Heating conductive filament and method for manufacturing the same

Abstract

This disclosure pertains to a method for manufacturing a heating conductive filament, comprising: (a) uniformly mixing carbon-based nanofillers (101) with a thermoplastic polymer matrix (103) to form a polymer mixture; (b) extruding the polymer mixture to form a continuously mixed filament (105; 106); (c) pelletizing the filament to form a granulate (107) and drying the granulate (107) to remove moisture; (d) re-extruding the granulate (107) to form an extruded filament, and (e) guiding the re-extruded filament through a drawing system comprising rollers and winders with a drawing rate between 3 and 9, to output the heating conductive filament in a wound form, the carbon-based nanofillers comprising carbon black and single-walled carbon nanotubes, the carbon black having a concentration range of 3% to 25% by weight and / or the single-walled carbon nanotubes having a concentration range of 0.3% to 5% by weight.

Description

[0001] Description

[0002] Title: Heating conductive filament and method for manufacturing the same

[0003] Technical field

[0004] The present disclosure relates to the field of electrical heating elements and conductive materials. In particular, the present disclosure pertains to heating conductive filaments and methods for their manufacturing.

[0005] It is known to use electrically conductive molding with a positive temperature coefficient (PTC) for various applications, such as electrically heated sheet materials. With these materials, significant rise in PTC intensity is achieved by utilizing a polymer composition with specific components. The molding process allows these materials to maintain structural integrity and service properties during PTC, which offers advantages in terms of electrical conductivity and temperature-dependent resistivity. Other processes involve producing electrically conductive thermoplastic resin monofilaments with precise temperature control during orientation, which ensures high strength and excellent electrical conductivity.

[0006] For instance, the US patent application No. 4,432,924 discusses a process for producing an electrically conductive thermoplastic monofilament containing electrically conductive carbon black through extrusion, cooling, and orientation steps. An aging step, in which the temperature of the monofilament is kept constant, is also carried out between the cooling step and the orientation step.

[0007] The Canadian patent application No. 3 029 093 A1 discusses electrically conductive moldings made of an electrically conductive polymer composition which has inherent positive temperature coefficient (PTC) and which comprises at least one organic matrix polymer, submicro- or nanoscale electrically conductive particles and at least one phase-change material he moldings are produced by the injection-molding process or are in particular electrically conductive monofilaments, multi-filaments, fibers, nonwoven fabrics, foams or films or foils which can by way of example be used in automobile heating systems or heating blankets or industrial textiles, and are self- regulating in respect of current. There is also discussed how to produce such moldings in a process involving melting if submicro- or nanoscale electrically conductive particles, together with a phase-change material which is advantageously combined in polymer network structures of a copolymer to give a masterbatch, and also with other compound- material components, form a thermoplastifiable mixture. However, the synthetic polymer wires and filaments that can be produced are not systematically applicable for use in electric vehicle (EV) batteries and smart home technologies, notably because these wires cannot be made lightweight and flexible. Another drawback is that it is not possible to weave these wires into fabrics, limiting their use in outdoor and athletic wear industries. Existing methods also face challenges in achieving uniform temperature gradients during the orientation process, affecting the overall quality and performance of the conductive monofilaments.

[0008] Summary

[0009] To address this or these drawbacks, it is proposed according to a first aspect of the present disclosure a method for manufacturing a heating conductive filament, comprising the steps of:

[0010] (a) mixing uniformly carbon-based nanofillers with a thermoplastic polymer matrix to form a respective polymer mixture,

[0011] (b) extruding the respective polymer mixture to form a continuously mixed filament,

[0012] (c) pelletizing the formed continuously mixed filament to form at least one respective granulate,

[0013] (d) re-extruding the at least one respective granulate to form a respective extruded filament, and

[0014] (e) guiding the respective re-extruded filament through a drawing system comprising a plurality of rollers and winders, said drawing system having a drawing rate larger than 3 and smaller than 9, to output the heating conductive filament in a wound form, wherein the carbon-based nanofillers are selected to comprise carbon black and singlewalled carbon nanotubes, the carbon black having a concentration range of 3% to 25% by weight and / or the single-walled carbon nanotubes having a concentration range of 0.3% to 5% by weight.

[0015] This allows to overcome the aforementioned drawbacks, as the present invention aims to provide a manufacturing method for a heating conductive filament that exhibits excellent conductive and heating features. Such ultra-thin filaments have optimized linear electrical resistance, in particular for generating heat, and using materials that significantly reduce energy consumption compared to existing solutions. The linear resistance and resistivity of the filament are controlled through precise amounts of carbon-based nanofillers in combination with an optimal sequence of compounding and drawing stages.

[0016] Herein, a "drawing rate" is defined as the ratio of the speed at which the re-extruded filament is drawn by a roller in the system to the speed at which the filament is extruded or drawn by a preceding roller. This measure indicates the efficiency of the drawing system in processing the filament from its initial extrusion to its subsequent handling by the roller system.

[0017] Surprisingly, a drawing rate between 3 and 9 provides a filament with optimal heating conductive features. A drawing rate smaller than 3 might result in too little modification of the filament properties whereas a drawing rate larger than 9 or 10 is excessively fast, potentially causing damage to the filament.

[0018] According to a possible embodiment, the filament is a monofilament. When the filament is a monofilament, the filament provides a single, continuous strand of material, preferably uniform in diameter.

[0019] Herein, a thermoplastic polymer matrix has the form of an organic matrix made out of a polymer.

[0020] According to a possible embodiment, rollers can be configured so that the properties, such as speed, of the guiding step can be selected and controlled precisely, are merely drawing to precisely control the drawing process.

[0021] According to a possible embodiment, in a non-limiting way, the carbon-black has a grade that can be selected among EC-300J, XC-72, SC Ultra, N990, etc.

[0022] According to possible embodiments, the carbon black is selected to be electrically conductive. Advantageously, the carbon black can also be selected to enable a high surface-area-to-volume ratio, providing optimal conductive properties.

[0023] According to a possible embodiment, the step (e) of guiding passing the re-extruded filament is carried out by guiding said re-extruded filament through a plurality of heated rollers and / or winders.

[0024] Herein, carrying out the guiding step (e) with heater rollers and / or winders means that the temperature of said rollers and / or winders can be controlled and adjusted.

[0025] According to a possible embodiment, heater rollers and / or winders comprise ovens and / or air heating means.

[0026] In a preferred embodiment, the pelletizing step (c) is directly followed by a drying step (c1) of the formed at least one respective granulate, said drying step comprising applying a temperature higher than 60 °C, the drying step preceding the re-extruding step (d).

[0027] In a preferred embodiment, the mixing step (a) is preceded by a preliminary step (aO) of selecting at least one material of the thermoplastic polymer matrix to be among polyethylene terephthalate, polyamide 6, polypropylene, low-density polyethylene, or high-density polyethylene.

[0028] Herein, low-density polyethylene, called LDPE, and high-density polyethylene, called HDPE, are types of polyethylene distinguished by their density and structure, which in turn affect their physical properties. This enables versatility in material choice, optimizing the filament for different applications and environments. Additionally, this selection provides a particular advantage for the production process, improving speed and reducing energy consumption, for instance if polyethylene is combined with polyamide 6 under conditions requiring special compatibilizers and compatible plasticizers.

[0029] In a preferred embodiment, the extruding step (b) comprises, when the mixing step (a) is preceded by the preliminary selecting step (aO), the step (aO) of selecting comprising selecting the at least one material of the thermoplastic polymer matrix to be polypropylene, low-density polyethylene, or high-density polyethylene, a step (a1) of cooling the extruded mixture in a water bath at a temperature controlled to be higher than 10 °C and lower than 25°C, and wherein the cooling step (a1) is carried out before the drying step (c).

[0030] According to a possible embodiment, the temperature of the water bath cooling is controlled to be equal to 20°C.

[0031] This enables rapid solidification of the extruded mixture, effectively preventing the agglomeration of the carbon-based nanofillers. This control mechanism is optionally adjusted depending on the specific polymer used, to inhibit additional crystallization and ensure the proper solidification of the filament, thereby maintaining its structural integrity and desired properties.

[0032] In a preferred embodiment, the mixing step (a) or the step (d) further comprises adding elastomeric structures, called modifiers, and other structures, called plasticizers, to the compound, wherein the concentration of said modifiers and / or plasticizers is strictly larger than 0% by weight and smaller than 10% by weight.

[0033] This enables the stabilization and modification of dispersion agents, achieving the required drawing properties and enhancing elongation during the drawing process, thereby improving the overall mechanical properties and processability of the filament.

[0034] According to various possible embodiments: the plasticizers can be directly added to the thermoplastic polymer matrix and carbonbased nanofillers in a controlled amount during the initial mixing step (a) and / or added to ensure uniform distribution throughout the compound, the plasticizers can be injected directly into the twin-screw extruder through a specialized injection port, allowing for precise control over the amount being incorporated into the compound, the plasticizers can be mixed with polymer granules before adding them, ensuring even distribution within the thermoplastic polymer matrix, the plasticizers can be dissolved or dispersed in a solvent, then sprayed onto the polymer and carbon-based nanofiller, with the solvent being subsequently evaporated to leave the plasticizers uniformly distributed, and / or the plasticizers can be added to a mixing vessel containing polymer and the carbon-based nanofillers, homogenized, and then provided to an extruder.

[0035] In a preferred embodiment, the method further comprises, after the guiding step (e), a step (f1) of electrically controlling that the linear electrical resistance of the formed heating conductive filament is larger than 3 kOhm / lin.m and is smaller than 10000 kOhm / lin.m.

[0036] Herein, the unit "kOhm / lin.m" stands for "kilo(o)hms per (linear) meter", defining a standard physical unit for measuring the electrical resistance, where kOhm equals 1000 ohms.

[0037] Herein, “Linear meter”, or “lin.m”, refers to a unit length measured in meters along a line.

[0038] When combined, "kOhm / lin.m" is used to measure the electrical resistance per unit of length of a given material.

[0039] In a preferred embodiment, the method further comprises, after the guiding step (e), a step (f2) of measuring that the linear density of the formed heating conductive filament is larger than 30 tex and is smaller than 55 tex.

[0040] This enables obtaining a filament with the desired mechanical properties.

[0041] Herein, the unit "tex" provides a standardized way of measuring the linear density, expressing the thickness or weight of the filaments, or of fibers and yarns. For example, if the formed filament has a linear density of 50 tex, it means that 50 centimeters of that filament weighs 0.025 grams.

[0042] Herein, the linear density of a filament can be measured on a winder directly, knowing the speed of winding and the dimensions of the winder. The filament can also be weighed using different techniques.

[0043] To address this or these drawbacks, it is proposed according to another aspect of the present disclosure an electrically conductive heating filament comprising a thermoplastic polymer matrix with carbon-based nanofillers, the carbon-based nanofillers being uniformly mixed with the thermoplastic polymer matrix, the carbon-based nanofillers including single-walled carbon nanotubes and carbon black, and wherein:

[0044] - the concentration of the single-walled carbon nanotubes is larger than 0.3% by weight and is smaller than 5% by weight, and / or

[0045] - the concentration of the carbon black is larger than 3% by weight and is smaller than 25% by weight. This enables optimal conductivity without significantly compromising the mechanical properties. Unlike filaments which rely on phase transition materials that alter conductivity during heating due to power voltage changes, this aspect ensures greater performance and predictability in heating parameters.

[0046] Advantageously, the amount of carbon-based nanofillers, with or without modifiers and / or plasticizers, provides an improved resistivity of the end material, while the drawing speed defines an improved resistance, resulting in stable and reliable properties, without the need of using phase change materials.

[0047] According to a possible embodiment, the single-walled carbon nanotubes are in raw form or in the form of pellets.

[0048] In a preferred embodiment, the concentration of the thermoplastic polymer matrix is larger than 60% by weight and is smaller than 96.7% by weight.

[0049] In a preferred embodiment, at least one material of the thermoplastic polymer matrix is selected among polyethylene terephthalate, polyamide 6, polypropylene, low-density polyethylene, or high-density polyethylene.

[0050] For instance, polyethylene terephthalate (PET) enables improved thermal stability and mechanical strength of the filament. Specifically, PET significantly enhances the thermal and mechanical properties of the resulting filament, ensuring it maintains its integrity and performance under high-temperature conditions and mechanical stress.

[0051] In a preferred embodiment, the electrically conductive heating filament further comprises elastomeric structures, called modifiers, and / or other structures, called plasticizers, and wherein the concentration of said modifiers and / or plasticizers is strictly larger than 0% by weight and smaller than 10% by weight.

[0052] In a preferred embodiment, at least one of the modifiers is made of styrene-butadiene rubber, SBR.

[0053] Herein, styrene-butadiene rubbers are defined as a family of synthetic rubbers derived from the copolymerization of styrene and butadiene. These rubbers function as elastomeric agents, improving the drawing process of the filament.

[0054] This enables better flexibility, elasticity, and stretchability during manufacturing, enhancing the overall mechanical properties and processability of the filament.

[0055] In a preferred embodiment, the diameter of the electrically conductive heating filament is larger than 0.15 millimeter and is smaller than 0.25 millimeters.

[0056] This enables adaptability to various heating applications requiring different filament diameters.

[0057] In a preferred embodiment, the linear density of the electrically conductive heating filament is larger than 30 tex and smaller than 55 tex.

[0058] In a preferred embodiment, wherein the linear electrical resistance of the formed heating conductive filament is larger than 3 kOhm / lin.m and smaller than 10000 kOhm / lin.m.

[0059] This allows to overcome the aforementioned drawbacks, providing eco-friendly heating solutions and expanding the applicability of such materials in various advanced technologies, including EV batteries, smart home systems, and wearable technology.

[0060] Improved conductivity is achieved by the incorporation of conductive carbon-based nanoparticles, while the resulting resistance, in particular the resulting linear resistance, and resistivity, are controlled by the quantity of carbon-based nano-fillers, by the extrusion parameters, and by the drawing processes parameters. This, in turn, provides an electrically conductive heating composite filament, comprising conductive carbon-based nanoparticles, for use in energy-efficient heating elements, in textiles such as mesh or fabrics, electromagnetic shielding constructions and anti-static applications.

[0061] Brief description of the drawings

[0062] Other features, embodiments, definitions and advantages will become apparent upon reading the detailed description below and analyzing the attached drawings, including the following figures.

[0063] Figure 1 represents the compounding stage, or step, of a method for manufacturing a heating conductive filament according to one embodiment.

[0064] Figure 2 represents the drawing stage, or step, for manufacturing a heating conductive filament according to one embodiment.

[0065] Unless otherwise indicated, common or analogous elements in the figures are denoted by the same reference numerals and exhibit identical or analogous features, so that common or analogous elements are generally not described again for the sake of clarity and conciseness. Description of the embodiments

[0066] According to various embodiments, a method for producing heating and self-heating conductive filaments comprises several steps, that can be classified in two main stages. The first main stage, called “compounding” stage, aims at combining and mixing components, including fillers and polymers of different nature, thermal properties and behavior, such as thermoplastics, and using different devices, in view of obtaining a compound. During the second stage, called “drawing” stage, the compound is subsequently extruded, processed, and drawn using different types of rollers and winders, involving the application of different temperatures and pressures, in view of obtaining a conductive heating filament and, in particular, a heating conductive monofilament.

[0067] Figure 1 illustrates a system configured to carry out the compounding steps, or first stage, of a method for manufacturing a heating conductive filament according to one embodiment.

[0068] For carrying out this first stage of compounding, a compounding system 100 is illustrated. The system 100 is designed to facilitate the mixing, melting, and extrusion of polymer materials, such as polylactic acid mixed with plasticizers, in a controlled manner.

[0069] The process begins with providing polymer parts 101 and plasticizer parts 103 to a feeder 112, the feeder 112 being responsible for introducing the raw materials into the system 100.

[0070] For instance, polylactic acid containing 10% by weight (10% wt.) of a nonionic surfactant plasticizer is fed into the extruder. The feeder 112 directs the polymer and plasticizer mixture into a twin-screw extruder 114, where the plasticizer molecules act as lubricants for the polymer chains, reducing their internal resistance to sliding and enhancing the processability of the material.

[0071] According to an embodiment, the compounding system 100 and, for instance, the feeder 112, comprises one or more powder gravimetric metering devices.

[0072] According to an embodiment, the compounding system 100 comprises a twin-screw extruder 114, which itself comprises two screws with interchangeable segments.

[0073] This enables providing the maximum possible mixing of the components along the entire length of the melt movement, die for one or multiple streams, depending on the capacity and torque of the twin-screw extruder 114, which is adjustable.

[0074] As part of the compounding system 100, a drive module 110 can power the twin-screw extruder 114, enabling a mechanical and preferably controllable mixing of the fed polymer 101 and of the fed plasticizer 103 in a melted state.

[0075] This enables carbon-based nanofillers, namely single-layer nanotubes and carbon black in powder form, to be provided by the powder gravimetric metering units to the twin-screw extruder 114. Further, in the twin-screw extruder 114, active mixing and uniform distribution of the components in the thermoplastic polymer matrix takes place. This is achieved preferably thanks to a properly selected combination of screw segments, extrusion temperatures, and pressures.

[0076] According to an embodiment, the twin-screw extruder 114 operates with a screw speed larger than 100 rounds per minute and smaller than 200 rounds per minute and a torque range of a few Newton meters.

[0077] According to an embodiment, the twin-screw extruder 114 is further equipped with heating zones 118, which are configured to maintain a precise temperature control. For instance, ten or eleven heating zones can provide temperature control up to 220°C. This temperature control ensures consistent melting and mixing of the polymer and plasticizer.

[0078] According to an embodiment, and after the polymer mixture is mixed and melted, it passes through a forming die 116, also called forming die, and preferably comprising a single orifice which shapes the melted polymer into a continuous filament 105.

[0079] According to an embodiment, the extruded filament 105 is immediately quenched in a water bath 120.

[0080] This enables a rapid cooling, which in turn solidifies the filament 105 into a solidified filament 106, maintaining its shape and enhancing its mechanical properties. The water bath 120 is preferably adapted to provide cold water circulation for active cooling.

[0081] According to an embodiment, after the quenching, the solidified filament 106 is cut into pellets 107 by a pelletizer 107.

[0082] According to an embodiment, the pellets 107 are subsequently air-dried at an ambient temperature of approximately 23 °C. Another step of drying, which can range from 24 to 60 hours, is subsequently applied at a temperature of approximately 35 °C, preferably under reduced pressure to remove any residual moisture. Said reduced pressure can be larger than 15 hectopascals and smaller than 30 hectopascals, for instance 20 hectopascals.

[0083] The pellets 107, also called granulates, as obtained from the compounding system 100, can subsequently be subjected to various thermal and mechanical characterizations, for instance scanning calorimetry, thermal gravimetric analysis or melt flow rate techniques. Such tests provide measurements defining the chemical structure of the result and give in particular information about the influence of the plasticizer parts 103 over the intermolecular interactions in the polymer, affecting its functional properties.

[0084] The compounding stage enables pre-mixing, distributing, and pre-orientating the nanotubes with carbon black, using a twin-screw extruder which applies a certain pressure during the mixing of the components and subsequent extrusion. The subsequent drawing stage is carried out separately, based on these granulates.

[0085] After the compounding stage and before the drawing stage, the granulates are preferably dried during an intermediary drying substage. According to an embodiment, the granulates obtained after compounding stage are dried up using one or more ovens heated up to 60 degrees Celsius.

[0086] According to an embodiment, depending on the components of the thermoplastic polymer matrix, the heating temperature for drying up the granulates can be higher than 60 degrees Celsius.

[0087] This enables properly removing some, if not all, of the moisture present in the granulates before carrying out the second stage of drawing.

[0088] According to an embodiment, the granulates can be dried from 1 hour up to 48 hours.

[0089] This ensures the proper quality of the subsequent filaments, improving the resulted mechanical features.

[0090] The subsequent drawing stage can also be is carried out separately, based on these dried up granulates.

[0091] Figure 2 illustrates a system configured to carry out the drawing steps, or second stage, of a method for manufacturing a heating conductive filament according to one embodiment.

[0092] Following the first stage of compounding, this second stage, called “drawing” stage, aims at uniformly drawing the compounds as obtained, to obtain as a end product a heating conductive filament with a given diameter and corresponding linear density.

[0093] For carrying out the second stage, a drawing system 2000 is illustrated in conjunction with an extrusion system 200, the pellets 107 being provided to said extrusion system 200 after the first stage of compounding. The extrusion system 200 serves as an entry point of the drawing system 2000.

[0094] In an embodiment, the extrusion system 200 comprises a feeder 212, configured to receive pellets, in particular the pellets 107 obtained during the compounding stage. The extrusion system 200 further comprises a single-screw extruder 214 configured to re-extrude a filament 10a from the provided pellets 107.

[0095] In an embodiment, the single-screw extruder 214 includes a venting zone to remove volatile components.

[0096] Optionally, the extrusion system 200 comprises a metering pump 216 enabling precise control over the extrusion process. The extrusion system 200 can also comprise a cooling water bath 220 which has, when present, a temperature actively maintained around 20-25 degrees Celsius.

[0097] This enables the compound to undergo a re-extrusion stage with a single-screw extruder without further introduction of components.

[0098] The re-extruded filament 10a is then passed to the drawing system 2000 using one or more guiding means, such as rollers. It is subsequently guided through the drawing system 2000, which comprises different devices selected among guiding cold rollers, one or more closed heating chambers, take-up hot rollers, and winders.

[0099] According to an embodiment, the extruded material 10a is firstly provided to a slow haul-off device 2200, which comprises a plurality of cold rollers. Said cold rollers are configured to maintain a desired tension and shape for the extruded filament 10a.

[0100] For instance, the slow haul-off device 220 comprises three, four, five, six or seven rollers rotating at a same speed. The necessary pressing force can be adjusted by the pressure roller, which is located above the first guide roller of the slow haul-off device 220 and presses the filament with the necessary force to avoid damaging the thread and avoid slippage.

[0101] Following the slow haul-off device 2200, the filament 10a is guided to one or more ovens 2400. Preferably, this or these ovens operate at temperatures lower than 200°C, ideally between 80°C and 160°C, the selected temperatures depending on the components of the thermoplastic polymer matrix.

[0102] This enables heating up the filament to the required temperature to soften it for proper drawing. Advantageously, this also enables removing residual moisture from the material of 10a, improving its stability and quality for subsequent processing, and outputting a modified filament 10b. The filament 10b is then passed to subsequent heating and / or haul-off devices, to draw the filament 10b under controlled temperatures and pressures.

[0103] For instance, the pre-drawn filament 10b can be fed into a closed-type heating chamber. Said heating can be provided by air heating, obtained with thermoelectric heaters, and enabling temperatures from 50 to 5 degrees below the melting point of the polymer thermoplastic polymer matrix.

[0104] In a particular embodiment, after being outputted by the one or more ovens 2400, the filament 10b is guided towards the first among a plurality of receiving rollers 2600. Specifically, a fast haul- off device 2600 comprises a plurality of heated roller, for instance six heated rollers. This enables adjusting the pressing force applied to the filament 10b, by one or more pressure rollers of the fast haul-off device 2600. As illustrated, pressure rollers can be located above the first, the fourth and the sixth guide rollers of the device 2600, which thereby ensures a fast haul-off, maintaining the shape and alignment of the filament.

[0105] According to an embodiment, the fast haul-off device 2600 comprises three pairs of independently speed- and temperature-controlled rollers. This enables bringing the filament as precisely as possible to the specified diameter. This further enables a “2” degree of draw, a “3” degree of draw and a “4” degree of draw to be controlled by adjusting the speed of each independent pair of rollers and exposing the rollers to temperatures ranging from 80 degrees to 5 degrees less than the melting point of the thermoplastic polymer matrix.

[0106] According to an embodiment, the first roller of the fast haul-off device 2600 is provided with a pressure roller to ensure that the yarn has the required pressing force and cannot slip on the roller surface.

[0107] After being drawn by the fast haul-off device 2600, the filament 10b is then drawn by another fast haul-off device 2800, which comprises a plurality of cold rollers, for instance three heated rollers.

[0108] According to an embodiment, the rollers of this other fast haul-off device 2600 define corresponding winders, which are configured to process the heating conductive filament at the end of the guiding step, leading to the wound filament 10.

[0109] Advantageously, the set 2600 of rollers and the set 2800 of winders together ensure that the filament achieves an optimal diameter and surface finish.

[0110] Still advantageously, after passing the filament through a group of hot rollers, passing through the filament through a group of cold rollers rotating at the same speed allows for precise control over the final properties of the filament, ensuring high-quality conductive filaments suitable for various applications such as heating elements.

[0111] Advantageously, the inventors have discovered as a surprising technical effect, that the alignment and anisotropic properties of the filament, induced by the aforementioned features, have a significant impact on the resulting conductivity.

[0112] In particular, the orientation of the carbon-based nanofillers along the axis of the filament enhances longitudinal conductivity while reducing transversal conduction, thereby improving the filament’s directional heating performance. This anisotropy obtained through the drawing process contributes to stable, tunable, and energy-efficient heating features, meeting the current needs of precision applications.

[0113] The filament obtained by drawing in a hot chamber after active cooling and after extrusion results in a significant reduction in its electrical conductivity, provided that the strain rate exceeds 5000%.

[0114] Surprisingly, the inventors have shown that even when the strain rate exceeds 5000%, it is possible to obtain stable electrically conductive properties.

[0115] As described above, a given selection of predetermined drawing parameters, such as the drawing rate or the applied temperatures and pressures, enables obtaining specific mechanical and electrical features of the filament formed at the end of the second stage, together with stable heating properties.

[0116] The electrically conductive filaments obtained by means of the present process have a high strength and an excellent electrical conductivity and, therefore, are suitable for industrial or practical use. The polymer heating filaments can then be used to weave a mesh or woven into fabric.

[0117] Depending on the value of the supply voltage, filaments of different linear resistance can then be heated with different intensities, to attain temperatures up to 80°C. By varying the length of the thread in the mesh or fabric, its resistance and frequency of arrangement, it is possible to achieve uniform heating over an entire surface of a product heated with the manufactured heating conductive filaments. Although the present disclosure and the embodiments described therein have been shown and described with reference to specific preferred embodiments, this is not to be construed as limiting the invention itself. Various changes may be made in form and details without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS1. A method for manufacturing a heating conductive filament (10), comprising the steps of:(a) mixing uniformly carbon-based nanofillers (101) with a thermoplastic polymer matrix (103) to form a respective polymer mixture,(b) extruding the respective polymer mixture to form a continuously mixed filament (105 ;106),(c) pelletizing the formed continuously mixed filament (105 ; 106) to form at least one respective granulate (107),(d) re-extruding the at least one respective granulate (107) to form a respective extruded filament (10a, 10b), and(e) guiding the respective re-extruded filament (10a, 10b) through a drawing system (2000) comprising a plurality of rollers and winders (2200, 2400, 2600, 2800), said drawing system (2000) having a drawing rate larger than 3 and smaller than 9, to output the heating conductive filament (10) in a wound form, wherein the carbon-based nanofillers are selected to comprise carbon black and singlewalled carbon nanotubes, the carbon black having a concentration range of 3% to 25% by weight and / or the single-walled carbon nanotubes having a concentration range of 0.3% to 5% by weight, and characterized in that the pelletizing step (c) is directly followed by a drying step (c1) of the formed at least one respective granulate (107), said drying step comprising applying a temperature higher than 60 °C, the drying step preceding the re-extruding step (d).

2. The method according to claim 1 , wherein the mixing step (a) is preceded by a preliminary step (aO) of selecting at least one material of the thermoplastic polymer matrix to be among polyethylene terephthalate, polyamide 6, polypropylene, low-density polyethylene, or high-density polyethylene.

3. The method according to claim 2, wherein the extruding step (b) comprises, when the mixing step (a) is preceded by the preliminary selecting step (aO), the step (aO) of selecting comprising selecting the at least one material of the thermoplastic polymer matrix to be polypropylene, low-density polyethylene, or high-density polyethylene, a step (a1) of cooling the extruded mixture in a water bath at a temperature controlled to be higher than10 °C and lower than 25°C, and wherein the cooling step (a1) is carried out before the drying step (c).

4. The method according to any of the preceding claims, wherein the mixing step (a) or the step (d) further comprises adding elastomeric structures, called modifiers, and other structures, called plasticizers, to the compound, wherein the concentration of said modifiers and / or plasticizers is strictly larger than 0% by weight and smaller than 10% by weight.

5. The method according to any of the preceding claims, further comprising, after the guiding step (e), a step (f1) of electrically controlling that the linear electrical resistance of the formed heating conductive filament is larger than 3 kOhm / lin.m and is smaller than 10000 kOhm / lin.m.

6. The method according to any of the preceding claims further comprising, after the guiding step (e), a step (f2) of measuring that the linear density of the formed heating conductive filament is larger than 30 tex and is smaller than 55 tex.

7. An electrically conductive heating filament comprising a thermoplastic polymer matrix with carbon-based nanofillers, the carbon-based nanofillers being uniformly mixed with the thermoplastic polymer matrix, the carbon-based nanofillers including single-walled carbon nanotubes and carbon black, and wherein:- the concentration of the single-walled carbon nanotubes is larger than 0.3% by weight and is smaller than 5% by weight, and / or- the concentration of the carbon black is larger than 3% by weight and is smaller than 25% by weight.

8. The electrically conductive heating filament according to claim 7, wherein the concentration of the thermoplastic polymer matrix is larger than 60% by weight and is smaller than 96.7% by weight.

9. The electrically conductive heating filament according to claim 7 or 8, wherein at least one material of the thermoplastic polymer matrix is selected among polyethylene terephthalate, polyamide 6, polypropylene, low-density polyethylene, or high-density polyethylene.

10. The electrically conductive heating filament according to claim 9, further comprisingelastomeric structures, called modifiers, and / or other structures, called plasticizers, and wherein the concentration of said modifiers and / or plasticizers is strictly larger than 0% by weight and smaller than 10% by weight.

11. The electrically conductive heating filament according to any of claims 7-10, wherein at least one of the modifiers is made of styrene-butadiene rubber, SBR.

12. The electrically conductive heating filament according to any of claims 8-12, wherein the diameter of the electrically conductive heating filament is larger than 0.15 millimeter and is smaller than 0.25 millimeters.

13. The electrically conductive heating filament according to any of claims 7-12, wherein the linear density of the electrically conductive heating filament is larger than 30 tex and smaller than 55 tex.

14. The electrically conductive heating filament according to any of claims 7-13, wherein the linear electrical resistance of the formed heating conductive filament is larger than 3 kOhm / lin.m and smaller than 10000 kOhm / lin.m.

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