JP2505897B2 - Mold for optical element molding - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element molding die used for press molding of an optical element made of glass, and in particular, an optical element which can easily realize high precision and has good durability. It relates to a molding die. Such an optical element molding die is suitably used, for example, as a high precision molding die for directly forming an optical surface.

[Prior Art] Generally, optical elements such as lenses, prisms, mirrors, and filters are formed by grinding a material such as glass into a desired outer shape, and then polishing a functional surface, that is, a surface through which light is transmitted and / or reflected. To produce an optical surface.

In the manufacture of the optical element as described above, it is necessary for a skilled worker to perform processing for a considerable time in order to obtain a desired surface accuracy by grinding and polishing. Also,
In the case of manufacturing an optical element having an aspherical functional surface, more advanced grinding and polishing techniques are required and the processing time has to be prolonged.

Therefore, recently, instead of the traditional optical element manufacturing method as described above, the optical element material is housed in a molding die having a predetermined surface accuracy, and the material is heated and pressed while being heated, thereby immediately performing press molding. A method for forming an overall shape including a functional surface is being used. According to this,
Even when the functional surface is aspherical, it is suitable for the continuous production of optical elements in a relatively simple and 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 fusion with the optical element material during molding. And it is difficult to form a reaction precipitate.

Therefore, conventionally, many types of such press-molding dies have been proposed such as metals, ceramics, and materials obtained by coating these with appropriate materials.

For example, JP-A-49-51112 discloses a mold using 13Cr martensitic steel.
Japanese Unexamined Patent Publication No. 60-2 discloses a mold using silicon carbide (Sic) and a mold using silicon nitride (Si ₃ N ₄ ).
Japanese Patent No. 46230 discloses a mold in which a cemented carbide is coated with a noble metal.

[Problems to be Solved by the Invention] However, the above 13Cr martensitic steel is apt to be oxidized, and further, there is a problem that Fe is diffused into the glass material during press forming at a high temperature and the glass is colored. In addition, the above Si
C and Si ₃ N ₄ are generally difficult to oxidize, but at high temperatures some oxidation occurs and a SiO ₂ film is formed on the mold surface, so fusion with glass tends to occur and hardness is too high. Therefore, the workability is extremely poor.

Further, a material having a surface coated with a noble metal has a disadvantage that it is easily damaged and easily deformed due to low hardness.

Therefore, in view of the above-mentioned conventional technique, it is an object of the present invention to provide a long-life optical element molding die that can be easily manufactured with high accuracy and has little deterioration in accuracy during press molding.

[Means for Solving the Problems] According to the present invention, in an optical element molding die used for press molding of an optical element made of glass, at least the molding surface of a mold base material is coated with a double nitride film. A mold for optical element molding is provided.

In the present invention, the “double nitride film” is a film in which a plurality of metals are mixed in a crystalline and / or amorphous nitride state.

Examples of the metal forming the double nitride film include aluminum (Al), boron (B), chromium (Cr), hafnium (Hf), niobium (Nb), tantalum (Ta), titanium (T).
i), vanadium (V), tungsten (W), zirconium (Zr).

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

To coat the surface of the die base material with the double nitride film, for example, a physical vapor deposition method (PVD method) such as a sputtering method or an ion plating method or a chemical vapor deposition method (CVD method) such as a plasma CVD method is used.

The double nitride film is preferably covered with an intermediate layer in order to improve the adhesion with the die base material, and the intermediate layer is made of the same metal as the metal forming the double nitride film. More preferable.

The film thickness of the double nitride film is appropriately set depending on the manufacturing conditions,
The film thickness may be such that sufficient durability is obtained in view of desired characteristics during use.

The double nitride film coated in this manner has high oxidation resistance at high temperatures, and thus has low fusion property with glass and good releasability, so that an optical element with good accuracy can be used even if it is repeatedly used. Obtainable.

When the metal constituting the double-nitride film is aluminum and the above-mentioned other metals, the aluminum nitride on the film surface portion reacts with the atmospheric gas and glass at a high temperature at which molding is performed,
It is oxidized to aluminum oxide (Al ₂ O ₃ ). However, since the generated Al ₂ O ₃ has a Knoop hardness of 1400 kg / mm ^2, which is harder than other oxides, the oxidation of the mold surface progresses due to many consecutive moldings, and the double nitride film remains as Al ₂ O _3. Even if the film is changed to a double oxynitride film composed of the above-mentioned nitride, the hardness of the film surface is not significantly reduced, and the film has good scratch resistance. In addition, the generated Al ₂ O
No. ₃ has a relatively low fusion property, and even if Al ₂ O ₃ is generated on the mold surface, the mold is unlikely to fuse with glass.

If aluminum nitride is present in the double nitride film,
The remaining nitride is less likely to be oxidized. This is the standard free energy temperature diagram for the formation of oxides {for example, JFElliott, M. Gleiser; Thermochemistry for Steelmaking by Elliott and Glazer.
Steelmaking, Vol.1 (1960), Addisons Wesley.)} Is clear that a comparison between aluminum (Al) and other metals suggests that Al is more easily oxidized than other metals.

When the metal constituting the double nitride film contains aluminum, the above preferable characteristics are that aluminum is 5 to 95 atoms.
%, More remarkable in the double nitride film in which the balance is other metal.

[Examples] The present invention will be described by examples with reference to the drawings.

Example 1 FIGS. 1 and 2 show one embodiment of an optical element molding die according to the present invention.

FIG. 1 shows a state before press molding of an optical element.
The figure shows the state after molding of the optical element. In FIG. 1, 1 and 2 are mold base materials, 1-a and 2-a are double nitride films formed on a molding surface of the mold base material in contact with the glass material, and 3 is a glass material, and FIG. Medium 4 is an optical element. By pressing the glass material 3 placed between the molds as shown in FIG. 1, an optical element 4 such as a lens is formed as shown in FIG.

Manufacturing of mold coated with double nitride film: Mold base material is made of cemented carbide [WC (90%) + Co (10%)], sintered SiC, processed into a predetermined shape, lens molding surface is mirror surface It is processed. The molding surface of the mold base material was coated with a double nitride film to manufacture a mold according to the present invention as follows. For comparison, a mold having no coating on the molding surface of the mold base material and a mold having an SiC layer formed on the molding surface were produced. Table 1 shows a list of the manufactured molds. In Table 1, N
o-1 to No. 3 are examples of the present invention.

Next, regarding No. 1 and No. 2 described above, an aluminum titanium nitride (TiAlN) film was formed on the molding surface of the mold base material by the reactive sputtering method using the apparatus shown in FIG.

In FIG. 3, reference numeral 20 denotes an airtight chamber of the sputtering apparatus. An exhaust port 21 is connected to the hermetic chamber 20, and the exhaust port 21
Reference numeral 21 is connected to a pressure reducing source (not shown). A heater 22 is disposed in an upper portion of the hermetic chamber 20, and a heater power supply 23 is connected to the heater. A mold base support 24 is disposed below the heater 22, and a mold base bias power supply 25 is connected to the support. The support base 24 supports a mold base material 26 with the molding surface facing downward. A nitrogen gas or ammonia introducing pipe 27 and a glow discharge generating coil 28 are arranged below the support 24, and a matching circuit is provided in the coil.
A high frequency power supply 30 is connected via 29. A cathode electrode 31 is arranged below the airtight chamber 20. A mixed target 32 of titanium and aluminum mixed in an area ratio of about 1: 1 is provided on the upper part of the electrode 31, and a cooling water pipe 33 is connected to the lower part. An argon gas introduction pipe 34 is disposed above the electrode 31, and a shutter 35 is disposed in the vicinity of above the target 32.

At the time of forming the aluminum titanium nitride (TiAlN) film, the mold base material 26 obtained as above is washed with acetone to remove the support.
After being supported by 24, the pressure inside the airtight chamber 20 was reduced to 1 × 10 ⁻⁵ Torr. Next, argon gas is supplied from the pipe 34 to 3 × 10 ⁻³ To
rr up to high frequency electric field (13.56MHz, 0.2k
(W · hr) is applied to generate argon glow discharge, and a negative bias (−50 V) is applied to the mold base material 26 by the bias power source 25 to perform sputter cleaning with argon ions. After that, while introducing argon gas from the pipe 34, a high frequency electric field (13.56MHz, 0.5kW ・ h) was applied to the cathode electrode 31.
r) is applied to generate a glow discharge of argon in the vicinity of the titanium / aluminum mixture target 32, and the titanium / aluminum mixture target is bombarded with argon ions to perform sputtering. Open the shutter 35 and pipe at the same time
Nitrogen gas was introduced at 5 × 10 ^-4 Torr by 27 and sprayed near the mold base material 26, and high frequency electric field (13.56MHz, 0.5kW) was applied to the coil 28.
・ Hr) is applied to form nitrogen plasma, and a negative bias (-50 V) is applied to the mold base material 26 by the bias electrode 25 to draw nitrogen ions into the mold base material 26 and reactive sputtering of a titanium-aluminum mixture. Then, an aluminum titanium nitride layer was formed on the surface of the mold base material 26. At this time, the temperature of the mold base material was 500 ° C. The thickness of the obtained aluminum titanium nitride layer was 1 μm. A similar aluminum titanium nitride layer was obtained by applying ammonia gas in place of the nitriding gas or applying a DC voltage to the cathode electrode in place of the high frequency electric field in the above example.

 In the same manner, No. 3 to No. 30 double nitride films were formed.

In the comparative example, a silicon carbide layer was formed on the molding surface of the mold base material in the same manner using the apparatus shown in FIG. At this time, the same amount of CH ₄ gas was introduced without introducing nitrogen gas, and a silicon target was used instead of the titanium / aluminum mixture target. The thickness of the silicon carbide layer was 1 μm.

Press-molding of lens with double-nitride film-covered mold: Using the mold thus obtained, a lens molding test was conducted by a molding apparatus shown in FIG.

In FIG. 4, reference numeral 51 denotes a vacuum chamber main body, 52 denotes a lid thereof, 53 denotes an upper die for molding an optical element, 54 denotes a lower die thereof, 55 denotes an upper die holder for holding down an upper die, and 56 denotes a trunk die. , 57 is a mold holder,
58 is a heater, 59 is a lifting rod for lifting the lower mold, 60 is an air cylinder for operating the lifting rod, 61 is an oil rotary pump, 62, 63, 64 are valves, 65 is an inert gas inflow pipe, 66
Is a valve, 67 is a leak pipe, 68 is a valve, 69 is a temperature sensor, 70 is a water cooling pipe, and 71 is a stand for supporting a vacuum chamber.

 The process of manufacturing the lens will be described below.

First, adjust the flint type optical glass (SF14) to a predetermined amount, place the spherical glass material in the mold cavity,
This is installed in the device.

After setting the mold into which the glass material has been placed in the apparatus, the lid 52 of the vacuum chamber 51 is closed, water is flowed through the water cooling pipe 70, and an electric current is passed through the heater 58. At this time, the nitrogen gas valves 66 and 68 are closed, and the exhaust system valves 62, 63 and 64 are also closed. The oil rotary pump 61 is always rotating.

Open the valve 62 and start evacuation. When it becomes 10 ^-2 Torr or less, close the valve 62 and open the valve 66 to introduce nitrogen gas into the vacuum chamber from the cylinder. When the temperature reaches a predetermined temperature, the air cylinder 60 is operated and pressurized at a pressure of 80 kg / cm ² for 5 minutes. After the pressure was removed, the cooling rate was cooled at -5 ° C / min to the transition point or lower, and then cooling was performed at a rate of -20 ° C / min or higher.When the temperature dropped to 200 ° C or lower, the valve 66 was closed. The air is introduced into the vacuum chamber 51 by opening the leak valve 63. Then, the lid 52 is opened, the upper mold retainer is removed, and the molded product is taken out.

As described above, the flint optical glass SF14 (softening point
Sp = 586 ° C., dislocation point Tg = 485 ° C.) were used to mold the lens 4 shown in FIG. FIG. 5 shows a molding condition, that is, a time-temperature relationship diagram at this time.

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

As described above, in the examples of the present invention, even when repeatedly used in press molding, good surface precision was sufficiently maintained, and an optical element having good surface precision was formed.

Although a flint type glass is used as the optical glass to be molded in the above-mentioned examples, other crown type glasses can be similarly molded with good accuracy.

In the above-described embodiment, the cemented carbide and sintered SiC are used as the mold base material. However, the mold base material is not limited to these two, and may be any material having high temperature and high strength.

In the above example, the double nitride film formed on the mold base material by the PVD method or the CVD method is used as it is, but the double nitride film is formed relatively thick by this method, and then the surface is mirror-polished. Can also be used. Further, even when a defect is generated on the surface by a number of presses, a good surface can be reproduced by such polishing.

Further, the atom ratio of the metal forming the double nitride film is not limited to the ratio of this embodiment, and the ratio can be changed appropriately by changing the mixing ratio of the target metal. Further, in the above-mentioned embodiment, AlN is always contained, but a combination not containing AlN is also possible. Examples of the present invention coated with a double nitride film containing no AlN are shown in Table 2 (No. 31).
~ 58).

Example 2 Production of Mold Coated with Double Nitride Film via Intermediate Layer: With respect to No. 29 and No. 30 described above, the molding surface of the mold base material was formed by the reactive sputtering method using the apparatus shown in FIG. An aluminum hafnium tantalum titanium nitride (AlHfTaTiN) layer was coated on top via an intermediate layer (AlHfTaTi).

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

The mold base material 26 obtained as described above was washed with acetone, and after being supported by the support 24, the inside of the airtight chamber 20 was filled with 1 × 10 ⁻⁵ To
The pressure was reduced to rr. Next, add 3 argon gas from the pipe 34.
Introduced up to × 10 ^-3 Torr and applied high frequency electric field (13.56M
Hz, 0.2 kW · hr) is applied to generate a glow discharge of argon, and a negative bias (-) is applied to the mold base material 26 by the bias power supply 25.
50 V) is applied to perform sputter cleaning with argon ions. After that, a high-frequency electric field (13.56 MHz, 0.5 μm) was applied to the cathode electrode 31 while introducing argon gas from the pipe 34.
5kW · hr) is applied to generate an argon glow discharge in the vicinity of the aluminum hafnium tantalum titanium target 32,
Sputtering is performed by bombarding the target 32 with argon ions. First, open the shutter 35 and set the middle layer to 0.
It was formed with a thickness of 2 μm. Next, nitrogen gas of 5 × 10 ⁻⁴ Torr was introduced by a pipe 27 and sprayed in the vicinity of the die base material 26, and a high frequency electric field (13.56 MHz, 0.5 kW · hr) was applied to the coil 28 to form nitrogen plasma. A negative bias (-50 V) is applied to the mold base material 26 by the bias electrode 25 to draw nitrogen ions into the mold base material 26, and reactive sputtering of aluminum hafnium tantalum titanium is performed to form aluminum nitride on the surface of the mold base material 26. A hafnium tantalum titanium layer was formed. At this time, the temperature of the mold base material was 500 ° C. The thickness of the obtained aluminum hafnium tantalum titanium nitride layer was 1 μm.
Similar aluminum hafnium tantalum nitride layers were obtained by applying ammonia gas instead of nitrogen gas or applying DC voltage to the cathode electrode instead of high-frequency electric field in the above-mentioned examples.

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

[Effects of the Invention] According to the present invention as described above, since the molding surface is covered with the double nitride film having the better oxidation resistance than the single metal nitride film, the accuracy in repeated press molding is improved. Little deterioration,
Further, there is provided a mold for molding an optical element having a long life which does not cause fusion with glass even when used at a particularly high temperature.

Furthermore, the Knoop hardness Hk of the double nitride film is about 2400 to 3000 kg / mm ² , and it is harder to scratch because it has higher hardness compared to the nitride film of a single metal. However, it is hard to be scratched, and therefore an optical element having good surface accuracy can be manufactured for a long period of time.

In addition, the mold of the present invention can be easily manufactured because a mold having good workability can be widely selected as a mold base material.

[Brief description of drawings]

1 and 2 are sectional views showing one embodiment of the optical element molding die according to the present invention. FIG. 1 shows a state before press molding, and FIG. 2 shows a state after press molding. FIG. 3 is a schematic view of a sputtering apparatus used for manufacturing the mold of the present invention. FIG. 4 is a sectional view showing a lens molding apparatus using the optical element molding die 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 nitride 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 ... Ammonia introduction pipe, 28 ... Glow discharge generating coil, 29 ... Matching circuit,
30 ... High frequency power source, 31 ... Cathode electrode, 32 ... Aluminum hafnium tantalum titanium target, 33 ... Cooling water pipe,
34 ... Argon gas introduction pipe, 35 ... Shutter, 51 ...
Vacuum tank body, 52 ... Lid, 53 ... Upper mold, 54 ... Lower mold, 55 ... Upper mold hold, 56 ... Body mold, 57 ... Mold holder, 58 ... Heater, 59
… Lifting rod, 60… Air cylinder, 61… Oil rotary pump,
62,63,64 ... Valve, 65 ... Inflow pipe, 66 ... Valve, 67 ...
Outflow pipe, 68 ... Valve, 69 ... Temperature sensor, 70 ... Water cooling pipe, 71 ... Stand.

Claims (4)

(57) [Claims] 1. An optical element molding die used for press molding of an optical element made of glass, wherein at least a molding surface of a mold base material is covered with a double nitride film. 2. The metal constituting the double nitride film is 5 to 95 atom%
Aluminum (Al) and the balance of boron (B), chromium (Cr), hafnium (Hf), niobium (Nb), tantalum (Ta), titanium (Ti), vanadium (V), tungsten (W), zirconium The optical element molding die according to claim 1, which is at least one selected from the group consisting of (Zr). 3. The optical element molding die according to claim 1, wherein the double nitride film is covered with an intermediate layer interposed therebetween. 4. The optical element molding die according to claim 3, wherein the intermediate layer is made of the same metal as the metal forming the double nitride film.