METHOD FOR JOINING THERMOPLASTIC OR COMPOSITE MATERIALS USING A CONDUCTIVE OPENWORK SUPPORT

Abstract

The present invention belongs to the field of manufacturing parts or objects from thermoplastic materials or composite materials, in particular the field of welding, heating or mechanical reinforcement of thermoplastic materials or composite materials. The invention relates to an assembly usable in fields such as aeronautics, aerospace, ballistic protection, automotive, oil and para-oil, food or energy. The invention relates to a method of assembling at least two parts made of thermoplastic materials comprising a step of bringing said parts into contact with at least one added support coated with graphene or based on graphene. Abstract figure: 1

Description

Title of the invention: METHOD FOR ASSEMBLING THERMOPLASTIC MATERIALS OR COMPOSITE MATERIALS USING A CONDUCTIVE OPENWORK SUPPORT Technical field of the invention

[0001] The present invention belongs to the field of manufacturing parts or objects from thermoplastic materials or composite materials, in particular the field of welding, heating or mechanical reinforcement of thermoplastic materials or composite materials. The invention relates to an assembly usable in fields such as aeronautics, aerospace, ballistic protection, automobiles, oil and para-oil, food and energy.

[0002] The invention relates to a method for assembling at least two parts made of thermoplastic materials or composite materials, comprising a step of bringing said parts into contact with at least one perforated support coated with graphene or based on graphene. Prior art

[0003] The assembly of thermoplastic or composite parts generally relies on methods such as riveting or induction welding. Riveting, characterized by the use of multiple metal rivets, resulted in labor difficulties and an increase in the mass of the final structure. On the other hand, induction welding, although commonly used, had disadvantages such as excessive and non-uniform localized heating, which could alter the strength of the bonding zone, thus inducing docking defects, especially in the case of conductive carbon fiber reinforced composites which heat by induction.

[0004] Thus, there is a need to improve the manufacture of composites of this type, in particular in order to improve the heating device and ensure uniform heating of the assembly surface, obtaining robust mechanical properties, thus eliminating the disadvantages of traditional methods. Statement of the invention

[0005] The present invention makes it possible to obtain a composite which surprisingly solves the drawbacks mentioned above. The composite obtained according to the method according to the invention allows uniform heating during the assembly of thermoplastic parts. The perforated support, integrated in the future welded area, improves the specific surface area at the composite weld and mechanically strengthens its final structure. This versatile approach is applicable to a variety of thermoplastics, providing exceptional flexibility. The method is compatible with many thermoplastic materials, reducing docking defects and providing a strong and uniform bond between parts. With wide applications in several sectors, the present invention provides a novel solution for welding and mechanical strengthening of thermoplastic materials. In addition, the possibility of disassembly (by reheating the perforated support within the composite) facilitates recycling, while the electrical connections allow precise control and monitoring of the process.

[0006] The method according to the invention thus makes it possible to provide an integrated solution, combining homogeneous heating, mechanical reinforcement, material versatility, precise control of the temperature input, and ease of recycling, thus surpassing existing solutions in the field of thermoplastic welding. The openwork support also provides mechanical reinforcement to the assembly.

[0007] The method according to the invention is distinguished by its versatility, suitable for the heat input that can lead to the welding of various thermoplastics over a wide range of melting temperatures, in various technical and artistic fields. The use of materials reinforced with electrically conductive elements, while insulating the electrically conductive openwork support, provides safety against short circuits. The mesh structure of the openwork support offers a double advantage by providing a structured support for the graphene while mechanically reinforcing the thermoplastic materials, resulting in a significant improvement in the mechanical properties of the final composite. The final composite can also be used as a heating element.

[0008] A first subject of the present invention is a method for manufacturing a composite comprising the assembly of at least two pieces of thermoplastic materials or composite materials via a step of bringing into contact at least one perforated support coated with a layer of graphene or based on graphene. The method for assembling a composite according to the invention, comprising pieces of thermoplastic material or composite material, comprises the steps of: a) bringing into contact and holding a first part and a second part with at least one perforated support comprising a graphene or graphene-based coating, said support being inserted between the two parts; b) heating the two parts, the heating being carried out by means of an electric current passing through the at least one perforated support, c) cooling and assembly, and obtaining the composite.

[0009] Advantageously, the contacting of step a) may further comprise the contacting of at least one thermoplastic film whose melting temperature is lower than that of the first and second parts, preferably a polyurethane film, said film being interposed between the two parts. According to the invention, the implementation of the method using at least one thermoplastic film is particularly advantageous when the first and second parts are made of a thermoplastic material having a high melting temperature, or a composite material having a high melting temperature or which does not have a melting point achievable without destruction, such as for example when the parts 1 and 2 are made of PEEK, or of carbon / PEEK composite, or even of aramid.

[0010] Advantageously, the thermoplastic film can either be arranged between two perforated supports, themselves inserted between the two parts, or the perforated support is arranged between two thermoplastic films. In a variant according to the invention, the perforated support can be inserted between two thermoplastic films, the assembly thus formed by the perforated support and the two thermoplastic films thus being inserted between the two parts, in accordance with step a). In another variant according to the invention, a thermoplastic film can be inserted between two perforated supports, the assembly formed by the perforated supports and the thermoplastic film thus being inserted between the two parts, in accordance with step a).In a third variant according to the invention, a thermoplastic film can be inserted between an openwork support and one of the first and second parts, the assembly formed by the openwork support and the thermoplastic film thus being inserted between the two parts, in accordance with step a). Other arrangements are possible depending on the number of thermoplastic films and openwork supports desired in the final composite.

[0011] Advantageously, the thermoplastic film may have a thickness ranging from 50 μm to 10 mm, preferably 60 μm to 1 mm. The melting temperature of the thermoplastic film is always lower than or equal to that of the first and second thermoplastic parts.

[0012] Advantageously, the duration of step b) of the method according to the invention may be within an interval ranging from 10 seconds to 1 hour. Preferably, the duration is a few minutes, i.e. within an interval ranging from 1 minute to 10 minutes. The duration of step b) will depend on the perforated support as well as the nature of the thermoplastic parts or films. Those skilled in the art will know how to adapt the duration of step b) according to the composite to be produced.

[0013] Advantageously, the duration of step c) of the method according to the invention may be within an interval ranging from 10 minutes to 2 hours, preferably 30 minutes. The duration of step c) will depend on the cooling system used. Those skilled in the art will know how to adapt the duration of step c) depending on the composite to be produced.

[0014] Advantageously, the heating temperature of step b) of the method according to the invention is equal to a value of 10 to 20 degrees above the melting temperature of the first and second parts or of the at least one thermoplastic film. Positioning the temperature just above the melting temperature of the first and second parts or of the at least one thermoplastic film makes it possible to obtain localized melting around the points of contact with the perforated support, without risk of deterioration of said parts.

[0015] Advantageously, the holding can be achieved by applying pressure on either side of the first and second parts (on the faces opposite the faces in contact with the at least one perforated support). Preferably, the pressure exerted is in a range from 0.5 to 100 bar, preferably from 1.1 bar to 2 bar. The holding is implemented in step a), and is maintained during steps b) and c). The holding ensures optimal contact during steps b) of heating and c) of cooling, ensuring a defect-free weld. According to the invention, after the power supply has been cut off, during step c), the cooling and the maintenance of the pressure seal the weld, the perforated support remains in the composite, thus increasing the specific surface area for optimal cohesion of the assembly according to the invention.

[0016] Advantageously, when implementing the method according to the invention, the perforated support is connected to a power supply. The power supply connected to the perforated support makes it possible to generate localized heat at the interface between the first and second parts, causing the thermoplastic material of the two parts or the thermoplastic film to melt. The power supply is connected to the perforated support by means of electrodes. The electrodes can be any type of compatible electrode, for example copper electrodes. The power supply and the electrodes can be any material known and usable under the conditions of the present invention. Those skilled in the art will know how to adapt the power supply and the electrodes.

[0017] Advantageously, the power supply can generate an electric current having a power in a range from 40 W to 10 kW, preferably in a range from 250 W to 1000 W.

[0018] Advantageously, the electrodes can be retained after implementation of the method according to the invention so as to facilitate the possible disassembly of the composite according to the invention, and thus contributing to more efficient recycling practices. Depending on the application, the electrical connection areas of the perforated support can also be retained for future use (composite used as a heating element). These connections can also be used to monitor and control the welded area (detection of defects or cracks). In addition, the possibility of cutting the connection areas offers additional aesthetic or safety flexibility to the composite according to the invention. The electrodes can alternatively be removed (for example disconnected or cut), during a step subsequent to the assembly of the composite.

[0019] Advantageously, the first and second parts can be of various shapes. They can be flat or complex. The areas involved in the assembly according to the method according to the invention are adapted, so that the contact surface is optimal. The method according to the invention thus applies to thermoplastic parts or composite materials having flat or curved contact shapes at the area to be heated and fixed. The flexibility of the material can allow optimal contact at the area to be fixed. The first and second parts can be plates, films, lamellae, thin sheets, parts with complex geometry, cylinders. By part with complex geometry, we mean for example curved, angular, serpentine, or arched parts.

[0020] Advantageously, the thermoplastic material of the first and second parts can be chosen from acetal (POM), acrylonitrile butadiene styrene (ABS) and other specialized styrenics, polyimides (PI) such as aramids, aromatic polyamides, cellulose CA (cellulose acetate), CAB (cellulose acetate butyrate), CAP (cellulose acetate propionate) and CN (cellulose nitrate), ethylene vinyl acetate (EVA), expanded polystyrene (EPS), expanded polypropylene (EPP), fluoroplastics PTFE (polytetrafluoroethylene) and FEP (fluorinated ethylene propylene), nylons (polyamides) PA, the family of polyaryletherketones such as PEEK (polyaryletheretherketone), polyetherketone (PEK), polyetheretherketoneketone (PEEKK) and polyetherketoneetherketoneketone (PEKEKK), polybutene-1 (PB-1), polycarbonate (PC), polyacetals, POM (polyoxymethylene), thermoplastic polyesters such as PETP (poly(ethylene terephthalate),PBT (polybutylene terephthalate) and PET (polyethylene terephthalate), high-density polyethylene (HDPE), low-density polyethylene (LDPE), LLDPE (linear low-density polyethylene), polypropylene (PP), polyphenylene oxide (PPO), polyphenylene sulfide PPS, polyphenylene sulfone (PPSU), polymethylpentene PMP, polystyrene (general purpose) GPPS and polystyrene (high impact) HIPS, poly(vinyl alcohol) (PVOH: polyvinyl alcohol homopolymer), PVA or PVAL: poly(vinyl alcohol), polyvinyl chloride (PVC), styrene acrylonitrile (SAN) and acrylonitrile styrene acrylate (ASA), thermoplastic elastomers TPE (thermoplastic rubber) and TPR (thermopropylene rubber) and a mixture thereof. ,

[0021] Advantageously, the composite material of the first and second parts can be chosen from carbon / epoxy, carbon / polyurethane, carbon / thermoplastic, thermoplastic / thermoplastic, thermoplastic / epoxy, thermoplastic / polyurethane, plant fiber / epoxy, plant fiber / polyurethane, plant fiber / thermoplastic, ceramic / epoxy, ceramic / polyurethane, ceramic / thermoplastic and a mixture of these.

[0022] Advantageously, the thermoplastic film may be chosen from acrylonitrile butadiene styrene films (Melting temperature: 130°C), polyacetal copolymer (Melting temperature: 165°C), polyurethane (Melting temperature: 80°C), polyamide 6,6 (Melting temperature: 255°C), polyamide 6 (PA6) - (Melting temperature: 220°C), polyamide 11 (Melting temperature: 185°C), polycarbonate (Melting temperature: 230°C), transparent thermoplastic polyester (Melting temperature: 255°C), polyetheretherketone (Melting temperature: 343 to 387°C), low density polyethylene (Melting temperature: 100°C), high density polyethylene 300 (Melting temperature: 130°C). °C), very high density polyethylene 500 (Melting temperature: 135 °C), very high density polyethylene 1000 (Melting temperature: 138 °C), polymethyl methacrylate (Melting temperature: 180 °C), polypropylene (Melting temperature: 163 °C),polystyrene (Melting temperature: (160 °C), polytetrafluoroethylene (Melting temperature: 325 °C), chlorinated polyvinyl chloride (Melting temperature: 190 °C), polyvinyl chloride (Melting temperature: 125 °C), polyvinylidene fluoride (Melting temperature: 173 °C), fluorinated ethylene propylene (Melting temperature: 260 °C), cellulose nitrate (Melting temperature: 160 °C), polyvinyl alcohol (Melting temperature: 200 °C), ethylene vinyl acetate (Melting temperature: 93 °C) and a mixture thereof.

[0023] Advantageously, the first and second parts, and possibly the at least one thermoplastic film, may be made of identical or different materials. When the melting temperatures are different, the part or film melting first will act as a glue during assembly. Thus, a higher temperature equal to or at 20°C can be maintained, taking into account the lowest melting temperature of the two parts or of the film.

[0024] Advantageously, the openwork support may comprise at least one element chosen from a perforated plate, a net, a grid, a mesh, a woven textile, regular or irregular. The openwork support may be in the form of a perforated plate, a net, a grid, a mesh, a woven textile or a related structure. The openwork support may be regular or irregular. When the openwork support is not made of graphene, it comprises a graphene coating. The three-dimensional arrangement of the graphene on the structure of the perforated plate, net, grid, mesh, woven textile or related structure gives this structure exceptional properties such as high electrical conductivity, thermal conductivity, flexibility and mechanical strength. The openwork support is configured so as to have sufficient permeability allowing good impregnation of the parts made of thermoplastic material. The control and management of the electrical and therefore thermal current is very precise on the area of ​​the parts to be assembled. The person skilled in the art will know how to adapt the shape of the perforated support according to the shape and nature of the first and second thermoplastic parts.

[0025] Advantageously, the perforated plate, the net, the grid, the netting or the woven textile may be made of graphene, fiberglass, quartz fiber, thermoplastic polyester, polyethylene terephthalate, glycolized polyethylene terephthalate, polyetheretherketone, aramids, polyamide, polytetrafluoroethylene, ceramic, plant fibers such as hemp, flax or cellulose and a mixture thereof.

[0026] Advantageously, the graphene coating can be obtained via all the techniques known to those skilled in the art (spraying, dipping, dip-coating, impregnation, pad printing, doctor blade, slot die, Layer by Layer (LBL or layer by layer deposition), screen printing, capillary deposition, inkjet or electrostatic deposition) with pure / functionalized graphene (solid or liquid), or from a graphene-based ink. The graphene coating can be deposited on the support via the methods described in patent applications FR3087432 or WO2020109380. The mesh, adjustable between 1 and 100 millimeters2, can be oriented in a specific manner to guarantee optimal heat distribution according to the geometric constraints of the desired weld.

[0027] Advantageously, the graphene coating may have a thickness ranging from 100 nm to 100 μm. The perforated support is coated with a graphene coating, when said support is not made of graphene.

[0028] Advantageously, the openwork support is made of material resistant to a temperature higher than the melting temperature of the first and second parts. Preferably, the melting temperature of the openwork support is at least 20°C higher than that of the thermoplastic parts or of the at least one thermoplastic film. This guarantees that the openwork support will not be damaged during the implementation of the method according to the invention.

[0029] Advantageously, the heating is resistive or by induction. The graphene mesh or the graphene coating acts as a resistive heating element. When electrically powered, the graphene of the grid generates heat uniformly over its surface. This localized heat locally melts the thermoplastic material to be assembled: the thermoplastic parts or the thermoplastic film(s), depending on the embodiment. In addition to its heating properties, the perforated support also contributes to the mechanical reinforcement of the final structure of the composite and allows the introduction of new functionalities, such as non-destructive diagnostic or heating systems.

[0030] Advantageously, the method according to the invention may further comprise a step d) of assembly with a third part made of thermoplastic material or composite material and comprising the sub-steps: - bringing into contact and maintaining the assembly obtained according to the invention and the third part with at least one second perforated support comprising a graphene or graphene-based coating, said support being interposed between said assembly and the third part; - heating of the element formed by the assembly, the openwork support and the third part, the heating being implemented by means of an electric current flowing through the at least one second openwork support, - cooling and assembly, and obtaining the composite.

[0031] Advantageously, the at least one second openwork support is identical to or different from the at least one openwork support described previously.

[0032] Advantageously, the third part is identical or different from the first and second parts described previously.

[0033] Advantageously, the method according to the invention can comprise n iteration(s) of step d) and obtaining an assembly comprising n+2 parts made of thermoplastic material, n being an integer. Preferably n is in a range from 1 to 40, and more preferably from 1 to 20. The nature of the second openwork support and of the third part can vary at each iteration.

[0034] Advantageously, step(s) d) may be implemented simultaneously or sequentially with respect to one another, as well as with respect to steps a), b) and c). When steps are implemented simultaneously, the heating and cooling phases are preferably synchronized.

[0035] Advantageously, by analogy with steps a), b) and c), step(s) d) can be implemented with or without thermoplastic film. The conditions of steps a), b) and c) on thermoplastic films also apply to steps d).

[0036] Another object of the present invention relates to a composite obtained according to the method according to the invention comprising a first part 1 and a second part 2 made of thermoplastic material or composite material, said parts being fixed to each other, and at least one perforated support 3 comprising a graphene or graphene-based coating, said support 3 being at the interface between the two parts 1, 2.

[0037] Advantageously, the composite according to the invention can comprise at least two openwork supports.

[0038] Advantageously, the composite according to the invention may further comprise one or more third part(s).

[0039] Advantageously, the composite of the invention may further comprise at least one thermoplastic film. The at least one thermoplastic film may be at the interface between the two parts 1, 2 and / or the at least one support 3, said parts being fixed to each other via said thermoplastic film.

[0040] Advantageously, the composite according to the invention may comprise a first part 1 and a second part 2 made of thermoplastic material, said parts being fixed to each other via a thermoplastic film, said thermoplastic film being interposed between at least two perforated supports 3 comprising a graphene or graphene-based coating, said supports 3 being at the interface between the two parts 1, 2.

[0041] Advantageously, the composite according to the invention may comprise a first part 1 and a second part 2 made of thermoplastic material, said parts being fixed to each other via at least two thermoplastic films, said thermoplastic films being at the interface between the two parts 1, 2, and an openwork support 3 comprising a graphene or graphene-based coating, said supports 3 being at the interface between the two thermoplastic films. Brief description of the figures

[0042] [Fig-1] [Fig. 1] represents the implementation of the method according to the invention and the assembly of a part 1 with a part 2 by means of an openwork support 3. The faces 12 and 22 of the respective parts 1 and 2 are in contact with the support 3. The pressure is exerted on the faces 11 and 21 of the respective parts 1 and 2. The openwork support 3 comprises copper electrodes 31 and 32. The electrodes 31 and 32 are connected to a power supply (not shown).

[0043] . [Fig.2] [Fig.2] represents a composite according to the invention comprising a first part 1, a second part 2 and an openwork support 3, said support being integrated into the structure of the composite, following the implementation of the method according to the invention.

[0044] [Fig.3] [Fig.3] represents the implementation of the method according to the invention comprising a first part 1, a second part 2, an openwork support 3, and a thermoplastic film 4. The polyester film 4 is in contact with the face 12 of the part 1 and the support 3. The support 3 is in contact with the face 22 and the thermoplastic film 4. The assembly formed by the openwork support 3 and the thermoplastic film 4 is thus interposed between the two parts 1, 2. The pressure is exerted on the faces 11 and 21 of the respective parts 1 and 2. The openwork support 3 comprises copper electrodes 31 and 32. The electrodes 31 and 32 are connected to a power supply (not shown). EXAMPLES

[0045] Other advantages, aims and particular characteristics of the present invention will emerge from the examples which follow, given for explanatory and in no way limiting purposes.

[0046] Example: Composite 1 made from two PEEK plates and a graphene-coated fiberglass grid

[0047] The first and second parts are two PEEK plates measuring 30 cm x 30 cm and 5 mm thick.

[0048] The openwork support is a graphene-coated fiberglass grid (mesh surface area 2 mm2, graphene layer thickness 4 pm).

[0049] Copper electrodes were used to electrically power the grid.

[0050] A power supply delivering a power of 900 watts was used to achieve a heating temperature of 350°C.

[0051] The graphene-coated fiberglass grid was placed between the two PEEK plates. The contact surface between the grid and the plates was uniform.

[0052] Pressure (1.5 bar) was applied to the plates to ensure good contact.

[0053] The copper electrodes were connected to the grid.

[0054] The grill was powered with a power of 900 watts to heat evenly to 350°C. The heating time is 3 minutes.

[0055] Under the effect of the heat generated by the grid, the surfaces of the PEEK plates in contact with the grid melted locally.

[0056] The pressure that was exerted promoted the mixing of the polymer chains, ensuring precise fusion.

[0057] After the electric current was turned off, the polymer cooled, thus sealing the weld. The cooling time is 30 minutes.

[0058] The graphene-coated fiberglass grid remained trapped in the welded area, contributing to the mechanical strengthening of the final composite.

[0059] The electrical connection areas of the fiberglass grid are retained for use as a resistive heating system, also allowing disassembly of the two plates to facilitate recycling when the composite is no longer useful.

[0060] Power connections can be used to monitor and control the welded area.

[0061] Example 2: Composite 2 made from two polycarbonate plates and a graphene-coated fiberglass grid:

[0062] The first and second parts are two polycarbonate plates measuring 30 cm x 30 cm and 10 mm thick to be welded.

[0063] The openwork support is a graphene-coated fiberglass grid (mesh surface area 2 mm2, graphene layer thickness 4 pm).

[0064] Copper electrodes were used to electrically power the grid.

[0065] A power supply delivering a power of 600 watts was used to achieve a heating temperature of 260°C.

[0066] The graphene-coated fiberglass grid was placed between the two polycarbonate plates.

[0067] The contact surface between the grid and the plates must be uniform.

[0068] Pressure (1.2 bar) was applied to the plates to ensure good contact.

[0069] The copper electrodes were connected to the grid.

[0070] The grill was powered with a power of 600 watts to heat evenly to 260°C. The heating time is 3 minutes.

[0071] Under the effect of the heat generated by the grid, the surfaces of the polycarbonate plates in contact with the grid melted locally.

[0072] The pressure that was exerted promoted the mixing of the polymer chains, ensuring precise fusion.

[0073] After the electric current was turned off, the polycarbonate cooled, thus sealing the weld. The cooling time is 30 minutes.

[0074] The graphene-coated fiberglass grid remained trapped in the welded area, contributing to the mechanical strengthening of the final composite.

[0075] The electrical connection areas of the fiberglass grid are retained to facilitate recycling when the composite is no longer useful.

[0076] The power connections may further be used to monitor and control the welded area.

[0077] Example 3: Composite 3 made from two polyester plates using a support consisting of a PU film interposed between two graphene-coated fiberglass grids:

[0078] The first and second parts are two polyester plates measuring 30 cm x 30 cm and 5 cm thick to be welded.

[0079] The openwork support is a set of two graphene-coated fiberglass grids (mesh area 2 mm2, graphene layer thickness 4 pm), in the middle of which is intercalated a polyurethane (PU, thickness 70 pm) film (melting temperature less than 90°C). The PU film is distributed uniformly between the two fiberglass grids.

[0080] A power supply delivering a power of 340 watts made it possible to heat to 150°C.

[0081] The power supply was connected to the resistive heating element.

[0082] The support was supplied with a power of 340 watts to heat to 150°C. The heating time is 3 minutes.

[0083] Under the effect of the heat generated by the support, the PU film melted. The PU thus allowed welding at a temperature well below the melting temperature of the polyester plates, without risk of altering the intrinsic properties of the polyester.

[0084] The pressure (1.5 bar) which was exerted ensured good contact between the melting surfaces of the plates.

[0085] After the electric current was turned off, the polyester and the PU film cooled, thus sealing the weld. The cooling time is 30 minutes.

[0086] The electrical connection areas of the support are preserved to measure the variation in conductivity as a function of moisture adsorption.

[0087] This method allows welding at a temperature lower than the melting temperature of the polyester, thus preserving the properties of the material.

[0088] Example 4: Composite 4 made from two carbon / epoxy composite plates using a support consisting of a graphene-coated fiberglass grid sandwiched between two polyurethane films:

[0089] The first and second parts are two carbon / epoxy composite plates measuring 30 cm x 30 cm and 10 cm thick to be welded.

[0090] The openwork support is a graphene-coated fiberglass grid (mesh surface area 2 mm2, graphene layer thickness 4 pm), sandwiched between two polyurethane (PU) films (melting temperature below 90°C).

[0091] A power supply delivering a power of 300 watts made it possible to heat to 100°C.

[0092] The power supply was connected to the support via copper electrodes.

[0093] The support was powered with a power of 300 watts to heat to 100°C. The heating time is 3 minutes.

[0094] Under the effect of the heat generated by the support, the polyurethane films (PU, thickness 70 μm) reached their melting point. In this composite, the molten PU fulfills a dual function by acting as a bonding agent between the two composites and by serving as a protective layer to prevent any contact between the conductive grid and the carbon fibers of the composite, thus avoiding any risk of short circuit.

[0095] The pressure (1.5 bar) which was exerted ensured good contact between the melting surfaces of the plates.

[0096] After the electric current was turned off, the polyester and the PU film cooled, thus sealing the weld. The cooling time is 30 minutes.

[0097] The electrical connection areas of the support are preserved for non-destructive diagnosis and provide the possibility of detecting a crack or defect by measuring the conductivity.

[0098] This method allowed welding at a temperature lower than the melting temperature of the two carbon / epoxy composite plates, thus preserving the properties of the material.

Claims

Claims

1. Method for assembling a composite, comprising parts made of thermoplastic material or composite material, comprising the steps: a) bringing into contact and holding a first part and a second part with at least one perforated support comprising a graphene or graphene-based coating, said support being interposed between the two parts; b) heating the two parts, the heating being carried out by means of an electric current flowing through the at least one perforated support, c) cooling and assembling, and obtaining the composite.

2. Method according to claim 1, in which the contacting of step a) further comprises contacting at least one thermoplastic film whose melting temperature is lower than that of the first and second parts, said film being interposed between the two parts.

3. Method according to the preceding claim, wherein the heating temperature of step b) is equal to 10 to 20 degrees above the melting temperature of the thermoplastic parts or film.

4. Method according to any one of the preceding claims, in which the thermoplastic material of the first and second parts is chosen from acetal, styrene acrylonitrile butadiene, polyimides, aromatic polyamides, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose nitrate, ethylene vinyl acetate, expanded polystyrene, expanded polypropylene, fluoroplastics such as polytetrafluoroethylene, fluorinated ethylene propylene, nylons such as polyamides, the family of polyaryletherketones such as polyaryletherketone, polyetherketone, polyetheretherketoneketone and polyetherketoneetherketoneketone, polybutene-1, polycarbonate, polyacetals, polyoxymethylene, poly(ethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate, high density polyethylene, low density polyethylene,low-density polyethylene, linear density, polypropylene, polyphenylene oxide, polyphenylene sulfide, polyphenylene polysulfone, polymethylpentene, polystyrene, high impact polystyrene HIPS, polyvinyl alcohol, polyvinyl alcohol homopolymer, polyvinyl chloride, styrene acrylonitrile and acrylonitrile styrene acrylate, thermoplastic elastomers such as thermoplastic rubber and thermopropylene rubber, and a mixture thereof.

5. A method according to any preceding claim, wherein the composite material of the first and second parts is selected from carbon / epoxy, carbon / polyurethane, carbon / thermoplastic, thermoplastic / thermoplastic, thermoplastic / epoxy, thermoplastic / polyurethane, plant fiber / epoxy, plant fiber / polyurethane, plant fiber / thermoplastic, ceramic / epoxy, ceramic / polyurethane, ceramic / thermoplastic and a mixture thereof.

6. A method according to any one of claims 2 to 5, wherein the thermoplastic film may be selected from acrylonitrile butadiene styrene, polyacetal copolymer, polyurethane, polyamide 6,6, polyamide 6, polyamide 11, polycarbonate, transparent thermoplastic polyester, polyetheretherketone, low density polyethylene, high density polyethylene 300, very high density polyethylene 500, very high density polyethylene 1000, polymethyl methacrylate, polypropylene, polystyrene, polytetrafluoroethylene, polyvinyl chloride, polyvinyl chloride, polyvinylidene fluoride, fluorinated ethylene propylene, cellulose nitrate, polyvinyl alcohol, ethylene vinyl acetate and a mixture thereof.

7. Method according to any one of the preceding claims, in which the first and second parts are plates, films, lamellae, thin sheets, parts with complex geometry, cylinders.

8. Method according to any one of the preceding claims, in which the openwork support comprises at least one element chosen from a perforated plate, a net, a grid, a wire mesh, a woven textile, regular or irregular.

9. A method according to the preceding claim, wherein the perforated plate, net, grid, netting or woven fabric is made graphene, fiberglass, quartz fiber, thermoplastic polyester, polyethylene terephthalate, polyethylene terephthalate glycol, polyetheretherketone, polyamide, polytetrafluoroethylene, ceramic, plant fibers such as hemp, flax or cellulose and a mixture thereof.

10. A method according to claim 8 or 9, wherein the perforated plate, net, grid, netting or woven fabric is not made of graphene and the graphene coating has a thickness ranging from 100 nm to 100 pm.

11. A method according to any preceding claim, wherein the electric current has a power in a range from 40 W to 10 kW, preferably in a range from 250 W to 1000 W.

12. Method according to any one of the preceding claims, in which the holding is achieved by applying pressure on either side of the first and second parts, preferably the pressure exerted is in a range from 0.5 to 100 bar, preferably from 1.1 bar to 2 bar.

13. Method according to any one of the preceding claims, further comprising a step d) of assembly with a third part made of thermoplastic material or composite material and comprising the sub-steps: - bringing into contact and maintaining the assembly obtained according to any one of the preceding claims and the third part with at least one second perforated support comprising a graphene or graphene-based coating, said support being interposed between said assembly and the third part; - heating the assembly and the third part, the heating being carried out by means of an electric current flowing through the at least one second perforated support, - cooling and assembly, and obtaining the composite.

14. Method according to the preceding claim comprising n iteration(s) of step d) and obtaining an assembly comprising n+2 parts made of thermoplastic material or composite material, n being an integer preferably ranging from 1 to 40, and more preferably from 1 to 20.

15. Composite obtained according to the method of any one of the preceding claims comprising a first part (1) and a second part (2), said parts being fixed to each other, and an openwork support (3) comprising a graphene or graphene-based coating, said support (3) being at the interface between the two parts (1, 2).

16. Composite according to the preceding claim, further comprising one or more third part(s).

17. Composite according to claim 15 or 16, further comprising at least one thermoplastic film at the interface between the two parts (1,2) and / or the at least one support (3), said parts being fixed to each other via said thermoplastic film.

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