JPS61256931A - Molding method for optical glass element - Google Patents

Abstract

PURPOSE:To make the production of a high-accuracy optical lens which does not require a polishing stage after molding possible by coating the surface of molding tools with a thin alloy film of a specifically composed noble metal in the stage of molding the optical glass element by using the molding tools under heating and pressurizing. CONSTITUTION:The optical glass element heated to a high temp. is put between an upper die 11 and a lower die 12 consisting essentially of a superhard material such as WC, TiC or TaC and is pressed and molded by the press forming surfaces 11', 12' of the upper and lower dies, by which the lens is produced. The thin film of the noble metal alloy contg. 40-95wt%. In and the balance elements of at least one kind selected from Pt, Os, Pd, Rh and Ru is coated on the surfaces 11', 12'. The lens consisting of the molded optical glass is molded to have the faces of the high accuracy to the extent f not requiring the subsequent polishing stage and the lens having the high-accuracy molding surface is easily produced with good productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for molding high-precision optical glass elements that does not require a polishing step after press molding in the production of optical glass elements such as lenses and prisms.

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 equipment and reduce the weight of the lens portion. In manufacturing this aspherical lens, processing and mass production are difficult using the polishing method, which is a conventional optical lens manufacturing method, and direct press molding is considered to be promising.

This direct press molding method involves heating and pressure molding a lump of optical glass on an aspherical mold that has been finished to the desired surface quality and surface precision, or molding a lump of glass that has been heated in advance. This is a method of manufacturing an optical lens by performing heat-pressure molding without requiring a subsequent polishing step (for example, Japanese Patent Publication No. 38126/1983).

Problems to be Solved by the Invention However, in manufacturing the above-mentioned optical glass lenses, it is necessary that the optical glass lenses obtained by press molding have excellent image forming performance, especially in the case of aspherical lenses. High surface accuracy is required. Therefore, as a mold for molding optical glass elements, the chemical action on optical glass at high temperatures is minimal, the pressing surface of the mold is not susceptible to damage such as scratches and abrasions, and high surface accuracy changes due to press molding. It is necessary to have characteristics such as not doing something.

Various materials have been studied for this purpose, but conventional mold materials do not sufficiently satisfy the requirements such as low reactivity with optical glass, oxidation resistance, and high strength at high temperatures. Molds coated with noble metals are considered promising as mold materials that are less reactive to optical glass and have excellent oxidation resistance.

Among precious metals, platinum (PT) is particularly excellent in terms of its reactivity with optical glass and oxidation resistance.
) belongs to the low hardness category. Iridium (Ir)
By alloying with high-hardness precious metal elements such as palladium (Pd) and ruthenium (Ru), the hardness of the precious metal alloy increases, and lead oxide is approximately 75% by weight. It becomes possible to press-form a highly reactive lead oxide-based optical glass containing lead oxide.

In this case, it contains approximately 75% by weight of lead oxide, making it extremely reactive, but the temperature is lower due to the higher amount of lead oxide (
Optical glass can be press-molded at a temperature of approximately 520°C.

On the other hand, for example, lead oxide is 36% by weight.

In the case of lead oxide glass consisting of 60% by weight of silicon dioxide and other trace components, the reactivity of the glass is low because the content of lead oxide is low, and the temperature at which press molding is possible rises to around 630°C. If the press molding surface of the mold does not have sufficient hardness even at this temperature, the press molding surface of the mold will be susceptible to damage such as scratches and abrasions. In other words, when press-molding optical glass at even higher temperatures,
Needless to say, it has low reactivity with optical glass and oxidation resistance.
It is necessary to use a mold for molding an optical glass element that has excellent high-temperature hardness.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a method for precisely molding an optical glass element by heating and pressurizing it. death,
The remainder is platinum (pt), osmium (OB), palladium (Pd), rhodium (Rh), and ruthenium (Ru).
The present invention provides a method for molding an optical glass element using a mold coated with a thin film of a noble metal alloy containing at least one element selected from the following.

As a result of research, the inventors found that iridium (Ir)
Coated with a noble metal alloy thin film containing 95% by weight and the remainder containing at least one element selected from platinum (pt), osmium (Os), palladium (Pd), rhodium (Rh) and ruthenium (Ru). By heating and pressurizing an optical glass element to precision mold it using the mold, it is possible to obtain an optical glass with extremely excellent shape accuracy and surface accuracy.

In the case of lead oxide optical glass, which consists of 36% by weight of lead oxide, 50% by weight of silicon dioxide, and other trace components, the reactivity of the glass is low because the content of lead oxide is relatively small, but silicon dioxide is 60% by weight. Since it contains % by weight, the temperature at which press molding is possible is extremely high at about 630°C. In order to precisely mold such optical glass, it is necessary that it does not react with the optical glass, that it has excellent oxidation resistance and that controlling the atmosphere is not difficult, and that the press forming surface of the mold does not change even when reverse molding is performed at high temperatures. It is necessary to use a mold with high strength and high hardness that does not change.

Example Examples are shown below.

FIG. 1 shows a mold for molding an optical glass element according to the present invention, and is a perspective view of an upper mold 1 and a lower mold 2 thereof. Both types 1 and 2 are made of cemented carbide whose main component is tungsten carbide (WC), with a composition of 10% by weight of titanium carbide (Tic), 10% by weight of tantalum carbide (TaC), and 8% by weight of cobalt (Co). (WC-10TiC-10
TaC-8Co) t7) Diameter 3゜■, length 50+m
Using a cylindrical material, the upper mold 1 has a concave molding surface 4 with a radius of curvature of 46 and four square notches 3 on its periphery, and the lower mold 2 has a radius of curvature of 200 m. Concave molding surfaces 5 were each formed by electric discharge machining, and these molding surfaces 4 and 5 were mirror-finished by lapping with ultrafine diamond powder.

Next, platinum 40 is placed on the mirror-finished molding surfaces 4 and 6.
Iridium-platinum alloy (Ir-40P) mixed with wt%
A noble metal layer having a thickness of 2 μm was formed by sputtering.

FIG. 2 is a partially cutaway view showing heaters 6 and 7 wound around the outer diameter surfaces of the upper and lower molding molds 1 and 2, respectively, and attached to upper and lower plungers 8 and 9 of a press. In addition,
Since press molding is performed in a nitrogen atmosphere, the work area is surrounded by a cover 1o. In the same figure, lead oxide (pbo
) is 35% by weight.

Silicon oxide (SiO, p is 50% by weight, potassium oxide (K
2O), a spherical lump 11 with a radius of 20 mm of lead oxide-based optical glass, the remainder of which is made up of trace components, is held in a raw material supply jig 12 and heated in a tunnel-shaped preheating furnace 13 set at 630°C. The molds 1 and 2, heated to 0.degree. C., are held at a press pressure of 40Ky/h for 2 minutes. After cooling both the upper and lower molds 1 and 2 to a temperature of 380° C. in that state, the upper plunger 8 is returned and the molded optical glass element is taken out from the take-out port 14.

After repeating such press molding 300 times, the upper and lower molding molds 1 and 2 were removed, and the surface roughness and Vickers hardness (
1(v) The surface condition of the optical glass element obtained by press molding was observed.

The above tests were repeated for a pair of molds with different noble metal alloy compositions, and the results are shown in Table 1.

For comparison, a mold was prepared in which a noble metal alloy thin film having a composition outside the scope of the claims of the present application was formed on a cemented carbide having the same composition as in this example, and the results of testing under the same press forming conditions are shown in the following. It is listed at the end of Table 1.

As is clear from Table 1, as the amount of iridium (Ir) in the precious metal alloy increases, the Vickers hardness increases, and even after 300 press moldings, there is no trace of reaction with optical glass. The highly accurate surface shape and surface roughness of the mold surface have hardly changed. Moreover, there were no minute scratches on the surface of the optical glass after press molding, and the optical properties were also very good.

On the other hand, if the iridium (Ir) content in the noble metal alloy is less than the claimed range, the mold surface will not be sufficiently hardened and the surface roughness of the mold will be approximately Q,06 μm. The optical properties of the obtained optical glass element were also deteriorated. If the iridium (Ir amount) in the noble metal alloy is higher than the claimed range, there will be traces of slight reaction between the mold and the optical glass, the optical glass element will be slightly colored, and the optical properties will deteriorate. Was.

In this example, WC-10TiC-10TaC-8
Although a cemented carbide having a CO composition was used, the base material for the molding die is not limited to the above composition; for example, a TiC-based cermet or a TfN-based cermet.

Cr3C2 base cermet, At203 base cermet.

Needless to say, ZrO2 ceramics or At2o3 ceramics may also be used. Further, the shape of the molding surfaces 4 and 6 is not limited to the shape of this embodiment, and it goes without saying that the shape of a prism, a filter, etc. may be used.

Table 1 Results of press molding of lead oxide-based optical glass elements Effects of the invention As is clear from the above explanation, the method and mold for molding optical glass elements of the present invention precisely mold optical glass by heating and pressurizing it. In the method, iridium (Ir) is contained more than 40% by weight and less than 96% by weight, and the balance is platinum (PT), osmium (O8), palladium (Pd),
It is characterized by using a mold coated with a thin film of a noble metal alloy containing at least one element selected from rhodium (Rh), ruthenium (Ru), and iridium (Ru) in the noble metal alloy. If the amount of Ir) is within the range claimed in the present patent application, the noble metal alloy thin film will be hardened.

As a result, even after molding lead oxide optical glass 300 times at 630°C, the shape accuracy and surface roughness of the press molding surface of the molding die hardly changed, and the optical properties of the obtained optical glass element was also very good.

Therefore, by the method for molding an optical glass element of the present invention, an optical glass element with very high precision can be easily manufactured, and its industrial value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a press molding die for an optical glass element in an embodiment of the present invention, and FIG. 2 is a diagram showing a press machine used in the same embodiment. 11... Upper mold, 12... Lower mold, 11'
...Press surface of upper die, 121...Press surface of lower die 11//...Notch part, 13.
...Heating heater for the upper mold, 14... Heater for the lower mold, 15... Piston cylinder for the upper mold, 16... Piston cylinder for the lower mold. , 17...
... Raw glass lumps, 18... Raw glass supply jig, 19... Molded glass outlet,
20... Raw glass preheating furnace, 21...
...Oi.

Claims (1)

[Claims] The press-molded surface of the optical glass element is made of iridium (Ir).
Contains more than 40% by weight and 96% by weight or less, with the balance being platinum (Pt), osmium (Os), and palladium (Pd).
, using a mold coated with a thin film of a noble metal alloy containing at least one element selected from rhodium (Rh) and ruthenium (Ru), to precisely mold optical glass by heating and pressurizing it. Characteristic method for molding optical glass elements.