JP2017062371A - Optical member having antireflection film and manufacturing method of the antireflection film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antireflection film having an excellent mechanical strength and adhesion even if a resin lens substrate having a comparatively low melting point where a deposition step including a high-temperature process of 90°C or higher cannot be applied is used and also to provide an optical member having the same.SOLUTION: An optical member includes a substrate and an antireflection film arranged on the substrate with a three-layer structure in an order from a first layer to a third layer. The first layer includes a dense film containing SiOand/or a silane coupling agent. The second and third layers include a silica aerogel film. In the light of wavelength 550 nm, a refractive index of the substrate is 1.6 or less, and a refractive index of the third layer is within 1.15-1.32. The refractive indices of the substrate, the first layer, the second layer and the third layer get lower in this order.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an optical member having an antireflection film having a three-layer structure and a method for producing the antireflection film having the three-layer structure.

  High-performance single-focus lenses and zoom lenses widely used in photographic cameras, broadcast cameras, and the like have a lens barrel configuration of a large number of lens groups. Generally, these lenses are composed of about 5 to 40 lenses. Some lenses, such as wide-angle lenses, target images with a wide angle of view, and the incident angle of light increases at the periphery of such wide-angle lenses. In addition, in terms of optical design, a lens having a lens surface having a smaller radius of curvature than the effective diameter is often included in the optical path. A dielectric film having a different refractive index is combined on the surface of an optical component such as a lens, and the thickness of each dielectric film is 1 / 2λ or 1 / 4λ with respect to the center wavelength λ. An antireflection treatment using a multilayer film utilizing the interference effect is performed.

Japanese Patent Laid-Open No. 10-319209 (Patent Document 1) discloses a step of forming a first antireflection layer of a first material on a substrate by a wet process or a dry process, and a second method of covering the first antireflection layer by a wet process. An antireflection film having a step of forming a second antireflection layer of the material is disclosed, and the antireflection film obtained by such a method has a small number of layers and high performance (wide antireflection film). (Wavelength band, low reflectance, and wide angle characteristics), and describes that it exhibits a high antireflection effect particularly in the ultraviolet region. Further, the cited document 1 discloses that one or more antireflection layers may be additionally formed under the first antireflection layer by a wet or dry process, and the dry process is selected from vacuum deposition, sputtering, and CVD. And that the wet process includes a sol-gel process, specifically, a first layer made of SiO ₂ formed by a dry process, and an SiO ₂ porous body formed by a sol-gel method An antireflection film having a two-layer structure consisting of a second layer made of is described. However, this antireflection film having a two-layer structure has a relatively high refractive index of the outermost layer (second layer) of 1.20 to 1.35, so that it is sufficient to withstand practical use when used in recent high-performance lenses. It cannot be said that it has antireflection performance.

  Japanese Patent Application Laid-Open No. 10-227902 (Patent Document 2) has at least two fluororesin layers laminated in order of a high refractive index layer and a low refractive index layer from the substrate side, and has a wavelength range of 350 to 1350 nm. A broadband antireflection film exhibiting a transmittance of 99.5% or more is disclosed, and it is described that this broadband antireflection film exhibits high antireflection performance even for visible light having a relatively high incident angle. Patent Document 2 describes that the luminous reflectance for light with an incident angle of, for example, 60 ° is about 1.6%. However, since this antireflection film is made of a fluororesin, it has a problem that it does not have a sufficient mechanical strength and cannot withstand practical use.

  JP-A-2006-227596 (Patent Document 3) and JP-A-2006-215542 (Patent Document 4) are composed of a dense layer and a porous layer made of silica aerogel formed in order on the surface of a substrate, and have a refractive index. Proposals have been made of antireflection coatings that become smaller in order from the base material to the silica airgel layer. This silica airgel layer consists of (i) a sol or gel silicon oxide reacted with an organic modifier to form an organic modified sol or organic modified gel, and (ii) an organic modified sol or organic modified gel made into a sol By coating the surface of the dense layer, causing a springback phenomenon in the resulting organically modified silica gel layer to form an organically modified silica airgel layer, and (iii) heat treating the organically modified silica airgel layer to remove the organically modified groups. Form. The refractive index of the silica airgel layer is as small as about 1.20, and the antireflection film having the silica airgel layer has excellent antireflection characteristics in a wide wavelength range. Further, since the silica airgel layer can be produced by a sol-gel method, it is excellent in cost performance. However, since the silica airgel layer has poor mechanical strength and adhesion to the substrate, it cannot be said that the scratch resistance is sufficient.

  JP-A-2009-237551 (Patent Document 5) is composed of a dense layer and a mesoporous silica porous film sequentially formed on the surface of a base material, and the refractive index decreases in order from the base material to the mesoporous silica porous film layer. An antireflection film and a method for manufacturing the same are disclosed. However, the production method described in Patent Document 5 requires a baking step at 500 ° C. or more to improve the removal of the surfactant and the adhesion and mechanical strength of the film, which may be melted or deformed. A resin lens or a lens containing a resin (for example, a hybrid lens obtained by bonding a special transparent resin to optical glass) cannot be used as a base material.

  In addition, since the antireflection films described in Patent Documents 3 to 5 have a film formed by a dry process in the first layer, the thickness of the film formed by the dry process is particularly large in a lens having a large curvature. However, there is a problem that the anti-reflective properties at the periphery of the lens deteriorates as the distance from the periphery increases.

Japanese Patent Application Laid-Open No. 2012-215790 (Patent Document 6) has an optical two-layer structure including an intermediate layer provided on a base material and a low refractive index layer provided on the surface of the intermediate layer. The refractive index layer is a layer in which hollow silica is bound by a binder, and the refractive index (n1) is 1.15 or more and 1.24 or less, and the refractive index (n2) of the intermediate layer is n (sub ), Formula (1):
n1 × [n (sub)] ^0.5 × 0.930 ≦ n2 ≦ n1 × [n (sub)] ^0.5 × 0.985
An antireflection film satisfying the above relationship is disclosed. In Patent Document 6, in the production of this antireflection film, it is preferable to perform heat treatment at 90 to 200 ° C. in order to volatilize the solvent and cure the film when forming the low refractive index layer. If so, it is described that the thermal expansion deformation of the substrate can be prevented. For example, in Examples 1 to 10, a coating solution containing hollow silica and an acrylic resin is applied, and pre-baking at 90 ° C. for 120 seconds and post-baking at 150 ° C. for 1 hour for volatilization of the solvent and curing of the film. The example which performed is described. However, since the antireflection film described in Patent Document 6 requires heat treatment at such a high temperature in order to volatilize the solvent and cure the film, it is applied to a resin substrate having a relatively low melting point. It is not possible.

Japanese Patent Laid-Open No. 10-319209 JP-A-10-227902 JP 2006-227596 A JP 2006-215542 A JP 2009-237551 A JP 2012-215790 A

  Accordingly, the first object of the present invention is to provide excellent mechanical strength and adhesion even for a resin lens substrate having a relatively low melting point, which cannot be applied to a film forming process including high-temperature treatment at 90 ° C. or higher. And an optical member having the same.

  The second object of the present invention is to provide an obliquely incident light beam in both the central portion and the peripheral portion (a portion where the substrate tilt angle is large), even if the lens substrate has a large curvature with a maximum substrate tilt angle of 30 ° or more. An antireflection film having excellent antireflection performance and an optical member having the same are provided.

As a result of diligent research in view of the above object, the inventors of the present invention have developed a first layer composed of a dense film containing SiO ₂ and / or a silane coupling agent on a substrate, and a silica airgel film formed by a wet process. The antireflection film composed of the second layer and the third layer is found to have excellent mechanical strength and adhesiveness that can withstand practical use even when formed by a film forming process of 90 ° C. or less. I came up with the invention.

That is, the optical member comprising the substrate of the present invention and the antireflection film having a three-layer structure provided in the order of the first layer to the third layer on the substrate,
The first layer comprises a dense film containing SiO ₂ and / or a silane coupling agent,
The second layer and the third layer are composed of a silica airgel film,
For light with a wavelength of 550 nm,
The refractive index of the substrate is 1.6 or less,
The third layer has a refractive index in the range of 1.15 to 1.32.
The refractive indexes of the substrate, the first layer, the second layer, and the third layer are lower in this order.

  The substrate is preferably made of resin or contains resin.

  The first layer preferably has an effect of improving adhesion between the substrate and the second layer.

  The refractive index of the third layer is preferably in the range of 1.15 to 1.25.

  The substrate is preferably a lens substrate having a maximum substrate tilt angle of 30 ° or more.

  The maximum substrate tilt angle of the lens substrate is preferably in the range of 30 to 65 °.

The lens optical thickness of the first layer at an arbitrary substrate inclination angle theta _t of the substrate D1 (θ _t), the optical thickness of the second layer D2 (θ _t), and the optical thickness of the third layer D3 (θ _t ) is
The following formula (1), formula (2) and formula (3) respectively:
_{D1 (θ t) = D1 0} × (cosθ t) α ··· (1)
_{D2 (θ t) = D2 0} × (cosθ t) β ··· (2)
_{D3 (θ t) = D3 0} × (cosθ t) γ ··· (3)
(Where D1 ₀ , D2 ₀ and D3 ₀ represent the optical film thicknesses of the first layer, the second layer and the third layer, respectively, at the center of the lens substrate, and α, β and γ are independently − It is preferably a numerical value in the range of 2.0 to 2.0.

  The film thickness of the first layer may be reduced from the center to the periphery of the lens substrate.

  The film thicknesses of the first to third layers are preferably constant regardless of the substrate tilt angle of the lens substrate, or increase in thickness from the center of the lens substrate to the periphery.

  The ratio D / R between the effective diameter D and the curvature radius R of the lens substrate is preferably in the range of 0.1-2.

A first layer composed of a dense layer containing SiO ₂ and / or a silane coupling agent, a second layer composed of silica airgel, and a third layer are sequentially laminated on the substrate, and the substrate is refracted by light having a wavelength of 550 nm. A three-layer configuration in which the refractive index is 1.6 or less, the refractive index of the third layer is in the range of 1.15 to 1.32, and the refractive indexes of the substrate, the first layer, the second layer, and the third layer are lower in this order. The method of the present invention for producing an antireflection film of
Forming the first layer by a dry process or a wet process, and forming the second layer and the third layer by a wet process,
All the steps of forming the first layer to the third layer are performed at 90 ° C. or lower.

  Preferably, the step of forming the first layer comprises a vacuum deposition method or a sol-gel method, and the step of forming the second layer and the third layer comprises a sol-gel method.

  The optical member of the present invention can be applied to a lens substrate made of a resin having a relatively low melting point because the antireflection film can be formed by a film forming process of 90 ° C. or less. Performance can be imparted.

  The optical member of the present invention has an excellent antireflection performance in a wide wavelength range even if it is a lens substrate having a maximum substrate tilt angle of 30 ° or more. It is suitable for a lens system including a lens surface, an optical disk pickup lens, and the like.

It is a schematic cross section which shows an example of the optical member of this invention. It is a schematic cross section which shows another example of the optical member of this invention. It is a schematic cross section for demonstrating the board | substrate inclination angle of an optical member. It is a schematic cross section for demonstrating the lens effective diameter and lens curvature radius of an optical member. It is a schematic cross section for demonstrating the light ray incident angle of an optical member. FIG. 3 is a schematic cross-sectional view illustrating a configuration of an optical member of Example 1. 6 is a graph showing antireflection characteristics in (a) a lens center portion and (b) a lens peripheral portion (a portion where the substrate tilt angle is 50 °) of the optical member of Example 1. It is a graph which shows the anti-reflective characteristic in (a) lens center part of the optical member of Example 2, and (b) lens peripheral part (part whose board | substrate inclination angle is 50 degrees). It is a schematic diagram which shows an example of the apparatus which forms an antireflection film by vacuum evaporation.

[1] optical members
(A) First Mode FIG. 1 includes a substrate 2 and an antireflection film 3 having a three-layer structure in which a first layer 3a, a second layer 3b, and a third layer 3c are sequentially provided on the substrate 2. The optical member 1 is shown. In the antireflection film 3, the first layer 3a is made of a dense film containing SiO ₂ and / or a silane coupling agent, and the second layer 3b and the third layer 3c are made of a silica airgel film. In light having a wavelength of 550 nm, the refractive index of the substrate 2 is 1.6 or less, the refractive index of the third layer 3c is in the range of 1.15 to 1.32, the substrate 2, the first layer 3a, the second layer 3c, and the third layer 3c. The refractive index of the layer 3c decreases in this order. FIG. 1 is an enlarged view of each layer in the thickness direction for easy understanding of the layer structure of the antireflection film 3. Further, the refractive index in this specification is a value in light having a wavelength of 550 nm unless otherwise specified.

  Each of the first layer 3a, the second layer 3b, and the third layer 3c is preferably made of a film formed by a film forming process of 90 ° C. or less.

(1) Antireflection film The first layer is preferably a dense film containing SiO ₂ and / or a silane coupling agent, and is preferably formed by a dry process or a wet process. In light having a wavelength of 550 nm, the refractive index of the first layer must be lower than the refractive index of the substrate and higher than the refractive index of the second layer, preferably in the range of 1.37 to 1.57, and preferably in the range of 1.37 to 1.53. A range is more preferred, with a range of 1.37 to 1.51 being most preferred. The optical film thickness of the first layer is preferably 1 to 100 nm, and more preferably 2 to 50 nm. The dry process is preferably a vacuum deposition method, and the wet process preferably includes a sol-gel method. When forming a dense film made of SiO _{2, a} dry process is preferable, and when forming a dense film containing a silane coupling agent, a wet process is preferable.

When the first layer is formed of a dense film containing SiO ₂ and / or a silane coupling agent, adhesion between the substrate and the second layer (silica airgel film) is improved. Due to the effect of improving the adhesion of the first layer, an optical member having an antireflection film with high mechanical strength can be obtained even when all processes for forming the antireflection film are performed at 90 ° C. or lower. The first layer is preferably composed of a dense film containing a silane coupling agent.

  The second layer is preferably made of a silica airgel film and formed by a wet process. The refractive index of the second layer needs to be lower than the refractive index of the first layer and higher than the refractive index of the third layer in light having a wavelength of 550 nm, preferably in the range of 1.30 to 1.50, and 1.35 to 1.45. Is more preferable, and the range of 1.37 to 1.42 is most preferable. The optical film thickness of the second layer is preferably 50 to 150 nm, and more preferably 100 to 140 nm. The wet process preferably includes a sol-gel method.

  The third layer is preferably made of a silica airgel film and formed by a wet process. The refractive index of the third layer is in the range of 1.15 to 1.32 for light having a wavelength of 550 nm, and needs to be lower than the refractive index of the second layer. The refractive index of the third layer is preferably in the range of 1.15 to 1.30, more preferably 1.15 to 1.28, and most preferably 1.15 to 1.25. The optical thickness of the third layer is preferably 90 to 170 nm, and more preferably 100 to 150 nm. By providing a layer having such a low refractive index as the outermost layer, an excellent antireflection effect is exhibited. The wet process preferably includes a sol-gel method.

  The silica airgel membrane constituting the second layer and the third layer is preferably a porous membrane having a pore diameter of 0.005 to 0.2 μm, and the average pore diameter is preferably 0.001 to 0.1 μm. The porosity of the silica airgel film is preferably 30 to 90%.

  In order to impart water resistance and durability to the antireflection film, a silica airgel composed of silica whose organic end is modified may be used. Further, a fluororesin film having water and oil repellency may be provided on the third layer made of the silica airgel film.

(2) Substrate The optical member of the present invention uses a substrate having a refractive index of 1.6 or less for light having a wavelength of 550 nm. The refractive index of the substrate is preferably in the range of 1.6 to 1.9. By forming the antireflection film on a substrate having a refractive index in such a range, an optical member having good antireflection performance in the visible light wavelength band can be obtained. The substrate is preferably made of a resin or contains a resin. The resin preferably has a melting point of 150 ° C. or lower, and specific examples include polymethyl methacrylate (PMMA), polycarbonate (PC), and chain or cyclic polyolefin. The shape of the substrate may be a flat plate or a lens. Examples of the substrate containing a resin include a hybrid lens obtained by bonding a transparent resin to optical glass. In the case of a hybrid lens, the substrate material on the surface on which the antireflection film is formed may be in the above refractive index range.

(B) Second Aspect In the first aspect of the optical member, a second aspect of a configuration using a lens-like substrate (lens substrate) having a maximum substrate inclination angle of 30 ° or more will be described.

  FIG. 2 shows an optical member 11 including a lens substrate 21 and an antireflection film 31 in which a first layer 31a, a second layer 31b, and a third layer 31c are provided on the lens substrate 21 in this order. The optical member 11 according to the second aspect is an aspect in which a lens substrate 21 having a maximum substrate inclination angle of 30 ° or more is used as a substrate, and is composed of a first layer 31a, a second layer 31b, and a third layer 31c. The configuration of the film 31 is basically the same except for the points described below. Therefore, differences from the first aspect will be described in detail.

The maximum substrate tilt angle of the lens substrate is preferably 30 ° or more, more preferably in the range of 30 to 65 °, and still more preferably in the range of 30 to 60 °. Here, as shown in FIG. 3, the substrate tilt angle is an angle (θ _t ) formed by a normal at an arbitrary point on the lens surface with respect to an axis C passing through the center of the lens and parallel to the optical axis. The angle is 0 ° at the center of the lens, and usually increases toward the periphery of the lens. 2 and 3 are enlarged views of each layer in the thickness direction for easy understanding of the layer structure of the antireflection film 31. FIG.

  The lens substrate 21 preferably has a ratio D / R between the lens effective diameter D and the lens curvature radius R in the range of 0.1 to 2. As shown in FIG. 4, the lens effective diameter D is the maximum diameter that can be effectively used when used as an optical member, and the radius of curvature R is a radius when the lens curved surface is approximated to a sphere. When the lens substrate having the ratio D / R in the range of 0.1 to 2 is used, the effect of the present invention is more exhibited.

Further, the light ray incident angle (θ _i ) at an arbitrary point on the lens surface is an angle formed by the normal and the light ray at that point. For example, at the center of the lens (point where the substrate tilt angle is 0 °), FIG. is an angle indicated by theta _i in a), in the portion of the substrate inclination angle theta _t, is the angle indicated by theta _i in FIG. 4 (b).

The optical thickness D1 (θ _t ) of the first layer, the optical thickness D2 (θ _t ) of the second layer, and the optical thickness D3 (θ _t ) of the third layer at an arbitrary substrate tilt angle θ _t of the lens substrate. Are the following formulas (1), (2) and (3):
_{D1 (θ t) = D1 0} × (cosθ t) α ··· (1),
_{D2 (θ t) = D2 0} × (cosθ t) β ··· (2), and
_{D3 (θ t) = D3 0} × (cosθ t) γ ··· (3)
(Where D1 ₀ , D2 ₀ and D3 ₀ represent the optical film thicknesses of the first layer, the second layer and the third layer, respectively, at the center of the lens substrate, and α, β and γ are independently − It is preferably a numerical value in the range of 2.0 to 2.0. α, β and γ are more preferably each independently in the range of −1.3 to 1.3, and most preferably are independently in the range of −0.5 to 1.2.

  As shown in FIG. 2, the optical film thickness of the first layer 31a may become thinner from the central part of the lens substrate 21 toward the peripheral part. The optical film thicknesses of the second layer 31b and the third layer 31c are preferably constant regardless of the substrate tilt angle of the lens substrate 21, or the peripheral portion is thicker than the center portion of the lens. Thus, by forming the first layer 31a as it goes to the peripheral portion, a good antireflection effect can be obtained regardless of the substrate tilt angle, and the reflection is less affected by the light incident angle at the tilt angle. A protective film is obtained. In particular, it is more effective when a lens substrate having a maximum substrate tilt angle of 30 ° or more is used.

  As another configuration of the antireflection film, the optical film thicknesses of the first layer 31a, the second layer 31b, and the third layer 31c are constant regardless of the substrate inclination angle of the lens substrate, or from the central portion of the lens substrate to the peripheral portion. There are cases where it gets thicker as you go.

(c) Antireflection property The optical member of the present invention has an antireflection property with a maximum reflectance of 0.24 to 0.3% or less in a visible light band of 400 to 700 nm. The optical component of the present invention is suitable for a lens, a prism, a diffraction element, and the like mounted on an optical device such as a television camera, a video camera, a digital camera, an in-vehicle camera, a microscope, and a telescope. In particular, an optical member formed by forming an antireflection film on a lens substrate having a maximum substrate tilt angle of 30 ° or more has good antireflection properties even in the periphery of the lens, so it is suitable for an ultra-wide angle lens, an optical disk pickup lens, etc. It is.

[2] Manufacturing method On the substrate, a first layer composed of a dense layer containing SiO ₂ and / or a silane coupling agent, a second layer composed of silica airgel, and a third layer are sequentially laminated, and light having a wavelength of 550 nm The refractive index of the substrate is 1.6 or less, and the refractive index of the third layer is in the range of 1.15 to 1.32. The refractive indexes of the substrate, the first layer, the second layer, and the third layer become lower in this order. The method for manufacturing the three-layer antireflection film is as follows:
Forming the first layer by a dry process or a wet process, and forming the second layer and the third layer by a wet process,
All the steps of forming the first layer to the third layer are performed at 90 ° C. or lower. By performing the manufacturing process at 90 ° C. or lower in this way, the substrate is not exposed to temperatures exceeding 90 ° C. Therefore, even when a resin having a relatively low melting point is used as the substrate, the antireflection of the present invention A film can be formed.

(1) Formation method of the first layer The first layer of the antireflection film is a layer composed of a dense layer containing SiO ₂ and / or a silane coupling agent, and is formed by a dry process or a wet process. Examples of the dry process include physical vapor deposition such as vacuum vapor deposition, sputtering, and ion plating, and chemical vapor deposition such as thermal CVD, plasma CVD, and photo CVD. A combination of these methods may be used as necessary. In particular, the vacuum deposition method is preferable in terms of manufacturing cost and processing accuracy. The wet process preferably includes a sol-gel method. In particular, the dense layer containing only SiO ₂ is preferably formed by a dry process, and the dense layer containing a silane coupling agent is preferably formed by a wet process.

  Examples of the vacuum deposition method include a resistance overheating method, an electron beam method, and the like, but an electron beam vacuum deposition method will be described below. As shown in FIG. 9, the electron beam vacuum deposition apparatus 130 includes a rotatable rotating rack 132 for placing a plurality of substrates 100 on the inner surface in a vacuum chamber 131, and a crucible for installing a deposition material 137. A vapor deposition source 133 having 136, an electron beam irradiator 138, a heater 139, and a vacuum pump connection port 135 connected to the vacuum pump 140 are provided. The antireflection film is formed by vapor-depositing the vapor deposition material 137 on the surface of the substrate 100 while reducing the pressure in the vacuum chamber 131. The substrate 100 is placed on the rotating rack 132 so that the surface faces the vapor deposition source 133 side, and the vapor deposition material 137 is placed on the crucible 136. The inside of the vacuum chamber 131 is depressurized by the vacuum pump 140 connected to the vacuum pump connection port 135, and the vapor deposition material 137 is heated and evaporated by irradiation of the electron beam from the electron beam irradiator 138. In order to form a uniform vapor deposition film, the rotating rack 132 is rotated by the rotating shaft 134 while the substrate 100 is heated by the heater 139.

  When vapor deposition is performed on the lens substrate using the vacuum deposition apparatus, the film thickness usually decreases from the center of the lens to the periphery of the lens. However, the lens substrate installation position, the position of the deposition source 133, the electron beam irradiation intensity, and the vacuum By adjusting the degree or the like, the thickness of the layer from the central part to the peripheral part of the lens substrate can be adjusted to some extent.

In the vacuum evaporation method, the initial degree of vacuum is preferably, for example, 1.0 × 10 ^{−6 to} 1.0 × 10 ⁻⁵ Torr. If the degree of vacuum is outside this range, the vapor deposition takes time, and the production efficiency is deteriorated, or the vapor deposition is insufficient and the film formation is not completed. The temperature of the substrate 100 during vapor deposition can be appropriately determined according to the heat resistance of the substrate and the vapor deposition rate, but is preferably 60 to 90 ° C, for example.

When the first layer is formed by a wet process, for example, a coating solution containing SiO ₂ obtained by a sol-gel method is applied by a method such as dip coating, spray coating, spin coating, or printing. Is preferred. The dense layer containing the silane coupling agent is preferably formed by applying a solution of the silane coupling agent by the above method. When forming a dense layer containing a silane coupling agent, it may be formed by applying only a silane coupling agent, or by applying a solution containing SiO ₂ and a silane coupling agent. May be.

(2) Formation method of 2nd layer and 3rd layer The 2nd layer and 3rd layer of an antireflection film consist of silica airgel, and are formed by a wet process. The wet process preferably includes a sol-gel method. By forming an ultra-low refractive index film made of silica aerogel by the sol-gel method, it is possible to obtain a refractive index lower than MgF ₂ (n = 1.39), which is a low refractive index material generally used in vacuum deposition, It is possible to obtain an antireflection film having a wide bandwidth and a wide angle (wide incident angle range) with a very low reflectance, which has been difficult to realize so far.

For example, when the MgF ₂ layer is formed as the second layer and the third layer by vacuum deposition on the lens substrate, the film thickness of the second layer and the third layer becomes thinner toward the lens periphery as in the first layer. For this reason, in the lens periphery where the substrate tilt angle is large, all the film thicknesses of the first layer to the third layer become thin, and good antireflection performance cannot be obtained.

  As the sol-gel method, an existing method can be applied. Particularly preferably, (i) an acidic solution is further added to an alkaline sol prepared by hydrolysis and condensation polymerization of alkoxysilane under a basic catalyst. A step of adding a first acidic sol having a median diameter of 100 nm or less, and (ii) a step of obtaining a second acidic sol having a median diameter of 10 nm or less by hydrolysis and condensation polymerization of alkoxysilane under an acidic catalyst. (iii) a step of mixing the first and second acidic sols, (iv) a step of applying and drying the obtained mixed sol on the lens substrate on which the first layer and the second layer are formed, (v It is preferable to form a third layer of silica airgel by an alkali treatment step, (vi) a washing step, and (vii) a humidity treatment step.

(i) Step of preparing the first acidic sol
(a) Alkoxysilane The alkoxysilane for the first acidic sol is preferably a tetraalkoxysilane monomer or oligomer (condensation product). When a tetrafunctional alkoxysilane is used, a sol of colloidal silica particles having a relatively large particle size can be obtained. Tetraalkoxysilane is represented by Si (OR) ₄ [R is an alkyl group having 1 to 5 carbon atoms (methyl, ethyl, propyl, butyl, etc.) or an acyl group having 1 to 4 carbon atoms (acetyl etc.)]. Those are preferred. Specific examples of tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, diethoxydimethoxysilane and the like. Of these, tetramethoxysilane and tetraethoxysilane are preferred. A small amount of trifunctional or lower functional alkoxysilane may be added to the tetraalkoxysilane as long as the effects of the present invention are not impaired.

(b) Hydrolysis and polycondensation in the presence of a basic catalyst Hydrolysis and polycondensation proceed by adding an organic solvent, a basic catalyst and water to the alkoxysilane. As the organic solvent, alcohols such as methanol, ethanol, n-propanol, i-propanol, and butanol are preferable, and methanol or ethanol is more preferable. As the basic catalyst, ammonia, amine, NaOH or KOH is preferable. Preferred amines are alcohol amines or alkyl amines (methylamine, dimethylamine, trimethylamine, n-butylamine, n-propylamine, etc.).

The amount ratio between the organic solvent and the alkoxysilane is preferably set so that the concentration of the alkoxysilane is 0.1 to 10% by mass (silica concentration) in terms of SiO ₂ . When the silica concentration is more than 10% by mass, the particle size of the silica particles in the obtained sol becomes too large. On the other hand, when the silica concentration is less than 0.1, the particle size of the silica particles in the obtained sol becomes too small. Note the range of 1 to 10 ⁴ are preferable as the molar ratio of the organic solvent / alkoxysilane.

The basic catalyst / alkoxysilane molar ratio is preferably 1 × 10 ⁻⁴ to 1, more preferably 1 × 10 ^{−4 to} 0.8, and particularly preferably 3 × 10 ^{−4 to} 0.5. . If the molar ratio of basic catalyst / alkoxysilane is less than 1 × 10 ⁻⁴ , hydrolysis reaction of alkoxysilane does not occur sufficiently. On the other hand, even if the molar ratio exceeds 1 and the base is added, the catalytic effect is saturated.

  The water / alkoxysilane molar ratio is preferably 0.1-30. If the water / alkoxysilane molar ratio is more than 30, the hydrolysis reaction proceeds too quickly, making it difficult to control the reaction and making it difficult to obtain a uniform silica airgel film. On the other hand, when it is less than 0.1, hydrolysis of alkoxysilane does not occur sufficiently.

  The alkoxysilane solution containing the basic catalyst and water is preferably aged by standing at 10 to 90 ° C. for about 10 to 60 hours or slowly stirring. By aging, hydrolysis and condensation polymerization proceed, and silica sol is generated. The silica sol includes, in addition to a dispersion of colloidal silica particles, a dispersion in which colloidal silica particles are aggregated in a cluster.

(c) Hydrolysis and polycondensation in the presence of an acidic catalyst An acidic catalyst, and water and an organic solvent as necessary are added to the obtained alkaline sol, and hydrolysis and polycondensation are further advanced in an acidic state. Examples of the acidic catalyst include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid and the like. The same organic solvent as above can be used. In the first acidic sol, the molar ratio of acidic catalyst / basic catalyst is preferably 1.1 to 10, more preferably 1.5 to 5, and most preferably 2 to 4. If the molar ratio of acidic catalyst / basic catalyst is less than 1.1, polymerization by acidic catalyst does not proceed sufficiently. On the other hand, if it exceeds 10, the catalytic effect is saturated. The organic solvent / alkoxysilane molar ratio and the water / alkoxysilane molar ratio may be the same as described above. The sol containing the acidic catalyst is preferably aged by standing at 10 to 90 ° C. for about 15 minutes to 24 hours or slowly stirring. By aging, hydrolysis and condensation polymerization proceed to produce a first acidic sol.

  The median diameter of the silica particles in the first acidic sol is 100 nm or less, preferably 10 to 50 nm. The median diameter is measured by a dynamic light scattering method.

(ii) Step of preparing the second acidic sol
(a) Alkoxysilane The alkoxysilane for the second acidic sol is Si (OR ¹ ) _x (R ² ) _4-x [x is an integer of 2 to 4. 2-4 functional groups represented by R ¹ is preferably an alkyl group having 1 to 5 carbon atoms (methyl, ethyl, propyl, butyl or the like) or an acyl group having 1 to 4 carbon atoms (acetyl or the like). R ² is preferably an organic group having 1 to 10 carbon atoms, for example, a hydrocarbon group such as methyl, ethyl, propyl, butyl, hexyl, cyclohexyl, octyl, decyl, phenyl, vinyl, allyl, and γ-chloropropyl, CF ₃ CH _2- , CF ₃ CH ₂ CH _2- , C ₂ F ₅ CH ₂ CH _2- , C ₃ F ₇ CH ₂ CH ₂ CH _2- , CF ₃ OCH ₂ CH ₂ CH _2- , C ₂ F ₅ OCH ₂ CH ₂ CH _2- , C ₃ F ₇ OCH ₂ CH ₂ CH _2- , (CF ₃ ) ₂ CHOCH ₂ CH ₂ CH _2- , C ₄ F ₉ CH ₂ OCH ₂ CH ₂ CH _2- , 3- (perfluoro (Cyclohexyloxy) propyl, H (CF ₂ ) ₄ CH ₂ OCH ₂ CH ₂ CH _2- , H (CF ₂ ) ₄ CH ₂ CH ₂ CH _2- , γ-glycidoxypropyl, γ-mercaptopropyl, 3,4 -Substituted hydrocarbon groups such as epoxycyclohexylethyl and γ-methacryloyloxypropyl.

  Specific examples of the bifunctional alkoxysilane include dimethyldialkoxysilane such as dimethyldimethoxysilane and dimethyldiethoxysilane. Specific examples of the trifunctional alkoxysilane include methyltrialkoxysilane such as methyltrimethoxysilane and methyltriethoxysilane, and phenyltrialkoxysilane such as phenyltriethoxysilane. Examples of the tetrafunctional alkoxysilane include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, and diethoxydimethoxysilane. The alkoxysilane is preferably trifunctional or more, more preferably methyltrialkoxysilane and tetraalkoxysilane.

(b) Hydrolysis and polycondensation in the presence of an acidic catalyst Hydrolysis and polycondensation proceed by adding an organic solvent, an acidic catalyst and water to an alkoxysilane monomer or oligomer (polycondensation product). The same organic solvent and acidic catalyst as described in the step of preparing the first acidic sol can be used. The acidic catalyst / alkoxysilane molar ratio is preferably 1 × 10 ⁻⁴ to 1, more preferably 1 × 10 ^{−4 to} 3 × 10 ^{−2, and} most preferably 3 × 10 ⁻⁴ to 1 × 10 ⁻² . The molar ratio of the organic solvent / alkoxysilane and the molar ratio of water / alkoxysilane may be the same as described in the step of preparing the first acidic sol.

  The alkoxysilane solution containing an acidic catalyst and water is preferably aged by standing at 10 to 90 ° C. for about 30 minutes to 60 hours or by slowly stirring. By aging, hydrolysis and condensation polymerization proceed to produce a second acidic sol. When the aging time exceeds 60 hours, the median diameter of the silica particles in the sol becomes too large.

  The resulting colloidal silica particles in the second acidic sol have a smaller median diameter than the first acidic sol. The median diameter of the colloidal silica particles in the second acidic sol is 10 nm or less, preferably 1 to 5 nm. The median diameter ratio between the silica particles in the first acidic sol and the silica particles in the second acidic sol is preferably 5 to 50, and more preferably 5 to 35. When the median diameter ratio is less than 5 or more than 50, the scratch resistance of the silica airgel film is lowered.

(iii) Step of preparing mixed sol It is preferable that the first acidic sol and the second acidic sol are mixed and slowly stirred at 1 to 30 ° C. for about 1 minute to 6 hours. You may heat a mixture at 80 degrees C or less as needed. The solid mass ratio of the first acidic sol and the second acidic sol is preferably 5 to 90, more preferably 5 to 80. When the solid content mass ratio is less than 5 or more than 90, the scratch resistance of the silica airgel film is lowered.

(iv) Application and drying process
(a) Application The mixed sol is applied to the surface of the lens substrate on which the first layer and the second layer are formed. Examples of the application method include dip coating, spray coating, spin coating, and printing. When applying to a three-dimensional structure such as a lens, a spin coating method or a dipping method is preferable, and a spin coating method is particularly preferable. The physical film thickness of the gel obtained can be controlled, for example, by adjusting the substrate rotation speed in the spin coating method, adjusting the concentration of the mixed sol, or the like. The rotation speed of the substrate in the spin coating method is preferably about 1,000 to 15,000 rpm.

  The organic solvent may be added as a dispersion medium in order to adjust the concentration and fluidity of the mixed sol and improve the coating suitability. The concentration of silica in the mixed sol at the time of application is preferably 0.1 to 20% by mass. If necessary, the mixed sol may be sonicated. Aggregation of colloidal particles can be prevented by ultrasonic treatment. The ultrasonic frequency is preferably 10 to 30 kHz, the output is preferably 300 to 900 W, and the treatment time is preferably 5 to 120 minutes.

(b) Drying The drying conditions for the coating film are appropriately selected according to the heat resistance of the substrate. In order to promote the polycondensation reaction, heat treatment may be performed at a temperature below the boiling point of water for 15 minutes to 24 hours, and then at a temperature of 100 to 200 ° C. for 15 minutes to 24 hours. The silica airgel film exhibits high scratch resistance by heat treatment.

(v) Alkali treatment step By treating the silica airgel membrane with alkali, the scratch resistance is further improved. The alkali treatment is preferably performed by applying an alkali solution or leaving it in an ammonia atmosphere. The solvent of the alkaline solution can be appropriately selected according to the alkali, and water, alcohol and the like are preferable. The concentration of the alkaline solution is preferably 1 × 10 ^{−4 to} 20N, and more preferably 1 × 10 ^{−3 to} 15N.

  Examples of the alkali include inorganic alkalis such as sodium hydroxide, potassium hydroxide, and ammonia; inorganic alkali salts such as sodium carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate; monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, Triethylamine, n-propylamine, di-n-propylamine, n-butylamine, di-n-butylamine, n-amylamine, n-hexylamine, laurylamine, ethylenediamine, hexamethylenediamine, aniline, methylaniline, ethylaniline, Cyclohexylamine, dicyclohexylamine, pyrrolidine, pyridine, imidazole, guanidine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, Organic alkalis such as trabutylammonium hydroxide, monoethanolamine, diethanolamine, triethanolamine, choline; organic acid alkali salts such as ammonium formate, ammonium acetate, monomethylamine formate, dimethylamine acetate, aniline acetate, pyridine lactate, guanidinoacetic acid Etc. can be used.

When alkali treatment is performed by application of an alkaline solution, it is preferable to apply 10 to 200 mL per 1 cm ^{2 of} the silica airgel film. The application can be performed by the same method as that for applying the silica airgel film, and the spin coating method is preferred. The substrate rotation speed in the spin coating method is preferably about 1,000 to 15,000 rpm. The film after applying the alkaline solution is preferably stored at 1 to 40 ° C, more preferably at 10 to 30 ° C. The storage time is preferably 0.1 to 10 hours, more preferably 0.2 to 1 hour.

When the alkali treatment is performed in an ammonia atmosphere, the treatment is preferably carried out in an ammonia gas partial pressure of 1 × 10 ⁻¹ to 1 × 10 ⁵ Pa. The treatment temperature is preferably 1 to 40 ° C, more preferably 10 to 30 ° C. The treatment time is preferably 1 to 170 hours, more preferably 5 to 80 hours.

  If necessary, the silica-treated airgel membrane is dried. Drying is preferably performed at a temperature of 50 to 200 ° C. for 15 minutes to 24 hours.

(vi) Cleaning step The silica airgel membrane after the alkali treatment is cleaned as necessary. The washing is preferably performed by a method of immersing in water and / or alcohol, a method of showering, or a combination thereof. You may ultrasonically treat, immersing. The washing temperature is preferably 1 to 40 ° C., and the time is preferably 0.2 to 15 minutes. The silica airgel membrane is preferably washed with 0.01 to 1,000 mL of water and / or alcohol per 1 cm ² . The silica airgel membrane after washing is preferably dried at a temperature of 50 to 200 ° C. for 15 minutes to 24 hours. As alcohol, methanol, ethanol, and isopropyl alcohol are preferable.

(vii) Humidity treatment step The silica airgel membrane after application, alkali treatment or washing is subjected to humidity treatment under high humidity conditions. It is thought that hydrolysis of unreacted alkoxysilane and polycondensation reaction of silanol groups proceed due to the humidity treatment, improving the mechanical strength of the silica airgel film and changing the refractive index over time after film formation. It is suppressed.

  Humidity treatment is performed by storing in an environment at a temperature of 35 ° C or higher and a relative humidity of 70% or higher for 1 hour or longer. If the humidity of the treatment is less than 70% RH, the above effect cannot be obtained sufficiently. The humidity is preferably 75% RH or more, more preferably 80% RH or more, and most preferably 90% RH or more. The treatment temperature is preferably 35 to 90 ° C, more preferably 40 to 80 ° C, and most preferably 50 to 80 ° C. When the treatment temperature is less than 35 ° C., the above effect cannot be obtained sufficiently, and even if it exceeds 90 ° C., the effect is saturated. Although the treatment time depends on the temperature condition and the humidity condition, the effect can be obtained by performing the treatment for 1 hour or more. Preferably it is 5-120 hours, More preferably, it is 5-48 hours. The effect is saturated when the treatment time exceeds 120 hours.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[1] Optical member fabrication example 1
As shown in FIG. 6, on a hybrid lens substrate 22 (a substrate formed by forming an aspheric surface with an acrylate resin 22b on the surface of a spherical glass lens 22a), an antireflection film 31 (first layer 31a, The optical member 11 (configuration shown in Table 1) formed by forming the second layer 31b and the third layer 31c) was produced by the method described below.

(1) Fabrication of substrate A photocurable resin (acrylate resin) is injected into the gap between the spherical glass lens substrate and the desired shape (aspherical surface) mold, and the resin is cured by light irradiation. After that, by releasing the photo-curable resin from the mold, a hybrid lens substrate (maximum substrate tilt) in which an aspheric surface is formed on the surface of the spherical glass lens substrate with an acrylate resin (refractive index: nd = 1.535). (Angle: 53.8 °, effective lens diameter: 43.1 mm, radius of curvature: 27.3 mm). The radius of curvature is a value obtained by approximating the aspheric surface to a sphere.

(2) Formation of antireflection film
(a) Formation of first layer A SiO ₂ film was formed on the surface of the acrylate resin by vacuum deposition (dry process) so as to have the structure shown in Table 1. The substrate heating temperature (set temperature) at this time was 100 ° C., and the temperature near the substrate in the vacuum chamber was about 60 to 80 ° C. Therefore, the temperature of the substrate was substantially 80 ° C. or lower.

(b) Formation of the second layer
(i) Preparation of first acidic sol After mixing 17.05 g of tetraethoxysilane and 69.13 g of methanol, 3.88 g of aqueous ammonia (3 N) was added and stirred at room temperature for 15 hours to prepare an alkaline sol. To 40.01 g of this alkaline sol, 2.50 g of methanol and 1.71 g of hydrochloric acid (12 N) were added and stirred at room temperature for 30 minutes to prepare a first acidic sol (solid content: 4.94% by mass).

(ii) Preparation of second acidic sol After mixing 30 ml of tetraethoxysilane, 30 ml of ethanol and 2.4 ml of water at room temperature, 0.1 ml of hydrochloric acid (1 N) was added and stirred at 60 ° C. for 90 minutes. A second acidic sol (solid content: 14.8% by mass) was prepared.

(iii) Preparation of mixed sol 0.22 g of the second acidic sol was added to the total amount of the first acidic sol so that the solid mass ratio of the first acidic sol and the second acidic sol was 67.1, A mixed sol was prepared by stirring at room temperature for 5 minutes.

(iv) Application and Alikari Treatment The obtained mixed sol was applied onto the first layer by spin coating so as to have the structure shown in Table 1, and a 0.3 N sodium methoxide methanol solution was applied immediately after application. Further application was performed by spin coating. Both of these spin coat applications were performed at room temperature (25 ° C.). The coated sample was allowed to stand for 30 minutes under constant temperature and humidity of 60 ° C. and 90% RH and dried. The substrate cooled to room temperature was thoroughly washed with water.

(c) Formation of third layer The same mixed sol as that used for forming the second layer was applied onto the second layer by spin coating so as to have the structure shown in Table 1, and immediately after the application. A 0.3 N sodium methoxide methanol solution was further applied by spin coating. Both of these spin coat applications were performed at room temperature (25 ° C.). The coated sample was allowed to stand for 24 hours under constant temperature and humidity of 60 ° C. and 90% RH and dried. A sodium methoxide methanol solution was spin-coated at room temperature on a substrate cooled to room temperature, and further allowed to stand at 60 ° C. and 90% constant temperature and humidity for 30 minutes. The substrate cooled to room temperature was thoroughly washed with water.

  Table 1 shows the refractive index, physical film thickness, and optical film thickness of each layer of the obtained antireflection film. A lens reflectometer (model number: USPM-RU, manufactured by Olympus Corporation) was used for the measurement of refractive index and physical film thickness.

The optical thickness of the first layer to the substrate inclination angle θ _t D1 (θ _t), a second layer having an optical thickness of D2 (theta _t) and a third layer having an optical thickness of D3 (theta _t) are respectively the following formulas ( 1.1), formula (1.2) and formula (1.3):
_{D1 (θ t) = D1 0} × (cosθ t) α ··· (1.1),
_{D2 (θ t) = D2 0} × (cosθ t) β ··· (1.2) and
_{D3 (θ t) = D3 0} × (cosθ t) γ ··· (1.3)
(Where D1 ₀ , D2 ₀ and D3 ₀ represent optical film thicknesses of the first layer, the second layer and the third layer, respectively, at the center of the lens substrate, and α, β and γ are all -2.0 to It was in the range of 2.0.)

注(1)：基板傾斜角度50°の箇所

Note (1): Location where the board tilt angle is 50 °

Example 2
Using the hybrid lens substrate produced in Example 1, an optical member (configuration shown in Table 2) formed by forming a three-layer antireflection film as shown below was produced.

(1) Formation of antireflection film
(a) Formation of first layer A UV curable silane coupling agent (KBM-5103 manufactured by Shin-Etsu Chemical Co., Ltd.) was applied by spin coating and cured by irradiation with ultraviolet rays to form a first layer.

(b) Formation of Second Layer A second layer was formed in the same manner as in Example 1 except that the film thickness was changed as shown in Table 2.

(c) Formation of third layer A third layer was formed in the same manner as in Example 1.

Table 2 shows the refractive index, physical film thickness, and optical film thickness of each layer of the obtained antireflection film. The refractive index and physical film thickness were measured in the same manner as in Example 1. The optical thickness of the first layer to the substrate inclination angle θ _t D1 (θ _t), a second layer having an optical thickness of D2 (theta _t) and a third layer having an optical thickness of D3 (theta _t) are respectively the following formulas ( 2.1), formula (2.2) and formula (2.3):
_{D1 (θ t) = D1 0} × (cosθ t) α ··· (2.1),
_{D2 (θ t) = D2 0} × (cosθ t) β ··· (2.2) and
_{D3 (θ t) = D3 0} × (cosθ t) γ ··· (2.3)
(Where D1 ₀ , D2 ₀ and D3 ₀ represent optical film thicknesses of the first layer, the second layer and the third layer, respectively, at the center of the lens substrate, and α, β and γ are all -2.0 to It was in the range of 2.0.)

注(1)：基板傾斜角度50°の箇所

Note (1): Location where the board tilt angle is 50 °

[2] Evaluation of optical components
(1) Evaluation of antireflection characteristics The antireflection characteristics of the optical member of Example 1 are shown in FIGS. 7 (a) and 7 (b), and the antireflection characteristics of the optical member of Example 2 are shown in FIGS. Shown in 8 (b). 7 (a) and 8 (a) show the antireflection characteristics at the center of the lens, and FIGS. 7 (b) and 8 (b) show the antireflection at the periphery of the lens (where the substrate tilt angle is 50 °). Show properties.

  From Examples 1 and 2, the optical member of the present invention has good antireflection performance with almost no change in the central portion and the peripheral portion even when a lens substrate having a large substrate tilt angle (50 ° or more) is used. It can be seen that

(2) Evaluation of scratch resistance A silica airgel film on the outermost surface of the antireflection film is applied to a nonwoven fabric of 20 mm x 20 mm at a rate of 3600 mm / min while applying a pressure of 1 kg / cm ² (trade name “Spic Lens Wiper”). , Manufactured by Ozu Sangyo Co., Ltd.) 30 times, surface scratches were visually confirmed and evaluated according to the following criteria.

<Criteria>
The silica aero membrane was not damaged at all ...
The silica aero film was scratched but did not peel off ...
Silica Aero membrane peeled off ×

  The results are shown in Table 3. From the results shown in Table 3, it can be seen that the optical members of Examples 1 and 2 are provided with an antireflection film having excellent mechanical strength and adhesion even when formed by a film forming process of 90 ° C. or less. It was.

1,11 ... Optical member 2 ... Substrate
21 ... Lens substrate
22 ... Hybrid lens substrate
21a ・ ・ ・ Spherical glass lens substrate
21b ・ ・ ・ Acrylate resin 3,31 ・ ・ ・ Antireflection film
3a, 31a ... 1st layer
3b, 31b ... 2nd layer
3c, 31c ・ ・ ・ 3rd layer
100 ... Board
130 ・ ・ ・ Electron beam vacuum evaporation system
131 ・ ・ ・ Vacuum chamber
132 ・ ・ ・ Rotating rack
133 ... Vapor deposition source
134 ・ ・ ・ Rotation axis
135 ・ ・ ・ Vacuum pump connection port
136 ... Crucible
137 ... Vapor deposition material
138 ... Electron beam irradiator
139 Heater
140 ... Vacuum pump

Claims (12)

An optical member comprising a substrate and an antireflection film having a three-layer structure provided in the order of the first layer to the third layer on the substrate,
The first layer comprises a dense film containing SiO ₂ and / or a silane coupling agent,
The second layer and the third layer are composed of a silica airgel film,
For light with a wavelength of 550 nm,
The refractive index of the substrate is 1.6 or less,
The third layer has a refractive index in the range of 1.15 to 1.32.
The optical member, wherein the refractive index of the substrate, the first layer, the second layer, and the third layer decreases in this order.   The optical member according to claim 1, wherein the substrate is made of a resin or contains a resin.   3. The optical member according to claim 1, wherein the first layer has an effect of improving adhesion between the substrate and the second layer. 4.   The optical member according to any one of claims 1 to 3, wherein the refractive index of the third layer is in the range of 1.15 to 1.25.   5. The optical member according to claim 1, wherein the substrate is a lens substrate having a maximum substrate inclination angle of 30 ° or more.   6. The optical member according to claim 5, wherein a maximum substrate inclination angle of the lens substrate is in a range of 30 to 65 [deg.]. 7. The optical member according to claim 5, wherein the optical thickness D1 (θ _t ) of the first layer and the optical thickness D2 (θ _{t of} the second layer at an arbitrary substrate tilt angle θ _t of the lens substrate. ), And the optical film thickness D3 (θ _t ) of the third layer is
The following formula (1), formula (2) and formula (3) respectively:
_{D1 (θ t) = D1 0} × (cosθ t) α ··· (1)
_{D2 (θ t) = D2 0} × (cosθ t) β ··· (2)
_{D3 (θ t) = D3 0} × (cosθ t) γ ··· (3)
(Where D1 ₀ , D2 ₀ and D3 ₀ represent the optical film thicknesses of the first layer, the second layer and the third layer, respectively, at the center of the lens substrate, and α, β and γ are independently − The numerical value is in the range of 2.0 to 2.0.   8. The optical member according to claim 5, wherein the first layer has a thickness that decreases from a center portion to a peripheral portion of the lens substrate. 9.   8. The optical member according to claim 5, wherein the film thicknesses of the first layer to the third layer are constant regardless of the substrate tilt angle of the lens substrate, or go from the central portion of the lens substrate to the peripheral portion. An optical member characterized by being thickened according to   10. The optical member according to claim 5, wherein a ratio D / R between an effective diameter D and a curvature radius R of the lens substrate is in a range of 0.1 to 2. 10. A first layer composed of a dense layer containing SiO ₂ and / or a silane coupling agent, a second layer composed of silica airgel, and a third layer are sequentially laminated on the substrate, and the substrate is refracted by light having a wavelength of 550 nm. A three-layer configuration in which the refractive index is 1.6 or less, the refractive index of the third layer is in the range of 1.15 to 1.32, and the refractive indexes of the substrate, the first layer, the second layer, and the third layer are lower in this order. A method of manufacturing an antireflection film of
Forming the first layer by a dry process or a wet process, and forming the second layer and the third layer by a wet process,
A method for producing an antireflection film, wherein the steps of forming the first layer to the third layer are all performed at 90 ° C. or lower.   12. The method of manufacturing an antireflection film according to claim 11, wherein the step of forming the first layer comprises a vacuum deposition method or a sol-gel method, and the step of forming the second layer and the third layer is a sol-gel. A process for producing an antireflection film, characterized by comprising:

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