JPS6251211B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for making a mold for molding an optical element. Conventionally, many optical elements such as lenses, prisms, and filters are manufactured by polishing glass. However, polishing requires considerable time and skill. In addition, manufacturing an aspherical lens by polishing requires a more sophisticated polishing technique and requires a longer processing time. In contrast to such a method of manufacturing an optical element by polishing, there is a method of manufacturing an optical element by molding by heating and pressing. According to this molding method, optical elements can be manufactured in a short time, and aspherical lenses can also be manufactured easily and in a short time in the same way as spherical lenses. There are still problems that need to be improved in the molding method. The problem is that it is not easy to mold an optical element with the surface precision necessary for an optical element. That is, conventionally, molds made of graphite have often been used, but when a mold made of graphite is used, optical glass elements with good surface precision can be manufactured. Nakatsuta. The present invention provides a mold member for glass molding as described above, in which a material containing tungsten carbide and cobalt as main components and at least 3 to 10 parts by weight of cobalt per 100 parts by weight of tungsten carbide is sintered into the shape of the mold member. Provided is a method for creating a mold for molding an optical lens, which is characterized by forming a mold, and then applying hot isostatic pressing treatment (HIP treatment) thereto to form a molding surface in which tungsten carbide is densely arranged. It is something to do. That is, the mold for molding an optical element created according to the present invention is made of a material mainly composed of tungsten carbide and cobalt, and has a molding surface on which tungsten carbide is densely arranged, so this mold is used. In this way, an optical element having high surface precision can be manufactured by heating and pressing. As mentioned above, many molds made from graphite have traditionally been used as molds for making optical elements, but because graphite is porous, no matter how much it is polished, it cannot be used as an optical element. Although it has not been possible to obtain a mold with an inner wall surface rough enough to produce a device with surface precision, in the present invention, this can be achieved by using a mold whose main components are tungsten carbide and cobalt. As a result, it is possible to obtain a mold having an inner wall surface with a surface roughness of R _nax 5/100 μm or less, and to produce an optical element having a surface precision that accurately corresponds to such surface roughness. Therefore, the surface roughness of the inner wall of the mold made according to the present invention is usually R _nax 5/100 μm or less, particularly R _nax 3/100 μm.
The following settings are preferable. In order to create a mold with such high surface precision, high pressure is applied to the surface of the sintered body of tungsten carbide and cobalt to ensure that there are no pores (cavities) that would impede the surface precision, and then the surface is polished. The manufactured one is suitable. The composition ratio of tungsten carbide and cobalt forming the mold is set appropriately, but in general, a range of 1 to 25 parts, particularly 3 to 10 parts of cobalt is suitable for 100 parts (by weight) of tungsten carbide. . Further, other components such as nickel may be added as appropriate.

In this way, by adding cobalt to tungsten carbide, it is possible to obtain a mold that is denser and does not change shape at high temperatures. However, materials whose main components are tungsten carbide and cobalt have a coefficient of linear expansion of 5 x 10 ^-6 , which is smaller than 8.2 x 10 ^-6 of flint-based optical glass (SF14), and that so-called shrinkage does not occur. does not stick to the mold (good mold releasability), has higher thermal conductivity than ceramics (0.91 cal/sec/cal), has high hardness (Hv1500) and has excellent durability, and has the high mirror finish mentioned above. It has the advantage of providing flexibility.

An optical element molded by heat and pressure using a mold created according to the present invention does not require post-polishing and can be used as an optical element as it is. In addition, the heating and pressurizing conditions in the forming process are appropriately set depending on the type of glass used and the type of crystalline material such as MgF ₂ , CaF ₂ , TiO ₂ , ZnS, etc.; The temperature of the glass is above the glass transition point. It may be heated in advance before being placed in the mold, or it may be heated together with the mold after being placed in the mold.

However, in order to prevent oxidation from occurring due to heating, this molding step is preferably carried out in a vacuum or in an inert atmosphere such as nitrogen gas or helium.

Hereinafter, an example of manufacturing an optical element using a mold made according to the present invention and a comparative example of manufacturing an optical element using a conventional mold made of graphite will be described.

Example 1 5 parts by weight of cobalt (Co) was mixed with 100 parts by weight of tungsten carbide (WC) pulverized to a particle size of 1 to 2μ, and the material was sintered after pressing into an outer diameter of 17 mm and a thickness of 15 mm. It was densified by pressure pressing (HIP) using gas (argon) as a pressure medium and applying a high pressure of 5000 kg/cm ² .

Next, using a curve generator (spherical surface generating machine), it was ground in the same manner as for generating the spherical surface of a lens, to obtain a surface roughness of about R _nax 10 μm. Further particle size 10
Lapping to 1μ using μm alumina abrasive grains
Rmax is obtained by polishing the surface with a diamond of 0.5 μm in diameter as shown in Figure 1A.
was set to 0.03 μm or less.

The lens molding apparatus and processing procedure will be explained with reference to FIG.

In Fig. 2, 1 is a sealed container, 2 is a lid thereof, 3 is an upper mold for molding an optical element, 4 is a lower mold, 5
6 is the upper mold holder to hold the upper mold, 6 is the body mold,
7 is a mold holder, 8 is a heater, 9 is a lifting rod that lifts up the lower mold, 10 is an air cylinder that operates the lifting rod, 11 is an oil rotary pump, 12, 1
3 and 14 are valves, 15 is a nitrogen gas introduction pipe,
16 is a valve, 17 is a discharge pipe, 18 is a valve, 19 is a temperature sensor, 20 is a water cooling pipe, 21
indicates a stand on which a sealed container is placed.

Before manufacturing an optical element, as a preliminary preparation, a disk-shaped piece of flint optical glass (SF14) with an outer diameter of 15.8 mm and a thickness of 2 mm is polished on both sides (this is called a blank). Open the lid 2 of the airtight container 1, place the blank 22 on the lower mold 4 and set the mold 3, then close the lid 2 of the airtight container and open the water cooling pipe 2.
0 and energize the heater 8. At this time, the nitrogen gas valves 16 and 18 are closed, and the exhaust system valves 12, 13, and 14 are also closed. Incidentally, the oil rotating pump 11 is constantly rotating.

The valve 12 is opened and exhaust begins, and when the temperature becomes below 10 ^-2 Torr, the valve 12 is closed and the valve 16 is opened to introduce nitrogen gas from the cylinder into the sealed container. When the temperature reaches 650°C, the air cylinder 10 is activated and molding is performed at a pressure of 10 kg/cm ² . Apply pressure until the temperature drops below the transition point, and during this time reduce the cooling rate to 10℃/
Control to min position. After that, cool at a rate of 20℃/min or more, and when the temperature drops to 200℃ or less, valve 1
6 and open the valve 13 to introduce air into the vacuum chamber 1. Then, open the lid 2, remove the upper mold presser 5, and take out the molded product.

As above, flint optical glass (SF14) (softening point SP = 586℃, transition point Tg = 485℃)
As a result of molding a lens having the shape and dimensions shown in FIG. 3 using the mold, it was possible to obtain a lens having a surface roughness almost the same as that of the mold shown in FIG. 1A.

FIG. 4 shows the molding conditions at this time, that is, a time-temperature relationship diagram.

Example 2 In the same manner as in Example 1, a material consisting of 5 parts by weight of cobalt and 5 parts by weight of nickel was used in 100 parts by weight of tungsten carbide pulverized to a particle size of 1 to 2 μm in the same manner as in Example 1. Surface roughness Rmax0.03μ
I made a mold less than m.

When a lens was molded using the same lens molding apparatus and processing procedure as in Example 1, the same results as in Example 1 were obtained.

Comparative Example A conventional graphite mold was polished and the same lens as in Example 1 above was molded using the same equipment. In this case, the surface roughness of the mold was Rmax 0.3 μm, as shown in Figure 1B, and the molded lens was
As shown in Figure C, only a surface roughness of Rmax 0.2 μm could be obtained.

As mentioned above, the mold for molding an optical element created according to the present invention is made of a material mainly composed of tungsten carbide and cobalt, with nickel added as necessary, and the optical element to be molded is welded to the mold. In other words, it was confirmed that the mold releasability was excellent, and that the mold releasability was further improved especially when nickel was added. In addition, this mold has excellent optical performance, and especially when the cobalt content is in the range of 3 to 10 parts, welding of glass and cobalt during molding is suppressed, and the mold is dense and does not change shape at high temperatures. Obtainable. Furthermore, this mold has good processing performance, which is the most desired condition in glass molding, and makes it easier to achieve a high mirror finish with an R _nax of 3 to 4/100 μm compared to molds made from conventional graphite. This enables precise molding of optical elements.

[Brief explanation of the drawing]

Figure 1A shows an example of the surface roughness of a mold made according to the present invention, and Figures 1B and 1C show the surface roughness of a conventional graphite mold and the surface roughness of a molded lens. 2 is a sectional view showing a lens molding apparatus, FIG. 3 is a diagram showing the shape and dimensions of an example of a lens to be molded, and FIG. 4 is a time-temperature relationship diagram during molding. 1... airtight container, 2... lid, 3... upper mold, 4...
...lower mold, 5...upper mold press, 6...body mold, 7...
Mold holder, 8... Heater, 9... Lifting rod,
10...Air cylinder, 11...Oil rotary pump,
12, 13, 14... Valve, 15... Nitrogen gas introduction pipe, 16... Valve, 17... Discharge pipe, 18... Valve, 19... Temperature sensor, 20
...Water cooling pipes, 21... units.

Claims (1)

[Claims] 1. Put the optical glass into a mold member having a molding surface to be formed on the functional surface of the optical lens, heat the optical glass and the mold member to a temperature equal to or higher than the transition point of the optical glass, and heat the molding surface of the mold member. A method for creating a mold for molding a lens by applying pressure to the mold member and displacing the molding surface of the mold member to the pressurized surface of the optical glass while maintaining R _nax at least 5/100 μm or less. The mold member is
It contains tungsten carbide and cobalt as main components, and the composition ratio is at least 3 to 10 parts by weight of cobalt per 100 parts by weight of tungsten carbide. 1. A method for making a mold for molding an optical element, comprising densifying a shape by hot isostatic pressing to form a molding surface of a mold member on which tungsten carbide is densely arranged.