JP6678008B2 - 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.

  A lens made of high-refractive-index low-dispersion glass can be combined with a lens made of ultra-low-dispersion glass to form a cemented lens, thereby making it possible to make the optical system compact while correcting chromatic aberration. Therefore, the high refractive index low dispersion glass occupies a very important position as an optical element constituting a projection optical system such as an imaging optical system and a projector. Such high-refractive-index low-dispersion glasses are described in, for example, Patent Documents 1 to 20.

JP 2007-063071 A JP 2007-230835 A JP 2007-249112 A JP 2007-261826 A JP 2003-267748 A JP 2009-203083 A JP-A-2011-230992 JP 2012-025638 A JP-A-54-090218 JP-A-56-160340 JP 2001-348244 A JP 2008-001551 A JP-T-2013-5366791A 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 glass for optical elements, an optical property map (also called Abbe diagram) is widely used to show the distribution of optical properties. The optical property map takes the Abbe number νd on the horizontal axis and the refractive index nd on the vertical axis, and the Abbe number νd increases from the right side to the left side of the horizontal axis, and the refractive index increases upward from below the vertical axis. Created to increase accordingly. In the following, the refractive index and Abbe number refer to the refractive index nd for the helium d-line (wavelength 587.56 nm) and the Abbe number νd for the helium d-line (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 shown generally. This is considered to be due to the following reasons.
Many high refractive index 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 the rare earth oxide must be increased. However, when the content of the rare earth oxide in the conventional high refractive index low dispersion glass is increased, the thermal stability of the glass is reduced, and the glass tends to be devitrified in the process of manufacturing the glass. For this reason, it has been difficult for conventional high-refractive low-dispersion glass 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 that the conventional high-refractive-index low-dispersion glass exhibits the above-described distribution in the optical property map.

On the other hand, in designing an optical system, glass having a high refractive index and a large Abbe number (low dispersion) is a very effective material for an optical element for correcting chromatic aberration, increasing the functionality of the optical system, and reducing its size. is there. Therefore, it is very meaningful to set a straight line that rises to the right on the optical property map and to provide a glass having a higher refractive index than the straight line and the straight line (located on the map on the left side of the straight line). Big.
From the above points, a glass whose Abbe number νd is 39.5 to 41.5 and whose refractive index nd is equal to or more than 2.0927-0.0058 × νd with respect to this Abbe number, 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 both Gd and Ta are rare elements, the demand in various industrial fields has been increasing in recent years, so that the supply in the market is insufficient. Therefore, from the viewpoint of stable supply of the high-refractive-index low-dispersion glass, it is desirable to reduce the content of Gd or Ta in the high-refractive-index low-dispersion glass.
On the other hand, in the conventional glass composition of a high-refractive-index low-dispersion glass, if the optical properties and the thermal stability are both to be maintained while reducing the content of Gd or Ta, the light absorption edge on the short wavelength side of the glass is reduced. The wavelength tends to be longer, and the transmittance of ultraviolet rays tends to decrease significantly.
By the way, in order to correct chromatic aberration, a method is known in which a plurality of lenses are formed using glasses having different optical characteristics, and these lenses are bonded to each other to form a cemented lens. In the process of making a cemented lens, an ultraviolet-curing adhesive is usually used to bond the lenses together. The details are as follows. An ultraviolet-curing adhesive is applied to the surface where the lenses are to be bonded, and the lenses are bonded. At this time, usually, an extremely thin coating layer of the ultraviolet curable adhesive is formed between the lenses. Next, the coating layer is irradiated with ultraviolet light through a lens to cure the ultraviolet-curable adhesive. Therefore, if the transmittance of the ultraviolet ray of the lens is low, a sufficient amount of the ultraviolet ray does not reach the coating layer through the lens, and the curing becomes insufficient. Or it takes a long time to cure.
Similarly, when a lens is adhered and fixed to a lens barrel or the like using an ultraviolet curable adhesive, similarly, if the ultraviolet transmittance of the lens is low, curing will be insufficient or long. It takes time.
Therefore, in order to obtain a glass having a transmittance characteristic suitable for manufacturing an optical system, it is desirable to suppress an increase in the wavelength of the light absorption edge on the short wavelength side of the glass.

  One embodiment of the present invention has an Abbe number νd of 39.5 to 41.5, satisfies a relationship of nd ≧ 2.0927−0.0058 × νd, can be supplied stably, and is used for manufacturing an optical system. It is an object to provide a suitable glass.

One embodiment of the present invention provides a cation% display:
The total content of B ³⁺ and Si ⁴⁺ is 43 to 65%,
The total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 25 to 50%;
The total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ is 3 to 12%,
Zr4 ⁺ content of 2 to 8%,
The 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 zero. .70-1.75,
The cation ratio {(B ³⁺ + Si ⁴⁺ ) / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} of the total content of B ³⁺ and Si ⁴⁺ to the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ is 9 .00 or less,
The cation ratio of Zn ²⁺ content to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ {Zn ²⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} less than 0.2;
The cation ratio of the La ³⁺ content to the total content of La ³⁺ , Y ³⁺ , G ³⁺ and Yb ³⁺ {La ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} is 0.50 to 0.95;
The cation ratio of the 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 0.10 to 0.50;
The cation ratio of the 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 0.10 or less;
The cation ratio of the Nb ⁵⁺ content to the total content of Nb ⁵⁺ , Ti ⁴⁺ and W ⁶⁺ {Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )} is 0.80 or more;
The cation ratio of the Ta ⁵⁺ content to the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ {Ta ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} is 0.2 or less;
Where 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
About.

The above glass satisfies the relationship of nd ≧ 2.0927−0.0058 × νd when the Abbe number νd is in the range of 39.5 to 41.5, and various components including Gd ³⁺ (that is, La ³⁺ , Y ³ The total content of ³⁺ , Gd ³⁺ , Yb ³⁺ ) and the various components including Ta ⁵⁺ (that is, Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ , W ⁶⁺ ) are within the above ranges, and Gd ³⁺ , Ta ⁵⁺ is within the above range. Satisfies the cation ratio contained in the denominator or numerator. Therefore, the ratio occupied by Gd and Ta in the glass composition is reduced. The above glass has a high thermal stability (devitrification) due to the composition adjustment satisfying the above content, total content and cation ratio in the composition satisfying the total content and cation ratio. Realization) and suppression of the longer wavelength of the light absorption edge on the shorter wavelength side.

  According to one embodiment of the present invention, glass having useful optical characteristics in an optical system, capable of being supplied stably, and having transmittance characteristics suitable for manufacturing an optical system can be provided. Further, according to one aspect 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 above glass.

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 that fills. Hereinafter, details of the above glass will be described.

  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. In the present specification and the present invention, a content of 0% or no or no introduction of a component means that the component is not substantially contained, and the content of the component is at an impurity level. Degree.

In the present invention, the glass composition is represented by cation% for the cation component. As is well known, the cation% is a percentage with the total content of all cation components contained in the glass being 100%.
Hereinafter, unless otherwise specified, the content of the cation component and the sum of the contents of a plurality of types of cation components (total content) are expressed as cation%. Further, in the cation% display, the ratio of the content of the cation components (including the total content of a plurality of types of cation components) is referred to as a cation ratio.
In the following, with respect to the numerical range, a (more) preferable lower limit and a (more) preferable upper limit may be shown in a table and described. In the table, the numerical values described at the bottom are more preferable, and the numerical values described at the bottom are most preferable. Unless otherwise specified, a (more) preferable lower limit means that it is (more) preferable that the value is not less than the described value, and a (more) preferable upper limit is that it is not more than the described value. (More) preferred. The numerical value 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 a numerical range.

<Glass composition>
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 43% or more, the thermal stability of the glass is improved, and the crystallization of the glass during production can be suppressed. On the other hand, when the total content of B ³⁺ and Si ⁴⁺ is 65% or less, a decrease in the refractive index nd can be suppressed, so that glass having the above-described optical characteristics can be manufactured. Therefore, the total content of B ³⁺ and Si ⁴⁺ in the above glass is in the range of 43 to 65%. The preferred lower limit and preferred upper limit of the total content of B ³⁺ and Si ⁴⁺ are as shown in the following table.

La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ are components having a function of increasing the refractive index while suppressing a decrease in Abbe number νd. These components also have the function of improving the chemical durability and weather resistance of glass and increasing the glass transition temperature.
When 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, a decrease in the refractive index nd can be suppressed, and thus the above-described optical characteristics. Can be produced. Furthermore, it is also possible to suppress a decrease in chemical durability and weather resistance of glass. When the glass transition temperature is lowered, the glass is liable to be broken (decreased in machinability) when the glass is mechanically processed (cut, cut, ground, polished, etc.), but La ³⁺ , Y ³⁺ , Gd ^When the total content of ³⁺ and Yb ³⁺ is 25% or more, a decrease in the glass transition temperature can be suppressed, so that the machinability can be improved. On the other hand, if the total content of each component of La ³⁺ , Y ³⁺ , Gd ^3+, and Yb ³⁺ is 50% or less, the thermal stability of the glass can be increased, so that crystallization of It is also possible to reduce the amount of unmelted raw material when glass is melted or when glass is melted. In addition, an increase in specific gravity can be suppressed. Therefore, in the above glass, the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is in the range of 25 to 50%. Preferred lower and upper limits of the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb 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 glass by containing an appropriate amount. If the total content of Ti ⁴⁺ , Nb ⁵⁺ , Ta ⁵⁺ and W ⁶⁺ (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ ) is 3% or more, the above-mentioned optical characteristics can be realized while maintaining thermal stability. it can. On the other hand, if the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ is 12% or less, it is possible to suppress a decrease in thermal stability and a decrease in Abbe number νd. Further, the increase in the degree of coloring λ5 described below can be suppressed, and the ultraviolet transmittance of the glass can be increased. Therefore, in the above glass, the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ is in the range of 3 to 12%. Preferred lower and upper limits for the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ 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 glass by containing an appropriate amount. Zr ⁴⁺ also has a function of increasing the glass transition temperature so that the glass is less likely to break during mechanical processing. In order to obtain these effects favorably, the content of Zr ^{4+ in} the above glass is set to 2% or more. On the other hand, when 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. . Therefore, the Zr ⁴⁺ content in the above glass is in the range of 2 to 8%. Preferred lower and upper limits for the Zr ⁴⁺ content are shown in the table below.

To improve the thermal stability of the glass while realizing 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 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⁺ ) ０．７ is set to 0.70 to 1.75. When the cation ratio ((B ³⁺ + Si ⁴⁺ ) / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )) is 0.70 or more, the thermal stability of the glass can be improved, so that the devitrification of the glass is suppressed. can do. In addition, an increase in specific gravity of glass can be suppressed. When the specific gravity of the glass increases, the optical element manufactured using the glass becomes heavier. As a result, an optical system incorporating this optical element becomes heavy. For example, when a heavy optical element is incorporated in an autofocus camera, power consumption for driving the autofocus increases, and the battery is quickly consumed. It is preferable to be able to suppress an increase in the specific gravity of the glass from the viewpoint of reducing the weight of the optical element manufactured using the glass and the 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 1.75 or less, the above optical characteristics can be realized. The preferable lower limit and the preferable upper limit of the cation ratio of ^{{(B 3+ + Si 4+)} / (La 3+ + Y 3+ + Gd 3+ + Yb 3+)}, shown in the following Table.

In order to improve the thermal stability of the glass while suppressing the decrease in the refractive index nd and realizing the above-mentioned optical characteristics, the above glass has a B content relative to the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ^6+. The cation ratio of the total content of ³⁺ and Si ⁴⁺ {(B ³⁺ + Si ⁴⁺ ) / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} is set to 9.00 or less.
In order to improve the thermal stability of the glass while suppressing the decrease in the Abbe number νd, the cation ratio {(B ³⁺ + Si ⁴⁺ ) / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} is set to 5.00 or more. Is preferred. Further, when the cation ratio {(B ³⁺ + Si ⁴⁺ ) / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} is 5.00 or more, the longer wavelength of the light absorption edge on the shorter wavelength side of the glass is further suppressed. It is preferable to As a result, when a glass lens is joined using an ultraviolet-curable adhesive, ultraviolet rays can more easily reach the coating layer of the adhesive through the lens. This makes it easier to cure the adhesive by ultraviolet irradiation.
The more preferable lower limit and the 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.

In order to improve the thermal stability of the glass and suppress the crystallization of the glass while realizing the above-mentioned optical characteristics, in the above glass, Zn relative to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is used. The cation ratio of the ²⁺ content {Zn ²⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} is less than 0.2. Preferred lower and upper limits of the cation ratio {Zn ²⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} are shown in the following table.

Among the rare earth elements La, Y, Gd and Yb, Gd belongs to the heavy rare earth element and is a component required to reduce the content in the glass from the viewpoint of stable supply of the glass. Gd is also a component having a large atomic weight and increasing the specific gravity of glass.
Yb also belongs to heavy rare earth elements and has a large atomic weight. Yb has absorption in the near infrared region. On the other hand, it is desirable that the interchangeable lens for a single-lens reflex camera and the lens of a surveillance camera have a high light transmittance in the near infrared region. Therefore, it is desirable to reduce the Yb content in order to obtain a 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 allocating an appropriate amount to the total content of rare earth elements, improve the thermal stability and improve the specific gravity. Is a component useful for suppressing an increase in the refractive index and providing a high-refractive-index low-dispersion glass.

Therefore, in the glass, the ^{La 3+ is,} La ^3+, Y 3+, the ^{La 3+} content of the cation ratio to the total content of ^{Gd 3+} and ^{Yb 3+ {La 3+ / (La} 3+ + Y 3+ + Gd 3+ + Yb 3+)}, The range is 0.50 to 0.95. The preferred lower limit and preferred upper limit of the cation ratio {La ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} are shown in the following table.

^Also, the ^{Y 3+,} La ^3+, Y 3+, the content of the cation ratio of ^{Y 3+} to the total content of ^{Gd 3+} and ^{Yb 3+} a ^{{Y 3+ / (La 3+ +} Y 3+ + Gd 3+ + Yb 3+)} 0.10 ０．５0.50. The preferred lower limit and preferred upper limit of the cation ratio {Y ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} are shown in the following table.

As described above, Gd ³⁺ is a component whose content in glass should be reduced from the viewpoint of stable supply of glass. In the glass, 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 above glass, the cation ratio of the content of Gd ³⁺ to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ from the viewpoint of stably supplying the high-refractive-index low-dispersion glass having the above-mentioned optical characteristics ΔGd ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} is set to 0.10 or less. Satisfying the above cation ratio can also contribute to lowering the specific gravity of glass. The preferred lower limit and preferred upper limit of the cation ratio {Gd ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} are shown in the following table.

The total content of La ³⁺ , Y ³⁺ , Gd ^3+, and Yb ³⁺ , and the cation ratio of the La ³⁺ content, the Y ³⁺ content, and the Gd ³⁺ content to the total content are as described above. Preferred lower and upper limits of the content of each component of La ³⁺ , Y ³⁺ , Gd ³⁺ , and Yb ³⁺ are shown in the following table. The lower limit of the Y ³⁺ content shown in the following table is preferable also from the viewpoint of improving the thermal stability and meltability of the glass.

Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ , when contained in appropriate amounts, serve to increase the refractive index and improve the thermal stability of the glass. However, when the content of Ti ⁴⁺ or W ⁶⁺ 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 shorter wavelength side of the glass has a longer wavelength. Therefore, in the above-mentioned optical glass, each of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ , and W ⁶⁺ is required to improve the thermal stability of the glass and to suppress the increase of the light absorption edge on the short wavelength side of the glass. The ratio of these contents is determined in consideration of the properties. The details are as follows.
Nb ⁵⁺ has the function of increasing the refractive index nd and improving the thermal stability of the glass without increasing the specific gravity, coloring and production cost of the glass. Nb ⁵⁺ is also a component that makes it difficult to increase the absorption edge on the short wavelength side of glass to longer wavelengths as compared to Ti ⁴⁺ and W ⁶⁺ . As is well known, the absorption edge on the short wavelength side of glass can be represented by an index called λ5. That is, Nb ⁵⁺ is a component that makes it difficult to increase λ5 as compared with Ti ⁴⁺ and W ⁶⁺ . Details of λ5 will be described later.
On the other hand, when the content of Ti ⁴⁺ increases, λ5 increases. Further, the transmittance of the glass in the visible region is reduced, and the coloring of the glass tends to increase.
Ta ⁵⁺ has a function of increasing the refractive index, and is a component that is harder to make the absorption end on the short wavelength side of glass longer than Nb ⁵⁺ , Ti ⁴⁺ , and W ⁶⁺ , but is an extremely expensive component. is there. Therefore, from the viewpoint of stable supply of glass, it is not preferable to actively use Ta ⁵⁺ . Further, when the content of Ta ⁵⁺ is large, the raw material tends to remain undissolved when the glass is melted. Also, the specific gravity of the glass increases.
As for the content of W ⁶⁺ , λ5 increases as the content increases. Further, the transmittance in the visible region decreases, and the specific gravity increases.

As described above, Ta ⁵⁺ is a component whose content should be reduced. Therefore, it is not preferable to use Ta ⁵⁺ positively. In order to improve the thermal stability and suppress the longer wavelength of the light absorption edge on the shorter wavelength side (preferably, reduce λ5), in the above glass, Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ The cation ratio {Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )} of the content of Nb ⁵⁺ to the total content of Nb ⁵⁺ , Ti ⁴⁺ and W ⁶⁺ excluding Ta ⁵⁺ is set to 0.80 or more. The preferred lower limit and preferred upper limit of the cation ratio {Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )} are shown in the following table.

As for Ta ⁵⁺ , in order to improve the thermal stability of the glass, reduce the dispersion of the refractive index and reduce the amount of Ta used, the content of Ta ^{5+ with} respect to the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ is improved. Cation ratio {Ta ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} is 0.2 or less. The preferred lower limit and more preferred upper limit of the cation ratio {Ta ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} are shown in the following table.

In addition, as for Nb ⁵⁺ , while reducing the content of Gd ³⁺ and Ta ⁵⁺ in order to enable stable supply of glass, desirably reducing the content of Yb ³⁺ together with Gd ³⁺ and Ta ⁵⁺ , the short wavelength Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ , W ^{6+ in} order to suppress a longer wavelength of the light absorption edge on the side (preferably reduce λ5) and to provide a high-refractive-index low-dispersion glass excellent in thermal stability. In consideration of the above-described action, the cation ratio of the content of Nb ⁵⁺ 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 set to 0. .4 or more. In order to further suppress the increase in the wavelength of the light absorption edge on the short wavelength side, it is preferable to increase the cation ratio {Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )}. More preferable lower and upper limits of the cation ratio {Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} are shown in the following table.

Furthermore, Nb ⁵⁺ and Ti ⁴⁺ are used in order to further suppress the longer wavelength of the light absorption edge on the shorter wavelength side (preferably further suppress the increase of λ5) and to promote the curing of the ultraviolet curable adhesive by the irradiation of ultraviolet rays. , The cation ratio of the Ti ⁴⁺ content to the total content of Ta ⁵⁺ and W ⁶⁺ {Ti ⁴⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} is preferably 0.6 or less. Preferred lower limits and more preferred upper limits of the cation ratio {Ti ⁴⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} are shown in the following table.

Similarly, from the viewpoint of further suppressing the longer wavelength of the light absorption edge on the shorter wavelength side (preferably, further suppressing the increase of λ5), W ⁶⁺ with respect to the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ It is preferable to set the content cation ratio {W ⁶⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} to 0.2 or less. The preferred lower limit and more preferred upper limit of the cation ratio {W ⁶⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} are shown in the following table.

Among Nb ⁵⁺ , Ti ⁴⁺ , and W ⁶⁺ , Ti ⁴⁺ has a strong tendency to increase the coloring of glass, and has a relatively strong effect of increasing λ5. In suppressing the increase in λ5, the cation ratio of the content of Ti ^{4+ to} the total content of Nb ⁵⁺ , Ti ⁴⁺ and W ⁶⁺ (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ ) {Ti ⁴⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )} Is preferably set to a preferable upper limit value shown in the following table. Note that the cation ratio {Ti ⁴⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )} can be set to zero.

In order to suppress the decrease in Abbe number νd while maintaining the thermal stability of the glass, La ³⁺ with respect to the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ ), Y ^3+, the lower limit of the total content of ^{Gd 3+} and ^{Yb 3+ (La 3+ + Y 3+} + Gd 3+ + Yb 3+) cation ratio of ^{{(La 3+ + Y 3+ +} Gd 3+ + Yb 3+) / (Nb 5+ + Ti 4+ + Ta 5+ + W 6+)} Is preferably a lower limit value shown in the following table.
On the other hand, in order to maintain the thermal stability of the glass while suppressing the decrease in the refractive index, the upper limit of the cation ratio {(La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ ) / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} is set. It is preferable to set the upper limit value as shown in the following table.

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

The total content of B ³⁺ and Si ⁴⁺ which are glass network forming components is as described above. Regarding B ³⁺ and Si ⁴⁺ , B ³⁺ has a better function of improving ^fusibility than Si ^4+, but is more likely to volatilize during melting. On the other hand, Si ⁴⁺ has a function of improving the chemical durability, weather resistance, and machinability of the glass, and increasing the viscosity of the glass at the time of melting.
Generally, in a high-refractive-index low-dispersion glass containing a rare earth element 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, it is easy to crystallize. Crystallization at the time of glass production is more stable when crystallized than in an amorphous state (amorphous state), and is caused by ions constituting the glass moving in the glass and arranged so as to have a crystal structure. Therefore, by adjusting the ratio of the content of each component of B ³⁺ and Si ⁴⁺ so as to increase the viscosity at the time of melting, it is difficult to arrange the ions so as to have a crystal structure, and the crystallization of glass is prevented. In addition, it is possible to further suppress the devitrification resistance of the glass.
From the above viewpoints, the preferred lower limit and preferred upper limit of the cation ratio {B ³⁺ / (B ³⁺ + Si ⁴⁺ )} of the B ³⁺ content to the total content of B ³⁺ and Si ⁴⁺ are as shown in the following table. It is preferable that the content be equal to or more than the lower limit shown in the following table from the viewpoint of improving the meltability of glass. 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, to be less than the upper limit shown in the following table, in order to reduce the fluctuation of the glass composition due to volatilization during melting and the fluctuation of the optical properties due to this, and also to the chemical durability, weather resistance and machinability of the glass It is also preferred from the viewpoint of one or more improvements.

For each of the B ³⁺ content and the Si ⁴⁺ content, a preferred lower limit and a preferred upper limit from the viewpoint of improving the devitrification resistance, melting property, moldability, chemical durability, weather resistance, machinability, and the like of the glass, It is shown in the table below.

Zn ²⁺ has a function of promoting the melting of the glass raw material when melting the glass, that is, a function of improving the melting property. Further, it also has functions of adjusting the refractive index nd and Abbe number νd and lowering the glass transition temperature. The value obtained by dividing the content of Zn ²⁺ by the total content of B ³⁺ and Si ⁴⁺ , that is, the cation ratio {Zn ²⁺ / (B ³⁺ + Si ⁴⁺ )} is the suppression of the decrease in Abbe number νd and the thermal property of the glass. From the viewpoints of improvement in stability and suppression of reduction in glass transition temperature (improvement in machinability), the content is preferably 0.15 or less. Since Zn is an optional component that may or may not be contained in the above glass, the cation ratio {Zn ²⁺ / (B ³⁺ + Si ⁴⁺ )} is preferably 0 or more. In order to improve the glass content and to easily produce a homogeneous glass, it is more preferable to include Zn to make the cation ratio {Zn ²⁺ / (B ³⁺ + Si ⁴⁺ )} more than 0. A more preferred lower limit and a more preferred upper limit of the cation ratio {Zn ²⁺ / (B ³⁺ + Si ⁴⁺ )} are shown in the following table.

From the standpoint of improving the meltability, thermal stability, moldability, machinability, etc. of the glass and realizing the above-mentioned optical characteristics, preferred lower and upper limits of the Zn ²⁺ content are as shown in the following table. .

From the viewpoints of further improving the thermal stability of the glass, suppressing the lowering of the glass transition temperature (improving the machinability), and improving the chemical durability, the sum of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ The cation ratio of the Zn ²⁺ content to the content {Zn ²⁺ / (Ti ⁴⁺ + Nb ⁵⁺ + Ta ⁵⁺ + W ⁶⁺ )} is preferably 1.0 or less. On the other hand, since Zn is an optional component, the lower limit of the cation ratio {Zn ²⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} is preferably 0, but the melting property is improved and the light absorption edge on the shorter wavelength side has a longer wavelength. From the viewpoint of further suppressing the formation of the compound (preferably, further suppressing the increase of λ5), it is more preferable to set the value to more than 0. In view of the above, more preferable lower limit and more preferable upper limit of the cation ratio {Zn ²⁺ / (Ti ⁴⁺ + Nb ⁵⁺ + Ta ⁵⁺ + W ⁶⁺ )} are as shown in the following table.

Regarding Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ , and W ⁶⁺ , taking into consideration the above-mentioned actions and effects, preferred ranges of the content of each component of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ , and W ⁶⁺ are shown in the following table.

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

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

Each of Na ⁺ , K ⁺ , Rb ⁺ , and Cs ⁺ has a function of improving the melting property of glass. However, when the content of these elements is increased, the thermal stability, chemical durability, and weather resistance of the glass are increased. In addition, the machinability tends to decrease. Therefore, the lower and upper limits of the respective contents of Na ⁺ , K ⁺ , Rb ⁺ , and Cs ⁺ are preferably as shown in the following table.

From the viewpoint of improving 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 ⁺ + Na ⁺ Preferred lower limits and preferred upper limits of + K ⁺ ) are as shown in the following table.

Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , and Ba ²⁺ are components having a function of improving the melting property of glass. However, when the content of these components increases, the thermal stability of the glass decreases, and the glass tends to be devitrified. Therefore, the content of each of these components is preferably not less than the lower limit shown below, and is preferably not more than the upper limit.

In addition, in order to maintain 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⁺ ) should be equal to or more than the lower limit shown in the following table. Is preferable, and it is preferable that it is 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 tendency to decrease the refractive index nd, a tendency to decrease the thermal stability of the glass, and a tendency to decrease the meltability may be observed. In consideration of the above points, the Al ³⁺ content is preferably equal to or greater than the lower limit shown in the following table, and is preferably equal to or less than the upper limit.

Ga ³⁺ , In ³⁺ , Sc ³⁺ , and Hf ⁴⁺ 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, each content of Ga ³⁺ , In ³⁺ , Sc ³⁺ , and Hf ⁴⁺ is preferably not less than the lower limit shown in the following table, and more preferably not more than the upper limit.

Lu ³⁺ has the function of increasing the refractive index nd, but is also a component that increases the specific gravity of glass. 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, preferable lower and upper limits of the Lu ³⁺ content are as shown in the following table.

Ge ⁴⁺ 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, preferred lower and preferred upper limits of the Ge ⁴⁺ content are as shown in the following table.

Bi ³⁺ is a component that increases the refractive index nd and decreases the Abbe number νd. It is also a component that tends to increase the coloring of the glass. The preferred lower limit and preferred upper limit of the Bi ³⁺ content for producing a glass having the above-mentioned optical properties and less coloring are as shown in the following table.

  In order to obtain the above-mentioned various actions and effects well, the sum of the contents of the cationic components described above (total content) is preferably more than 95%, and more than 98%. More preferably, it is more preferably more than 99%, and even more preferably more than 99.5%.

Among the cation components other than the cation components described above, P ⁵⁺ is a component that lowers the refractive index nd and is a component that lowers the thermal stability of glass. May improve thermal stability. Preferable lower and upper limits of the ^{P5 +} content for producing a glass having the above-mentioned optical properties and excellent thermal stability are as shown in the following table.

Te ⁴⁺ is a component that increases the refractive index nd, but is a toxic component, so it is preferable to reduce the content of Te ⁴⁺ . Preferred lower and upper limits for the Te ⁴⁺ content are as shown in the following table.

  In addition, in each of the above tables, the component in which the (lower) preferable lower limit or 0% is described is preferably also 0% in content. 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 include these elements, that is, not to introduce these elements into glass as glass components.
U, Th, and Ra are all radioactive elements. Therefore, it is preferable not to include these elements, that is, not to introduce these elements into 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 glass or become a source of fluorescence. However, it is not preferable as an element to be contained in glass for an optical element. Therefore, it is preferable not to include these elements, that is, not to introduce these elements into glass as glass components.

Sb and Sn are arbitrarily addable elements that function as fining agents.
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%, It is more preferably in the range of 0.01 to 0.08% by mass, and still more preferably in the range of 0.02 to 0.05% by mass.
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, and further preferably in the range of 0% by mass.

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

Since the glass is an oxide glass, it contains O ²⁻ as an anionic 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%, and still more preferably 100 anion%.
Examples of the anion component other than O ²⁻ include F ⁻ , Cl ⁻ , Br ⁻ , and I ⁻ . However, all of F ⁻ , Cl ⁻ , Br ⁻ , and I ⁻ tend to volatilize during melting of the glass. Due to the volatilization of these components, the properties of the glass fluctuate, and the homogeneity of the glass tends to be reduced, and the melting equipment tends to be significantly consumed. Therefore, it is preferable to suppress the total content of F ⁻ , Cl ⁻ , Br ⁻ and I ⁻ to a value obtained by subtracting the content of O ²⁻ from 100 anion%.
In addition, as is well known, the anion% is a percentage with the total content of all anion components contained in the glass being 100%.

<Glass properties>
(Optical properties of glass)
The above glass has Abbe number νd in the range of 39.5 to 41.5, and refractive index nd satisfies the following expression (1) with respect to Abbe number νd.
nd ≧ 2.0927−0.0058 × vd (1)
Glass having an Abbe number νd of 39.5 or more is effective in correcting chromatic aberration as a material for an optical element. On the other hand, when the Abbe number νd is larger than 41.5, unless the refractive index is reduced, the thermal stability of the glass is significantly reduced, and the glass tends to be devitrified in the course of manufacturing. Preferred lower and upper limits of the Abbe number νd are shown in the following table.

The above glass has a refractive index nd satisfying the expression (1) with respect to the Abbe number νd. Glass whose Abbe number νd is in the range of 39.5 to 41.5 and whose refractive index nd satisfies the expression (1) is a highly useful glass in designing 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 is hardly devitrified, the refractive index nd preferably satisfies the following expression (2).
nd ≦ 2.1270−0.0058 × vd (2)
The lower limit and the 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 shown in the following table, and is preferably not more than the upper limit.

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

(Glass-transition temperature)
The glass transition temperature of the above glass is not particularly limited, but is preferably 640 ° C. or higher. By setting the glass transition temperature to 640 ° C. or higher, the glass can be hardly damaged when the glass is mechanically processed such as cutting, cutting, grinding, and polishing. Further, since it is not necessary to contain a large amount of components such as Li and Zn which have a strong effect of lowering the glass transition temperature, even if the content of Gd and Ta is reduced, the content of Yb is also reduced. In addition, thermal stability can be easily improved.
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 will be significantly consumed. Further, when molding glass, molding must be performed at a high temperature, and the mold used for molding is significantly consumed.
The preferred lower limit and preferred upper limit of the glass transition temperature are as shown in the following table from the viewpoint of improving the machinability and reducing the burden on the annealing furnace and the mold.

(Light transmittance of glass)
The suppression of the light transmittance of the glass, more specifically, the suppression of the longer wavelength of the light absorption edge on the shorter wavelength side can be evaluated by the degree of coloring λ5. The coloring degree λ5 indicates a wavelength at which the spectral transmittance (including surface reflection loss) of a 10-mm-thick glass becomes 5% from the ultraviolet region to the visible region. Λ5 shown in Examples described later is a value measured in a wavelength range of 250 to 700 nm. The spectral transmittance is, for example, more specifically, using a glass sample having planes parallel to each other polished to a thickness of 10.0 ± 0.1 mm, and entering light from the direction perpendicular to the polished surface. Is the spectral transmittance obtained as a result, 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 bonding lenses with an ultraviolet-curing adhesive to produce a cemented lens, the adhesive is irradiated with ultraviolet rays through the optical element to cure the adhesive. 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 range. The coloring degree λ5 can be used as an index for quantitatively evaluating the absorption edge on the short wavelength side. The above glass can exhibit λ5 of preferably 335 nm or less, more preferably 332 nm or less, further preferably 330 nm or less, more preferably 328 nm or less, and still more preferably 326 nm or less, by the composition adjustment described above. The lower limit of λ5 may be, for example, about 315 nm, but is preferably as low as possible and is not particularly limited.

On the other hand, as an index of the degree of coloring of glass, there is a degree of coloring λ70. λ70 represents a wavelength at which the spectral transmittance measured by the method described for λ5 is 70%. From the viewpoint of making the glass less colored, the preferable range of λ70 is 420 nm or less, the more preferable range is 400 nm or less, the more preferable range is 390 nm or less, and the still more preferable range is 380 nm or less. The standard of the lower limit of λ70 is 350 nm, but the lower the standard, the better, and there is no particular limitation.
Further, as an index of the degree of coloring of glass, a degree of coloring λ80 may also be mentioned. λ80 represents the wavelength at which the spectral transmittance measured by the method described for λ5 is 80%. From the viewpoint of making the glass less colored, the preferred range of λ80 is 550 nm or less, the more preferred range is 500 nm or less, the more preferred range is 490 nm or less, and the still more preferred range is 480 nm or less. The standard of the lower limit of λ80 is 355 nm, but the lower the lower, the more preferable, and there is no particular limitation.

(Specific gravity of glass)
In an optical element (lens) constituting an optical system, a refractive power is determined by a refractive index of glass constituting a lens and a curvature of an optical functional surface (a surface on which a light beam to be controlled enters / exits) of the lens. To increase the curvature of the optical function surface, the thickness of the lens also increases. As a result, the lens becomes heavier. 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.
As described above, if the refractive index can be increased while suppressing an increase in the specific gravity of glass, the weight of an optical element having a constant refractive power can be reduced.
The contribution of the refractive index nd to the refractive power is determined by taking 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 a vacuum from the refractive index nd of the glass. It can be used as an index when 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 by reducing this value, the weight of the lens can be reduced.
In the above glass, the ratio of Gd and Ta, which causes an increase in specific gravity, is small, and the ratio of Yb can be reduced, so that the specific gravity can be reduced 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, when d / (nd-1) is excessively reduced, the thermal stability of the glass tends to decrease. Therefore, d / (nd-1) is preferably set to 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, preferred lower limits and preferred upper limits of the specific gravity d of the glass are shown in the following table. It is preferable that the specific gravity d be equal to or less than the upper limit shown in the following table from the viewpoint of reducing the weight of the optical element made of 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)
One of the indicators of the thermal stability of glass is the liquidus temperature. From the viewpoint of suppressing crystallization and devitrification during glass production, the liquidus temperature LT is preferably 1300 ° C. or lower, more preferably 1250 ° C. or lower. The lower limit of the liquidus temperature LT is, for example, 1100 ° C. or higher, but 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 Abbe number νd, and is useful as a glass material for an optical element. Further, by the composition adjustment described above, it is possible to homogenize the glass and to reduce the coloring. Therefore, the above glass is suitable as an optical glass.

<Glass manufacturing method>
The above-mentioned glass is prepared by weighing and mixing raw materials such as oxides, carbonates, sulfates, nitrates, hydroxides and the like so that a desired glass composition can be obtained, and thoroughly mixing to form a mixed batch. 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 glass is a high-refractive-index low-dispersion glass having the above-described optical characteristics, but also has excellent thermal stability, and thus can be stably manufactured by using a known melting method and molding method.

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

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

  The optical element blank is similar to the shape of the target optical element, and is polished to the shape of the optical element (a 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 embodiment, an optical element blank can be produced by a method of press-molding a molten glass obtained by melting an appropriate amount of the above glass (referred to as a direct press 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 glass material for press molding and press molding the produced glass material for press molding.

  The press molding of the glass material for press molding can be performed by a known method in which the glass material for press molding which has been softened by heating is pressed with a press mold. Both heating and press molding can be performed in the air. By annealing after press molding to reduce distortion inside the glass, a homogeneous optical element blank can be obtained.

  The glass material for press molding is a glass gob for press molding that is subjected to mechanical processing such as cutting, grinding, polishing, etc. And those 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 local pressure is applied to the groove portion from the back surface of the grooved surface, and the glass portion is formed at the groove portion. There are a method of breaking a plate and a method of cutting a glass plate with a cutting blade. Further, as a grinding and polishing method, barrel polishing and the like can be mentioned.

  The glass material for press molding can be produced, for example, by molding a molten glass into a mold, casting it into a glass plate, and cutting this 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 press-molding a glass gob for press molding by reheating and softening. A method of producing an optical element blank by reheating and softening glass and press-molding the glass 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,
The present invention relates to an optical element made of the above glass.
The optical element is manufactured using the glass described above. 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 embodiment of the present invention,
A method for producing an optical element, comprising a step of producing an optical element by grinding and / or polishing the optical element blank described above,
Is also provided.

  In the method for manufacturing the optical element, grinding and polishing may be performed by a known method, and by sufficiently washing and drying the surface of the optical element after processing, it is possible to obtain an optical element having high internal quality and surface quality. it can. Thus, an optical element made of the above glass can be obtained. Examples of the optical element include various lenses such as a spherical lens, an aspherical lens, and a micro lens, a prism, and the like.

  Further, the optical element made of the above glass is also suitable as a lens constituting a cemented optical element. Examples of the junction optical element include an element in which lenses are joined (joint lens), an element in which a lens and a prism are joined, and the like. For example, in the case of a bonded optical element, the bonding surface of two optical elements to be bonded is precisely processed (for example, spherical polishing) so that the shape becomes an inverted shape, and an ultraviolet curable adhesive used for bonding the bonded lens is used. Is applied and bonded, and then irradiated with ultraviolet light through a lens to cure the adhesive. The glass is preferable for producing the bonded optical element as described above. A plurality of optical elements to be bonded are manufactured using a plurality of types of glass having different Abbe numbers νd, respectively, and bonded to form an element suitable for correction of chromatic aberration.

As a result of quantitative analysis of the glass composition, the glass component may be represented on an oxide basis, and the content of the glass component may be represented by mass%. The composition expressed in mass% on the oxide basis as described above can be converted into a composition expressed in cation% and anion% by the following method, for example.
If it contains N species of the glass component in the glass, a k-th of the glass component is denoted as A (k) _m O _n. Here, k is any integer from 1 to N.
A (k) is a cation, O is oxygen, and m and n are stoichiometrically determined integers. For example, when the oxide standard is B ₂ O ₃ , m = 2 and n = 3, and when it is SiO ₂ , m = 1 and n = 2.
Next, the content of A _(k) m _{O n,} and X (k) [wt%]. Here, _assuming that the atomic weight of A (k) is P (k) and the atomic number of oxygen O is Q, the formal molecular weight R (k) of A (k) _{m On} is
R (k) = P (k) × m + Q × n
Becomes
further,
B = 100 / {[mxX (k) / R (k)]}
Then, the content (cation%) of the cation component A (k) ^{s +} is [X (k) / R (k)] × m × B (cation%). Here, Σ means the sum of m × X (k) / R (K) from k = 1 to k. m changes according to k. s is 2 n / m.
Further, the molecular weight R (k) may be calculated using a value rounded to the fourth decimal place and displayed to the third decimal place. Table 60 below shows the molecular weights of some glass components and additives based on oxide standards.

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

(Example 1)
Compounds such as oxides and boric acid were weighed as raw materials and mixed sufficiently to produce batch raw materials so that glasses having the compositions shown in the following table were obtained.
This batch raw material was put in a platinum crucible and heated together with the crucible 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 agitated and homogenized, the molten glass was cast into a preheated mold, allowed to cool to near the glass transition temperature, and immediately placed together with the mold in an annealing furnace. Then, annealing was performed at about the glass transition temperature for about 1 hour. After annealing, it was allowed to cool to room temperature in an annealing furnace.
Observation of the glass thus produced revealed no precipitation of crystals, no bubbles, no striae, and no undissolved raw materials. In this way, a highly homogeneous glass could be produced.

(Comparative Examples 1-4)
In order to obtain glasses having the respective compositions of Comparative Examples 1 to 4 shown in the following table, oxides, compounds such as boric acid were weighed as raw materials, and sufficiently mixed to prepare batch raw materials. A glass was obtained in the same manner as in Example 1.
The composition of Comparative Example 1 is the same as that of Glass No. A composition obtained by converting the composition of No. 11 into a glass composition expressed by cation%;
Comparative Example 2 is the glass No. A composition obtained by converting the composition of No. 25 into a glass composition expressed by cation%;
Comparative Example 3 is the glass No. A composition obtained by converting the composition of No. 45 into a glass composition expressed by cation%;
Comparative Example 4 is glass No. A composition obtained by converting the composition of No. 49 into a glass composition expressed by cation%;
It is.

The glass properties of the obtained glass were measured by the following methods. 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 a refractive index measurement method specified by the Japan Optical Glass Industrial Association. The Abbe number νd was calculated using the measured values of the refractive indexes nd, nF, and nc.
(2) Glass transition temperature Tg
The measurement was performed at a heating rate of 10 ° C./min using a differential scanning calorimeter (DSC).
(3) Specific gravity Measured by 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 facing each other, light having an intensity Iin is incident on the polished surface in a direction perpendicular to the polished surface using a spectrophotometer. Is measured, 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. % Was 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. After cooling, the inside of the glass was observed with an optical microscope of 100 times, and the liquidus temperature was determined from the presence or absence of crystals.

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

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

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

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

(Comparative Example 5)
No. 1 shown in Table 8 of JP-A-2014-62026. 51 glasses (hereinafter, referred to as glass I) were reproduced. Λ5 of Glass I described in Table 8 of JP-A-2014-62026 is 337 nm.
Next, in the same manner as in Example 5, a spherical lens made of glass I was produced, and an attempt was made to produce a cemented lens using the produced spherical lens. However, when the ultraviolet curable adhesive applied to the bonding surface was irradiated with ultraviolet light through a lens made of glass I, the adhesive could not be sufficiently cured because the ultraviolet light transmittance of glass I was low.

(Comparative Example 6)
The glass according to one embodiment of the present invention has a cation ratio of {Zn ²⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} of less than 0.2.
On the other hand, No. 1 shown in Table 1 of JP-A-2014-62026. The cation ratio of the glass No. 6 is 0.578. No. 1 shown in Table 1 of JP-A-2014-62026. In order to make the glass composition of the glass of No. 6 have a cation ratio of less than 0.2, Zn ²⁺ is reduced, and the reduced amount is replaced with another component so that the balance of the content of the other component does not change significantly. The glass was prepared by allocating and adjusting the composition as shown in Table 62 below. The ratio between the glass components in Table 62 is the cation ratio. Specifically, a glass raw material was prepared, 170 g of the prepared raw material was put in a platinum crucible, and melted and refined at 1400 ° C. for 2 hours. After the molten glass was agitated and homogenized, the molten glass was cast into a preheated mold, allowed to cool to near the glass transition temperature, and immediately placed together with the mold in an annealing furnace. Then, annealing was performed at about the glass transition temperature for about 1 hour. After annealing, it was allowed to cool to room temperature in an 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 the glass became cloudy and lost transparency.
On the other hand, in the glass according to one embodiment of the present invention, the crystal adjustment can be suppressed by performing the composition adjustment described in detail above.

  Finally, each of the above-described embodiments will be summarized.

According to one embodiment, in terms of cation%, the total content of B ³⁺ and Si ⁴⁺ is 43 to 65%, the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 25 to 50%, Nb The total content of ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ is 3 to 12%, the content of Zr ⁴⁺ is 2 to 8%, and the content of B ³⁺ and Si with respect to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ^{3+. 4+} total content of the cation ratio of ^{{(B 3+ + Si 4+)} / (La 3+ + Y 3+ + Gd 3+ + Yb 3+)} is ^0.70~1.75, Nb ^5+, Ti ^4+, total ^{Ta 5+} and ^{W 6+} The cation ratio of the total content of B ³⁺ and Si ⁴⁺ to the content {(B ³⁺ + Si ⁴⁺ ) / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} is 9.00 or less, La ³⁺ , Y The cation ratio of Zn ²⁺ content to the total content of ³⁺ , Gd ³⁺ and Yb ³⁺ {Zn ²⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} is less than 0.2, La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ^{La 3+} content content of the cation ratio to the total content of ^{3+ {La 3+ / (La 3+} + Y 3+ + Gd 3+ + Yb 3+)} is ^{0.50~0.95, La 3+, Y 3+,} Gd 3+ and ^{Yb 3+} the total content relative ^{Y 3+} content of the cation ratio of ^{{Y 3+ / (La 3+ +} Y 3+ + Gd 3+ + Yb 3+)} is 0.10 to ^0.50, La ^3+, total content of Y 3+, ^{Gd 3+} and ^{Yb 3+ Gd 3+} content of the cation ratio to the amount ^{{Gd 3+ / (La 3+ +} Y 3+ + Gd 3+ + Yb 3+)} is 0.10 or less, b ^{5+, Ti 4+} and ^{W 6+ Nb 5+} content of the cation ratio to the total content of ^{{Nb 5+ / (Nb 5+ +} Ti 4+ + W 6+)} is 0.80 or ^{more, Nb 5+, Ti 4+, Ta} 5+ , and ^{W 6+} the cation ratio of ^{Ta 5+} content to the total content of ^{{Ta 5+ / (Nb 5+ +} Ti 4+ + Ta 5+ + W 6+)} is 0.2 or less, a, in the range of Abbe number νd is 39.5 to 41.5 It is possible to provide a glass that is an oxide glass having a refractive index nd that satisfies the above formula (1) with respect to the Abbe number νd.

  The above glass is a glass satisfying the expression (1), and is a high-refractive-index low-dispersion glass useful in an optical system. The above glass can be supplied stably because the ratio of Gd and Ta in the glass composition is reduced, and obtain high thermal stability by satisfying the above-mentioned contents, total contents and cation ratio. And the longer wavelength of the light absorption edge on the shorter wavelength side can be suppressed.

In one aspect, from the viewpoint of stable supply of glass, the content of Gd ³⁺ in the above glass is preferably 3 cation% or less.

In one aspect, from the viewpoint of stable supply of glass, the Ta ⁵⁺ content in the glass is preferably 3.0 cation% or less.

  In one aspect, it is preferable that in the glass, the increase in 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.

  From the glass 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, there is provided a glass material for press molding comprising the above glass, an optical element blank, and an optical element.

  According to another aspect, there is also provided a method of manufacturing a glass material for press molding, comprising a step of forming the glass into a glass material for press molding.

  According to still another aspect, there is also provided a method for producing an optical element blank, comprising a step of producing 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, comprising a step of forming the glass into an optical element blank.

  According to still another aspect, there is also provided a method of 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 in all respects as illustrative 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 according to one embodiment of the present invention can be obtained by performing the composition adjustment described in the specification on the above-described glass composition.
In addition, it is of course possible to arbitrarily combine two or more of the items described as examples or preferable ranges in the specification.

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

Claims (7)

In cation% display,
The total content of B ³⁺ and Si ⁴⁺ is 43 to 65%,
The total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 25 to 50%;
The total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ is 3 to 12%,
Zr4 ⁺ content of 2 to 8%,
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 0.70 to 1.75;
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 9.00 or less,
The cation ratio of Zn ²⁺ content to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ {Zn ²⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} is 0. Less than 2.
Cation ratio of La ³⁺ content to total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ {La ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} Is 0.50 to 0.95,
The cation ratio {Y ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} of the Y ³⁺ content to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 0. .10 to 0.50,
The cation ratio {Gd ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} of the Gd ³⁺ content to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 0. .10 or less,
The cation ratio of the Nb ⁵⁺ content to the total content of Nb ⁵⁺ , Ti ⁴⁺ and W ⁶⁺ {Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )} is 0.80 or more;
The cation ratio {Ta ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} of the Ta ⁵⁺ content to the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ is 0. .2 or less,
And
Coloring degree λ5 is 335 nm or less,
Abbe number νd is in the range of 39.5 to 41.5, and refractive index nd is the following formula (1) with respect to Abbe number νd:
nd ≧ 2.0927−0.0058 × νd (1)
A glass that is an oxide glass that satisfies In cation% display,
The total content of B ³⁺ and Si ⁴⁺ is 43 to 65%,
The total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 25 to 50%;
The total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ is 3 to 12%,
Zr4 ⁺ content of 2 to 8%,
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 0.70 to 1.75;
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 9.00 or less,
The cation ratio of Zn ²⁺ content to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ {Zn ²⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} is 0. Less than 2.
Cation ratio of La ³⁺ content to total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ {La ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} Is 0.50 to 0.95,
The cation ratio {Y ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} of the Y ³⁺ content to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 0. .10 to 0.50,
The cation ratio {Gd ³⁺ / (La ³⁺ + Y ³⁺ + Gd ³⁺ + Yb ³⁺ )} of the Gd ³⁺ content to the total content of La ³⁺ , Y ³⁺ , Gd ³⁺ and Yb ³⁺ is 0. .10 or less,
The cation ratio of the Nb ⁵⁺ content to the total content of Nb ⁵⁺ , Ti ⁴⁺ and W ⁶⁺ {Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )} is 0.80 or more;
The cation ratio {Ta ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + Ta ⁵⁺ + W ⁶⁺ )} of the Ta ⁵⁺ content to the total content of Nb ⁵⁺ , Ti ⁴⁺ , Ta ⁵⁺ and W ⁶⁺ is 0. .2 or less,
The cation ratio of the content of Nb ⁵⁺ to the total content of Nb ⁵⁺ , Ti ⁴⁺ and W ⁶⁺ {Nb ⁵⁺ / (Nb ⁵⁺ + Ti ⁴⁺ + W ⁶⁺ )} is 0.90 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 formula (1) with respect to the Abbe number νd:
nd ≧ 2.0927−0.0058 × νd (1)
And a ratio d / (nd-1), which is a ratio of specific gravity d to a value obtained by subtracting 1 from the refractive index nd, is 5.70 or less. The glass according to claim 1 or 2 , wherein the content of Gd ³⁺ is 3 cation% or less. The glass according to any one of claims 1 to 3 , wherein the ^{Ta5 +} content is 3.0 cation% or less. Claim 1 glass material for press molding comprising a glass according to any one of 4. Optical element blank formed of a glass according to any one of claims 1-4. Optical elements of glass according to any one of claims 1-4.