JPH06166525A - Mold for forming optical element - Google Patents

Abstract

PURPOSE:To obtain a mold for forming an optical element having high denseness and thermal conductivity by using a sintered compact containing AlN as a principal component and a specific amount of CaO as a sintering assistant. CONSTITUTION:This mold for forming an optical element is formed from a sintered compact containing AlN as a principal component and 0.5-5wt.% CaO. The sintered compact having a high thermal conductivity and a high density is obtained with a lower content of the CaO than that of Y2O3 which is a conventionally used sintering assistant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical glass element, and more particularly to an optical element molding die used for manufacturing a high precision optical glass element which does not require a polishing step after press molding.

[0002]

2. Description of the Related Art Generally, in designing an optical glass element, an aspherical surface is used to simplify a lens portion. However, in the manufacturing method of this aspherical optical glass element, mass production was difficult by the conventional polishing method.
Therefore, in recent years, a method has been developed in which the optical glass is softened by heating and press-molded with a mold having a highly accurate aspherical shape.

In this press molding, since the glass is softened at a high temperature to form the optical surface only by pressing, a material which does not react with the glass at a high temperature is required. Therefore, the mold material is required to have poor wettability with glass. In order to satisfy the characteristics, conventionally, for example, as disclosed in Japanese Patent Application Laid-Open No. 3-83825, the above-mentioned problem is solved by a molding die in which at least a molding surface is formed with AlN.

[0004]

The AlN material has a heat conductivity of 100 W in addition to the poor wettability with the glass.
/ M · K or more. For materials with high thermal conductivity, heating and cooling can be controlled easily, so temperature control during molding can be performed easily. However, JP-A-3-8
The molding die disclosed in Japanese Patent No. 3825 is Y ₂ O ₃ · T.
Since hO ₂ is used as an auxiliary agent, it has poor wettability with glass and is unlikely to cause fusion, but it is necessary to contain the auxiliary agent in an amount of 5 to 10 wt% in order to enhance the thermal conductivity. Also, Y ₂
In order to make AlN into a dense sintered material by using O ₂ · ThO ₂ as an auxiliary agent, it is necessary to contain the auxiliary agent in an amount of 5 to 10 wt% or more.

The sintering step is based on the following steps. When AlN is sintered, grain growth occurs. Grain growth does not become a dense sintered material by confining pores existing between grains. Therefore, an auxiliary agent is contained. Upon sintering, the auxiliary agent becomes a liquid phase and precipitates at grain boundaries. This suppresses the growth of particles and facilitates the movement of internal pores to the outside.
It becomes a precise material. At the interface between the particles and the auxiliary agent, apparently high-purity AlN can be sintered due to the characteristic that solid solution oxygen and impurities are taken into the liquid phase. In the above conventional method, Y ₂
Since O ₃ · ThO ₂ is used as an auxiliary agent, the above proportion is necessary for sintering the dense structural material.

Therefore, a large amount of an auxiliary agent is required in order to obtain a mold material having both the denseness and the thermal conductivity. However, when the amount of the auxiliary agent is large, contact with high temperature glass causes the problem that the auxiliary agent precipitated between particles is decomposed and the surface is deteriorated. In particular, the durability was remarkably reduced when the glass was continuously formed for a long time or when the glass was formed at a high temperature. Further, when Y ₂ O ₃ and ThO ₂ are contained in an amount of ₅ to 10 wt%, the characteristics of AlN are weakened by Y ₂ O ₃ and ThO ₂ , and the thermal conductivity of the molding surface of the molding die having the above composition is low. It became easier to burn.

The present invention has been made in view of the above-mentioned problems, and the above-mentioned high compactness, which is the above-mentioned problem with a low amount of auxiliary agent,
An object is to provide an optical element molding die having high thermal conductivity.

[0008]

In order to solve the above problems, the present invention forms an optical element by a sintered body containing AlN as a main component and 0.5 to 5 wt% CaO as a sintering aid. It was decided to form a mold. This makes it possible to solve the problems of denseness and thermal conductivity with a low content of auxiliary agent.

[0009]

FIG. 1 shows the relationship between the amount of CaO added and the relative density. From FIG. 1, it is confirmed that the auxiliary agent of CaO has a higher relative density than Y ₂ O _{3 with} a lower amount of the auxiliary agent. Also C
When the thermal conductivity of a sintering agent having aO of 1 to 2 wt% was measured, it was 150 W / m · K, but Y ₂ O ₃ was 1 to ₂ w.
When the thermal conductivity of the t% sintering agent was measured, it was 100 W /
m · K, the CaO auxiliary has a low content and high thermal conductivity,
A high density was obtained.

[0010]

Example 1 (Mold forming method) High-purity AlN powder (purity 99.9%)
The above) and CaO were mixed at a weight ratio of 97: 3, ethanol was added as a dispersion medium, and the mixture was dried at 100 ° C. for 3 hours. Then, it shape | molded in the shape (blank) approximated to the shape shown in FIG. The molding pressure was 1.5 ton. The molded blank 1 is 650-7 in a nitrogen atmosphere.
Degreasing was performed by heating in the range of 00 ° C. After degreasing for 3 hours, the temperature was raised to 1800 ° C., held at that temperature for 5 hours, and then fire-bonded. After heating and holding, it was cooled for 10 hours. The outer shape of the sintered blank 1 was ground with a diamond grindstone to finish the shape. Also, the glass lens molding surface is polished with diamond powder and the surface is rounded.
It was finished to max = 0.08 μm or less.

(Molding Method) A glass material of LaK8 having a low softening point was molded with this optical element molding die. A schematic diagram of the apparatus is shown in FIG. The glass was heated and melted at 1080 ° C. in the crucible 3. 2 is molten glass. After the glass was melted, it was discharged, cut by the shear 4, and then the cut glass gob 5 was received by the carrying dish 6. The carrier plate 6 was kept at a temperature corresponding to a glass viscosity of 10 ⁵ to 10 ⁷ poise by passing through the heater 7. After being heated and held by the heater 7, the transfer tray 6 was fixed by the transfer arm 10, transferred and rotated between the pair of molding dies 8 and 9 of the present embodiment, and the heated glass was supplied between the dies. The molding dies 8 and 9 are formed of AlN, and are kept at a temperature corresponding to a glass viscosity of 10 ¹² to 10 ¹⁴ poises. After dropping onto the molding die 9, which is the lower die, the pressing time is 5 seconds and the pressing pressure is 5 kgf / cm ^2.
After that, it was pressed at a pressing pressure of 160 kgf / cm ² and pressed for 15 seconds.

(Effect) When continuous molding was carried out by this molding method, no auxiliary agent was deposited on the molding surface and no deterioration of the surface was observed even after continuous molding for 25,000 shots or more. The above mold has good thermal conductivity, and has a characteristic that the molding surface is not easily deteriorated even when continuous molding is performed because the sintering aid is small even at high temperature molding of molten glass or the like.

The weight percentage of AlN and CaO is 97: 3.
The same effect was obtained even if the weight% of CaO was reduced to 0.5 wt%. However, if the amount is less than that, the amount of the auxiliary agent decreases, and grain growth of AlN occurs, so that a dense sintered material cannot be obtained. Further, even if the weight percentage of CaO was increased to 5 wt%, the same effect as above was obtained, but if it is more than that, the problem that the thermal conductivity decreases,
There was a problem that O was precipitated and the surface was deteriorated.

[0015]

Example 2 An example is shown in which softened glass having a high softening point such as BK type is molded with the above molding die. The manufacturing method of the molding die is the same as that of the first embodiment.

(Molding Method) The molding method is shown in FIG. A BK7 glass material having a high softening point was molded. The glass material 12 whose both surfaces had been flat-polished was inserted into a carrying jig 13 and further installed on a carrying arm 14. The glass material 12 and the transfer jig 13 were heated by the heater 11 by the transfer arm 14.
It was softened by heating to a temperature corresponding to a glass viscosity of 10 ⁷ to 10 ⁹ poise. After heating, the transfer arm 14 was moved and transferred between the molding dies 16 and 17. Molds 16, 17
Is heated and maintained at a temperature corresponding to a glass viscosity of 10 ¹² to 10 ¹⁴ poise. Press time 20 seconds, press pressure 25
It was molded at 0 kgf / cm ² . Reference numeral 15 is a molded lens.

(Effect) When continuous molding was carried out by this molding method, deterioration of the molding surface did not occur as in Example 1 even after continuous molding of 30,000 shots or more.
Since the above mold material has good heat conduction, heat absorption from the mold surface is good even at high temperature molding of high temperature glass etc., and the temperature difference between the glass and the mold becomes small immediately, so there is a characteristic that glass cracking due to the temperature difference does not occur easily. .

As in Example 1, the weight percentage of AlN and CaO was 97: 3, but the weight percentage of CaO was 0.
Similar effects were obtained even when the amount was reduced to 5 wt%. However, if the amount is less than that, the amount of the auxiliary agent decreases, and grain growth of AlN occurs, so that a dense sintered material cannot be obtained. Also Ca
Even if the weight percentage of O was increased to 5 wt%, the same effect as described above was obtained, but if it was more than that, there was a problem that the thermal conductivity was lowered and that CaO was precipitated and deteriorated from the surface.

[0019]

As described above, according to the present invention, the optical element molding die contains AlN as a main component and CaO of 0.5 to 0.5%.
Since it was formed from a sintered body containing 5 wt%, even if the content of CaO used as an auxiliary agent is 0.5 to 5 wt%, it is possible to have the same compactness and durability as the conventional molding die. Since the content of the auxiliary agent with respect to AlN is smaller than that of the composition of the conventional molding die, the properties of AlN are further emphasized and the thermal conductivity of the molding die is increased.
That is, since a dense sintered body can be obtained with a low amount of auxiliary agent as compared with a conventional molding die, deterioration at high temperature is reduced, and further thermal conductivity is improved, so that temperature control can be easily performed, It is possible to manufacture a highly accurate molded lens.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of CaO added and the relative density.

FIG. 2 is a vertical sectional view showing a molding die molded in Example 1 of the present invention.

FIG. 3 is a schematic configuration diagram showing a molding apparatus used in the first embodiment.

FIG. 4 is a schematic configuration diagram showing a molding apparatus used in Example 2 of the present invention.

[Explanation of symbols]

 1 Blank 8, 9, 16, 17 Mold for molding

Claims (1)

[Claims] 1. A main component of AlN and CaO of less than 0.
An optical element molding die, which is formed of a sintered body containing 5 to 5 wt%.