JP2010189269A - Optical glass, preform for precise press forming and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide optical glass which is optically homogeneous, has high quality and, when manufacturing preform for precise press forming, does not generate striae. <P>SOLUTION: The optical glass is fluorine-containing glass, characterized in that, when the refractive index value of the glass is represented by nd<SP>(1)</SP>and the refractive index value of the glass obtained by remelting the glass at 900°C for 1 h in a nitrogen atmosphere, cooling the glass to the glass transition temperature and, thereafter, cooling the glass to 25°C at a cooling rate of 30°C/h is represented by nd<SP>(2)</SP>, nd<SP>(1)</SP>and nd<SP>(2)</SP>are substantially the same. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical glass, a precision press-molding preform made of the optical glass and a manufacturing method thereof, and an optical element made of the optical glass and a manufacturing method thereof.

  A precision press molding method is known as a method for producing a glass optical element by press molding glass without grinding or polishing. In this method, by accurately transferring the shape of the inner surface of the press mold to the glass material to be molded, optical elements that are difficult to produce by grinding and polishing, such as aspherical lenses, microlenses, and diffraction gratings, are produced with high productivity. This is a method that enables mass production.

  The glass material to be molded used in the precision press molding method is called a preform, and is a glass molded body made of glass having a weight exactly equal to the weight of the press-molded product. When the process from the melting of the glass to the molding of the optical element is viewed as a series of processes, if the preform can be molded directly from the molten glass, the productivity of the entire process can be further improved.

  By the way, fluorine-containing glass such as fluorophosphate glass is an optical glass that is very useful as a low-dispersion glass. As such a fluorophosphate optical glass, a glass as described in Patent Document 1 is known. .

Japanese National Patent Publication No. 3-500162

  When producing a precision press-molding preform (sometimes referred to as a glass molding) by heating and melting a glass raw material and molding the resulting molten glass, the above-mentioned fluorine-containing materials such as a conventional fluorophosphate glass are used. When glass is used, fluorine in the glass is volatilized from the surface of the high-temperature glass, and an optically nonuniform portion called striae is generated in the near-surface layer of the resulting preform.

Therefore, there is a problem that unless the surface layer of the preform is removed by any method, it cannot be used as a material for manufacturing an optical element.
In addition to the case where the preform is molded, when a glass sheet or a rod-shaped glass is molded from molten glass, there is a problem that a highly volatile substance is volatilized from the high-temperature glass surface to cause striae.
Thus, when a glass raw material was heated and melted to produce a fluorine-containing glass, there was a problem that the optical homogeneity of the glass was impaired.

  The present invention has been made to solve the above-mentioned problems, and provides an optically homogeneous and high-quality fluorine-containing optical glass, a precision press-molding preform made of the optical glass, and a method for producing the same, and It aims at providing the optical element which consists of the said optical glass, and its manufacturing method.

The present invention that achieves the above object provides the following (1) to (17).
(1) Fluorine-containing glass, the refractive index value of which is nd ⁽¹⁾ , the glass is remelted in a nitrogen atmosphere at 900 ° C. for 1 hour, cooled to the glass transition temperature, and thereafter 30 hours per hour the value of the refractive index after cooling to 25 ° C. at a cooling rate of ° C. when a nd ^(2), optical glass nd ⁽¹⁾ and nd ⁽²⁾ and is characterized in that substantially equal,
(2) The optical glass according to (1) above, wherein the absolute value of nd ⁽²⁾ -nd ⁽¹⁾ is 0.00300 or less.
(3) The optical glass according to (1) or (2), wherein the fluorine-containing glass is a fluorophosphate glass,
(4) The fluorophosphate glass is expressed in terms of cation%,
P ⁵⁺ 5-50%,
Al ³⁺ 0.1-40%,
Mg ²⁺ 0-20%,
Ca ²⁺ 0-25%,
Sr2 ⁺ 0-30%,
Ba ²⁺ 0~30%,
Li ⁺ 0-30%,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-10%,
La ³⁺ 0-5%
Gd ³⁺ 0-5%
The optical glass according to (3) above,
(5) F ^- and ^{O 2-F} to the total amount of ^- the molar ratio ^F of the content of - ^/ (F - ^{+ O 2-)} is from 0.25 to 0.95, (3) or (4) Optical glass as described in
(6) The optical glass according to any one of (3) to (5) above, containing 2 to 30 cations of Li ⁺ .
(7) The optical index according to any one of (1) to (6) above, wherein the refractive index value nd ⁽¹⁾ of the glass is 1.40000 to 1.60000, and the Abbe number (νd) is 67 or more. Glass,
(8) The optical glass according to (3), wherein the fluorophosphate glass contains Cu ²⁺ ,
(9) In cation% display,
P ⁵⁺ 11-45%,
Al ³⁺ 0-29%,
Li ⁺ , Na ⁺ and K ⁺ in total 0 to 43%,
Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ and Zn ²⁺ in total 14 to 50%,
Cu ²⁺ 0.5-13%,
In addition, in anionic% display,
F ^- 17-80%
The optical glass according to (8) above,
(10) The optical glass according to (1) or (2) above, wherein the fluorine-containing glass is a fluoroborate glass or a fluorosilicate glass,
(11) A precision press-molding preform comprising the optical glass according to any one of (1) to (10) above,
(12) The precision press-molding preform according to (11) above, wherein the entire surface is formed by solidification of a molten glass surface,
(13) The molten glass made of the optical glass according to any one of the above (1) to (10) is allowed to flow out, the molten glass lump is separated, and the preform is formed in the process of cooling the glass. A method for producing a precision press-molding preform,
(14) An optical element comprising the optical glass according to any one of (1) to (10) above,
(15) The precision press-molding preform described in (11) or (12) above or the precision press-molding preform obtained by the method described in (13) above is heated, and precision press molding is performed using a press mold. A method of manufacturing an optical element,
(16) A method for producing an optical element as described in (15) above, wherein a precision press molding preform is introduced into a press mold and heated together to perform precision press molding, and (17) the heated press mold The method for producing an optical element according to (15) above, wherein a separately heated precision press molding preform is introduced and precision press molding is performed.
Is to provide.

According to the present invention, a fluorine-containing optical material suitable for producing a high-quality precision press-molding preform from molten glass and further suitable for producing an optical element by precision press-molding the obtained preform. Glass can be provided.
Moreover, it is possible to provide a precision press-molding preform made of the optical glass and a method for producing the same, and an optical element made of the optical glass and a method for producing the optical element.
Further, since the amount of volatile substances is reduced, it is possible to provide an optical glass with little fluctuation in optical properties such as refractive index during melting and molding.

It is the schematic of the precision press molding apparatus used in the Example of this invention.

  When a glass raw material is melted to obtain a preform made of a fluorine-containing glass such as fluorophosphate glass, intense volatilization occurs from the surface of the molten glass, and the volatilization causes striae in the vicinity of the preform surface. Volatilization is suppressed and the striae can be expected to be eliminated by reducing easily volatile substances from the glass used for preform molding by some means. However, reducing the substances that are likely to volatilize may change the glass composition desired.

  As a result of considering how to reduce the concentration of volatile substances in the glass and eliminate the striae while realizing the desired glass composition, the present inventors obtained some knowledge. It was. The knowledge of the present inventors is as follows.

(1) It is considered that a volatile substance and a non-volatile substance exist in the molten glass obtained by heating and melting a glass raw material.

(2) Volatile substances in glass are produced when glass raw materials are heated and melted, and then are not produced, or even if they are produced, compared to the amount produced when the raw materials are heated and melted. It is considered that only a negligible amount is generated.

(3) In order to reduce the concentration of the volatile substance, the volatile substance may be volatilized from the molten glass accumulated in the container. The glass should not flow out until the concentration of volatiles is sufficiently reduced.

(4) Molding a molten glass with a reduced concentration of volatile substances to produce a preform, cooling it to room temperature, heating and re-melting, the vitrification from the raw material is already achieved by the first melting. Since it has been completed, the concentration of volatile substances is not expected to increase. In fact, even if the glass with a reduced concentration of volatile substances is remelted, there is not much volatilization.

(5) It is not easy to determine whether the concentration of volatile substances has decreased to a level necessary for striae reduction. Theoretically, volatile substances are identified and the concentration of volatile substances is measured, and the amount of volatile substances that volatilize from the glass per unit volume when re-melted is measured and evaluated by the amount of the quantity. It is possible to do this, but it is not realistic. Fortunately, the glass of the present invention is an optical glass, and its refractive index is determined with high accuracy.
The refractive index of glass reflects the composition, and the refractive index changes with the change of the composition. The change in the concentration of the volatile substance is very slight in terms of composition, but in an optical glass in which the refractive index is determined with high accuracy, such a slight change can be monitored as a change in refractive index. For example, if the refractive index of the glass is accurately measured before and after remelting and the refractive index difference between before and after remelting is large, a large amount of volatile substances remain in the glass before remelting. Conversely, if the refractive index difference is small, there will be less volatile material in the glass before remelting.

(6) Relating the difference in refractive index before and after remelting and the possibility of canceling the pulse understanding, making the refractive index substantially the same before and after remelting, more specifically, refraction before and after remelting. By making the absolute value of the difference of the ratios equal to or less than a predetermined value, it is possible to provide an optical glass that enables understanding of the pulse.

  Based on the above inference, the inventors measured the refractive index difference before and after remelting, and eliminated the striae during molding by suppressing the absolute value of this refractive index difference to a predetermined value or less.

Hereinafter, the present invention will be specifically described.
[Optical glass]
The optical glass of the present invention is a fluorine-containing glass having a refractive index value of nd ⁽¹⁾ , the glass is remelted at 900 ° C. for 1 hour in a nitrogen atmosphere, and cooled to a glass transition temperature. Thereafter, when the value of the refractive index after cooling to 25 ° C. at a cooling rate per hour 30 ° C. was ^{nd (2), nd (1} ) shall nd ⁽²⁾ and is characterized in that substantially equal It is.

Here, nd ⁽¹⁾ and nd ⁽²⁾ are substantially equal means that in the optical glass, nd ⁽¹⁾ and nd ⁽²⁾ are approximated so as not to cause striae. .

In the optical glass of the present invention, the absolute value of nd ⁽²⁾ -nd ⁽¹⁾ is preferably 0.00300 or less. When the absolute value of nd ⁽²⁾ -nd ⁽¹⁾ exceeds 0.00300, striae occur on the surface of the preform when the molten glass is formed into a preform. When the absolute value is 0.00300 or less, a glass material capable of preventing striae can be provided. A preferable range of the absolute value is 0.00200 or less, a more preferable range is 0.00150 or less, and a further preferable range is 0.00100 or less. In the fluorine-containing glass, since fluorine is a component that relatively lowers the refractive index of the glass, the value of nd ⁽²⁾ -nd ⁽¹⁾ is generally positive.

The atmosphere at the time of remelting performed to measure nd ⁽²⁾ is nitrogen in order to prevent the refractive index of the glass from being influenced by factors other than volatilization due to the reaction between the glass and the atmosphere. The remelting is performed under a predetermined condition at 900 ° C. for 1 hour, and then cooled to the glass transition temperature. Since the value of nd ⁽²⁾ is also influenced by the cooling rate during cooling, the cooling is performed at a predetermined cooling rate of 30 ° C. per hour and cooled to 25 ° C.

  A known method can be used for measuring the refractive index, and it is desirable to measure with an accuracy of 6 significant digits (5 digits after the decimal point). As an example of measuring the refractive index, Japanese Optical Glass Industry Association Standard JOGIOS01-1994 “Measurement Method of Refractive Index of Optical Glass” can be applied.

  Depending on the shape and volume of the glass, for example, if the glass is small spherical or molded into a thin lens, the glass cannot be processed into a sample with the shape and dimensions specified in the above standards There is also. In that case, the glass is heated, softened, press-molded, and annealed to form a prism shape in which two planes intersect at a predetermined angle. Then, based on the same measurement principle as the above standard, the refractive index is measured. The heating temperature at the time of molding into a prism shape by press molding is a temperature range that is sufficient if the glass can be softened at most, and is extremely lower than the temperature at which the glass melts, so the influence on the concentration of volatile substances is negligible. The refractive index change amount before and after the heating can be ignored.

  In order to reduce or eliminate the striae of glass, it is more effective to lower the molding temperature in addition to lowering the concentration of volatile substances.

Next, the preferable aspect in the optical glass of this invention is demonstrated.
The optical glass of the present invention is made of fluorine-containing glass, and specific examples thereof include fluorophosphate glass, fluoroborate glass, and fluorosilicate glass. Hereinafter, the optical glass made of fluorophosphate glass is called optical glass I, and the optical glass made of fluoroborate glass or fluorosilicate glass is called optical glass II.

A preferred first embodiment of the optical glass I made of fluorophosphate glass (hereinafter referred to as optical glass IA) is:
In cation% display,
P ⁵⁺ 5-50%,
Al ³⁺ 0.1-40%,
Mg ²⁺ 0-20%,
Ca ²⁺ 0-25%,
Sr2 ⁺ 0-30%,
Ba ²⁺ 0~30%,
Li ⁺ 0-30%,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-10%,
La ³⁺ 0-5%
Gd ³⁺ 0-5%
Is an optical glass containing

In the optical glass I-A, the anion component F ^- and ^{O 2-} allocations, F ^- and ^{O 2-} F to the total amount of ^- the molar ratio of the content of ^{F - / (F - + O} 2-) is 0. A range of 25 to 0.95 is preferred. By setting the amount of the anion component as described above, low dispersion characteristics can be imparted to the glass.

According to the optical glass IA, optical characteristics having a refractive index value nd ⁽¹⁾ of 1.40000 to 1.60000 and an Abbe number (νd) of 67 or more can be realized. The upper limit of the Abbe number (νd) is not particularly limited, but it is preferable to set the Abbe number (νd) to 100 or less from the viewpoint of stably producing the glass.

In the optical glass I-A, 2 divalent cationic components ^{(R 2+)} as ^Ca 2+, those containing two or more of ^{Sr 2+} and ^{Ba 2+} preferred.

The optical glass IA preferably has a total content of 1 cation% or more of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ which are divalent cation components (R ²⁺ ), Mg ²⁺ , Ca ^2+, and more preferably the content of ^{Sr 2+} and ^{Ba 2+} is respectively 1 or more cationic%.

  Hereinafter, the composition of the optical glass IA will be described in detail. The ratio of each cation component is expressed in% cation based on the molar ratio, and the ratio of each anion component is also expressed in% anion based on the molar ratio. It shall be.

P ⁵⁺ is an important cation component as a glass network former. If it is less than 5%, the stability of the glass is lowered, and if it exceeds 50%, P ⁵⁺ needs to be introduced as an oxide raw material, so the oxygen ratio increases. Does not meet the target optical characteristics. Therefore, the amount is 5% to 50%, more preferably 5% to 40%, and particularly preferably 5% to 35%. When introducing P ^5+, the use of PCl ₅ is not appropriate because it erodes platinum and is volatile, which hinders stable production and is preferably introduced as a phosphate.

Al ³⁺ is a component that improves the stability of fluorophosphate glass. If it is less than 0.1%, the stability decreases, and if it exceeds 40%, the glass transition temperature (Tg) and the liquidus temperature (LT) increase greatly. As a result, the molding temperature rises and striae due to surface volatilization during molding occurs strongly, making it impossible to obtain a homogeneous glass molded body, particularly a press molding preform. Therefore, the amount is 0.1% to 40%, more preferably 5% to 40%, and particularly preferably 10% to 35%.

Introduction of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , and Ba ²⁺ , which are divalent cation components (R ²⁺ ), contributes to improvement of the stability of the glass. However, since the stability as glass decreases due to excessive introduction, it is preferable to set Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , and Ba ²⁺ in the following ranges.

First, the preferable content of Mg ²⁺ is 0 to 20%, more preferably 1 to 20%, still more preferably 5 to 15%, and particularly preferably 5 to 10%.

The preferable content of Ca ²⁺ is 0 to 25%, more preferably 1 to 25%, still more preferably 5 to 20%, and particularly preferably 5 to 16%.

The preferred content of Sr ²⁺ is 0-30%, more preferably 1% to 30%, more preferably 5-25%, particularly preferably 10 to 20%.

The preferable content of Ba ²⁺ is 0 to 30%, more preferably 1 to 30%, still more preferably 1 to 25%, still more preferably 5 to 25%, and particularly preferably 8 to 25%.

It is preferable to introduce two or more of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ , rather than introducing each singly, and more than two of Ca ²⁺ , Sr ²⁺ and Ba ²⁺ are introduced. preferable. In order to further enhance the effect of introducing the divalent cation component (R ²⁺ ), the total content of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ is preferably 1 cation% or more. Moreover, when it introduces exceeding each upper limit, stability will fall rapidly. Ca ²⁺ and Sr ²⁺ can be introduced in a relatively large amount, but Mg ²⁺ and Ba ²⁺ particularly lower the stability. However, since Ba ²⁺ is a component capable of realizing a high refractive index while maintaining low dispersion, it is preferably introduced in a large amount within a range not impairing stability.

Li ⁺ is a component that lowers the glass transition temperature (Tg) without impairing the stability. However, if it exceeds 30%, the durability of the glass is impaired and at the same time the workability is lowered. Therefore, the amount is 0-30%. A preferable range is 0 to 25%, and a more preferable range is 0 to 20%.

  However, when it is desired to further reduce the glass transition temperature, such as for precision press molding applications, the amount of Li + is preferably 2 to 30%, more preferably 5 to 25%, and more preferably 5 to 20%. More preferably.

Na ⁺ and K ⁺ have the effect of lowering the glass transition temperature (Tg), respectively, like Li ⁺ , but at the same time, the thermal expansion coefficient tends to be larger than that of Li ⁺ . Moreover, since NaF and KF have a very high solubility in water as compared with LiF, the water resistance is also deteriorated. Therefore, the amounts of Na ⁺ and K ⁺ are 0 to 10%, respectively. A preferable range for both Na ⁺ and K ⁺ is 0 to 5%, and it is more preferable not to introduce them.

Y ^{3+, La} 3+, ^{Gd 3+} stability of the glass, improves the durability, but an effect of increasing the refractive ^{index, Y 3+} is more than ^10%, La 3+, stability in ^{Gd 3+} 5 percent is On the contrary, the glass transition temperature (Tg) is greatly increased, so the amount is 0 to 10% in the case of Y ³⁺ and 0 to 5% in the case of La ³⁺ and Gd ³⁺ . Preferred ranges are 0 to 3% for Y ³⁺ , 0 to 3% for La ³⁺ and Gd ³⁺ .

Incidentally, from the top to stably produce a high quality optical ^{glass, P 5+, Al 3+, Mg} 2+, Ca 2+, Sr 2+, Ba 2+, Li + and ^{Y 3+,} La 3+, cation the total amount of ^{Gd 3+} % Is preferably over 95%, more preferably over 98%, further preferably over 99%, and even more preferably 100%.

  The optical glass IA can contain a cation component such as Ti, Zr, Zn, or a lanthanoid, or a cation component such as B, in addition to the above-described cation component, as long as the object of the present invention is not impaired.

Ratio of anionic components, while realizing the desired optical properties, in order to obtain an optical glass having excellent stability, F ^- and O ^2-F to the total amount of ^- the molar ratio of the content of F ^- / ( F ⁻ + O ²⁻ ) is set to 0.25 to 0.95.

  The optical glass IA is an excellent glass even when viewed as glass for producing an optical element by grinding or polishing, or as glass for producing an optical element by precision press molding.

As an aspect of the optical glass IA, there is a glass containing 2 to 30 cation% Li ⁺ (hereinafter referred to as an optical glass IAa). According to the optical glass IAa, The viscosity at the phase temperature can be lowered and the molding temperature can be lowered. By introducing ²⁺ cation% or more of Li ⁺ , the glass molding temperature and glass transition temperature can be further lowered, and volatilization from the surface of the preform can be further reduced. On the other hand, when the amount of Li ⁺ exceeds 30 cation%, durability and workability are lowered. By introducing Li ⁺ , the precision press molding temperature can be lowered, so the time required to heat the preform and the time required to cool down after press molding can be shortened. Will improve. Further, the reaction between the glass and the press mold can be suppressed by lowering the press molding temperature, the surface condition of the press molded product can be improved, and the life of the press mold can be extended.

  The optical glass I of the present invention made of fluorophosphate glass exhibits a high transmittance in the visible light region, except for the case where a colorant is added, on a sample having a thickness of 10 mm that is flat on both sides and parallel to each other. On the other hand, the transmittance at a wavelength of 400 nm to 2000 nm when light is incident from the vertical direction (excluding reflection loss on the sample surface) is 80% or more, preferably 95% or more.

Since the optical glass IA-a contains a predetermined amount of Li ⁺ , its glass transition temperature (Tg) is 470 ° C. or lower, preferably 430 ° C. or lower.

Further, the optical glass IA-a positively contains Li ⁺ among the alkali metal ions, and therefore has a relatively small coefficient of thermal expansion and relatively excellent water resistance. Accordingly, the glass surface can be polished and processed into a press-molding preform, or the optical element can be processed into a smooth and high-quality glass surface.

  Since the optical glass IA (including the optical glass IA-a) exhibits excellent water resistance and chemical durability, from the preparation of the precision press molding preform to the press molding, Even if stored for a long time, the surface of the preform does not change. In addition, since the surface of the optical element is hardly changed, the optical element can be used in a good state where the surface is not clouded for a long time.

  Also, according to the optical glass IA-a, the glass melting temperature can be lowered by about 50 ° C. compared to the glass having the same optical constant as that of the glass of the above aspect and not containing Li. Problems such as coloring of glass, mixing of bubbles, and striae due to platinum melting from the container at the time can be reduced and eliminated.

  Generally, fluorophosphate glass has a high viscosity at the time of outflow, and when a molten glass lump of a desired weight is separated from the outflowing molten glass and molded to produce a preform, the glass draws a thin thread at the separated portion. There arises a problem such that the thread-like portion remains on the surface of the formed glass lump and forms a protrusion. When trying to solve such problems by lowering the efflux viscosity, the effluent temperature of the glass must be raised, and as mentioned above, the volatilization of fluorine from the glass surface is promoted and the striae becomes significant. .

  In order to eliminate such problems, the optical glass IA-a lowers the temperature suitable for molding molten glass, so that the temperature exhibiting a predetermined viscosity is lower than that of a conventional fluorophosphate glass. The glass composition is determined. Although the glass transition temperature is much lower than the molding temperature of molten glass, glass with a low glass transition temperature can also lower the above molding temperature, thus reducing and eliminating problems such as stringing and striae during molding. The glass composition is adjusted so that the glass transition temperature is in the above range.

  In addition, by lowering the glass transition temperature, it is possible to reduce the heating temperature of the glass in the press molding of the preform, particularly the precision press molding as described above, and the reaction between the glass and the press molding die is relaxed, Effects such as extending the life of the press mold can also be obtained.

Therefore, the optical glass IA-a is suitable as a glass material for press molding, particularly as a glass material for precision press molding, but is also suitable as a glass material for making an optical element by grinding and polishing. . In addition, the preferable aspect of optical glass IAa is the same as optical glass IA except the quantity of Li ^<+> having been said range.

A preferred second embodiment of the optical glass I made of fluorophosphate glass (hereinafter referred to as optical glass IB) is fluorophosphate glass containing Cu ²⁺ , and this glass functions as a near-infrared absorbing glass. The optical glass IB is particularly suitable as a color correction filter for a semiconductor image sensor such as a CCD or a CMOS, and when used for the above-mentioned purposes, the content of Cu ²⁺ is 0.5 to 13 cation%. Is desirable.

A particularly preferred composition of the optical glass IB is expressed in terms of cation%,
P ⁵⁺ 11-45%,
Al ³⁺ 0-29%,
Li ⁺ , Na ⁺ and K ⁺ in total from 0 to 43%,
Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ and Zn ²⁺ in total 14 to 50%,
Cu ²⁺ 0.5-13%,
In addition, in anionic% display,
F ^- 17~80%
Is included.

In the above composition, the remaining amount of the anionic component is preferably O ²⁻ .

In the above composition, P ⁵⁺ is a basic component of fluorophosphate glass and an important component that brings about absorption of Cu ^{2+ in} the infrared region. If the content of P ⁵⁺ is less than 11%, the color deteriorates to be greenish. Conversely, if it exceeds 45%, the weather resistance and devitrification resistance deteriorate. Therefore, the content of P ⁵⁺ is preferably 11 to 45%, more preferably 20 to 45%, and still more preferably 23 to 40%.

Al ³⁺ is a component that improves the devitrification resistance, heat resistance, thermal shock resistance, mechanical strength, and chemical durability of fluorophosphate glass. However, if it exceeds 29%, the near infrared absorption characteristics deteriorate. Therefore, the content of Al ³⁺ is preferably 0 to 29%, more preferably 1 to 29%, still more preferably 1 to 25%, and even more preferably 2 to 23%. .

Li ⁺ , Na ⁺ and K ⁺ are components that improve the meltability and devitrification resistance of the glass and improve the transmittance in the visible light region, but if the total amount exceeds 43%, the durability of the glass, Workability deteriorates. Therefore, the total content of Li ⁺ , Na ⁺ and K ⁺ is preferably 0 to 43%, more preferably 0 to 40%, and still more preferably 0 to 36%.

Among the alkali components, Li ⁺ is excellent in the above action, and the amount of Li ⁺ is preferably 15 to 30%, more preferably 20 to 30%.

Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ^2+, and Zn ²⁺ are useful components that improve the devitrification resistance, durability, and workability of the glass. However, since the devitrification resistance decreases due to excessive introduction, Mg The total amount of ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ and Zn ²⁺ is preferably 14 to 50%, more preferably 20 to 40%.

A preferable range of the Mg ²⁺ content is 0.1 to 10%, and a more preferable range is 1 to 8%.

A preferable range of the Ca ²⁺ content is 0.1 to 20%, and a more preferable range is 3 to 15.

A preferable range of the Sr ²⁺ content is 0.1 to 20%, and a more preferable range is 1 to 15%.

A preferable range of the Ba ²⁺ content is 0.1 to 20%, a more preferable range is 1 to 15%, and a further preferable range is 1 to 10.

Cu ²⁺ is a bearer of near-infrared light absorption characteristics. If the amount is less than 0.5%, the near-infrared absorption is small. Conversely, if it exceeds 13%, the devitrification resistance deteriorates. Therefore, the content of Cu ²⁺ is preferably 0.5 to 13%, more preferably 0.5 to 10%, still more preferably 0.5 to 5%, and even more preferably 1 to 5%.

F ⁻ is an important anion component that lowers the melting point of the glass and improves the weather resistance in the optical glass IB. By containing F ⁻ , the optical glass IB can lower the glass melting temperature, suppress the reduction of Cu ²⁺ , and obtain the required optical characteristics. If it is less than 17%, the weather resistance deteriorates. On the other hand, if it exceeds 80%, the content of O ²⁻ decreases, so that coloring near 400 nm with monovalent Cu ⁺ occurs. Therefore, the content of F ⁻ is preferably 17 to 80%. In order to further improve the above characteristics, the amount of F ⁻ is more preferably 25 to 55%, and further preferably 30 to 50%.

O ²⁻ is an important anion component in the optical glass IB, and it is preferable that the entire remaining amount excluding F ^{− of the} total anion component is composed of the O ²⁻ component. Therefore, the preferable amount of O ²⁻ is a range obtained by subtracting the preferable amount of F− from 100%. If the amount of O ²⁻ is too small, divalent Cu ²⁺ is reduced to monovalent Cu ⁺ , so that the absorption in the short wavelength region, particularly near 400 nm, becomes large, and the color becomes green. On the other hand, if the amount is excessive, the viscosity of the glass is high and the melting temperature is high, so the transmittance is deteriorated.
Note that Pb and As are not harmful because they are highly harmful.

Preferred transmittance characteristics of the optical glass IB are as follows.
The spectral transmittance at a wavelength of 500 to 700 nm is converted into a thickness at which the wavelength showing a transmittance of 50% is 615 nm, and the spectral transmittance at a wavelength of 400 to 1200 nm exhibits the following characteristics.

Wavelength 400nm 78% or more, preferably 80% or more, more preferably 83% or more, still more preferably 85% or more,
Wavelength 500 nm 85% or more, preferably 88% or more, more preferably 89% or more,
Wavelength 600 nm 51% or more, preferably 55% or more, more preferably 56% or more,
Wavelength 700 nm 12% or less, preferably 11% or less, more preferably 10% or less,
Wavelength 800 nm 5% or less, preferably 3% or less, more preferably 2.5% or less, still more preferably 2.2% or less, even more preferably 2% or less,
Wavelength 900 nm 5% or less, preferably 3% or less, more preferably 2.5% or less, still more preferably 2.2% or less, even more preferably 2% or less,
Wavelength 1000 nm 7% or less, preferably 6% or less, more preferably 5.5% or less, still more preferably 5% or less, even more preferably 4.8% or less,
Wavelength 1100 nm 12% or less, preferably 11% or less, more preferably 10.5% or less, still more preferably 10% or less,
The wavelength is 1200 nm 23% or less, preferably 22% or less, more preferably 21% or less, and still more preferably 20% or less.

  That is, absorption of near-infrared light having a wavelength of 700 to 1200 nm is large, and absorption of visible light having a wavelength of 400 to 600 nm is small. Here, the transmittance is assumed to be a glass sample having two planes that are parallel to each other and optically polished, and when light is incident on one of the planes perpendicularly, the intensity of the light emitted from the other of the planes is expressed as follows. It is a value divided by the intensity of the incident light before entering the sample, and is also called external transmittance.

  With such characteristics, color correction of a semiconductor image sensor such as a CCD or CMOS can be performed satisfactorily.

  The optical glass of the present invention includes an optical glass (optical glass II) made of fluoroborate glass or fluorosilicate glass.

Since the optical glass II also contains fluorine and boron or silicon in the glass raw material, easily volatile substances are generated by heating and melting the glass raw material. Therefore, as in the case of the optical glass I made of fluorophosphate glass, the volatile substances at the time of molding are substantially eliminated by forming the molten glass and substantially excluding volatile substances (volatile substances) before producing the preform. The generation of striae due to the volatilization of and the change in refractive index can be reduced or prevented. Also in the optical glass II, the value of the refractive index of the glass is nd ⁽¹⁾ , the glass is remelted at 900 ° C. for 1 hour in a nitrogen atmosphere, cooled to the glass transition temperature, and then the rate of temperature decrease at 30 ° C. per hour. When the refractive index value after cooling to 25 ° C. is nd ⁽²⁾ , nd ⁽¹⁾ and nd ⁽²⁾ are substantially equal. More specifically, nd ⁽²⁾ −nd ^{(1 The} glass having an absolute value of ⁾ of 0.00300 or less can be considered as a standard of glass from which volatile substances are substantially excluded. The measuring method of the refractive index, remelting conditions, and the preferable range of the absolute value are the same as those of the optical glass I.

In both cases of optical glasses I and II, volatile substances are excluded and reduced from the glass. Therefore, when preparing the raw materials, care must be taken to introduce a large amount of substances lost due to volatilization. Such composition correction is performed so that the absolute value of nd ⁽²⁾ -nd ⁽¹⁾ is not more than a predetermined value and nd ⁽¹⁾ becomes a desired value. A typical component reduced by volatilization is fluorine. Since other components vary depending on the target glass composition, the composition may be corrected based on the above guidelines.

The optical glass of the present invention is manufactured by heating and melting a glass raw material, and then flowing out and molding after reducing the concentration of a volatile substance in a container. What is necessary is just to set each melting condition suitably so that the absolute value of nd ⁽²⁾ -nd ⁽¹⁾ of the glass obtained may be 0.00300 or less.

  At the time of molding, the high-temperature glass easily reacts with moisture in the atmosphere, and the quality of the glass is lowered by this reaction. Therefore, it is preferable that the molten glass flows out and is molded in a dry atmosphere. The amount of water in the dry atmosphere is preferably equivalent to a dew point of -30 ° C or lower. The type of gas may be an inert gas such as nitrogen or argon.

  The glass molded body thus formed is subjected to mechanical processing such as cutting, grinding and polishing to form a glass material for press molding and a precision press molding preform described in detail below, and optical elements such as lenses, prisms and filters. Can be.

[Preform for precision press molding and its manufacturing method]
The precision press-molding preform of the present invention comprises the optical glass of the present invention described above. Here, the precision press-molding preform is formed by pre-molding glass having a weight equal to the weight of the press-molded product into a shape suitable for precision press molding.

  Fluorophosphate glass has properties that it has a higher degree of wear and a higher thermal expansion coefficient than other general optical glasses. Such a property is not preferable for polishing. When the degree of wear is large, processing accuracy is lowered, and scratches during polishing are likely to remain on the glass surface. Polishing is performed while the cutting fluid is applied to the glass. However, if the cutting fluid is applied to the glass whose temperature has been increased by polishing, or if glass having scratches due to polishing on the surface is added to the cleaning liquid whose temperature has increased during ultrasonic cleaning, A fluorophosphate glass that is exposed to a large temperature change and has a large coefficient of thermal expansion is likely to break the glass due to thermal shock. Therefore, it is desirable to manufacture by a method that does not depend on polishing, whether it is a preform for precision press molding or an optical element. From this point of view, it is desirable that the precision press-molding preform has a surface formed by solidifying glass whose entire surface is melted, and the optical element is preferably produced by precision press-molding.

  Preventing and reducing damage to the preform when it is cleaned or heated prior to precision press molding by making the entire surface of the preform a surface formed by solidifying glass in the molten state Can do.

Next, the manufacturing method of the press molding preform of this invention is demonstrated.
The first aspect of the method for producing a press-molding preform of the present invention (hereinafter referred to as preform manufacturing method I) is a process in which molten glass is caused to flow out of a pipe, the molten glass lump is separated, and the glass is cooled. It is characterized by being molded into a preform.

  The production of the molten glass may be carried out in the same manner as in the optical glass manufacturing method of the present invention described above, regardless of the preform manufacturing method I or the preform manufacturing method II described later. The molten glass with a reduced concentration of volatile substances flows out continuously from a platinum alloy or platinum pipe heated to a predetermined temperature at a constant flow rate. The molten glass lump having a weight obtained by adding the weight of one preform or the weight of one preform to the weight of the removal portion described later is separated from the molten glass that has flowed out. When separating the molten glass lump, it is desirable to avoid the use of a cutting blade so that no cut marks remain. It is preferable to use a method in which the molten glass lump is separated from the front end of the molten glass flow by using the surface tension of the molten glass by suddenly dropping the support at a timing at which the molten glass lump of the target weight can be separated.

  The separated molten glass lump is formed into a desired shape in the process of cooling the glass on the recess of the preform mold. At that time, in order to prevent wrinkles on the preform surface or breakage in the glass cooling process called can cracking, it is preferable to mold the glass lump in a state of being lifted by applying upward wind pressure to the glass block. In that case, it is preferable from the viewpoint of reducing and preventing striae to spray the gas on the surface of the glass lump to promote the cooling of the surface.

  After the temperature of the glass is lowered to a temperature range that does not deform even when an external force is applied to the preform, the preform is taken out from the preform mold and gradually cooled.

  In order to further reduce volatilization from the glass surface, glass outflow and preform molding should be performed in a dry atmosphere (dry nitrogen atmosphere, dry air atmosphere, dry mixed gas atmosphere of nitrogen and oxygen, etc.) as described above. Is preferred.

  A second aspect of the method for producing a press-molding preform of the present invention (preform production method II) is a method of forming a glass molded body by molding a molten glass, and machining the glass molded body. It is the manufacturing method of the preform for press molding which produces the preform which consists of optical glass of invention.

  Here, the production of the molten glass is as described above. In the preform production method II, first, molten glass is continuously discharged from a pipe and poured into a mold disposed below the pipe. As the mold, a flat bottom and a side wall that surrounds the bottom from three sides and one side of which is open are used. The side walls that sandwich the opening side and bottom from both sides face each other in parallel, and the mold is placed, fixed, and poured into the mold so that the center of the bottom is positioned vertically below the pipe and the bottom is horizontal. The molten glass is spread so as to have a uniform thickness in the region surrounded by the side walls, and after cooling, the glass is drawn out horizontally from the opening on the side surface of the mold at a constant speed. The drawn glass molded body is sent into an annealing furnace and annealed. In this way, a plate-like glass molded body made of the optical glass of the present invention having a certain width and thickness is obtained. In this way, a glass molded body with reduced and suppressed surface striae is obtained.

  Next, the plate-like glass molded body is cut or cleaved and divided into a plurality of glass pieces called cut pieces, and these glass pieces are ground and polished to finish a preform for press molding with a target weight.

  As another method, a mold having a cylindrical through-hole is disposed and fixed vertically below the pipe so that the central axis of the through-hole faces the vertical direction. At this time, it is preferable to arrange | position a casting_mold | template so that the central axis of a through-hole may be located in the vertically downward direction of a pipe. Then, molten glass is poured from the pipe into the mold through-hole at a constant flow rate to fill the through-hole with glass, and the solidified glass is drawn vertically downward from the lower end opening of the through-hole at a constant speed and gradually cooled. A cylindrical rod-shaped glass molded body is obtained. After annealing the glass molded body thus obtained, a plurality of glass pieces are obtained by cutting or cleaving from a direction perpendicular to the central axis of the cylindrical bar. Next, the glass piece is ground and polished to finish a preform for press molding with a desired weight. Also in these methods, it is preferable to perform the outflow and shaping of the molten glass in a dry atmosphere as described above. Furthermore, also in these methods, it is effective to reduce and prevent striae by accelerating cooling by blowing a gas onto the glass surface during molding.

  Since both preform production methods I and II can produce a high-quality and highly accurate preform, this method is suitable as a method for producing a preform for precision press molding.

  Preform production method II adds 100% of the glass molded body to the glass molded body for machining. However, if the striation on the surface of the glass molded body can be reduced or suppressed, the glass molded body can be used. The effective use volume of can be increased. Since fluorophosphate glass has a high raw material cost among optical glasses, production costs of preforms and optical elements can be reduced by effectively using the glass.

  The preform may be produced using any one of the optical glasses I and II of the present invention depending on the purpose.

[Optical element and manufacturing method thereof]
The optical element of the present invention is characterized by comprising the optical glass of the present invention. Since the optical element of the present invention is composed of the above-described optical glass of the present invention, according to the present invention, an optical element utilizing low dispersion characteristics can be provided. Further, since the optical element of the present invention is made of glass having excellent water resistance and chemical durability, according to the present invention, it is possible to provide an optical element that does not cause problems such as clouding of the surface even after long-term use. it can.

  The type and shape of the optical element are not particularly limited, but are suitable for aspherical lenses, spherical lenses, microlenses, lens arrays, prisms, diffraction gratings, prisms with lenses, lenses with diffraction gratings, and the like.

From the viewpoint of application, it is suitable for an optical element constituting an imaging system, for example, a digital camera lens, a camera lens for a camera-equipped mobile phone, an optical pickup lens, a collimator lens, and the like.
If necessary, an optical thin film such as an antireflection film may be formed on the surface of the optical element.

Next, the manufacturing method of the optical element of this invention is demonstrated.
The optical element manufacturing method of the present invention comprises heating a precision press molding preform of the present invention or a precision press molding preform produced by the preform manufacturing method of the present invention, and performing precision press molding with a press mold. It is characterized by.

  The precision press molding is also called mold optics molding, and is a well-known method in the technical field. In an optical element, a surface that transmits, refracts, diffracts, or reflects light is an optical functional surface (a lens surface such as an aspherical surface of an aspherical lens or a spherical surface of a spherical lens is taken as an example of a lens). It corresponds to the optical function surface), but according to precision press molding, the optical function surface can be formed by press molding by precisely transferring the molding surface of the press mold to glass, and the optical function surface is finished. Therefore, it is not necessary to add machining such as grinding and polishing.

  Therefore, the optical element manufacturing method of the present invention is suitable for manufacturing optical elements such as lenses, lens arrays, diffraction gratings, and prisms, and is particularly suitable as a method for manufacturing aspherical lenses with high productivity. Yes.

  According to the method for producing an optical element of the present invention, both optical elements having the above optical characteristics can be produced, and since the glass transition temperature (Tg) is low, the press molding temperature can be lowered. Damage to the molding surface of the mold is reduced, and the life of the mold can be extended. Further, since the glass constituting the preform has high stability, devitrification of the glass can be effectively prevented even in the reheating and pressing steps. Furthermore, a series of steps for obtaining a final product from glass melting can be performed with high productivity.

  As a press mold used for precision press molding, known molds such as silicon carbide, zirconia, alumina and other heat-resistant ceramic molds provided with a release film can be used. A silicon press mold is preferable, and a carbon-containing film or the like can be used as the release film. In view of durability and cost, a carbon film is particularly preferable.

  In precision press molding, it is desirable that the molding atmosphere be a non-oxidizing gas in order to keep the molding surface of the press mold in a good state. The non-oxidizing gas is preferably nitrogen or a mixed gas of nitrogen and hydrogen.

  Next, as the modes of precision press molding used in the method for producing an optical element of the present invention, the following two modes of precision press molding 1 and 2 can be shown.

(Precision press molding 1)
The precision press molding 1 is one in which a preform is introduced into a press mold, heated together, and precision press molded.
In this precision press molding 1, precision press molding is performed by heating the temperature of the press mold and the preform to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁶ to 10 ¹² dPa · s. It is preferable.
The glass is preferably cooled to a temperature showing a viscosity of 10 ¹² dPa · s or more, more preferably 10 ¹⁴ dPa · s or more, and even more preferably 10 ¹⁶ dPa · s or more. It is desirable to remove from the mold.
Under the above conditions, the shape of the molding surface of the press mold can be accurately transferred with glass, and the precision press molded product can be taken out without being deformed.

(Precision press molding 2)
The precision press molding method 2 is a method in which a separately heated preform is introduced into a preheated press mold and precision press molding is performed.
According to this precision press molding 2, since the preform is preheated before being introduced into the press mold, it is possible to manufacture an optical element having a good surface accuracy without surface defects while shortening the cycle time. it can.

  The preheating temperature of the press mold is preferably set lower than the preheating temperature of the preform. Thus, by lowering the preheating temperature of the press mold, it is possible to reduce the wear of the press mold.

In the precision press molding 2, it is preferable that the glass constituting the preform is preheated to a temperature exhibiting a viscosity of 10 ⁹ dPa · s or less, more preferably 10 ⁹ dPa · s.

The preform is preferably preheated while floating, more preferably preheated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ^5.5 to 10 ⁹ dPa · s ^. It is more preferable to preheat to a temperature showing a viscosity of ⁵ dPa · s or more and less than 10 ⁹ dPa · s.
Moreover, it is preferable to start cooling the glass simultaneously with the start of pressing or in the middle of pressing.
The temperature of the press mold is adjusted to a temperature lower than the preheating temperature of the preform, and the temperature at which the glass exhibits a viscosity of 10 ⁹ to 10 ¹² dPa · s may be used as a guide.

In this method, it is preferable that after the press molding, the glass is cooled to a viscosity of 10 ¹² dPa · s or more and then released.
The precision press-molded optical element is taken out from the press mold and gradually cooled as necessary. When the molded product is an optical element such as a lens, an optical thin film may be coated on the surface as necessary.

  The above is the method for manufacturing the optical element of the present invention. In addition to the method described above, for example, the glass molded body is formed by flowing out the molten glass, annealed, and then machined to manufacture the optical element of the present invention. You can also For example, the cylindrical rod-shaped glass molded body described above can be sliced from a direction perpendicular to the cylinder axis, and the obtained cylindrical glass can be ground and polished to produce optical elements such as various lenses.

  In addition, what is necessary is just to use the glass of either optical glass I and II for the said optical element according to the objective.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
Example 1 ( Example of optical glass production)
As raw materials for glass, phosphates and fluorides corresponding to the respective glass components were used. The raw materials were weighed so as to be a glass having a composition of 1 to 11, and sufficiently mixed.

  The above prepared raw material was melted at 850 ° C. for 1 hour using a platinum crucible, then rapidly cooled and pulverized, and used as a rough melt cullet. 10 kg of this rough melt cullet was put into a platinum crucible sealed with a lid, heated to 900 ° C. and melted. Next, a sufficient amount of drying gas was introduced into the platinum crucible and the molten glass was clarified at 1100 ° C. for 2 hours while maintaining a dry atmosphere. Examples of the dry gas include an inert gas such as nitrogen, a mixed gas of an inert gas and oxygen, oxygen, and the like.

  After clarification, the temperature of the glass was lowered to 850 ° C., which is lower than the temperature at the time of clarification, and then the glass was caused to flow out from a pipe connected to the bottom of the crucible. The gas introduced into the crucible was cleaned through a filter and discharged to the outside. In each of the above steps, the glass in the crucible was stirred to obtain a homogeneous glass.

  The obtained molten glass was cast into a carbon mold in a dry nitrogen atmosphere. The cast glass was allowed to cool to the transition temperature and immediately placed in an annealing furnace, annealed for 1 hour near the transition temperature, and gradually cooled to room temperature in the annealing furnace. Each optical glass of 1-11 was obtained.

  Each optical glass No. When 1 to 11 were magnified and observed with a microscope, no crystal precipitation or unmelted raw material was observed.

The obtained optical glass No. For 1 to 11, the refractive index (nd), Abbe number (νd), and glass transition temperature (Tg) were measured as follows. The measurement results are shown in Tables 1-2.
(1) Refractive index (nd) and Abbe number (νd)
Refractive index (nd) and Abbe number (νd) were measured for optical glass obtained at a slow cooling rate of -30 ° C / hour.

In addition, regarding refractive index nd, optical glass No. measured on the said conditions. The refractive index values of 1 to 11 are nd ^(1), and optical glass No. Re melting of 1 to 11, refractive index after cooling ^{nd (2)} was measured as follows.

The optical glass No. 30 g of each of 1 to 11 was put into a glassy carbon crucible in a quartz glass chamber with a capacity of 2 liters into which dry nitrogen gas was introduced at a rate of 2 liters / min. Remelted for hours. Then, it cooled to glass transition temperature vicinity in a chamber, and cooled to room temperature 25 degreeC with the temperature-fall rate of 30 degreeC / hour after that. And the optical glass No. obtained in this way. Each refractive index nd ⁽²⁾ of 1 to 11 was measured.

Optical glass No. About 1 to 11 of the glass indicate the absolute value of ^{nd (2) -nd (1)} and ^{nd (2) -nd (1)} in Table 1 and Table 2.
(2) Glass transition temperature (Tg)
The glass transition temperature (Tg) was measured using a thermomechanical analyzer manufactured by Rigaku Corporation with a heating rate of 4 ° C./min.

As shown in Tables 1 and 2, the optical glass No. 1 of the present invention. Each of 1 to 11 had a desired refractive index, Abbe number and glass transition temperature, exhibited excellent low-temperature softening properties and meltability, and was suitable as an optical glass for press molding.
In addition, the absolute values of nd ⁽²⁾ -nd ⁽¹⁾ and nd ⁽²⁾ -nd ⁽¹⁾ were both smaller than 0.00300.

Example 2 (Production Example of Optical Glass)
As raw materials for glass, phosphates, fluorides, oxides and the like corresponding to the respective glass components were used. The raw materials are weighed so as to be a glass having the composition of 12 and 13, mixed well, then put into a platinum crucible sealed with a lid, and stirred in an electric furnace at 790 to 850 ° C. as in Example 1. Then, the mixture was heated and melted in a dry inert gas atmosphere, and after clarification, the temperature was lowered and then the outflow was started. The gas exhausted from the crucible was cleaned through a filter and discharged outside.

  The obtained molten glass is cast into a carbon mold, and the obtained glass is allowed to cool to the transition temperature and immediately put into an annealing furnace, annealed for 1 hour near the transition temperature, and gradually cooled to room temperature in the annealing furnace. Optical glass No. 1 shown in Table 3. 12 and 13 were obtained. In addition, optical glass No. Table 3 shows the glass transition temperature Tg of 12 and 13 and the transmittance at typical wavelengths. The transmittance is a value at a thickness at which the transmittance is 50% at a wavelength of 615 nm. Optical glass No. 12, the thickness is 1.0 mm. In 13, the thickness is 0.45 mm. The transmittance was measured with a spectrophotometer using a sample having a flat plate shape and optically polished surfaces facing each other in parallel.

Optical glass No. 12 and also ^nd (2) About 13 ^{-nd (1)} is 0.00300 or ^less, nd (2) the absolute value of ^{-nd (1)} was also 0.00300 or less.

Comparative Example 1
Although the glass raw material was melted so that the glass of Comparative Example 1 shown in Table 4 was obtained, no dry inert gas was allowed to flow into the crucible during melting. A continuous melting furnace with a capacity of 50 liters was used, the melting temperature was 1100 ° C., and the residence time of the glass in the furnace from melting to the start of outflow was 20 hours. Thus was prepared a glass from a molten glass was prepared in the same flow as above procedure, nd ⁽²⁾ is significantly increased relative to nd ⁽¹⁾ as shown in Table 4, nd ⁽²⁾ -nd The absolute value of ⁽¹⁾ was greater than 0.00300.

Example 3 (Preform production example)
Each molten glass made of optical glass Nos. 1 to 11 and the glass of Comparative Example 1 has a constant flow rate from a platinum alloy pipe whose temperature is adjusted to a temperature range in which stable outflow is possible without devitrification of the glass. The molten glass lump having the weight of the target preform was separated by a method in which the molten glass flow tip was supported by dropping or supporting the molten glass using a support and then rapidly dropping the support to separate the glass lump. Next, each of the obtained molten glass lumps was received by a receiving mold having a gas outlet at the bottom, and a gas was ejected from the gas outlet and molded while the glass lumps floated to prepare a precision press-molding preform. The shape of the preform was made spherical or flat spherical by adjusting and setting the separation interval of the molten glass. The weights of the obtained preforms precisely matched the set values, and all of the preforms were smooth and the surfaces were formed by solidification of the molten glass.

  Next, when the inside of the preform was observed, the optical glass No. 1 of the present invention was observed. No striae were observed in 1 to 11, but striking striae were observed radially on the surface of the glass of Comparative Example 1.

  Separately, the surface of a glass piece obtained by casting molten glass into a mold, blowing a dry gas onto the glass surface to form a glass plate or cylindrical rod while promoting cooling, annealing, and then cutting the glass. Were ground and polished to obtain a preform having a smooth entire surface. In this case as well, no striae was found on the surface of the glass sheet or cylindrical rod formed by casting the molten glass obtained by atmosphere substitution. Reason was accepted.

Example 4 ( Example of optical element production)
Each preform made of optical glass Nos. 1 to 11 obtained in Example 3 was precision press-molded using the press apparatus shown in FIG. 1 to obtain an aspheric lens. Specifically, after the preform 4 is placed between the lower mold 2 and the upper mold 1 of the press mold composed of the upper mold 1, the lower mold 2 and the body mold 3, the inside of the quartz tube 11 is placed in a nitrogen atmosphere to form a heater 12. Was energized to heat the inside of the quartz tube 11. The temperature inside the press mold is set to a temperature at which the glass to be molded exhibits a viscosity of 10 ⁸ to 10 ¹⁰ dPa · s, and while maintaining the same temperature, the push bar 13 is lowered and the upper mold 1 is pressed to form. The preform set in the mold was pressed. The press pressure was 8 MPa, and the press time was 30 seconds. After pressing, the pressure of the press is released, and the glass molded product that has been press-molded is kept in contact with the lower mold 2 and the upper mold 1 until the viscosity of the glass reaches 10 ¹² dPa · s or more. It was cooled and then rapidly cooled to room temperature, and the glass molded product was taken out of the mold and an aspherical lens was obtained. The obtained aspherical lens had extremely high surface accuracy.
In FIG. 1, reference numeral 9 is a support rod, reference numeral 10 is a lower mold, a barrel holder, and reference numeral 14 is a thermocouple.
An aspherical lens obtained by precision press molding was provided with an antireflection film as required.

Example 5 (Production Example of Optical Element)
Each preform made of optical glass No. 1 to 11 obtained in practical example 3 was precision press-molded by a method different from that in Example 4. In this method, first, the preform was preheated to a temperature at which the viscosity of the glass constituting the preform was 10 ⁸ dPa · s while the preform floated. On the other hand, a press mold having an upper mold, a lower mold, and a body mold is heated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁹ to 10 ¹² dPa · s, and the preheated preform is pressed. It was introduced into the mold cavity and precision press-molded at 10 MPa. Cooling of the glass and the press mold was started at the start of pressing, and the glass was cooled until the viscosity of the molded glass reached 10 ¹² dPa · s or more, and then the molded product was released to obtain an aspheric lens. The obtained aspherical lens had extremely high surface accuracy.
An aspherical lens obtained by precision press molding was provided with an antireflection film as required. In this way, a glass optical element with high internal quality could be obtained with high productivity and high accuracy.

Example 6 (Production Example of Sheet Glass and Optical Element)
Each molten glass consisting of optical glass Nos. 1 to 11 was continuously poured from a pipe into a mold, formed into a sheet glass in a dry nitrogen atmosphere, and slowly cooled. Next, when the inside of the glass was observed, no striae was observed.
Next, the plate glass was cut, ground, and polished to obtain a material for press molding, and this material was heated, softened, and press molded to produce an optical element blank. The blank was annealed and then ground and polished to obtain a spherical lens.
An antireflection film or a near infrared light reflection film may be appropriately formed on the surface of these optical elements.

Example 7
The optical glass No. Preforms, sheet glass, and round bar glass made of 12 and 13 were prepared by the methods described in the above-mentioned practical examples 3, 6 and the like. Next, a plate glass made of optical glass No. 12 was sliced and processed into a flat plate shape, and main surfaces parallel to each other were optically polished to obtain a near infrared light absorption filter having a thickness of 1.0 mm. The near-infrared absorption filter for bonding the near-infrared light absorbing filter and a crystal flat plate whose main surfaces parallel to each other to optical polishing and two flat plates made of optical glass (borosilicate glass BK-7) are bonded together and incorporated into an imaging device. A composite filter with both filter function and optical low-pass filter function was fabricated.

  Similarly, optical glass No. After slicing the plate-like glass composed of 13, both sides were optically polished to form a flat plate having a thickness of 0.45 mm. This flat plate was bonded to a crystal flat plate and an optical glass (borosilicate glass BK-7) flat plate to produce a composite filter.

  In addition, optical glass No. After slicing 12 or 13 round bar glass, both sides optically polished may be bonded to a quartz plate and an optical glass (borosilicate glass BK-7) plate to form a composite filter.

Next, optical glass no. Preforms 12 and 13 were precision press molded to produce an aspherical lens having a near infrared light absorption function.
Various optical elements obtained as described above were optically homogeneous, and no striae were observed.

  According to the present invention, a fluorine-containing optical glass having no striae can be obtained. An optical glass having low dispersion and low glass transition temperature and capable of precision press molding and having low temperature softening properties can be obtained. Preforms for precision press molding using the optical glass, and various lenses, etc. The optical element can be manufactured.

DESCRIPTION OF SYMBOLS 1 ... Upper type | mold 2 ... Lower type | mold 3 ... Body type | mold 4 ... Preform 9 ... Support rod 10 ... Lower type | mold, body type | mold holder 11 ... Quartz tube 12 ... Heater 13 ... Push rod 14 ... Thermocouple

Claims (11)

In a method for producing optical glass in which a glass raw material is heated and melted to form molten glass, and the molten glass is formed to produce a fluorine-containing glass.
Volatile substances contained in the molten glass are volatilized and the concentration thereof is lowered, and then the molten glass is molded, so that the refractive index value of the obtained glass is nd (1), and the glass is placed in a nitrogen atmosphere. When the refractive index value after re-melting at 900 ° C. for 1 hour, cooling to the glass transition temperature, and then cooling to 25 ° C. at a cooling rate of 30 ° C. per hour is nd (2), nd (1) An optical glass having an absolute value (| nd (2) −nd (1) |) of the difference between nd and nd (2) of 0.00300 or less is manufactured. In a method for producing optical glass in which a glass raw material is heated and melted to form molten glass, and the molten glass is formed to produce a fluorine-containing glass.
A method for producing an optical glass, comprising: volatilizing a volatile substance contained in a molten glass, reducing the concentration thereof, and then forming the molten glass to form an optical glass having no striae. The manufacturing method of the optical glass of Claim 1 or 2 which introduce | transduces dry gas into a container and reduces the density | concentration of the volatile substance of the molten glass in this container.   The manufacturing method of the optical glass of any one of Claims 1-3 whose fluorine-containing glass is a fluorophosphate glass. Fluorophosphate glass is expressed as cation%,
P ⁵⁺ 5~50%,
Al ³⁺ 0.1-40%,
Mg ²⁺ 0-20%,
Ca ²⁺ 0-25%,
Sr2 ⁺ 0-30%,
Ba ²⁺ 0~30%,
Li ⁺ 0-30%,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-10%,
La ³⁺ 0-5%
Gd ³⁺ 0-5%
The manufacturing method of the optical glass of Claim 4 containing this. F ^- and ^{O 2-F} to the total amount of ^- the molar ratio ^F of the content of ^{- / (F - + O 2-} ) to prepare a fluorophosphate glass is from 0.25 to 0.95, according to claim 4 or 5 The manufacturing method of optical glass as described in any one of. The manufacturing method of the optical glass of any one of Claims 4-6 which produces the fluorophosphate glass containing 2-30 cation% of Li ⁺ . An optical glass is produced by the method according to any one of claims 1 to 7, a molten glass made of the obtained optical glass is allowed to flow out, a molten glass lump is separated, and a preform is cooled in the process of cooling the glass. A method for manufacturing a precision press-molding preform that eliminates the striae, characterized by being molded into a mold.   A method for producing an optical element, comprising: producing a precision press-molding preform by the method according to claim 8; heating the obtained preform; and performing precision press-molding with a press mold.   The optical element manufacturing method according to claim 9, wherein a precision press-molding preform is introduced into a press mold and heated together to perform precision press molding. The optical element manufacturing method according to claim 9, wherein a separately heated precision press molding preform is introduced into a heated press mold and precision press molding is performed.

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