JP2612621B2 - 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 press forming dies have been proposed, such as metals, ceramics, and materials obtained by coating these materials with appropriate materials.

For example, JP-A-49-51112 discloses a mold using 13Cr martensitic steel.
No. 3 discloses a mold using silicon carbide (SiC) and a mold using silicon nitride (Si ₃ N ₄ ).
No. 46230 discloses a mold in which a hard metal is coated with a noble metal.

[Problems to be Solved by the Invention] However, the above 13Cr martensitic steel is liable to be oxidized, and there is a problem that Fe diffuses 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 hard to be oxidized, but at high temperatures, a certain degree of oxidation occurs and a SiO ₂ film is formed on the mold surface, so that fusion with glass tends to occur and the hardness is too high Therefore, there is a disadvantage that 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.

In view of the above, it is an object of the present invention to provide a long-life optical element molding die that can be easily manufactured with high precision and has less deterioration in precision 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 a molding surface of a mold base material has tantalum (Ta), boron (B), hafnium. (Hf), zirconium (Zr), vanadium (V),
Aluminum (Al), niobium (Nb), molybdenum (M
o), a mold for forming an optical element, characterized by being coated with a double carbonized film of at least two metals selected from the group consisting of chromium (Cr).

In the present invention, a “multi-carbide film” is a film in which a plurality of metals are mixed in a crystalline and / or amorphous carbide state, and includes, for example, a film made of TaC and TiC,
A film in which a so-called interstitial carbide structure such as C and (TaTi) ₂ C is mixed, and a film in which a metal element or carbon is mixed without being bonded to another element are also included. Hereinafter, TaC-TiC and the like mainly represent the metal composition of the double carbonized film meaning these films collectively.

As the form of the carbide contained in the multiple carbonized film, the usual
_{TaC, B 4 C, HfC,} ZrC, VC, Al 4 C 3, NbC, Mo 2 C, and Cr ₃ C _2, etc., etc. These so-called interstitial carbides and the like.

The composition of the double carbonized film can change the atomic ratio between metal and carbon within a considerable range. However, as a practical range, a metal content of about 30 to 50 atom% is preferable.

The thickness of the multiple carbonized film is appropriately set according to the manufacturing conditions.
A film thickness (preferably,
0.1 to 10 μm, more preferably about 1 μm).

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.

In order to coat the double carbonized film on the surface of the mold base material, 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.

In order to improve the adhesion to the mold base material, the multiple carbonized film is preferably coated via an intermediate layer, and the intermediate layer is preferably made of the same metal as the metal constituting the multiple carbonized film. More preferred.

The double carbonized film coated in this way has high oxidation resistance, especially at high temperatures, has extremely low adhesion to glass, and has good mold release properties. It can be applied well to molding using high melting glass, which is considered to be difficult to carry out precision molding industrially.Furthermore, the primary molded glass or molten glass is housed in a mold device and pressed. There is an advantage that an optical element with good accuracy can be obtained even when used repeatedly for manufacturing an optical element to be molded.

[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 of the optical element before press molding, and FIG.
The figure shows the state after molding of the optical element. In FIG. 1, reference numerals 1 and 2 denote a mold base material, 1-a and 2-a denote double carbonized films formed on a molding surface of the mold base material in contact with a glass material, and 3 denotes a glass material. Reference numeral 4 denotes 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.

Manufacture of mold coated with multiple carbonized film: The mold base material is made of cemented carbide [WC (90%) + Co (10%)] and sintered SiC, processed into a predetermined shape, and the lens molding surface is mirror-finished It has been processed. A mold according to the present invention was manufactured as follows by coating a forming surface of the mold base material with a double carbonized film. 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,
No. 1 to No. 30 are examples of the present invention.

Next, for the above Nos. 1 and 2, a titanium tantalum carbide layer (TaC-TiC) film was formed on the molding surface of the mold base material by a 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. Below the support 24, a methane and acetylene gas introduction pipe 27 and a glow discharge generating coil 28 are arranged.
The high-frequency power supply 30 is connected via the. A cathode power supply 31 is disposed below the hermetic chamber 20. A mixed target 32 of titanium and tantalum mixed at an area ratio of about 1: 1 is provided at an upper portion of the power supply 31, and a cooling water pipe 33 is connected to a lower portion. 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.

When forming a titanium tantalum carbide (TaC-TiC) film, the mold base material 26 obtained as described above is washed with acetone and supported by the support 24, and then the inside of the hermetic chamber 20 is 1 × 10 ^−5. The pressure was reduced to Torr. Next, argon gas (3 × 10
^-3 Torr) and a high frequency electric field (13.56 MHz,
0.2 kW · hr) to generate an argon glow discharge, and a bias power supply 25 applies a negative bias (−50) to the mold base material 26.
V) is applied to perform sputter cleaning using argon ions. Thereafter, a high-frequency electric field (13.56 MHz, 0.5 k
W · hr) to apply a titanium / tantalum mixture target 32
, A glow discharge of argon is generated in the vicinity of the target, and sputtering is performed by bombarding the titanium / tantalum mixture target with argon ions. The shutter 35 is opened, and at the same time, hydrocarbon gas (methane and acetylene) is introduced at 1 × 10 ⁻³ Torr through the pipe 27 and sprayed near the mold base material 26,
A high-frequency electric field (13.56 MHz, 0.5 kW · hr) is applied to the coil 28 to form carbon plasma, and a negative bias (−50 V) is applied to the mold base material 26 by the bias electrode 25 to remove carbon ions from the mold base material 26. Then, reactive sputtering of a titanium / tantalum mixture was performed to form a titanium tantalum carbide layer on the surface of the mold base material 26. At this time, the temperature of the mold base material is 300 ° C
Met. The thickness of the obtained titanium tantalum carbide layer is 1 μm.
m. 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 the high-frequency electric field.

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

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, a silicon target was used instead of the titanium / aluminum mixture target. The thickness of the silicon carbide layer is 1
μm.

Press molding of lens by double carbonized film coating 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
Denotes a valve, 67 denotes a leak pipe, 68 denotes a valve, 69 denotes a temperature sensor, 70 denotes a water cooling pipe, and 71 denotes a base for supporting a vacuum tank.

 The steps for manufacturing the lens will be described below.

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

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

The valve 62 is opened and exhaust is started. When the pressure becomes 10 ^-2 Torr or less, the valve 62 is closed, the valve 66 is opened, and nitrogen gas is introduced from the cylinder into the vacuum chamber. 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.

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

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

In the above embodiment, a flint-based optical glass is used as the optical glass to be molded. However, other types of glass such as a crown-based glass 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 embodiment, the double carbonized film formed on the mold base material by the PVD method or the CVD method is used as it is.However, the double carbonized film is formed relatively thick by the 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 constituting the multiple carbonized film is not limited to the ratio of this embodiment, and can be changed as appropriate by changing the mixing ratio of the target metal.

Example 2 Manufacture of a mold coated with a multiple carbonized film via an intermediate layer: For No. 27 and No. 28, the molding surface of the mold base material by a reactive sputtering method using the apparatus shown in FIG. On top, a tantalum titanium hafnium carbide (25TaC-25TiC-50HfC) layer was coated via an intermediate layer (TaTiHf).

However, in FIG. 3, a tantalum titanium hafnium target mixed in a ratio of tantalum: titanium: hafnium = 1: 2: 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, argon gas (3
× 10 ^-3 Torr) and a high frequency electric field (13.56M
Hz, 0.2 kW · hr) to generate an argon glow discharge, and a bias power supply 25 applies a negative bias (−
50V) is applied to perform sputter cleaning using 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.
5 kW · hr) is applied to generate a glow discharge of argon in the vicinity of the tantalum titanium hafnium target 32, and the target 32 is bombarded with argon ions to perform sputtering. First, open the shutter 35 to make the middle layer 0.2 μm
The thickness was formed. Next, 1 × 10 ⁻³ Torr of hydrocarbon gas (methane and acetylene) was introduced through the pipe 27 and the mold base material was introduced.
26, and a high-frequency electric field (13.56 MH)
z, 0.5 kW · hr) to form a carbon plasma, and apply a negative bias (−50 V) to the mold base material 26 by the bias electrode 25 to draw carbon ions into the mold base material 26 while applying tantalum titanium hafnium. A tantalum titanium hafnium carbide layer was formed on the surface of the mold base material 26 by performing reactive sputtering. At this time, the temperature of the mold base material was 300 ° C. The metal content in the obtained tantalum carbide titanium hafnium layer is 50 at
om%. The thickness of the multiple carbonized film was 1 μm. In the above embodiment, a similar tantalum titanium hafnium carbide layer was obtained even when a DC voltage was applied to the cathode electrode instead of the high-frequency electric field.

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 forming surface is covered with a double carbonized film having better oxidation resistance than a single metal carbonized film, the accuracy in repeated press forming is improved. Less degradation,
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, double carbide film is Knoop hardness Hk is 2400~3000kg / mm ² approximately, as compared with carbide film of a single metal hardly scratched because of high hardness, repeated cleaning in use for this Even when the optical element is hardly damaged, 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 the 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 carbonized film, 3 ... glass material, 4 ... molded lens, 20 ... airtight chamber, 21 ... exhaust port, 22 ... ... heater, 23 ... heater power supply, 24 ... mold base material support, 25 ... bias power supply, 26 ... mold base material, 27 ... hydrocarbon gas introduction pipe, 28 ... glow discharge generating coil 29 Matching circuit 30 High-frequency power supply 31 Cathode power supply 32 Target 33 Pipe for cooling water 34 Argon gas introduction pipe 35 Shutter 51 Vacuum Tank body, 52 ... Lid, 53 ... Upper mold, 54 ... Lower mold, 55 ... Upper mold retainer, 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 Nsa, 70 ...... water-cooled pipe, 71 ...... table.

Claims (1)

(57) [Claims] 1. An optical element molding die used for press molding an optical element made of glass, wherein at least a molding surface of a mold base material has tantalum (Ta), boron (B), hafnium (Hf), zirconium (Zr). , Vanadium (V), aluminum (Al), niobium (Nb), molybdenum (Mo), and chromium (Cr). For forming optical elements.