JP4165703B2 - Precision press molding preform manufacturing method and optical element manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a precision press-molding preform, a precision press-molding preform, an optical element, and a method for manufacturing the same. More specifically, the present invention relates to a method for efficiently producing a high-quality glass precision press-molding preform, a high-quality precision press-molding preform made of Bi-containing fluorophosphate glass, and these preforms. The present invention relates to an optical element obtained by precision press molding and a manufacturing method thereof.

Various optical systems including imaging optical systems require lenses made of low-dispersion glass. Such low-dispersion optical glass generally contains fluorine for the purpose of reducing dispersion.
In recent years, the demand for lenses such as aspherical lenses made of low-dispersion glass has been increasing as digital still cameras and digital video cameras become smaller, have higher pixels, and have higher performance. In order to meet such demand, the method of grinding and polishing the shape of the optical functional surface such as the lens surface is not in time, and the glass called the preform is heated and softened, pressed with a press mold, and the optical functional surface A mass production method with high productivity is effective by a precision press molding method (also referred to as a mold optics molding method) for molding (see, for example, Patent Document 1).
When a lens made of low-dispersion glass containing fluorine is produced by a precision press molding method, first a glass molded body called a preform is produced. The preform is required to have a mass equal to the mass of the target precision press-molded product and have no defects such as devitrification, striae, and scratches inside and on the surface.

The following two methods are conceivable for producing the preform. One is a method of forming a glass block, cutting out a portion free from defects such as striae, and chamfering or optically polishing the surface to form a preform. In this method, since the surface of each preform is optically polished, it takes a lot of time and labor, and there is a problem that the cost is increased. There is also a problem that the mass of the glass must be strictly controlled as the grinding and polishing progress.
Another method is a method in which a molten glass lump having a mass equal to the mass of the target preform is separated from the molten glass and formed into a preform in the course of cooling the molten glass lump. It is what is called. In the hot forming method, a preform can be made directly from molten glass, so that productivity can be improved. Moreover, a molten glass lump can be isolate | separated with high mass accuracy by dripping a molten glass from an outflow nozzle, or supporting the front-end | tip of the molten glass which flows down from an outflow nozzle, and removing the said support at predetermined timing.
Also, in order to prevent the glass lump surface from touching other objects as much as possible during molding, it is possible to make a preform with an extremely smooth surface by molding in a state where the glass is floated by applying wind pressure. .

As described above, the hot forming method is extremely excellent as a method for producing a preform, but it has been difficult to apply to a glass containing a highly volatile component such as fluorine.
For example, high demand glass having ultra-low dispersion characteristics has obtained the above characteristics by including fluorine in the glass structure, but in a glass at a very high temperature in a molten state, fluorine is replaced with oxygen in the air. The fluorine in the glass is reduced and the ultra-low dispersibility is lost. In a glass whose composition has been adjusted so as to obtain thermal stability, the stability is impaired by the replacement of fluorine with oxygen. Therefore, although it is a method that can produce a preform with high productivity, it is a fact that it has not been put into practical use to form a high-temperature-reactive glass such as fluorine-containing glass by a hot forming method. .
Although there is a difference in the mechanism of volatilization, there is a problem of volatilization when a preform is hot-formed using glass containing an easily volatile component such as boron.
Japanese Patent No. 3153871

  Under such circumstances, the first object of the present invention is to efficiently produce a high-quality glass precision press-molding preform and a high-quality precision press-molding made of fluorophosphate glass. The second object is to provide an optical element obtained by precision press-molding these preforms and a method for producing the same.

  The inventors of the present invention have made extensive studies on the possibility of hot forming of precision press-molding preforms using glass that shows high reactivity and volatility in the molten state, such as fluorine-containing glass and boron-containing glass. It was. During this process, a preform was hot-molded from fluorophosphate glass, and the surface was examined in detail, and even a preform that seemed to be well-formed at first glance was magnified with a microscope. It was recognized that they were lined up. Furthermore, when this preform was precision press-molded to produce a lens, it was found that the irregularities of the preform remained as fine irregularities on the surface of the lens. The unevenness of the lens surface is also a level that cannot be visually recognized, but is inappropriate as an optical element.

It is considered that fine irregularities on the surface of the preform are generated because fluorine in the glass in a high temperature state evaporates from the surface of the molten glass during cooling. The release of fluorine from the glass is thought to occur as a result of the reaction with oxygen in the atmosphere. Therefore, in order to prevent the unevenness from occurring, it is only necessary to prevent the glass immediately after flowing out from coming into contact with the atmosphere that is rich in air or oxygen as much as possible.
Further, even if evaporation of easily volatile components in the glass is prevented, if the glass is molded in contact with the mold, traces of contact with the mold remain uneven on the preform surface.

Therefore, to make a high-quality preform by hot forming a glass that is highly reactive at high temperatures such as fluorine-containing glass,
(I) Glass in a high temperature state is handled in a sealed space filled with a non-oxidizing atmosphere.
(Ii) When the glass has a relatively large mass that is difficult to cool naturally, the molten glass that has flowed out is brought into direct contact with an object that takes heat away from the glass and cooled, and then molding into a preform is started. In order to avoid contact with other objects as much as possible, the preform is formed while applying wind pressure to the glass and floating it.
(Iii) In the case of a molten glass lump having a relatively small mass dripped from the outflow pipe, the preform is cooled to a temperature at which easily volatile components do not evaporate in the process of dropping the molten glass lump and then floated by applying wind pressure. Can be started.
(Iv) When the floating gas for floating molding blows to the outlet of the outflow pipe, it causes mass fluctuation of the preform, striae, devitrification, etc., and therefore the outlet is blocked from the floating gas.
(V) It is desirable to limit the movement path of the molten glass lump in the vertical direction from the separation from the molten glass to the start of levitation so that no folding occurs.
As a result of the above considerations, it has been found that a precision press-molding preform made of optical glass having no fine irregularities on the surface and good internal quality can be stably produced.
The present invention has been completed based on such findings.

That is, the present invention
(1) a glass melt gob of predetermined weight from a molten glass flowing out from the outlet of the outflow pipe are separated, a gas wind pressure applied by the gas undergoing those the glass gob in the mold for ejecting, glass while floating In the manufacturing method of a precision press molding preform to be molded into a preform,
The molten glass support disposed under the outflow pipe is directly supported by receiving the tip of the molten glass flow while shielding the outflow pipe from the gas ejected from the mold , and the support by the molten glass support is removed and melted. A method for producing a precision press-molding preform, wherein the step of separating the molten glass mass from the tip of the glass stream is performed in a sealed space filled with a non-oxidizing gas;
(2) In a method for producing a precision press-molding preform in which molten glass droplets are dropped from an outflow pipe, received by a molding die that ejects gas, and wind pressure is applied by the gas to form a glass preform while floating.
The dropping of the molten glass droplet is performed in a sealed space filled with a non-oxidizing gas, and a shield is provided so as to cross the dropping path of the molten glass droplet to shield the outflow pipe from the gas ejected from the mold. And a method for producing a precision press-molding preform, wherein the shield is removed from the dropping path in synchronization with the dropping of the molten glass droplet,
(3) In a method for producing a precision press-molding preform in which a molten glass droplet is dropped from an outflow pipe, received by a molding die that ejects a gas, and formed into a glass preform while being lifted by applying wind pressure with the gas,
The molten glass droplet is dropped in a sealed space filled with a non-oxidizing gas, and a support is provided so as to cross the molten glass droplet dropping path to shield the outflow pipe from the gas ejected from the mold. In addition, a molten glass droplet is dropped on the support, and the support is removed from the dropping path in synchronization with the dropping of the molten glass droplet.
A method for producing a precision press-molding preform,
(4) A molten glass lump or molten glass droplet having a constant mass is separated from the molten glass flowing out from the outlet of the outflow pipe, and received by a molding die that ejects a gas for applying wind pressure to the glass lump or glass droplet . In the manufacturing method of a precision press molding preform that is molded into a glass preform while levitating,
A space including an outlet is covered with a cover having an opening that can be opened and closed vertically below the outlet, and the space is sealed when the opening is closed, and a non-oxidizing gas is contained in the space. The glass is applied to a molding die that separates a molten glass lump or molten glass droplet with the opening closed, and opens the opening and ejects a non-oxidizing gas disposed close to the opening. A method for producing a precision press-molding preform, which is characterized by transferring a lump or glass droplet and molding,
(5) Preform for precision press molding according to any one of (1) to (4) above, wherein molten glass ingots or molten glass droplets are separated one after another and dropped into a plurality of molding dies in order. Manufacturing method,
(6) The method for producing a precision press-molding preform according to any one of (1), (2), (3) and (5) above, wherein the gas for applying wind pressure is a non-oxidizing gas ,
(7) The molten glass support or the support is composed of two split members, and a recess for storing molten glass is formed on the mating surface of the split member in a state where the split members are in close contact with each other. The method for producing a precision press-molding preform according to any one of (1), (3) and (5) above,
(8) The sealed space is formed by the molten glass support or shield and a cover disposed on the molten glass support or shield (1), (2), (3) and ( A method for producing a precision press-molding preform according to any one of items 5),
(9) The method for producing a precision press-molding preform according to any one of (1) to (8) above, wherein a preform made of glass containing fluorine is molded.
(10) The method for producing a precision press-molding preform according to any one of (1) to (9) above, wherein a preform comprising a glass containing Bi is molded.
(11) (1) to (10) was prepared Risei tight press-molding preform by the process according to any one of clauses, heating the preform for precision press molding obtained, A method of manufacturing an optical element, characterized by precision press molding using a press mold,
( 12 ) A method for producing an optical element as described in ( 11 ) above, wherein a precision press-molding preform is introduced into a press mold, the preform and the press mold are heated together, and precision press molding is performed. 13 ) Provided is a method for producing an optical element as described in ( 11 ) above, wherein the preform for precision press molding and the press mold are separately heated, and then the preform is introduced into the press mold and precision press molding is performed. Is.

According to the method for producing a precision press-molding preform of the present invention, a high-quality and high-mass-accuracy preform can be obtained directly from a molten glass containing a component having high volatility and high reactivity such as fluorine-containing glass. Can be produced.
Further, according to the precision press molding preform of the present invention, it is possible to provide a high-quality glass optical element both on the surface and inside by precision press molding.
Furthermore, according to the optical element of the present invention, it is possible to provide an optical element made of fluorophosphate glass having excellent surface and internal quality, which does not require any grinding or polishing for the shape processing of the optical functional surface.
In addition, according to the method for manufacturing an optical element of the present invention, there is provided a method for manufacturing an optical element made of fluorophosphate glass having excellent surface and internal quality, which does not require any grinding or polishing for the shape processing of the optical functional surface. can do.

First, a method for producing a precision press-molding preform will be described in detail.
[Precision press molding preform manufacturing method]
In the present invention, precision press molding refers to a press molding method in which an optical functional surface having an optical function of refracting, reflecting, diffracting or transmitting light is formed by press molding. This is called molding or mold press molding. In precision press molding, the shape of optical functional surfaces (for example, aspherical surfaces of aspherical lenses, surfaces with fine irregularities of diffraction gratings, etc.) are determined by press molding. There is no need to machine the functional surface into the design shape. In precision press molding, a glass molded body adjusted to be equal to the mass of the press-molded product is heated and pressed with a press mold at a temperature that can be deformed by pressurization. This glass molded body is called a precision press-molding preform (hereinafter sometimes simply referred to as a preform).

As described above, the preform has a high mass accuracy, and is used only with good internal quality and surface condition free from striae, devitrification, scratches, cracks and the like.
(About preform manufacturing method 1)
In the first embodiment of the preform manufacturing method (hereinafter referred to as preform manufacturing method 1), a molten glass lump of a constant mass is separated from the molten glass flowing out from the outlet of the outflow pipe, and the wind pressure is applied to the glass lump. In addition, in a method for manufacturing a precision press-molding preform that is molded into a glass preform while floating, the molten glass support is directly received and supported by a molten glass support disposed under the outflow pipe, The step of removing the support by the support and separating the molten glass lump from the tip of the molten glass flow is performed in a sealed space filled with a non-oxidizing gas.

Highly reactive components such as fluorine contained in the glass in the molten state change the composition of the glass surface due to substitution of oxygen with highly reactive components near the surface when the oxygen concentration in the atmosphere is high. When the highly reactive component is detached from the glass, scale-like fine irregularities as described above are generated. Therefore, in the preform manufacturing method 1, the glass immediately after flowing out is handled in a sealed space filled with a non-oxidizing gas.
Examples of the non-oxidizing gas include nitrogen gas, inert gas (eg, argon gas, helium gas), carbon dioxide gas, or a gas obtained by mixing the above gases. The amount of oxygen in the non-oxidizing gas is preferably suppressed to 15% or less by volume ratio, more preferably 10% or less, still more preferably 5% or less, and more preferably 0.1 to 5%. That's fine.

  In this method, a clarified and homogenized molten glass is prepared, and the molten glass is continuously flowed down from a temperature-controlled outflow pipe made of a platinum alloy or the like at a constant outflow rate. And it receives and directly supports the front end of the molten glass flow flowing down on the upper surface of the molten glass support that stands by below the outflow pipe. That is, the support is performed in a state where the tip of the molten glass flow and the molten glass support are in contact with each other. The molten glass support is composed of a plurality of split members, and each split member has a function of being spaced apart from each other or closely contacting. When receiving the front end of the molten glass flow, the split members are brought into close contact with each other, and the front end of the molten glass flow is received and supported at the boundary portion of the split member. In this state, since the support and the tip of the molten glass flow are in direct contact with each other, the viscosity of the tip of the molten glass flow increases even if the glass has a low viscosity at the time of outflow, and may enter between the split members. Absent. Further, since the viscosity of the molten glass lump is increased by the contact with the split member, it is possible to effectively prevent the glass from being bent easily when the molten glass lump is transferred to the molding die described below. Moreover, volatilization of easily volatile components such as fluorine from the surface can be reduced by increasing the viscosity (temperature decrease) of the molten glass lump. The split member is preferably cooled to prevent fusion with the molten glass and to easily obtain the above effect. Examples of the cooling method include a method of cooling the split member with water, a method of cooling the split member with air, a method of increasing the emissivity by making the surface of the split member black, and a combination of the above methods. When the split member is water-cooled or air-cooled, a flow path may be provided inside the split member, and cooling water or cooling gas may flow through it. Examples of the molten glass support include heat-resistant metals, carbon, and ceramics. Of these, heat resistant stainless steel is preferable in consideration of heat resistance and thermal conductivity.

  After receiving and supporting the tip of the molten glass flow, the support by the molten glass support is removed at a timing when a predetermined amount of molten glass lump is obtained, and the molten glass lump is separated. As a specific method for removing the support by the molten glass support, there is a method in which the molten glass support is lowered vertically. In order to make the amount of the molten glass lump constant, the position for receiving the tip of the molten glass flow and the descent condition of the molten glass support are constant, and the descent period is also constant. The distance and speed of the descent may be selected such that the molten glass flow can be cut. When the molten glass support is lowered vertically, a constriction occurs between the tip of the molten glass flow and the outflow pipe side, and the constriction increases as the descent continues, and the tip separates and is placed on the molten glass support. A certain amount of molten glass ingot is obtained. Next, the split members are separated from each other, and the molten glass lump is dropped vertically downward from between the separated split members. Before the separation of the molten glass flow is completed, the split member may be separated to drop the molten glass lump. Alternatively, the glass can be cut by opening the split member at regular intervals without lowering the split member, or the molten glass lump is separated by a combination of lowering the split member and separating the split member at regular intervals. May be.

Any number of split members may be used, but it is preferable that the molten glass support is composed of two split members from the viewpoint of reliably and easily performing the above series of operations. In that case, it is preferable that the boundary of the split member in a state where the split member is in close contact is a straight line from the viewpoint of bringing both members into close contact. The upper surfaces of the two split members are flat, and the angle between the two upper surfaces is 90 ° to 180 °. The two surfaces are symmetrical with respect to a virtual plane passing through the boundary between the two split members. It is desirable. By using such a molten glass support, the tip of the molten glass flow can be stably supported, and the molten glass lump can be dropped vertically downward when the split member is separated.
Before the lowering, the molten glass support may be lowered vertically downward at a speed lower than the outflow speed of the molten glass flow. By such an operation, it is possible to prevent the end of the outflow pipe from being buried in the molten glass pool and causing striae.

A mold waits below the molten glass support and receives the falling molten glass lump. The molten glass flows out from the outflow pipe and follows a path along the vertically lower side until it falls into the mold. Therefore, the horizontal component of the external force acting on the molten glass flow and the molten glass lump can be minimized, and the occurrence of defects such as folding into the glass molded body can be prevented.
A gas outlet is provided at the bottom of the mold for receiving the molten glass lump and forming it into a glass molded body, and from there upwards the glass on the mold (the molten glass lump and the glass molded body are collectively called). The molding is performed while the glass is floated by jetting a gas for floating by applying a wind pressure of. When the gas (hereinafter referred to as levitation gas) is blown onto the outflow pipe, the temperature of the molten glass flow or the flowing down glass flow decreases, or the molten glass lump falls to make it unstable. After that, it is desirable to immediately block the floating gas by bringing the split members into close contact with each other.

It is preferable to use a non-oxidizing gas as the floating gas. In that case, it is desirable to use the same kind of gas as the non-oxidizing gas filling the sealed space.
The gas outlet may be one in which a plurality of pores are selectively opened or may be one pore. In the method of ejecting gas from a plurality of selectively opened fine pores, an upward wind pressure is applied to the molten glass lump over a wide range, so that there is one rotational symmetry axis and the contour in the cross section including the rotational symmetry axis is This is suitable for forming glass on a rotating body that is convex outward. In this case, it is preferable to arrange a plurality of pores in the recess of the mold so as to be symmetric with respect to the center of the recess.

On the other hand, by forming one pore at the center of the recess of the mold and ejecting gas, the glass can be molded while rotating in the recess of the mold. This method is suitable for forming a spherical glass molded body.
As the material of the mold, a heat resistant metal such as stainless steel, carbon, or the like can be used. Moreover, although the molten glass lump transferred to the mold is lower in temperature than when it flows out, it is still at a high temperature and there is a risk of fusion. Therefore, it is preferable that the temperature of the mold is controlled to 300 ° C. or lower to reliably prevent fusion. In order to prevent fusion, it is desirable to provide a film such as a diamond-like carbon film on the surface of the mold.

  In order to prevent fusion, it is desirable to provide a film such as a diamond-like carbon film on the surface of the molten glass support that contacts the molten glass and the surface of the mold that contacts the molten glass lump. Moreover, it is desirable that the surface is mirror-finished. When the molten glass support is separated and the molten glass lump is dropped, if the glass is fused on the surface of the split member or the molten glass slips poorly, the horizontal component of the external force acting on the molten glass lump is This increases the risk of defects such as folding in the glass molded body. Therefore, for the purpose of preventing fusion and improving slipping, it is particularly preferable to coat the surface of the split member with diamond-like carbon, cool the split member, and polish the surface of the split member.

Moreover, it is preferable to drop a molten glass lump to the center of a shaping | molding die from the viewpoint of performing prevention of glass folding more reliably, and said means becomes a point.
In order to receive the molten glass lump which is separated and dropped one after another, a plurality of molding dies are sequentially transferred below the molten glass support. Specifically, a plurality of molding dies may be arranged at equal intervals on the turntable so that an empty molding die waits when the molten glass lump is dropped. In this way, the molten glass lump is distributed to a plurality of molds to form a glass molded body.
The molded glass molded body is cooled on the mold to a temperature at which it is not deformed by an external force, and then taken out and gradually cooled.

Here, FIG. 1 is a production process diagram showing an example of a method for producing a precision press-molding preform according to the present invention, wherein the step of separating the molten glass lump is a sealed space filled with a non-oxidizing gas. In order to perform the inside, as shown in FIG. 1, the space formed by the tip of the outflow pipe 2 and the molten glass support 3a (the split member in the figure) is filled with a non-oxidizing gas. A method in which all the molds 1 for molding the preform are put in a sealed container and filled with a non-oxidizing gas is desirable, but a method in which a non-oxidizing gas is allowed to flow in the space for molding the glass of the mold 1 But it is effective enough. In order to minimize the sealed space, the cover 5 (a glass cover in the figure) is covered so as to surround the tip of the outflow pipe 2 and the portion of the molten glass support 3a on which the molten glass lump 4a is placed. A sealed space is formed by the cover 5 and the molten glass support 3 a in a state where the split members constituting the molten glass support 3 a are in close contact with each other. It satisfies the sealed space in a non-oxidizing gas 6 (N ₂ gas atmosphere in the figure), since the separation of the molten glass gob 4a is performed in a state where the split members 3a are in close contact with each other, and high ambient temperature of the glass The step of separating the molten glass ingot at a high reactive level can be performed in a sealed space filled with a non-oxidizing gas. FIG. 2 is an explanatory view showing another example of the shape of the split member that receives the molten glass flow. In FIG. 2, the molten glass support 3 b is constituted by two split members and receives the molten glass 4. The surface is inclined. Then, at a timing at which a predetermined amount of molten glass lump 4a can be separated, the support of the lower end portion of the molten glass is removed by separating them from each other without lowering the split member 3b, and the molten glass lump 4a is separated. Let it fall naturally in the center.

The cover 5 is preferably a transparent container such as a glass container. By making the cover 5 transparent, the outflow state can be observed from the outside. In FIGS. 1 and 2, in order to improve the hermeticity in the glass cover 5, the skirt 8 composed of a resilient material such as Teflon is used to connect the glass cover 5 and the split members 3a and 3b without gaps. Even when they are lowered or separated from each other, there is no gap between the glass cover 5 and the split members 3a and 3b. As described above, by reducing the gap, the internal pressure in the cover can be made higher than the external pressure, and the air is less likely to enter the cover.
In some cases, the molten glass wets around the outer periphery of the end of the outflow pipe. In such a case, it is preferable that a portion where the molten glass gets wet is included in the sealed space.
Furthermore, it is preferable to use a dry gas as the non-oxidizing gas. This is because, if moisture is contained in the gas, moisture and fluorine in the glass are combined to easily volatilize from the glass. For example, the dry gas may be prepared by removing moisture in the gas through the desiccant or evaporating the liquefied gas. As examples of the liquefied gas, liquid nitrogen and liquid carbon dioxide can be shown as preferred examples. The liquid carbon dioxide is obtained by liquefying carbon dioxide under high pressure.

  The dry gas preferably has a moisture content of 400 ppm or less, and more preferably 380 ppm or less. The lower limit of the moisture content of the dry gas is not particularly limited, and is ideally 0 ppm, but the moisture content of the dry gas available in large quantities is 100 ppm or more. It is also preferable to use a gas having a dew point of −30 ° C. or lower as the dry gas. Although there is no restriction | limiting in particular in the lower limit of the dew point of dry gas, The lower limit of the dew point of the gas which can be obtained in large quantities is about -80 degreeC. Further, a high-pressure gas can be used as the drying gas. For example, when high-pressure helium gas or high-pressure argon gas is used, a grade having a dew point of −60 ° C. or an ultra-high purity grade (dew point of −80 ° C.) may be designated. Therefore, gas can be used as dry gas from these high-pressure gases. However, since the dew point of the high-pressure gas may increase depending on the storage condition of the container, it is preferable to use the gas from the well-controlled high-pressure gas container. In addition, even if the gas has a moisture content or dew point that does not fall within the above range, it passes through a column filled with a desiccant such as synthetic zeolite, and the gas whose moisture content or dew point reaches a predetermined value is dried gas. It can also be used as

Next, the temperature of the non-oxidizing gas supplied into the sealed container will be described. When supplying the non-oxidizing gas to a position away from the outflow pipe, the temperature of the drying gas is not particularly limited and may be about room temperature. When supplying the gas from the vicinity of the outflow pipe, it is preferable to set the temperature of the gas to be equal to or higher than the softening temperature of the glass to be formed in order to prevent adhesion of volatile components to the pipe, and it is more preferable to set the outflow glass temperature. preferable.
As shown in FIG. 1, after the split members constituting the molten glass support 3a are separated and the molten glass lump 4a is dropped vertically downward and introduced into the center of the mold 1, the split members immediately adhere to each other. Let Therefore, even if the cover 5 is used to seal the tip of the outflow pipe 2 and the upper part of the molten glass support 3a, the space covered with the cover 5 can be kept sealed except when the molten glass lump is dropped. . Even when the split member is separated, the non-oxidizing gas flows out from the inside of the cover, so that the floating gas 9 (N _{2 in the} figure) does not easily flow into the space covered with the cover 5. Further, even if the floating gas flows in, the gas is also a non-oxidizing gas, so that the sealed space can be kept filled with the non-oxidizing gas.

As described above, according to the preform manufacturing method 1, since the molten glass immediately after the outflow having high reactivity with the atmosphere is handled in the sealed space filled with the non-oxidizing gas, the preform having a smooth surface and having no defects is formed. be able to. In addition, by directly contacting the molten glass block with the molten glass support in the above-mentioned sealed space, the heat of the glass is taken away, and highly reactive components such as fluorine and easily volatile components are less likely to occur later before being introduced into the mold. The glass surface can be cooled to a temperature range. Therefore, the glass whose entire surface is melted is formed by solidification, and a smooth preform can be produced even when viewed microscopically without scale-like fine irregularities.
On the other hand, by forming one pore at the center of the recess of the mold and ejecting gas, the glass can be molded while rotating in the recess of the mold. This method is suitable for forming a spherical glass molded body.

Note that the preform manufacturing method 1 is suitable for manufacturing a preform having a relatively large mass. The preferred range of preform mass is 200 mg to 10 g. The mass accuracy is preferably within ± 2%, more preferably within ± 1%.
(About preform manufacturing method 2)
In a second embodiment of the preform manufacturing method (hereinafter referred to as preform manufacturing method 2), molten glass droplets are dropped from an outflow pipe and received by a molding die that ejects gas, and the wind pressure is applied by the gas and floated. In the method for manufacturing a precision press-molding preform that is molded into a glass preform, the molten glass droplet is dropped in a sealed space filled with a non-oxidizing gas, and the molten glass droplet dropping path is crossed. In this manufacturing method, the shielding body is provided to shield the outflow pipe from the gas ejected from the mold, and the shielding body is removed from the dropping path in synchronization with the dropping of the molten glass droplet.
In the preform manufacturing method 2, the same non-oxidizing gas as in the manufacturing method 1 is used for the same reason as in the preform manufacturing method 1.

FIG. 3 is a production process diagram showing another example of a method for producing a precision press-molding preform of the present invention.
Also in the preform manufacturing method 2, as shown in FIG. 3, a clarified and homogenized molten glass is prepared, and the molten glass 4 is allowed to flow out from the outflow pipe 2 made of temperature-controlled platinum alloy or the like at a constant outflow rate. . And a molten glass drop is dripped at the shaping | molding part in which the gas jet nozzle of the shaping | molding die 1 which waits under the outflow pipe 2 was provided. A plurality of forming dies 1 are prepared, and when the molten glass droplet 4b is received at a position (referred to as a dropping position) for receiving the molten glass droplet below the outflow pipe 2, it is unloaded from the dropping position and an empty forming mold is conveyed to the dropping position. The In this way, the plurality of molds are sequentially conveyed to the dropping position to receive the molten glass droplets 4b one after another. The molten glass droplet on the molding die is subjected to upward wind pressure by a gas (floating gas) 9 (N _{2 in the} drawing) ejected upward from the gas ejection port, and is molded into a glass molded body while floating. The solidified glass molded body is taken out from the mold and returned to the dropping position again.

In this way, a plurality of molds are circulated and used, but since the floating gas is ejected from the gas outlet, the floating gas sprays on the outflow pipe when the mold reaches the dripping position, and the outflow conditions, dripping Make the condition unstable.
Here, the meaning that the outflow condition becomes unstable will be specifically described. When the floating gas blows to the tip of the outflow pipe, the end of the outflow pipe is cooled by the gas, so that the temperature of the outflow pipe fluctuates and the outflow amount of glass fluctuates. However, the dripping weight does not vary greatly when the fluctuation range of the outflow amount of glass is small (the reason will be described later). On the other hand, when the temperature at the tip of the outflow pipe decreases, crystals of the molten glass may precipitate at the outflow port. In this case, the dripping weight increases or striae occurs in the glass molded body. Since the glass composition described above is generally easy to crystallize in the outflow temperature range, a temperature drop at the end of the outflow pipe is a serious problem.

  Next, the meaning that the dripping condition becomes unstable will be specifically described. The weight of the droplet is determined by the outer diameter (D) of the outlet, the surface tension (γ) of the glass, and the gravitational acceleration (g) (Equation 1). Strictly speaking, the larger the glass flow rate, the heavier the droplet weight, but when the flow rate change is small, the droplet weight does not change and the influence can be ignored. On the other hand, since γ depends on temperature, a large temperature fluctuation causes fluctuation in droplet weight. Although g is constant on the earth, it becomes a force that lifts the droplet when the floating gas is applied to the tip of the droplet, so that it is apparently affected by the same effect as when g is reduced. That is, when floating gas is applied from below the droplet, the weight of the droplet increases. However, since the flow of the floating gas is disturbed and the force for lifting the droplet is not constant, the drop weight is more likely to fluctuate than when the floating gas is blocked.

Droplet weight = πDγ / g (1)
In the present invention, in order to prevent the floating gas 9 from blowing to the outflow pipe 2, as shown in FIG. 3, a shield or a support 3 c (a split member in the figure) is provided between the outflow pipe 2 and the mold 1. The outflow pipe 2 is shielded from the floating gas 9, and at the same time, the cover 5 and the shield 3c form a sealed space including the tip of the outflow pipe. In order to fill the non-oxidizing gas in the sealed space, a non-oxidizing gas 6 (N ₂ gas atmosphere in the figure) is allowed to flow through the cover. By controlling the flow rate of the non-oxidizing gas to be constant, the temperature fluctuation at the tip of the outflow pipe can be reduced. Moreover, in order to make the said shielding sufficient, the shielding body 3c is arrange | positioned across the dripping path | route of a molten glass droplet, and it removes the shielding body 3c from a dripping path | route synchronizing with dripping. Specifically, the shield 3c is composed of a plurality of split members, shields the outflow pipe 2 from the gas 9 ejected by bringing the split members into close contact with each other, and synchronizes with the split of the molten glass droplet 4b. The members are separated from each other, and the shield 3c is arranged so that the molten glass droplet 4b falls between the separated split members. Alternatively, the shield is used as a support, receives and supports the dropped glass droplets, cools to some extent, and then separates the split members as the support from each other, and the molten glass droplets between the separated split members. Position the support so that it falls. In order to perform the above operation reliably and easily, it is preferable that the shield is constituted by two split members.
By shielding the outflow pipe from the floating gas in this way, it is possible to stabilize the outflow condition of the molten glass and the dripping condition of the molten glass droplet, and improve the mass accuracy of the glass molded body. The mass accuracy is preferably within a range of ± 1% of the target mass.

The second form of the preform manufacturing method 2 is a manufacturing method of a preform in which molten glass droplets are dropped from an outflow pipe and received by a molding die that ejects gas, and the preform manufacturing method 2 is formed. This is the same as the first embodiment. FIG. 4 is a manufacturing process diagram showing still another example of the method for manufacturing a precision press-molding preform according to the present invention. As shown in FIG. 4, it is supported so as to cross the dropping path of the molten glass droplet 4b. A body 3b (a split member in the figure) is provided to shield the outflow pipe 2 from the gas 9 ejected from the mold 1, and after the dropped molten glass droplet 4b is directly received by the support 3b, the support 3b The molten glass droplet 4b falling vertically downward is received by the molding die 1 and molded. The support 3b also functions to directly receive and support the molten glass droplet 4b that has been dropped, together with the function of the shield in the first form of the preform manufacturing method 2. In the method shown in FIG. 4, the surface of the support 3 b that receives the molten glass droplet is inclined so that the molten glass droplet 4 b can be stably seated at the position where the two split members are brought into close contact with each other. By doing so, the molten glass droplet 4b is allowed to fall naturally at a desired position of the mold 1, preferably at the center of the mold.
In FIGS. 3 and 4, a skirt made of a resilient material such as Teflon may be attached between the glass cover 5 and the split members 3c and 3b without any gap to further improve the sealing performance in the cover.
The structure, shape, material, and cooling method of the support may be the same as in the preform manufacturing method 1.

  In the first form of the preform manufacturing method 2, it is preferable to drop molten glass droplets from the outflow pipe into the forming part provided with the gas outlet of the molding die. In the second aspect, the gas outlet of the molding die is It is preferable to drop the molten glass droplets received by the support on the formed part. The glass dropped or dropped from the outflow pipe to the mold may be solidified to some extent. The glass dropped or dropped including such a case is called a molten glass drop.

  The second embodiment has the following advantages. When glass with extremely low viscosity when flowing down is directly inserted into a molding die that blows out gas, even if it is inserted into the center of the die, it may fold and cause striae or bubbles. In particular, when a spherical preform is molded, it is necessary to rotate the molten glass at a high speed in the mold, which may cause folding striae and bubbles. Therefore, it is necessary to increase the viscosity of the molten glass as much as possible before spheroidizing with a mold. In this method, the molten glass is held on the support before being inserted into the mold, and the molten glass is cooled by removing the heat of the molten glass from the contact surface. In this way, it is possible to reduce easily volatilized and highly reactive components such as fluorine from glass while preventing folding striae and generation of bubbles. Although other cooling means are conceivable, for example, in the method of blowing gas, there is a risk of cooling the outlet. Further, a method of supporting and cooling the molten glass in a non-contact state with a gas blown from the porous material using a support made of a porous material is also conceivable. However, in addition to the danger of cooling the outlet with gas, there is a problem that productivity is reduced because the cooling rate is low in the non-contact state, so that the dropping interval must be delayed. That is, the second embodiment is preferable because the viscosity of the molten glass is reliably increased in a short time and there is no possibility of cooling the outlet. Further, as described above, when the molten glass is dropped and inserted into the mold, it is desirable that the molten glass be dropped at the lowest possible speed, that is, spontaneously dropped into the center of the mold. In order to realize such a condition, the support is composed of a plurality of split members, the split members are brought into close contact with each other, molten glass is received at the contact portion, the split members are separated from each other, and the separated split members are separated. A method in which molten glass droplets are dropped between them is used. In this way, the falling distance of the molten glass droplet can be reduced, the molten glass droplet can be naturally dropped, and the molten glass droplet can be naturally dropped directly below without giving an impact to the molten glass droplet. In addition, the same thing as the molten glass support body used by the preform manufacturing method 1 can be used for a support body.

In the second embodiment, the split member constituting the support is made of a heat-resistant metal material, carbon, ceramics, etc. and processed into a thin plate shape. The contact portion with the molten glass is cooled by flowing water or gas inside to prevent fusion with the glass. In order to control the cooling rate, it is also effective to control the water temperature. In addition, the split member is inclined toward the contact portion so that the position of the dropped molten glass lump is stabilized, and the support position of the molten glass is lowered. The surface does not need to be a flat surface, and may be a curved surface. Moreover, you may form a hollow in a contact part with molten glass.
Further, in order to reduce the horizontal force applied to the molten glass when the split member is separated, it is desirable that the surface supporting the molten glass is a polished surface, and coating having anti-fusing and low friction characteristics is performed.
The material of the mold, the film provided on the molding surface, and the method of transferring the mold may be the same as in the preform manufacturing method 1.
The above-described method is also suitable for molding glass whose mass accuracy and quality are likely to deteriorate due to fluctuations in molten glass outflow conditions and molten glass droplet dropping conditions.

Here, in order to perform the step of dripping the molten glass in a sealed space filled with a non-oxidizing gas, all the molds for molding the tip of the outflow pipe, the shield, and the preform are placed in a sealed container. The inside may be filled with a non-oxidizing gas. Alternatively, in order to minimize the sealed space as described above, the space including the tip of the outflow pipe is covered with a cover, an opening is provided at the bottom of the cover so as not to prevent the molten glass droplet from falling, and the cover is covered with the shield. Close the opening. Except when dropping the molten glass drop into the mold, the space including the tip of the outflow pipe is sealed by the cover and the shield. The sealed space is filled with a dry gas and molten glass is dropped.
Note that a transparent container is preferably used as the cover, and a glass container may be used. In this way, the outflow state can be observed from the outside.
In this way, it is possible to handle the molten glass droplets in a non-oxidizing gas atmosphere until they are sent to the mold.
The non-oxidizing gas may be the same as the non-oxidizing gas used in the preform manufacturing method 1.
Further, it is desirable to use the non-oxidizing gas as the levitation gas.
As described above, according to the preform manufacturing method 2, since the molten glass immediately after flowing out is handled in the sealed space filled with the non-oxidizing gas, a preform having a smooth surface and no defects can be formed.

Moreover, since the calorie | heat amount which the molten glass droplet of about dripping weight has is small compared with the calorie | heat amount which the molten glass lump obtained by the preform manufacturing method 1, before introducing into a shaping | molding die, easily volatile components, such as a fluorine, do not volatilize easily. The glass surface can be cooled to a temperature range. However, since the cooling of the glass is further promoted by the second mode in which the molten glass droplet is brought into direct contact with the shield, volatilization of the easily volatile component can be further reduced. As described above, according to the preform manufacturing method 2, the glass whose entire surface is melted is formed by solidification, and a preform that is smooth even when viewed microscopically without scale-like fine irregularities. Can be manufactured.
Also in the non-oxidizing gas of the preform manufacturing method 2, the dry gas of the preform manufacturing method 1 can be used.
The preform manufacturing method 2 is suitable for manufacturing a preform having a relatively small mass. The preferred range of preform mass is 5 to 600 mg.

In either of the preform production methods 1 and 2, the molten glass lump (droplet) is at a high temperature when it is dropped into the mold, not as soon as it flows out. Since the floating gas is applied only to the lower surface of the glass, it is preferable to perform molding with the atmosphere around the mold as the non-oxidizing gas atmosphere. Although it is a simpler method, the method of spraying any one of the above gases onto the upper surface of the glass on the mold is effective.
Both preform manufacturing methods 1 and 2 are also suitable for forming glass with low outflow viscosity, which is likely to be folded, and has high mass accuracy from molten glass with a viscosity at the time of flow of about 0.5 to 50 dPa · s. High quality preforms can also be molded.

In the case of a glass having a low outflow viscosity as described above, when a spherical preform is formed, a molten glass lump (droplet) is inserted into a mold having a funnel-shaped hole as shown in FIG. If a molten glass lump (droplet) can be inserted in the center of the mold when the molten glass lump (drop) is inserted, it will be supported by the gas flow that blows up and land, so there is a risk that the molten glass will break and foam and striae will occur. Lower. However, if a molten glass lump (drop) falls on the entrance of a funnel-shaped hole or a wall, the molten glass lump (drop) may be stretched due to frictional resistance or instantaneous fusion between the wall and glass. . In such a case, the glass breaks before landing and bubbles and striae are likely to occur. Such a problem is a problem peculiar to a glass having a low viscosity when flowing down, and hardly becomes a problem in a glass having a viscosity of 50 dPa · s or more. Therefore, a molding die is arranged directly under the outflow pipe to prevent folding and foaming when a molten glass lump (droplet) is inserted into the die. However, if the floating gas from the mold is applied to the outlet of the outflow pipe, problems such as mass fluctuation of the preform and deterioration of the quality of the glass occur. Therefore, in the preform manufacturing method 1, the gas for floating the glass is used. In the preform manufacturing method 2, the molten glass support is blocked by a shield so as not to be applied to the outflow pipe. In the preform manufacturing method 2, it is desirable that the shield used only for the purpose of shielding the floating gas should be a thin plate, and the falling distance of the molten glass droplet should be as small as possible. The material of the shielding plate may be a heat resistant metal material in consideration of the case where the molten glass comes into contact. In addition, it is desirable to use a split member with a short moving distance in order to shield and remove at high speed in synchronization with dropping.
(About preform manufacturing method 3)
In a third aspect of the preform manufacturing method (hereinafter referred to as preform manufacturing method 3), a molten glass lump of a constant mass is separated from the molten glass flowing out from the outlet of the outflow pipe, and the wind pressure is applied to the glass lump. In a manufacturing method of a precision press-molding preform that is received by a molding die that blows out a gas to be added and formed into a glass preform while being floated, a cover having an opening that can be opened and closed vertically below the outlet The space including the outlet is covered, and the space is sealed when the opening is closed, and a non-oxidizing gas is supplied into the space, and the molten glass lump is formed in the state where the opening is closed. The glass lump is transferred to a molding die that separates and opens the opening and injects a non-oxidizing gas disposed in the vicinity of the opening, and is molded.
As the non-oxidizing gas, the same one as in the preform production method 1 or 2 can be used.

Since the preform manufacturing method 3 can move the molten glass lump from the sealed space to the mold in a state where the opening of the sealed space and the mold are close to each other, the glass in a high temperature state is kept in a non-oxidizing gas atmosphere for a long time. A good preform can be formed even with glass that can be handled and exhibits high reactivity at high temperatures.
From the above viewpoint and from the viewpoint of preventing the occurrence of defects such as folding by minimizing the fall distance of the molten glass lump, the opening is opened after the opening and the upper end of the mold are brought into close contact with each other. It is preferable to drop.
Further, in order to prevent folding, it is desirable that the molten glass block is dropped freely in the vertical direction, and is preferably dropped at the center of the molding part of the mold.
In order to more stably produce a high-quality preform, a method combining the preform manufacturing methods 1 and 3 or a method combining the preform manufacturing methods 2 and 3 is more desirable.

As the glass suitable for the method for producing the preform of the present invention, fluorine-containing glass, fluorophosphate glass, boron-containing glass, boron and fluorine-containing glass, Bi-containing glass, Bi and fluorine-containing glass, Bi-containing fluorophosphate glass, Bi and boron-containing glass, Bi, boron and fluorine-containing glass can be exemplified.
In the present invention, it is desirable to introduce Bi into the glass component in order to reduce the wetting of the molten glass to the outer periphery of the outflow pipe tip and to improve the high temperature stability of the glass. The wet glass is considered to stay on the outer periphery of the pipe for a relatively long time, during which the easily volatile and highly reactive components such as fluorine and boron are detached and deteriorated. When the glass thus altered is taken into the molten glass lump or molten glass droplet, a heterogeneous portion is generated in the preform and becomes a defect. Therefore, it is desired to reduce the wetting up as much as possible.

By introducing Bi, the surface tension of the molten glass is increased, and not only the above-described reduction in wetting, but also a preform having a reduced striae and a microscopically smooth surface can be efficiently produced. In order to reduce the above wetting, it is desirable to use a gold-containing platinum alloy outflow pipe.
In addition, melting of fluorine-containing glass (for example, fluorophosphate glass) is performed in a non-oxidizing gas atmosphere in which the oxygen content is suppressed to 15% or less by volume, or in an atmosphere such as nitrogen gas or argon gas that does not react with molten glass. It is preferable to carry out with. It can also be melted in a dry non-oxidizing gas atmosphere. In this way, a preform made of fluorophosphate glass having a refractive index (nd) in the range of 1.4 to 1.65 and an Abbe number (νd) in the range of 65 to 97 can be manufactured. .

Next, the preform of the present invention will be described.
[preform]
The first preform of the present invention is a preform produced by the production method of the present invention, and the second preform is made of Bi-containing fluorophosphate glass, and the glass whose entire surface is molten is solidified. It is a preform characterized by being formed.
The preform of the present invention is formed by solidifying glass whose entire surface is in a molten state, and there are no fine scratches such as polishing marks and latent scratches. Further, since there are no fine irregularities, the surface is microscopically smooth. By such a preform, the surface of the precision press-molded product, particularly the surface of the optical functional surface, can be made into a good surface free of irregularities that are not intended microscopically. Performance degradation can be prevented. In addition, as the preform of the present invention, a preform whose entire surface is a free surface is preferable.

Next, a preferable shape of the preform will be described. During precision press molding, the preform can be expanded isotropically as much as possible, and the main use of optical elements, which are the main applications of precision press-molded products, has a rotational symmetry axis. Therefore, a shape having a sphere or one rotational symmetry axis is preferable. A preferable shape having one rotational symmetry axis is as follows.
Consider a straight line connecting a point on the contour of the preform and the center of gravity of the preform in a cross section including the axis of symmetry, and a tangent line that touches the contour at the point on the contour. A preferable shape is one in which the angle θ formed by the straight line and the tangent line changes as follows. That is, θ is 90 ° at the intersection of the rotationally symmetric axis and the contour line, and as the point on the contour line is moved from this intersection point, θ increases monotonically, then decreases monotonically, and after it reaches 90 ° again. Monotonously decreases. It then proceeds monotonically and returns to 90 ° at the other intersection of the rotational symmetry axis and the contour line. In this case, since the preform is a rotating body, θ becomes 90 ° again at the intersection of the start points while exhibiting the same behavior as the above behavior. When θ is set to the complementary angle of θ, a behavior in which monotonic increase and monotonic decrease are interchanged is shown.
With such a shape, the atmosphere gas is confined between the preform and the press mold during precision press molding, and the risk of a gas trap that causes molding defects can be reduced. In order to further reduce the risk of such a gas trap, the preform surface may be formed so that the radius of curvature of the preform surface is smaller than the radius of curvature of the press mold forming surface.
Next, the case where the preform of the present invention is made of fluorophosphate glass will be described. Taking advantage of the fact that this optical glass is a fluorophosphate glass, it is preferable that the optical glass has a low dispersion characteristic with an Abbe number (νd) of 65 or more. Particularly, the refractive index (nd) is 1.4 to 1.65, and the Abbe number. Those having (νd) of 65 to 97 are preferred.

Then, the preferable composition of optical glass is demonstrated.
(Preferred composition I)
The first preferred fluorophosphate glass contains Bi ions as the cation component. Bi ion introduction has the effect of improving the high temperature stability of the glass and reducing the wetting of the outflow pipe. Furthermore, the introduction of Bi increases the surface tension, so that it is possible to efficiently produce a preform that not only reduces the above wetting, but also reduces striae and has a microscopically smooth surface. The amount of Bi introduced is 0.2 to 20 mol% for BiF _{3 and} more than 0 mol% to 10% or less for Bi ₂ O ₃ .
(Preferred composition II)
The second preferred fluorophosphate glass comprises P ⁵⁺ , Al ³⁺ , Ba ²⁺ , Ca ²⁺ , Sr ²⁺ as essential cation components and Mg ²⁺ , Zn ²⁺ , Li ⁺ , Na ⁺ , K ⁺ , Si as optional cation components. ^{Fluorophosphate} containing ⁴⁺ , B ³⁺ , La ³⁺ , Gd ³⁺ , Y ³⁺ , W ⁶⁺ , Nb ⁵⁺ , Bi ³⁺ , O ²⁻ , F ⁻ as essential anion components, and Cl ⁻ , Br ⁻ as optional anion components It is glass. Specifically, by _{mol%, Al (PO 3) 3 0~15} %, Ba (PO 3) 2 1~25%, AlF 3 2~45%, YF 3 0~15%, LaF 3 0~ 10%, GdF ₃ 0-10%, MgF ₂ 0-20%, CaF ₂ 2-45%, SrF ₂ 2-45%, BaF ₂ 0-20%, ZnF ₂ 0-30%, LiF 0-10% , NaF 0-15%, KF 0-15%, SiO ₂ 0-5%, B ₂ O ₃ 0-5%, 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%, 0~5% ZnO, Y 2 O 3 0~5%, Al 2 O 3 0~5% , Gd ₂ O ₃ 0-5%, Nb ₂ O ₅ 0-5%, WO ₃ 0-5%.
The reason why the composition range of each component is limited is as follows.

Al (PO ₃ ) ₃ is a component that constitutes the network structure of glass, and is the most important component that improves the weather resistance of glass. However, if its content exceeds 15%, the thermal stability of the glass decreases. The liquid phase temperature and the optical properties (dispersion becomes high) may be greatly deteriorated, so the amount introduced is 15% or less. More preferably, it is 0.5 to 12% of range.

Ba (PO ₃ ) ₂ is a component that constitutes a network structure of glass, and at the same time, an essential component for improving the weather resistance of glass. If the content is less than 1%, the weather resistance of the glass is significantly lowered and the stability is also deteriorated. On the other hand, if it exceeds 25%, the optical constant (Abbe number) of the glass is lowered, and the weather resistance is also deteriorated due to an increase in P ₂ O ₅ . Therefore, the amount introduced is 1 to 25%. More preferably, it is 2 to 20% of range.

AlF ₃ is a component that stabilizes and lowers the dispersion of glass. However, if its content exceeds 45%, the stability of the glass is remarkably deteriorated and the meltability is deteriorated. Is not obtained, the amount of introduction is in the range of 2 to 45%. More preferably, it is 4 to 40% of range.

Although YF _{3, GdF} 3, LaF ₃ has a high effect of devitrification resistance improved by a small amount of _additives, YF _3, GdF 3, LaF respectively 15% introduction amount of _3, 10%, more than 10%, the glass On the contrary, it becomes unstable and tends to devitrify, so the amount of introduction is limited to 15%, 10% and 10% or less, respectively. More preferably, the content of YF ₃ is 12% or less, the content of GdF ₃ is 8% or less, and the content of LaF ₃ is 7% or less.

If MgF ₂ is introduced in a large amount exceeding 20%, the crystallization tendency of the glass increases and the glass becomes unstable. Therefore, the amount introduced is set to 0 to 20%. The introduction of a small amount of MgF ₂ contributes to the improvement of the stability of the glass and greatly contributes to the low dispersion of the glass.

CaF ₂ and SrF ₂ are indispensable components for maintaining the glass devitrification resistance and reducing the dispersion. In particular, CaF ₂ plays a role of strengthening the glass structure in combination with AlF ₃ and is an indispensable component for stabilizing the glass. However, when the amount of CaF ₂ and SrF ₂ introduced is less than 2%, the stability of the glass deteriorates, and it becomes difficult to obtain a desired optical constant. Therefore, the amount of introduction should be in the range of 2 to 45%. More preferably _CaF 2 5 to _40%, in the range of SrF 2 3 to 35%.

ZnF ₂ is a component that is introduced to increase the stability and weather resistance of the glass. However, if the amount of introduction exceeds 20%, the glass becomes unstable, so the amount of introduction is 0 to 20%. To do. A more preferable introduction amount is in the range of 1 to 16%.

BaF ₂ is a very useful component for enhancing the stability of the glass and improving the refractive index. However, when introduced in an amount of more than 30%, the glass tends to be crystallized and is difficult to dissolve. The amount is 0-30%. A more preferable introduction amount is in the range of 2 to 25%.

  LiF, NaF, and KF have the effect of improving the devitrification resistance and dispersibility of the glass by adding a small amount. However, when introduced in a large amount, the stability of the glass deteriorates rapidly and the durability also deteriorates. , NaF and KF are suppressed to 10%, 15% and 15% or less, respectively. More preferably, they are 0 to 5%, 0 to 10%, and 0 to 10%, respectively.

_{SiO 2, B 2 O 3,} Li 2 O, Na 2 O, K 2 O, MgO, CaO, SrO, BaO, ZnO, Y 2 O 3, Al 2 O 3, Gd 2 O 3, Nb 2 O 5, WO ₃ is an optional component and has the effect of improving the stability, weather resistance and durability of the glass by introducing a small amount of the above components, but may deteriorate the meltability of the glass or the dispersibility. Therefore, the amount of introduction should be 5% or less. More preferably, it is 4% or less.
Furthermore, a small amount of a compound such as Cl or Br can be introduced for the purpose of defoaming or adjusting the optical constant.

In addition, the preferable glass composition II and the preferable glass composition I can be combined, and the preferable glass composition II containing Bi can also be made.
The water resistance of the fluorophosphate glass constituting the preform is preferably less than 0.25 in terms of weight loss (%) in a water resistance test according to the Japan Optical Glass Industry Association standard.
Further, the fluorophosphate glass constituting the preform is held in a thermo-hygrostat filled with clean air having a temperature of 65 ° C. and a relative humidity of 90% in a state where both sides are optically polished, It is desirable to have weather resistance such that the intensity ratio of scattered light / transmitted light when transmitting white light is 8.0 or less.
Furthermore, fluorophosphate glass having a glass transition temperature (Tg) of 500 ° C. or lower is preferred from the viewpoint of precision press moldability.

Moreover, the thing in which the wavelength from which the internal glass transmittance (thickness 10mm conversion) which does not include the reflection and scattering loss in a glass surface will be 80% is in the range of 300-370 nm is preferable.
In addition, when introduce | transducing an absorber into glass and providing a filter function, a coloring component can also be introduce | transduced in glass. For example, by introducing an appropriate amount of Cu ions, near infrared absorption characteristics can be imparted, and an optical element having a near infrared absorption function can also be obtained by precision press molding.
The preform obtained by molding and slow cooling from the molten glass is washed and dried as necessary. Further, a film having a lubrication action may be formed on the preform surface so that the mold release action and the glass easily spread on the surface of the press mold. Such a film is desirably formed on the entire preform surface. Examples of the film include a carbon-containing film and a self-assembled film. Examples of the carbon-containing film include a deposited carbon film and a carbon film formed by CVD.

Next, the optical element of the present invention will be described.
[Optical element]
The optical element of the present invention is an optical element produced by heating the preform produced by the production method of the present invention or the preform of the present invention and precision press molding. Examples of such an optical element include a lens, a prism, a prism with a lens, a diffraction grating, and a polygon mirror. Examples of the lens include a spherical lens, an aspheric lens, a micro lens, a pickup lens, a collimator lens, and a lens array.

  By using a preform having high mass accuracy, an element in which the entire surface of the optical element is a surface formed by precision press molding can be obtained. By forming the entire surface of the optical element by precision press molding, it is not necessary to shape the precision press-molded product by mechanical processing such as grinding or polishing. A non-optical functional surface (referred to as a lens peripheral portion) around the optical functional surface of the lens may be used to fix the lens to the holder. In order to use the lens peripheral portion as a reference for positioning when fixing the lens peripheral portion to the holder, the relative positional relationship and the angle between the optical axis of the lens and the lens peripheral portion must be accurately formed in a predetermined relationship. If the optical functional surface and the lens peripheral part are simultaneously molded by precision press molding, the lens positioning reference function can be imparted to the lens simultaneously with press molding.

When the entire surface of the optical element is formed by precision press molding, the mass accuracy of the precision press molding preform used is preferably within ± 1% of the target value.
When the optical element is made of fluorophosphate glass, a low dispersion or ultra-low dispersion optical element can be provided. In addition, fluorophosphate glass has high ultraviolet transmittance, so lenses for optical control of ultraviolet rays (spherical lenses, aspherical lenses, microlenses, pickup lenses, collimator lenses, lens arrays, etc.), prisms, and lenses Suitable for prisms.
Moreover, the optical element which has a light absorption function can also be obtained by using the preform which introduce | transduced the coloring agent as mentioned above. As such an element, an optical element having a near-infrared absorption function to which Cu ions are added, for example, the above-described various optical elements can be provided.

An optical multilayer film such as an antireflection film, a partial reflection film, or a high reflection film or a single layer film may be formed on the surface of the optical element as necessary.
[Method for Manufacturing Optical Element]
The optical element manufacturing method of the present invention is characterized in that the preform produced by the manufacturing method of the present invention or the preform of the present invention is heated and precision press-molded using a press mold.
By the above method, a high-quality optical element free from defects such as fine irregularities, alteration, striae, devitrification, etc., which are not intended for the optical function surface can be produced. It is particularly suitable for producing an optical element made of fluorophosphate glass.

A first aspect of the optical element manufacturing method (referred to as optical element manufacturing method 1) is a method of introducing a preform into a press mold, heating the preform and the press mold together, and performing precision press molding. It is.
In a second aspect of the optical element manufacturing method (referred to as optical element manufacturing method 2), the preform and the press mold are heated separately, and then the preform is introduced into the press mold and precision press molding is performed. It is a method.

In manufacturing method 1 of the optical element, it is preferable that the temperature of the press mold and the temperature of the preform are set to temperatures at which the glass constituting the preform exhibits a viscosity of 10 ⁸ to 10 ¹² dPa · s. Further, it is preferable that the glass is cooled to a temperature exhibiting a viscosity of 10 ¹² dPa · s or more and then taken out from the press mold, and the glass is cooled to a temperature exhibiting a viscosity of 10 ¹⁴ dPa · s or more. It is more preferable to take out from the press mold, and it is even more preferable to take out from the press mold after cooling to a temperature exhibiting a viscosity of 10 ¹⁶ dPa · s or more.

The optical element manufacturing method 1 is a method in which a preform preheated to a temperature higher than that of the press mold is introduced into the press mold and precision press molding is performed. In this method, it is preferable to release the mold after press forming after the glass constituting the preform has a viscosity of 10 ¹² dPa · s or more.
In addition, it is preferable to preheat the preform while floating, and it is more preferable to preheat to a temperature at which the glass exhibits a viscosity of 10 ^5.5 to 10 ⁹ dPa · s. Moreover, it is preferable to start cooling the glass simultaneously with the start of the press or in the middle of the press.
In the preheating of the preform, the preheating temperature is preferably a temperature at which the glass exhibits a viscosity of 10 ⁹ dPa · s or less, and more preferably a temperature at which a viscosity of 10 ^5.5 to 10 ⁹ dPa · s is exhibited. The temperature of the press mold is preferably a temperature at which the glass exhibits 10 ⁹ to 10 ¹² dPa · s.

In any of the above methods, a press mold using a mold material made of SiC, cemented carbide, heat-resistant metal or the like and provided with a release film such as a carbon film or a noble metal film on the molding surface as necessary. The press molding can be performed in an atmosphere of nitrogen, a mixed gas of nitrogen and hydrogen, an inert gas, or the like. The press-molded optical element may be provided with the above-described film as necessary after being gradually cooled.
As described above, according to the method for manufacturing an optical element of the present invention, since a high-quality preform is used, a good optical element free from surface defects and internal defects can be produced. Furthermore, since the mass accuracy of the preform is high, an optical element can be produced without machining any surface other than the optical functional surface.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
Various physical properties of the glass were measured as follows.
(1) Refractive index (nd) and Abbe number (νd)
It measured about the optical glass obtained by cooling at the temperature fall rate of 30 degreeC per hour.
(2) Glass transition temperature (Tg) and yield point (Ts)
Using a thermomechanical analyzer, the temperature was increased at a rate of 4 ° C./min.
Example 1
A glass raw material prepared by mixing a predetermined amount of batch is heated and melted, defoamed and clarified, and stirred and homogenized to continuously flow down from a temperature-controlled platinum alloy nozzle at a constant flow rate. At this time, the amount of glass pulled up was 9.5 kg / day. In addition, the composition and characteristics of the glass obtained from the above molten glass are as shown in Table 1.

The molten glass stream flowing down is formed into a preform by the apparatus shown in FIGS.
The molten glass support used in this example is composed of two flat plate-shaped split members, and the surface that receives the tip of the molten glass flow is mirror-finished. Is configured. Further, in order to control the outlet and the support to the N ₂ atmosphere, a SiO ₂ glass cover is attached as shown in FIGS. 1 and 2, and the N ₂ atmosphere is controlled until the glass melt is sent to the mold. Further, a water channel is provided inside the molten glass support to prevent fusion with the molten glass, and cooling is performed by flowing cooling water. The temperature of the support was controlled by controlling the amount of water-cooled water and the water temperature. The surface of the molten glass support was coated with diamond-like carbon.

  First, as shown in FIG. 1, the molten glass support is raised in a state where the split members are in close contact with each other, moved to 4 mm below from the surface receiving the tip of the molten glass flow and the outlet pipe outlet, and then stopped. In this state, the surface that receives the tip of the molten glass flow is kept in a horizontal state (the state in which the receiving surface faces vertically upward). Next, the tip of the flowing molten glass flow is received and supported by the boundary portion between the two split members that are in close contact with each other. The size of the molten glass supported on the molten glass support increases with time. If the amount of molten glass is large, the pipe tip may be buried in the molten glass, and striae may occur. Therefore, in order to maintain the distance between the molten glass and the outflow nozzle, the support may be lowered in the vertical direction at a low speed. When molten glass of a desired mass is collected on the support, the support is rapidly lowered vertically with the support in close contact with the split member, and the glass flow is cut and separated by the surface tension of the glass. A molten glass lump having a predetermined mass is obtained on the body. The descending distance of the support may be a distance at which the molten glass flow can be cut. Next, the split members were separated from each other, and the molten glass lump was dropped vertically downward from between the two split members. The fallen molten glass lump falls into a mold waiting under the support, and is molded into a preform while being floated by a gas ejected from the bottom of the mold.

After dropping the molten glass block from the molten glass support, the split members are immediately returned to the state of being in close contact with each other. By this operation, the support can block the gas and prevent the gas from being blown to the outflow pipe. The support then rises again to receive the tip of the molten glass flow.
The glass molded body cooled and solidified with time on the mold is sucked out from the mold, transferred onto a pallet, and gradually cooled. In this way, preforms having a predetermined mass are successively produced from the molten glass that continuously flows out.

In addition, as shown in FIG. 2, the molten glass lump of a predetermined mass is separated without using a cutting blade by separating the split members from each other, and spontaneously falls to the center of the mold and is continuously discharged from the molten glass. A method of manufacturing preforms having a predetermined mass one after another was also performed. The split member is tapered, and the opening angle when the split member is in close contact is 150 °. By attaching this taper, the position of receiving the molten glass was further stabilized, and the accuracy of the dropping position of the molten glass lump was improved.
In this way, the preform production cycle was set to 3.2 seconds, a 350 ± 3 mg spherical glass molded body made of optical glass was produced, and a preform made of fluorophosphate glass was obtained.
The preform did not show defects such as kanware and other scratches, striae, folds, and devitrification.
Furthermore, when the preform surface was magnified and observed with an optical microscope, the entire surface was smooth.

In addition, since the glass flow is cut by one split member, the cutting accuracy of the glass flow is greatly improved compared to the case where the glass flow is cut by a plurality of molds, and the temperature of the outflow pipe tip is increased by the gas blown from the mold. Since it does not fluctuate, the mass accuracy is also high within ± 1% of the target value as described above.
Example 2
The prepared glass raw material is melted by heating, defoaming clarification and stirring and homogenization, and the same molten glass as in Example 1 is continuously flowed down from a temperature-controlled platinum alloy pipe at a constant flow rate. The amount of glass pulled up at this time was 8 kg / day.
The molten glass flow flowing down is formed into a press-forming preform by the apparatus shown in FIG.

  The shield used in this example is composed of two flat plate-shaped split members. The split members are in close contact with each other and shield the tip of the outflow pipe from the flow of gas and air coming from below, but the split members are separated from each other in accordance with the timing when the molten glass droplet drops from the top of the outflow pipe. The molten glass droplet falls into the mold through the space between the split members. As soon as the molten glass droplet passes between the split members, the split members are brought into close contact with each other to shield the outflow pipe from the gas.

Moreover, it can also shape | mold into the preform for press molding with the apparatus shown by FIG.
The support used in FIG. 4 is composed of two split members whose surfaces for receiving molten glass droplets are inclined. The split members are in close contact with each other and shield the tip of the outflow pipe from the flow of gas and air coming from below, and after the molten glass droplet has dropped on the support from the tip of the outflow pipe, the glass melted droplet is somewhat discharged. After cooling, the split members are separated from each other, and molten glass droplets drop into the mold through the spaced apart split members. As soon as the molten glass droplet passes between the split members, the split members are brought into close contact with each other to shield the outflow pipe from the gas.

The molten glass drop that has fallen on the mold is formed into a glass molded body in a spherical shape while being floated while being rotated by the floating gas. Next, the cooled and solidified glass molded body is sucked and taken out from the mold, transferred onto a pallet and gradually cooled. Thus, the molten glass which flows out continuously is dripped, and the glass molded object of a predetermined mass is manufactured one after another.
In this way, a 350 ± 1.4 mg spherical preform made of fluorophosphate glass was produced.
The preform did not show defects such as kanware and other scratches, striae and devitrification. Further, the weight accuracy was also high within ± 1% of the target value as described above.

Furthermore, when the preform surface was magnified and observed with an optical microscope, fine irregularities were not seen and the surface was smooth. Further, the entire surface was a free surface.
Example 3
The preforms made of fluorophosphate glass molded in Examples 1 and 2 were washed and dried, and then precision press molding was performed to produce an aspheric lens. In the press molding, a press mold in which a carbon film was formed on the surface of a SiC mold material was used, and the atmosphere was a nitrogen atmosphere. The press molding was performed by heating the preform to a temperature of 600 ° C. or lower and pressing it at a pressure of 10 MPa for 60 seconds. After press molding, the aspherical lens was removed from the press mold and gradually cooled. The obtained lens was in good condition both on the inside and on the surface. Even when the lens surface was magnified, fine irregularities were not recognized. The lens does not need to be centered, and can be used as a positioning reference when fixing a lens peripheral portion formed by precision press molding to a holder. An antireflection film may be formed on the surface thus obtained.
In the precision press molding, the preform may be introduced into the press mold, and the preform and the press mold may be heated at the same time, or the heated press mold may be put into the preheated press mold. You may press.

Although this embodiment relates to a method for manufacturing an aspheric lens, it can also be applied to manufacturing other optical elements such as prisms and diffraction gratings.
Comparative Example Molten glass from which the glass having the same composition as in Examples 1 and 2 is obtained is dropped from the outflow pipe in the atmosphere, dropped into a mold for injecting the floating gas waiting under the outflow pipe, and spherical while floating. Molded into a preform. When this preform was cooled slowly, it was magnified and observed with an optical microscope. As a result, fine scale irregularities were observed over the entire surface.
Subsequently, when this preform was precision press-molded in the same manner as in Example 3, fine irregularities were observed on the obtained lens surface. In addition, the mass accuracy of the preform deteriorated because levitation gas was blown onto the outflow pipe.

Moreover, the molten glass from which the glass of the same composition as Example 1 and 2 is obtained flows out from an outflow pipe in air | atmosphere, the front-end | tip is received with the shaping | molding die which ejects a floating gas, and it is predetermined at the timing at which glass of a predetermined mass is obtained. The mold was lowered by a distance of 1 to obtain a molten glass lump on the mold. The molten glass lump was molded into a spherical preform while levitating. When this preform was cooled slowly, it was magnified and observed with an optical microscope. As a result, fine scale irregularities were observed over the entire surface.
Subsequently, when this preform was precision press-molded in the same manner as in Example 3, fine irregularities were observed on the obtained lens surface.

  According to the preform manufacturing method of the present invention, a high-quality glass precision press-molding preform can be efficiently manufactured. Then, by performing precision press molding of the preform, it is possible to produce various optical elements that do not require shape processing by mechanical processing such as grinding and polishing.

It is a manufacturing process figure which shows an example of the manufacturing method of the preform for precision press molding of this invention. It is explanatory drawing which shows another example of the shape of the split member which receives a molten glass flow. It is a manufacturing process figure which shows another example of the manufacturing method of the preform for precision press molding of this invention. It is a manufacturing process figure which shows another example of the manufacturing method of the preform for precision press molding of this invention.

Explanation of symbols

1 mold 2 flow pipe 3a, 3b, 3c split member 4 molten glass 4a molten glass gob 4b molten glass drop 5 cover 6 N ₂ gas atmosphere 7 waterway 8 Teflon skirt 9 floating gas

Claims (13)

The glass melt gob of predetermined weight from a molten glass flowing out from the outlet of the outflow pipe are separated, in the mold for ejecting the gas undergoing those the glass gob to wind pressure applied by the gas, the glass preform while floating In the manufacturing method of the precision press molding preform to be molded,
The molten glass support disposed under the outflow pipe is directly supported by receiving the tip of the molten glass flow while shielding the outflow pipe from the gas ejected from the mold , and the support by the molten glass support is removed and melted. A method for producing a precision press-molding preform, wherein the step of separating the molten glass block from the tip of a glass stream is performed in a sealed space filled with a non-oxidizing gas. In a manufacturing method of a precision press-molding preform in which a molten glass droplet is dropped from an outflow pipe, received by a molding die that ejects gas, and formed into a glass preform while being floated by applying wind pressure with the gas,
The dropping of the molten glass droplet is performed in a sealed space filled with a non-oxidizing gas, and a shield is provided so as to cross the dropping path of the molten glass droplet to shield the outflow pipe from the gas ejected from the mold. And the manufacturing method of the preform for precision press molding characterized by removing the said shield from the said dripping path | route synchronously with dripping of a molten glass droplet. In a manufacturing method of a precision press molding preform for dropping a molten glass droplet from an outflow pipe, receiving it with a molding die for jetting gas, and forming a glass preform while floating by applying wind pressure with the gas,
The molten glass droplet is dropped in a sealed space filled with a non-oxidizing gas, and a support is provided so as to cross the molten glass droplet dropping path to shield the outflow pipe from the gas ejected from the mold. In addition, a molten glass droplet is dropped on the support, and the support is removed from the dropping path in synchronization with the dropping of the molten glass droplet.
A method for producing a precision press-molding preform. While separating a molten glass lump or molten glass drop of a certain mass from the molten glass flowing out from the outlet of the outflow pipe and receiving it with a molding die that blows out a gas for applying wind pressure to the glass lump or glass drop , In a method for manufacturing a precision press-molding preform to be molded into a glass preform,
A space including an outlet is covered with a cover having an opening that can be opened and closed vertically below the outlet, and the space is sealed when the opening is closed, and a non-oxidizing gas is contained in the space. The glass is applied to a molding die that separates a molten glass lump or molten glass droplet with the opening closed, and opens the opening and ejects a non-oxidizing gas disposed close to the opening. A method for producing a precision press-molding preform, wherein a lump or glass droplet is transferred and molded. The manufacturing method of the precision press molding preform of any one of Claims 1-4 which isolate | separate a molten glass lump or a molten glass drop one after another, and it falls and shape | molds to a some shaping | molding die one by one. The method for producing a precision press-molding preform according to any one of claims 1, 2, 3, and 5, wherein the gas for applying wind pressure is a non-oxidizing gas. The molten glass support or the support is composed of two split members, and a recess for storing the molten glass is formed on the mating surface of the split members with the split members in close contact with each other. The method for producing a precision press-molding preform according to any one of claims 1, 3, and 5. The said sealed space is formed of the said molten glass support body or shielding body, and the cover arrange | positioned on the said molten glass support body or shielding body of Claim 1, Claim 2, Claim 3 and Claim 5. The manufacturing method of the preform for precision press molding of any one of Claims 1. The method for producing a precision press-molding preform according to any one of claims 1 to 8, wherein a preform made of glass containing fluorine is molded. The method for producing a precision press-molding preform according to any one of claims 1 to 9, wherein a preform made of glass containing Bi is molded. After producing the Risei tight press-molding preform by the process according to any one of claims 1 to 10, heating the preform for precision press molding obtained, precisely by using a pressing mold A method for producing an optical element, comprising press molding. The optical element manufacturing method according to claim 11 , wherein a precision press-molding preform is introduced into a press mold, and the preform and the press mold are heated together to perform precision press molding. The method for producing an optical element according to claim 11 , wherein the precision press molding preform and the press mold are separately heated, and then the preform is introduced into the press mold and precision press molding is performed.

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