HEATABLE PANEL AND ITS MANUFACTURING METHOD

Abstract

 The present invention consists of a heating panel which uses, as a power source, electrical energy that is to be converted into thermal energy. To that end, the obtained solution is based on obtaining a sheet (1) of recyclable, lightweight conductive polymer which, as a result of the addition of conductive additives, can change its thermal and electrical properties and replace heat-generating metallic resistors when this type of heating is required.
The sheet with conductive particles added as additive forms part of a heatable panel which produces thermal energy when an electric current is applied, such that in order to carry out this process, said panel comprises, in addition to the conductive sheet, metallic electrodes (6) mechanically connected to the sheet, a first temperature-insulating layer (3), a second electricity-insulating layer (2), and a thermocouple sensor (5) attached to the sheet configured for measuring the internal temperature of the heatable panel.

Description

Object of the invention and field of application

[0001] The present invention relates to heatable panels produced by means of conventional plastic transformation processes based on conductive thermoplastic compounds. The panel is heated as a result of Joule effect whereby an electrically conductive material is heated when an electric current is applied. These panels can be used as a heating system in different sectors such as automotive, construction, aerospace, and packaging sectors. The panels can be obtained by means of extrusion, injection, or compression molding and then shaped to enable adapting to different geometries.

Background of the invention

[0002] Different protected systems to be used as Joule heating or resistive heating are known up until now. None of the reviewed inventions refer to thermoplastic polymers obtained by means of extrusion, injection, or compression, since the high electrical conductivity required to achieve the Joule effect is much more difficult to obtain by means of conventional plastic processing processes. Several inventions, the novelty of which lies in the development of conductive coatings on different substrates, have thus been found.

[0003] Invention ES2574622 uses, as a heatable material, a thermosetting elastomer with a high percentage of carbon nanotubes (CNTs) (between 20 and 45% by weight) added as additive. This elastomer is used as a coating in different substrates. The invention indicates the importance of copper electrodes which are deposited by means of electrochemical electrodeposition on the conductive material.

[0004] In invention WO 2007089118, a highly conductive film that can be heated is obtained by spraying an aqueous solution of carbon nanotubes (CNTs) on a polymer sheet. Invention DE102011086448(A1) is also based on the deposition of layers of an aqueous solution of carbon nanotubes (CNTs) for obtaining a heatable coating.

[0005] Invention WO2002076805 A1 describes a steering wheel that can be heated by means of applying carbon particle-based conductive coatings. In invention ES2402034B1, work is also performed with different layers of conductive coatings, and it also contemplates the encapsulation of heatable elements and electrodes.

[0006] Inventions US2005172950 and WO 2009011674 relate to heatable fabrics or clothing. The former is based on impregnating fabrics with conductive coatings and the latter obtains the conductive fabric from long carbon nanotube fibers.

[0007] In invention DE102007004953 (A1), carbon nanotubes and intrinsically conductive polymers are used as a heatable coating in glasses.

[0008] In invention ES 2537400 B1, conductive coatings are applied in heatable automobile elements, specifically in rear-view mirrors.

[0009] Claim 2 of patent DE102011003012 refers to a cross-linked polymer and the example specifies the use of a silicone. These materials are thermally stable and cannot be processed by extrusion. Thermoplastic polymers can be partially cross-linked to obtain an extruded sheet but, in that case, they cannot be melted again, leading to the inability to recycle same.

[0010] In the present invention the materials are in no case cross-linked, with recyclability being a very novel feature of the panel. Furthermore, it relates to soft materials such as silicone, whereas the materials of the present invention are rigid panels.

[0011] The materials developed in the present invention have a much lower resistivity, being much more conductive than the materials specified in said German invention DE102011003012. The low conductivity conditions the design of the electrodes, resulting in said electrodes having to be relatively close and have a large size (similar to the geometry of the heatable sheet).

[0012] In invention GR1449261, the process of obtaining a highly conductive film is very different from that developed in the present invention. It is based on annealing which is performed on the polymer after the extrusion of the film. This annealing can last up to 24 h.

[0013] The present invention does not contemplate this technology because good conductivity is achieved by properly dispersing the conductive charge and correctly processing the material to obtain the final film or part with the desired conductive properties. Therefore, a PTC plastic is obtained by means of conventional processes as a result of the good dispersion of the conductive particles which are achieved by applying certain specific processing conditions, which also allows producing larger geometries with a greater distance of the electrodes.

[0014] Invention CN201610317174 relates to solvent-based conductive pastes without being thermoplastic polymers. The polymeric material produced by means of extrusion is the (non-conductive) substrate on which the conductive paste is applied. It is a functional ink printing process that is very different from thermoplastic processing.

[0015] Therefore, the inventions that are found are based on the application of conductive paints or varnishes that finally form a conductive coating or on the extrusion of materials with worse electrical conductivities, which subsequently makes the configuration of the electrodes difficult and complicated. The application of coatings is a manual process and the final behavior of the heating element depends on different factors, such as: the number of layers of the conductive solution or paint, the worker who applies the paint, the homogeneity of the solution, given that if the conductive particles decant over time, the first applied layer may have a much higher concentration of conductive particles than the last applied layer. Therefore, the heating homogeneity and the reproducibility of the heating elements produced are not stable.

[0016] In the present invention, the conductive particles are dispersed in the thermoplastic die in a co-rotating twin-screw extruder. A homogeneous nanocompound with high electrical conductivity is obtained, allowing the electrodes to be positioned at a great distance. In a subsequent processing, this material is melted to obtain a conductive sheet. Said process can be an extrusion, compression, or injection. The obtained part will have a homogeneous concentration of conductive particles, ensuring a reproducible and homogeneous behavior. Furthermore, as it is based on thermoplastic materials, the sheet can be ground and reprocessed, assuring recycling at the end of the product's service life. Recycling is not contemplated in the state of the art since different materials and thermosetting coatings that do not allow recycling are combined.

[0017] Unlike the inventions mentioned in the prior art, the materials developed and the manufacturing process carried out in the present invention provide a lower resistivity of the conductive sheet of 10¹ Ohm.cm, which is much lower with respect to patent DE102011003012A1, which mentions resistances between 10³ and 10⁶ ohm.cm, implying a greater conduction by the developed panel.

Description of the invention

[0018] The present invention has been devised as a heating panel which uses, as a power source, electrical energy that is to be converted into thermal energy. The novelty lies in the type of material making up the heatable panel and in its manufacturing process.

[0019] The conceived solution is based on obtaining a sheet of recyclable, lightweight conductive polymer to be used in a wide variety of designs depending on the sizes and geometries required according to the application.

[0020] The polymer materials are usually insulating materials; however, as a result of the addition of conductive additives, they can change their thermal and electrical properties and replace heat-generating metallic resistors when this type of heating is required.

[0021] The heatable panel produces thermal energy when an electric current is applied, such that in order to carry out this process, the panel comprises:

• a sheet made of thermoplastic material with temperature conducting particles added as additive, providing the sheet with a PTC (Positive Temperature Coefficient) behavior, wherein the geometry of the sheet can be adaptable by means of thermoforming processes used in the manufacture thereof and wherein said sheet is recyclable;
• metallic electrodes mechanically connected to the sheet and configured for applying an electric current going through said sheet;
• a first temperature- and electricity-insulating layer configured for preventing heat energy losses in the direction opposite the desired direction;
• a second electricity-insulating layer configured for preventing direct contact with the sheet; and
• a thermocouple sensor attached to the sheet configured for measuring the internal temperature of the heatable panel;

such that the sheet is attached to the first insulating layer on one side and to the second insulating layer on the opposite side. The metallic electrodes are attached on opposite longitudinal ends of the sheet and the thermocouple sensor is attached in the central part of the sheet.

[0022] All these components forming the heatable panel, i.e., the sheet, the first insulating layer, the second insulating layer, the thermocouple sensor, and the metallic electrodes, are reusable to form part of another heatable panel or to form part of another system.

[0023] Since the sheet has a PTC thermistor behavior, when an electrical current is applied to the metallic electrodes, the sheet works by increasing the electrical resistance with the increase of temperature. In other words, once the desired temperature is reached, it stabilizes and no temperature peaks are generated, making it a safe heating system. This feature gives it the particularity of being self-regulating, dispensing with the need for thermostats that are necessary in other heating systems.

[0024] The conductive particles added as additive to the thermoplastic material of the sheet have directly proportional percentages in the mixture with the thermoplastic material, depending on the final temperature required by the heatable panel and on the type of conductive particles used. Once the material has been formulated, the temperature of the panels can be regulated by adapting the input voltage or cutting off the current supply, without having to adapt the formulation to each of the applications.

[0025] These temperature conducting particles of the sheet can be carbon black, graphite, graphene, carbon nanotubes, or a combination of the foregoing.

[0026] In one embodiment, the conductive particles added as additive to the thermoplastic material of the sheet are carbon nanotubes and have a concentration comprised between 5 and 10% with respect to the total weight of the sheet.

[0027] In other embodiments, when the conductive particles are of graphite material, the concentration is comprised between 20 and 40%, when they are of carbon black, the concentration is between 10 and 30%, when they are of graphene, between 3 and 10%, all these percentages being with respect to the total weight of the mixture forming the sheet.

[0028] The thermoplastic materials of the sheet can be polyolefins, polyesters, polyamides, thermoplastic elastomers, polysulfones, polyetherimides, or a combination of all the foregoing, since all of them allow mixing with the temperature conducting particles and have structural and mechanical characteristics suitable for the use of the heatable panel, although a type of polyolefin, i.e., polypropylene, is preferably used.

[0029] Furthermore, since it is a polymeric compound, the composite layer can adopt several forms by means of thermoforming, obtaining a lightweight final compound, allowing the use thereof for spaces with special geometries. Furthermore, machining operations can be applied thereto to make the adjustment with other elements.

[0030] In one embodiment, the heatable panel also comprises a coating fabric partially or completely covering the panel, said coating fabric being an electrically insulating material that is resistant to temperature changes and selected depending on the characteristics of the installation of the panel.

[0031] The conductive materials of the metallic electrodes can be copper or silver, although other metallic materials that can be mechanically attached to the sheet to be reused can be selected.

[0032] The manufacturing process for manufacturing the sheet made of thermoplastic material with temperature conducting particles added as additive is carried out by means of plastic and thermoplastic transformation processes.

[0033] To that end, the conductive particles in the form of powder and the thermoplastic material in the form of pellets are first introduced in a heated container of a co-rotating twin-screw extruder.

[0034] Once the conductive particles and the thermoplastic material have been introduced in the container, they are hot mixed, melting the thermoplastic material in the extruder, to achieve a homogeneous mixture, applying a specific mechanical energy of at least 0.5 kWh/kg while melting the thermoplastic material.

[0035] The purpose of this process is to disperse the conductive charge in the polymer die to achieve optimal electrical properties homogeneously throughout the volume of the sheet.

[0036] To achieve optimum dispersion, the thermoplastic material is melted at a temperature of 210°C, for the preferred case of a polypropylene die, and the screws rotate at a speed greater than 600 rpm, for a material input of 10 kilograms per hour in the co-rotating extruder measuring 25 mm diameter and with a length to diameter ratio equal to 40.

[0037] Once a homogeneous mixture is achieved, said mixture of molten plastic with the conductive particles is passed through an extruder head configured for generating filaments of thermoplastic material with conductive particles added as additive.

[0038] Once cooled, these filaments of thermoplastic material with added additive are cut using a shear to obtain pellets of said material.

[0039] In order not to lose electrical conductivity, processing must be optimized, assuring slow cooling of the material at the head outlet. The calender rollers must be at a high temperature, assuring that the carbon nanotubes have enough time to be distributed into the polymer die and form the conductive network.

[0040] In a subsequent manufacturing process, said pellets are melted to obtain the sheet of heatable panel by means of a new extrusion, drawing, roller lamination, or a combination of these manufacturing processes, all these processes being hot processes to facilitate the molding of the sheet, although it can also be performed by means of injection into plastic dies or compression molding. With these manufacturing processes, the geometry of the sheet can be adaptable to any geometry depending on the shape and size requirements.

[0041] In another embodiment, the thermoplastic material conductive sheet with conductive particles added as additive can be obtained in a single step, coupling a co-rotating extruder to a flat sheet head. The panel is therefore more cost-effective and faster to manufacture.

[0042] Furthermore, as it is based on thermoplastic materials, the sheet can be ground to obtain pellets again, and reprocessed, assuring recycling at the end of the product's service life. This recycling is not contemplated in the prior art found since different embedded materials and thermosetting coatings that do not allow recycling are combined.

[0043] In this described sheet manufacturing method, the conductive particles do not coat any material, but are dispersed in the die of the co-rotating twin-screw extruder with the thermoplastic material, unlike these inventions mentioned in the prior art, so the materials developed in the present invention obtain the mentioned resistivity of 10¹ Ohm.cm, and a greater thermal conduction.

[0044] This good conductivity is only achieved by properly dispersing the conductive charge and correctly processing the conductive particles to obtain the sheet with the desired conductive properties.

[0045] Therefore, with this process a PTC plastic sheet is achieved by means of manufacturing processes as a result of the dispersion of the conductive particles, which are achieved by applying certain specific processing conditions. This also allows producing geometries having a larger size than those found and a greater distance between the electrodes.

[0046] When all the materials have been manufactured, the heating panel is constructed by means of custom machining according to the desired geometry of the final panel or by means of thermoforming, connecting the electrodes to the sheet and placing the insulation layers on the sides of said sheet.

[0047] Once these layers have been attached to the sheet, the assembly is covered by means of the coating fabric customized according to the design and the final application, with fabrics that are resistant to temperature changes or possible iterations that they may have with the exterior to provide a finish suitable for use.

[0048] All the parts of the heating panel are therefore completely recyclable due to their nature and reusable for the same or another application.

BRIEF DESCRIPTION OF THE FIGURES

[0049] 

• Figure 1 shows an elevation view and another profile view of the heatable panel.
• Figure 2 shows the temperature reached by heatable panels with heat conducting sheets of different sizes and geometries.
• Figure 3 shows a graph indicating how the temperature levels of the material of a sheet manufactured from polypropylene with carbon nanotubes vary when 48 V are applied starting from a temperature of - 21°C.

PREFERRED DESCRIPTION OF THE INVENTION

[0050] As can be seen in Figure 1, the heatable panel of the present invention is formed by a sheet (1), manufactured from a thermoplastic material, metallic electrodes (6) mechanically connected on the sides to the sheet (1), a first insulating layer (3) located on one side of the sheet (1), preventing the sheet from losing temperature on the side opposite the desired side and also preventing the passage of electric current on that side, a second electricity-insulating layer (2) for limiting the passage of electric current on the opposite side of the sheet (1) where heat is emitted, and a thermocouple sensor (5) attached to the sheet (1) measuring the internal temperature of the heatable panel.

[0051] In the preferred embodiment, said heatable panel is partially or completely coated by a coating fabric (4) made of an electrically insulating material for two purposes. Preventing a user who is close to the panel from coming into unwanted contact with the electrically conductive heatable sheet (1) and providing a finish according to the panel installation location.

[0052] This coating fabric (4) can be of many types, but a natural fabric is preferably selected.

[0053] Despite being made from a thermoplastic material, the sheet (1) is capable of emitting heat because electrically conductive particles are added as additive, providing the sheet (1) with PTC behavior. These temperature conducting particles of the sheet (1) can be of different types such as carbon black, graphite, graphene, carbon nanotubes, and a combination of the foregoing, carbon nanotubes (CNTs) preferably being used due to their heat conduction properties.

[0054] The percentage of these carbon nanotube particles is comprised between 5 and 10% with respect to the total weight of the sheet, which is completed with thermoplastic materials selected from polyolefins, polyesters, polyamides, thermoplastic elastomers, polysulfone, polyetherimide, or a combination of all of the foregoing, although polypropylene, a compound from the groups of polyolefins, is preferably used.

[0055] Figure 2 shows the temperature that the heatable panel can reach using carbon nanotubes (CNTs) in different percentages and different sizes as additive particle, so that the higher the percentage of nanotubes, the higher the temperature reached by the panel.

[0056] The thermoplastic material used in this case, shown in Figure 2, is a polypropylene in which different percentages of carbon nanotubes (CNTs) from 3% to 10% by weight have been mixed. Different temperatures in degree Celsius are generated by applying a voltage of 48 V to the heatable panel, reaching up to 100°C if the panel has a smaller surface with sides measuring 15 x 15 cm.

[0057] In the graph of Figure 3, the operation of a sheet manufactured from polypropylene with carbon nanotubes is shown, to which a voltage of 48 volts has been applied gradually during the first minute, establishing that constant voltage until minute 6. Due to the applied load, the temperature of the panel begins to go up in a logarithmic growth, going from -21°C to 75°C within those 6 minutes, in which the indicated voltage is applied. The temperature drops gradually in an exponential decrease when the voltage is removed.

[0058] With these materials used in the sheet of the heatable panel, the test of which is shown in Figure 3, 45°C is reached within 4 minutes starting at a temperature of -21°C.

[0059] The energy consumption of said heatable panel is 120 W for a rectangular geometry measuring 350 cm on one side by 250 cm on the other side and by 2 cm wide, applying 48 V and 64 W, for the same geometry, applying 24 V. For a smaller geometry of a square panel measuring 15 cm on each side and by 1 cm wide, the energy consumption is 20 W at 48 V and 5 W at 24 V.

[0060] To manufacture the sheet (1) a series of processes is followed to achieve the mentioned operating characteristics. Since the sheet (1) is formed by a thermoplastic material and particles added as additive, firstly the mixing of both components is performed, so that they are blended together in the state of pellets and powder, and heated to melt the plastic material, where it is stirred inside an extruder applying a specific mechanical energy of at least 0.5 kWh/kg.

[0061] The thermoplastic material is melted at a temperature of at least 210°C when polypropylene is used and the screws rotate at a speed of at least 600 rpm for a material input of 10 kilograms per hour in a co-rotating extruder measuring 25 mm in diameter and with a length to diameter ratio equal to 40.

[0062] Once the correct homogenization of the mixture has been achieved, the material is extruded to obtain filaments that are cooled and solidified in rollers, to be subsequently cut using a shear and to obtain new pellets but from the mixture of components.

[0063] Said pellets are used to obtain the sheet (1) following one or different plastic transformation processes, such as extrusion, drawing, compression molding, roller lamination, or die injection.

[0064] Once the sheet (1) has been manufactured, it is attached to the rest of the components forming the heatable panel and is ready for use.

EXAMPLES

Example 1: Polypropylene- and carbon nanotube (CNT)-based heatable panel

[0065] The present example refers to a sheet made of polypropylene and carbon nanotubes obtained by means of flat sheet extrusion. In this process, the plastic material is melted by means of heat and shear in an extruder and is forced to pass through a head, giving it the shape of a sheet. The sheet is passed through a roller system or calender. The cooling of the material is controlled by varying the temperature of these rollers.

[0066] The key parameters for processing the sheet with high electrical conductivity by means of extrusion are shown in Table 1.

Table 1: Optional extrusion parameters

Parameter	Value
Area 1 (°C)	180
Area 2 (°C)	185
Area 3 (°C)	195
Area 4 (°C)	200
Area 5 (°C)	210
Head (°C)	220
Melt temperature (°C)	211
Pressure (bar)	57
Speed (rpm)	60
Torque (N/m2)	4.5 - 23%
Drawing (%)	1.0
Die Gap (µm) (Nozzle opening)	900
Roller temperature (°C)	80
Film thickness (µm)	900

[0067] The percentage of carbon nanotubes is determined according to the temperature of use required by the application. The optimal range being between 5 and 10% of nanotubes to reach temperatures between 25 and 100°C.

Example 2: Polypropylene- and graphite-based heatable panel

[0068] In this second example, the sheet is obtained by means of compression molding. The main parameters involved in the process are the pressure exerted on the mold, the cycle time, and the temperature during processing.

[0069] Table 2 shows the processing conditions to achieve optimum electrical conductivity in the graphite plates.

Table 2: Compression molding processing parameters

Units	BIPOLAR
Min	E1	E2	E3	E4	E5
	4	2	2	4	15
bar	P1	P2	P3	P4	P5
	4	40	75	150	70
°C	T1	T2	Dry samples for 2 h at 80°C
	190	190

[0070] Table 3 shows the temperatures reached in three areas of the heatable panel when a certain voltage is applied. In this case, the panels have a geometry of 15 x 15 cm and they were obtained by means of compression molding.

Table 3: Thermal behavior of panels containing polypropylene and graphite

	PP+20%graphite	PP+30%graphite	PP+40%graphite
T1	45.9	96.6	102
T2	45.7	100	86.9
T3	46.3	80.6	60.7
V	48	48	38
Current (A)	0.24	5.12	5.11
Power (W)	11.52	245	195

Claims

1. A heatable panel or sheet, capable of producing heat energy when an electric current is applied, characterized in that it comprises:

- a sheet (1) made of thermoplastic material with electrically conductive particles added as additive, providing the sheet (1) with a PTC behavior, wherein said sheet (1) is recyclable;

- metallic electrodes (6) mechanically connected to the sheet (1) and configured for applying an electric current going through said sheet (1);

- a first temperature- and electricity-insulating layer (3) configured for preventing heat energy losses in the direction opposite the desired direction;

- a second electricity-insulating layer (2) configured for preventing direct contact with the sheet (1); and

- a thermocouple sensor (5) attached to the sheet (1) configured for measuring the internal temperature of the heatable panel;

wherein the sheet (1) is attached to:

- the first insulating layer (3) on one side of said sheet (1);

- the second insulating layer (2) on the opposite side of the attachment of said sheet (1) with the first insulating layer (3);

- the metallic electrodes (6) on opposite longitudinal ends of said sheet (1); and

- the thermocouple sensor (5) in the central part of the sheet (1), the sheet (1), the first insulating layer (3), the second insulating layer (2), the thermocouple sensor (5), and the metallic electrodes (6) being reusable.

2. The heatable panel according to claim 1, characterized in that the temperature conducting particles of the sheet (1) are selected from the group consisting of carbon black, graphite, graphene, carbon nanotubes and a combination of the foregoing.

3. The heatable panel according to claim 2, characterized in that the conductive particles added as additive to the thermoplastic material of the sheet (1) are carbon nanotubes with a concentration comprised between 5 and 10% with respect to the total weight of the sheet.

4. The heatable panel according to claim 2, characterized in that the conductive particles added as additive to the thermoplastic material of the sheet (1) are of graphite material with a concentration comprised between 20 and 40% with respect to the total weight of the sheet.

5. The heatable panel according to claim 2, characterized in that the conductive particles added as additive to the thermoplastic material of the sheet (1) are of carbon black with a concentration comprised between 10 and 30% with respect to the total weight of the sheet.

6. The heatable panel according to claim 2, characterized in that the conductive particles added as additive to the thermoplastic material of the sheet (1) are of graphene with a concentration comprised between 3 and 10% with respect to the total weight of the sheet.

7. The heatable panel according to any one of the preceding claims, characterized in that the thermoplastic materials of the sheet (1) are selected from the group consisting of polyolefins, polyesters, polyamides, thermoplastic elastomers, polysulfone, polyetherimide, and a combination of all the foregoing.

8. The heatable panel according to any one of the preceding claims, characterized in that the heatable panel additionally comprises a coating fabric (4) partially or completely covering the panel, said coating fabric (4) being an electrically insulating material selected from a group consisting of polyvinyl chloride, polyurethane, natural fabrics, and a combination of all the foregoing.

9. The heatable panel according to any one of the preceding claims, characterized in that the conductive materials of the metallic electrodes (6) are selected from the group consisting of copper and silver.

10. A manufacturing process for manufacturing the sheet (1) made of thermoplastic material with temperature conducting particles added as additive by means of plastic and thermoplastic transformation processes, characterized in that the process comprises:

a) Introducing the conductive particles in the form of powder and the thermoplastic material in the form of pellets in a heated container of a co-rotating twin-screw extruder;

b) Hot mixing, melting the thermoplastic material in the extruder, configured for obtaining a homogeneous mixture of said thermoplastic material with the conductive particles, applying a specific mechanical energy of at least 0.5 kWh/kg while melting the thermoplastic material.

11. The manufacturing process for manufacturing the sheet (1) according to claim 10, characterized in that the manufacturing process additionally comprises:

c1) Forcing the passage of the mixture of the molten plastic with the conductive particles through an extruder head configured for generating filaments of thermoplastic material with conductive particles added as additive;

d1) Cutting said filaments of thermoplastic material with added additive using a shear for obtaining pellets of said material;

e1) Melting said pellets for obtaining the sheet (1) of the heatable panel in a process selected from a group consisting of extrusion, drawing, compression molding, roller lamination, and injection.

12. The manufacturing process for manufacturing the sheet (1) according to claim 10, characterized in that the manufacturing process additionally comprises:
c2) Extruding the thermoplastic material with conductive particles added as additive through the extruder, producing the sheet (1) of the heatable panel.

13. The manufacturing process for manufacturing the sheet (1) according to claim 10, characterized in that the sheet (1) is recycled, being ground into the form of pellets which are added to the conductive particles in the form of powder and to the thermoplastic material in the form of pellets into the heated container of the extruder of phase a).

14. The manufacturing process for manufacturing the heatable panel according to claim 10, characterized in that the thermoplastic material is melted at a temperature of at least 210°C for polypropylene and the screws rotate at a speed of at least 600 rpm for a material input of 10 kilograms per hour in a co-rotating extruder measuring 25 mm in diameter and with a length to diameter ratio equal to 40.

Drawing