Anticorrosive Coating Composition Comprising Graphene

Field of the Invention

The present invention relates to anticorrosive coating compositions, particularly those that comprise an epoxy resin, a solvent and graphene.

Background

Corrosion is the gradual degradation of a metal due to oxidation. As a metal corrodes, it is converted from a refined form into the corresponding metal oxide. Corrosion readily occurs under natural conditions due to the relative stability of metal oxides compared to their refined counterparts. As a result, corrosion is a widespread and well-known problem that affects metal structures across a variety of industries.

One technique for reducing the rate of corrosion of a metal surface is to coat it with a composition that resists corrosion. This creates a physical barrier between the corrosive external environment and the metal structure. For anticorrosive coatings to be effective they must be impermeable to the environment that causes the corrosion, which may be air, salt water or acids, for example. If a coating is at all permeable then the metal surface underneath it can be damaged even if the coating is applied with good coverage and without defects.

It is also a desirable property of anticorrosive coatings that they adhere tightly to the substrate onto which they are coated, and that they have sufficient mechanical strength to resist the spread of corrosion from localised areas of damage. Such systems have extended service lifetimes and require less regular maintenance.

Graphene has been subject to extensive research since it was first isolated in 2004. One application of graphene that has been suggested is its use as an additive in anticorrosive coating compositions to enhance their anticorrosive property.

However, there remains a need to improve the anticorrosive property of coating compositions comprising graphene. One reason for this is that graphene is prone to agglomeration, which leads to an uneven distribution through a (for example) liquid phase. Reducing agglomeration of graphene, and thereby improving its dispersibility in a liquid phase, is key to the efficacy and efficiency of the graphene present in a coating film.

The present invention has been devised in light of the above considerations.

Summary of the Invention

At its broadest, the present invention relates to an anticorrosive coating composition.

The anticorrosive coating composition uses a graphene-based additive in an epoxy coating formulation. The subject of the present invention is a coating composition that exhibits better corrosion creep performance than a leading commercial anticorrosive epoxy. In a first aspect, the coating composition comprises (a) epoxy resin, (b) a main solvent and (c)(i) graphene, wherein the graphene is present in the coating composition in an amount 0.01 wt% to 0.4 wt% by weight of the coating composition, and the graphene as a raw material has a median flake diameter of 0.5 pm to 55 pm or a mean flake diameter of 0.01 pm to 55 pm, or (c)(ii) graphite, wherein the graphite is present in the coating composition in an amount 0.01 wt% to 0.4 wt%, and the graphite has a median flake diameter of 0.5 pm to 55 pm or a mean flake diameter of 0.01 pm to 55 pm. “wt%” is used to refer to the amount of a component present in the coating composition by weight of the coating composition.

The inventors have found that the corrosion creep performance of the coating composition is improved at least when the graphene is present, and particularly when graphene having a flake diameter of 0.5 pm to 55 pm is used.

The inventors have also found that the corrosion creep performance of the coating composition is improved at least when the graphene is present in the coating composition in an amount 0.01 wt% to 0.4 wt%, for example 0.04 wt% to 0.3 wt% or 0.06 wt% to 0.14 wt%.

In another aspect, the coating composition according to the first aspect comprises (a) epoxy resin, (b) a main solvent, and (c)(i) graphene, wherein the graphene is present in the coating composition in an amount 0.01 wt% to 0.4 wt%, and the graphene has a median flake diameter of 0.5 pm to 55 pm or a mean flake diameter of 0.01 pm to 55 pm.

In another aspect, the coating composition according to the first aspect comprises (a) epoxy resin, (b) a main solvent, and (c)(ii) graphite, wherein the graphite is present in the coating composition in an amount 0.01 wt% to 0.4 wt%, and the graphite has a median flake diameter of 0.5 pm to 55 pm or a mean flake diameter of 0.01 pm to 55 pm.

In another aspect, the coating composition comprises (a) epoxy resin, (b) a main solvent and (c)(i) graphene, wherein the graphene is present in the coating composition in an amount 0.01 wt% to 0.4 wt% by weight of the coating composition, and the graphene as a raw material has a median flake diameter of 0.01 pm to 55 pm or a mean flake diameter of 0.01 pm to 55 pm, or (c)(ii) graphite, wherein the graphite is present in the coating composition in an amount 0.01 wt% to 0.4 wt%, and the graphite has a median flake diameter of 0.01 pm to 55 pm or a mean flake diameter of 0.01 pm to 55 pm.

In some embodiments, the graphene and/or graphite has a flake diameter of 0.5 to 55 pm, preferably 0.1 to 25 pm, or 0.12 to 20 pm, or 0.14 pm to 12 pm, or 0.2 pm to about 10 pm.

In some embodiments, the graphene has a flake diameter of 0.5 to 55 pm, preferably 3 to 25 pm, more preferably 5 to 20 pm, even more preferably 8 pm to 12 pm, and most preferably about 10 pm.

The graphene may also preferably have a thickness of no more than 7 nm, or no more than 5 nm, or no more than 4 nm, or no more than 3.5 nm.

The graphene may also preferably have a thickness of 2 nm to 7 nm, preferably 2.5 nm to 5 nm and most preferably 3 nm to 4 nm.

Accordingly, in some embodiments the graphene suitably has an aspect ratio of 70 to 27,500, or 100 to 25,000, preferably 1000 to 8000, more preferably 1500 to 5000 and most preferably 2000 to 4000.

In some preferred embodiments of the present invention, the epoxy resin is present in the coating composition in an amount 15 wt% to 20 wt%. In some preferred embodiments of the present invention, the main solvent comprises an oxygenated solvent and an aromatic solvent.

Preferably, the oxygenated solvent is present in the coating composition in an amount 2 wt% to 15 wt%. Preferably, the aromatic solvent is present in the coating composition in an amount 1 wt% to 10 wt%.

Preferably, the total weight composition of the main solvent present in the coating composition is an amount 3 wt% to 25 wt%. That is, the total weight composition of solvent, not including any curing agent solvent, present in the coating composition.

In those embodiments in which the main solvent comprises oxygenated solvent and aromatic solvent, the total weight composition of the main solvent is at least the sum of the weight compositions of the oxygenated solvent and the aromatic solvent, but not including the weight composition of any curing agent solvent.

In those embodiments in which the main solvent comprises oxygenated solvent or aromatic solvent, the total weight composition of the main solvent is at least the weight composition of the oxygenated solvent or the aromatic solvent, but not including the weight composition of any curing agent solvent.

In some embodiments, the oxygenated solvent is propylene glycol methyl ether. In some embodiments, the aromatic solvent is xylene. In some embodiments the oxygenated solvent is propylene glycol methyl ether and the aromatic solvent is xylene.

In some embodiments of the present invention, the graphene is provided in or introduced into the coating composition as a graphene dispersion. Preferably, the dispersion medium is an epoxy resin, which may suitably be the epoxy resin which is component (a) of the coating composition. Preferably, the content of graphene in the graphene dispersion is in the range of 5 - 10% by weight, most preferably about 5% by weight.

Preferably, the graphene provided in the coating composition is unfunctionalized graphene.

The coating composition may further comprise at least one of epoxy type 1 provided as 75% solids in xylene, a thixotropic agent, a dispersing agent, a colouring pigment, a mineral extender, a diluent, an amine-based curing agent, an amine accelerator or a curing agent solvent; or multiple of these in any combination thereof.

A second aspect of the present invention relates to a coating system for coating a surface of a substrate, wherein the coating system comprises at least one coating layer produced from the present coating composition.

The coating system may have only a single coating layer (that being produced from the present coating composition). Alternatively it may have multiple coating layers, or be included as part of a multi coat / multi product coating system.

Whilst each coating layer of the coating system according to the present invention may comprise different coating compositions, so long as at least one is produced from the present coating composition, it may be advantageous for the coating system to include at least two coating layers produced from the present coating composition. In some embodiments, the coating system comprises one layer produced from the present coating composition and one layer produced from a different coating composition.

A third aspect of the present invention relates to a kit of parts comprising the disclosed coating composition and a plurality of containers, wherein a first container contains part B components, as described herein and the other container(s) (that is, the remaining ones of said plurality of containers other than the aforementioned first container) contain part A components, as described herein.

That is, the components of the given coating composition, other than the amine-based curing agent and the (if present) curing agent solvent and/or amine accelerator, are distributed to be contained within the other containers in the kit. For example, there may be a single further container (a second container) which includes all these other components. There may be a series of further containers each containing a respective single one of these other components. There may be further containers which include any two of these other components, or any three of these other components, and so on.

A fourth aspect of the present invention relates to a method of coating a surface of a substrate, comprising the step of applying one or more layers of the present coating composition to at least a part of the substrate. It will be recognised that the substrate is suitably metal. It might be an alloy, a refined metal, and so on.

A fifth aspect of the present invention relates to a coated substrate comprising a substrate and a coating system as described herein. That is, at least a part of the substrate has a coating produced from the present coating composition.

The invention includes all combinations of the aspects and preferred/suitable features of embodiments described herein except where such a combination is clearly impermissible or expressly avoided.

Summary of the Figures

Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

Figure 1 illustrates a cross-section of a coated substrate according to an exemplary embodiment of the present invention prepared for corrosion creep measurement in accordance with ISO 12944-6 Annex A requirements;

Figure 2 displays photographs of panels that have been coated by a 2 x 150 pm epoxy coating prepared in accordance with Example 1 , and a 1 x 50 pm polyurethane topcoat. The panels are photographed after being subjected to cyclic corrosion test conditions for 4200 hours in accordance with ISO 12944-9:2018 Annexe B Cyclic Testing. . Photographs are annotated with panel numbers P1 , P2 and P3 accordingly;

Figure 3 illustrates the average corrosion creep results of different coatings each provided as a 2 x 150 pm epoxy coating system and a 1 x 50 pm polyurethane topcoat, after being subjected to cyclic corrosion test conditions for 4200 hours in accordance with ISO 12944- 9:2018 Annexe B Cyclic Testing. . Figure 4 illustrates mechanical test data for coating sample S6, wherein graphene is present in 0.1 wt%.

Figure 5 illustrates mechanical test data for coating sample S5, wherein the coating does not comprise graphene and has additional epoxy resin.

Figure 6 illustrates mechanical test data for coating sample S4, wherein the coating sample does not comprise graphene.

Detailed Description of the Invention

Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

Graphene

Initially it is worth discussing the meaning of various terms that are used herein.

In particular, “graphene” is used to refer not only to monolayer graphene but also to few layer graphene.

Techniques for measuring the flake thickness of graphene are well known and include, for example, atomic force microscopy.

The flake thickness of graphene is no more than 7 nm.

In some embodiments, the flake thickness of graphene is no more than 6.3 nm, or 5.6 nm, or 5 nm, or 4.9 nm, or 4.2 nm, or 4 nm, or 3.5 nm, or 3.15 nm, or 2.8 nm, or 2.45 nm, or 2.1 nm, or 1.75 nm, or 1.4 nm, or 1.05 nm, or 0.7 nm, or 0.35 nm.

In some embodiments, the flake thickness of graphene is no less than 0.35 nm, or 0.7 nm, or 1.05 nm, or 1.4 nm, or 1.75 nm, or 2.1 nm, or 2.45 nm, or 2.8 nm, or 3.15 nm, or 3.5 nm, or 4.2 nm, or 4.9 nm, or 5.6 nm, or 6.3 nm, or 7 nm.

The number of layers of graphene is no more than about 20 layers.

In some embodiments, the graphene has a number of layers no more than 18, or 16, or 14, or 12, or 10, or 9, or 8, or 7, or 6, or 5, or 4, or 3, or 2, or 1.

In some embodiments, the graphene has a number of layers no less than 1, or 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10, or 12, or 14, or 16, or 18, or 20.

The graphene used herein preferably has a flake thickness of 2 nm to 7 nm, which corresponds to about 6 and 20 layers assuming a layer separation of 0.345 nm. As used herein, flake thickness for a graphene sample refers to the t ₅ o average thickness (i.e. the value where 50% of the graphene flakes are thinner and 50% of the graphene flakes are thicker). Of course, skilled technician in this field understands a suitable sampling regime to obtain a representative average for such properties of graphene. In some other embodiments, the graphene preferably has a flake thickness of less than 3.5 nm, for example about 0.35 nm or about 0.7 nm, which corresponds to less than about 10 layers, for example 1 or 2 layers.

“Graphene” is used to refer not only to unfunctionalized graphene but also to functionalized graphene. Unfunctionalized graphene is graphene that is substantially free of chemical functionalization. A characterisable feature of unfunctionalized graphene is that is has a close to 100% carbon composition.

The graphene present in the coating composition according to the present invention is suitably unfunctionalized graphene.

The graphene used herein preferably has an oxygen content as a percentage of the carbon composition of at most 3.0%, preferably 2.5%, more preferably 2%, and even more preferably no greater than 1%. This is considered important at least to assist the graphene to form a stable dispersion in liquid epoxy resin.

The “flake diameter” of a graphene sample refers to the average lateral flake dimension of the graphene flakes in the sample. Techniques for measuring the flake diameter (or lateral flake dimensions) of graphene are well known and include, for example, scanning electron micrography. The lateral flake dimension of graphene is generally measured at the longest dimension of the flake. The “average” lateral flake dimension (i.e. flake diameter as used herein) refers to the dso median average or, where stated, the mean average.

The aspect ratio of a graphene refers to the value calculated by dividing the flake diameter of the graphene by the flake thickness of graphene.

Graphene, provided either as a raw material or as a dispersion, is routinely supplied by manufacturers with information about the flake diameter(s) contained. Manufacturers may list the average flake diameter of graphene in terms of its median average diameter, or in terms of its mean average diameter, or in terms of another kind of measurement.

In an embodiment of the present invention the graphene has a flake diameter of 0.5 pm to 55 pm, preferably 3 pm to 25 pm, more preferably 5 pm to 20 pm, even more preferably 8 pm to 12 pm and most preferably about 10 pm.

In some embodiments of the present invention the graphene has a mean average flake diameter of at least 0.01 pm, or 0.02 pm, or 0.03 pm, or 0.04 pm, or 0.05 pm, or 0.06 pm, or 0.07 pm, or 0.08 pm, or 0.09 pm, or 0.1 pm, or 0.12 pm, or 0.14 pm, or 0.16 pm, or 0.18 pm, or 0.2 pm, or 0.22 pm, or 0.24 pm, or 0.26 pm, or 0.28 pm, or 0.3 pm, or 0.35 pm, or 0.4 pm, or 0.45 pm, or 0.5 pm, or 0.6 pm, or 0.7 pm, or 0.8 pm, or 0.9 pm, or 1 pm, or 2 pm, or 3 pm, or 4 pm, or 5 pm, or 6 pm, or 7 pm, or 8 pm, or 9 pm, or 10 pm.

In some embodiments of the present invention the graphene has a mean average flake diameter of no more than 100 pm, or 90 pm, or 80 pm, or 70 pm, or 60 pm, or 55 pm, or 50 pm, or 45 pm, or 40 pm, or 35 pm, or 30 pm, or 25 pm, or 20 pm, or 18 pm, or 16 pm, or 14 pm, or 12 pm, or 10 pm, or 9 pm, or 8 pm, or 7 pm, or 6 pm, or 5 pm, or 4 pm, or 3 pm, or 2 pm, or 1 pm, or 0.9 pm, or 0.8 pm, or 0.7 pm, or 0.6 pm, or 0.5 pm, or 0.4 pm, or 0.3 pm, or 0.2 pm, or 0.1 pm, or 0.09 pm, or 0.08 pm, or 0.07 pm, or 0.06 pm, or 0.05 pm, or 0.04 pm, or 0.03 pm, or 0.02 pm, or 0.01 pm. In one embodiment, the mean average flake diameter of graphene is 0.2 pm ± 0.04 pm.

In another embodiment, the mean average flake diameter of graphene is 0.2 pm ± 0.05 pm.

In an embodiment of the present invention the graphene has a flake thickness of 2 nm to 7 nm, preferably 2.5 nm to 5 nm, most preferably 3 nm to 4 nm. This corresponds to a number of graphene layers of 6 and 14 layers, preferably 7 and 13 layers, most preferably 9 and 12 layers.

In an embodiment of the present invention the aspect ratio of graphene is 100 to 25,000, preferably 1000 to 8000, more preferably 1500 to 5000 and most preferably 2000 to 4000.

In another embodiment of the present invention the aspect ratio of graphene is 1 to 30,000, or 10 to 15,000, or 25 to 5,000, or 50 to 2,000.

In a preferred embodiment of the present invention the graphene is provided in the coating composition as a graphene dispersion.

Graphene products meeting these criteria are readily commercially available, and various methods of making graphene are well known.

Graphite

“Graphite” is used to refer to multilayer graphene having an average thickness of more than 7 nm, which corresponds to more than about 20 layers assuming a layer separation of 0.345 nm. Graphite is distinguishable from graphene by its flake thickness. The graphene used here has a flake thickness of 7 nm or less.

Techniques for measuring the flake thickness of graphite are well known. Like graphene, these techniques include, for example, atomic force microscopy. The graphite used herein has a flake thickness of more than 7 nm to 35 nm or less, which corresponds to more than about 20 layers and about 100 layers or less assuming a layer separation of 0.345 nm.

The flake thickness of graphite is more than 7 nm.

In some embodiments, the flake thickness of graphite is more than 7 nm and 31.5 nm or less, or more than 7 nm and 28 nm or less, or more than 7 nm and 24.5 nm or less, or more than 7 nm and 21 nm or less, or more than 7 nm and 17.5 nm or less, or more than 7 nm and 14 nm or less, or more than 7 nm and 10.5 nm or less.

In some embodiments, the flake thickness of graphite is more than 10.5 nm, or is more than 14 nm, or is more than 17.5 nm, or is more than 21 nm, or is more than 24.5 nm, or is more than 28 nm, or is more than 31.5 nm, or is more than 35 nm.

The number of layers of graphene in graphite is more than about 20 layers.

In some embodiments, the number of layers of graphene in graphite is more than about 20 layers to 100 layers or less, or more than about 20 layers to 90 layers or less, or more than about 20 layers to 80 layers or less, or more than about 20 layers to 70 layers or less, or more than about 20 layers to 70 layers or less, or more than about 20 layers to 60 layers or less, or more than about 20 layers to 50 layers or less, or more than about 20 layers to 40 layers or less, or more than about 20 layers to 30 layers or less.

In some embodiments, the number of layers of graphene in graphite is more than is about 30 layers, or is about 40 layers, or is about 50 layers, or is about 60 layers, or is about 70 layers, or is about 80 layers, or is about 90 layers, or is about 100 layers.

Flake thickness of graphite refers to the same tso average thickness value used to refer to the flake thickness of graphene. Again, the skilled technician in the field understands a suitable sampling regime to obtain a representative average for such properties of graphite, as they also do for graphene.

“Graphite” is used to refer not only to unfunctionalized graphite but also to functionalized graphite. Unfunctionalized graphite is graphite that is substantially free of chemical functionalization and so has a composition close to 100% carbon.

The graphite present in the coating composition according to the present invention is suitably unfunctionalized graphite.

Similarly to graphene, the “flake diameter” of a graphite sample refers to the average lateral flake dimension of the graphite flakes in the sample. Techniques for measuring the flake diameter (or lateral flake dimensions) of graphite are well known and include, for example, scanning electron micrography.

The lateral flake dimension of graphite is measured in a similar way as it is for graphene.

The lateral flake dimension of graphite is generally measured at the longest dimension of the graphite flake. The “average” lateral flake dimension, or flake diameter, refers to the d ₅ o median average, or, where stated, the mean average.

The aspect ratio of graphite is calculated in a similar way as it is for graphene. The aspect ratio of graphite refers to the value calculated by dividing the flake diameter of the graphite by the flake thickness of graphite.

As with graphene, graphite is routinely supplied by manufacturers with information about its flake diameter(s) contained. Manufacturers may list the average flake diameter of graphite in terms of its median average diameter, or in terms of its mean average diameter, or in terms of another kind of measurement.

In some embodiments of the present invention the graphite has a mean average flake diameter of at least 0.01 pm, or 0.02 pm, or 0.03 pm, or 0.04 pm, or 0.05 pm, or 0.06 pm, or 0.07 pm, or 0.08 pm, or 0.09 pm, or 0.1 pm, or 0.12 pm, or 0.14 pm, or 0.16 pm, or 0.18 pm, or 0.2 pm, or 0.22 pm, or 0.24 pm, or 0.26 pm, or 0.28 pm, or 0.3 pm, or 0.35 pm, or 0.4 pm, or 0.45 pm, or 0.5 pm, or 0.6 pm, or 0.7 pm, or 0.8 pm, or 0.9 pm, or 1 pm, or 2 pm, or 3 pm, or 4 pm, or 5 pm, or 6 pm, or 7 pm, or 8 pm, or 9 pm, or 10 pm.

In some embodiments of the present invention the graphite has a mean average flake diameter of no more than 100 pm, or 90 pm, or 80 pm, or 70 pm, or 60 pm, or 55 pm, or 50 pm, or 45 pm, or 40 pm, or 35 pm, or 30 pm, or 25 pm, or 20 pm, or 18 pm, or 16 pm, or 14 pm, or 12 pm, or 10 pm, or 9 pm, or 8 pm, or 7 pm, or 6 pm, or 5 pm, or 4 pm, or 3 pm, or 2 pm, or 1 pm, or 0.9 pm, or 0.8 pm, or 0.7 pm, or 0.6 pm, or 0.5 pm, or 0.4 pm, or 0.3 pm, or 0.2 m, or 0.1 pm, or 0.09 pm, or 0.08 pm, or 0.07 pm, or 0.06 pm, or 0.05 pm, or 0.04 pm, or 0.03 pm, or 0.02 pm, or 0.01 pm.

In some embodiments of the present invention the aspect ratio of graphite is 0.2 to 15,000, or 2 to 7000, or 5 to 2500, or 7.5 to 100.

In a preferred embodiment of the present invention the graphite is provided in the coating composition as a graphite dispersion.

Graphite products meeting these criteria are readily commercially available, and various methods of making graphite are well known.

Components

Described herein is a multi-component composition. The composition is made, broadly, by mixing the various components together; however the order and grouping of those mixings may vary.

For example, it is well understood in the art that coating compositions made be formed by mixing a ‘Part A’ set of components and, optionally, a ‘Part B’ set of components. In turn, ‘Part A’ may be made by mixing the individual components, or subsets of those, until all the ‘Part A’ components are together. ‘Part B’, if used, may be made by mixing the individual components, or subsets of those, until all the ‘Part B’ components are together.

Mixing ‘Part A’ and ‘Part B’ components initiates an epoxy/amine curing reaction. The coating composition according to the present invention was found to have a usable lifetime of up to 1 hour at 25 °C after ‘Part A’ and ‘Part B’ were mixed together.

In the present invention, a graphene dispersion or graphite dispersion is used as one of the components of 'Part A’, in order to introduce a desired amount of graphene into the final coating composition. Herein, the components of 'Part A’ may be split (notionally, or physically pre-mixing) into the ‘graphene dispersion’ or ‘graphite dispersion’ and ‘everything else except the graphene dispersion or graphite dispersion’, this latter sometimes being referred to herein as the Main Coating Formulation.

The graphene dispersion is, in general, a dispersion of graphene (discussed above) in epoxy resin.

The graphite dispersion is, in general, a dispersion of graphite (discussed above) in epoxy resin.

“Epoxy resin” is used to refer to the combination of one or more epoxy resins. In some embodiments, the epoxy resin is provided as a liquid epoxy resin. In some embodiments, the epoxy resin is provided as a solid epoxy resin. In some embodiments, the epoxy resin is provided comprising a combination of liquid epoxy resin and solid epoxy resin. Preferably, the epoxy resin comprises a bisphenol A epoxy resin, for example it is a bisphenol A epoxy resin. Most preferably, the epoxy resin comprises at least one of a bisphenol A diglycidyl ether (DGEBA) and a difunctional bisphenol A/epichlorohydrin derived epoxy resin, for example EPON 828 manufactured by Hexion.

Within the main coating formulation is included a main solvent. The “Main Solvent” is used to refer to a combination of one or more solvents which is suitable for reducing the viscosity of the coating composition. The main solvent does not include any curing agent solvent included in the coating composition described herein.

Preferably, the main solvent comprises an oxygenated solvent and/or an aromatic solvent. An oxygenated solvent is a solvent comprising oxygen-containing functional groups. An aromatic solvent is a solvent comprising aromatic functional groups. A single solvent species may be both aromatic and oxygenated, and hence fulfil both of these functions. Therefore, in certain embodiments the main solvent is a single solvent which is both oxygenated and aromatic. However, in other embodiments it may be preferable for the main solvent to comprise two distinct chemical species, one being an oxygenated solvent (which is not aromatic) and the other being an aromatic solvent (which is not oxygenated).

In a preferred embodiment of the present invention the oxygenated solvent comprises propylene glycol methyl ether and the aromatic solvent comprises xylene.

That is, in some embodiments, the present invention relates to a coating composition, comprising:

(a) epoxy resin;

(b’) xylene;

(b”) Propylene glycol methyl ether; and

(c)(i) graphene, wherein the graphene is present in the coating composition in an amount 0.01 wt% to 0.4 wt%, and the graphene has a median flake diameter of 0.5 pm to 55 pm or a mean flake diameter of 0.01 pm to 55 pm, or

(c)(ii) graphite, wherein the graphite is present in the coating composition in an amount 0.01 wt% to 0.4 wt%, and the graphite has a median flake diameter of 0.5 pm to 55 pm or a mean flake diameter of 0.01 pm to 55 pm.

The main coating formulation may include other optional components as well, such as a thixotropic agent, a dispersing agent, a colouring pigment, a mineral extender, or a diluent, or any combination thereof. It may also include an amount of epoxy resin, and/or epoxy type 1.

“Thixotropic agent” is used to refer to the combination of one or more thixotropes. The thixotropic agent is suitable for reducing settling of solid components of the coating composition and to reduce sag tendency during application of the coating composition.

In a suitable embodiment of the present invention the thixotropic agent comprises a polyamide wax thixotrope.

"Dispersing agent” is used to refer to the combination of one or more dispersing agents. A suitable dispersing agent comprises a solution of a salt of unsaturated polyamine amides and low-molecular acidic polyesters, for example ANTI-TERRA-U manufactured by BYK. “Colouring pigment” is used to refer to the combination of one or more colouring pigments.

A suitable colouring pigment is titanium dioxide, for example Tiona 595 manufactured by Cristal.

“Mineral extender” is used to refer to the combination of one or more mineral extenders. In a preferred embodiment of the present invention the mineral extender comprises talc. A suitable talc is, for example, Talc A450 manufactured by Omya.

“Diluent” is used to refer to the combination of one or more diluents. The diluent may comprise, for example, a liquid hydrocarbon resin. In a preferred embodiment of the present invention the diluent comprises an aromatic hydrocarbon resin, for example NOVARES LA 700 manufactured by Rutgers Chemicals.

“Epoxy type 1” refers to an epoxy resin that is preferably provided as a 75% solids solution in xylene. The epoxy type 1 is suitable for assisting in wetting the substrate and developing good adhesion of the cured coating film after application of the coating composition onto the substrate.

In a preferred embodiment the epoxy type 1 comprises an EPON 1001 resin manufactured by Hexion, for example EPON 1001-X-75.

Part B components, where used, generally include those ingredients directly related to curing of the coating composition. For example, Part B may comprise an amine-based curing agent, and optionally a curing agent solvent, and optionally an amine accelerator.

“Amine-based curing agent” is used to refer to the combination of one or more amine-based curing agents. In a preferred embodiment of the present invention the amine-based curing agent comprises a polyamide resin adduct such as polyamide 125, for example Polymid 125 manufactured by Allnex.

“Curing agent solvent” is used to refer to the combination of one or more curing agent solvents. The curing agent solvent is suitable for reducing the viscosity of the curing agent and optionally the amine accelerator. The inventors found that this improves pourability.

A suitable curing agent solvent comprises an oxygenated solvent. In a preferred embodiment of the present invention the curing agent solvent comprises propylene glycol methyl ether.

“Amine accelerator” is used to refer to the combination of one or more amine accelerators.

A suitable amine accelerator is 2,4,6-tris(dimethylaminomethyl)phenol (D P30), for example ANCAMINE K54 manufactured by Evonik.

In some embodiments of the present invention, no components of part B are present in the coating component. In these embodiments, the coating composition comprises part A only.

In an embodiment of the present invention, the main coating formulation has a density of no less than 1 g/L to no greater than 2 g/L, preferably no less than 1.2 g/L to no greater than 1.8 g/L, most preferably no less than 1.4 g/L to no greater than 1 .7 g/L. In an embodiment of the present invention, graphene is present in the coating composition in an amount 0.01 wt% to 0.4 wt%, preferably 0.01 wt% to 0.3 wt%, more preferably 0.01 wt% to 0.2 wt%, most preferably 0.01 wt% to 0.15 wt%.

In an embodiment of the present invention, graphite is present in the coating composition in an amount 0.01 wt% to 0.4 wt%, preferably 0.01 wt% to 0.3 wt%, more preferably 0.01 wt% to 0.2 wt%, most preferably 0.01 wt% to 0.15 wt%.

In an embodiment of the present invention, the epoxy resin is present in the coating composition in an amount 14 wt% to 20 wt%, preferably 15 wt% to 19 wt%, most preferably 16 wt% to 18 wt%.

In an embodiment of the present invention, the oxygenated solvent is present in the coating composition in an amount 2 wt% to 15 wt%, preferably 8 wt% to 15 wt%, more preferably 9 wt% to 14 wt%, most preferably 10 wt% to 12 wt%. In some embodiments no oxygenated solvent is included.

In an embodiment of the present invention, the aromatic solvent is present in the coating composition in an amount 1 wt% to 10 wt%, preferably 1 wt% to 5 wt%, more preferably 1 wt% to 4 wt%, most preferably 1 wt% to 3 wt%. In some embodiments no aromatic solvent is included.

In an embodiment of the present invention, the total weight composition of the main solvent present in the coating composition is in an amount 3 wt% to 25 wt%, preferably 9 wt% to 20 wt%, more preferably 10 wt% to 18 wt%, most preferably 11 wt% to 15 wt%.

In an embodiment of the present invention, the epoxy type 1 is present in the coating composition in an amount 3 wt% to 10 wt%, preferably 3 wt% to 8 wt%, most preferably 4 wt% to 5 wt%. In some embodiments no epoxy type 1 is included.

In an embodiment of the present invention, the thixotropic agent is present in the coating composition in an amount 0.2 wt% to 2 wt%, preferably 0.4 wt% to 1 wt%, most preferably 0.6 wt% to 1 wt%. In some embodiments no thixotropic agent is included.

In an embodiment of the present invention, the dispersing agent is present in the coating composition in an amount 0.2 wt% to 1 wt%, preferably 0.2 wt% to 0.8 wt%, most preferably 0.2 wt% to 0.6 wt%. In some embodiments no dispersing agent is included.

In an embodiment of the present invention, the colouring pigment is present in the coating composition in an amount 8 wt% to 25 wt%, preferably 8 wt% to 20 wt%, most preferably 8 wt% to 15 wt%. In some embodiments no colouring pigment is included.

In an embodiment of the present invention, the mineral extender is present in the coating composition in an amount 15 wt% to 40 wt%, preferably 25 wt% to 40 wt%, most preferably 25 wt% to 35 wt%. In some embodiments no mineral extender is included.

In an embodiment of the present invention, the diluent is present in the coating composition in an amount 3 wt% to 10 wt%, preferably 3 wt% to 8 wt%, most preferably 4 wt% to 7 wt%. In some embodiments no diluent is included. In an embodiment of the present invention, the amine-based curing agent is present in the coating composition in an amount 5 wt% to 20 wt%, preferably 5 wt% to 15 wt%, most preferably 8 wt% to 15 wt%. In some embodiments no amine-based curing agent is included.

In an embodiment of the present invention, the curing agent solvent is included in the coating composition in an amount 0 wt% to 2 wt%, preferably 0 wt% to 1.5 wt%, most preferably 0 wt% to 1 wt%.

In an embodiment of the present invention, the total amount of solvent included in the coating composition (main solvent plus curing agent solvent, if present) is 9 wt% to 22 wt%, preferably 10 wt% to 19.5 wt%, most preferably 11 wt% to 16 wt%.

In an embodiment of the present invention, the total amount of epoxy included in the coating composition (any epoxy resin present plus any epoxy type 1 present) is 14 wt% to 30 wt%, preferably 15 wt% to 27 wt%, most preferably 16 wt% to 23 wt%.

In an embodiment of the present invention, the amine accelerator is included in the coating composition in an amount 0 wt% to 2 wt%, preferably 0 wt% to 1.5 wt%, most preferably 0 wt% to 1 wt%.

Graphene Dispersion

In a preferred embodiment of the present invention the graphene is provided in the coating composition as a graphene dispersion. That is, a graphene dispersion may be mixed or blended with other components (for example other Part A components, and then Part B if present) to form the coating composition; that dispersion may persist in the mixed or blended coating composition.

A graphite dispersion may be provided similarly.

The inventors have identified several technical advantages related to providing graphene into the coating composition in the form of a graphene dispersion.

A first advantage is that graphene in the form of a dispersion is easier to control and to handle than graphene provided as a solid powder.

A second advantage is that the likelihood of exposure to airborne flakes of graphene are reduced when graphene is provided in the form of a dispersion compared to graphene provided as a solid powder. This mitigates any potential adverse health related risks associated with handling graphene materials.

A third advantage relates to the economic loss caused by graphene lost as airborne flakes. When handled as a solid powder, a substantial quantity of graphene can be lost into the air, particularly in well ventilated environments or where extraction systems are present. This loss of graphene is mitigated when the graphene is provided as a dispersion.

A fourth advantage is that graphene has been found to be more completely and efficiently dispersed in the coating composition when it is provided as a dispersion as compared to graphene provided as a solid powder. A fifth advantage is that the graphene dispersion can be incorporated with the components of the main coating formulation by low shear mechanical mixing, for example stirring. That is, high shear dispersion techniques are not necessary when the graphene is provided as a graphene dispersion. This is because graphene has already been dispersed in the graphene dispersion, so high shear dispersion techniques are not necessary when combining the graphene dispersion with the main coating formulation.

These advantages may also be found when providing graphite into the coating composition in the form of a graphite dispersion.

Preferably, the dispersion medium of the graphene dispersion or the graphite dispersion is an epoxy resin. Preferably, the weight composition of graphene in the graphene dispersion or graphite in the graphite dispersion provided in the coating composition (or by which the graphene or graphite is introduced into the coating composition) is in the range of 5 - 10% by weight, most preferably about 5% by weight.

In some embodiments the weight composition of the graphene dispersion or the graphite dispersion in the coating composition is 0.2 wt% to 8 wt%, preferably 0.2 wt% to 6 wt%, more preferably 0.2 wt% to 4 wt% and most preferably 0.2 wt% to 3 wt%.

Methods of preparing a graphene dispersion from graphene and a liquid medium will be well known to those skilled in the art. In addition, standard equipment appropriate for dispersing graphene in a liquid medium will be known to the skilled person, for example the SHRED In- Line Rotor/Stator, the Silverson Flashmix, the NETZSCH Inline Disperser PSI-Mix, the CMX solid-liquid mixer, the ILD INLINE DIMINISHEAR and the Quadro Ytron inline mixing technology. These same methods and equipment may also be used to prepare a graphite dispersion from graphite and a liquid medium.

The graphene dispersion may be manufactured by dispersing the graphene in a portion of the epoxy resin component of the coating composition. That dispersion may then be added to the other desired components of the coating composition, in any order, including the remaining portion of the epoxy resin component. The skilled person in this technical field will be aware of suitable methods for producing such mixtures.

In a preferred embodiment the epoxy resin in which the graphene is to be dispersed is preheated to reduce its viscosity. Preferably, the epoxy resin is pre-heated to 40 °C. Graphene may then be introduced into the pre-heated epoxy resin. The epoxy resin is in a liquid state after it is pre-heated.

In a preferred embodiment the graphene is introduced to the epoxy resin while it is stirred, preferably at low speed. Dispersing the graphene into the epoxy resin by high-shear mixing such as by using the standard equipment appropriate for dispersing graphene in a liquid medium described above has been found to form a homogeneous dispersion.

It would be apparent to the skilled person that for each of these equipment a range of dispersing blade diameters, dispersing blade speeds, stirring speeds, and dispersing durations can be used.

A graphite dispersion can be prepared similarly from graphite.

Measuring anticorrosive property In order to quantitatively define the extent of corrosion protection provided by the coating it is necessary to specify the requirements for the coating system along with the laboratory tests used to assess its performance.

Assessment in this work consists of scribe corrosion creep measurements as well as a general assessment of panel condition (excluding scribe areas) using the methods recommended in ISO 12944 (paints and varnishes - corrosion protection of steel structures by protective paint systems) in order to provide a more complete picture of corrosion performance.

Scribe Corrosion Creep is a key measure of coating performance and is a good indication of the long-term durability of a coating system that may be subject to mechanical damage during service. It is used as a pass fail criterium in ISO 12944 coating system evaluation, as well as other industry standards and prequalification systems.

Scribe Corrosion Creep describes the degree to which corrosion proceeds from a deliberately cut narrow rectangular flaw in a coating film (see Figure 1) and is measured after subjecting the test panels to periods of exposure in known corrosive conditions.

The rate of corrosion creep is influenced by the adhesion of the coating to the substrate and the level of mechanical properties of the coating. These can vary during the course of the testing.

Before exposure to the corrosive environment, the coating remains tightly adhered to the substrate in the scribe area, as it does over the rest of the panel face. The adhesion at the coating/substrate interface is largely a function of the chemistry at the interface.

Once the test panel is placed into the test environment, external stresses may be introduced due to e.g. heat expansion and water absorption. At the edges of the scribe, which are acting as anodic areas in the corrosion cell, adhesion is decreased by dissolution of the iron. At some point, the induced stresses in the coating are greater than the adhesion at the scribe boundaries, loss of coating adhesion results and corrosion advances. The extra volume occupied by corrosion product formed (rust) applies additional force to the film. The better the inherent coating adhesion and the more resilient the coating film is, the slower the rate of corrosion creep will be.

Uses of the coating composition

The presently described coating composition may be present in a coating system for coating a surface of a substrate. The coating system according to the present invention comprises one or more coatings produced from the present coating composition. The coating system may have one, but generally has two or more coating layers.

In a coating system according to the present invention that comprises at least two coatings, one or two of the coatings may be produced from the present coating composition. The anticorrosive property is improved in a coating system comprising two coatings, and particularly where the two coatings are produced from the present coating composition. That is, it is particularly advantageous for the coating system to comprise a plurality of coatings produced from the present coating composition, and most preferred for all coatings of the coating system to be produced from the present coating composition. In some embodiments the coating system comprises a protective topcoat layer on the outermost surface (that is, furthest from the substrate). The topcoat may be coated onto one of the coating layers produced from the present coating composition. In some preferred embodiments the protective topcoat is a polyurethane topcoat.

A particular usage of the coating composition as part of a coating system is for coating a surface of a metal substrate to reduce the rate of corrosion of that metal substrate. Suitable metal substrates include, non-limitingly, steel and aluminium. In particular cold rolled steel and hot rolled steel are suitable substrates. The cold rolled steel and the hot rolled steel may in some embodiments be smooth (that is, the coating system or coating is applied to the substrate without that substrate having been subjected to a roughening procedure such as abrasive blast cleaning). In other suitable embodiments, the substrate (such as cold rolled steel or hot rolled steel) may be ones which has been subjected to abrasive blast cleaning.

As mentioned above, the coating composition as according to the present invention may comprise an amine-based curing agent and optionally a curing agent solvent and/or an amine accelerator. The skilled person would be aware that the amine-based curing agent and optionally a curing agent solvent and/or an amine accelerator may be mixed with the remaining components of the coating composition in situ, shortly prior to being coated on a substrate.

Hence, another aspect of the present invention regards a kit of parts. The kit of parts comprises a plurality of containers, wherein a first container contains part B components and further containers contain part A components of the presently described coating composition. In one embodiment of the present invention, the amine-based curing agent and optionally the curing agent solvent and/or the amine accelerator are provided in a first container and all of the remaining components are provided in a second container.

Another aspect of the present invention relates to a method of coating a surface of a substrate, whereby one or more layers of the presently described coating composition are applied to at least a part of the substrate. The skilled person would be aware of normal methods of coating a surface of a substrate, including but not limited to brushing, spraying or rolling techniques. The coating composition may be applied onto a surface of a substrate in one or more layers, to form a single or multi-layered coating system.

Another aspect of the present invention relates to a method of coating a surface of a substrate, whereby one or more layers of the presently described coating composition are applied to at least a part of the substrate. The method involves combining the containers of the present kit of parts, then applying the combined composition onto a surface of a substrate in one or more layers to form a single or multi-layered coating system. Preferably, the combined composition is applied onto the surface of the substrate immediately after combination of the containers.

Hence, another aspect of the present invention is the provision of a coated substrate comprising a substrate and a coating system as discussed herein; that is, wherein at least a part of the substrate has a coating produced from the presently described coating composition.

One advantage of the present invention is that the present coating composition has been found to exhibit an excellent anticorrosive property even without a primer coating being coated between the surface of the substrate and the coating of the present coating composition.

Therefore, in some embodiments, the present invention relates to methods or coated substrates where the present coating composition is applied directly to an otherwise uncoated substrate. For example, where the substrate is formed from a metal material, in some embodiments the coating composition is applied directly to the metal surface in a method of the present invention. Thus, in some embodiments a coating layer formed from the present coating composition is formed directly upon the metal surface in a coated substrate of the present invention.

The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” 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. 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. The term “about” in relation to a numerical value is optional and means for example +/- 10%. Examples

EXAMPLE 1 - coating preparation

Suitable graphene is obtainable from any one of Levidian, NanoXplore, First Graphene, Anhui Juguang Information Technology Co., Ltd (formerlyXuanCheng HengWang New Materials Co. Ltd.), The Sixth Element, Neograf, Applynano and the Graphene Manufacturing Group (GMG).

The graphene used herein is HW-POW unfunctionalized graphene supplied by Anhui Juguang Information Technology Co., Ltd (formerlyXuanCheng HengWang New Materials Co. Ltd ). The average flake diameters of the graphene grades used are about 10 pm (graphene grade 1, HW-POW-Z005), about 20 pm (graphene grade 2, HW-POW-Z006) and about 50 pm (graphene grade 3, HW-PGW-Z0050). The thickness of each of the graphene grades is 3 to 5 nm. Graphene grade 1, graphene grade 2 and graphene grade 3 only substantially differ from each other by their average flake diameter property.

Suitable epoxy resins used herein are DGEBA and Epon 828 supplied by Hexion.

Suitable epoxy type 1 used herein is Epon 1001 supplied by Hexion.

Xylene and 1 -butanol used herein are each supplied by Redox.

Suitable hydrogenated castor oil used herein is THIXATROL ST supplied by Elementis.

Suitable dispersing agent used herein is ANTI-TERRA-U supplied by BYK.

Suitable titanium dioxide used herein is Tiona 595 supplied by Cristal.

Suitable talc used herein is Talc A450 supplied by Omya.

Suitable liquid hydrocarbon resin used herein is NOVARES LA 700 supplied by Rutegers.

Suitable polyamide 125 used herein is Polymid 125 supplied by Allnex.

Suitable DMP30 used herein is ANCAMINE K54 supplied by Evonik.

Suitable alternative graphenes are Levidian G1 and G3 graphene supplied by Levidian.

Levidian G1 substantially comprises non-functionalized monolayer graphene, with some double and few layer non-functionalized graphene present.

Levidian G3 comprises few layer non-functionalized graphene.

Levidian G1 has a bulk density of 30 ± 5 g/L and a specific surface area of 320 ± 20 m ² /g.

Levidian G3 has a bulk density of 60 ± 5 g/L and a specific surface area of 130 ± 5 m ² /g.

Levidian G1 graphene has a carbon content of more than 97.5% and an oxygen content of less than 2.5%. Levidian G3 graphene has a carbon content of more than 97.5% and an oxygen content of less than 2.5%.

Levidian G1 graphene has a mean lateral particle size of 0.2 ± 0.04 pm.

Levidian G3 graphene has a mean lateral particle size of 0.2 ± 0.05 pm.

SI

Coating sample S1 was prepared as follows. 1 kg of a 5% graphene dispersion in epoxy resin was prepared by dispersing 50 g of graphene grade 1 in 950 g of epoxy resin using a 100 mm diameter dispersion blade at 4000 rpm at a blade tip speed of 21 ms ^-1 . Appropriate alternative high shear dispersing equipment may be used. The skilled person in this field would certainly be aware of appropriate equipment.

A main coating formulation comprising epoxy resin 16.66 wt%; epoxy type 1 4.47 wt%; xylene 6.91 wt%; 1-butanol 5.04 wt%; hydrogenated castor oil 0.81 wt%; dispersing agent 0.41 wt%; titanium dioxide 13.54 wt%; talc 32.34 wt%; and liquid hydrocarbon resin 5.42 wt% was prepared by a high speed dispersion process commonly used in the coatings industry. The graphene dispersion produced above was incorporated into the main coating formulation at a level of 1 .34 wt% to form a part A. This could be mixed to distribute the components using high speed dispersion techniques typically used in the manufacture of common paints that may or may not comprise graphene. The graphene dispersion does not necessarily need to be subjected to high speed dispersion at this stage, but can be mixed in at low shear after all of the other solid components have been dispersed. A person skilled in this field would certainly be aware of appropriate techniques.

This part A was combined with part B curing agent components comprising polyamide 125 11.72 wt%; DMP30 0.68 wt%; and 1-butanol 0.66 wt% prior to application of the coating. It was found that the usable lifetime of the coating composition after part A was combined with part B, and hence the epoxy/amine reaction was initiated, was 1 hour at 25 °C.

S2

Coating sample S2 was prepared identically to S1 , except that graphene grade 3 was used instead of graphene grade 1.

S3

Control coating sample S3 was prepared as follows. A coating composition comprising epoxy resin 17.94 wt%; epoxy type 1 4.47 wt%; xylene 6.91 wt%; 1-butanol 5.05 wt%; hydrogenated castor oil 0.81 wt%; dispersing agent 0.41 wt%; titanium dioxide 13.59 wt%; talc 32.35 wt%; and liquid hydrocarbon resin 5.42 wt% was prepared by a high speed dispersion process commonly used in the coatings industry to form a part A.

This part A was combined with part B curing agent components comprising polyamide 125 11.72 wt%; DMP30 0.68 wt%; and 1-butanol 0.66 wt% prior to application of the coating.

Sa

Coating sample Sa was prepared identically to S1 , except that Levidian G1 was used instead of graphene grade 1. Sb

Coating sample Sb was prepared identically to S1 , except that Levidian G3 was used instead of graphene grade 1.

EXAMPLE 2 - corrosion test results

Three panels were prepared for testing to determine the performance of corrosion resistant coatings used in industrial and marine applications.

Each panel comprises 2 x 150 pm coatings prepared with the coating samples described in Example 1 , and a 1 x 50 pm polyurethane topcoat (i.e. 350 pm total).

(As explained above, graphene grade 1 refers to graphene having an average flake diameter of about 10 pm; graphene grade 3 refers to graphene having an average flake diameter of about 50 pm.)

Epoxy coating systems of 2 x 150 pm coatings and a 1 x polyurethane topcoat (i.e. 350 pm total) are typical of those used to provide high durability (15 - 25 years life as per ISO12944) in immersion and aggressive atmospheric conditions (categories as described in ISO 9223 and ISO 12944 — Im1 , Im2, Im3, C4, C5, Cx).

The evaluation method used in this screening work was largely based on the testing requirements ISO 12944 (paints and varnishes - corrosion protection of steel structures by protective paint systems) to highlight differences in performance between the various coating samples.

Sample preparation

All coating systems were applied to steel panels by a commercial coating contractor using standard pressure pot spray equipment in an industrial coating environment. The 150 mm x 100 mm x 6 mm test panels were first prepared by degreasing, then abrasive blast cleaned with garnet to surface standard ISO 8501-1 Sa 2.5, with a final surface profile of 35 pm.

The reverse sides of the panels were coated with a commercial epoxy mastic to minimise corrosion during testing.

Surface preparation and coating operations were monitored by a NACE CIP Level 3 Coating Inspector and the appropriate records are available.

All panels had a scribe introduced according to the requirements of ISO 12944-6 Annex A, see Figure 1. Panel edges were provided additional protection by dip applying a thin bead of high solids epoxy coating. All panels were cured for a minimum of two weeks before the commencement of testing.

Test Procedure

All test panels were subjected to 4200 hours cyclic corrosion testing as described in ISO 12944-9:2018 Annexe B

At 4200 hours test duration, all panels were removed, washed with fresh water and dried.

All panels were photographed at this point.

Corrosion creep was assessed according to ISO 12944-6:2018 Annex A. All scribe areas were photographed after removal of loosely adhered coating. Scribe-creep measurement was made with digital Vernier calipers that had 0.01 mm precision, at 5 mm gaps between samples.

Photographs were taken using a Sony a6000 24.3 MP APSC sensor camera using a Sony SAL50M28 50 mm macro lens with E-mount adaptor on a tripod in ambient fluorescent light. Autoexposures in the range of % s to 1 s were observed at a fixed aperture of about f-11 .

Discussion

Photographs of all panels appear in Figure 2. One panel per sample was prepared.

Results

Test Type ISO 12944-9:2018 Annexe B Cyclic Testing (4200 Hrs)-

Substrate 150 mm x 100 mm x 6 mm Hot Rolled Steel

Preparation Degrease, Abrasive Blast Clean (Garnet) to ISO 8501.1 Sa 2.5 Final

Surface Profile 35 pm

These results are illustrated in Figure 3.

Coat 1 and coat 2 refer to the first and second epoxy coatings of the 2 x 150 pm coatings prepared in accordance with Example 1. Each sample further comprises a 1 x 50 pm polyurethane topcoat. Corrosion creep refers to the corrosion creepage distance emanating from the scribe position.

Corrosion creep vs S3 refers to the corrosion creepage distance of a coating sample relative to the corrosion creepage distance of the S3 sample.

Corrosion Creep Improvement vs S3 refers to the improvement in the corrosion creepage distance of a coating sample relative to the corrosion creepage distance of the S3 sample. That is, the percentage reduction in corrosion creep distance relative to the corrosion creep distance of the S3 sample.

Observations

Small and isolated rust spots do not represent a general failure of the coating, with all panels behaving similarly.

The corrosion creep performance of coating samples P2 and P3 are significantly better than coating sample P1, having corrosion creep improvements of 45% and 43% respectively.

The corrosion creep values of coating samples P2 (3.51 mm) and P3 (3.59 mm) themselves are excellent results under these test conditions.

P2 and P3 only differ from P1 because coat 1 and coat 2 comprise graphene. P2 comprises graphene grade 1, having an average flake diameter of about 10 pm and P3 comprises graphene grade 3, having an average flake diameter of about 50 pm. It can be concluded that the improved corrosion creep performance of P2 and P3 compared with P1 is caused by the presence of graphene in the coating composition, prepared in the way as set out above.

Conclusions

Example 2 shows that the use of graphene as an additive in the epoxy coating formulation enhances its anticorrosive property. The corrosion creep performance of the 2 x 150 pm epoxy coating; 1 x 50 pm polyurethane coating systems P2 and P3 was significantly improved relative to the comparable coating where graphene is absent, P1 .

It is particularly notable that P2 and P3 demonstrate excellent creep performances with coating systems comprising 2 x 150 pm epoxy coatings comprising graphene and a 1 x 50 pm polyurethane coating (350 pm total). This is because higher film thickness systems that are designed to provide better overall barrier properties typically suffer from excessive scribe creep because of the high levels of internal stress inherent in their composition. This is a particular problem where high film thickness coatings are subject to mechanical damage during service, for example epoxy coatings at 1000 pm and above used on decks and used in work areas of offshore structures. The use of graphene in the coating composition may improve the performance of coatings in these areas.

The results obtained to date indicate the potential for graphene to enhance the properties of high-performance epoxy coating systems. In particular, scribe corrosion creep can be significantly reduced. In two epoxy coat systems, the improvement due to graphene is significant at least when present in both coats.

We infer that this is the positive result of greater tensile strength in a graphene-containing coating layer being able to better maintain adhesion, despite internal tensile stress created by solvent-evaporation induced shrinkage of the coating and under test conditions (Piens and De Deurwaerder, Progress in Organic Coatings, 2001, 43(1-3), 18-24).

EXAMPLE 3 - mechanical properties

54 is Interseal 670HS supplied by AkzoNobel.

Interseal 670HS is a widely known commercial epoxy coating. It comprises two components, namely a base (code EGA236) and a curing agent (EGA247). The base is comparable with the main coating formulation described throughout the present specification. The Curing Agent is comparable with “part B” described throughout the present specification.

S6 was prepared firstly by incorporating a graphene dispersion prepared as set out in Example 1 into the base of the Interseal 670HS formulation by a high speed dispersion process commonly used in the coatings industry. This forms the “part A” component. The graphene dispersion was incorporated into the Interseal 670HS such that the amount of graphene in the coating composition was 0.1 wt%.

The coating composition could then be mixed to distribute the components in the same way as that set out in Example 1.

Part A was combined with the curing agent of Interseal 670HS prior to application of the coating.

55 was prepared in the same way as S6 except that it does not comprise graphene. S5 was prepared by incorporating epoxy resin into the Interseal 670HS formulation in an amount equivalent to the amount of epoxy resin that comprised the graphene dispersion according to the preparation of S6.

S5 is different from S4 because it comprises an additional quantity of epoxy resin.

S5 is different from S6 only because it does not comprise graphene.

The graphene used in S6 is graphene grade 2. That is, the average flake diameter of the graphene in S6 is about 20 pm.

Mechanical testing of isolated coating films has shown that optimised levels of graphene modification can increase tensile strength by up to 44%, increase extension before break up to 103% and reduce modulus by up to 10% vs unmodified coating films (see Figures 4, 5 and 6). These results indicate the graphene modification is producing stronger, more pliable coating films.

Three coating samples were prepared for testing to determine the performance of corrosion resistant coatings used in industrial and marine applications.

Sample S6 was prepared using HW-POW grade unfunctionalized graphene supplied by Anhui Juguang Information Technology Co., Ltd (formerly XuanCheng HengWang New Materials Co. Ltd). The graphene used is graphene grade 2 and has an average flake diameter of about 20 pm. The thickness of the graphene is 3 to 5 nm.

Average measurements were obtained over 5x repeats. Individual measurements are shown as S4-1 to S4-5; S5-1 to S5-5; and S6-1 to S6-5 (Figures 4-6).