JPH02188432A - Molding die for optical parts - Google Patents

Abstract

PURPOSE:To prevent both oxidative deterioration of the surface of a die and melt-sticking of glass by coating the surface layer of tungsten carbide on the surface of the molding die for the optical parts which consists of sintered hard alloy incorporating tungsten carbide as a main component. CONSTITUTION:The base material 1 of sintered hard alloy incorporating tungsten carbide as a main component is produced by adding powder of Co, etc., as a binder to tungsten carbide powder, molding and sintering this mixture. Then the face of this base material 1 used for a press is ground and worked into a recessed curved face and polished. Then the film 2 of tungsten carbide is uniformly coated on the surface by a CVD method, etc., and furthermore the surface is polished by utilizing diamond grinding granules, etc., and a molding die for the optical parts is obtained. Further as the base material 1 of the die made of sintered hard alloy, the material having <=2X10<-6>/ deg.C difference of thermal expansion coefficient for the coating material 2 of tungsten carbide is preferably utilized.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a mold for optical components, and in particular to a mold for forming an optical element by directly hot press molding an optical glass lens or the like without the need for a mechanical polishing process. The present invention relates to a mold for optical components suitable for high-precision processing and long life.

[Prior Art] In recent years, there has been an increasing demand for aspheric lenses as optical glass lenses. This is because by adopting an aspherical shape, the optical system can be simplified, making it possible to reduce the size, weight, and cost. However, this aspherical lens cannot be manufactured by conventional grinding and
It is extremely difficult to process using polishing technology, and this has been a barrier to mass production.

Therefore, recently, a method of manufacturing an aspherical glass lens by hot press molding has been attempted.

The method of manufacturing aspherical glass lenses by hot press molding involves inserting a glass material into a mold finished with a predetermined aspherical shape, then heating the material in the mold to the molding temperature, and then processing. It is pressed and press-molded.

Therefore, the press mold material described above must have properties such as high strength at high temperatures, easy mold shape accuracy and surface roughness, and no reaction with glass at high temperatures.

In addition, as such an optical element mold, for example, 1f-
As described in Jikai No. 59-123631, a cemented carbide containing tungsten carbide (WC) and cobalt (Go) has been proposed.

[Problem to be solved by the invention] Although optical glass contains a large amount of SiO, B, O, BaO, etc., the softening temperature of the glass is 650℃.
Because the temperature is ~750°C, the reaction between the mold and the glass and the oxidation of Co are intense (i.e.

When the cemented carbide itself is directly used as a press mold for high-temperature forming, the G contained in the cemented carbide.

(begins to oxidize when the temperature reaches about 400°C), and even with a press mold made of cemented carbide, it was difficult to prevent the mold from deteriorating.

An object of the present invention is to solve the problems of the prior art described above, to prevent the mold surface from deteriorating due to oxidation even when glass is press-molded at high temperatures, and to eliminate the reaction between the glass and the mold so that the mold surface does not deteriorate. An object of the present invention is to provide a mold for an optical component that does not cause glass fusion phenomenon.

[Means for Solving the Problems] The above object is achieved by a structure in which the surface of a cemented carbide mold whose main component is tungsten carbide is coated with a surface layer of tungsten carbide.

[Effect] In general, cemented carbide is made of G compared to fine grain powder of WC.

It is made by molding powder using a binder and then sintering it, so the powder is in a solidified state.

However, as the cemented carbide is heated, the CO particles begin to oxidize at temperatures above about 400°C, lose their effectiveness as a binder, and fall off the surface of the press mold.

Further, as this falling off progresses, WC also begins to fall off from the press mold surface, deteriorating the mold surface, worsening the roughness of the mold surface, and shortening the life of the mold. In particular, for optical glass lenses obtained by press molding, the surface roughness of the molded product must be 0.02 μm or less, an extremely mirror-like condition, so even slight oxidation on the surface of the press mold is a problem. Become. Furthermore, when Co is heated to a high temperature, it tends to react with glass, and a phenomenon in which the glass is fused to the surface of the press mold also occurs.

As described above, there are many problems in press-forming glass at high temperatures using cemented carbide as a press-forming surface.

In contrast, in this project, as mentioned above, the processed surface of the cemented carbide is coated with WC on the mold surface without directly contacting the glass material. During press molding, almost no reaction between the mold surface obtained as described above and the glass was observed.

This has made it possible to create a mold for pressing optical parts that has excellent oxidation resistance at high temperatures.

[Example] Hereinafter, an example of the present invention will be described in detail using FIGS. 1 to 3.

Example 1 FIG. 1 is a longitudinal cross-sectional view showing an example of a press molding mold for an optical component according to the present invention, and shows a mold coated with WC coating. This mold was processed in the following steps. The pressed surface of the sintered cemented carbide base material (composition of 9°4% WC and 50% Go) was formed into a cylinder with a diameter of 30m and a height of 40m1, with a curvature of half a50! The concave curved surface was ground with a shape accuracy of ±1 μm using ll11. After that, it is polished with diamond abrasive grains while maintaining the shape accuracy, and the surface roughness is Rma.
Finished x to 0°1 μm.

The processed surface was uniformly coated with WC film 2 to a thickness of about 6 μm by CVD, and further polished to a surface roughness of 0.001 μm or less using diamond abrasive grains to produce a press mold.

After that, 40wt, %Ba○-39wt%Si
○, -15wt%B20. A cylindrical material of optical glass with a diameter of 16 m and a thickness of 15 m5, which is mainly made of Press molding was performed by applying a load of 2 tonf for 2 minutes. The shape accuracy and surface roughness of the molded product at this time are almost the same as those of the mold, and there is no reaction between the glass and the mold. Figure 2 shows the change in surface roughness of the mold during repeated press molding. is shown in comparison with Change 3 in the surface roughness of the cemented carbide metal mold. As can be seen, in the case of the present invention type, there was almost no deterioration over time as in change 4, and a longer life could be achieved.

Example 2 69wt%Sint-10wt%B, O, -9wt%N
A, a cylindrical (diameter 16 m x thickness 15 m) material of optical glass containing 0-8 wt% O as the main component was placed between the concave surfaces of the WC type similar to Example 1, and placed in a nitrogen atmosphere. After heating to about 650'C, a load of about 2 tonf was applied and press molding was performed.

In this case, as in Example 1, the shape accuracy and surface roughness of the molded product are almost the same as those of the mold, and no reaction between the glass and the mold is observed.

When repeatedly press-molded to No. 3 IxI.

As can be seen, the change in surface roughness of the mold 4 is shown.
Compared to change 3 in the surface roughness of the cemented carbide association mold shown in the same figure, the lifespan has been extended by several orders of magnitude.

As described above, the WC coating mold according to the present invention is effective for hot forming glass.

5 In this example, a cemented carbide with a composition of tungsten carbide and cobalt was used as the base material, but cemented carbide or metal with a composition other than this may be used if the coefficient of thermal expansion is close to that of the coating material (WC). good.

The reason for this is that if there is a large difference in the coefficient of thermal expansion between the base material and the coating material, large tensile or compressive stress is likely to occur in the film when it is cooled after forming the CVD film at high temperatures.
The reason is that the coating is easily destroyed, or that the coating is easily destroyed by repeated use.

When coating by CVD method is applied at 1000° C., the thermal expansion coefficient difference is preferably 2×10 −”/′C or less to prevent destruction of the film.

The coating method is not limited to the CVD method, and may be ion mixing, PVD, or the like.

In addition, although the coating thickness was 6 μm in this example, it may be about 0.5 μm in the final polishing method, and the minimum thickness is 1 μm.
Good to have.

[Effects of the Invention] According to the present invention described above, by using a press mold whose surface is coated with a WC film as a hot press mold material for optical components, the mold surface does not deteriorate due to oxidation. Furthermore, since the melting M phenomenon of glass on the mold surface due to reaction with glass does not occur, the life of the mold can be extended, and optical parts can be mass-produced.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a longitudinal sectional view showing an embodiment of the press mold for optical components of the present invention, and FIG.
wt%BaO-39wt%SiO. -15wt%B□O1 type glass is a diagram showing the change in surface roughness when molded. Figure 3 is a diagram showing the change in surface roughness when molding 69wt%5in2-10wt%B, 0. -9w
It is a diagram showing the change in surface roughness when O-based glass is molded to t% Na and 0-8 wt%. 1... Cemented carbide base material, 2... WC coating material. Shuko M2 figure ^ Select hill Shiga"50'& CN)

Claims (1)

[Scope of Claims] 1. A mold for an optical component, characterized in that it has a structure in which the surface of a cemented carbide mold whose main component is tungsten carbide is coated with a surface layer of tungsten carbide. 2. The base material of the cemented carbide mold is made of a material having a thermal expansion coefficient difference of 2×10^-^6/°C or less with respect to the coating material. Molding mold for optical parts.