Lens unit and in-vehicle camera

Abstract

To provide a lens unit capable of reducing leakage of air within a lens barrel and intrusion of the fresh air into the lens barrel even after exposure to a high-temperature atmosphere for a long time or exposure to a repetitive temperature change in a wide temperature range.SOLUTION: A lens unit is adopted, which includes multiple optical elements lined up along a light axis and a lens barrel for holding the multiple optical elements, the lens barrel has a diameter-reduced portion for disposing at least one optical element, at least one non-optical effective part in an object side or an image-forming side of at least the one optical element interposes a sealing material with thermoelastic elastomer as a main constituent between the diameter-reduced portion and itself, and a position in the light axis direction of at least the one optical element is fixed by urging force to the other non-optical effective part differing from the one non-optical effective part.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a lens unit and an in-vehicle camera.

Background Art

[0002] As a lens unit mounted on an in-vehicle camera, a lens barrel holding a plurality of optical elements is known. For example, Patent Document 1 discloses a lens unit in which a glass lens, at least one resin lens, and an infrared cut filter (hereinafter referred to as an "IR cut filter") are held in the lens barrel in this order from the object side. The glass lens is fixed in a state where an O-ring is sandwiched between the glass lens and a first lens support surface provided at an opening on the object side of the lens barrel, and seals the opening on the object side of the lens barrel. The IR cut filter is fixed to a filter fixing portion provided at an opening on the object side of the lens barrel, and seals the opening on the imaging side of the lens barrel. Then, a resin lens is fixed in a sealed space inside the lens barrel formed by sealing both openings.

[0003] The ambient temperature around an in-vehicle camera equipped with such a lens unit can be assumed as follows. For example, a rear view monitor installed outside the vehicle body has a relatively low maximum achievable ambient temperature. On the other hand, in the case of an in-vehicle camera installed on the inner surface of the front windshield, the maximum achievable ambient temperature is high. Especially in the latter case, it is exposed to a high-temperature atmosphere for a long time. When a resin lens is adopted for the lens unit used in an in-vehicle camera used at such an ambient temperature, there is a problem that yellowing occurs due to auto-oxidation. Therefore, in the lens unit disclosed in Patent Document 1, the surface of the resin lens is prevented from yellowing by covering the resin lens itself with an oxygen permeation prevention film to prevent oxygen from reaching the surface of the resin lens. Patent Document 1 also proposes filling the sealed space with nitrogen gas using a sealing material or disposing an oxygen scavenger in the sealed space.

[0004] Generally, lens units are equipped with sealing materials such as O-rings made of vulcanized rubber to prevent dust and water from entering through the interface and gaps between optical elements with different coefficients of thermal expansion and the lens barrel. For such applications, ethylene propylene diene rubber (EDPM), which has heat and cold resistance, is widely known. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-105194 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, an effective oxygen permeability barrier film, such as the one described in Patent Document 1, is an inorganic layer with few defects. The difference in the coefficient of linear expansion between this inorganic layer and the optical resin is very large. Therefore, there is a difficult challenge in preventing delamination and cracking of the oxygen permeability barrier film over a wide temperature range, such as from -40°C to 125°C.

[0007] Furthermore, when filling the sealing space inside the telescope tube with nitrogen gas, it must be considered that the rubber used for sealing will have reduced sealing performance due to plastic deformation that occurs over time, characterized by compression set, since it is a seal based on compressive stress. In addition, it is required to have excellent gas barrier properties, cold resistance, and not contaminate the inside of the telescope tube by bleeding or blooming.

[0008] EPDM, widely used for dustproof and waterproof purposes, offers good barrier properties against polar gases like water molecules, but is not a suitable choice when considering gas barrier properties against nonpolar gases like nitrogen and oxygen molecules.

[0009] Isobutylene-isoprene rubber (IIR) is an example of a rubber with excellent gas barrier properties and cold resistance, but it has the problem of poor heat aging resistance and high compression set. Furthermore, high-nitrile rubbers with a high polymerization fraction of acrylonitrile among butadiene-acrylonitrile copolymers and fluororubbers with a high fluorine content are examples, but their cold resistance is compromised.

[0010] As can be understood from the above, the present invention aims to provide a lens unit that can reduce leakage of air inside the lens barrel and intrusion of outside air into the lens barrel, even when exposed to a high-temperature atmosphere for a long period of time or to repeated temperature changes over a wide temperature range. [Means for solving the problem]

[0011] Therefore, in order to solve the above-mentioned problems, the inventors of this case have diligently conducted research and arrived at the lens unit and sealing material described below.

[0012] The lens unit according to the present invention comprises a plurality of optical elements arranged along the optical axis and a lens barrel that holds the plurality of optical elements, wherein the lens barrel has a diameter-reducing portion for arranging at least one optical element, and a sealing material mainly composed of a thermoplastic elastomer is interposed between the object side or the image-forming side of the at least one optical element and the diameter-reducing portion, and the position of the at least one optical element in the optical axis direction is fixed by a biasing force on the other non-optical effective portion which is different from the one non-optical effective portion.

[0013] The in-vehicle camera according to the present invention employs an in-vehicle camera characterized by being equipped with the lens unit according to the present invention. [Effects of the Invention]

[0014] The lens unit according to the present invention interposes a sealing material mainly composed of thermoplastic elastomer between the non-optically effective portion of the optical element and the reduced diameter portion of the lens barrel, fixing the position of the optical element in the optical axis direction by a biasing force. As a result, the sealed space formed within the lens barrel is protected from leakage of air inside the lens barrel and intrusion of outside air into the lens barrel, even when exposed to high-temperature atmospheres for extended periods or repeated temperature changes over a wide temperature range. This maintains the inert gas filling the sealed space and suppresses yellowing of the resin lens placed in the sealed space. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic cross-sectional view of the lens unit according to the present invention. [Figure 2] This is a schematic cross-sectional view of the lens unit according to the present invention. [Figure 3] This is a schematic cross-sectional view of the lens unit according to the present invention. [Figure 4] This is a schematic cross-sectional view of the lens unit used experimentally in the examples and comparative examples. [Modes for carrying out the invention]

[0016] 1. Embodiment of the lens unit The lens unit according to the present invention comprises a plurality of optical elements arranged along the optical axis and a lens barrel that holds the plurality of optical elements, the lens barrel having a diameter-reducing portion for positioning at least one optical element. The non-optical effective portion of at least one optical element, either on the object side or the image-forming side, has a sealing material mainly composed of thermoplastic elastomer interposed between it and the diameter-reducing portion, and has a structure that fixes the position of at least one optical element in the optical axis direction by a biasing force on the other non-optical effective portion which is different from the other non-optical effective portion. In this invention, the optical elements include glass lenses and resin lenses, as well as optical filters such as IR cut filters and bandpass filters, and cover glass.

[0017] 〔Structure of the lens unit〕 Fig. 1 shows a schematic cross-sectional view of a lens unit 1 according to an embodiment of the present invention. The lens barrel 10a includes a reduced-diameter portion 11a and a reduced-diameter portion 13 for arranging optical elements. At this time, the shape and structure of the lens barrel 10a do not have openings other than the openings on the object side and the imaging side, and any shape and structure may be used as long as high gas barrier properties can be maintained by the sealing according to the present invention. In particular, it is not limited to the lens unit described below, and it may be any one, such as an optical path bending optical system.

[0018] The lens unit 1 includes a glass lens 20, a glass lens 21, a glass lens 22, a glass lens 23, a resin lens 24, a resin lens 25, and an IR cut filter 26 in order from the object side. A sealing material 50a mainly composed of a thermoplastic elastomer is inserted between the non-optical effective portion on the imaging side of the glass lens 20 and the arrangement surface 12a of the reduced-diameter portion 11a, and a pressing force is applied to the non-optical effective portion on the object side of the glass lens 20 using a pressing ring 40, thereby fixing the positions of a plurality of optical elements, namely, the glass lens 20, the glass lens 21, the glass lens 22, the glass lens 23, the resin lens 24, and the resin lens 25, in the optical axis direction.

[0019] Also, a sealing material 51 mainly composed of a thermoplastic elastomer is inserted between the non-optical effective portion on the object side of the IR cut filter 26 and the arrangement surface 14 of the reduced-diameter portion 13, and a pressing force is applied to the non-optical effective portion on the imaging side of the IR cut filter 26 using a pressing ring 41, thereby fixing the position of the IR cut filter 26 in the optical axis direction. In this way, a space sealed by the glass lens 20, the IR cut filter 26, the lens barrel 10a, the sealing material 50a, and the sealing material 51 is formed.

[0020] And the resin lens only needs to be arranged within the sealed space, and the number of sheets and the arrangement location are not particularly limited. In FIG. 1, the case where two resin lenses, resin lens 24 and resin lens 25, are resin lenses will be described as an example, but the present invention is not limited to this, and at least one other than the glass lens 20 is a resin lens. Thus, since it is sufficient that the resin lens is arranged within the sealed space, the optical element used for sealing is not limited to the glass lens 20 and the IR cut filter 26 as long as a sealing material is inserted between the reduced diameter portion.

[0021] As described above, the shape and structure of the lens barrel 10a do not have openings other than the openings on the object side and the imaging side. That is, the path of the outside air entering the above-described sealed space or the path of the gas leaking from the sealed space is the interface between the optical element used for sealing and the lens barrel or the gap between the optical element used for sealing and the lens barrel. Therefore, it is sufficient to insert the sealing material according to the present invention that exhibits gas barrier properties at the interface between the optical element used for sealing and the lens barrel or the gap between the optical element used for sealing and the lens barrel. That is, when inserting the sealing material at the interface between the optical element used for sealing and the lens barrel or the gap between the optical element used for sealing and the lens barrel, the sealing material may be inserted on any optical surface on the object side or the imaging side of the optical element used for sealing.

[0022] Furthermore, the lens unit 1 may insert an adjustment mechanism such as a spacer ring 30 or a fixed aperture 31 to fix the position of the optical element in the optical axis direction.

[0023] The materials of encapsulating materials 50a and 51 are mainly composed of thermoplastic elastomers. Generally, compared to vulcanized rubber, thermoplastic elastomers have a larger compression set and significantly lose their initial compressive stress over time at high temperatures. For example, the compression set at 70°C for 22 hours according to JIS K6262 is often 40% or more, and even the smallest is around 25%. Furthermore, for example, the styrene-based elastomer described below has a glass transition temperature of 90-100°C for its hard segment, the polystyrene block. Therefore, when exposed to a temperature environment exceeding 100°C with applied load, extensional flow occurs, and its function as an elastic body is clearly impaired.

[0024] The inventors focused on the fact that thermoplastic elastomers have high adhesion to the surfaces of aluminum alloys, resins, and organic glass. Specifically, when exposed to a high-temperature atmosphere for a long period of time, or when subjected to repeated temperature changes over a wide temperature range, such as from -40°C to 125°C, a encapsulant mainly composed of thermoplastic elastomer expands in volume at high temperatures, loses its initial compressive stress, and then contracts in volume as it cools. Even in such cases, the encapsulant mainly composed of thermoplastic elastomer maintains its compressive stress and, instead of resisting the tensile stress associated with volume contraction, possesses sufficient interfacial adhesion and cold resistance. Therefore, it was found that there is no delamination at the "interface between the optical element and the encapsulant" and the "interface between the encapsulant and the placement surface" (hereinafter, these two interfaces are referred to as "contact surfaces"), preventing gas leakage and inflow due to cracking inside the encapsulant, and resulting in excellent gas barrier properties. In other words, by using thermoplastic elastomer as the main component, the encapsulant exhibits excellent gas barrier properties, cold resistance, and heat aging resistance over a wide temperature range, such as from -40°C to 125°C. Thus, once the lens unit according to the present invention is exposed to a high-temperature environment, the adhesion force of the contact surfaces no longer depends on the compressive stress of the sealing material. Therefore, it can maintain high gas barrier properties regardless of the compression set of the sealing material.

[0025] [Positioning structure for optical elements in the optical axis direction] In the non-optically effective portion of an optical element interposed between the diameter-reduced portion of the lens barrel and the optical element, it is preferable that the region other than the region where the sealant is interposed contacts at least one of the diameter-reduced portion and an adjacent optical element along the optical axis, thereby positioning the optical element interposed between the diameter-reduced portion of the lens barrel and the optical element in the optical axis direction. Sealant, mainly composed of thermoplastic elastomer, exhibits large compression set in high-temperature environments, and clearly undergoes extensional flow at temperatures above the glass transition temperature of the hard segment. Therefore, in a structure where the optical element is positioned in the optical axis direction solely by the sealant, it is difficult to maintain the optical axis position of the optical element interposed by the sealant.

[0026] [Structure that applies a biasing force] The lens unit 1 fixes the optical axis position of the glass lens 20 by inserting a sealing material 50a mainly composed of thermoplastic elastomer between the non-optically effective portion on the image-forming side of the glass lens 20 and the diameter-reducing portion 11a on the arrangement surface 12a, and by applying a biasing force to the non-optically effective portion on the object side of the glass lens 20 using a retaining ring 40. Furthermore, the lens unit 1 also fixes the optical axis positions of the glass lenses 21 to 23, the resin lens 24, and the resin lens 25 by the biasing force of the retaining ring 40.

[0027] Furthermore, a sealing material 51 mainly composed of thermoplastic elastomer is interposed on the arrangement surface 14 between the non-optically effective portion on the object side of the IR cut filter 26 and the reduced diameter portion 13, and a biasing force is applied to the non-optically effective portion on the image-forming side of the IR cut filter 26 using a retaining ring 41, thereby fixing the position of the IR cut filter 26 in the optical axis direction. The biasing force is preferably applied by a retaining ring that can be screwed onto the lens barrel. The screwing method may be a self-tapping or other method using multiple screws, and is not limited to cases where both the lens barrel and the retaining ring are directly screwed, as in lens units 1 to 3 and lens unit 101.

[0028] The biasing force described above may also be applied by temporarily tightening the telescope tube. In particular, when using a metal telescope tube, the structure can be made simpler and production can be simplified.

[0029] [Main components of sealing material] The sealing materials 50a and 51 of the lens unit 1 preferably have a thermoplastic elastomer as their main component. The brittle temperature of the thermoplastic elastomer is preferably -40°C or lower, and more preferably -50°C or lower. Furthermore, the thermoplastic elastomer is preferably a styrene-based elastomer with excellent adhesive properties. By using a styrene-based elastomer as the main component of the sealing material, the adhesion between the contact surfaces is high, and delamination of the contact surfaces is less likely to occur even in usage environments with large temperature changes from low to high temperatures, for example, when the sealing material is exposed to a high temperature environment exceeding 100°C from a room temperature environment and then plastically deformed, and then exposed to a low temperature environment of -40°C.

[0030] Styrene-based elastomers include styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene copolymers, etc., depending on the difference in the soft segment, in which the hard segment is styrene. Furthermore, hydrogenated styrene-based elastomers such as styrene-ethylene-butylene-styrene block copolymers (SEBS), styrene-ethylene-propylene-styrene block copolymers (SEPS), and styrene-ethylene-ethylene-butylene-styrene block copolymers (SEEPS) are also included. In terms of heat aging resistance, hydrogenated styrene-based elastomers are preferred.

[0031] Furthermore, the thermoplastic elastomer is more preferably an isobutylene-based block copolymer. In isobutylene-based block copolymers, the soft segment is composed of molecular chains mainly composed of isobutylene, and the hard segment is known to be made of aromatic vinyl compounds, polyamides, and polyurethanes. In addition, examples of hard segments using styrene as the aromatic vinyl compound include styrene-isobutylene block copolymer (SIB), which is a diblock copolymer, and styrene-isobutylene-styrene block copolymer (SIBS), which is a triblock copolymer.

[0032] The isobutylene-based block copolymer preferably contains one or more of SIB and SIBS. This is because SIBS, or compositions using SIB and SIBS, have good flexibility, tackiness, thermal stability, and vibration damping performance despite having low migration, and possess gas barrier properties comparable to IIR. SIBS and SIBS / SIB are marketed under the trade name "SIBSTAR" by Kaneka Corporation. Furthermore, since the hard segment of SIB and SIBS is a styrene block, they are also included in styrene-based elastomers.

[0033] In other words, the thermoplastic elastomer preferably contains one or more of the following: styrene-based elastomer, hydrogenated styrene-based elastomer, and isobutylene-based block copolymer. This is because the appropriate combination can be selected depending on the usage environment of the lens unit. There are no particular limitations on the mixing ratio, etc.

[0034] [Additives for sealing materials] The rate of gas permeation through polymer compounds exhibits a temperature dependence according to Arrhenius's equation; therefore, an increase in the gas permeability coefficient with increasing temperature is unavoidable. Consequently, when only styrene-based elastomers are used as encapsulants, the gas permeability coefficient in high-temperature environments cannot be said to be sufficiently low. For this reason, alloying of styrene-based elastomers with gas barrier resin materials or composite formation with nanofillers is preferable. Examples of gas barrier resins used in this alloying include polyvinyl alcohol-based resins with excellent gas barrier properties, such as polyvinyl alcohol (PVOH), ethylene-vinyl alcohol copolymer (EVOH), and butenediol-vinyl alcohol copolymer. In other words, it is preferable that the encapsulant contains a polyvinyl alcohol-based resin.

[0035] Furthermore, it is even more preferable that the polyvinyl alcohol-based resin is EVOH, which is easily partially compatible with styrene-based elastomers and is easily melt-molded. The higher the vinyl alcohol unit content in EVOH, the higher the gas barrier properties and elasticity of the EVOH. This is also true for alloys with styrene-based elastomers; as the vinyl alcohol unit content in the encapsulant composition increases, the gas barrier properties of the encapsulant increase. On the other hand, as the vinyl alcohol unit content in the encapsulant composition increases, the flexibility of the composition decreases, making it more susceptible to delamination at the contact surface due to temperature changes and crack formation inside the encapsulant when used as an encapsulant. Therefore, in order to maintain sufficient flexibility and cold resistance as an encapsulant, and to maintain adhesion at the contact surface, it is necessary to keep the vinyl alcohol unit content in the encapsulant composition within an appropriate range.

[0036] The vinyl alcohol unit content in EVOH is preferably 5 parts by weight or more and 60 parts by weight or less, when the total weight of the sealing material to be mixed is 100 parts by weight. If the vinyl alcohol unit content of EVOH is less than 5 parts by weight, it is undesirable because the effect of strengthening the gas barrier properties is insufficient. If the vinyl alcohol unit content of EVOH exceeds 60 parts by weight, the flexibility of the composition decreases as described above. Therefore, it is undesirable because the gas barrier properties as a sealing material decrease under repeated temperature change environments such as thermal shock tests. Furthermore, although the vinyl alcohol unit component contributes to the capture of oxygen dissolved in the composition, it is also undesirable because the initial physical properties of the composition, such as the elastic modulus, change significantly due to crosslinking reactions and gelation of the composition due to auto-oxidation. For the reasons mentioned above, the vinyl alcohol unit content of EVOH is more preferably 10 parts by weight or more and 30 parts by weight or less.

[0037] Furthermore, it is preferable to include an inorganic layered compound that has undergone organic pretreatment as a sealing material. Examples of inorganic layered compounds include clay minerals such as smectite group (montmorillonite, saponite, beidelite, nontronite, hectorite, souconite, stevensite), vermiculite (vermiculite, etc.), mica group, and talc. The inorganic layered compound that has undergone organic pretreatment according to the present invention is preferably montmorillonite powder. Montmorillonite is a clay mineral whose main component is hydrated aluminum silicate, and it is a white or gray powder mass. Montmorillonite powder is obtained by powdering this mass. Layered montmorillonite is dispersed in the composition in a state of interlayer delamination. This is because by including montmorillonite in the sealing material, it is possible to maintain high gas barrier properties even when the lens unit is exposed to high temperatures, while also maintaining high adhesion of the contact surfaces.

[0038] The montmorillonite powder content is preferably in the range of 5 parts by weight to 30 parts by weight when the total weight of the sealing material composition is 100 parts by weight. This is because it can enhance the gas barrier properties while maintaining high adhesion between the contact surfaces. If the montmorillonite powder content is less than 5 parts by weight, the gas barrier properties of the sealing material cannot be considered sufficient, which is undesirable. On the other hand, if the montmorillonite powder content exceeds 30 parts by weight, it will cause a decrease in flexibility and adhesion between the contact surfaces, which is also undesirable.

[0039] Furthermore, by incorporating tackifiers such as hydrogenated petroleum resins into the thermoplastic elastomer as additives, within a range that does not significantly impair its gas barrier properties, the adhesion between contact surfaces can be increased.

[0040] [Second sealing material] When the sealing material contains a PVOH-based resin, moisture absorption may occur due to the domains of the PVOH-based resin, potentially leading to a decrease in gas barrier properties, including moisture resistance. In this case, a "second sealing material" for moisture protection may be inserted closer to the outside air than the location where the PVOH-based resin-containing sealing material is installed. While vulcanized rubber such as O-rings may be used for this sealing material, it is preferable to use a sealing material mainly composed of a styrene-based elastomer and a polyolefin alloy. In this case, examples of polyolefins include polyethylene, polypropylene, poly-4-methylpentene, and alicyclic polyolefins, but polyethylene is preferred due to its good heat aging resistance, cold resistance, and water vapor barrier properties.

[0041] [Hardness of sealing material] The International Rubber Hardness (IRHD) of the sealing material, as determined by the M method (micro-size test for medium hardness) as described above, is preferably between 55 IRHD and 95 IRHD. If the IRHD of the sealing material is less than 55 IRHD, it is undesirable because when the sealing material is inserted between the placement surface and the optical element and the optical element is pressed, the deformation of the sealing material will be large, which may interfere with the optically effective area of ​​the optical element. If the IRHD of the sealing material exceeds 95 IRHD, it is undesirable because when the sealing material is inserted between the placement surface and the optical element and the optical element is pressed, the deformation of the sealing material will be small, which may not adequately fit the shape, curvature, and roughness of the optical element and the placement surface, potentially reducing adhesion.

[0042] For the reasons stated above, a lower limit of the International Rubber Hardness (IRHD) of the sealing material is more preferably 60 IRHD. Furthermore, a higher upper limit of the International Rubber Hardness (IRHD) of the sealing material is more preferably 80 IRHD, and even more preferably 75 IRHD.

[0043] [Method for manufacturing sealing material] The sealing material according to the present invention can be prepared and manufactured as follows. As an example, SIBS and EVOH with an ethylene content of 27 mol% are mixed (dry blended) in a mass ratio of 8.5:1.5, and then molded into a resin sheet of a predetermined thickness using a twin-screw extruder. Subsequently, the obtained sheet is cut into a predetermined shape to obtain a sheet-like sealing material for bonding optical elements. However, the above-mentioned mixing ratio and manufacturing method are examples only and are not limited thereto.

[0044] [Shape and dimensions of sealing material] The shape of the sealing material may be circular, rectangular, or an irregular ring shape, as long as it can achieve a gas barrier. Furthermore, if the sealing material can be laid in such a way that it can achieve full contact around the entire circumference of the optical element with the sealing material interposed, the shape of the sealing material may be strip-shaped. The dimensions should be such that they fit within the placement surface 12a.

[0045] When the sealing material is ring-shaped, a larger difference between the outer and inner diameters of the ring-shaped sealing material is advantageous for gas barrier properties. This is because a ring-shaped sealing material with a large difference between the outer and inner diameters allows for a longer distance for gas to travel within the sealing material. For this reason, a structure that allows for a large area of ​​the reduced-diameter portion 11a and the non-optically effective portion of the optical element, thereby ensuring a large area of ​​the placement surface 12a, and interposing a ring-shaped sealing material 50a with a large difference between the outer and inner diameters, can provide higher gas barrier properties. However, in practice, the outer and inner diameters of the sealing material should be determined within an appropriate range that is dimensionally acceptable for the lens unit and optical element.

[0046] The thickness of the sealing material should be such that it allows for high adhesion of the contact surface, taking into account the curvature of the optical element, the lens thickness, etc. More specifically, the thickness that allows for high adhesion is the thickness that, when a biasing force is applied with the appropriate torque, includes sufficient "compression allowance" of the sealing material for the contact surface to adhere properly. Furthermore, the biased optical element should be in contact with the reduced diameter portion of the lens barrel or another optical component, fixing its position in the optical axis direction.

[0047] Furthermore, it is preferable to determine the size of the placement surface 12a in relation to the dimensions of the sealing material 50a so that even if dimensional changes occur due to deformation of the sealing material when a biasing force is applied, or if volume expansion of the sealing material occurs in a high-temperature environment, the sealing material 50a does not protrude from the space formed by the placement surface 12a.

[0048] Figure 2 shows a schematic cross-sectional view of lens unit 2. The sealing material 50b of lens unit 2 has a larger difference between its outer diameter and inner diameter compared to the sealing material 50a of lens unit 1. In this way, the dimensions of the sealing material 50b and the dimensions of the placement surface 12b suitable for the dimensions of the sealing material 50b can be determined within the range permitted by the dimensions of the reduced diameter portion 11b. Furthermore, since the resin lens only needs to be placed in the sealed space sealed by the glass lens 20, the IR cut filter 26, the lens barrel 10b, the sealing material 50b, and the sealing material 51, in lens unit 2, not only the resin lenses 24 and 25, but also the resin lenses 21b to 23b are resin lenses.

[0049] [Telescope tube] The material of the lens barrel 10a can be a non-ferrous metal such as aluminum alloy or magnesium alloy. On the other hand, as a resin material, one or more alloy materials from among poly(ester) carbonate, polyphenylene ether, aromatic polyamide, polyethylene terephthalate, syndiotactic polystyrene, polyphenylene sulfide, polyetheretherketone, polysulfone, polyethersulfone, polyamideimide, polyetherimide, and liquid crystal polymer are preferred. In particular, from the viewpoint of gas barrier properties, aromatic polyamide, polyphenylene sulfide, and liquid crystal polymer are preferred as the main components. These may be compounded with glass fibers, carbon fibers, potassium titanate fibers, and other fillers, and furthermore, materials to which inorganic layered compounds such as mica, talc, kaolin, and montmorillonite have been pre-treated to become organic may be used.

[0050] The inside of the lens barrel is a sealed space that maintains high gas barrier properties. As long as high gas barrier properties can be maintained, the shape and structure of the lens barrel can be anything. A lens unit using this lens barrel has, for example, an objective-side aperture at one end and an imaging-side aperture at the other end. Various lenses and optical filters can be attached to the aforementioned apertures. Intermediate lenses can also be placed between these. These intermediate lenses may be fixed inside the lens barrel or may be configured to be movable. Movable intermediate lenses can be used to change the optical magnification or adjust the focus.

[0051] The sealed space constructed in this manner is then assembled in an inert gas environment, which fills it with an inert gas containing very little oxygen, thus preventing the yellowing of the resin lens. It is preferable to use nitrogen gas as the inert gas, as nitrogen gas has a low gas permeability coefficient for polymer materials in general.

[0052] Furthermore, since it is sufficient to form the sealed space described above, a configuration like the lens unit 3 shown in the schematic cross-sectional view of Figure 3 is also possible. In the lens unit 3, a sealing material 50c is interposed on the placement surface 12c, and a biasing force is applied to the non-optically effective portion on the object side between the glass lens 20 and the glass lens 21c using a retaining ring 40, thereby fixing the positions of the multiple optical elements in the optical axis direction, namely the glass lens 20, glass lens 21c, glass lens 22c, resin lens 23c, resin lens 24, and resin lens 25. In this way, a sealed space is formed by the glass lens 21c, the IR cut filter 26, the lens barrel 10c, the sealing material 50c, and the sealing material 51. In this case, the resin lenses only need to be placed within the sealed space, and in the lens unit 3, the glass lens 22c is a glass lens, while the resin lenses 23c, 24, and 25 are resin lenses.

[0053] As can be understood from the above, the lens unit according to the present invention, which interposes a sealing material mainly composed of thermoplastic elastomer between the non-optically effective portion and the reduced diameter portion of the optical element, and fixes the position of multiple optical elements in the optical axis direction by biasing force on the non-optically effective portion, can reduce leakage of air inside the lens barrel and intrusion of outside air into the lens barrel even when exposed to a high-temperature atmosphere for a long period of time or to repeated temperature changes over a wide temperature range. As a result, the inert gas filling the sealing space configured in the lens unit is maintained, and yellowing of the resin lens placed in the sealing space can be suppressed.

[0054] [Optical elements] Next, the optical elements included in lens units 1 to 3 described above will be explained. There are no particular limitations on these optical elements; they can be appropriately selected and used depending on the application. For example, the lens units mounted on the in-vehicle cameras and surveillance cameras described above will be exposed to the outside air, depending on the installation and usage environment. Therefore, it is preferable to use inorganic glass for the objective lens, which is positioned closest to the object, considering scratch resistance.

[0055] Furthermore, for optical elements used to seal by applying a biasing force, such as the glass lenses 20 of lens unit 1 and lens unit 2, and the glass lenses 20 and 21c of lens unit 3, inorganic glass is preferred because at least one of the surfaces, either the object side or the image-forming side, is exposed to oxygen. This is because gas molecules such as oxygen and nitrogen do not permeate the inside of the optical element's medium.

[0056] The trailing lens following the lens closest to the object, which is directly exposed to the outside air, is generally used to correct various aberrations that occur in the lens closest to the object. Such trailing lenses are generally composed of a combination of a concave lens and a convex lens. When one of these lenses is made of a high Abbe number optical material, it is preferable to use a low Abbe number optical material for the other to correct chromatic aberration. In particular, when the aberrations that occur in the lens closest to the object are large, it is preferable to arrange multiple combinations of concave and convex lenses as trailing lenses.

[0057] Furthermore, the coefficient of linear expansion and temperature dependence of the refractive index of resin are significantly greater than those of glass. Therefore, in such cases, by using resin lenses for both the concave and convex lenses that constitute the subsequent lens, aberration correction becomes possible over a wide temperature range.

[0058] The glass transition temperature (extracorporeal glass transition onset temperature) of the resin used in these resin lenses is preferably 10°C or more higher than the maximum temperature reached by the lens unit, and more preferably 20°C or more higher, in order to suppress deformation in high-temperature environments.

[0059] Examples of resins for resin lenses with a high Abbe number include those made of alicyclic aliphatic polymers such as amorphous polyolefins (APO). Amorphous aliphatic polymers, when they adopt a molecular structure that results in a high glass transition temperature, can lead to a decrease in resistance to yellowing. However, as long as the optical element is used within the sealed space according to the present invention, it is preferable to select a resin material with a high glass transition temperature as described above.

[0060] On the other hand, aromatic compounds such as poly(ester) carbonates can be used as resins for resin lenses with low Abbe numbers.

[0061] The IR cut filter 26 is generally provided to cut infrared rays from the light rays that have passed through the lens group. In order to ensure gas barrier properties by interposing a sealing material 51 between the IR cut filter 26 and the lens barrel 10a, it is preferable to use an IR cut filter 26 made of inorganic glass.

[0062] Furthermore, as long as they are used within the sealed space of lens units 1 to 3, the optical elements are not limited to thermoplastic resins. Energy-curable optical resins such as polymers containing crosslinked structures, functional groups with poor heat aging resistance such as epoxy groups, and sulfur-containing polymers may be used for the lenses, the lens surface, or microstructures formed on the lens surface, as long as the glass transition temperature is within a suitable range.

[0063] 2. Embodiment of an in-vehicle camera The in-vehicle camera according to the present invention is equipped with the lens unit according to the present invention described above. In this lens unit, a sealing material mainly composed of thermoplastic elastomer is interposed between the non-optically effective portion and the reduced diameter portion of the optical elements, and the position of the multiple optical elements in the optical axis direction is fixed by the biasing force applied to the non-optically effective portion.

[0064] Therefore, even if the in-vehicle camera is exposed to a high-temperature atmosphere for a long period of time, or to repeated temperature changes over a wide temperature range, leakage of air from inside the lens barrel of the lens unit equipped with the in-vehicle camera and intrusion of outside air into the lens barrel can be reduced. As a result, the inert gas filling the sealed space configured in the lens unit equipped with the in-vehicle camera is maintained, and yellowing of the resin lens placed in the sealed space can be suppressed.

[0065] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the following examples. [Examples]

[0066] To improve testing efficiency, the test lens unit 101 used a simulated lens barrel 102, which is open only on the objective side and closed on the image-forming side, as shown in the schematic cross-sectional view in Figure 4, instead of a lens barrel that is open at both ends. In Example 1, a round bar made of A5056 aluminum alloy was machined into the shape shown in Figure 4 and then anodized as the simulated lens barrel 102. In this specification, this will be referred to as lens barrel A.

[0067] The retaining ring 105 was made by machining a round bar made of A5056 aluminum alloy into the shape shown in Figure 4. The glass lens 103 is a single-sided convex lens made of inorganic glass, with optical surface 103a being convex and optical surface 103b being flat.

[0068] The ring-shaped and sheet-shaped sealing material 104 was manufactured as follows. First, 90 parts by weight of SIBS (SIBSTAR® 062T, Kaneka Corporation) and 10 parts by weight of EVOH (EVAL® L171B, Kuraray Co., Ltd.) with an ethylene content of 27 mol% were weighed out to 100 parts by weight of the total sealing material and mixed (dry blended). In this case, the vinyl alcohol unit is 8.1 parts by weight. The mixed (dry blended) material was then extruded to form resin pellets.

[0069] Then, these resin pellets were fed into an injection molding machine to obtain a sheet-like molded product with a thickness of 1 mm. Subsequently, this 1 mm thick sheet was compression-molded in a furnace heated to 125°C to obtain a resin film with a thickness of 0.1 mm. The obtained resin film was then cut into a ring shape with dimensions that would not cause overhang from the placement surface 102 g, taking into account dimensional changes when biasing force is applied and changes due to volume expansion in a high-temperature environment. Thus, a ring-shaped and sheet-like sealing material 104 was obtained.

[0070] Test specimen 107 is a molded body made of amorphous polyolefin (ZEONEX® E48R, Zeon Corporation), processed to a diameter of 9 mm and a thickness of 2 mm.

[0071] Next, the lens unit 101 was assembled in a glove box where the inside was purged with nitrogen to reduce the oxygen concentration to 100 ppm or less. First, the test piece 107 was placed on the bottom surface 102e of the cylindrical part 102b of the simulated lens barrel 102. Subsequently, a ring-shaped and sheet-shaped sealing material 104 was placed on the placement surface 102g of the simulated lens barrel 102, and then the glass lens 103 was attached, and the retaining ring 105, which is a biasing member, was screwed in with a tightening torque of 2 N·m. In this way, with the sealing material 104 sandwiched between the glass lens 103 and the placement surface 102g, the glass lens 103 was pressed against the contact surface 102c of the simulated lens barrel 102. As a result, the glass lens 103 was fixed to the simulated lens barrel 102 with nitrogen sealed in the sealing space 106 of the simulated lens barrel 102. In this way, the lens unit of Example 1 was manufactured. [Examples]

[0072] The material for the encapsulant 104 in Example 2 was prepared by weighing 85 parts by weight of SIBS (SIBSTAR® 062T, Kaneka Corporation) and 15 parts by weight of EVOH (EVAL® L171B, Kuraray Co., Ltd.) with an ethylene content of 27 mol% for 100 parts by weight of the total encapsulant material, and then mixing (dry blending) them together. In this case, the vinyl alcohol unit is 12.1 parts by weight. The lens unit of Example 2 was prepared using the same materials as in Example 1, except for the material for the encapsulant 104. [Examples]

[0073] The material for the encapsulant 104 in Example 3 was prepared by weighing 80 parts by weight of SIBS (SIBSTAR® 062T, Kaneka Corporation) and 20 parts by weight of EVOH (EVAL® L171B, Kuraray Co., Ltd.) with an ethylene content of 27 mol% for 100 parts by weight of the total encapsulant material, and then mixing (dry blending) them together. In this case, the vinyl alcohol unit is 16.2 parts by weight. The lens unit of Example 3 was prepared using the same materials as in Example 1, except for the material for the encapsulant 104. [Examples]

[0074] The material for the encapsulant 104 in Example 4 was prepared by weighing 75 parts by weight of SIBS (SIBSTAR® 062T, Kaneka Corporation) and 25 parts by weight of a masterbatch containing 50 wt% organically modified montmorillonite (product name nanoMax-PP, manufactured by Nanocor) (12.5 parts by weight as montmorillonite) to 100 parts by weight of the total encapsulant material, and then mixing (dry blending) them together. The lens unit of Example 4 was prepared using the same materials as in Example 1, except for the material for the encapsulant 104. [Examples]

[0075] The materials for the encapsulant 104 in Example 5 were prepared by weighing 70 parts by weight of SIBS (SIBSTAR® 062T, Kaneka Corporation), 10 parts by weight of EVOH (EVAL® L171B, Kuraray Co., Ltd.) with an ethylene content of 27 mol%, and 20 parts by weight of a masterbatch containing 50 wt% organically modified montmorillonite (product name nanoMax-PP, manufactured by Nanocor Corporation) (10.0 parts by weight as montmorillonite), and then mixing (dry blending) them. Except for the materials for the encapsulant 104, the lens unit of Example 5 was prepared using the same materials as in Example 1. [Examples]

[0076] In Example 6, the simulated lens barrel 102 was prepared by machining a round bar made of glass fiber and mineral-reinforced polyphenylene ether-modified polyphenylene sulfide. In this specification, this will be referred to as lens barrel B. The lens unit of Example 6 was fabricated in the same manner as in Example 1, except for the lens barrel. [Examples]

[0077] In Example 7, the simulated lens barrel 102 was prepared as lens barrel B. Except for the lens barrel, the lens unit for Example 7 was fabricated using the same components as in Example 3. [Examples]

[0078] In Example 8, a simulated lens barrel 102 was prepared using lens barrel B. For the sealing material 104, 70 parts by weight of SIBS (SIBSTAR® 062T, Kaneka Corporation) and 30 parts by weight of EVOH (EVAL® L171B, Kuraray Co., Ltd.) with an ethylene content of 27 mol% were weighed and mixed (dry blended) for every 100 parts by weight of the total sealing material. In this case, the vinyl alcohol units were 24.3 parts by weight. Except for the materials of the lens barrel and sealing material 104, the lens unit of Example 8 was manufactured using the same materials as in Example 1. [Examples]

[0079] In Example 9, the simulated lens barrel 2 was prepared as lens barrel B. For the sealing material 104, 60 parts by weight of SIBS (SIBSTAR® 062T, Kaneka Corporation) and 40 parts by weight of EVOH (EVAL® L171B, Kuraray Co., Ltd.) with an ethylene content of 27 mol% were weighed and mixed (dry blended) for a total of 100 parts by weight of the sealing material materials. In this case, the vinyl alcohol units were 32.4 parts by weight. Except for the materials of the lens barrel and sealing material 104, the lens unit of Example 9 was made in the same way as in Example 1. [Examples]

[0080] In Example 10, the lens unit of Example 10 was fabricated in the same manner as in Example 7, except that the glass lens 103 was fixed to the simulated lens barrel 102 with air components the same as normal atmosphere sealed in the sealing space 106 of the simulated lens barrel 102 instead of nitrogen. Comparative Example

[0081] In the comparative example, test piece 107 was used as is, without being placed in the lens unit.

[0082] [Evaluation Test 1] The lens units of Examples 1 to 10 and the test piece 107 of the comparative example were left in a constant temperature chamber filled with air and maintained at a temperature of 125°C for 500 hours. After this test, the lens units of Examples 1 to 10 were disassembled and the test piece 107 was removed. Subsequently, the light transmittance at a wavelength of 400 nm was measured for the test pieces 107 of Examples 1 to 10 and the comparative example using a spectrophotometer U-4100 (Hitachi High-Technologies Corporation).

[0083] Table 1 shows the change in light transmittance (Δ%T) of test specimen 107 at a wavelength of 400 nm after leaving the lens units of Examples 1 to 10 and the comparative example test specimen 107 in a constant temperature bath maintained at 125°C for 500 hours. The change in light transmittance (Δ%T) refers to the difference in light transmittance of test specimen 107 before and after the test. A negative value for the change in light transmittance (Δ%T) indicates a deterioration in the light transmittance of test specimen 107.

[0084] [Table 1]

[0085] The results shown in Table 1 clearly show that the change in light transmittance (Δ%T) in Examples 1 to 9 was smaller than that in the comparative example. In other words, by interposing the sealing material 104 between the non-optically effective portion and the reduced diameter portion of the optical element, and fixing the position of the optical element in the optical axis direction by biasing force on the non-optically effective portion, the nitrogen gas filling the sealing space formed in the lens unit was maintained, and it became clear that yellowing of the test piece 107 was suppressed even when left in a high-temperature environment of 125°C for a long time.

[0086] Furthermore, since the change in light transmittance (Δ%T) in Examples 1 to 9 was smaller than that in Example 10, it was confirmed that the yellowing of the test piece 107 could be further suppressed by inserting the sealing material 104 between the non-optically effective part and the reduced diameter part of the optical element, as well as by sealing nitrogen in the sealing space of the lens unit.

[0087] Furthermore, under the same material conditions for the sealing material, the change in light transmittance (Δ%T) of lens barrel B was slightly larger than the change in light transmittance (Δ%T) of lens barrel A, but smaller than the change in light transmittance (Δ%T) of the comparative example. In other words, it was confirmed that the sealing material according to the present invention exhibits gas barrier properties even with lens barrels made of different materials.

[0088] In Example 7, the change in light transmittance (Δ%T) when the sample was left in a constant temperature bath at 120°C for 3000 hours was -4.8.

[0089] [Evaluation Test 2] A thermal shock test was performed on the lens units of Examples 3 and 6 through 9, and on the comparative example test piece 107, using the test conditions of "-40°C for 30 minutes, 125°C for 30 minutes" repeated 500 times. The thermal shock apparatus used was the TSE-12 (manufactured by ESPEC Corporation). The thermal shock apparatus was kept in an air atmosphere. After the above tests were performed, the lens units of Examples 3 and 6 through 9 were disassembled and test piece 107 was removed. Subsequently, the light transmittance at a wavelength of 400 nm was measured for the test pieces 107 of Examples 3, 6 through 9, and the comparative example using a spectrophotometer U-4100 (Hitachi High-Technologies Corporation).

[0090] Table 2 shows the change in light transmittance (Δ%T) of test piece 107 at a wavelength of 400 nm after repeating the cycle of "-40°C for 30 minutes, 125°C for 30 minutes" 500 times for the lens units of Examples 3 and 6 to 9, and the comparative example test piece 107.

[0091] [Table 2]

[0092] The results shown in Table 2 clearly show that the change in light transmittance (Δ%T) in Examples 3 and 6 to 9 was smaller than that of the comparative example. In other words, by interposing the sealing material 104 between the non-optically effective part and the reduced diameter part of the optical element, and fixing the position of the optical element in the optical axis direction by biasing force on the non-optically effective part, the nitrogen gas filling the sealing space configured in the lens unit was maintained, and it became clear that yellowing of the test piece 107 was suppressed even when subjected to repeated thermal shocks of "-40°C for 30 minutes, 125°C for 30 minutes" 500 times.

[0093] From the above evaluation results, it was found that a lens unit in which the sealing material 104 is interposed between the non-optically effective part and the reduced diameter part of the optical element, and the position of the optical element in the optical axis direction is fixed by a biasing force on the non-optically effective part, can maintain its gas barrier properties even when exposed to a high-temperature atmosphere for a long period of time, and can reduce leakage of air inside the lens barrel and intrusion of outside air into the lens barrel even when exposed to repeated temperature changes over a wide temperature range. Furthermore, it was found that the sealing material does not break down because it maintains its elasticity even at low temperatures, and the adhesion of the contact surface can be maintained. In addition, it was confirmed that the yellowing of the test piece 107 can be further suppressed by sealing nitrogen in the sealing space. [Industrial applicability]

[0094] The lens unit according to the present invention comprises a plurality of optical elements arranged along the optical axis and a lens barrel that holds the plurality of optical elements. The lens barrel has a diameter-reducing section for positioning at least one optical element. A sealing material mainly composed of thermoplastic elastomer is interposed between the object-side or image-forming side of the at least one optical element and the diameter-reducing section, thereby fixing the position of the at least one optical element in the optical axis direction by the biasing force applied to the non-optical effective section. As a result, as demonstrated in the examples, it has excellent gas barrier performance that prevents oxygen contained in the atmospheric atmosphere from passing through, suppressing yellowing of the resin lens inside the lens barrel. Therefore, the lens unit according to the present invention can be suitably used in in-vehicle cameras and surveillance cameras used in high-temperature atmospheres. [Explanation of symbols]

[0095] 1 Lens Unit 2 Lens Units 3 Lens Units 10a Telescope tube 11a Reduced diameter part 12a Placement surface 10b Telescope Tube 11b Reduced diameter part 12b Placement plane 10c Telescope Tube 11c Reduced diameter part 12c Placement plane 13 Reduced diameter part 14 Placement plane 20 Glass lenses 21 Glass lenses 21b Resin lens 21c glass lens 22 Glass lenses 22b Resin lens 22c glass lens 23 Glass lenses 23b Resin lens 23c resin lens 24 resin lenses 25 Resin lenses 26 IR cut filters 30 Interval rings 31 Fixed aperture 40 Retaining ring 41 Retaining ring 50a Sealing material 50b Encapsulant 50c Encapsulant 51. Sealing material 101 Lens Unit 102 Simulated Telescope Tube 102a Objective lens opening 102b Cylindrical part 102c Contact surface 102d Inner surface 102e Bottom 102f Male thread section 102g placement surface 103 Glass lens 103a Optical surface 103b Optical surface 104 Sealing material 105 Retaining ring 105a Female thread section 106 Sealed space 107 Test specimens

Claims

1. A lens unit used in an in-vehicle camera, It comprises a plurality of optical elements arranged along the optical axis, and a lens barrel that holds the plurality of optical elements, The lens barrel is provided with a reduced diameter section for arranging at least one optical element, The non-optical effective portion of at least one optical element, either on the object side or the image-forming side, is interposed between it and the diameter-reduced portion with a sealing material mainly composed of a thermoplastic elastomer and having high tackiness at the contact surface between the non-optical effective portion and the diameter-reduced portion, in a manner independent of compressive stress. The position of the at least one optical element in the optical axis direction is fixed by a biasing force applied to the other non-optical effective part, which is different from the other non-optical effective part. A lens unit characterized in that at least one resin lens is arranged in a space sealed using the lens barrel, the at least one optical element, and the sealing material.

2. The lens unit according to claim 1, wherein the area of ​​the non-optical effective portion other than the area in which the sealing material is interposed is in contact with at least one of the reduced diameter portion and an adjacent optical member along the optical axis.

3. The lens unit according to claim 1 or claim 2, wherein the at least one optical element is made of inorganic glass.

4. The lens unit according to any one of claims 1 to 3, wherein the biasing force is provided by a retaining ring that can be screwed onto the lens barrel.

5. The lens unit according to any one of claims 1 to 4, wherein the biasing force is due to the temporary tightening of the lens barrel.

6. A lens unit according to any one of claims 1 to 5, wherein nitrogen is sealed in a space sealed using the lens barrel, the at least one optical element, and the sealing material.

7. The lens unit according to any one of claims 1 to 6, wherein the thermoplastic elastomer contains one or more of styrene-based elastomers, hydrogenated styrene-based elastomers, and isobutylene-based block copolymers.

8. The lens unit according to claim 7, wherein the isobutylene-based block copolymer contains one or more of styrene-isobutylene block copolymers and styrene-isobutylene-styrene block copolymers.

9. The lens unit according to any one of claims 1 to 8, wherein the sealing material contains a polyvinyl alcohol-based resin.

10. The lens unit according to claim 9, wherein the polyvinyl alcohol resin is an ethylene-vinyl alcohol copolymer, and the content of vinyl alcohol units in the ethylene-vinyl alcohol copolymer is 5 parts by weight or more and 60 parts by weight or less when the total weight of the sealing material to be mixed is 100 parts by weight.

11. The lens unit according to any one of claims 1 to 10, wherein the sealing material contains polyolefin.

12. The lens unit according to any one of claims 1 to 11, wherein the sealing material contains an inorganic layered compound that has undergone organic pretreatment.

13. The lens unit according to any one of claims 1 to 12, wherein the International Rubber Hardness (IRHD) of the sealing material is 55 IRHD or more and 95 IRHD or less.

14. An in-vehicle camera characterized by comprising a lens unit according to any one of claims 1 to 13.

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