APPLICATIONS CROSS-REFERENCETORELATEDAPPLICATIONS

[0001] This application claims priority to and the benefit of the provisional patent application titled “Development of Low-Cost Epoxy Composites for Electromagnetic Interference Shielding Applications,” application number 202141009368, filed in the Indian Patent Office on March 05, 2021. The specification of the above referenced patent application is incorporated herein by reference in its entirety.

BACKGROUND

Technical Field

[0002] The embodiments herein are generally related to electromagnetic interference (EMI) shielding. The embodiments herein are particularly related toa composite sheet developed by the use of a continuous matrix with randomly dispersed conductive particulates along with a flexible graphite sheet (FGS). The embodiments herein are more particularly related to a composite sheet, which is formable and is of sufficient strength to act as a structural component and is suitable for use in automotive components that require EMI shielding. Description of Related Art

[0003] One of the most common issues encountered in various electronic systems is Electromagnetic Interference (EMI). This can disrupt the normal working of the electronic systems. These disruptions occur due to the generation of undesirable currents by outside electromagnetic radiations. To overcome these issues and protect the electronic systems, it is generally favoured to use an EMI shielding material in different forms such as coatings, gaskets, composites, conductive enclosures, etc.

[0004] The EMI shielding materials are unique because they do not let electromagnetic waves of undesired wavelength pass through and reflect them, thereby protecting the sensitive components.

[0005] Additionally, within the device as well, EM radiation can interfere with precise circuitry and may adversely affect its efficiency, energy consumption, and may result in a sudden breakdown.

[0006] Another class of EMI shielding materials absorbs electromagnetic waves rather than reflecting them. This class of EMI shielding materials is mostly used for stealth and radar applications. Modem-day EMI shielding materials require greater performance whilst consuming less space and having lightweight properties.

[0007] Hence, there is a need for an efficient and lightweight EMI shielding material capable of providing a comprehensive shielding performance over existing ones. [0008] The shortcomings mentioned above, disadvantages, and problems are addressed herein, which will be understood by reading and studying the following specifications.

OBJECTIVES OF THE EMBODIMENTS HEREIN [0009] The primary objective of the embodiments herein is to provide a technique to develop a low-cost composite sheet for electromagnetic interference (EMI) shielding.

[0010] Another objective of the embodiments herein is to provide a composite sheet comprising of a continuous polymer matrix with randomly dispersed conductive particulates along with a flexible graphite sheet (FGS). [0011] Yet another object of the embodiments herein is to provide a composite sheet developed by layer-by-layer assembly of the polymer matrix.

[0012] Yet another object of the embodiments herein is to provide a composite sheet in which a polymer matrix is composited with conductive particulates, which comprises of various carbon derivatives.

[0013] Yet another object of the embodiments herein is to provide a composite sheet in which polymer matrix composited with carbon derivatives is laminated with a flexible graphite sheet (FGS).

[0014] Yet another object of the embodiments herein is to provide a composite sheet in which the polymer matrix is made up of epoxy.

[0015] Yet another object of the embodiments herein is to provide a composite sheet in which the carbon derivatives comprise materials such as, but not limited to, multi-walled carbon nanotubes (MWCNTs), expanded graphite (EG), or graphene nanoplatelets (GNPs). [0016] Yet another object of the embodiments herein is to provide a composite sheet with FGS of a thickness of 0.1 to 1.0 mm.

[0017] Yet another object of the embodiments herein is to provide a composite sheet which is developed by a simple hand lay-up technique.

[0018] Yet another object of the embodiments herein is to provide a composite sheet that has a total shielding effect of 35 - 55 dB at 12.5 GHz inthe Ku - band.

[0019] Yet another object of the embodiments herein is to provide a composite sheet with high heat dissipation capacity.

[0020] Yet another object of the embodiments herein is to provide a composite sheet that has the capability to come down to 27°C from 60-80°C in 20-60 seconds. [0021] Yet another object of the embodiments herein is to provide a composite sheet, which is made up by preparing a mixture of epoxy and carbon derivatives.

[0022] Yet another object of the embodiments herein is to provide a composite sheet in which 0.1 - 5 % of carbon derivative is mixed in a solvent like ethanol by sonication while preparing the composite sheet for 10 - 60 minutes.

[0023] Yet another object of the embodiments herein is to provide a composite sheet in which epoxy resin is added to the carbon derivative mixture by sonication for 30 - 120 minutes under continuous stirring at 100 - 500 rpm while preparing the composite sheet. [0024] Yet another object of the embodiments herein is to provide a composite sheet for which the temperature is kept 40 - 80°C while preparing the composite sheet.

[0025] Yet another object of the embodiments herein is to provide a composite sheet in whicha hardener such as (1,2,3,6-tetrahydromethyl methanophthalic anhydride) is added in ratio from 100: 10 to 100:70 under stirring for 10 - 60 minutes while preparing the composite sheet.

[0026] Yet another object of the embodiments herein is to provide a composite sheet for which the mixture is poured in a mould and cured for 2 -6 hours at 60 - 150°C while preparing the composite sheet.

[0027] Yet another object of the embodiments herein is to provide a composite sheet for which the mould can be of metal such as aluminum, steel, or the iron with a coating of a material such asTeflon.

[0028] Yet another object of the embodiments herein is to provide a composite sheet for which post-curing is done at 100-200°C for 1-5 hours. [0029] Yet another object of the embodiments herein is to provide a composite sheet that is formable and is of sufficient strength to act as a structural component and is suitable for use in automotive components that require efficient EMI shielding.

[0030] These and other objects and advantages of the embodiments herein will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

SUMMARY

[0031] The following details present a simplified summary of the embodiments herein to provide a basic understanding of the several aspects of the embodiments herein. This summary is not an extensive overview of the embodiments herein. It is not intended to identify key /critical elements of the embodiments herein or delineate the embodiments' scope herein. Its sole purpose is to present the concepts of the embodiments herein in a simplified form as a prelude to the more detailed description that is presented later.

[0032] The other objects and advantages of the embodiments herein will become readily apparent from the following description taken in conjunction with the accompanying drawings. However, it should be understood that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

[0033] The various embodiments herein provide a low-cost composite for electromagnetic interference shielding. A composite sheet is developed, comprising a continuous matrix with randomly dispersed conductive particulates and a flexible graphite sheet. The composite sheets are formable and are of sufficient strength to act as structural components and are suitable for use in automotive components that require efficient EMI shielding.

[0034] According to an embodiment herein, the method of synthesizing a low- cost composite flexible graphite sheet (FGS) for electromagnetic interference (EMI) shielding, comprises the following steps. Carbon derivatives are dispersed in ethanol by bath sonication for a time period of 10-60 minutes to obtain a solution. Epoxy resin is added to the solution and the solution is mixed mechanically for a time period of 30-120 minutes at a stirring speed of 100-500 rpm and at a temperature range 40-80°C to obtain solution mixture. The anhydride -based hardener is added to the solution mixture. The solution mixture comprising anhydride-based hardener is mixed mechanically for a time period of 10-60 minutes at a stirring speed of 100-500 rpm. The flexible graphite sheet (FGS) is placed in Teflon coated metallic mould and the solution mixture comprising anhydride -based hardener and epoxy resin is poured to obtain a sample composite sheet. The sample composite sheet is cured at a temperature range of 60°C-150°C for 2-6 hours.

The sample composite sheet is post-curated at a temperature range of 100-200°C for 1-5 hours. The composite sheet is removed from the mould for EMI shielding. The synthesized flexible graphite sheet (FGS) is analyzed for total shielding effectiveness and for physic-chemical properties [0035] According to an embodiment herein, the carbon derivatives are selected from a group consisting of exfoliated graphene (EG), graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (CNTs). The carbon derivatives are dispersed in a solvent. The solvent is ethanol. The carbon derivatives are individually added in ethanol in an amount ranging 0.1 wt%-5 wt%. [0036] According to an embodiment herein, the anhydride -based hardener which is added to the solution mixture is 1, 2, 3, 6-tetrahydromethyl methanophthalic anhydride. The hardener is a cross-linking agent. The anhydride-based hardener is added to the solution mixture in a ratio of 100:10 to 100:70. [0037] According to an embodiment herein, the synthesized Flexible Graphite

Sheet (FGS) provides shielding effectiveness in a range of 35 - 55 dB at 12.6 GHz in Ku - band. The synthesized Flexible Graphite Sheet (FGS) has a thickness of 0.1 -1.0 mm. The synthesized Flexible Graphite Sheet (FGS) attains a temperature of 27 °C from a temperature of 60-80°C in a time period of 20-60 seconds. [0038] According to an embodiment herein, a technique is given to developing a composite sheet comprising a continuous matrix with randomly dispersed conductive particulates and a flexible graphite sheet.

[0039] According to an embodiment herein, a composite sheet is developed by layer-by-layer assembly of a polymer matrix where the polymer matrix is made up of epoxy.

[0040] According to an embodiment herein, the polymer matrix is composited with carbon derivatives such as, but not limited to, multi-walled carbon nanotubes (MWCNTs), exfoliated graphite (EG), or graphene nanoplatelets (GNPs).

[0041 ] According to an embodiment herein, the composite sheet was developed by dissolving the carbon derivatives in a solvent such as ethanol by the use of sonication for 10 - 60 minutes, followed by the addition of epoxy resin and mechanical mixing using an overhead stirrer equipped with a bath sonicator at 100 - 500 rpm for 30 - 120 minutes.

[0042] According to an embodiment herein, 0.1-5 weight % of carbon derivative is mixed in a solvent such as ethanol by sonication. [0043] According to an embodiment herein, the temperature is maintained at

40-80°C during mechanical stirring to evaporate the solvent.

[0044] According to an embodiment herein, an anhydride-based hardener is added in 100:10 - 100:70 ratio with mixing at 100 -500 rpm for 10-60 minutes. [0045] According to an embodiment herein, an anhydride-based hardener such as (1,2,3,6-tetrahydromethyl methanophthalic anhydride) is added to the mixture.

[0046] According to an embodiment herein, the mixture is poured in a Teflon coated metal mould made up of materials, but not limited to, such as aluminum, steel, iron and cured at 60 - 150°C for 2 - 6 hours followed by post-curing at 100 - 200°C for 1-5 hours.

[0047] According to an embodiment herein, the polymer matrix composited with conductive carbon derivatives is laminated with a flexible graphite sheet (FGS).

[0048] According to an embodiment herein, the flexible graphite sheet is, but not limited to, of 0.1- 1.0mm thickness. [0049] According to an embodiment herein, the composite sheet made by the simple hand lay-up technique has a total shielding effect of 35-55 dB at 12.5 GHz in Ku - band.

[0050] According to an embodiment herein, a composite sheet is developed with high heat dissipation capability, which can come down to 27°C from 60 - 80°C in 20 - 60 seconds.

[0051] According to an embodiment herein, the developed composite sheet can be used in an automotive application, biomedical application, energy production, and storage application, electrochemical applications for efficient EMI shielding.

[0052] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by referencing the drawings and the following detailed description.

[0053] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. However, it should be understood that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The other objects, features, and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:

[0055] FIG.l illustrates a schematic representation of the method of fabricating an EMI shielding composite sheet, according to one embodiment herein.

[0056] FIG.2 is a flow chart illustrating a method of fabricating an EMI shielding composite sheet with a simple hand lay-up technique, according to one embodiment herein.

[0057] The features of the embodiments herein are described in drawings and of which a few are not shown in all. These features can be combined with any or all other features that exist in the embodiments herein.

DETAILED DESCRIPTION OF THE EMBODIMENTS HEREIN

[0058] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other changes may be made without departing from the scope of the embodiments. The following detailed description is, therefore, not to be taken in a limiting sense.

[0059] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted to necessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of how the embodiments herein may be practiced and enable those of skill in the art to practice the embodiments further herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0060] The various embodiments herein provide a low-cost composite sheet and method for EMI shielding application based on a simple hand lay-up technique. The composite sheet consists of a continuous polymer matrix with randomly dispersed conductive particulates along with a Flexible Graphite Sheet (FGS), which provides total shielding effectiveness of 35 - 55 dB at 12.6 GHz in Ku - band.

[0061] According to an embodiment herein, the method of synthesizing a low- cost composite flexible graphite sheet (FGS) for electromagnetic interference (EMI) shielding, comprises the following steps. Carbon derivatives are dispersed in ethanol by bath sonication for a time period of 10-60 minutes to obtain a solution. Epoxy resin is added to the solution and the solution is mixed mechanically for a time period of 30-120 minutes at a stirring speed of 100-500 rpm and at a temperature range 40-80°C to obtain solution mixture. The anhydride -based hardener is added to the solution mixture. The solution mixture comprising anhydride-based hardener is mixed mechanically for a time period of 10-60 minutes at a stirring speed of 100-500 rpm. The flexible graphite sheet (FGS) is placed in Teflon coated metallic mould and the solution mixture comprising anhydride -based hardener and epoxy resin is poured to obtain a sample composite sheet.

The sample composite sheet is cured at a temperature range of 60°C-150°C for 2-6 hours. The sample composite sheet is post-curated at a temperature range of 100-200°C for 1-5 hours. The composite sheet is removed from the mould for EMI shielding. The synthesized flexible graphite sheet (FGS) is analyzed for total shielding effectiveness and for physic-chemical properties

[0062] According to an embodiment herein, the carbon derivatives are selected from a group consisting of exfoliated graphene (EG), graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (CNTs). The carbon derivatives are dispersed in a solvent. The solvent is ethanol. The carbon derivatives are individually added in ethanol in an amount ranging 0.1 wt%-5 wt%.

[0063] According to an embodiment herein, the anhydride -based hardener which is added to the solution mixture is 1, 2, 3, 6-tetrahydromethyl methanophthalic anhydride. The hardener is a cross-linking agent. The anhydride-based hardener is added to the solution mixture in a ratio of 100:10 to 100:70. [0064] According to an embodiment herein, the synthesized Flexible Graphite

Sheet (FGS) provides shielding effectiveness in a range of 35 - 55 dB at 12.6 GHz in Ku - band. The synthesized Flexible Graphite Sheet (FGS) has a thickness of 0.1 -1.0 mm. The synthesized Flexible Graphite Sheet (FGS) attains a temperature of 27 °C from a temperature of 60-80°C in a time period of 20-60 seconds. [0065] FIG.l illustrates a schematic representation of the method of fabricating an EMI shielding composite sheet, according to one embodiment herein. In a glass beaker 102, a mixture 101 of 0.1 - 5wt% of carbon derivatives such as, but not limited to multi- walled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs), exfoliated graphite (EG) is prepared with a solvent such as ethanol by bath sonication for 10 - 60 minutes. In another beaker, 103 epoxy resin 104 is taken. The mixture 101 and epoxy resin 104 are mixed in a glass beaker 106 to prepare a solution 105 by mechanical mixing by using overhead stirrer at 100 - 500 rpm and continuous bath sonication for 30 - 120minutes at a temperature of 40 - 80°C.

[0066] According to an embodiment herein, the anhydride -based hardener (1,2,3,6-tetrahydromethyl methanophthalic anhydride), which acts as a cross-linking agent, is added in the beaker 106 in 100: 10 - 100:70 ratio with continuous mixing at 100 - 500 rpm for 10 - 60 minutes.

[0067] According to an embodiment herein, the final mixture 105 is poured from the beaker 106 over the flexible graphite sheet 107, which provides strength and enhances the EMI shielding effect and the heat dissipation capability, contained in a metallic mould made of materials such as aluminum, steel, or iron with a coating of Teflon and is cured at 60 - 150 °C for 2 - 6 hours.

[0068] According to an embodiment herein, the final composite sheet 108 is prepared by performing a post-curing at 100-200°C for 1- 5 hours. The developed composite sheet 108 is removed from the mould and is directly used for EMI shielding applications.

[0069] FIG.2 is a flow chart illustrating a method of fabricating an EMI shielding composite sheet with a simple hand lay-up technique, according to one embodiment herein. At 201, carbon derivatives such as EG, MWCNTs, GNPs are dispersed in a solvent such as ethanol by bath sonication for 10 - 60 minutes. At 202, epoxy resin is added and mechanically mixed at 100 - 500 rpm for 30 - 120 minutes and at 40 - 80°C. At 203, anhydride - based hardener is added. At 204, mechanical mixing is done for 30 - 120 minutes at 100 - 500 rpm. At 205, the mixture is poured into a Teflon coated metallic mould holding a flexible graphite sheet. At 206, curing is performed for 2 - 6 hours at 60-150°C. At 207, post-curing is performed at 100 - 200 °C for 1 - 5 hours. At 208, the composite sheet is removed from the metallic mould for use in EMI shielding.

[0070] According to an embodiment herein simple carbon derivatives are used to fabricate flexible graphite sheet (FGS) such as exfoliated graphene (EG), graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (CNTs). The other materials are easily available. Further a simple process is used to fabricate exfoliated graphene (EG), graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (CNTs) without using any complex machinery.

[0071] According to an embodiment herein, the performance of flexible graphite sheet (FGS) is enhanced when compared to existing solutions. The flexible graphite sheet (FGS) illustrates extremely high thermal conductivity. The materials used to fabricate flexible graphite sheet (FGS) are fire retardant materials.

[0072] The embodiments herein provide a technique to prepare a composite sheet comprising of a continuous polymer matrix with randomly dispersed conductive particulates along with a flexible graphite sheet (FGS).

[0073] The embodiments herein provide flexible graphite sheet (FGS) which are fabricated with low-cost raw materials. The flexible graphite sheet (FGS) illustrates high leap in EMI shielding performance capabilities. The flexible graphite sheets (FGS) illustrate high thermal conductivity. The flexible graphite sheet (FGS) is highly scalable and easy to manufacture in bulk.

IB [0074] The embodiments herein provide a composite sheet which can be used in electromagnetic interference shielding application. The composite sheet is formable and is of sufficient strength to act as a structural component and is suitable for use in automotive components that require efficient EMI shielding.

[0075] The embodiments herein provide a composite sheet that can also be used in biomedical applications, energy production and storage applications, fire retardant applications, gaskets and high-temperature seals, and sensors.

[0076] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.

[0077] It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope.

[0078] Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications.

[0079] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the appended claims' spirit and scope. [0080] Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications.

[0081] It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications. However, all such modifications are deemed to be within the scope of the claims.