POLLUTION-REDUCING COATINGS

This application claims priority from GB 1423090.8 filed 23 December 2014, the contents of which are incorporated herein in their entirety.

Field of the Invention

The present invention relates to pre-coated metal sheets that have NO _x abatement activity and to coatings and compositions that have NO _x abatement activity. The invention further relates to kits comprising two compositions for mixing to provide NO _x abatement coatings. In other words, the invention one component systems for applying coatings to a substrate in a factory or similar and two component systems for mixing at the site of application to provide ΝΟχ abatement coatings. Background

The modern world relies heavily on the burning of fossil fuels for the provision of energy. However, negative effects associated with the burning these fuels are well known. For example, the release of carbon dioxide (C0 ₂ ) into an environment that is increasingly less able to absorb is generally recognised to be contributing to global warming. Carbon monoxide (CO) is poisonous and oxides of nitrogen (NO and N0 ₂ , collectively referred to herein as NO _x ) and sulphur (S0 ₂ and others) have a negative effect on air quality, and are known to be associated with smog, acid rain, and reduced water quality. Oxides of nitrogen are also implicated in climate change. To reduce the emission of these pollutants, exhaust gas scrubbers have been fitted to static facilities such as power stations, and catalytic converters can be used on vehicles to encourage the reduction of oxides of nitrogen and the oxidation of CO and unburnt hydrocarbons. However, catalytic converters are not always an effective solution, not least because engines, especially diesel engines, are running hotter which results in more NO _x in the exhaust and less hydrocarbon. The end result is that European cities, such as London, have unacceptable levels of NO _x and are being prosecuted by the EU Commission in an attempt to force the authorities into action.

Titanium dioxide is widely used as a pigment in paints and coatings. The photo-catalytic effect of titanium dioxide has been known for many years. It is common knowledge that if the titanium dioxide pigment particles are not encapsulated by silica and other inorganic oxides such as alumina or zirconia, then the particles will initiate photo-degradation reactions in the organic coatings into which they are incorporated. This results in undesirable

"chalking" and negatively impacts the appearance of the coating. Ultimately, it results in erosion and a need to clean and recoat the surface more frequently than is desirable. Typically, therefore, this problem of photo-catalytic degradation is addressed by

encapsulation of the titanium dioxide particles. Encapsulation isolates most of the titanium dioxide surface, which reduces the photo-catalytic activity to acceptable levels.

The photo-catalytic activity of titanium dioxide has been exploited to provide NO _x abatement by adding directly to concrete used to form walls so that the walls themselves are active against NO _x . Chemi-luminesence spectroscopy has been used to demonstrate that these surfaces are effective in reducing the local NO _x levels with the titanium dioxide acting as a photo-catalyst driving the reaction of NO _x and water to produce nitric acid. The resultant acid is then washed away by rain or by spraying regularly with water in the case of tunnels. It was recently demonstrated that provided tunnel lighting is of the correct wavelength it does not have to have a great intensity in order for the photoactive titanium dioxide to be active against NO _x . Of course, it will be appreciated that in this context the associated photo- catalytic degradation that is such a problem in organic coatings is not an issue in these concrete structures.

Concrete, while useful for many applications, is not always a preferred or even feasible material for many construction applications. Pre-coated metal is often a material of choice used by the construction industry, especially when the building being assembled is similar to a warehouse or factory and so a large area needs to be protected from the elements. The substrate is often galvanised steel coated with a paint system that is applied under factory conditions for consistent quality. However, aluminium and steels coated with different metallic coatings (for example, Galfan and Galvalume) can be used also as substrates. These are usually sold in rolls and are referred to in the industry as "coil" or "coils"/ The most common coatings are based around thermosetting polymers such as polyesters cross-linked with hexa-methoxymethyl melamines, although polyesters cross-linked with isocyanates are also used. Thermoplastic coatings can be used and these are normally based on either plasticised polyvinyl chloride or poly vinylidene difluoride alloyed with an acrylic resin or fluoro-polymers consisting of alternating fluoro-ethylene and alkyl vinyl ether segments. Pigments are added to give colour and sometimes functionalities such as near infrared (NIR) reflectivity. Coatings that are intended for use on the exterior surfaces of the building envelope are carefully formulated from raw materials that are known to deliver good outdoor durability. Thus for white and light coloured coatings encapsulated titanium dioxide is used to ensure photo degradation is kept to a minimum.

Those skilled in the art of paint formulation will at once recognise the dichotomy of having an active paint film containing titanium dioxide that is sufficiently effective against NO _x and yet is stable or at least resistant to photo-degradation. Previous patents have described how this can be circumvented in coil coatings by separating the photoactive coating from the organic layer using a relatively thin inorganic barrier layer. This elegant solution has its benefits. However, in order to achieve the activity required while retaining acceptable durability for a coated coil, the metal strip to be coated must be passed down the coating line at least twice.

1 ) Photocatalytic coating

Pub.No.:US2009/0061246 A1 (Pub. Date: March 5, 2009) 2) Depolluting coating composition

Pub. No.:US2008/0097018 A1 (Pub Date: April 24, 2008)

3) Coating composition having surface depolluting properties.

Pub No.:US2007/0167551 A1 (Pub Date: Jul 19, 2007)

4) Composition for use NOx removing translucent coating

Pub.No.:US2007/0155622 (Pub Date: Jul 5, 2007)

5) De-polluting and self-cleaning expoxy siloxane coating

Pub No.:US2009/0281207 A1 (Pub.date: Nov.12, 2009)

6) Self-Cleaning substrate and methods for making the same.

Pub No.:US201 1/0027485 A1 (Pub.date: Feb.3, 201 1 ) Summary of the Invention

The present invention is based on the inventors' insight that a single coating having both ΝΟχ abatement properties and good resistance to degradation would be desirable in terms of cost of production of pre-coated materials, environmental impact (less waste, both of energy and scrap metal) and manufacturing ease and efficiency. The invention further provides kits comprising compositions that may be mixed at the point of use to enable NO _x abatement coatings to be applied to substrates by, for example, brush or spray application. In other words, the invention further provides two component systems. The present invention provides this by using binders that are somewhat resistant to the degradation chemistry associated with photoactive titanium. The inventors have observed that after an initial degradation of the organic binder reveals the naked titanium dioxide particle the film remains intact for a considerable period of time. Embodiments of the present invention provide coatings that reduce NO _x levels and have durability ratings that meet the Ruv2 classification (EN10169-2). This durability makes the materials and compositions described herein suitable for coating coil for the construction industry and / or for applying to surfaces by brush or spray application either during construction or later as a maintenance or repair application.

In a first aspect, the present invention provides a coated metal substrate wherein the coating comprises a NO _x active material, the NO _x active material comprising photoactive titanium dioxide and a binder, the binder comprising a silicone and a polymer, wherein the silicone content of the binder is at least 30%wt of the solids in the binder.

The present invention further provides a coated metal substrate wherein the coating comprises a NO _x active material, the NO _x active material comprising photoactive titanium dioxide and a binder, the binder comprising a silicone and a polymer, wherein the material has a NO _x abatement value of 5% or more, more preferably 10% or more (measured as described herein) after 1000 h of cycling 4 h UV exposure, 4 h condensation (EN 13523-10 specification).

The present invention further provides a coated metal substrate wherein the coating comprises a NO _x active material, the NO _x active material comprising photoactive titanium dioxide and a binder, the binder comprising a silicone and a polymer, wherein the material is formed from a composition comprising at least 5%wt silicone of the total weight of the composition (prior to application and drying to form the coating), more preferably at least 7%wt, more preferably at least 10%wt. For example, the silicone content of the composition prior to application and drying may be 7-15%wt, for example, 9-13%wt.

The present invention further provides compositions for application to substrates. These compositions, when dried, form NO _x active material, for example, coatings. Suitably, the NO _x active coatings have a NO _x abatement value of >5%, more preferably, greater than 10% (measured as described herein) after 1000 h of cycling 4 h UV exposure, 4 h condensation (EN-13523-10 specification). Accordingly, in a further aspect, the present invention provides a composition for applying to a substrate to form a NO _x active coating, the composition comprising photoactive titanium dioxide and a binder, the binder comprising a silicone and a polymer, wherein the silicone content of the binder is at least 30%wt of the solids in the binder.

The present invention further provides a composition for applying to a substrate to form a ΝΟχ active coating, the composition comprising a binder comprising a silicone and a polymer, wherein the material is formed from a composition comprising at least 5%wt silicone of the total weight of the composition (prior to application and drying to form the coating), more preferably at least 7%wt, more preferably at least 10%wt. For example, the silicone content of the composition prior to application and drying may be 7-15%wt, for example, 9-13%wt.

Liquid compositions according to the present invention may be provided as "one pot" (1 K) or "two pot" (2K) systems. Suitably, the two pot system may be provided as a kit comprising a composition comprising photoactive titanium dioxide and a binder, the binder comprising a silicone and a polymer, wherein the silicone content of the binder is at least 30%wt of the solids in the binder (the first pot); and a hardener (the second pot). Suitably the hardener is a cross-linker which may be provided in a solvent.

Accordingly, the present invention further provides a kit including:

(i) a composition comprising photoactive titanium dioxide and a binder, the binder comprising a silicone and a polymer, wherein the silicone content of the binder is at least 30%wt of the solids in the binder; and

(ii) a hardener composition comprising a cross-linker in a solvent, optionally wherein the cross linker is an unblocked isocyanate.

Suitably, compositions (i) and (ii) are provided in separately sealed containers (which may also be described as pots), optionally within instructions for a method as described herein. Of course, the containers may be supplied unsealed, for example, in pails. These two component systems are suitable for manual application on site using conventional equipment. Accordingly, the kit may include an applicator, for example, a spray gun or a brush. The following optional features and preferences apply to NO _x active materials and compositions for applying to a substrate to form a NO _x active coating, except where context dictates otherwise. The ΝΟχ active materials of the invention may comprise a pigment, for example, pigmentary titanium dioxide. Similarly, the compositions of the invention may further comprise a pigment such as pigmentary titanium dioxide. Other pigments are of course envisaged.

It will be appreciated that suitable pigments may be selected to afford the desired colour and durability.

Suitably, the binder may comprise a silicone and a polyester. Preferably, the binder does not significantly absorb UV light > 300 nm wavelength. More preferably, the binder does not significantly absorb UV light > 290 nm wavelength. Without wishing to be bound by any particular theory, the present inventors believe that low or no absorbance at these wavelengths increases the durability of the coating.

Accordingly, in some embodiments the binder comprises a polyester formed from a diacid component in which the two acid moieties are not in electronic conjugation. It will be appreciated that binders may be formed using more than one diacid and / or more than one polyol. In some embodiments, the binder comprises only one diacid and only one polyol.

For example, the binder may comprise a polyester formed of isophthalic acid and a polyol. For example, the binder may comprise a polyester formed of hexahydrophthalic anhydride and a polyol.

In some embodiments, the polyol is trimethylolpropane. The coated metal substrate of the invention may have one, two, three, or even more layers. To improve cost efficiency, it may be preferable to use only one or two layers. Preferably, the coated metal substrate of the invention has two layers, for example, a primer and the ΝΟχ active material, wherein the NO _x active material is applied directed to the primer.

Suitably, the NO _x active material forms a topcoat.

The present inventors have found that the NO _x activity and / or durability of the coatings is often improved with increased surface area and / or more uniform particle size of the photoactive titanium dioxide. Accordingly, in some preferred embodiments, the photoactive titanium dioxide is micronized.

The present inventors have found that it may be advantageous to pre-treat the binder to effect reaction of the silicone and the polymer. In other words, the silicone and polymer (for example, polyester) of the binder may be heated or otherwise treated to effect covalent bond formation between the two. Accordingly, in some embodiments the binder is silicon and polyester at least partially bound together by covalent bonds. The present invention further provides coatings formed using compositions of the invention.

The compositions of the invention are suitably applied to metal substrates either as a topcoat on a suitable primer or as a single coat by continuous coil coating and / or other suitable application methods including, but not restricted to, spray application, electrostatic spray application, powder coating application and brush application.

Accordingly, the present invention further relates to methods of manufacturing a substrate having a NO _x active coating applied as described. Accordingly, in a further aspect the present invention may provide a method of

manufacturing a substrate having a NO _x active coating, the method comprising:

optionally, applying a primer coating to a surface of the substrate to form a primer coat;

providing a composition for applying to a substrate to form a NO _x active coating according to the present invention;

applying said composition to a surface of the substrate or, if present, on top of the primer coat;

drying the composition to provide a NO _x active coating on the substrate. The step of providing the composition may comprising mixing compositions (i) and (ii) to provide a composition for applying to a substrate. In other words, the composition that is applied may be a one pot composition (for cross-linking at high temperatures, for example on a coil line), or a two pot composition that has been mixed and cross-links under ambient conditions.

Suitably the substrate is sheet metal as described herein. For example, the method may be a method of manufacturing coil. Accordingly, in some embodiments, the coated metal substrate is a coated metal coil. The application of the composition to the metal substrate or primer coat on the metal substrate may therefore use a roll coating process. Typical roll coating processes are known in the art in the field of metal coil manufacture. The present invention also provides coated metal substrates manufactured by methods as described herein.

Coated metal substrates of the invention may be used in the construction industry to assist pollution control. Accordingly, in a further aspect the present invention provides use of a coated metal substrate of the invention in the abatement of NO _x .

Coated metal substrates of the invention may be used near roads or railway lines to assist pollution control. For example, the coated metal substrates of the invention may be located in tunnels. The tunnels may be vehicular and/or rail tunnels. The coated metal substrates of the invention may also be used in other suitable locations. For example, they may be used to line walls alongside roads or railway lines. For example, they may be provided as panels, or a component of panels, provided near roads or railway lines. Definitions

ΝΟχ refers to oxides of nitrogen, also referred to a nitrogen oxides, that may be common pollutants in exhaust fumes. Typically, x is 1 or 2; that is, NO _x may refer to nitric oxide (NO) and nitrogen dioxide (N0 ₂ ) and mixtures thereof. Unless stated otherwise, NO _x refers to the total concentration of NO and N0 ₂ in the atmosphere surrounding the coating.

NOy active material

As used herein, this term refers to a material that has NO _x abatement activity. In other words, to a material that reduces the total amount of NO _x gases in the atmosphere surrounding the surface of the material. The materials described herein are suitably coatings formed by application of compositions that are then dried. Throughout this application, references to coatings apply generally to NO _x active materials of the present invention. Suitable compositions are described herein, and the invention relates to both materials (i.e. after application and drying) and compositions (liquid formulations including solvent prior to application and drying).

Suitably, the NO _x active material is a coating on a substrate, for examples, a metal substrate. Non-limiting examples of suitable metal substrates include Hot Dip Galvanised Steel, Galfan ^® , Galvalume ^® , Zinc aluminium magnesium alloy metal coatings as well as aluminium and cold rolled steel. These coated substrates may be provided as coils. Suitably, the N0 _X active material is provided as the uppermost coat (topcoat). It may be the only coat, or may be used in association with further coats. For example, a primer coat may be provided. Preferably, a surface of the substrate is coated with a primer and a NO _x active topcoat.

Coil

As used herein, coil refers a pre-coated metal substrate produced on a coil coating line using a coil coating process, for example as described as follows. Coil coating is a continuous, automated process for coating metal before fabrication into end products. The substrate, typically steel or aluminum, is delivered in coil form from the rolling mills. The metal coil is positioned at the beginning of the coating line, and in one continuous process, the coil is unwound, cleaned, pre-treated, primed, and/or painted (as appropriate); it is then re-coiled at the end of the line. These rolled coils are then supplied ready for cutting and shaping to the construction industry.

Suitably, the coils of the present invention are "two coat" coils. These two coat coils comprise a 1 ^st coat which is a primer and a 2 ^nd coat which is a top coat. In coils of the present invention, this 2 ^nd coat is a NO _x active topcoat. Suitably, the primer cost is

6-8 microns in thickness, which the top coat is around 20 microns in thickness. Of course, other thicknesses may be envisaged. A backing coat can be applied to the reverse side of the strip to suit the intended end use.

Advantageous, the provision of a NO _x active top coat that may be applied directly to the primer reduces the number of runs needed to produce the coil as compared to conventional three coat systems.

Photoactive titanium dioxide

Also referred to herein as photoactive Ti0 ₂ , PA Ti0 ₂ and PA. This refers to ultrafine titanium dioxide having high surface area and high purity. Suitably, the photoactive titanium dioxide is predominantly anatase titanium dioxide. For example, more than 75% by weight of the total Ti0 ₂ may be in the anatase form. Suitably, the Ti0 ₂ content of the powder is greater than 80%wt, for example ~85%wt or around ~95%wt.

Suitably, the surface area is at least 20 m ² /g, preferably at least 50 m ² /gm, more preferably at least 70 m ² /g, most preferably at least 90 m ² /g, as measured by the 5 point BET method. In some embodiments, the surface area is at least 100 m ² /g, for example at least 150 m ² /g or even greater, for example, at least 200 m ² /g, at least 250 m ² /g, or even at least 300 m ² /g. Suitably, the photoactive titanium dioxide has a particle size of less than 150 nm, preferably less than 50 nm, for example 5-50 nm, 5-40 nm, 5-30 nm, 5-25 nm, or even 5-20 nm. The photoactive titanium dioxide may be micronized. In these cases, the particle size may be 15 nm or less, for example, 5-15 nm or even 5-10 nm.

References to particle size will be understood to mean the average particle size of the titanium dioxide particulates. The particle sizes may be measured by suitable methods apparent to those skilled in the art, and it will be understood that the above values should be read to embrace proximal values that may be attributed to experimental error. The particle sizes may be measured by, for example, transmission electron microscopy (TEM) or X-ray diffraction (XRD). Suitable photoactive titanium dioxide commercially available includes CristalACTIV™PC500, CristalACTIV™PC105, CristalACTIV™PC105M (micronized), and PCX4 (all available from Cristal). Further sources include Aeroxide ^® Ti0 ₂ PA25 and Aeroxide ^® Ti02 P90 both from Evonik, Kronoclean 7000 and 7050 from Kronos. Suitably, the photoactive titanium dioxide is present in coatings and compositions of the invention. Owing to the cost of photoactive titanium dioxide, preferably the amount is equal to or less than 1 1 %wt of the total formulation. For example, photoactive titanium dioxide may be present in coatings and compositions of the invention in an amount from 1 -1 1 %wt, for example, 3-1 1 %wt, preferably 3-8wt%. The preferred amount may vary with the exact nature of the composition and its intended use. For compositions applied on a coil coating line (as a one pot system) the amount is preferably, 5-8%wt, most preferably around 7.5%wt. For compositions provided for application as a two pot system, the amount is preferably lower; around 3-5%wt, for example around 4%wt. The numbers given are %wt of the composition and prior to application and drying to form the coating.

Pigmentary titanium dioxide

Also referred to herein as pigmentary Ti0 ₂ . This refers to titanium dioxide pigment, as may be included in, for example, coil coatings, protective coatings, powder coating, automotive, OEM and refinishing systems. Suitably, the pigmentary titanium dioxide is rutile titanium dioxide, for example, chloride process rutile titanium dioxide. Pigmentary titanium dioxide may have a larger average particle size than photoactive titanium dioxide. For example, the average particle size may be about 0.2 to 0.35 microns. Commercially available pigmentary titanium dioxide suitable for use in the present invention includes TiONA ^® 696 (available from Cristal) and Ti-Pure R-960 ^® (available from DuPont ^® ).

Suitably, the NO _x active coatings and compositions of the invention, include pigmentary titanium dioxide. However, its inclusion is not essential. For example, the pigmentary titanium dioxide content of the NO _x active coatings and compositions of the invention may be 0-50%wt, preferably 5-50%wt, more preferably 5-40%wt, more preferably 10-40%wt, more preferably 20-40%wt, more preferably 25-40%, more preferably 30-40%, most preferably 35-37%wt. The numbers given are %wt of the composition and prior to application and drying to form the coating.

It will be appreciated that other pigments conventionally used in compositions and coatings may be included, for example, to give a coating of a different colour.

Other pigments may be in addition to pigmentary titanium dioxide. Alternatively, no pigmentary titanium dioxide may be present, and only one or more other pigments provided. Suitable pigments are known in the art and may include iron oxide reds, yellows and blacks. Other suitable pigments may be modified titanium dioxide, for example, spinel titanates in which ΤΊ02 has been modified with other elements such as nickel and antimony.

Suitably, the pigment to binder ratio may be in the range 1 :1 to 1 .5:1 , preferably 1 .3:1 to 1 .4:1 .

Binder

The coatings and compositions of the invention comprise a binder. Suitably, the binder comprises a silicone and a polymer. The polymer is an organic polymer; in other words, it has a carbon-containing backbone. In some embodiments, the polymer is a polyester, as described herein, although it will be appreciated that other polymers may be used, for examples, acrylates and methacrylates. Suitably, the binder comprises only silicone and polymer. For forming compositions, the binder may include a solvent. Suitable solvents are known in the art. This facilitates manufacture and application of the compositions to the substrates. For convenience, except where context dictates otherwise, references to the binder herein refer to solids in the binder. Of course, it will be appreciated that dried materials (coatings) formed from the compositions described herein are substantially free of solvent, that is, the binder in the coatings described herein may comprise only solids. It follows that for such substantially solvent-free materials (coatings), references to solids in the binder refer to the binder.

Suitable silicone-modified saturated polyesters include Benester SL compositions

commercially available from N. Benasedo S.p.A.

As described herein, the present inventors speculate (without wishing to be bound to any particular theory) that comparatively high silicone content contributes to the desirable durability profile for the NO _x active coats and compositions of the present invention.

Accordingly, suitably, the binder comprises at least 30%wt silicone, preferably at least 35%wt silicone, more preferably, at least 40%wt silicone, more preferably at least 45%wt, more preferably at least 50%wt. The silicone content of the binder may be less than 80%wt, for example less than 70%, for example less than 60% The silicone is provided in combination with a polymer, preferably a polyester, in the binder. Suitably, the binder comprises at least 30% polymer. These percentages refer to % by weight in the binder. Any solvent provided is not, for the ratios and %wt values given herein, considered a part of the binder. For example, the binder in the composition, or composition prior to application and drying to form the material, may comprise silicone and polymer in a ratio between 3:7 and 7:3. In other embodiments, the binder comprises silicone and polymer in a ratio of between 1 :1 and 7:3, for example between 7:6 and 5:3, for example, between 4:3 and 5:4. In some preferred embodiments, the binder comprises silicone and polymer in a ratio of around 6:4.

In some embodiments, the binder may comprise the silicone as an oil; that is, the binder may be a blend of silicone oil and polymer. However, it may be preferable to pre-treat the binder so as to pre-react the silicone and the polymer, for example, to cause reaction between the silicone and the hydroxyl groups on the polymer (in the case of a polyester or similar) to form covalent bonds. This pre-treatment step may comprise a heating step. Suitably, the polymer may be thinned in a suitable solvent (i.e. one that will provide compatibility without interrupting the course of the reaction) and the silicone adding during heating. A suitable solvent is 1 -methoxy-2-propyl acetate. This solvent component is, for the ratios and %wt values given herein, not considered a part of the binder. Suitably, a catalyst, for example, a titanate is added. Suitably, the catalyst may be added at 0.01 to 0.1 %wt of the total monomers. This catalyst is, for the ratios and %wt values given herein, not considered a part of the binder. Similarly, any solvent added to thin the polymer is not considered a part of the binder. Rather, this solvent is considered part of the solvent content of the formulations.

Suitably, the heating step is at a temperature above 100 °C, for example, around 140 °C until viscosity and non-volatile requirements are met.

Silicone

Silicones are polymeric structures made up of repeating units of siloxane. The silicones described herein are mixed inorganic-organic polymers in which silicon atoms bear organic R substituents, where each R is an organic group such as methyl or phenyl. They may also be referred to as polymerized siloxanes or polysiloxanes.

The present inventors have found that through controlling the nature of R, it is possible to control and even "fine tune" the properties of the coating including its heat resistance, compatibility and hardness. Suitably, the silicone of the binders described herein comprises both methyl and phenyl groups. Suitably, the ratio of phenyl to methyl groups is in the range 0.5:1 to 1 :1 , for example 0.6:1 , 0.7:1 , 0.8:1 or 0.9:1 . Preferably, it is about 1 :1. Higher methyl group content formulations are cheaper and react faster, but the inclusion phenyl groups in the ratios specified aids handling and / or mechanical properties of the end product (high methyl content leads to hard resins). Appropriate selection for the desired cost performance relationships are within the remit of the skilled person.

Suitably, the silicone content in the compositions and NO _x active material described is at least 5%wt of the total weight of the composition prior to application and drying to form the material, more preferably at least 7%wt, more preferably at least 10%wt. For example, it may be 7-15%wt, for example, 9-13%wt.

Polyester

As used herein, polyester refers generally to any and all polymers that contain an ester functional group in their main chain. Preferably, the term polyester, as used herein, refers to thermoset polyesters. Certain preferred polyesters include polyesters formed from

dicarboxylic acid monomers including orthophthalic acid, isophthalic acid, and terephthalic acid, and hydrogenated versions thereof, and other aliphatic acids including succinic acid, glutaric acid and adipic acid. It will be appreciated that anhydrides of these dicarboxylic acid monomers may be present and indeed may be used as starting materials. Especially preferred dicarboxylic acid monomers include isophthalic acid and hexahydrophthalic anhydride and 1 ,3 and 1 ,4-CHDAs.

Without wishing to be bound by any particular theory, the present inventors attribute poor durability at least in part to significant absorption of the binder in the UV region 290-400 nm. Suitably, therefore, the polyester does not absorb significantly at wavelengths over 300 nm, more preferably, at wavelengths over 290 nm. For this reason, dicarboxylic acids in which the two acid moieties are not in conjugation are preferred. These include hexahydrophthalic anhydride and other aliphatic diacids including cyclohexane 1 ,3 and 1 ,4 dicarboxylic acid, and isophthalic acid (owing to the meta configuration).

Any suitable polyol may be used, for example, a diol or triol. Certain preferred diols include neopentyl glycol (NPG), 1 ,6-hexane diol (HD), ethylene glycol (EG), 1 ,2 propylene glycol, 1 ,3 propylene glycol, 1 ,4 butandiol, 2 methyl propane diol (MP diol), and butylethylpropylene diol (BEPD).

Certain preferred triols include trimethylolpropane (TMP), glycerol, and trimethylolethane (TME, also known as pentaglycerol). Preferably, the triol is trimethylolpropane (TMP).

In some preferred embodiments, the polyester is formed from isophthalic acid and trimethylolpropane (TMP). In some preferred embodiments, the polyester is formed from hexahydrophthalic anhydride and trimethylolpropane (TMP). Suitably, the polyester is formed of dicarboxylic acid monomer and polyol in a ratio of 7:3 to 3:7. Preferably, a slight excess of polyol is used, that is preferably the ratio of dicarboxylic acid monomer to polyol is 1 :>1 , for example about 4:6, for example about 4.5:5.5.

Cross-linkers

Suitably, cross-linkers are used in the coatings and compositions of the present invention. Suitable cross-linkers include melamine cross-linkers and isocyanate cross-linkers, which may be blocked or unblocked.

The invention provides both "one pot" and "two pot" systems. A one pot system refers to a composition that includes a cross-linker. Suitably, the one pot compositions are applied and cross-linked with heating up to a peak metal temperature of 250 °C. This heating will activate the cross-linker. For example, one pot systems may be used on a coil coating line to produce pre-coated metal strip. A two pot system is provided as two compositions. One of the compositions is a hardener composition including a cross-linker. The two

compositions are mixed prior to application. Two pot systems are sometimes referred to in the art as two-component or 2K systems and generally cross-link at ambient temperatures. Preferred cross-linkers include melamine cross-linkers, for example, methylated melamine monomers. Where appropriate, blocked isocyanates may also be used.

Preferably, for processes involving application with heating (as the 1 K systems are used) the cross-linker is blocked. For example, the acid used to catalyse the melamine cross-linkers may be amine blocked, such that they unblock at temperatures above 140 °C. Isocyanate cross-linkers may be blocked by chemicals such as methyl ethyl keto-oxime or caprolactam. Again, the blocking agent is released by thermal treatment. Both melamine and isocyanate cross-linkers are used in coil coating applications. A commercially available cross-linker suitable for use is Cymel ^® 303 LF Resin (commercially available from a number of sources including Allnex).

For two pot systems, isocyanate cross-linkers may be preferred. For example, the cross- linker may be an aliphatic polyisocyanate such as an isocyanate based on hexamethylene diiocyanate trimer (HDI polymer). Such a cross-linker is commercially available as

Tolonate™ HDT-LV2 from Vencorex ^® . The cross-linker may be used in combination with a catalyst. For example, in the two pot systems, the composition may include a catalyst, while the hardener composition includes an isocyanate cross-linker. Suitable catalysts are known the art and include organometallic catalysts such as organo tin compounds. The catalyst may be selected to adjust the pot life and drying time of the mixed composition. Suitably, the pot life is around 20 minutes.

Suitably, the mixed composition when applied at a thickness of 15-20 microns (dried value) is surface dry in about 1 hour, and hard dry in about 4 hours.

Suitably, cross-linkers are present at 2-8%wt, more preferably, 3-6%wt, most preferably 3-4%wt. The numbers given are %wt of the composition and prior to application and drying to form the coating.

Other additives

It will be appreciated that other additives may be included. These may include catalysts, wetting agents, matting agents, flow agents and solvents.

Catalysts for polyester melamine systems are typically amine-blocked aromatic sulphonic acids. Suitably, they comprise 0.05% by wt of the total composition. Pigment wetting aids may be used to help improve the dispersion of the pigment in the binder. For example, suitable wetting agents are known in the art and include DisperByk 180 (available from Altana). If present, a wetting agent may comprise 0.5%wt, but as the skilled person will appreciate, the amount included may depend on the amount of pigment and its surface area. Waxes may be used to modify the surface characteristics. These are typically blends of PTFE and polyethylene (for example, Shamrock S-381 available from Shamrock) or even pure PTFE (for example, FluoroSLIP 225, also available from Shamrock). Matting agents such as silica are commonly used. Suitable matting agents include Syloid® ED5, available from Grace). If present, a matting agent may comprise 5%wt of the formulation depending upon the efficiency of the matting agent and the desired gloss level. Flow agents are added to aid the appearance of the final film by equalising surface tension. Suitably, high molecular weight acrylate or polyester materials are used and may comprise 0.5% by wt of the total composition.

The amounts and identities of such additives may vary with the desired result. Appropriate choices of additives and amounts are within the remit of the skilled person. Suitably, compositions are formulated with about 60%wt solid content. That is, the non- solvent content of the compositions, also referred to as the resin component or solid component of the dried product, forms about 60%wt of the compositions. Solvent as used herein may refer to a single solvent, or a combination of solvents. Suitable solvent blends for coil coatings are known in the art and typical consist of a mixture of aromatic solvents (for example Solvesso™ 150, available from ExxonMobil Chemical) and oxygenated solvents (for example, propylene glycol methyl ether acetate) in a 1 :1 ratio. Durability

Also referred to herein as retention and maintenance of aesthetic appearance. As used herein, this is determined by two methods, the percentage gloss retention level and chalking.

Outdoor durable systems are classified according to EN 10169-2 by the percentage gloss retention level attained after 2 years exposure in Florida or 2000 hours in a cabinet irradiated with UV light using fluorescent tubes as the source with a peak irradiance at 340 nm, operated on a 4 hours light and 4 hours humidity cycle.

A product with more than 30% gloss retention after 2000 hours in a cabinet irradiated with UV light using fluorescent tubes as the source is classified as an Ruv2 class material (EN10169-2).

A product with over 60% gloss retention after 2000 hours in a cabinet irradiated with UV light using fluorescent tubes as the source is classified as an Ruv3 class material.

Suitably, the coatings described herein are Ruv2 class materials. Similarly, suitably, the coating formed using compositions as described herein are Ruv2 class materials.

Durability may also be determined by determining the extent of chalking (graded on a 0-10 scale as described herein).

Coated substrates were exposed to UV A conditions of cycling 4 h UV, 4 h condensation (EN13523-10 specification) or cycling 8 h UV or 4 h condensation (ASTM G154 Cycle 1 ). The temperature during UV irradiation was controlled at 60 °C for both procedures but the temperature during condensation was 40 °C for the EN 13523-10 test and 50 °C for the ASTM G154. The extent of chalking was determined according to ASTM D4214 Section 7.2.1 by running a finger along the surface then pressing the finger to a black sheet of paper, then visually quantifying the deposit.

Scale No 10 - None

Scale No 8 - Visible

Scale No 6 - 4 - 2 - 0 - Severe

Suitably, the coatings described herein are rated 6 or more in the chalking test, more preferably 8 or more, more preferably 10. Similarly, suitably coatings produced by compositions described herein are rated 6 or more in the chalking test, more preferably 8 or more, more preferably 10.

NOy abatement

This term as used herein refers to the property of materials as described herein to facilitate reaction of NO _x gases to reduce the total amount of NO _x gases in the atmosphere

surrounding the surface.

ΝΟχ abatement performance was assessed by Cristal using a ranking system, in each case as described herein.

QUV A exposure

1 . Panels (15 cm by 7.5 cm) with the 2 coat coil system (primer and Ti0 ₂ containing coat) were exposed in QUV tester with Solar Eye 230V with UV A exposure conditions of cycling 4 h UV, 4 h condensation (EN 13523-10 specification) or cycling 8 h UV or 4 h condensation (ASTM G154 Cycle 1 ). The temperature during UV irradiation was controlled at 60 °C for both procedures but the temperature during condensation was 40 °C for the EN 13523-10 test and 50 °C for the ASTM G154.

2. Gloss retention and colour measurements were made using a gloss meter, with checks every 250 hours up to 2000 hours:

· Gloss measurement every 250 hours up to 2000 hours to give % gloss

retention.

• Colour measurement CI ELAB (DE Specular Component Excluded SPEX ) : colour difference c.f. unexposed panel (EN 13523-3).

• Chalking is an important issue. (ASTM D4214) Determination of NO/NO ₂ abatement by coatings

The paint films were irradiated with 0.89 W/m ² UV at 340 nm for 1000, 1500 and 2000 hours using a filtered QUV A -340 light source (QUV Tester with Solar Eye 230V) before carrying out the test. This activates or increases the activity of the coatings over and above the un- exposed coatings. For the NO _x measurements, the samples were irradiated with a UV fluorescent tube which emits 10 W/m ² UV in the range of 300 to 400 nm. The NO _x that is used is NO at 225 ppb in nitrogen.

Measurement:

1 . Equipment

Nitrogen Oxides Analyser Model ML9841 B - ex Monitor Europe

UV Lamp Model VL-6LM 365 & 312 nanometre wavelength -ex BDH

Air-tight sample chamber 3 channel gas mixer - ex Brooks Instruments, Holland

2. Gases

NO Nitric Oxide

Compressed air containing water vapour to give 50% Relative Humidity in mixed stream. 3. Method

1 . Switch on Analyser and exhaust pump. Ensure exhaust pipe goes to atmosphere.

2. Allow to warm-up. Several internal components need to reach operating temperature before the analyser will begin operation. The process will, typically, take 60 minutes from cold start and the message START-UP SEQUENCE ACTIVE will be displayed until operating conditions are met.

3. After warm-up turn on air and test gas supply to the gas mixer.

4. Calibrate the Analyser on the Test gas supply only, (turn the air channel to zero on the gas mixer), according to the manufacturer's instructions

5. After calibration turn OFF the test gas supply at the gas mixer.

6. Place test sample in the test chamber and seal chamber.

7. Turn on both air and test gas and adjust each until required level of test gas is reached, shown by the Analyser output. RECORD level. Check that the Relative Humidity is 50% within plus or minus 5%.

8. Switch on the UV lamp when test gas levels are at desired point.

9. Allow the irradiated sample value to reach equilibrium, typically up to

3 minutes.

10. RECORD the value shown on the analyser. 1 1 . Report "Initial Value" i.e. no UV, "Final Value" after UV exposure for set period,

12. % NOx Removed = INITIAL VALUE - FINAL VALUE ^* 100

INITIAL VALUE The % results are presented in a ranking system, so absolute values cannot be taken. Examples UV absorption

To determine the extent of UV absorption of different binders, a series of clear coatings

(denoted C) (without either pigmentary titanium or photoactive titanium) were produced and their UV absorbance measured.

Clear free films at 18-20 microns thickness were cast on to PTFE coated panels and stoved to a Peak Metal Temperature (PMT) 232-241 °C. The dry film thickness was approximately 20 microns. The films were then cut to 40 mm x 70 mm panels and placed in a

measurement window 47 mm x 75 mm (designed to fit the holder in the FTIR and

UVA is/NIR spectrophotometers) with a window of 25mm diameter. The UV absorbance was evaluated at each wavelength by scanning through the UV wavelengths from 190-450 nm at a speed of 1 19 nm/min. Readings were recorded by the instrument and plotted on an absorbance vs wavelength chart. The absorbance at 290 and 300nm was then recorded manually (Table 1 ). For convenience, the numbers 1 , 2, 3, 4, and 5 will be used generally to refer to those binders as described.

Silicone Phenyhmethyl Polyester composition UV absorbance at content of ratio in Silicone 300 nm binder (%wt

of the

binder) ^*

Terephthalic acid (35%)

1 C 50 0.5:1 Ethylene glycol (12%) > 2.0

Trimethylolpropane (53%)

Isophthalic acid (23%)

Adipic acid (18%)

2C 30 0.5:1 > 1.0

Neopentylglycol (19%)

Trimethylolpropane (40%)

Isophthalic acid (42%)

3C 61 0.5:1 > 0.5

Trimethylolpropane (58%)

Isophthalic acid (46%)

4C 51 1 :1 < 0.5

Trimethylolpropane (54%)

Hexahydrophthalic

5C 51 1 :1 anhydride (45%) < 0.2

Trimethylolpropane (55%)

* %wt refers to the bine er and not the binder + solvent.

Table 1

Similar results were obtained when corresponding clear films were produced using the two pot system for 2C, 4C, and 5C.

Correlation of chalking and UV absorbance

As discussed herein, the present inventors speculate (without wishing to be bound in any way) that increased UV absorbance in the region >300 nm contributes to loss of gloss and / or degradation/breakdown of the coatings.

The binders 1 -5 described above for the clear coatings were tested in for coatings of the invention, used as a one pot system (Table 2). Pigmentary

Photoactive UV QUV A Ruv2

titanium Chalking titanium absorbance EN10169-2

Binder dioxide (as 2000 h QUV A dioxide (as % of binder 2000 h

% of (ASTM D4214) of composition) (as above) Gloss Retention

composition)

1 26 9(M) > 2.0 <20% Severe (0)

2 28 9 > 1.0 <20% Severe (0)

3 28 10(M) > 0.5 <30% Severe (0)

4 28 9 < 0.5 <25% Severe (6)

4 28 9 (M) < 0.5 >30% Visible (8)

5 29 10 (M) < 0.2 >30% None (10)

Table 2

Advantageous effects associated with micronized photoactive titanium dioxide

The present inventors have found that using micronized photoactive titanium dioxide is advantageous in terms of durability and/or NO _x performance (M in all cases denotes micronized), as can be seen by a comparison of the two examples using binder 4 in Table 2 (above). The inventors attribute this to an increase in photo-activity owing to increased available surface area and the decrease in the unevenness of degraded surfaces leading to better gloss retention results.

Importance of pigmentary titanium dioxide and photoactive titanium dioxide

To determine the importance of the presence of both pigmentary titanium dioxide and photoactive titanium dioxide, a series of comparator experiments were run. Each had a 51 % silicone content in the binder resin, a 1 :1 ratio of phenyl to methyl groups in the silicone and a polyester composition of isophthalic acid (46%) and trimethylolpropane (54%) (i.e. the same binder as example 4C (above)). 4(XY) contained only a very small amount of photoactive titanium dioxide and no pigmentary titanium dioxide; 4(YX) contained

pigmentary titanium dioxide but no photoactive titanium dioxide, while 4(YY) contained both (Table 3). It should be noted that each of the binders described above was tested as a (YX) example (that is, containing pigmentary titanium dioxide but no photoactive titanium dioxide). Not one of these (YX) examples showed any appreciable NO _x abatement.

ΝΟχ reduction was determined using the Cristal ranking system (measured on the QUV (EN 13523-10 specification)). The QUV-A gloss retention and chalking were measured as described herein. The results clearly demonstrate the desirability of including both pigmentary titanium dioxide and photoactive titanium dioxide. Without wishing to be bound to any particular theory, the present inventors speculate that the inclusion of pigmentary titanium dioxide assists the activity of the photoactive titanium dioxide within the coating through internally reflecting the incident light so that more of the incident light is absorbed by the photoactive Ti0 ₂ . Of course, it will be appreciated that the inclusion of pigmentary titanium dioxide, while preferred, is not essential. For example, other pigments may be included and / or the amount of photoactive titanium may be increased.

Further examples

Each of the binders 1 -5 was used to produce a coating having NO _x activity. Binders 1 , 2, and 3 gave active coatings, while binders 4 and 5 gave active coatings having good durability (gloss retention) and excellent chalking results (Table 4). Each coating was produced as a one pot system.

Photoactive QUV A RUV2 Chalking

Pigmentary NO _x

titanium EN10169-2 2000 h titanium dioxide reduction

Binder dioxide (as 2000 h QUV A

(as %wt of 1000 h

%wt of Gloss (ASTM composition) QUV A

composition) Retention D4214)

1 26 9(M) >10%, good <20% Severe (0)

2 28 9 >10%, good <20% Severe (0)

3 28 10(M) >10%, good <30% Severe (0)

4 28 9 >10%, good <25% Severe (6)

4 28 9 (M) >10%, good >30% Visible (8)

5 29 10 (M) >10%, good >30% None (10)

Table 4

Coated panels according to the present invention have been exposed in Kuala Lumpur and Florida in private locations for 6 and 12 month periods. In each case, NO _x reduction activity was measured on the unwashed panels and washed panels (washing removes dirt and particulate build up on the surface).

After 6 months' exposure in Florida a panel according to the invention (using a one pot system) exhibited 16% NO _x reduction after washing (15% unwashed). After 12 months' exposure, NO _x reduction for the washed panel was higher at 21 % (17% unwashed). This higher activity after washing may be attributed to removal of slight chalking exposing the active titanium. There was virtually no change in film thickness, indicating that this chalking did not cause significant degradation of the coating over the test period. Kuala Lumpur showed a greater difference between the washed and unwashed panels, perhaps attributable to levels of air pollution. After 6 months' exposure in Kuala Lumpur a panel according to the invention (same formulation as the Florida test) exhibited 8% NO _x reduction after washing (4% unwashed). After 12 months' exposure, NO _x reduction for the washed panel was virtually unchanged at 7%, while dirt build up resulted in only 2% for the unwashed panel.

In each case, sufficient / good NO _x abatement activity was observed over the period. Two Pot (2K) Systems

Similar results were observed with two pot air drying compositions for binders 2, 4, and 5. For analogous clear compositions, the following results were obtained:

Table 5 Two pot (2K) compositions according to the invention:

Formulations

Compositions of the present invention and compositions to form NO _x active top coats of the present invention may be formed as follows:

Composition clear coatings

The following describes an exemplary protocol for producing a one pot liquid composition according to the invention:

Composition is applied to substrate at 35-55 microns wet film thickness using a suitable wire wound bar drawn through a pool of the coating placed at the far end of the panel to be coated. The coated panel is then placed in an electric convection oven and baked to a PMT of 232 -241 °C with a dwell time 30-35 s. The oven temperature is 265 °C. The panel is then extracted from the oven and quenched in a water bath at room temperature. The end result is a panel coated with a film of paint between 18 and 20 microns thick. Extent of reaction is determined using an MEK double rub test with adequate reaction being defined by more than 150 MEK double rubs (EN13523-1 1 ).

Two pot compositions may be produced in a similar manner, omitting the cross-linker. A separate hardener composition is provided. The two compositions are combined before application. Binder as supplied in

1 solvent (silicone and Pre-mix items 1 -3

polymer pre-reacted)

2 Solvent 1

3 Solvent 2

4 Flow Aid Add items 5-7 with stirring

mix for 10 minutes at slow speed under

5 Solvent 5/6

mixer

6 Catalyst 2

7 Solvent 4

Separately, a composition comprising a suitable cross-linker in solvent is provided as a hardener composition. The composition may be applied using a bar coater, brush or spray gun. It will be appreciated that solvents may be selected to suit the application method. The selection of suitable solvents in apparent to one of skill in the art.

Composition Pigmented Coatings

The following describes an exemplary protocol for producing a one pot liquid composition according to the invention:

Binder as supplied in

1 solvent (silicone and Pre-mix items 1 -2

polymer pre-reacted)

2 Dispersant

Add pigments with stirring then high

3 Pigment

speed disperse for 10 minutes

4 Solvent 1

then bead mill composition if necessary

5 Solvent 2 until agglomerates/particles are reduced

to below the level specified

Take mill base (premixed items 1 -5) and

6 Resin as supplied in solvent

stir in items 6-12

7 Cross-linker

8 Flow Aid Add items 5-9 with stirring

mix for 10 minutes at slow speed under

9 Solvent 3

mixer

10 Catalyst

1 1 Solvent 4

12 Matting Agent Add more to adjust gloss as necessary

Composition should be applied to substrate at 35-55 microns wet film thickness using a suitable wire wound bar drawn through a pool of the coating placed at the far end of the panel to be coated. The coated panel is then placed in an electric convection oven and baked to a PMT of 232-241 °C with a dwell time 30-35s. The oven temperature is 265 °C. The panel is then extracted from the oven and quenched in a bucket of water at room temperature. The end result is a panel coated with a film of paint between 18 and 20 microns thick. Extent of reaction is determined using an MEK double rub test with adequate reaction being defined by more than 150 MEK double rubs (EN13523-1 1 ).

Of course those skilled in the art will be aware that on-line application is effected by roller coating techniques with roller speeds and configurations adjusted for specific lines. Bake schedules may be adjusted for individual lines. Two pot compositions according to the invention may be produced in a similar manner, omitting the cross-linker. A separate hardener composition is provided. The two

compositions are combined before application.

Separately, a composition comprising a suitable cross-linker in solvent is provided as a hardener composition. The composition may be applied using a bar coater, brush or spray gun. It will be appreciated that solvents may be selected to suit the application method. The selection of suitable solvents in apparent to one of skill in the art.

— oOo—

Any one or more of the aspects of the present invention may be combined with any one or more of the other aspects of the present invention. Similarly, any one or more of the features and optional features of any of the aspects may be applied to any one of the other aspects. Thus, the discussion herein of optional and preferred features may apply to some or all of the aspects. In particular, optional and preferred features relating to the composition, methods of making the composition and methods of using the composition, etc apply to aspects related to the coated substrate and material. Throughout this specification, including the claims which follow, unless the context requires otherwise, the word "comprise," and variations such as "comprises" and "comprising," will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a polyol" includes mixtures of two or more such polyol, and the like. Ranges may be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent "about," it will be understood that the particular value forms another embodiment.

This disclosure includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

A number of publications are cited herein in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Each of these references is incorporated herein by reference in its entirety into the present disclosure, to the same extent as if each individual reference was specifically and individually indicated to be incorporated by reference.