Optical element manufacturing method

Abstract

A manufacturing method for efficiently producing high-precision optical elements using simple equipment is provided. The method involves placing a core member in a cavity surrounded by surfaces including a surface C of a first portion of a mold and a surface D of a second portion, and while forming a layer on surface A by injection molding, pressing surface B of the core member opposite surface A against surface D, which has been heated to a temperature higher than the glass transition temperature of the plastic of the core member, and then cooling surface D to mold surface B into a surface Bd of a target shape. The core member is placed in the cavity with only a portion of surface B in contact with surface D, and the core member is placed in the cavity with only a portion of surface B in contact with surface D so that a gap exists between surfaces B and D. The shape of the core member is determined so that the ratio of the volume of the gap to the volume of the space is 0.15 or less.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing optical elements, including lenses, diffraction gratings, prisms, and microlens arrays. [Background technology]

[0002] In the manufacturing method of plastic injection molding, the molten plastic injected into the mold must be sufficiently cooled before the molded product can be removed, so production efficiency depends on the cooling time. If the molded product is thick, the cooling time will be longer, which will reduce production efficiency. In the case of optical elements, the mold temperature must be relatively high to maintain high shape precision, so the cooling time has a particularly large impact on production efficiency.

[0003] For this reason, a manufacturing method for optical elements by injection molding has been developed in which molding is divided into multiple steps, a core member is manufactured in the first molding step, and a thin layer is formed on the surface of the core member in the second and subsequent molding steps (for example, Patent Document 1). According to this method, the optical surface, which requires high shape accuracy, is formed as the surface of a thin layer in a separate molding step, thereby shortening the cooling time and improving production efficiency.

[0004] However, in the above manufacturing method, it is usually necessary to separately perform the molding steps of thin layers on both sides of the core member while the core member is fixed in a mold, which requires a complex mechanism of the mold and auxiliary equipment.

[0005] As described above, a manufacturing method capable of efficiently manufacturing high-precision optical elements using simple equipment has not been developed. Therefore, there is a need for a manufacturing method capable of efficiently manufacturing high-precision optical elements using simple equipment. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JPH09225961(A)(JP 9-225961) Summary of the Invention [Problem to be solved by the invention]

[0007] A technical object of the present invention is to provide a manufacturing method that can efficiently manufacture high-precision optical elements using a simple apparatus. [Means for solving the problem]

[0008] A method for manufacturing an optical element of the present invention uses a mold having a first portion and a second portion. In the manufacturing method of the present invention, a core member is placed in a cavity of the mold surrounded by a surface including surface C of the first portion and surface D of the second portion facing surface C. Molten plastic is poured into the space surrounded by surfaces including surfaces A and C of the core member to form a layer on surface A by injection molding. Meanwhile, surface B of the core member opposite surface A is pressed against surface D, which has been heated to a temperature higher than the glass transition temperature of the plastic of the core member, and surface D is then cooled to mold surface B into a surface Bd of a desired shape. In the manufacturing method of the present invention, the core member is placed in the cavity so that only a portion of surface B is in contact with surface D, leaving a gap between surfaces B and D. The shape of the core member is determined so that the ratio of the volume of the gap to the volume of the space is 0.15 or less.

[0009] In the method for manufacturing an optical element of the present invention, a layer is formed on surface A by injection molding, while surface B of the core member opposite surface A is pressed against surface D, which has been heated to a temperature higher than the glass transition temperature of the plastic of the core member, thereby press-molding surface B into surface Bd of the desired shape, thereby allowing high-precision optical elements to be obtained using simple equipment.

[0010] Furthermore, the manufacturing method of the present invention can improve the surface accuracy of the optical surface of the optical element corresponding to surface B.

[0011] In the method for manufacturing an optical element according to the first embodiment of the present invention, the maximum distance between the surface B and the surface D in the thickness direction of the optical element is ⅓ or less of the maximum thickness of the optical element.

[0012] In the method for manufacturing an optical element according to the second embodiment of the present invention, the maximum thickness of the optical element is 5 millimeters or more.

[0013] The method of the present invention is particularly effective for producing optical elements with a center thickness or maximum thickness of 5 mm or more, in which deformation of surface B of the core member is unlikely to occur due to the filling pressure of the molten plastic alone.

[0014] In the method for manufacturing an optical element according to the third embodiment of the present invention, the ratio of the volume of the gap to the volume of the space is 0.015 or more and 0.08 or less.

[0015] According to this embodiment, the pressure after the expansion of the plastic, that is, the pressure at the end of molding of surface B, can be set to a sufficient value, thereby further improving the precision of the optical surface of the optical element corresponding to surface B.

[0016] In the method for manufacturing an optical element according to the fourth embodiment of the present invention, the surface A is a plane perpendicular to the central axis of the core member.

[0017] In the method for manufacturing an optical element according to the fifth embodiment of the present invention, the surface Bd is a convex surface or a concave surface.

[0018] In the method for manufacturing an optical element according to the sixth embodiment of the present invention, the surface Bd and the surface B are symmetrical about their respective central axes.

[0019] In the method for manufacturing an optical element according to the seventh embodiment of the present invention, the surface Bd is an aspherical surface.

[0020] In the method for manufacturing an optical element according to the eighth embodiment of the present invention, the material of the core member and the material of the layer formed on surface A by injection molding are the same.

[0021] In the method for manufacturing an optical element according to the ninth embodiment of the present invention, the filling pressure is 50 megapascals or more.

[0022] If the filling pressure is less than 50 MPa, a sufficient pressure value cannot be secured at the end of molding of surface B, and the precision of the optical surface cannot be further improved. [Brief explanation of the drawings]

[0023] [Figure 1] 1A and 1B are diagrams showing an example of a mold used in the manufacturing method of the optical element of the present invention. [Figure 2] 3 is a flowchart illustrating a method for manufacturing an optical element according to the present invention. [Figure 3] FIG. 2 shows a core member installed in a cavity between a first part and a second part of a mold. [Figure 4] 10 is a diagram showing a state in which molten plastic is poured into the space between surface C of the first portion and surface A of the core member. FIG. [Figure 5] FIG. 10 is a diagram showing the state after press forming is performed. [Figure 6A] FIG. 2 is a perspective view of an example core member. [Figure 6B] FIG. 6B is a longitudinal cross-sectional view of the core member of FIG. 6A. [Figure 6C] FIG. 6B is a cross-sectional view of the core member of FIG. 6A. [Figure 7A] FIG. 2 is a perspective view of an example optical element. [Figure 7B] FIG. 7B is a longitudinal cross-sectional view of the optical element of FIG. 7A. [Figure 7C] FIG. 7B is a cross-sectional view of the optical element of FIG. 7A. [Figure 8] FIG. 2 is a view showing a core member disposed in a mold. [Figure 9A] This is a graph showing the relationship between pressure, volume, and temperature for plastic (PMMA, polymethyl methacrylate). [Figure 9B] FIG. 10 is a diagram showing the relationship between the temperature and pressure of plastic and the theoretical value of the ratio of volume Vg to volume V, assuming that volume Vg is filled by the volume expansion of plastic. [Figure 10] 1 is a flow chart illustrating a prior art method for manufacturing an optical element. [Figure 11A] FIG. 2 is a perspective view of a core member as a primary molded product. [Figure 11B] FIG. 2 is a longitudinal cross-sectional view of a core member as a primary molded product. [Figure 11C] FIG. 2 is a cross-sectional view of a core member as a primary molded product. [Figure 12A] FIG. 1 is a perspective view of a secondary molded product. [Figure 12B] FIG. 2 is a longitudinal cross-sectional view of a secondary molded product. [Figure 12C] FIG. 1 is a cross-sectional view of a secondary molded product. [Figure 13A] This is a perspective view of a tertiary molded product. [Figure 13B] FIG. 1 is a longitudinal cross-sectional view of a tertiary molded product. [Figure 13C] This is a cross-sectional view of a tertiary molded product. [Figure 14] FIG. 2 shows a core member placed in a cavity between a first part and a second part of a mold when manufacturing a concave lens. [Figure 15] 10 is a diagram showing a state in which molten plastic is poured into the space between surface C of the first portion and surface A of the core member when manufacturing a concave lens. FIG. [Figure 16] FIG. 10 is a diagram showing the state after press molding is performed when manufacturing a concave lens. [Figure 17] FIG. 10 shows a core member placed in a cavity between a first part and a second part of a mold when manufacturing an optical element such as a prism in which one surface is inclined relative to the other surface. [Figure 18] This is a diagram showing the state in which molten plastic is poured into the space between surface C of the first part and surface A of the core member when manufacturing an optical element such as a prism in which one surface is inclined relative to the other surface. [Figure 19] 10A and 10B are diagrams showing a state after press molding is performed when manufacturing an optical element such as a prism in which one surface is inclined relative to the other surface. DETAILED DESCRIPTION OF THE INVENTION

[0024] FIG. 1 shows an example of a mold used in the method for manufacturing an optical element of the present invention. The mold includes a first portion 110 and a second portion 120 configured to face each other and form a cavity therebetween. The second portion 120 includes a press-molding portion 121 equipped with a heater 123 and an outer portion 127 surrounding the press-molding portion 121. The press-molding portion 121 and the outer portion 127 are separated by a heat insulating material 125. The heater 123 may be a commercially available electric heater. The heat insulating material 125 may be a sheet-like material made of, for example, glass cloth. The press-molding portion 121 and the heat insulating material 125 are configured to be stored in the outer portion 127.

[0025] FIG. 2 is a flow chart illustrating the method for manufacturing an optical element according to the present invention.

[0026] 2, the core member 210 is molded. The core member 210 is made of plastic and may be molded by injection molding, for example.

[0027] In step S1020 of FIG. 2, the core member 210 is placed in the cavity of the mold shown in FIG.

[0028] 3 is a diagram showing core member 210 placed in the cavity between first portion 110 and second portion 120 of the mold. Core member 210 has surface A and an opposite surface B. A space 115 is formed between surface C of first portion 110 and surface A of core member 210. In the state shown in FIG. 3, the apex of surface B of core member 210 and the portion (valley bottom) corresponding to the apex of surface D of second portion 120 are in contact.

[0029] In step S1030 of FIG. 2, molten plastic is poured into the space 115 between the surfaces C and A, forming a layer on the surface A of the core member 210 by injection molding. ,corePress molding is performed by pressing surface B, which is the opposite side of surface A of core member 210, against surface D of press-molding portion 121, which has been heated to a temperature higher than the glass transition temperature of the plastic of core member 210. Through press molding, the shape of surface D of the mold is transferred to surface B of the core member, forming surface B'. The side surfaces of core member 210 other than surfaces A and B are in contact with the inner surface of the second portion in a state in which core member 210 can move inside the second portion.

[0030] FIG. 4 is a diagram showing a state in which a portion of molten plastic has been poured into the space 115 between the surface C of the first portion 110 and the surface A of the core member 210. The poured molten plastic forms a layer on the surface A of the core member 210. back, core Surface B of member 210 opposite surface A is pressed against surface D of a mold heated by heater 123 to a temperature higher than the glass transition temperature of the plastic of core member 210, thereby performing press molding.

[0031] 5 is a diagram showing the state after press molding has been carried out. Surface B' is formed by transferring the shape of surface D of the mold to the core member through press molding.

[0032] Table 1 shows an example of conditions for the method of manufacturing an optical element of the present invention. [Table 1] Since the heating temperature of the forming heater is set to 150°C, the temperature of surface D is higher than the glass transition temperature of the material of the core member, and the shape is transferred with high precision.

[0033] In the above-described embodiments, the material of the core member and the material of the layer formed by injection molding are the same. In general, the material of the core member may be different from the material of the layer formed by injection molding. Specifically, for example, when the material of the layer formed by injection molding is PMMA, PC (polycarbonate), which has a relatively high glass transition temperature, may be used as the material of the core member.

[0034] In step S1040 of FIG. 2, heating by the heater 123 is stopped, and the surface D of the press-molding portion 121 and the molded product are cooled to a temperature below the glass transition temperature of the material.

[0035] The molded product is removed from the mold in step S1050 of Fig. 2. After the molded product is removed from the mold, heating by heater 123 begins for the next molding process.

[0036] Normally, the above-mentioned cooling time of the press-molding part 121 and the molded product does not affect the molding time because it falls within the time required to solidify the molten plastic of the layer formed by injection molding on surface A. If necessary, the above-mentioned cooling time can be shortened by providing water-cooling piping in the press-molding part 121.

[0037] 6A is a perspective view of an example of a core member 210. The length and width of the bottom surface of the core member 210 are 62 millimeters and 40 millimeters, respectively, and the height of the core member is 18 millimeters.

[0038] FIG. 6B is a longitudinal cross-sectional view of the core member of FIG. 6A.

[0039] FIG. 6C is a cross-sectional view of the core member of FIG. 6A.

[0040] 7A is a perspective view of an example of optical element 300. Optical element 300 comprises a portion 215 corresponding to a core member after press molding and an additional portion 220 formed as a layer by injection molding. The length, width, and height (thickness) of additional portion 220 are 75 millimeters, 50 millimeters, and 2.5 millimeters, respectively. The height of optical element 300 is 20.5 millimeters.

[0041] FIG. 7B is a longitudinal cross-sectional view of the optical element of FIG. 7A.

[0042] FIG. 7C is a cross-sectional view of the optical element of FIG. 7A.

[0043] In this example, surface B' is a lens surface. The shape of surface Bd, which is the target shape of the lens surface, can be expressed by the following formula (1). The unit of length is millimeters.

number

number

number

number

number

[0044] The shape of the surface Bd, which is the target shape of the lens surface, is symmetrical about the central axis. Next, the shape of the core member 210 will be described.

[0045] 8 is a diagram showing the core member 210 placed in a mold, which shows the same state as that shown in FIG.

[0046] The contour of surface D in FIG. 8 is the same as the contour of surface Bd. The shape of surface B of core member 210 corresponding to surface Bd is also symmetrical around the central axis. As described with reference to FIG. 3, the vertex of surface B of core member 210 and the portion (valley bottom) of second portion 120 corresponding to the vertex of surface D are in contact. Since the contours of surface D and surface B are different, a gap 117 is created between surface D and surface B. In the example shown in FIG. 8, when coordinates in a plane perpendicular to the central axis are represented by (x, y), the shape of surface B is determined so that the difference g in coordinates in the central axis direction between points on surface D and surface B with the same (x, y) coordinates increases with distance from the central axis.

[0047] The shape of surface Bd and the shape of surface B of core member 210 are axially symmetric, but the shapes of core member 200 and lens 300 differ in length in the vertical direction and length in the horizontal direction, as shown in Figures 6A-6C and 7A-7C, respectively. The value of g reaches a maximum value gmax at the end of core member 200 in Figure 8, which shows a vertical cross section of core member 200.

[0048] The difference between the center thickness of the molded lens and the center thickness of the core member 210 is t. The volume of the space 115 between surface C of the first portion 110 and surface A of the core member 210, where the plastic is poured, is denoted by V, and the volume of the gap 117 between surface B of the core member 210 and surface D of the second portion 120 is denoted by Vg.

[0049] The deviation width e from the design value for surface B of the core member and surface B' of the optical element 300 will be explained. Surface B' is a lens surface. Surface Bd and the surface of the measured shape (hereinafter referred to as the measurement surface) are superimposed with their vertices and central axes aligned. An xyz Cartesian coordinate system is defined with the vertex of the lens surface as the origin and the central axis of the lens surface as the z axis. The shape of surface Bd is expressed by equation (1). r in equation (1) can be expressed by the following equation.

number

[0050] The deviation width e of surface B of core member 210 shown in Figure 6 with respect to the design surface is 595 micrometers. The deviation width e of surface B' of optical element 300 manufactured by the present invention shown in Figure 7 is 75 micrometers. The deviation width of surface B' is significantly reduced compared to the deviation width of surface B.

[0051] Ga It is thought that surface B of the core material, which is in contact with surface D, which has a temperature higher than the lath transition temperature, remelts, causing deformation and flow at surface B, reducing the range of deviation.

[0052] The inventors of the present application have newly discovered that, in order to manufacture a high-precision optical element by the above-mentioned method, it is important to set an appropriate value for the ratio of the volume Vg of the gap 117 between surfaces B and D to the volume V of the space 115 between surfaces C and A into which the molten plastic is poured, when the core member 210 is placed in the cavity with part of surface B of the core member 210 in contact with surface D of the second portion 120 (the state shown in FIG. 8). This discovery will be explained below.

[0053] When the core member is relatively thick and has relatively high rigidity, the filling pressure of the molten plastic poured into the space between surfaces C and A alone does not cause deformation of surface B of the core member. In this case, deformation of surface B occurs as follows: When the plastic poured into the space between surfaces C and A expands and applies pressure to the core member, surface B of the core member is pressed against surface D of second portion 120, which has been heated to a temperature higher than the glass transition temperature of the plastic of core member 210. This causes deformation and flow of surface B, and gap 117 between surfaces B and D shown in FIG. 8 is filled by the core member, causing surface A of the core member to move toward the second portion. At that time, the plastic in the space between surfaces C and A expands from the state shown in FIG. 4 to the state shown in FIG. 5.

[0054] Figure 9A shows the relationship between pressure, volume, and temperature for a plastic (PMMA, polymethyl methacrylate). The horizontal axis of Figure 9A represents temperature, and the vertical axis of Figure 9A represents specific volume. At a temperature of 250°C, the specific volume at a filling pressure of 200 MPa is 0.853, the specific volume at a filling pressure of 100 MPa is 0.886, the specific volume at a filling pressure of 50 MPa is 0.910, and the specific volume at a filling pressure of 0 MPa is 0.942. Therefore, the volume expansion rate when the pressure is completely released is as follows: 200 megapascals: 1.104 100 Megapascals: 1.062 50 megapascals: 1.036 As described above, the plastic poured into the space between surface C and surface A expands, exerting pressure on the core member, causing surface B of the core member in contact with surface D, which has been heated to a temperature higher than the glass transition temperature, to remelt, and surface B to deform and flow, filling volume Vg with the core member, and surface A of the core member moving toward surface B. In other words, volume Vg is equal to the expansion of the plastic in volume V of space 115 between surfaces C and A in the state shown in Figure 8. Therefore, the ratio Vg / V of volume Vg to volume V is related to the above-mentioned volumetric expansion rate of core member 200. In the above process, the pressure decreases as the plastic expands.

[0055] 9B is a diagram showing the relationship between the temperature and pressure of the plastic and the theoretical value of the ratio of volume Vg to volume V, assuming that volume Vg is equal to the expansion of the plastic in volume V of space 115 between surface C and surface A in the state of FIG. 8. The horizontal axis of FIG. 9B represents temperature, and the vertical axis of FIG. 9B represents the theoretical value of the ratio of volume Vg to volume V. When the temperature is 250°C, the theoretical value of the ratio Vg / V of volume Vg to volume V is as follows: 200 MPa: 0.104 100 megapascals: 0.062 50 megapascals: 0.036

[0056] Considering the types of plastic materials that have large volume changes, the upper limit of the ratio Vg / V is 0.15.

[0057] In the above-described embodiment, the condition regarding the ratio Vg / V of the volume Vg to the volume V is as follows: Molding temperature: 250℃ Filling pressure: 70 MPa Expansion coefficient: 1.046 (when pressure is reduced from 70 MPa to 0 MPa) Vg: 9375mm 3 (cubic millimeter) V: 210mm 3 (cubic millimeter) Vg / V: 0.0224 When Vg / V is the above value, the pressure after the plastic expands will not drop to 0. Generally, to obtain sufficient shape precision for the optical surface of surface B', the pressure after the plastic expands, i.e., the pressure at the end of molding surface B, should preferably be 30 MPa or higher. Also, to obtain an optical surface with sufficient shape precision, it is preferable that Vg / V be 0.015 or higher.

[0058] The method of the present invention is particularly effective for manufacturing optical elements with a center or maximum thickness of 5 millimeters or more, where deformation of surface B of the core member is unlikely to occur due to the filling pressure of the molten plastic alone. The maximum value gmax of the gap g in the thickness direction of the optical element, i.e., the direction in which surface A of the core member moves when pressed, is 1 / 3 or less of the center thickness (maximum thickness) of the optical element.

[0059] In the above-described embodiment, the values ​​of the center thickness of the optical element and the maximum value gmax of the gap g are as follows: Center Thickness: 20.5 mm gmax: 0.15 mm

[0060] Here, a conventional method for manufacturing an optical element will be described.

[0061] FIG. 10 is a flow chart illustrating a prior art method for manufacturing an optical element.

[0062] In step S2010 of FIG. 10, a core member 210' is manufactured as a primary molded product.

[0063] FIG. 11A is a perspective view of a core member 210' as a primary molded product.

[0064] FIG. 11B is a vertical cross-sectional view of a core member 210' as a primary molded product.

[0065] FIG. 11C is a cross-sectional view of a core member 210' as a primary molded product.

[0066] The length and width of the bottom of the primary molded product are 57 mm and 35 mm, respectively, and the height of the primary molded product is 15.5 mm.

[0067] 10, a core member 210' as a primary molded product is placed in a mold, and an additional portion 220' is formed on the bottom surface of the core member 210' to produce a secondary molded product. An example of the mold used is the mold shown in FIG. 1 of Patent Document 1.

[0068] FIG. 12A is a perspective view of the secondary molded product.

[0069] FIG. 12B is a vertical cross-sectional view of the secondary molded product.

[0070] FIG. 12C is a cross-sectional view of the secondary molded product.

[0071] The length, width and height (thickness) of the additional portion 220' are 75 mm, 50 mm and 2.5 mm, respectively, and the height of the secondary molded product is 18 mm.

[0072] In step S2030 of Figure 10, with the secondary molded product placed in the above-mentioned mold, an outer layer 230' is formed on the surface of the core member 210' opposite to the bottom surface on which the additional portion 220' is formed, thereby producing a tertiary molded product.

[0073] FIG. 13A is a perspective view of the tertiary molded product.

[0074] FIG. 13B is a vertical cross-sectional view of the tertiary molded product.

[0075] FIG. 13C is a cross-sectional view of the tertiary molded product.

[0076] The length and width of the bottom surface of the portion of the third molded article covered with the outer layer 230' are 62 mm and 40 mm, respectively. The thickness of the outer layer 230' is 2.5 mm, and the height of the portion of the third molded article covered with the outer layer 230' from the surface of the additional portion 220' is 18 mm. The height of the third molded article is 20.5 mm.

[0077] The width of deviation e of surface B" of optical element 300' manufactured by the manufacturing method of the prior art shown in FIG. 13A is 104 micrometers. Therefore, when forming an aspheric lens surface as shown in formula (1), the width of deviation e of surface B' of optical element 300 manufactured by the manufacturing method of the present invention is 75 micrometers as described above, which is smaller than the width of deviation e of surface B" of optical element 300' manufactured by the manufacturing method of the prior art.

[0078] Another embodiment of the present invention will now be described. Figures 14 to 16 are diagrams showing a core member and a mold for manufacturing a concave lens.

[0079] 14, like FIG. 3, shows core member 210 installed in the cavity between first portion 110 and second portion 120 of the mold. Core member 210 has a surface A and an opposite surface B. A space 115 is formed between surface C of first portion 110 and surface A of core member 210.

[0080] The shape of surface D in Figure 14 is the same as the shape of surface Bd, which is the target shape of the lens surface. The shape of surface B of the core member 210, which corresponds to surface Bd, which is symmetrical about the central axis, is also symmetrical about the central axis. In the state shown in Figure 14, the vertex of surface B of the core member 210 and the part of the second portion 120 corresponding to the vertex of surface D are in contact. Because the outline of surface D differs from the outline of surface B, a gap occurs between surface D and surface B. If coordinates in a plane perpendicular to the central axis are represented as (x, y), the difference g in the coordinates in the central axis direction between a point on surface D and a point on surface B with the same (x, y) coordinates is set to increase with the distance from the central axis. The value of g reaches a maximum value gmax at the end of the core member 200 in Figure 15, which shows a longitudinal cross section of the core member 200.

[0081] FIG. 15 , like FIG. 4 , is a diagram illustrating a state in which a portion of molten plastic has been poured into the space 115 between surface C of the first portion 110 and surface A of the core member 210. This diagram illustrates a state in which a portion of molten plastic has been poured into the space 115 between surface C of the first portion 110 and surface A of the core member 210. The poured molten plastic forms a layer on surface A of the core member 210. When the plastic poured into the space between surfaces C and A expands and applies pressure to the core member 210, surface B of the core member 210 is pressed against surface D of the second portion 120, which has been heated to a temperature higher than the glass transition temperature of the plastic of the core member 210. This causes surface B to deform and flow, filling the gap between surfaces B and D with the core member 210, and surface A of the core member 210 to move toward the second portion. In this manner, surface B is press-molded.

[0082] Fig. 16 is a diagram showing the state after press molding has been carried out, similar to Fig. 5. Surface B' is formed by transferring the shape of surface D of the mold to the core member through press molding.

[0083] 17 to 19 are diagrams showing a core member and a mold when manufacturing an optical element such as a prism in which one surface is inclined relative to the other surface.

[0084] FIG. 17, like FIG. 3, shows a core member 210 placed in a cavity between the first portion 110 and the second portion 120 of a mold. The core member 210 has a surface A and an opposite surface B. A space 115 is formed between surface C of the first portion 110 and surface A of the core member 210. In the state shown in FIG. 17, the end of surface B of the core member 210 contacts the end of surface D of the second portion 120. Surface D is inclined relative to surface B, so a gap is created between the two surfaces. The gap (the distance between surfaces B and D) in the direction in which surface A of the core member moves when pressed increases with the distance from the portion where surfaces B and D contact each other.

[0085] FIG. 18 , like FIG. 4 , is a diagram illustrating a state in which a portion of molten plastic has been poured into the space 115 between surface C of the first portion 110 and surface A of the core member 210. This diagram illustrates a state in which a portion of molten plastic has been poured into the space 115 between surface C of the first portion 110 and surface A of the core member 210. The poured molten plastic forms a layer on surface A of the core member 210. When the plastic poured into the space between surfaces C and A expands and applies pressure to the core member 210, surface B of the core member 210 is pressed against surface D of the second portion 120, which has been heated to a temperature higher than the glass transition temperature of the plastic of the core member 210. This causes surface B to deform and flow, filling the gap between surfaces B and D with the core member 210, and surface A of the core member 210 to move toward the second portion. In this manner, surface B is press-molded.

[0086] Fig. 19 is a diagram showing the state after press molding has been carried out, similar to Fig. 5. Surface B' is formed by transferring the shape of surface D of the mold to the core member through press molding.

[0087] The apparatus used in the manufacturing method of the present invention is, as shown in FIG. 1, a simple heater added to a normal mold, and does not require a press mechanism or the like.

[0088] On the other hand, the apparatus used in the prior art manufacturing method includes a complex mechanism for performing two molding steps to form thin layers on both sides of the core member while the core member is fixed in a mold, as shown in FIG. 1 of Patent Document 1.

[0089] When the apparatus used in the manufacturing method of the present invention shown in FIG. 1 is compared with the apparatus shown in FIG. 1 of Patent Document 1, the former is much simpler.

[0090] Therefore, according to the manufacturing method of the present invention, optical elements with high precision equal to or higher than that of the prior art can be efficiently manufactured using equipment simpler than that of the prior art.

Claims

1. A method for manufacturing an optical element using a mold comprising a first part and a second part, The core member is placed within the cavity of the mold, which is surrounded by the surface C of the first portion and the surface D of the second portion facing surface C. Molten plastic is poured into the space enclosed by the surfaces A and C of the core member and a layer is formed on surface A by injection molding, and the surface B of the core member opposite to surface A is pressed against surface D, which is heated to a temperature higher than the glass transition temperature of the plastic of the core member. The manufacturing method involves then cooling the surface D and shaping the surface B to form a surface Bd of the target shape. A manufacturing method comprising: placing the core member in the cavity such that a gap exists between surface B and surface D; filling the space with molten plastic; the gap still exists after filling with molten plastic; then the filled plastic expands, surface B is pressed against surface D and remelted, deformation and flow occur on surface B, and the gap is filled by the core member.

2. The method for manufacturing an optical element according to Claim 1, wherein the surface Bd is a lens surface, and the core member is placed in the cavity such that a gap exists between the surface B and the surface D, with the portion of the surface B corresponding to the vertex of the lens surface in contact with the surface D.

3. The method for manufacturing an optical element according to claim 1, wherein the maximum distance between the surface B and the surface D in the thickness direction of the optical element is 1 / 3 or less of the maximum thickness of the optical element.

4. The method for manufacturing an optical element according to claim 1, wherein the maximum thickness of the optical element is 5 millimeters or more.

5. The method for manufacturing an optical element according to Claim 1, wherein the core member is placed in the cavity such that a gap exists between the surface B and the surface D, and the ratio of the volume of the gap to the volume of the space is 0.015 or more and 0.08 or less.

6. The method for manufacturing an optical element according to claim 1, wherein the surface A is a plane perpendicular to the central axis of the core member.

7. The method for manufacturing an optical element according to claim 1, wherein the surface Bd is a convex or concave surface.

8. A method for manufacturing an optical element according to claim 1, wherein the surface Bd and the surface B are symmetrical about their respective central axes.

9. The method for manufacturing an optical element according to claim 1, wherein the surface Bd is aspherical.

10. The method for manufacturing an optical element according to claim 1, wherein the material of the core member and the material of the layer formed on the surface A by injection molding are the same.

11. A method for manufacturing an optical element according to claim 1, wherein the injection molding filling pressure is 50 megapascals or more.

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