JP7050294B2 - Optical glass, preforms for precision press molding, and optical elements - Google Patents

Description

The present invention relates to optical glass, preforms for precision press molding, and optical elements.

High-refractive-index, high-dispersible glass having a refractive index (nd) of 1.800 or more and an Abbe number (νd) of 32.0 or less is in demand for a wide range of applications. It is manufactured.
Further, among the above-mentioned high refractive index and high dispersibility glasses, the glass having a relatively low dispersibility with respect to the refractive index (the number of abbreviations is relatively large) when viewed in terms of the balance between the refractive index and the dispersibility is more specific. Specifically, in an orthogonal coordinate system having the Abbe number (νd) as the x-axis and the refractive index (nd) as the y-axis, the points at (25.0, 1.860) and (30.0, 1.800). There is a specific need for a high refractive index high dispersibility glass having an abbreviation number and a refractive index located on the high refractive index side of a straight line drawn so as to pass through the point. More specifically, the above-mentioned high-refractive index and high-dispersion glass is in demand for optical components such as digital cameras, projectors, and camera interchangeable lenses.

As such a highly refractive index and highly dispersible glass, for example, Patent Document 1 contains SiO ₂ and B ₂ O ₃ as basic components, and ZnO, rare earth oxides, TiO ₂ and Nb ₂ O ₅ in predetermined proportions, respectively. The glass contained in is disclosed. The glass disclosed in Patent Document 1 is so-called borosilicate glass, and a glass having an Abbe number (νd) of 29 or more and 32 or less and a refractive index (nd) of 1.83 or more was actually obtained. Is disclosed.

However, in general, in the production of borosilicate glass, it is necessary to heat the raw material to a relatively high temperature of 1300 ° C. or higher, and this is no exception to the glass of Patent Document 1 described above. Therefore, the above-mentioned glass has a problem in that the temperature at which the raw material is melted at the time of manufacturing (hereinafter, may be referred to as “melting temperature”) is lowered, and the cost and energy saving in the manufacturing are achieved.

On the other hand, it is known that phosphoric acid-based glass generally has a lower melting temperature than borosilicate glass. As phosphoric acid-based glass having a high refractive index and high dispersibility, for example, Patent Document 2 describes P ₂ O ₅ , B ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, CaO, TiO ₂ , Bi. Disclosed is a glass containing ₂ O ₃ , Nb ₂ O ₅ and WO ₃ in a predetermined composition. Similarly, as phosphoric acid-based glass having a high refractive index and high dispersibility, for example, Patent Document 3 describes P ₂ O ₅ , B ₂ O ₃ , WO ₃ , Nb ₂ O ₅ , TiO ₂ , Li ₂ O and Na ₂ . A glass containing O as an essential component in a predetermined ratio is disclosed.

Japanese Unexamined Patent Publication No. 2007-254197 Japanese Unexamined Patent Publication No. 2008-303112 Patent No. 3798268

However, although the glass having the composition disclosed in Patent Document 2 and Patent Document 3 can be recognized as having a high refractive index and high dispersibility, the refractive index is relatively small with respect to the Abbe number, which is more specific. Since the Abbe number (νd) and the refractive index (nd) are located on the lower refractive index side than the above-mentioned straight line in the above-mentioned orthogonal coordinate system, they do not meet specific needs.

From the above, it is required to develop a glass having an optical constant that can meet the above-mentioned specific needs and having a low melting temperature.

The present invention has been developed in view of the above-mentioned current situation, and has a high refractive index and high dispersibility with a refractive index (nd) of 1.800 or more and an Abbe number (νd) of 32.0 or less. It is an object of the present invention to provide an optical glass having a high optical constant index and which does not require an excessively high temperature when melting a raw material. Another object of the present invention is to provide a preform for precision press molding and an optical element using the above optical glass.

As a result of diligent studies to achieve the above object, the present inventor has P ₂ O ₅ , Li ₂ O, Nb ₂ O ₅ , and BaO as basic compositions, and the total of BaO, SrO, CaO, and MgO. By adjusting the balance between the total of alkali metal oxides and the total amount of alkali metal oxides, an optical glass having a desired optical constant without using a predetermined component such as TiO ₂ and having a relatively low melting temperature of the raw material can be obtained. I found that I could get it.

That is, the optical glass of the present invention is
By mass%,
P ₂ O ₅ : 10% or more and 30% or less,
B ₂ O ₃ : 0% or more and 10% or less,
Li ₂ O: 1% or more and 5% or less,
K ₂ O: 0% or more and 10% or less,
Nb ₂ O ₅ : 25% or more and 50% or less,
WO ₃ : 0% or more and less than 9%,
Ta ₂ O ₅ : 0% or more and 10% or less,
BaO: 5% or more and 40% or less,
SrO: 0% or more and 20% or less,
CaO: 0% or more and 10% or less,
MgO: 0% or more and 10% or less,
ZnO: 0% or more and 10% or less,
Bi ₂ O ₃ : 0% or more and 15% or less,
Y ₂ O ₃ : 0% or more and 10% or less,
La ₂ O ₃ : 0% or more and 5% or less,
Gd ₂ O ₃ : 0% or more and 5% or less,
SiO ₂ : 0% or more and 5% or less,
Has a composition containing
Does not contain Ti and Na
When the total content of BaO, SrO, CaO and MgO is RO and the total content of Li ₂ O and K ₂ O is _R'2 O,
It is characterized in that RO is more than 20% and 40% or less, and RO / _R'2 O is more than 3.1. Such an optical glass has a high refractive index and high dispersibility with a refractive index (nd) of 1.800 or more and an Abbe number (νd) of 32.0 or less, and has an optical constant with a relatively high refractive index. Moreover, an excessively high temperature is not required when melting the raw materials.

The optical glass of the present invention has a refractive index (nd) and an Abbe number (νd) in a Cartesian coordinate system having the Abbe number (νd) as the x-axis and the refractive index (nd) as the y-axis at point A (25. 0, 1.860), point B (30.0, 1.800), point C (32.0, 1.820), point D (27.0, 1.880) connected by a straight line. It can be located in the area surrounded by AB, BC, CD, DA.

Further, the preform for precision press molding of the present invention is characterized in that the above optical glass is used as a material.

Further, the optical element of the present invention is characterized in that the above optical glass is used as a material.

According to the present invention, it has an optical constant with a relatively high refractive index even though it has a high refractive index and high dispersibility with a refractive index (nd) of 1.800 or more and an Abbe number (νd) of 32.0 or less. Moreover, it is possible to provide an optical glass that does not require an excessively high temperature when melting the raw materials. Further, according to the present invention, it is possible to provide a preform for precision press molding and an optical element using the above optical glass.

It is a figure which shows the range of the Abbe number (νd) and the refractive index (nd) which an optical glass of one Embodiment of this invention can have.

(Optical glass)
Hereinafter, the optical glass of one embodiment of the present invention (hereinafter, may be referred to as “optical glass of the present embodiment”) will be specifically described. The optical glass of this embodiment is based on mass%.
P ₂ O ₅ : 10% or more and 30% or less,
B ₂ O ₃ : 0% or more and 10% or less,
Li ₂ O: 1% or more and 5% or less,
K ₂ O: 0% or more and 10% or less,
Nb ₂ O ₅ : 25% or more and 50% or less,
WO ₃ : 0% or more and less than 9%,
Ta ₂ O ₅ : 0% or more and 10% or less,
BaO: 5% or more and 40% or less,
SrO: 0% or more and 20% or less,
CaO: 0% or more and 10% or less,
MgO: 0% or more and 10% or less,
ZnO: 0% or more and 10% or less,
Bi ₂ O ₃ : 0% or more and 15% or less,
Y ₂ O ₃ : 0% or more and 10% or less,
La ₂ O ₃ : 0% or more and 5% or less,
Gd ₂ O ₃ : 0% or more and 5% or less,
SiO ₂ : 0% or more and 5% or less,
Has a composition containing
Does not contain Ti and Na
When the total content of BaO, SrO, CaO and MgO is RO and the total content of Li ₂ O and K ₂ O is _R'2 O,
It is characterized in that RO is more than 20% and 40% or less, and RO / _R'2 O is more than 3.1.

The optical glass of the present embodiment may contain other components (described later) other than the above-mentioned components. However, the optical glass of the present embodiment has the above-mentioned components (P ₂ O ₅ , B ₂ O ₃ , Li ₂ O, K ₂ ) from the viewpoint of more reliably expressing the desired optical constant and reduction of the melting temperature. O, Nb ₂ O ₅ , WO ₃ , Ta ₂ O ₅ , BaO, SrO, CaO, MgO, ZnO, Bi ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ and SiO ₂ ) only It is preferable to have a composition consisting of.
Here, "consisting only of the above-mentioned components" includes a case where an impurity component other than the component is inevitably mixed, specifically, the ratio of the impurity component is 0.2% by mass or less. And.

First, in the present embodiment, the reason why the composition of the optical glass is limited to the above range will be described. In addition, unless otherwise specified, the "%" indication regarding a component shall mean mass%.

<P ₂ O ₅ >
P ₂ O ₅ is an essential component in the optical glass of the present embodiment, and is a main component forming a network structure that forms the skeleton of the glass. However, when the content of P ₂ O ₅ in the optical glass exceeds 30%, the refractive index decreases and the desired optical constant cannot be obtained, and the glass transition temperature (Tg) and the yield temperature (At) increase. do. Further, when the content of P ₂ O ₅ in the optical glass exceeds 30%, the liquid phase temperature and the melting temperature also rise. On the other hand, if the content of P ₂ O ₅ in the optical glass is less than 10%, the glass cannot be stabilized and the tendency of devitrification increases. Therefore, in the optical glass of the present embodiment, the content of P ₂ O ₅ is set in the range of 10% or more and 30% or less. From the same viewpoint, the content of P ₂ O ₅ in the optical glass of the present embodiment is preferably 12% or more, more preferably 13% or more, and preferably 28% or less. , 26% or less is more preferable.

<B ₂ O ₃ >
In the optical glass of the present embodiment, B ₂ O ₃ is an effective component for forming a glass network structure and using an appropriate amount in the same manner as P ₂ O ₅ for homogenizing the glass and improving the meltability. However, when the content of B ₂ O ₃ in the optical glass exceeds 10%, the glass becomes unstable and the tendency of devitrification increases. Therefore, in the optical glass of the present embodiment, the content of B ₂ O ₃ is set in the range of 0% or more and 10% or less. From the same viewpoint, the content of B ₂ O ₃ in the optical glass of the present embodiment is preferably 8% or less, and more preferably 6% or less.

<Li ₂ O>
Li ₂ O is an essential component in the optical glass of the present embodiment, and is effective in reducing the melting temperature and increasing the refractive index, and is also an effective component in reducing the glass transition temperature (Tg). In particular, Li ₂ O can increase the polarizability of non-crosslinked oxygen in the glass, so that the refractive index can be improved more effectively. However, if the Li ₂ O content in the optical glass exceeds 5%, the devitrification resistance and chemical durability of the glass deteriorate, and the expansion coefficient of the glass becomes large, so that the lens surface is formed during precision press molding. Accurate transfer of is difficult. On the other hand, if the Li ₂ O content in the optical glass is less than 1%, at least the effects of increasing the refractive index and reducing the glass transition temperature (Tg) cannot be sufficiently obtained. Therefore, in the optical glass of the present embodiment, the Li ₂ O content is set in the range of 1% or more and 5% or less. From the same viewpoint, the Li ₂ O content in the optical glass of the present embodiment is preferably 1.5% or more, more preferably 2% or more, and more preferably 4% or less. It is preferably 3.8% or less, and more preferably 3.8% or less.

<K ₂ O>
K ₂ O is effective in reducing the melting temperature and the glass transition temperature (Tg) in the optical glass of the present embodiment, and by using an appropriate amount in combination with Li ₂ O, the liquid phase temperature of the glass due to the mixed alkali effect. It is an ingredient that can lower the temperature. However, if the K ₂ O content in the optical glass exceeds 10%, the devitrification resistance and chemical durability of the glass may deteriorate, and the expansion coefficient of the glass becomes large. Moreover, even if the devitrification resistance is maintained, it becomes impossible to maintain a high refractive index. Therefore, in the optical glass of the present embodiment, the content of K ₂ O is set in the range of 0% or more and 10% or less. From the same viewpoint, the content of K ₂ O in the optical glass of the present embodiment is preferably 8% or less, more preferably 6% or less.

<Nb ₂ O ₅ >
Nb ₂ O ₅ is an essential component in the optical glass of the present embodiment, and is an essential component effective for increasing the refractive index and improving the chemical durability. However, when the content of Nb ₂ O ₅ in the optical glass exceeds 50%, the melting temperature becomes significantly high. On the other hand, if the content of Nb ₂ O ₅ in the optical glass is less than 25%, the refractive index cannot be sufficiently increased and the desired optical constant cannot be obtained. Therefore, in the optical glass of the present embodiment, the content of Nb ₂ O ₅ is set in the range of 25% or more and 50% or less. From the same viewpoint, the content of Nb ₂ O ₅ in the optical glass of the present embodiment is preferably 30% or more, more preferably 33% or more, and preferably 45% or less. , 40% or less is more preferable.

<WO ₃ >
WO ₃ is effective in obtaining a desired optical constant in the optical glass of the present embodiment, and when used in an appropriate amount in combination with Nb ₂ O ₅ , the refractive index does not increase the yield temperature (At). Is an ingredient that can be adjusted. However, when the content of WO ₃ in the optical glass is 9% or more, the dispersibility becomes too high, and there is a possibility that the glass is colored, the chemical durability is deteriorated, and the glass specific gravity is increased. Therefore, in the optical glass of the present embodiment, the content of WO ₃ is set in the range of 0% or more and less than 9%. From the same viewpoint, the content of WO ₃ in the optical glass of the present embodiment is preferably 8.8% or less, and more preferably 8.6% or less.

<Ta ₂ O ₅ >
Ta ₂ O ₅ is an effective component for increasing the refractive index and improving the chemical durability in the optical glass of the present embodiment. However, when the content of Ta ₂ O ₅ in the optical glass exceeds 10%, the meltability of the glass is significantly deteriorated and the glass becomes unstable. Therefore, in the optical glass of the present embodiment, the content of Ta ₂ O ₅ is set in the range of 0% or more and 10% or less. From the same viewpoint, the content of Ta ₂ O ₅ in the optical glass of the present embodiment is preferably 9% or less, more preferably 8% or less.

<BaO>
BaO is an essential component in the optical glass of the present embodiment, and is an effective component for increasing the refractive index and lowering the liquidus temperature to improve the devitrification resistance. However, when the BaO content in the optical glass exceeds 40%, the glass becomes unstable, the tendency to devitrify increases, and the chemical durability of the glass deteriorates. On the other hand, if the BaO content in the optical glass is less than 5%, the refractive index cannot be sufficiently increased and a desired optical constant cannot be obtained. Therefore, in the optical glass of the present embodiment, the BaO content is set in the range of 5% or more and 40% or less. From the same viewpoint, the content of BaO in the optical glass of the present embodiment is preferably 6% or more, more preferably 8% or more, and preferably 35% or less, preferably 30%. The following is more preferable.

<SrO>
SrO is an effective component for increasing the refractive index and lowering the liquidus temperature to improve the devitrification resistance in the optical glass of the present embodiment. However, when the SrO content in the optical glass exceeds 20%, the glass becomes unstable, the tendency to devitrify increases, and the chemical durability of the glass deteriorates. Therefore, in the optical glass of the present embodiment, the content of SrO is set in the range of 0% or more and 20% or less. From the same viewpoint, the content of SrO in the optical glass of the present embodiment is preferably 19% or less, more preferably 18% or less.

<CaO>
CaO is an effective component for lowering the liquidus temperature and improving the devitrification resistance in the optical glass of the present embodiment. However, when the CaO content in the optical glass exceeds 10%, the glass becomes unstable, the tendency to devitrify increases, and the chemical durability of the glass deteriorates. Therefore, in the optical glass of the present embodiment, the CaO content is set in the range of 0% or more and 10% or less. From the same viewpoint, the CaO content in the optical glass of the present embodiment is preferably 8% or less, and more preferably 5% or less.

<MgO>
MgO is an effective component for lowering the liquidus temperature and improving the devitrification resistance in the optical glass of the present embodiment. However, when the content of MgO in the optical glass exceeds 10%, the glass becomes unstable, the tendency of devitrification increases, and the meltability of the glass deteriorates. Therefore, in the optical glass of the present embodiment, the MgO content is set in the range of 0% or more and 10% or less. From the same viewpoint, the content of MgO in the optical glass of the present embodiment is preferably 8% or less, and more preferably 5% or less.

<Total of BaO, SrO, CaO and MgO>
Here, the optical glass of the present embodiment requires that the total content of BaO, SrO, CaO and MgO (represented by "RO" in the present specification) is more than 20% and 40% or less. .. When the total content exceeds 40%, the glass becomes unstable and the tendency to devitrify increases. On the other hand, if the total content is 20% or less, the refractive index cannot be sufficiently increased and a desired optical constant cannot be obtained.
The total content of BaO, SrO, CaO and MgO in the optical glass of the present embodiment is preferably 35% or less, preferably 33% or less, from the viewpoint of more effectively suppressing devitrification of the glass. It is more preferably 20.5% or more, and more preferably 21% or more from the viewpoint of further increasing the refractive index.

<Ratio of RO and _R'2 O>
Further, in the optical glass of the present embodiment, when the total content of BaO, SrO, CaO and MgO is RO and the total content of Li ₂ O and K ₂ O is _R'2 O, RO / _R'2 O needs to exceed 3.1. The present inventor has a tendency that metal ions such as Ba, Sr, Ca and Mg have a higher ionic electric field strength than alkali metal ions and can further increase the polarizability of unbridged oxygen in glass. Based on this finding, by optimizing the ratio of RO and _R'2 O while limiting the content of each component while considering the influence of density, the refractive index is high even in high dispersibility. Found that a relatively high optical constant can be obtained. If RO / _R'2 O is 3.1 or less, the refractive index cannot be sufficiently increased and a desired optical constant cannot be obtained. In this regard, a method of compensating for the increase in the refractive index can be considered by adding a large amount of components (for example, Nb ₂ O ₅ , WO ₃ , etc.) having a large valence and which can contribute to the increase in the refractive index. However, since all of these components have a function of increasing dispersibility (reducing the Abbe number), even if a large amount is added, the desired optical constant cannot be obtained. Moreover, since all of the above-mentioned components are difficult to melt, the addition of a large amount causes an increase in the melting temperature and a long boiling time.
Further, the RO / _R'2 O in the optical glass of the present embodiment is preferably more than 3.5 and more than 4.0 from the viewpoint of obtaining a desired optical constant by further increasing the refractive index. Is more preferable.

<ZnO>
ZnO is an effective component for increasing the refractive index, lowering the bending temperature (At), and reducing the expansion coefficient in the optical glass of the present embodiment. However, when the ZnO content in the optical glass exceeds 10%, the tendency of the glass to devitrify increases and the melting temperature also rises. Therefore, in the optical glass of the present embodiment, the ZnO content is set in the range of 0% or more and 10% or less. From the same viewpoint, the ZnO content in the optical glass of the present embodiment is preferably 9% or less, more preferably 8% or less.

<Bi ₂ O ₃ >
Bi ₂ O ₃ is an effective component for increasing the refractive index and also for reducing the glass transition temperature (Tg) in the optical glass of the present embodiment. However, if the content of Bi ₂ O ₃ in the optical glass exceeds 15%, the specific gravity of the glass may increase, and the noble metal constituting the melting vessel may be easily eroded, resulting in coloring of the glass. be. Further, if the Bi ₂ O ₃ content in the optical glass exceeds 15%, the surface of the lens after press molding may become cloudy. Therefore, in the optical glass of the present embodiment, the content of Bi ₂ O ₃ is set in the range of 0% or more and 15% or less. From the same viewpoint, the content of Bi ₂ O ₃ in the optical glass of the present embodiment is preferably 13% or less, more preferably 11% or less.

<Y ₂ O ₃ >
Y ₂ O ₃ is an effective component for increasing the refractive index and improving the chemical durability in the optical glass of the present embodiment. However, when the content of Y ₂ O ₃ in the optical glass exceeds 10%, the meltability of the glass is significantly deteriorated and the glass becomes unstable. Therefore, in the optical glass of the present embodiment, the content of Y ₂ O ₃ is set in the range of 0% or more and 10% or less. From the same viewpoint, the content of Y ₂ O ₃ in the optical glass of the present embodiment is preferably 8% or less, and more preferably 5% or less.

<La ₂ O ₃ >
La ₂ O ₃ is an effective component for increasing the refractive index and improving the chemical durability in the optical glass of the present embodiment. However, when the content of La ₂ O ₃ in the optical glass exceeds 5%, the meltability of the glass is significantly deteriorated and the glass becomes unstable. Therefore, in the optical glass of the present embodiment, the content of La ₂ O ₃ is set in the range of 0% or more and 5% or less. From the same viewpoint, the content of La ₂ O ₃ in the optical glass of the present embodiment is preferably 4.5% or less, and more preferably 4% or less.

<Gd ₂ O ₃ >
Gd ₂ O ₃ is an effective component for increasing the refractive index and improving the chemical durability in the optical glass of the present embodiment. However, when the content of Gd ₂ O ₃ in the optical glass exceeds 5%, the meltability of the glass is significantly deteriorated and the glass becomes unstable. Therefore, in the optical glass of the present embodiment, the content of Gd ₂ O ₃ is set in the range of 0% or more and 5% or less. From the same viewpoint, the content of Gd ₂ O ₃ in the optical glass of the present embodiment is preferably 4.5% or less, and more preferably 4% or less.

<SiO ₂ >
SiO ₂ is a component that can increase the viscosity of the melt and stabilize the glass in the optical glass of the present embodiment. However, when the content of SiO ₂ in the optical glass exceeds 5%, the refractive index decreases, the desired optical constant cannot be obtained, and the glass transition temperature (Tg) and the yield temperature (At) increase. Further, when the content of SiO ₂ in the optical glass exceeds 5%, the liquid phase temperature and the melting temperature also rise. Therefore, in the optical glass of the present embodiment, the content of SiO ₂ is set in the range of 0% or more and 5% or less. From the same viewpoint, the content of SiO ₂ in the optical glass of the present embodiment is preferably 3% or less, and more preferably 2% or less.

<Ti (non-containing component)>
The optical glass of the present embodiment needs to be free of Ti. In the optical glass containing the above-mentioned components, if Ti (for example, TiO ₂ ) is used, the refractive index can be increased, but the dispersibility is correspondingly increased, and the desired optical constant cannot be obtained. Moreover, the melting temperature is significantly increased.

<Na (non-containing component)>
Further, it has been found that in an optical glass containing the above-mentioned components, Na (for example, Na ₂ O) may significantly deteriorate the devitrification resistance and hinder the achievement of a desired optical constant. Therefore, it was decided that the optical glass of the present embodiment does not contain Na.

<Other ingredients>
The optical glass of the present embodiment contains a small amount (for example, 5% each) of other components other than the above-mentioned components, such as ZrO ₂ , Sb ₂ O ₃ , GeO ₂ , and Ga ₂ O ₃ , unless the purpose is not deviated. Can be included (below).
The optical glass of the present embodiment preferably does not contain components having a high environmental load or adverse effect on the human body, such as PbO, TeO ₂ , As ₂ O ₃ , and CdO.

Next, various characteristics of the optical glass of the present embodiment will be described.

<Refractive index (nd) and Abbe number (νd)>
The optical glass of the present embodiment has a high refractive index and high dispersibility with a refractive index (nd) of 1.800 or more and an Abbe number (νd) of 32.0 or less, and has an optical constant with a relatively high refractive index. Can have. More specifically, as shown in FIG. 1, the refractive index (nd) and the Abbe number (νd) of the optical glass of the present embodiment have the Abbe number (νd) as the x-axis and the refractive index (nd) as the y-axis. In the Cartesian coordinate system, the position is on a straight line drawn so as to pass through points A (25.0, 1.860) and B (30.0, 1.800) or on the higher refractive index side than the straight line. can do. Therefore, the optical glass of the present embodiment can meet a specific need.

Further, the optical glass of the present embodiment preferably has a refractive index (nd) of 1.800 or more, and preferably 1.805 or more, from the viewpoint of greatly expanding the degree of freedom in optical design using the optical glass. It is more preferably 1.810 or more, still more preferably 1.880 or less, still more preferably 1.875 or less, still more preferably 1.870 or less. Similarly, the optical glass of the present embodiment preferably has an Abbe number (νd) of 25.0 or more, preferably 25.5 or more, from the viewpoint of greatly expanding the degree of freedom in optical design using the optical glass. Is more preferably 26.0 or more, more preferably 32.0 or less, still more preferably 31.0 or less, still more preferably 30.0 or less.

The refractive index (nd) and Abbe number (νd) of the optical glass of the present embodiment are not particularly limited, and as shown in FIG. 1, points A (25.0, 1.860) and points B (30). .0, 1.800), point C (32.0, 1.820), point D (27.0, 1.880) connected by a straight line, line segments AB, BC, CD , Can be located within the area surrounded by DA.
The above "inside the region" includes the line segments of AB, BC, CD, and DA. Further, the refractive index (nd) and Abbe number (νd) of the optical glass of the present embodiment can be adjusted, for example, by appropriately adjusting the content of each of the above-mentioned components within a predetermined range. ..

<Glass transition temperature (Tg)>
The optical glass of the present embodiment preferably has a glass transition temperature (Tg) of 560 ° C. or lower. When the glass transition temperature (Tg) of the optical glass is 560 ° C. or lower, the softening temperature is also lowered, and precision press molding can be performed more easily. From the same viewpoint, the glass transition temperature (Tg) of the optical glass of the present embodiment is more preferably 555 ° C or lower, further preferably 550 ° C or lower.
The glass transition temperature (Tg) can be measured by the procedure described in Examples. Further, the adjustment of the glass transition temperature (Tg) of the optical glass of the present embodiment can be achieved, for example, by appropriately adjusting the content of each of the above-mentioned components within a predetermined range.

<Manufacturing method of optical glass>
Next, a method for manufacturing the optical glass of the present embodiment will be described.
Here, the optical glass of the present embodiment may be manufactured according to a conventional manufacturing method without particular limitation as long as the composition of each component satisfies the above-mentioned range.
For example, first, as a raw material for each component that can be contained in the optical glass of the present embodiment, an oxide, a hydroxide, a carbonate, a nitrate, a phosphate, etc. are weighed at a predetermined ratio, and a glass is sufficiently mixed. Used as a compounding ingredient. Next, this raw material is put into a melting container (for example, a crucible made of a precious metal such as platinum) that does not react with a glass raw material or the like, and heated to 900 to 1150 ° C. in an electric furnace to melt. After that, the optics of the present embodiment are subjected to timely stirring for homogenization, clarification, casting into a mold preheated to an appropriate temperature, and then slowly cooling in an electric furnace to remove strain. Glass can be manufactured. Further, since the optical glass of the present embodiment does not require an excessively high temperature when melting the raw materials, the heating temperature can be as high as 1150 ° C. as described above, and it is possible to reduce the manufacturing cost and save energy. can. For defoaming, a very small amount (for example, an amount of less than 1% in optical glass) of a clearing agent such as Sb ₂ O ₃ can be added.

(Preform for precision press molding)
Hereinafter, the preform for precision press molding of one embodiment of the present invention (hereinafter, may be referred to as “preform of the present embodiment”) will be specifically described.
Here, the precision press-molding preform is a preformed glass material used in a well-known precision press molding method, that is, a glass reserve that is heated and used for precision press molding. It means a molded product.

Here, precision press molding is also called mold optics molding as is well known, and is a method of forming an optical functional surface of a finally obtained optical element by transferring a molding surface of a press molding mold. The optical functional surface means a surface of the optical element that refracts, reflects, diffracts, and emits light to be controlled. For example, the lens surface of the lens is the optical surface. It corresponds to the functional aspect.

The preform of the present embodiment is characterized in that the above-mentioned optical glass is used as a material. As described above, since the preform of the present embodiment uses the above-mentioned optical glass as a material, it is possible to meet the above-mentioned specific needs, and it is possible to reduce the cost and save energy in manufacturing. From the viewpoint of more reliably obtaining the desired optical constant, the preform of the present embodiment preferably satisfies the essential requirements regarding the composition of each component described above for the optical glass of the present invention, and the optical of the present invention. It is more preferable to meet the various preferable requirements described above for glass.

The method for producing the preform of the present embodiment is not particularly limited. However, it is desirable that the preform of the present embodiment be produced by the following production method by taking advantage of the excellent characteristics of the above optical glass.

The first method for producing a preform (referred to as "preform manufacturing method I") is to melt optical glass as a material, flow out the obtained molten glass, separate the molten glass ingot, and separate the molten glass ingot. It is a method of forming into a preform in the process of cooling.

In the second method for producing a preform (referred to as "preform manufacturing method II"), optical glass as a material is melted, and the obtained molten glass is molded to produce a glass molded body, and the molded body is used. It is a method of processing to obtain a preform.

Both the preform manufacturing methods I and II are common in that they include a step of obtaining a homogeneous molten glass from optical glass as a material. In this step, for example, an optical glass raw material prepared and manufactured so as to obtain desired characteristics is placed in a platinum melting container, heated, melted, clarified, homogenized to prepare a homogeneous molten glass, and the temperature is adjusted. It can flow out of a conditioned platinum or platinum alloy outflow nozzle or outflow pipe. It should be noted that even if the optical glass raw material is roughly melted to produce a cullet, and the cullet is mixed and heated, melted, clarified, and homogenized to obtain a homogeneous molten glass, the glass is discharged from the outflow nozzle or outflow pipe. good.

Here, when producing a small preform or a spherical preform, for example, a method in which molten glass is dropped from an outflow nozzle as molten glass droplets having a desired mass, and the molten glass is received by a mold or the like and molded into a preform. Can be adopted. Alternatively, a method of forming a preform by dropping molten glass droplets having a desired mass onto liquid nitrogen or the like from an outflow nozzle can be adopted.
On the other hand, when producing a medium-sized or large preform, for example, a molten glass flow is made to flow down from an outflow pipe, the tip of the molten glass flow is received by a preform molding die, etc., and a nozzle and a preform forming die of the molten glass flow are received. After forming a constricted part between the glass and the constricted part, the preform molding die is swooped down directly below, the molten glass flow is separated at the constricted part by the surface tension of the molten glass, and the molten glass ingot having a desired mass is received by the receiving member. It is possible to adopt a method of molding into a preform.

In order to obtain a preform having a smooth surface without scratches, stains, wrinkles, surface deterioration, etc., for example, a preform having a free surface, the molten glass block is floated by applying wind pressure on a preform molding die or the like. A method of molding into a preform, or putting molten glass droplets in a medium obtained by cooling a gaseous substance into a liquid at room temperature such as liquid nitrogen and under normal pressure to form a preform is used.

Here, when the molten glass ingot is molded into a preform while floating, a gas (referred to as floating gas) is blown to the molten glass ingot, and an upward wind pressure is applied to the molten glass ingot. At this time, if the viscosity of the molten glass block is too low, the floating gas enters the glass and remains as bubbles in the preform. However, by setting the viscosity of the molten glass gob to 3 to 60 dPa · s, the glass gob can be levitated without the floating gas entering the glass.

Examples of the gas used when the floating gas is blown onto the preform include air, N ₂ gas, O ₂ gas, Ar gas, He gas, and water vapor. Further, the wind pressure is not particularly limited as long as the preform can float without coming into contact with a solid such as the surface of a molding die.

Since many precision press-molded products (for example, optical elements) manufactured from preforms have a rotation symmetry axis like a lens, it is desirable that the shape of the preform also has a rotation symmetry axis. As a specific example, a sphere or a device having one axis of rotational symmetry can be shown. As a shape having one axis of rotational symmetry, a shape having a smooth contour line with no corners or dents in the cross section including the axis of rotational symmetry, for example, an ellipse whose short axis coincides with the axis of rotational symmetry in the above cross section is defined as a contour line. A shape in which the sphere is flattened (a shape in which one axis passing through the center of the sphere is defined and the dimensions are reduced in the axial direction) can also be mentioned.

In the preform manufacturing method I, since the optical glass is molded in a temperature range in which the optical glass can be plastically deformed, the preform may be obtained by press-molding the glass block. In that case, since the shape of the preform can be set relatively freely, it can be approximated to the shape of the target precision press-molded product, for example, one of the facing surfaces may be convex and the other may be concave, or both. Can be concave, one surface can be flat and the other surface can be convex, one surface can be flat, the other surface can be concave, or both sides can be convex.

In the preform manufacturing method II, for example, after molding by casting molten glass into a mold, the strain of the molded body is removed by annealing, cutting or cutting is performed, and the glass is divided into predetermined dimensions and shapes, and a plurality of glasses are formed. Pieces can be made and the glass pieces polished to smooth the surface and a preform made of glass of a given mass can be obtained. It is preferable to cover the surface of the preform thus produced with a carbon-containing film for use. The preform manufacturing method II is suitable for manufacturing a spherical preform, a flat plate-shaped preform, and the like that can facilitate grinding and polishing.

In any of the manufacturing methods, since the melting temperature of the optical glass used is low, it is possible to reduce the manufacturing cost and save energy.

Next, a more preferable preform will be described in order to further enhance the mass productivity of molded products such as optical elements by precision press molding.

In the production of the preform of the present embodiment, by reducing the amount of deformation of the glass in the precision press molding, the temperature of the glass and the molding die during the precision press molding is lowered, the time required for the press molding is shortened, and the press pressure is pressed. Can be reduced. As a result, the reactivity between the glass and the molding surface of the molding die is lowered, defects that occur during precision press molding are reduced, and mass productivity is further improved.

Here, in the case of producing a lens by precision press molding of a preform, a preferable preform has a surface to be pressed (a surface pressed by a molding mold facing surface facing each other during precision press molding). A preform which is a reform and further has a rotation symmetry axis penetrating the centers of the two pressed surfaces is more preferable. Among these preforms, those suitable for precision press molding of meniscus lenses are preforms in which one of the pressed surfaces is a convex surface, the other is a concave surface, a flat surface, or a convex surface when the curvature is smaller than the convex surface.

Further, a preform suitable for precision press molding of both concave lenses is a preform in which one of the pressed surfaces is either a convex surface, a concave surface, or a flat surface, and the other is a convex surface, a concave surface, or a flat surface.
On the other hand, a preform suitable for precision press molding of a biconvex lens is a preform in which one of the pressed surfaces is a convex surface and the other is a convex surface or a flat surface.

In any case, the preform is preferably a preform having a shape that more closely resembles the shape of the precision press-molded product.

When a molten glass block is molded into a preform using a preform molding die, the lower surface of the glass on the molding die is largely determined by the shape of the molding surface in the molding die. On the other hand, the upper surface of the glass has a shape determined by the surface tension of the molten glass and the weight of the glass itself. Here, in order to reduce the amount of deformation of the glass during precision press molding, it is necessary to control the shape of the upper surface of the glass being molded in the preform molding die. The shape of the upper surface of the glass, which is determined by the surface tension of the molten glass and the weight of the glass itself, is a convex free surface. To make the upper surface flat, concave, or a convex surface with a smaller curvature than the free surface, the upper surface of the glass. Pressure can be applied to the glass. Specifically, the upper surface of the glass can be pressed with a molding die having a molding surface having a desired shape, or the upper surface of the glass can be molded into a desired shape by applying wind pressure. When pressing the upper surface of the glass with the molding die, a plurality of gas outlets are provided on the molding surface of the molding die, and gas is ejected from these gas ejection ports to form a gas cushion between the molding surface and the upper surface of the glass. The upper surface of the glass may be pressed through the gas cushion. Alternatively, when it is desired to form the upper surface of the glass on a surface having a curvature larger than that of the free surface, the upper surface of the glass may be formed so as to raise the upper surface by generating a negative pressure in the vicinity thereof.

Further, since the preform has a shape that more closely resembles the shape of the precision press-molded product, it is also preferable that the preform has a polished surface. For example, a preform polished so that one of the pressed surfaces is a flat surface or a part of a spherical surface and the other is a part of a spherical surface or a flat surface is preferable. Here, a part of the spherical surface may be a convex surface or a concave surface, but it is desirable to determine whether the spherical surface is a convex surface or a concave surface depending on the shape of the precision press-molded product as described above.

Each of the above preforms can be preferably used for molding a lens having a diameter of 10 mm or more, and can be preferably used for molding a lens having a diameter of 20 mm or more. It can also be preferably used for molding a lens having a central wall thickness of more than 2 mm.

(Optical element)
Hereinafter, the optical element of one embodiment of the present invention (hereinafter, may be referred to as “optical element of the present embodiment”) will be specifically described.
The optical element of the present embodiment is characterized in that the above-mentioned optical glass is used as a material. As described above, since the optical element of the present embodiment uses the above-mentioned optical glass as a material, it is possible to meet the above-mentioned specific needs, and to reduce the cost and energy in manufacturing. From the viewpoint of more reliably obtaining the desired performance, the optical element of the present embodiment preferably satisfies the essential requirements regarding the composition of each component described above for the optical glass of the present embodiment, and the optical of the present embodiment. It is more preferable to meet the various preferable requirements described above for glass.

The type of optical element is not limited, but is typically a non-spherical lens, a spherical lens, or a lens such as a plano-concave lens, a plano-convex lens, a biconcave lens, a biconvex lens, a convex meniscus lens, a concave meniscus lens; A lens array; a lens with a diffraction grid; a prism; a prism with a lens function; and the like can be exemplified. As the optical element, preferably, a lens such as a convex meniscus lens, a concave meniscus lens, a biconvex lens, a biconcave lens, a plano-convex lens, a plano-concave lens, a prism, and a diffraction grating can be exemplified. Each of the above lenses may be an aspherical lens or a spherical lens. If necessary, an antireflection film or a partially reflective film having wavelength selectivity may be provided on the surface.

<Manufacturing method of optical element>
Next, a method of manufacturing the optical element of the present embodiment will be described.
The optical element of this embodiment can be manufactured, for example, by precision press molding the above preform using a press molding mold.

Here, in precision press molding, a press molding die in which the molded surface is preliminarily processed into a desired shape with high accuracy can be used, but the molded surface is molded while preventing the fusion of glass during pressing. A release film may be formed to ensure good elongation of the glass along the surface. The release film includes a precious metal (platinum, platinum alloy) film, an oxide (Si, Al, Zr, Y oxide, etc.) film, a nitride (B, Si, Al nitride, etc.) film, and the like. Examples include carbon-containing films. As the carbon-containing film, it is desirable that the film contains carbon as a main component (when the element content in the film is expressed in atomic%, the carbon content is higher than the content of other elements), and specifically. Can exemplify a carbon film, a hydrocarbon film, or the like. As a method for forming a carbon-containing film, a known method such as a vacuum vapor deposition method using a carbon raw material, a sputtering method, an ion plating method, or a known method such as thermal decomposition using a material gas such as a hydrocarbon can be used. It may be used. For other films, it is possible to form a film by using a vapor deposition method, a sputtering method, an ion plating method, a sol-gel method, or the like.

Further, the press molding die and the preform heating and precision press molding steps are performed with nitrogen gas or nitrogen gas in order to prevent oxidation of the molding surface of the press molding die or the release film suitably provided on the molding surface. It is preferably performed in a non-oxidizing gas atmosphere such as a mixed gas of hydrogen gas. In the non-oxidizing gas atmosphere, the release film covering the surface of the preform, particularly the carbon-containing film, is not oxidized, and the film remains on the surface of the precision press-molded molded product. This film should be removed in the end, but in order to remove the release film such as a carbon-containing film relatively easily and completely, the precision press-molded product should be removed in an oxidizing atmosphere, for example, in the atmosphere. You just have to heat it. The release film such as the carbon-containing film should be removed at a temperature at which the precision press-molded product is not deformed by heating. Specifically, it is preferable to remove the release film such as a carbon-containing film in a temperature range lower than the transition temperature of the glass.

The method for manufacturing the optical element of the present embodiment is not particularly limited, and examples thereof include the following two manufacturing methods. Here, in the production of the optical element of the present embodiment, it is preferable to repeat the step of precision press molding the above-mentioned preform for precision press molding using the same press molding mold from the viewpoint of mass production of the optical element. ..

In the first method for manufacturing an optical element (referred to as "optical element manufacturing method I"), a preform is introduced into a press molding die, and the preform and the press molding die are heated together for precision press molding. This is a method for obtaining an optical element.
The second method for manufacturing an optical element (referred to as "optical element manufacturing method II") is a method in which a heated preform is introduced into a preheated press-molding mold and precision press-molded to obtain an optical element.

In the optical element manufacturing method I, after the preform is supplied between the pair of the upper and lower dies facing each other in which the molded surface is precisely shaped, the viscosity of the glass is a temperature equivalent to ^{105 to 10 9 dPa} · s. By heating both the molding die and the preform to soften the preform and then pressure molding the preform, the molding surface of the molding die can be precisely transferred to the glass. The optical element manufacturing method I is a recommended method when improvement of molding accuracy such as surface accuracy and eccentricity accuracy is important.

^In the optical element manufacturing method II, the temperature was raised to a temperature corresponding to 104 to ¹⁰⁸ dPa · s in advance with the viscosity of the glass between the pair of the upper and lower dies facing each other in which the molded surface was precisely shaped. By supplying the preform and pressure-molding it, the molding surface of the molding die can be precisely transferred to the glass. The optical element manufacturing method II is a recommended method when productivity improvement is important.

The pressure and time at the time of pressurization can be appropriately determined in consideration of the viscosity of the glass and the like. For example, the press pressure can be about 5 to 15 MPa and the press time can be 10 to 300 seconds. Pressing conditions such as pressing time and pressing pressure may be appropriately set within a well-known range according to the shape and dimensions of the molded product.

After that, the molding die and the precision press-molded product are cooled, and when the temperature is preferably equal to or lower than the strain point, the mold is released and the precision press-molded product is taken out. In addition, in order to precisely adjust the optical characteristics to a desired value, the annealing treatment conditions of the molded product at the time of cooling, for example, the annealing speed and the like may be appropriately adjusted.

The optical element of the present embodiment can be manufactured without going through a press molding step. For example, uniform molten glass is cast into a mold to form a glass block, which is annealed to remove strain, and the annealing conditions are adjusted so that the refractive index of the glass becomes a desired value to adjust the optical characteristics. After that, it can be obtained by cutting or cutting the glass block to make a glass piece, and further grinding and polishing to finish the optical element.

Hereinafter, the optical glass of the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Oxides, hydroxides, carbonates, nitrates, phosphates, etc. corresponding to each of the raw materials of each component are weighed so as to have the compositions shown in Tables 1 to 4 after vitrification, and are sufficiently mixed. Then, it was put into a platinum crucible and melted at 900 to 1150 ° C. in an electric furnace. Then, the optical glass of each example was obtained by stirring at appropriate times to homogenize, clarifying, casting in a mold preheated to an appropriate temperature, and then slowly cooling in an electric furnace.
When melting in an electric furnace, as an evaluation of meltability, after heating at 1150 ° C. for 30 minutes, the platinum crucible was taken out from the electric furnace without stirring, and the presence or absence of unmelted residue in the glass was confirmed. Then, the meltability was evaluated as "○" when no unmelted residue was confirmed and as "x" when unmelted residue was confirmed. The results are shown in Tables 1 to 4.

Next, the refractive index (nd), Abbe number (νd), and glass transition temperature (Tg) of each of the obtained optical glasses were measured according to the procedure shown below. The results are shown in Tables 1 to 4.

The refractive index (nd) and Abbe number (νd) were measured using "KPR-200" manufactured by Shimadzu Device Co., Ltd. For reference, in FIG. 1, the refractive index (nd) and the Abbe number of the optical glasses of Examples 1 to 35 in a Cartesian coordinate system having the Abbe number (νd) as the x-axis and the refractive index (nd) as the y-axis ( The plot of νd) is shown.

The glass transition temperature (Tg) was measured by raising the temperature at 5 ° C. per minute using a thermal expansion measuring instrument.

From Table 1 and Table 2 and FIG. 1, the optical glasses of Examples 1 to 35 all have a high refractive index and high dispersibility with a refractive index (nd) of 1.800 or more and an Abbe number (νd) of 32.0 or less. In addition, the Abbe number (νd) and refractive index (nd) are subtracted so as to pass through points A (25.0, 1.860) and B (30.0, 1.800) in the orthogonal coordinate system. It can be seen that it is located on a straight line or on the higher refractive index side than the straight line. Further, from Tables 1 and 2, the optical glasses of Examples 1 to 35 all have good meltability, and more specifically, all of the raw materials can be melted by heating at 1150 ° C. I understand.

Further, from Tables 1 and 2, since the optical glass of Examples 1 to 35 has a glass transition temperature (Tg) of 560 ° C. or lower, the softening temperature is also low, and precision press molding can be performed more easily. I know I can do it.

On the other hand, from Table 3, the optical glass of Comparative Example 1 had a relatively low refractive index in relation to the Abbe number and had poor meltability. This is because it contains TiO ₂ , it contains Na ₂ O, RO is too low, RO / _R'2 O is too small, Nb ₂ O ₅ is too low, and WO ₃ is high. It is thought that it is due to too much.
Further, the optical glass of Comparative Example 2 had a relatively low refractive index in relation to the Abbe number and had poor meltability. It is considered that this is due to the fact that it contains TiO ₂ , that it contains Na ₂ O, that RO is too low, that RO / _R'2 O is too small, that WO ₃ is too high, and so on. Be done.
Further, the optical glass of Comparative Example 3 had a relatively low refractive index in relation to the Abbe number. It is considered that this is due to the fact that Na ₂ O is contained, RO is too small, RO / _R'2 O is too small, WO ₃ is too large, and the like.
Further, the optical glass of Comparative Example 4 had a relatively low refractive index in relation to the Abbe number. This is due to the fact that it contains Na ₂ O, RO is too low, RO / _R'2 O is too small, Nb ₂ O ₅ is too low, and WO ₃ is too high. Conceivable.

Further, the optical glasses of Comparative Examples 5 and 6 had poor meltability. It is considered that this is because the obtained optical glass was so-called borosilicate glass and contained a large amount of TiO ₂ .
Further, the optical glass of Comparative Example 7 had a relatively low refractive index at least in relation to the Abbe number. This is considered to be due to the fact that RO is too small. Further, the optical glass of Comparative Example 7 had poor meltability. It is considered that this is because the melting temperature has risen as a result of adding a relatively large amount of components having a large valence in order to increase the refractive index to some extent.
Further, the optical glass of Comparative Example 8 was devitrified and could not obtain a desired optical constant. This is considered to be due to the fact that there are too many ROs.
Further, the optical glass of Comparative Example 9 could not achieve a high refractive index. This is considered to be due to the fact that RO / _R'2 O is too small.
Further, the optical glass of Comparative Example 10 corresponds to the one in which K ₂ O is replaced with Na ₂ O in the composition of the optical glass of Example 8, but devitrification occurs and a desired optical constant can be obtained. I didn't. It is considered that this is also due to the fact that it contains Na ₂ O and the like.

Further, the optical glass of Comparative Example 11 could not have a high refractive index and had poor meltability. This is considered to be due to the fact that there are too many P ₂ O ₅ and the like. Further, the optical glass of Comparative Example 11 had a relatively high glass transition temperature (Tg) because it contained too much P ₂ O ₅ .
Further, the optical glass of Comparative Example 12 had devitrification and could not obtain a desired optical constant. This is considered to be due to the fact that P ₂ O ₅ is too small.
Further, the optical glass of Comparative Example 13 was devitrified and could not obtain a desired optical constant. This is considered to be due to the fact that there are too many B ₂ O ₃ .
Further, the optical glass of Comparative Example 14 could not achieve a high refractive index. This is considered to be due to the fact that the amount of Li ₂ O is too small. Further, the optical glass of Comparative Example 14 had a relatively high glass transition temperature (Tg) because the amount of Li ₂ O was too small.

Further, the optical glass of Comparative Example 15 had devitrification and could not obtain a desired optical constant. This is considered to be due to the fact that there is too much Li ₂ O.
Further, the optical glass of Comparative Example 16 was devitrified and could not obtain a desired optical constant. This is considered to be due to the fact that there is too much K ₂ O.
Further, the optical glass of Comparative Example 17 could not achieve a high refractive index. This is considered to be due to the fact that Nb ₂ O ₅ is too small.
Further, the optical glass of Comparative Example 18 had at least poor meltability. It is considered that this is due to the fact that Nb ₂ O ₅ is too much.
Further, the optical glass of Comparative Example 19 had a relatively low refractive index in relation to the Abbe number. This is thought to be due to the fact that there is too much WO ₃ .
Further, the optical glass of Comparative Example 20 had at least poor meltability. It is considered that this is due to the fact that Ta ₂ O ₅ is too much.

Further, the optical glass of Comparative Example 21 had devitrification, a desired optical constant could not be obtained, and the meltability was poor. It is considered that this is due to the fact that there is too much ZnO.
Further, the optical glass of Comparative Example 22 had at least poor meltability. This is considered to be due to the fact that there are too many Y ₂ O ₃ .
Further, the optical glass of Comparative Example 23 had at least poor meltability. This is considered to be due to the fact that there are too many La ₂ O ₃ and the like.
Further, the optical glass of Comparative Example 24 had at least poor meltability. It is considered that this is due to the fact that Gd ₂ O ₃ is too much.
Further, the optical glass of Comparative Example 25 had at least poor meltability. It is considered that this is due to the fact that the amount of SiO ₂ is too large.

According to the present invention, it has an optical constant with a relatively high refractive index even though it has a high refractive index and high dispersibility with a refractive index (nd) of 1.800 or more and an Abbe number (νd) of 32.0 or less. Moreover, it is possible to provide an optical glass that does not require an excessively high temperature when melting the raw materials. Further, according to the present invention, it is possible to provide a preform for precision press molding and an optical element using the above optical glass.

Claims (3)

By mass%,
P ₂ O ₅ : 10% or more and 30% or less,
B ₂ O ₃ : 0% or more and 10% or less,
Li ₂ O: 1% or more and 5% or less,
K ₂ O: 0% or more and 10% or less,
Nb ₂ O ₅ : 25% or more and 50% or less,
WO ₃ : 0% or more and less than 9%,
Ta ₂ O ₅ : 0% or more and 10% or less,
BaO: 5% or more and 40% or less,
SrO: 0% or more and 20% or less,
CaO: 0% or more and 8% or less,
MgO: 0% or more and 10% or less,
ZnO: 0% or more and 10% or less,
Bi ₂ O ₃ : 0% or more and 15% or less,
Y ₂ O ₃ : 0% or more and 10% or less,
La ₂ O ₃ : 0% or more and 5% or less,
Gd ₂ O ₃ : 0% or more and 5% or less,
SiO ₂ : 0% or more and 5% or less,
Has a composition containing
Does not contain Ti and Na
When the total content of BaO, SrO, CaO and MgO is RO and the total content of Li ₂ O and K ₂ O is _R'2 O,
RO is more than 20% and 40% or less, and RO / _R'2 O is more than 3.1.
Point A (25.0, 1.860) in a Cartesian coordinate system in which the Abbe number (νd) has the Abbe number (νd) as the x-axis and the Abbe number (nd) has the y-axis. Lines AB, BC connecting points B (30.0, 1.800), point C (32.0, 1.820), and point D (27.0, 1.880) in sequence with a straight line. An optical glass, characterized in that it is located within a region surrounded by, CD, DA . A preform for precision press molding, characterized in that the optical glass according to claim 1 is used as a material. An optical element according to claim 1, wherein the optical glass is used as a material.

Images