JPS6287B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical glass element.

Conventionally, many optical glass elements such as lenses, prisms, and filters are manufactured by polishing glass. However, the polishing process requires considerable time and skill. Furthermore, manufacturing an aspherical lens by polishing requires a more sophisticated polishing technique and also requires a longer processing time. In contrast to such a method of manufacturing an optical glass element by polishing, there is a method of manufacturing an optical glass element by molding by heating and pressing. According to this molding method, optical glass 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. Even in the pressure molding method, there are still problems that need to be improved. The problem is that it is not easy to mold an optical glass element with the surface precision required for an optical glass 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 main object of the present invention is to provide a method of manufacturing an optical glass element having good surface precision by selecting a mold material.

In the method for manufacturing an optical glass element according to the present invention, glass is housed in an upper mold, a lower mold, and a body mold made of molybdenum whose inner wall surfaces have a surface roughness of R _nax 5/100 μm or less, and the heated glass is heated. It is characterized by pressure molding.

That is, the present invention is a method of manufacturing an optical glass element having high surface precision by heating and pressing by using a mold made of molybdenum. As mentioned above, many molds made from graphite have traditionally been used as molds for making optical glass elements, but since graphite is porous, no matter how much it is polished, it cannot be used as an optical glass element. Although it has not been possible to obtain a mold with an inner wall surface rough enough to make an element with sufficient surface precision, in the present invention, by using a mold made of molybdenum, the surface roughness can be improved. SaR
It is possible to obtain a mold having an inner wall surface of _nax 5/100 μm or less, and to produce an optical glass element having a surface precision that accurately corresponds to such surface roughness. Therefore, the surface roughness of the inner wall of the molybdenum mold used in the present invention that houses the glass is R _nax 5/100.
The surface roughness is set to .mu.m or less, and thereby optical glass elements can be manufactured with precision corresponding to this surface roughness. To create a mold with a surface roughness that corresponds to the high surface precision of such optical glass elements, high pressure is applied to the surface of a molybdenum sintered body to make the surface free of pores that would impede surface precision. , and those manufactured by further polishing are suitable.
The surface roughness of the mold is R _nax 3/100 depending on the surface precision required for the optical glass element to be manufactured.
μm, furthermore, R _nax is set to 1/100 μm or less. The optical glass element molded by heat and pressure using this molybdenum mold does not require post-polishing and can be used as an optical glass element as it is.

However, molybdenum has a linear expansion coefficient of 6×10 ^-6
Even though the coefficient of linear expansion is smaller than that of flint-based optical glass (SF14), 8.2×10 ^-6 , it does not cause burning, has good machinability, and has high thermal conductivity (0.35 cal/sec/cal). Therefore, temperature control is easy, processing time can be shortened, and high productivity can be obtained.It has a high melting point (2620℃) and therefore has good heat resistance.
Moreover, it has the advantage that the high specularity mentioned above can be obtained. In this respect, the mold and the parts surrounding the mold are all made of molybdenum. The heating and pressurizing conditions in the molding process are set appropriately depending on the type of glass used, but in general, the temperature of the glass during pressurization is above the glass transition point, and the glass is heated in advance before being placed in the mold. It may be left 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.

Examples of the method of manufacturing an optical glass element using a molybdenum mold according to the present invention and comparative examples of a conventional method of manufacturing an optical glass element using a graphite mold will be described below.

EXAMPLE A molybdenum material obtained by sintering was cut to approximately the size of a mold, heated to approximately 1000°C, and simultaneously subjected to high pressure (5000 Kg/cm ² ) to make the surface dense.

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
R _na by lapping using μm alumina abrasive grains.
The maximum roughness _R nax was obtained by polishing the surface to a surface roughness of approximately 1 μm and polishing it with a diamond with a particle size of 0.5 μm, using the stylus roughness measurement method 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 optical glass elements, the outer diameter of flint-based optical glass (SF14) is
Polish both sides of a disk of 15.8 mm and 2 mm thick (this is called a blank). Airtight container lid 2
Open the blank 22 and place it on the lower mold 4.
After setting, the lid 2 of the airtight container is closed, water is allowed to flow through the water cooling pipe, and the heater 8 is energized. 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 . Continue to 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 closed container 1. Then, open the lid 2, remove the upper mold presser 5, and take out the molded product.

By the above method, flint-based 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 this method, it was possible to obtain a lens with a surface roughness R _nax of 0.05 μm, as shown in FIG. 1B. FIG. 4 shows the molding conditions at this time, that is, a time-temperature relationship diagram.

Comparative Example The same lens as in the above example was molded using the same equipment using a conventional graphite mold.
In this case, the surface roughness of the mold was R _nax 0.3 μm as shown in Figure 1 C, and the molded lens had a surface roughness R _nax 0.2 μm as shown in Figure 1 D. I couldn't help it.

As described above, in the method for manufacturing an optical glass element according to the present invention, an upper mold, a lower mold, and a body mold made of molybdenum are used. As mentioned above, molybdenum has a smaller coefficient of linear expansion than glass, so the shrinkage of the body during cooling after molding is smaller than that of glass, and therefore, the molded glass can be easily removed from the body. can. In addition, the glass material to be molded has a high softening point (500 to 800°C), and its viscosity decreases, making it easy to fuse with the mold, but molybdenum is difficult to fuse with the glass, so the fusion between the glass and the mold is difficult. The problem of adhesion can be solved by using molybdenum upper, lower, and body molds. Furthermore, molybdenum has excellent workability and can be made into complex shapes.For example, in order to attach the body mold to a mold holder, or to attach the upper mold to an upper mold holder, screw holes are inserted into the molybdenum mold. It is also easy to cut.

[Brief explanation of the drawing]

Figures 1A and 1B are diagrams showing examples of the surface roughness of a mold and the surface roughness of a molded lens in the method of the present invention, and Figures 1C and 2 are diagrams showing the surface roughness of a similar mold and molding in the conventional method. Fig. 2 is a cross-sectional view showing the lens molding device;
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.

Claims (1)

[Claims] 1. An optical system characterized by housing glass in an upper mold, a lower mold, and a body mold made of molybdenum whose inner wall surfaces have a surface roughness of R _nax 5/100 μm or less, and press-molding the heated glass. Method for manufacturing glass elements.