JP2018180264A - Wide-angle lens unit and vehicle-mounted camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide-angle lens unit which uses hydrophilic-coated lenses with improved durability, and to provide a vehicle-mounted camera.SOLUTION: A wide-angle lens unit 10 for a vehicle-mounted camera comprises multiple lenses 11-14 arranged along an optical axis, out of the lenses 11-14, a first lens 11 located at the most object side is made of a reinforced glass having a Mohs hardness of 6 or greater. The first lens 11 has a hydrophilic coating 32 that provides a contact angle no greater than 20 degrees. The hydrophilic coating 32 is provided with an antistatic property providing a surface resistivity that is no greater than 1×10Ωcm. An AR coating 31 is provided between the first lens 11 and the hydrophilic coating 32.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wide-angle lens unit and an on-vehicle camera.

  An on-vehicle camera is known which has a wide-angle lens unit for displaying an image around the car on a monitor at the time of parking or the like. The wide angle is a lens unit with an angle of view of, for example, 60 to 100 degrees, but may include a super wide-angle lens unit that exceeds 100 to 180 degrees, or a lens unit of about 50 to 60 degrees. May be included. The on-vehicle camera having such a wide-angle lens unit is arranged such that at least the lens on the object side is exposed to the outside of the vehicle. Therefore, in the wide-angle lens unit of such a vehicle-mounted camera, the lens closest to the object is wetted with rain water, water at the time of car washing, and cleaning liquid. In this case, if a drop of water remains on the lens closest to the object side, the captured image is distorted and blurred.

  Therefore, a water repellent coating is applied to the object side surface of the lens on the most object side of the wide angle lens unit. The water repellent coat allows water to be repelled and to fall relatively easily from the lens, thus making the camera image clearer. However, there have been cases where water droplets may stay at the boundary between the lens and the lens barrel, or fine water droplets may not remain on the surface of the lens, making the image to be photographed unclear.

  In addition, it has been proposed to form a hydrophilic film (hydrophilic coat) on the lens surface of a vehicle-mounted camera (see, for example, Patent Document 1). In Patent Document 1, not a titanium oxide-containing hydrophilic film which does not exhibit hydrophilicity unless irradiated with ultraviolet light, but a hydrophilic film consisting of silicon dioxide particles that can be used without ultraviolet light and a binder is formed on the lens There is. If a hydrophilic film is provided on the lens exposed outside the car, the contact angle when water droplets adhere to the lens will be small, and the water droplets adhering to the lens surface will spread in the surface direction, covering the lens surface and becoming water droplets Since the three-dimensional shape of the lens collapses, the optical influence on the lens is reduced, and distortion of the photographed image can be suppressed.

JP, 2015-49281, A

  By the way, in the hydrophilic film, the decrease in hydrophilicity becomes a problem. The main cause of the decrease in hydrophilicity is, for example, adhesion of dust. The portion to which dust adheres is lower in hydrophilicity than the hydrophilic film, and the portion of the adhered dust repels water, and the hydrophilicity decreases. Further, for example, a hydrophilic film of an acrylic polymer or a hydrophilic film obtained by solidifying the above-mentioned particles of silicon dioxide with a binder can not be said to have a strong structure, and for example, it is scratched by rubbing at the time of car washing etc. Do. If the hydrophilicity is reduced, the image of the on-vehicle camera is likely to be disturbed by water droplets and the like. Even in an on-vehicle camera used for a vehicle such as a car, a certain service life is required, and it is difficult to use a hydrophilic film whose hydrophilicity decreases relatively quickly.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a wide-angle lens unit and an on-vehicle camera using a lens having a hydrophilic coat with improved durability.

In order to solve the above-mentioned subject, a lens unit of the present invention is provided with a plurality of lenses arranged along an optical axis,
The first lens on the most object side of the lenses is made of tempered glass having a Mohs hardness of 6 or more,
The first lens is provided with a hydrophilic coat having a contact angle of 20 degrees or less, and the hydrophilic coat is provided with an antistatic property having a surface resistance value of 1 × 10 ¹⁰ Ω · cm or less. .

According to such a configuration, when the water adheres, the water coat is prevented from forming a ball by the hydrophilic coating having a contact angle of 20 degrees or less, and the water is spread on the object side surface of the lens. By doing this, the image quality can be maintained even in a wet state. By using a hydrophilic coating having a contact angle of 20 degrees or less, even when a small water droplet such as mist is attached to the lens, the deterioration of the image quality of the image photographed by sufficiently spreading the water is suppressed. Can. In addition, by providing the hydrophilic coating with an antistatic property such that the surface resistance value is 1 × 10 ¹⁰ Ω · cm or less, charging of the first lens is prevented, adhesion of dust due to static electricity is suppressed, and adhesion of dust is caused. It is possible to suppress the decrease in hydrophilicity. Furthermore, when the first lens is a tempered glass having a Mohs hardness of 6 or more, the scratch of the hydrophilic coat on the surface of the first lens reaches the glass of the first lens and the scratch further deepens, so the surface area of the scratch is large. Can be prevented. For example, in the case where the wound has a shape close to a cross section, the deeper the wound, the wider the wound on the surface side. Therefore, by hardening the first lens as tempered glass, it is formed in the hydrophilic coating by suppressing the damage of the hydrophilic coating from reaching the first glass lens and becoming deeper and reducing the surface area of the damage. It is possible to suppress the decrease in hydrophilicity due to the scratch. Further, in this case, it is possible to suppress the state in which the flow of electricity is cut off due to the damage, and to suppress the reduction in the antistatic property.
The contact angle means that, as shown in FIG. 3, when the solid S surface is in contact with the liquid (water droplets) W and the gas G, the liquid W surface is the solid S surface at the boundary line where these three phases contact. The angle formed is called the contact angle (θ). A contact angle of 90 ° or less is said to be wet, a property with a small contact angle is called hydrophilic, and a large property is called water repellency. A contact angle of 10 degrees or less is called super-hydrophilic. In the present invention, the contact angle of the hydrophilic coat is 20 degrees or less, and more preferably 10 degrees or less. The hydrophilic coat is desirably formed on the entire surface of the object side lens surface of the first lens, but may be partially formed. In this case, it is preferable to provide a hydrophilic coat at the center of the lens surface which is particularly susceptible to rubbing.

In the configuration of the present invention, it is preferable that an antireflective coating be provided between the first lens and the hydrophilic coating.
According to such a configuration, the anti-reflection function can be provided to the first lens on the most object side of the wide-angle lens unit while maintaining the hydrophilicity of the hydrophilic coat.

An on-vehicle camera according to the present invention is characterized by having the wide-angle lens unit of the above-described configuration.
According to such a configuration, by using the above-described wide-angle lens, it is possible to suppress the deterioration of the image quality of the image captured even when wet due to rain or the like, and to extend the lifetime.

  According to the present invention, it is possible to suppress the influence of rain or the like on a captured image over a long period of time.

It is a schematic sectional drawing which shows the wide-angle lens unit and vehicle-mounted camera which concern on embodiment of this invention. It is a figure for demonstrating the flaw of a lens, Comprising: (a) shows a reference example, (b) is a figure which shows an Example. It is a figure for demonstrating a contact angle.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The wide-angle lens unit of the present embodiment is provided in an on-vehicle camera mounted on a vehicle such as a car. As shown in FIG. 1, the wide-angle lens unit 10 according to the present embodiment includes a substantially cylindrical lens barrel 18 and a lens group 17 including a plurality of lenses 11 to 14 disposed in the lens barrel 18. ing. The lens group 17 has a first lens 11, a second lens 12, a third lens 13 and a fourth lens 14 from the object side to the image side, and the first lens 11 is a glass lens. The third lens 13 and the fourth lens 14 are resin lenses. The fourth lens 14 is a cemented lens in which the resin lens 15 on the object side and the resin lens 16 on the image side are bonded with an adhesive.
Further, diaphragms 21 and 22 are provided between the second lens 12 and the third lens 13 and between the third lens 13 and the fourth lens 14.

  The plurality of lenses 11 to 14 fixed and supported by the lens barrel 18 are disposed in a state in which the respective optical axes are aligned, and the respective lenses 11 to 14 are arranged along one optical axis. In this state, one lens group 17 used for imaging is configured.

The lens barrel 18 is a cylindrical member with both ends open, has an opening 18a at the end (one end) on the object side (outside, incident side), and the end (inside, emission side) on the image side The other end portion has an opening 18b. Further, a reduced diameter portion 18 c formed to narrow the opening 18 b is provided at an end of the lens barrel 18 on the image side. The opening 18 b is smaller than the opening 18 a and smaller than the outer diameter of the fourth lens 14. The inner diameter of the lens barrel 18 gradually increases from the image side to the object side in correspondence with the outer diameters of the first lens 11 to the fourth lens 14. Further, lenses are press-fitted into the lens barrel 18 in the order of the fourth lens 14, the third lens 13, the second lens 12, and the first lens 11 from the opening 18 a on the object side. The glass lens may not be press-fit, but may be loose-fit. In the state where the fourth lens 14 to the first lens 11 are installed in the lens barrel 18, the opening 18a on the object side is crimped to fix the first lens 11 to the fourth lens 14 to the lens barrel. An annular seal member 19 is disposed between the outer periphery of the first lens 11 and the inner periphery of the lens barrel 18.
Further, for example, an infrared cut filter 23 is provided in the opening 18 b on the image side of the lens barrel 18. An image sensor 25 is disposed on the image side of such a lens unit, whereby an on-vehicle camera is configured. The image sensor 25 is mounted on a substrate (not shown), and the lens unit is fixed to the substrate having the image sensor 25 via a mounting member (not shown).

An AR coat 31 as an antireflective film is formed on the surface of the first lens 11, and a hydrophilic coat 32 is formed on the AR (antireflection) coat 31. That is, the AR coat 31 is provided between the first lens 11 and the hydrophilic coat 32. The AR coating 31 is a transparent thin film applied to the surface to reduce the reflection of light at the surface of the material.
For example, in the case of a single-layer thin film, the condition of n0>n1> n2 (or n0 <n1 <n2), where n0 is the refractive index of the substance, n1 is the refractive index of the thin film, and n2 is the refractive index of the external medium Then, assuming that the thickness of the thin film is d, when the optical thickness n1d of the thin film is 1/4 wavelength, the reflectance is minimized, and the condition of the refractive index n1 = (n0 · n2) 1/2 of the thin film The value of minimum reflectance is 0 when Furthermore, a multilayer antireflective film is used for complete antireflective. It is made by a vacuum evaporation method or the like. Examples of the material of the AR coat 31 include MgF ₂ and SiO ₂ . Further, as the AR coating 31, there is also a wet method as a method other than vacuum deposition, and for example, a method of applying a fluorocarbon resin material is known. The AR coat 31 is not limited to the above-described one, and various AR coats can be used. For example, it is preferable that the AR coat 31 be formed by vapor deposition and have as high hardness as possible.

The hydrophilic coat 32 preferably exhibits hydrophilicity with a contact angle of 20 degrees or less, more preferably superhydrophilic with a contact angle of 10 degrees or less. This makes it possible to suppress the adverse effect of fine water droplets on imaging. That is, in the hydrophilic film, extended wetting occurs in which the water expands the area so that the interface between the lens surface and air is replaced with the interface between the lens surface and water, and the water does not gather in a rounded state. Can be reduced. The hydrophilic coat 32 may be, for example, an acrylic polymer as a hydrophilic polymer, but is not limited thereto. Basically, it is possible to use one that exhibits hydrophilicity with a known contact angle of 20 degrees or less. If the contact angle is 20 degrees or less, the hydrophilic coating 32 does not need to use a hydrophilic polymer, and may be an inorganic hydrophilic coating, for example, a silica-based hydrophilic coating 32 It is also good. In addition, the hydrophilic coating 32 has a surface resistance value of 1 × 10 ¹⁰ Ω · cm or less, and has an antistatic property. The provision of the antistatic property may be, for example, adding a transparent conductive metal oxide to the hydrophilic coating material, for example, using one or more of tin oxide, indium oxide, zinc oxide and antimony oxide. It is also good. The antistatic property may be imparted by adding a surfactant to the hydrophilic polymer.

  The first lens 11 is a glass lens, but is made of tempered glass. The tempered glass is manufactured, for example, by an ion exchange method, a wind cooling method, or the like. In addition, since it is difficult to process tempered glass, it is strengthened after the shape of the glass is determined (after being formed into a lens). In the ion exchange method, by immersing a glass containing sodium (Na) ions in an aqueous solution containing potassium (K) ions, Na ions in the glass surface are exchanged with K ions in the solution. At this time, K ions larger than Na ions enter a narrow space where Na ions originally existed, and a layer of compressive stress is generated on the glass surface. Then, in order to break the glass, not only the force to break the bond between molecules but also the force to remove the surface compressive stress is required. For this reason, a greater force is required to break this glass than ordinary glass.

  Moreover, in the air-cooling method, after heating glass to about 650-700 degreeC, air is blown on the glass surface and it produces | generates by rapidly cooling. It is the same as the ion exchange method in that a compressive stress layer is formed on the surface, but in the case of the air-cooling reinforcement method, a stress field is formed by giving a density difference between the surface layer and the inside by heat treatment. In the present embodiment, the first lens 11 is made of tempered glass, and the Mohs hardness is 6 or more. Here, as a reference example, when the glass of the first lens 11 is not reinforced, when the coating on the lens surface is damaged by car wash etc., as shown in FIG. There is a possibility that the glass of the first lens 11 may be reached beyond 31 and the hydrophilic coat 32. On the other hand, as an example, when the glass of the first lens 11 is strengthened and the Mohs hardness is 6 or more, as shown in FIG. 2B, the scratch 35 is the glass surface of the first lens 11 The possibility of being stopped is high. In this case, in the case where the flaw 35 has a rough cross-section, the width along the cross-sectional direction of the flaw 35 becomes shorter as the first lens 11 is made of tempered glass. As a result, when the scratch 35 is generated, the remaining amount of the hydrophilic coating 32 is larger when the first lens 11 is made of tempered glass than when the tempered glass is not used. That is, by using the first lens 11 as a reinforced glass, the amount of loss of the hydrophilic coat 32 due to a scratch can be reduced. As a result, it is possible to reduce the attenuation of the hydrophilicity due to the scratch of the hydrophilic coat and the attenuation of the antistatic property. In particular, in order to keep the surface resistance value of the hydrophilic coating low, it is preferable that the flaw be as small as possible. By using tempered glass, the antistatic property is maintained as long as possible, and adhesion of dust to the first lens 11 is achieved. It can be prevented.

According to the present embodiment, in the wide-angle lens unit 10 to which the first lens 11 of the in-vehicle camera is exposed, by imparting hydrophilicity, the influence of water droplets on a photographed image can be reduced more than water repellency. In the embodiment, by using the hydrophilic coat 32 having a contact angle of 20 degrees or less, the influence on the image can be reduced. In addition, by imparting the antistatic property having a surface resistance value of 1 × 10 ¹⁰ Ω · cm or less, it is possible to prevent the decrease in hydrophilicity due to the adhesion of dust to the first lens 11, and it is possible to extend the lifetime. In addition, by forming the first lens 11 of tempered glass, it is possible to reduce the damage caused to the hydrophilic coating and to delay the attenuation of the hydrophilicity and the antistatic property.

In the present embodiment, the AR coat 31 and the hydrophilic coat 32 are formed on the object side surface of the first lens 11 closest to the object side in the lens group 17, but fogging due to water vapor present in the internal space is prevented From the viewpoint of the above, it may be formed on the image side of the first lens 11 as well. At this time, it is preferable to provide an AR coat in the lower layer of the hydrophilic coat from the viewpoint of preventing ghosting also on the image side of the first lens.
Further, although the second lens 12 to the fourth lens 14 are resin lenses, all or part of them may be glass lenses. The lens barrel 18 is made of, for example, resin, but may be made of metal.

Reference Signs List 10 wide-angle lens unit 11 first lens 12 second lens 13 third lens 14 fourth lens 17 lens group (a plurality of lenses)
31 Antireflective Coating 32 Hydrophilic Coating

Claims (3)

With multiple lenses aligned along the optical axis,
The first lens on the most object side of the lenses is made of tempered glass having a Mohs hardness of 6 or more,
The first lens is provided with a hydrophilic coat having a contact angle of 20 degrees or less, and the hydrophilic coat is provided with an antistatic property having a surface resistance value of 1 × 10 ¹⁰ Ω · cm or less. Wide-angle lens unit.   The wide angle lens unit according to claim 1, wherein an antireflective coating is provided between the first lens and the hydrophilic coating.   An on-vehicle camera having the wide-angle lens unit according to claim 1 or 2.

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