JP2013121893A - Method of producing glass with low reflective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a glass with a low reflective film, wherein: the method can solves the problem that when the low reflective film is formed on a soda lime silicate glass plate through a sol-gel method, the low reflective film is eroded due to sodium ion elution; and the method can provide the low reflective film that has low refractive index, is excellent in optical properties and has robustness.SOLUTION: A coating liquid for forming a low reflective film has an organic solvent containing a colloidal silica and a tungsten compound, wherein the tungsten compound accounts for 5 to 40 mass% of the mass of colloidal silica on an oxide conversion basis. A method of producing a glass with the low reflective film includes: a first step of coating the coating liquid on a soda lime silicate glass plate to form a coated film; a second step of burning and curing the coated film formed on the soda lime silicate glass to obtain the low reflective film; and a third step of cleaning, with water, the soda lime silicate glass on which the coated film is burned and cured.

Description

  The present invention relates to a method for producing a glass with a low reflection film in which a low reflection film is formed on the surface of soda lime silicate glass, which is a glass containing sodium. The glass with a low reflection film according to the method for producing a glass with a low reflection film of the present invention is used for an automobile glass or a protective member of a lighting fixture, and is particularly preferably used for the production of a cover glass for a solar cell.

  The low-reflection film prevents the surface reflection of the substrate, eliminates the loss of light transmittance (hereinafter sometimes simply referred to as transmittance) due to surface reflection, and improves the transmittance of a transparent substrate such as glass. In addition, it is formed on the substrate surface. The low-reflection film is not limited to the lens surfaces of optical devices such as still cameras, video cameras, and liquid crystal projectors, but is formed on general-purpose solar cell cover glass, architectural window glass, showcases, and automotive window glass. It is going to be done. By forming a low-reflection film on the glass plate, the solar cell cover glass has an effect of improving the output of the solar cell by improving the transmittance, and preventing the reflection of the architectural window glass, showcase or automobile window glass. It is done.

For example, Patent Document 1 discloses at least one component selected from the group consisting of silica sol (a) having a particle size of 5 to 30 nm, a hydrolyzate of alkoxysilane, a hydrolyzate of metal alkoxide, and a metal salt. (B) and (a) 100 parts by weight of SiO _2, a coating solution containing (b) in an organic solvent at a ratio of 10 to 50 parts by weight in terms of a metal oxide, A low-refractive-index antireflection film obtained by curing after coating is disclosed. Patent Document 2 discloses a method for depositing a porous antireflection layer by a sol-gel method, using a titanium-containing precursor, and adding particles, particularly nanoparticles, to a sol-gel solution. A method of depositing the prevention layer is disclosed.

  However, there are the following three problems in forming a low reflection film on the above-mentioned general-purpose product.

  The first problem is that optical glass, alkali-free glass and the like are expensive and need to be manufactured at a high temperature, and for general-purpose products that are required to be inexpensive, the roll-out method and the float method are industrially used. It is unavoidable to use a soda rim silicate glass plate having a sodium content that is inexpensive and produced in large quantities. The second problem is that, when using a sodalim silicate glass plate, the low reflective film is attacked by the dissolved sodium content due to the action of moisture and carbon dioxide in the atmosphere. A third problem is that it is necessary to manufacture a glass with a low reflection film in a large area by a simple method.

The first problem will be specifically described. Glass materials such as lenses and prisms used in optical instruments are usually selected from high-purity raw materials that do not contain impurities, and the composition adjustment is performed. Optical glass such as dispersion flint glass, low refractive index and low dispersion crown glass, and white glass having high light transmittance by reducing the content of components such as iron ions and sodium ions are used. The liquid crystal display substrate uses a general formula MO-Al ₂ O ₃ —SiO ₂ (M is divalent such as calcium) in which calcium and aluminum are used instead of sodium as a glass raw material in order not to attack the thin film transistor and the Cr film. Alkali-free glass having an alkali content represented by less than 0.5% by mass has been used. However, these glasses are difficult to use in the above-mentioned general-purpose products because the raw materials are more expensive than soda lime silicate glasses, and the melting temperature is high and the production is difficult and expensive.

  When a low-reflection film is formed as it is on a soda lime silicate glass plate that is mainly used for general-purpose products, the low-reflection film is affected by the sodium content. As a countermeasure for the second problem, the sodium content is usually eluted as the base of the low-reflection film. An undercoat film is formed as an alkali passivation film for prevention.

Such an undercoat film is, for example, a wet coating method typified by a sol-gel method, colloidal silica, tetraethoxysilane (hereinafter sometimes abbreviated as TEOS), methyltriethoxysilane (hereinafter abbreviated as MTES). The silica coating solution containing the above may be applied and coated on the surface of the soda lime silicate glass plate and then fired and baked, or by the dry coating method typified by vapor deposition and sputtering on the surface of the soda lime silicate glass plate. It is formed. Such silica-coated film, those containing SiO _{2 mainly,} SiO 2 -ZrO _{2 combination,} SiO 2 -TiO ₂ combinations, are known by polysilazane.

  For example, Patent Document 3 discloses an organic-inorganic hybrid coating material that prevents the elution of sodium components from glass coated on the surface by coating and curing an organic-inorganic hybrid substance (precursor) containing an organic substituent and a siloxane bond. Is disclosed.

  Moreover, as a method of suppressing alkali elution from a soda lime glass silicate glass plate without using an undercoat film, a method of reducing the sodium content in advance by contacting or washing the surface with an acid, the surface sodium ions as lithium ions, etc. The method of exchange is mentioned. In addition, a method of attaching a metal thin film such as tin or zinc to the surface of soda lime silicate glass can be mentioned. For example, if the soda lime silicate glass plate is manufactured with a float plate that unfolds and flushes the glass raw material on the molten tin bath, the bottom surface that comes in contact with the molten tin will have an effect of preventing sodium elution due to the adhesion of tin. It has been known. However, the top surface that does not come into contact with the molten tin is free from tin adhesion, so that sodium is easily eluted, and the low-reflection film is easily affected.

  In any case, when a functional thin film, particularly a metal thin film, is formed directly on a soda lime silicate glass plate that has not been surface-treated, the sodium content is diffused by heat, high humidity, or the surface is wet. Due to the elution, there was a problem that the thin film was damaged and desired characteristics could not be obtained.

  Next, the third problem will be specifically described. On the surface of a glass material such as a lens and a prism used in an optical apparatus, a multi-coated low reflection film is formed by a multilayer film in which different metal oxide thin films are stacked. Multi-coating is performed by vapor deposition, etc., and requires a vacuum film-formation device. Mass production of glass with a low-reflection film by attaching a multilayer film to a general-purpose product using a large-scale vacuum film-formation device Is expensive, and it is difficult and difficult to precisely control the thickness of each thin film.

  A single-layer low-reflection film is simpler to form on a substrate than a multilayer film, and has a single-layer and low-refractive-index low-reflection film that is advantageous for easily producing a low-reflection member with a large area at low cost. An attached glass is obtained.

  For example, in a single-layer low-reflection film, a method of lowering the refractive index of the film by taking air having a refractive index of 1 inside the film as microvoids (voids) or metapores has been attempted. A membrane and a silica membrane using hollow silica fine particles have been studied.

  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 by. 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 4, 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 5 includes silica and 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 , or WO A composite oxide sol in which a composite oxide colloidal particle having an average particle size of 5 nm to 300 nm and an inorganic oxide other than silica selected from ₃ is dispersed in water and / or an organic solvent, the colloidal particle Is characterized in that part of elements 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. A composite 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.

  However, the composite oxide sol described in Patent Document 4 or Patent Document 5 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.

Japanese Patent Laid-Open No. 08-122501 JP 2010-134462 A JP 2008-273783 A International Patent Publication No. WO00 / 37359 JP 2006-117526 A

  There is a need for inexpensive low-reflection coated glass for solar cell cover glass, architectural glass, showcases and automotive glass.

When the low-reflection film or the undercoat film is a film containing a siloxane bond, sodium ions are generated from the soda lime silicate glass plate over time by the action of water or carbon dioxide gas during film formation by heating and baking or outdoors. It dissolves and becomes sodium hydroxide by the action of moisture in the atmosphere, and siloxane bonds are invaded by the following reaction to produce sodium silicate (Na ₂ SiO ₃ ), which becomes a water glass and dissolves.

SiO ₂ + 2NaOH → Na ₂ SiO ₃ + H ₂ 0
In particular, when the low reflective film is a porous film and the film has a low refractive index due to the low refractive index air taken into the void, the silica content becomes sodium silicate (Na ₂ SiO ₃ ). As a result, the film becomes brittle, the strength is lowered, voids in the film are clogged, the refractive index of the film is increased, the effect of low reflection is lost, and the low reflection film is even peeled off. In addition, titanium alkoxides and zirconium alkoxides, which are widely used as binders for silica fine particles in the low reflection film or undercoat film, have a problem that they are weak against elution of sodium ions.

  The present invention solves the above-mentioned problem that a low reflection film is affected by elution of sodium ions when a low reflection film is formed on a soda lime silicate glass plate by a sol-gel method. The present invention provides a method for producing a glass with a low reflection film that provides a reflection film.

  In addition, the method for producing a glass with a low reflection film according to the present invention facilitates film formation on a large area that stably forms a low reflection film capable of obtaining a sufficient low reflection effect with a single layer film on a soda lime silicate glass plate. Provide a simple method. In order to stably form a low reflection film, a coating liquid for forming a low reflection film that is excellent in liquid life without generation of solid content over time is desired.

  That is, this invention consists of the following inventions 1-8.

  In an actual production site, it is usually not washed immediately after forming a functional thin film on glass. In particular, when a metal thin film is formed with a vacuum device, the film surface is sufficiently clean, and there is a move, shipment, acceptance, etc. when entering the next process, unless there are special circumstances such as taking time. Do not wash. Further, even when an undercoat film as an alkali passivation film for preventing elution of sodium was formed, cleaning was not performed immediately after the film formation.

In the method for producing a glass plate with a low reflection film according to the present invention, when a low reflection film is formed on a soda lime silicate glass plate, the low reflection film is not affected by elution of sodium ions. Thus, sodium ions and tungsten alkoxide were reacted to form water-soluble sodium tungstate (Na ₂ WO ₄ ), so that sodium ions eluted by calcination were quickly removed by washing with water.

  The low-reflection film obtained in the method for producing a glass plate with a low-reflection film of the present invention is a performance decrease such as an increase in refractive index or a decrease in film strength, dissolution or clogging due to elution of sodium ions by moisture and carbon dioxide in the atmosphere. It was a low reflection film excellent in moisture resistance in which the occurrence of defects such as the above was suppressed.

As described above, in the method for producing a glass with a low reflection film of the present invention, the above-described problems caused by elution of sodium ions from the soda lime silicate glass plate are suppressed by the action of moisture and carbon dioxide gas, and the moisture resistance is excellent. The low reflection film was obtained by using a coating liquid for forming a low reflection film obtained by adding a tungsten compound to colloidal silica. If the water is washed immediately after firing, the excess sodium content including water-soluble sodium tungstate (Na ₂ WO ₄ ) generated during firing of the low-reflection film is washed away, so that the moisture resistance of the subsequent low-reflection film Improved. In addition, sodium tungstate (Na ₂ WO ₄ ) is washed away by washing, resulting in a more porous film, and the film has a lower refractive index, so that the transmittance immediately after film formation is improved.

  Moreover, the robust film excellent in moisture resistance was obtained by using colloidal silica of a specific shape and particle diameter for colloidal silica.

[Invention 1]
For forming a low reflection film comprising colloidal silica and a tungsten compound in an organic solvent, wherein the tungsten compound is contained in the range of 5% by mass or more and 40% by mass or less in terms of oxide with respect to the mass of the colloidal silica. Apply the coating solution
A first step of applying a soda lime silicate glass plate to form a coating;
A second step of obtaining a low reflection film by baking and curing a film formed on a soda lime silicate glass plate;
A third step of washing the soda lime silicate glass plate with the coating fired and cured,
A method for producing a glass with a low reflection film.

[Invention 2]
The method of Invention 2, wherein the colloidal silica is a rod-like 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 as observed by a scanning electron microscope.

[Invention 3]
The method of Invention 2, wherein the mass ratio of rod-shaped colloidal silica: spherical colloidal silica is 20:80 to 80:20.

[Invention 4]
The tungsten compound is W (OR ¹ ) _6-n X _n
(N is 1 ≦ n ≦ 6, R ¹ is each independently a 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, s-amyl group, 2-ethylhexyl group, methoxyethyl group, methoxypropyl group, ethoxymethyl group, ethoxyethyl group, ethoxypropyl group or phenyl group, X Is a halogen atom.)
The method of inventions 1-3.

[Invention 5]
The tungsten compound is W (OR ² ) _6-n Cl _n
(N is 1 ≦ n ≦ 6, R ² is each 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.
The method of invention 1-4 which is.

[Invention 6]
The tungsten compound is converted into the following reaction WCl ₆ + 5Na (OR ² ) → W (OR ² ) ₅ Cl + 5NaCl in an isopropyl alcohol solvent.
(R ² is each independently a 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.)
In synthesized ^{W (OR} ₂₎ 5 is Cl, the method of the invention 1-5.

[Invention 7]
The method according to any one of Inventions 1 to 6, wherein the low reflective film has a refractive index of 1.20 or more and 1.40 or less.

[Invention 8]
The cover glass for solar cells with a low reflection film obtained by the method of invention 1-7.

  In addition, the method of invention 1-8 is effective also when forming a low reflection film in the soda-lime silicate glass plate in which the said undercoat film is formed.

  According to the present invention, when forming a low-reflection film on a soda lime silicate glass plate by a sol-gel method, the problem that the low-reflection film is affected by elution of sodium ions is solved, and a glass with a low reflection film excellent in moisture resistance is obtained. A manufacturing method was provided.

  That is, in the method for producing a glass with a low reflection film according to the present invention, since the low reflection film is not affected by elution of sodium ions, the sodium content eluted by baking at the time of forming the low reflection film is quickly removed by washing with water.

  Further, in the method for producing a glass with a low reflection film of the present invention, by using a coating solution for forming a low reflection film in which a tungsten compound is added to colloidal silica, an alkali elution and low reflection film at the time of baking soda lime silicate glass plate is used. Thus, a glass with a low reflection film having a low reflection film having a low refractive index and excellent moisture resistance was obtained.

  In addition, according to the method for producing a glass with a low reflection film of the present invention, it is easy to stably form a film on a large area to form a low reflection film capable of obtaining a sufficient low reflection effect with a single layer film on a soda lime silicate glass plate. Provided. In order to stably form a low reflection film, a coating liquid for forming a low reflection film having excellent liquid life without generation of a solid content with time was used.

It is a drawing substitute SEM (scanning electron microscope) photograph of the reflective film of the soda-lime silicate board with a low reflective film. It is the transmittance | permeability curve of the soda-lime silicate glass plate with a low reflection film.

1. The manufacturing method of the glass plate with a low reflection film Invention 1 of the present invention comprises colloidal silica and a tungsten compound in an organic solvent, and the tungsten compound is 5% by mass or more in terms of oxide with respect to the mass of the colloidal silica. A coating solution for forming a low reflection film, contained in a range of 40% by mass or less,
A first step of applying a soda lime silicate glass plate to form a coating;
A second step of obtaining a low reflection film by baking and curing a film formed on a soda lime silicate glass plate;
A third step of washing the soda lime silicate glass plate with the coating fired and cured,
And a method for producing a glass with a low reflection film.

Usually, if the low-reflection film is a film containing a siloxane bond, sodium ions are eluted from the soda lime silicate glass plate during film formation by heating and baking or due to the action of water outdoors, and the following reaction As a result, the siloxane bond is eroded, soda silicate (Na ₂ SiO ₃ ) is produced and dissolved as water glass, the surface of the low reflection film or the glass plate is eroded, and the low reflection film is no longer used or peeled off.

SiO ₂ + 2NaOH → Na ₂ SiO ₃ + H ₂ O
However, as described above, when a low-reflective film-forming coating solution in which a tungsten compound is added to colloidal silica is used to form a low-reflective film on a soda-lime silicate glass plate, soda-lime silicate is formed during firing. Sodium ions eluted from the glass plate react with tungsten to form sodium tungstate (Na ₂ WO ₄ ). Na ₂ WO ₄ was water-soluble, and was washed with water after firing. Na ₂ WO ₄ and excess sodium ions were washed away, and a low reflection film excellent in moisture resistance was obtained. By washing, Na ₂ WO ₄ is washed away, resulting in a more porous film with a lower refractive index, and tungsten oxide (WO ₃ ) is bonded to silica as a binder to obtain a porous film that is porous but hard. It was.

  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 substrate surface in order to prevent reflection of light on the substrate surface. is there. The refractive index is a measured value obtained by spectroscopic ellipsometry measurement using an ellipsometer.

  Moreover, the average transmittance and the average reflectance were measured using a spectrophotometer to measure the light wavelength range, 380 nm to 1200 nm transmittance and reflectance, and the average transmittance and average reflectance in the wavelength range were calculated. Value. The transmittance curve is a curve obtained by continuously plotting measured values of transmittance with a spectrophotometer in a certain wavelength region.

2. Next, a coating solution for forming a low reflection film used in the method for producing a glass with a low reflection film according to the present invention will be described.

  The coating liquid for forming a low reflection film is a liquid for coating on the surface of a substrate to form a low reflection film on the substrate. 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 formed with a low reflective film on the surface has a higher transmittance as the refractive index is lower, the light receiving efficiency of the solar cell is improved, and the energy conversion efficiency from light to electricity is increased. .

  The low reflection type coating solution used in the method for forming a low reflection film of the present invention contains colloidal silica and a tungsten compound.

In the low reflection film obtained by applying and baking the coating liquid for forming the low reflection film on a soda lime silicate glass plate, fine voids are formed by bonding WO ₃ to the silica fine particles. It is generated when the content of the tungsten compound is less than 5% by mass in terms of oxide (WO ₃ ) with respect to the mass of the colloidal silica (the mass of the solid content, hereinafter the same) in the coating solution for forming the low reflection film. There are few voids and a low refractive index film cannot be obtained. When the content of the tungsten compound is more than 40% by mass in terms of oxide (WO ₃ ), the resulting film has a high refractive index and is unlikely to be a low reflection film. Preferably, they are 10 mass% or more and 30 mass% or less.

In the method for producing a glass plate with a low reflection film of the present invention, WO ₃ is at the interface of silica fine particles, and the silica fine particles are bonded as a binder. In addition, a binder means what is combined.

  Moreover, when mass-producing the low reflection member which formed the low reflection film on the base-material surface, the liquid stability of the coating liquid for low reflection film formation is important.

2.1. Preparation of coating liquid for forming low reflection film The preparation of the coating liquid for forming low reflection film is characterized by mixing, for example, a dispersion containing a tungsten compound and a dispersion containing colloidal silica. The colloidal silica is preferably at least two types of colloidal silica having different shapes.

  In preparing the colloidal silica dispersion and the tungsten compound dispersion, the alcohol in the colloidal silica dispersion is methanol, ethanol, n-propanol or IPA, ester as the alcohol in the colloidal silica dispersion. Is ethyl acetate, an organic solvent such as acetone is used as the polar solvent, and an alcoholic organic solvent such as methanol, ethanol, n-propanol, or IPA is used in the dispersion of the tungsten compound, and these are used in combination. May be. In order to promote the hydrolysis of colloidal silica and to quickly form a low-reflection film during the condensation of colloidal silica during firing, or to reduce the risk of fire, water, preferably pure water, is added. Also good.

2.2 Coating method and firing method of coating system for forming low reflection film Next, in the method for producing a glass plate with a low reflection film of the present invention, a coating method for coating liquid for forming a low reflection film and a low reflection film formation after coating The firing method will be described.

  It is difficult to form a film having several kinds of compositions on the substrate surface by a single film formation in a vacuum film formation method such as a vapor deposition method and a sputtering method, but in a wet coating method such as a sol-gel method, It is easy to form a film by coating once. Wet coating methods are expected to have a wide range of applications for low reflection films and light control films for the ultraviolet, visible and infrared regions, starting with the production of cover glass for solar cells, steppers, lasers, organic EL, liquid crystal display elements, LEDs In addition to precision optical equipment such as a lens, a member having a low-reflection film and a light control film such as a lighting fixture, and the like, it is suitably used for the production of general-purpose automotive glass, particularly windshields and lighting fixture protection members. In the method for producing a glass plate with a low reflection film of the present invention, a sol-gel method is suitably employed.

  When the sol-gel method is employed in the method for producing a glass plate with a low reflection film of the present invention, the coating solution for forming the low reflection film on the soda lime silicate glass plate is a dip-up method, that is, only a dip coating method. Instead, various coating methods such as a spin coating method, a spray coating method, a roller coating method using a reverse roll coater, a screen printing method, a brush coating method, an ink jet method, and the like are applied.

  It is preferable that the coating film formed on the soda lime silicate glass plate by the coating method is dried at 80 ° C. or higher and 150 ° C. or lower for 10 minutes to 6 hours, and then further heated and fired to form a low reflection film. As a preferred embodiment of the heating and baking, a low reflection film excellent in wear resistance was obtained by heating and baking at 500 ° C. or more and 700 ° C. or less for 2 to 3 minutes, that is, 120 to 180 seconds. In particular, by using colloidal silica and a tungsten compound at the same time, and firing and washing with water, a low reflective film having a low refractive index and excellent heat resistance, moisture resistance and wear resistance was obtained. The water used for washing may be acidic as long as it dissolves sodium tungstate and does not attack the low-reflection film.

2.3. Component 2.3.1 Colloidal Silica Containing Low Reflective Film Forming Coating Liquid Colloidal silica contained in the low reflective film forming coating liquid used in the method for producing a glass with a low reflective film of the present invention will be described.

  Colloidal silica is a colloid in which silicon oxide or its hydrate is agglomerated, and is usually a colloid obtained by dehydration condensation using alkoxysilane as a raw material, or a colloid obtained by removing alkali from an alkali silicate by ion exchange. Is mentioned. The coating solution for forming a low reflection film used in the present invention comprises a dispersion containing a tungsten compound and colloidal silica. The colloidal silica is at least two types of colloidal silica having different shapes, for example, rod-shaped colloidal silica and spherical colloidal silica. Preferably there is.

  The rod-shaped colloidal silica refers to a long and narrow colloidal silica, and may be on a bead or curved. Further, the spherical colloidal silica refers to a round colloidal silica, and may not be a perfect sphere but a distorted ellipsoid. The maximum diameter of the colloidal silica fine particles is referred to as a long diameter in rod-shaped colloidal silica, and is referred to as a particle diameter in spherical colloidal silica. Moreover, the minimum diameter of rod-shaped colloidal silica is called a short diameter.

  When forming a silica film containing silica fine particles, if the silica fine particles are spherical, it is easy to fill, and if the particle size distribution of the silica fine particles is uniform, the packing density can be increased. The film can ensure a packing density of 70% or more by close packing. However, spherical silica fine particles are bonded to each other by point contact, and if they receive stress from the outside and a shearing force acts between the fine particles, they are brittle and easily broken, and have a poor wear resistance when used as a silica film. was there.

  On the other hand, the rod-like silica fine particles are bulky particles having a large aspect ratio, the packing density of the rod-like silica is low, and the rod-like particles are entangled three-dimensionally to form a three-dimensional bridge structure. Has a low filling rate, is bulky and has a high porosity. 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.

  Therefore, it is preferable to use both rod-like colloidal silica and spherical colloidal silica in the coating solution for forming a low-reflection film used in the method for producing a glass with a low-reflection film. Assuming that a coating liquid in which colloidal silicas with different shapes coexist is used, the gap formed by the rod-shaped colloidal silica entangled and bonded onto the bridge due to the Brownian motion of the colloidal silica in the liquid when coated on the substrate. In addition, it is considered that a film having a low refractive index, that is, a low reflection film is formed by the effect that the coating film is formed in the state where the spherical silica fine particles are captured and the air having the refractive index of 1 is taken into the gap.

  Specifically, in the coating drying process, fine spherical silica particles enter the gap as the solvent evaporates due to capillarity of the voids between the rod-shaped colloidal silica and the spherical colloidal silica, resulting in more silica with different shapes. Therefore, a low-reflective film with excellent frictional strength is formed, which is denser using only rod-shaped colloidal silica and coarser porosity using only spherical colloidal silica, and has more contacts and stronger bonding. it is conceivable that.

  However, when colloidal silicas having different shapes coexist, there is a problem that a sol is easily formed and the life of the coating liquid for forming a low reflection film cannot be obtained.

Low reflection film obtained by the production method of the low reflective film coated glass of the present invention, different silica particle shapes, the interface with WO ₃ is the refractive index 1 incorporated into microvoids produced by bonding as a binder A low refractive index is obtained by air. A rod-shaped colloidal silica prepared in the range of 5 nm or more and 100 nm or less in the major axis, a spherical colloidal silica prepared in a range of 5 nm or more and 50 nm or less, and a tungsten compound are dispersed. By using the applied coating liquid for forming a low reflection film, it was easy to generate microvoids made of air in the low reflection film, and the adhesion strength of the low reflection film to the glass plate was improved.

  The colloidal silica used in the present invention is preferably at least two types of silica having different shapes. Specifically, it is preferable to use 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 the colloidal silica having different shapes.

  In the rod-shaped colloidal silica, if the major axis is shorter than 5 nm, the resulting low reflection film is unlikely to be a film having many minute voids, and if the major axis is longer than 100 nm, minute voids are hardly formed. The aspect ratio of the rod-shaped colloidal silica, 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 or larger than 10, microvoids are hardly formed in the low reflection film. In spherical colloidal silica, if the particle size is smaller than 5 nm, the resulting low reflection film is unlikely to be a film having many minute voids, and if the particle size is larger than 50 nm, minute voids are not easily formed.

  Among all colloidal silicas including rod-shaped colloidal silica and spherical colloidal silica contained in the coating liquid for forming a low reflection film used in the method for producing a glass with a low reflection film of the present invention, a scanning electron microscope (hereinafter referred to as SEM) It is preferable that 90% or more of the total number of colloidal silica falls within the above range by visual observation. The remainder does not satisfy the above range, in other words, is colloidal silica outside the above range, and if more than 10% of colloidal silica outside the above range is contained, not only the formation of microvoids will be hindered, but the upper limit. When colloidal silica having a diameter of 5 times or more of the value is included, the formed film is not uniform, which is not preferable.

  The following are mentioned as a silicon compound for producing | generating the colloidal silica for containing the silica fine particle used for the coating liquid for low reflection film formation used for the manufacturing method of the glass with a low reflection film of this invention.

Preferred silicon compounds include alkoxides, and are represented by the general formula Si (OR) ₄ (wherein R is independently methyl, ethyl, normal propyl, isopropyl, normal butyl, secondary butyl, methoxy Or an 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 -OR of alkoxide by halogen atoms, such as a chlorine atom, may be mentioned, for example, chloro triethoxysilane, dichloro di normal butoxy silane, or trichloro normal butoxy silane etc. are mentioned. In the present invention, rod-shaped colloidal silica prepared by dehydrating and condensing these silicon compounds to have a major axis of 5 nm or more and 100 nm or less, and spherical colloidal silica prepared by a particle diameter of 5 nm or more and 50 nm or less are preferably used.

2.3.2 Tungsten compound The colloidal silica contained in the coating solution for forming a low reflection film used in the method for producing a glass with a low reflection film of the present invention will be described.

  In order to contain tungsten oxide in the low reflective film in the coating liquid for forming the low reflective film, it is preferable to use a tungsten compound that has excellent liquid stability in the coating liquid and is less likely to cause solid analysis.

Tungsten compounds include W (OR ¹ ) ₆ and halides, hydrates, alkoxides or chelate compounds typified by tungsten chlorides containing WX _{6. In} the present invention, more stable dispersion is possible. it is preferable to use _{^{W (OR 1) 6-n}} X n to give a liquid. Here, n is 1 ≦ n ≦ 6, and R ¹ is independently methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, s-butyl group, i-butyl group, t -Represents a butyl group, n-amyl group, i-amyl group, s-amyl group, 2-ethylhexyl group, methoxyethyl group, methoxypropyl group, ethoxymethyl group, ethoxyethyl group, ethoxypropyl group or phenyl group, Is a halogen atom. In addition, the tungsten compound includes calcium tantalate, that is, CaWO ₄ , iron tungstate, that is, FeWO ₄ , manganese tungstate, and the like after calcination in the presence of inorganic alkoxides such as Ca, Fe, and Mn and alkoxide in the tungsten alkoxide. that like those that generate MnWO tungstate compounds such as _4.

Among them, tungsten chloride and alkoxide, W (OR ² ) _6-n Cl _n, is a tungsten compound that is easy to synthesize and easy to use in the present invention. N is 1 ≦ n ≦ 6, and R ² is independently methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, i-butyl, t- A butyl group, an n-amyl group, an i-amyl group or an s-amyl group;

In the coating liquid for forming a low reflective film used in the present invention, W (OR ² ) ₅ Cl is particularly useful for liquid stability, and in the coating liquid for forming a low reflective film of the present invention, dispersion dispersed in IPA It is preferable to use it as a liquid mixed with a dispersion of colloidal silica. R ² is preferably a methyl group, an ethyl group, an n-propyl group, or an i-propyl group.

W (OR ² ) ₅ Cl can be synthesized in a methanol solvent or an ethanol solvent, but by using IPA as a solvent, it is mixed with a dispersion containing colloidal silica, 1% by mass or more, Even if water is added so as to be 50% by mass or less, a solid content hardly precipitates, and a coating solution for forming a low reflection film having good stability is obtained.

W (OR ² ) ₅ Cl is synthesized by the following reaction in an IPA solvent.

WCl ₆ + 5Na (OR ² ) → W (OR ² ) ₅ Cl + 5NaCl
R ² is independently a methyl group, ethyl group, n-propyl group or 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.

2.4 Stability of the coating solution for forming the low-reflection film Normally, the coating solution for forming the low-reflection film for forming the low-reflection film on the transparent substrate should be stable for a long time without change over time and without precipitation of solids. Stability is important and it is preferable that it can be stored for at least 30 days at room temperature. For example, when comparing the stability of metal oxide precursors in sols, such as metal alkoxides, Si-based alkoxides such as alkoxysilanes are relatively stable without gelation and solids precipitation over time. It is known to those skilled in the art that alkoxides based on Zr, Zr, Ti, and Sn are unstable. Specifically, when comparing the stability of metal oxide precursors in sols, such as metal alkoxides, Si-based alkoxides such as alkoxysilanes are slow to hydrolyze, without gelation and precipitation of solids over time. Although relatively stable, Al-based, Zr-based, Ti-based, Sn, transition metal, and rare earth-based alkoxides are unstable. In the case of using these metals, there are not only metals in the coating solution for forming a low reflection film that have only a compound that cannot be stably dispersed, but also in the liquid stability, there is precipitation of solids, the life of the liquid is short, and the low reflection film There are concerns about performance degradation. Moreover, the obtained low reflection film is inferior in hardness and inferior in heat resistance, moisture resistance and wear resistance.

  The coating solution for forming a low reflection film used in the method for producing a glass with a low reflection film of the present invention is a mixture of colloidal silica and a tungsten compound, particularly an alkoxide of tungsten, and a combination of colloidal silica and tungsten alkoxide. It was found to be stable in the long term.

  The coating solution for forming a low reflection film used in the present invention in which colloidal silica and a tungsten compound are dispersed has good liquid stability. Specifically, even when water is added up to 50% by mass, the coating liquid is stable. Yes, it is easy to adjust volatility, viscosity adjustment, and solid content concentration using various organic solvents. Preferably, it is 30 mass% or less, More preferably, it is 1 mass% or more and 10 mass% or less. Compared to a coating containing only colloidal silica, in which solid content precipitates as the water content increases, by coexisting with a tungsten compound, it is stable even when water is added to a concentration of 50% by mass, and safety And is compatible with various coating methods.

  For example, when water is added to a dispersion of colloidal silica, colloidal silica becomes unstable and solid content often precipitates, and water is not used, but low reflective film formation using both colloidal silica and tungsten alkoxide is used. In the coating liquid for coating, solids are hardly precipitated even when water is added up to 50 mass% with respect to the total mass of the liquid due to the action of the alkoxide. Further, by adding 1% by mass or more of water to the coating solution for forming a low reflection film, the wettability with a glass plate is improved. In the present invention, the coating for forming a low reflection film using both colloidal silica and tungsten alkoxide is used. Using the liquid, the water content can be arbitrarily adjusted between 1% by mass and 50% by mass with respect to the total mass. Preferably, they are 1 mass% or more and 30 mass% or less, More preferably, they are 1 mass% or more and 10 mass% or less.

  The coating solution for forming a low reflection film comprising the tungsten compound of the present invention and a dispersion of at least two or more types of colloidal silica having different shapes is prepared such that the water content is in the range of 1% by mass to 50% by mass, Even when water is added, it exhibits excellent liquid stability, and the solid content does not precipitate over a long period of time. Preferably, they are 1 mass% or more and 30 mass%, More preferably, they are 1 mass% or more and 10 mass% or less.

  Specifically, the zeta potential is generally important for the stability of colloids, and colloidal particles dispersed in a liquid are often charged positively or negatively due to their ionicity, dipole characteristics, etc. The colloidal particles are surrounded by charges having the opposite sign of the 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 potential of the “slip surface” where liquid flow begins to occur in the electric double layer formed around the colloidal particles in the colloid. 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 interface properties. In particular, it is an important index for controlling the stability of colloidal dispersion / aggregation and interaction. To control 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 the stability of the colloid and the 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 in the solution as extremely small fine particles, 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 an electrostatic repulsive force acts between the particles. This repulsive force tends to disperse in the colloidal particles. Since the zeta potential increases in proportion to the magnitude of this electrostatic repulsive force, it becomes an index of the stability of the colloidal particles. When the zeta potential approaches zero, the colloidal particle agglomeration force overcomes the electrostatic repulsive force, and colloidal particle aggregation occurs. Conversely, an additive that increases the absolute value of the zeta potential can be adsorbed on the colloid surface, and a stable colloid can be obtained by pH control.

3. Reflective film and low-reflective member By using the coating liquid for forming a low-reflective film, the method for producing a glass with a low-reflective film according to the present invention has a refractive index of 1.20 or more and 1.40 or less. A low reflection film was obtained.

In addition, in the method for producing a glass with a low reflection film of the present invention, by including WO ₃ in a range of 5% by mass or more and 40% by mass or less with respect to silica fine particles, heat resistance and moisture resistance that can withstand outdoor use. Thus, a low reflective film excellent in durability such as abrasion resistance was obtained.

At this time, to the mass of silica, containing a range of WO ₃ is preferably 5 mass% or more, in the range of 40 wt% or less. In the low reflection film, voids are formed around the metal oxide. When the content of the metal oxide is less than 5% by mass with respect to the mass of the colloidal silica, less voids are produced and a film having a low refractive index cannot be obtained. When the content of the metal oxide is more than 40% by mass, the resulting film has a high refractive index and does not become a low reflection film. Preferably, it is the range of 10 mass% or less and 30 mass% or more.

In the low reflection film produced by the method for producing a glass with a low reflection film of the present invention, the low reflection film containing WO ₃ in a range of 5 mass% or more and 40 mass% or less with respect to the silica fine particles is minute in the film. The voids are formed and become a dense film while being porous, and the refractive index is lowered by taking in air having a refractive index of 1, and the presence of WO ₃ as described above is responsible for increasing the transmittance in a certain wavelength range, By increasing the transmittance in the wavelength range, a film having a low refractive index and extremely transparency was obtained, and the transmittance was improved from the visible light to the infrared light region of the low reflection member formed by the low reflection film. . The low reflection base material formed by forming this transparent low reflection film has sufficient low reflection performance even when the low reflection film is a single layer film.

The low reflection film is different silica fine particles in shape by joining the WO ₃ as a binder, while containing microvoids become dense film, silica and WO ₃ at the interface with refractive index 1 taken as the void air Due to the effect of the layer, the refractive index was lowered.

  Moreover, the mass ratio of the rod-shaped colloidal silica: spherical colloidal silica which can produce | generate the said low reflection film and a void easily and was excellent in the adhesive strength with respect to a glass plate is 20: 80-80: 20. In other ranges, void formation is small and a low reflection film is difficult to obtain, and adhesion strength is poor.

  Moreover, the preferable film thickness in the base | substrate surface of the said low reflection film 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.

  Compared with the prior art (Patent Documents 4 and 5), the method for producing a glass with a low reflection film according to the present invention is a composite without removing the inorganic oxide and without covering the surface of the colloidal particles with silica. After preparing the oxide sol, it is possible to form a low reflection film by directly coating the substrate surface with a single layer film without coating the substrate surface.

  In addition, the low reflection member in which the low reflection film is formed by the method for producing a glass with a low reflection film of the present invention is useful as a cover glass for a solar cell using a low Fe high-transmission glass plate whose Fe content is reduced as much as possible. is there. When used as a cover glass for solar cells, high transmittance and low reflectance are required, and since solar cells are constantly exposed to sunlight, the material has both antifouling properties, water resistance and weather resistance, etc. Is desired. As described above, the glass with a low reflection film produced using the colloidal silica having a different shape of the present invention and a coating solution for forming a low reflection film using a tungsten compound, particularly tungsten alkoxide, is antifouling and heat resistant. Excellent in moisture resistance, wear resistance and weather resistance.

4). Optical Characteristics of Glass with Low Reflective Film Next, optical characteristics of the glass with a low reflective film produced by the method for producing a glass with a low reflective film of the present invention will be described.

When a metal oxide such as silica (refractive index 1.46) and WO ₃ (refractive index 1.75) coexists in the low reflection film, the combination tends to increase the transmittance in a specific wavelength range. . Although the wavelength range cannot be strictly defined, when the refractive index of the metal oxide is low, the peak shifts slightly longer than the peak of the maximum value of the transmittance curve of silica alone. As the refractive index of the metal oxide increases, the peak further appears on the longer wavelength side.

Therefore, in the case of a low reflection film in which WO ₃ having a high refractive index of 1.75 is bonded to silica particles and dispersed in the silica film by utilizing the property that the peak of the maximum value of this transmittance curve is shifted, The presence of WO ₃ increases the transmittance in the long wavelength region of the low reflective member on which the low reflective film is formed, and increases the transmittance in a wide wavelength region.

In the method for producing a glass with a low reflection film according to the present invention, a coating for forming a low reflection film in which a dispersion containing colloidal silica having a different shape is mixed with a dispersion containing tungsten alkoxide, for example, W (OR ² ) ₅ Cl. The low reflection film formed by baking the film after applying the liquid to the base material has a tendency to increase the transmittance in the long wavelength region of the low reflection member on which the low reflection film is formed. In the wavelength region of 1200 nm or less, the average transmittance of the low reflection member on which the low reflection film was formed was improved.

This is due to the effect of inclusion of WO _{3 in} the low reflection film produced by baking tungsten alkoxide, for example, W (OR ² ) ₅ Cl. R ² represents a methyl group, an ethyl group, an n-propyl group, or an i-propyl group.

Specifically, the low reflection member formed by forming a silica coat film made only of silica has a high transmittance at a wavelength of 500 nm, and similarly, a low reflection film formed by mixing silica fine particles and WO ₃ is formed. Even in a low reflection member, it was analogized that a transmittance curve having a peak at a wavelength of 550 nm was given, but when actually mixed with WO ₃ , the peak of maximum transmittance shifted between 500 nm and 900 nm on the long wavelength side. As a result, the transmittance in the long wavelength region increases. This is also a factor in increasing the visible light transmittance of the low reflection member in which the low reflection film is formed by the method for producing a glass with a low reflection film of the present invention. Moreover, if the peak of the maximum transmittance is shifted between 500 nm and 900 nm, if the glass with a low reflection film according to the method for producing a glass with a low reflection film of the present invention is used for a cover glass for a solar cell, Conversion efficiency increases.

  In addition, CIS thin film solar cells and crystalline silicon, which have been developed in recent years, have a wide absorption of wavelengths of 400 nm or more and 1200 nm or less, and have a longer wavelength range than conventional amorphous silicon systems. It can absorb light, and its absorption peak is around 900 nm. As described above, the low reflection member having a low reflection film formed by the method for producing a glass with a low reflection film of the present invention has an ultraviolet / visible wavelength range of 300 nm to 800 nm, and a near infrared wavelength range of 800 nm. As described above, since it has high light transmittance at 1200 nm or less, it can be suitably used as a cover glass for solar cells having absorption in a long wavelength region as well as amorphous silicon solar cells.

  Hereinafter, based on an Example and a comparative example, the manufacturing method of the glass with a low reflection film of this invention is demonstrated. The present invention is not limited to the following examples.

  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]
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, Comparative Example 1), a coating solution for forming a low reflection film having a tungsten alkoxide content of 40% by mass in terms of oxide relative to colloidal silica (Example 2, Comparative Example 2) In the production of the glass with a low reflection film, the evaluation results of the moisture resistance with and without cleaning (Examples 1 and 2) (Comparative Examples 1 and 2) were compared.

  Subsequently, only the rod-shaped colloidal silica and tungsten alkoxide were used, and 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 only 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. A coating solution for low reflection film formation (Comparative Example 4) in which the content of tungsten alkoxide with respect to colloidal silica was 50% by mass in terms of oxide was prepared.

[Coating liquids of Comparative Examples 4 to 6]
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. Moreover, the coating liquid (comparative example 6) which consists only of tungsten alkoxides was prepared.

The composition of the coating liquid for forming a low reflection film in Examples 1 to 4 and the coating liquid in Comparative Examples 3 to 6 are summarized in Table 1 above.

Subsequently, the coating liquid for forming a low reflection film of Examples 1 to 4 and the coating liquid of Comparative Examples 3 to 6 were colorless and transparent soda lime silicate glass plates (hereinafter simply referred to as glass plates) having a thickness of 3 mm and a size of 100 mm × 100 mm. The glass with a low reflection film having a low reflection film formed on both sides was obtained, and physical properties of the obtained glass with a low reflection film were evaluated. Table 2 shows the physical property evaluation methods.

  Examples 1-4 of the present invention and Comparative Examples 1-4 will be described in detail.

Example 1
<Preparation of colloidal silica dispersion>
In a three-necked flask with a capacity of 1000 ml, weighed 16.34 g of a rod-shaped colloidal silica IPA dispersion (manufactured by Nissan Chemical Industries, Ltd., product number, IPA-ST, solid content concentration 30.3 mass%, major axis 10 nm to 20 nm), 231.21 g of ethanol was added with stirring. Next, 111.50 g of ethanol was added to 12.28 g of a spherical colloidal silica dispersion (manufactured by JGC Catalysts and Chemicals, product number: OSCAL1432, solid content 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.

<Preparation of glass with low reflection film>
The surface of the soda lime silicate glass plate was wet-polished with alumina particles, washed with distilled water and then with IPA, and then heated to 100 ° C. to dry. 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 plate by a dip method.

  The washed glass plate was immersed 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 plate. 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, cooled at room temperature (20 ° C., the same applies hereinafter), washed with tap water, and has a light blue reflective color. A glass with a low reflection film formed by forming a reflection film on both sides was obtained.

  FIG. 1 shows a SEM photograph substituting for a drawing of the low reflection film on the glass surface with the low reflection film.

It is an enlarged photograph by SEM of the low reflection film formed on the glass plate using the said 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. After film formation, washing with water removed not only extra sodium ions but also sodium silicate (Na ₂ SiO ₃ ) and sodium tungstate (Na ₂ WO ₄ ).

<Evaluation of glass with low reflection film>
FIG. 2 shows a transmittance curve of the glass with a low reflection film.

  The transmittance | permeability curve of the glass plate with a low reflection film which performed water washing after forming a low reflection film on the surface of a soda lime silicate glass glass plate by the sol-gel method using the said coating liquid for low reflection film formation is shown. The transmittance curve of No. 1 was obtained by applying the coating solution for forming a low reflection film on a soda lime silicate glass plate at a lifting speed of 3 mm / sec from the coating tank filled with the coating solution for forming a low reflection film. The transmittance curve of the glass-coated glass, similarly, the transmittance curve of 2 is the transmittance curve of the glass with a low reflection film at a lifting speed of 5 mm / sec, and the transmittance curve of 3 is the low reflection film at the lifting speed of 7 mm / sec. It is a transmittance | permeability curve of attached glass. As the pulling speed increases, the film thickness increases, and the peak of the maximum transmittance shifts to the long wavelength side. Compared with the transmittance curve (represented by R) of the soda lime silicate glass plate without the reference low reflection film, the transmittance was improved in all wavelength regions.

  Next, 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 with a low reflective film formed on both surfaces under the above-described pulling speed of 3.4 mm / sec. Was 98.0%, and the average transmittance was improved by 7.5% compared to the average transmittance of 90.5% of the glass plate 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 with an ellipsometer, n = 1.302, and satisfactory performance was obtained as a glass with a low reflection film.

Next, the frictional strength of the low-reflection film was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to a pad by a wear tester. The friction strength of 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.

  Next, a high-temperature and high-humidity test was performed at 85 ° C. and a relative humidity of 85% in order to evaluate the moisture resistance of the low reflective film. The average transmittance after exposure for 1000 hours was 97.5%, which was only 0.5% lower than that before the test, and the appearance and color tone of the film were hardly changed.

Further, when the surface resistance value of this low reflective film-coated glass 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.

Comparative Example 1
These measured values are values after the glass plate is washed with water after film formation. When a high temperature and high humidity test is performed for evaluating the moisture resistance without washing with excess sodium ions, sodium silicate (Na ₂ SiO ₃ ) and sodium tungstate (Na ₂ WO ₄ ) attached, exposure to 1000 hr The later average transmittance was 94.4%, which was 3.6% lower than that before the test, and the appearance and color tone of the film were also changed. Sodium ion, sodium silicate (Na ₂ SiO ₃ ) and sodium tungstate It was found that the desired moisture resistance could not be obtained when (Na ₂ WO ₄ ) was adhered.

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 soda lime silicate glass plate in the same procedure as in Example 1, heated and fired, cooled, and then washed with tap water to obtain a glass plate with a low reflection film. . After film formation, washing with water removed not only extra sodium ions but also sodium silicate (Na ₂ SiO ₃ ) and sodium tungstate (Na ₂ WO ₄ ).

  When the physical property values were measured according to the physical property evaluation methods in Table 2, the low reflective film-coated glass was formed by forming low reflective films on both sides 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 with the average transmittance of 90.5% for the glass plate 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 with a low reflection film.

Next, the frictional strength of the low-reflection film was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to a pad by a wear tester. The friction strength of 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.

  Next, a high-temperature and high-humidity test was performed at 85 ° C. and a relative humidity of 85% in order to evaluate the moisture resistance of the low reflective film. The average transmittance after exposure for 1000 hours was 96.8% after only a 0.5% decrease compared to before the test, and the appearance and color tone of the film were hardly changed.

Further, when the surface resistance value of this low reflective film-coated glass 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 2
These measured values are values after the glass plate is washed with water after film formation. When a high-temperature and high-humidity test was conducted for moisture resistance evaluation in a state where unnecessary sodium ions, sodium silicate (Na ₂ SiO ₃ ) and sodium tungstate (Na ₂ WO ₄ ) were not washed, The average transmittance is 93.7%, which is 4.2% lower than that before the test, and the appearance and color tone of the film are also changed. Sodium ion, sodium silicate (Na ₂ SiO ₃ ) and sodium tungstate (Na It was found that the desired moisture resistance could not be obtained when ₂ WO ₄ ) was adhered.

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 soda lime silicate glass plate in the same procedure as in Example 1, heated and fired, cooled, and then washed with tap water to obtain a glass with a low reflection film.

  When the physical property values were measured in accordance with the physical property evaluation methods shown in Table 2, the average of the low reflective film-coated glasses formed by forming the low reflective film on both sides in the same manner as in Example 1 under the pulling rate of 3.4 mm / sec. The transmittance was 97.5%, and the average transmittance was improved by 7.0% compared to the average transmittance of 90.5% for the glass plate 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 112 nm. Moreover, when the refractive index n was measured with the ellipsometer, it was n = 1.292 and the desired performance was obtained as glass with a low reflection film.

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

  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 plate in the same procedure as in Example 1, heated and fired, cooled, and then washed with tap water to obtain a glass with a low reflection film.

  According to the physical property evaluation method of Table 2, the physical property value was measured. Under the conditions of a pulling rate of 3.0 mm / sec, a low reflective film with a low reflective film formed on both sides in the same manner as in Example 1 was obtained. 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 plate 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 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 the low-reflection film was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to a pad by a wear tester. The friction strength of was evaluated. The frictional strength of the low reflective film is cloudy and partially peeled after 3000 reciprocating rubs according to the nell cloth abrasion test, and compared with the frictional strength of the glass with the low reflective film of Example 1 and Example 2. It was inferior.

  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 3
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 soda lime silicate glass plate in the same procedure as in Example 1, heated and fired, cooled, and then washed with tap water to obtain a glass 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 glass plate formed on both surfaces in the same manner as in Example 1 under the pulling speed of 3.4 mm / sec was The soda lime silicate glass plate before the film was provided was 1.6% higher than that of the soda lime silicate glass plate, 92.1%, and the desired performance as a glass with a low reflection film could not be 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.

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 soda lime silicate glass plate in the same manner as in Example 1, heated and fired, cooled, and then tap water To obtain glass with a film. Unlike Examples 1 to 4 and Comparative Example 1, tungsten alkoxide is not used.

  Next, the film-coated glass 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 6.9% higher than the soda lime silicate glass plate before the film was provided. As for the frictional strength of the film, the appearance after 3000 reciprocating frictions in the flannel abrasion test was cloudy, and the haze increased by 5.7% compared to before the test, and there was partial peeling and the frictional strength was inferior.

  The average transmittance of the glass with film after 1000 hr exposure by the high temperature and high humidity test (85 ° C., relative humidity 85%) is 95.4%, which is 2.0% lower than before the test, and the appearance Was discolored. This is a result of not using tungsten alkoxide.

  The film-coated glass was inferior in film strength, and as a result of the high-temperature and high-humidity test, it was 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 corodal silica was 20% by mass. After coating on a soda lime silicate glass plate in the same procedure as in Example 1, it was heated and fired to obtain glass with a film. Unlike Examples 1-4 and Comparative Examples 1-3, tungsten alkoxide is not used.

  Subsequently, the film-coated glass plate 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 the soda lime silicate glass plate before the 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 average transmittance of the glass plate with a film after 1000 hr exposure by the high temperature and high humidity test (temperature 85 ° C., relative humidity 85%) is 91.6%, which is 2.0% lower than before the test. The appearance was discolored. This is a result of not using tungsten alkoxide.

Comparative Example 6
Only the tungsten alkoxide solution prepared in Example 1 was applied to a soda lime silicate glass plate and heated and fired in the same manner as in Example 1 to obtain a glass with a tungsten oxide film. A haze of 46.8% became a cloudy ground glass glass plate.

[result]
The evaluation results are shown in Table 3.

  The glass with a low reflection film in which the low reflection film is formed by the method for producing a glass with a low reflection film of the present invention is excellent in hydrophilicity and antifouling properties, has antistatic properties, and is hardly stained. In particular, as shown in Table 3, the glass with a low reflection film of Examples 1 and 2 showed high average transmittance, and the average transmittance deteriorated as a result of the frictional strength of the film by the flannel abrasion test and the high temperature and high humidity test. It showed excellent durability without doing.

[Addition of water to coating solution]
Coating solution for forming low reflection film used in Example 1, coating solution used in Comparative Example 2 using only colloidal silica having a different shape, and coating of Comparative Example 3 in which TEOS was added to a dispersion of colloidal silica having a different shape Water was added to the liquid, and precipitation of solid content with time was observed.

  Specifically, 10.0% by mass of pure water is added to the coating solution for forming a low reflection film of Example 1 and the coating solutions of Comparative Example 2 and Comparative Example 3, and stored at room temperature (20 ° C.). The presence or absence of white turbidity and solid content was observed.

  Low reflection film forming coating solution used in Example 1 in which tungsten alkoxide is added in a preferred ratio to two types of colloidal silica (rod-shaped colloidal silica + spherical colloidal silica), only for two types of colloidal silica having different shapes The coating solution used in Comparative Example 2 was added with 10.0% by mass of pure water, and no change was observed after 90 days.

  In comparison, the coating liquid used in Comparative Example 3 in which TEOS was added to two types of colloidal silica dispersions having different shapes was added with 10% of pure water, and after 1 week, it gelled and became a coating liquid. It was not usable.

  Subsequently, 10.0 mass% of pure water was added, and the soda lime silicate was used in the same manner as in Example 1 using the coating solution for forming a low reflection film prepared in Example 1 after 90 days (referred to as Example 5). The physical properties of the obtained glass with a low reflection film were evaluated by coating on a glass plate.

Example 5
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 is applied to a soda lime silicate glass plate in the same procedure as in Example 1, heated and baked, cooled, washed with tap water, and glass with a low reflection film Got.

  When the physical property values were measured according to the physical property evaluation methods in Table 2, the low reflective film-coated glass was formed by forming low reflective films on both sides 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 with the average transmittance of 90.5% for the glass plate 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 112 nm. Further, when the refractive index n was measured with an ellipsometer, n = 1.285, and satisfactory performance was obtained as a glass with a low reflection film.

Next, the frictional strength of the low-reflection film was rubbed back and forth 3000 times with a load of 15 g / cm ² using a flannel cloth attached to a pad by a wear tester. The friction strength of 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.

  Next, a high-temperature and high-humidity test was performed at 85 ° C. and a relative humidity of 85% in order to evaluate the moisture resistance of the low reflective film. The average transmittance after 1000 hr exposure was 96.7% only by a 1.0% decrease compared to before the test, and the appearance and color tone of the film were hardly changed.

  The results are summarized in Table 4. To the glass with a low reflection film formed on both sides with the low reflection film forming coating solution used in Example 1 to which pure water was not added, 10.0% by mass of pure water was added, and 90% The result of the physical property evaluation of the glass with a low reflection film formed by forming the low reflection film on both sides with the coating liquid for forming the low reflection film of Example 5 after the passage of days is not inferior to the glass with the low reflection film of Example 1. Met.

Comparative Example 7
These measured values are values after the glass plate is washed with water after film formation. In the state where extra sodium ions, sodium silicate (Na ₂ SiO ₃ ) and sodium tungstate (Na ₂ WO ₄ ) are adhered, these measured values cannot be obtained. In particular, when a high temperature and high humidity test is performed for moisture resistance evaluation without washing with water, the average transmittance after 1000 hr exposure is 94.4%, which is 3.6% lower than that before the test. The appearance and color tone of the film also changed, and it was found that the desired moisture resistance could not be obtained when sodium ions, sodium silicate (Na ₂ SiO ₃ ), and sodium tungstate (Na ₂ WO ₄ ) were attached.

  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.

  According to the method for producing a glass with a low reflection film of the present invention, a glass with a low reflection film excellent in low refractive index, heat resistance, abrasion resistance, moisture resistance and antifouling property, which uses a soda lime silicate glass plate, is obtained. Obtained.

The glass plate with a low reflection film according to the method for producing a glass plate with a low reflection film of the present invention can be used in a cover glass for solar cells, a showcase, a window, glass for automobiles, or the like. In particular, the peak wavelength of transmitted light can be shifted in accordance with the characteristics of the solar cell to improve the conversion rate of the solar cell, which is useful as a cover glass for a solar cell. Specifically, the peak of the maximum transmittance of the glass with a low reflection film having a low reflection film made only of silica is usually around 500 nm, but by including WO ₃ , the peak is reduced to 500 nm to 900 nm. The low reflection member excellent in use as a cover glass for solar cells was obtained.

  In the method for producing a glass with a low reflection film of the present invention, the coating liquid for forming a low reflection film has no solid content precipitation, has a long liquid life, and can contain water. It has good wettability and supports various application methods.

Claims (8)

For forming a low reflection film comprising colloidal silica and a tungsten compound in an organic solvent, wherein the tungsten compound is contained in the range of 5% by mass or more and 40% by mass or less in terms of oxide with respect to the mass of the colloidal silica. Apply the coating solution
A first step of applying a soda lime silicate glass plate to form a coating;
A second step of obtaining a low reflection film by baking and curing a film formed on a soda lime silicate glass plate;
A third step of washing the soda lime silicate glass plate with the coating fired and cured,
A method for producing a glass with a low reflection film. The method according to claim 1, wherein the colloidal silica is a rod-like 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 as observed with a scanning electron microscope. The method according to claim 2, wherein the mass ratio of rod-shaped colloidal silica: spherical colloidal silica is 20:80 to 80:20. The tungsten compound is W (OR ¹ ) _6-n X _n
(N is 1 ≦ n ≦ 6, R ¹ is each independently a 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, s-amyl group, 2-ethylhexyl group, methoxyethyl group, methoxypropyl group, ethoxymethyl group, ethoxyethyl group, ethoxypropyl group or phenyl group, X Is a halogen atom.)
The method according to any one of claims 1 to 3, wherein: The tungsten compound is W (OR ² ) _6-n Cl _n
(N is 1 ≦ n ≦ 6, R ² is each 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.
The method according to any one of Inventions 1 to 4, wherein: The tungsten compound is converted into the following reaction WCl ₆ + 5Na (OR ² ) → W (OR ² ) ₅ Cl + 5NaCl in an isopropyl alcohol solvent.
(R ² is each independently a 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.)
The method according to claim 1, which is W (OR ² ) ₅ Cl synthesized by: The method according to any one of claims 1 to 6, wherein the low reflection film has a refractive index of 1.20 or more and 1.40 or less. A solar cell cover glass with a low reflection film obtained by the method according to any one of claims 1 to 7.

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