JPH0224770B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a mold for molding a glass lens with high shape accuracy and fine surface roughness that does not require grinding and polishing after press molding, and a method for manufacturing the same. .

[Prior Art] As a mold for molding a glass lens having high shape accuracy and fine surface roughness that does not require grinding and polishing after press molding, the mold described in U.S. Pat. No. 4,139,677 is known. ing. In this specification, silicon carbide (SiC) or silicon nitride (Si ₃ N ₄ ) is used to form a mold surface for glass forming by a hot press method, CVD method, etc., and then the glass product to be obtained is described. The mold surface was finished by grinding and polishing to match the final shape.

In the hot press method, raw material powder of silicon carbide or silicon nitride is placed in a molding die and pressed to form a mold using high temperature plasticity.

On the other hand, in the CVD method, coating is carried out by deposition on a suitable type of substrate material, and when silicon carbide or silicon nitride is deposited, the reaction is carried out at a temperature of around 1350°C. After deposition, the coating layer had to be deposited to a sufficient thickness for finishing, and a thickness of at least 10 μm was required.

[Problems to be Solved by the Invention] The hot pressing method has problems in that it is not possible to produce products with complex shapes, and it is extremely difficult to prevent the formation of pores.

On the other hand, in the CVD method, no pores are generated, but the reaction temperature when depositing on the substrate is high, around 1350°C, so the grown particles are large in size and finishing processing is required. However, since silicon carbide and silicon nitride are very hard and brittle, there is a problem in that they tend to chip during finishing.

In addition, if the coating layer is relatively thick (10 μm or more), the mold surface of the substrate to be coated must also be processed with high precision, and in addition to the finishing process after coating, two precision processes are required. I had to do it.

The present invention has been made with the aim of solving the above-mentioned problems.

[Means for solving the problem] The present invention provides a silicon nitride layer with a thickness of 0.2 to 2 μm, which does not impair the surface roughness of the mirror surface, on the mirror surface of a substrate finished with a surface roughness of 200 Å or less. A glass lens mold is manufactured by coating.

When carrying out the present invention, a silicon nitride layer is applied to the mirror surface of a substrate processed to a surface roughness of 200 Å or less at a reaction temperature of approximately 900°C using a low-temperature plasma CVD method.
to form a coating layer on the mirror surface of the substrate.

[Operation] First, the glass molding surface of the substrate is molded with high shape accuracy.
Processed into a mirror surface with fine surface roughness. Next, silicon nitride, which has excellent oxidation resistance, is deposited on the processed mirror surface at approximately 900°C using low-temperature plasma CVD.
The thickness of the silicon nitride coating layer is 0.2 to 2 μm.
While conventional CVD methods deposit silicon nitride at around 1350°C, low-temperature plasma CVD methods deposit silicon nitride at around 1350°C.
Since the process is carried out at a low temperature of 900°C, fine particles with a grown particle size of 100 Å or less are deposited and do not affect the surface roughness. Furthermore, since the coating layer is thin and uniformly coats the mirror surface, it does not affect the shape accuracy. Therefore, no finishing work is required after coating.

Next, the substrate material will be explained.

The substrate material may be any material as long as it is dense, can be mirror-finished, and has a coefficient of thermal expansion not significantly different from that of silicon nitride, and may be molybdenum, stainless steel, sintered silicon carbide, etc., but tungsten carbide is more preferable. For example, tungsten carbide with cobalt (Co) as a binder cannot be said to have sufficient oxidation resistance to be used as a mold as it is, but it is possible to create a mold surface with high shape accuracy and a surface roughness of about 100 Å. By depositing a silicon nitride layer of approximately 0.2 to 2 μm on the mold surface using the low-temperature plasma CVD method at approximately 900°C, a transparent film with a uniform thickness is formed on the mold surface and the shape accuracy is maintained, allowing growth. Particle size is 100
Since it is less than Å, almost no change is observed in the surface roughness as mentioned above. The coating layer is pure silicon nitride, has no pores, and has excellent oxidation resistance. However, in order to prolong the life in molding, it is desirable to use it in an inert gas atmosphere. In addition, tungsten carbide, which is relatively easy to process, can be processed with high precision, and the silicon nitride layer, which is a material that is prone to chipping, does not need to be processed. There is no need to worry about chipping during molding. If the thickness of the silicon nitride layer is made thicker than 2 μm, the diameter of the grown particles gradually increases, making it difficult to make the film thickness uniform, and the difference in coefficient of thermal expansion with the substrate material becomes a problem, so approximately 0.2 A thickness of ~2 μm is desirable. In this way, finishing processing such as repolishing after coating is not required.

[Examples] Examples of the present invention will be described below with reference to the drawings.
The plasma CVD apparatus used in this example for depositing silicon nitride is shown in FIG.

The plasma CVD apparatus has a structure in which a supply system for supplying raw material gas is arranged at the lower part of a reaction tube 1 in which silicon nitride is deposited, and an exhaust system is arranged at the upper part.

A vertical reaction tube 1 is made of quartz, and a lens molding mold substrate 2 is installed inside the reaction tube 1. The substrate 2 is heated by a heater 3 attached to the outside of the reaction tube 1. The temperature of the substrate 2 is detected by a thermocouple 4 and kept constant.

The raw material gas is supplied to the reaction tube 1 by a gas supply system installed at the bottom of the reaction tube 1. A bubbler 5 that vaporizes silicon chloride as a raw material is installed in a constant temperature bath 6 maintained at 20°C. Silicon chloride as a raw material is vaporized in a bubbler 5, and a carrier gas whose flow rate is adjusted by a mass flow controller 7a is used.
It is fed into the mixer 8 together with H ₂ . On the other hand, the flow rate of the raw material N ₂ gas is also regulated by the mass flow controller 7b and flows into the mixer 8. carrier gas
H ₂ , raw material silicon chloride and N ₂ are mixed in a mixer 8
mixed in.

The mixed N ₂ , H ₂ and silicon chloride are introduced into the reaction tube 1 from the lower part of the reaction tube 1 . Also, in order to keep the overall amount of _H2 constant, from another line,
H ₂ whose flow rate is adjusted by the mass flow controller 7c is supplied into the reaction tube 1 from the lower part of the reaction tube 1.

Silicon chloride as a raw material supplied to reaction tube 1 and
_N2 is turned into plasma by the RF generator 9, matching box 10, and work coil 11, and silicon nitride is deposited on the mirror surface of the substrate 2.

The interior of the reaction tube 1 is evacuated by the oil rotary pump 12. Unreacted gas and reaction by-products present in the discharged gas are removed by a trap 13 installed between the oil rotary pump 12 and the reaction tube 1.

Further, the pressure inside the reaction tube 1 is controlled by a Pirani gauge 14.

Using the plasma CVD equipment explained above,
As a first example, silicon nitride was deposited on a tungsten carbide substrate under the following conditions. The reaction temperature was 900°C, the pressure inside reaction tube 1 was 0.3 torr, the mixed gas flow rate of silicon chloride and H ₂ was 300 ml/min, and N ₂
The gas flow rate was 100 ml/min, the gas flow rate of H ₂ supplied from a separate line was 450 ml/min, and the reaction time was 1 hour. The substrate 2 used was one processed into an engineering mirror surface with a surface roughness of about 100 Å. As a result of the reaction, silicon nitride with a thickness of about 1 μm was deposited on the mirror surface of the substrate 2. The surface roughness of the mirror surface coated with silicon nitride was 120 ÅRz, as shown in FIG. 2, and the surface roughness of the mirror surface was maintained.

Further, as a second example, silicon nitride was deposited on a tungsten carbide substrate 2 under the following conditions. The reaction temperature is 1050℃, and the pressure inside reaction tube 1 is
Mixed gas flow rate of silicon chloride and _H2 at 1 torr
The reaction time was adjusted to 300 ml/min, the N ₂ gas flow rate to 60 ml/min, and the H ₂ gas flow rate supplied from a separate line to 150 ml/min, and the reaction time was 30 minutes.

As a result of the reaction, silicon nitride was deposited on the substrate 2, forming a coating layer with a thickness of about 1.8 μm, and the same optical performance as in the first example was obtained.

On the other hand, the following experiment was conducted to investigate the oxidation resistance of the silicon nitride coating layer.

A tungsten carbide substrate sample without any coating layer and a sample in which a tungsten carbide substrate was coated with silicon nitride to a thickness of about 1 μm were left in the atmosphere maintained at 600° C. for 10 hours. After that, we measured the surface roughness and found that there was no change in the surface roughness of the sample coated with silicon nitride, but the surface roughness of the uncoated sample was 550 Å due to roughness due to oxidation.
It had changed to Rz.

[Effects of the invention] Tungsten carbide, which is relatively easy to process, is processed into a mirror surface with high shape accuracy and fine surface roughness (200 Å or less), and a thin silicon nitride layer with a thickness of 0.2 to 2 μm is applied to the mirror surface using a low-temperature plasma CVD method. Even if it is covered with
There is no need for finishing machining after coating, as it does not affect surface roughness or shape accuracy. Therefore, there is no need to process the silicon nitride layer, which is prone to chipping. Furthermore, since the coating layer is very thin, there is no possibility that the coating layer will cause chipping during molding of the glass lens. Furthermore, coating the substrate with a silicon nitride layer significantly improves oxidation resistance, thereby extending the life of the mold.

[Brief explanation of drawings]

Figure 1 shows low-temperature plasma for mold manufacturing according to the present invention.
The CVD apparatus diagram and FIG. 2 are diagrams showing the measurement results of the surface roughness after coating with silicon nitride. DESCRIPTION OF SYMBOLS 1... Reaction tube, 2... Substrate, 3... Heater, 4... Thermocouple, 5... Bubbler, 6... Constant temperature bath, 7a, 7b,
7c...Mass flow controller, 8...Mixer, 9
...RF generator, 10...Matching box, 11...Work coil, 12...Oil rotary pump,
13...Trap, 14...Pirani gauge.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a mold for a glass lens, which comprises coating a substrate finished with an optical mirror surface with a surface roughness of 200 Å or less with a silicon nitride layer having a thickness of 0.2 to 2 μm. 2. The method for manufacturing a glass lens mold according to claim 1, wherein the material of the substrate having a mirror surface is tungsten carbide. 3 After polishing the glass molding surface of the substrate to an optical mirror surface, apply plasma to an extent that does not impair mirror precision.
2. A method for manufacturing a mold for molding a glass lens according to claim 1, wherein the mold is coated with silicon nitride using a CVD method. 4. The method for manufacturing a mold for molding a glass lens according to claim 1, wherein the silicon nitride coating is carried out at about 900° C. by plasma CVD.