JPH0379299B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a mold used for molding optical glass elements such as optical lenses.

PRIOR TECHNOLOGY Japanese Patent Publication No. 11624/1983 discloses that glass can be formed into a desired molded product by hot pressing. Surface properties have not been achieved. This is because the mold releasability largely depends on the wettability of the glass, which is attributable to the material of the press mold.

Recently, the use of molds made of glassy carbon, tungsten alloy, or quartz glass has been disclosed in US Pat. It is disclosed in the specification of Patent No. 316861.

In these conventional molds, metals such as stainless steel, for example, undergo growth of cohesive grains due to temperature cycles during glass molding and hot pressing, changing the crystal structure, resulting in a rough surface. It has the drawback of deteriorating the shape and mold releasability, damaging the smoothness and gloss of the product in the early stage of molding, and extremely shortening the life of the mold.

On the other hand, glassy carbon is easily oxidized, structurally weak, susceptible to surface scratches, and has low thermal conductivity.
It also has low fracture impact resistance. All of these physical properties are undesirable for heating, softening and pressure forming the glass. Furthermore, since quartz glass has wettability and low thermal conductivity, it is not sufficient as a mold material like glassy carbon.

Therefore, there is a strong need to develop mold materials that have desirable glass forming properties and improved structural and thermal properties.

OBJECT OF THE INVENTION The object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to meet the above-mentioned needs, an optical fiber is provided which forms a glass molded surface having the final optical surface performance without the need for grinding and polishing steps. The present invention aims to provide a mold for molding glass elements.

Summary of the Invention The mold for molding an optical glass element according to the present invention includes:
At least the molded surface is formed of TiB _two- base ceramics. In particular, TiB ₂ single-layer high-density ceramics, _{TiB 2}
-(Ni, B) based cermet and TiB ₂ -(Ni,
Zr) based cermets are preferably used.

The present invention is based on ultra-fine particles already developed by one of the inventors.
TiB ₂ powder (1981 Powder and Powder Metallurgy Association 52nd Lecture Conference, Special Feature on Lectures (2-36)
Ultra-fineness by Metallothemic Reduction method
By pressureless sintering using TiB ₂ powder (preparation and sinterability), TiB ₂ ceramics with a sintered density of almost 100% can be obtained, and this can be used to create molds with excellent surface quality (structure). This is based on the fact that it has become possible to manufacture

According to the present invention, a mold having a glass molding surface that does not require final grinding or polishing is made of TiB _two- base ceramics, or at least the molding surface of the mold is formed with a thin film layer of TiB _two- base ceramics. do. Since this thin film layer has sufficient surface quality, it can be used as is, but it can be processed by grinding, polishing, etc., if necessary. To form a thin film layer of TiB _di- ceramics, a TiB _di- ceramic raw material is deposited on a mold body made of a suitable material that is commonly used, such as chemical vapor deposition, vapor deposition using a high-power CO ₂ laser, ion plating method, etc. It may be deposited by a well-known method. The molding surface of the thin film layer formed in this way matches the finished shape of the optical glass element to be molded, and the glass that has been heated and softened in air or a non-oxidizing atmosphere can be used to mold the optical element into the desired shape. can be formed into

In particular, ceramics made of TiB ₂ monomer are produced by using the above-mentioned ultra-fine TiB ₂ powder 100% by hot pressing.
Use a high-density one.

Example Next, the present invention will be explained in detail.

In the present invention, the mold for molding the optical glass element may be made entirely of _TiB ceramics including the molding surface, or the mold body may be made of a suitable material. TiB ₂ on the surface
It may also have a structure in which a thin film layer of base ceramics is provided.

Figure 1 shows the entire structure made of TiB ₂ single high-density ceramics, TiB ₂ -(Ni, B) cermet, and TiB ₂
This figure shows the structure of an example of the molding die of the present invention, which is composed of an upper mold 1 and a lower mold 2 made of TiB _two- base ceramics selected from -(Ni, Zr)-based cermets. When the entire structure is made of TiB _two- base ceramics as in this example, it is preferable to grind or polish each molding surface 1a, 2a to obtain a desired curved surface and to smooth it. In the figure, 3 is glass softened by heating.

FIG. 2 shows another example of the molding die of the present invention. In this example, the upper mold 4 and the lower mold 5 of the mold are
After forming these molded surfaces with a suitable material, thin film layers 6 and 7 of TiB _dibase ceramics are coated by well-known methods such as chemical vapor deposition, high-power CO ₂ laser vapor deposition, and ion plating. wear. The molding surface coated with the thin film layers 6 and 7 in this way has sufficient surface quality and can of course be used as a mold surface as is, but it can be ground, polished, etc. as necessary. The surface quality can also be further improved by processing.

In order to determine the releasability from the mold, which is one of the important features of the mold according to the present invention, the wettability of the flint-based glass to the mold was examined. Figure 3 shows a simple diagram of wetting. In this case, the wetting angles between the TiB _dibase ceramic 8 and the molten glass 9 are θ ₁ (a) and θ ₂ (b), and if θ ₁ >90°, there is no wetting, and if θ ₂ <
If it is 90 degrees, it is considered wet.

Next, in order to conduct a comparative test of the wetting of the molding surface of the present invention and the conventional molding surface, a heating furnace in which nitrogen gas was introduced at a rate of 7/min and kept in a non-oxidizing atmosphere was heated at a rate of 2/min.
When heated at a temperature increase rate of .degree. C., the contact angle due to wetting of the flint glass against the molding surface made of various materials of the mold placed in the heating furnace was measured. The measurement results are shown as a graph in FIG.

As is clear from FIG. 4, according to the present invention
A mold with a molding surface made of TiB _two- base ceramics has a larger wetting angle θ over a wider temperature range than those made of stainless steel or quartz glass.
It turns out that it doesn't get wet easily.

Next, the oxidation resistance and mechanical strength of the mold of the present invention having a molding surface made of TiB _two- base ceramics and a conventional mold were compared.

Comparative tests were conducted by holding TiB _dibase ceramics, stainless steel, and cast iron in an air atmosphere at 750°C for 100 hours. As a result, stainless steel and cast iron were significantly oxidized and their surfaces differed from their original surfaces, while TiB _two- base ceramics showed almost no change. In addition, the oxidation resistance of TiB ₂ ceramics is as follows: TiB ₂ high-density ceramics > TiB ₂
-(Ni, Zr) system>TiB ₂ -(Ni, B) system.

As a result, the TiB _two- base ceramic used in the present invention has excellent oxidation resistance, does not oxidize when used up to 750°C, and has good roughening resistance.

Furthermore, the mechanical strength of TiB _two- base ceramics was investigated in terms of transverse rupture strength and micro-Vickers hardness (Hv scale).

First, in order to examine the transverse rupture strength, the strength was measured using a transverse rupture test material using TiB _two- base ceramics with a width of 4 mm, a thickness of 2 mm, and a distance between fulcrums of 10 mm. The loading speed was 0.4 mm/min.

As a result of the transverse rupture strength test, the high-density TiB ₂ sintered body has a strength of 75 to 85 Kg/mm ² , and the TiB ₂ − (Ni, Zr) system has a strength of 75 to 85 Kg/mm 2
85Kg/mm ² , and the TiB ₂ -(Ni,B) system showed a strength of 50 to 70Kg/mm ² . In addition, the micro-Vickers hardness is 3300 to 3400 for high-density TiB ₂ sintered bodies, and TiB ₂ −
The values were 2000 to 2700 for the (Ni, Zr) system, and 1800 to 2500 for the TiB ₂ -(Ni, B) system. These values are C-
The value was the same as or close to that of BN (cubic boron nitride) tool materials. From this, the TiB _two- base ceramic used in the present invention has sufficient hardness and strength, and is promising for use as a mold for glass molding or for forming the molding surface of a mold.

From the above results, TiB _two- base ceramics has excellent mirror workability, oxidation resistance, roughness resistance, and mechanical strength, and these are favorable properties compared to conventional metal molds. There is.

Next, nitrogen gas is introduced into the heating furnace at a rate of 3/min to maintain the inside of the furnace in a non-oxidizing atmosphere.
A mold coated with _two TiB ceramics was placed, and a flint-based glass lump, which had been brought to a suitable temperature for molding in a separate furnace, was transferred onto the _two TiB ceramic coated surface of the mold to form optical glass parts. No foreign matter was observed on the surface of the optical glass component obtained by molding in this way, it had a fire polish appearance and the surface precision was extremely good.

In contrast, the surfaces of optical glass parts obtained by molding with conventional molds had foreign matter attached to them and many irregularities, making them unusable as-is and requiring finishing work. .

Further, after using a mold having a molding surface made of the TiB _two -base ceramic of the present invention several thousand times, the condition of the molding surface was examined, and as a result, no change was observed in the surface.

Effects of the Invention According to the present invention, a single TiB ₂ high-density ceramic having excellent properties for use as a mold for molding optical glass elements and for molding optical glass parts;
Since a mold is used in which at least the molding surface is made of TiB _2- based ceramics selected from TiB ₂ - (Ni, B) and TiB ₂ - (Ni, Zr) systems, there is no adhesion of foreign matter. It is possible to mold optical glass parts with optically smooth molding surfaces. Therefore, it is possible to omit post-processing after pressure molding of optical glass parts, which was conventionally required, thereby simplifying the process and having the effect of greatly contributing to cost reduction. Furthermore, the mold having a molding surface made of the TiB _two- base ceramic according to the present invention is durable and has a long service life, and in particular, the mold having the molding surface formed of a thin film layer of the TiB _two- base ceramic mentioned above has features such as durability and long life. By using this method, it is easy to reduce the cost of a high-precision mold, and it becomes possible to reduce the cost of producing optical glass parts with high precision and stable quality.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an example of an optical lens molding mold of the present invention whose entire structure is made of TiB _two -base ceramics, and Fig. 2 is a lens-molding mold of the present invention whose molding surface is made of TiB _two- base ceramics. A cross-sectional view showing another example of the mold, Figures 3a and b are schematic diagrams showing the wetting of the flint-based glass to the mold molding surface, and Figure 4 shows the wetting of the flint-based glass to the molding surface of TiB _two- base ceramics, quartz glass, and stainless steel. It is a graph showing the temperature dependence of wetting angle. 1, 4... Upper mold, 2, 5... Lower mold, 1a, 2a
... Molding surface, 3 ... Heated softened glass, 6,7
...Thin film layer of TiB _dibase ceramics.

Claims (1)

[Scope of Claims] 1. A mold for molding an optical glass element, characterized in that at least a molding surface is formed of _two- TiB ceramics. 2. Claim 1 describes the use of a TiB ₂ monolithic high-density ceramic, a TiB ₂ -(Ni, B)-based cermet, and a TiB ₂ -(Ni, Zr)-based cermet as the TiB 2 _- based ceramic. A mold for molding optical glass elements.