JPH07101737A - Forming die for optical element - Google Patents

Abstract

PURPOSE:To provide a forming die for an optical element with which generation of cracks or irregular colors can be prevented and a formed surface having a uniform grain diameter can be obtd. CONSTITUTION:The forming die 1 for an optical element consists of a forming plane 2 of a sintered body essentially comprising AlN joined with a base body 3 by diffusion 4. The base body 3 consists of a nonoxide material having 3.5X10<-6> to 5.5X10<-6>/C deg.C coefft. of linear expansion and sintered at 1500-2000 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element molding die particularly suitable for use in press molding of aspherical lenses.

[0002]

2. Description of the Related Art In press molding an aspherical lens,
The optical surface is formed only by pressing on the heat-softened glass. Therefore, it is required that the mold used for this does not react with high temperature glass and has poor wettability to glass.

As a mold for molding an optical element having such characteristics, the applicant of the present invention discloses in Japanese Patent Laid-Open No. 3-83825.
It has been proposed to form the molding surface with a compound containing AlN (aluminum nitride) as a main component. That is, in Example 1 of the publication, sputtering is performed to form an AlN film on the molding surface of the molding die. Further, in Example 2, the entire molding die is manufactured by processing a sintered body using AlN powder and an auxiliary material as raw materials.

[0004]

However, the above-mentioned prior art optical element molding die has the following problems. (1) With respect to the molding die of Example 1, AlN ionized AlN was collided with the surface of the base material by sputtering.
Since the N film is formed, there is a problem that it is difficult to form a compound at the interface between the AlN film and the base material. Also, Al
Since stress is generated at the interface between the N film and the base material, when high-temperature glass adheres at a high pressure, there is a problem that film peeling may occur due to the external force.

(2) With respect to the molding die of Example 2, it is difficult to sinter a thick member such as the molding die.
There is a problem in that oxygen and carbon inside remain without reacting, resulting in uneven sintering or cracking after sintering. In particular, there is a problem that the surface roughness PV does not become 0.1 μm or less even after polishing, because the particle diameter is different in the uneven sintering portion. Further, since the occurrence of sintering unevenness cannot be seen from the surface, there is a problem that defects are not revealed until after processing into a molding die.

The present invention has been made in view of the above problems, and an object thereof is to provide an optical element molding die capable of preventing the occurrence of cracks and color unevenness and obtaining a molding surface having a uniform particle diameter. To do.

[0007]

In order to achieve the above object, the optical element molding die of the present invention has a linear expansion coefficient of 3.5 × 1.
Sintering temperature of 1500 to 20 at 0 ^{-6 to} 5.5 x 10 ^-6 / ° C
The base material made of a non-oxide material at 00 ° C. was diffusion-bonded to a molding surface made of a sintered body containing AlN as a main component.

[0008]

In the optical element molding die of the present invention having the above-mentioned structure, the molding surface is composed of a thin plate-shaped AlN sintered body which is easy to manufacture. This forming surface and the base material are separately pre-sintered,
After shape processing, main sintering is performed while applying pressure in the mold. As a result, the dissimilar members are diffusion-bonded. Here, the following conditions are required to perform the diffusion bonding properly.

(1) The linear expansion coefficient of the AlN sintered body is 4.5 ×
Since it is 10 ^-6 / ° C, the linear expansion coefficient of the base material is 3.5 x 10
Must be ^{-6 to} 5.5 x 10 ^-6 / ° C. This is because when materials having greatly different linear expansion coefficients are joined together, cracks occur due to interfacial stress after sintering. According to an experiment by the inventor, no crack was generated within the above range.

(2) The sintering temperature of the base material must be in the same range as the sintering temperature of AlN (1500 to 2000 ° C.). This is because the main sintering of both is performed at the same time. If the temperature of the main sintering is 1500 ° C. or lower, the sintering of AlN becomes incomplete and pores and color unevenness occur. On the other hand, when the main sintering temperature exceeds 2000 ° C., AlN decomposes and cannot be sintered.

(3) The base material must be a non-oxide type material. This is because the sintering of AlN must be performed in a non-oxidizing atmosphere, and if the base material is an oxide here, oxygen in the base material reacts with AlN to generate Al ₂ O _3. .

[0012]

Embodiment 1 An embodiment of an optical element molding die according to the present invention will be described below with reference to the accompanying drawings. First, a first embodiment of the present invention will be described. FIG. 1 is a sectional view showing a mold for molding an optical element. As shown, this optical element molding die 1 is made of Al
A molding surface 2 made of a sintered body containing N as a main component is diffusion-bonded 4 to a base material 3. Hereinafter, a method for manufacturing the optical element molding die 1 will be described.

First, the AlN sintered body forming the molding surface is pre-sintered. High-purity AlN powder (purity 99.9% or more) having an average particle diameter of 1.3 μm and Y ₂ O ₃ are mixed at a weight ratio of 97: 3, ethanol is added as a dispersion medium, and the mixture is kneaded for 15 hours. This is cast into a disc-shaped mold having an outer diameter of 16 mm and a thickness of 7 mm, and dried at 250 ° C. for 3 hours. After drying, the mixture is heated to 650 to 700 ° C. in a nitrogen atmosphere to degrease, and then temporarily sintered in a nitrogen atmosphere at 1300 ° C. for 2 hours (see FIG. 2a).

Next, the sintered body forming the base material is pre-sintered. High-purity sialon powder with an average particle size of 1.0 μm (purity 9
9.9% or more), Y ₂ O ₃ , Al ₂ O ₃ , and MgO are mixed at a weight ratio of 95: 2: 2: 1, ethanol is added as a dispersion medium, and the mixture is kneaded for 10 hours. This is cast into a mold having the shape of a base material and dried at 250 ° C. for 3 hours. After drying, after heating to 650 to 700 ° C. in a nitrogen atmosphere to degrease,
Pre-sintering is performed in a nitrogen atmosphere at 1300 ° C. for 2 hours (see FIG. 2b).

Next, the temporary sintered body of AlN and sialon was placed in a HIP mold, and main sintering and diffusion bonding were carried out by a HIP molding machine in a nitrogen atmosphere of 1800 ° C. and a pressure of 150 kgf / cm ² for 1 hour. After heating, it was gradually cooled over 2 hours (see FIG. 2c).

The blank thus sintered is ground with a diamond grindstone to finish the outer diameter. Then, the lens molding surface 2a was polished with diamond powder to finish the surface roughness Rmax = 0.08 μm or less (see FIG. 2d).

Using the optical element molding die having the above-described structure, lens molding was performed to test the durability. The optical element molding die tested has a molding surface with an outer diameter of 15 mm,
The AlN sintered body, which is a concave surface of an effective system of 14.5 mm and is a molding surface, has a thickness of 6 mm. Glass material of SK8, outer diameter φ1
A biconvex lens having a size of 5 mm and a center thickness of 4 mm was molded. The outline of the apparatus is shown in FIG. The glass in the crucible 7 is heated and melted by the heater 5 so that the viscosity becomes 10 ² to 10 ³ poise, the plunger 8 is raised, the molten glass 6 is discharged quantitatively from the nozzle, and cut by the shear 9 to cut the lower mold. Drop it on 11. Here, the lower mold 11 is heated by a heater (not shown) to a temperature at which the glass viscosity becomes 10 ¹² to 10 ¹⁴ poises. The upper mold 12 is also made of the same material as the lower mold and is heated to the same temperature. After the molten glass gob 10 was supplied, the lower mold 11 was moved coaxially with the upper mold 12, and was molded under a pressing time of 5 seconds and a pressing pressure of 5 kgf / cm ² , and 3 seconds after the pressing was started, the outer peripheral portion of the mold had a glass viscosity of 10%. After heating the outer peripheral portion of the mold by blowing an inert gas at a temperature corresponding to ⁷ to 10 ⁹ poise for 5 seconds, the pressing pressure is further 80 kgf / cm.
^An optical element was obtained by pressurizing to ² and molding with a pressing time of 20 seconds.

In the optical element molding die of this example, the AlN sintered body, which is the molding surface, had no cracks or color irregularities, the particle size was uniform, and abnormalities such as cracks on the diffusion bonding surface were observed. I couldn't do it. After the molding of 15,000 shots, no problem occurred and it was in a state in which it could be used sufficiently.

On the other hand, for comparison with this example, when an optical element molding die entirely made of AlN alone was manufactured with the same component amounts as described above, cracks were extremely generated. Further, even when no cracks were generated, color unevenness was observed on the polished molding surface. The particle diameter is different in the uneven color portion, and the optical element can be molded at the initial stage of molding, but large particles are likely to fall off after 6000 shot molding.

In this embodiment, sialon having a low coefficient of linear expansion was used as the base material, but Si having the same coefficient of linear expansion was used.
₃ N ₄ (coefficient of linear expansion 3.5 × 10 ^-6 / ° C), HI of SiC
Similar effects were obtained with P sintered bodies (coefficient of linear expansion 4.2 × 10 ⁻⁶ / ° C.) and B 4 C (coefficient of linear expansion 4.5 × 10 ⁻⁶ / ° C.). However, when sintered with a material having a coefficient of linear expansion of less than 3.5 × 10 ⁻⁶ / ° C., cracks were generated from the joint surface.

The main sintering temperature is 1500 ° C.
When the materials of less than 1 were used, AlN was not sintered and pores were formed on the lens molding surface. On the other hand, AlC was not decomposed and could not be sintered in the normal pressure sintered SiC having a temperature higher than 2000 ° C.

Further, although a nitride base material was used in the present embodiment, when sintered with an oxide (Al ₂ O ₃ ),
It could not be used as a mold because AlN reacted to form an oxide.

[0023]

Second Embodiment Next, a second embodiment of the present invention will be described. Figure 4
FIG. 3 is a cross-sectional view showing an optical element molding die. The optical element molding die 1 of this embodiment has a convex shape, and the molding surface 2 and the base material 3 are different from those of the first embodiment. Less than,
A method of manufacturing the optical element molding die 1 will be described.

First, the AlN sintered body forming the molding surface is pre-sintered. High-purity AlN powder (purity 99.9% or more) having an average particle diameter of 1.3 μm and CaO are mixed at a weight ratio of 97: 3, ethanol is added as a dispersion medium, and the mixture is kneaded for 10 hours. This is cast into a disc-shaped mold having an outer diameter of 24 mm and a thickness of 6 mm, and dried at 250 ° C. for 3 hours. After drying, the mixture is heated to 650 to 700 ° C. in a nitrogen atmosphere to degrease, and then temporarily sintered in a nitrogen atmosphere at 1300 ° C. for 2 hours (see FIG. 2a).

Next, the sintered body forming the base material is pre-sintered. High-purity AlN powder with an average particle diameter of 1.3 μm (purity 99.9
%), BN powder, and auxiliary agent Y ₂ O ₃ at 94: 5:
Mix in a weight ratio of 1 and add ethanol as the dispersion medium,
Knead for 10 hours. This is cast into a mold in the shape of the base material, 2
Dry at 00 ° C. for 3 hours. After drying, 6 in a nitrogen atmosphere
After heating to 50 to 700 ° C. and degreasing, nitrogen atmosphere 13
Pre-sinter at 00 ° C. for 2 hours (see FIG. 2b).

Next, the pre-sintered body of AlN and AlN-BN composite material was placed in a HIP mold, and a HIP molding machine was used to carry out a nitrogen atmosphere at 1750 ° C. and a pressure of 200 kgf / cm ² ,
Main sintering and diffusion bonding were carried out for 1.5 hours, and after heating, they were gradually cooled over 3 hours (see FIG. 2c).

The blank thus sintered is ground with a diamond grindstone to finish the outer diameter. Then, the lens molding surface 2a was polished with diamond powder to finish the surface roughness Rmax = 0.08 μm or less (see FIG. 2d).

Using the optical element molding die configured as described above, lens molding was performed to test the durability. The optical element molding die tested has a molding surface with an outer diameter of 23 mm,
The AlN sintered body, which has a concave shape with an effective diameter of 22.5 mm and is a molding surface, has a thickness of 6 mm. A biconcave lens having an outer diameter of 23.4 mm and a center thickness of 2 mm was molded. As a result, the same effect as in Example 1 was confirmed.

In this embodiment, AlN having a high linear expansion coefficient is used.
Although -BN was used as the base material, the same effect can be obtained with other materials having the same linear expansion coefficient. However, when sintered with a material having a coefficient of linear expansion exceeding 5.5 × 10 ⁻⁶ / ° C., cracks were generated from the joint surface.

[0030]

As described above, according to the present invention, A
Since the molding surface made of 1N sintered body is bonded to the base material to form the optical element molding die, the AlN sintered body can be formed of a thin plate, and as a result, cracks and color unevenness can be prevented, and uniform A molding surface having a different particle diameter can be obtained. Also, since the thermal conductivity of AlN is as high as about 150 W / mK, if the thermal conductivity of the base material is changed, the thermal conductivity of the entire mold will change, and the glass cooling rate during molding can be set arbitrarily. I was able to do it.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an optical element molding die according to Example 1 of the present invention.

FIG. 2 is a diagram showing a manufacturing process of the optical element molding die of the present invention.

FIG. 3 is a diagram illustrating lens molding using the optical element molding die of the present invention.

FIG. 4 is a sectional view showing an optical element molding die according to Example 1 of the present invention.

[Explanation of symbols]

 1 Optical Element Mold 2 Molding Surface 2a Lens Molding Surface 3 Base Material 4 Diffusion Bonding Surface

Claims (1)

[Claims] 1. The coefficient of linear expansion is 3.5 × 10 ^{−6 to} 5.5 × 1.
For optical element molding, in which a molding surface made of a sintered body containing AlN as a main component is diffusion-bonded to a base material made of a non-oxide material having a sintering temperature of 0 ^-6 / ° C and a temperature of 1500 to 2000 ° C. Type.