JP6735402B2 - Optical glass, optical element and optical glass material - Google Patents

Description

The present invention relates to a phosphate optical glass having a refractive index (nd) of 1.620 to 1.700 and an Abbe number (νd) of 53 to 65. The present invention also relates to an optical element and an optical glass material made of such optical glass.

In recent years, with the spread of imaging devices such as digital cameras and surveillance cameras, there is an increasing demand for optical elements mounted in these devices. In particular, phosphate optical glass having a predetermined refractive index and low dispersibility is effectively used as an optical element material for such imaging devices. For example, the phosphate optical glass described in Patent Document 1 is known.

When attempting to further increase the refractive index and lower the dispersion based on such a phosphate optical glass, the selection of glass components becomes important.

By the way, optical glass is widely used as an optical element such as an optical lens or an optical glass material for an optical element. Glass is a viscous substance at a glass transition temperature Tg (hereinafter sometimes simply referred to as “glass transition temperature”, “Tg”, or “temperature Tg”), and has a property that the viscosity decreases with an increase in temperature, that is, Tg. It has the property of softening when heated to a high temperature. Utilizing this property, as a molding method of an optical element, a press molding method is known in which glass softened by heating is pressed into a desired shape. Such press molding methods are roughly classified into three methods: a direct press molding method, a reheat press molding method, and a precision press molding method (also called a mold press molding method).

Among these molding methods, the direct press molding method and the reheat press molding method are press molding of a molten or softened glass material in a short time to form an optical element blank close to the target optical element shape, and then, This is a method of finishing the optical element blank by grinding and polishing. On the other hand, the precision press molding method is a method of producing a target optical element by transferring a precision-processed molding surface shape to glass softened in a non-oxidizing atmosphere. No grinding or polishing is required.

In addition, the direct press molding method is a method of pressing the molten glass without producing a glass material, whereas the reheat press molding method and the precision press molding method cool the molten glass once to solidify it. After molding the glass material, the glass material is reheated to be softened and press-molded.

Generally, in the case of a method of reheating a glass material once solidified to soften it, such as a reheat press method or a precision press molding method, when the heating temperature is too high, a defect due to crystallization occurs in the molded product after pressing. There is. Therefore, if the heating temperature is too low to avoid crystallization of the glass, the viscosity of the glass is high, so that the shape of the glass is defective due to insufficient deformation of the glass during press molding, or the glass is pressed due to an increase in the press pressure to deform the glass Defects such as cracks may occur.

These problems are that precise temperature control can be performed in an open atmosphere rather than precision press molding, which involves press molding in a non-oxidizing atmosphere at a relatively low temperature for a long time under precise temperature control. Reheat press molding, in which the glass material is heated to a relatively high temperature (for example, the viscosity of glass is equivalent to 10 ⁴ to 10 ⁶ dPa·s), which is difficult and press-molded in a high temperature in a short time. It becomes remarkable in the case of the law.

Note that the crystal of glass includes a surface crystal that often occurs on the glass surface and an internal crystal that entirely occurs from the glass surface to the inside. For optical glass, it is preferable that both surface crystals and internal crystals are absent or extremely small.

Particularly for phosphate optical glass, it is important to ensure the thermal stability of the glass when manufacturing optical elements.

In the present invention, the thermal stability of glass includes devitrification resistance when molding a glass melt and devitrification resistance when glass once solidified is reheated.

Japanese Patent No. 4533069

However, in the phosphate optical glass, there is a trade-off relationship between attaining a high refractive index and a low dispersion and ensuring the thermal stability of the glass. Without considering such a trade-off relationship, for example, when a large amount of a glass component for increasing the refractive index is introduced, the internal crystal of the glass tends to easily occur, which causes the deterioration of the quality of the glass product. ..

As a result of intensive studies to solve the above problems, the present inventors have found a phosphate optical glass having a high refractive index, a low dispersion, and excellent thermal stability. Specifically, the inventors have invented a phosphate optical glass having thermal stability such that internal crystals of glass do not occur during reheat press molding while giving priority to achieving a high refractive index.

An object of the present invention is to provide a phosphate optical glass having a relatively high refractive index nd and excellent thermal stability. A further object of the present invention is to provide an optical element and an optical glass material made of such optical glass.

That is, the gist of the present invention is as follows.
[1] An oxide glass having a total content [P ⁵⁺ +B ³⁺ +Al ³⁺ ] of P ⁵⁺ , B ³⁺ and Al ³⁺ of 60 cation% or less,
Ba ²⁺ ,
Any one or more selected from Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ ,
And any one or more selected from Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ ,
The cation ratio α [Ba ²⁺ /(Mg ²⁺ +Ca ²⁺ +Zn ²⁺ +Sr ²⁺ )] of the content of Ba ²⁺ to the total content of Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ is 0.80 or less,
The cation ratio β[(P ⁵⁺ +B ³⁺ +Al ³⁺ )/(Gd ³⁺ +Y ³⁺ +La ³⁺ +Yb ⁺ of the total content of P ⁵⁺ , B ³⁺ and Al ³⁺ with respect to the total content of Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ^{3+. 3+} )] is less than 14.0,
An optical glass having a refractive index nd of 1.620 to 1.700 and an Abbe number νd of 53 to 65.
[2] The optical glass according to [1] above, wherein the total content [Gd ³⁺ +Y ³⁺ +La ³⁺ +Yb ³⁺ ] of Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ is 2 to 20 cation %.
[3] The optical glass according to the above [1] or [2], wherein the content of P ⁵⁺ is 10 to 45 cation %.
[4] The optical glass as described in any of [1] to [3] above, wherein the content of Ba ²⁺ is 5 to 25 cation %.
[5] The optical glass as described in any of [1] to [4] above, wherein the content of Zn ²⁺ is 15 cation% or less.
[6] The content of the cation ratio of ^{P 5+} to the content of ^{B 3+ [P 5+ / B 3+} ] is 0.2 to 10.0, optics according to any one of [1] to [5] Glass.
[7] An optical element comprising the optical glass according to any one of the above [1] to [6].
[8] An optical glass material comprising the optical glass according to any one of [1] to [6] above.

According to the present invention, it is an optical glass having a relatively high refractive index (refractive index nd is 1.620 or more), and due to its excellent thermal stability, even when reheated under severe conditions. Thus, an optical glass that hardly crystallizes can be obtained. Further, an optical element and an optical glass material made of such optical glass can be obtained.

It is a schematic diagram which shows the differential scanning calorimetric curve of optical glass.

Hereinafter, modes for carrying out the present invention (hereinafter, simply referred to as “the present embodiment”) will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be appropriately modified and implemented within the scope of the gist. In the present specification, each content is represented by cation% unless otherwise specified.

In the present invention, the cation% means the ratio of individual cations to all the cations contained in the glass as a molar percentage. Further, since the optical glass of the present invention is an oxide glass, the anion is mainly oxygen (O ^{2 −} ), but a part of the anion can be replaced with an anion other than oxygen (for example, halogen).

Optical Glass The optical glass of the present invention is an oxide glass having a total content of P ⁵⁺ , B ³⁺ and Al ³⁺ [P ⁵⁺ +B ³⁺ +Al ³⁺ ] of 60% or less, and is Ba ²⁺ , Mg ²⁺ , Ca ^2+. comprises of any one or more selected from ^{Zn 2+,} and ^{Sr 2+, Gd 3+, Y 3+} , and any one or more selected from ^{La 3+} and ^{Yb 3+, and,} Mg ^2+, Ca 2+, ^{Zn 2+} and the cation ratio of the content of ^{Ba 2+} to the total content of ^{Sr 2+ α [Ba 2+ / (} Mg 2+ + Ca 2+ + Zn 2+ + Sr 2+)] is 0.80 or ^{less, Gd 3+, Y 3+, La} 3+ and Yb ^P 5+ to the total content of ^{3+, B 3+} and the cation ratio of the total content of ^{Al 3+ β [(P 5+ +} B 3+ + Al 3+) / (Gd 3+ + Y 3+ + La 3+ + Yb 3+)] There are less than 14.0 The refractive index nd is 1.620 to 1.700 and the Abbe number νd is 53 to 65.

In general, the components that constitute glass can be roughly classified into a network component that forms a network structure of glass and a modifying component that controls the properties of glass. Of these, the network component mainly contributes to the stability of the glass (for example, structural stability, thermal stability, and glass meltability). Therefore, from the viewpoint of obtaining stable glass, it is desirable that the ratio of the network component in the glass be relatively large.

On the other hand, the modifying component mainly contributes to the functionality of glass (for example, optical properties such as refractive index and dispersibility, and chemical durability such as weather resistance). Therefore, it is desirable to appropriately select and adjust the type and amount of the modifying component added according to the function and characteristics required for the glass. However, if the proportion of the modifying component in the glass is increased, the proportion of the network component is reduced as a result, and the stability of the glass may be reduced. Further, depending on the modifying component, even if it is effective from the viewpoint of improving the properties, the addition of a small amount thereof may significantly reduce the stability of the glass.

As described above, the stability and functionality of glass are greatly influenced by the balance between the network component and the modifying component.

Conventionally, phosphate optical glass has been expected to be used as an optical element such as an optical lens because it exhibits a high refractive index and low dispersibility, but it has low weather resistance and can be used as a glass for press molding. There wasn't. In order to solve such a problem, in the invention described in Patent Document 1 (Reference Example 4), by adding Ba ²⁺ as a modifying component and increasing the proportion of Ba ²⁺ in the glass, a high refractive index (refractive index) The weather resistance was improved while securing the rate nd of 1.620 or more).

However, although such an optical glass has improved weather resistance and is suitable as a glass for precision press molding, it tends to cause crystallization due to a modifying component (for example, Ba ²⁺ ) introduced in a large amount, so that the glass is There was a problem that the thermal stability of was deteriorated. Therefore, even if the glass is once solidified once, if it is softened again under severe conditions, crystals may occur in the glass after cooling, and such glass is an optical element such as a reheat press molding method. Was not suitable for the production method.

In particular, when the ratio of the network component (for example, P ⁵⁺ etc.) in the optical glass is lowered and the ratio of the modifying component (for example, the component enhancing weather resistance or the component enhancing refractive index) is increased, the thermal stability of the glass is improved. Sex tends to deteriorate. Therefore, crystallization of the glass occurs due to reheating in the reheat press molding, and it has been difficult to obtain a phosphate optical glass having a high refractive index, which is excellent in weather resistance and thermal stability. Such a problem remarkably appears when trying to obtain a relatively high refractive index (refractive index nd is 1.620 or more, further 1.630 or more).

Therefore, as a result of intensive studies to solve the above problems, the present inventors have found that the proportion of the modifying component in the glass increases and the proportion of the network component decreases (P ⁵⁺ , B ³⁺ and Al). ^{Even if} the total content of ³⁺ [P ⁵⁺ +B ³⁺ +Al ³⁺ ] is 60% or less), the thermal stability of the glass can be improved by mixing Ba ²⁺ and other divalent components in a well-balanced manner. The present invention has been completed and the present invention has been completed.

That is, the optical glass according to the present invention, along with containing ^{Ba 2+, Mg 2+, Ca 2+} , include any one or more selected from ^{Zn 2+,} and ^{Sr 2+,} Mg ^2+, Ca 2+, ^{Zn 2+} and ^{Sr 2+} One feature is that the cation ratio α[Ba ²⁺ /(Mg ²⁺ +Ca ²⁺ +Zn ²⁺ +Sr ²⁺ )] of the Ba ²⁺ content to the total content of is 0.80 or less.

By setting the cation ratio α in the above range, it is possible to prevent the specific modifying component (Ba ²⁺ ) from being excessively introduced into other modifying components, and thus prevent the crystal generated due to the specific modifying component. it can. Therefore, the thermal stability of the glass can be secured.

According to the optical glass of the present invention as described above, it is possible to effectively prevent the generation of internal crystals of the glass in the reheat press molding performed in the air atmosphere in which precise temperature control is difficult.

Further, the optical glass according to the present invention has Gd ³⁺ and Y ^{3+ in} order to effectively increase the refractive index (nd) while maintaining the thermal stability obtained by setting the cation ratio α in the predetermined range. , La ³⁺ and Yb ³⁺ , and a total of P ⁵⁺ , B ³⁺ and Al ³⁺ with respect to the total content of Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ^3+. One of the features is that the cation ratio β [(P ⁵⁺ +B ³⁺ +Al ³⁺ )/(Gd ³⁺ +Y ³⁺ +La ³⁺ +Yb ³⁺ )] of the content is less than 14.0.

The ratio (cation ratio β) of the total content of the network components (P ⁵⁺ , B ³⁺ and Al ³⁺ ) to the total content of the rare earth elements (Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ ) is set within the above range. As a result, the total content of the rare earth elements is relatively increased, so that the refractive index of the glass can be set high.

Such an optical glass according to the present invention is particularly suitable for producing an optical element having a high refractive index by using a reheat press molding method.

The optical glass in the present invention is a glass composition containing a plurality of metal oxides and may be in any form (bulk, plate, sphere, etc.) and application (material for optical element, optical element, etc.). Instead, they are collectively called optical glass.

<Glass composition>
Next, the glass composition of the optical glass according to the present invention will be described in detail. The content rate of the constituent components of the glass can be measured by a method such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry).

The analytical value (for example, in atomic% notation) obtained by performing the quantitative analysis for each element based on the ICP-AES analysis may include a measurement error of about ±5% of the analytical value. Further, based on the above analysis value, it can be converted into a value expressed in oxide or a cation component in glass can be converted into a value expressed in cation %, and the conversion method will be described later.

Further, in the present specification, the content of the constituent component being 0% or not contained or not introduced means that the constituent component is substantially not contained, and the content of the constituent component is not more than the impurity level. It refers to something.

P ⁵⁺ is a network component that forms the network structure of glass, and is an essential component for giving the glass thermal stability that can be manufactured. However, when P ⁵⁺ is excessively contained, the glass transition temperature, the yield point and the glass melting temperature rise, and the refractive index and weather resistance tend to decrease. On the other hand, if the content of P ⁵⁺ is too small, the Abbe number (νd) of the glass decreases, the low dispersibility is impaired, and the glass tends to devitrify and become unstable. Therefore, in the optical glass of the present invention, the upper limit of the content of P ⁵⁺ is preferably 40%, more preferably 37%, 35%, 34% and 33% in this order. Further, the lower limit of the content of P ⁵⁺ is preferably 10%, more preferably 12%, 13%, 14% and 15% in this order.

B ³⁺ is a very effective component for improving the meltability of the glass and homogenizing the glass, and at the same time, for improving the devitrification resistance and weather resistance of the glass, increasing the refractive index, and promoting low dispersion. It is an effective ingredient. However, if B ³⁺ is excessively introduced, there is a possibility that the glass transition temperature and the yield point are increased, the devitrification resistance is deteriorated, and the low dispersibility is lost. Therefore, in the optical glass of the present invention, the upper limit of the B ³⁺ content is preferably 35%, and more preferably 32%, 30%, 28%, 27%, and 26% in this order. If the amount of B ³⁺ introduced is too small, the melting property and devitrification resistance of the glass decrease. Therefore, in the optical glass of the present invention, the lower limit of the B ³⁺ content is preferably 0.1%, and further 1.0%, 2.0%, 3.0%, 5.0%, 7%. Preferred in the order of 0.0. In the optical glass of the present invention, B ³⁺ forms a network structure of glass together with P ⁵⁺ , and thus it is preferable that B ³⁺ be contained as an essential component from the viewpoint of glass stability.

Al ³⁺ is a network component that forms a network structure of glass, and is used as an effective component for improving the weather resistance of glass. However, if the amount of introduction is excessive, the glass transition temperature and the yield point become high, the stability and meltability of the glass deteriorate, and the refractive index may decrease. Therefore, in the optical glass of the present invention, the upper limit of the Al ³⁺ content is preferably 10%, more preferably 8%, 7%, 5% and 4% in this order. The lower limit of the content of Al ³⁺ is preferably 0%, more preferably 0.1%, 0.5% and 1.0% in this order.

When the total content of P ⁵⁺ , B ³⁺ and Al ³⁺ [P ⁵⁺ +B ³⁺ +Al ³⁺ ] exceeds 60%, the refractive index is lowered, the melting temperature of the glass is increased, and the quality is deteriorated due to volatilization of the glass. There is a risk. On the other hand, when the total content of these components is too small, devitrification resistance is deteriorated, vitrification becomes difficult, and low dispersibility may be deteriorated. In the optical glass of the present invention, the upper limit of the total content [P ⁵⁺ +B ³⁺ +Al ³⁺ ] is 60%, and 55%, 52%, 50%, 48% and 47.5% are preferable in that order. Further, the lower limit of the total content [P ⁵⁺ +B ³⁺ +Al ³⁺ ] is preferably 27%, more preferably 32%, 35%, 38%, 40% and 41% in this order.

Further, in the optical glass of the present invention, from the viewpoint of simultaneously providing the glass with low dispersibility and enhancing thermal stability, the ratio of the content of P ^{5+ to} the content of B ³⁺ : the cation ratio. The upper limit of [P ⁵⁺ /B ³⁺ ] is preferably 12, and more preferably 10, 8, 6, 5, and 4 in that order. Further, the lower limit of the cation ratio [P ⁵⁺ /B ³⁺ ] is preferably 0.2, more preferably 0.3, 0.4, 0.5, and 0.6 in this order. As described above, in the optical glass according to the present invention, by balancing the proportion of P ⁵⁺ and B ³⁺ that predominantly act on the formation of the glass network structure, excellent thermal stability is obtained while achieving low dispersion. be able to.

Ba ²⁺ is a very effective essential component for increasing the refractive index of glass and improving the weather resistance when introduced in an appropriate amount. However, if the amount introduced is too large, the thermal stability of the glass is significantly impaired, the glass transition temperature is increased, and the low dispersibility tends to be impaired. On the other hand, if the amount introduced is too small, the desired refractive index cannot be obtained and the weather resistance is further deteriorated. Therefore, in the optical glass of the present invention, Ba ²⁺ is an essential component, and the upper limit of its content is preferably 25%, and further 22%, 20%, 18%, 17%, 16%, 15 The order of% is preferable. The lower limit of the content of Ba ²⁺ is preferably 5%, more preferably 6%, 8%, 9% and 10% in this order.

Further, from the viewpoint of enhancing the thermal stability and weather resistance of the glass, the upper limit of the total content of Ba ²⁺ and P ⁵⁺ [Ba ²⁺ +P ⁵⁺ ] is preferably 60%, further 55%, 53%, 51%, 50% and 48% are preferable in this order. The lower limit of the total content [Ba ²⁺ +P ⁵⁺ ] is preferably 20%, more preferably 22%, 25%, 27%, 29%, 30%.

Furthermore, the upper limit of the ratio of the content of Ba ^{2+ to} the content of B ³⁺ : the cation ratio [Ba ²⁺ /B ³⁺ ] is preferably 10 from the viewpoint of ^lowering the glass dispersion and increasing the thermal stability of the glass. And more preferably in the order of 7, 5, 3, 2, 1.7 and 1.6. The lower limit of the cation ratio [Ba ²⁺ /B ³⁺ ] is preferably 0.1, and more preferably 0.2, 0.3, 0.4 and 0.5 in that order.

Mg ²⁺ is a component introduced in order to achieve both high weather resistance and low dispersion of glass. The introduction of a small amount of Mg ²⁺ has the effect of lowering the glass transition temperature, the yield point or the liquidus temperature. However, when it is introduced in a large amount, the thermal stability of the glass is significantly deteriorated and the liquidus temperature is increased. Therefore, in the optical glass of the present invention, the upper limit of the Mg ²⁺ content is preferably 25%, more preferably 22%, 20%, 18%, 16% and 15% in this order. The lower limit of the content of Mg ²⁺ is preferably 0%, more preferably 1%, 2%, 5%, 7%, 8%.

Ca ²⁺ is a component that is introduced in order to promote low dispersion of glass, improve the thermal stability of glass, and lower the liquidus temperature. However, if Ca ²⁺ is excessively introduced, not only the chemical durability of the glass is deteriorated, but also the thermal stability of the glass is rather deteriorated and the refractive index is also likely to be decreased. Therefore, in the optical glass of the present invention, the upper limit of the Ca ²⁺ content is preferably 22%, more preferably 20%, 17%, 15%, 13%, and 12% in this order. The lower limit of the Ca ²⁺ content is preferably 0%, and more preferably 1%, 2%, 5%, 7%, 8% in this order.

From the viewpoint of achieving both low dispersion of glass, thermal stability, and weather resistance, the upper limit of the total content [Mg ²⁺ +Ca ²⁺ ] of Mg ²⁺ and Ca ²⁺ in the optical glass of the present invention is preferably 40. %, more preferably 35%, 32%, 30% and 27% in this order. The lower limit of the total content [Mg ²⁺ +Ca ²⁺ ] is preferably 5%, and more preferably 10%, 12%, 14% and 15% in this order.

Sr ²⁺ is an effective component that increases the refractive index of glass without impairing the low dispersibility of glass. It is also effective as a component that enhances the weather resistance of glass. However, if Sr ²⁺ is excessively introduced, the liquidus temperature tends to rise and the thermal stability of the glass tends to deteriorate. Therefore, in the optical glass of the present invention, the upper limit of the Sr ²⁺ content is preferably 15%, more preferably 10%, 7%, 5%, and 4% in this order. The lower limit of the Sr ²⁺ content is preferably 0%, more preferably 0.1%, 1.0%, 1.5%, 2.0%.

Zn ²⁺ is a component used to increase the refractive index of glass, improve the thermal stability of glass, and lower the liquidus temperature and the glass transition temperature by proper introduction. However, if Zn ²⁺ is excessively introduced, the low dispersibility is greatly impaired and the chemical durability of the glass is deteriorated. Therefore, in the optical glass of the present invention, the upper limit of the Zn ²⁺ content is preferably 15%, more preferably 14%, 12%, 10% and 9% in this order. If the amount of Zn ²⁺ introduced is too small, the liquidus temperature and the glass transition temperature tend to increase. Therefore, the lower limit of the Zn ²⁺ content is preferably 0%, more preferably 1.0%, 2.0%, 2.5%, and 3.0% in this order.

The optical glass of the present invention contains, in addition to Ba ²⁺ , one or more kinds selected from Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ as a divalent component. At that time, from the viewpoint of improving the weather resistance of the glass and obtaining desired optical characteristics, the total content of Mg ²⁺ , Ca ²⁺ , Zn ²⁺ , Sr ²⁺ and Ba ²⁺ R=[Mg ²⁺ +Ca ²⁺ +Zn ²⁺ +Sr ²⁺ +Ba The upper limit of [ ²⁺ ] is preferably 53%, more preferably 50%, 47%, 45%, 44%, 43% and 42% in this order. The lower limit of the total content R is preferably 26%, more preferably 30%, 33%, 35%, 36%, 38% in this order.

In the optical glass of the present invention, from the viewpoint of improving the thermal stability of the glass while increasing the refractive index, the ratio of the content of Ba ²⁺ to the total content of Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ : cation The ratio α[Ba ²⁺ /(Mg ²⁺ +Ca ²⁺ +Zn ²⁺ +Sr ²⁺ )] is 0.80 or less. Moreover, the preferable upper limit of the cation ratio α is 0.75, and further, 0.70, 0.65, 0.60, 0.55 and 0.50 are preferable in this order. From the viewpoint of improving the weather resistance of the glass, the lower limit of the cation ratio α is preferably 0.10, and further 0.20, 0.25, 0.30, 0.35, 0.40 in this order. preferable. By satisfying such a condition, the Ba ²⁺ content is not remarkably excessively introduced with respect to the content of the other divalent components, so that the precipitation of crystals due to Ba ²⁺ can be suppressed. Therefore, even if the components that increase the refractive index are increased and the components that form the network structure are reduced by mixing Ba ²⁺ and the other divalent components in a well-balanced manner in this way, The stability can be improved.

Further, the optical glass of the present invention having a cation ratio α of 0.80 or less may be referred to as a crystallization peak temperature Tc (hereinafter, simply referred to as “crystallization peak temperature”, “Tc” or “temperature Tc”). ) And the glass transition temperature Tg (Tc-Tg) are relatively wide, and both Tc-Tg are 145°C or higher. By setting this cation ratio α within the above range, Tc-Tg is consequently increased, and when resoftening the glass, the glass can be softened at a temperature lower than the temperature Tc, so that the glass is crystallized. Without, the thermal stability of the glass can be improved.

Further, from the viewpoint of improving the thermal stability of the glass, the upper limit of the ratio of the content of Ba ²⁺ to the total content of Mg ²⁺ and Sr ²⁺ :cation ratio [Ba ²⁺ /(Mg ²⁺ +Sr ²⁺ )] is preferably Is 2.5, more preferably 2.0, 1.7, 1.5, 1.2, 1.1, 1.0 in this order. The lower limit of the cation ratio [Ba ²⁺ /(Mg ²⁺ +Sr ²⁺ )] is preferably 0.1, and more preferably 0.2, 0.3, 0.4.

From the viewpoint of improving the thermal stability of glass and obtaining desired optical characteristics, the ratio of the total content of Sr ²⁺ and Ba ^{2+ to} the total content of Mg ²⁺ and Ca ²⁺ : cation ratio [(Sr ²⁺ +Ba ²⁺ ). The upper limit of /(Mg ²⁺ +Ca ²⁺ )] is preferably 2.5, and more preferably 2.0, 1.7, 1.5, 1.2, 1.1, 1.0. Further, the lower limit of the cation ratio [(Sr ²⁺ +Ba ²⁺ )/(Mg ²⁺ +Ca ²⁺ )] is preferably 0.1, and further 0.2, 0.3, 0.4, 0.5 in this order. preferable.

Note that among the divalent components consisting of Mg ²⁺ , Ca ²⁺ , Zn ²⁺ , Sr ²⁺ and Ba ²⁺ , Ba ²⁺ effectively enhances the refractive index and weather resistance of the glass, but excessive introduction thereof causes thermal stability of the glass. Sex is significantly impaired. On the other hand, Zn ²⁺ improves the thermal stability of the glass, but its excessive dispersion greatly impairs the low dispersibility. Therefore, in view of obtaining the thermal stability of the glass desired optical constants, proportion of the content of ^{Zn 2+} to the content of ^{Ba 2+:} The upper limit of the cation ratio of ^[Zn 2+ / ^{Ba 2+]} is preferably 0. 90, more preferably 0.80, 0.75, 0.70, 0.65, 0.60 in this order. The lower limit of the cation ratio [Zn ²⁺ /Ba ²⁺ ] is preferably 0.05, and more preferably 0.10, 0.15, 0.20, 0.25 in that order.

Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ are all components that contribute to improving the weather resistance of glass and increasing the refractive index. However, if these components are excessively introduced, the thermal stability of the glass may be deteriorated. Therefore, in the optical glass of the present invention, the upper limit of the Gd ³⁺ content is preferably 15%, and more preferably 12%, 10%, 9%, 8%, 7%, 6%. The lower limit of the content of Gd ³⁺ is preferably 0%, more preferably 0.5%, 1%, 2%, 3%. The upper limit of the Y ³⁺ content is preferably 10%, more preferably 7%, 5%, 4% and 3% in this order. The lower limit of the Y ³⁺ content is preferably 0%, more preferably 0.5% and 1.0%. The upper limit of the La ³⁺ content is preferably 10%, more preferably 7%, 5%, 4% and 3% in this order. The lower limit of the La ³⁺ content is preferably 0%, more preferably 0.05%. The upper limit of the Yb ³⁺ content is preferably 5%, more preferably 4%, 3%, 2%, and 1.5% in this order. Further, the lower limit of the content of Yb ³⁺ is preferably 0%, more preferably 0.05%. It should be noted that Yb ³⁺ has an absorptivity in the near infrared region, so it is preferable not to introduce it when using a light beam in the near infrared region.

The rare earth elements such as Gd ³⁺ , Y ³⁺ , La ^3+, and Yb ³⁺ are preferably introduced appropriately from the viewpoint of effectively increasing the refractive index. Therefore, the optical glass of the present invention contains at least one selected from Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ . However, if these components are excessively introduced, the thermal stability of the glass tends to deteriorate. Therefore, the upper limit of the total content Re=[Gd ³⁺ +Y ³⁺ +La ³⁺ +Yb ³⁺ ] of Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ is preferably 20%, further 15%, 12% and 10%. , 9% in that order. The lower limit of the total content Re is preferably 2.0%, more preferably 2.5%, 3.0%, 3.5%, 4.0% in this order. The thermal stability of the glass may be improved by introducing two or more kinds of rare earth elements, rather than introducing a single rare earth element. Therefore, the optical glass of the present invention preferably contains any two or more kinds of rare earth elements selected from Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ .

Further, the optical glass according to the present invention, while ensuring the thermal stability of the glass obtained by setting the cation ratio α in a predetermined range, from the viewpoint of effectively increasing the refractive index, the total content of the rare earth elements is contained. The ratio of the total content of P ⁵⁺ , B ³⁺ and Al ^{3+ to} the amount Re: the cation ratio β[(P ⁵⁺ +B ³⁺ +Al ³⁺ )/Re] is less than 14.0. Moreover, the preferable upper limit of the cation ratio β is 13.5, and further, 13.0, 12.5, 12.0, 11.5, and 11.0 are preferable in that order. The lower limit of the cation ratio β is preferably 2.0, more preferably 3.0, 4.0, 4.5, 5.0, 5.5.

In the present invention, the cation ratio α and the cation ratio β are closely related from the viewpoint of obtaining desired optical characteristics and improving the thermal stability of the glass. The explanation will be given below.

In the optical glass according to the present invention, relatively high total content Re of rare earth elements, which is a component that effectively increases the refractive index, is introduced in consideration of increasing the refractive index of the glass. On the other hand, when the total content Re of rare earth elements becomes excessive, the thermal stability of the glass tends to deteriorate as described above. Therefore, there is a predetermined limit on the introduction amount of the total content Re of rare earth elements, and this limit is defined by the cation ratio β (the cation ratio β is less than 14.0). By thus defining the cation ratio β in a predetermined range, desired optical characteristics (high refractive index) can be obtained, but the thermal stability of the glass is improved as the total content Re of rare earth elements increases. It tends to get worse.

On the other hand, excessive introduction of a rare earth element deteriorates thermal stability. Therefore, in the optical glass according to the present invention, the thermal stability is improved by setting the cation ratio α within a predetermined range. However, if the introduced amount of Ba ²⁺ with respect to the total content of Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ is too large, the thermal stability will be impaired. Therefore, in the present invention, the upper limit of the cation ratio α is defined (cation. The ratio α is 0.80 or less).

In this way, by adjusting the glass composition so that the cation ratio α and the cation ratio β fall within the predetermined ranges, it is possible to obtain desired optical characteristics and improve the thermal stability of the glass.

Si ⁴⁺ is an effective component for improving chemical durability while maintaining low dispersibility. However, if the amount introduced is too large, the glass transition temperature and the yield point tend to increase, and the refractive index tends to decrease. Therefore, in the optical glass of the present invention, the upper limit of the Si ⁴⁺ content is preferably 3%, more preferably 2%, 1.5%, and 1.0% in this order. Although Si ⁴⁺ is a network component together with P ⁵⁺ , B ³⁺ and Al ³⁺ , Si ⁴⁺ does not necessarily have to be introduced into the optical glass of the present invention.

Li ⁺ is a component that lowers the glass transition temperature and the yield point and is effective for lowering the dispersion. In particular, coexistence of P ⁵⁺ , B ³⁺ and Li ⁺ is very effective for lowering the dispersion of glass. However, if Li ⁺ is excessively introduced, the chemical durability (weather resistance, alkali resistance, etc.) of the glass deteriorates, and the refractive index tends to sharply decrease. Therefore, in the optical glass of the present invention, the upper limit of the content of Li ⁺ is preferably 23%, and further preferably 20%, 17%, 15%, and 14% in this order. The lower limit of the Li ⁺ content is preferably 0%, and more preferably 1%, 2%, 5%, 7%, 8%.

Both Na ⁺ and K ⁺ are optional components that are introduced to improve the devitrification resistance of the glass, lower the glass transition temperature, the yield point, and the liquidus temperature, and improve the meltability of the glass. The introduction of appropriate amounts of Na ⁺ and K ⁺ improves the stability of the glass and lowers the liquidus temperature and the transition temperature. However, when it is introduced in excess, the chemical durability is significantly deteriorated and the refractive index is also reduced. There is a tendency. Therefore, in the optical glass of the present invention, the upper limits of the contents of Na ⁺ and K ⁺ are preferably 10%, and further preferably 5%, 3%, and 2% in this order. In addition, it is particularly preferable that Na ⁺ and K ⁺ are not substantially introduced.

Further, if the total content of Li ⁺ , Na ⁺ and K ⁺ is too small, the glass transition temperature and the yield point rise, and the meltability deteriorates. Therefore, in the optical glass of the present invention, the upper limit of the total content R ₂ =[Li ⁺ +Na ⁺ +K ⁺ ] of Li ⁺ , Na ⁺ and K ⁺ is preferably 23%, and further 20%, 17 %, 15% and 14% are preferable in this order. The lower limit of the total content R ₂ is preferably 0%, more preferably 1%, 2%, 5%, 7%, 8%.

Further, in the optical glass of the present invention, it is not always necessary to introduce Cs ⁺ which is an alkali metal component, and it is not necessary because it is disadvantageous in terms of raw material cost. Also, Cs ⁺ lowers the refractive index, since significantly impairing weather resistance, it is preferred not to introduce Cs ^+.

From the viewpoint of achieving both meltability and thermal stability of the glass, the upper limit of the ratio of the P ⁵⁺ content to the total content R ₂ of the alkali metal components: the cation ratio [P ⁵⁺ /R ₂ ] is 30. It is preferable, and more preferable is 25, 20, 15, 10, and 8 in that order. The lower limit of the cation ratio [P ⁵⁺ /R ₂ ] is preferably 1.0, and more preferably 1.5, 2.0, and 2.5.

The optical glass of the present invention preferably contains substantially no Pb, As, Cd, U, Th, or Tl from the viewpoint of reducing the load on the environment.

Further, the optical glass of the present invention may contain halogen, that is, F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ as an optional component. The content can be represented by the anion fraction of anions (for example, [F ⁻ /(O ^{2 −} +F ⁻ )]). The upper limit of the content of F ⁻ is preferably 10%, more preferably 5%, 3%, 2%, 1%, 0.5%, 0.1%. ^{Furthermore, Cl -, Br -, I} - upper limit of the content of, preferably 5%, respectively, and further, 3%, 2%, 1%, 0.5%, preferably in the order of 0.1% .. When the glass contains halogen, it is preferable to set the upper limit of B ^{3+ in} the glass to 25% in order to suppress volatilization of the glass, further preferably 20%, 15%, 10% and 5% in this order, and most preferably It is preferably substantially free. However, this does not apply when a small amount of halogen of 1% or less is added. In particular, in order to suppress volatilization of the components from the glass and improve the homogeneity of the glass, it is preferable that the halogen is not substantially contained.

Further, the optical glass of the present invention may contain an easily reducing component composed of W ⁶⁺ , Ti ⁴⁺ , Bi ³⁺ and Nb ⁵⁺ as an optional component. These easily reducing components are effective components for increasing the refractive index. However, W ⁶⁺ , Ti ⁴⁺ , Bi ³⁺ and Nb ⁵⁺ significantly reduce the Abbe number (νd) of the glass. Therefore, the upper limit of the total content [W ⁶⁺ +Ti ⁴⁺ +Bi ³⁺ +Nb ⁵⁺ ] of the easily reducing components is preferably 5%, more preferably 3%, 2%, 1%, and 0.5% in this order. .. In addition, it is particularly preferable that substantially no easy reducing component is introduced.

The optical glass of the present invention as described above is basically P ⁵⁺ , B ³⁺ , Si ⁴⁺ , Al ³⁺ , Li ⁺ , Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , Zn ²⁺ , Sr ²⁺ , Ba ^2+. , Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ are preferred. The total content of these components [P ⁵⁺ +B ³⁺ +Si ⁴⁺ +Al ³⁺ +Li ⁺ +Na ⁺ +K ⁺ +Mg ²⁺ +Ca ²⁺ +Zn ²⁺ +Sr ²⁺ +Ba ²⁺ +Gd ³⁺ +Y ³⁺ +La ³⁺ +Yb can be Yb ³⁺ +Yb. It is more preferably 98% or more, still more preferably 99% or more, still more preferably 100%.

It is preferable that the optical glass of the present invention is basically composed of the above-mentioned components, but it is possible to introduce other components as long as the action and effect of the present invention are not impaired. Further, in the present invention, inclusion of inevitable impurities is not excluded.

In addition, "substantially not contained" can be based on the fact that the content is less than 0.2%. Components and additives that are not substantially contained are preferably not contained in the glass, so the content is preferably less than 0.1%, more preferably less than 0.08%, and 0.1. It is more preferably less than 05%, even more preferably less than 0.01%, and even more preferably less than 0.005%.

Further, when the optical glass of the present invention is composed of the above components and the total amount is 100% by mass, even if a fining agent such as Sb ₂ O ₃ , SnO ₂ or CeO _{2 is} introduced in an amount of 4% by mass or less. Good. The upper limit of the content of Sb ₂ O ₃ is preferably 4% by mass, more preferably 3% by mass, 2% by mass, 1% by mass, 0.5% by mass and 0.1% by mass in this order. The lower limit of the Sb ₂ O ₃ content is preferably 0%, and more preferably 0.01% by mass, 0.02% by mass, and 0.04% by mass. Further, since SnO ₂ and CeO ₂ may deteriorate the transmittance of glass, it is preferable to introduce 1% by mass or less, and it is particularly preferable not to introduce them.

In the present specification, the glass composition of the optical glass is mainly described in terms of cation %. However, the analytical values obtained by quantitatively analyzing each component by ICP-AES analysis or the like are used as follows. Can be converted to the cation% display.

As a result of the quantitative analysis of the glass composition, the content ratio of the cation element in the glass component composed of the cation and the anion may be displayed as a percentage of atomic %. Such a composition display can be converted into the cation% display of the present invention by the following method, for example.

That is, the content (atomic %) of each cation in the quantified glass component is divided by the specific atomic weight to obtain the mole percentage of each cation, and the ratio of the cations to be calculated to all the contained cations. Is expressed as a mole percentage to convert it to a cation% display.

For example, the content (atomic %) of n cations is quantified by quantitative analysis as m ₁ , m ₂ ,..., M _i ,..., M _n, and the atomic weight of each cation is M ₁ , When M ₂ ,..., M _i ,..., M _n , the cation content rate (cation %) of one component (m _i , M _i ) can be obtained by the following formula.
[(M _i /M _i )/{(m ₁ /M ₁ )+(m ₂ /M ₂ )+・・・+(m _i /M _i )+・・・+(m _n /M _n )} ] X 100
Although the content (atomic %) of the anionic element may be quantified by the quantitative analysis, it can be converted into the anion content (anion %) of the anion in the same manner as above.

Further, as a result of the 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 displayed in mass %. The display of such a composition can be converted into a cation% display by the following method, for example.

The oxide composed of the cation A and oxygen is referred to as “A _m O _n ”. m and n are integers determined stoichiometrically. For example, for B ³⁺ , the oxide-based notation is B ₂ O ₃ , m=2, n=3, and for Si ⁴⁺ , SiO _{2 is} m=1, n=2.

First, the content of A _m O _n in mass% is divided by the molecular weight of A _m O _n , and then m is multiplied. Let this value be Q. Then, the Q values for all the glass components are summed. When the sum of Q values is ΣQ, the value obtained by normalizing the Q value of each glass component so that ΣQ is 100% is the content of As ⁺ in the cation% display. In addition, s is 2n/m.

<Optical properties of optical glass (refractive index, Abbe number)>
The upper limit of the refractive index nd of the optical glass of the present invention is 1.700, more preferably 1.690, 1.685, 1.680, 1.670, and 1.660 in that order. Moreover, the lower limit of the refractive index nd is 1.620, and further, 1.625, 1.630, 1.635, and 1.640 are preferable in that order.

The upper limit of the Abbe number νd of the optical glass of the present invention is 65, more preferably 62 and 61 in that order. Further, the lower limit of the Abbe number νd is 53, and further preferred is 54, 55, 56, 57, 58, 59 in this order.

By constructing an optical system using an optical element made of such an optical glass having a high refractive index and a low dispersion, it becomes possible to make the optical system compact, have high functionality, and improve chromatic aberration.

<Thermal stability of optical glass>
The thermal stability of glass includes devitrification resistance when molding a glass melt and devitrification resistance when glass once solidified is reheated. The devitrification resistance when molding a glass melt is based on the liquidus temperature, and the lower the liquidus temperature, the more excellent the devitrification resistance. In glass with a high liquidus temperature, in order to prevent devitrification, the temperature of the glass melt must be maintained at a high temperature, which leads to deterioration of quality and productivity due to volatilization of glass components. It may end up. Therefore, the optical glass of the present invention preferably has a liquidus temperature of 1350° C. or lower, more preferably 1300° C. or lower, further preferably 1250° C. or lower, and even more preferably 1200° C. or lower. It is preferably 1100° C. or lower, and even more preferably 1.

On the other hand, with respect to devitrification resistance when the glass once solidified is reheated, the larger the temperature difference (Tc-Tg) between the crystallization peak temperature Tc and the glass transition temperature Tg, the better the devitrification resistance. .. For example, in the reheat press molding method, it is necessary to heat the optical glass material to a temperature higher than the temperature Tg to soften it to an appropriate viscosity (about 10 ⁴ to 10 ⁶ dPa·s). However, when the temperature of the heated glass material reaches the temperature Tc, internal crystals are generated, so glass having a small temperature difference (Tc-Tg) is disadvantageous in performing reheat press molding. On the other hand, glass having a large temperature difference (Tc-Tg) is likely to soften at a temperature lower than the temperature Tc, so that the reheat press molding can be performed in a state where the glass does not devitrify.

In general, the "softening point" of glass is a temperature at which the glass starts to significantly deform due to its own weight, and is a temperature corresponding to a viscosity of about 10 ^7.6 dPa·s. On the other hand, in the reheat press molding method, “the temperature Tp at which the glass softens” (hereinafter, may be simply referred to as “the temperature at which the glass softens”, “Tp”, or “temperature Tp”) is higher than the “softening point”. It is the temperature at which the viscosity of the glass corresponds to a viscosity of 10 ⁴ to 10 ⁶ dPa·s. The temperature corresponding to the viscosity of 10 ⁴ to 10 ⁶ dPa·s can be uniquely obtained from the viscosity curve.

The glass transition temperature Tg, which is an index of the thermal stability of glass, the crystallization peak temperature Tc, and the endothermic peak temperature Tk associated with the glass transition (hereinafter, simply referred to as “endothermic peak temperature”, “Tk”, or “temperature Tk”). The crystallization start temperature Tx (hereinafter sometimes simply referred to as “crystallization start temperature”, “Tx” or “temperature Tx”) will be described with reference to FIG. 1.

FIG. 1 is a schematic diagram showing a differential scanning calorimetric curve of optical glass (phosphate optical glass). In the figure, the horizontal axis represents temperature and the vertical axis represents the amount of differential heat corresponding to the exothermic heat absorption of the glass. The glass transition temperature Tg, the endothermic peak temperature Tk associated with the glass transition, the crystallization start temperature Tx, and the crystallization peak temperature Tc are all measured by a differential scanning calorimeter [DSC (Differential Scanning Calorimetry)].

The endothermic peak temperature Tk accompanying the glass transition in the present invention means the temperature of the peak of the endothermic reaction that occurs in the vicinity of Tg to (Tg+100° C.). The crystallization peak temperature Tc means the temperature at which the crystallization exothermic peak at the lowest temperature is exhibited when powdering glass and performing differential scanning calorimetry from room temperature to a predetermined temperature at a temperature rising rate of 10° C./min. The crystallization start temperature Tx means the rising temperature on the low temperature side of the crystallization peak.

The glass transition temperature Tg of the optical glass of the present invention is preferably within the following range. That is, the upper limit of Tg is preferably 630°C, more preferably 600°C, 580°C, 560°C, and 540°C in this order. The lower limit of Tg is not particularly limited, but is preferably 400°C, more preferably 440°C, 460°C, 480°C, and 490°C in this order.

The crystallization peak temperature Tc of the optical glass of the present invention is preferably within the following range. That is, the lower limit of Tc is preferably 640°C, more preferably 650°C, 660°C, 67°C, and 675°C in this order. The upper limit of Tc is preferably 820°C, more preferably 810°C, 800°C, 790°C, 785°C, and 780°C in this order.

Usually, in the press molding method, the glass material is heated and adjusted to have a viscosity suitable for press molding. In particular, since the reheat press molding method deforms the glass in a shorter time than the precision press molding method, it is generally necessary to reheat the glass at a relatively high temperature so that good press molding can be performed and to sufficiently reduce the viscosity of the glass. Target.

In the case of press molding for a short time, if the heating temperature is insufficient and the viscosity of the glass is high, the molded product may crack under the pressure during pressing, or a defective shape due to insufficient deformation may occur. The non-defective rate may decrease. Therefore, in order to perform favorable press molding, particularly in the reheat press molding method, it is necessary to sufficiently heat the glass material and adjust it to an appropriate temperature (the temperature at which the glass viscosity is 10 ⁴ to 10 ⁶ dPa·s). There is.

On the other hand, when the glass is heated to a temperature higher than the crystallization peak temperature Tc of the glass, crystals (internal crystals or surface crystals) will be generated in the glass molded product after press molding, and the glass will be defective. There is a risk of becoming. Therefore, when heating the glass material, it is necessary to perform the heating at a temperature at which the viscosity is suitable for press molding and lower than the temperature Tc.

However, in the glass which is easily crystallized in the reheat press molding method, the temperature difference between Tg and Tc is often small, and the temperature Tc may be exceeded when heated to a temperature at which the viscosity is suitable for press molding.

Therefore, as the temperature difference (Tc-Tg) between the temperature Tc and the temperature Tg is larger, the crystallization of the glass is less likely to occur. The optical glass of the present invention has Tc-Tg of 145° C. or higher, does not generate internal crystals due to reheating, and has excellent thermal stability, as shown in Examples described later. That is, in the optical glass of the present invention, since the temperature Tc is sufficiently higher than the temperature Tg, the glass material is softened at a temperature lower than the crystallization peak temperature Tc during reheat press molding, and crystals are not generated. ..

In other words, the crystallization peak temperature Tc of the optical glass of the present invention is sufficiently higher than the temperature Tp at which the glass softens. In the optical glass of the present invention, as shown in Tables 1 to 3 described later, no internal crystal was generated in any of the samples (Samples 1 to 37). Therefore, by using the optical glass of the present invention, it becomes possible to favorably perform reheat press molding under severe reheating conditions.

Further, looking at the relationship between the temperature difference (Tc-Tg) and the temperature difference (Tc-Tp), since the temperature Tp is higher than the temperature Tg, the temperature difference (Tc-Tg) is the temperature difference (Tc- Tp), and the larger these temperature differences are, the more preferable. The optical glass of the present invention has a high temperature Tc and a large temperature difference (Tc-Tg) due to the above glass composition. Therefore, as a result, the temperature difference (Tc-Tp) also becomes large, and the thermal stability can be improved.

In the optical glass of the present invention, the temperature difference (Tc-Tg) between the temperature Tc and the temperature Tg is preferably 145°C or higher, more preferably 150°C or higher, further preferably 160°C or higher, Particularly preferably, it is 180°C or higher, and more preferably 200°C or higher.

Further, the temperature difference (Tc-Tp) between the temperature Tc and the temperature Tp is preferably 1°C or more, and the temperature difference (Tc-Tp) is preferably 5°C or more, more preferably 10°C or more. Yes, it is more preferably 20°C or higher, still more preferably 30°C or higher, and even more preferably 50°C or higher.

The optical glass of the present invention has a crystallization peak in a reheat press molding method in which the glass material is heated to a temperature higher than Tg to soften the glass material to an appropriate viscosity (about 10 ⁴ to 10 ⁶ dPa·s). Since it softens sufficiently at a temperature lower than the temperature Tc, generation of internal crystals can be effectively prevented. Further, since the optical glass of the present invention has excellent thermal stability, it can be applied to a reheat press molding method in an open atmosphere where precise temperature control is difficult.

As described above, in the optical glass of the present invention, the quantitative relationship between the content of Ba ²⁺ contained in the optical glass and the total content of divalent components other than Ba ²⁺ (cation ratio α[Ba ²⁺ /( Mg ²⁺ +Ca ²⁺ +Zn ²⁺ +Sr ²⁺ )]) is set to a range of 0.80 or less so that the glass does not devitrify even under severe reheating conditions such as reheat press molding. The thermal stability can be improved.

Further, the optical glass of the present invention contains any one or more kinds of rare earth elements selected from Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ , and P ^{5+ with} respect to the total content Re of these rare earth elements. The thermal stability of the glass by setting the quantitative relationship of the total content of B, B ³⁺ and Al ³⁺ (cation ratio β[(P ⁵⁺ +B ³⁺ +Al ³⁺ )/Re]) to be less than 14.0. At the same time, the refractive index can be effectively increased.

The thermal stability of glass obtained from a differential scanning calorimeter (DSC) can also be evaluated by the peak intensity Δ of crystallization. Specifically, the smaller the exothermic peak of crystallization, the smaller the tendency of the glass to change into crystals, and thus the higher the thermal stability of the glass, which is preferable for the glass of the present invention. In consideration of the sensitivity of the apparatus, the peak intensity Δ of crystallization is A when the absolute value of the difference between the amounts of heat of Tk and Tg is A and the absolute value of the difference of the amount of heat between Tx and Tc is B. Can be represented by a relative value such as peak intensity Δ=B/A (times). The height of the crystallization peak can be calculated from the difference between the calorific value at the peak temperature and the baseline of the differential scanning calorimeter, but in this case, it depends on how to draw the baseline, and therefore, in the present embodiment, the former The peak intensity Δ of crystallization was calculated by the method described in 1.

The glass having higher thermal stability and less likely to be crystallized has a smaller peak intensity Δ because less heat is generated when the glass is transformed into crystals. Therefore, the peak intensity Δ is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, even more preferably 4 or less, even more preferably 2 or less, still more preferably 1 or less. In the most preferable glass, no crystallization peak is observed and the peak intensity cannot be defined. Even if the peak intensity Δ is relatively large, if the temperature difference [Tc−Tg] between the temperature Tc and the temperature Tg is 145° C. or higher, crystallization is performed even if the glass is heated to a higher temperature to reduce the viscosity. Does not occur, crystallization is less likely to occur during reheat press molding.

Further, the optical glass of the present invention is also excellent in weather resistance. The weather resistance of glass can be expressed using a haze value as an index. The haze value is the degree of cloudiness of the glass when the glass is kept under a high temperature and high humidity environment for a predetermined time. Specifically, the haze value is the ratio of the scattered light intensity to the total transmitted light intensity when white light is transmitted perpendicularly to the polished surface of a double-sided optically polished glass flat plate, that is, [scattered light intensity/transmitted light intensity ] Is displayed as a percentage. The optical glass of the present invention preferably has a haze value of 10 or less, more preferably 5 or less, still more preferably 2 or less, and still more preferably less than 1. Glass with a large haze value is so-called chemical durability, which has a high rate of eroding the glass and forming reactants on the glass surface due to various chemical components such as water droplets and water vapor adhering to the glass and glass in the usage environment. It is a glass with low properties. On the contrary, a glass having a small haze value like the optical glass of the present invention is a glass having high chemical durability (weather resistance).

Production of Optical Glass The optical glass according to the present invention may be produced according to a known glass production method by mixing the raw materials so as to have the above-mentioned predetermined composition.

The raw material of each component in the glass (glass raw material) is not particularly limited, but examples thereof include oxides, carbonates, nitrates, and hydroxides of each metal.

Manufacture of Optical Element, etc. In order to manufacture an optical element using the optical glass according to the present invention, a known method may be applied. For example, the optical glass according to the present invention is melted to form a plate-shaped glass material, and the plate-shaped glass material is subdivided into a predetermined volume to produce a press-molding glass material. Alternatively, a glass gob of a predetermined volume is continuously molded from a molten state of the optical glass according to the present invention to produce a glass material for press molding. Next, this glass material is reheated and press-molded (reheat press molding) to produce an optical element blank. Further, the optical element blank is processed by a process including polishing to produce an optical element or a glass material for precision press molding.

Alternatively, the glass melt is hot-molded to produce a precision press-molding glass material (preform), and the glass material is heated and precision press-molded to produce an optical element.

Alternatively, the glass melt is directly molded (direct press molding) to prepare a glass molded body, and the molded body is polished to fabricate an optical element.

The optical function surface of the produced optical element may be coated with an antireflection film, a total reflection film or the like depending on the purpose of use.

Examples of the optical element include spherical lenses, aspherical lenses, microlenses, various lenses such as lens arrays, prisms, and diffraction gratings.

Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and it goes without saying that the present invention can be implemented in various modes without departing from the scope of the present invention. ..

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1 and Comparative Example 1)
Tables 1 to 3 show optical glasses according to the examples of the present invention (Samples 1 to 37), and Table 4 shows optical glasses according to the comparative example of the present invention (Sample 38). Samples 6 and 18 shown in Table 4 are the same as the samples shown in Table 1 and Table 2, and are also shown for comparison between the example and the comparative example.

These optical glasses were manufactured by the following procedures and various evaluations were performed.

[Manufacture of optical glass]
First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of glass are prepared as raw materials, and the glass composition of the resulting optical glass is as shown in Tables 1 to 4 in terms of cation%. The above raw materials were weighed and prepared so that the raw materials were sufficiently mixed. The blended raw material (batch raw material) thus obtained was charged into a platinum crucible, and melted in an electric furnace in a temperature range of 1200 to 1400° C. according to the melting property of the raw material, stirred to homogenize, and clarified. The molten glass was flown out from the outflow nozzle and cast into a mold preheated to an appropriate temperature. The cast glass was put into a slow cooling furnace and cooled to room temperature according to a predetermined slow cooling schedule to obtain each optical glass (Samples 1 to 38).

[Evaluation of optical glass]
Regarding the obtained optical glass (Samples 1 to 38), the glass composition was confirmed, the refractive index (nd), the Abbe number (νd), the glass transition temperature (Tg), and the crystallization start temperature (Tx) by the following methods. ), crystallization peak temperature (Tc), crystallization peak intensity (Δ), and the presence or absence of internal crystals were evaluated. A weather resistance (D _H ) test was also performed on Sample 6.

[1] Confirmation of glass composition An appropriate amount of each optical glass obtained as described above was sampled, treated with acid and alkali, and subjected to inductively coupled plasma mass spectrometry (ICP-AES method) to analyze each component. It was measured by quantifying the content, and it was confirmed that it matches the glass composition of each sample shown in Tables 1 to 4 in terms of cation %.

[2] Refractive index (nd) and Abbe number (νd)
The optical glass cooled to room temperature is again held at a temperature between the glass transition temperature (Tg) and the yield point (Ts) by the refractive index measurement method specified by the Japan Optical Glass Industry Association, and the temperature is lowered at a temperature lowering rate of -30°C/hour. The refractive index (nd) and the Abbe's number (νd) of the optical glass obtained by removing the strain in the glass were measured [[GMR-1] sold by Shimadzu Device Manufacturing Co., Ltd. use〕. The results are shown in Tables 1 to 4.

[3] Glass transition temperature (Tg), crystallization peak temperature (Tc) and peak intensity (Δ)
It was measured with a differential scanning calorimeter manufactured by Bruker AXS Co., Ltd. at a heating rate of 10° C./min. Furthermore, the temperature difference (Tc-Tg) was calculated from the measured Tg and Tc. Further, the peak intensity (Δ) was calculated based on the differential scanning calorimeter curve shown by the differential scanning calorimeter. The results are shown in Tables 1 to 4.

[4] Presence or absence of internal crystal Glass is cast from a molten state to a mold in the atmosphere to prepare a glass molded body having a flat free surface on the upper surface, and the glass molded body is cut to 1×1×1 cm ³ A cubic glass sample of was obtained. This glass sample is put into a heating furnace and held at a temperature Tg for 10 minutes (primary heating), then held at a temperature (Tp) at which the glass softens (second heating), and the glass sample is taken out from the heating furnace. And let it cool. Next, the glass sample was polished, and the inside of the glass was observed from the polished surface with a microscope to observe the presence or absence of internal crystals. From this observation, a crystal having no diameter of 0.1 μm or more was evaluated as “no crystal”, and a crystal having a diameter of 0.1 μm or more was evaluated as “with crystal”. Although the temperature Tp varied depending on each sample, it was confirmed that all the samples were softened at a temperature within the range of (Tg+about 130° C.) to (Tg+about 180° C.). The results are shown in Tables 1 to 4.

[5] Weather resistance (D _H ) test Regarding the obtained optical glass (Sample 6), a glass sample (30×30×3 mm) whose main surface was face-polished was molded according to Japan Optical Glass Industry Association Standard JOGIS07, The treatment was carried out for 48 hours in a temperature cycle environment of high temperature and high humidity. Thereafter, the haze value of the glass sample was measured using a haze meter (TC-HIIIDPK) manufactured by Tokyo Denshoku Co., Ltd. The haze value can be obtained by the scattered light intensity/transmitted light intensity×100 (unit: %). The results will be described later.

As shown in Tables 1 to 4, the optical glasses (Samples 1 to 37) according to the examples of the present invention have a refractive index nd in the range of 1.620 to 1.700 and an Abbe number νd in the range of 53 to 65. , In particular, the cation ratio α[Ba ²⁺ /(Mg ²⁺ +Ca ²⁺ +Zn ²⁺ +Sr ²⁺ )] and the cation ratio β [(P ⁵⁺ +B ³⁺ +Al ³⁺ )/Re] are within the desired range (cation ratio α is 0. A glass having a cation ratio β of 80 or less and a cation ratio β of less than 14.0).

In the optical glass according to the example of the present invention, the average value of the temperature difference (Tc-Tg) between the temperature Tg and the temperature Tc is about 210° C., and the temperature Tp of each sample is higher than the crystallization peak temperature Tc. It was also confirmed that the temperature was low (that is, Tp<Tc), no internal crystal was generated in the solidified glass, and the thermal stability was high.

In particular, Sample 18 has the lowest temperature difference (Tc-Tg) among Samples 1 to 37, but even in this case, the glass does not soften, internal crystals do not occur, and it is thermally stable. It was confirmed that the property is high.

Further, although the sample 6 is a sample very close to the sample 38 (comparative example) in terms of the refractive index and the Abbe number, the temperature difference (Tc-Tg) is 192° C. and the internal crystal is It was confirmed that it did not occur and the thermal stability was high like other samples.

On the other hand, in the sample 38 which is the optical glass according to the comparative example of the present invention, the temperature difference (Tc-Tg) is 139° C., which is a temperature Tp (much higher than the crystallization peak temperature Tc (667° C.). It softened at 710 degreeC. That is, in this sample 38, the temperature Tp and the temperature Tc had a relationship of Tp>Tc. Then, it was confirmed that internal crystals were generated in the glass of the solidified sample 38 and the thermal stability was inferior.

The reason why the above difference occurs is that the sample 38, which is the optical glass according to the comparative example, has the cation ratio β of less than 14, but the cation ratio α, which is an index of the thermal stability of the glass, is within the predetermined range (0. It is considered to be because it is out of (80.80 or less).

As described above, the optical glass according to the example of the present invention has a sufficiently large temperature difference (Tc-Tg). Therefore, the glass can be surely softened at the temperature Tp lower than the temperature Tc. Therefore, the optical glass of the present invention can be applied to reheat press molding in which precise temperature control is difficult.

On the other hand, in the optical glass according to the comparative example (Sample 38), the temperature difference (Tc-Tg) is relatively small, and the softening temperature Tp is higher than the crystallization peak temperature Tc. Therefore, the optical glass according to the comparative example is softened. If so, internal crystals are generated, and it is difficult to apply the optical glass according to the comparative example to reheat press molding.

In addition, as a result of the weather resistance ( _DH ) test, it was confirmed that the optical glass (Sample 6) according to this example had no surface alteration even after being treated for a long time under high temperature and high humidity, and was excellent in transparency. It was The haze value was 0.1%.

From these results, it was confirmed that the optical glass according to the present invention has excellent weather resistance.

(Example 2)
An optical lens was produced using the optical glass (Samples 1 to 37) produced in Example 1. Specifically, each optical glass of Example 1 was processed into a predetermined shape to prepare an optical glass material. Then, the optical glass material is heated and softened, press-molded into a shape similar to the shape of the target lens, after press molding, the glass is annealed, and the optical lens is finished by processing steps including a polishing step. It was As the glass press molding method, annealing method, and processing step, known methods may be appropriately applied.

It was confirmed that the optical lens thus obtained did not crystallize the glass even when it was heated at a relatively high temperature in the reheat press molding, and a good optical lens was obtained.

(Comparative example 2)
An optical lens was tried to be produced by using the optical glass (Sample 38) produced in Comparative Example 1 in the same manner as in Example 2.

However, it was confirmed that the optical glass according to the comparative example has low thermal stability, crystallization occurs due to heating during reheat press molding, and internal crystals are generated in the obtained optical lens.

The present invention is summarized below.
As shown in Tables 1 to 4, the optical glass of the present invention (Samples 1 to 37) is a glass in which the total content of P ⁵⁺ , B ³⁺ and Al ³⁺ [P ⁵⁺ +B ³⁺ +Al ³⁺ ] is 60 cation% or less. There
Ba ²⁺ ,
Any one or more selected from Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ ,
And any one or more selected from Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ ,
The cation ratio α [Ba ²⁺ /(Mg ²⁺ +Ca ²⁺ +Zn ²⁺ +Sr ²⁺ )] of the content of Ba ²⁺ to the total content of Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ is 0.80 or less,
The cation ratio β[(P ⁵⁺ +B ³⁺ +Al ³⁺ )/(Gd ³⁺ +Y ³⁺ +La ³⁺ +Yb ⁺ of the total content of P ⁵⁺ , B ³⁺ and Al ³⁺ with respect to the total content of Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ^{3+. 3+} )] is less than 14.0,
It is satisfied that the refractive index nd is 1.620 to 1.700 and the Abbe number νd is 53 to 65.

From another aspect, Samples 1 to 17, which are examples of the optical glass according to the present invention, are selected as the optical glass particularly excellent in low dispersibility and thermal stability. When the present invention is viewed with reference to these samples, these optical glasses satisfy the following conditions.
A glass having a total content of P ⁵⁺ , B ³⁺ and Al ³⁺ [P ⁵⁺ +B ³⁺ +Al ³⁺ ] of 60 cation% or less,
Ba ²⁺ ,
Any one or more selected from Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ ,
And any one or more selected from Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ ,
The cation ratio α [Ba ²⁺ /(Mg ²⁺ +Ca ²⁺ +Zn ²⁺ +Sr ²⁺ )] of the content of Ba ²⁺ to the total content of Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ is 0.50 or less,
Gd ^{3+, Y 3+, La 3+} and ^{Yb 3+ P} 5+ to the total content ^{of, B 3+} and the total content of the cation ratio of ^{Al 3+ β [(P 5+ +} B 3+ + Al 3+]) / (Gd 3+ + Y 3+ + La 3+ +Yb ³⁺ )] is 12.0 or less,
An optical glass having a refractive index nd of 1.635 to 1.660 and an Abbe number νd of 59 to 62.

According to these samples, Tc-Tg is as large as 180° C. or higher, the peak intensity Δ is suppressed to be low, the thermal stability is excellent, and the optical index is 1.635 or more and Abbe number is 59 or more. Optical glass having characteristics can be manufactured.

Tg Glass transition temperature Tk Endothermic peak temperature Tx Crystallization start temperature Tc Crystallization peak temperature A Absolute value of heat quantity difference between Tk and Tg B Absolute value of heat quantity difference between Tx and Tc

Claims (7)

An oxide glass in which the total content of P ⁵⁺ , B ³⁺ and Al ³⁺ [P ⁵⁺ +B ³⁺ +Al ³⁺ ] is 38 to 60 cation % ,
Ba ²⁺ ,
Any one or more selected from Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ ,
And any one or more selected from Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ ,
The cation ratio α [Ba ²⁺ /(Mg ²⁺ +Ca ²⁺ +Zn ²⁺ +Sr ²⁺ )] of the content of Ba ²⁺ to the total content of Mg ²⁺ , Ca ²⁺ , Zn ²⁺ and Sr ²⁺ is 0.80 or less,
The cation ratio β[(P ⁵⁺ +B ³⁺ +Al ³⁺ )/(Gd ³⁺ +Y ³⁺ +La ³⁺ +Yb ⁺ of the total content of P ⁵⁺ , B ³⁺ and Al ³⁺ with respect to the total content of Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ^{3+. 3+} )] is less than 14.0,
^Contains B ³⁺ ,
The content of the cation ratio of ^{P 5+} to the content of ^{B 3+ [P 5+ / B 3+} ] is 0.2 to 10.0,
An optical glass having a refractive index nd of 1.620 to 1.700 and an Abbe number νd of 53 to 65. The optical glass according to claim 1, wherein the total content of Gd ³⁺ , Y ³⁺ , La ³⁺ and Yb ³⁺ [Gd ³⁺ +Y ³⁺ +La ³⁺ +Yb ³⁺ ] is 2 to 20 cation %. The optical glass according to claim 1, wherein the content of P ⁵⁺ is 10 to 45 cation %. The optical glass according to claim 1, wherein the content of Ba ²⁺ is 5 to 25 cation %. The optical glass according to claim 1, wherein the content of Zn ²⁺ is 15 cation% or less. An optical element comprising the optical glass according to claim 1. An optical glass material comprising the optical glass according to claim 1.

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