JP2012148950A - Low-reflective film, method for formation thereof, and low-reflective member equipped therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-reflective film to be formed on a transparent base material and a method for forming the low-reflective film, specifically to provide a low-reflective film having a low refractive index and low reflectance in the form of a monolayered film and easily forming a large surface area film in a simpler manner, a method for forming the low-reflective film, and a low-reflective member equipped with the low-reflective film.SOLUTION: There are provided the low-reflective film comprising silica microparticles and at least one metal oxide selected from the group consisting of tungsten oxide, niobium oxide, tantalum oxide, titanium oxide, zirconium oxide, tin oxide, aluminum oxide, hafnium oxide, chromium oxide, cerium oxide, molybdenum oxide and lanthanum oxide as a binder in an amount of ≥5 mass% and ≤40 mass% relative to the amount of the silica microparticles and having a refractive index of ≥1.20 and ≤1.40; and a method for producing the low-reflective film.

Description

  The present invention relates to a low reflection film, a method for forming the same, and a low reflection member using the same. Specifically, the present invention relates to a solar cell cover glass, an automobile glass, or a protective member for a lighting fixture as a low reflective member having a low reflective film formed on the surface of a transparent substrate, and particularly to a solar cell cover glass. .

  The low-reflection film prevents the surface reflection of the substrate, eliminates the loss of light transmittance due to surface reflection (hereinafter sometimes referred to simply as transmittance), and increases the transmittance of a transparent substrate such as glass or transparent plastic. In order to improve, it is formed on the substrate surface.

  The low reflection film is formed on the surface of the cover glass for solar cells, the surface of lenses for optical devices such as still cameras, video cameras, and liquid crystal projectors, image display surfaces such as cathode ray tubes and liquid crystal display devices, or copying machines, It is formed on the surface of an imaging tube, an LED display element, illumination, an organic EL, a window or a showcase, a reflector member of an automobile headlamp, or the like.

  When solar cells are used outdoors, the solar cells are constantly exposed, so that they are required to have weather resistance such as heat resistance, water resistance and wear resistance, which is resistant to differences in temperature and wind and rain, and preferably as a protective member Of solar cell cover glass. The cover glass for a solar cell is required to have transparency and low reflectivity in order to obtain high light receiving efficiency in the solar cell and not to reduce the conversion efficiency. Therefore, since the glass plate is used as the substrate and the low reflection film is formed on the surface of the glass plate, a solar cell cover glass is commercially available because it is hardly deteriorated and can maintain the performance over a long period of time. By forming a low reflection film on the surface, if the substrate is transparent, the transmittance increases without loss due to surface reflection. For example, a solar cell cover glass with a low-reflection film formed on the surface has a higher transmittance as the refractive index of the low-reflection film is lower, and the solar cell has better light reception efficiency and energy conversion from light to electricity. Increases efficiency.

  Still cameras, video cameras, and the like use a plurality of lenses in a multi-group for correcting aberrations. If surface reflection is not suppressed, resolution is lowered and flare and ghost are caused. Therefore, it is important to form a low reflection coating on the lens surface, in other words, a low reflection film. In a display device, a showcase, or the like, unless the surface reflection is reduced by the low reflection film, the visibility deteriorates due to reflection of the reflected image.

  Conventionally, for optical lenses and prisms, a multilayer film in which thin films having different refractive indexes and thicknesses are superimposed on a transparent substrate, that is, a multi-coat has been often used. If the reflective film has a multilayer structure, reflection can be prevented in a wide wavelength range. However, when forming a plurality of thin films by vacuum deposition or the like, it is necessary to precisely control the thickness of each thin film in order to achieve low reflection. Furthermore, in order to perform multi-coating on a large plate glass, a large-sized vacuum film forming apparatus is required, which is technically difficult and expensive.

  Therefore, recently, development of a single-layer and low-refractive-index low-reflecting film that is advantageous for producing a low-reflection member having a large area easily at low cost has been desired. A single-layer low-reflection film is easier to form on the substrate surface than a multilayer film, and can be used for a solar cell cover glass to improve light receiving efficiency and light-to-electricity conversion efficiency. Further, it is suitably used for preventing reflection of automobile glass, particularly windshields, and for improving illuminance when used for protective members of lighting fixtures such as cover glasses and transparent plastics.

  In a single-layer low-reflection film, a method of reducing the refractive index of the film by incorporating air having a refractive index of 1 as microvoids (voids) or metapores into the film formed on the substrate surface is attempted. It has been. For example, it has been studied to form a low reflection film comprising a porous silica film or a silica film using hollow silica fine particles on the substrate surface.

  A porous silica film is formed by applying a raw material liquid obtained by mixing a silica sol and a surfactant or a high boiling point solvent to a substrate, and then forming a mesopore in the silica film by forming a film by a sol-gel method. It is obtained with. In addition, the sol-gel method means that a sol composed of silicon alkoxide and colloidal silica obtained by dehydrating and condensing it is gelled after being applied to the surface of the body, and then heated and fired to obtain amorphous, polycrystalline, etc. This is a technique for forming a relatively hard film.

  The hollow silica fine particles are silica fine particles containing fine voids or mesopores by using an alkoxysilane having a specific alkyl group or the like and aggregating and condensing the same. A film formed on the substrate using these hollow silica fine particles has voids or mesopores derived from the hollow silica fine particles, and becomes a low reflection film by the air contained in the voids or mesopores.

  However, the hollow silica fine particles have a problem that the production process is complicated. Therefore, it is difficult to adopt as a cover glass for solar cells, a protective member for lighting equipment, and an automobile glass, which are general-purpose products.

  For example, in Patent Document 1, porous composite oxide particles composed of silica and an inorganic oxide other than silica are coated with a porous silica-based inorganic oxide layer having a thickness of 0.5 nm to 20 nm. Disclosed is a fine particle characterized in that By forming a film containing the fine particles on the surface of the substrate, it is said that a substrate with a film having a low refractive index and excellent adhesion to a resin, strength, antireflection ability, etc. can be provided. .

Patent Document 2 includes silica, Al ₂ O ₃ , B ₂ O ₃ , TiO ₂ , ZrO ₂ , SnO ₂ , Ce ₂ O ₃ , P ₂ O ₅ , Sb ₂ O ₃ , MoO ₃ , and WO _3. A composite oxide colloidal sol in which a composite oxide colloidal particle having an average particle size composed of an inorganic oxide other than silica selected in the range of 5 nm to 300 nm is dispersed in water and / or an organic solvent, A composite in which a part of an element other than silica constituting the inorganic oxide is removed and the particle surface is coated with a silica coating, and the refractive index is in the range of 1.36 to 1.44. An oxide sol is disclosed. The composite oxide sol can be used to provide a substrate for low reflection in which a coating film having a low refractive index is formed.

  Specifically, the surface of the particles from which a part of the inorganic oxide has been removed and voids are formed are hollow silica fine particles coated with a silica film, and the composite oxide colloidal particles as the hollow silica fine particles are converted into water and / or an organic solvent. It is a dispersed complex oxide sol.

  However, the composite oxide sol described in Patent Document 1 or Patent Document 2 has a process of removing a part of the inorganic oxide and a process of coating the surface of the colloidal particles with silica in its production, and the process is complicated. There is a problem that there is a problem, and it is difficult to employ it as a protective member for solar cell cover glass, automobile glass and lighting equipment.

International Patent Publication No. WO00 / 37359 JP 2006-117526 A

  An object of this invention is to provide the low reflection member excellent in heat resistance, abrasion resistance, and antifouling property. It is another object of the present invention to provide a low reflection film having a low refractive index and low reflectance in a single layer film.

  Furthermore, an object of the present invention is to provide a method for forming a low-reflection film that allows easy formation of a large-area low-reflection film on the surface of a substrate by a simpler method.

  Furthermore, the present invention can form a film with a large area by a simpler method for use in improving the light receiving efficiency of a solar cell, preventing reflection of an automobile windshield, and improving illuminance as a protective member of a lighting fixture. An object of the present invention is to provide a low reflection film, a method for forming the same, and a low reflection member using the same.

  Further, when forming a silica film containing silica fine particles, it is easy to fill the silica fine particles in a spherical shape, and if the particle size distribution of the silica fine particles is uniform, the packing density can be increased and obtained. Further, the silica film can ensure a packing density of 70% or more by close packing. However, even if a binder is used, spherical silica fine particles are bonded together with a narrow contact area. If a shear force acts between the fine particles under external stress, they are brittle and easily broken, and the formed silica film There was a problem of poor wear resistance.

  On the other hand, the rod-like silica fine particles are bulky particles having a large aspect ratio, and the rod-like silica fine particles are three-dimensionally entangled to form a three-dimensional bridge structure. Therefore, the obtained silica film is bulky and has a large porosity. Become. The silica film is porous, rich in air layer, and exhibits an excellent low reflection performance with an apparent refractive index of 1.25 or less, but the friction strength is extremely brittle, and it can be easily peeled off with light friction and can withstand practical use. There was a problem that was not.

  Furthermore, an object of the present invention is to provide a low reflection film, a method for forming the low reflection film, and a low reflection member using the same, which solve the above problems.

  As a result of intensive studies in view of the above problems, the present invention uses a specific metal oxide as a binder to which silica fine particles are bound when formed into a film, so that the film strength is low and the weather resistance is poor, and the film tends to deteriorate. Thus, a low reflection film having a low refractive index is obtained.

  Furthermore, the present invention finds a low reflection film having excellent optical performance such as low reflection performance and excellent friction strength by coexisting silica fine particles having different shapes of rod-like silica particles and spherical silica fine particles in the low reflection film. It is a thing.

  In particular, in the present invention, a low-reflection film formed by forming a low-reflection film on a transparent substrate such as a glass plate by coexisting silica fine particles having different shapes and a metal oxide as a binder for joining the silica fine particles in a low-reflection film. The optical characteristics and the friction strength of the reflecting member were suitable for the cover glass application of the solar cell.

  In the present invention, the rod-like silica fine particles refer to elongated silica fine particles, which may be beaded or curved. In addition, the spherical silica fine particles are round silica fine particles, and may be a perfect ellipsoid or a distorted ellipsoid. The maximum diameter of the silica fine particles is referred to as a long diameter in the case of rod-shaped silica fine particles, and is referred to as a particle diameter in the case of spherical silica fine particles. Further, the minimum diameter of the rod-like silica fine particles is referred to as the short diameter. The same applies to rod-shaped colloidal silica and spherical colloidal silica. The fine particles are particles having a maximum diameter of approximately 100 nm or less. Colloidal silica is a colloid in which silicon oxide or its hydrate is agglomerated, and is usually obtained by dehydration condensation using alkoxysilane (tetraethoxysilane or the like) as a raw material or by ion exchange from alkali silicate. The colloid is obtained by removing the alkali component.

  Further, the binder means what is bonded, and the metal oxide joins the silica fine particles at the interface of the silica fine particles.

  In the present invention, the low reflection film is a film having a low refractive index (refractive index (nD) measured by an ellipsometer (nD) = 1.40 or less) formed on the surface of the substrate to prevent reflection of light on the surface of the substrate. is there.

  Further, in the present invention, the refractive index is a measured value obtained by spectroscopic ellipsometry measurement using an ellipsometer, and the average transmittance and average reflectance are measured using a spectrophotometer in the wavelength range of light, 380 nm to 1200 nm. This is a value obtained by measuring the transmittance and the reflectance of the light and calculating the average transmittance and the average reflectance in the wavelength region. The transmittance curve is a curve obtained by continuously plotting measured values of transmittance with a spectrophotometer in a certain wavelength region.

  In the low reflection film of the present invention, the binder of silica fine particles is selected from tungsten oxide, niobium oxide, tantalum oxide, titanium oxide, zirconium oxide, tin oxide, aluminum oxide, hafnium oxide, chromium oxide, molybdenum oxide, cerium oxide, and lanthanum oxide. By using at least one metal oxide selected from the group, a low reflective film excellent in frictional strength and free from strength reduction was formed on the substrate surface due to heat firing, wetting and aging.

  In particular, tungsten compounds, niobium compounds, and tantalum compounds are hard when they become particles, and the friction strength such as wear resistance is improved. In addition, the optical characteristics can be adjusted by including the low reflection film.

  That is, the present invention is the low reflection film of the inventions 1 to 4 below.

[Invention 1]
At least one selected from the group consisting of silica fine particles and tungsten oxide, niobium oxide, tantalum oxide, titanium oxide, zirconium oxide, tin oxide, aluminum oxide, hafnium oxide, chromium oxide, molybdenum oxide, cerium oxide, and lanthanum oxide. A binder composed of a metal oxide is contained, and the content ratio of the binder composed of the metal oxide to the silica fine particles is 5% by mass or more and 40% by mass or less, and the refractive index is 1.20 or more and 1.40 or less. A low reflective film characterized by the above.

[Invention 2]
Silica fine particles are rod-shaped silica fine particles having a major axis of 5 nm or more and 100 nm or less, and spherical silica having a particle size of 5 nm or more and 50 nm or less as observed with a scanning electron microscope (hereinafter abbreviated as SEM). The low reflective film of invention 1 characterized by comprising mainly fine particles.

[Invention 3]
The low reflection film according to invention 2, wherein the mass ratio of the rod-like silica particles to the spherical silica particles is rod-like silica particles: spherical silica particles = 20: 80 to 80:20.

[Invention 4]
The low reflection film according to any one of inventions 1 to 3, wherein the metal oxide is at least one metal oxide selected from the group consisting of tungsten oxide, niobium oxide and tantalum oxide.

  The transparent substrate forming the low reflection film of the present invention includes a transparent resin plate such as a glass plate, a polycarbonate plate, an acrylic plate, and polyethylene terephthalate. However, a glass plate is a preferable material because it is hard and hardly scratched and has excellent heat resistance and weather resistance. In particular, the low-reflection film of the present invention can provide a highly durable low-reflection member even when a glass plate is used as the substrate, and can be particularly preferably used for a solar cell cover glass.

  By forming the low reflection films of the inventions 1 to 4 on the surface of the transparent substrate, the low reflection members of the inventions 5 and 6 were obtained.

[Invention 5]
A low reflection member in which the low reflection film of Inventions 1 to 4 is formed on the surface of a transparent substrate.

[Invention 6]
The low reflective member according to invention 5, wherein the transparent substrate is a glass plate, and the average transmittance in the light wavelength range of 380 nm to 1200 nm is 95% or more.

  Usually, the peak position indicating the maximum value of the transmittance curve of the low reflection member having a low reflection film made only of silica is around 500 nm, but by adding a metal oxide to the low reflection film formed on the surface, When the peak position is shifted to 500 nm or more and 900 nm or less, the transparency of the low reflection film is increased, and the solar cell cover glass is used, the conversion efficiency of the solar cell is increased, and the low reflection is excellent for the solar cell cover glass. A member was obtained.

[Invention 7]
The low reflection member according to invention 5 or 6, wherein the peak of the maximum value of the transmittance curve is in the range of 500 nm or more and 900 nm or less.

  The low reflection member described in the inventions 5 to 7 is particularly suitable for use as a solar cell cover glass.

[Invention 8]
The cover glass for solar cells which consists of the low reflection member of the invention 5-7.

  Moreover, this invention is the formation method of the low reflection film for forming the low reflection film of the invention 1-4 in a base | substrate.

  In the method for forming a low reflection film of the present invention, it is preferable to use a dispersion of colloidal silica, which is a precursor, in order to incorporate silica fine particles in the low reflection film.

  In order to allow silica fine particles having different shapes to coexist, it is preferable to use a coating solution for forming a low reflection film having colloidal silica having different shapes as a precursor. The low reflection film forming coating solution is a liquid that is applied to the surface of a substrate to form a low reflection film on the substrate.

  In the present invention, a liquid in which colloidal silica and a specific metal compound are dispersed is applied to a substrate as a coating liquid for forming a low reflection film, and then heated and fired, whereby colloidal silica is made into silica fine particles, and the metal compound is made into a metal oxide, A low reflective film in which silica fine particles were bonded using a metal oxide as a binder was obtained.

  In the method for forming a low reflection film of the present invention, in addition to the colloidal silica dispersion on the substrate, the material is selected from the group consisting of tungsten, niobium, tantalum, titanium, zirconium, tin, aluminum, hafnium, chromium, molybdenum, cerium and lanthanum. By using the dispersion liquid of at least one kind of metal compound, a low reflection film excellent in frictional strength was formed on the surface of the substrate without any decrease in adhesion strength due to heating, baking, wetting or aging.

  In particular, tungsten, niobium and tantalum compounds are themselves hard when they become particles, and it is considered that frictional strength such as wear resistance is improved by containing them in a low reflection film.

  Inventions 9 to 14 show a method for forming a low reflection film of the present invention.

[Invention 9]
A dispersion containing a metal compound of at least one metal selected from the group consisting of tungsten, niobium, tantalum, titanium, zirconium, tin, aluminum, hafnium, chromium, molybdenum and rare earth is added to the dispersion containing colloidal silica. A coating solution for forming a low reflection film is applied to a substrate to form a coating film, and then heated and fired to form colloidal silica as silica fine particles and a metal compound as a metal oxide to form a low reflection film. Method.

  The method of the invention 9 is, for example, a method of forming the low reflection film of the invention 1 on a substrate.

[Invention 10]
Colloidal silica is a rod-shaped colloidal silica having a major axis of 5 nm or more and 100 nm or less, and a spherical colloidal silica having a particle diameter of 5 nm or more and 50 nm or less is 90% or more of the total number of the colloidal silica, as observed by SEM. The method of Invention 9, wherein the compound content is 5% by mass or more and 40% by mass or less in terms of oxide.

  The method of the invention 10 is, for example, a method of forming the low reflection film of the invention 2 on a substrate.

[Invention 11]
The method of Invention 10, wherein the mass ratio of the rod-shaped colloidal silica to the spherical colloidal silica is rod-shaped colloidal silica: spherical colloidal silica = 20: 80 to 80:20 in terms of oxide.

  The method of the invention 11 is, for example, a method of forming the low reflection film of the invention 3 on a substrate.

[Invention 12]
The method according to any of inventions 9 to 11, wherein the metal compound is a metal compound of at least one metal selected from the group consisting of tungsten, niobium and tantalum.

  The method of the invention 12 is, for example, a method of forming the low reflection film of the invention 4 on a substrate.

[Invention 13]
A low reflection member obtained by forming a low reflection film having a refractive index of 1.20 or more and 1.40 or less on a transparent substrate surface by the method of inventions 9-12.

[Invention 14]
The low reflection member according to invention 13, wherein the transparent substrate is a glass plate, and the average transmittance in the light wavelength range of 380 nm to 1200 nm is 95% or more.

[Invention 15]
The low reflection member according to invention 13 or 14, wherein the maximum peak of the transmittance curve is in the range of 500 nm or more and 900 nm or less.

[Invention 16]
The cover glass for solar cells which consists of a low reflection member of invention 13-15.

  According to the present invention, a low reflection film as a single layer film capable of forming a large area by a simple method, a method for forming the same, and a low reflection member using the same are provided. The low reflection member in which the low reflection film is formed on the transparent substrate surface by the low reflection film forming method of the present invention has a high average transmittance.

  According to the present invention, a low reflection film having a sufficiently low reflection effect with a single layer film can be obtained, and a method for forming a low reflection film that can be easily formed over a large area is obtained. The low reflection member obtained by the method is suitably used for a solar cell cover glass, an automotive glass (particularly a windshield), or a protective member for a lighting fixture.

It is a drawing SEM photograph of a glass substrate with a low reflective film using tungsten alkoxide. It is the transmittance | permeability curve of the glass substrate with a low reflection film using a tungsten alkoxide. It is a drawing SEM photograph of a glass substrate with a low reflection film using niobium alkoxide. It is the transmittance | permeability curve of the glass substrate with a low reflection film using niobium alkoxide. It is a SEM photograph substituting for a drawing of a glass substrate with a low reflection film using tantalum alkoxide. It is a transmittance | permeability curve of the glass substrate with a low reflection film using a tantalum alkoxide.

1. Low Reflective Film First, the low reflective film of the present invention will be described.

  The present invention is selected from the group consisting of silica fine particles and tungsten oxide, niobium oxide, tantalum oxide, titanium oxide, zirconium oxide, tin oxide, aluminum oxide, hafnium oxide, chromium oxide, molybdenum oxide, cerium oxide and lanthanum oxide. A binder comprising at least one metal oxide is contained, the content ratio of the binder comprising the metal oxide to the silica fine particles is 5% by mass or more and 40% by mass or less, and the refractive index is 1.20 or more. The low reflection film is 40 or less. The refractive index is preferably as low as possible, more preferably 1.35 or less, and still more preferably 1.30 or less.

  Furthermore, the present invention is characterized in that the silica fine particles are mainly rod-like silica fine particles having a major axis of 5 nm to 100 nm and spherical silica fine particles having a particle size of 5 nm to 50 nm as observed by SEM. This is the low reflection film. “Mainly” means 90% or more of the total number of colloidal silica, and the rest are silica fine particles having a shape not satisfying the above range.

  The present invention is also the above low reflection film, wherein the mass ratio of the rod-like silica particles and the spherical silica particles is rod-like silica particles: spherical silica particles = 20: 80 to 80:20.

  The present invention is also the above low reflection film, wherein the metal oxide is at least one metal oxide selected from the group consisting of tungsten oxide, niobium oxide and tantalum oxide.

  In the low reflection film of the present invention, the content of the metal oxide in the low reflection film is 5% by mass or more and 40% by mass with respect to the mass of the silica (solid mass) of the rod-like silica fine particles and the spherical silica fine particles. % Or less. If it is less than 5% by mass, the resulting film is inferior in frictional strength, and if it is more than 40% by mass, the refractive index of the resulting film will be high and a low reflection film will not be obtained. Preferably, they are 10 mass% or more and 30 mass% or less.

  Further, in the low reflection film of the present invention, containing a metal oxide in the silica film has an effect of shifting the peak of the maximum value of the transmittance curve to the long wavelength side. Further, since the metal oxide itself is hard, there is an effect of improving the wear resistance.

  At this time, since the metal oxide does not fill the voids of the silica fine particles, the metal oxide exists in the film as fine particles having substantially the same particle diameter of 5 nm or less and 50 nm or more, or the metal oxide is present. At the grain boundary of the silica fine particles, it is required that the silica fine particles are bonded to give strength to the low reflection film, and that the metal oxide does not change due to a high temperature environment, water adhesion and ultraviolet irradiation.

Such metal oxides include tungsten oxide (WO ₃ , refractive index 1.75), niobium oxide (niobium pentoxide: Nb ₂ O ₅ , refractive index 1.9), tantalum oxide (tantalum pentoxide: Ta _2). O ₅ , refractive index 2.0), titanium oxide (TiO ₂ , refractive index 2.2), zirconium oxide (zirconia: ZrO ₂ , refractive index 1.85), tin oxide (SnO ₂ , refractive index 1.7), Aluminum oxide (alumina: Al ₂ O ₃ , refractive index 1.65), hafnium oxide (hafnia: HfO ₂ , refractive index 1.90), chromium oxide (Cr ₂ O ₃ , refractive index 2.1), molybdenum oxide ( MoO ₂ , MoO ₃ , refractive index 1.80), cerium oxide (ceria: CeO ₂ , refractive index 1.8) and lanthanum oxide (La ₂ O ₃ , refractive index 1.75).

  The low reflection film of the present invention is obtained by joining silica fine particles having different shapes as a binder with a metal oxide as a binder, and obtaining a low refractive index by air having a refractive index of 1 taken into a minute void (gap). According to observation, it is preferable that the major axis of the rod-like silica fine particles is 5 nm or more and 100 nm or less. If the major axis is smaller than 5 nm or larger than 100 nm, it is difficult to form minute voids in the film. In this case, the aspect ratio of the rod-like silica fine particles, that is, the major axis / minor axis is preferably 2 or more and 10 or less. When the major axis / minor axis is smaller than 2 and larger than 10, it is difficult to form minute voids made of air in the film.

  On the other hand, the spherical silica fine particles preferably have a particle size of 5 nm or more and 50 nm or less. If the particle size is smaller than 5 nm or larger than 50 nm, it is difficult to form minute voids in the film.

  In the present invention, among all the silica particles including rod-like silica particles and spherical silica particles, 90% or more of the total number of silica particles having a shape falling within the above range is necessary when observed by SEM. The rest are silica fine particles having a shape that does not satisfy the above range. If it is included more than 10%, the formation of minute voids is hindered.

  In the low reflection film of the present invention, the mass ratio of the rod-like silica fine particles to the spherical silica fine particles is rod-like silica fine particles: spherical silica fine particles = 80: 20 to 20:80. In other ranges, void formation is small and it is difficult to obtain a low reflection film, and the adhesion strength of the low reflection film to a substrate, particularly a glass plate, is poor.

  The preferred film thickness on the substrate surface of the low reflection film of the present invention is 20 nm or more and 500 nm or less. If the film thickness is thinner than 20 nm, the wear resistance is inferior and film formation is difficult. On the other hand, if it is thicker than 500 nm, the film thickness becomes non-uniform and it is difficult to form a film. Preferably, they are 50 nm or more and 150 nm or less. In order to obtain a low reflectance with respect to visible light, the thickness is preferably 100 nm or more and 120 nm or less.

  The low reflection film of the present invention is a film containing a large number of microvoids. Specifically, voids are formed by joining silica particles of different shapes as a binder with a metal oxide, and due to the effect of air having a refractive index of 1 taken into the voids, a low refractive index ( A low reflection film of 1.20 or more and 1.40 or less) was obtained. In addition, a hard film can be obtained by including a metal oxide in the low reflection film, and it is hydrophilic with good adhesion to the substrate, is conductive, and is not easily charged with static electricity. The formed low reflection member is difficult to get dirty.

  Specifically, as observed by SEM, 90% or more of the total number of silica fine particles is rod-like silica fine particles having a major axis of 5 nm or more and 100 nm or less, and spherical silica fine particles having a particle diameter of 5 nm or more and 50 nm or less. The low reflection film of the present invention containing at least one metal oxide selected from niobium or tantalum in a range of 5% by mass to 40% by mass with respect to all silica fine particles, in addition to antifouling property, Excellent heat resistance, durability to withstand outdoor use, and wear resistance. Moreover, by including a metal oxide, it is hydrophilic and conductive, is hardly charged with static electricity, and has excellent antifouling properties.

2. Method for Forming Low Reflective Film Next, a method for forming the low reflective film of the present invention that provides the above low reflective film will be described.

  That is, the present invention provides at least one metal compound selected from the group consisting of tungsten, niobium, tantalum, titanium, zirconium, tin, aluminum, hafnium, chromium, molybdenum, cerium and lanthanum in a dispersion containing colloidal silica. A coating solution for forming a low reflection film comprising a dispersion liquid containing a coating material is applied to a substrate to form a coating film, and then heated and fired to colloidal silica as silica fine particles and a metal compound as a metal oxide to be cured. This is a method for forming a low reflection film.

  Further, according to the present invention, the colloidal silica is 90% or more of the total number of the colloidal silica, and the colloidal silica is rod-shaped colloidal silica having a major axis of 5 nm or more and 100 nm or less and spherical colloidal silica having a particle diameter of 5 nm or more and 50 nm or less. In the above method, the metal compound content relative to the colloidal silica is 5% by mass or more and 40% by mass or less in terms of oxide.

  Moreover, this invention is said method characterized by the mass ratio of rod-shaped colloidal silica and spherical colloidal silica being rod-shaped silica colloidal silica: spherical colloidal silica = 20: 80-80: 20.

  The present invention is also the above method, wherein the metal compound is a metal compound of at least one metal selected from the group consisting of tungsten, niobium and tantalum.

  In the method for forming a low reflection film of the present invention, when forming a low reflection film on a substrate, a coating liquid for forming a low reflection film in which a dispersion of colloidal silica and a specific metal compound are dispersed is used.

  In the method for forming a low reflection film of the present invention, the content of the metal compound in the coating solution for forming the low reflection film is the mass of colloidal silica, which is a combination of rod-shaped colloidal silica and spherical colloidal silica (mass of solid content, hereinafter the same). ) In terms of oxide, it is in the range of 5 mass% or more and 40 mass% or less. Preferably it is the range of 10 mass% or less and 30 mass% or more. If it is less than 5% by mass, the resulting film is inferior in abrasion resistance, and if it is more than 40% by mass, the refractive index of the obtained film is high and it is difficult to form a low reflection film. Preferably, they are 10 mass% or more and 30 mass% or less.

  Assuming the film formation mechanism in the method for forming a low reflection film of the present invention, the coating liquid for forming a low reflection film in which colloidal silica having different shapes coexisted was coated on the substrate, so that the colloidal silica in the liquid was coated. In the film formed by heating and baking the coating film, the coating is formed in a state where the spherical silica particles are trapped in the gap formed by the Brownian motion, in which the rod-shaped colloidal silica having a large aspect ratio is entangled and joined in a bridge shape It is considered that a film having a low refractive index, that is, a low reflection film was formed by the effect that air having a refractive index of 1 was taken into the gaps in the microvoids.

  Specifically, in the drying process of the coating film, the solvent filled by capillarity in the voids between the rod-shaped colloidal silica and the spherical colloidal silica has the effect of strongly bonding the contact points between them, and as the solvent evaporates, the rod-shaped It is considered that fine spherical colloidal silica is trapped in the gaps between the colloidal silicas, and shrinks and dries while rearranging so that silicas of different shapes are adjacent to each other at more contacts. In this way, by using two types of colloidal silica having different shapes, a denser film than when only rod-shaped colloidal silica is used, and a coarser porosity film than when only spherical colloidal silica is used, and It is presumed that a porous film having many contacts and stronger bonding and excellent in friction strength is formed.

  However, if a porous film composed of two types of silica fine particles having different shapes and air is formed on the transparent substrate surface, it exhibits excellent low reflectivity with respect to visible light having a wavelength of about 500 nm to 550 nm, When forming a low reflection film on a solar cell cover glass, it was difficult to control the transmittance over a wide range of wavelengths from 380 nm to 1200 nm in order to improve the conversion efficiency. For this purpose, it is preferable to add a metal compound as a refractive index adjusting material, hydrolyze it, and then condense it.

  In the method for forming a low reflection film of the present invention, the coating liquid for forming the low reflection film is dispersed in a dispersion containing colloidal silica having different shapes, such as tungsten, niobium, tantalum, titanium, zirconium, tin, aluminum, hafnium, chromium, A dispersion containing at least one metal compound selected from the group consisting of molybdenum, cerium and lanthanum was added to obtain a coating solution for forming a low reflection film. In addition, the simple substance of these metals is hydrophobic, and even if it makes it fine particle, it is difficult to disperse | distribute it in a coating liquid. These metal oxides or hydrates, like the fine particles of simple metals, generally have poor dispersibility when used as a coating solution and tend to be inferior in stability, such as precipitation of crystals and solids, Often there is a problem with the liquid life.

  Therefore, in the method for forming a low reflection film of the present invention, a metal alkoxide is preferably used as the metal compound. In particular, an alkoxide of tungsten, niobium or tantalum provides a coating solution for forming a low reflection film having excellent liquid stability and excellent liquid life.

In the tungsten compound, silicotungstic acid (SiO ₂ · 12WO ₃ · 26H ₂ O) may be used, and silicotungstic acid is soluble in water and alcohol and has excellent liquid stability and liquid life.

  In the formation of a low reflection film, for example, tetraethoxysilane (hereinafter abbreviated as TEOS) is cured to form a film unless the content of colloidal silica in the coating solution is 5 mass% or less. However, for example, tungsten alkoxide, niobium alkoxide, or tantalum alkoxide can be contained in an arbitrary ratio with respect to colloidal silica.

Thus, the metal compound is made of tungsten oxide (WO ₃ , refractive index 1.75), niobium oxide (niobium pentoxide: Nb _2). O ₅ , refractive index 1.9), tantalum oxide (tantalum pentoxide: Ta ₂ O ₅ , refractive index 2.0), titanium oxide (TiO ₂ , refractive index 2.2), zirconium oxide (zirconia: ZrO ₂ , Refractive index 1.85), tin oxide (SnO ₂ , refractive index 1.7, aluminum oxide (alumina: Al ₂ O ₃ , refractive index 1.65), hafnium oxide (hafnia: HfO ₂ , refractive index 1.90) , chromium oxide _(Cr 2 _{O 3,} the refractive index 2.1), molybdenum oxide _(MoO 2, MoO _3, refractive index 1.80), cerium oxide (ceria: CeO _2, refractive index 1.8) or oxidation Lanta _(La 2 _{O 3,} the refractive index 1.75), and as a binder to bond the silica fine particles.

  In the present invention, the inclusion of the metal oxide in the low reflection film has the effect of shifting the peak of the maximum transmittance curve to the long wavelength side, and the wear resistance of the low reflection member on which the low reflection film is formed. It is thought that it brought about the effect of improving. When the metal compound in the coating liquid for forming the low reflection film becomes a metal oxide in the film, the silica fine particles were adhered as a binder at the grain boundary of the silica fine particles to give strength to the low reflection film. The metal oxide is required not to change at high temperatures and ultraviolet rays.

  In view of the above points, at least one metal compound selected from the group consisting of tungsten, niobium, tantalum, titanium, zirconium, tin, aluminum, hafnium, chromium, molybdenum, cerium, and lanthanum was selected. In particular, tungsten, niobium and tantalum compounds such as tungsten, niobium and tantalum alkoxides or silicotungstic acid are excellent. Due to the effect of adding these metal compounds to the coating solution for forming a low reflection film, the adhesion strength to the glass plate is improved when a low reflection film is formed.

  Further, in the method for forming a low reflection film of the present invention, a low reflection film forming coating solution having a specific colloidal silica having a different shape and a specific metal compound is heated and fired to form a metal having silica fine particles as a binder. A low reflective film bonded with an oxide is obtained. At this time, in order to obtain a low refractive index by air having a refractive index of 1 taken into microvoids (gap), a rod-like colloidal silica having a major axis of 5 nm or more and 100 nm or less and a particle diameter of 5 nm or more are observed by SEM. The rod-shaped colloidal silica of 50 nm or less is preferably 90% or more of the total number of colloidal silica. If the major axis is smaller than 5 nm or larger than 100 nm, the above-mentioned effects are not obtained, and the above-mentioned minute voids are hardly formed in the film. When the aspect ratio of the rod-shaped colloidal silica, that is, the major axis / minor axis is smaller than 2 or larger than 10, the above-mentioned effects are not obtained, and the above-mentioned minute voids are hardly formed in the film. In spherical colloidal silica, if the particle size is smaller than 5 nm or larger than 50 nm, minute voids are hardly formed in the film. In order to obtain minute voids, it is necessary that the colloidal silica having a shape falling within the above range as observed by SEM is 90% or more of the total number. If it is included more than 10%, the formation of minute voids is hindered. Further, if there is a material greatly deviating to the large diameter side, specifically 5 times or more, that is, a material having a particle size of 500 nm or more, the film thickness becomes non-uniform, which is not preferable.

  As observed by SEM, the major axis is 5 nm or more and 100 nm or less, the major axis / minor axis = 2 or more and 10 or less is rod-shaped colloidal silica, and the spherical colloidal silica having a particle size of 5 nm or more and 50 nm or less is the total number of colloidal silica. By using a coating solution for forming a low reflection film that is 90% or more and is made of a dispersion containing the above metal compound, voids can be easily generated.

  In the method for forming a low reflection film of the present invention, by using colloidal silica that gives silica particles having different shapes as described above, silica particles having different shapes and tungsten oxide, niobium oxide, tantalum oxide, titanium oxide, zirconium oxide, Refractive index of 1.20 or more and 1.40 or less comprising at least one metal oxide selected from the group consisting of tin oxide, aluminum oxide, hafnium oxide, chromium oxide, molybdenum oxide, cerium oxide and lanthanum oxide A low reflection film was obtained. More preferably, it is a low reflective film comprising at least one metal oxide selected from the group consisting of tungsten oxide, niobium oxide and tantalum oxide as the metal oxide.

  Further, in the method for forming a low-reflection film of the present invention, a rod-shaped colloidal silica in a coating solution for forming a low-reflection film that gives a low-reflection film that easily generates voids and has excellent adhesion strength to a glass plate: The mass ratio is 80:20 to 20:80 in terms of oxide. In other ranges, void formation is small and it is difficult to obtain a low reflection film, and the adhesion strength of the low reflection film to the substrate is inferior.

  Specifically, the present invention relates to a rod-shaped colloidal silica having a major axis of 5 nm or more and 100 nm or less, and a major axis / minor axis of 2 or more and 10 or less, as observed by SEM. At least one selected from the group consisting of tungsten, niobium, tantalum, titanium, zirconium, tin, aluminum, hafnium, chromium, molybdenum, cerium and lanthanum in a dispersion containing spherical colloidal silica having a diameter of 5 nm or more and 50 nm or less A low-reflective coating solution obtained by adding a dispersion containing a metal compound such as metal alkoxide so that the content of the metal compound relative to colloidal silica is 5% by mass or more and 40% by mass or less in terms of oxide. After being coated onto a coating film, it is heated and fired to convert a metal compound such as a metal alkoxide into a metal oxide. A method of forming a low-reflection film, which is then cured.

  In the method for forming a low reflection film of the present invention, a member with a low reflection film having a low reflection film having a refractive index of 1.20 or more and 1.40 or less, that is, a low reflection member is obtained in this way. It was.

  For example, when the low reflection film was formed on both surfaces of a 3 mm thick soda lime silicate glass plate as a substrate by a float method, the average transmittance was improved by 8% compared to the case where it was not formed. The average transmittance of the glass plate is about 90%, and the average transmittance when a conventional silica coat film made of colloidal silica and TEOS is formed on both surfaces of the glass plate is about 92%.

  In addition, the colloidal silica dispersion and the metal compound, for example, a metal alkoxide dispersion, have liquid stability, so that in the colloidal silica dispersion, methanol, ethanol, n-propanol, i-propanol (also known as isopropyl alcohol). Or an alcohol solvent such as 2-propanol (hereinafter abbreviated as IPA), an ester solvent such as ethyl acetate, or an organic solvent typified by a polar solvent such as acetone, and a dispersion of a metal compound, particularly a metal alkoxide. Is preferably an organic solvent typified by alcohol such as methanol, ethanol, n-propanol or IPA, and is preferably used in the method for producing a low reflection film of the present invention.

  Usually, when water is added to a dispersion of colloidal silica, the colloidal silica becomes unstable and solid content often precipitates, and although it is not usually added, it is composed of colloidal silica and tungsten, niobium and tantalum. In the coating solution for forming a low reflection film using an alkoxide selected from the group, a solid content hardly precipitates even when water is added up to 50% by mass with respect to the total weight due to the action of the alkoxide. Further, by adding 1% by mass or more of water to the low reflection film forming coating solution, the wettability with the glass plate is improved and the coating is facilitated. In the coating solution for forming a low reflection film used in the method for forming a low reflection film of the present invention, the water content can be arbitrarily adjusted between 1% by mass and 50% by mass with respect to the total mass.

  Therefore, in the method for forming a low reflection film of the present invention, it is possible to use a coating solution for forming a low reflection film having a water content of 1% by mass to 50% by mass. Preferably, they are 1 mass% or more and 30 mass% or less. Furthermore, Preferably, they are 1 mass% or more and 10 mass% or less.

  The low-reflection film according to the method of forming a low-reflection film of the present invention is a film containing a large number of microvoids, and a refractive index of 1 incorporated into voids formed by joining silica particles having different shapes as binders with metal oxides. Due to the effect of the air layer, the refractive index becomes low.

  In the method for forming a low reflection film of the present invention, the low reflection film forming coating solution can be applied to a substrate by a sol-gel method.

  For example, in a film forming method in a vacuum such as a vapor deposition method and a sputtering method, it is difficult to obtain a mixed film having several types of compositions by a single film formation on the surface of a substrate, but a wet coating method such as a sol-gel method. Can be easily formed by a single coating on the substrate surface, and is expected to be applied to a wide range of light control films in the ultraviolet, visible and infrared regions. The sol-gel method is suitably used for the production of a protective member, particularly a solar cell cover glass.

  Application of the coating solution for forming a low reflection film on a substrate, particularly a substrate, is a spine coater method, a dip-up method, that is, a dip coating method, a spray method, a roller coating method, a flow coating method, a screen printing method, a brush coating, It can be performed by a method such as inkjet.

  It is preferable that the coating formed on the substrate by various coating methods is dried at 80 ° C. or higher and 150 ° C. or lower for 10 minutes to 6 hours, and then further heated and fired. The heating temperature is determined according to the heat-resistant temperature of the substrate. Baking is preferably performed in a temperature range in which characteristics such as hydrophilicity can be maintained. In the case of a plastic transparent substrate, it is preferable to treat at approximately 300 ° C. or lower. In addition, the inorganic glass plate can be fired at a high temperature of about 750 ° C. by adjusting the firing time. As a preferred embodiment, a film excellent in wear resistance can be obtained by baking at 500 ° C. or higher and 800 ° C. or lower for 2 to 3 minutes, that is, 120 seconds to 180 seconds.

  When preparing a coating solution for forming a low reflection film, tungsten, niobium, and tantalum compounds, in particular, alkoxides of these metals and silicotungstic acid can be arbitrarily mixed with colloidal silica.

  In particular, in the method for forming a low reflection film according to the present invention, when a coating solution for forming a low reflection film contains a compound of tungsten, niobium, or tantalum, that is, a low-reflection film using an alkoxide or silicotungstic acid of these metals. After applying the coating liquid for forming a reflective film on a glass plate, it is preferably heated and fired to obtain a low reflective member on which a low reflective film is formed. The upper limit is 800 ° C. or lower in consideration of glass deformation, and does not need to be higher than 800 ° C. or higher. After reaching the desired firing temperature, a hard low-reflection film is obtained by heating and holding for 2 to 3 minutes, that is, 120 to 180 seconds.

  In this way, after using a glass plate for the substrate, and applying a coating solution for forming a low reflection film, which is a combination of the colloidal silica and at least one metal compound selected from tungsten, niobium or tantalum, to the substrate by the above method, By heat-firing, a low reflection member excellent in wear resistance was obtained.

3. Next, a dispersion containing colloidal silica used in the coating solution for forming a low reflection film in the present invention will be described.

  The following are mentioned as a silicon compound for producing | generating colloidal silica for making the low anti-film of this invention contain a silica particle.

For example, the silicon compound is preferably an alkoxide, and is represented by the general formula Si (OR) ₄ , wherein R is independently a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, or a secondary butyl group. , A methoxyethyl group, an ethoxyethyl group or a phenyl group), or a hydrolyzate or partial hydrolyzate thereof, particularly tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, Tetranormal propoxysilane, tetranormalbutoxysilane, tetratertiarybutoxysilane or the like or a hydrolyzate thereof is preferable. Moreover, what substituted the -OR group of alkoxide by halogen atoms, such as a chlorine atom, may be used, for example, chlorotriethoxysilane, dichloro dinormal butoxy silane, trichloro normal butoxy silane, etc. are used. In the method for producing a low reflection film of the present invention, these silicon compounds are dehydrated and condensed to form a rod-like colloidal silica having a major axis of 5 nm or more and 100 nm or less, a major axis / minor axis of 2 or more and 10 or less, a particle size of 5 nm or more, What was prepared in spherical colloidal silica of 50 nm or less is used as a raw material.

4). Metal Alkoxide Next, various metal alkoxides as metal compounds used in the coating solution for forming a low reflection film in the present invention will be described in order.

[Tungsten alkoxide]
In the present invention, in order to contain tungsten oxide in the low reflection film, it is preferable to use tungsten alkoxide which is excellent in stability without being precipitated in the coating liquid for forming the low reflection film.

Such tungsten alkoxide includes W (OR) ₆ or W (OR) _6-n X _n (n is 1 ≦ n ≦ 5, R is independently a methyl group, an ethyl group, or an n-propyl group. I-propyl group, n-butyl group, s-butyl group, i-butyl group, t-butyl group, n-amyl group, i-amyl group, s-amyl group, 2-ethylhexyl group, methoxyethyl group, A methoxypropyl group, an ethoxymethyl group, an ethoxyethyl group, an ethoxypropyl group, or a phenyl group, and X represents a halogen atom). In addition, calcium tungstate obtained by firing in the presence of inorganic and organic salts such as Ca, Fe, Mn and alkoxide in the tungsten alkoxide, that is, CaWO ₄ , iron tungstate, that is, FeWO ₄ , manganese tungstate, That is, a tungstic acid compound such as MnWO ₄ can be used.

In the low reflection manufacturing method of the present invention, it is particularly preferable to use W (OR) _6-n Cl _n . n is 1 ≦ n ≦ 5, and R is independently methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, s-butyl group, i-butyl group, t-butyl group, n-amyl group, i-amyl group or s-amyl group.

Among these, W (OR) ₅ Cl is preferable. R is independently methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, i-butyl, t-butyl, n-amyl, i -Amyl group or s-amyl group.

W (OR) ₅ Cl is useful for the liquid stability of the coating solution for forming a low reflection film, and is used as a dispersion dispersed in methanol, ethanol or IPA, and mixed with a dispersion containing colloidal silica. preferable.

W (OR) ₅ Cl is synthesized by the following reaction in an IPA solvent.

WCl ₆ + 5Na (OR) → W (OR) ₅ Cl + 5NaCl
[Niobium alkoxide]
In the present invention, in order to contain niobium oxide in the low reflection film, it is preferable to use a niobium alkoxide that is excellent in stability without being precipitated in the coating liquid for forming the low reflection film.

As such a niobium alkoxide, Nb (OR) ₅ , Nb (OR) _5-n X _n (n is 1 ≦ n ≦ 4, R is independently a methyl group, an ethyl group, an n-propyl group, i-propyl group, n-butyl group, s-butyl group, i-butyl group, t-butyl group, n-amyl group, i-amyl group, s-amyl group, 2-ethylhexyl group, methoxyethyl group, methoxy A propyl group, an ethoxymethyl group, an ethoxyethyl group, an ethoxypropyl group or a phenyl group, X is a halogen atom) or a mixed alkoxide (Fe, Mn) with Fe and Mn: Nb = 1: 2. is there.

In the present invention, it is particularly preferable to use Nb (OR) _5-n Cl _n . n is 1 ≦ n ≦ 4, and R is independently methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, s-butyl group, i-butyl group, t-butyl group, n-amyl group, i-amyl group or s-amyl group.

Among these, Nb (OR) ₄ Cl is preferable. R is independently methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, i-butyl, t-butyl, n-amyl, i -Amyl group or s-amyl group.

Nb (OR) ₄ Cl is useful for the stability of the coating solution for forming a low reflection film, and is used by mixing with a dispersion containing colloidal silica as a dispersion dispersed in methanol, ethanol or IPA. It is preferable.

Nb (OR) ₄ Cl is synthesized by the following reaction in an IPA solvent.

NbCl ₅ + 4Na (OR) → Nb (OR) ₄ Cl + 4NaCl
[Tantalum alkoxide]
In the present invention, in order to contain tantalum oxide in the low reflection film, it is preferable to use tantalum alkoxide that is excellent in stability without being precipitated in the coating liquid for forming the low reflection film.

As such a tantalum alkoxide, Ta (OR) ₅ , Ta (OR) _{5- nXn} (n is 1 <= n <= 4, R is respectively independently a methyl group, an ethyl group, n-propyl group, i-propyl group, n-butyl group, s-butyl group, i-butyl group, t-butyl group, n-amyl group, i-amyl group, s-amyl group, 2-ethylhexyl group, methoxyethyl group, methoxy A propyl group, an ethoxymethyl group, an ethoxyethyl group, an ethoxypropyl group, or a phenyl group, and X is a halogen atom.) Or a mixed alkoxide with Fe and Mn (Fe, Mn): Ta = 1: 2 Can be mentioned.

In the present invention, among others, Ta _(OR) is preferably used _5-n Cl n. n is 1 ≦ n ≦ 4, and R is independently methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, s-butyl group, i-butyl group, t-butyl group, n-amyl group, i-amyl group or s-amyl group.

Of these, Ta (OR) ₄ Cl is preferable, and each R is independently a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an s-butyl group, an i-butyl group, t- A butyl group, an n-amyl group, an i-amyl group or an s-amyl group;

Ta (OR) ₄ Cl is useful for the liquid stability of a coating solution for forming a low reflection film, and is used by mixing with a dispersion containing colloidal silica as a dispersion dispersed in methanol, ethanol or IPA. Is preferred.

Ta (OR) ₄ Cl is synthesized by the following reaction in an IPA solvent.

TaCl ₅ + 4Na (OR) → Ta (OR) ₄ Cl + 4NaCl
[Titanium alkoxides and complexes]
In the present invention, in order to contain titanium oxide in the low reflection film, it is preferable to use a titanium alkoxide that is excellent in stability without being precipitated in the coating solution for forming the low reflection film.

As such a titanium alkoxide, the general formula Ti (OR) ₄ (R is independently methyl group, ethyl group, normal propyl group, isopropyl group, normal butyl group, secondary butyl group, methoxyethyl group, ethoxyethyl) Group or a phenyl group) or a hydrolyzed sol thereof, and tetraethoxytitanium, tetranormalpropoxytitanium, tetraisopropoxytitanium or tetranormalbutoxytitanium is preferably used. Moreover, those polycondensed dimer to dimer are also used.

  Moreover, what substituted -OR of titanium alkoxide by halogen atoms, such as a chlorine atom, may be used, for example, chlorotriethoxy titanium, dichloro dinormal butoxy titanium, or trichloro normal butoxy titanium may be used.

The titanium metal complex is represented by the general formula Ti (OR) _n Y _4-n . In the formula, OR represents an alkoxy group, and Y: represents a chelate. n: An integer of 0 to 3 is shown. Each R is independently a methyl group, ethyl group, normal propyl group, isopropyl group, normal butyl group, secondary butyl group, methoxyethyl group, ethoxyethyl group or phenyl group.

[Zirconium alkoxide]
In the present invention, in order to contain zirconium oxide in the low reflection film, it is preferable to use a zirconium alkoxide that is excellent in stability without being precipitated in the coating solution for forming the low reflection film.

Such a zirconium alkoxide has the general formula Zr (OR) ₄ , where R is independently methyl, ethyl, normal propyl, isopropyl, normal butyl, secondary butyl, methoxyethyl, ethoxy And an alkoxy compound thereof or a hydrolysis sol thereof.

  As such Zr alkoxide, tetraethoxyzirconium, tetranormalpropoxyzirconium, tetraisopropoxyzirconium, tetranormalbutoxyzirconium, and zirconium hydroxide sol which is a hydrolyzate thereof are preferably used.

  Moreover, what substituted -OR of Zr alkoxide by the halogen may be sufficient, for example, chloro triethoxy zirconium, dichloro di normal butoxy zirconium, or trichloro normal butoxy zirconium etc. are mentioned.

[Tin alkoxide]
In the present invention, in order to contain tin oxide in the low reflection film, it is preferable to use a tin alkoxide that is excellent in stability without being precipitated in the coating solution for forming the low reflection film.

Examples of such tin alkoxides include tin alkoxides such as tetraethoxytin, tetranormalpropoxytin, tetraisopropoxytin, and tetranormalbutoxytin, or hydrolyzed sols thereof. SnO ₂ is a semiconductor, and imparts an antistatic function to the hydrophilic low reflection film of the hydrophilic low reflection member of the present invention.

[Aluminum alkoxide]
In the present invention, in order to contain aluminum oxide in the low reflection film, it is preferable to use an aluminum alkoxide that is excellent in stability without being precipitated in the coating solution for forming the low reflection film.

Such an aluminum alkoxide is represented by the general formula Al (OR) ₃ (R is each independently a methyl group, an ethyl group, an isopropyl group, a normal butyl group, a secondary butyl group, a methoxyethyl group, an ethoxyethyl group, or a phenyl group. )), Or hydrolyzed sols thereof, such as triethoxyaluminum, triisopropoxyaluminum, trinormalpropoxyaluminum, or trisecondary butylaluminum, which can be suitably used.

  Moreover, what substituted -OR of aluminum alkoxide by halogen atoms, such as a chlorine atom, may be sufficient, and chloro diisopropoxy aluminum, chloro disecondary butyl aluminum, dichloro isopropoxy aluminum, or dichloro secondary butyl aluminum is mentioned.

The aluminum metal complex is represented by the general formula Al (OR) _n Y _3-n , 1 ≦ n ≦ 3. In the formula, OR represents an alkoxide, and Y: represents a chelate. Here, n represents an integer of 0 to 3. R is each independently a methyl group, an ethyl group, an isopropyl group, a normal butyl group, a secondary butyl group, a methoxyethyl group, an ethoxyethyl group, or a phenyl group. Examples of the chelate include acetylacetone (hereinafter sometimes abbreviated as acac), ethyl acetoacetate, methyl acetoacetate, propyl acetoacetate, trifluoroacetylacetone, hexafluoroacetylacetone, methanesulfonic acid, or trifluoromethanesulfonic acid. Furthermore, the aluminum alkoxide and the condensation-polymerized 2-3 trimer of these aluminum metal complexes are also mentioned.

[Hafnium alkoxide]
In the present invention, in order to contain hafnium oxide in the low reflection film, it is preferable to use hafnium alkoxide that is excellent in stability without being precipitated in the coating liquid for forming the low reflection film.

In the method for producing a low reflection film according to the present invention, the hafnium alkoxide for containing hafnium oxide in the low reflection film includes a general formula Hf (OR) ₄ (R is each independently a methyl group, an ethyl group, or a normal propyl group). Group, isopropyl group, normal butyl group, secondary butyl group, methoxyethyl group, ethoxyethyl group or phenyl group.) Or a hydrolyzed sol thereof.

  As such a hafnium alkoxide, tetraethoxyhafnium, tetranormalpropoxyhafnium, tetraisopropoxyhafnium, tetranormalbutoxyhafnium, and a hafnium hydroxide sol which is a hydrolyzate thereof are preferably used.

  In addition, one in which —OR of hafnium alkoxide is substituted with halogen may be used, and examples thereof include chlorotriethoxyhafnium, dichlorodinormalbutoxyhafnium, and trichloronormalbutoxyhafnium.

[Chromium alkoxides and complexes]
In the present invention, in order to contain chromium oxide in the low reflection film, it is preferable to use a chromium alkoxide that is excellent in stability without being precipitated in the coating solution for forming the low reflection film.

Such a chromium alkoxide includes a general formula Cr (OR) ₃ (wherein R is independently a methyl group, an ethyl group, an isopropyl group, a normal butyl group, a secondary butyl group, a methoxyethyl group, an ethoxyethyl group, or a phenyl group). And triethoxypropoxychromium, triisopropoxychromium, trinormalpropoxychrome or trisecondary butylchromium, which are hydrolyzed sols thereof, and can be suitably used.

  In addition, chromium acetylacetone is used as a complex, chromium nitrate, chromium chloride, chromium acetate, and chromium phosphate are used as inorganic salts, and octylate and naphthenate are used as organic salts.

[Molybdenum alkoxide]
In the present invention, in order to contain molybdenum oxide in the low reflection film, it is preferable to use molybdenum alkoxide that is excellent in stability without being precipitated in the coating solution for forming the low reflection film.

Molybdenum alkoxide is Mo (OR) ₆ , Mo (OR) _6-n X _n , (1 ≦ n ≦ 5, and R is independently methyl group, ethyl group, normal propyl group, isopropyl group, normal Butyl group, secondary butyl group, t-butyl group, 2-ethylhexyl, methoxyethyl group, methoxypropyl group, ethoxymethyl group, ethoxyethyl group, ethoxypropyl group or phenyl group, X is fluorine atom, chlorine atom, bromine It is an atom or an iodine atom.) The molybdenum alkoxides obtained Ca, Fe, after firing coexist inorganic or organic salts and alkoxides of Mn or the like, calcium molybdate, i.e. CaMoO _4, iron molybdate, i.e. FeMoO _4, molybdenum, manganese, i.e. MnMoO ₄ A molybdate compound such as the above may be used.

[Rare earth alkoxide complex]
In the present invention, in order to contain a rare earth in the low reflection film, it is possible to use a rare earth alkoxide that is excellent in stability without being precipitated in the coating liquid for forming the low reflection film, and use cerium alkoxide or lanthanum alkoxide. Can do.

The rare earth alkoxide is represented by the general formula M (OR) ₃ (M represents a rare earth element: La, Y, Ce, Pr, Nd, Sm or Eu, and R is independently a methyl group, an ethyl group, an isopropyl group, or a normal butyl group. Group, secondary butyl group, methoxyethyl group, ethoxyethyl group or phenyl group). Examples of the cerium alkoxide include triethoxycerium, triisopropoxycerium, and trinormalpropoxycerium. The lanthanum alkoxide includes triethoxy lanthanum, and tri-propoxy yttrium and triethoxy samarium are also used.

  In addition, acetylacetone salts as cerium or lanthanum complexes, nitrates, chlorides, acetates and phosphates as rare earth inorganic salts, octylates and naphthenates as organic salts are also used.

[Silica sol]
Silica and metal sols produced by solvent substitution of oxides obtained by hydrolyzing silicon or metal chlorides or alkoxides are commercially available. In the method for producing a low reflection film of the present invention, silica fine particles are used as raw materials. Can be used.

  For example, organosilica sol is trade name, Oscar 1132, Oscar 1232, Oscar 1332, Oscar 1432 or Oscar 1632 from JGC Catalysts & Chemicals Co., Ltd., trade name, methanol silica sol, IPA-ST, IPA from Nissan Chemical Industries, Ltd. -ST-UP, IPA-ST-ZL, EG-ST, NPC-ST-30, DMAC-ST, MEK-ST, commercially available. As the organoalumina sol, trade names, Aluminum Sol-CSA55 and Aluminum Sol-CSA110AD are commercially available from Kawaken Fine Chemical Co., Ltd.

  Furthermore, as the organic solvent-based antimony oxide sol, trade names, Sun Colloid ATL-130 and Sun Colloid AMT-130 are commercially available from Nissan Chemical Industries, Ltd.

  Alternatively, a commercially available sol as an aqueous dispersion can be used after solvent substitution.

  Such an aqueous sol is commercially available from Nissan Chemical Industries, Ltd. under the trade name, Snowtex 40, Snowtex O, Snowtex C or Snowtex N, and from JGC Catalysts & Chemicals Co., Ltd. -30H, Cataloid SI-30, Cataloid SN or Cataloid SA are commercially available from Asahi Denka Kogyo Co., Ltd. under the trade name, Adelite AT-30, Adelite AT-20N, Adelite AT-20A or Adelite AT-20Q, Product names, silica dol-30, silica doll-20A or silica doll-20B are commercially available from Nippon Chemical Industry Co., Ltd., and water-based silicon oxide sols are trade names, alumina sol-100, alumina sol- 200 or alumina sol-520 is commercially available, water Alumina sol is commercially available from Kawaken Fine Chemical Co., Ltd. under the trade name, alumina clear sol, aluminum sol-10, aluminum sol-20, aluminum sol-SV-102, or aluminum sol-SH5. , Trade names, A-1550 and A-2550 are commercially available. Aqueous zirconium oxide sol is commercially available from Nissan Chemical Industries, Ltd. NZS-30A and NZS-30B are commercially available. Aqueous tin oxide sol is available from Taki Chemical Co., Ltd. Trade names, Cerames S-8 and Cerames C-10 are commercially available, and water-based titanium oxide sols are commercially available from Taki Chemical Co., Ltd. under the trade names, Tynock A-6, Tynock M-6, tin oxide and antimony oxide. The water-based sol consisting of is commercially available from Taki Chemical Co., Ltd. under the trade name Cerames F-10. It is.

5. Stability of Low Reflective Film Forming Coating Liquid The low reflective film forming coating liquid applied to a transparent substrate needs long-term stability and is preferably stored at room temperature for 30 days or longer. When mixing the above hydrolyzable metal alkoxide with the coating solution for forming a low reflection film, it is not possible to reduce the refractive index of the target wavelength in the low reflection film by mixing only one type of metal alkoxide. It is necessary to mix 2-4 types of metal compounds. In such mixing, even if there is only one kind of metal compound, it can exist as a relatively stable sol, but if the mixed metal compound does not match, gelation, aggregation and precipitation will occur uniformly. It may be difficult to obtain a simple coating film.

  In general, the zeta potential is important for the stability of the colloid, and the colloidal particles dispersed in the liquid are often charged positively or negatively due to their own ionicity, dipole characteristics, etc. These colloidal particles are surrounded by charges of the opposite sign in an amount that neutralizes the surface charge, and form an electric double layer composed of a fixed layer and a diffusion layer.

  The zeta potential is defined as the “slip surface” potential at which liquid flow starts to occur in the electric double layer formed around the fine particles in the solution. As the zeta potential approaches zero, the repulsive forces of the colloidal particles weaken and eventually aggregate. The zeta potential is an important value in evaluating the properties of the interface. In particular, it is an important index for controlling the stability of colloidal dispersion / aggregation and interaction. In controlling the aggregation and dispersion of colloidal particles, when a plurality of metal alkoxides are mixed and used, it is necessary to carefully select the metal alkoxide to be used in consideration of colloidal stability and pot life.

  Colloidal particles are more stable when the surface area is made as small as possible. When the surface area is large, the colloidal particles tend to aggregate. It is presumed that the metal alkoxide exists as very small fine particles in the solution, and the colloidal particles are more dispersed and stabilized by surrounding the relatively large colloidal particles such as colloidal silica.

  On the other hand, colloidal particles are charged, and electrostatic repulsion works between the particles. The zeta potential is an indicator of stability such as colloidal dispersion / aggregation and interaction. As the zeta potential approaches zero, the tendency of the colloidal particles to aggregate overcomes the electrostatic repulsion, causing the colloidal particles to aggregate. Conversely, an additive that increases the absolute value of the zeta potential can be adsorbed on the surface of the colloidal particles, and a stable colloid can be obtained by pH control.

  In addition, when comparing the stability of metal oxide precursors in sols, such as metal alkoxides, Si-based alkoxides such as alkoxysilanes are slow to hydrolyze and are relatively stable without gelation and solids precipitation over time. However, it is known to those skilled in the art that Al, Zr, Ti, Sn, transition metal, and rare earth alkoxides are unstable.

  The coating solution for forming a low reflection film used in the method for forming a low reflection film of the present invention includes colloidal silica having different rod-like and spherical shapes, tungsten, niobium, tantalum, titanium, zirconium, tin, aluminum, hafnium, chromium, It is a mixture of at least one metal alkoxide selected from molybdenum or rare earth (lanthanum, cerium) or a hydrolyzate thereof, and in particular, at least one selected from the colloidal silica and tungsten, niobium or tantalum. It has been found that the combination of metal alkoxides is stable for a long time.

6). Low Reflective Member A low reflective member formed on the surface of a silica coat film made only of silica has a high transmittance at a wavelength of 500 nm. The low reflection member formed on the surface of the low reflection film of the present invention in which silica fine particles having different shapes are bonded to each other using a metal oxide as a binder is presumed to give a transmittance curve having a peak at a wavelength of 500 nm. However, in practice, the peak of maximum transmittance slightly shifts in the range of 500 nm to 900 nm on the long wavelength side, and accordingly, the transmittance in the long wavelength region tends to increase. This is a factor that increases the average transmittance of the low reflection member on which the low reflection film of the present invention is formed.

  90% or more of the total number of silica fine particles includes rod-like silica fine particles having a major axis of 5 nm to 100 nm and a major axis / minor axis = 2 to 10 and spherical silica particles having a particle diameter of 5 nm to 50 nm. A dispersion liquid containing at least one metal compound selected from the group consisting of tungsten, niobium, tantalum, titanium, zirconium, tin, aluminum, hafnium, chromium, molybdenum, cerium, and lanthanum is mixed with the dispersion liquid. This tendency is conspicuous in the low reflection formed by applying the low reflection film-forming coating liquid on the transparent substrate and then baking by heating to form a low reflection film. In the wavelength region of 500 nm or more and 1200 nm or less, the transmittance Improved. This is due to the inclusion effect of the metal oxide generated by firing the metal alkoxide.

Silica fine particles and metal oxides, that is, tungsten oxide (WO ₃ , refractive index 1.75), niobium oxide (niobium pentoxide: Nb ₂ O ₅ , refractive index 1.9), tantalum oxide (tantalum pentoxide: Ta ₂ O ₅ , refractive index 2.0), titanium oxide (TiO ₂ , refractive index 2.2), zirconium oxide (zirconia: ZrO ₂ , refractive index 1.85), tin oxide (SnO ₂ , refractive index 1.7). Aluminum oxide (alumina: Al ₂ O ₃ , refractive index 1.65), hafnium oxide (hafnia: HfO ₂ , refractive index 1.90), chromium oxide (Cr ₂ O ₃ , refractive index 2.1), molybdenum oxide _(MO0 2, MO0 _3, refractive index 1.80), cerium oxide: for (ceria CeO _2, refractive index 1.8) or lanthanum oxide _(La 2 _{O 3,} the refractive index 1.75), respectively In combination, it does not become a simple average value of refractive index.When silica fine particles and metal oxide coexist, the combination tends to increase the transmittance in a specific wavelength range. Although the range cannot be strictly defined, when the refractive index of the metal oxide is low, the shift is slightly longer than the peak indicating the maximum value of the transmittance curve of silica alone. As the refractive index increases, the peak of the maximum value is further shown on the longer wavelength side.

  Therefore, using this property, when several kinds of metal oxides having different refractive indexes are mixed with silica fine particles, for example, a metal oxide having a relatively low refractive index has a higher transmittance in the visible region. Higher metal oxides tend to increase the transmittance in a longer wavelength region, so by combining them appropriately, the metal oxides will act as a refractive index adjuster and will increase the transmittance over a wide range of wavelengths. .

For the transparent substrate as the substrate for forming the low reflection film of the present invention, an organic plastic substrate or the like can be used in addition to the inorganic glass substrate. As an example of the inorganic glass substrate, a plate-like material such as soda lime silicate glass, borosilicate glass, aluminosilicate glass, barium borosilicate glass or quartz glass can be used. Furthermore, these glass substrates also use clear glass products, colored glass products such as green and bronze, functional glass products such as UV and IR cut glass, and safety glass products such as tempered glass, semi-tempered glass, and laminated glass. Can be done. As the ceramic _Si 3 _N 4, SiC, sapphire, Si wafers, GaAs, also used in the substrate, such as InP or AlN.

  Examples of the plastic substrate include polycarbonate (PC), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), triacetyl cellulose (TAC), and polyimide.

  Since the low reflection film of the present invention exhibits an extremely low reflectance even in a single layer film, a low reflection member having a high average transmittance was obtained when formed on one or both surfaces of a transparent substrate.

  The low reflection member of the present invention is useful as a cover glass for solar cells. When used as a cover glass for solar cells, high average transmittance and low average reflectance are required, and since solar cells are constantly exposed to sunlight, antifouling properties, water resistance, weather resistance, etc. The material which it has together is desired. As described above, the glass plate with a low reflection film as the low reflection member of the present invention using the colloidal silica having a different shape according to the present invention and at least one metal compound selected from tungsten, tantalum, or niobium is provided. Excellent weather resistance such as dirtiness, heat resistance or wear resistance.

  In addition, CIS thin film solar cells and crystalline silicon, which have been developed in recent years, have wide absorption at wavelengths of 400 nm or more and 1200 nm or less, and light in a longer wavelength range than conventional amorphous silicon systems. The absorption peak is in the vicinity of 900 nm. As described above, the low reflection film according to the method of forming a low reflection film of the present invention has high light transmission in the ultraviolet / visible wavelength range, 300 nm to 800 nm, and the near infrared wavelength range, 800 nm to 1200 nm. Therefore, it is suitably used as a cover glass for solar cells having absorption in a long wavelength region as well as amorphous silicon solar cells.

  Although the low reflective film of this invention, its formation method, and the low reflective member using the same are shown based on an Example, this invention is not limited to a following example.

  First, a coating solution for forming a low reflection film for forming a low reflection film on a substrate will be described.

[Coating solution for forming low reflection film using tungsten alkoxide]
A coating solution for forming a low reflection film using two types of colloidal silica (rod-shaped colloidal silica + spherical colloidal silica) and tungsten alkoxide having different shapes, and the tungsten alkoxide content relative to the colloidal silica is 14% by mass in terms of oxide. A coating solution for forming a low reflection film (Example 1), a coating solution for forming a low reflection film (Example 2) in which the content of tungsten alkoxide in colloidal silica is 40% by mass in terms of oxide, and tungsten alkoxide in colloidal silica. A coating solution for low reflection film formation (Comparative Example 1) containing 50% by mass in terms of oxide was prepared.

  Next, using a rod-shaped colloidal silica and tungsten alkoxide, a coating solution for forming a low reflection film (Example 3) having a tungsten alkoxide content of 20 mass% with respect to the rod-shaped colloidal silica was prepared.

  Next, using a spherical colloidal silica and tungsten alkoxide, a coating solution for forming a low reflection film (Example 4) having a tungsten alkoxide content of 20 mass% with respect to the spherical colloidal silica was prepared.

[Coating solution for forming low reflection film using niobium alkoxide]
A coating solution for forming a low-reflection film using two types of colloidal silica (rod-shaped colloidal silica + spherical colloidal silica) and niobium alkoxide having different shapes, and the niobium alkoxide content relative to the colloidal silica is 25% by mass in terms of oxide. A coating solution for forming a low reflection film (Example 5), a coating solution for forming a low reflection film having a niobium alkoxide content of 40 mass% in terms of oxide (Example 6), and a niobium alkoxide for colloidal silica. A coating solution for forming a low reflection film (Comparative Example 2) containing 50% by mass in terms of oxide was prepared.

  Next, using a rod-shaped colloidal silica and niobium alkoxide, a coating solution for forming a low reflection film (Example 7) having a niobium alkoxide content of 20 mass% with respect to the rod-shaped colloidal silica was prepared.

  Next, using a spherical colloidal silica and niobium alkoxide, a coating solution for forming a low reflection film (Example 8) having a niobium alkoxide content of 20 mass% with respect to the spherical colloidal silica was prepared.

[Preparation of coating solution for forming low reflection film using tantalum alkoxide]
A coating solution for forming a low reflection film using two types of colloidal silica (rod-shaped colloidal silica + spherical colloidal silica) and tantalum alkoxide having different shapes, and the content of tantalum alkoxide with respect to colloidal silica is 20% by mass in terms of oxide. A coating solution for forming a low reflection film (Example 9), a coating solution for forming a low reflection film (Example 10) in which the content of tantalum alkoxide with respect to colloidal silica is 40% by mass in terms of oxide, and tantalum alkoxide with respect to colloidal silica. A coating liquid for forming a low reflection film (Comparative Example 3) containing 50% by mass in terms of oxide was prepared.

  Next, using a rod-shaped colloidal silica and tantalum alkoxide, a coating solution for forming a low reflection film (Example 11) having a tantalum alkoxide content of 20 mass% with respect to the rod-shaped colloidal silica was prepared.

  Next, using a spherical colloidal silica and tantalum alkoxide, a coating solution for forming a low reflection film (Example 12) having a tungsten alkoxide content of 20 mass% with respect to the spherical colloidal silica was prepared.

[Coating liquid of comparative example]
Next, a coating solution (Comparative Example 4) using only two types of colloidal silica and not using a metal alkoxide was prepared. Moreover, the coating liquid (Comparative Example 5) using two types of colloidal silica and TEOS was prepared. Also, a coating solution consisting of only tungsten alkoxide (Comparative Example 6), only niobium alkoxide (Comparative Example 7) or tantalum alkoxide (Comparative Example 8) was prepared.

  The glass substrate was coated with the coating solution for forming a low reflection film according to Examples 1 to 12 and the coating solution of Comparative Examples 1 to 8 to form a low reflection film, and physical properties of the obtained glass substrate with a low reflection film were evaluated. . In addition, soda-lime silicate glass by the float process was used for the glass substrate.

The compositions of the low reflection film forming coating solutions of Examples 1 to 12 and the coating solutions of Comparative Examples 1 to 8 are summarized in Table 1.

Subsequently, the coating liquid for forming a low reflection film of Examples 1 to 12 and the coating liquid of Comparative Examples 1 to 8 were applied to a colorless and transparent glass substrate having a thickness of 3 mm and a size of 100 mm × 100 mm to obtain a glass substrate with a low reflection film. Obtained. Table 2 shows a method for evaluating physical properties of the obtained glass substrate with a low reflection film.

  Hereinafter, Examples 1 to 12 and Comparative Examples 1 to 5 of the present invention will be described in detail.

[Examples 1 to 4, Comparative Example 1 (example using tungsten alkoxide)]
Hereinafter, Examples 1 to 4 and Comparative Example 2 using tungsten alkoxide are shown.

Example 1
<Preparation of colloidal silica dispersion>
In a three-necked flask with a volume of 1000 ml, a rod-shaped colloidal silica isopropanol (hereinafter abbreviated as IPA) dispersion (manufactured by Nissan Chemical Industries, Ltd., product number, IPA-ST, solid content concentration 30.3 mass%, major axis 10 to 20 nm). ) 16.34 g was weighed in and 231.21 g of ethanol was added with stirring. Subsequently, 111.50 g of ethanol was added to 12.28 g of a spherical colloidal silica dispersion (manufactured by JGC Catalysts & Chemicals, product number, OSCAL1432, solid concentration 20.2 mass%, particle size 5 nm to 10 nm) with stirring. Those were mixed to obtain 371.3 g of a colloidal silica dispersion.

  The mixing ratio of the rod-shaped colloidal silica and the spherical colloidal silica was 67:33 by mass ratio.

<Preparation of tungsten alkoxide dispersion>
Under a nitrogen stream, 5.86 g of tungsten hexachloride (WCl ₆ ) was collected in a 300 ml three-necked flask, and 79.5 g of IPA cooled to 5 ° C. was added. To this was added 1.70 g of metallic sodium (manufactured by Wako Pure Chemical Industries, Ltd.), then refluxed in a nitrogen atmosphere at 75 ° C. for 24 hours, and cooled to room temperature (about 20 ° C.). Subsequently, pressure filtration was performed, and tungsten alkoxide (W (OCH ₂ (CH ₃ ) ₂ ) ₅ Cl) and NaCl as a by-product were separated by filtration. The concentration of tungsten in the filtrate was 4.22% by mass in terms of WO ₃ . In this way, about 70 g of a dispersion of tungsten alkoxide (W (OCH ₂ (CH ₃ ) ₂ ) ₅ Cl) was obtained.

<Preparation of coating solution for forming low reflection film>
While stirring at room temperature in a nitrogen atmosphere at room temperature in 179.8 g of the colloidal silica dispersion, 13.9 g of the tungsten alkoxide dispersion synthesized above was gradually added dropwise over 3 hours to give a pale brown transparent liquid. Obtained. After mixing, the mixture is further refluxed at 70 ° C. for 6 hours under a nitrogen atmosphere, and the colloidal silica and tungsten alkoxide in terms of mass ratio in terms of oxide are SiO ₂ : WO ₃ = 86: 14, that is, tungsten alkoxide in terms of oxide. A coating solution for forming a low reflection film having a solid concentration of 2.2% by mass was prepared to 14% by mass.

<Production of glass substrate with low reflection film>
The surface of a glass substrate having a thickness of 3 mm and a size of 100 mm × 100 mm was wet-polished with alumina particles, washed with distilled water and then with IPA, and then heated to 100 ° C. and dried. When the contact angle of pure water was measured in order to confirm the surface state, it showed a strong hydrophilic property with a contact angle of 5 ° or less and was clean.

  Next, a low reflection film was formed on the surface of the glass substrate by a dip method.

  The washed glass substrate was dipped in the low reflection film forming coating solution and pulled upward at a speed of 3.4 mm / sec to apply the low reflection film forming coating solution to both surfaces of the glass substrate. It was dried at 50 ° C. for 30 minutes and further dried at 110 ° C. for 60 minutes. This is put into a baking furnace heated to 750 ° C., held for 150 seconds, taken out, rapidly cooled at room temperature, and formed with a low reflection film having a light blue reflection color on both sides, and a glass with a low reflection film A substrate was obtained.

  FIG. 1 shows a drawing-substitute SEM photograph of the surface of a glass substrate with a low reflection film using tungsten alkoxide.

  It is an enlarged photograph by SEM of the low reflection film formed on the glass substrate using the coating liquid for low reflection film formation. The ordered particles are silica fine particles, and the silica fine particles are bonded by tungsten oxide serving as a binder and are a porous film containing a microvoid and a hard film.

<Evaluation of glass substrate with low reflection film>
FIG. 2 shows a transmittance curve of a glass substrate with a low reflection film obtained using tungsten alkoxide.

  A low reflection film was formed on the surface of the glass substrate by the sol-gel method using the coating liquid for forming the low reflection film. A transmittance curve of 1 is a transmittance curve of a glass substrate with a low reflection film applied to the glass substrate at a lifting speed of 3 mm / sec from the coating tank, and similarly, a transmittance curve of 2 is a lifting speed of 5 mm / sec. The transmittance curve of the glass substrate with a low reflection film is a transmittance curve of the glass substrate with a low reflection film at a pulling rate of 7 mm / sec. As the pulling speed increases, the film thickness increases, and the peak of the maximum transmittance shifts to the long wavelength side. Compared to the transmittance curve (represented by R) of a glass substrate that does not have a reference low-reflection film, the transmittance is improved in the entire wavelength region.

  When the physical property values were measured in accordance with the physical property evaluation methods shown in Table 2, the average transmittance of the glass substrate with a low reflection film formed by forming the low reflection film on both surfaces under the above-described pulling speed of 3.4 mm / sec was The average transmittance was 98.0%, and the average transmittance was improved by 7.5% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflection film.

  Next, the film thickness was measured with a stylus type surface shape measuring instrument and found to be 108 nm. Further, when the refractive index n was measured by an ellipsometer, n = 1.298, and satisfactory performance was obtained as a glass substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The appearance was slightly scratched and a haze was seen, but the film was not peeled off and the average transmittance was measured to be 97.4%, which was 0.6% lower than that before the test. Moreover, when the contact angle of the pure water was measured, it was 6.5 °, indicating strong hydrophilicity.

Moreover, when the surface resistance value of this low reflective film-coated glass substrate after 30 days at room temperature (25 ° C.) and 50% relative humidity was measured, it was 9.0 exp10 ⁸ Ω. cm, and it was confirmed that excellent antistatic performance was maintained.

Example 2
A colloidal silica dispersion containing colloidal silica having different shapes was prepared in the same manner as in Example 1. Next, the tungsten alkoxide dispersion prepared in Example 1 is added to the colloidal silica dispersion so that 40% by mass of tungsten alkoxide in terms of oxide is contained with respect to the mass of the colloidal silica, that is, SiO _2. : WO ₃ = 60: 40 was added, and a coating solution for forming a low reflection film having a solid content concentration of 1.9% by mass was prepared. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 1 and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured according to the physical property evaluation methods in Table 2, a low reflective film-coated glass substrate was formed on both surfaces in the same manner as in Example 1 under the condition of a pulling speed of 3.4 mm / sec. The average transmittance was 97.3%, and the average transmittance was improved by 6.8% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflective film. Subsequently, when the film thickness was measured with a stylus type surface shape measuring instrument, it was 105 nm. Further, when the refractive index n was measured with an ellipsometer, it was n = 1.279, and satisfactory performance was obtained as a glass substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The appearance was slightly scratched and a haze was seen, but the film was not peeled off, and the average transmittance was measured to be 96.6%, which was 0.7% lower than before the test. Moreover, when the contact angle of the pure water was measured, it was 12 °, indicating strong hydrophilicity.

In addition, when the surface resistance value of this low reflective film-coated glass substrate after 30 days was measured at room temperature (25 ° C.) and a relative humidity of 50%, it was 5.2 exp10 ⁸ Ω. cm, and it was confirmed that excellent antistatic performance was maintained.

Comparative Example 1
A colloidal silica dispersion containing colloidal silica having different shapes was prepared in the same manner as in Example 1. Next, the tungsten alkoxide dispersion prepared in Example 1 is added to the colloidal silica dispersion so that 50% by mass of tungsten alkoxide in terms of oxide is contained with respect to the mass of the colloidal silica, that is, SiO _2. : WO ₃ = 50: 50 and a coating solution for forming a low reflection film having a solid content concentration of 1.9% by mass was prepared. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 1 and heated and fired to obtain a glass substrate with a film.

  When the physical property values were measured in accordance with the physical property evaluation methods in Table 2, the average transmittance of the film-coated substrate formed on both surfaces in the same manner as in Example 1 under the condition of a pulling rate of 3.4 mm / sec, The glass substrate was improved 1.6% from the glass substrate before the film was provided, and was 92.1%, and the desired performance as a glass substrate with a low reflection film was not obtained.

  Subsequently, when the film thickness was measured with a stylus type surface shape measuring instrument, it was 122 nm. Further, the refractive index of the film was measured with an ellipsometer, and n = 1.362. The refractive index was higher than desired.

  This is a result of the content of the tungsten compound with respect to the colloidal silica deviating from the preferable content range of 5% by mass or more and 40% by mass or less in terms of oxide.

Example 3
After diluting the rod-shaped colloidal silica IPA dispersion used in Example 1 (manufactured by Nissan Chemical Industries, Ltd., product number, IPA-ST, solid content concentration 30.3% by mass, major axis 10 nm to 20 nm) with ethanol, tungsten alkoxide Is a mass ratio in terms of oxide, SiO ₂ : WO ₃ = 80: 20, that is, a tungsten alkoxide is prepared so as to be 20% by mass in terms of oxide, and a low reflection film having a solid content concentration of 2.0% by mass A forming coating solution was obtained. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 1 and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured in accordance with the physical property evaluation methods in Table 2, a low reflective film-coated glass substrate formed by forming low reflective films on both sides in the same manner as in Example 1 under the pulling rate of 3.4 mm / sec. The average transmittance was 97.5%, and the average transmittance was improved by 7.0% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflective film. Next, the film thickness was measured with a stylus type surface shape measuring instrument and found to be 112 nm. Further, when the refractive index n was measured with an ellipsometer, n = 1.292, and the desired performance was obtained as a substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The frictional strength of the low reflective film is that the appearance after 3000 reciprocating frictions in the flannel cloth abrasion test is cloudy and partially peeled, and the frictional strength of the glass substrate with the low reflective film of Example 1 and Example 2 It was inferior compared.

  This is a result of forming a film having inferior frictional strength because the colloidal silica (rod-like colloidal silica + spherical colloidal silica) having a different specific particle size shape is not used but only the rod-like colloidal silica is used.

Example 4
After diluting the IPA dispersion of spherical colloidal silica used in Example 1 (manufactured by JGC Catalysts and Chemicals, product number, OSCAL1432, solid concentration 20.2 mass%, particle size 5 nm to 10 nm) with ethanol, tungsten alkoxide was obtained. SiO ₂ : WO ₃ = 80: 20 by mass ratio in terms of oxide, that is, a tungsten alkoxide is prepared so as to be 20% by mass in terms of oxide, and a low reflective film having a solid content concentration of 2.0% by mass is formed. A coating solution was obtained. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 1 and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured according to the physical property evaluation methods in Table 2, a low reflective film-coated glass substrate was formed on both surfaces in the same manner as in Example 1 under the condition of a pulling rate of 3.0 mm / sec. The average transmittance was 96.9%, and the average transmittance was improved by 6.4% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflective film. Next, the film thickness was measured with a stylus type surface shape measuring instrument and found to be 109 nm. Further, when the refractive index n was measured with an ellipsometer, n = 1.303, and the desired performance as a low reflection film was obtained.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The frictional strength of the low reflective film is that the appearance after 3000 reciprocating frictions in the flannel cloth abrasion test is cloudy and partially peeled, and the frictional strength of the glass substrate with the low reflective film of Example 1 and Example 2 It was inferior compared.

  This is a result of forming a film having inferior frictional strength because only the spherical colloidal silica was used without using colloidal silica (rod-like colloidal silica + spherical colloidal silica) having a specific particle size.

[Examples 5 to 8, Comparative Example 2 (example using niobium alkoxide)]
Examples where niobium alkoxide is used are shown in Examples 5 to 8 and Comparative Example 2 below.

Example 5
<Preparation of colloidal silica dispersion>
IPA dispersion of rod-shaped colloidal silica (IPA-ST-UP manufactured by Nissan Chemical Industries, Ltd., solid content concentration 15.2% by mass, major axis 40 nm to 100 nm) was weighed into a 1000 ml three-necked flask, and IPA 186.6 g was added with stirring. Next, IPA, 194.8 g added to 23.41 g of spherical colloidal silica (manufactured by JGC Catalysts and Chemicals, product number, OSCAL1632, solid concentration 20.5 mass%, particle size 8 nm to 15 nm) with stirring. By mixing, 436 g of colloidal silica dispersion was obtained.

  The mixing ratio of the rod-shaped colloidal silica and the spherical colloidal silica was 50:50 by mass ratio.

<Preparation of niobium alkoxide dispersion>
Under a nitrogen stream, 9.76 g of niobium pentachloride (NbCl ₅ ) was collected in a 500 ml three-necked flask, and 205 g of IPA cooled to 5 ° C. was added. To this was added 3.32 g of metallic sodium (manufactured by Wako Pure Chemical Industries, Ltd.) to obtain 218 g of a slurry in which niobium alkoxide (Nb (OCH ₂ (CH ₃ ) ₂ ) ₄ Cl) and by-product NaCl were mixed.

Next, the mixture was refluxed in a nitrogen atmosphere at 75 ° C. for 24 hours and cooled to room temperature (about 20 ° C.). Then, pressure filtration was performed, and niobium alkoxide (Nb (OCH ₂ (CH ₃ ) ₂ ) ₄ Cl) and NaCl as a by-product were separated by filtration. The concentration of niobium in the filtrate was 2.3% by mass in terms of Nb ₂ O ₅ . This filtrate was used as a dispersion of niobium alkoxide (Nb (OCH ₂ (CH ₃ ) ₂ ) ₄ Cl).

<Preparation of coating solution for forming low reflection film>
While stirring at room temperature in a nitrogen atmosphere at room temperature, the niobium alkoxide dispersion synthesized above, 139.74 g, was gradually added dropwise to the colloidal silica dispersion over 3 hours to obtain a milky white transparent liquid. After mixing, the mixture is further refluxed under 70 in a nitrogen atmosphere for 8 hours, so that colloidal silica and niobium alkoxide are in a mass ratio of oxide equivalent to SiO ₂ : Nb ₂ O ₅ = 3: 1, ie niobium alkoxide is equivalent to oxide. To 25 mass%, and this was used as a coating solution for forming a low reflection film.

<Production of glass substrate with low reflection film>
The surface of a glass substrate having a thickness of 3 mm and a size of 100 mm × 100 mm was wet-polished with alumina particles, washed with distilled water and then with IPA, and then heated to 100 ° C. and dried. When the contact angle of pure water was measured in order to check the surface condition, it showed a strong hydrophilic property with a contact angle of 5 ° or less and was clean.

  The washed glass substrate was immersed in the low reflection film forming coating solution, and pulled upward at a speed of 3.0 mm / sec by a dipping method to apply the low reflection film forming coating solution to both surfaces of the glass substrate. It was dried at 50 ° C. for 30 minutes and further dried at 110 ° C. for 60 minutes. This is put into a baking furnace heated to 750 ° C., held for 150 seconds, taken out, rapidly cooled at room temperature, and a low reflection film having a light blue reflection color is formed on both sides. A glass substrate was obtained.

  FIG. 3 shows a drawing-substitute SEM photograph of the surface of the glass substrate with a low reflection film using niobium alkoxide.

  It is an enlarged photograph by SEM of the low reflection film formed on the glass substrate using the coating liquid for low reflection film formation. The ordered particles were silica, and the silica fine particles were joined by niobium oxide serving as a binder, and became a hard film while being a porous film containing microvoids.

<Evaluation of glass substrate with low reflection film>
FIG. 4 shows a transmittance curve of a glass substrate with a low reflection film using niobium alkoxide.

  A low reflection film was formed on the surface of the glass substrate by the sol-gel method using the coating liquid for forming the low reflection film. A transmittance curve of 1 is a transmittance curve of a glass substrate with a low reflection film applied to the glass substrate at a lifting speed of 3 mm / sec from the coating tank. Similarly, a transmittance curve of 2 is a lifting speed of 5 mm / sec. The transmittance curve of the glass substrate with a low reflection film is a transmittance curve of the glass substrate with a low reflection film at a pulling rate of 7 mm / sec. As the pulling speed increases, the film thickness increases, and the peak of the maximum transmittance shifts to the long wavelength side. Compared to the transmittance curve (represented by R) of a glass substrate that does not have a reference low-reflection film, the transmittance is improved in the entire wavelength region.

  Subsequently, according to the physical property evaluation method of Table 2, the average transmittance of the glass substrate with a low reflection film formed by forming a low reflection film on both surfaces in the same manner as in Example 5 under the condition of a lifting speed of 3.0 mm / sec. As a result, the average transmittance was 98.2%, and the average transmittance was improved by 7.7% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflection film. . Then, the film thickness was measured with a stylus type surface shape measuring instrument and found to be 113 nm. Further, when the refractive index n was measured with an ellipsometer, n = 1.275, which was satisfactory as a glass substrate with a low reflection film.

The friction strength of this coating film was rubbed back and forth 3000 times with a load of 15 g / cm ^{2 on} the surface of the glass substrate with a low reflection film using a flannel cloth wear tester, and the friction of the low reflection film. The strength was evaluated. The appearance had a slight haze, but the color tone did not change, and the average transmittance was 97.7%, which was slightly decreased by 0.5% compared to before the test. When the pure water contact angle was measured, it showed a strong hydrophilic property at 6.5 °.

Further, when the surface resistance value of this low reflective film-coated glass substrate after 30 days at 25 ° C. and 50% relative humidity was measured, it was 6.7 exp10 ⁸ Ω. cm, and it was confirmed that excellent antistatic performance was maintained.

Example 6
A colloidal silica dispersion containing colloidal silica having different shapes was prepared in the same manner as in Example 5. Next, the niobium alkoxide dispersion prepared in Example 1 is added to the colloidal silica dispersion so that the niobium alkoxide is contained in an amount of 40% by mass in terms of oxide with respect to the mass of the colloidal silica, that is, Nb ₂ A coating solution for forming a low reflection film having a solid content concentration of 1.9% by mass was prepared so that O ₅ : WO ₃ = 60: 40. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 1 and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured in accordance with the physical property evaluation methods shown in Table 2, a low reflective film-coated glass substrate formed by forming low reflective films on both sides in the same manner as in Example 5 under the condition of a pulling speed of 3.0 mm / sec. The average transmittance was 98.0%, and the average transmittance was improved by 7.5% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflective film. Next, the film thickness was measured with a stylus type surface shape measuring instrument and found to be 108 nm. Further, when the refractive index n was measured with an ellipsometer, n = 1.281, which was a satisfactory performance as a low reflective film glass substrate.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The appearance was slightly scratched and a haze was seen, but the film was not peeled off, and the average transmittance was measured to be 97.1%, which was 0.9% lower than before the test. Moreover, when the contact angle of the pure water was measured, it was 18 °, indicating strong hydrophilicity.

Further, when the surface resistance value of this low reflective film-coated glass substrate after 30 days at room temperature (25 ° C.) and 50% relative humidity was measured, it was 11.2 exp10 ⁸ Ω. cm, and it was confirmed that excellent antistatic performance was maintained.

Comparative Example 2
A colloidal silica dispersion containing colloidal silica having different shapes was prepared in the same manner as in Example 5. Next, the niobium alkoxide dispersion prepared in Example 5 is added to the colloidal silica dispersion so that the niobium alkoxide is 50% by mass in terms of oxide with respect to the mass of the colloidal silica. A coating solution for forming a low reflection film having a solid content concentration of 2.0% by mass was prepared so that SiO ₂ : Nb ₂ 0 ₅ = 50: 50. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 3 and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured in accordance with the physical property evaluation methods in Table 2, the average transmittance of the film-coated substrate formed on both surfaces in the same manner as in Example 5 under the condition of a pulling speed of 3.0 mm / sec is The glass substrate was -0.9% lower than the glass substrate before the film was provided, and was 89.6%, which was not a glass substrate with a low reflection film.

  Subsequently, when the film thickness was measured with a stylus type surface shape measuring instrument, it was 115 nm. Further, when the refractive index of the film was measured with an ellipsometer, n = 1.353, and the refractive index was higher than desired.

  This is a result of the content of niobium alkoxide with respect to colloidal silica deviating from the preferable content range of 5% by mass or more and 40% by mass or less in terms of oxide.

Example 7
After diluting the IPA dispersion of rod-shaped colloidal silica used in Example 5 (IPA-ST-UP manufactured by Nissan Chemical Industries, Ltd., solid content concentration 15.2 mass%, major axis 40 nm to 100 nm) with IPA, niobium alkoxide SiO ₂ : Nb ₂ O ₅ = 80: 20 by mass ratio in terms of oxide, that is, niobium alkoxide is prepared to be 20% by mass in terms of oxide, and low reflection with a solid content concentration of 2.0% by mass A coating solution for film formation was obtained. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 1 and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured according to the physical property evaluation methods shown in Table 2, a low reflection film was formed on both surfaces under the condition of a pulling speed of 3.0 mm / sec. The average transmittance of the low reflective film-coated glass substrate is 97.2%, and the average transmittance of the glass substrate without the low reflective film is 96.7%, which is 6.7%. % Improved. Next, the film thickness was measured with a stylus type surface shape measuring instrument and found to be 102 nm. Further, when the refractive index n was measured with an ellipsometer, it was n = 1.296, which was satisfactory as a glass substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The frictional strength of the low reflective film is cloudy and partially peeled after 3000 reciprocating frictions according to the flannel abrasion test, and compared with the frictional strength of the substrates with the low reflective film of Example 5 and Example 6. It was inferior.

  This is a result of forming a film having inferior frictional strength because only spherical colloidal silica was used without using spherical colloidal silica.

Example 8
After diluting the IPA dispersion of spherical colloidal silica used in Example 5 (manufactured by JGC Catalysts and Chemicals, product number, OSCAL1632, solid concentration 20.5 mass%, particle size 8 nm to 15 nm) with IPA, niobium alkoxide SiO ₂ : Nb ₂ O ₅ = 80 in terms of mass ratio in terms of oxide
: 20, that is, niobium alkoxide was prepared so as to be 20% by mass in terms of oxide, and a coating solution for forming a low reflection film having a solid content concentration of 2.0% by mass was obtained. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 1 and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured according to the physical property evaluation methods in Table 2, the average of the glass substrates with low reflection films formed on both surfaces in the same manner as in Example 5 under the condition of a pulling speed of 3.0 mm / sec. The transmittance was 97.6%, and the average transmittance was improved by 7.1% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflective film. Subsequently, when the film thickness was measured with a stylus type surface shape measuring instrument, it was 117 nm. Further, when the refractive index n was measured with an ellipsometer, it was n = 1.284, which was a satisfactory performance as a glass substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The frictional strength of the low reflective film is that the appearance after 3000 reciprocating frictions in the flannel cloth abrasion test is cloudy and partially peeled. It was inferior compared.

  This is a result of forming a film having inferior frictional strength because only the spherical colloidal silica was used without using colloidal silica (rod-like colloidal silica + spherical colloidal silica) having a specific particle size.

[Examples 9 to 12, Comparative Example 3 (example using tantalum alkoxide)]
Examples where tungsten alkoxide is used in Examples 9 to 12 and Comparative Example 3 are shown below.

Example 9
<Preparation of colloidal silica dispersion>
14.28 g of a rod-shaped colloidal silica IPA dispersion (manufactured by Nissan Chemical Industries, product number, IPA-ST-UP, solid content concentration 15.2 mass%, major axis 40 nm to 100 nm) is weighed into a three-neck flask with a capacity of 1000 ml. And IPA 106.14 g was added with stirring. Next, IPA264.2g was added to spherical colloidal silica (manufactured by Nissan Chemical Industries, Ltd., trade name, methanol silica sol, solid content concentration 30.2 mass%, particle size 10 nm to 20 nm) with stirring. By mixing, 401 g of colloidal silica dispersion, 401 g, was obtained.

Thus, in the colloidal silica dispersion, the mass ratio in terms of oxide between the rod-shaped colloidal silica and the spherical colloidal silica in terms of oxide (SiO ₂ ) is rod-shaped colloidal silica: spherical colloidal silica = 30: 70. Prepared. The solid content concentration is 1.8% by mass.

<Preparation of tantalum alkoxide dispersion>
Under a nitrogen stream, 8.20 g of tantalum pentachloride was collected in a 500 ml three-necked flask, and 255.10 g of methanol cooled on ice at 5 ° C. was added. To this was added 28% by mass sodium methoxide (Wako Pure Chemical Industries, Ltd.) and 17.66 g, and tantalum alkoxide (Ta (OCH ₂ (CH ₃ ) ₂ ) ₄ Cl) and by-product NaCl were mixed. 281 g of slurry was obtained.

Next, the mixture is refluxed at 65 ° C. for 16 hours in a nitrogen atmosphere, cooled to room temperature (about 22 ° C.), and then tantalum alkoxide (Ta (OCH ₂ (CH ₃ ) ₂ ) ₄ by pressure filtration while flowing nitrogen. Cl) and by-product NaCl were filtered off. The concentration of tantalum in the filtrate was 1.8% by mass in terms of Ta ₂ O ₅ .

<Preparation of coating solution for forming low reflection film>
While stirring at room temperature in a nitrogen atmosphere at room temperature in 401 g of the colloidal silica dispersion, 100.3 g of the tantalum alkoxide dispersion synthesized above was gradually added dropwise over 2 hours at room temperature to give a slightly milky white transparent liquid. Obtained. After mixing, the mixture is further refluxed at 60 ° C. for 8 hours under a nitrogen stream, so that the colloidal silica and the tantalum alkoxide are in a mass ratio of oxide equivalent to SiO ₂ : Ta ₂ O ₅ = 80: 20, that is, tantalum alkoxide. Was prepared so as to be 20% by mass in terms of oxide and used as a coating solution for forming a low reflection film.

<Production of glass substrate with low reflection film>
The surface of a glass substrate having a thickness of 3 mm and a size of 100 mm × 100 mm was wet-polished with alumina particles, washed with distilled water and then with IPA, and then heated to 100 ° C. and dried. When the contact angle of pure water was measured in order to check the surface condition, it showed a strong hydrophilic property with a contact angle of 5 ° or less and was clean.

  The washed glass substrate was immersed in the low reflection film forming coating solution and coated on both sides by a dipping method at a lifting speed of 4.0 mm / sec. It was dried at 50 ° C. for 30 minutes and further dried at 110 ° C. for 60 minutes. This is put into a baking furnace heated to 750 ° C., held for 150 seconds, taken out, rapidly cooled at room temperature, and a low reflection film having a light blue reflection color is formed on both sides. A glass substrate was obtained.

  FIG. 5 shows a drawing-substitute SEM photograph of the surface of the glass substrate with a low reflection film using tantalum alkoxide.

  It is an enlarged photograph by the SEM mirror of the low reflection film formed on the glass substrate using the said coating liquid for low reflection film formation. The ordered particles are silica, and the silica fine particles are bonded by tantalum oxide serving as a binder, and are a porous film containing a microvoid and a hard film.

<Evaluation of glass substrate with low reflection film>
FIG. 6 shows a transmittance curve of a glass substrate with a low reflection film using tantalum alkoxide.

  A low reflection film was formed on a glass substrate by the sol-gel method using the low reflection film forming coating solution. A transmittance curve of 1 is a transmittance curve of a glass substrate with a low reflection film applied to the glass substrate at a lifting speed of 3 mm / sec from the coating tank, and similarly, a transmittance curve of 2 is a lifting speed of 5 mm / sec. The transmittance curve of the glass substrate with a low reflection film is a transmittance curve of the glass substrate with a low reflection film at a pulling rate of 7 mm / sec. As the pulling speed increases, the film thickness increases, and the peak of the maximum transmittance shifts to the long wavelength side. Compared to the transmittance curve (represented by R) of a glass substrate that does not have a reference low-reflection film, the transmittance is improved in the entire wavelength region.

  When the average transmittance of the glass substrate with a low reflection film at the above-described pulling speed of 4.0 mm / sec was measured, the average transmittance was 97.9%, and the average transmittance of the glass substrate without the low reflection film was 90%. Compared to .5%, the average transmittance was improved by 7.4%. Next, when the film thickness was measured with a stylus type surface shape measuring instrument, it was 121 nm. Further, when the refractive index n was measured with an ellipsometer, the refractive index was n = 1.260, which was satisfactory as a glass substrate with a low reflection film.

Next, the friction strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. Although the appearance was somewhat haze, the color tone was unchanged, and the average transmittance was measured to be 97.5%, which was 0.4% lower than before the test. Moreover, when the contact angle of the pure water was measured, it was 8.0 ° and showed strong hydrophilicity.

Further, when the surface resistance value of this low reflective film-coated glass substrate after 30 days at 25 ° C. and 50% relative humidity was measured, it was 9.0 exp10 ⁸ Ω. cm, and it was confirmed that excellent antistatic performance was maintained.

Example 10
A colloidal silica dispersion containing colloidal silica having different shapes was prepared in the same manner as in Example 9. Next, the tantalum alkoxide dispersion prepared in Example 1 is added to the colloidal silica dispersion so that 40% by mass of tantalum alkoxide is contained in terms of oxide with respect to the mass of colloidal silica, that is, Ta ₂ A coating solution for forming a low reflection film having a solid content concentration of 1.9% by mass was prepared so that O ₅ : WO ₃ = 60: 40. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 9, and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured in accordance with the physical property evaluation methods shown in Table 2, a low reflective film-coated glass substrate was formed on both surfaces in the same manner as in Example 9 under the condition of a pulling speed of 3.4 mm / sec. The average transmittance was 97.1%, and the average transmittance was improved by 6.6% compared to the average transmittance 90.5% of the glass substrate not provided with the low reflective film. Next, the film thickness was measured with a stylus type surface shape measuring instrument and found to be 109 nm. Further, when the refractive index n was measured with an ellipsometer, n = 1.279, which was a satisfactory performance as a glass substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The appearance was slightly scratched and a haze was seen, but the film was not peeled off, and the average transmittance was measured to be 96.5%, which was 0.6% lower than that before the test. Further, when the contact angle of pure water was measured, it was 19.3 ° and showed strong hydrophilicity.

Further, when the surface resistance value of this low reflective film-coated glass substrate after 30 days was measured at room temperature (25 ° C.) and a relative humidity of 50%, it was 3.6 exp10 ⁸ Ω. cm, and it was confirmed that excellent antistatic performance was maintained.

Comparative Example 3
A colloidal silica dispersion containing colloidal silica having different shapes was prepared in the same manner as in Example 9. Next, the tantalum alkoxide dispersion prepared in Example 5 is added to the colloidal silica dispersion so that the tantalum alkoxide is contained in an amount of 50% by mass in terms of oxide with respect to the mass of the colloidal silica, that is, SiO _2. : Ta ₂ O ₅ = 50: 50, and a coating solution for forming a low reflection film having a solid content concentration of 1.7% by mass was prepared. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 9, and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured in accordance with the physical property evaluation methods in Table 2, the average transmittance of the film-coated substrate formed on both surfaces in the same manner as in Example 9 under the condition of a pulling rate of 3.0 mm / sec is The glass substrate was 2.7% higher than the glass substrate before the film was formed, and it was 93.3%, and the desired performance as a glass substrate with a low reflection film could not be obtained.

  Next, the film thickness was measured with a stylus type surface shape measuring instrument to be 107 nm. Moreover, when the refractive index of the film was measured with an ellipsometer, it was n = 1.310, and the refractive index was higher than desired.

  This is a result of the content of the tantalum compound with respect to the colloidal silica deviating from the preferable content range of 5% by mass to 40% by mass in terms of oxide.

Example 11
After diluting the IPA dispersion of rod-shaped colloidal silica used in Example 9 (IPA-ST-UP, manufactured by Nissan Chemical Industries, Ltd., solid concentration 15.2% by mass, major axis 40 nm to 100 nm) with IPA, tantalum alkoxide was obtained. SiO ₂ : Ta ₂ O ₅ = 80: 20 in terms of mass in terms of oxide, that is, tantalum alkoxide is prepared to be 20% by mass in terms of oxide, and low reflection with a solid content concentration of 2.0% by mass A coating solution for film formation was obtained. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 1 and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured according to the physical property evaluation methods in Table 2, the average of the glass substrates with low reflection films formed on both surfaces in the same manner as in Example 9 under the condition of a pulling rate of 3.0 mm / sec. The transmittance was 96.9%, and the average transmittance was improved by 6.5% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflective film. Subsequently, when the film thickness was measured with a stylus type surface shape measuring instrument, it was 115 nm. Further, when the refractive index n was measured with an ellipsometer, it was n = 1.294, which was a satisfactory performance as a glass substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The frictional strength of the low-reflection film is that the appearance after 3000 reciprocating frictions in the flannel cloth abrasion test is cloudy and partially peeled. It was inferior compared.

  This is a result of forming a film having inferior frictional strength because the colloidal silica (rod-like colloidal silica + spherical colloidal silica) having a different specific particle size shape is not used but only the rod-like colloidal silica is used.

Example 12
The IPA dispersion of spherical colloidal silica used in Example 9 (manufactured by Nissan Chemical Industries, Ltd., trade name, methanol silica sol, solid content concentration 30.2 mass%, particle size 10 nm to 20 nm) was diluted with IPA, and then tantalum. The alkoxide was prepared in such a way that the oxide ratio in terms of mass ratio was SiO ₂ : Nb ₂ O ₅ = 80: 20, that is, the tantalum alkoxide was 20 mass% in terms of oxide, and the solid content concentration was 2.0 mass%. A coating solution for forming a low reflection film was obtained. The low reflection film forming coating solution was applied to a glass substrate in the same procedure as in Example 9, and heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured according to the physical property evaluation methods in Table 2, the average of the glass substrates with low reflection films formed on both surfaces in the same manner as in Example 9 under the condition of a pulling rate of 3.0 mm / sec. The transmittance was 97.0%, and the average transmittance was improved by 6.5% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflective film. Then, the film thickness was measured with a stylus type surface shape measuring instrument and found to be 113 nm. Further, when the refractive index n was measured with an ellipsometer, n = 1.307, which was a satisfactory performance as a glass substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The frictional strength of the low reflective film is that the appearance after 3000 reciprocating frictions in the flannel cloth abrasion test is cloudy and partly peeled off, and compared to the glass substrates with the low reflective film of Examples 5 and 6. It was inferior in strength.

  This is a result of forming a film having inferior frictional strength because only the spherical colloidal silica was used without using colloidal silica (rod-like colloidal silica + spherical colloidal silica) having a specific particle size.

Comparative Example 4
In the same manner as in Example 1, a colloidal silica dispersion containing colloidal silica having a different shape was prepared, applied to a glass substrate in the same procedure as in Example 1, and then heated and fired to obtain a glass substrate with a low reflection film. . Unlike Examples 1-12, a metal oxide is not contained in a low reflection film.

  Subsequently, the glass substrate with a low reflection film was evaluated in the same manner as in Example 1.

  When the physical property values were measured according to the physical property evaluation method, the average transmittance was 97.4%, which was 7.6% higher than the glass substrate before the low reflective film was provided. The frictional strength of the low reflective film is cloudy in appearance after 3000 reciprocating rubs according to the nell cloth abrasion test, haze is increased by 5.7% compared to before the test, and there is partial peeling and inferior frictional strength. It was.

  The glass substrate with a low reflection film of Comparative Example 4 was inferior in film strength, poor in durability, and could not withstand practical use.

Comparative Example 5
In the same manner as in Example 1, a colloidal silica dispersion containing colloidal silica having a different shape was prepared, and TEOS was added so that the mass ratio with respect to the colloidal silica was 20% by mass. After coating on a glass substrate in the same procedure as in Example 1, it was heated and fired to obtain a glass substrate with a low reflection film. Unlike Examples 1-12, a metal oxide is not contained in a low reflection film.

  Subsequently, the glass substrate with a low reflection film was evaluated in the same manner as in Example 1.

  When the physical property values were measured according to the physical property evaluation method, the average transmittance was 94.6%, which was 4.1% higher than that of the glass substrate before the low reflective film was provided. The frictional strength of the low reflective film is cloudy in appearance after 3000 reciprocating rubs according to the nell cloth abrasion test, haze is increased by 5.7% compared to before the test, and there is partial peeling and inferior frictional strength. It was.

Comparative Example 6
Only the tungsten alkoxide solution prepared in Example 1 was applied to a glass substrate and heated and fired in the same manner as in Example 1 to form a film, thereby obtaining a glass substrate with a tungsten oxide film. A cloudy ground glass substrate having a haze of 46.8% was obtained.

Comparative Example 7
When only the niobium alkoxide solution prepared in Example 5 was applied to a glass substrate and heated and fired in the same manner as in Example 5 to form a film and measured with an ellipsometer to obtain a glass substrate with a niobium oxide film, the film was refracted. The rate was 1.90, and the average transmittance was lower than that of a glass substrate on which a low reflective film was not formed.

Comparative Example 8
Only the tantalum alkoxide solution prepared in Example 9 was applied to a glass substrate and heated and fired in the same manner as in Example 9 to form a film, thereby obtaining a glass substrate with a tantalum oxide film. The refractive index of the film was 1.86, and the average transmittance was lower than that of the glass substrate on which the low reflection film was not formed.

(result)
The evaluation results are shown in Table 3.

  The glass substrate with a low reflection film on which the low reflection film of the present invention is formed is excellent in hydrophilicity and antifouling properties, has antistatic properties, and is hardly contaminated. In particular, as shown in Table 3, the substrates with low reflective films of Examples 1, 2, 5 and 6 and Examples 9 and 10 showed high average transmittance, and the results of film strength tests by flannel abrasion tests. It showed excellent durability without deteriorating the average transmittance.

  The magnifications of the SEM photographs in FIGS. 1, 3, and 5 are the same.

[Addition of water to coating solution]
The coating liquid for forming a low reflection film of Examples 1, 5, and 9, the coating liquid of Comparative Example 4 containing only colloidal silica having a different shape, and the coating liquid of Comparative Example 5 in which TEOS was added to a dispersion of colloidal silica having a different shape. Water was added to the coating solution to which water was added, and precipitation of solid content over time was observed.

  Specifically, 10.0% by mass of pure water was added to the coating solutions for forming a low reflection film of Examples 1, 5, 9 and Comparative Examples 4, 5, and stored at room temperature (20 ° C.). The presence or absence of white turbidity and solid content was observed.

  The low-reflective film-forming coating liquid of Example 1 in which tungsten alkoxide is added to two types of colloidal silicas (rod-shaped colloidal silica + spherical colloidal silica) in different ratios, and the niobium alkoxide is added in the low-reflective film of Example 5 The coating solution for forming a low reflection film of Example 9 to which tantalum alkoxide was added as a forming coating solution was added 10.0% by mass of pure water to the coating solution of Comparative Example 4 containing only two types of colloidal silica having different shapes. No change was observed after 90 days.

  In comparison, the coating solution of Comparative Example 5 in which TEOS was added to two types of colloidal silica dispersions having different shapes was added with 10% pure water, and after 1 week, it gelled and was not used as a coating solution. It was possible.

  Next, 10.0% by mass of pure water was added, and the coating solution for forming a low reflection film prepared in Examples 1, 5 and 9 after 90 days (respectively, Examples 13, 14, and 15) was used. In the same manner as in Examples 1, 5, and 9, coating and film formation were performed on a glass substrate, and physical properties of the obtained glass substrate with a low reflection film were evaluated.

Example 13
A coating solution for forming a low reflection film in which a tungsten alkoxide dispersion is added to a colloidal silica dispersion containing colloidal silica having different shapes is prepared in the same manner as in Example 1, and then pure water is added to the total weight of the liquid. 10.0 mass% was added and it left still for 90 days under room temperature (20 degreeC). The coating solution for forming a low reflection film after standing was applied to a glass substrate in the same procedure as in Example 1, and then heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured according to the physical property evaluation methods in Table 2, a low reflective film-coated glass substrate was formed on both surfaces in the same manner as in Example 1 under the condition of a pulling speed of 3.4 mm / sec. The average transmittance was 97.7%, and the average transmittance was improved by 7.2% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflective film. Next, the film thickness was measured with a stylus type surface shape measuring instrument and found to be 112 nm. Further, when the refractive index n was measured with an ellipsometer, it was n = 1.285, and satisfactory performance was obtained as a glass substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The appearance was slightly scratched and a haze was seen, but the film was not peeled off, and the average transmittance was measured to be 96.8%, which was 0.9% lower than that before the test. Further, when the contact angle of pure water was measured, it was 15.2 °, indicating strong hydrophilicity.

Example 14
A coating solution for forming a low reflection film obtained by adding a niobium alkoxide dispersion liquid to a colloidal silica dispersion liquid containing colloidal silica having different shapes was prepared in the same manner as in Example 5, and then pure water was added to the total weight of the liquid. 10.0 mass% was added and it left still for 90 days under room temperature (20 degreeC). The coating solution for forming a low reflection film after standing was applied to a glass substrate in the same procedure as in Example 1, and then heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured according to the physical property evaluation methods shown in Table 2, a low reflective film-coated glass substrate was formed on both surfaces in the same manner as in Example 5 under the condition of a pulling rate of 3.0 mm / sec. The average transmittance was 96.8%, and the average transmittance was improved by 6.3% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflective film. Next, the film thickness was measured with a stylus type surface shape measuring instrument and found to be 108 nm. Further, when the refractive index n was measured with an ellipsometer, it was n = 1.277, and satisfactory performance was obtained as a glass substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The appearance was slightly scratched and a haze was seen, but the film was not peeled off and the average transmittance was measured to be 96.1%, which was 0.7% lower than before the test. Further, when the contact angle of pure water was measured, it was 13.6 °, indicating strong hydrophilicity.

Example 15
A coating solution for forming a low reflection film obtained by adding a tantalum alkoxide dispersion liquid to a colloidal silica dispersion liquid containing colloidal silica having different shapes was prepared in the same manner as in Example 9, and then pure water was added to the total weight of the liquid. 10.0 mass% was added and it left still for 90 days under room temperature (20 degreeC). The low reflection film forming coating solution after standing was applied to a glass substrate in the same procedure as in Example 9, and then heated and fired to obtain a glass substrate with a low reflection film.

  When the physical property values were measured according to the physical property evaluation methods in Table 2, a low reflective film-coated glass substrate was formed on both surfaces in the same manner as in Example 1 under the condition of a pulling speed of 3.4 mm / sec. The average transmittance was 96.6%, and the average transmittance was improved by 6.1% compared to the average transmittance of 90.5% for the glass substrate not provided with the low reflective film. Subsequently, when the film thickness was measured with a stylus type surface shape measuring instrument, it was 115 nm. Further, when the refractive index n was measured with an ellipsometer, it was n = 1.264, and satisfactory performance was obtained as a glass substrate with a low reflection film.

Next, the frictional strength of this coating was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to the pad by a wear tester. The friction strength was evaluated. The appearance was slightly scratched and haze was visible, but the film was not peeled off and the average transmittance was measured to be 95.8%, which was 0.8% lower than before the test. Further, when the contact angle of pure water was measured, it was 14.4 ° and showed strong hydrophilicity.

The results are summarized in Table 4. 10.0% by mass of pure water was added to a glass substrate with a low reflection film formed on both surfaces with the low reflection film forming coating liquids of Examples 1, 5, and 9 in which pure water was not added. In addition, the results of physical property evaluation of the glass substrate with a low reflection film formed by forming the low reflection film on both surfaces with the coating liquid for forming the low reflection film of Examples 13, 14, and 15 after 90 days have passed are as follows. No. 9 was a result not inferior to the substrate with a low reflection film.

By adding water, it is easy to adjust the viscosity of the coating solution for forming a low reflection film, and the choice of coating methods that can be handled increases. In addition, the safety against fire tends to increase.

  By the method for forming a low reflection film of the present invention, a low reflection member having a durable low hydrophilic film having a low refractive index formed on the surface was obtained. The low reflection member of the present invention is a cover glass for solar cells, an optical material such as a lens, an image display surface such as a cathode ray tube or a liquid crystal display device, a glass plate or transparent glass such as a window or a showcase, a skylight material, a water heater or a lighting fixture. It can be used in a wide range of fields that require hydrophilicity, antifouling properties, and low reflection antistatic properties such as plastics. Moreover, since it is excellent in the transmittance | permeability not only in an ultraviolet to visible light and a wavelength range but a near-infrared wavelength range, it is especially useful especially as a cover glass for solar cells.

  Specifically, the low reflection member formed on the surface of the low reflection film of the present invention has an effect of improving the illuminance due to high average transmittance as a protection member for the luminaire, preventing reflection of the windshield, When used for solar cell cover glass, the optical characteristics can be adjusted, the light reception efficiency is improved by improving the average transmittance due to the effect of forming a low reflection film, and in particular, the power generation efficiency is improved. It is used very suitably as a cover glass for solar cells.

  In addition, the low reflection member formed with the low reflection film of the present invention is excellent in durability without deterioration of the strength of the low reflection film even when the substrate is a glass plate, and is used as a cover glass for solar cells. Ideal for.

Claims (16)

At least one selected from the group consisting of silica fine particles and tungsten oxide, niobium oxide, tantalum oxide, titanium oxide, zirconium oxide, tin oxide, aluminum oxide, hafnium oxide, chromium oxide, molybdenum oxide, cerium oxide, and lanthanum oxide. A binder composed of a metal oxide is contained, and the content ratio of the binder composed of the metal oxide to the silica fine particles is 5% by mass or more and 40% by mass or less, and the refractive index is 1.20 or more and 1.40 or less. A low reflective film characterized by the above. The silica fine particles are mainly rod-like silica fine particles having a major axis of 5 nm to 100 nm and spherical silica fine particles having a particle size of 5 nm to 50 nm as observed with a scanning electron microscope. 2. The low reflection film according to 1. 3. The low reflection film according to claim 2, wherein the mass ratio of the rod-like silica particles and the spherical silica particles is rod-like silica particles: spherical silica particles = 20: 80 to 80:20. 4. The low oxide according to claim 1, wherein the metal oxide is at least one metal oxide selected from the group consisting of tungsten oxide, niobium oxide, and tantalum oxide. 5. Reflective film. A low-reflection member, wherein the low-reflection film according to any one of claims 1 to 4 is formed on a transparent substrate surface. 6. The low reflection member according to claim 5, wherein the transparent substrate is a glass plate, and an average transmittance in a light wavelength range of 380 nm to 1200 nm is 95% or more. The peak of the maximum value of a light transmittance curve is 500 nm or more and 900 nm or less, The low reflection member of Claim 5 or Claim 6 characterized by the above-mentioned. A solar cell cover glass comprising the low reflection member according to claim 5. A dispersion containing a metal compound of at least one metal selected from the group consisting of tungsten, niobium, tantalum, titanium, zirconium, tin, aluminum, hafnium, chromium, molybdenum and rare earth is added to the dispersion containing colloidal silica. A coating solution for forming a low reflection film is applied to a substrate to form a coating film, and then heated and fired to form colloidal silica as silica fine particles and a metal compound as a metal oxide to form a low reflection film. Method. Colloidal silica is 90% or more of the total number of rod-shaped colloidal silica having a major axis of 5 nm or more and 100 nm or less and spherical colloidal silica having a particle diameter of 5 nm or more and 50 nm or less as observed by a scanning electron microscope. The method according to claim 9, wherein the content of the metal compound is 5% by mass or more and 40% by mass or less in terms of oxide. The method according to claim 10, wherein the mass ratio of the rod-shaped colloidal silica to the spherical colloidal silica is rod-shaped silica colloidal silica: spherical colloidal silica = 20: 80 to 80:20. The method according to claim 9, wherein the metal compound is a metal compound of at least one metal selected from the group consisting of tungsten, niobium and tantalum. A low reflection member in which a low reflection film having a refractive index of 1.20 or more and 1.40 or less is formed on the transparent substrate surface by the method according to any one of claims 9 to 12. The low reflection member according to claim 13, wherein the transparent substrate is a glass plate, and an average transmittance in a wavelength range of 380 nm to 1200 nm is 95% or more. The peak of the maximum value of a light transmittance curve is 500 nm or more and 900 nm or less, The low reflection member of Claim 13 or Claim 14 characterized by the above-mentioned. The cover glass for solar cells which consists of a low reflection member of any one of Claim 13 thru | or 15.

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