JPH0729782B2 - Optical element molding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for molding optical elements such as lenses, prisms, mirrors and filters, and in particular from a molten glass material without going through steps such as grinding and polishing. The present invention relates to a method of molding an optical element having an optical functional surface with good surface accuracy by pressing.

[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 the production of the optical element as described above, in order to obtain a desired surface precision (that is, precision such as surface shape and surface roughness) by grinding and polishing, a skilled worker needs a considerable amount of time to process the surface. It was necessary to do. 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, press molding is performed by accommodating the optical element material in a molding die device having a predetermined surface accuracy and heating and pressing. Immediately thereafter, it is becoming possible to form an overall shape including a 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 optical functional surface by press molding, a preform product (preform) is once obtained by making an optical glass material into an approximate shape to a target shape, and then the preform is molded by a molding apparatus. There are a method in which the molten optical glass is housed inside and pressed into a final target shape, and a method in which the molten optical glass is immediately housed in a 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 for obtaining the preform, and therefore, it is not sufficient in terms of manufacturing cost.

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

By the way, in order to form a highly accurate optical function surface by press molding, in addition to improving the surface accuracy of the mold member, it is necessary to strictly control the temperature of the mold member and the glass material during pressing. . In particular, in the method in which the molten glass is directly contained in the mold and press-molded, the temperature changes greatly, so that sufficient temperature control is necessary.

In order to facilitate such temperature control, press molding is
It has been proposed that the above steps be divided and performed continuously. For example, in Japanese Patent Laid-Open No. 60-118639, the first molding (glass viscosity 10 to 10 ³ poise, press pressure ² to 10 kg / cm ² ) is performed to obtain a roughly external shape, and the first molding is performed. While the viscosity of the obtained molded product is 10 ^8.5 to 10 ¹¹ poise, the second molding is performed by using the mold member having the temperature of the glass transition temperature or higher, and thus the optical element having the desired shape and accuracy is obtained. A method of obtaining is disclosed.

However, in such a conventional press molding method, the outer diameter dimension tolerance is within 0.05 mm, and the surface roughness of the optical surface is Rmax0.02.
μm or less, the surface accuracy of the optical surface is within 2 Newton rings, and the asymmetry (as) and partial surface change (habit) of the optical surface are within 0.5 Newton rings. It is difficult to stably obtain an optical element.

Furthermore, it is preferable that the following points be satisfied in order to favorably obtain a highly accurate optical element by press molding.

That is, in order to extend the life of the mold exposed to high temperature, to reduce the cost of the mold as much as possible, to prevent deformation of the molded optical element due to sink marks, burrs, cracks, etc., and to prevent surface contamination of the molded optical element. To prevent fusion with the mold member without using a mold release agent, etc., the thickness of the surface change layer due to volatilization of glass material components, etc. to such an extent that optical applications are not hindered. The surface accuracy does not decrease even after taking out the element from the mold, the surface accuracy can be maintained even if fine annealing for adjusting the refractive index is performed, and the molding is performed with sufficient accuracy regardless of the type of glass material, It is preferable that the temperature cycle is less wasteful and continuous molding is possible with low energy consumption.

The present invention has been made in view of the above circumstances, and an object thereof is to obtain a stable and highly accurate optical element from a molten glass material by press molding with good efficiency.

[Means for Solving the Problems] According to the present invention, the above-mentioned object is to perform a primary molding of a glass material by using a primary molding die device to obtain a primary molded product, and A method of molding an optical element, wherein a secondary molding product is obtained by subjecting the primary molding product to secondary molding using a secondary molding die device. Primary molding by accommodating and molding a molten glass material in the mold device while maintaining the temperature of the mold member of the device at a temperature between the glass transition temperature of the glass material and a temperature 110 ° C. lower than the temperature. In a second molding process, the temperature of the mold member of the second molding device is maintained at a temperature between the glass transition temperature and a temperature 50 ° C. lower than the glass transition temperature in the second molding device. A method for molding an optical element, characterized in that the primary molded article is housed and molded to obtain a secondary molded article. It is achieved.

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

FIG. 1 is a configuration diagram of a main part of an embodiment of a molding die apparatus for carrying out an optical element molding method according to the present invention. This device has an optical element as shown in Fig. 2 (the radius of curvature of the first surface).
It is used for the primary molding of a biconvex lens 2 having a diameter of 52 mm and a radius of curvature of 40 mm on the second surface.

In FIG. 1, reference numeral 12 is an upper mold member, and the lower surface of the upper mold member 12 has a molding working surface 12a having a shape corresponding to the first surface of the optical element 2.
Are formed. Reference numeral 14 denotes a lower mold member, the upper surface of which has a molding surface 14 having a shape corresponding to the second surface of the optical element 2.
a is formed. These mold members are made of, for example, SUS310S. Measuring points of thermocouples 16 and 18 for measuring the temperature of the mold members are embedded in the upper and lower mold members, respectively, and around each mold member for heating the mold members. Heaters 20 and 22 are attached. The heater 20 is controlled in heat generation amount by a controller 24, and the heater 22 is controlled in heat generation amount by a controller 26. The detected temperature signal is input from the thermocouple 16 to the controller 24, and similarly, the detected temperature signal is input from the thermocouple 18 to the controller 26. Reference numeral 28 is a power source for supplying electric power to the heaters 20 and 22 for heating the die members via the controllers 24 and 26.

The upper mold member 12 is supported by a supporting member 30 and is moved in the vertical direction by a drive source (not shown) connected to the supporting member. Similarly, the lower mold member 14 is supported by a support member 32, and is vertically moved by a drive source (not shown) connected to the support member. The mold is opened and closed by the vertical movement of the upper mold member 12 and / or the lower mold member 14 as described above.

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. The center thickness of the shape is 3.05 mm, which is about 5% thicker than the center thickness of 2.9 mm.

The surface roughness of the molding working surfaces 12a, 14a of the mold members 12, 14 is Rmax 10μ.
m or less, for example, 6.3 μm. Such a mold member can be easily manufactured by ordinary machining.

3 and 4 are views for explaining the steps up to the primary molding performed using the molding die apparatus of FIG.

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. The viscosity of the glass G is, for example, 10 ⁴ poise or less. At this time, an optical glass having higher homogeneity can be obtained by appropriately stirring and performing defoaming treatment if necessary.

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 apparatus shown in FIG. 1 is arranged below the outlet.

The lower mold member 14 is previously adjusted by a heater 22 to a temperature between a temperature at which the optical glass exhibits a viscosity of 10 ¹³ poise (glass transition temperature) and a temperature 110 ° C. lower than the temperature.

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.

Next, as shown in FIG. 4, the upper mold member 12 is pressed against the lower mold member 14 to close the mold, and the primary molding is performed.
The next molded product 6 is obtained. In addition, prior to this molding, the upper die member
Similarly to the lower mold member 14, the heater 12 is adjusted to a temperature between the glass transition temperature of the optical glass and 110 ° C. lower than the glass transition temperature by the heater 20 in advance.

In the above-described primary molding, since the mold members 12 and 14 are adjusted to a temperature between the glass transition temperature and a temperature 110 ° C. lower than the temperature, the temperature of the high temperature supplied between the mold members is high. The temperature of the molten glass block 4 is rapidly lowered only at the surface portion and solidified. For this reason, the surface roughness of the molding action surfaces 12a, 14a of the mold member is not faithfully transferred to the primary molded product 6, and the surface roughness of the molded product becomes relatively small. No burr is generated. Then, by setting the surface roughness of the molding action surfaces 12a, 14a of the mold member to Rmax of 10 μm or less, it is possible to obtain a secondary molded product having a sufficiently good surface roughness in the secondary molding. Therefore, it is not necessary to mirror-finish the molding operation surface of the mold member of the primary molding mold device,
The cost of manufacturing the mold member can be reduced.

Further, in the above-mentioned primary molding, since the temperature of the glass material is rapidly lowered and solidified only in the surface portion, the surface-altered layer formed on the surface of the primary molded article 6 due to volatilization of the glass component from the glass surface or the like. It is possible to make the thickness sufficiently thin that there is no problem for normal use.

Further, in the above-mentioned primary molding, the temperature of the glass material is rapidly lowered only at the surface portion and solidifies, but since the temperature does not drop so much inside, a large deformation is possible.

Then, in the above-mentioned primary molding, the mold member and the glass block 4 are
Since there is a certain temperature difference between and, a sink mark is partially generated on the surface of the primary molded product. However, by using the above-mentioned primary molding conditions, the sink mark will not be generated in the secondary molding. It can be sufficiently solved with a vertical pressing margin of 2% or more.

When the mold member temperature at the start of the primary molding is set to a temperature higher than the glass transition temperature, there is an advantage that the number of sink marks is reduced, but fusion between the mold member and glass is likely to occur. Burrs are remarkable at the mold member mating portion of the primary molded product. Furthermore, since the fidelity of the transfer of the molding member working surface is enhanced, it becomes necessary to make the surface roughness of the molding working surface sufficiently high (for example, mirror finish).

On the other hand, when the mold temperature at the start of the primary molding is less than 110 ° C. lower than the glass transition temperature, cracks and pits are likely to occur on the primary molded product, and sink marks cannot be eliminated by the secondary molding. It may increase to some extent.

5 and 6 are views for explaining the steps from the primary molding to the secondary molding. Secondary molding is performed using the same mold device as that shown in FIG. However, as the upper mold member 13 and the lower mold member 15, those different from the mold members 12 and 14 of the apparatus shown in FIG. 1 are used. The mold members 13 and 15 are made of, for example, cemented carbide represented by tungsten carbide. Further, when the upper mold member 13 and the lower mold member 15 are closed, the shape of the cavity formed between the molding action surfaces 13a and 15a of both mold members becomes the final lens shape shown in FIG. It is shaped.

The surface roughness of the molding action surface of the mold members 13 and 15 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 or less.

The primary molded product 6 obtained by the above-mentioned primary molding has a viscosity of 10 ⁸ to 10 ^14.5 poise near its surface,
As shown in the drawing, it is preferable to place the secondary molding device on the molding surface 15a of the lower mold member 15 in a predetermined posture. At this point, the viscosity of the central part of the primary molded product 6 is
It is preferably 10 ⁵ to 10 ¹² poise.

If the viscosity of the vicinity of the surface of the primary molded product 6 at the time of taking out from the mold device is less than 10 ⁸ poise, the deformation caused at the time of taking out from the mold and at the time of carrying in to the secondary molding die device becomes large. However, the secondary molding may not be performed well in some cases. Further, when the viscosity of the surface of the primary molded product 6 near the surface when it is taken out from the mold device exceeds 10 ^14.5 poise, cracks are likely to occur at the time of being taken out from the mold and at the time of secondary molding. It takes a long time to get there. Such disadvantages can be eliminated by taking out from the mold device under the above conditions.

Prior to the secondary molding, the upper mold member 13 of the secondary molding mold device 13
The lower mold member 15 is adjusted in advance by the heaters 21 and 23 to a temperature between the glass transition temperature and a temperature 50 ° C. lower than the glass transition temperature.

Next, as shown in FIG. 6, the upper mold member 13 is pressed against the lower mold member 15 to close the mold and perform the second molding. At the end of this secondary molding, the upper mold member 13 and the lower mold member 15 reach a temperature at which the viscosity of the secondary molded product 8 shows 10 ^8.5 to 10 ¹¹ poise, and the upper mold member 13 and the lower mold member 15 and 20
It is preferable that the heating amount of the heaters 21 and 23 is appropriately adjusted so that the temperature difference converges to within a temperature of 0 ° C., and the heating is performed at an appropriate pressure for an appropriate time. As a result, the secondary molded product 8 is obtained by maintaining the temperature difference in the molded product 8 within the temperature difference range of the mold member at the time of completion of the secondary molding. In order to improve the surface accuracy, it is preferable to gradually increase the temperature of the mold member, gradually decrease the glass temperature, and further gradually increase the press pressure during this molding.

In the secondary molding as described above, when the viscosity of the molded product 8 at the time of completion of molding is less than 10 ^8.5 poise, sink marks tend to be remarkable during cooling, and the viscosity of the molded product 8 at the time of completion of molding is When it exceeds 10 ¹¹ poise, the molding time becomes long, and the molded product 8 tends to partially recover elastic properties after molding, so that good surface accuracy may not be obtained. Such a disadvantage can be eliminated by setting the range of 10 ^8.5 to 10 ¹¹ poise.

Further, when the temperature difference between the upper mold member 13 and the lower mold member 15 at the end of molding exceeds 20 ° C., the temperature difference between both surfaces of the molded product 8 becomes large, and the warp stress generated in the molded product 8 at the time of cooling becomes large. Too good surface accuracy may not be obtained. Such disadvantages are eliminated by keeping the temperature difference below 20 ° C.

Further, when the temperature of the upper mold member and the lower mold member at the start of the secondary molding exceeds the glass transition temperature, the sink marks generated in the primary molding cannot be sufficiently eliminated and a good surface is obtained. There is a disadvantage that it is difficult to obtain accuracy. On the other hand, if the mold temperature at the start of the secondary molding is less than 50 ° C. lower than the glass transition temperature, the secondary molded product is likely to be cracked or splintered, and the time required for molding becomes longer. There is a disadvantage. Such a disadvantage can be eliminated by setting the temperature within the above range.

Furthermore, since the mold member temperature of the mold device when the molded product is taken out from the second mold device after the cooling step described below is the temperature at which the viscosity of the molded product shows 10 ^14.5 poise, Subsequently, it is not necessary to heat the mold member largely when accommodating the primary molded product of the next cycle.

Further, since the temperature of the primary molded product is higher than that of the mold member at the time of starting the secondary molding, the mold member is heated by the molded product, and therefore, the heating of the mold member by the heater need not be so strong. It is possible to further reduce the cycle time because the temperature can be easily controlled and the heat cycle does not become unreasonable.

Further, the temperature of the mold member becomes the highest in the secondary molding at the end of molding, and at this time, the mold member is sufficiently covered with the glass molded product, so that the degree of oxidation is small.
It is possible to improve the durability of the mold member.

After the secondary molding, cooling is performed while the secondary molded product 8 is kept in the mold device. Cooling is preferably performed in the following two stages.

The first cooling is a stage up to the glass transition temperature, and the second
The secondary cooling is a stage up to the temperature at which the secondary molded product 8 exhibits a viscosity of 10 ^14.5 poise (hereinafter, referred to as “de straining lower limit temperature”).

The primary cooling is performed while appropriately adjusting the cooling rate so that the difference between the temperature of the upper mold member 13 and the temperature of the lower mold member 15 is within 5 ° C., preferably within 2 ° C. at the end of the primary cooling. As a result, the temperature of the molded product is also kept within the above temperature range. The cooling rate is adjusted by controlling the amount of heat generated by the heaters 21 and 23 by a controller (not shown) similar to the controllers 24 and 26 used for the primary molding.

During the secondary cooling, the heaters 21 are respectively controlled by the controller so that the difference between the temperature of the upper mold member 13 and the temperature of the lower mold member 15 during the process does not become larger than that at the end of the primary cooling process but becomes gradually smaller. , 23 while controlling the calorific value. At this time, the temperature of the molded product is maintained at the same temperature as the mold member temperature.

The final molded product obtained by cooling as described above has almost no residual strain, and is extremely faithful to the surface accuracy of the molding member molding working surface of the secondary molding (for example, within 2 Newton rings). Even if fine annealing for adjusting the refractive index is performed subsequently, the surface accuracy does not significantly decrease.

Some examples in which the optical element molding method according to the present invention is actually carried out as described above are shown below.

Example 1: A glass lens for a camera having a shape as shown in FIG. 2 was manufactured by press molding.

As the glass material, a flint type optical glass F8 having a refractive index n (d) of 1.59551 and an Abbe number υ (d) of 39.2 was used.

First, the raw material of the glass material is the crucible 33 shown in FIG.
It is housed inside, heated and melted at 1400 ℃ to vitrify, and then
It was rapidly cooled to 1350 ° C, and further slowly cooled to 1335 ° C at a rate of 7.5 ° C / h to perform defoaming treatment. Before and after this defoaming treatment, homogenization treatment was performed by a stirring operation.

Next, the molten glass was subjected to primary molding using a primary molding die device as shown in FIG. The mold members 12 and 14 of the molding mold device are made of SUS310S, and their molding working surfaces 12a,
The surface roughness of 14a is Rmax 6.3 μm.
The cavity formed when 4 is closed has a vertical center thickness corresponding to the target lens shape shown in Fig. 2.
It was 3.05mm, which is about 5% thicker than 9mm. The material of the mold members 13 and 15 of the secondary molding mold device was cemented carbide.

FIG. 7 shows the lower mold member 1 of the primary molding mold device in this example.
4, upper mold member 13 and lower mold member 15 of the secondary molding mold device,
3 is a graph showing a temporal change in temperature of glass as a material to be molded.

In the first molding, at the beginning (time 0), the upper mold member 12 and the lower mold member 14 of the first molding mold device are adjusted to 430 ° C., which is 15 ° C. lower than the glass transition temperature Tg (445 ° C.) of the glass material. Was done.

The temperature of the glass flowing down from the glass outflow portion 36 shown in FIG. 3 was set to 920 ° C. At this temperature the viscosity of the glass is about 1
0 ^3.8 Poise. The glass was supplied onto the lower mold member 14 as the glass block 4 having a predetermined weight by the cutting operation of the cutter 40.

There is a preferable range for the viscosity of the glass supplied to the mold device in the primary molding. That is, if the glass viscosity is too small, it becomes difficult to obtain a proper block because of excessive fluidity, while if the glass viscosity is too large, bubbles are caught in the glass block or striae in the block when it is supplied to the mold device. Tend to occur. For example, for flint type glass and crown type glass, the preferable range is 10 ^3.0.
10 ^5.0 about. Examples, 10 ^0.5-10 about ^3.5 preferred range is lanthanum-based glass can be exemplified.

The glass is supplied to the lower mold member 14 at time t ₁ , the lower mold member is moved to a position corresponding to the upper mold member 12, and immediately thereafter, the upper mold member is aligned with the lower mold member, Primary molding was performed until t ₂ . During this process, the viscosity inside the glass changes from about 10 ^3.8 poise to about 10 ⁶ to 10 ⁷ poise, and the temperature drops sharply. At the same time, the temperature of the mold member 14 rises sharply from 430 ° C. The primary molding was carried out for about 5 seconds, during which the pressing pressure was gradually increased up to 25 Kg / cm ² .

On the other hand, the upper mold member 13 and the lower mold member 15 of the secondary molding mold device.
Is 5 from the glass transition temperature of the glass material by time t _3.
The temperature was adjusted to 440 ° C, which is lower by ℃.

Taken out primary molded article 6 from the primary mold apparatus in the time t _2, the supply on the lower mold member 15 of the at time t ₃ said first molded product secondary mold apparatus. At time t ₂ , the viscosity of the molded product 6 is about 10 ^6.6 poise inside and about 1 on the surface.
0 ⁹ poise, the viscosity of the molded article at the time t ₃ is about 10 ¹⁰ poise at the surface portion at about ¹⁰⁷ poise internally.

At time t ₄ , the upper mold member 13 was aligned with the lower mold member 15 of the secondary molding die device, and the secondary molding was performed until time t ₅ . During this process, the temperatures of the upper mold member 13, the lower mold member 15, and the molded product are 515 ° C. (glass viscosity of about 10 ° C.
^9.4 Poise), and the variation was controlled to be within 20 ° C. at time t _{5 at the} end of the secondary molding.

The secondary molding was carried out for about 15 seconds, during which the pressing pressure was gradually increased up to 80 kg / cm ² . By this secondary molding, a pressing margin of 5% in the thickness direction is made,
The surface roughness was reduced and sink marks were eliminated, and a secondary molded product 8 having a shape as shown in FIG. 2 was obtained.

Next, the primary cooling was performed from time t ₅ to t ₆ while the secondary molded product was kept in the secondary molding die device. This cooling was performed at a rate of 10 ° C./min up to the glass transition temperature so that the temperature difference among the upper mold member 13, the lower mold member 15, and the secondary molded product 8 was within 5 ° C. at time t ₆ .

Next, in the same manner, the secondary cooling was carried out from time t ₆ to time t ₇ while the secondary molded product 8 was still housed in the secondary molding die device. This cooling was carried out at a rate of 5 ° C./min up to the lower temperature limit of strain removal so that the temperature difference among the upper mold member 13, the lower mold member 15 and the secondary molded product 8 became gradually smaller.

After the completion of the secondary cooling, the molded product was taken out from the secondary molding die device and naturally cooled to room temperature.

The outer dimension accuracy of the lens thus obtained was measured and found to be within the tolerance shown in FIG. 2. Further, the surface roughness of the optically functional surface of the lens was Rmax 0.02 μm or less, and the astigmatism and habit of the surface were All were within 0.5 Newton rings.

Furthermore, after performing fine annealing to obtain a desired refractive index n (d) = 1.59551, this lens was similarly subjected to surface accuracy measurement of the optically functional surface. There was no change, and the deviation in curvature was within 2 Newton rings. Furthermore, the thickness of the surface change layer of the molded product generated during the molding and cooling process is 400
It was Å and could be used satisfactorily as a camera lens as it was.

As shown in FIG. 7, the mold member of the second molding mold device is heated to 440 ° C. by the heater from time t ₈ to t ₉ and press molding of the next cycle is started immediately from time t ₉ be able to.

Example 2: Using the same glass material (F8) and the same device as in Example 1 above, the outer diameter was 25 mm, the center thickness was 11 mm ± 0.05 mm, the radius of curvature of the optically functional surface was the first surface 20 mm, the second surface A biconvex lens having a surface of 40 mm was press-molded.

The surface roughness of the optically functional surface molding working surface of the mold member of the primary molding machine is Rmax 10 μm, and the surface roughness of the optical function surface molding working surface of the mold member of the secondary molding machine is Sa is Rmax
It was set to 0.01 μm.

First, in the same manner as in Example 1 above, vitrification treatment was performed in the crucible,
Defoaming treatment and homogenization treatment were performed.

In the primary molding, the center thickness is about 2% larger than the target shape.
It was set to 11.22 mm.

In the first molding, at the beginning (time 0), the upper mold member 12 and the lower mold member 14 of the first molding die device were adjusted to 350 ° C, which is 95 ° C lower than the glass transition temperature (445 ° C) of the glass material. It was

The temperature of the glass supplied to the mold device during the first molding is 88.
It was set to 0 ° C. At this temperature the viscosity of the glass is about 10 ^4.1 poise.

The primary molding was carried out for about 5 seconds, during which the pressing pressure was gradually increased to a maximum of 20 kg / cm ² .

The surface roughness of the primary molded product thus obtained is Rmax 5 μm
The peak of the concave and convex portions on the surface was the first
Compared with the surface of the mold member of the next molding mold device, the mold member had a roundness, and surface waviness due to sink marks was very slight.

On the other hand, the upper mold member 13 and the lower mold member 15 of the secondary molding mold device.
Was adjusted to 390 ° C., which was 45 ° C. lower than the glass transition temperature of the glass material, by the time when the second molding was started.

The primary molded product was taken out of the primary molding die device and transferred into a nitrogen atmosphere while maintaining the temperature so as not to lower the temperature. Then, the subsequent steps were all performed under a nitrogen atmosphere.

The viscosity of said primary molded article at the time of accommodating the primary molded article in the secondary mold apparatus was about ¹⁰¹⁰ poise at the surface portion is from about 10 ⁸ poises internally.

In the secondary molding, the temperatures of the upper mold member 13, the lower mold member 15 and the molded product 8 are made to converge toward 510 ° C. (the temperature corresponding to a glass viscosity of about 10 ^9.5 poise), and the secondary molding is completed. The variation was controlled to be within 20 ° C at the time of.

The secondary molding was carried out for about 18 seconds, during which the pressing pressure was gradually increased up to 80 kg / cm ² . By this secondary molding, pressing with a pressing margin of 2% in the thickness direction was performed, and a secondary molded product having the target shape was obtained.

The primary cooling was performed at a rate of 10 ° C./min so that the temperature difference between the mold member and the molded product converged within 2 ° C. at the end of the primary cooling.

The secondary cooling was performed at a rate of 5 ° C./min so that the temperature difference between the mold member and the molded product was further reduced.

After the completion of the secondary cooling, the molded product was taken out from the secondary molding die device, naturally cooled to room temperature, and further subjected to fine annealing for making the lens have a desired refractive index.

The surface roughness of the optically functional surface of the lens thus obtained is Rm.
The ax was 0.02 μm or less, the deviation of curvature was within 2 Newton rings, and the astigmatism and habit of the surface were within 0.5 Newton rings.

Example 3: A lens having the same shape as in Example 1 above, with a refractive index n (d) of 1.
A 77250 press-molded lanthanum optical glass LaSF016 having an Abbe number υ (d) of 49.6 was used.

As the primary molding die device and the secondary molding die device, the same devices as in Example 1 were used. Further, the primary molding was carried out in a nitrogen atmosphere and the secondary molding was carried out in vacuum.

First, in the same manner as in Example 1 above, vitrification treatment was performed in the crucible,
Defoaming treatment and homogenization treatment were performed.

In the first molding, at the beginning (time 0), the upper mold member 12 and the lower mold member 14 of the first molding die device are adjusted to 600 ° C., which is 100 ° C. lower than the glass transition temperature (700 ° C.) of the glass material. It was

The temperature of the glass supplied to the mold during the primary molding is 90
It was set to 0 ° C. At this temperature the viscosity of the glass is about 10 ^2.9 poise. The glass block was supplied from the glass outflow part to the primary molding die device through a frame curtain for blocking the atmosphere and the nitrogen atmosphere.

The primary molding was carried out for about 5 seconds, during which the pressing pressure was gradually increased to a maximum of 20 kg / cm ² .

On the other hand, the upper mold member 13 and the lower mold member 15 of the secondary molding mold device.
Was adjusted to 675 ° C., which is 25 ° C. lower than the glass transition temperature of the glass material, by the time of the second molding.

The primary molded product was taken out from the above-mentioned primary molding die device and supplied to the secondary molding die device while maintaining the temperature so that the temperature would not decrease.

The viscosity of the primary molded product when the primary molded product was housed in the secondary molding die device was about 10 ⁹ poise inside and about 10 ¹¹ poise at the surface portion.

In the secondary molding, the temperatures of the upper mold member 13, the lower mold member 15 and the molded product are converged toward 720 ° C. (the temperature corresponding to a glass viscosity of about 10 ^10.0 poise), respectively, and the secondary molding is completed. The time was controlled so that the variation was within 10 ° C.

The secondary molding was performed for about 15 seconds, during which the pressing pressure was gradually increased up to 120 Kg / cm ² . By this secondary molding, a pressing margin of 5% in the thickness direction is made,
A secondary molded product having the target shape was obtained.

At the end of the first cooling, the glass transition temperature is 5 ° C. so that the temperature difference between the mold member and the molded product converges within 2 ° C.
It was performed at a speed of / min.

The secondary cooling was performed at a rate of 3 ° C./min up to the lower limit temperature of the strain removal point (685 ° C.) so that the temperature difference between the mold member and the molded product was further reduced.

After the completion of the secondary cooling, the molded product was taken out from the secondary molding die device, naturally cooled to room temperature, and further subjected to fine annealing for making the lens have a desired refractive index.

The surface roughness of the optically functional surface of the lens thus obtained is Rm.
The ax was 0.02 μm or less, the deviation of curvature was within 2 Newton rings, and the astigmatism and habit of the surface were within 0.5 Newton rings.

EFFECTS OF THE INVENTION According to the present invention as described above, a high-precision optical element represented by a camera lens can be obtained with good efficiency by direct press molding from a molten glass material, and thus obtained. The precision of the optical element does not deteriorate even during processing such as fine annealing and vacuum deposition.

Further, the present invention can be sufficiently applied even to glass having a high molding temperature without being restricted by the type of glass used.

Further, since the temperature of the mold member at the time of molding is relatively low, fusion of the glass and the mold member does not occur, the life of the mold member can be extended, and the thickness of the surface change layer in the molded product can be reduced. It can be made sufficiently thin, and continuous molding can be performed with low energy consumption without waste in the temperature cycle of the mold.

Furthermore, in the present invention, an inexpensive primary molding die member can be used, and the relatively expensive secondary molding die member also has sufficient durability because the temperature of high temperature is extremely short. Thus, the device cost can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of a molding die device. FIG. 2 is a diagram showing the shape of the optical element. 3 to 6 are explanatory views of the molding process. FIG. 7 is a graph showing changes over time in the temperatures of the mold member and the glass during molding. 4: Glass block, 6: Primary molded product, 8: Secondary molded product,
12,13: Upper mold member, 14,15: Lower mold member, 16,18: Thermocouple, 20,2
1,22,23,34,38: Heater, 24,26: Controller, 33: Crucible, 36: Outflow part.

Claims (2)

[Claims] 1. A glass material is subjected to a primary molding using a primary molding die device to obtain a primary molded product, and the primary molded product is further subjected to a secondary molding die device. A method of molding an optical element, which comprises a secondary molding to obtain a secondary molded product, wherein the temperature of a mold member of a primary molding mold device in the primary molding is set to a glass transition temperature of a glass material and the temperature. The molten glass material is housed and molded in the mold device maintained at a temperature lower than 110 ° C. to obtain a primary molded product, and a secondary molding mold device is used in the secondary molding. Secondary molded product obtained by accommodating and molding the above-mentioned primary molded product in the mold device in a state where the temperature of the mold member is maintained between the glass transition temperature and a temperature lower than the glass transition temperature by 50 ° C. A method of molding an optical element, comprising: 2. The viscosity of the primary molded product near the surface is 10 ⁸ to 10
^The method for molding an optical element according to claim 1, wherein the primary molded product is housed in a secondary molding die device at the time of ^14.5 poise.