JP3140260B2 - Method for manufacturing optical glass element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical glass element having excellent surface quality, which can be used as a glass material for precision press molding from molten glass flowing down from an outlet (orifice) of a nozzle. .

[0002]

2. Description of the Related Art In recent years, a glass element or the like that has been ground and polished to a certain shape and surface accuracy is housed in a molding die having a predetermined surface accuracy, and is subjected to press molding under heating to form lenses, prisms and the like. A method for obtaining an optical element having a high-precision optical function surface has been developed. In this method, molten glass is caused to flow out of an orifice through a glass outflow nozzle installed in a glass melting furnace, and cut by a shear (cutting blade) to form a fixed amount of molten glass lump (hereinafter referred to as a gob). create. Then, the gob is preliminarily molded with a mold close to the shape of the final molded article, and the preformed body is ground and polished.

[0003] However, in this method, a shear mark (cut mark) is generated when the molten glass flow is cut, which does not disappear even when preformed, so that long grinding and polishing are required, and the cost is high. There were drawbacks.

On the other hand, JP-A-2-34525 discloses a method for obtaining a gob having no shear mark on the surface from a molten glass flow.
No. 6,086,045. This method utilizes a method in which glass having an appropriate viscosity is received in a mold, and when a predetermined weight is accumulated, the mold is lowered to separate the glass flow upward and downward due to the surface tension of the glass. In this method, after the glass flow is separated, the cast molten glass is cooled in a mold until at least its surface is solidified.

[0005]

However, in the method of receiving a high-temperature molten glass flow with a mold as in the above-described method, the following problems occur.

In the above-mentioned shearless cutting, the viscosity of glass must be about 90 dPa · s or less in order to enable good separation without pulling a thread.
0 dPa · s is adopted. On the other hand, commercially available optical glasses exhibit a relationship between temperature and viscosity as shown in FIG. The temperature of the glass at which the viscosity of the glass becomes 90 dPa · s or less is
In the figure, SF58 (manufactured by Schott) on the lowest temperature side is about 800 ° C. or higher, and about 100 ° C.
The temperature is as high as 0 ° C or higher.

[0007] When such a high-temperature molten glass flow is received by a mold, the components volatilize violently from the glass surface.
A large amount of volatiles is likely to accumulate on the mold, requiring frequent mold cleaning, and shortening the mold life.

On the other hand, if the temperature of the mold receiving the glass flow is set lower than the temperature of the glass flow, the life of the mold tends to be longer. However, wrinkles called sink marks are generated on the glass surface received by the mold, which causes a problem that surface defects such as residual gas are caused in the subsequent precision press molding. Conversely, bringing the mold temperature closer to the glass flow temperature is effective in preventing sink marks, but the reactivity at the contact surface between the glass and the mold, and the reactivity between the mold and the atmosphere before receiving the glass, increase Life is shortened.

That is, an object of the present invention is to provide an optical glass capable of producing a glass material for precision press free of surface defects such as shear marks and sink marks by receiving a glass flow in a mold and extending the life of the mold. An object of the present invention is to provide a device manufacturing method.

[0010]

An object of the present invention is to discharge molten glass from an outflow port and receive it in a receiving mold without using a cutting blade.
In the method for manufacturing an optical glass element having a step of dish squat, the petri dish squat pre glass out flow
While maintaining a constant region below 10 ^2.5, under the outflow glass
This can be achieved by a method for producing an optical glass element, characterized in that the surface viscosity is from 10 ^2.5 to 10 ^7.65 dPa · s.

[0011]

In the present invention, since the viscosity in a specific range of 10 ^2.5 ~10 ^{7. 65} dPa · s before receiving in receiving mold outflow glass, if the portion in contact with this part receiving-type, receiving-type The dirt on the mold surface due to the volatile matter from the glass in contact with the glass is drastically reduced, and fusion of the glass and the mold can be prevented. As a result, a glass material for precision press without surface defects such as shear marks and sink marks can be manufactured, and the life of the mold can be extended.

The portion having a viscosity of 10 ^2.5 to 10 ^7.65 dPa · s may be a lower portion of the outflow glass which is in contact with the receiving mold. On the other hand, the upper part of the outflow glass has a viscosity of 10
It is desirable to maintain the value at less than ^2.5 so that good cutting by shearless cutting is possible.

As described above, the viscosity is 10 ^2.5 to 10 ^7.65 dPa.
As a method of making the s flow, by setting the ambient temperature outside the outlet to room temperature or the like, for example, controlling the flow rate of the outflow glass slower than usual or exposing the glass to the atmosphere outside the outlet for a predetermined time, There is a way to lower the temperature below the glass. There is also a method of lowering the temperature below the outflow glass by a cooling means (cooling gas spraying means or the like) specially provided with the outflow glass.

The viscosity of the lower part of the outflow glass is particularly 10
It is preferably from ⁴ to ^10.7.6 dPa · s, and more preferably from 10 ⁵ to ^7.65 dPa · s.

[0015]

Embodiments of the present invention will be described below in detail.

Example 1 In this example, the outflow of glass was controlled by adjusting the pressure in the vicinity of the orifice, whereby the desired glass viscosity was obtained.

FIGS. 1 to 4 are views showing each process of this embodiment. 1 to 4, 1 is a glass melting furnace, 2 is a glass melting crucible, 3 is a molten optical glass (SK12, manufactured by OHARA), 4 is an orifice (outflow port), 5 is a hermetic seal, 8 is a receiver. A mold, 40 is a removable pressure chamber, 41 is a pressure vessel, 11 is a pressure control gas inlet / outlet, 50 is a measurement window (made of CaF ₂ ), and 51 is a radiation thermometer. Here, the temperature of the molten glass in the orifice 4 is 1180 ° C. (the glass viscosity is 10 ^2.1 dPa · s), the inner diameter of the orifice 4 is 6 mm, and the glass flow rate is 70 g / min (the state where the pressure vessel 41 is removed; ).

First, as shown in FIG. 1, the outflow of the dripping glass 3a from the orifice 4 was started.

Next, as shown in FIG. 2, the pressure vessel 41 was moved below the orifice 4 from the standby position and immediately connected to the lower portion of the glass melting furnace 1 to form a pressure chamber 40.
Next, a non-oxidizing gas at room temperature (nitrogen gas is used in this embodiment) is introduced from the pressure control gas inlet / outlet 11 and the pressure chamber 4 is opened.
The air pressure within 0 was increased by 2000 to 50,000 Pa, and the outflow of the molten glass was stopped. By changing the stop time, the temperature (measured by the radiation thermometer 51) of the lower surface of the glass 3a exposed at the orifice can be changed. In this embodiment, the stop time was changed from 5 to 180 seconds as shown in Table 1 below.

Next, as shown in FIG. 3, the receiving die 8 was raised and stopped at a predetermined distance from the orifice 4.
In this embodiment, the distance is set within 10 mm (specifically, 8 mm).

Next, the gas was exhausted from the pressure control gas inlet / outlet 11 to reduce the pressure to the atmospheric pressure, and the outflowing molten optical glass was received for 2 seconds to form the staying glass 3b on the wall surface (temperature of the receiving die 8 of 500 ° C.). .

Next, as shown in FIG.
The glass was lowered at a speed of mm / sec, and the molten glass was cut without shearing to form a glass gob 3c weighing 2.3 g. Thereafter, the pressure vessel 41 was removed from the glass melting furnace 1, and another detachable pressure vessel was connected to the lower part of the glass melting furnace 1.

In the above steps, the temperature and the viscosity of the lower surface of the molten glass 3a were changed by changing the stop time of the molten glass 3a (time during which the outflow of the glass was stopped) from 5 to 180 seconds. (Examples 1-1 to 1-4 and Comparative Example 1-2
~ 1-3).

Also, the life of the mold in the case of leaving the natural outflow without using a pressure chamber or the like as in the present embodiment (Comparative Example 1-1) is also shown. In Comparative Example 1-1, the stop time of the glass 3a means the time from when the shears are cut to when the next mold comes into contact with the glass.

The results thus obtained are shown in Table 1 below.
Here, the life of the receiving die 8 was determined to be either the time when the surface of the die became dirty due to the adhesion of volatiles from the glass or the time when fusion of the glass and the die occurred, whichever was earlier.

[0026]

[Table 1] * 1 Stop time of glass outflow from orifice 4 * 2 Temperature of lower surface of outflowing molten glass 3a * 3 Viscosity of lower surface of outflowing molten glass 3a.

As shown in Table 1, the viscosity of the lower surface of the glass was
Is within the specified range of the present invention (10^2.5 -10^7.65dPa ・
Examples 1-1 to 1-4 in s) have a long mold life.
I understand. On the other hand, Comparative Example 1 in which the viscosity of the lower surface of the glass was too low
1 to 1-2 have short mold life and high viscosity
In Comparative Example 1-3, which was too long, the outflow of glass stopped.
It should be noted that the glass cut during the charles cutting
The viscosity of the fin portion was determined in any of the Examples and Comparative Examples.
Also 10^2.5 lower than dPa · s, 10^2.1 -10 ^2.4 d
Pa · s and good shearless cutting is possible
Was.

<Embodiment 2> In this embodiment, the outflow amount of glass was controlled by using the apparatus shown in FIG. 5, thereby obtaining a desired glass viscosity.

The apparatus shown in FIG. 5 includes a rotating screw 62 (3 turns, φ6) in a glass melting crucible 61 having an outflow chamber 60 (inner diameter 100 mm, depth 100 mm).
0 mm). By rotating the screw 62, the molten glass 3 is pushed upward,
The outflow of molten glass can be stopped. Also, the screw 62
The outflow can be resumed by reducing the number of revolutions.

In this embodiment, the temperature of the glass was measured by the radiation thermometer 51 in the same manner as in the first embodiment, and a glass gob was collected by the receiving die 8. The temperature of the molten glass at the orifice 4 ′ is 1180 ° C. (the glass viscosity is 10 ^2.1 dPa ·
s), the inner diameter of the orifice 4 ′ is 8 mm, and the glass flow rate is 1
It was set to 00 g / min. When stopping the outflow of the molten glass, the screw 150 was set to 70 rpm, and when resuming the outflow, the screw 150 was set to 30 rpm. The direction of rotation of the screw is set to a direction in which the glass is pushed upward. However, it is also possible to repeat the restart of the outflow by changing the number of rotations.

In accordance with the above steps, the temperature and viscosity of the lower surface of the molten glass 3a were changed by changing the stop time of the molten glass 3a (time during which the outflow of glass was stopped) from 5 to 180 seconds (Example 2-1). ~ 2-3, and Comparative Examples 2-1 ~ 2-
3).

The results thus obtained are shown in Table 2 below.
Here, the life of the receiving die 8 was evaluated and determined in the same manner as in Example 1.

[0033]

[Table 2] * 1 Stop time of glass outflow from orifice 4 * 2 Temperature of lower surface of outflowing molten glass 3a * 3 Viscosity of lower surface of outflowing molten glass 3a.

As shown in Table 2, the viscosity of the lower surface of the glass is within the specified range of the present invention (10 ^2.5 to 10 ^7.65 dPa ·
It can be seen that Examples 2-1 to 2-3 in s) have a long mold life. On the other hand, the viscosity of the lower surface of the glass is too low in Comparative Example 2-
In Comparative Examples 2-3, in which the life of the mold was short and the viscosity of the lower surface of the glass was too high, the outflow of the glass was stopped.
In addition, the viscosity of the constriction of the glass cut at the time of the shearless cutting was 1 in each of the examples and the comparative examples.
Lower than 0 ^2.5 dPa · s, 10 ^2.1 to ^102.3 dPa
-S and good shearless cutting was possible.

Example 3 In this example, the outflowing glass was cooled and heated using the apparatus shown in FIG. 6 to obtain a desired glass viscosity.

In FIG. 6, reference numeral 71 denotes a heating nozzle, 72 denotes a cooling nozzle, 73 and 74 denote temperature control devices, 75 denotes a gas combustion chamber, 76 and 77 denote gas flow controllers, 78 denotes an oxygen cylinder, 79 Indicates a hydrogen cylinder. The glass used in this example is the same as that in Example 1.

In this embodiment, the temperature of the glass was measured by a radiation thermometer (not shown) in the same manner as in the first embodiment, and a glass gob was collected by a receiving mold (not shown). Here, the wavelength range used in the radiation thermometer was 4 to 5 μm so as not to be affected by the gas flow for temperature control. The temperature of the molten glass in the orifice 4 was set at 1180 ° C. (glass viscosity: 10 ^2.1 dPa · s), the inner diameter of the orifice 4 was set to 6 mm, and the glass flow rate was set to 18 g / min. The weight of one glass gob was set to 0.9 g.

Under the above conditions, a glass gob was manufactured without using a temperature controlling gas, but the temperature of the lower surface of the glass was 10 ^2.4 even if the timing of bringing the receiving mold into contact with the glass was delayed as much as possible. It did not become larger than dPa · s.

Then, after collecting the glass gob and before the next receiving mold comes into contact with the glass 3a, the room temperature air is blown from the cooling nozzle 72 toward the lower surface of the glass at 600 ml / min. From 71, an oxygen-hydrogen flame adjusted to 2400 ° C. was cooled to 600 m in the same amount as the cooling gas.
It was sprayed directly below the orifice 4 at 1 / min.

In the above steps, the temperature and viscosity of the lower surface of the molten glass 3a are changed by changing the time of spraying with the cooling gas (that is, the time until the next receiving mold comes into contact with the glass 3a) from 0.4 to 2 seconds. Was changed (Example
3-1 to 3-3 and Comparative Example 3-1).

The results thus obtained are shown in Table 3 below.
Here, the life of the receiving die 8 was evaluated and determined in the same manner as in Example 1.

[0042]

[Table 3] * 1 Time for blowing the cooling gas to the lower surface of the outflowing molten glass 3a * 2 Temperature of the lower surface of the outflowing molten glass 3a * 3 Viscosity of the lower surface of the outflowing molten glass 3a.

As shown in Table 3, the viscosity of the lower surface of the glass was within the specified range of the present invention (10 ^2.5 to 10 ^7.65 dPa ·
It can be seen that Examples 3-1 to 3-3 in s) have a long mold life. On the other hand, Comparative Example 3-
1 has a short mold life. Note that the viscosity of the constriction of the glass cut during the shearless cutting is lower than 10 ^2.5 dPa · s in any of the examples and the comparative examples.
^2.1 to ^102.3 dPa · s, and good shearless cutting was possible.

In particular, the use of the cooling nozzle as in this embodiment is effective when the viscosity of the lowermost surface of the glass flow does not easily increase. At this time, if a heating nozzle is appropriately used, it is useful to maintain a preferable viscosity distribution in the glass flow.

In the embodiments described above, for example, the type of glass, the diameter of the orifice, the flow rate of the glass, the shape of the mold, and the like are not limited to the above conditions, and can be appropriately set according to the purpose. .

[0046]

As described above, according to the present invention, the viscosity of the outflow glass before receiving it in the receiving mold is 10 ^2.5 to 10 ^7.65.
Since this is a specific range of dPa · s, if this part is a part in contact with the receiving mold, dirt on the mold surface due to volatile matter from the glass in contact with the receiving mold is drastically reduced, and the melting of the glass and the mold is performed. Wear can be prevented. As a result, a glass material for precision press without surface defects such as shear marks and sink marks can be manufactured, and the life of the mold can be extended.

[Brief description of the drawings]

FIG. 1 is a view showing each step of Example 1.

FIG. 2 is a view showing each step of Example 1.

FIG. 3 is a view showing each step of Example 1.

FIG. 4 is a view showing each step of Example 1.

FIG. 5 is a diagram showing an apparatus used in Example 2.

FIG. 6 is a diagram showing an apparatus used in Example 3.

FIG. 7 is a graph showing a relationship between temperature and viscosity of a commercially available optical glass.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass melting furnace 2 Glass melting crucible 3 Melted optical glass 4 Orifice (outflow port) 5 Hermetic seal 8 Receiving mold 11 Pressure control gas inlet / outlet 40 Detachable pressure chamber 41 Pressure vessel 50 Measurement window 51 Radiation thermometer 60 Outflow chamber 61 Glass melting crucible 62 Rotating screw 71 Heating nozzle 72 Cooling nozzle 73, 74 Temperature controller 75 Gas combustion chamber 76, 77 Gas flow controller 78 Oxygen cylinder 79 Hydrogen cylinder

Continuation of the front page (72) Inventor Hiroyuki Kubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A 1-153539 (JP, A) JP-A 3-223123 ( JP, A) JP-A-1-224232 (JP, A)

Claims (3)

(57) [Claims] 1. A received by type received by the outflow of the molten glass from the outlet, in the manufacturing method of an optical glass element having a step of dish squat without a cutting blade, 10 a petri dish squat proposed site of glass out flow ^2.5 Keep less than
And while the lower surface of the viscosity of 10 ^2.5 to 10 of the outflow glass
^{7. A} method for producing an optical glass element, which is performed at a pressure of ^7.65 dPa · s. 2. A pressure chamber is formed around the outlet, and a pressure chamber is formed.
By temporarily stopping the outflow of molten glass by pressure
The viscosity of the lower surface of the outflow glass is 10 ^2.5 to 10 ^7.65 dPa
The method for producing an optical glass element according to claim 1, wherein 3. An outflow chamber is provided above the outflow port, and the outflow chamber is provided.
Insert a screw and rotate the screw to
Push the glass upwards to prevent molten glass from flowing out.
By temporarily stopping, the viscosity of the lower surface of the outflow glass becomes 10
^2. The optical gas according to claim 1, wherein the pressure is ^2.5 to ^10.65 dPa · s.
A method for manufacturing a lath element.