DESC:FIELD OF THE INVENTION:
The present invention relates to thermal control. More specifically, the present invention relates to a structurally modified graphite comprising a single crystal-based graphite having a hexagonal structure aligned in columnar form and a process for preparation of structurally modified graphite. The invention further relates to a multi layered graphite sheet (ML) having improved in-plane and through-plane thermal conductivity for uniform heat distribution in thermoelectric module having both "warming" and "cooling" effects.

BACKGROUND OF THE INVENTION:
Thermal controlling is a very essential technical requirement in various industries. Thermoelectric module also known as Peltier device/module is used in various industries to provide both "warming" and "cooling" effects. Further, thermal controlling is very much required in technical areas where customers require comfort such as automotive industries, healthcare, wellness and/or hospitality industry.

The current industrial trend is focusing on the health and comfort of customers. For example, Peltier based hot and cool seats actively heat and cool the seat of automotive vehicle to help maintain the core body temperature of the rider/driver in harsh weather. These Peltier modules along with a graphite sheet are mounted in the seat foam. However, during product testing uneven heating distribution and formation of areas with high heat flux density was observed. These high heat flux areas can cause product damage and can also have negative health impacts. Therefore, a solution for their elimination and uniform heat distribution is required.

Similarly in other industries such as healthcare, wellness and/or hospitality the existing solution involves using metallic heat sinks. However, metallic heat sinks usually do not have good in-plane thermal conductivity. Further, metallic heat sinks can also add weight and are corrosion prone and rigid. Accordingly, there is a need for a Peltier device having improved in-plane and through-plane thermal conductivity for uniform heat distribution at the same time having good flexibility.

Therefore, there exists a need for designing and developing an improved graphite sheet that can overcome the above-mentioned challenges. In fact, there is a requirement to provide a thermoelectric module with an improved graphite sheet which improves in-plane and through-plane thermal conductivity for uniform heat distribution at the same time having good flexibility.

OBJECTIVES OF THE PRESENT INVENTION:
The primary objective of the present invention is improvement in cooling and heating rate of a system.

A further objective of the present invention is to provide an in-plane and through-plane thermal conductivity enhancement of the system.

A further objective of the present invention is to provide a multi-layered graphite sheet (ML) having improved in-plane and through-plane thermal conductivity for uniform heat distribution, wherein the multi layered graphite sheet comprises a synthetic single crystal based graphite.

A further objective of the present invention is to provide a process for the preparation of structurally modified graphite sheet comprising a single crystal based graphite, with high purity and thermal conductivity tailored between 450-2000 W/m-K.

A further objective of the present invention is to provide a thermoelectric module which can be used for uniform heat distribution.

SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the description of the invention. This summary neither intended to identify key or essential inventive concepts of the invention and nor it is intended to determine the scope of the invention.

The present invention provides a structurally modified graphite comprising a single crystal-based graphite having a hexagonal structure aligned in columnar form. The structurally modified graphite has high purity in the range of 99 to 99.9 %, show no outgassing, and has thermal conductivity tailored between 450-2000 W/m-K.

The present invention also provides a multi-layered graphite sheet (ML) for uniform heat distribution, wherein the multi-layered graphite sheet (ML) comprises a first outer layer (L1) of a polymer polytertrafluoroethylene (PTFE) for the protection of underlying layers in the seat; a first middle layer (L2) of a structurally modified graphite comprising a single crystal-based graphite having a hexagonal structure aligned in columnar form for uniform in-plane and through-plane thermal conductivity across the seat; a second middle layer (L3) of an acrylic polymer for providing stability, strength, and protection from stress and strain; and an inner layer (L4) of an adhesive for proper placement of the multi-layered graphite sheet. The multi-layered graphite sheet is for use in automotive industry in Peltier based automotive hot and cool seats, in healthcare, wellness and/or hospitality in thermal bedding, thermal blanket, thermal belts and similar applications.

The present invention also provides a process for preparing the multi-layered sheet (ML), wherein the process comprises preparing a structurally modified graphite in the first step. Further, placing the structurally modified graphite and a polymer film between rollers of a calendaring machine, wherein the structurally modified graphite at one side is in contact with the polymer film. When passing through rollers of the calendaring machine at a temperature in the range of 200 to 300 °C, a bonded PTFE-Graphite composite layer is obtained in which the polymer film forms the first outer layer (L1) and the structurally modified graphite forms the first middle layer (L2). In the next step, an acrylic polymer layer and an adhesive layer sequentially laminated over the cooled structurally modified graphite side of the bonded PTFE-Graphite composite layer to obtain a laminated PTFE-Graphite composite layer. The acrylic polymer layer forms the second middle layer (L3) and the adhesive layer forms the inner layer (L4). Then the laminated PTFE-Graphite composite layer is subjected to pressing at a temperature in the range of 100°C to 150°C to obtain the multi-layered sheet (ML).

The present invention also provides a process for the preparation of a structurally modified graphite comprising preparing a graphite powder from non-graphitic graphitizable carbon forms comprises hydrocarbon through chemical vapour deposition; and rolling the graphite powder in the transverse direction using rollers to obtain the structurally modified graphite, wherein the structurally modified graphite is a synthetic single crystal-based graphite having a hexagonal structure aligned in columnar form, the single crystal-based graphite has high purity in the range of 99 to 99.9 %, no outgassing and thermal conductivity between 450-2000 W/m-K.

The present invention also provides a thermoelectric module for automotive hot and cool seat comprising a thermoelectric device, a multi-layered graphite sheet (ML) comprising a structurally modified graphite, and a cover, wherein the multi-layered graphite sheet is placed in between the thermoelectric device and the cover for thermal distribution.

BRIEF DESCRIPTION OF THE DRAWING:
The detailed description below will be better understood when read in conjunction with the appended drawings. For the purpose of assisting in the explanation of the invention, there are shown in the drawings embodiments which are presently preferred and considered illustrative.
It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown therein.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Figure 1: illustrates a pictorial representation of measuring the thermal conductivity of conventional graphite sheets;
Figure 2a: illustrates a conventional graphite structure which has a misaligned honeycomb structure; Figure 2b: illustrates a synthetic graphite structure which has an aligned honeycomb structure, according to one embodiment of the present disclosure;
Figure 3: illustrates the schematic diagram of the invented multi-layered graphite sheet with PTFE, acrylic and adhesive layer, according to one embodiment of the present disclosure;
Figure 4: illustrates the schematic diagram of the thermoelectric module having the invented multi-layered graphite sheet, according to one embodiment of the present disclosure;
Figures 5a-5c: illustrates the pictorial diagram of the graphite sheet without any PTFE or Acrylic layer according to one embodiment of the present disclosure;
Figure 6a-6b: illustrates the pictorial diagram of the invented multi-layered graphite sheet with PTFE, acrylic and adhesive layer, according to one embodiment of the present disclosure;
Figure 7: illustrates the schematic diagram of testing the thermal conductivity of the invented multi-layered graphite sheet with PTFE, acrylic and adhesive layer, according to one embodiment of the present disclosure;
Figure 8a: illustrates the graphical diagram of heating temperature difference observed on conventional graphite sheet, according to one embodiment of the present disclosure;
Figure 8b: illustrates the graphical diagram of cooling temperature difference observed on conventional graphite sheet, according to one embodiment of the present disclosure;
Figure 9a: illustrates the graphical diagram of heating temperature difference observed on invented multi-layered graphite sheet with PTFE and acrylic layer but without adhesive layer, according to one embodiment of the present disclosure;
Figure 9b: illustrates the graphical diagram of cooling temperature difference observed on invented multi-layered graphite sheet with PTFE and acrylic layer but without adhesive layer, according to one embodiment of the present disclosure;
Figure 10a: illustrates the graphical diagram of heating temperature difference observed on invented multi-layered graphite sheet with all layers, according to one embodiment of the present disclosure; and
Figure 10b: illustrates the graphical diagram of cooling temperature difference observed on invented multi-layered graphite sheet with all layers, according to one embodiment of the present disclosure.

DESCRIPTION OF THE INVENTION:
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated process, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, methods, and examples provided herein are illustrative only and not intended to be limiting.

The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

The term “some” as used herein is defined as “none, or one, or more than one, or all”. Accordingly, the terms “none”, “one”, “more than one”, “more than one, but not all” or “all” would all fall under the definition of “some”. The term “some embodiments” may refer to no embodiments or to one embodiment or to several embodiments or to all embodiments. Accordingly, the term “some embodiments” is defined as meaning “no embodiment, or one embodiment, or more than one embodiment, or all embodiments”.

More specifically, any terms used herein such as but not limited to “includes”, “comprises”, “has”, “consists” and grammatical variants thereof is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. The specification will be understood to also include embodiments which have the transitional phrase “consisting of” or “consisting essentially of” in place of the transitional phrase “comprising”. The transitional phrase “consisting of” excludes any element, step, or ingredient not specified in the claim, except for impurities associated therewith. The transitional phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention.

Whether or not a certain feature or element was limited to being used only once, either way it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element”. Furthermore, the use of the terms “one or more” or “at least one” feature or element do NOT preclude there being none of that feature or element, unless otherwise specified by limiting language such as “there NEEDS to be one or more” or “one or more element is REQUIRED”.

Use of the phrases and/or terms such as but not limited to “a first embodiment”, “a further embodiment”, “an alternate embodiment”, “one embodiment”, “an embodiment”, “multiple embodiments”, “some embodiments”, “other embodiments”, “further embodiment”, “furthermore embodiment”, “additional embodiment” or variants thereof do NOT necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

Thermoelectric module also known as Peltier device/module is used in the automotive seat or any other industrial article for hot and cool function. This device is placed directly below the seat cover and/or industrial article. Since seat foam and seat cover are polymer based and/or the industrial article have metals, the heat spread throughout the seat or article is uneven. The area directly above the thermoelectric module has reported high temperature as compared to the other areas.

Accordingly, there is a need for uniform heat distribution that can distribute and conduct heat evenly in x, y and z directions i.e., have great in-plane and through-plane thermal conductivity.

Graphite is an allotrope of Carbon. Graphite is formed of a layered structure with strong covalent bonds within the layers, and weak Van der Waals bonds connecting the layers. It has anisotropic physical properties. The thermal conductivity of natural graphite is approximately 1000 W/(m-K) in the plane and around 5 W/(m-K) through the thickness, making it a good heat spreader.

However, natural/conventional graphite sheets have static imperfections, limited columnar structure, point defects, dislocation, and misalignment of hexagonal structure. These problems result in reduced thermal conductance and limited thickness of 1.5 mm. Due to structure imperfections natural/conventional graphite sheets also have mechanical strength limitations and thus cannot be used in industrial applications as there are many factors such as high vibrations, requirements of flexibility and adaptability in different industrial applications. Further, uneven thermal variation was also observed in experiments conducted with natural/conventional graphite sheets. The thermal conductivity of natural/conventional graphite sheets is measured and illustrated as in figure 1 and in table 1 below.

Table 1
X Y
Sample 1 10.1 Deg. Celsius 16.8 Deg. Celsius
Sample 2 8.8 Deg. Celsius 19.4 Deg. Celsius

As illustrated in Figure 1, in an experiment, sample 1 (S1) and sample 2 (S2) of natural/conventional graphite sheets are placed on thermal environment (TE). This experiment is performed to measure the temperature in X and Y direction with the help of thermistors S1A, S1B, S2A and S2B. As evident by the readings in table 1, huge variation in temperature is observed. This indicates that natural/conventional graphite sheets are not efficient in heat spreading as per industrial requirements.

In view of the above drawbacks of the natural graphite and for improving the graphite sheet functionality, a structurally modified graphite comprising a synthetic single crystal-based graphite is used in the present invention. In an embodiment, the present invention discloses a structurally modified graphite comprising a single crystal-based graphite having a hexagonal structure aligned in columnar form. The structurally modified graphite has high purity in the range of 99 to 99.9 %, show no outgassing, and has thermal conductivity tailored between 450-2000 W/m-K. Further, the structurally modified graphite having improved in-plane and through-plane thermal conductivity for uniform heat distribution.

In an embodiment of the present invention, the structurally modified graphite is a single crystal-based graphite having a hexagonal structure aligned in columnar form. Figure 2a and 2b illustrate the difference in structure of natural/conventional and synthetic graphite sheets respectively. Figure 2a illustrates the hexagonal structure of natural graphite sheet which is a misaligned hexagonal structure and figure 2b illustrates the hexagonal structure of synthetic graphite sheet which is an aligned in columnar manner.

Further, to improve on the shortcomings of nature/conventional graphite sheets in automotive seat or any other industrial article for hot and cool function, a multi-layered graphite sheet (ML) is made. The multi-layered sheet (ML) includes 4 layers. For better industrial adaptability, the construction of multi-layered graphite sheets (ML) includes the synthetic single crystal-based graphite sheet (L2) as second layer. The first layer was a polymer film (L1) that acted as a protector of the entire sheet. The synthetic single crystal-based graphite sheet (L2) is the next layer. The thickness of the synthetic single crystal-based graphite sheet is in the range of 20 to 40 micron and approximate density is in the range of 1.5 to 2.0 g/cm3. During experimentation it is observed that thinner and denser the layer, better would be the thermal conductivity. An acrylic layer (L3) is given below the synthetic single crystal-based graphite sheet (L2) to provide stability, strength and protection from vibrations of the automotive. The next layer consisted of an adhesive (L4) that helped in proper placement of the sheet, wherein the layer consisted of the adhesive (L4) is an optional layer. However, the adhesive layer (L4) is a must have function for applications where the product undergoes vibrations. Moreover, the adhesive layer (L4) ensures that there are no air gaps between the surface to be placed and the multi-layered graphite sheets (ML). These air gaps are working as bad conductors of heat and can negatively impact heat distribution. In an embodiment, the complete thickness of the multi-layered graphite sheet (ML) with L1-L4 is in the range of 70 to 80 micron .

The present invention provides a multi-layered graphite sheet (ML) for uniform heat distribution, wherein the sheet comprises:
a. a first outer layer (L1) of a polymer for the protection of underlying layers in the seat;
b. a first middle layer (L2) of a structurally modified graphite for uniform in-plane and through-plane thermal conductivity across the seat;
c. a second middle layer (L3) of an acrylic polymer for providing stability, strength, and protection from stress and strain; and
d. an inner layer (L4) of an adhesive for proper placement of the multi-layered graphite sheet.

In an embodiment of the present invention, the first outer layer (L1) is made of the polymer selected from a group comprising polytertrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), polypropylene, and chlorinated polyethylene.

In an embodiment of the present invention, there is provided a multi-layered graphite sheet (ML) wherein the structurally modified graphite is a synthetic single crystal-based graphite having a hexagonal structure aligned in columnar form. The structurally modified graphite has high purity, show no outgassing, and has thermal conductivity tailored between 450-2000 W/m-K.

In an embodiment of the present invention, the acrylic polymer is selected from a group comprising poly(methacrylate) (PMA), poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(2-hydroxyethyl methacrylate) (poly-HEMA).

In an embodiment, the present invention discloses a multi-layered graphite sheet (ML) for an automotive hot and cool seat. The multi-layered graphite sheet (ML) is placed in between the thermoelectric module based on Peltier effect and seat cover for providing the heating and cooling effect through effective heat distribution. The multi-layered graphite sheet (ML) is made of a first layer (L1), a second layer (L2), a third layer (L3), and a fourth layer (L4). The first layer (L1) is made of a polytertrafluoroethylene (PTFE) for the protection of underlying layers in the seat. The second layer (L2) is made up of a synthetic single crystal-based graphite sheet (a structurally modified graphite) for uniform in-plane and through-plane thermal conductivity across the seat. The third layer is made of a polymer (acrylic) for providing stability, strength, and protection from the vibrations of the automotive. For manufacturing this, the preformed graphite sheets which is nothing, but the structurally modified graphite (L2) are rolled between a thin PTFE sheet (L1) and flexible acrylic sheet (L3). The compression force from rolling results in a dense graphite inner layer (L3). The fourth layer (L4) is made of an adhesive which is applied at the last process. This adhesive layer ensures proper placement of the graphite sheet on seat and avoids formation of any air gaps. Figure 3 illustrates the schematic diagram of the invented multi-layered sheet.

In an embodiment of the present invention, the multi-layered graphite sheet (ML) is for used in automotive industry in Peltier based automotive hot and cool seats, in healthcare, wellness and/or hospitality in thermal bedding, thermal blanket, thermal belts, EMI shielding, thermal management, energy storage, gaskets for leak proofing and similar applications.

The present invention also provides a process for preparing the multi-layered sheet (ML), wherein the process comprises:
i. preparing a structurally modified graphite;
ii. placing the structurally modified graphite and a polymer film between rollers of a calendaring machine, wherein the structurally modified graphite and the polymer film are in contact with each other, the polymer film forms the first outer layer (L1) and the structurally modified graphite forms the first middle layer (L2);
iii. passing through the rollers of the calendaring machine to obtain a bonded PTFE-Graphite composite layer;
iv. cooling the bonded PTFE-Graphite composite layer;
v. laminating an acrylic polymer layer and an adhesive layer sequentially over the structurally modified graphite side of the bonded PTFE-Graphite composite layer to obtain a laminated PTFE-Graphite composite layer, wherein the acrylic polymer layer forms the second middle layer (L3) and the adhesive layer forms the inner layer (L4); and
vi. subjecting the laminated PTFE-Graphite composite layer to pressing to obtain the multi-layered sheet (ML).

In an implementation of specific embodiment of the present invention, the calendaring machine is operated at a temperature in the range of 200 to 300 °C to obtain a bonded PTFE-Graphite composite layer.

In an implementation of specific embodiment of the present invention, the acrylic polymer layer and adhesive layer are aligned sequentially and then subjected to a heat press or roller press, with a controlled temperature range of 100°C to 150°C.

In an embodiment of the present invention, the structurally modified graphite is prepared by a process comprises steps of:
i. preparing a graphite powder from non-graphitic graphitizable carbon forms; and
ii. rolling the graphite powder in the transverse direction using rollers to obtain the structurally modified graphite,
wherein the structurally modified graphite is a synthetic single crystal-based graphite having a hexagonal structure aligned in columnar form, the single crystal-based graphite has high purity, no outgassing and thermal conductivity between 450-2000 W/m-K.

In an embodiment of the present invention, the synthetic single crystal-based graphite also known as structurally modified graphite is manufactured by graphitization via chemical vapor deposition using non-graphitic graphitizable carbon forms, for example, but not limiting to, hydrocarbons. The obtained graphite powder is then preformed using rollers to convert into sheet form. The rolling using rollers is carried out in the transverse direction and the mechanical force results in binding hexagonal structure in columnar manner of the graphite powder. Binders are not used in the rolling process which results in synthetic single crystal-based graphite sheets having pure graphite exhibiting good thermal properties. This kind of processing results in reduced point defects and dislocations in the graphite sheets. Moreover, the rolling process results in arranging the hexagonal structure of graphite in columnar manner. This enables the synthetic single crystal-based graphite sheets (L2) to have high purity, no outgassing and thermal conductivity that can be tailored between 450-2000 W/m-K.

In an embodiment of the present invention, the non-graphitic graphitizable carbon forms comprises hydrocarbons. In an embodiment of the present invention hydrocarbons comprises methane. In an embodiment of the present invention the non-graphitic carbon are hard carbon or charcoals selected from a group comprising glassy carbons, pitch cokes, activated carbon and coal.

In an embodiment of the present invention, the graphite powder is prepared through chemical vapour deposition. Chemical vapour deposition is used to prepare graphene with excellent high value thermal conductivity values. The chemical vapour deposition of the present invention uses the transition metal catalyst selected from a group comprising Cu, Ni, and Fe along with the hydrocarbon gas at a temperature in the range of 1000 to 1200 ?. The hydrocarbon gas is methane gas used as source of carbon. Subsequently, scotch method is used to obtain the graphite powders.

In an embodiment of the present invention, the polymer film is selected from a group comprising polytertrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), polypropylene, and chlorinated polyethylene, the acrylic polymer layer is an acrylic polymer sheet, or a liquid acrylic polymer selected from a group comprising poly(methacrylate) (PMA), poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(2-hydroxyethyl methacrylate) (poly-HEMA).

In an embodiment, the present invention discloses a thermoelectric module (Peltier device) having synthetic single crystal-based graphite sheet (L2) which improves in-plane and through-plane thermal conductivity for uniform heat distribution.

The present invention also provides a thermoelectric module for automotive hot and cool seat comprising a thermoelectric device, a multi-layered graphite sheet (ML) comprising a structurally modified graphite, and a cover, wherein the multi-layered graphite sheet is placed in between the thermoelectric device and the cover for thermal distribution.

EXAMPLES
The disclosure will now be illustrated with working examples, which is intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods, the exemplary methods, devices and materials are described herein. It is to be understood that this disclosure is not limited to particular methods, and experimental conditions described, as such methods and conditions may vary.

Example 1: Preparation of structurally modified graphite
The synthetic single crystal-based graphite sheet (L2) also known as structurally modified graphite (L2) is manufactured by graphitization via chemical vapor deposition using non-graphitic graphitizable carbon forms, for example, but not limiting to, hydrocarbons, The chemical vapour deposition is used to prepare graphene with excellent high value thermal conductivity values. The chemical vapour deposition is carried out at a temperature in the range of 1000 to 1200 ?. The hydrocarbon gas is methane gas used as source of carbon. A transition metal catalyst selected from a group comprising Cu, Ni, and Fe is used along with the methane gas. Subsequently, scotch method is used to obtain the graphite powders.

The obtained graphite powder is then preformed using rollers to convert into sheet form. The rolling using rollers is carried out in the transverse direction and the mechanical force results in binding hexagonal structure in columnar manner of the graphite powder. Binders are not used in the rolling process which results in synthetic single crystal-based graphite sheets having pure graphite exhibiting good thermal properties. This kind of processing results in reduced point defects and dislocations in the graphite sheets. Moreover, the rolling process results in arranging the hexagonal structure of graphite in columnar manner. This enables the synthetic single crystal-based graphite sheets to have high purity, no outgassing and thermal conductivity that can be tailored between 450-2000 W/m-K.

Example 2: Preparation of multi-layered graphite sheet (ML)
The steps for preparing the multi-layered sheet is given below :
Step 01 : Preparation of graphite sheet as mentioned in example 1.
Step 02 : Calendaring process between L1 ( PTFE sheet) and L2 (Graphite sheet).
The graphite sheet and PTFE film is placed between the rollers of the calendaring machine. The graphite sheet is placed in such a way that its one side is in contact with the PTFE film. The materials are then passed slowly through the calendaring rollers to ensure smooth and uniform bond ( automatically by the machine). The moderate pressure and heat from the machine bonds the layers together. Usually, the temperature used is between the range of 200 – 300 °C. This temperature range is used to make sure the PTFE layer has softened up for proper bonding. Once the calendaring is over, the layers are allowed to air cool so that the bond between the layers stabilizes.
Step 03 : L3 ( Acrylic sheet) and L4 ( adhesive layer) bonding.
The next step involves the lamination of an acrylic sheet (L3) and an adhesive layer (L4) onto the composite PTFE-Graphite sheet. The acrylic sheet and adhesive layer are aligned sequentially and then subjected to a heat press or roller press, with a controlled temperature range of 100°C to 150°C. The applied heat softens both the acrylic and adhesive layers, allowing them to bond firmly to the PTFE-Graphite composite. The moderate temperature ensures that the acrylic layer maintains its structural integrity while forming a strong bond with the underlying materials.

Alternatively, liquid acrylic and adhesive can also be used. They are sprayed evenly onto the surface of the PTFE-Graphite composite. After application, the layers are allowed to cure. This curing process is crucial to ensure that the liquid acrylic and adhesive fully harden and form a permanent bond.

Figure 4 illustrates the schematic diagram of the thermoelectric Module (TEM) / Peltier device having the multi-layered graphite sheet (ML) of the present invention, wherein, the multi-layered graphite sheet (ML) shows improved in-plane and through-plane thermal conductivity for uniform heat distribution. The multi-layered graphite sheet (ML) is placed below the seat cover and above the thermoelectric module. This location enables proper heat distribution at seat cover, giving the customer the optimum heating and cooling effect.

Figure 4 also illustrate a schematic representation of Design of Experiment setup. Design of Experiments are conducted using these synthetic single crystal-based graphite sheets (L2). Thermistors are used to measure the dynamic temperature change on thermal environment (TE), preferably on a working prototype of the hot and cool seat. A huge decrease in temperature delta at x, y and z directions was observed. This indicates even heat spreading throughout the surface of the seat and elimination of high heat flux dense areas.

Further, figures 5a-5c show the graphite sheet without any PTFE, acrylic and adhesive layer. Figures 5a-5b show that the graphite sheet without any PTFE or Acrylic layer is extremely brittle and breaks immediately during manual bend test. For the test, the edge of the sheet was bent manually. As per observations, the sheet immediately broke with the powdery graphite residue on the fingers. Furthermore, to check the resistance of graphite sheet for water, few droplets of water were splashed on the sheet and then the area was wiped with a tissue paper. Black residue of graphite was observed on the tissues. Graphite peel off was observed. Figure 5c shows that the graphite sheet without any PTFE or Acrylic layer when subjected to water droplets, then the graphite peels off.

Further, figures 6a-6b show the multi-layered graphite sheet (ML) with PTFE (L1), the structurally modified graphite (L2), acrylic (L3) and adhesive layer (L4). Further Figure 6a shows that the addition of PTFE (L1) and acrylic layer (L3) to the structurally modified graphite (L2) results in flexible and less brittle sheet. Figure 6b shows that due to PTFE top layer, no graphite peel off is observed when the sheet is subjected to water droplets.

In an exemplary embodiment, figure 7 illustrates testing of the multi-layered graphite sheet (ML) was conducted by simulating vehicle conditions. Four thermistors (TC-1, TC-2, TC-3 and TC-4) were connected to different parts of the multi-layered graphite sheet (ML) to evaluate dynamic temperature change. TC-1 and TC-2 were placed directly above the thermoelectric module (not shown in Figure 7) while TC-3 and TC-4 were placed on the side away from the thermoelectric module (not shown in Figure 7). The temperature outputs from thermistors were reordered every 0.2 second interval.

Figures 8a and figure 8b show graphs which illustrate experiments with the natural/conventional graphite sheet. The temperature difference observed on natural/conventional graphite sheet, which is 30°C and -17.25°C in heating and cooling cycle respectively. Wherein, figure 8a illustrates heating having maximum temperature is 59.25°C and ?T= Maximum Temperature - Minimum Temperature (69 – 39 = 30 °C). Wherein, Figure. 8b illustrates cooling having Minimum Temperature: 6.5 and ?T = Minimum Temperature - Maximum Temperature (6.5 -23.75 = -17.25°C). These huge variation/differences in temperature indicates that there is an uneven distribution of heat. The area with high heat temperature has high flux density which creates hotspots on the surface of the seat.

Figures 9a and figure 9b show graphs which illustrate experiments with the present invented graphite sheet with PTFE and acrylic layer but without adhesive layer. The temperature difference observed on this sheet is 18.5°C and -7.5°C in heating and cooling cycle respectively. Wherein, figure 9a illustrates heating having maximum temperature is 69.75°C (through plane conductivity) and ?T (in-plane thermal conductivity) = Maximum Temperature - Minimum Temperature (69.75 – 51.25 = 18.5°C). Wherein, figure 9b illustrates cooling having Maximum Temperature: 13°C (through plane conductivity) and ?T (in-plane thermal conductivity) = Maximum Temp-Minimum Temp (13.0-21.5 = -7.5°C). Decrease in value of ?T indicates that improved thermal conductivity both in-plane and through-plane can be achieved using the synthetic single crystal-based graphite sheet (L2) with columnar structure. However, lack of adhesive resulted in formation of air gaps between seat foam and the synthetic single crystal-based graphite sheet with PTFE and acrylic layer. These air gaps can result in airflow between TC-3 and TC-4 which negatively affects the uniform heat spreading.

Figure 10a and figure 10b illustrate experiments with the presently invented multi-layered graphite sheet (ML) which has all 4 layers. The temperature difference observed on the multi-layered graphite sheet (ML) is 11.25°C and -6°C in heating and cooling cycle respectively. Wherein, figure 10a illustrates heating having maximum temperature is 55.5°C (through plane conductance) and ?T (in plane thermal conductance) = Maximum Temperature - Minimum Temperature (55.5 - 44.25 = 11.25°C). Wherein, Fig. 10b illustrates cooling having Minimum Temperature 16.75°C and ?T= Minimum Temp - Maximum Temp (16.75 - 23.00 = -6.25°C). As per observation, the newly developed multi-layered graphite sheet (ML) made of the synthetic graphite sheet (L2) with PTFE (L1), acrylic (L3) and adhesive layer (L4) shows enhanced in-plane and through-plane conductivity. With respect to natural graphite sheet, the invented multi-layered graphite sheet (ML) resulted in 60-70 % decrease in ?T. Low value ?T indicates even distribution on the surface of seat i.e., reduction in high heat flux density areas.

Advantages of the present invention:
The multi-layered graphite sheet (ML) as disclosed herein has many advenatages such as a wider range of tailorable thermal conductivities (450-2000 W/m-K), protection from vibrations, and desirable flexiblity as well as strength. Further, the multi-layered graphite sheet (ML) as disclosed herein does not use any additional fillers for heat distribution accordingly the making the multi-layered sheet light weight. Further, the multi-layered graphite sheet (ML) as disclosed herein has improved in-plane and through-plane thermal conductivity for uniform heat distribution, improvement in cooling and heating rate, quick, dynamic and powerless working and easy fitment and detachment.
,CLAIMS:1. A structurally modified graphite comprising a synthetic single crystal-based graphite having a hexagonal structure aligned in columnar form, wherein the structurally modified graphite has high purity in the range of 99 to 99.9 %, show no outgassing, and has a thermal conductivity tailored between 450-2000 W/m-K.

2. A multi-layered graphite sheet (ML) for uniform heat distribution, wherein the sheet comprises:
a. a first outer layer (L1) of a polymer for the protection of underlying layers in the seat;
b. a first middle layer (L2) of a structurally modified graphite for uniform in-plane and through-plane thermal conductivity across the seat;
c. a second middle layer (L3) of an acrylic polymer for providing stability, strength, and protection from stress and strain; and
d. an inner layer (L4) of an adhesive for proper placement of the multi-layered graphite sheet.

3. The multi-layered graphite sheet (ML) as claimed in claim 2, wherein the first outer layer (L1) is made of the polymer selected from a group comprising polytertrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), polypropylene, and chlorinated polyethylene.

4. The multi-layered graphite sheet (ML) as claimed in claim 2, wherein the structurally modified graphite is a synthetic single crystal-based graphite having a hexagonal structure aligned in columnar form, the structurally modified graphite has high purity in the range of 99 to 99.9 %, show no outgassing, and has thermal conductivity tailored between 450-2000 W/m-K.

5. The multi-layered graphite sheet (ML) as claimed in claim 2, wherein the first middle layer (L2) of a structurally modified graphite has a thickness in a range of 20 to 40 micron and density in a range of 5 to 2.0 g/cm3.

6. The multi-layered graphite sheet (ML) as claimed in claim 2, wherein the multi-layered graphite sheet (ML) has a thickness from L1-L4 in the range of 70 to 80 micron.

7. The multi-layered graphite sheet (ML) as claimed in claim 2, wherein the acrylic polymer is selected from a group comprising poly(methacrylate) (PMA), poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(2-hydroxyethyl methacrylate) (poly-HEMA).

8. The multi-layered graphite sheet (ML) as claimed in claim 2, wherein the multi-layered sheet (ML) is for used in automotive industry in Peltier based automotive hot and cool seats, in healthcare, wellness and/or hospitality in thermal bedding, thermal blanket, thermal belts, EMI shielding, thermal management, energy storage, gaskets for leak proofing and similar applications.

9. A process for preparing the multi-layered sheet (ML), wherein the process comprises:
i. preparing a structurally modified graphite;
ii. placing the structurally modified graphite and a polymer film between rollers of a calendaring machine, wherein the structurally modified graphite and the polymer film are in contact with each other, the polymer film forms the first outer layer (L1) and the structurally modified graphite forms the first middle layer (L2);
iii. passing through the rollers of the calendaring machine to obtain a bonded PTFE-Graphite composite layer, wherein the calendaring machine is operated at a temperature in the range of 200 to 300 °C;
iv. cooling the bonded PTFE-Graphite composite layer;
v. laminating an acrylic polymer layer and an adhesive layer sequentially over the structurally modified graphite side of the bonded PTFE-Graphite composite layer to obtain a laminated PTFE-Graphite composite layer, wherein the acrylic polymer layer forms the second middle layer (L3) and the adhesive layer forms the inner layer (L4); and
vi. subjecting the laminated PTFE-Graphite composite layer to pressing to obtain the multi-layered sheet (ML).

10. The process as claimed in claim 9, wherein the structurally modified graphite is prepared by a process comprises steps of:
i. preparing graphite powder from non-graphitic graphitizable carbon forms; and
ii. rolling the graphite powder in the transverse direction using rollers to obtain the structurally modified graphite,
wherein the structurally modified graphite is a single crystal-based graphite having a hexagonal structure aligned in columnar form, the single crystal-based graphite has high purity in the range of 99 to 99.9 %, no outgassing and thermal conductivity between 450-2000 W/m-K.

11. The process as claimed in claim 10, wherein the non-graphitic graphitizable carbon form is selected from a group comprising hydrocarbons, glassy carbons, pitch cokes, activated carbon and coal, and wherein the hydrocarbons comprises methane.

12. The process as claimed in claim 10, wherein the graphite powder is prepared through chemical vapour deposition carried out at a temperature of 1000 to 1200 ?, a transition metal catalyst selected from a group comprising Cu, Ni, and Fe is used along with a hydrocarbon gas, wherein the hydrocarbon gas is methane gas.

13. The process as claimed in claim 9, wherein the polymer film is selected from a group comprising polytertrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), polypropylene, and chlorinated polyethylene, the acrylic polymer layer is an acrylic polymer sheet or a liquid acrylic polymer selected from a group comprising poly(methacrylate) (PMA), poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(2-hydroxyethyl methacrylate) (poly-HEMA), wherein the pressing is carried out at a temperature in the range of 100°C to 150°C.

14. A thermoelectric module for automotive hot and cool seat comprising a thermoelectric device, a multi-layered graphite sheet (ML) as defined in claim 2, and a cover, wherein the multi-layered graphite sheet is placed in between the thermoelectric device and the cover for uniform thermal distribution.