JPH0776095B2 - Optical element manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing optical elements such as lenses, prisms, mirrors and filters, and in particular from a molten glass material without undergoing steps such as grinding and polishing. The present invention relates to a method for efficiently producing an optical element having an optical functional surface with good surface accuracy and durability at low cost using press molding.

[Prior Art] Generally, in optical elements such as lenses, prisms, mirrors, and filters, after a glass material is ground to have a desired external shape, a functional surface, that is, a surface through which light is transmitted and / or reflected is polished. It is manufactured by making it an optical surface.

In order to obtain desired surface accuracy (that is, accuracy of surface shape, surface roughness, etc.) by grinding and polishing in the production of the optical element as described above, a skilled worker performs processing for a considerable time. Was necessary. Further, in the case of manufacturing an optical element having an aspherical functional surface, more sophisticated 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 metal device having a predetermined surface accuracy and heated and pressed to perform press molding. Immediately, it is becoming common to form the overall shape including the functional surface. According to this, an optical element can be manufactured relatively easily and in a short time even when the functional surface is an aspherical surface.

In the method of manufacturing an optical element by forming an optically functional surface by press molding, an optical glass material is once made into an approximate shape of a target shape to obtain a preform (preform), and then the preform is molded into a molding die. There are a method in which the molten optical glass is housed in the apparatus and formed into a final target shape by pressing, and a method in which the molten optical glass is immediately housed in the molding die apparatus and pressed to perform molding.

In the method using a preform, as described in JP-B-61-32263, a preform is obtained by an appropriate method such as grinding and polishing, and the preform and the mold member of the final molding die device are separately provided. Alternatively, it is necessary to heat the preform in a mold apparatus to a predetermined temperature, press the softened preform with a mold apparatus at an appropriate pressure, and then cool the preform.

However, this method requires the same steps as those in the conventional method when obtaining the preform, and therefore, it cannot be said that the manufacturing cost is still sufficiently satisfactory.

On the other hand, the method in which the molten glass is directly housed in the mold apparatus and press-molded reduces the time required for the process and is particularly suitable for continuous molding.

By the way, in the optical element press-molded as described above, generally, for the purpose of improving the functionality or durability of the optical functional surface, an antireflection film or a reflective film is formed on the functional surface by a vacuum deposition method or the like. Often a surface treatment is applied to coat the incremental film.

Conventionally, such a thin film forming surface treatment is carried out by once cooling the molded product obtained by the press molding to near room temperature, then carrying the molded product into a surface treatment apparatus and heating it to an appropriate temperature. Is done above.

However, in the conventional method for manufacturing a coated optical element as described above, it takes a considerably long time from the time when the molded optical element is taken out from the mold device until the actual vapor deposition is performed,
For this reason, carbon dioxide gas or water in the air may act on the molding surface to cause burns, and foreign matter such as dust often adheres to the molding surface of the molded optical element. Although the process is performed, since the cleaning process is also exposed to the cleaning liquid, the frequency of occurrence of burns increases.

As described above, the conventional method is liable to cause burns on the optically functional surface in the process before vapor deposition, and thus has a drawback that the defective product generation rate increases depending on the type of glass material. Further, there are some glass species that cannot be practically used because they have a remarkable burning effect even though they have characteristic optical characteristics.

Further, in the above-mentioned conventional method, since the press-formed product is once cooled to near room temperature and then re-heated for surface treatment, there is a problem that a large amount of heat energy is lost.

The present invention has been made in view of the above circumstances, and an object thereof is to stably manufacture a surface-treated high-precision optical element with good efficiency and low energy consumption.

[Means for Solving the Problems] According to the present invention, a molded article having an optical functional surface is formed by press molding a molten glass material using a molding die apparatus in order to achieve the above objects. Obtained, by performing a film forming process on the optical functional surface of the molded product under heating,
In a method for producing an optical element having an optical functional surface on which a thin film is formed on the surface, the molded product at a temperature higher than the lower limit of strain removal after press molding is lower than the lower limit of strain removal for the film forming process. An optical element having an optical functional surface having a thin film formed on the surface is obtained by immediately performing the heating film forming process at the heating film forming process temperature after cooling to the heating film forming process temperature. A method for manufacturing an optical element is provided.

Examples of the heating film forming process used in the present invention include CVD under heating or PVD such as vacuum deposition and sputtering.

[Examples] Specific examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a graph showing the time change of the glass temperature for explaining the first embodiment of the optical element manufacturing method according to the present invention. Incidentally, FIG. 1 also shows the case of the conventional method for comparison.

FIG. 2 is a diagram showing an optical element 2 manufactured in this example, which is a biconvex lens having a first surface with a radius of curvature of 52 mm and a second surface with a radius of curvature of 40 mm.

Note that the present embodiment is PbO-B ₂ O ₃ is known as a low-melting glass
-This relates to the case where glass containing ZnO as a main component is used.

FIG. 3 and FIG. 4 are explanatory views of press molding by the molding die device in this embodiment.

In these drawings, the molding die apparatus has an upper die member 12 and a lower die member 14, and a lower surface of the upper die member has a molding action surface having a shape corresponding to the first surface of the optical element 2. 12a is formed, and a molding action surface 14a having a shape corresponding to the second surface of the optical element 2 is formed on the upper surface of the lower mold member 14. The surface roughness of these molding action surfaces 12a, 14a is set to be equal to or less than the surface roughness of the optically functional surface of the target optical element (mirror finish), for example, Rmax 0.01 μm.
It is said that

The upper mold member 12 and the lower mold member 14 are respectively moved in the vertical direction by a driving source (not shown), whereby the mold is opened and closed.

Although not shown, the mold device is provided with an appropriate heating means, and the mold member and the glass material can be controlled to a desired temperature by the heating means.

In the above mold apparatus, when the upper mold member 12 and the lower mold member 14 are closed, the shape of the cavity formed between the molding action surfaces 12a and 14a of both mold members is the final lens shown in FIG. It is shaped like a shape.

FIG. 3 shows the step of supplying the molten glass to the mold device.

In FIG. 3, 33 is a glass melting tank (crucible),
A heater 34 is attached around the crucible. Crucible
An outflow portion 36 is connected to the lower portion of 32, and a heater 38 is attached around the outflow portion. And the outflow part
Below the 36, a cutter 40 for cutting the continuously flowing molten glass into an appropriate length is arranged.

Put the raw material of the desired optical glass in the crucible 33 and
To heat to an appropriate temperature. As a result, the fused optical glass G is formed in the crucible 33. At this time, an optical glass with higher homogeneity can be obtained by appropriately stirring and performing defoaming treatment as needed.

The molten glass gradually flows down in the outflow portion 36 due to the action of gravity, and is extruded from the outflow port at the lower end of the outflow portion. At this time, the lower mold member 14 of the mold device is arranged below the outlet.

The melted and softened glass is extruded from the outlet of the outflow section 36, and when the tip reaches an appropriate height below the cutter 40, the cutter is operated to cut the molten glass. The glass block 4 thus cut falls on the molding surface 14a of the lower mold member 14 at time t ₁ .

FIG. 4 is a diagram showing a state during pressing.

As shown in FIG. 4, the lower mold member 14 on which the glass block 4 is placed is moved to a position corresponding to the upper mold member 12, and is moved to the lower mold member 14 at a temperature of 370 ° C. from time t ₂ to t _3. On the other hand, upper die member 1
Molding is performed by pressing 2 to close the mold to obtain a molded product 6 having a desired final shape.

After the above-mentioned molding, cooling is performed. The cooling is achieved by controlling the amount of heat by the heating means of the mold device.

For cooling, the molded product 6 has a lower temperature limit of strain removal (glass has a viscosity of 10 ^14.5
(Temperature indicating Poise) 300 ° C. The molded product is accommodated in the mold device relatively slowly from time t ₃ to t ₄ , and after reaching a temperature lower than the temperature t ₄ to t _Five
To cool at a relatively high rate. This is because if the cooling is performed too rapidly above the lower limit temperature of the strain elimination, internal strain occurs, and the strain is not effectively removed below the lower limit temperature of the strain elimination point. Since internal strain does not substantially occur below the temperature of the lower limit point of the strain removal, there is no problem even if cooling is performed rapidly.

Before the temperature reaches 200 ℃, open the above mold equipment and mold 6
The product is taken out, carried into the vacuum vapor deposition apparatus, and vacuum vapor deposition is started. For example, as shown in Fig. 1, during the period from time t ₄ to t ₅ when the temperature reaches 250 ° C, the molded product is carried into the vacuum deposition device from the mold device, and from time t ₅ to t _6. Then, vacuum-deposit MgF ₂ on both optically functional surfaces.

After that, the coated optical element is taken out from the vacuum vapor deposition apparatus and cooled to room temperature.

In order to continuously and efficiently perform such a series of press molding, cooling and vacuum vapor deposition steps, it is preferable to perform the press molding and cooling in a vacuum and arrange the vacuum vapor deposition apparatus in the same vacuum system. However, it is preferable to provide a gate valve between these devices so that the valve is opened only when the optical element is transported.

On the other hand, in FIG. 1, the dotted line indicates the steps of press molding, cooling to room temperature, cleaning, loading into a vacuum evaporation apparatus, heating, vacuum evaporation and cooling by the conventional method of press molding using a preform. An example in which an optical element similar to that of the above-mentioned embodiment of the present invention is manufactured will be shown.

As can be seen from FIG. 1, in the conventional example, the cooling process from time t ₅ , the cleaning process, and the reheating process before vapor deposition (that is, from P ₁
It takes more time than the embodiment of the present invention by the amount up to P ₂ ) and the energy loss is larger than that of the embodiment of the present invention by the consumed heat energy of this time. Therefore, according to the embodiment of the present invention, the cost can be considerably reduced.

Further, according to the embodiment of the present invention, since the vacuum deposition is immediately performed immediately after the cooling after the molding after the cooling, the foreign matter such as dust may be attached to the optically functional surface before the vacuum deposition. Since it is extremely small, the embodiment of the present invention does not require a cleaning step as in the conventional example, and because of this and because the time until vacuum deposition is short, burns may occur due to contact with the cleaning liquid and air. There is no such thing.

The optical element obtained in the embodiment of the present invention, the temperature of 30 ℃, humidity
When stored for one month in a 100% atmosphere, no optical defects such as spiders were observed on the optically functional surface.

On the other hand, in the case of the above-mentioned conventional example, the occurrence of burns was recognized after the cleaning step, and a partial defect was recognized on the optically functional surface after vacuum deposition.

As described above, according to the examples of the present invention, it is possible to obtain a good optical element by using glass which cannot obtain a good optical element by the conventional method due to insufficient optical durability.

FIG. 5 is a graph showing the time change of the glass temperature for explaining the second embodiment of the optical element manufacturing method according to the present invention. Incidentally, FIG. 5 also shows the case of the conventional method for comparison.

This embodiment differs from the first embodiment only in that fine annealing for fine adjustment of the refractive index is performed after vacuum evaporation.

In this embodiment, fine annealing is performed immediately after the vapor deposition process. The annealing is performed at a temperature higher than the vapor deposition temperature for a desired time (maximum temperature 320 ° C.), while the dotted line in FIG. 5 indicates the steps of further cleaning, heating and fine annealing following the conventional example of FIG. An example in which an optical element similar to that of the above-described embodiment of the present invention is manufactured is shown.

As can be seen from FIG. 5, in the conventional example, the cooling process from time t ₅ , the cleaning process, and the reheating process before vapor deposition (that is, from P ₁
Cooling step after minute) and deposition of up to P _2, and takes extra time than minutes) by the present invention the embodiments of the minute (i.e. P ₃ washing steps and re-heating step to P _4, and this time The energy loss is larger than that in the embodiment of the present invention by the consumed heat energy. Therefore, according to the embodiment of the present invention, the cost can be considerably reduced.

In the embodiment of the present invention shown in FIG. 5, vacuum evaporation was performed before fine annealing, but it is also possible to perform fine annealing first and then vacuum evaporation in the cooling process. According to this, the heat energy loss is further reduced, and the cost can be further reduced.

[Effects of the Invention] According to the present invention as described above, a molded product having a temperature higher than the lower limit of strain elimination after press molding is cooled to a heating film forming treatment temperature lower than the lower limit of strain elimination for film forming treatment. Immediately thereafter, the heating film forming process is performed at the heating film forming temperature, so that it is possible to sufficiently prevent surface defects such as burning and adhesion of foreign matter during the manufacturing process, which results in low chemical durability. Therefore, it is possible to manufacture optical elements using glass, which was not suitable for conventional optical element manufacturing, and to provide an optical functional surface with a thin film formed on the surface with good efficiency and low energy consumption. An optical element having the same can be manufactured.

[Brief description of drawings]

FIG. 1 and FIG. 5 are graphs showing the time change of glass temperature for explaining the method for manufacturing an optical element according to the present invention. FIG. 2 is a diagram showing an optical element. FIG. 3 and FIG. 4 are explanatory views of press molding by the molding die device according to the present invention. 4: Glass block, 6: Molded product, 12: Upper mold member, 14: Lower mold member, 33: Crucible, 36: Outflow part.

Claims (1)

[Claims] 1. A molded product having an optical functional surface is obtained by press-molding a molten glass material using a molding die device, and a film-forming treatment is performed on the optical functional surface of the molded product under heating. In the method for producing an optical element having an optical functional surface on which a thin film is formed on the surface, the molded article at a temperature higher than the lower limit of strain removal after press molding is treated from the lower limit of strain removal for the film forming process. An optical element having an optical functional surface having a thin film formed on the surface is obtained by immediately performing the heating film forming process at the heating film forming process temperature after cooling to a low heating film forming process temperature. And a method for manufacturing an optical element.