JPH04175231A - Production of optical element - Google Patents

Abstract

PURPOSE:To prevent the adhesion of an easily volatile component in a glass material to the surface of a mold to provide a cloudless optical element having an excellent surface precision by specifying the atmospheric gas pressure in the mold, when the softened glass material is press-molded to directly prepare the optical element. CONSTITUTION:For example, the spherical blank of optical glass is loaded on a lower mold 4 in a closed container 1, and an upper mold 3 and an upper press 5 are attached. After a lid 2 is closed, water is passed through a water-cooling pipe 20, and an electric current is applied to heaters 8. An oil rotary pump 11 is operated, and a valve 12 is opened to evacuate the container 1. After a desired vacuum degree is obtained, the valve 12 is closed, and valves 16 and 18 are opened to charge the container 1 with nitrogen gas from a bomb. In the process the pressure of the nitrogen gas is controlled to a pressure of >=1.5 atm. The pressure is constantly maintained by the automatic opening of a leak valve attached to the container 1 and by the automatic opening of the valve 16 when temperature is raised and lowered, respectively. The glass is press-molded at a desired temperature and subsequently cooled. The valves 16, 18 are subsequently closed, and a valve 13 is opened to charge the container 1 with air, followed by taking out the molded optical element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of manufacturing an optical element that is directly formed by press-molding a softened glass body without requiring finishing by grinding, polishing, etc.

[Prior Art] Conventionally, in order to manufacture glass optical elements, it has been common to grind a glass material into a predetermined shape using a diamond grindstone or the like, and then polish the ground surface with cerium oxide or the like. However, as the need for aspherical lenses continues to grow, there is a limit to the ability to manufacture large quantities of optical elements at low cost using conventional methods. The manufacturing technology is being put into practical use.

However, when a large number of heat-softened glass materials are manufactured by continuous pressure molding in one set of molds, lead-based glass (flint glass) contains lead in the glass material. Even in glass that does not contain lead, easily volatile components (e.g. alkali, alkaline earth, boron, etc.) may volatize and adhere or fuse to the surface of the mold, causing visible damage to the mold and the optical element after molding. A phenomenon occurs in which clouding occurs on the surface, which significantly reduces the surface precision of the optical element after molding. To counter this problem, various molding glass materials have been proposed.

For example, in JP-A No. 57-4735, a glass material for molding is coated in advance with a coating layer made of a thermoplastic material such as glass or plastic that can be easily removed by a specific chemical treatment. Removal of the coating layer (eg with nitric acid) is indicated.

Furthermore, JP-A No. 62-297225 discloses the use of a molding glass material coated with a glass surface layer having a glass transition temperature higher than that of the inner glass and having substantially the same coefficient of thermal expansion and refractive index. There is.

Furthermore, in JP-A-62-207728, the easily volatile components (B, Os, P) in the surface layer were immersed in hydrofluoric acid and nitric acid.
It has been shown to use a glass material for molding with reduced bO, etc.).

[Problems to be Solved by the Invention] However, in JP-A-57-4735, a step of removing the coating layer is required after press molding, resulting in an extremely time-consuming and expensive optical element. Furthermore, when processing with acid, the surface precision of the optical element itself may be deteriorated, causing a decrease in yield.

Furthermore, in JP-A-62-297225, it is effective for optical elements in which the amount of deformation from the glass material for molding is very small, but it is effective for optical elements with a large amount of deformation, since the glass material is in an unsoftened state during molding. Microscopic cracks are likely to occur in the surface layer, and glass pieces resulting from these cracks may adhere to the mold, making it difficult to continuously manufacture high-precision optical elements.

Furthermore, in JP-A-62-207728, when a glass material for molding is immersed in hydrofluoric acid, 5iO= is decomposed at the same time as easily volatile components such as lead, so the volume changes and the pressure-molded optical element There is a problem that variations occur in dimensional accuracy.

In addition, when applying some type of anti-fogging coating to the surface of glass material for molding for boat fishing, it is mainly applied by vapor deposition, which is expensive, and moreover, the coating is torn from the glass surface during molding and the inner glass is exposed. This has the disadvantage that the anti-fogging effect is not sufficient because of this. Furthermore, if the coating film is too thick, the mold may be contaminated or the coating may crack. If it is too thin, there is a drawback that the anti-fogging effect is not sufficient. Furthermore, due to the slight difference in the coefficient of thermal expansion between the glass and the coating material, the membrane cracks when heated, and when pressurized, the inner glass protrudes, resulting in partial fogging.

Therefore, an object of the present invention is to continuously produce optical elements in large quantities that do not allow easily volatile components such as lead, alkali, alkaline earth metals, and boron to adhere to the mold, and that are free from clouding, that is, have excellent surface precision. An object of the present invention is to provide a method for manufacturing an optical element that can be molded with high yield.

[Means and effects for solving the problem] That is, the present invention presses a moldable optical element molding material placed in a molding mold with the molding mold to improve the functional aspect of the optical element. In the pressure molding method for molding, the method of manufacturing an optical element is characterized in that the atmospheric gas pressure inside the mold is 1.5 atmospheres or more.

In the present invention, the atmospheric gas pressure inside at least the mold in the molding apparatus is set to 1.5 atm or more, preferably 1.5 atm or more.
By setting the pressure to 5 atm or more and 3 atm or less, volatilization of easily volatile components from the glass is suppressed and fogging of the mold and molded product is prevented.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a pressurizing/heating device used to examine the volatilization amount of easily volatile components in a glass material. In the same figure, 23 is a heater, 24 is an SUS recyling 5
is made of copper, 26 is a mirror-polished upper mold, 27 is the same lower mold, 28
is a glass material (a material for molding an optical element), and there is a gap of about 50 μm between the glass material 28 and the upper mold 26. The apparatus shown in FIG. 1 is located in a chamber (not shown), and the atmospheric gas pressure in the chamber can be set arbitrarily. Note that the mold materials for the upper and lower molds were cemented carbide, and the glass material was SK12 manufactured by OHARA (Tg=sso°C).

Hereinafter, the method of the present invention will be explained step by step.

First, as shown in Figure 1, a glass material is placed between the molds.

Next, the evacuation of the chamber is started and the pressure reaches 3 x 1.
When the temperature reaches 0-2 Torr, nitrogen gas is introduced into the chamber as an atmospheric gas. Nitrogen gas pressure is lXl
There were five levels: 0-' Torr, 1 atm, 1.5 atm, 2 atm, and 3 atm.

Next, the heater is energized to heat the mold and glass to 620
Do not raise the temperature to ℃. After holding the temperature at 620°C for 30 minutes, electricity supply was stopped. After the temperature was lowered to room temperature, the upper mold was taken out from the chamber. Easily volatile components that had evaporated from the 5K12 glass were attached to the upper mold that was taken out. The amount of this deposit was evaluated by the change in cloudiness of the upper mold (change in reflectance).

Figure 2 shows the results of reflectance measurements. The reflectance value is a relative value with the reflectance of the upper mold before molding being 100%. As is clear from FIG. 2, the fogging of the upper mold decreased as the nitrogen gas pressure increased, and at 1°5 atm or higher, the amount remained within normal permissible limits (reflectance of 90% or more).

From the above results, it has become clear that by increasing the atmospheric gas pressure in the molding apparatus, volatilization of easily volatile components from the surface of the glass material can be suppressed.

Next, an example in which an optical element was press-molded by the method of the present invention will be shown.

FIG. 3 is a sectional view showing the apparatus used for press molding.

In Fig. 3, 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 is an upper mold holder, 6 is made of copper, 7 is a mold holder, and 8 is a heater. , 9 is a lower die push-up rod, 10 is an air cylinder that drives the push-up rod, 11 is an oil rotary pump, 12, 13, and 14 are valves, 1
5 is an inert gas introduction pipe, 16 is a valve, 17 is an exhaust pipe, 18 is a valve, 19 is a temperature sensor, 20 is a water cooling pipe, and 21 is a stand that supports the closed container.

First, crown-based optical glass (■ OHARA 5K12, softening point 5p = 672°C, glass transition point Tg = 550°C) or flint-based optical glass (■ OHARA!!! SF8, softening point 5p = 567°C, glass transition point A blank for molding was prepared in the form of a sphere with a predetermined weight (Tg=443°C).

Next, open the lid 2 of the airtight container 1, remove the upper mold 3 and the upper mold holder 5, place the blank on the lower mold 4, and place the blank on the upper mold 4.
And the upper mold presser foot 5 was attached. After closing the lid 2 again,
Water was flowed through the water cooling pipe 20, and the heater 8 was energized. At this time, the nitrogen gas valves 16, 18, and exhaust system valves 12, 13, and 14 were closed. Next, the oil rotary pump 11 was activated, the valve 12 was opened, and the inside of the container 1 was evacuated. After the degree of vacuum in the container 1 reached 1 o-'' Torr, the valve 12 was closed and the valve 16.18 was opened to introduce nitrogen gas from the cylinder into the closed container 1. At this time, the nitrogen gas pressure was 1 The pressure was set at .5 atm or 3 atm.The degree of vacuum reached 10-'' Torr when the temperature of the mold and glass material was approximately 150°C. In addition, when the temperature rises, a leak valve (not shown) attached to the closed container 1 automatically opens to allow leakage to keep the N2 pressure constant, and when the temperature falls, the valve 16 automatically opens to keep the N2 pressure constant. It has become.

After the temperature reached a predetermined temperature, the air cylinder 10 was operated and press molding was performed at a pressure of 80 kg/cm for 5 minutes.The applied pressure was removed, and the molding was cooled at a rate of approximately ℃/min until the temperature reached below the glass transition point. After that, cooling was performed at a rate of 20° C./min or more, and after the temperature dropped to 200° C. or less, valves 16 and 18 were closed, and leak valve 13 was opened to introduce air into the sealed container 1.Next, , open the lid 2, and remove the upper mold 3.
Then, the upper mold presser 5 was removed and the molded optical element was taken out.

Table 1 shows the results of a visual inspection of the surface of the optical element obtained. Note that No. 5.6 is a comparative example.

Table 1 *1 Usable level *2 As shown above, in the examples of the present invention, optical elements with good surface precision (surface roughness) could be molded.

In the above embodiments, flint-based and crown-based glass materials were used, but other glass materials can be similarly molded with good precision.

Although nitrogen gas was used as the atmospheric gas for pressurization, any non-oxidizing atmospheric gas may be used, such as argon gas or helium gas, for example. Of course, the atmospheric gas pressure may exceed 3 atmospheres.

The optical element to be molded may have any shape.

Although cemented carbide was used as the mold material, any material with high strength may be used, such as a titanium nitride coated mold, a silicon nitride mold, or a silicon carbide mold.

[Effects of the Invention] As is clear from the above examples, the present invention suppresses the volatilization of easily volatile components from the glass material, so even when pressure molding is performed multiple times, the easily volatile components in the glass material for molding are suppressed. It is possible to obtain an optical element with no clouding, that is, with excellent surface precision, without adhering to the surface of the mold. Further, optical elements can be press-molded in large quantities at a high yield while maintaining the surface precision of the glass material for molding. Furthermore, since it is molded from one type of glass material, even shapes with a large degree of asphericity can be molded continuously and with high precision without producing defects such as cracks. Therefore, optical elements such as aspherical lenses, which conventionally tended to be expensive, can now be molded in large quantities at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a pressurizing/heating device used to examine the volatilization amount of easily volatile components in a glass material. FIG. 2 is a diagram showing the relationship between the volatilization amount of easily volatile components in the glass material and the atmospheric gas pressure. FIG. 3 is a schematic cross-sectional view of an example of an optical element molding apparatus used in the present invention. 1: Airtight container, 2: Lid, 3: Upper mold, 4: Lower mold, -5: Upper mold holder, 6: Copper, 7: Mold holder, 8: Heater, 9: Lower mold push-up rod, 10: Air Cylinder, 11: Oil rotary pump, 12.13, 14: Valve, 15: Inert gas introduction pipe, 16: Valve, 17: Discharge pipe, 18: Valve, 19: Temperature sensor, 20: Water cooling pipe,
21: Stand. 23: Heater, 24: Ring 25: Copper, 26: Upper mold, 27: Lower mold, 28 Glass material. Agent Patent Attorney Jo Taira Yamashita Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) In a pressure molding method in which a moldable optical element molding material placed in a mold is pressurized by the mold to mold the functional surface of the optical element, at least A method for manufacturing an optical element, characterized in that the internal atmospheric gas pressure is 1.5 atmospheres or more. (2) The method for manufacturing an optical element according to claim 1, wherein the atmospheric gas pressure is 1.5 atm or more and 3 atm or less.