JPS63310735A - Method for forming optical element - Google Patents

Abstract

PURPOSE:To stably obtain a formed optical element article having excellent surface precision and appropriate for a camera lens, etc., with high efficiency by forming molten optical glass adjusted at a specified temp., primarily cooling the glass at a controlled rate, and then secondarily cooling the glass. CONSTITUTION:The molten optical glass G which has been heated and melted in a crucible 33 through a heater 34, having <=10<4> p viscosity, and kept at a specified temp. is defoamed, as required, and then extruded through an outflow part 36. A specified amt. of the glass blocks 4 cut by a cutter 40 is dropped onto a lower die member 14 previously adjusted by a heater 22 to the temp. between the temp. at which the glass G exhibits 10<3> p viscosity and the temp. 110 deg.C lower than the former temp. An upper die member 12 adjusted at the same temp. as the lower die member 14 is pressed on the member 14 to quench and solidify only the surface part, and then primary forming is carried out to obtain a primary formed article while controlling the temp. difference between the die members 14 and 12 to <=20 deg.C. The formed article is primarily cooled to the glass transition point so that the temp. of die member and that of the formed article are gradually converged, and then secondarily cooled in the same way to the stress relieving lower-limit temp. of the glass material. The formed article is then taken out.

Description

[Detailed description of the invention] [Industrial application field] Book 3? [This article relates to a method of molding optical elements such as lenses, prisms, mirrors, and filters, and particularly relates to a method of molding optical elements having optical surfaces with good surface precision by pressing.

[Prior Art] Generally, optical elements such as lenses, prisms, mirrors, and filters are manufactured by grinding a glass material to give a desired external shape, and then polishing the machined surface, that is, the surface through which light is transmitted and/or reflected. It is manufactured by forming an optical surface.

On the other hand, in recent years, there has been a demand for improvements in optical performance, and for this reason, there has been an increasing demand for optical elements having an aspherical surface.

In the manufacture of such aspherical optical elements, highly skilled workers must spend long hours processing to obtain the desired surface precision (i.e. precision of surface shape and surface roughness) through grinding and polishing. It is necessary to do so.

Therefore, recently, instead of the traditional optical element manufacturing method as described above, press molding is performed by housing the optical element material in a mold device with a predetermined surface accuracy and heating and pressurizing it. Increasingly, the overall shape including the functional aspects is immediately formed. According to this method, an optical element can be manufactured relatively easily and in a short time even when the fffi surface is an aspherical surface.

In the method of manufacturing an optical element by forming an optically functional surface by glass molding, an optical glass material is first obtained as a pre-molded product (preform) in an approximate shape of a single shape, and then the preform is There are two methods: one is to place the molten optical glass in a mold device and press it into the final desired shape, and the other is to immediately put the molten optical glass in the mold device and press it to form the glass.

In the method using preform, the Japanese Patent Publication No. 61-3226
As described in Publication No. 3, a preform is obtained by an appropriate method such as grinding and polishing, and the preform and the mold member of a mold device for final molding are placed separately or the preform is housed in the mold device. The preform is then heated to a predetermined temperature and the thus softened preform is pressed with a suitable pressure using a molding device and allowed to cool.

By the way, in order to form a highly accurate optically clear surface by press molding, in addition to improving the surface precision of the mold member, it is necessary to strictly control the temperature of the mold member and the glass material during pressing. be.

In particular, in the method in which the molten glass is placed directly in a mold and press-formed, sufficient temperature control is required because temperature changes are large.

In order to facilitate this kind of temperature control, press forming is carried out in two ways.
It has been proposed to perform the above steps sequentially. For example, in Japanese Patent Application Laid-open No. 60-118639,
First molding to obtain the approximate external shape (glass viscosity 10-10
3 poise, press pressure 2-10 Kg/cm2),
The viscosity of the molded product obtained in the primary molding is 108.5 to I
A method is disclosed in which a second molding is performed using a mold member at a temperature north of the glass transition point temperature during QLI poise, thereby obtaining an optical element having the desired shape and precision.

However, in this conventional press forming method, the outer diameter tolerance is within 0.05 mm and the surface roughness of the optical surface is R.
maxo, 02 gm 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 both Newton ring 0.5.
It is difficult to stably obtain highly accurate optical elements such as photographic lenses.

The present inventors have discovered that the surface precision of the optically functional surface of a molded article is largely influenced by the cooling process after pressing, and has arrived at the present invention.

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

That is, to extend the life of the mold that is exposed to high temperatures, to reduce the cost of the mold as much as possible, to prevent deformation due to sink marks, cracks, cracks, etc. in the molded optical element, and to prevent surface contamination of the molded optical element. The thickness of the surface-changed layer due to volatilization of glass material components must be at a level that does not interfere with optical applications. The surface precision does not deteriorate even after the element is removed from the mold, and the surface precision can be maintained even when fine annealing is performed to adjust the refractive index, and molding can be performed with sufficient precision regardless of the type of glass material. It is preferable that the continuous molding be done in circular motion with little waste in temperature cycles and low energy consumption.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to stably obtain a high-precision optical element with good efficiency by press molding.

[Means for Solving the Problems] According to the present invention, the above object is to obtain a molded product by molding a glass material using a molding device, and at the end of the molding, the mold of the molding device is The temperature difference between the member and the molded product is maintained within 20°C, and the temperature of each mold member and the molded product are adjusted to the glass transition temperature of the glass material while the molded product is housed in the mold device. The first cooling is performed at the first cooling rate so as to gradually converge, and then, while the molded product is housed in the mold device, the temperatures of each mold member and molding are increased to the lower limit temperature of removal strain of the glass material. Light 7: Performing secondary cooling at a second cooling rate d higher than the first cooling rate so that the product temperature gradually converges, and then removing the molded product from the mold device. This is achieved by a method of molding the element.

[Example] Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1 is a structural diagram of the main parts of this embodiment of a molding body for carrying out the optical element molding method according to the present invention. still,
This example shows a case in which molding is performed in two stages: primary molding and secondary molding.

The apparatus shown in Fig. 1 is used for the primary molding of an optical element 2 (biconvex lens with a radius of curvature of the first surface of 52 mm and a radius of curvature of the second surface of 40 mm) as shown in Fig. 2. .

In FIG. 1, reference numeral 12 denotes an upper mold member, and its lower surface has a molding action surface 1 having a shape corresponding to the first surface of the optical element 2.
2a is formed. Reference numeral 14 denotes a lower mold member, on the upper surface of which a molding surface 14a having a shape corresponding to the second surface of the optical element 2 is formed. These mold members are made of, for example, 5US31O8. There is a thermocouple 1 in each of the upper and lower mold members to measure the temperature of those mold members.
6.18 measurement points are embedded, and around each mold member there are heaters 20, 20 for heating the mold member, respectively.
22 is attached. The heater 20 is connected to the controller 2
The amount of heat generated by the heater 22 is controlled by a controller 26. A detected temperature signal is inputted from the thermocouple 16 to the controller 24,
Similarly, a detected temperature signal is inputted to the controller 26 from the thermocouple 18 . Further, 28 is a power source for supplying electric power to the heaters 20 and 22 for heating each mold member listed in L through the controllers 24 and 26.

The upper mold member 12 is supported by a support member 30, and is driven by a drive source (not shown) connected to the support member.
It is forced to move in two downward directions. Similarly, the lower mold member 1
4 is supported by a support member 32, and is moved in the vertical direction by a driving source (not shown) connected to the support member to move the upper and lower parts of the mold member 12 and/or the lower mold member 14 such as 0 or more. The directional movement causes the mold to open and close.

In the above mold device, the upper mold member 12 and the lower mold member 14
When the mold members are closed, the molding working surfaces 12a, 14a of both mold members
The shape of the cavity formed between them is about 5% thicker than the center thickness of 2.9 mm of the final lens shape shown in FIG.
．． The shape is such that the center thickness is 0.05 mm.

The surface roughness of the molding working surfaces 12a, 14a of the mold member 12.14 is set to RmaxlOμm or less, for example, 6°3 gm. Such a mold member can be easily manufactured by ordinary machining.

53 and 4 are diagrams for explaining the steps up to the primary molding performed using the molding device shown in FIG. 1 above.

In FIG. 3, 33 is a glass melting tank (crucible), and a heater 34 is attached around the crucible. An outflow section 36 is connected to the lower part of the crucible 32, and a heater 38 is attached around the outflow section. and,
A cutter 40 is disposed below the outflow portion 36 to cut the molten glass into an appropriate length while continuously flowing out.

A raw material for a desired optical glass is placed in the crucible 33, and heated to an appropriate temperature by operating the heater 34. This results in
Molten optical glass G is formed in the crucible 33. The viscosity of the glass G is, for example, 104 poise or less. still,
At this time, by stirring and defoaming as necessary, optical glass with higher homogeneity can be obtained.

The molten glass gradually flows down in the outflow section 36 due to the eastward action and is pushed out from the outlet at the lower end of the outflow section. At this time, the lower mold member 14 of the apparatus shown in FIG.
Place it.

The lower mold member 14 is heated in advance by a heater 22 to a temperature at which the optical glass exhibits a viscosity of 1013 poise (glass transition point temperature).
and a temperature 110″C lower than the above temperature.

2. The molten and softened glass is pushed out from the outlet of the outlet section 36, and when its tip reaches an appropriate height below the cutter 40, the cutter is activated to cut the molten glass. .

The thus cut glass block 4 falls onto the molding surface 14a of the lower ffi 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 perform primary molding.
A primary molded product 6 is obtained. Incidentally, prior to this molding, the upper mold member 12 as well as the lower mold member 14 is heated in advance to the glass transition point temperature of the optical glass by the heater 20 at 110°C.
It is preferable to adjust the temperature to a temperature between 0.5°C and a lower temperature.

In the primary forming described below, since the mold members 12 and 14 are adjusted to a temperature between the glass transition point temperature and a temperature 110° C. lower than the glass transition temperature, the mold members 12 and 14 are supplied between the mold members. The temperature of only the surface portion of the high-temperature molten glass block 4 rapidly decreases and solidifies. For this reason, the molding surface 12a of the mold member
, 14a is not faithfully transferred to the primary molded product 6, and the surface roughness of the molded product becomes relatively small.
Furthermore, occurrence of flash at the mold matching portion is also eliminated. Then, the surface roughness of the molding working surfaces 12a and 14a of the mold member is set to Rmax
By setting it to 1Opm or less, it is possible to obtain a secondary molded product with sufficiently good surface roughness in the secondary molding. Therefore, there is no need to mirror-finish the molding surface of the mold member of the primary molding mold device, and the cost of manufacturing the mold member can be reduced.

In addition, in the above-mentioned primary forming, only the surface portion of the glass material rapidly decreases in temperature and solidifies. The thickness can be made thin enough to be completely acceptable for normal applications.

Furthermore, in the above-mentioned primary forming, the temperature of the glass material sharply decreases only at the surface portion and solidifies, but the inside temperature does not decrease so much, so that large deformations are possible.

In the above primary molding, the mold member and the glass block 4 are
Because there is a certain temperature difference between the This problem can be sufficiently resolved with a vertical push distance of 2% or more.

If the temperature of the mold member at the start of the above-mentioned primary molding is set to a temperature exceeding the glass transition point temperature, the above-mentioned sink marks will be reduced, but this will tend to cause fusion between the mold member and the glass. Moreover, the occurrence of flashing at the mold member mating portion of the primary molded product becomes noticeable. Furthermore, since the fidelity of transfer of the molding working surface of the mold member is increased, it becomes necessary to make the surface roughness of the molding working surface sufficiently high (for example, mirror finished).

For example, if the mold temperature at the start of the primary molding is set to less than 110° C. below the glass transition point temperature.

The primary molded product is likely to develop cracks and tingles, and furthermore, there is a risk that sink marks will increase to the extent that they cannot be eliminated by the secondary molding.

FIGS. 5 and 6 are diagrams for explaining the steps from primary molding to secondary molding. The secondary molding is performed using a mold apparatus similar to that shown in FIG. 1 above. However, as the upper mold member 13 and the lower mold member 15, the mold members 12 and 14 of the apparatus shown in FIG.
When the mold members 5 and 5 are closed, the molding working surfaces 13a and 15 of both mold members
The shape of the cavity formed between a is such that it becomes the final lens shape shown in Figure 52.

The surface roughness of the molding surface of the mold member 13.15 is equal to or lower than the surface roughness of the optically flexible surface of the target optical element (mirror finish), for example, Rmaxo, 01.
It is considered to be less than uLm.

When the primary molded product 6 obtained in the above primary molding has a viscosity of 108 to 1Q14.5 poise near its surface, it is transferred to the secondary molding mold as shown in FIG. It is preferable that the primary molded product 6 is placed in a predetermined position on the molding surface 15a of the lower mold member 15 of the device.At this point, the viscosity of the center portion of the primary molded product 6 is 105 to 1Q12 poise. is preferable.

If the viscosity near the surface of the primary molded product 6 when taken out from the mold device is less than 108 poise, deformation that occurs when taken out from the mold and when carried into the mold device for secondary molding tends to be large. Therefore, good molding may not be possible in the secondary molding. Furthermore, if the viscosity near the surface of the primary molded product 6 when ejected from the mold device exceeds 1014·5 poise, cracks are likely to occur during ejection from the mold and during secondary molding, and The time required for subsequent molding also tends to be long. Such disadvantages can be eliminated by removing the mold from the molding device under the above conditions.

Prior to the second molding, the upper mold member 1 of the mold device for the second molding
3 and the lower mold member 15 are preferably adjusted in advance to a temperature between the above-mentioned glass transition point temperature and a temperature 50° C. lower than the above-mentioned glass transition temperature using heaters 21 and 23, respectively.

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 secondary molding.
At the end of this :52 molding, the upper mold member 1
3 and the lower mold member 15 have a viscosity of 108.
While adjusting the heat generation amount of the heaters 21 and 23 as appropriate, so that the temperature becomes 5 to IQII poise and the temperature difference between the mold member 13 and the lower mold member 15 converges to within 20 ° C. It is preferable to apply an appropriate pressure and measure an appropriate amount of time.Thereby, at the end of the second molding, the temperature difference within the molded product 8 is maintained within the temperature difference range of the mold member, and the second molded product 8 is is obtained. In order to improve the surface accuracy, it is preferable to gradually increase the temperature of the mold member, gradually lower the glass temperature, and gradually increase the press pressure during this molding.

In the above-mentioned secondary molding, if the viscosity of the molded product 8 at the end of molding is less than 108.5 poise, the occurrence of sink marks during cooling tends to be significant. If the viscosity exceeds 1011 poise, the molding time becomes long and the molded product 8 tends to undergo partial elastic recovery after molding, making it impossible to obtain good surface accuracy. This kind of disadvantage is the above l Q 8.5 ~ IQII
This problem can be solved by setting it within the Poise range.

Furthermore, if 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 sides of the molded product 8 will increase, and the warping stress generated in the molded product 8 during cooling will increase. If it is too high, good surface accuracy may not be obtained.

Such disadvantages can be eliminated by setting the temperature difference to 20° C. or less.

Furthermore, when the temperature of the upper mold member and the lower mold member at the start of the secondary molding is a temperature exceeding the glass transition point temperature,
There is a disadvantage that the sink marks caused in the above-mentioned primary forming are not sufficiently eliminated and it is difficult to obtain good surface accuracy. On the other hand, the second
) at the start of the next molding! i humidity temperature 50 from glass transition point temperature
If the temperature is lower than 0.degree. C., there are disadvantages in that cracks and tingles are likely to occur in the secondary molded product, and the time required for molding is also increased. Such disadvantages can be eliminated by keeping the temperature within the above range.

Furthermore, since the temperature of the mold member of the second mold device when the molded product is taken out from the second mold device after the cooling process described later is a temperature at which the viscosity of the molded product is 1014·5 poise, this mold device There is no need to heat the mold member significantly when storing the primary molded product for the next cycle.

Furthermore, since the temperature of the primary molded product is higher than that of the mold member at the start of the second molding, the mold member receives heat from the molded product, so there is no need to heat the mold member so strongly by the heater, and the temperature of the mold member is higher than that of the mold member. It is possible to easily control the temperature without causing any strain on the thermal cycle, and to further shorten the cycle time.

Furthermore, in the secondary molding, the temperature of the mold member reaches its highest at the end of molding, and at this point the mold member is sufficiently covered with the glass molded product, so the degree of oxidation is low.
It is possible to improve the durability of mold members.

After the secondary molding, cooling is performed while the secondary molded product 8 remains in the mold device. Cooling is performed in two stages as described below.

The first cooling is the stage to the glass transition temperature, and the second
The next cooling is a stage to a temperature at which the second molded product 8 exhibits a viscosity IQ of 14.5 poise (hereinafter referred to as "strain removal lower limit temperature").

At the end of the first cooling, 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 2°C.
The cooling rate is adjusted as appropriate so that the cooling rate is within the following range. In this way, 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 using controllers (not shown) similar to the controllers 24 and 26 used for primary molding.

During the second cooling process, the heater 21 is 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 does not become larger than that at the end of the first cooling process and gradually decreases. ,．． This is done while controlling the amount of heat generated. At this time, the temperature of the molded product is also maintained at the same level as the temperature of the mold member.

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 mold member forming working surface of the above-mentioned secondary forming (for example, within 2 Newton rings). It has an optically functional surface, and even if fine annealing is subsequently performed to adjust the refractive index, the surface precision will not deteriorate significantly.

Some examples of actually implementing the optical element molding method according to the present invention as described above will be shown below.

Example 1: A glass lens for a camera having the shape shown in FIG. 2 was manufactured from molten glass by two-step press molding.

The glass material has a refractive index n (d) of 1.5955.
Flint type optical glass F8 with an Atsbe number υ(d) of 39.2 was used.

First, the raw material of the glass material is placed in a crucible 3 shown in FIG.
3, heated and melted at 1400°C to vitrify it,
That V! 7. Rapidly cool to 1350°C and further to 1335°C.
Degassing treatment was carried out by slow cooling at a rate of 5° C./h. Before and after this defoaming treatment, homogenization treatment by stirring operation was performed.

Next, the molten glass was first formed using a first forming mold apparatus as shown in FIG. The mold members 12 and 14 of the mold device are made of 5US310S, and the surface roughness of their molding surfaces 12a and 14a is Rmax6.3μ.
m, and the cavity formed when the mold member 12.14 is closed has a center thickness in the downward direction of about 5 mm, which is smaller than the corresponding center thickness of the objective lens shape shown in the second factor, 2.9 mm.
% thicker at 3.05mm. The material of the mold members 13 and 15 of the primary mold device was cemented carbide. Figure 7 shows the lower mold member 1 of the primary mold device in this example.
4. Upper mold member 13 and lower mold member 1 of the mold device for secondary molding
5 and is a graph showing temporal changes in the temperature of glass, which is a material to be molded.

In the primary molding, initially (time 0), the upper mold member 12 and lower mold member 14 of the primary molding mold device are adjusted to 430°C, which is 15°C lower than the glass transition point temperature Tg (445°C) of the glass material. It was done.

The temperature of the glass flowing down from the glass outlet 36 shown in FIG. 3 was 920°C. At this temperature the viscosity of the glass is approximately IQ 3.8 poise. Cutter 4 for glass
The glass block 4 having a predetermined weight was supplied onto the lower mold member 14 by a cutting operation of 0.

There is a preferable range for the viscosity of the glass supplied to the mold device in the primary molding. In other words, if the glass viscosity is too low, the fluidity will be excessive and it will be difficult to form a suitable block41), while if the glass viscosity is too high, bubbles will be drawn into the glass block when it is fed to the molding device, or the block will be damaged. It tends to cause striae. For example, for flint glass and crown glass, the preferred range is 1
An example is about 03.0-105·Q, and a preferable range for lanthanum glass is 100·5 to IQ 3.5.
The degree can be exemplified.

The glass is supplied to the lower mold member 14 at time 11, and the lower mold member is moved to a position corresponding to the upper mold member 12, and then the upper mold member is immediately aligned with the upper mold member, and at time t2. Primary molding was performed up to this point. During this process, the viscosity inside the glass changes from about 103.8 poise to about 1
The temperature suddenly drops to 0G-107゛poise. At the same time, the temperature of the mold member 14 rises rapidly from 430°C. The primary forming was carried out for about 5 seconds, during which time the press pressure was gradually increased to a maximum of 25 kg/cm2.

On the other hand, the upper mold member 13 and lower mold member 15 of the secondary mold device were adjusted to a temperature of 4.40° C., which is 5° C. lower than the glass transition point temperature of the glass material, by time t3.

At time t2, the primary molded product 6 is taken out from the primary molding device, and at time t3, the primary molded product is supplied onto the lower mold member 15 of the secondary molding device, at time t.
At time t3, the viscosity of the molded article 6 was about IQ 6.6 poise inside and about 109 poise at the surface, and at time t3 the viscosity of the molded article was about 107 poise inside and about 1Q10 poise at the surface. Ta.

At time t4, the lower mold member 15 of the secondary molding mold device
Then, the upper mold member 13 was added and secondary molding was performed until time t5. In this process, the upper mold member 13, the lower mold member 15
and the temperature of the molded product is 515°C (as shown in the figure).
The temperature was converged toward a temperature corresponding to 109.4 poise in terms of glass viscosity), and the variation was controlled to be within 20° C. at time t5 at the end of the second molding.

The secondary forming was carried out for about 15 seconds, during which time the press pressure was gradually increased to a maximum of 80 kg/cm2. Through this secondary forming, a pressing distance of 596 in the thickness direction is performed, the surface roughness is reduced and sink marks are eliminated, and a secondary molded product 8 having a shape as shown in FIG. 2 is obtained. It was done.

Next, primary cooling was performed from time t5 to t6 while the secondary molded product remained housed in the mold device for secondary molding. This cooling was carried out at a speed of 10'07 m1n to the glass transition temperature so that the temperature difference between the upper mold member 13, the lower mold member 15, and the secondary molded product 8 was within 5° C. at time t6.

Next, secondary cooling was performed from time t6 to t7 while the secondary molded product 8 was similarly housed in the secondary molding mold device. This cooling is performed at a rate of 5°C/5°C so that the temperature difference between the upper mold member 13, the lower mold member 15, and the secondary molded product 8 gradually decreases.
The strain removal was carried out at a speed of min up to the lower limit temperature.

After the secondary cooling was completed, the molded product was taken out from the secondary molding mold device and allowed to cool naturally to room temperature.

When the external dimensional accuracy of the thus obtained lens was measured, it was within the tolerance shown in FIG.
The surface roughness of the part was Rmaxo, 024 m or less, and the asperities and irregularities of the mirror surface were all within 0.5 Newton's ring.

Furthermore, this lens has a desired refractive index n (d) = 1.5
After performing fine annealing to obtain 9551, we similarly measured the surface accuracy of the optical functional surface, and found that the surface roughness, asperity, and texture were the same as on the plate, and that the deviation in curvature was similar to that of Newton's ring. It was less than two. Furthermore, the thickness of the surface change layer of the molded product produced during the molding and cooling process was 400 mm, and it could be used satisfactorily as a camera lens as it is.

As shown in FIG. 7, the mold member of the second molding mold device is heated to 440° C. from time t8 to t9, and the next cycle of press molding can be started immediately from time t9. .

Example 2: Using the same glass material (F8) and the same equipment as in Example 1, a plate with an outer diameter of 25 mm and a center thickness of 11 mm ± 0.0
A biconvex lens having a radius of curvature of 20 mm on the first surface and 40 mm on the second surface was press-molded.

In addition, the surface roughness of the optically functional surface of the mold member of the second mold device is RmaxlOgm, and the surface roughness of the optically functional surface of the mold member of the second mold device is RmaxlOgm. was taken as Rmaxo, 01 gm.

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

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

In the primary molding, at the beginning (time O), the L-shaped member 12 and the lower mold member 14 of the primary molding mold device are adjusted to 350°C, which is 95°C lower than the glass transition point temperature (445°C) of the glass material. Ta.

The temperature of the glass supplied to the molding device during primary molding is 8.
The temperature was set at 80°C. At this temperature the viscosity of the glass is approximately IQ
It is 4.1 poise.

The primary forming was carried out for about 5 seconds, during which time the press pressure was gradually increased to a maximum of 20 kg/cm2.

The surface roughness of the primary molded product thus obtained was Rmax5.
The peaks of the concave and convex portions on the surface were rounder than the surface of the mold bag material for the TJ primary molding, and there was very little waviness on the surface due to sink marks.

On the other hand, the upper mold member 13 and lower mold member 15 of the secondary molding mold device were adjusted to a temperature of 390° C., which is 45° C. lower than the glass transition point temperature of the glass material, by the time of starting the secondary molding.

The primary molded product was taken out of the primary molding device and transferred to a nitrogen atmosphere while being kept warm so as not to drop in temperature. All subsequent steps were performed in a kyosine atmosphere.

The viscosity of the primary molded product when it was placed in the secondary mold device was about 108 poise inside and about 108 poise at the surface.

In the second molding, the temperature of the upper mold member 13, the f-type member 15, and the molded product 8 is 510°C (100°C in terms of glass viscosity).
09.5 poise), with a variation of 20°C at the end of the second molding.
It was controlled to be within the range.

The secondary molding was carried out for about 18 seconds, during which time the press pressure was gradually increased to a maximum of 80 kg/cm2. Through this secondary molding, pressing was performed with a pressing amount of 2% in the thickness direction, and a secondary molded product having the desired shape was obtained.

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

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

After the secondary cooling was completed, the molded product was removed from the secondary molding mold device and allowed to cool naturally to room temperature, and further fine annealing was performed to give the lens a desired refractive index.

The surface roughness of the optically functional surface of the lens thus obtained is R
maxo was 02 gm or less, the deviation in curvature was within 2 Newton rings, and the asperity and curl of the mirror surface were both within 0.5 Newton rings.

Example 3: A lens with the same shape as in Example 1 above has a refractive index n(d) of 1.
．． Press molding was carried out using lanthanum-based optical glass La5F016, which had a 77,250 mm diameter and a roughness number υ(d) of 49.6.

Incidentally, as the primary molding mold device and the secondary molding mold device 4, the same ones as in Example 1 were used. Further, the first molding was performed in a nitrogen atmosphere, and the second molding was performed in a vacuum.

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

In the primary molding, initially (time O), the upper mold member 12 and lower mold member 14 of the primary molding mold device are heated to 600° C., which is 100°C lower than the glass transition point temperature (700'C) of the glass material.
It was adjusted to Ci.

The temperature of the glass supplied to the molding device during primary molding is 9
It was assumed to be 00℃. At this temperature the viscosity of the glass is about 102
・It is 9 poise. The glass blocks were supplied from the glass outlet to the primary molding device through a frame curtain to block the atmosphere and nitrogen atmosphere.

The primary forming was carried out for about 5 seconds, during which time the press pressure was gradually increased to a maximum of 20 kg/cm2.

On the other hand, the L5 member 13 and the lower mold member 15 of the second mold device were adjusted to 675° C., which is 25° C. lower than the glass transition point temperature of the glass material, by the time the second molding started.

Take out the primary molded product from the upper primary molding mold device,
The mixture was supplied to a mold device for secondary molding while being kept warm so as not to drop in temperature.

The viscosity of the primary molded product when it was placed in the secondary mold device was about 109 poise inside and about 1011 poise at the surface.

In the second molding, the temperature of the upper mold member 13, lower mold member 15, and molded product is 720°C (glass viscosity IQ
temperature corresponding to IO・O poise), with a variation of 10°C at the end of the second molding.
It was controlled to be within the range.

The secondary molding was carried out for about 15 seconds, during which time the press pressure was gradually increased to a maximum of 120 kg/cm2.

Through this secondary molding, pressing was performed with a pressing amount of 5% in the thickness direction, and a secondary molded product having the desired shape was obtained.

The first cooling is carried out by 5℃ to the glass transition point temperature so that the temperature difference between the mold member and the molded product converges within 2℃ at the end of the first cooling.
/ min.

The secondary cooling is carried out at 3℃/m until the strain relief lower limit temperature (685℃) so that the temperature difference between the mold member and the molded product is further reduced.
It was done at a speed of i n.

After the secondary cooling was completed, the molded product was removed from the secondary molding mold device and allowed to cool naturally to room temperature, and further fine annealing was performed to give the lens a desired refractive index.

The surface roughness of the optical mechanical surface of the thus obtained lens is Rmaxo, 02 μm or less, the deviation in curvature is within 2 Newton rings, and the asperities and irregularities of the mirror surface are both within 0.5 Newton rings. Met.

Example 4: An optical element 3 having a shape as shown in FIG. 8 (biconvex lens with a first surface having a radius of curvature of 78 mm and a second surface having a radius of curvature of 60 mm) was manufactured by press molding using a preform.

The vehicle equipment for molding shown in FIG. 9 was used.

In FIG. 9, reference numeral 43 denotes an upper mold member, and a molding surface 43a having a shape corresponding to the first surface of the bipedal optical element 3 is formed on its lower surface.

Reference numeral 45 denotes a lower mold member, on the upper surface of which a molding surface 45a having a shape corresponding to the second surface of the optical element 3 is formed. These mold members are made of cemented carbide, and the molding surface 4
The surface roughness of 3a and 45a is Rmaxo, 01 pm or less. Note that 47 is an A-shaped member integrally fixed with the lower mold member 45, and 16 and 18 are thermocouples similar to those in FIG. 1 above. The mold members 43 and 45 are each moved downward by driving means (not shown).

As a glass material, the refractive index n (d) is 1.7725.
A lanthanum-based optical glass La5FO16 having an average number υ(d) of 49.6 was used.

First, a round rod-shaped glass material with an outer diameter of just under 24 mm was cut, and both cut surfaces were ground and polished to obtain a preform with a thickness of about 4 mm.

The preform was placed in the mold device, placed in a vacuum heating furnace, and the entire mold device, including the preform, was heated from room temperature to 718° C. (temperature corresponding to a glass viscosity of 1010, 2 poise) over 20 minutes. At this point, the temperatures of the upper mold member 43 and the lower mold member 45 were maintained within the range of 718°C±3°C.

Next, at this temperature, a pressure of 100 kg/cm2 was applied between the upper mold member 43 and the lower mold member 45 for 3 minutes to obtain a molded product.

Next, the press pressure was released, and primary cooling and secondary cooling were performed continuously while the molded product was kept in the mold device.

The first cooling is carried out at a glass transition point temperature (700℃) so that the temperature difference between the mold member and the molded product converges within 2℃ at the end of the
°C) at a rate of 5 °C/min.

The secondary cooling is carried out at 3℃/m until the strain removal lower limit temperature (685℃) so that the temperature difference between the mold member and the molded product is further reduced.
It was done at a speed of i n.

Subsequently, the lens was rapidly cooled at 30°C to 30°C, the molded product was removed from the molding device, and further fine annealing was performed to give the lens a desired refractive index.

The surface roughness of the optically functional surface of the lens thus obtained is R
maxo was 02 uLm or less, the deviation in curvature was within 2 Newton rings, and the asperities and curls of the mirror surface were both within 0.5 Newton rings.

On the other hand, for comparison, a lens (Comparative Example 1) obtained by immediately rapidly cooling from 718° C. to room temperature without performing the above-mentioned primary cooling and secondary cooling in this example, and A similar measurement was made for a lens obtained by rapidly cooling from 700°C to room temperature without cooling (Comparative Example 2), and it was found that the lens of Comparative Example 1 had already developed asymmetry and aspendium before fine annealing.
Both habits have two or more Newton rings, and Comparative Example 2
Before fine annealing, both asperities and quirks were within 0.5 Newton rings, but after fine annealing, both asperities and quirks became 2 or more Newton links.
All of them had insufficient precision as photographic lenses.

[Effects of the Invention] According to the present invention as described above, a high-precision optical element such as a camera lens can be obtained with good efficiency by press molding, and the optical element thus obtained can be fine-annealed. There is no deterioration in the quality of the melon even during treatments such as vacuum deposition and vacuum deposition.

Further, the present invention is not limited to the type of glass used, and can be sufficiently applied to glass having a high molding temperature.

[Brief explanation of drawings]

FIG. 1 and FIG. 9 are main part configuration diagrams of a molding device. FIG. 2 and FIG. 8 are diagrams showing the shape of the optical element. FIGS. 3 to 6 are explanatory diagrams of the molding process. FIG. 7 is a graph showing temporal changes in temperature of the mold member and glass during molding. 4 Nigarasu block, 6: Primary molded product. , 8: Secondary molded product, 12.13, 43: Upper mold member, 14.15, 45: Lower mold member, 16.18: Thermocouple, 20. 21, 22, 23, 34, 38: Heater, 24.26: Controller, 33 nil acupuncture point, 36; Outflow part. Agent: Patent Attorney Minoru Yamashita, Figure 5, Figure 6

Claims (3)

[Claims] (1) A molded product is obtained by molding a glass material using a molding device, and at the end of the molding, the temperature difference between the mold member of the molding device and the molded product is maintained within 20°C. While the molded product is housed in the mold device, primary cooling is performed at a first cooling rate so that the temperature of each mold member and the temperature of the molded product gradually converge to the glass transition point temperature of the glass material, and then a second cooling rate that is slower than the first cooling rate so that the temperature of each mold member and the temperature of the molded product gradually converge to the lower limit removal strain temperature of the glass material while the molded product is housed in the mold device; 1. A method for molding an optical element, which comprises performing secondary cooling in a step and then removing the molded product from a mold device. (2) A molded product is obtained from the molten glass material by performing primary molding using a mold member for primary molding, and then performing secondary molding using a mold member for secondary molding. ,
A method for molding an optical element according to claim 1. (3) The method for molding an optical element according to claim 1, wherein a molded product is obtained by performing molding using a preformed product.