JP5364435B2 - 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 didysprosium trioxide film 3. By forming the didysprosium trioxide 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 the 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 Tg point (glass transition point) and therefore has a high molding temperature (for example, 800 ° 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.
The optical element molding die of the present invention is a film layer in which at least the outermost layer of the optical element molding die is made of didysprodium trioxide in the optical element molding die used for press molding of an optical element made of glass. Tona is, is characterized in that the outermost layer of the film layer is a thickness of less than 2000nm or 50nm.
It should be noted that the film layer made of didysprodium trioxide is likely to vary in the way of oxidation during production, but if the oxidation number of the dysprodium atom is x and is within the range of + 2.5 ≦ x ≦ + 3.5 good. 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 this invention, paying attention to the action of didysprodium trioxide (Dy ₂ O ₃ ), the life of the mold is extended by forming a film layer made of didysprodium trioxide on at least the outermost layer of the mold. Yes. As a deterioration factor of the mold, there is oxidation of the mold surface by oxygen in the atmosphere. However, since didysprodium trioxide is originally a stable oxide, 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 didysprodium trioxide on at least the outermost layer of the mold, the releasability of the glass is good, and the chemical reaction with oxidation or glass Deterioration due to reaction and element 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 didysprodium trioxide having a melting point of about 2400 ° C., the molding can be performed at a high temperature of about 1000 ° C., for example.

Film layer trioxide dysprosium as a membrane used in the outermost layer of the mold of the molding surface, if more than 50nm thick can be obtained sufficiently advantages thereof. 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 dysprodium target by an RF sputtering method in a state where the pressure in the vacuum chamber is 10 ⁻² Pa. Sputtered particles of metal dysprodium are oxidized by oxygen gas in the atmosphere, most of which becomes stable didysprodium trioxide (Dy ₂ O ₃ ), and didysprodium trioxide is formed on the molding part surface 2 a of the mold base 2. The membrane 3 is formed. In the present embodiment, since only one film layer is formed on the molding part surface 2a of the mold base material 2, the didysprodium trioxide film 3 becomes the outermost film layer and, at the same time, the didysprodium trioxide film. After the formation of 3, the surface of this film becomes the molding surface of the optical element molding die 1. In addition, since the melting point of didysprodium trioxide is about 2400 ° 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 are 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 layer of dysprodium trioxide film 3. did.

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. The thickness of the didysprodium trioxide film 3 is 50 nm for the sample 1 and 200 nm for the sample 2 and the sample 3.
The thickness of the didysprodium trioxide film 3 is preferably 50 nm or more and 2000 nm or less. If the thickness of the didysprodium trioxide 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 didysprodium trioxide film 3 exceeds 2000 nm, the thickness of the didysprodium trioxide film 3 becomes too thick and the strength of the didysprodium trioxide film 3 is lowered.

This optical element molding die 1 is assembled in a circulation type isothermal molding machine, and a lanthanum-based L-LAH85 (manufactured by OHARA) is used as a glass material to perform a press molding test of glass as an optical element at a molding temperature of 700 ° C. It was.
Note that L-LAH85 has a Tg point of 614 ° C. and an At point (glass deformation point) of 659 ° 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 didysprodium trioxide 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-LAH85 is heated and softened, a part of the contained components volatilizes. Therefore, generally, a small amount of volatile components 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-LAH85 and the didysprodium trioxide film 3 are in direct contact with each other, but both the glass material and the didysprodium trioxide film 3 are oxides. It has been found that chemical bonding is difficult to occur between each other, and the optical element can be satisfactorily molded without causing seizure of the optical element or deposition of volatile components on the didysprodium trioxide film 3.

Thus, according to the optical element molding die 1 of the first embodiment of the present invention, the dysprodium trioxide film 3 is formed on the mold base material 2 and the outermost surface layer of the molding surface of the optical element molding die 1 is divided into three layers. By using the didysprodium oxide film 3, the releasability of the glass is good, and 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, by setting the outermost layer of dysprodium trioxide film 3 to a thickness of 50 nm or more, the function and 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 dysprodium trioxide film 3 made of didysprodium trioxide having a melting point of about 2400 ° 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.
In the optical element molding die 6 of this embodiment, an intermediate layer 4 is formed between the die base material 2 and the didysprodium trioxide film 3. And as shown in Table 2, as the optical element molding die 6 of this embodiment, the material of the mold base material 2, the material of the intermediate layer 4, and the material and thickness of the outermost layer were changed, and the samples 4 to 4 were changed. 8, Comparative Example 1 and Comparative Example 2 were produced.

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. 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 most bismuth trioxide. The film layer on the dysprodium film 3 side is formed of tantalum oxide (Ta ₂ O ₅ ). In the four film layers constituting the intermediate layer 4, the proportion of oxygen atoms in the composition of the film layer increases at a constant rate as it moves from the mold base 2 side to the didysprodium trioxide film 3 side. It is configured. 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%.
In this manner, the intermediate layer 4 in the samples 4 to 7 is formed by four film layers, with the composition being changed in four steps from the mold base material 2 side to the didysprodium trioxide film 3 side. Yes.
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 didysprodium trioxide film 3 side. The total thickness of 4 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 didysprodium trioxide 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.

Similarly to 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-LAH85 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 didysprodium trioxide film 3. In the sample 4 in which the thickness of the didysprodium trioxide film 3 was 30 nm, the didysprodium trioxide 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 didysprodium trioxide film 3 was 50 nm, 200 nm, and 500 nm, there was no problem in the optical element mold 1 even when the optical element was molded into 1000 shots. Sample 8 is obtained by continuously changing the composition of the intermediate layer 4 and setting the thickness of the outermost layer of dysprodium trioxide film 3 to 200 nm. There was no.

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 2 in which the intermediate layer 4 was formed of metal titanium and the outermost layer was formed of TiN having a thickness of 100 nm, the optical element was seized and spoiled when 10 shots of the optical element were formed.
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 material 2 and the thickness of the outermost layer of the dysprodium trioxide film 3 are the same, By providing an intermediate layer 4 having a metal tantalum composition on the mold base 2 side and a tantalum trioxide composition on the mold base material 2 side between the material 2 and the didysprodium trioxide film 3, trioxide It was found that the didysprodium film 3 was difficult to peel from the mold base material 2.

  Thus, according to the mold 6 for an optical element of the second embodiment of the present invention, the mold base 2 side of the intermediate layer 4 is made of metal tantalum that can be easily bonded to WC, and the didysprodium trioxide film 3 side is Tantalum oxide is easy to bond with didysprodium trioxide. For this reason, in addition to the effect of the first embodiment, the adhesion between the mold base material 2 and the didysprodium trioxide 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 the intermediate layer 4 is moved from the mold base material 2 side to the outermost layer of the dysprodium trioxide film 3 side. It is formed so as to increase the proportion of oxygen atoms in 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 such that the proportion of oxygen atoms in the intermediate layer 4 increases monotonously without decreasing as it moves from the mold base 2 side to the didysprodium trioxide film 3 side. The ratio of oxygen atoms in the intermediate layer 4 does not have to increase monotonously from the mold base 2 side toward the didysprodium trioxide film 3 side, and there is a region where the ratio of oxygen atoms is constant. You may do it.
Moreover, in the said embodiment, the composition of the intermediate | middle layer 4 was changed from the metal tantalum to the tantalum oxide as the intermediate | middle layer 4 moved to the dysprodium trioxide film | membrane 3 side from the type | mold base material 2 side. However, the composition of the intermediate layer 4 is not limited to this. For example, the metal chromium is changed from chromium oxide to metal oxide and from titanium metal to titanium oxide as the mold base material 2 side is moved to the didysprodium trioxide film 3 side. You may comprise.

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 first embodiment and the second embodiment, lanthanum-based L-LAH85 is used as 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, you may form a didysprodium trioxide film | membrane on the whole surface of the shaping | molding die for optical elements. 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, although the rhenium dioxide film was used for the shaping | molding surface of an optical element shaping | molding die, not only this but the didysprodium trioxide film | membrane 3 was shape | molded by RF sputtering method. However, the formation of the dysprodium trioxide film 3 is not limited to the RF sputtering method, but includes ion plating, arc ion plating, reactive plasma deposition, deposition using ruthenium oxide as a target, and the like. Any means capable of forming dysprodium can be used.
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 outermost layer is made of trioxide dysprosium 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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