JP2014238468A - Imaging lens, imaging lens unit and camera module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a weld line from being formed in an imaging lens that is relatively thin and large in a thickness difference.SOLUTION: Since an imaging lens 100 is formed of a plastic material by an injection molding, when a thickness deviation index is equal to or less than 0.1 mm, the imaging lens has a tendency to have a weld line formed. However, selection of the plastic material for the injection molding so as to make a refractive index nd equal to or less than 1.52 results in reduction in a molecular weight of the plastic material, and fluidity of molten resin J upon injection is made easy to be sufficiently high. As a result, by causing the fluidity of the resin to be enhanced, occurrence of the weld line can be easily prevented.

Description

  The present invention relates to an imaging lens formed by injection molding from a plastic material, and an imaging lens unit and a camera module incorporating such a lens.

  Recent imaging optical systems are a combination of a large number of lenses, and a lens shape is adopted in which the central part becomes thinner and the peripheral part becomes thicker, depending on the lens configuration, especially with the reduction in height and accuracy. There is a tendency to. In this way, in molding with a shape that is thin in the center and thick in the periphery, the molten resin that has passed through the gate in the mold is divided into multiple directions, and a resin trace called a weld line tends to remain on the opposite gate side. There is a disadvantage that the process yield is lowered as an appearance defect.

  In addition, the weld line itself is a problem in other fields including a high NA optical pickup lens and the like, and attempts have been made to improve the molding process by various methods (Patent Documents 1 to 4). However, since either method leads to an increase in molding cycle time or an increase in equipment costs, it is rarely introduced in practice.

  For example, in Patent Document 1, in the injection molding of a thermoplastic resin, a resin in which carbon dioxide is melted is used to improve the fluidity of the resin so that transfer defects and weld lines are less likely to occur. Resin is limited, such as using a molten resin, and is not common. In Patent Document 2, the molding space is compressed at the time of injection to improve transferability and reduce weld lines. Moreover, in patent document 3, it is supposed that it fills resin not only from one direction with a gate but the whole outer periphery of molding space with respect to the lens which is easy to generate | occur | produce a weld like a concave lens. Further, in Patent Document 4, the mold surface is preheated when heat cycle molding is performed on an injection molded product having a thin portion and a thick portion and a ratio of 1/30 to 1/2. In any of the methods, there is a problem that a facility for compression or heating is required or it takes time for compression or heating.

Japanese Patent Laid-Open No. 10-538386 International Publication WO2007 / 000930 Japanese Patent Laid-Open No. 03-39218 JP-A-10-44203

The present invention has been made in view of the above-described problems of the background art, and an object thereof is to suppress the formation of a weld line in an imaging lens that is relatively thin and has a large thickness difference.
Another object of the present invention is to provide an imaging lens unit and a camera module incorporating the above-described imaging lens.

In order to achieve the above object, an imaging lens according to the present invention is formed from a plastic material by injection molding, has a thickness deviation index of 0.1 mm or less, and a d-line refractive index of 1. 52 or less. The uneven thickness index is given by Tmin ² / Tmax, where Tmax is the thickness of the thickest part and Tmin is the thickness of the thinnest part.

  The imaging lens is formed by injection molding from a plastic material. By selecting a plastic material for injection molding whose d-line refractive index is 1.52 or less, its molecular weight is lowered. Therefore, it becomes easy to sufficiently increase the fluidity of the molten resin at the time of injection, and the fluidity of the resin is improved, so that even an imaging lens having a thickness deviation index of 0.1 mm or less is welded. Generation of lines can be prevented.

  In a specific aspect or aspect of the present invention, the imaging lens is formed by a side gate method in which a resin is supplied along the mold-matching surfaces of a pair of molds. In this case, the molten resin is more likely to be unevenly filled into the molding space corresponding to the lens shape with a small deviation index, but the plastic material that can easily improve the fluidity of the molten resin can cause the generation of weld lines. It can be surely prevented. Further, since the gate is arranged in the lens outer shape portion because the side gate method is adopted, even if the gate cut remains, the optical portion is hardly affected.

  In another aspect of the present invention, the thickness Tmin of the thinnest part is 0.25 mm or less. In this case, the flow of the molten resin tends to avoid the molding space corresponding to the thinnest portion, but the weld line is less likely to be generated by the molten resin having high fluidity as described above.

  In still another aspect of the present invention, the thinnest part is disposed at the center of the circular contour. When the thinnest part is in the central part, the melted resin that has circulated from the surroundings tends to form a weld line here by meeting on the side opposite to the gate, so that the significance of using a plastic material having a low refractive index is increased.

  In yet another aspect of the present invention, the thickness Tmax of the thickest portion is 1.0 mm or less. In some cases, the molten resin does not easily flow in the entire molding space and is likely to be filled unevenly. However, as described above, a weld line is less likely to be generated by the molten resin having high fluidity.

  In yet another aspect of the present invention, the thickest portion is disposed between the optical axis and the outer edge portion. In this case, the molten resin does not flow easily in the thinnest part near the optical axis and tends to form a weld line here by meeting on the side opposite to the gate, so that the significance of using a plastic material having a low refractive index is increased.

  In still another aspect of the present invention, the plastic material is formed of a cycloolefin resin. In this case, the fluidity of the molten resin can be easily improved, and the optical performance can be high, such as low water absorption. In addition, it is considered that the molten resin is relatively difficult to cool, and once the weld line image is formed, it disappears or becomes inconspicuous.

  In order to achieve the above object, an imaging lens unit according to the present invention includes the imaging lens described above.

  According to the imaging lens unit, since the imaging lens described above is provided, high imaging performance can be realized with a low cost by using a low-cost lens that easily improves fluidity during molding and eliminates the weld line.

  In order to achieve the above object, a camera module according to the present invention includes the above-described imaging lens unit and an imaging element that detects an image by the imaging lens unit.

  According to the camera module, since the imaging lens unit described above is provided, the imaging lens unit that is thin but has high imaging performance and is easy to manufacture satisfies the requirements of low cost and high performance while supporting low profile. be able to.

(A) is a side sectional view of an imaging lens according to an embodiment of the present invention, and (B) is a plan view of the imaging lens. (A) And (B) is a figure explaining the principal part etc. of the metal mold | die for forming the lens for imaging shown in FIG. 1 (A) by injection molding, (C) is supply of molten resin. FIG. It is a conceptual diagram explaining the imaging lens unit and camera module incorporating the imaging lens shown in FIG.

  Hereinafter, an imaging lens and the like according to an embodiment of the present invention will be described with reference to the drawings.

  An imaging lens 100 shown in FIGS. 1 (A) and 1 (B) has a circular outline in a plan view, and has a lens body 10 that exhibits an optical function, and is around the lens body 10 and is used for support. The flange portion 20 is provided. The lens body 10 is a biconcave element as a whole, and has a first optical surface 11 and a second optical surface 12. Both optical surfaces 11 and 12 are both aspherical surfaces. In particular, the first optical surface 11 has a concave shape at the central portion 10a and an annular convex shape at the peripheral portion 10b. The flange portion 20 has a relatively large thickness, but has a narrow radial width.

The thinnest part 14a having the smallest thickness in the optical axis AX direction exists in the central part 10a of the lens body 10, and the thickest part 14b having the largest thickness in the optical axis AX direction is present in the peripheral part 10b of the lens body 10. Exists. The thinnest part 14a is provided on the optical axis AX, and the thickest part 14b is provided between the central part 10a and the outer edge part 10c. That is, the lens body 10 is thin at the central portion 10a and thick at the peripheral portion 10b. The imaging lens 100 or the lens body 10 is thin as a whole and has an uneven thickness index of 0.1 mm or less. Further, the thickness Tmin of the thinnest portion 14a is 0.25 mm or less, and the thickness Tmax of the thickest portion 14b is 1.0 mm or less. The outer diameter D1 of the imaging lens 100 is about 4 to 10 mm, and the main body diameter D2 of the lens body 10 is about 2 to 8 mm. In a specific manufacturing example, the thickness Tmin of the thinnest part 14a is 0.29 mm, the thickness Tmax of the thickest part 14b is 0.8 mm, the outer diameter D1 is 5.3 mm, and the body diameter D2 Is about 4.2 mm. In this case, the thickness ratio Tmax / Tmin of the lens body 10 is 2.75, and the thickness index Tmin ² / Tmax is 0.1 mm. The thickness deviation index Tmin ² / Tmax is obtained by multiplying the thickness ratio of the thinnest part 14a and the thickest part 14b by the thickness of the thinnest part 14a, and represents the thickness difference and the degree of thinness. In other words, the smaller the thickness deviation index Tmin ² / Tmax is, the thinner the thinnest portion 14a is compared to the surrounding area, which means that the absolute value is thin.

  The imaging lens 100 is formed by injection molding from a plastic material. The imaging lens 100 has a refractive index at d-line of 1.52 or less. That is, the imaging lens 100 is formed of a relatively low molecular weight plastic material. A specific material of the imaging lens 100 is a cycloolefin resin. Cycloolefin resin is based on cyclic olefin polymer (COP) resin and cyclic olefin copolymer (COC) resin, and is used to improve the performance of additives and products to facilitate molding as required. Additives can be included. Cyclic olefin polymer (COP) is an amorphous polymer synthesized from cycloolefins such as norbornene. Cyclic olefin copolymer (COC) resin is an amorphous polymer obtained by copolymerizing cycloolefins such as norbornene and other monomers such as ethylene.

  FIG. 2A is a view for explaining a mold for molding the imaging lens 100. The mold apparatus 70 includes a first mold 71 and a second mold 72. The first mold 71 and the second mold 72 are mold-matched at the mold-matching surface PL, and a cavity 70 a is formed between the molds 71 and 72. A transfer surface 71a for transferring the shape of the first optical surface 11 of the imaging lens 100 is formed on the first mold 71 so as to face the cavity 70a. A transfer surface 72a for transferring the shape of the second optical surface 12 of the lens 100 is formed. The transfer surfaces 71 a and 72 a are also portions for transferring the surface of the flange portion 20. In the mold apparatus 70, a gate GA communicating with the cavity 70a is formed. In this case, the gate GA is disposed not on the center of the transfer surfaces 71a and 72a but on the side, and injection molding is performed by a side gate method.

  FIG. 2B is a cross-sectional view illustrating the entire structure of the mold apparatus 70. A runner RA is connected to the cavity 70a also shown in FIG. 2A through a gate GA, and the runner RA is connected to the sprue SP on the resin supply side. As a result, the molten resin J from the sprue SP obtained by melting the thermoplastic resin fills the runner RA and fills the cavity 70a through the gate GA. By separating the first mold 71 and the second mold 72 after cooling the molten resin J, a sprue portion 81 corresponding to the sprue SP, a runner portion 82 corresponding to the runner RA, and a gate corresponding to the gate GA. A molded product 80 including the portion 83 and a molded product main body 84 corresponding to the cavity 70a is formed. Thereafter, the gate portion 83 is subjected to a gate cut process, and the imaging lens 100 is obtained by the molded product main body 84 at the end of the gate portion 83.

  As shown in FIG. 2C, in the injection molding using the mold apparatus 70, the molten resin J injected into the cavity 70a from the gate GA has a refractive index nd of d-line of 1.52 or less. When formed of a relatively low molecular weight material and sufficiently low in viscosity, the molten resin J spreads relatively uniformly as shown by the solid line. On the other hand, when the molten resin J is formed of a material that is not so low in molecular weight that the refractive index nd of the d line is larger than 1.52 and the viscosity is not so low, the molten resin J has a thin central portion as shown by a one-dot chain line. The tendency to fill in two hands to avoid CA increases. As a result, in the region AR opposite to the gate portion 83, the molten resin J divided into two hands joins, so that the weld line 91 is easily formed.

  FIG. 3 is a diagram illustrating an imaging lens unit 200 in which the imaging lens 100 shown in FIG. 1A and the like is incorporated, and a camera module 300 or an imaging apparatus 400 including the imaging lens unit 200.

  The imaging lens unit 200 includes, in order from the object side, an aperture stop ST, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and an IR cut filter FL. With. The imaging lens unit 200 has a function of forming a subject image on the image plane or the imaging plane I of the imaging element 51. The camera module 300 also includes the imaging lens unit 200 that forms a subject image, an imaging element 51 that detects the subject image formed by the imaging lens unit 200, and holds the imaging element 51 from behind and wiring and the like. A wiring board 52 having an imaging lens 100 and the like, and a lens barrel portion 54 having an opening OP through which a light beam from the object side is incident are provided.

  In the imaging lens unit 200, at least the fifth lens L5 corresponds to the imaging lens 100 shown in FIG. In other words, the fifth lens L5 has the thinnest part in the central part and the thickest part in the peripheral part, and the deviation index is 0.1 mm or less. The fifth lens L5 is formed by injection molding from a plastic material, and the refractive index nd at the d-line is 1.52 or less.

  The image sensor 51 is a sensor chip made of a solid-state image sensor. The photoelectric conversion unit 51a of the image sensor 51 is composed of a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor), photoelectrically converts incident light for each RGB, and outputs an analog signal thereof. The surface of the photoelectric conversion unit 51a as the light receiving unit is an image plane or an imaging plane (projected plane) I.

  The wiring board 52 may have a role of aligning and fixing the image sensor 51 to other members (for example, the lens barrel portion 54). The wiring board 52 can receive a voltage and a signal for driving the image pickup device 51 and the driving mechanism 55a from an external circuit, and can output a detection signal to the external circuit.

  The lens barrel portion 54 houses and holds the imaging lens unit 200 including the imaging lens 100. The lens barrel portion 54 enables the focusing operation of the imaging lens unit 200 by moving any one or more of the lenses L1 to L5 constituting the imaging lens unit 200 along the optical axis AX. Therefore, for example, a drive mechanism 55a is provided. The drive mechanism 55a includes, for example, a voice coil motor and a guide, and reciprocates a specific lens along the optical axis AX.

  The imaging apparatus 400 includes a control unit 63, an optical system driving unit 65, an imaging element driving unit 67, an image memory 68, and the like in addition to the camera module 300 described above.

  The control unit 63 controls each unit of the imaging device 400. The control unit 63 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like, and various types of programs are read out from the ROM and expanded in the RAM, in cooperation with the CPU. Execute the process.

  The optical system driving unit 65 controls the state of the lens 100 by operating the driving mechanism 55 a of the imaging lens 100 when performing focusing, exposure, and the like under the control of the control unit 63. The optical system driving unit 65 operates the driving mechanism 55a to appropriately move a specific lens in the lens 100 along the optical axis AX, thereby causing the lens 100 to perform a focusing operation.

  The image sensor driving unit 67 controls the operation of the image sensor 51 when performing exposure or the like under the control of the control unit 63. Specifically, the image sensor driving unit 67 controls the image sensor 51 by scanning the image sensor 51 based on the timing signal. Further, the image sensor driving unit 67 converts, for example, a detection signal output from the image sensor 51 or an analog signal as a photoelectric conversion signal into digital image data. Further, the image sensor driving unit 67 can perform various image processing such as distortion correction, color correction, and compression on the image signal detected by the image sensor 51.

  The image memory 68 receives the digitized image signal from the image sensor driving unit 67 and stores it as readable and writable image data.

上記表１において対ウェルド効果欄の○は、工程が良好であることを意味し、明確なウェルドラインが形成されないことを意味する。また、対ウェルド効果欄の×は、工程が良好でないこと（ウェルドが無視できない程度に顕著）を意味する。また、顕微鏡観察結果は、射速を変えて射出成形した複数のサンプルについて、光学顕微鏡によって横方向からの照明下で４０倍の観察を行った結果である。ここで、ウェルドラインの長さは、レンズ外径部（外縁）から中央よりのウェルドライン先端までの距離とした。なお、工程の管理上は、４０倍の低倍観察で足り、４０倍の低倍観察で観察されないウェルドラインが存在しても、光学的性能に悪影響を及ぼす程のものではない。実際、実施例１、２でも、２００倍の高倍観察を行うことにより、微細なウェルドラインが形成されていることを確認した。
以上の結果から、屈折率ｎｄが１．５１５、１．５１２の材料で成形したレンズでは、ウェルドラインが発生しても、問題ない程度の微かなものであることが分かる。一方、屈折率ｎｄが１．５４４、１．５２３、１．５３２、１．５３１の材料で成形したレンズでは、ある程度目立つウェルドラインが発生することが分かる。 Specific examples will be described below. Example 1 according to the present invention was a COP (cyclic olefin polymer) having a refractive index nd of 1.515 at the d-line wavelength, and Example 2 was a COP having a refractive index nd of 1.512. On the other hand, Comparative Example 1 is a COC (cyclic olefin copolymer) having a refractive index nd of 1.544 at the d-line wavelength, and Comparative Example 2 is a COP having a refractive index nd of 1.523. Was a COP with a refractive index nd of 1.532, and Comparative Example 4 was a COP with a refractive index nd of 1.531. For example, the molding conditions of Example 1 were a mold temperature of 120 ° C. and a resin temperature of 280 ° C. (glass transition point Tg of 128 ° C.). The molding conditions of Comparative Example 1 were a mold temperature of 128 ° C. and a resin temperature of 280 ° C. (glass transition point Tg of 137 ° C.). The injection speed of the resin was set to 50 mm / s, 100 mm / s, and 150 mm / s. Table 1 below summarizes the occurrence of weld lines and the like.
[Table 1]

In Table 1 above, “o” in the column for the weld effect column means that the process is good and a clear weld line is not formed. Further, x in the anti-weld effect column means that the process is not good (conspicuous enough that the weld cannot be ignored). Further, the microscope observation result is a result of performing 40 times observation with a light microscope under illumination from the lateral direction with respect to a plurality of samples injection-molded at different firing speeds. Here, the length of the weld line was the distance from the lens outer diameter portion (outer edge) to the tip of the weld line from the center. In terms of process management, observation at a low magnification of 40 times is sufficient, and the presence of a weld line that is not observed at a low magnification of 40 times does not adversely affect the optical performance. In fact, also in Examples 1 and 2, it was confirmed that a fine weld line was formed by performing 200 times high magnification observation.
From the above results, it can be seen that a lens molded with a material having a refractive index nd of 1.515 or 1.512 is fine enough to cause no problem even if a weld line is generated. On the other hand, it can be seen that a weld line that is noticeable to some extent is generated in a lens molded with a material having a refractive index nd of 1.544, 1.523, 1.532, or 1.531.

  As described above, since the imaging lens 100 according to the embodiment is formed by injection molding from a plastic material, a weld line tends to be easily formed when the deviation index is 0.1 mm or less. Arise. However, since the molecular weight of the molten resin J is reduced by selecting a plastic material for injection molding so that the refractive index nd is 1.52 or less, the fluidity of the molten resin J should be sufficiently increased. It becomes easy to improve the fluidity of the resin and easily prevent the generation of weld lines.

  Although the imaging lens 100 and the like as the embodiment according to the present invention have been described above, the imaging lens according to the present invention is not limited to the above. For example, the shape of the imaging lens 100 is not limited to those illustrated in FIGS. 1A and 1B, and may have various surface shapes determined by optimizing the optical design. For example, the lens 100 is not limited to the thinnest part 14a provided on the optical axis AX of the central part 10a, and the thinnest part 14a is provided on the outer side adjacent to the central part 10a. It may be a thing.

  In the above embodiment, the fifth lens L5, which is the most image-side lens (final lens) in the imaging lens unit 200, has a thickness index of 0.1 mm or less and a refractive index nd of 1.52. Although the following COP is used for injection molding, any of the other lenses L1 to L4 that are not closest to the image side may be a lens having the same properties as the fifth lens L5. The configuration of the imaging lens unit 200 shown in FIG. 3 is merely an example, and the number of lenses constituting the imaging lens unit 200 can be 3, 4, 6, or more.

  The manufacturing method of the imaging lens 100 and the like described in the above embodiment is merely an example, and various methods not illustrated can be used.

  DESCRIPTION OF SYMBOLS 10 ... Lens body, 10a ... Center part, 10b ... Peripheral part, 10c ... Outer edge part, 11, 12 ... Optical surface, 14a ... Thinnest part, 14b ... Thickest part, 20 ... Flange part, 51 ... Imaging element, 52 DESCRIPTION OF SYMBOLS ... Wiring board 54 ... Optical-barrel part 65 ... Optical-system drive part 67 ... Imaging device drive part 70 ... Mold apparatus 70a ... Cavity 71 ... Mold 71, 72 ... Mold, 71a, 72a ... Transfer surface 80 ... Molded product 82 ... Runner portion 83 ... Gate portion 84 ... Molded product body 91 ... Weld line 100 ... Imaging lens 200 ... Imaging lens unit 300 ... Camera module 400 ... Imaging Device, AR ... opposite side region, AX ... optical axis, CA ... center part, D1 ... outer diameter, D2 ... main body diameter, FL ... IR cut filter, I ... imaging surface, J ... molten resin L1 ... lens, L1-L4 ... lens

Claims (9)

An imaging lens formed by injection molding from a plastic material,
When the thickness of the thickest part is Tmax and the thickness of the thinnest part is Tmin, the thickness deviation index Tmin ² / Tmax is 0.1 mm or less,
An imaging lens having a d-line refractive index of 1.52 or less.   The imaging lens according to claim 1, wherein the imaging lens is formed by a side gate method in which a resin is supplied along a mold-matching surface of a pair of molds.   The imaging lens according to any one of claims 1 and 2, wherein a thickness Tmin of the thinnest portion is 0.25 mm or less.   The imaging lens according to claim 3, wherein the thinnest part is disposed at a central part of a circular outline.   The imaging lens according to any one of claims 1 to 4, wherein the thickness Tmax of the thickest portion is 1.0 mm or less.   The imaging lens according to claim 5, wherein the thickest portion is disposed between an optical axis and an outer edge portion.   The imaging lens according to any one of claims 1 to 6, wherein the plastic material is formed of a cycloolefin-based resin.   An imaging lens unit comprising the imaging lens according to any one of claims 1 to 7.   A camera module comprising: the imaging lens unit according to claim 8; and an imaging device that detects an image by the imaging lens unit.

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