BR112015007053B1 - ELECTRICALLY CONDUCTIVE COATING COMPOSITION, ELECTRICALLY CONDUCTIVE COATING AND METHOD FOR MAKING AN ELECTRICALLY CONDUCTIVE COATING COMPOSITION - Google Patents

Abstract

electrically conductive coating composition, electrically conductive coating and method for making an electrically conductive coating composition. coating compositions containing graphene carbon particles are disclosed. graphene carbon particles can be thermally produced and dispersed in thermoset coatings and/or thermoset polymer film coatings. the cured coatings exhibit desired properties such as increased electrical conductivity.

Description

field of invention

[0001] The present invention relates to electrically conductive coatings containing graphene carbon particles.

Invention history

[0002] Many different types of coatings are subjected to environments where electrical conductivity is desired. For example, the improved conductivity properties can be advantageous for many types of clear coatings, color coatings, primer coatings, static dissipative coatings and printed electronics, batteries, capacitors, electrical traces, antennas, electrical heating coatings, and the like.

Invention Summary

[0003] One aspect of the invention provides an electrically conductive coating composition comprising a film-forming resin and thermally produced graphene carbon particles. When the coating composition is cured, it has an electrical conductivity greater than an electrical conductivity of the same coating composition without the thermally produced graphene carbon particles.

[0004] Another aspect of the invention provides an electrically conductive coating comprising a polymeric resin film and thermally produced graphene carbon particles dispersed in the polymeric resin film.

[0005] A further aspect of the invention provides a method of realizing an electrically conductive coating composition comprising mixing the thermally produced graphene carbon particles with a film-forming resin.

Brief description of the drawings

[0006] Figure 1 is a graph illustrating the electrical conductivity properties of various coatings containing graphene carbon particles thermally produced in accordance with the embodiments of the present invention compared to coatings containing other types of commercial graphene particles; and

[0007] Figure 2 is a graph illustrating the electrical conductivity properties of various coatings containing one type of commercially available graphene carbon particles in combination with the thermally produced graphene carbon particles of the present invention or other types of carbon particles of commercially available graphene.

Detailed description of the invention's achievements

[0008] In accordance with the embodiments of the present invention, graphene carbon particles are added to coating compositions to provide desirable properties such as increased electrical conductivity. As used herein, the term "electrically conductive" when referring to a coating containing graphene carbon particles means that the coating has an electrical conductivity of at least 0.001 S/m. For example, the coating can have a conductivity of at least 0.01, or at least 10 S/m. Typically, the conductivity can be from 100 to 100,000 S/m or higher. In certain embodiments, the conductivity can be at least 1,000 S/m or at least 10,000 S/m. For example, the conductivity can be at least 20,000 S/m, or at least 30,000 S/m, or at least 40,000 S/m.

[0009] In accordance with certain embodiments, coatings do not exhibit significant electrical conductivity in the absence of the addition of graphene carbon particles. For example, a conventional touch-up colorless layer may have conductivity that is not measurable, while coatings of the present invention including graphene carbon particles may exhibit conductivities as noted above. In certain embodiments, the addition of graphene carbon particles increases the conductivity of coatings by more than a factor of 10, typically greater than a factor of 1,000 or 100,000 or greater.

[0010] In certain embodiments, graphene carbon particles can be added to film-forming resins in amounts from 0.1 to 95 weight percent based on total coating solids. For example, graphene carbon particles can comprise from 1 to 90 percent by weight, or from 5 to 85 percent by weight. In certain embodiments, the amount of graphene carbon particles contained in the coatings can be relatively large, such as from 40 or 50 weight percent to 90 or 95 weight percent. For example, graphene carbon particles can comprise from 60 to 85 percent by weight, or from 70 to 80 percent by weight. In certain embodiments, the conductivity properties of coatings can be significantly increased with relatively minor additions of graphene carbon particles, for example, less than 50 weight percent, or less than 30 weight percent. In certain embodiments, the present coatings have sufficiently high electrical conductivities at relatively low loadings of the graphene carbon particles. For example, the electrical conductivities noted above can be achieved in graphene carbon particle loadings of less than 20 or 15 percent by weight. In certain embodiments, particle loadings can be less than 10 or 8 percent by weight, or less than 6 or 5 percent by weight. For example, for coatings comprising film-forming polymers or resins which, by themselves, are not conductive, the addition of from 3 to 5 weight percent of the thermally produced graphene carbon particles can provide an electrical conductivity of at least 0.1 S/m, e.g., or at least 10 S/m.

[0011] The coating compositions may comprise any of a variety of thermoplastic and/or thermoset compositions known in the art. For example, coating compositions can comprise film-forming resins selected from epoxy resins, acrylic polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyether polymers, bisphenol A-based epoxy polymers , polysiloxane polymers, styrenes, ethylenes, butylenes, their copolymers, and mixtures thereof. Generally speaking, such polymers can be any such polymer made by any method known to one of skill in the art. Such polymers can be solvent-borne, water-soluble or water-dispersible, emulsifiable or of limited water solubility. Furthermore, polymers can be supplied in sol-gel systems, can be supplied in core-shell polymer systems, or can be supplied in powder form. In certain embodiments, the polymers are dispersions in a continuous phase comprising water and/or organic solvent, for example, emulsion polymers or non-aqueous dispersions.

[0012] Thermoset or curable coating compositions typically comprise film-forming polymers or resins having functional groups that are reactive with themselves or a cross-linking agent. The functional groups on the film-forming resin can be selected from any of a variety of reactive functional groups, including, for example, carboxylic acid groups, amine groups, epoxide groups, hydroxyl groups, thiol groups, carbamate groups, amide groups, urea groups, isocyanate groups (including isocyanate and tris-alkylcarbamoyltriazine blocked groups) mercaptan groups, styrenic groups, anhydride groups, acetoacetate acrylates, uretidione and combinations thereof.

[0013] Thermoset coating compositions typically comprise a cross-linking agent which can be selected from, for example, aminoplastics, polyisocyanates including blocked isocyanates, polyepoxides, beta-hydroxyalkylamides, polyacids, anhydrides, organometallic acid functional materials , polyamines, polyamides and mixtures of any of the above. Suitable polyisocyanates include multifunctional isocyanates. Examples of multifunctional polyisocyanates include aliphatic diisocyanates like hexamethylene diisocyanate and isophorone diisocyanate and aromatic diisocyanates like toluene diisocyanate and 4,4'-diphenylmethane diisocyanate. Polyisocyanates can be blocked or unblocked. Examples of other suitable polyisocyanates include isocyanurate trimers, allophanates and diisocyanate uretdiones. Examples of commercially available polyisocyanates include DESMODUR N3390, which is sold by Bayer Corporation, and TOLONATE HDT90, which is sold by Rhodia Inc. Suitable aminoplastics include condensates of amines and/or amides with aldehyde. For example, melamine condensate with formaldehyde is a suitable aminoplastic. Suitable aminoplasts are well known in the art. A suitable aminoplast is disclosed, for example, in U.S. Pat. No. 6,316,119 at column 5, lines 45-55, incorporated herein by reference. In certain embodiments, the resin can be self cross-linked. Self cross-linking means that the resin contains functional groups that are capable of reacting with themselves, such as alkoxysilane groups, or that the reaction product contains functional groups that are coreactive, for example, alkoxysilane groups. hydroxyl and isocyanate blocked groups.

[0014] The dry film thickness of cured coatings can typically range from less than 0.5 microns to 100 microns or more, for example from 1 to 50 microns. As a particular example, the cured coating thickness can range from 1 to 15 microns.

[0015] In accordance with certain embodiments, when the coating compositions are cured, the resulting coatings comprise a continuous matrix of the cured resin with the graphene carbon particles dispersed therein. Graphene carbon particles can be evenly dispersed throughout the thickness of the coating. Alternatively, the graphene carbon particles may be non-uniformly distributed, e.g., with a particle distribution gradient across the coating thickness and/or across the coating.

[0016] As used herein, the term "graphene carbon particles" means carbon particles having structures comprising one or more layers of one atom thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The average number of stacked layers can be less than 100, for example, less than 50. In certain embodiments, the average number of stacked layers is 30 or less, such as 20 or less, 10 or less, or, in some cases 5 or less. The graphene carbon particles may be substantially flat, however, at least a portion of the planar sheets may be substantially curved, curled, wrinkled, or warped. Particles typically do not have a spheroidal or equiaxed morphology.

[0017] In certain embodiments, the graphene carbon particles present in the coating compositions of the present invention have a thickness, measured in a direction perpendicular to the carbon atom layers, of no more than 10 nanometers, no more than 5 nanometers, or, in certain embodiments, no more than 4 or 3 or 2 or 1 nanometer, such as no more than 3.6 nanometers. In certain embodiments, graphene carbon particles can be from 1 atom layer up to 3, 6, 9, 12, 20, or 30 atom layer thickness, or more. In certain embodiments, the graphene carbon particles present in the compositions of the present invention have average particle sizes, ie, widths and lengths, measured in a direction parallel to the carbon atom layers, of at least 10 or 30 nanometers, such as like, more than 50 nanometers, in some cases more than 100 nanometers up to 1000 nanometers. For example, the average particle size of graphene carbon particles can be from 200 to 800 nm, or from 250 to 750 nm. Graphene carbon particles can be supplied in the form of ultra-thin flakes, platelets or sheets having relatively high average aspect ratios (aspect ratio being defined as the ratio of the longest dimension of a particle to the shortest dimension of the particle) greater than 3:1 such as greater than 10:1 to 2000:1. For example, aspect ratios can be greater than 15:1, or greater than 25:1, or greater than 100:1 or greater than 500:1.

[0018] In certain embodiments, graphene carbon particles used in the coating compositions of the present invention have relatively low oxygen content. For example, graphene carbon particles used in certain embodiments of the compositions of the present invention may, even when having a thickness of no more than 5 or no more than 2 nanometers, have an oxygen content of no more than 2 percent atomic weight, such as, not more than 1.5 or 1 percent atomic weight, or not more than 0.6 percent atomic weight, such as, about 0.5 percent atomic weight. The oxygen content of graphene carbon particles can be determined using X-Ray Photoelectron Spectroscopy, as described in D.R. Dreyer et al., Chem. Soc. Rev. 39, 228-240 (2010).

[0019] In certain embodiments, the graphene carbon particles used in the coating compositions of the present invention have a specific surface area of B.E.T. of at least 50 square meters per gram, such as at least 70 square meters per gram, or, in some cases, at least 100 square meters per gram. For example, the surface area can be from 100 or 150 to 500 or 1000 square meters per gram, or from 150 to 300 or 400 square meters per gram. In certain embodiments, the surface area is less than 300 square meters per gram, for example, less than 250 square meters per gram. As used herein, the term "B.E.T. specific surface area." refers to a specific surface area determined by nitrogen adsorption according to ASTMD 3663-78 based on the Brunauer-Emmett-Teller method described in the journal “The Journal of the American Chemical Society”, 60, 309 ( 1938).

[0020] In certain embodiments, graphene carbon particles used in the coating compositions of the present invention have a Raman spectroscopy 2D/G peak ratio of at least 1.1, e.g., at least 1.2 or 1.3. As used herein, the term "2D/G peak ratio" refers to the ratio of the 2D peak intensity at 2692 cm-1 to the intensity of the G peak at 1580 cm-1.

[0021] In certain embodiments, graphene carbon particles used in the coating compositions of the present invention have a relatively low bulk density. For example, graphene carbon particles used in certain embodiments of the present invention are characterized by having a bulk density (tap density) of less than 0.2 g/cm3, such as, no more than 0.1 g/cm3. For the purposes of the present invention, the bulk density of the graphene carbon particles is determined by placing 0.4 grams of the graphene carbon particles into a glass measuring cylinder having a readable scale. The cylinder is lifted approximately one inch and squeezed 100 times by pressing the base of the cylinder onto a hard surface to allow the graphene carbon particles to settle into the cylinder. The volume of the particles is then measured, and the bulk density is calculated by dividing 0.4 grams by the measured volume, where the bulk density is expressed in terms of g/cm3.

[0022] In certain embodiments, graphene carbon particles used in the coating compositions of the present invention have a tapped density and a percent densification that is less than the tapped density and percent densification of graphite powder and certain types of carbon particles. substantially flat graphene carbon. Lower compressed density and lower percent densification are each currently believed to contribute better dispersion and/or rheological properties than graphene carbon particles exhibiting higher compressed density and higher percent densification. In certain embodiments, the tap density of the graphene carbon particles is 0.9 or less, such as less than 0.8, less than 0.7, such as from 0.6 to 0.7 . In certain embodiments, the percent densification of the graphene carbon particles is less than 40 percent, such as, less than 30 percent, such as, from 25 to 30 percent.

[0023] For the purposes of the present invention, the compressed density of graphene carbon particles is calculated from a measured thickness of a given mass of the particles after compression. Specifically, the measured thickness is determined by subjecting 0.1 gram of the graphene carbon particles to the cold press under 15,000 pounds force in a 1.3 centimeter mold for 45 minutes, where the contact pressure is 500 MPa . The compressed density of the graphene carbon particles is then calculated from that measured thickness according to the following equation: Compressed density (g/cm3) = 0.1 gram π*(1,3cm/2)2*(thick. measure in cm)

The percent densification of the graphene carbon particles is then determined as the calculated compressed density ratio of the graphene carbon particles, as determined above, to 2.2 g/cm3, which is the density of graphite.

[0025] In certain embodiments, graphene carbon particles have a measured bulk net conductivity of at least 10 microSiemens, such as at least 30 microSiemens, such as at least 100 microSiemens immediately after mixing and at later points in time , such as in 10 minutes, or 20 minutes, or 30 minutes, or 40 minutes. For the purposes of the present invention, the net bulk conductivity of the graphene carbon particles is determined as follows. First, a sample comprising a 0.5% solution of graphene carbon particles in butyl cellosolve is sonicated for 30 minutes with a bath sonicator. Immediately after sonication, the sample is placed in a standard calibrated electrolyte conductivity cell (K=1). A Fisher Scientific AB 30 conductivity meter is introduced to the sample to measure the sample's conductivity. Conductivity is arranged over the course of about 40 minutes.

[0026] In accordance with certain embodiments, percolation, defined as long-range interconnectivity, occurs between conductive carbon particles of graphene. Such percolation can reduce the resistivity of coating compositions. Conductive graphene particles can occupy a minimal volume within the coating so that the particles form a continuous, or nearly continuous, network. In such a case, the aspect ratios of the graphene carbon particles may affect the minimum volume required for percolation. Furthermore, the surface energy of graphene carbon particles can be the same or similar to the surface energy of elastomeric rubber. Otherwise, the particles may tend to flake or lose their mixture as they are processed.

The thermally produced graphene carbon particles used in the coating compositions of the present invention are made by thermal processes. In accordance with embodiments of the invention, thermally produced graphene carbon particles are made from carbon-containing precursor materials that are heated to high temperatures in a thermal zone, such as a plasma. As more fully described below, the carbon-containing precursor materials are heated to a sufficiently high temperature, e.g., above 3,500°C, to produce the graphene carbon particles having the characteristics as described above. Carbon-containing precursor, such as a hydrocarbon supplied in gaseous or liquid form, is heated in the thermal zone to produce graphene carbon particles in the thermal zone or downstream therefrom. For example, thermally produced graphene carbon particles can be made by the systems and methods disclosed in U.S. Patent Nos. 8,486,363 and 8,486,364.

[0028] In certain embodiments, thermally produced graphene carbon particles can be made using the mechanism and method described in U.S. Patent No. 8,486,363 in [0022] through [0048] wherein (i) one or more hydrocarbon precursor materials capable of forming a two-carbon fragment species (such as n-propanol, ethane, ethylene, acetylene, vinyl chloride, 1,2-dichloroethane, allyl alcohol, propionaldehyde, and/or vinyl bromide ) is introduced into a thermal zone (such as a plasma), and (ii) the hydrocarbon is heated in the thermal zone to a temperature of at least 1000°C to form graphene carbon particles. In other embodiments, thermally produced graphene carbon particles can be made using the mechanism and method described in U.S. Patent No. 8,486,364 in [0015] through [0042] wherein (i) a methane precursor material (such as, a material comprising at least 50 percent methane, or, in some cases, gaseous or liquid methane of at least 95 or 99 percent purity or greater) is introduced into a thermal zone (such as a plasma ), and (ii) the methane precursor is heated in the thermal zone to form graphene carbon particles. Such methods can produce graphene carbon particles having at least some, in some cases all, of the characteristics described above.

[0029] During the production of graphene carbon particles by the thermal production methods described above, a carbon-containing precursor is provided as a feed material that can be contacted with an inert carrier gas. The carbon-containing precursor material can be heated in a thermal zone, for example, by a plasma system. In certain embodiments, the precursor material is heated to a temperature of at least 3,500°C, for example, from a temperature greater than 3,500°C or 4,000°C to 10,000°C or 20,000°C. Although the thermal zone can be generated by a plasma system, it should be understood that any other suitable heating system can be used to create the thermal zone, such as several types of ovens, including electrically heated tube ovens and the like.

[0030] The gas stream may be contacted with one or more quench streams which are injected into the plasma chamber through at least one quench current injection port. The quench stream can cool the gas stream to facilitate the formation or control of the particle size or morphology of the graphene carbon particles. In certain embodiments of the invention, after contacting the product gas stream with quench streams, the ultrafine particles may be passed through a converging member. After the graphene carbon particles leave the plasma system, they can be collected. Any suitable means can be used to separate graphene carbon particles from the gas stream, such as, for example, a bag filter, cyclone separator or deposition on a substrate.

[0031] Without being bound by any theory, it is currently believed that the preceding methods of fabricating the thermally produced graphene carbon particles are partially suitable for producing graphene carbon particles having relatively low thickness and relatively high aspect ratio in combination with relatively low oxygen content as described above. Furthermore, such methods are currently believed to produce a substantial amount of graphene carbon particles having a substantially curved, curled, wrinkled, or warped morphology (referred to herein as a "3D" morphology), as opposed to predominantly producing particles having a substantially two-dimensional (or flat) morphology. This characteristic is believed to be reflected in the previously described compressed density characteristics and is believed to be beneficial in the present invention as it is currently believed, when a significant portion of the graphene carbon particles have a 3D morphology, the "edge to edge contact" ” and “edge to face” between the graphene carbon particles within the composition can be promoted. This is thought to be due to particles having a 3D morphology less likely to be aggregated into the composition (due to lower Van der Waals forces) than particles having a two-dimensional morphology. Furthermore, it is currently believed that even in the case of “face to face” contact between particles having a 3D morphology, as particles may have more than one face plane, the entire particle surface is not engaged in a single “face to face” interaction with another single particle, however, may instead participate in interactions with other particles, including other “face to face” interactions on other planes. As a result, graphene carbon particles having a 3D morphology are currently thought to provide the best conductive path in the present compositions and are currently thought to be useful for obtaining the electrical conductivity characteristics pursued by the embodiments of the present invention, particularly when the particles of Graphene carbons are present in the composition in relatively low amounts.

[0032] In certain embodiments, thermally produced graphene carbon particles can be combined with other types of graphene particles, such as those obtained from commercial sources, for example, from Angstron, XG Sciences and other commercial sources. In such embodiments, commercially available graphene carbon particles may comprise exfoliated graphite and have different characteristics compared to thermally produced graphene carbon particles, such as different size distributions, thicknesses, aspect ratios, structural morphologies, content of oxygen and chemical functionality in the basal planes/edges.

[0033] When thermally produced graphene carbon particles are combined with commercially available graphene carbon particles in accordance with the embodiments of the invention, a bimodal distribution, tri-modal distribution, etc. of the carbon particle characteristics of graphene can be achieved. For example, graphene carbon particles contained in coatings can have multimodal particle size distributions, aspect ratio distributions, structural morphologies, edge functionality differences, oxygen content, and the like. The following Table 1 lists the average particle sizes, thicknesses and aspect ratios for thermally produced graphene carbon particles compared to certain commercially available graphene carbon particles produced from exfoliated graphite.

[0034] In an embodiment of the present invention wherein both thermally produced graphene carbon particles and commercially available graphene carbon particles, e.g., from exfoliated graphite, are added to a coating composition to produce a bimodal graphene particle size distribution, the relative amounts of different types of graphene carbon particles are controlled to produce the desired conductivity properties of the coatings. For example, thermally produced graphene particles can comprise from 1 to 50 weight percent, and commercially available graphene carbon particles can comprise from 50 to 99 weight percent, based on the total weight of the Graphene carbon particles. In certain embodiments, the thermally produced graphene carbon particles can comprise from 2 to 20 weight percent, or from 5 to 10 or 12 weight percent.

[0035] In addition to the resin and graphene carbon particle components, coatings of the present invention may include additional components conventionally added to coating compositions, such as crosslinking agents, pigments, paints, flow aids, defoamers, dispersants, solvents , UV absorbers, catalysts and surface active agents.

[0036] In certain embodiments, coating compositions are substantially free of certain components such as polyalkyleneimines, graphite or other components. For example, the term "substantially free of polyalkyleneimines" means that the polyalkyleneimines are not purposely added, or are present as impurities or in trace amounts, e.g., less than 1 weight percent or less than 0. 1 percent by weight. The coatings of the present invention have been found to have good adhesion properties without the need to add polyalkyleneimines. The term "substantially free of graphite" means that the graphite is not purposely added, or is present as an impurity or in trace amounts, e.g., less than 1 percent by weight or less than 0.1 by weight percent of weight. In certain embodiments, graphite in smaller amounts may be present in the coatings, e.g., less than 5 weight percent or less than 1 weight percent of the coating. If graphite is present, it is typically in an amount less than graphene, eg less than 30 percent by weight based on the combined weight of graphite and graphene, eg less than 20 or 10 percent weight.

[0037] The coating compositions of the present invention can be made by various standard methods in which graphene carbon particles are mixed with the film-forming resins and other components of the coating compositions. For example, for two-part coating systems, the graphene carbon particles can be dispersed in part A and/or part B. In certain embodiments, the graphene carbon particles are dispersed in part A by various mixing techniques. , such as sonication, high-speed mixing, middle milling, and the like. In certain embodiments, graphene carbon particles can be blended into coating compositions using high energy and/or high shear techniques such as sonication, 3-cylinder cutter, ball cutter, agitator cutter, rotor/mixers stator and the like.

[0038] In accordance with certain embodiments, the coatings of the present invention have desirable mechanical properties, increased IR absorption, increased "color depth", increased thermal conductivity, decreased permeability for small molecules such as water and oxygen, may also be advantageous for these same coatings.

[0039] The following examples are intended to illustrate various aspects of the invention, and are not intended to limit the scope of the invention.

Example 1

[0040] The electrical conductivities of coatings containing thermally produced graphene carbon particles were compared with similar coatings containing commercial graphene particles, and no such particle. Coating compositions were made with aqueous latex particles that are stable in N-methyl pyrrolidone (NMP) solvent. Acrylic latex particles are crosslinked and functionalized by epoxy, but do not need to be functionalized to operate. The latex forms a film at elevated temperatures and serves as the binder to hold the film together. Thermally produced graphene carbon particles, labeled PPG A and PPG B, were produced by the thermal plasma production method using methane as a precursor material disclosed in U.S. Patent No. 8,486,364. Thermally produced PPG A and PPG B graphene carbon particles have a surface area of about 250 - 280 m 2 /g and are about 100-200 nm in size. Commercially available graphene carbon particles included: XG-M5 (from XG Sciences having an average particle size of 5 microns, thickness about 6 nm, and BET surface area from 120 to 150 square meters per gram ); XG-C750 (from XG Sciences having an average particle size of about 1.5 microns, thickness of about 2 nm, and BET surface area of 750 square meters per gram); and PDR (from Angstron Materials having an average particle size of about 10 microns, thickness of about 1 nm and BET surface area from 400 to 800 square meters per gram). Prior to addition of graphene carbon particles to the coating solution, samples are diluted to 0.25 - 2.5 weight percent in NMP solvent and sonicated by horn for 15 min. The PPG B sample was dispersed at twice the sonication energy per unit graphene compared to the PPG A sample. The final coating composition is then made by mixing latex, NMP solvent and the predispersed graphene carbon particles. The samples are then bath sonicated for 15 minutes. After sonication, samples are passed through a 150 mesh filter and then extracted onto the glass substrates in a 6 mil wet film construction. Wet films are flashed at room temperature for 15 minutes, followed by an oven cure at 100°C for 30 minutes.

[0041] Figure 1 graphically illustrates the conductivities of coatings containing the thermally produced PPG A and PPG B graphene carbon particles in various loads, compared to other commercial graphene carbon particles and a control coating containing no such particle, which did not measure any conductivity. Although PPG A and PPG B particles are about an order of magnitude smaller than M5 particles, they produce similar electrical conductivities. As the particles get smaller, the resistance should increase in the film at a similar loading, i.e., comparing the M5 with PDR, which is an average particle size of ~10 microns vs. 5 micron and the C750 which is 1.5 micron. However, the thermally produced graphene particles provide a lower coating of strength. This may be due to the extremely low oxygen content of the thermally produced graphene carbon particles and the fact that their edge functionality may be limited to C-H vs. C-O, C-N bonds observed in commercial graphene samples, producing a lower particle-particle contact resistance for the thermally produced graphene. Thermally produced graphene can also be inherently more conductive due to its turbostratic crystal structure.

Example 2

[0042] Coatings comprising a type of commercially available graphene carbon particles alone, and in combination with other graphene carbon particles (including the thermally produced graphene carbon particles), were produced and measured for electrical conductivity. The coating compositions were made with 10 weight percent graphene carbon particles: xGnP C-300 (from XG Sciences having an average particle size of 1.5 microns, thickness of about 2 nm and surface area of 300 square meters BET per gram), xGnP C750 (from XG Sciences as described in Example 1), xGnP M25 (from XG Sciences having an average particle size of 25 microns, thickness of 6-8 nm, and BET surface area 120-150 square meters per gram) or thermally produced PPG graphene carbon particles, 1.67 weight percent ethyl cellulose (Aqualon, Ashland), and 88.33 weight percent deionized water. These coating compositions were dispersed by adding 70g of each to 8 oz. glass jars with 220g of SEPR Ermil 1.0-1.25mm cutter medium. The samples in the jars were shaken for 4 hours using a Lau disperser (Model DAS 200, Lau, GmbH). The milling medium was then filtered from the coating compositions. Blends of these coating compositions were then prepared so that of the total 10 percent by weight graphene carbon in each of the blends, there are two types of graphene carbon particles in the following weight percentages: 92% xGnP M-25 and 8% thermally produced PPG graphene carbon particles, 92% M-25 xGnP and 8% C-300 xGnP and 92% M-25 xGnP and 8% C-750 xGnP. Each of these mixtures as well as the M-25 xGnP only coating composition was applied as 1-2 mm wide lines in a serpentine circuit pattern to a 2 x 3 inch glass slide (Fisherbrand, Plain, Precleaned) using a dispensing jet (PICO valve, MV-100, Nordson, EFD) and a tabletop robot (2504N, Janome) and then dried in an oven at 212°F for 30 minutes. The electrical conductivity of each coated sample was determined by first measuring the coil circuit resistance vs. the length of the circuit line. Then, the cross-sectional area of the serpentine lines was measured using a style profilometer (Dektak). Using the measured values for the cross-sectional area (A) and the resistance (R) for a given length (L) of the circuit, the resistivity (p) was calculated using the equation p = RA/L. Then, the conductivity (a) was calculated by obtaining the reciprocal of the resistivity, α = 1/p.

[0043] The results are shown in Figure 2. The addition of a small amount of the thermally produced PPG graphene carbon particles significantly increases the conductivity, by about 200%, above that of a coating composition containing only one carbon of large platelet-type graphene (xGnP M-25). Figure 2 shows that small additions of other commercially available graphene carbon particles do not increase the conductivity as significantly (only about 50% increase for xGnP C-300 and only about 90% increase for xGnP C-750).

[0044] For the purposes of this description, it is to be understood that the invention may assume several alternative variations and step sequences, except where expressly specified otherwise. Furthermore, except in any operational examples, or where otherwise indicated, all numbers expressing, for example, amounts of ingredients used in the specification and claims are to be understood to be modified in all instances by the term “about”. Accordingly, unless otherwise indicated, the numerical parameters set forth in the following specification and appended claims are approximations which may vary depending on the desired properties to be achieved by the present invention. At the very least, and not in an attempt to limit the application of the equivalents doctrine to the scope of the claims, each numerical parameter should at least be interpreted in light of the number of significant digits reported and when applying ordinary rounding techniques.

[0045] Notwithstanding that the numerical variations and parameters establishing the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as accurately as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective test measurements.

[0046] Likewise, it is to be understood that any numerical variation mentioned herein is intended to include all subvariations included therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and including) the stated minimum value of 1 and the stated maximum value of 10, i.e. having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

[0047] In this application, the use of the singular includes the plural and the plural includes the singular, unless specifically stated otherwise. Furthermore, in this application, the use of “or” means “and/or”, unless specifically stated otherwise, although “and/or” may be explicitly used in certain instances.

[0048] It will be readily appreciated by those skilled in the art that modifications can be made to the invention without deviating from the concepts disclosed in the foregoing description. Such modifications shall be considered to be included within the following claims, unless the claims, by their language, expressly state otherwise. Correspondingly, the particular embodiments described in detail herein are only illustrative and not limiting to the scope of the invention which are to receive the full breadth of the appended claims and any and all of their equivalents.

Claims (20)

1. Electrically conductive coating composition, characterized in that it comprises: - a film-forming resin; and - thermally produced graphene carbon particles, in combination with another type of graphene carbon particles, the thermally produced graphene carbon particles being produced by: - introducing a precursor material comprising a methane or hydrocarbon material capable of form a kind of two-carbon fragment in a thermal zone having a temperature greater than 3,500°C to 20,000°C; - heating the precursor material in the thermal zone to form graphene carbon particles from the precursor material; and - collecting graphene carbon particles having an average aspect ratio greater than 3:1; and wherein another type of graphene carbon particles comprise exfoliated graphite graphene carbon particles; and when the coating composition is cured, it has an electrical conductivity greater than an electrical conductivity of the same coating composition without the thermally produced graphene carbon particles. 2. An electrically conductive coating composition according to claim 1, characterized in that the thermally produced graphene carbon particles comprise from 1 to 95 percent by weight of the coating composition based on the total solids content of the coating. 3. The electrically conductive coating composition of claim 1, wherein the thermally produced graphene carbon particles comprise more than 40 percent by weight of the coating composition based on the total solids content of the coating composition. coating. 4. The electrically conductive coating composition of claim 1, wherein the thermally produced graphene carbon particles comprise less than 20 weight percent of the coating composition based on the total solids content of the coating composition . 5. Electrically conductive coating composition according to claim 1, characterized in that the thermally produced graphene carbon particles have an oxygen content of less than 1.5 atomic percent. 6. Electrically conductive coating composition according to claim 1, characterized in that the thermally produced graphene carbon particles have a BET surface area of less than 300 square meters per gram. 7. Electrically conductive coating composition according to claim 1, characterized in that the thermally produced graphene carbon particles comprise from 1 to 20 percent by weight, and the exfoliated graphite carbon particles comprise 80 up to 99 percent by weight, based on the total weight of the graphene carbon particles. 8. Electrically conductive coating composition according to claim 1, characterized in that the film-forming resin comprises epoxy resins, acrylic polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyether polymers, bisphenol A based epoxy polymers, polysiloxane polymers, styrenes, ethylenes, butylenes, coreshell polymers, non-aqueous dispersed polymer particles, their copolymers, and mixtures thereof. 9. Electrically conductive coating composition, according to claim 1, characterized in that the film formation comprises a latex resin or a non-aqueous dispersed resin. 10. Electrically conductive coating composition, according to claim 1, characterized in that the coating is free of graphite. 11. Electrically conductive coating composition according to claim 1, characterized in that the coating is free of polyalkyleneimines. 12. Electrically conductive coating composition according to claim 1, characterized in that the electrical conductivity of the cured coating composition is at least 1,000 S/m. 13. Electrically conductive coating composition according to claim 12, characterized in that the electrical conductivity of the cured coating composition is at least 10,000 S/m. 14. Electrically conductive coating, characterized in that it comprises: - a polymeric resin film; and - thermally produced graphene carbon particles in combination with another type of graphene carbon particles dispersed in the polymeric resin film, the thermally produced graphene carbon particles being produced by: - introducing a precursor material comprising a material of methane or hydrocarbon capable of forming a kind of two-carbon fragment in a thermal zone having a temperature greater than 3,500°C to 20,000°C; - heating the precursor material in the thermal zone to form graphene carbon particles from the precursor material; and - collecting graphene carbon particles having an average aspect ratio greater than 3:1; and Wherein another type of graphene carbon particles comprise exfoliated graphite graphene carbon particles; and wherein another type of graphene carbon particles comprises exfoliated graphite carbon particles. 15. Electrically conductive coating according to claim 14, characterized in that the electrically conductive coating has an electrical conductivity of at least 10 S/m. 16. Electrically conductive coating according to claim 15, characterized in that the electrically conductive coating has an electrical conductivity of at least 1,000 S/m. 17. Electrically conductive coating according to claim 16, characterized in that the electrically conductive coating has an electrical conductivity of at least 10,000 S/m. 18. Electrically conductive coating according to claim 14, characterized in that the polymeric resin comprises epoxy resins, acrylic polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyether polymers, epoxy based polymers in bisphenol A, polysiloxane polymers, styrenes, ethylenes, butylenes, core-shell polymers, non-aqueous dispersed polymer particles, their copolymers, and their mixtures. 19. Electrically conductive coating according to claim 14, characterized in that the coating has a dry film thickness of 1 to 100 microns. 20. Method for making an electrically conductive coating composition as defined in claim 1, characterized in that it comprises mixing the thermally produced graphene carbon particles in combination with another type of graphene carbon particles with a film-forming resin , whereby the thermally produced graphene carbon particles are produced by: - introducing a precursor material comprising a methane or hydrocarbon material capable of forming a kind of two-carbon fragment in a thermal zone having a temperature greater than 3,500°C up to 20,000°C; - heating the precursor material in the thermal zone to form graphene carbon particles from the precursor material; - collect graphene carbon particles having an average aspect ratio greater than 3:1; another type of graphene carbon particles comprising exfoliated graphite graphene carbon particles; and wherein another type of graphene carbon particles comprises exfoliated graphite carbon particles.

Images