JP2002114526A - Method for manufacturing molding die for optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve releasing property as a molding die member. SOLUTION: In this method for forming a molding die for an optical element to deposit at least a hard carbon film as a release layer on the molding face by an ion beam vapor deposition method, the hard carbon film is deposited under the conditions of 6 to 21 kV acceleration voltage in the initial stage of film deposition and 0.4 to 4 kV acceleration voltage in the final stage of film deposition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art The technology of manufacturing a lens by press molding a glass material without the need for a polishing step eliminates the complicated steps required in conventional manufacturing, and makes it easy and inexpensive to manufacture a lens. In recent years, it has been used for manufacturing not only lenses but also optical elements made of prisms and other glasses.

[0003] The properties required of such a mold used for press molding of a glass optical element include hardness,
It is excellent in heat resistance, mold release properties, mirror workability and the like. Conventionally, many proposals have been made for this type of mold material, such as metals, ceramics, and materials coated with them.

[0004] To give some examples, see JP-A-49-49
No. 51112 discloses a 13Cr martensitic steel,
JP-A-52-45613 discloses SiC and Si ₃
N ₄ is, in JP-A-60-246230, the coating material of the noble metal in cemented carbide, also, JP 6
1-1183134, JP-A-61-281030 and JP-A-1-301864, respectively,
JP-A-64-83529 proposes a material in which a diamond thin film or a diamond-like carbon film is coated with a hard carbon film.

In Japanese Patent Publication No. 2-31012,
It has been proposed to form a carbon film of 5 to 500 nm on either the lens or the mold. Further, according to Japanese Patent Application Laid-Open No. 6-72728 filed by the present inventors,
By using a carbon ion beam of high ion energy to form a mixing layer made of carbon and at least one or more elements constituting an intermediate layer formed on the mold base material or the base material surface, peeling and cracking of the film It describes a method for producing a mold that does not cause the occurrence of.

[0006]

However, 13 martensitic steel has a disadvantage that it is easily oxidized, and furthermore, Fe diffuses into the glass at a high temperature and the glass is colored. SiC
And Si ₃ N ₄ are generally considered to be hardly oxidized. However, at high temperatures, oxidation occurs, SiO ₂ is formed on the surface, and glass fusion occurs. A material coated with a noble metal does not easily fuse, but has a disadvantage that it is easily damaged and easily deformed because it is extremely soft.

In general, a diamond-like carbon film, a
-C: The mold using the H film and the hard carbon film has good mold-releasability between the mold and the glass and is unlikely to cause fusion with the glass. However, the adhesion between the mold and the film is generally low, and the molding operation is difficult. When repeated several hundred times or more, the film is partially peeled off, and there is a problem in durability such that a molded product may not have sufficient molding performance. Further, the diamond thin film has high hardness and excellent thermal stability, but has a smaller shape than amorphous carbon films such as the diamond-like carbon film, aC: H film and hard carbon film. The mold releasability between glass and glass is poor, and further improvement in mold releasability has been desired.

In Japanese Patent Application Laid-Open No. Hei 1-301864, a film made of diamond crystal, graphite crystal and amorphous carbon is formed at a carbon source gas concentration of 3% or more, and the maximum surface roughness is set to 20 nm or less. Although it has been proposed, the presence of graphite crystals in the film
Deterioration of hardness and oxidation resistance occurs, which causes deterioration of mold durability.

Further, the carbon film obtained by the forming method (vacuum vapor deposition method) used in the example of Japanese Patent Publication No. 2-31012 generally has a weak adhesion between the film and the substrate, and is difficult to form. There may be a problem in durability such as peeling of the film inside.

The method described in Japanese Patent Application Laid-Open No. 6-72728 is a preferable method as compared with other methods for manufacturing a mold for molding an optical element.
C: Compared to a mold using an H film or a hard carbon film, the mold releasability may be inferior, and glass with low strength, a thin lens with a large diameter, a lens with a large thickness ratio, etc. may cause glass breakage. It has been desired to further improve the releasability.

The present invention has been made based on the above circumstances, and an object of the present invention is to further improve the releasability of the problem.

[0012]

Therefore, in the present invention,
In a method of forming an optical element molding die in which at least a hard carbon film is formed as a release layer on a molding surface by an ion beam evaporation method, an acceleration voltage of 6 to
It is characterized in that a film is formed by applying an acceleration voltage of 0.4 to 4 kV at the end of the film formation at 21 kV.

In this case, as an embodiment of the present invention,
When forming the film at an acceleration voltage of 6 to 21 kV at the initial stage of film formation, the film thickness is set to 10 to 80 nm, and at the end of the film formation, the film thickness at the acceleration voltage of 0.4 to 4 kV is set to 5 to 5
It is effective to set the acceleration voltage to 0 nm and to change the acceleration voltage in two or more steps.

[0014]

Next, the operation of the present invention will be described below, together with the knowledge obtained when the present invention is carried out. In view of the problems of the conventional optical element molding die, the present inventor continued detailed experiments on the formation conditions of the hard carbon film formed as the release layer by the ion beam evaporation method. The effect of the acceleration voltage on the molding performance was clarified.

That is, in a method of manufacturing an optical element molding die in which at least a hard carbon film is formed as a release layer on a molding surface by an ion beam evaporation method, an acceleration voltage of 6 to 21 kV is applied at the initial stage of forming the hard carbon film. By applying an accelerating voltage of 0.4 to 4 kV at the end of film formation and forming a film, there is no fusion with glass, high hardness, excellent surface smoothness, and high mold durability. They have found that an optical element molding die can be realized.

Conventional hard carbon films and diamond crystal thin films containing an amorphous component as a main component have smaller adhesion to glass and are superior in releasability than other ceramic and metal thin films. The adhesion between the base material and the film was weak, and the film was sometimes peeled off due to the stress of the film, the difference in the coefficient of thermal expansion, and the pressure during molding. This is because carbon materials such as hard carbon film and diamond crystal thin film have good releasability from glass, but these films generally have large film stress, and due to heat and molding force, It is considered that peeling easily occurs.

According to the method described in JP-A-6-72728, carbon ions can be ion-implanted to increase the adhesion between the film and the mold base material. was there. This is because, due to the ion implantation, carbon atoms penetrate into the mold base material, thereby improving the adhesion between the film and the mold base material, but the proportion of carbon atoms present on the outermost surface of the mold decreases. In addition, it is considered that the releasability from glass deteriorates.

The inventors of the present invention have repeatedly studied the conditions for forming the hard carbon film by the ion beam evaporation method.
It has been found that high releasability and high film adhesion are simultaneously realized by applying a voltage of 21 kV and applying an acceleration voltage of 0.4 to 4 kV at the end of film formation to form a film.

As a result, the present invention has been problematic in terms of mold releasability and durability, particularly in the case of large-diameter glass lenses, low-strength glass lenses, thin-wall glass lenses, and high-thickness glass lenses. It is most suitable for the molding of the lens.

[0020]

Embodiments of the present invention will be specifically described below with reference to the drawings. Here, FIG. 1 shows a schematic cross section of the optical element molding die of the present invention. In the figure, reference numeral 11 denotes a mold base material having a hard carbon film 13 on a molding surface. Although FIG. 1 shows the convex lens molding die,
In the present invention, the present invention is not limited to a convex lens molding die, but can be used for a concave lens molding die, an aspherical lens molding die, a cylindrical lens molding die, and the like.

The hard carbon film referred to in the present invention is also called a diamond-like carbon film because it is basically amorphous, has high hardness and high transparency in the infrared region. is there. Since this hard carbon film is amorphous, it has a very smooth surface, and by being formed on the surface of the mold base material, it has the same or higher surface smoothness as that of the mold base material. Smoothness can be obtained.

Although the hard carbon film usually does not have any crystallinity, it can be measured in a fine region (n
When observing (m order) in detail, microcrystalline diamond or graphite having a size of about several nm may be observed. The amount of these crystallites is also very difficult to estimate, but seems to be at most a few percent of the total volume.

The "hard carbon film" referred to in the present invention is a carbon film containing only a carbon crystal phase (diamond or graphite) of almost negligible amount or less. For forming this hard carbon film, an ion beam evaporation method is used. The ion beam deposition method uses a carbon source gas and
Diluent gas such as hydrogen, oxygen, chlorine, fluorine, rare gas,
By applying a hot filament or high frequency, and further applying a magnetic field, etc., it is turned into plasma, and from this plasma, ions are accelerated using an electric field to form an ion beam, and this ion beam is irradiated onto a mold base material. And forming a hard carbon film on the molding surface.

At this time, the acceleration voltage is set to 6 to 21 at the beginning of the film formation.
A voltage of 0.4 to 4 kV is applied at the end of film formation to form a hard carbon film. By increasing the acceleration voltage of the ion beam at the early stage of film formation, the adhesion between the mold base material and the hard carbon film can be increased, and peeling of the film can be prevented. By lowering the acceleration voltage at the end of film formation, It increases the carbon concentration on the molding surface and improves the releasability. For example, the hard carbon film formed at the end of film formation becomes a “release layer”, and the layer of the hard carbon film formed at the beginning of film formation has a good adhesion between the “release layer” and the mold base material. It acts as an “intermediate layer” for

The accelerating voltage at the initial stage of film formation is 6 to 2
1 kV, preferably 7-18 kV, optimally 8-15 k
V. If the acceleration voltage at the initial stage of film formation is lower than 6 kV, the adhesion between the mold base material and the hard carbon film is low, and there is a fear that the film may peel off. If the voltage is higher than 21 kV, a layer having a small amount of carbon atoms is formed, and peeling may occur between the hard carbon film formed at an early stage of the film formation and the hard carbon film formed at the end of the film formation. is there. Further, the film thickness when forming the film at an acceleration voltage of 6 to 21 kV in the initial stage of film formation is 10 to 10 kV.
80 nm, preferably 20 to 50 nm. 10 nm
If it is less than 30, sufficient adhesion may not be obtained, and if it is more than 80 nm, the surface roughness of the mold material may be deteriorated.

When the film thickness is larger than 80 nm, the surface roughness of the mold material deteriorates because the film is formed at a high accelerating voltage. This is because fine roughness is generated. As a result, when used for an optical element that requires particularly high surface properties, sufficient optical characteristics may not be obtained.

The accelerating voltage at the end of the film formation is 0.4 to 4
kV, preferably 0.5-3 kV, optimally 0.8-2
kV. If the acceleration voltage at the end of the film formation is lower than 0.4 kV, the hard carbon film cannot have sufficient hardness, is likely to be damaged during molding, and the surface properties of the molded product may be deteriorated. On the other hand, if it is larger than 4 kV, the carbon concentration on the molding surface becomes low, so that the releasability is deteriorated and the glass may be broken.

The thickness of the hard carbon film is 20 nm.
Not less than 200 nm, preferably not less than 30 nm and 10
0 nm or less, optimally 40 nm or more and 80 nm or less. If the thickness is more than 200 nm, film peeling or the like is likely to occur, and the mold durability may deteriorate. If the thickness is less than 20 nm, sufficient releasability may not be obtained.

In the final stage of the film formation, the accelerating voltage is set to 0.4 to
At 4 kV, the film thickness is 5 to 50 nm, preferably 10 to 40 nm, and most preferably 15 to 35 nm.
This is because if the thickness is less than 5 nm, sufficient releasability may not be obtained, and if the thickness is more than 50 nm, film peeling or the like is likely to occur, and mold durability may deteriorate.

Further, the accelerating voltage is set in two or more stages, optimally in three stages.
Change more than steps. The acceleration voltage is set to 6 to 21 at the beginning of film formation.
In addition to the so-called two steps of kV and 0.4 to 4 kV at the end of film formation, the acceleration voltage may be reduced stepwise between the initial stage and the end of film formation. For example, if the acceleration voltage is 15 kV
It can be changed stepwise, for example, 10 kV → 5 kV → 2 kV.

As in this case, when the acceleration voltage is gradually reduced, the adhesion between the mold base material and the film tends to be improved. Even when the accelerating voltage is changed stepwise, increasing the accelerating voltage on the way is problematic in terms of improving the adhesion, and conversely, it may cause peeling of the film, so it is better to avoid it.

In the formation of the hard carbon film by the ion beam evaporation method of the present invention, various carbon-containing gases and liquid organic compounds can be vaporized and used as a carbon source. As the liquid organic compound, alcohols such as methanol and ethanol, ketones such as acetone, aromatic hydrocarbons such as benzene, ethers such as dimethyl ether, and organic acids such as formic acid and acetic acid can be used. As the carbon-containing gas, hydrocarbon gas such as methane, ethane, ethylene, and acetylene, carbon monoxide, and halogenated carbon can be used.

The mold base material used in the present invention is alumina
Oxide ceramics such as zirconia, silicon carbide
Carbide / nitride-based ceramics such as silicon nitride / titanium carbide / titanium nitride / tungsten carbide; furthermore, WC-based hard alloys and metals such as molybdenum / tungsten / tantalum can be used. The shape of the mold base material (substrate)
It can be arbitrarily determined depending on the shape of the molding device and the molded lens.For example, when molding a lens, the molding surface is
A curved surface is formed in accordance with the curvature of the lens diameter, and the hard carbon film is formed on the curved surface by using an ion beam evaporation method.

The hard carbon film may be formed directly on the mold base material, but preferably, an intermediate layer is formed on the mold base material,
It is preferable to form a hard carbon film thereon. This is because cemented carbide such as WC-Co used as a mold base material, Si
In a sintered body such as C and Si ₃ N ₄ , missing particles and voids are unavoidable, and holes of several μm or more are present on the surface. Therefore, when a hard carbon film is formed on such a surface, This is because an extremely thin portion may be formed in the hole.

In such a portion, the adhesion of the hard carbon film formed thereon is reduced, and the portion tends to be a starting point of peeling and cracking of the film. For this reason, it is desirable to fill the hole in the surface or to form an intermediate layer having a thickness sufficient to reduce the depth of the hole on the mold base material. The optimum thickness of the intermediate layer varies depending on the surface condition of the mold base material, but is generally 0.5 μm or more, preferably 0.8 μm or more.
Suitable materials for the intermediate layer are Ti, Ta, Si
At least one compound or mixture of carbides, nitrides, and carbonitrides. These materials have an effect of improving the adhesion of the hard carbon film, in addition to the effect of filling the hole on the surface of the mold base material.

[0036]

Next, the present invention will be described in detail with reference to examples.

(Embodiment 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 the optical element, and FIG. 2 shows a state after molding the optical element. Here, reference numeral 11 denotes a mold base material, reference numeral 12 denotes a glass material, reference numeral 13 denotes a release film made of the hard carbon film of the present invention, and reference numeral 2 in FIG.
1 is an optical element. As shown in FIG. 1, an optical element 21 such as a lens is formed by press-molding a glass material 12 placed between molds.

Next, the optical element molding die of the present invention will be described in detail. In this example, a hard carbon film was formed by using an ion beam evaporation method. FIG. 3 is a schematic diagram showing an ion beam evaporation apparatus, and 31 is a vacuum chamber, 3
2 is an ion source, 33 is an acceleration grid, 34 is an ion beam, and 35 is a mold.
A gas exhaust port 36 is connected to a valve, an oil diffusion pump, and a rotary pump (all not shown).
37 is a valve, 38 is a gas flow regulator, 39 is a pressure regulator, 310 is a gas cylinder (in the figure, 2 is a gas cylinder).
Although only one gas cylinder is described, various gases such as methane, hydrogen, argon, oxygen, and nitrogen are actually connected.)

As a mold base material, after processing a binderless WC-based cemented carbide sintered body (trade name: TJ-05, manufactured by Fuji Dice) into a predetermined shape, the molding surface is Rmax = 0.04 μm.
Mirror-polished, and then a titanium nitride film was formed by a known ion plating method. After the mold base material was thoroughly washed, it was set in an ion beam evaporation apparatus shown in FIG. The gas flow rate was methane: 10 ml / min, hydrogen: 20 ml / min, the substrate temperature was no heating (water cooling), and the pressure was 5 × 10 ⁻² Pa. In addition, film formation was performed by changing the acceleration voltage to 15 kV for 5 minutes and 2 kV for 3 minutes.

The thickness of the evaluation sample separately prepared under the same conditions as the film forming conditions in the molding die was 55 nm as a whole. Further, the film thickness of the evaluation sample separately prepared under the film formation conditions of 3 kV at an acceleration voltage of 2 kV was 22 nm as measured.

The molding glass is a crown type optical glass SK.
12 (softening point Sp = 672 ° C., transition point Tg = 550 ° C.)
Then, an extremely thin convex lens having a diameter radius of φ32 mm, a center portion having a thickness of 2.5 mm, and an outermost periphery having a thickness of 1.4 mm is formed. The molding conditions are a nitrogen atmosphere, a press temperature of 620.
C. During the molding, the mold releasability between the mold and the molded optical element was good. In addition, when the surface of the mold after molding was observed with a scanning electron microscope, no peeling of the film, no generation of cracks, and no fusion of glass were observed, indicating that the mold had good surface properties. Also, the molded glass lens did not show any cracks in the glass and had good surface roughness.

A mold for forming an optical element was prepared in the same manner as described above except that the acceleration voltage was fixed at 15 kV, and glass molding was performed using the same glass material and shape. The mold force was large, and the glass was broken. In general, a hard carbon film having sufficient releasability from glass, a lens with a small diameter, and a sufficient thickness has sufficient characteristics as an optical element molding die. However, in the case of a large-diameter and extremely thin lens as in this embodiment,
Due to the large molding amount of the glass and easy distortion, the glass may be broken or the durability of the mold may be deteriorated (film peeling).

(Other Examples 2-5 and Comparative Example 1-
2) In this example and the comparative example, the acceleration voltage in the initial stage of film formation was variously changed, and the effect was evaluated. As a mold base material, after processing a WC-based cemented carbide into a predetermined shape, the formed surface is mirror-polished to Rmax = 0.04 μm, and thereafter, a silicon carbide (SiC) film is formed as an intermediate layer by a known sputtering method. Was formed with a thickness of 0.8 μm. After the mold base material was thoroughly washed, it was set in the apparatus shown in FIG. 3 to form a hard carbon film. At this time, the raw material gas flow rate was hydrogen: 10 ml.
/ Min, acetylene: 10 ml / min. The other film forming conditions are as follows: the substrate temperature is not heated (water cooling).
Pressure: 4.5 × 10 ^-2 Pa. The acceleration voltage at the initial stage of film formation was changed as shown in Table 1 below, and the film formation time at that time was 7 minutes at the beginning of film formation, and then 3 kV at 2 kV. As a result, a hard carbon film having a thickness of 80 to 95 nm was formed.

Next, press molding of a glass lens was performed using this optical element molding die. For the press molding, a continuous molding apparatus was used, and the molded glass was crown optical glass SK12 (softening point Sp = 672 ° C., transition point Tg = 55).
0 ° C), diameter: 32 mm, center: 2.5 mm
Thickness, outermost circumference: An extremely thin convex lens having a thickness of 1.4 mm is formed. The molding conditions are a nitrogen atmosphere, a press temperature of 620.
C. and 500 times of press molding. The lens shape is the same as in the first embodiment. Table 1 shows the results.

[0045]

[Table 1] ◎; very good ○; good △; practically acceptable ×;

In Example 2-5, the acceleration voltage in the initial stage of film formation was set to 6 to 21 kV according to the present invention (the range described in the claims).
By doing so, sufficient surface properties and molding durability of a molded product were obtained as a mold for optical element molding. On the other hand, in Comparative Example 1-2, since the acceleration voltage was out of the above range, deterioration of the surface properties and molding durability of the molded product was confirmed. In Comparative Example 1-2, the adhesion of the hard carbon film to the mold was low, partial film peeling occurred, and deterioration of the mold durability was confirmed.

In Comparative Example 1, the film peeling occurred on the entire hard carbon film, and in Comparative Example 2, it occurred at the interface between the hard carbon film at the early stage of film formation and the hard carbon film at the last stage of film formation. Was observed. For this reason, in Comparative Example 1, the surface properties of the molded glass were deteriorated, and some of them were not suitable for practical use. As described above, as shown, by setting the accelerating voltage, which is within the scope of the present invention at the initial stage of film formation, as an optical element molding die,
Sufficient molded product surface properties and molding durability were obtained.

(Other Examples 6-9 and Comparative Example 3-
4) In this example and the comparative example, the acceleration voltage at the end of the film formation was changed variously, and the effect was evaluated. That is,
The hard carbon film was formed by the same ion beam evaporation method as in Example 1. Further, after working a WC cemented carbide into a predetermined shape as a mold base material, the forming surface was changed to Rmax = 0.04.
Then, a titanium carbide (TiC) film is formed as an intermediate layer by a known sputtering method to a thickness of 0.5 μm.
It was formed with a thickness of μm.

After the mold base material was thoroughly washed, it was set in the apparatus shown in FIG. 3 to form a hard carbon film. The raw material gas flow rates are as follows: hydrogen: 10 ml / min, methane: 10 ml / mi
n. The other synthesis conditions were such that the substrate was not heated (water-cooled) and the pressure was 4 × 10 ⁻² Pa. The acceleration voltage at the end of the film formation was changed as shown in Table 2, and the synthesis time at that time was an acceleration voltage of 12 kV at the beginning of the film formation for 7 minutes, and then the end of the film formation for 3 minutes. As a result, a hard carbon film having a thickness of about 80 nm was formed.

Next, press molding of a glass lens was performed using this optical element molding die. The molding is performed using a continuous molding device, and the crown-based optical glass SK is used as the molding glass.
12 (softening point Sp = 672 ° C., transition point Tg = 550 ° C.)
, Diameter: 32 mm, thickness at the center: 2.5 m
m, an extremely thin convex lens having an outermost thickness of 1.4 mm. The molding was performed 500 times under a nitrogen atmosphere at a press temperature of 620 ° C. Table 2 shows the results.

[0051]

[Table 2] ◎; very good ○; good △; practically acceptable ×;

In Example 6-9, by setting the accelerating voltage at the final stage of the formation of the hard carbon film to 0.4 to 4 kV, sufficient molding surface property and molding durability as an optical element molding die were obtained. was gotten. On the other hand, Comparative Example 3,
In No. 4, since the accelerating voltage at the end of the film formation was out of the above range, deterioration of the molded product surface properties and molding durability was confirmed. In Comparative Example 3, since the acceleration voltage at the end of the film formation was low, the hardness of the hard carbon film was low, the mold was flawed, and the deterioration of the molded article surface properties and molding durability was confirmed. Further, in Comparative Example 4,
The acceleration voltage at the end of the film formation was high, and the releasability was deteriorated.
As a result, the molded glass was cracked, and the glass adhered to the mold, and the mold had to be cleaned during the molding test.

As described above, the acceleration voltage in the range specified in the present invention, that is, the acceleration voltage at the end of the formation of the hard carbon film is set to 0.1.
By setting the voltage to 4 to 4 kV, sufficient surface properties and molding durability of a molded product as an optical element molding material were obtained.

(Other Examples 10-13 and Comparative Examples 5-6) In this example and comparative examples, the acceleration voltage at the end of the film formation in the hard carbon film was set to 0.4 to 4 kV, and the film thickness was formed. Was changed variously, and the effect was evaluated. The hard carbon film was formed by the same ion beam deposition method as in Example 1.

A mold base material made of a super hard material processed into a predetermined shape is put into the apparatus shown in FIG. 3 to form a hard carbon film.
The formation conditions were as follows: gas flow rate: benzene: 5 ml / min, hydrogen: 10 ml / min, substrate temperature: room temperature, pressure: 3
× 10 ^-2 Pa, acceleration voltage is 15 kV for the first 5 minutes of film formation.
And the final stage of film formation was 1 kV. The synthesis time at the final stage of film formation was variously changed, and the film thickness was changed as shown in Table 3.
The film thickness at the final stage of film formation was measured on an analysis sample separately prepared separately from the molding die.

Next, press molding of a glass lens was performed using this optical element molding die. The molding was performed using a continuous molding apparatus, and the crown glass optical glass SK1 was used as the molded glass.
2 (softening point Sp = 672 ° C., transition point Tg = 550 ° C.), diameter: φ32 mm, center thickness: 2.5 m
m, an extremely thin convex lens having an outermost thickness of 1.4 mm is formed. The molding conditions were as follows: under nitrogen atmosphere, press temperature: 62
Press molding was performed 500 times at 0 ° C. Table 3 shows the results.

[0057]

[Table 3] ◎; very good ○; good △; practically acceptable ×;

In Examples 10-13, by setting the film thickness at the final stage of the formation of the hard carbon film to 5 to 50 nm, sufficient molded article surface properties and molding durability as an optical element molding die were obtained. Was done. On the other hand, Comparative Example 5,
In No. 6, since the film thickness at the final stage of film formation was out of the above range, deterioration of the molded product surface properties and molding durability was confirmed. In Comparative Example 5, since the film thickness at the end of film formation was small, the mold releasability between the mold and the glass was poor, and the mold releasability was deteriorated. For this reason, cracks in the molded glass occurred, and the glass adhered to the mold, and the mold had to be cleaned during the molding test. In Comparative Example 6,
Since the film thickness at the end of film formation was large, the adhesion of the hard carbon film to the mold was low, and peeling occurred at the portion of the hard carbon film formed at the end of film formation. For this reason, the surface properties of the molded product were deteriorated, and fine glass adhered to the peeled portion of the mold, so that the mold had to be cleaned during the molding test.

As described above, within the range specified in the present invention, that is, the thickness of the hard carbon film at the final stage of film formation is 5 to 50 nm.
As a result, sufficient mold surface properties and molding durability were obtained as a mold for an optical element molding die.

(Other Examples 14-17 and Comparative Examples 7-8) In this example and comparative examples, the acceleration voltage in the initial stage of film formation in the hard carbon film was set to 6 to 21 kV, and the film thickness was varied. And evaluated its effect. The hard carbon film was formed by the same ion beam deposition method as in Example 1.

A mold base made of a super-hard material processed into a predetermined shape is put into the apparatus shown in FIG. 3 to form a hard carbon film.
The formation conditions are as follows: gas flow rate is benzene: 10 ml / min;
Substrate temperature: 200 ° C., pressure: 3 × 10 ⁻² Pa, acceleration voltage: 12 kV during the initial 5 minutes of film formation, ² kV at the end of film formation
And The synthesis time in the initial stage of film formation was changed variously, and the film thickness was changed as shown in Table 4. The film thickness at the final stage of film formation was measured on an analysis sample separately prepared separately from the molding die.

Next, press molding of a glass lens was performed using the optical element molding die. The molding was performed using a continuous molding apparatus, and the crown glass optical glass SK1 was used as the molded glass.
2 (softening point Sp = 672 ° C., transition point Tg = 550 ° C.), diameter: φ32 mm, center thickness: 2.5 m
m, an extremely thin convex lens having an outermost thickness of 1.4 mm is formed. The molding conditions were as follows: under nitrogen atmosphere, press temperature: 62
Press molding was performed 500 times at 0 ° C. Table 4 shows the results.

[0063]

[Table 4] ◎; very good ○; good △; practically acceptable ×;

In Examples 14-17, by setting the film thickness at the final stage of the formation of the hard carbon film to 20-80 nm, sufficient mold surface properties and molding durability as an optical element molding die were obtained. Was done. In contrast, Comparative Example 7,
In No. 8, since the film thickness at the initial stage of film formation was out of the above range, deterioration of the molded product surface properties and molding durability was confirmed. In Comparative Example 7, since the film thickness at the initial stage of film formation was small, the adhesion of the hard carbon film to the mold was low, and peeling occurred at the interface between the mold and the hard carbon film. For this reason, the surface properties of the molded product were deteriorated, and fine glass adhered to the peeled portion of the mold, so that the mold had to be cleaned during the molding test. In Comparative Example 8, since the film thickness at the initial stage of film formation was large, the surface roughness of the molded product was deteriorated, and sufficient characteristics as an optical element could not be obtained.

As described above, within the range specified in the present invention, that is, the film thickness of the hard carbon film at the initial stage of film formation is 20 to 80 n.
By setting it to m, sufficient molded article surface properties and molding durability were obtained as a mold material for an optical element molding die.

(Embodiment 18) In this embodiment, the acceleration voltage for forming the hard carbon film was changed in three stages. First, as a mold base material, after processing a sintered body of an inderless WC-based cemented carbide (trade name: TJ-05, manufactured by Fuji Die) into a predetermined shape, the formed surface is mirror-polished to Rmax = 0.04 μm,
A titanium nitride film formed by a known ion plating method was used. After thoroughly cleaning the mold base material, FIG.
Was installed in the ion beam evaporation apparatus shown in FIG.

At this time, the gas flow rate was methane: 12 ml /
min, hydrogen: 15 ml / min, temperature of the substrate without heating (water cooling), pressure: 4.8 × 10 ⁻² Pa.
In addition, as shown in FIG. 4, film formation was performed by changing the acceleration voltage to 12 kV for 6 minutes, 6 kV for 2 minutes, and 1 kV for 2 minutes.

In addition, under the same conditions as the synthesis conditions of the molding die,
When the film thickness of the separately prepared evaluation sample was measured, it was 110 nm in total. Furthermore, acceleration voltage 1
The film thickness was measured for a separately prepared evaluation sample under a film forming condition of kV for 2 minutes, and it was 15 nm.

As the molded glass, crown optical glass SK12 (softening point Sp = 672 ° C., transition point Tg = 55)
0 ° C), diameter: φ32 mm, thickness at the center:
An extremely thin convex lens having a thickness of 2.5 mm and an outermost thickness of 1.4 mm is formed. The molding was performed under a nitrogen atmosphere at a press temperature of 620 ° C. During molding, the mold releasability between the mold and the molded optical element was very good. When the surface of the mold after molding was observed with a scanning electron microscope, no exfoliation of the film, no generation of cracks, and no fusion of the glass were observed, and the mold had very good mold surface properties. Also, the molded glass lens did not show any cracks in the glass and had very good surface roughness. Further, the molding durability is also very good, and is 1.3 to 1.
Five times the molding durability was obtained.

[0070]

According to the method of manufacturing an optical element molding die of the present invention, the method of forming an optical element molding die in which at least a hard carbon film is formed as a release layer on a molding surface by ion beam evaporation is provided. The acceleration voltage of the hard carbon film is set to 6 to 21 kV at the initial stage of the film formation, and the acceleration voltage is set to 0.4 to 21 kV at the end of the film formation.
By forming a film at 4 kV, a mold for molding an optical element can be manufactured at low cost and without deterioration of the film or deterioration of the surface roughness of the formed glass.

As a result, using a mold using the above-described manufacturing method,
When the glass optical element is molded, the mold releasability of the glass and the mold is extremely good, and a molded article having excellent surface roughness, surface accuracy, transmittance, and shape accuracy can be obtained. Furthermore, even if press molding is repeated using these molds for a long time, an extremely durable optical element molding die free from defects such as film peeling, cracking, and scratching can be obtained.

As described above, by using the mold for molding an optical element obtained by the present invention and the method for producing the same, it has become possible to realize an improvement in productivity and a reduction in cost.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an optical element molding die according to the present invention, showing a state before press molding.

FIG. 2 is a sectional view showing an example of an optical element molding die according to the present invention, showing a state after press molding.

FIG. 3 is a schematic diagram of forming a hard carbon film by an ion beam evaporation method.

FIG. 4 is an example of a temporal change of an acceleration voltage when manufacturing an optical element molding die according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Type base material 12 Glass material 13 Hard carbon film 21 Molded glass 31 Vacuum container 32 Ion beam apparatus 33 Acceleration electrode 34 Ion beam 35 Base 36 Gas exhaust port 37 Valve 38 Gas flow meter 39 Pressure regulator 310 Gas cylinder

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Nao Miyazaki 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 4G015 HA01 4K029 BA34 BA56 BB02 BD03 CA03 CA05 EA09

Claims (4)

[Claims] 1. A method for producing an optical element molding die in which at least a hard carbon film is formed as a release layer on a molding surface by an ion beam vapor deposition method, wherein an acceleration voltage of 6 to 21 kV is applied at an early stage of forming the hard carbon film. And applying an accelerating voltage of 0.4 to 4 kV at the end of film formation to form a film. 2. The optical element molding die according to claim 1, wherein the film thickness is 10 to 80 nm when the film is formed at an acceleration voltage of 6 to 21 kV in the initial stage of film formation. Method. 3. The optical element molding die according to claim 1, wherein the film thickness is 5 to 50 nm when the film is formed at an acceleration voltage of 0.4 to 4 kV at the end of the film formation. Manufacturing method. 4. The method for manufacturing an optical element molding die according to claim 1, wherein the acceleration voltage is changed in two or more steps.