JP2003104737A - Mold for forming optical element and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold for forming an optical element with prolonged service life by suppressing the progress of deterioration by oxidation, and the occurrence of a crack or peeling off of the surface layer, and to provide a method for manufacturing the mold. SOLUTION: This mold for forming an optical element uses an ultra-hard alloy metal essentially comprising tungsten carbide as a base material 9, and a predetermined surface of the base material 9 including at least a forming surface is irradiated with nitrogen ion to be infiltrated so that the outermost surface layer of the predetermined surface is converted to a modified layer 10 containing nitrogen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element molding die used for manufacturing optical elements such as lenses and prisms made of glass by press molding of a glass material, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the growing need for inexpensively manufacturing optical elements made of glass, even glass with relatively small diameters has been press-molded directly from glass using a molding die. The characteristics required for the mold used for molding such an optical element of glass include excellent characteristics such as hardness, thermal oxidation resistance, releasability, mirror surface workability, and abrasion resistance. .

Conventionally, materials such as ceramics and cemented carbide have been used as this kind of material, and a mold-releasing wear-resistant film of metal or ceramic is formed on the molding surface of a glass lens to be formed. It has been attempted to prevent fusion and improve mold durability. As an example, Japanese Patent Publication No. 6-102
In Japanese Patent No. 553, a tungsten carbide is formed on a cemented carbide base material made of tungsten carbide by a sputtering method.
A mold for molding an optical element, which has a coating of up to 1.5 μm, is disclosed.

[0004]

However, when glass is press-molded by the above-mentioned optical element molding die,
Since the outermost layer of this optical element molding die is composed of a tungsten carbide film formed by a sputtering method, the crystallized tungsten carbide film is oxidized by the influence of a slight amount of oxygen contained in the glass and the deterioration progresses. There was a problem. Further, there is a problem that a crack occurs in the tungsten carbide film or film peeling occurs due to the influence of glass flow.

The present invention has been made by paying attention to the problems of the above-mentioned prior art, and it is possible to extend the life of the mold by suppressing the progress of deterioration due to oxidation, the generation of cracks and peeling of the film. An object is to provide a molding die and a method for producing the same.

[0006]

In order to solve the above problems, an optical element molding die according to claim 1 of the present invention is an optical element having a molding surface formed of a compound containing tungsten carbide as a main component. In the molding die, the outermost surface layer of the molding surface contains nitrogen.

An optical element molding die according to a second aspect of the present invention is an optical element molding die having a molding surface on which a thin film containing tungsten carbide is formed. In the outermost layer of the thin film, ions containing nitrogen are contained. It is characterized in that it is an injected layer.

An optical element molding die according to a third aspect of the present invention is an optical element molding die having a molding surface formed of a compound containing tungsten carbide as a main component, and an ion containing nitrogen on the molding surface. And a mixed layer containing tungsten carbide and a layer into which tungsten is implanted, a layer containing tungsten carbide is provided on the mixed layer, and a layer formed by implanting nitrogen-containing ions into this layer is used as the outermost layer. Is characterized by.

According to a fourth aspect of the present invention, there is provided an optical element molding die manufacturing method, wherein at least the molding surface of the optical element molding die base material having a molding surface formed of a compound containing tungsten carbide as a main component, The method is characterized by including a step of implanting ions containing nitrogen.

A method of manufacturing an optical element molding die according to a fifth aspect of the present invention comprises a step of forming a thin film containing tungsten carbide on at least the molding surface of the optical element molding die, and the above-mentioned step formed on the molding surface. Implanting ions containing nitrogen into the outermost layer of the thin film.

According to a sixth aspect of the present invention, there is provided an optical element molding die which has a molding surface formed of a compound containing tungsten carbide as a main component. A first step of implanting ions containing nitrogen, a second step of forming a film containing tungsten carbide while continuing the implantation of ions containing nitrogen, and stopping the implantation of ions containing nitrogen. It is characterized by including a third step of continuing the film formation containing the tungsten, and a fourth step of stopping the film formation containing the tungsten carbide and implanting the ions containing the nitrogen again.

The operation of claims 1 and 2 will be described. As shown in the above-mentioned prior art, the molding surface made of tungsten carbide does not cause fusion with glass at high temperature, can be mirror-finished, has appropriate hardness, and is known to be hard to be oxidized. As a result of research, the present inventor has found that by including nitrogen in the surface of tungsten carbide, the mold life can be significantly extended as compared with a mold in which the surface is made of a thin film of tungsten carbide.

Tungsten carbide reduces the frictional resistance on the surface by injecting nitrogen into the outermost layer. This makes it possible to prevent cracks and film peeling caused by the flow of glass, and greatly reduce the wear of the mold due to the flow.

Also, due to the effect of implantation, the tungsten carbide crystal on the surface is destroyed and a fine crystal structure or
It can be an amorphous surface. Compared with the crystal structure of tungsten carbide formed by a simple sputtering method, this surface is less likely to undergo crystal growth or deterioration due to oxidation. As a result, deterioration of the molding surface due to oxidation is delayed, and the life of the mold can be significantly improved.

The operation of claim 3 will be described. Mixing the sputtered tungsten carbide particles while injecting nitrogen ions onto the molding surface, and then sputtering only tungsten carbide to form a tungsten carbide film, the mixed surface being mixed, the molding surface and the tungsten carbide film. There is no clear interface between. Then, by implanting nitrogen ions into the outermost layer of the tungsten carbide film, the prevention of film peeling is enhanced.
An optical element molding die having the same effect as described above can be obtained.

The operation of claims 4 and 5 will be described. Ion implantation is a technique of accelerating ions to forcibly add an element to the surface. When nitrogen ions are implanted into the surface of a thin film containing tungsten carbide as a main component, some of the bonds in the tungsten carbide are broken, and the tungsten is excited by collision and recoil of the tungsten and nitrogen ions. Is possible. Further, carbon generated by breaking the bond between the injected nitrogen and tungsten carbide is also present as a single substance. Further, the nitrogen ions collide with the tungsten carbide crystal, so that the crystal becomes fine and becomes amorphous.

By implanting ions containing nitrogen in this manner, nitrogen can be made to exist on the outermost surface of tungsten carbide. In addition, the crystal of tungsten carbide in the outermost layer can be made fine by the injection, and the optical element molding die according to the first and second aspects can be manufactured.

The operation of claim 6 will be described. Mixing sputtered tungsten carbide particles while implanting nitrogen ions on the molding surface and then sputtering only tungsten carbide to form a tungsten carbide film creates a clear interface between the molding surface and the tungsten carbide film. There will be a mixed layer that does not allow it. Then, by implanting nitrogen ions into the outermost layer of the tungsten carbide film, the optical element molding die according to claim 3 having the functions of claims 1 and 2 and further strengthening the prevention of film peeling. It can be manufactured.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) Embodiment 1 of the present invention will be described. FIG. 1 is a diagram showing a conceptual configuration of an apparatus for performing ion implantation in the method of manufacturing an optical element molding die according to the present embodiment.

As shown in FIG. 1, the apparatus for performing the ion implantation includes a vacuum container 7 which can be depressurized to a predetermined pressure by a vacuum pump 6, and the vacuum container 7 has an optical element molding die. A holder 2 for holding the base body 1 is fixedly arranged on a cooling plate (not shown). The holder 2 is connected to a cooling water supply device (not shown) and can be cooled by cooling water.

In the present embodiment, the base 1 is a cemented carbide containing tungsten carbide as a main component and containing no metal binder, and contains 5 wt% of a ceramic of titanium carbide and tantalum carbide as a binder.

An ion source 3 for irradiating the substrate 1 supported by the holder 2 with ions (nitrogen ions in this embodiment) 8 is provided in the vacuum container 7, and the ion source 3 is provided with the ion source 3. An inlet 4 for introducing the ions 8 is installed. Further, inside the vacuum container 7, an ion current measuring device 5 for measuring the number of ions with which the substrate 1 is irradiated is arranged.

Next, a case of manufacturing an optical element molding die having the above-mentioned structure will be described. The substrate 1 containing tungsten carbide as a main component is processed into a concave shape having a predetermined radius of curvature (70 mm), and the molding surface is mirror-finished so that the maximum surface roughness Rmax is 0.04 μm or less by using diamond abrasive grains or the like. Polishing process. Then, with the substrate 1 held in the holder 2,
The vacuum vessel 7 is evacuated by the vacuum pump 6 and 6 × 10 ⁻⁴
A high vacuum of Pa or less is used.

After that, the desired surface of the substrate 1 is irradiated with nitrogen ions 8 from the ion source 3. In this embodiment, nitrogen gas is introduced into an ionizer (not shown) at a flow rate of 1 to 5 SCCM to generate plasma, which is ionized and mass-separated to obtain a desired ratio of ions from the ion introduction port 4. It is introduced into the ion source 3. The acceleration energy of nitrogen ions to be irradiated was 35 KeV, and the beam current density of the ions was 10 μA / cm ² . Further, the ion irradiation dose is 7 × 10 ¹⁷ ions / cm ²
And The method of the ion source 3 is not limited to the method used in this embodiment, and a Kauffman type, a bucket type or the like may be adopted.

The substrate 1 ion-implanted by the above method has nitrogen implanted on its outermost surface. Further, the bond of the tungsten carbide of the substrate 1 is cut by the implantation of the nitrogen ions 8, and the tungsten nitride is formed by the collision and recoil of the tungsten and the nitrogen ions 8. In addition, there are also carbons whose bonds have been broken from tungsten carbide.

The surface of the tungsten carbide formed according to the present embodiment, into which nitrogen ions were implanted, had a fine crystal structure due to collision of nitrogen ions 8. In this case, the acceleration energy of the irradiated nitrogen ions 8 is preferably 5 KeV or more. If the acceleration energy is 5 KeV or less, the etching effect on the surface causes excessive damage to the treated surface, which is not preferable. Also, the acceleration energy is 20
In case of 0 KeV or more, or the beam current density is 200
When μA / cm ² or more, the treated surface is heated and the substrate 1
It is not preferable because it affects the Further, in the case of implanting into the cemented carbide of the sintered body as in the present embodiment, when the beam current density is 30 μA / cm ² or more, the treated surface becomes rough, so that the precision metal It is not preferable for the function of the mold. For the same reason, the ion dose is set to 1.5 × 10 ¹⁸ i
The case of ons / cm ² or more is also not preferable.

The holder 2 for supporting the base 1 is
By flowing water through a cooling plate (not shown), it is possible to cool the substrate 1 during processing, and thus it is possible to further prevent thermal deformation of the substrate 1 during film formation.

The optical element molding die formed according to the present embodiment, as shown in FIG.
There is a modified layer 10 modified by nitrogen ions. The modified layer 10 contains tungsten nitride, nitrogen, carbon, and tungsten as described above.

According to the present embodiment, by implanting nitrogen ions into the surface containing tungsten carbide as a main component,
Nitrogen could be contained in the outermost layer of the molding surface of the optical element molding die. By using ion implantation in this way, the ratio of nitrogen on the molding surface can be easily set, and the distribution in the depth direction can also be easily set, so the molding surface state can be changed depending on the optical element to be molded and molding conditions. Also when doing, the desired setting can be easily obtained.

The coefficient of friction of the surface of this embodiment was measured by the ball-on-disk method. For comparison, the friction coefficient of the optical element molding die manufactured in the present embodiment was measured without nitrogen ion implantation (Comparative Example 1). Alumina balls having a diameter of 4 inches were used as test balls, and the friction coefficient was measured by moving the balls at a speed of 5.23 cm / sec with a load of 2N. The friction coefficient of the cemented carbide of Comparative Example 1 in which nitrogen ions were not injected was 0.56,
The coefficient of friction of the surface of the present embodiment was as small as 0.35, and it was confirmed that the coefficient of friction was lowered by implanting nitrogen ions.

Using this optical element molding die, a glass material SK
A preform of 11 (transition point: 535 ° C, softening point: 630 ° C) was press-molded. The above preform is placed between the molds, heated while being pressed, and cooled to take out the optical element. This process was repeated 10,000 times to measure the surface roughness of the molding surface after use, but the optical element molding die of the present embodiment remained substantially as it was initially.

As a result of performing the same molding using the mold of Comparative Example 1, the maximum molding surface roughness before use was Rmax: 0.04.
After 10,000 times with respect to μm, the surface roughness of the molding surface is 0.23
It deteriorated to μm.

By using the optical element molding die of this embodiment, the deterioration of the die is slowed down, and the life of the die can be extended while maintaining good releasability.

(Second Embodiment) A second embodiment of the present invention will be described. In the present embodiment, nitrogen ions are implanted into the substrate of the optical element molding die on which the tungsten carbide film has been formed by the same apparatus and method as in the first embodiment.

For the substrate 1 (see FIG. 1) of the optical element molding die according to the second embodiment, a cemented carbide containing nickel and chromium as binders and containing tungsten carbide as a main component is used. A tungsten carbide film was formed on this substrate 1 in advance by an ion beam sputtering method to a thickness of 8000 Å. The film forming conditions are a substrate temperature of 500 ° C. and an anode current of 0.
3A, acceleration voltage 900V, acceleration current 40mA.
Then, nitrogen ions were implanted using the apparatus shown in FIG. 1 as in the first embodiment.

Next, a method for manufacturing the optical element molding die of this embodiment will be described. The substrate 1 coated with the tungsten carbide film is housed in a vacuum container 7, and the inside of the vacuum container 7 is evacuated to a high vacuum of 4 × 10 ⁻⁴ Pa or less. The acceleration energy of nitrogen ions to be irradiated was 40 KeV, and the beam current density was 50 μA / cm ² . Further, the ion irradiation dose was set to 1 × 10 ¹⁸ ions / cm ² . Other conditions are the same as those in the first embodiment.

FIG. 3 is a cross-sectional view of the substrate 1 of the optical element molding die of this embodiment formed by the above method. In the present embodiment, a tungsten carbide thin film 12 formed by an ion beam sputtering method is separately formed on a cemented carbide base material 11 containing nickel and chromium as binders.
The modified layer 13 in which nitrogen ions are implanted by the apparatus shown in FIG.
Are formed.

In the modified layer 13, tungsten nitride is formed by collision and recoil of the thin film element tungsten and nitrogen ions. The modified layer 13 becomes a tungsten carbide thin film 12 as it becomes deeper from the surface and decreases in a tilted manner, and there is no clear interface. This modified layer 13 contains nitrogen tungsten, nitrogen, carbon, and tungsten as in the first embodiment.

According to the present embodiment, nitrogen ions can be implanted into the tungsten carbide thin film 12, and the molding surface of the optical element molding die can be formed by excluding tungsten, carbon, and nitrogen. You can Therefore, the reduction of the friction coefficient, which is the effect of nitrogen ion implantation on the surface of tungsten carbide, can be sufficiently exhibited. Further, a uniform surface can be formed by implanting ions into the tungsten carbide thin film 12.

The coefficient of friction of the surface of this embodiment was measured by the ball-on-disk method. For comparison, the friction coefficient of the optical element molding die produced in the second embodiment was measured without performing nitrogen ion implantation (Comparative Example 2).
An alumina ball having a diameter of 4 inches was used as a test ball, and a friction coefficient was measured by moving the ball at a speed of 5.23 cm / sec with a load of 2N.

The surface of the tungsten carbide of the present embodiment in which nitrogen ions are implanted has an alumina ball moving distance of 6
No abrasion was observed and film peeling did not occur even when the length exceeded 00 m. Also, the friction coefficient was as small as 0.28.
On the other hand, on the surface of the tungsten carbide film of Comparative Example 2 in which nitrogen ions were not implanted, film peeling occurred and the base material 11 was generated when the movement distance of the alumina ball was less than 80 m.
Has worn out. The coefficient of friction also showed a large value of 0.42.

Using the optical element molding die of this embodiment, a preform of LaSF03 (transition point: 730 ° C., softening point: 808 ° C.) was pressed as a glass material. Place the preform between the molds, heating while pressing,
Cool and take out the optical element. This pressing step was repeated 30,000 times to measure the surface roughness after molding, but it was substantially the same as the initial state. Moreover, neither cracking nor film peeling occurred.

As a result of performing the same molding using the mold of Comparative Example 2, the maximum molding surface roughness before use was Rmax: 0.03.
After 300 times, the surface roughness of the molding surface was 0.
It deteriorated to 18 μm. When the press was further continued, cracks occurred 8000 times and film peeling occurred from the cracks.

This is because in the mold of Comparative Example 2, a slight amount of oxygen from the glass material adheres to the mold surface at the time of molding and deteriorates due to oxidation, but the mold of the present embodiment suffers from oxidation deterioration due to nitrogen injection. It was delayed. Further, the stress generated at the interface between the base material 11 and the tungsten carbide film 12 due to the decrease in the friction coefficient due to the nitrogen ion implantation is reduced,
It prevents cracks and film peeling.

The effect that the progress of mold deterioration is delayed and the mold life can be extended while maintaining good mold releasability is the same as in the first embodiment.

In this embodiment, the tungsten carbide film is formed by the ion beam sputtering method.
The same effect can be obtained by forming a tungsten carbide film by a film forming method such as the D method or the CVD method and implanting nitrogen ions.

(Third Embodiment) A third embodiment of the present invention will be described. FIG. 4 is a diagram showing a conceptual configuration of an apparatus for performing ion implantation in the method of manufacturing the optical element molding die according to the present embodiment.

As shown in FIG. 4, the apparatus for performing the ion implantation includes a vacuum container 21 that can be depressurized to a predetermined pressure by a vacuum pump 20, and the vacuum container 21 has an optical element molding die. Holder 15 for holding the substrate 14 of
Are fixedly arranged on a cooling plate (not shown). The holder 15 is connected to a cooling water supply device (not shown) and can be cooled by cooling water.

In the present embodiment, as in the first embodiment, the base 14 is a cemented carbide containing no metal binder but 5% by weight of a ceramic of titanium carbide and tantalum carbide as a binder.

An ion source 16 for irradiating the substrate 14 supported by the holder 15 with ions (nitrogen ions in the present embodiment) 22 is provided in the vacuum container 7, and the ion source 16 is provided in the ion source 16. An inlet 17 for introducing the ions 22 is installed. Furthermore, in the vacuum container 7,
An ion current measuring device 18 for measuring the number of ions 22 with which the substrate 14 is irradiated is arranged, and a tungsten carbide target 19 is arranged so as to be connected to a power source (not shown).

Next, a case of manufacturing the optical element molding die having the above-mentioned structure will be described. In FIG. 4, the base 14 of the optical element molding die is processed into a predetermined shape, and the molding surface is formed by using diamond abrasive grains or the like, and the maximum surface roughness Rmax: 0.03 μm.
Mirror-polishing processing is performed so that it becomes m or less. Then the base 1
With 4 held in the holder 15, the vacuum container 21 is evacuated by the vacuum pump 20 to obtain a high vacuum of 6 × 10 ⁻⁴ Pa or less.

After that, the desired surface of the substrate 14 is irradiated with nitrogen ions 22 from the ion source 16. In this embodiment, 1 to 5 SCCM of nitrogen gas is supplied to an ionizer (not shown).
Is introduced into the ion source 16 from the ion introduction port 17 through the ion introduction port 17 in a desired ion ratio by mass-separating it. The acceleration energy of the nitrogen ions 22 to be irradiated is 25K.
eV, the beam current density of the above ions is 5 μA / cm
^{It was set to 2} .

Nitrogen ions 22 are added to the surface of the substrate 14 in an amount of 2 × 1.
After the implantation of 0 ¹⁷ ions / cm ² (first step), the tungsten carbide target 19 is sputtered by applying a high frequency while continuing the implantation of the nitrogen ions 22 to form a film on the substrate 14 (second step). Process). Film thickness is 1000Å
When the temperature reaches, the implantation of the nitrogen ions 22 is stopped and the film formation is continued (third step). After that, the film thickness is 5000Å
Then, the film formation is stopped and nitrogen ions are implanted again (fourth step). At this time, the acceleration energy of nitrogen ions to be irradiated is 35 KeV, the current density of the ions is 15 μA / cm ² , and the implantation amount is 3.5 × 10 5.
^{It was set to 17} ions / cm ² .

In the optical element molding die formed by the above method, as shown in FIG. 5, the surface layer of the die base material 23 is mixed by nitrogen ion implantation and tungsten carbide film formation. There is a mixed layer 26 with the tungsten film 24, and a tungsten carbide film 24 is formed thereon. Thus, there is no clear interface between the mold base 23 and the tungsten carbide film 24. Further, on the surface of the tungsten carbide film 24, there is a modified layer 25 into which nitrogen ions have been implanted. Other operations are similar to those of the second embodiment.

(Effect) According to the optical element molding die of the present embodiment, since there is no clear interface between the tungsten carbide film 24 and the mold base material 23, the mold base material 23 and the tungsten carbide film 24 are separated from each other. It is possible to prevent film peeling that occurs between the two.

Using the optical element molding die of this embodiment, the glass material SK11 (transition point: 535 ° C., softening point: 630
C) preforms were pressed. The above preform is placed between the molds, heated while being pressed, and cooled to take out the optical element. The pressing process was repeated 50,000 times, but no film peeling occurred. Other effects are similar to those of the second embodiment.

[0057]

According to claims 1 and 4 of the present invention, since the outermost surface layer of the molding surface is a layer into which ions containing nitrogen are implanted, the coefficient of friction is lowered and the abrasion due to the flow of glass is greatly reduced. Can be reduced. This can significantly extend the life of the optical element molding die.

According to the second and fifth aspects of the present invention, a thin film containing tungsten carbide is formed on at least the molding surface, and ions containing nitrogen are implanted into the outermost surface layer of the thin film containing tungsten carbide. In addition to the above effects, the tungsten carbide crystals on the surface of the thin film are scraped, resulting in a fine crystal structure or an amorphous surface, the friction coefficient is further reduced, and cracks and film peeling are prevented. it can. Further, by implanting nitrogen-containing ions into the thin film surface, the deterioration of the molding surface caused by the oxidation of oxygen contained in the glass and the deterioration due to the flow of the glass are delayed, and the mold life is significantly improved.

According to claims 3 and 6 of the present invention, in addition to the above effects, since ions containing nitrogen are implanted into the interface between the substrate and the thin film and the surface of the thin film, Since there is no clear interface with the thin film, film peeling can be prevented. Therefore, the life of the mold is further improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a conceptual configuration of an apparatus for performing ion implantation in a method for manufacturing an optical element molding die according to a first embodiment of the present invention.

FIG. 2 is an enlarged view showing a surface layer of the optical element molding die according to the first embodiment of the present invention.

FIG. 3 is an enlarged view showing a surface layer of an optical element molding die according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a conceptual configuration of an apparatus for performing ion implantation in the method for manufacturing an optical element molding die according to the third embodiment.

FIG. 5 is an enlarged view showing a surface layer of an optical element molding die according to a third embodiment of the present invention.

[Explanation of symbols]

1,14 Base 2,15 holder 3,16 Ion source 4,17 Ion inlet 5,18 Ion current measuring instrument 6,20 vacuum pump 7,21 Vacuum container 8,22 Nitrogen ion 9 Carbide substrate 10,25 Modified layer 11 Base material 12,24 Tungsten carbide film 19 Tungsten Carbide Target 23 type base material

Claims (6)

[Claims] 1. An optical element molding die having a molding surface formed of a compound containing tungsten carbide as a main component, wherein the outermost layer of the molding surface contains nitrogen. 2. An optical element molding die having a molding surface on which a thin film containing tungsten carbide is formed, wherein the outermost layer of the thin film is a layer into which ions containing nitrogen are implanted. Mold for molding. 3. An optical element molding die having a molding surface formed of a compound containing tungsten carbide as a main component, and a mixed layer containing a layer in which ions containing nitrogen are implanted on the molding surface and tungsten carbide. Along with
A mold for forming an optical element, wherein a layer containing tungsten carbide is provided on the mixed layer, and a layer formed by implanting ions containing nitrogen into this layer is an outermost layer. 4. An optical device comprising a step of implanting ions containing nitrogen into at least the molding surface of an optical element molding die base material having a molding surface formed of a compound containing tungsten carbide as a main component. A method for manufacturing an element molding die. 5. A step of forming a thin film containing tungsten carbide on at least the molding surface of an optical element molding die, and a step of implanting nitrogen-containing ions into the outermost surface layer of the thin film formed on the molding surface. A method for producing a mold for molding an optical element, which comprises: 6. An optical element molding die having a molding surface formed of a compound containing tungsten carbide as a main component, the first step of implanting nitrogen-containing ions into at least the molding surface, and the nitrogen A second step of forming a film containing tungsten carbide while continuing the implantation of the ions containing silicon; a third step of stopping the injection of the ions containing nitrogen and continuing the film forming containing the tungsten; A fourth step of stopping the film formation containing tungsten and re-implanting the ions containing nitrogen, the method for manufacturing an optical element molding die.