JPH03153535A - Mold for forming optical element - Google Patents

Abstract

PURPOSE:To obtain a mold for forming which is high in oxidation resistance and can be produced at high precision and is little in deterioration of precision by coating a compositely carbonized film on the molding face of the base material of the mold. CONSTITUTION:In a mold for molding which is utilized for press-molding of an optical element made of glass, a compositely carbonized film is coated at least on the molding face of the base material of a mold. The compositely carbonized film is formed of a film wherein a plurality of metals are mixed in a state of crystalline and/or amorphous carbide. For example, Ti, Ta, B and Hf, etc., are shown as metal for forming the compositely carbonized film. For example, sintered hard alloy and sintered SiC are utilized as the base material of the mold. In order to coat the compositely carbonized film, e.g. a physical vapor deposition method such as the sputtering and ion plating methods and a chemical vapor deposition method such as a plasma CVD method. The compositely carbonized film is preferably coated via an intermediate layer to enhance the adhesive property to the base material of the mold.

Description

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

[Prior Art] Generally, optical elements such as lenses, prisms, mirrors, and filters are manufactured by grinding a material such as glass to give a desired external shape, and then polishing the functional surface, that is, the surface that transmits and/or reflects light. It is manufactured by forming an optical surface.

In manufacturing such optical elements as described above, in order to obtain the desired surface precision by grinding and polishing, it is necessary for skilled workers to carry out processing for a considerable amount of time. 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, optical element materials are placed in a mold with a predetermined surface accuracy and pressurized while heating. More and more methods are being used to form the overall shape, including the functional aspects. According to this, even when the functional surface is an aspherical surface, it is suitable for continuous production of optical elements relatively easily and in a short time.

The properties required of the mold used in press molding as described above include sufficient hardness, good heat resistance, oxidation resistance, good mirror workability, and the ability to avoid fusion with optical element materials during molding. First, it is difficult to form reaction precipitates.

Therefore, conventionally, such press molding molds were made of metal,
Many types of materials have been proposed, including ceramics and materials coated with appropriate materials.

For example, in JP-A-49-51112, 13Cr
A mold using martensitic steel is disclosed, and JP-A No. 52-45613 discloses a mold using silicon carbide (SiC) and a mold using silicon nitride (simN4). Japanese Patent No. 60-246230 discloses a mold made of cemented carbide coated with a noble metal.

[Problems to be Solved by the Invention] However, the above-mentioned 13C martensitic steel is easily oxidized and has the disadvantage that Fe diffuses into the glass material during high-temperature press forming, causing the glass to become colored. 5isN4 is generally not oxidized, but at high temperatures it oxidizes to some extent and forms SiO on the mold surface.
Since a film of □ is formed, it is easy to fuse with the glass, and furthermore, the hardness is too high, resulting in extremely poor workability.

Furthermore, materials whose surfaces are coated with precious metals have low hardness and are easily damaged (and easily deformed).

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, an object of the present invention is to provide a mold 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 the Problems] According to the present invention, an optical element molding die used for press molding an optical element made of glass is characterized in that at least the molding surface of the mold base material is coated with a double carbide film. A mold for molding an optical element is provided.

In the present invention, a "double carbide film" refers to a film in which multiple metals are mixed in the form of crystalline and/or amorphous carbides. It also includes films in which so-called interstitial carbide structures such as (TaTi)sC are mixed, and films in which metal elements or carbon are mixed in a state where they are not bonded to other elements.

Hereinafter, TaC-TiC and the like mainly refer to the metal composition of the double carbide film, which is a general term for these films.

As the metal constituting the double carbide film, for example, titanium (Ti
), tantalum (Ta), boron (B), hafnium (H
f), zirconium (Zr), vanadium (V), aluminum (Al), tungsten (W), niobium (Nb)
), molybdenum (Mo), and chromium (Cr). Therefore, the forms of carbides contained in the double carbide film include ordinary TiC, TaC, B4C, HfC, ZrC, V
C.

A14CI, WC, NbC, MotC, Cr1Ct, etc., and these so-called interstitial carbides (TaTiC, (TaT
i) IC etc.).

In the composition of the double-carbide film, the atomic ratio of metal to carbon can be varied over a considerable range, but for practical purposes, a metal content of about 30 to 50 atoa+% is preferable.

The film thickness of the double-carbonized film is appropriately set depending on the manufacturing conditions, but the film thickness is such that the desired characteristics can be exhibited during use (preferably 0
．． The thickness may be 1 to 10 μm (more preferably about 1 μm).

As the material of the mold base material, for example, cemented carbide or sintered SiC can be used. These materials are processed into a desired external shape by cutting, grinding, polishing, etc., and in particular, the molding surface is finished to a desired surface accuracy and used as a mold base material.

In order to coat the surface of the mold base material with a double carbide film, physical vapor deposition methods such as sputtering method and ion blasting method (
Chemical vapor deposition methods (PVD method) and plasma CVD method (CVO method)
method).

The double-carbide film is preferably coated with an intermediate layer in order to improve its adhesion to the base material, and this intermediate layer is preferably made of the same metal as the metal constituting the double-carbide film. More preferred.

The double-carbide film coated in this way has high oxidation resistance, especially at high temperatures, and has extremely low fusion properties with glass (because it has good mold releasability, It can be successfully applied to molding using glass with a high melting point, which is considered difficult to perform industrially with high precision molding, and can even accommodate primary molded glass or molten glass in a mold device. It has the advantage that it can be applied to the manufacture of optical elements by press molding, and optical elements with good precision can be obtained even if they are used repeatedly.

[Example 1 The present invention will be explained by way of examples with reference to the drawings.

Example 1 FIGS. 1 and 2 show a mold for molding an optical element according to the present invention.
2 shows two embodiments.

Figure 1 shows the state of the optical element before press molding, and Figure 2 shows the state of the optical element after molding. A double carbon film formed on the molding surface in contact with the base glass material, 3 is the glass material,
4 in FIG. 2 is an optical element. By press-molding a glass material 3 placed between molds as shown in FIG. 1, an optical element 4 such as a lens is formed as shown in FIG. 2.

The mold base material was made of cemented carbide [WC (90%) + Co (10
%)l, made of sintered SiC, processed into a predetermined shape,
The lens molding surface is mirror-finished. A mold according to the present invention was manufactured as follows by coating the molding surface of the mold base material with a double carbonized film. In addition, for comparison, a mold in which the molding surface of the mold base material was not coated and a mold in which a SiC layer was formed on the molding surface were manufactured. A list of the manufactured molds is shown in Table 1. In Table 1, No. 1 to No. 30 are examples of the present invention.

Next, regarding No. 1 and No. 002 above, the third
Using the apparatus shown in the figure, a titanium tantalum carbide layer (TaC-
A Tic) film was formed.

In FIG. 3, 20 is an airtight chamber of the sputtering apparatus. An exhaust port 21 is connected to the airtight chamber 20, and the exhaust port 21 is connected to a decompression source (not shown). Airtight room 2
A heater 22 is placed in the upper part of the heater 0, and a heater power source 23 is connected to the heater. Heater 22
A mold base material support 24 is disposed below, and a mold base material bias power source 25 is connected to the support. A mold base material 26 is supported on the support body 24 with the molding surface facing downward. A vibrator 27 for introducing methane and acetylene gas and a coil 28 for generating glow discharge are arranged below the support 24, and a high frequency power source 3 is connected to the coil via a matching circuit 29.
0 is connected.

A cathode electrode 31 is arranged at the bottom of the airtight chamber 20. A mixed target 32 of titanium and tantalum mixed at an area ratio of 1:1 is provided on the upper part of the electrode 31, and a cooling water vibe 33 is connected to the lower part.

A vibrator 34 for introducing argon gas is arranged above the electrode 31, and a shutter 35 is arranged above and near the target 32.

When forming a titanium tantalum carbide (TaC-TiC) film, the mold base material 26 obtained as above is washed with acetone and supported by the support 24, and then the airtight chamber 20 is heated to an I.
The pressure was reduced to X 10"' Torr. Next, the vibrator 34
Argon gas (3X 10-” Torr) is introduced into the coil 28, and a high-frequency electric field (13.56MHz, 0.2
kW-hr) is applied to generate an argon glow discharge, and the bias power supply 25 applies a negative bias (-
50 V) is applied to perform sputter cleaning using argon ions. Thereafter, while introducing argon gas from the vibrator 34, a high frequency electric field (13
, 56MHz, 0.5kW-hr) was applied to titanium.
Argon glow discharge is generated near the tantalum mixture target 32, and the titanium/tantalum mixture target is bombarded with argon ions to perform sputtering. The shutter 35 is opened, and at the same time, hydrocarbon gas (methane and acetylene) is pumped in at 1 x 10 by the vibrator 27.
-" Torr is introduced and sprayed near the mold base material 26, and a high frequency electric field (13.56 MHz, 0.5 kW) is applied to the coil 28.
hr) is applied to form a carbon plasma, and a negative bias (-50V) is applied to the mold base material 26 through the bias electrode 25 to draw carbon ions into the mold base material 26 while reactive sputtering of the titanium/tantalum mixture is performed. A titanium tantalum carbide layer was formed on the surface of the mold base material 26. At this time, the temperature of the mold base material was 300°C. The thickness of the obtained titanium tantalum carbide layer was 1 μm. In the above example, a similar titanium tantalum carbide layer was obtained even when a DC voltage was applied to the cathode electrode instead of a high frequency electric field.

Thereafter, double-carbonized films No. 3 to No. 30 were formed in the same manner.

As for a comparative example, a silicon carbide layer was similarly formed on the molding surface of the mold base material using the apparatus shown in FIG. At this time, a silicon target was used instead of the titanium/aluminum mixture target. The thickness of the silicon carbide layer is II
It was Lm.

Lens Breathing: Using the mold thus obtained, a lens molding test was conducted using the molding apparatus shown in FIG.

In Fig. 4, 51 is the vacuum chamber main body, 52 is its lid, 53 is an upper mold for molding optical elements, 54 is a lower mold, 55 is an upper mold holder for holding down the upper mold, 56 57 is a mold holder, 58 is a heater, 59 is a lifting rod that lifts up the lower mold, 60 is an air cylinder that operates the lifting rod, 61 is an oil rotary pump, 62, 63, and 64 are valves.
65 is an inert gas inflow vibe, 66 is a valve, 67 is a leak vibe, 68 is a valve, 69 is a temperature sensor, 70
71 indicates a water-cooled vibrator, and 71 indicates a stand supporting a vacuum chamber.

The process of manufacturing the lens will be described below.

First, a flint-based optical glass (SF14) is adjusted to a predetermined amount, and a spherical glass material is placed in a mold cavity, and this is installed in the apparatus.

After the mold containing the glass material is placed in the apparatus, the lid 52 of the vacuum chamber 51 is closed, water is allowed to flow through the water-cooled vibrator 70, and electric current is passed through the heater 58. At this time, the nitrogen gas valve 66
and 68 are closed, and the exhaust system valves 62, 63, and 64 are also closed. Note that the oil rotary pump 61 is constantly rotating.

The valve 62 is opened to begin exhaustion, and when the temperature drops below 10-'' Torr, the valve 62 is closed, and the valve 66 is opened to introduce nitrogen gas from the cylinder into the vacuum chamber. When the temperature reaches a predetermined temperature, the air cylinder 60 is activated. Pressure is applied for 5 minutes at a pressure of 80 kg/cm''. After removing the pressure, the cooling rate is 1 °C/win until the temperature drops below the transition point, and then cooling is performed at a rate of 0 °C/win or more, and when the temperature drops to 200 °C or less, the valve 66 is closed. , the leak valve 63 is opened to introduce air into the vacuum chamber 51. Then lid 5
Step 2: Remove the upper mold holder and take out the molded product.

As described above, the lens 4 shown in FIG. 2 was molded using flint optical glass 5F14 (softening point Sp = 586°C, dislocation point Tg = 485°C). FIG. 5 shows the molding conditions at this time, that is, a time-temperature relationship diagram.

The surface roughness of the molding surfaces of the mold members 53 (upper mold) and 54 (lower mold) before and after press molding (n = 5000) as described above, the surface roughness of the optical surface of the molded optical element, and the molding Table 1 shows the mold releasability between the optical element and the mold members 53 and 54.

Table 1 *The coating value indicates the mole percent of the component.

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.

In the above embodiment, carbide and sintered SiC are used as the mold base material, but the mold base material is not limited to these two (any material with high temperature and high strength may be used).

In the above example, the double carbide film formed on the mold base material by the PVD method or CVD method is used as it is, but the double carbide film is formed relatively thick by this method, and then the surface is mirror-polished. It can also be used as

In addition, even if defects occur on the surface due to multiple presses, a good surface can be regenerated by such polishing.

Further, the atom ratio of the metals constituting the double carbide film is not limited to the ratio of this embodiment, but can be changed as appropriate by changing the mixing ratio of the metals in the target.

Example 2 What was done No. 2 above
7, No. 28, on the molding surface of the base material by reactive sputtering method using the apparatus shown in FIG.
intermediate layer (TaTiHfJ, 25TiC-50HfC
) layer was coated.

However, in FIG. 3, a tantalum titanium hafnium target mixed in an area ratio of tantalum:titanium:hafnium=1:2:2 was used as the target 32.

After cleaning the mold base material 26 obtained as described above with acetone and supporting it with the support body 24, the inside of the airtight chamber 20 was cleaned with IX.
After the pressure was reduced to 10-'Torr, argon gas (3X 10-'Torr) was introduced from the vibrator 34, and a high-frequency electric field (13.56MHz, 0.2kW) was applied to the coil 28.
・hr) is applied to generate an argon glow discharge, and the bias power supply 25 applies a negative bias (-50
V) is applied to perform sputter cleaning with argon ions. Thereafter, while introducing argon gas from the vibrator 34, a high frequency electric field (13, 56
First, the shutter 3
5 was opened to form an intermediate layer with a thickness of 0.2 μm.Next, hydrocarbon gas (methane and acetylene) was introduced at 1×10-” Torr using a vibrator 27 and sprayed near the mold base material 26, and the coil 28 is a high frequency electric field (13,56M
Hz, 0.5 hr) is applied to form a carbon plasma, and a negative bias (-50V) is applied to the mold base material 26 by the bias electrode 25 to draw carbon ions into the mold base material 26 while injecting tantalum titanium. A tantalum titanium hafnium carbide layer was formed on the surface of the mold base material 26 by reactive sputtering of hafnium. At this time, the temperature of the mold base material is 300
It was ℃. The metal content in the obtained tank titanium hafnium carbide layer was 50 atom%. Further, the film thickness of the double-carbonized film was 1 μm. In the above embodiment,
A similar tantalum titanium hafnium carbide layer was obtained by applying a DC voltage instead of a high frequency electric field to the cathode electrode.

When these molds were repeatedly used for press molding in the same manner as in Example 1, good surface precision could be sufficiently maintained as in Example 1, and an optical element with good surface precision could be molded.

[Effects of the Invention] According to the present invention as described above, since the molding surface is coated with a double carbide film that has better oxidation resistance than a single metal carbide film, accuracy can be improved during repeated press forming. Provided is a mold for molding an optical element that has a long life, is less susceptible to deterioration, and does not cause fusion with glass even when used at high temperatures.

Furthermore, the Knoop hardness Hk of the double carbonized film is 2400 to 3000.
It is approximately 7 mm" in weight and has a high hardness compared to a single metal carbide film, so it is less likely to be scratched. Therefore, it is less likely to be scratched even after repeated cleaning during use, and therefore has a good surface precision. can be manufactured over a long period of time.

Furthermore, the mold of the present invention is easy to manufacture because a wide range of materials with good workability can be selected as the mold base material.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing one embodiment of the mold for molding an optical element according to the present invention, with FIG. 1 showing the state before press molding, and FIG. 2 showing the state after press molding. FIG. 3 is a schematic diagram of the sputtering apparatus used to manufacture the mold of the present invention. FIG. 4 is a sectional view showing a lens molding apparatus using the optical element mold according to the present invention. FIG. 5 is a time-temperature relationship diagram during lens molding. 1.2... Mold base material, 1-a, 2-a... Double carbide film, 3... Glass material, 4... Molded lens, 20... Airtight chamber, 21...・Exhaust port, 22・
...Heating heater, 23...Heater power supply, 24...
- Mold base material support, 25...bias power supply, 26...
Mold base material, 27... Vibrator for introducing hydrocarbon gas, 28... Coil for generating glow discharge, 29... Matching circuit, 30... High frequency power supply, 31
... Cathode electrode, 32 ... Target, 33 ... Vibrator for cooling water, 34 ... Vibrator for introducing argon gas, 35 ... Shutter 51 ... Vacuum chamber body, 52 ... Lid, 53...
Upper mold, 54...Lower mold, 55...Upper mold presser, 56...Mold, 57...Mold holder, 58...
・Heater 59... Lifting rod, 60... Air cylinder, 61... Oil rotary pump, 62.63.64
...Valve, 65...Inflow vibe, 66...Valve, 67...Outflow vibe, 68...Valve, 6
9...Temperature sensor, 70...Water cooling vibe, 71.
...stand.

Claims (1)

[Claims] 1. In an optical element molding mold used for press molding an optical element made of glass, at least the molding surface of the mold base material,
A mold for molding an optical element characterized by being coated with a double-carbonized film. 2. The metals that make up the double carbide film are titanium (Ti), tantalum (Ta), boron (B), hafnium (Hf), zirconium (Zr), vanadium (V), aluminum (Al), and tungsten (W). 2. The mold for molding an optical element according to claim 1, wherein the mold is at least two selected from the group consisting of , niobium (Nb), molybdenum (Mo), and chromium (Cr). 3. The mold for molding an optical element according to claim 1, wherein the double-carbonized film is coated with an intermediate layer interposed therebetween. 4. The mold for molding an optical element according to claim 3, wherein the intermediate layer is made of the same metal as the metal constituting the double carbide film.