WO2012105692A1 - Objective lens, method for manufacturing objective lens, and mold - Google Patents

Abstract

The purpose of the present invention is to provide an objective lens wherein a fine pattern or the like is transferred with high precision but the amount of molten resin poured into a mold space corresponding to the optically functional part of the lens is constrained. The elements involved in the process of molding the objective lens (10) satisfy conditions (1) to (3), resulting in the molded objective lens (10) having a fine pattern transferred with high precision. That is, when the objective lens (10) is molded, incomplete filling due to insufficient injection pressure and optical-performance degradation due to excessive pressure are prevented. Also, in a gate-cut step at the end of the manufacturing process, the cutting margin for a flange part (12) is minimized, thereby avoiding adverse effects on first and second optical surfaces (OS1 and OS2). Alignment near neck parts (13) of said first and second optical surfaces (OS1 and OS2) is also controlled.

Description

Objective lens, objective lens manufacturing method, and molding die

The present invention relates to an objective lens having a fine shape on an optical surface, in particular, an objective lens incorporated in a notebook computer, a manufacturing method thereof, and a molding die used in the manufacturing method.

In an objective lens formed by injection molding, generally, a gate portion that is an inlet through which molten resin flows into a mold space corresponding to the objective lens is disposed on the outer periphery of the flange portion of the objective lens (see, for example, Patent Document 1). ). This is because the gate portion is separated from the optical surface so that molding distortion or the like of the gate portion does not affect the optical surface of the objective lens. The molten resin that has flowed in from the gate portion provided on the outer periphery of the flange portion passes through the neck portion connecting the optical surface of the lens and the flange portion from the gate portion having a relatively small cross-sectional area, and has a relatively wide cross-sectional area. It flows into the mold space corresponding to the optical function part of the lens, and the optical surface is transferred by filling this mold space.

However, when the objective lens as disclosed in Patent Document 1 is a small one that is incorporated into, for example, a notebook computer and is compatible with a plurality of types of discs, the transfer accuracy of the lens is particularly problematic. Become. That is, since such an objective lens is compatible with a plurality of types of disks, it has a fine shape with a small diameter, and there is a problem that transfer to the fine shape is incomplete. This is because, in the lens having a small diameter and a fine shape as described above, the neck portion has a high degree of necking, and the amount of molten resin flowing into the mold space corresponding to the optical function portion is limited. In addition, when the molten resin passes through the gate portion, the molten resin that comes in contact with the mold surface such as the gate wall surface is cooled by the mold to increase the viscosity, and only the central portion of the gate portion serves as a passage to form the molten resin. It will flow into the mold space. Therefore, the greater the degree of constriction of the neck portion, the more the amount of molten resin flowing in is limited.When the amount is significantly limited, the amount of molten resin flowing into the optical function portion is insufficient, and the mold is in an unfilled state. Transfer to fine diffractive shape is incomplete.

JP 2008-213397 A

An object of the present invention is to provide an objective lens in which a fine shape or the like is transferred with high accuracy while suppressing restriction of the amount of molten resin flowing into a mold space corresponding to the optical function portion of the lens.

Another object of the present invention is to provide an objective lens manufacturing method for manufacturing the objective lens and a molding die used in the manufacturing method.

In order to achieve the above object, an objective lens according to the present invention has an optical function part having a fine shape on an optical surface and a flange part provided around the optical function part, and is provided on the outer peripheral edge of the flange part. An objective lens that is injection-molded by a resin introduced into the mold space from the gate portion and is used for reading and / or writing information on BD, DVD, and CD, and the optical function portion includes a first optical surface and A second optical surface having a smaller curvature than the first optical surface, a neck portion between the optical function portion and the flange portion, and a lens outer diameter in a direction perpendicular to the lens optical axis as G (mm In the optical function portion, the thickness on the lens axis in the direction parallel to the lens optical axis is t (mm), and in the neck portion, the minimum thickness of the neck portion in the direction parallel to the lens optical axis is T (mm). When G ≦ 4.05 (mm), The thickness deviation ratio t / T indicating the degree of squeezing is greater than 4.0. In the gate portion, the gate width in the direction perpendicular to the lens optical axis is W (mm), and the thickness in the direction parallel to the lens optical axis is When the gate depth is D (mm), the following conditional expressions (1) to (3) are satisfied.
0.5T ≦ D ≦ 1.33T (1)
1.5T ≦ W ≦ 3T (2)
D · W ≧ 1.5T ² (3)

The objective lens with a lens outer diameter G satisfying G ≦ 4.05 (mm) is a relatively small lens, and the smaller the lens outer diameter G, the smaller the cross-sectional area of the neck portion. In addition, the objective lens satisfying the thickness t on the lens axis and the minimum thickness T of the neck portion of t / T> 4.0 has a relatively large thickness deviation ratio and the amount of molten resin flowing in is limited. The challenge becomes bigger.

Even in an objective lens having such a large problem, when the objective lens is molded, the elements satisfy the conditional expressions (1) to (3), so that the objective lens has a fine shape transferred with high accuracy. Specifically, by increasing the gate depth D to 0.5T or more, setting the gate width W to 1.5T or more, and setting the gate cross-sectional area (D · W) to 1.5T ² or more. When the objective lens is molded, the cross-sectional area through which the molten resin passes at the center of the gate portion fills the mold without excessive injection pressure when the molten resin passes through the gate portion. It will be large enough to be able to. Therefore, it is possible to prevent optical performance deterioration due to unfilling due to insufficient injection pressure and excessive pressure. In addition, by setting the gate width W to 3T or less, it is possible to suppress the cut margin of the flange portion when finishing the gate cut, and to avoid adverse effects on the optical surface. Further, by reducing the gate depth D to 1.33 T or less, a resin that deteriorates optical performance caused by a turbulent flow caused by the flow of the molten resin hitting the convex step portion of the neck portion in the vicinity of the neck portion of the optical surface. Can be suppressed.

In a specific aspect or aspect of the present invention, in the objective lens, the flange portion has a first flange surface on the first optical surface side and a second flange surface on the second optical surface side, and the second flange. The surface is disposed lower than the vertex of the second optical surface. In this case, the ratio of the thickness of the flange portion to the minimum thickness T of the neck portion becomes relatively small, and when the objective lens is molded, the molten resin flowing from the gate portion is suppressed from flowing excessively at the neck portion. This can prevent the deterioration of the optical performance in the vicinity of the neck portions of the first and second optical surfaces.

In another aspect of the present invention, the outer periphery of the second optical surface is formed inside the outer periphery of the first optical surface. In this case, when the objective lens is molded, the molten resin flows into the first optical surface side earlier than the second optical surface side, and the molten resin can easily flow to the first optical surface side.

In still another aspect of the present invention, the neck portion has a first end surface on the first optical surface side and a second end surface on the second optical surface side, and connects the first flange surface and the first end surface. At least one of the surfaces connecting the second flange surface and the second end surface is inclined with respect to the lens optical axis. In this case, the surface connecting the flange surface and the end surface becomes gentle, and the molten resin can smoothly flow into the neck portion.

In still another aspect of the present invention, at least one of the first end surface and the second end surface has a mirror surface. In this case, since the end surface is a mirror surface, the molten resin can flow smoothly when the objective lens is molded.

In yet another aspect of the present invention, one of the first flange surface and the second flange surface is arranged to be recessed from either the corresponding first end surface or second end surface on the neck portion side. In this case, in the neck portion on the optical surface side where the flange surface is recessed, the convex step portion of the neck portion that hinders the flow of the molten resin is eliminated during the molding of the objective lens, so the flow of the molten resin becomes a turbulent flow. It flows smoothly. Therefore, it is possible to suppress the deterioration of the optical performance in the vicinity of the neck portion of the first and second optical surfaces.

In yet another aspect of the present invention, the flange portion has a step shape that changes the thickness in the direction parallel to the lens optical axis on at least one of the first flange surface and the second flange surface. In this case, the inclined portion that is the boundary between the flange surface and the end surface becomes gentle, and the molten resin can smoothly flow into the neck portion.

In yet another aspect of the present invention, the second end face has a convex mark for mold identification. In this case, since the objective lens has the above configuration, a mark that is difficult to be transferred with a small-diameter lens can be transferred with high accuracy.

In yet another aspect of the present invention, a convex mark for mold identification is provided on the second flange surface. In this case, since the objective lens has the above configuration, a mark that is difficult to be transferred with a small-diameter lens can be transferred with high accuracy.

In yet another aspect of the present invention, when the thickness on the lens axis in the direction parallel to the lens optical axis is t (mm) and the focal length of a light beam having a wavelength of 500 nm or less is f (mm), 0.8 ≦ t / f ≦ 2.0. Thus, in the case of a lens having a relatively large lens axis thickness t in a direction parallel to the lens optical axis of the objective lens, transfer to a fine diffractive shape becomes more difficult, but the objective lens has the above configuration, Transfer with high accuracy. It is more preferable that t / f is 1.0 ≦ t / f ≦ 1.8, which enables transfer with higher accuracy.

In order to solve the above-described problems, an objective lens manufacturing method according to the present invention includes an optical function unit having a fine shape on an optical surface and a flange unit provided around the optical function unit. A method of manufacturing an objective lens that is injection-molded by a resin introduced into a mold space from a gate portion provided at a peripheral edge, and is used for recording and / or reproducing information on BD, DVD, and CD. Injecting molten resin into a mold space formed by a first mold for forming the first optical surface and a second mold for forming the second optical surface of the objective lens, and molding the objective lens; Removing the objective lens from the mold space by opening the first mold and the second mold relatively apart from each other, and the objective lens includes an optical function section and a flange section. Has a neck between the lens light The lens outer diameter in a direction perpendicular to the lens is G (mm), the thickness on the lens axis in the direction parallel to the lens optical axis is t (mm) in the optical function unit, and the direction in the neck portion is parallel to the lens optical axis. When the minimum thickness of the neck portion is T (mm), G ≦ 4.05 (mm), the uneven thickness ratio t / T indicating the degree of necking is larger than 4.0, and in the gate portion, When the gate width in the direction perpendicular to the lens optical axis is W (mm) and the gate depth in the direction parallel to the lens optical axis is D (mm), the following conditional expressions (1) to (3) are satisfied: Fulfill.
0.5T ≦ D ≦ 1.33T (1)
1.5T ≦ W ≦ 3T (2)
D · W ≧ 1.5T ² (3)

In the objective lens manufacturing method, an objective lens having a fine shape transferred with high accuracy can be manufactured by satisfying the conditional expressions (1) to (3). That is, when the objective lens is molded, it is possible to prevent optical performance deterioration due to unfilling due to insufficient injection pressure or excessive pressure. Further, it is possible to suppress the cutting margin of the flange portion at the time of finishing gate cutting, and to avoid adverse effects on the optical surface. Moreover, the flow orientation of the resin which degrades the optical performance caused by the turbulent flow caused by the flow of the molten resin hitting the convex portion of the neck portion in the vicinity of the neck portion of the optical surface can be suppressed.

In order to solve the above-described problems, a molding die according to the present invention has an optical function part having a fine shape on an optical surface, and a flange part provided around the optical function part, on the outer periphery of the flange part. A molding die for molding an objective lens that is injection-molded by a resin introduced into a mold space from a provided gate and is used for reading and / or writing information on BD, DVD, and CD. A first mold having a first transfer surface forming a first optical surface of the lens and a first molding surface forming a first flange surface extending around the first optical surface; A second gold having a second transfer surface forming a second optical surface having a smaller curvature than the optical surface, and a second molding surface forming a second flange surface extending around the second optical surface. And an objective lens between the first transfer surface and the first molding surface. A third molding surface that forms a neck portion of the objective lens, a fourth molding surface that forms a neck portion of the objective lens between the second transfer surface and the second molding surface, The dimension of the mold space formed by the mold and the second mold is such that the lens outer diameter in the direction perpendicular to the lens optical axis is G (mm), and the optical function unit has a dimension in the direction parallel to the lens optical axis. When the thickness on the lens axis is t (mm) and the minimum thickness of the neck in the direction parallel to the optical axis of the lens is T (mm), G ≦ 4.05 (mm), the degree of necking Is a thickness ratio t / T greater than 4.0, and in the gate portion, the gate width in the direction perpendicular to the lens optical axis is W (mm), and the gate depth in the direction parallel to the lens optical axis is When D is D (mm), the following conditional expressions (1) to (3) are satisfied. Here, the mold space has a shape obtained by inverting the contour of the objective lens.
0.5T ≦ D ≦ 1.33T (1)
1.5T ≦ W ≦ 3T (2)
D · W ≧ 1.5T ² (3)

By satisfying the conditional expressions (1) to (3), the molding die can be a molding die capable of molding an objective lens having a fine shape transferred with high accuracy. That is, when the objective lens is molded, it is possible to prevent optical performance deterioration due to unfilling due to insufficient injection pressure or excessive pressure. Further, it is possible to suppress the cutting margin of the flange portion at the time of finishing gate cutting, and to avoid adverse effects on the optical surface. Moreover, the flow orientation of the resin which degrades the optical performance caused by the turbulent flow caused by the flow of the molten resin hitting the convex portion of the neck portion in the vicinity of the neck portion of the optical surface can be suppressed.

In a specific aspect or side surface of the present invention, in the molding die, the second molding surface is from a die-matching surface of the first die and the second die rather than the apex of the second transfer surface. It is formed in a shallow position.

In another aspect of the present invention, the outer periphery of the second transfer surface is formed inside the outer periphery of the first transfer surface.

In still another aspect of the present invention, at least one of the surface connecting the first molding surface and the third molding surface and the surface connecting the second molding surface and the fourth molding surface is a lens optical axis. It is inclined with respect to.

In yet another aspect of the present invention, one of the first molding surface and the second molding surface is disposed so as to be recessed from either the third molding surface or the fourth molding surface.

In still another aspect of the present invention, a transfer surface that forms a step shape that changes the thickness in a direction parallel to the lens optical axis is provided on at least one of the first molding surface and the second molding surface.

In still another aspect of the present invention, the fourth molding surface has a concave transfer surface for transferring a convex mark for mold identification.

In yet another aspect of the present invention, the second molding surface has a concave transfer surface for transferring a convex mark for identifying a mold.

FIG. 1A is a partial side sectional view of the objective lens according to the first embodiment, and FIG. 1B is a plan view of the second optical surface side of FIG. 1A. FIG. 1B is a partial side cross-sectional view illustrating a molding die for forming the objective lens of FIG. 1A. It is a figure explaining the flow path space for resin supply, and the type | mold space for objective lens shaping | molding. FIG. 4A is a partial side sectional view of the objective lens of the second embodiment, and FIG. 4B is a partially enlarged view for explaining a molding die for forming the objective lens of FIG. 4A. FIG. 5A is a partial side cross-sectional view of the objective lens of the third embodiment, and FIG. 5B is a partially enlarged view for explaining a molding die for forming the objective lens of FIG. 5A. FIG. 6A is a partial side cross-sectional view of the objective lens of the fourth embodiment, and FIG. 6B is a partially enlarged view for explaining a molding die for forming the objective lens of FIG. 6A. FIG. 7A is a partial side cross-sectional view of the objective lens of the fifth embodiment, and FIG. 7B is a partially enlarged view for explaining a molding die for forming the objective lens of FIG. 7A.

[First Embodiment]
Hereinafter, an objective lens and a method for manufacturing the objective lens according to the present invention will be described with reference to the drawings.
An objective lens 10 shown in FIGS. 1A and 1B is made of plastic and has a circular optical function part 11 having an optical function, an annular flange part 12 provided radially outward from the outer edge of the optical function part 11, and an optical An annular neck portion 13 is provided between the functional portion 11 and the flange portion 12. In FIG. 1A, since the objective lens 10 has a symmetrical shape around the lens optical axis OA, only half of the objective lens 10 is shown and the remaining illustration is omitted. This objective lens 10 is an objective lens with NA of 0.75 or more. Specifically, the objective lens 10 is, for example, a single-wave objective lens of a three-wavelength compatible type. In this case, for example, the objective lens 10 can read or write optical information corresponding to the BD (Blu-Ray Disc) standard with a wavelength of 405 nm and NA of 0.85, and also has a DVD (Digital Versatile Disc) and optical information corresponding to the CD (Compact Disc) standard with a wavelength of 780 nm and NA of 0.53 can be read or written.

The optical function unit 11 of the objective lens 10 has a convex first optical surface OS1 having a relatively large curvature on the front side, and a convex second optical surface OS2 having a smaller curvature than the first optical surface OS1 on the back side. . Among these, the first optical surface OS1 is arranged closer to the laser light source for writing (recording) or reading (reproducing) when the objective lens 10 is operated by being incorporated in an optical pickup device such as a notebook personal computer. Further, the second optical surface OS2 is disposed to face a BD or the like that is an optical information recording medium when the objective lens 10 is incorporated in an optical pickup device and operated. The first optical surface OS1 is provided with a fine structure or fine shape FS that is a diffractive structure. The fine shape FS is formed in a concentric annular zone, and the outermost periphery thereof reaches a position near the outer edge of the optical function unit 11. On the other hand, the second optical surface OS2 is a mirror surface having no diffractive structure.

In addition, the diffractive structure referred to in this specification is a general term for structures that have a step and have a function of converging or diverging a light beam by diffraction. For example, a plurality of unit shapes are arranged around the optical axis, and a light beam is incident on each unit shape, and the wavefront of the transmitted light is shifted between adjacent annular zones, resulting in new It includes a structure that converges or diverges light by forming a simple wavefront. The diffractive structure preferably has a plurality of steps, and the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. In addition, when the objective lens provided with the diffractive structure is a single aspherical lens, the incident angle of the light beam to the objective lens differs depending on the height from the optical axis, so the step amount of the diffractive structure is slightly different for each annular zone. It will be. For example, when the objective lens is a single aspherical convex lens, even if it is a diffractive structure that generates diffracted light of the same diffraction order, generally, the distance from the optical axis tends to increase.

By the way, it is preferable that the diffractive structure has a plurality of concentric annular zones around the optical axis. In general, the diffractive structure can have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shape including the optical axis is a blaze structure, a staircase structure, or a staircase structure and a blaze structure. There is a structure in which is superimposed.

The flange portion 12 includes an annular protruding portion 14 provided on the radially outer side of the neck portion 13. The protruding portion 14 is a portion that is relatively thicker than the neck portion 13. The protruding portion 14 protrudes from the neck portion 13 toward the laser light source, that is, the first optical surface OS1, and also protrudes toward the optical information recording medium, that is, the second optical surface OS2. The protruding portion 14 has, on the first optical surface OS1 side, a first flange surface 12a perpendicular to the lens optical axis OA and an inner diameter surface 14a facing the fine shape FS (first optical surface OS1) of the optical function unit 11. And has a second flange surface 12b perpendicular to the lens optical axis OA and an inner diameter surface 14b facing the second optical surface OS2 of the optical function unit 11 on the second optical surface OS2 side. 2 It has the outer-diameter surface 14c arrange | positioned on the opposite side of inner- diameter surface 14a, 14b on both sides of 12 flange surface 12a, 12b. That is, the inner diameter surface 14a is a surface that connects the first flange surface 12a and a first end surface EP1 of the neck portion 13 described later, and the inner diameter surface 14b is the second flange surface 12b and the second end surface EP2 of the neck portion 13. It is a surface to connect. The inner diameter surface 14a extends with an inclination with respect to the lens optical axis OA and has a tapered shape spreading on the laser light source side, and the inner diameter surface 14b extends with an inclination with respect to the lens optical axis OA. It has a tapered shape that widens on the information recording medium side. The outer diameter surface 14c extends in parallel to the lens optical axis OA and has a cylindrical shape. The first and second flange surfaces 12a and 12b are flat surfaces extending perpendicular to the lens optical axis OA. The first flange surface 12a is disposed lower than the vertex Q1 of the first optical surface OS1, and the second flange surface 12b is disposed lower than the vertex Q2 of the second optical surface OS2. That is, the first optical surface OS1 protrudes closer to the laser light source than the first flange surface 12a, and the second optical surface OS2 protrudes closer to the information recording medium than the second flange surface 12b.

The neck part 13 is a thinner part than the optical function part 11 and the flange part 12. A ring-shaped first end surface EP1 is formed on the laser light source side of the neck portion 13, that is, the first optical surface OS1, and a ring-shaped second end surface EP1 is formed on the optical information recording medium side, that is, the second optical surface OS2. An end face EP2 is formed. The first and second end surfaces EP1, EP2 are mirror surfaces. The boundary between the second optical surface OS2 and the second end surface EP2 (the outer periphery of the second optical surface OS2) is inward of the boundary between the first optical surface OS1 and the first end surface EP1 (the outer periphery of the first optical surface OS1). Is formed. That is, the outer diameter of the second optical surface OS2 is smaller than the outer diameter of the first optical surface OS1. Thereby, when the objective lens 10 is molded, the molten resin flows into the first optical surface OS1 side earlier than the second optical surface OS2 side. The first end surface EP1 or the second end surface EP2 has a region formed of a flat surface that regularly reflects collimated light, for example, and is used when the objective lens 10 is aligned.

Hereinafter, the dimensions of the objective lens 10 will be described. In the optical function unit 11, the lens outer diameter in the direction perpendicular to the lens optical axis OA is G (mm) (see FIG. 1B), and the thickness on the lens axis in the direction parallel to the lens optical axis OA is t (mm) (FIG. 1)), and G ≦ 4.05 (mm) and t / mm when the minimum thickness of the neck in the direction parallel to the lens optical axis OA is T (mm) (see FIG. 1A). T> 4.0, and in the gate portion GP, the gate width in the direction perpendicular to the lens optical axis OA is W (mm) (see FIG. 1B), and the gate depth is parallel to the lens optical axis OA. Is D (mm) (see FIG. 1A), the following conditional expressions (1) to (3) are satisfied. The lens axis thickness t is the thickness of the thickest portion of the optical function unit 11 that is parallel to the lens optical axis OA.
0.5T ≦ D ≦ 1.33T (1)
1.5T ≦ W ≦ 3T (2)
D · W ≧ 1.5T ² (3)

The objective lens 10 has a thickness on the lens axis in a direction parallel to the lens optical axis OA as t (mm), and a focal length of the objective lens 10 in a light beam having a wavelength of 500 nm or less as f (mm). 0.8 ≦ t / f ≦ 2.0, preferably 1.0 ≦ t / f ≦ 1.8. The objective lens 10 in which t / f satisfies the above range has a relatively large lens axis thickness t in a direction parallel to the lens optical axis OA.

Hereinafter, a mold for manufacturing the objective lens 10 shown in FIGS. 1A and 1B will be described with reference to FIG. 2 and the like. The illustrated mold 40 includes a movable mold 41 as a first mold and a fixed mold 42 as a second mold. The movable mold 41 is driven by the mold opening / closing drive device 51 and can move forward and backward in the AB direction, and can be opened / closed with the fixed mold 42. A mold space for injection molding can be formed as will be described in detail below by clamping the molds 41 and 42 together with the parting surfaces PS1 and PS2.

As shown in FIG. 3, by clamping the movable mold 41 and the fixed mold 42, a mold space CV for molding the objective lens 10 and a flow path space FC for supplying resin to the mold space CV. And are formed. Among these, the mold space CV corresponds to the shape of the objective lens 10 shown in FIG. 1A and the like. The flow path space FC is a space corresponding to the runner portion RP and the like of the molded product before the objective lens 10 is separated, and the gate portion GS is a space corresponding to the gate portion GP of the molded product. In the objective lens 10 shown in FIG. 1A and the like, the gate portion GP is completely removed by finishing.

The mold space CV includes a main body space CV1, a flange space CV2, and a neck space CV3. The main body space CV1 is defined by the first and second transfer surfaces S1, S2, and the flange space CV2 is the third, fourth, fifth, sixth, and seventh transfer surfaces S3, S4, S5, S6, S7. The neck space CV3 is defined by the eighth and ninth transfer surfaces S8 and S9. Here, the pair of opposing first and second transfer surfaces S1 and S2 facing the main body space CV1 form the first and second optical surfaces OS1 and OS2 of the optical function unit 11 in the center of the objective lens 10, respectively. This corresponds to the end faces of core dies 64a and 74a described later. The outer periphery of the second transfer surface S2 is formed inside the outer periphery of the first transfer surface S1. The first transfer surface S1 is deeper and has a larger curvature than the second transfer surface S2. Further, a mold surface portion S11 corresponding to the fine shape FS of the objective lens 10 is provided on the first transfer surface S1.

A pair of opposing third and fourth transfer surfaces S3 and S4 facing the flange space CV2 are first and second for forming the first and second flange surfaces 12a and 12b of the flange portion 12 of the objective lens 10, respectively. 2 corresponding to the end surfaces of the outer peripheral molds 64b and 74b described later. The fifth and sixth transfer surfaces facing the flange space CV2 are for forming the inner diameter surfaces 14a and 14b of the flange portion 12, respectively, and correspond to the end surfaces of the outer peripheral molds 64b and 74b. The fifth and sixth transfer surfaces S5 and S6 are formed to be inclined with respect to the lens optical axis OA of the objective lens 10. The seventh transfer surface S7 facing the flange space CV2 is for forming the outer diameter surface 14c of the objective lens 10, and corresponds to the end surfaces of the outer peripheral molds 64b and 74b. The fourth transfer surface S4 is formed at a position shallower from the parting surface than the vertex Q3 of the second transfer surface S2.

A pair of opposed eighth and ninth transfer surfaces S8, S9 facing the neck space CV3 are the third and fourth for forming the first and second end surfaces EP1, EP2 of the neck portion 13 of the objective lens 10, respectively. And corresponds to the end surfaces of the outer peripheral molds 64b and 74b. The eighth and ninth transfer surfaces S8, S9 are flat surfaces so that the first and second end surfaces EP1, EP2 of the neck portion 13 are mirror surfaces.

Returning to FIG. 2, the movable mold 41 on the movable side includes a mold plate 61 that forms the parting surface PS <b> 1, a receiving plate 62 that supports the mold plate 61 from behind, and an attachment plate that supports the receiving plate 62 from behind. 63, a core mold 64a as a mold insert that forms the mold space CV (particularly the main body space CV1) shown in FIG. 3, and a peripheral part that forms the mold space CV (particularly the flange space CV2 and the neck space CV3). And an outer peripheral mold 64b. Further, the movable mold 41 has a protruding pin 65 that protrudes and releases the runner portion RP of the molded product before separating the objective lens 10, a movable rod 67a that pushes the core mold 64a from the back, and the protruding pin 65 behind. A movable rod 67b that pushes from the front and a movable member 67 that moves the movable rods 67a and 67b back and forth. Here, the core mold 64a is driven by the advancing movable rod 67a to advance toward the fixed mold 42, and automatically retracts and returns to the original position as the movable rod 67a retracts. Further, the ejecting pin 65 is driven by the moving movable rod 67b to move forward to the fixed mold 42 side, and automatically retracts and returns to the original position as the movable rod 67b moves backward. The advancing / retracting member 68 is driven by the advancing / retreating drive device 52 and moves forward and backward in the AB direction at an appropriate timing and amount.

In the movable mold 41, a mold plate 61 that is a mold part on the mold surface side includes a runner recess 61b that forms the runner portion RP shown in FIGS. 1A and 1B, a gate recess 61c that forms the gate portion GP, and an outer peripheral mold. 64b and the protruding pin 65 are provided with through holes 61e and 61f provided for insertion.

The fixed mold 42 on the fixed side forms a mold plate 71 that forms the parting surface PS2, a mounting plate 72 that supports the mold plate 71 from behind, and a mold space CV (particularly a main body space CV1) shown in FIG. A core die 74a as a mold insert and an outer peripheral die 74b as a peripheral part forming a die space CV (particularly, a flange space CV2 and a neck space CV3) are provided.

In the fixed mold 42, a mold plate 71 which is a mold part on the mold surface side includes a runner recess 71b for forming the runner part RP shown in FIGS. 1A and 1B, a gate surface 71c for forming the gate part GP, and an outer peripheral mold. And a through hole 71e provided for inserting 74b.

Hereinafter, the dimensions of the mold space CV and the flow path space FC will be described with reference to FIG. The mold space CV has a shape obtained by inverting the contour of the objective lens 10, and the dimensions of the mold space CV correspond to the dimensions of the objective lens 10 described above. That is, in the main body space CV1 corresponding to the optical function unit 11, the lens outer diameter in the direction perpendicular to the lens optical axis OA is G (mm) (see FIG. 1B), and the lens axis on the lens axis in the direction parallel to the lens optical axis OA. When the thickness is t (mm) and the minimum thickness of the neck portion in the direction parallel to the lens optical axis OA in the neck space CV3 corresponding to the neck portion 13 is T (mm), G ≦ 4.05 (mm ) And t / T> 4.0, and in the flow path space FC (gate portion GS) formed by the gate recess 61c and the gate surface 71c corresponding to the gate portion GP, it is perpendicular to the lens optical axis OA. When the gate width in the direction is W (mm) and the gate depth in the direction parallel to the lens optical axis OA is D (mm), the following conditional expressions (1) to (3) are satisfied.
0.5T ≦ D ≦ 1.33T (1)
1.5T ≦ W ≦ 3T (2)
D · W ≧ 1.5T ² (3)

Here, as already explained, when the molten resin passes through the gate portion GS in the molding of the objective lens 10, the molten resin that comes into contact with the mold surface such as the wall surface of the gate portion GS is the first and second gold. Cooled by the molds 41 and 42, the viscosity increases. Therefore, the molten resin substantially flows only through the central portion of the gate portion GS and flows into the mold space CV. In the mold space CV and the flow path space FC, the gate depth D is increased to 0.5T or more and the gate width W is set to 1.5T or more so as to satisfy the conditional expressions (1) to (3). gate cross-sectional area of (D · W) by such a 1.5T ² or more, the cross sectional area of passage of the molten resin at the center of the gate portion GS is excessive when passing the molten resin in the gate portion GS The mold space CV can be fully filled without requiring a high injection pressure. Thereby, it is possible to prevent optical performance deterioration due to unfilling due to insufficient injection pressure and excessive pressure.

In addition, by setting the gate width W to 3T or less, it is possible to suppress the cutting margin of the flange portion 12 when finishing gate cutting, and to avoid adverse effects on the first and second optical surfaces OS1 and OS2. Furthermore, by setting the gate depth D to 1.33 T or less, the turbulence caused by the flow of the molten resin hits the inclined surfaces of the inner diameter surfaces 14 a and 14 b of the protruding portion 14 provided on the radially outer side of the neck portion 13. It is possible to suppress the flow orientation of the resin that deteriorates the optical performance of the first and second optical surfaces OS1 and OS2 caused by the flow.

In particular, the objective lens 10 for a small pickup device such as a notebook personal computer has G ≦ 4.05 (mm) and t / T> with respect to the lens outer diameter G, the lens axis thickness t, and the minimum thickness T of the neck portion. 4.0. For this reason, the cross-sectional area of the neck portion 13 is relatively small, and it is necessary to prevent the molten resin from flowing in the neck portion 13. When the dimensions of the mold space CV and the flow path space FC (the dimensions of the objective lens 10) satisfy the conditional expressions (1) to (3), the flow of the molten resin in the neck portion 13 is not extremely hindered, and high accuracy is achieved. In addition, it is possible to obtain a lens that ensures transferability. The lens outer diameter G is preferably 1.45 (mm) ≦ G ≦ 4.05 (mm). By setting the lens outer diameter G to 1.45 (mm) or more, it is possible to prevent the fine shape provided on the lens optical surface from becoming too small, and thus it is possible to perform transfer with higher accuracy. Further, the uneven thickness ratio t / T is preferably 9.0> t / T> 4.0. By making t / T smaller than 9.0, the uneven thickness ratio does not become too large, so that it is possible to prevent the flow rate of the molten resin from being extremely limited.

On the other hand, when the gate depth D is smaller than 0.5T, the gate width W is smaller than 1.5T, and the gate cross-sectional area D · W is smaller than 1.5T ² , the central portion of the gate portion GS The cross-sectional area of the molten resin cannot fill the mold space CV, that is, the area cannot sufficiently transfer the first and second transfer surfaces S1 and S2. Thereby, in order to maintain the injection speed for fully filling the mold space CV with the molten resin, a large injection pressure for allowing the molten resin to pass through the gate portion GS is required. Thus, since a larger injection pressure is required to prevent a decrease in speed when the molten resin passes through the neck portion 13, a large injection pressure is required when the molten resin is filled in the mold space CV. This causes the resin to be oriented in the flow direction. As a result, birefringence occurs, and the optical performance of the molded objective lens 10 deteriorates. If the gate width W is wider than 3T, the gate width W becomes too large with respect to the flange width F, which is the distance from the outer diameter of the optical function portion 11 of the molded objective lens 10 to the outer diameter of the flange portion 12. . Therefore, the cutting margin of the flange portion 12 increases at the time of gate cut (D cut), the cut surface approaches the first and second optical surfaces OS1 and OS2, and the adverse effects of stress strain generated at the time of gate cut are adversely affected by the first and second optical surfaces. Surfaces OS1 and OS2 will receive. Further, when the gate depth D is deeper than 1.33T, the molten resin flowing smoothly from the gate portion GS is excessively flowed into the mold space CV at the convex step portion of the neck space CV3 that hinders the flow of the molten resin. To be suppressed. As a result, a turbulent flow is generated at the convex step portion of the neck space CV3, and flow orientation caused by the flow of the molten resin is generated on the first and second optical surfaces OS1, OS2 in the vicinity of the neck portion 13 of the molded objective lens 10. As a result, optical performance deteriorates.

Hereinafter, a method for manufacturing the objective lens 10 will be briefly described. First, the movable mold 41 and the fixed mold 42 are appropriately heated by a mold temperature controller (not shown). Thereby, the temperature of the mold part that forms the mold space CV in both molds 41 and 42 is set to a temperature state suitable for molding. Next, the mold opening / closing drive device 51 is operated, the movable mold 41 is advanced to the fixed mold 42 side to be in the mold closed state, and the closing operation of the mold opening / closing drive device 51 is further continued, whereby the movable mold 41 is moved. The mold is clamped to clamp the fixed mold 42 with a necessary pressure. Next, by operating an injection device (not shown), the molten resin is injected into the mold space CV between the clamped movable mold 41 and the fixed mold 42 with a necessary pressure through the gate portion GS or the like. Let the injection to inject. After the molten resin is introduced into the mold space CV, the molten resin in the mold space CV is gradually cooled by heat dissipation, so that the molten resin is solidified with the cooling and waits for completion of molding. Next, the mold opening / closing drive device 51 is operated to retract the movable mold 41 and perform mold opening to separate the movable mold 41 from the fixed mold 42. As a result, the objective lens 10, which is a molded product, is released from the fixed mold 42 while being held by the movable mold 41. Next, the advancing / retreating drive device 52 is operated, and the objective lens 10 is projected by the core mold 64a and the ejection pin 65 via the movable rods 67a and 67b. As a result, the objective lens 10 is urged by the movable rod 67a or the like and pushed out toward the fixed mold 42, and the objective lens 10 is released from the movable mold 41. The objective lens 10 released from both molds 41 and 42 is carried out of the molding apparatus by gripping a sprue portion extending from the runner portion RP of the objective lens 10. Further, the objective lens 10 after being carried out is subjected to external processing such as removal of the gate portion GP to be a product for shipment.

In the objective lens and the objective lens manufacturing method according to the present embodiment described above, the molded objective lens 10 is obtained by satisfying the conditional expressions (1) to (3) described above when the elements for molding the objective lens 10 satisfy the conditional expressions (1) to (3). It has a fine shape transferred with high precision. That is, when the objective lens 10 is molded, it is possible to prevent unfilling due to insufficient injection pressure and optical performance deterioration due to excessive pressure. Further, it is possible to suppress the cutting margin of the flange portion 12 at the time of finishing gate cutting, and to avoid adverse effects on the first and second optical surfaces OS1 and OS2. Furthermore, it suppresses the flow orientation of the resin that deteriorates the optical performance caused by the turbulent flow caused by the flow of the molten resin hitting the convex portion of the neck near the neck 13 of the first and second optical surfaces OS1, OS2. can do. In particular, an objective lens having a small diameter and a fine shape as used in, for example, a notebook personal computer can be transferred with high accuracy and have good optical characteristics.

Hereinafter, an example of a test for considering the external dimensions and optical performance of the example and the comparative example of the objective lens 10 will be described. Here, two examples of “light utilization efficiency” and “wavefront aberration” are adopted as examples of targets for optical performance evaluation, and optical performances of objective lenses having different gate depths D and gate widths W as external dimensions. Consider. “Light utilization efficiency” is defined as the ratio of the amount of light of the spot light that passes through the objective lens and is collected with respect to the amount of light incident on the optical surface of the objective lens that is the target optical lens. . Specifically, the light utilization efficiency is obtained by using, for example, a measuring device similar to a microscope, and without using an objective lens as a test lens, that is, using a light amount value L1 in a state without a test lens as a reference as an eyepiece. It is measured by measuring with a power meter arranged at the corresponding position, and then measuring the light quantity value L2 in the same manner with the lens to be tested, and calculating from both measurement results as L2 ÷ L1 × 100 [%]. “Wavefront aberration” is based on “spherical aberration”, “coma aberration”, and “astigmatism” among objective lenses that are optical lenses to be measured using an interferometer. Aberration is adopted. As the light source light, BD light (wavelength 405 nm), DVD light (wavelength 660 nm), and CD light (wavelength 785 nm) are used for both light utilization efficiency and wavefront aberration.
Table 1 shows the test results of the above test regarding the relationship between the external dimensions of the objective lens and the optical performance. Here, in the evaluation of the test results, “◯” indicates that the optical performance is good, “×” indicates that the objective lens is distorted by the gate cut, and “XX” indicates that the molten resin is disturbed. It indicates that the optical performance has deteriorated due to the flow, and “xxx” indicates that a transfer failure has occurred on the optical surface. More specifically, “○” means that “light utilization efficiency” satisfies the required standard range of light utilization efficiency, and a specific example of the numerical value is BD light (wavelength 405 nm). Satisfying 87% ± 5%, DVD light (wavelength 660 nm) 75% ± 5%, and CD light (wavelength 785 nm) 61% ± 5%, and “spherical aberration” as measured by an interferometer, It means that “coma” and “astigmatism” satisfy the required standard range. “X” means that at least “coma” is a value out of the standard. “XX” means that at least “astigmatism” is a value deviating from the standard. “XXX” means that at least “light utilization efficiency” is a value out of the standard. Note that there may be a plurality of “x”, “xxx”, and “xxx”.

As shown in Table 1, the optical performance of the objective lens is “good” because (D, W) = (1.0T, 1.5T), (1.33T, 1.5T), (1. 0T, 2.0T), (1.33T, 2.0T), (0.5T, 3.0T), (1.0T, 3.0T), (1.33T, 3.0T) Met. This satisfies the conditional expressions (1) to (3).

In Table 1, any combination that did not satisfy the above conditional expressions (1) to (3) caused a problem in optical performance due to poor transfer of the optical surface.

Hereinafter, examples of specific dimensions of the objective lens 10 will be described.
In this embodiment, the objective lens 10 has the following dimensions: the lens outer diameter G is 4.00 (mm), the gate width W is 0.80 (mm), the gate depth D is 0.44 (mm), and the thickness on the lens axis. t was 2.0 (mm), and the minimum thickness T of the neck was 0.475 (mm). All dimensions satisfy the above conditions (1) to (3) and the range of t / T> 4.0. The objective lens 10 having a fine shape transferred with high accuracy was obtained by molding the objective lens 10 with a molding die corresponding to the objective lens 10 having the above dimensions.

In this embodiment, the objective lens 10 has a lens outer diameter G of 4.00 (mm), a gate width W of 1.1 (mm), a gate depth D of 0.38 (mm), and a thickness on the lens axis. t was 2.0 (mm), and the minimum thickness T of the neck was 0.475 (mm). All dimensions satisfy the above conditions (1) to (3) and the range of t / T> 4.0. The objective lens 10 having a fine shape transferred with high accuracy was obtained by molding the objective lens 10 with a molding die corresponding to the objective lens 10 having the above dimensions.

In this embodiment, the objective lens 10 has a lens outer diameter G of 4.00 (mm), a gate width W of 0.66 (mm), a gate depth D of 0.50 (mm), and a thickness on the lens axis. t was 2.0 (mm), and the minimum thickness T of the neck was 0.42 (mm). All dimensions satisfy the above conditions (1) to (3) and the range of t / T> 4.0. The objective lens 10 having a fine shape transferred with high accuracy was obtained by molding the objective lens 10 with a molding die corresponding to the objective lens 10 having the above dimensions.

In the present embodiment, the objective lens 10 has a lens outer diameter G of 4.00 (mm), a gate width W of 0.75 (mm), a gate depth D of 0.48 (mm), and a thickness on the lens axis. t was 2.0 (mm), and the minimum thickness T of the neck was 0.38 (mm). All dimensions satisfy the above conditions (1) to (3) and the range of t / T> 4.0. The objective lens 10 having a fine shape transferred with high accuracy was obtained by molding the objective lens 10 with a molding die corresponding to the objective lens 10 having the above dimensions.

[Second Embodiment]
Hereinafter, the objective lens according to the second embodiment will be described. The objective lens according to the second embodiment is a modification of the objective lens according to the first embodiment, and parts not specifically described are the same as those in the first embodiment.

As shown in FIG. 4A, in the flange portion 212 of the present embodiment, the first flange surface 12 a is disposed so as to be recessed from the first end surface EP <b> 1 of the neck portion 13. That is, the protruding portion 214 of the flange portion 212 has a shape in which only the optical information recording medium side, that is, the second optical surface OS2 side protrudes. In the flange portion 212, the inner diameter surface 214a has a tapered shape that narrows on the laser light source side.

As shown in FIG. 4B, the molding die 40 for molding the objective lens 210 corresponds to the dimensions of the objective lens 210. In the movable mold 41, the fifth transfer surface S5 is formed so as to be inclined with respect to the lens optical axis OA corresponding to the inner diameter surface 214a of the flange portion 212.

In the objective lens 210 according to the present embodiment, the convex portion of the neck portion 13 that obstructs the flow of the molten resin is eliminated in the neck portion 13 on the first optical surface OS1 side where the first flange surface 12a is recessed. When the objective lens 210 is molded, turbulent flow due to inhibition of the flow of the molten resin does not occur, and the objective lens 210 flows smoothly. Therefore, it is possible to suppress the deterioration of the optical performance in the vicinity of the neck portion 13 of the first and second optical surfaces OS1, OS2.

In addition, in the flange part 212, you may arrange | position not 2nd flange surface 12b rather than 1st flange surface 12a rather than 2nd end surface EP2 of the neck part 13. FIG.

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

As shown in FIG. 5A, the flange portion 312 of the present embodiment has a step shape 315 that changes the thickness in the direction parallel to the lens optical axis OA on the second flange surface 12b side. The step shape 315 is formed in two steps on the inner diameter surface 14 b of the flange portion 312. Specifically, a first step 315a is formed on the inner side of the second flange surface 12b, that is, on the optical function unit 11 side, and a second step 315b is disposed on the outer side of the second flange surface 12b adjacent to the first step 315a. Is formed. The first step portion 315a is provided at a position far from the information recording medium side, and the second step portion 315b is provided at a position closer to the information recording medium side than the first step portion 315a. That is, the step shape 315 has a staircase shape in which the flange thickness increases toward the outside of the flange portion 12. A surface 315c connecting the first step portion 315a and the second step portion 315b is a tapered surface extending toward the information recording medium side. A surface 315d adjacent to the inside of the first step portion 315b is a tapered surface extending toward the information recording medium side.

As shown in FIG. 5B, the molding die 40 for molding the objective lens 310 corresponds to the dimensions of the objective lens 310. In the fixed mold 42, the sixth transfer surface S6 is formed with a step-shaped transfer surface ST1 corresponding to the step shape 315 of the flange portion 312.

In the objective lens 310 according to the present embodiment, the stepped shape 315 that is an inclined portion that is the boundary between the second flange surface 12b and the second end surface EP2 becomes gentle, and the molten resin is more smoothly formed when the objective lens 310 is molded. Can flow into the neck portion 13.

In the flange portion 312, a step shape 315 may be provided on the first flange surface 12a side.

[Fourth Embodiment]
The objective lens according to the fourth embodiment will be described below. The objective lens according to the fourth embodiment is a modification of the objective lens according to the first embodiment, and parts not specifically described are the same as those according to the first embodiment.

As shown in FIG. 6A, the neck portion 13 of the present embodiment has a convex mark M for mold identification on the second end face EP2. The mark M is substantially hemispherical, and is arranged near the boundary between the neck portion 13 and the optical function portion 11 on the information recording medium side. Thus, even if the objective lens 410 has the mark M on the neck portion 13 where the molten resin is difficult to pass during molding, the objective lens 410 satisfies the conditional expressions (1) to (3). The mark M can also be transferred with high accuracy. The place where the mark M is disposed is not limited to the second end surface EP2, and may be disposed on the second flange surface 12b.

As shown in FIG. 6B, the molding die 40 for molding the objective lens 410 corresponds to the dimensions of the objective lens 410. In the fixed mold 42, the ninth transfer surface S9 is formed with a concave transfer surface PT corresponding to the mark M of the neck portion 13.

[Fifth Embodiment]
The objective lens according to the fifth embodiment will be described below. Note that the objective lens of the fifth embodiment is a modification of the objective lens of the second embodiment, and parts not specifically described are the same as those of the second embodiment.

7A, in the flange portion 512 of the present embodiment, the first flange surface 12a has a step shape 515 that changes the thickness parallel to the lens optical axis OA. The step shape 515 is formed in two steps on the inner diameter surface 14 a of the flange portion 512. Specifically, a first step 515a is formed on the inner side of the first flange surface 12a, that is, on the optical function unit 11 side, and a second step 515b is disposed on the outer side of the first flange surface 12a adjacent to the first step 515a. Is formed. The first step portion 515a is provided at a position closer to the laser light source side, and the second step portion 515b is provided at a position farther from the laser light source side than the first step portion 515a. That is, the step shape 515 has a stepped shape in which the flange thickness decreases toward the outside of the flange portion 12. A surface 515c that connects the first step portion 515a and the second step portion 515b is a tapered surface that narrows toward the laser light source side. A surface 515d adjacent to the outside of the second step portion 515b is a surface in a direction parallel to the lens optical axis OA. In the flange portion 512, a step shape 515 may be provided on the second flange surface 12b.

As shown in FIG. 7B, the molding die 40 for molding the objective lens 510 corresponds to the dimensions of the objective lens 510. In the movable mold 41, a step-shaped transfer surface ST2 corresponding to the step shape 515 of the flange portion 512 is formed on the fifth transfer surface S5.

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 above embodiment, if the shape of the mold space CV provided in the injection mold constituted by the fixed mold 42 and the movable mold 41 satisfies the conditional expressions (1) to (3), Various shapes can be used. That is, the shape of the mold space CV formed by the core molds 64a and 74a is merely an example, and can be appropriately changed according to the purpose of the objective lens 10 and other optical elements. For example, the first optical surface OS1 of the objective lens 10 may be molded with the fixed mold 42, and the second optical surface OS2 having a smaller curvature than the first optical surface OS1 may be molded with the movable mold 41. it can.

Further, in the above embodiment, the fine shape FS formed in the optical function unit 11 of the objective lens 10 is not limited to the illustrated one, and various diffractive structures and the like according to applications can be used.

In the above embodiment, the second flange surface 12b is arranged lower than the vertex Q2 of the second optical surface OS2, but if the molten resin flow at the neck portion 13 is not hindered, The second flange surface 12b may be disposed higher than the vertex Q2 of the second optical surface OS2. That is, the second flange surface 12b may protrude beyond the second optical surface OS2.

In the above embodiment, the outer periphery of the second optical surface OS2 is formed inside the outer periphery of the first optical surface OS1, but the outer periphery of the second optical surface OS2 is the same as the outer periphery of the first optical surface OS1. They may be formed at substantially the same position on the vertical line. Moreover, you may form outside the outer periphery of 1st optical surface OS1.

Moreover, in the said embodiment, although 1st and 2nd end surface EP1, EP2 of the neck part 13 had a mirror surface, it does not need to be a mirror surface. Moreover, it is good also considering either one of 1st and 2nd end surface EP1, EP2 as a mirror surface.

Claims (25)

1. Resin introduced into a mold space from a gate portion provided at an outer peripheral edge of the flange portion, having an optical function portion having a fine shape on an optical surface and a flange portion provided around the optical function portion An objective lens that is injection molded by and used to read and / or write information on BD, DVD, and CD,
   The optical function unit includes a first optical surface and a second optical surface having a smaller curvature than the first optical surface,
   A neck portion is provided between the optical function portion and the flange portion,
   The lens outer diameter in the direction perpendicular to the lens optical axis is G (mm), and in the optical function unit, the thickness on the lens axis in the direction parallel to the lens optical axis is t (mm),
   When the minimum thickness of the neck portion in the direction parallel to the lens optical axis is T (mm), G ≦ 4.05 (mm) and t / T> 4.0. ,
   In the gate portion, when the gate width in the direction perpendicular to the lens optical axis is W (mm) and the gate depth in the direction parallel to the lens optical axis is D (mm), the following conditional expression is satisfied. Objective lens characterized by satisfying.
   0.5T ≦ D ≦ 1.33T
   1.5T ≦ W ≦ 3T
   D · W ≧ 1.5T ²
2. The flange portion has a first flange surface on the first optical surface side and a second flange surface on the second optical surface side,
   The objective lens according to claim 1, wherein the second flange surface is disposed lower than a vertex of the second optical surface.
3. 3. The objective lens according to claim 1, wherein an outer periphery of the second optical surface is formed on an inner side than an outer periphery of the first optical surface.
4. The neck portion has a first end surface on the first optical surface side and a second end surface on the second optical surface side,
   At least one of a surface connecting the first flange surface and the first end surface and a surface connecting the second flange surface and the second end surface is inclined with respect to the lens optical axis. The objective lens according to any one of claims 1 to 3.
5. The objective lens according to claim 4, wherein at least one of the first end surface and the second end surface has a mirror surface.
6. One of the first flange surface and the second flange surface is disposed on the neck portion side so as to be recessed from either the corresponding first end surface or the second end surface. Item 6. The objective lens according to any one of Items 4 and 5.
7. The said flange part has a level | step difference shape which changes the thickness of the direction parallel to the said lens optical axis in at least any one side of a said 1st flange surface and a said 2nd flange surface. The objective lens according to any one of 6 to 6.
8. The objective lens according to any one of claims 4 to 7, wherein a convex mark for identifying a mold is provided on the second end face.
9. The objective lens according to any one of claims 1 to 7, wherein a convex mark for identifying a mold is provided on the second flange surface.
10. When the thickness on the lens axis in the direction parallel to the lens optical axis is t (mm) and the focal length of a light beam having a wavelength of 500 nm or less is f (mm), 0.8 ≦ t / f ≦ 2.0. The objective lens according to any one of claims 1 to 9, wherein
11. Resin introduced into a mold space from a gate portion provided at an outer peripheral edge of the flange portion, having an optical function portion having a fine shape on an optical surface and a flange portion provided around the optical function portion A method of manufacturing an objective lens that is injection-molded by and used for recording and / or reproducing information of BD, DVD, and CD,
    Molten resin is injected into a mold space formed by a first mold that molds the first optical surface of the objective lens and a second mold that molds the second optical surface of the objective lens, and the objective Forming a lens;
    Removing the objective lens from the mold space by relatively opening the first mold and the second mold apart from each other; and
    With
    The objective lens has a neck portion between the optical function portion and the flange portion,
    The lens outer diameter in the direction perpendicular to the lens optical axis is G (mm), and in the optical function unit, the thickness on the lens axis in the direction parallel to the lens optical axis is t (mm),
    When the minimum thickness of the neck portion in the direction parallel to the lens optical axis is T (mm), G ≦ 4.05 (mm) and t / T> 4.0. ,
    In the gate portion, when the gate width in the direction perpendicular to the lens optical axis is W (mm) and the gate depth in the direction parallel to the lens optical axis is D (mm), the following conditional expression is satisfied. An objective lens manufacturing method characterized by satisfying:
    0.5T ≦ D ≦ 1.33T
    1.5T ≦ W ≦ 3T
    D · W ≧ 1.5T ²
12. The optical function unit includes a first optical surface and a second optical surface having a smaller curvature than the first optical surface,
    The flange portion has a first flange surface on the first optical surface side and a second flange surface on the second optical surface side,
    The method of manufacturing an objective lens according to claim 11, wherein the second flange surface is disposed lower than a vertex of the second optical surface.
13. 13. The method of manufacturing an objective lens according to claim 11, wherein an outer periphery of the second optical surface is formed inside an outer periphery of the first optical surface.
14. The neck portion has a first end surface on the first optical surface side and a second end surface on the second optical surface side,
    At least one of a surface connecting the first flange surface and the first end surface and a surface connecting the second flange surface and the second end surface is inclined with respect to the lens optical axis. The method for manufacturing an objective lens according to any one of claims 11 to 13.
15. 15. The method of manufacturing an objective lens according to claim 14, wherein at least one of the first end surface and the second end surface has a mirror surface.
16. One of the first flange surface and the second flange surface is disposed in the neck portion so as to be recessed from either the corresponding first end surface or the second end surface. The manufacturing method of the objective lens as described in any one of 14 and 15.
17. Resin introduced into a mold space from a gate portion provided at an outer peripheral edge of the flange portion, having an optical function portion having a fine shape on an optical surface and a flange portion provided around the optical function portion A molding die for molding an objective lens that is injection-molded by and used to read and / or write information on BD, DVD, and CD,
    A first mold having a first transfer surface forming a first optical surface of the objective lens and a first molding surface forming a first flange surface extending around the first optical surface; ,
    A second transfer surface that forms a second optical surface having a smaller curvature than the first optical surface; and a second molding surface that forms a second flange surface extending around the second optical surface. A second mold,
    With
    A third molding surface forming a neck portion of the objective lens between the first transfer surface and the first molding surface;
    A fourth molding surface that forms a neck portion of the objective lens between the second transfer surface and the second molding surface;
    The dimension of the mold space formed by the first mold and the second mold is as follows:
    The lens outer diameter in the direction perpendicular to the lens optical axis is G (mm), and in the optical function unit, the thickness on the lens axis in the direction parallel to the lens optical axis is t (mm),
    When the minimum thickness of the neck portion in the direction parallel to the lens optical axis is T (mm), G ≦ 4.05 (mm) and t / T> 4.0. ,
    In the gate portion, when the gate width in the direction perpendicular to the lens optical axis is W (mm) and the gate depth in the direction parallel to the lens optical axis is D (mm), the following conditional expression is satisfied. A molding die characterized by corresponding to the objective lens to be filled.
    0.5T ≦ D ≦ 1.33T
    1.5T ≦ W ≦ 3T
    D · W ≧ 1.5T ²
18. The second molding surface is formed at a position shallower than a die-mating surface between the first mold and the second mold than an apex of the second transfer surface. Item 18. A mold according to Item 17.
19. The molding die according to any one of claims 17 and 18, wherein an outer periphery of the second transfer surface is formed inside an outer periphery of the first transfer surface.
20. At least one of a surface connecting the first molding surface and the third molding surface and a surface connecting the second molding surface and the fourth molding surface is inclined with respect to the lens optical axis. The molding die according to any one of claims 17 to 19, wherein the molding die is provided.
21. The one of the first molding surface and the second molding surface is disposed so as to be recessed from either the third molding surface or the fourth molding surface. 20. A molding die according to 20.
22. The transfer surface for forming a step shape that changes the thickness in a direction parallel to the lens optical axis is provided on at least one of the first molding surface and the second molding surface. The molding die according to any one of 20 and 21.
23. The molding die according to any one of claims 17 to 22, wherein the fourth molding surface has a concave transfer surface for transferring a convex mark for mold identification.
24. The molding die according to any one of claims 17 to 22, further comprising a concave transfer surface for transferring a convex mark for mold identification to the second molding surface.
25. The dimension of the mold space is such that the thickness on the lens axis in the direction parallel to the lens optical axis of the objective lens is t (mm), and the focal length of the objective lens in a light beam having a wavelength of 500 nm or less is f (mm). Furthermore, it corresponds to the objective lens which is 0.8 <= t / f <= 2.0, The molding die as described in any one of Claim 17-24 characterized by the above-mentioned.

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