JP2009210739A - Antireflection film, forming method therefor, and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a uniform antireflection film having a low refractive index, and having excellent antireflectance in a wide wavelength range of a light beam, a forming method therefor, and an optical element having the antireflection film. <P>SOLUTION: This antireflection film has a meso-porous silica porous film aggregated with a meso-porous silica nanoparticle formed on a base material or a surface of a dense film formed thereon, and has 1.10 or less of refractive index. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an antireflection film formed on the surface of a substrate, and particularly has a low refractive index and excellent antireflection properties for light in a wide wavelength range, a method for forming the same, and an antireflection film thereof The present invention relates to an optical element having a film.

  An optical antireflection film is applied to an optical substrate such as an objective lens, an eyeglass lens, an optical reflector, or a low-pass filter of an optical pickup device or a semiconductor device for the purpose of improving light transmittance. Conventionally, the antireflection film has been formed by a physical method such as vacuum deposition, sputtering, or ion plating. However, these film-forming methods have the disadvantage that they are expensive because they require vacuum equipment.

The single-layer antireflection film is designed to have a refractive index smaller than that of the base material and larger than that of an incident medium such as air. It is said that a refractive index of 1.2 to 1.25 is ideal for an antireflection film of a lens made of glass having a refractive index of about 1.5. However, since there is no substance having such an ideal refractive index in an antireflection film that can be formed by a physical method, MgF ₂ having a refractive index of 1.38 is widely used as an antireflection film material.

  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. The antireflection film having a multilayer structure has a disadvantage that the cost is higher.

  Therefore, a method for forming an antireflection film by a wet method using a sol-gel method using dehydration polycondensation (dip coating method, roll coating method, spin coating method, flow coating method, spray coating method, etc.) is proposed. Has been.

  For example, Japanese Patent Laid-Open No. 2006-215542 (Patent Document 1) includes a dense layer and a silica airgel porous layer that are sequentially formed on the surface of a base material, and the refractive index decreases in order from the base material to the silica airgel porous layer. Proposed anti-reflection coating. This silica airgel porous layer comprises (i) a sol or gel silicon oxide reacted with an organic modifier to form an organic modified sol or an organic modified gel, and (ii) the organic modified sol or the organic modified gel as a sol The resulting organically modified silica gel layer is subjected to a springback phenomenon to form an organically modified silica airgel layer, and (iii) the obtained organically modified silica airgel layer is heat treated to form an organically modified silica airgel layer. It is formed by removing the modifying group.

  The silica airgel porous layer has a refractive index as small as about 1.20, and the antireflection film having it has excellent antireflection characteristics in a wide wavelength range. And since it can produce by the sol-gel method, it is excellent also in cost performance. However, an antireflection film having a lower refractive index is desired.

Therefore, “Chemical Industry”, Chemical Industry Co., Ltd., September 2005, Vol. 56, No. 9, pp. 688-693 (Non-patent Document 1) describes hydrochloric acid as a mesoporous silica nanoparticle integrated film having high light transmittance. Tetraethoxysilane, cationic surfactant (cetyltrimethylammonium chloride) and nonionic surfactant [HO (C ₂ H ₄ O) _106- (C ₃ H ₆ O) _70- (C ₂ H _{4 under} acidic conditions After aging the mixed solution of O) ₁₀₆ H], a solution of mesoporous silica nanoparticles coated with a nonionic surfactant and having a cationic surfactant in the pores was prepared by adding aqueous ammonia. Describes a mesoporous silica nanoparticle integrated film obtained by coating this solution on the surface of a substrate, drying and baking to remove the cationic surfactant and the nonionic surfactant. However, the mesoporous silica nanoparticle integrated film of Non-Patent Document 1 has a relatively low nonionic surfactant / tetraethoxysilane molar ratio of about 0.009 in the raw material and a high firing temperature of 600 ° C., so that it has a low refractive index of 1.1 or less. Have no rate.

  Therefore, Japanese Patent Laid-Open No. 2006-130889 (Patent Document 2) is formed on the substrate surface as a transparent inorganic porous film having a low refractive index and a high transmittance of 90% or more in the visible light region to the near infrared region, A mesoporous silica thin film having nanoscale micropores and a refractive index of 1.05 to 1.3 is proposed. This mesoporous silica thin film is prepared by applying a mixture of a surfactant, a silica raw material such as tetraethoxysilane, water, an organic solvent, and an acid or alkali to a base material to prepare an organic-inorganic composite film. Manufactured by drying and photooxidation to remove organic components.

  Japanese Patent No. 3668126 (Patent Document 3) discloses a ceramic precursor such as tetraethoxysilane, a catalyst, a method of forming a ceramic film having a low dielectric constant (due to high porosity and low refractive index). A method has been proposed in which a liquid comprising a surfactant and a solvent is prepared and applied to a substrate, and the solvent and the surfactant are removed to form a porous silica film.

  However, the mesoporous silica thin film of Patent Document 2 and the porous silica film of Patent Document 3 form a silicate network around the micelles of the surfactant when the coating film is dried, and proceed with hydrolysis and polycondensation. Since the network is formed by a process of forming a solid thin film, it takes a long time for hydrolysis and polycondensation after coating, and is non-uniform.

JP 2006-215542 A JP 2006-130889 Japanese Patent No. 3668126 Specification “Chemical Industry”, Chemical Industry, September 2005, Vol. 56, No. 9, pp.688-693

  Accordingly, an object of the present invention is to provide a uniform antireflection film having a low refractive index and excellent antireflection properties for light in a wide wavelength range, a method for forming the same, and an optical element having the antireflection film. is there.

  As a result of diligent research in view of the above object, the present inventors include an alkoxysilane, a cationic surfactant and a nonionic surfactant, and the molar ratio of the nonionic surfactant / alkoxysilane is a predetermined value or more. A mesoporous silica porous film comprising an aggregate of mesoporous silica nanoparticles obtained by hydrolyzing alkoxysilane in a solution of The present inventors have found that a uniform antireflection film having a low refractive index and excellent antireflection property for light in a wide wavelength range can be obtained when formed on the surface of a dense film formed in the present invention.

  That is, the first antireflection film of the present invention is a mesoporous silica porous film formed by aggregating mesoporous silica nanoparticles formed on the surface of a substrate, and has a refractive index of 1.10 or less.

  The second antireflection film of the present invention comprises a dense film and a mesoporous silica porous film formed in order on the surface of the substrate, and the mesoporous silica porous film is composed of an aggregate of mesoporous silica nanoparticles, and is 1.10 or less. It has the refractive index of.

  The mesoporous silica nanoparticles preferably have an average particle size of 200 nm or less. The mesoporous silica nanoparticles preferably have a hexagonal structure.

  The mesoporous silica porous membrane preferably has a structure in which a pore size distribution curve obtained by a nitrogen adsorption method has two peaks. The mesoporous silica porous membrane preferably has a peak due to intraparticle pore diameter in the range of 2 to 10 nm and a peak due to interparticle pore diameter in the range of 5 to 200 nm in the pore size distribution curve. . The pore volume ratio between the intraparticle pores and the interparticle pores is preferably 1/15 or more and less than 1/2. The mesoporous silica porous membrane preferably has a physical film thickness of 15 to 500 nm. The porosity of the mesoporous silica porous membrane is preferably 75 to 90%.

  In a preferred example of the second antireflection film, the dense film is a single layer, and the refractive index decreases in order from the base material to the mesoporous silica porous film. In another preferred example of the second antireflection film, the dense film is a multilayer and is formed by combining a plurality of films having different refractive indexes.

The first method of forming the antireflection film of the present invention is a method of forming an antireflection film composed of a mesoporous silica porous film in which mesoporous silica nanoparticles are aggregated on the surface of a substrate, comprising: (i) a solvent , Acidic catalyst, alkoxysilane, cationic surfactant and nonionic surfactant, wherein the molar ratio of the nonionic surfactant / the alkoxysilane is 2.5 × 10 ^{−2 to} 5 × 10 ⁻² The mixed solution is aged to hydrolyze and polycondensate the alkoxysilane, and (ii) by adding a basic catalyst to the obtained acidic sol containing silicate, the nonionic surfactant is coated, and Preparing a solution of mesoporous silica nanoparticles having a cationic surfactant in the pores; (iii) coating the resulting solution on the surface of the substrate; (iv) drying to remove the solvent; v) baked And removing the cationic surfactant and the nonionic surfactant was.

The second method of forming the antireflection film of the present invention is to form an antireflection film comprising a single-layer or multilayer dense film and a mesoporous silica porous film in which mesoporous silica nanoparticles are aggregated on the surface of a substrate. (1) After forming a single-layer or multilayer dense film made of an inorganic material on the surface of the substrate by vapor deposition, (2) (i) solvent, acidic catalyst, alkoxysilane, cationic An alkoxysilane is obtained by aging a mixed solution containing a surfactant and a nonionic surfactant, wherein the molar ratio of the nonionic surfactant / the alkoxysilane is 2.5 × 10 ^{−2 to} 5 × 10 ^−2. Hydrolysis and polycondensation, and (ii) by adding a basic catalyst to the obtained acidic sol containing silicate, the nonionic surfactant is coated, and the cationic surfactant is placed in the pores. Mesoporous silica Preparing a solution of nanoparticles, (iii) coating the resulting solution on the surface of the single-layer or multilayer dense membrane, (iv) drying to remove the solvent, and (v) firing to cation the cation The surfactant is removed, and the nonionic surfactant is removed.

It is preferable to use n-hexadecyltrimethylammonium chloride as the cationic surfactant. The nonionic surfactant is represented by the formula: RO (C ₂ H ₄ O) _a- (C ₃ H ₆ O) _b- (C ₂ H ₄ O) _c R (where a and c are each from 10 to 120) And b represents 30 to 80, and R represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms. The molar ratio of the cationic surfactant / the nonionic surfactant is preferably 4-8.

  It is preferable to use hydrochloric acid as the acidic catalyst. Ammonia is preferably used as the basic catalyst. Tetraethoxysilane is preferably used as the alkoxysilane. The firing is preferably performed at a temperature of 500 ° C. or lower.

  The optical element of the present invention has the antireflection film on the surface of an optical substrate.

  The antireflection film of the present invention has a low refractive index of 1.10 or less, is excellent in antireflection properties for light in a wide wavelength range, and is uniform. 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. Furthermore, the antireflection film of the present invention has a low production cost and a good yield.

[1] Optical element having antireflection film The antireflection film is formed on the surface of an optical substrate (simply referred to as a substrate). The first antireflection film is composed of a mesoporous silica porous film, and the second antireflection film is composed of a dense film and a mesoporous silica porous film formed in this order from the substrate side.

(1) Optical element having first antireflection film FIG. 1 shows a first antireflection film 2 formed on the surface of a substrate 1. The first antireflection film 2 is composed of a mesoporous silica porous film 20. 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, LASF01, LASF016, LAK14, and SF5, Pyrex (registered trademark) glass, quartz, blue plate glass, white plate glass, and the like. The refractive index of these base materials 1 is in the range of 1.45 to 1.85.

  The mesoporous silica porous film 20 is formed by aggregating mesoporous silica nanoparticles. FIG. 2 shows an example of mesoporous silica nanoparticles. The particle 200 includes a silica skeleton 200b having mesopores 200a, and has a porous structure in which the mesopores 200a are regularly arranged in a hexagonal shape. However, the mesoporous silica nanoparticles 200 are not limited to those having a hexagonal structure, and may have a cubic structure or a lamellar structure. Therefore, the mesoporous silica membrane 20 may be made of any one of these three types of particles or a mixture thereof, but is preferably made of hexagonal particles 200. Since the mesoporous silica nanoparticles 200 are uniformly formed with mesopores 200a having excellent regularity, the mesoporous silica porous film 20 has excellent transparency and crack resistance.

  The average particle size of the mesoporous silica nanoparticles 200 is preferably 200 nm or less, and more preferably 20 to 50 nm. If the average particle size exceeds 200 nm, it is difficult to adjust the film thickness, and the flexibility of thin film design is low. In addition, the anti-reflection characteristic and crack resistance of the mesoporous silica porous film 20 are also low. The average particle diameter of the mesoporous silica nanoparticles 200 is determined by a dynamic light scattering method. The refractive index of the mesoporous silica porous film 20 depends on the porosity, and the refractive index is smaller as the porosity is larger. The porosity of the mesoporous silica porous membrane 20 is preferably 75 to 90%. The refractive index of the mesoporous silica porous film 20 having a porosity in this range is 1.05 to 1.10. This porosity is more preferably 76.5 to 85%.

  As shown in FIG. 3, the mesoporous silica membrane 20 preferably has two peaks in the pore size distribution curve obtained by the nitrogen adsorption method. Specifically, an isothermal desorption curve of nitrogen is obtained for the mesoporous silica porous membrane 20, and this is analyzed by the BJH method. The pore size distribution curve is expressed with the horizontal axis as the pore diameter and the vertical axis as the log differential pore volume. It preferably has two peaks. The BJH method is described in, for example, “Method for obtaining mesopore distribution” (E. P. Barrett, L. G. Joyner, and P. P. Halenda, J. Am. Chem. Soc., 73, 373 (1951)). The log differential pore volume is a change amount of the differential pore volume dV with respect to the logarithmic difference value d (logD) of the pore diameter D, and is expressed by dV / d (logD). The first peak on the small pore diameter side indicates the diameter of the intraparticle pores, and the second peak on the large pore diameter side indicates the diameter of the interparticle pores. The mesoporous silica membrane 20 preferably has a distribution in which the intraparticle pore diameter is in the range of 2 to 10 nm and the interparticle pore diameter is in the range of 5 to 200 nm.

Preferably, the ratio of pore volume within a particle V ₁ and inter-particle pore volume V ₂ is less than 1/15 or more and 1/2. The mesoporous silica porous membrane 20 having this ratio in the above range has a small refractive index of 1.10 or less. This ratio is more preferably 1/10 or more and less than 1/2. The ratio V ₁ / V ₂ passes through the point E of the minimum value between the first and second peak (minimum value of the ordinate), the horizontal axis and a straight line parallel to the base line L _0, of each peak calculated coordinate along the horizontal axis (D _a to D _D) at the intersection A~D the L ₁ ~L ₄ and the baseline L ₀ (tangential line at the maximum inclination point) the maximum slope line, respectively the analysis data by the BJH method, D _a Calculate the total volume of pores with a diameter in the range of ~ D _B as V ₁ and calculate the total volume of pores with a diameter in the range of D _{C -D D} as V ₂ and the ratio of these It is obtained by calculating.

  The preferred physical film thickness of the mesoporous silica porous membrane 20 is 15 to 500 nm, more preferably 100 to 150 nm.

(2) Optical element having second antireflection film FIG. 4 shows an example of the second antireflection film. The second antireflection film 2 is composed of a dense film 21 and a mesoporous silica porous film 20 formed in this order from the base material 1 side. The mesoporous silica porous membrane 20 may be the same as described above.

The refractive index is preferably ascending in order from the substrate 1 to the dense film 21, the mesoporous silica porous film 20, and the incident medium A. The optical film thicknesses d ₁ and d ₂ of the dense film 21 and the mesoporous silica porous film 20 are preferably 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 two layers of the dense film 21 and the mesoporous silica porous film 20 provided so that the refractive index decreases in order from the base material 1, the optical film thickness of each layer 21 and 20 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 20 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 20 is increased. The optical film thicknesses d ₁ and d ₂ of the dense film 21 and the mesoporous silica porous film 20 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 film 21, between the dense film 21 and the mesoporous silica porous film 20, and between the mesoporous silica porous film 20 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 film 21 is a layer made of an inorganic material such as a metal oxide (referred to as “inorganic layer”). 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.

The dense film 21 of the second antireflection film 2 may be a multilayer. FIG. 6 shows an example of a second antireflection film having a multilayer dense film 21. The antireflection film 2 in this example is the same as the antireflection film 2 having a two-layer structure shown in FIG. 4 except that the dense film 21 has a five-layer structure including a first layer 210 to a fourth layer 214. However, the multilayer dense film 21 is not limited to a five-layer structure. The multilayer dense film 21 is preferably designed so that the reflected light generated at the interface between the layers and the light incident on each layer cancel each other out by interference. Specifically, the antireflection efficiency can be further increased by appropriately combining a plurality of films having different refractive indexes. When forming the multilayer dense film 21, for example, SiO ₂ , TiO ₂ , Al ₂ O ₃ , MgF ₂ , SiN, CeO ₂ , ZrO ₂ , HfO ₂ , Ta ₂ O _{5 and the} like can be used. As a specific example of the dense film 21 having a multilayer structure, there are a structure in which four to six layers of TiO ₂ and MgF ₂ are alternately coated by a vacuum deposition method and a structure in which four to six layers of TiO ₂ and SiO ₂ are alternately coated. Can be mentioned.

[2] Method for forming antireflection film
(1) Formation of porous mesoporous silica membrane A porous mesoporous silica membrane is obtained by aging a mixed solution of (i) a solvent, an acidic catalyst, an alkoxysilane, a cationic surfactant and a nonionic surfactant to form an alkoxysilane. Hydrolyzed and polycondensed, and (ii) by adding a basic catalyst to the obtained acidic sol containing silicate, which is coated with a nonionic surfactant and has a cationic surfactant in the pores Prepare a solution (sol) of mesoporous silica nanoparticles (hereinafter sometimes referred to as “surfactant-mesoporous silica nanoparticle composite”), (iii) coat the sol on the surface of the substrate or dense film, and (iv) dry And (v) calcination to remove the cationic surfactant and the nonionic surfactant.

(a) Raw material
(a-1) Alkoxysilane 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, a mesoporous silica porous 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 etc. are mentioned. As the alkoxysilane oligomer, polycondensates of the above-mentioned monomers are preferable. The alkoxysilane oligomer is obtained by hydrolysis and polycondensation of an alkoxysilane monomer. Specific examples of the alkoxysilane oligomer include silsesquioxane represented by the general formula RSiO _1.5 (where R represents an organic functional group).

(a-2) Surfactant
(i) Cationic surfactant Examples of the cationic surfactant include halogenated alkyltrimethylammonium, halogenated alkyltriethylammonium, halogenated dialkyldimethylammonium, halogenated alkylmethylammonium, and halogenated alkoxytrimethylammonium. Examples of the alkyl trimethyl ammonium halide include lauryl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride, cetyl trimethyl ammonium bromide, stearyl trimethyl ammonium chloride, benzyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride and the like. Examples of the halogenated alkyltrimethylammonium include n-hexadecyltrimethylammonium chloride. Examples of the dialkyldimethylammonium halide include distearyldimethylammonium chloride and stearyldimethylbenzylammonium chloride. Examples of the halogenated alkylmethylammonium include dodecylmethylammonium chloride, cetylmethylammonium chloride, stearylmethylammonium chloride, and benzylmethylammonium chloride. Examples of the halogenated alkoxytrimethylammonium include octadecyloxypropyltrimethylammonium chloride.

(ii) Nonionic surfactant Examples of the nonionic surfactant include block copolymers of ethylene oxide and propylene oxide, polyoxyethylene alkyl ethers, and the like. As a block copolymer of ethylene oxide and propylene oxide, for example, the formula: RO (C ₂ H ₄ O) _a- (C ₃ H ₆ O) _b- (C ₂ H ₄ O) _c R (where a and c are each 10 To 120, b represents 30 to 80, and R represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms). Examples of commercially available block copolymers include Pluronic (registered trademark, BASF). Examples of the polyoxyethylene alkyl ether include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether and the like.

(a-3) Catalyst
(i) Acidic catalyst Examples of the acidic catalyst include inorganic acids such as hydrochloric acid (hydrochloric acid), sulfuric acid and nitric acid, and organic acids such as formic acid and acetic acid.

(ii) Basic catalyst Examples of the basic catalyst include ammonia, amine, NaOH and KOH. Examples of preferred amines include alcohol amines and alkyl amines (eg, methylamine, dimethylamine, trimethylamine, n-butylamine, n-propylamine, etc.).

(a-4) Solvent Pure water is used as the solvent.

(b) Formation method
(b-1) Hydrolysis and polycondensation under acidic conditions After preparing an acidic solution by adding an acidic catalyst to pure water, and then adding a cationic surfactant and a nonionic surfactant to prepare a mixed solution Then, alkoxysilane is added, followed by hydrolysis and polycondensation. The pH of the acidic solution is preferably about 2. Since the isoelectric point of the silanol group of alkoxysilane is about pH 2, the silanol group stably exists in an acidic solution near pH 2. The solvent / alkoxysilane molar ratio is preferably 30-300. When this molar ratio is less than 30, the degree of polymerization of alkoxysilane becomes too high. On the other hand, if it exceeds 300, the degree of polymerization of alkoxysilane becomes too low.

The molar ratio of the cationic surfactant / solvent is preferably 1 × 10 ^{−4 to} 3 × 10 ⁻³ , whereby mesoporous silica nanoparticles having excellent mesopore regularity can be obtained. This molar ratio is more preferably 1.5 × 10 ⁻⁴ to 2 × 10 ⁻³ .

The molar ratio of cationic surfactant / alkoxysilane is preferably 1 × 10 ^{−1 to} 3 × 10 ⁻¹ . If this molar ratio is less than 1 × 10 ⁻¹ , the mesoporous silica nanoparticle mesostructure (hexagonal array structure) will be insufficiently formed. On the other hand, if it exceeds 3 × 10 ^−1, the particle size of the mesoporous silica nanoparticles becomes too large. This molar ratio is more preferably 1.5 × 10 ^{−1 to} 2.5 × 10 ⁻¹ .

The nonionic surfactant / alkoxysilane molar ratio is 2.5 × 10 ^{−2 to} 5 × 10 ⁻² . When this molar ratio is less than 2.5 × 10 ⁻² , the refractive index of the porous mesoporous silica film exceeds 1.10.

  The molar ratio of the cationic surfactant / nonionic surfactant is preferably 4 to 8, whereby mesoporous silica nanoparticles having excellent mesopore regularity can be obtained. This molar ratio is more preferably 5-7.

  The solution containing alkoxysilane is aged for 1 to 24 hours. Specifically, the solution is vigorously stirred at 20 to 25 ° C. Hydrolysis and polycondensation proceed by aging, and a sol containing silicate (an oligomer starting from alkoxysilane) is generated.

(b-2) Hydrolysis and polycondensation under basic conditions A basic catalyst is added to the obtained acidic sol to make the solution basic, and then the hydrolysis and polycondensation are performed to complete the reaction. Thereby, mesoporous silica nanoparticles having an average particle size of 200 nm or less are obtained. The pH of the solution is preferably adjusted to 9-12.

  By adding a basic catalyst, a silicate skeleton is formed around the cationic surfactant micelle, and a regular hexagonal array grows to form particles in which silica and the cationic surfactant are combined. The As the composite particles grow, the effective charge on the surface decreases, so that the nonionic surfactant is adsorbed on the surface. As a result, a solution (sol) of mesoporous silica nanoparticles coated with a nonionic surfactant and having a cationic surfactant in the pores (see FIG. 2 for particle shape) is obtained [for example, Imai Hiroaki, “Chemical Industry”, Chemical Industry, September 2005, Vol. 56, No. 9, pp.688-693]. In the formation process of the mesoporous silica nanoparticles, the growth of the composite particles is suppressed by the adsorption of the nonionic surfactant. Therefore, the mesoporous silica nanoparticles obtained by the preparation method using the above two types of surfactants The particles have an average particle size of 200 nm or less and excellent regularity of mesopores.

(b-3) Application The surface of the substrate is coated with a solution (sol) of a surfactant-mesoporous silica nanoparticle composite. Examples of the sol coating method include spin coating, dip coating, spray coating, flow coating, bar coating, reverse coating, flexo coating, gravure coating, printing, and a combination of these. The thickness of the obtained porous film can be controlled, for example, by adjusting the substrate rotation speed in the spin coating method, the pulling speed in the dipping method, or the concentration of the coating solution. The substrate rotation speed in the spin coating method is preferably about 500 to about 10,000 rpm, for example.

  A basic aqueous solution having the same pH as that of the sol may be added as a dispersion medium before coating so that the concentration and fluidity of the sol are in an appropriate range. The ratio of the surfactant-mesoporous silica nanoparticle composite in the coating solution is preferably 10 to 50% by mass. If it is out of this range, it is difficult to form a uniform thin film.

(b-4) Drying The solvent is evaporated from the applied sol. The drying conditions for the coating film are not particularly limited, and may be appropriately selected according to the heat resistance of the substrate. Natural drying may be performed, or drying may be promoted by heat treatment at a temperature of 50 to 200 ° C. for 15 minutes to 1 hour.

(b-5) Firing The dried membrane is fired to remove the cationic surfactant and the nonionic surfactant, thereby forming a mesoporous silica porous membrane. The firing temperature is preferably from 300 ° C to 500 ° C. If the firing temperature exceeds 500 ° C., the refractive index may exceed 1.10. The upper limit of the firing temperature is more preferably 450 ° C. or less. The lower limit of the firing temperature is more preferably 350 ° C. The firing time is preferably 1 to 6 hours, more preferably 2 to 4 hours. Since the bond between the mesoporous silica particles and the bond between the mesoporous silica particles and the substrate are strengthened during firing, adhesion to the substrate and crack resistance are improved.

(2) Formation of dense film The inorganic layer can be formed by physical vapor deposition such as vacuum vapor deposition, sputtering or ion plating, chemical vapor deposition such as thermal CVD, plasma CVD or photo-CVD.

  When using a vapor deposition method, the vapor deposition material which consists of inorganic materials is evaporated by heating, and it adheres to a base material in a vacuum, and forms an inorganic layer. There is no particular limitation on the method for making the vapor deposition material vapor, for example, a method using an energization heating type source, a method of applying an electron beam by an E-type electron gun, a method of applying a large current electron beam by a hollow cathode discharge, a laser applying 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.

  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
To pH 2 hydrochloric acid (0.01N) 40 g, n-hexadecyltrimethylammonium chloride (manufactured by Kanto Chemical Co., Inc.) 1.21 g (0.088 mol / L), and block copolymer HO (C ₂ H ₄ O) _106- (C ₃ 7.56 g (0.014 mol / L) of H ₆ O) _70- (C ₂ H ₄ O) ₁₀₆ H (trade name “Pluronic F127”, Sigma-Aldrich) was added, and the mixture was stirred at 23 ° C. for 1 hour. Add Silane (Kanto Chemical Co., Ltd.) 4.00 g (0.45 mol / L), stir at 23 ° C for 3 hours, then add 3.94 g (1.51 mol / L) 28 mass% aqueous ammonia to adjust the pH to 11. And stirred at 23 ° C. for 0.5 hour. The obtained surfactant-mesoporous silica nanoparticle composite solution was applied to the surface of a flat plate (φ30 mm) made of BK7 glass having a refractive index of 1.518 by spin coating, dried at 80 ° C. for 0.5 hour, and then 400 Baked at 3 ° C. for 3 hours. The properties of the obtained antireflection film are shown in Table 1. A lens reflectometer (model number: USPM-RU, manufactured by Olympus Corporation) was used to measure the refractive index and physical film thickness.

Example 2
A surfactant-mesoporous silica nanoparticle composite solution was prepared in the same manner as in Example 1 except that the concentration of the block copolymer was 0.016 mol / L. A mesoporous silica porous film was formed on the surface of a flat plate (φ30 mm) made of LAK14 having a refractive index of 1.700 in the same manner as in Example 1 except that this solution was used. The properties of the obtained antireflection film are shown in Table 1.

Example 3
A magnesium fluoride layer (refractive index: 1.388) with a physical film thickness of 93 nm was formed on the surface of the BK7 glass (refractive index: 1.518) by vacuum deposition using an apparatus having an electron beam evaporation source (optical) Film thickness: 130 nm). On this magnesium fluoride dense film, a mesoporous silica porous film was formed in the same manner as in Example 1. Table 1 shows the layer structure and characteristics of the obtained antireflection film.

Example 4
Using the above apparatus, a magnesium fluoride layer (refractive index: 1.388) having a physical thickness of 93 nm was formed on the surface of the LAK14 glass flat plate (refractive index: 1.700) by vacuum deposition (optical thickness 130 nm). A mesoporous silica porous film was formed on the magnesium fluoride dense film in the same manner as in Example 2. Table 1 shows the layer structure and characteristics of the obtained antireflection film.

Example 5
A multilayer dense film was formed on the surface of the BK7 glass flat plate (refractive index: 1.518) by vacuum deposition using the above apparatus so as to have the configuration shown in Table 1. A mesoporous silica porous membrane was formed on the resulting multilayer dense membrane in the same manner as in Example 1.

Example 6
A multilayer dense film was formed on the surface of the LAK14 glass flat plate (refractive index: 1.700) by the vacuum evaporation method using the above apparatus so as to have the configuration shown in Table 1. A mesoporous silica porous membrane was formed on the resulting multilayer dense membrane in the same manner as in Example 2.

Comparative Example 1
Using the above equipment, form a magnesium fluoride layer (refractive index 1.388) with a physical film thickness of 100 nm (optical film thickness 139 nm) on the surface of the BK7 glass flat plate (refractive index 1.518) by vacuum evaporation. Thus, an antireflection film was prepared. The properties of the obtained antireflection film are shown in Table 1.

Comparative Example 2
Using the above equipment, form a magnesium fluoride layer (refractive index 1.388) with a physical film thickness of 99 nm (optical film thickness 137 nm) on the surface of the LAK14 glass flat plate (refractive index 1.700) by vacuum evaporation. Thus, an antireflection film was prepared. The properties of the obtained antireflection film are shown in Table 1.

Comparative Example 3
On the surface of the BK7 glass flat plate (refractive index 1.518), an antireflection film was prepared by forming a multilayer dense film by vacuum deposition using the above apparatus so as to have the structure shown in Table 1.

Comparative Example 4
On the surface of the LAK14 glass flat plate (refractive index: 1.700), an antireflection film was prepared by forming a multilayer dense film by vacuum deposition using the above apparatus so as to have the structure shown in Table 1.

Comparative Example 5
In the same manner as in Example 1 of JP-A-2006-215542, an antireflection film comprising an MgF ₂ layer and a silica airgel porous layer was formed on the surface of the BK7 glass flat plate. The properties of the obtained antireflection film are shown in Table 1.

Note: (1) η represents the refractive index.

Measurement of Spectral Reflectance For the antireflection films of Examples 1 to 6 and Comparative Examples 1 to 5, a spectral reflectance of a light beam having an incident angle of 0 ° in the wavelength range of 380 to 780 nm is measured with a lens reflectometer (model number: USPM-RU, manufactured by Olympus Corporation) was used for measurement. The spectral reflectance was measured in the same manner for Comparative Example 6 only for the BK7 glass flat plate (refractive index: 1.518) and for Comparative Example 7 only for the LAK14 glass flat plate (refractive index: 1.700). The results are shown in FIGS. The antireflection films of Examples 1 to 6 have a spectral reflectance of 5% or less with respect to a light beam having an incident angle of 0 °. In particular, the antireflection films of Examples 1 and 3 to 6 have a spectral reflectance of approximately 2%. It was the following. On the other hand, in Comparative Examples 1 to 4, since only the dense antireflection film is formed, the spectral reflectance is compared with the antireflection films of Examples 3 to 6 made of a dense and mesoporous silica porous film. Was inferior. Since the antireflection film of Comparative Example 5 has a silica airgel porous layer (refractive index 1.20), it is compared with the antireflective films of Examples 3 to 6 consisting of dense and mesoporous silica porous films (refractive indices 1.088 and 1.091). Spectral reflectance was inferior. In Comparative Examples 6 and 7, since the antireflection film was not formed, the spectral reflectance was clearly inferior to Examples 1 to 6 having the antireflection film.

Measurement of pore size distribution For the anti-reflective coatings of Examples 1 and 2, an isothermal desorption curve of nitrogen gas was obtained with an automatic non-surface area / pore distribution measurement device “Tristar 3000” (Shimadzu Corporation), and this was calculated by the BJH method. The pore size distribution curve by log differential pore volume distribution was obtained by analysis. The results are shown in FIG.

As is clear from FIG. 11, the antireflection films of Examples 1 and 2 each have two peaks in the pore size distribution curve, and the intraparticle pore diameter is in the range of 2 to 10 nm. The pore size had a distribution in the range of 5 to 200 nm. Antireflection film of Example 1, and 2.1 nm to D _A shown in FIG. 3, and 3.1 nm to D _B, a D _C and 12.2 nm, a D _D a 40.6 nm, respectively the analysis data by the BJH method, 2.1 ～3.1 a pore volume within a particle V ₁ to find the total volume of pores having a diameter in the range of nm, between the particles seek total volume of pores having a diameter in the range of 12.2 to 40.6 nm pore volume V ₂ and the ratio V ₁ / V ₂ was found to be 1 / 2.1. Antireflection film of Example 2, the D _A and 1.9 nm, a D _B and 3.0 nm, a D _C and 17.3 nm, in the same manner as above except that the 64.3 nm and D _D, the ratio V ₁ / V ₂ As a result, it was 1 / 6.0.

It is sectional drawing which shows an example of the optical element which has the reflection preventing film of this invention. It is a perspective view which shows an example of the mesoporous silica particle which comprises the anti-reflective film of FIG. It is a graph which shows a typical pore size distribution curve. It is sectional drawing which shows another example of the 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 FIG. It is sectional drawing which shows another example of the optical element which has the antireflection film of this invention. It is a graph which shows the spectral reflectance of the antireflection film of Examples 1-3. It is a graph which shows the spectral reflectance of the anti-reflective film of Examples 4-6. It is a graph which shows the spectral reflectance of the anti-reflective film of Comparative Examples 1-3. It is a graph which shows the spectral reflectance of the multilayer antireflection film of Comparative Examples 4 and 5, and the glass flat plate of Comparative Examples 6 and 7. 3 is a graph showing a pore size distribution curve of an antireflection film of Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical base material 2 ... Antireflection film
20 ... Mesoporous silica porous membrane
200 ・ ・ ・ Mesoporous silica nanoparticles
200a ・ ・ ・ Meso hole
200b ・ ・ ・ Silica skeleton
21, 210, 211, 212, 213, 214 ... Dense film

Claims (18)

An antireflection film comprising a porous mesoporous silica film formed by aggregating mesoporous silica nanoparticles formed on a surface of a substrate, and having a refractive index of 1.10 or less. A reflection film characterized by comprising a dense film and a mesoporous silica porous film sequentially formed on the surface of the substrate, wherein the mesoporous silica porous film is an aggregate of mesoporous silica nanoparticles and has a refractive index of 1.10 or less. Prevention film. The antireflection film according to claim 2, wherein the dense film is a single layer, and the refractive index decreases in order from the base material to the mesoporous silica porous film. 3. The antireflection film according to claim 2, wherein the dense film is a multilayer and is formed by combining a plurality of films having different refractive indexes. 5. The antireflection film according to claim 1, wherein the mesoporous silica nanoparticles have an average particle size of 200 nm or less. The antireflection film according to any one of claims 1 to 5, wherein the mesoporous silica nanoparticles have a hexagonal structure. 7. The antireflection film according to claim 1, wherein the mesoporous silica porous film has a structure in which a pore size distribution curve obtained by a nitrogen adsorption method has two peaks. . 8. The antireflection film according to claim 7, wherein the mesoporous silica porous film has a peak due to an intraparticle pore diameter in a range of 2 to 10 nm and a peak due to an interparticle pore diameter of 5 in the pore diameter distribution curve. An antireflection film characterized by being in a range of ˜200 nm. The antireflection film according to claim 8, wherein a pore volume ratio between the intraparticle pores and the interparticle pores is 1/15 or more and less than 1/2. The antireflection film according to claim 1, wherein the mesoporous silica porous film has a physical film thickness of 15 to 500 nm. 11. The antireflection film according to claim 1, wherein the porosity of the porous mesoporous silica film is 75 to 90%. A method for forming an antireflection film comprising a mesoporous silica porous film in which mesoporous silica nanoparticles are aggregated on the surface of a substrate, comprising: (i) a solvent, an acidic catalyst, an alkoxysilane, a cationic surfactant, Hydrolysis and polycondensation of alkoxysilane by aging a mixed solution containing an ionic surfactant and having a molar ratio of the nonionic surfactant / alkoxysilane of 2.5 × 10 ^{−2 to} 5 × 10 ⁻² (Ii) mesoporous silica nanoparticles coated with the nonionic surfactant and having the cationic surfactant in the pores by adding a basic catalyst to the obtained acidic sol containing the silicate (Iii) coating the obtained solution on the surface of the substrate, (iv) drying to remove the solvent, and (v) firing to cation the surfactant and the Method characterized by removing the ionic surfactant. A method of forming an antireflection film comprising a single layer or multilayer dense film and a mesoporous silica porous film formed by aggregating mesoporous silica nanoparticles on the surface of a substrate, comprising: (1) an inorganic material by vapor deposition (2) (i) comprising a solvent, an acidic catalyst, an alkoxysilane, a cationic surfactant and a nonionic surfactant, (Ii) The resulting silicate by hydrolyzing and polycondensing alkoxysilane by aging a mixed solution having a nonionic surfactant / alkoxysilane molar ratio of 2.5 × 10 ^{−2 to} 5 × 10 ⁻² A solution of mesoporous silica nanoparticles coated with the nonionic surfactant and having the cationic surfactant in the pores by adding a basic catalyst to the acidic sol containing (iii) Obtained melt (Iv) drying to remove the solvent, and (v) firing to remove the cationic surfactant and the nonionic surfactant. A method characterized by: 14. The method of forming an antireflection film according to claim 12 or 13, wherein n-hexadecyltrimethylammonium chloride is used as the cationic surfactant, and the formula: RO (C ₂ H ₄ O is used as the nonionic surfactant. ) _a- (C ₃ H ₆ O) _b- (C ₂ H ₄ O) _c R (where a and c each represent 10 to 120, b represents 30 to 80, and R represents a hydrogen atom or a carbon number) A block copolymer represented by 1 to 12 alkyl groups). 15. The method for forming an antireflection film according to claim 12, wherein hydrochloric acid is used as the acidic catalyst, ammonia is used as the basic catalyst, and tetraethoxysilane is used as the alkoxysilane. Method. 16. The method for forming an antireflection film according to claim 12, wherein a molar ratio of the cationic surfactant / the nonionic surfactant is 4 to 8. 17. The method for forming an antireflection film according to claim 12, wherein the baking is performed at a temperature of 500 ° C. or lower. 12. An optical element comprising the antireflection film according to claim 1 on the surface of an optical substrate.

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