Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
  • B29C45/14—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
  • B29C45/16—Making multilayered or multicoloured articles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
  • B29D11/00—Producing optical elements, e.g. lenses or prisms
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
  • B29L2011/00—Optical elements, e.g. lenses, prisms

Definitions

• the present invention relates to a method for manufacturing optical elements.
• Optical elements include lenses, diffraction gratings, prisms, and microlens arrays.
• 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.
• the thicker the molded product the longer the cooling time, which reduces production efficiency.
• the mold temperature needs to be relatively high to maintain high shape precision, so the cooling time has a particularly large impact on production efficiency.
• the core member must be fixed in a mold and the thin layer molding steps must usually be carried out separately on both sides of the core member. This requires a complex mechanism for the mold and associated equipment.
• the technical objective of the present invention is to provide a manufacturing method that can efficiently produce high-precision optical elements using simple equipment.
• the method for manufacturing an optical element of the present invention uses a mold having a first portion and a second portion.
• a plastic core member is inserted into 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 then poured into the space formed by the surface including surface A of the core member and surface C of the first portion to form a layer on surface A by injection molding.
• the filling pressure of the molten plastic presses 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, thereby performing press molding.
• the surface of the optical element is formed by pressing surface B of the core member against 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 producing a highly accurate optical element.
• surface A of the core member is formed on surface A of the core member by injection molding
• surface B of the core member is press-molded using the filling pressure of the molten plastic, making it possible to efficiently manufacture high-precision optical elements using relatively simple equipment.
• the temperature of surface B is at least 30 degrees higher than the glass transition temperature of the plastic of the core member.
• the maximum value of the filling pressure is in the range of 30 MPa to 100 MPa.
• the shape of the second surface is aspherical.
• FIG. 1A and 1B are diagrams showing an example of a mold used in the manufacturing method of an optical element of the present invention.
• 3 is a flowchart illustrating a method for manufacturing an optical element according to the present invention.
• FIG. 2 shows a core member installed in a cavity between a first portion and a second portion of a mold.
• 10 is a diagram showing a state in which molten plastic is poured into the space between surface C of the first portion 110 and surface A of the core member.
• FIG. 5 is a diagram showing the state after press molding using the filling pressure of the molten plastic is performed.
• FIG. 10 is a diagram showing an example of the shape of a core member.
• FIG. 2 is a diagram illustrating an example of the shape of an optical element.
• FIG. 1 is a flow chart illustrating a prior art method for manufacturing an optical element.
• FIG. 2 is a perspective view of a core member as a primary molded product.
• FIG. 2 is a longitudinal cross-sectional view of a core member as a primary molded product.
• FIG. 2 is a cross-sectional view of a core member as a primary molded product.
• FIG. 2 is a longitudinal cross-sectional view of a secondary molded product.
• FIG. 2 is a cross-sectional view of a secondary molded product.
• FIG. 1 is a perspective view of a tertiary molded product.
• FIG. 1 is a longitudinal cross-sectional view of a tertiary molded product.
• FIG. 1 is a cross-sectional view of a tertiary molded product.
• FIG. 1 shows an example of a mold used in the method for manufacturing an optical element of the present invention.
• the mold comprises a first part 110 and a second part 120 that face each other and are configured to form a cavity therebetween.
• the second part 120 comprises a press-molding part 121 equipped with a heater 123, and an outer part 127 that surrounds the press-molding part 121.
• the press-molding part 121 and the outer part 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 in the form of a sheet made of, for example, glass cloth.
• the press-molding part 121 and the heat insulating material 125 are configured to be stored in the outer part 127.
• Figure 2 is a flow chart illustrating the method for manufacturing optical elements of the present invention.
• the core member 210 is molded.
• the core member 210 may be made of plastic and molded by injection molding, for example.
• step S1020 of Figure 2 the core member 210 is placed in the cavity of the mold shown in Figure 1.
• Figure 3 shows a core member 210 installed in a cavity between the first part 110 and the second part 120 of the mold.
• the core member 210 has a surface A and an opposite surface B.
• the core member 210 may be fixed to the outer part 127 by a plunger (not shown) or the like.
• a space 115 is formed between surface C of the first part 110 and surface A of the core member 210.
• step S1030 of Figure 2 molten plastic is poured into the space 115 between surfaces C and A to form a layer on surface A of core member 210 by injection molding, while the filling pressure of the molten plastic presses surface B, the side of core member 210 opposite surface A, 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, 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'.
• Figure 4 shows the 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.
• the filling pressure of the molten plastic presses surface B of the core member 210 opposite surface A against surface D of the mold, which 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.
• Figure 5 shows the state after press molding using the filling pressure of molten plastic has been performed.
• Surface B' has been formed by transferring the shape of surface D of the mold to the core member through press molding.
• Table 1 shows an example of conditions for the method of manufacturing an optical element of the present invention.
• 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.
• the material of the core member and the material of the layer formed by injection molding are the same.
• the material of the core member may be different from the material of the layer formed by injection molding.
• a material such as PC (polycarbonate), which has a relatively high glass transition temperature may be used as the material of the core member.
• step S1040 of Figure 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.
• step S1050 of Figure 2 the molded product is removed from the mold. After the molded product is removed from the mold, heating by heater 123 begins for the next molding process.
• the above cooling time for the press-molding portion 121 and molded product falls within the time required to solidify the molten plastic in the layer formed by injection molding on surface A, and therefore does not affect the molding time. If necessary, the above cooling time can be shortened by providing water-cooling piping in the press-molding portion 121.
• Figure 6 shows 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.
• the height of the core member is 18 millimeters.
• Figure 7 shows an example of the shape of optical element 300.
• Optical element 300 consists of a portion 215 that corresponds to the 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 50 millimeters, 75 millimeters, and 2.5 millimeters, respectively.
• the height of optical element 300 is 20.5 millimeters.
• 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.
• Figure 8 is a flow chart illustrating a conventional method for manufacturing optical elements.
• step S2010 of Figure 8 the core member 210' is manufactured as a primary molded product.
• Figure 9A is a perspective view of the core member 210' as a primary molded product.
• Figure 9B is a vertical cross-sectional view of the core member 210' as a primary molded product.
• Figure 9C is a cross-sectional view of the core member 210' as a primary molded product.
• the length and width of the bottom surface of the primary molded product are 35 millimeters and 57 millimeters, respectively.
• the height of the primary molded product is 15.5 millimeters.
• step S2020 of Figure 8 the core member 210' serving as the 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 Figure 1 of Patent Document 1.
• Figure 10A is a perspective view of the secondary molded product.
• Figure 10B is a vertical cross-sectional view of the secondary molded product.
• Figure 10C is a cross-sectional view of the secondary molded product.
• 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 secondary molded product is 18 millimeters.
• step S2030 of Figure 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.
• Figure 11A is a perspective view of the tertiary molded product.
• Figure 11B is a vertical cross-sectional view of the tertiary molded product.
• Figure 11C is a cross-sectional view of the tertiary molded product.
• the length and width of the bottom surface of the portion of the tertiary molded product covered with outer layer 230' are 40 millimeters and 62 millimeters, respectively.
• the thickness of outer layer 230' is 2.5 millimeters, and the height of the portion of the tertiary molded product covered with outer layer 230' is 18 millimeters from the surface of additional portion 220'.
• the height of the tertiary molded product is 20.5 millimeters.
• 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.
• the width of deviation e of surface B of core member 210 shown in Figure 6 is 595 micrometers.
• the width of deviation e of surface B' of optical element 300 manufactured by the manufacturing method of the present invention shown in Figure 7 is 75 micrometers.
• the width of deviation e of surface B" of optical element 300' manufactured by the manufacturing method of the prior art shown in Figure 11A is 104 micrometers. Therefore, when forming an aspherical lens surface as shown in equation (1), the width of deviation e of surface B' of optical element 300 manufactured by the manufacturing method of the present invention is smaller than the width of deviation e of surface B" of optical element 300' manufactured by the manufacturing method of the prior art.
• the equipment used in the manufacturing method of the present invention simply adds a simple heater to a regular mold and does not require a press mechanism or the like.
• the apparatus used in the conventional manufacturing method is equipped with a complex mechanism for carrying out two molding steps to form thin layers on both sides of the core member while the core member is fixed in a mold.
• the manufacturing method of the present invention makes it possible to efficiently manufacture optical elements with high precision equal to or greater than that of conventional technology using equipment simpler than that of conventional technology.

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• Health & Medical Sciences (AREA)
• Ophthalmology & Optometry (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)

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