WO2015170721A1

WO2015170721A1 - Optical element molding method, molding mold, and optical element

Info

Publication number: WO2015170721A1
Application number: PCT/JP2015/063238
Authority: WO
Inventors: 富波徹; 古田勝己
Original assignee: コニカミノルタ株式会社
Priority date: 2014-05-09
Filing date: 2015-05-07
Publication date: 2015-11-12
Also published as: JP6409870B2; CN106457622B; CN106457622A; JPWO2015170721A1

Abstract

Provided is an optical element molding method which can prevent the burrs on an optical element obtained from a molding material from blocking assembly with other components. An inner wall (37) is provided to a lower molding mold (30), and thus the spreading of a photocurable resin (molding material) (RA) can be easily contained within the inner wall (37). The angle (θ1) of a lower outer wall (38) is set to be greater than 180° with respect to the inner wall (37), and thus it becomes easier to block the spreading of the photocurable resin (RA) when the same overflows the inner wall (37) and the like. An end part (E1) of the lower outer wall (38) side of the inner wall (37) is located farther outward than an end part (E2) of an upper outer wall (48) side of a perimeter flat wall (46), and thus even if the photocurable resin (RA) comes into contact with the inner wall (37) and reaches the end part (E1), it becomes easier for the photocurable resin (RA) to extend inward from the inner wall (37) and reach the perimeter flat wall (46). The angle (θ2) of the upper outer wall (48) is set to be greater than 180° with respect to the perimeter flat wall (46), and thus even if the photocurable resin (RA) which has reached the perimeter flat wall (46) reaches a location farther outward than the end part (E2), the amount of the photocurable resin that spreads outward can be made less.

Description

Optical element molding method, mold, and optical element

The present invention relates to a method for molding an optical element using a molding die, and more particularly to a molding method and a molding die for an optical element suitable for molding an energy curable resin, and an optical element obtained by these.

In lenses used for imaging elements, extreme miniaturization is required due to the spread of mobile terminals. Along with this, a thin and uneven lens is also required for the lenses used therefor. However, it has been found difficult to mold thin and uneven lenses by injection molding. Therefore, it is conceivable to mold the lens using a photocurable resin or other energy curable resin that has an advantage with respect to a thin and uneven molded product.

As a method of molding a lens made of a photocurable resin, an ultraviolet ray from a light source incorporated in a stage that supports the upper mold and the lower mold by sandwiching an ultraviolet curable resin between the upper mold and the lower mold made of a transparent material. There is a technique for forming a lens by irradiating an ultraviolet curable resin between molds (see, for example, Patent Document 1).

Also, there is a molding method of a composite element in which an ultraviolet curable resin is attached to a base material such as a glass lens with a molding die (for example, see Patent Document 2). In this molding method, the resin is supplied onto the transfer surface of the mold, the substrate is brought close to the mold until the resin thickness is appropriate, and the ultraviolet light is applied from the outside of the mold while maintaining the appropriate proximity. Irradiate light.

In the molding of energy curable resins such as ultraviolet curable resins, it is difficult to form a precise outer shape because a mold with an open outer periphery is used, and the resin leaks outside the target outer shape of the lens. A burr is formed. When such a burr | flash is formed, when incorporating a lens in a holder, it will interfere with the inner wall surface or inner surface of a holder. That is, it becomes difficult to assemble the lens, or the accuracy of assembling the lens decreases. In addition, although the process of cutting a burr | flash can also be provided, a process increases, it causes a cost increase, and eccentricity may arise in a cutting process.

JP 2011-242478 A JP 2007-15240 A

The present invention has been made in view of the above-mentioned problems of the background art, and is an optical element that can prevent burr of an optical element obtained by an energy curable resin or other molding material from interfering with assembly to other parts. An object is to provide a forming method.

Another object of the present invention is to provide a mold for realizing the above-described method for molding an optical element, and an optical element manufactured thereby.

In order to achieve the above object, a method for molding an optical element according to the present invention is to solidify a molding material between a lower mold and an upper mold, and the lower mold is a lower optical mold. The upper mold has a transfer surface, an inner wall forming an outer side surface of the optical element, and a lower outer wall adjacent to the outer side of the inner wall. The upper mold extends substantially perpendicular to the upper optical transfer surface and a vertical reference axis. An angle θ1 of the lower outer wall with respect to the inner side wall is larger than 180 °, and an angle θ2 of the upper outer wall with respect to the circumferential wall. Is larger than 180 °, and the end portion on the lower outer wall side of the inner wall is outside the end portion on the upper outer wall side of the circumferential flat wall in a state where the lower mold and the upper mold are positioned.

In the above molding method, since the inner wall is provided in the lower mold, it is easy to keep the spread of the resin in the inner wall. Furthermore, the angle θ1 of the lower outer wall with respect to the inner wall is larger than 180 °, and it is easy to prevent the resin from spreading over the inner wall and the peripheral flat wall. At this time, since the end on the lower outer wall side of the inner wall is outside the end on the upper outer wall side of the circumferential flat wall, even if there is a molding material that contacts the inner wall and reaches the end, It becomes easy to reach the peripheral flat wall which extends in the opposite direction. Moreover, since the angle θ2 of the upper outer wall with respect to the circumferential flat wall is larger than 180 °, the amount of outward spreading can be reduced even if the molding material that has reached the circumferential flat wall reaches outside the end portion. As described above, it becomes easy to prevent the molding material from spreading from the end of the inner wall to the outside, so the optical element after molding can be easily and precisely assembled to a holder or the like using the side surface corresponding to the inner wall. It will be a thing.

According to a specific aspect of the present invention, in the molding method, the inner wall has a portion extending in a cylindrical shape along the reference axis on the upper end side. In this case, a cylindrical side surface can be formed on the optical element, and the assembly to the holder or the like can be further stabilized.

According to another aspect of the present invention, in a state where the lower optical transfer surface and the upper mold are positioned, the end portion on the lower outer wall side of the inner wall and the end portion on the upper outer wall side of the circumferential wall are substantially the same. Placed at height. In this case, the molding material can be accumulated on the lower molding die side, and the molding material can be kept inside by the upper molding die, so that the molding material can be more reliably prevented from spreading outward from the end portion of the inner wall.

According to still another aspect of the present invention, the viscosity of the molding material before solidification is 5000 mPa · s or less. By setting the viscosity of the molding material to 5000 mPa · s or less, good shape transferability can be maintained.

According to still another aspect of the present invention, the molding material is an energy curable resin. In this case, the viscosity at the time of supplying the molding material between the molds can be sufficiently lowered even at a low temperature, and a thin optical element with a biased thickness can be molded with relatively high accuracy.

According to still another aspect of the present invention, the molding material is a photocurable resin. In this case, a highly accurate optical element can be molded at a low temperature.

In order to achieve the above object, a molding die according to the present invention includes a lower molding die for receiving a molding material, and an upper molding die arranged to face the lower molding die, and the lower molding die and the upper molding die. A molding die for cast molding in which a molding material is sandwiched between molds, and the lower molding die is adjacent to the lower optical transfer surface, the inner side wall forming the outer side of the optical element, and the outer side of the inner side wall. The upper mold has an upper optical transfer surface, a peripheral flat wall extending substantially perpendicular to a vertical reference axis to form a peripheral plane of the optical element, and an upper outer wall adjacent to the outside of the peripheral flat wall. The angle θ1 of the lower outer wall with respect to the inner wall is greater than 180 °, the angle θ2 of the upper outer wall with respect to the circumferential flat wall is larger than 180 °, and the end on the lower outer wall side of the inner wall is above the circumferential flat wall. It is outside the end on the outer wall side.

In the above mold, since the inner wall is provided in the lower mold, it is easy to keep the spread of the resin in the inner wall. Furthermore, the angle θ1 of the lower outer wall with respect to the inner wall is larger than 180 °, and it is easy to prevent the resin from spreading over the inner wall and the peripheral flat wall. Furthermore, since the end portion on the lower outer wall side of the inner wall is outside the end portion on the upper outer wall side of the circumferential flat wall, even if there is a molding material that contacts the inner wall and reaches the end portion, the inner wall is inward from the inner wall. It becomes easy to extend and to reach the opposing surrounding flat wall. Moreover, since the angle θ2 of the upper outer wall with respect to the circumferential flat wall is larger than 180 °, the amount of outward spreading can be reduced even if the molding material that has reached the circumferential flat wall reaches outside the end portion. As described above, it becomes easy to prevent the molding material from spreading from the end of the inner wall to the outside. Therefore, the optical element molded by this molding die can be assembled to a holder or the like using the side surface corresponding to the inner wall. Simple and precise.

In order to achieve the above object, the optical element according to the present invention is formed by cast molding using the above-described mold and has an outer shape reference corresponding to the inner wall.

1A and 1B are an end view and a side cross-sectional view of a lower mold among molds for carrying out the optical element molding method of the embodiment. 2A and 2B are a side sectional view and an end view of the upper mold among the molds. It is a conceptual diagram explaining the shaping | molding apparatus incorporating a shaping | molding die. It is a sectional side view explaining the arrangement | positioning relationship of the upper and lower shaping die mutually positioned at the time of cast shaping | molding. 5A and 5B are a side cross-sectional view and a partially enlarged cross-sectional view for explaining a casting process in which a resin is supplied. 6A and 6B are conceptual diagrams for explaining the spread state of the resin around the upper and lower molds. It is side sectional drawing explaining the assembly | attachment to an optical element holder.

Hereinafter, an optical element molding method according to an embodiment of the present invention will be described with reference to the drawings.

The lower mold 30 shown in FIGS. 1A and 1B is one mold part that constitutes a mold for carrying out the optical element molding method according to the present embodiment. The lower mold 30 shown in the figure is formed of a glass or other material having optical transparency. The lower mold 30 includes a transfer portion 31 on the center side of the surface and a substrate portion 32 that supports the transfer portion 31 from behind. The transfer portion 31 protrudes from the substrate portion 32 and has an outer ring protrusion 33 on the outermost side. The substrate portion 32 has a flat plate shape and has a circular outline as shown in the figure, but may have a rectangular outline.

The transfer portion 31 includes a lower optical transfer surface 35 for forming an optical surface of the optical element, a peripheral flat wall 36 for forming a peripheral plane of the optical element, an inner wall 37 for forming an outer side surface of the optical element, and an inner wall. 37 and a lower outer wall 38 adjacent to the outside of 37. The lower optical transfer surface 35 has a convex aspheric shape as a whole, but is not limited thereto, and may be a concave surface or a spherical shape. The circumferential flat wall 36 is an annular plane extending perpendicularly to the vertical reference axis AX, and surrounds the lower optical transfer surface 35 at a low position. In the illustrated example, a step is formed between the lower optical transfer surface 35 and the peripheral flat wall 36, but the step can be eliminated depending on the shape of the lower optical transfer surface 35. The inner wall 37 includes a cylindrical surface portion 37a extending in a cylindrical shape parallel to the vertical reference axis AX, and a tapered surface portion 37b inclined inward with respect to the cylindrical surface portion 37a. The lower outer wall 38 is a donut surface-like annular surface and constitutes an annular side surface of the transfer portion 31. The lower outer wall 38 is continuously formed so as to protrude from the surface 32 a of the substrate portion 32.

2A and 2B, the upper mold 40 is the other mold part constituting the mold for carrying out the optical element molding method of the embodiment. The upper mold 40 is made of light-transmitting glass or other material. The upper mold 40 includes a transfer portion 41 on the center side of the surface and a substrate portion 42 that supports the transfer portion 41 from behind. The transfer portion 41 protrudes from the substrate portion 42 and has an outer ring protrusion 43 on the outermost side. The substrate portion 42 has a flat plate shape and has a circular outline as shown in the figure, but may have a rectangular outline.

The transfer portion 41 has an upper optical transfer surface 45 for forming an optical surface of the optical element, a peripheral flat wall 46 forming a peripheral plane of the optical element, and an upper outer wall 48 adjacent to the outside of the peripheral flat wall 46. The upper optical transfer surface 45 has a concave aspherical shape as a whole, but is not limited thereto, and may be a convex surface or a spherical shape. The circumferential flat wall 46 is an annular plane extending perpendicularly to the vertical reference axis AX, and surrounds the upper optical transfer surface 45 at a higher position or a more protruding position. In the illustrated example, the upper optical transfer surface 45 and the peripheral flat wall 46 are continuously connected, but a step can be formed between them. The upper outer wall 48 is a tapered annular surface extending on the base side, and constitutes an annular side surface of the transfer portion 41. The upper outer wall 48 is continuously formed so as to protrude from the surface 42 a of the substrate portion 42.

FIG. 3 is a conceptual diagram for explaining a manufacturing apparatus in which the

molds

30 and 40 of FIG. 1 are incorporated, and a method for molding an optical element, specifically, cast molding is performed. The illustrated manufacturing apparatus 100 stores a lower stage 11, a lower drive unit 12, an upper stage 13, and an upper drive unit 14 in a processing chamber 10. Outside the processing chamber 10, there are provided a UV light source 22 that irradiates the appropriate position of the work from the back side of the lower stage 11 during the curing process, and a main driving unit 23 that moves the upper driving unit 14 up and down. Yes. Note that the inside of the processing chamber 10 can be an environment of vacuum or nitrogen purge. In this case, it is possible to perform molding using an anaerobic photocurable resin RA.

The lower stage 11 has a chuck portion (not shown) and the like, and holds the lower molding die 30 as a workpiece. The lower drive unit 12 moves the lower stage 11 up and down. The upper stage 13 has a chuck portion (not shown) and the like, and holds an upper mold 40 as a workpiece. The upper drive unit 14 adjusts the position and posture of the upper stage 13. That is, the upper drive unit 14 is provided with a triaxial drive unit, an inclination drive unit that adjusts an inclination posture, and the like. Accordingly, the upper stage 13 can be displaced three-dimensionally while supporting the upper mold 40 and can be rotated, for example, around the vertical axis. In the adjustment, the vertical axis of the upper drive unit 14 is set to coincide with the reference axis AX of the lower mold 30. The upper drive unit 14 is driven by the main drive unit 23 to move up and down.

In the manufacturing apparatus 100, the three-dimensional translation and rotation of the lower mold 30 and the upper mold 40 can be aligned, and alignment marks (not shown) formed on both

molds

30 and 40 are used. Thus, the relative arrangement relationship between the lower mold 30 and the upper mold 40 can be set precisely.

An optical element molding method using the manufacturing apparatus 100 of FIG. The lower mold 30 and the upper mold 40 are set apart from each other in the manufacturing apparatus 100, and an appropriate amount of a photocurable resin RA (energy curable resin) that is a molding material is supplied onto the lower mold 30. . At this time, the viscosity of the photocurable resin (molding material) RA is set to 1000 to 5000 mPa · s or less. By setting the viscosity of the photocurable resin RA to 5000 mPa · s or less, good shape transferability can be maintained. Thereafter, the upper mold 40 is gradually lowered to set the lower mold 30 and the upper mold 40 at an appropriate distance. That is, both

molds

30 and 40 are positioned for molding. Thereafter, by operating the UV light source 22, the photocurable resin RA between the

molds

30 and 40 can be cured or solidified by the curing light KK. Thereafter, the molded product obtained from the photocurable resin RA is taken out by opening the mold that separates the lower mold 30 and the upper mold 40. This molded product can be post-processed to achieve a stable state by further curing by heat treatment.

FIG. 4 is a diagram for explaining the shapes and arrangement relationships of the upper and lower molding dies 30 and 40. In the lower mold 30, the angle θ <b> 1 of the lower outer wall 38 adjacent to the inner wall 37 is set to be greater than 180 ° and is equal to or greater than 270 °. On the other hand, in the upper mold 40, the angle θ2 of the upper outer wall 48 adjacent to the peripheral flat wall 46 is set to be larger than 180 °, and is 210 ° or more and 270 ° or less. As shown in the drawing, in a state where the upper mold 40 is positioned with respect to the lower mold 30, the end E1 on the lower outer wall 38 side of the inner wall 37 is more than the end E2 on the upper outer wall 48 side of the circumferential wall 46. Is also on the outside by a width h. That is, the outer diameter of the inner wall 37 is larger than the outer diameter of the circumferential flat wall 46 by a width 2h that is greater than or equal to a predetermined value. The width 2h is adjusted in consideration of the variation of the photocurable resin RA. Similarly, with the upper mold 40 positioned relative to the lower mold 30, the end E1 on the lower outer wall 38 side of the inner wall 37 and the end E2 on the upper outer wall 48 side of the circumferential flat wall 46 are Arranged at approximately the same height. More specifically, the end E1 of the inner wall 37 is slightly higher than the end E2 of the circumferential flat wall 46 disposed on the inner side. However, the end E1 of the inner wall 37 can be made lower than the end E2 of the circumferential flat wall 46. When the end E1 of the inner wall 37 is made higher than the end E2 of the circumferential flat wall 46, the end E1 does not contact the upper mold 40 or the end E2 does not contact the lower mold 30. Like that.

FIGS. 5A and 5B are views for explaining a state before the photocurable resin (molding material) RA is sandwiched between the lower mold 30 and the upper mold 40 and cured. The photocurable resin RA supplied on the lower mold 30 is spread by the upper mold 40 and fills the inside of the inner wall 37, but gets over the end E <b> 1 of the inner wall 37 to the lower outer wall 38 side. Not enough to overflow. In the upper mold 40, the photocurable resin RA fills the lower side of the peripheral flat wall 46 and gets over the end E <b> 2 of the peripheral flat wall 46, but receives a force that prevents it from spreading greatly toward the upper outer wall 48.

As shown in FIG. 6A, in the lower mold 30, the photocurable resin RA supplied to the inner wall 37 rises along the inner wall 37, but the angle θ1 at the end E1 greatly exceeds 180 °. Therefore, the pinning effect by the end E1 prevents the photocurable resin RA from getting over the end E1 and overflowing to the lower outer wall 38 side.
As shown in FIG. 6B, in the upper mold 40, the photocurable resin RA spreads outward along the peripheral flat wall 46. When the supply amount of the photocurable resin RA is not so large, the angle θ2 at the end portion E2 exceeds 180 °, so that the photocurable resin RA gets over the end portion E2 due to the pinning effect by the end portion E2. The overflow to the upper outer wall 48 side is prevented. However, when the supply amount of the photocurable resin RA is larger, the angle θ2 at the end portion E2 does not greatly exceed 180 °, so that even if the photocurable resin RA does not get over the end portion E1, A state occurs in which the curable resin RA gets over the end E2 and spreads toward the upper outer wall 48 side. However, since the angle θ2 at the end portion E2 exceeds 180 °, the photocurable resin RA can be prevented from greatly spreading to the upper outer wall 48 side, and spread beyond the end portion E1 of the lower mold 30 to the outside. Can be surely prevented. Note that the discharge or dropping of the photocurable resin RA may cause a variation of several percent or less, but it is certain that the photocurable resin RA gets over the end E2 and greatly spreads toward the upper outer wall 48 as described above. It can be prevented.

As shown in FIG. 7, a molded product (optical element) 50 formed by curing the photocurable resin RA between the lower mold 30 and the upper mold 40 includes a pair of opposed optical transfer surfaces 35, And a flange portion 52 formed by a pair of opposed peripheral

flat walls

36 and 46 and an inner wall 37. The main body 51 has a pair of

optical surfaces

51a and 51b. A burr-like protruding portion 53 caused by the upper outer wall 48 is formed on the upper portion of the flange portion 52, but extends upward and extends outward beyond the side surface 52a of the flange portion 52. Absent. The inner side surface 53a of the burr-like protrusion 53 forms an angle γ with respect to the upper surface 52u of the flange portion 52, and this angle γ is 90 to 180 °. Note that the side surface 52 a of the flange portion 52 is an outer shape reference of the molded product (optical element) 50. In addition, the optical axis OA of the molded product (optical element) 50 coincides with the reference axis AX of the

molds

30 and 40.

The molded product 50 is assembled so as to be stored in the holder 60. The holder 60 has a cylindrical side wall 61 and an annular bottom wall 62. The flange portion 52 of the molded product 50 is held by the side wall 61 so as to be prevented from moving outward, and the side surface 52a that is the outer side surface is in contact with the inner surface 61a. In addition, the bottom wall 62 is held so as to prevent downward movement, and the lower surface 52b is in contact with the bottom surface 62a.

As described above, according to the method for molding an optical element according to the present embodiment, since the inner wall 37 is provided in the lower mold 30, the spread of the photocurable resin (molding material) RA is increased in the inner wall 37. Easy to stay. Furthermore, the angle θ1 of the lower outer wall 38 with respect to the inner wall 37 is larger than 180 °, and it is easy to prevent the photocurable resin RA from spreading over the inner wall 37 and the like. At this time, since the end E1 on the lower outer wall 38 side of the inner wall 37 is outside the end E2 on the upper outer wall 48 side of the circumferential flat wall 46, the photocuring property that contacts the inner wall 37 and reaches the end E1. Even if the resin RA is present, it extends from the inner side wall 37 to the inside and easily reaches the peripheral flat wall 46. Moreover, since the angle θ2 of the upper outer wall 48 with respect to the circumferential flat wall 46 is larger than 180 °, the amount of outward spreading is reduced even if the photocurable resin RA reaching the circumferential flat wall 46 reaches outside the end E2. be able to. As described above, it is easy to prevent the photocurable resin (molding material) RA from spreading outward from the end E1 of the inner wall 37, so that the molded product (optical element) 50 after molding corresponds to the inner wall 37. Assembling to the holder 60 or the like using the side surface 52a is simple and precise.

The optical element molding method and mold according to the present embodiment have been described above, but the optical element molding method and the like according to the present invention are not limited to those described above. For example, in the upper mold 40 of the above-described embodiment, the peripheral flat wall 46 is not limited to extending perpendicularly to the reference axis AX, and may have a slight inclination or curvature with respect to a plane orthogonal to the reference axis AX. Further, the inner wall 37 of the lower mold 30 can also be a tapered surface that is inclined with respect to the reference axis AX and spreads upward.

The

transfer portions

31 and 41 and the optical transfer surfaces 35 and 45 are not limited to a circle but may be an ellipse, a rectangle, or another polygon.

In the above, a case has been described in which a photocurable resin RA is supplied as a molding material between the

molds

30 and 40 to obtain a molded product. However, instead of the photocurable resin RA, a thermosetting resin or the like may be used. it can. When the thermosetting resin is used, the

molds

30 and 40 do not need to transmit ultraviolet rays or other light.

In FIG. 3, the pair of

molds

30 and 40 are positioned using the

stages

11 and 13. However, the

molds

30 and 40 may be positioned and fixed using a positioning jig. it can.

The

molds

30 and 40 may be capable of molding a large number of optical elements at once, and may be a lens array having a large number of lens portions.

Claims

A molding method for an optical element that solidifies by sandwiching a molding material between a lower mold and an upper mold,
The lower mold has a lower optical transfer surface, an inner wall that forms the outer side of the optical element, and a lower outer wall adjacent to the outside of the inner wall,
The upper mold has an upper optical transfer surface, a peripheral flat wall extending substantially perpendicular to a vertical reference axis to form a peripheral plane of the optical element, and an upper outer wall adjacent to the outside of the peripheral flat wall,
The angle θ1 of the lower outer wall with respect to the inner wall is larger than 180 °, and the angle θ2 of the upper outer wall with respect to the peripheral wall is larger than 180 °,
The end of the inner wall on the lower outer wall side is a molding of an optical element located outside the end of the peripheral flat wall on the upper outer wall side in a state where the lower molding die and the upper molding die are positioned. Method.
The method for molding an optical element according to claim 1, wherein the angle θ1 is 270 ° to 360 °, and the angle θ2 is 210 ° to 270 °.
The method for molding an optical element according to any one of claims 1 and 2, wherein the inner wall has a portion extending in a cylindrical shape along the reference axis on an upper end side.
In a state where the lower optical transfer surface and the upper mold are positioned, the end on the lower outer wall side of the inner wall and the end on the upper outer wall side of the peripheral wall are disposed at substantially the same height. The method for molding an optical element according to any one of claims 1 to 3, wherein:
The method for molding an optical element according to any one of claims 1 to 4, wherein a viscosity of the molding material before solidification is 5000 mPa · s or less.
The method for molding an optical element according to any one of claims 1 to 5, wherein the molding material is an energy curable resin.
The method for molding an optical element according to claim 6, wherein the molding material is a photocurable resin.
A casting mold comprising: a lower mold for receiving a molding material; and an upper mold disposed to face the lower mold; and sandwiching the molding material between the lower mold and the upper mold A mold,
The lower mold has a lower optical transfer surface, an inner wall that forms the outer side of the optical element, and a lower outer wall adjacent to the outside of the inner wall,
The upper mold has an upper optical transfer surface, a peripheral flat wall extending substantially perpendicular to a vertical reference axis to form a peripheral plane of the optical element, and an upper outer wall adjacent to the outside of the peripheral flat wall,
The angle θ1 of the lower outer wall with respect to the inner wall is larger than 180 °, and the angle θ2 of the upper outer wall with respect to the peripheral wall is larger than 180 °,
The mold on the lower outer wall side of the inner wall is located outside the end of the peripheral wall on the upper outer wall side.
An optical element formed by cast molding using the mold according to claim 8 and having an outer shape reference corresponding to the inner wall.