PROCESS FOR MAKING AN ANTI-SOILING COATING COMPOSITION AND A COATING MADE THEREFROM

Abstract

The disclosure relates to a process to provide a substrate having improved anti-soiling properties. The disclosure also relates to an anti-soiling coating composition, and to a process of making an anti-soiling coating composition. Use of the coating composition to improve anti-soiling properties of a substrate.

Description

The disclosure relates to a process to provide a substrate having improved anti-soiling properties. The disclosure further relates to a process for making an anti-soiling (AS) coating composition comprising the steps of preparing an aqueous dispersion of organic-inorganic core-shell nano-particles, and optionally adding an inorganic or organic polymeric or polymerisable compound as binder. The disclosure also relates to an anti-soiling coating. The disclosure also relates to the anti-soiling coating. having anti-reflective properties.

The disclosure also relates to an AS coating composition (ASC composition) as obtained with said process, and to a process of applying an anti-soiling coating (ASC) on a substrate using such composition, and to the resulting coated substrate. The disclosure also relates to a substrate comprising the anti-soiling coating. Another aspect of the disclosure 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 of the disclosure includes the use of a coating formulation as described herein for improving anti-soiling properties of a substrate. In another aspect the use of a coating formulation as described herein also provides anti-reflective properties to the substrate, i.e. provides increased transmission of the coated substrate as compared to a reference. In an aspect the reference is uncoated glass.

Coated substrates (such as coated cover glass of solar modules) 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 composition demonstrating improved anti-soiling properties after application of such composition on a substrate and converting the dried coating composition into a coated substrate. The coating of the coated substrate is referred to herein as anti-soiling coating (ASC) provides a coating composition demonstrating improved anti-soiling properties after application of such composition on a substrate and converting the dried coating composition into a coated substrate is referred to herein as Anti-Soiling Coating composition (ASC composition)

Practice of the inventive process may provide a solar module demonstrating improved anti-soiling properties. A coating composition may also be referred to herein as coating formulation.

Improved anti-soiling properties may be demonstrated via reduced frequency of cleaning, e.g. compared to uncoated substrates, whilst having the same power output over a period of time e.g. 3 months. Improved anti-soiling properties may be demonstrated via an improved power output at the same frequency of cleaning, e.g. compared to uncoated substrates, over a period of time e.g. 3 months.

The anti-soiling coating (ASC) may be a porous coating. In an aspect the ASC is a porous coating further providing AR properties. A typical example of a coating proving AR properties (an anti-reflective coating, also referred to as ARC) is a thin layer of porous inorganic oxide—for example a layer of less than 0.2 μm thickness-which substantially consists of an inorganic oxide like silica and has certain porosity. Such coatings may be applied to a transparent substrate to reduce the amount of light being reflected from its surface, i.e. from the air-substrate interface, and thus increase the amount of light being transmitted through the substrate. Such coatings can be used as single layer or as part of a multi-layer coating (or coating stack). Typical single layer ARCs based on thin porous silica layers have been described in e.g. EP0597490, U.S. Pat. Nos. 4,830,879, 5,858,462, EP1181256, WO2007/093339, WO2008/028640, EP1674891, WO2009/030703, WO2009/140482, US2009/0220774, and WO2008/143429.

A single layer ARC on a transparent substrate typically has a refractive index between the refractive indices of the substrate and air, in order to effectively reduce the amount of light reflected. For example, in case of a glass with refractive index 1.5 the AR layer typically has a refractive index of about 1.2-1.3, and ideally of about 1.22. A porous silica (or other inorganic oxide) layer having sufficiently high porosity can provide such a low refractive index and function as AR coating, if its layer thickness is about ¼ of the wavelength of the light; meaning that in the relevant wavelength range of 300-800 nm the thickness preferably is in the range 70-200 nm.

Optimum porosity and pore size in an ARC is not only depending on the coating layer thickness, but also on other desired performance characteristics. For example, pore size should not be too large, to minimise light scattering and optimise transparency. On the other hand, if the layer contains very small pores, this may result—under ambient use conditions—in non-reversible moisture up-take via capillary condensation; affecting refractive index and making the coating layer more prone to fouling. Such capillary condensation effects have been reported for so-called meso-porous silica, especially having pores in the range 1-20 nm. Porosity is needed to reduce refractive index, but too high porosity level may deteriorate mechanical strength of the coating, e.g. reduce (pencil) hardness and abrasion resistance.

By inorganic oxide precursor is herein meant a compound that contains metal and can be converted into a metal oxide for example by hydrolysis and condensation reaction.

Porous coatings can be made from a solvent borne coating composition comprising an inorganic or organic binder material and a pore forming agent. In case of an inorganic binder, for example based on an inorganic oxide precursor, typically a sol-gel process is used for making a (porous) inorganic oxide layer, wherein a precursor compound in solution or colloid (or sol) form is formed into an integrated network (or gel) of either discrete particles or network polymers. In such process, the sol gradually evolves to a gel-like diphasic system containing both a liquid and solid phase. Removing remaining liquid is generally accompanied by shrinkage and densification, and affects final microstructure and porosity. Furthermore exposure to elevated temperature is often applied to also enhance further condensation reactions and secure mechanical and structural stability. Typical inorganic oxide precursors used are metal alkoxides and metal salts, which can undergo various forms of hydrolysis and condensation reactions. Metal is understood to include silicon within the context of this description.

Such solvent borne coating composition contains solvent and organic ligands from organo-metallic inorganic oxide precursors, which compounds as such will induce some porosity to the inorganic oxide layer; but typically with pores smaller than 10 nm. The further presence of a pore forming agent in the coating composition will help in generating suitable porosity level and pore sizes in the final layer to provide the desired refractive index and as a result therefrom anti-reflective properties. Suitable pore forming agents, also called porogens, known from prior art publications include organic compounds, like higher boiling solvents, surfactants, organic polymers, and inorganic particles having sub-micron particle size, including porous particles and organic-inorganic core-shell nano-particles.

Use of porous or hollow nano-particles in a binder or matrix material represents an elegant way to control porosity level and pore sizes in a porous coating layer. Various different synthetic strategies for making hollow inorganic particles can be distinguished, as for example described in Adv. Mater. 2008, 20, 3987-4019. A typical approach applies a micro- or nano-sized organic structure in a solvent system as a template or scaffold for forming an inorganic oxide outer layer (also referred to as coating with inorganic oxide), resulting in hybrid organic-inorganic core-shell (or coated) nano-particles as intermediate product. Shell layers comprising silica are generally made with a sol-gel process based on the so-called Stober method, wherein an alkoxy silane is hydrolysed and condensed in water/alcohol mixtures containing ammonia.

There remains a need in industry for an anti-soiling coating composition based on organic-inorganic core-shell nano-particles, which composition can be made into an ASC at relatively low temperatures, for example on thermally sensitive substrates.

The present invention provides a process to provide a substrate having improved anti-soiling properties. The present invention also provides a process to provide a substrate having improved anti-soiling properties, an AS coating composition and a process of making such composition.

The present invention provides a process to provide a substrate having improved anti-soiling properties comprising the steps:

• • a) Providing a substrate having a surface;
  • b) Providing a coating composition comprising
    • i. organic-inorganic core shell nanoparticles having a core comprising an emulsion stabilizer C and a shell comprising inorganic oxide;
    • ii. at least 5 wt % water based on the total weight of the coating composition;
    • iii. at least one water soluble solvent; and
    • iv. an organic compound A;
  • c) Applying a layer of the composition to the surface to obtain a coated substrate.
  • d) Drying the applied layer to obtain a dried coated substrate

Improved anti-soiling properties may be determined via visual assessment. In this assessment may include:

• • a) Providing a substrate with a surface to be tested;
  • b) Cleaning the surface to be tested to obtain a cleaned surface;
  • c) Soiling the surface to be tested with dust to obtain a dusted soiled surface;
  • d) Oscillating the substrate having the dusted surface;
  • e) removing excess dust from the dusted surface to obtain a soiled surface; and
  • f) making a visual assessment of the soiled surface

In step d) of the soil test Oscillating may be done by 300 cycles at a speed of 100 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 e) 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 is followed by cleaning the non-soiled side of the soiled substrate 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 40%.

Soil test and soiling test are used interchangeably herein.

In step f) Visual assessment may be made using values in a range from 0 to 3 where 0 is none to minor soiling, 1 low soiling, 2 acceptable soiling and 3 is high soiling.

In step f) visual assessment may be done by visually comparing the surface to be tested with a reference surface also exposed to steps a) to e) and determine in step f) which surface contains less dust particles under the same lighting conditions.

Less particles indicate improved anti-soiling properties, in particular improved anti-soiling properties as compared to the reference surface. The reference surface may be an uncoated substrate of the same material as the substrate of the coated substrate. Both the surface to be tested and the reference surface are determined under the same conditions. For example by assessing the reflection of a light source on the surface. For example by placing the reference substrate and the coated substrate to be tested next to each other with both surfaces to be compared facing a light source. Tilting the reference substrate and the coated substrate to be tested under the same angle such that a ceiling light reflects its light on the surfaces and comparing the gloss. In case the surface of the coated substrate to be tested demonstrates more gloss that the surface of the reference substrate the surface of coated substrate to be tested demonstrates improved anti-soiling.

In an aspect the soil test, in particular step c) and d) above, is performed using a Taber Oscillating Abrasion Tester (such as model 6160), at 20° C., 40% relative humidity using Arizona coarse sand.

Anti-soiling properties may be determined via measuring the transmittance of the 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 or a Perkin Elmer 1050 UV/VIS spectrophotometer.

A soil test may include:

• • a) Providing a substrate with a surface to be tested;
  • b) Cleaning the surface to be tested to obtain a cleaned surface;
  • c) Measuring the transmittance from 400-1200 nm of the cleaned surface before soiling and determining the average transmittance in the range from 400 to 1200 nm (TO);
  • d) Soiling the surface to be tested with dust to obtain a dusted soiled surface;
  • e) Oscillating the substrate having the dusted surface;
  • f) removing excess dust from the dusted surface to obtain a soiled surface; and
  • g) measuring the transmittance from 400-1200 nm of the soiled surface after soiling (transmittance after soiling) and determining the average transmittance in the range from 400 to 1200 nm (Tsoil).

This way the following values may be obtained:

• • in step c) T_Substrate,0: the average transmittance from 400-1200 nm of the uncoated glass surface (substrate without coating) before soil test;
  • in step g) T_{Substrate,soil}: the average transmittance from 400-1200 nm of the uncoated glass surface after soil test;
  • in step c) T_Coating,0: the average transmittance from 400-1200 nm of the coated glass surface (coating with double sides coating) before soil test;
  • in step g) T_Coating,soil: the average transmittance from 400-1200 nm of the coated glass surface after soil test.

In step e) of the soil test Oscillating may be done by 300 cycles at a speed of 100 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 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 40%.

Soil test and soiling test are used interchangeably herein.

Herein the average transmittance from 400-1200 nm means the average transmittance value in the wavelength range of 400 to 1200 nm.

In an aspect the transmittance is measured using a Perkin Elmer 1050 UV/VIS 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 6160).

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 50%. In an aspect the ASR is at least 75%, in an aspect the ASR is at least 80%, in an aspect at least 85%, in an aspect the ASR is at least 90%.

The improved anti-soiling properties may be demonstrated by an increased Anti-Soiling Ratio (ASR) as defined by:

$\mathrm{ASR}=\frac{\left(T_{\mathrm{Substrate},0}-T_{\mathrm{Substrate},\mathrm{soil}}\right)-\left(T_{\mathrm{Coating},0}-T_{\mathrm{Coating},\mathrm{soil}}\right)}{\left(T_{\mathrm{Substrate},0}-T_{\mathrm{Substrate},\mathrm{soil}}\right)}\times 100\%,$

where “T” is the average transmittance from 400-1200 nm measured by a spectrophotometer, Substrate refers to substrate without coating, Coating refers to the substrate with double sided coating. “0” refer to the measured transmittance before the soil test and “soil” refers to transmittance after soil test. From 400-1200 nm means from 400 to 1200 nm including 1200 nm. In an aspect the coated substrate demonstrates an ASR of at least 50%. In an aspect the coated substrate demonstrates an ASR of at least 75%. In an aspect the coated substrate demonstrates an ASR of at least 80%. In an aspect the coated substrate demonstrates an ASR of at least 90%.

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

with ARE=T_Coating,0−T_Substrate,0,

where T is the is the average transmittance from 400-1200 nm, Substrate refers to substrate without coating, Coated substrate refers to the substrate with double sided coating and 0 refers to before soil test.

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 2%, in an aspect the ARE is at least 3%, in an aspect the ARE is at least 4%, in an aspect the ARE is at least 5%. In an aspect the ARE is at least 6%.

The degree of soiling of the coatings may be determined by providing substrate being partially coated using a coating composition as described herein (i.e. a partially coated substrate), said composition comprising

• • organic-inorganic core shell nanoparticles as described herein having a core comprising an emulsion stabilizer C as described herein and a shell comprising inorganic oxide as described herein;
  • at least 5 wt % water, based on the weight of the total coating composition;
  • at least one water soluble solvent as described herein; and
  • an organic compound A as described herein.

And thereafter visually comparing an uncoated part of the partially coated substrate with a coated part of the partially coated substrate. Improved anti-soiling properties are demonstrated if coated part shows more gloss than the uncoated part.

In an aspect the anti-soiling coating demonstrates anti-reflective (AR) properties as well.

In an aspect the anti-soiling coating demonstrates a TMax of at least 97.5%.

In an aspect the anti-soiling coating demonstrates an T average of at least 96%.

In an aspect the anti-soiling coating demonstrates a TMax of at least 96%.

In an aspect the anti-soiling coating demonstrates an T average of at least 95%.

Where Tmax is the value of highest transmission % measured from 400 to 1200 nm.

Where T average is the average transmittance from 400 to 1200 nm.

The present invention provides a process of making an anti-soiling coating composition comprising the steps of

• 1) Preparing an oil-in-water emulsion by mixing
  • an apolar organic compound A;
  • a cationic addition copolymer C as emulsion stabilizer; and
  • aqueous medium of pH 2-6;
  • at a mass ratio C/A of 0.1 to 2, to result in 1-50 mass % (based on emulsion) of emulsified droplets of particle size 30-300 nm;
• 2) Providing an inorganic oxide shell layer to the emulsified droplets by adding to the emulsion obtained in step 1) at least one inorganic oxide precursor, to result in organic/inorganic core-shell nano-particles with mass ratio core/shell of from 0.2 to 25;
• 3) Optionally combining the core-shell nanoparticles thus obtained with water and/or water soluble solvent;
• 4) Optionally adjusting pH; and
• 5) Optionally adding an organic or inorganic polymeric or polymerizable binder.

At the end of step 2) typically the core comprises, the at least one water soluble solvent, such as for example methanol or ethanol or a mixture thereof originating from hydrolyzed inorganic oxide precursors.

With the process of making the anti-soiling coating composition of the invention it is found possible to make a coating composition comprising core-shell particles based on emulsified droplets, having a particle size in the range of 30 to 300 nm, that contain a liquid apolar organic compound This particle size can be controlled by the type of organic compound and the monomer composition of the cationic addition copolymer, and/or by selecting conditions like temperature, pH, aqueous medium composition, and to a lesser degree stirring rate. A further advantage of the present process is that the dispersion of core-shell nano-particles obtained is stable under different conditions; increasing its shelf life or storage time, and allowing for example altering its concentration and solvent system, and addition of different binders and auxiliary components. The coating composition obtained with the process according to the invention can be advantageously used for making, ASC, in particular porous ASCs at a wide range of temperatures on different substrates, including thermoplastic substrates that have low temperature resistance; because the organic compound can be easily removed from the core-shell particles by solvent extraction or evaporation at relatively low temperature, and low temperature curable binder can be used. In an aspect the porous ASC demonstrates anti-reflective properties.

In an aspect a process to make a ASC composition comprises a step 1) wherein an apolar organic compound A; a cationic addition copolymer C; and an amount of an aqueous medium of pH 2-6 are mixed at a mass ratio C/A of 0.1 to 2 to prepare an oil-in-water emulsion. The apolar organic compound A used herein is typically a liquid at temperatures above 0° C., preferably above 10 or 20° C. in order to make an oil-in water emulsion. Compound A preferably retains liquid character under conditions of making the emulsion, and during subsequent process and storage steps. On the other hand, it is an advantage that during making an ARC from the composition, especially during a drying step, compound A can be easily removed from the coating by evaporation to create porosity. Therefore, compound A has preferably a boiling point of at least 30, 40, 60, 80, or 100° C., and of at most 350, 300, 250, 200 or 150° C.

Compound A used herein has an apolar (or hydrophobic) character, meaning that it has solubility in water at room temperature of at most 5 kg/m³ and can form a separate phase from water. Compound A is preferably a compound that can be dispersed in water in the presence of copolymer C as described hereinafter. Preferably compound A has a solubility in water at room temperature of at most 4, 3, 2, or 1 kg/m³.

It is highly preferred that compound A is non-polymeric. By non-polymeric is herein understood that A is not built from more than 2 repeating monomer units as it was found that particularly for applications where high temperature drying is not acceptable, it may require extended time to extract or evaporate compound A from the core-shell nano particles when compound A is a polymer.

Compound A preferably is inert with regard to other components used in the process or composition of the invention. If Compound A is an ester, Compound A may be partially extracted from the dispersed core-shell particle into the medium of the final coating composition that may also contain binder.

Examples of apolar compound A include hydrocarbon compounds, fatty acids, alcohols, esters, ethers, vinyl compounds, and the like. Suitable examples include cyclohexane, decane, toluene, trimethyl benzene, isoamyl acetate, C8-C22 alcohols, styrene, alkyl (meth)acrylates, butanediol dimethacrylate, hexanediol dimethacrylate, and the like.

Herein one compound may be used as compound A, but also a mixture of compounds as defined above may be applied. It is also possible to use a compound A wherein a minor amount, for example less than 4, or 2 mass %, of a hydrophobic compound not satisfying above definition is dissolved, which may aid in dispersing compound A. An example of a suitable mixture is cyclohexane containing 1 mass % of heptadecane.

In step 1) of the process of making anti-soiling coating composition according to the invention an oil-in-water emulsion is prepared of compound A and a cationic addition copolymer C. Cationic addition copolymer C, emulsion stabilizer C, cationic copolymer C and copolymer C are used interchangeably herein. Copolymer C is obtained from at least one monomer unit having a cationic charge and at least one neutral or non-ionic monomer, preferably an apolar monomer of which the corresponding homopolymer shows limited or no solubility in water.

In an aspect, the cationic copolymer has a positive zeta potential. Preferably, cationic copolymer C is not readily soluble in water, but tends to form colloidal aggregates, which enhances its functioning as emulsion stabilizer. The copolymer may be a random, but also a block copolymer, and may comprise styrenic, acrylic, methacrylic, olefinic, and/or vinylic comonomers. Within the context of this application all these monomers are together referred to as ethylenically unsaturated monomers or vinyl monomers; that is including a.o. methacrylates which comprise a methyl-vinyl group. Acrylic and methacrylic compounds are together typically referred to as (meth)acrylic monomers in the art. The addition copolymer can advantageously be made using various polymerisation techniques as known to a skilled person, and from a great number of suitable vinyl monomers; offering a wide range of compositions for the copolymer. Suitable examples include bulk, solution and emulsion polymerisations using radical initiators. The copolymer is preferably provided as dispersion in aqueous medium, which may have resulted from an emulsion polymerisation of selected monomers, but also from polymerisation in organic solvent followed by dispersing the copolymer obtained in aqueous medium of pH 2-6; as is known in the art.

Copolymer C is preferably a copolymer obtained from:

• • at least one cationic or basic monomer (M1), including compounds with a pending group that can combine with a proton to form a cationic group; like monomers with a tertiary amine group;
  • at least one neutral or non-ionic monomer (M2); preferably an apolar monomer of which the corresponding homopolymer is not readily soluble in aqueous medium; and
  • optionally at least one polar, anionic or acidic monomer (M3).

Copolymer obtained from described monomers means the copolymer is formed by polymerizing a composition that comprises the described monomers.

E.g. Copolymer C is preferably a copolymer formed by polymerizing a composition that comprises:

• • at least one neutral or non-ionic monomer (M2); preferably an apolar monomer of which the corresponding homopolymer is not readily soluble in aqueous medium; and
  • optionally at least one polar, anionic or acidic monomer (M3).

Too high an amount of M2 may result in insolubility and/or precipitation of the copolymer in an aqueous medium. The type and amount of comonomers is thus preferably chosen such that the copolymer can be dispersed in an aqueous medium into colloidal particles or aggregates. It is an advantage of present invention that random copolymers of such monomers can already function as emulsion stabilizers in an aqueous medium; thus omitting the need for using more complex synthetic routes of making block copolymers. The skilled person will be able to select a suitable copolymer composition, also depending on the compound A to be emulsified and composition of the aqueous medium.

In an embodiment, the copolymer C herein is a copolymer obtained from

• • 1-25 mole % of at least one monomer M1;
  • 50-99 mole % of at least one monomer M2; and
  • 0-25 mole % of at least one monomer M3 (with the sum of M1, M2, and M3 adding up to 100%).

If a comonomer M3 is used in preparing the copolymer, especially an anionic M3, monomer M1 is used in such amount, for example in a molar excess over M3, to result in an ionic copolymer having a net positive charge.

In an embodiment copolymer used herein is a cationic copolymer obtained from

• • 5-15 mole % of at least one monomer M1;
  • 75-95 mole % of at least one monomer M2; and
  • 0-10 mole % of at least one monomer M3.

In further preferred embodiments, the copolymer used herein is such a cationic copolymer obtained from at least 5, 6, 7, 8, 9 or 10 mole %, and at most 25, 20, 15, 12 or 10 mole % of at least one monomer M1; and at least one monomer M2 in such amount that the sum of M1 and M2 is 100 mole %.

Cationic monomers M1 that can be suitably used in forming copolymer C used the process according to the invention via addition polymerisation include vinyl monomers with a pending amino functional group; which can be non-ionic monomers that can be neutralised during or after forming the copolymer, monomers with an already neutralised amino functional group, or vinyl monomers with a permanent quaternary ammonium group.

Examples of vinyl monomers bearing non-ionic amino functional groups include N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminohexyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N-methyl-N-butyl-aminoethyl (meth)acrylate, tert-butylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, 2-(1,1,3,3,-tetramethylbutylamino)ethyl (meth)acrylate, beta-morpholinoethyl (meth)acrylate, 4-(beta-acryloxyethyl) pyridine, vinylbenzylamines, vinyl phenylamines, 2-vinylpyridines or 4-vinylpyridines, p-aminostyrenes, dialkyaminostyrenes such as N,N,-diaminomethylstyrene, substituted diallylamines, N-vinylpiperidines, N-vinylimidazole, N-vinylimidazoline, N-vinylpyrazole, N-vinylindole, N-substituted (meth)acryl amides like 2-(dimethylamino)ethyl (meth)acrylamide, 2-(t-butylamino)ethyl (meth)acrylamide, 3-(dimethylamino)propyl (meth)acrylamide, (meth)acryl amide, N-aminoalkyl (meth)acrylamides, vinyl ethers like 10-aminodecyl vinyl ether, 9-aminooctyl vinyl ether, 6-(diethylamino)hexyl vinyl ether, 5-aminopentyl vinyl ether, 3-aminopropyl vinyl ether, 2-aminoethyl vinyl ether, 2-aminobutyl vinyl ether, 4-aminobutyl vinyl ether, 2-di methylaminoethyl vinyl ether, N-(3,5,5,-triethylhexyl)aminoethyl vinyl ether, N-cyclohexylaminoethyl vinyl ether, N-tert-butylaminoethyl vinyl ether, N-methylaminoethyl vinyl ether, N-2-ethylhexylaminoethyl vinyl ether, N-t-octylaminoethyl vinyl ether, beta-pyrrolidinoethyl vinyl ether, or (N-beta-hydroxyethyl-N-methyl) aminoethyl vinyl ether. Cyclic ureido or thiourea containing ethylenically unsaturated monomers like (meth)acryloxyethyl ethyleneurea, (meth)acryloxyethyl ethylenethiourea (meth)acrylamide ethyleneurea, (meth)acrylamide ethylenethiourea and alike can also be used. Preferred monomers are amino-functional (meth)acrylates and (meth)acrylamides; especially N,N,-dialkylaminoalkyl (meth)acrylates, more specifically t-butylaminoethyl methacrylate, dimethylaminopropyl methacrylate, dimethylaminoethyl methacrylate (DMAEMA) or diethylaminoethyl methacrylate (DEAEMA), more preferably DMAEMA and DEAEMA.

The above given examples of suitable and preferred M1 monomers can also be used in their ionised form, by treating with for example an acid, preferably an organic acid like a carboxylic acid, prior to polymerisation.

Suitable examples of M1 monomers with a permanent quaternary ammonium group include methacrylamidopropyl trimethylammonium chloride (MAPTAC), diallyl dimethyl ammonium chloride (DADMAC), 2-trimethyl ammonium ethyl methacrylic chloride (TMAEMC) and quaternary ammonium salts of substituted (meth)acrylic and (meth)acrylamido monomers.

Neutral or non-ionic monomers M2 that can be suitably used in forming the copolymer used the process according to the invention via addition polymerisation include a wide range of ethylenically unsaturated monomers or vinyl monomers, including various styrenic, (meth)acrylic, olefinic, and/or vinylic comonomers. The at least one monomer M1 is preferably hydrophobic. Preferably, the cationic copolymer comprises a certain amount of non-water soluble or hydrophobic comonomers that will promote the copolymer, not being fully water soluble, to self-assemble into colloidal particles or aggregates in an aqueous medium. The skilled person will be able to select suitable combinations of monomers and their contents based on the information disclosed in this description and experiments, possibly assisted by some further experiments; and depending on copolymer composition (like M1 and M2 types and amounts), conditions (like solvent composition, temperature, pH), and type of compound A.

Suitable styrene monomers M2 include styrene, alpha-methyl styrene and other substituted styrenes. Suitable (meth)acrylic monomers M2 include alkyl or cycloalkyl (meth)acrylates, preferably C₁-C₁₈ alkyl (meth)acrylates or C₁-C₈ alkyl (meth)acrylates, like methyl(meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate (all isomers), isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isopropyl (meth)acrylate, propyl (meth)acrylate (all isomers), or isobornyl (meth)acrylate. Most preferred (meth)acrylic monomers include methyl methacrylate (MMA), ethyl methacrylate (EMA), n-butyl methacrylate (BMA). Similarly, N-alkyl (meth)acrylamides can be used as monomer M2. Also other monomers that can be copolymerized with M1 can be used as monomer M2, including butadiene; vinyl monomers like vinyl chloride, vinyl laurate, vinyl alkyl ethers, and the like.

As monomer M3 various compounds that can be copolymerized with M1 and M2 can be used, including acrylonitrile, methacrylonitrile, vinyl monomers like vinyl pyrrolidone, vinyl esters such as vinyl acetate or vinyl propionate, and the like. Also anionic or acidic monomers M3 may be used in forming the copolymer used in the method according to the invention; like monomers with a pending phosphoric, sulfonic, or carboxylic acid group. Suitable monomers include vinyl monomers with a carboxylic acid group, examples being ethylenically unsaturated monocarboxylic and/or dicarboxylic acids, like fumaric acid, itaconic acid, maleic acid, and especially (meth)acrylic monomers with a carboxylic acid group, such as acrylic acid (AA), methacrylic acid (MAA) and β-carboxy ethylacrylate. A copolymer comprising both anionic and cationic groups can be referred to as a polyampholyte. Resulting intra- and intermolecular interactions between the ionic groups may enhance their functioning as emulsion stabilizer C in the process of the invention.

In an aspect the emulsion stabilizer C is an cationic addition copolymer comprising at least one monomer unit having a cationic charge and at least one monomer unit being neutral or non-ionic and having an overall positive zeta potential.

In an embodiment of the invention, the cationic copolymer may be obtained from 5-15 mole % of at least one monomer M1 selected from the group consisting of amino-functional (meth)acrylates and (meth)acrylamides; and 85-95 mole % of at least one monomer M2 selected from the group of C1-C18 alkyl (meth)acrylates.

In a further embodiments of the invention, a cationic copolymer is applied which comprises 5-10 mole % of dimethylaminoethyl methacrylate (DMAEMA) as monomer M1, and 90-95 mole % of MMA as monomer M2; or a copolymer made from 5-12 mole % of DMAEMA and 88-95 mole % of isobornyl acrylate (IBOA).

The molar mass of copolymer C can vary widely. Typically, the copolymer has a weight averaged molar mass (Mw) in the range 1-500 kDa (kg/mol), preferably Mw is at least 2, 5, 10, 15 or even 20 kDa, but at most 250, 200, 150, 100, 50 or even 40 kDa to optimise activity as emulsion stabilizer. The molar mass of the copolymer can be determined by gel permeation chromatography (GPC) using polymethylmethacrylates of known molar masses as a standard and THF or hexafluoro iso-propanol as an eluting solvent.

In step 1) of the process according to make an ASC composition an oil-in-water emulsion is prepared by mixing compound A and copolymer C in an aqueous medium of pH 2-6, resulting from organic and/or inorganic acid or buffer compounds being present. Within this pH range the copolymer C will be cationically charged, also if M1 monomer has a (neutralized) tertiary amine pending group. Temperature for mixing is not critical, but is generally from ambient to about 50° C.

By aqueous medium is herein meant a liquid comprising water. The aqueous medium may in addition to water comprise at least one water soluble solvent such as alcohols, ketones, esters, or ethers. Examples include 1,4-dioxane, acetone, ethyl acetate, propanol, ethanol, methanol, butanol, methyl ethyl ketone, methyl propyl ketone, and tetrahydrofuran and mixtures thereof. Preferably, the aqueous medium comprises water and a lower (C1-C8) aliphatic alcohol, like methanol, ethanol, iso-propanol or 1-methoxypropan-2-ol or mixture thereof; more preferably ethanol or iso-propanol or mixtures thereof. If water soluble solvent is present, its amount is chosen such that compound A and copolymer C will not be dissolved, securing formation of emulsified droplets of compound A and copolymer C. Preferably the amount of water soluble solvent is at most 10 mass %, more preferably at most 8, 6 or 4 mass % (based on total composition). Preferably the solvent composition of the aqueous medium is also suitable for the subsequent step 2) of forming a shell layer.

In the process to make an ASC composition the manner and order in which components A and C are added to and mixed with the aqueous medium is not particularly critical. For example compound A and copolymer C may be added simultaneously or sequentially, optionally under stirring. Formation of emulsified droplets may be facilitated by stirring, for example with a stirring bar at relatively low speed, with a high-speed mixer, with a high-pressure homogenizer, or with sonication. The actual stirring rates (or similar settings when using alternative mixing devices as exemplified above) can vary and is chosen to realize an oil-in-water emulsion as determined by routine experimentation by the skilled person.

In the step 1) of preparing an oil-in-water emulsion by mixing organic compound A and copolymer C in aqueous medium the mass ratio of C to A is from 0.1 to 2. A certain minimum amount of cationic copolymer is needed to stabilize the emulsion, but also to provide the emulsified droplets with a certain charge level relevant for forming a shell layer of at least partially reacted inorganic oxide precursor in subsequent step 2). Too high an amount of copolymer, that is a relatively low amount of compound A, could reduce potential porosity level that can be formed in a coating layer from the composition as obtained. Mass ratio C/A is therefore preferably at least 0.15, 0.2, 0.3 or 0.4, and at most 1.5, 1.2, 1.0, 0.9, 0.8, 0.7, 0.6 or 0.5.

If desired, in the process to make an ASC composition a further conventional surfactant of low molar mass may be added in step 1), to assist formation of dispersed droplets and to further stabilise the emulsion obtained. The surfactant used may be non-ionic, cationic or anionic, or a combination thereof. Preferably none, or only small amount of surfactant is used, like 0.1-3, more preferably 0.2-1.5 mass %.

The process to make an ASC composition results in step 1) in a dispersion of 1-50 mass % of emulsified droplets (based on total emulsion). The emulsion may be prepared with a wide range of concentration of emulsified particles, depending subsequent steps and uses. Generally a relatively high concentration is preferred in step 1), allowing further dilution with water or other solvents as desired during subsequent steps. Preferably, a dispersion is made in step 1) containing at least 2, 4, 6, 8 or 10 mass % of emulsified droplets, and at most 40, 30, 25 or 20 mass %. Based on the information provided above, the skilled person can determine the relative amounts of compound A, copolymer C, aqueous medium and optionally other compounds to be used in the process.

The process of the invention results in step 1) in a dispersion of emulsified droplets of particle size 20-300 nm. Formation and size of emulsified droplets can be monitored by various techniques; for example by Dynamic Light Scattering (DLS). In view of using the composition obtained with the process according to the invention to make an AR coating, variables of the process as described above are chosen such that particle size is preferably at least 25, 30, 35, 40, 45 or 50 nm, and at most 250, 200, 175, 150 or 125 nm (as measured with DLS).

The process to make an ASC composition comprises a step 2) of providing an inorganic oxide shell layer to the emulsified droplets, by adding to the emulsion obtained in step 1) at least one inorganic oxide precursor to result in organic/inorganic core-shell nanoparticles with mass ratio core/shell of from 0.2 to 25. The core is here the sum of compound A and emulsion stabilizer C and shell is SiO₂ equivalent of inorganic oxide precursor. By metal oxide equivalent of inorganic oxide precursor is here meant the mass of oxides that the precursors is converted to by complete conversion into metal oxides, such as TMOS and TEOS each counting as one SiO₂, titanium tetraisopropoxide counting as one TiO₂ and aluminium nitrate counting as a half Al₂O₃. In the step 2) of the process according to the invention, the emulsified droplets act as template on which a shell layer is formed from sol particles of partially reacted precursor. Such formation of an inorganic shell layer by a sol-gel process has been described in many publications, including documents cited in this application, and publications referenced therein. Suitable inorganic oxide precursors include metal salts, metal chelates and organo-metallic compounds, preferably metal alkoxides, and combinations thereof. Such compounds can undergo various hydrolysis and/or condensation reactions in aqueous medium to finally form corresponding oxides or mixed oxides. Within the present application silicon (Si) is considered to be a metal. Suitable metals include Si, Al, Bi, B, In, Ge, Hf, La and lanthanoids, Sb, Sn, Ti, Ta, Nb, Y, Zn and Zr, and mixtures thereof. Preferably the metal is at least one of Si, Al, Ti, and Zr. Preferred precursors include alkoxy silanes, preferably tetra- or tri-alkoxy silanes like tetramethoxy silane (TMOS), tetraethoxy silane (TEOS), methyltrimethoxy silane, methyltriethoxy silane, titanium tetraisopropoxide, aluminium nitrate, aluminium butoxide, yttrium nitrate and zirconium butoxide. Such precursor compounds can be partially pre-reacted or pre-hydrolysed to form oligomeric species, typically in the form of nano-sized particles of about 1-20, 1-10 or even 1-5 nm; also called sol particles.

In an embodiment of the invention, the at least one inorganic precursor comprises an alkoxy silane, more preferably TMOS and/or TEOS. Preferably, the shell layer formed substantially consists of silica (precursor) as inorganic oxide; the shell for example comprises at least 80, 85, or 90 mole % of Si as metal in the inorganic oxide, more preferably at least 95 mole % of Si.

In the process to make an ASC composition the step of forming a shell layer from the precursor on the template to result in core-shell nano-particles is typically performed under mild conditions. As mentioned above, the aqueous medium may comprise an water soluble solvent such as alcohols, ketones, esters, or ethers; preferably an alcohol like methanol, ethanol or iso-propanol. Water serves as solvent or diluent for the composition, but will also react with the inorganic oxide precursor; for example with an alkoxy silane. The amount of water present in the composition is therefore at least the amount needed for such desired reaction(s), like (partial) hydrolysis of for example tetraethoxy silane. In case complete hydrolysis of TEOS would be aimed at, the composition should contain water in at least a 4:1 molar ratio to Si.

The temperature is not very critical in this step of the process to make an ASC composition and can be varied widely as long as the emulsion is not disrupted. Temperature can be up to 100° C., but is typically ambient, i.e. from about 15 to 40° C. As said hydrolysis reaction is exothermic, cooling may be used to control temperature in this step. The pH is in the range 2-6, preferably 3-5 or 3-4.5. An advantage of applying such conditions is that nanoparticles formed from the precursor typically having a negative charge and will at least partly deposit on the outside of emulsified droplets of opposite charge. This way an open or ‘fluffy’, or more condensed layer of inorganic oxide (precursor) may form around the emulsion particles, depending on reaction conditions.

In the process to make an ASC composition forming a shell layer from the precursor on the template droplets is performed at such mass ratio of inorganic oxide precursor to organic template that organic/inorganic core-shell nano-particles with mass ratio core/shell of from 0.2 to 25 result. It is preferred that the mass ratio core/shell is from 0.2 to 5 and particularly from 0.2 to 2. More preferably, the process results in core-shell nano-particles with mass ratio core/shell of 0.3-2, more preferably 0.4-1.8. The high mass ratio of core/shell such as 2 to 25 and particularly from 4 to 23 is particularly advantageous when no separate binder addition step 5) is included in the method according to the invention. In this case, oxide precursor added in step 2) may also act as an integrated binder, in the sense that some of the oxide precursor will form the shell of the core-shell nanoparticles and some of the oxide precursor will remain unbonded or only very loosely bonded to the nanoparticles and during preparation of the ASC will act as a binder.

Formation of a shell layer from the precursor on the template may be monitored by measuring change in dimensions of the emulsified droplets, eg. by DLS. Although the DLS technique has its draw-backs, for example mainly detecting the larger particles, and particle size may also change as result of compounds liberated from the precursor, like an alcohol, which could be absorbed in the core, it is a simple and convenient method to observe shell formation. Shell formation may slow down or stop when the net charge of the emulsified core particle has decreased by the inorganic oxide (precursor) having charge opposite to that of the copolymer. A certain charge level will likely remain to keep the particles dispersed. As shell formation is thought to result from complexing of inorganic nanoparticles with the outer layer of emulsified droplet comprising cationic copolymer, an open or fluffy structure is expected to be formed in the aqueous medium rather than a dense shell (as in dried particles).

In embodiments of the process to make an ASC composition the structure of the shell formed, like its density or surface properties, may be further optimized by extending reaction time, reacting with a coupling agent or other treatment as known from the art. Thickness of the shell layer thus formed is typically in the range of 1-20 nm, preferably 2-10 nm. Shell thickness of core-shell nano-particles, and their morphology can be assessed on particles with techniques like TEM, especially cryo-TEM, SAXS, or SANS. Considering the relatively thin shell layer, particle size of the core-shell particles is in ranges similar to those of the emulsified droplets.

With the process to make an ASC composition dispersed core-shell nano-particles are obtained, which composition is found to show remarkably good storage and handling stability, meaning the composition shows little tendency to changing viscosity or gelling compared to other sol-gel process based dispersions. It was further found that the solids content of the dispersion may be adjusted by evaporation or dilution with water or water soluble solvent such as an alcohol; which greatly increases the possibilities for adjusting composition to match requirements for coating applications.

Examples of the water soluble solvent as described herein include 1,4-dioxane, acetone, ethyl acetate, propanol, ethanol, methanol, butanol, isopropanol, methyl ethyl ketone, methyl propyl ketone, dimethylsulfoxide, dimethylformamide, and tetrahydrofuran and mixtures thereof. Preferably, the water soluble solvent is selected from a lower (C1-C8) aliphatic alcohol, like methanol, ethanol, iso-propanol or 1-methoxypropan-2-ol or mixtures thereof; more preferably from ethanol or iso-propanol or mixtures thereof.

The process to make an ASC composition may comprise a further step 5) of adding 2-70 mass % of at least one polymeric or polymerisable compound as binder (mass % based on the sum of core-shell particles and binder). Preferably an amount of between 2 and 20 mass % of at least one polymeric or polymerisable compound as binder is used. In principle the composition obtained after step 2, 3 or 4 can be used to form an ASC on the substrate, showing a certain level of adhesion to the surface of the substrate after drying, resulting from further reaction of the inorganic oxide precursor, which generally has not fully reacted during preparing the shell layer. Preferably, a binder is added in step 5) to the AS coating composition, which binder can be at least one inorganic or organic polymeric or polymerisable compound. In forming an ASC from the composition, the binder may act as film former and hold together the core-shell nano-particles, resulting in improved mechanical properties of the coating formed and in better adhesion to the substrate upon drying. Addition of binder will reduce the level of porosity of a coating made from the composition. Thus in step 5) of the process preferably at least 2, 5, 10, 15, 20, or 25 mass % of binder is added; but at most 65, 55, 50, 40, or 30 mass % (based on the sum of solid SiO2 content of the core-shell particles and of the binder) of binder is used. Using too much binder may reduce the anti soiling performance of the AS coating.

Suitable organic binders in the process to make an ASC composition include a range of different polymers and thermally or radiation—e.g. UV—curable monomers, as known to the skilled person. Organic binders, especially radiation curable binders generally have the advantage that they can be cured when exposed to UV light or to elevated temperatures of preferably below 250° C., compatible with e.g. thermoplastic substrates, and at which also the organic compound A may be evaporated from the nano-particles to in situ create hollow particles. Use of inorganic binders may be preferred to result in coatings with improved mechanical properties and durability. If desired, the organic binder may be cured with UV light after the drying step of the ASC.

It is an advantage of present invention that the process allows the skilled person to select and use a binder that provides the properties desired for a certain application of the coating.

Examples of suitable organic binders that may be applied include radical curable—peroxide- or photo-initiated—compositions comprising vinyl monomers and vinylpolymers having unsaturated groups, like acrylates, methacrylates, maleate/vinyl ethers, etc.), or radical curable unsaturated polyesters or polyurethanes in styrene and/or (meth)acrylates.

Suitable inorganic binders in the process of making an AS coating composition of the invention include inorganic oxide precursors like metal alkoxides, metal chelates, metal salts, and mixtures thereof. Suitable metals include at least one element selected from Si, Al, Be, Bi, B, Fe, Mg, Na, K, In, Ge, Hf, La and lanthanoids, Sb, Sn, Ti, Ta, Nb, Y, Zn and Zr; preferably the metal is at least one element selected from Si, Al, Ti, and Zr. Suitable inorganic oxide precursors include those compounds that can react via hydrolysis and/or condensation reactions to form the corresponding oxide, as is well known in the art. The inorganic oxide precursor (which in the context of the present invention is considered polymerisable through for example hydrolysis and/or condensation, or polymerized in a glass, sol-gel or crystal stage) can be a metal salt or an organo-metallic compound, like an alkoxy, an aryloxy, a halogenide, a nitrate, or a sulphate compound, and combinations thereof. Preferred precursors include alkoxy silanes, including halogenated—especially fluorinated—derivates, like tetramethoxy silane (TMOS), tetraethoxy silane (TEOS), methyltrimethoxy silane, methyltriethoxy silane, fluoroalkoxy silanes like trifluoropropyl trimethoxy silane, titanium tetraisopropoxide, aluminium nitrate, aluminium butoxide, yttrium nitrate and zirconium butoxide. More preferably, the precursor comprises TMOS and/or TEOS.

The inorganic oxide precursor can be a mixture of inorganic oxide precursor compound and corresponding inorganic oxide. Such mixture may for example result in case a precursor compound partially pre-reacts or pre-hydrolyses in aqueous medium during making the composition to form oligomeric species, typically in the form of nano-sized particles; which is a well-known procedure in sol-gel technology. Examples of preferred polymeric inorganic binder include pre-oligomerized TEOS, pre-oligomerized TMOS and combinations thereof.

In a further preferred embodiment, the binder used in the process to make an ASC composition comprises a mixture of different inorganic oxide precursors, in which case typically a mixed inorganic oxide is formed as is known for e.g. different glasses. In such mixed oxide the elements are connected via oxygen atoms to form part of an ionic or covalent network, rather than that they are present as a physical mixture of different oxides. Within the context of the present disclosure, mixed inorganic oxide refers to such definition. Formation of a mixed oxide may e.g. be determined by assessing changes in iso-electric point of oxides—e.g. in the form of thin layers—formed from different compositions, or by analytical techniques, like IR and solid-state NMR. Nevertheless, it is customary in the art to define the composition of such mixed inorganic oxide by the theoretical amounts of inorganic oxide for each metal present; e.g. the composition of an aluminosilicate made from Si- and Al-oxide precursors is typically expressed in silica and alumina contents. In case of a mixed oxide as binder, a main metal element is preferably selected from Si, Al, Ti, and Zr, and a second element selected from Si, Al, Be, Bi, B, Fe, Mg, Na, K, In, Ge, Hf, La and lanthanoids, Sb, Sn, Ti, Ta, Nb, Y, Zn and Zr; with a molar ratio of main to second element of about 75:25 to 99:1.

Preferably, the binder used in step 5) of the process comprises a mixture of a silica precursor and a precursor for Al-oxide or Y-oxide, as the mixed oxide formed shows high outdoor resistance or durability.

The alumina precursor may include

• • Al(III) complexes such as halogen-based salts of Al(III) in the form of AIX3 where X can be F, C1, Br, I and their hydrate form;
  • Al(III) inorganic salts such as Al(III) nitrates, nitrites, sulfites, sulfates, phosphates, chlorates, perchlorates, carbonates and their hydrate form;
  • Al(III) complexes bearing oxygen or nitrogen donor based ligands which are hydrolysable such as alkoxides or amides; and
  • combinations thereof.

The alumina precursor may include any of Al(isopropoxide)3, Al(sec-butoxide)3, Al(NO3)3, AlCl3 or a combination thereof.

In an aspect the coating composition comprises from 0.1 to 30 wt-% aluminium oxide equivalents of aluminium containing compound. This may (further) improve the anti-soiling properties.

In an aspect the coating composition comprises from 0.5 to 30 wt-% aluminium oxide equivalents of aluminium containing compound.

In an aspect the coating composition comprises from 1 to 15 wt-% aluminium oxide equivalents of aluminium containing compound.

In an aspect of the invention the anti-reflective coating layer comprises at least 0.1 wt %, at least 0.5 wt %, at least 1 wt %, at least 2 wt %, at least 3 wt %, at least 5 wt % at least 7 wt % at least 10 wt %, at least 12 wt % aluminium oxide equivalents of aluminium containing compound.

In an aspect of the invention the anti-reflective coating comprises 30 wt % or less, 25 wt % or less, 20 wt % or less, 15 wt % or less, 10 wt % or less aluminium oxide equivalents of aluminium containing compound.

In an aspect the aluminium oxide equivalents of aluminium containing compound are based on total ash rest after combustion at 600° C., 2 min 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 1.0 to 25 wt-% aluminium oxide equivalents of aluminium containing compound.

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 SiO₂ irrespective if the species present is tetraethoxysilane, partially hydrolysed tetraethoxysilane or SiO₂. 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 SiO₂ equivalent irrespective if the species present is tetraethoxysilane, partially hydrolysed tetraethoxysilane or SiO₂. Analogous for Alumina, one calculates the amount of pure Al₂O₃ that could be formed. Aluminum oxide equivalents are calculated back to theoretical Al₂O₃ amount based on the alumina precursor added to the formulation.

The alumina precursor may include any of Al(isopropoxide)3, Al(sec-butoxide)3, Al(NO3)3, AlCl3 or a combination thereof.

The silica precursor may include TEOS (tetraethoxysilane), TMOS (tetramethoxysilane), alkylsilanes such as (R)x)Si(OCH3)4−x where R=CH3; C2H5; OCH3 of OC2H5 or a combination thereof.

For instance for silica, one starts from alkoxysilane. When it is referred to oxide equivalents, the assumption is made that only pure SiO₂ is formed. Analogous for Alumina, if started from Al(NO3)3 one calculates the amount of pure Al₂O₃ that could be formed.

For example for 10 grams of tetraethyl orthosilicate (TEOS), the amount of inorganic oxide equivalents is calculated as follows:

$\mathrm{eq}.{\mathrm{SiO}}_2=\frac{\mathrm{amount}\mathrm{TEOS}\left[g\right]}{\mathrm{MwTEOS}}*\mathrm{Mw}{\mathrm{SiO}}_2$ $i.e.\mathrm{eq}.{\mathrm{SiO}}_2=\mathrm{oxide}\mathrm{equivalents}\mathrm{of}\mathrm{inorganics}=10/{208.33}^{*}60.08=2.88g$

Alternatively it may be measured. As result in an aspect the inorganic oxide equivalents are based on total ash rest after combustion at 600° C., 2 min in air. As the skilled person knows total ash rest after combustion at 600° C., 2 min in air is the total residual solid material after combustion at 600° C., 2 min in air.

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.

The improved anti-soiling properties may be demonstrated by an increased Anti-Soiling Gain (ASG) with,

$\mathrm{ASG}=\left[1-\frac{\left(T_{\mathrm{coated}\mathrm{substrate}\mathrm{with}\mathrm{Al},0}-T_{\mathrm{coated}\mathrm{substrate}\mathrm{with}\mathrm{Al},\mathrm{soil}}\right)}{T_{\mathrm{coated}\mathrm{substrate}\mathrm{with}\mathrm{out}\mathrm{Al},0}-T_{\mathrm{coated}\mathrm{substrate}\mathrm{without}\mathrm{Al},\mathrm{soil}}}\right]\times 100\%$

where T is the is the average transmittance from 400-1200, Coated Substrate with Al refers to a double side coated substrate with the coating comprising alumina and Coated Substrate without Al refers to a double side coated substrate with same coating where the alumina is excluded, 0 refers to before soil test and soil refers to after soil test.

The process to make an ASC composition may also comprise adding a combination of inorganic and organic binders, to for example further improve properties of the resulting coating, like anti-fouling behaviour, or enhance adhesion to the substrate. These binders may form polymers or networks on their own, but can also co-react.

In an embodiment, the binder comprises at least one inorganic oxide precursor. In a further embodiment the binder consists of at least one inorganic oxide precursor.

The process to make an ASC composition may optionally comprise a further step of adding at least one auxiliary component, which typically is a non-volatile or solid component. Preferably, auxiliary components are added in an amount of less than 20 mass % based on the sum of core-shell particles and binder, more preferably less than 10 or 5 mass %. These components may be added to assist in processing of the coating composition or to affect other functionalities of the coating to be made from the composition. Examples of auxiliary components include acids, buffer agents, catalysts, coupling agents, surfactants, anti-foaming agents, chelating agents, slip agents, thickening agents, and levelling agents.

The process to make an ASC composition optionally comprises a further step of adjusting the solids content of the coating composition by removing or adding water and/or water soluble solvent. The AS coating composition made with the process of the invention typically has solids content of less than about 20, 15, 10, 5 or even 3 mass %, and a minimum solids content of about 0.1 mass %, preferably at least 0.2, 0.5 or 1.0 mass %. Within the context of this application solids content means the total of components added excluding compound A, water and water soluble solvents, that is the sum of copolymer C, inorganic oxide precursor, binder and auxiliary components. The solids content may be determined as known to person skilled in the art by drying at 130° C. until a constant weight after drying is obtained (e.g. by using an infrared moisture analyser/balance; Ohaus MB45). The solids content=(initial weight−the constant weight after drying) divided by the initial weight×100.

The composition made with the process make an ASC composition comprises water and water soluble solvent as defined above, water and water soluble solvent are together also referred to as solvent. The solvent of the coating composition obtained with the process is a liquid component that contains the other coating components in dissolved, dispersed or colloidal states, and could thus also be referred to as diluent. The amount of solvent can be varied to obtain a desired viscosity of the coating composition, which viscosity may be relatively low to allow easy application to the substrate in thin films, e.g. for use as AS coating. Typically the viscosity of the coating composition is at least about 0.6 mPa·s, preferably at least 1.0 or 2.0 mPa·s. Depending on the deposition technology applied, the viscosity may as high as 1000 mPa·s. Preferably viscosity is at most 500, 300 or 200 mPa·s. for making thin layers of homogeneous thickness. The viscosity can be measured with known methods, for example with an Ubbelohde PSL ASTM IP no 1 (type 27042) especially for low viscosity ranges, or with a Brookfield viscometer. Solids content may be adjusted by removing solvent by e.g. evaporation or by adding solvent.

In a further preferred aspect of the process make an ASC composition the pH of the coating composition obtained is changed to a level at which inorganic oxide and/or its precursor—present in core-shell particles and/or as binder—will not react, including reacting at least only very slowly, to prevent agglomeration of core-shell particles; in case of silica precursors preferably to a pH of about 2-3, or even below 2 (as measured with a standard pH electrode on aqueous or alcoholic dispersion). This way the process results in a composition with favourable storage properties and extended shelf-life. For adjusting pH an inorganic or organic acid may be added, like nitric acid solution.

Storage at temperature of below room temperature, more preferably below 15 or 10° C. but above freezing temperature, will also increase shelf-life of the coating composition obtained.

The above described steps of the process according to the invention are typically performed at ambient pressure, but the skilled person will realise that increased (or reduced) pressure may also be applied.

The invention further relates to an AS coating composition obtained with the process to make an ASC composition as described hereinabove, including all combinations and perturbations of indicated steps, components, features and embodiments.

In a further aspect the invention also relates to a process for making an ASC on a substrate comprising the steps of

• • applying the AS coating composition as described herein according to the invention or obtained with the process make an ASC composition to the substrate; and
  • drying the applied coating layer.

The substrate on which the coating composition according to the invention can be applied may vary widely, and can be organic or inorganic and of various geometries. In an aspect the substrate is a transparent substrate. Preferably, the substrate is transparent for at least visible light. In an aspect transparent means at least 80% transmission as measured using a spectrophotometer in a range from 200-2000 nm, in an aspect a range from 400-1200 nm. Suitable substrates include inorganic glasses (e.g. borosilicate glass, soda lime glass, glass ceramic, aluminosilicate glass) and plastics (e.g. PET, PC, TAC, PMMA, PE, PP, PEN, PVC and PS) or composite materials like laminates. Preferably the substrate is a glass, like borosilicate glass; preferably a flat glass like float glass with smooth or patterned surface.

The substrate may be float glass or textured glass (for example SM or MM glass). The substrate may be wood or metal. The substrate may be flexible.

The ASC coating composition herein can be applied directly to the substrate, but also to another coating layer already present on the substrate; such as a barrier layer for alkali ions, an adhesion promoting layer, a hard coat layer, or a layer having a higher refractive index (than the substrate).

The present in invention provides a process to provide a substrate having improved anti-soiling properties comprising the steps

• • a) Providing a substrate having a surface;
  • b) Providing a coating composition comprising
    • i. organic-inorganic core shell nanoparticles having a core comprising an emulsion stabilizer C and a shell comprising inorganic oxide; and
    • ii. a water soluble solvent
    • iii. an organic compound A;
  • c) Applying a layer of the composition to the surface to obtain a coated substrate.
  • d) Drying the applied layer to obtain a dried coated substrate.

The process to provide a substrate having improved anti-soiling properties may include applying more than one coating layer, preferably with intermediate drying performed after the application of each layer. In some embodiments, intermediate drying is performed after applying some or all of the layers.

In the process to provide a substrate having improved anti-soiling properties the AS coating composition can be applied to the substrate with various deposition techniques, as known to a skilled person for making thin homogeneous coating layers. Suitable methods include spin-coating, dip-coating, spray-coating, roll-coating, slot die-coating, aerosol coating and the like. Preferred methods are dip-coating, roll-coating and spray coating. The thickness of the wet coating layer to be applied depends on the amount of solid film forming components in the coating composition, and on the desired layer thickness after subsequent drying. The skilled person will be able to select appropriate methods and conditions depending on the situation.

In an aspect a dried applied AS coating layer has a thickness of at least 50 nm and at most 1 mm as determined using cross section SEM (Scanning Electron Microscopy). In an aspect a dried applied AS coating layer has a thickness of at least 50 nm and at most 500 nm as determined using cross section SEM.

In case the AS coating is also to provide AR properties coating composition is preferably applied to the substrate in a wet thickness that will result, after applying a single layer, in a thickness after drying of about 20 nm or more, preferably the applied dried coating has a layer thickness of at least about 50 or 70 nm and of at most about 200, 180, 160 or 140 nm. In case of a multi-layer coating the skilled person may select different layer thicknesses.

In the coating process according to the invention the step of drying the applied layer of coating composition will comprise drying to evaporate at least part of the water soluble solvent and other volatile components including compound A and/or water. Further exposure to elevated temperature may be used to complete reaction of the binder into for example inorganic oxide(s), and removing residual volatiles and optionally non-volatile organic components such as the emulsion stabilizer C; depending on drying temperature.

Drying preferably takes place under ambient conditions (e.g. 15-30° C.), although elevated temperatures (e.g. up to about 250° C., more preferably up to 100, 50 or 40° C.) may also be used to shorten the total drying time, or effectuate complete or partial volatilization of less volatile components. Drying may be promoted by applying an inert gas flow, or reducing pressure. Specific drying conditions may be determined by a person skilled in the art based on components to be evaporated.

Therefore in an aspect the process according to the invention in step d) the applied layer is exposed to a temperature of at least 5 degrees Celsius, for the duration of at least at least one hour.

It is possible to apply the ASC composition before the tempering step of for example 650 degrees Celsius and still obtain an anti-soiling effect after a short time (e.g. of from 1 to 10 minutes) of exposure to such temperature.

Therefore in an aspect the process according to the invention in step d) the applied layer may be exposed to a temperature of at most 700 degrees Celsius, for the duration of at most 10 minutes.

In an aspect the process according to the invention in step d) the applied layer is exposed to a temperature of at most 250 degrees Celsius, for the duration of at most 10 minutes.

In an aspect the process according to the invention in step d) the applied layer is exposed to a temperature in a range of 15 to 80 degrees Celsius, for the duration of at least 1 hour.

During drying also compound A and water and water soluble solvent contained in the dispersed core-shell particles may at least partially be removed; resulting in porous or hollow particles which generate voids >20 nm in diameter. It is a specific advantage of the invention that an AS coating can be made at relatively low temperature, allowing use of substrates with limited thermal resistance, like plastic substrates. In such way of performing the process of the invention, also the drying step is performed at a temperature compatible with the substrate. After drying a substrate provided with a porous coating and showing AR properties is thus obtained.

Drying may be performed using a number of techniques including thermal drying, flash heating, UV aided drying, laser-induced drying, plasma treatment, microwave drying or combinations thereof. Drying conditions are depending on the coating composition, and on the type of substrate. The skilled person is able to select proper techniques and conditions. Thermally drying coatings at e.g. temperatures above 250° C. is preferred for inorganic oxide precursors as binder to result in e.g. better mechanical properties. Such conditions are often not possible for drying a plastic substrate in an oven; and also not needed to generate a desired porosity level with the AR coating composition of the invention. If high temperature drying is desired, a surface heating technique like flash heating may advantageously be applied to minimise exposure of the substrate to high temperature; as is for example described in WO2012037234.

In a preferred way of operating the process of the invention, drying is performed at a temperature of at most 300° C., more preferably at most 250, or 200° C. After drying the coating, residual organics including copolymer C can be optionally further removed by known methods; for example by exposing the coating to a solvent and extracting the organic compound from the coating.

Alternatively, especially in case of inorganic binder and glass substrate, drying may be performed by heating at temperatures from about 250 to 700° C., preferably above 300, 400, 450, 500, 550 or 600° C., during at least 1 minute. Such heating will result in porosity, and also promote formation of oxides from inorganic oxide precursors, especially when in the presence of oxygen; resulting in both drying and removing organics by calcination. In case of an inorganic glass substrate drying can be performed at relatively high temperatures; of up to the softening temperature of the glass. Such drying by heating is preferably performed in the presence of air, and is often referred to as firing in e.g. glass industry. If desired, the air may comprise increased amounts of water (steam) to further enhance drying and formation of an inorganic oxide coating. The product obtained by such process is typically a fully inorganic porous coating.

In a further preferred embodiment of the coating process of the invention such drying step is combined with a glass tempering step; i.e. heating the coated glass substrate to about 600-700° C. during a few minutes, followed by quenching, to result in AR-coated toughened or safety glass.

The invention further relates to an AS coated transparent substrate that is obtainable by or is obtained with the process according to the invention and as described hereinabove, including all combinations and perturbations of indicated features and embodiments.

An anti-reflective (AR) or light reflection reducing coating is a coating that reduces the reflection of light from the surface of a substrate at one or more wavelengths between 400 and 1200 nm, as measured at 5° incident angle. Measurements are carried out on the coated and uncoated substrate. Preferably the reduction in reflection is about 30% or more, preferably about 50% or more, more preferably about 70% or more, even more preferably about 85% or more. The reduction in reflection as expressed in a percentage is equal to 100×(reflection of the uncoated substrate−the reflection of the coated substrate)/(reflection of uncoated substrate).

The AS coated substrate obtainable by the process according to the invention may also show very good AR properties. In an aspect in combination with good mechanical performance, like abrasion resistance passing the felt test as defined in EN1096-2. AR properties may be demonstrated by a coated substrate having a minimum reflection of 2% or less at a certain wavelength, preferably about 1% or less, and more preferably of at most about 1.4, 1.2, 1.0, 0.8 or 0.6% (for two-sided coated substrate). The average reflection over a 425-675 nm wavelength range for a two-sided coated substrate is preferably about 3% or less, and more preferably at most about 2.5, 2, 1.8, 1.7, 1.6 or 1.5%.

The AS coated substrate according to the invention may be used in many different applications and end-uses, like window glazing, cover glass for solar modules, including thermal and photo-voltaic solar systems, or cover glass for TV screens and displays. The invention thus further relates to an article comprising the AS coated substrate obtained with the process according to the invention. Examples of such articles include solar panels, like a thermal solar panel or a photo-voltaic module, monitors, touch-screen displays for mobile phones, tablet pc's or all-in-one pc's, and TV sets.

The organic core may comprise compound A, at least one water soluble solvent, copolymer C, and water. Optionally the core may comprise an other surfactant. This core can be at least partly removed by evaporating volatile components; and/or by solvent extraction or etching, thermal degradation, catalytic decomposition, photo-degradation, electron beam or laser irradiation, and combinations thereof; optionally followed by evaporating the degradation products. Core material may be removed, partially or virtually completely, while the nano-particles are still in dispersed form, but also during or after separating the particles from the dispersion for a subsequent use

The nano-particles described herein typically have an particle size of at most 300 nm, more preferably at most 250, 200, 150, or 100 nm. Preferably, the particle size is preferably at least 25, 30, 35, 40, 45 or 50 nm. The size and shape of the individual core-shell nano particles varies considerably for nano particles of a coating composition according to the invention. It is therefore emphasized that particle size herein refer to the Z-averaged hydrodynamic diameter measured by determined by Dynamic Light Scattering (DLS) on dispersions on a Malvern Nano ZS as discussed above.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description, embodiments and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular or preferred aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless stated otherwise or obviously incompatible therewith.

The invention will be further illustrated by the following examples and comparative experiments, without being limited thereto.

The present invention includes the following embodiments.

• • 1. A process to provide a substrate having improved anti-soiling properties comprising the steps:
    • a) Providing a substrate having a surface;
    • b) Providing a coating composition comprising
      • i. organic-inorganic core shell nanoparticles having a core comprising an emulsion stabilizer C and a shell comprising inorganic oxide;
      • ii. at least 5 wt % water based on the total weight of the coating composition;
      • iii. at least one water soluble solvent; and
      • iv. an organic compound A;
    • c) Applying a layer of the composition to the surface to obtain a coated substrate.
    • d) Drying the applied layer to obtain a dried coated substrate.
  • 2. The process according to any one of the preceding embodiments, wherein in step d) the applied layer is exposed to a temperature in the range of 20-40 degrees C., for the duration of at least 10 minutes, preferably 30 min, most preferably at least one hour.
  • 3. The process according to any one of the preceding embodiments, wherein in step d) the applied layer is exposed to a temperature of at least 5 degrees Celsius, for the duration of at least at least one hour.
  • 4. The process according to any one of the preceding embodiments, wherein in step d) the applied layer is exposed to a temperature of at most 700 degrees Celsius, for the duration of at most 10 minutes.
  • 5. The process according to any one of the preceding embodiments, wherein in step d) the applied layer is exposed to a temperature of at most 250 degrees Celsius, for the duration of at most 10 minutes.
  • 6. The process according to any one of the preceding embodiments, wherein in step d) the applied layer is exposed to a temperature in a range of 15 to 80 degrees Celsius, for the duration of at least 1 hour.
  • 7. The process according to any one of the preceding embodiments, wherein the dried applied layer has a thickness of at least 50 nm and at most 1 mm as determined using SEM.
  • 8. The process according to any one of the preceding embodiments, wherein the substrate is selected from glass, polymer, wood and metal.
  • 9. The process according to any one of the preceding embodiments, wherein the substrate is a transparent substrate.
  • 10. The process according to any one of the preceding embodiments, wherein the coating composition is an anti-reflective coating composition.
  • 11. The process according to any one of the preceding embodiments, wherein the composition comprises a binder, preferably the binder comprises an inorganic oxide binder, preferably the inorganic oxide binder comprises inorganic oxide precursor is selected from metal alkoxides, metal chelates, metal salts, and mixtures thereof, preferably the inorganic oxide binder comprises an alkoxy silane.
  • 12. The process according to any one of the preceding embodiments, wherein the ratio of organic-inorganic core shell nanoparticles:binder is in a range of 100:0 to 20:, pref. 99:1 to 50:50 based on weight.
  • 13. The process according to any one of the preceding embodiments, wherein the composition comprises 2-70 mass % of at least one polymeric or polymerisable compound as binder, wherein mass % is based on the sum of core-shell particles and binder, preferably 5-50 mass % of at least one compound as binder.
  • 14. The process according to any one of the preceding embodiments, wherein the composition comprises between 0 to 30 wt-%, preferably between 0.1 to 30 wt-%, pref between 1 and 15 aluminium oxide equivalents of aluminium containing compound, preferably the coating formulation comprises between 0.5 to 30 wt-% aluminium oxide equivalents of aluminium containing compound.
  • 15. The process according to any one of the preceding embodiments, wherein in step a) the surface of the substrate is not coated, at least partially coated or fully coated.
  • 16. Process according to any one of the preceding embodiments, wherein the organic-inorganic core shell nanoparticles have particle size is in a range of from 25 to 300 nm as measured using DLS, preferably from 25 to 150 nm.
  • 17. The process according to any one of the preceding embodiments, wherein compound A is a non-polymeric compound.
  • 18. The process according to any one of the preceding embodiments, wherein compound A has a boiling point of at least 10° C. and at most 300° C., preferably compound A has a boiling point of at least 30° C. and at most 200° C.
  • 19. The process according to any one of the preceding embodiments, wherein compound A has solubility in water at room temperature of at most 3 kg/m′.
  • 20. The process according to any one of the preceding embodiments, wherein compound A comprises a solvent.
  • 21. The process according to any one of the preceding embodiments, wherein compound A is selected from hydrocarbon compounds, fatty acids, alcohols, esters, ethers and vinyl compounds and mixtures thereof, Preferably selected from cyclohexane, decane, toluene, trimethyl benzene, isoamyl acetate, C8-C22 alcohols, styrene, alkyl (meth)acrylates, butanediol dimethacrylate, hexanediol dimethacrylate and mixtures thereof.
  • 22. The process according to any one of the preceding embodiments, wherein emulsion stabiliser C is a cationic addition copolymer which is cationic at pH<6.
  • 23. Process according to any one of the preceding embodiments, wherein copolymer C comprises:
    • 1-25 mole % of at least one cationic or basic monomer M1, like vinyl monomers with a tertiary amine group;
    • 50-99 mole % of at least one non-ionic apolar monomer M2; and
    • 0-25 mole % of at least one polar, anionic or acidic monomer M3; with the sum of M1, M2, and M3 adding up to 100%.
  • 24. Process according to any one of the preceding embodiments, wherein copolymer C comprises from
    • 5-15 mole % of at least one monomer M1;
    • 75-95 mole % of at least one monomer M2; and
    • 0-10 mole % of at least one monomer M3; with the sum of M1, M2, and M3 adding up to 100%.
  • 25. Process according to any one of the preceding embodiments, wherein copolymer C is obtained from comprises 5-15 mole % of at least one monomer M1 selected from the group consisting of amino-functional (meth)acrylates and (meth)acrylamides; and 85-95 mole % of at least one monomer M2 selected from the group of C1-C18 alkyl (meth)acrylates.
  • 26. Process according to any one of the preceding embodiments, wherein mass ratio C/A is 0.15-1.0.
  • 27. The process according to any one of the preceding embodiments, wherein the composition is a coating composition comprising organic-inorganic core-shell nano-particles having a particle size of 35-300 nm, wherein the particle size is the Z-averaged hydrodynamic diameter measured by DLS, organic-inorganic core-shell nano-particles having a mass ratio core/shell of from 0.2 to 25 where core is the sum of an organic compound A and an emulsion stabilizer C at a mass ratio C/A of 0.1 to 2 and shell is the metal oxide equivalent of inorganic oxide precursor, wherein compound A is an apolar organic compound having a solubility in water of at most 5 kg/m³, and the emulsion stabilizer C is a cationic addition copolymer obtained from at least one monomer unit having a cationic charge and at least one monomer unit being neutral or non-ionic and having an overall positive zeta potential, wherein compound A is a non-polymeric compound and wherein the at least one inorganic precursor comprises a precursor selected from metal salts, metal chelates and organo-metallic compounds, preferably metal alkoxides, and combinations thereof.
  • 28. Process according to any one of the preceding embodiments, wherein metals include at least one element selected from Si, Al, Be, Bi, B, Fe, Mg, Na, K, In, Ge, Hf, La and lanthanoids, Sb, Sn, Ti, Ta, Nb, Y, Zn and Zr.
  • 29. The process according to any one of the preceding embodiments, wherein applying is done via spin-coating, dip-coating, spray-coating, roll-coating, slot die-coating or aerosol coating.
  • 30. The process according to any one of the preceding embodiments, wherein drying is done outdoor.
  • 31. The process according to any one of the preceding embodiments, wherein the anti-soiling coating demonstrates a TMax of at least 97.5%.
  • 32. The process according to any one of the preceding embodiments, wherein the anti-soiling coating demonstrates an T average of at least 96%.
  • 33. A coated substrate obtained with the process according to any one of the preceding embodiments.
  • 34. Use of a composition as defined in any one of the preceding embodiments, to improve anti-soiling properties of a substrate.
  • 35. Use of a coating composition to improve anti-soiling properties of a substrate, wherein the coating composition comprises organic-inorganic core-shell nano-particles having a particle size of 35-300 nm, wherein the particle size is the Z-averaged hydrodynamic diameter measured by DLS, organic-inorganic core-shell nano-particles having a mass ratio core/shell of from 0.2 to 25 where core is the sum of an organic compound A and an emulsion stabilizer C at a mass ratio C/A of 0.1 to 2 and shell is the metal oxide equivalent of inorganic oxide precursor, wherein compound A is an apolar organic compound having a solubility in water of at most 5 kg/m³, and the emulsion stabilizer C is a cationic addition copolymer obtained from at least one monomer unit having a cationic charge and at least one monomer unit being neutral or non-ionic and having an overall positive zeta potential, wherein compound A is a non-polymeric compound and wherein the at least one inorganic precursor comprises a precursor selected from metal salts, metal chelates and organo-metallic compounds, preferably metal alkoxides, and combinations thereof.
  • 36. An anti-soiling coating composition comprising
    • i. organic-inorganic core shell nanoparticles as defined herein; having a core comprising an emulsion stabilizer C as defined herein;
      • and a shell comprising inorganic oxide as defined herein;
    • ii. an organic compound A as defined herein;
    • iii. at least 5 wt % water based on the total weight of the coating composition;
    • iv. at least one water soluble solvent as defined herein; and
    • v. optionally a binder as defined herein.
  • 37. The composition according to any one of the preceding embodiments, wherein the composition comprises between 0 to 30 wt-%, preferably between 0.1 to 30 wt-%, pref between 1 and 15 aluminium oxide equivalents of aluminium containing compound, preferably the coating formulation comprises between 0.5 to 30 wt-% aluminium oxide equivalents of aluminium containing compound.
  • 38. Process of making an anti-soiling coating composition comprising the steps of
    • 1) Preparing an oil-in-water emulsion by mixing an organic compound A; an emulsion stabilizer C; and aqueous medium of pH 2-6; at a mass ratio C/A of 0.1 to 2, to result in 1-50 mass % based on emulsion of emulsified droplets of particle size 30-300 nm wherein the particle size is the Z-averaged hydrodynamic diameter measured by DLS; and
    • 2) Providing an inorganic oxide shell layer to the emulsified droplets by adding to the emulsion obtained in step 1) at least one inorganic oxide precursor, to result in organic-inorganic core-shell nano-particles with mass ratio core/shell of from 0.2 to 25 where the core is the sum of compound A and emulsion stabilizer C and shell is metal oxide equivalent of inorganic oxide precursor,
      • wherein compound A is an apolar organic compound having a solubility in water of at most 5 kg/m³, and the emulsion stabilizer C is a cationic addition copolymer obtained from at least one monomer unit having a cationic charge and at least one monomer unit being neutral or non-ionic.
  • 39. Process according to any one of the preceding embodiments, wherein compound A is a non-polymeric compound.
  • 40. Process according to any one of the preceding embodiments, wherein compound A has a boiling point of at least 10° C. and at most 300° C.
  • 41. Process according to any one of the preceding embodiments, wherein compound A has solubility in water at room temperature of at most 3 kg/m³.
  • 42. Process according to any one of the preceding embodiments, wherein copolymer C is obtained from
    • 1-25 mole % of at least one cationic or basic monomer M1, like vinyl monomers with a tertiary amine group;
    • 50-99 mole % of at least one non-ionic apolar monomer M2; and
    • 0-25 mole % of at least one polar, anionic or acidic monomer M3; with the sum of M1, M2, and M3 adding up to 100%.
  • 43. Process according to any one of the preceding embodiments, wherein copolymer C is obtained from
    • a) 5-15 mole % of at least one monomer M1;
    • b) 75-95 mole % of at least one monomer M2; and
    • c) 0-10 mole % of at least one monomer M3; with the sum of M1, M2, and M3 adding up to 100%.
  • 44. Process according to any one of the preceding embodiments, wherein copolymer C is obtained from 5-15 mole % of at least one monomer M1 selected from the group consisting of amino-functional (meth)acrylates and (meth)acrylamides; and 85-95 mole % of at least one monomer M2 selected from the group of C1-C18 alkyl (meth)acrylates.
  • 45. Process according to any one of the preceding embodiments, wherein mass ratio C/A is 0.15-1.0.
  • 46. Process according to any one of the preceding embodiments, wherein the emulsified droplets have average particle size of 35-200 nm.
  • 47. Process according to any one of the preceding embodiments, wherein the at least one inorganic precursor comprises an alkoxy silane.
  • 48. Process according to any one of the preceding embodiments, comprising a further step 3) of adding 2-70 mass % of at least one polymeric or polymerisable compound as binder, wherein mass % is based on the sum of core-shell particles and binder.
  • 49. Process according to any one of the preceding embodiments, comprising adding 5-50 mass % of at least one compound as binder.
  • 50. Process according to any one of the preceding embodiments, wherein the binder is at least one inorganic oxide precursor.
  • 51. Anti-soiling coating composition obtained with the process according to any one of the preceding embodiments.
  • 52. Process for making an anti-soiling coating on a transparent substrate comprising the steps of applying the coating composition obtained with the process according to any one of the preceding embodiments to the substrate; and drying the applied coating layer.
  • 53. Process to any one of the preceding embodiments, wherein drying is performed at a temperature of at most 250° C.
  • 54. Anti-soiling coated transparent substrate obtained with the process according to any one of the preceding embodiments.

EXPERIMENTS

Organic Compounds

Table 1 provides relevant data on compounds A that are applied in experiments as organic core or template.

	TABLE 1
			Melting	Boiling	Solubility
			point	point	in water
	Reference	Compound	(° C.)	(° C.)	(kg/m3)
	A1	Cyclohexane	6.5	81	0.04
	A2	Toluene	−93	110	0.5
	A3	Isoamyl	−78	142	1.1
		acetate

Cationic Copolymers

Table 2 presents monomer composition for a number of cationic copolymers C, which are obtained following the procedure described in the experimental part of EP2178927, which is incorporated herein by reference. Copolymers were used as aqueous dispersion with a concentration of about 20 mass %, with pH of about 4 (acidified with formic acid). The copolymers had Mw in the range 25-40 kDa (GPC).

	TABLE 2
	C1	C2	C3	C4	C5
	monomer	Comonomer content (mole %)
	DMAEMA	10.1	38.3	17.5	10.3	8.3
	MMA	89.9	61.7	82.5	—	91.7
	IBOA	—	—	—	89.7

DLS Measurements

A Malvern Nano ZS dynamic light scattering instrument was used to measure particle size of dispersed particles on 1 drop of dispersion in 10 ml aqueous KCl solution (1 mmol/L) at 25° C. and in back-scattering mode. Particle size herein refers to average particle size measured as Z-averaged hydrodynamic diameter.

For formulations (example 10) made in isopropanol the DLS measurements were performed in isopropanol as the diluting solvent. For these measurements 10 drops of formulation was added to 10 ml of isopropanol.

Felt Test

Scratch resistance of applied coating layers is evaluated by the felt test according to EN1096-2.

Optical Properties

Reflection and transmission of coated transparent substrates is evaluated with a Shimadzu UV-2450 spectrophotometer. Relative specular reflectance is measured at an incident angle of 5° with a reflectance attachment. For measuring transmission the integrating sphere attachment is installed in the sample compartment, and incidence angle was 0° (normal to the sample surface). Average reflection values are calculated for the wavelength range 425-675 nm. Measurements are performed on two-sided coated plates. Transmission measurements in example 10 were performed on a Schimadzu 2600 or Perkin Elmer 1050 spectrophotometer. Average transmission values are calculated for the wavelength range 400-1200 nm.

Example 1

20 grams of cyclohexane (p.a.) containing 1 mass % of heptadecane was dispersed using a Ultra-turrax unit T25 into a mixture of 14 grams Milli-Q water, 1 gram of 2-propanol and 15 grams of a dispersion containing 21.5 mass % of cationic copolymer C1 (Mw about 30 kDa). The resulting coarse emulsion was further dispersed using a high-pressure homogenizer (DeBee, operated at a pressure 30 kPsi, using diamond orifice and applying water cooling) in 9 cycles of about 15 strokes each and allowing the temperature to decrease after each cycle to 40° C. This resulted in a stable emulsion with emulsion droplets of particle size (DLS Z-averaged hydrodynamic diameter) of 265 nm (Polydispersity Index, PDI 0.28). To this emulsion 2 grams of copolymer C1 were added, rendering a clear positive charge of the droplets, indicated by the zeta potential >+11 mV (pH 4). Silication was then performed by gradually adding (90 minutes) by perfusor pump 41.5 g of tetramethoxy silane (TMOS) to a mixture of 35 g of the resulting emulsion and 80 g Milli-Q water, under firmly stirring with magnetic stirring bar. After the addition was completed stirring was continued for another 90 minutes. 100 g of the mixture was diluted with 100 g of Milli-Q water and acidified with 6 drops of concentrated HNO₃. The DLS size of the final product was 255 nm (PDI 0.20) and TEM analysis revealed spherical silica particles with particle size in the range 60-120 nm. (see FIG. 1).

Cyclohexane could be removed by rota-evaporation treatment, while gradually increasing the water temperature of the water bath from 30 to 40° C., and reducing the pressure from 300 to 100 mbar. The final dispersion contained 6.4 mass % of hollow silica particles with DLS size of 219 nm (PDI 0.35) and zeta potential of 12 mV (pH=4); and was found to be stable in time.

Example 2

Example 1 was repeated, but now 20.7 g of TMOS was used. After evaporation of cyclohexane TEM analysis showed hollow silica spheres of similar size as in Example 1, but the particles appeared to be partly collapsed; likely due to limited strength of the silica shell during sample preparation for the TEM analysis.

Comparative Experiment 3

Example 1 was repeated, but now copolymer C2 was used. It appeared not possible to obtain a stable emulsion of cyclohexane; polymer C2 apparently being too hydrophilic to function as emulsion stabilizer.

Example 4

Example 1 was repeated, but now copolymer C3 was used. After evaporation of cyclohexane TEM analysis showed hollow silica particles of similar size as in Example 1, but the particles appeared to be less regularly shaped.

Example 5

21 g of cyclohexane containing 1 mass % of heptadecane was dispersed using a Ultra-turrax unit T25 into 51.3 g of a dispersion containing 17.4 mass % of cationic copolymer C4 (Mw about 31 kDa). This resulted in a stable emulsion (>1 week) with emulsion droplets of DLS size of 202 nm (PDI 0.02). Silication was performed by gradually adding (90 min) 41.5 g of TMOS to a mixture of 35 g of the resulting emulsion and 80 g Milli-Q water, while firmly stirring with magnetic stirring bar. After the addition was completed the dispersion was stirred for another 90 minutes. 135 g of the mixture was diluted in 750 g Milli-Q water and acidified with 15 drops of concentrated HNO₃. The final dispersion of 2.2 mass % displayed a DLS size of 200 nm (PDI 0.06), a zeta potential of +19 mV at pH 4.0 and was stable for more than one week. A TEM micrograph on the resulting dispersion after sample preparation showed spherical hollow silica particles of about 100-150 nm and a shell thickness of about 10 nm; also showing some collapsed particles.

Cyclohexane was removed from the dispersion by spray-drying (Büchi Mini Spray drying B-191) at an evaporation temperature of 130-150° C., flow rate at 270 mL/h in combination with an air flow of 640 normal L/h. TEM performed on the obtained white powder showed aggregated particles having multi-hollow structure. The product showed opacifier (whitening) power, when applied as a simple paint formulation on black photo paper.

Example 6

23.3 g of toluene was mixed with 52.6 g of a dispersion of copolymer C5 (19 mass % in water, pH 3.9, particle size 44 nm (PDI 0.06) by DLS) using a Dispermat mixing unit, and then diluted with 180 grams of water; resulting in about 13 mass % emulsified droplets in water. To 100 g of this emulsion 52 g of TMOS was added drop-wise over 2 hours at ambient temperature under stirring. Particle size of resulting particles was about 82 nm (according to DLS). The obtained dispersion was acidified with 50% nitric acid to a pH of 1.8; and showed stability over time. A TEM micrograph revealed spherical particles showing a core-shell structure, and particle size in the range 30-80 nm (see FIG. 3).

Example 7

50 g of isoamyl acetate was mixed with 113 g of a dispersion of copolymer C5 (19 mass % in water, pH 3.9, particle size 44 nm (PDI 0.06) by DLS) using a Dispermat mixing unit, and then diluted with 385 grams of water; resulting in about 13 mass % emulsified droplets in water. To 180 g of this emulsion 70 g of TMOS was added drop-wise over 2 hours at ambient temperature under stirring. Particle size of resulting particles was about 100 nm (according to DLS). The obtained dispersion was acidified with 50% nitric acid to a pH of 1.9; and showed stability over time. Moreover, the dispersion could be diluted with water, ethanol, or isopropanol and remain stable (no visual flocculation or sedimentation).

A Cryo-TEM micrograph revealed spherical particles showing a core-shell structure, and particle size in the range 30-70 nm (see FIG. 4).

Several coatings were prepared from the dispersion obtained, by diluting with isopropanol and adding different amounts of a sol made from tetraethoxy silane (TEOS) as binder.

The sol of TEOS was prepared by adding to a solution of TEOS in iso-propanol a molar excess of water while stirring, to pre-hydrolyse the silane compound. After cooling back to room temperature glacial acetic acid was added, and after 24 hrs stirring at ambient conditions more iso-propanal and nitric acid (65%) were added. The resulting dispersion contained about 4 mass % of silica particles of about 3-5 nm size.

Composition 7-1 was made by diluting the core-shell particles dispersion with 5-fold amount of acidified isopropanol, followed by adjusting pH of the final dispersion to 1.5 by adding nitric acid (50%).

Compositions 7-2, 7-3, 7-4 and 7-5 were prepared by mixing an amount of above prepared core-shell particles dispersion with different amounts of the TEOS sol as binder and iso-propanol, after which the pH was adjusted to about 1.5 by adding nitric acid (50%). The amount of binder was calculated as mass of SiO₂ resulting from TEOS relative to the sum of binder and core-shell particles.

The obtained coating compositions were used to provide coating layers to glass plates by dip-coating in a dust-free room. Pilkington Optiwhite S glass plates of 2 mm thickness were cleaned with water and household cleaner, then rinsed with water and demi-water, and then dip-coated by immersing in a container with coating composition; the coating bath being kept at room temperature (at about 21° C.) and 50% relative humidity. The plate was then vertically pulled up from the bath at a rate of about 2.5 mm/s. The coated plate was subsequently dried at ambient conditions for at least 5 minutes.

After application the coated glass was dried at 125° C. during 15 minutes in an air circulation oven, or dried at 650° C. during 2.5 minutes. All samples passed the felt test. Minimum reflection of the samples dried at 650° C. was between 0.5 and 1%. As an example the reflection curve measured for sample 7-1 is shown in FIG. 2. In case the coated plates were dried at 125° C. the average reflection was between 1.7 and 3.2%. This difference in reflection can be attributed to different porosity levels, resulting from the copolymer (emulsion stabiliser C) present in the core-shell particles being pyrolyzed (or depolymerized) and evaporated at 650° C.; but not at the low drying temperature, whereas drying at 125° C. will result in evaporation of the organic compound contained in the core-shell particles dispersion, and thus in some porosity. Reflection data are summarized in Table 3.

Comparative Experiment 8

52.6 g of dispersion of copolymer C5 (19 mass % in water, pH 3.9, particle size 44 nm (PDI 0.06) by DLS) was mixed with 173.3 g of water (˜5% emulsion stabilizer in water), and subsequently 20 g of TMOS was drop-wise added over 2 hours at ambient temperature. Increase of particle size to about 84 nm (according to DLS) was observed. The obtained dispersion was acidified with 50% nitric acid to a pH of 1.8; and showed stability over time. A cryo-TEM micrograph shows spherical, but somewhat aggregated particles having core-shell structure, with particle size in the range 25-90 nm (see FIG. 5).

Analogously to Example 7, coating compositions were made by combining the obtained dispersion with different amounts of TEOS sol and iso-propanol; and used for preparing coated glass samples. For the products obtained average reflection is about 1% when dried at 650° C., but is above about 5.8% when dried at 125° C. This difference indicates that at low temperature hardly any porosity is obtained, whereas at high temperature porosity may result from calcination of organic copolymer in the coating; demonstrating the advantage of the coating composition according to the invention as prepared in e.g. Example 7 particularly when prepared at dried at low temperature where the emulsion stabilizer is not pyrolysed or evaporated. Results are summarized in Table 3.

TABLE 3
	Amount of	Average reflection	Average reflection
	binder	(%)	(%)
Sample	(mass %)	(dried at 125° C.)	(dried at 650° C.)
Example 7-1	0	1.7	0.8
Example 7-2	9	2.3	0.8
Example 7-3	16	2.4	0.8
Example 7-4	23	2.7	1.1
Example 7-5	28	3.2	1.8
Comp. exp. 8-1	0	5.8	0.8
Comp. exp. 8-2	21	7.1	0.9
Comp. exp. 8-3	36	5.9	0.8
Comp. exp. 8-4	45	6.0	1.2
Comp. exp. 8-5	52	6.1	1.1

Humidity sensitivity: For the comparative coating compositions, where only the emulsion stabilizer and no component A is present, the minimum reflection is below 1% when dried at 650° C., but increases to above 3% at 90% relative humidity. It could be theorized (without being limited thereto) that this may be due the mesoporosity of the coating. When coating compositions wherein component A is present in the nano particles are dried at 650° C. the minimum reflections stay below 1.5% even at 90% relative humidity.

Outdoor durability: After accelerated outdoor durability tests (1000 hours @ 85% relative humidity and 85° C.) the coatings are off white possibly due to sodium and calcium salts having diffused out of the glass plates, but after washing with water and ethanol the AR properties are retained.

Mechanical properties: The scratch resistance of the coating compositions 13.1-13.4 as well as on the comparative coating composition pass the felt test according to EN 1096-2 with a change in transmission of less than 0.5%.

Example 9

Several coating formulations were prepared by mixing core-shell particle dispersions of Example 6 (with toluene as component A) with isopropanol and varying amounts of binder in the form of the sol of TEOS prepared as described in Example 7.

Coating formulation 9.1: (No binder): To 500 grams of isopropanol 6.5 grams of 1:1 65% nitiric acid/water was added after which 90 grams of the core-shell particle dispersion of Example 6. Final pH of the formulation is 1.6 and particle size of 87 nm according to DLS. After 6 weeks at room temperature the DLS value was increase less than 10 nm indication good storage stability of the particles. The formulation contains an equivalent SiO₂ content of 1.27%.

Comparative coating formulation 9.2: (100% binder): Binder in the form of the sol of TEOS prepared as described in Example 7 containing an equivalent amount of silica of 4% was diluted with isopropanol to a relative amount of 1.27% SiO₂.

Coating formulation 9.3: (35% binder): To 200 grams of the core-shell particle dispersion of Example 6, 107.8 grams of binder in the form of the sol of TEOS prepared as described in Example 7 was added so a SiO₂ equivalence ratio of 35/65 was obtained.

Coating formulation 9.4: (65% binder): To 100 grams of the core-shell particle dispersion of Example 6, 185.9 grams of binder in the form of the sol of TEOS prepared as described in Example 7 was added so a SiO₂ equivalence ratio of 65/35 was obtained.

Coating formulation 9.5: (90% binder): To 100 grams of the core-shell particle dispersion of Example 6, 900.7 grams of binder in the form of the sol of TEOS prepared as described in Example 7 was added so a SiO₂ equivalence ratio of 90/10 was obtained.

The pH of the formulations was maintained at 1.5+/−0.2 and adjusted with nitric acid if needed.

Coating formulations 9.1-9.5 were dip coated and assessed on the optical properties via optical transmission measurements relative to glass (type Pilkington Optiwhite S; average transmission between 350 and 850 nm of 91.4%). Morphology of the coatings (only dried at room temperature) was determined via cross-section SEM analysis. To achieve complete drying and hardness, the transmission was measured after 1 week.

TABLE 4
		Average
	Cross	transmission
Sample	section	gain	Observations
coating	FIG. 6	6.02%	Many core-shell particles
formulation			with rather rough coating
9.1			surface
Comparative	FIG. 7	2.27%	No pores observed. Nano
coating			pores between binder particles
formulation			may be present but are too
			small to be observed with
			this technique.
			Very smooth surface
coating	FIG. 8	5.5%	Core-shell particles
formulation			observedand some surface
9.3			roughness
coating	FIG. 9	5.05%	Core-shell particles
formulation			observedand some surface
9.4			roughness
coating	FIG. 10	4.05%	Only limited number of
formulation			core-shell particles observed.
9.5			Smooth surface

In FIG. 11, the average transmission gain is plotted as a function of the origin of the silica. Each sample composition is indicated with number. Surprisingly, a highly un-linear behavior is observed in that the transmission gain remains high even at very binder contents and that the transmission gain only is reduced substantially when more than 90% of the silica originates from the binder.

Mechanical performance was evaluated using abrasion test performed according to NEN-EN 1096-2). For all formulation above >50% POT only minor changes (<0.5%) in transmission gain were observed after the test. Hence, even after the abrasion test, good optical properties are obtained that are of interest for commercial application in for example the solar cell cover glass market.

Example 10

Several coating formulations were prepared by mixing core-shell particle dispersions of Example 6 (with toluene as component A) [referred to below as CSP-EX6] with isopropanol and varying amounts of binder in the form of the sol of TEOS prepared as described in Example 7.

Several coating formulations were prepared by mixing core-shell particle dispersions of Example 7 (with isoamyl acetate as component A) [referred to below as CSP-EX7] and varying amounts of binder in the form of the sol of TEOS prepared as described in Example 7.) [referred to below as binder-EX7]

10-1: Coating Formulation 100% CSP: 100% Core-Shell Particle Dispersion CSP EX6

41.6 g of CSP-EX6 was diluted with 280.0 g of IPA and acidified with 65% nitric acid to pH<2. The [SiO₂] is 1.7 wt %.

10-2: Coating Formulation 50% CSP: 50 wt % Core-Shell Particle Dispersion and 50 wt % Binder

25.0 g of CSP-EX6 was diluted with 143.3 g of IPA to a [SiO₂] of 2.0 wt %. Then, 168.3 g of binder was added (this is binder EX7 diluted in isopropanol (1:1) to [SiO₂] of 2.0 wt %). The formulation was stirred to obtain good mixing. pH=1.6

10-3: Coating Formulation 30% CSP: 30 wt % Core-Shell Particle Dispersion 70 wt % Binder

13.4 g of CSP-EX6 was diluted with 76.7 g of IPA to a [SiO₂] of 2.0 wt %. Then, 210.0 g of binder (of EX7 diluted 1:1 in isopropanol to [SiO₂] of 2.0 wt %) was added, and the formulation was stirred. pH=1.5

10-4: Coating Formulation 70% CSP: 70 wt % Core-Shell Particle Dispersion and 30 wt % Binder

31.3 g of CSP-EX6 was diluted with 178.9 g of IPA to a [SiO₂] of 2.0 wt %. Then, it was mixed with 89.9 g of binder (of Ex7 diluted 1:1 in isopropanol to [SiO₂] of 2.0 wt %). The pH=1.7

10-5: Coating Formulation 100% CSP: 100% Core-Shell Particle Dispersion CSP EX7

54.5 g of CSP-EX7 was diluted with 245.5 g of IPA to a [SiO₂] of 2.0 wt %. pH was adjusted with nitric acid to <2.0. DLS=93 nm

10-6: 50% Coating Formulation 50% CSP: 50 wt % Core-Shell Particle Dispersion and 50 wt % Binder

27.3 g of CSP-EX7 was diluted with 122.8 g of IPA to a [SiO₂] of 2.0 wt %. This was mixed with 150.0 g of binder (of Ex7 diluted 1:1 in isopropanol to [SiO₂] of 2.0 wt %). pH=1.8

DLS=95 nm

10-7: Coating Formulation 100% Binder

Binder-EX7 was diluted 1:1 with IPA to a [SiO₂] of 2.0 wt %.

Dipcoating experiments were performed on Pilkington Optiwhite S float glass with, 3.2 mm thickness and size of 10×10 cm with coating formulations 10-1 to 10-7 as described above.

Dip-coating was done in a dust-free room. Pilkington Optiwhite S glass plates of 3.2 mm thickness were cleaned with water and household cleaner, then rinsed with water and demi-water, and then dip-coated by immersing in a container with coating composition; the coating bath being kept at room temperature (at about 21° C.) and 40% relative humidity. The plate was then vertically pulled up from the bath at a rate (as indicated in tables 5-7 below). The coated plate was subsequently dried at ambient conditions for at least 5 minutes. After drying as indicated in the tables below the soiling measurement as described below was performed.

Method of Soiling Measurement

Soiling procedure: The anti-soiling properties of the coatings were tested with a Taber Oscillating Abrasion Tester (model 6160) using commercially available Arizona test dust from quartz A4 coarse (size varying from 1 to 200 μm) as soiling medium, commercially available from KSL Staubtechnik GMBH. The 10×10 cm 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, 20 g of Arizona test dust is gently dispersed over the whole glass plate using a brush. The soiling procedure (300 cycles at a speed of 100 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 40% RH and the temperature was 20° C.

Soiling Evaluation: Soiling Score—Visual Assessment (Table 5-8):

The degree of soiling of the coatings was determined by visually assessing the soiled substrate using the following soiling scale:

3: high soiling
2: acceptable soiling
1: low soiling
0: zero to minor soiling

Soiling Evaluation—Transmission Measurement to Determine AS Loss/ARE/ASR (Table 9)

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 400-1200 nm was established from the spectra. Based on the resulting differences between the before and after values of the average transmittance over 400-1200 nm recorded in the spectra, conclusions regarding the level of soiling and hence the effectiveness of the anti-soiling coatings could be drawn.

TABLE 5
Code			Dip	Drying
(coating	CSP-		speed	time	Soiling
formulation)	EX6	Binder	(mm/sec)	(20° C.)	score
10-1	100	0	3.5	1	day	0-1
	100	0	3.5	5	days	0-1
10-4	70	30	3.5	1	day	0-1
10-2	50	50	3.5	1	day	1-2
	50	50	3.5	5	days	1-2
10-3	30	70	3.5	1	day	2
10-7	0	100	3.0	1	day	3
(Binder
EX7)

TABLE 6
Code			Dip	Drying
(coating	CSP		speed	time	Soiling
formulation)	EX7	Binder	(mm/sec)	(20° C.)	score
10-5	100	0	2.5	1 day	0
10-6	50	50	2.5	1 day	2

TABLE 7
Code		Dip
(coating	Drying	speed	Drying	Soiling
formulation)	temperature	(mm/sec)	time	scale
10-4	20° C.	2.5	1	day	0-1
10-4	650° C.	3.2	1	minute	1
10-4	650° C.	3.4	2	minutes	1
10-4	650° C.	3.6	3	minutes	1-2
10-4	650° C.	3.8	4	minutes	1-2
10-4	650° C.	4.0	5	minutes	2

TABLE 8
			Average
			T %
	Average		after	Max	AS
	T %	Max T %	soil	T %	loss*
Sample	400-	(λ at	400-	after	(%-
Float glass	1200 nm	Max)	1200 nm	soil	points)	ASR	ARE
0	92.7	—	87.6	—	5.1	—	—
10-1	96.8	98.3	96.6	98.1	0.2	96.1	4.1
		(689)
10-4	96.1	97.3	95.9	97.1	0.2	96.1	3.4
		(703)
		97.4
10-2	95.9	(610)	95.1	96.5	0.8	84.3	3.2
10-3	95.4	96.9	94.2	95.5	1.2	76.5	2.7
		(586)
*AS loss is transmission loss after soiling on the same plate, Tprior soil minus Tafter soil based on Average T % 400-1200 nm

FIG. 12 shows a photograph of a glass plate coated with coating formulation 10-1 as described above: 100% CSP EX6 (soiling score 0-1) with an uncoated edge at the top (soiling score 3).

Claims

1. A process to provide a substrate having improved anti-soiling properties comprising the steps

a) Providing a substrate having a surface;

b) Providing a coating composition comprising: i. organic-inorganic core shell nanoparticles having a core comprising an emulsion stabilizer C and a shell comprising inorganic oxide; and ii. at least one water soluble solvent; iii. at least 5 wt % water based on the total weight of the coating composition; and iv. an organic compound A;

c) Applying a layer of the composition to the surface to obtain a coated substrate; and

d) Drying the applied layer to obtain a coated substrate.

2. The process according to claim 1, wherein in step d) the applied layer is exposed to a temperature of at least 5 degrees Celsius, for the duration of at least at least one hour.

3. The process according to claim 1, wherein the composition comprises a binder, preferably the binder comprises an inorganic oxide binder, preferably the inorganic oxide binder comprises inorganic oxide precursor is selected from metal alkoxides, metal chelates, metal salts, and mixtures thereof, preferably the inorganic oxide binder comprises an alkoxy silane.

4. The process according to claim 1, wherein the composition comprises between 0 to 30 wt-%, preferably between 0.1 to 30 wt-%, pref between 1 and 15 aluminium oxide equivalents of aluminium containing compound, preferably the coating formulation comprises between 0.5 to 30 wt-% aluminium oxide equivalents of aluminium containing compound.

5. Process according to claim 1, wherein the organic-inorganic core shell nanoparticles have particle size is in a range of from 20 to 300 nm as measured using DLS.

6. The process according to claim 1, wherein compound A is a non-polymeric compound.

7. The process according to claim 1, wherein compound A has a boiling point of at least 10° C. and at most 300° C., preferably compound A has a boiling point of at least 30° C. and at most 200° C.

8. The process according to claim 1, wherein compound A has solubility in water at room temperature of at most 3 kg/m3.

9. Process according to claim 1, wherein copolymer C is obtained form

1-25 mole % of at least one cationic or basic monomer M1, like vinyl monomers with a tertiary amine group;

50-99 mole % of at least one non-ionic apolar monomer M2; and

0-25 mole % of at least one polar, anionic or acidic monomer M3; with the sum of M1, M2, and M3 adding up to 100%.

10. Process according to claim 1 wherein mass ratio C/A is 0.15-1.0.

11. Process according to claim 1 wherein metals include at least one element selected from Si, Al, Be, Bi, B, Fe, Mg, Na, K, In, Ge, Hf, La and lanthanoids, Sb, Sn, Ti, Ta, Nb, Y, Zn and Zr.

12. A coated substrate obtained with the process according to claim 1.

13. Use of the coating composition as defined in claim 1 to improve anti-soiling properties of a substrate

14. An anti-soiling coating composition comprising

i. organic-inorganic core shell nanoparticles having a core comprising and an emulsion stabilizer C and a shell comprising inorganic oxide;

ii. at least 5 wt % water based on the total weight of the coating composition;

iii. at least one water soluble solvent; and

iv. an organic compound A.

15. Process of making an anti-soiling coating composition comprising the steps of

1) Preparing an oil-in-water emulsion by mixing an apolar organic compound A; a cationic addition copolymer C as emulsion stabilizer; and aqueous medium of pH 2-6;

at a mass ratio C/A of 0.1 to 2, to result in 1-50 mass % (based on emulsion) of emulsified droplets of particle size 30-300 nm;

2) Providing an inorganic oxide shell layer to the emulsified droplets by adding to the emulsion obtained in step 1) at least one inorganic oxide precursor, to result in organic/inorganic core-shell nano-particles with mass ratio core/shell of from 0.2 to 25;

3) Optionally combining the core-shell nanoparticles thus obtained with water and/or water soluble solvent;

4) Optionally adjusting pH; and

5) Optionally adding an organic or inorganic polymeric or polymerizable binder.