JP2718452B2 - Glass optical element molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention does not require grinding, polishing, and the like by heating and softening a molding material of a glass optical element and then pressing it with a molding die. The present invention relates to a method for forming a glass optical element capable of forming a glass optical element having high surface accuracy and surface roughness.

[Conventional technology]

2. Description of the Related Art Conventionally, many optical elements such as lenses, prisms, and filters have been formed mainly by grinding and polishing a glass material. However, such processing requires a considerable amount of time and skill, and in particular, in order to form an aspherical lens by polishing or the like, more advanced polishing or the like is required, and the processing time becomes longer and shorter. It has been difficult to produce large quantities of glass optical elements in time. Therefore, as disclosed in, for example, JP-A-61-132525, a glass material is heated and softened between a pair of molding dies, transferred and disposed, and this is simply pressed by a molding die to form a lens or the like. A method for molding a glass optical element has been developed and implemented, and has attracted attention.

FIG. 5 shows an apparatus used in the above-mentioned molding method, in which an upper die 1 and a lower die 2 which are coaxially opposed to each other in a pair.
Is provided. Molding surfaces 1a and 2a having a shape corresponding to a desired lens shape are formed on the opposing surfaces of the upper mold 1 and the lower mold 2, respectively. The upper mold 1 and the lower mold 2 are connected to a drive device (not shown), and are allowed to approach and move away from each other. The upper mold 1 and the lower mold 2 have release members 3 and 4 slidably fitted to respective outer peripheral surfaces thereof and are supported by guide members 5 and 6.

Between the upper mold 1 and the lower mold 2, a support table 9 for supporting a mounting table 8 on which the glass material 7 is mounted is arranged. On both sides of the support 9, a heating furnace 10 for heating and softening the glass material 7, a press-molded glass optical element, and a slow cooling furnace 11 for slow cooling are arranged. Further, a pair of transfer members for holding the mounting table 8 on which the glass material 7 is mounted and transporting the glass optical element to the heating furnace 10 and the support table 9 and transporting the glass optical element after press molding from the support table 9 to the annealing furnace. 12,13 are provided.

A method of molding a glass optical element by the molding apparatus having the above configuration will be described. First, a glass material 7 cut into a column shape is placed on a mounting table 8, and the mounting table 8 is mounted on a pair of transport members.
The material is conveyed into the heating furnace 10 while being sandwiched between 12 and 13. Then, the glass material is heated and softened to a temperature near the inflection point (a temperature at which the viscosity of the glass material becomes approximately 10 ⁶ to 10 ⁸ poise) determined by a viscosity-temperature curve obtained by the intrusion method, and then, is conveyed through the transfer members 12 and 13. The glass table 7 is transferred to the support table 9 by the
The lower and upper dies 1 and 2 are pressed between the upper and lower dies 1 and 2 which are placed between the upper and lower dies 2 and heated and maintained at a temperature near the transition point of the glass material 7. Next, when the press molding is completed, the release member 3 of the upper mold 1 descends to press the outer peripheral portion of the glass optical element after the press molding downward, and the upper mold 1 ascends to put the glass optical element on the molding surface. At the same time, the release member 4 of the lower mold 2 rises and presses the outer peripheral portion of the glass optical element upward, and the lower mold 2 descends and separates the glass optical element from the molding surface 2a. After the mold release, the glass optical element is mounted on the mounting table 8 and conveyed into the annealing furnace 11 via the conveying members 12 and 13 to gradually cool the glass optical element to obtain a final product.

[Problems to be solved by the invention]

The conventional molding method has the following problems.

First, the optical contact is easily generated by the optical contact at the interface between the molding surfaces 1a, 2a and the glass optical element, and a strong release force is required at the time of release, so the glass optical element pressed by the release members 3, 4 There was a problem that chips were generated on the outer peripheral portion of the above, and it became a defective product. In addition, the chips of the glass are
There is a problem that the glass optical element that is adhered to the substrate and then pressed and formed has a poor appearance and the life of the mold is shortened.

Further, there is a problem that the shape precision of the glass optical element is reduced when the mold is released by a strong releasing force. For example, in the case of a camera lens, the accuracy of the curvature is required to be within ± 1 μm, and the shape indicating the asymmetry of the shape and the characteristic indicating the partial change of the curvature are required to be within ± 0.1 μm. If the molding force is large, there is a problem that the deformation at the time of release causes a significant reduction in shape accuracy, and a lens having a desired shape cannot be obtained.

Further, since a high-rigidity release member is required to cope with a strong release force, there has been a problem that the molding apparatus is complicated and the size is increased.

The present invention has been made in view of the above-described conventional problems, and improves the releasability to reduce the defective product incidence rate of the glass optical element and extend the life of the molding die. It is another object of the present invention to provide a method for molding a glass optical element capable of producing a large amount of a high-precision glass optical element with stable shape accuracy at low cost.

[Means for solving the problem]

In order to achieve the above object, the method for forming a glass element of the present invention is performed by using a pair of upper and lower molding dies heated near the transition temperature of the glass material to be molded, to a temperature higher than the molding die. In a method of molding a glass optical element by press-molding a heat-softened glass material, a method of press-molding the vicinity of an upper mold and a lower mold of a glass material heated and softened to a temperature higher than the molding die at the same cooling rate. The method includes a first forming step and a second forming step of press-forming the vicinity of the upper mold and the lower mold of the glass material while changing the cooling rate.

Here, in the first molding step, it is necessary to control the temperature difference between the upper mold and the lower mold to 5 ° C. or less, preferably 1 ° C. or less. When there is a temperature difference of 5 ° C or more between the upper and lower molds, the surface of the glass material in contact with the low-temperature mold is rapidly cooled and solidified and shrinks as soon as the heat-softened glass material comes into contact with the molding die. In addition, since sufficient pressure is not applied to the surface of the glass material and the molding surface of the mold, the molding surface shape is not accurately transferred, and the shape accuracy of the glass optical element is reduced.

(Operation)

In the method for molding a glass optical element according to the present invention, the glass material that has been heated and softened is subjected to pressure molding in two steps that are continuous with the first molding step and the second molding step.

In the first molding step, the upper mold and the lower mold are controlled to the same temperature, and the glass material in the heat-softened state is transferred with high precision to a mold molding surface having a shape corresponding to a desired optical element. Starts sharply with the start of press molding, and is cooled to the temperature of the molding die in just a few seconds.

In the second molding step, the glass material is press-formed while partially changing the cooling rate. The cooling rate is changed between the vicinity of the upper mold and the lower mold of the glass material, or the difference in the temperature is obtained immediately before the completion of the press molding. Since it is provided to change the amount of temperature decrease, elastic deformation corresponding to “warpage” caused by a difference in the amount of shrinkage occurs inside the glass. That is, the glass shrinks with cooling, and in the relationship between the cooling rate and the amount of shrinkage, as the cooling rate increases, the glass does not substantially deform, that is, shrinks to a temperature near the glass strain point (10 ¹⁴ poise). Is smaller, and the smaller the amount of temperature decrease in the cooling process, the smaller the amount of shrinkage. Such elastic deformation, when opening the upper and lower molds, acts to release the glass optical component after press molding,
Reduce release force.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First Embodiment FIG. 1 shows a molding apparatus used for carrying out a first embodiment of a method for molding a glass optical element according to the present invention. A molding die including the mold 21 and the lower mold 22 is configured. Upper mold 21 and Lower mold 22
Molding surfaces 21a and 22a having a shape corresponding to a desired optical element shape are formed on each of the opposed surfaces.

The upper mold 21 incorporates a thermocouple 23 in the center,
A heater 24 is mounted on the outer periphery. Thermocouple 23 and heater 24 are temperature controller 25 that can be set to any heat history.
And the temperature of the upper mold 21 is controlled using a thermocouple 23 and a heater 24.

The lower mold 22 is connected to a mold drive device 27 via a mold drive shaft 26 and is held so as to be vertically movable, and is capable of approaching and separating from the upper mold 21. The mold driving device 27 is connected to a pressure controller 28 that can be set to any pressure process. A load cell 29 connected to the pressure controller 28 is provided between the mold drive shaft 26 and the mold drive device 27, and is configured to control the pressing force at the time of press forming the glass optical element. The lower mold 22 has a thermocouple 30 buried in the center and a heater 31 mounted on the outer periphery, like the upper mold 21. The thermocouple 30 and the heater 31 are connected to a temperature controller 32 which can be set to an arbitrary heat history, and the temperature of the lower mold 21 is controlled by the thermocouple 30 and the heater 31. The temperature controllers 25 and 32 and the pressure controller 28 are connected to one sequencer 33 and are operated by the sequencer 33 in conjunction with each other.
Other configurations are the same as those of the conventional molding apparatus described above, and therefore, the same portions are denoted by the same reference numerals and description thereof will be omitted.

Next, a method for forming the glass optical element of the present embodiment using the forming apparatus having the above configuration will be described. In the present embodiment, in the crown glass, using an optical glass material having a glass transition point Tg: 535 ° C., a softening point Sp: 639 ° C., and a sag point At: 559 ° C. Then, an aspherical lens for a camera having a thickness of 3 mm was pressed and formed.

First, the surface of the glass material 7 is preliminarily processed by a polishing process in advance into a spherical surface approximating a desired optical element shape. Next, the glass material 7 is placed on the mounting table 8, and the glass table 7 is conveyed into the heating furnace 10 while the mounting table 8 is sandwiched between the pair of conveying members 12 and 13. Then, the viscosity of the glass material 7 is reduced to about
After softening by heating to 640 ° C., which is a temperature of 10 ⁶ to 10 ⁸ poise, the material is transferred between the upper die 21 and the lower die 22 via the transfer members 12 and 13 to be supported on the support 9 and to be driven. The lower die 22 is raised by operating the device 27. Then, the temperatures of the upper mold 21 and the lower mold 22 are set to 530 ° C., which is near the glass transition temperature of the glass material 7.
The glass material 7 is cooled to the mold temperature of the upper and lower molds 21 and 22 while the glass material 7 is molded by pressing with a pressing force of 200 kg / cm ² for 5 seconds (first molding step). Next, following the first molding step, only the mold temperature of the lower mold 22 is gradually lowered until it reaches 500 ° C., and while the temperature near the lower mold 22 of the glass material 7 is gradually cooled, a pressing of 200 kg / cm ² is performed. Press molding with pressure for 10 seconds (second molding step). After that, the upper mold 21 and the lower mold 22 are opened to complete the press molding, and the molded glass optical element (not shown) is mounted on the mounting table 8. Then, the glass optical element is transported together with the mounting table 8 into the annealing furnace 11 via the transport members 12 and 13, and the glass optical element as the final product after the annealing is taken out.

Next, the operation of the molding method will be described with reference to FIG.

FIG. 2 is a graph showing a change over time in the thermal history of the upper mold 21, the lower mold 22, and the glass material 7 near the upper mold and the lower mold.

First, in the first molding step, the glass material 7 heated and softened to 640 ° C. is rapidly cooled at the same time as the press molding by the upper mold 21 and the lower mold 22 is started, and the mold temperature of the upper and lower molds 21 and 22 is 530 ° C. It is almost the same temperature. At this time, the glass material 7 is transferred with high accuracy to the shapes of the molding surfaces 21a and 22a of the upper and lower molds 21 and 22 corresponding to a desired optical element.

Next, in the second molding step, only the lower mold 22 is continuously lowered from 530 ° C. to 500 ° C., and at the end of the second molding step, that is, at the time of mold release, the glass material 7 is moved near the upper mold and the lower mold. It is gradually cooled so as to have a temperature difference of about 30 ° C. with the vicinity. At this time, due to the difference in the cooling rate inside the glass material and the difference in the amount of shrinkage due to the temperature difference at the time of mold release, elastic deformation corresponding to the “warp” generated inside the glass optical element occurs, and the upper and lower molds 21 , 22 and the glass optical element are reduced in adhesion.

According to the present embodiment, the adhesion force generated at the interface between the molding die and the glass optical element at the time of release can be reduced by a simple means for lowering the mold temperature only in the lower mold 22. The glass optical element can be released without using the glass. further,
The temperature of the lower mold 22 can be raised to a predetermined temperature in a short time, the next glass material 7 can be continuously pressed and molded, and a large number of glass optical elements can be manufactured in a short time.

(Second Embodiment) The feature of the method for forming a glass optical element of this embodiment is as follows.
The point is that in the molding step, the mold temperature of both the upper mold and the lower mold is lowered by making the temperature gradient different, and press molding is performed. The molding apparatus used in the embodiment is configured in the same manner as the molding apparatus shown in FIG. 1, so that the description and illustration are omitted, and the embodiment is described using the same reference numerals.

Hereinafter, the molding method of the glass optical element of the present embodiment will be described as a third method.
This will be described with reference to the drawings.

FIG. 3 is a graph showing the change over time in the heat history of the upper mold 21, the lower mold 22 and the temperature near the upper mold and the temperature near the lower mold of the glass material 7 and the molding pressure.

First, the same procedure as in the first embodiment is performed up to the first molding step. That is, the glass material 7 which has been polished in advance is heated and softened in a heating furnace 10 to 640 ° C. at a temperature at which the viscosity becomes 10 ⁶ to 10 ⁸ poise, and then the upper and lower molds 21 and 22 which are set at 530 ° C. and 200 kg / cm. Press molding for 5 seconds with a pressing force of ²
To cool.

Next, the upper mold 21 is kept at 520 ° C.
The lower mold 22 is gradually cooled until the temperature reaches 500 ° C., and the molding pressing force is reduced to 100 kg / cm ² to perform press molding for 10 seconds. Thereafter, the upper mold 21 and the lower mold 22 are opened to complete the molding. Then, similarly to the first embodiment, the glass optical element as a final product is taken out after being conveyed in the annealing furnace 11 and gradually cooled.

In the present embodiment, a difference is set in the temperature gradient for cooling the upper mold 21 and the lower mold 22 in the second molding step so that the glass material 7 is cooled.
Is gradually cooled, an elastic deformation corresponding to the "warp" generated inside the glass optical element occurs as in the first embodiment.

According to the present embodiment, similarly to the first embodiment, the adhesion force generated at the interface between the molding die and the glass optical element at the time of releasing the glass optical element is reduced. The glass optical element can be released without using it.

Further, the shape accuracy (transfer accuracy) is further improved by a simple means of reducing the molding pressing force in the second molding process from that in the first molding process, and a high quality glass optical element can be molded.

In this embodiment, in the second molding step, the upper mold 21
Although the example in which the pressure molding is performed while simultaneously cooling the upper mold 21 and the lower mold 22 has been described, the present invention can be implemented by changing the timing of the time for cooling the upper mold 21 and the lower mold 22. Further, the cooling means of the lower mold 22 is not limited to the means using the temperature controller 32,
It can be carried out while cooling the lower mold 22 by means of blowing a cooling gas (for example, nitrogen gas or the like) or the like onto the lower mold 22.

(Third Embodiment) The characteristic of the optical element molding method of the present embodiment is that the temperature of the mounting table on which the glass material is placed is maintained without changing the mold temperatures of the upper and lower molds in the first molding step and the second step. The point is that the temperature of the glass material in the second forming step is changed.

FIG. 4 is a sectional view showing a main part of a molding apparatus used for carrying out the molding method.

In the figure, reference numeral 40 denotes a temperature control member for controlling the temperature of the mounting table 8, which is arranged vertically above the support table 9 by a driving device (not shown). The temperature control member 40 is
It is configured to surround the outer shape of the mounting table 8 supported on the support table 9 via the transfer members 12 and 13. The temperature control member 40 includes a temperature control material 41 composed of a heater and a cooling pipe and a thermocouple 42.
Has been formed. The temperature control member 41 and the thermocouple 42 are connected to a temperature controller 43 so that the temperature of the temperature control member 40 can be controlled. In the above-mentioned molding apparatus, since it can be implemented by a configuration substantially similar to that of the molding apparatus shown in FIG. 5, the same parts are denoted by the same reference numerals.

Next, a method for forming the glass optical element of the present embodiment using the forming apparatus having the above configuration will be described. In the present embodiment, a glass transition point T commonly called SF8 as a glass material
An aspheric objective lens for an optical disk pickup having an outer diameter of 7 mm and a thickness of 5 mm was press-formed using flint glass having a g of 443 ° C., a softening point Sp: 567 ° C., and a sag point At: 470 ° C.

First, while placing the glass material 7 on the mounting table 8,
The mounting table 8 is held between the transfer members 12 and 13 and transferred into the heating furnace 10. Then, after the glass material 7 is heated and softened to 550 ° C., the mounting table 8 is transferred onto the support table 9 via the transfer members 12 and 13, and the upper and lower molds 1 and 2 set at 400 ° C. Press molding. As a first forming step in this press forming, first, a glass material 7 is pressed at a pressing force of 100 kg / cm ² for 5 minutes.
Press molding for seconds. Next, as a second molding step, the temperature of the lower part of the glass material 7 adjacent to the lower mold 2 via the mounting table 8 is gradually cooled by the temperature control member 41 until the temperature reaches 390 ° C. While maintaining the upper temperature at 400 ° C., press molding is performed for 10 seconds with a pressing force of 80 kg / cm ² . After that, the upper mold 1 and the lower mold 2 are opened to complete the press molding, and the formed glass optical element (not shown) is transported together with the mounting table 8 into the annealing furnace 11 via the transport members 12 and 13 and gradually cooled. Then, the glass optical element as the final product is taken out.

In the present embodiment, only the lower part of the glass material 7, that is, only the vicinity of the lower mold, is gradually cooled in the second molding step, so that the glass has the same operation as the first and second embodiments. The optical element is pressed.

According to this embodiment, the adhesive force generated at the interface between the molding die and the glass optical element is reduced as in the first and second embodiments, and the mold can be released without using means such as a release member. .

Further, since it is not necessary to change the temperature of the lower mold or the upper and lower molds, the next glass material can be continuously pressed in a shorter time, and the cycle time of the press molding can be shortened.

〔The invention's effect〕

As described above, according to the method for molding a glass optical element of the present invention, after pressing the glass material at the same cooling rate,
Since the second forming step of pressing and forming while changing the cooling rate between the vicinity of the upper mold and the vicinity of the lower mold in the glass material is provided, elastic deformation corresponding to the "warpage" caused by the difference in the amount of shrinkage occurs inside the glass Therefore, the mold can be released without using means such as a release member due to the elastic deformation. Accordingly, generation of chips or the like on the glass optical element due to pressing of the release member can be prevented, and the life of the mold can be extended without the chips of the glass adhering to the molding surface of the mold. Further, shape deformation when the mold is released with a strong release force can be prevented, and the shape accuracy can be improved.
Also, since the release member is not required, the molding device can be simplified,
The size can be reduced. As a result, high-quality glass optical elements with stable shape accuracy can be manufactured in large quantities at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a molding apparatus used for carrying out the first embodiment of the method for molding a glass optical element according to the present invention, and FIG.
FIG. 3 is a graph showing a forming step in the first embodiment, FIG. 3 is a graph showing a forming step in the second embodiment of the method for forming a glass optical element according to the present invention, and FIG. FIG. 5 is a cross-sectional view showing a main part of a molding apparatus used for carrying out a method for molding an optical element, and FIG. 5 is a cross-sectional view showing a conventional molding apparatus. 7 Glass material 21 Upper mold 22 Lower mold 23,30 Thermocouple 24,31 Heater 25,32 Temperature controller

Continuation of the front page (72) Inventor Eiji Kawamura 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd. (56) References JP-A-2-59449 (JP, A) JP-A-1- 208334 (JP, A)

Claims (1)

(57) [Claims] 1. A glass optical element for press-molding a glass material heated and softened to a temperature higher than the molding die by a pair of upper and lower molding dies heated near the transition point temperature of the glass material to be molded. In the molding method, a first molding step of press-molding the vicinity of the upper mold and the vicinity of the lower mold in the glass material heated and softened to a temperature higher than the molding die at the same cooling rate, and the vicinity of the upper mold in the glass material. A second molding step of press-molding the vicinity of the lower mold while changing the cooling rate, and a method of molding a glass optical element.