Imaging lens unit

Abstract

To provide an imaging lens unit which can suppress degradation of optical performance even by water absorption of a plastic lens.SOLUTION: An imaging lens unit 1 includes a lens barrel 2 formed of a resin material, and a first plastic lens 10 to a seventh plastic lens 70 stored in the lens barrel 2. At least two adjacent plastic lenses among the first plastic lens 10 to the seventh plastic lens 70 have different coefficients of water absorption. In the two plastic lenses having different coefficients of water absorption, conical fit inclination surfaces around an optical axis X are formed outside optical effective parts of each of the lenses so as to be fitted thereto. When the fit inclination surfaces are formed, the fit inclination surface of a high water absorption side plastic lens on a side having a high coefficient of water absorption is formed outside the fit inclination surface of a low water absorption side plastic lens on a side having a low coefficient of water absorption.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an imaging lens unit that forms a subject image on a solid-state imaging element such as a CCD sensor or a CMOS sensor. [Background technology]

[0002] Imaging lens units are installed in mobile information devices such as smartphones, home appliances, and automobiles to realize camera functions. Imaging lens units are units that form subject images on solid-state imaging elements such as CCD sensors and CMOS sensors, and have multiple lenses inside a lens barrel. The optical performance of an imaging lens unit depends not only on the optical characteristics of each lens, but also on the degree of coincidence of the optical axes of each lens housed inside the lens barrel, the degree of inclination, and the degree of deviation from the design value of the surface spacing.

[0003] As a method for adjusting the optical axis, tilt and lens surface interval between the lenses, there is a method in which a fitting structure is formed on the edge of each lens, and these adjustments are made by fitting the lenses together using this fitting structure. For example, the imaging lens unit described in Patent Document 1 has such a fitting structure. In this imaging lens unit, a fitting inclined surface centered on the optical axis and a flat portion connected to the fitting inclined surface are formed on the edge of each lens. When assembling the imaging lens unit, first, the fitting inclined surface of the first lens is fitted to the fitting inclined surface of the second lens, and the flat portion of the first lens is abutted against the flat portion of the second lens. Furthermore, the fitting inclined surface of the second lens is fitted to the fitting inclined surface of the third lens, and the flat portion of the second lens is abutted against the flat portion of the third lens. The optical axis of each lens is adjusted by fitting the fitting inclined surfaces, and the tilt adjustment and the lens surface interval are adjusted by abutting the flat portions. According to the imaging lens unit described in Patent Document 1, it is possible to control the position and orientation of each lens within the lens barrel with high precision. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2018 / 335607 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, plastic lenses have been widely used to reduce the weight and cost of imaging lens units, as well as to improve optical performance by using aspheric surfaces. Plastic lenses have an inherent water absorption rate. In the lens fitting structure described in Patent Document 1, when lenses with different water absorption rates are combined, there is a risk of optical performance being degraded. For example, when two plastic lenses with different water absorption rates are combined using the above-mentioned fitting structure, stress based on the difference in water absorption rate occurs inside each lens due to the water absorption of each lens. The stress generated inside the lens affects the lens surface interval and lens surface shape. Even if the lens absorbs water, if the water is released from the lens by leaving it thereafter, the effect on optical performance is small, but if internal stress remains even when left after absorbing water, or if the surface shape and surface interval of the lens change due to internal stress, the optical performance of the imaging lens unit is degraded.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to provide an imaging lens unit capable of suppressing deterioration in optical performance even when a plastic lens absorbs water. [Means for solving the problem]

[0007] The imaging lens unit according to the present invention includes a lens barrel made of a resin material and a plurality of plastic lenses housed in the lens barrel. At least two adjacent plastic lenses among the plurality of plastic lenses have different water absorption rates, and have conical fitting inclined surfaces centered on the optical axis that can be fitted to the outside of the respective optically effective portions. In addition, in the adjacent plastic lenses, the fitting inclined surface of the high water absorption side plastic lens having a higher water absorption rate is formed outside the fitting inclined surface of the low water absorption side plastic lens having a lower water absorption rate.

[0008] At least two adjacent plastic lenses among the plurality of plastic lenses have conical fitting inclined surfaces centered on the optical axis formed on the outer side of the optically effective portion, i.e., on the so-called edge portion. During assembly, the optical axes of the lenses can be aligned by fitting the fitting inclined surfaces formed on the edge portion of each lens. That is, the imaging lens unit of the present invention has a structure in which the optical axes of the plastic lenses are aligned by fitting the fitting inclined surfaces. It is not necessary to provide fitting inclined surfaces for all the plastic lenses in the lens barrel, and the optical axis of some plastic lenses may be adjusted by fitting the outer peripheral surface of the lens with the inner wall surface of the lens barrel.

[0009] However, plastic lenses with high water absorption have a larger volume change due to water absorption than plastic lenses with low water absorption. In a conventional imaging lens unit, when plastic lenses with different water absorption rates are adjacent to each other, the volume change of the plastic lens with the higher water absorption rate in the outward direction, i.e., in the direction perpendicular to the optical axis, is restricted by the fitting inclined surface formed on the plastic lens with the lower water absorption rate. This restriction causes stress due to the difference in water absorption rate inside each lens, leading to a deterioration in the optical performance of the imaging lens unit.

[0010] In the imaging lens unit according to the present invention, in at least two adjacent plastic lenses, the fitting inclined surface of the plastic lens with higher water absorption is formed outside the fitting inclined surface of the plastic lens with lower water absorption. With this configuration, even if the plastic lens with higher water absorption changes in volume due to water absorption, it is not interfered with by the fitting inclined surface of the plastic lens with lower water absorption, so that the stress generated inside the lens can be suitably suppressed. For convenience, in this specification, among the plastic lenses with different water absorption rates, the plastic lens with higher water absorption rate is called the "high water absorption side plastic lens" and the plastic lens with lower water absorption rate is called the "low water absorption side plastic lens".

[0011] In the imaging lens unit having the above configuration, it is desirable to satisfy the following conditional expressions (1) and (2), where the water absorption rate of the low water absorption side plastic lens is β1 and the water absorption rate of the high water absorption side plastic lens is β2. β1<0.1% (1) β2>0.2% (2)

[0012] The stress generated inside the plastic lens increases as the difference between the water absorption rate of the high water absorption side plastic lens and the water absorption rate of the low water absorption side plastic lens increases. When plastic lenses satisfying conditional expressions (1) and (2) are adjacent to each other, the configuration of the imaging lens unit according to the present invention is particularly effective.

[0013] In the imaging lens unit having the above configuration, it is desirable that the lens barrel has a higher water absorption rate than the plurality of plastic lenses.

[0014] If the water absorption rate of the lens barrel is lower than that of the multiple plastic lenses, when the plastic lenses expand in volume due to water absorption, there is a risk that stress will be generated inside the lenses due to contact between the outer peripheral surface of the plastic lenses and the inner wall surface of the lens barrel. By making the water absorption rate of the lens barrel higher than that of the plastic lenses, it is possible to avoid the generation of such stress inside the lenses.

[0015] In the imaging lens unit having the above configuration, when the water absorption rate of the lens barrel is β3, it is desirable to satisfy the following conditional expression (3). β3>0.4% (3)

[0016] In the imaging lens unit having the above configuration, it is desirable that the linear expansion coefficient of the high water absorption side plastic lens is greater than the linear expansion coefficient of the low water absorption side plastic lens.

[0017] There is a close relationship between the volume expansion of a plastic lens due to water absorption and its linear expansion coefficient. When the linear expansion coefficient of the high water absorption side plastic lens is greater than the linear expansion coefficient of the low water absorption side plastic lens, the configuration of the imaging lens unit according to the present invention is effective.

[0018] In the imaging lens unit having the above configuration, it is desirable that at least one of the outer peripheral surfaces of the high water absorption plastic lens is fitted into the inner wall surface of the lens barrel.

[0019] By fitting at least one of the outer peripheral surfaces of the highly water-absorbent plastic lens into the inner wall surface of the lens barrel, the optical axis of the plastic lens can be made to coincide with the central axis of the lens barrel. Effect of the Invention

[0020] According to the imaging lens unit of the present invention, it is possible to provide an imaging lens unit capable of suppressing deterioration in optical performance even when the plastic lens absorbs water. [Brief description of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view that shows a schematic cross section of an imaging lens unit according to an embodiment of the present invention. [Diagram 2] 2 is an exploded cross-sectional view of a lens assembly portion of the imaging lens unit shown in FIG. 1. [Diagram 3] 3 is an exploded cross-sectional view illustrating a second lens, a third lens, and a fourth lens of the lens assembly shown in FIG. 2 in comparison with a conventional configuration. FIG. [Figure 4] 3 is an exploded cross-sectional view illustrating a fourth lens, a fifth lens, and a sixth lens of the lens assembly shown in FIG. 2 in comparison with a conventional configuration. FIG. [Diagram 5] 2 is a graph showing the results of a simulation of the maximum stress occurring in each lens during temperature rise in the imaging lens unit shown in FIG. [Figure 6] 2 is a graph showing the results of a simulation of the amount of change in surface spacing between lenses that occurs when the temperature drops in the imaging lens unit shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the configuration described in the following embodiment is merely an example, and may be freely modified or changed, and is not intended to limit the technical scope of the present invention.

[0023] As shown in Fig. 1, an imaging lens unit 1 according to this embodiment is combined with a solid-state imaging element S and an infrared cut filter F, and is mounted on a camera of a portable information device such as a smartphone. The imaging lens unit 1 has a lens barrel 2 and a lens etc. housed within the lens barrel 2. For convenience in the following description, the left side in Figs. 1 to 4 is defined as the front (or object side), and the right side as the rear (or image side).

[0024] The lens barrel 2 is formed from a black, opaque resin material, such as polycarbonate with added carbon. The lens barrel 2 has a substantially cylindrical peripheral wall 3 that opens along the optical axis X, and a front wall 4 that is formed integrally with the peripheral wall 3 so as to close the front opening. An opening 4A is formed in the center of the front wall 4, with the optical axis X as its center. A receiving surface 4B that is perpendicular to the optical axis X is formed behind the front wall 4.

[0025] In the imaging lens unit 1 according to this embodiment, seven plastic lenses are housed in the lens barrel 2. Specifically, from the object side to the image side, a first plastic lens 10, a second plastic lens 20, a third plastic lens 30, a fourth plastic lens 40, a fifth plastic lens 50, a sixth plastic lens 60, and a seventh plastic lens 70 are housed in this order. Note that, although this embodiment is configured to house seven plastic lenses in the lens barrel 2, the present invention can be applied to any lens configuration having at least two plastic lenses, and a configuration including a glass lens as part of the lens configuration is also acceptable.

[0026] Resin light shielding plates 80-85 are inserted between the first plastic lens 10 to the seventh plastic lens 70. The light shielding plates 80-85 have a disk shape with an opening in the center, and block unnecessary light between the lenses. A spacer ring 90 is inserted between the sixth plastic lens 60 and the seventh plastic lens 70. The spacer ring 90 is an annular member and has an opening with a diameter larger than the diameter of the optically effective portion on the image side of the sixth plastic lens 60 and the diameter of the optically effective portion on the object side of the seventh plastic lens 70. The surface distance between the sixth plastic lens 60 and the seventh plastic lens 70 is determined by the light shielding plate 85 and the spacer ring 90. After the first plastic lens 10 to the seventh plastic lens 70, the light shielding plates 80-85, and the spacer ring 90 are stored in the lens barrel 2, an annular press ring 91 is fixed to the peripheral wall portion 3 of the lens barrel 2 from the rear of the seventh plastic lens 70 with an adhesive or the like.

[0027] Fig. 2 is an exploded cross-sectional view of a lens assembly consisting of first plastic lens 10 to seventh plastic lens 70, light shielding plates 80 to 85, and spacer ring 90 housed in lens barrel 2. As shown in Fig. 2, an annular step is formed around the optical axis X on the outside of the optically effective portions of first plastic lens 10 to fifth plastic lens 50, that is, on the so-called edge portions. By fitting the annular step portions of each plastic lens together, the position and orientation of each plastic lens can be maintained with high precision within lens barrel 2.

[0028] The first plastic lens 10 integrally has a lens portion 11 having a lens function and an edge portion 12 located on the periphery of the lens portion 11. An abutment surface 13 perpendicular to the optical axis X is formed on the object side of the edge portion 12. This abutment surface 13 is formed at a position where it abuts against the receiving surface 4B of the lens barrel 2. When the first plastic lens 10 is stored in the lens barrel 2, the abutment surface 13 abuts against the receiving surface 4B of the lens barrel 2. On the other hand, an annular step portion 14 is formed on the image side of the edge portion 12, which is made up of an inwardly facing conical fitting inclined surface 14A centered on the optical axis X and an annular flat surface 14B facing the image side and connected to the outer periphery of the fitting inclined surface 14A. The annular flat surface 14B is formed so as to be perpendicular to the optical axis X.

[0029] The second plastic lens 20 integrally has a lens portion 21 having a lens function and an edge portion 22 located on the periphery of the lens portion 21. An annular step portion 23 is formed on the object side of the edge portion 22, which is composed of an outward conical fitting inclined surface 23A centered on the optical axis X and an annular flat surface 23B that connects to the outside from the end of the fitting inclined surface 23A. The fitting inclined surface 23A is formed at a position where the vertical distance from the optical axis X is approximately the same as that of the fitting inclined surface 14A of the first plastic lens 10. The annular flat surface 23B is formed so as to be perpendicular to the optical axis X. On the other hand, an annular step portion 24 is formed on the image side of the edge portion 22, which is composed of an outward conical fitting inclined surface 24A centered on the optical axis X and an annular flat surface 24B that connects to the outside from the end of the fitting inclined surface 24A. Of these, the annular flat surface 24B is formed so as to be parallel to the annular flat surface 23B.

[0030] During assembly, the fitting inclined surface 23A of the second plastic lens 20 is fitted into the fitting inclined surface 14A of the first plastic lens 10, and the annular flat surface 23B of the second plastic lens 20 is abutted against the annular flat surface 14B of the first plastic lens 10. This causes the optical axes of the first plastic lens 10 and the second plastic lens 20 to coincide, and determines the surface spacing between the first plastic lens 10 and the second plastic lens 20.

[0031] The third plastic lens 30 integrally has a lens portion 31 having a lens function and an edge portion 32 located on the periphery of the lens portion 31. An annular step portion 33 is formed on the object side of the edge portion 32, which is composed of an inward conical fitting inclined surface 33A centered on the optical axis X and an annular flat surface 33B connected to the outside from the end of the fitting inclined surface 33A. The fitting inclined surface 33A is formed at a position where the vertical distance from the optical axis X is approximately the same as that of the fitting inclined surface 24A of the second plastic lens 20. The annular flat surface 33B is formed so as to be perpendicular to the optical axis X. On the other hand, an annular step portion 34 is formed on the image side of the edge portion 32, which is composed of an inward conical fitting inclined surface 34A centered on the optical axis X and an annular flat surface 34B connected to the outside from the end of the fitting inclined surface 34A. Of these, the annular flat surface 34B is formed so as to be parallel to the annular flat surface 33B.

[0032] During assembly, the fitting inclined surface 33A of the third plastic lens 30 is fitted into the fitting inclined surface 24A of the second plastic lens 20, and the annular flat surface 33B of the third plastic lens 30 is abutted against the annular flat surface 24B of the second plastic lens 20. This causes the optical axis of the second plastic lens 20 and the optical axis of the third plastic lens 30 to coincide, and determines the surface spacing between the second plastic lens 20 and the third plastic lens 30.

[0033] The fourth plastic lens 40 integrally has a lens portion 41 having a lens function and an edge portion 42 located on the periphery of the lens portion 41. An annular step portion 43 is formed on the object side of the edge portion 42, which is composed of an outward conical fitting inclined surface 43A centered on the optical axis X and an annular flat surface 43B that connects to the outside from the end of the fitting inclined surface 43A. The fitting inclined surface 43A is formed at a position where the vertical distance from the optical axis X is approximately the same as that of the fitting inclined surface 34A of the third plastic lens 30. The annular flat surface 43B is formed so as to be perpendicular to the optical axis X. On the other hand, an annular step portion 44 is formed on the image side of the edge portion 42, which is composed of an outward conical fitting inclined surface 44A centered on the optical axis X and an annular flat surface 44B that connects to the outside from the end of the fitting inclined surface 44A. Of these, the annular flat surface 44B is formed so as to be parallel to the annular flat surface 43B.

[0034] During assembly, the fitting inclined surface 43A of the fourth plastic lens 40 is fitted into the fitting inclined surface 34A of the third plastic lens 30, and the annular flat surface 43B of the fourth plastic lens 40 is abutted against the annular flat surface 34B of the third plastic lens 30. This causes the optical axes of the third plastic lens 30 and the fourth plastic lens 40 to coincide, and determines the surface spacing between the third plastic lens 30 and the fourth plastic lens 40.

[0035] The fifth plastic lens 50 integrally has a lens portion 51 having a lens function and an edge portion 52 located on the periphery of the lens portion 51. On the object side of the edge portion 52, an annular step portion 53 is formed, which is composed of an inward conical fitting inclined surface 53A centered on the optical axis X and an annular flat surface 53B connected to the end of the fitting inclined surface 53A and outward. The fitting inclined surface 53A is formed at a position where the vertical distance from the optical axis X is approximately the same as that of the fitting inclined surface 44A of the fourth plastic lens 40. The annular flat surface 53B is formed so as to be perpendicular to the optical axis X. In addition, on the image side of the edge portion 52, an annular flat surface 54 is formed which is parallel to the annular flat surface 53B. Furthermore, the outer peripheral surface of the fifth plastic lens 50 is formed so as to be able to fit with the inner wall surface of the peripheral wall portion 3 of the lens barrel 2.

[0036] During assembly, the fitting inclined surface 53A of the fifth plastic lens 50 is fitted into the fitting inclined surface 44A of the fourth plastic lens 40, and the annular flat surface 53B of the fifth plastic lens 50 is abutted against the annular flat surface 44B of the fourth plastic lens 40. This causes the optical axis of the fourth plastic lens 40 and the optical axis of the fifth plastic lens 50 to coincide, and determines the surface spacing between the fourth plastic lens 40 and the fifth plastic lens 50. Furthermore, by fitting the fifth plastic lens 50 into the lens barrel 2, the optical axes of the first plastic lens 10 to the fifth plastic lens 50 coincide with the central axis of the lens barrel 2.

[0037] The sixth plastic lens 60 integrally has a lens portion 61 having a lens function and an edge portion 62 located on the periphery of the lens portion 61. An annular plane 63 perpendicular to the optical axis X is formed on the object side of the edge portion 62. An annular plane 64 parallel to the annular plane 63 is formed on the image side of the edge portion 62. In addition, the outer circumferential surface of the sixth plastic lens 60 is formed so as to be able to fit into the inner wall surface of the peripheral wall portion 3 of the lens barrel 2.

[0038] The seventh plastic lens 70 integrally has a lens portion 71 having a lens function, and an edge portion 72 located on the periphery of the lens portion 71. An annular plane 73 perpendicular to the optical axis X is formed on the object side of the edge portion 72. An annular plane 74 parallel to the annular plane 73 is formed on the image side of the edge portion 72. A pressing ring 91 abuts against the annular plane 74. The outer peripheral surface of the seventh plastic lens 70 is formed so as to be able to fit with the inner wall surface of the peripheral wall portion 3 of the lens barrel 2.

[0039] When the outer peripheral surfaces of the sixth plastic lens 60 and the seventh plastic lens 70 are fitted to the inner wall surface of the peripheral wall portion 3 of the lens barrel 2, the optical axes of both lenses coincide. Furthermore, by sandwiching a shielding plate 84 between the fifth plastic lens 50 and the sixth plastic lens 60, the surface spacing between the fifth plastic lens 50 and the sixth plastic lens 60 is determined. Similarly, by sandwiching a spacing ring 90 and a shielding plate 85 between the sixth plastic lens 60 and the seventh plastic lens 70, the surface spacing between the sixth plastic lens 60 and the seventh plastic lens 70 is determined.

[0040] As described above, due to the engagement and abutment of the annular steps formed on the edges of each plastic lens and the engagement between the outer peripheral surfaces of the lenses and the inner wall surface of the lens barrel 2, the optical axes of each of the lenses, first plastic lens 10 to seventh plastic lens 70, are aligned inside the lens barrel 2 and the surface spacing between each lens is set to a constant value.

[0041] Next, the behavior of each lens in the imaging lens unit 1 according to the present embodiment when the lens absorbs water will be described in comparison with a conventional imaging lens unit.

[0042] Fig. 3 shows a comparison between the conventional structure and the structure according to the present embodiment with respect to the edge structures of the second to fourth plastic lenses. The exploded view on the left side of Fig. 3 shows the conventional second plastic lens 120, third plastic lens 130, and fourth plastic lens 140. Of these, the second plastic lenses 20, 120 and the fourth plastic lenses 40, 140 are low water absorption side plastic lenses, and the third plastic lenses 30, 130 are high water absorption side plastic lenses.

[0043] In the conventional lens configuration, the fitting inclined surface 124A of the second plastic lens 120 and the fitting inclined surface 133A of the third plastic lens 130 are fitted together, and the annular flat surface 124B of the second plastic lens 120 and the annular flat surface 133B of the third plastic lens 130 are in contact with each other. The fitting inclined surface 124A is an inwardly facing conical surface centered on the optical axis X, and the fitting inclined surface 133A is an outwardly facing conical surface centered on the optical axis X. Therefore, in the relationship between the second plastic lens 120 and the third plastic lens 130, the fitting inclined surface 133A of the high water absorption side plastic lens is located more inward than the fitting inclined surface 124A of the low water absorption side plastic lens.

[0044] Furthermore, the fitting inclined surface 134A of the third plastic lens 130 and the fitting inclined surface 143A of the fourth plastic lens 140 fit together, and the annular flat surface 134B of the third plastic lens 130 and the annular flat surface 143B of the fourth plastic lens 140 abut against each other. Of these, the fitting inclined surface 134A is an inward-facing conical surface centered on the optical axis X, and the fitting inclined surface 143A is an outward-facing conical surface centered on the optical axis X. Therefore, in the relationship between the third plastic lens 130 and the fourth plastic lens 140, the fitting inclined surface 134A of the high water absorption side plastic lens is located outside the fitting inclined surface 143A of the low water absorption side plastic lens.

[0045] In this configuration, when the second plastic lens 120 to the fourth plastic lens 140 expand due to water absorption, the third plastic lens 130 tends to expand outward more than the other two low water absorption plastic lenses. At this time, the fitting inclined surface 124A of the second plastic lens 120 restricts the outward expansion of the third plastic lens 130. As a result, stress is generated inside the second plastic lens 120 and the third plastic lens 130.

[0046] On the other hand, in the configuration according to the present embodiment, in the relationship between the second plastic lens 20 and the third plastic lens 30, the fitting inclined surface 33A of the high water absorption side plastic lens is located outside the fitting inclined surface 24A of the low water absorption side plastic lens. Therefore, even if the second plastic lens 20 to the fourth plastic lens 40 expand due to water absorption, the outward expansion of the third plastic lens 30 is not restricted by the fitting inclined surface 24A. In this way, the second plastic lens 20 and the third plastic lens 30 are not subjected to stress due to interference between the low water absorption side plastic lens and the high water absorption side plastic lens as in the conventional lens configuration.

[0047] Fig. 4 shows a comparison between the conventional structure and the structure according to the present embodiment with respect to the edge structure of the fourth to sixth plastic lenses. The exploded view on the left side of Fig. 4 shows the conventional fourth plastic lens 140, fifth plastic lens 150, and sixth plastic lens 160. Of these, the fourth plastic lenses 40 and 140 are low water absorption side plastic lenses, and the fifth plastic lenses 50 and 150 and the sixth plastic lenses 60 and 160 are high water absorption side plastic lenses.

[0048] In the conventional lens configuration, the fitting inclined surface 144A of the fourth plastic lens 140 and the fitting inclined surface 153A of the fifth plastic lens 150 are fitted together, and the annular flat surface 144B of the fourth plastic lens 140 and the annular flat surface 153B of the fifth plastic lens 150 abut against each other. The fitting inclined surface 144A is an inwardly facing conical surface centered on the optical axis X, and the fitting inclined surface 153A is an outwardly facing conical surface centered on the optical axis X. Therefore, in the relationship between the fourth plastic lens 140 and the fifth plastic lens 150, the fitting inclined surface 153A of the high water absorption side plastic lens is located more inward than the fitting inclined surface 144A of the low water absorption side plastic lens.

[0049] Additionally, fitting inclined surface 154A of fifth plastic lens 150 and fitting inclined surface 163A of sixth plastic lens 160 fit together, and annular flat surface 154B of fifth plastic lens 150 and annular flat surface 163B of sixth plastic lens 160 abut against each other. Of these, fitting inclined surface 154A is an inward-facing conical surface centered on optical axis X, and fitting inclined surface 163A is an outward-facing conical surface centered on optical axis X. Therefore, in terms of the relationship between fifth plastic lens 150 and sixth plastic lens 160, fitting inclined surface 154A is located outside fitting inclined surface 163A.

[0050] In this configuration, when the fourth plastic lens 140 to the sixth plastic lens 160 expand due to water absorption, the fifth plastic lens 150 tends to expand outward more than the fourth plastic lens 140. At this time, the fitting inclined surface 144A of the fourth plastic lens 140 restricts the outward expansion of the fifth plastic lens 150. As a result, stress is generated inside the fourth plastic lens 140 and the fifth plastic lens 150.

[0051] On the other hand, in the configuration according to the present embodiment, in the relationship between the fourth plastic lens 40 and the fifth plastic lens 50, the fitting inclined surface 53A of the high water absorption side plastic lens is located outside the fitting inclined surface 44A of the low water absorption side plastic lens. Therefore, even if the fourth plastic lens 40 to the sixth plastic lens 60 expand due to water absorption, the outward expansion of the fifth plastic lens 50 is not restricted by the fitting inclined surface 44A. In this way, the fourth plastic lens 40 and the fifth plastic lens 50 are not subjected to stress due to interference between the low water absorption side plastic lens and the high water absorption side plastic lens as in the conventional lens configuration.

[0052] Next, we will explain the results of simulating the stress caused by water absorption and the amount of change in lens surface spacing for each plastic lens in the imaging lens unit 1. Here, we substituted material property values ​​in a high-temperature, high-humidity environment and simulated water absorption in the lenses using nonlinear static analysis (thermal analysis). Note that the content shown below is merely the result of a simulation under certain conditions, and various factors must be taken into consideration for the phenomenon that occurs in each plastic lens in a real environment.

[0053] In this simulation, the temperature is raised from 25°C to 85°C, kept at 85°C, and lowered from 85°C to 25°C, and the maximum stress generated in each lens and the change in the inter-lens surface spacing are evaluated under these environments. The temperature rise time, heat retention time, and temperature drop time are the same. From the temperature rise to the heat retention, a value obtained by adding the linear expansion coefficient converted from the volume expansion coefficient due to water absorption to the linear expansion coefficient of the material, that is, the linear expansion coefficient considering water absorption (hereinafter referred to as "converted linear expansion coefficient") is used, and during temperature drop, the linear expansion coefficient of the material is used. The volume expansion coefficient here is a value when it is assumed that the volume expands to the saturated water absorption rate. The linear expansion coefficient, volume expansion coefficient due to water absorption, and converted linear expansion coefficient of the first plastic lens 10 to the seventh plastic lens 70 and the lens barrel 2 in this embodiment are shown below. The first plastic lens 10 to the seventh plastic lens 70 and the first plastic lens to the seventh plastic lens in the conventional lens configuration are shown as L1 to L7. Linear expansion coefficient [1 / K] Volume expansion rate [%] Converted linear expansion rate [1 / K] L1 6.000E-05 0.030 6.167E-05 L2 6.000E-05 0.030 6.167E-05 L3 6.600E-05 0.380 8.711E-05 L4 6.000E-05 0.030 6.167E-05 L5 6.600E-05 0.320 8.378E-05 L6 7.000E-05 0.360 9.000E-05 L7 6.000E-05 0.030 6.167E-05 Tube 2 7.000E-05 0.600 10.333E-05

[0054] In the imaging lens unit 1 according to this embodiment, the third plastic lens 30 (L3), the fifth plastic lens 50 (L5), and the sixth plastic lens 60 (L6) correspond to the high water absorption side plastic lenses, and the first plastic lens 10 (L1), the second plastic lens 20 (L2), the fourth plastic lens 40 (L4), and the seventh plastic lens 70 (L7) correspond to the low water absorption side plastic lenses, The linear expansion coefficient of the high water absorption side plastic lens is greater than the linear expansion coefficient of the low water absorption side plastic lens.

[0055] When the water absorption rate of the low water absorption side plastic lens is β1 and the water absorption rate of the high water absorption side plastic lens is β2, the first plastic lens 10 to the seventh plastic lens 70 satisfy the following conditional expressions (1) and (2). β1<0.1% (1) β2>0.2% (2)

[0056] Furthermore, the water absorption rate of the lens barrel 2 is higher than that of the first plastic lens 10 to the seventh plastic lens 70, and when the water absorption rate of the resin material of the lens barrel 2 is β3, the lens barrel 2 satisfies the following conditional formula (3). β3>0.4% (3)

[0057] The following shows the results of a simulation of the maximum stress that occurs inside the lens when the temperature rises. Conventional lens configuration Maximum stress [MPa] 1st plastic lens 0.2802 Second plastic lens 120 4.6287 3rd plastic lens 130 4.1456 4th plastic lens 140 3.8646 5th Plastic Lens 150 3.1516 6th Plastic Lens 160 0.9464 7th plastic lens 1.2458 Lens configuration of this embodiment Maximum stress [MPa] 1st Plastic Lens 10 7.27E-06 Second plastic lens 20 6.42E-06 3rd plastic lens 30 7.38E-06 4th Plastic Lens 40 4.94E-06 5th Plastic Lens 50 5.00E-06 6th Plastic Lens 60 4.66E-06 No. 7 Plastic Lens 70 1.66E-06

[0058] Fig. 5 is a graph showing the maximum stress generated inside the lens when the temperature is increased. In the graph, the maximum stress value in the conventional lens configuration is shown by a dashed line, and the maximum stress value in the lens configuration of this embodiment is shown by a solid line. As shown in Fig. 5, according to the lens configuration of this embodiment, the stress generated inside each plastic lens can be reduced to almost zero.

[0059] Next, the results of a simulation of the amount of change in lens surface spacing on the optical axis when the temperature is decreased are shown. Note that the surface spacing between the first and second plastic lenses is shown as "L1-L2," the surface spacing between the second and third plastic lenses is shown as "L2-L3," and the surface spacing between the other plastic lenses is shown in a similar manner. Conventional lens configuration Change [μm] Between L1-L2 2.2681 Between L2 and L3: 2.9313 Between L3 and L4 1.7682 Between L4 and L5: 1.4240 Between L5 and L6 -4.1091 Between L6-L7 -0.6189 Lens configuration of this embodiment Change [μm] Between L1-L2 0.0142 Between L2 and L3 -0.1316 Between L3 and L4: 0.6221 Between L4 and L5: 0.4051 Between L5-L6 0.4115 Between L6 and L7 -0.4266

[0060] Fig. 6 is a graph showing the amount of change in the lens surface spacing on the optical axis when the temperature is decreased. In the graph, the amount of change in the lens surface spacing in a conventional lens configuration is shown by a dashed line, and the amount of change in the lens surface spacing in the lens configuration of this embodiment is shown by a solid line. As shown in Fig. 6, according to the lens configuration of this embodiment, the amount of change in the lens surface spacing can be made smaller than that of the conventional lens configuration. [Industrial Applicability]

[0061] The present invention can be mounted on cameras built into portable information devices such as smartphones, home appliances, and automobiles, and can be applied to fields requiring stable optical performance. [Explanation of symbols]

[0062] 1 Imaging lens unit 2. Telescope tube 3 Peripheral wall part 4 Front wall 4A opening 4B Receiving surface 10 First plastic lens 11 Lens section 12 Edge 13 Contact surface 14 Annular step 14A Mating slope 14B Circular plane 20, 120 Second plastic lens 21 Lens section 22 Edge 23, 24 Annular step 23A, 24A, 124A mating slope 23B, 24B, 124B Circular plane 30, 130 3rd plastic lens 31 Lens section 32 Edge 33, 34 Annular step 33A, 34A, 133A, 134A mating slope 33B, 34B, 133B, 134B Circular plane 40, 140 4th plastic lens 41 Lens section 42 Edge 43, 44 Annular step 43A, 44A, 143A, 144A mating slope 43B, 44B, 143B, 144B Circular plane 50, 150 5th plastic lens 51 Lens section 52 Edge 53 Annular step 53A, 153A, 154A mating slope 53B, 54, 153B, 154B Circular plane 60, 160 6th plastic lens 61 Lens section 62 Edge 63, 64, 163B Circular plane 163A Mating slope 70 7th Plastic Lens 71 Lens section 72 Edge 73, 74 Circular plane 80, 81, 82, 83, 84, 85 shielding plate 90 interval ring 91 Presser Ring F Infrared cut filter S Image sensor

Claims

1. An imaging lens unit mounted on a smartphone camera, The lens barrel is made of a resin material, and seven plastic lenses are housed in the lens barrel. The seven plastic lenses have aspheric surfaces on both sides, The first plastic lens to the seventh plastic lens are arranged in this order from the subject side, and at least five lenses from the first plastic lens to the fifth plastic lens have conical fitting inclined surfaces centered on the optical axis formed on the outside of their respective optically effective portions, an imaging lens unit, wherein the water absorption rate of a material of a third plastic lens and a fifth plastic lens is greater than 0.2%, the water absorption rate of a material of a second plastic lens and a fourth plastic lens is less than 0.1%, the water absorption rate of a material of the lens barrel is greater than 0.4%, and the mating inclined surfaces formed on the third plastic lens and the fifth plastic lens are mated only outside the mating inclined surfaces of the lenses with which they are mated.

2. The imaging lens unit according to claim 1 , wherein an outer peripheral surface of the fifth plastic lens is fitted into an inner wall surface of the lens barrel.

Images