Graphene-based coating composition for electromagnetic interference shielding, method and use thereof

Abstract

The present invention relates to a graphene-based coating composition suitable for electromagnetic interference shielding at frequencies between 30 MHz and 300 GHz, the composition comprising graphene nanoplates.The present invention also relates to a method of applying the ink composition as a coating to a substrate and to uses of the ink composition.

Description

[Technical field]

[0001] The present disclosure relates to the field of coating compositions, preferably ink compositions, comprising graphene for shielding electromagnetic interference at frequencies between 30 MHz and 300 GHz, articles coated with the compositions, methods and uses thereof. [Background technology]

[0002] Man-made and natural sources of electromagnetic interference (EMI) can cause temporary disruptions, data loss, and failure of electronic devices, equipment, and systems. These issues create many challenges and are of paramount importance to the automotive, aerospace, defense, and medical industries.

[0003] The rapid increase in density of electronic devices can dramatically increase EMI, degrading device performance, adjacent systems, and even affecting human health.

[0004] Nanotechnology and miniaturization have further exacerbated the problem of EMI, as interactions between components or chip elements of a device can result in minute interference effects. The most common example of EMI in daily life is the crosstalk between a laptop screen or a wireless microphone in a conference room and a mobile phone signal, resulting in flickering images and noise distortion. Due to the effects of EMI, the use of mobile phones is prohibited on airplanes and in certain locations or buildings. This has prompted the development of appropriate measures to suppress (or eliminate) the effects of EMI. Essentially, there are three main mechanisms for EMI shielding: reflection, absorption, and multiple reflections. Reflection is recognized as the primary EMI shielding mechanism, and the shield must contain mobile charge carriers (such as electrons and holes provided by metals, offshoot carbon, and conductive polymer-based materials). The secondary EMI shielding mechanism is absorption, and the shield may contain electric and / or magnetic dipoles that can interact with the electric or magnetic fields of EM radiation.

[0005] The tertiary mechanism is multiple reflections, which are facilitated by high interfacial area. Existing shielding methods that address these issues use brittle, inflexible, heavy systems and rigid housings, meshes, and foils made from heavy and expensive metals such as silver, copper, aluminum, and nickel.

[0006] Metals are the most common materials for EMI shielding due to their high electrical conductivity. However, metals suffer from issues such as high reflectivity, susceptibility to corrosion, heavy weight, large carbon footprint, and uneconomical processing. In light of this, polymer-based blends and composites have attracted significant attention due to their unique combination of electrical, thermal, dielectric, magnetic, and / or mechanical properties that lend themselves to efficient electromagnetic shielding response.

[0007] Nanoscale materials based on single / multilayer graphene sheets have attracted much attention due to their unique properties. Graphene is known to be the thinnest (one carbon atom thick) yet strongest (based on specific strength) material compared to other carbon allotropes such as graphite, carbon fibers, fullerenes, CNTs, and conventional metals. Moreover, graphene also possesses excellent electrical and thermal properties, making it a promising candidate for electronics and EMI shielding applications. Recently, several attempts have been made to harness the attractive and promising properties of these individual carbon sheets by uncovering how to manipulate graphene and forming graphene-based nanocomposites, especially for electrical and electromagnetic shielding applications. The use of graphene, which has a large aspect ratio and high electrical conductivity, can provide high EMI shielding.

[0008] In summary, graphene has unique properties that make it a promising material for a variety of applications, due to its advantages over conventional shielding solutions, which are mainly based on heavy, stiff, time- and energy-intensive metals: in particular, its high electrical conductivity makes it suitable for applications in sensors, batteries, transistors, capacitors, etc.

[0009] Structures based on graphene sheets have been the focus of many researches due to their excellent electrical and mechanical properties. This high electrical conductivity leads to a thin skin depth, which degrades the electromagnetic field due to absorption losses in the shielding material. In addition, the reflection losses at the interface between two materials depend on the difference in the characteristic impedance of the shield and the surrounding material, which requires a highly conductive material (Henry W. Ott, Electromagnetic Compatibility Engineering. John Wiley & Sons, 2011). From the point of view of absorption and reflection losses, graphene may be an optimal shielding material. Moreover, due to its mechanical properties, graphene has been considered a promising candidate for EMI shielding (C. Acquarelli, Rinaldi, Tamburrano, G. De Bellis, GDAloia, MSSarto, pp. 488-493, 2014). Compared to traditional metal shields, graphene itself is robust, lightweight and flexible, making it suitable for commercial applications (J. Liang, Y. Wang, Y. Huang, Y. Ma, Z. Liu, J. Cai, vol. 47, no. 3, pp. 92-2925, 2008).

[0010] Graphene-based conductive coatings have emerged as an effective solution to replace metallic coatings, foils, meshes and enclosures with lighter and more flexible coatings.

[0011] The document CN103113786 discloses a graphene conductive ink and its manufacturing method that can be used for electrical purposes including EMI shielding. However, the document describes the use of polycarbonate and an entirely different formulation. Furthermore, the document CN103113786 describes the weight percentage of graphene in the range of 0.1-95%, which may be considered an ineffective ink for shielding applications.

[0012] The document China Patent No. 105001716 discloses a graphene-based low resistance conductive printing ink and its manufacturing method, but without disclosing the complete application, although a more complex ink formulation is used, i.e., the use of 5-20 wt% of a specific auxiliary conductive agent.

[0013] The document EP 3703479 A1 discloses a composite material for shielding electromagnetic radiation, a raw material for additive manufacturing processes, a product comprising the composite material, and a method for manufacturing the product.

[0014] These facts are disclosed to explain the technical problem addressed by the present disclosure. Summary of the Invention

[0015] The present invention relates to a graphene-based composition for shielding electromagnetic interference at frequencies between 30 MHz and 300 GHz.Preferably, the present invention relates to a graphene-based coating composition.

[0016] Additionally, the present disclosure also provides customized electrical conductivity and wave attenuation levels.The coating can be applied to flexible or rigid materials on smooth or textured surfaces by using conventional spraying, brushing techniques, spray coating, paint brushing, roll coating, bar coating, drop casting, blade coating, doctor blade, dip coating, screen printing, and spin coating.

[0017] The compositions of the present invention are also suitable for application to parasitic elements, board level shields, patches, and thin films.

[0018] The composition of the present disclosure comprises: Over 75% weight reduction by replacing heavy metal shields with lightweight polymers; Excellent electrical conductivity with planar electrical resistivity of 0.01 to 500 ohms / sq inch; >95% attenuation within the radio and microwave frequency range of 30MHz to 300GHz, Good adhesion to hard, flexible, smooth, rough and soft materials; Benefits include:

[0019] The present disclosure enables the use of graphene in a wide range of manufacturing and technology sectors, including aerospace and defense, communications and IT, energy, healthcare, consumer electronics, automotive, packaging, maritime, sports and protective equipment, and biotechnology.

[0020] The compositions may be applied as EMI shielding coatings in industrial equipment, electronic components, medical devices, communication equipment, office equipment, military equipment, automotive parts, aerospace equipment, EMI / RFI shielding enclosures, automotive cables, RFID tags, solar panels, consumer electronics, mobile and flexible electronics, conductive paints, medical devices, sensors, wearable electronics, touch screens, and the like.

[0021] The present disclosure relates to a method for producing a composite material comprising: 0.1 to 30 weight percent graphene as a first carbon-based material; 0.1 to 30 weight percent of a second carbon-based conductive material; 0 to 20% by weight of a dispersant, preferably an alkoxysilane; 0.1-40% by weight of a polymer as a binder selected from the list of silicone-based polymers, polyetherimides, polysiloxanes, polyethyleneimines, ethylcellulose, or mixtures thereof; 0.1 to 10% by weight of polyoxyethylene; 10-85% by weight of a solvent selected from the list consisting of xylene, kerosene, toluene, water, dimethyl sulfoxide, butanone, diethylene glycol monoethyl ether acetate, silane, tetrahydrofuran, ethanol, polyacrylic acid, polyvinyl acid, terpineol, or mixtures thereof; The present invention relates to a graphene-based coating composition for shielding electromagnetic interference at frequencies between 30 MHz and 300 GHz, comprising:

[0022] The graphene-based coating composition of the present disclosure surprisingly ensures that this combination of materials stabilizes the dispersion of graphene and other conductive fillers, promotes electrical penetration, and improves electrical conductivity when the coating composition is applied as an electromagnetic shield.

[0023] In one embodiment, the binder influences the level of electrical conductivity and EMI shielding. Furthermore, different binders (or mixtures) have different adhesion behavior to the substrate. Preferably, the polymer used as binder is a silicone-based polymer. For better results, the binder is a polysiloxane, more preferably a polydimethylsiloxane.

[0024] In the graphene-based coating composition of the present disclosure, polyoxyethylene acts as a surfactant, alkoxysilane is a dispersant, and xylene is a solvent.

[0025] In an embodiment for obtaining better results, the solvent is in the range of 20 to 60% by weight, preferably 20 to 50% by weight, and more preferably 20 to 30% by weight.

[0026] In an embodiment for better results, the solvent is selected from the list consisting of xylene, water or a mixture thereof, preferably xylene.

[0027] In embodiments for better results, the graphene is selected from nanoplate graphene, few layer graphene, multi-layer graphene, graphene oxide, or combinations thereof.

[0028] In an embodiment for better results, the graphene is nanoplate graphene.

[0029] In an embodiment for better results, the graphene nanoplates have a diameter particle size of 1 μm to 25 μm, preferably 0.3 to 8 μm.

[0030] In an embodiment for better results, the graphene nanoplates have a D50 size of 2.0 μm and a D90 size of 7.8 μm.

[0031] In an embodiment for better results, the thickness of the graphene flakes is less than 100 nm, more preferably 0.33 to 15 nm. Measurements were performed using a scanning electron microscope (SEM) and a transmission electron microscope (TEM).

[0032] In one embodiment, the graphene nanoplates have an average size of 1.0-10.0 μm, preferably 2.0-6.0 μm, more preferably 4.0 μm. Measurements were performed using a scanning electron microscope (SEM).

[0033] In an embodiment for obtaining better results, the amount of polymer ranges from 1 to 40% by weight, preferably from 10 to 35% by weight, more preferably from 15 to 25% by weight.

[0034] In an embodiment for better results, the polymer is a polysiloxane.

[0035] In an embodiment for better results, the polysiloxane is polydimethylsiloxane.

[0036] In an embodiment for obtaining better results, the amount of alkoxysilane is in the range of 0.1 to 20% by weight, preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight.

[0037] In an embodiment for better results, the second carbon-based conductive material is selected from the list consisting of graphite, carbon black, carbon nanotubes, carbon nano-onions, graphene oxide, carbon nanospheres, and mixtures thereof.

[0038] In an embodiment for better results, the polyoxyethylene is polyoxyethylene 10 tridecyl ether. Polyoxyethylene 10 tridecyl ether is a non-ionic surfactant and an effective wetting agent.

[0039] In an embodiment for better results, the alkoxysilane is (3-aminopropyl)triethoxysilane.

[0040] Another aspect of the present disclosure relates to an ink comprising the composition of the present disclosure.

[0041] Another aspect of the present disclosure relates to a coated article comprising the graphene-based coating composition of the present disclosure. Preferably, the coated article is industrial equipment, electronic components, medical devices, communication devices, office equipment, military equipment, automotive parts, aerospace and defense equipment, EMI / RFI shielding enclosures, cables, RFID tags, solar panels, consumer electronics, mobile devices and flexible electronics, sensors, wearable electronics, touch screens, parasitic elements, board level shields, patches, thin films.

[0042] In an embodiment for obtaining better results, the thickness of the coating composition is in the range of 15 to 20,000 μm, preferably 50 to 500 μm, 100 to 300 μm.

[0043] In an embodiment for obtaining better results, the thickness of the coating composition is in the range of 100 to 250 μm.

[0044] Another aspect of the present disclosure is a process for obtaining the graphene-based coating composition of the present disclosure, comprising: mixing a polymer binder in a solvent; adding graphene to the mixture; adding a second carbon-based conductive material to the mixture; adding polyoxyethylene to the mixture; In a process comprising: The polymer as the binder is selected from silicone-based polymers, polyetherimides, polysiloxanes, polyethyleneimines, ethylcellulose, or mixtures thereof, and is in the range of 0.1 to 40% by weight; The graphene range is 1-30 wt.%. the second carbon-based conductive material is in the range of 0.1 to 30 wt. %; The polyoxyethylene is in the range of 0.1 to 10% by weight. The solvent is selected from the list consisting of xylene, kerosene, toluene, water, dimethyl sulfoxide, butanone, diethylene glycol monoethyl ether acetate, silane, tetrahydrofuran, ethanol, polyacrylic acid, polyvinyl acid, terpineol, or mixtures thereof, in the range of 10-85% by weight.

[0045] In an embodiment for better results, the method further comprises the step of adding a dispersant to the mixture, preferably 0.1-20% by weight of an alkoxysilane.

[0046] Another aspect of the present disclosure relates to a method of applying a graphene-based coating composition as described herein or obtained by a method as described herein, comprising the steps of applying the coating composition to a substrate by spray coating, paint brush, roll coating, spin coating, blade coating, bar coating, doctor blade, dip coating, screen printing, or drop casting techniques, and curing the coating layer by heating at a temperature of up to 250° C., preferably by air drying.

[0047] In one embodiment, the graphene-based coating composition for electromagnetic interference shielding at frequencies between 30 MHz and 300 GHz comprises: 0.1-30 wt.% graphene nanoplates; 0.1-30% by weight of other carbon-based materials; 0.1 to 20% by weight of an alkoxysilane, 0.1 to 40% by weight of a polysiloxane or other silicone-based polymer, 0.1 to 10% by weight of polyoxyethylene, Contains 10 to 30 weight percent xylene compounds.

[0048] In one embodiment, the graphene nanoplatelets have a particle size distribution of 1 μm to 25 μm and a flake thickness of less than 100 nm.

[0049] In one embodiment, the polysiloxane is polydimethylsiloxane.

[0050] In one embodiment, the carbon-based material is selected from natural and synthetic graphite, carbon black, carbon nanotubes, carbon nano-onions, graphene oxide, and carbon nanospheres.

[0051] In one embodiment, the polyoxyethylene is polyoxyethylene 10 tridecyl ether.

[0052] In one embodiment, the composition further comprises a solvent selected from kerosene, toluene, water, dimethyl sulfoxide, butanone, diethylene glycol monoethyl ether acetate, silane, tetrahydrofuran, ethanol, polyacrylic acid, polyvinyl acid, terpineol, or a mixture thereof.

[0053] In one embodiment, the solvent is present in the range of 0.1 to 85% by weight.

[0054] In one embodiment, the composition further comprises a polymer selected from polyetherimide, polysiloxane, polyethyleneimine, ethylcellulose, or a mixture thereof.

[0055] In one embodiment, the polymer is present in the range of 1-40% by weight.

[0056] In one embodiment, the composition further comprises an additive selected from an alkoxysilane, such as (3-aminopropyl)triethoxysilane.

[0057] In one embodiment, the additive is present in the range of 1-20% by weight.

[0058] In one embodiment, the compositions are used as coatings for industrial equipment, electronic components, medical devices, communication equipment, office equipment, military equipment, automotive parts, aerospace and defense equipment, EMI / RFI shielding enclosures, cables, RFID tags, solar panels, consumer electronics, mobile devices and flexible electronics, sensors, wearable electronics, touch screens, parasitic elements, board level shielding, patches, thin films.

[0059] In one embodiment, the coating has a thickness of 15 to 20000 μm, preferably 50 to 500 μm, and more preferably 100 to 300 μm.

[0060] The invention also relates to a process in which the composition is applied as a coating by spray coating, paint brush, roll coating, spin coating, blade coating, bar coating, doctor blade, dip coating, screen printing or drop casting techniques, followed by air drying or curing by heating at temperatures up to 250°C.

[0061] The composition of the present disclosure comprises: It can be stored for a long time at low temperatures. Can be used immediately after mixing by hand. We offer a wide range of coating techniques, including spray coating, blade coating, bar coating, doctor blade, paint brush, roll coating, drop casting, dip coating, screen printing, spin coating, etc. Can be dried at room temperature (RT). Low surface resistivity, It is characterized by notable properties such as: [Brief description of the drawings]

[0062] The following drawings depict preferred embodiments for illustrating the present disclosure and should not be construed as limiting the scope of the invention.

[0063] [Figure 1] FIG. 1 illustrates an embodiment. (a), (b) are optical images of exfoliated graphene nanoplates (GNPs), and (c)-(g) are scanning electron microscope (SEM) images of the same type of exfoliated GNPs drop-cast onto a Si substrate. [Diagram 2] FIG. 13 is a graphical representation of an embodiment of a lateral size histogram of GNPs, dimensions of 160 individual flakes measured from an SEM image. [Diagram 3] Bright-field transmission electron microscopy (BFTEM) images of GNPs. Insets in (a) and (c) represent the areas where images in (b) and (d) were taken. [Figure 4] (a) Raman spectra (average of 15 spectra, normalized to the G peak) of as-received graphite (4a) and exfoliated GNP powder (4b). (b) Detailed view of the D, G, and D' peaks and the corresponding Lorentzian fits. (c) Detailed view of the 2D peak fitted with three Lorentzian fits. [Diagram 5] X-ray photoelectron spectroscopy (XPS) spectra of graphite (5a) and GNP (5b) powders: (a) survey spectrum normalized to maximum intensity, (b) high-resolution C 1s spectrum. [Figure 6] Optical images of GNPs from different commercially available materials: (a) K1, (b) K2, (c) F1, and (d) F2. [Figure 7] (a) One embodiment of the graphene-based composition of the present disclosure; (b) K1, (c) K2, (d) F1, and (e) Raman spectroscopy spectra (maximum intensity peak, normalized to G band) of GNP powders from commercial sources. [Figure 8] High-resolution C 1s XPS spectra of GNP powder samples from reference pure graphite (a) and three commercial materials, Graphenest ((b) the present invention), (c) K1, (d) K2), (e) F1, (f) F2. All spectra were individually normalized to the highest intensity value. [Figure 9] (a) A sample of Coating #A (or Ink A) blade coated on a Mylar substrate. (b) Optical image of a cross section of a free-standing Coating #A revealing its heterogeneous nature, with the bright areas corresponding to the polymer matrix. (c)-(f) SEM images of the surface of Coating #A. [Figure 10] Fourier transform infrared spectroscopy (FTIR) spectrum of coating #A. The numbers in the figure represent the functional groups associated with PDMS. The weak peaks around 2850, 1794, and 1571 cm-1 correspond to the symmetric C-H stretching vibration (a), C=O stretching vibration (b), and C=C aromatic ring (c), respectively. [Figure 11] Variation of EM attenuation (right y-axis, EM reflection (a), EM absorption (b), and total EM attenuation (c)) and surface resistivity (left y-axis, R sheet (d)) with thickness of coating #A. EM attenuation was calculated from the average value of S-parameters measured with a VNA up to 3 GHz. [Figure 12] FIG. 1(a)-(i) Outline of TEM images of graphene flakes. [Figure 13] TEM images of the graphene materials used for morphology analysis. [Figure 14] TEM images of the graphene materials used for morphology analysis. [Figure 15] TEM images of the graphene materials used for morphology analysis. [Figure 16] TEM images of the graphene materials used for morphology analysis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0064] The present invention relates to a graphene-based coating composition, preferably an ink composition, suitable for electromagnetic interference shielding at frequencies between 30 MHz and 300 GHz, which comprises graphene nanoplates. The present invention also relates to a method of applying the ink composition as a coating to a substrate / article, and to uses of the ink composition.

[0065] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which are not intended to limit the scope of the present invention.

[0066] The present invention relates to a coating composition, preferably an ink composition, containing graphene for shielding electromagnetic interference at frequencies from 30 MHz to 300 GHz.

[0067] The properties of graphene are shown below.

[0068] Optical images are shown in Figures 1a and 1b, where exfoliated nanoplatelets with various dimensions and morphologies can be observed. Further investigation by scanning electron microscopy (SEM) (Figures 1c-g) and surface analysis at high resolution show a layered structure of graphene nanoplatelets (GNPs) with folded edges.

[0069] In one embodiment, Figure 2 shows lateral size measurements of 160 flakes. The average size of the GNPs can be calculated to be 4.0 μm, with 50% of the flakes less than 2.0 μm and 90% less than 7.8 μm.

[0070] In one embodiment, using bright-field (BF) TEM, it is possible to see overlapping layers of graphene flakes floating on a carbon holey grid (Figure 3a-c). Figure 3d shows an image taken at high magnification where multiple folded nanosheets are visible overlapping, exhibiting moiré patterns resulting from crystal mismatch.

[0071] Raman spectroscopy of the pristine graphite powder and the GNP powder after exfoliation is shown in Figure 4. A detailed view of the peaks and their corresponding fittings can be seen in Figures 4b and 4c. Due to the few-layer / multilayer nature of the samples, fitting of the 2D peaks needs to be done using three separate Lorentzians, as opposed to the characteristic single symmetric Lorentzian shape of monolayer graphene.

[0072] The positions, full and half width (FWHM) and intensity ratio values ​​of the characteristic peaks are given in Table 1. The characteristic D, G and 2D modes of graphite are at 1350.9, 1581.0 and 2703.6 cm, respectively. -1 Comparing GNPs with graphite, there are no significant changes in the peak positions or shapes, except for a slight decrease in the D / G band intensity ratio from 0.18 to 0.14. The lower D band intensity indicates the absence of defects and a significantly larger crystal size. This feature may be related to edge effects, which are more easily observed in extensively exfoliated graphene with small sheet sizes (A.C. Ferrari, J.C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri, F. Mauri, S. Piscane, D. Jiang, K.S. Vosselov, S. Roth, A.K. Geim, 187401 (2006), M. Lotya, Y. Hernandez, P.J. King, R.J. Smith, V. Nicolosi, L.S. Karlsson, F.M. Blighe, S. De, Z. Wang, I.T.c.Govern, G.S. Duesberg, J.N. Coleman, J.Am. Chem. Soc. 131 (2009) 3611-3620).

[0073] Table 1: Raman peak characteristics of GNP powder of one embodiment of a graphene-based coating composition extracted from fitting of the peaks using a single Lorentzian curve.

[0074] [Table 1]

[0075] X-ray photoelectron spectroscopy (XPS) allows for extremely selective characterization of the surface chemical properties of materials. In the case of carbon-based materials, it is particularly useful to quantify the amount of oxygen groups and identify the various functional groups. The XPS spectra of both pure graphite (a) and GNP (b) powder contained no elements other than carbon and oxygen, thus indicating the absence of impurities or contaminants. From the normalized survey spectra in Figure 5a and Table 2, it can be noticed that the O 1s peak is slightly reduced from 5.4% to 4.9% when graphite is exfoliated to GNPs. Figure 5b shows the high-resolution spectrum of the C 1s peak of the same sample. Besides the characteristic asymmetric peaks assigned to C-C and C-H bonds, a small peak at 248.8 eV due to O-C=O groups was detected in the graphite sample (a) but not in the GNP powder (b). A secondary peak corresponding to a plasmon / shake-up feature was also detected at a higher binding energy around 291 eV. The binding energy, FWHM, and atomic percentage values ​​of the peaks adapted from Fig. 5b are shown in Table 3. No significant peak shifts were detected, strengthening the hypothesis that the exfoliation process does not introduce new functional groups / contaminants or change the chemical nature of the materials.

[0076] Table 2: Binding energies, full width at half maximum (FWHM), and atomic percentage C 1s and O 1s values ​​obtained from the survey spectra in Figure 5a for both graphite and GNP samples of the present disclosure.

[0077] [Table 2]

[0078] Table 3: Percentage of XPS fitting peaks obtained from the high-resolution C 1s spectrum in Figure 5b.

[0079] [Table 3]

[0080] The thermal stability of the GNP powders of the present disclosure was determined by TGA, and the percentage of mass loss is shown in Table 2. The structural and chemical properties of the carbon-based powders (e.g., particle size / thickness, defects, presence of functional groups, oxygen content level) can affect the TGA characteristics. For example, graphene oxide (GO) typically exhibits 2-3 significant mass loss events at temperatures below 300 °C, which can be explained by the removal of moisture (below 100 °C) and the removal of oxygen functional groups (100-360 °C) (F. Farivar, PLYap, RU Karunagaran, D. Losic, C 2021, Vol. 7, 41.7 pages (2021)). As expected, these phenomena were not observed in the GNP samples of the present invention, which showed a mass loss of about 2% at temperatures below 100 °C and an almost linear mass change behavior up to 250 °C. This result is consistent with other GNP powders reported by Hack et al. (R. Hack, CHG Correia, RA de S. Zanon, SHPezzin, Mate'ria (Rio Janeiro). 23 (2018)).

[0081] Table 4: TGA analysis of GNP powders of the present disclosure.

[0082] [Table 4]

[0083] Below is a comparison with other commercially available graphene nanoplates.

[0084] Samples of different commercially available materials, namely K1, K2, F1, F2 (comparative data), are shown in Table 5. K1 corresponds to K-Nano (KNG-150) from K-NANO. KNG-150 graphene nanoplatelets are stacks of multi-layer graphene sheets with platelet morphology. K2 corresponds to TA-001A, which consists of a large number of single-layer sheets and a small number of few-layer graphene. F1 corresponds to PureGRAPH™ 5 from FirstGraphene, characterized by large plate size, and F2 corresponds to PureGRAPH™ 10 from FirstGraphene, characterized by graphene nanoparticles.

[0085] From the optical inspection shown in Figure 6, it was possible to confirm that K1(a) and F1(c) are the smallest flakes, with the majority of them having a lateral size of less than 5 μm. K2(b) and F2(d) have similar dimensions, although the size and thickness of the newest one seems to be slightly larger. These conclusions are in line with the data available from the supplier listed in Table 5.

[0086] Table 5: Comparison of thickness and lateral size of samples from different suppliers. Data for the GNP embodiment was taken from the characteristics shown in the previous section, while data for the other samples was collected from the supplier's website and data sheets.

[0087] [Table 5]

[0088] By comparing the Raman spectroscopy of all samples (Figure 7), the low D peak intensity and slightly higher I2D / IG ratio of the GNP embodiments of the present disclosure are highlighted. All spectra are very similar and characteristic of multi-layered GNPs, with the exception of K1(a), where the small lateral dimensions of the flakes have a large impact on the intensity of the D and D' peaks, and the shape of the 2D band reflects a thickness of a few layers (2-5 layers) despite the supplier's statement that the flakes should be multi-layered (>10 layers) due to the thin flakes (D. Yoon, H. Moon, H. Cheong, JS Choi, JA Choi, BH Park, J. Korean Phys. Soc. 55 (2009) 1299-1303).

[0089] The chemical and structural properties of the GNP samples of the present invention were compared by XPS, and no elements other than C and O were detected. The high-resolution C 1s spectrum (Figure 8) shows the similarity of all plots, and no O-containing functional groups were detected. The only difference between the samples is the percentage of oxygen detected. The K1 and K2 samples contain about 4-5% oxygen, which is similar to the GNPs of the present invention, while the F1 and F2 samples contain higher levels of oxygen, 8-9%, as shown in Table 6. This could be related to various factors, such as different production methods, the solvent / liquid medium used, and the properties of the raw graphite. Graphene with lower oxygen content may be associated with better electrical properties (C. Mattevi, G. Eda, S. Agnoli, S. Miller, K. A. Mkhoyan, O. Celik, D. Mastrogiovanni, G. Granozzi, E. Carfunkel, M. Chhowalla, Adv. Funct. Mater. 19 (2009) 2577-2583).

[0090] Table 6: XPS data obtained from survey spectra of K1 and K2, F1 and F2 GNPs. No elements other than carbon and oxygen were detected.

[0091] [Table 6]

[0092] In one embodiment, the graphene material used in the coating composition disclosed herein is in the form of nanoplatelets with particle sizes ranging from 1 μm to 25 μm (as shown in FIG. 2 above) and flake thicknesses of less than 100 nm.

[0093] Table 7 shows the lateral particle size distribution of the graphene samples used in the present invention.

[0094] Table 7: Lateral size distribution of particles in samples of graphene nanoplatelets of the present invention.

[0095] [Table 7]

[0096] Figure 12(a)-(i) show overview TEM images of graphene flakes. These TEM images show grain sizes of about 5 μm, dark contrast areas indicating different thicknesses, and folded flakes that may cause an increased grain thickness reading. Also shown are some overlapping and twisted flakes with different crystal orientations, showing a moiré effect.

[0097] Figure 13 shows an overview of different sections of graphene material, where further morphological analysis was performed on transparent particle types.

[0098] Figures 14, 15, and 16 show the TEM images of the graphene material used for morphology analysis. Figure 15 shows the graphene material where it is observable that some graphene flakes are elongated in a rod morphology. It has been shown that some graphene particles as shown in Figure 16 are formed by folded flakes, i.e. the same flakes are folded several times to form a zigzag morphology. As shown in Figure 16, the particle size was measured to be about 5 μm. The dark contrast reveals that there is a difference in thickness and the thickness of the particles increases due to the folded flakes. The graphene sample consists of a particle size distribution of 1 μm to 20 μm, with the flake thickness being less than 10 nm. The smaller particles are formed from the exfoliated flakes of the larger particles and the thickness of the smaller particles is related to the way the flakes are folded, i.e. the number of times they are folded.

[0099] In one embodiment, approximately 90% of the graphene nanoplatelets are in the lateral size range of 0.3-8 μm. Smaller particles have a higher total surface area and require less graphene to achieve the percolation threshold. Smaller particles also have a lower viscosity, which is a good property for coating applications.

[0100] Below are examples of coating compositions.

[0101] In one embodiment, the Coating #A (or Ink #A) composition comprises: 2% by weight of graphene nanoplates, 6% by weight of graphite, 0.5% by weight of alkoxysilane, 21.5% by weight of polysiloxane, 20% by weight of polyoxyethylene, 50% by weight of xylene, Includes.

[0102] In one embodiment, Coating #B (or Ink #B) composition comprises: 15% by weight of graphene nanoplates, 2% by weight of carbon black, 23% by weight polyimide; 60% by weight of water, Includes.

[0103] In one embodiment, Coating #C (or Ink #C) composition comprises: 10% by weight of graphene nanoplates, 3% by weight of carbon nanotubes; 2% by weight of alkoxysilane, 28% by weight of polysiloxane, 27% by weight of polyoxyethylene, 30% by weight of xylene, Includes.

[0104] The coating composition (ink) may generally be prepared using a mixing device.

[0105] In one embodiment, the disclosed graphene-based composition for EMI shielding comprises: 0.1-30 wt.% graphene nanoplatelets; 0.1-30% by weight of other carbon-based materials; 0.1 to 20% by weight of an alkoxysilane, 0.1 to 40% by weight of a polysiloxane or other silicone-based polymer, 0.1 to 10% by weight of polyoxyethylene, 10 to 30% by weight of a xylene compound; This includes compounds of the formula:

[0106] In one embodiment, the polysiloxane is polydimethylsiloxane (PDMS).

[0107] In one embodiment, the carbon-based material is selected from natural and synthetic graphite, carbon black, carbon nanotubes, carbon nano-onions, graphene oxide, and carbon nanospheres.

[0108] In one embodiment, the xylene compound is a mixture of xylene and ethylbenzene.

[0109] In one embodiment, the polyoxyethylene is polyoxyethylene 10 tridecyl ether.

[0110] In one embodiment, the composition, preferably the ink, further comprises a solvent selected from, but not limited to, kerosene, toluene, water, dimethylsulfoxide, butanone, diethylene glycol monoethyl ether acetate, silane, tetrahydrofuran, ethanol, polyacrylic acid, polyvinyl acid, terpineol, or mixtures thereof.

[0111] The solvent is present in the range of 0.1 to 85% by weight.

[0112] In one embodiment, the composition further comprises a polymeric binder selected from, but not limited to, polyetherimide, polysiloxane, polyethyleneimine, ethylcellulose, or mixtures thereof.

[0113] The polymer is present in the range of 1 to 40% by weight, preferably 10 to 35% by weight.

[0114] In one embodiment, the composition includes an additive selected from, but not limited to, an alkoxysilane, such as (3-aminopropyl)triethoxysilane.

[0115] The additive, ie, alkoxysilane, is present in the range of 0.1 to 20% by weight, preferably 0.2 to 5% by weight.

[0116] Next, the properties of the coating, and in particular the properties of the ink, will be described.

[0117] Due to the excellent electrical and thermal properties of GNPs, their use as conductive additives and fillers in coatings, especially inks, can be beneficial for a variety of applications, such as sensors, batteries, medical devices, electromagnetic interference (EMI) shielding, electric vehicles, and aerospace.

[0118] The compositions of the present invention are paintable coatings and are ideal for use in EMI shielding.

[0119] In one embodiment, Figure 9a shows an example of a RT dried Coating #A (or Ink #A) layer blade coated on a Mylar substrate. When examining a cross section of this layer (Figure 9b), the non-uniform domains of the coating can be observed. The polymer matrix can be seen as bright areas with high contrast, allowing for the formation of a thick, structurally integrated coating, as well as surrounding the GNPs in continuous pathways, forming a conductive network and enabling electro-osmosis.

[0120] Inspection of the coating surface with SEM (Figures 9c-f) reveals that the flakes are very densely interconnected, with no visible defects or gaps within the layer. When the graphene flakes are viewed at higher magnification (Figure 9f), evaporation of the solvent results in the formation of air pockets within the polymer passivation coating of the graphene flakes, resulting in in some cases in a spherical surface texture.

[0121] In one embodiment, FIG. 10 shows the FTIR spectrum of Coating #A (or Ink #A). The FTIR provides evidence of the presence of silicon and oxygen-containing functional groups attached to the graphene-based material. The numbers in the figure represent the functional groups associated with PDMS, as described in Table 8. 2850, 1794, and 1571 cm -1 The weak peaks in the vicinity correspond to the symmetric CH stretching vibration (a), C=O stretching vibration (b), and C=C aromatic ring (c), respectively.

[0122] Table 8: Functional groups of the PDMS matrix for coating #A (or ink #A).

[0123] [Table 8]

[0124] Due to the high electrical conductivity of Coating #A (or Ink #A), it can be used as an effective EM shielding material. The shielding effectiveness depends not only on the electrical conductivity of the material, but also on its thickness, as shown in Equation 1:

[0125]

number

[0126] where t is the sample thickness and δ is the skin depth.

[0127] Therefore, three samples with three different thicknesses (~108 μm (Sample A), ~154 μm (Sample B), ~287 μm (Sample C)) were fabricated on a Mylar substrate. S-parameters were extracted using a VNA from 100 MHz to 3 GHz, and conductivity was extracted using a four-tip probe and a source meter.

[0128] Table 9: Conductivity and EM attenuation of coating compositions of the present disclosure samples - Coating #A (or Ink #A) sample.

[0129] [Table 9]

[0130] From these measurements, it is observable that by increasing the film thickness by about 50%, from about 108 μm (Sample A) to about 154 μm (Sample B), the resistivity is significantly reduced by half, from about 61 Ω / sq to about 30 Ω / sq. By further increasing the thickness to about 287 μm (Sample C), no significant change in bulk resistivity was detected, but the sheet resistance was almost halved compared to Sample B.

[0131] With regard to the EM shielding effectiveness, as expected, an increase in thickness is reflected in an increase in the EM absorption values, reaching about 22 dB for the thickest sample (C). This represents more than 99% attenuation of the electric field, a level that exceeds the adequate requirements for most commercial applications. It is worth noting that most of the EM attenuation of Coating #A (or Ink #A) is done by EM absorption, with the amount of reflection decreasing as the thickness of the sample increases, a property of conductive carbon-based materials and unlike metal shields, which mostly prevent the transmission of EM waves via a reflection mechanism, which can affect adjacent unprotected systems.

[0132] The EM shielding properties of the bare Mylar substrate were also measured, but no significant signal loss was detected, so the effect from the substrate can be neglected.

[0133] A plot of the data in Table 9 is better visualized in Figure 11.

[0134] In one embodiment, the compositions of the present disclosure are suitable for use as coatings, preferably ink coatings, on flexible or rigid materials, smooth or textured surfaces.

[0135] In one embodiment, the compositions are used as coatings for industrial equipment, electronic components, medical devices, communication equipment, office equipment, military equipment, automotive parts, aerospace and defense equipment, EMI / RFI shielded enclosures, cables, RFID tags, solar panels, consumer electronics, mobile devices and flexible electronics, sensors, wearable electronics, touch screens.

[0136] In one embodiment, the composition is applied by spray coating, paint brush, roll coating, spin coating, blade coating, bar coating, doctor blade, dip coating, screen printing, or drop casting techniques.

[0137] Table 10 shows the application of the compositions using various coating techniques and the coating thickness.

[0138] [Table 10]

[0139] Table 11 shows the results of the ink composition samples using various coating techniques and coating thickness.

[0140] [Table 11]

[0141] After application, the composition may be allowed to dry naturally or cured by heating at temperatures up to 250°C.

[0142] Methods of applying the disclosed compositions include applying the coating composition, preferably an ink, as a coating by spray coating, paint brush, roll coating, spin coating, blade coating, bar coating, doctor blade, dip coating, screen printing, or drop casting, followed by air drying or curing by heating at temperatures up to 250°C.

[0143] In one embodiment, the ink composition coating has a thickness of 15 to 20000 μm.

[0144] When ranges are specified, the endpoints are included. Moreover, unless otherwise indicated or clear from the context and / or understanding of one of ordinary skill in the art, it is to be understood that values ​​expressed as ranges can take any particular value within the ranges defined in different embodiments of the invention, down to one tenth of the unit of the lower limit of the range, unless otherwise clearly indicated by the context and / or understanding of one of ordinary skill in the art. It is also to be understood that values ​​expressed as ranges can assume any subrange within the given range, with the endpoints of the subranges being expressed to the same precision as one tenth of the unit of the lower limit of the range, unless otherwise indicated or clear from the context and / or understanding of one of ordinary skill in the art.

[0145] The term "comprising" as used in this document is intended to indicate the presence of stated features, integers, steps or components, but does not exclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0146] Those skilled in the art will appreciate that, unless otherwise stated herein, the particular order of steps described is merely illustrative and may be varied without departing from the disclosure. Thus, unless otherwise stated, the steps described are unordered, implying that, where possible, steps may be performed in any convenient or desirable order.

[0147] This description is of course in no way limited to the embodiments presented in this specification, which may offer a person of average knowledge in the field many possibilities for modifying them without departing from the general concept defined in the claims.

[0148] The above-described embodiments may be combined with each other, and the appended claims further define particular embodiments of the present disclosure.

Claims

1. 0.1 to 30 wt. % of graphene as a first carbon-based material; 0.1 to 30 wt. % of a second carbon-based conductive material; 0 to 20 wt. % of a dispersant, preferably an alkoxysilane; 0.1 to 40 wt. % of a polymer as a binder selected from the list of silicone-based polymers, polyetherimides, polysiloxanes, polyethyleneimines, ethylcellulose, or mixtures thereof; 0.1 to 10% by weight of polyoxyethylene; 10 to 85 wt. % of a solvent selected from the list consisting of xylene, kerosene, toluene, water, dimethyl sulfoxide, butanone, diethylene glycol monoethyl ether acetate, silane, tetrahydrofuran, ethanol, polyacrylic acid, polyvinyl acid, terpineol, or mixtures thereof; 1. A graphene-based coating composition for shielding electromagnetic interference at frequencies between 30 MHz and 300 GHz, comprising:

2. The composition of claim 1, wherein the solvent is in the range of 20 to 60% by weight, preferably 20 to 50% by weight, more preferably 20 to 30% by weight.

3. 2. The composition of claim 1, wherein the solvent is selected from the list consisting of xylene, water, or a mixture thereof, preferably xylene.

4. 10. The composition of claim 1, wherein the graphene is selected from nanoplate graphene, few layer graphene, multilayer graphene, oxide graphene, or a combination thereof.

5. 10. The composition of claim 1, wherein the graphene is nanoplate graphene.

6. The composition of claim 1, wherein the graphene nanoplates have a diameter particle size of 1 μm to 25 μm, preferably 0.3 to 8 μm.

7. 6. The composition of claim 5, wherein the graphene nanoplates have a D50 size of 2.0 μm and a D90 size of 7.8 μm.

8. 2. The composition of claim 1, wherein the thickness of the graphene flakes is less than 100 nm, more preferably 0.33 to 15 nm.

9. The composition of claim 1, wherein the amount of said polymer ranges from 1 to 40% by weight, preferably from 10 to 35% by weight, more preferably from 15 to 25% by weight.

10. The composition of claim 1 , wherein the polymer is a polysiloxane.

11. The composition of claim 1 , wherein the polysiloxane is polydimethylsiloxane.

12. The composition of claim 1, wherein the amount of alkoxysilane ranges from 0.1 to 20% by weight, preferably from 0.2 to 10% by weight, more preferably from 0.5 to 5% by weight.

13. 10. The composition of claim 1, wherein the second carbon-based conductive material is selected from the list consisting of graphite, carbon black, carbon nanotubes, carbon nano-onions, graphene oxide, carbon nanospheres, and mixtures thereof.

14. 2. The composition of claim 1, wherein the polyoxyethylene is polyoxyethylene 10 tridecyl ether.

15. The composition of claim 1, wherein the alkoxysilane is (3-aminopropyl)triethoxysilane.

16. An ink comprising the composition of any one of claims 1 to 15.

17. A coated article comprising a graphene-based composition according to any one of claims 1 to 15.

18. 18. The coated article of claim 17, which is industrial equipment, electronic components, medical devices, communications equipment, office equipment, military equipment, automotive parts, aerospace and defense equipment, EMI / RFI shielding enclosures, cables, RFID tags, solar panels, consumer electronics, mobile devices and flexible electronics, sensors, wearable electronics, touch screens, parasitic elements, board level shielding, patches, thin films, and the like.

19. The coated article according to claim 18, wherein the thickness of the coating composition is in the range of 15 to 20,000 μm, preferably 50 to 500 μm, more preferably 100 to 300 μm.

20. 20. The coated article of claim 19, wherein the coating composition has a thickness in the range of 100 to 250 μm.

21. mixing a polymer binder in a solvent; adding graphene to the mixture; adding a second carbon-based conductive material to the mixture; adding polyoxyethylene to the mixture; Including, the polymer as binder is selected from silicone-based polymers, polyetherimides, polysiloxanes, polyethyleneimines, ethylcellulose, or mixtures thereof, in the range of 0.1 to 40% by weight; The graphene range is 1 to 30 wt. %; the second carbon-based conductive material is in the range of 0.1 to 30 wt. %; the polyoxyethylene is in the range of 0.1 to 10% by weight, the solvent is selected from the list consisting of xylene, kerosene, toluene, water, dimethyl sulfoxide, butanone, diethylene glycol monoethyl ether acetate, silane, tetrahydrofuran, ethanol, polyacrylic acid, polyvinyl acid, terpineol, or mixtures thereof, in the range of 10 to 85% by weight; 10. A method for obtaining the graphene-based coating composition of claim 1.

22. The process further comprising the step of adding a dispersant to said mixture, preferably 0.1 to 20 wt. % of an alkoxysilane.

23. 22. A method of applying the graphene-based coating composition of any one of claims 1 to 15 or claim 21, comprising the steps of applying the coating composition to a substrate by spray coating, paint brush, roll coating, spin coating, blade coating, bar coating, doctor blade, dip coating, screen printing, or drop casting techniques, and curing the coating layer by heating at a temperature of up to 250°C, preferably by air drying.

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