JP4511221B2 - Precision press molding preform manufacturing method and optical element manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a precision press-molding preform used when producing a glass optical element or the like by precision press molding, and a method for producing an optical element for precision press-molding the preform.

  With the widespread use of digital cameras and camera-equipped mobile phones, there is an increasing demand for glass optical elements such as aspheric lenses that constitute an imaging optical system. In addition, with the widespread use of DVD devices and personal computers, there is an increasing demand for small glass lenses that guide light beams for reading and writing data on optical recording information recording media.

As a method for manufacturing such a glass optical element with high productivity with high accuracy, there is a glass precision press molding method (also referred to as a mold optics molding method).
In the precision press molding method, a glass preform having a predetermined shape and weight, a smooth surface and high internal quality is produced. Then, the preform is heated and precision press-molded to mold the optical element.
Looking back at the production of optical elements back to the production of glass materials, it is necessary to increase the productivity of preforms in order to improve productivity. Incidentally, as a method for producing a preform with high productivity, there is a method called a hot preform molding method as disclosed in Patent Document 1. In this method, a molten glass that does not contain bubbles and is made homogeneous, flows out from a heat-resistant nozzle called an outflow nozzle at a constant flow rate, and a molten glass lump of a predetermined weight is separated from the outflowing molten glass stream. The preform is formed in the process of cooling the molten glass lump. In the hot preform molding method, it is not necessary to cut or polish the glass block, so the process can be simplified, and if the molten glass lump is separated under certain conditions, a large amount of preform with a certain weight can be obtained. Can also be made. Further, since there is no need for machining, there is a feature that glass waste such as sludge can be dispensed with.

As described above, the hot preform molding method is an excellent method, but the surface of the high-temperature glass lump that eventually becomes the preform surface is exposed to the atmosphere for a long time, so the components in the glass volatilize and the surface. May change, or the surface composition of the glass block may change slightly, resulting in uneven refractive index called surface striae. A preform containing such a defect becomes a defective product because defects remain in the molded product when precision press molding is performed. In particular, when a glass containing a readily volatile component such as fluorine, boric acid or alkali metal oxide is formed, there is a problem that defective products are particularly likely to occur.
Japanese Examined Patent Publication No. 7-51446

  The present invention has been made to solve the above-described problems, and a method for producing a precision press-molding preform for hot-forming a high-quality preform with high productivity, and using the preform. Another object of the present invention is to provide a method for producing a high-quality glass optical element with high productivity.

Means for achieving the object of the present invention is as follows.
[Claim 1] A precision press molding process including a step of separating a predetermined amount of glass from the molten glass flowing out to form a glass lump, and forming the glass lump while floating by applying wind pressure. In the manufacturing method of renovation,
By continuously supplying a non-oxidizing gas containing a carbon-containing compound to a space where the molten glass flows out and separates the glass , at least the molten glass flows and glass is separated from the non-oxidizing atmosphere containing the carbon-containing compound. A method for producing a precision press-molding preform, characterized in that it is carried out in-house.
[2] The method for producing a precision press-molding preform according to [1], wherein the glass is any one of fluorine-containing glass, boric acid-containing glass and alkali metal oxide-containing glass.
[Claim 3] In the method of manufacturing an optical element including a step of heating a glass preform and precision press molding,
A method for producing an optical element, comprising: producing a preform by the production method according to claim 1 or 2; and precision-pressing the produced preform.
[4] The method for producing an optical element according to [3], wherein a preform is introduced into a press mold, the mold and the preform are heated together, and precision press molding is performed.
[5] The method for producing an optical element according to [3], wherein a preheated preform is introduced into a press mold and precision press molding is performed.

  According to the method for producing a precision press-molding preform of the present invention, the generation of surface striae in hot forming and the deterioration of the quality of the glass surface caused by the reaction of moisture in the atmosphere with the glass surface are prevented. Simple preforms can be manufactured. Furthermore, according to the method for producing an optical element of the present invention, the preform produced by the above method is heated and precision press-molded, so that a high-quality optical element can be produced with high productivity.

Hereinafter, the present invention will be described in more detail.

(Precision press molding preform manufacturing method)
The method for producing a precision press-molding preform according to the present invention includes a step of separating a predetermined amount of glass from a molten glass flowing out to form a glass lump, and molding the glass lump to obtain a preform. In the method for producing a preform for use, at least the outflow of the molten glass and the separation of the glass are performed in an atmosphere containing a carbon-containing compound.
Here, the “press-forming preform” is a glass molded body that is heated and softened for use in press molding, and is made of glass having a required weight corresponding to the weight of the press-formed product. The shape is formed so as to be suitable for press molding, and examples thereof include a spherical shape, a flat spherical shape, and a spheroid. As a preferable shape, one having a rotationally symmetric axis and having a smooth contour line having no corners or depressions in a cross section including the rotationally symmetric axis, for example, an ellipse whose short axis coincides with the rotationally symmetric axis in the cross section. The line can be mentioned. Further, as shown in FIG. 1, a line connecting a point on the contour of the preform in the cross section and a center of gravity G of the preform on the rotational symmetry axis, and a tangent that touches the contour at the point on the contour. When the angle of one of the angles is θ, when the point moves on the contour starting from the point a on the rotational symmetry axis, θ monotonically increases from 90 ° and subsequently monotonously decreases. Thereafter, a shape that increases monotonically and becomes 90 ° at the other point b where the contour line intersects the rotational symmetry axis is further preferable. In an arbitrary cross section including the rotational symmetry axis, it is desirable that the angle θ is as described above.
“Precision press molding” is also called a mold optics molding method as described above, and is a method of forming the shape of an optical functional surface by press molding. Details thereof will be described later.

The precision molding preform manufacturing method of the present invention is characterized in that at least the molten glass is discharged and the glass is separated in an atmosphere containing a carbon-containing compound. In this way, at least the outflow of molten glass and the separation of glass are performed in an atmosphere containing a carbon-containing compound, thereby preventing the occurrence of surface striae and the reaction between moisture contained in the atmosphere and the glass surface, and high quality. Can be obtained. This is because when the molten glass is discharged and the glass is separated in an atmosphere containing a carbon-containing compound, the carbon-containing compound is thermally decomposed on the high-temperature glass surface, and carbon is deposited on the surface of the glass lump. By coating the surface with a carbon film, volatilization of easily volatile components contained in the glass can be prevented, and the occurrence of striae due to volatilization can be reduced. This is thought to be because the reaction on the surface can be prevented. If the entire surface is covered with the carbon film until the volatile component is cooled to a temperature at which the volatile component does not volatilize, striae due to volatilization of the volatile component can be prevented. The temperature at which the readily volatile component does not volatilize depends on the composition of the raw glass. For example, when fluorine-containing glass is used as the raw glass, for example, 500 ° C. or lower, and when boric acid-containing glass is used, for example, 600 ° C. or lower, alkaline When the metal oxide-containing glass is used, it is sufficient that the entire surface is covered with the carbon film until the glass block is cooled to a temperature of 700 ° C. or lower, for example. In addition, it is preferable that the atmosphere at the time of shaping | molding a glass lump and obtaining a preform is also the atmosphere containing the above-mentioned carbon containing compound. Although the shape of the glass changes in the process of forming the glass block into a preform, the entire surface of the glass can always be covered with the carbon film by setting the forming atmosphere as described above.
The carbon film on the surface thus formed can be removed by annealing the preform in an atmosphere containing oxygen (for example, air). Moreover, you may utilize as a mold release film for improving the mold release property at the time of precision press molding, without removing.

The atmosphere containing the carbon-containing compound in the method may be a hydrocarbon gas-containing atmosphere. As the hydrocarbon gas, acetylene, xylene, methane, ethane, propane, butane, or the like can be used. In addition, when an active gas such as oxygen is present, the hydrocarbon gas is decomposed before being thermally decomposed on the glass surface. Further, when H ₂ O or the like generated by the reaction comes into contact with the glass surface, it has an undesirable effect on the glass surface such as unevenness and striae. Therefore, the atmosphere containing the carbon-containing compound is preferably a non-oxidizing atmosphere. Specifically, an atmosphere in which a hydrocarbon gas is mixed with an inert gas (such as nitrogen or argon) is preferable. The mixing ratio (volume ratio) between the hydrocarbon gas and the inert gas can be, for example, hydrocarbon gas: inert gas = 100: 0 to 1: 1000. When using liquid hydrocarbons at room temperature such as xylene, an inert gas is bubbled into the liquid to create a mixed gas of hydrocarbon gas and inert gas, and the mixed gas is supplied as an atmosphere. Good. The hydrocarbon gas concentration in the atmosphere is preferably 1000 ppm or more.

  The temperature of the atmosphere containing the carbon-containing compound is desirably not too high, and specifically, it is preferably 400 ° C. or lower. If the atmospheric temperature is too high, the carbon-containing compound is decomposed before thermal decomposition on the glass surface, adheres to the glass as carbon fine particles, and causes surface irregularities. Moreover, it is preferable to apply the method of this invention to the glass whose glass forming temperature exceeds 500 degreeC. By applying to such a glass, formation of a carbon film by the thermal decomposition of the carbon-containing compound on the glass surface proceeds well.

  In the method of the present invention, a hydrocarbon gas or a gas containing a hydrocarbon gas (for example, a mixed gas of a hydrocarbon gas and an inert gas) can be introduced into the container by continuous supply (flow). By introducing the gas in a flow, it is possible to obtain an effect of removing by-products generated by thermal decomposition from the atmosphere.

Next, a process of forming a glass lump from the flowing molten glass and forming the glass lump to obtain a preform will be described.
First, in order to form a glass lump, a sufficiently clarified and homogenized molten glass is prepared, and the molten glass is discharged from the pipe at a constant flow rate. Then, a desired amount of glass is separated from the molten glass flowing out. As a separation method, a method of dropping molten glass from a pipe and separating it into a desired amount of glass droplets (referred to as a dropping method), a tip of the molten glass flow flowing out of the pipe is supported by a support, and the glass flow A method of making a constriction between the pipe side and the tip of the glass, then lowering the support rapidly and separating the glass on the tip side from the constriction (referred to as a descending cutting method), cutting the molten glass flow flowing out of the pipe There is a method of cutting with a blade and separating glass having a desired weight (referred to as a mechanical cutting method). By keeping the glass outflow rate from the pipe per unit time constant, a glass lump of equal weight can be obtained if the separation interval is constant.

Next, the separated glass is received by a mold or temporarily supported by a support, and then transferred to a mold and molded to obtain a preform having a predetermined shape. As a forming method, using a method of forming while floating on a mold by applying wind pressure (referred to as a floating forming method), a smooth surface free from scratches, dirt, surface alteration, etc. However, it is preferable because a preform which is a surface formed by solidifying molten glass or a preform whose entire surface is a free surface can be produced. In addition, “the surface formed by solidifying the glass whose entire surface is melted” may be a portion where the mold surface is transferred in contact with the mold for molding, "The whole surface is a free surface" means that there is no portion where the mold surface is transferred by contact with the mold.
For example, using a molding die having a recess provided with a port for jetting the gas for applying the wind pressure (called floating gas) to the bottom, the glass lump is supplied to the recess, and the glass lump is moved up and down in the recess. The spherical preform can also be formed by rotating it. Also, a recess or recess having a large number of gas ejection ports is formed of a porous body, and a floating gas is ejected from the entire inner surface of the recess to float the glass, and a preform is formed into a shape along the shape of the recess. You can also.
After being molded on the mold, the preform can be taken out without being deformed by being cooled to a glass transition temperature or a temperature lower than the above temperature and then taken out from the mold.

As described above, according to the method for producing a precision press-molding preform of the present invention, a precision press-molding preform with reduced surface striae can be obtained. In order to further reduce the surface striae, the gas flows along the outer periphery of the outflow pipe and in the direction of the glass outflow (vertically below) to reduce the wetting of the glass to the outer periphery of the outflow pipe, In order to prevent water vapor from reacting with the high-temperature glass surface, it is preferable that the molten glass flows out in a dry atmosphere. However, in order to perform outflow of molten gas and separation of glass in an atmosphere containing a carbon-containing compound, the gas used here is the hydrocarbon gas described above or a mixed gas of hydrocarbon gas and inert gas. It is preferable that
The method of flowing gas along the outer periphery of the pipe is also effective in reducing the weight of the molten glass droplet obtained by the dropping method. In the dropping method, dripping occurs when the balance between the gravity acting on the glass and the surface tension at which the glass tries to stay at the tip of the pipe is lost and the gravity increases. By constantly flowing a gas at a constant flow rate along the pipe periphery as described above, the downward force applied to the glass is increased, so that it is possible to drop a glass drop having a smaller weight than when no gas is flowed. it can. In addition, it is preferable to flow gas so that it may become a laminar flow near the pipe front-end | tip all over a pipe periphery.

  In addition, when eluting molten glass from an outflow nozzle, the problem that a molten glass wets to the outer peripheral part of a nozzle tip may generate | occur | produce. The wet glass is taken in by the newly flowing glass over time. As described above, when the glass wets or the wet glass is taken into the outflow glass, it is difficult to separate a predetermined amount of the molten glass lump, and the weight of the separated glass lump changes. Further, the wet glass is exposed to the atmosphere at a high temperature for a longer time than the glass that is molded immediately after flowing out. Therefore, the volatile component in the glass volatilizes and becomes a deteriorated glass, and when it is taken into the outflowed glass, the quality of the preform is deteriorated. Therefore, in the method for producing a precision press-molding preform of the present invention, as a nozzle for causing molten glass to flow out, at least the outer peripheral surface in the vicinity of the outlet is a non-oxide ceramic, specifically, silicon carbide, carbon, It is preferable to use a nozzle made of either silicon nitride or silicon. By using such a nozzle, wetting of the outflow glass can be suppressed and the above problem can be avoided. Moreover, it is preferable that the non-oxide ceramic constituting at least the outer peripheral surface in the vicinity of the outlet has heat resistance enough to withstand long-time glass outflow.

  In the nozzle, the whole nozzle may be formed of a non-oxide ceramic, or the tip of the nozzle (a portion including the outflow port where the molten glass may get wet) may be formed of a non-oxide ceramic. . Alternatively, the entire nozzle may be formed of platinum or a platinum alloy, and a coat made of the above material may be provided on the outer peripheral surface near the outflow port. All the materials are materials that are difficult to wet with molten glass. In the nozzle, silicon carbide is most preferable as a material constituting at least the outer peripheral surface in the vicinity of the outlet (hereinafter referred to as an outer peripheral surface constituent material), and carbon is then preferable.

In addition, when coat | covering an outer peripheral surface constituent material to a nozzle outer peripheral surface, it is preferable that the thickness shall be 10 nm or more, and it is preferable to set it as 100 nm or more. However, if the film thickness becomes too thick, the coating may be damaged due to a large thermal stress, so the film thickness is preferably 3 mm or less.
The nozzle can be used by being attached to a platinum or platinum alloy pipe connected to a container for storing molten glass by means such as welding.

Moreover, you may form the nozzle inner peripheral surface which is a flow path of molten glass with non-oxide ceramics, specifically, any of silicon carbide, carbon, silicon nitride, and silicon. Hereinafter, the material forming the inner peripheral surface is referred to as an inner peripheral surface constituting material.
The molten glass outflow nozzle having an inner peripheral surface made of the inner peripheral surface constituent material can obtain the following effects regardless of whether or not the outer peripheral surface constituent material is provided on the outer peripheral surface. When glass with low viscosity at the time of outflow is discharged, the glass is discharged at a temperature suitable for forming by lowering the outflow temperature. In addition to such properties, glass having a property of being easily devitrified is formed by flowing out at a temperature slightly higher than the liquidus temperature. However, if the outflow temperature fluctuates for some reason and falls below the liquidus temperature, the glass may be devitrified before flowing out, resulting in a decrease in fluidity and clogging. Since the nozzle portion has the lowest temperature in the glass flow path, glass clogging often occurs in the nozzle. Therefore, by taking advantage of the property that non-oxide ceramics are difficult to wet with glass, the inner peripheral surface of the nozzle is made of non-oxide ceramic to reduce the trouble of clogging in the nozzle even if the glass has poor fluidity. it can. Such a nozzle can be made by coating the inner peripheral surface constituting material on the inner peripheral surface of a platinum alloy nozzle, for example. The nozzle may be formed of a non-oxide ceramic at least on the outer peripheral surface in the vicinity of the outlet. In that case, at least the outer peripheral surface in the vicinity of the outlet may be coated with the inner peripheral surface constituent material on the inner peripheral surface of the nozzle made of non-oxide ceramic, or the outer peripheral surface constituent material and the inner peripheral surface constituent material may be the same. As a material, the nozzle may be composed of the material.

  When the surface of the glass block thus obtained is magnified and observed with an optical microscope, striae may be observed over the entire surface of the glass block. This striae is a surface stria localized near the surface. The alteration layer on the surface of the glass lump, such as burns, is limited to a portion having a depth of 0.1 μm or less from the surface, but the surface striae have reached a depth that can be recognized by visual observation using an optical microscope. It is desired to etch from the glass lump surface to a depth of at least 0.5 μm or more. A more preferable depth is 1 μm or more, a further preferable depth is 10 μm or more, a still more preferable depth is 20 μm or more, and a particularly preferable depth is 50 μm or more. Etching is performed until the entire glass is optically homogeneous without striae and to a depth where a glass mass of the desired weight is obtained. Although there is no particular limitation on the upper limit of the etching depth, it is not necessary to remove even optically homogeneous glass, so a depth of up to 5 mm may be used as a guide. Alternatively, the upper limit of the etching depth may be managed by the ratio of preform weight / glass lump weight. In that case, the ratio of preform weight / glass lump weight is desirably 80% or more, and more desirably 85% or more. As described above, since the weight of the glass lump is slightly reduced by the etching, it is preferable to form a glass lump having a weight obtained by adding the above weight reduction to the target weight so that a preform having a desired weight can be obtained.

  Since the glass lump after etching has a smooth surface and is optically homogeneous, the glass lump after etching can be used as a preform for precision press molding. Note that if the hot-formed glass lump is etched without annealing, the glass may crack due to residual stress. Therefore, it is desirable to anneal or remove the glass lump before etching to reduce or remove the residual stress inside the glass. Annealing may be performed while maintaining the glass block at a temperature near the annealing point. Phosphate glass has a large coefficient of thermal expansion, and stress tends to remain in the process of forming a glass block. Therefore, the annealing is effective for preventing cracks during etching.

Etching on the surface of the glass lump uniformly removes the entire surface of the glass lump, so that the shape of the preform is similar to that of the glass lump. Therefore, a preform having a desired shape can be easily obtained by forming the glass block into a similar shape to the preform.
As optical elements manufactured by precision press molding, an optical element having a shape having one rotational symmetry axis such as a lens is overwhelmingly many. Therefore, the shape of the preform is also desired to be a spherical shape or a shape having one rotationally symmetric axis (for example, a spheroid, a shape obtained by extending a sphere in a certain axial direction, a crushed shape, or the like). In order to produce a preform having such a shape, a glass lump having a shape similar to the target preform shape may be formed and etched. If the method of the present invention is not used, the striae reach even deeper layers, increasing the amount that must be removed by the etching process. In contrast, by using the method of the present invention, even if surface striae occur, the portion that must be removed by etching or the like can be minimized.

  As described above, the method for producing a precision press-molding preform of the present invention can prevent volatilization of easily volatile components and prevent occurrence of surface striae by providing a carbon film coat on the entire surface of the glass lump. Therefore, it is particularly preferable to apply to a glass containing an easily volatile component. Examples of such glass include fluorine-containing glass, boric acid-containing glass, and alkali metal oxide-containing glass. Below, these glass is demonstrated.

(Fluorine-containing glass)
Examples of the fluorine-containing glass used in the present invention include fluorophosphate glass, fluorine-containing silicate glass, fluorine-containing borosilicate glass, and fluorine-containing borate glass.
Among these, fluorophosphate glass is a very important glass as a material for a low dispersion glass preform having an Abbe number (νd) of 65 or more. Further, by containing copper ions, near-infrared absorption characteristics can be imparted, and the glass is also useful as a color correction filter material for semiconductor imaging devices.
Fluorophosphate glass has a relatively low glass transition temperature and is suitable for precision press molding. From the viewpoint of precision press formability and hot formability, and from the viewpoint of imparting low dispersion characteristics with an Abbe number (νd) of 65 or more, a preferred fluorophosphate glass has Al, Ca, and Sr as cation components as anion components. A particularly preferred fluorophosphate glass (hereinafter referred to as “glass A”) contains F and O as essential components. Al (PO ₃ ) ₃ 0 to 20%, Ba (PO ₃ ) _{2 in} terms of mol%. _{0~30%, Mg (PO 3)} 2 0~30%, Ca (PO 3) 2 0~30%, Sr (PO 3) 2 0~30%, Zn (PO 3) 2 0~30%, NaPO ₃ 0-15%, AlF ₃ 2-45%, ZrF ₄ 0-10%, YF ₃ 0-15%, YbF ₃ 0-15%, GdF ₃ 0-15%, BiF ₃ 0-15%, LaF _{3 0~10%, MgF 2 0~20%,} CaF 2 2~45%, Sr _{2 2~45%, BaF 2 0~20,} ZnF 2 0~30%, LiF 0~10%, 0~15% NaF, KF 0~15%, Li 2 O 0~5%, Na 2 O 0~ _{5%, K 2 O 0~5%} , 0~5% MgO, CaO 0~5%, SrO 0~5%, BaO 0~5%, is intended to include 0 to 5% ZnO.

The composition range will be described in detail. The content of each component is expressed in mol% unless otherwise specified.
Al (PO ₃ ) ₃ is a component constituting a glass network structure, and is the most important component for enhancing the weather resistance of glass. If the content is 20% or less, the glass is high in thermal stability, and the liquid phase temperature and optical properties (low dispersibility) are also preferable. Therefore, the introduction amount is preferably 20% or less. More preferably, it is 0.5 to 15% of range.

Ba (PO ₃ ) ₂ , Mg (PO ₃ ) ₂ , Ca (PO ₃ ) ₂ , and Sr (PO ₃ ) ₂ , as well as Al (PO ₃ ) ₃ , are components that constitute a glass network structure. It is an important component for improving the weather resistance of glass. If the content exceeds 30%, the dispersion of the glass becomes high, and the weather resistance tends to deteriorate due to an increase in P ₂ O ₅ . Therefore, the amount of each introduced is preferably 30% or less. A more preferable content of each component of Ba (PO ₃ ) ₂ , Mg (PO ₃ ) ₂ , Ca (PO ₃ ) ₂ , and Sr (PO ₃ ) ₂ is in the range of 0 to 25%. In order to obtain a desired optical constant, the total amount of the components (Mg (PO ₃ ) ₂ + Ca (PO ₃ ) ₂ + Sr (PO ₃ ) ₂ + Ba (PO ₃ ) ₂ ) should be 35% or less. Is preferable, and it is more preferable to set it as 32% or less.

Zn (PO ₃ ) ₂ is important as a component for improving the stability of glass. If it is introduced in excess of 30%, the dispersion of the glass tends to increase and the durability tends to deteriorate. Therefore, an introduction amount of 30% or less is desirable.

NaPO ₃ is a component that improves the stability of the glass and improves the optical properties. In order to obtain high durability, the introduction amount is desirably 15% or less.

AlF ₃ is a component that improves the stability of the glass and lowers the dispersion. The introduction amount is preferably in the range of 2 to 45%, more preferably in the range of 4 to 40%. If the content of AlF ₃ is 45% or less, the stability and solubility of the glass is high, and if it is 2% or more, desired optical characteristics can be obtained.

ZrF ₄ is a component that constitutes a network structure of glass, and is a component that improves stability and durability. However, in order to obtain desired optical characteristics and stability, the introduction amount is desirably 10% or less.

YF ₃ , YbF ₃ , GdF ₃ , BiF ₃ and LaF ₃ can obtain a high effect of improving devitrification resistance by adding a small amount. However, if the amount of YF ₃ , YbF ₃ , GdF ₃ , or LaF ₃ exceeds 15%, 15%, 15%, 15%, 10%, respectively, the glass becomes unstable on the contrary, and it tends to devitrify. The introduction amounts are desirably suppressed to 0 to 15%, 0 to 15%, 0 to 15%, 0 to 15%, and 0 to 10%, respectively. More preferably, the content of YF ₃ 0 to 12%, and the content of YbF ₃ 0 to 12%, and the content of GdF ₃ 0 to 10%, and the content of BiF ₃ is 0-10%, LaF ₃ The content of is 0 to 7%, and more preferably, the content of GdF ₃ is 0 to 8%.

MgF ₂ is a component for reducing the dispersion of glass. However, if it is introduced in excess of 20%, the glass may become unstable, so the content is preferably 20% or less.

CaF ₂ and SrF ₂ are important components for achieving low dispersion while maintaining devitrification resistance. In particular, CaF ₂ plays a role of strengthening the glass structure in combination with AlF ₃ and is an essential component for stabilizing the glass. If the introduction amount of each of CaF ₂ and SrF ₂ is 2% or more, sufficient glass stability can be obtained and a desired optical constant can be obtained. If both CaF ₂ and SrF ₂ are 45% or less, the stability of the glass can be maintained. Therefore, the amounts of CaF ₂ and SrF ₂ introduced are both preferably in the range of ₂ to 45%, more preferably 5 to 40% for CaF ₂ and ₃ to 35% for SrF ₂ .

BaF ₂ is effective in stabilizing the glass and increasing the durability. In order to maintain the stability of the glass, the introduction amount is desirably 20% or less.

ZnF ₂ is effective in improving durability and reducing dispersion. In order to maintain the glass stability, the amount introduced is preferably 30% or less.

  LiF, NaF, and KF have the effect of improving the devitrification resistance and dispersibility of the glass by adding a small amount. However, due to excessive introduction, the stability of the glass deteriorates rapidly and the durability tends to deteriorate. The introduction amounts of LiF, NaF, and KF are preferably 0 to 10%, 0 to 15%, and 0 to 15%, respectively. More preferable amounts of LiF, NaF, and KF are 0 to 5%, 0 to 10%, and 0 to 10%, respectively.

Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO, BaO, and ZnO are not essential components of glass A, but the effect of improving the stability, weather resistance, and durability of glass by introducing a small amount. There is. However, since there is a possibility that the melting property of the glass is deteriorated or the dispersibility is deteriorated due to excessive introduction, each introduction amount is set to Li ₂ O 0 to 5%, Na ₂ O 0 to 5%, K ₂ O. It is preferable to set it as 0-5%, MgO 0-5%, CaO 0-5%, SrO 0-5%, BaO 0-5%, ZnO 0-5%. More preferably, Li ₂ O 0-4%, Na ₂ O 0-4%, K ₂ O 0-4%, MgO 0-4%, CaO 0-4%, SrO 0-4%, BaO 0-4. %, ZnO 0 to 4%.

  In addition to the above components, a small amount of a compound such as Cl or Br can be introduced for the purpose of defoaming or adjusting the optical constant. However, it is desirable not to introduce a lead compound or an arsenic compound in consideration of environmental impact.

  Copper-containing fluorophosphate glass is also preferable as the glass used in the present invention. By introducing copper oxide based on fluorophosphate glass, near infrared absorption characteristics can be imparted. An optical element having near-infrared absorption characteristics can also be produced by precision press-molding a preform made of the above copper-containing fluorophosphate glass. Examples of the glass serving as the base include the glass A. Such an optical element can also be used as a color correction filter for a semiconductor image sensor such as a CCD or CMOS. For example, it can be formed into a thin plate to form the above filter, or a diffraction grating can be used to form an optical low-pass filter, or a lens can be formed into an optical element having both a color correction filter and a lens function, or can be diffracted on the lens surface. An optical element having both an optical low-pass filter function with a grating function, a lens function, and a color correction filter function can be provided.

Glass A is stable as glass. The glass melt is poured into a 40 × 70 × 15 mm carbon mold, allowed to cool to the glass transition temperature, annealed at the glass transition temperature for 1 hour, and then room temperature. Even if it is further allowed to cool, crystals that can be observed with a microscope do not precipitate.
As the fluorine-containing glass, it is preferable to use a glass having high weather resistance having a haze value of 8% or less after being left for 350 hours under the conditions of a temperature of 60 ° C. and a relative humidity of 90%. By using glass having high weather resistance, the surface of the preform produced by the production method of the present invention can be kept good over a long period of time, and the weather resistance of an optical element produced from the glass can also be improved. . The haze value is an amount defined in Japan Optical Glass Industry Association Standard JOGIS07-1975 “Method for Measuring Chemical Durability of Optical Glass (Surface Method)”.

When molding a glass lump made of glass A, after melting and refining at a temperature of 800 to 1100 ° C., oxygen gas is mixed in the air, in a dry atmosphere, or in an inert gas such as nitrogen or a rare gas such as argon. In this case (in this case, the proportion of oxygen is preferably 0.1 to 50% by volume), for example, glass is flowed out through an outflow pipe made of platinum alloy, and a preform is produced by the above-described float forming method. can do.
By using the glass having the above composition, it is made of an optical glass having an optical constant in the range of refractive index (nd) of 1.42 to 1.6 and Abbe number (νd) of 65 or more, preferably 65 to 97. A preform can be made. Moreover, in the said glass, it is more preferable to use the glass whose yield point (Ts) is 500 degrees C or less from the viewpoint of improving precision press moldability more.

(Boric acid-containing glass)
Examples of the boric acid-containing glass that can be suitably used as the raw glass in the production method of the present invention include glass containing B ₂ O _{3 in an amount} of 10 mol% or more, particularly 15 mol% or more. An example of such a glass, by mol%, as a glass _{component, B 2 O 3 15~60%,} SiO 2 0~40%, La 2 O 3 5~22%, Gd 2 O 3 0~20 %, ZnO 0-45%, Li ₂ O 0-15%, Na ₂ O 0-10%, K ₂ O 0-10%, ZrO ₂ 0-15%, Ta ₂ O ₅ 0-15%, WO _{3 0~15%, Nb 2 O 5 0~10} %, 0~15% MgO, CaO 0~15%, SrO 0~15%, BaO 0~15%, Y 2 O 3 0~15%, Yb 2 O _{3 to} 15%, TiO ₂ 0 to 20%, Bi ₂ O ₃ 0 to 10% glass (hereinafter referred to as glass B). The glass contains B ₂ O ₃ which is a readily volatile component, and since the viscosity of the glass when it flows out is low, surface striae easily occur. However, by applying the production method of the present invention, the easily volatile component can be obtained. Therefore, high quality preform can be molded.

Hereinafter, the content of each component is expressed in mol% unless otherwise specified.
B ₂ O ₃ is an essential component for forming a glass network structure in a boric acid-containing glass. In particular, when a large amount of a high refractive index component such as La ₂ O ₃ or Gd ₂ O ₃ is introduced, it is a component necessary as a main network structure formation for the formation of glass. If the content is 60% or less, highly refractive glass can be obtained, and if it is 15% or more, sufficient stability against devitrification can be obtained, and the meltability is improved. Therefore, the introduction amount is preferably in the range of 15 to 60%. More preferably, it is 20 to 60%, and still more preferably 20 to 45%.

Although SiO ₂ is an optional component, it is a glass network structure-forming component like B ₂ O ₃ . When glass containing a large amount of La ₂ O ₃ or Gd ₂ O ₃ is replaced with the main component B ₂ O ₃ and added in a small amount, the liquidus temperature of the glass is lowered, the high temperature viscosity is increased, and the glass Can be greatly improved. However, if it is introduced in excess of 40%, the refractive index of the glass is lowered, and the glass transition temperature becomes high and precision press molding may be difficult. Therefore, the amount introduced is in the range of 0 to 40%. It is preferable to make it. More preferably, it is 0-30%, More preferably, it is 0-10% of range.

La ₂ O ₃ is a component that increases the refractive index and improves the chemical durability without decreasing the stability of the glass against devitrification and without increasing the dispersion. If the content is 5% or more, the above effect can be sufficiently obtained, and if it is 22% or less, high stability against devitrification can be obtained. Therefore, the introduction amount is preferably in the range of 5 to 22%. More preferably, it is 5 to 20%, and more preferably 7 to 18%.

Gd ₂ O ₃ works like La ₂ O ₃ to increase the refractive index and improve chemical durability without increasing the stability and dispersion of the glass against devitrification. In particular, the stability of the glass can be further improved by allowing La ₂ O ₃ and Gd ₂ O ₃ to coexist. Therefore, the glass B preferably contains Gd ₂ O ₃ . If the content is 20% or less, high stability against devitrification can be obtained, and since the glass transition temperature does not increase and the precision press formability does not deteriorate, the introduction amount is 0-20. % Is preferable. More preferably, it is 1 to 18%, and further preferably 2 to 16%.

  ZnO lowers the melting temperature, liquidus temperature and transition temperature of glass, and is a useful component for adjusting the refractive index. In order to obtain the expected effect, it is preferable to introduce 1% or more. However, if introduced over 45%, the dispersion also increases, the stability against devitrification tends to deteriorate, and the chemical durability tends to decrease, so the amount introduced should be in the range of 0 to 45%. Preferably, the range of 1 to 45% is more preferable, the range of 1 to 32% is further preferable, and the range of 1 to 20% is even more preferable.

Li ₂ O is a component that significantly lowers the glass transition temperature without significantly lowering the refractive index and chemical durability compared to other alkali metal oxide components. In particular, even when introduced in a small amount, a great effect can be obtained, and it is an effective component for adjusting the thermal properties (glass transition temperature, yield point, etc.) of glass. If the content is 15% or less, high stability against devitrification of the glass can be obtained, and since the liquidus temperature is low, the introduction amount is preferably 0 to 15%. It is more preferably 10%, still more preferably in the range of 0.5-15%, even more preferably 1-12%, and even more preferably in the range 2-12%.

Na ₂ O and K ₂ O are components introduced to lower the glass transition temperature. However, since these components all tend to lower the refractive index of the glass, the introduction amount is preferably 0 to 10%. More preferably, it is 0 to 8%.

ZrO ₂ can be used as a component for obtaining a glass having a high refractive index and low dispersion. By introducing a small amount of ZrO ₂ , there is an effect of improving the stability against high temperature viscosity and devitrification without lowering the refractive index of the glass. However, if it is introduced in excess of 15%, the liquidus temperature rises rapidly and the stability against devitrification tends to deteriorate, so the amount introduced is preferably 0 to 15%. More preferably, it is the range of 0-10%, More preferably, it is the range of 1-10%.

Ta ₂ O ₅ can be used as a component imparting high refractive index and low dispersion. By introducing a small amount of Ta ₂ O ₅ , there is an effect of improving the stability against high temperature viscosity and devitrification without lowering the refractive index of the glass. However, if introduced over 15%, the liquidus temperature rises rapidly and the dispersion tends to increase, so the amount introduced is preferably 0 to 15%. More preferably, it is 0 to 10% of range, More preferably, it is 1 to 8% of range.

WO ₃ is a component introduced as appropriate in order to improve the stability and meltability of the glass and improve the refractive index. However, if the amount introduced exceeds 15%, dispersion tends to increase, and the necessary low dispersion characteristics tend not to be obtained. Therefore, the amount introduced is preferably 0 to 15%. More preferably, it is more than 0% and 15% or less, more preferably in the range of 1 to 15%, still more preferably in the range of 1 to 12%.

Nb ₂ O ₅ is a component introduced as appropriate in order to improve the stability and refractive index of the glass. However, if the amount introduced exceeds 10%, the dispersion becomes large and the required low dispersion characteristics may not be obtained. Therefore, the amount introduced is preferably in the range of 0 to 10%. More preferably, it is 0-8%, More preferably, it is 0-5% of range.

MgO, CaO, and SrO are components introduced to lower the liquidus temperature and the transition temperature of the glass, and are particularly effective in glasses into which Nb ₂ O ₅ has been introduced. However, since these components may deteriorate the stability and optical properties of the glass, the introduction amount is preferably 0 to 15%. More preferably, it is the range of 0-12%, More preferably, it is the range of 0-10%.

  BaO is used as a component that imparts high refractive index and low dispersion. When introduced in a small amount, BaO can increase the stability of the glass and improve the chemical durability. However, if introduced more than 15%, the stability of the glass against devitrification is greatly impaired, and the transition temperature and yield point temperature tend to be increased. Therefore, the amount introduced is preferably 0 to 15%. More preferably, it is 0 to 10% of range.

Y ₂ O ₃ and Yb ₂ O ₃ can also be used as components having a high refractive index and low dispersion, and when introduced in a small amount, the stability of the glass can be improved and the chemical durability can be improved. However, if it is introduced in an amount of more than 15%, the stability of the glass against devitrification is greatly impaired, and the transition temperature and yield point temperature tend to increase. Therefore, the amount of introduction is preferably 0 to 15%. More preferably, it is 0 to 10% of range. Y ₂ O ₃ and Yb ₂ O ₃ coexist with La ₂ O ₃ to increase the function of improving glass stability.

TiO _{2 is} also a component that increases the refractive index. However, since glass stability tends to decrease and glass tends to color due to excessive introduction, 0 to 20% is preferably introduced.

Bi ₂ O ₃ functions to increase the refractive index and improve the glass stability. However, since glass tends to be colored by excessive introduction, introduction of 0 to 10% is preferable.

Sb ₂ O ₃ is used as a defoaming agent, but a sufficient effect can be obtained by introduction of 1% or less. Further, when the content of Sb ₂ O ₃ is increased, the molding surface of the press mold may be damaged during precision press molding. Therefore, the introduction amount is preferably in the range of 0 to 1%.

In a glass containing each component of B ₂ O ₃ , SiO ₂ , La ₂ O ₃ , Gd ₂ O ₃ , ZnO, Li ₂ O, ZrO ₂ , Ta ₂ O ₅ , high refractive index and low dispersion (n _d > 1. 75 and ν _d > 25), the total amount of La ₂ O ₃ + Gd ₂ O ₃ is preferably 12% or more, and the total amount is in the range of 12 to 35%. More preferably.

Further, the ratio of the content of La ₂ O ₃ expressed in mol% to the total content expressed in mol% of lanthanoid oxide, Ln ₂ O ₃ (Ln = La, Gd, Yb, Y, Sc) in glass (min Ratio) La ₂ O ₃ / Ln ₂ O ₃ is preferably in the range of 0.3 to 1, and more preferably in the range of 0.4 to 0.9. The reason is as follows.
As the glass for precision press molding, there is a glass containing Li ₂ O, which is a component that renders the glass unstable, while imparting suitability for precision press molding, that is, a low glass transition temperature. In such a glass, glass formation becomes difficult when the amount of lanthanoid oxide that can impart high refractive index and low dispersibility is increased. However, it is possible to obtain a stable glass while increasing the amount of lanthanoid oxide added by making the distribution (above fraction) of La ₂ O ₃ in the lanthanoid oxide 0.3 to 1. Thus, it is possible to stably form a glass even for a glass to which a component such as Li ₂ O that lowers the stability is added. Moreover, by maintaining this ratio, it greatly contributes to the reduction of the liquid phase temperature and the improvement of the high temperature viscosity. When La ₂ O ₃ / ΣLn ₂ O ₃ is set in the above range, it is possible to obtain a much more stable glass compared to a glass having a large ratio even if the total amount of Ln ₂ O ₃ is the same. Furthermore, it is preferable for the above reason that the total content (ΣLn ₂ O ₃ ) of La ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , Y ₂ O ₃ , Sc ₂ O ₃ is 12 to 35%.

GeO ₂ can also be introduced into the glass. Like SiO ₂ , GeO ₂ is a component that stabilizes glass and gives a higher refractive index than SiO ₂ , and is appropriately introduced when achieving a high refractive index. However, it is expensive and the amount introduced is preferably 0 to 8% in order to increase dispersion. More preferably, it is 0 to 1%, and it is more preferable not to introduce.

  Since PbO is a component that is easily reduced, it precipitates due to reduction during precision press molding and becomes cloudy on the surface of the molded product. Moreover, since it is also an environmentally undesirable substance, it is desirable to exclude PbO from the glass.

Lu ₂ O ₃ is less frequently used than other components. Further, since it is a rare substance, it is expensive as an optical glass raw material, and it is a component that is not desired in terms of cost. Moreover, since it is not necessary to introduce it, it is desirable not to introduce Lu ₂ O ₃ .
Moreover, it is desirable not to contain environmentally harmful elements such as cadmium, chromium and mercury, radioactive elements such as thorium, and toxic elements such as arsenic.
In order to adjust physical properties in the glass, the total amount of 5% or less of _{TiO 2, Al 2 O 3,} Ga 2 O 3 , etc. may be introduced.

The glass coexist _{La 2 O 3, Gd 2 O} 3 in the boric acid-containing glass, it is possible to increase the stability of the glass by coexistence effect of La ₂ O ₃ and Gd ₂ O _3, resistance at the time of preform Devitrification is improved. The glass in which La ₂ O ₃ and ZnO coexist can improve the low-temperature softening property suitable for precision press molding without lowering the refractive index due to the effect of ZnO. La ₂ O ₃ , Gd ₂ O ₃ , ZnO coexisting, La ₂ O ₃ , Gd ₂ O ₃ , ZnO, Li ₂ O coexisting, SiO ₂ , La ₂ O ₃ , Gd ₂ O ₃ , ZnO In the case where Li ₂ O, ZrO ₂ and Ta ₂ O ₅ coexist, the coexistence effects of the above components can be obtained.
Any one of the above-mentioned glasses, B ₂ O ₃ , SiO ₂ , ZnO, Li ₂ O, La ₂ O ₃ , Gd ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , WO ₃ , Y ₂ O ₃ More preferably, the total content of Yb ₂ O ₃ is 95% or more, more preferably 99% or more, and still more preferably 100%.

(Alkali metal oxide-containing glass)
An example of an alkali metal oxide-containing glass that can be suitably used as a raw material glass in the production method of the present invention is a glass containing 1 mol% or more of Li ₂ O, Na ₂ O, and K ₂ O in total. Can do. Since Li ₂ O is the component that most improves the low-temperature softening property with respect to a fixed introduction amount (introduction amount expressed in mol%), 1 mol% of Li ₂ O is used as the glass for precision press molding. The glass containing above is preferable.

Surface striae are likely to occur with glass containing readily volatile components, but are also likely to occur with glass with low outflow viscosity. An optical glass having a refractive index (nd) of 1.65 or more and an Abbe number (νd) of 35 or less and containing P ₂ O ₅ , Nb ₂ O ₅ and Li ₂ O corresponds to such a glass. By using such glass as a raw glass in the method for producing a precision press-molding preform of the present invention, a remarkable effect of reducing surface striae can be obtained.

The glass containing P ₂ O ₅ , Nb ₂ O ₅ and Li ₂ O contains P ₂ O ₅ as a glass network structure forming component and Nb ₂ O ₅ as a high refractive index and high dispersion imparting component. Moreover, it contains Li ₂ O as a low-temperature softening imparting component, and realizes a high refractive index characteristic with a refractive index (nd) of 1.65 or more, preferably 1.75 or more.
P ₂ O ₅ is a glass network structure formed as described above, and is a component for imparting stability that can be produced to glass. If 45 mole% or less the content of P ₂ O _5, transition temperature and sag of the glass is low, thereby improving the weather resistance. Moreover, if it is 15 mol% or more, glass which is hard to devitrify and has high stability can be obtained. Therefore, the content of P ₂ O ₅ is preferably in the range of 15 to 45%, and more preferably in the range of 17 to 40 mol%. Hereinafter, the content of each component is expressed in mol% unless otherwise specified.

Nb ₂ O ₅ is a component for imparting characteristics such as high refractive index and high dispersion as described above. If the amount introduced is 35% or less, the glass transition temperature and yield point are lowered, the stability and high-temperature solubility are improved, and foaming and coloring are less likely to occur during precision pressing. Moreover, if the introduction amount is 3% or more, the durability of the glass is high and the required high refractive index can be obtained. Therefore, the introduction amount is preferably in the range of 3 to 35%, and more preferably in the range of 5 to 30%.

As described above, Li ₂ O is the most effective component for lowering the glass transition temperature, and is less likely to lower the refractive index than other alkalis and does not deteriorate durability. If the amount introduced is 2% or more, the transition temperature can be lowered, and if it is 35% or less, the stability of the glass is high and the durability is improved. Therefore, the amount of Li ₂ O introduced is preferably in the range of 2 to 35%. More preferably, it is 5 to 30% of range.

Next, components that can be arbitrarily introduced into the alkali metal oxide-containing glass will be described.
TiO ₂ has the effect of imparting high refractive index and high dispersibility and improving devitrification stability. However, if its content exceeds 20%, the devitrification stability and transmittance of the glass deteriorates rapidly, the yield point and the liquidus temperature also increase rapidly, and the glass tends to be colored during precision press molding. . Therefore, the introduction amount is preferably 0 to 20%, and more preferably 0 to 15%.

WO ₃ is an effective component for imparting high refractive index, high dispersion characteristics and low-temperature softening properties. WO ₃ works to lower the glass transition temperature and yield point and to raise the refractive index, like alkali metal oxides. And since there exists an effect which suppresses the wettability of glass and a press-molding die, there exists an effect that the mold release property of glass becomes very good in the case of precision press molding. However, if WO ₃ is excessively introduced, for example, exceeding 40%, the glass tends to be colored, while the high-temperature viscosity of the glass also decreases, which may make hot molding difficult. Therefore, the content is preferably 0 to 40%, more preferably 0 to 35%.

Bi ₂ O ₃ is a component that imparts high refractive index and high dispersibility, is a component that has the effect of greatly expanding and stabilizing the glass generation region, and is a component that increases the weather resistance of the glass. . Therefore, by introducing Bi ₂ O ₃ , it is possible to vitrify even a glass having a low P ₂ O ₅ content. Further, by introducing Bi ₂ O ₃ , the wetting angle when the molten glass is placed on the platinum plate can be increased. The increase in the wetting angle makes it difficult for the glass to get wet on the outer periphery of the outflow pipe. Therefore, it is also effective in reducing the surface striae of the preform. Moreover, the weight accuracy of a glass lump can also be improved by reducing wetting. However, if the amount introduced exceeds 20%, the glass tends to be devitrified and colored at the same time, so the Bi ₂ O ₃ content is preferably 0 to 20%. It is more preferable to set it to -15%. Incidentally, in order to obtain the above effect by Bi ₂ O ₃ introduced in the above range, it is preferable that the Bi ₂ O ₃ in an amount of 0.2% or more, more preferably 0.5% or more.

B ₂ O ₃ is an effective component for improving the glass meltability and homogenizing the glass. At the same time, the introduction of a small amount changes the bondability of the OH inside the glass to reduce the foaming of the glass during precision press molding. The effect of suppressing is acquired. However, if B ₂ O ₃ is introduced in an amount of more than 30%, the weather resistance of the glass may deteriorate or the glass may become unstable. Therefore, the amount introduced is preferably in the range of 0 to 30%. . A more preferred range is from 0 to 25%.

BaO is a component having an effect of imparting a high refractive index, improving devitrification stability, and lowering the liquidus temperature. When WO ₃ is introduced, particularly when a large amount of WO ₃ is introduced, the introduction of BaO has a great effect of suppressing the coloring of the glass and improving the devitrification stability. When the content of P ₂ O ₅ is small, the weather resistance of the glass There is also an effect of improving the nature. However, when the introduced amount of BaO exceeds 25%, not only the glass becomes unstable, but also the transition temperature and the yield point tend to increase. Therefore, the introduced amount of BaO is preferably 0 to 25%. 0 to 20% is more preferable.

  ZnO is a component that can be introduced to increase the refractive index and dispersion of the glass. The introduction of a small amount of ZnO also has the effect of lowering the glass transition temperature, yield point, and liquidus temperature. However, when introduced excessively, the devitrification stability of the glass is remarkably deteriorated, and the liquidus temperature may be increased. Therefore, the amount of ZnO introduced is preferably 0 to 25%, more preferably 0 to 20%, and still more preferably 0 to 15%.

  MgO, CaO, and SrO are components that are introduced to adjust the stability and weather resistance of the glass. However, if an excessive amount is introduced, the glass tends to become very unstable. 20% is preferable, and 0 to 15% is more preferable.

Na ₂ O and K ₂ O are components that can be introduced to improve the devitrification resistance of the glass and to lower the glass transition temperature, yield point, and liquidus temperature, and to improve the meltability of the glass. is there. However, if any of Na ₂ O and K ₂ O is more than 30%, or if the total amount of Li ₂ O, Na ₂ O and K ₂ O is more than 45%, the stability of the glass is deteriorated. In addition, since the weather resistance and durability of the glass may be deteriorated, the amounts of Na ₂ O and K ₂ O introduced are preferably 0 to 30%, respectively. Li ₂ O, Na ₂ O and K ₂ The total amount of O is preferably 0 to 45%. Na ₂ O 0-20%, more preferably containing K ₂ O 0 to 25%, it is most preferable to set the Na ₂ O 0 to 5 wt%.

Al ₂ O ₃ , SiO ₂ , La ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , ZrO ₂ , Ta ₂ O ₃ are components that can be introduced to adjust the stability and optical constants of glass. is there. However, all of these components increase the glass transition temperature and may reduce precision press formability. Accordingly, the introduction amounts are less than 15% for Al ₂ O ₃ and SiO ₂ , and 0 to 10% for La ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , ZrO ₂ , and Ta ₂ O ₃ , respectively. it is desirable to keep the, Al ₂ O _3, 0~12% respectively for the SiO _2, the _{La 2 O 3, Gd 2 O3} , Yb 2 O 3, ZrO 2, Ta 2 O 3 in 0 to 8%, respectively More preferably.

Sb ₂ O ₃ is effective as a glass refining agent. However, if added in excess of 1%, the glass tends to foam during precision press molding, so the amount introduced is preferably 0 to 1%. Further, other components such as TeO ₂ and Cs ₂ O can be introduced up to 5% in total. However, since TeO ₂ is toxic, it is desirable not to use it from the viewpoint of environmental impact. Similarly, it is desirable not to use compounds such as PbO, As ₂ O ₃ , CdO, Tl ₂ O, radioactive substances, Cr, and Hg. . Also, Ag ₂ O is not particularly necessary and is preferably not introduced.
Thus, as an example of the _{P 2 O 5 -Nb 2 O 5} -Li 2 O -based glass, by _{mol%, P 2 O 5 15~45%,} Nb 2 O 5 3~35%, Li 2 O 2 _{~35%, B 2 O 3 0~25} %, SiO 2 0~15%, Al 2 O 3 0~15%, Na 2 O 0~30%, K 2 O 0~30% ( provided that Li ₂ O, Na ₂ the total amount of O and K ₂ O is less 45%), 0~20% MgO, CaO 0~20%, SrO 0~20%, BaO 0~25%, 0~25% ZnO, TiO 2 0~ 20%, WO ₃ 0-40%, Bi ₂ O ₃ 0-20%, La ₂ O ₃ 0-10%, Gd ₂ O ₃ 0-10%, Yb ₂ O ₃ 0-10%, ZrO ₂ 0 An optical glass containing 5%, Ta ₂ O ₅ 0-10% can be shown.
In addition, in the said glass, the glass whose refractive index (nd) is 1.75 or more is more preferable, and 1.8 or more is further more preferable. The upper limit of the refractive index (nd) is not particularly limited, but may be 2.1 or less. On the other hand, the Abbe number (νd) is more preferably 30 or less, and further preferably 25 or less. The lower limit of the Abbe number (νd) is not particularly limited, but may be 15 or less.

  Further, in order to improve precision press formability, those having a glass transition temperature (Tg) of 550 ° C. or lower are preferable, and those having a yield point (Ts) of 600 ° C. or lower are preferable. The precision press molding is preferably performed at a temperature 30 to 60 ° C. higher than the yield point of the glass used. Accordingly, the low temperature softening property enables precision press molding at a low temperature of 700 ° C. or lower. When the yield point exceeds 650 ° C and the press temperature exceeds 700 ° C, OH adhering to the surface of the preform reacts with the press mold and decomposes, leaving many bubbles on the surface of the precision press-molded product. May end up. Such bubbles not only lower the surface accuracy of the molded optical element, but also damage the molding surface of the press mold. However, the use of the glass imparted with the low-temperature softening property can solve the above problem.

  Furthermore, since the method for producing a precision press-molding preform of the present invention can suppress surface striae, a high-quality preform can be produced even when glass having a low viscosity at the liquidus temperature is used. it can. Therefore, the production method is preferably applied to glass having a liquidus temperature viscosity (referred to as liquid phase viscosity) of 10 dPa · s or less, and more preferably applied to glass having a liquidus viscosity of 6 dPa · s or less. More preferably, it is applied to a glass of 5 dPa · s or less. There is no particular limitation on the lower limit of the liquid phase viscosity, but it may be 1 dPa · s or more.

As the glass material, H ₃ PO ₄ for P ₂ O _5, metaphosphates, such as phosphorus pentoxide, using a HBO _3, B ₂ O ₃ for B ₂ O _3, for the other components Carbonates, nitrates, oxides, and the like can be used as appropriate. These raw materials are weighed at a predetermined ratio and mixed to prepare a mixed raw material, which is put into a melting furnace heated to, for example, 1000 to 1400 ° C., melted, clarified, stirred, and homogenized. Glass can be used.

  As described above, according to the method for manufacturing a precision press-molding preform of the present invention, surface striae can be prevented by covering the entire surface with a carbon film in the process of molding glass. . However, if surface striae occur for some reason, the surface striae are localized in the surface layer from the surface of the formed glass lump to a certain depth, so if the surface layer is removed by etching, optical It is also possible to make a uniform preform. Etching of the glass lump may be dry etching using an etching gas or wet etching using an etching solution, but it is preferable to immerse the glass lump in the etching solution in order to uniformly remove the entire surface of the glass lump. Is preferably performed by immersing the entire glass mass.

  One of the advantages of etching over mechanical polishing is that the etching depth (the depth removed by etching) can be made constant by making the etching conditions constant. By combining this superiority and the superiority of hot forming, it is possible to produce a high-quality and highly accurate preform from molten glass with high productivity. For example, a molten glass lump is separated from the molten glass flowing out, and a process of forming the glass lump is repeated to produce a plurality of glass lumps having a constant weight. Then, the plurality of glass lumps are etched under a certain condition to produce a preform having a constant weight from which the surface layer has been removed. Since a certain amount of glass is removed under certain etching conditions, a large amount of preforms having a certain weight can be easily produced. This method is easy by making the time for immersing the glass block in the etching solution constant, or by immersing a plurality of glass blocks in the etching solution in a lump, and taking out from the etching solution after a predetermined time. It can be carried out.

As the etching solution, an acid solution or an alkali solution can be used. Examples of the acid solution include HNO ₃ , HCl, H ₂ SO ₄ , HF, H ₂ SiF ₆ , or the like, or HNO ₃ , HCl, H ₂ SO ₄ , HF, and H ₂ SiF _6. The mixed solution which mixed the above acid can be illustrated. Examples of the alkaline solution include a solution of NaOH, KOH, Na ₂ CO ₃ or the like, or an alkali solution in which two or more kinds of alkalis selected from NaOH, KOH, and Na ₂ CO ₃ are mixed. You may mix adjuvants, such as a chelating agent and surfactant, with the said acid solution or alkali solution. By adding a chelating agent to the etching solution, metal ions generated by melting of the glass during etching can be taken in and etching can be performed more uniformly.

When glass containing an alkaline earth metal oxide is etched with an H ₂ SO ₄ solution, a hardly soluble salt (sulfide salt such as BaSO ₄ ) is generated on the glass lump surface by the reaction between the etching solution and the glass. When such a salt accumulates on the glass lump surface, the progress of the etching is hindered, so it is desirable to stir the etching solution.
On the other hand, even when the glass contains an alkaline earth metal oxide such as BaO, when etching with an HCl solution, since the alkaline earth metal chloride is water-soluble, it dissolves in the etching solution and does not hinder the progress of the etching. From such a viewpoint, it is preferable to use an HCl solution as the acid solution, and then to use an HNO ₃ solution. On the other hand, it is also possible to utilize the generation of a hardly soluble salt. Since the hardly soluble salt precipitates in the solution, the etching solution is saturated and the etching rate is unlikely to decrease. Moreover, if a deposit is also removed, it can also be used repeatedly as etching liquid.

Using the fact that the etching rate increases with HCl solution and HNO _{3 solution,} the etching rate in H 2 SO ₄ solution is decreased, the mixed solution of HCl and H ₂ SO _4, mixing of HNO ₃ and H ₂ SO ₄ The etching rate can be adjusted by mixing solutions having different etching rates, such as a solution, a mixed solution of HCl, HNO ₃ , and H ₂ SO ₄ .

  After the preform thus prepared is washed, a thin film such as a release film may be formed on the surface as necessary. Examples of the release film include a carbon-containing film and a self-assembled film.

[Method for Manufacturing Optical Element]
The optical element manufacturing method of the present invention is a method of manufacturing an optical element including a step of heating and precision press molding a glass preform, and the preform manufactured by the method of manufacturing a precision press molding preform of the present invention. Is characterized by precision press molding.
As described above, precision press molding is also called a mold optics molding method, which 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.

According to the present invention, various lenses such as a spherical lens, an aspheric lens, and a micro lens, a diffraction grating, a lens with a diffraction grating, a lens array, various optical elements such as a prism, and applications include a digital camera and a camera with a built-in film. Various lenses such as lenses constituting imaging optical systems, imaging lenses mounted on camera-equipped mobile phones, and lenses for guiding light rays used for data reading and / or data writing on optical recording media such as CDs and DVDs An optical element can be manufactured.
These optical elements may be provided with an optical thin film such as an antireflection film, a total reflection film, a partial reflection film, or a film having spectral characteristics, if necessary.

  Examples of the press mold used for the precision press molding method include known molds, for example, those having a release film on the molding surface of a mold material such as silicon carbide or super hard material. Among these, it is preferable to use a press mold made of silicon carbide. As the release film, a carbon-containing film, a noble metal alloy film, or the like can be used, but a carbon-containing film is preferable from the viewpoint of durability and cost. Moreover, in the manufacturing method of the above-mentioned precision press molding preform of the present invention, a carbon film formed on the entire surface of the glass lump can be used as a release film.

In the precision press molding method, 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. As the non-oxidizing gas, it is preferable to use nitrogen, a mixed gas of nitrogen and hydrogen, or the like.
The press pressure may be appropriately adjusted, and a range of 50 to 150 kgf / cm ² can be used as a guide. Moreover, what is necessary is just to adjust press time suitably, and can set the range of 10 to 300 second as a standard.

Next, a precision press molding method particularly suitable for the method for producing an optical element of the present invention will be described.
(Precision press molding method 1)
In this method, the preform is introduced into a press mold, the mold and the preform are heated together, and precision press molding is performed (referred to as precision press molding method 1).
In the precision press molding method 1, it is preferable to perform precision press molding 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 dPaS.
Further, it is desirable that the precision press-molded product is taken out from the press mold after the glass is cooled to a temperature at which the glass exhibits a viscosity of 10 ¹² dPaS or more, more preferably 10 ¹⁴ dPaS or more, and even more preferably 10 ¹⁶ dPaS or more.
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 method 2)
In this method, after heating the preform, the preform is introduced into a press mold and precision press molding is performed. That is, the press mold and the preform are separately preheated, and the preheated preform is introduced into the press mold. Precision press molding (referred to as precision press molding method 2).
According to this method, since the preform is preliminarily heated before being introduced into the press mold, it is possible to manufacture an optical element with good surface accuracy free from surface defects while shortening the cycle time.
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, the consumption of the mold can be reduced.
Further, according to this method, since it is not necessary to perform preform heating in the press mold, the number of press molds to be used can be reduced.

In the precision press molding method 2, it is preferable that the glass constituting the preform is preheated to a temperature showing a viscosity of 10 ⁹ dPaS or less, more preferably 10 ⁹ dPaS.
The preform is preferably preheated while floating, and the glass constituting the preform is preheated to a temperature showing a viscosity of 10 ^5.5 to 10 ⁹ dPaS, more preferably 10 ^5.5 dPaS or more and less than 10 ⁹ dPaS. More preferably.
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 dPaS may be used as a guide.
In this method, it is preferable that after press molding, the glass is cooled until the viscosity becomes 10 ¹² dPaS or more and then released.

  The precision press-molded optical element is taken out from the press mold and gradually cooled as necessary. Further, when the lens is molded, centering may be performed. Moreover, you may coat an optical thin film on the surface as needed.

In this way, an alkali such as fluorine-containing glass, B ₂ O ₃ borate containing glasses, such -La ₂ O ₃ based _{glass, P 2 O 5 -Nb 2 O} 5 -Li 2 O -based glass, such as fluoric phosphate glass High-quality optical elements made of various glasses such as metal oxide-containing glass can be produced with high productivity.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

[Manufacture of precision press-molding preforms]
The composition of the glass used is shown in Table 1 together with optical constants (refractive index nd, Abbe number νd), transition temperature (Tg), and yield point (Ts). Although the optical constant changes only slightly depending on the temperature history, the composition, optical constant (refractive index nd, Abbe number νd), transition temperature (Tg), and yield point (Ts) are also different in preforms and optical elements. You can think of it as the same.
In order to make the glass, the corresponding oxides, carbonates, sulfates, nitrates, fluorides, hydroxides, etc., as the raw materials of each component, such as Al (PO ₃ ) ₃ , Ba (PO ₃ ) ₂ , Using AlF ₃ , YF ₃ , MgF ₂ , CaF ₂ , SrF ₂ , BaF ₂ , weigh 250 to 300 g at the prescribed ratios shown in Table 1 and mix well to prepare a batch, which is put in a platinum crucible. In an electric furnace maintained at 1200 to 1450 ° C., 0.1 to 50% by volume of oxygen gas is mixed with a gas called inert gas such as nitrogen, a rare gas such as argon, or a rare gas such as argon while stirring. In the atmosphere, heating and melting were performed for 2 to 4 hours. 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 near the glass transition temperature, and then in the furnace Allowed to cool to room temperature. In the obtained glass, crystals that can be observed with a microscope were not precipitated.

The refractive index (nd), Abbe number (νd), transition temperature (Tg), and yield point (Ts) of the glass shown in Table 1 were measured as follows.
(1) Refractive index (nd) and Abbe number (νd)
The glass obtained by lowering the glass held at a temperature between the glass transition temperature and the yield point at a temperature lowering rate of −30 ° C./hour was measured.
(2) Transition temperature (Tg) and yield point (Ts)
The temperature increase rate was measured at 4 ° C./min with a thermomechanical analyzer from Rigaku Corporation.
(3) Degree of glass wear (FA)
The degree of wear (FA) of the glass was measured according to “Japan Optical Glass Industry Association Standard JOGIS 10-1994 Measuring Method of Abrasion of Optical Glass”. The unit is dimensionless, and the larger the degree of abrasion (FA), the more easily the glass is worn.

次に表１に示したガラスが得られる熔融ガラスを熔融温度８００〜１１００℃にて多量に熔融し、清澄、均質化して一定の流量で白金合金製の流出パイプから流出した。
熔融ガラスの流出および成形を、炭素含有化合物を含む雰囲気中で行うために、流出ノズル先端を含む熔融ガラス塊の移動経路を密閉した。そして、２０℃に保たれたキシレンに２０℃の窒素をバブリングしてキシレン蒸気と窒素の混合ガスを作り、この混合ガスを前述の密閉した空間に連続供給（フロー）して、キシレン・窒素混合ガス雰囲気中で熔融ガラスを流出した。このようにして全表面が炭素膜で覆われているガラス塊を成形した。次に、炭素膜を酸化して除去した後、ガラス塊を観察したところ、内部にも表面にも脈理は見られなかった。
更に、キシレンの代わりにアセチレンガスを使用して同様の操作を行い、全表面が炭素膜で被覆されたガラス塊を成形した。炭素膜を除去した後、ガラス塊を観察したところ、内部にも表面にも脈理は見られなかった。

Next, the molten glass from which the glass shown in Table 1 was obtained was melted in large quantities at a melting temperature of 800 to 1100 ° C., clarified and homogenized, and flowed out from the platinum alloy outflow pipe at a constant flow rate.
In order to discharge and form the molten glass in an atmosphere containing a carbon-containing compound, the moving path of the molten glass lump including the tip of the outflow nozzle was sealed. Then, nitrogen at 20 ° C. is bubbled into xylene kept at 20 ° C. to make a mixed gas of xylene vapor and nitrogen, and this mixed gas is continuously supplied (flowed) into the above-mentioned sealed space to mix xylene and nitrogen. The molten glass flowed out in a gas atmosphere. In this way, a glass lump whose entire surface was covered with a carbon film was formed. Next, after the carbon film was oxidized and removed, the glass lump was observed, and no striae was found inside or on the surface.
Furthermore, the same operation was performed using acetylene gas instead of xylene, and a glass lump whose entire surface was covered with a carbon film was formed. After removing the carbon film, the glass lump was observed, and no striae were found inside or on the surface.

Similarly, B ₂ O ₃ 46% by _{mol%, La 2 O 3 13%,} Gd 2 O 3 6%, 16% ZnO, Li 2 O 3%, ZrO 2 5%, Ta 2 O 5 4% , WO ₃ 4%, SiO ₂ 3%, refractive index (nd) 1.82, Abbe number (νd) 43.0, glass transition temperature (Tg) 590 ° C., liquidus temperature 1010 ° C. or preform formed of the optical glass, P ₂ O ₅ 24% by _{mol%, Nb 2 O 5 18%,} WO 3 5%, TiO 2 3%, Bi 2 O 3 3%, Li 2 O 20%, Na _{2 O 13%, K 2 O} 2%, B 2 O 3 6%, BaO 2%, includes 2% ZnO, refractive index (nd) of 1.83, an Abbe's number ([nu] d) 23.9, a glass transition When a preform made of optical glass with a temperature (Tg) of 450 ° C. and a liquidus temperature of 890 ° C. is molded, there is no striation on the inside or on the surface. It is did not.

[Manufacture of optical elements]
The steps from molten glass outflow to glass lump formation were carried out by performing the following operations in a gas atmosphere in which xylene vapor was mixed with nitrogen. A molten glass lump of a predetermined weight was separated from the flowing molten glass by a dropping method and received by a glass lump forming die that ejected gas, and the glass was moved up and down to form a spherical preform. The preforms having a constant weight were formed one after another by receiving the molten glass droplets dropped at a constant time interval one after another by a glass lump molding die. After cooling to a temperature at which the preform did not deform, it was removed from the mold. In this way, a plurality of spherical preforms made of each glass shown in Table 1, the B ₂ O ₃ —La ₂ O ₃ containing glass, and the P ₂ O ₅ —Nb ₂ O ₅ containing glass were produced.

  In addition, the molten glass lump is separated by a descending cutting method, received by a glass lump forming die having a recess formed by a porous material, and gas is ejected from the fine pores of the porous material, so that each glass shown in Table 1 A preform was formed. Also in this method, a plurality of preforms having a constant weight were produced by repeating the above steps with a constant separation time interval. In addition, the shape of the preform formed by this method is a shape that has one rotational symmetry axis, has a major axis and a minor axis, and is composed of curved surfaces with different curvatures, and has a shape that approximates a flat sphere. Equivalent to.

  All preforms thus molded were cooled to room temperature, then placed in an annealing furnace and annealed at a temperature about 10 ° C. lower than the glass transition temperature for 1 hour, at a rate of 30 ° C./hour. The temperature was lowered to reduce distortion. The preform formed by any of the above methods had high weight accuracy.

A release film may be provided on the entire surface of the preform thus obtained in order to improve the mold release property during precision press molding. Examples of such a release film include a carbon film and a self-assembled film.
The preform thus obtained was heated, and an aspherical lens was obtained by precision press molding (aspherical precision pressing) using the press apparatus shown in FIG. The details of precision press molding are as follows. The preform was allowed to stand between the lower die 2 and the upper die 1 made of SiC having an aspherical shape, and then the quartz tube 11 was heated by energizing the heater 12 with the inside of the quartz tube 11 being a nitrogen atmosphere. The temperature inside the molding die is set to a temperature at which the glass yield point is +20 to 60 ° C., and while maintaining the same temperature, the push bar 13 is lowered and the upper die 1 is pushed to precisely perform the preform in the press molding die. Press molded. A glass transition temperature in a state where the aspherical lens made of fluorophosphate glass formed by reducing the molding pressure after pressing, with the molding pressure of 8 MPa and the molding time of 30 seconds, is kept in contact with the lower mold 2 and the upper mold 1. It was gradually cooled to a temperature of −30 ° C. and then rapidly cooled to room temperature. Thereafter, the aspherical lens was taken out from the press mold and subjected to shape measurement and appearance inspection. The obtained aspherical lens was a highly accurate lens.

When the surface of this lens was magnified and observed with an optical microscope, it was confirmed that it was a high-quality lens with no surface or internal striae as in the preform used.
The aspherical lens made of a high-quality and high-precision fluorophosphate glass could be formed by introducing the preheated preform into a press mold and performing precision press molding.
The shape and dimensions of the preform may be appropriately determined depending on the shape of the precision press-molded product to be produced. Further, in the case of a preform having surface striae, the entire surface may be etched as described above to remove the surface layer where striae are present, and the preform may be optically homogeneous before use. In that case, it is preferable to etch by immersing the entire preform in an etching solution as described above.

According to this example, even if surface striae occur, the striae-existing layer can be limited to a very shallow layer, so that the amount of glass removed by etching can be reduced. Since the etching time can be shortened, the productivity of the preform can be improved.
In the above embodiment, an aspheric lens is molded, but by using a press mold that matches the shape of the final product, a concave meniscus lens, a convex meniscus lens, a plano-convex lens, a biconvex lens, a plano-concave lens, a biconcave lens, etc. Various aspherical lenses or various spherical lenses, or optical elements such as prisms, polygon mirrors, and diffraction gratings can be manufactured.

Also, various optical elements made of near-infrared absorbing glass can be produced by preparing a preform in the same manner using copper-containing fluorophosphate glass and precision press-molding in the same manner as described above. Such an optical element can be used as a color correction filter for a semiconductor imaging element.
In addition, an optical multilayer film such as an antireflection film or a high reflection film can be formed on the optical functional surface of each optical element obtained as necessary.

  The method for producing a precision press-molding preform of the present invention is suitable for producing a preform made of glass such as fluorine-containing glass containing easily volatile components, boric acid-containing glass, or alkali metal oxide-containing glass. Furthermore, according to the method for producing an optical element of the present invention, the preform produced by the above method is heated and precision press-molded, so that a high-quality optical element can be produced with high productivity.

It is the schematic which shows an example of the shape of the preform obtained by the manufacturing method of this invention. It is sectional explanatory drawing of a precision press apparatus.

Claims (5)

In a method for producing a precision press-molding preform including a step of forming a glass lump by separating a predetermined amount of glass from the molten glass flowing out and forming the glass lump while floating by applying wind pressure. ,
By continuously supplying a non-oxidizing gas containing a carbon-containing compound to a space where the molten glass flows out and separates the glass , at least the molten glass flows and glass is separated from the non-oxidizing atmosphere containing the carbon-containing compound. A method for producing a precision press-molding preform, characterized in that it is carried out in-house. The method for producing a precision press-molding preform according to claim 1, wherein the glass is any one of fluorine-containing glass, boric acid-containing glass, and alkali metal oxide-containing glass. In the manufacturing method of the optical element including the step of heating the glass preform and precision press molding,
A method for producing an optical element, comprising: producing a preform by the production method according to claim 1 or 2; and precision-pressing the produced preform. 4. The method of manufacturing an optical element according to claim 3, wherein a preform is introduced into a press mold, the mold and the preform are heated together, and precision press molding is performed. 4. The method of manufacturing an optical element according to claim 3, wherein a preheated preform is introduced into a press mold and precision press molding is performed.

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