JPS623030A - Method for forming optical glass element - Google Patents

Abstract

PURPOSE:To obtain an optical glass element without necessitating polishing process after molding, by forming a pair of press molds using a cemented carbide as the matrix, coating the mold with SiC having a specific composition and pressing a heated and softened glass gob with the mold pair. CONSTITUTION:A cemented carbide composed mainly of WC is used as a matrix and formed to a press mold having the form of the optical glass element to be formed. The press mold is coated with an SiC coating film having a C/Si ratio of 0.7-1.2. A glass gob heated above the softening temperature in an inert atmosphere or in vacuum is pressed with a pair of the above coated molds. An optical lens can be produced by this process without necessitating the grinding and polishing processes.

Description

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

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 processability and mass production, and direct press moldability 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 with a coating film of silicon carbide or silicon nitride 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 and Si3N4 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 materials conventionally used for these molding materials are sintered types, mu1203. Since it uses substances such as B2O3 that are relatively easy to react with glass, it has the disadvantage that lenses cannot be molded due to the high sugar content.

On the other hand, the composition ratio (C/Eii value) of molds made by coating silicon carbide etc. on carbon moldings varies considerably depending on the forming conditions, and the properties of the resulting SiC thin film are not constant. There were problems with bonding strength with the base material and reactivity with glass.

Means to Solve the Problems In order to solve the above-mentioned problems, the present invention provides a method for forming an optical glass element by using cemented carbide as a base material, processing this into a mold in the shape of a lens to be molded, and further A silicon carbide coating film having a uniform thickness and a carbon to silicon composition ratio (C/Si value) in the range of 0.7 to 1°2 is formed thereon.

Here, the cemented carbide used as the base material is not only capable of electrical discharge machining, but also can be used for general grinding using silicon carbide, which has high hardness and is conventionally used as a mold 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 strong enough to withstand the repeated thermal cycles of mold heating, press molding, and cooling during glass press forming. It has the characteristic of providing film adhesion.

Operation The present invention overcomes the difficulty of high-precision machining due to the drawbacks of molds using sintered bodies of SiC or 5i5N4, which have been conventionally used as molds for the same purpose, by the method described above, and Even when glass containing a large amount of alkali elements such as barium is molded, there is an advantage that there is little reaction between the mold and the glass. This makes it possible to create an optical glass element with a long life and high reliability by direct press molding.

Example Two cylindrical rods of WC cemented carbide containing 2% by weight of cobalt (Go), each having a diameter of 30 mm and a length of 60 cm, were prepared, and the curvature of the rods was cut by electric discharge machining. The upper mold has a concave shape with a radius of 46m111 and a radius of curvature of 2
It was processed into the shape of a pair of press molding molds consisting of a lower mold with a concave shape of 0.00 mm.

As a result of polishing the press-formed surfaces of each pair of blocks using ultrafine diamond abrasive grains, it was possible to mirror-finish the surfaces to an accuracy of 0.02 μm (maximum roughness Rmax) within 2 hours. Next, an amorphous silicon carbide film having a thickness of 2 μm and a composition ratio of carbon to silicon (C/Si value) of 0.8 was formed on this mirror surface by sputtering to prepare a mold for glass press molding.

The mold thus created is shown in FIG. This mold is set in the press machine shown in Fig. 2, and 5102 is es
%r B2O3 11%, Na2O 10%.

Borosilicate alkali optical glass consisting of 8 parts of N20 and the rest of trace components, and 8102 strength of 81%.

Two types of spherical lumps of barium borosilicate optical glass each having a radius of 20 ml+ were pressed and formed into a biconvex lens shape, each consisting of 17 pieces of B2O5, 0 pieces of BaO, and the remaining trace components. The molding conditions were as follows: Molding was carried out in a N2 atmosphere with a mold temperature of 4 kg/af, and the mold was cooled to 400°C together with the mold, and the molded product was taken out. The pressing results for acid-alkali glass are shown in Sample No. 3 in Table 1, and the pressing results for the above barium borosilicate glass are shown in Table 2, Sample N19.

A vacuum atmosphere ( Table 1 shows the results of press forming at 162 Torr). 11-2, 4-6 and Table 2 sample positive 7-8
, 10-12. Here, for comparison, films with a C/Si value of 0.6 and 1.4 are shown, but these cannot be put to practical use because they react with glass or the film itself peels off.

In addition, conventionally used silicon carbide and silicon nitride sintered molds were prepared and set in the press and machine shown in Fig. 2 instead of the molds of the present invention, and the same glass lumps as described above were processed under the same conditions. The silicon carbide and silicon nitride sintered bodies were press-formed with O. After electrical discharge machining, the sintered bodies were finished by grinding, and the surfaces were polished to a mirror finish using the same diamond abrasive grains as described above. Even in this mirror polishing process alone, the maximum surface roughness can be finished to 0.02 μm, which is 20 to
It took 40 to 60 hours, 26 times longer. The results of press forming using the silicon carbide and silicon nitride sintered molds are also shown in Samples N113 and 14 in Table 2 as comparative examples. These were difficult to put to practical use because they reacted with the glass during pressing and adhered to the mold.

(Hereinafter referred to as Kinpaku) As can be seen from Tables 1 and 2, samples M2 to 6 of this example
The press molds of Nos. , 8 to 11 were able to provide optical glasses with significantly superior press moldability compared to conventionally used silicon carbide and silicon nitride sintered molds. Here, when the C/Si value of SiC is 1.4 or more (that is, excessive C), the Vickers hardness (Hv) of the sputtered film does not decrease much, but the film becomes brittle and the adhesive force with the substrate becomes weak.
The heating, cooling, and pressing pressure caused by the press cause peeling of the film. Furthermore, when the C/Si value becomes 0.6 or less (that is, excessive Si), free Si increases, and therefore the Vickers hardness decreases significantly. It easily reacts with this waste glass component, causing the mold and glass to adhere.

Based on the above (7), the SiC C/Si value is 0.7 to 1.
It can be seen that good moldability can be obtained by controlling the temperature between 2 and 2.

In addition, the constituent elements of the base material are mainly we, and GOlTi
It can be seen that it is effective for all substances including C and TaG. Furthermore, in the examples, the cemented carbide used as the base material has been described as having we as the main component, but it is not limited to this, and may include TiC, TiN, A12, etc.
It has been confirmed that all cermets whose main components are cermets such as 05+ and Or502 are also effective.

Effects of the Invention As is clear from the above explanation, the direct press molding method and mold for optical glass of the present invention uses a cemented carbide whose main component is WC as a base material, and presses the mold into the shape of the optical glass to be molded. A pair of molds on which a silicon carbide coating film with a uniform thickness and a carbon to silicon composition ratio (G/Si value) in the range of 0.7 to 1.2 is formed. It is characterized in that it is heated to a temperature above the softening point of the glass to be molded and then pressure-formed in an inert gas atmosphere or under vacuum, so it is different from conventionally used sintered materials mainly made of silicon carbide or silicon nitride. Compared to molds using solid bodies, this method not only has less reactivity when molding glass, but also has the advantage of being able to more easily form high-precision mold shapes than before when performing general grinding processing. be.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a press-molding mold for an optical glass element 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. 11... Upper mold, 12... Lower mold, 11'
...Press surface of upper die, 12'...Press surface of lower die, 11''...Cut part, 13...
... Heater for upper mold, 14 ... Heater for lower mold, 16 ... Piston cylinder for upper mold,
16... Piston cylinder for lower mold, 17...
... Raw glass lumps, 18 ... Raw glass supply jig, 19 ... Molded glass outlet, 2
0... Raw glass preheating furnace, 21...
・Oi. Name of agent: Patent attorney Toshio Nakao and 1 other person11
−1st upper die 12′−−°press surface of lower die

Claims (2)

[Claims] (1) Using cemented carbide as a base material, process this into a mold in the shape of the optical glass element to be molded, and then apply a uniform thickness to the mold with a carbon to silicon composition ratio (C/Si value). 0.7
Using a pair of molds coated with a silicon carbide (SiC) coating having a temperature in the range of ~1.2, the glass to be molded is heated to above its softening temperature under an inert gas atmosphere or vacuum, and then pressurized. A method for molding an optical glass element, characterized by molding. (2) Claim (1) characterized in that the cemented carbide has tungsten carbide (WC) as a main component.
A method for molding an optical glass element as described in .