Chemical resistance

Abstract

A coating composition for protecting a substrate from chemical attack, the composition comprising a carrier medium; glass flakes; and 2D material nanoplates having at least one nanoscale dimension. Pr

Description

TECHNOLOGICAL FIELD Embodiments of the present disclosure relate to chemical resistance. Some relate to coating compositions for protecting a substrate from chemical attack. BACKGROUND In some environments, such as construction, petrochemical, infrastructure, or marine environments, a substrate requires heavy duty protection from harsh chemicals, in order to prolong the life of the substrate. The substrate could be for instance flooring, a bridge, part of a power plant or a waste water treatment plant, decking, a storage tank, chemical bunding, a concrete structure, a beam or a pipe. A coating is often applied to these substrates to provide protection against harsh chemicals, such as acids, alkalis or solvents. Known chemical resistant coatings are generally polymer-based coatings. However, many of these known coatings do not provide adequate protection for the substrate, require a thick coat, or require multiple coats. The use of thicker coatings can cause significant stress within the coating, leading to microcracking and / or disbondment, which leads to further degradation in the performance or the coating. It is therefore desirable to provide improved chemically resistant coatings to provide better protection of the substrate from chemical attack by harsh chemicals. BRIEF SUMMARY According to various, but not necessarily all, embodiments there is provided a coating composition for protecting a substrate from chemical attack, the composition comprising: a carrier medium; glass flakes; and 2D material nanoplates, the 2D material nanoplates having at least one nanoscale dimension. The 2D material nanoplates and glass flakes may be present in the composition in a ratio of between 1:10 and 1:200 by weight. Possibly, the 2D material nanoplates and glass flakes are present in the composition in a ratio of between 1:20 and 1:100 by weight. Possibly, the 2D material nanoplates and glass flakes are present in the composition in a ratio of between 1:20 and 1:50 by weight. The composition may comprise 0.01 wt.% to 1 wt.% of the 2D material nanoplates. Possibly, the composition comprises 0.02 wt.% to 0.5 wt.% of the 2D material nanoplates. Possibly, the composition comprises 0.02 wt.% to 0.1 wt.% of the 2D material nanoplates. Possibly, the composition comprises 0.03 wt.% to 0.08 wt.% of the 2D material nanoplates. The composition may comprise 1 wt.% to 25 wt.% of the glass flakes. Possibly, the composition comprises 2 wt.% to 18 wt.% of the glass flakes. Possibly, the composition comprises 5 wt.% to 15 wt.% of the glass flakes. The carrier medium may comprise a curable resin. The carrier medium may comprise at least one of an epoxy resin, a thermosetting acrylic, a phenolic resin, chlorinated rubber, an aminoplast, a urethane, a carbamate, a polyester, an alkyd resin, coal tar epoxy, a polyaspartic resin, a polyurea resin, non-isocyanate resins formed by Michael addition, a silicone, a novolak, a polyurea, a silicate, a vinyl ester, a fluoropolymer, an unsaturated polyester, or mixtures and / or combinations thereof. The 2D material nanoplates may comprise one or more of graphene, graphene oxide, reduced graphene oxide, hexagonal boron nitride (hBN), molybdenum disulphide (MoS2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), Graphyne (C), borophene (B), phosphorene (P), or a 2D in-plane or vertical heterostructure of two or more of the aforesaid materials. The 2D material nanoplates may comprise graphene-based nanoplates. The graphene-based nanoplates may comprise graphene nanoplates with 5 to 25 layers of carbon atoms. According to various, but not necessarily all, embodiments there is provided a chemical-resistant coating system comprising a coating formed from the coating 3 composition of any of the preceding paragraphs, the coating being formed on a substrate. The coating may have a dry film thickness of 50 microns to 250 microns. Possibly, the coating has a dry film thickness of 75 to 125 microns. In some embodiments, the system comprises a single layer of the coating. In other embodiments, the system comprises multiple layers of the coating. In some embodiments, the substrate is non-metallic. In other embodiments, the substrate is metallic. According to various, but not necessarily all, embodiments there is provided a method of coating a substrate comprising: applying the coating composition of any of the preceding paragraphs to the substrate. In some embodiments, the substrate is non-metallic. In other embodiments, the substrate is metallic. According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims. BRIEF DESCRIPTION Some examples will now be described with reference to the accompanying figures in which: FIG. 1 shows a graph illustrating the hardness values of various example coatings; FIG. 2 shows a graph illustrating the gloss values of various example coatings; FIG. 3 shows pictures of samples coated with a first comparative example coating after immersion in 10% lactic acid solution for 28 days; FIG. 4 shows pictures of samples coated with a first example coating after immersion in 10% lactic acid solution for 28 days; FIG. 5 shows pictures of samples coated with a second example coating after immersion in 10% lactic acid solution for 28 days; FIG. 6 shows pictures of samples coated with a third example coating after immersion in 10% lactic acid solution for 28 days; FIG. 7 shows pictures of samples coated with a fourth example coating after immersion in 10% lactic acid solution for 28 days; FIG. 8 shows a graph illustrating the retention of hardness and gloss of various example and comparative example coatings after immersion in 10% lactic acid solution for 28 days, along with the dry film thickness values for each coating; FIG. 9 shows pictures of samples coated with a first comparative example coating after immersion in 10% sodium hypochlorite solution for 28 days; FIG. 10 shows pictures of samples coated with a first example coating after immersion in 10% sodium hypochlorite solution for 28 days; FIG. 11 shows pictures of samples coated with a second example coating after immersion in 10% sodium hypochlorite solution for 28 days; FIG. 12 shows pictures of samples coated with a third example coating after immersion in 10% sodium hypochlorite solution for 28 days; FIG. 13 shows pictures of samples coated with a fourth example coating after immersion in 10% sodium hypochlorite solution for 28 days; and FIG. 14 shows a graph illustrating the retention of hardness and gloss of various example and comparative example coatings after immersion in 10% sodium hypochlorite solution for 28 days, along with the dry film thickness values for each coating. DETAILED DESCRIPTION Examples of the disclosure provide a coating composition for protecting a substrate from chemical attack, the composition comprising: a carrier medium; glass flakes; and 2D material nanoplates, the 2D material nanoplates having at least one nanoscale dimension. The glass flakes comprise a glass platelet material. The glass platelets have a high aspect ratio (i.e., a low thickness to surface area ratio). The glass flakes typically have a thickness of between 100 nm and 10 microns and lateral dimensions (i.e., width) ranging from around 15 microns to 2000 microns. In some examples, the glass 5 platelets may be made from a borosilicate glass. The glass flakes may have a thickness of 0.5 microns to 10 microns. Preferably, the glass flakes have a thickness of 1 micron to 7 microns, such as 5 microns. The glass flakes may have a D50 particle size of 5 microns to 100 microns, and preferably have a D50 particle size of 10 microns to 50 microns. Most preferably, the glass flakes have a D50 particle size of 20 microns to 40 microns. The D50 particle size can be determined using dynamic light scattering. The thickness and lateral dimensions (i.e., width) of the glass flakes referred to herein are the mean values as determined using scanning electron microscopy or atomic force microscopy. In some examples, the glass flakes are coated, in order to facilitate a stronger interaction of the glass flakes with the carrier medium. The glass flakes may be coated with a polymeric material, such as vinyl ester, acrylic or epoxy resin. In some examples, the coating composition comprises 0.5 wt.% to 30 wt.%, 1 wt.% to 20 wt.%, 2 wt.% to 18 wt.%, 5 wt.% to 15 wt.%, 7 wt.% to 13 wt.%, at least 3 wt.%, at least 5 wt.%, or 7 wt.% to 13 wt.% of the glass flakes. In some examples, the coating composition comprises 5 wt.%, 10 wt.%, or 20 wt.% of the glass flakes. The 2D material nanoplates comprise 2D materials or layered 2D materials. 2D materials (sometimes referred to as single layer materials) are crystalline materials consisting of a single layer of atoms. Layered 2D materials consist of layers of 2D materials weakly stacked or bound to form three dimensional structures. Some 2D materials or layered 2D materials might not be wholly crystalline and thus can include some amorphous content. For instance, synthetic or exfoliated graphene is known to include some amorphous content. Nanoplates of 2D materials and layered 2D materials have thicknesses within the nanoscale (i.e., less than 100 nm) or smaller and their other two dimensions are generally at scales larger than the nanoscale (i.e., greater than 100 nm). The 2D material nanoplates could also be considered as 2D material nanosheets. In some examples, the coating composition comprises 0.01 wt.% to 2 wt.%, 0.01 wt.% to 1 wt.%, 0.025 wt.% to 1 wt.%, 0.1 wt.% to 1 wt.%, 0.1 wt.% to 0.5 wt.%, 0.02 wt.% to 0.5 wt.%, 0.02 wt.% to 0.1 wt.%, at least 0.03 wt.%, at least 0.05 wt.%, or 0.03 wt.% to 0.08 wt.% of the 2D material nanoplates. In some examples, the coating composition comprises 0.025 wt.%, 0.05 wt.%, 0.1 wt.%, or 0.5 wt.% of the 2D material nanoplates. In some examples, the 2D material nanoplates and glass flakes are present in the composition in a ratio of between 1:10 and 1:200 by weight (wt.% 2D material platelets: wt.% glass flakes). Preferably, the 2D material nanoplates and glass flakes are present in the composition in a ratio of between 1:20 and 1:100 by weight (wt.% 2D material platelets: wt.% glass flakes). Most preferably, the 2D material nanoplates and glass flakes are present in the composition in a ratio of between 1:20 and 1:50 by weight (wt.% 2D material platelets: wt.% glass flakes). 2D materials may be graphene, graphene oxide, reduced graphene oxide, hexagonal boron nitride (hBN), molybdenum disulphide (MoS2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), Graphyne (C), borophene (B), phosphorene (P), or a 2D in-plane heterostructure of two or more of the aforesaid materials. Layered 2D materials may be layers of graphene (C), graphene oxide, reduced graphene oxide, hexagonal boron nitride (hBN), molybdenum disulphide (MoS2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), Graphyne (C), borophene (B), phosphorene (P), or a 2D vertical heterostructure of two or more of the aforesaid materials. The 2D material nanoplates may comprise up to 40 layers, and preferably comprise up to 25 layers. In some embodiments, the 2D material nanoplates (such as graphenebased nanoplates) have a D50 particle size of less than 45 pm, less than 30 pm, or less than 15 pm, as measured by a Mastersizer 3000. Preferably, the 2D material nanoplates are graphene-based nanoplates, such as graphene nanoplates, graphene oxide nanoplates, or reduced graphene oxide nanoplates. The graphene-based nanoplates could also be considered as carbon nanosheets. The graphene-based nanoplates typically have a thickness of between 0.3 nm and 12 nm and lateral dimensions ranging from around 100 nm to 100 pm. The graphene-based nanoplates may comprise up to 40 layers of carbon atoms, and preferably comprise up to 25 layers of carbon atoms. Most preferably, the graphenebased nanoplates comprise 5 to 25 layers of carbon atoms. Graphene-based nanoplates have been shown to provide protection from UV light, which can further protect the substrate and the remainder of the coating. The thickness of the 2D material nanoplates referred to herein is the mean thickness value as determined using scanning electron microscopy or atomic force microscopy. The number of layers in the 2D material nanoplates referred to herein is the mean number of layers as determined using scanning electron microscopy or atomic force microscopy. Graphene has many forms and growth of a film by CVD (Chemical Vapor Deposition) is well understood and can give rise to graphene films of 1-3 atomic layers. Such films are used frequently in experimentation in connection with graphene. Such techniques have limited commercial applicability because they enable only relatively small areas of film to be created or substrate to be coated. In commercial applications it is more typical for graphene to be used in the form of graphene-based nanoplates. Graphenebased nanoplates may be produced by either exfoliation of graphite or via synthetic solvothermal processes. Such graphene-based nanoplates may vary substantially in number of atomic layers, surface area, functionality and sp2 content. Such variations impact on the physical properties of the graphene such as the conductivity of the graphene. In some examples, the 2D material nanoplates comprise synthetic graphene nanoplates. In some other examples, the 2D material nanoplates comprise exfoliated graphene nanoplates. In some examples, the graphene-based nanoplates comprise graphene nanoplates, graphene oxide nanoplates, reduced graphene oxide nanoplates, bilayer graphene nanoplates, bilayer graphene oxide nanoplates, bilayer reduced graphene oxide nanoplates, few-layer graphene nanoplates, few-layer graphene oxide nanoplates, few-layer reduced graphene oxide nanoplates, graphene nanoplates of 6 to 14 layers of carbon atoms, graphene nanoplates with 5 to 25 layers of carbon atoms, graphene nanoplates with 40 or less layers of carbon atoms, graphene nanoplates with 25 to 30 layers of carbon atoms, graphene nanoplates with 20 to 35 layers of carbon atoms, graphene nanoplates with 20 to 40 layers of carbon atoms, graphene oxide nanoplates of 6 to 14 layers of carbon atoms, graphene oxide nanoplates with 40 or less layers of carbon atoms, graphene oxide nanoplates with 25 to 30 layers of carbon atoms, graphene oxide nanoplates with 20 to 35 layers of carbon atoms, graphene oxide nanoplates with 20 to 40 layers of carbon atoms, reduced graphene oxide nanoplates of 6 to 14 layers of carbon atoms, reduced graphene oxide nanoplates with 40 or less layers of carbon atoms, reduced graphene oxide nanoplates with 25 to 30 layers of carbon atoms, reduced graphene oxide nanoplates with 20 to 35 layers of carbon atoms, and / or reduced graphene oxide nanoplates with 20 to 40 layers of carbon atoms. The glass flakes and 2D material nanoplates are preferably homogeneously dispersed within the carrier medium. In some examples, the carrier medium comprises a curable resin, which may be in the form of a liquid curable resin. The curable resin may comprise an epoxy resin, a thermosetting acrylic, a phenolic resin, chlorinated rubber, an aminoplast, a urethane, a carbamate, a polyester, an alkyd resin, coal tar epoxy, a polyaspartic resin, a polyurea resin, non-isocyanate resins formable by Michael addition, a silicone, a novolak, a polyurea, a silicate, a vinyl ester, a fluoropolymer, an unsaturated polyester, or mixtures and / or combinations thereof. The resin is generally present in the coating composition in the form of the resin precursor(s) (i.e., a curable resin), rather than the cured resin. In some examples, the carrier medium comprises additional components as is conventional, such as wetting agents, dispersing agents, surfactants, solvents, adhesion promoters and / or rheology modifiers. The solvent may comprise an organic solvent such as xylene or butanol. The carrier medium may also comprise a surface wetting agent such as Tego® Wet 270. The adhesion promoter may comprise an aminosilane or an epoxysilane (such as Addid ® 911). Alternatively, or additionally, the adhesion promoter may comprise a phosphate ester (such as Lubrizol ® 2061), a zirconate (such as Manchem ® 441), a titanate (such as Ken-React® KR® 12), or a chlorinated paraffin. Some comparative example coating compositions are provided in Table 1 below, and some example inventive coating compositions are provided in Table 2 below. Table 1 Specific Comparative Comparative Comparative Comparative Comparative Component example of Example 1 Example 2 Example 3 Example 4 Example 5 component (wt.%) (wt.%) (wt.%) (wt.%) (wt.%) Curable resin Epikote ® 828 39.83% 47.92% 46.04% 42.28% 47.42% Solvent Xylene 14.94% 17.97% 17.27% 15.85% 17.78% Solvent Butanol 4.64% 5.58% 5.36% 4.92% 5.52% Wetting agent Tego ® Wet 270 0.10% 0.10% 0.10% 0.10% 0.10% Glass flake ECR Glassflake - Micronised - Grade GF003 20.00% None None None None 2D material nanoplates Genable ® G1200 1 wt.% Graphene nanoplate dispersion None 2.50% (0.025 wt.% graphene nanoplates) 5.00% (0.05 wt.% graphene nanoplates) 10.00% (0.1 wt.% graphene nanoplates) None 2D material nanoplates Genable ® G1400 15 wt.% Graphene nanoplate dispersion None None None None 3.33% (0.5 wt.% graphene nanoplates) Curing agent Curamine 32- 805 20.49% 25.93% 26.23% 26.85% 25.85% Table 2 Component Specific example of component Example 1 (wt.%) Example 2 (wt.%) Example 3 (wt.%) Example 4 (wt.%) Curable resin Epikote ® 828 37.95% 41.06% 39.79% 42.43% Solvent Xylene 14.23% 15.40% 14.92% 15.91% Solvent Butanol 4.42% 4.78% 4.63% 4.94% Wetting agent Tego ® Wet 270 0.10% 0.10% 0.10% 0.10% Glass flake ECR Glassflake - Micronised - Grade GF003 20.00% 10.00% 5.00% 10.00% 2D material nanoplates Genable ® G1200 1 wt.% Graphene 2.50% (0.025 wt.% graphene nanoplates) 5.00% (0.05 wt.% graphene nanoplates) 10.00% (0.1 wt.% graphene nanoplates) None nanoplate dispersion 2D material nanoplates Genable ® G1400 15 wt.% Graphene nanoplate dispersion None None None 3.33% (0.5 wt.% graphene nanoplates) Curing agent Curamine 32-805 20.80% 23.67% 25.56% 23.29% The example coating compositions of Table 2 comprise a carrier medium, glass flakes, and 2D material nanoplates, the 2D material nanoplates having at least one nanoscale dimension. The carrier medium in the examples of Tables 1 and 2 comprises one or more curable resins. These example compositions of Tables 1 and 2 can be formed by combining a first part with a second part. The first part comprises a curable resin and the second part comprises a curing agent. The remaining components are generally provided in the first part, but could alternatively or additionally be provided in the second part. The first and / or second parts may also comprise additional components as is conventional, such as wetting agents, dispersing agents, surfactants, solvents, or rheology modifiers. The reaction to form a coating according to some examples of the disclosure is initiated by combining the first and second parts. The curable resin reacts with the curing agent to form a cured resin, thereby forming a solid coating. In other examples, the coatings according to examples of the disclosure may be formed from a one-part composition, for example, which cures in response to exposure to an environmental stimulus. The environmental stimulus may be heat (such as a “stoving finish”), UV light, or alternatively the presence of moisture and / or oxygen on exposure to the atmosphere. In these examples, the curable resin could optionally be a self-crosslinking polymer, such that a curing agent is not required. Example resins formed from one-part compositions include alkyd resins. In the example coating compositions of Table 2, the curable resin is an epoxy resin. The composition may comprise 20 to 70 wt.% of the curable resin. Preferably, the composition comprises 30 to 55 wt.% of the curable resin. In the example coating compositions of Table 2, the 2D material nanoplates comprise graphene nanoplates. The graphene nanoplates are added to the composition as part of a dispersion. The Genable® G12001 wt.% dispersion of Tables 1 &2 is a dispersion containing 1 wt.% of commercially available synthetic graphene nanoplates (A-GNP35 which has 6 to 14 layers of carbon atoms, available from Applied Graphene Materials UK Limited, United Kingdom) stabilised in an epoxy resin matrix. The Genable ® G1400 15 wt.% dispersion of Tables 1 &2 is a dispersion containing 15 wt.% of commercially available exfoliated graphene nanoplates (A-GNP45 which has 10 to 18 layers of carbon atoms, available from Applied Graphene Materials UK Limited, United Kingdom) stabilised in an epoxy resin matrix. In the examples coating compositions of Table 2, the carrier medium further comprises a solvent. In these examples, the carrier medium includes an organic solvent, such as a xylene solvent and / or a butanol solvent. The composition may comprise 10 to 50 wt.% of the solvent. Preferably, the composition comprises 15 to 30 wt.% of the solvent. The example coating compositions of Table 2 further comprise a wetting agent, which is Tego ® Wet 270 in this case. The coating composition may comprise 0.01 wt.% to 1 wt.% of the wetting agent. Preferably, the coating composition comprises 0.05 wt.% to 0.2 wt.% of the wetting agent. In the example coating compositions of Table 2, the curing agent is an amine-based epoxy curing agent, such as Curamine 32-805. Preparation of the coating The example coating compositions of Tables 1 and 2 can be prepared firstly by making up the carrier medium. In one example method, the carrier medium is prepared by mixing the curable resin and solvents in a high-speed disperser at 700-800 rpm to ensure effective mixing, but to avoid splashing. The wetting agent, glass flake, and 2D material nanoplates are then mixed into the carrier medium at 700-800 rpm in a highspeed disperser for 30 minutes, or longer than 30 minutes if required, in order to provide a homogeneous mixture. The curing agent is then added to the composition, 12 and the composition is mixed in the high-speed disperser at 2000 rpm for 4 minutes, followed by a 2200 rpm defoaming stage. The example coating compositions described herein can be applied to a substrate, to provide a chemical-resistant coating system once the carrier medium has cured and / or dried. In some examples, the coating compositions may be applied to the substrate using a drawdown bar, with the drawdown bar thickness set to 300 microns. In other examples, the coating compositions can be sprayed onto the substrate. In some examples, the substrate is non-metallic (i.e. the bulk of the substrate is made from a non-metallic material, such as concrete, brick, or stone). In other examples, the substrate is metallic (i.e. the bulk of the substrate is made from a metallic material, such as steel or zinc). The substrate could be for instance flooring, a bridge, part of a power plant or a waste water treatment plant, decking, a storage tank, chemical bunding, a concrete structure, a beam or a pipe. In some examples, only a single layer of the coating is applied to the substrate. In other examples, multiple layers of the coating are applied to the substrate. After curing and / or drying, the 2D material nanoplates may be encased within the solidified carrier medium in the coating. Furthermore, the 2D material nanoplates and glass flakes may be homogeneously dispersed through the solidified carrier medium. The applied coating may have a dry film thickness of 50 microns to 250 microns. Preferably, the coating has a dry film thickness of 75 to 125 microns. Most preferably, the coating has a dry film thickness of 80 to 100 microns. The dry film thickness values referred to herein are the mean values. The mean dry film thickness of the coating can be measured using an ultrasonic coating thickness gauge. When the coating is applied to ferrous substrates, electromagnetic induction or a magnetic pull-off gauge can also be used to measure the mean dry film thickness. Experimental The example and comparative example coating compositions of Tables 1 and 2 were applied to blasted steel panels using a 300 micron application bar, and then were allowed to cure to provide example and comparative example coatings. Firstly, the hardness of the example and comparative example coatings were tested using a pencil hardness test. Graphite pencils of varying hardness (shown in Table 3 below) were moved across the surface of the coating. The hardness of the coating 5 relative to the graphite pencils is determined by the softest pencil that will leave a scratch on the surface of the coating. The various hardness ratings are shown in Table 3 below. Table 3 Pencil Scale Rating N / A None None 0 9B Softer B - Black 1 8B 2 7B 3 6B 4 5B 5 4B ! HB - Hard Black 6 3B 7 2B 8 B 9 HB 10 F 11 H F - Firm 12 2H 13 3H 14 4H 15 5H 16 6H Harder H -Hard 17 7H 18 8H 19 9H 20 10H 21 The hardness of the example and comparative example coatings is shown in Fig. 1. The name of the example and comparative example coatings correspond to the name of the coating composition of Table 1 or 2 from which the coating is formed (for instance, the coating titled “example 1” is formed from the coating composition titled 15 “example 1” of Table 2, and the “comparative example 2” coating is formed from the “comparative example 2” coating composition of Table 1, etc.). As shown in Fig. 1, the coating containing only glass flake (comparative example 1) with no 2D nanoplates is harder than the other coatings shown in Fig. 1. The remaining coatings have a generally similar hardness level. The gloss of the coatings was also tested using a gloss meter. The 60° gloss values for the example coatings are shown in Fig. 2. As illustrated by Fig. 2, the coatings containing glass flake (comparative example 1, and examples 1 to 4) illustrate improved gloss relative to those without glass flake. Immersion testing was then carried out on the sample coatings, to assess the chemical resistance of the various coatings when applied to a blasted steel plate. The lower half of the coated steel plates were immersed in a bath of 10% lactic acid solution for 28 days at 23 °C, and the resultant coatings following the immersion were then tested. Fig. 3 shows the plate coated with comparative example coating 1 after 28 days in the lactic acid solution. Fig. 4 shows the plate coated with example coating 1 after 28 days in the lactic acid solution. Fig. 5 shows the plate coated with example coating 2 after 28 days in the lactic acid solution. Fig. 6 shows the plate coated with example coating 3 after 28 days in the lactic acid solution. Fig. 7 shows the plate coated with example coating 4 after 28 days in the lactic acid solution. As illustrated in Figures 3 to 7, the plate coated in comparative example coating 1 shows the most visual degradation. The plate coated in example coating 1 shows less visual degradation, whilst the example coatings 2 to 4 show no substantial visual degradation. Fig. 8 is a graph illustrating the dry film thickness (DFT), the retention of hardness, and the retention of gloss of the coating samples after immersion in the lactic acid solution. The % retention of hardness is calculated by dividing the hardness value of the sample measured after immersion by the hardness value from before the immersion, and multiplying by 100. Similarly, the % retention of gloss is calculated by dividing the gloss value of the sample measured after immersion by the gloss value from before the immersion, and multiplying by 100. Comparative example coating 1 and example coating 1 were not tested after immersion in the lactic acid solution due to significant breakdown of these coatings. Example coatings 2, 3 and 4 show improved hardness 15 after immersion when compared to the comparative examples, and also show much improved gloss retention when compared to the comparative examples. Further immersion tests were carried out on steel plates coated in the example and comparative example coatings. The further tests involved immersing the lower half of the freshly coated plates in a bath of 10% sodium hypochlorite solution for 28 days at 23 °C, and then testing the resultant coatings. Fig. 9 shows the plate coated with comparative example coating 1 after 28 days in the sodium hypochlorite solution. Fig. 10 shows the plate coated with example coating 1 after 28 days in the sodium hypochlorite solution. Fig. 11 shows the plate coated with example coating 2 after 28 days in the sodium hypochlorite solution. Fig. 12 shows the plate coated with example coating 3 after 28 days in the sodium hypochlorite solution. Fig. 13 shows the plate coated with example coating 4 after 28 days in the sodium hypochlorite solution. As illustrated in Figures 9 to 13, the plate coated in comparative example coating 1 shows the most visual degradation. The example coatings 1 to 4 show no substantial visual degradation after immersion in the sodium hypochlorite solution. Fig. 14 is a graph illustrating the dry film thickness, the retention of hardness, and the retention of gloss of the coating samples after immersion in the sodium hypochlorite solution. The % retention of hardness is calculated by dividing the hardness value of the sample measured after immersion by the hardness value from before the immersion, and multiplying by 100. Similarly, the % retention of gloss is calculated by dividing the gloss value of the sample measured after immersion by the gloss value from before the immersion, and multiplying by 100. Example coatings 1 to 4 show no significant decrease in hardness after immersion. Comparative examples 4 and 5 show significant decreases in hardness after immersion in the sodium hypochlorite solution, particularly when compared to examples 3 and 4 respectively. All of the coatings show a decrease in gloss to similar levels following the immersion in the sodium hypochlorite solution. 16 There is thus described a coating composition, a chemical resistant coating system, and a method of coating a substrate with a number of advantages as detailed above and below. The coating formed from the coating composition provides a coating that is highly resistant to degradation from chemical attack by different harsh chemicals. The coating can thus provide improved protection fora substrate. The coating provides a high initial gloss value, and demonstrates improved hardness and gloss when compared to known coatings. These advantages can be achieved using a relatively thin (i.e., low dry film thickness) coating, when compared to known coatings, thereby requiring less of the coating material. Furthermore, the advantages can be achieved using a single coat, whereas known coating systems often utilise two or more coats. Without being bound by theory, it is thought that the 2D material nanoplates and glass flakes work in combination to provide a particularly effective barrier to inhibit the passage of moisture and to inhibit chemical diffusion through the coating. Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. Different carrier mediums could be used as required. For instance, the carrier medium could comprise water soluble polymers or emulsion polymers, which may be crosslinked as required. Particles of emulsion polymers are generally formed from very high molecular weight polymers, and the particles are generally not crosslinked with one another. However, if desired, polymer particles within emulsion coatings can be crosslinked using self-crosslinking reactions, such as keto-hydrazide crosslinking. The coating composition may be applied to the substrate in a number of different ways, for instance using a brush, using a roller, or by spray coating. Types of spray coating include compressed air spray methods, high volume low pressure (HVLP) spraying methods or airless spray methods. The chemical-resistant coating may be used in combination with a different type of coating on the substrate. The term coating composition used in relation to various examples herein could describe compositions prior to the addition of a curing agent, and also describe compositions after the addition of a curing agent. The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one” or by using “consisting”. In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example. Features described in the preceding description may be used in combinations other than the combinations explicitly described above. Where multiple ranges in the format "X to Y" are described in relation to a certain feature, it is understood that all ranges combining the different endpoints are also contemplated. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. The term ‘a’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon.

Claims

28 06 241. A coating composition for protecting a substrate from chemical attack, the composition comprising:5 a carrier medium;glass flakes; and2D material nanoplates, the 2D material nanoplates having at least one nanoscale dimension and a D50 particle size of less than 45 pm, less than 30 pm, or less than 15 pm, and the 2D material nanoplates comprising graphene-based 10 nanoplates which comprise 5 to 25 layers of carbon atoms.

2. A coating composition according to claim 1, wherein the 2D material nanoplates and glass flakes are present in the composition in a ratio of between 1:10 and 1:200 by weight.

153. A coating composition according to claim 2, wherein the 2D material nanoplates and glass flakes are present in the composition in a ratio of between 1:20 and 1:100 by weight.20 4. A coating composition according to claim 3, wherein the 2D material nanoplatesand glass flakes are present in the composition in a ratio of between 1:20 and 1:50 by weight.

5. A coating composition according to any of the preceding claims, wherein the 25 composition comprises 0.01 wt.% to 1 wt.% of the 2D material nanoplates.

6. A coating composition according to claim 5, wherein the composition comprises 0.02 wt.% to 0.5 wt.% of the 2D material nanoplates.30 7. A coating composition according to claim 6, wherein the composition comprises0.02 wt.% to 0.1 wt.% of the 2D material nanoplates.

8. A coating composition according to claim 7, wherein the composition comprises 0.03 wt.% to 0.08 wt.% of the 2D material nanoplates.3528 06 249. A coating composition according to any of the preceding claims, wherein the composition comprises 1 wt.% to 25 wt.% of the glass flakes.

10. A coating composition according to claim 9, wherein the composition comprises 2 wt.% to 18 wt.% of the glass flakes.

11. A coating composition according to claim 10, wherein the composition comprises 5 wt.% to 15 wt.% of the glass flakes.

12. A coating composition according to any of the preceding claims, wherein the carrier medium comprises a curable resin.

13. A coating composition according to any of the preceding claims, wherein the carrier medium comprises at least one of an epoxy resin, a thermosetting acrylic, a phenolic resin, chlorinated rubber, an aminoplast, a urethane, a carbamate, a polyester, an alkyd resin, coal tar epoxy, a polyaspartic resin, a polyurea resin, nonisocyanate resins formed by Michael addition, a silicone, a novolak, a polyurea, a silicate, a vinyl ester, a fluoropolymer, an unsaturated polyester, or mixtures and / or combinations thereof.

14. A coating composition according to any of the preceding claims, wherein the 2D material nanoplates comprise one or more of graphene, graphene oxide, reduced graphene oxide, hexagonal boron nitride (hBN), molybdenum disulphide (MoS2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), Graphyne (C), borophene (B), phosphorene (P), or a 2D in-plane or vertical heterostructure of two or more of the aforesaid materials.

15. A coating composition according to any of the preceding claims, wherein the glass flakes have a D50 particle size of 5 microns to 100 microns.

16. A coating composition according to any of the preceding claims, wherein the graphene-based nanoplates comprise graphene nanoplates with 5 to 25 layers of carbon atoms.28 06 2417. A chemical-resistant coating system comprising a coating formed from the composition of any of the preceding claims, the coating being formed on a substrate.

18. A chemical-resistant coating system according to claim 17, wherein the coating has a dry film thickness of 50 microns to 250 microns.

19. A chemical-resistant coating system according to claim 18, wherein the coating has a dry film thickness of 75 to 125 microns.

20. A chemical-resistant coating system according to any of claims 17 to 19, wherein the system comprises a single layer of the coating.

21. A chemical-resistant coating system according to any of claims 17 to 19, wherein the system comprises multiple layers of the coating.

22. A chemical resistant coating system according to any of claims 17 to 21, wherein the substrate is non-metallic.

23. A chemical resistant coating system according to any of claims 17 to 21, wherein the substrate is metallic.

24. A method of coating a substrate comprising: applying the coating composition of any of claims 1 to 16 to the substrate.

25. A method according to claim 24, wherein the substrate is a non-metallic substrate.

Images