JP6903994B2 - Optical element and its manufacturing method - Google Patents

Description

The present invention relates to an optical element provided with an antireflection film having an antifogging property on the surface and a method for manufacturing the same.

Interchangeable lenses such as single focus lenses and zoom lenses used in imaging devices such as photographic and broadcast cameras have multiple lenses that are reflected at the interface with air even if there is only one lens in the lens barrel. The reflection is further amplified in the sheet. Therefore, when the amount of reflected light on each lens surface is large, not only the amount of transmitted light is lost, but also flare and ghost due to multiple reflections in or between lenses are likely to occur, and the contrast is low. Further, with digitalization, the image pickup portion of a camera or the like is replaced with an image sensor from a film, and the light reflected on the image sensor surface is also a factor of flare and ghost.

Therefore, an antireflection film is applied to the surface of an optical element such as an interchangeable lens or an image sensor. As the antireflection film, dielectric films having different refractive indexes are combined, and the optical film thickness of each dielectric film is set to 1 / 2λ or 1 / 4λ with respect to the center wavelength λ, and a multilayer film utilizing the interference effect. Anti-reflection treatment is applied depending on the configuration. In the antireflection film having such a multilayer structure, magnesium fluoride (MgF ₂ ) having a refractive index of 1.38 is generally applied to the outermost layer in order to improve the antireflection performance. In recent years, a method has been developed in which a silica airgel having a refractive index as low as 1.30 or less is _{used as a substitute for MgF 2} and heat-treated to apply an antireflection film.

However, in the conventional antireflection film, since the surface of the outermost magnesium fluoride layer and the silica airgel layer is smooth, there is a problem that the surface area is small and the wettability of water is not improved.

Japanese Patent Application Laid-Open No. 2006-221144 (Patent Document 1) states that a silica airgel layer having antireflection performance is fired at a temperature equal to or higher than the decomposition temperature of an organic group and lower than the glass transition temperature of a substrate to which the silica airgel layer is applied. It is disclosed that it will be processed. However, the problem that the surface shape of the outermost surface is smooth and the surface area is small and the wettability (anti-fog effect) is not improved has not been solved.

Republished Patent WO 2006/030848 (Patent Document 2) discloses that a porous film having a low refractive index is applied to the outermost layer of the antireflection film. The porous membrane used in Patent Document 2 is similar to the silica airgel layer disclosed in Patent Document 1, and is _{realized by depositing spherical nanoparticles (here, MgF 2} nanoparticles) having a uniform particle size. ing. That is, spherical nanoparticles having a uniform particle size are deposited to form a porous film, and the outermost surface of the film is a smooth surface with small irregularities. This also applies to the silica airgel used in Patent Document 1, and the problem that the surface area of the outermost layer is small and the wettability of water is not improved has not been solved.

Japanese Unexamined Patent Publication No. 2006-221144 Republished Patent WO 2006/030848 Gazette

Therefore, an object of the present invention is to provide an optical element provided with an antireflection film having an antifogging property and a method for manufacturing the same.

As a result of diligent research in view of the above objectives, the present inventor has a dense layer made of an inorganic material on a base material and a nanoporous film or a nanoparticle film on the substrate, and has an arithmetic average roughness (Ra) of 2.5 to. It is 50 nm, has a maximum height (Ry) of 15 to 200 nm, has a fine uneven structure with a water contact angle of 10 ° or less, is composed of SiO ₂ , and has a plurality of elongated anti-fog layers having a low refractive index. By accumulating nanoparticles having a shape and forming a low refractive index antifogging layer in which the surface of the nanoparticles is hydrophilic, an optical element having an antireflection film having antifogging properties can be obtained. I found that and came up with the present invention.

That is, the optical element of the present invention is a nanoporous film or nanoparticle film having a base material, a dense layer made of an inorganic material formed on the base material, and a fine concavo-convex structure formed on the dense layer. An optical element having an antireflection film having a low refractive index antifogging layer composed of, the low refractive index antifogging layer made of SiO ₂ , and the low refractive index antifogging layer having a plurality of elongated shapes. The nanoparticles are deposited, the surface of the nanoparticles is hydrophilic, the arithmetic average roughness (Ra) of the microconcavo-convex structure is 2.5-50 nm, and the maximum height (Ry) is 15-200 nm. It is characterized in that the contact angle of water of the antireflection film is 10 ° or less.

The average major axis of the nanoparticles is 30 to 200 nm, the average and short diameter is a 10 to 50 nm, the average major axis / average minor diameter is preferably from 1 to 20.

The porosity of the low refractive index antifogging layer is preferably 20 to 35%, and the refractive index is preferably 1.29 to 1.35. The thickness of the low refractive index antifogging layer is preferably 80 to 170 nm in terms of optical film thickness (nd).

The dense layers are MgF ₂ , SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , ZnO, Ta ₂ O ₅ , Nb ₂ O ₅ , HfO ₂ , CeO ₂ , SnO ₂ , In ₂ O ₃ , Y ₂ It is preferably a single layer or a multilayer consisting of at least one selected from the group consisting of _{O 3} , Pr ₆ O ₁₁ and Sb ₂ O _3.

Whether the substrate is made of glass, molten quartz glass, synthetic quartz glass, silicon or chalcogenide inorganic material, cycloolefin polymer, cycloolefin copolymer, polymethylmethacrylate resin, polycarbonate resin, polypropylene, polyethylene, ultraviolet curable resin or It is preferably made of an organic material of a thermosetting resin, or a combination of these inorganic materials and an organic material.

The shape of the base material is not particularly limited, but is preferably a flat plate shape, a lens shape, a prism shape, or a diffraction element shape. The haze value of the optical element is preferably 0.3% or less.

In the method of the present invention for producing such an optical element, the dense layer is formed on the base material by a physical film forming method, the low refractive index antifogging layer is formed by a wet method, and then at room temperature to 200 ° C. or lower. It is characterized by drying.

It is preferable that the physical abdominal method is a vacuum vapor deposition method or a sputtering method, and the wet method is a sol-gel method.

According to the present invention, a dense layer made of an inorganic material is formed on a base material, and a nanoporous film or a nanoparticle film is formed on the dense layer, and the arithmetic average roughness (Ra) is 2.5 to 50 nm and the maximum height (Ry) is high. ) is a 15 to 200 nm, the contact angle of water forms a low refractive index anti-fog layer having a 10 ° or less of the fine unevenness, the low refractive index anti-fogging layer is made of SiO _2, a low refractive Ritsubokumoriso becomes deposited nanoparticles having a plurality of elongated shape, the surface of the nanoparticles hydrophilic der Runode while suppressing damage to the substrate, improve the degree of freedom in designing the anti-reflection film It is possible to obtain an optical element provided with an antireflection film having antifogging properties while improving the hydrophilic effect.

It is the schematic which shows the optical element provided with the antireflection film which has the antifogging property by one Example of this invention. It is a graph which shows the spectral characteristic of the reflectance of the antireflection film of Example 1. It is a graph which shows the spectral characteristic of the reflectance of the antireflection film of Example 2. It is a graph which shows the spectral characteristic of the reflectance of the antireflection film of Example 3. It is a graph which shows the spectral characteristic of the reflectance of the antireflection film of Example 4. It is a perspective view which shows the 3D image which measured the surface of the antireflection film of Example 3 using an atomic force microscope (AFM). It is a front view which shows the 3D image which measured the surface of the antireflection film of Example 3 using an atomic force microscope (AFM). It is a graph which shows the shape of the AA cross section of the analysis part in the three-dimensional image which measured the surface of the antireflection film of Example 3 using an atomic force microscope (AFM). It is a perspective view which shows the 3D image which measured the surface of the antireflection film of the comparative example 1 using an atomic force microscope (AFM). It is a front view which shows the 3D image which measured the surface of the antireflection film of the comparative example 1 using an atomic force microscope (AFM). It is a graph which shows the shape of the BB cross section of the analysis part in the three-dimensional image which measured the surface of the antireflection film of the comparative example 1 using an atomic force microscope (AFM).

The optical element of the present invention has a low refractive index protection consisting of a base material, a dense layer made of an inorganic material formed on the base material, and a nanoporous film or a nanoparticle film having a fine concavo-convex structure formed on the base material. It is composed of an antireflection film having a cloudy layer, the low refractive index antifogging layer is _{composed of SiO 2} , and the low refractive index antifogging layer is composed of nanoparticles having a plurality of elongated shapes deposited on the surface of the nanoparticles. It is hydrophilic, the arithmetic average roughness (Ra) of the fine concavo-convex structure is 2.5 to 50 nm, the maximum height (Ry) is 15 to 200 nm, and the contact angle of water of the antireflection film is 10 ° or less. It is characterized by being. Such an antireflection film has both excellent antireflection performance and antifogging property.

FIG. 1 shows a schematic view of an optical element provided with an antireflection film having antifogging properties according to an embodiment of the present invention. In FIG. 1, a dense layer 2 is formed on a base material 1, and a low refractive index antifogging layer 3 is formed on the dense layer 2.

The material of the base material 1 is not particularly limited, but is preferably composed of an inorganic material, an organic material, or a combination thereof. Examples of the inorganic material include glass, fused silica glass, synthetic quartz glass, silicon, chalcogenide and the like. Examples of the organic material include cycloolefin polymer (COP), cycloolefin copolymer (COC), polymethylmethacrylate resin (PMMA), polycarbonate resin (PC), polypropylene (PP), polyethylene (PE) and the like. Examples of the ultraviolet curable resin include radical polymerization type acrylate resin, urethane acrylate, polyester acrylate, polybutadiene acrylate, epoxy acrylate, silicon acrylate, amino resin acrylate, en-thiol resin, cationic polymerization type vinyl ether resin, and alicyclic epoxy resin. , Glycidyl ether epoxy resin, urethane vinyl ether, polyester vinyl ether and the like, and examples of the thermosetting resin include epoxy resin, phenol resin, unsaturated polyester resin, urea resin, melamine resin, silicon resin and polyurethane. The base material 1 may have a film made of an organic material formed on an inorganic material such as glass. The refractive index of the base material 1 is not particularly limited, but is preferably 1.45 to 1.95. The shape of the base material is not particularly limited, and examples thereof include a flat plate shape, a lens shape, a prism shape, and a diffraction element shape.

The material and refractive index of the dense layer 2 can be appropriately selected according to the types of the base material 1 and the low refractive index antifogging layer 3, but MgF ₂ , SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , and so on. From at least one selected from the group consisting of ZnO, Ta ₂ O ₅ , Nb ₂ O ₅ , HfO ₂ , CeO ₂ , SnO ₂ , In ₂ O ₃ , Y ₂ O ₃ , Pr ₆ O ₁₁ and Sb ₂ O _3. Is preferable. The dense layer 2 may be a single layer or a multi-layer. By providing a dense layer made of an inorganic material between the base material 1 and the low refractive index antifogging layer 3 in this way, the adhesion of the low refractive index antifogging layer 3 can be improved. The effect of the dense layer is particularly exhibited when the base material 1 is made of an organic material such as an organic panel. In order to further improve the adhesion, the layer in contact with the low refractive index antifogging layer 3 of the dense layer 2 is a mixed film of _{TiO 2} , SiO ₂ or Ta ₂ O ₅ , Y ₂ O ₃ and Pr ₆ O _11. Is more preferable. The method for producing the dense layer 2 is not particularly limited, but chemical vapor deposition such as a physical vapor deposition method (PVD) such as a vacuum vapor deposition method or a sputtering method, a chemical vapor deposition method (CVD), a sol-gel method, or a spin-on glass (SOG). The method (CLD) can be used.

In the optical element of this embodiment, the low refractive index antifogging layer 3 is formed by depositing a large number of nanoparticles 4. The nanoparticles 4 have an elongated shape. Since nanoparticles 4 having a large number of elongated shapes are deposited, voids are formed between adjacent particles as shown in FIG. 1, and the elongated shape of the nanoparticles 4 is formed on the surface of the low refractive index antifogging layer 3. A fine concavo-convex structure is formed. As a result, the low refractive index antifogging layer 3 can obtain a low refractive index.

The surface of each nanoparticles 4 is hydrophilic. As a result, a hydrophilic fine concavo-convex structure is imparted to the surface of the low refractive index antifogging layer 3. By providing the surface of the low refractive index antifogging layer 3 with a fine concavo-convex structure having hydrophilicity in this way, the surface area of the low refractive index antifogging layer 3 is increased, and the hydrophilic effect (wetting property) is improved. Is obtained. The contact angle of water in the low refractive index antifogging layer 3 is preferably 10 ° or less. If the contact angle is larger than 10 °, the anti-fog effect will be weakened. The contact angle of the low refractive index antifogging layer 3 having antifogging properties is more preferably 5 ° or less.

（ただしX_L〜X_Rは測定面の任意の座標であるX座標の範囲であり、F（X）はX座標上の測定点（X）における高さであり、Z₀は測定面内の平均高さである。）により表される。 The arithmetic mean roughness Ra of the fine uneven structure of the low refractive index antifogging layer 3 is 2.5 to 50 nm. Arithmetic mean roughness Ra is the center line average roughness obtained based on JIS B 0601 using an atomic force microscope (AFM), and is based on the following equation (1):

(However, X _{L to} X _R is the range of the X coordinate, which is an arbitrary coordinate of the measurement surface, F (X) is the height at the measurement point (X) on the X coordinate, and Z ₀ is in the measurement surface. It is represented by the average height.).

If the arithmetic mean roughness Ra of the low refractive index antifogging layer 3 is less than 2.5 nm, the high antifogging property of the low refractive index antifogging layer 3 cannot be obtained, and if the arithmetic mean roughness Ra exceeds 50 nm, the light Scattering occurs, making it unsuitable for optical elements. Further, since the surface of the low refractive index antifogging layer 3 is provided with a fine concavo-convex structure having an arithmetic average roughness Ra of 2.5 to 50 nm, the refractive index gradually changes from the incident medium to the optical element, and the refractive index becomes the incident medium. The reflected light at the interface of the optical element is reduced, and the antireflection effect can be obtained in a wide wavelength range. The arithmetic mean roughness Ra is preferably 2.5 to 30 nm, more preferably 2.5 to 15 nm.

The maximum height Ry of the fine uneven structure on the surface of the low refractive index antifogging layer 3 is 15 to 200 nm. Maximum height Ry is synonymous with maximum height defined by JIS B 0601. If the maximum height Ry of the low refractive index antifogging layer 3 is less than 15 nm, the high antifogging property of the low refractive index antifogging layer 3 cannot be obtained, and if the maximum height Ry exceeds 200 nm, light scattering occurs. However, it becomes unsuitable for optical elements. Further, when the maximum height Ry of the fine uneven structure on the surface of the low refractive index antifogging layer 3 is 15 to 200 nm, the refractive index is gradually changed from the incident medium to the optical element, so that the antireflection effect is obtained in a wide wavelength range. Is obtained. The maximum height Ry is preferably 20 to 150 nm, more preferably 25 to 100 nm.

The average period of the fine uneven structure on the surface of the low refractive index antifogging layer 3 (the average value of the distances between adjacent peaks) is preferably shorter than the wavelength of light used. As a result, the fine concavo-convex structure functions as a sub-wavelength structure, and an excellent antireflection effect can be obtained in a wide wavelength range.

The porosity of the low refractive index antifogging layer 3 is preferably 20 to 35%. When the porosity of the low refractive index antifogging layer 3 is in this range, it has sufficient strength and a low refractive index can be obtained. The refractive index of the low refractive index antifogging layer 3 is preferably 1.29 to 1.35.

Examples of the shape of the nanoparticles 4 having an elongated shape include an ellipsoidal shape, a tubular shape, a rugby ball shape, and a shape in which spherical particles are connected. By depositing nanoparticles 4 having an elongated shape rather than a spherical shape in this way, as shown in FIG. 1, the nanoparticles 4 are not regularly arranged, the gaps between the particles are increased, and the surface is uneven. Becomes larger. Therefore, the low refractive index antifogging layer 3 on which the nanoparticles 4 are deposited has a large porosity, and a fine uneven structure having a large arithmetic mean roughness is formed on the surface. The average major axis of the nanoparticles 4 having an elongated shape is preferably 30 to 200 nm, and the average minor axis is preferably 10 to 50 nm. The aspect ratio of the nanoparticles 4 defined by the average major axis / average minor axis is preferably 1 to 20, more preferably 2 to 15.

The nanoparticles 4 are particularly _{preferably silica nanoparticles containing SiO 2} as a main component, and the silica nanoparticles are preferably hydrophilic due to the effect of silanol groups (Si-OH) present on the surface of the material. As a result, the obtained low refractive index antifogging layer 3 can have both low refractive index and antifogging property while having sufficient strength.

The thickness of the low refractive index antifogging layer 3 can be appropriately set depending on the material of the base material 1 and the dense layer 2, but the optical film thickness (nd) is preferably 80 to 170 nm. Since the low refractive index antifogging layer 3 has a fine uneven structure having a large arithmetic mean roughness on its surface and is porous, it can have excellent antifogging and antireflection performance even with a thickness of 100 nm or less. ..

The low refractive index antifogging layer 3 can be formed by applying a coating liquid containing a layer material by a wet method and then drying the obtained coating film at room temperature to 200 ° C. or lower. As the coating liquid containing the layer material, for example, Excel Pure manufactured by Chuo Motor Co., Ltd. can be used.

Examples of the method for applying the coating liquid to the substrate include a spin coating method, a spray coating method, a dip coating method, a flow coating method, a bar coating method, a reverse coating method, a flexographic method, a printing method, and a method in which these are used in combination. .. Of these, the spin coating method and the spray coating method are preferable because they can easily make the film uniform and control the film thickness. The physical film thickness of the obtained coating film can be controlled, for example, by adjusting the base rotation speed in the spin coating method, adjusting the concentration of the layer material, and the like. The rotation speed of the base material in the spin coating method is preferably about 500 to 10000 rpm.

As the wet method, a sol-gel method may be used. As the sol-gel method, an existing method can be applied, but a sol containing a layer material (for example, silica sol) is applied to the dense layer 2, and the obtained gel film is dried at room temperature to 200 ° C. or lower. Is preferable.

The antireflection film used in the present invention is a low nanoporous film or nanoparticle film having a fine concavo-convex structure with an arithmetic mean roughness (Ra) of 2.5 to 50 nm and a maximum height (Ry) of 15 to 200 nm. Since the outermost layer is provided with a refractive index antifogging layer, it has high antifogging properties and antireflection performance in a wider wavelength range. The optical element of the present invention provided with such an antireflection film can be suitably used for light rays having a wide wavelength range of 300 nm to 2000 nm.

The haze value of the optical element of the present invention is preferably 0.3% or less. If the haze value exceeds 0.3%, there is a problem that the transmittance is lowered and the contrast of the captured image is lowered.

The optical element of the present invention preferably has a high antireflection effect in the visible to infrared regions applied to optical components such as lenses, prisms, and diffraction elements. Such optical elements are suitably used for interchangeable lenses and imaging devices such as television cameras, video cameras, digital cameras, security cameras, and in-vehicle cameras, and projection optical systems and projection devices such as projectors.

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.

In the evaluation methods of the samples prepared in the examples and comparative examples shown below, a lens reflectance measuring machine (model number: USPM-RU, manufactured by Olympus Co., Ltd.) was used to measure the optical film thickness and the refractive index. An atomic force microscope (AFM) manufactured by Seiko Instruments Co., Ltd. is used to evaluate the average roughness (Ra) and maximum height (Ry), and the haze value (so-called cloud value) is measured by Co., Ltd. A haze meter HM-150 manufactured by Murakami Color Technology Laboratory was used, and a contact angle measuring device manufactured by Kyowa Kagaku Co., Ltd. was used to measure the pure water contact angle.

(Example 1)
[1-1 Formation of dense layer]
A 6-layer dense layer 2 shown in Table 1 was formed on a base material 1 made of a BK7 glass flat plate (diameter 30 mm, refractive index: 1.518) by a vacuum vapor deposition method using an apparatus having an electron beam type vapor deposition source.

[1-2 Formation of anti-fog layer with low refractive index]
As the low refractive index antifogging layer 3, Excel Pure [DB-01] manufactured by Chuo Motor Co., Ltd. was spin-coated on the dense layer 2 and then dried with warm air at 80 ° C. for 30 minutes to form a silica nanoparticle film. Formed. The low refractive index antifogging layer 3 had a refractive index of 1.305 and an optical film thickness of 136 nm. Table 2 shows the arithmetic mean roughness (Ra), maximum height (Ry), pure water contact angle, and haze value of the optical element of the obtained low refractive index antifogging layer 3.

(Example 2)
[2-1 Formation of dense layer]
A UV curable resin (radical polymerization type acrylate resin) having a refractive index of 1.532 was applied to a BK7 glass flat plate (diameter 30 mm, refractive index: 1.518) to a thickness of 2 mm and cured by UV irradiation to prepare a base material 1. .. Next, the 7-layer dense layer 2 shown in Table 1 was formed on the base material 1 in the same manner as in the example.

[2-2 Formation of anti-fog layer with low refractive index]
As the low refractive index antifogging layer 3, Excel Pure [DB-01] manufactured by Chuo Motor Co., Ltd. is spin-coated on the dense layer 2 and then naturally dried at 25 ° C. for 30 minutes to form a silica nanoparticle film. did. The low refractive index antifogging layer 3 had a refractive index of 1.310 and an optical film thickness of 138 nm. Table 2 shows the arithmetic mean roughness (Ra), maximum height (Ry), pure water contact angle, and haze value of the optical element of the obtained low refractive index antifogging layer 3.

(Example 3)
[3-1 Formation of dense layer]
The nine dense layers 2 shown in Table 1 were formed on the base material 1 made of a J-LAF010 glass flat plate (diameter 30 mm, refractive index: 1.746) in the same manner as in the examples.

[3-2 Formation of anti-fog layer with low refractive index]
As the low refractive index antifogging layer 3, Excel Pure [DB-01] manufactured by Chuo Motor Co., Ltd. was spin-coated on the dense layer 2 and then dried with warm air at 80 ° C. for 30 minutes to form a silica nanoparticle film. Formed. The low refractive index antifogging layer 3 had a refractive index of 1.298 and an optical film thickness of 122 nm. Table 2 shows the arithmetic mean roughness (Ra), maximum height (Ry), pure water contact angle, and haze value of the optical element of the obtained low refractive index antifogging layer 3.

(Example 4)
[4-1 Formation of dense layer]
The eight dense layers 2 shown in Table 1 were formed on the base material 1 made of a LaFK55 glass flat plate (diameter 30 mm, refractive index: 1.697) in the same manner as in the examples.

[4-2 Formation of anti-fog layer with low refractive index]
As the low refractive index antifogging layer 3, Excel Pure [DB-01] manufactured by Chuo Motor Co., Ltd. was spin-coated on the dense layer 2 and then dried with warm air at 80 ° C. for 30 minutes to form a silica nanoparticle film. Formed. The low refractive index antifogging layer 3 had a refractive index of 1.295 and an optical film thickness of 139 nm. Table 2 shows the arithmetic mean roughness (Ra), maximum height (Ry), pure water contact angle, and haze value of the optical element of the obtained low refractive index antifogging layer 3.

(Comparative Example 1)
[(5-1) Preparation of organically modified silica wet gel (surface modification by TMCS)]
(5-1-1) Preparation of silica wet gel 5.90 g of methyl silicate 51 (average tetramer of tetramethoxysilane) manufactured by Fuso Chemical Industries, Ltd. and 50.55 g of methanol (special grade) manufactured by Wako Pure Chemical Industries, Ltd. To the mixture was added 3.20 g of 0.10 N ammonia water prepared from 28% ammonia (special grade) manufactured by Wako Pure Chemical Industries, Ltd., and the mixture was stirred for 10 minutes. Then, it was allowed to stand at room temperature for 3 days to promote the hydrolysis polycondensation reaction and aged.

(5-1-2) Solvent replacement of silica wet gel The silica wet gel prepared in the step (5-1-1) was cut into a size of about 2 cm square, placed in a crystal dish, and manufactured by Wako Pure Chemical Industries, Ltd. Ethanol (special grade) was added and stirred slowly at 300 rpm for 1 day using a magnetic stirrer to replace the solvent in the silica wet gel with ethanol. By decantation after the substitution, a silica wet gel substituted with an ethanol solvent was obtained. Ethanol used for solvent substitution was added at a ratio of 100 ml to 20 g of silica wet gel.

Subsequently, 4-methyl-2-pentanone (special grade) manufactured by Wako Pure Chemical Industries, Ltd. was added to the silica wet gel solvent-substituted with ethanol, and the mixture was slowly stirred at 300 rpm for 1 day using a magnetic stirrer. The solvent in the silica wet gel was replaced with 4-methyl-2-pentanone. Decantation after substitution gave a silica wet gel solvent-substituted with 4-methyl-2-pentanone. 4-Methyl-2-pentanone used for solvent substitution was added at a ratio of 100 ml to 20 g of silica wet gel.

(5-1-3) Surface modification of silica wet gel 60 g of wet gel prepared in step (5-1-2) was placed on a crystal dish, and trimethylchlorosilane manufactured by Tokyo Kasei Kogyo Co., Ltd. and Wako Pure Chemical Industries, Ltd. A mixed liquid consisting of 4-methyl-2-pentanone (special grade) was added, and the silicon oxide terminals in the silica wet gel were organically modified by stirring slowly at 300 rpm for 1 day using a magnetic stirrer. By decantation after organic modification, an organically modified silica wet gel was obtained. To prepare a mixed solution of trimethylchlorosilane and 4-methyl-2-pentanone, the mixture was mixed at a volume ratio of 5 ml: 95 ml. For organic modification of the silica wet gel, a mixture of trimethylchlorosilane and 4-methyl-2-pentanone was added at a ratio of 100 ml to 20 g of the silica wet gel.

(5-1-4) Cleaning of Organically Modified Silica Wet Gel Take 60 g of the wet gel prepared in the step (5-1-3) on a crystal dish and take 4-methyl-2-pentanone manufactured by Wako Pure Chemical Industries, Ltd. (5-1-4). (Special grade) was added, and the organically modified silica wet gel was washed by stirring slowly at 300 rpm for 1 day using a magnetic stirrer. Then, by decantation, an organically modified wet gel from which the organic modifier and by-products were removed was obtained. The 4-methyl-2-pentanone used for washing was added at a ratio of 100 ml to 20 g of the silica wet gel.

[(5-2) Preparation of ultrasonic dispersion of organically modified silica wet gel]
Take the organically modified silica wet gel prepared in step (5-1) in a 100 ml disposable beaker, add 4-methyl-2-pentanone (special grade) manufactured by Wako Pure Chemical Industries, Ltd., and use a magnetic stirrer at 700 rpm. The ultrasonic waves were dispersed for 2 hours with an ultrasonic disperser (rated output 600 W, oscillation frequency 19.5 KHz ± 1 KHz) manufactured by Nippon Seiki Seisakusho Co., Ltd. The concentration of the dispersion solution was adjusted so that the solid content concentration was 3.5% by weight. The solid content concentration of the dispersion solution was prepared from the solid content calculated from the mass before and after drying when the organically modified silica wet gel was placed in a blower constant temperature incubator (inert oven) at 120 ° C. for 2 hours and dried.

[(5-3) Application of sol to substrate and hardening of coating film]
The coating liquid for producing a porous silica film prepared in step (5-2) was applied to the surface of a parallel flat plate (diameter 30 mm, thickness 1.5 mm) made of BK7 glass having a refractive index of 1.518 by a spin coating method. Table 2 shows the arithmetic mean roughness (Ra), maximum height (Ry), pure water contact angle, and haze value of the optical element of the obtained silica porous film.

(Comparative Example 2)
After applying the coating liquid for forming a porous silica film prepared in Comparative Example 1 to the surface of a parallel flat plate (diameter 30 mm, thickness 1.5 mm) made of 1.518 BK7 glass in the same manner as in Comparative Example 1 by the spin coating method. , The coated substrate was heated at 400 ° C. Table 2 shows the arithmetic mean roughness (Ra), maximum height (Ry), pure water contact angle, and haze value of the optical element of the obtained silica porous film.

As is clear from Tables 1 and 2, it was found that the arithmetic mean roughness (Ra) and the maximum height (Ry) of the antireflection coatings of Examples 1 to 4 were larger than those of Comparative Examples. Further, the haze value of the optical elements of Examples 1 to 4 was 0.1% of a level that can be used for optical applications, as in Comparative Examples 1 and 2. As a result, the contact angle of the pure water of the antireflection film of Examples 1 to 4 was significantly lower than that of Comparative Examples 1 and 2, and it was found that the antifogging effect was excellent.

[Scratch resistance evaluation method]
The antireflection film on the surface of the base material is rubbed 10 times with a non-woven fabric (trade name "Spic Lens Wiper", manufactured by Ozu Corporation) at a speed of 150 times / minute while applying a pressure of ^{1 kg / cm 2 to scratch the surface.} It was visually confirmed and evaluated according to the following criteria. The results are shown in Table 3.
<Criteria>
A part of the antireflection film was scratched, but it did not peel off ... ○
The anti-reflection film was scratched and partly peeled off or the reflected color changed ... △
All the anti-reflection film has peeled off ... ×

[Evaluation of adhesion]
After attaching the cellophane tape to the area of 1 cm × 1 cm of the antireflection film, the adhesion was evaluated by peeling the cellophane tape while pulling it in the direction of 45 degrees. The evaluation was performed according to the following criteria by visually observing the peeling of the surface. The results are shown in Table 3.
<Criteria>
The antireflection film did not peel off at all ... ○
Part of the antireflection film was peeled off ... △
All the anti-reflection film has peeled off ... ×

As is clear from Table 3, the antireflection films of Examples 1 to 4 were also excellent in the mechanical strength (scratch resistance and adhesion) of the film. On the other hand, in Comparative Example 1, since the outermost silica porous film had an ultra-low refractive index but low strength, both scratch resistance and adhesion were poor. In Comparative Example 2, since the strength of the silica porous film of the outermost layer was also small, both scratch resistance and adhesion were insufficient.

[Surface observation]
A three-dimensional image obtained by measuring the surface of the antireflection film of Example 3 using an atomic force microscope (AFM) manufactured by Seiko Instruments Co., Ltd. and cross-sectional shapes of analysis points are shown in FIGS. Figures 9 to 11 show a three-dimensional image of the surface of the antireflection film 1 measured using an atomic force microscope (AFM) manufactured by Seiko Instruments Co., Ltd., and the cross-sectional shape of the analysis site. As shown in FIGS. 6 and 7, the antireflection film of Example 3 has an uneven shape having an average period of about 100 to 300 nm, and as shown in FIG. 8, the arithmetic mean roughness (Ra) and the maximum height. All of (Ry) had a large value. On the other hand, as shown in FIGS. 9 to 11, the fine uneven structure of Comparative Example 1 had both small arithmetic mean roughness (Ra) and maximum height (Ry). As described above, the low refractive index antifogging layer of Example 3 has a large arithmetic average roughness (Ra) and maximum height (Ry), and has a small average period of the uneven shape, so that it has excellent antifogging properties and also has excellent antifogging properties. An anti-reflection effect was obtained in a wide wavelength range.

Claims (14)

A low refractive index antifogging layer composed of a base material, a dense layer made of an inorganic material formed on the base material, and a nanoporous film or a nanoparticle film having a fine concavo-convex structure formed on the dense layer. An optical element having an antireflection film
The low refractive index antifogging layer is made of SiO ₂ , and the low refractive index antifogging layer is formed by depositing nanoparticles having a plurality of elongated shapes, and the surface of the nanoparticles is hydrophilic.
The arithmetic mean roughness (Ra) of the fine uneven structure is 2.5 to 50 nm, the maximum height (Ry) is 15 to 200 nm, and the contact angle of water of the antireflection film is 10 ° or less. An optical element characterized by. The optical element according to claim 1 , wherein the nanoparticles have an average major axis of 30 to 200 nm, an average minor axis of 10 to 50 nm, and an average major axis / average minor axis of 1 to 20. .. The optical element according to claim 1 or 2 , wherein the average period of the fine concavo-convex structure is shorter than the wavelength of light used. The optical element according to any one of claims 1 to 3 , wherein the low refractive index antifogging layer has a porosity of 20 to 35%. The optical element according to any one of claims 1 to 4 , wherein the low refractive index antifogging layer has a refractive index of 1.29 to 1.35. The optical element according to any one of claims 1 to 5 , wherein the thickness of the low refractive index antifogging layer is 80 to 170 nm in terms of optical film thickness (nd). The dense layers are MgF ₂ , SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , ZnO, Ta ₂ O ₅ , Nb ₂ O ₅ , HfO ₂ , CeO ₂ , SnO ₂ , In ₂ O ₃ , Y ₂ The optical element according to any one of claims 1 to 6 , wherein the optical element is a single layer or a multilayer composed of at least one selected from the group consisting of O ₃ , Pr ₆ O ₁₁ and Sb ₂ O _3. The optical element according to any one of claims 1 to 7 , wherein the haze value is 0.3% or less. The optical element according to claim 8 , wherein the base material is made of an inorganic material such as glass, fused silica glass, synthetic quartz glass, silicon or chalcogenide. 8. The eighth aspect of claim 8, wherein the substrate is made of an organic material such as a cycloolefin polymer, a cycloolefin copolymer, a polymethylmethacrylate resin, a polycarbonate resin, polypropylene, polyethylene, an ultraviolet curable resin or a thermosetting resin. Optical element. The base material is glass, molten quartz glass, synthetic quartz glass, silicon or chalcogenide inorganic material, cycloolefin polymer, cycloolefin copolymer, polymethylmethacrylate resin, polycarbonate resin, polypropylene, polyethylene, ultraviolet curable resin or thermosetting. The optical element according to claim 8 , further comprising a combination of a curable resin with an organic material. The optical element according to any one of claims 1 to 11 , wherein the base material has a flat plate shape, a lens shape, a prism shape, or a diffraction element shape. In the method for manufacturing an optical element according to any one of claims 1 to 12, the dense layer is formed on the base material by a physical film forming method or a wet method, and the low refractive index antifogging layer is formed by a wet method. A method for manufacturing an optical element, which comprises drying at room temperature to 200 ° C. or lower. The method for manufacturing an optical element according to claim 13 , wherein the physical film forming method is a vacuum vapor deposition method or a sputtering method, and the wet method is a sol-gel method.

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