JPS627639A - Method for molding optical glass element - Google Patents

Abstract

PURPOSE:To facilitate the high-accuracy working of a mold form and to reduce remarkably the reaction between the mold and glass even when high m.p. glass is molded by forming a film of a specified metallic oxide on the molding surface of a die using a sintered hard alloy as the base material and further forming an SiC film thereon. CONSTITUTION:A sintered hard alloy is used as the base material and the material is worked into a die in the same form as an optical glass element to be molded. Then, a coating film contg. >=1 kind among Al2O3, SiO2, ZrO2 and TiO2 is formed in uniform thickness on the compression-molding surface of the die and an SiC coating film is further formed thereon in uniform thickness. Glass is heated at a temp. above the m.p. of the glass and then compression-molded in an inert gas atmosphere by using a couple of the obtained dies. The C/Si ratio of the SiC coating film is preferably regulated to 0.7-1.2. The sintered hard alloy to be used as the base material is preferably composed of tungsten carbide (WC).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing an optical glass element, and in particular to a method of manufacturing an optical glass element, particularly an optical glass element that does not require a polishing process after press molding.

The present invention relates to a method for molding an optical glass element.

2. Description of the Related Art In recent years, there has been a trend toward aspheric optical glass lenses, which can simultaneously simplify the lens structure of optical instruments and reduce the weight of the lens portion. For manufacturing this aspherical lens, the optical polishing method, which is a conventional optical lens manufacturing method, is inferior in workability and mass production, and direct press molding is considered to be promising.

This direct press molding method uses an aspherical mold that has been finished to the desired surface quality and precision in advance.
This is a method of manufacturing optical lenses by heating or pre-heating a lump of optical glass and press-molding the glass lump, without requiring any further polishing or polishing process after press-molding. .

However, the method for manufacturing the optical glass lens described above,
After press molding, the image forming quality of the obtained lens must be excellent to the extent that it is not impaired. Especially in the case of an aspherical lens, it is required that it can be molded with high precision.

Therefore, the mold material must have minimal chemical effects on the glass at high temperatures, be resistant to damage such as scratches on the glass press surface of the mold, and have high resistance to destruction due to thermal shock. It is.

For this purpose, molds made of materials such as silicon carbide or silicon nitride, or molds in which a coating film of silicon carbide or silicon nitride is completely formed on high-density carbon are considered suitable, and various studies have been conducted. ing. (For example, JP-A-62-45613).

Problems to be Solved by the Invention However, since materials such as SiC, Si, and N4 have extremely high hardness, it is extremely difficult to process these materials into molds for molding spherical or aspherical lenses with high precision. Moreover, since all of the mold materials conventionally used for these molds are sintered types, M1206. is used as a sintering aid. This method uses a substance such as B2O3 that reacts relatively easily with glass, which has the disadvantage that lenses cannot be molded with high precision.

On the other hand, molds made by coating silicon carbide on a carbon molded product may also react with the glass or cause peeling of the film, depending on the type of press glass and pressing conditions.

In order to overcome these drawbacks, by using a mold made by coating silicon carbide by sputtering on a cemented carbide whose main component is WC containing Go as a base material, there is extremely little reaction with glass. The adhesive strength of the film was also very strong. However, since the pressing temperature is extremely high at around 800°C, as the number of presses increases, GO in the base material diffuses into the SiC sputtered film, and eventually the Si
There was a problem that the C reached the surface of the film and reacted with the glass, resulting in poor durability of the mold.

Means for Solving the Problems The present invention In order to solve the problems, a mold for molding uses cemented carbide as a base material, processes this into a mold in the shape of a lens to be molded, and then presses a uniform mold onto the mold. Al2O, SiO2 in thickness
, ZrO□O and TiO□(1) or a mixture thereof, and furthermore, a coating film of a type or a mixture thereof is formed with a uniform thickness and a composition ratio of carbon to silicon (C/Si value) of 0.7 to
Amorphous SiC, α-5, such that in the range of 1.2
This method is characterized by forming a coating film of any one of a mixture of iC, amorphous SiC, and α-SiC.

Here, the cemented carbide used as the base material is not only capable of electrical discharge machining, but also can be used in general grinding processes using silicon carbide, which has high hardness and is conventionally used as a material for direct press molding of glass lenses. It has the characteristic that it can be processed into mold shapes with higher precision than silicon nitride or silicon nitride. Also,
The cemented carbide used as the base material has a coefficient of thermal expansion that closely matches that of the silicon carbide used as the coating film, so it is suitable for repeating the thermal cycle of mold heating, press forming, and cooling during press forming of glass. It has the characteristic of providing strong and durable film adhesion.

Function The present invention overcomes the difficulty of high-precision machining, which was a drawback of molds using SiC or Si3N4 sintered bodies, which were conventionally used as molds for the same purpose.
- This has the advantage that there is very little reaction between the mold and the glass even when molding high melting point glass.
16. .

The direct press molding method has a longer life and higher reliability.
4) It becomes possible to create an optical glass element.
′,
; ゎyu 3゜22, 2 g 60MM (D yo ua, 2 □. '□'s copal) (Go) Prepare two each of WC cemented carbide rods contained in ', and cut around the periphery by electrical discharge machining. A pair of press molding molds were formed, each consisting of a concave upper mold with a certain radius of curvature of 46 m and a concave lower mold with a radius of curvature of 200 mm.

The press-molded surfaces of each pair of blocks were mirror-polished using ultra-fine diamond abrasive grains. As a result, the surfaces could be mirror-finished to an accuracy of maximum roughness Rm2Lx) of 0.02 μm within 2 hours. Next, a 205 film with a thickness of 0.2 μm is formed on this mirror surface by sputtering, and then a 205 film with a carbon to silicon composition ratio (C/Si value) of 0.7 is further deposited on this mirror with a thickness of 2 μm by sputtering. An amorphous silicon carbide film was formed to prepare a mold for glass press molding.

The mold thus created is shown in FIG. This mold was set in the press machine shown in Figure 2, and 5in2 was 68mm.
%, B20. is 11%, H2L20 is 10%, and 20
A spherical lump of alkali borosilicate optical glass having a radius of 2Off and consisting of 8% and the remainder of trace components was pressed and molded into a biconvex lens shape.

At this time, the molding atmosphere of the press machine was N2,
Press molding was carried out at a mold temperature of 800°C and a press pressure of 4°kg/ci, and the molded product was then cooled to 40°C together with the mold and taken out. The results for the above borosilicate alkali glass are shown in Table 1, sample f2. AI again! 20. After forming other sputtered films (intermediate thin films) such as SiO2, ZrO2 and Tie2f, press molding was performed in the same manner using molds formed in the same manner.The results are shown in Table 1 Samples & 3 to 6. Further, as a comparative example, the results in the case where there was no intermediate layer thin film are shown in Table 1 Sample Consideration 1. Furthermore, we used cemented carbide as the main component of the base material with different constituent elements, and on top of the material with a different combination of intermediate thin films.
Table 1 Samples &6 to 16 show the results of press molding using molds made by forming SiC thin films with different composition ratios and crystal systems of C and C. Among these molds that do not use an intermediate layer, the mold of sample JIL1゜6.12 has a press count of 1.
The surface condition was good up to oO times, but after 1oOo times, part of the mold surface turned brown and discolored, and elemental analysis of this part detected cobalt, silicon, sodium, and potassium. From this, it can be seen that the cobalt in the base material diffuses into the SiC thin film, reacts with the glass, and adheres to the mold, resulting in a worsening of the surface roughness (Rmax). In addition, samples f14 and 1 were used in the mold without an intermediate layer.
Sample No. 6 reacted with glass or peeled off the film after several press experiments, and subsequent press experiments could not be conducted. Here, when the C/Si value of SiC is 1.4 or more (that is, excessive C), the sputtered film becomes brittle and its adhesion to the substrate becomes weak, and the film peels off due to heating, cooling, and press pressure by pressing. do. Furthermore, when the C/Si value is 0.6 or less (that is, Si is excessive), free Si increases, which makes it easier to react with glass components and cause the mold and glass to adhere. This example sample f2-5, 7-11 and 1
In the press mold No. 3, by forming an oxide layer between the WC base material and the SiC coating film, it was possible to obtain an optical glass with extremely excellent press moldability.

In addition, we created the conventionally used silicon carbide sintered mold,
The mold of the present invention was set in the press machine shown in FIG. 2, and a glass lump similar to that described above was press-molded under the same conditions.

The mold of this silicon carbide sintered body was manufactured by electrical discharge machining, followed by grinding, and the surface was polished to a mirror finish using the same diamond abrasive grains as described above. Even in this mirror polishing process alone, the maximum roughness of the surface is 0.02 μm''!
It took ~50 hours. The results of press molding of this silicon carbide sintered body are also shown in Table 1 (Sample & 16
)It was shown to. This could not be put to practical use because it reacted with the glass during pressing and adhered to the mold.

(Left below) Effects of the Invention As is clear from the above explanation, the direct press molding method and mold for Hikari 9 glass of the present invention uses a cemented carbide as a base material mainly composed of WC, and molds the same. Processed into a press mold in the shape of yellow glass, and then stamped on it with a uniform thickness, k120. , S
After forming iO2, ZrO□, and Tio2(7) -8 or more, fumorphous SiC is further formed on top of which the Si and C composition seal (c/Si value) is between 0.7 and 1.2.
, a-8iO and a mixture of amorphous-SiC and α-SiC, the glass to be formed is heated in an inert gas atmosphere to a temperature at which the glass is softened and then heated. Since it is characterized by being pressure-formed, when molding glass, C
Not only is reactivity reduced, but it is also easier to create a highly accurate mold shape. Furthermore, the formation of an oxide intermediate layer has a very large advantage in terms of mold life.

In addition, in the examples, the cemented carbide used as the base material has been described as having all the WC components, but it is not limited to this.
It has been confirmed that all cermets containing r, 02, etc. as main components are also effective.

[Brief Description of the Drawings] Fig. 1 is a diagram showing a press-molding mold for an optical glass element 1 in an embodiment of the present invention, and Fig. 2 is a partially cutaway front view of a press machine used in the same embodiment. be. 11... Upper mold, 12... Lower mold, 11'
...Press surface of upper die, 12'...Press surface of lower die, 11'...Notch part, 13...
... Heater for upper mold, 14 ... Heater for lower mold, 15 ... Piston cylinder for upper mold,
16... Piston cylinder for lower mold, 17...
... Raw glass lumps, 18 ... Raw material glass, supply jig, 19 ... Molded glass outlet, 2° ... Raw material glass preheating furnace, 21.・
...Wow. 1. Name of agent: Patent attorney Toshio Nakao and one other person 12'-m-Bottom mold brace surface Figure 2

Claims (4)

[Claims] (1) Use cemented carbide as a base material, process this into a mold in the shape of the optical glass element to be molded, and place it on top of it with a uniform thickness.
Aluminum oxide (Al_2O_3), silicon oxide (S
Using a pair of molds, a coating film containing one or more of zirconium oxide (ZrO_2), zirconium oxide (ZrO_2), and titanium oxide (TiO_2) is formed, and a silicon carbide (SiC) coating film is further formed with a uniform thickness on top of the coating film. A method for forming an optical glass element, which comprises heating the glass to a temperature equal to or higher than the softening point of the glass to be formed in an inert gas atmosphere, and then press-forming the glass. (2) Claim 1, characterized in that the silicon carbide coating film is silicon carbide having a carbon to silicon composition ratio (C/Si value) in the range of 0.7 to 1.2. A method for forming optical glass elements. (3) The silicon carbide coating film is made of amorphous silicon carbide (A-SiC), alpha silicon carbide (a-S
2. The method for molding an optical glass element according to claim 1, wherein the glass element is made of one of iC) or a mixture of amorphous silicon carbide and alpha silicon carbide. (4) The method for molding an optical glass element according to claim 1, wherein the cemented carbide used as the base material has tungsten carbide (WC) as a main component.