JPH09197239A - Production of plastic lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a plastic lens capable of easily making fine adjustment of molds for adjusting the relative positions of both side lens faces with a holding frame and the spacing between both side lens faces and making the refractive index in the lens part uniform with good resin flow without a large change to the shape over the entire part of the lens. SOLUTION: In the process for producing the plastic lens by integrally molding the holding frame on the circumference of the lens part and providing the inner periphery end of the holding frame with a cylindrical part parallel with the optical axis, the two split segmental molds 20, 21 capable of molding the holding frame on the side nearer the outer periphery than the cylindrical part and columnar cores 23, 24 capable of setting the insertion depth into the circular holes 22 formed in the respective segmental molds 20, 21 with high accuracy are used and concave curvilinear surfaces 25 forming the effective lens faces are formed at the front ends of the respective cores 23, 24 by using these dies and cores. Further, annular planes 26 are formed on the circumferences of these surfaces and tapered surfaces 27 are formed on the outer peripheries of annular planes 26. The respective cores 23, 24 are provided with outer peripheral surfaces 28 for molding the cylindrical parts. The thickness of the lens part and the relative positions in the optical axis direction of the lens part with respect to the holding frame are set by adjusting the insertion depth of the cores 23, 24 into the respective segmental molds 20, 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact and high performance for focusing a laser beam when writing and reading optical information on an optical information recording medium such as a compact disc (CD), an optical disc and an optical card. Plastic lenses.

[0002]

2. Description of the Related Art Conventionally, various types of plastic lenses have been provided which are integrally formed with a holding frame around a lens portion and have good mountability and handleability on an optical device body.
No. 617 discloses it. However, in the conventional plastic lens, since an acute angle concave portion is formed at the boundary between the lens portion and the holding frame, the performance of the lens, that is, the high accuracy of the reference point in the measurement of the curvature of the effective lens surface is high. Setting was impossible. Here, it is considered that the lens portion and the holding frame are continuously formed with a smooth curved surface. However, similarly to the above, it is impossible to set the reference point with high accuracy in measuring the curvature of the effective lens surface. .

[0003] Regarding the moldability, the flow of the injected acrylic resin or the like is disturbed in the acute concave portion at the boundary between the lens portion and the holding frame, causing a phenomenon that the resin is cooled unevenly. Local distortion of refractive index occurs due to internal distortion and uneven density, which may seriously affect the performance of the lens, and the sharp edge on the mold makes it difficult to manufacture In addition, the edge may be damaged, and there is a problem in durability.

Further, since the side surface of the holding frame facing the lens surface is generally formed as an inclined surface which is expanded outward, both lens surfaces are oriented in the optical axis direction with respect to the holding frame fixed to the optical device body. If it becomes necessary to perform the molding by moving the mold in parallel, the mold must be remade, which tends to increase the cost.

[0005]

SUMMARY OF THE INVENTION In view of the above situation, the present invention is to solve the problems such as the curvature of the effective lens surface of a lens molded by trial, and the like. Fine adjustment of the mold for adjusting the relative position of the lens surfaces on both sides to the holding frame and the distance between the lens surfaces on both sides can be easily performed without causing it, and the resin flow such as acrylic resin is good and the refractive index in the lens part The point is to provide a method of manufacturing a plastic lens capable of making uniform.

[0006]

In order to solve the above-mentioned problems, the present invention integrally forms a holding frame around the lens portion, and a cylindrical portion parallel to the optical axis at the inner peripheral end of the holding frame. A method of manufacturing a plastic lens comprising: a split mold capable of molding a holding frame on the outer peripheral side of the cylindrical portion; and a highly accurate insertion depth in a circular hole formed in each split mold. With a cylindrical core that can be set to, a concave curved surface for molding an effective lens surface is formed at the tip of each core, an annular flat surface is formed around it, and a tapered surface is formed on the outer periphery of the annular flat surface. , Each core is provided with an outer peripheral surface for molding the cylindrical part, and the thickness of the lens part and the relative position of the lens part with respect to the holding frame in the optical axis direction are set by adjusting the insertion depth of the core into each split mold. The manufacturing method of the plastic lens It was.

Here, the method of manufacturing a plastic lens according to the present invention is such that a concave curved surface for molding an effective lens surface is formed at the tip end of a split mold capable of molding a holding frame on the outer peripheral side from a cylindrical portion. The insertion depth of each core can be set with high precision, so the effective lens surfaces on both sides are moved in parallel in the optical axis direction to adjust the relative position of the effective lens surfaces on both sides to the holding frame and the distance between the lens surfaces on both sides However, even if the insertion depth of each core into the split mold is adjusted, only the length of the cylindrical portion parallel to the optical axis formed at the inner peripheral end of the holding frame changes. No significant change occurs in the overall shape of the lens. In addition, since there is no sharp edge in the mold, the resin flows well and the resin is injected uniformly into the mold, so that there is no internal distortion, the density is uniform, and the local variation in the refractive index is eliminated. . Furthermore, since an annular flat surface is formed around the concave curved surface that forms the effective lens surface of each core, a flat portion orthogonal to the optical axis is formed between the holding frame and the outer peripheral edges of both lens surfaces by this annular flat surface. The portion can be used as a reference point for measuring the curvature and minute irregularities when evaluating the performance of the effective lens surface.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the embodiments shown in the accompanying drawings. FIG. 1 shows a representative embodiment of the present invention, in which A denotes a plastic lens, 1 denotes a lens portion, and 2 denotes a holding frame.

In the plastic lens A according to the present invention, a holding frame 2 is integrally formed around a lens portion 1 which is an aspheric lens widely used in the field of micro optics, and both sides of the lens portion 1 are effective. An annular flat portion 5 perpendicular to the optical axis 4 between the outer peripheral edge of the lens surfaces 3 and 3 and the holding frame 2
And cylindrical portions 6, 6 parallel to the optical axis 4 are formed at inner peripheral ends of the holding frame 2 facing the both effective lens surfaces 3, 3. Here, the width of the flat portion 5 orthogonal to the optical axis 4 is preferably 0.2 to 0.5 mm. If the width is smaller than 0.2 mm, it is difficult to become a measurement reference point, and the width is smaller than 0.5 mm. Wide and plastic lens A
It is not suitable for miniaturization.

The holding frame 2 is formed so as to protrude from the effective lens surface 3 in the direction of the optical axis 4 to form holding rings 7 and 7 which also have a function of protecting the effective lens surface 3. An annular mounting ring 8 protruding laterally is formed. The distance between the flat portions 5 and 5 is set substantially equal to or wider than the width of the mounting ring 8 in the optical axis direction so that the resin flow is improved. Further, a tapered inclined surface 9 which is expanded outward from the outer edge of the flat portion 5 to the cylindrical portion 6 is formed to widen the field of view, and an antireflection film is formed on the inclined surface 9. Thus, it is possible to prevent the incident light irradiated on the inclined surface 9 from being reflected again toward the effective lens surface 3 and becoming stray light.

In the plastic lens A, as shown in FIG. 2, one holding ring 7 is fitted in a mounting hole 11 opened in the main body 10 of the optical device, and one side of the mounting ring 8 is attached to the periphery of the mounting hole 11. Alternatively, the mounting reference planes 12 formed on both sides and orthogonal to the optical axis 4 are fixed in a state of being in contact with each other, and the laser light 13 incident from one effective lens surface 3 is recorded on an optical information such as a compact disc, an optical disc or an optical card. The light is focused on the medium 14, and the reflected light is again detected by the photodetector through the effective lens surface 3 to read the optical information. The optical information recording medium 14 is formed by laminating a recording film 17 in which pits 16 are formed on tracks by forming fine irregularities or locally changing the light reflectance and the direction of magnetization on a substrate 15. And a protective film 18 on the upper surface that is transparent to the wavelength of the laser light used.
Are laminated.

Usually, this type of pickup lens has a very short focal length of several mm, and the spot diameter is set to be as small as possible in consideration of the increase in the amount of information. Since the diameter is converged as small as that, and is set to, for example, 1 μm or less, high precision is required for attachment to the optical device body 10,
Furthermore, uniformity of the refractive index within the lens unit 1 is required. For that purpose, the optical axis 4 of each of the effective lens surfaces 3 and 3 on both sides is required.
It is required to set the relative positions of the effective lens surfaces 3 and 3 with respect to the mounting reference surface 12 with high accuracy, as well as to set the thickness d of the lens portion 1 with high accuracy. It is necessary to design the mold into an excellent shape, and accordingly, the shape and structure of the mold 19 require special measures.

The plastic lens A has been invented so as to satisfy all of the above requirements, and a method of manufacturing the plastic lens A will be described with reference to FIG. As shown in FIG. 3, the mold 19 has two divided molds 20 and 21 that can form the outer peripheral side of the cylindrical portion 6 of the plastic lens A, and circular holes 22 formed in the divided molds 20 and 21. And cores 23 and 24, which can set the insertion depth with high precision.
A concave curved surface 25 corresponding to the effective lens surface 3 is formed at the tip of the lens 24, an annular flat surface 26 corresponding to the flat portion 5 is formed around the concave curved surface 25, and a tapered surface 27 corresponding to the inclined surface 9 is further formed on the outer periphery.
The outer peripheral surface 28 corresponding to the cylindrical portion 6 is
The structure is the same as that of the outer peripheral surface. An injection path 29 for injecting a resin such as an acrylic resin that can be used as a lens is formed between the split molds 20 and 21 so as to communicate with a portion of the holding frame 2 located on the side of the mounting ring 8. I have.

The cores 23 and 24 are fitted into the circular holes 22 and 22 of the split molds 20 and 21, respectively, and the holding frame 2 is inserted.
The insertion depth of one core 23 is adjusted with respect to the portion of the split mold 20 corresponding to the mounting reference surface 12 of the other core.
The thickness d of the lens unit 1 is adjusted by adjusting the distance between the lens unit 24 and the core 23.
Is set so that the focal position with respect to the mounting reference plane 12 of the holding frame 2 can be set with high accuracy. Since the insertion depth of the cores 23 and 24 with respect to the split molds 20 and 21 can be adjusted, the operation of optimally setting the plastic lens A in the trial production stage can be performed in a very short time, and the holding frame 2 can be adjusted. Can easily change the focal position with respect to the mounting reference plane 12.

As described above, if the cylindrical portion 6 parallel to the optical axis 4 is provided at the inner peripheral end facing the lens surfaces 3 on both sides of the holding frame 2, a mold for forming the lens surface 3, ie, a mold, is provided. Core 23, 24
Is moved in parallel in the optical axis direction, and the holding frame 2
And the distance between the lens surfaces 3 and 3 can be adjusted to optimally set the focal position with respect to the holding frame 2 and the thickness d of the lens portion 1, and fine adjustment of the mold is required after trial production. In such a case, even when the lens surface 3 is slightly moved in parallel in the optical axis direction, a large change does not occur in the overall shape.

Further, since the structure is such that the tips of the cores 23, 24 enter the cavities formed by the split molds 20, 21, the gap between the cores 23, 24 and the split molds 20, 21 That is, no burrs are formed on the outer edge of the cylindrical portion 6.

[0017]

According to the method of manufacturing a plastic lens of the present invention as described above, the holding frame is integrally molded around the lens portion, and the cylindrical portion parallel to the optical axis is formed at the inner peripheral end of the holding frame. A method of manufacturing a plastic lens comprising: a split mold capable of molding a holding frame on the outer peripheral side of the cylindrical portion; and a highly accurate insertion depth in a circular hole formed in each split mold. With a cylindrical core that can be set to, a concave curved surface for molding an effective lens surface is formed at the tip of each core, an annular flat surface is formed around it, and a tapered surface is formed on the outer periphery of the annular flat surface. , Each core is provided with an outer peripheral surface for molding the cylindrical part, and the thickness of the lens part and the relative position of the lens part with respect to the holding frame in the optical axis direction are set by adjusting the insertion depth of the core into each split mold. So the lens surface is formed Adjusting the insertion depth of each core to the split mold, that is, the lens surface is moved in parallel in the optical axis direction to adjust the relative position of the effective lens surface on both sides with respect to the holding frame and the distance between the effective lens surfaces on both sides. Not only can the focus position and the thickness of the lens portion with respect to the holding frame be optimally set, but even if the insertion depth of each core into the split mold is adjusted, the light formed at the inner peripheral end of the holding frame can be adjusted. Only the length of the cylindrical portion parallel to the axis changes, but the overall shape of the lens does not change significantly.

Further, since there is no sharp edge in the mold, the resin can be injected into the mold with a good flow of the resin, and the resin can be uniformly cooled, so that the sink is small and the density is low. In addition, the refractive index can be made uniform. Furthermore,
The flat portion can be used as a reference point for measuring the curvature and minute unevenness when evaluating the performance of the effective lens surface.

[Brief description of drawings]

FIG. 1 is a sectional view of a plastic lens according to the present invention.

FIG. 2 is an omitted partial cross-sectional view showing a use state of a plastic lens.

FIG. 3 is an omitted partial cross-sectional view of a mold for molding a plastic lens.

[Explanation of symbols]

 A plastic lens, 1 lens part 2 holding frame 3 effective lens surface 4 optical axis 5 flat part 6 cylindrical part 7 holding ring 8 mounting ring 9 inclined surface 10 optical device body 11 mounting hole 12 mounting reference surface 13 laser light 14 optical information recording Medium 15 Substrate 16 Pit 17 Recording film 18 Protective film 19 Mold 20 Divided mold 21 Divided mold 22 Circular hole 23 Core 24 Core 25 Concave curved surface 26 Annular flat surface 27 Tapered surface 28 Outer peripheral surface 29 Injection path

Claims (1)

[Claims] 1. A method of manufacturing a plastic lens, wherein a holding frame is integrally molded around the lens portion, and a cylindrical portion parallel to the optical axis is provided at an inner peripheral end portion of the holding frame. The tip part of each core is composed of a split mold that can mold the holding frame on the outer peripheral side and a cylindrical core that can set the insertion depth in the circular holes formed in each mold with high precision. In addition to forming a concave curved surface for molding an effective lens surface, forming an annular flat surface around it and forming a tapered surface on the outer periphery of the annular flat surface, each core is provided with an outer peripheral surface for molding the cylindrical portion, A method of manufacturing a plastic lens, characterized in that the thickness of the lens portion and the relative position of the lens portion with respect to the holding frame in the optical axis direction are set by adjusting the insertion depth of the core into the split mold.