JPH0445458B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a mold for molding an optical element. [Prior Art] In general, it is widely practiced to mold optical glass by hot pressing to obtain a desired optical element. By the way, when using this hot press means, it is very important that the mold has good mold releasability, and the mold releasability usually depends largely on the wettability of the glass to the material on the mold surface. Conventionally, as disclosed in, for example, Japanese Unexamined Patent Publication No. 62-87423, there has been known a mold for molding an optical element in which at least the molding surface is made of chromium nitride. This mold for molding optical elements has good mold releasability because the glass does not easily wet, and in fact maintains its initial performance even after more than 5,000 molding shots. [Problem to be solved by the invention] However, the conventional mold for molding optical elements described above has a diameter of
Although it is suitable for obtaining optical elements with a small diameter of up to about 10 mm, problems have arisen when obtaining optical elements with an even larger diameter. In other words, when forming a large-diameter optical element by hot pressing, in order to prevent the glass from deforming during heating, the heating temperature cannot be raised as much as when forming a small-diameter optical element, and the viscosity is high. must be molded. For this reason, during pressing, greater energy must be applied to the glass through press pressure and mold temperature. Therefore, the bonds of the compounds constituting the glass are broken, making them more likely to adhere to the mold. When this was repeated for each shot, a phenomenon called burn-in finally occurred. The present invention has been made in view of such conventional problems, and provides a mold for molding an optical element that does not cause seizure for a long period of time even when a large diameter optical element is molded by hot press. The purpose is to [Means for Solving the Problems] In order to achieve the above object, the present invention provides an optical element molding die in which at least the outermost layer of the molding surface is made of a material containing chromium (Cr) and nitrogen (N) as main components. was heated in an oxidizing atmosphere to form dichromium trioxide (Cr ₂ O ₃ ) on the outermost layer to form a mold for molding an optical element. The first requirement for a material that does not easily wet glass is that it must be thermodynamically stable and inert.
Whether or not it is thermodynamically stable can be determined by the standard Gibbs energy of formation. Secondly, it is better that the atoms on the outermost surface of the mold have a smaller ionicity. This is because the greater the ionicity, the more active it is, and the easier it is for glass to adhere to it. In the case of metal oxides, the ionicity is smaller as the polarization is larger (the ionic radius of the metal is smaller). Furthermore, in order to be satisfactory as a mold, it must have good hardness and adhesion. Table 1 shows the standard Gibbs energies of formation (ΔG) for six types of substances, and Table 2 shows the ionic radii of three types of ions.

【table】

[Effect]

In the optical element molding mold of the present invention having the above configuration, at least the outermost layer of the molding surface is formed of Cr ₂ O ₃ made by oxidizing CrN etc. No burn-in occurs for a long time. [Example] (First example) The mold base material was made of cemented carbide, and the diameter was 14 mm and R46.
A CrN layer was formed on the mirror-finished molding surface by sputtering. The thickness of the CrN layer was 5000 Å. Next, the mold was placed in an electric furnace and heated to 600℃ in the atmosphere.
Heated for 2 hours to oxidize the topmost part of the CrN layer.
It was made into ₃ layers of Cr ₂ O. The mold for molding an optical element thus obtained is shown in FIG. In Figure 1, 1
is the mold base material, 2 is the molding surface, 3 is the CrN layer, 4 is Cr ₂ O ₃
It is a layer. Furthermore, FIG. 2 shows the results of X-ray diffraction of this mold for molding an optical element. As can be seen from FIG. 2, Cr ₂ O ₃ is produced. Further, as a result of depth direction analysis using Auger electron spectroscopy, the thickness of the Cr ₂ O ₃ layer 4 was approximately 120 Å. When optical glass was molded using the mold for molding an optical element of this example, good mold releasability was exhibited even after 5,000 shots or more, and no seizure of the glass occurred. Further, a test was conducted in which the surface of the Cr ₂ O ₃ layer 4 was brought into contact with hydrofluoric acid during 5000 shots, but no surface deterioration was observed. (Second example) The mold base material is made of cemented carbide, diameter 14 mm, R46
A Cr layer was formed on the mirror-finished molding surface by ion beam sputtering. Next, a CrN layer was formed on the Cr layer by ion beam sputtering. The combined thickness of the Cr layer and CrN layer was 5000 Å. The reason why the Cr layer was formed here was to improve the adhesion between the mold base material and the CrN layer. Thereafter, the mold was placed in an electric furnace and heated at 600° C. for 4 hours in an N ₂ gas atmosphere to oxidize the outermost part of the CrN layer to form a Cr ₂ O ₃ layer. The thickness of this Cr ₂ O ₃ layer was about 60 Å. In this example, heating is performed in an N ₂ gas atmosphere, but even in an N ₂ gas atmosphere, water is contained, so the water becomes an oxidizing agent and forms a Cr ₂ O ₃ layer. I can do it. Note that when optical glass was molded using the mold for molding an optical element of this example, it had good mold releasability and no seizure occurred in the glass, similar to that of the first example. Further, a hydrofluoric acid test was conducted in the same manner as in the first example, but no surface deterioration was observed. (Third Example) A mold base material was formed from a SiC sintered body, and the diameter was 18 mm.
A CrN layer was formed on the mirror-finished R120 molding surface by ion plating. The thickness of the CrN layer was 7000 Å. Next, the mold was placed in an electric furnace and heated at 700°C for 2 hours in an Ar gas atmosphere.
The outermost part of the layer was oxidized to form _three Cr ₂ O layers. this
The thickness of the Cr ₂ O ₃ layer was approximately 150 Å. In this example, heating is performed in an Ar gas atmosphere, but N ₂
As with gases, moisture is present, so Cr ₂ O ₃
layers can be formed. In addition, when the hardness of the Cr ₂ O ₃ layer surface (molding surface) of the optical element mold of this example was measured using a microhardness meter, Hv = 1500Kgf/mm ² (25gf load)
and had good hardness. Furthermore, when the optical glass was molded, it had good mold releasability similar to the first example, and no seizure of the glass occurred. [Effects of the Invention] As described above, according to the mold for molding an optical element of the present invention, at least the outermost layer of the molding surface is made of Cr and N.
Since it is formed from Cr ₂ O ₃ by heating and oxidizing a material whose main component is It also has sufficient surface hardness and good adhesion, making it usable for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a first embodiment of the mold for molding an optical element of the present invention, and FIG. 2 is a chart showing the results of X-ray diffraction of the mold for molding an optical element shown in FIG. 1... Mold base material, 2... Molding surface, 3... CrN layer, 4...
_{Cr2O 3} layers.

Claims (1)

[Claims] 1. Dichromium trioxide is formed on the outermost layer by heating an optical element molding mold in which at least the outermost layer of the molding surface is made of a material mainly composed of chromium and nitrogen in an oxidizing atmosphere. A mold for molding optical elements.