JP5364433B2 - Mold for optical elements - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mold for an optical element which is excellent in releasability in molding under a high temperature and is long in service life. <P>SOLUTION: The mold 1 for an optical element is used for press-molding an optical element made of glass, wherein the outermost surface layer on at least the molding face of the mold 1 comprises a rhenium dioxide film 3. By forming the rhenium dioxide film 3 as the outermost surface of the mold base 2, good releasing property for glass is obtained and degradation caused by oxidation, chemical reaction with glass or diffusion of elements is improved, thereby extending service life of the mold 1 for an optical element. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an optical element mold used for press molding 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 optical elements at a low cost, it is essential to extend the life of the mold. However, because highly reactive glass containing various metal oxides and alkali components is used at high temperatures, The deterioration of

The temperature at which the optical glass material is press-molded is generally 400 ° C. to 800 ° C., although it depends on the glass transition point. In the molding at this temperature, element diffusion is likely to occur, and in particular, components such as alkali metals contained in the optical glass material and oxygen molecules in the atmosphere easily undergo chemical reaction and grain boundary diffusion. Therefore, the deterioration of the molding surface where the mold and the glass are in contact affects the life of the molding die, and in order to counter this, the surface of the molding die is treated with a hard film or the like.
Conventionally, for a mold used for such glass molding, as described in Patent Document 1, a TiN layer is formed on the surface of a mold substrate, or as described in Patent Document 2, A platinum alloy film is coated.

  However, in the case where the TiN layer is formed on the surface of the mold base, TiN is oxidized by oxygen supply from oxygen in the atmosphere or oxides in the glass when the mold temperature increases. In particular, in continuous molding at high temperatures (for example, 500 ° C. or higher), the releasability from glass is deteriorated due to the effect of oxidation, and as a result, fusion with the glass occurs and the releasability is reduced. .

  On the other hand, a mold coated with a platinum-based alloy film has good mold releasability from glass, but film peeling occurs in continuous molding. This is because oxygen and glass component elements easily penetrate into the platinum-based alloy due to grain boundary diffusion, and the diffused and penetrated components react with the elements of the intermediate layer and the base material to form a compound. As a result, film peeling occurs due to the reactive growth of the compound components that have reacted under the platinum-based alloy film and the thermal cycle during glass forming.

  In any of the above conventional molds, the mold deteriorates due to reaction with oxygen and glass components during continuous molding, so the mold has a very short life, and this problem is solved. In order to achieve this, there has been proposed a mold for an optical element, as shown in Patent Document 3, in which a molding surface of a mold base material is a film layer mainly composed of iridium oxide.

JP 59-123629 A JP 62-3031 A JP 2001-89164 A

  However, the optical element molding die shown in Patent Document 3 also has a high molding temperature due to a high Tg point (glass transition point) (for example, 600 ° C. or higher). For example, when a glass material such as a lanthanum is used. The iridium oxide on the molding surface may be sublimated and consumed.

  The present invention has been made in consideration of such conventional problems, and an object thereof is to provide a mold for an optical element that has good releasability in molding at high temperature and has a long life. To do.

In order to solve the above problems, the present invention proposes the following means.
Mold for an optical element of the present invention is a mold for an optical element used in the press molding of the optical element made of glass, the outermost layer of at least the molding surface of the mold for the optical element Ri Do from the membrane layer consisting dioxide rhenium The outermost film layer has a thickness of 50 nm or more and 2000 nm or less .
In addition, the film layer made of rhenium dioxide is likely to vary in the way of oxidation during production, but it may be in the range of + 3.8 ≦ x ≦ + 4.5, where the oxidation number of rhenium atoms is x. In addition, there is no problem in performance even if inevitable trace amounts of impurities are mixed.

In glass molding, the deterioration of the molding surface where the mold and glass are in contact mainly affects the life. In the present invention, attention is paid to the action of rhenium dioxide (ReO ₂ ), and the life of the mold is extended by forming a film layer made of rhenium dioxide on at least the outermost layer of the mold. As a cause of deterioration of the mold, there is oxidation of the mold surface by oxygen in the atmosphere, but rhenium dioxide is originally a stable oxide, so there is no deterioration due to the progress of oxidation.

Therefore, according to the mold for optical elements of the present invention, by forming a film layer made of rhenium dioxide on at least the outermost layer of the mold, the releasability of the glass is good, and oxidation, chemical reaction with glass and elements Deterioration due to diffusion is improved. Therefore, the lifetime of the mold can be extended and the optical element can be provided at low cost.
Further, by forming the outermost layer with rhenium dioxide having a melting point of about 900 ° C., the molding can be performed at a high temperature of about 700 ° C., for example.

If the film layer of rhenium dioxide as a film used as the outermost layer of the molding surface of the mold is 50 nm or more in thickness, the effect can be sufficiently obtained. However, if the thickness is less than 50 nm, the film thickness becomes very close to the size of the crystal grains, which increases the possibility of partial defects due to particle dropout and the like, which is not preferable.

Further, in the above optical element molding die, an intermediate layer is provided between the mold base material and the outermost layer, the intermediate layer contains tantalum atoms, and moves from the mold base side to the outermost layer side. More preferably, the intermediate layer is configured to increase the proportion of oxygen atoms.
According to this invention, the adhesive force between the mold base material and the outermost layer can be improved by the intermediate layer.

  According to the optical element molding die of the present invention, it is possible to improve the releasability in molding at a high temperature and to prolong the life of the die.

It is sectional drawing of the shaping | molding die for optical elements of 1st Embodiment of this invention. It is sectional drawing of the shaping | molding die for optical elements of 2nd Embodiment of this invention.

(First embodiment)
Hereinafter, a first embodiment of an optical element molding die according to the present invention will be described with reference to FIG.
The mold base material 2 of the optical element mold 1 is processed into a shape substantially similar to the shape corresponding to the desired final product, and then the concave molded portion surface 2a is ground by using a diamond grindstone. It is fabricated by processing into a shape corresponding to the above and then mirror polishing.

Next, the mold base material 2 is installed in the vacuum chamber, and the mold base material 2 is heated to 200 ° C. and kept warm. Then, oxygen gas is introduced into the vacuum chamber, and sputtering is performed using a metal rhenium target by RF sputtering in a state where the pressure in the vacuum chamber is 10 ⁻² Pa. The sputtered particles of metal rhenium are oxidized by oxygen gas in the atmosphere, and most of them become stable rhenium dioxide (ReO ₂ ), and the rhenium dioxide film 3 is formed on the forming portion surface 2 a of the mold base 2. In the present embodiment, since only one film layer is formed on the molding part surface 2a of the mold base material 2, the rhenium dioxide film 3 becomes the outermost film layer, and at the same time, after the rhenium dioxide film 3 is formed, The surface of this film becomes the molding surface of the optical element molding die 1. Since the melting point of rhenium dioxide is about 900 ° C., it can be used up to a molding temperature of about 700 ° C. without any problem.

  As shown in Table 1, Samples 1 to 3 were manufactured as the optical element molding die 1 of the present embodiment by changing the material of the mold base material 2 and the thickness of the outermost rhenium dioxide film 3.

As the material of the mold base material 2, WC (tungsten carbide) was used in sample 1, lanthanum-based glass (Tg point is 738 ° C.) in sample ₂ , and SiO ₂ (silicon dioxide) was used in sample 3. Further, the thickness of the rhenium dioxide film 3 is 50 nm for the sample 1 and 200 nm for the sample 2 and the sample 3.
The thickness of the rhenium dioxide film 3 is preferably 50 nm or more and 2000 nm or less. If the thickness of the rhenium dioxide film 3 is less than 50 nm, the film thickness becomes very close to the size of the crystal grains, so that the possibility of partial defects due to particle dropping increases. On the other hand, when the thickness of the rhenium dioxide film 3 exceeds 2000 nm, it becomes too thick and the strength of the rhenium dioxide film 3 is lowered.

This optical element molding die 1 is assembled in a circulation type isothermal molding machine, and lanthanum L-LAH53 (manufactured by OHARA INC.) Is used as a glass material, and the glass is press molded as an optical element at a molding temperature of 640 ° C. A test was conducted.
L-LAH53 has a Tg point of 574 ° C. and an At point (glass deformation point) of 607 ° C.

The results of molding the optical element in a nitrogen atmosphere are shown in the moldability column of Table 1.
In Sample 1, the rhenium dioxide film 3 was peeled off when the optical element was molded into 500 shots. In Sample 2 and Sample 3, there was no problem in the optical element mold 1 even when the optical element was 1000 shot-molded.
In the above test, only the atmosphere was changed to the atmosphere, and the result of molding the optical element using the above Sample 1 to Sample 3 also showed the same moldability as the test result in the nitrogen atmosphere shown in Table 1. .

Since L-LAH53 is heated and softened, a part of the contained components volatilizes, and therefore, a small amount of volatile components generally adhere to the optical element mold 1 during molding of the optical element.
At the time of molding by the optical element molding die 1, the glass material which is L-LAH53 and the rhenium dioxide film 3 are in direct contact, but since the glass material and the rhenium dioxide film 3 are both oxides, they are chemically bonded to each other. It was found that the optical element can be satisfactorily molded without causing seizure of the optical element or deposition of volatile components on the rhenium dioxide film 3.

Thus, according to the optical element molding die 1 of the first embodiment of the present invention, the rhenium dioxide film 3 is formed on the mold base material 2, and the outermost layer of the molding surface of the optical element molding die 1 is the rhenium dioxide film 3. By making it, the releasability of the glass is good, and the deterioration due to oxidation, chemical reaction with glass and element diffusion is improved. Therefore, the lifetime of the optical element mold 1 can be extended, and the optical element can be provided at low cost.
Further, when the outermost rhenium dioxide film 3 has a thickness of 50 nm or more, the effect can be sufficiently obtained. However, if the thickness is less than 50 nm, the film thickness becomes very close to the size of the crystal grains, which increases the possibility of partial defects due to particle dropout and the like, which is not preferable.
Further, by using the rhenium dioxide film 3 of rhenium dioxide having a melting point of about 900 ° C. as the outermost layer, molding can be performed at a high temperature.

(Second Embodiment)
Hereinafter, the second embodiment of the optical element molding die according to the present invention will be described with reference to FIG. Only the differences will be described.
An intermediate layer 4 is formed between the mold base 2 and the rhenium dioxide film 3 in the optical element mold 6 of the present embodiment. And as shown in Table 2, as the optical element molding die 6 of the present embodiment, the material of the intermediate layer 4 and the material and thickness of the outermost layer were changed, and Sample 4 to Sample 8, Comparative Example 1 and Comparison Example 2 was prepared.

In Samples 4 to 7, the intermediate layer 4 is formed in a state where four film layers having a thickness of 100 nm are stacked, and the thickness of the intermediate layer 4 as a whole is 400 nm.
The intermediate layer 4 contains tantalum atoms in its entirety, and among the four film layers constituting the intermediate layer 4, the film layer closest to the mold base material 2 is formed of metal tantalum, and the most rhenium dioxide film. The film layer on the third side is formed of tantalum oxide (Ta ₂ O ₅ ). The four film layers constituting the intermediate layer 4 are configured such that the proportion of oxygen atoms in the composition of the film layer increases at a constant rate as the film layer moves from the mold base 2 side to the rhenium dioxide film 3 side. ing. That is, since the proportion of oxygen atoms in the composition of tantalum oxide is about 71% according to the formula (5/7), the proportion of oxygen atoms in the second film layer from the mold base material 2 side is about 24%. The proportion of oxygen atoms in the third film layer from the mold base material 2 side was configured to be about 48%.
As described above, the intermediate layer 4 in the samples 4 to 7 is formed by four film layers, the composition of which is changed stepwise in four steps from the mold base material 2 side to the rhenium dioxide film 3 side.
Further, in the sample 8, the oxygen atom ratio in the intermediate layer 4 is continuously changed from 0 to 71% as it moves from the mold base material 2 side to the rhenium dioxide film 3 side. The thickness was 400 nm.
Thus, the intermediate layer 4 in the sample 8 is formed by changing the composition continuously.
Further, the intermediate layer 4 in Comparative Example 1 is formed of metal chromium with a thickness of 100 nm, and the intermediate layer 4 in Comparative Example 2 is formed of metal titanium with a thickness of 100 nm.

  These intermediate layers 4 are formed in a vacuum chamber before the outermost layer such as the rhenium dioxide film 3 is formed. For example, the intermediate layer 4 in the samples 4 to 7 is formed by a known technique of increasing the oxygen gas concentration in the vacuum chamber every time each film layer is formed using a metal tantalum target by RF sputtering.

As in the first embodiment, the optical element molding die 6 was assembled in a circulation type isothermal molding machine, and an optical element molding test was performed using L-LAH53 as a glass material. The outermost layer of Comparative Example 1 is a film layer composed of Ir and Pt having the same number of moles.
The results of molding the optical element in a nitrogen atmosphere are shown in the moldability column of Table 2.
Samples 4 to 7 are obtained by changing only the thickness of the rhenium dioxide film 3. In Sample 4 in which the thickness of the rhenium dioxide film 3 was 30 nm, the rhenium dioxide film 3 was peeled off when 300 shots of the optical element were formed. In Sample 5, Sample 6, and Sample 7 in which the thickness of the rhenium dioxide film 3 was 50 nm, 200 nm, and 500 nm, there was no problem in the optical element mold 1 even when 1000 shots of the optical element were formed. In Sample 8, the composition change of the intermediate layer 4 was made continuous, and the thickness of the outermost rhenium dioxide film was 200 nm. However, there was no problem even when the optical element was formed into 1000 shots.

On the other hand, in Comparative Example 1 in which the intermediate layer 4 is made of metallic chromium and the outermost layer is made of Ir-Pt having a thickness of 200 nm, the optical element is seized and spoiled from the time when the optical element is molded 100 shots. Was not obtained. In Comparative Example 1 in which the intermediate layer 4 was formed of titanium metal and the outermost layer was formed of TiN having a thickness of 100 nm, the optical element was burned and spoiled at the time when the optical element was formed into 10 shots.
In addition, the result of having shape | molded the optical element using said sample 4-sample 8, the comparative example 1 and the comparative example 2 also changed the atmosphere in air | atmosphere in the said test also with the test result in nitrogen atmosphere shown in Table 2. Similar moldability was exhibited.

  From the test result of the sample 5 and the test result of the sample 1 in the first embodiment, even if the material of the mold base 2 and the thickness of the rhenium dioxide film 3 which is the outermost layer are the same, the mold base 2 By providing an intermediate layer 4 between the rhenium dioxide film 3 and the metal base tantalum 2 on the mold base material 2 and tantalum oxide on the rhenium dioxide film 3 side, the rhenium dioxide film 3 is peeled from the base metal 2. I found it difficult to do.

  Thus, according to the optical element molding die 6 of the second embodiment of the present invention, the metal base tantalum 2 side of the intermediate layer 4 is made of metal tantalum that can be easily bonded to WC, and the rhenium dioxide film 3 side is made of rhenium dioxide. The tantalum oxide is easy to join. For this reason, in addition to the effect of the first embodiment, the adhesion between the mold base material 2 and the rhenium dioxide film 3 can be improved.

In the above embodiment, the intermediate layer 4 of the samples 4 to 7 is composed of four film layers, and oxygen atoms in the intermediate layer 4 are moved from the mold base material 2 side to the rhenium dioxide film 3 side which is the outermost layer. It is formed so as to increase the ratio to four stages. However, the number of intermediate layers 4 is not limited as long as the number of steps is two or more and the number of steps of increasing the proportion of oxygen atoms in the intermediate layer 4 is two or more. Further, the sample 8 is configured so that the proportion of oxygen atoms in the intermediate layer 4 increases monotonously without decreasing as it moves from the mold base material 2 side to the rhenium dioxide film 3 side. The proportion of oxygen atoms in 4 need not be monotonically increased from the mold base 2 side to the rhenium dioxide 3 side, and there may be a region where the proportion of oxygen atoms is constant.
In the above embodiment, the composition of the intermediate layer 4 is changed from metal tantalum to tantalum oxide as the intermediate layer 4 moves from the mold base material 2 side to the rhenium dioxide film 3 side. However, the composition of the intermediate layer 4 is not limited to this. For example, as the composition moves from the mold base 2 side to the rhenium dioxide film 3 side, the metal chromium is changed to chromium oxide, and the metal titanium is changed to titanium oxide. May be.

As mentioned above, although 1st Embodiment and 2nd Embodiment of this invention were explained in full detail with reference to drawings, the concrete structure is not restricted to this embodiment, The structure of the range which does not deviate from the summary of this invention Changes are also included.
For example, in the said 1st Embodiment and 2nd Embodiment, the lanthanum type | system | group L-LAH53 was used for the glass material. However, without being limited thereto, for example, titanium oxide-based L-TIM28 (manufactured by OHARA) may be used as the glass material. When an optical element molding test was performed with the optical element molds of the first and second embodiments using L-TIM 28, the test results shown in Tables 1 and 2 were almost the same. .

  Moreover, in the said 1st Embodiment and 2nd Embodiment, although the rhenium dioxide film was used for the shaping | molding surface of the shaping | molding die for optical elements, not only this but a rhenium dioxide film | membrane is formed in the whole surface of the shaping | molding die for optical elements. You may do it. With this configuration, the optical element molding die can be used in the air without using a non-oxidizing atmosphere gas such as nitrogen, so that the manufacturing cost of the optical element can be reduced.

Moreover, in the said 1st Embodiment and 2nd Embodiment, the rhenium dioxide film | membrane 3 was shape | molded by RF sputtering method. However, the rhenium dioxide film 3 is not limited to the RF sputtering method, but rhenium dioxide film formation such as ion plating method, arc ion plating method, reactive plasma film formation, film formation targeting rhenium oxide and the like can be performed. Any means is possible.
Further, as the material of the mold base material 2 in the first and second embodiments, silicon nitride, aluminum nitride, alumina or the like may be used.

1, 6 Optical element molding die 2 Mold base material 2a Molded part surface

Claims (2)

In the mold for an optical element used in the press molding of the optical element made of glass, Ri Do from the membrane layer on its outer surface consisting dioxide rhenium of at least the molding surface of the mold for the optical element,
The outermost film layer has a thickness of not less than 50 nm and not more than 2000 nm . An intermediate layer is provided between the mold base material and the outermost layer,
Claim 1, wherein the intermediate layer contains tantalum atom, according proceeds from the basic material side to the outermost layer side, characterized in that it is configured to increase the proportion of oxygen atoms in the intermediate layer The mold for optical elements described.

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