CABLE COMPRISING AN ELECTRICALLY CONDUCTIVE ELEMENT CONTAINING METALLIZED CARBON FIBERS

Description

[0001] The invention relates to an electrical cable comprising at least one elongated electrically conductive element comprising a metallized carbon fiber or at least one set of metallized carbon fibers.

[0002] Electrical cables are widely used for the transmission of electrical energy as well as for data transmission. Electrical cables must have different properties depending on their use, including good electrical conductivity, good mechanical strength, and being as light as possible.

[0003] An electrical cable typically comprises a single-strand or multi-strand electrically conductive element, most often surrounded by an insulating material. The electrically conductive element is generally made of metallic materials such as, for example, copper or aluminum. However, the use of these metallic materials in electrical cables has several disadvantages. Indeed, these metals can have mechanical properties that are not always suited to needs, low availability and a high price. Furthermore, metals are high-density materials, which poses problems for the manufacture and installation of electrical cables, particularly long ones (over 2 km), and in applications where minimizing the mass of the systems is sought, such as for example in aeronautical systems.

[0004] US 2011 / 209894 A1 describes a composite material formed from electrically conductive metallized carbon fibers.

[0005] WO 2013 / 016445 A1 describes a carbon-based conductive substrate.

[0006] US 2009 / 194313 A1 describes a coaxial cable comprising a core, an insulating layer, a shielding layer, a sheathing layer.

[0007] EP 3 367 390 A1 describes a metal-coated electrically conductive carbon nanotube wire and methods of forming the same.

[0008] The aim of the present invention is to overcome the drawbacks of the prior art by proposing a light and inexpensive electrically conductive element while having very good electrical conductivity and improved mechanical properties.

[0009] The present invention thus relates to an electric cable in accordance with claim 1.

[0010] Thanks to the electric cable of the invention, the use of solid metal conductors is limited or even avoided. The electric cable of the invention has good specific conductivity while having significantly improved mechanical properties, such as tensile strength, thermal resistance, and / or flexibility (e.g. necessary for its winding and installation). In addition, another advantage is that the electric cable of the invention has, in particular, very good physicochemical properties, such as low thermal expansion of the electrically conductive element. Furthermore, the electric cable of the invention advantageously takes advantage of the low density of carbon fibers compared to the densities of metals.In addition, it has a lower linear mass than an electric cable comprising one or more metallic conductor(s) as the only conductive element(s), and has a comparable manufacturing cost. Elongated electrically conductive element

[0011] A carbon fiber is composed mainly of crystalline carbon atoms aligned more or less parallel to the axis of the carbon fiber. The carbon content of a carbon fiber is generally between 90% and 99%, and depends mainly on the stages of the manufacturing process.

[0012] The metallized carbon fiber used in the present invention comprises a carbon fiber surrounded by one or more metal layers.

[0013] The metallized carbon fiber assembly used in the present invention comprises a plurality of metallized carbon fibers, each of said metallized carbon fibers comprising a carbon fiber surrounded by one or more metal layers.

[0014] The carbon fiber of the metallized carbon fiber or the carbon fibers of the set of metallized carbon fibers may be one or more fibers called carbon-based. "Carbon-based" means a fiber that may be composed of carbon, and more particularly carbon nanofibers, carbon nanotubes and / or graphene.

[0015] A set of carbon fibers according to the invention comprises several carbon fibers which can be conventionally organized into carbon threads commonly called "strands". A carbon thread can comprise several thousand carbon fibers designated by the letter K, for example a thread of 12,000 carbon fibers is called "12K".

[0016] The specific conductivity of at least 8% of the metallized carbon fiber or of the set of metallized carbon fibers advantageously allows said metallized carbon fiber or said set of metallized carbon fibers to be used as an elongated electrically conductive element in an electric cable according to the invention.

[0017] The elongated electrically conductive element may preferably have a specific conductivity of at least 15%, preferably at least 25%, and more preferably at least 35%.

[0018] The specific conductivity of a material is expressed in Sm 2< .kg -1< , and corresponds to the ratio of its electrical conductivity expressed in siemens per meter (S / m) divided by its density expressed in kg / m 3< .

[0019] The specific conductivity of a material, expressed in %, is determined in relation to the specific conductivity at 20°C of pure annealed copper which is 6524.71 Sm 2< .kg -1< . The density at 20°C of pure annealed copper is 8890 kg.m -3< . Electrical conductivity (S / m) characterizes the ability of a material to allow the electrons it contains to move freely under the effect of an electric field and therefore allow the passage of an electric current.

[0020] In the invention, a set of metallized carbon fibers is defined as several metallized carbon fibers organized, for example, in parallel to each other. According to a possible variant, the carbon fibers of a set can be twisted or braided.

[0021] In the electrical cable of the invention, the set of metallized carbon fibers may comprise at least 2 metallized carbon fibers, preferably at least 1000 metallized carbon fibers, preferably at least 3000 metallized carbon fibers, preferably at least 6000 metallized carbon fibers, and more preferably at least 12000 metallized carbon fibers.

[0022] In the electric cable of the invention, the set of metallized carbon fibers may comprise at most 48000 metallized carbon fibers, or even the set of metallized carbon fibers may comprise more than 48000 metallized carbon fibers.

[0023] In the present invention, the elongated electrically conductive element may comprise: only one metallized carbon fiber, and / or a single set or several sets of metallized carbon fibers, in particular at most 10 sets of metallized carbon fibers.

[0024] In a particular embodiment, the elongated electrically conductive element of the invention may further comprise at least one metallic conductor.

[0025] Where the elongated electrically conductive element comprises a plurality of sets of metallized carbon fibers, each set may comprise a different number of metallized carbon fibers and / or a different metal constituting the metal layer surrounding the carbon fibers.

[0026] In the present invention, the elongated electrically conductive element may advantageously be the most central element of the cable.

[0027] More particularly, the elongated electrically conductive element preferably does not surround an insulating or polymeric material, in particular of the insulating or polymeric layer type.

[0028] The elongated electrically conductive element may also comprise additional elements such as, for example, one or more non-metallized carbon fiber(s).

[0029] In the present invention, the metal layer(s) of the metallized carbon fiber(s) may comprise at least one metal chosen from copper, zinc, tin, silver, aluminum, and one of their alloys. By "alloy" is meant the combination or mixture of at least two metals, in particular chosen from those listed above.

[0030] Preferably, the metal layer may comprise only copper or only a copper alloy.

[0031] When the metallized carbon fiber or the metallized carbon fibers of a set of metallized carbon fibers are surrounded by several metallic layers, at least one of the metallic layers may comprise copper or a copper alloy, the other metallic layer(s) may comprise a different metal, in particular chosen from zinc, nickel, tin, silver, aluminum, and a mixture thereof.

[0032] The metal layer may be in direct physical contact with the carbon fiber of the metallized carbon fiber or with each carbon fiber of said set of metallized carbon fibers.

[0033] The metal layer may be bonded by physical and / or chemical interactions, preferably by covalent bonding, to the carbon fiber to enable good adhesion of the metal layer to the carbon fiber.

[0034] An intermediate layer called an "adhesion" layer may be placed between the carbon fiber and the metal layer of the metallized carbon fiber, in order to improve the adhesion of the metal layer around the carbon fiber. The intermediate layer may be a metal layer, which may comprise one or more metals selected from tin, nickel, copper, aluminum, silver, and a mixture thereof.

[0035] In the invention, the metal layer has an average thickness of at least 100 nm, preferably at least 500 nm, and more preferably at least 1 µm. In a particular embodiment, the average thickness of the metal layer may be at most 5 µm.

[0036] More particularly, the average thickness of the metal layer is the number average thickness between at least two thicknesses measured respectively at two different points along the carbon fiber(s). If the thickness of the metal layer is substantially constant along the carbon fiber(s), the average thickness of the metal layer is equal to the thickness of the metal layer at any point of the carbon fiber(s).

[0037] The average thickness of the metal layer can be readily determined by techniques well known to those skilled in the art.

[0038] Preferably, the metal layer may have a constant thickness along the entire length of the carbon fiber or carbon fiber(s) of a set of metallized carbon fibers. A constant thickness means that the thickness of the metal layer may vary by at most ±30% relative to the average thickness of the metal layer, preferably by at most ±20% relative to the average thickness of the metal layer, and more preferably by at most ±10% relative to the average thickness of the metal layer.

[0039] In the invention, the thickness of the metal layer can be adapted according to the nature of the metal or metals it comprises and according to the desired conductivity. In particular, a metal layer comprising a metal having a low conductivity can be thicker than a metal layer comprising a metal having a higher conductivity.

[0040] The metallization of the carbon fiber or carbon fiber(s) of a set of carbon fibers can be carried out by a process chosen from electrodeposition, electroplating (known by the Anglicism " electroplating "), electroplating without electric current (known by the Anglicism " electroless plating "), thermal evaporation under vacuum (" heated evaporation "), electron beam evaporation (" electron beam evaporation "), cathode sputtering (" sputtering "), ion beam assisted deposition (" ion-assisted deposition "). According to a preferred embodiment, the metallization of the carbon fiber(s) can be carried out by electrodeposition.

[0041] In the invention, the metallized carbon fiber(s) may have a length ranging from 100 m to 200 km, preferably ranging from 100 m to 10 km, and more preferably ranging from 100 m to 3 km. By using a metallized carbon fiber or a set of metallized carbon fibers, good specific conductivity and good mechanical properties are maintained over the entire length of the electrical cable.

[0042] The (non-metallized) carbon fiber of a metallized carbon fiber or the (non-metallized) carbon fibers constituting the set of metallized carbon fibers has / have a diameter ranging from 0.5 µm to 100 µm, preferably ranging from 1 µm to 50 µm, and more preferably ranging from 5 µm to 10 µm. These values are given for the carbon fiber without taking into account any possible metallic layer(s) covering it.

[0043] The metallized carbon fiber or set of metallized carbon fibers may have a cross-section ranging from 0.2 µm 2< to 1000 µm 2< , preferably ranging from 1 µm 2< to 500 µm 2< , and more preferably ranging from 10 µm 2< to 100 µm 2< .

[0044] According to the invention, the elongated electrically conductive element may have a direct current electrical conductivity of at least 3% IACS, preferably at least 5% IACS, and more preferably at least 10% IACS. According to the invention, the elongated electrically conductive element may have a direct current electrical conductivity of at most 50% IACS.

[0045] The electrical conductivity of a material is expressed in siemens per meter (S / m).

[0046] The electrical conductivity of a material, expressed in % IACS (IACS corresponding to the anglicism " International Annealed Copper Standard »), is determined in relation to the electrical conductivity at 20°C of pure annealed copper which is 5.8001x10 7< S / m. Polymeric layer

[0047] In the invention, the elongated electrically conductive element is surrounded by at least one polymeric layer. Preferably, the polymeric layer is an electrically insulating layer. The term "electrically insulating layer" means a layer whose electrical conductivity can be at most 1.10 -9 < S / m (siemens per meter) (at 25°C).

[0048] According to a first possible variant, the elongated electrically conductive element may comprise a single metallized carbon fiber surrounded by at least one polymeric layer.

[0049] According to a second possible variant, the elongated electrically conductive element may comprise several metallized carbon fibers, all of said metallized fibers being surrounded by at least one polymeric layer.

[0050] A polymeric layer is understood to mean a layer comprising at least one polymer, the term "polymer" as such generally meaning homopolymer or copolymer (e.g. block copolymer, statistical copolymer, terpolymer, etc.).

[0051] In the invention, the polymer may advantageously be an olefin polymer (polyolefin) or, in other words, an olefin homo- or co-polymer, and may in particular be a thermoplastic or crosslinked polymer.

[0052] Preferably, the olefin polymer is an ethylene or propylene polymer.

[0053] The polymeric layer of the invention may comprise at least one polymer selected from linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), ethylene vinyl acetate copolymer (EVA), ethylene butyl acrylate copolymer (EBA), methyl acrylate (EMA), 2-hexylethyl acrylate (2HEA), ethylene alpha olefin copolymer, ethylene propylene copolymer (EPR), polyurethane, fluoropolymer, chlorinated polymer such as polyvinyl chloride (PVC), polyphenylene oxide (PPO), engineering polymer, and mixtures thereof.

[0054] Examples of ethylene and alpha-olefin copolymers include polyethylene octene (PEO).

[0055] Examples of ethylene-propylene copolymers (EPR) include ethylene-propylene diene terpolymers (EPDM).

[0056] The term “technical polymer” means a polymer having improved properties, which may be chosen in particular from a polyphenylethylene ether, a polyamide, polyetheretherketone (PEEK), a polyimide, a fluorinated ethylene copolymer (FEP), a polyethylene furanoate (PEF), and one of their mixtures.

[0057] The polymeric layer may further comprise at least one additive chosen from antioxidants, stabilizers, crosslinking agents, scorch retarders, co-crosslinking agents, processing aids such as lubricants or waxes, compatibilizing agents, coupling agents, filler stabilizers, and a mixture thereof.

[0058] Preferably, the polymeric layer is a so-called “HFFR” layer for the Anglicism “ Halogen-Free Flame Retardant» according to IEC 60754 Parts 1 and 2 (2011).

[0059] The polymeric layer may further comprise at least one filler. The filler of the invention may be a mineral or organic filler. It may be chosen from a flame-retardant filler, an inert filler, and one of their mixtures.

[0060] For example, the flame retardant filler may be a hydrated filler, chosen in particular from metal hydroxides such as, for example, magnesium dihydroxide (MDH) or aluminum trihydroxide (ATH). These flame retardant fillers act mainly physically by decomposing endothermically (e.g., release of water), which has the effect of lowering the temperature of the polymer layer and limiting the propagation of flames along the electrical device. We speak in particular of flame retardant properties, well known by the Anglicism " flame retardant » .

[0061] The inert filler can be chalk, talc, clay (e.g. kaolin), carbon black, or carbon nanotubes.

[0062] The polymeric layer can preferably be extruded.

[0063] The polymeric layer may be crosslinked or not crosslinked. Crosslinking may be carried out by conventional crosslinking techniques well known to those skilled in the art, such as, for example, peroxide crosslinking and / or hydrosilylation under the action of heat; silane crosslinking in the presence of a crosslinking agent; crosslinking by electron beams, gamma rays, X-rays, or microwaves; crosslinking by photochemical means such as irradiation under beta radiation, or irradiation under ultraviolet radiation in the presence of a photoinitiator. Crosslinking is preferably carried out according to the silane crosslinking technique.

[0064] The polymeric layer may have a thickness ranging from 10 µm to 2 mm, preferably from 100 µm to 1 mm, and more preferably from 100 µm to 700 µm. Sheath

[0065] The electrical cable of the invention may further comprise a sheath, in particular a protective sheath, surrounding the polymeric layer(s).

[0066] Preferably, the sheath may be the outermost layer of the electrical cable of the invention.

[0067] The sheath is in particular a continuous and uniform layer around at least said polymeric layer. It provides protection for the insulated elongated electrically conductive element(s), in particular against humidity, mechanical damage and / or chemical damage. It can also protect against mechanical damage. This sheath can be conventionally made from suitable thermoplastic materials such as HDPE (high density polyethylene), MDPE (medium density polyethylene) or LLDPE (linear low density polyethylene); or materials that retard the spread of flame or are resistant to the spread of flame.

[0068] The polymers cited for the polymeric layer of the invention can also be used for the sheath.

[0069] Preferably, the outer protective sheath is an electrically insulating sheath.

[0070] The sheath may have a thickness ranging from 100 µm to 2 mm, preferably from 100 µm to 1.5 mm, and more preferably from 100 µm to 1 mm. Electric cable

[0071] The electrical cable of the invention can be applied typically, but not exclusively, to the fields of low voltage (in particular less than 6 kV), medium voltage (in particular from 6 to 45-60 kV) or high voltage (in particular greater than 60 kV, and up to 800 kV) power cables, whether they are direct or alternating current.

[0072] Other characteristics and advantages of the present invention will appear in the light of the description of non-limiting examples of electric cables according to the invention, made with reference to the figure 1 .

[0073] There figure 1 represents a cross-sectional view of an electrical cable according to one embodiment of the invention.

[0074] For reasons of clarity, only the elements essential for understanding the invention have been represented schematically, and this without respecting the scale.

[0075] There figure 1 represents a cross-sectional view of an electric cable 1 according to a particular embodiment of the invention.

[0076] The electrical cable 1 comprises a central elongated electrically conductive element 2 comprising an assembly of 12,000 metallized carbon fibers 3, each carbon fiber of said assembly being surrounded by a metallic layer of copper.

[0077] The elongated electrically conductive element 2 is surrounded by a polymeric layer 4.

[0078] An electrically insulating sheath 5 is placed around the polymeric layer 4.

[0079] In this particular example, the polymeric layer 4 is in direct physical contact with the elongated electrically conductive element 2 and the electrically insulating sheath 5 is in direct physical contact with the polymeric layer 4. Examples

[0080] In order to demonstrate the technical effects of the present invention, tests were carried out using metallized carbon fibers according to the invention and so-called “comparative” carbon fibers. Formation of the elongated electrically conductive element Example 1 (comparative example)

[0081] Example 1 consists of preparing an elongated electrically conductive element comprising 12,000 non-metallized carbon fibers marketed by Toray under the reference TORAYCA T300. The diameter of each carbon fiber is 7 µm. Their length is 200 meters or more.

[0082] The density of the elongated electrically conductive element is determined by densimetric measurement according to ASTM D792-08, and is 1.76 g / cm 3< . Example 2 (comparative example)

[0083] Example 2 is to prepare an elongated electrically conductive element comprising 12,000 nickel-plated carbon fibers marketed by Teijin Company under the reference TOHO TENAX HTS40. The diameter of each carbon fiber alone (without the nickel layer) is 7 μm, and the nickel layer has a thickness of 1 μm around each carbon fiber. The length of the nickel-plated carbon fibers is 200 meters or more.

[0084] The density of the elongated electrically conductive element is determined by densimetric measurement according to ASTM D792-08, and is 2.7 g / cm 3< . Example 3 (example according to the invention)

[0085] Example 3 involves preparing an elongated electrically conductive element comprising 12,000 copper-clad carbon fibers.

[0086] The metallization of carbon fibers with copper is carried out by electrodeposition, with metallic copper (Cu (0) < ) marketed by the company SIFCO under the reference CUIVRE ALCALIN DEPOT EPAIS CODE 5280, around respectively 12000 non-metallized carbon fibers marketed by the company Toray under the reference TORAYCA T300. The diameter of each non-metallized carbon fiber is 7 µm and their length is 200 meters or more.

[0087] Electrodeposition is carried out with a current generator type device from the TTI brand under the reference QPX600DP, for approximately 5 minutes, to obtain a copper layer approximately 1 µm thick around the carbon fibers.

[0088] An elongated electrically conductive element is formed from the copper-plated carbon fibers with 12,000 of said fibers.

[0089] The density of the elongated electrically conductive element is determined by densimetric measurement according to ASTM D792-08, and is 4.4 g / cm 3< . Measurement of the specific conductivity of the elongated electrically conductive elements of Examples 1 to 3

[0090] The measurement of the specific conductivity (%) of the elongated electrically conductive elements of Examples 1, 2 and 3 is carried out by measuring 4 points according to ASTM B193 and ISO 3915.

[0091] The calculation of the specific conductivity is then determined from the value of the electrical conductivity and the density of the elongated electrically conductive element.

[0092] The results are collected in the table below: Specific conductivity (%) Example 1: 12000 unmetallized carbon fibers 0,6 Example 2: 12,000 nickel-plated carbon fibers 7,4 Example 3: 12,000 copper-clad carbon fibers 39,9

[0093] Thus, the electrically conductive element of the invention, as exemplified in Example 3, has a specific conductivity much higher than that of Example 1 and Example 2.

[0094] The electrically conductive element of the invention in an electric cable makes it possible to significantly limit, or even avoid, the use of solid metal conductors, while having very good mechanical and physicochemical properties.

Claims

1. Electric cable (1) comprising at least one elongate electrically conductive element (2) surrounded by at least one polymer layer (4), said elongate electrically conductive element (2) comprising a metallised carbon fibre or at least one set of metallised carbon fibres (3), characterised in that the metallised carbon fibre or said set (3) of metallised carbon fibres has a specific conductivity of at least 8%, in that the metallised carbon fibre or the set of metallised carbon fibres comprise one or more carbon fibres, respectively, surrounded by at least one metal layer, the metal layer having an average thickness of at least 100 nm, and in that the carbon fibre of the metallised carbon fibre or the carbon fibres making up the set of metallised carbon fibres has / have a diameter ranging from 0.5 µm to 100 µm.

2. Electric cable (1) according to claim 1, characterised in that said elongate electrically conductive element (2) has a specific conductivity of at least 15%, preferably at least 25%, and more preferably at least 35%.

3. Electric cable (1) according to any of the preceding claims, characterised in that said set of metallised carbon fibres (3) comprises at least 1,000 metallised carbon fibres, preferably at least 6,000 metallised carbon fibres, and more preferably at least 12,000 metallised carbon fibres.

4. Electric cable (1) according to any of the preceding claims, characterised in that said metal layer comprises copper or a copper alloy.

5. Electric cable (1) according to any of the preceding claims, characterised in that the metal layer is in direct physical contact with the carbon fibre of said metallised carbon fibre or with each carbon fibre of said set of metallised carbon fibres.

6. Electric cable (1) according to any of the preceding claims, characterised in that the metal layer has an average thickness of at least 500 nm, and more preferably at least 1 µm.

7. Electric cable (1) according to any of the preceding claims, characterised in that it further comprises a sheath (5) surrounding the polymer layer (4).

8. Electric cable (1) according to any of the preceding claims, characterised in that the metallised carbon fibre(s) have a length ranging from 100 m to 200 km, preferably ranging from 100 m to 10 km, and more preferably ranging from 100 m to 3 km.

9. Electric cable (1) according to any of the preceding claims, characterised in that the carbon fibre of the metallised carbon fibre or the carbon fibres making up the set of metallised carbon fibres has / have a diameter ranging from 1 µm to 50 µm, and more preferably ranging from 5 µm to 10 µm.

10. Electric cable (1) according to any of the preceding claims, characterised in that said elongate electrically conductive element (2) has a direct current electrical conductivity of at least 3% IACS, preferably at least 5% IACS, and more preferably at least 10% IACS.

11. Electric cable (1) according to any of the preceding claims, characterised in that the elongate electrically conductive element (2) is the element closest to the centre of the cable.

12. Electric cable (1) according to any of the preceding claims, characterised in that the elongate electrically conductive element (2) does not surround any insulating or polymer material.