JPH10330121A - Molding of optical element and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide process and machine for molding optical elements that can avoid leaving defects due to the air stagnation on the surface of the optical element and has no risk of oxidation of the molds, when they are press-molded. SOLUTION: When an optical element is press molded, a glass blank is set between a couple of molds 4, 11 in the molding chamber 17, the couple of molds 4, 11 and the glass blank are heated and the couple of the molds 4, 11 are used to press-mold the glass blank. In this case, the molding chamber 17 is reduced in its pressure down to a prescribed level before the press-molding operation. In a preferred embodiment, the molding chamber 17 is evacuated down to <=5 Pa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for manufacturing an optical element by press molding.

[0002]

2. Description of the Related Art Methods of manufacturing optical elements such as glass lenses which require high precision are roughly classified into two types: a method of manufacturing by grinding and polishing, and a method of manufacturing by reheat press. Generally, a method of forming an optical surface by grinding and polishing a glass material is often used as a method of manufacturing an optical element. However, the formation of a curved surface by grinding and polishing requires a large number of processes, which are more than a dozen processes, and generates a large amount of glass grinding powder that is harmful to workers. There are many problems such as difficulty in mass-producing glass lenses having high aspheric optical surfaces with the same accuracy.

On the other hand, in a reheat press, a glass blank (a glass material previously divided into a predetermined size) manufactured by cooling a molten glass once is heated and pressed to change the shape of the glass into a glass. This is a method of manufacturing an optical element such as an optical lens by transferring the image to an optical element, and has an advantage that the step directly related to the formation of a curved surface is only one step of press molding. Further, once the mold is manufactured, any number of molded products corresponding to the accuracy of the mold can be manufactured.

In recent years, devices such as cameras and video cameras have been reduced in size, and compact discs and CD-ROMs have been
With the spread of optical communication technology and the development of optical communication technology, the requirements for optical elements are becoming stricter. For this reason, in addition to spherical lenses that have been widely used as optical elements up to now, those with complicated shapes such as aspherical lenses and micro lens arrays, and various sizes from ultra-small to large are also available. It is becoming required.

[0005] The steps of the reheat press are roughly as follows. After setting the glass blank between the upper and lower molds and replacing the inside of the molding chamber containing the mold and the glass blank with an inert gas such as nitrogen gas in order to prevent oxidation of the mold, use an infrared lamp (or high-frequency The mold and the glass blank are heated using a heating device. After reaching the predetermined temperature, the glass blank is pressed using the upper and lower molds, and finally cooled to take out the product. By the way, when the optical element is molded by the above-mentioned reheat press, the inert gas remains trapped between the mold and the glass blank depending on the shape, and a defect called air pocket occurs on the surface of the molded optical element. May be. Further, if oxygen remains in the molding chamber after the inside of the molding chamber accommodating the mold and the glass blank is replaced with the inert gas, there is a problem that the mold is oxidized by the residual oxygen at a high temperature.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the conventional reheat press, and an object of the present invention is to provide an optical element for forming an optical element by the reheat press. Another object of the present invention is to provide a method and apparatus for molding an optical element that does not leave air pockets on the surface of the optical element and does not cause oxidation of the mold.

[0007]

According to a method of molding an optical element of the present invention, a glass blank is set between a pair of molds housed in a molding chamber, and the pair of molds and the glass blank are heated. In a molding method of an optical element for performing press molding of a glass blank using a pair of molds, the pressure in the molding chamber is reduced to a predetermined pressure prior to press molding of the glass blank.

[0008] Preferably, the predetermined pressure is 5P
a or less. As described above, by evacuation of the inside of the molding chamber prior to press molding of the glass blank, during press molding, an inert gas such as nitrogen gas is not trapped between the mold and the optical element. The occurrence of defects due to pooling can be prevented. At the same time,
Since the amount of residual oxygen in the molding chamber can be reduced,
The life of the mold can be extended.

As a specific procedure for reducing the pressure in the molding chamber, for example, any of the following three procedures can be adopted. (A) First, the inside of the molding chamber is reduced to a predetermined pressure, and then the pair of molds and the glass blank are heated.

(B) First, the molding chamber is replaced with an inert gas such as nitrogen gas, and then the molding chamber is evacuated and evacuated in parallel with the heating of the pair of molds and the glass blank. (C) First, the molding chamber is replaced with an inert gas such as nitrogen gas, and then, in parallel with the heating of the pair of molds and the glass blank, a small amount of the inert gas is supplied into the molding chamber. Is evacuated.

After the end of press molding, an inert gas such as nitrogen gas may be flowed into the molding chamber to cool the pair of molds and the glass blank. Further, the optical element molding apparatus of the present invention is an optical element molding apparatus that performs press molding of a glass blank heated to a temperature equal to or higher than the glass transition point by using a pair of molds in a molding chamber. In addition, the airtightness is provided, and a decompression evacuation means for decompressing and exhausting the inside thereof is provided.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an optical element press molding apparatus used for carrying out an optical element molding method according to the present invention. Upper plate 1 on top of frame 1
The fixed shaft 2 extends downward from the upper plate 1c, and the upper die assembly 4 is attached to the lower end of the fixed shaft 2 via a heat insulating cylinder 3 made of ceramic.
The upper die assembly 4 includes a metal die plate 5, a ceramic (or cemented carbide) upper die 6, and a fixed die 7 that fixes the upper die 6 to the die plate 5 and forms a part of the die. It is configured.

A base 1a is disposed below the frame 1, a screw jack 8 is disposed above the base 1a, and a load cell 8b is disposed above the screw jack 8.
The moving shaft 9 is attached via the. The screw jack 8 uses the servo motor 8a as a drive source, and converts the rotational motion of the servo motor 8a into a linear motion. Moving axis 9
Extends upward facing the fixed shaft 2 and penetrates the intermediate plate 1b provided in the middle stage of the frame 1 and the intermediate block 1d attached to the upper surface of the intermediate plate 1b. A lower mold assembly 11 is attached to the upper end of the moving shaft 9 via a heat insulating cylinder 10. The moving shaft 9 moves up and down with its position, speed, torque, and the like controlled according to a program previously input to the control panel 26. Similar to the upper die assembly 4, the lower die assembly 11 includes a metal die plate 12, a ceramic lower die 13, and a moving die that fixes the lower die 13 to the die plate 12 and forms a part of the die. 14.

A bracket 15 that can be moved up and down by a driving device (not shown) is slidably mounted around the fixed shaft 2. A transparent quartz tube 16 is attached to the lower surface of the bracket 15 so as to surround the upper mold assembly 4 and the lower mold assembly 11. Quartz tube 1
Reference numeral 6 has upper and lower flange portions. Further, an outer tube 18 is attached to the lower side of the bracket 15 so as to surround the outer periphery of the quartz tube 16, and a lamp unit 19 is arranged along the inner wall of the outer tube 18. The lamp unit 19 includes an infrared lamp 20, a reflection mirror 21 disposed behind the infrared lamp 20, a water cooling pipe (not shown) for cooling the reflection mirror 21, and the like. The upper die assembly 4 and the lower die assembly 11 is radiantly heated from outside the quartz tube 16.

The flange on the upper end side of the quartz tube 16 is fixed to the bracket 15 by a clamp 35, and the contact surface between the flange and the bracket 15 is sealed by an O-ring fitted on the lower surface of the bracket 15. On the other hand, the lower flange of the quartz tube 16 is pressed against the upper surface of the intermediate block 1b, and the contact surface between the flange and the upper surface of the intermediate block 1b is sealed by an O-ring fitted on the upper surface of the intermediate block 1b. . In this manner, the inside of the quartz tube 16 constitutes a molding chamber 17 that blocks the periphery of the upper mold assembly 4 and the lower mold assembly 11 from the outside.

When the flange on the lower end side of the quartz tube 16 is pressed against an O-ring fitted into the upper surface of the intermediate block 1b, the outer tube 18 is not damaged so that the quartz tube 16 is not damaged.
Are supported by the intermediate plate 1a via the movable clamp 36. An extendable upper shaft bellows 29 is attached between the upper plate 1c and the bracket 15 to block the upper side of the molding chamber 17 from the outside world. Lower bellows 30
Is attached, and shields the lower side of the molding chamber 17 from the outside.

The interior of the fixed shaft 2 and the movable shaft 9 is filled with an inert gas such as nitrogen gas in the molding chamber 17 or a gas supply for cooling the upper mold assembly 4 and the lower mold assembly 11. Channels 22 and 23 are formed to supply the inert gas to the inside of the molding chamber 17 via a flow controller (not shown). The inert gas supplied into the molding chamber 17 is exhausted through an exhaust port 24 formed in the intermediate block 1d. The molding chamber 17
A vacuum valve (not shown) is attached to the gas supply paths 22 and 23 so that the inert gas does not flow into the molding chamber 17 from the gas supply paths 22 and 23 when the inside of the chamber is evacuated. ing. A vacuum gauge 34 and vacuum valves 31 and 32 are attached to the exhaust port 24, and the vacuum valve 32 is connected to a vacuum pump 33. Also, lower die assembly 11
, A thermocouple 25 is attached.

Next, a method for press-molding a glass optical element using this molding apparatus will be described. First, the vacuum pump 33 is started while the vacuum valve 32 for evacuation is closed, and a glass blank is set between the upper mold 6 and the lower mold 13 of the molding apparatus. Next, the bracket 15 is lowered, and the flange on the lower end side of the quartz tube 16 is pressed against the O-ring fitted on the upper surface of the intermediate block 1b using the movable clamp 36, thereby forming the molding chamber 17.

Thereafter, press molding of the glass blank can be performed by the following three different procedures. (A) A method in which the inside of the molding chamber 17 is depressurized to a predetermined pressure before heating is started, then heated, and after reaching a predetermined temperature, press molding is performed.

(B) First, after the interior of the molding chamber 17 is replaced with an inert gas such as nitrogen gas, the interior of the molding chamber 17 is evacuated and evacuated. After reaching, press molding.

(C) First, after the inside of the molding chamber 17 is replaced with an inert gas such as nitrogen gas, the inside of the molding chamber 17 is evacuated and evacuated while supplying a small amount of the inert gas into the interior of the molding chamber 17. A method in which heating is performed in parallel with this, and after reaching a predetermined pressure and temperature, press molding is performed.

Next, the results of the press molding of the aspherical lens made of glass according to the above procedures will be described. FIG. 2 shows an overview of the types used. (A)
(B) shows a state where the glass blank 37 is set between the upper and lower dies, and (b) shows a state where the glass blank is pressed by the upper and lower dies. When an aspheric lens 38 as shown in FIG. 2B is formed, a defect 39 called an air pocket is likely to occur on the surface of the lens as shown in FIG. In addition, BK-7 (manufactured by OHARA CORPORATION, transition point 553 ° C, yield point 614 ° C) was used as a glass material.

In the case of the method (a), the vacuum valve (not shown) for supplying nitrogen gas and the vacuum valve 31 for exhausting nitrogen gas were closed, and the vacuum valve 32 for exhausting vacuum was opened. The inside of the molding chamber 17 is depressurized by the vacuum pump 33,
7 is reduced to 5 Pa, while the vacuum pump 33 is operated, the molds 6, 7, 1
Heating of 3, 14, and the glass blank 37 was started. After the mold and the glass blank reached 690 ° C., the glass blank was pressed. After the pressing, the vacuum valve 32 for evacuation is closed, the vacuum valve (not shown) for supplying nitrogen gas is opened, nitrogen gas is supplied for several seconds, and the pressure in the molding chamber 17 becomes higher than the atmospheric pressure. At this point, the vacuum valve 31 for exhausting nitrogen gas is opened, and while exhausting nitrogen gas,
The mold and molded optics were cooled.

In the case of the method (b), after supplying nitrogen gas into the molding chamber 17 for 10 seconds, the vacuum valve (not shown) for supplying nitrogen gas and the vacuum valve 31 for exhausting nitrogen gas are closed, and the vacuum exhaust is performed. Vacuum valve 32 was opened. While the inside of the molding chamber 17 was depressurized by the vacuum pump 33, the molds 6, 7, 13, 14 and the glass blank 37 were heated using the infrared lamp 20. After the mold and the glass blank reached 690 ° C., and the pressure in the molding chamber was reduced to 5 Pa, the glass blank was pressed. After the pressing, the vacuum valve 32 for evacuation is closed, the vacuum valve (not shown) for supplying nitrogen gas is opened, nitrogen gas is supplied for several seconds, and the pressure in the molding chamber 17 becomes higher than the atmospheric pressure. At this point, the vacuum valve 31 for exhausting nitrogen gas was opened, and the mold and the formed optical element were cooled while exhausting nitrogen gas.

In the case of the method (c), after supplying nitrogen gas as an inert gas into the molding chamber 17 for 10 seconds, the vacuum valve 31 for evacuating the inert gas is closed, and then the vacuum valve 32 for evacuating the gas is turned on. At the same time, the inside of the molding chamber 17 was evacuated and evacuated by the vacuum pump 33, and at the same time, a small amount of nitrogen gas was supplied while being adjusted by a flow rate adjusting device (not shown). In this state, the molds 6, 7, 13, 14 and the glass blank 37 were heated using the infrared lamp 20. After the mold and the glass blank reached the molding temperature and the pressure in the molding chamber 17 was reduced to 5 Pa, the glass blank was pressed. After pressing, the vacuum valve 32 for vacuum evacuation is closed. When the pressure in the molding chamber 17 becomes equal to or higher than the atmospheric pressure, the vacuum valve 31 for evacuation of the inert gas is opened, and the mold and the gas are exhausted while evacuating nitrogen gas. The formed optical element was cooled.

Using the above three kinds of procedures, 3
When the press molding of the aspherical lens was performed 00 times,
In any case, no occurrence of defects due to air accumulation was observed in the molded product. It was also confirmed that the oxidation of the mold was less than that of the conventional method.

For comparison, using a conventional method,
Similarly, press molding was performed 300 times. In this case, the inside of the molding chamber 17 was replaced with nitrogen gas, and then the temperature was raised to 690 ° C., and then press molding was performed. As a result, occurrence of defects due to air accumulation was observed in all the molded products.

[0028]

According to the method for molding an optical element of the present invention,
It is possible to manufacture an aspherical lens or an optical element having a complicated shape with high accuracy and without the risk of defects due to air accumulation.

Further, since the amount of residual oxygen in the molding chamber is reduced, oxidation of the mold at a high temperature is suppressed, and the life of the mold is greatly extended. Further, since the consumption of the inert gas during the temperature rise can be reduced, the running cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a press molding apparatus used in a method for molding an optical element of the present invention.

FIG. 2 is a diagram showing an example of forming an aspheric lens using upper and lower molds, (a) showing a state in which a glass blank is set between upper and lower molds, and (b) showing a state in which the glass blank is pressed Represents

FIG. 3 is a diagram showing an example of a defect called air pocket generated on the surface of an optical element when an aspheric lens is press-formed by a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Frame, 1a ... Base, 1b ... Intermediate plate, 1c ... Upper plate, 1d ... Intermediate plate, 2 ... Fixed shaft, 3 ... Heat insulation cylinder, 4 ...・ Assembly of upper mold, 5 ・ ・ ・ die plate, 6 ・ ・ ・ upper mold, 7
... fixed die, 8 ... screw jack, 8a
..Servo motor, 8b load cell, 9 moving axis, 10 heat insulating cylinder, 11 lower die assembly, 1
2 ... die plate, 13 ... lower mold, 14 ... moving die, 15 ... bracket, 16 ... quartz tube, 1
7 ... molding chamber, 18 ... outer cylinder, 19 ... lamp unit, 20 ... infrared lamp, 21 ... reflection mirror, 22, 23 ... gas supply path, 24 ... exhaust mouth,
25 ... thermocouple, 26 ... control panel, 29 ... upper shaft bellows, 30 ... lower shaft bellows, 31, 32
..Vacuum valve, 33 ... Vacuum pump, 34 ... Vacuum gauge, 35 ... Fixed clamp, 36 ... Movable clamp, 37 ... Glass blank, 38 ... Press molded product (aspherical surface) Lens), 39 ... air pool.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Isao Matsuzuki 2068-3 Ooka, Numazu-shi, Shizuoka Pref.

Claims (7)

[Claims] 1. An optical system for setting a glass blank between a pair of molds housed in a molding chamber, heating the pair of molds and the glass blank, and then press-molding the glass blank using the pair of molds. A method for molding an optical element, comprising reducing the pressure in the molding chamber to a predetermined pressure prior to press molding of a glass blank. 2. The method for molding an optical element according to claim 1, wherein the pressure in the molding chamber is reduced to 5 Pa or less before press molding the glass blank. 3. The method according to claim 1, wherein the pressure in the molding chamber is first reduced to a predetermined pressure, and then the pair of molds and the glass blank are heated. . 4. The method according to claim 1, wherein the molding chamber is first replaced with an inert gas, and then the molding chamber is evacuated and decompressed in parallel with the heating of the pair of molds and the glass blank. A method for forming an optical element according to claim 2. 5. The molding chamber is first replaced with an inert gas, and then the inside of the molding chamber is depressurized while supplying the inert gas into the molding chamber in parallel with the heating of the pair of molds and the glass blank. The method for forming an optical element according to claim 1, wherein the gas is evacuated. 6. The molding of the optical element according to claim 1, wherein an inert gas is flowed into the molding chamber after the completion of the press molding to cool the pair of molds and the glass blank. Method. 7. An optical element molding apparatus for performing press molding of a glass blank heated to a temperature equal to or higher than a glass transition point using a pair of molds in a molding chamber, wherein the molding chamber has airtightness, An optical element molding apparatus, comprising: a vacuum evacuation unit for evacuating the inside of the optical element.