WO2014065225A1

WO2014065225A1 - Fluorophosphate glass, preform for press molding, and optical element

Info

Publication number: WO2014065225A1
Application number: PCT/JP2013/078421
Authority: WO
Inventors: 茂輝澤村; 賢治北岡
Original assignee: 旭硝子株式会社
Priority date: 2012-10-23
Filing date: 2013-10-21
Publication date: 2014-05-01
Also published as: JPWO2014065225A1; CN104755439A

Abstract

Disclosed is fluorophosphate glass. This glass contains, in cation %, 10-45% of P⁵⁺, 1-40% of Al³⁺, 0-20% of Mg²⁺, 0-25% of Ca²⁺, 0-25% of Sr²⁺, 0-35% of Ba²⁺, 24-60% of Li⁺, 0-10% of Na⁺, 0-10% of K⁺, 0-10% of Y³⁺, 0-15% of B³⁺, and F^- in such an amount that the anion ratio of F^- to the total of F^- and O^2-, namely F^-/(F^- + O^2-) is 0.25-0.85.

Description

Fluorophosphate glass, press-molding preform, and optical element

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

In recent years, methods for manufacturing optical elements by press molding have become mainstream due to improvements in press molding technology. Press molding is a technique in which spherical or cylindrical glass (hereinafter referred to as a preform) is heated in a mold to a glass transition temperature or a yield point or higher and pressed into a specific shape.

The optical glass used for the optical element has different glass main components for each desired optical property. As a glass having low refractive index and low dispersion optical properties, fluorophosphate glass is mainly used since it exhibits high visible light transmittance and anomalous dispersion (for example, see Patent Document 1). Low dispersion and anomalous dispersion are effective for correcting chromatic aberration, and a high visible light transmittance is an advantageous characteristic as an optical element material constituting an imaging optical system.

On the other hand, fluorophosphate glass contains fluorine, which is an easily volatile component, as an essential component. Therefore, in the fluorophosphate glass, in addition to desired optical characteristics, desired thermal characteristics that suppress volatilization of fluorine are required in order to improve preform molding and production efficiency and yield of optical elements.

For example, if the molding temperature becomes too high during press molding, the components are volatilized from the preform surface, and volatilized components such as fluoride adhere to the mold surface. When this volatile component adheres to the glass surface, it scatters light and becomes a spider defect. Therefore, in order to improve the durability of the mold and prevent spider defects, it is desirable that the fluorophosphate glass has a low glass transition temperature and yield point.

That is, fluorophosphate glass is required to lower the glass transition temperature and the yield point from the viewpoint of having the above-described optical characteristics and increasing the production efficiency.

As fluorophosphate glass suitable for press molding, for example, P ⁵⁺ , Al ³⁺ , two or more divalent cation components selected from Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ and Li ⁺ are essential. together comprising as cationic components of, F ^- F to the total amount of and the ^{O ^2--} the molar ratio ^{^{^{F - / (F - + O}}} 2-) glass is 0.25 to 0.85 has been proposed (For example, refer to Patent Document 2). However, since this glass has a low Li ⁺ content, it has a high glass transition temperature and is not sufficient in terms of ease of production.

Japanese Patent Laid-Open No. 10-139454 JP 2010-042998 A

The present invention is a fluorophosphate glass suitable for the production of optical elements, has low refractive index and low dispersion optical properties, is less likely to cause striae during preform molding, and is less likely to cause devitrification during press molding. The purpose is to provide glass.

The fluorophosphate glass of the present invention is expressed in terms of cation%,
P ^{5+ 10-45} %,
Al ^{3+ 1-40} %,
Mg ^{2+ 0-20} %,
Ca ^{2+ 0-25} %,
Sr ^{2+ 0-25} %,
Ba ^{2+ 0-35} %,
Li ⁺ 24-60%,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-10%,
B ^{3+ 0-15} %,
Containing
F ^- the F ^- anion ratio to the total amount of the ^{^{^{^{O 2- (F - / (F}}}} - + O 2-)) , characterized in that it contains at from 0.25 to 0.85.

The fluorophosphate glass of the present invention has low refractive index and low dispersion optical characteristics. Moreover, since there is much content of Li ^<+> , a glass transition temperature and a yield point can be made low. Therefore, the molding temperature can be lowered, the volatilization of components from the glass surface can be suppressed, and the durability of the mold can be enhanced. Furthermore, it is thermally stable and exhibits high liquid phase viscosity. Therefore, even a preform having a large volume can produce a preform having no internal defects such as devitrification, and a large-diameter lens can be produced by a press molding method using the preform.

(Optical glass)
The fluorophosphate glass (hereinafter abbreviated as the present glass) of the present invention will be described below. In the present specification, unless otherwise specified, the ratio of the cation component is expressed as cation% based on the molar ratio, and the ratio of each anion component is expressed as% anion based on the molar ratio. To do.

P ⁵⁺ is a glass network former and is an essential component. The content of P ⁵⁺ is 10 to 45%. If it is less than 10%, the stability of the glass may be lowered. In order to increase the content of P ⁵⁺ , it is preferable to introduce it with normal phosphoric acid as a raw material. If P ⁵⁺ exceeds 45%, the water in orthophosphoric acid may react with fluorine and volatilize as HF gas. In the case of introducing the oxide raw material, the oxygen ratio becomes too large, so that there is a possibility that desired optical characteristics are not satisfied. The upper limit of P ⁵⁺ is preferably 40% or less, more preferably 35% or less, and even more preferably 33% or less. The lower limit of P ⁵⁺ is preferably 12% or more, and more preferably 15% or more. As the P ⁵⁺ raw material, it is preferable to use a phosphate from the viewpoint of suppressing the erosion of the platinum crucible and suppressing the volatilization of the components.

Al ³⁺ is a component that improves the stability of the glass and is an essential component. The content of Al ³⁺ is 1 to 40%. If it is less than 1%, the stability of the glass is lowered, and if it exceeds 40%, the glass transition temperature and the liquidus temperature may be increased. The upper limit of Al ³⁺ is preferably 37% or less, more preferably 35% or less, still more preferably 33% or less, and even more preferably 30% or less. The lower limit of Al ³⁺ is preferably 3% or more, and more preferably 5% or more.

Mg ²⁺ is a component that improves the stability of the glass, but is not an essential component. The Mg ²⁺ content is 0 to 20%. From the viewpoint of devitrification resistance, the upper limit of Mg ²⁺ is preferably 15% or less, more preferably 10% or less, and even more preferably 7% or less. The lower limit of Mg ²⁺ is preferably more than 0%, more preferably 1% or more.

Ca ²⁺ is a component that improves the stability of the glass, but is not an essential component. The content of Ca ²⁺ is 0 to 25%. From the viewpoint of devitrification resistance, the upper limit of Ca ²⁺ is preferably 22% or less, more preferably 15% or less, and even more preferably 10% or less. The lower limit of Ca ²⁺ is preferably more than 0%, more preferably 1% or more.

In the present glass, Sr ²⁺ is a component that improves the stability of the glass, but is not an essential component. The content of Sr ²⁺ is 0 to 25%. From the viewpoint of devitrification resistance, the upper limit of Sr ²⁺ is preferably 22% or less, more preferably 15% or less, and even more preferably 10% or less. The lower limit of Sr ²⁺ is preferably more than 0%, more preferably 0.5% or more, and further preferably 1% or more.

Ba ²⁺ is a component that can improve the stability of the glass and achieve a high refractive index while maintaining low dispersion, but is not an essential component. The content of Ba ²⁺ is 0 to 35%. The upper limit of Ba ²⁺ is preferably 31% or less, more preferably 30% or less, still more preferably 29% or less, and even more preferably 25% or less from the viewpoint of devitrification resistance. The lower limit of Ba ²⁺ is preferably more than 0%, more preferably 1% or more, and further preferably 3% or more.

In order to enhance the effect of the alkaline earth metal cation component (R ²⁺ ), the total content (Mg ²⁺ + Ca ²⁺ + Sr ²⁺ + Ba ²⁺ ) is preferably 1 to 31%. When the content is 1% or more, the effect of increasing the stability of the glass is enhanced. On the other hand, if it exceeds 31%, the stability of the glass is rather lowered. The upper limit of the total amount of R ²⁺ is preferably 30% or less, and more preferably 29% or less.

When R ²⁺ is contained in the above total amount, it is preferable to use two or more selected from Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ . From the viewpoint of enhancing the effect of the inclusion of the alkaline earth metal, it is preferable to use Ba ²⁺ as an essential component and to use one or more selected from Mg ²⁺ , Ca ²⁺ and Sr ²⁺ . Although Sr ²⁺ and Ba ²⁺ can be introduced in a relatively large amount, the introduction of a large amount of Mg ²⁺ and Ca ²⁺ may reduce the stability of the glass.

Li ⁺ is a component that lowers the glass transition temperature without impairing stability, and is an essential component. The content of Li ⁺ is 24 to 60%. If the content of Li ⁺ is less than 24%, the glass transition temperature cannot be lowered sufficiently and the stability is also lowered. If it exceeds 60%, the durability of the glass is impaired, and the workability also decreases. Although the effect of lowering the glass transition temperature can be obtained even if the following alkali metal component is contained, it is preferable to contain Li ⁺ because the water resistance of the glass is excellent. The upper limit of Li ⁺ is preferably 50% or less, more preferably 45% or less, still more preferably 43% or less, still more preferably 41% or less, and particularly preferably less than 40%. The lower limit of Li ⁺ is preferably more than 25%, more preferably 27% or more, and even more preferably more than 30%. When importance is attached to the stability of the glass, the Li + content is preferably more than 30% to 60%. At this time, the upper limit of Li ⁺ is more preferably 59% or less, still more preferably 57% or less, and even more preferably 55% or less. The lower limit of Li ⁺ is more preferably 31% or more and even more preferably 32% or more. When importance is attached to striae suppression of glass, the Li + content is preferably 24 to 30%. At this time, the upper limit of Li ⁺ is more preferably 29% or less, even more preferably 28% or less, and even more preferably 27% or less. The lower limit of Li ⁺ is more preferably more than 24% and even more preferably 25% or more.

In this glass, in order to obtain the effects of glass stability and striae suppression, the ratio of the content of Li ^{+ to} the total amount of alkaline earth metal components Li ⁺ / ΣR ²⁺ , that is, Li ⁺ / (Mg ²⁺ + Ca ²⁺ + Sr ²⁺ + Ba ²⁺ ) is preferably more than 0.8 and less than 16. In particular, when importance is attached to the stability of the glass, it is preferable that Li ⁺ / ΣR ²⁺ be 1 or more and less than 16. By stabilizing the glass, it is possible to produce a preform having a large volume, and it is also possible to produce a large-diameter lens by a press molding method. The upper limit of Li ⁺ / ΣR ²⁺ is more preferably 15 or less, even more preferably 14 or less, and even more preferably 13 or less. The lower limit of Li ⁺ / ΣR ²⁺ is more preferably more than 1, and even more preferably 2 or more. When importance is attached to striae suppression of glass, it is preferable that Li ⁺ / ΣR ²⁺ be more than 0.8 and less than 1. In this case, the upper limit of Li ⁺ / ΣR ²⁺ is more preferably 0.98 or less, and even more preferably 0.97 or less. The lower limit of Li ⁺ / ΣR ²⁺ is more preferably 0.82 or more, and even more preferably 0.85 or more.

Na ⁺ and K ⁺ are components that lower the glass transition temperature in the same manner as Li ⁺ , but are not essential components. The contents of Na ⁺ and K ⁺ are both 0 to 10%. Since Na ⁺ and K ⁺ have a larger thermal expansion coefficient than that of Li ⁺ , a low content is preferable, and it is more preferable that they are not substantially contained. In the present specification, the term “substantially does not contain” means to allow contamination by inevitable impurities although not actively containing.

Y ³⁺ is a component that improves the stability or durability of the glass, but is not an essential component. The content of Y ³⁺ is 0 to 10%. If it exceeds 10%, the stability of the glass is rather lowered and the glass transition temperature is increased. The upper limit of Y ³⁺ is preferably 7% or less, and more preferably 5% or less.

B ³⁺ is a vitrification component and has the effect of stabilizing the glass, but is not an essential component. The content of B ³⁺ is 0 to 15%. From the viewpoint of ensuring the durability of the glass and suppressing the volatilization of the components, B ³⁺ is preferably 15% or less. The upper limit of B ³⁺ is preferably 10% or less, and more preferably 5% or less. In order to reduce the volatilization of components, 0.5% or less is more preferable, and it is particularly preferable that the component is not substantially contained. The raw material of B ³⁺ is preferably B ₂ O ₃ from the viewpoint of suppressing the volatilization of components and preventing the striae of glass.

The glass may contain components other than the above components as long as the object of the invention is not impaired, but P ⁵⁺ , Al ³⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Li ⁺ can be used as the cation component. And the total amount of Y ³⁺ is preferably 95% or more from the viewpoint of stably producing a high-quality optical glass. The total amount of the cation component is preferably 98% or more, more preferably 99% or more, substantially from P ⁵⁺ , Al ³⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Li ⁺ and Y ^3+. It is particularly preferred that

Examples of components other than the above components include lanthanoids such as Ti ⁴⁺ , Zr ⁴⁺ , Zn ²⁺ , Bi ⁵⁺ , W ⁵⁺ , Nb ⁵⁺ , Sb ³⁺ , La ³⁺ , and Gd ³⁺ . The total content of these is preferably 5% or less, more preferably 2% or less, and even more preferably 1% or less.

Si ⁴⁺ may also be included for the purpose of stabilizing the glass. However, in the production of fluorophosphate glass, since the melting temperature of the glass is low, if it is introduced excessively, the raw material remains undissolved in the glass melt, and volatilization increases during melting, which may impair the production stability. Accordingly, the content of Si ⁴⁺ is preferably 0 to 10%, more preferably 0 to 8%, and further preferably 0 to 5%.

Sn ²⁺ is preferably not substantially contained since the glass may be colored. Moreover, in order to suppress environmental load, it is preferable not to contain Pb2 ⁺ substantially.

In the present glass, the proportion of the anionic component, while achieving the desired optical properties, in order to obtain a glass having excellent stability, F ^- the F ^- and anion ratio to the total amount of the O ^2-( F ⁻ / (F ⁻ + O ²⁻ )) 0.25 to 0.85. The anion ratio is preferably 0.3 to 0.8, more preferably 0.35 to 0.75. Further, the total amount of F ⁻ and O ²⁻ in the anion is preferably 99% or more, and more preferably substantially consists of F ⁻ and O ²⁻ .

The anionic component, F ^- and O ^2- Besides, containing halogen is permitted. However, the chloride raw material has higher deliquescence than the fluoride raw material and easily contains moisture. Therefore, when used simultaneously with the fluoride raw material, it may become hydrogen fluoride and promote volatilization of fluorine. In general, a chloride raw material has a high vapor pressure and is likely to volatilize. Therefore, in the present glass, it is preferable that Cl ⁻ is not substantially contained.

The optical constant of the present glass is preferably 1.4 to 1.58 for the refractive index (n _d ) and 60 to 90 for the Abbe number (ν _d ). The refractive index is more preferably 1.45 to 1.575, and further preferably 1.48 to 1.56. The Abbe number is more preferably 65 to 85, and further preferably 70 to 82.

Since the present glass has a large Li ⁺ content, the glass transition point can be lowered. The glass transition temperature is preferably 380 ° C. or lower. In order to suppress deterioration of the mold during press molding and volatilization of components from the preform and prevent a decrease in productivity, the lower the glass transition temperature, the better. Therefore, the glass transition temperature is more preferably 370 ° C. or less, further preferably 360 ° C. or less, and particularly preferably 350 ° C. or less.

The yield point of this glass is preferably 420 ° C. or lower. In order to prevent deterioration of the mold during press molding and volatilization of components from the preform and prevent a decrease in productivity, a lower yield point is preferable. Therefore, the yield point is more preferably 410 ° C. or lower, further preferably 400 ° C. or lower, and particularly preferably 380 ° C. or lower.

The liquidus temperature of this glass is preferably 750 ° C. or lower for good preform molding. When the liquidus temperature is higher than 750 ° C., components are volatilized from the surface of the glass melt at the time of preform molding, which may cause striae. The lower the liquidus temperature, the more preferable, 730 ° C. or lower is more preferable, 670 ° C. or lower is further preferable, and 650 ° C. or lower is particularly preferable. In the present specification, the term “liquid phase temperature” refers to the lowest temperature at which crystals are not generated from a glass melt when held at that temperature for 1 hour.

The linear expansion coefficient of the present glass is preferably 140 to 200 × 10 ⁻⁷ / ° C. When the thermal expansion coefficient exceeds 200 × 10 ⁻⁷ / ° C., there is a possibility that a problem that the glass surface is missing at the time of molding may occur.

In the composition range of the present glass, the fluorophosphate glass (the present glass I), which emphasizes stability, is expressed in terms of cation%,
P ^{5+ 10-45} %,
Al ^{3+ 1-40} %,
Mg ^{2+ 0-20} %,
Ca ^{2+ 0-25} %,
Sr ^{2+ 0-25} %,
Ba ^{2+ 0-35} %,
Li ⁺ more than 30-60%,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-10%,
B ^{3+ 0-15} %,
Containing
F ^- the F ^- anion ratio to the total amount of the ^{^{^{O 2- (F - / (F}}} - + O 2-)) with those containing at from 0.25 to 0.85.

In addition, in the composition range of this glass, fluorophosphate glass (present glass II) that emphasizes striae suppression is expressed in terms of cation%,
P ^{5+ 10-45} %,
Al ^{3+ 1-40} %,
Mg ^{2+ 0-20} %,
Ca ^{2+ 0-25} %,
Sr ^{2+ 0-25} %,
Ba ^{2+ 0-35} %,
Li ⁺ 24-30%,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-10%,
B ^{3+ 0-15} %,
Containing
F ^- the F ^- and anion ratio to the total amount of the ^{^{^{^{O 2- (F - / (F}}}} - + O 2-)) are those containing at from 0.25 to 0.85.

(preform)
The preform of the present invention is preferably obtained by molding the present glass or further polishing the molded product.

Hereinafter, although an example of the manufacturing method of the preform of this invention is demonstrated, it is not limited to this.
A glass raw material of the present glass is melted in a tank to form a glass melt, and this glass melt is discharged from a nozzle tip attached to the tank to a forming die to produce a molten glass lump (gob). At that time, the glass melt is received and collected by the receiving surface of the mold, but the mold is slowly lowered so that the glass tip does not wet the tip of the nozzle. When the gob reaches the target volume, the mold is lowered quickly and the glass flow is cut by surface tension. In order to produce a gob with a desired volume, during the production of the gob, an inert gas such as nitrogen gas is passed through the porous mold, and the gob is lifted by the force of the gas outflow to make it elliptical or spherical, etc. Cool and mold the preform.

As the mold, for example, the radius of curvature R of the surface that receives the glass melt is 8 mm, the concave depth of the curved surface of the portion that receives the glass is 4 mm, and is formed of a porous material. Those configured to be ejected are used. An inert gas such as nitrogen gas is ejected only from the R portion. An inert gas such as nitrogen gas may not only float the gob but also fill it around the gob. By increasing the size of the mold, a preform having a larger volume can be formed.

In the present invention, since the glass composition is thermally stable and exhibits high liquid phase viscosity, even a large preform having a volume of 1 to 1.5 cm ³ does not have internal defects such as devitrification and foreign matter. Is obtained. In particular, according to the above method, a preform free from striae, surface wrinkles and scratches can be obtained. If the preform has a volume of 1.5 cm ³ , a lens having a diameter of about 25 mm can be manufactured by press molding.

(Optical element)
The optical element of the present invention is preferably obtained by molding a preform formed from the present glass. Since the present glass has the optical characteristics described above, the optical design is easy when used as an optical element. Examples of such optical elements include aspherical lenses and spherical lenses used in digital cameras and the like.

As a manufacturing method of the optical element, a press molding method is preferable from the viewpoint of improving mass productivity. In the press molding method, a press molding die whose molding surface is processed into a desired shape in advance is used. A pair of molds face each other, the preform of the present invention described above is placed between them, and both the mold and the preform are heated to a temperature at which the glass falls to a viscosity suitable for molding. Soften the renovation. And by pressing this, the shaping | molding surface of a shaping | molding die is precisely transcribe | transferred to glass. Since the present glass has a sufficiently low glass transition temperature, the heating temperature of the preform can be lowered. Therefore, durability of a metal mold | die can be made high and the volatilization of the component from the glass surface at the time of a press can be suppressed. In addition, as described above, the present glass is free from internal defects such as devitrification and foreign matter, and is free from striae and surface wrinkles and scratches even in a large preform having a volume of 1 to 1.5 cm ^3. Since a preform can be obtained, it is possible to manufacture a lens having a large aperture, which has been difficult in the past, by a press molding method. That is, a lens with a diameter of 8 mm from a preform with a volume of about 0.6 cm ³ , a lens with a diameter of 15 mm from a preform with a volume of about 1.0 cm ³ , a lens with a diameter of about 25 mm from a preform with a volume of about 1.5 cm ³ Each can be manufactured by press molding.

The atmosphere during press molding is preferably non-oxidizing to protect the mold surface and preform surface. As the non-oxidizing atmosphere, an inert gas such as argon or nitrogen, a reducing gas such as hydrogen, or a mixed gas of an inert gas and a reducing gas can be used. Preferably, nitrogen gas or nitrogen gas mixed with a small amount of hydrogen gas can be used. The pressure and time during pressurization can be appropriately changed according to the viscosity of the glass. After heating and pressurizing, the mold and the press-molded product are cooled, and when the temperature is preferably below the strain point, the mold is released and the press-molded product is taken out.

Hereinafter, specific embodiments of the present invention will be described. However, the present invention is not construed as being limited to these. Examples 1 to 61 are examples of the present invention, and examples 62 and 63 are comparative examples. Examples 62 and 63 are glasses having the compositions described in Examples 17 and 19 of JP2010-42998A. The produced glass was measured by the method described below. Tables 1 to 7 show the cation% and anion% of each glass and the measured values obtained by the following measurements. For data not measured, “-” is shown in the table.

(Production of glass)
The raw materials were weighed so as to obtain glasses having chemical compositions shown in Tables 1 to 7. As a glass raw material, a phosphate raw material, a fluoride raw material, an oxide raw material, and a carbonate raw material were used and prepared so as to have a target composition. The prepared raw material was put into a platinum crucible having an internal volume of about 300 cc, and melted, clarified and stirred at about 900 to 1000 ° C. for 1 hour. Then, after casting into a rectangular mold having a length of 100 mm and a width of 50 mm preheated to about 320 to 370 ° C., it was gradually cooled at about 1 ° C./min to obtain a sample.

(Evaluation methods)
The resultant glass refractive index at a wavelength of 587.6 nm (helium d line) and _{(n d)} Abbe's number ([nu _d), the glass transition temperature _{(T g,} Unit: ° C.), yield point (At, Unit: ° C. ), Liquid phase temperature (L _T , unit: ° C.), linear expansion coefficient (α, unit: × 10 ⁻⁷ / ° C.) and specific gravity were measured. These measurement methods are described below.

Optical constant (refractive index, Abbe number): A sample processed into a rectangular parallelepiped shape having a side of 20 mm and a thickness of 10 mm was used and measured with a refractometer (trade name: KPR-2000, manufactured by Kalnew Optical Industry Co., Ltd.). Refractive index values are rounded to the fifth decimal place by rounding to the sixth decimal place.
The Abbe number (ν _d ) was calculated by ν _d = (n _d −1) / (n _F −n _C ), rounded to the first decimal place by rounding off the second decimal place. n _F and n _C are refractive indexes for hydrogen F line and C line, respectively. These refractive indexes were similarly measured using the refractometer.

Thermal characteristics (glass transition temperature, yield point): A sample processed into a cylindrical shape having a diameter of 5 mm and a length of 20 mm was subjected to thermal expansion using a thermomechanical analyzer (trade name: TMA4000SA, manufactured by Bruker AXS). The measurement was performed at a heating rate of 5 ° C./min.

Liquid phase temperature: About 5 g of a glass sample was put in a platinum dish, and each of the glass samples held at 600 ° C. to 800 ° C. in increments of 10 ° C. for 1 hour was cooled by natural cooling, and then the presence or absence of crystal precipitation was observed with a microscope. The lowest temperature at which no crystal was observed was defined as the liquidus temperature.

Linear expansion coefficient: A sample processed into a cylindrical shape having a diameter of 5 mm and a length of 20 mm, using a thermomechanical analyzer (trade name: TMA4000SA, manufactured by Bruker AXS), using quartz as a standard data, 5 ° C / The average value of 50 to 200 ° C. was calculated from the thermal expansion curve obtained at a rate of temperature increase of minutes.

Specific gravity: The ratio between the mass of the sample and the mass of 4 ° C. pure water of the same volume under a pressure of 101.325 kPa (standard atmospheric pressure) is displayed as SG, and JIS standard Z8807 (1976, weighed in liquid) Measurement method).

As a result of visual observation at the time of sample preparation, it was confirmed that all the glasses of the examples had no problem in solubility, and the obtained glass sample had no bubbles or striae.

(Preparation of preform for press molding)
The glass material of Example 52 was heated and melted and clarified at 900 ° C. in a glass melting furnace, homogenized at 800 ° C., and introduced into the outflow pipe. The molten glass introduced into the outflow pipe was caused to flow out from the nozzle and supplied onto the mold to produce a press molding preform. In the mold, the molten glass was shaped into an ellipse or a sphere while being floated with nitrogen gas. The produced preform was observed with a polarizing microscope (trade name: BX50, manufactured by OLYMPUS), and it was confirmed that there was no devitrification. The volume was 1.5 cm ³ .

An optical glass suitable as an optical element used in an optical system such as a digital camera can be provided.

Claims

In cation% display,
P 5+ 10-45 %,
Al 3+ 1-40 %,
Mg 2+ 0-20 %,
Ca 2+ 0-25 %,
Sr 2+ 0-25 %,
Ba 2+ 0-35 %,
Li + 24-60%,
Na + 0-10%,
K + 0-10%,
Y 3+ 0-10%,
B 3+ 0-15 %,
Containing
F - the F - and anion ratio to the total amount of the O 2- (F - / (F - + O 2-)) fluorophosphate glass characterized by containing at 0.25 to 0.85.
2. The fluorophosphate glass according to claim 1, wherein a cation ratio (Li + / (Mg 2+ + Ca 2+ + Sr 2+ + Ba 2+ )) of the content of Li + to the total amount of the alkaline earth metal component is more than 0.8 and less than 16. .
The fluorophosphate glass according to claim 1, comprising Li + in an amount of more than 30 to 60 cations.
4. The fluorophosphate glass according to claim 3, wherein a cation ratio (Li + / (Mg 2+ + Ca 2+ + Sr 2+ + Ba 2+ )) of the content of Li + to the total amount of the alkaline earth metal component is 1 or more and less than 16. 5.
The fluorophosphate glass according to claim 1, comprising Li + in an amount of 24 to 30 cations.
6. The fluorophosphate glass according to claim 5, wherein the cation ratio (Li + / (Mg 2+ + Ca 2+ + Sr 2+ + Ba 2+ )) of the content of Li + to the total amount of the alkaline earth metal component is more than 0.8 and less than 1. .
The fluorophosphate glass according to any one of claims 1 to 6, which has a refractive index (n d ) of 1.4 to 1.58 and an Abbe number (ν d ) of 60 to 90.
The fluorophosphate glass according to any one of claims 1 to 7, wherein the total amount of the alkaline earth metal component (Mg 2+ + Ca 2+ + Sr 2+ + Ba 2+ ) is 1 to 31 cation%.
Alkaline earth metal component
Mg 2+ 0-20 %
Ca 2+ 0-25 %,
Sr 2+ 0-25 %,
Ba 2+ 1-31 %,
The fluorophosphate glass according to any one of claims 1 to 8, wherein
Alkaline earth metal component
Mg 2+ 0-20 %
Ca 2+ more than 0-22 %,
Sr 2+ 0-25 %,
Ba 2+ 3-30 %,
The fluorophosphate glass according to any one of claims 1 to 9, wherein
Alkaline earth metal component
Mg 2+> 0 to 10%
Ca 2+ over 0-10%,
Sr 2+> 0 to 10%,
Ba 2+ 3 to 29%,
The fluorophosphate glass according to any one of claims 1 to 10, wherein
The fluorophosphate glass according to any one of claims 1 to 11, which has a glass transition temperature (T g ) of 380 ° C or lower.
The fluorophosphate glass according to any one of claims 1 to 12, which has a yield point (At) of 420 ° C or lower.
The fluorophosphate glass according to any one of claims 1 to 13, wherein a preform for press molding having a volume of 1 cm 3 or more free from devitrification is obtained.
A press-molding preform comprising the fluorophosphate glass according to any one of claims 1 to 14.
An optical element formed by press-molding the preform according to claim 15.
The optical element according to claim 16, which is a lens having a diameter of 8 mm or more.