JP2001318209A - Optical element and molding tool for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the release of an optical element such as a convex lens or a convex meniscus from a molding tool by designing the shape of the transfer faces of the element, other than the region of the optical effective diameter. SOLUTION: In a biconvex lens or a meniscus, at least one of both lens faces deviates from the elongations of a curved line which sets the curved surface in the optical effective diameter toward the lens side, with respect to the optical axis direction in regions at the outsides of the optical effective diameter and has such a shape of a face as to be transferred that the reduction of lens thickness is made larger than that of lens thickness formed by the elongations, in accordance with the increase of diameter in directions orthogonal to the optical axis and the face to be transferred is formed up to at least the required outside diameter of the lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element obtained by hot press-molding glass using mold members facing each other, and a mold for the optical element.

[0002]

2. Description of the Related Art In a conventional press molding method, in order to absorb a variation in gob capacity, an excess glass portion serving as an edge portion of a lens is flowed out of a region of an optical effective diameter of the lens.
In order to form the mold so that it can be retracted, a structure of a mold having a sufficient internal space has been used. Here, the surplus glass portion refers to a glass portion that has protruded outside the region of the optical effective diameter during press molding, and is schematically shown in FIG. 7 as a longitudinal sectional view. In the drawing, reference numeral 22 denotes an upper mold member, 23 denotes a lower mold member, and 24 denotes a press lens as a molded product.

When the thickness of the edge portion of the present invention is a lens shape in which the thickness of the edge portion is smaller than the center thickness of the lens, that is, a so-called convex lens shape, it is necessary to prevent the lens from cracking around the surplus glass portion. Usually, the surplus glass portion is designed to be as thick as possible. For example, as shown in FIG. 7, the molding surface of the mold member is applied to the outer periphery of the mold member from outside the optically effective diameter region. In many cases, the transfer molding portion was formed into a flat shape.

However, in the case of a convex lens shape, the thickness of the central portion is larger than the edge portion of the lens, so that a difference occurs between the heat shrinkage amounts in the cooling process. For example, FIG.
If the Δl center and Δl edge in the above are the thermal contraction amounts of the lens center and the edge in the press axis direction, respectively, Δ
The relationship of 1 center> Δl edge always holds during cooling. Therefore, if the upper and lower mold members are not restrained up and down during the cooling process, a stress state in which the difference in the amount of thermal contraction between the center portion of the lens and the edge portion is supported by the edge portion, that is, the upper and lower mold members As a result, a state is obtained in which a compressive force in the press axis direction is applied to the edge portion of the lens.

That is, the transfer molding portion of the molding surface of the mold member in the surplus glass portion is perpendicular to the press axis direction (in FIG. 7,
If they face each other (horizontal planes), the compressive force in the press axis direction generated by the difference in the amount of thermal contraction between the lens center portion and the edge portion acts perpendicularly on the glass / mold interface. Therefore, a problem arises in that the surplus glass portion is sandwiched between the upper and lower mold members, making it difficult to release the mold.

In addition to this, as shown in the figure, a portion where the flat portion and the curved portion are discontinuous (intersection between the above-mentioned horizontal plane and a curve extending outside the optical effective diameter area) is formed in the surplus glass portion. Therefore, cracking of the glass is likely to occur due to stress concentration at the site. Therefore, regarding the convex lens shape, even if the surplus glass portion is made flat and the lens edge portion is made as thick as possible, it is not possible to fundamentally solve the crack.

Therefore, in order to prevent the convex lens from cracking,
The outer diameter of the lens is made smaller than the diameter of the lens molding surface where the extension of the curve that sets the curved surface in the area of the optical effective diameter reaches, that is, a lens shape that does not provide the above-described discontinuous portion. The method is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-46021.

However, this does not necessarily improve the releasability of the outer peripheral portion of the lens. Even if cracks can be prevented at discontinuous portions, cracks due to non-releasing cannot be prevented. As described above, in the conventional methods, the releasability is improved, and furthermore, cracking is prevented.
An effective device for the shape of the surplus glass portion has not been proposed.

[0009]

As described above, in the prior art described above, in the case of a convex lens shape, the compressive force in the press axis direction is reduced due to the difference in heat shrinkage of the glass between the center portion of the lens and the edge portion. , The releasability of the edge portion deteriorates, and cracks easily occur. Further, there is a problem that even if the thickness of the edge portion is increased, cracking cannot be prevented unless the shape of the edge portion is appropriate.

The present invention has been made based on the above circumstances, and is directed to an optical element such as a convex lens or a convex meniscus lens, and devising a shape of a transfer surface outside an area of an optical effective diameter, The purpose is to facilitate release.

[0011]

Therefore, in the present invention,
In an optical element that is a biconvex lens or a convex meniscus lens having a spherical or aspherical lens surface facing in the optical axis direction, at least one of the two lens surfaces is in a region outside the optical effective diameter thereof. From the extension of the curve that sets the curved surface within the optical effective diameter, deviates toward the lens in the optical axis direction, and as the diameter in the direction perpendicular to the optical axis increases, the lens thickness formed by the extension increases. The transfer surface shape is such that the amount of reduction in thickness is large, and the transfer surface is formed to at least a required lens outer diameter.

Further, according to the present invention, an optical element which is a biconvex lens or a convex meniscus lens having a spherical or aspherical lens surface facing in the optical axis direction is press-formed by two mold members facing each other. In the mold, at least one of the two lens surfaces deviates from the extension line of the curve defining the curved surface within the effective optical diameter toward the lens in the optical axis direction in a region outside the effective optical diameter. At least one of the mold members so that the transfer surface shape is such that the amount of decrease in lens thickness is greater than that formed by the extension line with an increase in the diameter in the direction orthogonal to the optical axis. A transfer molding portion for the surface to be transferred is formed at least to a required lens outer diameter outside the transfer area having a predetermined optical effective diameter on the molding surface of .

According to this configuration, the compressive force acting on the edge of the lens (optical element) in the press axis direction is converted into a shear stress or a tensile stress,
It is possible to increase the stress that positively contributes to the release. The degree of the effect obtained by changing the shape of the edge portion of the lens differs depending on the shape.

That is, with regard to converting the compressive stress generated in the edge portion into the shear stress, the maximum effect can be obtained by configuring the edge portion with a surface inclined by 45 degrees from the press axis direction. The reason for this is that generally, on a plane inclined at 45 degrees from the direction in which the compressive stress is applied, all the compressive stress is converted into a shear stress.

On the other hand, the greatest effect can be obtained by converting the compressive stress generated in the edge into a tensile stress by forming the edge in a plane parallel to the press axis. The reason for this is that, as in the case of the conversion of the shearing stress, on the surface inclined 90 degrees from the direction in which the compressive stress acts, all the compressive stress is converted into the tensile stress, and the thermal stress in the radial direction of the lens is reduced. This is because it works perpendicular to the part.

Outside the region of the optical effective diameter, the line deviates from the extension of the curve defining the curved surface within the region of the optical effective diameter, and is formed by the extension with the increase in the diameter in the direction orthogonal to the optical axis. The shape of the optical element having the transferred surface shape such that the reduction amount of the lens thickness becomes larger, the compressive stress generated in the press axis direction and the heat shrinkage force of the lens in the direction perpendicular to the press axis can be at least released. Shown are shapes that can be converted to advantageous stresses. This conversion is effective not only for the force due to the shrinkage of the glass but also for the external force that compresses the press lens via the mold.

As described above, in the present invention, cracks in the edge portion are prevented by improving the releasability by the transfer surface shape of the lens (optical element) outside the optical effective diameter region. It is.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) An embodiment of the present invention will be specifically described below with reference to the drawings.
FIG. 1 schematically shows the structure of a molding die in the press molding apparatus according to the first embodiment. Where 1
Is an upper mold member, and 2 is a lower mold member. As the material used for these mold members, any material such as ceramic and metal may be used. However, the higher the elastic modulus, the better the deformation of the molding die is suppressed, and the more advantageous the stress for releasing the mold is.

Reference numeral 3 denotes a press-molded lens as an optical element, and there is no particular limitation on the type of material. In this embodiment, SK-12 (Tg = 550 ° C.) is used. 4
Is a barrel die for guiding the mold members 1 and 2, and the material used is not particularly limited as long as it has excellent heat resistance. A resistance heating element indicated by reference numeral 5 is built in the body mold 4 so that the gob can be heated to a softening temperature.

The mold members 1 and 2 are not fixed in the direction of the press axis, and can freely slide up and down in the body mold 4. Press molding is performed in a nitrogen atmosphere to suppress the reaction between the mold and the glass.

The lens (optical element) forming step in this embodiment can be roughly divided into the following two steps.

(1) A pressing press step of transferring an optically functional surface (a region of an effective optical diameter) to a heated and softened glass gob. (2) A step of cooling a lens after the pressing press. The schematic configuration of the mold at the stage 2) is shown. Here, symbols 6 and 7 are respectively
An upper mold member and a lower mold member. Reference numeral 8 denotes a press-molded lens, and a portion 9 indicated by a thin broken line denotes an extension of a curve that sets a curved surface within the area of the optical effective diameter. In addition, the portion 10 indicated by the thick broken line is outside the region of the optical effective diameter.
From the extension, the lens deviates to the lens side in the optical axis direction of the lens, and as the diameter in the direction orthogonal to the optical axis increases, the amount of decrease in lens thickness becomes larger than that formed by the extension. The figure shows an area of a transfer surface shape, and the transfer surface is formed at least to a required lens outer diameter. Reference numeral 11 denotes a free surface of the glass left at the time of pressing and pressing, and the shape of the molding surface of the upper and lower mold members is not transferred.

When cooled from the state shown in FIG. 2, since the lens of this embodiment has a convex shape, the compressive force in the press axis direction on the edge portion of the lens increases. If the edge portion is formed between planes perpendicular to the press axis (horizontal planes parallel to each other in the figure), the compression force in the press axis direction becomes a stress component that hinders mold release. If the entire edge is in the region indicated by reference numeral 10, it can be converted into shear or tensile stress on the glass / mold interface. In this way, when the glass and the mold member are separated from each other by the generated shear or tensile stress, a lens (optical element) without cracks can be obtained.

The conventional lens shape including a flat portion outside the optical effective diameter region and the extension of a curve for setting a curved surface within the optical effective diameter region outside the optical effective diameter region shown in FIG. Deviated from the line, with the increase in the diameter in the direction perpendicular to the optical axis, the lens shape having a transferred surface shape such that the amount of reduction in lens thickness becomes greater than that formed by the extension line, Compare the release temperature and cracking rate. The results are shown below.

FIG. 3 shows a flat portion (part 1 shown by hatching) in the lens shape of FIG.
4) is added (this is referred to as B shape).
That is, reference numeral 12 denotes a flat portion, and reference numeral 13 denotes an A-shaped edge portion transfer surface shape.

As described above, when the hatched portion 14 is added, a lens shape having a flat portion outside the region of the effective optical diameter, that is, a B shape, which is a comparison object, is obtained. Regarding each molding condition at the time of press molding, in both cases, the pressing press temperature was 614 ° C., and the cooling rate was 10 ° C./min.

Table 1 shows the results of the press molding experiments performed under the above conditions. The mold release temperature is the temperature of the mold when mold release occurs, and the cracking rate was calculated from 100 samples. As a result, the shape A of the present invention had a higher mold release temperature than the shape B, and was more effective in preventing cracking of the lens.

[0028]

[Table 1] (Second Embodiment) FIG. 4 shows a shape of a molding die used in a second embodiment of the present invention. Here, the convex meniscus lens 15 is formed. In the lens 15, the curved surface 16 that constitutes the area outside the optical effective diameter indicated by the thick broken line is an extension of the curve (for example, a curve drawn with a constant radius of curvature) that sets the curved surface within the optical effective diameter (thin broken line). ), The transferred image is deviated to the lens side in the optical axis direction, and as the diameter in the direction perpendicular to the optical axis increases, the amount of decrease in the lens thickness becomes larger than that formed by the extension line. The transfer surface is formed at least to a required lens outer diameter (free surface during molding).

In this embodiment, the compression press converts the compressive force applied to the edge of the lens in the axial direction of the press into a stress contributing to mold release on the curved surface 16 to promote mold release. We examined whether or not. For this reason, the free surface portion 17 is left on the outer edge of the lens after the pressing, so that the press allowance (lens thickness) during cooling is secured.

FIG. 5 is a molding process diagram including a cooling press process, showing the relationship between temperature and time at this time. Here, the pressing press temperature is 614 ° C., and the cooling rate is 10 ° C./m.
in, the cooling press temperature range is 580-550 ° C.
Based on this molding process, the difference between the mold release temperature and the crack generation rate was compared between the lens shape of the present invention shown in FIG. 4 and the conventional lens shape. Further, as for the shape shown in FIG. 4, the case where the cooling press is not performed was also examined.

Here, the above-mentioned conventional shape is different from the shape shown in FIG. 4 in that the transferred portion of the molding surface that forms the area outside the optically effective diameter has a curved surface that sets a curved surface within the optically effective diameter area. It refers to the shape of the transfer surface formed by the extension line, and the diameter is set to be the same as in the case of the present invention. The glass material used for molding was SK12 (Tg = 550 ° C.).

An experiment was conducted under the above conditions, and the results obtained are shown in Table 2. The mold release temperature is the temperature of the mold when mold release occurs, and the crack generation rate is calculated from 100 samples. Comparing the mold release temperatures, the lens shape of the present invention subjected to the cooling press was the highest, the second was the lens shape of the present invention without the cooling press, and the lowest was the conventional lens subjected to the cooling press. It was a shape.

[0033]

[Table 2] According to the results, the mold release temperature was low even when the cooling press was performed on the conventional shape, so the release temperature was not increased by the cooling press, but the cooling press was performed on the lens shape of the present invention. It is clear that the release temperature was increased by performing. That is, it can be said that the compression force in the press axis direction generated by the cooling press was converted into the stress contributing to the release at the portion indicated by the curved surface 16.

Cracking of the lens occurs only in the conventional lens shape having the lowest release temperature, and in the shape in which the release temperature is increased by the shape of the present invention, cracking can be completely prevented.

(Third Embodiment) FIG. 6 is a schematic diagram of a molding die used in a third embodiment of the present invention. That is,
The upper and lower mold members were used to form a convex meniscus lens shape in which one transfer surface was a flat surface and the other transfer surface was a convex surface. In the figure, reference numeral 18 denotes a press lens, 19 denotes a transfer surface (molding surface) of an upper die member processed into a concave surface, and 20 denotes a transfer surface (molding surface) of a lower die member processed into a flat surface. In the lens formed here, the portion 21 outside the region of the optical effective diameter is shifted from the extension line (indicated by a thin dotted line) of the curve defining the curved surface within the region of the optical effective diameter to the lens side in the optical axis direction. Deviated, with an increase in the diameter in the direction perpendicular to the optical axis, has a transferred surface shape such that the amount of decrease in lens thickness is greater than that formed by the extension line, the transferred surface, It is formed to at least the required lens outer diameter.

Here, the above-described transfer surface shape is set only on the upper mold member to improve the releasability. In order to compare the effect of this lens shape (see FIG. 6), the transfer surface portion of the molding surface outside the region of the optical effective diameter is an extension of the curve 19 that sets the curved surface within the region of the optical effective diameter. Molding was also performed on a conventional shape.

Similar to the steps in the first embodiment,
For this embodiment, when the lens is molded, when the mold reaches 540 ° C., mold release occurs on the convex surface,
The plane was released at 480 ° C. At this time, no crack was generated. On the other hand, in the conventional shape of the comparative example, 3
At 80 ° C., both the convex surface and the flat surface were released, and cracks occurred in the molded product.

From these results, it can be seen that when one side is released and the thermal strain in the glass is released, cracking of the lens hardly occurs. In this way, any one of the upper and lower transfer surface shapes is outside the optically effective diameter area, from the extension of the curve that sets the curved surface within the optically effective diameter area, deviating toward the lens in the optical axis direction, As the diameter in the direction perpendicular to the optical axis increases, the transfer surface shape has a shape in which the amount of reduction in lens thickness is greater than that formed by the extension line, and the transfer surface is at least a required surface. When the lens is formed up to the outer diameter of the lens, the releasability is improved, and cracking of the lens can be prevented.

[0039]

As described above, according to the present invention, when the optical element is molded into the specified shape, the compressive stress in the press axis direction is converted into shear or tensile stress at the glass / mold interface. The effect that the mold release easily occurs is obtained. Further, when the outer edge of the lens is a free surface during molding, an external force in the press axis direction can be applied to the edge of the lens, and the mold release is promoted.

As described above, when the area outside the optically effective diameter is released from the mold, the area within the optically effective diameter is easily released, which is effective in preventing the lens from cracking. In addition, since the mold release occurs at a higher temperature, the cycle time of the entire molding can be shortened, so that the mold durability can be improved, and inexpensive, high-precision optical elements can be mass-produced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a structure of a molding die used in a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing an example of a biconvex lens shape corresponding to the present invention.

FIG. 3 is a diagram illustrating a biconvex lens shape, similarly illustrating a state where a flat portion is added to the lens shape used in the first embodiment.

FIG. 4 is a longitudinal sectional view showing a convex meniscus lens shape according to a second embodiment of the present invention.

FIG. 5 is a process chart of the molding.

FIG. 6 is a longitudinal sectional view showing a convex meniscus lens shape according to a third embodiment of the present invention.

FIG. 7 is a schematic longitudinal sectional view of a convex lens shape having a surplus glass portion including a conventional problem.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 upper mold member 2 lower mold member 3 press-molded lens (biconvex) 4 body mold 5 resistance heating element 6 upper mold member 7 lower mold member 8 press-molded lens (biconvex) 9 curved surface in optical effective diameter area 10 A transfer surface shape corresponding to the present invention 11 Free surface portion 12 Flat portion perpendicular to the press axis 13 Edge portion of the lens shape of FIG. 2 14 Different between the shape of FIG. 2 and the shape of FIG. Area 15 Press-molded lens (convex meniscus shape) 16 Transfer surface shape applicable to the present invention 17 Free surface portion 18 Press lens (convex meniscus shape) 19 Transfer surface of upper mold 20 Transfer surface of lower mold 21 Applicable to the present invention Transfer surface shape example 22 Upper mold 23 Lower mold 24 Press lens (biconvex)

Claims (3)

[Claims] In an optical element which is a biconvex lens or a convex meniscus lens having a spherical or aspherical lens surface facing in the optical axis direction, at least one of the lens surfaces has an optical effective diameter. In the outer region, the lens is deviated from the extension line of the curve defining the curved surface within the optical effective diameter toward the lens in the optical axis direction, and is formed by the extension line with an increase in the diameter in the direction orthogonal to the optical axis. An optical element having a shape of a transferred surface such that the amount of reduction in lens thickness is larger than required, and wherein the transferred surface is formed to at least a required lens outer diameter. 2. The optical element according to claim 1, wherein the outer edge of the lens has a portion formed as a free surface portion during molding. 3. The two mold members facing each other,
In a molding die for press-molding an optical element which is a biconvex lens or a convex meniscus lens having a spherical or aspherical lens surface facing in the optical axis direction, at least one of the two lens surfaces has its optical surface. In the region outside the effective diameter, the extension from the extension of the curve that sets the curved surface within the optical effective diameter deviates toward the lens in the optical axis direction, and the extension increases with an increase in the diameter in the direction orthogonal to the optical axis. The transfer surface is formed on a molding surface of at least one of the mold members outside a transfer region having a predetermined effective optical diameter so that the transfer surface shape is such that the amount of reduction in lens thickness is greater than that formed by a line. A molding die, wherein a transfer molding part for a surface is formed at least to a required lens outer diameter.