WO2021057708A1

WO2021057708A1 - A coating dispersion, a process for preparing the same and use thereof

Info

Publication number: WO2021057708A1
Application number: PCT/CN2020/116774
Authority: WO
Inventors: He He; Yunxin GU
Original assignee: Saint-Gobain Glass France
Priority date: 2019-09-23
Filing date: 2020-09-22
Publication date: 2021-04-01
Also published as: CN111826002A

Abstract

A coating dispersion comprises from 0.02 to 1.2 wt% of a photocatalytic metal compound, from 1.5 to 10 wt% of a granular silicon dioxide; and from 0.2 to 2 wt% of a binder, wherein the photocatalytic metal compound comprises photocatalytic metal sulfide, photocatalytic metal oxide or a combination thereof, and the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is from 3 to 500.

Description

A coating dispersion, a process for preparing the same and use thereof

Technical Field

The present disclosure is related to the technical field of coating and particularly related to a coating dispersion for use in coating, a process for preparing the same and a substrate which is covered with a coating prepared from the coating dispersion and has good self-cleaning capability and total transmission energy difference.

Background

With the development of clean energy, photovoltaic cell panels have been widely used. Photovoltaic cell panels are exposed to the air and easily polluted by dust and dirt, reducing the sunlight incident on the photovoltaic cell panels and the amount of generated electricity. Panel cleaning is a common process to restore photovoltaic power generation, but it is a time and energy consuming process. The self-cleaning coating is beneficial for photovoltaic cell panels to maintain high power generation and reduce cleaning costs. Therefore, there is a demand for photovoltaic power plants to apply the self-cleaning coating of photovoltaic cell panels directly.

TiO ₂ is a material with good photocatalytic properties and hydrophilicity, which can be applied to self-cleaning coatings. CN106046863A discloses a process for preparing a TiO ₂ nano-coating, including 1) preparation of TiO ₂ solution: TiO ₂ solution is prepared by using butyl titanate as titanium source, isopropanol as solvent, and diethanolamine as hydrolysis inhibitor, and 2) dispersion and surface modification of TiO ₂ nano solution: for the TiO ₂ solution obtained in step 1) , sodium silicate is used as dispersant, silane as coupling agent, and the surface of TiO ₂ is modified to obtain the TiO ₂ nano-coating. CN104745025A discloses an environmentally friendly multifunctional nano modified coating, which is prepared from the following materials in ratio by weight: nano titanium dioxide particle slurry at 50 to 200 portions, acrylic acid film former at 30 to 100 portions, dispersant at 5 to 30 portions, thickener at 10 to 50 portions, defoamer at 5 to 10 portions, and appropriate amount of water. CN108948802A discloses a self-cleaning coating with enhanced light transmittance, and the coating suspension for preparation the self-cleaning coating includes in ratio by weight: nano-silicon dioxide particles at 15 to 20 portions, nano-titanium dioxide particles at 8 to 10 portions, metal quantum dots at 3 to 5 portions, amino silane coupling agent at 1 to 1.8 portions, butyl acetate at 8 to 10 portions, ethanol at 150 to 180 portions.

Summary

In the first aspect, provided is a coating dispersion, wherein based on the total weight of the coating dispersion, the coating dispersion comprises: from 0.02 to 1.2 wt%of a photocatalytic metal compound, from 1.5 to 10 wt%of a granular silicon dioxide; and from 0.2 to 2 wt%of a binder; wherein the photocatalytic metal compound comprises photocatalytic metal sulfide, photocatalytic metal oxide or a combination thereof, and the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is from 3 to 500.

In an embodiment, the photocatalytic metal compound in the coating dispersion according to the present disclosure is zinc oxide, zirconia, tin oxide, titanium dioxide, zinc sulfide, lead sulfide or a combination thereof, preferably titanium dioxide.

In a preferable embodiment, in the coating dispersion according to the present disclosure, the particle size of the photocatalytic metal compound is from 10 to 100 nm.

In another embodiment, the coating dispersion according to the present disclosure comprises a granular silicon dioxide having a particle size of from 10 to 30 nm.

In another embodiment, in the coating dispersion according to the present disclosure, the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is from 5 to 100.

In another embodiment, in the coating dispersion according to the present disclosure, the weight ratio of the granular silicon dioxide to the binder is from 1 to 19, preferably from 3 to 15.

In another embodiment, in the coating dispersion according to the present disclosure, the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder is from 1 to 19, preferably from 3 to 15.

In yet another embodiment, the solid content of the coating dispersion according to the present disclosure is from 1.72 to 13.2 wt%, preferably from 2 to 10 wt%.

In an embodiment, in the coating dispersion according to the present disclosure, the content of anatase type titanium dioxide in titanium dioxide is 80 wt%or more, preferably 90 wt%or more, more preferably 95 wt%or more.

In another embodiment, in the coating dispersion according to the present disclosure, the binder is one or more selected from the group consisting of: sol-type silica, silane coupling agent.

In a preferable embodiment, the sol-type silica is prepared by one or more selected from the group consisting of: tetraethoxysilane, sodium silicate, lithium silicate, potassium silicate.

In another preferable embodiment, the silane coupling agent is prepared by an organosilane precursor with the following formula or a combination thereof:

R ² _nSi (OR ¹) _4-n;

wherein n is an integer of from 0 to 2, R ¹ is a C _XH _2X+1 type alkyl functional group, R ² is an organic group containing alkyl, epoxy, acrylate, methacrylate, amine, phenyl or vinyl functional group.

In an embodiment, in the coating dispersion according to the present disclosure, based on the total weight of the coating dispersion, the coating dispersion comprises from 0.04 to 0.8 wt%of a photocatalytic metal compound.

In another embodiment, in the coating dispersion according to the present disclosure, based on the total weight of the coating dispersion, the coating dispersion comprises from 4 to 8 wt%of a granular silicon dioxide.

In another embodiment, in the coating dispersion according to the present disclosure, based on the total weight of the coating dispersion, the coating dispersion comprises from 0.4 to 1.8 wt%of a binder.

In an embodiment, the coating dispersion according to the present disclosure further comprises dispersion medium, the dispersion medium is aqueous solution, water-containing solution or water.

In an embodiment, the pH of the coating dispersion according to the present disclosure is from 1 to 7, preferably from 2 to 5.

In the second aspect, provided is a process for preparing the coating dispersion according to the present disclosure, comprising

(1) providing a photocatalytic metal compound, a granular silicon dioxide and a binder solution;

(2) adding the photocatalytic metal compound and the granular silicon dioxide into the binder solution and performing mixing,

wherein, based on the total weight of the coating dispersion,

the content of the photocatalytic metal compound is from 0.02 to 1.2 wt%;

the content of the granular silicon dioxide is from 1.5 to 10 wt%;

the content of the binder solution is from 88.8 to 98.4 wt%.

In an embodiment, in the process for preparing the coating dispersion according to the present disclosure, the particle size of the photocatalytic metal compound is from 10 to 100 nm.

In another embodiment, in the process for preparing the coating dispersion according to the present disclosure, the particle size of the granular silicon dioxide is from 10 to 30 nm.

In an embodiment, in the process for preparing the coating dispersion according to the present disclosure, the content of the binder in the binder solution is from 0.2 to 4 wt%, preferably from 0.5 to 2.5 wt%.

In another embodiment, in the process for preparing the coating dispersion according to the present disclosure, the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is from 3 to 500, preferably from 5 to 100.

In another embodiment, in the process for preparing the coating dispersion according to the present disclosure, the weight ratio of the granular silicon dioxide to the binder is from 1 to 19, preferably from 3 to 15

In yet another embodiment, in the process for preparing the coating dispersion according to the present disclosure, the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder is from 1 to 19, preferably from 3 to 15.

In the third aspect, provided is a covered substrate, wherein at least one surface of the substrate is at least partially covered with a coating prepared by the coating dispersion according to the present disclosure.

In an embodiment, at least one surface of the substrate is covered with the coating for 80%or more, preferably 90%or more, more preferably 95%or more.

In another embodiment, the substrate is photovoltaic cell panel, glass, plastic, metal, polymer or semiconductor.

In yet another embodiment, the coating comprising a coating composition, the coating composition comprises a photocatalytic metal compound, a granular silicon dioxide and a binder,

wherein based on the total weight of the coating dispersion,

the content of the photocatalytic metal compound is from 0.5 to 30 wt%,

the content of the granular silicon dioxide is from 50 to 94 wt%,

the content of the binder is from 5 to 45 wt%,

wherein the weight ratio of the granular silicon dioxide to the photocatalytic metal compound in the coating composition is from 3 to 500.

In the fourth aspect, provided is a process for preparing the covered substrate according to the present disclosure, comprising applying the coating dispersion according to the present disclosure to at least one surface of the substrate and performing drying.

In an embodiment, the application includes spin coating, spray coating, roll coating, dip coating, flow coating or a combination thereof.

In the fifth aspect, provided is use of the coating dispersion according to the present disclosure in the preparation of a photovoltaic cell panel.

Beneficial Effect

The coating dispersion according to the present disclosure can be directly coated on a substrate like a photovoltaic cell panel and can be dried naturally without further heat treatment. It will not affect the binding or adhesion of the coating and can be used for online production of coated glass manufacturers.

The coating in the covered substrate according to the present disclosure has good self-cleaning ability, enhanced transmission anti-reflection and large total transmission energy difference, solving the problem of increased reflection of photovoltaic panel by using TiO ₂ as photocatalyst and adverse effects to power generation in the prior art. Application of the coating dispersion on the substrate according to the present disclosure is beneficial for reducing cleaning costs and increasing power generation.

The coating on the covered substrate according to the present disclosure has good photocatalytic performance and super-hydrophilicity. The total transmission energy difference of the substrate before and after applications of the coating dispersion according to the present disclosure can be 1.6%. The coating on the covered substrate according to the present disclosure has good stability, which can withstand high temperature such as 650 ℃ heat treatment, and has good durability, scratch resistance and environmental stability.

The preparation process of the coating dispersion and the covered substrate according to the present disclosure is simple and convenient, suitable for large-scale production, and it can be widely used in photovoltaic cell panel, construction, greenhouse and other fields.

Brief Description of the Drawings

The foregoing and other aspects of the present application can be more fully understood from the detailed description described below in combination with the following drawings. It should be noted that the scales of the figures may be different for the purpose of clarity, but this does not affect the understanding of the present application.

Figure 1: Schematic diagram of the covered substrate.

Figure 2: Spectrum of absorption of Methylene Blue solution after UV irradiation (abscissa represents wavelength, ordinate represents absorbance) .

Figure 3: Total transmission energy difference of the samples of Example 4-8.

Figure 4: Total transmission energy difference of the samples of Example 1, 4, 9-10.

Figure 5: Results of outdoor tests of the samples of Example 1 and Comparative Example 1.

Detailed Description

General Definition and Terms

The present disclosure will be described in details below, and it should be noted that the description is provided for the purposed of illustration rather than limitation.

Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by a person skilled in the art. If there is a contradiction, the definition provided in this application shall prevail. When expressing a certain amount, concentration or other value or parameter in the form of a range, a preferable range, or a preferable range upper limit and a preferable range lower limit, it should be understood that it is corresponds to specifically revealing any range by combining any pair of upper limit of the range or preferable range value with the lower limit of any range or preferable range value, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical ranges listed herein are intended to include the endpoints of the range and all integers and fractions (decimals) within the range.

When used with a numerical variable, the term “approximate” or “about” usually refers to the value of the variable and all the values of the variable within the experimental error (for example, within an average 95%confidence interval) or within ± 10%of the specified value, or a wider range.

The term “optional” or “optionally” means the event described subsequent thereto may or may not happen. This term encompasses the cases that the event may or may not happen, and that the contents are selected in an arbitrary manner.

Unless otherwise stated, the percentages, parts or the like herein are on a weight basis.

The expression “comprise” or its synonyms “contain” , “include” , “have” or the like are meant to be inclusive, which does not exclude other unlisted elements, steps or ingredients. The expression “consist of” excludes any unlisted elements, steps or ingredients. The expression “substantially consist of” refers to specified elements, steps or ingredients within a given range, together with optional elements, steps or components which do not substantively affect the basic and novel feature of the claimed subject matter. It should be understood that the expression “comprise” encompasses the expressions “substantially consist of” and “consist of” .

The term “substantially” as used herein refers to a range within 10%preferably 5%of a standard value or a reference value.

The term “room temperature” as used herein refers to about 20 to 30 ℃, for example about 25 ℃.

The term “coating dispersion” used herein may also be known as coating dispersion liquid, which is a liquid form where one or more substances are dispersed in another medium. A coating dispersion may also be known as coating composition or coating. A coating dispersion generally contains two parts of dispersion medium and dispersed phase. A dispersion medium may also be known as dispersing agent, continuous phase. The dispersion medium includes but is not limited to water, water-containing solution, aqueous solution, organic solvent like ethanol, acetone, isopropanol. A dispersed phase may also be known as dispersed substance, dispersed mass. A dispersed phase refers to the substance dispersed by dispersion medium, for example the remained dry substance after the dispersion medium volatilizes. The dispersed phase herein includes a photocatalytic metal compound, a granular silicon dioxide and a binder.

The term “sol-type silica” used herein refers to silicon dioxides present in a silicon dioxide collosol. Such silica has chain or network structure which is different from the granular silicon dioxide as mentioned herein.

The term “particle size” as used herein refers to the size or diameter of particles. When a certain physical characteristic or physical behavior of the measured particle is closest to a homogeneous sphere (or combination) with a certain diameter, the diameter (or combination) of the sphere is considered as the equivalent particle size (or particle distribution) of the measured particle. The particle size may be measured by laser method, sedimentation method, photon cross-correlation spectroscopy method, sieving method, microscope method, ultrasonic particle size analysis method, X-ray small-angle diffraction method or the like. The particle size herein is measured by laser method, and the measuring instrument is Malvern laser particle size analyzer.

The term “solid content” used herein refers to the mass percentage of the remaining part of the coating dispersion after drying. For example, in the present disclosure, the solid content of the coating dispersion refers to the total weight of photocatalytic metal compound, granular silicon dioxide and binder in the coating dispersion, based on the total weight of the coating dispersion.

The term “total transmission energy” as used herein includes the sum of the solar radiation energy directly transmitted through a glass and the subsequent heat radiated by the glass, expressed as TE. ISO9050 standard herein is used to count the total transmission energy value in the wavelength range of from 300 to 1200 nm. The measuring instrument is, for example, a spectrophotometer, such as model Perkin Elmer Lambda 950. As used herein, ΔTE is the total transmission energy difference, that is, the TE value of the covered substrate (i.e. the substrate covered by the coating or the coated substrate) minus the TE value of the uncovered substrate. It is usually used to measure the optical performance of the coating.

The term “chromatic aberration” used herein is also known as chromatism, expressed as ΔE. Measured by CIE 1976 chromatic aberration formula, ΔE = ( (L* ₁-L* ₂) ²+ (a* ₁-a* ₂) ²+ (b* ₁-b* ₂) ²) ^1/2 (L is luminosity, A represents red and green, B represents yellow and blue) . The smaller the ΔE, the more subtle the difference. When ΔE<2, there is almost no visual difference. Chromatic aberration is measured with a colorimeter.

The term “contact angle” as used herein can be used to characterize the interaction between water molecules and the surface of different solid materials. At the intersection of the three phases of water (liquid phase) , material (solid phase) and air (gas phase) , the angle θ formed by the tangent to the surface of the water droplet and the contact surface between the water and the material is called contact angle. The degree of wetting can be estimated from θ angle. The smaller the θ angle, the better the wettability. The contact angle is usually measured using methods commonly used in the field, such as a profile image analysis method. The droplet is dropped on the surface of the sample at room temperature, the shape image of the droplet is obtained through the microscope lens and camera, and then digital image processing and algorithms are used to calculate the contact angle of the droplet in the image. Unless otherwise specified, the contact angle herein uses water as the measuring droplet. The contact angle measured herein is static contact angle. The device for measuring the contact angle can be, for example, a contact angle measuring instrument.

Coating Dispersion

Provided is a coating dispersion. The coating dispersion comprises dispersed phase and dispersion medium. The dispersed phase comprises a photocatalytic metal compound, a granular silicon dioxide and a binder. Based on the total weight of the coating dispersion, the coating dispersion comprises about 0.02 to 1.2 wt%of a photocatalytic metal compound, about 1.5 to 10 wt%of a granular silicon dioxide, and about 0.2 to 2 wt%of a binder.

Photocatalytic metal compound

Photocatalytic metal compound is a metal compound with photocatalytic capability. Under suitable irradiation, usually under ultraviolet (UV) radiation, it can catalyze the degradation reaction of organic compounds. For example, such photocatalytic activity is triggered in the layer by generating electron-hole pairs. This is helpful for decomposing organic contaminants adhering to the coating surface. In addition, the photocatalytic metal compound has good hydrophilicity, which allows pollutants or decomposed pollutants to be easily removed by the washing of water such as rainwater.

The photocatalytic metal compound used herein comprises photocatalytic metal sulfide, oxide or a combination thereof, and includes but is not limited to zinc oxide, zirconia, tin oxide, titanium dioxide, zinc sulfide, lead sulfide or a combination thereof, preferably titanium dioxide.

The titanium dioxide generally has rutile type or anatase type. There is difference between the refractive indexes of these two crystal forms of titanium dioxide. The anatase type titanium dioxide is preferable herein. In an embodiment, the content of anatase type titanium dioxide in the titanium dioxide is about 80 wt%or more, preferably about 90 wt%or more, more preferably about 95 wt%or more.

The shape of the photocatalytic metal compound includes but is not limited to sphere shape, dodecahedron, triacontahedron or irregular polyhedron, but it is necessary to keep gaps between the photocatalytic metal compound particles when they are stacked in the coating to facilitate the incidence of sunlight and the resulting increase in the total transmission energy difference of the coating, and the sphere shape is preferable. The particle size of the photocatalytic metal compound herein is about 10 to 100 nm. The preferable particle size is helpful for obtaining a photocatalytic metal compound with an appropriate total specific surface area, which is beneficial to obtain a stable coating dispersion, to obtain the photocatalytic performance of the coating, and to obtain a coating with a suitable thickness and a suitable refractive index, so as to achieve a coating with a higher total transmission energy difference. An excessively large particle size of the photocatalytic metal compound will decrease the specific surface area, thereby reducing the photocatalytic performance, meanwhile the refractive index will increase, and the total transmission energy will decrease. A excessively small particle size of the photocatalytic metal compound will make the particles easy to agglomerate. Preferably, the lower limit of the particle size of the photocatalytic metal compound is about 12 nm or more, such as 15 nm or more. Preferably, the upper limit of the particle size of the photocatalytic metal compound is about 60 nm or less, more preferably 40 nm or less. For example, about 20 nm. The photocatalytic metal compound herein has a relatively concentrated particle size distribution. In a preferable embodiment, the photocatalytic metal compound is monodispersed.

In an embodiment, based on the total weight of the coating dispersion, the content of photocatalytic metal compound is about 0.02 to 1.2 wt%. A suitable content of photocatalytic metal compound is helpful for obtaining a coating with good photocatalytic performance and self-cleaning performance. An excessively high content of photocatalytic metal compound goes against the film-forming performance of the final coating and will lead to a decrease in the total transmission energy difference of the coating. An excessively low content of photocatalytic metal compound will reduce the photocatalytic performance of the obtained coating and weaken the hydrophilicity of the coating. Preferably, based on the total weight of the coating dispersion, the lower limit of the content of the photocatalytic metal compound is about 0.04 wt%or more, more preferably about 0.06 wt%or more. Preferably, based on the total weight of the coating dispersion, the upper limit of the content of the photocatalytic metal compound is about 0.8 wt%or less, more preferably about 0.6 wt%or less. For example, about 0.08, 0.16, 0.24, 0.4, 0.8 wt%.

Granular silicon dioxide

Silicon dioxide has a high light transmittance, which contributes to the reduction of the final refractive index of the coating dispersion or the coating obtained through the coating dispersion, and reduces the adverse effects of the relatively high refractive index of the photocatalytic metal compound on the photovoltaic cell panel efficiency.

In an embodiment, the refractive index of the granular silicon dioxide is about 1.3 to 1.5, preferably about 1.4 to 1.5.

The granular silicon dioxide herein refer to solid silicon dioxide in granular form. The shape of granular silicon dioxide includes but is not limited to sphere, dodecahedron, triacontahedron or irregular polyhedron, and it is necessary to keep gaps between the granular silicon dioxide when it is accumulated in the coating to facilitate the incidence of sunlight, and the sphere is preferable. The particle size of the granular silicon dioxide is about 10 to 30 nm.The preferable particle size is helpful for obtaining silicon dioxide with a suitable total specific surface area, which is beneficial to obtain a stable coating dispersion, so as to obtain a coating with good hydrophilicity, suitable thickness, refractive index and air or void volume, to obtain a relatively higher total transmission energy difference of the obtained coating. An excessively large particle size of the granular silicon dioxide will increase the refractive index of the obtained coating and reduce the air or void volume in the coating, which goes against the incidence of sunlight, thereby reducing the total transmitted energy difference. An excessively small particle size of the granular silicon dioxide will make the particles easy to agglomerate. Preferably, the lower limit of the particle size of the granular silicon dioxide is about 12 nm or more, more preferably about 15 nm or more. Preferably, the upper limit of the particle size of the granular silicon dioxide is about 25 nm or less, more preferably about 20 nm or less. For example, about 18 nm. The granular silicon dioxide herein have a relatively concentrated particle size distribution. In a preferred embodiment, the silicon dioxide is monodispersed.

In an embodiment, based on the total weight of the coating dispersion, the content of granular silicon dioxide is about 1.5 to 10 wt%. A suitable content of granular silicon dioxide is helpful for obtaining a coating with good hydrophilicity and optical properties such as the total transmission energy difference. An excessively high silicon dioxide content goes against the film-forming performance of the coating, and goes against the photocatalytic performance. An excessively low silicon dioxide content will reduce the transmission energy of the obtained coating and weaken the hydrophilicity of the coating. Preferably based on the total weight of the coating dispersion, the lower limit of the content of granular silicon dioxide is about 3 wt%or more, more preferably about 4 wt%or more. Preferably based on the total weight of the coating dispersion, the upper limit of the content of granular silicon dioxide is about 9 wt%or less, more preferably about 8 wt%or less. For example, about 5.7, 6.4, 7.2 wt%.

The combination of granular silicon dioxide and photocatalytic metal compound is helpful for obtaining a coating obtained by coating dispersion with good hydrophilicity, thereby beneficial for maintaining the self-cleaning ability of the coating for a long time. In an embodiment, the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is about 3 to 500. A preferable weight ratio of the granular silicon dioxide to the photocatalytic metal compound is advantageous for obtaining a coating with good photocatalytic performance, self-cleaning performance and optical properties such as a higher total transmission energy difference. An excessively low weight ratio will reduce the total transmission energy difference of the obtained coating, and an excessively high weight ratio will reduce the photocatalytic performance of the coating. Preferably, the lower limit of the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is about 4 or more, preferably about 5 or more, and more preferably about 6 or more. Preferably the upper limit of the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is about 300 or less, preferably about 200 or less, more preferably about 100 or less. For example, about 7, 15, 30, 45, 90.

Binder

The binder herein is preferably a material with a relatively small refractive index or a relatively high light transmittance. In an embodiment, the binder is selected from the group consisting of sol-type silica, silane coupling agent or a combination thereof. In a preferable embodiment, the sol-type silica is prepared by one or more selected from the group consisting of:tetraethoxysilane (TEOS) , sodium silicate, lithium silicate, potassium silicate. In another preferable embodiment, the silane coupling agent is prepared by an organosilane precursor with the following formula or a combination thereof: R ² _nSi (OR ¹) _4-n;

wherein n is an integer of from 0 to 2, R ¹ is a C _XH _2X+1 type alkyl functional group, R ² is an organic group containing for example alkyl, epoxy, acrylate, methacrylate, amine, phenyl or vinyl functional group. x is an integer of from 1 to 20, for example 1, 3, 5, 7, 9, 11, 13, 15, 17, 19. The alkyl has generally from 1 to 20 carbon atoms.

In a more preferable embodiment, the binder is a silicon dioxide collosol prepared by tetraethoxysilane.

A suitable binder content is helpful for obtaining a stable coating dispersion. An excessively high binder content will reduce the light transmittance and total transmission energy difference. An excessively low binder content will affect the coating adhesion performance. In an embodiment, based on the total weight of the coating dispersion, the content of the binder is about 0.2 to 2 wt%. Preferably, the lower limit of the binder content is about 0.4 wt%or more, more preferably about 0.6 wt%or more. Preferably, the upper limit of the binder content is about 1.8 wt%or less, more preferably about 1.6 wt%or less. For example, about 0.7, 1.5 wt%. The binder content herein refers to the content of the compound in the binder solution which can actually participate in the binding reaction, for example, the content of sol-type silica in the silicon dioxide collosol.

In an embodiment, the weight ratio of the granular silicon dioxide to the binder is about 1 to 19. A preferable ratio of the granular silicon dioxide to the binder is helpful for forming a coating with a certain amount of air or voids inside. A certain amount of air or voids inside the coating is advantageous for the incidence of sunlight and forming a coating with a good total transmission energy difference. Preferably, the lower limit of the weight ratio of the granular silicon dioxide to the binder is about 2 or more, preferably about 3 or more, and more preferably about 5 or more. Preferably, the upper limit of the weight ratio of the granular silicon dioxide to the binder is about 17 or less, preferably about 15 or less, more preferably about 12 or less. For example, about 4, 9.

In another embodiment, the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder is about 1 to 19. A preferable ratio of the granular silicon dioxide and the photocatalytic metal compound to the binder is beneficial for forming a coating with good adhesion. Preferably, the lower limit of the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder is about 2 or more, preferably about 3 or more, and more preferably about 5 or more. Preferably, the upper limit of the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder is about 17 or less, preferably about 15 or less, more preferably about 12 or less. For example, about 4, 9. For example, about 4, 10.

The coating dispersion herein is preferably an aqueous coating dispersion. The dispersion medium in the coating dispersion is preferably aqueous solution, water-containing solution or water. The aqueous solution refers to a solution, wherein water is the main dispersion medium. In an embodiment, the dispersion medium according to the present disclosure is an acidic water solution, preferably an inorganic acid aqueous solution. Inorganic acids include but is not limited to hydrochloric acid, sulfuric acid, and nitric acid.

In an embodiment, the pH of the coating dispersion is about 1 to 7. A preferable pH of the coating dispersion is helpful for forming a stable coating dispersion solution. Preferably, the lower limit of the pH is about 2 or more. Preferably, the upper limit of the pH is about 5 or less. For example, 3.

In an embodiment, based on the total weight of the coating dispersion, it comprises from 86.8 to 98.28 wt%of a dispersion medium. Preferably, the lower limit of the dispersion medium is about 90 wt%or more. Preferably, the upper limit of the dispersion medium is about 98 wt%, preferably about 97 wt%or less. For example, 96 wt%, 94 wt%, 92 wt%.

In an embodiment, the solid content of the coating dispersion is about 1.72 to 13.2 wt%. Preferably, the lower limit of the solid content of the coating dispersion is about 2 wt%or more, more preferably about 3 wt%or more. Preferably, the upper limit of the solid content of the coating dispersion is about 10 wt%or less. For example, about 4, 6, 8 wt%. A suitable solid content is helpful for forming a coating with a suitable thickness and good optical properties such as total transmission energy difference.

Process for preparing the coating dispersion

Provided is a process for preparing the coating dispersion according to the present disclosure, comprising

(2) adding the photocatalytic metal compound and the granular silicon dioxide into the binder solution and performing mixing.

The particle size and content of the photocatalytic metal compound are as described in the section of Coating Dispersion, thus the particle size and content of the photocatalytic metal compound will not be repeated here.

The particle size and content of the granular silicon dioxide are as described in the section of Coating Dispersion, thus the particle size and content of the granular silicon dioxide will not be repeated here.

In another embodiment, the content of the binder solution is about 88.8 to 98.4 wt%. Preferably, the lower limit of the content of the binder solution is about 92 wt%or more. Preferably, the upper limit of the content of the binder solution is about 98 wt%or less, preferably about 96 wt%or less, more preferably about 94 wt%or less. For example, about 93 wt%.

In yet another embodiment, the content of the binder in the binder solution is about 0.2 to 4 wt%. Preferably, the lower limit of the content of the binder is about 0.5 wt%or more, more preferably about 0.7 wt%or more. Preferably, the upper limit of the content of the binder is about 2.5 wt%or less, more preferably about 1.7 wt%or less. For example, about 0.8, 1.5 wt%. A preferable binder content in the binder solution is advantageous for adhesion of the coating on the substrate and obtaining the desired total transmission energy difference of the coating.

In an embodiment, the binder solution is selected from the group consisting of silicon dioxide collosol, silane coupling agent solution and a combination thereof. In a preferable embodiment, the silicon dioxide collosol is prepared by one or more selected from the group consisting of: tetraethoxysilane, sodium silicate, lithium silicate, potassium silicate. The silane coupling agent solution is prepared by an organosilane precursor with the following formula or a combination thereof: R ² _nSi (OR ¹) _4-n;

In an embodiment, the binder solution is silicon dioxide collosol. The silicon dioxide collosol is selected from the silicon dioxide collosol, which is prepared by tetraethoxysilane, sodium silicate, lithium silicate or potassium silicate.

Preferably, the silicon dioxide collosol can be prepared, for example, according to the process described in CN 101626989A, which is incorporated herein by reference in its entirety.

In a specific embodiment, the silicon dioxide collosol is prepared by the following process:

(i) mixing acidic aqueous solution with tetraethoxysilane,

(ii) optionally, diluting the product of step (i) .

The acidic aqueous solution in step (i) includes but is not limited to hydrochloric acid, sulfuric acid, nitric acid. The acidic aqueous solution has a pH of about 1 to 4, for example about 2. A suitable pH range is helpful for obtaining a silicon dioxide collosol with good stability. The weight ratio of the tetraethoxysilane to the acidic aqueous solution is about 1: 15 to 5: 1, preferably about 1: 5 to 2: 1, for example about 1: 1.5. The tetraethoxysilane is also known as ethyl orthosilicate.

The dilution in step (ii) makes that the solid content is about 1.72 to 13.2 wt%in the coating dispersion after addition of photocatalytic metal compound and granular silicon dioxide. Preferably, the lower limit of the solid content is about 2 wt%or more, preferably about 3 wt%or more, and the upper limit of the solid content is about 10 wt%or less. For example, about 8 wt%. Water can be used for dilution, or an acidic aqueous solution with a pH of 7 or less can be used for dilution.

In an embodiment, the order of addition in step (2) is not particularly limited. In an embodiment, the photocatalytic metal compound and the granular silicon dioxide are successively added into the binder solution. In another embodiment, the photocatalytic metal compound and the granular silicon dioxide are added into the binder solution at the same time. In yet another embodiment, the photocatalytic metal compound and granular silicon dioxide are mixed and then added into the binder solution. The weight ratio of the granular silicon dioxide to the photocatalytic metal compound, the weight ratio of the granular silicon dioxide to the binder in the binder solution, the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder in the binder solution are as described above.

In the process for preparing the coating dispersion according to the present disclosure, after the mixing in step (2) , it optionally further comprises the step of subjecting the coating dispersion to ultrasonic treatment.

Covered substrate

Provided is a covered substrate, wherein at least one surface of the substrate is at least partially covered with a coating prepared by the coating dispersion according to the present disclosure. For example, it is as shown in Figure 1.

The substrate according to the present disclosure can be any suitable material, which includes but is not limited to photovoltaic cell panel, glass, plastic, metal, polymer or semiconductor or the like. Glass includes but is not limited to borosilicate glass, soda-lime glass, aluminosilicate glass, or the like. The substrate can have any suitable shape, such as a plane or a curved surface, such as a sheet, a flat plate, a tube or any irregular shape.

In an embodiment, the thickness of the coating is about 50 to 200 nm. Preferably, the lower limit of the thickness of the coating is about 60 nm or more, preferably about 70 nm or more. Preferably, the upper limit of the thickness of the coating is about 180 nm or less, preferably about 150 nm or less. For example, about 100 nm. Preferably, the selection of the components and their contents in the coating dispersion according to the present disclosure is helpful for obtaining a coating which has a relatively thin coating thickness and maintains good optical properties such as total transmission energy difference.

The coating comprises coating composition, and the coating composition comprises a photocatalytic metal compound, a granular silicon dioxide and a binder.

In an embodiment, based on the total weight of the coating composition, in the coating composition, the content of the photocatalytic metal compound is from 0.5 to 30 wt%, the content of the granular silicon dioxide is from 50 to 94 wt%, and the content of the binder is from 5 to 45 wt%. In a preferable embodiment, based on the total weight of the coating composition, in the coating composition, the lower limit of the content of the photocatalytic metal compound is about 1 wt%or more, preferably about 2 wt%or more. Based on the total weight of the coating composition, the upper limit of the content of the photocatalytic metal compound is about 20 wt%or less, preferably about 10 wt%or less. For example, about 2, 5, 10 wt%.

In another preferable embodiment, based on the total weight of the coating composition, the lower limit of the content of the granular silicon dioxide is about 60 wt%or more, preferably about 65 wt%or more, more preferably about 70 wt%or more. Based on the total weight of the coating composition, the upper limit of the content of the granular silicon dioxide is about 92 wt%or less, preferably about 90 wt%or less. For example, about 72, 80, 90 wt%.

In yet another preferable embodiment, based on the total weight of the coating composition, the lower limit of the content of the binder is about 7 wt%or more, preferably about 8 wt%or more. Based on the total weight of the coating composition, the upper limit of the content of the binder is about 40 wt%or less, preferably about 30 wt%or less, more preferably about 25 wt%or less. For example, about 9, 20 wt%. The photocatalytic metal compound and the binder are selected as described above.

In an embodiment, the particle size of the photocatalytic metal compound in the coating composition is about 10 to 100 nm. Preferably, the lower limit of the particle size of the photocatalytic metal compound is about 12 nm or more, such as 15 nm or more. Preferably, the upper limit of the particle size of the photocatalytic metal compound is about 60 nm or less, more preferably 40 nm or less. For example, about 20 nm.

In another embodiment, the particle size of the granular silicon dioxide is about 10 to 30 nm.Preferably, the lower limit of the particle size of the granular silicon dioxide is about 12 nm or more, more preferably about 15 nm or more. Preferably, the upper limit of the particle size of granular silicon dioxide is about 25 nm or less, more preferably about 20 nm or less. For example, about 18 nm.

As mentioned above, preferably, the content and particle size of the photocatalytic metal compound and the granular silicon dioxide, the type and content of the binder, and the ratio of the granular silicon dioxide and the photocatalytic metal compound to the binder are advantageous for obtaining a coating with good adhesion, good photocatalytic performance, hydrophilicity, optical properties such as higher total transmission energy difference, and self-cleaning properties.

In an embodiment, in the coating composition, the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is about 3 to 500. Preferably, the lower limit of the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is about 4 or more, preferably about 5 or more, and more preferably about 6 or more. Preferably, the upper limit of the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is about 300 or less, preferably about 200 or less, more preferably about 100 or less. For example, about 7, 15, 30, 45, 90.

In another embodiment, in the coating composition, the weight ratio of the granular silicon dioxide to the binder is about 1 to 19. Preferably, the lower limit of the weight ratio of the granular silicon dioxide to the binder is about 2 or more, preferably about 3 or more, and more preferably about 5 or more. Preferably, the upper limit of the weight ratio of the granular silicon dioxide to the binder is about 17 or less, preferably about 15 or less, and more preferably about 12 or less. For example, about 4, 9.

In yet another embodiment, in the coating composition, the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder is about 1 to 19. Preferably, the lower limit of the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder is about 2 or more, preferably about 3 or more, more preferably about 5 or more. Preferably, the upper limit of the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder is about 17 or less, preferably about 15 or less, more preferably about 12 or less. For example, about 4, 9. For example, about 4, 10.

In an embodiment, the coating according to the present disclosure is obtained by drying the coating dispersion according to the present disclosure.

In an embodiment, the coating contains a certain amount of air or voids. Preferably, the air or voids in the coating are helpful for reducing the refractive index of the coating and increasing the incidence of sunlight. The amount of air or voids in the coating can be characterized by the total transmission energy difference of the coating. In an embodiment, the total transmission energy difference (ΔTE) of the coating is about 1.0 or more. Preferably, the lower limit of ΔTE is about 1.1 or more, more preferably about 1.2 or more, and further preferably about 1.3 or more. ΔTE is for example about 1.2 to 1.8, such as about 1.4, 1.5, 1.6, 1.7. ΔTE of the coating is the TE value of the covered substrate minus the TE value of the uncovered substrate.

In an embodiment, the contact angle of the coating is 10° or less, preferably 5° or less, for example about 2°, 2.5°, 3°.

Process for preparing the covered substrate

Provided also is a process for preparing the covered substrate, comprising applying the coating dispersion according to the present disclosure to at least one surface of the substrate and drying.

The drying temperature should not cause the coating dispersion to decompose. It is usually above about room temperature and below 120 ℃. For example, about 100 ℃, drying at room temperature. Drying can be done with any suitable means, such as in an oven.

The application includes but is not limited to spin coating, spray coating, roll coating, flow coating, dip coating or a combination thereof.

In an embodiment, spin coating is used to apply the coating dispersion to the substrate. For example, the coating dispersion can be deposited with a spin coating machine. The rotation speed can be, for example, about 500 to 2000 rpm.

In another embodiment, spray coating is used to apply the coating dispersion on the substrate.

In yet another embodiment, roll coating is used to apply the coating dispersion on the substrate.

The coating according to the present disclosure can withstand high temperature treatment. In an embodiment, the coating dispersion is applied to the glass substrate. The obtained glass covered by the coating can withstand glass tempering treatment at about 650 ℃.

Provide is further use of the coating dispersion according to the present disclosure in the preparation of a photovoltaic cell panel.

Example

Specific examples are given below to illustrate the marked glass product and its preparation process according to the present disclosure, but not to constitute any limitation.

Materials

Unless otherwise specified, the raw materials and instruments described herein are commercially available.

Photocatalytic metal compound: titanium dioxide, purchased from Efuchem Co. Ltd., with the tradename of EFU-GY02 and particle size of 20 nm.

Granular silicon dioxide, purchased from FUSO Chemical Co. Ltd., with the tradename of NS-24 and particle size of 18 nm.

Binder solution: silicon dioxide collosol

Tetraethoxysilane (TEOS) , purchased from Sinopharm.

Hydrochloric acid, purchased from Sinopharm.

Example 1-3 and Comparative Example 1

The formulations of the coating dispersions of Example 1-3 and Comparative Example 1 are shown in Table 1.

Table 1

*wt% (based on total weight of coating dispersion)

Preparing procedures

(1) Mixing TEOS with hydrochloric acid (pH=2) , wherein the weight ratio of TEOS to hydrochloric acid was 1: 1.5. Stirring at room temperature for at least 2 h to obtain a transparent solution, which was silicon dioxide concentrated collosol.

(2) Diluting the silicon dioxide concentrated collosol obtained in step (1) with water or acidic water and adding titanium dioxide and granular silicon dioxide such that the solid content in the liquid mixture was 8%. The content of each component was described in Table 1.

(3) Mixing the mixture of step (2) in an ultrasonic cleaner for about 30 min to obtain the coating dispersions of Example 1-3 and Comparative Example 1. The pH of the coating dispersion was 3.

(4) Depositing the coating dispersion obtained in step (3) using a spin coating machine with a rotation speed of 1000 rpm. The substrate was selected as glass. The final coating thickness was 100 nm.

(5) Putting the coated glass in an oven and drying at 100 ℃ for 20 min.

The compositions of the coatings were shown in Table 2.

Table 2

Photocatalytic performance test

The coated glasses of Example 1-3 and Comparative Example1 were placed into 2.73 mg/L methylene blue solution and were irradiated with 254 nm UV for 24 h. A spectrophotometer was then used to determine the absorption peak of the methylene blue solution after UV irradiation.

The coated glass of Example 1 showed the original color of the methylene blue solution before UV irradiation, i.e. blue, but the color of the methylene blue solution faded after UV irradiation and become very light blue.

As shown in Figure 2, it can be observed that with the increase of the content of titanium dioxide in the coating/coating dispersion, the absorption of methylene blue solution decreases after irradiation. Therefore, the coated glasses of Example 1-3 show good photocatalytic properties.

Example 4-10

The formulations of the coating dispersions of Example 4-10 were shown in Table 3.

Table 3

*wt% (based on total weight of coating dispersion)

Preparing procedures

The preparing procedures of Example 4-10 were identical to those of Example 1-3 and Comparative Example 1 and the compositions of the coatings were shown in Table 4.

Table 4

Optical performance test

The total transmission energy (TE) of the coated glasses of Examples 1, 4-10 were tested, and the testing instrument was Perkin Elmer Lambda 950 spectrophotometer. The tests were performed with the ISO9050 standard to calculate the total transmission energy values in the wavelength range of from 300 to 1200 nm, which were compared with the total transmission energy values of the glasses without coating, as shown in Figure 3 and Figure 4 (ΔTE (Total Transmission Energy Difference) in Figure 3 and Figure 4 = TE of glass covered by coating -TE of glass not covered by coating) .

It can be observed from Figure 3 and Figure 4 that, compared with the glasses without coating, the total transmission energy (TE) of the coated glasses of Examples 1, 4-10 are improved. In particular, when the content of titanium dioxide in the coating is 10%or less, it shows a higher ΔTE value, which is about 1.5%. It can be observed from Figure 4 that when the weight ratio of granular silicon dioxide to binder is 9 (Example 4) , compared with the weight ratio of granular silicon dioxide to binder is 3.99 (Example 1) , 4 (Example 9) or 3 (Example 10) , a higher ΔTE value can be seen.

Adhesion test

The coating surface of the coated glass of Example 1 was scratched hard back and forth for 20 cycles with a non-woven fabric. There was no change in the coating, no visual scratch, and no change in the total transmission energy difference.

The coated glass of Example 1 was tempered at 650℃. The coated glass after treatment was subjected to scratch resistance test (using a Taber linear scratch tester) , after testing the scratch resistance of the coated glass, the coating chromatic aberration of the coated glass was tested using CIE 1976. The difference of chromatic aberration before and after scratching ΔE=0.96, that is, there is no obvious difference. That is, the coated glass has good scratch resistance.

Contact angle test

A contact angle tester was used to determine the contact angles of the samples of Example 1-10, and the results are shown in Table 5.

It can be seen from Table 5 that the samples of Example 1-10 all has lower contact angle values.

Table 5

Outdoor test

The samples of Example 1 and Comparative Example 1 were subject to outdoor test (i.e. exposed to the atmosphere for a period of time) . The attenuation of ordinate in Figure 5 was the difference between the TEs after the sample was exposed to the atmosphere and before the exposure. It can be found that the attenuation of the total transmission energy of the sample of Example 1 is always lower than that of Comparative Example 1. And the TE has recovered after rainfall. For example, after being placed outdoor for 70 days, the attenuation of the total transmission energy of Example 1 was about 1.5%, while the attenuation of the total transmission energy of Comparative Example 1 was about 2.3%. Therefore, the sample of Example 1 shows excellent self-cleaning ability and low attenuation of total transmission energy over time.

Although the specific embodiments of the present disclosure have been described above, a person skilled in the art should understand that they are provided for illustration only, and the protection scope is defined by the appended claims. A person skilled in the art without departing the principle and essence of the invention, can make various changes or modifications to these embodiments and these changes and modifications all fall within the protection scope of the present invention.

Claims

A coating dispersion, wherein

based on the total weight of the coating dispersion, the coating dispersion comprises

from 0.02 to 1.2 wt%of a photocatalytic metal compound,

from 1.5 to 10 wt%of a granular silicon dioxide, and

from 0.2 to 2 wt%of a binder;

wherein,

the photocatalytic metal compound comprises photocatalytic metal sulfide, photocatalytic metal oxide or a combination thereof, and

the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is from 3 to 500.
The coating dispersion according to claim 1, wherein

the photocatalytic metal compound is zinc oxide, zirconia, tin oxide, titanium dioxide, zinc sulfide, lead sulfide or a combination thereof, preferably titanium dioxide.
The coating dispersion according to claim 1 or 2, wherein

the particle size of the photocatalytic metal compound is from 10 to 100 nm.
The coating dispersion according to any one of claims 1 to 3, wherein

the coating dispersion comprises a granular silicon dioxide having a particle size of from 10 to 30 nm.
The coating dispersion according to any one of claims 1 to 4, wherein

the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is from 5 to 100; and/or

the weight ratio of the granular silicon dioxide to the binder is from 1 to 19, preferably from 3 to 15; and/or

the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder is from 1 to 19, preferably from 3 to 15; and/or

the solid content of the coating dispersion is from 1.72 to 13.2 wt%, preferably from 2 to 10 wt%.
The coating dispersion according to any one of claims 2 to 5, wherein

the content of anatase type titanium dioxide in the titanium dioxide is 80 wt%or more, preferably 90 wt%or more, more preferably 95 wt%or more.
The coating dispersion according to any one of claims 1 to 6, wherein

the binder is one or more selected from the group consisting of: sol-type silica, silane coupling agent;

preferably,

the sol-type silica is prepared by one or more selected from the group consisting of: tetraethoxysilane, sodium silicate, lithium silicate, potassium silicate;

the silane coupling agent is prepared by an organosilane precursor with the following formula or a combination thereof:

R ² _nSi (OR ¹) _4-n;

wherein n is an integer of from 0 to 2, R ¹ is a C _XH _2X+1 type alkyl functional group, R ² is an organic group containing alkyl, epoxy, acrylate, methacrylate, amine, phenyl or vinyl functional group.
The coating dispersion according to any one of claims 1 to 7, wherein

based on the total weight of the coating dispersion, the coating dispersion comprises

from 0.04 to 0.8 wt%of a photocatalytic metal compound, and/or

from 4 to 8 wt%of a granular silicon dioxide; and/or

from 0.4 to 1.8 wt%of a binder.
The coating dispersion according to any one of claims 1 to 8, wherein

the coating dispersion further comprises a dispersion medium, the dispersion medium is aqueous solution, water-containing solution or water; and/or

the pH of the coating dispersion is from 1 to 7, preferably from 2 to 5.
A process for preparing the coating dispersion according to any one of claims 1 to 9, comprising

(1) providing a photocatalytic metal compound, a granular silicon dioxide and a binder solution;

(2) adding the photocatalytic metal compound and the granular silicon dioxide into the binder solution and performing mixing,

wherein, based on the total weight of the coating dispersion,

the content of the photocatalytic metal compound is from 0.02 to 1.2 wt%;

the content of the granular silicon dioxide is from 1.5 to 10 wt%;

the content of the binder solution is from 88.8 to 98.4 wt%.
The process for preparing the coating dispersion according to claim 10, wherein

the particle size of the photocatalytic metal compound is from 10 to 100 nm; and/or

the particle size of the granular silicon dioxide is from 10 to 30 nm.
The process for preparing the coating dispersion according to claim 10 or 11, wherein

the content of the binder in the binder solution is from 0.2 to 4 wt%, preferably from 0.5 to 2.5 wt%.
The process for preparing the coating dispersion according to any one of claims 10 to 12, wherein

the weight ratio of the granular silicon dioxide to the photocatalytic metal compound is from 3 to 500, preferably from 5 to 100; and/or

the weight ratio of the granular silicon dioxide to the binder is from 1 to 19, preferably from 3 to 15; and/or

the ratio of the total weight of the granular silicon dioxide and the photocatalytic metal compound to the weight of the binder is from 1 to 19, preferably from 3 to 15.
A covered substrate, wherein

at least one surface of the substrate is at least partially covered with a coating prepared by the coating dispersion according to any one of claims 1 to 9.
The covered substrate according to claim 14, wherein

at least one surface of the substrate is covered with the coating for 80%or more, preferably 90%or more, more preferably 95%or more.
The covered substrate according to claim 14 or 15, wherein

the substrate is photovoltaic cell panel, glass, plastic, metal, polymer or semiconductor.
The covered substrate according to any one of claims 14 to 16, wherein

the coating comprises a coating composition, the coating composition comprises a photocatalytic metal compound, a granular silicon dioxide and a binder,

wherein based on the total weight of the coating dispersion,

the content of the photocatalytic metal compound is from 0.5 to 30 wt%,

the content of the granular silicon dioxide is from 50 to 94 wt%,

the content of the binder is from 5 to 45 wt%,

wherein the weight ratio of the granular silicon dioxide to the photocatalytic metal compound in the coating composition is from 3 to 500.
A process for preparing the covered substrate according to any one of claims 14 to 17, comprising applying the coating dispersion according to any one of claims 1 to 9 to at least one surface of the substrate and performing drying.
The process for preparing the covered substrate according to claim 18, wherein

the application includes spin coating, spray coating, roll coating, dip coating, flow coating or a combination thereof.
Use of the coating dispersion according to any one of claims 1 to 9 in the preparation of a photovoltaic cell panel.