TWI889723B - Optical glass, preform, optical element, and optical machine - Google Patents

Abstract

The present invention provides an optical glass having a partial dispersion ratio (θg,F) within a desired range, high devitrification resistance, and good re-hot pressing formability. The optical glass of the present invention contains, in terms of mass % of the oxide-converted composition, 10.0% to 35.0% of SiO ₂ , 10.0% to 40.0% of Nb ₂ O ₅ , 1.0% to 15.0% of ZrO ₂ , 1.0% to 15.0% of Li ₂ O , and 1.0% to 20.0% of Ln ₂ O ₃ (wherein Ln is at least one selected from the group consisting of La, Y, Gd, and Yb). The mass ratio (Li ₂ O + La ₂ O ₃ ) / SiO ₂ is 0.35 or more, the mass ratio Li ₂ O / (Li ₂ O + Na ₂ O + K ₂ O) is 0.50 or more, and the relationship between the partial dispersion ratio (θg, F) and the Abbe number (ν _d ) satisfies (-0.00162×ν _d +0.624) (θg,F) The relationship is (-0.00162×ν _d +0.654).

Description

Optical glass, preforms, optical components, and optical machines

The present invention relates to optical glass and optical components.

Optical systems such as digital cameras and video cameras contain some degree of blur, known as aberration. These aberrations are categorized as monochromatic aberrations and chromatic aberrations. Chromatic aberration, in particular, strongly depends on the material properties of the lenses used in the optical system.

Chromatic aberration is typically corrected by combining a low-dispersion convex lens with a high-dispersion concave lens. However, this combination only corrects aberrations in the red and green regions, leaving aberrations in the blue region. This incompletely eliminated aberration in the blue region is called the secondary spectrum. Correcting the secondary spectrum requires optical design that incorporates the blue g-ray (435.835nm). The partial dispersion ratio (θg,F) is used as an indicator of the optical properties that are important in optical design. In the aforementioned optical system combining low-dispersion and high-dispersion lenses, the secondary spectrum is effectively corrected by using optical materials with a large partial dispersion ratio (θg, F) for the low-dispersion lens and optical materials with a small partial dispersion ratio (θg, F) for the high-dispersion lens.

In recent years, demand for glass with a low partial dispersion ratio (θg,F) has increased significantly in optical design.

The partial dispersion ratio (θg,F) is expressed by the following equation (1).

θg,F=(n _g -n _F )/(n _F -n _C )……(1)

For optical glass, there is a roughly linear relationship between the partial dispersion ratio (θg,F), which represents the partial dispersion properties in the short-wavelength region, and the Abbe number (ν _d ). On an orthogonal coordinate system with the partial dispersion ratio (θg,F) on the vertical axis and the Abbe number (ν _d ) on the horizontal axis, the line representing this relationship is drawn by connecting the two points plotted for the partial dispersion ratio and Abbe number of NSL7 and PBM2. This line is called the normal line. Although the standard glass used as the benchmark for normal lines varies among optical glass manufacturers, each company defines them with nearly identical slopes and intercepts (NSL7 and PBM2 are optical glasses manufactured by Ohara Co., Ltd.; PBM2 has an Abbe number (ν _d ) of 36.3 and a partial dispersion ratio (θg,F) of 0.5828, while NSL7 has an Abbe number (ν _d ) of 60.5 and a partial dispersion ratio (θg,F) of 0.5436).

Known methods for producing optical components from optical glass include: grinding and polishing a ball-on-brick (GOB) or glass block formed from optical glass to obtain the desired shape of the optical component; reheating and shaping the ball-on-brick or glass block (rehot pressing) the resulting glass molded body, followed by grinding and polishing; and forming a preform material obtained from the ball-on-brick or glass block using an ultra-precision mold (precision press molding) to obtain the desired shape of the optical component. In all cases, stable glass is required when forming the ball-on-brick or glass block from molten glass raw material. If the stability (devitrification resistance) of the glass constituting the resulting paste ball or glass block decreases and crystallization occurs within the glass, glass suitable for use as an optical element will no longer be obtained.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2006-248897.

[Patent Document 2] Japanese Patent Application Laid-Open No. 2012-240909.

It is difficult to obtain a glass with a small partial dispersion ratio (θg,F) using the glass disclosed in Patent Document 1, and devitrification properties are also easily degraded.

Although the glass of Patent Document 2 shares the commonality of reducing the partial dispersion ratio (θg,F), it contains _Ta2O5 as _an essential component, resulting in high manufacturing costs, and poor meltability, resulting in poor formability.

The present invention was developed in view of the above-mentioned problems, and its object is to obtain an optical glass having a partial dispersion ratio (θg,F) within the required range, high devitrification resistance, and good re-hot pressing formability.

More specifically, the present invention is to obtain a partial dispersion ratio (θg,F) and the Abbe number (ν _d ) satisfying (-0.00162×ν _d +0.624) (θg,F) (-0.00162×ν _d +0.654), and the liquidus temperature is below 1150℃, and the optical glass has good formability after hot pressing.

To address the above-mentioned issues, the inventors conducted repeated and intensive experimental research and discovered that by adjusting the relationship between the contents of _{Ln2O3 and Li2O} in glass containing _SiO2 and _Nb2O5 , it is possible to obtain optical glass that exhibits a low partial dispersion ratio, high resistance to devitrification, and good rehot pressing properties, leading _to the completion of the present invention.

(1) An optical glass comprising, in terms of mass % of the oxide-converted composition, 10.0% to 35.0% of _SiO2 , 10.0% to _40.0 % of _Nb2O5 , 1.0% to 15.0% of _ZrO2 , 1.0% to 15.0% of _{Li2O ,} and 1.0% to 20.0% of _Ln2O3 (wherein Ln is at least one selected from the group consisting of La, Y, Gd, and Yb); a mass ratio ( _Li2O + _La2O3 )/ _SiO2 of 0.35 or greater; a mass ratio _Li2O /( _Li2O + _Na2O + _K2O ) of 0.50 or greater; and a _relationship between the partial dispersion ratio (θg,F) and the Abbe number ( _νd ) satisfying (-0.00162× _νd +0.624) (θg,F) The relationship is (-0.00162×ν _d +0.654).

(2) The optical glass described in (1), which contains, in terms of mass % of the composition converted into _oxides , 0% to 20.0% of _B2O3 , 0% to 20.0% of _La2O3 , 0% to 20.0% of _CaO , 0% to 20.0% of SrO, 0% to 20.0% of BaO, and 0% to 10.0% of _Na2O .

(3) The optical glass described in (1) or (2) contains more _SiO2 than _B2O3 ; the mass ratio (ZnO+ _TiO2 + _P2O5 )/ _{( ZrO2} + _La2O3 + _Li2O ) is less than _0.15 ; and the mass sum of BaO+CaO+SrO is 5.0% to _20.0 %.

(4) The optical glass as described in any one of (1) to (3), wherein the refractive index (n _d ) is 1.70000 to 1.80000 and the Abbe number (ν _d ) is 30.00 to 40.00.

(5) The optical glass as described in any one of (1) to (4), wherein the liquidus temperature is below 1150°C.

(6) An optical element composed of the optical glass described in any one of (1) to (5).

(7) A preform made of the optical glass described in any one of (1) to (5) and used for grinding and/or precision pressing.

(8) An optical machine comprising an optical element as described in (6) or (7).

According to the present invention, an optical glass having a low partial dispersion ratio (θg,F), a low liquidus temperature, and good re-hot pressing formability can be obtained.

FIG1 is a graph showing the relationship between the partial dispersion ratio (θg,F) and the Abbe number (ν _d ) of the glass of the embodiment of the present case.

While embodiments of the optical glass of the present invention are described in detail, the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the present invention. Furthermore, overlapping descriptions may be omitted, but this does not limit the scope of the invention.

[Glass composition]

The following describes the composition ranges of the components that comprise the optical glass of the present invention. Unless otherwise specified, the content of each component is expressed as a percentage by mass relative to the total mass of the glass in terms of oxide-equivalent composition. The term "oxide-equivalent composition" herein refers to the composition of each component contained in the glass, assuming that all oxides, complex salts, and metal fluorides used as raw materials for the glass components of the present invention decompose and transform into oxides during melting. The total mass of the resulting oxides is 100 mass%, and the composition is expressed based on the assumption that all oxides, complex salts, and metal fluorides used as raw materials for the glass components of the present invention decompose and transform into oxides during melting.

[About essential ingredients and optional ingredients]

_SiO2 is an essential component that promotes stable glass formation and reduces devitrification (the formation of crystals), which is undesirable for optical glass.

In particular, by setting the _SiO₂ content to 10.0% or higher, glass with excellent devitrification resistance can be achieved without significantly increasing the partial dispersion ratio. Furthermore, the liquidus temperature can be lowered. Therefore, the _SiO₂ content is preferably 10.0% or higher, more preferably 13.0% or higher, further preferably 15.0% or higher, further preferably 18.0% or higher, and most preferably 20.0% or higher as the lower limit.

On the other hand, by setting the _SiO2 content to 35.0% or less, the increase in the partial dispersion ratio can be suppressed. Therefore, the upper limit of the _SiO2 content is preferably 35.0% or less, more preferably 33.0% or less, and most preferably 31.0% or less.

Nb ₂ O ₅ is an essential component that can increase the refractive index and reduce the Abbe number.

In particular, by setting the content _{of Nb2O5} to 10.0% or more, the refractive index can be increased. Therefore, the content _{of Nb2O5} is preferably 10.0% or more, more preferably 12.0% or more, further preferably 15.0% or more, further preferably 20.0% or more, and most preferably 23.0% or more as the lower limit.

On the other hand, by setting _{the Nb2O5} content to 40.0% or less, thermal stability can be achieved, reducing the material cost of the glass. Furthermore, devitrification of the glass _can be reduced. Therefore, the upper limit of the _Nb2O5 content is preferably 40.0% or less, more preferably 38.0% or less, further preferably 36.0% or less, and most preferably 34.0% or less.

_ZrO2 is an essential component that can increase the refractive index and Abbe number of the glass and reduce the dispersion ratio.

In particular, by setting the _ZrO2 content to 1.0% or higher, the partial dispersion ratio can be reduced, resulting in a stable glass. Therefore, the _ZrO2 content is preferably at least 1.0%, more preferably at least 2.0%, even more preferably at least 3.0%, even more preferably at least 5.0%, and most preferably at least 6.0% as the lower limit.

On the other hand, by setting the _ZrO2 content to 15.0% or less, devitrification can be reduced, and a more homogeneous glass can be easily obtained. Therefore, the upper limit of the _ZrO2 content is preferably 15.0% or less, more preferably 12.0% or less, even more preferably 11.0% or less, further preferably 10.0% or less, and most preferably 9.0% or less.

Unlike other alkali metals, Li ₂ O is a necessary component to reduce the dispersion ratio.

In particular, by setting the _Li2O content to 1.0% or more, the meltability of the glass can be improved and the dispersion ratio can be reduced. Therefore, the _Li2O content can be preferably 1.0% or more, more preferably 1.5% or more, further preferably 2.0% or more, and most preferably 2.5% or more as the lower limit.

On the other hand, by setting the content of the Li ₂ O component to 15.0% or less, devitrification caused by excessive inclusion of the Li ₂ O component can be reduced, and devitrification during re-hot pressing can also be reduced.

Therefore, the upper limit of the content of the Li ₂ O component is preferably 15.0% or less, more preferably 12.0% or less, further preferably 10.0% or less, further preferably 9.0% or less, and most preferably 8.0% or less.

B ₂ O ₃ is an optional component that promotes stable glass formation, lowers the liquidus temperature, improves devitrification resistance, and improves the solubility of glass raw materials.

In particular, by setting the _B2O3 content to 0% or more, the rise in liquidus temperature _can be suppressed. Therefore, the _B2O3 content can be preferably 0% or more, _more preferably more than 0%, more preferably 0.1% or more, further preferably 0.2% or more, and most preferably 0.3% or more as the lower limit.

On the other hand, by setting the _B2O3 content to 20.0% or less, a decrease in the refractive index and an increase in the partial dispersion ratio can be suppressed. Therefore, the upper limit _{of the B2O3 content} is preferably 20.0% or less, more preferably 18.0% or less, more preferably 16.0% or less, even more preferably 14.0% or less, further preferably 12.0% or less, and most preferably 11.0% or less.

The SiO ₂ component is preferably contained in a larger amount than the B ₂ O ₃ component. If the B ₂ O ₃ component is greater than the SiO ₂ component, the partial dispersion ratio increases. Therefore, by containing a larger amount of SiO ₂ than the B ₂ O ₃ component, the glass can be stabilized and the partial dispersion ratio can be reduced.

La ₂ O ₃ is a component that can reduce devitrification and partially reduce the dispersion ratio. By containing this La ₂ O ₃ component, it exhibits an effect different from other rare earth elements that are prone to devitrification.

In particular, by setting the _La₂O₃ content to 0% or higher, _the refractive index can be increased, and by adjusting the content within the range of the present invention, anomalous dispersion can be reduced. Therefore, the _La₂O₃ content is preferably 0 _% or higher, more preferably 1.0% or higher, even more preferably 2.0% or higher, further preferably 3.0% or higher, further preferably 4.0% or higher, and most preferably 5.0% or higher as the lower limit.

On the other hand, by setting the _La₂O₃ content to 20.0% or less, the increase in the Abbe number can be _suppressed , devitrification can be reduced, and coloration can be minimized. Therefore, the upper _limit of the _La₂O₃ content is preferably 20.0% or less, more preferably 19.0% or less, further preferably 17.0% or less, and most preferably 16.0% or less.

The Gd ₂ O ₃ component, the Y ₂ O ₃ component, and the Yb ₂ O ₃ component are arbitrary components capable of increasing the refractive index and reducing the partial dispersion ratio by containing at least one of them in an amount exceeding 0%.

On the other hand, when a large amount of Gd ₂ O ₃ , Y ₂ O ₃ , and Yb ₂ O ₃ components are contained, the liquidus temperature decreases, causing the glass to devitrify.

In particular, by setting the content of each of _{the Gd2O3} component, _{the Y2O3} component, and _{the Yb2O3} component to 10.0% or less, devitrification and coloration can be reduced. Therefore, the upper limit of each _of the _Gd2O3 component, _{the Y2O3} component, and _{the Yb2O3} component is preferably 10.0% or less, more preferably 8.0% or less, further preferably 5.0% or less, and most preferably 3.0% or less.

Na ₂ O and K ₂ O are optional components that, when contained in an amount exceeding 0%, can improve the solubility of glass raw materials and reduce coloring.

On the other hand, if Na ₂ O and K ₂ O components are contained in large amounts, the stability of the glass deteriorates and the devitrification resistance is reduced.

On the other hand, by setting the contents of _Na2O and _K2O components to 10.0% or less, devitrification can be reduced. Therefore, the upper limit of the contents of _Na2O and _K2O components is preferably 10.0% or less, more preferably 8.0% or less, further preferably 7.0% or less, further preferably 6.0% or less, and most preferably 5.0% or less.

MgO is an optional component that improves solubility and lowers the liquidus temperature, but its inclusion in large amounts can cause glass devitrification.

On the other hand, by setting the MgO content to 10.0% or less, devitrification can be reduced. Therefore, the upper limit of the MgO content is preferably 10.0% or less, more preferably 8.0% or less, further preferably 5.0% or less, further preferably 3.0% or less, and most preferably 2.0%.

CaO is an optional component that can improve the stability of glass.

In particular, by setting the CaO content to 0% or higher, meltability can be improved. Therefore, the lower limit of the CaO content is preferably 0% or higher, more preferably 0.1% or higher, further preferably 0.5% or higher, further preferably 1.0% or higher, and most preferably 2.0% or higher.

On the other hand, by setting the CaO content to 20.0% or less, press formability improves and increases in the partial dispersion ratio can be suppressed. Therefore, the upper limit of the CaO content is preferably 20.0% or less, more preferably 17.0% or less, further preferably 14.0% or less, further preferably 12.0% or less, and most preferably 10.0% or less.

SrO is an optional component that can improve the stability of glass.

On the other hand, by setting the SrO content to 20.0% or less, press-formability improves and increases in the partial dispersion ratio can be suppressed. Therefore, the upper limit of the SrO content is preferably 20.0% or less, more preferably 17.0% or less, further preferably 14.0% or less, further preferably 12.0% or less, and most preferably 10.0% or less.

BaO is an optional component that can improve the stability of glass.

On the other hand, by setting the BaO content to 20.0% or less, press-formability improves and increases in the partial dispersion ratio can be suppressed. Therefore, the upper limit of the BaO content is preferably 20.0% or less, more preferably 17.0% or less, further preferably 14.0% or less, further preferably 12.0% or less, and most preferably 10.0% or less.

_TiO2 is an optional component that increases the refractive index and reduces the Abbe number. On the other hand, if a large amount of _TiO2 is contained, the partial dispersion ratio increases.

In particular, by setting the _TiO2 content to 10.0% or less, the increase in the partial dispersion ratio can be suppressed and the Abbe number can be lowered. Therefore, the upper limit of the _TiO2 content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and most preferably 2.0% or less.

ZnO is an inexpensive, optional component that can be adjusted toward high dispersion. However, if a large amount of ZnO is included, the partial dispersion ratio increases.

In particular, by setting the ZnO content to 10.0% or less, devitrification and coloration can be reduced. Therefore, the upper limit of the ZnO content is preferably 10.0% or less, more preferably 5.0% or less, further preferably less than 3.0%, and most preferably 1.0% or less.

Ta ₂ O ₅ is an optional component that increases the refractive index, reduces the Abbe number and the partial dispersion ratio, and improves the resistance to devitrification.

In particular, by setting the _Ta₂O₅ content to 10.0% or less, the use of _{Ta₂O₅ ,} a rare mineral resource, is reduced, and the glass _can be melted at a lower temperature, thereby reducing the production cost of the glass. Furthermore, devitrification of the glass caused _by excessive _Ta₂O₅ content can be reduced. Therefore, the _upper limit of the _Ta₂O₅ content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and most preferably 1.0% or less. From the perspective of reducing the material cost of the glass, _Ta₂O₅ may be _omitted .

_WO3 is an optional component that increases the refractive index, lowers the Abbe number, and improves the solubility of the glass raw materials. By limiting the _WO3 content to 10.0% or less, the partial dispersion ratio of the glass is minimized, coloring is reduced, and internal transmittance is improved. Therefore, the upper limit of the _WO3 content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and most preferably 1.0% or less.

_P2O5 is an optional component _that can improve the stability of glass.

On the other hand, by setting the _P2O5 content to 10.0% or less, the increase in the partial dispersion ratio caused _by excessive _{P2O5 can} be reduced. Therefore, the upper limit of _{the P2O5} content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, further preferably less than 2.0%, and most preferably 1.0% or less.

_GeO₂ is an optional component that can increase the refractive index and reduce devitrification. By limiting the _GeO₂ content to 10.0% or less, the use of expensive _GeO₂ can be reduced, thereby lowering the material cost of the glass. Therefore, the upper limit of the _GeO₂ content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and most preferably 1.0% or less.

Al ₂ O ₃ is an optional component that can increase the refractive index and improve the devitrification resistance.

On the other hand, by setting the _Al2O3 content to 10.0% or less, devitrification caused by excessive _{Al2O3 can} be reduced. Therefore, the upper limit of _{the Al2O3} content is preferably _10.0 % or less, more preferably 5.0% or less, further preferably 3.0% or less, and most preferably 1.0% or less.

Ga ₂ O ₃ is an optional component that can increase the refractive index and improve the resistance to devitrification.

On the other hand, by setting the _Ga2O3 content to 10.0% or less, devitrification caused by excessive _{Ga2O3 can} be reduced. Therefore, the upper limit _of the _Ga2O3 content is preferably _10.0 % or less, more preferably 5.0% or less, further preferably 3.0% or less, and most preferably 1.0% or less.

_Bi2O3 is _an optional component that can increase the refractive index, lower the Abbe number, and reduce the glass transition point. By setting _{the Bi2O3} content to 10.0% or less, the partial dispersion ratio can be minimized, glass coloration can be reduced, and internal transmittance _can be improved. Therefore, the upper limit of the _Bi2O3 content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and most preferably 1.0% or less.

_TeO₂ is an optional component that can increase the refractive index, reduce the partial dispersion ratio, and lower the glass transition point. By limiting the _TeO₂ content to 10.0% or less, glass coloration can be reduced, thereby increasing internal transmittance. Furthermore, by reducing the use of expensive _TeO₂ , glass with lower material costs can be obtained. Therefore, the upper limit of the _TeO₂ content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0%, and most preferably 1.0% or less. In particular, from the perspective of reducing the material cost of the glass, _TeO₂ may be omitted.

_SnO2 is an optional component that can clarify (defoam) molten glass and increase the visible light transmittance of the glass. By setting the _SnO2 content to 1.0% or less, the glass can be less likely to be discolored or devitrified by the reduction of the molten glass. In addition, by reducing the alloying of _SnO2 with melting equipment (especially precious metals such as Pt), the life of the melting equipment can be extended. Therefore, the upper limit of the _SnO2 content is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less.

_Sb2O3 promotes defoaming and clarifies the glass, and is an optional component in the optical glass of the present invention. By limiting the _Sb2O3 content to 1.0% _or less relative to the total mass of the glass, excessive foaming during melting _can be minimized, and _{the Sb2O3} component can be less likely to alloy with melting materials (particularly precious metals such as Pt). Therefore, the upper limit of the _Sb2O3 content relative to the total mass of the glass (calculated as oxide) is preferably _1.0 % or less, more preferably 0.5% or less, further preferably 0.3% or less, and most preferably 0.1% or less.

Furthermore, the component for clarifying and defoaming the glass is not limited to the aforementioned Sb ₂ O ₃ component, and any clarifier or defoaming agent known in the field of glass manufacturing, or a combination thereof, may be used.

When the total amount (by mass ₎ of _Ln2O3 (where Ln is one or more selected from the group consisting of La, Y, Gd, and Yb) is 1.0% or more, it can increase the refractive index and reduce the dispersion ratio. Therefore, the lower limit of the total amount _{of Ln2O3} is preferably 1.0% or more, more preferably 3.0% or more, further preferably 5.0% or more, and most preferably 7.0% or more.

On the other hand, by setting the total content (mass sum) of _{the Ln2O3} component to 20.0% or less, devitrification caused _by excessive _Ln2O3 can be reduced. Therefore, the upper limit is preferably 20.0% or less, more preferably 18.0% or less, further preferably 17.0% or less, and most preferably 16.0% or less.

The stability of the glass can be improved when the sum (mass) of the _Rn2O component (wherein Rn is one or more selected from the group consisting of Li, Na, and K) is 1.0% or greater. Therefore, the lower limit of the sum of the _Rn2O components is preferably 1.0% or greater, more preferably 2.5% or greater, further preferably 3.0% or greater, and most preferably 3.5% or greater.

On the other hand, by setting the total content (mass sum) of the Rn ₂ O component to 15.0% or less, a decrease in the refractive index can be suppressed, and devitrification caused by excessive inclusion of the Rn ₂ O component can be reduced. Therefore, the upper limit is preferably 15.0% or less, more preferably 14.0% or less, further preferably 13.0% or less, and most preferably 12.0% or less.

When the sum of the RO components (where R is one or more selected from the group consisting of Mg, Ca, Sr, and Ba) is 5.0% or greater, low-temperature meltability can be improved. Therefore, the sum of the RO components has a lower limit of preferably 5.0%, more preferably 5.3% or greater, further preferably 5.8% or greater, and most preferably 6.0% or greater.

On the other hand, to prevent a decrease in devitrification resistance due to excessive inclusion, the total content of the RO components is preferably 20.0% or less. Therefore, the upper limit of the total mass of the RO components is preferably 20.0% or less, more preferably 19.0% or less, further preferably 18.0% or less, and most preferably 16.0% or less.

When the mass ratio of BaO+CaO+SrO is set at 5.0% or higher, low-temperature meltability can be improved. Therefore, the mass ratio of BaO+CaO+SrO is preferably 5.0% or higher, more preferably 5.3% or higher, further preferably 5.8% or higher, and most preferably 6.0% or higher as the lower limit.

On the other hand, excessive amounts of BaO, CaO, and SrO increase the refractive index and dispersion, making it difficult to achieve the desired optical properties and deteriorating the devitrification properties. Therefore, the content is preferably 20.0% or less. Therefore, the upper limit of the content of BaO, CaO, and SrO is preferably 20.0% or less, more preferably 19.0% or less, further preferably 18.0% or less, and most preferably 16.0% or less.

When the mass ratio ( _Li2O + _La2O3 )/ _SiO2 is set to 0.35 or higher, the glass can be stabilized and the partial dispersion _ratio can be reduced. Therefore, the mass ratio ( _Li2O + _La2O3 )/ _SiO2 has a lower limit of _preferably 0.35 or higher, more preferably 0.36 or higher, further preferably 0.38 or higher, and most preferably 0.40 or higher.

On the other hand, in order to suppress the increase in liquidus temperature, the mass ratio _{( Li2O} + _La2O3 )/ _SiO2 is preferably 1.00 or less. Therefore, the upper limit of _the mass ratio ( _Li2O + _La2O3 )/ _SiO2 is preferably 1.00 or less, more preferably 0.90 or less, further preferably 0.88 or less, and most preferably 0.85 or less.

When the mass ratio _Li2O /( _Li2O + _Na2O + _K2O ) is 0.50 or greater, the _Li2O component's effect in reducing the partial dispersion ratio is most effectively exerted, improving meltability and suppressing devitrification. Therefore, the lower limit of the mass ratio _Li2O /( _Li2O + _Na2O + _K2O ) is preferably 0.50 or greater, more preferably 0.52 or greater, further preferably 0.54 or greater, and most preferably 0.55 or greater.

_When the mass ratio ( _SiO2 + _B2O3 + _Ln2O3 ) / _Rn2O is set to 3.50 or higher, devitrification can be suppressed and the liquidus temperature _can be lowered. Therefore, the lower limit of the mass ratio ( _SiO2 + _{B2O3 + Ln2O3} ) / _Rn2O is preferably 3.50 or higher, more preferably 3.55 or higher, further preferably exceeding 3.58, _and most preferably 3.60 or higher.

On the other hand, when the mass ratio (SiO ₂ + B ₂ O ₃ + Ln ₂ O ₃ ) / Rn ₂ O is set to 12.0 or less, the Abbe number (ν _d ) can be maintained. Therefore, the upper limit of the mass ratio (SiO ₂ + B ₂ O ₃ + Ln ₂ O ₃ ) / Rn ₂ O is preferably 12.0 or less, more preferably 11.80 or less, further preferably 11.50 or less, and most preferably 11.20 or less.

When the mass ratio (ZnO + TiO ₂ + P ₂ O ₅ ) / (ZrO ₂ + La ₂ O ₃ + Li ₂ O) is set to less than 0.15, an increase in the partial dispersion ratio caused by the ZnO component, TiO ₂ component, and P ₂ O ₅ component can be suppressed. Therefore, the upper limit of the mass ratio (ZnO + TiO ₂ + P ₂ O ₅ ) / (ZrO ₂ + La ₂ O ₃ + Li ₂ O) is preferably less than 0.15, more preferably 0.12 or less, further preferably 0.10 or less, and most preferably 0.08 or less.

[About ingredients that should not be contained]

Next, we explain the components that the optical glass of the present invention should not contain and the components that are not desirable to contain.

Other components may be added as needed without compromising the properties of the glass of the present invention. However, the inclusion of small amounts of transition metal components other than Ti, Zr, Nb, W, La, Gd, Y, Yb, and Lu, such as V, Cr, Mn, Fe, Co, Ni, Cu, Ag, and Mo, either alone or in combination, can cause coloration of the glass and absorption at specific wavelengths in the visible light region. Therefore, it is particularly preferred that optical glass used for wavelengths in the visible light region be substantially free of these transition metal components.

In addition, lead compounds such as PbO and arsenic compounds such as As ₂ O ₃ are components with high environmental loads, so it is ideal that they are substantially free of them, that is, they are not contained at all except for unavoidable contamination.

Furthermore, in recent years, the use of Th, Cd, Tl, Os, Be, and Se has been regulated as hazardous chemicals. Environmental measures are required not only in glass manufacturing but also in processing and post-production handling. Therefore, when environmental impact is a concern, it is best to substantially eliminate these components.

[Manufacturing method]

The optical glass of the present invention is produced, for example, by uniformly mixing the aforementioned raw materials so that the respective components are within a predetermined content range. The resulting mixture is then placed in a platinum crucible, a quartz crucible, or an alumina crucible for rough melting. The mixture is then placed in a gold crucible, a platinum crucible, a platinum alloy crucible, or an indium crucible and melted at a temperature between 1000°C and 1400°C for 2 to 5 hours. The mixture is then stirred for homogenization and degassing. The temperature is then lowered to between 950°C and 1250°C, followed by fine stirring to remove ripples. The mixture is then cast into a mold and slowly cooled.

[physical properties]

The optical glass of the present invention has a refractive index (n _d ) and Abbe number (ν _d ) within a predetermined range.

The refractive index ( _nd ) of the optical glass of the present invention preferably has a lower limit of 1.70000 or higher, more preferably 1.73000 or higher, and even more preferably 1.75000 or higher. The upper limit of the refractive index is preferably 1.80000 or lower, and even more preferably 1.79000 or lower.

The Abbe number (ν _d ) of the optical glass of the present invention has a lower limit of preferably 30.00 or higher, more preferably 32.00 or higher, and even more preferably 33.00 or higher. On the other hand, the Abbe number (ν _d ) of the optical glass of the present invention has an upper limit of preferably 40.00 or lower, more preferably 38.00 or lower, and even more preferably 37.00 or lower.

The optical glass of the present invention, with such a refractive index and Abbe number, is useful in optical design, particularly in achieving high imaging properties and enabling miniaturization of optical systems, thereby expanding the degree of freedom in optical design.

The optical glass of the present invention has a low partial dispersion ratio (θg,F).

More specifically, the lower limit of the partial dispersion ratio (θg, F) of the optical glass of the present invention is not particularly limited, but is preferably 0.560 or greater, more preferably 0.565 or greater. On the other hand, the upper limit of the partial dispersion ratio (θg, F) of the optical glass of the present invention is preferably 0.600 or less, more preferably 0.595 or less, and even more preferably 0.593 or less. Furthermore, the relationship between the partial dispersion ratio (θg, F) and the Abbe number (ν _d ) of the optical glass of the present invention preferably satisfies (-0.00162×ν _d +0.624). (θg,F) The relationship is (-0.00162×ν _d +0.654).

Thus, the optical glass of the present invention contains a relatively large amount of _SiO2 and _Nb2O5 and has a lower partial dispersion ratio (θg,F) _than conventional glasses. Therefore, optical devices formed from this optical glass can be preferably used to correct chromatic aberration.

Here, the lower limit of the partial dispersion ratio (θg,F) in the relationship between the optical glass of the present invention and the Abbe number (ν _d ) is not particularly limited, but is preferably (-0.00162×ν _d + 0.624) or greater, more preferably (-0.00162×ν _d + 0.627) or greater, and even more preferably (-0.00162×ν _d + 0.630) or greater. On the other hand, the upper limit of the partial dispersion ratio (θg,F) in the relationship between the optical glass of the present invention and the Abbe number (ν _d ) is preferably (-0.00162×ν _d + 0.654) or less, more preferably (-0.00162×ν _d + 0.651) or less, and even more preferably (-0.00162×ν _d + 0.648) or less.

The optical glass of the present invention preferably has a high transmittance for visible light, especially for light with short wavelengths, thus exhibiting less coloration.

In particular, if the optical glass of the present invention is expressed in terms of glass transmittance, the wavelength (λ ₈₀ ) at which the spectral transmittance is 80% for a sample with a thickness of 10 mm is preferably below 420 nm, more preferably below 417 nm, and even more preferably below 410 nm as the upper limit.

In addition, the shortest wavelength (λ ₅ ) at which the optical glass of the present invention exhibits a spectral transmittance of 5% for a sample having a thickness of 10 mm is preferably 345 nm or less, more preferably 343 nm or less, and even more preferably 342 nm or less as an upper limit.

As a result, the glass's absorption edge is located near the ultraviolet region, increasing its transparency to visible light. This makes the optical glass ideal for use in light-transmitting optical components such as lenses.

The optical glass of the present invention preferably has high resistance to devitrification, and more specifically, has a low liquidus temperature.

Specifically, the upper limit of the liquidus temperature of the optical glass of the present invention is preferably 1150°C or lower, more preferably 1148°C or lower, and even more preferably 1145°C or lower. This reduces crystallization of the produced glass even when the molten glass is discharged at a lower temperature, thereby minimizing devitrification during glass forming from the molten state and reducing the impact on the optical properties of optical devices using the glass. Furthermore, since the glass can be formed even at a lower melting temperature, the energy consumed during glass forming can be reduced, thereby reducing glass manufacturing costs.

[Preform and optical components]

A glass molded article can be produced from the produced optical glass using a molding method such as re-hot pressing or precision pressing. Specifically, a preform for press molding can be produced from the optical glass, and this preform can be re-hot pressed and then polished to produce a glass molded article. Alternatively, the polished preform can be precision pressed to produce a glass molded article. The method for producing a glass molded article is not limited to these methods.

The glass molded article produced in this manner is useful for various optical components, particularly lenses and prisms. This reduces color blurring caused by chromatic aberration in light passing through an optical system incorporating the optical component. Consequently, when the optical component is used in a camera, the photographic subject can be more accurately represented, while when used in a projector, the desired image can be projected with higher definition.

[Example]

The compositions of Examples (No. 1 to No. 20) and Comparative Example A of the present invention, as well as the refractive index (n _d ), Abbe number (ν _d ), partial dispersion ratio (θg,F), liquidus temperature, transmittance λ ₅ , and transmittance λ ₈₀ are shown in Tables 1 and 2. The following examples are for illustrative purposes only and are not intended to be limiting.

For the glasses of the Examples and Comparative Examples, high-purity raw materials such as oxides, hydroxides, carbonates, nitrates, fluorides, and metaphosphates commonly used in optical glass were selected as raw materials for each component. The raw materials were weighed and mixed evenly in the composition ratios shown in the table for each Example and Comparative Example, and then placed in a stone crucible (the melting point of the glass was adjusted according to the melting point). Similarly, platinum crucibles and alumina crucibles can also be used. Depending on the melting difficulty of the glass components, the melt is melted in an electric furnace at a temperature range of 1100°C to 1400°C for 0.5 to 5 hours. The melt is then transferred to a platinum crucible, stirred and homogenized, and degassing is performed. The temperature is then lowered to 1000°C to 1200°C. After stirring and homogenization, the melt is cast into a mold and slowly cooled to produce glass.

The refractive index (n _d ), Abbe number (ν _d ), and partial dispersion ratio (θg,F) of the glasses used in the Examples and Comparative Examples were measured using the V-block method specified in JIS (Japanese Industrial Standards) B 7071-2:2018. The refractive index (n _d ) is expressed as the value measured for the d-ray (587.56 nm) of a helium lamp. The Abbe number (ν _d ) was calculated using the refractive index for the d-ray (n _d ) of a helium lamp, the refractive index for the F-ray (486.13 nm) of a hydrogen lamp (n _F ), and the refractive index for the C-ray (656.27 nm) (n _C ) using the formula: Abbe number (ν _d ) = [(n _d -1)/(n _F -n _C )]. The partial dispersion ratio (θg,F) is calculated using the refractive index for g-rays from a mercury (Hg) lamp ( _ng ), the refractive index for F-rays (486.13 nm) from a hydrogen lamp ( _nF ), and the refractive index for C-rays (656.27 nm) ( _nC ) using the formula: partial dispersion ratio (θg,F) = ( _{ng -nF} ) / ( _{nF -nC} ). These refractive indices ( _nd ), Abbe numbers ( _νd ), and partial dispersion ratio (θg,F) are determined by measuring glass obtained by slow cooling at a rate of -25°C/hr.

Next, based on the measured Abbe number (ν _d ) and partial dispersion ratio (θg,F), the intercept b ₂ when the slope a ₂ is 0.00162 in the relationship (θg,F) = -a ₂ × ν _d +b ₂ is determined.

The transmittance of the glass used in the Examples and Comparative Examples was measured in accordance with the Japan Optical Glass Industries Association Standard JOGIS02-2003. Furthermore, in the present invention, the presence and degree of coloration of the glass are determined by measuring the transmittance of the glass. Specifically, the spectral transmittance of a parallel-surface polished glass with a thickness of 10 mm ± 0.1 mm was measured in accordance with JIS Z8722 from 200 nm to 800 nm, and the wavelengths (λ ₈₀ and λ ₅ ) at which the spectral transmittance reached 80% and 5% were determined.

The liquidus temperatures of the glasses used in the Examples and Comparative Examples were measured as follows: A crushed glass sample was placed on a platinum plate at a 10 mm interval. The plate was then placed in a furnace with a temperature gradient of 800°C to 1200°C for 30 minutes before removal. After cooling, the glass sample was observed under an 80x magnification microscope to determine whether crystals were present. For this purpose, optical glass was crushed into particles approximately 2 mm in diameter as a sample.

As shown in the table, the refractive index ( _nd ) of the optical glass of the embodiments of the present invention is greater than or equal to 1.70000 and less than or equal to 1.80000, which is within the required range.

In addition, the Abbe number (ν _d ) of the optical glass of the embodiments of the present invention is greater than or equal to 30.00 and less than or equal to 40.00, which is within the required range.

As shown in the table, the optical glass of the embodiment of the present invention satisfies the relationship between the Abbe number (ν _d ) and the partial dispersion ratio (θg,F) (-0.00162×ν _d +0.624) (θg,F) (-0.00162×ν _d +0.654).

As shown in the table, the optical glass of the embodiment of the present invention has a liquidus temperature of 1150°C or less. Furthermore, due to its low liquidus temperature, the optical glass of the embodiment of the present invention is presumed to have high re-hot press formability.

As shown in the table, the optical glasses of the embodiments all exhibit a spectral transmittance of 80% at a wavelength (λ ₈₀ ) of 420 nm or less, and a spectral transmittance of 5% at a wavelength (λ ₅ ) of 345 nm or less.

The glass of Comparative Example A has a mass ratio of (Li ₂ O + La ₂ O ₃ )/SiO ₂ less than 0.35, so it devitrifies severely and does not undergo vitrification.

The present invention has been described in detail above for illustrative purposes. However, this embodiment is for illustrative purposes only, and it should be understood that various modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention.

All documents described in this specification and the disclosures of the Japanese application specification (including the specification, drawings, and patent claims) that form the basis for the Paris priority right of this application are incorporated herein by reference.

Claims (6)

An optical glass comprising, in terms of oxide-converted composition by mass, 10.0% to 30.0% _SiO2 ; 10.0% to 40.0% _Nb2O5 ; 1.0 _% to 15.0% _ZrO2 ; 1.0% to 15.0% _Li2O ; and 1.0% to 20.0% _Ln2O3 (wherein Ln is at least one selected from the group consisting _of La, Y, Gd, and Yb); wherein the _SiO2 component is greater than _{the B2O3} component; the mass sum of BaO+CaO+SrO is 5.0% to _20.0 %; the mass ratio ( _Li2O + _La2O3 )/ _SiO2 is 0.53 or greater; the mass ratio _Li2O /( _Li2O + _Na2O +K ₂ O) is 0.50 or more; the mass ratio (SiO ₂ ＋B ₂ O ₃ ＋Ln ₂ O ₃ )/Rn ₂ O is greater than 3.58 and less than 12.0 (wherein Rn is one or more selected from the group consisting of Li, Na, and K); the mass ratio (ZnO + TiO ₂ ＋P ₂ O ₅ )/(ZrO ₂ ＋La ₂ O ₃ ＋Li ₂ O) is 0.12 or less; the refractive index (n _d ) is 1.70000 to 1.80000, and the Abbe number (ν _d ) is 30.00 to 40.00; the partial dispersion ratio (θg,F) and the Abbe number (ν _d ) satisfy the following relationship: (-0.00162×ν _d +0.624)≤(θg,F)≤(-0.00162×ν _d +0.654). The optical glass described in claim 1 contains, in terms of mass % of the composition converted into oxides: 0% to _20.0 % of _B2O3 ; 0% to 20.0% of _La2O3 ; 0% to 20.0% of _CaO ; 0% to 20.0% of SrO; 0% to 20.0% of BaO; and 0% to 10.0% of _Na2O . The optical glass as recited in claim 1 or 2, wherein the liquidus temperature is 1150°C or less. An optical element is composed of the optical glass as described in any one of claims 1 to 3. A preform is made of the optical glass as recited in any one of claims 1 to 3 and is used for grinding and/or precision pressing. An optical machine comprises the optical element as described in claim 4.