JP4497460B2 - Method for manufacturing antireflection film - Google Patents

Description

  The present invention relates to an antireflection film formed on a surface of a substrate, and particularly to an antireflection film suitable for a lens having a large numerical aperture (NA) used in an optical pickup device or a semiconductor device, and an optical element having the antireflection film. About.

  The surface of the objective lens of the optical pickup device or the semiconductor device is coated with an antireflection film to efficiently transmit incident light. For example, in a single-layer antireflection film, the optical path difference between the reflected light on the surface of the antireflection film and the reflected light at the boundary between the antireflection film and the lens is an odd multiple of half the wavelength, and these lights are It is designed to have a thickness that cancels out due to interference. In general, it is often designed to have a film thickness that maximizes the anti-reflection effect near the center of the lens (light incident angle is 0 °). The minimum value is shown in a region where light is perpendicular to the antireflection film. The objective lens is arranged so that light to be collected is incident perpendicularly to the center of the surface (light incident angle is 0 °). However, since the lens surface of the objective lens is a curved surface, only the extremely limited range around the optical axis satisfies the normal incidence condition. For this reason, the light incident angle is large in the lens peripheral portion, so that the lens is greatly deviated from the design condition of the single-layer antireflection film, and the reflectance of incident light is high.

  On the other hand, the antireflection film (multilayer antireflection film) composed of a plurality of layers 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 Japanese Patent Application No. 9-335909 (Patent Document 1), a conductive light absorbing film is formed on the substrate side, and a plurality of high refractive index transparent films and low refractive index transparent films are alternately arranged in this order. A layered anti-reflective coating is described. The preferred thicknesses of the high refractive index transparent film and the low refractive index transparent film are 15-30 nm (high refractive index layer), 15-30 nm (low refractive index layer), 10-314 nm (high Refractive index layer), 60 to 120 nm (low refractive index layer). The antireflection film having layers having different thicknesses causes interference between reflected light and incident light in a wide wavelength range. Therefore, when it is formed on the surface of the objective lens, an antireflection effect can be obtained even at a position away from the optical axis to some extent.

  However, since an objective lens such as an optical pickup device has a large numerical aperture and has a light incident angle of 60 ° or more in the lens peripheral portion, even if it is composed of layers having different thicknesses as in Patent Document 1. In the peripheral portion, an effective antireflection effect cannot be shown. Furthermore, when an antireflection film is formed on the curved surface of a lens, etc., the physical film thickness at the lens periphery tends to be smaller than at the lens center, and when the film thickness is designed based on the lens center, antireflection at the lens periphery is prevented. There is also a problem that the film thickness greatly deviates from the design film thickness. Since the antireflection characteristic greatly depends on the film thickness, if it deviates from the design film thickness, an effective antireflection effect cannot be shown. Therefore, in the lens peripheral portion, the light incident angle is large and the deviation from the designed film thickness is large, so that a sufficient antireflection effect cannot be obtained.

Japanese Patent Application No. 9-335909 (Japanese Patent Laid-Open No. 11-171596)

  Accordingly, an object of the present invention is to provide an antireflection film having excellent antireflection characteristics for light having a large incident angle and having a small film thickness dependence of the antireflection characteristics, and an optical element having such an antireflection film. Is to provide.

  As a result of diligent research in view of the above object, the present inventors have developed an antireflection film composed of a plurality of layers, each of which has a refractive index that decreases in order from the base material, and a plurality of layers having different porosity on the incident medium side. Those having the porous layer of the present invention have been found to have excellent antireflection properties, and have arrived at the present invention.

  That is, the antireflection film of the present invention is formed on the surface of a base material and is composed of a plurality of layers, and the refractive index of the base material and each layer decreases in order from the base material, and the layer and its adjacent The refractive index difference between the layer and the substrate and the layer in contact therewith is 0.02 to 0.2, the physical layer thickness of each layer is 15 to 200 nm, and at least two layers formed on the incident medium side of each layer are ( a) a porous layer, characterized in that (b) it has different porosity.

  The porous layer is preferably a silica airgel layer. The porosity of the silica airgel layer is preferably 30 to 90%. The silica airgel layer is preferably hydrophobized. Each layer is preferably formed by a wet method.

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

  The antireflection film of the present invention is an antireflection film formed on the surface of a base material and comprising a plurality of layers, and the refractive index of the base material and each layer gradually decreases from the base material in order. Specifically, the refractive index difference between adjacent layers and the refractive index difference between the base material and the layer in contact with the base material are 0.02 to 0.2, and the physical layer thickness of each layer is 15 to 200 nm. In addition, at least two layers on the surface side of each layer are porous layers and have different porosity. Such an antireflection film is in a state close to that in which the refractive index smoothly decreases from the base material to the incident medium, and hardly reflects light rays at the interface of each layer. Accordingly, the film thickness dependency of the reflectance is small, and the change in the reflectance is small even if the physical film thickness is increased or decreased. Moreover, it can have an excellent antireflection characteristic for light having a large light incident angle.

  The optical element of the present invention has the antireflection film of the present invention on the lens surface. For this reason, even a lens having a large numerical aperture has excellent antireflection characteristics in the peripheral portion, and is suitable for an objective lens such as an optical pickup.

[1] Optical element having antireflection film FIG. 1 shows an optical element having an antireflection film. This optical element includes a lens 1 and an antireflection film 2 formed on the surface 11 of the lens 1. The antireflection film 2 in the drawing is drawn thicker than the actual thickness. The antireflection film 2 shown in FIG. 1 has a six-layer structure, but the present invention is not limited to this, and includes those having 2 to 5 layers and 7 or more thin layers.

  A first layer 21 is formed on the surface 11 of the lens 1, and a second layer 22, a third layer 23, a fourth layer 24, a fifth layer 25, and a sixth layer 26 are formed thereon in this order. . The first layer 21, the second layer 22, and the third layer 23 are dense layers, and the fourth layer 24, the fifth layer 25, and the sixth layer 26 are porous layers. The sixth layer 26 is in contact with the incident medium a. The thickness of each layer is maximum at the center 110 of the lens 1 and gradually decreases toward the peripheral portion 12. In the present specification, the peripheral portion 12 of the lens 1 is a portion having a distance from the central axis of 2R / 5 to R / 2, where R is the effective diameter of the lens 1. The thickness of the antireflection film 2 that is the sum of the thicknesses of the respective layers also gradually decreases from the center 110 to the peripheral portion 12.

The physical film thickness of the antireflection film 2 depends on the substrate tilt angle θ. As shown in FIG. 3, the substrate inclination angle θ represents an angle formed by a surface Fo that contacts the center 110 of the lens 1 and a surface F that contacts the point t on the surface 11. The physical film thickness D (θ) of the antireflection film 2 at the substrate tilt angle θ is expressed by the following equation (1)
D (θ) = D ₀・ (cosθ) ^x ... (1)
(Where θ represents the substrate tilt angle, D ₀ represents the physical film thickness of the antireflection film 2 at the center of the lens, X represents a constant of 0 or more and 1 or less, and 0 ° <θ < 90 °. ). The physical film thickness D (θ) decreases as θ increases. X is a constant depending on the film formation conditions (film formation method, film formation material, film formation apparatus, etc.) of the antireflection film 2. When the light beam L is parallel light, the incident angle on the lens surface 11 is equal to the substrate tilt angle θ.

FIG. 4 shows an example of the relationship between the substrate tilt angle θ and the film thickness ratio D (θ) / D ₀ of the antireflection film 2. This antireflection film 2 was formed on the surface of a lens 1 having a radius of curvature of about 2 mm by vacuum evaporation (depressurization n degree 1 × 10 ⁻⁶ Torr, vacuum evaporation 4 minutes). Is. This graph is approximated to (cosθ _m ) ^0.7 .

  FIG. 2 schematically shows the relationship between the physical film thickness of the antireflection film 2 and the refractive index. The physical layer thickness d of each layer at the center 110 of the lens 1 is substantially equal. In the present specification, “physical layer thickness” indicates the physical thickness of each layer constituting the antireflection film 2. The physical layer thickness d of each layer is 15 to 200 nm. The refractive index is the largest in the lens 1, the smallest in the incident medium a, and decreases in order from the first layer 21 to the sixth layer 26. The refractive index differences r between the layers, between the first layer 21 and the lens 1, and between the sixth layer 26 and the incident medium a are substantially equal, and are 0.02 to 0.2, respectively. For this reason, the change of the refractive index with respect to the physical layer thickness is stepped and smooth enough to be approximated by a straight line. Since the change in the refractive index with respect to the physical layer thickness from the lens 1 to the incident medium a is smooth as described above, the refractive index gradually decreases from the lens 1 to the incident medium a when viewed macroscopically. In addition, reflection of incident light hardly occurs at the interface of each layer. Therefore, the antireflection film 2 can exhibit an excellent antireflection effect. Although depending on the number of constituent layers, the physical film thickness D of the antireflection film 2 at the center 110 is preferably about 100 to 1000 nm.

  If the physical layer thickness d is not in the range of 15 to 200 nm, or the refractive index difference r is not in the range of 0.02 to 0.2, the change in the refractive index with respect to the physical layer thickness d of each layer is not smooth. For this reason, the reflectance at the interface increases. For example, if the physical layer thickness d of the second layer 22 is less than 15 nm, the effect obtained by the second layer 22 is too small, so the refractive index suddenly changes from the refractive index of the first layer 21 to the third layer 23. It will be the same as you did. If the physical layer thickness d of the second layer 22 is more than 200 nm, interference by the second layer 22 occurs in the visible range, and the antireflection effect is impaired.

  Of the layers of the antireflection film 2, the dense layer may be a layer made of only an inorganic material such as a metal oxide, or a composite layer made of inorganic fine particles and a binder (hereinafter referred to as an inorganic fine particle-binder composite layer). Alternatively, a layer made of resin may be used. The material of each layer can be selected from those having a refractive index smaller than that of the lens 1 and larger than that of the incident medium a. However, the refractive index difference r between adjacent layers needs to be 0.02 to 0.2.

  For example, when the lens 1 is made of lanthanum crown glass (LaK glass) and the incident medium a is air, the refractive index of the lens 1 is 1.72, and the refractive index of the incident medium a is 1. Therefore, the material of each layer is 1.02. Selected from those having a refractive index of ˜1.7. Examples of inorganic materials having a refractive index of 1.02 to 1.7 include calcium fluoride, magnesium fluoride, aluminum fluoride, sodium fluoride, lithium fluoride, cerium fluoride, silicon oxide, aluminum oxide, cryolite, thiolite and these A mixture is mentioned.

  Examples of inorganic fine particle-binder composite layers include calcium fluoride, magnesium fluoride, aluminum fluoride, sodium fluoride, lithium fluoride, cerium fluoride, silicon oxide, aluminum oxide, zirconium oxide, cryolite, thiolite, titanium oxide, Examples thereof include those in which at least one inorganic fine particle selected from the group consisting of indium oxide, tin oxide, antimony oxide, cerium oxide, hafnium oxide and zinc oxide is dispersed in a binder. The refractive index of the inorganic fine particle-binder composite layer depends on the composition and content of the inorganic fine particles and the composition of the binder.

  Examples of the resin having a refractive index of 1.02 to 1.7 include a fluororesin, an epoxy resin, an acrylic resin, a silicone resin, and a urethane resin. Commonly known fluororesins include polytetrafluoroethylene resin, perfluoroethylenepropylene resin, perfluoroalkoxy resin, polyvinylidene fluoride resin, ethylene-tetrafluoroethylene resin, and polychlorotrifluoroethylene resin. Although these resins can be used, since many of them have crystallinity, it is not so preferable for forming the transparent antireflection film 2. On the other hand, a layer made of an amorphous fluororesin 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.

  As the porous layer, a silica airgel layer is particularly preferable. The porosity of the silica airgel layer is preferably 90% or less. When the porosity exceeds 90%, the mechanical strength is too small. The refractive index of the silica airgel layer depends on the porosity. A silica airgel layer having a larger porosity has a smaller refractive index. For example, a silica airgel layer with a porosity of 35% has a refractive index of about 1.3, and a silica airgel layer with a porosity of 78% has a refractive index of about 1.1. The refractive index of the silica airgel layer having a porosity of 90% or less is approximately 1.05 to 1.35. The silica airgel layer is preferably hydrophobized. The silica airgel layer subjected to the hydrophobization treatment has excellent water resistance and durability.

  As an example of the layer configuration of the antireflection film 2, the first layer 21 is made of aluminum oxide (refractive index 1.64), the second layer 22 is made of silicon oxide (refractive index 1.46), and the third layer 23 is magnesium fluoride ( The refractive index is 1.38), and the fourth to sixth layers 24, 25, and 26 are made of porous silicon oxide. As another example of the layer structure, the first layer 21 is composed of zirconium oxide and a binder, the second layer 22 is composed of colloidal silica and a binder, the third layer 23 is composed of a fluorine-containing ultraviolet curable resin, the fourth layer to Examples include those in which the sixth layers 24, 25, and 26 are made of silica airgel.

The antireflection characteristic of the antireflection film 2 hardly depends on the physical film thickness. In the present specification, “antireflection property” indicates reflectance and transmittance, and “having excellent antireflection property” indicates that it has a small reflectance and a large light transmittance. If the film thickness dependence of the antireflection characteristic is small, the antireflection characteristic excellent in the peripheral portion 12 can be exhibited. Also when forming the anti-reflection film 2, there is no need to precisely control the physical thickness D _0. For example, when the physical film thickness D ₀ of the antireflection film 2 is shifted by ± 50%, the variation in reflectance at the center 110 of the lens 1 is less than 2%, and the variation in light transmittance is also less than 2%.

  The antireflection characteristic of the antireflection film 2 hardly depends on the light incident angle. The antireflection film 2 exhibits excellent antireflection characteristics even in a portion where the substrate tilt angle θ is large. The increase in reflectance at the position of the substrate tilt angle θ65 ° is less than 6% with respect to the reflectivity at the center 110 where the substrate tilt angle θ0 °.

  The antireflection film 2 exhibits excellent antireflection characteristics for light in a wide wavelength range. Specifically, even when light having a wavelength of the design wavelength to ± 200 nm is irradiated, the reflectance falls within the range of the reflectance of the design wavelength + about 2%.

  Although the lens peripheral portion 12 has a large substrate tilt angle θ and the antireflection film 2 formed on the peripheral portion 12 has a physical film thickness smaller than the center 110, the antireflection characteristics of the antireflection film 2 are physical as described above. Since it has a small dependency on the film thickness and the light incident angle, the peripheral portion 12 also has excellent antireflection characteristics. Accordingly, the optical element having the antireflection film 2 is relatively less likely to reflect light rays even at the peripheral portion 12 of the lens 1. Since such an optical element transmits a large amount of light as the entire element, it can be said that the entire element has excellent antireflection characteristics.

[2] Manufacturing method of antireflection film A layer made of only an inorganic substance can be formed by physical vapor deposition such as vapor deposition, sputtering, ion plating, chemical vapor deposition such as thermal CVD, plasma CVD, and photo-CVD. it can. The inorganic fine particle-binder composite layer can be formed by a wet method such as a dipping method, a spin 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. When each layer is formed by a wet method, the antireflection film 2 can be manufactured at low cost.

(1) Formation of dense layer A method for producing an inorganic fine particle-binder composite layer and a fluororesin layer will be described taking a wet method as an example.

(a) Inorganic fine particle-binder composite layer
(a-1) Preparation of inorganic fine particle-containing slurry A slurry containing inorganic fine particles and a binder component is prepared. In this specification, the binder component refers to a monomer and / or oligomer that becomes a binder by polymerization.

  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 antireflection film is too poor in transparency. Those having an average particle size of less than 5 nm are difficult to produce. Examples of preferred inorganic fine particles include those made of the above-mentioned inorganic materials. More preferable inorganic fine particles include those made of colloidal silica. The colloidal silica is preferably surface-treated. Colloidal silica can be surface treated with a silane coupling material or the like.

  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 layer to be formed is too brittle. If the mass ratio is less than 0.05, it is difficult to achieve a desired refractive index.

  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, the anti-reflective film 2 containing a binder can also be provided on the non-heat resistant substrate 1. Examples of the ultraviolet curable and / or thermosetting compound include a radical polymerizable compound, a cationic polymerizable compound, and an anion polymerizable compound. These compounds may be used in combination. The binder component may be a monomer or an oligomer.

  As the radical polymerizable compound, an acrylate ester is preferable. Specific examples of the radical polymerizable compound include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, hydroxybutyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, carboxypolycaprolactone acrylate, acrylic acid, methacrylic acid and Monofunctional (meth) acrylates such as acrylamide, diacrylates such as pentaerythritol triacrylate, ethylene glycol diacrylate and pentaerythritol diacrylate monostearate, tri (meth) acrylates such as trimethylolpropane triacrylate, pentaerythritol triacrylate, Multifunctional (meth) acrylates such as pentaerythritol tetraacrylate derivatives and dipentaerythritol pentaacrylate Rate, 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 a radically polymerizable and / or cationically polymerizable binder component, a radical polymerization initiator and / or a cationic polymerization initiator are 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 benzyl, benzophenone and derivatives thereof, 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.

  You may mix | blend 2 or more types of inorganic fine particles and / or a binder with a 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 thin film to be formed. 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 20 to 10,000 parts by mass per 100 parts by mass in total of the inorganic fine particles and the binder component.

(a-2) Thinning A layer of inorganic fine particle-containing slurry is formed on a substrate by dipping, spinning, spraying, roll coating, screen printing, or the like. For example, in the case of the dipping method, the thickness of the layer to be formed can be controlled by the slurry concentration, the dipping time, the pulling time, 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 3000 mJ / cm ² using a UV irradiation apparatus, the binder component is polymerized to form a thin 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) Fluororesin layer
(b-1) Preparation of fluorine-containing composition solution To form a fluororesin layer, a solution of a composition containing (a) a fluorine-containing olefin polymer and a crosslinkable compound was applied to a substrate or the like. It may be crosslinked later, or may be polymerized after applying a solution of a composition containing (b) a fluorine-containing olefin compound and a monomer copolymerized therewith. 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 / or fluorine-containing olefin compound is preferably 5 to 80% by mass.

(b-2) Thinning Since the method for forming the fluororesin layer is almost the same as the above (a-2) 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. and held for about 30 to 60 minutes. In the case of the ultraviolet curing type, UV irradiation is performed at about 50 to 3000 mJ / cm ² using a UV irradiation apparatus. Although depending on the thickness of the layer, the irradiation time is usually about 0.1 to 60 seconds.

(c) Multi-layering After forming the first layer, a step of forming a layer comprising an inorganic fine particle-containing slurry or a fluorine-containing composition solution thereon, and a step of polymerizing by irradiating the obtained thin layer with ultraviolet rays By repeating, a dense layer can be laminated. If the refractive index condition is satisfied, a fluororesin layer may be laminated on the inorganic fine particle-binder composite layer, or an inorganic fine particle-binder composite layer may be laminated on the fluororesin layer.

(2) Formation of porous layer A method for producing a porous layer will be described by taking as an example the case of laminating a hydrophobized silica airgel layer.

(a) Raw material for silica airgel layer
(a-1) Alkoxysilane and silsesquioxane Silica sol and silica gel are produced by hydrolysis polymerization of alkoxysilane and / or silsesquioxane. The alkoxysilane may be a monomer or an oligomer. The alkoxysilane monomer preferably has three 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 alkoxysilane monomers include methyltrimethoxysilane, methyltriethoxysilane, phenyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, tetrapropoxysilane, dimethoxydiethoxysilane, dimethyldimethoxysilane and 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 polymerization of monomers.

Even when silsesquioxane is used as a starting material, an antireflection film having excellent uniformity can be obtained. Silsesquioxane is a general term for network-like polysiloxanes represented by the general formula RSiO _1.5 (where R represents an organic functional group). Examples of R include an alkyl group (which may be linear or branched, and having 1 to 6 carbon atoms), a phenyl group, and an alkoxy group (for example, a methoxy group, an ethoxy group, etc.). Silsesquioxane is known to have various structures such as a ladder type and a cage type, and some have vacancies in the molecule. It also has excellent weather resistance, transparency and hardness, and is suitable as a starting material for silica airgel.

(a-2) Solvent A preferred solvent is a mixture 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 volume ratio of the solvent is preferably 1-2. When the water / alcohol ratio is more than 2, it takes too much time for the solvent to volatilize. When the water / alcohol ratio is less than 1, 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. Specific examples include hydrochloric acid, ammonia, amine, NaOH, and KOH. Preferred amines include alcohol amines and alkyl amines (for example, methylamine, dimethylamine, trimethylamine, n-butylamine, n-propylamine).

(b) Preparation of silica gel Dissolve alkoxysilane or the like in a solvent composed of water and alcohol. The solvent / alkoxysilane molar ratio is preferably 5-40. When the molar ratio is less than 5, it is difficult to dissolve alkoxysilane or the like. If the molar ratio is more than 40, it takes too much time to dry the silica gel. The molar ratio of catalyst / alkoxysilane and the like is preferably 1 × 10 ^{−3 to} 3 × 10 ⁻² , and more preferably 3 × 10 ⁻³ to 1 × 10 ⁻² . If the molar ratio is less than 1 × 10 ⁻³ , hydrolysis of alkoxysilane or the like does not occur sufficiently. Even if the molar ratio ^exceeds 3 × 10 ⁻² , the catalytic effect does not increase.

  When an aqueous solution containing a catalyst and a solvent such as alkoxysilane is stirred (or stirred and aged), a wet gel is formed. An aqueous solution containing an alkoxysilane or the like and a catalyst and a solvent is stirred at 15 to 60 ° C. for 60 to 120 minutes, and after adding an alcohol and a basic catalyst, the mixture is stirred at 15 to 30 ° C. for 20 to 60 hours, Aging for 20 to 60 hours is preferred. For aging, it is preferable to stir slowly at a temperature of 40 to 60 ° C. or to stand still. The wet gel is a sparsely formed secondary particle of silica gel having a diameter of about 20 to 50 nm that forms a three-dimensional network. The wet gel can be dehydrated (solvent substitution) by washing with alcohol and / or hexane.

(c) Hydrophobic treatment The surface is hydrophobized by immersing silica gel in the hydrophobization solution. Preferred hydrophobizing agents 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, an alkyl group, or an aryl group, and the alkyl group is substituted or unsubstituted. And an aryl group is substituted or unsubstituted and has a carbon number of 5 to 18.) and a mixture thereof.

  Specific examples of hydrophobizing agents include triethylchlorosilane, trimethylchlorosilane, diethyldichlorosilane, dimethyldichlorosilane, acetoxytrimethylsilane, acetoxysilane, diacetoxydimethylsilane, methyltriacetoxysilane, phenyltriacetoxysilane, diphenyldiacetoxysilane, trimethyl Ethoxysilane, trimethylmethoxysilane, 2-trimethylsiloxypent-2-en-4-one, n- (trimethylsilyl) acetamide, 2- (trimethylsilyl) acetic acid, n- (trimethylsilyl) imidazole, trimethylsilylpropiolate, nonamethyltri Silazane, hexamethyldisilazane, hexamethyldisiloxane, trimethylsilanol, triethylsilanol, triphenylsilanol, t-butyldimethylsila Noles and diphenylsilane diols.

  The solvent of the hydrophobization solution is hydrocarbons such as hexane, cyclohexane, pentane, and heptane, alcohols such as methanol, ethanol, n-propyl alcohol, and 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 hydrophobizing agent, the hydrophobizing treatment is preferably performed at 10 to 40 ° C. If it is less than 10 ° C., the hydrophobizing agent will not sufficiently react with silica. If it exceeds 40 ° C., the hydrophobizing agent reacts with substances other than silica and easily produces by-products. 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 hydrophobizing 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 silanol group modification rate is preferably about 10 to 30%.

  After completion of the hydrophobization reaction, the hydrophobized silica gel is washed. It is preferable to use hexane, heptane, pentane, cyclohexane or the like for washing.

(d) Preparation of Hydrophobized Silica-Containing Sol To prepare the hydrophobized silica-containing sol, a dispersion medium is added to the hydrophobized silica gel, and then mechanical stirring or ultrasonic irradiation is performed. For ultrasonic irradiation, 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, and the output of the ultrasonic irradiation apparatus is preferably 300 to 900 W.

  The ultrasonic irradiation time is preferably 5 to 120 minutes. The longer the ultrasonic irradiation time, the finer the hydrophobized silica gel and the less agglomeration occurs. For this reason, the hydrophobized silica is almost monodispersed in the sol. When the ultrasonic irradiation time is less than 5 minutes, the fine particles are not sufficiently dissociated. Even when the ultrasonic irradiation time is longer than 120 minutes, the dissociation state of the hydrophobized silica is hardly changed.

  The ratio of the hydrophobized silica gel to the dispersion medium is preferably 0.1 to 20% by mass. If the ratio of the hydrophobized silica gel to the dispersion medium is not in the range of 0.1 to 20% by mass, it is difficult to form a uniform thin layer with the hydrophobized silica-containing sol.

(e) Thinning A hydrophobized silica-containing sol is applied onto a dense layer or a porous layer. Examples of the coating method include a spray coating method, a spin coating method, a dip method, and a flow coating method. Of these, the dip method exhibits relatively good coatability both when the sol concentration is large and small.

  When a sol containing hydrophobized silica in a state close to monodispersion is used, a silica airgel layer having a small porosity can be formed. When a sol containing hydrophobized silica in an aggregated state is used, a silica airgel layer having a large porosity can be formed. That is, it can be said that the ultrasonic irradiation time affects the porosity of the silica airgel layer. When the sol irradiated with ultrasonic waves for 5 to 120 minutes is dip-coated, a silica airgel layer having a porosity of 25 to 90% can be obtained.

  After applying the silica gel-containing sol and drying the coating layer, baking is performed at 80 to 300 ° C. If the firing temperature is less than 80 ° C., gelation does not proceed sufficiently. If it exceeds 300 ° C., silica becomes too hydrophilic due to the elimination of hydrophobic groups. The sol becomes a gel by drying and baking, and a hydrophobized silica airgel layer is formed.

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

Example 1
A multilayer antireflection film was formed on the surface of the lens having the shape shown in FIG. 1 as shown in the following (1) and (2), and the light transmittance and water resistance were examined.

(1) Formation of dense layer
(i) 1st layer Titanium oxide fine particles (average particle size 20 nm) 1 g, pentaerythritol triacrylate 15 g, polymerization initiator (2-methyl-1- [4- (methylthio) phenyl] -2-monforinoprop Non-1) 0.5 g, methanol 300 mL, and propylene glycol monoethyl ether 75 mL were mixed to obtain a titanium oxide-containing slurry. After dip-coating a titanium oxide-containing slurry on the surface of a lens made of LaFK55 (refractive index at a wavelength of 550 nm: 1.697) having the shape shown in FIG. 1, a UV irradiation device (Fusion Systems Inc.) The first layer was formed by irradiation with ultraviolet rays at 1500 mJ / cm ² . The refractive index of the first layer was 1.64, and the physical layer thickness was 91 nm.

(ii) Second layer Silicone hard coat solution (trade name UVHC 8558, manufactured by GE Toshiba Silicone Co., Ltd.) 30 mL and i-propyl alcohol 270 mL were mixed, and the resulting solution was dip-coated on the first layer. A second layer was formed in the same manner as (i) above except that this was irradiated with ultraviolet rays. The refractive index of the second layer was 1.47, and the physical layer thickness was 102 nm.

(iii) Third layer 30 g of a copolymer of perfluoroethylene and vinylidene fluoride, polymerization initiator (2-methyl-1- [4- (methylthio) phenyl] -2-monfolinopropanone-1) 1.5 g and 1000 mL of methyl i-butyl ketone were mixed, and the resulting fluorine-containing copolymer solution was dip-coated on the second layer, and the third layer was treated in the same manner as in (i) above except that this was irradiated with ultraviolet rays. Formed. The refractive index of the third layer was 1.39, and the physical layer thickness was 108 nm.

(2) Formation of porous layer
(i) Preparation of Hydrophobized Silica Gel After mixing 5.21 g of tetraethoxysilane and 4.38 g of ethanol, 0.4 g of hydrogen chloride (0.01 N) was added and stirred for 60 minutes. 44.35 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 temperature of the mixture was aged at 46 ° C. for 46 hours. Since a wet gel was formed in the mixture, it was washed with ethanol and hexane. The silica gel after solvent exchange was placed in a hexane solution of triethylchlorosilane (concentration: 5% by volume), stirred for 30 hours to organically modify the silica gel, and the resulting hydrophobized silica was washed with hexane.

(ii) Hydrophobized silica-containing sol Hexane was added to hydrophobized silica gel, and the resulting mixture was divided into three parts. Each gel was then dispersed by sonication (20 Hz, 500 W). The ultrasonic irradiation time was 5 minutes, 10 minutes, and 100 minutes, respectively. For convenience, the ultrasonic irradiation time of 5 minutes is referred to as liquid A, the liquid for 10 minutes is liquid B, and the liquid for 100 minutes is liquid C.

(iii) Dip coating The third layer obtained in the above (1) (iii) was dip coated with the solution C, and then air-dried at room temperature for 5 minutes. Next, solution B was dip coated and air dried at room temperature for 5 minutes, then solution A was dip coated and air dried at room temperature for 5 minutes. When this was baked at 100 ° C. for 5 minutes, a silica airgel layer was formed.

注１ 「層No.」は、レンズ側から順にNo.１、No.２、・・・・No.６とする。
注２ 「−」は、緻密層を示す。 Table 1 shows the structure of the antireflection film.

Note 1 “Layer No.” shall be No. 1, No. 2,.
Note 2 “-” indicates a dense layer.

注１ 「層No.」は、レンズ側から順にNo.１、No.２、・・・・No.６とする。 Table 2 shows the ultrasonic irradiation time and refractive index of each silica airgel layer.

Note 1 “Layer No.” shall be No. 1, No. 2,.

  It was found that a silica airgel layer having a small refractive index is formed as the ultrasonic irradiation time is shorter.

(3) Measurement of light transmittance and reflectance The lens with a multilayer antireflection film was irradiated with laser light having a wavelength of 405 nm, and the light transmittance was measured to be 98.7%. Further, the spectral reflectance at the lens center 110 was measured. The results are shown in FIG.

(4) Water resistance test
A lens with a multilayer antireflection film was placed in a constant temperature and humidity chamber set at 60 ° C. and 90 RH%. After maintaining in a thermo-hygrostat for 48 hours, the lens with the multilayer antireflection film was taken out and irradiated with laser light having a wavelength of 405 nm, and the light transmittance was measured to be 98.6%.

It is sectional drawing which shows an example of the anti-reflective film of this invention. It is a graph which shows the relationship between the physical film thickness and refractive index of the antireflection film of this invention. It is an expanded sectional view which shows the A section of FIG. 5 is a graph showing a relationship between a substrate tilt angle θ and a film thickness ratio D (θ) / D ₀ . It is a graph which shows the relationship between the wavelength irradiated to the lens with an antireflection film, and spectral reflectance.

Explanation of symbols

1 ... Lens
11 ... surface
110 ・ ・ ・ Center
12 ... Peripheral part 2 ... Antireflection film
21 ... First layer
22 ... Second layer
23 ... Third layer
24 ... Fourth layer
25 ... Fifth layer
26 ・ ・ ・ 6th layer

Claims (3)

It consists of a plurality of layers formed on the curved surface of the lens, and the refractive index of the lens and each layer decreases in order from the lens, and the refractive index difference between the layer, the adjacent layer, the lens and the layer in contact with it Is 0.02 to 0.2, the physical layer thickness of each layer is 15 to 200 nm, and at least two layers formed on the incident medium side among the plurality of layers are porous layers each having a different porosity. A method of manufacturing a prevention film,
Wherein the porous layer, a dispersion comprising hydrophobic treatment of silica gel from 0.1 to 20 wt% with respect to the dispersion medium, each hydrophobic silica-containing sol was prepared by ultrasonic irradiation at different times, ultrasonic irradiation A method for producing an antireflection film, characterized by adjusting by forming dip coats in descending order of time , drying and firing. The method for producing an antireflection film according to claim 1, wherein all of the plurality of layers are formed by dip coating. 3. The method of manufacturing an antireflection film according to claim 1, wherein the ultrasonic irradiation is performed at a frequency of 10 to 30 kHz and an irradiation time of 5 to 120 minutes.

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