JPH02267127A - Method for forming optical element and device therefor - Google Patents

Abstract

PURPOSE:To prevent occurrence of temperature distribution of glass raw material and forming mold, reduction of molding conditions (temperature and pressure) and improve transferring properties of shape by specifying atmosphere temperature in a forming chamber in which a forming mold is arranged. CONSTITUTION:A glass raw material 12 is heated and softened in a heat oven 14 and the heat-treated raw material 12 is carried between upper and lower molds 2 and 3 in a forming chamber 1 by advance of a carrying arm 17 and the raw material 12 is subjected to press forming by raising the lower mold 3 to provide the optical element. During the press forming process, the interior of the forming chamber 1 is held to N2 gas atmosphere heated at temperature (t) close to transition point of a raw material 12 by a heater of the forming chamber. N2 gas heated to temperature t by a N2 gas heating oven 26 is fed into the forming chamber 1, because outside air is sent to the molding chamber 1 as an arm 17 and lower mold 3 are moved. Furthermore, upper and lower molds 2 and 3 are heated to temperature t.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical element molding method and apparatus in which a glass material is softened by heating and press-molded using a pair of molds.

[Conventional technology]

Conventionally, when a glass material that has been heated and softened in a heating furnace is transferred between a pair of molds and an optical element is press-molded by the mold, it is necessary to prevent oxidation of the mold and to prevent the glass material and mold from oxidizing. In order to prevent fusion of
A technique related to Japanese Patent No. 525 is described.

[Problem to be solved by the invention]

However, in the above-mentioned conventional press molding, the outer periphery and surface of the glass material are exposed to a non-oxidizing gas atmosphere during the process of conveying the glass material heated and softened in a heating furnace between molds and press forming it. This caused a temperature distribution between the surface and interior of the glass material, which adversely affected the transferability of the molding. In addition, since the mold is cooled in a non-oxidizing gas atmosphere and heated to a predetermined temperature, there is a temperature distribution on the surface (molding surface), and there is a difference between the center and the periphery of the molding surface. The temperature difference had an adverse effect on the molding process.

Therefore, in order to obtain good transferability, it is necessary to increase the temperature of the mold and the molding pressure to a higher temperature, resulting in a problem that the molding conditions place a higher load on the mold. In particular, for lenses with a large outer diameter or lenses with a large uneven thickness (difference between the middle thickness and the outer peripheral thickness), the adverse effect on shape transferability was significant.

The present invention has been made in view of the problems of the prior art described above, and it is possible to prevent temperature distribution from occurring in the glass material and molding die, and to reduce molding conditions (temperature, pressing force). It is an object of the present invention to provide an optical element molding method and a molding apparatus that have good molding transferability and can perform high-precision transcription even for lenses with a large outer diameter or large uneven thickness.

[Failure to solve the problem]

In order to achieve the above object, the optical element molding method of the present invention is an optical element molding method in which a glass material is heated and softened, and the glass material is conveyed between a pair of molding molds and press-molded. Pressure molding is performed while controlling the atmospheric temperature in the molding chamber to a temperature near the transition point of the glass material to be molded.

Further, the optical element molding apparatus of the present invention is an optical element molding apparatus that heats and softens a glass material and press-molds it with a pair of molding molds. It is constructed by providing means for controlling heating to a temperature near the transition point of the glass material.

[For production]

In the optical element molding method having the above configuration, the inside of the molding chamber in which the molding die is arranged is heated to a temperature close to the transition point of the glass material. Therefore, the glass material heated above the glass softening point is less likely to be cooled in the molding chamber, and temperature differences are less likely to occur between the glass surface and the interior, and between the center and the outer periphery due to cooling. Furthermore, since the amount of heat taken away from the mold is reduced, temperature distribution is less likely to occur in the mold.

Therefore, the temperature distribution of the glass material immediately before press molding and the surface temperature distribution of the molding die become extremely small, making it possible to perform molding with good transferability.

Further, in the optical element molding apparatus described above, the inside of the molding chamber is heated to a temperature near the transition point of the glass material by the heating control means. Therefore, a molding method having the above effects can be implemented.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

(First Embodiment) FIG. 1 is a longitudinal sectional view showing a first embodiment of an optical element molding apparatus according to the present invention.

In the figure, 1 indicates a molding chamber, and within the molding chamber 1, an upper mold 2 and a lower mold 3, which are molds for molding, are housed. Upper mold 2
is fixed to the lower surface of the upper plate 1a of the molding chamber 1, and the lower mold 3 is
It is fixed to the upper surface of the lower mold installation stand 4. And upper mold 2
．． The lower molds 3 are arranged coaxially in a pair and facing each other, and molding surfaces 2a and 3a having a high surface shape and surface roughness corresponding to a desired optical element are formed on the opposing surfaces. That is, the molding surfaces 2a and 3a are formed by "2 molds 2. Part of the upper mold temperature monitor that measures the temperature of the lower mold 3 6. It is formed at the tip of the lower mold temperature monitor part 7.

On the other hand, the lower mold 3 has holes 8 drilled in the lower plate 1b of the molding chamber l.
The drive shaft 9 is fixed to the tip of the drive shaft 9 provided through the lower mold installation stand 4, and is moved toward and away from the upper mold 2 by the operation of the drive section 10 connected to the other end of the drive shaft 9. It is set freely.

The lower die installation stand 4 and the drive shaft 9 are fixed to each other via a heat insulating material 11.

The side wall 1c of the molding chamber 1 is provided with a window 13 through which the glass material 12 and press-molded optical elements (not shown) are carried into and out of the molding chamber 1. and,
A glass material 12 is placed on the side wall IC at a position corresponding to the window 13.
A heating furnace 14 equipped with a glass material heater 14a for heating and softening the glass material to a predetermined temperature is connected thereto. This window 1
A heat insulating shutter 15 is provided between the heating furnace 3 and the heating furnace 14 . The heat insulating shack 15 is connected to a drive unit 16, and is moved downward by -1 by the operation of the drive 16, so that the window 13 can be opened or closed.

17 is a transport arm for carrying the glass material 12 into the heating furnace 14 and a forming point between the upper and lower molds 2.3 in the molding chamber 1, and carrying out the optical element after press molding from the molding chamber 1; A mounting portion 19 is formed at the tip of the transport arm 17 on which a transport tool 18 for holding the glass material 12 and the optical element is placed.

A heat insulating board 20 is provided on the entire inner wall of the molding chamber 1, and a heat insulating board 21 is also provided on the upper surface of the lower plate 1b,
Heat within the molding chamber 1 is prevented from being released to the outside. A molding chamber heater 22 for heating the inside of the molding chamber 1 to a predetermined temperature is installed on the entire inner wall of the heat insulating plate 21 . Furthermore, the side wall 1 of the molding chamber 1 on the opposite side of the heating furnace 14
d, a molding room temperature monitor 2 for measuring the temperature inside the molding chamber 1 and controlling the heating state by the molding chamber heater 22;
3 is installed. The molded room temperature monitor 23 is a quartz tube 2
The molding room temperature monitor 23 directly measures the temperature of the molding chamber 1 which fluctuates due to outside air flowing into the molding chamber 1 when the lower mold 3 is raised and lowered and the transfer arm 17 is carried in and out. When controlled, it is possible to prevent a large overshoot, that is, a state in which the inside of the molding chamber 1 is heated to a temperature exceeding the set temperature due to the influence of the temperature of the outside air flowing in.

On the other hand, a nitrogen gas heating furnace 26 communicating with the inside of the molding chamber 1 is connected to the lower plate 1b of the molding chamber 1 through a stainless steel pipe 25 covered with a heat insulating material.

The nitrogen gas heating furnace 26 is configured in a tubular shape with a nitrogen gas heater 27, and one end is connected to a nitrogen gas supply device (for example, a nitrogen gas tank) 28, and the other end is connected to the stainless steel pipe 25. A nitrogen gas temperature monitor section 29 is provided.

The nitrogen gas temperature monitor unit 29 measures the temperature of the nitrogen gas fed into the molding chamber 1 and controls the nitrogen gas heater 27 so that the nitrogen gas fed does not affect the temperature of the molding chamber 1. The temperature is set to be approximately the same as the temperature of the molding chamber 1. The temperature-controlled nitrogen gas flows from below the lower mold installation table 4 through the stainless steel pipe 25 so as not to affect the temperature inside the molding chamber 1 and the temperature of the molding mold. It is sent into the molding chamber 1 in this state.

Next, a method of press molding an optical element using the molding apparatus having the above configuration will be described. In this example, Atte used glass type LLF6 (softening point: 637 degrees Celsius, yield point: 501 degrees Celsius, transition point: 453 degrees Celsius) as the glass material 12 to mold a biconvex lens.

First, a glass material 12 that has been mirror-finished by grinding and polishing is placed on the mounting portion 19 of the transport arm 17 while being held by the transport tool 18 . Next, the transport arm 17 is moved by a drive device (not shown), and the glass material 12 is transferred to the heating furnace 14 set at 650'C, which is the temperature during molding, and heated for 2 minutes to 640°C. Heat nearby.

Thereafter, the transport arm 17 is further advanced to transport the glass material 12 to the molding point between the upper and lower molds 2.3.

Then, the lower mold 3 is raised by the drive of the drive unit 1o, and in cooperation with the upper mold 2, the glass material 1 is formed on the molding surfaces 3a, 2a.
2 to form a desired optical element.

During the press molding process, the inside of the molding chamber 1 is heated to around 400°C (the transition point of the glass material -5) by the molding chamber heater 22.
It is maintained in a nitrogen gas atmosphere at 0'C). In addition, as outside air flows into the molding chamber 1 as the transfer arm 17 and the lower die 3 move, the nitrogen gas supplied from the nitrogen gas supply device 28 flows into the molding chamber 1 heated to around 400°C by the nitrogen gas heating furnace 26. Supplied. In addition, upper mold 2. The lower mold 3 is maintained at a temperature near the transition point of the glass material 12.

In this embodiment, the glass material 12 heated to around 640°C in the heating furnace 14 is transferred to both the upper and lower molds 2.3 by the transfer arm 17.
During the process of conveyance, heat is removed by the atmosphere inside the molding chamber 1 and the glass material 12 is cooled. However, since the inside of the molding chamber 1 is heated to around 400°C, the degree of cooling of the glass material 12 is small, and the glass material 12 is cooled. Temperature distribution between the inside and surface of the material becomes difficult to achieve. Furthermore, both the upper and lower molds 2.3 are equipped with mold heaters (
(not shown), the molding surfaces 2a and 3a
The temperature depends on the atmosphere inside the molding chamber 1. However, since both the upper and lower dies 2 and 3 are held near the transition point, heat release is suppressed in the molding chamber 1 controlled at around 400°C, making it difficult for temperature distribution to occur on the molding surface 2a3a. , is maintained in a nearly uniform state.

FIG. 2 shows the shape of the optical element molded by the molding method of this example. As is clear from the figure, the molded optical element did not have any sink marks and had very good transferability.

Figure 3 shows the shape of an optical element molded under the same conditions as this example without controlling the temperature inside the molding chamber, in order to compare with the shape of the optical element molded according to this example. It is something. In this case, the ambient temperature inside the molding chamber was 230° C. due to the effects of the molding heater, heating furnace, and the like.

As is clear from the figure, a sink mark had occurred in the center.

The reason why the glass material is molded under such conditions is that the heating softening temperature of the glass material is considerably higher than the ambient temperature of the conveyance path of the glass material and the molding mold, and that a temperature distribution occurs in the glass material due to the cooling effect during the conveyance process. This is due to the fact that the temperature of the molding die is considerably higher than the ambient temperature of the molding chamber, resulting in a radial temperature distribution on the molding surface.

In other words, the temperature distribution of the glass material occurs on the inside and outside of the glass material, and in the case of the biconvex lens molded in this example, since the thickness of the center and the outer periphery are different, In extreme cases, the outer surface and peripheral surface may solidify before press molding. on the other hand,
The temperature distribution of the molding die occurs in the radial direction around the optical axis of the molding surface, and the temperature drop in the outer circumference is large. Therefore,
When press-molding the above glass material and mold, the outer periphery of the glass material solidifies faster than the center.
Since the outer periphery solidifies first, the entire pressing force of the mold acts on the outer periphery, and a uniform pressing force no longer acts on the surface of the optical element. Thereafter, solidification of the central portion progresses and the glass material contracts, but no pressing force is applied, making it difficult to form an optical element surface with good transferability.

Therefore, in order to obtain good transferability without controlling the ambient temperature inside the molding chamber, it is necessary to increase the mold temperature, increase the pressing force, and increase the heating furnace temperature, which causes a load on the mold. becomes large, and the durability of the mold is significantly reduced due to deterioration of the molding surface. The time required for pressing is the time from when the glass material is completely physically cooled and solidified (e.g., cooled to below the transition point) to when it is released from the mold, in order to prevent deformation after mold release. If the ambient temperature in the room is not controlled, it takes time to cool down due to increases in mold temperature, heating furnace temperature, etc., and the pressing time becomes longer, resulting in an extension of the cycle time. In particular, in the case of lenses with a pronounced biconvex shape (large uneven thickness) or lenses with a large outer diameter, the temperature distribution of the glass material becomes large, so if the molding room temperature is not controlled, the press molding of the optical element will be difficult. Difficult cases arise.

Therefore, according to this embodiment, the cycle time can be shortened and
A good optical element as shown in FIG. 2 can be molded while reducing the load on the mold.

(Second Example) In this example, using the molding apparatus shown in FIG.
F11 (softening point 568°C1 yielding point 503°C transition point 4
67°C) for the glass material 12 to mold a meniscus-shaped lens.

In this example, the atmosphere in the molding chamber 1 was controlled to around 417°C (the transition point of the glass material -50°C), and the lenses were press-molded. Other molding steps and the like are the same as those in the first embodiment, so their explanation will be omitted.

In this embodiment, a glass material 1 heated in a heating furnace 14 is used.
2 is transferred between the upper and lower molds 2 and 3 by the transfer arm 17, and is cooled by the atmosphere inside the molding chamber 1, but the inside of the molding chamber 1 is heated to around 417°C. Therefore, the degree of cooling of the glass material 12 is small, and temperature distribution between the inside and surface of the glass material is less likely to occur.

FIG. 4 shows the shape of the optical element molded by the molding method of this example. As is clear from the figure, the molded optical element did not have any sink marks and had very good transferability.

Figure 5 shows the shape of an optical element molded under the same conditions as this example without controlling the temperature inside the molding chamber, in order to compare with the shape of the optical element molded according to this example. It is something. In such a case, the inside of the molding chamber is heated for molding.
The ambient temperature was 235°C due to the influence of the heater, heating furnace, etc.

As is clear from the figure, the outer periphery of the lens is not transferred well and is molded. The reason why the glass is molded in such a state is caused by the temperature distribution of the glass material during transportation and the temperature distribution of the molding surface of the mold, as in the first embodiment.

That is, the temperature distribution of the glass material occurs not only on the inside and the outer surface of the glass material, but also in the center and the outer periphery because the center is thinner than the outer periphery in the meniscus lens molded in this example. In extreme cases, the center and outer surface may solidify before press molding. Therefore, when such a glass material is press-molded, the center of the glass material solidifies faster than the outer periphery, and the center solidifies first, so the pressing force of the mold acts only on the center and does not affect the outer periphery. Since it does not act on the glass surface material of the mold, the transferability to the glass surface material of the mold deteriorates.

Therefore, in order to obtain good transferability without controlling the ambient temperature inside the molding chamber, it is necessary to increase the mold temperature, increase the pressing force, and increase the heating furnace temperature, which causes a load on the mold. becomes large, and the durability of the mold is significantly reduced due to deterioration of the molding surface. The time required for pressing is the time until the glass material is completely physically cooled and solidified (for example, cooled to below the transition point) and released from the mold, in order to prevent deformation after mold release. If the ambient temperature in the room is not controlled, it takes time to cool down due to increases in mold temperature, heating furnace temperature, etc., and the pressing time becomes longer, resulting in an extension of the cycle time.

Furthermore, by increasing the temperature of the heating furnace, the deformation of the glass material due to heating increases, and the glass material, which has been finished into a close-fitting shape by grinding and polishing, is greatly deformed and the amount of deformation due to pressure increases. This may cause surface deterioration.

In addition, in some cases, lenses with a pronounced meniscus shape (large uneven thickness) or lenses with larger outer diameters may have a wide temperature distribution in the glass material, making it difficult to press mold optical elements unless the molding room temperature is controlled. Cases may occur.

Therefore, according to this embodiment, the cycle time can be shortened and
A good optical element as shown in FIG. 4 can be molded while reducing the load on the mold.

(Third Example) This example uses the molding apparatus shown in FIG.
A biconvex lens was molded using F11 (softening point: 568°C, yield point: 503°C, transition point: 467°C) as the glass material 12.

In this example, the atmosphere in the molding chamber 1 was controlled to around 5.degree. 0.degree. C. (the transition point of the glass material -35.degree. C.), and the lenses were press-molded. Other molding steps and the like are the same as those in the first embodiment, so their explanation will be omitted.

In this example as well, an optical element having good transferability could be press-molded as in the first example.

In addition, effects such as improved durability of the mold and shortened cycle time were confirmed.

On the other hand, when molding was performed with the temperature inside the molding chamber at 260"C without controlling the ambient temperature in the molding chamber, the result was similar to the case where the atmosphere in the molding chamber was not controlled as described in the first embodiment. The lens was molded.

In addition, SKI 1 has a large slope of the temperature-viscosity curve,
Since the viscosity changes greatly with a slight temperature change, the effect of this example is even greater, and the temperature distribution of the glass material may cause cracks on the surface or, in the worst case, completely wear out. However, by controlling the ambient temperature as in this embodiment, cracks and the like can be prevented.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to reduce the molding conditions, improve the durability of the mold, and shorten the molding cycle time. In addition, lenses with more extreme shapes and lenses with large outer diameters can be molded with good transferability, and the number of shapes that can be molded can be increased.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing a first embodiment of a molding apparatus according to the present invention, FIG. 2 is an explanatory diagram showing the shape of an optical element molded by the first embodiment of a molding method according to the present invention, FIG. 3 is an explanatory diagram showing the shape of an optical element molded by a conventional method, FIG. 4 is an explanatory diagram showing the shape of an optical element molded by a second embodiment of the molding method according to the present invention, and FIG. The figure is an explanatory diagram showing the shape of an optical element molded by a conventional method. ■...Molding chamber 2...Upper mold 3...Lower mold 22...Molding chamber heater 26
...Nitrogen gas heating furnace

Claims (2)

[Claims] (1) In an optical element molding method in which a glass material is softened by heating and then conveyed between a pair of molding molds and press-molded, the ambient temperature in the molding chamber in which the molding molds are arranged is set near the transition point of the glass material to be molded. An optical element molding method characterized by press molding while controlling heating to a temperature of . (2) In an optical element molding device that heats and softens a glass material and press-forms it using a pair of molding dies, the ambient temperature in the molding chamber in which the molding dies are placed is set to a temperature near the transition point of the glass material to be molded. An optical element molding apparatus characterized by being provided with means for controlling heating.