Method for manufacturing optical element

Abstract

A method for manufacturing an optical element according to the present invention involves using a mold comprising a first portion and a second portion. In this method for manufacturing an optical element , a plastic core member is inserted into a cavity of said mold surrounded by surfaces including a surface C of said first portion and a surface D of said second portion that faces said surface C, and molten plastic is poured into a space formed by surfaces including a surface A of said core member and the surface C of said first portion to form a layer on said surface A by injection molding; meanwhile, a surface B of said core member on the opposite side from said surface A is press-molded by being pressed, due to the filling pressure of said molten plastic, against a surface D of said second portion, which has been set to a temperature higher than the glass transition temperature of the plastic of said core member.

Description

Optical element manufacturing method

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

[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 that 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.

[0006] JPH09225961(A) (Patent Publication No. 9-225961)

[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.

[0008] The method for manufacturing an optical element of the present invention uses a mold having a first portion and a second portion. In the method for manufacturing an optical element of the present invention, a plastic core member is inserted into a cavity of the mold surrounded by a surface including a surface C of the first portion and a surface D of the second portion facing surface C, and molten plastic is poured into a space formed by a surface including a surface A of the core member and a surface C of the first portion to form a layer on surface A by injection molding, while press-molding is performed by pressing a surface B of the core member opposite surface A against surface D of the second portion, which has been heated to a temperature higher than the glass transition temperature of the plastic of the core member, using the filling pressure of the molten plastic.

[0009] In the method for manufacturing an optical element of the present invention, the surface of the optical element is formed by pressing the surface B of the core member against the surface D of a mold that has been heated to a temperature higher than the glass transition temperature of the plastic of the core member, thereby obtaining an optical element with high precision.

[0010] Furthermore, since a layer is formed on surface A of the core member by injection molding, and surface B of the core member is press-molded using the filling pressure of the molten plastic, high-precision optical elements can be efficiently manufactured using relatively simple equipment.

[0011] In the method for manufacturing an optical element according to the first embodiment of the present invention, the temperature of the surface B is 30 degrees or more higher than the glass transition temperature of the plastic of the core member.

[0012] In the method for manufacturing an optical element according to the second embodiment of the present invention, the maximum value of the filling pressure is in the range of 30 megapascals to 100 megapascals.

[0013] In the method for manufacturing an optical element according to the third embodiment of the present invention, the shape of the second surface is aspherical.

[0014] According to this embodiment, high shape accuracy can be obtained even when the lens surface of the optical element is aspherical.

[0015] FIG. 5 is a diagram showing an example of a mold used in the manufacturing method of an optical element of the present invention. FIG. 6 is a flow chart explaining the manufacturing method of an optical element of the present invention. FIG. 7 is a diagram showing a core member placed in a cavity between a first part and a second part of a mold. FIG. 8 is a diagram showing a state in which molten plastic has been poured into the space between surface C of the first part 110 and surface A of the core member. FIG. 9 is a diagram showing a state after press molding has been performed using the filling pressure of the molten plastic. FIG. 10 is a diagram showing an example of the shape of the core member. FIG. 11 is a diagram showing an example of the shape of an optical element. FIG. 12 is a flow chart explaining a manufacturing method of an optical element according to the prior art. FIG. 13 is a perspective view of a core member as a primary molded product. FIG. 14 is a longitudinal cross-sectional view of a core member as a primary molded product. FIG. 15 is a transverse cross-sectional view of a core member as a primary molded product. FIG. 16 is a perspective view of a core member as a primary molded product. FIG. 17 is a transverse cross-sectional view of a core member as a primary molded product. FIG. 18 is a perspective view of a secondary molded product. FIG. 19 is a longitudinal cross-sectional view of a secondary molded product. FIG. 19 is a transverse cross-sectional view of a secondary molded product. FIG. 19 is a perspective view of a tertiary molded product. FIG. 19 is a longitudinal cross-sectional view of a tertiary molded product. FIG. 19 is a transverse cross-sectional view of a tertiary molded product.

[0016] 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 that 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.

[0017] FIG. 2 is a flow chart illustrating the method for manufacturing an optical element according to the present invention.

[0018] 2, the core member 210 is molded. The core member 210 is made of plastic and may be molded by injection molding, for example.

[0019] In step S1020 of FIG. 2, the core member 210 is placed in the cavity of the mold shown in FIG.

[0020] 3 is a diagram showing a core member 210 installed 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. The core member 210 may be fixed to the outer portion 127 by a plunger (not shown) or the like. A space 115 is formed between the surface C of the first portion 110 and the surface A of the core member 210.

[0021] 2, molten plastic is poured into the space 115 between surfaces C and A to form a layer on surface A of the core member 210 by injection molding, while the filling pressure of the molten plastic presses surface B of the core member 210 opposite surface A against surface D of the press-molding part 121, which has been heated to a temperature higher than the glass transition temperature of the plastic of the core member 210, to perform press molding. The shape of surface D of the mold is transferred to surface B of the core member by press molding, forming surface B'.

[0022] 4 is a diagram showing 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. As the molten plastic continues to be poured, the filling pressure of the molten plastic presses surface B of the core member 210 opposite surface A against surface D of a mold that has been heated by heater 123 to a temperature higher than the glass transition temperature of the plastic of the core member 210, thereby performing press molding.

[0023] 5 is a diagram showing the state after press molding using the filling pressure of molten plastic is performed. By press molding, the shape of surface D of the mold is transferred to the core member, forming surface B'.

[0024] Table 1 shows an example of conditions for the method of manufacturing an optical element of the present invention. Generally, when the temperature of surface D is 30 degrees or more higher than the glass transition temperature of the core member material and the maximum value of the filling pressure is in the range of 30 to 100 megapascals, the shape of surface D of the mold can be transferred with high accuracy.

[0025] In the above-described embodiment, the core material and the layer formed by injection molding are the same material. In general, the core material may be different from the layer formed by injection molding. Specifically, for example, when the layer formed by injection molding is made of PMMA, the core material may be made of PC (polycarbonate), which has a relatively high glass transition temperature.

[0026] In step S1040 of FIG. 2, heating by the heater 123 is stopped, and the press-molding portion 121 and the molded product are cooled to a temperature below the glass transition temperature of the material.

[0027] 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.

[0028] Normally, the above-mentioned cooling time of the press-molding part 121 and the molded product does not affect the molding time because it is 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 a water-cooling pipe to the press-molding part 121.

[0029] 6 is a diagram showing an example of the shape of the core member 210. The length and width of the bottom surface of the core member 210 are 40 millimeters and 62 millimeters, respectively, and the height of the core member is 18 millimeters.

[0030] 7 is a diagram showing an example of the shape of an optical element 300. The 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 the additional portion 220 are 50 millimeters, 75 millimeters, and 2.5 millimeters, respectively. The height of the optical element 300 is 20.5 millimeters.

[0031] In this example, surface B' is a lens surface. The shape of the lens surface can be expressed by the following formula (1): where the unit of length is millimeters. z represents the coordinate in the direction of the central axis based on the vertex of the lens surface, r represents the distance from the central axis to a point on the surface, and A1-A4 represent coefficients.

[0032] Here, a conventional method for manufacturing an optical element will be described.

[0033] FIG. 8 is a flow chart illustrating a prior art method for manufacturing an optical element.

[0034] In step S2010 of FIG. 8, a core member 210' is manufactured as a primary molded product.

[0035] FIG. 9A is a perspective view of a core member 210' as a primary molded product.

[0036] FIG. 9B is a vertical cross-sectional view of the core member 210' as the primary molded product.

[0037] FIG. 9C is a cross-sectional view of the core member 210' as a primary molded product.

[0038] The length and width of the bottom surface of the primary molded product are 35 mm and 57 mm, respectively, and the height of the primary molded product is 15.5 mm.

[0039] 8, 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 manufacture a secondary molded product. An example of the mold used is the mold shown in FIG. 1 of Patent Document 1.

[0040] FIG. 10A is a perspective view of the secondary molded product.

[0041] FIG. 10B is a vertical cross-sectional view of the secondary molded product.

[0042] FIG. 10C is a cross-sectional view of the secondary molded product.

[0043] The length, width and height (thickness) of the additional portion 220' are 50 mm, 75 mm and 2.5 mm, respectively, and the height of the secondary molded product is 18 mm.

[0044] In step S2030 of FIG. 8, with the secondary molded product placed in the mold, an outer layer 230' is formed on the surface of the core member 210' opposite the bottom surface on which the additional portion 220' is formed, thereby producing a tertiary molded product.

[0045] FIG. 11A is a perspective view of the tertiary molded product.

[0046] FIG. 11B is a vertical cross-sectional view of the tertiary molded product.

[0047] FIG. 11C is a cross-sectional view of the tertiary molded product.

[0048] The length and width of the bottom surface of the portion of the third molded article covered with the outer layer 230' are 40 mm and 62 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' is 18 mm from the surface of the additional portion 220'. The height of the third molded article is 20.5 mm.

[0049] The width e of deviation 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. The vertices and central axes of the surface of the designed shape (hereinafter referred to as the design surface) and the surface of the measured shape (hereinafter referred to as the measurement surface) are aligned and superimposed. 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 the design surface is expressed by equation (1). r in equation (1) can be expressed by the following equation: Let P be a point on the design surface, and find the value obtained by subtracting the z coordinate of point P from the z coordinate of a point on the measurement surface that has the same (x, y) coordinate as point P. Find the above value for each point on the design surface. In the set of the above values ​​for points on the design surface, the difference between the maximum and minimum values ​​is taken as the range e of deviation from the design value.

[0050] The width e of the deviation of surface B of core member 210 shown in FIG. 6 is 595 micrometers. The width e of the deviation of surface B' of optical element 300 manufactured by the manufacturing method of the present invention shown in FIG. 7 is 75 micrometers. On the other hand, the width e of the deviation of surface B" of optical element 300' manufactured by the manufacturing method of the prior art shown in FIG. 11A is 104 micrometers. Therefore, when forming an aspherical lens surface as shown in formula (1), the width e of the deviation of surface B' of optical element 300 manufactured by the manufacturing method of the present invention is smaller than the width e of the deviation of surface B" of optical element 300' manufactured by the manufacturing method of the prior art.

[0051] The apparatus used in the manufacturing method of the present invention is, as shown in FIG. 1, merely a simple heater added to a normal mold, and does not require a press mechanism or the like.

[0052] On the other hand, the apparatus used in the conventional 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.

[0053] 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.

[0054] 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, A plastic core member is inserted into the cavity of the mold, which is surrounded by the surface C of the first part and the surface D of the second part facing surface C. This method involves injecting molten plastic into the space enclosed by surfaces A and C of the core member and forming a layer on surface A by injection molding, while simultaneously press-molding the surface B of the core member opposite to surface A against surface D, which is heated to a temperature higher than the glass transition temperature of the plastic of the core member, using the filling pressure of the molten plastic. A method for manufacturing an optical element, in which the surface of the optical element after press molding of surface B is called surface B', and the surface with the designed shape is called surface Bd, an xyz Cartesian coordinate system is defined with the vertices of each surface B, B', and Bd as the origin and the central axis as the z axis, and the value obtained by subtracting the z coordinate of point P from the z coordinate of the point on surface B or surface B' obtained by measurement at the (x,y) coordinate of surface B or surface B' corresponding to the (x,y) coordinate of point P on surface Bd, the difference between the maximum and minimum values ​​of the above set of values ​​is determined, this difference is called the deviation width of surface B or surface B', and the optical element is press molded so that the deviation width of surface B' is smaller than the deviation width of surface B.

2. 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.

3. The method for manufacturing an optical element according to claim 1, wherein the temperature of surface B is 30 degrees or more higher than the glass transition temperature of the plastic of the core member.

4. The method for manufacturing an optical element according to claim 1, wherein the maximum value of the filling pressure is in the range of 30 megapascals to 100 megapascals.

5. The method for manufacturing an optical element according to claim 1, wherein the shape of the second surface is aspherical.