JP2006248873A - Method for manufacturing preform for press molding, method for manufacturing optical element and apparatus for flowing molten glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a high quality preform for press molding by a hot molding method, an apparatus for allowing a molten glass to flow out which can be used in the above method and a method for manufacturing an optical element from the resultant preform. <P>SOLUTION: The method for manufacturing a preform for press molding involves a step that a molten glass block which is obtained by allowing a molten glass to flow out from a flow outlet located at a nozzle end through a glass flow path in a nozzle to flow glass is separated and a step that the separated molten glass block is molded into the preform on a molding die. The nozzle for allowing glass to flow has a molten glass guide rod which is projected from the inside of the glass flow path to the outside of the flow outlet. The molten glass is allowed to flow from the glass flow path along the molten glass guide rod and a gas is sprayed on a molten glass surface for cooling acceleration. The nozzle for the effusion of glass is heated by heating means involving an induction heating means and the molten glass is allowed to flow from the glass flow outlet along the molten glass guide rod. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a press-molding preform, a molten glass outflow apparatus that can be used in the method, and a method for manufacturing an optical element from the press-molding preform obtained by the manufacturing method.

In recent years, as a method of manufacturing a high-precision optical lens, a method of forming a lens by press molding has been put into practical use, and aspherical lenses, rhythms, irregularly shaped lenses, and the like can be manufactured at low cost. As a method for producing a glass preform used for such press molding, there is a method of performing processing such as cutting, grinding and polishing on a glass material (referred to as a cold working method). Further, in order to reduce the cost of the preform and the optical element, a method (called a hot forming method) in which molten glass flows out of the nozzle and is molded into a preform having high weight accuracy and few surface defects is also used (referred to as hot forming method). Patent Document 1).
JP 2003-40632 A

The hot forming method achieves higher productivity than the cold working method, and can reduce the cost of the preform and thus the optical elements, but requires higher technical capabilities to produce a high-quality preform. To do.
One of the reasons is that an optical component called striae is formed on the surface of the preform due to volatilization of easily volatile components (easily volatiles) contained in the glass from the surface of the high-temperature glass flowing out from the nozzle. Inhomogeneous portions are generated. Since the striae remain in the optical element obtained by press-molding the preform, the preform cannot be used for manufacturing the optical element and becomes a defective product.

Further, during hot forming, the glass may wet up to the outer periphery of the outflow nozzle. When glass wets around the nozzle periphery, the wet glass is exposed to a high-temperature atmosphere on the nozzle surface for a long time, so when some of the components in the glass volatilize and change in quality or crystallize. There is. When the deteriorated glass or precipitated crystals are washed and taken in by the glass that has flowed out of the nozzle, the deteriorated glass of the molded preform is mixed mainly on the surface. Thus, if a heterogeneous portion is formed in the preform, the optical homogeneity of the preform is remarkably impaired, resulting in a defective product.
As described above, it has been extremely difficult to produce a high-quality press-molding preform by a hot forming method.

  The present invention has been made to solve the above problems, and provides a method for producing a high-quality press-molding preform by a hot forming method and a molten glass outflow device that can be used in the method. Another object of the present invention is to provide a method for producing an optical element from a preform produced by the above method.

Means for solving the above problems are as follows.
[1] A step of flowing molten glass out of an outlet provided at the nozzle tip through a glass flow path in the glass outflow nozzle to separate the molten glass lump, and forming the separated molten glass lump into a preform on a mold. In a method for producing a press-molding preform including:
The glass outflow nozzle has a molten glass guide rod protruding from the glass flow path to the outside of the outlet,
Let the molten glass flow flowing out from the outlet flow down along the molten glass guide rod; and
A method for producing a preform for press molding, characterized in that gas is blown onto the molten glass that has flowed out to promote cooling of the surface of the molten glass.
[2] The method for manufacturing a press-molding preform according to [1], wherein the glass outflow nozzle is heated by a heating unit including an induction heating unit.
[3] Press for separating molten glass lump by letting molten glass flow out from the outlet provided at the nozzle tip through the glass flow path in the glass outflow nozzle, and forming the separated molten glass lump into a preform on a mold In the manufacturing method of the preform for molding,
The glass outflow nozzle has a molten glass guide rod protruding from the glass flow path to the outside of the outlet, and is heated by heating means including induction heating means,
A method for producing a preform for press molding, characterized by causing molten glass flowing out from the outlet to flow down along the molten glass guide rod.
[4] The method for manufacturing a press-molding preform according to [3], wherein a high-frequency induction coil is disposed around the glass outflow nozzle, and a lower end of the molten glass guide rod protrudes downward from a lower end of the coil.
[5] The method for producing a press-molding preform according to [4], wherein gas is blown to the molten glass flowing out from the outlet to promote cooling of the surface of the molten glass.
[6] The method for producing a press-molding preform according to any one of [1] to [5], wherein a preform made of B ₂ O ₃ and / or rare earth oxide-containing glass is molded.
[7] The method for producing a press-molding preform according to any one of [1] to [5], wherein a preform made of phosphate glass or fluorophosphate glass is molded.
[8] A support is disposed below the molten glass guide rod,
The molten glass tip flowing down along the molten glass guide rod is supported by the support, and then
The preform for press molding according to any one of [1] to [7], wherein the support is lowered or the support by the support is removed to separate the tip of the molten glass to obtain a molten glass lump. Manufacturing method.
[9] Manufacture of a preform for press molding according to any one of [1] to [7], wherein molten glass lump is separated from the outflowing molten glass by dropping molten glass from a tip of the molten glass guide rod. Method.
[10] A method for manufacturing an optical element comprising a step of heating a press-molding preform produced by the production method according to any one of [1] to [9] and a step of press-molding.
[11] In a molten glass outflow apparatus comprising a glass outflow nozzle for flowing out the molten glass flow from the outflow port through the glass flow path, and heating means for heating the glass outflow nozzle,
The heating means includes induction heating means, and
The molten glass outflow apparatus, wherein the glass outflow nozzle includes a molten glass guide rod protruding from the inside of the glass flow path to the outside of the outflow port.

According to the present invention, a high-quality press-molding preform can be manufactured from molten glass with high productivity by hot forming.
Furthermore, according to the present invention, a high-quality optical element can be produced from the press molding preform with high productivity.

Hereinafter, the present invention will be described in more detail.
[Method of manufacturing preform for press molding]
The first method for producing a press-molding preform of the present invention (hereinafter also referred to as “method 1”) is as follows.
A press including a step of flowing molten glass from an outlet provided at the tip of a nozzle through a glass flow path in a glass outflow nozzle, separating the molten glass lump, and forming the separated molten glass lump into a preform on a mold. In the manufacturing method of the preform for molding,
The glass outflow nozzle has a molten glass guide rod protruding from the glass flow path to the outside of the outlet,
Let the molten glass flow flowing out from the outlet flow down along the molten glass guide rod; and
A method for producing a preform for press molding, characterized in that gas is blown onto the molten glass that has flowed out to promote cooling of the surface of the molten glass.

The second method for producing a press-molding preform of the present invention (hereinafter also referred to as “method 2”) is as follows:
A press molding process that separates the molten glass lump by letting the molten glass flow out from the outlet provided at the nozzle tip through the glass flow path in the glass outflow nozzle, and molding the separated molten glass lump into a preform on the mold. In the manufacturing method of renovation,
The glass outflow nozzle has a molten glass guide rod protruding from the glass flow path to the outside of the outlet, and is heated by heating means including induction heating means,
A method for producing a preform for press molding, wherein the molten glass flowing out from the outlet is caused to flow down along the molten glass guide rod.
In the present invention, the molten glass that has flowed out is at least one of a molten glass flow and a molten glass that has not yet been separated from the molten glass flow and has accumulated below the molten glass flow (hereinafter also referred to as “molten glass pool”). Means.
Hereinafter, method 1 and method 2 will be described in detail.

Method 1
In Method 1, molten glass is caused to flow out from an outlet provided at the tip of the nozzle through a glass flow path in the glass outflow nozzle, the molten glass lump is separated, and the separated molten glass lump is formed into a preform on a mold. This is a method for producing a press-molding preform.
First, clarified and homogenized molten glass is accumulated in a container, and the molten glass is poured into a pipe made of, for example, platinum or a platinum alloy, the upper part of which is connected to the container. From the elution nozzle), it is preferably discharged continuously at a constant flow rate. The molten glass flowing out from the outlet flows down along the molten glass guide rod protruding from the inside of the glass flow path to the outside of the outlet. Thus, the molten glass lump is separated from the molten glass flowing down along the molten glass guide rod. The separation of the molten glass lump will be described later.

When producing preforms from molten glass containing readily volatile materials by hot forming, the volatiles volatilize when the glass flows out, resulting in surface striae in the resulting preform and obtaining a high quality preform. It becomes difficult.
Therefore, in the method 1, as described above, while the molten glass flow is caused to flow down along the guide rod, gas is blown to the molten glass that has flowed out to promote cooling of the surface of the molten glass (hereinafter also referred to as “air cooling”). ). In Method 1, by cooling with air, cooling of the molten glass flowing out from the outlet is promoted to suppress volatilization of easily volatile substances. Here, by using the guide rod, it is possible to elongate the molten glass flow longer than the natural flow, so heat can be efficiently taken from the molten glass flowing out from the outlet, further promoting the air cooling efficiency. can do. Thereby, volatilization of easily volatile substances can be reduced, and a high-quality preform with reduced striae can be obtained.

Next, the air cooling will be described.
An example of an apparatus used for air cooling of a molten glass flow in the present invention is shown in FIG. The apparatus shown in FIG. 1 has an air-cooling nozzle composed of a double pipe, and a gas is blown to the molten glass flowing out from the outlet by introducing the molten glass outflow nozzle into the internal through hole of the double pipe. It has a structure that can. The air cooling nozzle shown in FIG. 1 is provided with an air cooling gas flow path over the entire circumference of the double pipe portion. However, it is also possible to provide an air-cooled gas flow path in a part of the double pipe portion. When using such an air-cooled nozzle composed of a double tube, it is preferable to arrange the molten glass outflow nozzle so as to be wrapped by the air-cooled nozzle, as shown in FIG. As a result, the gas used for air cooling (hereinafter also referred to as “air-cooled gas”) is directly blown to the outflow nozzle, thereby avoiding the deterioration of the quality of the preform due to crystallization of the glass at the nozzle portion. Can do.

  The air cooling method in the present invention is not limited to the above-described embodiment. For example, the air outlet is placed in a container so as not to apply cooling gas directly to the air outlet, and is kept warm, and another air cooling nozzle (such as a glass tube) is used. Air-cooled gas may be blown to the molten glass stream, the molten glass pool, or both the molten glass stream and the molten glass pool. In this case, it is desirable to prepare a plurality of nozzles and arrange them so as to face each other. Further, even when the air-cooled gas is blown without covering the outlet, there may be no problem if the molten glass has good devitrification resistance.

  The air cooling is performed by blowing air cooling gas to the molten glass that has flowed out from the outlet of the glass outflow nozzle. In particular, in order to increase the cooling efficiency by air cooling, it is preferable to blow the air cooling gas on the portion flowing down along the guide rod of the molten glass flow. It is also possible to blow air-cooled gas on the molten glass block on the mold. Thereby, the surface striae of the preform can be further reduced.

  As will be described later, in Method 1, the molten glass outflow nozzle is preferably induction-heated. However, since the purpose of air cooling is to cool the molten glass flow, it is desirable that the air cooling nozzle itself is not induction-heated. Therefore, it is desirable that the air-cooled nozzle is made of an insulator such as quartz glass or ceramics, not a metal that is induction-heated at a high frequency. In particular, quartz glass is preferable as a material for the air-cooled nozzle because it is transparent, allows easy observation of the outflow nozzle, and has a low processing cost.

  The type of air-cooled gas is not particularly limited as long as the molten glass that has flowed out can be cooled, but nitrogen and clean air are desirable from the viewpoint of cost. The flow rate of the cooling gas is about 2 to 10 liters / minute, and more preferably about 3 to 6 liters / minute. However, it should be optimized as appropriate depending on the design of the air cooling nozzle (the width of the gap between the blowout nozzles) and the type of glass.

Next, the glass outflow nozzle having a guide rod used in the present invention will be described.
As a material of the glass outflow nozzle, a general noble metal or a noble metal alloy which is difficult to wet with glass to be molded such as platinum or a platinum alloy (platinum-gold, platinum-rhodium-gold) can be used. As will be described later, in Method 1, since the nozzle is preferably induction-heated, it is preferable to use a nozzle made of a material capable of induction heating.
On the other hand, as the material of the molten glass guide rod, it is preferable to use a material that easily wets with the glass to be molded. Specifically, a material that easily wets the glass to be formed may be selected from precious metals such as platinum, rhodium, and palladium, and alloys of these precious metals and other precious metals (for example, gold).

In the glass outflow nozzle, the inner diameter of the glass flow path and the opening diameter of the glass outlet may be the same, the former may be larger than the latter, or the former may be smaller than the latter. In particular, it is preferable that the opening diameter of the glass outlet at the tip is larger than the inner diameter of the glass flow path. When the molten glass flows through the nozzle, the glass flow velocity at the glass outlet can be made smaller than the glass flow velocity at the glass passage by making the opening diameter of the glass outlet larger than the inner diameter of the glass passage. . In such a state, the molten glass flow that has reached the glass outlet flows so as to wet the molten glass guide rod protruding from the inside of the glass flow path to the outside of the glass outlet, and the guide rod before getting wet to the outer periphery of the nozzle. It flows down along. When a guide rod made of a material that easily wets the glass is placed in the center of the nozzle tip, the glass is pulled to the lower center of the nozzle in an attempt to wet the surface of the guide rod, and as a result, wetting up to the outer periphery of the nozzle is suppressed. . Further, by increasing the opening diameter of the nozzle outlet, it is possible to suppress the tendency of the glass to get wet on the outer periphery of the nozzle along the lower end surface of the nozzle. Therefore, it is desirable that the opening diameter of the nozzle outlet is as close as possible to the outer diameter of the nozzle, that is, the nozzle tip is thin. In addition, it is easier to suppress the wetting of the nozzle periphery when the opening diameter is widened in a funnel shape at the nozzle tip. In this way, it is possible to reduce or prevent the glass from getting wet around the nozzle periphery.
It is considered that the nozzle outer diameter has an influence on the difficulty of wetting the glass nozzle periphery. The glass outflow nozzle used in the present invention has an outer diameter of 4 mm or more, preferably 5 to 15 mm, and a nozzle thickness at the tip of 0.5 mm or less, preferably 0.2 to 0.4 mm. Is appropriate. Moreover, it is preferable to set it as 3.0-14.6 mm, and, as for the opening diameter of an outflow port, it is more preferable to set it as 4.0-14.6 mm. On the other hand, the inner diameter of the glass flow path may be selected in consideration of the outflow viscosity of the glass by obtaining an appropriate glass flow rate from the capacity of the glass lump to be formed.

  The glass outflow nozzle has a molten glass guide rod protruding from the glass flow path to the outside of the outlet. The length of the portion of the molten glass guide rod protruding from the glass outlet is preferably 1 to 2 times the outer diameter of the glass outlet. The glass outflow nozzle preferably has an inner diameter that gradually increases in the portion from the glass flow path to the glass outlet, and the inner diameter spread angle at the nozzle tip is preferably 130 ° or less. FIG. 8 shows a schematic view of the nozzle tip (inner diameter spreading angles 25 °, 70 °, 130 °). When the spread angle of the nozzle tip inner diameter exceeds 130 °, the molten glass that has flowed out of the nozzle spreads abruptly. Therefore, in glass with low outflow viscosity, a difference in flow velocity occurs between the molten glass at the center side and the outside of the nozzle. Tends to occur. On the other hand, if the spread angle is 100 ° or less, the above problem does not occur, but the length of the tapered hole is increased, so that the length of the inner diameter portion of the nozzle is shortened, and the flow rate of the molten glass at the nozzle is adjusted. There is a tendency for capacity to decline. However, since the above problem can be solved by increasing the total length of the nozzle, there is no major inconvenience. The tip of the guide rod is preferably rounded so that the molten glass can flow smoothly.

  The thickness of the guide rod is preferably in the range of 0.4 to 2.5 mm, more preferably in the range of 0.6 to 1.5 mm, and still more preferably in the range of 0.7 to 1.2 mm. If the thickness of the guide bar is less than 0.4 mm, the effect of cooling the molten glass tends to be reduced, and it is too thin to handle. On the other hand, if the thickness of the guide rod exceeds 2.5 mm, the guide rod is too thick, and thus the flow of glass tends to be disturbed to cause striae.

It is preferable that the glass outflow nozzle having the guide rod can be disposed so that the molten glass guide rod can be exchanged and can be easily manufactured. An example of such a nozzle will be described with reference to FIG. However, the present invention is not limited to this embodiment.
As shown in FIG. 7, a guide rod engaging portion having an inner diameter larger than the inner diameter of the flow passage is provided at the upper portion of the glass flow passage of the nozzle, and the upper portion of the molten glass guide rod main body is disposed in the glass flow passage in one direction. An engaging portion having a width equal to the outer diameter of the main body is provided in the other direction so that the width is wider than the inner diameter of the guide rod and narrower than the inner diameter of the guide rod engaging portion. A molten glass guide rod is inserted into the nozzle from the part side.

  Such an engaging portion of the guide rod can be easily processed by the following method. An end portion of a wire (for example, platinum wire) having a diameter of about 0.5 to 1.0 mm is melted by heating with an oxyhydrogen burner, and a round ball is formed at the end portion of the wire by surface tension. An engagement part can be formed by pressing the ball part hydraulically after cooling to form a disk. Precious metal rods of 1 mm or less are easily bent, so that precise machining is difficult. A practical and inexpensive method as described above is desirable. Of course, the engaging portion may be formed in a T-shape or the like.

  The molten glass guide rod produced as described above is engaged with the guide rod engaging portion, and the molten glass guide rod is installed on the glass outflow nozzle with its tip protruding from the glass outlet of the nozzle. To do. If the nozzle is fixed in the vertical direction so that the glass outlet is directed downward, the molten glass guide rod can be kept stable at the central axis position of the nozzle. Since the engaging portion of the guide bar has the same width as the outer diameter of the main body in the other direction, the engaging portion does not hinder the flow of glass.

  In this way, the molten glass guide rod can be stably installed without being fixed to the glass outflow nozzle, and the molten glass guide rod can be easily inserted and removed. According to the structure, even when the molten glass guide rod is consumed, it can be easily replaced. Prepare multiple types of molten glass guide rods with different outer diameters and lengths, and select the appropriate molten glass guide rod according to the type of glass that flows out, the amount of glass flowing out, etc. It can also be set.

  The glass outflow nozzle can be induction-heated or can be heated by energization. The induction heating is a heating method in which a conductor is heated by arranging a coil around the conductor and generating an induction current by flowing a high-frequency current through the coil. This is a heating method in which the above-mentioned conductor is heated by Joule heat by connecting a current electrode to an electrical conductor and passing a current between the electrodes. What is necessary is just to select the material of a glass outflow nozzle and a molten glass guide rod with a heating method. In particular, in the method 1, it is preferable to heat the glass outflow nozzle by a heating unit including an induction heating unit. According to the induction heating, by producing the air-cooled nozzle with a material that is not induction-heated, the air-cooled nozzle is not directly heated, and the molten glass stream can be cooled well. In addition, in the case of induction heating, unlike the case where the glass outflow nozzle is directly energized and heated, there is an advantage that the glass outflow nozzle can be attached and detached.

  Furthermore, the induction heating has an advantage that the temperature of the guide rod can be adjusted by the relative position of the high frequency induction coil and the guide rod. Specifically, the portion included in the coil of the guide rod (the portion surrounded by the coil) can be heated to substantially the same temperature as the nozzle, and the portion protruding from the coil lower end of the guide rod is set lower than the nozzle temperature. be able to. Thus, by adjusting the relative position of the guide rod and the high-frequency induction coil, the temperature of the guide rod protruding from the nozzle can be set lower than the temperature of the glass outflow nozzle, and the guide rod ( In particular, the lower end portion of the guide rod takes away the heat of the molten glass flow, so that the cooling of the molten glass flow can be efficiently promoted. In particular, it is preferable that the molten glass guide rod protrudes below the lower end of the high frequency induction coil, and the high frequency induction coil is arranged so that the lower end of the high frequency induction coil and the lower end of the glass outflow nozzle are at the same height. More preferably.

  In the method 1, the molten glass lump is separated from the molten glass flowed down along the molten glass guide rod as described above. As a separation method, when producing a relatively lightweight preform, a molten glass drop is dropped from the tip of a molten glass guide rod, and a molten glass lump is obtained by receiving the glass drop with a preform mold. It is preferable to use it. This method is called a dropping method.

When a molten glass droplet is dropped from the nozzle tip using a nozzle that does not have a guide rod, the mass of the glass droplet is m, the gravitational acceleration is g, the outer diameter of the nozzle tip is 2r, and the surface tension of the molten glass is δ. Then, the relational expression of mg = 2π · r · δ holds. If the surface tension of the molten glass is known from this relational expression, the minimum mass m of the molten glass droplet obtained by natural dripping can be determined by measuring the outer diameter 2r of the nozzle tip. As can be seen from this relational expression, when the minimum outer diameter of the glass outflow nozzle is 0.5 mm, it is difficult to obtain a lightweight glass drop of 50 mg or less with ordinary optical glass.
In particular, in the case of glass that tends to wet up around the nozzle, such as phosphate glass, the glass adheres thickly around the outer circumference of the thin nozzle, so it is very possible to obtain molten glass droplets of 100 mg or less by the natural dripping method. difficult.
On the other hand, by dropping a molten glass droplet from the tip of the molten glass guide rod, it is possible to naturally drop a molten glass droplet that is lighter than the conventional method. Moreover, using a glass outflow nozzle having a guide rod also has an advantage that a molten glass lump can be obtained from a low viscosity molten glass stream by a dropping method.

  In the above dripping method, in order to further improve the effect of reducing and preventing the molten glass from getting wet around the nozzle periphery, the molten glass guide rod is not completely buried in the molten glass hanging from the glass outlet. It is preferable to project from the glass outlet with a sufficient length. Since the weight of the molten glass hanging from the glass outlet of the nozzle is determined by the outer diameter of the glass outlet of the nozzle, it is preferable to change the protruding length of the molten glass guide rod for each outer diameter. On the other hand, when the projection length of the molten glass guide rod from the glass outlet of the nozzle is too long, striae that seems to be caused by the molten glass flow at the lower end of the molten glass guide rod becoming too thin is likely to occur inside the glass. Tend to be. Therefore, it is desirable to optimize the protrusion length of the molten glass guide rod from the glass outlet of the nozzle in consideration of the above matters. As a guideline, as described above, the length (projection length) of the molten glass guide rod protruding from the glass outlet of the nozzle is preferably 1 to 2 times the outer diameter of the glass outlet.

  Further, when producing a preform having a relatively large weight, it is preferable to use the following method. A molten glass flow is continuously flowed down from the tip of the molten glass guide rod, and the lower end portion of the molten glass flow is supported by a support close to the tip of the molten glass guide rod, and between the molten glass guide rod side and the support side. Constriction is formed in the molten glass flow. Next, the molten glass lump is obtained by lowering the support vertically downward to separate the molten glass below the constricted portion and receiving it on the support. This method is called descending cutting method. If a preform mold is used as the support, the separated molten glass lump can be directly molded into the preform on the preform mold. When the support is used as a separate article from the preform mold, it is preferable to transfer the molten glass lump on the support to the preform mold and mold it into a preform so as not to impact the glass as much as possible.

  In both the dropping method and the falling cutting method, the molten glass lump can be separated without leaving a cut mark on the glass. In both methods, the glass outflow from the glass outflow nozzle is kept constant, and in the descent cutting method, the distance between the two when the support is brought close to the tip of the molten glass guide rod, the timing of approaching, the timing of lowering the support, and support By making the moving distance when the body descends constant, etc., it is possible to achieve separation of the molten glass lump with high weight accuracy, and as a result, it is possible to increase the weight accuracy of the preform to be molded. In addition, instead of rapidly dropping the support by the descent cutting method, the molten glass lump can be separated by moving the support rapidly in the horizontal direction and rapidly removing the support at the lower end of the molten glass flow. .

  The separated molten glass block is formed into a preform on a mold. For example, it is possible to use a molding die having a concave portion that accommodates the glass lump and introduce the molten glass lump into the concave portion to be molded into a preform. In the molding process, it is desirable to mold the preform while floating the glass. Specifically, a plurality of gas ejection holes are provided at the bottom of the recess of the preform mold, and gas is ejected, and the gas is blown onto the glass in the recess to apply upward wind pressure, so that the glass floats up. Can be molded into a renovation. The levitation does not have to maintain the state where the glass floats on the recess, and the contact time between the glass and the press mold is set so that the preform surface does not wrinkle or breakage called can cracking occurs. What is necessary is just to reduce. This is because when the glass lump comes into contact with the mold, the contact portion is locally quenched and shrinks, causing the formation of wrinkles on the preform surface at the beginning of molding, or causing cracking in the latter half of the molding process. Because. On the other hand, if the glass is floated as described above, it is possible to reduce the contact between the mold and the glass that causes the above-mentioned problems.

  One of the preferred embodiments of the molding method used in the present invention is that gas is ejected upward from a gas ejection hole provided at the bottom of the recess of the preform mold, and a molten glass lump is introduced into the recess and ejected. This is a method in which a glass is rotated by a wind pressure of gas to form a spherical preform. In this method, the recess is composed of a bottom having a gas outlet and a smooth slope surrounding the bottom, the inside diameter of the recess is continuously increased from the bottom to the top, and the slope is symmetrical with respect to an arbitrary rotation angle. A certain mold can be used. Examples of such a mold include a mold having a bottom near the apex of a right cone and a conical slope corresponding to a concave slope, a mold having a trumpet-shaped concave part, and a mold having a venturi-shaped concave part. it can. As described above, in the case where the bottom of the recess has the gas outlet and the inner diameter of the recess becomes larger from the bottom to the top, the wind pressure of the gas ejected from the gas outlet becomes stronger in the recess as it approaches the bottom. When molten glass is introduced into the concave portion, it rises by receiving a strong upward wind pressure due to the jet gas when it descends to some extent. When the glass rises, the wind pressure it receives becomes weaker and the glass rolls down the slope. Since such movement is repeated and the rotation direction of the glass is random, the glass is formed into a spherical shape. Thus, a spherical preform can be formed.

In addition to the above-described embodiment, the glass is levitated and formed by forming a recess with a porous body, ejecting gas from the entire surface of the recess through the porous body, and applying upward wind pressure to the glass introduced into the recess. There is also a method of forming into a preform.
In this way, a preform for press molding can be obtained by forming the glass into a preform shape on the concave portion, cooling to a temperature at which the glass does not deform even when an external force is applied, and then removing the glass from the mold.

  A preferable method for forming a preform from a molten glass ingot obtained one after another is a method in which a plurality of preform forming dies are arranged at equal intervals on the same circumference around a rotation axis on a turntable that rotates with an index. is there. In this method, each mold is rotated and transferred in one direction while being stopped at a predetermined stop position by index rotation. One of the same number of stop positions as the number of preform molds is set as the casting position, and the preform mold that stops at this position receives the molten glass lump, and the mold that received the molten glass lump together with the glass. Mold into a preform while transporting. The molded preform is removed from the mold before the mold returns to the casting position, and the process of transferring the emptied molding mold to the casting position and receiving the molten glass gob is repeated. Thereby, a preform can be mass-produced from the molten glass flow which flows out continuously. The obtained preform can be subjected to press molding after slow cooling.

Method 2
In Method 2, while the glass outflow nozzle having a molten glass guide rod protruding from the inside of the glass flow path to the outside of the outlet is heated by the heating means including the induction heating means, the molten glass flowing out from the outlet is Flow down along the glass guide rod. According to the method 2, the advantage by the induction heating described above can be obtained. Furthermore, also in Method 2, it is preferable to cool the molten glass that has flowed out in the same manner as Method 1 in order to reduce or prevent striae. Details of the nozzle, guide rod, nozzle heating method, air cooling method, glass lump separation method, molding method and the like used in Method 2 are as described for Method 1 above.

Next, the glass used in the present invention will be described.
The glass suitable for the method of the present invention, particularly the method 1 for carrying out air cooling, is a glass that contains many components that are likely to volatilize at high temperatures and causes striae when discharged at high temperatures. Examples of such glass include B ₂ O ₃ and / or rare earth oxide-containing glass. According to the method of the present invention, since the distance between the nozzle and the mold can be increased particularly by using the guide rod, the cooling effect of the molten glass flow by the air cooling method can be obtained more efficiently. be able to.

  Further, as described above, since the method of the present invention can obtain the effect of suppressing and preventing wetting, glass that easily wets around the nozzle periphery, such as phosphate glass, fluorine-containing glass, and fluorophosphate glass is used. Also suitable in some cases. In particular, phosphate glass and fluorophosphate glass are remarkably wet, and when using a conventional nozzle that does not have a guide rod, the glass is wetted to a high position on the outer periphery of the pipe connected to the top of the nozzle. Is particularly effective.

Such phosphate glasses include P ₂ O ₅ and Nb ₂ O ₅ containing glass, P ₂ O ₅ and TiO ₂ containing glass, P ₂ O ₅ and WO ₃ containing glass, P ₂ O ₅ and Bi ₂ O _3. Containing glass, P ₂ O ₅ , Nb ₂ O ₅ and TiO ₂ containing glass, P ₂ O ₅ , Nb ₂ O ₅ , TiO ₂ and WO ₃ containing glass, P ₂ O ₅ , Nb ₂ O ₅ and Bi ₂ O ₃ Containing glass, P ₂ O ₅ , Nb ₂ O ₅ , Bi ₂ O ₃ and WO ₃ containing glass, P ₂ O ₅ , Nb ₂ O ₅ , Bi ₂ O ₃ and TiO ₂ containing glass, P ₂ O ₅ , Nb ₂ Examples include O ₅ , Bi ₂ O ₃ , TiO ₂ and WO ₃ containing glasses.

  Furthermore, as described above, according to the method of the present invention, a molten glass lump can be obtained from a low-viscosity molten glass stream, preferably by a dropping method. Specifically, a molten glass lump can be obtained from a molten glass flow having an outflow viscosity of 10 dPa · s or less, preferably 1 to 8 dPa · s, more preferably 1 to 5 dPa · s. Thereby, a preform having a weight of 100 mg or less, which has been difficult to produce by the conventional method, can be stably produced. The outflow viscosity can be determined as follows. The viscosity of the glass at each temperature is measured in advance, and a graph of temperature and viscosity (viscosity curve) is created. The liquid phase temperature is measured separately, and the viscosity at that temperature is read from the graph and is defined as the liquid phase viscosity. Similarly, the viscosity of the glass at the outflow temperature is read from the above graph and is defined as the outflow viscosity.

As described above, according to the present invention, a high-quality press-molding preform, particularly a preform suitable for precision press-molding can be produced with high productivity.
Examples of the shape of the preform that can be manufactured by the method of the present invention include those suitable for precision press molding of an optical element, such as a sphere and a rotating body.
In particular, the present invention relates to a preform used when manufacturing a small optical element requiring high weight accuracy, such as an imaging lens and a pickup lens mounted on a camera-equipped mobile phone, and a lens mounted on a digital camera. It is suitable for the manufacture of a preform used when manufacturing an optical element such as by precision press molding.

[Fused glass outflow equipment]
The molten glass outflow device of the present invention is
In a molten glass outflow apparatus comprising a glass outflow nozzle for flowing out a molten glass flow from an outlet through a glass channel, and a heating means for heating the glass outflow nozzle,
The heating means includes induction heating means, and
The glass outflow nozzle includes a molten glass guide rod that protrudes from the inside of the glass channel to the outside of the outflow port. According to the molten glass outflow apparatus of the present invention, as described above, a glass melt that easily causes striae, a glass that easily wets up, and a molten glass lump is separated from a molten glass flow having a low viscosity to obtain a high-quality preform. Can do. The details of the molten glass outflow device of the present invention are as described above.

[Method of manufacturing optical element]
The method for producing an optical element of the present invention includes:
It is a manufacturing method of an optical element provided with the process of heating the press molding preform produced by the manufacturing method of the press molding preform of the present invention, and the process of press molding.
As described above, according to the method for producing a press-molding preform of the present invention, a high-quality preform can be produced with high productivity. Therefore, the press-molding preform obtained by this method is used. As a result, the optical element can be manufactured with high productivity.

  In the method for producing an optical element of the present invention, a preform having high weight accuracy and high quality can be used as a whole. Therefore, it is preferable to produce an optical element by precision press molding. The precision press molding is also called a mold optics molding method, and is a method of forming the shape of the optical functional surface by press molding, 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.

  As a press mold used in the precision press molding method, a known mold, for example, a mold having a release film on a molding surface of a mold material such as silicon carbide or super hard material can be used. Among these, it is preferable to use a press mold made of silicon carbide. As the release film, a carbon-containing film, a noble metal alloy film, or the like can be used. From the viewpoint of durability and cost, it is preferable to use a carbon-containing film.

  In the precision press molding method, it is desirable that the molding atmosphere be a non-oxidizing gas atmosphere in order to keep the molding surface of the press mold in a good state. As the non-oxidizing gas, it is preferable to use nitrogen, a mixed gas of nitrogen and hydrogen, or the like.

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 (hereinafter referred to as precision press molding method 1).
In precision press molding method 1, precision press molding may be performed by heating the temperature of the press mold and the preform to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁶ to 10 ¹² dPa · s. preferable.
Also the glass can 10 ¹² dPa · s or more, more preferably 10 ¹⁴ dPa · s or more, more preferably from press mold the precision press molded article is cooled to a temperature at which a viscosity of more than 10 ¹⁶ dPa · s 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 (hereinafter referred to as precision press molding method 2).
According to this method, since the preform is preliminarily heated before being introduced into the press mold, it is possible to manufacture an optical element with good surface accuracy free from surface defects while shortening the cycle time.
The preheating temperature of the press mold is preferably set lower than the preheating temperature of the preform. Thus, by lowering the preheating temperature of the press mold, the consumption of the mold can be reduced.
Further, according to this method, since it is not necessary to perform preform heating in the press mold, the number of press molds to be used can be reduced.

In the precision press molding method 2, it is preferable 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 less than 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.
Thus, according to the present invention, various lenses such as spherical lenses, aspherical lenses, and micro lenses, diffraction gratings, lenses with diffraction gratings, various optical elements such as lens arrays and prisms, and digital cameras as applications Guides light used for data reading and / or data writing on optical recording media such as lenses that constitute imaging optical systems for cameras with built-in cameras and cameras, camera-equipped mobile phones, and CDs and DVDs Therefore, various optical elements such as lenses can be manufactured. In addition, if a preform made of copper-containing glass is used, an optical element having a color correction function of a semiconductor imaging element can be produced. Among them, it is suitable as a method for producing a lens mounted on a digital camera.
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 Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 (FIG. 1)
A platinum alloy outflow nozzle, a high-frequency induction heating coil, and an air cooling nozzle were set as follows. An outflow nozzle (inner diameter of the tip: 6.0 mm, spread angle 90 °) as shown in FIG. 1 was processed from a platinum-gold alloy base material containing 5% by mass of gold. As shown in FIG. 1, a counterbore portion having a diameter of 3 mm and a depth of 3 mm was processed at the upper end of the outflow nozzle. On the other hand, a tapered hole was formed at the lower end (outlet) of the outflow nozzle, and the thickness of the outer periphery of the tip was reduced to 0.25 mm. In addition, a through hole of φ1.3 mm was processed in the central portion excluding both ends.

  Next, the end of a 0.8 mm platinum wire was heated and melted with an oxygen-hydrogen burner to form a spherical portion of φ2.1 mm at the end of the platinum wire. The spherical portion was sandwiched between metal flat plates and hydraulically pressed to form a circular plate portion having a diameter of 2.7 mm and a thickness of 0.8 mm at the tip of the platinum wire to obtain a molten glass guide rod. This platinum molten glass guide rod with a disc was inserted into the outflow nozzle from the counterbore side, and a disc portion of φ2.7 mm was engaged with the counterbore portion of φ3.0 mm. The platinum molten glass guide rod was protruded from the lower end of the outflow nozzle, and the projection amount of the platinum molten glass guide rod was determined and cut. Thereafter, the platinum molten glass guide rod was taken out, the cut portion of the platinum molten glass guide rod was heated and melted with an oxygen-hydrogen burner, and the cut portion was rounded, and then returned to the outflow nozzle. The outflow nozzle into which the platinum molten glass guide rod was inserted was abutted against the lower end of the outflow pipe and fixed with a fixing jig made of platinum alloy.

    Next, quartz glass was processed to produce a double tube (diameter φ39.5 mm) as shown in FIG. The upper part of the double pipe was closed, and an introduction pipe for introducing air-cooled gas was attached to the double pipe part. On the other hand, the lower part of the double pipe was open, and the diameter of the double pipe part was reduced at the lower end side. Such an air cooling nozzle made of quartz glass was arranged so as to wrap the outflow nozzle as shown in FIG. In such a state, a cooling gas (for example, nitrogen) is passed through a quartz glass-made air cooling nozzle to cool the top surface of the molten glass mass being cast on the molten glass flow or the mold that has just come out of the outflow nozzle. be able to. Moreover, since the outflow nozzle is wrapped with an air cooling nozzle made of quartz glass, the air cooling gas is not blown onto the outflow nozzle, and the glass is not crystallized at the nozzle portion.

  Next, a high frequency induction heating coil (also referred to as a high frequency induction coil or a high frequency coil) for heating the outflow nozzle will be described. A high frequency induction heating coil having an inner diameter of 40 mm, a height of 50 mm, and a number of turns of 7 was prepared, and a quartz glass air-cooled nozzle was fitted into the high frequency coil and physically fixed. In this state, the outflow nozzle was inserted into the air cooling nozzle and physically fixed. The lower end of the high-frequency induction heating coil, the lower end of the outflow nozzle (excluding the platinum molten glass guide rod), and the lower end of the air cooling nozzle were adjusted so as to have the same height. Therefore, the molten glass guide rod made of platinum protruding from the outflow nozzle was also protruded from the lower end of the coil.

Next, a molten glass and its outflow method are demonstrated. At nd: 1.85, νd: 40, glass cullet containing B ₂ O ₃ , ZnO, and La ₂ O ₃ as main components was put into a 3 liter platinum crucible, melted at 1100 ° C., and then at 1300 ° C. Defoaming clarification and stirring were performed to obtain molten glass. This molten glass was continuously flowed out at a flow rate of 1.2 kg / hr from a platinum alloy flow-out nozzle which was temperature-controlled at 1060 ° C. by induction heating through a temperature-controlled platinum pipe connected to the bottom of the platinum crucible. The liquid phase temperature of the present glass is 1050 ° C., and the viscosity at the liquid phase temperature is 4.5 dPa · s. Further, at the outflow temperature of 1060 ° C., the viscosity of the glass is 3.9 dPa · s.

Next, a preform molding method and a molding apparatus will be described. Twelve molds for directly casting the molten glass were evenly arranged on the outer periphery of the rotary table that rotated the index by 30 °. The depression of the casting mold cast part is made of a porous material, and a floating gas (for example, nitrogen) was flowed 0.3 liter / min toward the concave surface side in order to keep the molten glass lump in a substantially floating state. Moreover, in order to adjust the cooling rate of the molten glass on a shaping | molding die, the shaping | molding die was heated at about 200-300 degreeC. With the above settings, 12 molds are distributed in order directly under the outlet, the mold is raised and the molten glass flow is received in the concave portion of the mold for 6.4 seconds, and then the mold is rapidly lowered to cause the molten glass flow to flow. Cutting was performed to obtain a molten glass lump of 425 mm ^{3 in} the concave portion of the mold. The same operation was repeated, and the molten glass was cast in order with 7.6 molds every 7.6 seconds. The molten glass lump was cooled and solidified in a substantially floating state on the mold, and then removed from the mold by a robot vacuum suction hand and arranged on a tray.

Next, the amount of projection of the platinum molten glass guide rod from the tip of the outflow nozzle will be described. When molten glass is dropped from an outflow nozzle having an outer diameter of 6 mm, the length of the molten glass hanging from the outflow nozzle is limited to about 6 mm, and dripping occurs at lengths longer than that. The platinum molten glass guide rod inserted into the outflow nozzle is used for the purpose of accelerating the cooling of the molten glass, and is used to stretch the glass flow narrower and longer than during natural dripping. Therefore, in order to drop molten glass, the amount of projection of the platinum molten glass guide rod should be 6 mm or more for a nozzle having an outer diameter of 6 mm. In addition, the preferable protrusion amount which obtains sufficient cooling effect with the molten glass guide rod made of platinum is 6 to 12 mm for an outflow nozzle having an outer diameter of 6 mm. The longer the amount of protrusion, the easier it is to obtain the effect of cooling the molten glass. However, if the amount of protrusion is 14 mm or more, the temperature of the glass is too low and the glass may be crystallized on the surface of the platinum molten glass guide rod. On the contrary, if the projection amount of the molten glass guide rod is not too long, the molten glass will not stay on the surface of the molten glass guide rod even if the surface temperature of the molten glass guide rod is below the liquidus temperature, Since it is located in the center of the molten glass having a high temperature, there is almost no risk of crystallization. Thus, it is necessary to optimize the protrusion amount of the molten glass guide rod from the outflow nozzle according to the outer diameter of the nozzle to be used. In this example, the amount of projection of the molten glass guide rod was 7 mm. Further, in this example, 5 liters / minute of nitrogen was passed through the air cooling nozzle, and air cooling was performed by blowing air cooling gas onto the part flowing down along the molten glass guide rod as shown in FIG.
In this example, the distance between the tip of the nozzle and the mold was about 5 mm longer than when a nozzle without a molten glass guide rod was used, and the glass flow could be cast in a thin state. The preform thus obtained had no striae on the surface and inside, and the quality was good.

Example 2 (FIG. 2)
A molten glass lump was separated from the molten glass stream using the apparatus shown in FIG. In this example, a 425 mm ³ preform was molded under the same conditions as in Example 1 except that no quartz glass air cooling nozzle was attached and no air cooling was performed. However, after the casting was completed, the mold was retracted from just below the outflow nozzle, and then 7 liters / minute of nitrogen was blown onto the molten glass lump from directly above the molten glass lump. In the obtained preform, thin striae were observed on the outermost peripheral surface. However, when the lens was molded with this preform, the striae on the surface existed outside the effective diameter of the lens, and the concentration of striae was at a non-defective level.

Example 3 (FIG. 3)
A glass cullet containing P ₂ O ₅ , R ₂ O (R: Li, Na, K) and Nb ₂ O ₅ as main components was put into a platinum crucible at nd: 1.8468 and νd: 23.5. After melting at 0 ° C., defoaming was clarified at 1100 ° C. and homogenized with stirring to obtain a molten glass. This molten glass is bonded to the bottom of the crucible, and a platinum alloy outflow nozzle with a molten glass guide rod at 900 ° C. through a platinum pipe whose temperature is controlled by induction heating (tip outer diameter: φ6.0 mm, center hole diameter: 1.2 mm, The nozzle tip was spread at a flow rate of 0.96 kg / hr from a nozzle tip spread angle of 90 °, a molten glass guide rod diameter: φ0.8 mm, and a protruding amount of the molten glass guide rod: 7 mm). The molten glass that flowed out under these flow conditions was molded into a 425 mm ³ preform at intervals of 6.5 seconds using the same apparatus as in Example 2. In FIG. 3, the schematic of the cutting | disconnection separation of the molten glass lump just before casting in a present Example is shown. The glass has a liquidus temperature of 880 ° C. and a liquidus viscosity of 5.3 dPa · s. Therefore, the outflow viscosity of the molten glass is 4.1 dPa · s. The obtained preform had no defects such as striae and had no problem in quality.

The molten glass of this composition has very good wettability with the above-described platinum-gold alloy nozzle. On the other hand, when an ordinary nozzle such as Comparative Example 3 described later is used, the molten glass wets at the tip of the nozzle and a thick surface striae is generated in the preform (see Comparative Example 3 and FIG. 6). In this embodiment, as shown in FIG. 3, the shape of the molten glass at the tip of the nozzle can be kept in a tapered state from just before casting to cutting and separation of the molten glass lump. This is a phenomenon that occurs because the molten glass wets along the molten glass guide rod. In order to obtain such an effect, it is desirable to use a molten glass guide rod whose wettability with molten glass is equal to or better than that of the nozzle material. That is, when a normal gold-platinum alloy nozzle (containing 5% gold) is used, it is not preferable to use a molten glass guide rod made of a noble metal that does not wet well, such as pure gold.
As described above, the shape of the molten glass at the tip of the nozzle is always kept in a tapered state from just before casting to cutting and separation of the molten glass lump, so that even a molten glass that easily wets the nozzle material does not get wet.

Comparative Example 1 (FIG. 4)
Only the outflow nozzle was changed to one without a molten glass guide rod (FIG. 4), and other conditions were the same as in Example 1 to form a 425 mm ³ preform. In the obtained preform, dark radial striae were observed on the outer periphery. Such stria is considered to occur because the outer periphery of the preform is not easily cooled by air. Therefore, when the outflow nozzle temperature was lowered to 1040 ° C., no striae was observed. However, crystals were deposited at the tip of the nozzle within about 30 minutes from the start of molding, and continuous molding was not possible.

Comparative Example 2 (FIG. 5)
Only the outflow nozzle was changed to a nozzle without a molten glass guide rod (FIG. 5), and other conditions were the same as in Example 2 to form a 425 mm ³ preform. In the resulting preform, a thick striae resembling the onion skin streak from the center to the outer periphery was observed and could not be used as a preform.

Comparative Example 3 (FIG. 6)
Only the outflow nozzle was changed to a nozzle without an molten glass guide rod (inner diameter 0.9 mm), and the other conditions were the same as in Example 3 to form a 425 mm ³ preform. On the surface of the preform thus obtained, suddenly strong surface striae occurred.
In FIG. 6, the schematic of the cutting-separation of the molten glass lump just before casting in the comparative example 3 is shown. As shown in FIG. 6, in the nozzle without the molten glass guide rod, the hanging droplets are not constricted. Each time the molten glass stream is cut, the molten glass is lifted upward by surface tension. Therefore, even if there is no wetting up at the initial stage of molding, the outer periphery of the nozzle tip gets wet with time. When the nozzle tip is covered with a thin glass layer, the glass stays and changes its quality. When the modified glass is mixed into the preform surface, a deep surface striae is generated.

  ADVANTAGE OF THE INVENTION According to this invention, a high quality preform for press molding can be manufactured by the hot forming method from the glass containing an easily volatile substance, or the glass which wets easily to a nozzle.

1 is a schematic view of an apparatus used in Example 1. FIG. FIG. 6 is a schematic view of an apparatus used in Example 2. It is the schematic of the cutting-separation of the molten glass lump just before casting in Example 3. 2 is a schematic view of an apparatus used in Comparative Example 1. FIG. 6 is a schematic view of an apparatus used in Comparative Example 2. FIG. It is the schematic of the cutting-separation of the molten glass lump just before casting in the comparative example 3. An example of the glass outflow nozzle which has a guide rod is shown. Schematic diagrams of nozzle tips (inner diameter spreading angles 25 °, 70 °, 130 °) are shown.

Claims (11)

A press including a step of flowing molten glass from an outlet provided at the tip of a nozzle through a glass flow path in a glass outflow nozzle, separating the molten glass lump, and forming the separated molten glass lump into a preform on a mold. In the manufacturing method of the preform for molding,
The glass outflow nozzle has a molten glass guide rod protruding from the glass flow path to the outside of the outlet,
Let the molten glass flow flowing out from the outlet flow down along the molten glass guide rod; and
A method for producing a preform for press molding, characterized in that gas is blown onto the molten glass that has flowed out to promote cooling of the surface of the molten glass. The said glass outflow nozzle is a manufacturing method of the preform for press molding of Claim 1 heated by the heating means containing an induction heating means. A press molding process that separates the molten glass lump by letting the molten glass flow out from the outlet provided at the nozzle tip through the glass flow path in the glass outflow nozzle, and molding the separated molten glass lump into a preform on the mold. In the manufacturing method of renovation,
The glass outflow nozzle has a molten glass guide rod protruding from the glass flow path to the outside of the outlet, and is heated by heating means including induction heating means,
A method for producing a preform for press molding, characterized by causing molten glass flowing out from the outlet to flow down along the molten glass guide rod. The manufacturing method of the press molding preform of Claim 3 which arrange | positions the high frequency induction coil around the said glass outflow nozzle, and makes the lower end of the said molten glass guide rod protrude below rather than the lower end of the said coil. The manufacturing method of the preform for press molding of Claim 4 which sprays gas on the molten glass which flows out out of the said outflow port, and accelerates | stimulates cooling of the said molten glass surface. The method of press-molding preform produced according to any one of claims 1 to 5, a preform consisting of B ₂ O ₃ and / or rare earth oxide-containing glass. The method for producing a press molding preform according to any one of claims 1 to 5, wherein a preform made of phosphate glass or fluorophosphate glass is molded. A support is disposed below the molten glass guide rod,
The molten glass tip flowing down along the molten glass guide rod is supported by the support, and then
The preform for press molding according to any one of claims 1 to 7, wherein the support is lowered or the support by the support is removed to separate the tip of the molten glass to obtain a molten glass lump. Manufacturing method. The manufacturing method of the preform for press molding of any one of Claims 1-7 which isolate | separate a molten glass lump from the molten glass which flows out by dripping molten glass from the front-end | tip of the said molten glass guide rod. The manufacturing method of an optical element provided with the process of heating the preform for press molding produced by the manufacturing method of any one of Claims 1-9, and the process of press molding. In a molten glass outflow apparatus comprising a glass outflow nozzle for flowing out a molten glass flow from an outlet through a glass channel, and a heating means for heating the glass outflow nozzle,
The heating means includes induction heating means, and
The molten glass outflow apparatus, wherein the glass outflow nozzle includes a molten glass guide rod protruding from the inside of the glass flow path to the outside of the outflow port.

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