NEW PRODUCT COMPRISING COATED SUBSTRATE PARTICLES

The present invention relates to particles having a new form of coating based on a graphitic material and/or an oxide of a graphitic material. It also relates to a method of preparing the coated particles. The coated particles of the invention have a range of advantageous properties and uses.

Background to the Invention

A number of different particulate forms of carbon and/or oxides thereof have been described in the art, along with combinations thereof with other materials. Often the other material may feature particles of a different type, with the carbon and/or oxide thereof being used to adjust the properties of the other particles.

For instance, US20130004752 describes methods for applying to a substrate a coating composition containing carbon in the form of carbon nanotubes, graphenes, fullerenes, or mixtures thereof and metal particles, which is said to be useful as an electromechanical component such as a strip conductor; US20130237404 describes a method of producing an aluminium-carbon composite material, e.g. by milling a mixture of aluminium powder and nano-graphite plates; US20140212685 describes an engine or an engine part made from Al, Mg or an alloy comprising one or more thereof, which is reinforced by nanoparticles, in particular carbon nanotubes; CN 105733318 describes a modified aluminium pigment comprising graphene oxide, which pigment is said to have good storage stability, silver- proof resistance and corrosion resistance; WO2017059866 describes a suspension containing at least one metallic, ceramic, polymeric, or solid carbon-containing material and one or more fatty acids or derivatives thereof, which is said to be useful in 3D printing processes; US20170225233 describes a method of producing a graphene-reinforced inorganic matrix composite, e.g. by high energy milling copper powder with flake graphite; WO2018051105 describes a method of forming a powder of composite material using a reinforcement precursor material containing carbon black; US20180126456 describes a nanostructure -metal matrix composite and method for production thereof, which composite includes a host metal and nanofiller dispersed in the grains of the metal, where the nanofiller can include, inter alia, carbon nanotubes, carbon nanorods and graphene; and it is reported in ACS Nano 2018, 12, 11, 11366-11375 that the optical ignition and combustion properties of micron-sized A1 particles can be enhanced by adding 20 wt% of graphene oxide.

A common feature of the approaches described in the above-mentioned documents and generally in the prior art is that when particles of carbon and/or oxides thereof are combined with substrate particles, the two particle types tend to be brought together in a way that results in a non-uniform distribution of the carbon on and/or around the substrate particles. For instance, US20130237404 describes an approach whereby aluminium powder and carbon material are added to a hexane solvent and ultrasonicated to prepare a powder mixture, which is then subjected to ball-milling for around 2 hours using zirconia balls having a diameter of about 5 mm. This yields a product which is described as deformed aluminium-carbon mixed particles.

Summary of the Invention

The present invention is based on the surprising finding that if substrate particles are milled in a certain way in the presence of a graphitic material and/or oxide thereof, it is possible to produce substrate particles having a uniform coating comprising the graphitic material and/or oxide thereof. It is also based on the finding that substrate particles featuring such a uniform coating have a range of advantageous properties and uses.

The particular milling technique needed to produce such uniformly coated particles may vary depending on, inter alia, the nature of the substrate particles and the graphitic material and/or oxide thereof, the relative amounts thereof, and the processing conditions (e.g. the apparatus, milling media, milling time, and the presence/absence of solvent and/or other additives). Generally, though, the production method is characterised in that it involves what may be considered lower energy milling than has generally been used in similar situations in the prior art. For instance, for a given combination of substrate particles, and graphitic material and/or oxide thereof, the milling techniques that can be used to produce substrate particles having a uniform coating of graphitic material and/or oxide thereof may be distinguished over those techniques that may have been used before in the art in that they are carried out using one or more of (i) a longer milling time; (ii) a lower (milling) rotational speed; and (iii) lighter milling media. Other potentially distinguishing features include the use of particular solvent types and/or further additives (such as a lubricant and/or dispersant), and/or the presence of an initial step in which the graphitic material and/or oxide thereof is dispersed in the/a solvent prior to being brought into contact with the substrate particles.

Thus, the present invention provides coated substrate particles, wherein the coating is a uniform coating comprising a graphitic material and/or oxide thereof.

The present invention also provides a method of applying to substrate particles a uniform coating comprising a graphitic material and/or oxide thereof, the method comprising milling the substrate particles in the presence of a graphitic material and/or oxide thereof; and it also provides coated substrate particles obtained or obtainable by such a method.

The present invention also provides the use of the coated substrate particles of the invention as a pigment, and it also provides (i) a product comprising coated substrate particles of the invention, which product is a varnish, paint, automobile finish, ink

(preferably a printing ink), powder coating material, polymer composition, ceramic, glass or cosmetic agent; (ii) article of manufacture which contains a coated component, wherein the coated component is obtained or obtainable by applying to said component a product as defined in point (i), and optionally further subjecting the thus applied product to one or more subsequent treatment steps; (hi) a product comprising a heat conducting component, wherein said heat conducting component comprises coated substrate particles of the invention; and (iv) a product comprising an electricity conducting component, wherein said electricity conducting component comprises coated substrate particles of the invention.

The present invention also provides a sintered material obtained or obtainable by sintering a composition comprising coated substrate particles of the invention.

The present invention also provides a printed product obtained or obtainable by printing a liquid composition comprising coated substrate particles of the invention.

Description of Figures Figure 1 shows an SEM image of A1 substrate particles, taken after 1 hour of milling in the presence of graphene nanoplatelets.

Figure 2 show the electrical conductivity in different planes for compact pellets for 2 examples of coated substrate particles.

The left hand image in Figure 3 shows an FIB cross-section by TEM of a coated substrate flake particle of the present invention, wherein the substrate particle is an A1 (aluminium) flake and the coating is graphene nanoplatelet (GNP or GnP). The GNP layer can be seen in black.

The right hand image in Figure 3 shows a bright-field image of a coated substrate flake particle, obtained using optical microscopy. The darker spots on the surface correspond to locations where the GNP deposits were relatively thick, but Raman microscopy showed signatures of GNP across the entire surface, correlating to the layer observed by TEM (in the left hand image in Figure 3).

Figure 4 shows the rate of H ₂ production for aluminium pigments in dilute acid. Evolution is fastest in the absence of the coating, and then is seen to get progressively slower as the amount of GNP used to coat the substrate particles is increased (though with the difference in going from 4 ® 8% less marked than the difference in going from 0 ® 1%, from 1 ® 2%, and from 2 ® 4%).

Figure 5 shows the change in appearance of paint compositions containing a range of different A1 flakes in terms of CIEL*a*b* after high-shear testing (relative to the equivalent untreated A1 pigment at 1). Moving left to right the bars in the graph correspond (in turn) to Examples 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 22 and 24.

Figures 6 and 7 show tensile strength test results for polycarbonate compositions and polystyrene compositions, respectively, containing A1 pigments (both coated and uncoated). In both Figures, the samples identified from top to bottom in the keys correspond to the bars moving left to right across the graphs. Detailed description

The substrate particles

Preferred features of the substrate particles for use in preparing the coated substrate particles of the invention are set out below.

The shape of the substrate particles that can be used to prepare the coated substrate particles of the invention is not particularly limited. Typically, the substrate particles comprise (and preferably are) at least one selected from flakes, spheroids, rods and platelets. In a preferred embodiment the substrate particles comprise (or are) flakes and/or spheroids, more preferably spheroids. Typically, the substrate particles are flakes or spheroids, and conveniently they are spheroids (as discussed below, spheroids may be converted into flakes during application of the coating).

The method of the present invention can be used to apply uniform coatings to substrate particles of relatively small size. Typically, the substrate particles have a d ₅₀ value (prior to application of the coating) of at least 0.01 mm, more preferably 0.05 mm and most preferably 0.1 mm. In some applications the substrate particles will typically have a higher d ₅₀ value such as at least 0.5 mm, at least 1 mm, at least 2 mm, or at least 5 mm, but in some cases smaller particle sizes may be appropriate.

Similarly, the method of the present invention can be used to apply uniform coatings to substrate particles of relatively large size. Typically, though, the substrate particles have a d ₅₀ value (prior to application of the coating) of no more than 5000 mm, such as no more than 4000 mm, no more than 3000 mm, no more than 2000 mm, no more than 1500 mm, no more than 1000 mm, no more than 500 mm, no more than 200 mm, no more than 150 mm, and usually no more than 120 mm. For some applications, d ₅₀ values of no more than 70 or no more than 50 mm are most appropriate.

Ranges of d ₅₀ values (prior to application of the coating) which may be preferred for some applications of the coated substrate particles are 0.1 to 200 mm, 0.5 to 150 mm, and 1 to 120 mm. The d ₅₀ value is preferably measured by a laser diffraction method, and more preferably it is measured in accordance with ASTM B822-17.

When the substrate particles comprise (or are) flakes and/or platelets, the aspect ratio of the flakes and/or platelets is not particularly limited. The average aspect ratio may be, for instance, at least 2, such as at least 5, at least 10, at least 25 or at least 50. Typically, it is no more than 2000, such as no more than 1500, no more than 1000, or no more than 500. The average aspect ratio may be measured by taking the average (mean) aspect ratio of 30 (preferably 50, more preferably 100) individual flakes or platelets in the flake or platelet products as measured by microscopy, such as by scanning electron microscopy (SEM), transmission electron microscopy (TEM) or atomic force microscopy (AFM), wherein the aspect ratio for a given flake or platelet is defined as the longest diameter of the flake or platelet divided by the thickness. Preferably, the aspect ratios of the individual flake or platelet products are measured by scanning electron microscopy, e.g. using a Hitachi TM 4000PLUS apparatus.

In one embodiment which is preferred for some applications, the substrate particles are flakes having a d ₅₀ value of 0.1 to 200 mm and an average aspect ratio of 2 to 500. For instance, in some cases the substrate particles may be flakes having a d ₅₀ value of 1 to 50 mm and an average aspect ratio of 5 to 50.

Typically, the substrate particles have an average (mean) Max Feret value (prior to application of the coating) of at least 0.01 mm, more preferably at least 0.05 mm, and most preferably at least 0.1 mm. In some applications the substrate particles will typically have a higher average Max Feret value such as at least 0.5 mm, at least 1 mm, at least 2 mm, or at least 5 mm, but in some cases smaller particle sizes may be appropriate.

Similarly, the method of the present invention can be used to apply uniform coatings to substrate particles of relatively large size. Typically, though, the substrate particles have an average Max Feret value (prior to application of the coating) of no more than 5000 mm, such as no more than 4000 mm, no more than 3000 mm, no more than 2000 mm, no more than 1500 mm, no more than 1000 mm, no more than 500 mm, no more than 200 mm, no more than 150 mm, and usually no more than 120 mm. For some applications, average Max Feret values of no more than 70 or no more than 50 mm are most appropriate. Ranges of average Max Feret values (prior to application of the coating) which may be preferred for some applications of the coated substrate particles are 0.1 to 200 mm, 0.5 to 150 mm, and 1 to 120 mm.

The average Max Feret value is preferably measured by optical microscopy. The average is the mean value, and is taken for at least 30 (preferably 50, more preferably 100) individual substrate particles. The relative standard deviation for the Max Feret value (calculated as 100 * standard deviation / mean) is preferably no more than 100 %, such as no more than 70%, or no more than 50%. There is no particular lower limit for the relative standard deviation though typically it is no less than 10 %, such as no less than 20 %.

The substrate particles preferably comprise (or are) a metal (e.g. aluminium or copper), alloy (e.g. steel or any alloy of Ni or Ti), metal oxide (e.g. iron oxide), ceramic (e.g. mica or glass, or other metalloid non-metal compounds) or polymer (e.g. polycarbonate, polystyrene or acrylic). Alternatively the substrate particles may comprise (or be) a mixture of one or more thereof, but typically it is convenient to use a single material.

When the substrate particles comprise (or are) metal they may optionally have an outer layer composed of an oxide of the metal.

In a preferred embodiment the substrate particles comprise (or are) at least one selected from (i) metal particles (e.g. aluminium or copper particles), (ii) alloy particles (e.g.

particles of steel or any alloy of Ni or Ti), (iii) metal oxide particles (e.g. iron oxide particles), (iv) ceramic particles (e.g. particles of mica or glass, or other metalloid non- metal compounds), and (v) polymer particles (e.g. polycarbonate, polystyrene or acrylic particles), wherein when the substrate particles are metal particles they may optionally have an outer layer composed of an oxide of the metal. For some applications the substrate particles are preferably metal particles and/or metal particles having an outer layer composed of an oxide of the metal. Illustrative options for the substrate particles include aluminium particles, bronze particles, copper particles, titanium particles and zinc particles (with aluminium particles being convenient for many applications), wherein in each case the metal particles optionally have an outer layer composed of an oxide of the metal.

When the substrate particles are metal particles which may optionally have an outer layer composed of an oxide of the metal, the average proportion of metal in the particles is preferably ³90%, such as ³95%, ³98%, ³99%, ³99.5% or ³99.9% by weight of the total weight of the uncoated metal particles.

In one preferred embodiment of the invention, the substrate particles are aluminium pigment flake particles. The preferred options outlined above for d ₅₀ and aspect ratio apply generally to all aspects of the invention but are particularly relevant to this embodiment. For instance, the pigment flakes preferably have a d ₅₀ value of 0.1 to 200 mm and an average aspect ratio of 2 to 500, and more preferably a d ₅₀ value of 1 to 50 mm and an average aspect ratio of 5 to 50.

The substrate particles for use in the invention may be produced by known means. For instance, when the substrate particles are metal flake particles (optionally having an outer layer composed of an oxide of the metal), they may be made by a conventional milling process, e.g. ball-milling, bead milling or horizontal milling, with ball-milling preferred (the starting material is not particularly limited, but may typically be a metal powder). Suitable substrate particles are also available commercially. Examples of suitable commercially available products include Sparkle Silver Ultra® 6555 (SSU 6555) aluminium flakes, Royal Metal Powders Cl 15, Grade 5 titanium powders, and Lexan- 121R.

The coating

The coating of the coated substrate particles of the invention comprises a graphitic material and/or oxide thereof.

A graphitic material is one that has a structure corresponding to or resembling that of graphite, and in particular a material which features planes of carbon atoms arranged in hexagonal arrays. Preferably the graphitic material and/or oxide thereof comprises at least one selected from graphite, graphene, graphene oxide, reduced graphene oxide, carbon black, carbon nanoparticles and carbon nanotubes. Typically, the graphitic material and/or oxide thereof is graphite, graphene, graphene oxide, reduced graphene oxide, carbon black, carbon nanoparticles and carbon nanotubes. For some applications graphene, graphene oxide and reduced graphene oxide may be preferred, particularly graphene. The coating is preferably obtained or obtainable by milling the (uncoated) substrate particles in the presence of a graphitic material and/or oxide thereof, for example graphite, graphene, graphene oxide, reduced graphene oxide, carbon black, carbon nanoparticles and/or carbon nanotubes. More preferably the coating is obtained or obtainable by milling (uncoated) substrate particles in the presence of at least one selected from graphene, graphene oxide and reduced graphene oxide, and most typically in the presence of graphene. In this regard, the graphitic material and/or oxide thereof may conveniently be in the form of nanoparticles, e.g. nanoflakes or nanoplatelets. For instance, when the graphitic material and/or oxide thereof is graphene, it may conveniently be in the form of graphene nanoplatelets (GNP). Suitable reagents for the graphitic material and/or oxide thereof - e.g. GNP reagents - are commercially available. The GNP reagents are typically aggregates (or stacks) of platelets having a d ₅₀ value of no more than 50 mm (typically no more than 25 mm). The platelets typically have a d ₅₀ value of at least 0.1 mm, such as at least 0.2 or at least 0.5 mm. The platelets typically have a thickness of 1 to 10 nanometers. The platelets typically have a surface area of at least 30 m ² /g. In some cases high surface areas are possible, such as up to 1000 m ² /g.

For the coated substrate particles of the invention, it is not necessary for the uniform coating to fully encapsulate the substrate particles in order for the beneficial effects of the invention to arise. Indeed, for many applications of the coated particles, once a relatively high level of surface coverage is achieved (e.g. at least 50 %), there may be limited benefit to further increasing the coverage with the aim of approaching complete coverage. Thus, the uniform coating on the coated substrate particles may cover the substrate particles partially or completely, provided of course that the coating is uniform (meaning it is not present, for instance, in the form of distinct lumps of graphitic material and/or oxide thereof which may be dotted over the surface of the substrate particles, separated by gaps where there is little or no graphitic material and/or oxide thereof).

Intraparticle properties of the coated substrate particles

Preferably the surface coverage of the coating as measured by Raman microscopy on an intraparticle basis is at least 20 %. In other words, there is present a plurality of coated substrate particles, for each of which the proportion of the surface of the substrate particle which is covered by the coating, as measured by Raman microscopy, is at least 20 %. More preferably the surface coverage is at least 30 %, such as at least 40 %, at least 50 %, at least 60 %, at least 70 % or at least 80 %.

Preferably the relative standard deviation for the intraparticle thickness of the coating (RSD ¹ ) is≤50 %, wherein RSD ¹ is calculated as follows:

RSD ¹ = 100 * a ¹ / m ¹ wherein:

- coating thickness is measured by transmission electron microscopy (TEM); m ¹ is the mean thickness of the coating; and

a ¹ is the standard deviation for the thickness of the coating.

More preferably RSD ¹ is≤45 %, such as≤40 % or≤35 %.

For embodiments wherein the intraparticle RSD ¹ is defined in the manner described above, it is particularly preferred for the coated substrate particles to have a d ₅₀ value ³0.1 mm, such as ³0.2 mm, ³0.5 mm or ³1 mm. Preferably the mean intraparticle thickness of the coating as measured by TEM (p ¹ ) is ≤100 nm, such as≤90,≤80,≤70,≤60, or≤50 nm. For some applications lower thicknesses may be suitable, such as≤45,≤40,≤35,≤30,≤25,≤20, or≤15 nm. As regards the lower limit for the mean intraparticle thickness, for some applications a coating be as thin as a single sheet of graphene may be enough to yield the beneficial effects of the present invention, though more typically the mean intraparticle thickness is ³0.5 nm, such as ³1 nm, ³ 2 nm, ³3 nm, ³4 nm, or ³5 nm.

Preferably the intraparticle relative intensity variation (RlY _Particle ) is≤ 50 %, wherein RIV _Particle is calculated as follows:

RlV _Particle ⁼ 100 * hlt.Var. _Particle / A Vg.Int. _Particle wherein: intensity refers to (the intensity of) light reflectance as measured by a microscope reflectance photometry method;

Int.Var. _Particle is the standard deviation of intensities in the target area; and Avg.Int. _Particle is the mean intensity in the target area.

More preferably RIV _Particle is≤45 %, such as≤40 %,≤35 % or≤30 %.

In a number of instances above and also generally herein, preferred intraparticle properties have been disclosed, i.e. the property at issue is one that is measured for an individual particle. The invention relates to such individual particles when present in the form of a plurality of such individual coated substrate particles. In this regard, in some instances the coated substrate particles of the invention may be present in combination with other particles that do not enjoy the specified intraparticle properties of the coated substrate particles of the present invention. For instance, a sample of coated substrate particles of the present invention may be mixed with a sample of coated substrate particle of another type having a non-uniform coating, and/or due to unavoidable variance in manufacturing methods carried out on an industrial scale the production of the particles of the invention may result in a product which includes a modest amount of particles that do not feature the uniform coating which characterises the particles of the present invention. For instance, in embodiments of the invention where the surface coverage of the coating as measured by Raman microscopy on an intraparticle basis is at least 60 %, the coated substrate particles may be present in the form of a sample which also contains some particles wherein the surface coverage of the coating as measured by Raman microscopy on an intraparticle basis is less than 60 %. For most applications, though, it is desired for the coated substrate particles of the invention to be present in the form of a plurality of coated substrate particles, the majority of which satisfy the preferred intraparticle properties. Thus, for each of the intraparticle properties mentioned herein, independently, the coated substrate particles of the invention are preferably present in the form of a plurality of coated substrate particles, at least 50% of which satisfy the intraparticle property, more preferably at least 60 %, such as at least 70 %, at least 80 %, at least 90 % or at least 95 %. In each case, the proportion of coated substrate particles which satisfy the intraparticle property is typically determined by measuring the property for 30 arbitrarily selected coated substrate particles. In instances where greater accuracy is required, it may alternatively by determined by measuring the property for 100 arbitrarily selected coated substrate particles.

Interparticle properties

Preferably, there is present a plurality of coated substrate particles, for each of which the proportion of the surface of the substrate particle which is covered by the coating, as measured by Raman microscopy, is at least 20 %. More preferably the surface coverage is at least 30 %, such as at least 40 %, at least 50 %, at least 60 %, at least 70 % or at least 80 %. Preferably, the relative standard deviation (which, when expressed as a percentage, equals 100 * standard deviation divided by mean) in terms of the surface coverage of the coating as measured by Raman microscopy (on an intraparticle basis) is≤50 %, such as ≤40 %,≤30 %,≤20 %, or≤15 %. Preferably the mean RlV _Particle value for the particles within a sample (Avg.RIV. _Sample ) is ≤30 %, wherein:

RIV _Particle is the relative intensity variation for an individual particle and is calculated as RlV _Particle = 100 * Int.Var. _Particle / Avg.Int. _Particle ;

Int.Var. _Particle is the standard deviation of intensities in the target area - Avg.Int. _Particle is the mean intensity in the target area; and

intensity refers to (the intensity of) light reflectance as measured by a microscope reflectance photometry method.

In other words, for a sample of the particles, the mean of the RlV _Particle values for each of the particles in the sample (Avg.RIV. _Sample ) is preferably≤30 %.

More preferably Avg.RIV. _Sample is≤28 %, such as≤26 %,≤24 %,≤22 %, or≤20 %.

The mean RlV _Particle value for the particles within a sample (Avg.RIV. _Sample ) may be calculated as:

Avg.RIV . _Sample 100 * å ((Int.Var. _Particle / Avg.Int. _Particle ) / N) wherein N is the number of particles analysed. Preferably the standard deviation in the RlV _Particle values for the particles within a sample ( SD (RIV) _Sample ) is≤10 %, wherein:

RIV _Particle is the relative intensity variation for an individual particle and is calculated as RlV _Particle = 100 * Int.Var. _Particle / Avg.Int. _Particle ;

Int.Var. _Particle is the standard deviation of intensities in the target area;

- Avg.Int. _Particle is the mean intensity in the target area; and

intensity refers to (the intensity of) light reflectance as measured by a microscope reflectance photometry method.

In other words, for a sample of the particles the standard deviation in the RlV _Particle values for each of the particles in the sample (SD(RIV) _Sample ) is preferably≤10 %.

More preferably SD(RIV) _Sample is≤9 %, such as≤8 %,≤7 %, or≤6 %.

Preferably the relative standard deviation in the RlV _Particle values for the particles within a sample (RSD(RIV) _Sample ) is≤30 %, wherein:

RlV _Particle is the relative intensity variation for an individual particle and is calculated as RlV _Particle = 100 * Int.Var. _Particle / Avg.Int. _Particle

Int.Var. _Particle is the standard deviation of intensities in the target area;

- Avg.Int. _Particle is the mean intensity in the target area; and

intensity refers to (the intensity of) light reflectance as measured by a microscope reflectance photometry method.

In other words, for a sample of the particles the relative standard deviation in the RlV _Particle values for each of the particles in the sample (RSD(RIV) _Sample ) is preferably≤30 %.

More preferably RSD(RIV) _Sample is≤27 %, such as≤24 %,≤21 %, or≤18 %.

The relative standard deviation in the RlV _Particle values for the particles within a sample (RSD(RIV) _Sample ) may be calculated as:

RSD(RIV) _Sample 100 * SD(RIV) _Sample / Avg.RIV _Sample wherein SD(RIV) _Sample is the standard deviation (SD) of the RlV _Particle values within the sample.

Preferably the relative standard deviation in the Avg.Int. _Particle values for the particles (RSD(Avg.Int.) _Sample ) is≤15 %, wherein:

- Avg.Int. _Particle is the mean intensity in the target area; and

intensity refers to (the intensity of) light reflectance as measured by a microscope reflectance photometry method. In other words, for a sample of the particles the relative standard deviation in the

Avg.Int. _Particle values of each of the individual particles (RSD(Avg.Int.) _Sample ) is≤15 %.

More preferably (RSD(Avg.Int.) _Sample ) is≤14 %, such as≤13 %,≤12 %,≤11 %,≤10 % or ≤9 %.

The relative standard deviation in the Avg.Int. _Particle values for the particles

(RSD(Avg.Int.) _Sample ) may be calculated as:

RSD(Avg.Int.) _Sample = 100 * SD(Avg.Int.) _Sample / Avg. (Avg.Int.) Sample wherein:

S D (Avg.Int.) _Sample is the standard deviation in the Avg.Int. _Particle values for each of the particles in the sample, and

- Avg. (Avg.Int.) _Sample is the mean of the Avg.Int. _Particle values for each of the particles in the sample.

Unless indicated otherwise, for any interparticle properties discussed herein the interparticle property is typically determined by measuring the property for 30 arbitrarily selected coated substrate particles. In instances where greater accuracy is required, it may alternatively by determined by measuring the property for 100 arbitrarily selected coated substrate particles.

Further preferred aspects of the coated substrate particles Preferred aspects relating to the size and shape of the coated substrate particles are generally in line with those set out above for the (uncoated) substrate particles, subject to allowing for the facts that (a) the substrate particles have a uniform coating applied to them and so will be larger in size (though often only by a relatively small amount) and (b) the fact that the application of the coating via the method of the invention (which involves milling) will usually modify the shape of the particles. The extent to which the shape of the particles is modified depends of course on the milling conditions - in some cases the changes may be relatively minor (e.g. when particularly low energy milling techniques are used), but in other cases more substantial changes can be effected. This gives rise to a further potential benefit of the method of the present invention, since the method of applying the coating to the substrate particles can be used to simultaneously adapt and control the shape of the substrate particles so as to optimise their suitability for whatever application is intended for them. In this regard, it is of course known in the art that milling techniques can be used to modify the shape of particles (e.g. as noted above, milling can be used to prepare metal flakes from metal powder), and a skilled person would be able to adjust the milling conditions so as to achieve any shape modifications that may be desired. For instance, this could involve using milling techniques which, while lower in energy than those generally used in the prior art, are high enough in energy to have a flattening effect on the starting substrate particles, thereby increasing their aspect ratio. Such an approach means that coated metal flakes of relatively high aspect ratio can be prepared directly from metal powder (or metal flakes of lower aspect ratio) in a single step, without the need to employ a separate milling step before the coating is applied.

Generally, the following may be noted in connection with the shape and size of the coated substrate particles of the invention.

The shape of the coated substrate particles is not particularly limited. Typically, the coated substrate particles comprise (and preferably are) at least one selected from flakes, spheroids, rods and platelets. In a preferred embodiment the coated substrate particles comprise (or are) flakes and/or spheroids, more preferably flakes. Typically, the coated substrate particles are flakes or spheroids, and usually they are flakes.

Typically the coated substrate particles have a d ₅₀ value of at least 0.01 mm, more preferably 0.05 mm and most preferably 0.1 mm. Also, in some applications the coated substrate particles may have a higher d ₅₀ value such as at least 0.5 mm, at least 1 mm, at least 2 mm, or at least 5 mm.

Typically, the coated substrate particles have a d ₅₀ value of no more than 5000 mm, such as no more than 4000 mm, no more than 3000 mm, no more than 2000 mm, no more than 1500 mm, no more than 1000 mm, no more than 500 mm, no more than 200 mm, no more than 150 mm, and usually no more than 100 mm. For some applications, d ₅₀ values of no more than 70 or no more than 50 mm are appropriate.

Ranges of d ₅₀ values which may be preferred for some applications of the coated substrate particles are 0.1 to 200 mm, 0.5 to 150 mm, and 1 to 100 mm.

As with the uncoated substrate particles, when the d ₅₀ value of the coated substrate particles is to be determined this is preferably measured by a laser diffraction method, and more preferably it is measured in accordance with ASTM B822-17.

When the coated substrate particles comprise (or are) flakes and/or platelets, the aspect ratio of the flakes and/or platelets is not particularly limited. The average aspect ratio may be, for instance, at least 2, such as at least 5, at least 10, at least 25 or at least 50. Typically it is no more than 2000, such as no more than 1500, no more than 1000, or no more than 500. The average aspect ratio may be measured by taking the average (mean) aspect ratio of 30 (preferably 50, more preferably 100) individual flakes or platelets in the flake or platelet products as measured by microscopy, such as by scanning electron microscopy (SEM), transmission electron microscopy (TEM) or atomic force microscopy (AFM), wherein the aspect ratio for a given flake or platelet is defined as the longest diameter of the flake or platelet divided by the thickness. Preferably, the aspect ratios of the individual flake or platelet products are measured by scanning electron microscopy, e.g. using a Hitachi TM 4000PLUS apparatus.

Typically, the coated substrate particles have an average (mean) Max Feret value of at least 0.01 mm, more preferably at least 0.05 mm, and most preferably at least 0.1 mm. In some applications the coated substrate particles will typically have a higher average Max Feret value such as at least 0.5 mm, at least 1 mm, at least 2 mm, or at least 5 mm, but in some cases smaller particle sizes may be appropriate. The coated substrate particles may be of relatively large size. Typically, the coated substrate particles have an average Max Feret value of no more than 5000 mm, such as no more than 4000 mm, no more than 3000 mm, no more than 2000 mm, no more than 1500 mm, no more than 1000 mm, no more than 500 mm, no more than 200 mm, no more than 150 mm, and usually no more than 120 mm. For some applications, average Max Feret values of no more than 70 or no more than 50 mm are most appropriate.

Ranges of average Max Feret values for the coated particles which may be preferred for some applications are 0.1 to 200 mm, 0.5 to 150 mm, and 1 to 120 mm.

The average Max Feret value is preferably measured by optical microscopy. The average is the mean value, and is taken for at least 30 (preferably 50, more preferably 100) individual coated substrate particles. The average Max Feret value is preferably measured by optical microscopy. The average is the mean value, and is taken for at least 30

(preferably 50, more preferably 100) individual substrate particles. The relative standard deviation for the Max Feret value (calculated as 100 * standard deviation / mean) is preferably no more than 100 %, such as no more than 70%, or no more than 50%. There is no particular lower limit for the relative standard deviation, though typically it is no less than 10 %, such as no less than 20 %.

In one embodiment which is preferred for some applications, the coated substrate particles are flakes having a d ₅₀ value of 0.1 to 200 mm and an average aspect ratio of 2 to 500. For instance, in some cases the coated substrate particles may be flakes having a d ₅₀ value of 1 to 50 mm and an average aspect ratio of 5 to 50.

The method of the invention

The present invention provides a method of applying to substrate particles a uniform coating comprising a graphitic material and/or oxide thereof, the method comprising milling the substrate particles in the presence of a graphitic material and/or oxide thereof.

In this regard, the nature of the coating (e.g. in terms of thickness, and/or the extent of coverage) which may be desired for the coated substrate particles of the invention will depend on the particular application which is envisaged for them, but may be controlled by the ratio of the mass of graphitic material and/or oxide thereof to the surface area ratio of the substrate particles, and also by the milling conditions. On that point, the method of the present invention preferably employs lower energy milling techniques than have typically been employed in the prior art, and in particular it is preferred to employ relatively long milling times and relatively low rotational speeds. This facilitates formation of the desired uniform coating. Thus, the graphitic material and/or oxide thereof is forced onto the surface during the milling process and is believed to remain there primarily by virtue of van der Waals forces. Over time, the milling is believed to mechanically exfoliate the graphitic material and/or oxide thereof, leading to a uniform distribution thereof over the surfaces of the substrate particles.

Preferably the method of the invention comprises milling the substrate particles in the presence of the graphitic material and/or oxide thereof for at least 4 hours, such as at least 5 hours, at least 6 hours, at least 7 hours, at least 8 hours, at least 9 hours, or at least 10 hours. The upper limit for the milling time is not particularly limited. Milling could be continued for up to 200 hours and sometimes more if it is desired to maximise uniformity of the coating to a very high level, though the gains in uniformity achieved with such extended milling times tend to fall off and so in practice milling times beyond 100 hours are unnecessary for many applications. For many applications, milling times of 5 to 80 hours (such as 10 to 20 hours) are suitable.

In a typical embodiment, the milling is carried out in a cascading mill. In this embodiment the method of the invention preferably comprises milling the substrate particles in the presence of the graphitic material and/or oxide thereof at≤100 rpm, such as≤90 rpm,≤80 rpm,≤70 rpm,≤60 rpm or≤50 rpm. For efficiency the rotational milling speed is desirably not too low, though. For many applications the method may typically involve milling the substrate particles in the presence of the graphitic material and/or oxide thereof at ³4 rpm, such as ³6 rpm, ³8 rpm, or ³10 rpm.

In a preferred embodiment the method of the invention comprises milling the substrate particles in the presence of the graphitic material and/or oxide thereof for ³5 hours at≤100 rpm. In the method of the invention the amount of graphitic material and/or oxide thereof is preferably at least 0.01 %, such as at least 0.02 %, at least 0.05 %, at least 0.1 %, at least 0.2 %, or at least 0.5 % by weight based on the weight of the substrate particles. The amount of the graphitic material and/or oxide thereof is preferably no more than 50 % by weight, such as no more than 40 %, no more than 30 %, or no more than 20 % by weight based on the weight of the substrate particles.

The milling is preferably carried out in the presence of a solvent. The solvent may be organic or aqueous, although it may be noted that water may not be appropriate with some milling apparatuses. Typically, the solvent is organic, such as an ester, alcohol or hydrocarbons (e.g. white spirit, which is mixture of C _? to C12 hydrocarbons).

In some cases when the milling is carried out in the presence of a solvent, it may be beneficial to form a suspension of the graphitic material and/or oxide thereof in the solvent prior to milling. This can facilitate formation of a uniform coating. For instance, the method of the invention may comprise a first step of forming a suspension of the graphitic material and/or oxide thereof in a solvent, and then a second step of milling the substrate particles in the presence of said suspension of the graphitic material and/or oxide thereof. The suspension of the graphitic material and/or oxide thereof may be formed, for instance, by mechanical agitation and/or sonication. In one embodiment a dispersant agent, e.g. a fatty acid (such as oleic acid) may be included in the mixture of the solvent plus the graphitic material and/or oxide thereof, in order to enhance formation of the dispersion. This may reduce the time it takes to form the dispersion using agitation and/or sonication. The milling is preferably carried out in the presence of a lubricant and/or a dispersant. For instance, it may be carried out in the presence of one or more fatty acids (such as oleic acid) which can act as both a lubricant and a dispersant. The amount of the lubricant and/or dispersant, when present, may be up to 100 %, such as up to 50 %, or up to 20 % by weight based on the weight of the substrate particles. The amount is typically at least 0.1 % by weight, such as at least 1% by weight based on the weight of the substrate particles.

The milling may preferably be carried out in the presence of an antioxidant. The amount of the antioxidant, when present, is typically 0.01 to 10 % by weight based on the weight of the substrate particles. The milling media to be used in the method of the invention are not particularly limited. They may be based on e.g. a metal, an alloy or a ceramic. For instance, they may be steel, a metal oxide (e.g. zirconium oxide), a metal silicate (e.g. zirconium silicate), or glass. Preferably the milling media have a density of≤8 g/cm ³ , such as≤7 g/cm ³ ,≤6 g/cm ³ ,≤5 g/cm ³ ,≤4 g/cm ³ , or≤3 g/cm ³ . Thus, in a preferred aspect of the invention the milling media are glass (although glass may not be appropriate for all cases, such as e.g. situations where the mill is operated at a relatively high speed which could risk breaking the glass milling media).

In a preferred embodiment, the method of the invention comprises milling the substrate particles in the presence of a graphitic material and/or oxide thereof for ³5 hours at≤100 rpm, also in the presence of

(i) a solvent, and

(ii) a lubricant and/or dispersant,

wherein the amount of graphitic material and/or oxide thereof is 0.01 to 20 % by weight based on the weight of the substrate particles, and

wherein the milling media have a density of≤6 g/cm ³ .

The apparatus to be used for the milling in the method of the present invention is not particularly limited. It may for example be a ball mill, bead mill, or horizontal mill.

Typically, it is a cascading mill. Suitable apparatuses are commercially available.

Benefits and uses of the invention

The method of the present invention produces uniform coatings on substrate particles rather than simply dispersing carbon content onto them. Thus, the coated substrate particles of the present invention differ from those of prior art products containing particles in combination with a graphitic material and/or oxide thereof by virtue of the fact that the graphitic material and/or oxide thereof are present in the form of a uniform coating.

Consequently, a much larger proportion of the graphitic material and/or oxide thereof is present on the surface of the particles than will be seen with prior art products prepared by bringing together substrate particles with a graphitic material and/or oxide thereof. In this regard, the presence on the surface of the particles of a uniform coating of graphitic material and/or oxide thereof imparts the coated substrate particles with a number of interesting properties, which in turn means the coated particles may lend themselves to a range of potential uses or applications. For instance, the application of the coating to the substrate particles can be used to provide increased chemical resistance, increased thermal conductivity, increased electrical conductivity, new optical properties, and/or enhanced mechanical properties. In some instances, in particular where the substrate particles are flakes, anisotropic properties may arise. Also, the uniformity of the coating means there is a relatively high level of contact between it and the surface of the underlying substrate particle, and there is less concern about the possibility of the uncontrolled migration of graphitic materials and/or oxide thereof (e.g.) during feeding processes involving the coated particles.

In addition, the use of low energy milling in accordance with the method of the present invention can enable a more precise control of particle morphology and size distribution than is possible with the sort of high energy milling approach that has been used in the prior art. Morphology and size distribution are both critical parameters in additive manufacturing. They are particularly important for materials softer than the common titanium or Inconel alloys which currently dominate additive manufacturing in the field. The method of the present invention thus enables the provision of highly refined products of excellent quality.

Further benefits of the invention, including additional explanatory comments on some of the advantages and uses noted above, are set out below. - Appearance - materials/ formulations comprising the coated substrate particles of the invention may enjoy improved optical properties as compared to prior art pigments. For instance, when used in a formulation, visual properties, particularly for flake

morphologies, may include a uniformly darker reflection, a reduction of total brightness whilst retaining the strong metallic angle-dependent effects on brightness, enhanced opacity and/or enhanced hiding power (in one aspect, the coated substrate particles may be used is as a pigment, wherein the particles may be added to a material or formulation to impart a visual - e.g. metallic - effect). In contrast, traditional black pigments are isotropic in appearance. Additionally, the coating present in the coated substrate particles of the invention may usefully provide a functional effect on colour position - a dark gonio-apparent coating (i.e. the visual appearance of a coating made with traditional dark pigment and metallic particles) can be obtained with a high total solar reflection, which also benefits LIDAR (light detection and ranging) and RADAR (radio detection and ranging) reflection potentials. (In coatings using traditional dark pigments such as carbon black, it has been found that a similar colour appearance to that of traditional pigments can be obtained, but with improved overall reflection

capabilities. In particular the coating may provide better LIDAR (or NIR) reflection.

So the coating may be used to provide a good gonio-apparent coating, and in particular the visual appearance of a coating made with traditional dark pigment and metallic particles.)

- High shear resistance - the coated substrate particles of the invention have high shear resistance, and also lend this property to materials/ formulations comprising them. This is particularly beneficial for coating applicators (consistency of the appearance of the applied coating is desired) that subject formulations to accelerated shear degradation due to recirculation/ recyc ling numerous times through the application system.

Typically, recirculation damage is very high for traditional malleable metal flake pigments, resulting in an inconsistent appearance for applied coatings, whereas formulations comprising the coated substrate particles of the invention do not experience this issue.

- Sintered materials - particle morphology and size distribution can be critical parameters for compressed and sintered materials, and so the invention provides improved sintered products and processes: sintered materials prepared from coated substrate particles of the invention can enjoy the properties of non-sintered materials (e.g. good thermal and electrical properties). Another advantage of the present invention is that heating the particles during sintering is less of a concern (e.g. as regards the combustion reactions that are possible with some metal powders) when the coating is present.

Thermal properties - the coated substrate particles of the invention have higher thermal conductivity and emissivity than corresponding uncoated particles. This can afford superior heat management for coatings/solid systems (e.g. heat exchange systems, radiators, cookware, etc.). In addition, coated substrate particles of the invention (which, by virtue of the control of particle size, morphology, etc. provided by the present invention, ensure proper flow, good contact, and good compaction if sintered or pressed) may advantageously be used in thermal pastes, which in turn can be used to provide good thermal contact between separate elements (e.g. an energy-intensive machine and a radiator).

- Anisotropic effects - by controlling particle morphology using the method of the invention, significant anisotropic effects can be achieved: coatings or materials which transfer thermal energy preferentially in one direction over another improve the efficiency with which systems reach stable operating temperatures with minimal undesirable loss. For example, coated substrate particles of the invention (in the form of a coating, solid material or thermal paste) may give rise to more efficient radiators. The anisotropy displayed by certain graphitic materials, namely the much higher thermal conductance observed in one plane over others in this instance, may be further exploited in product design, because the present invention enables preferential alignment of graphitic materials such as graphene on the substrate interface (e.g.

through the use of an electric field).

- Electrical properties - as well as for thermal conductivity, graphitic materials display anisotropic behaviour for electrical conductivity, wherein electrical conductivity may several orders of magnitude greater in the transverse plane. It is known that conductive particles in a dielectric medium experience polarisation in an alternating electric field. For particles that contain crystalline regions or that have shape anisotropy in

polarisation, this induces a torque that acts to align the polarisation moment with the electric field; graphene and similar materials have such a shape anisotropy due to their 2D or semi-crystalline structure. Thus, the invention provides a means to preferentially align the graphitic materials to the substrate interface and, using appropriately designed morphology, coated substrate particles of the invention may be aligned in specific patterns. Using the same torque, disorientation or dispersion of particles may be introduced. Desirable appearances in coatings such as very high metallic travel in paint systems may therefore be achieved; similar effects may be obtained in resins or plastics. In cases where improved mechanical strength is desirable, electric fields may be used to provide orientation and thus increase strength by alignment, or to provide disorientation to reduce brittleness in one or more directions. The coated substrate particles of the invention also provide a means of producing electrically conductive materials, as the electric ally-c onductive carbon coating is concentrated on the surface of the substrate particles and thus exposed to electrical contact. Along with the improved control of particle morphology and size afforded by the method of the present invention, this is conducive to producing an efficient electrically-conductive ink, paste, pigment, sintered or solid material; possible applications include a conductive - potentially flexible - printed electrical contact, an EMI (electromagnetic interference) or anti-static additive, and an electrically- conductive paste for electrical systems. The coated substrate particles of the invention may also be useful in the metal paste contacts of photovoltaic devices.

The anisotropy displayed by certain graphitic materials, namely the much higher electrical conductance observed in one plane over others in this instance, may be further exploited in product design, because the present invention enables preferential alignment of graphitic materials such as graphene on the substrate interface.

Chemical resistance - the coated substrate particles of the invention, particularly at higher levels of surface coverage, can enjoy increased chemical resistance (as compared to corresponding uncoated substrate particles) to oxidising, acidic, basic, aqueous and/or other reactive environments. This property is especially useful in encapsulated systems where chemical resistance is desirable (both in end-use and formulation stability), for example sol-gels or polymer powder coating systems. Materials comprising coated substrate particles of the invention (e.g. as a coating, sintered, or solid part) may resist corrosion and therefore possible end-use applications include coatings for exposed environments, such as marine or industrial environments, and vehicle or room interiors which may be repeatedly exposed to foodstuff and/or sanitising products.

- Mechanical strength - coated substrate particles of the invention can enjoy superior tensile and mechanical strength (vs uncoated substrate particles). Thus, materials comprising the coated substrate particles may experience corresponding improvements in this regard as compared to (a) materials comprising the uncoated substrate particles alone, or (b) materials comprising the uncoated substrate particles plus an equivalent amount of graphitic material and/or oxide thereof (which is present in combination with the substrate particles, but not in the form of a uniform coating). - Downstream uses - the coated substrate particles of the invention may be used for a wide range of purposes in view of their beneficial properties. Thus, they may be incorporated into products such as varnishes, automobile finishes, paints, printing inks, powder coating materials, architectural paints, polymer compositions, security printing inks, ceramics, glass and cosmetic agents.

The present invention provides the use of the coated substrate particles of the invention as a pigment. Preferably in this regard the pigment is used in a varnish, paint, automobile finish, ink (preferably a printing ink), powder coating material, polymer, ceramic, glass or cosmetic agent.

The present invention also provides a product comprising the coated substrate particles of the invention, which product is a varnish, paint (e.g. a paint for imparting to a surface particular optical properties and/or functional/ structural performance such as chemical and/or heat resistance, such as an architectural paint), automobile finish, ink (preferably a printing ink, e.g. a security printing ink), powder coating material, polymer composition (e.g. a resin composition or a plastic composition), ceramic, glass or cosmetic agent.

The present invention also provides an article of manufacture which contains a coated component, wherein the coated component is obtained or obtainable by applying to said component a product as defined in the preceding paragraph, and optionally further subjecting the thus applied product to one or more subsequent treatment steps (e.g. a drying step, a curing step, and/or a heating step).

The present invention also provides a product comprising a heat conducting component, wherein said heat conducting component comprises the coated substrate particles of the invention.

The present invention also provides a product comprising an electricity conducting component, wherein said electricity conducting component comprises the coated substrate particles of the invention. The amount of the coated substrate particles of the invention in the products set out above is not particularly limited and may vary depending on the context and desired effect.

Typically, the coated substrate particles of the invention are present in the product (or component) in an amount of at least 0.001 % by weight, such as at least 0.01 %, or at least 0.1 % by weight. It is also typical for the coated substrate particles of the invention to be present in the product (or component) in an amount of up to 100 % by weight, such as up to 70 % or up to 50 % by weight.

The polymer compositions of the present invention comprise a polymer together with the coated substrate particles of the invention. The polymer may be polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyacrylate, polycarbonate, fibreglass or nylon.

The present invention also provides a sintered material obtained or obtainable by sintering a composition comprising the coated substrate particles of the invention.

The present invention also provides a printed product obtained or obtainable by printing a liquid composition comprising the coated substrate particles of the invention.

Examples

PREPARATION OF COATED SUBSTRATE PARTICLES OF THE INVENTION

A range of different coated substrate particle types were prepared. Unless indicated otherwise, the particles were prepared by milling substrate particles in a cascading mill in the presence of a graphitic material or an oxide thereof, dispersed in a solvent (white spirit was used as the solvent in these Examples, though of course other solvents can be used too), as set out below in Table 1, following which the milling apparatus was emptied and the coated substrate particles were duly extracted from the mixture. Examples 1 and 2 are Comparative Examples.

CHARACTERIZATION OF THE PARTICLES

Particle Size Analysis

Substrate particles may be characterised before and/or after (and/or during) application of the coating. The appropriate analysis of size and shape characteristics is often determined by the size class and/or the shape parameters which affect the end-use of the particles. For instance, in additive manufacturing, diameter and sphericity may be important parameters, whereas for rod or flake-type particles, elongation and Max Feret can be more relevant. Also, possible measurement methods may vary depending on the nature of the sample. For larger particles, d ₅₀ may be a convenient particle size parameter - unless indicated otherwise, d ₅₀ is measured using laser diffraction according to ASTM B822-17.

In addition, it is possible to carry out shape parameter analysis to characterise the particles, in particular for (e.g.) relatively small (such as≤0.4 mm) and/or non-spherical (e.g. rod) type particles - appropriate calibrated microscopy techniques such as optical microscopy and scanning electron microscopy (SEM) may be employed. Optical microscopy is preferred. For such shape parameter analysis, both static and dynamic image analysis may be employed. 100 particles (at least) are preferably analysed. In such a shape parameter analysis the instrument is adjusted to capture a substantially in-focus image of a particle, and the appropriate methodology is used to assign the boundary of the particle, typically through brightness contrast with the background. A number of parameters can then be calculated from the resulting object, including maximum fret (or Max Feret - the longest straight-line length in the object from edge to edge), equivalent diameter (the diameter of a circle with the same area as the object), ISO-defined circularity (the ratio of the inscribed and circumscribed circles for an object’s boundary), elongation (the ratio of the longest feret length perpendicular to the Max Feret length), and roughness (ratio of the perimeter of the circle of equivalent diameter to the measured perimeter length). ISO 14488 should be followed when possible for sampling.

Particle size analysis results for some of the particles from Table 1 above are set out below in Table 2. Transmission Electron Microscopy (TEM)

TEM may be used to measure the relative standard deviation for the thickness of the coating (RSD ¹ ) and the mean thickness of the coating (m ¹ ). Particles may be prepared for TEM examination by cutting them with a focused ion beam (FIB) so as to give the largest possible interface distance on the sample particle (e.g. for a flake this would be along the max fret and through the thickness of the flake, whereas for a spheroid this would be across the diameter of the sphere). FIB instruments can use a variety of ion beams to etch a target - a person of skill in the art of TEM sample preparation would be able to select appropriate conditions to provide a clean cut.

In order to measure m ¹ and RSD ¹ , the maximum magnification at which it is possible to clearly see the carbon layer-substrate interface should be used. The examined interface distance is at least 75% of the largest possible interface distance cut in the sample preparation (ideally it is 100%, i.e. all the way around), and measurements are taken every 0.5% of said distance (meaning 150 to 200 measurements at evenly spaced intervals along the interface distance are taken). Cruder forms of analysis are also possible, whereby measurements are taken (e.g.) every 5 % of said distance (meaning 15 to 20 measurements are taken), though preferably the measurements are taken every 0.5% of said distance as just mentioned above.

A coated substrate particle of Example 24 as described above in Table 1 was analysed by TEM in the following manner. A single flake lying flat on an A1 substrate was located. A 100 nm layer of protective platinum-carbon was deposited over the target area using an electron beam (to prevent ion implantation when using an ion beam). On top of this, 1.5 mm of platinum carbon was deposited using a 30 kV ion beam. The target area was then etched using the ion beam until the flake could be lifted out from the mounting substrate and placed onto a copper TEM grid. The ion beam was then used to thin the target area until the thickness normal to the carbon-substrate interface layer was sufficiently low for TEM imaging. The m ¹ (i.e coating thickness) for this flake was measured as 50.6 nm and the RSD ¹ value was 48.8%.

The left-hand side of Figure 3 shows a TEM image of a coated substrate particle of the invention (a particle from Example 24 in Table 1 above). Microscope Reflectance Photometry (MRP)

MRP may be used to measure intraparticle relative intensity variation (RlV _Particle ), the mean RIV _Particle value for a sample of the particles (Avg.RIV _Sample ), the standard deviation in the RIV _Particle values for a sample of the particles (SD(RIV) _Sample ), the relative standard deviation in the RlV _Particle values for a sample of the particles (RSD(RIV) _Sample ), the mean

Avg. Int . _Parti ( Avg.Int. _Sample ), and also the relative standard deviation in the Avg.Int. _Particle values for a sample of the particles (RSD(Int.) _Sample ).

Particles may be characterised by their light reflection properties in these ways using a microscope equipped with a camera utilising a charge-coupled device detector (CCD).

This method is particularly well suited to flakes and similar particle morphologies, where a substantial portion of the particles have planes lying within focus.

The area on individual particles which must be viewable should be at least 1/6 of the total particle surface area in focus, using an appropriate magnification level. An appropriate magnification level may be determined by resolution, wherein the target particle area should be in focus with a pixel resolution of at least 0.1 mm ² per pixel. The minimum bit depth is suitably 8-bit. For typical RGB (red, green, and blue) three-channel cameras or other multichannel CCD cameras, the preferred option is to use only one channel, preferably only the green colour channel (to avoid differences in white balancing).

Samples for examination are first washed with an appropriate solvent to prevent milling solvents, dispersants, lubricants etc. contributing to the signal. Samples are then dispersed onto a substantially flat, smooth, inert substrate, preferably glass, using air-dispersion or dispersed when suspended in a liquid. The substrate must not influence or distort the particle under examination. The dispersion should leave dry particles with enough distance between them that their perimeters are clearly distinguishable from each other.

The camera may be focused onto the plane of one particle (or multiple particles, if more than one particle target plane is in focus). Still images are taken with camera settings chosen to maintain the sample within the dynamic range of the camera under fixed illumination. For sample comparisons, the illumination and camera settings should be quantitation only if the target area is in focus and the perimeter contained completely inside the usable focus area of the camera. Unless the apparatus product literature indicates otherwise, the centre area comprising 50% of the total viewable area, in the same aspect ratio of the CCD, should be used.

The target particle area(s) may be specified by the operator or by using software functions and parameters that can be chosen to automatically identify target areas - this may include functions such as edge detection and thresholding of pixel values. For sample

comparisons, it is required to choose settings for these and similar features which can be applicable to all samples being compared.

MRP data was recorded for some coated substrate particles of the invention from Table 1 as described above and also (for comparative purposes) some other particle types. The results are set out below in Table 3. For each of the results, interparticle properties are indicated (as a general matter, interparticle properties are denoted by the presence of the term“Sample” in subscript, whereas in contrast the term“Particle” in subscript refers to intraparticle properties), and in each case N was equal to 100 (i.e. 100 particles were analysed).

Table 3: MRP results

mean of the Int.Var. _Particle values within the sample

standard deviation of the Int.Var. _Particle values within the sample

Raman Microscopy

A confocal Raman microscopy analysis was performed to evaluate the percent carbon coverage of coated substrate particles of the present invention. Confocal Raman microscopy is a high-resolution imaging technique that is used for the characterisation of materials based on their chemical composition. Raman spectra of carbon were obtained using an alpha300 RA confocal Raman and Fluorescence ZEISS microscope equipped with a thermoelectrically-cooled video charge-coupled device camera.

Samples for examination are first washed with an appropriate solvent to prevent milling solvents, dispersants, lubricants etc. contributing to the signal. Samples are then dispersed onto a substantially flat, smooth, inert substrate, preferably glass, using air-dispersion or dispersed when suspended in a liquid. The substrate must not influence or distort the particle under examination.

The objective should be chosen such that at least one whole particle may be imaged with a resolution of ³1 pixel/mm. Before irradiating the samples, the laser beam (l=532 nm) was focused using an X50 objective lens. The area for examination and integration time should be selected (whether it includes one or multiple particles) so as to give a signal to noise ratio ³0.5, wherein the signal to noise ratio is defined as the difference in peak and background signal divided by the square root of the background signal. The total collection time may depend on the laser power, area size, and integration time. To prevent damage to samples, the laser power should be≤54 mW.

The microscopy image can be colour coded to distinguish between the Raman signals from the substrate and the carbon. Image processing software, such as ImageJ, may be used to process the colour coded images to determine the percentage total area of the carbon coverage on a given particle. This percentage may be calculated by dividing the total carbon Raman signal by the surface area of the particle. Using this method, as a screener method it can be possible to obtain an indication of average surface coverage by examining at least 5 particles, more preferably at least 10 particles, such as 15 particles. As noted above, though, the property is typically determined by analysing 30 (sometimes 100) arbitrarily selected coated substrate particles. Raman microscopy examination was performed on six Examples of coated substrate particles of the invention (Examples 6, 7, 12, 17, 18 and 24 from Table 1 above), along with the particles of Example 2 (which is a Comparative Example wherein the carbon was not present in the form of a uniform coating - this was prepared using the same starting 5 substrate particles as were used to make the aforementioned coated substrate particles of the invention, and the particles were also similarly mixed wet in excess solvent with a dispersed GNP1 slurry before being filtered and dried as typical of the other examples, however no low energy milling step was not carried out). The results are summarised below in Tables 4 and 5.

PROPERTIES OF THE COATED SUBSTRATE PARTICLES, AND USES THEREOF

High speed shear degradation

To simulate the recirculation of an automotive paint through a paint-applicator system, particle pigments were subjected to accelerated shear degradation. Thin aluminium flake pigments are susceptible to damage by high shear, which in turn affects the appearance of the material, including reduced reflection at near-specular angles and increased reflection at angles far from specular. Other changes to the visual appearance may be loss of gloss, loss of‘face’ (near-specular) brightness, increase in‘flop’ (far from specular) brightness and reduction in‘travel’ (flop index or rate of change in brightness from near- to far-from- specular angles). Test results may not be directly interpretable as mechanical strength but can be compared against a desired performance rating (i.e. the amount of change in an appearance measurement caused by the relevant modification to the composition). Paints were formulated using coated substrate particles and comparable uncoated substrate particles in an acrylic thermoset resin. The same resin was used when applying a protective topcoat. The flow rate of the coating formulations was measured and adjusted to 17 seconds using a #4 Ford cup using a xylene solvent. Using a Waring Blender base with explosion-proof motor (5BA 60VL66, Type BA) and a water-jacketed stainless steel blender (Waring SS510C), a portion of the formulated paints were exposed to high-speed shear for 8 minutes at 15,300 rpm. Paints were then applied to uncoated steel Q-panels, using identical spraying parameters on an automated spray applicator, and cured. After curing, the topcoat was applied using identical spraying parameters for all panels on an automated spray applicator, and then cured.

Colour data was collected according to ASTM E 2194-14(2017), using a BYK-mac i 23 mm multiangle spectrometer. The anormal illumination angle was fixed at 45°.

Observations were taken at the -15°, 15°, 25°, 45°, 75° and 110° aspecular angles. A D65 illuminant, as specified in ASTM D 1729 (2016), was used as the light source.

Different application methods and conditions (including environmental conditions, substrates and resin variations) may influence test results. Insofar as possible, samples of equivalent, uncoated substrates were prepared and tested identically to each sample to provide standards. Values derived from standards may be used to compare previous results to confirm the quality of the testing conditions, and to normalise results. For instance, the absolute L ^* a ^* b ^* of a particular aspecular angle for a given sample may instead be reported 5 as DL ^* Da ^* Db ^* with reference to the standard. For most samples, å _{All Angles} DL ^*

where 1 and 2 refer to sample measurements on systems with and without

shear applied, is sufficient information to characterise the degradation of a sample. For normalisation between application conditions, the results for samples containing coated particles of the invention are reported as a percentage, %AL*standard, of the comparable 10 uncoated particles standard’s å _{All Angles} DL ^* . Lower values of %DL ^* standard indicate less shear-induced change to the appearance of the applied coating.

Some of the particles described above in Table 1 were tested in accordance with the above protocol. The results are summarised below in Table 6 and also in Figure 5.

15

Table 6: Shear resistance test results

Example Shear resistance improvement compared to standard (%AL*standard )

1 0.0

2 13.1

3 61.0

4 89.2

5 93.8

6 96.9

7 90.3

8 81.5

9 91.9

10 81.8

11 95.9

12 92.7

13 80.0

14 68.9

15 86.0

16 61.3

17 89.9

18 93.4

22 92.2

24 70.2

For samples which experience (or are expected to experience) significant colour shifts in hue or chroma with shear damage, total colour difference calculations are performed using the CIE76 DE ^* formula. DE ^* is calculated between samples sprayed with identical formulations prepared with and without shear. For normalisation between application conditions, the results for samples containing coated substrate particles are reported as a percentage, %DE ^* _standard , of the comparable uncoated particles standard’s DE ^* . Lower values of %DE ^* _standard indicate less shear-induced change to the appearance of the applied coating. Thirteen different sample types were tested in this manner and the results summarised in Figure 5.

The test data discussed above illustrate that the coated substrate particles of the invention enjoy significantly enhanced resistance to shear degradation, and that this enhanced resistance is attributable to the fact that the graphitic material is present in the form of a uniform coating.

Chemical resistance

Aluminium materials tend to be sensitive to corrosion by acidic and/or basic solutions.

Such corrosion generally leads to the evolution of H ₂ gas. Samples of the particles of Examples 1, 5, and 24 from Table 1 above (all of which were based on the same A1 pigment as the starting substrate particle) were tested for corrosion resistance, by measuring the time taken for 10 ml of H ₂ gas to evolve from samples in a 0.5 M HCl (aq) solution at standard temperature and pressure. The same starting A1 substrate (pigment) particles were used in each case, but the amount of graphitic material present in the form of a uniform coating was varied. The testing apparatus consisted of a sealed testing vessel connected by a tube to a glass burette. The burette was then suspended upside down, with the lower portion containing the tube submerged in deionised water, and water was drawn up into the burette by vacuum. Before sealing, the testing vessel was filled with 40 ml of 0.5 M HCl, to which 0.5 g of the particles being tested had been added. The vessel was connected to the burette and gently agitated to ensure the material wetted, and the time taken to evolve 10 ml of gas was recorded. The results are summarised in Figure 4 and show that application of the coating of the present invention improves the chemical resistance of the A1 particles.

Thermal Conductivity Thermal conductivity and effusivity measurements were taken for a sample of coated substrate particles of the invention plus a sample of corresponding uncoated substrate particles, using a C-Therm TCi Thermal Conductivity Analyser with the Modified

Transient Plane Source (MTPS) configuration. The MTPS method is well-suited for the analysis of solids, liquids, powders, pastes, textiles and similar materials. The system was operated in accordance with a modified ASTM D7984 protocol (humidity not controlled and temperature kept at 23 °C). A liquid test cell was used for powder sample

measurements as follows: the liquid test cell accessory was placed over a sensor housing, powder was placed into the cell over the sensor surface, ¼ of a teaspoon at a time, until the cell was full of powder, and then a 75 g powder compaction weight was applied to the sample to ensure sufficient consistency of measurement. The results are summarised in Table 7. The composite sample showed a 12.1% higher thermal conductivity and 19.9% higher effusivity for the coated substrate particles of the invention as compared to the

corresponding uncoated particles. For both parameters the results are significant given that the accuracy rating for the MTPS method is within 5% or better of the measurement. Table 7: Thermal conductivity test results (N=5).

Tensile strength

Metal effect pigments are often combined with polymers. However, adding metal pigments to a polymer (e.g. a plastic material) can affect the tensile strength of the polymer. The tensile strength of plastics comprising various different types of particles were assessed according to ASTM D638M. First 3% metal pigment was mixed in polycarbonate and general purpose polystyrene, then the plastic was extruded to produce metal-containing polycarbonate and polystyrene pellets. The pellets were added to a Boy 55A injection moulding machine and dogbone-shaped plastic specimens, with thickness under 14 mm, were produced. The dogbone shaped plastics were then tested using a Lloyd T5K series tensile tester. A minimum of five specimens within a sample were tested. The results are summarised in Figures 6 and 7. In the case of polycarbonate (Figure 6), the addition of the metal pigments increases the tensile strength, with the coated metal pigments of the invention performing better than uncoated metal pigments at each of the different amounts used (i.e. when the metal pigments are added in an amount of 1 %, 3 %, and also 5 %). In the case of polystyrene (Figure 7), the addition of the metal pigments reduces the tensile strength, but the coating of the present invention was found to significantly reduce this loss of tensile strength. Improvements are seen relative to both (a) uncoated metal particles, and also (b) metal particles which are used in combination with a graphitic material but wherein the graphitic material is not present in the form of a uniform coating. Impact strength

Adding metal effect pigments to polymers can adversely affect the impact resistance of the polymers. Polymer compositions containing coated substrate particles of the invention wherein the substrate is a metal pigment have been found to enjoy greater impact resistance than equivalent compositions wherein corresponding uncoated particles are used, when tested according to ASTM D6110. In each case, 3% by weight of the particles was mixed with general purpose polystyrene and then plastic extrusion was carried out to produce metal-containing polystyrene pellets. The pellets were then added into an injection molding machine to produce specimens with a dimension! 25.7 x 12.1 x 6.5 mm using a Boy 55A injection molding machine. The specimens were then V-notched before being subjected to impact testing. A first composition comprising particles of Example 11 as set out in Table 1 above was found to lead to increased impact resistance as compared to a second composition containing corresponding uncoated particles instead. Electrical conductivity

Compact pellets comprising two different types of coated (Al) substrate particles were subjected to electrical conductivity testing. Conductivity was measured both parallel and perpendicular to test for the possible presence of an anisotropic properties. In particular, pellets were prepared by cold-pressing coated substrate particles of the invention at 10.8 kN (approximately 850 MPa for 12.7 mm diameter cylindrical samples). A 2-point probe was used to test the conductivity through the center of the pellet using the maximum straight-line distance at mid-height. Due to the morphology of the particles, there are orientations in which this path is substantially parallel to the largest facets of the coated particles or perpendicular to them. The results are set out in Figure 2.

Sintered materials

Sintered materials prepared from coated substrate particles of the invention can offer improved chemical resistance, thermal conductivity, tensile strength, thermal degradation, impact strength and shear degradation. The procedure and conditions for preparation of such sintered materials may vary depending on the exact nature of the particles being used and the intended application. However, methods of preparing sintered materials (e.g. using a hot press, isostatic hot press, or cold press and sinter approach) are known in the art and persons of skill in the art would be able to apply these known techniques to processes of making sintered materials using coated substrate particles of the invention.

A sintered product was prepared using coated substrate particles of the present invention in the following manner. The coated metal pigments were first washed with acetone to remove lubricant (oleic acid) on the surface and dried to completion using oven. The metal pigments in the form of 20mm x 20mm samples were cold-pressed at 107.9 kN (giving a pressure of approximately 270 MPa). The green density for the pellets was ³85% before sintering. The pellets were then sintered at 540°C ±5° for 6 hours under nitrogen flow.

An illustrative design of experiment (DOE) for identifying further suitable sintering methods for a given situation is set out below.

Exemplary DOE for sintered products Pellets are prepared by cold-pressing coated substrate particles of the invention at 107.9 kN (approximately 850 MPa) for 12.7 mm diameter cylindrical samples. To identify suitable conditions for a given coated substrate particle, nine pellet samples may be heated to sintering in an inert atmosphere under the following temperatures and pressures:

Optimum process conditions may then be identified depending on the objective (e.g. level of performance desired vs practical and/or cost considerations).

The following two prophetic Examples A and B could serve as a starting point on which an alternative DOE for identifying a suitable sintering process could be based. A A sintered material could be prepared using the coated substrate particles of the invention wherein the substrate particles are aluminium flakes having a d ₅₀ value of 15 mm. The mixture is then compacted under a pressure of 350 MPa, followed by sintering at 560 °C for 2 hours under a nitrogen atmosphere and a reduced pressure of 400 Pa.

B An alternative sintered material could be prepared using coated substrate particles of the invention wherein the substrate particles are aluminium-copper alloy spheroids having a d ₅₀ value of 50 mm. The mixture is then compacted under a pressure of 350 MPa, followed by sintering at 600 °C for 2 hours under a nitrogen atmosphere and a reduced pressure of 150 Pa.

Other processes Any end-use that relies heavily on the packing and flow mechanics of the feed (such as pressing, 3D selective laser sintering and hot extrusion) may be enhanced by utilising coated substrate particles of the invention. Thus, the fact that the present invention enables excellent control over particle morphology and size distribution means the disclosed 5 methods may be used to provide spherical (coated) particle morphologies which may be particularly advantageous in the context of such processes.