JP7472562B2 - Optical Glass - Google Patents

Description

The present invention relates to optical glass suitable for use in optical elements such as lenses.

In recent years, as optical systems used in cameras, microscopes, endoscopes, etc. have become smaller and lighter, there is a demand for higher refractive indexes as optical properties of the glass used in the optical lenses.

In order to make glass have a higher refractive index, _{it is} necessary to reduce the content of _SiO2 and _{B2O3 ,} which are glass skeleton components, and to include a large amount of rare earth oxides such as _La2O3 , _Gd2O3 , and _{Ta2O5 ,} or _Nb2O5 and _TiO2 . However, in this case, vitrification becomes difficult. This is because optical glass is generally produced by melting raw materials in a melting vessel such as a crucible and cooling _them , and in glass systems with a small amount of glass skeleton components, crystallization tends to proceed from the contact interface with the melting vessel.

Even if the composition is difficult to vitrify, it can be vitrified by eliminating contact at the interface with the melting vessel. As such a method, a containerless levitation method (containerless solidification method) is known in which the raw material is melted and cooled in a floating state. By using this method, the molten glass hardly comes into contact with the melting vessel, so that crystallization originating from the interface with the melting vessel can be prevented, and vitrification becomes possible. For example, in Patent Document 1, a glass containing only _TiO2 and BaO as a glass composition is produced by the containerless levitation method.

Japanese Patent No. 4789086

The glass described in Patent Document 1 is relatively susceptible to devitrification, so even when the containerless floating method is used, it is difficult to make it larger in diameter (for example, to a major axis of 2 mm or more). In addition, since it devitrifies before it softens and deforms when heated, it is also difficult to mold it using a mold press.

In view of the above, the present invention aims to provide a new optical glass that has a high refractive index, excellent resistance to devitrification, and can be made large in diameter and molded by press molding.

As a result _of intensive research, the present inventors have found that the above problems can be solved by an optical glass containing _La2O3 , _Nb2O5 , _{TiO2 and B2O3} as essential _components in prescribed ranges, and propose this in the present invention.

That is, the optical glass of the present invention is characterized by containing, in mole percent, 10 to 50% La ₂ O ₃ , 10 to 70% Nb ₂ O ₅ , more than 0 to 60% TiO ₂ , and more than 0 to 40% B ₂ O ₃ .

The optical glass of the present invention preferably contains, in mol %, at least 60% of La ₂ O ₃ +Nb ₂ O ₅ +TiO ₂ . In this specification, "x+y+..." means the total amount of the corresponding components.

The optical glass of the present invention preferably has a refractive index (nd) of 2.05 to 2.35 and an Abbe number (νd) of 10 to 40.

The optical glass of the present invention preferably has a glass transition point (Tg) of 750°C or less. This makes it easy to perform mold press molding.

The optical glass of the present invention is suitable for use in mold press molding.

The present invention provides a new optical glass that has a high refractive index, excellent resistance to devitrification, and can be made large in diameter and molded by press molding.

FIG. 1 is a schematic cross-sectional view showing one embodiment of an apparatus for producing an optical glass of the present invention. 1 is a photograph showing the appearance of a glass sample No. 8 before and after pressing in an example.

The optical glass of the present invention is characterized by containing, in mol %, 10-50% La ₂ O ₃ , 10-70% Nb ₂ O ₅ , more than 0 to 60% TiO ₂ , and more than 0 to 40% B ₂ O ₃ . The reasons for limiting the glass composition range in this way are explained below. In the following explanation of the content of each component, "%" means "mol %" unless otherwise specified.

La ₂ O ₃ is a component that increases 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 10 to 50%, preferably 12 to 40%, more preferably 15 to 35%, and even more preferably 20 to 30%. If the content of La ₂ O ₃ is too low, it is difficult to obtain the above effects. On the other hand, if the content of La ₂ O ₃ is too high, the glass transition point becomes high, making mold press molding difficult. It also becomes difficult to vitrify.

Nb ₂ O ₅ is a component that has a large effect of increasing the refractive index, and also has the effect of widening the vitrification range. It also has the effect of lowering the glass transition point. The content of Nb ₂ O ₅ is 10 to 70%, preferably 15 to 67%, and more preferably 20 to 65%. If the content of Nb ₂ O ₅ is too low, it becomes difficult to obtain the above effect. On the other hand, if the content of Nb ₂ O ₅ is too high, it becomes difficult to vitrify the glass.

_TiO2 is a component that has a large effect of increasing the refractive index, and also has an effect of increasing chemical durability. The content of _TiO2 is more than 0 to 60%, preferably 1 to 55%, more preferably 3 to 50%, even more preferably 5 to 45%, particularly preferably 5 to 40%, and most preferably 5 to 25%. If the content of _TiO2 is too small, it is difficult to obtain the above effect. On the other hand, if the content of _TiO2 is too large, it is easy to devitrify and it is difficult to obtain a glass material of the desired size. In addition, when the effect of increasing the refractive index is prioritized, the content of _TiO2 is preferably more than 40%, more preferably 45% or more.

From the viewpoint of obtaining optical properties of high refractive index and high dispersion, the content of _La2O3 + _Nb2O5 + _TiO2 is preferably 60% or more, 65% or more, particularly 70% or more. There is no particular _upper limit, but if it is too much, it becomes difficult to vitrify and it becomes difficult to increase _the diameter (for example, the major axis is 2 mm or more, 3 mm or more, 4 mm _or more, or even 5 mm or more), or the glass transition point becomes high _and mold press molding tends to become difficult. Therefore, it is preferable that the content of _La2O3 + _Nb2O5 + _TiO2 is less than 100%, 99% or less, 95% or less, particularly 90% or less.

From the viewpoint of the thermal stability of the glass, the molar ratio of the contents of Nb ₂ O ₅ and La ₂ O ₃ (Nb ₂ O ₅ /La ₂ O ₃ ) is preferably 1 to 3.5, 1 to less than 2.5, particularly 1 to 2.4, so that devitrification during mold press forming can be suppressed.

B ₂ O ₃ is a component that forms a glass skeleton and expands the vitrification range. It also has the effect of lowering the glass transition point. The content of B ₂ O ₃ is more than 0 to 40%, preferably 5 to 35%, and more preferably 10 to 30%. If the content of B ₂ O ₃ is too low, it becomes difficult to obtain the above effect. On the other hand, if the content of B ₂ O ₃ is too high, the refractive index decreases and it becomes difficult to obtain the desired optical characteristics.

From _the viewpoint of obtaining _{a glass having a high refractive index, excellent resistance to devitrification, and capable of being made large in diameter or molded by press molding, the content of La2O3 + Nb2O5} + _TiO2 + _B2O3 is preferably 70% or more, ₇₅ % or more, and particularly preferably 80% or more. The upper limit may be 100%, but when other components are contained, it may be less than 100%, 99% or less, 95% or less, or even 90% or less.

In addition to the above components, the optical glass of the present invention may contain the following components.

Gd ₂ O ₃ is a component that increases the stability of vitrification and increases the refractive index. However, if the content of Gd ₂ O ₃ is too high, vitrification becomes more difficult. Therefore, the content of Gd ₂ O ₃ is preferably 0 to 20%, more preferably 0.1 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 high, vitrification becomes difficult and the raw material cost tends to increase. Therefore, the content of Ta ₂ O ₅ is preferably 0 to 20%, more preferably 0.1 to 5%.

Y ₂ O ₃ is a component that increases the stability of vitrification and increases the refractive index. However, if the content of Y ₂ O ₃ is too high, vitrification becomes more difficult. 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 high, vitrification becomes difficult. Therefore, the content of Yb ₂ O ₃ is preferably 0 to 20%, more preferably 0 to 10%.

_ZrO2 is a component that increases the refractive index and also has the effect of increasing chemical durability. However, if the content of _ZrO2 is too high, the glass transition point becomes high. Also, it becomes difficult to vitrify. Therefore, the content of _ZrO2 is preferably 0 to 10%, more preferably 0 to 5%.

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 high, the refractive index decreases and it becomes difficult to obtain the desired optical properties. In addition, the glass transition point becomes high. Therefore, the content of Al ₂ O ₃ is preferably 0 to 20%, more preferably 0 to 10%.

_SiO2 is a component that forms the glass skeleton and expands the vitrification range. It also has the effect of improving weather resistance. However, if the _SiO2 content is too high, the refractive index decreases and it becomes difficult to obtain the desired optical characteristics. Therefore, the _SiO2 content is preferably 0 to 30%, more preferably 0 to 20%.

_GeO2 is a component that increases the refractive index and also has the effect of widening the vitrification range. However, if the _GeO2 content is too high, the raw material cost tends to be high. Therefore, the _GeO2 content is preferably 0 to 10%, more preferably 0 to 5%.

_WO3 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 widening the vitrification range. However, if the content of _WO3 is too high, it tends to be more prone to devitrification and to make it difficult to increase the diameter. Therefore, the content of _WO3 is preferably 0 to 10%, more preferably 0 to 5%.

_SnO2 is a component that has a great effect of increasing the refractive index. However, it is prone to cause devitrification due to reduction. Therefore, the content of _SnO2 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 widening the vitrification range. However, if the content is too high, 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 increasing the stability of vitrification and increasing chemical durability. However, if the content is too high, the refractive index decreases and it becomes difficult to obtain the desired optical characteristics. Therefore, the content of these components is preferably 0 to 10% each, and more preferably 0 to 5% each.

Li ₂ O, Na ₂ O, K ₂ O and Cs ₂ O have the effect of lowering the melting temperature, but also lower the refractive index, so their total content is preferably 0 to 10%, more preferably 0 to 5%.

Sb ₂ O ₃ can be contained as a fining agent. However, in order to avoid coloration or in consideration of environmental aspects, the content of Sb ₂ O ₃ is preferably 1% or less, and more preferably is substantially not contained.

Considering the environmental impact, it is preferable that PbO is not substantially contained.

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

The refractive index (nd) of the optical glass of the present invention is preferably 2.05 or more, more preferably 2.07 or more, and even more preferably 2.10 or more. For example, when the optical glass of the present invention is used as a lens, the higher the refractive index, the thinner the lens can be made, which is advantageous in miniaturizing optical devices. The upper limit of the refractive index is preferably 2.35 or less, more preferably 2.30 or less, taking into account the stability of vitrification.

Taking into consideration the stability of vitrification, the Abbe number (νd) of the optical glass of the present invention is preferably 10 to 40, 12 to 38, and particularly preferably 15 to 37.

The glass transition point (Tg) of the optical glass of the present invention is preferably 750°C or lower, more preferably 740°C or lower, and even more preferably 735°C or lower. If the glass transition point is too high, mold press molding becomes difficult. Specifically, the press mold and the glass are more likely to react during mold press molding, and deterioration of the press mold is more likely to be accelerated.

The optical glass of the present invention can be processed by mold press molding into optical elements such as lenses and prisms for use.

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

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 outlets 10b opening into the molding surface 10a. The gas outlets 10b are 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 outlets 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, a raw material lump 12 prepared to become glass of the above composition is placed on the molding surface 10a. Examples of raw material lump 12 include a pressed compact of raw material powder, a sintered compact of raw material powder, and an aggregate of crystals having a composition equivalent to the target glass composition.

Next, gas is ejected from the gas ejection holes 10b to float the raw material lump 12 on the molding surface 10a. In other words, the raw material lump 12 is held in a state where it is not in contact with the molding surface 10a. In this state, the raw material lump 12 is irradiated with laser light from the laser light irradiation device 13. This heats and melts the raw material lump 12 to vitrify it, and molten glass is obtained. The molten glass is then cooled to obtain a glass material. In the process of heating and melting the raw material lump 12 and the process of cooling the molten glass and the glass material until the temperature of the molten glass and the glass material is at least below the softening point, it is preferable to continue ejecting at least gas and suppress contact between the raw material lump 12, the molten glass, and the glass material and the molding surface 10a. In addition to the method of irradiating laser light, the method of heating and melting may be radiation heating.

The optical glass of the present invention will be described in detail below using examples, but the present invention is not limited to the following examples.

Tables 1 and 2 show examples of the present invention (Nos. 1 to 17) and comparative examples (Nos. 18 to 20).

First, raw materials were mixed to produce raw material batches with the glass compositions shown in the table. 0.2 to 0.7 g of each raw material was weighed out, press molded, and then fired at 800 to 1100°C for 3 to 12 hours to produce raw material blocks.

Using the raw material lump obtained above, a roughly spherical glass sample (major axis 3.5-6.5 mm) was prepared by a containerless levitation method using an apparatus similar to that shown in FIG. 1. A 100 W _CO2 laser oscillator was used as the heat source. Oxygen gas was used as the gas for levitating the raw material lump, and was supplied at a flow rate of 1-15 L/min. The obtained glass sample was annealed at 680-750°C, and then the refractive index (nd), Abbe number (νd), and glass transition point (Tg) were measured by the following method.

The refractive index (nd) and Abbe number (νd) were measured using a KPR-2000 (Shimadzu Corporation) after polishing the glass sample at a right angle. The refractive index (nd) was evaluated using the measured value for the helium lamp d line (587.6 nm). The Abbe number (νd) was calculated from the refractive index of the d line and the refractive index of the hydrogen lamp F line (486.1 nm) and C line (656.3 nm) using the formula Abbe number (νd) = {(nd-1)/(nF-nC)}.

The glass transition temperature (Tg) was determined by crushing the glass sample and performing DTA (differential thermal analysis).

A simple evaluation of mold press molding was also performed on glass sample No. 8. Specifically, a glass sample with a major axis of 6.5 mm and a minor axis of 3.5 mm was placed in a cylindrical tungsten carbide press mold with a diameter of 8 mm, and uniaxial pressure was applied from above and below, followed by heating at 755°C (Tg+45°C). As a result, the glass sample was deformed to a shape with a major axis of 8 mm and a minor axis of 2 mm. Photographs before and after pressing are shown in Figure 2. After pressing, the surfaces of the glass sample and the press mold were checked, and no abnormalities such as deterioration of the press mold or reaction between the glass sample and the press mold were found.

As shown in Tables 1 and 2, the glass samples No. 1 to 17, which are examples, had the desired optical properties, with a refractive index of 2.1206 to 2.2985 and an Abbe number of 18.15 to 22.01. In addition, it can be seen that the glass transition points were low, at 654 to 740°C, making them suitable for mold press molding. On the other hand, the glass samples No. 18 and 19, which are comparative examples, had high glass transition points of 783°C or higher and were not suitable for mold press molding. In addition, glass sample No. 18 had a refractive index of 1.9510, which was inferior in optical properties to the examples. Glass sample No. 20 did not vitrify.

Claims (4)

An optical glass comprising, in mole percent, 10-50% La ₂ O ₃ , 10-70% Nb ₂ O ₅ , more than 0-25% TiO ₂ , more than 0-15 % B ₂ O ₃ , and 85% or more La ₂ O ₃ +Nb ₂ O ₅ +TiO ₂ . The optical glass according to claim 1, characterized in that it has a refractive index (nd) of 2.05 to 2.35 and an Abbe number (νd) of 10 to 40. The optical glass according to claim 1 or 2, characterized in that the glass transition point (Tg) is 750°C or less. The optical glass according to any one of claims 1 to 3, characterized in that it is for use in mold press molding.