JP2010082838A - Lens manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens manufacturing method capable of transferring uniformly step difference structure on a lens at a high transfer rate, over the whole area, and capable of making precise a macroscopic surface shape of the lens. <P>SOLUTION: An injection rate of a resin is brought into 1.2 cm<SP>3</SP>/sec or more when filling a cavity CV, and the resin is thereby prevented from being solidified under the condition where the resin is not filled sufficiently into micro-fine structure SS corresponding to the ring-band-like step difference structure over the whole of the cavity CV. A transfer rate and lens transmission luminous energy are thereby restrained from getting low over the whole of a diffraction pattern FP. Surface shape precision is also enhanced in macroscopic view of the lens OL, by bringing the injection rate into 30 cm<SP>3</SP>/sec or less, while filling an inside of the cavity CV moderately to prevent a transfer rate of the diffraction pattern FP from getting low ununiformly. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lens manufacturing method for performing injection molding by injecting a resin into a cavity formed by a pair of molds.

  As a conventional lens manufacturing method, in order to mold a high-precision plastic lens with a short cycle time, a mold having a ceramic score having a lower thermal conductivity than that of general stainless steel is used, and the mold internal temperature is set to a resin level. Some have a temperature of 5 to 20 ° C. lower than the glass transition point Tg (see Patent Document 1).

  As another lens manufacturing method, in order to produce a high-precision diffractive lens with high transferability, a mold in which the thermal conductivity of a core material having a fine structure is set to 20 W / mK or less, and this core is compared. Some use a metal mold coated with high thermal conductivity (see Patent Document 2).

Yet another lens manufacturing method is a mold in which a surface processing layer having a fine shape is formed on a heat insulating layer of a ceramic material in order to transfer a diffractive lens structure to a molded body with high accuracy. Some use a mold having a conductivity of 10 W / mK or less and a thickness of 0.1 to 3 mm (see Patent Document 3).
Japanese Patent Laid-Open No. 5-200789 JP 2004-284110 A JP2002-96335

  The present inventor relates to a compatible objective lens that is shared for recording or reproduction on a plurality of recording media such as a BD (Blu-Ray Disc) and a DVD (Digital Versatile Disc), and has an annular shape on an aspheric surface. He has been involved in the development of diffractive lenses with a step structure. For such a diffractive lens with a ring-shaped step structure, a side gate that injects resin from the side surface along the parting line into a cavity formed with the fixed mold and movable mold clamped for ease of molding. The method is adopted. At this time, a technique is used in which a heat insulating layer is provided on the core of a mold having a diffractive lens structure to improve transferability.

  As a result of trying various molding conditions in the course of development of a diffractive lens using the side gate type molding method as described above, the present inventor has ensured uniform transferability of the diffractive structure of the diffractive lens and reduced the amount of transmitted light. It was confirmed that it was not easy to suppress the decrease. As a result of intensive studies on the non-uniformity of transferability of the diffractive structure and the reduction in transmitted light, the present inventor has found that such characteristic deterioration is related to the injection rate of the resin.

  Specifically, when the above-described side gate molding method is used, the direction in which the resin easily flows into the step structure as viewed from the gate into which the resin flows (that is, the direction perpendicular to the gate; the resin flow direction is the extension of the step structure) And a direction in which the resin hardly flows into the step structure (that is, a gate direction; a direction in which the resin flow direction is substantially orthogonal to the extending direction of the step structure). The present inventor considered that there is a tendency that transferability is relatively deteriorated with respect to the gate direction in forming the diffractive lens. That is, in the gate direction of the diffractive lens, it is considered that the step structure is solidified in a state where the resin does not enter, and the transfer rate of the step structure is locally insufficient. When the transfer of the step structure is insufficient, light diffraction and refraction in the step structure are not manifested as designed, and scattered light is generated, so that the amount of transmitted light that contributes to image formation is reduced.

In the method of Patent Document 1, since the injection rate is too low at 1 cm ³ / sec or less, even if a step structure is provided on the surface of the core having low thermal conductivity, the amount of heat of the fluid resin is easily lost. The viscosity of the resin will increase. Therefore, the resin is solidified in a state where the resin does not enter the entire step structure, and the overall transfer rate of the step structure on the lens becomes insufficient, and there is a possibility that the transmitted light amount of the lens may be low. It is done.

  In the methods of Patent Documents 2 and 3 above, the transferability of the ring-shaped step structure on the diffractive lens can be improved as a whole, but if the injection rate at the time of filling the cavity is too low, the flow into the ring-shaped step structure It is considered that solidification begins to occur before the resin enters, and the resin is solidified in a state where the resin does not enter the entire step structure, resulting in insufficient transfer of the step structure and a decrease in the amount of light transmitted through the lens. On the other hand, if the injection rate at the time of filling the cavity is too high, the inertia in the flow line direction of the fluid resin itself becomes strong, so it is easy to jump over without filling the groove of the step structure in the gate direction, and the step structure is transferred. The transfer rate in the gate direction is relatively inferior, and the amount of transmitted light through the lens is considered to be lower than when the transfer is uniformly performed over the whole. In addition, it may be difficult to obtain surface shape accuracy on both sides of the lens when the lens is viewed macroscopically.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a lens manufacturing method that can uniformly transfer a step structure on a lens over the entire area and that can highly accurately make a macroscopic surface shape of the lens.

In order to solve the above problems, a lens manufacturing method according to the present invention is a lens manufacturing method in which a lens having a ring-shaped step structure is injection-molded by injecting a resin into a cavity formed by a pair of molds. And at least one metal mold | die which has a transfer surface corresponding to a ring zone-shaped level | step difference structure among a pair of metal mold | dies is the heat insulation formed with the low heat conductive material which has a heat conductivity of 10 W / m * K or less. A transfer portion on the transfer surface side, injecting resin into the cavity from the outer peripheral side surface of the cavity, and setting the injection rate of the resin when filling the cavity to 1.2 cm ³ / sec or more and 30 cm ³ / sec or less Features. In the above, the time when the cavity is filled refers to the time from when the resin flow front passes through the gate which is the entrance of the cavity to the time when the cavity is filled with the resin. It refers to the volume of resin that the plasticizing mechanism injects per unit time. Further, the heat insulating part includes both a case where the mold base is itself and a case where the heat insulating portion is provided as a heat insulating layer on the mold base. In addition, when a metal mold | die is comprised with several metal mold members, such as a core part and an outer periphery type | mold, a heat insulation part is provided with respect to the metal mold | die base material of the core part which has a transfer surface for transferring the optical surface of a lens. Can be provided.

In the above lens manufacturing method, at least one mold has a heat insulating part formed of a low thermal conductive material having a thermal conductivity of 10 W / m · K or less on the transfer surface side, so that the fluid resin introduced into the cavity Can be gradually cooled to a desired level without being rapidly cooled, and this can contribute to an improvement in the transferability of the concave-convex shape constituting the annular zone-shaped step structure of the lens while preventing an increase in molding cycle time. At this time, since the injection rate of the resin at the time of filling the cavity is set to 1.2 cm ³ / sec or more, it is possible to prevent the resin from solidifying in a state where the resin does not sufficiently enter the step structure over the entire cavity. As a result, it is possible to suppress a decrease in the overall transfer rate of the step structure and a decrease in the amount of light transmitted through the lens. Further, since the injection rate of the resin at the time of filling the cavity is set to 30 cm ³ / sec or less, the resin was introduced into the cavity in the gate direction of the lens (the direction in which the resin flow direction is orthogonal to the direction in which the step structure extends). It is possible to prevent the transfer resin from jumping over without filling the groove of the step structure and causing the transfer rate to be relatively deteriorated in a specific gate direction. As a result, it is possible to suppress non-uniformity in the transfer rate of the step structure that is biased in a specific direction on the lens and a decrease in the amount of transmitted light through the lens. Further, by setting the injection rate to 30 cm ³ / sec or less, the cavity can be filled gently, and the surface shape accuracy when the lens is viewed macroscopically can be improved. In other words, even when molding a lens having a fine annular zone-shaped step structure, it achieves more uniform transferability, and a uniform light quantity distribution of transmitted light when the lens is irradiated with light, and good wavefront aberration. The lens which has can be obtained. Furthermore, for example, when diffracted light with a ring-shaped step structure is used, the amount of light transmitted through the lens can be further increased, for example, the diffraction efficiency can be improved.

  In a specific aspect or viewpoint of the present invention, in the lens manufacturing method, at least one mold has a surface processed layer provided on the heat insulating portion. In this case, a desired step structure can be formed with high accuracy on the transfer surface of the mold. The surface processed layer is a layer for providing a concavo-convex shape constituting a step structure, and refers to a layer whose surface is processed into a desired shape with a diamond bit after coating a plating layer or the like. On the surface of the transfer surface, a protective layer or a release layer may be further provided on this surface processed layer.

  In another aspect of the present invention, the heat insulating portion is formed of 6-4Ti and has a thickness of 3 mm or more. In this case, the heat insulating part can be easily processed and incorporated into the mold.

  In still another aspect of the present invention, the heat conductivity of the heat insulating portion is 3 W / m · K or less. In this case, the transferability of the step structure can be improved.

  In still another aspect of the present invention, the heat insulating portion is formed of zirconia ceramics and has a thickness of 0.1 mm or more. In this case, the transferability of the step structure can be improved.

  In still another aspect of the present invention, the heat insulating portion is formed by thermal spraying. In this case, it is easy to cope with various mold shapes.

  In still another aspect of the present invention, the internal temperature of the pair of molds when the resin is injected into the cavity is −3 ° C. or higher and + 5 ° C. or lower with respect to the glass transition point. In this case, since the resin is introduced into the cavity with an appropriate viscosity, not only can the transfer rate be improved, but the resin is not rapidly cooled, so that birefringence is reduced.

In still another aspect of the present invention, the injection rate of the resin when filling the cavity is 1.2 cm ³ / sec or more and 27 cm ³ / sec or less. In this case, more uniform transfer is possible in the gate direction and the gate orthogonal direction, and the macroscopic surface shape accuracy can be further improved.

  In still another aspect of the present invention, the pressure of the cavity at the time of filling the cavity is 0.05 MPa or more lower than the atmospheric pressure. In this case, not only the overall transfer rate of the lens can be improved, but also a uniform transfer can be secured, and appearance defects such as weld lines can be reduced.

In still another aspect of the present invention, the resin injected into the cavity is a cycloolefin resin, and the injection rate of the cycloolefin resin at the time of filling the cavity is 2.5 cm ³ / sec or more and 24.5 cm ³ / sec. It is as follows. In this case, birefringence over the entire lens can be reduced, and appearance defects such as flow marks and jetting can be reduced, and good optical characteristics can be obtained.

In still another embodiment of the present invention, the injection rate of the resin when filling the cavity is 17 cm ³ / sec or more and 24.5 cm ³ / sec or less. In this case, even with an optical pickup objective lens having an NA of 0.8 or more, appearance defects such as weld lines can be further reduced.

[First Embodiment]
The lens manufacturing method according to the first embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is a front view for explaining an injection molding machine 10 for carrying out the lens manufacturing method of the present embodiment. The injection molding machine 10 includes a side gate type molding die 40 including a fixed die 41 as a first die and a movable die 42 as a second die. Injection molding is performed by injecting resin from the side of the fixed mold 41 to produce a molded product having a plurality of diffraction lenses.

  The injection molding machine 10 includes a fixed platen 11, a movable platen 12, an opening / closing drive device 15, an injection device 16, a temperature adjustment device 18, a decompression device 19, and a control device 20. The injection molding machine 10 sandwiches a fixed mold 41 and a movable mold 42 between the movable platen 12 and the fixed platen 11 and clamps both the molds 41 and 42 to mold space, that is, a cavity CV (FIG. 2) and enables injection molding using the cavity CV. Here, in the injection molding machine 10, the mold opening and closing of the molding die 40 are in the horizontal direction, that is, the horizontal direction. The molding die 40 can be incorporated into an injection molding machine that opens and closes in the vertical direction.

  The fixed platen 11 is fixed to the upper surface on the center side of the support frame 14, and the inside of the fixed platen 11 detachably supports the fixed mold 41. The movable platen 12 is supported by an opening / closing drive device 15 to be described later so as to be capable of moving forward and backward. Inside the movable platen 12, a movable mold 42 is detachably supported. In addition, an ejector 45 is incorporated in the movable platen 12. The ejector 45 is for extruding a molded product remaining in the movable mold 42 when the mold is opened from the movable mold 42 to the fixed mold 41 side.

  The opening / closing drive device 15 includes a linear guide 15a, a power transmission unit 15d, and an actuator 15e. The linear guide 15 a supports the movable platen 12 and enables the movable platen 12 to smoothly reciprocate with respect to the advancing and retreating direction with respect to the fixed platen 11. The power transmission unit 15d expands and contracts in response to the driving force from the actuator 15e. As a result, the movable platen 12 can be freely displaced toward and away from the mold clamping plate 13, and as a result, the movable platen 12 and the fixed platen 11 can be closed so as to be close to each other. Both can be clamped with a desired clamping force.

  The injection device 16 includes a cylinder 16a, a raw material storage unit 16b, a screw 16c, a resin injection end 16d, and a drive unit 16e. The injection device 16 can discharge the molten resin from the nozzle-shaped resin injection end 16d in a state in which the temperature is controlled to be higher than the mold temperature. The injection device 16 can detachably connect the resin injection end 16d of the cylinder 16a to the sprue portion SP (see FIG. 2) of the fixed mold 41 via the fixed platen 11, and is movable with the fixed mold 41. The molten resin can be supplied at a desired timing into the cavity CV formed with the mold 42 being clamped.

  The temperature adjusting device 18 is connected to both molds 41 and 42 constituting the molding die 40, and circulates a heating medium in a flow path formed adjacent to the cavity in both molds 41 and 42. By doing so, the temperatures of both molds 41 and 42 are appropriately maintained during molding including closing and clamping of both molds 41 and 42.

  The decompression device 19 is connected to the movable mold 42 side of the molding die 40 and has a desired cavity CV (see FIG. 2) formed in the clamping mold 40 in a clamped state compared to the atmosphere. The pressure can be reduced to an extent.

  The control device 20 includes an injection device control unit 22, an opening / closing control unit 25, a decompression control unit 26, and an ejector control unit 27.

The injection device control unit 22 operates the drive unit 16e and the like to heat and melt the resin introduced into the cylinder 16a from the raw material storage unit 16b to an appropriate viscosity, and is formed between both molds 41 and 42. Molten resin is supplied into the cavity CV (see FIG. 2) at a desired injection rate. That is, the amount and temperature of extrusion of the resin by the drive unit 16e can be adjusted under the control of the injection device control unit 22. Specifically, the injection rate of the resin when filling the cavity CV is 1.2 cm ³ / sec. It is 30 cm ³ / sec or more and preferably 1.2 cm ³ / sec or more and 27 cm ³ / sec or less. As a result, the step structure formed on the transfer surfaces of both molds 41 and 42 can be transferred uniformly and sufficiently over the entire surface. The resin injected by the injection device 16 and supplied into the cavity CV of the molding die 40 is, for example, a cycloolefin resin in which birefringence hardly occurs. In this case, the injection rate of the resin when filling the cavity CV is preferably 2 It is set to ⁵ cm ³ / sec or more and 24.5 cm ³ / sec or less.

  The injection device control unit 22 keeps the resin at a necessary temperature by extending the cylinder 16a when the resin is plasticized by appropriately energizing a heater formed around the cylinder 16a, for example.

  The mold temperature control unit 24 operating under the control of the control device 20 appropriately keeps the internal temperatures of the molds 41 and 42 during molding by appropriately operating the temperature adjusting device 18. Specifically, under the control of the mold temperature control unit 24, at the time of molding, for example, at the time of filling the cavity CV (see FIG. 2), the internal temperature of the molding die 40 is −3 ° C. or more with respect to the glass transition point of the resin. + 5 ° C or less. As a result, the resin introduced into the cavity CV comes into contact with the transfer surface with an appropriate viscosity, and the resin solidifies slowly without being rapidly cooled.

  The opening / closing control unit 25 controls the operation of the opening / closing drive device 15 and adjusts the opening / closing timing and the mold clamping force of both molds 41, 42.

  The decompression control unit 26 adjusts the pressure in the cavity CV (see FIG. 2) formed between the molds 41 and 42 during molding by appropriately operating the decompression device 19. Specifically, under the control of the decompression control unit 26, during the molding, for example, before the filling of the cavity CV of the molding die 40 is started, the inside of the cavity CV is maintained at a state lower than the atmospheric pressure by 0.05 MPa or more. The replacement of the space in the cavity CV with the resin is facilitated.

  The ejector control unit 27 controls the operation of the ejector 45 incorporated in the movable platen 12. When the mold is opened, a molded product remaining in one movable mold 42 is pushed out from the movable mold 42 and released. The molded product having the diffractive lens can be carried out of the injection molding machine 10.

  FIG. 2 is a side sectional view for explaining the structure of the molding die 40. 3A to 3C are enlarged sectional views around the cavity, and FIG. 4 is a side sectional view of the lens OL molded by the molding die 40 shown in FIG.

  As shown in FIG. 2, the fixed mold 41 and the movable mold 42 constituting the molding mold 40 can be opened and closed with a parting line PL as a boundary. A plurality of cavities CV for molding the lens OL shown in FIG. 4 are formed by mold-clamping the fixed mold 41 and the movable mold 42 and supplying resin to each cavity CV. A flow path portion FC is formed. The flow path portion FC includes a sprue portion SP, a runner portion RP, and a gate portion GP. Here, the gate portion GP is a resin introduction path that opens to the outer peripheral side surface of the cavity CV, but has a smaller cross-sectional area than the runner portion RP. Although details are omitted in the drawing, the molded product injection-molded by the molding die 40 includes a plurality of lenses OL, and the resin filling space corresponding to the molded product has an axial sprue. A plurality of runner portions RP diverge radially from the portion SP, and a cavity CV communicates with the tip of each branched runner portion RP via a gate portion GP. The gate portion GP is provided with a decompression slit communicating with the decompression device 19, an opening with a valve, and the like, so that the inside of the cavity CV can be decompressed immediately before injection.

  As shown in FIG. 3A, the cavity CV, which is a space between the molds 41 and 42, corresponds to the shape of the lens OL (see FIG. 4 and the like) that is the main body portion of the molded product. ing. The lens OL includes a center portion OLa as an optical function portion having an optical function, and an annular flange portion OLb extending from the center portion OLa in the outer diameter direction. This lens OL is an objective lens for an optical pickup device, is compatible with BD, DVD, and CD, and satisfies NA 0.85 with respect to a light beam having a wavelength for BD.

  The fixed die 41 includes a core portion 52 as a nesting on the fixed side, an outer peripheral die 51 having a structure capable of supporting and fixing the nesting on the fixed side, and the outer peripheral die 51 and the core portion 52. And a receiving plate (not shown) fixed integrally.

  The outer periphery mold | type 51 has the end surface 51a which forms the parting line PL of FIG. Further, a flange forming part FF is provided at the tip of the outer peripheral mold 51, and a molding surface 56b for defining the cavity CV is formed on the surface of the flange forming part FF. The molding surface 56b is a transfer surface that molds the flange surface F1 of the flange portion OLb of the lens OL. In addition, a core insertion hole 55 that is a cylindrical through hole for inserting and supporting the core portion 52 is formed in the outer peripheral mold 51.

  The core portion 52 has a cylindrical outer peripheral side surface that can be fitted into the core insertion hole 55, and an optical surface for defining a cavity CV is provided at the distal end surface provided at the distal end portion 52 b of the core portion 52. A molding surface 56a is provided. The optical surface molding surface 56a is a concave surface and is a transfer surface for molding one optical surface Sa of the center portion OLa of the lens OL.

  In the fixed mold 41 described above, the outer peripheral mold 51 has a high thermal conductivity material having a thermal conductivity higher than 10 W / m · K, for example, pre-hardened steel, that is, low carbon steel (thermal conductivity: 60.0 W / m · K). Etc. Moreover, the core part 52 is also comprised with the high heat conductive material whose heat conductivity is larger than 10 W / m * K, specifically, the base material of low carbon steel or stainless steel. The end surface of the core portion 52 on the cavity CV side can be covered with a nickel phosphorous plating layer formed by using an electroless nickel plating method, and the optical surface molding surface 56a is formed by this nickel phosphorous plating layer. Can do. Further, the optical surface molding surface 56a can be coated with a thin release film formed of a resin material.

  The movable mold 42 projects a core portion 62 as a movable core mold, an outer peripheral mold 61 having a structure capable of supporting and fixing the movable core mold integrally, and a molded product OL. A movable pin 64 as an extruding member to be released, a receiving plate (not shown) for integrally fixing the outer peripheral die 61 and the core 62, and a transmission mechanism (not shown) that allows the movable pin 64 to move forward and backward. Is provided. The movable mold 42 can be reciprocated along the axis AX by the opening / closing drive device 15 of FIG.

  In addition, the outer periphery type | mold 61 is comprised by the high heat conductive material in which heat conductivity is larger than 10 W / m * K, for example, prehardened steel, ie, low carbon steel. On the other hand, the core portion 62 is made of a lower heat conductive material than the outer peripheral die 61. The base material of the core part 62, that is, the low thermal conductivity material constituting the base material has a thermal conductivity of 0.05 W / m · K or more and 10 W / m · K or less, for example, 6-4Ti is used as the base material. be able to.

  The outer peripheral mold 61 has an end face 61a that forms the parting line PL of FIG. In addition, a core insertion hole 65 for inserting and supporting the core portion 62 and a pin insertion hole 65b for inserting and supporting the movable pin 64 are formed in the outer peripheral mold 61. Here, the core insertion hole 65 is a columnar through hole, and the pin insertion hole 65b is a smaller diameter through hole. A flange forming portion FM is provided at the tip of the outer peripheral mold 61, and a molding surface 66b for defining the cavity CV is formed on the surface of the flange forming portion FM. The molding surface 66b is a transfer surface for molding the flange surface F2 of the flange portion OLb of the lens OL, that is, one annular end surface.

  The core part 62 itself functions as a heat insulating part that prevents rapid cooling of the resin during injection. The core portion 62 has a cylindrical outer peripheral side surface that can be fitted into the core insertion hole 65, and an optical surface for defining a cavity CV is provided on the distal end surface provided at the distal end portion 62 b of the core portion 62. A molding surface 66a is provided. The optical surface molding surface 66a is a concave surface and is a transfer surface for molding one optical surface Sb of the center portion OLa of the lens OL. The optical surface molding surface 66a has a fine structure SS corresponding to a ring-shaped step structure, and forms a diffraction pattern FP corresponding to the ring-shaped step structure on the optical surface Sb of the central portion OLa. The end surface on the cavity CV side of the core portion 62 is covered with a nickel phosphorous plating layer 67 formed by using an electroless nickel plating method in order to improve machinability. By processing, an optical surface molding surface 66 a including the microstructure SS is formed as the surface of the nickel phosphorus plating layer 67. Furthermore, the optical surface molding surface 66a can be coated with a thin release film formed of a resin-based material.

  The movable pin 64 is inserted into the pin insertion hole 65b, and is movable along the axis AX within the pin insertion hole 65b. That is, the movable pin 64 is driven by the ejector 45 in FIG. 1 via a transmission mechanism (not shown), and moves forward or backwards in the pin insertion hole 65b of the outer peripheral die 61 toward the fixed die 41. can do. The tip of the pin insertion hole 65b constitutes a part of the molding surface 66b that defines the cavity CV. Four movable pins 64 are arranged at equal intervals along the annular molding surface 66b of the outer peripheral die 61, and the flange portion OLb of the lens OL can be pushed out along the axis AX with good balance.

  Note that the number of movable pins 64 is not limited to four, but may be various three or more according to specifications such as the size of the lens OL and allowable accuracy. Further, the core portion 62 can be used in place of the movable pin 64 and the center portion OLa of the lens OL can be directly pushed out of the movable mold 42.

  FIG. 5 is an enlarged cross-sectional view illustrating the resin injection end 16d of the cylinder 16a provided in the injection device 16 and the internal structure around it. The resin injection end 16d has a nozzle hole 81, and the resin heated to a desired temperature can be discharged from the nozzle hole 81 at a desired injection rate by operating the screw 16c inserted into the cylinder 16a. it can. A head 82 is attached to the tip of the screw 16c. A check ring 84 is provided between the head 82 and the screw main body 83 to allow the resin to be sent out to the front of the head 82, while the resin sent out to the front of the head 82 is the screw main body. The return to the 83 side is prevented.

The injection device 16 stores molten resin suitable for injection in front of the head 82 in the cylinder 16a by rotating the screw 16c at an appropriate speed while supplying the resin into the cylinder 16a. When the molten resin is injected, that is, the resin injection end 16d is hermetically connected to the end portion FCa of the flow path portion FC provided in the fixed mold 41 shown in FIG. 2, and the flow path portion FC and the cavity CV are connected. The screw 16c is advanced in a state where the pressure is moderately reduced. The forward speed of the screw 16c at this time is V [cm / sec], the cross-sectional area determined by the inner diameter (barrel inner diameter) of the cylinder 16a is A [cm ² ], and the injection rate IR of the molten resin is V × A [cm ³ / sec]. That is, the injection rate IR can be arbitrarily set by the forward speed V of the screw 16c.

  FIG. 6 is a schematic diagram showing how the cavity CV shown in FIG. 2 and the like is filled with molten resin. With the start of resin filling, the molten resin MP is injected into the cavity CV through the gate portion GP. The molten resin MP gradually fills the cavity CV so as to spread uniformly from the position of the gate portion GP. At this time, the molten resin MP on the center side moves so as to pass through the center of the cavity CV along the gate direction D1, and crosses the groove of the ring-shaped microstructure SS formed on the surface of the core portion 62 at that time. Flowing. On the other hand, the molten resin MP on the peripheral side moves along the periphery of the cavity CV, and flows along the groove of the ring-shaped microstructure SS formed on the surface of the core portion 62 at that time. That is, in the cavity CV, the ring-shaped microstructure SS in the gate direction D1 flows and fills so that the resin traverses, and the ring-shaped microstructure SS in the gate orthogonal direction D2 flows and fills along the resin. The As described above, since the ring-shaped microstructure SS is filled in different flow states with respect to the gate direction D1 and the gate orthogonal direction D2, the transfer rate of the microstructure SS, that is, the uniformity of the shape accuracy of the diffraction pattern FP on the lens OL is ensured. In view of the above, it is very important to control the injection rate IR. By appropriately setting the injection ratio IR of the resin, the diffraction pattern on the lens OL obtained can be obtained even if the filling process of the grooves constituting the ring-shaped microstructure SS is different between the gate direction D1 and the gate orthogonal direction D2. The FP can be made substantially uniform, and a local decrease in the amount of light transmitted through the lens OL can be suppressed. Further, the surface shape accuracy of the optical surfaces Sa and Sb when the lens OL is viewed macroscopically can be improved.

  FIG. 7 is a flowchart for explaining the outline of the method for manufacturing the objective lens OL using the molding apparatus shown in FIG. First, the fixed mold 41 and the movable mold 42 are heated to a temperature suitable for molding by a mold temperature controller (not shown) (step S10). Thereby, the temperature of the surface of the metal mold | die part which forms the cavity CV in both metal mold | dies 41 and 42, or its vicinity is made into the temperature state suitable for shaping | molding.

  Next, the opening / closing drive device 15 is operated to advance the movable mold 42 toward the fixed mold 41 to start the mold closing (step S11). By continuing the closing operation of the opening / closing drive device 15, the mold is brought into a closed state in which the fixed mold 41 and the movable mold 42 are in contact with each other. By further continuing the closing operation of the opening / closing drive device 15, Clamping is performed to clamp the movable mold 42 with a necessary pressure (step S12).

  Next, by operating an injection device (not shown), the molten resin is required via the gate portion GP or the like in the cavity CV formed between the fixed mold 41 and the movable mold 42 that are clamped. Injection is performed at a pressure and an injection rate (step S13). At this time, the decompression device 19 is operated as appropriate so that the inside of the cavity CV is decompressed to a desired degree in comparison with the atmosphere in advance.

  After the molten resin is introduced into the cavity CV, the molten resin in the cavity CV is gradually cooled by heat dissipation, so that it waits for the molten resin to solidify and complete molding with the cooling (step S14).

  Next, the opening / closing drive device 15 is operated to retract the movable mold 42 and perform mold opening to separate the movable mold 42 from the fixed mold 41 (step S15). As a result, the objective lens OL as a molded product is released from the fixed mold 41 while being held by the movable mold 42.

  Next, the ejector 45 is operated to project the objective lens OL by the ejection pin 64 (step S16). As a result, the objective lens OL is urged against the distal end surface of the protruding pin 64 and pushed toward the fixed mold 41, and the objective lens OL is released from the movable mold 42.

  The objective lens OL released from both molds 41 and 42 is carried out of the molding apparatus by gripping a sprue portion or the like extending from the gate portion (not shown) of the objective lens OL (step). S17). Further, the objective lens OL after being carried out is subjected to external processing such as removal of the gate portion to be a product for shipment.

According to the lens manufacturing method of the first embodiment described above, one movable mold 42 has an optical surface molding surface 66a formed of a core portion 62 formed of a low thermal conductive material having a thermal conductivity of 10 W / m · K or less. Therefore, the fluid resin introduced into the cavity CV can be gradually cooled to a desired level without being rapidly cooled, and an annular shape provided in the lens OL is prevented while preventing an increase in molding cycle time. This can contribute to improvement in transferability of the diffraction pattern FP as a step structure. At this time, since the injection rate of the resin at the time of filling the cavity CV is set to 1.2 cm ³ / sec or more, the resin cannot sufficiently enter the groove of the fine structure SS corresponding to the ring-shaped step structure over the entire cavity CV. It can be prevented from solidifying in the state. In addition, it is possible to suppress a decrease in the overall transfer rate of the diffraction pattern FP and a decrease in the amount of light transmitted through the lens. On the other hand, by making the injection rate 30 cm ³ / sec or less, the lens OL was viewed macroscopically while gently filling the cavity CV and preventing the transfer rate of the diffraction pattern FP from being reduced unevenly. In this case, the surface shape accuracy can be improved.

  In particular, the lens OL obtained by the manufacturing method of the present embodiment is an objective lens for an optical pickup device with a three-wavelength compatible fine step structure that is compatible with BD, DVD, and CD. In the case of a three-wavelength compatible objective lens, it has a microstructure SS, which is a complicated and dense annular structure, so that not only a uniform and high transfer rate is required for such an objective lens, but also a high NA. The shape accuracy of the optical surface Sb having a very high curvature is also required. According to the present embodiment, it is possible to provide a lens OL that satisfies these requirements relatively easily.

[Second Embodiment]
The lens manufacturing method according to the second embodiment will be described below. The lens manufacturing method according to the second embodiment is a modification of the first embodiment, and parts that are not particularly described are the same as those in the first embodiment.

  FIG. 8A is a partially enlarged cross-sectional view of the fixed mold 41 and the movable mold 42 in the present embodiment, and shows a mold closed state and a mold clamped state. FIG. 8B shows a state in which the lens OL is protruded after the fixed mold 41 and the movable mold 42 are opened.

  In this case, a heat conduction suppressing layer 162c made of a low heat conductive material is provided as a heat insulating portion at the tip end portion 62b of the core portion 62. The heat conduction suppression layer 162c is sandwiched between the nickel phosphorus plating layer 67 as a surface layer and the base material portion 162d as a base material, and has a role of preventing rapid cooling of the molded lens OL.

  Specifically, the heat conduction suppressing layer 162c is made of a low heat conductive material having a thermal conductivity of 0.05 W / m · K or more and 10 W / m · K or less, for example, a metal material such as 6-4Ti, It can be formed using a resin material such as polyimide, or a ceramic such as zirconia or alumina. When the heat conduction suppressing layer 162c is formed of 6-4Ti, the thickness is set to 3 mm or more, for example. Moreover, when the heat conduction suppression layer 162c is formed of zirconia ceramics, the thickness is set to 0.1 mm or more. On the other hand, the base material portion 162d is made of a high heat conductive material having a thermal conductivity higher than 10 W / m · K, specifically, a base material of low carbon steel or stainless steel.

[Third Embodiment]
Hereinafter, the lens manufacturing method according to the third embodiment will be described. The lens manufacturing method according to the third embodiment is a modification of the first embodiment, and parts that are not particularly described are the same as those in the first embodiment.

FIG. 9 is a view showing a modification of the injection device 16 shown in FIGS. In this case, an injection cylinder part 16B is provided separately from the plasticizing cylinder part 16A provided with the cylinder 16a and the screw 16c. The plasticizing cylinder portion 16A supplies molten resin to the injection cylinder portion 16B by a screw 16c that rotates but does not advance. The injection cylinder portion 16B includes a cylinder 116a and a plunger 116c. The injection cylinder portion 16B receives supply from the plasticizing cylinder portion 16A and stores molten resin suitable for injection in the front portion of the plunger 116c in the cylinder 116a. Then, at the injection timing of the molten resin, the resin injection end 116d is hermetically connected to the end portion FCa of the flow path portion FC provided in the fixed mold 41, and the plunger 116c is advanced. In this case, the forward speed of the plunger 116c is V [cm / sec], the cross-sectional area determined by the inner diameter (barrel inner diameter) of the cylinder 116a is A [cm ² ], and the injection rate IR of the molten resin is V × A [cm ³ / sec]. That is, the injection rate IR can be arbitrarily set by the forward speed V of the plunger 116c.

[Description of Specific Examples]
Hereinafter, specific examples of the production method of the present invention will be described.

以上の表１において、３つのタイプの成形金型（コア部６２）について測定結果をまとめている。第１タイプの成形金型は、ステンレス鋼を母材部１６２ｄすなわち基材とし、溶射によって形成したジルコニアセラミックスを熱伝導抑制層１６２ｃすなわち断熱部としたものである。また、第２タイプの成形金型は、焼結によって形成したジルコニアセラミックスをコア部６２としたものである。さらに、第３タイプの成形金型は、６−４Ｔｉをコア部６２としたものである。熱伝導率の欄は、断熱部を構成する低熱伝導性材料の常温における熱伝導率を表している。また、断熱部厚さの欄は、熱伝導抑制層１６２ｃを特に設けた場合はその厚みとし、熱伝導抑制層１６２ｃを特に設けていない場合はコア部６２全体の厚みとしている。実験では、射出率を０．５〜４０〔ｃｍ^３／ｓｅｃ〕の範囲で変化させ、評価項目として透過光量と収差性能とを調べた。 [Example 1]
The object of the lens manufacturing method of this example was a BD / DVD / CD three-wavelength compatible objective lens for optical pickup (lens diameter 5 mmφ). This optical pickup objective lens has an annular step structure only on one side. In this production example, the material resin was a cycloolefin resin. The glass transition point Tg of the material resin was 123 ° C., the resin was injected at a resin temperature of 260 ° C., and the mold temperature when the molding die 40 was injected was 123 ° C. Table 1 below summarizes the experimental results.

In Table 1 above, the measurement results for three types of molding dies (core portion 62) are summarized. The first type molding die uses stainless steel as a base material portion 162d, that is, a base material, and zirconia ceramics formed by thermal spraying as a heat conduction suppressing layer 162c, that is, a heat insulating portion. Further, the second type molding die has a core portion 62 made of zirconia ceramics formed by sintering. Further, the third type mold has 6-4 Ti as the core portion 62. The column of thermal conductivity represents the thermal conductivity at room temperature of the low thermal conductivity material constituting the heat insulating portion. The column of the heat insulating portion thickness is the thickness when the heat conduction suppressing layer 162c is particularly provided, and is the thickness of the core portion 62 as a whole when the heat conduction suppressing layer 162c is not particularly provided. In the experiment, the emission rate was changed in the range of 0.5 to 40 [cm ³ / sec], and the amount of transmitted light and aberration performance were examined as evaluation items.

また、収差性能の評価は、目的とする集光特性からのズレを透過波面収差として計測した。評価ランクの記号は、以下の表３のように設定されている。なお、波面収差の測定には、コニカミノルタオプト社製の干渉計（ＫＶＩＩ４０５Ａ）を用いた。

以上の実施例１から、熱伝導率が１０Ｗ／ｍ・Ｋ以下で、射出率を１．２〔ｃｍ^３／ｓｅｃ〕以上３０〔ｃｍ^３／ｓｅｃ〕以下とすることで、従来に比較して転写性が向上して透過光量が高くなるとともに、射出率が適正に調整されることで、レンズの両光学面について必要な表面形状精度を得ることができることが分かる。特に、射出率を１．２〔ｃｍ^３／ｓｅｃ〕以上２７〔ｃｍ^３／ｓｅｃ〕以下とすることは、透過光量を向上させ、かつ、レンズ両面の形状精度（収差の少なさとして評価）を向上させるので、より好ましい。さらに、本実施例のようにシクロオレフィン系樹脂を用いる場合、射出率が２．５〔ｃｍ^３／ｓｅｃ〕以上２４．５〔ｃｍ^３／ｓｅｃ〕以下とすることで、レンズ全体の複屈折率を低減できることを確認しており、かつ、外観不良（低射出率のときに発生するフローマーク、高射出率のときに発生するジェッティング）を低減できることを確認している。さらに、射出率を１７〔ｃｍ^３／ｓｅｃ〕以上２４．５〔ｃｍ^３／ｓｅｃ〕以下とすることで、ＮＡ０．８５の光ピックアップ用対物レンズにおいてウェルドラインと呼ばれる外観不良を低減できるので好ましい。なお、ステンレス鋼で形成したコア部からなる従来型の金型の場合、熱伝導率が高すぎる結果として、レンズ収差性能をある程度確保できても、十分な転写性が得られないことを実験的に確認している。 Here, the evaluation of the amount of transmitted light was based on the amount of transmitted light of a lens molded with a conventional mold in which a nickel phosphor plating layer for transfer was formed on the surface of a core portion made of stainless steel. Specifically, when the transmitted light amount of the lens formed with the conventional mold is T1, and the transmitted light amount of the lens formed with the mold of the example is T2, the transmitted light amount evaluation value is E = (T2 / T1). X100 [%] is given, and the symbol of the evaluation rank is set as shown in Table 2 below. For measurement of the amount of transmitted light, a spot image analyzer (KVSA1000A) manufactured by Konica Minolta Opto was used.

In addition, the aberration performance was evaluated by measuring the deviation from the intended light collecting characteristic as transmitted wavefront aberration. The evaluation rank symbols are set as shown in Table 3 below. The wavefront aberration was measured using an interferometer (KVII405A) manufactured by Konica Minolta Opto.

From Example 1 above, the thermal conductivity is 10 W / m · K or less and the injection rate is 1.2 [cm ³ / sec] or more and 30 [cm ³ / sec] or less, compared with the conventional case. It can be seen that the required surface shape accuracy can be obtained for both optical surfaces of the lens by improving the transferability and increasing the amount of transmitted light and adjusting the emission rate appropriately. In particular, when the emission rate is set to 1.2 [cm ³ / sec] or more and 27 [cm ³ / sec] or less, the amount of transmitted light is improved and the shape accuracy of both surfaces of the lens (evaluated as low aberration). Since it improves, it is more preferable. Further, when a cycloolefin-based resin is used as in this embodiment, the birefringence of the entire lens is adjusted by setting the injection rate to 2.5 [cm ³ / sec] or more and 24.5 [cm ³ / sec] or less. In addition, it has been confirmed that appearance defects (flow marks generated at a low injection rate, jetting generated at a high injection rate) can be reduced. Furthermore, it is preferable to set the emission rate to 17 [cm ³ / sec] or more and 24.5 [cm ³ / sec] or less because an appearance defect called a weld line can be reduced in an NA0.85 optical pickup objective lens. In the case of a conventional mold consisting of a core formed of stainless steel, as a result of thermal conductivity being too high, even if lens aberration performance can be secured to some extent, it is experimentally impossible to obtain sufficient transferability. Have confirmed.

  In particular, in the objective lens for a three-wavelength compatible type optical pickup, a complicated and dense annular zone step is provided on the lens surface, so it is generally not easy to obtain uniform and high transferability, but also from the above evaluation As is apparent, the manufacturing method of the present invention can achieve uniform and high transferability required for an objective lens for a three-wavelength compatible type optical pickup.

  In addition, in a lens with a high NA including the objective lens for a three-wavelength compatible type optical pickup, a lens surface with a very high curvature is formed. However, the manufacturing method of the present invention increases the lens surface with a high curvature. Can be formed with accuracy.

以上の表４において、実施例１と同様に、３つのタイプの成形金型（コア部６２）について測定結果をまとめている。熱伝導率の欄は、断熱部を構成する低熱伝導性材料の常温における熱伝導率を表している。また、断熱部厚さの欄は、熱伝導抑制層１６２ｃを特に設けた場合はその厚みとし、熱伝導抑制層１６２ｃを特に設けていない場合はコア部６２全体の厚みとしている。実験では、射出率を０．５〜４０〔ｃｍ^３／ｓｅｃ〕の範囲で変化させ、評価項目として透過光量と収差性能とを調べた。 [Example 2]
The object of the lens manufacturing method of this example was a collimator lens for a BD optical pickup having a lens diameter of 5 mmφ. This collimator lens has an annular step structure on only one side. The conditions of this production example were the same as the production conditions of Example 1. That is, the material resin was a cycloolefin resin, the glass transition point Tg thereof was 123 ° C., the resin temperature at the time of injection was 260 ° C., and the mold temperature was 123 ° C. Table 4 below summarizes the experimental results.

In Table 4 above, similar to Example 1, the measurement results are summarized for three types of molding dies (core part 62). The column of thermal conductivity represents the thermal conductivity at room temperature of the low thermal conductivity material constituting the heat insulating portion. The column of the heat insulating portion thickness is the thickness when the heat conduction suppressing layer 162c is particularly provided, and is the thickness of the core portion 62 as a whole when the heat conduction suppressing layer 162c is not particularly provided. In the experiment, the emission rate was changed in the range of 0.5 to 40 [cm ³ / sec], and the amount of transmitted light and aberration performance were examined as evaluation items.

From the above Example 2, the thermal conductivity is 10 W / m · K or less and the injection rate is 1.2 [cm ³ / sec] or more and 30 [cm ³ / sec] or less, compared with the conventional case. It can be seen that the required surface shape accuracy can be obtained for both optical surfaces of the lens by improving the transferability and increasing the amount of transmitted light and adjusting the emission rate appropriately. In particular, when the emission rate is set to 1.2 [cm ³ / sec] or more and 27 [cm ³ / sec] or less, the amount of transmitted light is improved and the shape accuracy of both surfaces of the lens (evaluated as low aberration). Since it improves, it is more preferable. Further, when a cycloolefin-based resin is used as in this embodiment, the birefringence of the entire lens is adjusted by setting the injection rate to 2.5 [cm ³ / sec] or more and 24.5 [cm ³ / sec] or less. In addition, it has been confirmed that appearance defects (flow marks generated at a low injection rate, jetting generated at a high injection rate) can be reduced.

以上の表５において、転写率とは、回折輪帯のピッチをＰｍとし、成形品であるレンズＯＬのダレ量をＷｍとして、
転写率＝（Ｐｍ−Ｗｍ）／Ｐｍ
で与えられる。ここで、ダレ量Ｗｍは、コア部６２に形成された回折パターンの溝ＤＰａにレンズＯＬの突起が十分入り込んでない部分ＰＬａの幅によって決定される。また、図６に示すゲート方向Ｄ１とゲート直交方向Ｄ２とに関してこれに交差する領域の微細構造ＳＳの転写性を確認した。 [Transfer rate of ring-shaped step structure]
Below, the test which confirms the tendency regarding the directivity of the transcription | transfer rate of a ring-shaped step structure is demonstrated. The object of the test was a collimator lens for a BD optical pickup having a lens diameter of 5 mmφ. The lens manufacturing conditions were the same as those in Examples 1 and 2. That is, the material resin was a cycloolefin resin, the glass transition point Tg thereof was 123 ° C., the resin temperature at the time of injection was 260 ° C., and the mold temperature was 123 ° C. The structure of the core portion 62 is such that stainless steel is used as a base material portion 162d, that is, a base material, and zirconia ceramics formed by thermal spraying is used as a heat conduction suppressing layer 162c, that is, a heat insulating portion. Table 5 below summarizes the experimental results regarding the transfer rate.

In Table 5 above, the transfer rate refers to the pitch of the diffraction zone as Pm, and the sagging amount of the lens OL as a molded product as Wm.
Transfer rate = (Pm−Wm) / Pm
Given in. Here, the sagging amount Wm is determined by the width of the portion PLa where the projection of the lens OL does not sufficiently enter the groove DPa of the diffraction pattern formed in the core portion 62. Further, the transferability of the microstructure SS in the region intersecting with the gate direction D1 and the gate orthogonal direction D2 shown in FIG. 6 was confirmed.

From the above experiments, it was found that the transferability was improved overall and uniformly under conditions where the injection rate was neither too low nor too high. In addition, when the injection rate is too low, that is, 1 [cm ³ / sec] (that is, smaller than 1.2 [cm ³ / sec]), the resin is cured without being completely transferred, and the transfer rate is reduced as a whole. I think that. If the injection rate is too high (32 [cm ³ / sec]) (ie, greater than 30 [cm ³ / sec]), the resin flow inertia is too strong, so that it becomes difficult for the resin to enter the step structure in the gate direction D1. It is considered that the transfer rate of the step structure in the direction D1 is relatively deteriorated as compared with the gate orthogonal direction D2.

In summary, it can be said that the overall transferability is improved when the thermal conductivity is 10 [W / m · K] or less. Furthermore, by setting the injection rate to 1.2 [cm ³ / sec] or more and 30 [cm ³ / sec] or less, there is no difference in the transfer rate of the annular zone step structure in the gate direction D1 and the gate orthogonal direction D2, It was confirmed that uniform transfer was achieved.
[Others]
Although description of a detailed Example is abbreviate | omitted, it has the core part 62 which has the heat insulation thickness 1mm of thermal conductivity 1.2 [W / m * K], and mold temperature is Tg-3 [degreeC] or more Tg + 5 [ [° C.] or less, the resin is introduced into the cavity with an appropriate viscosity, so that not only the transfer rate can be improved, but also the resin is not rapidly cooled.

  Although detailed description of the embodiment is omitted, the core portion 62 having a heat insulation thickness of 1 mm with a thermal conductivity of 1.2 [W / m · K] is provided, and the resin temperature is increased within a range in which the resin does not deteriorate. Thus, the resin viscosity can be reduced, the transfer rate is further improved, and the amount of transmitted light is preferably increased.

  Although the present invention has been described based on the above embodiments, the present invention is not limited to the above embodiments, and various modifications are possible. For example, in the said embodiment, the core part 62 or the heat conduction suppression layer 162c of the movable mold 42 is formed of a low heat conductive material having a heat conductivity of 0.05 W / m · K or more and 10 W / m · K or less. However, the heat insulating part can also be provided by using the core part 52 of the fixed mold 41 as a similar structure.

  In the above description, an objective lens for an optical pickup device that is compatible with BD, DVD, and CD is assumed as the lens OL. However, a lens OL for other purposes may be obtained by the same manufacturing method. it can. For example, an objective lens for an optical pickup device that is compatible with other types of recording media can be manufactured by the above manufacturing method. In addition, a collimator lens with a fine step structure, a correction optical element, an imaging optical element, and a viewfinder optical element can be similarly manufactured by the above manufacturing method.

  In addition, the shape of the cavity CV provided in the injection mold composed of the fixed mold 41 and the movable mold 42 is not limited to the illustrated one, and various shapes can be used. That is, the shape of the cavity CV formed by the core portions 52, 62 and the like is merely an example, and can be appropriately changed according to the use of the lens OL.

It is a front view explaining the shaping | molding apparatus of 1st Embodiment. It is a sectional side view explaining the structure of the shaping die comprised with a fixed die and a movable die. (A)-(C) are sectional drawings explaining the metal mold | die and manufacturing method of 1st Embodiment. It is a side view of the lens by which injection molding is carried out. It is an expanded sectional view explaining the resin injection end of the cylinder of an injection device, and the internal structure of the periphery. It is a schematic diagram which shows a mode that the cavity shown in FIG. 2 etc. is filled with molten resin. It is a flowchart explaining the basic flow of the lens manufacturing method of this embodiment. (A), (B) is sectional drawing explaining the metal mold | die and manufacturing method of 2nd Embodiment. It is an expanded sectional view explaining the injection device of a 3rd embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Injection molding machine, 11 ... Fixed platen, 12 ... Movable platen, 15 ... Opening / closing drive device, 16 ... Injection device, 18 ... Temperature control device, 19 ... Depressurization device, 41 ... Fixed mold, 42 ... Movable die, CV ... mold space, GP ... gate part, OL ... lens

Claims (11)

A lens manufacturing method for injection molding a lens having a ring-shaped step structure by injecting resin into a cavity formed by a pair of molds,
Of the pair of molds, at least one mold having a transfer surface corresponding to the ring-shaped step structure has a heat insulating portion formed of a low thermal conductive material having a thermal conductivity of 10 W / m · K or less. On the transfer surface side,
A method for manufacturing a lens, comprising injecting a resin into the cavity from an outer peripheral side surface of the cavity, and an injection rate of the resin at the time of filling the cavity being 1.2 cm ³ / sec or more and 30 cm ³ / sec or less .   The lens manufacturing method according to claim 1, wherein the at least one mold has a surface processed layer provided on the heat insulating portion.   The lens manufacturing method according to any one of claims 1 and 2, wherein the heat insulating portion is formed of 6-4Ti and has a thickness of 3 mm or more.   The lens manufacturing method according to claim 1, wherein the heat conductivity of the heat insulating portion is 3 W / m · K or less.   The lens manufacturing method according to claim 4, wherein the heat insulating portion is formed of zirconia ceramics and has a thickness of 0.1 mm or more.   The lens manufacturing method according to claim 5, wherein the heat insulating portion is formed by thermal spraying.   The internal temperature of the pair of molds when the resin is injected into the cavity is -3 ° C or higher and + 5 ° C or lower with respect to the glass transition point. A lens manufacturing method according to claim 1. 8. The lens manufacturing method according to claim 1, wherein an injection rate of the resin at the time of filling the cavity is 1.2 cm ³ / sec or more and 27 cm ³ / sec or less. .   9. The lens manufacturing method according to claim 1, wherein a pressure of the cavity at the time of filling the cavity is 0.05 MPa or more lower than an atmospheric pressure. The resin injected into the cavity is a cycloolefin resin, and the injection rate of the cycloolefin resin when filling the cavity is 2.5 cm ³ / sec or more and 24.5 cm ³ / sec or less, The lens manufacturing method according to any one of claims 1 to 9. 5. The lens manufacturing method according to claim 4, wherein an injection rate of the resin at the time of filling the cavity is 17 cm ³ / sec or more and 24.5 cm ³ / sec or less.

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