JP7132589B2 - Optical glass, preforms for precision press molding, and optical elements - Google Patents

Description

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

Optical glass classified as so-called BK type, which has a refractive index (nd) of 1.48 to 1.54 and an Abbe number (νd) of about 58 to 67, has been mass-produced for a long time and is still used today. , imaging lenses for digital cameras, optical pickup lenses, and optical communication lenses.

Here, optical glasses are often used to produce preforms for precision press molding. Preforms for precision press molding using optical glass can be produced by the conventional method of grinding and polishing, and the method of directly dropping molten glass and receiving it with a mold (dropping method). Among them, the dropping method does not require grinding and polishing, so it is a more excellent manufacturing method that is low in cost and can be expected to have the effect of reducing the environmental load.
However, in principle, the dropping method is difficult to implement when the viscosity of the glass melt (for example, the viscosity at 1300° C.) is excessively high. Under these circumstances, there is a demand for an optical glass having desired optical constants and a low melt viscosity for use in the dropping method.

For example, in Patent Document 1, by setting SiO ₂ , B ₂ O ₃ , R ₂ O (R: Li, Na, K) and Al ₂ O ₃ to specific composition ranges, the viscosity becomes lower in a high temperature range. discloses a BK type borosilicate glass suitable for making preforms by the dropping method.

Japanese Patent Application Laid-Open No. 2002-201037

By the way, in precision press molding, cemented carbide molds are often used. It is preferable that the modulus difference is small, that is, it has low expansibility. Furthermore, even when such low-expansion glass is bonded to low-expansion materials such as ceramics and metal alloys, the risk of breakage caused by the difference in expansion coefficient is low, so the sealing material and the lens barrel are integrated. It can be preferably used as a lens material for molding.
In the field of optical glass, "low expansion" generally means that the average coefficient of linear expansion (α _{100-300° C.} ) is approximately 80×10 ⁻⁷ /° C. or less.

However, as a result of intensive studies by the present inventors, it has become clear that the conventional optical glass described in Patent Document 1 has a relatively large coefficient of expansion. Or, it was found that the probability of occurrence of chipping is relatively high. In addition, it has been found that the conventional optical glass described in Patent Document 1 tends to have insufficient water resistance. Such water resistance is an extremely important quality in terms of the fact that many optical elements, such as lenses, are placed close to the atmosphere and used, and the fact that water is used in the manufacturing process (polishing process). is one.
Therefore, the above conventional optical glasses have room for improvement at least in terms of low expansion and improvement in water resistance.

The present invention has been developed in view of the above-mentioned current situation. The object is to provide reform and optical elements.

As a result of intensive studies to achieve the above object, the inventors of the present invention have found that, in a composition of borosilicate glass, particularly containing a large amount of B ₂ O ₃ , SiO ₂ and Al ₂ O ₃ are added to B ₂ O ₃ . are included in a predetermined ratio, and the total content of Li ₂ O, Na ₂ O, and K ₂ O is within an appropriate range, so that the viscosity of the melt is low, and the melt has low expansion and water resistance. It was found that an optical glass having excellent properties can be produced.

That is, the optical glass of the present invention is
in % by mass,
SiO ₂ : 30% or more and 50% or less,
B ₂ O ₃ : 25% or more and 38% or less,
Al ₂ O ₃ : 2% or more and 12% or less,
Li ₂ O: 0% or more and 5% or less,
Na ₂ O: 0% or more and 12% or less,
K ₂ O: 0% or more and 10% or less,
MgO: 0% or more and 10% or less,
CaO: 0% or more and 10% or less,
SrO: 0% or more and 5% or less,
BaO: 0% or more and 5% or less,
ZnO: 0% or more and 15% or less,
having a composition containing TiO ₂ : 0% or more and 5% or less and ZrO ₂ : 0% or more and 5% or less,
The mass ratio represented by B ₂ O ₃ /(SiO ₂ +Al ₂ O ₃ ) is 0.53 or more and 0.72 or less, and
The total content of Li ₂ O, Na ₂ O, and K ₂ O is 6% or more and 17% or less. Such an optical glass has a low melt viscosity, a low expansion property, and excellent water resistance.

The optical glass of the present invention preferably has an average coefficient of linear expansion (α _{100-300° C.} ) of 80×10 ⁻⁷ /° C. or less as measured according to JOGIS08-2003 of the Japan Optical Glass Industry Standard.

The optical glass of the present invention preferably has a viscosity of 20 dPa·s or less at 1300°C.

The optical glass of the present invention preferably has a water resistance class of 1 to 4 as measured according to JOGIS06-2009 of the Japan Optical Glass Industry Standard.

The optical glass of the present invention preferably has a refractive index (nd) of 1.48 or more and 1.54 or less and an Abbe number (νd) of 58 or more and 67 or less.

Further, a preform for precision press molding of the present invention is characterized by using the above optical glass as a raw material.

Further, an optical element of the present invention is characterized by using the above optical glass as a material.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an optical glass having a low melt viscosity, a low expansion property, and excellent water resistance, as well as a precision press-molding preform and an optical element using the optical glass. can.

(optical glass)
Hereinafter, the optical glass of one embodiment of the present invention (hereinafter sometimes referred to as "optical glass of the present embodiment") will be specifically described. The optical glass of the present embodiment has, in mass %,
SiO ₂ : 30% or more and 50% or less,
B ₂ O ₃ : 25% or more and 38% or less,
Al ₂ O ₃ : 2% or more and 12% or less,
Li ₂ O: 0% or more and 5% or less,
Na ₂ O: 0% or more and 12% or less,
K ₂ O: 0% or more and 10% or less,
MgO: 0% or more and 10% or less,
CaO: 0% or more and 10% or less,
SrO: 0% or more and 5% or less,
BaO: 0% or more and 5% or less,
ZnO: 0% or more and 15% or less,
having a composition containing TiO ₂ : 0% or more and 5% or less and ZrO ₂ : 0% or more and 5% or less,
The mass ratio represented by B ₂ O ₃ /(SiO ₂ +Al ₂ O ₃ ) is 0.53 or more and 0.72 or less, and
The total content of Li ₂ O, Na ₂ O, and K ₂ O is 6% or more and 17% or less.

In addition, the optical glass of the present embodiment may contain other components (described later) other than the components described above. However, the optical glass of the present embodiment preferably has a composition consisting only of the above-described components, from the viewpoint of reducing the viscosity of the melt and more reliably developing low-expansion properties and improved comet resistance.
Here, "consisting only of the above-described components" includes the case where impurity components other than the components are inevitably mixed, specifically, the ratio of the impurity components is 0.2% by mass or less. and

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

< _SiO2 >
In the optical glass of the present embodiment, SiO ₂ forms a network structure of the glass, gives the glass devitrification resistance that can be manufactured, and is useful in that it can increase the low expansion and water resistance of the glass. is an ingredient. However, when the content exceeds 50%, the viscosity of the glass melt increases, while when the content is less than 30%, the stability against devitrification, low expansion, and water resistance are improved. Not enough effect. Therefore, in the optical glass of the present embodiment, the content of SiO ₂ is set in the range of 30% or more and 50% or less. From the same viewpoint, the content of SiO ₂ in the optical glass of the present embodiment is preferably 32.5% or more, more preferably 35% or more, and 47.5% or less. is preferred, and 45% or less is more preferred.

< _{B2O3 >}
In the optical glass of the embodiment, B ₂ O ₃ forms a network structure of the glass, gives the glass devitrification resistance that can be manufactured, reduces the viscosity of the glass melt, and improves the low expansibility. It is a useful component that can provide However, if the content exceeds 38%, the water resistance is lowered, while if the content is less than 25%, the effect of improving the low expansion property cannot be obtained. Therefore, in the optical glass of this embodiment, the content of B ₂ O ₃ is in the range of 25% or more and 38% or less. From the same viewpoint, the content of B ₂ O ₃ in the optical glass of the present embodiment is preferably 26% or more, more preferably 27% or more, and preferably 37% or less. , 36% or less.

< _{Al2O3 >}
In the optical glass of the present embodiment, Al ₂ O ₃ suppresses the phase separation of the glass, gives the glass devitrification resistance that can be manufactured, and can improve the low expansion property and water resistance of the glass. It is a useful ingredient that can However, when the content exceeds 12%, the viscosity of the glass melt increases, while when the content is less than 2%, the stability against devitrification, low expansion, and water resistance are improved. Not enough effect. Therefore, in the optical glass of this embodiment, the content of Al ₂ O ₃ is in the range of 2% or more and 12% or less. From the same viewpoint, the content of Al ₂ O ₃ in the optical glass of the present embodiment is preferably 3% or more, more preferably 4% or more, and preferably 11% or less. , 10% or less.

<Relationship among SiO ₂ , B ₂ O ₃ and Al ₂ O ₃ contents>
Here, the optical glass of the present embodiment requires that the mass ratio represented by _B2O3 / _{( SiO2 + Al2O3} ) is 0.53 or more and 0.72 or less. If the mass ratio is less than 0.53, even if the respective contents of SiO ₂ , B ₂ O ₃ and Al ₂ O ₃ are within the above ranges, the low expansion property is deteriorated, and the glass melt There is a risk that the viscosity of the Further, if the mass ratio is more than 0.72, water resistance may deteriorate even if the respective contents of SiO ₂ , B ₂ O ₃ and Al ₂ O ₃ are within the ranges described above. The mass ratio in the optical glass of the present embodiment is preferably 0.54 or more from the viewpoint of more effectively improving the low expansibility and sufficiently reducing the viscosity of the glass melt. , from the viewpoint of more effectively improving the water resistance, it is preferably 0.68 or less.

< _Li2O >
In the optical glass of this embodiment, Li ₂ O is a component capable of reducing the viscosity of the glass melt. However, when the content exceeds 5%, the low expansibility and water resistance of the glass are remarkably lowered, and the raw material cost is increased (the price has been on the rise in recent years). Therefore, in the optical glass of the present embodiment, the content of Li ₂ O is in the range of 0% or more and 5% or less. From the same point of view, the content of Li ₂ O in the optical glass of the present embodiment is preferably 3% or less, more preferably less than 3%.

< _Na2O >
In the optical glass of this embodiment, Na ₂ O is a component that can reduce the viscosity of the glass melt. However, when the content exceeds 12%, the low expansibility and water resistance of the glass deteriorate. Therefore, in the optical glass of the present embodiment, the content of Na ₂ O is in the range of 0% or more and 12% or less. From the same point of view, the content of Na ₂ O in the optical glass of the present embodiment is preferably 11% or less, more preferably 10% or less.

< _K2O >
In the optical glass of this embodiment, K ₂ O is a component capable of reducing the viscosity of the glass melt. However, when the content exceeds 10%, the low expansibility and water resistance of the glass deteriorate. Therefore, in the optical glass of this embodiment, the content of K ₂ O is set within the range of 0% or more and 10% or less. From the same point of view, the content of K ₂ O in the optical glass of the present embodiment is preferably 9% or less, more preferably 8% or less.

<Total of Li ₂ O, Na ₂ O, and K ₂ O>
Here, in the optical glass of the present embodiment, the total content of Li ₂ O, Na ₂ O and K ₂ O should be 6% or more and 17% or less. If the total content exceeds 17%, the low expansibility and water resistance of the glass are lowered, while if it is less than 6%, the effect of reducing the viscosity of the glass melt cannot be sufficiently obtained. In addition, the total content of Li ₂ O, Na ₂ O, and K ₂ O in the optical glass of the present embodiment is preferably 7% or more from the viewpoint of further increasing the low viscosity of the glass melt. It is more preferably 8% or more, and from the viewpoint of sufficiently suppressing a decrease in the low expansibility and water resistance of the glass, it is preferably 16% or less, and more preferably 15% or less. .

<MgO>
In the optical glass of the present embodiment, MgO is a component capable of increasing the water resistance without impairing the low viscosity of the glass melt. However, when the content exceeds 10%, the low expandability deteriorates. Therefore, in the optical glass of the present embodiment, the content of MgO is set in the range of 0% or more and 10% or less. From the same point of view, the content of MgO in the optical glass of the present embodiment is preferably 9% or less, more preferably 8% or less.

<CaO>
In the optical glass of this embodiment, CaO is a component capable of increasing the low viscosity of the glass melt. However, when the content exceeds 10%, the water resistance and low expansion properties deteriorate. Therefore, in the optical glass of the present embodiment, the content of CaO is set in the range of 0% or more and 10% or less. From the same point of view, the CaO content in the optical glass of the present embodiment is preferably 9% or less, more preferably 8% or less.

<SrO>
In the optical glass of this embodiment, SrO is a component that can increase the low viscosity of the glass melt. However, when the content exceeds 5%, the water resistance and low expansion properties deteriorate. Therefore, in the optical glass of the present embodiment, the content of SrO is set in the range of 0% or more and 5% or less. From the same point of view, the content of SrO in the optical glass of the present embodiment is preferably 4% or less, more preferably 3% or less. Note that the optical glass of this embodiment may not contain SrO.

<BaO>
In the optical glass of this embodiment, BaO is a component that can increase the low viscosity of the glass melt. However, when the content exceeds 5%, the water resistance and low expansion properties deteriorate. Therefore, in the optical glass of the present embodiment, the content of BaO is in the range of 0% or more and 5% or less. From the same point of view, the content of BaO in the optical glass of the present embodiment is preferably 4% or less, more preferably 3% or less. Note that the optical glass of this embodiment may not contain BaO.

<ZnO>
In the optical glass of the present embodiment, ZnO is a component capable of enhancing water resistance and low expansion properties without impairing the low viscosity of the glass melt. However, if the content exceeds 15%, the water resistance decreases and the refractive index (nd) increases, making it difficult to produce optical glass having the desired optical constants. Therefore, in the optical glass of the present embodiment, the content of ZnO is set in the range of 0% or more and 15% or less. From the same point of view, the content of ZnO in the optical glass of the present embodiment is preferably 12.5% or less, more preferably 10% or less.

< _TiO2 >
In the optical glass of this embodiment, TiO ₂ is a component that can improve water resistance. However, if the content exceeds 5%, the refractive index (nd) increases, making it difficult to produce optical glass having the desired optical constants. Therefore, in the optical glass of the present embodiment, the content of TiO ₂ is in the range of 0% or more and 5% or less. From the same point of view, the content of TiO ₂ in the optical glass of the present embodiment is preferably 4% or less, more preferably 3% or less.

< _ZrO2 >
In the optical glass of this embodiment, ZrO ₂ is a component capable of enhancing water resistance. However, if the content exceeds 5%, the refractive index (nd) increases, making it difficult to produce optical glass having the desired optical constants. Therefore, in the optical glass of this embodiment, the content of ZrO ₂ is set in the range of 0% or more and 5% or less. From the same point of view, the content of ZrO ₂ in the optical glass of this embodiment is preferably 4% or less, more preferably 3% or less.

<Other ingredients>
The optical glass of the present embodiment may contain other components other than the components described above, such as GeO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ , Bi ₂ O ₃ , Y ₂ O, as long as the purpose is not deviated. ₃ , La ₂ O ₃ , Gd ₂ O ₃ and the like can be contained in small amounts.

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

<Refractive index (nd) and Abbe number (νd)>
The optical glass of this embodiment can have so-called BK type optical constants.
Specifically, the refractive index (nd) of the optical glass of this embodiment is preferably 1.48 or more and 1.54 or less. Further, the refractive index (nd) of the optical glass of the present embodiment is more preferably 1.485 or more, further preferably 1.49 or more, and more preferably 1.535 or less. , 1.53 or less.
On the other hand, the Abbe number (νd) of the optical glass of this embodiment can be 58 or more and 67 or less. Further, the Abbe number (νd) of the optical glass of the present embodiment is more preferably 59 or more, still more preferably 60 or more, more preferably 66 or less, and 65 or less. is more preferred.

<Average coefficient of linear expansion (α _100-300°C )>
The optical glass of this embodiment has low expansibility as described above. Specifically, the optical glass of the present embodiment preferably has an average coefficient of linear expansion (α _{100-300° C.} ) of 80×10 ⁻⁷ /° C. or less, more preferably 78×10 ⁻⁷ /° C. or less. is more preferable, and 76×10 ⁻⁷ /° C. or less is even more preferable.
The above-mentioned "average coefficient of linear expansion (α _{100-300° C.} )" refers to a value measured in accordance with the Japan Optical Glass Industry Standard JOGIS08-2003 "Method for measuring thermal expansion of optical glass".

<Viscosity of Melt>
As described above, the optical glass of this embodiment has a low melt viscosity. Specifically, the optical glass of the present embodiment preferably has a viscosity at 1300° C. of 20 dPa·s or less, more preferably 17.5 dPa·s or less, and further preferably 15 dPa·s or less. preferable.

<Water resistance>
As described above, the optical glass of this embodiment has excellent water resistance. Specifically, the optical glass of the present embodiment has chemical durability ( Water resistance) is preferably 1-4.

<Method for producing optical glass>
Next, a method for manufacturing the optical glass of this embodiment will be described.
Here, the optical glass of the present embodiment may be manufactured according to a conventional manufacturing method without any particular limitation as long as the composition of each component satisfies the ranges described above.
For example, first, as raw materials for each component that can be contained in the optical glass of the present embodiment, oxides, hydroxides, carbonates, nitrates, and the like are weighed in predetermined proportions and sufficiently mixed to obtain a glass preparation raw material. . Next, this raw material is put into a melting vessel (for example, a precious metal crucible) that does not react with glass raw materials, etc., heated to 1200 to 1500° C. in an electric furnace to melt, and stirred appropriately. Next, the glass is clarified and homogenized in an electric furnace, cast into a mold preheated to an appropriate temperature, and then slowly cooled in an electric furnace to remove distortion, thereby producing the optical glass of the present embodiment. be able to. In order to improve the coloration of the glass and eliminate bubbles, a very small amount (for example, an amount of 0.5% or less in the optical glass) of industrially known components such as Sb ₂ O ₃ can be added.

As will be described later, the optical glass of this embodiment can be used as a preform for precision press molding and as a material for optical glass. However, since the optical glass of the present embodiment has a low expansion property, it can be adhered to sealing materials, more specifically, low expansion materials such as ceramics and metal alloys, in addition to the above materials. It can also be used as a sealing material.

(preform for precision press molding)
A preform for precision press molding according to one embodiment of the present invention (hereinafter sometimes referred to as "preform of the present embodiment") will be specifically described below.
Here, the precision press-molding preform is a preformed glass material used in a well-known precision press molding method, that is, a glass preform that is heated and subjected to precision press molding. means a molded body.

Here, precision press molding is also known as mold optics molding, and is a method of forming the optically functional surface of the finally obtained optical element by transferring the molding surface of a press mold. In addition, the optical function surface means a surface of an optical element that refracts, reflects, diffracts, enters and exits the light to be controlled. It corresponds to the functional aspect.

The preform of this embodiment is characterized by using the optical glass described above as a material. As described above, the preform of the present embodiment uses the above-described optical glass as a raw material, and therefore has low expansibility and excellent water resistance.
From the viewpoint of obtaining desired performance, the preform of the present embodiment preferably satisfies the essential requirements regarding the composition of each component already described for the optical glass of the present invention. , it is more preferable to satisfy various requirements that are considered preferable.

The method for producing the preform of this embodiment is not particularly limited. However, the preform of the present embodiment is desirably produced by the following production method, taking advantage of the excellent properties of the optical glass.

A first preform manufacturing method (referred to as "preform manufacturing method I") comprises melting an optical glass as a raw material, flowing out the obtained molten glass to separate a molten glass lump, and separating the molten glass lump. It is a method of molding into a preform in the process of cooling.

A second preform manufacturing method (referred to as "preform manufacturing method II") comprises melting an optical glass as a raw material, molding the obtained molten glass to produce a glass molded body, and manufacturing the molded body. It is a method of processing to obtain a preform.

Preform manufacturing methods I and II are common in that they include a step of obtaining homogeneous molten glass from optical glass as a raw material. In this step, for example, optical glass raw materials prepared by mixing so as to obtain desired properties are placed in a platinum melting vessel, heated, melted, clarified, and homogenized to prepare a homogeneous molten glass. Outflow can be from a tuned platinum or platinum alloy outflow nozzle or outflow pipe. Alternatively, raw materials for optical glass may be roughly melted to produce cullet, and this cullet may be mixed, heated, melted, clarified, and homogenized to obtain homogeneous molten glass, which is discharged from the outflow nozzle or outflow pipe. good.

Here, in the case of producing a small preform or a spherical preform, for example, a method in which molten glass droplets of a desired mass are dropped from an outflow nozzle, received in a mold or the like, and molded into a preform. can be adopted. Alternatively, a method of forming a preform by dripping molten glass droplets of a desired mass from an outflow nozzle into liquid nitrogen or the like can be adopted.
On the other hand, when producing a medium or large sized preform, for example, the glass melt flow is made to flow down from an outflow pipe, the tip of the glass melt flow is received by a preform molding die or the like, and the nozzle of the glass melt flow and the preform molding die are connected. After forming a constricted portion between the preform mold and the preform, the preform mold is rapidly lowered to separate the molten glass flow at the constricted portion due to the surface tension of the molten glass. A method of molding into a preform can be adopted.
All of these methods are classified as dropping methods. And, as described above, since the viscosity of the melt of the optical glass used as the raw material is low, it is possible to suitably carry out these dropping methods.

In order to obtain a preform having a smooth surface free of scratches, stains, wrinkles, surface alterations, etc., for example, a preform having a free surface, air pressure is applied to the molten glass gob on a preform mold or the like to float it. A method of molding into a preform, or a method of molding into a preform by placing molten glass droplets in a medium, such as liquid nitrogen, which is gaseous at normal temperature and normal pressure by cooling to liquid, is used.

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

Air, N ₂ gas, O ₂ gas, Ar gas, He gas, water vapor, etc., can be cited as the gas used when the floating gas is blown onto the preform. Moreover, the wind pressure is not particularly limited as long as the preform can float without coming into contact with a solid such as the mold surface.

Since many precision press-molded products (for example, optical elements) manufactured from preforms have an axis of rotational symmetry, such as lenses, it is desirable that the shape of the preform also has an axis of rotational symmetry. As a specific example, a sphere or one having one axis of rotational symmetry can be shown. As a shape having one axis of rotational symmetry, a shape having a smooth outline without corners or dents in a cross section containing the axis of rotational symmetry, for example, an ellipse whose short axis coincides with the axis of rotational symmetry in the cross section is defined as the outline. A shape in which a sphere is flattened (a shape in which one axis passing through the center of the sphere is determined and the dimension is reduced in the direction of the axis) can also be mentioned.

In the preform production method I, the optical glass is molded in a temperature range in which plastic deformation is possible, so the preform may be obtained by press-molding a glass lump. In that case, the shape of the preform can be set relatively freely, so that it can be approximated to the shape of the desired precision press-molded product. can be concave, one flat and the other convex, one flat and the other concave, or both convex.

In the preform manufacturing method II, for example, after the molten glass is cast into a mold and molded, the distortion of the molded body is removed by annealing, the molded body is cut or cleaved, divided into predetermined dimensions and shapes, and a plurality of glass pieces are obtained. is produced, and the glass piece is polished to have a smooth surface, and a preform made of glass of a predetermined mass can be obtained. The surface of the preform thus produced is also preferably coated with a carbon-containing film before use. Preform manufacturing method II is suitable for manufacturing spherical preforms, flat preforms, and the like that can be easily ground and polished.

In either manufacturing method, the optical glass used has excellent low expansion and water resistance, so it is difficult to produce defective products due to glass cracking, chipping, devitrification, etc., and high-quality preforms can be stably produced. In addition, the mass productivity of the entire optical element manufacturing process can be improved.

Next, a more preferable preform will be described from the viewpoint of further improving the mass productivity of molded articles such as optical elements by precision press molding.

The optical glass of this embodiment provides excellent precision press moldability from the standpoint of the glass material. can be reduced, the time required for press molding can be shortened, and the press pressure can be reduced. As a result, the reactivity between the glass and the molding surface of the molding die is reduced, the above-mentioned defects that occur during precision press molding are reduced, and mass productivity is further enhanced.

Here, a preferable preform when manufacturing a lens by precision press molding a preform has surfaces to be pressed facing opposite directions (surfaces pressed by molding surfaces facing each other during precision press molding). A preform that is a preform and has an axis of rotational symmetry passing through the centers of the two surfaces to be pressed is more preferable. Among these preforms, those suitable for precision press molding of meniscus lenses are preforms in which one of the surfaces to be pressed is convex and the other is concave, flat, or convex if the curvature is smaller than that of the convex surface.

A preform suitable for precision press molding of a biconcave lens is a preform in which one of the surfaces to be pressed is convex, concave, or flat, and the other is convex, concave, or flat.
On the other hand, a preform suitable for precision press molding of a biconvex lens is a preform in which one of the surfaces to be pressed is convex and the other is convex or flat.

In any case, it is preferable that the preform has a shape that more closely approximates the shape of the precision press-molded product.

When a glass melt gob is formed into a preform using a preform mold, the lower surface of the glass on the mold is generally determined by the shape of the molding surface of the mold. On the other hand, the upper surface of the glass has a shape determined by the surface tension of the molten glass and the weight of the glass itself. Here, in order to reduce the amount of deformation of the glass during precision press molding, it is also necessary to control the shape of the upper surface of the glass being molded in the preform mold. The shape of the upper surface of the glass, which is determined by the surface tension of the molten glass and the weight of the glass itself, is a convex free surface. pressure can be applied to Specifically, the upper surface of the glass can be pressed with a mold having a molding surface of a desired shape, or the upper surface of the glass can be molded into a desired shape by applying air pressure. When pressing the upper surface of the glass with the molding die, a plurality of gas ejection ports are provided on the molding surface of the molding die, and gas is ejected from these gas ejection ports to form a gas cushion between the molding surface and the upper surface of the glass, A gas cushion may be used to press the upper surface of the glass. Alternatively, if it is desired to form the upper surface of the glass on a surface having a larger curvature than the free surface, the upper surface of the glass may be formed by generating a negative pressure in the vicinity of the upper surface of the glass so as to raise the upper surface.

Further, the preform is preferably a preform with a polished surface in order to make the shape more similar to the shape of the precision press-molded product. For example, it is preferable to use a preform in which one of the surfaces to be pressed is polished to become a flat surface or a portion of a spherical surface, and the other surface is polished to become a portion of a spherical surface or a flat surface. Here, a part of the spherical surface may be convex or concave, but it is desirable to decide whether it is convex or concave depending on the shape of the precision press-molded product as described above.

Each of the above preforms can be preferably used for molding a lens with a diameter of 10 mm or more, and more preferably used for molding a lens with a diameter of 20 mm or more. Moreover, it can be preferably used for molding lenses having a center thickness exceeding 2 mm.

(optical element)
Hereinafter, an optical element according to one embodiment of the present invention (hereinafter sometimes referred to as "optical element according to this embodiment") will be specifically described.
The optical element of this embodiment is characterized by using the above-described optical glass as a material. As described above, the optical element of the present embodiment uses the optical glass described above as a material, and thus has low expansibility and excellent water resistance.
From the viewpoint of obtaining desired performance, the optical element of the present embodiment preferably satisfies the essential requirements regarding the composition of each component already described for the optical glass of the present embodiment. More preferably, it satisfies the various desirable requirements mentioned above.

The types of optical elements are not limited, but typical ones include lenses such as aspherical lenses, spherical lenses, plano-concave lenses, plano-convex lenses, biconcave lenses, biconvex lenses, convex meniscus lenses, and concave meniscus lenses; microlenses; A lens array; a lens with a diffraction grating; a prism; a prism with a lens function; Examples of the optical element are preferably lenses such as a convex meniscus lens, a concave meniscus lens, a biconvex lens, a biconcave lens, a planoconvex lens, and a planoconcave lens, a prism, and a diffraction grating. Each of the lenses may be an aspherical lens or a spherical lens. An anti-reflection film, a wavelength-selective partial reflection film, or the like may be provided on the surface, if necessary.

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

Here, in precision press molding, it is possible to use a press mold whose molding surface has been preliminarily processed into a desired shape with high precision. A release film may be formed in order to allow the glass to spread well along the surface. Release films include films of noble metals (platinum, platinum alloys), films of oxides (such as oxides of Si, Al, Zr, and Y), films of nitrides (such as nitrides of B, Si, and Al), Examples include carbon-containing films. As the carbon-containing film, a film containing carbon as a main component (a film containing more carbon than other elements when the element content in the film is expressed in atomic %) is desirable. can be exemplified by a carbon film, a hydrocarbon film, or the like. As a method for forming a carbon-containing film, there are known methods such as a vacuum deposition method, a sputtering method, an ion plating method, etc. using a carbon raw material, and a known method such as thermal decomposition using a material gas such as a hydrocarbon. You can use it. Other films can be formed using a vapor deposition method, a sputtering method, an ion plating method, a sol-gel method, or the like.

In addition, in the heating of the press mold and the preform and the precision press molding process, nitrogen gas or nitrogen gas is used to prevent oxidation of the mold surface of the press mold or the mold release film suitably provided on the mold surface. It is preferable to carry out in a non-oxidizing gas atmosphere such as a mixed gas of hydrogen gas. In a non-oxidizing gas atmosphere, the release film, particularly the carbon-containing film, covering the surface of the preform is not oxidized and remains on the surface of the precision press-molded product. This film should be removed eventually, but in order to remove the release film such as the carbon-containing film relatively easily and completely, the precision press-molded product must be placed in an oxidizing atmosphere, such as the air. Just heat it up. The release film such as the carbon-containing film should be removed at a temperature that does not cause deformation of the precision press-molded product due to heating. Specifically, it is preferable to remove a release film such as a carbon-containing film in a temperature range below the glass transition temperature.

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

A first optical element manufacturing method (referred to as "optical element manufacturing method I") includes introducing a preform into a press mold, heating the preform and the press mold together, and performing precision press molding. A method of obtaining an optical element.
The second optical element manufacturing method (referred to as "optical element manufacturing method II") is a method in which a heated preform is introduced into a preheated press mold and subjected to precision press molding to obtain an optical element.

In the optical element manufacturing method I, after supplying a preform between a pair of opposing upper and lower molds whose molding surfaces are precisely shaped, the viscosity of the glass reaches a temperature equivalent to 10 ⁵ to 10 ⁹ dPa s. By heating both the mold and the preform to soften the preform and pressure molding it, the molding surface of the mold can be precisely transferred to the glass. Optical element manufacturing method I is a recommended method when improvement of molding accuracy such as surface accuracy and eccentricity accuracy is emphasized.

In the optical element manufacturing method II, the temperature was raised in advance to a temperature corresponding to 10 ⁴ to 10 ⁸ dPa·s in viscosity of glass between a pair of opposing upper and lower molds whose molding surfaces were precisely shaped. By supplying a preform and pressure-molding it, the molding surface of the mold can be precisely transferred to the glass. Optical element manufacturing method II is a recommended method when productivity improvement is emphasized.

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

After that, the mold and the precision press-molded product are cooled, and when the temperature becomes lower than the strain point, the mold is released and the precision press-molded product is taken out. In order to match the optical properties precisely to desired values, the annealing conditions of the molded product during cooling, such as the annealing rate, may be appropriately adjusted.

Note that the optical element of this embodiment can be manufactured without the press molding process. For example, homogenous molten glass is cast into a mold to form a glass block, which is then annealed to remove distortion and to adjust the optical properties by adjusting the annealing conditions so that the refractive index of the glass reaches a desired value. After that, the glass block is cut or cleaved to form a glass piece, which is further ground and polished to obtain an optical element.

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

As raw materials for each component shown in Tables 1 and 2, oxides, hydroxides, carbonates, nitrates, etc. corresponding to each are vitrified, weighed to 100 g, thoroughly mixed, and placed in a platinum crucible. It was put in and melted in an electric furnace at 1200-1500° C. for 1-2 hours. After that, it was stirred at a suitable time, homogenized, clarified, cast in a mold preheated to an appropriate temperature, and then slowly cooled in an electric furnace to remove distortion, thereby performing Examples 1 to 17 and Optical glasses of Comparative Examples 1 to 12 were obtained. For each optical glass, the refractive index (nd), Abbe number (νd), average coefficient of linear expansion (α _{100-300° C.} ), viscosity at 1300° C., and water resistance were measured according to the following procedures. Tables 1 and 2 show the results.

The refractive index (nd) and Abbe's number (νd) were measured according to the Japan Optical Glass Industry Association standard "JOGIS01-2003 Method for measuring the refractive index of optical glass".

The average coefficient of linear expansion (α _{100-300° C.} ) was measured according to JOGIS08-2003 “Method for Measuring Thermal Expansion of Optical Glass” of the Japan Optical Glass Industry Association Standard. A smaller value indicates better low-expansion properties.

The measurement of the viscosity at 1300°C was performed by the rotating cylinder method. Specifically, a platinum cylinder was immersed in a glass melt at 1300° C., and the viscosity was obtained from the rotational force (torque) received by the cylinder when the cylinder was rotated.

The measurement of water resistance is performed in accordance with the Japan Optical Glass Industry Standard JOGIS06-2009 "Method for measuring chemical durability of optical glass (powder method)", and evaluates whether it corresponds to any of classes 1 to 6. did. The smaller the class number, the better the water resistance.

As can be seen from Table 1, all of the optical glasses of Examples 1 to 17 according to the present invention have an average coefficient of linear expansion (α _{100-300° C.} ) of 80×10 ⁻⁷ /° C. or less, which is low expansion. Viscosity at 1300° C. is 20 dPa·s or less, and water resistance grade is 1 to 4, indicating excellent water resistance.

On the other hand, from Table 2, the optical glass of Comparative Example 1 has a large average coefficient of linear expansion (α _{100-300° C.} ) and is inferior in water resistance. This is believed to be due to the too low content of SiO ₂ .
Also, the optical glass of Comparative Example 2 has a high viscosity at 1300°C. This is probably due to the excessive SiO ₂ content.
Further, the optical glass of Comparative Example 3 has a large average coefficient of linear expansion (α _{100-300° C.} ). It is considered that this is due to the content of B ₂ O ₃ being too small.
Further, the optical glass of Comparative Example 4 has a water resistance class of 5, and is inferior in water resistance. It is believed that this is due to the excessive B ₂ O ₃ content.

In addition, the optical glass of Comparative Example 5 was devitrified during production, so various measurements could not be performed. It is considered that this is due to the absence of Al ₂ O ₃ .
Moreover, the optical glass of Comparative Example 6 has a high viscosity at 1300°C. This is probably due to the excessive Al ₂ O ₃ content.
Moreover, the optical glass of Comparative Example 7 has a high viscosity at 1300°C. It is believed that this is due to the total content of Li ₂ O, Na ₂ O and K ₂ O being too low.
The optical glass of Comparative Example 8 has a large average coefficient of linear expansion (α _{100-300° C.} ) and has a water resistance class of 5, which means that it is inferior in water resistance. It is believed that this is due to the total content of Li ₂ O, Na ₂ O and K ₂ O being too high.

Further, the optical glass of Comparative Example 9 has a large average coefficient of linear expansion (α _100-300°C ) and a high viscosity at 1300°C. This is probably because the mass ratio represented by B ₂ O ₃ /(SiO ₂ +Al ₂ O ₃ ) is too small.
Moreover, the optical glass of Comparative Example 10 has a water resistance class of 5, and is inferior in water resistance. This is probably because the mass ratio represented by B ₂ O ₃ /(SiO ₂ +Al ₂ O ₃ ) is too large.
Further, the optical glass of Comparative Example 11 has a large average coefficient of linear expansion (α _100-300°C ) and a high viscosity at 1300°C. This is probably because the content of B ₂ O ₃ is too small, the mass ratio represented by B ₂ O ₃ /(SiO ₂ +Al ₂ O ₃ ) is too small, and the like.
The optical glass of Comparative Example 12 has a large average coefficient of linear expansion (α _100-300°C ) and a high viscosity at 1300°C. This is probably because the SiO ₂ content is too large, the mass ratio represented by B ₂ O ₃ /(SiO ₂ +Al ₂ O ₃ ) is too small, and the like.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an optical glass having a low melt viscosity, a low expansion property, and excellent water resistance, as well as a precision press-molding preform and an optical element using the optical glass. can.

Claims (6)

in % by mass,
SiO ₂ : 30% or more and 45 % or less,
B ₂ O ₃ : 25% or more and 38% or less,
Al ₂ O ₃ : 2% or more and 12% or less,
Li ₂ O: 0% or more and 5% or less,
Na ₂ O: 0% or more and 12% or less,
K ₂ O: 0% or more and 10% or less,
MgO: 0% or more and 10% or less,
CaO: 0% or more and 10% or less,
SrO: 0% or more and 5% or less,
BaO: 0% or more and 5% or less,
ZnO: 0% or more and 15% or less,
TiO ₂ : 0% or more and 5% or less and ZrO ₂ : having a composition consisting only of 0% or more and 5% or less,
The mass ratio represented by B ₂ O ₃ /(SiO ₂ +Al ₂ O ₃ ) is 0.53 or more and 0.72 or less, and
An optical glass having a total content of Li ₂ O, Na ₂ O, and K ₂ O of 6% or more and 17% or less,
An optical glass characterized by having an average coefficient of linear expansion (α _{100-300° C.} ) of 80×10 ⁻⁷ /° C. or less as measured according to JOGIS08-2003 of the Japan Optical Glass Industry Association Standard. The optical glass according to claim 1, which has a viscosity of 20 dPa·s or less at 1300°C. 3. The optical glass according to claim 1, which has a water resistance grade of 1 to 4 as measured according to JOGIS06-2009 of the Japan Optical Glass Industry Association. 4. The optical glass according to claim 1, which has a refractive index (nd) of 1.48 or more and 1.54 or less and an Abbe number (νd) of 58 or more and 67 or less. A preform for precision press molding, characterized in that the optical glass according to any one of claims 1 to 4 is used as a raw material. An optical element characterized by using the optical glass according to any one of claims 1 to 4 as a material.