JP5986938B2 - Optical glass, glass material for precision press molding, optical element and manufacturing method thereof - Google Patents

Description

  The present invention relates to optical glass, a precision press-molding preform, an optical element, and a method for producing the same. Specifically, it is a phosphoric acid optical glass having a high refractive index and a high dispersion characteristic, and is suitable for precision press molding, a precision press molding preform and optical element made of this optical glass, and this precision press molding. The present invention relates to a method for manufacturing an optical element for precision press-molding a preform.

  As a so-called phosphoric optical glass containing a large amount of phosphoric acid as a glass network former, those having various refractive indexes as described in Patent Documents 1 to 7 are known. Among these, optical glass having high refractive index and high dispersion characteristics (low Abbe number) is in high demand as an optical element material for various lenses. This is because, for example, a compact and highly functional optical system for correcting chromatic aberration can be configured by combining with a lens having a high refractive index and low dispersion. Furthermore, by making the optical functional surface of a lens having a high refractive index and high dispersion characteristics aspherical, it is possible to further enhance the functions and compactness of various optical systems.

JP 2003-238197 A JP 2003-160355 A JP 2008-303112 A JP 2009-96646 A JP 2012-17261 A JP-A-8-157231 JP-A-6-345481

  As a method for manufacturing an optical element, a precision press molding method is known. The precision press molding method is a method of forming the optical functional surface of an optical element without performing mechanical processing such as grinding and polishing, and glass optics that requires labor and cost in processing such as aspherical lenses such as grinding and polishing. This is a method by which an element can be efficiently manufactured. Therefore, the above-mentioned phosphoric acid-based optical glass has high refractive index and high dispersion characteristics, as well as properties suitable for precision press molding (good precision press moldability). Desirable for manufacturing.

Thus, one embodiment of the present invention provides a phosphate-based optical glass that has high refractive index and high dispersion characteristics and is suitable for a precision press molding method.
Furthermore, according to one aspect of the present invention, there are provided a precision press-molding preform and optical element made of the above-described optical glass, and a method of manufacturing an optical element for precision press-molding the precision press molding preform.

One aspect of the present invention is an oxide-based glass composition,
P ₂ O ₅ 24-34% by weight,
B ₂ O ₃ more than 0% by mass and 4% by mass or less,
Na ₂ O, K ₂ O, and Li ₂ O in total 12 to 20% by mass,
Nb ₂ O ₅ 15-30% by mass,
TiO ₂ 8-15% by mass,
Bi ₂ O ₃ 4-25% by mass,
Including
The mass ratio (TiO ₂ / Nb ₂ O ₅ ) is in the range of 0.36 to 1.00,
The mass ratio (Bi ₂ O ₃ / Nb ₂ O ₅ ) is in the range of 0.16 to 1.67,
An optical glass having a refractive index nd of 1.78 or more and less than 1.83 and an Abbe number νd of 20 to 25;
About.

The optical glass according to the above-described embodiment includes, as essential components, P ₂ O ₅ , B ₂ O ₃ , Nb ₂ O ₅ , TiO ₂ , Bi ₂ O ₃ , alkali metal oxides (Na ₂ O, K ₂ O, And at least one selected from the group consisting of Li ₂ O) and a ratio of TiO ₂ and Nb ₂ O ₅ , which are useful components for imparting high refractive index and high dispersion characteristics to the optical glass, good precision The ratio of Bi ₂ O ₃ and Nb ₂ O ₅ , which are components capable of imparting press formability, is defined. Thus, it is possible to obtain a phosphoric acid-based optical glass having a high refractive index and high dispersion characteristic of a refractive index nd of 1.78 or more and less than 1.83 and an Abbe number νd in the range of 20 to 25 and suitable for precision press molding. It becomes.

  According to one aspect of the present invention, it is possible to provide a phosphate-based optical glass having a high refractive index and a high dispersion characteristic that is suitable for obtaining a precision press-molding preform. According to a further aspect, a precision press-molding preform and an optical element made of the above-described optical glass are also provided.

[Optical glass]
The optical glass according to one embodiment of the present invention has an oxide-based glass composition in which P ₂ O ₅ is 24 to 34% by mass, B ₂ O ₃ is more than 0% by mass and 4% by mass or less, Na ₂ O, K _2. A total of 12 to 20% by mass of O and Li ₂ O, 15 to 30% by mass of Nb ₂ O ₅ , 8 to 15% by mass of TiO ₂ , and 4 to 25% by mass of Bi ₂ O ₃ , TiO ₂ / Nb ₂ O ₅ ) is in the range of 0.36 to 1.00, the mass ratio (Bi ₂ O ₃ / Nb ₂ O ₅ ) is in the range of 0.16 to 1.67, and the refractive index nd Is an optical glass in which the Abbe number νd is in the range of 20 to 25.
The details will be described below.

As described above, in the present invention, the glass composition of the optical glass is displayed on the basis of oxide. Here, the “oxide-based glass composition” refers to a glass composition obtained by converting all glass raw materials to be decomposed during melting and existing as oxides in the optical glass. Unless otherwise specified, the glass composition is displayed on a mass basis.
The glass composition in the present invention is determined by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). The analysis value obtained by this analysis method includes a measurement error of about ± 5%.
In the present specification and the present invention, the content of the constituent component of 0% means that the constituent component is substantially not included, and the content of the constituent component is about the impurity level or less. Point to.

P ₂ O ₅ is an essential component as a glass forming component in phosphate glass. Phosphate glass has the characteristics that it can melt glass at a relatively low temperature and has high transmittance in the visible region. Further, P ₂ O ₅ is a component located on the high dispersion side as compared with SiO ₂ and B ₂ O ₃ which are the same glass forming components, and the content thereof is obtained in order to obtain the high dispersion characteristic showing the above Abbe number νd. Is 24% or more. Preferably it is 27% or more, more preferably 28% or more. However, if an excessive amount is introduced, the glass tends to devitrify, so the content is set to 34% or less. Preferably it is 31% or less, More preferably, it is 30% or less.

SiO ₂ is an optional component that can be added to the above-described optical glass, and has an effect of increasing devitrification resistance. From the viewpoint of obtaining a high refractive index characteristic, if the above-mentioned optical glass includes SiO _2, is preferably SiO ₂ content is 1.2% or less. More preferably, it is 1.0% or less, more preferably less than 0.5%, still more preferably 0.4% or less, and it may not be introduced (even if the SiO ₂ content is 0%).

B ₂ O ₃ is a component having an effect of increasing devitrification resistance by adding an appropriate amount to the phosphate glass. Therefore, more than 0% is introduced into the above optical glass as an essential component. The B ₂ O ₃ content is preferably 0.4% or more, more preferably 0.7% or more. However, if an excessive amount is included, it is difficult to realize a high refractive index and a high dispersion characteristic, so the content is made 4% or less. Preferably it is 3% or less, More preferably, it is 1.5% or less.
Here, the B ₂ O ₃ content of 0% includes a case where B ₂ O ₃ is contained in glass in a trace amount to the impurity level. Therefore, the content of B ₂ O ₃ is greater than 0% refers to the B ₂ O ₃ is contained in an amount exceeding about impurity levels. Specifically, it is 700 ppm (mass ratio) or more, or 1000 ppm (mass ratio) or more, for example.

The glass characteristics that the glass suitable for precision press molding desirably has include a low glass transition temperature. This is because it is necessary to increase the press molding temperature in order to press-mold a glass having a high glass transition temperature Tg. However, if the precision press molding temperature is increased, it is provided on the molding die itself or the molding surface of the molding die. It is because the release film which exists is damaged. In the precision press molding method, an optical functional surface is formed by transferring a molding die molding surface without machining such as grinding and polishing. Therefore, when the molding die or the release film is damaged and the molding surface becomes rough, the rough surface shape is transferred to the optical element, and an optical functional surface having high surface smoothness cannot be obtained.
From the above points, the above-described optical glass preferably has a relatively low glass transition temperature, specifically, a glass transition temperature of 520 ° C. or lower. The glass transition temperature is more preferably 510 ° C. or lower, further preferably 500 ° C. or lower, and further preferably 490 ° C. or lower. From the viewpoint of glass stability, the glass transition temperature is preferably higher than 460 ° C, more preferably 465 ° C or higher, and further preferably 470 ° C or higher.

In order to realize a low Tg suitable for precision press molding as described above, the mass ratio (B ₂ O ₃ / P ₂ O ₅ ) between the P ₂ O ₅ content and the B ₂ O ₃ content is set to 0 It is preferable to be over 0.1. More preferably, it is more than 0 and 0.083 or less.

Further, from the viewpoint of realizing a low glass transition temperature, the total content of the alkali metal oxides Na ₂ O, K ₂ O, and Li ₂ O in the above optical glass is 12% or more. On the other hand, from the viewpoint of maintaining devitrification resistance, the total content is 20% or less. Preferably it is 17% or less, More preferably, it is 16% or less.

The optical glass described above may contain one or more selected from the group consisting of Li ₂ O, Na ₂ O and K ₂ O as an alkali metal oxide. Introducing at least Na ₂ O as the alkali metal oxide is advantageous for obtaining an optical glass exhibiting a low glass transition temperature. From the viewpoint of lowering the glass transition temperature, the Na ₂ O content in the optical glass is preferably 2% or more, more preferably 4% or more, and further preferably 5% or more. On the other hand, from the viewpoint of devitrification resistance of the glass, the Na ₂ O content is preferably 12% or less, more preferably 9% or less, and even more preferably 8% or less.

Other alkali metal oxides, K ₂ O and Li ₂ O are all components that can be added to lower the glass transition temperature. The K ₂ O content of the optical glass described above can be, for example, 2% or more, and is preferably 4% or more. The Li ₂ O content can be, for example, 1% or more, and is preferably 2% or more. From the viewpoint of devitrification resistance, the K ₂ O content can be, for example, 8% or less, and preferably 7% or less. The Li ₂ O content can be, for example, 5% or less, and is preferably 4% or less.

Nb ₂ O ₅ is an essential component for obtaining a high refractive index and a high dispersion characteristic, and is also a component having an effect of improving durability. If Nb ₂ O ₅ is less than 15%, it is difficult to obtain the desired high refractive index and high dispersion characteristics, and if it exceeds 30%, the devitrification resistance of the glass is lowered. Therefore, in the above optical glass, the Nb ₂ O ₅ content is in the range of 15 to 30%. From the viewpoint of realizing more preferable high refractive index and high dispersion characteristics, the Nb ₂ O ₅ content is preferably 25% or less, more preferably 22% or less, and even more preferably 20% or less. . Further, from the viewpoint of devitrification resistance, the Nb ₂ O ₅ content is preferably 16% or more, and more preferably 18% or more.

TiO ₂ is a component that can impart high refractive index and high dispersion characteristics to the glass when added in an appropriate amount, and 8% or more is introduced into the optical glass. The TiO ₂ content is preferably 9% or more, more preferably 10% or more. However, if the content exceeds 15%, the devitrification resistance decreases, so the TiO ₂ content in the optical glass is set to 15% or less. Preferably it is 13% or less, More preferably, it is 12% or less.

Bi ₂ O ₃ is a useful component for lowering the glass transition temperature and improving precision press molding. Therefore, 4% or more of Bi ₂ O ₃ is introduced into the above optical glass. The Bi ₂ O ₃ content is preferably 6% or more, more preferably 10% or more. However, since the devitrification resistance is lowered when an excessive amount is introduced, the Bi ₂ O ₃ content in the optical glass is set to 25% or less. Preferably it is 20% or less, More preferably, it is 15% or less.

The contents of Nb ₂ O ₅ , TiO ₂ , and Bi ₂ O ₃ are as described above. Furthermore, in the above optical glass, the mass ratio (TiO ₂ / Nb ₂ O ₅ ) is in the range of 0.36 to 1.00, and the mass ratio (Bi ₂ O ₃ / Nb ₂ O ₅ ) is 0.16 to The range is 1.67. The ratio of Nb ₂ O ₅ and TiO ₂ , which are useful components for imparting high refractive index and high dispersion characteristics, and Bi ₂ O ₃ , which is a component useful for improving precision press moldability, are within the above range. The phosphoric acid optical glass having a high refractive index / high dispersion characteristic of a refractive index nd of 1.78 or more and less than 1.83 and an Abbe number νd in the range of 20 to 25 and suitable for precision press molding Can be obtained. From the viewpoint of achieving both high refractive index / high dispersion characteristics and precision press formability, the lower limit of the mass ratio (TiO ₂ / Nb ₂ O ₅ ) is preferably 0.40 or more, and preferably 0.50 or more. Is more preferably 0.55 or more. The upper limit is preferably 0.80 or less, more preferably 0.70 or less, and even more preferably 0.60 or less. On the other hand, from the same viewpoint, the lower limit of the mass ratio (Bi ₂ O ₃ / Nb ₂ O ₅ ) is preferably 0.20 or more, more preferably 0.40 or more, and 0.50 or more. More preferably, it is more preferably 0.60 or more. The upper limit is preferably 0.87 or less, more preferably 0.80 or less, and even more preferably 0.70 or less.

The optical glass described above may contain one or more of the alkaline earth metal oxides MgO, CaO, SrO and BaO. Alkaline earth metal oxides are components that have the effect of enhancing glass stability, but may cause a decrease in refractive index and a decrease in dispersibility. Therefore, the total content of the alkaline earth metal oxides MgO, CaO, SrO and BaO is preferably suppressed to 2% or less, and may be 0%.
The total content of alkali metal oxides and alkaline earth metal oxides (Li ₂ O + Na ₂ O + K ₂ O + MgO + CaO + SrO + BaO) may be in the range of 12 to 17% from the viewpoint of realizing high refractive index and high dispersion characteristics. preferable. The upper limit value is more preferably 17% or less, and still more preferably 16% or less.
Moreover, about content of each alkaline-earth metal oxide, the preferable lower limit of MgO content is 0% or more, and a preferable upper limit is 2% or less. The preferable lower limit of the CaO content is 0% or more, and the preferable upper limit is 2% or less, more preferably less than 1%. The preferable lower limit value of the SrO content is 0% or more, and the preferable upper limit value is 2% or less. The preferable lower limit of the BaO content is 0% or more, and the preferable upper limit is 2% or less.

WO ₃ is an optional component that can be added to the glass described above, and has the effect of contributing to the low Tg of the glass and improving the precision press formability. From the viewpoint of forming an optical glass suitable for precision press molding, it is preferable that 3% or more of WO ₃ is contained in the optical glass. More preferably, it is 6% or more, More preferably, it is 10% or more. On the other hand, from the viewpoint of devitrification resistance, the content of WO ₃ is preferably 23% or less, more preferably 20% or less, and even more preferably less than 13%.

From the viewpoint of lowering the glass Tg, the ratio of the WO ₃ content to the Nb ₂ O ₅ content is such that the mass ratio (WO ₃ / Nb ₂ O ₅ ) is in the range of 0.12 to 0.92. It is preferable to adjust. From the viewpoint of achieving both high refractive index / high dispersion characteristics and low Tg, the lower limit of the mass ratio (WO ₃ / Nb ₂ O ₅ ) is more preferably 0.20, still more preferably 0.50, and more More preferably, it is 0.55. The upper limit value is more preferably 0.80, and still more preferably 0.70.

ZnO, Al ₂ O ₃ , and Ta ₂ O ₅ can also be added to the optical glass as an optional component for adjusting the refractive index. The contents of ZnO, Al ₂ O ₃ and Ta ₂ O ₅ can be, for example, in the range of 0 to 5%, preferably in the range of 0 to 3%. Further, La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ , Cs ₂ O, ZrO ₂ , PbO and the like are each added in an amount of, for example, 0 to 1%, so that the object of the present invention is not impaired. You may add in the range. Further, SnO ₂ and Sb ₂ O ₃ may be added to the above-mentioned optical glass in amounts in the range of, for example, 0 to 1%, respectively, as the external addition amount.

  The glass composition of the above optical glass has been described above. Next, the glass characteristics of the above optical glass will be described.

  The above optical glass is a high refractive index and high dispersion optical glass having a refractive index nd of 1.78 or more and less than 1.83 and an Abbe number νd in the range of 20-25. The lower limit of the refractive index nd is preferably 1.790 or more, more preferably 1.795 or more, and further preferably 1.800 or more. The upper limit is preferably 1.820 or less, more preferably 1.815 or less, and still more preferably 1.810 or less. The lower limit of the Abbe number νd is preferably 21.0 or more, and more preferably 22.0 or more. The upper limit is preferably 24.0 or less, and more preferably 23.5 or less. The optical glass having the above refractive index nd and Abbe number νd is useful in an optical system.

As the high refractive index and high dispersion glass, the smaller the Abbe number νd at the same refractive index nd, the higher the usefulness in the optical system. From this point, a preferred embodiment of the above-described optical glass includes a glass having a refractive index and an Abbe number νd satisfying the following formula (1). nd ≦ 15 / νd + 1.18 (1)
By performing the composition adjustment described above, it is possible to obtain an optical glass that has the refractive index nd and Abbe number νd in the above-described ranges and satisfies the formula (1).

As other glass physical properties, the glass transition temperature of the optical glass described above is as described above. Examples of compositions effective for lowering Tg include the following compositions. Although the Tg can be lowered simply by increasing the content of alkali metal oxide or alkaline earth metal oxide, the weather resistance may deteriorate as a result. On the other hand, the following composition is mentioned as a preferable composition which can aim at low Tg suitable for precision press molding, maintaining a weather resistance.
(A) The total content of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO and BaO is in the range of 12 to 17%, and the mass ratio (B ₂ O ₃ / P ₂ O ₅ ) In the range of more than 0 and 0.1 or less. Preferably, the total content of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO and BaO is in the range of 12 to 17%, and the mass ratio (B ₂ O ₃ / P ₂ O ₅ ) Is preferably a composition in the range of more than 0 and 0.083 or less.
(B) The total content of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO and BaO is in the range of 12 to 17%, and the mass ratio (Bi ₂ O ₃ / Nb ₂ O ₅ ) In the range of 0.16-1.67. Preferably, the total content of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO and BaO is in the range of 12 to 17%, and the mass ratio (Bi ₂ O ₃ / Nb ₂ O ₅ ) In the range of 0.16 to 0.87.
(C) The total content of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO and BaO is in the range of 12 to 17%, and the mass ratio (WO ₃ / Nb ₂ O ₅ ) is 0 A composition that is in the range of 12 to 0.92.
(D) The total content of Li ₂ O, Na ₂ O and K ₂ O is in the range of 12 to 20%, and the mass ratio (WO ₃ / Nb ₂ O ₅ ) is in the range of 0.12 to 0.92. Composition.
(E) The total content of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO and BaO is in the range of 12 to 20%, and the mass ratio (WO ₃ / Nb ₂ O ₅ ) is 0 A composition that is in the range of 12 to 0.92.

Moreover, the following composition can be mentioned as an example of a composition effective in achieving both high dispersion characteristics and low Tg.
(F) The mass ratio (TiO ₂ / Nb ₂ O ₅ ) is in the range of 0.36 to 1.00, and the total content of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO and BaO A composition whose amount ranges from 12 to 17%. Preferably, the mass ratio (TiO ₂ / Nb ₂ O ₅ ) is in the range of 0.40 to 0.80, and the total content of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO and BaO A preferred range of amounts is a composition in the range of 12-17%.

  The glass characteristics that the optical glass desirably has from the point of precision press moldability can also include a low liquidus temperature. Glass having a low liquidus temperature has high devitrification stability in the vicinity of the softening point. Therefore, the preform is heated to be softened and precision press-molded to obtain an optical element having high transparency without devitrification. Because it can. From this point, it is preferable that the above-mentioned optical glass has a liquidus temperature of 1000 ° C. or lower. The liquidus temperature is more preferably 970 ° C. or less, and still more preferably 960 ° C. or less. Further, from the viewpoint of glass stability, the liquidus temperature is preferably 850 ° C. or higher, and more preferably 880 ° C. or higher.

  As described above, the above-described optical glass is an optical glass having high refractive index and high dispersion characteristics and suitable for precision press molding.

  Optical glass is prepared by weighing and preparing raw materials such as oxides, carbonates, sulfates, nitrates and hydroxides so that the desired glass composition can be obtained. It can be obtained by heating, melting, defoaming and stirring to make a molten glass free of bubbles and molding it. Specifically, it can be made using a known melting method.

[Preform for precision press molding]
One aspect of the present invention relates to a precision press-molding preform made of the above-described optical glass. A precision press-molding preform (hereinafter also referred to as a preform) means a glass lump to be subjected to precision press molding, and is a glass molded body corresponding to the mass of a precision press-molded product. Precision press molding is also called mold optics molding, and is a method of forming an optical functional surface of an optical element by transferring a molding surface of a press mold. The optical functional surface means a surface in the optical element that refracts, reflects, diffracts, or enters and exits light to be controlled. The lens surface in the lens corresponds to this optical function surface.

  The preform may be manufactured through cold processing such as grinding and polishing, or by hot processing (also referred to as hot forming) in which a molded product is obtained from molten glass without undergoing cold processing such as grinding and polishing. It may be produced. In order to stably supply a large amount of aspherical lenses using high-performance glass at a low cost, it is preferable to precisely press-mold a preform obtained by hot working. Glass properties suitable for this hot working include low Tg and low liquidus temperature. Since the above-mentioned optical glass can have these glass characteristics, it is also suitable for obtaining a preform by hot working.

  According to one embodiment of producing a preform by hot working, a uniform molten glass is produced by melting, clarifying, and stirring a glass raw material from which the above optical glass can be obtained. Thereafter, the molten glass is allowed to flow out from a platinum or platinum alloy pipe to produce a glass lump from a predetermined amount of molten glass, and a hot-formed product is formed using the glass lump. In this embodiment, the molten glass is continuously discharged from the outlet of the above-mentioned pipe, and the tip portion of the glass that has flowed out of the outlet is separated to obtain a predetermined amount of glass lump. The obtained glass lump is formed into a preform shape while the glass is in a temperature range where plastic deformation is possible. Examples of the method for separating the tip portion of the outflow glass include a dropping method and a descending cutting method. By using the optical glass described above, it is possible to separate the tip portion of the glass flowing out from the pipe outlet without devitrifying the glass. By keeping the outflow speed and outflow temperature constant, and keeping the dripping condition or descent condition constant, a preform with a constant weight can be manufactured with high reproducibility and high accuracy. According to this embodiment, for example, a preform having a mass of 1 to 5000 mg can be manufactured with high mass accuracy.

  In one embodiment, the separated glass tip is received by a molding die in which gas is ejected from a concave molding surface, and is molded into a preform such as a sphere or an ellipsoid by levitation and rotation by the wind pressure of the gas. . Such a molding method is called a floating molding method. Alternatively, a method of obtaining a preform by press-molding a molten glass lump with a lower mold and an upper mold is also known, and can be used for the above-described hot forming. The hot-formed product thus manufactured may be provided with a known release film on the surface as necessary.

[Optical element and manufacturing method thereof]
Another aspect of the present invention is:
An optical element comprising the optical glass described above; and
An optical element manufacturing method comprising a step of producing an optical element by precision press molding using a press mold in a state where the above-described precision press molding preform is softened by heating,
About.

  The precision press molding method is also called a mold optics molding method, and is already well known in the technical field to which the present invention belongs. A surface that transmits, refracts, diffracts, or reflects light rays of the optical element is called an optical functional surface. For example, taking a lens as an example, a lens surface such as an aspherical surface of an aspherical lens or a spherical surface of a spherical lens corresponds to an optical function surface. The precision press molding method is a method of forming an optical functional surface by press molding by precisely transferring a molding surface of a press mold to glass. That is, it is not necessary to add machining such as grinding or polishing to finish the optical functional surface. The precision press molding method is suitable for manufacturing optical elements such as lenses, lens arrays, diffraction gratings, and prisms, and is particularly suitable as a method for manufacturing an aspheric lens with high productivity.

  Since the above-mentioned preform can have a low Tg, which is a glass characteristic suitable for precision press molding, the glass can be pressed at a relatively low temperature. Therefore, since the burden on the molding surface of the press mold is reduced, the life of the molding die can be extended and the molding surface of the molding die can be prevented from being damaged and roughened.

In one embodiment of the precision press molding method, the preform having a clean surface was reheated so that the viscosity of the glass constituting the preform was in the range of 10 ⁵ to 10 ¹¹ Pa · s, and reheated. The preform is press-molded with a mold having an upper mold and a lower mold. A mold release film may be provided on the molding surface of the mold as necessary. The press molding is preferably performed in an atmosphere of nitrogen gas or inert gas in order to prevent oxidation of the molding surface of the mold. The press-molded product is taken out from the 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.

  Thus, a lens made of phosphate optical glass having a refractive index nd of 1.78 or more and less than 1.83, an Abbe number νd of 20 to 25, and suitable for precision press molding, Optical elements such as lens arrays, diffraction gratings, and prisms can be manufactured with high accuracy and high productivity.

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

1. Examples relating to optical glass and precision press-molding preform, comparative example In order to obtain optical glass having the composition shown in Table 1, oxides, carbonates, sulfates, nitrates, hydroxides and the like corresponding to the respective glass components 150 to 300 g of a glass raw material was weighed in a predetermined ratio and mixed well to obtain a blended batch. This was put in a platinum crucible, and the glass was melted in air for 2 to 4 hours while stirring at 1000 to 1250 ° C. After melting, the molten glass is poured into a 40 × 70 × 15 mm carbon mold, allowed to cool to the glass transition temperature, immediately put into an annealing furnace, annealed for about 1 hour in the glass transition temperature range, and room temperature in the furnace. Each optical glass was produced.
The refractive index, Abbe number, glass transition temperature, and liquidus temperature of each optical glass were measured by the following methods.

Measuring method (1) Refractive index (nd) and Abbe number (νd)
It measured about the optical glass obtained by making slow cooling temperature-fall rate -30 degreeC / hour.
(2) Glass transition temperature Tg
A differential scanning calorimetry (DSC (Differential Scanning Calorimetry)) was used to measure at a heating rate of 10 ° C./min.
(3) Liquidus temperature LT
The glass sample was held in a test furnace set to an arbitrary temperature for 2 hours, the presence or absence of crystals was observed with a microscope having a magnification of 10 to 100 times, and the liquidus temperature was measured.

  The measurement results are shown in Table 1.

  A high-quality and homogenized molten glass from which optical glasses of Examples shown in Table 1 were obtained was continuously discharged from a platinum alloy pipe. The molten glass flowing out was dropped from the pipe outlet, received one after another by a plurality of preform molding dies, and a plurality of spherical preforms were molded by a floating molding method. In addition, the temperature of the glass at the time of outflow was made several degree C higher than liquidus temperature.

  The preform obtained from the optical glass of the example was transparent and homogeneous with no crystal observable with a microscope. None of these preforms was devitrified, and a material with high mass accuracy was obtained.

  From the optical glass of the example, a preform was produced by using the falling cutting method instead of the dropping method. Similarly, devitrification was not observed in the preform obtained by the descending cutting method, and a preform with high mass accuracy was obtained. Moreover, the trace at the time of isolation | separation was not recognized in the preform by the dropping method and the descent cutting method. Even when the platinum pipe was used, the pipe was not damaged by the outflow of the molten glass, like the platinum alloy pipe.

2. Examples relating to optical elements The surface of the above-mentioned preform is coated as necessary, and introduced into a press mold including an upper and lower mold made of SiC and a body mold provided with a carbon-based release film on the molding surface, and nitrogen. A mold and preform are heated together in an atmosphere to soften the preform, precision press-molded and aspherical convex meniscus lens, aspherical concave meniscus lens, aspherical biconvex lens, aspherical both Various lenses of concave lenses were prepared. In addition, each condition of precision press molding was adjusted in the above-mentioned range.

  Observation of the various lenses thus produced revealed no scratches, spiders, or breakage on the lens surface.

  This process was repeated and mass production tests of various lenses were carried out. However, defects such as glass and press mold fusion did not occur, and high-quality lenses on both the surface and inside could be produced with high precision. . The surface of the lens thus obtained may be coated with an antireflection film.

  Next, the same preform as the above-mentioned preform is heated and softened, and separately introduced into a pre-heated press mold, precision press-molded, and aspherical convex meniscus lens, aspherical concave meniscus lens, Various lenses such as a spherical biconvex lens and an aspherical biconcave lens were prepared. In addition, each condition of precision press molding was adjusted in the above-mentioned range.

  When the various lenses thus prepared were observed, no white turbidity due to phase separation was observed, and no scratches, spiders, or damages were observed on the lens surface.

  This process was repeated and mass production tests of various lenses were carried out. However, defects such as glass and press mold fusion did not occur, and high-quality lenses on both the surface and inside could be produced with high precision. . The surface of the lens thus obtained may be coated with an antireflection film.

  Various shapes of optical elements such as prisms, microlenses, and lens arrays can be produced by appropriately changing the shape of the molding surface of the press mold.

  Finally, the above-described aspects are summarized.

According to one embodiment, P ₂ O ₅ is 24 to 34%, B ₂ O ₃ is more than 0% and 4% or less, Li ₂ O, Na ₂ O and K ₂ O are combined in a total of 12 to 20%, Nb ₂ O ₅ to 15 to 30%, TiO ₂ to 8 to 15% and Bi ₂ O ₃ to 4 to 25% by mass, and the mass ratio (TiO ₂ / Nb ₂ O ₅ ) is 0.36 to 1.00 By setting the range and mass ratio (Bi ₂ O ₃ / Nb ₂ O ₅ ) in the range of 0.16 to 1.67, the refractive index nd is 1.78 or more and less than 1.83, and the Abbe number νd is 20 to An optical glass suitable for precision press molding having a high refractive index and high dispersion characteristic of 25 can be obtained.

From the viewpoint of realizing more preferable high refractive index and high dispersion characteristics, the above optical glass is a total of 12 to 17% of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO, and BaO. It is preferable to include.

The above optical glass preferably has a mass ratio (B ₂ O ₃ / P ₂ O ₅ ) in the range of more than 0 and 0.1 or less from the viewpoint of realizing a glass transition temperature suitable for precision press molding. From the same viewpoint, it is also preferable that the mass ratio (WO ₃ / Nb ₂ O ₅ ) is in the range of 0.12 to 0.92, and the WO ₃ content is in the range of ₃ to 23% by mass.

  From the viewpoint of realizing more preferable high refractive index / high dispersion characteristics, it is also preferable that the CaO content is less than 1% by mass, and the total content of MgO, CaO, SrO, and BaO is less than 2% by mass. .

  The optical glass described above can have a glass transition temperature Tg of 520 ° C. or lower suitable for precision press molding by adjusting the composition described above.

  Since the optical glass described above has glass properties such as low Tg suitable for precision press molding, a precision press molding preform and an optical element obtained by precision press molding the preform are obtained. It is suitable as glass.

  That is, according to another aspect, a precision press-molding preform and an optical element made of the above-described optical glass are provided.

  According to another aspect, an optical element manufacturing method comprising a step of producing an optical element by precision press molding using a press mold in a state where the above-described precision press molding preform is softened by heating. Is also provided.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is useful in the field of manufacturing optical elements such as glass lenses, lens arrays, diffraction gratings, and prisms.

Claims (11)

In the oxide-based glass composition,
P ₂ O ₅ 24-34 wt%,
B ₂ O ₃ more than 0% by mass and 4% by mass or less,
Li ₂ O, Na ₂ O and K ₂ O in total 12 to 20% by mass,
Nb ₂ O ₅ 15-30% by mass,
TiO ₂ 8-15% by mass,
Bi ₂ O ₃ 4-25% by mass,
Including
The mass ratio (TiO ₂ / Nb ₂ O ₅ ) is in the range of 0.36 to 1.00,
The mass ratio (Bi ₂ O ₃ / Nb ₂ O ₅ ) is in the range of 0.16 to 1.67,
An optical glass having a refractive index nd of 1.78 or more and less than 1.83 and an Abbe number νd of 20 to 25. The optical glass according to claim 1, wherein the total content of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO and BaO is in the range of 12 to 17% by mass. The optical glass according to claim 1 or 2, wherein a mass ratio (B ₂ O ₃ / P ₂ O ₅ ) is in a range of more than 0 and 0.1 or less. The optical glass according to claim 1, wherein a mass ratio (WO ₃ / Nb ₂ O ₅ ) is in a range of 0.12 to 0.92. The optical glass according to any one of claims 1 to 4, wherein the content of WO3 is in the range of ₃ to 23 mass%. The optical glass according to any one of claims 1 to 5, wherein the CaO content is less than 1% by mass. The optical glass according to any one of claims 1 to 6, wherein the total content of MgO, CaO, SrO, and BaO is less than 2 mass%. The optical glass according to claim 1, which has a glass transition temperature Tg of 520 ° C. or lower. A precision press-molding preform made of the optical glass according to claim 1. The optical element which consists of optical glass of any one of Claims 1-8. An optical element manufacturing method comprising a step of producing an optical element by performing precision press molding using a press mold in a state where the precision press molding preform according to claim 9 is softened by heating.