JP2006215542A - Anti-reflection coating and optical element having such anti-reflection coating for imaging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anti-reflection coating having an excellent anti-reflection characteristic with respect to a light beam with a broad wavelength region and a wide variety of incident angles, and having sufficient mechanical strength, and also to provide an optical element for imaging system, having the anti-reflection coating. <P>SOLUTION: The anti-reflection coating comprises a dense layer 21 and a porous silica aerogel layer 22 formed in this order on the surface 11 of a substrate 1. The anti-reflection coating 2, in which the refractive index successively decreases from the substrate 1 to the respective layers 21 and 22, has a visual reflectance of 2% or less with respect to the light beam at incident angle of 0 to 60°, and excellent scratch resistance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an antireflection film formed on the surface of a substrate, and in particular, an antireflection film having excellent antireflection characteristics for light rays in a wide wavelength range and a wide incident angle range, and an imaging system having the antireflection film The present invention relates to an optical element.

  An antireflection film is applied to the surface of a base material such as a lens or prism constituting the optical apparatus for the purpose of improving the light transmittance. If the reflection in the visible region is suppressed by the antireflection film, the brightness and visibility of the image can be improved. Since many optical devices use light in a specific narrow wavelength range, the antireflection film provided on the optical element is designed to have an excellent antireflection effect at the wavelength used. For example, in a single-layer antireflection film, the optical path difference between the reflected light at the antireflection film surface and the reflected light at the boundary between the antireflection film and the lens is an odd multiple of 1/2 of the wavelength, and these rays are It is designed to have a thickness that cancels out due to interference.

  However, in recent years, optical devices using light beams in a wide wavelength range have been manufactured, and an antireflection film having excellent optical characteristics in a wide wavelength range has been desired. Moreover, since an optical element is often composed of a plurality of lens groups, a multilayer antireflection film is generally provided in order to prevent a loss of transmitted light amount due to reflection on each lens surface. The multilayer antireflection film is designed so that the reflected light generated at the interface of each layer and the light incident on each layer cancel each other out by interference.

  In recent years, lenses used in imaging optical devices such as cameras have been made to have a high numerical aperture (NA) in response to demands for miniaturization and high performance. However, for example, if the numerical aperture of the objective lens of the camera is increased, the lens curvature increases, and the light incident angle at the lens periphery increases. For this reason, the amount of reflected light at the lens periphery increases, and the amount of transmitted light and transmitted light colors differ between the center and the periphery of the lens, or a ghost caused by the reflected light at the lens periphery occurs. is there. Therefore, an antireflection film having excellent characteristics with respect to light rays having a wide range of incident angles is desired.

  In addition, when an antireflection film is formed on a curved surface such as a convex lens by a physical film forming method, the antireflection film is generally thinner in the peripheral portion than in the central portion of the lens. For this reason, the spectral characteristics shift to the shorter wavelength side than the design condition in the peripheral portion as compared with the center of the lens, and the amount of reflected light particularly in the red region increases. In addition, unlike the central part, obliquely incident light is mostly used in the peripheral part. However, since the interference length is shortened depending on the incident angle, the spectral characteristics are further shifted to the short wavelength side. End up. From this point of view, it is desired to provide an antireflection film having antireflection characteristics for light rays having a wide range of incident angles.

  Therefore, in Japanese Patent Laid-Open No. 2003-43202 (Patent Document 1), a low refractive index material is formed on the first and eighth layers counted from the substrate side, and an intermediate refractive index material is formed on the second, fourth, and sixth layers. A high refractive index material is formed on the third, fifth, and seventh layers, and the optical film thickness nd of each layer with respect to the design wavelength λd is (0.9 to 2.4) × λd / 4, (0.9 to 1.2) × λd / 4 for the second layer, (0.27 to 0.50) × λd / 4 for the third layer, and (0.17 to 0.27) × λd / 4 for the fourth layer. Yes, the fifth layer is (1.34 to 2.14) × λd / 4, the sixth layer is (0.35 to 0.45) × λd / 4, and the seventh layer is (0.26 to 0.38) × λd / 4, In the eighth layer, an antireflection film of (1.03 to 1.13) × λd / 4 is proposed. This antireflection film exhibits a reflectance of less than 1.0% for light having a wavelength of 340 to 900 nm. However, antireflection performance for light with a high incident angle is insufficient. For example, luminous reflectance for light with an incident angle of 60 ° [obtained from the spectral reflectance based on the XYZ color system standard of CIE (International Commission on Illumination). Y value] is over 4%.

  Japanese Patent Laid-Open No. 10-227902 (Patent Document 2) proposes a broadband antireflection film having at least two fluororesin layers laminated in the order of a high refractive index layer and a low refractive index layer from the substrate side. This broadband antireflection film exhibits a transmittance of 99.5% or more in the wavelength range of 350 to 1350 nm. This broadband antireflection film also exhibits high antireflection performance for visible light having a relatively high incident angle. For example, the luminous reflectance for light with an incident angle of 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.

  Japanese Patent Application Laid-Open No. 2003-119052 (Patent Document 3) proposes a light-transmitting sheet in which an airgel layer is formed on one surface of a light-transmitting sheet body. Patent Document 3 specifically describes silica airgel as an airgel. Since silica airgel has a low refractive index of 1.35 or less, the light-transmitting sheet of Patent Document 3 is excellent in antireflection properties. Patent Document 3 also describes providing a plurality of silica airgel layers so that the refractive index of the layer on the sheet body side increases. However, since this optically transparent sheet does not optimize the optical film thickness of each layer with respect to incident light, high antireflection performance cannot always be obtained for light beams having a wide range of incident angles.

JP2003-43202A JP-A-10-227902 JP2003-119052

  Accordingly, an object of the present invention is to provide an antireflection film having excellent antireflection characteristics with respect to light having a wide incident angle in a wide wavelength range and sufficient mechanical strength, and an imaging system having the antireflection film. It is to provide an optical element.

  As a result of intensive studies in view of the above object, the present inventors have formed a dense layer and a silica airgel porous layer on the surface of the base material in order so that the refractive index decreases in order from the base material. The present inventors have found that an antireflection film having excellent antireflection characteristics with respect to light rays having a wide range of incident angles and sufficient mechanical strength can be obtained, and the present invention has been conceived.

  That is, the antireflection film of the present invention is composed of a dense layer and a silica airgel porous layer formed in order on the surface of the substrate, and the refractive index decreases in order from the substrate to the porous layer. And

  The dense layer is preferably an inorganic layer, an inorganic fine particle-binder composite layer, or a resin layer. The inorganic layer is preferably formed by a vapor deposition method. The inorganic vapor deposition layer is preferably made of magnesium fluoride or silicon oxide.

  The silica airgel porous layer is preferably formed by heat-treating an organically modified silica airgel layer. The silica airgel porous layer preferably has a refractive index of 1.05 to 1.35. The porosity of the silica airgel porous layer is preferably 30 to 90%. The contact angle of the silica airgel porous layer with respect to pure water is preferably 15 ° or less.

  The optical film thickness of the dense layer and the porous layer is preferably in the range of λd / 5 to λd / 3 with respect to the design wavelength λd. The antireflection film of the present invention preferably exhibits a luminous reflectance of 2% or less for light rays having an incident angle of 0 to 60 ° in the wavelength range of the design wavelength λd ± 100 nm.

  The imaging system optical element of the present invention has the antireflection film.

  The antireflection film of the present invention consists of a dense layer and a silica airgel porous layer formed in order on the surface of the substrate, and the refractive index decreases in order from the substrate to the porous layer. It has excellent antireflection characteristics for light beams with a wide range of incident angles, and has sufficient mechanical strength. When the antireflection film of the present invention having such an excellent antireflection characteristic is provided on the lens, it is caused by a difference in transmitted light amount or transmitted light color between the central portion and the peripheral portion or reflected light at the lens peripheral portion. Problems such as ghosting can be significantly reduced. When an optical element having such excellent characteristics is used in a camera, endoscope, binoculars, projector, etc., the image quality can be remarkably improved. In particular, the antireflection film of the present invention has excellent antifogging properties because the outermost silica airgel porous layer has many voids and is hydrophilic. Furthermore, since the antireflection film of the present invention comprises two layers, the production cost is low and the yield is good.

[1] Imaging optical element having antireflection film FIG. 1 shows an antireflection film 2 formed on a surface 11 of an optical substrate (simply referred to as a substrate) 1. As shown in FIG. 1, the antireflection film 2 has a two-layer structure including a dense layer 21 and a silica airgel porous layer 22 in order from the substrate 1 side. In the example shown in FIG. 1, a flat plate is used as the base material 1, but the present invention is not limited to this, and a lens, a prism, a light guide, a film, or a diffraction element may be used. The material of the substrate 1 may be any of glass, crystalline material, and plastic. Specific examples of the material of the substrate 1 include optical glass such as BK7, LASF016, LAK14, and SF5, Pyrex (registered trademark) glass, quartz, blue plate glass, white plate glass, PMMA resin, PC resin, and polyolefin resin. The refractive index of these substrates is in the range of 1.45 to 1.85.

The refractive index decreases in the order of the base material 1, the dense layer 21, the silica airgel porous layer 22, and the incident medium A. The optical film thicknesses d ₁ and d ₂ of the dense layer 21 and the silica airgel porous layer 22 are in the range of λd / 5 to λd / 3 with respect to the design wavelength λd. The optical film thickness is the product of the refractive index of the film and the physical film thickness. The design wavelength λd used for determining the configuration of the thin film can be appropriately set according to the wavelength used for the optical element. For example, the visible wavelength [wavelength of 380 to 780 nm as defined by the CIE (International Commission on Illumination)] It is preferable that the center wavelength is substantially the same.

In the antireflection film 2 composed of a dense layer 21 and a silica airgel porous layer 22 provided so that the refractive index decreases in order from the base material 1, the optical film thickness of each layer 21 and 22 with respect to the design wavelength λd. When the range is λd / 5 to λd / 3, the optical film thickness D of the antireflection film 2 (the sum of the optical film thicknesses d ₁ and d ₂ ) is in the range of 2λd / 5 to 2λd / 3, and is incident from the base material 1. The change in the refractive index with respect to the optical film thickness over the medium A has a smooth step shape as shown in FIG. When the optical film thickness D of the antireflection film 2 is in the range of 2λd / 5 to 2λd / 3, the reflected light on the surface of the antireflection film 2 and the reflected light on the boundary between the antireflection film 2 and the substrate 1 Since the optical path difference is approximately 1/2 of the design wavelength λd, these rays cancel each other out due to interference. If the change in the refractive index with respect to the optical film thickness from the substrate 1 to the incident medium A is made into a smooth stepped shape, the change in the refractive index with respect to the optical film thickness can be made smooth, and the reflection of incident light that occurs at the boundary of each layer has a wide wavelength. Can be reduced in the area. Further, the reflected light generated at the interface of each layer cancels out by interfering with the light ray incident on each layer. Therefore, the antireflection film 2 exhibits an excellent antireflection effect for light rays in a wide wavelength range and a wide incident angle range. If the optical film thickness of each layer 21 and 22 is not in the range of λd / 5 to λd / 3, the change in the refractive index with respect to the optical film thickness from the substrate 1 to the incident medium A is not smooth. For this reason, the reflectance at the interface between the layers 21 and 22 is increased. The optical film thicknesses d ₁ and d ₂ of the dense layer 21 and the silica airgel porous layer 22 are more preferably λd / 4.5 to λd / 3.5 with respect to the design wavelength λd.

Refractive index differences R ₁ , R ₂ , R between the substrate 1 and the dense layer 21, between the dense layer 21 and the silica airgel porous layer 22, and between the silica airgel porous layer 22 and the incident medium A Each of ₃ is preferably 0.02 to 0.4, so that the change in refractive index with respect to the optical film thickness can be made smooth enough to approximate a straight line. Therefore, the antireflection effect of the antireflection film 2 is further improved.

  The dense layer 21 is a layer composed of an inorganic material such as a metal oxide (referred to as “inorganic layer”), a composite layer composed of inorganic fine particles and a binder (referred to as “inorganic fine particle-binder composite layer” or simply “composite layer”). Or a layer made of resin. The material of the dense layer 21 is selected from those having a refractive index smaller than the refractive index of the substrate 1 and larger than the refractive index (1.05 to 1.35) of the silica airgel porous layer 22.

  Examples of inorganic materials that can be used for the inorganic layer include magnesium fluoride, calcium fluoride, aluminum fluoride, lithium fluoride, sodium fluoride, cerium fluoride, silicon oxide, aluminum oxide, cryolite, thiolite, and mixtures thereof. Can be mentioned.

  Examples of inorganic fine particles that can be used in the composite layer include calcium fluoride, magnesium fluoride, aluminum fluoride, sodium fluoride, lithium fluoride, cerium fluoride, silicon oxide, aluminum oxide, zirconium oxide, cryolite, thiolite, Examples thereof include at least one inorganic fine particle selected from the group consisting of titanium oxide, indium oxide, tin oxide, antimony oxide, cerium oxide, hafnium oxide, and zinc oxide. The silicon oxide is preferably colloidal silica, and the colloidal silica may be surface-treated with a silane coupling agent or the like. The refractive index of the inorganic fine particle-binder composite layer depends on the composition of the inorganic fine particles and the binder composition as well as the content.

  Examples of the resin layer include a fluororesin layer, an epoxy resin layer, an acrylic resin layer, a silicone resin layer, and a urethane resin layer. The fluororesin includes crystalline fluororesins such as polytetrafluoroethylene resin, perfluoroethylene propylene copolymer, perfluoroalkoxy resin, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, and polychlorotrifluoroethylene. However, the amorphous fluororesin is preferable because it has excellent transparency. Specific examples of the non-crystalline fluororesin include a fluoroolefin copolymer, a polymer having a fluorine-containing aliphatic ring structure, and a fluorinated acrylate copolymer. Examples of the fluoroolefin copolymer include those obtained by copolymerization of 37 to 48% by mass of tetrafluoroethylene, 15 to 35% by mass of vinylidene fluoride, and 26 to 44% by mass of hexafluoropropylene. . Examples of the polymer having a fluorinated alicyclic structure include those obtained by polymerizing a monomer having a fluorinated alicyclic structure, and those obtained by cyclopolymerizing a fluorinated monomer having at least two polymerizable double bonds.

  The silica airgel porous layer 22 preferably has uniform pores having small pore diameters. Such a silica airgel porous layer 22 has high transparency. The refractive index of the silica airgel porous layer 22 depends on the porosity, and the higher the porosity, the smaller the refractive index. The porosity of the porous layer 22 is preferably 30 to 90%. The refractive index of the silica airgel layer having a porosity of 30 to 90% is usually 1.05 to 1.35. For example, the refractive index of a silica airgel layer having a porosity of 78% is about 1.1. When the porosity exceeds 90%, the mechanical strength is too small. If the porosity is less than 30%, the refractive index is too large.

  The silica airgel porous layer 22 has many voids, and moisture easily enters therein. Therefore, the silica airgel porous layer 22 is hydrophilic and exhibits antifogging properties. The contact angle of the silica airgel porous layer 22 with respect to pure water is 15 ° or less, and preferably 12 ° or less. When water enters the voids, the refractive index of the silica airgel porous layer 22 is somewhat increased, but there is no practical problem. Here, the “contact angle” means an angle between the tangent of the water droplet at the contact point with the apparent horizontal plane of the silica airgel porous layer 22 and the apparent horizontal plane. The method for measuring the contact angle is not particularly limited as long as it is a method using a general contact angle measuring device capable of measuring a water droplet that has been left immediately after dropping. As a measurement environment for the contact angle, it is preferable that the temperature is 21 to 24 ° C., the relative humidity is 45 to 55%, and the sample amount is 1 μL to 10 μL.

As described above, the antireflection film 2 composed of the two layers of the dense layer 21 and the silica airgel porous layer 22 exhibits excellent antireflection characteristics with respect to light rays having a wide incident angle in a wide wavelength range from the visible range to the infrared range. Here, the “excellent antireflection characteristic” means a small reflectance and a large light transmittance. Specifically, in the desired antireflection wavelength region, the luminous reflectance of the antireflection film 2 for light rays having an incident angle of 0 to 60 ° is preferably 2% or less. Here, “luminous reflectance” means the Y value obtained by measuring the spectral reflectance of the antireflection film and obtaining the obtained spectral reflectance according to the CIE (International Lighting Commission) XYZ color system standard. . The Y value is generally given by equation (1):
Y = ∫ρ (λ) dλ (1)
(Where λ is the wavelength and ρ (λ) is the spectral reflectance expressed as a function of wavelength). For example, if the antireflection wavelength range is 380 to 780 nm, and the design wavelength λd is approximately 550 nm, the wavelength λ used to calculate the Y value in equation (1) is centered on λd. The desired range is, for example, λd ± 100 nm = 450 to 650 nm, or λd ± 50 nm = 500 to 600 nm. On the other hand, when the wavelength range in which the luminous reflectance is 2% or less is obtained, the optimum optical film thicknesses d ₁ and d of the dense layer 21 and the silica airgel porous layer 22 are obtained by setting the center wavelength to the design wavelength λd. ₂ can be set. Further, the antireflection wavelength band of the antireflection film 2 can be shifted or widened by changing the design wavelength λd.

[2] Manufacturing method of antireflection film
(1) Formation of a dense layer A layer made of only an inorganic material may be formed by a physical vapor deposition method such as a vacuum vapor deposition method, a sputtering method, or an ion plating method, or a chemical vapor deposition method such as thermal CVD, plasma CVD, or photo-CVD. it can. The inorganic fine particle-binder composite layer can be formed by a wet method such as a dip coating method, a spin coating method, a spray method, a roll coating method, or a screen printing method. The resin layer can be formed by a chemical vapor deposition method or a wet method. Among these methods, a method for producing an inorganic layer by vapor deposition will be described first, and then a method for producing an inorganic fine particle-binder composite layer and a fluororesin layer by dip coating will be explained.

(a) Vapor deposition method In the case of using a vapor deposition method, a vapor deposition material made of an inorganic material is evaporated by heating and attached to a substrate in a vacuum to form an inorganic layer. There are no particular restrictions on the method of making the vapor deposition material vapor. For example, a method using an electrically heated source, a method of applying an electron beam with an E-type electron gun, a method of applying a high-current electron beam by hollow cathode discharge, a laser that applies a laser pulse Ablation etc. are mentioned. The substrate is preferably installed so that its film formation surface faces the vapor deposition material, and is preferably rotated during vapor deposition in that state. A layer having a desired thickness can be formed by appropriately setting the deposition time, the heating temperature, and the like.

(b) Dip coat method
(b-1) Inorganic fine particle-binder composite layer
(i) Preparation of inorganic fine particle-containing slurry

  The average particle size of the inorganic fine particles is preferably about 5 to 80 nm. When the average particle size is more than 80 nm, the resulting antireflection film is too low in transparency. On the other hand, it is difficult to produce inorganic fine particles having an average particle size of less than 5 nm.

  The mass ratio of inorganic fine particles / binder component is preferably 0.05 to 0.7. If the mass ratio of the inorganic fine particles / binder component is more than 0.7, it is difficult to apply uniformly and the resulting layer is too brittle. If the mass ratio is less than 0.05, it is difficult to obtain a desired refractive index.

  Here, the “binder component” refers to a monomer or oligomer that becomes a binder by polymerization. The binder component is preferably an ultraviolet curable or thermosetting compound, and more preferably an ultraviolet curable compound. When an ultraviolet curable compound is used, an antireflection film containing a binder can be provided even when the substrate is non-heat resistant. Examples of the ultraviolet curable or thermosetting compound include a radical polymerizable compound, a cationic polymerizable compound, and an anion polymerizable compound. These compounds may be used in combination.

  As the radical polymerizable compound, an acrylate ester is preferable. Specific examples of the radical polymerizable compound include (a) 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, Monofunctional (meth) acrylates such as carboxypolycaprolactone (meth) acrylate, (meth) acrylic acid, (meth) acrylamide, (b) pentaerythritol di (meth) acrylate, ethylene glycol di (meth) acrylate and pentaerythritol di ( Di (meth) acrylate such as (meth) acrylate monostearate, trimethylolpropane tri (meth) acrylate, tri (meth) acrylate such as pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meta) Acrylates, polyfunctional (meth) acrylates such as dipentaerythritol penta (meth) acrylate, and these include oligomers obtained by polymerizing.

  As the cationic polymerizable compound, an epoxy compound is preferable. Specific examples include phenyl glycidyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, vinylcyclohexene dioxide, 1,2,8,9-diepoxy limonene, 3,4-epoxy cyclohexyl methyl 3 ', 4'-epoxy. And cyclohexanecarboxylate and bis (3,4-epoxycyclohexyl) adipate.

  When using the binder component of a radically polymerizable compound or a cationically polymerizable compound, a radical polymerization initiator or a cationic polymerization initiator is added to the inorganic fine particle-containing slurry. As the radical polymerization initiator, a compound that generates radicals upon irradiation with ultraviolet rays is used. Examples of preferable radical polymerization initiators include benzyls, benzophenones, thioxanthones, benzyl dimethyl ketals, α-hydroxyalkylphenones, hydroxyketones, aminoalkylphenones, and acylphosphine oxides. The addition amount of the radical polymerization initiator is about 0.1 to 20 parts by mass with respect to 100 parts by mass of the radical polymerizable compound.

  As the cationic polymerization initiator, a compound that generates a cation by ultraviolet irradiation is used. Examples of the cationic polymerization initiator include onium salts such as a diazonium salt, a sulfonium salt, and an iodonium salt. The addition amount of the cationic polymerization initiator is about 0.1 to 20 parts by mass with respect to 100 parts by mass of the cationic polymerizable compound.

  Two or more inorganic fine particles and a binder component may be blended in the slurry. In addition, general additives such as a dispersant, a stabilizer, a viscosity modifier, and a colorant can be used as long as the physical properties are not impaired.

  The concentration of the slurry affects the thickness of the layer that forms. Examples of solvents include alcohols such as methanol, ethanol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, 2-butyl alcohol, i-butyl alcohol, t-butyl alcohol, 2-ethoxyethanol, 2-butoxy Alkoxy alcohols such as ethanol, 3-methoxypropanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, ketols such as diacetone alcohol, ketones such as acetone, methyl ethyl ketone, methyl i-butyl ketone, toluene And aromatic hydrocarbons such as xylene, and esters such as ethyl acetate and butyl acetate. The amount of the solvent used is about 20 to 10,000 parts by mass per 100 parts by mass in total of the inorganic fine particles and the binder component.

(ii) Coating A layer of inorganic fine particle-containing slurry is formed on the substrate by dip coating, spin coating, spraying, roll coating, screen printing, or the like. For example, in the case of the dip coating method, the thickness of the layer to be formed can be controlled by the slurry concentration, the dipping time, the pulling speed, and the like.

The binder component in the inorganic fine particle-containing slurry layer is polymerized. When the binder component is ultraviolet curable, when the UV irradiation is performed at about 50 to 3,000 mJ / cm ² using a UV irradiation device, the binder component is polymerized to form a layer composed of inorganic fine particles and the binder. Although depending on the thickness of the layer, the irradiation time is usually about 0.1 to 60 seconds.

  The solvent of the inorganic fine particle-containing slurry is volatilized. In order to volatilize the solvent, the slurry may be kept at room temperature or heated to about 30 to 100 ° C.

(b-2) Fluororesin layer
(i) Preparation of fluorine-containing composition solution To form a fluororesin layer, (a) a composition solution containing a fluorine-containing olefin polymer and a crosslinkable compound is applied to a substrate and then crosslinked. Alternatively, (b) a solution of a composition containing a fluorine-containing olefin compound and a monomer copolymerizable therewith may be applied and then polymerized. Methods for forming a fluororesin layer using a fluorine-containing composition are described in detail in JP-A Nos. 07-126552, 11-228631, 11-337706, and the like.

  A commercially available fluorine-containing composition may be mixed with an appropriate solvent. Examples of usable fluorine-containing compositions include Opstar (manufactured by JSR Corporation) and Cytop (manufactured by Asahi Glass Co., Ltd.). Preferred solvents include ketones such as methyl ethyl ketone, methyl i-butyl ketone and cyclohexanone, and esters such as ethyl acetate and butyl acetate. The concentration of the fluorine-containing olefin polymer and the fluorine-containing olefin compound is preferably 5 to 80% by mass.

(ii) Coating Since the method for forming the fluororesin layer is substantially the same as the above-mentioned (b-1) inorganic fine particle-binder composite layer except that a fluorine-containing composition solution is used, only the differences will be described below. After the layer of the fluorine-containing composition solution is formed, a crosslinking reaction or a polymerization reaction is performed. When the crosslinkable compound or the fluorine-containing olefin compound is a thermosetting type, it is preferably heated to 100 to 140 ° C. for about 30 to 60 minutes. In the case of the UV curable type, UV irradiation is performed at 50 to 3,000 mJ / cm ² . Although depending on the thickness of the layer, the irradiation time is usually about 0.1 to 60 seconds.

(2) Formation of a silica airgel porous layer A silica airgel porous layer is obtained by reacting (a) a sol-like or gel-like silicon oxide with an organic modifier to form an organically modified sol or an organically modified gel. The modified sol or the organic modified gel in the form of a sol is coated on the surface of the dense layer, and a springback phenomenon is generated in the obtained organic modified silica gel layer to form an organic modified silica airgel layer. It can be formed by heat-treating the modified silica airgel layer to remove the organic modifying group.

(a) Raw material for silica airgel layer
(a-1) Alkoxysilane and silsesquioxane Silica sol or silica gel is produced by hydrolysis and polymerization of alkoxysilane and / or silsesquioxane. The alkoxysilane may be a monomer or an oligomer. The alkoxysilane monomer preferably has 3 or more alkoxyl groups. By using an alkoxysilane having three or more alkoxyl groups as a starting material, an antireflection film having excellent uniformity can be obtained. Specific examples of the alkoxysilane monomer include methyltrimethoxysilane, methyltriethoxysilane, phenyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, tetrapropoxysilane, diethoxydimethoxysilane, dimethyldimethoxysilane, dimethyldi An ethoxysilane is mentioned. As the alkoxysilane oligomer, a polycondensation product of the above-mentioned monomers is preferable. The alkoxysilane oligomer is obtained by hydrolysis and polymerization of an alkoxysilane monomer.

Even when silsesquioxane is used as a starting material, an antireflection film having excellent uniformity can be obtained. Silsesquioxanes formula RSiO _1.5 (wherein R is. Of an organic functional group) is represented by a generic term for a network polysiloxane. Examples of R include an alkyl group (which may be a straight chain or a branched chain and having 1 to 6 carbon atoms), a phenyl group, and an alkoxy group (such as a methoxy group and an ethoxy group). Silsesquioxane is known to have various structures such as a ladder type and a saddle type. It also has excellent weather resistance, transparency and hardness, and is suitable as a starting material for silica airgel.

(a-2) Solvent The solvent is preferably composed of water and alcohol. As the alcohol, methanol, ethanol, n-propyl alcohol, and i-propyl alcohol are preferable, and ethanol is particularly preferable. The water / alcohol molar ratio of the solvent is preferably 0.01-2. If the water / alcohol molar ratio is more than 2, the hydrolysis reaction proceeds too quickly. When the water / alcohol molar ratio is less than 0.01, hydrolysis of alkoxysilane and / or silsesquioxane (hereinafter simply referred to as “alkoxysilane etc.”) does not occur sufficiently.

(a-3) Catalyst It is preferable to add a catalyst to an aqueous solution of alkoxysilane or the like. By adding an appropriate catalyst, the hydrolysis reaction of alkoxysilane or the like can be promoted. The catalyst may be acidic or basic. Examples of acidic catalysts include hydrochloric acid, nitric acid and acetic acid. Examples of basic catalysts include ammonia, amines, NaOH and KOH. Examples of preferred amines include alcohol amines and alkyl amines (eg methylamine, dimethylamine, trimethylamine, n-butylamine, n-propylamine).

(b) Preparation of sol or gel Dissolve alkoxysilane or the like in a solvent composed of water and alcohol. The solvent / alkoxysilane molar ratio is preferably 3-100. When the molar ratio is less than 3, the degree of polymerization of alkoxysilane or the like becomes too high. If the molar ratio exceeds 100, the degree of polymerization of alkoxysilane or the like becomes too low. The molar ratio of catalyst / alkoxysilane or the like is preferably 1 × 10 ^{−4 to} 3 × 10 ⁻² , and more preferably 3 × 10 ⁻⁴ to 1 × 10 ⁻² . If the molar ratio is less than 1 × 10 ⁻⁴ , hydrolysis reaction of alkoxysilane or the like does not occur sufficiently. Even if the molar ratio ^exceeds 3 × 10 ⁻² , the catalytic effect does not increase.

  A solution containing alkoxysilane or the like is aged for about 20 to 60 hours. Specifically, the solution is allowed to stand at 25 to 90 ° C. or slowly stirred. Gelation proceeds by aging, and a sol or gel containing silicon oxide is generated. In this specification, “sol containing silicon oxide” includes not only those in which colloidal particles made of silicon oxide are in a dispersed state but also those in which sol clusters made of aggregated colloidal particles are in a dispersed state. It is.

(c) Organic modification Add a solution of an organic modifier to the sol or gel, and bring the sol or gel and the organic modifier solution into sufficient contact with each other, so that a hydroxyl group at the terminal of silicon oxide constituting the sol or gel The hydrophilic group is replaced with a hydrophobic organic group. Preferred organic modifiers are the following formulas (2) to (7)
M _p SiCl _q ... (2)
M ₃ SiNHSiM ₃・ ・ ・ (3)
M _p Si (OH) _q・ ・ ・ (4)
M ₃ SiOSiM ₃ ... (5)
M _p Si (OM) _q・ ・ ・ (6)
M _p Si (OCOCH ₃ ) _q・ ・ ・ (7)
(Where p is an integer of 1 to 3, q is an integer of 1 to 3 that satisfies q = 4-p, M is hydrogen, a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms, or a carbon number 5 to 18 substituted or unsubstituted aryl groups) and a mixture thereof.

  Specific examples of organic modifiers include triethylchlorosilane, trimethylchlorosilane, diethyldichlorosilane, dimethyldichlorosilane, acetoxytrimethylsilane, acetoxysilane, diacetoxydimethylsilane, methyltriacetoxysilane, phenyltriacetoxysilane, diphenyldiacetoxysilane, trimethylethoxy Silane, trimethylmethoxysilane, 2-trimethylsiloxypent-2-en-4-one, n- (trimethylsilyl) acetamide, 2- (trimethylsilyl) acetic acid, n- (trimethylsilyl) imidazole, trimethylsilylpropiolate, nonamethyltrisilazane , Hexamethyldisilazane, hexamethyldisiloxane, trimethylsilanol, triethylsilanol, triphenylsilanol, t-butyldimethylsilano And diphenylsilanediol.

  The solvent of the organic modifier solution is hydrocarbons such as hexane, cyclohexane, pentane, heptane, alcohols such as methanol, ethanol, n-propyl alcohol, i-propyl alcohol, ketones such as acetone, and aromatics such as benzene and toluene. Group compounds are preferred.

  Although depending on the type and concentration of the organic modifier, the organic modification reaction is preferably allowed to proceed at 10 to 40 ° C. If it is less than 10 ° C., the organic modifier is too difficult to react with silicon oxide. If it exceeds 40 ° C., the organic modifier will easily react with substances other than silicon oxide. During the reaction, it is preferable to stir the solution so that there is no distribution in the temperature and concentration of the solution. For example, when the organic modifier solution is a hexane solution of triethylchlorosilane, the silanol group is sufficiently silyl-modified when held at 10 to 40 ° C. for about 20 to 40 hours (for example, 30 hours). The modification rate is preferably 10 to 30%.

(d) Substitution of solvent Before or after organic modification, in order to increase the dispersibility of the sol or gel, it is preferable to substitute the solvent (dispersion medium) in the sol or gel with another solvent for high dispersion. In the case of a gel, it is preferable to repeat the operation of pouring a high dispersion solvent into a container containing the gel, shaking, and then decanting. In this case, since the solvent in the gel is usually water + ethanol, it may be substituted with ethanol first, and then with another solvent for high dispersion (for example, ketone). In the case of a sol, a low-boiling solvent that azeotropes with the solvent in the sol is added, the original solvent is removed by azeotropic distillation, and then a high dispersion solvent is added as a new solvent. The azeotropic solvent may be the same as or different from the solvent for high dispersion.

  Solvents for high dispersion include water, ethanol, methanol, propanol, butanol, hexane, heptane, pentane, cyclohexane, toluene, acetonitrile, acetone, dioxane, methyl i-butyl ketone, propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethyl acetate And mixtures thereof are preferably used. More preferred solvents for high dispersion are ketones.

  If the solvent is replaced with a highly dispersing solvent by the ultrasonic treatment step described later, a highly dispersible organic-modified silica-containing sol can be obtained. For example, since ketones have excellent affinity for silica (silicon oxide) and organically modified silica, silica or organically modified silica is well dispersed in ketones. The substitution with the high dispersion solvent may be performed either before or after the organic modification, but is preferably performed before the organic modification from the viewpoint of reducing the number of steps.

  More preferable ketones have a boiling point of 60 ° C. or higher. Ketones having a boiling point of less than 60 ° C. (for example, acetone) not only makes it difficult to adjust the concentration of the dispersion because it volatilizes too much in the ultrasonic irradiation process described later. There is also a problem that sufficient film formation time cannot be obtained. Furthermore, acetone is known to be harmful to the human body and is not preferable from the viewpoint of worker health.

  Of the ketones, particularly preferred are asymmetric ketones having different substituents on both sides of the carbonyl group. Since asymmetric ketones have a large polarity, they have a particularly excellent affinity for silica and organically modified silica. The substituent that the ketone has may be an alkyl group or an aryl group. Preferred alkyl groups are those having about 1 to 5 carbon atoms. Specific examples of the ketone solvent include methyl i-butyl ketone, ethyl i-butyl ketone, and methyl ethyl ketone.

(e) Ultrasonic treatment By ultrasonic treatment, the gel-form or sol-form organic modified silica can be brought into a state suitable for coating. In the case of gel-like organically modified silica, it is considered that the gel aggregated by electrical force or van der Waals force is dissociated by ultrasonic treatment, or the covalent bond between metal and oxygen is broken, resulting in a dispersed state. It is done. Even in the case of a sol, aggregation of colloidal particles can be reduced by ultrasonic treatment. For the ultrasonic treatment, a dispersion device using an ultrasonic transducer can be used. The frequency of the ultrasonic wave to be irradiated is preferably 10 to 30 kHz. The output is preferably 300 to 900 W.

  The ultrasonic treatment time is preferably 5 to 120 minutes. The longer the ultrasonic wave is irradiated, the finer the gel or sol cluster becomes, and the less aggregated it becomes. For this reason, colloidal particles of organically modified silica are in a state close to monodispersion in a silica-containing sol obtained by ultrasonic treatment. When it is less than 5 minutes, the colloidal particles are not sufficiently dissociated. Even when the sonication time is longer than 120 minutes, the dissociation state of the organically modified silica colloidal particles hardly changes.

  In the organic-modified silica-containing sol thus obtained, the organic-modified silica preferably has a particle size of 200 nm or less. When the particle diameter of the organically modified silica is larger than 200 nm, it is difficult to form a substantially smooth silica airgel film.

  The organic solvent may be further added as a dispersion medium before or during the ultrasonic treatment so that the concentration and fluidity of the organic-modified silica-containing sol are in an appropriate range. The mass ratio of the organically modified silica to the solvent is preferably 0.1 to 20%. Outside this mass ratio range, it is difficult to form a uniform thin layer, which is not preferable.

(f) Coating The surface of the dense layer is coated with an organically modified silica-containing sol. Examples of the coating method of the organic-modified silica-containing sol include spray coating, spin coating, dip coating, flow coating, and bar coating. The solvent is volatilized from the applied organic-modified silica-containing sol, and an organic-modified silica airgel layer is formed. The porosity of the organically modified silica airgel layer decreases due to the gel shrinkage caused by capillary pressure while the solvent is volatilized, but recovers by the springback phenomenon when the solvent is volatilized. For this reason, the porosity of the organic modified silica airgel layer is almost the same as the original porosity of the gel network, and shows a large value. The shrinkage and springback phenomenon of the silica gel network is described in detail in US Pat. No. 5,948,482.

  When a sol containing silicon oxide colloidal particles in a state close to monodispersion is used, an organically modified silica airgel layer having a small porosity can be formed. When a sol containing colloidal particles in a large agglomerated state is used, an organic modified silica airgel layer having a large porosity can be formed. That is, it can be said that the ultrasonic treatment time affects the porosity of the organic modified silica airgel layer and the silica airgel layer obtained by heat-treating it. An organic modified silica airgel layer having a porosity of 30 to 90% can be obtained by dip coating a sol which has been subjected to ultrasonic treatment for 5 to 120 minutes.

(g) Heat treatment The obtained organic-modified silica airgel porous layer is heat-treated to remove the organic modification group. The heat treatment temperature is preferably in the range from the desorption temperature of the organic modifying group to the glass transition temperature of the substrate. When the heat treatment temperature is higher than the glass transition temperature of the substrate, the substrate is deformed. The upper limit of the heat treatment temperature is preferably a glass transition temperature of the substrate −100 ° C. or lower. Specifically, when the heat treatment temperature is higher than 150 ° C., the organic group can be sufficiently decomposed to obtain a hydrophilic silica airgel layer. The heat treatment temperature is preferably 300 ° C. or higher, more preferably 400 ° C. or higher.

  The heat treatment time is preferably in the range of 10 minutes to 4 hours. By such heat treatment, the organic modification group of the organic modified silica airgel porous layer is sufficiently removed. By removing the organic group, the silica airgel layer becomes hydrophilic, and water easily enters the voids. Further, since the bonds between the particles constituting the silica airgel become stronger during the heat treatment, the scratch resistance is also improved. Therefore, antifogging properties and scratch resistance can be imparted to the antireflection film by forming the hydrophilic silica airgel porous layer.

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

Example 1
An antireflection film was formed on the surface of the BK7 glass plate by the following steps (1) and (2). The design wavelength λd was 550 nm.
(1) Formation of dense layer Using a device with an electron beam evaporation source, the physical film thickness is 94 nm (optical) on the surface of a flat plate made of BK7 glass (refractive index at wavelength 550 nm: 1.518) by vapor deposition. A magnesium fluoride layer (refractive index: 1.38) having a film thickness of 130 nm was formed.

(2) Formation of porous layer
(i) Preparation of organic modified silica-containing sol After mixing 5.21 g of tetraethoxysilane and 4.38 g of ethanol, 0.4 g of hydrochloric acid (0.01 N) was added and stirred for 90 minutes. 44.3 g of ethanol and 0.5 g of an aqueous ammonia solution (0.02 N) were added and stirred for 46 hours, and then the mixture was heated to 60 ° C. and aged for 46 hours to produce a wet gel. After decanting the solvent, ethanol was quickly added and shaken, and the decantation replaced the wet gel solvent with ethanol. Further, methyl isobutyl ketone (MIBK) was added, shaken, and decanted to replace ethanol with MIBK. A MIBK solution of trimethylchlorosilane (concentration: 5% by volume) was added to gel-like silica and stirred for 20 hours to organically modify the terminal of silicon oxide. The obtained organically modified silica gel was washed with isopropyl alcohol (IPA). IPA was added to organically modified silica gel to a concentration of 10% by mass, and then sol was formed by ultrasonic irradiation (20 kHz, 500 W). The ultrasonic irradiation time was 40 minutes.

(ii) Dip coating On the magnesium fluoride dense layer obtained in the above step (1), the organic modified silica-containing sol obtained in the above step (2) is dip coated so that the physical film thickness is 145 nm. After air drying at room temperature, heat treatment was performed at 150 ° C. for 1 hour to form an organically modified silica airgel porous layer.

(iii) Hydrophilization treatment The glass flat plate on which the organically modified silica airgel porous layer was formed was heat treated at 450 ° C. for 1 hour to form a hydrophilic silica airgel porous layer. The obtained silica airgel porous layer had a refractive index of 1.20 and a physical film thickness of 115 nm (optical film thickness: 138 nm).

Table 1 shows the layer structure and characteristics of the obtained antireflection film.

Example 2
A multilayer antireflection film was formed on the surface of the LAK14 glass plate by the following steps (1) and (2). The design wavelength λd was 550 nm.
(1) Dense layer formation Using a device with an electron beam evaporation source, the physical film thickness is 90 nm (optical) on the surface of a flat plate (refractive index at wavelength 550 nm: 1.697) made of LAK14 glass by vapor deposition. A silicon oxide layer (refractive index: 1.46) having a film thickness of 131 nm was formed.

(2) Formation of porous layer
(i) Preparation of organic-modified silica-containing sol An organic-modified silica-containing sol was prepared in the same manner as in Example 1, except that the organic modification treatment with trimethylchlorosilane in MIBK solution was 40 hours and the ultrasonic irradiation time was 20 minutes. .

(ii) Dip coating On the silicon oxide layer obtained in the above step (1), the organic modified silica-containing sol obtained in the above step (2) is dip coated so as to have a physical film thickness of 145 nm. After air drying at 150 ° C. for 1 hour, an organically modified silica airgel porous layer was formed.

(iii) Hydrophilization treatment The glass flat plate on which the organically modified silica airgel porous layer was formed was heat treated at 450 ° C. for 1 hour to form a hydrophilic silica airgel porous layer. The obtained silica airgel porous layer had a refractive index of 1.15 and a physical film thickness of 115 nm (optical film thickness: 132 nm).

Table 2 shows the layer structure and characteristics of the obtained antireflection film.

Comparative Example 1
In the same manner as in step (1) of Example 1, an antireflection film consisting only of a dense layer was formed on the surface of the BK7 glass flat plate by vapor deposition. Table 3 shows the layer structure and properties of the obtained dense antireflection film.

Comparative Example 2
The process of Example 1 except that an SF5 glass substrate (refractive index at a wavelength of 550 nm: 1.68) was used as the substrate, and silicon oxide and titanium oxide were alternately laminated by vapor deposition so as to have the configuration shown in Table 4. ) To form an antireflection film consisting only of a dense layer. Table 4 shows the layer structure and characteristics of the resulting dense antireflection film.

Comparative Example 3
In the same manner as in step (1) of Example 1, an antireflection film consisting only of a dense layer was formed on the surface of the BK7 glass flat plate by vapor deposition. Table 5 shows the layer structure and characteristics of the obtained dense antireflection film.

  With respect to the antireflection films of Examples 1 and 2 and Comparative Examples 1 to 3, the spectral reflectance of light beams having incident angles of 0 ° and 60 ° in the wavelength region of 350 to 800 nm was measured with a spectrophotometer (type: U4000, Measured using Hitachi, Ltd. The results are shown in FIGS. In Examples 1 and 2, the spectral reflectance for a light beam having an incident angle of 0 ° was 2% or less, and the spectral reflectance for a light beam having an incident angle of 60 ° was 5% or less. On the other hand, in Comparative Examples 1 to 3, since the dense multilayer antireflection film was formed, the spectral reflectance with respect to a light beam having an incident angle of 0 ° or 60 ° was remarkably inferior.

  Luminous reflectance in the wavelength range of 500 to 600 nm (Y value according to CIE XYZ color system standard) was determined from the obtained spectral reflectance. The results are shown in Table 6.

  The antireflection films of Examples 1 and 2 were rubbed 5 times with a non-woven fabric (product name: Bemcot Lint Free, manufactured by Asahi Kasei Co., Ltd.) wetted with water, and the appearance of the surface was observed. Further, pure water was dropped on each antireflection film, and the contact angle was measured. The results are shown in Table 6.

  As can be seen from Table 6, in Examples 1 and 2, the luminous reflectance for light rays with incident angles of 0 ° and 60 ° was both 2% or less. On the other hand, in the multilayer antireflection film consisting only of the dense materials of Comparative Examples 1 to 3, the spectral reflectance with respect to a light beam having an incident angle of 60 ° was 4% or more. The antireflection films of Examples 1 and 2 were not scratched even after being rubbed with a lint-free wiper wetted with water 5 times, and were excellent in scratch resistance. Further, the antireflection films of Examples 1 and 2 had a contact angle with respect to pure water of 15 ° or less, and were excellent in hydrophilicity.

It is sectional drawing which shows an example of the imaging type | system | group optical element which has an antireflection film of this invention. It is a graph which shows the relationship between the optical film thickness and refractive index of the antireflection film of this invention. 6 is a graph showing the spectral reflectance of the multilayer antireflection film of Example 1. 6 is a graph showing the spectral reflectance of the multilayer antireflection film of Example 2. 5 is a graph showing the spectral reflectance of a dense multilayer antireflection film of Comparative Example 1. 5 is a graph showing the spectral reflectance of a dense multilayer antireflection film of Comparative Example 2. 6 is a graph showing the spectral reflectance of a dense multilayer antireflection film of Comparative Example 3.

Explanation of symbols

1 ... Optical base material
11 ... Surface 2 ... Anti-reflective coating
21 ... Dense layer
22 ... Silica airgel porous layer

Claims (11)

  An antireflection film comprising a dense layer and a silica airgel porous layer formed in order on the surface of a substrate, and having a refractive index that decreases in order from the substrate to the silica airgel porous layer.   2. The antireflection film according to claim 1, wherein the dense layer is an inorganic layer, an inorganic fine particle-binder composite layer, or a resin layer.   3. The antireflection film according to claim 2, wherein the inorganic layer is formed by a vapor deposition method.   The antireflection film according to claim 3, wherein the inorganic vapor deposition layer is made of magnesium fluoride or silicon oxide.   The antireflection film according to claim 1, wherein the silica airgel porous layer is formed by heat-treating an organically modified silica airgel layer.   6. The antireflection film according to claim 1, wherein the silica airgel porous layer has a refractive index of 1.05 to 1.35.   The antireflection film according to any one of claims 1 to 6, wherein the silica airgel porous layer has a porosity of 30 to 90%.   The antireflection film according to claim 1, wherein a contact angle of the silica airgel porous layer with respect to pure water is 15 ° or less.   9. The antireflection film according to claim 1, wherein the optical thicknesses of the dense layer and the silica airgel porous layer are in the range of λd / 5 to λd / 3 with respect to the design wavelength λd, respectively. An antireflection film characterized by.   10. The antireflection film according to claim 9, wherein a luminous reflectance for a light ray having an incident angle of 0 to 60 ° in the wavelength range of the design wavelength λd ± 100 nm is 2% or less. .   An imaging system optical element comprising the antireflection film according to claim 1.

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