JPH0226844A - Method for forming optical element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to a method for molding, for example, lenses, prisms, and other optical elements, and particularly relates to mold releasability between an optical element forming material and a mold. Regarding technology to improve

(Prior Art) Conventionally, in manufacturing optical elements such as lenses, glass or other optical element forming materials (hereinafter sometimes simply referred to as optical materials) have been polished and molded. It's here. However, in recent years, effective molding surfaces have been formed on molds made of various materials in accordance with the design of optical elements.
Techniques for molding optical elements into virtually the same shape are widely used.

Hereinafter, conventional optical element molding techniques will be explained with reference to the drawings. In the following description, an example of the configuration of a mold used for manufacturing an optical element will be described.

FIG. 2 is an explanatory diagram showing a schematic cross-section of a mold whose effective molding surface is a concave surface, as an example of the configuration of the mold.

As can be understood from this figure, the mold 10 is composed of a base material 12 and a thin film 14, and usually, after polishing and forming an effective molding surface a on the base material 12 using a machine tool such as a precision lathe, this It is generally produced by depositing a thin film on the surface of the effective molding surface a.

The thin film 14 is deposited by sputtering, ion blasting, chemical vapor deposition (CVD), or any other suitable technique depending on the thin film material.
The process is performed to a uniform film thickness of about m), and the process is performed so that the surface shape of the thin film 14 and the shape of the effective molding surface a of the base material 12 described above are substantially the same. Therefore, in the following description, The surface shape of the thin film 14 is referred to as an effective molding surface, and the surface b8 is referred to as an effective molding surface of the mold 10.

When molding an optical element using such a mold 10, first, the mold and the optical material are heated at least until the material softens.

Thereafter, this softened optical material is pressed against the aforementioned effective molding surface to mold the optical material into a shape corresponding to the surface. Here, when molding one optical element, it is common to use two or more molds. Therefore, during this press molding, the effective molding surfaces are pressed against the softened optical material in a state in which they are in contact with each other.

Subsequently, in order to harden the optical material which is molded into a predetermined shape according to the effective molding surface and is in a softened state, the mold and the optical material are allowed to cool or are cooled to obtain an optical element.

The material of the base material 12 constituting the above-mentioned mold 10 is as follows:
Materials that satisfy heat resistance, mechanical strength, workability, etc. are used, such as those disclosed in JP-A-52-45613 and JP-A-6.
Carbide-based compounds disclosed in Japanese Patent No. 0-195026, stainless steel, various heat-resistant alloys containing nickel as a main component, various ceramics, voxels, cermets, and the like are known.

Examples of the materials for the thin film 14 mentioned above include various ceramics including titanium nitride (TiN), alumina (AQ203), and silicon nitride (Sin), and gold (
Au), platinum (Pt), platinum group metals (e.g. rhodium (
Noble metals including Rh)) are known.

In such a technique, the thin film 1 constituting the mold 10
4 is provided for the purpose of increasing the durability of the effective molding surface and the workability of optical elements by ensuring the oxidation resistance and reaction resistance of the effective molding surface.

Furthermore, another function of the thin film 14 is to improve the wettability of the softened optical material to the effective molding surface. In this way, by improving the wettability between the mold and the optical material, it is possible not only to improve the processability described above but also to improve the releasability between the optical element and the mold.

(Problems to be Solved by the Invention) As can be understood from the above explanation, the conventional molding method using a mold is to heat the material for forming an optical element to a temperature intended to soften it, press-form it, and then press-form it. In order to take out the optical element, the temperature is lowered to, for example, room temperature. Therefore, due to the temperature difference between the time of press molding and the time of removal, the optical element and the mold undergo dimensional shrinkage according to their respective coefficients of thermal expansion.

Therefore, depending on the shape of the effective molding surface and the difference in the thermal expansion coefficients mentioned above, there is a problem that the optical element may clamp the mold, or the mold may clamp the optical element, reducing mold release properties. There was.

In order to deal with such deterioration in mold releasability, mechanical removal of the optical element from the mold has also been achieved. However, in such a case, there arise problems such as damage to the optical element, resulting in a decrease in yield, or, from the standpoint of mass production, a long time being required for the molding cycle, resulting in a decrease in molding efficiency.

This invention was developed in view of the above-mentioned conventional problems, and it is possible to mold an optical element that can improve the yield and molding efficiency by improving the releasability between the optical element and the mold. The purpose is to provide technology.

(Means for Solving the Problem) In order to achieve this object, according to the method for molding an optical element according to the first invention of this application, a mold having an effective molding surface consisting of a concave surface is heated. When molding an optical element by pressing the softened material for forming an optical element, the coefficient of thermal expansion of the base material constituting the mold described above is α1, and the coefficient of thermal expansion of the material for forming an optical element is 02, and these It is characterized in that it is molded under conditions where the coefficient of thermal expansion satisfies α, ≦α2'Fr.

Further, according to the method for molding an optical element according to the second invention of this application, an optical element forming material softened by heating is pressed onto a mold having an effective molding surface consisting of a convex surface to mold an optical element. In doing so, it is assumed that the thermal expansion coefficient of the base material constituting the mold described above is α1 and the thermal expansion coefficient of the optical element forming material is 02, and that the molding is performed under the condition that these thermal expansion coefficients satisfy α1≧α2. It is a feature.

In general, when carrying out the method of the first invention or the method of the second invention according to this application, on the surface of the above-mentioned base material,
It is preferable to use a mold on which a thin film of ceramics or noble metal is deposited to constitute the effective molding surface described above.

(Function) According to the method for molding an optical element according to the first invention of this application, when molding an optical element having a convex shape with a mold having an effective molding surface consisting of a concave surface, Between the coefficient of thermal expansion α and the coefficient of thermal expansion α2 of the optical material, α,
The configuration satisfies the relationship ≦α2. Therefore, if the temperature difference between the above-mentioned press molding and take-out is 8T, the dimensional shrinkage 1 of the base material and the dimensional shrinkage 2 of the optical material are expressed by α1ΔT or α2ΔT.

Therefore, the relationship between these dimensional shrinkages and L2 is ≦. bawl.

In such a dimensional shrinkage relationship, in the case of an optical element having a convex shape, the dimensional shrinkage L1 of the optical element is greater than the dimensional shrinkage L1 of the base material corresponding to the center of curvature of the effective molding surface.
is larger or these two values are equal, so that no clamping occurs between the optical element and the mold.

Further, according to the method for molding an optical element according to the second invention of this application, when molding an optical element having a concave shape using a mold in which an effective molding surface consisting of a convex surface is formed, heat of the base material is The structure is such that the relationship α,≧α2 is satisfied between the coefficient of expansion α1 and the coefficient of thermal expansion α2 of the optical material. For this reason, the dimension of the base material shrinks when the temperature difference mentioned above is set at 6.
and the dimensional shrinkage of the thin film, the relationship of 2 becomes ≧L2.

As can be understood from this relationship of dimensional shrinkage, in the case of an optical element having a concave shape, the dimensional shrinkage of the optical element is greater than the dimensional shrinkage L1 of the base material corresponding to the center of curvature of the effective molding surface. Since 2 is smaller or these two values are equal, no tightening strain occurs between the optical element and the mold.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, preferred specific conditions of the present invention such as materials, shapes, M distribution relationships, numerical conditions, and others will be illustrated and explained, but the present invention is limited only to these specific conditions. I want you to understand that this is not a thing.

In addition, in the following examples, various optical glasses are used as examples of materials for forming optical elements, and two different molds (hereinafter referred to as upper molds and lower molds) are used to mold optical elements. explain.

As already explained, in the method according to the present invention, the difference in thermal expansion coefficient between the base material and the optical element forming material is utilized to improve the releasability between the mold and the optical element. Therefore, in order to facilitate understanding of the explanation, prior to the example of the molding method, the thermal expansion coefficient α of the material constituting the base material,
For the thermal expansion coefficient α2 of the material constituting the optical element, −
Give an example.

Table 1 (i) Base material materials First, we will list conventionally known examples of materials constituting the base material, and list the material names and coefficients of thermal expansion. (ii) Materials for forming optical elements. Table 2 shows the thermal expansion coefficient α2 of main optical glasses and the transition point (temperature necessary for softening) of each material as an example of materials for forming optical elements.

Table 2 In this first example, a case will be described in which an optical element having a concave shape and a convex shape is molded using optical glass F2 (manufactured by Ohara Optical Glass Co., Ltd.) as the material for forming the optical element.

FIGS. 1(A) to (C) are for explaining the first embodiment.
FIG. 3 is an explanatory diagram showing a schematic cross section of the constituent components in each molding step.

First, in this first embodiment, as can be understood from FIG. 1(A), the upper mold 10a is a mold in which an effective molding surface consisting of a convex surface is formed, and an effective molding surface consisting of a roughly concave surface is used as the upper mold 10a. Each mold was produced using the mold in which the surface b2 was formed as the lower mold 10b.

In producing the upper mold 10a, the thermal expansion coefficient α2 of the optical glass F2 used as the optical material is 99X In-7 (deq
-'
dec+-') was used for the 5US4207a base material 12a.

Specifically, first, an effective molding surface consisting of a convex surface (corresponding to the effective molding surface a in FIG. 2 described above) is formed using an ultra-precision lathe, and then polished with a diamond abrasive to improve the surface roughness R, , lax is 0.01 (un) to obtain the base material 12a.

Next, using sputtering technology, the above-mentioned base material 1
A film of platinum (Pt) with a thickness of 2 (μ
The thin film 14a of m) was deposited to produce an upper mold 10a.

In addition, when producing the lower mold + ob, as mentioned above,
Since the thermal expansion coefficient α2 is 99x 1O-7 (deq-'), the method according to the first invention of this application is applied,
As an example of a material satisfying the condition α,≦α2, tungsten carbide having a thermal expansion coefficient α of 47×10−′ (de9−′) was used for the base material 12b.

The lower mold +ob was manufactured in the same manner as the upper mold 10a. First, an effective molding surface consisting of a concave surface was formed using an ultra-precision lathe, and then the surface roughness Rmax was adjusted to 0.01 (um). The base material 12b is obtained by polishing.

After that, the above-mentioned base material 12 is formed by sputtering technology.
A thin film +4b made of titanium nitride (TiN) with a thickness of 1 (urn) is deposited on the effective molding surface of the lower mold 10b.
I got it.

Next, the above-mentioned upper mold 10a and lower mold 10b! The process of actually molding an optical element using the method will be described in detail.

First, with reference to FIG. 1(A) mentioned above, press molding 1
To briefly explain the configuration of the device used, 16a and +6b indicate hydraulic cylinders installed in the heating furnace of the press molding device, and the upper hydraulic cylinder 16a is connected to the upper die 10a.
, and a lower mold 10b is attached to the lower hydraulic cylinder 16b, respectively. Reference numeral 18 indicates a thermocouple for measuring the temperature of the upper mold 10a or the lower mold 10b, and the thermocouple 18 is arranged in each of the above-mentioned hydraulic cylinders 16a and +6b. Further, 20 is a heater provided in the heating furnace, 22 is a molding section, and 24 is a gas inlet communicating with the molding section.

First, the above-mentioned optical element forming material (optical glass F2
) and polish it into a spherical shape. After silence, lower mold 10
An optical material 26 polished into a spherical shape is placed above the concave portion constituting the effective molding surface b2 of b, and the molded portion 22 is isolated from the outside air. Next, while measuring the temperatures of the upper mold 10a and the lower mold tab with the thermocouple 18, heating is performed using the heater 20 (heating is performed by the heater 20) until the temperature of the mold reaches approximately 500°C. In order to reduce deterioration of the lower mold 10b, silicon gas was introduced into the molding section 22 through the gas inlet 24 and heated to create a non-oxidizing atmosphere.

Subsequently, as can be understood from FIG. 1(B), after the temperature of the upper mold 10a and the lower mold +ob reached the above-mentioned predetermined value by heating, a pressure of about 70 (9/cm') was applied. The cylindrical molds are brought into pressure contact with each other by the hydraulic cylinders 16a and +61), and the optical material 26 described above is press-molded.

Next, the heater 20 is stopped and the optical material 2 after press molding is heated.
6, the upper mold 10a, and the lower mold 10t) are left to cool.

After that, the upper mold 10a and the lower mold 10b are connected by the thermocouple 18.
When it is confirmed that the temperature of Get 28.

By repeating the above steps, tightening between the two molds and the optical element was avoided, and a highly accurate optical element could be manufactured with good yield and high reproducibility.

Mth Example Next, as a second example, a case will be described in which optical glass F4 (manufactured by Koya Optical Glass Co., Ltd.) is used as the optical element forming material and an optical element having a concave shape and a convex shape is molded.

In this embodiment, similarly to the first embodiment described with reference to FIGS. 1(A) to (C), the upper mold 10a is a mold in which an effective molding surface b1 consisting of a convex surface is formed. The mold on which the effective molding surface b2 consisting of a roughly concave surface is formed is the lower mold +
The case where each is prepared and used as an ob will be explained.

First, in manufacturing the upper mold 10a, the thermal expansion coefficient α2 of the optical glass F4 used as the optical material is 95×10'' (d
e9-'
'(de9-') nickel is used for the base material 12a,
It was produced under the same conditions as in the first example. Next, using sputtering technology, a film of platinum-gold (Pt-Au) alloy with a thickness of 2 (u
The thin film 14a of n) was deposited to obtain an upper mold 10a.

In addition, in manufacturing the lower mold 10b, as proposed by the applicant of this application in Japanese Patent Application No. 62-306937, the base material is made of glass, and the effective molding surface of the base material is A mold was constructed by depositing a thin film on the material.

To explain in detail, as mentioned above, since the thermal expansion coefficient α2 of the optical material is 95x 10-'(deq-'), the method according to the first invention of this application is applied, and α, ≦
As an example of a material that satisfies the condition of α2, the thermal expansion coefficient α1
Optical glass La whose is 68×10-'(deq-')
S F 014 (manufactured by Koya Optical Glass, transition point approximately 695 (
"C)) was used for the base material +2t).

The lower mold 10b is manufactured by first using a bond having an effective molding surface consisting of a concave surface and molding it under the same conditions as the above-mentioned upper mold 10a.
A lower mold tab was obtained by depositing a thin film +4b made of t-Au alloy and having a thickness of 2 (um).

Using the upper mold 10a and lower mold 1 (H) thus produced, an optical element was molded in the same manner as in the first example.
As described above, a highly accurate optical element could be manufactured with good yield and high reproducibility.

Comparison Example Next, in order to make a comparison with the above-mentioned example in which the method of the present invention was applied, we will explain how to form an optical element having a planar shape and a convex shape. Molding into a convex shape was performed using a conventional molding technique (not shown).

To explain the configuration of the mold in detail, first, using optical glass 5FSOI as the optical element forming material, the upper mold 10a is
, the thermal expansion coefficient α2 of the material SFS○] is +
oox+o-F (dec+-' did. Next, using sputtering technology, nickel-chromium (Ni-
A thin film with a thickness of 0.2 (um) made of a Cr) alloy and a thin film with a thickness of 1.8 (um) made of the above-mentioned Pt-Au alloy were sequentially deposited to form a thin film 14a, and an upper mold 10a was obtained. Ta.

In such an upper mold 10a, N is sandwiched between the base material and the Pt-Au alloy film that substantially constitutes the effective molding surface.
The i-Cr alloy film was provided for the purpose of increasing the bonding force between the base material made of quartz and the Pt-Au alloy film.

In addition, when producing the lower mold tab, as mentioned above,
The thermal expansion coefficient 02 of the optical material is +00 Xl0-7 (de
+;+-'), so α is 120 x 10
-'(deq-') is 5US420! Base material + 2b, film thickness made of TiN by sputtering technology]
A thin film +4b of (um) was deposited to form a lower mold 10b.

When an optical element was molded in the same manner as in the first and second embodiments using the upper mold 10a and lower mold 10b thus produced, it was possible to mold a planar shape without causing the aforementioned tightening. Ta.

However, when molding a concave shape, clamping occurs between the mold and the optical element, resulting in a decrease in yield due to damage to the optical element and a decrease in molding efficiency over time. In addition, when such a lower mold was repeatedly used for molding, it was observed that the mold could not be released after several thousand molding cycles.

The embodiments of the invention related to this application have been described above, but
The method for molding an optical element according to this application is not limited only to the above-mentioned embodiments, and the materials, shapes, mounting configurations, numerical conditions, M arrangement relationships, and other conditions are within the scope of the present invention. It will be obvious that any suitable design changes and modifications may be made therein.

(Effects of the Invention) As is clear from the above description, according to the method for molding an optical element according to the first invention of this application, a mold having an effective molding surface consisting of a concave surface and a convex surface shape can be used. When molding an optical element, the structure is such that the relationship α1≦02 is satisfied between the thermal expansion coefficient α of the base material and the thermal expansion coefficient α2 of the optical material.

Therefore, in the case of an optical element having a convex shape, the dimensional shrinkage L2 of the optical element is larger than the dimensional shrinkage L1 of the base material corresponding to the center of curvature of the effective molding surface, or Since the two values are equal, no clamping occurs between the optical element and the mold.

Further, according to the method for molding an optical element according to the second invention of this application, when molding an optical element having a concave shape using a mold in which an effective molding surface consisting of a convex surface is formed, heat of the base material is The structure is such that the relationship α blindness≧α2 is satisfied between the expansion coefficient α and the thermal expansion coefficient α2 of the optical material.

Therefore, in the case of an optical element having a concave shape, the dimensional shrinkage of the optical element (2) is smaller than that of the base material corresponding to the center of curvature of the effective molding surface, or Since the two values are equal, no clamping occurs between the optical element and the mold.

As described above, according to the invention of this application, the condition between the thermal expansion coefficient α of the base material constituting the mold and the thermal expansion coefficient α2 of the optical element forming material is determined by adjusting the shape of the effective molding surface. By setting the settings according to Optical elements can be provided at low cost.

[Brief explanation of the drawing]

Figures 1 (A) to (C) are explanatory diagrams showing schematic cross-sections of each optical element molding process in order to explain the present invention in detail, and Figure 2 is to explain the prior art and embodiments. FIG. 2 is an explanatory diagram schematically showing, in cross section, an example of the configuration of a mold. 10, lOa, l0b-... mold, 12.12
a, 12b----base material 14, 14a, 14b...
...Thin film, 16a, 16b...Hydraulic cylinder 18
...Thermocouple, 20...Heater, 22...
Molding part 24...Gas inlet 26...Optical (for element formation) material 28...Optical elements a, b, b,, b2...Effective molding surface. ■12a Figure 1 (A) Procedural amendment

Claims (3)

[Claims] (1) A mold with an effective molding surface consisting of a concave surface,
When molding an optical element by pressing the optical element forming material softened by heating, the thermal expansion coefficient of the base material constituting the mold is α_1, and the thermal expansion coefficient of the optical element forming material is α_2, A method for molding an optical element, characterized in that molding is performed under conditions in which the coefficient of thermal expansion satisfies α_1≦α_2. (2) A mold with an effective molding surface consisting of a convex surface,
When molding an optical element by pressing the optical element forming material softened by heating, the thermal expansion coefficient of the base material constituting the mold is α_1, and the thermal expansion coefficient of the optical element forming material is α_2, A method for molding an optical element, characterized in that molding is performed under conditions in which the coefficient of thermal expansion satisfies α_1≧α_2. (3) The optical element according to claim 1 or 2, wherein the mold comprises the base material and a thin film made of ceramic or noble metal for forming the effective molding surface. Molding method.