JPH0597449A - Method for molding optical element - Google Patents

Abstract

PURPOSE:To reduce a cost by press molding a glass blank in an oxygen atmosphere using a specific mold release agent by means of a mold member formed with a metal oxide or ceramics as a mold base material or the coating layer of the molding surface. CONSTITUTION:The coating layer 132 consisting of a material contg. >=1 kinds among the oxides of Al, Ti, Cr, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Hf, Ta and W, such as Al2O3, and ceramics, such as SiC, AlN and Si3N4, having a prescribed thickness is formed by a sputtering method on the surface of the mold base material 130, such as superalloy, and then finished to a prescribed shape. The coating layer 132 may be formed after a Ta layer, etc., of 0.01 to 5mum thickness to decrease residual internal stress on the mold base material 130 at need. The glass blank is then pressed to the molding surface coated with the mold base material 130 via the mold release agent layer of 5 to 500Angstrom consisting of ZnS, etc., having the m. p. higher than the glass softening point and is press molded in the oxygen atmosphere, by which the optical element is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of an optical element in which the surface shape of a precision-processed mold is transferred to an optical element material by pressure molding so as to form a desired functional surface of the optical element. Concerning the law.

[0002]

2. Description of the Related Art In general, optical elements such as lenses, prisms, mirrors, and filters are formed by molding a glass material into a given outer shape and grinding it, and then the functional surface, that is, the surface through which light is transmitted and / or reflected is precisely ground. It is manufactured by the procedure to make it an optical functional surface.

However, in the production of the optical element as described above, a skilled worker takes a considerable amount of time in order to obtain a desired surface accuracy (that is, accuracy of surface shape and surface roughness) by grinding and polishing. It was necessary to carry out processing work. In particular, when manufacturing an optical element whose functional surface is an aspherical surface, more advanced grinding and polishing techniques are required and the processing time must be extended.

Therefore, recently, in place of the traditional optical element manufacturing method as described above, the optical element material is housed in a molding die having a predetermined surface precision and heated and pressed. Immediately, a method for forming an overall shape including a functional surface has been performed by press molding. According to this, even when the functional surface is an aspherical surface, the optical element can be manufactured relatively easily and in a short time. Such a press molding method is suitable for continuous production of optical elements.

The conditions required for the above-mentioned press molding include that the mold member and the optical element material do not fuse or react with each other, and the molding die can withstand repeated impacts.

In order to satisfy such conditions, in the conventional method for manufacturing an optical element, it is necessary to perform molding in a non-oxidizing atmosphere in order to prevent clouding and fusion defects of the molded product due to oxidative deterioration of the mold. was there. Therefore, there are problems that the molding apparatus becomes complicated and the cost of the molded product increases, it is difficult to prevent oxygen inflow during molding, and stable production becomes difficult.

[0007]

SUMMARY OF THE INVENTION Therefore, the present invention has been made based on the above circumstances, and it is possible to reduce the cost of a molded product by eliminating the need to control the atmosphere during molding by selecting the mold material and the surface treatment of the glass to be molded. An object of the present invention is to provide a molding method of an optical element, which enables easy and long-term manufacture of the optical element with stable accuracy.

[0008]

Therefore, in the present invention,
As a mold member for molding, a metal compound or ceramic having excellent oxidation resistance is used as a mold base material or a coating layer of the molding surface thereof, and a glass blank as an optical element material has a melting point from its glass softening point. The molding surface of the above-mentioned mold member is pressed through the mold release layer of a high material, and pressure molding is performed in the atmosphere in which oxygen exists.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first mold member according to the present invention.
Examples of are shown. Here, reference numeral 130 indicates a die base material, and 132 indicates an aluminum oxide coating layer formed on the molding surface of the die base material 130. The above mold base material 13
0 is made of cemented carbide and has a desired outer shape by machining such as cutting, grinding and polishing in advance. Particularly, the molding surface has a desired surface accuracy and surface roughness R _max = 0.02 μ.
It is finished in m.

In this embodiment, the die base material 130 is also used.
A sputtering method is used to form the aluminum oxide layer 132 on the surface of the. The aluminum oxide layer obtained by this method is amorphous represented by the chemical formula Al ₂ O ₃ having a composition ratio of Al = 2: 0 = 3, and has a thickness of, for example, 1.
The surface roughness is 0 μm and the surface roughness is R _max = 0.02 μm.

On the other hand, in order to clarify the superiority of the present invention as compared with the conventional example, the same mold base material as the above-mentioned mold base material was used as a comparative mold, and TiN was formed on the surface by sputtering. The thing which formed the layer was prepared. The surface roughness of this mold is R _max = 0.02 μm, which is equivalent to the mold of the present invention.

The present inventor conducted a molding test using these molds. The optical element material used for the molding step is glass SF8, and the surface thereof is coated with a release layer containing ZnS as a main component to a thickness of 200Å.

FIG. 4 shows an example of a sputtering apparatus for forming such an aluminum oxide layer. In FIG. 4, reference numeral 140 is a vacuum chamber. An exhaust port 142 is connected to the vacuum chamber, and the exhaust port is connected to a decompression source (not shown). A heater 144 is arranged in the upper portion of the vacuum chamber 140, and a reference numeral 145 is a power source for the heater. A mold base material support member 146 is disposed below the heater 144, and a mold base material 148 is supported by the support member with the molding surface facing downward. Reference numeral 149 is a bias power source for applying a bias voltage to the die base material. A coil 150 for glow discharge generation is arranged below the die base material 148. Note that reference numeral 15
Reference numeral 1 is the high frequency power supply, and 152 is the matching circuit.
A cathode electrode 154 is arranged in the lower part of the vacuum chamber 140, and an aluminum oxide target 156 is arranged on the electrode. Reference numeral 157 is a power source for applying a voltage to the cathode electrode 154,
Reference numeral 158 is a pipe for supplying argon gas toward the tantalum target 156.

When forming the aluminum oxide layer, the mold base material 148 finished to a predetermined accuracy is washed with an organic solvent and then supported by the mold base material support 146. Next, the vacuum chamber 140 is evacuated to a predetermined degree of vacuum, argon gas is introduced from the pipe 158, and the coil 150 is supplied by a high frequency power source.
A high frequency voltage is applied to generate a glow discharge, and a negative voltage is applied to the mold base material 148 by a bias power source 149 to perform sputter cleaning of the mold base material 148 with argon ions. After that, a high frequency or direct current voltage is applied to the cathode electrode 154 by the power source 157 to generate a glow discharge of argon in the vicinity of the aluminum oxide target 156, and an argon ion bombards the aluminum oxide target. Further, a high frequency voltage is applied to the coil 150 by the power supply 151 to form aluminum oxide plasma, and a negative bias voltage is applied to the mold base material 148 by the bias power supply 149 to remove oxygen and aluminum ions in the plasma. It is drawn toward the mold base material 148. In this way, sputtering is performed. As a result, an aluminum oxide layer is formed on the surface of the mold base material 148. Further, a TiN target may be used instead of the aluminum oxide target 156 for forming the TiN layer of the mold member prepared for comparison.

A continuous molding test was carried out using the above-mentioned two types of mold members thus obtained and glass as an optical element material by a molding apparatus shown in FIG. In the above molding apparatus, reference numeral 4 is an intake table,
Reference numeral 4 is a heat shield plate. Further, reference numeral 6 is a molding chamber,
Reference numeral 18 is a rail, and 20 is a pallet that can be transported on the rail in the direction of arrow A. Each reference numeral 24, 38,
Reference numerals 40 and 50 are hydraulic cylinders, and 28 is a heater arranged along the rail 18 in the molding chamber 6.

The inside of the molding chamber 6 is divided into a heating zone 6-1, a press zone 6-2, and a slow cooling zone 6-3 in this order along the pallet conveying direction. In the press zone 6-2, the upper molding member 30 is fixed to the lower end of the rod 34 of the hydraulic cylinder 38, and the lower molding member 32 is fixed to the upper end of the rod 36 of the hydraulic cylinder 40. ing. These upper mold member 30 and lower mold member 32
Corresponds to the mold member in the embodiment of FIG. 1 described above.

In order to obtain a blank to be put into this molding apparatus, a flint type optical glass (SF8 (PBM2
8) It is necessary to roughly process the softening point Sp = 567 ° C. and the transition point Tg = 443 ° C. into a predetermined shape and size.

This glass blank is placed on the pallet 20 and placed at the position 20-1 on the intake table. Then, this pallet is pushed in the direction A by the rod 22 of the hydraulic cylinder 24 to pass over the heat shield plate 12 and move to the 20-
It is conveyed to the position 2 and further to the next position. Thereafter, similarly, a pallet is newly placed on the loading table 4 at predetermined timing in the same manner, and each time the pallet is placed in the molding chamber 6 by 20-1.
→ ・ ・ ・ ・ ・ → Transfer to the position 20-8 sequentially. Meanwhile, in the heating zone 6-1, the glass blank is placed on the heater 2
8 is gradually heated to a temperature equal to or higher than the softening point at the position 20-4, and then conveyed to the press zone 6-2 where hydraulic cylinders 38 and 40 are operated to operate the upper mold member 30 and the lower mold member. 32, for example, 5 at a pressure of 10 kg / cm ^2.
Press for minutes, then release the pressure and cool to below the glass transition point. Then, the hydraulic cylinders 38 and 40 are operated to release the upper mold member 30 and the lower mold member 40 from the glass molded product. At the time of the pressing, the pallet is used as a body member for molding. Thereafter, the glass molded product is gradually cooled in the slow cooling zone 6-3.

The pallet that has reached the position 20-8 in the molding chamber 6 is transferred to the position 20-20 on the unloading table 10 over the heat shield plate 14 in the next transfer, and then to the next position. At the time of conveyance, the hydraulic cylinder 50 is operated to take out the above glass molded product from the molding device 2 by the rod 48.

After that, light polishing is performed to the extent that the shape of the surface of the molded optical element is not destroyed, and the film on the surface is removed. For example, in the case of an aspherical lens molding surface, soft felt is attached to the approximate spherical shape, and the surface is polished by copying using an abrasive or the like.

The press molding as described above is continuously performed 2000 times, and the surface roughness of the molding surface of the mold members 30 and 32 and the surface roughness of the optical surface after the coating film of the molded optical element is removed in the process. Table 1 shows the result of measurement of the hardness.

[0022]

[Table 1] As shown in Table 1, when the mold member coated with Al ₂ O ₃ of the present invention was used, the functional surface of the molded optical element was not deteriorated after the coating film was removed even after 2000 molding tests. I can't. On the other hand, in the comparative example using the mold member coated with TiN, the glass was fused to the mold within the initial 10 shots. This is because it is exposed to high temperatures in the presence of oxygen, so that TiN is oxidized and partially TiO ₂
It is considered that this is because the surface of the coating layer deteriorated.

Further, when the surface of the Al ₂ O ₃ coating layer is examined in detail with an optical microscope after 2000 shots,
A large number of minute peelings were generated in the peripheral portion of the molding surface of the mold member. It is considered that this is because a relatively large internal stress remained in the aluminum oxide layer and the adhesive force with the die base material was weakened.

The surface of the TiN coating layer of the comparative example is
When observed in detail with an optical microscope, a titanium oxide film is formed in a mottled pattern on the TiN layer at the fifth shot. In addition, at the 10th shot, the TiN layer was almost entirely oxidized and corroded to be in a tattered state.

[0025]

[Other Embodiments] FIG. 2 is a schematic sectional view showing a second embodiment of the mold member according to the present invention. Here, reference numeral 130 denotes a die base material, 131 denotes a tantalum layer formed on the molding surface of the die base material, and 132 denotes an aluminum oxide coating layer formed on the tantalum layer 131.

The thickness of the tantalum layer 131 is appropriately set depending on the manufacturing conditions, but is a thickness (for example, 0.01 to 5 μm, preferably 0.2 μm) so that desired characteristics can be exhibited during use.
m)).

The tantalum layer 131 functions to increase the bonding force between the mold base material 130 and the aluminum oxide layer 132 and prevent the coating layer from peeling off during use. That is, when the aluminum oxide layer is formed directly on the mold base material 130 without forming the tantalum layer 131, a relatively large internal stress remains in the aluminum oxide layer. Therefore, by interposing the tantalum layer 131 between the mold base material 130 and the aluminum oxide layer 132, it becomes possible to reduce the residual internal stress of the coating layer composed of the aluminum oxide layer 132 and the tantalum layer 131. Of. Thus, even if the press molding is repeated at a relatively high temperature during use, a heat-resisting thermal history can easily provide a mold member with good durability that does not cause peeling of the coating layer.

As a result of carrying out a molding test similar to that of the first embodiment using the above mold member, the surface roughness of the molded product and the mold was the same as in Table 1 this time, but 2000 shots. In the subsequent observation result of the die molding surface, fine peeling of the peripheral portion which occurred in the first embodiment did not occur.

A material having a melting point higher than the softening point of glass as an optical element material used therein is used for the release agent used in the above embodiments. It adheres to the surface of the molded part as a thin film when the glass blank is separated from the mold member, which is later peeled off. The selection criteria are that it is easy to coat on glass, that it does not accumulate on the mold during repeated molding to cause defective moldings, that it does not react with glass near the molding temperature to cause residual defects after film removal, molding Do not decompose or burn at temperature. For example, Al ₂ O ₃ , MgF _2, MgO, CuO, Z
Examples include nS, CaF ₂ , ZnSe, and ZnO. Also,
The thickness is preferably 5Å to 500Å from the viewpoints of fusion prevention, adhesion to a mold, and ease of removal.

In the above embodiment, cemented carbide is used for the mold member, but for example, Al, Ti, Cr, Fe, C
o, Ni, Cu, Zn, Zr, Nb, Mo, Hf, T
a, W metal oxide, or SiC, AlN, B
It may be made of a material containing at least one or more ceramics such as N and Si ₃ N _{4. In} this case, the coating layer on the molding surface may not be formed. Further, although aluminum oxide is mentioned as the coating layer in the above-mentioned embodiments, it may be constituted by the same material as described above for the mold base material.

By the way, when the oxidation reaction start temperature of the material selected here is measured by thermogravimetric analysis, the results are shown in Table 2 below.

[0032]

[Table 2] Thus, it will be understood that the ceramic will not oxidize when used in the press molding process if the oxidation initiation temperature of the ceramic is higher than the glass forming temperature. On the other hand, the oxide does not undergo oxidation even in the presence of high temperature oxygen. Deterioration of the mold at the time of molding is due to the fact that the change in the deposition near the surface occurs due to the oxidation, and the peeling and roughening progresses as a whole. Therefore, the aforementioned metal oxide does not deteriorate.

[0033]

As described above, the present invention provides a mold member of a molding mold in which a cemented carbide or the like is used as a mold base material and a metal oxide such as an aluminum oxide layer or ceramic is coated on the molding surface. Or the mold base material itself is composed of the metal oxide or ceramic as described above, the mold surface is coated with a mold release layer, and a glass blank as an optical element material is obtained by using the mold release layer and the mold member. With the combination function of and, it is possible to perform pressure molding without controlling the atmosphere, that is, even in the presence of oxygen. Therefore, the molding apparatus becomes cheaper and the cost of the molded product can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing another embodiment.

FIG. 3 is a conceptual diagram of a molding apparatus for carrying out the present invention.

FIG. 4 is a conceptual diagram of a film forming apparatus for making the molding die of the present invention.

[Explanation of symbols]

 130 type base material 132 aluminum oxide layer 131 tantalum layer 30 type member 32 type member 148 type base material 156 aluminum oxide target

Claims (2)

[Claims] 1. A metal compound or ceramic having excellent oxidation resistance is used as a mold member for molding as a mold base material or a coating layer on the molding surface thereof, and a glass blank as an optical element material A method for molding an optical element, which comprises applying a molding surface of the mold member through a release agent made of a material having a melting point higher than the glass softening point and performing pressure molding in an atmosphere containing oxygen. 2. As the metal compound, Al, Ti, C
r, Fe, Co, Ni, Cu, Zn, Zr, Nb, M
At least one of SiC, AlN, BN, and Si ₃ N ₄ is used as an oxide of o, Hf, Ta, W, or ceramic.
The molding method of an optical element according to claim 1, wherein the molding base member formed by forming the molding base material or the coating layer on the molding surface from a material containing three or more materials is used. ..