Patent Description:
A coated substrate comprising a coating layer with inorganic oxide and pores is disclosed herein, the coating layer demonstrates improved anti-soiling properties. The coated substrate may for example be used in solar modules. Further a coating formulation and use of the coating formulation are disclosed.

Anti-reflective (AR) coatings are coatings deposited on substrates, which require high transmission of light such as cover glasses for solar modules and green house glass, and said coatings are able to reduce the reflectivity of said substrates. Performance of solar modules tend to decrease over time amongst other reasons also due to soiling of the surface where light is transmitted through. In areas with high soiling rates, it was found that build-up of sand and dust particles provides a substantial contribution to the decreased performance.

It is the object of the invention to provide an improved coating.

In another aspect of the invention, it is an object of the invention to provide an improved coating formulation.

In a further aspect of the invention, it is an object of the invention to provide a method of improving anti-soiling properties of a coating.

The improvement may for example be achieving of improved anti-soiling properties of the coating, or another feature of the invention.

The subject-matter of the present invention is described in claims <NUM>-<NUM> as attached.

The invention is explained below with reference to exemplary embodiments as well as the drawings, in which.

The invention relates to an improved coating.

Such improved coating may be obtained by converting a coating formulation into a functional coating for example by heating.

Typically by converting the coating formulation on a substrate into a coated substrate.

Coated substrates, such as a cover glass of a solar module comprising an anti-reflective coating, usually need cleaning at some point in time. In particular in arid areas of the world. Cleaning involves among others time and costs and creates waste cleaning materials. There is therefore a need to reduce the cleaning frequency of coated substrates. This invention addresses the reduction of cleaning via improved anti-soiling properties of the coated substrate. The invention provides a coated substrate demonstrating improved anti-soiling properties. The invention provides a coating formulation demonstrating improved anti-soiling properties after application of such formulation on a substrate and converting the dried coating formulation into a coated substrate. The invention provides a solar module demonstrating improved anti-soiling properties.

Improved anti-soiling properties may be demonstrated via reduced frequency of cleaning whilst having the same power output over a period of time e.g. <NUM> months. Improved anti-soiling properties may be demonstrated via an improved power output at the same frequency of cleaning over a period of time e.g. <NUM> months.

Anti-soiling properties may be determined via measuring the transmittance of the anti-reflective coating on a transparent substrate by means of a transmission measurement using a spectrophotometer. The spectrophotometer can be any spectrophotometer which is suitable to analyse a coated substrate. A suitable spectrophotometer includes a Shimadzu UV2600 spectrophotometer. Another suitable spectrophotometer includes an Optosol Transpec VIS-NIR spectrophotometer.

The improved anti-soiling properties may be demonstrated by an increased Anti-Soiling Ratio (ASR) as defined herein. Improved anti-soiling properties may be demonstrated by an increased substrate-coating anti-soiling ratio, ASR, as compared to a reference coated substrate. In an aspect improved anti-soiling properties may be demonstrated by a substrate-coating anti-soiling ratio, ASR, of at least <NUM>%. In an aspect the ASR is at least <NUM>%, in an aspect the ASR is at least <NUM>%, in an aspect at least <NUM>%, in an aspect the ASR is at least <NUM>%.

In an aspect improved anti-soiling properties may be demonstrated by an increased substrate-coating anti-reflective effect, ARE, as defined herein.

Improved anti-soiling properties may be demonstrated by an increased ARE,as compared to a reference coated substrate. In an aspect the ARE is at least <NUM>%, in an aspect the ARE is at least <NUM>%, in an aspect the ARE is at least <NUM>%, in an aspect the ARE is at least <NUM>%.

In an aspect improved anti-soiling properties may be demonstrated by an increased Antisoiling gain, ASG, as defined herein. Improved anti-soiling properties may be demonstrated by an increased ASG, as compared to a reference coated substrate. In an aspect the ASG is at least <NUM>%, in an aspect the ASG is at least <NUM>%, in an aspect the ASG is at least <NUM>%.

The coating formulation according to the invention provides improved anti-soiling properties.

The coating formulation according to the invention provides improved anti-soiling properties to a coating obtained from such formulation after curing i.e. by converting the coating formulation on a substrate into a coated substrate for example by heating, such as by heating above <NUM> degrees Celsius.

The method according to the invention provides a coated substrate demonstrating improved anti-soiling properties.

The present invention relates to a coating formulation according to claim <NUM>.

In an aspect of the invention the coating formulation comprises at least <NUM> wt%, at least 4wt%, at least 5wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least 14wt %, at least <NUM> wt% or at least <NUM> wt % based on inorganic oxide equivalents of elongated dense inorganic oxide particles with an aspect ratio of at least <NUM> and a smaller diameter in the range of <NUM> to <NUM>.

In an aspect of the invention the coating formulation comprises at least <NUM> wt-%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt% based on inorganic oxide equivalents of elongated dense inorganic oxide particles with an aspect ratio of at least <NUM> and a smaller diameter in the range of <NUM> to <NUM>.

In an aspect of the invention the coating formulation comprises at most <NUM> wt%, at most <NUM> wt %, at most <NUM> wt%, at most <NUM> wt%, at most <NUM> wt%, at most <NUM> wt%, at most <NUM> wt% at most <NUM> wt% based on inorganic oxide equivalents of elongated dense inorganic oxide particles with an aspect ratio of at least <NUM> and a smaller diameter in the range of <NUM> to <NUM>. According to the invention the coating formulation comprises between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound, In an aspect of the invention the coating formulation comprises between <NUM> to <NUM> wt-% aluminium oxide. equivalents of aluminium containing compound. In an aspect of the invention the coating formulation comprises between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound, comprises between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound, between <NUM> and <NUM> wt% aluminium oxide equivalents of aluminium containing compound.

In an aspect of the invention the coating formulation comprises at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least 7wt% at least 10wt%, at least <NUM> wt % aluminium oxide equivalents of aluminium containing compound.

In an aspect of the invention the coating formulation comprises <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt % or less aluminium oxide equivalents of aluminium containing compound.

According to the present invention it is provided a method of preparing a coated substrate according to claim <NUM> which comprises the steps of:.

In an aspect a base coating as described herein forms at least a part of the first surface of the substrate. In an aspect a base coating as described herein forms the first surface of the substrate.

Also described herein is a coated substrate obtainable by a method as described herein, including a method comprising the steps of.

Also described herein is a coated substrate comprising:.

wherein the anti-reflective coating layer comprises.

Also described herein is the use of a coating formulation comprising elongated inorganic oxide particles with an aspect ratio of at least <NUM> and a smaller diameter in the range of <NUM> to <NUM> for improving anti-soiling properties of a substrate, where the coating formulation comprising core-shell nanoparticle as porogen where the core comprises an organic compound, such as a polymer like a cationic polymer or an organic compound with a boiling point below <NUM>, and the shell comprises an inorganic oxide, and between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound based on total ash rest after combustion at <NUM>, <NUM> in air.

Also described herein is the use of a coating formulation comprising elongated dense inorganic oxide particles with an aspect ratio of at least <NUM> and a smaller diameter in the range of <NUM> to <NUM> for improving anti-soiling properties of a substrate, wherein the coating formulation comprises core-shell nanoparticles as porogen, wherein the core comprises an organic compound, such as a polymer or an organic compound with a boiling point below <NUM>, the shell comprises a inorganic oxide; and the formulation comprises between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound.

The coating disclosed herein is a porous coating. The coating may be manufactured using a coating formulation comprising a binder and a porogen. The binder comprises inorganic binder particles, such as metaloxide particles, and or an inorganic oxide precursor. A porogen typically is an organic material that will decompose, burn, evaporate or be otherwise removed upon exposure to elevated temperature. Typically the elevated temperature is <NUM> degrees Celcius or more, such as <NUM> degrees Celsius or more, such as <NUM> degrees Celsius or more. Typically the organic material is an organic polymer. A porogen can comprise an organic material comprising an organic polymer such as an organic neutral, an organic cationic an organic anionic polymer, an polylectrolytes or a combination thereof. A porogen typically comprises an organic polymer core and an inorganic oxide shell around the core. The coating according to the disclosure comprises inorganic particles such as elongated inorganic dense oxide particles. It is noted that elongated inorganic dense oxide particles and elongated dense inorganic oxide particles are used interchangeably herein. It is noted that elongated inorganic dense oxide particles and elongated massive metal oxide particles are used interchangeably herein.

In an aspect of the coating formulation according to the invention the elongated dense inorganic oxide particles accounts for <NUM> to <NUM> wt-% of the total amount of inorganic oxide equivalents in the coating formulation, preferably for <NUM> to <NUM> wt-% of the total amount of inorganic oxide equivalents in the coating formulation, more preferably for <NUM> to <NUM> wt-% of the total amount of inorganic oxide equivalents in the coating formulation, and most preferably for <NUM> to <NUM> wt-% of the total amount of inorganic oxide equivalents in the coating formulation. In an aspect of the coating formulation according to the invention the elongated dense inorganic oxide particles accounts for <NUM> to <NUM> wt-% of the total amount of inorganic oxide equivalents in the coating formulation.

In an aspect of the coating formulation according to the invention the elongated dense inorganic oxide particles accounts for at least <NUM> wt% , at least <NUM> wt% <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least 14wt %, at least <NUM> wt%, at least <NUM> wt % , at least <NUM> wt-%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt based of the total amount of inorganic oxide equivalents in the coating formulation.

In an aspect of the coating formulation according to the invention the elongated dense inorganic oxide particles accounts for <NUM> wt% or less, <NUM> wt % or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less or <NUM> wt% or less of the total amount of inorganic oxide equivalents in the coating formulation.

The coating formulations of the present invention comprise a porogen capable of forming pores with a diameter in the range of <NUM> to <NUM>, which porogen is a core-shell nanoparticle where the core comprises an organic compound, such as a polymer or an organic compound with a boiling point below <NUM>, and the shell comprises an inorganic oxide.

The coating according to the invention comprises pores with a diameter in the range <NUM> to <NUM>.

The pores may be open pores, such as an opening along a boundary between two particles and optionally connecting to the surface of the coating, and/or the pores may be closed, such as a (closed) hollow particle.

For pores with a diameter of more than <NUM>, the pore diameter can be estimated by electron microscopy. For pores with a diameter below <NUM>, ellipsometry can be used to determine the size. Porogen pores are preferably of substantially regular shape, such as spherical or ellipsoidal (with one or two long axes) pores. In an aspect, porogen pores are preferably of substantially regular shape, such as spherical or ellipsoidal (with one or two long axes) pores, but should not have an aspect ratio of more than <NUM> as this may negatively influence the mechanical properties of the coating. A hollow particle, such as an hollow inorganic oxide particle may be defined as a particle with an inorganic oxide shell with a hollow core. Porogen pores may be defined by a hollow inorganic oxide particle, such as for example hollow inorganic oxide particles and may originate from core-shell particles having an inorganic oxide (or inorganic oxide precursor) shell and an organic polymer based core, so that upon curing of the coating the polymer will be removed. Upon curing of the coating formulation the polymer will be decomposed/removed and the coating is formed. Porogen pores may be defined by a hollow inorganic oxide particle, such as for example hollow inorganic oxide particles and may originate from core-shell particles having an inorganic oxide (or inorganic oxide precursor) shell and a core material comprising an organic polymer and/or an organic compound, so that upon curing of the coating the core material will be removed. Upon curing of the coating formulation the core material will be decomposed/removed such that a porous coating is formed. The pore typically originates from an organic porogen, that during conversion of the coating formulation into a functional coating typically will be decomposed, burned, evaporated or otherwise removed.

In an aspect a suitable curing temperature is at least <NUM> degrees Celsius. In an aspect a suitable curing temperature is at least <NUM>, in an aspect at least degrees <NUM> Celsius. Pores may also be defined by a combination of inorganic binder particles and/or dense inorganic oxide particles. In this case, the pore typically originates from an organic porogen, such as a polymer particle or another porogen, that during conversion of the coating formulation into a functional coating typically will be decomposed, burned, evaporated or otherwise removed. Porogens include organic neutral, cationic and anionic polymers or polylectrolytes (see e.g. <NPL>; <NPL>).

A pore may originate from an organic porogen, such as a polymer particle or another porogen, that during conversion of the coating formulation into a functional coating typically will be decomposed, burned, evaporated or otherwise removed. It should be observed that conversion does not encompass polymerization of organic (monomeric) compounds as the binder is an inorganic oxide based binder and the conversion therefore is of a sintering type conversion where organics are at least partially removed and metal oxide particles at least partially sinter together.

In addition to porogen pores, smaller pores are also present at least in the binder. In the context of the present invention, binder pores are therefore pores with a diameter of <NUM> to below <NUM>. Binder pores are typically not regular but extended pores in non-contacting regions between adjacent particles of binder, dense inorganic oxide particles and hollow nano particles (if present) and may form a network, which may or may not be in connection with the surface of the coating or with the porogen pores.

The coating according to the invention is a porous coating. By porous is herein meant that the coating has pores and a porosity of at least <NUM>%. The maximum porosity depends on mechanical requirements of the coating layer and is typically <NUM>% or less, preferably the porosity is less than <NUM>% and more preferably the porosity is less than <NUM>%. In an aspect such coating layer has a porosity of <NUM> to <NUM>%. A high porosity generally increases anti-reflective performance but may reduce mechanical strength of a coating. In an aspect the porous anti-reflective coating layer has of porosity of <NUM>% or more, <NUM>% or more, <NUM>% or more,<NUM>% or more, <NUM>% or more, <NUM>% or more, <NUM>% or more. In an aspect the porous anti-reflective coating layer has of porosity <NUM>% or less, <NUM>% or less, <NUM>% or less. In an aspect the porous anti-reflective coating layer has of porosity of <NUM> to <NUM>%. In an aspect the porous anti-reflective coating layer has of porosity of <NUM> to <NUM>%. As is well known by the skilled person, image analysis may suitably be performed on a SEM photo. The person skilled in the art known how to identify pores and the amount of pores and is able to calculate the porosity therefrom.

Alternatively the skilled person may calculate the porosity from a measured refractive index (RI). Knowing the RI of a coating material without any pores, the skilled person can calculate how much air/pore volume is present in the coating layer. The coating material herein is the total inorganic oxide material after convert the coating formulation into a functional coating for example by heating.

Total inorganic oxide material includes all inorganic oxide material in the coating e.g. material of the binder, plus the material of the inorganic oxide shell, plus aluminium containing compound(s).

In an aspect porosity is determined by image analysis on a SEM photo of a cross section of the coating layer orthogonal to the substrate.

In an aspect of the invention the coating layer of the coated substrate has a porosity of <NUM> to <NUM>%.

The coating according to the invention also comprises elongated dense inorganic oxide particles with an aspect ratio of at least <NUM>, and a smaller diameter in the range of <NUM> to <NUM>. Preferably the smaller diameter is in the range of <NUM> to <NUM>. By elongated is meant that at least one of the dimensions of the particle is much longer, such as at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> times the length of another dimension of the particle. It is preferred that the length of the elongated dense inorganic oxide particle is less than <NUM> times the length of another dimension of the particle, such as at most, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> times the length of another dimension of the particle. When the particle has an irregular shape, the aspect ratio is calculated as the length of the longest straight line from one side of the particle to the other side of the particle (even though this may mean that the straight line may be outside the particle) divided by the shortest dimension of the particle transverse to the longest straight line anyway along the straight line. Examples of elongated dense inorganic oxide particles are IPA-ST-UP (Nissan Chemical) and Bindzil <NUM>/750LS (Akzo Nobel) and others are commercially available.

The elongated particle has an aspect ratio of at least two and may, without being limited thereto, have an ellipsoidal, a rod-like or an irregular shape. The elongated particle as used in the invention has a longer axis (which may also be referred to as major) having length x1; and a shorter axis perpendicular to the longer axis (which may also be referred to as minor) having a length x2; and an aspect ratio (x1/x2) of at least two.

The aspect ratio is calculated by dividing the length of the longest axis by the smaller axis. The longest axis may also be referred to as major axis. The smaller axis may also be referred to as the minor axis, the smaller diameter or the shortest dimension of the particle.

Typically for determining the length of an axis of a particle the outside surface of the particle is used.

By dense is meant that the inorganic oxide particle has low or no porosity, such as a porosity of less than <NUM> vol-% or no porosity. In an aspect the elongated dense inorganic oxide particle has a porosity of <NUM> - <NUM> vol-%, in an aspect <NUM>-<NUM> vol-%, in an aspect <NUM>-<NUM> vol-% porosity.

By porogen is herein meant an entity capable of forming pores with a diameter of <NUM> to <NUM>, preferably <NUM> to <NUM>, in the final coating may for example be hollow particle; a core-shell particle with a core with a boiling point below the curing temperature of the coating formulation or a core, which is combustable or depolymerizable below the curing temperature; a particle, which is combustable or depolymerizable below the curing temperature. Porogen may also be referred to as pore forming agent. A core with a boiling point below the curing temperature boiling point has a decomposition temperature of below the curing temperature. A core which is combustable or depolymerizable below the curing temperature is a core that is decomposed or depolymerized, or a combiantion thereof, during curing, i.e. at a temperature which is below the curing temparature. As a result the core is removed and a pore is formed.

Thus by porogen, or pore forming agent, is herein meant an entity capable of forming pores with a diameter of <NUM> to <NUM>, preferably <NUM> to <NUM>, in the final coating. The porogen may be a polymer particle e.g. a polystyrene particle, Pluronic P123 and / or a PMMA particle. The porogen may for example be hollow particle. The porogen may for example be a hollow silica particle. The porogen may for example be a core-shell particle with a core having a boiling point below the curing temperature of the coating formulation. The porogen may be a core-shell particle with a core that is combustable or depolymerizable below the curing temperature or a particle, that is combustable or depolymerizable below the curing temperature. A core having a boiling point below the curing temperature comprises a material having boiling point of below the curing temperature. A core which is combustable or depolymerizable below the curing temperature comprises a material that is decomposed or depolymerized, or a combination thereof, during curing, i.e. at a temperature below the curing temperature. As a result the compound is removed and a pore is formed.

By oxide equivalents of inorganics is herein meant the metal oxides including silicon oxide irrespective of the actual compound that the inorganic species is present in so for example tetraethoxysilane would count as SiO<NUM> irrespective if the species present is tetraethoxysilane, partially hydrolysed tetraethoxysilane or SiO<NUM>. i.e. by oxide equivalents of inorganics is herein meant the equivalent amount of metal oxides including silicon oxide that can be formed from the actual compound or inorganic oxide precursor used. So for example a certain amount of tetraethoxysilane would be expressed as SiO<NUM> equivalent irrespective if the species present is tetraethoxysilane, partially hydrolysed tetraethoxysilane or SiO<NUM>. Analogous for Alumina, one calculates the amount of pure Al<NUM>O<NUM> that could be formed. Aluminum oxide equivalents are calculated back to theoretical Al<NUM>O<NUM> amount based on the alumina precursor added to the formulation.

The alumina precursor may include any of Al(isopropoxide)<NUM>, Al(sec-butoxide)<NUM>, Al(NO3)<NUM>, AlCl3 or a combination thereof.

The silica precursor may include TEOS (tetraethoxysilane), TMOS (tetramethoxysilane), alkylsilanes such as (R)x)Si (OCH3)<NUM>-x where R=CH3; C2H5; OCH3 of OC2H5 or a combination thereof.

In an aspect the inorganic oxide equivalents are based on total ash rest after combustion at <NUM>, <NUM> in air. As the skilled person knows total ash rest after combustion at <NUM>, <NUM> in air is the total residual solid material after combustion at <NUM>, <NUM> in air.

For instance for silica, one starts from alkoxysilane. When it is refered to oxide equivalents, the assumption is made that only pure SiO<NUM> is formed. Analogous for Alumina, if started from Al(NO3)<NUM> one calculates the amount of pure Al<NUM>O<NUM> that could be formed.

For example for <NUM> grams of tetraethyl orthosilicate (TEOS), the amount of inorganic oxide equivalents is calculated as follows: <MAT> <MAT>.

For example for <NUM> gram elongated dense inorganic oxide particles with an aspect ratio of at least <NUM> and an average smaller diameter in the range of <NUM> to <NUM>),
the amount of inorganic oxide equivalents is calculated as follows:
The elongated particles used in the examples are considered to be pure SiO2. So <NUM> gram elongated particles, is equivalent to <NUM> inorganic oxide ( here <NUM> gram SiO2).

In one embodiment, the porogen account for a significant part of the total amount of inorganic oxide in the coating formulation. Preferably, the porogen accounts for <NUM> to <NUM> wt-% of the total amount of inorganic oxide in the coating formulation, and more preferably the porogen accounts for <NUM> to <NUM> wt-% of the total amount of inorganic oxide in the coating formulation. This may for example be the situation when the porogen is a core shell particle or a hollow particle.

In another embodiment, the elongated dense inorganic oxide particles account for a significant amount of the inorganic oxide in the coating formulation. Preferably the elongated dense oxide particles account for <NUM> to <NUM> wt-% of the total amount of inorganic oxide in the coating formulation, more preferably for <NUM> to <NUM> wt-% of the total amount of inorganic oxide in the coating formulation, and even more preferably for <NUM> to <NUM> wt-% of the total amount of inorganic oxide in the coating formulation, such as <NUM> to <NUM> wt-% of the total amount of inorganic oxide in the coating formulation. In an aspect of the coating formulation according to the invention the elongated dense inorganic oxide particles accounts for <NUM> to <NUM> wt-% of the total amount of inorganic oxide in the coating formulation. In an aspect of the coating formulation according to the invention the elongated dense inorganic oxide particles accounts for at least <NUM> wt% , at least <NUM> wt% <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least 14wt %, at least <NUM> wt%, at least <NUM> wt % , at least <NUM> wt-%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt based of the total amount of inorganic oxide in the coating formulation. In an aspect of the coating formulation according to the invention the elongated dense inorganic oxide particles accounts for <NUM> wt% or less, <NUM> wt % or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less or <NUM> wt% or less of the total amount of inorganic oxide in the coating formulation.

The inorganic oxide may be any oxide known from glass coatings. The inorganic oxide may be any known from glass coatings including metal oxides such as for example Al<NUM>O<NUM>, SiO<NUM>, TiO<NUM>, ZrO<NUM>, oxides of lanthanides and mixtures (including mixed oxides) thereof. The inorganic oxide may be any known from glass coatings including metal oxides, compounds and mixtures comprising for example Al<NUM>O<NUM>, SiO<NUM> and optionally one or more of of Li2O, BeO, BaO, MgO, K2O, CaO, MnO, NiO SrO, FeO, Fe2O3, CuO, Cu2O, CoO, ZnO, PbO, GeO2, SnO2, Sb2O3, Bi2O3. It is preferred that the inorganic oxide contains silica, preferably the inorganic oxide contains at least <NUM> wt-% silica and more preferably the inorganic oxide is at least <NUM> wt-% silica, such as the inorganic oxide consisting of silica.

The coated substrate described herein may for example be prepared by a method comprising the steps of providing a substrate; providing a coating formulation according to the first aspect of the invention; apply the coating formulation on the substrate; drying the coating formulation on the substrate; and converting the coating formulation on the substrate into a coated substrate. It should be observed that the conversion does not involve polymerization of an organic polymer but rather a consolidation of the binder and/or conversion of the porogen into a pore in the coating. This may be by heating for example combined with a tempering process of a glass substrate, but may alternatively involve evaporation of solvent in a solvent templated particle, which may take place at a much lower temperature.

In case the core comprises a solvent, e.g. in a solvent templated particle, conversion of the porogen into a pore may involve evaporation of solvent, for example at temperature below <NUM>. The solvent may have a boiling point of at most <NUM>, or at most <NUM>, <NUM> or <NUM>. In such situation, a substrate comprising an applied coating formulation according to the invention is converted into a coated substrate comprising a coating layer on the first surface by exposing the applied coating formulation to a temperature of below <NUM>. In an aspect by exposing the applied coating formulation to a temperature of below <NUM>, below <NUM> or below <NUM>.

An anti-reflective coating comprising IPA-ST-UP particles (elongated particles) and inorganic binder is disclosed in <CIT>. However, <CIT> does not indicate any relevance to anti-soiling properties and does not disclose presence of pores having a diameter of <NUM>-<NUM> in the coating, and particularly not pores of a diameter of <NUM>-<NUM>.

When the coating is applied to a substrate, such as a glass sheet, the coating will have an inner surface facing towards the substrate and an outer surface facing away from the substrate. In one embodiment, the elongated dense inorganic oxide particles are not distributed homogeneously in the coating. Particularly, it was found to be advantageous that the mass ratio of inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating is higher in or near the outer surface of the coating. Here, outer surface refers to the surface of the coating away from the substrate, which surface typically is exposed to the atmosphere.

The distribution may for example be determined by STEM-EDX or by depth profiling. Thus the distribution of elongated dense inorganic oxide particles in a coating may for example be determined by STEM-EDX or by depth profiling. This is particularly advantageous when the chemical composition of the dense inorganic oxide particles and the overall formulation is not the same.

In an aspect of the coating according to the invention the mass ratio of inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating is higher in or near the outer surface of the coating as compared to a reference coating. A suitable reference coating may be a coating without elongated dense inorganic oxide particles.

It was found to be advantageous if the ratio is higher in the <NUM> of the coating closest to the outer surface than the average mass ratio of the inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating. In an aspect the ratio of inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating is at least <NUM>% higher in the <NUM> of the coating closest to the outer surface compared to the average ratio of the inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating. Particularly, it was found to be advantageous when the ratio is higher in the <NUM> of the coating closest to the outer surface that the average mass ratio of the inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating. Preferably the ratio of inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating is at least <NUM>% higher in the <NUM> of the coating closest to the outer surface that the average ratio of the inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating, and more preferably the ratio of inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating is at least twice as high in the <NUM> of the coating closest to the outer surface that the average ratio of the inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating. It could be theorized without being limited thereto that improved anti-soiling properties associated with this distribution of the elongated dense inorganic oxide particles is related to the slight change in surface morphology observed when elongated dense inorganic oxide particles are arrange near or at the surface of the coating.

In an aspect the coated substrate according to the invention demonstrates the mass ratio of inorganic oxide originating from the elongated dense inorganic oxide particles to total inorganic oxide of the coating being higher in a <NUM> thick top layer of the coating closest to the outer surface of the coated substrate than the average mass ratio of the inorganic oxide originating from dense inorganic oxide particles to total inorganic oxide of the coating.

In an aspect the mass ratio of inorganic oxide originating from the dense inorganic oxide particles to total inorganic oxide of the coating is at least <NUM>% higher in the top layer of the coating than the average mass ratio of the inorganic oxide originating from elongated dense inorganic oxide particles to total inorganic oxide of the coating.

In an aspect the mass ratio of inorganic oxide originating from the elongated dense inorganic oxide particles to total inorganic oxide of the coating is at least twice as high in the top layer the coating than the average mass ratio of the inorganic oxide originating from dense inorganic oxide particles to total inorganic oxide of the coating.

The coating according to the invention shows improved anti-soiling properties. The improved anti-soiling properties may be demonstrated by an increased Anti-Soiling Ratio (ASR) as defined by: <MAT> where "T" is the average transmittance from <NUM>-<NUM> measured by a spectrophotometer, Substrate refer to substrate without coating, Coating refers to the substrate with double sided coating. "<NUM>" refer to the measured transmittance before the soil test and "soil" refers to transmittance after soil test. From <NUM>-<NUM> means from <NUM> to <NUM> including <NUM>. In an aspect "T" is the average transmittance from <NUM>-<NUM> measured by a Shimadzu UV2600 spectrophotometer. In an aspect "T" is the average transmittance from <NUM>-<NUM> measured by an Optosol Transpec VIS-NIR spectrophotometer. In an aspect the coated substrate demonstrates an ASR of at least <NUM>%. In an aspect the coated substrate demonstrates an ASR of at least <NUM>%. In an aspect the coated substrate demonstrates an ASR of at least <NUM>%. In an aspect the coated substrate demonstrates an ASR of at least <NUM>%.

The improved anti-soiling properties may be demonstrated by an increased Anti-Soiling Ratio (ASR) as defined by: <MAT> where "T" is the average transmittance from <NUM>-<NUM> measured by a spectrophotometer, Substrate refer to substrate without coating, Coating refers to a double side coated substrate with the coating with alumina and elongated particles, "<NUM>" refers to the measured transmittance before the soil test and "soil" refers to transmittance after soil test. In an aspect "T" is the average transmittance from <NUM>-<NUM> measured by a Shimadzu UV2600 spectrophotometer. In an aspect "T" is the average transmittance from <NUM>-<NUM> measured by an Optosol Transpec VIS-NIR spectrophotometer. In an aspect the coated substrate demonstrates an ASR of at least <NUM>%. In an aspect the coated substrate demonstrates an ASR of at least <NUM>%. In an aspect the coated substrate demonstrates an ASR of at least <NUM>%. In an aspect the coated substrate demonstrates an ASR of at least <NUM>%. For the avoidance of doubt it is noted that "Coating with Al" refers to a double side coated substrate with the coating comprising alumina and elongated particles.

In an aspect the invention provides a coated substrate demonstrating a substrate-coating anti-soiling ratio, ASR, with <MAT> of at least <NUM>%, preferably the substrate-coating ASR is at least <NUM>%, more preferably the substrate-coating ASR is at least <NUM>%, and most preferably the substrate-coating ASR is at least <NUM>%, wherein T is the average transmittance from <NUM>-<NUM>, Substrate refers to substrate without coating, Coating refers to the substrate with double sided coating, <NUM> refers to before soil test and soil refers to after soil test.

The coating according to the invention was found to be particularly advantageous when the coating is an anti-reflective coating on a transparent substrate and the coating exhibit a substrate-coating anti-soiling ratio, ASR, with <MAT> was at least <NUM>%. Here "T" is the average transmittance from <NUM>-<NUM> measured by a Shimadzu UV2600 spectrophotometer, Substrate refer to substrate without coating, Coating refer to the substrate with double sided coating. "<NUM>" refer to the measured transmittance before the soil test and "soil" refer to transmittance after soil test. The soil test is conducted as described in the experimental part.

This way the following values may be obtained:.

TCoating,<NUM> may also be referred to herein as Tcoated substrate,<NUM> or Tcoated substrate with Al,<NUM> or Tcoated substrate without Al,<NUM>.

TCoating,soil may also be referred to herein as Tcoated substrate,soil or Tcoated substrate with Al,soil or Tcoated substrate without Al,soil.

In step e) of the soil test Oscillating may be done by <NUM> cycles at a speed of <NUM> cycles per minute; one cycle being defined as a full revolution of the circular drive disk: one completed back-and-forth movement of the tray of a Taber Oscillating table.

In step f) of the soil test removing excess dust may be done by manually gently tapping a thin edge of the substrate (the side of the glass plate) on a hard surface, such as a table top.

Removing excess dust may be followed by cleaning the back side (the front side being the surface to receive the incident light in the spectrophotometer) of the soiled substrate (soiled glass plate) by gently wiping the back side surface with a soft cloth;.

In an aspect cleaning comprises: cleaning with deionized water and a soft cloth, rinsing with laboratory grade ethanol and leaving to dry overnight.

Preferably cleaning is done at a relative humidity of below <NUM>%.

Soil test and soiling test are used interchangeably herein.

Herein the average transmittance from <NUM>-<NUM> means the average transmittance value in the wavelength range of <NUM> to <NUM>.

In an aspect the transmittance is measured using an Optosol Transpec VIS-NIR spectrophotometer.

In an aspect the transmittance is measured using an Shimadzu UV2600 spectrophotometer.

In an aspect the soil test, in particular step d) and e) above, is performed using a Taber Oscillating Abrasion Tester (such as model <NUM>).

ASR indicates how well the coating improves the anti-soiling properties of the substrate. An ASR of <NUM>% hence means that the coating only loses half the transmittance compared to the transmittance loss of the naked substrate. A naked substrate herein is a substrate without a coating layer, e.g. an uncoated piece of glass. Preferably the substrate-coating ASR of the coating is at least <NUM>%, more preferably the substrate-coating ASR is at least <NUM>%, and most preferably the substrate-coating ASR is at least <NUM>%. ASR cannot be higher than <NUM>% since this would mean that the coating is better after soiling, so the ASR should be maximum <NUM>%.

The improved anti-soiling properties may be demonstrated by an increased Anti-Soiling Gain (ASG) with, ASG = <MAT> where T is the is the average transmittance from <NUM>-<NUM>, Coated Substrate with Al refers to a double side coated substrate with the coating with alumina and elongated particles and Coated Substrate without Al refers to a double side coated substrate with same coating where the alumina and dense inorganic oxide particles are excluded, <NUM> refer to before soil test and soil refer to after soil test, <NUM> refers to before soil test and soil refer to after soil test.

In an aspect the coated substrate demonstrates by an Anti-Soiling Gain (ASG) of at least <NUM>%, in an aspect of at least <NUM>%. The invention provides a coated substrate having an Anti-Soiling Gain, ASG, with <MAT> of at least <NUM>%, preferably the ASG is at least <NUM>%, where T is the is the average transmittance from <NUM>-<NUM>, Coated Substrate with Al refers to a double side coated substrate with the coating with alumina and elongated particles and Coated Substrate without Al refers to a double side coated substrate with same coating where the alumina and dense inorganic oxide particles are excluded, <NUM> refers to before soil test and soil refers to after soil test.

The coating was also found to often fulfill the requirement that the antisoiling gain, ASG Coated substrate according to any one of the embodiments <NUM> to <NUM> as disclosed herein, wherein the coated substrate has an Antisoiling gain, ASG, <MAT> of at least <NUM>%, preferably the ASG is at least <NUM>%, where T is the is the average transmittance from <NUM>-<NUM> measured by a Shimadzu UV2600 spectrophotometer. Coated Substrate with Al refer to a double side coated substrate with the coating with alumina and elongated particles and Coated Substrate withoutAl refer to a double side coated substrate with same coating except the alumina and dense inorganic oxide particles are excluded, <NUM> refer to before soil test and soil referto after soil test. <NUM> refer to before soil test and soil refer to after soil test.

In an aspect the invention provides a coated substrate obtainable by the method of preparing a coated substrate according to the invention, demonstrating improved anti-soiling properties.

Herein it is described a coated substrate comprising:.

wherein the anti-reflective coating comprises.

In an aspect of the invention the anti-reflective coating layer comprises at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt% at least 7wt% at least 10wt%, at least <NUM> wt % aluminium oxide equivalents of aluminium containing compound.

In an aspect of the invention the anti-reflective coating comprises <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt % or less aluminium oxide equivalents of aluminium containing compound.

The porous anti-reflective coating layer may also be referred to herein as coating.

In a preferred embodiment of the coated substrate according to the invention, the coated substrate has an onset dust removal below <NUM>/s, preferably the onset dust removal is between <NUM>/s and <NUM>/s. This allows for ready removal of the dust that settle on the coated substrate by wind as well as facilitate cleaning of the coated substrate. An onset dust removal as described herein is the wind speed for onset of soiling removal, i.e. the wind speed at which a soiling medium, which has been deposited on the surface, starts to be blown away from the surface. Soiling medium may also be referred to as dust herein.

The onset dust removal may be determined e.g. in a closed-return wind tunnel. For example by placing glass slides horizontal on the floor ( at <NUM>° tilt angle) and applying the soiling medium. A suitable amount of soiling medium includes <NUM>-<NUM> gram/m<NUM>, such as <NUM> / m<NUM>. Relative humidity may be kept in a predetermined range e.g. between <NUM> and <NUM>%. The quantity of remaining dust may be measured by a high-precision balance. The windspeed at which the soiling started to be blown away from the surface is referred to as the onset dust removal. This means the weight of the plate including dust after applying the wind at a certain speed is lower than the weight before applying such wind. Suitable soiling medium includes Belgian Brabrantian loess. Suitable soiling medium includes Arizona test dust from quartz A4 coarse (size varying from <NUM> to <NUM>), Suitable soiling medium includes Arizona ISO12103-<NUM> A2 fine sand, Arizona ISO12103-<NUM> A4 coarse sand, Dust Mix "China fine", Dust Mix "China coarse", all commercially available at KSL staubtechnik gmbh, Germany.

The substrate is a solid material, such as a polymer sheet or a glass member. The substrate may include quartz or polymer foil, such as glass foil. Examples of polymer substrates are plastic foils and polymers based on one or more of the polymers selected from Polyethylene terephthalate (PET), Polymethyl methacrylate (PMMA), Polyethylene naphthalate (PEN). A further example of a polymer substrate includes polyimide (PI). Polymer substrates are advantageous for flexible solar cells. Preferably the substrate is transparent. Preferably, the substrate is a glass member being selected from the group of float glass, chemically strengthened float glass, borosilicate glass, structured glass, tempered glass and thin flexible glass having thickness in the range of for example <NUM> to <NUM> such as <NUM> to <NUM> as well as substrates comprising a glass member, such as a partially or fully assembled solar module and an assembly comprising a glass member. The glass member may be SM glass or MM glass. A commercially available MM glass includes Interfloat GMB SINA <NUM> solar glass for photovoltaic applications.

In an aspect of the invention the coated substrate is a cover glass for a solar module.

The invention further relates to a solar module comprising a coated substrate as described herein.

Examples of partially or fully assembled solar modules are modules comprising a glass member forming at least a part of the first surface of the substrate and at least one member selected from the group consisting of thin film transparent conductive and/or semiconductor layers, a back sheet, an encapsulant, an electrical conducting film, wiring, controller box and a frame wherein the glass member being selected from the group of float glass, chemically strengthened float glass, borosilicate glass, structured glass, tempered glass and thin flexible glass having thickness in the range of for example <NUM> to <NUM> such as <NUM> to <NUM>. Preferred substrates for the method according to the invention are hence tempered glass, chemically strengthened glass and substrates comprising temperature sensitive components, such as partially or fully assembled solar cell modules. In one embodiment, the substrate comprises a transparent solid sheet member with a base coating on a first side of the sheet member so the base coating forms at least a part of the first surface of the substrate, to be coated with the single non-laminated layer coating layer. Preferably, the base coating is selected from the group of barrier coatings, such as sodium barrier coatings, and anti-reflective coatings.

In an aspect the coated substrate according to the invention comprises a transparent solid sheet member, and a base coating layer interposed between the first surface and the coating layer on the first coating, preferably the base coating is selected from the group of barrier coatings and anti-reflective coatings.

In an aspect the substrate is transparent solid sheet member with a base coating on a first side of the sheet member so the base coating forms at least a part of the first surface of the substrate. In an aspect the substrate is transparent solid sheet member with a base coating on a first side of the sheet member so the base coating forms the first surface of the substrate.

The improved anti-soiling properties may be demonstrated by an increased ARE with <MAT> where T is the is the average transmittance from <NUM>-<NUM>, Substrate refers to substrate without coating, Coated substrate refers to the substrate with double sided coating and <NUM> refers to before soil test.

Tcoating,<NUM> and T coated substrate,<NUM> are used interchangeably herein. As a result ARE may also be phrased as: ARE = TCoated substrate,<NUM> - TSubstrate,<NUM>.

The coating according to the invention is preferably an anti-reflective coating. In an aspect according to the invention the coated substrate demonstrates an ARE of at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%.

In an aspect the coated substrate according to the invention demonstrates a substrate-coating anti-reflective effect, ARE, with <MAT> of at least <NUM>%, preferably the ARE is at least <NUM>%, more preferably the ARE is at least <NUM>%, where T is the is the average transmittance from <NUM>-<NUM>, Substrate refers to substrate without coating, Coated substrate refers to the substrate with double sided coating and <NUM> refers to before soil test. In an aspect T is the average transmittance from <NUM>-<NUM> measured by a Shimadzu UV2600 spectrophotometer. In an aspect T is the average transmittance from <NUM>-<NUM> measured by an Optosol Transpec VIS-NIR spectrophotometer.

It is highly preferred that when the coating is arranged on a transparent substrate the coating will have a substrate-coating anti-reflective effect, ARE, <MAT> of at least <NUM>%, preferably the ARE is at least <NUM>%, more preferably the ARE is at least <NUM>%, where T is the is the average transmittance from <NUM>-<NUM> measured by a Shimadzu UV2600 spectrophotometer. Here, "Substrate" refer to substrate without coating, and "Coating" refer to the substrate with double sided coating.

The coating according to the invention is particularly suitable for lowering the reflectivity of a transparent substrate for example any type of glass substrate, hence being used as an anti-reflective coating.

Herein it is also described a coating formulation comprising a porogen capable of forming pores with a diameter of <NUM>-<NUM>, elongated dense inorganic oxide particles with an aspect ratio of at least <NUM> and a smaller diameter in the range of <NUM> to <NUM>, an inorganic binder, a solvent and <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound. Aluminium and aluminum are used interchangeably herein. In an aspect the aluminium oxide equivalents of aluminium containing compound are based on total ash rest after combustion at <NUM>, <NUM> in air. The aluminium may be provided for example as metal oxide powder, but more preferably as an organic or inorganic salt optionally in solution or suspension. In a preferred embodiment, the coating formulation comprises between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound as it was found that the stability in the sense of shelf life was best for aluminium concentrations in this range. Stability refers to the stability of the coating formulation. The stability of the coating formulation may be assessed by looking at the homogeneity of the coating formulation. An inhomogeneous coating formulation indicates a low stability and low shelf life. The inhomogeneity of the formulation can be directly observed by the presence of sediments or gellation in the liquid formulation or can be measured by DLS (Dynamic Light Scattering) via the growth or aggregation of colloidal particles in the suspension over time. Using an inhomogeneous coating formulation typically results in a non-homogeneous coating.

In an aspect the coating formulation described herein comprises.

wherein the coating formulation comprises between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound based on total ash rest after combustion at <NUM>, <NUM> in air, preferably the coating formulation comprises between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound based on total ash rest after combustion at <NUM>.

The porogen may for example be hollow inorganic oxide particles, or core-shell particles having an inorganic oxide (or inorganic oxide precursor) shell and a core comprising an organic compound, such as a cationic polymer or an organic compound with a boiling point below <NUM>. The porogen may also be an organic porogen, such as organic nano particle like for example an organic polymeric nanoparticle or another porogen, that during conversion of the coating formulation into a functional coating typically will be decomposed, burned, evaporated or otherwise removed. By organic nano particle is herein meant a particle comprising one or more organic molecules and having a size in the range of <NUM> to <NUM>. Examples of organic molecules are polymers, such as acrylic polymers and latexes; and oligomers. The elongated dense inorganic oxide particle is discussed above.

In an aspect the porogen accounts for <NUM> to <NUM> wt-% of the total amount of inorganic oxide equivalents in the coating formulation. In an aspect the porogen accounts for <NUM> to <NUM> wt-% of the total amount of inorganic oxide equivalents in the coating formulation.

The inorganic binder typically comprises inorganic oxide particles with a diameter in the range of <NUM> to <NUM> and/or an inorganic oxide precursor with a diameter in the range of <NUM> to <NUM>. The inorganic binder is preferably an inorganic oxide particle or inorganic oxide precursor with a diameter in the order of <NUM> to <NUM>.

It is noted that the inorganic oxide particles may have a diameter of more than <NUM>, e.g. in the range of <NUM> to <NUM>. It is noted that the inorganic oxide precursor may have a diameter of more than <NUM>, e.g. in the range of <NUM> to <NUM>.

The inorganic binder comprises inorganic oxide nano particles with an average diameter in the range of <NUM> to <NUM>.

The inorganic binder typically comprises inorganic oxide particles with a diameter in the range of <NUM> to <NUM> and/or an inorganic oxide precursor with a diameter in the range of <NUM> to <NUM>.

The diameter of the inorganic oxide particle and/ or the inorganic oxide precursor may be measured with Dynamic Light Scattering (DLS). Examples are pre oligomerized silicium alkoxide such as pre oligomerized tetraethoxysilane, pre oligomerized titanium alkoxide and metal oxide sol gels. An example of an inorganic oxide particle and/ or the inorganic oxide precursor includes metal oxide sols. Pre oligomerized silicium alkoxide is also referred to by the skilled person as pre oligomerized silicon alkoxide. An inorganic binder may for example be prepared as described in <CIT> (incorporated herein by reference).

The coating formulation according to the invention comprises a solvent. The solvent can be any solvent, combination of solvents or combination of solvents and additives, such as surfactants and stabilizers, that can realize a stable dispersion of the coating formulation. Typically, the solvent accounts for <NUM> - <NUM>% of the mass of the coating formulation. Highly suitable solvents are isopropanol (IPA), water or combinations of solvents including IPA and/or water.

The coating formulations according to the invention comprises elongated dense inorganic oxide particles with an aspect ratio of at least <NUM>, and a smaller diameter in the range of <NUM> to <NUM> in a coating on a substrate for improving anti-soiling properties of a substrate. It was highly unexpected that the shape of the dense inorganic oxide particles appeared to have a major influence on the anti-soiling properties of the coating and that it hence was possible to reduce the sensitivity to soiling of a substrate by coating it with a coating where elongated dense inorganic oxide particles were included. A coating prepared from a coating formulation comprising non-spherical particles such as elongated particles, in particular elongated dense inorganic oxide particles, demonstrates improved anti-soiling properties as compared to a coating prepared from a coating formulation without elongated dense inorganic oxide particles. In an aspect a coating prepared from a coating formulation comprising non-spherical particles such as elongated particles, in particular elongated dense inorganic oxide particles, demonstrates improved anti-soiling properties as compared to a coating prepared from a coating formulation comprising spherical particles. In other words, this method of reducing sensitivity to soiling of a substrate includes the steps of applying a coating formulation containing elongated dense inorganic oxide particles to a substrate, and convert the coating formulation into a functional coating for example by heating.

Another aspect of the invention concerns a solar module comprising a coated substrate according to the first aspect of this invention. Another aspect of the invention concerns a solar module comprising a coated substrate as described herein. Such solar module exhibits significantly better performance over time at lower operational costs. The reason for that being the reduced frequency of cleaning or the improved power output at the same frequency of cleaning, all of which become possible due to the enhanced anti-soiling properties of the coating of the invention that significantly reduces the soiling of said solar module. Other advantageous devices comprising the coated substrate according to the invention are greenhouse glass (or polymer membrane), concentrated solar modules, windows, displays. In some applications, such as for example roof top coating or container surfaces, the substrate may be non-transparent and the advantage of the invention is there focused on the ability of the anti-soiling coating to reduce collection of dirt on the substrate or to enhance cleanability of the coated substrate as compared to the uncoated substrate.

The coating formulation may be applied to a substrate by any known technique in the art, for example dipping, brushing, spraying, spinning, slot die coating, aerosol coating or via the use of a roller. Spraying can be airless or with the use of conventional air, or electrostatic, or high volume/low pressure (HVLP) or aerosol coating. It is preferred that the coating formulation is applied by roll coating, aerosol coating or dip coating.

By functional coating is meant a coating that enhances mechanical, optical and/or electrical properties of the substrate to which the functional coating is attached. Examples of possible enhanced mechanical properties of a substrate coated with the coating of the invention are increased surface hardness, increased stiffness or wear properties as compared to the mechanical properties of the uncoated substrate. Examples of possible enhanced optical properties of a substrate coated with the coating of the invention are increased light transmittance from air through the functional coating and substrate compared to light transmittance directly from air through the substrate, and reduced reflectance from the interphase from air to the functional coating and the functional coating to the substrate compared to the reflectance directly from air to uncoated substrate. Examples of possible enhanced electrical properties of a substrate coated with the coating of the invention are increased conductivity as compared to the unconverted coating and/or to the uncoated substrate.

Another aspect described herein concerns the use of a coating formulation comprising elongated inorganic oxide particles with an aspect ratio of at least <NUM> and a smaller diameter in the range of <NUM> to <NUM> for improving anti-soiling properties of a substrate. Particularly, this embodiment concerns a coating formulation comprising core-shell nanoparticle as porogen where the core comprises an organic compound, such as a cationic polymer or an organic compound with a boiling point below <NUM>, and the shell comprises an inorganic oxide, and between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound based on total ash rest after combustion at <NUM>, <NUM> in air. Another aspect described herein includes the use of a coating formulation as described herein for improving anti-soiling properties of a substrate, such as a cover glass for a solar module.

Another aspect described herein includes the use of a coating formulation comprising elongated dense inorganic oxide particles with an aspect ratio of at least <NUM> and a smaller diameter in the range of <NUM> to <NUM> for improving anti-soiling properties of a substrate, wherein the coating formulation comprises core-shell nanoparticles as porogen, wherein the core comprises an organic compound, such as a polymer or an organic compound with a boiling point below <NUM>, the shell comprises a inorganic oxide; and the formulation comprises between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound.

Another aspect described herein includes the use of the combination of.

Another aspect described herein includes the use of elongated dense inorganic oxide particles with an aspect ratio of at least <NUM>, and a smaller diameter in the range of <NUM> to <NUM> to reduce the soiling of a solar module.

Additionally, herein are described the following embodiments <NUM>-<NUM>:.

The optical properties were measure from <NUM>-<NUM> using a Shimadzu UV2600 and the maximum transmittance was established.

Soiling procedure: The anti-soiling properties of the coatings were tested with a Taber Oscillating Abrasion Tester (model <NUM>) using commercially available Arizona test dust from quartz A4 coarse (size varying from <NUM> to <NUM>) as soiling medium, commercially available from KSL Staubtechnik GMBH. The <NUM> x <NUM> glass plate to be tested was first cleaned with deionized water and a soft cloth, rinsed with laboratory grade ethanol and left to dry overnight. The coated sample was then placed in the tray of the Taber Oscillating table so that the top surface of the glass plate is at the same height as the sample holder inside the tray. Next, <NUM> of Arizona test dust is gently dispersed over the whole glass plate using a brush. The soiling procedure (<NUM> cycles at a speed of <NUM> cycles per minute; one cycle was defined as a full revolution of the circular drive disk: one completed back-and-forth movement of the tray) was performed. The test sample was then removed from the tray and gently tapped to remove the excess of sand on its surface. The relative humidity in the testing environment was at <NUM> %RH and the temperature was <NUM>.

Soiling evaluation: The degree of soiling of the coatings was determined by relative loss in transmittance after soiling, measured with Optosol Transpec VIS-NIR. To that end, transmittance spectra were recorded prior and post artificial soiling via the Taber Oscillating Abrasion Tester. Subsequently, the maximum of transmittance over <NUM>-<NUM> spectra was established. Based on the resulting differences between the before and after values of the maximum transmittance over <NUM>-<NUM> recorded in the spectra, conclusions regarding the level of soiling and hence the effectiveness of the anti-soiling coatings could be drawn.

Cured sample was scraped off substrate with razorblade. The scrapings were rinsed from the substrate with ethanol and collected. One drop of ethanol suspension was transferred to carbon grid and dried, where after the elemental composition was determined by STEM EDX on scrapings arranged on the edge of the carbon grid. At least components Si, O, Al, and Ti were measured and amounts were determined by the software Esprit <NUM>.

Pore size of porogen pores, i.e. pores with a diameter in the range of <NUM> to <NUM>, is defined as the length of a line indicating the longest distance between walls of the pore on a cross section orthogonal to the surface of the substrate as measured by SEM. For irregular pore, the line indicating the longest distance may go outside pore. As is well known SEM stands for Scanning Electron Microscopy.

For binder pores with a pore size between <NUM> to <NUM>, ellipsometry is used to measure the pore size, using the method indicated herein. Since the method utilizes sorption of water in the pores, the measured size corresponds to the smallest diameter of the pore.

The size of the binder particles and the size of the elongated dense inorganic particles are measured using CryoTEM. The average size is the number average size based on ten randomly selected particles.

The volume fraction and pore size distribution of binder pores were determined by water sorption under variation of relative partial pressure of water. In a pore size regime ranging from <NUM> to <NUM>, the saturation pressure (and hence condensation/evaporation of water in the pores) is a function of the smallest dimension of the pore as described by the Kelvin equation. Condensation of water in the pores drastically changes the optical properties of the coating due to the difference in density between water and air, which optical properties were measured by ellipsometry.

Sample preparation depends on substrate type. For float glass, a scotch tape was applied on the backside of the glass to reduce backside reflections. For SM glass, measurement was done using focusing probes to reduce light scattering induced by the sample roughness. No scotch tape was applied at the backside in the case of SM glass. SM glass used was Interfloat GMB SINA <NUM>,<NUM> glass.

The ellipsometer used was a Woollam M-<NUM> UI running CompleteEase (Woollam) version <NUM>.

The experimental data were analyzed by fitting to optical models built using CompleteEase. The bare, uncoated substrate was measured first and then fitted using a b-spline model. The coating layer was described by a Cauchy model, using the first two terms of the series development, A and B. For the evaluation of the model, the data measured at <NUM>% rH was used.

Core-shell particles were prepared by the same method as disclosed in <CIT> using isopropanol instead of ethanol. The solution was further diluted with isopropanol to a concentration of <NUM> wt-% silica equivalents and had a particle size of <NUM>.

Silica based inorganic binder was prepared from tetraethoxysilane was prepared by the same method as disclosed in <CIT> and further diluted with isopropanol to achieve a binder solution of about <NUM> wt-% silica equivalents and a particle size of <NUM>-<NUM>.

Titania based inorganic binder was prepared from titanium(IV)propoxide by mixing diluted HCl with ethanol and titanium(IV)propoxide into a transparent liquid. This mixture was added to ethanol and water at room temperature to achieve a transparent binder solution with particle size of about <NUM>-<NUM> and a concentration of <NUM> wt-% of titania equivalents. To overcome limited shelf life issues, the titanium based binder was used in preparing coating formulations within <NUM> of preparation of the inorganic binder.

Al-Stock solution was prepared by dissolving Al(NO<NUM>)<NUM>. 9H2O (Fluka, Lot SZBG0830V) into a mixture of isopropanol (Sigma Aldrich, Lot K46556366515) and methoxypropanol (Alfa Aesar, Lot Q14C027) to a solid content of <NUM>%. Thereafter the solution was further diluted with isopropanol to <NUM> wt-% alumina equivalents.

Stock solution of elongated IPA-ST-UP particles was prepared by diluting IPA-ST-UP (Nissan Chemical, Lot <NUM>) with isopropanol to a concentration of <NUM> wt-% of oxide equivalents. This stock solution was used to prepare the samples in Table <NUM>.

Stock solution of elongated Bindzil <NUM>/750LS silica-based particles was prepared by diluting Bindzil particles in a glacial acetic acid / water mixture of pH <NUM> followed by addition of nitric acid to pH <NUM>. The mixture is further diluted with isopropanol to a final concentration of <NUM> wt-% of inorganic oxide. <NUM> wt-% of inorganic oxide equivalents. Bindzil <NUM>/750LS silica-based was obtained from Akzo Nobel (Netherlands).

All formulations were made in a <NUM> semi-transparent HDPE bottle with lid. Amounts of each component are indicated in Table <NUM>. Core-shell solution weighted and <NUM>-propanol was added and the bottle shaken. To this mixture, the inorganic binder was added and the bottle shaken. Subsequently the diluted Al-stock solution was added, and finally the stock solution of elongated particles was added.

Coatings was prepared with coating formulation that were maximum <NUM> old. All samples were soiled within <NUM> after preparation of the coating. Formulations were filled into a rectangular shaped container, with an inner size of <NUM>*<NUM>*<NUM>. filled with approximately <NUM> of coating formulation.

The coating formulations used to make the coated samples used in the soiling test were maximum <NUM> hours old.

Glass used was <NUM> Optiwhite float glass cut into <NUM>*<NUM> plates. Plates were washed and dried prior to coating application. Dipping conditions were: <NUM>-<NUM>; relative humidity <<NUM>% rH; dipping speed was varied between <NUM>-<NUM>/s as indicated in Table <NUM>. The Optiwhite float glass used was Optiwhite S.

The coated samples were cured by heating in an oven at <NUM> for <NUM> minutes. This treatment is similar to the thermal conversion realized during the tempering process typically used for cover glass for PV solar modules.

Examples of transmission measurement for a comparative sample (sample <NUM>) before and after soiling is shown in <FIG>. It is observed that soiling dramatically reduced the transmission. In <FIG>, the transmission measurement for a sample according to the invention is shown. Here, the transmission before and after soiling are very close.

From Table <NUM> it is observed that if elongated particles are present, then more than <NUM>% wt-% equivalent of Al<NUM>O<NUM> were needed to achieve a stable coating formulation with a shelf life of more than a few days. For alumina contents up to about <NUM>,<NUM>% equivalent Al<NUM>O<NUM>, it was observed that increasing the Al<NUM>O<NUM> content lead to an increase in optical properties and AS performance (lower loss after soiling test). From <NUM>,<NUM>%, the properties seem to reach a plateau. At higher Al<NUM>O<NUM> loading, from <NUM>,<NUM>% to <NUM>,<NUM>%, a decrease in optical performance was observed. In general, the observations are summarized in Table <NUM>.

It is observed that a stable coating formulation leading to an even coating was achieved for a coating formulation containing core-shell particles and inorganic binder, whereas the same coating formulation became unstable leading to un-even coatings and sedimentation in the coating formulation starting within days when elongated particles was added. When this formulation further contained aluminum species, the resulting coating formulation was stable and the achieved coating showed both anti-reflection and anti-soiling behavior.

For coating formulations containing inorganic oxide binder based on titanium and silicon species as well as core-shell particles, it was observed that if no elongated particles and no aluminum source was added, the coating formulation was unstable leading to un-even coatings. By adding an aluminum source, a stable formulation leading to a coating with anti-reflective properties was obtained. By further adding elongated particles, also anti soiling properties was achieved.

The windspeed for onset of soiling removal was determined in the closed-return wind tunnel of the Geography Research Group at KU Leuven, Belgium using Belgian Brabrantian loess as test dust. Clean, coated and uncoated <NUM> x <NUM> x <NUM> Pilkington Optiwhite glass slides were placed horizontal on the floor of the large test section of the wind tunnel, more than <NUM> downwind from the entrance of the test section and at <NUM>° tilt angle. <NUM>/m<NUM> of dust were applied. Relative humidity is kept between <NUM> and <NUM>%. Thereafter, the samples were moved to a section where wind speed could be increased progressively from <NUM>/s to <NUM>/s. For each step of wind speed, the quantity of remaining dust was measured by a high-precision balance and the onset dust removal was determined. In <FIG>, a plot of the results is shown. It is observed that for sample z according to the invention, onset dust removal is at a surprisingly much lower wind speed as compared to an uncoated sample (sample z, corresponding to sample XX in Table <NUM>) and the commercially available anti-reflective coating T2 of DSM. In Table <NUM>, the results are summarized.

The Optiwhite float glass used was Optiwhite S.

The transmittance was measured from <NUM>-<NUM> using an Optosol Transpec VIS-NIR. The average transmittance and Max T% (λ at Max) were determined. The results are listed below.

Soiling procedure: The anti-soiling properties of the coatings were tested with a Taber Oscillating Abrasion Tester (model <NUM>) using commercially available Arizona test dust from quartz A4 coarse (size varying from <NUM> to <NUM>) as soiling medium, commercially available from KSL Staubtechnik GMBH. The <NUM> x <NUM> glass plate to be tested was first cleaned with deionized water and a soft cloth, rinsed with laboratory grade ethanol and left to dry overnight. The coated sample was then placed in the tray of the Taber Oscillating table so that the top surface of the glass plate is at the same height as the sample holder inside the tray. Next, <NUM> of Arizona test dust was gently dispersed over the whole glass plate using a brush. The soiling procedure (<NUM> cycles at a speed of <NUM> cycles per minute; one cycle was defined as a full revolution of the circular drive disk: one completed back-and-forth movement of the tray) was performed. The test sample was then removed from the tray and gently tapped to remove the excess of sand on its surface. The back side of the tested glass plate was gently wiped with a soft cloth to remove any dust adhering under the plate. The relative humidity in the testing environment was at <NUM> %RH and the temperature was <NUM>.

Soiling evaluation: The degree of soiling of the coatings was determined by relative loss in transmittance after soiling, measured with an Optosol Transpec VIS-NIR spectrophotometer. To that end, transmittance spectra were recorded prior and post artificial soiling via the Taber Oscillating Abrasion Tester. Subsequently, the average of transmittance over <NUM>-<NUM> was established from the spectra. Based on the resulting differences between the before and after values of the average transmittance over <NUM>-<NUM> recorded in the spectra, conclusions regarding the level of soiling and hence the effectiveness of the anti-soiling coatings could be drawn.

The coated samples listed in table <NUM> were dried at least <NUM> minute at room temperature and thereafter cured by heating in an oven at <NUM> for <NUM> minutes.

This treatment is similar to the thermal conversion realized during the tempering process typically used for cover glass for PV solar modules. The results of the optical measurements are listed in Table <NUM>.

Preparation of core-shell particle solution was done as described in example <NUM> above. Preparation of inorganic binder was done as described in example <NUM> above.

Preparation of coating formulations was done as described above in Example <NUM>. Amounts of each component are indicated in Table <NUM>.

Coating of samples (coating glass with coating formualtion) was done as described above in Example <NUM>.

For the results in Table <NUM> the glass used was <NUM> Optiwhite S float glass was used. The glass was cut into <NUM>*<NUM> plates. Plates were washed and dried prior to coating application. Dipping conditions were: <NUM>; relative humidity <<NUM>% rH; dipping speed was varied between <NUM>-<NUM>/s as indicated in Table <NUM>.

For the results in Table <NUM> Interfloat MM glass (textured glass) was used. The dipping speed was set such that an optical thickness of about <NUM> was obtained.

The coated samples listed in table <NUM> were dried at least <NUM> minute at room temperature and thereafter cured by heating in an oven at <NUM> for <NUM>,<NUM> minutes. This treatment is similar to the thermal conversion realized during the tempering process typically used for cover glass for PV solar modules. The results of the optical measurements are listed in Tables <NUM> and <NUM>.

Method of optical measurement: same as under "Method of optical measurement used in example <NUM>" (see above).

Method of soiling measurement (soil test) : same as under "Method of soiling measurement (soil test) example <NUM>"(see above).

Claim 1:
A coating formulation comprising
i. at least <NUM> wt-% based on inorganic oxide equivalents of elongated dense inorganic oxide particles with an aspect ratio of at least <NUM> and a smaller diameter in the range of <NUM> to <NUM> as determined by CryoTEM;
ii. a porogen capable of forming pores with a diameter in the range of <NUM> to <NUM> as determined by SEM (Scanning Electron Microscopy), which porogen is a core-shell nanoparticle where the core comprises an organic compound, such as a polymer or an organic compound with a boiling point below <NUM>, and the shell comprises an inorganic oxide;
iii. an inorganic oxide binder; and
iv. a solvent,
wherein the coating formulation comprises between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound, preferably the coating formulation comprises between <NUM> to <NUM> wt-% aluminium oxide equivalents of aluminium containing compound.