WATERBORNE COATINGS

TECH NOLOGICAL FI ELD

This invention relates to waterborne coating systems and in particular to waterborne coating systems which include 2D material/graphitic nanoplatelets.

BACKGROU N D

2D materials as referenced herein are comprised of one or more of the known 2D materials and / or graphite flakes with a† leas† one nanoscale dimension, or a mixture thereof. They are collectively referred †o herein as “2D material/graphitic nanopla†ele†s” or“2D material/graphitic nanoplates”.

2D materials (sometimes referred†o as single layer materials) are crystalline materials consisting of a single layer of atoms or up†o several layers. Layered 2D materials consist of 2D layers weakly stacked or bound†o form three dimensional structures. Nanoplates of 2D materials have thicknesses within the nanoscale or smaller and their other two dimensions are generally a† scales larger than the nanoscale.

Known 2D nanomaterials, include bu† are no† limited to, graphene (C), graphene oxide, reduced graphene oxide, hexagonal boron nitride (hBN), molybdenum disulphide (M0S2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), Graphyne (C), borophene (B), phosphorene (P), or 2D vertical or in-plane he†eros†ruc†ures of two of the aforesaid materials.

Graphite flakes with a† leas† one nanoscale dimension are comprised of between 10 and 40 layers of carbon atoms and have lateral dimensions ranging from around 100 nm†o 100 Mm.

Waterborne coating systems have been central†o coating technology

development since the introduction of new regulations brought in†o address the impact of volatile organic compounds (VOCs) on air qualify, the environment and human health. Waterborne coating systems have been developed utilizing a range of chemistries seeking†o achieve performance levels comparable†o those of traditional coating systems which comprise one or more VOCs as the solvent for the coating system (hereafter referred†o as“organic solvent-based coating systems”) .

Waterborne coating systems provide advantages over organic solvent-based coating systems because they are better for worker health and safety, and have less impact on the environment. Waterborne coating systems are easy†o clean, can be thinned with wafer, and, if they comprise any organic solvents a† all, use solvents that are lower in odour, toxicity and flammability than are used in organic solvent- based coating systems. Waterborne coating systems such as lower-VOC acrylic coatings also dry faster than organic solvent-based coatings, which allows for faster recoafing times.

A particular form of waterborne coating systems which are of increasing importance given the regulations brought in†o address the impact of VOCs on air qualify are waterborne protective coating systems.

Protective coating systems, whether waterborne or organic solvent-based, have two key functions which are: the provision of protection against the prevailing elements / the environment, and their aesthetic appearance. Protection against the prevailing elements / the environment is, a† leas† in par†, protection against corrosion or degradation of the substrate†o which the coating is applied. The mechanism of corrosion or degradation which coating is preventing will depend on the substrate. The most important types of substrate are metal, concrete, and wood / wood composites.

The problem of corrosion of metal is well documented with metallic corrosion being estimated†o cos† about 3% of global GDP which constitutes a significant aspect of the global economy. There is substantial interest in the development of new and improved anticorrosive coating systems. Anticorrosive coating systems for metal are generally classified in accordance with the mechanisms by which they operate: barrier protection, inhibition (passivation of the substrate), and sacrificial protection (galvanic effect) . The mechanism of operation of each type of mefal anticorrosive coating system is well known. For coating systems providing barrier protection, the mechanism is that the coating or film formed once the coating system has been applied and dried prevents or inhibits the passage of water across the coating to the surface of the substrate.

Concrete is a construction material which is widely used in the construction of infrastructure (for example in bridges, buildings, and highways) and is subjected to steady degradation as a result of exposure to the elements / the environment with the result that there is a significant and ongoing need for maintenance of the concrete.

Concrete structures globally undergo different forms of damage as a result of exposure to wetting and drying, freezing and thawing, and extreme temperature changes. These exposures may cause the concrete to experience damage such as surface scaling, spalling, and corrosion-induced cracking. The damage to concrete is generally greater if water has soaked into the surface of the concrete than if no water has soaked into the surface of the concrete. The damage to concrete is also generally greater if the environment in which the concrete is situated includes chloride and / or sulphate ions than if such ions are absent. The chloride and / or sulphate ions commonly originate from anti-icing or de-icing salts, seawater and or the soil.

To prevent this damage or deterioration, it is often specified that pigmented coatings should be applied to concrete structures to seek to prevent the ingress of water and substances carried in the water into the concrete structure. Such coatings may include both smooth and textured finishes, and range in technology from solvent-borne coatings (including coatings based on epoxies, acrylics and vinyltoluene resins, Michael addition resins) to waterborne coatings (including acrylics, epoxies, epoxy esters, alkyds, Michael addition resins and hybrids of these) .

The application of a protective coating system to the surface layer of concrete can protect the surface layer of the concrete by retarding the ingress of water and water-laden harmful agents such as chloride and / or sulphate ions and / or de-icing chemicals info the concrete.

Wood a traditional building material is once again increasingly being seen as a material of interest for construction and the firs† wood-based skyscrapers have already been constructed. Of wider impact is the extensive use of wood in home construction, especially in north America and Asia. Unless wood is protected from exposure†o the elements / the environment it can, however, easily take up water and suffer from ro† as a consequence. If this occurs, significant remedial action is required†o maintain the structure.

A challenge associated with waterborne coating systems, and in particular waterborne protective coating systems, is†ha† application conditions can affect the appearance and performance of the final coating once it has been applied. For example, low temperatures and or extremes of humidity (high or low) must be avoided for optimal application appearance and film formation.

For waterborne protective coating systems†ha† have barrier properties, the ability of waterborne coatings†o provide the desired barrier performance is a† leas† partially dependent on the qualities of the coating or film created once the coating system has been applied†o the substrate and dried.

A firs† factor†ha† affects the quality of the film is the nature of the binder in the coating system when it is ready for application†o a substrate: various chemistries might be used and may include alkyd emulsions which are polyesters modified with unsa†ura†ed drying oils. On application these may crosslink through a catalysed oxidative reaction. Acrylic dispersions may be used and are frequently the copolymers of esters of acrylic and methacrylic acid. These may be thermoplastic or crosslinking systems. Two pack crosslinking systems (systems in which a hardener is mixed with the other components of the coating system immediately prior†o application of the coating) are frequently used where a high level of performance is required. Typical two pack crosslink systems may combine isocyanate and hydroxyl functional acrylics. Single pack acrylic crosslinking systems (systems in which the coating does no† require the addition of an external hardener) have also been developed, an example being systems that exploit the keto-hydrazide crosslinking reaction. Waterborne epoxy coatings (both Type 1 and Type 2) are a well-known waterborne chemistry for use in primer and direct†o metal applications where higher performance is required. Hybridisation of these chemistries is also used in order†o deliver optimized performance in individual applications.

A second factor that affects the qualify of the film is the effectiveness of the film formation when the coating system dries. The process of film formation where the binder comprises a polymer which was dispersed in wafer as a coating system is described by a mechanism which includes three consecutive stages:

(i) the concentration of the particles of binder (for example a polymer) dispersed through the coating system by evaporation,

(ii) the deformation of the particles of the binder (eg polymer) and the irreversible contact between the particles, and

(iii) the inferdiffusion of the binder (eg polymer chains) across the particle boundaries leading†o the formation of a continuous and mechanically stable film.

When the coating system is applied†o a substrate the dispersed particles of polymer are surrounded by a layer of surfactants which are critical†o their stability through the manufacturing process and their final form. In Figure 1 the different stages towards film formation are illustrated. In greater detail:

Phase (i) is characterised by a constant loss of wafer with time. The concentration of the particles continually increases and, dependent on the nature and strength of particle stabilisation and the ionic strength of the serum, the dispersed particles come info close contact and pack in a more or less ordered way. The closes† packing of monodisperse spheres would have an effective particle volume fraction of 0.74. The effective particle volume depends on the thickness of the enveloping hydrophilic surfactant layer on each particle. Phase (ii) starts when the undeformed particles of polymer firs† come into contact. A† this point, significant particle deformation can only take place if drying is taking place a† a temperature well above the polymer’s minimum film forming

temperature (MFT) and close†o or above its glass transition temperature (Tg) . Only then can the particles behave like a viscous fluid which is synonymous†o a slow water evaporation compared†o the stress relaxation time of the polymer. For a space filling structure†o form, spherical particles would have†o deform into rhombic dodecahedrons.

If drying occurs a† close†o the minimum film forming temperature, it is possible†ha† particle deformation will only partially occur and incomplete film formation will result. A† this stage, the particle boundaries will still be present and there will often be a layer of surfactants still surrounding the particles. Although such a final film is transparent and optically clear, it may be a porous structure of unsatisfactory quality.

According†o many authors there exists a phase (ii) (b), where a rupture of the surfactant layer, separating the deformed polymer particles, is prerequisite†o further polymer interdiffusion and full development of mechanical strength.

In phase (iii), the desired film properties are achieved long after the water has let† the film. Flere, the polymer chain mobility is understood†o depend on the difference between the temperature a† which the film dries and the polymer’s glass transition temperature (Tg) . The time needed for sufficient polymer interdiffusion is lower for sot† lattices or films than for hard lattices or films.

The contribution of other components of the formulation for the waterborne protective coating system can also affect the quality of the film. Some components contribute†o the hydrophilicity of the coating, these are generally wetting agents or surfactants.

The use of wetting agents or surfactants is essential for the control of colloidal stability during synthesis, storage, application and film formation of waterborne coating systems. In waterborne coating systems wetting agents or surfactants are used for several reasons, they help disperse pigments, and may assist in reduction of foaming of the coating system or settling of other components out of the dispersion that is in the coating system. Typical concentrations of wetting agents or surfactants are in the range 0.5 to 5 w†% of the resin matrix used in the coating formulation, with up to 25% of those surfactants being in the continuous (water) phase.

During film formation, phase separation of the wetting agents or surfactants occurs and the wetting agents or surfactants may be mobilized with the potential to accumulate at interfaces between particles depending on their chemistry.

Accumulation of the wetting agents or surfactants at the film / air boundary might result in the wetting agents or surfactants being removed during ageing of the film, this will create micropores in the film. The existence of micropores in the film will support water uptake which is undesirable.

High levels of wetting agents or surfactants in a film that results from a waterborne coating system may thus result in a film that is sensitive to water and reduce the barrier properties of the film. Other properties of the film, such as scrub resistance, may also be reduced by the levels of wetting agent or surfactant.

BRIEF SUMMARY

According†o a firs† aspect of the present invention there is provided a waterborne protective coating system that comprises at least one binder, water, and a dispersion of 2D material/graphitic nanoplatelets.

In some embodiments of the first aspect of the present invention the 2D

material/graphitic nanoplatelets are comprised of one or more of graphene or graphitic nanoplatelets, in which the graphene nanoplatelets are comprised of one or more of graphene nanoplates, reduced graphene oxide nanoplates, bilayer graphene nanoplates, bilayer reduced graphene oxide nanoplates, trilayer graphene nanoplates, trilayer reduced graphene oxide nanoplates, few-layer graphene nanoplates, few-layer graphene oxide nanoplates, few-layer reduced graphene oxide nanoplates, and graphene nanoplates of 6 to 10 layers of carbon atoms, and the graphitic nanoplatelets are comprised of graphite nanoplafes with a† leas† 10 layers of carbon atoms.

In some embodiments the present invention one or both of the graphene

nanopla†ele†s and the graphitic nanopla†ele†s have lateral dimensions ranging from around 100 nm†o 100 Mm.

In some embodiments of the firs† aspect of the present invention the 2D

material/graphitic nanopla†ele†s are comprised of one or more of graphitic nanopla†ele†s, in which the graphitic nanopla†ele†s are graphite nanoplates with 10 †o 20 layers of carbon atoms, graphite nanoplates with 10 to 14 layers of carbon atoms, graphite nanoplates with 10 to 35 layers of carbon atoms graphite

nanoplates with 10 to 40 layers of carbon atoms, graphite nanoplates with 25 to 30 layers of carbon atoms, graphite nanoplates with 25 to 35 layers of carbon atoms, graphite nanoplates with 20 to 35 layers of carbon atoms, or graphite nanoplates with 20 to 40 layers of carbon atoms.

In some embodiments of the firs† aspect of the present invention the 2D

material/graphitic nanopla†ele†s are comprised of one or more of 2D material nanopla†ele†s, in which the 2D material nanopla†ele†s are comprised of one or more of hexagonal boron nitride (hBN), molybdenum disulphide (M0S2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), Graphyne (C), borophene (B), phosphorene (P), or a 2D in-plane or vertical he†eros†ruc†ure of two or more of the aforesaid materials.

Few-layer graphene / reduced graphene oxide nanoplates have between 4 and 10 layers of carbon atoms, where a monolayer has a thickness of 0.035 nm and a typical interlayer distance of 0.14 nm.

In some embodiments of the firs† aspect of the present invention the 2D

material/graphitic nanopla†ele†s are comprised of graphene / graphitic

nanopla†ele†s and a† leas† one 1 D material. In some embodiments the 1 D material comprises carbon nanotubes. In some embodiments of the present invention the dispersion of 2D

maferial/graphific nanoplafelefs is one of the commercially available products Genable (trade mark) 1050 or Genable (trade mark) 1250 or a mixture thereof.

Genable 1050 is a dispersion of 10.0 w†% A-GNP10 graphitic nanoplafelefs stabilised in wafer (A-GNP10 is commercially available from Applied Graphene Materials UK Pic, UK and comprises reduced graphitic oxide nanoplafelefs of between 25 and 35 layers of atoms thick). Genable 1250 is a dispersion of 0.5 w†% A-GNP35 graphene nanoplafelefs stabilised in water (A-GNP35 is commercially available from Applied Graphene Materials UK Pic, UK and comprises graphene nanoplafelefs of between 5 and 15 layers of atoms thick). Both Genable 1050 and Genable 1250 are

commercially available from Applied Graphene Materials Pic, United Kingdom.

In some embodiments of the firs† aspect of the present invention the waterborne protective coating system further comprises one or more additives in which the additives is a dispersing additive for grinding inorganic and organic pigments in water, defoamer, pigment, rheology modifier, resin or binder, drier, levelling agent, substrate wetting agent, flow additive, skinning preventor, flash rus† inhibitor, or a mixture of two or more of the aforesaid additives.

The resin or binder may be a one par† resin or binder, or may be a two part resin or binder, or may comprise more than two parts.

In some embodiments the resin or binder is an acrylic resin.

In some embodiments the resin or binder is an epoxy resin. The epoxy resin may be a one par† epoxy resin or a two par† epoxy resin. The epoxy resin may be one of a UV curable resin, an oxidative curable resin†ha† air dries†o form a thermose† film, or a two par† epoxy resin†ha† may be cured a† ambient or elevated temperature†o form a thermose† film.

In some embodiments of the firs† aspect of the present invention the a† leas† one binder comprises one of an acrylic resin, an alkyd resin, an acrylic-alkyd hybrid resin, an epoxy resin, a polyester resin, a vinyl ester resin, a polyurethane resin, an aminoplas† resin, a urethane resin, a polyamide resin, or a mixture of two or more of the aforesaid resins.

In some embodiments of the first aspect of the present invention the af leas† one binder comprises an acrylic-alkyd hybrid resin.

One embodiment of the firs† aspect of the present invention is as example 1 below.

In some embodiments of the firs† aspect of the present invention the dispersion of 2D material/graphitic nanopla†ele†s has a stable shelf life of a† leas† two, three, four, five or six months under ambient storage conditions. This will have the effect†ha† the waterborne protective coating system will have a shelf life of a† leas† the shelf life of the dispersion of 2D material/graphitic nanopla†ele†s because the dispersion of 2D material/graphitic platelets will be agitated in the formulation of the waterborne protective coating system.

In some embodiments of the firs† aspect of the present invention the dispersion of 2D material/graphitic nanopla†ele†s comprises 2D material/graphitic nanopla†ele†s, water, a† leas† one wetting agent, and a† leas† one grinding media.

In some embodiments of the firs† aspect of the present invention the a† leas† one grinding media of the dispersion of 2D material/graphitic platelets is a grinding media†ha† is water soluble or functionalised†o be water soluble.

In some embodiments, the grinding media is a polymer modified with strong anchoring groups. In some embodiments the grinding media is an aqueous solution of a modified aldehyde resin having a† leas† one amine group. In some

embodiments the grinding media is a low molecular weigh† styrene/maleic anhydride copolymer.

In some preferred embodiments, the grinding media of the dispersion of 2D material/graphitic platelets is Laropal (trade mark) LR 9008 which is a water-soluble modified aldehyde resin commercially available from BASF, Dispersions & Resins Division, North America, ADDITOL (trade mark) XL 6515 a modified alkyd polymer, ADDITOL XW 6528 a polyester modified acrylic polymer, ADDITOL XW 6535 a high polymeric, aufo emulsifying pigment grinding medium, ADDITOL XW 6565 a high polymeric, aufo-emulsifying pigment grinding medium, ADDITOL XW 6591 a polyester modified acrylic polymer. The ADDITOL products are commercially available from the Allnex group of companies.

In some embodiments of the firs† aspect of the present invention the wetting agent or agents of the dispersion of 2D material/graphitic nanoplafelefs may be one of a polymeric wetting agent, an ionic wetting agent, a polymeric non-ionic dispersing and wetting agent, a cationic wetting agent, an amphoteric wetting agent, a Gemini wetting agent, a highly molecular resin-like wetting and dispersing agent or a mixture of two or more of these wetting agents. Gemini wetting agents have two polar centres or head groups in the polyether segment which are connected by a spacer segment.

Preferred wetting agents in the dispersion of 2D material/graphitic nanoplafelefs include bu† are no† limited†o ADDITOL (trade mark) VXW 6208/60, a modified acrylic copolymer which is a polymeric non-ionic dispersing and wetting additive

commercially available from Allnex Belgium SA/NV; and DISPERBYK-2150 (trade mark) a block copolymer with basic, pigment-affinic groups commercially available from BYK-Chemie GmbH, and Surfynol (trade mark) 104 a Gemini wetting agent and molecular defoamer commercially available from Evonik Nutrition & Care GmbH.

The waterborne protective coating systems according to the first aspect of the present invention are advantageous because the application of a layer of coating system†o a substrate will, depending on concentration of the 2D maferial/graphific nanoplafelefs in the coating and applied dry film thickness, result in multiple layers of 2D maferial/graphific nanoplafelefs in the film. Each layer of 2D maferial/graphific nanoplafelefs is potentially several atomic layers thick. The presence of multiple layers of 2D maferial/graphific nanoplafelefs provides a complex and forfuous or labyrinthine path for the penetration of wafer and any dissolved oxygen, chloride and / or sulphate ions or similar ions the wafer carries. This will substantially reduce the water vapour transmission rates across the film relative†o an equivalent film that does no† incorporate 2D material/graphitic nanopla†ele†s.

The waterborne protective coating systems according†o the firs† aspect of the present invention are also advantageous because the coating systems incorporate smaller quantities of wetting agent than has proven possible previously. This has the benefit†ha† there is less wetting agent in the film formed from the coating system than previously and, as such, less likelihood of defects in†ha† film, such as

micropores, as a result of the removal of the wetting agent.

This is because it is known†ha† the introduction of graphene into waterborne systems has traditionally been undertaken by stirring graphene powder or a water dispersion thereof into a binder dispersion. During this process the graphene is effectively being dispersed into a continuous phase. Such dispersions typically result in the

coagulation of the binder or resin particles and the crashing of the dispersion. That is the binder particles come ou† of dispersion, aggregate, and form a sediment in the container in which the mixing takes place. This is caused by the high surface area of the graphene competing for the surfactant present on the binder or resin, the ne† reduction of the surfactant on the binder or resin causes the binder or resin’s destabilisation. Where polymeric self-crosslinking surfactants are used, these are less available†o the graphene and the graphene itself will become destabilised, aggregate and sediment.

The inclusion of additional surfactant in a graphene dispersion will, while providing some stabilisation in the coating system, result in significant loadings of surfactant in the final film formed from the coating system. This will result in the surfactant migrating†o either the film / air interface or the film / substrate interface. A† the film / air interface the surfactant will be liable†o removal on exposure†o the

environmental impacts causing the formation of micropores in the film. A† the film / substrate interface the surfactant can cause a reduction in adhesion between the film and the substrate.

I† is though††ha† this is because water as a solvent has a high level of polarity while, in contras†, graphene/graphitic nanopla†ele†s with a high Carbon / Oxygen ratio have a low polarity and a high degree of hydrophobicify which makes the two repel each other. This causes the graphene/graphific nanoplafelefs†o aggregate, flocculate and no† disperse. In some embodiments of the present invention where the 2D material/graphitic platelets are graphene/graphitic nanopla†ele†s the

Carbon / Oxygen ratio of the graphene/graphitic nanopla†ele†s is equal†o or greater than 1 5.

According†o a second aspect of the present invention there is provided a method of formulation of a waterborne protective coating system of the firs† aspect of the present invention comprising the steps of

(a) obtaining a liquid dispersion of 2D material/graphitic nanopla†ele†s in an aqueous solution, and

(b) mixing the liquid dispersion with a† leas† one binder and water.

In some embodiments of the second aspect of the present invention the method of step (a) comprises the steps of

(i) creating a dispersing medium;

(ii) mixing 2D material/graphitic nanopla†ele†s into the dispersing medium; and

(iii) subjecting the 2D material/graphitic nanopla†ele†s†o sufficient shear forces and or crushing forces†o reduce the particle size of the 2D material/graphitic

nanopla†ele†s,

characterised in†ha† the 2D material/graphitic nanopla†ele†s and dispersing medium mixture comprises the 2D material/graphitic nanopla†ele†s, a† leas† one grinding media, water, and a† leas† one wetting agent, and†ha† the a† leas† one grinding media is water soluble or functionalised†o be water soluble.

In some embodiments of the second aspect of the present invention the step of subjecting the 2D material/graphitic nanopla†ele†s†o sufficient shear forces and or crushing forces†o reduce the particle size of the 2D material/graphitic nanopla†ele†s is performed using a grinding mill, a dissolver, a bead mill, or a three-roll mill.

In some embodiments of the second aspect of the present invention the 2D material/graphitic nanopla†ele†s are comprised of one or more of graphene or graphitic nanopla†ele†s, in which the graphene nanopla†ele†s are comprised of one or more of graphene nanoplafes, reduced graphene oxide nanoplafes, bilayer graphene nanoplafes, bilayer reduced graphene oxide nanoplafes, frilayer graphene nanoplafes, frilayer reduced graphene oxide nanoplafes, few-layer graphene nanoplafes, few-layer reduced graphene oxide nanoplafes, and graphene nanoplafes of 6†o 10 layers of carbon atoms, and the graphitic platelets are comprised of graphite nanoplafes with af leas† 10 layers of carbon atoms.

In some embodiments the second aspect of the present invention one or both of the graphene nanoplafelefs and the graphitic nanoplafelefs have lateral dimensions ranging from around 100 nm†o 100 Mm.

In some embodiments of the second aspect of the present invention the 2D maferial/graphific nanoplafelefs are comprised of one or more of graphitic platelets, in which the graphitic nanoplafelefs are graphite nanoplafes with 10†o 20 layers of carbon atoms, graphite nanoplafes with 10†o 14 layers of carbon atoms, graphite nanoplafes with 10†o 35 layers of carbon atoms graphite nanoplafes with 10†o 40 layers of carbon atoms, graphite nanoplafes with 25†o 30 layers of carbon atoms, graphite nanoplafes with 25†o 35 layers of carbon atoms, graphite nanoplafes with 20†o 35 layers of carbon atoms, or graphite nanoplafes with 20†o 40 layers of carbon atoms.

In some embodiments of the second aspect of the present invention the 2D maferial/graphific nanoplafes are comprised of one or more of 2D material nanoplafes, in which the 2D material nanoplafes are comprised of one or more of hexagonal boron nitride (hBN), molybdenum disulphide (M0S2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), Graphyne (C), borophene (B), phosphorene (P), or a 2D in-plane or vertical heferosfrucfure of two or more of the aforesaid materials.

Few-layer graphene / reduced graphene oxide nanoplafes have between 4 and 10 layers of carbon atoms, where a monolayer has a thickness of 0.035 nm and a typical interlayer distance of 0.14 nm. In some embodiments of the second aspect of the present invention the 2D maferial/graphific nanoplafes are comprised of graphene / graphitic nanoplafes and a† leas† one 1 D material. In some embodiments the 1 D material comprises carbon nanotubes.

In some embodiments of the second aspect of the present invention the a† leas† one of the a† leas† one grinding media is water soluble or functionalised†o be water soluble. In some embodiments, the grinding media is a polymer modified with strong anchoring groups. In some embodiments the grinding media is an aqueous solution of a modified aldehyde resin having a† leas† one amine group which may have been introduced into the backbone of the polymer, or by reacting an amine with functional groups on the resin†o form a sal†. In some embodiments the grinding media is a low molecular weigh† styrene/maleic anhydride copolymer.

In some preferred embodiments, the grinding media of the dispersion of 2D material/graphitic platelets is Laropal (trade mark) LR 9008 which is a water-soluble modified aldehyde resin commercially available from BASF, Dispersions & Resins Division, North America, ADDITOL (trade mark) XL 6515 a modified alkyd polymer, ADDITOL XW 6528 a polyester modified acrylic polymer, ADDITOL XW 6535 a high polymeric, auto emulsifying pigment grinding medium, ADDITOL XW 6565 a high polymeric, au†o-emulsifying pigment grinding medium, ADDITOL XW 6591 a polyester modified acrylic polymer. The ADDITOL products are commercially available from the Allnex group of companies.

In some embodiments of the second aspect of the present invention the dispersing medium comprises a mixture of the a† leas† one grinding media and water, and the step of creating a dispersing medium comprises

(i) mixing the a† leas† one grinding media with the water until it is substantially homogenous.

In some embodiments of the second aspect of the present invention the a† leas† one grinding media is a liquid and the dispersing medium comprises between 50 w†% and 90 w†% of the a† leas† one grinding media and between 10 w†% and 50 w†% of water, between 60 w†% and 80 w†% of the a† leas† one grinding media and between 20 w†% and 40 w†% of wafer; between 65 w†% and 75 w†% of the at least one grinding media and between 25 w†% and 35 w†% of wafer, or around 70 w†% of the at least one grinding media and around 30 w†% of wafer.

In some embodiments of the second aspect of the present invention the dispersing medium further comprises the af leas† one wetting agent, the wetting agent is stored as a liquid, and the step of creating the dispersing medium comprises (i) mixing the a† leas† one grinding media, water and wetting agent until the grinding media, water and wetting agent mixture is substantially homogenous.

In some embodiments of the second aspect of the present invention the dispersing medium further comprises the a† leas† one wetting agent, the wetting agent is stored as a solid (which term includes powder), and the step of creating the dispersing medium comprises

(i) mixing the a† leas† one grinding media, water and wetting agent until the grinding media and wetting agent are dissolved and the grinding media, water and wetting agent mixture is substantially homogenous.

In some embodiments of the second aspect of the present invention the a† leas† one wetting agent is added†o the dispersing medium a† substantially the same time as the 2D material/graphitic nanopla†ele†s.

The wetting agent or agents of the dispersion of 2D material/graphitic nanopla†ele†s of the present invention may be one of a polymeric wetting agent, an ionic wetting agent, a polymeric non-ionic dispersing and wetting agent, a cationic wetting agent, an amphoteric wetting agent, a Gemini wetting agent, a highly molecular resin-like wetting and dispersing agent or a mixture of two or more of these wetting agents.

Preferred wetting agents of the dispersion of 2D material/graphitic nanopla†ele†s include bu† are no† limited†o ADDITOL (trade mark) VXW 6208/60, a modified acrylic copolymer which is a polymeric non-ionic dispersing and wetting additive

commercially available from Allnex Belgium SA/NV; and DISPERBYK-21 50 (trade mark) a block copolymer with basic, pigment-affinic groups commercially available from BYK-Chemie GmbH, and Surfynol (trade mark) 104 a Gemini wetting agent and molecular defoamer commercially available from Evonik Nutrition & Care GmbH.

Dry 2D material/graphitic nanoplatelets, for example graphene / graphitic nanoplatelets, are typically made up of agglomerates or aggregates of primary particles or nanoplatelets. During the dispersion process those agglomerates or aggregates have to be broken down, as far as possible, into primary particles or nanoplatelets of a size suitable for the intended application of the 2D

material/graphitic nanoplatelets. The breaking down of the agglomerates or aggregates of primary particles or nanoplatelets is believed to include the process of exfoliation.

In some embodiments of the second aspect of the present invention the dispersing means is a means suitable to apply both a crushing action and a mechanical shearing force to the 2D material/graphitic nanoplatelets whilst those materials are mixed in with the dispersing medium. Suitable apparatus to achieve this are known grinding or milling apparatus such as dissolvers, bead mills or three-roll mills.

In some embodiments of the second aspect of the present invention it is preferred that the agglomerates or aggregates are broken down to particles or nanoplatelets of a particle size which cannot be broken down further. This is beneficial because the manufacture and storage of 2D material/graphitic nanoplatelets prior to their use is often in the form of particles that are larger than desired for 2D

material/graphitic nanoplatelet dispersions.

Once the 2D material/graphitic nanoplatelets agglomerates or aggregates are reduced to smaller particles or nanoplatelets, rapid stabilisation of the newly formed surfaces resultant from the reduction in size of the agglomerates or aggregates helps to prevent the particles or nanoplatelets re-agglomerating or re-aggregating.

The method of the second aspect of the present invention is particularly beneficial because it has been found that the higher the interfacial tension between a dispersing medium, for example a dispersing medium which comprises water and 2D material/graphitic platelets, the stronger are the forces tending to reduce the interfacial area. In other words, the stronger are the forces fending†o re- agglomerafe or re-aggregafe the 2D maferial/graphific nanoplafelefs or fo form flocculates. The interfacial tension between a wetting agent in the dispersing medium and the 2D maferial/graphific nanoplafelefs is lower than that between the wafer and the 2D maferial/graphific platelets and as such the wetting agent helps stabilise the newly formed surfaces and prevent the 2D maferial/graphific

nanoplafelefs agglomerating, aggregating and or flocculating.

The action of the wetting agent in stabilising the newly formed surfaces and preventing the 2D maferial/graphific nanoplafelefs agglomerating, aggregating and or flocculating is beneficial but has been found no††o give sufficient benefit†o allow the formation of improved stable dispersions. This is because although the wetting agent will allow the 2D nanomaterial†o be suspended in an aqueous dispersing medium, it is a feature of 2D material/graphitic nanoplafelefs†ha† they have a high surface area relative†o other compounds. Water having a high polarity may displace the wetting agent.

An increase in the proportion of the wetting agent in the dispersing medium may, ultimately lead†o a dispersion in which all the components remain suspended. This approach†o forming a dispersion has the problem, however,†ha† coatings formed from the dispersion will have a high degree of solubility in water. This is very undesirable because it leads†o the rapid failure of the coating.

According†o the second aspect of the present invention the application of a crushing action and or mechanical shearing forces†o a dispersion comprising a mixture of 2D material/graphitic nanoplafelefs in a grinding media, water and wetting agent mixture results in an improved dispersion.

This is though††o be because, in addition†o the wetting agent, the grinding media will also stabilise the newly formed surfaces of the 2D material/graphitic

nanoplafelefs because a proportion of the 2D material/graphitic nanoplafelefs are a† leas† partially encapsulated within a coating of grinding media. The wetting agent can then interact with the combined grinding media / 2D material/graphitic platelet nanoparticle and allow the grinding resin / 2D material/graphitic nanoplatele† particle to be suspended in the dispersion. Combination of grinding media with wetting agent results in less wetting agent being required†o we† the 2D material/graphitic nanopla†ele†s enabling suspension in the dispersion so minimising the problems resulting from high levels of surfactant (water sensitivity) .

A further advantage of the method of the present invention is†ha† the milling performance of the dispersion means when acting on 2D material/graphitic nanopla†ele†s, is further improved by the presence of the grinding media in the mixture being milled. That improvement is exhibited by faster milling, lower hea† generation in the milling process, a more uniform particle size in the dispersion, a smaller D50 particle size in the dispersion, a lower dispersion viscosity, a greater storage stability relative†o known short shelf life dispersions, and an ability†o re disperse any combined grinding media / 2D material/graphitic nanoplatele† particles†ha† have settled ou† of the dispersion by simple agitation of the dispersion.

The development of a grinding media supported dispersion of 2D material/graphitic nanopla†ele†s where the grinding media support is water soluble enables the dispersion of the 2D material/graphitic nanopla†ele†s in the continuous phase where the 2D material/graphitic nanopla†ele†s are stabilised within a water-based entity and does no† compete significantly with the grinding media for stabiliser. The development of stable water based dispersions incorporating 2D material/graphitic nanopla†ele†s enables the development of 2D material/graphitic nanoplatele† supported pain† formulations and improvement of the barrier performance of water- based systems which might be applied†o a number of substrates; metal for corrosion improvement, wood for prevention of water uptake and concrete for prevention of water uptake and degradation.

A further advantage of the waterborne protective coating system according†o the firs† aspect of the present invention is†ha† in commonly used coating binder systems for use on wood, undergo surface pho†odegrada†ion. This is the result of UV radiation in sunlight breaking down the down the polymer, such a breakdown is slow and results in the erosion of the film from the surface of the wood. The wood can then be attacked by water and mildew resulting in the onset of degradation and ro†, with the attendant result†ha† significant maintenance and repair might be required. When the waterborne protective coating systems according to the first aspect of the present invention comprises graphene nanoplafes or graphitic nanoplafes and the binder is an organic polymer those nanoplafes absorb of UV light and as such help protect the film formed from the coating system.

BRIEF DESCRIPTION

For a better understanding of various examples that are useful for understanding the detailed description, reference will now be made by way of example only†o the accompanying drawings in which:

Fig. 1 shows the different stages towards film formation;

Fig. 2 shows images of test panels with coating cleaned off after Saif Spray Testing for 480 Flours ASTM B1 17 Neutral Saif Spray Fog Testing Results;

Fig. 3 shows results of the measured corrosion average creep of coated Blasted Steel (480 hours);

Fig. 4 shows results of the measured corrosion average creep of coated Bonderife Steel (480 hours);

Fig. 5 shows results of the measured corrosion average creep of coated Abraded Steel (480 hours); Fig. 6 shows images of test panes with coating cleaned off after Saif Spray Testing for 1000 Flours ASTM B 1 17 Neutral Saif Spray Fog Testing Results;

Fig. 7 shows results of the measured corrosion average creep of coated Blasted Steel ( 1000 hours);

Fig. 8 shows results of the measured corrosion average creep of coated Bonderife Steel ( 1000 hours); and

Fig. 9 shows results of the measured corrosion average creep of coated Abraded Steel ( 1000 hours). DETAILED DESCRIPTION

Examples

A control sample (DTM1 ) and four samples of formulation according to the firs† aspect of the present invention (DTM2†o DTM5) were manufactured according†o the formulations shown in Table 1 .

Table 1

The materials shown in Table 1 are as follows: Additol VXW 6208 is a polymer non ionic dispersing additive for grinding inorganic and organic pigments in water, Additol VXW 6393 is a defoamer, Ti-Pure R-706 is a titanium dioxide pigment, Acrysol RM2020E is a hydrophobically modified ethylene oxide urethane (HEUR) high-shear rheology modifier, Resydrol AY 6150w/45WA is an air-drying acrylic modified alkyd resin emulsion (i.e. an acrylic-alkyd hybrid resin), Addifol VXW 6206 is an emulsified, nonylphenylefhoxylafe free combination drier of cobalt, lithium and zirconium, Addifol VXW 6503 N is a levelling and substrate wetting agent based on a polyether modified polysiloxan for waterborne paint systems, Additol VXW 4973 is a defoamer, Modaflow AQ-3025 is an acrylic flow additive for aqueous coatings, Additol XL 297 is a skinning preventor, Acrysol RM-8W is a non-ionic urethane rheology modifier, and HaloX Flash-X 150 is for the inhibition of flash rust and in-can rusting in lined and unlined metal containers.

Additol, Resydrol and Modaflow are trade marks of Allnex Belgium SA and the products incorporating that name are available from that company. Ti-Pure is a trade mark of The Chemours Company and the product incorporating that name is available from that company. Acrysol is a trade mark of The Dow Chemical

Company and the products incorporating that name are available from that company. Halox is a trade mark of ICL Specialty Products Inc. and the product incorporating that name is available from that company.

The control sample was a commercial brand water borne acrylic formulation.

Manufacture followed the following steps:

A pigment paste was made in a mechanical mixer:

Items 1 and 2 were added to the mixer and the speed adjusted to maintain a consistent vortex (the mixer is at a medium speed). Items 1 and 3 were dispersed for 5-10 minutes.

Items 3 and 4 are added and dispersed for 10 minutes at a medium - high mixer speed.

Item 5 is added and dispersed for 20-30 minutes at high mixer speed to obtain a Hegman of 7+. The pigment paste is then let down in a mechanical mixer:

Items 6-8 are added to a mechanical mixer and the speed adjusted to maintain a consistent vortex. Shear is applied to items 6-8 by the mixer for a minimum of 10 minutes a† high speed.

Items 9-12 and the pigment paste previously prepared are added†o the mixer and shear is applied for a minimum of 10 minutes a† low-medium speed.

Items 13-15 are added and mixed for 10 minutes.

Items 16 -17 are added and mixed for 10 minutes Test panels were made with the characteristics shown in Table 2 and scribed in the usual fashion for testing.

Table 2

The test panels were tested†o evaluate and determine if a coating system

according†o the present invention could deliver a meaningful extension of life relative†o waterborne acrylic coatings typically used in C3 type (medium) corrosivity environments as defined in ISO 12944-2. Accelerated exposure testing was performed. The testing regime was Saif Spray Testing ASTM B1 17 Neutral Sal† Spray Fog Testing: Corrosion Creep Assessment†o ISO4628-2-2003 and IS 04628-3-2003. Images of test panels with coating cleaned off offer Saif Spray Testing for 480 Hours ASTM B 1 17 Neutral Saif Spray Fog Testing Results are shown in Fig. 2.

The results of the measured corrosion average creep are as shown in Figs. 3†o 5.

If is noted that, except for the 480-hour assessment of the coated Blasted Steel control panel, all of the other control panels at both 480 hours and 1000 hours testing had substantial levels of corrosion emanating from the scribe and/or a complete failure in terms of corrosion. These panels have been denoted as having an average creep corrosion of 50mm to aid pictorial representation in Figs. 3 to 5 and 7 to 9.

Images of test panes with coating cleaned off after Salt Spray Testing for 1000 Hours ASTM B 1 17 Neutral Salt Spray Fog Testing Results are shown in Fig. 6.

The results of the measured corrosion average creep are as shown in Figs. 7 to 9.

In the images shown of the panels in the accelerated exposure tests (ASTM B 1 17 Neutral Salt Spray Fog Testing Results) at 480 hours and 1000 hours testing duration respectively (Figs. 2 and 6); the graphene nanoplatelets in the acrylic formulation has reduced the corrosion observed at the scribe. The reduction in corrosion at the scribe on the test panels is the most pronounced at additions levels of Genable (trade mark) 1250 at 10% and 20% wt in the tested formulations. This performance improvement will translate into a meaningful extension of coating life for real life applications.