High-efficiency planar heating element using graphene-based nanohybrid structure, and manufacturing method therefor

Abstract

The present invention relates to a planar heating element comprising: a heating layer including graphene flakes, functionalized graphene and a nanohybrid material; and an electrode electrically connected to the heating layer, wherein the nanohybrid material has the functionalized graphene self-adsorbed on the surfaces of thermally conductive inorganic particles.

Description

High-efficiency planar heating element using a graphene-based nanohybrid structure and method for manufacturing the same

[0001] The present invention relates to a planar heating element that converts electrical energy into thermal energy and a method for manufacturing the same. More specifically, it relates to a planar heating element and a method for manufacturing the same that utilizes a nano-hybrid structure of graphene and inorganic materials to enable efficient heating even with low power consumption, enable high-temperature heating of 500°C or higher, have excellent electrical connectivity, and facilitate mass production.

[0002] Generally, heating elements are devices that transfer energy by converting electrical energy into thermal energy and radiating it outwards, and they are widely utilized across a wide range of industries, from home appliances to various industrial sectors. Heating elements are broadly classified into metal heating elements, non-metal heating elements, and other heating elements based on their material.

[0003] Representative materials for metal heating elements include Fe-Cr-Al and Ni-Cr alloys, and high-melting-point metals such as platinum (Pt), molybdenum (Mo), tungsten (W), and tantalum (Ta) are also used. Non-metal heating elements include silicon carbide, molybdenum silicide, lanthanum chromite, and carbon, while other heating elements include ceramics, barium carbonate, and thick film resistors.

[0004] Heating elements can also be classified into linear and planar heating elements based on their external form. Linear heating elements are commonly referred to as "heating wires," and representative examples include filaments and nichrome wires. Planar heating elements have a structure in which metal electrodes are installed at both ends of a thin planar conductive heating element and insulated with insulating material, allowing heat to be generated across the entire surface. Materials used for planar heating elements include metal foil, heating paint (carbon black), and carbon fiber.

[0005] Planar heating elements have excellent heating efficiency and structural characteristics of excellent flatness and durability, while consuming 20 to 40 percent less power than conventional electric heating devices. Due to these advantages, planar heating elements are widely applied in various industrial heating devices, ranging from residential heating devices such as bedding mats, cushions, and home dry saunas to agricultural drying systems, road de-icing devices, and anti-fogging devices for automobile windows.

[0006] Recently, research on nanocarbon film heaters composed of carbon allotropes such as carbon nanotubes and graphene, which have various advantages over conventional heaters, is actively underway. Nanocarbon heating materials operate by releasing thermal energy in regions where electrons collide with phonons, impurities, and carbon defects when an electric field is applied. As the strength of the electric field increases, the scattering effect of electrons increases, causing the mean free path of electrons to decrease, which in turn causes the heating temperature to rise.

[0007] Nanocarbon film heaters possess excellent mechanical properties, being very lightweight and flexible, in addition to the advantages of conventional planar heating elements. They also have the advantage of enabling fast and efficient heating. In particular, graphene is a two-dimensional material composed of carbon atoms with a honeycomb-like structure; it is the thinnest material currently available, has a higher current density than copper, and possesses excellent strength, thermal conductivity, and electron mobility.

[0008] However, current nanocarbon planar heating elements face difficulties in commercialization due to issues such as a low heating temperature limit of 200°C or less and non-uniform electrical connectivity between the planar heating element and the wiring. Additionally, graphene manufactured using the CVD method currently applied to transparent heating elements has limitations in terms of reproducible quality and mass production capabilities required for commercialization. In particular, commercialization is difficult due to defects occurring during the process of transferring CVD graphene synthesized on copper foil onto a substrate and stacking multiple layers of graphene to achieve electrical performance.

[0009] To solve these problems, it is necessary to develop planar heating element technology using a new approach.

[0010] The present invention is intended to solve the problems of the prior art as described above, and the objectives of the present invention for this purpose are as follows.

[0011] One objective of the present invention is to provide a planar heating element capable of achieving a high heating temperature at a rapid speed even with low power consumption through a network structure of two-dimensional graphene and three-dimensional nanohybrid materials.

[0012] Another objective of the present invention is to provide a planar heating element capable of generating high temperatures of over 500°C, which cannot be achieved with commercial CVD graphene, through a nanohybrid structure of functionalized graphene and inorganic materials.

[0013] Another objective of the present invention is to provide a planar heating element that improves electrical connectivity between the planar heating element and the wiring and has excellent adhesion to the substrate.

[0014] Another objective of the present invention is to provide a method for manufacturing a planar heating element that can be mass-produced without complex processes through a spontaneous hybridization process between functionalized graphene colloid and inorganic particles.

[0015] Meanwhile, other unspecified objects of the present invention will be further considered to the extent that they can be easily inferred from the following detailed description and effects.

[0016]

[0017] To solve the problem described above, the following solution is proposed.

[0018] A planar heating element according to one embodiment of the present invention comprises a heating layer comprising graphene flakes, functionalized graphene, and a nanohybrid material; and an electrode electrically connected to the heating layer, wherein the nanohybrid material is a self-adsorbed functionalized graphene on the surface of a thermally conductive inorganic particle.

[0019] In one embodiment, the content of functionalized graphene self-adsorbed on the nanohybrid material may be 0.1 to 5 wt% based on the nanohybrid material.

[0020]

[0021] In one embodiment, the weight ratio of the graphene flakes, functionalized graphene, and nano-hybrid material may be 3.0 to 20 : 0.001 to 0.1 : 0.05 to 20.

[0022] In one embodiment, the graphene flakes may include reduced graphene and non-oxidized graphene.

[0023] In one embodiment, the thermally conductive inorganic particle may be at least one selected from the group consisting of Al2O3, SiO2, MoS2, MMT (montmorillonite), BN (boron nitride), AlN, ZnO, TiO2, and MgO.

[0024] A method for manufacturing a planar heating element according to one embodiment of the present invention comprises: (a) a step of manufacturing a paste for a planar heating element; (b) a step of applying and curing the paste for a planar heating element; and (c) a step of forming an electrode on the cured paste for a planar heating element, wherein step (a) may include: (a-1) a step of manufacturing a nanohybrid material by mixing a first functionalized graphene colloid and a thermally conductive inorganic particle; (a-2) a step of manufacturing a functionalized graphene dispersion by mixing a second functionalized graphene colloid and a resin in a solvent; (a-3) a step of manufacturing a high-concentration graphene flake dispersion by mixing and dispersing graphene flakes in a solvent and then concentrating them; and (a-4) a step of mixing the nanohybrid material, the functionalized graphene dispersion, and the high-concentration graphene flake dispersion.

[0025] In one embodiment, after performing step (b), a step of removing the resin through heat treatment may be further performed.

[0026] In one embodiment, the heat treatment may include a step of performing a first heat treatment at 200 to 300 ℃; and a step of performing a second heat treatment at 600 to 800 ℃.

[0027] In one embodiment, step (a-1) allows the first functionalized graphene to self-adsorb onto the surface of the inorganic particle by having a positive zeta potential of the first functionalized graphene and a negative zeta potential of the inorganic particle.

[0028] In one embodiment, the graphene flakes may include reduced graphene and non-oxidized graphene.

[0029] A planar heating element according to one embodiment of the present invention forms a dense network of two-dimensional graphene and three-dimensional nanohybrid materials to provide an efficient electrical and thermal transfer path, thereby enabling a higher heating temperature with half the power compared to commercial carbon nanotube heating elements and realizing a fast heating speed.

[0030] A planar heating element according to another embodiment of the present invention is capable of generating high temperatures of 500°C or higher, which cannot be achieved with commercial CVD graphene, through a stable three-dimensional network formed by a nanohybrid structure of functionalized graphene and an inorganic material.

[0031] A planar heating element according to another embodiment of the present invention spontaneously forms a uniform nanohybrid structure by means of electrostatic attraction between positively charged functionalized graphene and a negatively charged inorganic material, thereby having excellent electrical connectivity and improved uniformity of heating temperature.

[0032] The method for manufacturing a planar heating element according to another embodiment of the present invention has the advantage of enabling mass production by forming a uniform nanostructure without complex processes through spontaneous hybridization utilizing electrostatic attraction between functionalized graphene colloid and inorganic particles.

[0033] Meanwhile, it should be added that even if an effect is not explicitly mentioned here, the effects described in the following specification and the provisional effects expected by the technical features of the present invention are treated as described in the specification of the present invention.

[0034] FIG. 1 is a schematic structural diagram of a planar heating element according to one embodiment of the present invention.

[0035] Figure 2 schematically illustrates the structure of a nano-hybrid material based on functionalized graphene.

[0036] FIG. 3 is a schematic flowchart of a method for manufacturing a planar heating element according to another embodiment of the present invention.

[0037] Figure 4 is a photograph showing the process of fabricating a graphene-alumina nanohybrid material.

[0038] Figure 5 is a graph showing the zeta potential measurement results of a graphene-alumina nanohybrid material.

[0039] Figure 6 shows the transmission electron microscope results of the graphene-alumina nanohybrid material.

[0040] Figure 7 is a schematic diagram of a planar heating element for a film heater and a photograph taken of the evaluation of heating performance after actual fabrication.

[0041] Figure 8 is a graph showing the results of a comparison of heat generation performance under 30V application conditions.

[0042] Figure 9 is a diagram showing the manufacturing process of a nano-hybrid planar heating element for high-temperature heating.

[0043] Figure 10 shows the results of surface optical microscope observation of a nano-hybrid planar heating element for high-temperature heating after heat treatment.

[0044] Figure 11 shows the scanning electron microscope observation results of the surface of a nanohybrid planar heating element.

[0045] Figure 12 is a schematic design of a nano-hybrid planar heating element for high-temperature heating.

[0046] It should be noted that the attached drawings are provided as examples for reference to help understand the technical concept of the present invention, and the scope of the rights of the present invention is not limited by them.

[0047] Hereinafter, with reference to the drawings, we will examine the configuration of the present invention as guided by various embodiments thereof and the effects derived therefrom. In describing the present invention, detailed descriptions of related known functions are omitted if they are deemed obvious to a person skilled in the art and could unnecessarily obscure the essence of the invention.

[0048] A heating element is a device that converts electrical energy into thermal energy and radiates it outward, and is classified into linear heating elements and planar heating elements depending on its shape. Planar heating elements have a structure in which metal electrodes are installed on a thin, planar conductive heating layer and insulated to ensure uniform heating across the entire surface. Due to these structural characteristics, planar heating elements exhibit excellent heating efficiency while showing a power consumption rate 20–40% lower than that of general electric heating devices.

[0049] Recently, research on nanocarbon film heaters composed of carbon allotropes such as carbon nanotubes and graphene, which have various advantages over conventional heaters, is actively underway. In particular, graphene is a two-dimensional material in which carbon atoms are arranged in a hexagonal honeycomb shape. It possesses excellent electrical conductivity, thermal conductivity (~5000 W / mK), and mechanical strength, and is attracting attention as a novel heating material because it has the characteristic of releasing thermal energy as electrons collide with phonons, impurities, and defects when an electric field is applied.

[0050] A representative planar heating element utilizing graphene is the CVD-type graphene heating element; however, CVD-type graphene heating elements face difficulties in ensuring reproducible quality and mass producibility, and defects frequently occur during the transfer and stacking processes. Furthermore, it is difficult to ensure long-term reliability of CVD-type graphene heating elements due to delamination caused by the difference in thermal expansion coefficients between the heating layer and the electrodes.

[0051] FIG. 1 is a schematic structural diagram of a planar heating element according to one embodiment of the present invention, and FIG. 2 is a schematic diagram of the structure of a nano-hybrid material based on functionalized graphene.

[0052] Referring to FIG. 1, the present invention relates to a planar heating element using a graphene-based nanohybrid structure, comprising a heating layer including graphene flakes, functionalized graphene, and a nanohybrid material, and an electrode electrically connected to the heating layer. In this case, the nanohybrid material has a structure in which functionalized graphene is self-adsorbed on the surface of thermally conductive inorganic particles.

[0053] Looking at nanohybrid materials in more detail, they possess a structure in which positively charged functionalized graphene is self-adsorbed onto the surface of thermally conductive inorganic particles. In this case, the functionalized graphene has a positive zeta potential, while the thermally conductive inorganic particles have a negative zeta potential, leading to spontaneous hybridization. When the thermally conductive inorganic particles have a positive zeta potential, carboxyl groups (-COOH) and sulfonyl groups (-SO3) - It can be modified to have a negative zeta potential by introducing hydroxyl groups (-OH) through surface treatment, or by adjusting the pH of the environment where the functionalized graphene is bonded.

[0054] The functionalized graphene used in the present invention may have a zeta potential of +25mV or higher, preferably 30mV or higher, and more preferably +60mV or higher.

[0055] Functionalized graphene refers to graphene in which functional groups are introduced during the manufacturing process, thereby controlling the elemental content of carbon, oxygen, and nitrogen in the graphene. The groups formed in the functionalized graphene may be at least one selected from the group consisting of silane, amide, azide, anhydride, urea, urethane, amine, alkylene, epoxide, and mercapto groups. Furthermore, the functionalized graphene of the present invention may have a carbon (C) elemental content of 76 to 83 atoms %, an oxygen elemental content of 5 to 10 atoms %, and a nitrogen (N) elemental content of 9 to 18 atoms %. In particular, the O / N ratio may satisfy 0.7 or less, preferably 0.5 or less, and more preferably 0.3 or less. The functionalized graphene of the present invention can satisfy the required zeta potential by satisfying such an elemental composition.

[0056] As thermally conductive inorganic particles, at least one selected from the group consisting of Al2O3, SiO2, MoS2, MMT (montmorillonite), BN (boron nitride), AlN, ZnO, TiO2, and MgO may be used. For example, the zeta potential of Al2O3 has a negative value, and montmorillonite is a layered silicate mineral that has a negative zeta potential due to naturally occurring ion substitution within its structure.

[0057] Therefore, as shown in Figure 2, simply by mixing functionalized graphene and thermally conductive inorganic particles in a solvent, the functionalized graphene is self-adsorbed onto the surface of the thermally conductive inorganic particles to form a core-shell structure.

[0058] Meanwhile, since the zeta potential of the nanohybrid material of the present invention is +25mV or higher, it has high dispersion, which has the advantage of facilitating the process.

[0059] The content of self-adsorbed functionalized graphene on the nanohybrid material of the present invention may be 0.1 to 5 wt% based on the nanohybrid material. If the content of self-adsorbed functionalized graphene on the nanohybrid material is less than 0.1 wt%, the powder resistance of the nanohybrid material is too high. On the other hand, as the content of functionalized graphene increases, the coating thickness increases as functionalized graphene is coated on thermally conductive inorganic particles, but from the point when the content of functionalized graphene exceeds 5 wt%, aggregation between particles occurs, causing secondary particles to form rapidly. In particular, there is a problem in that the formation of secondary particles increases further during the drying process after coating with functionalized graphene.

[0060] In one embodiment of the present invention, the weight ratio of graphene flakes, functionalized graphene, and nano-hybrid material may be 3.0 to 20 : 0.005 to 0.1 : 0.05 to 20.

[0061] When the weight ratio of the nano-hybrid material is less than 0.05 based on graphene flakes, functionalized graphene, and nano-hybrid materials, cracks occur when the heating element is bent, and there is a problem of cracks occurring due to shrinkage when the temperature is raised to a high temperature (600 degrees) and then cooled. When the weight ratio of the nano-hybrid material is greater than 20 based on graphene flakes, functionalized graphene, and nano-hybrid materials, cracks occur when the heating element is bent, and there is a problem of the sheet resistance increasing rapidly. Therefore, it is desirable that the weight ratio of the nano-hybrid material is 0.05 to 20 based on graphene flakes, functionalized graphene, and nano-hybrid materials.

[0062] If the content ratio of functionalized graphene is less than 0.005 based on graphene flakes, functionalized graphene, and nano-hybrid materials, a decrease in film strength occurs due to insufficient formation of a graphene network, and the adhesion of the inter-plane heating element weakens, causing delamination during use, as well as a decrease in thermal stability and electrical performance. Therefore, it is desirable that the content ratio of functionalized graphene based on graphene flakes, functionalized graphene, and nano-hybrid materials be 0.005 or higher. Meanwhile, it is acceptable for the content ratio of functionalized graphene based on graphene flakes, functionalized graphene, and nano-hybrid materials to exceed 0.1, but above that level, performance becomes saturated, and consequently, there is a problem of reduced economic feasibility. Therefore, more preferably, the content ratio of functionalized graphene based on graphene flakes, functionalized graphene, and nano-hybrid materials may be between 0.005 and 0.1.

[0063] Graphene flakes serve as fillers to form a graphene network together with nanohybrid materials and functionalized graphene within the heating layer. Graphene flakes include reduced graphene (RGO) and non-oxidized graphene (LEG). Reduced graphene can be used with a thickness of 5 nm or less and a lateral size of 10 μm [D50] or less, while non-oxidized graphene can be used with a thickness of 100 nm or less and a lateral size of 15 μm [D50] or less. Reduced graphene plays a role in increasing the conductivity of the graphene flakes, while non-oxidized graphene primarily serves as a filler when forming the graphene network.

[0064] FIG. 3 is a schematic flowchart of a method for manufacturing a planar heating element according to another embodiment of the present invention.

[0065] A method for manufacturing a planar heating element according to another embodiment of the present invention comprises the steps of manufacturing a paste for a planar heating element, applying and curing the paste for a planar heating element, and forming an electrode on the cured paste for a planar heating element.

[0066] The step of manufacturing a paste for a planar heating element comprises: a step of preparing a nanohybrid material by mixing a first functionalized graphene colloid and thermally conductive inorganic particles; a step of preparing a functionalized graphene dispersion by mixing a second functionalized graphene colloid and a resin in a solvent; a step of preparing a high-concentration graphene flake dispersion by mixing and dispersing graphene flakes in a solvent and then concentrating them; and a step of mixing the nanohybrid material, the functionalized graphene dispersion, and the high-concentration graphene flake dispersion.

[0067] First, the step of manufacturing the nanohybrid material is performed.

[0068] A first functionalized graphene colloid having a positive charge is prepared.

[0069] The first functionalized graphene is manufactured as follows. Other functionalized graphene used in the present invention can also be manufactured by the following method.

[0070] Prepare an aqueous graphene oxide solution. The aqueous graphene oxide solution can be prepared by fabricating graphite oxide using the Hummers and Improved Methods or by performing an exfoliation process using commercially available graphite oxide.

[0071] Next, functional groups are imparted to the graphene oxide. An additive for forming functional groups is added to an aqueous solution of graphene oxide, stirred, and then ultrasonically dispersed to impart functional groups to the graphene oxide, thereby forming functionalized graphene. Specifically, 50 to 150 parts by weight of the additive are added to 100 parts by weight of an aqueous solution of graphene oxide, and the mixture is stirred at 90 to 120°C for 12 to 36 hours to form functionalized graphene.

[0072] The functional groups to be imparted to graphene can be determined by the additives.

[0073] As an additive for forming a silane group, an organic silane compound capable of forming a silane group may be used, for example, triethoxysilane, tetraethoxysilane, aminopropyltriethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, octadecyltrimethoxysilane, (3-methacryloxy)propyltrimethoxysilane, 3-glycidoxypropyl methyldimethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl methyldiethoxysilane, 3-glycidoxypropyl triethoxysilane. Any one selected from the group consisting of 3-isocyanate propyltriethoxysilane and 3-(Trimethoxysilyl)propylsuccinic anhydride may be used.As additives, organic monomers or polymers capable of forming amine or amide groups may be used, for example, ethylenediamine, triethylamine, paraphenylenediamine, o-phenylenediamine, mesophenylenediamine, 3,3',4,4'-tetraaminobiphenyl, 3,3',4,4'-tetraaminoterphenyl, benzidine, 1,5-diaminonaphthalene, (E)-4,4'-(diazene-1,2-diyl)dianiline, ethylenediamine, Any one selected from the group consisting of 1,6-diaminohexane, 1,8-diaminooctane, and 4,4-oxidianiline may be used.

[0074] As an additive for forming an amine or amide group, organic monomers or polymers capable of forming an amine or amide group may be used, for example, ethylenediamine, triethylamine, paraphenylenediamine, o-phenylenediamine, mesophenylenediamine, 3,3',4,4'-tetraaminobiphenyl, 3,3',4,4'-tetraaminoterphenyl, benzidine, 1,5-diaminonaphthalene, (E)-4,4'-(diazene-1,2-diyl)dianiline, Any one selected from the group consisting of ethylenediamine, 1,6-diaminohexane, 1,8-diaminooctane, and 4,4-oxidianiline may be used.

[0075] As an additive for forming an anhydride (anhydrous) functional group, an organic monomer or polymer capable of forming an anhydride functional group may be used, and, for example, any one selected from the group consisting of maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, pyromellitic anhydride, naphthalic anhydride, and trimellitic anhydride may be used.

[0076] Organic monomers or polymers can be used as additives capable of forming an azide group, and, for example, any one selected from the group consisting of sodium azide, methyl azidoacetate, phenyl azide, 2-azidoethanol, azidoacetic acid, and 2-azidoethylamine can be used.

[0077] Organic monomers or polymers may be used as additives capable of forming urea groups or urethane groups, and, for example, any one selected from the group consisting of isocyanate, polyol, ethoxysilane, polyethylene glycol, tolylene diisocyanate, methylene diphenyl diisocyanate, polytetramethylene ether glycol, and poly-caprolactone may be used.

[0078] Any one selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, and 1,8-octanediol may be used.

[0079] As an additive capable of forming an epoxide group, an epoxidized organic monomer or polymer may be used, for example, any one selected from the group consisting of epoxidized alkylene oxide, glycidyl methacrylate, styrenized epoxide, glycidyl amine, bisphenol A epoxy, epoxidized novolac, and epoxidized polyethylene oxide may be used.

[0080] Organic monomers or polymers can be used as additives capable of forming a mercapto group, for example, any one selected from the group consisting of 2-mercaptoethanol, 1-thioglycerol, 3-mercaptopropanesulfonic acid, D-pentaerythritol tetra(3-mercaptopropionate), 4-mercaptophenol, methyl 3-mercaptopropionate, 6-thioguanine, 1-hexanethiol, ethanethiol, and benzylmercaptan.

[0081] For reference, the amount of functional groups introduced can be determined by adjusting the amount of additive, stirring temperature, and stirring time. More specifically, the ratio of additive to graphene oxide, the timing and rate of additive addition at the beginning of the reaction, and the stirring speed and time are important.

[0082] Once stirring is complete, 1 ton of functionalized graphene colloid is produced per hour through a large-capacity circulating ultrasonic dispersion system.

[0083] The concentration of the first functionalized graphene colloid is 0.3 to 3.0 wt%, and at least one selected from the group consisting of deionized water, ethanol, methanol, IPA, DMF, and NMP is used as a solvent at a concentration of 70 to 90%, and the mixture is dispersed and homogenized by ultrasonic treatment for 20 to 40 minutes. Meanwhile, at least one thermally conductive inorganic particle selected from the group consisting of Al2O3, SiO2, MoS2, MMT, AlN, BN, ZnO, TiO2, and MgO is dispersed at a concentration of 8 to 12 wt%. Subsequently, the two solutions are mixed and homogenized at room temperature at 2500 to 3500 rpm for 20 to 40 minutes, after which spontaneous hybridization is carried out at 800 to 1200 rpm for 1.5 to 2.5 hours. The co-precipitate formed by the formation of the nanohybrid material is centrifuged. After that, the nanohybrid material is prepared by washing, vacuum filtration, and drying at 60°C for 10 hours in a vacuum atmosphere.

[0084] Next, a functionalized graphene dispersion is prepared. The second functionalized graphene colloid is formulated to be 0.05 to 3.0 wt% relative to the resin solid content. As the resin, at least one selected from the group consisting of epoxy resin, phenolic resin, melamine resin, silicone resin, polyurethane resin, unsaturated polyester resin, polyimide, polyetherimide, polyetheretherketone, polysulfone, polyphenylene sulfide, and liquid crystal polymer may be used. The second functionalized graphene can be prepared by the method described above for the first functionalized graphene. The functionalized graphene colloid is dispersed by ultrasound for 25 to 35 minutes using at least one solvent selected from the group consisting of ethanol, methanol, IPA (Isopropyl Alcohol), DMF (Dimethylformamide), and NMP (N-Methyl-2-pyrrolidone) at a concentration of 0.5 to 1.5 wt%. Then, a functionalized graphene dispersion having a solid content of 45 to 65 wt% is prepared by stirring at 40 to 60 rpm for 1.5 to 2.5 hours with at least one solvent and resin selected from the group consisting of DGMEA (Diethylene Glycol Monobutyl Ether Acetate), PGMEA (Propylene Glycol Monomethyl Ether Acetate), DHT (Diethylene Glycol Monobutyl Ether), and DHTA (Diethylene Glycol Monoethyl Ether Acetate) in a 3-axis stirrer, followed by stirring for 3.5 to 4.5 hours at 55 to 65°C under vacuum.

[0085] Next, a high-concentration graphene flake dispersion is prepared. Reduced graphene and non-oxidized graphene are mixed in at least one solvent selected from the group consisting of DGMEA (Diethylene Glycol Monobutyl Ether Acetate), PGMEA (Propylene Glycol Monomethyl Ether Acetate), DHT (Diethylene Glycol Monobutyl Ether), DHTA (Diethylene Glycol Monoethyl Ether Acetate), NMP (N-Methyl-2-pyrrolidone), DMF (Dimethylformamide), MEK (Methyl Ethyl Ketone), Toluene, and Xylene. To improve dispersion stability, a dispersion aid of 10 to 200 wt% relative to the total amount of graphene is included, along with at least one additive selected from the group consisting of a silane coupling agent, a curing accelerator, a leveling agent, and a CTBN (Carboxyl-Terminated Butadiene Nitrile)-based toughening agent to improve organic-inorganic bonding strength. This is subjected to high-pressure dispersion at 400 to 1200 bar with 25 to 55 passes. Subsequently, a high-concentration graphene flake dispersion with a graphene concentration of 15 to 45 wt% is prepared by stirring in a 3-axis stirrer at 45 to 55 rpm, 55 to 65°C, and under vacuum conditions for 7 to 9 hours.

[0086] The nanohybrid material, functionalized graphene dispersion, and high-concentration graphene flake dispersion are pre-dispersed in a 3-axis stirrer at 45 to 55 rpm for 1.5 to 2.5 hours. Subsequently, a hydraulic 3-roll mill process is carried out under conditions of 5 to 20 bar and 4 to 10 passes, and the final paste is completed by homogenization and degassing treatment using high-speed rotational stirring.

[0087] The composition of the manufactured paste for planar heating elements is as shown in Table 1 below.

[0088]

[0089] No. Composition Content [wt.%] 1 Nano-hybrid Material 0.05 ~ 202 Positively Charged Functionalized Graphene 0.001 ~ 0.13 Graphene Flakes (Reduced Graphene + Non-Oxidized Graphene) 3.0 ~ 204 Resin 5.0 ~ 205 Curing Agent 3.0 ~ 126 Catalyst (Controls curing reaction rate) < 17 Additive (Dispersion aid, Organic-inorganic coupling, Toughening, Curing acceleration, Leveling, etc.) < 38 Surfactant 1.0 ~ 209 Solvent 20 ~ 80

[0090]

[0091] Next, step (b) of applying and curing the manufactured paste for a planar heating element onto a substrate is performed. The substrate may be made of at least one material selected from the group consisting of PI (Polyimide), PET (Polyethylene Terephthalate), PEN (Polyethylene Naphthalate), PI (Polyimide), and Quartz. The applied paste is dried at 75 to 85°C for 8 to 12 minutes and at 115 to 125°C for 8 to 12 minutes, and then cured at 180 to 220°C for 0.8 to 1.2 hours. The temperature and time for drying and curing may vary depending on the resin used and the surrounding environment.

[0092] Next, step (c) of forming an electrode on the cured planar heating element is performed. The electrode is formed using at least one sintered conductive paste selected from the group consisting of silver, copper, aluminum, nickel, and alloys thereof, and dried at 115 to 125°C for 25 to 35 minutes.

[0093] Meanwhile, in the case of high-temperature heating elements, a step of removing the resin through additional heat treatment is performed. In the manufacture of high-temperature heating elements, heat treatment is carried out in two stages. The first heat treatment is performed at a relatively low temperature of 180 to 320°C, which is intended for the initial decomposition of the resin and the debinding process. In this stage, structural stress on the heating element can be minimized by avoiding a rapid rise in temperature, and the basic framework of the structure is formed while gradually removing organic materials (solvents, additives, etc.).

[0094] The second heat treatment is carried out at a high temperature of 550 to 850°C, and the second heat treatment can be performed in at least one inert gas atmosphere selected from the group consisting of argon, nitrogen, helium, and mixtures thereof. In the second heat treatment step, residual organic matter is completely removed and the graphene network is stabilized. In addition, the sintered silver paste used as an electrode is sintered and the densification of the inorganic structure proceeds.

[0095] By performing heat treatment in two stages during the manufacturing process of high-temperature heating elements, cracks caused by a rapid increase in temperature can be prevented and residual stress can be minimized. In addition, stable electrical and mechanical properties at high temperatures can be secured, thereby improving the long-term reliability of the heating element.

[0096] Finally, a protective layer can be formed with at least one material selected from the group consisting of inorganic silicane, polyimide, epoxy, and silicone.

[0097]

[0098] Examples

[0099] To demonstrate the effects of the present invention, a nanohybrid material was prepared as follows.

[0100] First, positively charged functionalized graphene colloid from Best Graphene was prepared. The functionalized graphene colloid has a zeta potential of +40 mV or higher and was prepared at a concentration of 0.5 to 2.0 wt%. Deionized water and ethanol were mixed in a ratio of 80:20 as the solvent, and sonication was performed for more than 30 minutes to achieve sufficient dispersion and homogenization.

[0101] Next, alumina (Al2O3) was prepared as a thermally conductive inorganic particle. The alumina was dispersed in a mixed solvent of deionized water and ethanol (80:20) at a concentration of 10 wt% and sufficiently dispersed for more than 30 minutes using a high-speed homogenizer.

[0102] Next, a nanohybrid material was prepared by mixing a functionalized graphene colloid and an alumina dispersion. Several samples were prepared such that the content of functionalized graphene was 0 to 8 wt% relative to the alumina. After mixing, homogenization was performed at 3000 rpm for 30 minutes, followed by stirring at 1000 rpm for 2 hours to allow the functionalized graphene to spontaneously adsorb onto the alumina surface.

[0103] Finally, the formed nanohybrid material was separated using a vacuum filter after undergoing three rounds of centrifugation and washing. The separated material was dried for 10 hours under vacuum conditions at 60°C to obtain the final nanohybrid material.

[0104] To evaluate the characteristics of the nanohybrid material manufactured by this method, the following analysis was performed.

[0105] Figure 4 is a photograph showing the process of fabricating a graphene-alumina nanohybrid material.

[0106] Referring to Figure 4, the state immediately after mixing Al2O3 and functionalized graphene colloid (left) and after spontaneous adsorption (right) can be compared. Immediately after mixing, the colloidal state is maintained, but after spontaneous adsorption proceeds, it can be seen that functionalized graphene is uniformly coated on the surface of Al2O3, forming a black nanohybrid material.

[0107] Figure 5 is a graph showing the zeta potential measurement results of a graphene-alumina nanohybrid material.

[0108] Referring to Figure 5, pure alumina exhibited a negative charge of -46.4 mV, and functionalized graphene exhibited a positive charge of +51.7 mV. The graphene-alumina nanohybrid material combined with them exhibited a positive charge of +27.7 mV, confirming that functionalized graphene was successfully adsorbed onto the alumina surface. In particular, since the zeta potential of the prepared graphene-alumina nanohybrid material is +25 mV or higher, dispersion is easy during processing.

[0109] Figure 6 shows the transmission electron microscope observation results of the graphene-alumina nanohybrid material. Referring to Figure 6, it can be seen that while a large number of aggregated particles appeared in the alumina (Figure 6 (left)), the particles in the graphene-alumina nanohybrid material existed individually. In particular, while pure alumina showed a particle size of approximately 1 μm, it increased to 3-4 μm after graphene coating, indicating that a graphene coating layer was formed on the surface of the alumina.

[0110] Table 2 shows the results of measuring powder resistivity and aggregation between individual particles according to the content of functionalized graphene in the nanohybrid material.

[0111]

[0112] Sample Nano-Hybrid Material Functionalized Graphene Powder Resistivity Content of Aggregation between Individual Particles [wt.%][Ω·m] 1010 12 No abnormal aggregation 20.14.3 x 105 No aggregation 30.5 2.7 x 10 4 No aggregation 412.1 x 10 3 No aggregation 525.2 x 10 2 No aggregation 637.8 x 10 1 No aggregation 741.2 x 10 1 No aggregation 855.1 x 10⁻⁶ 0 No aggregation 964.3 x 10⁻⁶ 0 Coagulation occurred 1085.4 x 10⁻⁶ 0 Coagulation occurred 11106.5 x 10 0 Aggregation occurs

[0113]

[0114] Referring to Table 2, as functionalized graphene is added, the powder resistivity is 10 12 4.3 x 10⁻⁶ at Ω·m 5 It can be observed that it decreases rapidly down to Ω·m. At a functionalized graphene content of 6 wt% or more, interparticle aggregation began to occur. Referring to Table 2, it is preferable that the content of functionalized graphene in the nanohybrid material be 0.1 to 5 wt%.

[0115] Next, a surface heating element paste was manufactured.

[0116] A functionalized graphene dispersion was prepared by mixing a functionalized graphene colloid with an epoxy resin. The functionalized graphene colloid was prepared at a concentration of 1.0 wt%, and a solvent consisting of ethanol and IPA mixed in a 1:1 ratio was used. After dispersion and homogenization by sonication for at least 30 minutes, the mixture was stirred at 50 rpm for 2 hours with the epoxy resin and DGMEA solvent in a tri-screw stirrer. Subsequently, the mixture was concentrated by stirring for 4 hours under vacuum conditions at 60°C to prepare a pre-dispersion with a solid content of 50–60 wt%.

[0117] Next, a high-concentration graphene flake dispersion was prepared. Reduced graphene with a thickness of 5 nm or less and a lateral size of 10 μm [D50] or less and non-oxidized graphene with a thickness of 100 nm or less and a lateral size of 15 μm [D50] or less were used, and were mixed in a DGMEA solvent with a dispersion aid of 15–150 wt% relative to the total amount of graphene. This was high-pressure dispersed at 500–1000 bar with 30–50 passes, and then stirred in a 3-screw stirrer at 50 rpm, 60°C, and under vacuum conditions for more than 8 hours to prepare a high-concentration graphene flake dispersion with a graphene concentration of 20–40 wt%.

[0118] Finally, a planar heating element paste was completed by mixing a nanohybrid material, a functionalized graphene pre-dispersion, and a graphene flake intermediate. Specifically, 5g of nanohybrid material, 10g of functionalized graphene-epoxy resin pre-dispersion, and 50g of high-concentration graphene intermediate were pre-dispersed in a 3-axis stirrer at 50 rpm for 2 hours, followed by a hydraulic 3-roll mill process under conditions of 6–15 bar and 5–8 passes. Lastly, the final paste was completed by homogenization and degassing treatment through high-speed rotational stirring.

[0119] The basic composition of the planar heating element paste of the present invention is prepared with a composition of 5 wt% nano-hybrid material, 0.05 wt% functionalized graphene, 10 wt% graphene flakes (reduced graphene:non-oxidized graphene = 1:1), 11.25 wt% resin and additives, 8 wt% surfactant, and 65.7 wt% solvent. In the case of Table 3 described below, the characteristics were evaluated while adjusting the nano-hybrid material content to 0.03 to 30 wt%, and in the case of Table 4, the characteristics were evaluated while adjusting the content of functionalized graphene to 0.003 to 0.3 wt%. In Table 5, the characteristics were evaluated for cases where only reduced graphene is present in the graphene flakes, cases where only non-oxidized graphene is present, cases where reduced graphene and non-oxidized graphene are present but functionalized graphene is absent, and cases where all are present. When controlling the content of nanohybrid materials, functionalized graphene, reduced graphene, and non-oxidized graphene, only the amount of solvent was controlled.

[0120] A planar heating element with a thickness of 20 μm was manufactured by applying a planar heating element paste to a polyimide film substrate with a thickness of 50 μm, drying it at 80°C for 10 minutes, drying it again at 120°C for 10 minutes, and then curing it at 200°C for 1 hour.

[0121] Table 3 below shows the results of evaluating the characteristics according to the content of the nano-hybrid material. Film strength was determined by checking the film condition when the heating element was formed on the substrate and folded more than 90˚, and thermal stability was evaluated by checking the film condition after heating at a rate of 10℃ per minute, maintaining at 600℃ for 10 minutes, and then cooling.

[0122]

[0123] Sample nanohybrid material functionalized graphene graphene flakes 2) Film Strength Thermal Stability Evaluation Surface Resistance Content [wt.%] 1)Content [wt.%] Content [wt.%] (Bending) (600℃) [Ω / sq] 1 20.0 30.0 510 Crack Occurrence Shrinkage-Crack Occurrence 19 1 30.0 40.0 510 Crack Occurrence Shrinkage-Crack Occurrence 19 1 40.0 50.0 510 Good Good 19.5 150.10.0 510 Good Good 20 16 10.0 510 Good Good 21 17 50.0 510 Good Good 21 18 100.0 510 Good Good 22 19 150.0 510 Good Good 23 20 200.0 510 Good Good 25 21 250.0 510 Crack Occurrence Good 100 22 300.0 510 Crack Occurrence Good 30 1) Depending on the change in the content of the nano-hybrid material, only the solvent content Adjusted. 2) The weight ratio of reduced graphene to non-oxidized graphene is 1:1.

[0124]

[0125] Referring to Table 3, when the weight ratio of the nano-hybrid material is less than 0.05 based on graphene flakes, functionalized graphene, and nano-hybrid material, cracks occur when the heating element is bent, and there is a problem of cracks occurring due to shrinkage when the temperature is raised to a high temperature (600 degrees) and then cooled. When the weight ratio of the nano-hybrid material is greater than 20 based on graphene flakes, functionalized graphene, and nano-hybrid material, cracks occur when the heating element is bent, and there is a problem of the sheet resistance increasing rapidly. Therefore, it is desirable that the weight ratio of the nano-hybrid material based on graphene flakes, functionalized graphene, and nano-hybrid material be between 0.05 and 20.

[0126] Table 4 below shows the results of evaluating the characteristics according to the content of functionalized graphene. Film strength was determined by checking the film condition when the heating element was formed on the substrate and folded more than 90°, and thermal stability was evaluated by checking the film condition after heating at a rate of 10°C per minute, maintaining at 600°C for 10 minutes, and then cooling.

[0127]

[0128] Sample nanohybrid material functionalized graphene graphene flakes 4)Film Strength Thermal Stability Evaluation Surface Resistance Content [wt.%] Content [wt.%] 3) Content [wt.%](Bending)(600℃)[Ω / sq] 235 0.00 310 Crack Occurrence Shrinkage-Crack Occurrence 31 245 0.00 410 Crack Occurrence Shrinkage-Crack Occurrence 30 255 0.00 510 Good Good 20 265 0.01 10 Good Good 19 275 0.05 10 Good Good 18 285 0.1 10 Good Good 18 295 0.2 10 Good Good 18 305 0.3 10 Good Good 18 3) Only the solvent content is adjusted according to the change in the content of functionalized graphene. 4) The weight ratio of reduced graphene to non-oxidized graphene is 1:1.

[0129]

[0130] Referring to Table 4, if the content ratio of functionalized graphene based on graphene flakes, functionalized graphene, and nano-hybrid materials is less than 0.005, a decrease in film strength occurs due to insufficient formation of a graphene network, and the adhesion of the inter-plane heating element weakens, causing delamination during use, as well as a decrease in thermal stability and electrical performance. Therefore, it is desirable that the content ratio of functionalized graphene based on graphene flakes, functionalized graphene, and nano-hybrid materials be 0.005 or higher. Meanwhile, it is acceptable for the content ratio of functionalized graphene based on graphene flakes, functionalized graphene, and nano-hybrid materials to exceed 0.1, but above that level, performance becomes saturated, and consequently, there is a problem of reduced economic feasibility. Therefore, more preferably, the content ratio of functionalized graphene based on graphene flakes, functionalized graphene, and nano-hybrid materials may be between 0.005 and 0.1.

[0131] Table 5 below shows the results of evaluating the characteristics of planar heating elements according to thickness based on the presence of reduced graphene, non-oxidized graphene, and functionalized graphene. In this invention, the adhesion strength of the planar heating element was evaluated using a cross-cut test according to ASTM D3359. The cross-cut test is a method for evaluating the degree of peeling of the coating film by making 100 squares on the surface of the coated planar heating element at 1mm intervals in vertical and horizontal directions, attaching a release-treated adhesive tape, and then peeling it off at a constant speed at a 180° angle. Adhesion strength is classified into six stages from 0B to 5B depending on the degree of peeling; 5B represents the highest adhesion strength where no peeling occurs, while 0B represents the lowest adhesion strength where more than 65% has peeled off.

[0132]

[0133] Number Reduced Graphene, Non-Oxidized Graphene and Functionalized Graphene Content Non-Plane Heating Element Surface Resistance Adhesion Reduced Graphene Non-Oxidized Graphene Functionalized Graphene Thickness [um][Ω / sq] Cross-cut 31 100 5180 3B 32 100 10 112 3B 33 100 205 13B 34 100 30 322B 35 100 40 27 2B 36 100 50 24 1B 370 10 5XX 380 10 10 1100 1B 390 10 206 52B 400 10 30 28 3B 41 10 40 21 3B 42 10 50 9 3B 4311051782B44110101093B4511020433B4611030253B4711040223B4811050152B49110.01 51224B50110.0110605B51110.0120325B52110.0130195B53110.0140115B54110.015085B

[0134]

[0135] Referring to Table 5, when examining the cases where only reduced graphene was used (numbers 31-36), the sheet resistance decreased from 180Ω / sq to 24Ω / sq as the thickness of the heating element increased from 5μm to 50μm. Regarding adhesion, it was maintained at the 3B level at thin thicknesses (5-20μm), but as the thickness increased, it was observed that the adhesion gradually decreased to 2B and 1B. This suggests that while reduced graphene enables the formation of a stable heating element at thin thicknesses, the adhesion decreases as the thickness increases due to a decrease in the bonding strength between the graphene layers.

[0136] When only non-oxidized graphene was used (Nos. 37-42), it was impossible to form a heating element at a thickness of 5 μm. At a thickness of 10 μm, the sheet resistance was very high at 1100 Ω / sq, and as the thickness increased, the sheet resistance decreased rapidly to 9 Ω / sq at 50 μm. The adhesion started at 1 B and improved to 3 B as the thickness increased. This means that in the case of non-oxidized graphene, a stable electrical network can be formed at a thick thickness, but a non-uniform heating element is formed at a thin thickness.

[0137] When reduced graphene and non-oxidized graphene were mixed in a 1:1 ratio (Nos. 43-48), the advantages of the two graphenes were mutually complemented, making it possible to form a heating element in all thickness regions. The sheet resistance was 178 Ω / sq at 5 μm and 15 Ω / sq at 50 μm. However, the adhesion strength remained at an intermediate level, similar to that of 2B-3B.

[0138] The most notable result is the case where 0.01 parts by weight of functionalized graphene was added to a 1:1 mixture of reduced graphene and non-oxidized graphene (Nos. 49-54). This composition exhibited the best characteristics across all thickness ranges. In particular, sheet resistance showed generally lower values ​​compared to other compositions, decreasing to 8 Ω / sq at a thickness of 50 μm. Additionally, adhesion was excellent at the 4B-5B level across all thicknesses. This is attributed to the functionalized graphene effectively performing the role of promoting three-dimensional connections between graphene networks and enhancing bonding strength with the substrate.

[0139] These results demonstrate that an appropriate mixture of reduced and non-oxidized graphene, combined with the addition of a small amount of functionalized graphene, is highly effective in optimizing the electrical properties and mechanical stability of planar heating elements. In particular, the addition of functionalized graphene was confirmed to play a key role in simultaneously improving the formation of the heating element's electrical network and its adhesion to the substrate.

[0140] Figure 7 is a schematic diagram of a planar heating element for a film heater and a photograph taken of the evaluation of heating performance after actual fabrication.

[0141] A planar heating element with a thickness of 20 μm and an area of ​​5 cm × 6 cm was manufactured by applying a planar heating element paste of the basic composition to a polyimide film substrate with a thickness of 50 μm, drying it at 80°C for 10 minutes, drying it again at 120°C for 10 minutes, and then curing it at 200°C for 1 hour. As shown in Fig. 7, a copper wire with a width of 1 cm and a thickness of 25 μm was attached to the planar heating element using silver adhesive and heat-treated at 150°C for 30 minutes to form terminal wiring, and a PEI film was pressure-attached to form a cover, thereby completing the planar heating element for evaluating heating performance. A commercial carbon nanotube heating paste was used as a comparative product. A DC power supply was applied to the planar heating elements of the example and the comparative example, and the temperature of the planar heating elements was measured using a thermal imaging camera to perform a comparative evaluation of heating performance.

[0142] Figure 8 is a graph showing the change in heating temperature over time for the graphene nanohybrid planar heating element of the present invention and a commercial carbon nanotube planar heating element under the condition of applying 30V. In the case of the commercial carbon nanotube planar heating element, the heating temperature was 125.4℃ at 10 seconds, 141.5℃ at 20 seconds, and 144.1℃ at 30 seconds after voltage application, and the power consumption was approximately 12.3W. On the other hand, the graphene nanohybrid planar heating element of the present invention showed a heating temperature of 155.3℃ after 10 seconds, 161.6℃ after 20 seconds, and 161.5℃ after 30 seconds after voltage application, and the power consumption was measured to be 6.0W.

[0143] These results demonstrate that the graphene nanohybrid planar heating element of the present invention can reach a higher heating temperature with approximately half the power compared to a commercial carbon nanotube planar heating element. In particular, it exhibited a characteristic of rapidly reaching the target temperature with a rapid temperature rise within the first 10 seconds. This is attributed to the fact that efficient electrical and thermal transfer pathways are secured through the dense network structure formed by the 2D graphene and 3D nanohybrid materials.

[0144] Table 6 below shows the results of comparing the heating temperatures of a commercial planar heating element and the planar heating element of the present invention after 30 seconds of voltage application.

[0145]

[0146] Comparison of heating temperature after 30 seconds of applied voltage Example of commercial planar heating element Planar heating element 20 V 79.2℃ 91.7℃ 30 V 144.1℃ 161.5℃

[0147]

[0148] As shown in Table 6, the planar heating element of the present invention exhibited superior heating performance compared to commercial planar heating elements even under different voltage conditions of 20V and 30V. When 20V was applied, the commercial planar heating element showed a heating temperature of 79.2℃, whereas the planar heating element of the present invention achieved a higher heating temperature of 91.7℃. When 30V was applied, the planar heating element of the present invention also recorded a higher heating temperature of 161.5℃ compared to 144.1℃ of the commercial planar heating element. These results indicate that the planar heating element of the present invention can demonstrate superior performance in various application fields.

[0149] Figure 9 shows the manufacturing process of a nano-hybrid planar heating element for high-temperature heating in steps.

[0150] First, a transparent quartz substrate with high heat resistance of over 1000°C was prepared in a size of 180 mm x 100 mm. A planar heating element paste with a basic composition was applied to the substrate in a size of 150 mm x 60 mm. The applied paste underwent a stepwise drying process: first, a first drying step was performed at 80°C for 10 minutes, followed by a second drying step at 120°C for 10 minutes. Finally, a basic heating layer was formed by curing at 250°C for 1 hour.

[0151] Next, an electrode was formed. An electrode was printed using a sintered silver paste. The width of the electrode was formed in the range of 0.5 mm to 10 mm, and the electrode layer was completed by drying at 120°C for 30 minutes.

[0152] After the electrode layer was completed, a first heat treatment step was performed. The first heat treatment was carried out at 300°C for 2 hours by increasing the temperature at a rate of 3°C per minute. During the first heat treatment process, the debinding of the silver paste proceeds simultaneously with the post-curing of the nanohybrid paste.

[0153] The second heat treatment step is carried out in an inert atmosphere with argon gas injected at a rate of 1 L / min. The temperature was increased at a rate of 3°C per minute and heat treatment was performed at 700°C for 30 minutes. At this stage, the sintering of the electrode is completed, and at the same time, the heat treatment of the nano-hybrid planar heating element for high-temperature heating is completed.

[0154] Finally, the final product was completed by coating the surface of the manufactured planar heating element with inorganic silazane to form a protective layer.

[0155] Figure 10 shows the results of observing the surface of a nanohybrid planar heating element with an optical microscope after heat treatment. It can be confirmed that a uniform surface state is maintained even after high-temperature heat treatment at 700°C. This demonstrates that the nanohybrid structure of the present invention is stably maintained even at high temperatures.

[0156] As shown in the scanning electron microscope (SEM) results of Fig. 11, it can be confirmed that the nanohybrid planar heating element has a structure in which spherical alumina particles are uniformly distributed within a graphene matrix. In particular, high-magnification observation revealed a core-shell structure in which a graphene sheet layer is clearly coated on the surface of the alumina particles, and it can be confirmed that a graphene network is densely formed between these nanohybrid particles.

[0157] Figure 12 shows the design of the planar heating element of the present invention and a commercial multilayer CVD graphene planar heating element to match the initial wiring resistance to the same level for the comparison of heating performance in Table 7. When aiming for the same wiring resistance (approx. 23.5 Ω), the nanohybrid planar heating element of the present invention was able to secure a large heating area of ​​45.0 mm due to a low sheet resistance of 80 Ω / sq. On the other hand, the heating area of ​​the commercial multilayer CVD graphene was limited to 10.5 mm due to a high sheet resistance of 330.5 Ω / sq.

[0158] Table 7 below compares the heating performance of a commercial multilayer CVD (Chemical Vapor Deposition) graphene planar heating element and the high-temperature planar heating element of the present invention.

[0159]

[0160] Heating temperature after 30 seconds of state voltage application and comparison of special features of multilayer CVD graphene nanohybrid planar heating element. Surface resistance of the heating element by surface (before polysilazane coating) 350.5 Ω / cm 2 80 Ω / cm 2 Initial Wiring Resistance 23.4 Ω 23.5 Ω Applied Voltage 30V 30 ℃ 29 ℃ Applied Voltage 60V 54 ℃ 52 ℃ Applied Voltage 110V Not Operating 133 ℃ Applied Voltage 150V Not Operating 229 ℃ Applied Voltage 220V Not Operating 459 ℃ Applied Voltage 230V Not Operating 510 ℃ Wiring Resistance After Heating Ends OPEN CIRCUIT 23.6 Ω

[0161]

[0162] As shown in the heating performance comparison results in Table 7, the two heating elements exhibited similar heating temperatures in the low-voltage range (30V, 60V), but showed a significant difference in the high-voltage range above 110V. In particular, the high-temperature planar heating element of the present invention was capable of generating heat of 469°C at 220V and 510°C at 230V, whereas the commercial multilayer CVD graphene was unable to operate above 110V. Furthermore, when measuring wiring resistance after heating ended, the nanohybrid planar heating element maintained its initial value (23.5Ω), whereas the multilayer CVD graphene experienced an electrical disconnection and became an OPEN Circuit. These results demonstrate that the graphene network structure of the present invention can maintain a stable electrical network even at high temperatures. Notably, the high-temperature planar heating element of the present invention showed almost no change in wiring resistance even after repeating the process of heating to over 500°C at an applied voltage of 230V and then cooling to room temperature 10 times.

[0163] As explained in detail above, the graphene-based nanohybrid planar heating element of the present invention can achieve excellent heating performance even with low power consumption through a graphene network structure implemented by nanohybrid materials, graphene flakes, and functionalized graphene.

[0164] In addition, electrical properties and mechanical stability are improved by a graphene network structure implemented by nanohybrid materials, graphene flakes, and functionalized graphene, making it possible to generate heat at high temperatures of over 500°C, which cannot be achieved with commercial CVD graphene.

[0165] In particular, since the planar heating element of the present invention does not utilize CVD, which has a high process difficulty, mass production is easy, and it is expected to be applicable to various fields ranging from film heaters for home appliances to high-temperature heaters for industrial use.

[0166] The scope of protection of the present invention is not limited to the description and expression of the embodiments explicitly described above. Furthermore, it is added once again that the scope of protection of the present invention cannot be limited by obvious changes or substitutions in the technical field to which the present invention belongs.

Claims

1. A heating layer comprising graphene flakes, functionalized graphene, and nanohybrid materials; and A planar heating element comprising an electrode electrically connected to the heating layer; wherein the nanohybrid material is a self-adsorbed functionalized graphene on the surface of a thermally conductive inorganic particle.

2. In Paragraph 1, A planar heating element in which the content of functionalized graphene self-adsorbed onto the nanohybrid material is 0.1 to 5 wt% based on the nanohybrid material.

3. In Paragraph 1, A planar heating element in which the weight ratio of the graphene flakes, functionalized graphene, and nano-hybrid material is 3.0 to 20 : 0.001 to 0.1 : 0.05 to 20.

4. In claim 1, the graphene flake is a planar heating element comprising reduced graphene and non-oxidized graphene.

5. In Paragraph 1, The above thermally conductive inorganic particle is a planar heating element selected from at least one of the group consisting of Al2O3, SiO2, MoS2, MMT (montmorillonite), BN (boron nitride), AlN, ZnO, TiO2, and MgO. 6.(a) Step for manufacturing paste for planar heating element; (b) a step of applying and curing the above-mentioned paste for a planar heating element; and (c) a step of forming an electrode on the cured paste for the planar heating element; comprising, The above step (a) is, (a-1) A step of preparing a nanohybrid material by mixing a first-functionalized graphene colloid and thermally conductive inorganic particles; (a-2) A step of preparing a functionalized graphene dispersion by mixing a second functionalized graphene colloid and a resin in a solvent; (a-3) A step of preparing a high-concentration graphene flake dispersion by mixing and dispersing graphene flakes in a solvent and then concentrating them; and (a-4) A method for manufacturing a planar heating element comprising the step of mixing a nanohybrid material, a functionalized graphene dispersion, and a high-concentration graphene flake dispersion.

7. In Paragraph 6, A method for manufacturing a planar heating element in which, after performing step (b) above, a step of removing the resin through heat treatment is further performed.

8. In Paragraph 7, The above heat treatment is, A step of performing a first heat treatment at 200 to 300 ℃; and A method for manufacturing a planar heating element comprising the step of performing a first heat treatment at 600 to 800 ℃.

9. In Paragraph 6, The above (a-1) step is, A method for manufacturing a planar heating element in which the first functionalized graphene has a positive zeta potential and the inorganic particle has a negative zeta potential, thereby causing the first functionalized graphene to self-adsorb onto the surface of the inorganic particle.

10. In Paragraph 6, The above graphene flakes are a method for manufacturing a planar heating element comprising reduced graphene and non-oxidized graphene.

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