JP6693726B2 - Glass, glass material for press molding, optical element blank, and optical element - Google Patents

Description

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

  By combining a lens made of high-refractive index low-dispersion glass with a lens made of ultra-low-dispersion glass to form a cemented lens, it is possible to make the optical system compact while correcting chromatic aberration. Therefore, the high refractive index and low dispersion glass occupies a very important position as an optical element that constitutes a projection optical system such as an imaging optical system or a projector. Such high refractive index and low dispersion glass is described in, for example, Patent Documents 1 to 20.

Japanese Patent Laid-Open No. 2007-063071 JP, 2007-230835, A JP, 2007-249112, A JP, 2007-261826, A JP, 2003-267748, A JP, 2009-203083, A JP, 2011-230992, A JP 2012-025638 A JP-A-54-090218 JP-A-56-160340 JP 2001-348244 A JP, 2008-001551, A Special table 2013-536791 gazette WO10 / 053214 JP, 2012-180278, A JP, 2012-236754, A JP, 2014-084235, A JP, 2014-062025, A JP, 2014-062026, A JP, 2011-93780, A

  For a glass for an optical element, an optical characteristic map (also called an Abbe chart) is widely used to show a distribution of optical characteristics. In the optical characteristic map, the horizontal axis represents the Abbe number νd and the vertical axis represents the refractive index nd. The Abbe number νd increases from the right side to the left side of the horizontal axis, and the refractive index increases from the lower side to the upper side of the vertical axis. It is created to increase accordingly. In the following, the refractive index and the Abbe number refer to the refractive index nd for the d line of helium (wavelength 587.56 nm) and the Abbe number νd for the d line of helium (wavelength 587.56 nm), unless otherwise specified.

In the optical characteristic map, the optical characteristics of the high-refractive-index low-dispersion glass (high nd high νd glass) show that the refractive index increases as the Abbe number decreases, and the refractive index decreases as the Abbe number increases. The distribution is generally shown. This is considered to be due to the following reasons.
Many high refractive index and low dispersion glasses contain rare earth oxides such as boron oxide and lanthanum oxide. In such a glass, in order to increase the refractive index without reducing the Abbe number, the content of rare earth oxide should be increased. However, when the content of the rare earth oxide is increased in the conventional high-refractive-index, low-dispersion glass, the thermal stability of the glass decreases and the glass tends to devitrify in the process of manufacturing the glass. Therefore, in the conventional high-refractive-index low-dispersion glass, it was difficult to increase both the Abbe number and the refractive index while suppressing devitrification of the glass for use as an optical element material. This is considered to be the reason why the conventional high-refractive-index, low-dispersion glass exhibits the above distribution in the optical characteristic map.

On the other hand, in the design of optical systems, glass with a high refractive index and a large Abbe number (low dispersion) is an extremely effective material for optical elements in order to correct chromatic aberration, improve the functionality of the optical system, and make it compact. is there. Therefore, it is very significant to set a straight-up straight line on the optical characteristic map and provide glass with a higher refractive index on this straight line and on the straight line (positioned on the left side of the straight line on the map). Is very large.
From the above points, a glass having an Abbe number νd of 39.5 to 41.5, and a refractive index nd of the Abbe number of 2.0927-0.0058 × νd or more, that is, nd ≧ 2 Glass satisfying the relationship of 0.0927-0.0058 × νd is a high-refractive-index, low-dispersion glass useful in an optical system.

On the other hand, among the glasses described in Patent Documents 1 to 20, the Abbe number νd is in the range of 39.5 to 41.5 and satisfies the relationship of nd ≧ 2.0927−0.0058 × νd. The high-refractive-index, low-dispersion glass contains one of Gd and Ta. However, although Gd and Ta are both rare elements, the demand in various industrial fields has been increasing in recent years, and thus the supply is insufficient with respect to the demand in the market. Therefore, from the viewpoint of stable supply of high-refractive-index, low-dispersion glass, it is desirable to reduce the content of Gd and Ta in the high-refractive-index, low-dispersion glass.
On the other hand, in the conventional glass composition of high refractive index and low dispersion glass, when it is attempted to maintain both optical characteristics and thermal stability while reducing the contents of Gd and Ta, the light absorption edge on the short wavelength side of the glass is There is a tendency that the wavelength becomes longer and the ultraviolet ray transmittance is greatly reduced.
By the way, in order to correct chromatic aberration, a plurality of lenses are made by using glasses having different optical characteristics, and a method for making these cemented lenses by bonding these lenses is known. An ultraviolet curable adhesive is usually used to bond the lenses together. Details are as follows. An ultraviolet curable adhesive is applied to the surfaces where the lenses are stuck together, and the lenses are stuck together. At this time, an extremely thin coating layer of the ultraviolet curable adhesive is usually formed between the lenses. Then, the coating layer is irradiated with ultraviolet rays through a lens to cure the ultraviolet curable adhesive. Therefore, when the ultraviolet ray transmittance of the lens is low, a sufficient amount of ultraviolet ray does not reach the coating layer through the lens, and the curing becomes insufficient. Alternatively, it takes a long time to cure.
Also, when a lens is bonded and fixed to a lens barrel using an ultraviolet curable adhesive, similarly, if the ultraviolet transmittance of the lens is low, the curing will be insufficient or the curing will take a long time. It takes time.
Therefore, in order to obtain a glass having a transmittance characteristic suitable for producing an optical system, it is desirable to suppress the lengthening of the light absorption edge on the short wavelength side of the glass.

  According to one embodiment of the present invention, the Abbe number νd is 39.5 to 41.5, the relationship of nd ≧ 2.0927−0.0058 × νd is satisfied, stable supply is possible, and an optical system can be manufactured. The purpose is to provide a suitable glass.

One aspect of the present invention, in mass% display,
The total content of B ₂ O ₃ and SiO ₂ is 17.5 to 35%,
_{La 2 O 3, Y 2 O} 3, the total content of _Gd 2 _{O 3} and _Yb 2 _{O 3} 45-70%
The total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ is ₃ to 16%,
ZrO ₂ content is 2 to 10%,
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 0.2 to 0.5,
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 2.8 or less,
Mass ratio of ZnO content to total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ {ZnO / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )} Is less than 0.10.
Mass ratio of La 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 {La ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )} is 0.55 to 0.98,
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 0.02 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 0.10 or less,
The mass ratio of the Nb ₂ O ₅ content to the total content of Nb ₂ O ₅ , TiO ₂ and WO ₃ {Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + WO ₃ )} is 0.81 or more,
Mass ratio of Ta ₂ O ₅ content to total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ {Ta ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} Is 0.3 or less,
And the Abbe number νd is in the range of 39.5 to 41.5, and the refractive index nd is the following Equation (1) with respect to the Abbe number νd:
nd ≧ 2.0927−0.0058 × νd (1)
A glass that is an oxide glass that satisfies the
Regarding

The above glass is a glass that satisfies the relationship of nd ≧ 2.0927−0.0058 × νd in the range where the Abbe number νd is 39.5 to 41.5, and various components containing Gd ₂ O ₃ (that is, La _{2 O 3, Y 2 O 3,} Gd 2 O 3, Yb 2 O 3) total content and various components comprising of _Ta 2 _{O 5 which has} a (i.e. _{Nb 2 O 5, TiO 2,} Ta 2 O 5, WO 3) Within the above range, the total content satisfies the above mass ratio including Gd ₂ O ₃ and Ta ₂ O ₅ in the denominator or numerator. Therefore, the ratio of Gd and Ta in the glass composition is reduced. The glass has high thermal stability (devitrification) due to composition adjustment satisfying the above-mentioned content, total content and mass ratio in the composition satisfying such total content and mass ratio. It is possible to achieve both the realization of (hard property) and the suppression of lengthening of the light absorption edge on the short wavelength side.

  According to one embodiment of the present invention, it is possible to provide a glass that has useful optical characteristics in an optical system, can be stably supplied, and has a transmittance characteristic suitable for producing an optical system. Further, according to one aspect of the present invention, it is possible to provide a press-molding glass material made of the above glass, an optical element blank, and an optical element.

FIG. 1 is a photograph of the glass evaluated in Comparative Example 6.

[Glass]
The glass according to one embodiment of the present invention has the above glass composition, has an Abbe number νd in the range of 39.5 to 41.5, and has a refractive index nd of the above formula (1) with respect to the Abbe number νd. It is an oxide glass to fill. Hereinafter, the details of the glass will be described.

In the present invention, the glass composition of glass is expressed on an oxide basis. Here, the "glass composition based on oxides" refers to a glass composition obtained by converting the glass raw materials to be all decomposed during melting and existing as oxides in the glass. Unless otherwise specified, glass compositions are expressed on a mass basis (mass%, mass ratio).
The glass composition in the present invention can be quantified by a method such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). The analytical value obtained by ICP-AES may include a measurement error of about ± 5% of the analytical value. Further, in the present specification and the present invention, the content of the constituent component being 0%, or not containing or not introducing means that the constituent component is substantially not contained, and the content of the constituent component is the impurity level. It means less than or equal to the degree.

  In the following, regarding the numerical range, a (more) preferred lower limit and a (more) preferred upper limit may be shown and described in the table. In the table, the numerical value described in the lower part is preferable, and the numerical value described in the lowermost part is most preferable. Further, unless otherwise specified, the (more) preferable lower limit means (more) preferably not less than the stated value, and the (more) preferable upper limit means not more than the stated value. (More) preferred. The numerical range described in the (more) preferable lower limit column and the numerical value described in the (more) preferable upper limit column in the table can be arbitrarily combined to define the numerical range.

<Glass composition>
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 17.5% or more, the thermal stability of the glass is improved and the crystallization of the glass during production is suppressed. be able to. On the other hand, when the total content of B ₂ O ₃ and SiO ₂ is 35% or less, the decrease in the refractive index nd can be suppressed, and thus the glass having the above-described optical characteristics can be manufactured. Therefore, the total content of B ₂ O ₃ and SiO ₂ in the above glass is in the range of 17.5 to 35%. The preferable lower limit and the preferable upper limit of the total content of B ₂ O ₃ and SiO ₂ are as shown in the following table.

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 the decrease of the Abbe number νd. Further, these components also have the functions of improving the chemical durability and weather resistance of glass and increasing the glass transition temperature.
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, the refraction is decreased. Since the decrease in the rate nd can be suppressed, the glass having the above-mentioned optical characteristics can be manufactured. Further, it is possible to suppress deterioration of chemical durability and weather resistance of the glass. It should be noted that when the glass transition temperature is lowered, the glass is apt to be damaged when mechanically working (cutting, cutting, grinding, polishing, etc.) (decrease in machinability), but La ₂ O ₃ , Y _{2 is used.} When the total content of O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ is 45% or more, the glass transition temperature can be prevented from lowering, so that the machinability can be improved. On the other hand, if the total content of each component of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ is 70% or less, the thermal stability of the glass can be increased, It is also possible to suppress crystallization at the time of producing glass and reduce unmelted residue of the raw material at the time of melting glass. It is also possible to suppress an increase in specific gravity. Therefore, in the above glass, the total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ is in the range of 45 to 70%. 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.

Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ are components having a function of increasing the refractive index, and by containing an appropriate amount, they also have a function of improving the thermal stability of the glass. When 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 3% or more, the thermal stability is maintained while maintaining the above. The optical characteristics described above can be realized. On the other hand, when the total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ is 16% or less, it is possible to suppress the decrease in thermal stability and the decrease in Abbe number νd. Further, it is also possible to suppress an increase in coloring degree λ5, which will be described later, and increase the ultraviolet transmittance of the glass. Thus, in the _glass, the total content of _{Nb 2 O 5, TiO 2,} Ta 2 O 5 and WO _3, the range 3 to 16%. The preferable lower limit and the 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.

ZrO ₂ is a component that has a function of increasing the refractive index, and when it is contained in an appropriate amount, it also has a function of improving the thermal stability of glass. ZrO ₂ also has a function of increasing the glass transition temperature so that the glass is less likely to be damaged during mechanical processing. In order to obtain these effects well, the content of ZrO _{2 in} the above glass is set to 2% or more. On the other hand, if the content of ZrO ₂ is 10% or less, the thermal stability of the glass can be improved, and therefore crystallization during glass production and the occurrence of unmelted residue during glass melting can be suppressed. .. Therefore, the ZrO ₂ content in the above glass is in the range of 2 to 10%. The preferable lower limit and the preferable upper limit of the ZrO ₂ content are shown in the following table.

In order to improve the thermal stability of glass and to realize the optical characteristics in which the Abbe number νd is 39.5 to 41.5 and the refractive index nd and the Abbe number νd satisfy the relationship of the above formula (1), In the glass, the 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 ) _/ a _{(La 2 O 3 + Y 2} O 3 + Gd 2 O 3 + Yb 2 O 3)} to 0.2 to 0.5. 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 0.2 or more, the thermal stability of the glass should be improved. Therefore, devitrification of the glass can be suppressed. It is also possible to suppress an increase in the specific gravity of the glass. When the specific gravity of glass increases, the optical element manufactured using this glass becomes heavy. As a result, the optical system incorporating this optical element becomes heavy. For example, if a heavy optical element is incorporated in an autofocus type camera, power consumption for 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 reduction of an optical element manufactured using this glass and an optical system incorporating this 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 0.5 or less, the above optical characteristics should be realized. You can The preferable lower limit and the preferable 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.

In order to suppress the decrease in the refractive index nd and realize the above-mentioned optical characteristics while improving the thermal stability of the glass, the above-mentioned glass contains Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ in total. The mass ratio of the total content of B ₂ O ₃ and SiO ₂ to the content {(B ₂ O ₃ + SiO ₂ ) / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} is set to 2.8 or less. ..
In order to improve the thermal stability of the glass while suppressing the decrease in Abbe number νd, the mass ratio {(B ₂ O ₃ + SiO ₂ ) / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} is set to It is preferably 1.2 or more. Further, by setting the mass ratio {(B ₂ O ₃ + SiO ₂ ) / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} to 1.2 or more, the length of the light absorption edge on the short wavelength side of the glass can be increased. It is preferable to further suppress the wavelength shift. As a result, when the glass lens is bonded using the ultraviolet curable adhesive, the ultraviolet rays are more likely to reach the coating layer of the adhesive through the lens. This makes it easier for the adhesive to be cured by irradiation with ultraviolet rays.
The more preferable lower limit and the preferable upper limit 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.

In order to improve the thermal stability of the glass and realize the above-mentioned optical properties, the above-mentioned glass contains ZnO in the total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O _3. The mass ratio of amounts {ZnO / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )} is less than 0.10. Mass ratio preferable lower limit and a preferred upper limit of the _{{ZnO / (La 2 O 3} + Y 2 O 3 + Gd 2 O 3 + Yb 2 O 3)}, shown in the following Table.

Among the rare earth elements La, Y, Gd and Yb, Gd belongs to the heavy rare earth elements and is a component required to reduce the content in the glass from the viewpoint of stable glass supply. Further, Gd has a large atomic weight and is a component that increases the specific gravity of glass.
Yb also belongs to heavy rare earth elements and has a large atomic weight. Further, Yb has absorption in the near infrared region. On the other hand, it is desirable that interchangeable lenses for single-lens reflex cameras and lenses for surveillance cameras have high light transmittance in the near infrared region. Therefore, it is desirable to reduce the content of Yb in order to make the glass useful for producing these lenses.
On the other hand, La and Y do not adversely affect the light transmittance in the near infrared region, and by distributing an appropriate amount with respect to the total content of rare earth elements, the thermal stability is improved and the specific gravity is improved. Is a component which is useful in suppressing the increase in the refractive index and providing a high refractive index and low dispersion glass.

Therefore, in the above glass, for La, the mass ratio of the 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 the _{2 O 3 + Y 2 O 3} + Gd 2 O 3 + Yb 2 O 3)}, in the range of 0.55 to 0.98. The preferable lower limit and the preferable upper limit 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.

As for Y, the mass ratio of the content of Y ₂ O ₃ to the 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)} to the range of 0.02 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.

As described above, Gd is a component whose content in glass should be reduced from the viewpoint of stable glass supply. In the above glass, the Gd content is determined by 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 with respect to the total content. In the glass, a high refractive index and low dispersion glass having optical properties described above from the stable _{supply, La 2 O 3, Y 2} O 3, Gd 2 O 3 and _Gd 2 to the total content of _Yb 2 _{O 3} O The mass ratio of the content of ₃ {Gd ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )} is set to 0.10. It should be noted that satisfying the above mass ratio can also contribute to lowering the specific gravity of glass. The preferable lower limit and the 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 , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ total content, and La ₂ O ₃ content, Y ₂ O ₃ content, Gd ₂ O ₃ content with respect to this total content. The mass ratio of is as described above. The preferable lower limit and the preferable upper limit of the content of each component of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ are shown in the following table. The Y ₂ O ₃ content is preferably the lower limit shown in the following table from the viewpoint of improving the thermal stability and meltability of the glass.

Nb, Ti, Ta and W function to increase the refractive index and improve the thermal stability of glass when they are contained in appropriate amounts. However, when the content of Ti or W is increased, the absorption edge on the short wavelength side in the visible region shifts to the long wavelength side. As a result, the light absorption edge on the short wavelength side of the glass has a long wavelength. Therefore, in the above optical glass, Nb, Ti, Ta, and W are taken into consideration in order to improve the thermal stability of the glass and suppress the lengthening of the light absorption edge on the short wavelength side of the glass. In addition, the ratio of these contents is determined. The details are as follows.
Nb has a function of increasing the refractive index nd and improving the thermal stability of the glass without increasing the specific gravity, coloring and manufacturing cost of the glass. In addition, Nb is also a component that makes it difficult for the absorption edge of the glass on the short wavelength side to have a longer wavelength than that of Ti and W. The absorption edge on the short wavelength side of glass can be represented by an index called λ5, as is well known. That is, Nb is a component that does not easily increase λ5 as compared with Ti and W. Details of λ5 will be described later.
On the other hand, as the Ti content increases, λ5 increases. Further, the transmittance of the glass in the visible region tends to decrease, and the coloring of the glass tends to increase.
Ta has a function of increasing the refractive index, and is a component that makes it difficult to make the absorption edge on the short wavelength side of the glass have a longer wavelength than Nb, Ti, and W, but is an extremely expensive component. Therefore, it is not preferable to positively use Ta ⁵⁺ from the viewpoint of stable glass supply. Further, when the content of Ta is high, the raw material is likely to remain unmelted when the glass is melted. Also, the specific gravity of the glass increases.
Regarding W, λ5 increases as its content increases. In addition, the transmittance in the visible region decreases and the specific gravity increases.

As described above, Ta is a component whose content should be reduced. Therefore, it is not preferable to positively use Ta. In order to improve the thermal stability and suppress the lengthening of the light absorption edge on the short wavelength side (preferably reduce λ5), in the above glass, Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ , the content weight ratio of _Nb 2 _{O 5} to the total content of _Nb 2 _O 5, TiO ₂ and WO ₃ excluding the _Ta 2 _{O 5} in the _{WO 3 {Nb 2 O 5 /} (Nb 2 O 5 + TiO 2 + WO ₃ )} is set to 0.81 or more. The preferable lower limit and the 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.

Regarding Ta, the total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ is used in order to improve the thermal stability of the glass, reduce the refractive index, and reduce the amount of Ta used. The mass ratio of the content of Ta ₂ O ₅ with respect to {Ta ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} is set to 0.3 or less. The preferable lower limit and more preferable upper limit of the mass ratio {Ta ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} are shown in the following table.

Regarding Nb, while reducing the contents of Gd and Ta in order to enable stable supply of glass, and desirably reducing the contents of Yb together with Gd and Ta, the light absorption edge of the short wavelength side In order to provide a high-refractive-index, low-dispersion glass with excellent long-wavelength suppression (preferably λ5 is small) and excellent thermal stability, Nb, Ti, Ta, and W are taken into consideration, and then Nb Mass ratio of the content of Nb ₂ O ₅ to the total content of 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 preferably 0.5 or more. Further, in order to further suppress the lengthening of the light absorption edge on the shorter wavelength side, it is preferable to increase the mass ratio {Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )}. .. The more preferable lower limit and the 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.

Furthermore, from the viewpoint of further suppressing the increase in the wavelength of the light absorption edge on the short wavelength side (preferably suppressing the increase of λ5) and accelerating the curing of the ultraviolet curable adhesive by ultraviolet irradiation, Nb ₂ O ₅ , The mass ratio of the TiO ₂ content to the total content of TiO ₂ , Ta ₂ O ₅ and WO ₃ {TiO ₂ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} may be 0.40 or less. preferable. The preferable lower limit and the more preferable upper limit of the mass ratio {TiO ₂ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} are shown in the following table.

Similarly, from the viewpoint of further suppressing the lengthening of the light absorption edge on the short wavelength side (preferably suppressing the increase of λ5), the total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ is contained. The mass ratio of WO ₃ content to the amount {WO ₃ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} is preferably 0.3 or less. The preferable lower limit and more preferable upper limit of the mass ratio {WO ₃ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} are shown in the following table.

Among Nb, Ti, and W, Ti has a strong tendency to increase the coloring of glass, and has a relatively strong effect of increasing λ5. In suppressing the increase of λ5, the mass ratio of the content of TiO _{2 to} the total content of Nb ₂ O ₅ , TiO ₂ and WO ₃ (Nb ₂ O ₅ + TiO ₂ + WO ₃ ) {TiO ₂ / (Nb ₂ O ₅ It is preferable to set the upper limit of + TiO ₂ + WO ₃ )} to the preferable upper limit values shown in the following table. The mass ratio {TiO ₂ / (Nb ₂ O ₅ + TiO ₂ + WO ₃ )} can be zero.

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) is maintained in order to suppress the decrease of the Abbe number νd while maintaining the thermal stability of the glass. Mass ratio of 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 ) to ₅ + WO ₃ ). The lower limit of (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ ) / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} may be set to a preferable lower limit value shown in the following table. preferable.
On the other hand, in order to maintain the thermal stability of the glass while suppressing the decrease in the refractive index, the mass ratio {(La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ ) / (Nb ₂ O ₅ + TiO ₂ ). The upper limit of ₂ + Ta ₂ O ₅ + WO ₃ )} is preferably set to the preferable upper limit values shown in the following table.

  The glass composition of the above glass will be further described below.

The total content of B ₂ O ₃ and SiO ₂ , which are the glass network-forming components, is as described above. Regarding B ₂ O ₃ and SiO ₂ , B ₂ O ₃ has a better function of improving the meltability than SiO _2, but is easily volatilized 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.
Generally, in a high-refractive-index, low-dispersion glass containing rare earth elements such as B and La, the viscosity of the glass at the time of melting is low. However, if the viscosity of the glass during melting is low, it tends to crystallize. Crystallization during glass production is more stable when crystallized than 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 that the viscosity at the time of melting becomes high, it becomes difficult to arrange the above ions so as to have a crystal structure, and the glass crystal Further, the devitrification resistance of glass can be further improved.
From the above viewpoints, the preferable lower limit and the preferable upper limit of 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 )} are It is as shown in the table below. It is preferable that the content is not less than the lower limit shown in the following table from the viewpoint of improving the glass meltability. Further, it is preferable that the content is not more than the upper limit shown in the following table in order to increase the viscosity of the glass at the time of melting. Further, the content of less than or equal to the upper limit shown in the following table reduces fluctuations in the glass composition due to volatilization at the time of melting and fluctuations in optical characteristics, and also in terms of chemical durability, weather resistance and machinability of the glass. It is also preferable from the viewpoint of one or more improvements.

Regarding each of the B ₂ O ₃ content and the SiO ₂ content, a preferable lower limit and a preferable upper limit from the viewpoint of improving devitrification resistance, meltability, moldability, chemical durability, weather resistance, machinability, etc. of glass. Is shown in the table below.

ZnO has a function of accelerating the melting of the glass raw material when melting the glass, that is, a function of improving the meltability. It also has a function of adjusting the refractive index nd and the Abbe number νd, and lowering the glass transition temperature. A value obtained by dividing the content of ZnO by the total content of B ₂ O ₃ and SiO ₂ , that is, the mass ratio {ZnO / (B ₂ O ₃ + SiO ₂ )}, suppresses the decrease of the Abbe number νd, From the viewpoint of improving the thermal stability and suppressing the decrease in the glass transition temperature (improving the machinability by this), it is preferably 0.30 or less. Since ZnO is an optional component which may or may not be contained in the above glass, it is preferable that the mass ratio {ZnO / (B ₂ O ₃ + SiO ₂ )} be 0 or more. In order to improve the property and to easily produce a homogeneous glass, it is more preferable that Zn is contained and the mass ratio {ZnO / (B ₂ O ₃ + SiO ₂ )} exceeds 0. The more preferable lower limit and the more preferable upper limit of the mass ratio {ZnO / (B ₂ O ₃ + SiO ₂ )} are shown in the following table.

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

From the viewpoint of further improving the thermal stability of the glass, suppressing the decrease of the glass transition temperature (improving the machinability by this), and improving the chemical durability, Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and The mass ratio of ZnO content to the total content of WO ₃ {ZnO / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} is preferably less than 0.61. On the other hand, since ZnO is an optional component, the lower limit of the mass ratio {ZnO / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} is preferably 0, but the meltability is improved and the light absorption edge on the short wavelength side is From the viewpoint of further suppressing the increase in the wavelength of (1) (preferably further suppressing the increase of λ5), it is more preferably 0 or more. Considering the above points, the more preferable lower limit and the more preferable upper limit of the mass ratio {ZnO / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} are as shown in the following table.

For _{Nb 2 O 5, TiO 2,} Ta 2 O 5, WO 3 , in consideration of the above-described action and _effect, the preferred content of each component of _{Nb 2 O 5, TiO 2,} Ta 2 O 5, WO 3 The ranges are shown in the table below.

  Next, optional components other than the components described above will be described.

Since Li ₂ O has a strong effect of lowering the glass transition temperature, the machinability tends to decrease as its content increases. In addition, chemical durability and weather resistance also tend to decrease. Therefore, the Li ₂ O content is preferably 5% or less. The preferable lower limit and the more preferable upper limit of the Li ₂ O content are shown in the following table. The content of Li ₂ O may be 0%.

Na ₂ O, K ₂ O, Rb ₂ O, and Cs ₂ O all have a function of improving the meltability of glass, but when the content of these 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 be as shown in the following table.

In order to improve the meltability of glass while maintaining the thermal stability, chemical durability, weather resistance and machinability of glass, the total content of Li ₂ O, Na ₂ O and K ₂ O (Li The preferable lower limit and the preferable upper limit of ( ₂ O + Na ₂ O + K ₂ O) are as shown in the following table.

  MgO, CaO, SrO, and BaO are all components that have the function of improving the meltability of glass. However, when the content of these components increases, the thermal stability of the glass decreases and the glass tends to devitrify. Therefore, the content of each of these components is preferably not less than the lower limit and not more than the upper limit shown below.

  Further, from the viewpoint of maintaining the thermal stability of the glass, the total content of MgO, CaO, SrO and BaO (MgO + CaO + SrO + BaO) is preferably equal to or higher than the lower limit shown in the following table, and is preferably equal to or lower 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, the refractive index nd may decrease, the thermal stability of the glass may decrease, and the meltability may decrease. In consideration of the above points, the Al ₂ O ₃ content is preferably not less than the lower limit and not more than the upper limit shown in the following table.

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 optical glass. Therefore, the content of each of Ga ₂ O ₃ , In ₂ O ₃ , Sc ₂ O ₃ , and HfO ₂ is preferably not less than the lower limit and not more than the upper limit shown in the following table.

Lu ₂ O ₃ has a function of increasing the refractive index nd, but is also a component that increases the specific gravity of glass. Further, since Lu is a heavy rare earth element like Gd and Yb, it is preferable to reduce the content of Lu. From the above points, the preferable lower limit and the preferable upper limit of the Lu ₂ O ₃ content are as shown in the following table.

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

Bi ₂ O ₃ is a component that raises the refractive index nd and lowers the Abbe number νd. It is also a component that tends to increase the coloring of glass. The preferable lower limit and the preferable upper limit of the Bi ₂ O ₃ content for producing a glass having the above-mentioned optical properties and little coloring are as shown in the following table.

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

Among the glass components other than the above-mentioned glass components, P ₂ O ₅ is a component that lowers the refractive index nd and is a component that lowers the thermal stability of the glass, but if it is introduced in an extremely small amount, It may improve the thermal stability of the glass. The preferable lower limit and the preferable upper limit of the P ₂ O ₅ content for producing a glass having the above-mentioned optical properties and excellent thermal stability are as shown in the following table.

TeO ₂ is a component that raises the refractive index nd, but since it is a component having toxicity, it is preferable to reduce the content of TeO ₂ . The preferable lower limit and the 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 0% in the (more) preferable lower limit or upper limit in each of the above tables has a content of 0%. The same applies to the total content of multiple components.

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

Sb and Sn are arbitrarily addable elements that function as a fining agent.
The addition amount of Sb is converted into _Sb 2 _{O 3,} when the total content of glass components other than _Sb 2 _{O 3} is 100 mass%, preferably in the range of 0 to 0.11 wt%, The range of 0.01 to 0.08 mass% is more preferable, and the range of 0.02 to 0.05 mass% is further preferable.
The addition amount of Sn is converted into SnO _2, when the total content of the glass component other than the SnO ₂ is 100 mass%, preferably in the range of 0 to 0.5 mass%, 0-0. It is more preferably in the range of 2% by mass, further preferably in the range of 0% by mass.

<Glass properties>
(Optical characteristics of glass)
The above glass is a glass having an Abbe number νd in the range of 39.5 to 41.5 and a refractive index nd satisfying the following formula (1) with respect to the Abbe number νd.
nd ≧ 2.0927−0.0058 × vd (1)
A glass having an Abbe number νd of 39.5 or more is effective as a material for an optical element in correcting chromatic aberration. On the other hand, if the Abbe's number νd is larger than 41.5, the thermal stability of the glass will be significantly lowered unless the refractive index is lowered, and devitrification is likely to occur in the glass manufacturing process. The preferable lower limit and the preferable upper limit of the Abbe number νd are shown in the following table.

In the above glass, the refractive index nd satisfies the expression (1) with respect to the Abbe number νd. A glass having an Abbe number νd in the range of 39.5 to 41.5 and a refractive index nd satisfying the formula (1) is a glass having a high utility value in the design of an optical system.
The upper limit of the refractive index nd is naturally determined by the glass composition. In order to improve the thermal stability and obtain a glass that does not easily devitrify, the refractive index nd preferably satisfies the following formula (2).
nd ≦ 2.1270-0.0058 × vd (2)
The preferable lower limit and more preferable upper limit of the refractive index nd with respect to the Abbe number νd are shown in the following table.

  Further, the refractive index nd is preferably not less than the lower limit and not more than the upper limit shown in the following table.

(Partial dispersion characteristics)
From the viewpoint of chromatic aberration correction, it is preferable that the glass has a small partial dispersion ratio when the Abbe number νd is fixed.
Here, the partial dispersion ratio Pg, F is expressed as (ng-nF) / (nF-nc) using the respective refractive indexes ng, nF, and nc at the g-line, F-line, and c-line.
The preferable lower limit and the preferable upper limit of the partial dispersion ratio Pg, f of the above glass are as shown in the following table in order to provide the glass suitable for the correction of high-order chromatic aberration.

(Glass-transition temperature)
The glass transition temperature of the glass is not particularly limited, but is preferably 640 ° C. or higher. By setting the glass transition temperature to 640 ° C. or higher, it is possible to make the glass less likely to be damaged when mechanically processing the glass such as cutting, cutting, grinding and polishing. Further, since it is not necessary to include a large amount of components such as Li and Zn having a strong function of lowering the glass transition temperature, it is possible to reduce the content of Gd and Ta, and further reduce the content of Yb. Also, it becomes easy to improve the thermal stability.
On the other hand, if the glass transition temperature is too high, the glass has to be annealed at a high temperature, and the annealing furnace is significantly consumed. Further, when the glass is molded, the molding has to be carried out at a high temperature, and the mold used for the molding is significantly consumed.
The preferable lower limit and the preferable upper limit of the glass transition temperature are shown in the following table from the viewpoint of improving the machinability and reducing the load on the annealing furnace and the molding die.

(Light transmittance of glass)
It is possible to evaluate that the light transmittance of glass, more specifically, the suppression of increasing the wavelength of the light absorption edge on the short wavelength side is evaluated by the coloring degree λ5. The coloring degree λ5 represents a wavelength at which the spectral transmittance (including surface reflection loss) of 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 the wavelength range of 250 to 700 nm. More specifically, the spectral transmittance is, for example, more specifically, a glass sample having parallel flat surfaces polished to a thickness of 10.0 ± 0.1 mm is used, and light is incident on the polished surface in a direction perpendicular to the surface. The spectral transmittance obtained by the above, that is, Iout / Iin when the intensity of light incident on the glass sample is Iin and the intensity of light transmitted through the glass sample is Iout.
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 cemented with each other by an ultraviolet curable adhesive for producing the cemented lens, the adhesive is irradiated with ultraviolet rays through the optical element to cure the adhesive. From the viewpoint of efficiently curing the ultraviolet curable adhesive, it is preferable that the absorption edge on the short wavelength side of the spectral transmittance is in the short wavelength range. The coloring degree λ5 can be used as an index for quantitatively evaluating the absorption edge on the short wavelength side. The above-mentioned glass can exhibit a λ5 of preferably 335 nm or less, more preferably 332 nm or less, still more preferably 330 nm or less, still more preferably 328 nm or less, still more preferably 326 nm or less, by adjusting the composition described above. As an example, the lower limit of λ5 can be set to 315 nm, but the lower limit is preferable and it is not particularly limited.

On the other hand, as an index of the coloring degree of glass, the coloring degree λ70 can be mentioned. λ70 represents the wavelength at which the spectral transmittance measured by the method described for λ5 is 70%. In order to obtain a glass with little coloring, the preferable range of λ70 is 420 nm or less, the more preferable range is 400 nm or less, the still more preferable range is 390 nm or less, and the still more preferable range is 380 nm or less. The lower limit of λ70 is 350 nm, but the lower limit is preferable and it is not particularly limited.
Further, as an index of the coloring degree of glass, the coloring degree λ80 can also be mentioned. λ80 represents a wavelength at which the spectral transmittance measured by the method described for λ5 is 80%. From the standpoint of making the glass less colored, the preferable range of λ80 is 550 nm or less, the more preferable range is 500 nm or less, the further preferable range is 490 nm or less, and the still more preferable range is 480 nm or less. The lower limit of λ80 is 355 nm, but the lower limit is preferable and it is not particularly limited.

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

  Further, preferable lower limit and preferable upper limit of the specific gravity d of the above glass are shown in the following table. Setting the specific gravity d to the upper limit or less shown in the following table is preferable from the viewpoint of reducing the weight of the optical element made of this glass. Further, it is preferable that the specific gravity is not less than the lower limit shown in the following table in order to further improve the thermal stability of the glass.

(Liquid phase temperature)
The liquidus temperature is one of the indexes of the thermal stability of glass. From the viewpoint of suppressing crystallization and devitrification during glass production, the liquidus temperature LT is preferably 1300 ° C. or lower, and more preferably 1250 ° C. or lower. The lower limit of the liquidus temperature LT is, for example, 1100 ° C. or higher, but it is preferably low and is not particularly limited.

  The glass according to one embodiment of the present invention described above has a large refractive index nd and an Abbe number νd, and is useful as a glass material for an optical element. Furthermore, homogenization and color reduction of glass are possible by adjusting the composition described above. Therefore, the above glass is suitable as an optical glass.

<Glass manufacturing method>
The above-mentioned glass is a raw material such as an oxide, a carbonate, a sulfate, a nitrate, and a hydroxide, which are weighed and mixed so that a desired glass composition can be obtained, and they are sufficiently mixed into a mixed batch in a melting vessel. It can be obtained by heating, melting, defoaming, and stirring to produce a homogeneous and bubble-free molten glass, which is then molded. Specifically, it can be produced using a known melting method. The above-mentioned glass is a high-refractive-index, low-dispersion glass having the above-mentioned optical characteristics, but since it has excellent thermal stability, it can be stably produced by a known melting method or molding method.

[Glass material for press molding, optical element blank, and manufacturing method thereof]
Another aspect of the present invention is
Glass material for press molding, which is made of the above-mentioned glass;
An optical element blank made of the above glass,
Regarding

According to another aspect of the present invention,
A method for producing a glass material for press molding, comprising a step of forming the above glass into a glass material for press molding;
A method for producing an optical element blank, which comprises a step of producing an optical element blank by press-forming the above-mentioned press-molding glass material using a press mold.
A method for manufacturing an optical element blank, which comprises a step of molding the above glass into an optical element blank,
Is also provided.

  The optical element blank is similar to the shape of the desired optical element, and the shape of the optical element should be polished (surface layer to be removed by polishing) and, if necessary, ground (to be removed by grinding). It is an optical element base material to which a surface layer) is added. The optical element is finished by grinding and polishing the surface of the optical element blank. In one aspect, an optical element blank can be produced by a method of forming a molten glass obtained by melting an appropriate amount of the above glass (called a direct pressing method). In another embodiment, an optical element blank can be produced by solidifying a molten glass obtained by melting an appropriate amount of the above glass.

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

  The 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 the strain inside the glass.

  In addition to what is called a press-molding glass gob that is used for press-molding for making optical element blanks, the press-molding glass material is subjected to mechanical processing such as cutting, grinding, and polishing to obtain a press-molding glass gob. Also included are those that are subjected to press molding through. As a cutting method, a groove is formed by a method called scribing on a portion of the surface of the glass plate to be cut, and a local pressure is applied to the groove portion from the back surface of the surface where the groove is formed, so that the glass is cut at the groove portion. There are methods such as breaking the plate and cutting the glass plate with a cutting blade. Moreover, barrel grinding etc. are mentioned as a grinding and polishing method.

  The glass material for press molding can be 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. 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 producing a press-molding glass gob by reheating, softening and press-molding. A method of reheating and softening glass and press-molding the glass to manufacture an optical element blank is called a reheat pressing method as opposed to a direct pressing 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 above glass.
The above optical element is produced using the above glass. In the above optical element, one or more coatings such as a multilayer film such as an antireflection film may be formed on the glass surface.

According to one aspect of the present invention,
A method for manufacturing an optical element, comprising a step of producing an optical element by grinding and / or polishing the above-mentioned optical element blank;
Is also provided.

  In the method for producing an optical element described above, known methods may be applied to grinding and polishing, and by sufficiently washing and drying the surface of the optical element after processing, an optical element having high internal quality and surface quality can be obtained. it can. In this way, an optical element made of the above glass can be obtained. Examples of the optical element include various lenses such as spherical lenses, aspherical lenses, microlenses, prisms, and the like.

  Further, the optical element made of the above glass is also suitable as a lens forming a cemented optical element. Examples of the cemented optical element include one in which lenses are cemented (cemented lens), one in which a lens and a prism are cemented, and the like. For example, a cemented optical element is an ultraviolet curable adhesive used for bonding a cemented lens by precisely processing (for example, spherical polishing) the cemented surfaces of two optical elements to be cemented so that the shape is an inverted shape. Can be prepared by coating and bonding and then irradiating ultraviolet rays through the lens to cure the adhesive. The above glass is preferable for manufacturing the cemented optical element in this manner. A plurality of optical elements to be joined are manufactured by using a plurality of types of glass having different Abbe numbers νd, respectively, and the elements are joined to each other, whereby an element suitable for correction of chromatic aberration can be obtained.

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

(Example 1)
As raw materials, compounds such as oxides and boric acid were weighed and sufficiently mixed to prepare a batch raw material so that a glass having a composition shown in the following table was obtained.
This batch raw material was put into a platinum crucible, and the crucible was heated to a temperature of 1350 to 1450 ° C., and the glass was melted and clarified for 2 to 3 hours. After the molten glass was stirred and homogenized, the molten glass was cast into a preheated mold and allowed to cool to near the glass transition temperature, and immediately the glass was put into an annealing furnace together with the mold. Then, it was annealed at about the glass transition temperature for about 1 hour. After annealing, it was left to cool to room temperature in the annealing furnace.
As a result of observing the glass thus produced, no precipitation of crystals, bubbles, striae, and unmelted material remained. In this way, glass with high homogeneity could be produced.

(Comparative Examples 1 to 4)
Except that compounds such as oxides and boric acid were weighed as raw materials and sufficiently mixed to prepare batch raw materials so that glasses having respective compositions of Comparative Examples 1 to 4 shown in the following table were obtained. Glass was obtained in the same manner as in Example 1.
The composition of Comparative Example 1 is the same as the glass No. 1 of Patent Document 20. 11 compositions,
Comparative Example 2 is a glass No. 1 of Patent Document 20. 25 compositions,
Comparative Example 3 is glass No. 1 of Patent Document 20. 45 compositions,
Comparative Example 4 is the glass No. 1 of Patent Document 20. 49 compositions,
Is.

The glass properties of the obtained glass were measured by the methods described below. The measurement results are shown in the table below.
(1) Refractive index nd, nF, nc, ng, Abbe number νd
The refractive index nd, nF, nc, and ng of the glass obtained by lowering the temperature at a temperature lowering rate of −30 ° C./hour were measured by the refractive index measuring method specified by the Japan Optical Glass Industry Association. The Abbe number νd was calculated using the respective measured values of the refractive indexes nd, nF, and nc.
(2) Glass transition temperature Tg
Using a differential scanning calorimeter (DSC), the temperature rising rate was set to 10 ° C./min and measurement was performed.
(3) Specific gravity It was measured by the Archimedes method.
(4) Coloring degree λ5, λ70, λ80
Using a glass sample having a thickness of 10 ± 0.1 mm having two optically polished flat surfaces opposed to each other, a spectrophotometer was used to make light having an intensity Iin incident on the polished surface from a direction perpendicular to the polished surface. The intensity Iout of the light transmitted through is measured and the spectral transmittance Iout / Iin is calculated. 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 which becomes% is set to λ80.
(5) Partial dispersion ratio Pg, F
It was calculated from the values of nF, nc, and ng measured in (1) above.
(6) Liquidus temperature The glass was placed in a furnace heated to a predetermined temperature and held for 2 hours, and after cooling, the inside of the glass was observed with a 100 × optical microscope to determine the liquidus temperature from the presence or absence of crystals.

(Example 2)
The various glass obtained in Example 1 was used to prepare a glass gob for press molding. This glass gob 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 subjected to mechanical processing including polishing to produce a spherical lens made of various glasses produced in Example 1.

(Example 3)
A desired amount of the molten glass produced in Example 1 was press-formed with a press die to produce a lens blank (optical element blank). The produced lens blank was taken out from the press mold, annealed, and subjected to mechanical processing including polishing to produce a spherical lens made of various glasses produced in Example 1.

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

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

(Comparative example 5)
No. 1 shown in Table 8 of JP-A-2014-62026. 51 glass (hereinafter referred to as glass I) was reproduced. The glass I described in Table 8 of JP-A-2014-62026 has λ5 of 337 nm.
Next, in the same manner as in Example 5, a spherical lens made of glass I was manufactured, and an attempt was made to manufacture a cemented lens using the manufactured spherical lens. However, when the ultraviolet curable adhesive applied to the bonding surface was irradiated with ultraviolet rays through a lens made of glass I, the adhesive could not be sufficiently cured because the glass I had a low ultraviolet transmittance.

(Comparative example 6)
In the glass according to one embodiment of the present invention, the mass ratio {ZnO / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )} is less than 0.10.
On the other hand, No. 1 shown in Table 1 of Japanese Unexamined Patent Publication No. 2014-62026. The mass ratio of the glass of No. 6 is 0.325. No. 1 shown in Table 1 of Japanese Patent Laid-Open No. 2014-62026. In order to make the glass composition of the glass of No. 6 have the above mass ratio of less than 0.10, ZnO is reduced, and the reduced amount is distributed to other components so that the balance of the content of other components does not change significantly. Then, the composition was adjusted as shown in Table 61 below to produce glass. The ratio of the glass components to each other in Table 61 is a mass ratio of the contents of the respective components in the oxide-based glass composition. Specifically, a glass raw material was prepared, 170 g of the prepared raw material was put into a platinum crucible, and the mixture was melted and clarified at 1400 ° C. for 2 hours. After the molten glass was stirred and homogenized, the molten glass was cast into a preheated mold and allowed to cool to near the glass transition temperature, and immediately the glass was put into an annealing furnace together with the mold. Then, it was annealed at about the glass transition temperature for about 1 hour. After annealing, it was left to cool to room temperature in the annealing furnace.
Then, the inside of the glass was observed.
FIG. 1 is a photograph of the glass evaluated in Comparative Example 6. As is clear from FIG. 1, a large number of crystals were precipitated in the glass and became cloudy and the transparency was lost.
On the other hand, in the glass according to one aspect of the present invention, crystal precipitation can be suppressed by the composition adjustment described in detail above.

  Finally, the above-mentioned aspects are summarized.

According to one aspect, the total content of B ₂ O ₃ and SiO ₂ is 17.5 to 35% in terms of mass%, La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O. the total content of _{3 45~70%, Nb} 2 _{O 5,} the total content of TiO 2, _Ta 2 _{O 5} and WO ₃ is 3 to 16%, ZrO ₂ content of 2~10%, _La 2 _{O 3} , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ 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 _{0.2~0.5, Nb 2 O 5, B} 2 O 3 to the total content of TiO 2, _Ta 2 _{O 5} and WO ₃ and SiO ₂ the total content of the mass ratio of _{{(B 2 O 3 + SiO} 2) / (Nb 2 O 5 + _{iO 2 + Ta 2 O 5 +} WO 3)} is 2.8 or _{less, La 2 O 3, Y 2} O 3, Gd 2 O 3 and the weight ratio of the ZnO content to the total content of _Yb 2 _{O 3} {ZnO / ( _{La 2 O 3 + Y 2 O} 3 + Gd 2 O 3 + Yb 2 O 3)} is less than _{0.10, La 2 O 3, Y} 2 O 3, Gd 2 O 3 and La ₂ to the total content of _Yb 2 _{O 3} O ₃ content of the mass ratio _{{La 2 O 3 / (La} 2 O 3 + Y 2 O 3 + Gd 2 O 3 + Yb 2 O 3)} is _{0.55~0.98, La 2 O 3, Y} 2 O 3 , The mass ratio of the Y ₂ O ₃ content to the total content of 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 _{0.02~0.45, La 2 O 3, Y} 2 O 3, G ₂ O ₃ and _Yb 2 _{O 3 Gd} 2 _{O 3} content of the mass ratio to the total content of _{{Gd 2 O 3 / (La} 2 O 3 + Y 2 O 3 + Gd 2 O 3 + Yb 2 O 3)} is 0. 10 or less, the mass ratio of the Nb ₂ O ₅ content to the total content of Nb ₂ O ₅ , TiO ₂ and WO ₃ {Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + WO ₃ )} is 0.81 or more, Mass ratio of Ta ₂ O ₅ content to total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ {Ta ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} Is 0.3 or less, the Abbe number νd is in the range of 39.5 to 41.5, and the refractive index nd is an oxide glass satisfying the above formula (1) with respect to the Abbe number νd. Can be provided.

The above glass is a glass satisfying the formula (1) and is a high refractive index and low dispersion glass useful in an optical system. The above-mentioned glass can be stably supplied because the proportion of Gd ₂ O ₃ and Ta ₂ O ₅ in the glass composition is reduced, and high heat can be obtained by satisfying the above-mentioned content, total content and mass ratio. Stability can be obtained, and the wavelength of the light absorption edge on the short wavelength side can be prevented from increasing.

In one aspect, the content of Gd ₂ O _{3 in} the glass is preferably 6% by mass or less from the viewpoint of stable glass supply.

In one aspect, the Ta ₂ O ₅ content in the glass is preferably 5% by mass or less from the viewpoint of stable glass supply.

  In one aspect, it is preferable that in the above glass, the wavelength of the light absorption edge on the short wavelength side of the glass is suppressed so that the coloring degree λ5 is 335 nm or less.

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

  Further, according to another aspect, there is also provided a method for producing a glass material for press molding, comprising a step of molding the above glass into a glass material for press molding.

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

  According to still another aspect, there is also provided a method of manufacturing an optical element blank including a step of molding the above glass into an optical element blank.

  According to still another aspect, there is also provided a method for manufacturing an optical element including a step of manufacturing an optical element by grinding and / or polishing the optical element blank.

The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.
For example, the glass according to one embodiment of the present invention can be obtained by adjusting the composition described in the specification for the above-exemplified glass composition.
Further, it is of course possible to arbitrarily combine two or more of the matters described as examples or preferable ranges in the specification.

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

Claims (8)

In mass% display,
The total content of B ₂ O ₃ and SiO ₂ is 17.5 to 35%,
_{La 2 O 3, Y 2 O} 3, the total content of _Gd 2 _{O 3} and _Yb 2 _{O 3} 45-70%
The total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ is ₃ to 16%,
ZrO ₂ content is 2 to 10%,
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 0.2 to 0.5,
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 2.8 or less,
Mass ratio of ZnO content to total content of La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ {ZnO / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )} Is less than 0.10.
Mass ratio of La 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 {La ₂ O ₃ / (La ₂ O ₃ + Y ₂ O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ )} is 0.55 to 0.98,
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 0.02 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 0.10 or less,
The mass ratio of the Nb ₂ O ₅ content to the total content of Nb ₂ O ₅ , TiO ₂ and WO ₃ {Nb ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + WO ₃ )} is 0.81 or more,
Mass ratio of Ta ₂ O ₅ content to total content of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and WO ₃ {Ta ₂ O ₅ / (Nb ₂ O ₅ + TiO ₂ + Ta ₂ O ₅ + WO ₃ )} Is 0.3 or less,
And
The coloring degree λ5 is 335 nm or less,
The Abbe number νd is in the range of 39.5 to 41.5, and the refractive index nd is the following Equation (1) with respect to the Abbe number νd:
nd ≧ 2.0927−0.0058 × νd (1)
A glass that is an oxide glass that satisfies the requirements. In mass% display,
B _Two O _Three And SiO _Two And a total content of 17.5 to 35%,
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three The total content of 45-70%,
Nb _Two O ₅ , TiO _Two , Ta _Two O ₅ And WO _Three The total content of 3-16%,
ZrO _Two Content is 2-10%,
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three B for the total content of _Two O _Three And SiO _Two Mass ratio of total content with {(B _Two O _Three + SiO _Two ) / (La _Two O _Three + Y _Two O _Three + Gd _Two O _Three + Yb _Two O _Three )} Is 0.2 to 0.5,
Nb _Two O ₅ , TiO _Two , Ta _Two O ₅ And WO _Three B for the total content of _Two O _Three And SiO _Two Mass ratio of total content with {(B _Two O _Three + SiO _Two ) / (Nb _Two O ₅ + TiO _Two + Ta _Two O ₅ ＋ WO _Three )} Is 2.8 or less,
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three Mass ratio of ZnO content to the total content of {ZnO / (La _Two O _Three + Y _Two O _Three + Gd _Two O _Three + Yb _Two O _Three )} Is less than 0.10.
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three Of the total content of La _Two O _Three Mass ratio of contents {La _Two O _Three / (La _Two O _Three + Y _Two O _Three + Gd _Two O _Three + Yb _Two O _Three )} Is 0.55 to 0.98,
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three Y for the total content of _Two O _Three Mass ratio of contents {Y _Two O _Three / (La _Two O _Three + Y _Two O _Three + Gd _Two O _Three + Yb _Two O _Three )} Is 0.02-0.45,
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three Gd relative to the total content of _Two O _Three Mass ratio of contents {Gd _Two O _Three / (La _Two O _Three + Y _Two O _Three + Gd _Two O _Three + Yb _Two O _Three )} Is less than 0.10,
Nb _Two O ₅ , TiO _Two And WO _Three Nb relative to the total content of _Two O ₅ Mass ratio of contents {Nb _Two O ₅ / (Nb _Two O ₅ + TiO _Two ＋ WO _Three )} Is 0.81 or more,
Nb _Two O ₅ , TiO _Two , Ta _Two O ₅ And WO _Three Ta for the total content of _Two O ₅ Mass ratio of contents {Ta _Two O ₅ / (Nb _Two O ₅ + TiO _Two + Ta _Two O ₅ ＋ WO _Three )} Is 0.3 or less,
Nb _Two O ₅ , TiO _Two , Ta _Two O ₅ And WO _Three Mass ratio of ZnO content to the total content of {ZnO / (Nb _Two O ₅ + TiO _Two + Ta _Two O ₅ ＋ WO _Three )} Is 0.01 or more,
And the Abbe number νd is in the range of 39.5 to 41.5, and the refractive index nd with respect to the Abbe number νd is the following formula (1):
  nd ≧ 2.0927−0.0058 × νd (1)
A glass that is an oxide glass that satisfies the requirements. In mass% display,
B _Two O _Three And SiO _Two And a total content of 17.5 to 35%,
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three The total content of 45-70%,
Nb _Two O ₅ , TiO _Two , Ta _Two O ₅ And WO _Three The total content of 3-16%,
ZrO _Two Content is 2-10%,
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three B for the total content of _Two O _Three And SiO _Two Mass ratio of total content with {(B _Two O _Three + SiO _Two ) / (La _Two O _Three + Y _Two O _Three + Gd _Two O _Three + Yb _Two O _Three )} Is 0.2 to 0.5,
Nb _Two O ₅ , TiO _Two , Ta _Two O ₅ And WO _Three B for the total content of _Two O _Three And SiO _Two Mass ratio of total content with {(B _Two O _Three + SiO _Two ) / (Nb _Two O ₅ + TiO _Two + Ta _Two O ₅ ＋ WO _Three )} Is 2.8 or less,
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three Mass ratio of ZnO content to the total content of {ZnO / (La _Two O _Three + Y _Two O _Three + Gd _Two O _Three + Yb _Two O _Three )} Is less than 0.10.
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three Of the total content of La _Two O _Three Mass ratio of contents {La _Two O _Three / (La _Two O _Three + Y _Two O _Three + Gd _Two O _Three + Yb _Two O _Three )} Is 0.55 to 0.98,
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three Y for the total content of _Two O _Three Mass ratio of contents {Y _Two O _Three / (La _Two O _Three + Y _Two O _Three + Gd _Two O _Three + Yb _Two O _Three )} Is 0.02-0.45,
La _Two O _Three , Y _Two O _Three , Gd _Two O _Three And Yb _Two O _Three Gd relative to the total content of _Two O _Three Mass ratio of contents {Gd _Two O _Three / (La _Two O _Three + Y _Two O _Three + Gd _Two O _Three + Yb _Two O _Three )} Is less than 0.10,
Nb _Two O ₅ , TiO _Two And WO _Three Nb relative to the total content of _Two O ₅ Mass ratio of contents {Nb _Two O ₅ / (Nb _Two O ₅ + TiO _Two ＋ WO _Three )} Is 0.81 or more,
Nb _Two O ₅ , TiO _Two , Ta _Two O ₅ And WO _Three Ta for the total content of _Two O ₅ Mass ratio of contents {Ta _Two O ₅ / (Nb _Two O ₅ + TiO _Two + Ta _Two O ₅ ＋ WO _Three )} Is 0.3 or less,
Nb _Two O ₅ , TiO _Two And WO _Three Nb relative to the total content of _Two O ₅ Mass ratio of the content of {Nb _Two O ₅ / (Nb _Two O ₅ + TiO _Two ＋ WO _Three )} Is 0.85 or more,
And the Abbe number νd is in the range of 39.5 to 41.5, and the refractive index nd is the following Equation (1) with respect to the Abbe number νd:
  nd ≧ 2.0927−0.0058 × νd (1)
Satisfies and
A glass that is an oxide glass having d / (nd-1), which is the ratio of the specific gravity d to the value obtained by subtracting 1 from the refractive index nd, of 5.70 or less. The glass according to any one of claims 1 to _{3, wherein} the content of Gd ₂ O ₃ is 6% by mass or less. The glass according to claim 1, wherein the content of Ta ₂ O ₅ is 5% by mass or less . Claim 1-5 glass material for press molding comprising a glass according to any one of. Optical element blank formed of a glass according to any one of claims 1-5. Optical elements of glass according to any one of claims 1-5.