JP2003137570A - Method for molding optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lengthen life of a mold by preventing oxidation of the mold when a quartz glass optical element is produced by a reheat press. SOLUTION: The upper and lower molds 4, 11 and a molding material 30 are heated with an inert gas flowing in an airtight molding chamber 17. The optical element is produced by press-molding of the molding material 30 using the molds 4, 11. The inert gas (for example gaseous nitrogen) stored beforehand in a gas storage tank 50 is circulated in the airtight molding chamber 17 from the time at which the temperature of the mold 11 is reached to a specific temperature (for example 500 deg.C) at the heating step to the time at which the temperature of the mold 11 is lowered to a specific temperature at a gradual cooling step. On the other hand, before the temperature of the mold 11 is reached to the specific temperature at the heating step and after the gradual cooling step is finished and the temperature of the mold is lowered to the specific temperature, a new inert gas is fed into the molding chamber 17 through a gas feeding path 22 and exhausted from a gas exhausting valve 53.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to, for example, a lens,
The present invention relates to a method of manufacturing glass optical elements such as prisms and parts for optical communication by press molding, and in particular, an inert gas supply method suitable for press molding a molding material having a high glass transition point such as quartz glass. Regarding

[0002]

2. Description of the Related Art In recent years, glass optical elements have been widely used in the fields of optical communication and medical care. In particular, an optical element made of quartz glass is attracting attention because it has excellent characteristics such as low thermal expansion, low impurities, and good ultraviolet transmittance. Quartz glass optical elements are used in various products such as microlens arrays with complicated shapes and from ultra-small to large sizes.

The method of manufacturing an optical element made of glass, which requires high precision, is roughly classified into two types, one is by grinding / polishing and the other is by press molding (called reheat press).

Of the two methods, the method of forming an optical surface by grinding / polishing has been widely used. However, this method has the problems that more than ten steps are required to form a curved surface by grinding and polishing, and that a large amount of glass grinding powder, which is harmful to the operator, is generated. Further, this method has a problem that it is difficult to mass-produce glass lenses having an aspherical optical surface with high added value with the same accuracy.

In the reheat press, the molten glass is cooled in a mold to produce a molding material (preform), and the molding material is placed between a pair of molds having a highly accurate molding surface, After heating the molding material to a temperature near the glass transition point, press molding is performed, and the shape of the mold is transferred to the molding material to manufacture an optical element. Therefore,
The reheat press has the advantage that the step directly involved in curved surface formation is only one step of press molding. Further, once the mold is manufactured, it is possible to manufacture many molded products according to the accuracy of the mold.

When the mold and the molding material are heated, it is necessary to prevent oxidation of the mold and the members adjacent to the mold. For this reason,
Oxygen is excluded from the periphery of the mold by accommodating the periphery of the mold and the vicinity of the tips of the upper and lower shafts in a molding chamber where the atmosphere can be adjusted, and flowing an inert gas into the molding chamber. An infrared lamp is used for heating the mold and the molding material.
For this reason, the side wall portion of the molding chamber is made of a quartz glass cylindrical member having high infrared transmittance (hereinafter referred to as a transparent quartz tube), and an infrared lamp is arranged outside the transparent quartz tube.

When press-molding quartz glass, the molding temperature is as high as about 1400 ° C., so that carbon or ceramics is used as the material of the mold. Considering the releasability of quartz glass, carbon is preferable. However, when the mold and the molding material are heated, the impurities contained in the inert gas oxidize the carbon, resulting in a problem that the life of the mold is short. For this reason, the optical element made of quartz glass has almost no result by the reheat press.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems when manufacturing an optical element made of quartz glass, and an object of the present invention is to provide an optical element made of quartz glass. It is an object of the present invention to provide a method for increasing the life of a mold by preventing the mold from being oxidized when it is manufactured by a reheat press.

[0009]

According to the method of molding an optical element of the present invention, after a glass molding material is placed between a pair of molds, the mold and the molding material are surrounded by an airtight enclosure wall. In the method for molding an optical element, which surrounds and heats the mold and the molding material while flowing an inert gas into the interior wall, and press-molds the molding material with the mold to manufacture an optical element, It is characterized in that the inert gas discharged from the inside is recovered and recirculated in the surrounding wall.

According to the method of the present invention, after the inert gas discharged from the surrounding wall is collected and stored in a tank or the like,
When recycled and used in the surrounding wall, the inert gas initially introduced into the surrounding wall contains oxygen and water as impurities, and thus the impurities slightly oxidize the surface of the mold. However, this removes oxygen and water from the inert gas. Therefore, oxygen or water is not contained in the inert gas that is recirculated into the surrounding wall next. As a result, the oxidation of the mold is prevented from progressing, and the life of the mold can be extended. Further, since the inert gas is reused, the consumption amount of the inert gas is reduced and the running cost can be reduced.

Preferably, when the temperature of the mold is equal to or higher than a preset temperature, the inert gas discharged from the inside of the surrounding wall is recovered and recirculated into the inside of the surrounding wall.

[0012] Preferably, when the temperature of the mold is 500 ° C or higher, the inert gas discharged from the inside of the enclosure is recovered and recirculated into the enclosure.

Preferably, the oxygen concentration of the inert gas discharged from the enclosure wall is measured, and when the value is 1 ppm or less, the inert gas is recovered and recirculated into the enclosure wall.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of a molding apparatus in which a method for molding an optical element according to the present invention is used. In the figure,
30 is a molding material, 4 is an upper mold unit, 11 is a lower mold unit, 2 is a fixed shaft, 9 is a movable shaft, 16 is a transparent quartz tube (enclosure), 17 is a molding chamber, 20 is an infrared lamp, and 29 is a thermocouple. , 40 is a vacuum exhaust device, 50 is a gas storage tank, 51
Is a gas supply valve, and 52 is a gas intake valve.

A fixed shaft 2 extends downward from the upper part of the frame 1, and an upper mold unit 4 is attached to a lower end surface of the frame 1 via a heat insulating cylinder 3 made of ceramics. The upper die unit 4 includes a die plate 5 made of metal (or carbon or ceramics), an upper die 6 made of ceramics (or carbon), and the upper die 6 fixed to the die plate 5 and The fixed die 7 is made of ceramics (or carbon or metal).

A drive device 8 (screw jack in this example) is provided at the bottom of the frame 1. The drive device 8 uses the servo motor 8a as a drive source and converts the rotational movement of the servo motor 8a into linear movement thrust. Drive device 8
Of the moving shaft 9 via the load detector 8b.
Is attached. The movable shaft 9 extends upward so as to face the fixed shaft 2. The speed, position, and axial load of the moving shaft 9 are controlled by a program input to the control device 26, and the moving shaft 9 can move in the vertical direction.

On the upper end surface of the moving shaft 9, a heat insulating cylinder 10 made of ceramics and having the same shape as the heat insulating cylinder 3 is attached. The lower mold unit 11 is made of metal (or
Die plate 1 made of carbon or ceramics
2, ceramic lower mold 1 (or carbon)
3 and a moving die 14 made of ceramics (or carbon or metal) that fixes the upper die 13 to the die plate 12 and forms a part of the die.

The fixed shaft 2 passes through an opening provided in the center of the upper plate 15. Upper plate 15
Are driven in the vertical direction by a driving device (not shown). An O-ring is attached to the above-mentioned opening, and the upper plate 15 can slide vertically between the outer periphery of the fixed shaft 2 and the outer periphery of the fixed shaft 2.

The moving shaft 9 penetrates through openings provided in the central portions of the lower frame 1a and the lower plate 1b, respectively. The lower frame 1a is fixed to the frame 1. The lower plate 1b is fixed to the upper surface of the lower frame 1a. An O-ring is attached to the opening of the lower frame 1a, and the moving shaft 9 is attached to the lower frame 1a.
It is possible to slide in the up-down direction while maintaining an airtight state with respect to the inner circumference.

The upper mold unit 4 and the lower mold unit 11 forming a pair, the heat insulating cylinder 3 and the heat insulating cylinder 10, the lower end of the fixed shaft 2 and the upper end of the movable shaft 9 are surrounded by a cylindrical member made of quartz glass. It is surrounded by (transparent quartz tube 16). The upper end surface of the transparent quartz tube 16 is abutted against the lower surface of the upper plate 15, and an O-ring is attached to the contact surface to ensure airtightness. Similarly, a transparent quartz tube 16
The lower end surface of the plate is abutted against the upper surface of the lower plate 1b, and an O-ring is attached to the contact surface to ensure airtightness. As a result, inside the transparent quartz tube 16,
A molding chamber 17 that is airtight to the outside is configured.

An outer cylinder 18 is arranged so as to surround the transparent quartz tube 16. The upper end of the outer cylinder 18 is connected to the lower side of the peripheral edge of the upper plate 15. A lamp unit 19 is attached to the middle part of the outer cylinder 18. The upper mold unit 4 and the lower mold unit 11 inside the transparent quartz tube 16 are heated by the radiant heat from the lamp unit 19.

A thermocouple 29 for temperature measurement is attached to the lower mold unit 11. The thermocouple 29 is the controller 2
Connected to 6.

The lamp unit 19 is the infrared lamp 2
0, a reflection mirror 21 arranged behind it, and a water cooling pipe (not shown) for cooling the reflection mirror 21. The infrared lamp 20 and the reflection mirror 21 are each configured by stacking a plurality of semi-arcuate parts into a ring shape and stacking them in a plurality of stages, and have an overall cylindrical shape.

Gas supply paths 22 and 23 are provided inside the fixed shaft 2 and the movable shaft 9, respectively. The die plate 5 and the die plate 12 are provided with gas supply paths 27 and 28, respectively. An exhaust port 24 is provided in the lower plate 16. This exhaust port 24
The vacuum exhaust device 40 is connected via a vacuum gauge 41 and a valve 42. The upper plate 15 has a gas outlet 2
5 are provided. The gas outlet 25 is connected to the gas storage tank 50 via a gas intake valve 52. A branch pipe is connected in the middle of a gas flow path 54 connecting the gas outlet 25 and the gas intake valve 52, and a gas exhaust valve 53 is provided at the end thereof. Further, the discharge side of the gas storage tank 50 is connected to the gas supply passage 23 via a gas supply valve 51.

Next, a method of supplying the inert gas to the molding chamber 17 in the above molding apparatus will be described.

After the molding material 30 is set between the molds 4 and 11, first, the gas in the molding chamber 17 is exhausted through the exhaust port 24 using the vacuum exhaust device 40, and then the inert gas is supplied from the source. The gas is supplied into the molding chamber 17 at a predetermined flow rate from a gas supply passage 22 (not shown). As a result, the inside of the molding chamber 17 is replaced with the inert gas. Next, while continuing to supply the inert gas, the inert gas is discharged from the gas exhaust valve 53 so that the pressure in the molding chamber 17 does not rise, and the temperature rise in the molding chamber 17 is started.

After the temperature of the lower mold 11 reaches a predetermined temperature, the gas exhaust valve 53 is closed to stop the exhaust while continuing to supply the inert gas into the molding chamber 17 through the gas supply passage 22. Instead, the gas intake valve 52 is opened. The inert gas supplied into the molding chamber 17 is recovered in the gas storage tank 50 via the gas outlet 25, the gas flow passage 54, the gas intake valve 52 and the gas flow passage 55. Such collection of the inert gas is continued until the pressing step is completed, the step is moved to the slow cooling step, and the temperature of the lower mold 11 is lowered to a predetermined temperature.

After the temperature of the lower mold 11 has dropped to a predetermined temperature, the gas intake valve 52 is closed, the gas exhaust valve 53 is opened to restart exhaust, and the gas is supplied from the gas supply passage 22 into the molding chamber 17. The flow rate of the inert gas is increased to quench the molds 4 and 11 (quenching process). After cooling the molds 4 and 11 and the molded product, the molding chamber 17 is opened, the press-molded product is taken out, and the next molding material is molded into the mold 4.
Set between 11.

In the next molding, before the temperature of the lower mold 11 reaches a predetermined temperature and after the slow cooling step is completed and the rapid cooling step is performed, the molding chamber 17 is subjected to the same route as described above. Inert gas is supplied and discharged. On the other hand, from the time when the temperature of the lower mold 11 reaches a predetermined temperature,
Until the slow cooling process is completed, the inert gas in the gas storage tank 50 is circulated and used in the molding chamber as follows. That is, the inert gas stored in the gas storage tank 50 during the first molding is supplied into the molding chamber 17 via the gas supply valve 51 and the gas supply passage 23. At the same time, the inert gas is discharged from the molding chamber 17 through the gas discharge port 25, and the discharged inert gas is collected in the gas storage tank 50 through the gas intake valve 52. Such collection of the inert gas is continued until the pressing step is completed, the step is shifted to the slow cooling step, and the temperature of the lower mold 11 is lowered to a predetermined temperature.

Next, a description will be given of the test results comparing the case where the inert gas is supplied according to the method of the present invention and the case where the conventional method is used. In this test, under the same conditions as when molding quartz glass, when heating and cooling of the mold were repeated without recirculating the inert gas, and when heating and cooling were repeated while recirculating the inert gas. A comparison of the weight change of the mold was carried out between and.

As the heating conditions, the mold was heated to 1400 ° C., held at that temperature for 120 seconds, gradually cooled to 500 ° C., and then rapidly cooled. The flow rate of inert gas during heating is 8 Nl / M, and the flow rate of inert gas during slow cooling is 40
N liter / M, the flow rate of the inert gas at the time of quenching is 220 N liter / M. Moreover, isotropic carbon (SFG-2: made by POCO GRAPHITE, Inc.) is used as the material of the mold,
Nitrogen gas (purity: 99.998% or more) obtained by vaporizing liquid nitrogen was used as the inert gas.

Under the above temperature conditions, from the time of heating to the time of rapid cooling, when the inert gas was not recirculated in all steps (Pattern 1: Conventional method), when heating above 500 ° C. and up to 500 ° C. In the case where the inert gas was recirculated during the slow cooling of 50 ° C., and the exhaust was performed without recirculating the inert gas during the heating at 500 ° C. or less and the rapid cooling (Pattern 2: the method according to the present invention), heating was performed 50 times each. -Cooling was repeated and the weight reduction amount of the mold before and after that was measured. Further, the oxygen concentration of the inert gas used during heating was measured. The results are shown in Table 1 below.

[0033]

[Table 1]

As shown in Table 1, in the case of pattern 2, the weight reduction amount of the mold is reduced to about 1/5 of that in pattern 1. This confirmed the effect of the method of the present invention.

[0035]

According to the optical element molding method of the present invention,
Oxidation of the mold is suppressed and the life of the mold can be extended.
As a result, the manufacturing cost can be reduced when molding the optical element made of quartz glass.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a molding apparatus in which a method for molding an optical element according to the present invention is used.

[Explanation of symbols]

1 ... frame, 1a ... lower frame, 1b ...
・ Lower plate, 2 ... Fixed shaft, 3 ... Insulation tube, 4
... Upper mold unit, 5 ... die plate, 6 ...
Upper mold, 7 ... Fixed die, 8 ... Driving device, 8a ...
・ Servo motor, 8b ... Load detector, 9 ... Moving shaft, 10 ... Adiabatic cylinder, 11 ... Lower mold unit, 12
... die plate, 13 ... lower mold, 14 ... moving die, 15 ... upper plate, 16 ... transparent quartz tube (cylindrical member), 17 ... molding chamber, 18 ... Outer cylinder, 1
9 ... Lamp unit, 20 ... Infrared lamp, 2
1 ... Reflective mirror, 22, 23, 27, 28 ... Gas supply path, 24, 25 ... Exhaust port, 26 ... Control device, 29 ... Thermocouple, 30 ... Molding material , 40 ...
-Vacuum exhaust device, 41 ... Vacuum gauge, 42 ... Valve, 50 ... Gas storage tank, 51 ... Gas supply valve, 52 ... Gas intake valve, 53 ... Gas exhaust valve , 54, 55 ... Gas flow paths.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shusaku Matsumura             2068 Ooka, Numazu City, Shizuoka Prefecture Toshiba Machine Co., Ltd.             In the company

Claims (4)

[Claims] 1. A glass molding material is arranged between a pair of molds, and the mold and the molding material are surrounded by an airtight surrounding wall, and an inert gas is flowed inside the surrounding wall. After heating the mold and the molding material, in a method of molding an optical element for manufacturing an optical element by press-molding the molding material with the mold, the inert gas discharged from the inside wall is recovered, and the surrounding wall is A method for forming an optical element, which comprises recirculating the inside. 2. The inert gas discharged from the inside of the surrounding wall is recovered and recirculated into the inside of the surrounding wall when the temperature of the mold is equal to or higher than a preset temperature. A method for molding an optical element as described above. 3. When the temperature of the mold is 500 ° C. or higher,
The method for molding an optical element according to claim 2, wherein the inert gas discharged from the inside of the surrounding wall is recovered and recirculated into the inside of the surrounding wall. 4. The oxygen concentration of the inert gas discharged from the inside of the enclosure is measured, and when the oxygen concentration is 1 ppm or less, the inert gas is recovered and recirculated into the enclosure. Item 2. A method for molding an optical element according to Item 1.