JP4834756B2 - Press molding preform manufacturing method, manufacturing apparatus, and optical element manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a press-molding preform. More specifically, in the present invention, boric acid and alkali components are easily volatilized in a molten state, such as glass based on boric acid-rare earth oxide or glass containing an alkali metal compound, and this volatilization causes striae. The present invention relates to a manufacturing method for manufacturing a preform for press molding while suppressing striae even if the glass system is easy to do. Furthermore, this invention relates to the method of manufacturing the optical element made from glass by precision press molding using the preform obtained by the said method. In addition, the present invention relates to an apparatus for manufacturing a press molding preform.

  As digital still cameras, digital video cameras, camera-equipped cell phones, etc. become smaller, higher pixels, and higher performance, they are made of high refractive index, high dispersion glass, high refractive index, low dispersion glass, and low refractive index, ultra low dispersion glass. A lens was required for the optical system. In addition, since the lens can be made aspherical, the optical system can be further miniaturized, and thus an aspherical lens having these optical characteristics is desired. On the other hand, as a manufacturing method of an aspheric glass lens, a method of precision press molding a glass preform as a raw material is the mainstream. Therefore, it has become necessary to develop a technique for hot-forming a preform from the glass and a technique for precision press-molding the preform. Here, the hot forming is a technique of directly preforming from molten glass, and preforming is performed by further forming a softened glass lump made from molten glass into a predetermined shape. However, optical glasses having the above optical constant have been known for some time, but due to the characteristics of the glass, there were many cases where the preform could not be hot-formed or precision press was difficult.

Japanese Patent Laid-Open No. 9-221329 (described later) JP-A-8-73229 (described later) JP 2000-154025 A (described later)

  In particular, glass and alkali metal compound-containing glasses mainly composed of boric acid-rare earth oxides tend to volatilize boric acid and alkali components in the molten state, and when these components volatilize, striae are likely to occur. . When trying to hot-form a preform using such glass, volatile components volatilize during hot-forming, and striae are likely to occur in the resulting preform.

  Specifically, when a boric acid-rare earth glass is molded at a temperature of about 1000 ° C., radial striae occur in the glass molded body. This striae will not occur if the forming temperature (the temperature at which the glass flows out of the pipe) is sufficiently lowered. However, when a liquid phase temperature is high (around 1000 ° C.) and a low-viscosity glass (less than 10 poise) is molded into a press-molding preform, the temperature of the molten glass can only be lowered to the vicinity of the liquid phase temperature. The liquidus temperature is the lowest temperature at which crystals precipitate when the molten glass is held. For this reason, the generation of radial surface striations is unavoidable with such high liquidus temperature and low viscosity glass, and press molded products obtained from such glass preforms can provide performance as optical components. I can't.

  Therefore, conventionally, it has been difficult to hot-form a preform from a glass system mainly containing these boric acid-rare earth oxides or glass containing an alkali metal compound. Until now, a method for producing a preform by hot forming from glass containing a large amount of volatile components has not been known. In the boric acid-rare earth glass, the above problem is remarkable, and it has been desired to provide a method for hot forming a preform while preventing the occurrence of surface striae. The same was true for glass containing an alkali metal compound that easily volatilizes.

  The present invention has been made to solve the above problems, and provides a method for producing a high-quality press-molding preform free from radial surface striae, and a production apparatus used for this method. Furthermore, it aims at providing the manufacturing method of the optical element which carries out precision press molding of the preform produced by the said method.

As a result of intensive investigations on the method of suppressing the radial surface striae found in the preform (glass molded body) as described above, the present inventors can suppress this striae by the following method. I found out that I can do it.
By blowing gas to the surface of the molten glass poured into the mold from the outflow pipe and lowering the temperature of the molten glass surface, the volatilization of volatile components can be suppressed, and as a result, the resulting glass molded body has a radial surface. The striae can no longer be seen. Moreover, about the molten glass lump obtained by cutting the molten glass flowing out from the outflow pipe into a predetermined weight, the glass molded body obtained by blowing gas immediately after the cutting to lower the temperature of the molten glass surface No radial striae can be seen.

The present invention for solving the above problems is as follows.
[Claim 1]
Including a step of allowing molten glass to flow out from an outflow pipe, separating the molten glass lump, and forming the obtained molten glass lump into a preform on a mold, wherein the preform is larger than a weight dropped from the outflow pipe. In a method for producing a press-molding preform having a weight,
A gas is blown from above and / or obliquely above the molten glass lump on the mold to promote cooling of the surface exposed to the atmosphere of the glass lump, while suppressing the occurrence of striae. A method for producing a press-molding preform.
[Claim 2]
Separation of the molten glass lump is performed by lowering the mold downward and separating and cutting the molten glass lump when the weight of the molten glass poured into the mold reaches a predetermined amount. The manufacturing method of the preform for press molding of Claim 1.
[Claim 3]
Including a step of allowing molten glass to flow out from an outflow pipe, separating the molten glass lump, and forming the obtained molten glass lump into a preform on a mold, wherein the preform is larger than a weight dropped from the outflow pipe. In a method for producing a press-molding preform having a weight,
The molten glass that has flowed out is received by the support, the molten glass lump is transferred from the support to a mold and a preform is formed, and the molten glass on the support and / or the mold is upward and / or oblique A method for producing a preform for press molding, characterized in that a preform is obtained by blowing a gas from above to promote cooling of the surface exposed to the glass atmosphere and suppressing occurrence of striae .
[Claim 4]
The transition from the support to the mold of the molten glass lump is performed by receiving the molten glass that has flowed out with the support, and when the predetermined amount of molten glass accumulates on the support, the support is rapidly lowered to melt from the molten glass stream. The method for producing a preform for press molding according to claim 3, wherein the molten glass lump obtained by cutting and separating the glass lump is transferred to a mold.
[Claim 5]
The method for producing a press-molding preform according to any one of claims 1 to 4, wherein the gas is blown so that the gas blown to the molten glass is not directly blown to the outflow pipe. .
[Claim 6]
The method for producing a press-molding preform according to any one of claims 1 to 5, wherein the glass lump being blown with gas is a glass lump formed on the mold.
[Claim 7]
The press molding press according to any one of claims 1 to 6, wherein when the viscosity of the glass is in a range of 1 to 10 ⁴ dPa · s, cooling promotion by spraying of the gas is started. Reform manufacturing method.
[Claim 8]
Forming into a preform while applying a wind pressure to the glass lump on the mold and allowing it to float, and starting cooling promotion by blowing the gas before the glass lump starts to swing on the mold The manufacturing method of the preform for press molding of any one of Claims 1-7.
[Claim 9]
The method for producing a press-molding preform according to any one of claims 1 to 8, wherein a temperature of the gas to be sprayed is equal to or lower than a glass transition temperature of the glass.
[Claim 10]
10. The method for producing a press-molding preform according to any one of 1 to 9, wherein a preform made of glass containing B ₂ O ₃ and / or an alkali metal oxide is molded.
[Claim 11]
A glass preform is prepared by the manufacturing method according to claim 1, the obtained preform is heated, and precision press molding is performed using a press mold. Device manufacturing method.
[Claim 12]
The optical element manufacturing method according to claim 11, wherein a preform is introduced into a press mold, and the mold and the preform are heated together to perform precision press molding.
[Claim 13]
The optical element manufacturing method according to claim 11, wherein a preform that has been heated in advance is introduced into a press mold and precision press molding is performed.
[Claim 14]
A plurality of molds for receiving a molten glass lump and forming it into a preform, provided that the molten glass lump is obtained by letting molten glass flow out from an outflow pipe and separating it, and the preform is extracted from the outflow pipe. Having a weight greater than the weight to be dripped,
A take-out device for taking out the preform from the mold, and a casting position for supplying the molten glass lump, a take-out position for taking out the preform, and a transfer device for sequentially circulating and transferring the preform to the cast position. In an apparatus for manufacturing a preform for press molding for molding a preform from a molten glass lump by the method according to claim 1,
A press characterized by comprising a cooling gas jetting mechanism for obtaining a preform while promoting the cooling of the glass from above and / or obliquely above the molten glass on the mold, while suppressing the occurrence of striae Manufacturing equipment for forming preforms.
[Claim 15]
A plurality of molds for receiving a molten glass lump and forming it into a preform, provided that the molten glass lump is obtained by letting molten glass flow out from an outflow pipe and separating it, and the preform is extracted from the outflow pipe. Having a weight greater than the weight to be dripped,
A take-out device for taking out the preform from the mold, and a casting position for supplying the molten glass lump, a take-out position for taking out the preform, and a transfer device for sequentially circulating and transferring the preform to the cast position. In a press molding preform manufacturing apparatus for molding a preform from a molten glass lump by the method according to claim 3,
A support for receiving the molten glass that has flowed out, a mechanism for transferring the molten glass lump from the support to a mold, and the glass on the support and / or the molten glass on the mold from above and / or obliquely from above An apparatus for producing a preform for press molding, comprising a cooling gas jetting mechanism for promoting the cooling of the substrate and obtaining a preform while suppressing the occurrence of striae.
[Claim 16]
When the transfer device is stopped at the stop position including the casting position and the take-out position, the moving device is repeatedly transferred and circulated.
The press molding according to claim 14 or 15, wherein the cooling gas ejection mechanism cools a molten glass lump on a molding die that is retained at a cast position and / or a stop position next to the cast position. Preform manufacturing equipment.

[Contrast with prior art]
By the way, as described above, the present invention aims to provide a method for producing a preform by hot forming from glass containing a large amount of volatile components. Gas is blown onto the molten glass stored on the mold or the support to lower the temperature of the molten glass surface.

  Among the techniques preceding the present invention, there is an invention that employs a technique of blowing gas to molten glass, although the object of the present invention is different. Although these inventions seem to be similar to the present invention at first glance, they are fundamentally different inventions. This point will be described below.

Difference from Japanese Patent Application Laid-Open No. 9-221329 (Patent Document 1) In the invention described in Patent Document 1, the object of preventing uneven wrinkles on the glass surface that occurs when the molten glass flowing out from a pipe is received by a receiving mold. Then, until the molten glass comes into contact with the receiving mold, a low temperature fluid (gas) is sprayed to the tip of the molten glass. The main object of the present invention is to obtain a preform free from wrinkle-like surface defects (such as gob-in marks) caused by rapid cooling of the glass surface by contact with a low temperature receiving mold. And as the solution, specifically, as shown in FIG. 1 of Patent Document 1, a ring-shaped gas blowing device is installed between the pipe and the receiving mold, and as shown in FIGS. 2 and 3, A gas (for example, a gas lower than the glass transition temperature) is sprayed on the tip of the molten glass that comes out of the pipe tip, and before the molten glass enters the receiving mold, that molten metal that may come into contact with the receiving mold. The bottom part is solidified.

  Also in the present invention, for example, an unheated nitrogen gas having a glass transition temperature or lower is continuously sprayed from the pipe to the surface of the molten glass cast into the mold. However, its purpose is to suppress surface striae, and the surface of the molten glass that blows the gas is mainly the surface opposite to the surface that contacts the mold, and the bottom of the molten glass that flows out of the pipe It does not cool the surface of the part. In the present invention, the surface of the molten glass (upper surface) while the molten glass is cast (poured) into the mold, and the surface of the molten glass (upper surface) after being cast into the mold A gas is sprayed on the surface to reduce the temperature of the surface of the molten glass to suppress volatilization of volatile components.

  In addition, in the invention described in Patent Document 1, a large amount of gas (30 liters / minute) is sprayed in a short time toward the molten glass hanging on the pipe to rapidly cool the molten glass at the tip of the pipe. It also sprays on the nozzle tip, making the outflow conditions and dripping conditions unstable. The temperature of the pipe tip from which the molten glass flows out is also lowered by the sprayed gas, the temperature of the outflow pipe varies, and the outflow amount of the glass varies. In addition, when the temperature at the tip of the outflow pipe decreases, crystals may precipitate on the molten glass at the outflow port, which may induce striae in the preform. Since the glass that is the main object of the present invention is a glass that is easily crystallized in the vicinity of the outflow temperature, a temperature drop at the end of the outflow pipe tends to cause the above-mentioned problem.

  In the invention described in Patent Document 1, in order to cool the molten glass hanging from the pipe tip, the injection port of the injection nozzle is below the outflow pipe, and the gas injection direction is upward from the horizontal (Patent Document 1). 2 and 3). On the other hand, the gas injection in the present invention is not intended to cool the bottom of the molten glass hanging from the tip of the pipe, but the upper surface of the molten glass hanging from the tip of the pipe and the molten glass contained in the mold. The purpose is to reduce the temperature of the glass on the upper surface of the glass. Therefore, the direction in which the gas is blown out is lower than the horizontal direction, and preferably the gas blow-out port is set at substantially the same height as the tip of the outflow pipe to suppress the temperature drop at the end of the outflow pipe.

Difference from Japanese Patent Laid-Open No. 8-73229 (Patent Document 2) In the invention described in Patent Document 2, non-oxidizing gas is circulated around the outflow pipe for the purpose of preventing the molten glass from getting wet to the outflow pipe. The molten glass is flowing out. In the invention described in Patent Document 2, the non-oxidizing gas is circulated around the outflow pipe while being heated together with the outflow pipe in the muffle for heating the outflow pipe. It is described that the temperature in the muffle is set based on the viscosity of the outflow glass and is controlled to be about 700 to 1300 ° C. Furthermore, in order to perform the outflow of the molten glass from the outflow pipe satisfactorily, the temperature of the non-oxidizing gas contacting the molten glass flowing out of the outflow pipe needs to be substantially equal to the temperature of the molten glass, at least It is not so low that the temperature of the molten glass can be lowered. On the other hand, in the present invention, a gas having a temperature lower than that of the molten glass is sprayed on the molten glass, thereby suppressing the volatilization of volatile components and suppressing the occurrence of striae.

  Japanese Patent Application Laid-Open No. 2000-154025 (Patent Document 3) also discloses an invention related to a molding apparatus having the same object as the invention described in Patent Document 2 and provided with a chamber for circulating gas around the outflow pipe. However, in the molding apparatus described in Patent Document 3, a heater is installed in the chamber, and the gas flowing through the chamber is heated more efficiently than the invention described in Patent Document 2, and flows out from the outflow pipe. The temperature at which the molten glass comes into contact is approximately the same as the temperature of the molten glass, and is not low enough to reduce the temperature of the molten glass.

  According to the method and apparatus for producing a preform for press molding of the present invention, even a glass containing a large amount of volatile components, for example, a lanthanum borate glass, has a high quality with no radial surface striae on the surface. It is possible to provide an inexpensive preform for precision press molding. Further, by producing an optical element by precision press molding the preform produced by the above method, a high-quality optical element can be mass-produced with high productivity.

Radial striae appearing on the surface of a press-molding preform composed of a boric acid-rare earth oxide-based glass. Explanatory drawing of pouring of the molten glass flow from the outflow pipe in a supply position to a shaping | molding die. An example of the manufacturing apparatus of the preform for press molding of this invention. The schematic explanatory drawing of the press apparatus used in the Example. Explanatory drawing of the pouring of the molten glass flow from the outflow pipe in a supply position to a shaping | molding die (example using a support body).

(Manufacturing method of preform for press molding)
The method for producing a press-molding preform of the present invention includes a step of allowing molten glass to flow out from an outflow pipe, separating the molten glass lump, and forming the obtained molten glass lump into a preform on a mold.

  Molten glass is allowed to flow out from the temperature-controlled platinum alloy outflow pipe at a constant outflow rate. Above the outflow pipe, prepare molten glass that has been clarified and homogenized in a melting furnace. And the molten glass flow which flows out is cut | disconnected and isolate | separated to the shaping | molding die which waits under the outflow pipe, and a molten glass lump is supplied. The molten glass flow that flows out of the outflow pipe is, for example, when the weight of the tip portion reaches a predetermined weight in the mold, the mold is inserted into the outflow pipe at a speed sufficiently higher than the outflow speed of the molten glass flow. By descending vertically from the outlet, it can be cut and separated.

  A plurality of molds 2 are prepared, and are arranged at regular intervals on the circumference of the turntable 10, for example, as shown in FIG. When the molten glass lump is supplied at a position (referred to as a supply position) for receiving the molten glass below the outflow pipe 1, the molten glass lump is carried out from the supply position, and an empty mold is conveyed to the supply position and stands by. In this way, the plurality of molds are sequentially conveyed to the supply position to supply the molten glass lump to the mold. It is preferable to mold into a preform while applying air pressure to the glass lump on the mold and allowing it to float. Therefore, the mold is made of, for example, a porous material, and gas is ejected by discharging gas from its pores or by providing one or more gas outlets on the surface holding the molten glass lump on the mold. Thus, an upward wind pressure is applied to the molten glass lump, and the molten glass lump is formed into a glass molded body while floating in the mold. The solidified glass molded body is taken out of the mold at the take-out position and returned to the supply position again. In addition, as a material of a shaping | molding die, heat resistant metals, such as stainless steel, carbon, ceramics, those porous bodies, etc. can be used. Examples of the levitation gas include nitrogen, air, and inert gas.

  The first aspect of the method for producing a press-molding preform according to the present invention is the surface on the side exposed to the atmosphere of the glass lump by blowing gas from above and / or obliquely above the molten glass lump on the mold. It is characterized by promoting cooling.

  In the case of boric acid-lanthanum glass, a radial striae as shown in FIG. 1 is often observed on the surface of a glass molded body (preform) formed from a molten glass lump by the above method. The form of this striae is the composition of the glass, the temperature of the outlet of the outlet pipe, the outlet speed of the molten glass, the weight of the preform, the flow rate of the gas that is blown out to float the molten glass mass in the mold It depends on the temperature of the mold.

  For this reason, it is necessary to change how the cooling gas is sprayed in accordance with the generation form of the striae generated under the above conditions. For example, when the striae is thin and the number thereof is small, gas can be blown onto the upper surface of the molten glass lump immediately after being supplied to the mold. Further, when the striae is deep and the number is large, gas can be blown onto the upper surface of the molten glass on the mold while the molten glass is being supplied to the mold. In order to further enhance the effect of generating striae, it is appropriate to blow gas onto the upper surface of the molten glass lump immediately after being supplied to the mold.

  In the first embodiment of the present invention, as shown in FIG. 2, at the supply position, the molten glass flow G is poured from the outflow pipe 1 into the mold 2 and the molten glass flow into which the molten glass below is poured from the constriction. A constriction is made on the way, and when it reaches a predetermined weight, the lower molten glass is separated from the constriction. From the point of time when the gas is continuously blown out from the first air-cooling nozzle 3 and the molten glass flow is poured into the mold, the first air-cooled nozzle is also blown into the molten glass stream G that is blown into the mold 2 Cooling gas is sprayed from 3 (state (B)). Further, the cooling gas is blown from the first air-cooling nozzle 3 to the molten glass block P immediately after the separation until it moves from the supply position to the next position (state (C)). The cooling gas blowout has no difference in the striatal suppression effect even if it starts from the time when the tip of the molten glass flow that has flowed out of the outflow pipe contacts the mold, and the apparatus has a mechanism for controlling the blowout timing. Therefore, the above timing control may not be performed.

When the viscosity of the glass is in the range of 1 to 10 ⁴ dPa · s, it is preferable to start cooling promotion by gas blowing.
Further, it is preferable that the glass block is formed into a preform while being floated by applying wind pressure to the glass block on the mold. It is preferable to start cooling by spraying.

  The air-cooling nozzle 3 which is a gas spraying device of the present invention is independent of the outflow pipe 1 and is usually not heated by a heater. Rather, it is preferably brought into contact with a low-frequency high-frequency heating coil in which water is flowing to increase the cooling efficiency. Moreover, it is preferable that the capacity | capacitance in a gas spraying instrument is also small, the gas introduce | transduced in the instrument stays in an instrument, and the time to heat is also shortened.

  That is, it is preferable to introduce the gas at room temperature into the nozzle without providing a specific heating source between the supply source such as a cylinder and the outlet of the air cooling nozzle. The first air-cooled nozzle 3 mounted on the high-frequency heating coil that heats the tip of the outflow pipe at the supply position is made of a material that is not heated by the high-frequency heating coil, such as glass or aluminum, and introduced into the gas. It is appropriate not to heat. In addition, the gas is cooled by putting a part of the path from the gas supply source to the spraying tool into the cooling medium, and the gas below the room temperature is introduced into the spraying tool and poured into the mold from the outlet. It is preferable to spray on the surface of the molten glass from the viewpoint of efficient cooling. Thus, even if low temperature gas below room temperature is sprayed, no striae is observed in the glass molded body and a striae suppression effect is obtained. The flow rate of the gas introduced into the air-cooled nozzle can be adjusted as appropriate by putting a flow meter in the pipe from the supply source to the spraying device.

  Examples of the gas include nitrogen, oxygen, air, argon, helium, carbon dioxide, and forming gas. However, since the purpose is to lower the surface temperature of the molten glass, the type of gas is not selected. An inexpensive and safe gas is desirable and does not need to be non-oxidizing at all. Moreover, it is preferable that the temperature of the gas to spray is below the glass transition temperature of the said glass.

  In the supply position, when the gas is blown onto the surface of the molten glass poured into the mold from the outlet of the outflow pipe, the gas blown to the molten glass is not directly blown onto the outflow pipe. It is preferable to perform spraying. Therefore, the position of the gas outlet of the first air-cooling nozzle is the same or higher in the vertical direction than the outlet of the molten glass, and the angle of spraying is downward from the horizontal, and the gas is directed toward the outlet. It is preferable not to spray. Moreover, it is preferable that the gas is sprayed continuously. If the cooling gas is sprayed only after the molten glass flow is cut until the next tip comes into contact with the mold, the striae suppressing effect generated in the glass molded body is hardly obtained.

  The second aspect of the method for producing a press-molding preform of the present invention is to receive the molten glass that has flowed out with a support, transfer the molten glass lump from the support to a mold, and mold the preform, and It is characterized in that cooling of the surface exposed to the glass atmosphere is promoted by blowing a gas from above and / or obliquely above the molten glass on the support and / or the mold.

  In the first aspect, the molten glass that has flowed out was supplied to the mold as it is, but in the second aspect, the molten glass that has flowed out is received by the support, and then the molten glass lump from the support is molded into the mold. To form a preform. Specific examples of cutting and separation of the molten glass lump using the support include the following two.

Example 1
As shown in FIG. 5, the support 5 is brought into a state in which two plate-like split members are butted together, and the tip of the outflow glass G is received on the upper surface of the boundary portion (state (B)). When a predetermined weight of molten glass accumulates on the support 5 (split member), it drops rapidly with the split member closed, and the molten glass lump is cut and separated from the glass stream (state (C)). Next, the split member is opened, the molten glass lump P is dropped, and the molten glass lump P is inserted into the concave portion of the preform mold 6 that is kept below the split member (state (D)).

Example 2
The tip of the spilled glass is received on the upper surface of the rectangular bar-shaped support. When a predetermined weight of molten glass accumulates on the support, the support member is rapidly lowered to cut and separate the molten glass lump from the glass stream. Next, the support member is rotated or inclined, and the molten glass lump is inserted into the concave portion of the preform mold that is kept under the split member.

The molten glass lump obtained from the above two specific examples can be inserted into a mold and preformed as follows.
As shown in FIG. 5, a forming die 6 having a gas ejection hole at the center of the bottom of a funnel-shaped recess (conical shape) is prepared. When the molten glass lump P is inserted into the recess while gas is ejected from the recess, the molten glass lump is spheroidized and solidified into a spherical preform P ′ while being roughly levitated and rotated by the airflow (state (D)) ).

  At that time, gas is blown onto the molten glass on the support and / or the mold from above and / or obliquely from above to promote cooling of the surface exposed to the glass atmosphere. The molten glass on the support and the mold can be cooled in the same manner as in the first embodiment. The cooling gas is continuously blown out from the first air-cooling nozzle 3, and the cooling gas is sprayed from the time when the molten glass stream flowing out from the outflow pipe 1 is poured into the support, and the support is being poured. The cooling gas is blown from the first air-cooling nozzle to the molten glass block P immediately after the glass is lowered and the molten glass is cut and separated until the molten glass moves from the support to the mold.

  Also in the second aspect, it is preferable that the gas blown onto the molten glass is blown so as not to blow directly onto the outflow pipe.

When the viscosity of the glass is in the range of 1 to 10 ⁴ dPa · s, it is preferable to start cooling promotion by blowing the gas.
Further, it is preferable that the glass block is formed into a preform while being floated by applying wind pressure to the glass block on the mold. It is preferable to start cooling by spraying.

In the third aspect of the method for producing a press-molding preform of the present invention, a gas is blown from above and / or obliquely upward to the glass block formed on the mold, and the glass block is exposed to the atmosphere of the glass block. The cooling of the side surface is promoted.
The third aspect of the present invention is mainly applied to the molten glass lump held by the molding die carried out from the supply position and the glass lump that has passed the molten state, from above and / or obliquely from above. By blowing this gas, cooling of the surface exposed to the glass lump atmosphere is promoted. For example, the molten glass lump P immediately after being unloaded from the supply position shown in FIG. 3 can be sprayed with a cooling gas from the second air cooling nozzle 4 disposed at a position after the supply position. In this case, it is preferable to provide the second air-cooling nozzle 4 shown in FIG. 3 so that its outlet comes vertically 5 to 10 mm above the liquid level of the glass lump, and to blow out the cooling gas therefrom.

  Ease of occurrence of radial striae seen on the surface of a glass molded body having a lanthanum borate composition varies depending on the glass composition and the outflow conditions. In order to produce a glass molded body with high productivity, it is preferable to adjust the outflow conditions such as the inner diameter and temperature of the tip of the outflow pipe according to the weight of the glass molded body. Depending on these conditions, the temperature of the glass melt poured into the mold differs, and the easiness of occurrence of striae depends on this temperature.

  In Examples, a method for suppressing radial striae generated on the surface of several glass molded articles having optical constants obtained from the composition range of lanthanum borate will be described in detail.

  As a method of spraying a low-temperature gas to the molten glass poured into the mold from the outflow pipe, a nozzle that blows out a cooling gas is provided in the vicinity of the outflow pipe, and the molten glass from which the cooling gas is poured into the mold To be sprayed on. A gas having a predetermined flow rate is sent from a gas generation source (not shown) to the nozzle via a gas flow rate regulator, and is blown out from the nozzle. The direction of the gas ejection port is preferably downward from the horizontal because the cooling gas is blown onto the molten glass poured into the mold.

  Molds are arranged at equal intervals on the turntable, and the molds are conveyed and carried out directly under the outflow pipe by the rotation of the table. Separation / cutting of molten glass lump from molten glass flowing out of the outflow pipe is a drop cutting in which the mold descends vertically and cuts when the weight of the molten glass poured into the mold reaches a predetermined amount. The mold that has been lowered and cut by the method is carried out from directly under the pipe, the next empty mold is carried, and the molten glass that exits from the pipe is received. It is held by a molding die carried out from directly under the outflow pipe.

  The present invention is particularly effective for molding a preform made of glass having a weight larger than the weight dropped from the pipe, as in the descending cutting method. This is because a glass having a large weight has a relatively low cooling speed, and therefore a large difference in quality is likely to occur depending on whether or not cooling is promoted by a cooling gas. Also in the second and third aspects, the temperature of the gas (cooling gas) sprayed on the upper surface of the glass is preferably not more than the glass transition temperature of the glass. In each aspect of the present invention, the temperature of the gas blown onto the glass during the period from the outflow until the preform is formed is preferably not higher than the glass transition temperature of the glass. Is appropriate.

(Press molding preform manufacturing equipment)
The press molding preform manufacturing apparatus of the present invention is an apparatus for molding a preform from a molten glass lump. This apparatus includes (1) a plurality of molding dies that receive molten glass lumps and mold them into preforms, (2) a take-out device that takes out the preforms from the molding dies, and (3) the plurality of molding dies as molten glass. A casting position for supplying the lump, a take-out position for taking out the preform, and a transfer device for sequentially circulating and transferring to the casting position are provided.

  An example of this manufacturing apparatus is shown in FIG. 3, for example, and has a plurality of molds 2 that receive a molten glass lump and mold it into a preform. Further, a take-out device (not shown) for taking out the preform from the mold is provided at the take-out position. Further, a turntable 10 is provided as a transfer device. By means of the turntable 10, the mold 2 is transferred again to the casting position (supply position) through the take-out position where the preform is taken out from the cast position (supply position) where the molten glass block is supplied.

  A first aspect of the press-molding preform manufacturing apparatus of the present invention is characterized in that the glass on the mold is provided with a cooling gas jetting mechanism for promoting cooling of the glass from above and / or obliquely from above. To do.

  The cooling gas ejection mechanism is shown as a first air cooling nozzle 3 and a second air cooling nozzle 4 in FIG. As shown in FIG. 2, the first air-cooling nozzle 3 has, for example, a double pipe structure for surrounding the outflow pipe 1, the upper end of the double pipe is sealed, the lower end is opened, and the opening is blown out of the cooling gas. It can be a mouth. A cooling gas introduction part (tube) (not shown) is provided in a part of the closed upper end part. In addition, the outer diameter near the upper end of the first air-cooling nozzle is designed so that it does not rattle in the high-frequency heating coil, and cooling gas is sprayed on the surface of the molten glass stream poured into the mold near the outlet. It is preferable to provide an angle for.

  Due to the rotation of the turntable, the mold 2 and the molten glass lump held in the mold 2 are carried out from under the outflow pipe 1, but after the mold 2 is carried out, the second air-cooled nozzle 4 is moved to the molten glass. It is arranged vertically above the lump, and a cooling gas with a predetermined flow rate is introduced into the second air cooling nozzle 4 by piping, and the cooling gas is blown out vertically from this position to cool the surface of the molten glass lump. Preferred (FIG. 2 (D)).

  The turntable receives the molten glass flow with the mold, stops at the supply position until it is cut and separated, then unloads the mold holding the molten glass lump from under the outflow pipe, and at the same time takes out the glass molded body at the takeout position. The mold that has been emptied is rotated to be conveyed under the outflow pipe. The second air-cooling nozzle 2 is individually provided as needed vertically above each mold located while the rotation of the turntable is stopped.

  Further, instead of individually arranging the cooling gas blowing positions at the positions of the respective molding dies when the turntable is stopped, it is possible to use those in which the blowing positions are continuously connected.

  The second aspect of the apparatus for producing a press-molding preform of the present invention comprises a support for receiving the molten glass that has flowed out, a mechanism for transferring the molten glass lump from the support to a mold, and the support. The glass on the body and / or the mold is provided with a cooling gas jetting mechanism for promoting cooling of the glass from above and / or obliquely from above.

  As shown in FIG. 5, the support 5 is composed of two split members, and each split member has a function of being separated from each other or closely attached. When receiving the tip of the molten glass flow G, the split member comes into close contact, and receives and supports the tip of the molten glass flow at the boundary portion of the split member. The split member is preferably cooled to avoid fusion with the molten glass. Examples of the support include heat-resistant metal, carbon, and ceramics.

  In addition, the entire support has a function of moving up and down (not shown), and after receiving and supporting the tip of the molten glass stream G, the support 5 is rapidly lowered vertically to form a predetermined amount of molten glass lump P. Can be cut and separated. In order to make the amount of molten glass lump constant, it is appropriate that the position for receiving the tip of the molten glass flow and the lowering condition of the support are constant, and the lowering period is also constant.

The split members are separated from each other, and the molten glass block P is dropped vertically downward from between the separated split members. A molding die 6 stands by below the support and receives the falling molten glass block P.
The cooling gas ejection mechanism is the same as in the first aspect of the present invention, and the first air cooling nozzle 3 and the second air cooling nozzle 4 are connected to the supply position and / or the stop position next to the supply position as shown in FIG. Can be arranged.

  Upon receiving the tip of the molten glass flow from the outflow pipe 1 on the support consisting of the two split members that are butted together, when a predetermined amount of molten glass G accumulates on the support 5, the support 5 suddenly descends and melts The tip of the glass is cut and separated as a molten glass lump P, and cooling gas is blown onto the molten glass with the first air-cooling nozzle 3 until the split members are separated from each other and the molten glass lump is dropped from there.

  The turntable stops at the supply position until the molten glass lump has been transferred from the support to the mold, and then the mold holding the molten glass lump is taken out from under the outflow pipe, and at the same time, the glass molded body is taken out at the takeout position. The emptied mold is rotated for transport under the spill pipe. The second air cooling nozzle 4 can be individually provided as needed vertically above each mold located while the rotation of the turntable is stopped.

  Further, instead of individually arranging the cooling gas blowing positions at the positions of the respective molds when the turntable is stopped, it is possible to use one in which the blowing positions are continuously connected.

  In the first and second aspects, the transfer device is configured to repeatedly circulate and transfer the moving mold after the mold is stopped at the stop position including the cast position and the take-out position. However, it is preferable to cool the glass on the mold that stops at the cast position and / or the stop position next to the cast position.

[Explanation about glass]
Hereinafter, the glass to which the method of the present invention is preferably applied will be described.
(Glass 1)
A first example of such glass (referred to as glass 1) is B ₂ O ₃ and rare earth oxide-containing glass. Specifically, there is a glass containing B ₂ O ₃ and one or more of rare earth oxides composed of La ₂ O ₃ , Gd ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , Sc ₂ O _3. .

In such glass, B ₂ O ₃ is an essential component for forming a glass network structure. In particular, when a large amount of a high refractive index component such as La ₂ O ₃ or Gd ₂ O ₃ is introduced, it is necessary as a main network structure formation for the formation of glass, but it is 60% (hereinafter, unless otherwise specified) If it is introduced in excess of%, the refractive index of the glass will decrease, making it unsuitable for the purpose of obtaining a highly refractive glass. In addition, since the meltability is lowered, the introduction amount is preferably 15 to 60%. More preferably, it is 20 to 60%, and still more preferably 20 to 45%.

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

La ₂ O ₃ is an essential component that increases the refractive index and improves the chemical durability without reducing the stability of the glass against devitrification and without increasing the dispersion. However, if it is less than 5%, a sufficient effect cannot be obtained, whereas if it exceeds 22%, the stability against devitrification is remarkably deteriorated. Therefore, the introduction amount is preferably in the range of 5 to 22%. More preferably, it is 5 to 20%, and more preferably 7 to 18%.

Like La ₂ O ₃ , Gd ₂ O ₃ functions to increase the refractive index and improve chemical durability without increasing the stability and dispersion of the glass to devitrification. In particular, the stability of the glass can be further improved by the coexistence of La ₂ O ₃ and Gd ₂ O ₃ . If the amount of Gd ₂ O ₃ introduced exceeds 20%, the stability against devitrification deteriorates, the glass transition temperature rises and the precision press formability decreases, so the amount introduced should be 0-20%. Is preferred. More preferably, it is 0 to 18%, still more preferably 0 to 16%.

  ZnO is a component useful for adjusting the refractive index by lowering the melting temperature, liquidus temperature and transition temperature of glass. In order to obtain the expected effect, it is preferable to introduce 2% or more. However, if introduced in excess of 45%, dispersion increases, stability against devitrification deteriorates, and chemical durability also decreases. Therefore, the amount introduced is preferably in the range of 0 to 45%. The range of ˜45% is more preferable, the range of 1 to 32% is more preferable, and the range of 1 to 20% is even more preferable.

Li ₂ O is a component that significantly lowers the glass transition temperature without significantly lowering the refractive index and chemical durability compared to other alkali metal oxide components. In particular, even when introduced in a small amount, a great effect is obtained, and it is an effective component for adjusting the thermal properties (glass transition temperature, yield point, etc.) of glass. However, when more than 15% of Li ₂ O is introduced, the stability of the glass against devitrification is drastically lowered and the liquidus temperature is also increased. Therefore, the introduced amount is preferably 0 to 15%, It is more preferably 10%, even more preferably 0.5 to 15%, even more preferably 1 to 12%, and even more preferably 2 to 12%.

Na ₂ O and K ₂ O are components introduced to lower the glass transition temperature, but these components all reduce the refractive index of the glass, so the amount introduced is 0-10% respectively. To do. More preferably, it is 0 to 8%.

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

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

WO ₃ is a component that is introduced as appropriate in order to improve the stability and meltability of the glass and improve the refractive index. However, if the amount introduced exceeds 15%, the dispersion becomes large and the required low dispersion Since the characteristics cannot be obtained, the introduction amount is set to 0 to 15%. More preferably, it is more than 0% and 15% or less, more preferably in the range of 1 to 15%, still more preferably in the range of 1 to 12%.

Nb ₂ O ₅ is a component that is introduced as appropriate in order to improve the stability and refractive index of the glass, but if the amount introduced exceeds 10%, the dispersion becomes large and the required low dispersion characteristics cannot be obtained. Therefore, the introduction amount is limited to 0 to 10% or less. More preferably, it is 0 to 8%, and still more preferably 0 to 5%.

MgO, CaO, and SrO are components introduced to lower the liquidus temperature and transition temperature of glass, and are particularly effective for glasses with Nb ₂ O ₅ introduced. Since the optical characteristics may be deteriorated, the introduction amount is set to 0 to 15%. More preferably, it is the range of 0-12%, More preferably, it is the range of 0-10%.

  BaO is used as a component that imparts a high refractive index and low dispersion. When introduced in a small amount, BaO increases the stability of the glass and improves the chemical durability. In order to increase the transition temperature and yield point temperature greatly, the introduction amount is set to 0 to 15%. More preferably, it is 0 to 10% of range.

Y ₂ O ₃ and Yb ₂ O ₃ are also used as components for imparting a high refractive index and low dispersion. When introduced in small amounts, the stability of the glass is improved and the chemical durability is improved. In order to greatly impair the stability against devitrification and raise the transition temperature and the yield point temperature, the introduction amount is set to 0 to 15%, respectively. More preferably, it is 0 to 10% of range. Y ₂ O ₃ and Yb ₂ O ₃ coexist with La ₂ O ₃ to increase the function of improving glass stability.

TiO _{2 is} also a component that increases the refractive index, but it is preferably introduced in an amount of 0 to 20% because the glass stability is lowered and the glass is colored by excessive introduction.

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

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

In a glass containing B ₂ O ₃ , SiO ₂ , La ₂ O ₃ , Gd ₂ O ₃ , ZnO, Li ₂ O, ZrO ₂ , Ta ₂ O ₅ components, high refractive index and low dispersion (n _d > 1.75 and In order to maintain high functionality of ν _d > 25), the total amount of La ₂ O ₃ + Gd ₂ O ₃ is preferably 12% or more, more preferably 12 to 35%.

The ratio of the content of La ₂ O ₃ expressed in mol% to the total content expressed in mol% of rare earth oxides, Ln ₂ O ₃ (Ln = La, Gd, Yb, Y, Sc) in glass (min Ratio) La ₂ O ₃ / Ln ₂ O ₃ is preferably in the range of 0.3 to 1, and more preferably in the range of 0.4 to 0.9. The reason is as follows.

As precision press-molding glass, it is necessary to add Li ₂ O, which is a component that destabilizes the glass, while imparting suitability for precision press molding, that is, a low glass transition temperature. Increasing the amount of rare earth oxide that is essential for high refractive index and low dispersibility makes glass formation difficult. However, by making the distribution of La ₂ O ₃ in the rare earth oxide (the above fraction) 0.3 to 1, it becomes possible to obtain a stable glass while increasing the amount of rare earth oxide added. It is possible to stably form a glass even for a glass to which a component such as Li ₂ O that lowers the degree is added. Moreover, by maintaining this ratio, it greatly contributes to the reduction of the liquid phase temperature and the improvement of the high temperature viscosity. When La ₂ O ₃ / ΣLn ₂ O ₃ is in the above range, it is possible to obtain a much more stable glass compared to a glass having a large ratio even when the total amount of Ln ₂ O ₃ is the same. Furthermore, the total content of La ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , Y ₂ O ₃ and Sc ₂ O ₃ (ΣLn ₂ O ₃ ) is preferably 12 to 35% for the above reason.

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

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

Lu ₂ O ₃ is less frequently used than other components. Further, since it is a rare substance, it is expensive as an optical glass raw material, and it is a component that is not desired in terms of cost. Moreover, since it is not necessary to introduce it, it is desirable not to introduce Lu ₂ O ₃ .

  It is desirable not to contain environmentally harmful elements such as cadmium, chromium and mercury, radioactive elements such as thorium, and toxic elements such as arsenic.

In addition, in order to adjust physical properties, the glass 1 may contain TiO ₂ , Al ₂ O ₃ , Ga ₂ O ₃ or the like in a total amount of 5% or less.

Hereinafter, some preferable examples of the glass 1 will be described. Such glasses include those in which B ₂ O ₃ , La ₂ O ₃ and Gd ₂ O ₃ coexist, those in which B ₂ O ₃ , La ₂ O ₃ and ZnO coexist, B ₂ O ₃ and La ₂ O ₃ , Gd ₂ O ₃ , ZnO coexisting, B ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , ZnO, Li ₂ O coexisting, B ₂ O ₃ , SiO ₂ , La ₂ O ₃ , Gd ₂ O ₃ , ZnO, Li ₂ O, ZrO ₂ , Ta ₂ O ₅ coexisting, or

B ₂ O ₃ 15~60% as glass _{components, SiO 2 0~40%, La 2} O 3 5~22%, Gd 2 O 3 0~20%, ZnO 0~45%, Li 2 O 0~15% _{, Na 2 O 0~10%, K} 2 O 0~10%, ZrO 2 0~15%, Ta 2 O 5 0~15%, WO 3 0~15%, Nb 2 O 5 0~10%, MgO 0~15%, CaO 0~15%, SrO 0~15%, BaO 0~15%, Y 2 O 3 0~15%, Yb 2 O 3 0~15%, TiO 2 0~20%, Bi 2 O ₃ glass containing 0 to 10%,

Furthermore, any one of the glasses, B ₂ O ₃ , SiO ₂ , ZnO, Li ₂ O, La ₂ O ₃ , Gd ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , WO ₃ , Y ₂ O ₃ , More preferably, the total content of Yb ₂ O ₃ is 95% or more, more preferably 99% or more, and even more preferably 100%.

  When the refractive index increases, it tends to be difficult to mold the preform. However, if the manufacturing method of the present invention is applied, a high-quality preform can be made with high productivity even with a glass having a high refractive index. According to the glass 1, a preform for precision press-molding an optical element made of high refractive index glass having a refractive index (nd) of 1.74 or more can also be made. (The refractive index (nd) can be reduced stepwise to 1.75 or more, 1.8 or more, or 1.85 or more. Although the upper limit is not particularly limited, the refractive index (nd) is 2.0. (As a guideline, the Abbe number (νd) is 25 to 50.)

[Method for Manufacturing Optical Element]
The method for producing an optical element of the present invention is a method for producing an optical element in which a glass preform is heated and precision press-molded, and the precision press-molding preform produced by the above production method is heated and precision press-molded. It is characterized by.

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

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

These optical elements may be provided with an optical thin film such as an antireflection film, a total reflection film, a partial reflection film, or a film having spectral characteristics, if necessary.
Examples of the press mold used in the precision press molding method include known ones, for example, those having a release film on the molding surface of a mold material such as silicon carbide or cemented carbide material. preferable. As the release film, a carbon-containing film, a noble metal alloy film, or the like can be used, but a carbon-containing film is preferable from the viewpoint of durability and cost.

In the precision press molding method, it is desirable that the molding atmosphere be a non-oxidizing gas in order to keep the molding surface of the press mold in a good state. The non-oxidizing gas is preferably nitrogen or a mixed gas of nitrogen and hydrogen.
The pressing pressure may be adjusted as appropriate, but a range of 50 to 150 kgf / cm ² can be used as a guide. The press time may be adjusted as appropriate, but a range of 10 to 300 seconds can be used as a guide.

  Next, a precision press molding method particularly suitable for the method for producing an optical element of the present invention will be described.

(Precision press molding method 1)
In this method, the preform is introduced into a press mold, the mold and the preform are heated together, and precision press molding is performed (referred to as precision press molding method 1).

In precision press molding method 1, the temperature of the press mold and the preform is heated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁶ to 10 ¹² dPa · s to perform precision press molding. preferable.
The glass is cooled to a temperature showing a viscosity of 10 ¹² dPa · s or more, more preferably 10 ¹⁴ dPa · s or more, more preferably 10 ¹⁶ dPa · s or more, and then the precision press-molded product is removed from the press mold. It is desirable to take it out.
Under the above conditions, the shape of the molding surface of the press mold can be accurately transferred with glass, and the precision press molded product can be taken out without being deformed.

(Precision press molding method 2)
In this method, after heating the preform, the preform is introduced into a press mold and precision press molding is performed. That is, the press mold and the preform are separately preheated, and the preheated preform is introduced into the press mold. Precision press molding (referred to as precision press molding method 2).
According to this method, since the preform is preliminarily heated before being introduced into the press mold, it is possible to manufacture an optical element with good surface accuracy free from surface defects while shortening the cycle time.

The preheating temperature of the press mold is preferably set lower than the preheating temperature of the preform. Thus, by lowering the preheating temperature of the press mold, the consumption of the mold can be reduced.
In addition, since it is not necessary to perform preform heating in the press mold, the number of press molds to be used can be reduced.

In the precision press molding method 2, it is preferable to preheat the glass constituting the preform to a temperature exhibiting a viscosity of 10 ⁹ dPa · s or less, more preferably 10 ⁹ dPa · s.
The preform is preferably preheated while floating, and the glass constituting the preform has a viscosity of 10 ^5.5 to 10 ⁹ dPa · s, more preferably 10 ^5.5 dPa · s to 10 ⁹ dPa · s. It is more preferable to preheat to a temperature indicating
Moreover, it is preferable to start cooling the glass simultaneously with the start of pressing or in the middle of pressing.

The temperature of the press mold is adjusted to a temperature lower than the preheating temperature of the preform, and the temperature at which the glass exhibits a viscosity of 10 ⁹ to 10 ¹² dPa · s may be used as a guide.
In this method, it is preferable that after the press molding, the glass is cooled to a viscosity of 10 ¹² dPa · s or more and then released.

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

Example 1
Example 1 is a case where the surface of the molten glass is air-cooled only at a supply position where a molten glass stream is poured from the outflow pipe shown in the figure into a mold. A quartz glass air-cooled nozzle is installed in a high-frequency heating coil that heats the outflow pipe by high-frequency induction, and nitrogen gas at room temperature is introduced into the air-cooled nozzle and poured from the outflow pipe into the mold as a cooling gas. The molten glass flow was sprayed to cool the surface of the molten glass. The blowing port of the air-cooling nozzle is directed in the direction for blowing the cooling gas toward the molten glass flow poured into the mold, and is not directed toward the tip portion of the outflow pipe.

Molten glass is an optical glass containing B ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ and ZnO with a refractive index of nd 1.77, an Abbe number νd 47, and a liquidus temperature of 990 ° C. It is melted, clarified, homogenized, and discharged. The temperature at the tip of the pipe was set to 990 ° C., and the liquid was discharged from the outlet at a viscosity of 10 or 7 dPa · s. The tip of the molten glass flow that flows out from the outlet of the outflow pipe is received by a (porous) mold, and when the molten glass received reaches a predetermined weight of 1950 mg, the mold is lowered downward and the molten metal flows out. Nitrogen gas is introduced into this air-cooled nozzle at the flow rate shown in Table 1 in a series of steps from cutting the glass flow to receiving the molten glass from the bottom of the outflow pipe by turning the turntable. A low-temperature nitrogen gas was sprayed as a cooling gas on the surface of the molten glass. Table 1 shows the radial striae seen on the surface of the gob-shaped glass molded body thus formed. As the gas flow rate of the cooling gas increased, the radial striae on the surface of the glass molded body became thinner, and disappeared at 4 liters / min or more. However, when the flow rate of the cooling gas was 8 liters / minute or more, the flow of the molten glass flow poured into the mold from the outflow pipe was disturbed, and surface stria caused by this was generated.

Example 2
In the second embodiment, the molten glass block held in the mold as shown in FIG. 2 (B) after the turntable rotates without being sprayed with the cooling gas to the molten glass at the supply position and is unloaded from the supply position. This is a case where the cooling gas is blown by the air cooling nozzle 2 from directly above to cool the surface.

Melting, clarifying, and homogenizing optical glass containing B ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ and ZnO with a refractive index of nd 1.81, Abbe number νd 41, and liquidus temperature of 950 ° C. A molten glass having a viscosity of 10 dPa · s was caused to flow out from the outlet at 970 ° C. The tip of the molten glass flow is received by a porous mold, and when the received molten glass reaches a predetermined weight of 1950 mg, the mold is lowered vertically to cut the flowing molten glass flow, The received mold was carried out from under the outflow pipe by rotation of the turntable. Nitrogen gas was sprayed from directly above the surface of the molten glass molded in the carried-out porous mold. Table 2 shows the relationship between the radial striae seen on the surface of the gob-shaped glass molding thus obtained and the flow rate of the sprayed nitrogen gas. The viscosity of the molten glass when starting to blow nitrogen gas is 10 ¹ to 10 ³ dPa · s.

  First, the flow rate of the cooling gas as a comparative example is 0 liter / minute, that is, the result of molding without air cooling will be described. A number of linear striae radiated on the surface of the glass molded body molded without air cooling. This striae was thick overall, and each one was long. On the other hand, when nitrogen gas was blown, the radial striae became thinner and shorter as the flow rate increased and became no more than 8 liters / minute.

  If the flow rate of the gas to be blown is too large, the molten glass blown with the gas is deformed into a concave shape due to wind pressure, rapidly cooled and solidified as it is, and becomes a glass molded body that is deformed into a concave shape, which is not preferable.

Example 3
In Example 3, as shown in FIG. 2, the tip of the outflow pipe is held by the air cooling nozzle 1 attached to the high frequency heating coil for high frequency induction heating, and the mold that is rotated from the bottom of the outflow pipe as the turntable rotates. The cooling gas is continuously blown out through the air-cooling nozzle 2 having the outlet immediately above the molten glass lump, and with the cooling gas of the air-cooling nozzle 1, the molten glass flow is poured from the outflow pipe into the mold. When the molten glass in the container reaches a predetermined weight, the mold is lowered vertically, the molten glass flow is cut and separated, and the mold holding the molten glass lump by rotating the turntable is directly below the outflow pipe. The molten glass is cooled by air until it is unloaded.

  The mold holding the molten glass block cooled by the air-cooling nozzle 1 moves directly under the air-cooling nozzle 2 and then supplies the molten glass to an empty mold that is conveyed directly under the outflow pipe. During this stop, the surface of the molten glass block cooled by the air-cooling nozzle 1 is further cooled at the spray destination.

Melting, clarifying and homogenizing optical glass containing B ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ and ZnO with refractive index nd 1.82, Abbe number νd 43 and liquidus temperature 1010 ° C A molten glass having a viscosity of 6 to 10 dPa · s was caused to flow out from the outlet at 1020 ° C. The tip of the molten glass flow that flows out from the outlet of the outflow pipe is received by a (porous) mold, and when the molten glass received reaches a predetermined weight of 1950 mg, the mold is lowered downward and the molten metal flows out. Nitrogen gas is introduced into this air-cooled nozzle at a flow rate shown in Table 3 in a series of steps from cutting the glass flow to receiving the molten glass receiving mold from the bottom of the outflow pipe by turning the turntable. A low-temperature nitrogen gas was sprayed as a cooling gas on the surface of the molten glass. The spraying at the stop position after carrying out was 10 liters / minute. The results are shown in Table 3.

Example 4
In the same manner as in Example 3, in Example 4, at the position where molten glass is supplied from the outflow pipe to the mold, the temperature of the tip of the outflow pipe is set to 1040 ° C., and air is poured into the molten glass poured into the mold from the outflow port. Cooling gas is blown from the cold nozzle 1, and then the molten glass that has been air-cooled at this supply position is carried out from directly under the outflow pipe by the rotation of the turntable, and nitrogen gas is blown from the air-cooling nozzle 2 at the next stop position. In the cooling molding method, the kind of cooling gas sprayed from the air cooling nozzle 1 was changed. Nitrogen, oxygen, air, argon, and helium were blown as cooling gas at a flow rate of 4 liters / minute. As shown in Table 5, the results showed that the striae was suppressed with any gas.

  Even when oxidizing (not non-oxidizing) oxygen or air is blown, the generation of radial striae is suppressed and the type of gas is not limited. Cooling the surface of the molten glass by blowing a low-temperature gas is important in suppressing the radial striae seen on the surface of the glass molded body of this composition system. Therefore, in detail, there is a difference in the suppression effect depending on the thermal conductivity of each gas, and when a gas having a high thermal conductivity, that is, helium gas is blown onto the molten glass, the surface of the molten glass is more effectively Lowers temperature and has great striae suppression effect. However, practically, it is desirable to use nitrogen gas or air in view of profitability (effect / cost).

The temperature of the gas is also important. If a high-temperature gas (hot air) is blown onto the surface of the molten glass, the cooling of the glass surface is slowed and no striae suppression effect is observed.
In each of the above examples, the temperature of the gas sprayed on the glass was 200 ° C. or lower.

Example 5
A carbon film was coated on the entire surface of the preform produced in each of the above examples.
The preform thus obtained was heated, and an aspherical lens was obtained by precision press molding (aspherical precision pressing) using the press apparatus shown in FIG. The details of precision press molding are as follows. The preform 24 was allowed to stand between the SiC lower mold 22 and the upper mold 21 having an aspherical shape, and then the quartz tube 11 was heated by energizing the heater 12 with the quartz tube 11 in a nitrogen atmosphere. . Set the temperature inside the molding die to a temperature at which the glass yield point + 20-60 ° C, and while maintaining the same temperature, lower the push bar 13 and press the upper die 1 to perform the preform in the press molding die. Precision press molding. A glass transition temperature with a molding pressure of 8 MPa and a molding time of 30 seconds, and after pressing, the aspherical lens made of fluorophosphate glass formed by reducing the molding pressure is kept in contact with the lower mold 22 and the upper mold 21. It was gradually cooled to a temperature of −30 ° C. and then rapidly cooled to room temperature. Thereafter, the aspherical lens was taken out from the press mold and subjected to shape measurement and appearance inspection. The obtained aspherical lens was a highly accurate lens.

  When the surface of this lens was magnified and observed with an optical microscope, it was confirmed that it was a high-quality lens with no surface or internal striae as in the preform used.

  The aspherical lens made of a high-quality and high-precision fluorophosphate glass could be formed by introducing the preheated preform into a press mold and performing precision press molding.

The shape and dimensions of the preform may be appropriately determined depending on the shape of the precision press-molded product to be produced. In the above embodiment, an aspheric lens is molded, but by using a press mold that matches the shape of the final product, various non-spherical lenses such as a concave meniscus lens, a convex meniscus lens, a plano-convex lens, a biconvex lens, a plano-concave lens, and a biconcave lens are used. An optical element such as a spherical lens or various spherical lenses, a prism, a polygon mirror, or a diffraction grating can also be manufactured.
In addition, an optical multilayer film such as an antireflection film or a high reflection film can be formed on the optical functional surface of each optical element obtained as necessary.

  The method for manufacturing a press-molding preform, the apparatus for manufacturing a press-molding preform, and the method for manufacturing an optical element of the present invention can be used in the field of manufacturing a glass optical element such as a small lens.

Claims (17)

Including a step of allowing molten glass to flow out from an outflow pipe, separating the molten glass lump, and forming the obtained molten glass lump into a preform on a mold, wherein the preform is larger than a weight dropped from the outflow pipe. In a method for producing a press-molding preform having a weight, a cooling gas ejection mechanism that surrounds the outflow pipe over the entire circumference of the molten glass lump on the molding die from above and / or obliquely above and has a cooling gas outlet A press characterized by accelerating the cooling of the surface exposed to the atmosphere of the glass lump by blowing gas from the cooling gas blowout port, and obtaining a preform while suppressing the occurrence of striae A method for manufacturing a preform for molding.   Separation of the molten glass lump is performed by lowering the mold downward and separating and cutting the molten glass lump when the weight of the molten glass poured into the mold reaches a predetermined amount. The manufacturing method of the preform for press molding of Claim 1. Including a step of allowing molten glass to flow out from an outflow pipe, separating the molten glass lump, and forming the obtained molten glass lump into a preform on a mold, wherein the preform is larger than a weight dropped from the outflow pipe. In a method for producing a press-molding preform having a weight,
The molten glass that has flowed out is received by a support, the molten glass lump is transferred from the support to a mold and a preform is formed, and the outflow pipe is formed on the molten glass on the support and / or the mold. Cooling of the surface exposed to the glass atmosphere by blowing gas from above and / or obliquely upward from the cooling gas blowing port of the gas blowing mechanism that surrounds the entire circumference and has a cooling gas blowing port. A method for producing a press-molding preform, wherein the preform is obtained while suppressing the occurrence of striae.   The molten glass lump transferred from the support to the mold receives the molten glass that has flowed out with the support, and when a predetermined weight of molten glass accumulates on the support, the support is rapidly lowered to move the molten glass lump from the molten glass stream. The method for producing a preform for press molding according to claim 3, wherein the preform is obtained by cutting and separating.   The method for producing a press-molding preform according to any one of claims 1 to 4, wherein the gas is blown so that the gas blown to the molten glass is not directly blown to the outflow pipe. .   The method for producing a press-molding preform according to any one of claims 1 to 5, wherein the glass lump being blown with gas is a glass lump formed on the mold. The press molding press according to any one of claims 1 to 6, wherein when the viscosity of the glass is in a range of 1 to 10 ⁴ dPa · s, cooling promotion by spraying of the gas is started. Reform manufacturing method.   Forming into a preform while applying a wind pressure to the glass lump on the mold and allowing it to float, and starting cooling promotion by blowing the gas before the glass lump starts to swing on the mold The manufacturing method of the preform for press molding of any one of Claims 1-7.   The method for producing a press-molding preform according to any one of claims 1 to 8, wherein a temperature of the gas to be sprayed is equal to or lower than a glass transition temperature of the glass. 10. The method for producing a press-molding preform according to any one of 1 to 9, wherein a preform made of glass containing B ₂ O ₃ and / or an alkali metal oxide is molded.   A glass preform is prepared by the manufacturing method according to claim 1, the obtained preform is heated, and precision press molding is performed using a press mold. Device manufacturing method.   The optical element manufacturing method according to claim 11, wherein a preform is introduced into a press mold, and the mold and the preform are heated together to perform precision press molding.   The optical element manufacturing method according to claim 11, wherein a preform that has been heated in advance is introduced into a press mold and precision press molding is performed. A plurality of molds for receiving a molten glass lump and forming it into a preform, provided that the molten glass lump is obtained by letting molten glass flow out from an outflow pipe and separating it, and the preform is extracted from the outflow pipe. Having a weight greater than the weight to be dripped,
A take-out device for taking out the preform from the mold, and a casting position for supplying the molten glass lump, a take-out position for taking out the preform, and a transfer device for sequentially circulating and transferring the preform to the cast position. In an apparatus for manufacturing a preform for press molding for molding a preform from a molten glass lump by the method according to claim 1,
The cooling gas is provided around the outflow pipe so as to surround the outflow pipe over the entire circumference, and has a cooling gas outlet mechanism having a cooling gas outlet, and the cooling gas is introduced into the molten glass on the mold from above and / or obliquely from above. from air outlet to facilitate cooling of the glass by blowing a cooling gas, manufacturing apparatus of a press-molding preform, wherein the benzalkonium obtain a preform while suppressing the generation of striae. A plurality of molds for receiving a molten glass lump and forming it into a preform, provided that the molten glass lump is obtained by letting molten glass flow out from an outflow pipe and separating it, and the preform is extracted from the outflow pipe. Having a weight greater than the weight to be dripped,
A take-out device for taking out the preform from the mold, and a casting position for supplying the molten glass lump, a take-out position for taking out the preform, and a transfer device for sequentially circulating and transferring the preform to the cast position. In a press molding preform manufacturing apparatus for molding a preform from a molten glass lump by the method according to claim 3,
A support body that receives the molten glass that has flowed out, a mechanism that moves the molten glass lump from the support body to a mold, and a periphery of the outflow pipe that is provided around the entire periphery of the outflow pipe, and a cooling gas outlet A cooling gas ejection mechanism having
Cooling of the glass is promoted by blowing a cooling gas from above and / or obliquely above the molten glass on the support and / or mold using the cooling gas jetting mechanism from above and / or obliquely upward. apparatus for producing a press-molding preform, wherein the benzalkonium obtain a preform while suppressing physical occurrence. When the transfer device is stopped at the stop position including the casting position and the take-out position, the moving device is repeatedly transferred and circulated.
The press molding according to claim 14 or 15, wherein the cooling gas ejection mechanism cools a molten glass lump on a molding die that is retained at a cast position and / or a stop position next to the cast position. Preform manufacturing equipment. The cooling gas ejection mechanism has a double tube structure, the upper end is sealed, the lower end is opened, and the lower end is used as the cooling gas outlet. An apparatus for manufacturing a preform for press molding as described in 1.

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