JP2008100885A - Optical element molding die - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element molding die on which a long-lived molding surface showing good releasability from an optical element is easily formed at a low cost. <P>SOLUTION: The optical element molding die 1 is the one which has the molding surface 1a and is used for press-molding of the optical element made of glass. The optical element molding die 1 is equipped with a die base material 2 and a film layer 3, provided that the die base material 2 has a molding base surface 2a serving as a base for the molding surface 1a, and the film layer 3 essentially comprises a tantalum oxide and is formed at least on the molding base surface 2a of the die base material 2. Here, the surface of the film layer 3 serves as the molding surface 1a. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical element molding die used for press molding of an optical element made of glass.

  A method of heating an optical glass material and press-molding it into a desired shape by a pressing means to form an optical element has been generally known. In particular, in recent years, with the improvement in performance of optical systems, it has been desired to produce optical elements having complicated shapes such as free-form surfaces as well as aspherical shapes in large quantities at low cost. In order to produce such an optical element at a low cost by press molding, it is an essential condition to extend the life of the mold. The life of the mold depends on the deterioration of the molding surface where the mold and the optical glass material come into contact. Therefore, in order to improve the durability of the molding surface, a TiN film, platinum alloy film, DLC is used as the mold base material. A film or the like is formed.

Here, although the temperature which press-molds an optical glass material is based also on the glass transition temperature of the optical glass material to be used, it is generally 400 to 800 degreeC. In molding at this temperature, element diffusion tends to occur, and when the film deteriorates due to heat cycle, components such as alkali metals contained in the optical glass material and oxygen molecules in the atmosphere undergo chemical reaction and grain boundary diffusion. It becomes easy. As a result, deterioration of the mold base material and film peeling are likely to occur. Therefore, the surface of the mold is treated with a hard film using iridium or the like (see, for example, Patent Document 1).
JP 2001-89164 A

However, since the conventional optical element molding die uses iridium, it is still not sufficient in terms of easy availability and reduction of acquisition / processing costs.
The present invention has been made in view of the above circumstances, and provides an optical element molding die that has a good releasability from an optical element and has a long-life molding surface that is easily and inexpensively formed. The purpose is to do.

The present invention employs the following means in order to solve the above problems.
An optical element molding die according to the present invention is an optical element molding die that has a molding surface and is used for press molding of an optical element made of glass, and has a molding base surface that is the basis of the molding surface. A mold base material having a tantalum oxide as a main component and at least a film layer provided on the molding base surface of the mold base material, the surface of the film layer being a molding surface .

  In this invention, since tantalum oxide is a stable oxide, deterioration of the film layer due to the progress of oxidation can be suppressed. In addition, tantalum oxide has a function of blocking the diffusion of chemical elements including oxygen against the diffusion of oxygen from the grain boundary. The moldability can be improved suitably.

The present invention is also the optical element molding die, wherein the film layer is formed to a thickness of at least 50 nm.
According to the present invention, since the thickness of the film layer is larger than the size of the crystal grains, partial defects due to particle dropping or the like can be suppressed.

Further, the present invention is the optical element molding die, wherein the film layer includes the outermost layer in which the molding surface is formed and the oxygen concentration of the tantalum oxide is substantially constant, and from the molding surface side. And an inclined layer in which the oxygen concentration decreases continuously or stepwise toward the mold base.
In the present invention, since there is an inclined layer, the adhesion between the outermost layer and the mold base material can be improved.

Further, the present invention is the optical element molding die, wherein an injection layer into which tantalum is injected is formed on the molding base surface, and the film layer is formed on the injection layer. And
The present invention can further improve the adhesion between the film layer and the mold base material.

  According to the present invention, it is possible to easily and inexpensively form a molding surface having good releasability from an optical element and having a long life.

A first embodiment according to the present invention will be described with reference to FIGS.
As shown in FIG. 1, an optical element molding die 1 according to the present embodiment has a molding surface 1a and is used for press molding of an optical element such as a lens (not shown) made of glass. A mold base material 2 having a molding base surface 2a to be a base of the surface 1a, and a film layer 3 having tantalum oxide as a main component and provided at least on the molding base surface 2a are provided. The surface of the film layer 3 is a molding surface 1a.

  The mold base material 2 is formed by, for example, a base material made of cemented carbide (WC 99%, TiC 1%) being processed into a shape substantially similar to a shape corresponding to a desired final product. After being processed into a shape corresponding to a desired final shape as a molding surface by grinding using, mirror polishing is performed.

  The film layer 3 has an outermost layer 5 in which the molding surface 1a is formed and the oxygen concentration of the tantalum oxide is substantially constant, and an inclination in which the oxygen concentration gradually decreases from the molding surface 1a side to the mold base material 2 side. And a layer 6. Here, the film layer 3 should just be formed in the thickness of at least 50 nm larger than a crystal grain.

  As shown in FIG. 2, the outermost layer 5 has a thickness of about 200 nm and is formed at an oxygen concentration such that the composition ratio of oxygen (O) to tantalum (Ta) in the tantalum oxide is 2.3. It is filmed. The oxygen concentration may be thermodynamically stable if the composition ratio in the outermost layer 5 is 2.1 or more, ideally 2.5.

  The graded layer 6 has a thickness of about 800 nm here, and is formed so that the composition ratio of oxygen and tantalum in the tantalum oxide changes every thickness of about 150 nm. That is, the oxygen concentration gradually decreases from the molding surface 1a side toward the mold base material 2 side, while the tantalum concentration conversely increases from the molding surface 1a side toward the mold base material 2 side. . In the present embodiment, the composition ratio is changed in four stages. However, if the oxygen concentration is a value between the state of 0 in the mold base material 2 and the composition ratio of the outermost layer 5, It may be changed at an arbitrary number of steps. Further, the thickness of the layer in which the composition ratio changes is not necessarily uniform, and any thickness may be used.

  Here, the film layer 3 is performed by a film forming apparatus 7 as shown in FIG. The film forming apparatus 7 includes a vacuum container 8 connected to a ground, a conductive sample holder 10 that is disposed in an upper part of the vacuum container 8 and holds a mold base material 2 to be formed, and a sample holder 10. A DC pulse bias power source 11 connected via the electrode, a solid target 12 disposed below the sample holder 10 for generating plasma, a trigger electrode 13 for causing an initial discharge for generating plasma, and a solid target An arc electrode 15 that discharges the target 12 to generate plasma is provided.

The vacuum vessel 8 is provided with exhaust ports 8A and 8B.
The trigger electrode 13 is separated from the solid target 12 at a predetermined interval via an insulator (not shown) so as not to be electrically connected to the solid target 12 and to be conductive by discharge when a high voltage is applied. Is provided. The trigger electrode 13 is connected to a trigger power source 16, and the arc electrode 15 is connected to an arc power source 17. The DC pulse bias power supply 11 is controlled by a computer (not shown) so as to generate a negative voltage at the same time or after the discharge of the arc electrode 15 starts.

A method for forming the film layer 3 will be described.
In this embodiment, tantalum having a purity of 99.9% is used as the solid target 12.
First, after the mold base material 2 is set in the sample holder 10, the pressure in the vacuum vessel 8 is exhausted from the exhaust ports 8A and 8B and the pressure is reduced to 1 × 10 ⁻⁴ Pa or less. Then, a voltage of 60 V is applied to the arc electrode 15 and a voltage of 4.5 kV is instantaneously applied to the trigger electrode 13 to cause trigger discharge.

  With this trigger discharge as a trigger, a discharge occurs from the arc electrode 15 to the solid target 12, and tantalum plasma is generated from the surface of the solid target 12. At that moment, the plasma reaches the molding base surface 2 a of the mold base 2 in the vacuum vessel 8. Thus, tantalum is deposited to a predetermined thickness after a predetermined time has elapsed.

  Thereafter, oxygen is introduced into the vacuum vessel 8 so that the oxygen partial pressure becomes a predetermined value. Then, the above-described film forming process is performed to form a tantalum oxide having a predetermined composition ratio of oxygen and tantalum with a predetermined film thickness.

  Furthermore, while the oxygen concentration in the vacuum vessel 8 is changed stepwise, the above-described film forming process is performed under each oxygen concentration to sequentially form the inclined layer 6 and the outermost layer 5. Finally, the film is gradually cooled after heating to 600 ° C. in an air atmosphere to remove the residual stress of the film.

  When the Bi-containing phosphate glass material is molded at a molding temperature of 560 ° C. in a nitrogen atmosphere using the optical element molding die 1 thus obtained, a product having a desired shape without seizure or spiders is produced. I was able to.

  According to this optical element molding die 1, since tantalum oxide is a thermodynamically stable oxide, deterioration of the film layer 3 due to the progress of oxidation can be suppressed. In addition, tantalum oxide has a function of blocking the diffusion of chemical elements including oxygen against the diffusion of oxygen from the grain boundary. The moldability can be improved suitably. Therefore, it is possible to easily and inexpensively form the molding surface 1a having a good releasability from the optical element to be molded and having a long life.

At this time, since the thickness of the film layer 3 is 1000 nm, that is, 50 nm or more, which is larger than the size of the crystal grains, it is possible to suppress partial defects due to particle dropping or the like on the molding surface 1a.
In addition, by changing the oxygen concentration introduced into the vacuum vessel 8 stepwise, the inclined layer 6 in which the oxygen composition ratio changes stepwise can be easily formed. Adhesion between the outermost layer 5 having a high oxygen concentration and the molding base surface 2a of the mold base material 2 having the lowest oxygen concentration can be enhanced.

Next, a second embodiment will be described with reference to FIG.
In addition, the same code | symbol is attached | subjected to the component similar to 1st Embodiment mentioned above, and description is abbreviate | omitted.
The difference between the second embodiment and the first embodiment is that the inclined layer 22 of the film layer 21 of the optical element molding die 20 according to the present embodiment is from the molding surface 20a side to the mold base material 2 side. That is, the oxygen concentration is continuously reduced.

  The graded layer 22 has a thickness of about 800 nm, as in the first embodiment. The oxygen concentration is continuously reduced from the molding surface 20a side toward the mold base material 2 side, while the tantalum concentration is conversely from the molding surface 20a side toward the molding base surface 2a side of the mold base material 2. Increase continuously.

This film layer 21 is also formed by the same method as in the first embodiment. However, oxygen is introduced into the vacuum container so that the oxygen concentration changes continuously rather than stepwise during the formation of the gradient layer 22.
According to this optical element molding die 20, since the composition ratio of oxygen continuously changes in the inclined layer 22, adhesion between the outermost layer 5 having the highest oxygen concentration and the mold base material 2 having the lowest oxygen concentration. The property can be improved more suitably.

Next, a third embodiment will be described with reference to FIGS.
In addition, the same code | symbol is attached | subjected to the component similar to other embodiment mentioned above, and description is abbreviate | omitted.
The difference between the third embodiment and the second embodiment is that an injection layer 32 in which tantalum is injected into the molding base surface 31a of the mold base 31 of the optical element molding die 30 according to this embodiment. The film layer 21 is formed on the injection layer 32.

A method for forming the injection layer 32 and the film layer 21 will be described.
First, the same solid target 12 as in the first embodiment is used.
After the mold base material 31 is set in the sample holder 10, the air pressure in the vacuum vessel 8 is exhausted from the exhaust ports 8A and 8B and depressurized to 1 × 10 ⁻⁴ Pa or less. Then, a voltage of 60 V is applied to the arc electrode 15 and a voltage of 4.5 kV is instantaneously applied to the trigger electrode 13 to cause trigger discharge.

With this trigger discharge as a trigger, a discharge occurs from the arc electrode 15 to the solid target 12, and tantalum plasma is generated from the surface of the solid target 12. At that moment, the plasma reaches the molding base surface 31 a of the mold base 31 in the vacuum vessel 8.
At the same time, a DC pulse bias voltage of −15 kV is applied 100 times to the mold base 31 by a DC pulse bias power supply 11 at intervals of 12 μsec and 13 μsec. As a result, ions contained in the plasma around the mold base material 31 are extracted by the DC pulse bias voltage and injected into the molding base surface 31 a of the mold base material 31. This injection operation was repeated 500 times. At this time, the extracted ions are accelerated by an electric field in a direction perpendicular to the surface of the molding base surface 31a. Therefore, even if the molding base surface 31a has a three-dimensional shape, all the surfaces are implanted in the direction perpendicular to the surface. The The composition ratio of tungsten and tantalum on the molded base surface 31a thus injected is set to 1: 1.

  Thereafter, the gradient layer 22 and the outermost layer 5 are formed by reducing the pulse bias voltage and performing the same film formation process as in the second embodiment while continuously changing the oxygen concentration in the vacuum vessel 8. . Finally, after heating to 600 ° C. in the air atmosphere, the film is gradually cooled to remove the residual stress of the film, and the molding surface 30a is obtained.

  According to the present invention, since the injection layer 32 is provided, the adhesion between the film layer 3 and the mold base material 31 can be improved more suitably.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, a cemented carbide is used as the mold base material. However, the present invention is not limited to this, and a heat-resistant metal such as stainless steel or Inconel or a tungsten alloy may be used.

It is sectional drawing which shows the optical element shaping die concerning the 1st Embodiment of this invention. It is a graph which shows the composition ratio in the film | membrane layer of the optical element shaping die concerning the 1st Embodiment of this invention. It is a block diagram which shows the apparatus for forming the film layer of the optical element shaping die which concerns on the 1st Embodiment of this invention. It is a graph which shows the composition ratio in the film | membrane layer of the optical element shaping die which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the optical element shaping die concerning the 3rd Embodiment of this invention. It is a graph which shows the composition ratio in the film | membrane layer and injection layer of the optical element shaping die which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20,30 Optical element shaping | molding metal mold | die 1a, 20a, 30a Molding surface 2,31 Mold base material 2a, 31a Molding base surface 3,21 Film layer 5 Outermost layer 6,22 Inclined layer 32 Injection layer

Claims (4)

An optical element molding die having a molding surface and used for press molding of an optical element made of glass,
A mold base material having a molding base surface to be a base of the molding surface;
Comprising a tantalum oxide as a main component and at least a film layer provided on the molding base surface of the mold base material,
An optical element molding die, wherein the surface of the film layer is a molding surface.   The optical element molding die according to claim 1, wherein the film layer is formed to a thickness of at least 50 nm. The film layer is an outermost layer in which the molding surface is formed and the oxygen concentration of the tantalum oxide is substantially constant,
An inclined layer in which the oxygen concentration decreases continuously or stepwise from the molding surface side toward the mold base side;
The optical element molding die according to claim 1 or 2, further comprising: An injection layer into which tantalum is injected is formed on the molding base surface,
4. The optical element molding die according to claim 1, wherein the film layer is formed on the injection layer.

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