JP2015078099A - Glass outflow device, glass outflow method, method of manufacturing preform for press molding, and method of manufacturing optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass outflow device including a diameter enlarged portion at a lower end of a pipe, capable of suppressing occurrence of a single flow of molten glass.SOLUTION: A glass outflow device 1 includes a pipe which flows out molten glass. The pipe includes a constant diameter portion 6 of which the inner diameter constantly extends in a vertical direction and a diameter enlarged portion 8 having a shape in which the inner diameter continuously extends and enlarges toward a lower end, both of which are formed in a glass flow passage 2 in which the molten glass flows. A diameter reduced portion 10 of which the inner diameter reduces toward an upper end is formed on the inner surface of the lower end edge of the diameter enlarged portion 8.

Description

  The present invention relates to a glass outflow device, a glass outflow method, a press molding preform manufacturing method, and an optical element manufacturing method, and in particular, a glass outflow device for manufacturing a glass molded product such as a preform, and The present invention relates to a glass outflow method, a method for manufacturing a press-molding preform using the glass outflow apparatus and method, and a method for manufacturing an optical element using the preform manufactured by the manufacturing method.

  2. Description of the Related Art Conventionally, a method is known in which molten glass is flowed out from an outflow pipe, a predetermined amount of molten glass lump is supplied onto a mold, and a preform for press molding is formed. A preform can be produced by molding and cooling the molten glass lump supplied on the mold.

  As such an outflow pipe, for example, in Patent Document 1 (particularly, FIG. 3), in order to increase the dripping weight of the molten glass and produce a large preform, a diameter-expanded portion whose inner diameter expands at the tip of the pipe. An outflow pipe formed of is disclosed.

  Further, for example, Patent Document 2 discloses a molten glass outflow pipe in which an enlarged diameter portion is formed such that the inner diameter increases toward the glass outlet in order to delay the dropping of the molten glass from the pipe. Yes. Furthermore, in Patent Document 2, in order to obtain a preform whose weight is larger than the weight by which the molten glass naturally drops from the tip of the outflow pipe, the tip of the molten glass that flows out is supported by a mold, and a desired amount is provided in the mold. When the molten glass is accumulated, the mold is suddenly lowered to separate the molten glass flowing out from the outflow pipe and the molten glass accumulated on the mold, thereby obtaining a desired amount of molten glass lump (hereinafter referred to as drop cutting). Law).

  In general, preform molding uses multiple molds, and these molds are sequentially moved below the outflow pipe and stopped to receive the molten glass lump, and the mold receiving the molten glass lump is taken out from the stop position. At the same time, the next mold is moved and stopped below the outflow pipe to supply a molten glass lump. According to the descending cutting method, it is possible to obtain a molten glass lump having a weight larger than that of the molten glass lump that is naturally dropped. In order to form a larger preform, it is necessary to increase the amount of molten glass flowing out per unit time (hereinafter referred to as the pulling amount). When the pulling amount is increased, the time during which the molten glass stays at the tip of the outflow pipe without dropping is shortened. As a result, the molten glass is dripped before the next mold moves below the outflow pipe, and the preform cannot be produced stably.

According to the outflow pipe as described in Patent Documents 1 and 2, even if the pulling amount is increased, the time during which the molten glass stays at the tip of the pipe without spontaneous dripping can be increased.
For these reasons, the methods described in Patent Documents 1 and 2 are effective in stably producing a large preform.

JP-A-8-188419 JP-A-10-36123

  Here, in order to manufacture a larger preform, while further increasing the amount of pull-up, increasing the diameter of the glass outlet of the spill pipe, the time for the molten glass to stay at the tip of the spill pipe without spontaneous dripping It needs to be long. However, when the diameter of the lower end of the pipe is further increased, as shown in FIG. 6, the molten glass 220 is separated from a part of the inner peripheral surface of the enlarged diameter portion 208, and the opposite peripheral surface (FIG. 6). Left side). Such a phenomenon is referred to as “single flow” in this specification.

  After the single flow is generated in this way, the molten glass 220 may return to the state of flowing again in contact with the entire inner peripheral surface of the enlarged diameter portion 208. However, if a single flow occurs, the inside of the molten glass 220 entrains gas, bubbles are mixed into the preform, or striae occur, resulting in a deterioration in the quality of the preform. There is.

  The present invention has been made in view of the above problems, and its purpose is to apply a glass outflow device having an enlarged diameter portion at the lower end of a pipe capable of suppressing the occurrence of a single flow of molten glass, and a glass outflow method. And a method for manufacturing a press-molding preform for forming a press-molding preform by flowing out the molten glass by the outflow method, and an optical element using the preform manufactured by the method for manufacturing the molding preform. It is to provide a manufacturing method.

  The glass outflow device of the present invention includes a constant diameter portion having a constant inner diameter extending in the vertical direction in a flow path through which the molten glass flows, and an enlarged diameter portion having a shape in which the inner diameter expands continuously toward the lower end. Is a glass outflow device for outflowing molten glass from a pipe in which is formed, and a reduced diameter portion whose inner diameter decreases toward the tip is formed on the inner surface of the lower end edge of the enlarged diameter portion.

  Further, the glass outflow method of the present invention has a constant diameter portion having a constant inner diameter extending in the vertical direction in the flow path through which the molten glass flows, and an enlarged diameter having a shape in which the inner diameter expands continuously toward the lower end. And a reduced diameter portion whose inner diameter is reduced toward the tip, on the inner surface of the lower end edge of the pipe.

  Although molten glass has a tendency to become thin due to surface tension, according to the present invention, since the reduced diameter portion is formed at the lower end edge of the enlarged diameter portion, the molten glass is also in the pipe inner periphery at the lower end portion of the enlarged diameter portion. The state which contacted the surface is maintained and generation | occurrence | production of the single flow of molten glass can be suppressed.

  According to the glass outflow apparatus and the glass outflow method of the present invention, it is possible to suppress the occurrence of a single flow of molten glass. Moreover, according to the method for manufacturing a press-molding preform of the present invention, a highly homogeneous preform can be manufactured. Moreover, according to the manufacturing method of the optical element of this invention, a high quality optical element can be manufactured stably through a preform from molten glass.

It is a vertical sectional view showing the glass outflow device of this embodiment. It is a vertical sectional view which expands and shows the diameter expansion part and diameter reduction part vicinity of the glass outflow device of this embodiment. It is a vertical sectional view which shows the shape of the lower end part of the diameter-expansion part of the glass outflow apparatus which is not provided with the diameter reduction part, and shows the state which is flowing out the molten glass. In the glass outflow apparatus of this embodiment, it is a vertical sectional view which expands and shows the lower end part of the enlarged diameter part in the state which is flowing out out of the molten glass. It is a vertical sectional view of an outflow pipe, molten glass, and a forming die when supplying molten glass flowing out from an outflow pipe to a recess provided on an upper surface of a forming die that is retained below the outflow pipe. It is a figure for demonstrating the single flow of a molten glass.

Hereinafter, one embodiment of a glass outflow device of the present invention is described in detail, referring to drawings.
FIG. 1 is a vertical cross-sectional view showing the vicinity of the lower end portion that flows out of the molten glass of the glass outflow device 1 of the present embodiment. The glass outflow apparatus 1 of this embodiment has a molten crucible (not shown) at the top, and has an outflow pipe 2 through which the molten glass accumulated in the molten crucible flows downward. The temperature of the outflow pipe 2 is controlled by a heating device (not shown) and a heat insulating material so that the molten glass flows out at a desired flow rate without devitrification. As for the heating device, a known device, for example, an energization heating mechanism for generating Joule heat by supplying current to the outflow pipe, a high-frequency coil disposed on the outer periphery of the outflow pipe, a high-frequency power source connected to the coil, It is possible to apply a high-frequency induction heating mechanism for inductively heating the outflow pipe. Moreover, a well-known thing can be used as a heat insulating material.

  As shown in FIG. 1, the outflow pipe 2 includes a glass flow path 3 extending in the vertical direction inside. The glass flow path 3 has an upper portion connected to the bottom of the melting crucible, a constant diameter portion 6 having a constant inner diameter, and an enlarged diameter portion 8 that has an inner diameter continuous from the lower end of the constant diameter portion 6 and increases downward. And have. The molten glass in the melting crucible flows down the glass flow path 3 and flows out from an opening provided below the enlarged diameter portion 8, that is, a glass outlet 9.

  FIG. 2 is an enlarged vertical cross-sectional view showing the lower end portion of the enlarged diameter portion 8 of the outflow pipe 2 of the glass outflow device 1 of the present embodiment. As shown in the figure, a reduced diameter portion 10 is formed at the lower end edge of the enlarged diameter portion 8 of the outflow pipe 2 so that the inner diameter decreases toward the tip over the entire circumference. The reduced diameter portion 10 is formed by projecting the inner surface of the glass flow path 3 in an annular shape toward the center of the glass flow path 3. The surface of the reduced diameter portion 10 has a substantially arc shape in the vertical cross section. In this embodiment, the constant diameter portion 6 extends directly from the connection portion with the melting crucible. However, the present invention is not limited to this, and the constant diameter portion 6 is fixed between the connection portion with the melting crucible and the constant diameter portion 6. A portion having an inner diameter different from the inner diameter of the diameter portion 6 may be provided. For example, in order to control the outflow amount of the molten glass, the inner diameter may gradually decrease from the connecting portion with the melting crucible toward the constant diameter portion 6. Further, a portion having an inner diameter smaller than the inner diameter of the fixed diameter portion 6 may be provided above the fixed diameter portion 6.

Hereinafter, the shape of the reduced diameter portion 10 in the present embodiment will be described in more detail.
FIG. 3 is a vertical cross-sectional view showing the shape of the lower end portion of the enlarged diameter portion of the glass outflow device not provided with the reduced diameter portion, and shows a state where the molten glass is flowing out. As shown in the figure, in the conventional glass outflow device 101, since the reduced diameter portion is not provided at the lower end of the enlarged diameter portion 108, the lower end of the glass flow path of the glass outflow device 101 faces substantially vertically downward. . When such a glass outflow device 101 is used, the molten glass 120 is separated from the inner surface of the pipe at a height position P ′ in the vicinity of the lower end of the enlarged diameter portion 108. At this time, as shown in FIG. 3, the outer peripheral surface of the molten glass 120 does not extend vertically downward from a position separated from the inner surface of the pipe, but is curved and reduced in diameter due to the influence of surface tension. . Here, the angle between the tangent L′ 0 of the pipe inner surface at the height position P ′ where the molten glass 120 is separated from the inner surface of the pipe and the tangent L′ 1 at the height position P of the outer peripheral surface of the molten glass is the contact angle θ. _Set to ₀ . The contact angle θ ₀ increases as the inner diameter at the lower end of the enlarged diameter portion 108 increases.

For example, when the molten glass is lanthanum borate-containing glass, the viscosity at the time of outflow is 5 to 6 dPas · s, and the inner diameter at the lower end of the pipe (the inner diameter of the glass outlet) is 9 mm, the above contact angle θ ₀ is approximately in the range of 30 to 35 degrees, and when the inner diameter at the lower end of the pipe is 16 mm, the contact angle θ ₀ is approximately in the range of 40 to 45 degrees.

  FIG. 4 is an enlarged vertical sectional view showing the lower end portion of the enlarged diameter portion 8 of the outflow pipe 2 in the present embodiment, and shows a state in which the molten glass 20 is flowing out. As shown in the figure, the glass outflow device 1 of the present embodiment is configured such that the upper end of the reduced diameter portion 10 is located at the height position P. This height position P is preferably equal to the height position P ′ at which the molten glass 120 in the glass dropping device not provided with the reduced diameter portion is separated from the pipe inner surface.

The reduced diameter portion 10 has a substantially arcuate surface shape (convex to the outside of the pipe) in the vertical cross section, and at the height position P that is the uppermost portion, the tangent of the surface of the reduced diameter portion 10 in the vertical cross section. It is preferable that the angle with respect to the vertical direction is maximized. In the present embodiment, the aperture angle θ is preferably 10 degrees or more, and when the inner diameter of the lower end of the pipe is 9 mm or more, the aperture angle θ is preferably 20 degrees or more. Further, it is more preferable that the aperture angle θ is not less than the contact angle θ ₀ .
The material of the outflow pipe 2 is preferably a platinum-based material such as platinum, a platinum alloy, or reinforced platinum that has excellent heat resistance and corrosion resistance, is electrically conductive, and can be heated by electric current and high-frequency induction.

Hereinafter, a method for producing a preform using the glass outflow device 1 will be described.
When manufacturing a preform, first, a glass melting apparatus is used, and a glass raw material is melted, clarified, and homogenized in a melting crucible in the glass melting apparatus to produce a molten glass. The molten glass flows into the outflow pipe 2 of the glass outflow device 1 from the connection with the bottom of the melting crucible. The molten glass flows down the glass flow path 3. The molten glass stays at the glass outlet 9 and does not drip until the mold receiving the molten glass is transferred below the outflow pipe 2.
While the molten glass stays at the glass outlet 9, the molding die is transferred and stopped below the outflow pipe 2, and the molten glass flows out into the concave portion on the molding die.

FIG. 5 shows the vertical flow of the outflow pipe 2, the molten glass and the mold 11 when the molten glass flowing out from the outflow pipe 2 is supplied to the recess 12 provided on the upper surface of the mold 11 that is retained below the outflow pipe 2. It is sectional drawing.
When the molten glass flows through the glass flow path 3 and flows out from the glass outlet 9, it is separated from the inner peripheral surface of the pipe so as to become thin due to surface tension, and a single flow tends to occur. Since the reduced diameter portion 10 is formed, the molten glass is kept in contact with the inner peripheral surface of the pipe at the lower end portion of the enlarged diameter portion 8 as shown in FIG. For this reason, generation | occurrence | production of the single flow of the molten glass 20 can be suppressed.

  When the molten glass that has flowed into the recess 12 of the mold 11 reaches a predetermined amount, the mold 11 is rapidly lowered by a lifting device (not shown) to melt the melt on the recess 12 from the molten glass that flows out of the glass outlet. Separate the glass (down-cut method). The separated molten glass lump floats by receiving upward wind pressure by a gas ejected from a large number of pores (not shown) formed in the recess 12 and is molded into a predetermined shape in this state to become a preform. A method of forming glass in a floating state on the forming die 11 in this way is called a floating forming method.

  The preform thus formed does not contain bubbles and striae and has high homogeneity, and is therefore suitable as a molding material for optical elements such as lenses. As a method for molding the preform into an optical element, a precision press molding method can be exemplified. In an example of the precision press molding method, first, a preform is heated and softened in a state of being accommodated in a mold, and then pressed by the mold. Thereby, an optical element having a shape corresponding to the mold is obtained.

  According to the glass outflow device 1 of the present embodiment, since the reduced diameter portion 10 is formed at the lower end edge of the enlarged diameter portion 8, the molten glass is in contact with the inner surface of the pipe also at the lower end portion of the enlarged diameter portion 8. Kept. For this reason, generation | occurrence | production of the single flow of a molten glass can be suppressed.

  Moreover, as for the diameter reducing part 10 of the glass outflow apparatus 1 of this embodiment, the aperture angle (theta) is more than the contact angle (theta) 0. Thereby, the surface of the reduced diameter part 10 will advance to an inner position rather than the surface of the molten glass flow in the case where the reduced diameter part is not provided. Thereby, it can suppress that molten glass leaves | separates from a pipe inner surface, and can suppress generation | occurrence | production of a single flow.

  Furthermore, by producing a preform using the glass outflow device of the present embodiment, it is possible to suppress the occurrence of a single flow of molten glass, thereby suppressing the occurrence of bubbles and striae inside the preform. In addition, a preform with high homogeneity can be produced. Thus, by manufacturing an optical element using a preform with high homogeneity, a high-quality optical element can be stably manufactured.

  In the above-described embodiment, the reduced diameter portion has a curved shape in a vertical sectional view, but the present invention is not limited to this and may have an inverted truncated cone shape or the like. In order to more reliably suppress the occurrence of a single flow, the enlarged diameter portion and the reduced diameter portion are smoothly connected in a vertical sectional view, that is, the tangential slope at the enlarged diameter portion and the tangential slope at the reduced diameter portion. Preferably varies continuously.

  Moreover, in the said embodiment, the height position P of the upper end of the diameter reducing part 10 demonstrates the case where the molten glass 120 in the glass dropping apparatus which is not equipped with the diameter reducing part is equal to the height position P 'which spaces apart from the pipe inner surface. However, the height position P is not limited to this, and the height position P is a low position even if the position is higher than the height position P ′ at which the molten glass 120 is separated from the inner surface of the pipe in the glass dropping device not provided with the reduced diameter portion. May be.

Here, the inventors have confirmed through experiments that the occurrence of a single flow can be suppressed according to the glass spill device of the present embodiment, which will be described below.
In this experiment, molten glass was flowed out using platinum pipes with different inner diameters and squeezing angles at the lower ends of the pipes, preforms were formed by the descent cutting method-floating molding method, and the frequency of occurrence of single flow in each pipe was determined. investigated. The frequency of occurrence of single flow is indicated by the number of single flows generated during the time when molten glass is allowed to flow out of the pipe for 24 hours to form a preform.

As glass materials, lanthanum borate containing glass MP-TAFD305 (refractive index nd = 1.8535, Abbe number νd = 40.1) and MP-BACD12 (refractive index nd = 1.58313, Abbe, manufactured by HOYA Corporation). The number νd = 59.46) was used. Moreover, the temperature of the pipe is set to a temperature at which the glass does not devitrify in the range of 1000 to 1100 ° C. when MP-TAFD305 is used as the glass material and 950 to 1100 ° C. when MP-BACD12 is used. did.
In addition, when the single flow generate | occur | produced, the outflow adjustment of the molten glass was performed and operation which restarts the outflow of glass in the state without a single flow was performed.

これら表１及び表２に示すように、絞り角度を大きくすることにより、パイプの径や硝材の種類によらず、片流れの発生頻度が低くなっている。このことから、パイプの下端縁に縮径部を設けることにより、片流れの発生を抑止できることが確認された。 Tables 1 and 2 are tables showing the frequency of single-flow occurrence when MP-TAFD305 and MP-BACD12 are used for the glass material, respectively.

As shown in Tables 1 and 2, by increasing the throttle angle, the frequency of occurrence of single flow is reduced regardless of the diameter of the pipe and the type of glass material. From this, it was confirmed that the occurrence of a single flow can be suppressed by providing a reduced diameter portion at the lower edge of the pipe.

  In addition, when MP-TAFD305 is used and the inner diameter of the lower end of the pipe is 16 mm, molding can be performed at a drawing angle of 20 degrees or more. It was confirmed that a preform could be created. From this, it was found that the aperture angle is preferably 10 degrees or more.

  Furthermore, when the aperture angle was 20 degrees or more, it was confirmed that a preform could be created under all conditions. From this, it was found that when the inner diameter of the lower end of the pipe is 9 mm or more, it is particularly preferable that the aperture angle is 20 degrees or more.

[Example of optical element production]
An optical element was manufactured using each of the above preforms. Here, a manufacturing example of an aspheric lens is shown as a manufacturing example of an optical element.
First, a press mold comprising parts such as an upper mold, a lower mold, and a body mold is prepared. The molding surfaces of the upper mold and the lower mold are precisely processed into a shape in which the irregularities of the shape of the optical function surface (lens surface) of the target aspherical lens are reversed, and are coated with a carbon film release film.

Next, the preform is introduced into the space surrounded by the upper mold, the lower mold, and the body mold, heated together until the glass is softened, the preform is pressed by the upper mold and the lower mold, and the shape of the molding surface is changed. It was precisely transferred to glass and precision press molded into an aspheric lens shape.
Further, after cooling the molded glass, the glass was taken out from the press mold to obtain an aspherical lens.
Note that known conditions and materials may be applied to the precision press molding conditions, the shape of the press mold, and others.

Finally, this embodiment will be summarized with reference to the drawings.
As shown in FIG. 1, the glass outflow device 1 of the present embodiment has a glass channel 3 through which molten glass flows, a constant diameter portion 6 having a constant inner diameter extending in the vertical direction, and a lower end continuous to the constant diameter portion 6. A glass outflow device 1 for dropping molten glass from an outflow pipe 2 formed with an expanded inner diameter portion 8 having an inner diameter expanding toward the inner surface of the lower diameter edge of the expanded diameter portion 8 toward the tip. Thus, a reduced diameter portion 10 whose inner diameter is reduced is formed.

DESCRIPTION OF SYMBOLS 1 Glass outflow apparatus 2 Outflow pipe 3 Glass flow path 6 Constant diameter part 8 Expanded part 9 Glass outflow port 10 Reduced diameter part 11 Mold 12 Recess 20 Molten glass

Claims (6)

A pipe in which a constant diameter portion having a constant inner diameter extending in the vertical direction and a diameter increasing portion having a shape in which the inner diameter expands toward the lower end is formed continuously in the flow path through which the molten glass flows. A glass outflow device for flowing out molten glass,
A glass outflow device in which a reduced diameter portion whose inner diameter decreases toward the tip is formed on the inner surface of the lower end edge of the enlarged diameter portion.   2. The glass outflow device according to claim 1, wherein when the maximum angle of the inner surface of the reduced diameter portion with respect to the vertical direction is a throttle angle, the throttle angle is 10 degrees or more.   The glass outflow device according to claim 2, wherein an inner diameter of a lower end of the pipe is 9 mm or more and the throttle angle is 20 degrees or more. A pipe in which a constant diameter portion having a constant inner diameter extending in the vertical direction and a diameter increasing portion having a shape in which the inner diameter expands toward the lower end is formed continuously in the flow path through which the molten glass flows. A glass outflow method for flowing out molten glass,
A glass outflow method in which a reduced diameter portion whose inner diameter decreases toward the tip is formed on the inner surface of the lower end edge of the pipe.   A method for producing a press-molding preform, wherein a molten glass is flowed out by the glass outflow method according to claim 4 to form a press-molding preform. A step of producing a press-molding preform by the method for producing a press-molding preform according to claim 5;
Heating the preform;
Press-molding the heated preform;
A method for manufacturing an optical element.

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