JPH09249424A - Molding of optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To readily obtain an optical element having the thinner midsection than the peripheral section by using a glass material of specific shape and structure in the production of an optical element by press-molding a glass material. SOLUTION: In the production of an optical element by press-molding a glass material with heat using a couple of forming molds comprising a top force 1 and a female force 2 which oppose to each other, 2 or more of cylindrical glass elements different in the diameter (for example 5 and 6) are stacked and press-molded between both forces 1, 2. The glass material has a diameter larger than the optically effective diameter of the mold to which contacts with the glass and is preferably smaller than the outer diameter of the molded lenses.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding an optical element, and more particularly to a method for molding an optical element for obtaining a lens having a thick edge and a thin inner wall by press molding.

[0002]

2. Description of the Related Art Conventionally, a method of press-molding a lens using a glass material for molding which has been processed into a cylindrical shape has been known. Here, instead of manufacturing an optical element such as a lens or a prism from a glass material by a polishing operation, the glass material for an optical element is put into a mold and heated and pressed. In this case, in order to accurately control the weight of the glass material, it is the simplest and cheapest method to make the glass material into a cylindrical shape in the preliminary processing.

A method of forming such a cylindrical glass material is described in, for example, Japanese Patent Laid-Open No. 60-246231.
There is a method described in the publication. Hereinafter, the molding method will be described with reference to the drawings.

Generally, when an optical element is manufactured by press molding, a glass material for an optical element is cut into a predetermined size and preheated to near the glass softening point. Next, when the glass material for an optical element is closed, the pre-heated optical element is placed between the upper and lower dies whose molding surfaces are processed so that they have almost the same shape as the finished optical element. A glass material for elements is supplied and pressure molding is performed at a predetermined temperature.

As described above, the glass material for forming an optical element is preferably as simple as possible in view of its manufacturing process or material processing cost.
It is optimal to use a glass rod that has been processed to have a predetermined outer diameter by centerless processing and cut it into a cylindrical body by cutting it into a predetermined width. However, when press molding is performed using such a glass material, as shown in FIG. 18, the corner portions 43 of the material are deformed first, and the portions that come into contact with the molding surfaces of the upper mold 41 and the lower mold 42 that face each other are smoothed. Thus, a closed space 44 is formed between the molding surface and the molding surface. Once the closed space is formed, the closed space exists until the completion of press molding, and the processed surface of the mold is not sufficiently transferred to the glass material, resulting in a defective optical element.

Various methods have been devised for the conventional method for preventing such a transfer failure, and, for example, the means shown in FIG. 17 is taken. Here, the lower mold 37 is the connecting rod 37.
It is fixed to the base 37B via A, and the upper mold 36
Is attached to the piston rod 36B via the connecting rod 36A. And the glass material 51 for optical elements is
First, the heating heater 40 heats the molding die to a molding temperature, and when it reaches a desired molding temperature, the heater contacts the upper mold 36 lowered by the operation of the hydraulic cylinder.

After that, the upper die vibrates and presses up and down by using, for example, a servo pulser. This oscillating pressurization is performed, for example, up to 90% of the total deformation amount of the glass material, and the remaining 10% is molded by steady pressure while the glass material is heated to the molding temperature. At the time when all the moldings of the total deformation amount are completed, the energization is stopped, and when the temperature falls to a desired temperature, the mold is opened, and after cooling, the molded optical element is taken out.

In particular, when the optical element is a lens having a large edge thickness and a thin inside thickness, such as a biconcave lens having a small curvature or a meniscus lens, a parallel plate or a glass cob is used.
In general, when molding from an inexpensive glass material, the flow volume of the glass material increases due to the amount of deformation during molding, so there is a drawback that distortion, cracks, and cans easily occur after molding due to stress accumulation due to molding.

Therefore, in order to solve this drawback, the following inventions have already been proposed. For example, JP
In the invention described in Japanese Patent Application Laid-Open No. 0-9716, the amount of deformation of the raw material during molding is reduced by performing final press molding using a preformed material finished to a shape close to the target shape of the molded lens. The generation of stress can be prevented, and secondary steps such as strain removal and shape correction can be omitted after the molding step.

[0010]

However, the invention described in Japanese Patent Application Laid-Open No. 60-246231 has the following drawbacks. That is, one surface and the other surface, the difference in the radius of curvature is large, particularly when forming a thin meniscus lens with a medium thickness with respect to the edge thickness, the glass material for the optical element, The side surface of the cylinder enters into the optically effective diameter of the lens to be molded due to deformation during press molding, so that there is a drawback that a part of the lens becomes cloudy after molding.

In other words, the glass material is flat-polished even if the flat plate portion of the cylinder is finished by polishing to a surface roughness that can be used for the optical surface. Since it can be processed in a large amount, it does not cost much, but polishing the side surface of the cylinder to a surface roughness that can be used for the optical surface is very expensive and loses the merit of making it into a cylindrical shape. Normally, the rough surface state is left, but this enters the optically effective diameter of the lens and causes fog.

Therefore, it is conceivable to make the diameter of the cylinder larger than the effective diameter of either of the two surfaces of the lens so that the side surface of the cylinder does not enter the optical effective diameter. In the case of a lens with a medium thickness compared to the edging, the height of the cylinder cannot be made thinner than the edging, so the volume of the glass material becomes too large and the deformation amount becomes large in order to satisfy the above requirements. As a result, during press molding, due to stress accumulation, the lens breaks or the required surface accuracy cannot be obtained. Moreover, the volume of the glass material is required to be many times larger than that of the lens to be molded, so that the material is wasted.

Further, the invention described in the above-mentioned JP-A-60-9716 has the following drawbacks. That is, in order to prepare a preformed glass material having a shape close to the target shape, it is necessary to perform preprocessing such as grinding / polishing or press molding on the parallel flat plate or the glass cob, which results in high cost.

Therefore, the present invention has been made in order to improve such conventional drawbacks, and the purpose thereof is to improve the edge thickness of a meniscus lens or the like, which is generally difficult to manufacture by press molding. On the other hand, an object of the present invention is to provide a method for molding an optical element, which enables an optical element having a thin inner wall to be easily obtained by press molding.

In other words, here, the amount of deformation of the glass material during press forming can be reduced to reduce the stress accumulation due to press forming, and prevent distortion and can after forming, and Instead of preparing a preformed glass material having a shape close to the target shape, an inexpensive cylindrical glass material is used as it is, so that the final molded product can be obtained at low cost.

[0016]

To achieve the above object, the present invention provides a glass material preformed by using a pair of molding dies each of which has a first mold and a second mold facing each other. In the method for molding an optical element, which comprises press molding under heating, the glass material is press-molded by stacking two or more cylindrical glass materials having different diameters between the molds. And

This makes it possible to reduce the amount of deformation at the time of molding when molding a lens such as a meniscus lens having a thick edge and a thin inner wall without increasing the volume of the glass material more than necessary. It is possible to prevent occurrence of a can and deterioration of surface accuracy due to accumulation of stress due to molding. In addition, the amount of wasted glass can be reduced.

In this case, it is preferable that the glass material has a diameter not less than the optically effective diameter of the molds in contact with each other and not more than the outer diameter of the lens to be molded. This prevents the side surface of the columnar surface from entering the optically effective surface of the molded product during press molding.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a diagram schematically showing a molding method of the present invention. In the figure, reference numeral 1 is an upper mold, and a diameter of a portion for molding a glass material is, for example, 18 mm, The radius of curvature is 9 mm. Further, reference numeral 2 is a lower mold, and the diameter of the portion for molding the glass material is, for example, 30 mm,
The radius of curvature is 40 mm. Further, reference numeral 3 is a barrel mold, which is adjusted to an arbitrary height so as to eliminate axial misalignment between the upper mold 1 and the lower mold 2 and to obtain a predetermined optical element thickness. In the figure, reference numeral 4 is a pressure ring, which is used in the case of a lens having a shape in which it is difficult to apply pressure to the peripheral portion of the lens as in this embodiment.

An air cylinder (not shown) is connected to the upper part of the upper mold 1 so that a desired pressure is applied. Further, the mold described above can be heated to a desired temperature by a heater (not shown). Then, in press molding, the following precision molding is performed.

In this precision molding, the set as shown in FIG.
Put the complete set into the chamber, N _TwoAfter replacing the gas,
The entire set of molds with a glass material, for example
Set between the deformation temperature and softening temperature of the SK12 glass described above.
Heated to a different temperature (for example, 620 ° C. in this embodiment)
When the temperature of the cylindrical glass material reaches 620 ° C
Then, press the upper mold 1 with the air cylinder to
Since press molding is performed until the upper edge of the hits the body mold 3.
is there. (Example 1) An optical element is molded by such a molding method.
Specific examples will be described below. Here, reference numeral 5,
6 is a columnar glass material for optical element molding.
16 mm in diameter x 6 mm in height, 24 mm in diameter x 1 in height
mm optical glass SK12 (glass transition point: 550 ° C.,
Deformation temperature: 588 ° C). Sides of glass materials 5 and 6
The part is finished by grinding and the roughness is # 10.
00, and the flat surface is mirror-finished by polishing.
The surface roughness is 0.1 μm.

With these configurations, as shown in FIG.
The biconcave lens 7 having a thick edge and a thin inside is molded. This lens 7 has a lens diameter of 24 mm, a first surface having a radius of curvature of 9 mm, an optical effective diameter of 16 mm, a second surface having a radius of curvature of 40 mm, an optical effective diameter of 24 mm, and a center thickness of 1 mm. The maximum thickness of the part is about 7 mm. The volume of this lens is 1616 mm ³ , and the weight is 5.
2 g.

As a comparative example for confirming the result of this example, the case where the cylindrical glass material shown in FIGS. 3, 4 and 5 is used is shown below. The glass material for molding shown in FIG.
The diameter of the side surface of the cylinder is set to 24 mm so that the upper surface and the lower surface do not go around the molding surface of the mold. The height of the lens is 7 mm including the thickest part of the lens to be molded.

The glass material for molding shown in FIG. 4 has a diameter of 16 m.
At m, the height is set to 8.1 mm so that it approximately matches the volume of the lens being molded. The glass material for molding shown in FIG. 5 has a diameter of 24 mm, and its height is set to 3.6 mm so as to approximately match the volume of the lens to be molded.

The molding results, including this Example 1, are shown in Table 1.
Shown in As is clear from Table 1, in the case where the diameter of the cylinder is the effective diameter of the lens to be molded, the side surface does not wrap around the effective diameter. From this, of course, if the diameter of the cylinder is made larger than the effective diameter of the lens,
Although the wraparound of the side surface does not occur, if it is too large, the difference between the glass material for molding and the actual volume of the lens becomes large, resulting in deterioration of surface accuracy and occurrence of cracks, which is not preferable.

As in Comparative Example 1, in order to prevent the side surface from wrapping and to secure the transfer area up to the effective diameter in the flat plate portion with one cylindrical glass material, the diameter of the cylinder and There is no choice but to increase the height, and in this example, the glass material for molding has a volume twice the volume of the lens.
As a result, the amount of deformation increases and the residual glass also increases due to the presence of excess glass, causing deterioration of surface accuracy and cracking.

When the diameter (bottom surface) of the cylindrical glass material is smaller than the effective diameter of the lens as in Comparative Example 2, the flat plate surface portion does not extend greatly during press molding, so the side surface of the cylinder The part enters the transfer area (lower surface) up to the effective diameter. As a result, a part of the lens becomes cloudy and becomes a defective product. In the case of Comparative Example 2,
Since the height is 7 mm, there is no shortage of the transfer area on the upper surface.

In the case of Comparative Example 3, since the diameter of the cylindrical material is equal to or larger than the effective diameter of the lens, there is no wraparound of the side surface portion to the transfer area up to the effective diameter. Moreover, since the volume of the material is only slightly larger than the volume of the lens, the amount of deformation is small and the surplus glass is also small, so that there is no occurrence of cracks and deterioration of surface accuracy. However, since the height is insufficient and the thickness of the glass material cannot be increased by press molding, the transfer area on the upper surface becomes insufficient, and the effective diameter is not satisfied, resulting in a defective product.

As is clear from Comparative Examples 1 to 3, in order to prevent cracks and ensure surface accuracy, it is necessary to reduce the amount of deformation and minimize the excess glass. That is, the volume of the glass material for molding needs to be slightly larger than the volume of the lens. Also,
It can be understood that the diameter of the column must be equal to or larger than the effective diameter in order to prevent the side surface from wrapping around the effective diameter. further,
It can be seen that it is not possible to secure the necessary transfer area if the height of the cylinder is not high enough.

It is impossible to satisfy the above conditions with one cylindrical glass material. On the other hand, in the two-tiered columnar material of this example, all of the above conditions are satisfied, and there is no side surface wrap around the effective diameter, sufficient surface accuracy, and a good lens with no cracks. Was obtained.

[0031]

[Table 1] (Second Embodiment) FIG. 9 is a diagram schematically showing a molding method according to a second embodiment of the present invention. In the drawing, reference numerals 17 and 18 denote an upper mold and a lower mold, respectively. And the diameter of the glass molding portion is 30 mm and the radius of curvature is 35 mm. Further, reference numeral 19 is a barrel mold, which is adjusted to an arbitrary height so as to eliminate the axis shift between the upper mold 17 and the lower mold 18 and to have a predetermined optical element thickness. Further, reference numerals 20 and 21 are pressure rings, and in this embodiment, they are used in the case of a lens having a shape in which it is difficult for pressure to be applied to the peripheral portion of the lens.

Further, reference numerals 22, 23 and 24 are glass materials for forming a cylindrical optical element, and the glass materials 22 and 24 have a structure as in Example 2 described below. (Example 2) Glass materials 22 and 24 in this example
Is a glass for optical: SK12 (physical properties are the same as in Example 1) having a diameter of 24 mm × height: 1 mm, and the glass material 23 has a diameter of 10 mm × height: 6.4 mm. Then, the side surface portions of these glass materials 22, 23, 24,
The flat plate portion is similar to that in the first embodiment.

With these configurations, it is possible to mold the biconcave lens 25 having a thick edge and a thin inner wall as shown in FIG. This lens 25 has a lens diameter of 2
4mm, both first and second surfaces have a radius of curvature of 35m
m, the effective optical diameter is 24 mm, the central thickness is 1 mm, and the peripheral thickness is about 5 mm at the maximum. The volume of this lens is 1402 mm ³ and the weight is 4.47 g.

In order to clarify the result of the second embodiment, a case where the cylindrical glass material shown in FIGS. 11, 12, and 13 is used alone will be described as a comparative example. In the glass material for molding of FIG. 11, the side surface of the cylinder has an upper surface and a lower surface,
The diameter is set to 24 mm so as not to go around the transfer area during press molding. The height is 5 mm, which corresponds to the thickest part of the lens to be molded.

The glass material for molding of FIG. 12 has a diameter of 16
In mm, its height is set to 7 mm so as to approximately match the volume of the lens to be molded. The glass material for molding shown in FIG. 13 has a diameter of 24 mm, and its height is set to 3.1 mm so as to approximately match the volume of the lens to be molded.

The molding results including Example 2 are shown in Table 2. Here, the same results as in Example 1 were obtained for Example 2.

[0037]

[Table 2]

[0038]

As described above, the present invention increases the volume of a preform by using, as a preform, two or more cylindrical optical element molding glass materials stacked together for press molding. Instead, it is possible to prevent the side part of the preform from getting around the transfer area within the effective diameter of the lens with the optimum volume and height.
The effect of eliminating defects such as generation of cracks due to accumulation of stress, deterioration of surface accuracy, and lack of transfer area due to insufficient height can be obtained.

Therefore, it is not necessary to use a polished preform that has been finished to a lens state as in the conventional case, and even a lens having a thick edge and a thin inner wall can be manufactured from an inexpensive cylindrical preform, resulting in a large cost. Down is achieved.

[Brief description of drawings]

FIG. 1 is a diagram of a mold structure for showing a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a molded lens obtained according to the first embodiment of the present invention.

FIG. 3 is a diagram of a glass material of a comparative example with respect to the specific example of the above embodiment.

FIG. 4 is likewise a diagram of a glass material of a comparative example.

FIG. 5 is likewise a diagram of a glass material of a comparative example.

FIG. 6 is a view showing a molded product of the cylindrical glass material of FIG.

FIG. 7 is a view showing a molded product of the cylindrical glass material of FIG.

FIG. 8 is a view showing a product obtained by molding the cylindrical glass material of FIG.

FIG. 9 is a diagram showing a mold structure according to a second embodiment of the present invention.

FIG. 10 is a cross-sectional view of a molded lens obtained in the second embodiment of the present invention.

FIG. 11 is a diagram of a glass material of a comparative example with respect to the specific example of the above embodiment.

FIG. 12 is also a diagram of a glass material in a comparative example.

FIG. 13 is likewise a diagram of a glass material in a comparative example.

FIG. 14 is a view showing the cylindrical glass material of FIG. 11 molded.

FIG. 15 is a view showing the cylindrical glass material of FIG. 12 molded.

FIG. 16 is a view showing the molded cylindrical glass material of FIG.

FIG. 17 is a cross-sectional view of a conventional molding device.

FIG. 18 is a diagram for explaining a problem in the conventional molding method.

[Explanation of symbols]

 1 Upper mold 2 Lower mold 3 Body mold 4 Pressure league 5 Glass material for forming cylindrical optical element 6 Glass material for forming cylindrical optical element 7 Lens 8 Glass material for forming cylindrical optical element 9 Glass for forming cylindrical optical element Material 10 Cylindrical optical element molding glass material 11 Molded product from glass material 8 12 Molded product from glass material 13 Molded product from glass material 10 14 Crack 15 Cloudy surface 16 Transfer area lacking part 17 Upper mold 18 Lower mold 19 Body type 20 Pressure ring 21 Pressure ring 22 Glass material for cylindrical optical element molding 23 Glass material for cylindrical optical element molding 24 Glass material for cylindrical optical element molding 25 Lens 26 Glass material for cylindrical optical element molding 27 Glass material for forming cylindrical optical element 28 Glass material for forming cylindrical optical element 29 Molded product from glass material 26 30 Moldings 32 crack 33 cloudy surface 34 transfer region lack portion from the molded article 31 glass material 28 from Las material 27

Claims (2)

[Claims] 1. In a method of molding an optical element, wherein a glass material is press-molded under heating using a pair of molding dies each of which is composed of a first mold and a second mold facing each other, and the glass material is Two or more cylindrical glass materials with different diameters,
A method for molding an optical element, characterized by stacking and press-molding between the two molds. 2. The optical element according to claim 1, wherein the glass material has a diameter that is equal to or larger than an optically effective diameter of a mold in contact with each other and equal to or smaller than an outer diameter of a lens to be molded. Element molding method.