JP7844112B2 - Lens unit and in-vehicle camera - Google Patents

Description

This invention relates to a lens unit and an in-vehicle camera.

A lens unit for in-vehicle cameras is known in which multiple optical elements are held in a lens barrel. 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 "IR cut filter") are held in the lens barrel in this order from the objective side. The glass lens is fixed with an O-ring in between between it and a first lens support surface provided at the objective side opening of the lens barrel, sealing the objective side opening of the lens barrel. The IR cut filter is fixed to a filter fixing part provided at the objective side opening of the lens barrel, sealing the image-forming side opening of the lens barrel. The resin lens is then fixed in the sealed space inside the lens barrel formed by the sealing of both openings.

The ambient temperature of an in-vehicle camera equipped with such a lens unit can be expected to be as follows. For example, rearview monitors installed on the exterior of the vehicle have a relatively low maximum ambient temperature. In contrast, in-vehicle cameras installed on the interior surface of the windshield, for instance, have a high maximum ambient temperature. In the latter case in particular, the camera is exposed to a high-temperature environment for extended periods. When a resin lens is used in a lens unit for an in-vehicle camera operating at such ambient temperatures, there is a problem of yellowing due to auto-oxidation. Therefore, in the lens unit disclosed in Patent Document 1, the resin lens itself is coated with an oxygen permeability-blocking film to prevent oxygen from reaching the surface of the resin lens and suppress yellowing of the resin lens. Patent Document 1 also proposes filling the sealed space with nitrogen gas using a sealing material or placing an oxygen absorber in the sealed space.

Generally, lens units are equipped with sealing materials such as O-rings made of vulcanized rubber to prevent dust and water leakage at the interfaces and gaps between optical elements with different coefficients of thermal expansion and the lens barrel. For this purpose, ethylene propylene diene rubber (EDPM), which has heat and cold resistance, is widely known.

Japanese Patent Publication No. 2016-105194

However, the oxygen permeability barrier film, as described in Patent Document 1, is an inorganic layer with few defects. The difference in the coefficient of thermal 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.

Furthermore, when filling the sealing space inside the telescope tube with nitrogen gas, it must be considered that the rubber used for sealing will experience a decrease in sealing performance due to plastic deformation over time, characterized by compression set, since the seal relies on compressive stress. Additionally, the rubber must possess excellent gas barrier properties, cold resistance, and prevent contamination of the inside of the telescope tube by bleed or bloom.

EPDM, widely used for dust and water resistance, 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.

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

As can be understood from the above, the present invention aims to provide a lens unit that can reduce leakage of internal air from the lens barrel and intrusion of external air into the lens barrel, even when exposed to high-temperature atmospheres for extended periods or to repeated temperature changes over a wide temperature range.

Therefore, in order to solve the aforementioned problems, the inventors of this case conducted diligent research and arrived at the lens unit and sealing material described below.

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 includes a diameter-reducing section for positioning at least one optical element. A sealing material primarily composed of a thermoplastic elastomer is interposed between the object-side or image-forming side of the at least one optical element and the diameter-reducing section. 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 section, which is different from the other non-optical effective section.

The in-vehicle camera according to this invention employs an in-vehicle camera characterized by being equipped with the lens unit according to this invention.

The lens unit according to this invention interposes a sealing material primarily 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 reduces leakage of internal air 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, suppressing yellowing of the resin lens placed within the sealed space.

This is a schematic cross-sectional view of the lens unit according to the present invention. This is a schematic cross-sectional view of the lens unit according to the present invention. This is a schematic cross-sectional view of the lens unit according to the present invention. This is a schematic cross-sectional view of the lens unit used experimentally in the examples and comparative examples.

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 structure in which a sealing material mainly composed of thermoplastic elastomer is interposed between it and the diameter-reducing portion, and the position of at least one optical element in the optical axis direction is fixed by a biasing force applied to 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.

[Lens unit structure]
Figure 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 diameter-reduced portion 11a and a diameter-reduced portion 13 for arranging optical elements. In this case, the shape and structure of the lens barrel 10a can be any shape and structure as long as it does not have any openings other than the openings on the object side and the image-forming side, and 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 can be any type, such as an optical path bending optical system.

The lens unit 1 comprises, in order from the object side, 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. A sealing material 50a, mainly composed of a thermoplastic elastomer, is interposed on the arrangement surface 12a between the non-optically effective portion and the diameter-reducing portion 11a of the glass lens 20. Furthermore, a biasing force is applied to the non-optically effective portion of the glass lens 20 on the object side using a retaining ring 40, thereby fixing the optical axis positions of the multiple optical elements: glass lens 20, glass lens 21, glass lens 22, glass lens 23, resin lens 24, and resin lens 25.

Furthermore, a sealing material 51, mainly composed of thermoplastic elastomer, is inserted between the non-optically effective portion on the object side of the IR cut filter 26 and the reduced-diameter portion 13 on the mounting surface 14. By applying a biasing force to the non-optically effective portion on the image-forming side of the IR cut filter 26 using a retaining ring 41, the position of the IR cut filter 26 in the optical axis direction is fixed. 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.

Furthermore, the resin lenses only need to be arranged within the sealed space, and there are no particular limitations on the number or placement of the lenses. Figure 1 illustrates an example where two resin lenses, resin lens 24 and resin lens 25, are present; however, the present invention is not limited to this, and at least one lens other than the glass lens 20 is a resin lens. Thus, since it is sufficient for the resin lenses to be arranged within the sealed space, the optical elements used for sealing are not limited to the glass lens 20 and the IR cut filter 26, as long as a sealing material is interposed between them and the reduced diameter portion.

As described above, the shape and structure of the lens barrel 10a do not have any openings other than the openings on the object side and the image-forming side. That is, the path for outside air to enter the sealed space, or the path for gas leakage 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, the sealing material according to the present invention, which exhibits gas barrier properties, should be interposed at the interface between the optical element used for sealing and the lens barrel, or at the gap between the optical element used for sealing and the lens barrel. In other words, when interposing the sealing material at the interface between the optical element used for sealing and the lens barrel, or at the gap between the optical element used for sealing and the lens barrel, the sealing material may be interposed on either the object-side or image-forming side optical surface of the optical element used for sealing.

Furthermore, the lens unit 1 may have adjustment mechanisms such as a spacing ring 30 or a fixed aperture 31 inserted to fix the position of the optical elements in the optical axis direction.

The materials of encapsulating materials 50a and 51 are primarily composed of thermoplastic elastomers. Generally, compared to vulcanized rubber, thermoplastic elastomers exhibit a larger compression set and significantly lose their initial compressive stress over time at high temperatures. For example, according to JIS K6262, the compression set at 70°C for 22 hours is often over 40%, and even the smallest values are 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 temperatures exceeding 100°C under applied load, tensile flow occurs, and its function as an elastic material is clearly impaired.

The inventors focused on the fact that thermoplastic elastomers have high adhesion to the surfaces of aluminum alloys, resins, and organic glass. That is, when exposed to a high-temperature atmosphere for a long time, or when exposed 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 and 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"), and gas leakage and inflow due to cracking inside the encapsulant can be suppressed, resulting in excellent gas barrier properties. In other words, by using a thermoplastic elastomer as the main component, the sealing material exhibits excellent gas barrier properties, cold resistance, and heat aging resistance over a wide temperature range of -40°C to 125°C. Thus, once the lens unit according to this 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, high gas barrier properties can be maintained regardless of the compression set of the sealing material.

[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.

[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-reduced 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.

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. The position of the IR cut filter 26 in the optical axis direction is fixed by applying a biasing force to the non-optically effective portion on the image-forming side of the IR cut filter 26 using a retaining ring 41. The biasing force is preferably applied by a retaining ring that can be screwed onto the lens barrel. Note that 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.

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 simplified, and production can be made easier.

[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 even in usage environments with large temperature changes from low to high temperatures, for example, even in harsh environments where the sealing material is subjected to plastic deformation from a room temperature environment to a high temperature environment exceeding 100°C and then subjected to a low temperature environment of -40°C, delamination of the contact surfaces is less likely to occur.

Styrene-based elastomers have a hard segment of styrene, and depending on the soft segment, examples include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene copolymer, etc. Furthermore, hydrogenated styrene-based elastomers such as styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene-butylene-styrene block copolymer (SEEPS) are also mentioned. Hydrogenated styrene-based elastomers are preferred in terms of heat aging resistance.

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, while the hard segment is known to use aromatic vinyl compounds, polyamides, and polyurethanes. Furthermore, examples of hard segments using styrene as the aromatic vinyl compound include diblock copolymers such as styrene-isobutylene block copolymer (SIB) and triblock copolymers such as styrene-isobutylene-styrene block copolymer (SIBS).

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

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 operating environment of the lens unit. There are no particular limitations regarding the mixing ratio, etc.

[Additives for sealing materials]
The rate of gas molecules permeating 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.

Furthermore, it is even more preferable that the polyvinyl alcohol-based resin be EVOH, which is easily partially compatible with styrene-based elastomers and easily melt-molded. The higher the vinyl alcohol unit content in EVOH, the higher its gas barrier properties and elasticity. This is also true for alloys with styrene-based elastomers; a higher vinyl alcohol unit content in the encapsulant composition increases the gas barrier properties of the encapsulant. On the other hand, a high vinyl alcohol unit content in the encapsulant composition reduces the flexibility of the composition, making it prone to delamination at the contact surface due to temperature changes and crack formation within the encapsulant when used as an encapsulant. Therefore, 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.

The vinyl alcohol unit content in this EVOH is preferably 5 parts by weight or more and 60 parts by weight or less, when the total weight of the sealing material materials to be mixed is 100 parts by weight. If the vinyl alcohol unit content of EVOH is less than 5 parts by weight, the effect of strengthening the gas barrier properties is insufficient, which is undesirable. 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 changes, such as in 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 caused by auto-oxidation. For the reasons stated above, the vinyl alcohol unit content of EVOH is more preferably 10 parts by weight or more and 30 parts by weight or less.

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

The montmorillonite powder content is preferably in the range of 5 parts by weight to 30 parts by weight, based on a total weight of 100 parts by weight of the sealing material composition. This is because it allows for enhanced gas barrier properties while maintaining high adhesion between the contact surfaces. A montmorillonite powder content of less than 5 parts by weight is undesirable because the gas barrier properties of the sealing material are not sufficient. On the other hand, a montmorillonite powder content exceeding 30 parts by weight is undesirable because it leads to a decrease in flexibility and adhesion between the contact surfaces.

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.

[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.

[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) 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.

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

[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.

[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.

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 gas travel distance within the sealing material. Therefore, by using a structure that ensures a large area for the reduced-diameter portion 11a and the non-optically effective portion of the optical element, and by ensuring a large area for the placement surface 12a, and inserting a ring-shaped sealing material 50a with a large difference between the outer and inner diameters, higher gas barrier properties can be obtained. However, in practical terms, 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.

The thickness of the sealing material should be such that it allows for high adhesion between the contact surfaces, 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" for the sealing material to ensure proper contact between the contact surfaces. Furthermore, the biased optical element should be in contact with the reduced diameter section of the lens barrel or another optical component, fixing its position in the optical axis direction.

Furthermore, it is preferable to determine the size of the placement surface 12a relative 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.

Figure 2 shows a schematic cross-sectional view of the lens unit 2. The sealing material 50b of lens unit 2 has a larger difference between its outer and inner diameters 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 resin lenses 24 and 25, but also resin lenses 21b to 23b are resin lenses.

[Telescope tube]
The material of the lens barrel 10a can be a non-ferrous metal such as an aluminum alloy or a 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.

The interior 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, for example, has 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 these apertures. Intermediate lenses can also be placed between these. These intermediate lenses may be fixed inside the lens barrel or configured to be movable. Movable intermediate lenses can be used to change the optical magnification or adjust the focus.

Furthermore, by assembling the sealed space in this manner under an inert gas environment, it becomes filled with an inert gas containing very little oxygen, which is the cause of 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.

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 inserted into the arrangement 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: 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; in the lens unit 3, glass lens 22c is a glass lens, while resin lenses 23c, 24, and 25 are resin lenses.

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 high-temperature atmospheres for long periods or to repeated temperature changes over a wide temperature range. This maintains the inert gas filling the sealing space configured in the lens unit, and suppresses yellowing of the resin lens placed in the sealing space.

[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, lens units mounted on the above-mentioned in-vehicle cameras and surveillance cameras are 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.

Furthermore, for optical elements used to seal by applying a biasing force, such as the glass lenses 20 of lens units 1 and 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. Therefore, gas molecules such as oxygen and nitrogen do not permeate the medium of the optical element.

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 typically consist of a combination of a concave lens and a convex lens. It is preferable to use a high Abbe number optical material for one of these lenses and a low Abbe number optical material for the other to correct chromatic aberration. In particular, when the aberrations in the lens closest to the object are large, it is preferable to arrange multiple combinations of concave and convex lenses as trailing lenses.

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, using resin lenses for both the concave and convex lenses constituting the subsequent lens allows for aberration correction over a wide temperature range.

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.

Examples of resins suitable for high Abbe number resin lenses include those made from alicyclic aliphatic polymers such as amorphous polyolefins (APOs). While amorphous aliphatic polymers exhibit reduced yellowing resistance if they adopt a molecular structure that results in a high glass transition temperature, it is preferable to select a resin material with a high glass transition temperature, as described above, for optical elements used within the sealed space according to the present invention.

On the other hand, examples of resins with low Abbe numbers for resin lenses include aromatic compounds such as poly(ester) carbonates.

The IR cut filter 26 is generally provided to cut infrared rays from the light rays that pass through the lens group. 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.

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 cross-linked 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, within a range where the glass transition temperature is suitable.

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 optical axis direction of the multiple optical elements is fixed by the biasing force on the non-optically effective portion.

Therefore, even if the in-vehicle camera is exposed to high-temperature environments for extended periods or to repeated temperature changes over a wide temperature range, leakage of air from inside the lens barrel of the lens unit and intrusion of outside air into the lens barrel can be reduced. This maintains the inert gas filling the sealed space within the lens unit of the in-vehicle camera, thereby suppressing yellowing of the resin lens located within that sealed space.

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.

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 with both ends open. In Example 1, the simulated lens barrel 102 was prepared by machining a round bar made of A5056 aluminum alloy into the shape shown in Figure 4, and then anodizing the entire bar. In this specification, this will be referred to as lens barrel A.

The retaining ring 105 was made by machining a round bar 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.

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 and mixed (dry blended) with 100 parts by weight of the total sealing material. In this case, the vinyl alcohol unit is 8.1 parts by weight. Then, the mixed (dry blended) material was extruded to form resin pellets.

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, taking into account dimensional changes when biasing force is applied and changes due to volume expansion in a high-temperature environment, so as not to protrude from the placement surface 102 g. Thus, a ring-shaped and sheet-like sealing material 104 was obtained.

Test specimen 107 was prepared by molding an amorphous polyolefin (ZEONEX® E48R, Zeon Corporation) to a diameter of 9 mm and a thickness of 2 mm.

Next, the lens unit 101 was assembled in a glove box where the internal oxygen concentration was purged with nitrogen to 100 ppm or less. First, the test piece 107 was placed on the bottom surface 102e of the cylindrical portion 102b of the simulated lens barrel 102. Then, a ring-shaped and sheet-shaped sealing material 104 was placed on the placement surface 102g of the simulated lens barrel 102, after which 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. This pressed the glass lens 103 against the contact surface 102c of the simulated lens barrel 102, with the sealing material 104 sandwiched between the glass lens 103 and the placement surface 102g. 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.

The material for the sealing material 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 sealing material materials, and then mixing (dry blending) them. In this case, the vinyl alcohol unit is 12.1 parts by weight. Except for the material for the sealing material 104, the lens unit of Example 2 was manufactured using the same materials as in Example 1.

The material for the sealing material 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 sealing material materials, and then mixing (dry blending) them. In this case, the vinyl alcohol unit is 16.2 parts by weight. Except for the material for the sealing material 104, the lens unit of Example 3 was manufactured using the same materials as in Example 1.

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 Corporation) (12.5 parts by weight as montmorillonite) to 100 parts by weight of the total encapsulant material, and then mixing (dry blending) them. Except for the material for the encapsulant 104, the lens unit of Example 4 was prepared using the same method as in Example 1.

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.

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. This will be referred to as lens barrel B in this specification. Except for the lens barrel, the lens unit of Example 6 was fabricated in the same manner as in Example 1.

In Example 7, a simulated lens barrel 102 was prepared using lens barrel B. The lens unit for Example 7 was fabricated using the same components as in Example 3, except for the lens barrel.

In Example 8, the simulated lens barrel 102 was prepared as 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) to a total of 100 parts by weight of the sealing material materials. In this case, the vinyl alcohol unit is 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.

In Example 9, the simulated lens barrel 2 was prepared as lens barrel B. The material for the sealant 104 was prepared by weighing and mixing (dry blending) 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% with weight of ethylene, for a total of 100 parts by weight of the sealant material. In this case, the vinyl alcohol unit is 32.4 parts by weight. Except for the materials for the lens barrel and sealant 104, the lens unit of Example 9 was manufactured using the same method as in Example 1.

In Example 10, the lens unit 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

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

[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).

Table 1 shows the change in light transmittance (Δ%T) of test specimen 107 at a wavelength of 400 nm after being left for 500 hours in a constant temperature bath maintained at 125°C for the lens units of Examples 1 to 10 and the comparative example test specimen 107. 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.

The results shown in Table 1 clearly demonstrate that the change in light transmittance (Δ%T) in Examples 1 to 9 was smaller than that in the comparative example. Specifically, 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 the non-optically effective portion, the nitrogen gas filling the sealing space in the lens unit was maintained, suppressing yellowing of the test piece 107 even when left for a long period in a high-temperature environment of 125°C.

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, in addition to interposing the sealing material 104 between the non-optically effective portion and the reduced-diameter portion of the optical element, sealing nitrogen in the sealing space of the lens unit further suppressed the yellowing of the test piece 107.

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.

Furthermore, 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.

[Evaluation Test 2]
A thermal shock test was performed on the lens units of Examples 3 and 6 through 9, and on the test piece 107 of the comparative example, using the test conditions of "-40°C for 30 minutes, 125°C for 30 minutes" repeated 500 times. The thermal shock apparatus used was named 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 the test piece 107 was removed. Subsequently, the light transmittance at a wavelength of 400 nm was measured for the test piece 107 of Examples 3, 6 through 9, and the comparative example using a spectrophotometer U-4100 (Hitachi High-Technologies Corporation).

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

The results shown in Table 2 clearly demonstrate that the change in light transmittance (Δ%T) in Examples 3 and 6 through 9 was smaller than that in the comparative examples. Specifically, by interposing the sealing material 104 between the non-optically effective portion and the reduced-diameter portion of the optical element, and fixing the optical axis position of the optical element by applying a biasing force to the non-optically effective portion, the nitrogen gas filling the sealing space in the lens unit was maintained. This suppressed yellowing of the test piece 107 even after repeated thermal shocks of "-40°C for 30 minutes, 125°C for 30 minutes" 500 times.

From the above evaluation results, it was revealed that a lens unit in which the sealing material 104 is interposed between the non-optically effective portion and the reduced-diameter portion 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 portion, can maintain its gas barrier properties even when exposed to high-temperature atmospheres for long periods of time. Furthermore, it was found that even when subjected to repeated temperature changes over a wide temperature range, leakage of internal air from the lens barrel and intrusion of external air into the lens barrel can be reduced. It was also revealed that the sealing material does not break down even at low temperatures because it maintains its elasticity, thus maintaining the adhesion of the contact surfaces. In addition, it was confirmed that the yellowing of the test piece 107 can be further suppressed by sealing nitrogen in the sealing space.

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 a 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. Therefore, as demonstrated in the examples, it possesses excellent gas barrier performance that prevents the passage of oxygen contained in the atmospheric environment, suppressing yellowing of the resin lens inside the lens barrel. Consequently, the lens unit according to the present invention is suitably usable in automotive cameras and surveillance cameras used in high-temperature atmospheres.

1 Lens unit 2 Lens unit 3 Lens unit 10a Lens barrel 11a Reduced diameter section 12a Arrangement surface 10b Lens barrel 11b Reduced diameter section 12b Arrangement surface 10c Lens barrel 11c Reduced diameter section 12c Arrangement surface 13 Reduced diameter section 14 Arrangement surface 20 Glass lens 21 Glass lens 21b Resin lens 21c Glass lens 22 Glass lens 22b Resin lens 22c Glass lens 23 Glass lens 23b Resin lens 23c Resin lens 24 Resin lens 25 Resin lens 26 IR cut filter 30 Interval ring 31 Fixed aperture 40 Retaining ring 41 Retaining ring 50a Sealing material 50b Sealing material 50c Sealing material 51 Sealing material 101 Lens unit 102 Simulated lens barrel 102a Objective lens opening 102b Cylindrical section 102c Contact surface 102d Inner circumferential surface 102e Bottom surface 102f Male threaded section 102g Placement surface 103 Glass lens 103a Optical surface 103b Optical surface 104 Sealing material 105 Retaining ring 105a Female threaded section 106 Sealing space 107 Test piece

Claims (14)

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. The lens unit according to claim 1, wherein the area of either of the non-optical effective portions 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. The lens unit according to claim 1 or 2, wherein at least one of the optical elements is made of inorganic glass. 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. The lens unit according to any one of claims 1 to 4, wherein the biasing force is provided by temporarily tightening the lens barrel. A lens unit according to any one of claims 1 to 5, wherein nitrogen is sealed in the space enclosed by the lens barrel, the at least one optical element, and the sealing material. 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. 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. The lens unit according to any one of claims 1 to 8, wherein the sealing material contains a polyvinyl alcohol-based resin. The lens unit according to claim 9, wherein the polyvinyl alcohol-based 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 materials of the sealing material to be mixed is 100 parts by weight. The lens unit according to any one of claims 1 to 10, wherein the sealing material contains polyolefin. 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. 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. An in-vehicle camera characterized by comprising a lens unit according to any one of claims 1 to 13.