WO2016114274A1

WO2016114274A1 - Glass, glass material for press molding, optical element blank, and optical element

Info

Publication number: WO2016114274A1
Application number: PCT/JP2016/050753
Authority: WO
Inventors: 智明根岸
Original assignee: Hoya株式会社
Priority date: 2015-01-13
Filing date: 2016-01-13
Publication date: 2016-07-21
Also published as: JP2023085359A; CN107207320B; JP6291598B2; JP2021008397A; JP2022050507A; CN108715512B; TWI671270B; TWI641572B; JP6812382B2; JP7250106B2; JP7514351B2; JP2018104283A; JPWO2016114274A1; CN107207320A; TW201904900A; TW201641456A; JP7003198B2; CN108715512A

Abstract

Provided is glass that is oxide glass which contains, in mass%, 15-35% by mass in total of B₂O₃ and SiO₂, 45-65% by mass in total of La₂O₃, Y₂O₃, Gd₂O₃ and Yb₂O₃, with the content of Yb₂O₃ being 3% by mass or less, 3-11% by mass of ZrO₂, 5% by mass or less of Ta₂O₅, and wherein the mass ratio of the B₂O₃ content to the total content of B₂O₃ and SiO₂ is 0.4-0.900; the mass ratio of the total content of B₂O₃ and SiO₂ to the total content of La₂O₃, Y₂O₃, Gd₂O₃ and Yb₂O₃ is 0.42-0.53; the mass ratio of the Y₂O₃ content to the total content of La₂O₃, Y₂O₃, Gd₂O₃ and Yb₂O₃ is 0.05-0.45; the mass ratio of the Gd₂O₃ content to the total content of La₂O₃, Y₂O₃, Gd₂O₃ and Yb₂O₃ is 0-0.05; and the mass ratio of the Nb₂O₅ content to the total content of Nb₂O₅, TiO₂, Ta₂O₅ and WO₃ is 0.5-1. This oxide glass has a refractive index nd within the range of 1.800-1.850 and an Abbe number νd of 41.5-44.

Description

Glass, glass material for press molding, optical element blank, and optical element

Cross-reference of related applications

This application claims the priority of Japanese Patent Application No. 2015-004542 and Japanese Patent Application No. 2015-004544 filed on January 13, 2015, the entire description of which is hereby specifically incorporated by reference.

The present invention relates to glass, a glass material for press molding, an optical element blank, and an optical element.

Glass having a high refractive index and low dispersion (high refractive index and low dispersion glass) having a refractive index nd in the range of 1.800 to 1.850 and an Abbe number νd in the range of 41.5 to 44 Are described in Patent Documents 1 to 18, for example. The entire description of Patent Documents 1 to 18 is specifically incorporated herein by reference.
Patent Document 1: JP 2002-12443 A Patent Document 2: JP 2003-267748 A Patent Document 3: JP 2005-281124 A Patent Document 4: JP 2005-298262 A Patent Document 5: JP Japanese Patent Application Laid-Open No. 55-121925 Patent Document 6: Japanese Patent Application Laid-Open No. 2009-203083 Patent Document 7: Japanese Patent Application Laid-Open No. 54-090218 Patent Document 8: Japanese Patent Application Laid-Open No. 56-160340 Patent Document 9: Japanese Patent Application Laid-Open No. 2009-167080 Patent Document 10: Japanese Patent Application Laid-Open No. 2009-167081 Patent Document 11: Japanese Patent Application Laid-Open No. 2009-298646 Patent Document 12: Japanese Patent Application Laid-Open No. 2010-111527 Patent Document 13: Japanese Patent Application Laid-Open No. 2010-111528 Patent Document 14: Japanese Patent Application Laid-Open No. 2010-111530 Patent Document 15: Japanese Patent Application Laid-Open No. 57-056344 Document 16: JP 61-163138 JP Patent Document 17: JP 2002-284542 JP Patent Document 18: JP 2007-269584 JP

Glass with a refractive index nd in the range of 1.800 to 1.850 and an Abbe number νd in the range of 41.5 to 44 is useful for correcting chromatic aberration, increasing the functionality of the optical system, and making it more compact. It is a material for an optical element. In the following, the refractive index means the refractive index nd at the d-line (helium wavelength 587.56 nm) unless otherwise specified. The Abbe number means νd unless otherwise specified. As is well known, νd is νd = (nd−1) / (nF−, where nF and nC are the refractive indexes of the F-line (hydrogen wavelength 486.13 nm) and the C-line (hydrogen 656.27 nm), respectively. nC).

In order to further increase the usefulness of the high refractive index and low dispersion glass having a refractive index and an Abbe number in the above ranges, it is desirable to satisfy the following points.

Stable supply is possible. For that purpose, it is desirable to reduce the ratio of Gd and Ta, which are elements having a high rare value, which are in short supply in recent years to the demand in the market, in the glass composition. On the other hand, the glass described in Patent Document 7 contains a large amount of Ta. Further, the glasses described in Patent Documents 8 to 14 and the glass having a refractive index and an Abbe number in the above-described ranges described in Patent Document 17 contain a large amount of Gd.

The proportion of Yb in the glass composition is low. This is due to the following reason.
Yb has absorption in the near infrared region. Therefore, glass containing a large amount of Yb (for example, glass described in Patent Document 16) is used for applications that require high transmittance from the visible range to the near-infrared range, such as surveillance cameras, night vision cameras, and in-vehicle camera lenses. It is not suitable as a material for optical elements. Yb belongs to a heavy rare earth element, has a large atomic weight as a glass component, and increases the specific gravity of the glass. As the specific gravity of the glass increases, the lens becomes heavier. As a result, when such a lens is incorporated into an autofocus camera lens, the power consumption increases and the battery consumption becomes severe. From the above points, it is desirable to reduce the proportion of Yb in the glass composition.

Excellent thermal stability. This is because the glass having low thermal stability has a tendency to devitrify in the process of producing the glass. However, according to the study of the present inventor, for example, the glass described in Patent Document 6 is inferior in thermal stability.

In view of the above, according to one embodiment of the present invention, the refractive index nd is in the range of 1.800 to 1.850, the Abbe number νd is in the range of 41.5 to 44, and the glass composition has Gd, Provided is a glass having a reduced proportion of Ta and Yb and excellent thermal stability.

In one aspect, it is also desirable that the glass further satisfy one or more of the following points.

The increase in the wavelength of the light absorption edge on the short wavelength side of the glass is suppressed. This is due to the following reason.
In order to correct chromatic aberration, a method is known in which a plurality of lenses are made using glass having different optical characteristics, and these lenses are bonded to form a cemented lens. In the process of making a cemented lens, an ultraviolet curable adhesive is usually used to bond the lenses together. Details are as follows. An ultraviolet curable adhesive is applied to the surface where the lenses are bonded together, and the lenses are bonded together. At this time, an extremely thin coating layer of an ultraviolet curable adhesive is usually formed between the lenses. Next, the coating layer is irradiated with ultraviolet rays through a lens to cure the ultraviolet curable adhesive. Therefore, when the transmittance of the ultraviolet ray of the lens is low, a sufficient amount of ultraviolet ray does not reach the coating layer through the lens, resulting in insufficient curing. Or it takes a long time to cure. Similarly, when an ultraviolet curable adhesive is used to adhere and fix a lens to a lens barrel or the like, if the lens has a low ultraviolet transmittance, curing may be insufficient or long. It takes time.
Therefore, in order to obtain a glass having transmittance characteristics suitable for the production of an optical system, it is necessary to increase the transmittance in the ultraviolet region of the glass, in other words, to increase the wavelength of the light absorption edge on the short wavelength side of the glass. It is desirable to suppress this.
However, according to the study of the present inventor, for example, in the glass described in Patent Document 5, the light absorption edge on the short wavelength side of the glass has a longer wavelength, and the transmittance in the ultraviolet region is reduced. In addition, in the glass composition of the conventional high refractive index and low dispersion glass, when trying to maintain both the high refractive index and low dispersion characteristics and the thermal stability while reducing the content of Gd and Ta, There was a tendency that the wavelength of the light absorption edge became longer and the transmittance of ultraviolet rays was greatly reduced.

Suitable for machining. Details are as follows. As a method for obtaining an optical element from glass, in addition to a precision press molding method (see, for example, Patent Documents 1 to 4), an optical element blank is formed from glass, and mechanical processing such as grinding and polishing is performed on the optical element blank. There is also a method of finishing the optical element by performing the above. If the glass is easily broken in such machining, the production yield is lowered. In general, glass for precision press molding has a low glass transition temperature, but a glass having a low glass transition temperature tends to be easily broken during machining. Therefore, in order to obtain a glass suitable for machining, it is desirable that the glass transition temperature is higher than that of the glass for precision press molding.

One embodiment of the present invention is represented by mass%,
The total content of B ₂ O ₃ and SiO ₂ is 15 to 35% by mass,
The total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ is 45 to 65% by mass, provided that the Yb ₂ O ₃ content is 3% by mass or less,
ZrO ₂ content is 3 to 11% by mass,
Ta ₂ O ₅ content is 5% by mass or less,
The mass ratio of B ₂ O ₃ content to the total content of B ₂ O ₃ and SiO ₂ (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) is 0.4-0.900,
Mass ratio of the total content of B ₂ O ₃ and SiO _{2 to} the total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ ((B ₂ O ₃ + SiO ₂ ) / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is 0.42 to 0.53,
Mass ratio of Y ₂ O ₃ content to total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ (Y ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is 0.05 to 0.45,
Mass ratio of Gd ₂ O ₃ content to total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ (Gd ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is 0 to 0.05,
Mass ratio of Nb ₂ O ₅ content to the total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ (Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) 0.5-1
A glass which is an oxide glass having a refractive index nd in the range of 1.800 to 1.850 and an Abbe number νd of 41.5 to 44 (hereinafter referred to as “glass 1”),
About.

Further, one embodiment of the present invention is represented by cation% display.
The total content of B ³⁺ and Si ⁴⁺ is 45 to 65%,
The total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 25-35%, provided that the Yb ³⁺ content is less than 2%;
Zr ⁴⁺ content is ^2-8 %,
Ta ⁵⁺ content is 3% or less,
The cation ratio of the B ³⁺ content to the total content of B ³⁺ and Si ⁴⁺ (B ³⁺ / (B ³⁺ + Si ⁴⁺ )) is 0.65 or more and less than 0.94,
Cation ratio of the total content of B ³⁺ and Si ⁴⁺ to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ ((B ³⁺ + Si ⁴⁺ ) / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) is 1.65 to 2.60,
The cation ratio of Y ³⁺ content to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ (Y ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) is 0 .05 to 0.45,
The cation ratio of Gd ³⁺ content to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ (Gd ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) is 0 ~ 0.05,
Cation ratio of Nb ⁵⁺ content to the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ (Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) is 0 .4 to 1,
A glass which is an oxide glass having a refractive index nd in the range of 1.800 to 1.850 and an Abbe number νd of 41.5 to 44 (hereinafter referred to as “glass 2”),
About.

The glass 1 is a glass having a refractive index nd and an Abbe number νd in the above range, and includes various components including Gd ₂ O ₃ (that is, La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O _3). ) Satisfies the above mass ratio with the Gd ₂ O ₃ content as the numerator and the total content of the various components as the denominator. Therefore, the proportion of Gd in the glass composition is reduced. Furthermore, the Ta ₂ O ₅ content and the Yb ₂ O ₃ content are as described above, and the proportion of Ta and Yb in the glass composition is also reduced. The above glass has a high thermal stability by adjusting the composition satisfying the above-mentioned content, total content and mass ratio in the composition in which the proportion of Gd, Ta and Yb is thus reduced. Can be realized. Further, it is possible to suppress the increase in the wavelength of the light absorption edge on the short wavelength side and to increase the glass transition temperature (Tg) (to increase the glass transition temperature).

The glass 2 is a glass having a refractive index nd and an Abbe number νd in the above range, and is a total content of various components including Gd ³⁺ (ie, La ³⁺ , Y ³⁺ , Gd ³⁺ , Yb ³⁺ ). Within the above range, the cation ratio is satisfied with the Gd ³⁺ content as the numerator and the total content of the various components as the denominator. Therefore, the proportion of Gd in the glass composition is reduced. Further, the Ta ⁵⁺ content and the Yb ³⁺ content are as described above, and the proportion of Ta and Yb in the glass composition is also reduced. The above glass has a high thermal stability by adjusting the composition satisfying the above-mentioned content, total content and cation ratio in the composition in which the proportion of Gd, Ta and Yb is reduced. Can be realized. Further, it is possible to suppress the increase in the wavelength of the light absorption edge on the short wavelength side and to increase the glass transition temperature (Tg) (to increase the glass transition temperature).

According to one embodiment of the present invention, it is possible to provide a glass that has high refractive index and low dispersion characteristics useful in an optical system, can be stably supplied, and is excellent in thermal stability. Furthermore, according to one embodiment of the present invention, it is possible to provide a glass material for press molding, an optical element blank, and an optical element made of the glass.

The spectral transmittance curve in the thickness 10.0mm of the glass A mentioned later is shown. The spectral transmittance curve in the thickness 10.0mm of the glass B mentioned later is shown.

The glass composition in the present invention can be quantified by a method such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). The analysis value obtained by ICP-AES may include a measurement error of about ± 5% of the analysis value, for example. Further, in the present specification and the present invention, that the content of the constituent component is 0% or does not contain or is not introduced means that the constituent component is substantially not contained, and the content of the constituent component is an impurity level. It means less than or equal to.

In the following, regarding the numerical range, a (more) preferable lower limit and a (more) preferable upper limit may be shown in a table. In the table, the numerical value described below is more preferable, and the numerical value described most downward is most preferable. In addition, unless otherwise specified, the (more) preferred lower limit means that it is (more) preferred to be greater than or equal to the stated value, and the (more) preferred upper limit is less than the stated value. (More) It is preferable. The numerical value range can be defined by arbitrarily combining the numerical values described in the (more) preferable lower limit column and the (more) preferable upper limit column in the table.

[Glass]
Glass 1 and glass 2 according to one embodiment of the present invention have the above-described glass composition, have an index of refraction nd of 1.800 to 1.850, and an Abbe number νd of 41.5 to 44. It is a physical glass. Hereinafter, the details of the glass 1 and the glass 2 will be described.

<Glass composition of glass 1>
In this invention, the glass composition of the glass 1 is displayed on an oxide basis. Here, the “oxide-based glass composition” refers to a glass composition obtained by converting all glass raw materials to be decomposed at the time of melting and existing as oxides in the glass. Unless otherwise specified, the glass composition of the glass 1 is expressed on a mass basis (mass%, mass ratio).

B ₂ O ₃ and SiO ₂ are glass network forming components. When the total content of B ₂ O ₃ and SiO ₂ (B ₂ O ₃ + SiO ₂ ) is 15% or more, the thermal stability of the glass is improved, and the crystallization of the glass during production is suppressed. it can. On the other hand, when the total content of B ₂ O ₃ and SiO ₂ is 35% or less, a decrease in the refractive index nd can be suppressed, so that the glass having the above-described optical characteristics, that is, the refractive index nd is 1 It is possible to produce a glass having a range of 800 to 1.850 and an Abbe number νd of 41.5 to 44. Therefore, the total content of B ₂ O ₃ and SiO ₂ in the glass 1 is in the range of 15 to 35%. The preferable lower limit and preferable upper limit of the total content of B ₂ O ₃ and SiO ₂ are as shown in the following table.

The content ratio of each component of B ₂ O ₃ and SiO ₂ , which are glass network forming components, is related to the thermal stability, meltability, formability, chemical durability, weather resistance, machinability, etc. of glass. Influence. B ₂ O ₃ is more excellent in improving the meltability than SiO ₂ , but easily volatilizes during melting. On the other hand, SiO ₂ has a function of improving the chemical durability, weather resistance, and machinability of glass and increasing the viscosity of glass during melting.
In general, in a high refractive index low dispersion glass containing rare earth elements such as B ₂ O ₃ and La ₂ O ₃ , the viscosity of the glass at the time of melting is low. However, when the viscosity of the glass at the time of melting is low, the thermal stability is lowered (it becomes easier to crystallize). Crystallization during glass production is more stable when crystallized than when it is in an amorphous state (amorphous state), and occurs when ions constituting the glass move in the glass and are arranged so as to have a crystal structure. Therefore, by adjusting the content ratio of each component of B ₂ O ₃ and SiO ₂ so as to increase the viscosity at the time of melting, it becomes difficult to arrange the ions so as to have a crystal structure, and the crystal of the glass The glass can be further suppressed and the thermal stability of the glass can be improved.
When the molten glass is poured into the mold and molded, if the viscosity of the molten glass is low, the solidified surface portion of the glass poured into the mold is entangled inside the glass that is still in the molten state, which causes striae. Homogeneity is reduced. The glass having excellent formability corresponds to a glass having a relatively high viscosity when a molten glass is poured into a mold among high refractive index and low dispersion glass containing rare earth elements.
If the mass ratio of the B ₂ O ₃ content to the total content of B ₂ O ₃ and SiO ₂ (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) is 0.900 or less, the viscosity at the time of melting Decline can be suppressed, thereby improving the thermal stability of the glass and suppressing volatilization during melting. Volatilization at the time of melting causes a large variation in glass composition and characteristics. As a result, it becomes difficult to form optically homogeneous glass. Therefore, it is preferable that the mass ratio (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) be 0.900 or less to suppress volatilization at the time of melting from the viewpoint of mass-producing glass with little variation in composition and characteristics. Further, the mass ratio _{_{(B 2 O 3 / (B}} 2 O 3 + SiO 2)) is equal to 0.900 or less, the chemical durability of the glass, weather resistance, it is also possible to suppress a decrease in machinability. On the other hand, in the glass composition described in Patent Document 15 (Japanese Patent Laid-Open No. 57-056344), the B ₂ O ₃ content is 28 to 30% by mass, and the SiO ₂ content is 1 to 3%. It is mass% (refer the claim of patent document 15). The mass ratio (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) calculated from the contents of these components is a large value of 0.903 to 0.968.
On the other hand, if the mass ratio (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) is 0.4 or more, it is possible to prevent unmelted glass raw material at the time of melting, thereby improving the meltability. it can.
From the above points, in the glass 1, the mass ratio (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) is set in the range of 0.4 to 0.900. The preferable lower limit and the preferable upper limit of the mass ratio (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) in the glass 1 are as shown in the following table.

For each of the content of B ₂ O _{3 and} the content of SiO ₂ , preferred lower limit and preferred for improving the thermal stability, meltability, moldability, chemical durability, weather resistance, machining, etc. of the glass The upper limit is shown in the table below.

La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ are components having a function of increasing the refractive index while suppressing a decrease in the Abbe number. These components also have the function of improving the chemical durability and weather resistance of the glass and increasing the glass transition temperature.
Refraction when the total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ ) is 45% or more Since the reduction in the rate can be suppressed, the glass having the above-described optical characteristics can be produced. Furthermore, it is possible to suppress a decrease in chemical durability and weather resistance of the glass. Note that when the glass transition temperature is lowered, the glass is likely to be damaged when mechanically processing the glass (cutting, cutting, grinding, polishing, etc.) (decrease in machinability), but La ₂ O ₃ , Y ₂ When the total content of O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ is 45% or more, a decrease in glass transition temperature can be suppressed, so that machinability can also be improved. On the other hand, if the total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ is 65% or less, the thermal stability of the glass can be increased, and thus glass is produced. It is also possible to suppress crystallization at the time, and to reduce the unmelted raw material when the glass is melted. Therefore, the total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O _{3 in} the glass 1 is in the range of 45 to 65%. The preferable lower limit and the preferable upper limit of the total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ are shown in the following table.

ZrO ₂ is a component having a function of increasing the refractive index, and also has a function of improving the thermal stability of the glass by containing an appropriate amount. ZrO ₂ also has a function of increasing the glass transition temperature and making it difficult for the glass to break during mechanical processing. In order to obtain these effects satisfactorily, the glass 1 has a ZrO ₂ content of 3% or more. On the other hand, if the content of ZrO ₂ is 11% or less, the thermal stability of the glass can be improved, so that crystallization during glass production and generation of unmelted glass during glass melting can be suppressed. . Therefore, the content of ZrO _{2 in} the glass 1 is in the range of 3 to 11%. The preferable lower limit and the preferable upper limit of the ZrO ₂ content are shown in the following table.

As described above, Ta ₂ O ₅ is a component that desirably reduces the proportion of the glass composition from the viewpoint of stable glass supply. Ta ₂ O ₅ is a component having a function of increasing the refractive index, but is also a component that increases the specific gravity of the glass and decreases the meltability. Therefore, the Ta ₂ O ₅ content in the glass 1 is set to 5% or less. The preferable lower limit and the preferable upper limit of the content of Ta ₂ O ₅ are shown in the following table.

In order to improve the thermal stability of the glass and suppress the increase in specific gravity while realizing the above optical characteristics, in the glass 1, La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O _{3 are used.} The mass ratio of the total content of B ₂ O ₃ and SiO _{2 to} the total content of ((B ₂ O ₃ + SiO ₂ ) / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is 0 The range is from 42 to 0.53. If the mass ratio ((B ₂ O ₃ + SiO ₂ ) / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is 0.42 or more, the thermal stability of the glass should be improved. Therefore, devitrification of the glass can be suppressed. Moreover, the increase in specific gravity of glass can also be suppressed. When the specific gravity of the glass increases, an optical element manufactured using the glass becomes heavy. As a result, an optical system incorporating this optical element becomes heavy. For example, if a heavy optical element is incorporated in an autofocus camera, the power consumption when driving the autofocus increases, and the battery is quickly consumed. The ability to suppress an increase in the specific gravity of glass is preferable from the viewpoint of reducing the weight of an optical element produced using the glass and an optical system incorporating the optical element. On the other hand, if the mass ratio ((B ₂ O ₃ + SiO ₂ ) / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is 0.53 or less, the above optical characteristics can be realized. Can do. In addition, the fact that the mass ratio ((B ₂ O ₃ + SiO ₂ ) / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is 0.53 or less indicates the chemical durability of the glass. It is also preferable from the viewpoint of improvement and high glass transition temperature (Tg). The preferred lower limit and preferred upper limit of the mass ratio ((B ₂ O ₃ + SiO ₂ ) / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) are shown in the following table.

Among La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ , Yb ₂ O ₃ is a desirable component for reducing the proportion of the glass composition for the reason described above. . Therefore, in the glass 1, the Yb ₂ O ₃ content is 3% or less. The preferable lower limit and the preferable upper limit of the Yb ₂ O ₃ content are shown in the following table.

Y ₂ O ₃ is a component that functions to improve the thermal stability of the glass without significantly reducing the light transmittance in the near infrared region. Moreover, since the atomic weight is small, it is a preferable component for suppressing an increase in the specific gravity of the glass. However, if the content of Y ₂ O ₃ is too large, the thermal stability of the glass is remarkably lowered and crystallization is likely to occur. Moreover, meltability falls. In order to improve the thermal stability and suppress the increase in specific gravity without significantly reducing the light transmittance in the near-infrared region and to make a glass having the above optical characteristics, in the glass 1, La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ , the mass ratio of Y ₂ O ₃ content to the total content (Y ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is in the range of 0.05 to 0.45. The preferable lower limit and the preferable upper limit of the mass ratio (Y ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) are shown in the following table.

Gd ₂ O ₃ is a component that desirably reduces the proportion of the glass composition for the reasons described above. Gd belongs to heavy rare earth elements like Yb, has a large atomic weight as a glass component, and increases the specific gravity of glass. Also from this point, it is desirable to reduce the proportion of Gd in the glass composition.
In glass 1, the content of Gd ₂ O ₃ depends on the total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ and the Gd ₂ O ₃ content relative to this total content. Determined. In the glass 1, La ₂ O ₃ and Y ₂ O are used in order to stably supply the high refractive index and low dispersion glass having the above-mentioned optical characteristics, and further to make a glass having a small specific gravity as the high refractive index and low dispersion glass. ₃ , the mass ratio of Gd ₂ O ₃ content to the total content of Gd ₂ O ₃ and Yb ₂ O ₃ (Gd ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) Is in the range of 0 to 0.05. The preferable lower limit and preferable upper limit of the mass ratio (Gd ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) are shown in the following table.

La ₂ O ₃ is useful for providing a high refractive index and low dispersion glass without significantly lowering the light transmittance in the near infrared region, improving the thermal stability and suppressing an increase in specific gravity. Is an essential ingredient. Therefore, in the glass 1, the mass ratio of La ₂ O ₃ content to the total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ (La ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is preferably in the range of 0.55 to 0.95. More preferable lower limits and more preferable upper limits of the mass ratio (La ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) are shown in the following table.

The preferable lower limit and preferable upper limit of the content of each component of La ₂ O ₃ , Y ₂ O ₃ and Gd ₂ O ₃ are shown in the following table.

Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ are components that have a function of increasing the refractive index, and also have a function of improving the thermal stability of the glass by containing an appropriate amount. The above optical characteristics are that the total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ ) is in the range of 3 to 15%. It is preferable for further improving the thermal stability of the glass while realizing it. The more preferable lower limit and the more preferable upper limit of the total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ are shown in the following table.

ZnO has a function of promoting melting of a raw material of glass when melting glass, that is, a function of improving meltability. It also has functions of adjusting the refractive index and Abbe number and lowering the glass transition temperature. The value obtained by dividing the ZnO content by the total content of B ₂ O ₃ and SiO ₂ , that is, the mass ratio (ZnO / (B ₂ O ₃ + SiO ₂ )) is 0.04 or more. It is preferable for improvement. On the other hand, it is preferable that the mass ratio (ZnO / (B ₂ O ₃ + SiO ₂ )) is 0.4 or less in order to suppress the decrease in Abbe number (high dispersion) and realize the above optical characteristics. It is preferred also on the thermal stability and improved high glass transition temperature (Tg) of the glass mass ratio _{_{(ZnO / (B 2 O 3}} + SiO 2)) is 0.4 or less. Therefore, the content of ZnO is set to 0.04 to 0.4 times the total content of B ₂ O ₃ and SiO ₂ by mass ratio, that is, mass ratio (ZnO / (B ₂ O ₃ + SiO ₂ )) Is preferably 0.04 to 0.4. More preferable lower limits and more preferable upper limits of the mass ratio (ZnO / (B ₂ O ₃ + SiO ₂ )) are shown in the following table.

In order to improve the meltability, thermal stability, moldability, machinability, etc. of the glass and realize the above optical characteristics, the preferred lower limit and preferred upper limit of the ZnO content are as shown in the following table.

Mass ratio of the total content of B ₂ O ₃ and SiO _{2 to} the total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ ((B ₂ O ₃ + SiO ₂ ) / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) is in the range of 2.65 to 10 in order to increase the ultraviolet transmittance of the glass while suppressing the increase in the coloring degree λ5 described later while realizing the above optical characteristics. It is preferable. In addition, in order to improve the thermal stability of the glass, the mass ratio ((B ₂ O ₃ + SiO ₂ ) / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) should be 2.65 or more. preferable. More preferable lower limits and more preferable upper limits of the mass ratio ((B ₂ O ₃ + SiO ₂ ) / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) are shown in the following table.

Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ serve to improve the thermal stability of the glass by containing appropriate amounts.
Among these components, when the content of TiO ₂ increases, the transmittance of the visible region of the glass tends to decrease, and the coloration of the glass tends to increase.
The action of Ta ₂ O ₅ is as described above.
As for the content of WO ₃ , when the content thereof increases, the transmittance in the visible region of the glass tends to decrease and the coloration of the glass tends to increase, and the specific gravity tends to increase.
On the other hand, Nb ₂ O ₅ has a function of hardly increasing the specific gravity, coloring, and production cost of the glass, increasing the refractive index, and improving the thermal stability of the glass. Therefore, the glass 1, excellent effect of Nb ₂ O _5, in order to utilize the effect, Nb ₂ O _5, by weight of the content of TiO _2, Ta ₂ O ₅ and WO Nb ₂ O ₅ to the total content of ₃ The ratio (Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) is set in the range of 0.5 to 1. The mass ratio (Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) is increased from the viewpoint of reducing the coloring degree λ5 and promoting the curing of the ultraviolet curable adhesive by ultraviolet irradiation. It is preferable. More preferable lower limit and more preferable upper limit of the mass ratio (Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) are shown in the following table.

It is not preferable to introduce Ta ₂ O ₅ into the glass positively for the reasons described above. Therefore, the content of Nb ₂ O ₅ with respect to the total content of Nb ₂ O ₅ , TiO ₂ and WO ₃ excluding Ta ₂ O ₅ among Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ The preferable range of the mass ratio (Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + WO ₃ )) will be described. The mass ratio (Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + WO ₃ )) must be in the range of 0.50 to 1 in order to produce a glass with excellent thermal stability and low coloration. Is preferred. More preferable lower limit and more preferable upper limit of the mass ratio (Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + WO ₃ )) are shown in the following table.

The mass ratio of ZnO content to the total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ (ZnO / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) improves the meltability. From the viewpoint of the above, it is preferably 0.1 or more. In addition, about the glass with low meltability, when the melting temperature of glass is raised or the melting time is lengthened so that there is no unmelted glass raw material, the coloring of the glass tends to increase. This is because, for example, when a glass is melted in a melting crucible made of a noble metal such as platinum, if the melting temperature is increased or the melting time is lengthened, the noble metal constituting the crucible melts into the molten glass, and light absorption by noble metal ions occurs. This is presumably because the coloration of the glass, particularly the value of λ5, increases. On the other hand, if the meltability is to be improved by adjusting the content of other glass components, the thermal stability may be lowered, or it may be difficult to obtain a homogeneous glass having the above optical characteristics. Therefore, in order to improve the meltability of the glass, it is preferable that the mass ratio (ZnO / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) is 0.1 or more from the viewpoint of suppressing the coloring of the glass. . From the viewpoint of further improving the thermal stability of the glass, suppressing the decrease in the glass transition temperature (improvement of machinability), and improving the chemical durability, the mass ratio (ZnO / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) is preferably 3 or less. More preferable lower limits and more preferable upper limits of the mass ratio (ZnO / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) are shown in the following table.

Preferred lower limits and preferred upper limits for each of Nb ₂ O ₅ content, TiO ₂ content, and WO ₃ content are shown in the following table.

The Li ₂ O content is 1% from the viewpoint of further improving the thermal stability of the glass, suppressing the lowering of the glass transition temperature (improvement of machinability by this), and improving the chemical durability and weather resistance. The following is preferable. The preferable lower limit and the more preferable upper limit of the Li ₂ O content are shown in the following table.

Na ₂ O, K ₂ O, Rb ₂ O, and Cs ₂ O all have a function of improving the meltability of the glass. However, when the content thereof increases, the thermal stability and chemical durability of the glass are increased. Property, weather resistance, and machinability tend to decrease. Therefore, it is preferable that the lower limit and the upper limit of each content of Na ₂ O, K ₂ O, Rb ₂ O, and Cs ₂ O are as shown in the following table.

Rb ₂ O and Cs ₂ O are expensive components and are not suitable for general-purpose glass compared to Li ₂ O, Na ₂ O, and K ₂ O. Therefore, in order to improve the meltability of the glass while maintaining the thermal stability, chemical durability, weather resistance, and machinability of the glass, the total content of Li ₂ O, Na ₂ O and K ₂ O The lower limit and the upper limit of (Li ₂ O + Na ₂ O + K ₂ O) are preferably as shown in the following table, respectively.

MgO, CaO, SrO, and BaO are all components that have a function of improving the meltability of glass. However, if the content of these components is increased, the thermal stability of the glass is lowered and a tendency to devitrification is exhibited. Accordingly, the content of each of these components is preferably set to be equal to or higher than the lower limit shown below, and is preferably set to be lower than the upper limit.

Further, in order to further improve the thermal stability of the glass, the total content of MgO, CaO, SrO and BaO (MgO + CaO + SrO + BaO) is preferably not less than the lower limit shown in the following table, and preferably not more than the upper limit. .

Al ₂ O ₃ is a component having a function of improving the chemical durability and weather resistance of glass. However, when the content of Al ₂ O ₃ increases, a refractive index decreasing tendency, a glass thermal stability decreasing tendency, and a meltability decreasing tendency may be observed. Considering the above points, the Al ₂ O ₃ content is preferably not less than the lower limit shown in the following table, and preferably not more than the upper limit.

Ga ₂ O ₃ , In ₂ O ₃ , Sc ₂ O ₃ , and HfO ₂ all have a function of increasing the refractive index nd. However, these components are expensive and are not essential components for obtaining the glass 1. Therefore, the contents of Ga ₂ O ₃ , In ₂ O ₃ , Sc ₂ O ₃ , and HfO ₂ are preferably not less than the lower limit shown in the following table, and preferably not more than the upper limit.

Lu ₂ O ₃ functions to increase the refractive index nd, but is also a component that increases the specific gravity of the glass. It is also an expensive component. From the above points, the preferred lower limit and the preferred upper limit of the content of Lu ₂ O ₃ are as shown in the following table.

GeO ₂ has a function of increasing the refractive index nd, but is a prominent and expensive component among commonly used glass components. From the viewpoint of reducing the production cost of glass, the preferred lower limit and preferred upper limit of the GeO ₂ content are as shown in the following table.

Bi ₂ O ₃ is a component that increases the refractive index nd and decreases the Abbe number. It is also a component that tends to increase the coloration of the glass. The preferred lower and preferred upper limits for the Bi ₂ O ₃ content are as shown in the following table from the viewpoint of producing a glass having the above-mentioned optical properties and little coloration.

In order to obtain the various functions and effects described above satisfactorily, the total content (total content) of the glass components described above is preferably more than 95%, more than 98%. More preferably, it is more preferably more than 99%, and still more preferably more than 99.5%.

Among the glass components described above, P ₂ O ₅ is a component that lowers the refractive index and is also a component that lowers the thermal stability of the glass. May improve stability. The preferred lower limit and preferred upper limit of the P ₂ O ₅ content are as shown in the following table for producing a glass having the above-mentioned optical characteristics and excellent thermal stability.

TeO ₂ is a component that increases the refractive index, but since it is a toxic component, it is preferable to reduce the content of TeO ₂ . The preferable lower limit and preferable upper limit of the TeO ₂ content are as shown in the following table.

In addition, it is also preferable that the content of (more) a preferred lower limit or 0% in each of the above tables is 0%. The same applies to the total content of a plurality of components.

Pb, As, Cd, Tl, Be, and Se each have toxicity. Therefore, it is preferable not to contain these elements, that is, not to introduce these elements into the glass as glass components.
U, Th, and Ra are all radioactive elements. Therefore, it is preferable not to contain these elements, that is, not to introduce these elements into the glass as glass components.
V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Ce increase the coloration of the glass and become a source of fluorescence. The element contained in the glass for optical elements is not preferable. Therefore, it is preferable not to contain these elements, that is, not to introduce these elements into the glass as glass components.

Sb and Sn are arbitrarily addable elements that function as fining agents.
The amount of Sb added is 0 to 0.11% by mass when converted to Sb ₂ O ₃ and the total content of glass components other than Sb ₂ O ₃ is 100% by mass in the oxide-based glass composition. The range is preferably 0.01 to 0.08% by mass, more preferably 0.02 to 0.05% by mass. Here, the “oxide-based glass composition” refers to a glass composition obtained by converting all glass raw materials to be decomposed during melting and existing as oxides in the glass. The Sb ₂ O ₃ content in the glass composition shown in the table described later is also the content calculated by the above method.
The addition amount of Sn should be in the range of 0 to 1.0% by mass when converted to SnO ₂ and the total content of glass components other than SnO ₂ is 100% by mass in the oxide-based glass composition. Preferably, the range is 0 to 0.5% by mass, more preferably 0 to 0.2% by mass, and still more preferably 0% by mass.

<Glass composition of glass 2>
In the present invention, the glass composition of the glass 2 is expressed in terms of cation% with respect to the cation component. As is well known, the cation% is a percentage in which the total content of all cation components contained in the glass is 100%.
The cation component is expressed as B ³⁺ , Si ⁴⁺ , La ³⁺ , for example, but the valence of the cation component (for example, the valence of B ³⁺ is ^{+3 and} the valence of Si ⁴⁺ is +4). The valence of La ³⁺ is a value determined by convention, and is the same as expressing B, Si, La as B ₂ O ₃ , SiO ₂ , La ₂ O ₃ on the oxide basis. . Cation A is expressed as A ^{s +} for a component expressed as A _m O _{n on the} oxide basis (A represents a cation, O represents oxygen, and m and n are stoichiometric integers). Is done. Here, s = 2n / m. Therefore, for example, when analyzing and quantifying the glass composition, it is not necessary to analyze the valence of the cation component. Hereinafter, unless otherwise specified, the content of the cation component and the total content (total content) of the plurality of types of cation components are expressed in cation%. Furthermore, in the cation% display, the ratio of the contents of cation components (including the total content of plural kinds of cation components) is referred to as a cation ratio.

B ³⁺ and Si ⁴⁺ are glass network forming components. When the total content of B ³⁺ and Si ⁴⁺ (B ³⁺ + Si ⁴⁺ ) is 45% or more, the thermal stability of the glass is improved, and the crystallization of the glass during production is suppressed. it can. On the other hand, when the total content of B ³⁺ and Si ⁴⁺ is 65% or less, a decrease in the refractive index can be suppressed, so that the glass having the above-described optical characteristics, that is, the refractive index nd is 1. It is possible to produce a glass having a range of 800 to 1.850 and an Abbe number νd of 41.5 to 44. Therefore, the total content of B ³⁺ and Si ⁴⁺ in the glass 2 is in the range of 45 to 65%. The preferable lower limit and the preferable upper limit of the total content of B ³⁺ and Si ⁴⁺ are as shown in the following table.

The ratio of the content of B ³⁺ and Si ⁴⁺ , which are glass network forming components, is related to the thermal stability, meltability, formability, chemical durability, weather resistance, machinability, etc. of glass. Influence. B ³⁺ is superior to Si ⁴⁺ in improving the meltability, but tends to volatilize during melting. On the other hand, Si ⁴⁺ has a function of improving the chemical durability, weather resistance, and machinability of glass and increasing the viscosity of glass during melting.
Generally, in a high refractive index and low dispersion glass containing rare earth elements such as B ³⁺ and La ³⁺ , the viscosity of the glass at the time of melting is low. However, when the viscosity of the glass at the time of melting is low, the thermal stability is lowered (it becomes easier to crystallize). Crystallization during glass production is more stable when crystallized than when it is in an amorphous state (amorphous state), and occurs when ions constituting the glass move in the glass and are arranged so as to have a crystal structure. Therefore, by adjusting the content ratio of each component of B ³⁺ and Si ⁴⁺ so as to increase the viscosity at the time of melting, it becomes difficult for the above ions to be arranged so as to have a crystal structure. The glass can be further suppressed and the thermal stability of the glass can be improved.
When the molten glass is poured into the mold and molded, if the viscosity of the molten glass is low, the solidified surface portion of the glass poured into the mold is entangled inside the glass that is still in the molten state, which causes striae. Homogeneity is reduced. The glass having excellent formability corresponds to a glass having a relatively high viscosity when a molten glass is poured into a mold among high refractive index and low dispersion glass containing rare earth elements.
If the cation ratio of the content of B ³⁺ to the total content of B ³⁺ and Si ⁴⁺ (B ³⁺ / (B ³⁺ + Si ⁴⁺ )) is less than 0.94, viscosity reduction during melting can be reduced. Thus, the thermal stability of the glass can be improved, and volatilization during melting can be suppressed. Volatilization at the time of melting causes a large variation in glass composition and characteristics. As a result, it becomes difficult to form optically homogeneous glass. Therefore, it is preferable that the cation ratio (B ³⁺ / (B ³⁺ + Si ⁴⁺ )) be less than 0.94 to suppress volatilization at the time of melting from the viewpoint of mass-producing glass with little variation in composition and characteristics. Furthermore, if the cation ratio (B ³⁺ / (B ³⁺ + Si ⁴⁺ )) is less than 0.94, it is possible to suppress the deterioration of the chemical durability, weather resistance, and machinability of the glass. On the other hand, in the glass composition described in Patent Document 15 (Japanese Patent Laid-Open No. 57-056344), the B ₂ O ₃ content is 28 to 30% by mass, and the SiO ₂ content is 1 to 3%. It is mass% (refer the claim of patent document 15). The cation ratio (B ³⁺ / (B ³⁺ + Si ⁴⁺ )) calculated from the contents of these components is as large as 0.942 to 0.981.
On the other hand, if the cation ratio (B ³⁺ / (B ³⁺ + Si ⁴⁺ )) is 0.65 or more, it is possible to prevent melting of the glass raw material at the time of melting, so that the meltability can be improved. .
From the above points, in the glass 2, the cation ratio (B ³⁺ / (B ³⁺ + Si ⁴⁺ )) is set to 0.65 or more and less than 0.94. The preferable lower limit and preferable upper limit of the cation ratio (B ³⁺ / (B ³⁺ + Si ⁴⁺ )) in the glass 2 are as shown in the following table.

For each of the B ³⁺ content and the Si ⁴⁺ content, the lower limit and preferable for improving the thermal stability, meltability, formability, chemical durability, weather resistance, machining, etc. of the glass. The upper limit is shown in the table below.

La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ are components having a function of increasing the refractive index while suppressing a decrease in the Abbe number. These components also have the function of improving the chemical durability and weather resistance of the glass and increasing the glass transition temperature.
If the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ ) is 25% or more, the decrease in refractive index can be suppressed. Therefore, it is possible to produce a glass having the above optical characteristics. Furthermore, it is possible to suppress a decrease in chemical durability and weather resistance of the glass. Note that when the glass transition temperature is lowered, the glass is likely to be damaged when mechanically processing the glass (cutting, cutting, grinding, polishing, etc.) (decrease in machinability), but La ³⁺ , Y ³⁺ When the total content of Gd ³⁺ and Yb ³⁺ is 25% or more, a decrease in glass transition temperature can be suppressed, so that machinability can also be improved. On the other hand, if the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 35% or less, the thermal stability of the glass can be increased. In addition, it is possible to reduce the remaining amount of raw materials when glass is melted or when melting glass. Therefore, in the glass 2, the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is in the range of 25 to 35%. The preferable lower limit and preferable upper limit of the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ are shown in the following table.

Zr ⁴⁺ is a component having a function of increasing the refractive index, and also has a function of improving the thermal stability of the glass by containing an appropriate amount. Zr ⁴⁺ also has a function of increasing the glass transition temperature and making it difficult for the glass to break during mechanical processing. In order to obtain these effects satisfactorily, the glass 2 has a Zr ⁴⁺ content of 2% or more. On the other hand, if the content of Zr ⁴⁺ is 8% or less, the thermal stability of the glass can be improved, so that crystallization during glass production and generation of unmelted residue during glass melting can be suppressed. it can. Therefore, the Zr ⁴⁺ content in the glass 2 is set in the range of 2 to 8%. The preferable lower limit and the preferable upper limit of the Zr ⁴⁺ content are shown in the following table.

As described above, Ta ⁵⁺ is a component that desirably reduces the proportion of the glass composition from the viewpoint of stable glass supply. Ta ⁵⁺ is a component having a function of increasing the refractive index, but is also a component that increases the specific gravity of the glass and decreases the meltability. Therefore, the Ta ⁵⁺ content in the glass 2 is 3% or less. The preferable lower limit and the preferable upper limit of the content of Ta ⁵⁺ are shown in the following table.

In order to improve the thermal stability of the glass and suppress the increase in specific gravity while realizing the above optical characteristics, the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ in the glass 2 The cation ratio ((B ³⁺ + Si ⁴⁺ ) / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) of the total content of B ³⁺ and Si ⁴⁺ with respect to 1.65 to 2.60 Range. If the cation ratio ((B ³⁺ + Si ⁴⁺ ) / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) is 1.65 or more, the thermal stability of the glass can be improved. Glass devitrification can be suppressed. Moreover, the increase in specific gravity of glass can also be suppressed. When the specific gravity of the glass increases, an optical element manufactured using the glass becomes heavy. As a result, an optical system incorporating this optical element becomes heavy. For example, if a heavy optical element is incorporated in an autofocus camera, the power consumption when driving the autofocus increases, and the battery is quickly consumed. The ability to suppress an increase in the specific gravity of glass is preferable from the viewpoint of reducing the weight of an optical element produced using the glass and an optical system incorporating the optical element. On the other hand, if the cation ratio ((B ³⁺ + Si ⁴⁺ ) / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) is 2.60 or less, the above optical characteristics can be realized. Further, the cation ratio ((B ³⁺ + Si ⁴⁺ ) / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) of 2.60 or less means that the chemical durability of the glass is improved and the high glass It is also preferable from the viewpoint of transition temperature (Tg). The preferable lower limit and the preferable upper limit of the cation ratio ((B ³⁺ + Si ⁴⁺ ) / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) are shown in the following table.

Of La ³⁺ , Y ³⁺ , Gd ^3+, and Yb ³⁺ , Yb ³⁺ is a component that desirably reduces the proportion of the glass composition for the reasons described above. Therefore, in the glass 2, the Yb ³⁺ content is less than 2%. The preferable lower limit and the preferable upper limit of the Yb ³⁺ content are shown in the following table.

Y ³⁺ is a component that functions to improve the thermal stability of the glass without significantly reducing the light transmittance in the near infrared region. Moreover, since the atomic weight is small, it is a preferable component for suppressing an increase in the specific gravity of the glass. However, if the content of Y ³⁺ is too large, the thermal stability of the glass is remarkably lowered and crystallization is likely to occur. Moreover, meltability falls. In order to improve the thermal stability and suppress the increase in specific gravity without significantly reducing the light transmittance in the near-infrared region and to make a glass having the above optical properties, in the glass 2, La ³⁺ , The cation ratio of the content of Y ³⁺ to the total content of Y ³⁺ , Gd ³⁺ and Yb ³⁺ (Y ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) is 0.05 The range is to 0.45. The preferable lower limit and the preferable upper limit of the cation ratio (Y ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) are shown in the following table.

Gd ³⁺ is a component that desirably reduces the proportion of the glass composition for the reasons described above. Gd belongs to heavy rare earth elements like Yb, has a large atomic weight as a glass component, and increases the specific gravity of glass. Also from this point, it is desirable to reduce the proportion of Gd in the glass composition.
In the glass 2, the Gd ³⁺ content, La ^3+, Y ^3+, and the total content of Gd ³⁺ and Yb ^3+, determined by Gd ³⁺ content for this total content. In the glass 2, La ³⁺ , Y ³⁺ , Y ³⁺ , Y 2 The cation ratio of the Gd ³⁺ content to the total content of Gd ³⁺ and Yb ³⁺ (Gd ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) is in the range of 0 to 0.05. . The preferable lower limit and the preferable upper limit of the cation ratio (Gd ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) are shown in the following table.

La ³⁺ does not significantly reduce the light transmittance in the near infrared region, improves thermal stability, suppresses an increase in specific gravity, and is useful for providing a high refractive index and low dispersion glass. It is an ingredient. Therefore, in the glass 2, the cation ratio of La ³⁺ content to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ (La ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ^{3) +} )) Is preferably in the range of 0.55 to 0.95. More preferable lower limits and more preferable upper limits of the cation ratio (La ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) are shown in the following table.

The preferable lower limit and the preferable upper limit of the content of each component of La ³⁺ , Y ³⁺ and Gd ³⁺ are shown in the following table.

Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ are components having a function of increasing the refractive index, and also have a function of improving the thermal stability of the glass by containing an appropriate amount. The total optical content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ ) is in the range of 2 to 10%. It is preferable for further improving the thermal stability of the glass while realizing it. The more preferable lower limit and the more preferable upper limit of the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ are shown in the following table.

Zn ²⁺ has a function of accelerating melting of the glass raw material when the glass is melted, that is, a function of improving the meltability. It also has functions of adjusting the refractive index and Abbe number and lowering the glass transition temperature. A value obtained by dividing the Zn ²⁺ content by the total content of B ³⁺ and Si ⁴⁺ , that is, the cation ratio (Zn ²⁺ / (B ³⁺ + Si ⁴⁺ )) is 0.01 or more. It is preferable for improving the meltability. On the other hand, the cation ratio (Zn ²⁺ / (B ³⁺ + Si ⁴⁺ )) is ^preferably 0.22 or less in order to suppress the decrease in Abbe number (high dispersion) and realize the above optical characteristics. . Further, the cation ratio (Zn ²⁺ / (B ³⁺ + Si ⁴⁺ )) is ^preferably 0.22 or less from the viewpoint of improving the thermal stability of the glass and increasing the glass transition temperature (Tg). Accordingly, the Zn ²⁺ content is set to 0.01 to 0.22 times the total cation ratio of B ³⁺ and Si ⁴⁺ , that is, the cation ratio (Zn ²⁺ / (B ^{3 +} + Si ⁴⁺ )) is preferably 0.01 to 0.22. More preferable lower limit and more preferable upper limit of the cation ratio (Zn ²⁺ / (B ³⁺ + Si ⁴⁺ )) are shown in the following table.

From the viewpoint of improving the meltability, thermal stability, moldability, machinability, etc. of the glass and realizing the above optical characteristics, the preferred lower limit and preferred upper limit of the Zn ²⁺ content are as shown in the following table. is there.

Cation ratio of the total content of B ³⁺ and Si ^{4+ to} the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ ((B ³⁺ + Si ⁴⁺ ) / (Nb ⁵⁺ + Ti ^{4 +} + Ta ⁵⁺ + W ⁶⁺ )) is in the range of 9.0 to 32 in order to increase the ultraviolet transmittance of the glass by suppressing the increase in the coloring degree λ5 described later while realizing the above optical characteristics. It is preferable. In addition, the cation ratio ((B ³⁺ + Si ⁴⁺ ) / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) should be 9.0 or more in order to improve the thermal stability of the glass. preferable. More preferable lower limit and more preferable upper limit of the cation ratio ((B ³⁺ + Si ⁴⁺ ) / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) are shown in the following table.

Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ serve to improve the thermal stability of the glass by containing appropriate amounts.
Among these components, when the content of Ti ⁴⁺ increases, the transmittance in the visible region of the glass tends to decrease and the coloration of the glass tends to increase.
The action of Ta ⁵⁺ is as described above.
With regard to W ⁶⁺ , when the content thereof increases, the transmittance in the visible range of the glass tends to decrease and the coloration of the glass tends to increase, and the specific gravity tends to increase.
On the other hand, Nb ⁵⁺ has a function of hardly increasing the specific gravity, coloring, and production cost of the glass, increasing the refractive index, and improving the thermal stability of the glass. Therefore, the glass 2, an excellent effect of Nb ^5+, in order to utilize the effect, Nb ^5+, Ti ^4+, Ta ^5+, and W ⁶⁺ content of the cation ratio of Nb ⁵⁺ to the total content of ( Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) is set in the range of 0.4 to 1. In order to reduce the coloring degree λ5 and promote the curing of the ultraviolet curable adhesive by ultraviolet irradiation, the cation ratio (Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) should be increased. Is preferred. More preferable lower limits and more preferable upper limits of the cation ratio (Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) are shown in the following table.

It is not preferable to introduce Ta ⁵⁺ into glass positively for the reason described above. Therefore, the content of Nb ⁵⁺ with respect to the total content of Nb ⁵⁺ , Ti ⁴⁺ and W ⁶⁺ excluding Ta ⁵⁺ in Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ A preferred range of the cation ratio (Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )) will be described. The cation ratio (Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )) should be in the range of 0.4 to 1 in order to produce a glass with excellent thermal stability and low coloration. Is preferred. More preferable lower limit and more preferable upper limit of the cation ratio (Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )) are shown in the following table.

The cation ratio of Zn ²⁺ content to the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ (Zn ²⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) is From the viewpoint of improving meltability, it is preferably 0.1 or more. In addition, about the glass with low meltability, when the melting temperature of glass is raised or the melting time is lengthened so that there is no unmelted glass raw material, the coloring of the glass tends to increase. This is because, for example, when a glass is melted in a melting crucible made of a noble metal such as platinum, if the melting temperature is increased or the melting time is lengthened, the noble metal constituting the crucible melts into the molten glass, and light absorption by noble metal ions occurs. This is presumably because the coloration of the glass, particularly the value of λ5, increases. On the other hand, if the meltability is to be improved by adjusting the content of other glass components, the thermal stability may be lowered, or it may be difficult to obtain a homogeneous glass having the above optical characteristics. Therefore, in order to improve the meltability of the glass, setting the cation ratio (Zn ²⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) to 0.1 or more can prevent the coloring of the glass. However, it is preferable. From the viewpoint of further improving the thermal stability of the glass, suppressing the lowering of the glass transition temperature (improvement of machinability), and improving the chemical durability, the cation ratio (Zn ²⁺ / (Nb ^{5 +} + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) is preferably 5 or less. More preferable lower limit and more preferable upper limit of the cation ratio (Zn ²⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) are shown in the following table.

Preferred lower limits and preferred upper limits for each of Nb ⁵⁺ content, Ti ⁴⁺ content, and W ⁶⁺ content are shown in the following table.

Li ⁺ content is 3% or less from the viewpoint of further improving the thermal stability of glass, suppressing the decrease in glass transition temperature (improvement of machinability), and improving chemical durability and weather resistance. It is preferable that The preferable lower limit and the more preferable upper limit of the Li ⁺ content are shown in the following table.

Na ⁺ , K ⁺ , Rb ⁺ , and Cs ⁺ all have a function of improving the meltability of the glass. However, as the content of these increases, the thermal stability, chemical durability, and weather resistance of the glass are increased. The machinability tends to decrease. Therefore, it is preferable that the lower limit and the upper limit of each content of Na ⁺ , K ⁺ , Rb ⁺ and Cs ⁺ are as shown in the following table.

Rb ⁺ and Cs ⁺ are expensive components, and are not suitable for general-purpose glass compared to Li ⁺ , Na ⁺ and K ⁺ . Therefore, in order to improve the meltability of the glass while maintaining the thermal stability, chemical durability, weather resistance, and machinability of the glass, the total content of Li ⁺ , Na ⁺ and K ⁺ (Li ⁺ The lower limit and the upper limit of (+ Na ⁺ + K ⁺ ) are each preferably as shown in the following table.

Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ are all components having a function of improving the meltability of glass. However, if the content of these components is increased, the thermal stability of the glass is lowered and a tendency to devitrification is exhibited. Accordingly, the content of each of these components is preferably set to be equal to or higher than the lower limit shown below, and is preferably set to be lower than the upper limit.

In order to further improve the thermal stability of the glass, the total content of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ (Mg ²⁺ + Ca ²⁺ + Sr ²⁺ + Ba ²⁺ ) is: It is preferable to be not less than the lower limit shown in the following table, and preferably not more than the upper limit.

Al ³⁺ is a component having a function of improving the chemical durability and weather resistance of glass. However, when the content of Al ³⁺ increases, a refractive index decreasing tendency, a glass thermal stability decreasing tendency, and a meltability decreasing tendency may be observed. Considering the above points, the Al ³⁺ content is preferably not less than the lower limit shown in the following table, and preferably not more than the upper limit.

Ga ³⁺ , In ³⁺ , Sc ³⁺ , and Hf ⁴⁺ all have a function of increasing the refractive index. However, these components are expensive and are not essential components for obtaining the glass 2. Accordingly, the contents of Ga ³⁺ , In ³⁺ , Sc ³⁺ , and Hf ⁴⁺ are preferably set to the lower limit or more shown in the following table, and preferably set to the upper limit or less.

Lu ³⁺ has a function of increasing the refractive index, but is also a component that increases the specific gravity of the glass. It is also an expensive component. From the above points, the preferred lower limit and the preferred upper limit of the Lu ³⁺ content are as shown in the following table.

Ge ⁴⁺ has a function of increasing the refractive index, but is a prominently expensive component among commonly used glass components. From the viewpoint of reducing the production cost of glass, the preferred lower limit and the preferred upper limit of the Ge ⁴⁺ content are as shown in the following table.

Bi ³⁺ is a component that increases the refractive index and decreases the Abbe number. It is also a component that tends to increase the coloration of the glass. The preferred lower and preferred upper limits for the Bi ³⁺ content are as shown in the following table from the viewpoint of producing a glass having the above optical properties and little coloration.

In order to obtain the various functions and effects described above satisfactorily, the total content (total content) of the cation components described above is preferably more than 95%, more than 98%. More preferably, it is more preferably more than 99%, and still more preferably more than 99.5%.

Among the cationic components other than the cationic components described above, P ⁵⁺ is a component that lowers the refractive index and is a component that lowers the thermal stability of the glass. May improve thermal stability. The preferred lower limit and preferred upper limit of the P ⁵⁺ content are as shown in the following table for producing a glass having the above-described optical properties and excellent thermal stability.

Te ⁴⁺ is a component that increases the refractive index, but since it is a toxic component, it is preferable to reduce the Te ⁴⁺ content. The preferable lower limit and preferable upper limit of the Te ⁴⁺ content are as shown in the following table.

The cationic component has been described above. Next, the anion component will be described.

Since glass 2 is an oxide glass, it contains O ²⁻ as an anion component. The content of O ²⁻ is preferably in the range of 98 to 100 anion%, more preferably in the range of 99 to 100 anion%, still more preferably 99.5 to 100 anion%, It is more preferable that it is% anion.
Examples of the anion component other than O ²⁻ include F ⁻ , Cl ⁻ , Br ⁻ and I ⁻ . However, all of F ⁻ , Cl ⁻ , Br ⁻ and I ⁻ are easily volatilized during melting of the glass. Due to volatilization of these components, the characteristics of the glass fluctuate and the homogeneity of the glass tends to decrease, or the melting equipment tends to be consumed significantly. Therefore, it is preferable to suppress the total content of F ⁻ , Cl ⁻ , Br ⁻ and I ⁻ to an amount obtained by subtracting the content of O ²⁻ from 100 anion%.
As well known, the anion% is a percentage with the total content of all anion components contained in the glass being 100%.

<Glass characteristics>
Next, glass characteristics common to the glass 1 and the glass 2 will be described. The glass described below refers to glass 1 and glass 2.

(Optical properties of glass)
The glass has a refractive index nd in the range of 1.800 to 1.850, and an Abbe number νd of 41.5 to 44.

Glass having a refractive index of 1.800 or more is suitable as a material for optical elements such as lenses having a large refractive power. On the other hand, when the refractive index is higher than 1.850, the Abbe number tends to decrease, the thermal stability of the glass tends to decrease, and the coloring tends to increase. The preferable lower limit and preferable upper limit of the refractive index are shown in the following table.

Glass with an Abbe number of 41.5 or more is effective for correcting chromatic aberration as a material for optical elements. On the other hand, when the Abbe number is larger than 44, the refractive index tends to decrease or the thermal stability of the glass tends to decrease. The preferable lower limit and preferable upper limit of the Abbe number are shown in the following table.

(Partial dispersion characteristics)
From the viewpoint of correcting chromatic aberration, the glass is preferably a glass having a small partial dispersion ratio when the Abbe number is fixed.
Here, the partial dispersion ratios Pg and F are (ng−nF) / (nF−nC) using the refractive indexes ng, nF and nC in the g-line (mercury wavelength 435.84 nm), F-line and C-line. ).
From the viewpoint of providing a glass suitable for high-order chromatic aberration correction, preferred lower limits and preferred upper limits of the partial dispersion ratios Pg, F of the glass are as shown in the following table.

(Glass-transition temperature)
The glass preferably has a glass transition temperature of 640 ° C. or higher from the viewpoint of improving machinability. By setting the glass transition temperature to 640 ° C. or higher, it is possible to make the glass difficult to break when mechanically processing the glass, such as cutting, cutting, grinding, and polishing.
On the other hand, if the glass transition temperature is too high, the glass must be annealed at a high temperature, and the annealing furnace is significantly consumed. Further, when glass is molded, it must be molded at a high temperature, and the consumption of the mold used for molding becomes significant.
From the viewpoint of improving machinability and reducing the burden on the annealing furnace and the mold, more preferable lower limit and preferable upper limit of the glass transition temperature are as shown in the following table.

(Light transmittance of glass)
It is possible to evaluate the light transmittance of glass, specifically, that the increase in the wavelength of the light absorption edge on the short wavelength side is suppressed by the coloring degree λ5. The coloring degree λ5 is a wavelength at which the spectral transmittance (including surface reflection loss) of a glass having a thickness of 10 mm is 5% from the ultraviolet region to the visible region. Λ5 shown in the examples described later is a value measured in a wavelength region of 250 to 700 nm. The spectral transmittance is, for example, more specifically, glass samples having mutually parallel planes optically polished to a thickness of 10.0 ± 0.1 mm, and light from a direction perpendicular to the optically polished surface. Is an intensity ratio Iout / Iin where Iin is the intensity of light incident on the glass sample and Iout is the intensity of light transmitted through the glass sample.
According to the coloring degree λ5, the absorption edge on the short wavelength side of the spectral transmittance can be quantitatively evaluated. As described above, when the lenses are bonded with an ultraviolet curable adhesive to produce a bonded lens, the adhesive is cured by irradiating the adhesive with ultraviolet rays through an optical element. In order to efficiently cure the ultraviolet curable adhesive, it is preferable that the absorption edge on the short wavelength side of the spectral transmittance is in a short wavelength region. As an index for quantitatively evaluating the absorption edge on the short wavelength side, the coloring degree λ5 can be used. The glass can exhibit a λ5 of preferably 335 nm or less, more preferably 332 nm or less, still more preferably 330 nm or less, more preferably 328 nm or less, and even more preferably 326 nm or less, by adjusting the composition described above. As an example, the lower limit of λ5 can be 315 nm, but it is not particularly limited as it is lower.

On the other hand, as an index of the coloring degree of glass, coloring degree λ70 is mentioned. λ70 is a wavelength at which the spectral transmittance measured by the method described for λ5 is 70%. From the viewpoint of making the glass with little coloration, a preferable range of λ70 is 420 nm or less, a more preferable range is 400 nm or less, a more preferable range is 390 nm or less, and a still more preferable range is 380 nm or less. A guideline for the lower limit of λ70 is 340 nm, but the lower limit is preferably not particularly limited.
Further, as an index of the coloring degree of the glass, a coloring degree λ80 is also mentioned. λ80 is a wavelength at which the spectral transmittance measured by the method described for λ5 is 80%. From the viewpoint of making the glass with little coloring, the preferable range of λ80 is 480 nm or less, the more preferable range is 460 nm or less, the more preferable range is 440 nm or less, and the still more preferable range is 420 nm or less. A guideline for the lower limit of λ80 is 350 nm, but the lower limit is preferably not particularly limited.

(Specific gravity of glass)
In the optical element (lens) constituting the optical system, the refractive power is determined by the refractive index of the glass constituting the lens and the curvature of the optical functional surface of the lens (the surface on which light to be controlled is incident and emitted). If the curvature of the optical function surface is increased, the thickness of the lens also increases. As a result, the lens becomes heavy. On the other hand, if a glass having a high refractive index is used, a large refractive power can be obtained without increasing the curvature of the optical function surface.
As described above, if the refractive index can be increased while suppressing an increase in the specific gravity of the glass, it is possible to reduce the weight of the optical element having a certain refractive power.
Regarding the contribution of the refractive index nd to the refractive power, by taking the ratio of the specific gravity d of the glass to the value obtained by subtracting 1 which is the refractive index in vacuum (nd-1) from the refractive index nd of the glass, It can be used as an index for weight reduction. That is, d / (nd-1) is used as an index for reducing the weight of the optical element, and by reducing this value, the lens can be reduced in weight.
Since the glass has a small proportion of Gd, Ta, and Yb that cause an increase in specific gravity, it is possible to reduce the specific gravity while being a high refractive index and low dispersion glass. Therefore, d / (nd-1) of the glass can be, for example, 5.70 or less. However, if d / (nd-1) is excessively decreased, the thermal stability of the glass tends to decrease. Therefore, d / (nd-1) is preferably set to 5.00 or more. More preferable lower limit and more preferable upper limit of d / (nd-1) are shown in the following table.

Furthermore, preferred lower limits and preferred upper limits of the specific gravity d of the glass are shown in the following table. Setting the specific gravity d to be equal to or higher than the upper limit shown in the following table is preferable from the viewpoint of reducing the weight of the optical element made of this glass. Moreover, it is preferable to make specific gravity more than the lower limit shown in the following table | surface in order to improve the thermal stability of glass more.

(Liquid phase temperature)
One indicator of the thermal stability of glass is the liquidus temperature. In order to suppress crystallization and devitrification during glass production, the liquidus temperature LT is preferably 1300 ° C. or lower, more preferably 1250 ° C. or lower, and further preferably 1200 ° C. or lower, 1150 It is still more preferable that it is below ℃. The lower limit of the liquidus temperature LT is 1100 ° C. or more as an example, but is preferably not low and is not particularly limited.

The glass (glass 1 and glass 2) according to one embodiment of the present invention described above is a high refractive index and low dispersion glass and is useful as a glass material for an optical element. Furthermore, it is possible to homogenize the glass and reduce coloring by adjusting the composition described above. In addition, the glass is easy to mold and mechanically work. Therefore, the above glass is suitable as an optical glass.

<Glass manufacturing method>
In order to obtain the desired glass composition, the glass is weighed and prepared as raw materials such as oxides, carbonates, sulfates, nitrates and hydroxides, and mixed well to form a mixed batch. It can be obtained by heating, melting, defoaming and stirring to make a molten glass free of bubbles and molding it. Specifically, it can be made using a known melting method. Although the above glass is a high refractive index low dispersion glass having the above-mentioned optical properties, it is excellent in thermal stability, and therefore can be stably produced using a known melting method and molding method.

[Press-molding glass material, optical element blank, and manufacturing method thereof]
Another aspect of the present invention is:
A glass material for press molding comprising the glass 1 or glass 2 described above;
An optical element blank made of the glass 1 or glass 2 described above,
About.

According to another aspect of the invention,
A method for producing a glass material for press molding comprising the step of forming the glass 1 or glass 2 described above into a glass material for press molding;
A method for producing an optical element blank comprising a step of producing an optical element blank by press-molding the above-described press-molding glass material using a press mold;
A method for producing an optical element blank, comprising the step of forming the glass 1 or glass 2 described above into an optical element blank,
Is also provided.
Since the glass material for press molding and the optical element blank are made of the glass 1 or glass 2 described above, the glass material for press molding and the optical element blank naturally correspond to the glass described above.

The optical element blank approximates the shape of the target optical element, and is polished to the shape of the optical element (surface layer to be removed by polishing) or ground as necessary (to be removed by grinding). An optical element base material to which a surface layer is added. The optical element is finished by polishing the surface of the optical element blank or by grinding and polishing. In one embodiment, an optical element blank can be produced by a method of pressing a molten glass obtained by melting an appropriate amount of the glass (referred to as a direct press method). In another aspect, an optical element blank can be produced by solidifying and further processing a molten glass obtained by melting an appropriate amount of the glass.

In another embodiment, an optical element blank can be produced by producing a press-molding glass material and press-molding the produced press-molding glass material.

Press molding of the glass material for press molding can be performed by a known method of pressing the glass material for press molding in a softened state by heating with a press mold. Both heating and press molding can be performed in the atmosphere. A uniform optical element blank can be obtained by annealing after press molding to reduce strain inside the glass.

The glass material for press molding is subjected to mechanical processing such as cutting, grinding, polishing, etc. in addition to what is called glass gob for press molding used for press molding for optical element blank production as it is. It includes those that are subjected to press molding via As a cutting method, a groove is formed in a portion of the surface of the glass plate to be cut by a method called scribing, and a local pressure is applied to the groove portion from the back surface of the surface on which the groove is formed. There are a method of breaking a plate and a method of cutting a glass plate with a cutting blade. Further, as the grinding and polishing methods, known processing methods such as barrel polishing can be mentioned.

The glass material for press molding is produced, for example, by casting molten glass into a mold to form a glass plate and cutting the glass plate into a plurality of glass pieces, or barrel-polishing these glass pieces. Can do. Alternatively, a glass gob for press molding can be produced by molding an appropriate amount of molten glass. An optical element blank can also be produced by repressing and softening a glass gob for press molding and press forming it. A method of producing an optical element blank by press-molding glass by reheating and softening is called a reheat press method as opposed to a direct press method.

[Optical element and manufacturing method thereof]
Another aspect of the present invention is:
The present invention relates to an optical element made of the glass 1 or the glass 2 described above.
The optical element is manufactured using the glass 1 or the glass 2 described above. In the optical element, one or more coatings such as a multilayer film such as an antireflection film may be formed on the glass surface.
Since the optical element is made of the glass 1 or glass 2 described above, it naturally corresponds to the glass described above. When a coating is formed on the glass surface of the optical element, the glass portion excluding the coating corresponds to the glass described above.

According to one embodiment of the present invention,
A method for producing an optical element comprising a step of producing an optical element by polishing at least the optical element blank described above,
Is also provided.

In the manufacturing method of the optical element, a known method may be applied for grinding and polishing, and an optical element having high internal quality and surface quality can be obtained by sufficiently washing and drying the surface of the optical element after processing. it can. In this way, an optical element made of the glass can be obtained. Examples of the optical element include various lenses such as a spherical lens, an aspheric lens, and a micro lens, a prism, and the like.

The optical element made of the glass 1 or the glass 2 is also suitable as a lens constituting the cemented optical element. Examples of the cemented optical element include those in which lenses are cemented (a cemented lens), and in which lenses and a prism are cemented. For example, in the bonding optical element, the bonding surface of two optical elements to be bonded is precisely processed so that the shape is inverted (for example, spherical polishing), and an ultraviolet curable adhesive is applied to the bonding surface. It can be produced by bonding the bonding surfaces to each other and then irradiating the adhesive on the bonding surface with ultraviolet rays through the optical element to cure the adhesive. In order to produce a bonded optical element in this way, the glass is preferable. A plurality of optical elements to be bonded are manufactured using a plurality of types of glasses having different Abbe numbers, and bonded to each other, whereby an element suitable for correcting chromatic aberration can be obtained.

As a result of the quantitative analysis of the glass composition, the glass component may be expressed on an oxide basis, and the content of the glass component may be displayed in mass%. Thus, the composition represented by mass% on the basis of oxide can be converted into the composition represented by cation% and anion%, for example, by the following method.
For example, an oxide consisting of cations A and oxygen is expressed as A _m O _n. m and n are integers determined stoichiometrically. For example, for B ³⁺ , the oxide standard is B ₂ O ₃ , m = 2 and n = 3, and for Si ⁴⁺ , SiO ₂ , m = 1 and n = 2.
First, the content of A _m O _n in mass percentage divided by the molecular weight of A _m O _n, further multiplied by m. Let this value be P. And P is totaled about all the cation components. When the total value of P is ΣP, the value obtained by standardizing the P value of each cation component so that ΣP is 100% is the content of As ⁺ in the cation% display. Here, s is 2 n / m.
Note that a trace amount of additive, for example, a clarifying agent such as Sb ₂ O ₃ may not be included in ΣP. In that case, the Sb content may be the externally divided content (mass%) converted to Sb ₂ O ₃ as described above. That is, the total content of the glass components excluding the Sb ₂ O ₃ content is 100% by mass, and the Sb ₂ O ₃ content is expressed as a value with respect to 100% by mass.
In addition, the molecular weight may be calculated using, for example, a value obtained by rounding off the fourth decimal place to the third decimal place. Incidentally, for example, the molecular weight of the oxide A _m O _n is the values and atomic weight of oxygen atom amount was multiplied by m elements A is the sum of the n-fold value. The following table shows the molecular weight of some glass components and additives in terms of oxide standards.

Hereinafter, the present invention will be further described based on examples. However, the present invention is not limited to the embodiment shown in the examples.

(Example 1)
In order to obtain a glass having the composition shown in the table below, compounds such as oxide and boric acid were weighed as raw materials and mixed sufficiently to prepare batch raw materials.
This batch raw material was put in a platinum crucible, and the whole crucible was heated to a temperature of 1350 to 1450 ° C., and the glass was melted and refined over 2 to 3 hours. After the molten glass was agitated and homogenized, the molten glass was cast into a preheated mold and allowed to cool to near the glass transition temperature, and then the glass together with the mold was placed in an annealing furnace. Then, annealing was performed for about 1 hour near the glass transition temperature. After annealing, it was allowed to cool to room temperature in an annealing furnace.
Observation of the glass thus prepared revealed no crystal precipitation, bubbles, striae, or unmelted raw material. In this way, highly homogenous glass could be made.
No. in Table 100 (Tables 100-1 to 100-7). Nos. 1-33 are Nos. 1 in Glass 1, Table 101 (Tables 101-1 to 101-6). 1 to 33 are the glass 2.

The glass characteristic of the obtained glass was measured by the method shown below. The measurement results are shown in the following table.
(1) Refractive index nd, nF, nC, ng, Abbe number νd
Refractive indexes nd, nF, nC, and ng were measured for the glass obtained by lowering the temperature at a temperature drop rate of −30 ° C./hour by the refractive index measurement method of the Japan Optical Glass Industry Association standard. The Abbe number νd was calculated using the measured values of the refractive indexes nd, nF, and nC.
(2) Glass transition temperature Tg
Using a differential scanning calorimeter (DSC), the heating rate was 10 ° C./min.
(3) Specific gravity Measured by Archimedes method.
(4) Degree of coloring λ5, λ70, λ80
Using a glass sample having a thickness of 10 ± 0.1 mm having two optically polished planes facing each other, a spectrophotometer is used to inject light having an intensity Iin from the direction perpendicular to the polished surface. The spectral transmittance Iout / Iin is calculated by measuring the intensity Iout of the light that has passed through λ5, the wavelength at which the spectral transmittance is 5% is λ5, the wavelength at which the spectral transmittance is 70% is λ70, and the spectral transmittance is 80 The wavelength at which% is obtained is λ80.
(5) Partial dispersion ratio Pg, F
It calculated from the value of nF, nC, and ng measured by said (1).
(6) Liquidus temperature The glass was placed in a furnace heated to a predetermined temperature and held for 2 hours. After cooling, the inside of the glass was observed with a 100-fold optical microscope, and the liquidus temperature was determined from the presence or absence of crystals.

(Example 2)
Various glasses obtained in Example 1 were used to produce a press-molding glass lump (glass gob). This glass lump was heated and softened in the atmosphere, and press-molded with a press mold to produce a lens blank (optical element blank). The produced lens blank was taken out from the press mold, annealed, and machined including polishing, and spherical lenses made of various glasses produced in Example 1 were produced.

(Example 3)
A desired amount of the molten glass produced in Example 1 was obtained, and while the obtained glass was in a softened state, it was press-molded with a press mold and cooled to produce a lens blank (optical element blank). The produced lens blank was taken out from the press mold, annealed, and machined including polishing, and spherical lenses made of various glasses produced in Example 1 were produced.

Example 4
A glass lump (optical element blank) produced by solidifying the molten glass produced in Example 1 was annealed and subjected to mechanical processing including polishing, and spherical lenses made of various glasses produced in Example 1 were produced.

(Example 5)
The spherical lens produced in Examples 2 to 4 was bonded to a spherical lens made of another type of glass to produce a cemented lens. The cemented surfaces of the spherical lenses produced in Examples 2 to 4 were convex spherical surfaces, and the cemented surfaces of spherical lenses made of other types of optical glass were concave spherical surfaces. The two joint surfaces were produced so that the absolute values of the curvature radii were equal to each other. An ultraviolet curable adhesive for optical element bonding was applied to the bonding surface, and the two lenses were bonded to each other at the bonding surfaces. Thereafter, the adhesive applied to the joint surface was irradiated with ultraviolet rays through the spherical lenses prepared in Examples 2 to 4, and the adhesive was solidified.
A cemented lens was produced as described above. The cemented lens had a sufficiently high bonding strength and a sufficient level of optical performance.

(Examination of the influence of Yb on the transmittance in the near infrared region)
A glass having a composition shown in Table 102 below (hereinafter referred to as “glass A”) and a glass having a composition shown in Table 103 (hereinafter referred to as “glass B”) were respectively melted and molded. And processed into a plate shape. These glass plates have two opposing flat surfaces. The two planes are parallel to each other and are optically polished. The distance between the two planes was 10.0 mm.
Using such a glass plate, the spectral transmittance was measured. The ratio of the intensity of the incident light incident on the glass plate and the intensity of the transmitted light transmitted through the glass plate while scanning the wavelength while vertically incident light on the two opposing planes (transmitted light intensity / incident light Intensity) was obtained, and a spectral transmittance curve of the glass plate was obtained. Spectral transmittance curves of these two types of glass at a thickness of 10.0 mm are shown in FIGS. 1 and 2, respectively (FIG. 1: glass A, FIG. 2: glass B).

Since the glass B does not contain Y ₂ O ₃ in the glass composition expressed by mass%, the mass ratio (Y ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is as described above. The glass is out of range. Further, since glass B does not contain Y ³⁺ in the glass composition represented by cation%, the cation ratio (Y ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) is outside the above range. It is glass. Accordingly, the glass B is does not correspond to the glass 2 in the glass 1 according to one embodiment of the present invention described above, increase or decrease the absorption of near-infrared region according to the magnitude of the Yb content, Y ₂ O ₃ And does not depend on the presence or absence of Y ³⁺ . Therefore, by comparing the glass A and the glass B, it is possible to confirm the influence of Yb on the transmittance in the near infrared region.
As shown in FIG. 1, in a glass A containing 0.1% by mass of Yb ₂ O ₃ in a glass composition represented by mass% and containing 0.04 cation% Yb ^{3+ in} a glass composition represented by cation%, Due to the light absorption of Yb centered around the wavelength of 950 nm, the transmittance in the vicinity thereof is lowered.
Further, as shown in FIG. 2, glass B containing 3.68% by mass of Yb ₂ O ₃ in the glass composition represented by mass% and glass composition containing 2.00% cation Yb ^{3+ in} the glass composition represented by cation%. Then, due to the light absorption of Yb centered around the wavelength of 960 nm, the transmittance in the vicinity thereof is greatly reduced.
As described above, as the Yb content increases, the transmittance in the near infrared region of the glass is greatly reduced. Therefore, as a glass used for applications requiring high transmittance from the visible region to the near infrared region, Yb Glass that contains a lot of is not suitable.

(Comparative Example 1)
An attempt was made to reproduce the glass of Example 4 of Patent Document 6 (Japanese Patent Application Laid-Open No. 2009-203083), but it crystallized during glass production. This is because the glass has a mass ratio (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) of 1 in the glass composition of mass%, and the cation ratio (B ³⁺ / Since (B ³⁺ + Si ⁴⁺ )) is 1, it is considered that the thermal stability is low.

(Comparative Example 2)
The glass of Example 28 (hereinafter referred to as “glass C”) in Patent Document 5 (Japanese Patent Laid-Open No. 55-121925) was reproduced, and λ5 was measured by the above method to be 348 nm.
A spherical lens was produced using glass C. Next, using the convex spherical surface of this spherical lens and the concave spherical surface of a spherical lens made of another type of optical glass as a bonding surface, an ultraviolet curable adhesive for optical element bonding was applied and the same as in Example 5 An attempt was made to produce a cemented lens. However, when the ultraviolet curable adhesive applied to the bonding surface was irradiated with ultraviolet rays through a lens made of glass C, the adhesive could not be sufficiently cured because the ultraviolet transmittance of glass C was low.

(Comparative Example 3)
The glass of Example 7 of Patent Document 17 (Japanese Patent Laid-Open No. 2002-284542) has a mass ratio (Gd ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) of 0. 09 and the mass ratio (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) is 0.92. This _{_{_{glass, La 2 O 3, Y 2}}} O 3, Gd 2 O 3 other than the content of the component constant, by substituting a part or all of Gd ₂ O ₃ to La ₂ O ₃ and Y ₂ O ₃ The change in the thermal stability of the glass was verified.
First, as an oxide-based glass composition, 5.15% by mass of Gd ₂ O ₃ is 0%, and the decrease in Gd ₂ O ₃ content is 5.15% by mass of La ₂ O ₃ . And Y ₂ O ₃ were distributed to La ₂ O ₃ and Y ₂ O ₃ , respectively. Specifically, it is calculated as 5.15% by mass × ((La ₂ O ₃ content / (La ₂ O ₃ content and Y ₂ O ₃ content)) ”. 09 wt% was replaced by Gd ₂ O ₃ to La ₂ O _3, 5.15 wt% × ((amount of Y ₂ O ₃ / (content of La ₂ O ₃ and Y ₂ O ₃ and the total content )) Was replaced by 1.06% by mass from Gd ₂ O ₃ to Y ₂ O _3. This composition is hereinafter referred to as “composition a”.
Next, Gd ₂ O ₃ contained in 5.15% by mass is reduced to 3% by mass, and the decrease in Gd ₂ O ₃ content is 2.15% by mass with the content of La ₂ O ₃ and Y ₂ O. respectively in accordance with the content of ₃ it was allocated to La ₂ O ₃ and Y ₂ O _3. Specifically, 2.15 wt% × ((amount of La ₂ O ₃ / (total content of the content and the Y ₂ O ₃ of La ₂ O ₃₎₎ 1.71 mass% calculated as was replaced from Gd ₂ O ₃ to La ₂ O _3, 5.15 wt% × ((amount of Y ₂ O ₃ / (total content of the content and the Y ₂ O ₃ of La ₂ O ₃₎₎ As a result, 0.44% by mass was substituted from Gd ₂ O ₃ to Y ₂ O _3. This composition is hereinafter referred to as “composition b”.
Table 104 shows the composition, “Composition a”, and “Composition b” of Example 7 of Patent Document 17.

Using 150 g of glass having the compositions a and b, a glass was produced according to the method described in the example of Patent Document 17, and the molten glass was poured into a mold to form a peripheral part of the glass, that is, by contact with the mold. Although no crystal deposition was observed in the rapidly cooled portion, a large number of crystals were deposited in the central portion of the glass, that is, in the portion where the cooling speed was lower than that in the peripheral portion. In addition, when the glass of the Example described previously was produced by the same method, the precipitation of the crystal | crystallization was not recognized not only the periphery part of glass but the whole.
The above results show that in the glass composition where the mass ratio (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) exceeds the previously described range, the thermal stability decreases when the Gd ₂ O ₃ content is decreased. It is thought that it is the result which shows doing.

(Comparative Example 4)
The glass of Example 7 of Patent Document 17 (Japanese Patent Laid-Open No. 2002-284542) has a cation ratio (Gd ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) of 0.08 and a cation ratio ( B ³⁺ / (B ³⁺ + Si ⁴⁺ )) is 0.95. This glass, La ^3+, Y ^3+, and a constant content of components other than Gd ^3+, when replacing a part or all of Gd ³⁺ into La ³⁺ and Y ^3+, glass heat The change of mechanical stability was verified.
First, Gd ³⁺ contained in 2.31 cation% is set to 0%, and the decrease in Gd ³⁺ content is 2.31 cation% according to La ³⁺ content and Y ³⁺ content, respectively. Allocated to La ³⁺ and Y ³⁺ . Specifically, 1.31 cation% calculated as 2.31 cation% × ((La ³⁺ content / (La ³⁺ content and Y ³⁺ content)) ”. Is replaced by Gd ³⁺ to La ³⁺ and calculated as 2.31 cation% × ((Y ³⁺ content / (La ³⁺ content and Y ³⁺ and total content)). 63 cation% was replaced from Gd ³⁺ to Y ³⁺ , and this composition is referred to as “Composition c” below.
Then it reduced the Gd ³⁺ contained 2.31 cations% to 1.5 cation%, the content of La ³⁺ the decrease 0.81 cations% of Gd ³⁺ content and the Y ³⁺ It distributed to ^La3 ⁺ and ^Y3 ⁺ according to content. Specifically, 0.81 cationic% × ((0.59 cations% calculated as content / (La ³⁺ content and total content of Y ³⁺⁾⁾ of La ³⁺ La ³ substituted to ^+, 0.81 cations% × ((Y ³⁺ content / (0.22 cations% calculated as the total amount)) of the content of La ³⁺ and Y ³⁺ Y ³ of ⁺ was replaced to. the composition, referred to as "composition d" in the following.
Table 105 shows the composition, “composition c”, and “composition d” of Example 7 of Patent Document 17.

Using 150 g of glass having compositions c and d, a glass was produced according to the method described in the example of Patent Document 17, and the molten glass was poured into a mold to form a peripheral part of the glass, that is, by contact with the mold. Although no crystal deposition was observed in the rapidly cooled portion, a large number of crystals were deposited in the central portion of the glass, that is, in the portion where the cooling speed was lower than that in the peripheral portion. In addition, when the glass of the Example described previously was produced by the same method, the precipitation of the crystal | crystallization was not recognized not only the periphery part of glass but the whole.
The above results show that the thermal stability decreases when the Gd ³⁺ content is decreased in a glass composition whose cation ratio (B ³⁺ / (B ³⁺ + Si ⁴⁺ )) exceeds the range described above. This is considered to be a result.

Finally, the above aspects will be summarized.

According to one embodiment, the total content of B ₂ O ₃ and SiO ₂ is 15 to 35% by mass, La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O _{3 in} terms of mass%. Total content of 45 to 65% by mass, provided that the Yb ₂ O ₃ content is 3% by mass or less, the ZrO ₂ content is 3 to 11% by mass, the Ta ₂ O ₅ content is 5% by mass or less, The mass ratio of B ₂ O ₃ content to the total content of B ₂ O ₃ and SiO ₂ (B ₂ O ₃ / (B ₂ O ₃ + SiO ₂ )) is 0.4 to 0.900, La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ in total mass ratio of total content of B ₂ O ₃ and SiO ₂ ((B ₂ O ₃ + SiO ₂ ) / (La ₂ O ₃ + Y _{_{_{_{2 O 3 + Gd 2 O 3}}}} + Yb 2 O 3)) is _{_{0.42 ~ 0.53, La 2 O 3}} , Y 2 O 3, Gd 2 O 3 and Y ₂ O ₃ to the total content of Yb ₂ O ₃ Including Mass ratio (Y ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) of 0.05 to 0.45, La ₂ O ₃ , Y ₂ O ₃ , Gd The mass ratio of the Gd ₂ O ₃ content to the total content of ₂ O ₃ and Yb ₂ O ₃ (Gd ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )) is 0 to 0.05, mass ratio of Nb ₂ O ₅ content to total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ (Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) is from 0.5 to 1, the refractive index nd is in the range from 1.800 to 1.850, and the glass is an oxide glass having an Abbe number νd of 41.5 to 44 (Glass 1 ) Can be provided.

According to one embodiment, the total content of B ³⁺ and Si ⁴⁺ is 45 to 65% in terms of cation%, and the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 25 to 35%, however, the Yb ³⁺ content is less than 2%, the Zr ⁴⁺ content is 2 to 8%, the Ta ⁵⁺ content is 3% or less, the total of B ³⁺ and Si ⁴⁺ The cation ratio of the B ³⁺ content to the content (B ³⁺ / (B ³⁺ + Si ⁴⁺ )) is 0.65 or more and less than 0.94, La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ The cation ratio of the total content of B ³⁺ and Si ⁴⁺ to the total content of ((B ³⁺ + Si ⁴⁺ ) / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) is 1.65 to 2.60, cation ratio of Y ³⁺ content to total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ (Y ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ ) Is 0.05 to 0.45, La ³⁺ , Y ³⁺ , Gd ^Cd ratio of Gd ³⁺ content to total content of ³⁺ and Yb ³⁺ (Gd ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ ) is 0 to 0.05, Nb ⁵⁺ , Ti The cation ratio of the Nb ⁵⁺ content to the total content of ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ (Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) is 0.4 to 1 In addition, a glass (glass 2) which is an oxide glass having a refractive index nd in the range of 1.800 to 1.850 and an Abbe number νd of 41.5 to 44 can be provided.

Glass 1 and glass 2 are high-refractive index, low-dispersion optical glasses having a refractive index nd and an Abbe number νd in the above ranges and useful as materials for optical elements constituting an optical system. The glass is a glass in which the contents of Gd, Ta, and Yb are reduced, and can exhibit high thermal stability.

In one aspect, the glass 1 is from the viewpoint of improving the meltability, further improving the thermal stability of the glass, suppressing the decrease in the glass transition temperature (improvement of machinability thereby), and improving the chemical durability. The mass ratio (ZnO / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )) is preferably in the range of 0.1 to 3.

In one aspect, the glass 2 is from the viewpoint of improving the meltability, further improving the thermal stability of the glass, suppressing the decrease in the glass transition temperature (thereby improving the machinability), and improving the chemical durability. The cation ratio (Zn ²⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )) is preferably in the range of 0.1 to 5.

In one embodiment, it is preferable that the glass 1 and the glass 2 have a suppressed light absorption edge on the short wavelength side of the glass so that the coloring degree λ5 is 335 nm or less.

In one aspect, it is preferable that the specific gravity d and the refractive index nd of the glass 1 and the glass 2 satisfy the above-described formula (A) from the viewpoint of enabling the weight reduction of an optical element having a constant refractive power.

In one embodiment, the glass 1 and the glass 2 preferably have a glass transition temperature of 640 ° C. or higher from the viewpoint of improving machinability.

From the glass 1 or glass 2 described above, a glass material for press molding, an optical element blank, and an optical element can be produced. That is, according to another aspect, a glass material for press molding made of glass 1 or glass 2, an optical element blank, and an optical element are provided.

Further, according to another aspect, there is also provided a method for producing a press-molding glass material comprising a step of molding glass 1 or glass 2 into a press-molding glass material.

According to still another aspect, there is also provided an optical element blank manufacturing method including a step of manufacturing an optical element blank by press-molding the press-molding glass material using a press mold.

According to still another aspect, there is also provided an optical element blank manufacturing method including a step of forming glass 1 or glass 2 into an optical element blank.

According to still another aspect, there is also provided an optical element manufacturing method including a step of manufacturing an optical element by polishing at least the optical element blank.

The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
For example, the glass concerning 1 aspect of this invention can be obtained by performing the composition adjustment as described in the specification with respect to the glass composition illustrated above.
Of course, it is possible to arbitrarily combine two or more of the matters described as examples or preferred ranges in the specification.
A certain glass may correspond to both the glass 1 and the glass 2.

The present invention is useful in the field of manufacturing various optical elements.

Claims

In mass% display
The total content of B 2 O 3 and SiO 2 is 15 to 35% by mass,
The total content of La 2 O 3 , Y 2 O 3 , Gd 2 O 3 and Yb 2 O 3 is 45 to 65% by mass, provided that the Yb 2 O 3 content is 3% by mass or less,
ZrO 2 content is 3 to 11% by mass,
Ta 2 O 5 content is 5% by mass or less,
The mass ratio of B 2 O 3 content to the total content of B 2 O 3 and SiO 2 (B 2 O 3 / (B 2 O 3 + SiO 2 )) is 0.4-0.900,
Mass ratio of the total content of B 2 O 3 and SiO 2 to the total content of La 2 O 3 , Y 2 O 3 , Gd 2 O 3 and Yb 2 O 3 ((B 2 O 3 + SiO 2 ) / (La 2 O 3 + Y 2 O 3 + Gd 2 O 3 + Yb 2 O 3 )) is 0.42 to 0.53,
Mass ratio of Y 2 O 3 content to total content of La 2 O 3 , Y 2 O 3 , Gd 2 O 3 and Yb 2 O 3 (Y 2 O 3 / (La 2 O 3 + Y 2 O 3 + Gd 2 O 3 + Yb 2 O 3 )) is 0.05 to 0.45,
Mass ratio of Gd 2 O 3 content to total content of La 2 O 3 , Y 2 O 3 , Gd 2 O 3 and Yb 2 O 3 (Gd 2 O 3 / (La 2 O 3 + Y 2 O 3 + Gd 2 O 3 + Yb 2 O 3 )) is 0 to 0.05,
Mass ratio of Nb 2 O 5 content to the total content of Nb 2 O 5 , TiO 2 , Ta 2 O 5 and WO 3 (Nb 2 O 5 / (Nb 2 O 5 + TiO 2 + Ta 2 O 5 + WO 3 )) 0.5-1
A glass which is an oxide glass having a refractive index nd of 1.800 to 1.850 and an Abbe number νd of 41.5 to 44.
The mass ratio of ZnO content to the total content of Nb 2 O 5 , TiO 2 , Ta 2 O 5 and WO 3 (ZnO / (Nb 2 O 5 + TiO 2 + Ta 2 O 5 + WO 3 )) is 0.1 to 3 The glass according to claim 1, which is in the range of
The glass according to claim 1 or 2, wherein the coloring degree λ5 is 335 nm or less.
Specific gravity d and refractive index nd are expressed by the following formula (A):
d / (nd-1) ≦ 5.70 (A)
The glass according to any one of claims 1 to 3, which satisfies:
The glass according to any one of claims 1 to 4, which has a glass transition temperature of 640 ° C or higher.
A glass material for press molding comprising the glass according to any one of claims 1 to 5.
An optical element blank made of the glass according to any one of claims 1 to 5.
An optical element made of the glass according to any one of claims 1 to 5.