JPH01172542A - Mold member for molding of optical element - Google Patents

Abstract

PURPOSE:To easily prepare an optical element with high efficiency and to manufacture a mold member having small deterioration of accuracy and having a longer service life by forming a tungsten carbide-chromium carbide layer onto the molding surface of the mold base metal. CONSTITUTION:The mold base metal 30 is formed with the sintered hard alloy consisting of tungsten carbide 41 having hard grains and chromium 42 as the binding phase thereof and is worked to the desired outer shape to finish the molding surface into the desired surface accuracy. The surface of the mold base metal 30 is then subjected to a carburizing treatment for about 0.5-2hr at about 800-1,000 deg.C to form a layer 31 of about 1-100mu thickness consisting of tungsten carbide 41 and chromium carbide 43. The layer is subjected to specular finishing. By this method, the mold member having high oxidizing resistance, low fusion characteristics with glass and good mold releasability and having good accuracy even used repeatedly can be obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a mold member used in an optical element molding apparatus,
In particular, the present invention relates to a mold member for molding optical elements that can easily achieve high precision and has good durability. Such a mold member for molding an optical element is suitably used, for example, as a mold member for high-precision molding to directly form an optical surface.

[Conventional technology and its problems]

In general, optical elements such as lenses, prisms, mirrors, and filters are made by grinding a material such as glass to give the desired external shape, and then polishing the functional surface, that is, the surface that originally transmits and/or reflects. It is manufactured by

However, in the production of optical elements such as those described above, in order to obtain the desired surface accuracy (i.e., accuracy of surface shape and surface roughness) through grinding and polishing, skilled workers spend a considerable amount of processing time. It was necessary to do it. Furthermore, when manufacturing an optical element whose functional surface is an aspherical surface, highly sophisticated grinding and polishing techniques are required and the processing time is unavoidably long.

Therefore, recently, instead of the traditional optical element manufacturing method as described above, thinless molding has been developed, in which the optical element material is housed in a mold with a predetermined surface accuracy and then heated and pressurized. Nowadays, methods of immediately forming the overall shape, including the functional aspects, are being used. According to this, an optical element can be manufactured relatively easily and in a short time even when the functional surface is an aspherical surface. Such a press molding method is suitable for continuous production of optical elements.

The properties required of mold members used in press molding as described above include sufficient hardness, good heat resistance, good mirror workability, and no fusion with optical element materials during molding. can be given.

Therefore, many types of mold members for press molding have been proposed in the past, such as metals, ceramics, and materials coated with appropriate materials.

For example, in JP-A-49-51112, 13Cr
A mold member using martensitic steel is disclosed, and JP-A No. 52-45613 discloses a mold member using martensitic steel.
A mold member using silicon nitride (st3N4) and a mold member using silicon nitride (st3N4) have been disclosed, and JP-A-60-246230 discloses a mold member in which a cemented carbide is coated with a noble metal.

However, the above-mentioned 13Cr martensitic steel has the disadvantage that it is easily solidified and, furthermore, F@ diffuses into the glass material during high-temperature press molding, causing the glass to become colored.

Moreover, the above SiC-? 513N4 is generally not easily oxidized, but at high temperatures it oxidizes to a certain extent and forms a SiO□ film on the surface of the mold member, which tends to cause fusion with glass and is too hard to work with. The problem is that it is extremely bad. Furthermore, materials whose surfaces are coated with precious metals have low hardness and are therefore easily damaged and deformed.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, it is an object of the present invention to provide a mold member for molding an optical element that can be easily manufactured with high precision and has a long life with little deterioration in precision during press molding.

[Means for solving problems]

According to the present invention, in order to achieve the above objects, in a mold member for molding an optical element, at least the molding surface of the mold base material is made of a mixture of tungsten carbide and chromium carbide (Cr2C2) as its binder phase. Provided is a mold member for molding an optical element, characterized in that the mold member is formed by a mold.

〔Example〕

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing one embodiment of a mold member according to the present invention. In this figure, 30 indicates a mold base material, and 31 a mixture of tungsten carbide and chromium carbide as its binder phase (hereinafter referred to as a tungsten carbide-chromium carbide layer) formed on the molding surface of the mold base material. ) is shown.

In the present invention, as the material for the mold base material, a cemented carbide consisting of tungsten carbide as hard particles and chromium as its binder phase is preferably used. The base material is previously given a desired external shape by cutting, grinding, polishing, etc., and in particular, the molded surface is finished to the desired surface precision.

In order to form the tungsten carbide-chromium carbide layer 31 on the surface of the base material 30, the surface of the base material 30 is carburized, for example.

FIG. 2 is an enlarged sectional view of the molding surface of the mold member used in the present invention before carburizing treatment. In this figure, 41 indicates tungsten carbide particles, and 42 indicates chromium.

FIG. 3 is an enlarged one-dimensional view of the molding surface after carburizing the mold member according to the present invention, where 43 indicates chromium carbide.The carburizing conditions are not particularly limited, but usually 800 to 1
It takes about 0.5 to 2 hours at 000°C.

The thickness of the tungsten carbide-chromium carbide layer is set appropriately depending on the manufacturing conditions, but it may be set to a thickness that provides sufficient durability considering the desired characteristics during use, for example, about 1 to 100 μm. The tungsten carbide-chromium carbide layer has high oxidation resistance at high temperatures, has low adhesion to glass, and has good mold releasability, so an optical element with good precision can be obtained even after repeated use.

Hereinafter, examples of manufacturing a mold member according to the present invention and glass molding using the same will be shown. At the same time, for comparison, an example of manufacturing a conventional mold member and glass molding using the same is also shown.

Cemented carbide Cwc (90%) + Cr (10%): A mold base material is made as the l-type base material material, and a tungsten carbide-chromium carbide layer is formed on the molding surface of the base material, and the following standard is prepared. A mold part according to the invention was manufactured. In addition, for comparison, a mold member that does not form a layer on the molding surface of the mold base material, a cemented carbide (WC)
(90%) + Co (10%), mold member and sintered SICf with l type base material! : A mold member was manufactured using the base material. A list of the manufactured mold members is shown in Part 1. In Table 1, /161 indicates an embodiment of the present invention, and 42.
, %3 and consideration 4 are comparative examples.

Table 1 First, the mold base material was cut, and then the molding surface corresponding to the functional surface (optical surface) of the molded optical element was processed to a desired surface precision. The molding surface of the mold base material was concave and was first ground to the desired curvature using a diamond grindstone.

Next, regarding the scrap 1, a tungsten carbide-chromium carbide layer was formed on the forming surface of the mold base material by carburizing using the apparatus shown in FIG.

In FIG. 4, 51 is a furnace, 52 is a heater, 53 is a stainless steel container, 54 is a carburizing agent, 55 is a mold base material, and 56 is a temperature sensor.

When forming the tungsten carbide-chromium carbide layer, the mold base material 55 obtained as described above was placed in a stainless steel container 53 and then carburized by maintaining the furnace temperature at 800° C. for 2 hours.

Next, the carburized mold base material was mirror-finished.

It was confirmed by X-ray diffraction that a tungsten carbide-chromium carbide layer as shown in FIG. 3 was formed on the surface of the mold member obtained. The thickness of the tungsten carbide-chromium carbide layer was approximately 1 μm.

Next, optical glass was press-molded using the mold member manufactured as described above.

FIG. 5 is a sectional view showing the apparatus used for press molding.

In FIG. 5, 1 is a closed container, 2 is its lid, 3 and 4 are the mold members for molding the optical element (biconvex lens), and 3 is an upper mold member. 4 is a lower die member, 5 is an upper die presser, 6 is a body die member υ, 7
8 is a heater, 9 is a lower mold pushing rod, and 10 is an air cylinder for driving the rod.

11 is an oil rotary pump], 12, 13, and 14 are pulp, 15 is a nitrogen gas introduction pipe, 16 is pulp, 17 is a discharge/4' eve, and 18 is pulp. Ah, 9.19 is the temperature sensor, 20 is the water cooling pipe, and 21 is the stand for the sealed container 1.

Flint optical glass (5F14, softening point 5p=58
A blank for molding was prepared in a spherical shape with a predetermined weight and a temperature of 6° C. (glass transition point Tg = 485° C.).

The lid 2 of the airtight container 1 was opened, the upper mold member 3 and the upper mold holder 5 were removed, the above-mentioned blank was placed on the trap of the lower mold member 4, and the upper mold member 3 and the upper mold holder 5 were attached.

Furthermore, after closing the lid 2, water was allowed to flow through the water cooling pipe 20, and the heater 8 was energized. At this time, the nitrogen gas pulp 16,
The pulp 18 and the exhaust system pulp 12°13.14 were kept closed. Next, the oil rotary pump 11 is operated, and the pulp 1
2 was opened, and the inside of the container 1 was evacuated. True 9 degrees inside container 1 is 1
After reaching 0'4 Torr, close the pulp 12, open the pulp 16.
introduced inside. After the temperature reached a predetermined temperature, the air cylinder 10 was operated and press molding was performed for 5 minutes at a pressure of 10'Q/cm.The press molding was performed at a rate of 5°C/min to below the glass transition point. Cool to 20
Cooling was carried out at a rate of .degree. C./min or higher, and after the temperature dropped to 200.degree. C. or lower, the pulps 16 and 18 were closed, the leak pulp 13 was opened, and air was introduced into the closed container 1. Next, the lid 2 was opened, the upper mold member 3 and the upper mold holder 5 were removed, and the molded optical element was taken out.

FIG. 6 is a diagram showing the temperature change of glass during press molding.

The optical surface roughness of the molding surface of the mold member 3゜4 before and after press molding as described above, the surface roughness of the optical surface of the molded optical element, and the release of the molded optical element from the mold members 3 and 4. The characteristics are shown in Table 2.

Table 2 shows 41. No fusion occurs. Regarding Ai2 and Mu3,
Press molding was performed 10,000 times using the same mold member, and the surface roughness of the molding surfaces of mold members 3 and 4 and the surface of the optical surface of the molded optical element after 200, 1,000, 5,000, and 10,000 times. The roughness is shown in Table 3.

As described above, in the examples of the present invention, good surface precision could be sufficiently maintained even when used in repeated press molding, and optical elements with good surface precision could be molded.

In the above embodiments, a flint-based optical glass is used as the optical glass to be molded, but other glasses such as crown-based glasses can also be molded with good precision.

〔Effect of the invention〕

According to the present invention as described above, by forming a tungsten carbide-chromium carbide layer on the molding surface of the mold base material, it is possible to provide a mold member for molding optical elements that has a long life and less accuracy deterioration during repeated press molding. .

Furthermore, the mold member of the present invention is easy to manufacture because the mold base material used has good workability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view showing an embodiment of a mold member according to the present invention. FIG. 2 is an enlarged sectional view of the molding surface of the mold member used in the present invention before carburizing treatment. FIG. 3 is an enlarged sectional view of the molding surface of the mold member according to the present invention after being carburized. FIG. 4 is a diagram showing an apparatus used for forming a tungsten carbide-chromium carbide layer in the production of a mold member according to the present invention. FIG. 5 is a sectional view of a press molding apparatus for optical elements. FIG. 6 is a diagram showing the temperature change of glass during press molding. 3.4: Mold member, 30 Type 2 base material, 31: Tungsten carbide-chromium carbide layer, 41; Tungsten carbide particles, 42
Nichrome, 43: Chromium carbide, 55: Mold member. Agent Patent Attorney Jo Taira Yamashita (Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6)

Claims (2)

[Claims] (1) A mold member for molding an optical element, characterized in that at least the molding surface of the mold base material is formed of a mixture of tungsten carbide and chromium carbide as its binder phase. Element. (2) The mold member for molding an optical element according to claim 1, wherein the mold base material is a cemented carbide made of tungsten carbide and chromium as its binder phase.