JPS638050B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing optical elements such as lenses and prisms by molding glass materials. A predetermined volume of glass material is placed between a pair of molds each having a mold surface, and the glass material is heated to the glass softening point and molded using the mold described above to manufacture optical elements such as lenses and prisms. It's about how to do it.

Conventionally, lenses and prisms have been produced by grinding the material with a diamond grindstone or the like, and then polishing it with cerium oxide or the like. However, as the need for aspherical lenses increased, it became difficult to produce large quantities of lenses at low cost using conventional methods. Therefore, methods of producing aspherical lenses by molding were researched in various countries, and Kodatsu of the United States proposed a method of molding in an inert gas (U.S. Patent Nos. 3,833,347 and 4,139,677). ing.

Optical glass has a high softening temperature of 500 to 800°C, and has a high surface precision (within 5 Newtons,
Although it is difficult to maintain a surface roughness (R _nax (1/100 μm or less)), Kodatsu's method, which does not oxidize the mold, is very promising.

As a result of numerous studies on methods of manufacturing optical elements by molding, the inventors of the present invention have found that, as described above, molding of glass materials is performed in a high degree of vacuum rather than in an inert gas. It was confirmed that excellent results could be obtained. In other words, when molding a glass material in an inert gas, defects such as minute holes may occur on the surface of the molded optical element, but when molding is performed in a vacuum, the molded optical element There is no fear of forming minute holes on the surface of the element, oxidation of the mold is prevented, and optical elements can be stably manufactured with surface precision equivalent to that in an inert atmosphere.

The method for manufacturing an optical element according to the present invention includes placing a predetermined volume of glass material between molds having a mold surface having a shape corresponding to a desired optical element and having high surface accuracy, and heating the glass material to the glass softening point. In the method of manufacturing an optical element by molding with the above-mentioned mold, the material of the mold is made of molybdenum, tungsten, or an alloy thereof, the mold made of the above-mentioned material, and glass placed between the molds. The material is placed in a vacuum chamber, and the temperature inside the vacuum chamber is 10 ^-1 to
This is characterized in that the molding is performed while maintaining a vacuum of 10 ^-5 Torr. 10 ^-1 above
A vacuum of between 10 -5 Torr and 10 ^-5 Torr is economically obtainable and sufficient to prevent entrainment of gas into the glass material and to prevent oxidation of the mold.

The drawing shows an example of a device for carrying out the method of the invention. In the figure, 1 is the main body of the vacuum chamber, 2 is its lid, 3 is an upper mold for molding optical elements, and 4
is the lower mold, 5 is the upper mold holder for holding the upper mold, 6 is the body mold, 7 is the mold holder, 8 is the heater, 9
1 is a lifting rod for lifting up the lower die; 10 is an air cylinder for operating the lifting rod; 11 is an oil diffusion pump; 12 is an oil rotary pump; 13 is a temperature sensor;
4 is the water cooling pipe, 15 is the main valve, 16,1
7, 18, and 19 indicate valves.

When manufacturing an optical element, first, the lid 2 of the vacuum chamber 1 is
, place a predetermined volume of glass material, for example, a flint glass material, on the lower mold 4 , set the upper mold 3 , close the lid 2 of the vacuum chamber 1 , and open the water cooling pipe 1 .
4, and turn on the heater 8.

At this time, the main valve 15, the valve 16, and the leak valves 18 and 19 are closed and the valve 17 is open. The oil diffusion pump 11 is always in operation, and the oil rotation pump 12 is also constantly rotating.

Open the valve 16 and begin exhaustion. When fluorescence appears on the Geissler tube or the vacuum gauge becomes less than 10 ^-1 Torr, close the valve 16 and open the main valve 15. When the temperature sensor 13 confirms that the glass has been heated above its softening point, the air cylinder 10
is activated to pressure-form the glass. The lower die 4 is made of the same material as the body die 6 and moves up and down while fitting with precision.

When the temperature drops below 200℃, main valve 1
5 is closed and the leak valve 18 is opened to introduce air into the vacuum chamber 1. Open the lid 2, remove the upper mold presser 5, and take out the molded product.

The upper and lower molds above are made of molybdenum (Mo)
Or made of tungsten (W) or its alloy. Conventionally, silicon carbide or the like has been generally used as such a mold material, but this material has high hardness, is difficult to process, and is brittle. The molybdenum, tungsten, and their alloys mentioned above are easy to cut, can be easily processed into desired shapes, and have good mold release properties, but when these materials are heated to high temperatures in air, they break out into needle-like crystals, making them unusable. Ta. However, according to the present invention, the molding ^can be
By performing the process in a vacuum of 10 ^-5 Torr to prevent mold oxidation, molybdenum (Mo), which has good mold releasability but cannot be used because needle-like crystals precipitate when heated in air at high temperatures, can be removed. A mold material such as tungsten (W) and its alloys can be used.

As described above, according to the method for manufacturing an optical element according to the present invention, molding is performed in a vacuum of 10 ^-1 to 10 ^-5 Torr, thereby improving the conventional method of molding in an inert gas. This eliminates the effects of gas remaining between the molded glass and the mold, and also prevents oxidation and reduces surface roughness.
Optical elements can be manufactured with high surface accuracy of R _nax 2/100 to 3/100 μm. As for this degree of vacuum
The best value is around 10 ^-2 Torr, which is not only economically advantageous because it can be obtained by a mechanical vacuum pump without using an expensive oil diffusion pump, but also sufficient to prevent oxidation. It is also possible to avoid adverse effects on the molded optical element due to the evaporation phenomenon of the lead content of the glass in a low oxygen concentration and in a high vacuum.

As described above, according to the present invention, optical elements such as lenses and prisms can be easily and accurately manufactured by molding glass materials, and in particular, it is possible to manufacture optical elements such as aspherical lenses by conventional mechanical grinding methods. Therefore, optical elements that are difficult to manufacture can be manufactured easily and accurately.

[Brief explanation of the drawing]

The drawing shows an example of the apparatus used to carry out the method of the invention. 1...Vacuum chamber, 2...Lid, 3...Upper mold, 4...
Lower mold, 8... Heater, 9... Lifting rod, 11
...Oil diffusion pump, 12...Oil rotation pump.

Claims (1)

[Claims] 1. A predetermined volume of glass material is placed between molds having a mold surface with a shape corresponding to a desired optical element and high surface precision, and the glass material is heated to the glass softening point while performing the above-mentioned process. In the method of manufacturing an optical element by molding with a mold, the material of the mold is made of molybdenum, tungsten, or an alloy thereof, and the mold made of the above material and the glass material placed between the molds are heated in a vacuum. 1. A method for manufacturing an optical element, characterized in that the molding is carried out by placing the optical element in a chamber and maintaining the vacuum chamber at a vacuum of 10 ^-1 to 10 ^-5 Torr.