JP3308720B2 - Mold for optical element molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold used for producing an optical element made of glass, such as a lens or a prism, by pressing a glass material.

[0002]

2. Description of the Related Art The technique of manufacturing a lens by press molding a glass material without the need for a polishing step eliminates the complicated steps required in the conventional manufacturing and makes it possible to manufacture a lens simply and inexpensively. Recently, not only lenses but also prisms and other optical elements made of glass have been used.

The properties required of a mold used for press molding of such a glass optical element include excellent hardness, heat resistance, mold releasability, mirror workability, and the like. Conventionally, many proposals have been made for metal, ceramics, and materials coated with them as mold materials of this kind. Some examples are given in JP-A-60-1985.
No. 246230 is made of a material obtained by coating a hard metal with a noble metal, as disclosed in Japanese Patent Application Laid-Open Nos. 61-183134 and 61-28103.
Japanese Patent Application Laid-Open No. 60-11838 discloses a diamond thin film or a diamond-like carbon film.
A coating with a titanium nitride film, a coating with tantalum nitride in JP-A-64-52623, and a coating with aluminum nitride in JP-A-61-197430.

[0004]

However, a mold coated with a noble metal does not easily fuse, but has the drawback that it is extremely soft and easily damaged and deformed. Further, although the diamond thin film has high hardness and excellent thermal stability, it is a polycrystalline film and therefore has a large surface roughness and needs to be mirror-finished. A mold using a DLC film, an aC: H film, and a hard carbon film has good mold-releasing property and does not cause fusion of glass, but when the molding operation is repeated several hundred times or more, In some cases, the film is partially peeled off, and a sufficient molding performance cannot be obtained in a molded product.

[0005] As one of the causes, an alloy is formed between the sintering aid in the sintered body represented by Co of WC-Co and the above-mentioned film by diffusion. Such a portion causes fusion of the glass at the time of molding and reacts with components contained in the glass to produce a precipitate, thereby causing deterioration in durability.

A mold coated with TiN or TaN has high hardness, but at 600 ° C. or higher, it is easily oxidized even in a nitrogen atmosphere, its surface becomes an oxide, and it easily fuses with glass. A mold coated with AlN is excellent in oxidation resistance, but has a drawback that the mold is deformed during repeated molding due to insufficient hardness. As described above, an optical element molding die excellent in moldability, durability, and economy has not been realized.

[0007]

According to the present invention, there is provided a combination of at least a molding surface of a mold base material, one of which is made of a material having excellent oxidation resistance and the other of which is made of a hard material.
Each of them is alternately stacked with a thickness of 1 to 3 nm to form 0.5 to 3
By forming a layered film having a thickness of μm, a mold having excellent oxidation resistance and high hardness is realized.

Specifically, materials having excellent oxidation resistance include aluminum nitride (AlN), and materials having high hardness include titanium nitride (TiN) and tantalum nitride (TaN). Note that tantalum nitride has better oxidation resistance than titanium nitride.

[0009] It is 0.5-
Since it is a 3 μm film, the film formation is 167 to 300
It becomes 0 times. Hereinafter, the present invention will be described using a combination of TiN and AlN as an example.

When a thin AlN layer is sandwiched between TiN layers from above and below, the crystal lattice of AlN is distorted and changes from hexagonal to cubic. Cubic AlN is stable and increases in hardness under ultra-high pressure (about 25 GPa).

[0011] The hardness also increases due to residual strain generated at the joint interface between TiN and AlN. For these two reasons, in the film of the present invention, a film having a hardness higher than TiN (about 2
Hv4000). Usually, TiN is 600
Oxidation starts at around 100 ° C.
Oxidation does not progress due to being sandwiched between AlN layers that do not oxidize to near 0 ° C., so that the oxidation start temperature is equivalent to that of the AlN film.

[0012]

【Example】

[Examples 1 to 20, Comparative Examples 1 to 26] Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of the mold according to the present invention. In FIG. 1, 1 indicates a mold base material, and 2 indicates a laminated film formed on a molding surface of the mold base material.

In the present invention, as a base material, a cemented carbide, cermet, or SiC can be used. These base materials are formed into a desired outer shape by processing such as cutting, grinding, and polishing, and the formed surface is particularly finished to a desired surface accuracy.

In order to form a laminated film on the surface of the base material 1, an ion plating method, a reactive sputtering method or the like, which is a kind of PVD method, is used. Switching between the two or three film-forming substances is performed by switching a shutter provided in the chamber.

Table 1 shows the molds used in this embodiment. In the table, the oxidation start temperature is a temperature at which the weight starts to increase in the thermal analysis.

Since the laminated film of the present invention has high oxidation resistance at high temperatures and low fusion bonding property with glass and good releasability, it is possible to obtain an optical element with good precision even when used repeatedly. Can be.

First, the mold base material was cut, and then the molding surface corresponding to the functional surface (optical surface) of the molding optical element was machined to a desired surface accuracy. The molding surface of the mold base material is concave,
First, it is processed to the desired curvature by grinding with a diamond grindstone, then it is polished using diamond powder with a particle size of 1 μm, and finished to the surface shape accuracy of about one Newton ring and the surface roughness accuracy of about R _max 0.02 μm. Was.

Next, the laminated films shown in Table 1 were formed on the molding surface of the mold base material by a reactive sputtering method using the apparatus shown in FIG.

In FIG. 2, reference numeral 3 denotes an airtight chamber of the sputtering apparatus. An exhaust port 4 is connected to the hermetic chamber 3, and the exhaust port 4 is connected to a pressure reducing source (not shown). A heater 5 is arranged in the upper part of the hermetic chamber 3, and a heater power supply 6 is connected to the heater. A mold base material support 7 is disposed below the heater 5, and a mold base material bias power supply 8 is connected to the support. The mold base material 9 is supported on the support 7 with the molding surface facing downward. A pipe 10 for introducing nitrogen gas or ammonia below the support 7;
A glow discharge generating coil 11 is arranged, and a high frequency power supply 13 is connected to the coil via a matching circuit 12. At the lower part of the hermetic chamber 3, cathode electrodes 14, 15,
16 are arranged. A titanium target 17 and an aluminum target 1 are provided on the electrodes 14, 15, and 16 respectively.
8, a tantalum target 19 is provided, and cooling water pipes 20, 21, 22 are connected to the lower portion, respectively. An argon gas introduction pipe 23 is arranged above the electrodes 14, 15, 16.

At the time of forming the laminated film, the mold base material 9 obtained as described above was washed with acetone, and after being supported by the support 7, the pressure in the hermetic chamber 3 was reduced to 2 × 10 ^-6 Torr. Next, argon gas was introduced from the pipe 23, and a high-frequency electric field (13.56 MHz, 0.2 kW
hr) to generate glow discharge of argon, and apply a negative bias (−50 V) to the mold base material 9 by the bias power supply 8 to perform sputter cleaning with argon ions. Thereafter, a high-frequency electric field (1) is applied to the cathode electrodes 14, 15, 16 while introducing argon gas from the pipe 23.
3.56 MHz, 0.5 kW · hr) to generate glow discharge of argon in the vicinity of each of the metal targets 17, 18, 19, and to generate a glow discharge of each of the targets 17, 18, 1.
9 is subjected to sputtering by bombarding with argon ions.

A shutter (not shown) was used so that sputtering was performed alternately from each target. The material of each laminated film and the thickness of each layer shown in Table 1 can be obtained according to the opening / closing speed and order of the shutter.

Simultaneously with the sputtering, a nitrogen gas is blown to the vicinity of the mold base material 9 by a pipe 10, and a high-frequency electric field (13.56 MHz, 0.5 kW · hr) is applied to the coil 11 to form a nitrogen plasma and a bias power supply. 8, a negative bias (−50 V) is applied to the mold base material 9 so that nitrogen ions and sputtered metal ions are alternately reactive-sputtered with aluminum, titanium and tantalum while drawing nitrogen ions and sputtered metal ions into the mold base material 9. A laminated film was formed on the surface. At this time, the temperature of the mold base material was 500 ° C. Table 1 shows the thickness of the obtained laminated film. In the above embodiment, a similar laminated film was obtained by applying ammonia gas instead of nitrogen gas, or applying DC voltage to the cathode electrode instead of the high-frequency electric field.

Next, the optical element was molded by using the mold shown in Table 1 obtained as described above.

The glass is borosilicate glass SK12 (n
d = 1.58313, vd = 59.4, transition point Tg = 5
50 ° C., yield point At = 588 ° C., see Table 2 for composition) and lanthanum glass LaK12 (nd = 1.67979)
0, νd = 55.3, transition point Tg = 554 ° C., yield point A
Using t = 596 ° C. and composition as shown in Table 3), a ball lens was formed.

FIG. 3 shows an outline of the apparatus used for the molding test. In FIG. 3, 24 is a chamber, 25 is an upper axis,
26 is a lower shaft, 27 is a block containing a heater (heater block), 28 is a heater block, 29 is an upper mold, 30 is a lower mold, 31 is glass, and 32 is a hydraulic cylinder.

After the chamber 24 is evacuated by a vacuum pump (not shown), N ₂ gas is introduced to make the inside of the chamber 24 an N ₂ atmosphere, and the upper and lower dies 29 and 30 are heated by the heater blocks 27 and 28. At a temperature corresponding to 10 ⁻⁹ d · Pa · s in the viscosity of the glass to be formed (SK12: 6
30 ° C., LaK12: 615 ° C.), the upper shaft 25 is pulled up by the hydraulic cylinder 32 and
A molding material (ball lens) was placed on the above by an automatic hand (not shown). After holding for 1 minute at the mold temperature as it is, the upper shaft 25 is lowered by the hydraulic cylinder 32, and the ball lens is moved with the force of 3000N by the upper mold 29 and the lower mold 30 for 3 minutes.
Pressed for minutes. Thereafter, cooling is performed at 50 ° C./min.
When the upper and lower mold temperatures reach 500 ° C., the upper mold 29 is raised, the molded article 31 on the lower mold 30 is taken out by an automatic hand (not shown), and then the molded article 31 is passed through a replacement device (not shown).
Was taken out of the chamber 24. The upper and lower molds were heated again, and the above operation was repeated, and 5000 shots were pressed.

Table 4 shows the results of the SK12 press test.

Table 4 shows that the thickness of each layer needs to be 1 to 3 nm. Note that a film thinner than 1 nm was not tested because it was difficult to prepare.

When the thickness of each layer is more than 3 nm, the AlN crystal lattice is not distorted and the hardness is not increased, so that the mold is deformed.

It is necessary that the thickness of the laminated film is 0.5 to 3 μm.

If the thickness of the laminated film is smaller than 0.5 μm, the laminated film does not have sufficient hardness, and the mold is deformed. On the other hand, when the thickness is more than 3 μm, the laminated film is easily peeled.

Similar results were obtained in the LaK12 press test.

Examples 21 to 40 and Comparative Examples 27 to 46
A mold in which an intermediate layer was formed between the laminated film and the base material was prepared, and a molding test was performed in the same manner as in Examples 1 to 20.

The material of the intermediate layer is titanium, nickel, chromium, tantalum, molybdenum, vanadium, tungsten, zirconia, hafnium or iron.

Table 5 shows the molds used for molding. Table 6 shows the molding test results. In the molds of Examples 1 to 20, 500
Although the 0 shot molding shows a good result, the mold provided with the intermediate layer did not peel off the film even when the 5000 shot molding test was repeated. That is, by providing the intermediate layer, the adhesion between the laminated film and the mold is improved, and the durability of the mold is greatly improved.

[Examples 41 to 60, Comparative Examples 47 to 68]
On the laminated film, a diamond thin film, a diamond-like carbon film (hereinafter, referred to as a DLC film), a hydrogenated amorphous carbon film (hereinafter, referred to as an aC: H film), and a hard carbon film were formed.

The diamond (thin) film is formed by a microwave plasma CVD method, a hot filament CVD method, a plasma jet method, an electron cyclotron resonance plasma CVD method or the like, and a DLC film, an aC: H film and a hard carbon film are formed.
It is formed by a plasma CVD method, an ion beam sputtering method, an ion beam evaporation method, a plasma sputtering method, or the like. Examples of the gas used for forming the film include hydrocarbons such as methane, ethane, propane, ethylene, benzene, and acetylene, which are carbon-containing gases; halogenated hydrocarbons such as methylene chloride, carbon tetrachloride, chloroform, and trichloroethane;
Alcohols such as methyl alcohol and ethyl alcohol; ketones such as (CH ₃ ) ₂ CO and (C ₆ H ₅ ) ₂ CO; gases such as CO and CO ₂ ;
_A mixture of gases such as ₂ , H ₂ , O ₂ , H ₂ O, and Ar may be used.

Table 7 shows the created models. A molding test was performed using the molds shown in Table 7 in the same manner as in Examples 1 to 20. Table 8 shows the results.

In Examples 1 to 20, the glass after molding was cooled to 500 ° C. in order to take out the glass, since at 500 ° C. or higher, the mold and the glass were stuck and did not come off. In Examples 41 to 60, since the adhesion between the mold and the glass was extremely low, it was possible to take out at 550 ° C.
As described above, by using the films of Examples 41 to 60, the cooling time can be reduced (tact reduction), and the cost is reduced.

That is, in Examples 41 to 60, not only the durability of the mold is increased, but also the effect of cost reduction by shortening the tact time is obtained.

Further, since there was no influence of the base material, there was no diffusion between the base material components, and no peeling or fusion occurred (see Comparative Examples 57 and 58).

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

[0046]

[Table 4]

[0047]

[Table 5]

[0048]

[Table 6]

[0049]

[Table 7]

[0050]

[Table 8]

[0051]

As described above, according to the present invention,
The hardness and oxidation resistance of the mold are obtained by alternately stacking at least two types of layers having a thickness of 1 to 3 nm on a molding surface of a mold base material of an optical element molding mold to a thickness of 0.5 to 3 μm. The performance was greatly improved. Even if press molding is repeated for a long time using this mold, an extremely durable optical element molding die which does not cause defects such as film peeling, cracking, scratching, and fusion due to oxidation can be obtained.

According to the second aspect of the present invention, by providing an intermediate layer between the laminated film and the mold base material, the adhesion between the laminated film and the mold base material is improved, and continuous molding for a longer time can be performed. It becomes possible.

According to the third aspect of the present invention, the mold is separated from the glass by coating any one of a diamond film, a diamond-like carbon film, a hydrogenated amorphous carbon film and a hard carbon film on the laminated film. The method is improved, the mold release at a higher temperature becomes possible, and the cost can be reduced by shortening the cooling time, that is, shortening the tact time. Further, the durability of the carbon-based film itself is also improved by the laminated film.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of the present invention.

FIG. 2 is a schematic sectional view showing an apparatus used for forming a laminated film in manufacturing a mold according to the present invention.

FIG. 3 is a schematic sectional view of a press forming apparatus for an optical element.

[Explanation of symbols]

 Reference Signs List 1 type base material 2 laminated film 3 airtight chamber 4 exhaust port 5 heater 6 heater power supply 7 type base material support 8 type base material bias power supply 9 type base material 10 nitrogen gas or ammonia introduction pipe 11 glow discharge generating coil 12 matching Circuit 13 High frequency power supply 14 Cathode electrode for titanium target 15 Cathode electrode for aluminum target 16 Cathode electrode for tantalum target 17 Titanium target 18 Aluminum target 19 Tantalum target 20 Pipe for cooling water 21 Pipe for cooling water 22 Pipe for cooling water 23 Argon gas introduction Pipe 24 Chamber 25 Upper shaft 26 Lower shaft 27 Heater block 28 Heater block 29 Upper die 30 Lower die 31 Glass 32 Hydraulic cylinder

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C03B 40/02 C03B 11/00 C03B 11/08

Claims (8)

(57) [Claims] 1. An optical element molding die used for press molding of an optical element made of glass, wherein at least two types of layers having a thickness of 1 to 3 nm are alternately superposed on at least a molding surface of the mold base material. An optical element molding die, wherein a laminated film having a thickness of 3 μm is formed. 2. The optical element according to claim 1, further comprising a film selected from the group consisting of a diamond film, a diamond-like carbon film, a hydrogenated amorphous carbon film, and a hard carbon film. Mold for molding. 3. The laminated film is made of aluminum nitride (Al).
3. The mold for molding an optical element according to claim 1, wherein N) and titanium nitride (TiN) are alternately stacked. 4. The laminated film is made of tantalum nitride (TaN).
3. The mold for molding an optical element according to claim 1, wherein the mold is formed by alternately stacking titanium nitride and titanium nitride (TiN). 5. The laminated film is made of tantalum nitride (TaN).
3. The mold for molding an optical element according to claim 1, wherein aluminum and aluminum nitride (AlN) are alternately stacked. 6. The laminated film is made of tantalum nitride (TaN).
And titanium nitride (TiN) and aluminum nitride (AlN)
3. The mold for molding an optical element according to claim 1, wherein 7. The optical element molding die according to claim 1, wherein an intermediate layer is further provided between the laminated film and the mold base material. 8. The intermediate layer is made of titanium (Ti), nickel (Ni), chromium (Cr), tantalum (Ta), molybdenum (Mo), vanadium (V), tungsten (W), zirconium (Zi), Hafnium (Hf),
8. The mold for molding an optical element according to claim 1, wherein the mold is made of one element selected from the group consisting of iron (Fe).