TW202222719A - Optical glass and optical elements made of optical glass wherein the optical glass has improved thermal stability and glass transition temperature characteristics while maintaining a high refractive index - Google Patents

Abstract

An object of the present invention is to provide an optical glass having improved thermal stability and glass transition temperature characteristics while maintaining a high refractive index, and an optical element made of the glass. The optical glass of the present invention contains B2O3, La2O3, Gd2O3, Ta2O5, Li2O, and ZnO as essential components, including, in mass %, 2.5 to 12% of SiO2, 0.70% or more of Li2O, 6% or more of ZnO, 25% or more of La2O3, 17.5% or less of Gd2O3, 6% or more of Ta2O5, 10% or more of Li2O and ZnO combined, 1.0% or more of Nb2O5 and WO3 combined. The mass ratio (La2O3+Gd2O3)/B2O3 is more than 2.2, and the mass ratio (Li2O/SiO2) is more than 0.200.

Description

Optical glass and optical elements formed from optical glass

The present invention relates to optical glass and optical elements formed from optical glass.

A lens formed of high-refractive-index, low-dispersion glass is combined with a lens formed of ultra-low-dispersion glass to form a cemented lens, which can correct chromatic aberrations and realize compact optical systems. Therefore, the high-refractive-index, low-dispersion glass occupies a very important position as an optical element constituting a projection optical system such as a photographing optical system and a projector.

In addition, as a method of producing an optical element, a method of producing a glass raw material for press molding from molten glass, and performing precise press molding of the glass raw material for press molding with a molding die to obtain an optical element (referred to as "precision pressing") is also known. molding method). In the precision press molding method, by transferring the shape of the molding surface of the molding die, the optical functional surface of the optical element can be formed without mechanical processing such as polishing and grinding. prior art literature Patent Literature

Patent Documents 1 and 2 disclose optical glasses suitable for precision press molding and having high refractive index and low dispersion. Patent Document 1: Japanese Patent Laid-Open No. 2006-137662; Patent Document 2: Japanese Patent Laid-Open No. 2003-267748.

Invention to solve problem

However, even in high-refractive-index, low-dispersion glass, when the refractive index of the glass is to be increased, the thermal stability of the glass tends to decrease and the glass transition temperature tends to increase. When the thermal stability is lowered, it is easy to devitrify when the glass is molded. In addition, in the case of glass having a high glass transition temperature, it is necessary to heat the glass to a high temperature during press molding, the glass reacts with the molding surface of the molding die, and the glass is foamed, etc., and the surface quality of the glass molding tends to deteriorate. . In particular, the deterioration of the surface quality tends to become conspicuous when large-scale molded articles are produced. The glasses described in Patent Documents 1 and 2 are both excellent as optical glasses, but there is room for improvement in terms of further improving thermal stability while maintaining high refractive index properties, and achieving both high refractive index and low glass transition temperature.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an optical glass having improved thermal stability and glass transition temperature characteristics while maintaining a high refractive index, and an optical element formed of the above-mentioned glass. solution to the problem

The inventors of the present invention have repeatedly conducted intensive studies, found that the glass having the following constitution can solve the above-mentioned problems, and completed the present invention. That is, the present invention includes the following. [1] An optical glass comprising B ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Ta ₂ O ₅ , Li ₂ O and ZnO as essential components, expressed in mass %, and containing 2.5 to 12% of SiO _2. 0.70% or more Li ₂ O, 6% or more ZnO, 25% or more La ₂ O ₃ , 17.5% or less Gd ₂ O ₃ , 6% or more Ta ₂ O ₅ , and the combination of Li ₂ O and ZnO The total content is 10% or more, the total content of Nb ₂ O ₅ and WO ₃ is 1.0% or more, the mass ratio (La ₂ O ₃ +Gd ₂ O ₃ )/B ₂ O ₃ is 2.2 or more, and the mass ratio (Li ₂ O/ SiO ₂ ) is 0.200 or more. [2] The optical glass according to [1], wherein the refractive index nd and the glass transition temperature Tg [° C.] satisfy the formula (1). Tg<1700×nd-2555 (1) [3] The optical glass according to [1], wherein the refractive index nd is 1.80 or more and the glass transition temperature Tg is 600° C. or less. [4] An optical element formed of the optical glass according to any one of [1] to [3]. Invention effect

According to the present invention, it is possible to provide an optical glass having improved thermal stability and glass transition temperature characteristics while maintaining a high refractive index, and an optical element formed of the glass.

In the present invention and this specification, unless otherwise specified, the glass composition of the optical glass is shown on the basis of oxides. Here, the "glass composition based on oxides" refers to the glass composition obtained by converting all the components that are decomposed when the glass raw material is melted to exist in the form of oxides in the optical glass, and the expression of each glass component is customary. , denoted as SiO ₂ , B ₂ O ₃ and so on. Unless otherwise specified, the content and total content of glass components are based on mass, and "%" means "mass %".

The content of the glass component can be quantified by a known method, for example, inductively coupled plasma emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), or other methods. In addition, in this invention and this specification, content of a structural component is 0%, It means that this structural component is not contained substantially, and it is permissible to contain this component at an unavoidable impurity level.

In addition, Abbe's number νd is a value for representing dispersion-related properties, and is represented by the following formula. Here, nF is the refractive index of the hydrogen blue line F (wavelength 486.13 nm), and nC is the refractive index of the hydrogen red line C (656.27 nm). νd=(nd-1)/nF-nC

The optical glass of the present embodiment contains B ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Ta ₂ O ₅ , Li ₂ O and ZnO as essential components, and contains 2.5 to 12% by mass of SiO ₂ , 0.70% or more Li ₂ O, 6% or more ZnO, 17.5% or less Gd ₂ O ₃ , 6% or more Ta ₂ O ₅ , and the total content of Li ₂ O and ZnO is 10% or more, Nb ₂ O ₅ The total content with WO ₃ is 1.0% or more, the mass ratio (La ₂ O ₃ +Gd ₂ O ₃ )/B ₂ O ₃ is 2.2 or more, and the mass ratio (Li ₂ O/SiO ₂ ) is 0.200 or more.

[Glass Composition] B ₂ O ₃ and SiO ₂ are network-forming components of glass. From the viewpoint of maintaining the thermal stability of the glass, the content of SiO ₂ is 2.5% or more, and from the viewpoint of maintaining the refractive index and keeping the glass transition temperature low, the content of SiO ₂ is 12% or less. The lower limit of the content of SiO ₂ is preferably 2.55% or more, 2.60% or more, 2.65% or more, 2.70% or more, and 2.75% or more in this order. In addition, the preferable upper limit of the content of SiO ₂ is preferably 11.0% or less, 10.75% or less, 10.50% or less, 10.25% or less, and 10.0% or less in this order.

From the viewpoint of maintaining thermal stability and meltability of the glass, the content of B ₂ O ₃ is preferably 10% or more, and from the viewpoint of maintaining the refractive index, the content of B ₂ O ₃ is preferably 20% or less. The lower limit of the content of B ₂ O ₃ is more preferably 7.92% or more, 8.50% or more, 9.0% or more, 9.50% or more, 10.0% or more, 10.5% or more, 11.0% or more, 11.46% or more, 12.0% or more, and 12.47% in this order. Above, above 13.0%, above 13.5%. Further, the upper limit of the content of B ₂ O ₃ is more preferably 20.0% or less, 19.5% or less, 19% or less, 18.5% or less, 18% or less, 17.5% or less, and 17.0% or less in this order.

Li ₂ O is a component that lowers the glass transition temperature while suppressing a decrease in the refractive index. In order to obtain this effect, the content of Li ₂ O is 0.70% or more. The lower limit of the content of Li ₂ O is more preferably 0.70% or more, 0.72% or more, 0.74% or more, 0.76% or more, 0.78% or more, and 0.80% or more in this order. The upper limit of the content of Li ₂ O is not particularly limited, but from the viewpoint of maintaining thermal stability and high refractive index properties of the glass, the upper limit of the content of Li ₂ O is more preferably 2.16% or less, 1.99% or less, 1.90% or less, 1.80% or less, 1.78% or less, 1.76% or less, 1.74% or less, 1.72% or less, 1.70% or less.

ZnO is also a component that lowers the glass transition temperature and improves the meltability while suppressing the decrease in the refractive index, and the content of ZnO is 6% or more in order to obtain this effect. The lower limit of the content of ZnO is more preferably 6.0% or more, 7.0% or more, 8.0% or more, 9.0% or more, 10.0% or more, and 11.0% or more in this order. The upper limit of ZnO is not particularly limited, but from the viewpoint of maintaining the chemical durability and thermal stability of the glass, the upper limit of the content of ZnO is more preferably 22.0% or less, 21.0% or less, 20.0% or less, 19.0% or less, and 18.0% or less in this order. , 17.0% or less, 16.0% or less.

In addition, from the viewpoint of achieving both high refractive index and low glass transition temperature, the total content of Li ₂ O and ZnO (content of Li ₂ O+ZnO) is 10% or more. The lower limit of the content of Li ₂ O+ZnO is more preferably 10.0% or more, 10.5% or more, 11.0% or more, 11.5% or more, 12.0% or more, and 12.5% or more in this order. The upper limit of the content of Li ₂ O+ZnO is not particularly limited, but is more preferably 23.0% or less, 22.0% or less, 21.0% or less, 20.0% or less, 19.0% or less, 18.0% or less, and 17.0% or less in this order.

La ₂ O ₃ and Gd ₂ O ₃ are components that increase the refractive index while maintaining low dispersion. From the viewpoint of maintaining the thermal stability of the glass, the content of Gd ₂ O ₃ is 17.5% or less. The upper limit of the content of Gd ₂ O ₃ is more preferably 17.25% or less, 17.0% or less, 16.75% or less, 16.50% or less, 16.25% or less, and 16.0% or less in this order. The lower limit of the content of Gd ₂ O ₃ is not particularly limited, but from the viewpoint of obtaining high refractive index and low dispersion properties excellent in thermal stability, the lower limit of the content of Gd ₂ O ₃ is preferably 3.0% or more, 3.5% or more, and 4.0% in this order. Above, above 4.5%, above 5.0%. In addition, from the viewpoint of further improving the thermal stability of the glass, the content of Gd ₂ O ₃ is preferably less than 13.0%, more preferably 12.5% or less, still more preferably 12.0% or less, and still more preferably less than 11.5%. In addition, when these preferable examples are expressed in mol %, the content of Gd ₂ O ₃ is preferably less than 6.7 mol %, more preferably 5.5 mol % or less, more preferably 4.9 mol % or less, and further preferably 4.8 mol % % or less, more preferably less than 4.5 mol%.

La ₂ O ₃ is a component that increases the refractive index and improves chemical durability without lowering the thermal stability of the glass and without increasing the dispersion, and its content is 25% or more. The lower limit of the content of La ₂ O ₃ is preferably 25.5% or more, 26.0% or more, 26.5% or more, 27.0% or more, 27.5% or more, 28.0% or more, and 28.5% or more in this order. In addition, the upper limit of the content of La ₂ O ₃ is not particularly limited, but the thermal stability tends to decrease due to excessive introduction in some cases. Therefore, it is preferably 41.0% or less, 40.5% or less, 40.0% or less, and 39.5% or less in this order. , 39.0% or less, 38.5% or less, 38.0% or less.

The lower limit of the total content of La ₂ O ₃ and Gd ₂ O ₃ (the content of La ₂ O ₃ + Gd ₂ O ₃ ) is preferably 37.0% or more, 37.5% or more, 38.0% or more, 38.5% or more, 39.0% or more, and 39.5% in this order. % or more, 40.0% or more. In addition, the upper limit of the total content of La ₂ O ₃ and Gd ₂ O ₃ (the content of La ₂ O ₃ + Gd ₂ O ₃ ) is preferably 50.0% or less, 49.5% or less, 49.0% or less, 48.5% or less, 48.0% or less, 47.5% or less.

Nb ₂ O ₅ is a component having functions of improving the thermal stability of glass and increasing the refractive index. Moreover, WO3 is a component which improves the thermal stability and meltability _of glass, and raises a refractive index. Therefore, in the present invention, from the viewpoint of obtaining high-refractive index glass, the lower limit of the total content of Nb ₂ O ₅ and WO ₃ (Nb ₂ O ₅ +WO ₃ ) is 1.0% or more, and the upper limit is not particularly limited. From the viewpoint of maintaining precision press formability, less is preferable. Taking the above into consideration, the lower limit of the content of Nb ₂ O ₅ +WO ₃ is preferably 1.00% or more, 1.25% or more, 1.50% or more, 1.75% or more, 2.00% or more, 2.25% or more, and 2.50% or more, in this order. In addition, the upper limit of the content of Nb ₂ O ₅ +WO ₃ is more preferably 10.0% or less, 9.5% or less, 9.0% or less, 8.5% or less, 8.0% or less, 7.5% or less, 7.0% or less, 6.5% or less, 6.0% in this order. the following.

The content of Nb ₂ O ₅ is not particularly limited as long as the content of Nb ₂ O ₅ + WO ₃ is satisfied. _The lower limit of the content of Nb ₂ O ₅ is ₀ %. 0.9% or more, 1.0% or more, 1.1% or more, 1.2% or more, 1.3% or more. When the amount of Nb ₂ O ₅ introduced is excessive, the dispersion may increase. Therefore, the upper limit of the content of Nb ₂ O ₅ is preferably 9.0% or less, 8.5% or less, 8.0% or less, 7.5% or less, 7.0% or less, in this order. 6.5% or less, 6.0% or less.

The content of WO ₃ is not particularly limited as long as the content of Nb ₂ O ₅ + WO ₃ is satisfied. The lower limit of the content of WO ₃ is 0%. When WO ₃ is contained, it is preferably 0.05% or more, 0.1% or more, and 0.15% in order Above, above 0.20%, above 0.25%. When the amount of WO ₃ introduced is excessive, the dispersion may increase, so the upper limit of the content of WO ₃ is preferably 9.0% or less, 8.5% or less, 8.0% or less, 7.5% or less, 7.0% or less, and 6.5% or less in this order.

The ratio of the total content of La ₂ O ₃ and Gd ₂ O ₃ to the content of B ₂ O ₃ (mass ratio (La ₂ O ₃ +Gd ₂ O ₃ )/B ₂ O ₃ ) is 2.2 or more. The lower limit of the mass ratio (La ₂ O ₃ +Gd ₂ O ₃ )/B ₂ O ₃ is more preferably 2.25% or more, 2.30% or more, 2.35% or more, 2.38% or more, 2.49% or more, 2.54% or more, and 2.58% in this order. Above, above 2.60%. The upper limit of the mass ratio (La ₂ O ₃ +Gd ₂ O ₃ )/B ₂ O ₃ ) is not particularly limited, but from the viewpoint of maintaining the thermal stability of the glass, it is preferably 5.1% or less, 4.9% or less, 4.7% or less, 4.5% or less, 4.2% or less, 4.1% or less, 4.0% or less, 3.9% or less, 3.8% or less, 3.7% or less.

The mass ratio (La ₂ O ₃ +Gd ₂ O ₃ )/(Li ₂ O + ZnO) is more preferably 4.00 or less, 3.90 or less, 3.80 or less, 3.70 or less, 3.60 or less, and 3.50 in this order from the viewpoint of suppressing an increase in the glass transition temperature. Hereinafter, from the viewpoint of maintaining the high refractive index and low dispersion characteristics, 2.00 or more, 2.10 or more, 2.20 or more, 2.30 or more, 2.40 or more, and 2.50 or more are more preferable in this order.

Ta ₂ O ₅ is a component that maintains high refractive index and low dispersion properties and thermal stability. In order to obtain the above-mentioned effects, the content of Ta ₂ O ₅ is 6.0% or more. The lower limit of Ta ₂ O ₅ is preferably 6.0% or more, 7.0% or more, 8.0% or more, 9.0% or more, and 10.0% or more in this order. The upper limit of the content of Ta ₂ O ₅ is not particularly limited, but from the viewpoint of maintaining the thermal stability of the glass, it is preferably 20.0% or less, 19.5% or less, 19.0% or less, 18.5% or less, 18.0% or less, and 17.5% or less in this order.

Furthermore, from the viewpoint of maintaining the thermal stability of the glass, the mass ratio (ZrO ₂ +Ta ₂ O ₅ +Nb ₂ O ₅ +WO ₃ )/(SiO ₂ +B ₂ O ₃ ) is more preferably 1.60 or less, 1.55 or less, and 1.50 or less in this order. , 1.45 or less, 1.40 or less, and 1.35 or less, from the viewpoint of maintaining high refractive index properties, more preferably 0.75 or more, 0.80 or more, 0.85 or more, 0.90 or more, 0.95 or more, and 1.00 or more.

TiO ₂ is a component that increases the refractive index and improves dispersion. The content of TiO ₂ is not particularly limited in the present invention. However, due to excessive introduction, it may react with the molding surface of the molding die during press molding, which tends to make the surface of the glass. Deterioration of quality, in addition to enhance the coloring of the glass. Therefore, the upper limit of the content of TiO ₂ is more preferably 3% or less, 2% or less, 1% or less, 0.5% or less, 0.1% or less, and 0% (excluding) in this order.

Y ₂ O ₃ is a high-refractive-index and low-dispersion component, which is not particularly limited in the present invention, but has a smaller effect of increasing the refractive index than Gd ₂ O ₃ which is the same rare earth oxide. When the total content of the rare earth oxides is excessive, the thermal stability of the glass tends to decrease. Therefore, La ₂ O ₃ and Gd ₂ O ₃ are preferably introduced rather than Y ₂ O ₃ from the viewpoint of maintaining high refractive index characteristics while maintaining thermal stability. From the above viewpoints, the upper limit of the content of Y ₂ O ₃ is preferably 3% or less, 2% or less, 1% or less, 0.5% or less, and 0.1% or less in this order, and may be 0%.

Yb ₂ O ₃ is an arbitrary component used as a high refractive index and low dispersion component. Excessive introduction causes a decrease in the thermal stability of the glass and an increase in the glass transition temperature. Furthermore, the absorption in the infrared region of the glass shows a tendency to increase. The preferable upper limit of the content of Yb ₂ O ₃ is more preferably 3%, 2%, 1%, 0.5%, and 0.1% in this order. Can also be 0%.

ZrO ₂ is an optional component in the present invention, and it is preferable to introduce ZrO ₂ in order to obtain the effect of improving the thermal stability of the glass without lowering the refractive index of the glass. The lower limit of the content of ZrO ₂ is more preferably 2.50% or more, 2.55% or more, 2.60% or more, 2.65% or more, 2.70% or more, and 2.75% or more in this order. The upper limit of the content of ZrO ₂ is more preferably 10.0% or less, 9.5% or less, 9.0% or less, 8.5% or less, 8.0% or less, 7.5% or less, 7.0% or less, and 6.5% or less in this order. In addition, when the content thereof increases, the liquidus temperature (deterioration of thermal stability) sharply rises.

Sb ₂ O ₃ acts as a clarifying agent. When the amount of addition thereof increases, the molding surface of the press-molding mold may be damaged during precision press molding, and the coloring of the glass tends to increase. The lower limit of the content of Sb ₂ O ₃ is preferably 0% or more, 0.01% or more, and 0.02% or more in this order, and the upper limit of the content of Sb ₂ O ₃ is preferably 1.0% or less, 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less. In addition, content of Sb ₂ O ₃ is a numerical value (Sb ₂ O ₃ ratio when the total mass of glass components other than Sb ₂ O ₃ is taken as 100).

From the viewpoint of lowering the glass transition temperature, the mass ratio (Li ₂ O/SiO ₂ ) of the content of Li ₂ O to the content of SiO ₂ is 0.200 or more. The lower limit of the mass ratio (Li ₂ O/SiO ₂ ) is preferably 0.200 or more, 0.210 or more, and 0.220 or more in this order. In addition, the upper limit of the mass ratio (Li ₂ O/SiO ₂ ) is preferably 0.300 or less, 0.290 or less, 0.280 or less, and 0.270 or less in this order from the viewpoint of suppressing an increase in the glass transition temperature and maintaining thermal stability.

Furthermore, from the viewpoint of solving the problem of the invention, the total content of the above-mentioned components and the clarifying agent is preferably 90% or more, and is preferably 93% or more, 95% or more, 96% or more, 98% or more, 99% or more, Above 99.5%, above 99.9%. From the viewpoint of solving the problems of the invention, the total content of Bi ₂ O ₃ , Ga ₂ O ₃ , Al ₂ O ₃ , BaO, SrO, CaO, MgO, Lu ₂ O ₃ , P ₂ O ₅ , and GeO ₂ is preferably 8 % or less, and more preferably 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, and 0.1% or less in this order.

The content of F is preferably 0.1% or less from the viewpoint of volatilization during glass melting, and more preferably no F is contained. From the viewpoint of suppressing the burden on the environment, it is preferable to substantially not contain Pb, Cd, Te, Tl, U, Th, Se, and As. Further, from the viewpoint of preventing coloration of glass, it is preferable that Fe, Cr, V, Co, Ni, Nd, Er, Eu, Cu, Tb, and Ho are not substantially contained.

[Characteristics of glass] In the optical glass of the present embodiment, it is preferable that the refractive index nd and the glass transition temperature Tg [° C.] satisfy the formula (1). Tg＜1700×nd-2555 (1) By satisfying the formula (1), both high refractive index characteristics and press moldability can be achieved. The optical glass of the present embodiment preferably has a refractive index nd of 1.80 or more, and preferably has a glass transition temperature Tg of 600°C or less. The lower limit of the refractive index nd is more preferably 1.805, 1.810, 1.815, 1.820, 1.825, 1.830, 1.835, 1.840, and 1.845 in this order. The more preferable upper limit of the refractive index is more preferably 1.880 or less, 1.875 or less, 1.870 or less, 1.865 or less, and 1.860 or less in this order. The more preferable lower limit of Abbe's number νd is more preferably 39.0 or more, 39.1 or more, 39.2 or more, 39.3 or more, 39.4 or more, and 39.5 or more in this order. The more preferable upper limit of Abbe's number νd is more preferably 41.0 or less, 40.9 or less, 40.8 or less, 40.7 or less, and 40.6 or less in this order. Increasing the refractive index of glass corresponds to expanding the degree of freedom that glass has when considering glass as a material of an optical element. From the viewpoint of expanding the degree of freedom described above, it is preferable to increase the refractive index. However, when the refractive index is increased while maintaining dispersion, the glass stability tends to decrease, so the above range is preferable.

The lower limit of the glass transition temperature Tg is more preferably 530°C or higher, 535°C or higher, 540°C or higher, 545°C or higher, and 550°C or higher in this order. The upper limit of the glass transition temperature Tg is more preferably 600°C or lower, 595°C or lower, 590°C or lower, and 585°C or lower in this order.

The glass transition temperature (Tg) is preferably low from the viewpoint of preventing consumption of the press-molding mold and damage to the release film, but when Tg is excessively lowered, the refractive index is lowered and the thermal stability of the glass is also lowered. Regarding glass stability, the difference (Tx-Tg) between the crystallization temperature Tx and the glass transition temperature Tg can be used as an index of the devitrification resistance when reheating the temporarily cured glass. It can be considered that the glass having a larger difference between the crystallization temperature Tx and the glass transition temperature Tg (Tx-Tg) is more excellent in the above-mentioned devitrification resistance.

The glass transition temperature Tg and the crystallization peak temperature Tx can be obtained as follows. In differential scanning calorimetry, when a glass sample is heated up, an endothermic behavior accompanied by a change in specific heat, that is, an endothermic peak appears, and when the temperature is further increased, an exothermic peak appears. In the differential scanning calorimetry analysis, a differential scanning calorimetry curve (DSC curve) in which the horizontal axis represents the temperature and the vertical axis represents the quantity corresponding to the exothermic and endothermic heat of the sample is obtained. In this curve, the intersection of the tangent at the point with the maximum slope when the endothermic peak appears from the base line and the above-mentioned base line is taken as the glass transition temperature Tg, and the intersection of the tangent at the point with the maximum slope when the exothermic peak appears and the above-mentioned baseline is taken as crystallization Peak temperature Tx. The glass transition temperature Tg and the crystallization peak temperature Tx can be measured using a high-temperature differential scanning calorimeter "DSC3300SA" manufactured by Bruker Co., Ltd., for example, after sufficiently pulverizing glass with a mortar as a sample. In the reheat press molding method of heating, softening, and molding a glass raw material into a desired shape, it is necessary to heat the glass raw material to a high temperature higher than the glass transition temperature. Since the temperature of the glass at the time of molding precipitates crystals when it reaches the crystallization temperature range, glass having a small (Tx-Tg) is disadvantageous in preventing devitrification and molding. On the contrary, glass with a large (Tx-Tg) is advantageous in that it can be molded by reheating and softening without devitrification.

From the above viewpoints, the lower limit of Tx-Tg is more preferably 130.0°C or higher, 135.0°C or higher, 140.0°C or higher, 145.0°C or higher, 150.0°C or higher, and 155.0°C or higher in this order. Tx-Tg can be, for example, 300.0°C or lower, 280.0°C or lower, 260.0°C or lower, 240.0°C or lower, or 220.0°C or lower, but may be higher than the values exemplified here.

The upper limit of the liquidus temperature is preferably 1210°C, 1200°C, 1190°C, and 1180°C in this order from the viewpoint of maintaining devitrification resistance (thermal stability at high temperature) during glass melting or molding of the glass melt. In addition, from the viewpoint of maintaining a high refractive index and a low glass transition temperature, the lower limit of the liquidus temperature is preferably 1080°C, 1090°C, 1100°C, and 1110°C in this order.

The optical glass of the present invention is not particularly limited, but preferably satisfies the following physical properties. The lower limit of the coloring degree λ80 is determined by the composition itself. The upper limit of the coloring degree λ80 is preferably 490 nm or less, 485 nm or less, 480 nm or less, and 475 nm or less in this order. The lower limit of the coloring degree λ70 is determined by the composition itself. The upper limit of the coloring degree λ70 is preferably 400 nm or less, 395 nm or less, 390 nm or less, and 385 nm or less in this order. The lower limit of the coloring degree λ5 is determined by the composition itself. The upper limit of the coloring degree λ5 is preferably 360 nm or less, 355 nm or less, 350 nm or less, and 345 nm or less in this order. The lower limit of the relative partial dispersion Pg,F is preferably 0.525 or more, 0.535 or more, 0.545 or more, and 0.555 or more in this order. With respect to the partial dispersion Pg, the upper limit of F is preferably 0.610 or less, 0.600 or less, 0.590 or less, and 0.580 or less in this order.

[Manufacture of Optical Glass] The optical glass of the embodiment of the present invention may be prepared from the glass raw material prepared according to the above-mentioned predetermined composition, and from the prepared glass raw material according to a conventionally known glass production method. For example, a variety of compounds are prepared, mixed thoroughly to prepare a batch of raw materials, and the batch of raw materials is put into a crucible such as a quartz crucible or a platinum crucible for rough melting. The melt obtained by the rough melting is rapidly cooled and pulverized to produce cullet. Furthermore, the cullet was put into a platinum crucible, heated and remelted to form a molten glass, and after clarification and homogenization, the molten glass was molded and gradually cooled to obtain optical glass. A well-known method may be used for shaping|molding and slow cooling of a molten glass. In addition, the compound used in preparing the batch raw material is not particularly limited as long as a desired content of the desired glass component can be introduced into the glass, and examples of such compounds include oxides, carbonates, nitrates, and hydroxides. Wait.

[Manufacture of optical elements, etc.] What is necessary is just to use a well-known method to produce an optical element using the optical glass of embodiment of this invention. For example, a glass raw material is melted into a molten glass, the molten glass is poured into a mold, formed into a plate shape, and annealed to produce a glass raw material made of the optical glass of the present invention. The obtained glass raw material is appropriately cut, polished, and ground to prepare a press-molded preform (preform) of a size suitable for press-molding. The preform is heated and softened, precision press-molded by a known method, and if necessary, centering is performed to produce optical elements such as an aspherical lens. The optical function surface of the produced optical element can be coated with an antireflection film, a total reflection film, or the like according to the purpose of use. As an optical element, various lenses, such as an aspherical lens, a lens, a diffraction grating, etc. can be illustrated. [Example]

[Production of glass samples] (Example 1) Compound raw materials corresponding to each component, that is, raw materials such as boric acid, carbonate, oxide, etc., are weighed to obtain compounds having the respective compositions shown in Tables 1 to 3 (Tables 4 to 6 are expressed in mol %) in % by mass. Glass, fully mixed to prepare raw materials. This preparation raw material was put into a platinum crucible, heated at 1300 to 1400° C. for 2 hours in an atmospheric environment, and melted, and homogenized and clarified by stirring to obtain a molten glass. The molten glass was cast into a molding die to be molded, and then slowly cooled to obtain a block-shaped glass sample. In addition, the raw material to be prepared may be roughly melted to produce cullet, the cullet may be remelted, homogenized and clarified by stirring, and the obtained molten glass may be cast into a molding die to be molded and slowly cooled.

[Evaluation of glass samples] [1] Glass composition About the obtained glass sample, the content of each glass component was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). In addition, in all the glass samples shown in Tables 1-3 (Tables 4-6 are shown in mol%), the content of F was 0%. [2] Refractive index nd, Abbe number νd and relative partial dispersion Pg,F According to the Japan Optical Glass Industry Association standard JOGIS-01, the refractive index at a predetermined wavelength was measured for a glass sample annealed at a slow cooling rate of -30°C/hour. Abbe's number νd and relative partial dispersion Pg,F were calculated from the measurement results of the refractive index. [3] Specific gravity Based on the standard JOGIS-05 of the Japan Optical Glass Industry Association. [4] λ80, λ70, λ5 The glass sample was processed to have a thickness of 10 mm, and had optically polished planes parallel to each other, and the spectral transmittance in the wavelength region of 280 nm to 700 nm was measured. The spectral transmittance B/A was calculated by setting the intensity of the light ray perpendicularly incident on one of the optically polished planes as the intensity A, and the intensity of the light ray emitted from the other plane as the intensity B. The wavelengths with spectral transmittances of 80%, 70%, and 5% are denoted as λ80, λ70, and λ5, respectively. In addition, the spectral transmittance also includes the reflection loss of light on the sample surface. [5] Glass transition temperature Tg, crystallization peak temperature Tx The glass is sufficiently pulverized in a mortar and used as a sample, and is measured using, for example, a high-temperature differential scanning calorimeter "DSC3300SA" manufactured by Bruker Co., Ltd. Crystallization was not observed on the surface and inside of each glass sample. [6] Liquidus temperature A 5-8 cc glass sample was placed in a furnace heated to 1300° C. and held for 20 minutes, fully melted, transferred to a furnace heated to a predetermined temperature, and held for 2 hours, and then cooled at room temperature. After cooling, the inside of the glass was observed with an optical microscope, and the liquidus temperature was determined by the presence or absence of crystals. In addition, the said glass physical properties measured are recorded in Tables 7-9.

[表2]

[表3]

[表4]

[表5]

[表6]

[表7]

[表8]

[表9]

[Table 1]

[Table 2]

[table 3]

[Table 4]

[table 5]

[Table 6]

[Table 7]

[Table 8]

[Table 9]

(Example 2) Each glass sample obtained in Example 1 was cut and ground to prepare a preform. The preform is heated, precisely press-molded, and precisely annealed to produce an aspherical lens. No foreign substances such as crystals and bubbles were found in the interior and surface of the produced aspherical lens, and an optical element with excellent interior and surface quality was obtained. In addition, well-known conditions, a shaping|molding die, a release film, etc. can be applied to precision press molding conditions, a shaping|molding die, a release film, and the like.

none.

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Claims (4)

An optical glass comprising B ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Ta ₂ O ₅ , Li ₂ O and ZnO as essential components, expressed in mass %, including 2.5-12% of SiO ₂ , 0.70 % or more of Li ₂ O, 6% or more of ZnO, 25% or more of La ₂ O ₃ , 17.5% or less of Gd ₂ O ₃ , 6% or more of Ta ₂ O ₅ , the total content of Li ₂ O and ZnO is 10% % or more, the total content of Nb ₂ O ₅ and WO ₃ is 1.0% or more, the mass ratio (La ₂ O ₃ +Gd ₂ O ₃ )/B ₂ O ₃ is 2.2 or more, and the mass ratio (Li ₂ O/SiO ₂ ) is Above 0.200. The optical glass according to claim 1, wherein the refractive index nd and the glass transition temperature Tg [°C] satisfy the formula (1), Tg<1700×nd-2555 (1). The optical glass according to claim 1, wherein the refractive index nd is 1.80 or more, and the glass transition temperature Tg is 600°C or less. An optical element formed of the optical glass according to any one of claims 1 to 3.