Electrical cable comprising a semiconductor layer with a smooth surface

Abstract

The present invention relates to an electrical cable comprising at least one semiconducting layer obtained from a polymer composition comprising at least 50% by weight of a propylene polymer, relative to the total weight of polymer(s) in the polymer composition, at least one conductive filler selected from acetylene blacks, and at most 10% by weight of polar polymer(s), relative to the total weight of polymer(s) in the polymer composition. Figure for the abstract: Fig. 1

Description

Title of the invention: Electric cable comprising a semi-conducting layer having a smooth surface

[0001] The present invention relates to an electric cable comprising at least one semi-conducting layer obtained from a polymer composition comprising at least 50% by weight of a propylene polymer, relative to the total weight of polymer(s) in the polymer composition, at least one conductive filler chosen from acetylene blacks, and at most 10% by weight of polar polymer(s), relative to the total weight of polymer(s) in the polymer composition.

[0002] The invention typically but not exclusively applies to electric cables intended for the transport of energy, in particular to medium voltage (in particular from 6 to 45-60 kV) or high voltage (in particular greater than 60 kV, and up to 800 kV) energy cables, whether in direct or alternating current, in the fields of aerial, underwater, terrestrial electricity transport, or even aeronautics. The invention applies in particular to electric cables comprising at least one semi-conductor layer having a smooth surface condition.

[0003] A semiconducting layer of an electric cable is generally obtained by dispersing conductive particles within a polymer matrix. However, during the manufacture of the compositions used to obtain these semiconducting layers, such particles are very often difficult to disperse in the polymers used as the polymer matrix. During the extrusion of the semiconducting layers either around the conductor of the cable or around the insulating layer, poorly incorporated carbon black particles may be found at the interface between a semiconducting layer and the insulating layer, and form protrusions surrounded by the insulating layer. These protrusions will lead to a localized increase in the electric field which may cause premature aging of the cable, said aging being able to induce electrical breakdown.

[0004] There is therefore a need for semi-conducting layers based on propylene polymer(s) for electric cables having an improved surface condition.

[0005] From international application WO2018 / 100409 A1, there is known an internal or external semiconducting layer for an electric cable obtained from a thermoplastic material based on a polypropylene matrix mixed with a dielectric liquid, the thermoplastic material having a melting enthalpy of 15 to 50 J / g, and the polypropylene matrix being obtained from a propylene material chosen from a heterophasic copolymer of propylene and ethylene having a melting enthalpy of 15 to 50 J / g, and an intimate mixture of said heterophasic copolymer and a homo- propylene polymer or propylene and ethylene copolymer having a fusion enthalpy greater than 50 J / g. In the examples, carbon black is used as a conductive filler. The surface condition of the semiconductor layer as described is not optimized.

[0006] An aim of the present invention is to overcome the drawbacks of the techniques of the prior art by proposing an electric cable, in particular medium or high voltage, based on propylene polymer(s), said cable having an improved surface condition (i.e. in which the protuberances are reduced and / or the surface condition has a smooth appearance), preferably while guaranteeing good thermomechanical properties.

[0007] This object is achieved by the invention which will be described below.

[0008] The first subject of the invention is an electric cable comprising at least one semi-conducting layer obtained from a polymer composition comprising at least 50% by weight of a propylene polymer and at most 10% by weight of polar polymer(s), relative to the total weight of polymer(s) in the polymer composition, and at least one conductive filler chosen from acetylene blacks.

[0009] Thus, thanks to the combination of at least 50% by weight of a propylene polymer relative to the total weight of polymer(s) in the polymer composition, and at least one conductive filler chosen from acetylene blacks, while having at most 10% by weight of polar polymer(s), relative to the total weight of polymer(s) in the polymer composition, the semi-conductive layer thus obtained has an improved surface condition, in particular a smooth appearance and / or having a reduction in the number of protuberances, preferably while guaranteeing good mechanical properties at high temperature.

[0010] The conductive charge

[0011] The polymer composition comprises at least one conductive filler chosen from acetylene blacks, in particular in a quantity sufficient to make the layer semi-conductive.

[0012] The polymer composition may comprise at least approximately 6% by weight of conductive filler, preferably at least approximately 15% by weight of conductive filler, and particularly preferably at least approximately 25% by weight of conductive filler, relative to the total weight of the polymer composition.

[0013] The polymer composition may comprise at most approximately 45% by weight of conductive filler, and preferably at most approximately 40% by weight of conductive filler, relative to the total weight of the polymer composition.

[0014] Conductive filler is an electrically conductive filler.

[0015] The conductive filler is chosen from acetylene blacks.

[0016] Unlike furnace blacks, graphites, or other fillers conductive, acetylene blacks have the advantages of having a lower quantity of chemical impurities (eg such as ionic contaminants and traces of oxides), good intrinsic electrical conductivity and allowing the achievement of good surface quality.

[0017] The conductive filler may be in the form of particles, nodules or aggregates, preferably with an average primary particle size having a dimension of at most 50 nm, preferably ranging from approximately 20 to 50 nm, and particularly preferably ranging from approximately 30 to 40 nm.

[0018] Considering several particles, nodules or aggregates of the conductive filler powder according to the invention, the term "dimension" represents the size distribution D50, this distribution being conventionally determined by methods well known to those skilled in the art.

[0019] The dimension of the conductive particle(s) according to the invention can be determined, for example, by microscopy, in particular by scanning electron microscope (SEM), by transmission electron microscope (TEM), or by laser diffraction.

[0020] The size distribution D50 is preferably measured by laser diffraction, for example using a laser beam diffraction granulometer. The size distribution D50 indicates that 50% by volume of the particle population has an equivalent sphere diameter less than the given value.

[0021] The presence of at least 50% by weight of a propylene polymer and at most 10% by weight of polar polymer(s) relative to the total weight of polymer(s) in the polymer composition makes it possible to incorporate sufficient conductive filler to make the layer semi-conductive, while ensuring good mechanical properties. Conversely, certain ethylene polymers such as LDPE do not allow a sufficient quantity of conductive filler to be incorporated without avoiding a degradation of the mechanical properties.

[0022] The conductive filler may have a specific surface area according to the BET method ranging from approximately 50 to 150 m2 / g, preferably from approximately 70 to 140 m2 / g, and particularly preferably from approximately 80 to 120 m2 / g.

[0023]

[0024] In the present description, the specific surface area of ​​the conductive inorganic filler can be easily determined according to DIN 9277 (2010).

[0025] The conductive filler preferably comprises a small amount of ionic substances, typically less than 100 ppm, for example less than 10 ppm. This amount can for example be determined by inductively coupled plasma spectroscopy or the method described in J. Tanaka, "Interfacial Aging Phenomena In Power Cable Insulation Systems", Institute of Materials Science, University of Connecticut, Progress Report No. 8 and 9, September 13, 1988 (

[0019] ).

[0026] The acetylene blacks of the invention are preferably chosen from those having at least one of the following characteristics: - an iodine absorption number ranging from approximately 45 g / kg to 300 g / kg, measured according to the standard (ASTM D-1510), - a DBP (dibutylphthalate) type oil absorption number ranging from approximately 100 cm3 / 100g to 300 cmVIOOg, measured according to ASTM D-2414, - an apparent density ranging from approximately 200 g / ml to 400 g / ml, measured according to ASTM D-1513, - a specific surface area CT AB (hexadecyltrimethyl ammonium bromide) ranging from approximately 40 to 300 m2 / g, measured according to standard ASTM D-6556, - a sulfur level of less than 200 ppm.

[0027] Propylene polymer

[0028] In the present description, the term “polymer” means any type of polymer, such as for example homopolymers or copolymers (e.g. block copolymer, random copolymer, terpolymer, etc.).

[0029] The polymer composition comprises at least about 50% by weight, preferably at least about 60% by weight, particularly preferably at least about 70% by weight, and more particularly preferably at least about 80% by weight, of propylene polymer(s) relative to the total weight of polymer(s) in the polymer composition.

[0030] The propylene polymer may be a homopolymer or a copolymer of propylene Pb and preferably a copolymer of propylene Pb

[0031] The propylene homopolymer Pi preferably has an elastic modulus ranging from 1250 at approximately 1600 MPa.

[0032] In the present description, the elastic modulus or Young's modulus of a polymer (known by the anglicism "Tensile Modulus") is well known to those skilled in the art, and can be easily determined according to the ISO 527-1, -2 (2012) standard. The ISO 527 standard has a first part, noted "ISO 527-1", and a second part, noted "ISO 527-2" specifying the test conditions relating to the general principles of the first part of the ISO 527 standard.

[0033] As examples of propylene copolymers Ph, mention may be made of copolymers of propylene and olefin, the olefin being chosen in particular from ethylene and an olefin ai other than propylene.

[0034] The ethylene or olefin ai other than propylene of the propylene-olefin copolymer preferably represents at most approximately 45 mol%, particularly preferably at most approximately 40 mol%, and more particularly preferably at most approximately 35 mol%, relative to the total number of moles of co- propylene and olefin polymer.

[0035] The mole percentage of ethylene or olefin ai in the propylene copolymer Pi can be determined by nuclear magnetic resonance (NMR), for example according to the method described in Masson et al., Int. J. Polymer Analysis & Characterization, 1996, Vol.2, 379-393.

[0036] The olefin ai other than propylene can correspond to the formula CH2=CH-R1, in which R1 is a linear or branched alkyl group having from 2 to 12 carbon atoms, notably chosen from the following olefins: 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and one of their mixtures.

[0037] Copolymers of propylene and ethylene are preferred as propylene copolymer Pb

[0038] The propylene copolymer Pi may be a homophasic propylene copolymer or a heterophasic propylene copolymer, and preferably a (heterophasic) propylene copolymer.

[0039] In the invention, the homophasic propylene copolymer Pi preferably has an elastic modulus ranging from approximately 600 to 1200 MPa, and particularly preferably ranging from approximately 800 to 1100 MPa.

[0040] The homophasic propylene copolymer Pi is advantageously a random propylene copolymer Pi.

[0041] The ethylene or olefin ai other than propylene of the homophasic propylene copolymer Pi preferably represents at most approximately 20 mol%, particularly preferably at most approximately 15 mol%, and more particularly preferably at most approximately 10 mol%, relative to the total number of moles of the homophasic propylene copolymer Pb.

[0042] The ethylene or olefin ai other than propylene of the homophasic propylene copolymer Pi may represent at least about 1 mol%, relative to the total number of moles of homophasic propylene copolymer Pb.

[0043] As an example of a statistical copolymer of propylene Ph, we can cite that marketed by the company Borealis under the reference Bormed® RB 845 MO or that marketed by the company Total Petrochemicals under the reference PPR3221.

[0044] The heterophasic (or heterophase) propylene copolymer Pi may comprise a thermoplastic phase of propylene type and a thermoplastic elastomer phase of ethylene copolymer and an olefin a2 type.

[0045] The olefin a2 of the thermoplastic elastomer phase of the heterophasic propylene copolymer Pi may be propylene.

[0046] The thermoplastic elastomer phase of the heterophasic propylene copolymer Pi may represent at least 20% by weight approximately, and preferably at least 45% by weight approximately, relative to the total weight of the heterophasic propylene copolymer P i-

[0047] The heterophasic propylene copolymer Pi preferably has an elastic modulus ranging from approximately 50 to 1200 MPa, and particularly preferably: either an elastic modulus ranging from approximately 50 to 550 MPa, and more particularly preferably ranging from approximately 50 to 300 MPa; or an elastic modulus ranging from approximately 600 to 1200 MPa, and more particularly preferably ranging from approximately 800 to 1200 MPa.

[0048] As an example of a heterophasic propylene copolymer, mention may be made of the heterophasic propylene copolymer marketed by the company LyondellBasell under the reference Adflex® Q 200 F, or the heterophasic copolymer marketed by the company LyondellBasell under the reference Moplen EP®2967.

[0049] The propylene homopolymer or copolymer Pi may have a melting temperature greater than approximately 110°C, preferably greater than approximately 130°C, particularly preferably greater than approximately 135°C, and more particularly preferably ranging from approximately 140 to 170°C.

[0050] The propylene homopolymer or copolymer Pi can have a fusion enthalpy ranging from approximately 20 to 100 J / g.

[0051] The propylene homopolymer Pi preferably has a fusion enthalpy ranging from approximately 80 to 90 J / g.

[0052] The homophasic propylene copolymer Pi preferably has a fusion enthalpy ranging from approximately 40 to 90 J / g, and particularly preferably ranging from 50 to 85 J / g.

[0053] The heterophasic propylene copolymer Pi preferably has a fusion enthalpy ranging from approximately 20 to 50 J / g.

[0054] The propylene homopolymer or copolymer Pi may have a melt flow index ranging from 0.5 to 3 g / 10 min; in particular determined at approximately 230°C with a load of approximately 2.16 kg according to the ASTM D1238-00 standard, or the ISO 1133 standard.

[0055] The homophasic propylene copolymer Pi preferably has a melt flow index ranging from 1.0 to 2.75 g / 10 min, and more preferably ranging from 1.2 to 2.5 g / 10 min; in particular determined at approximately 230°C with a load of approximately 2.16 kg according to the ASTM D1238-00 standard, or the ISO 1133 standard.

[0056] The heterophasic propylene copolymer Pi may have a melt flow index ranging from 0.5 to 3 g / 10 min, and preferably ranging from 0.6 to 1.2 g / 10 min approximately; in particular determined at approximately 230°C with a load of approximately 2.16 kg according to the ASTM D1238-00 standard, or the ISO 1133 standard.

[0057] The propylene homopolymer or copolymer Pi may have a density ranging from approximately 0.81 to 0.92 g / cm3; in particular determined according to standard ISO 1183A (at a temperature of 23°C).

[0058] The propylene copolymer Pi preferably has a density ranging from 0.85 to 0.91 g / cm3, and particularly preferably ranging from 0.87 to 0.91 g / cm3; in particular determined according to standard ISO 1183A (at a temperature of 23°C).

[0059] The polymer composition may comprise several propylene polymers, and in particular several different propylene Pi copolymers, in particular two different propylene Pi copolymers, said propylene Pi copolymers being as defined above.

[0060] In particular, the polymer composition may comprise a homophasic propylene copolymer (as a first propylene copolymer Pi) and a heterophasic propylene copolymer (as a second propylene copolymer Pi), or two different heterophasic propylene copolymers, and preferably a homophasic propylene copolymer and a heterophasic propylene copolymer.

[0061] When the polymer composition comprises a homophasic propylene copolymer and a heterophasic propylene copolymer, said heterophasic propylene copolymer preferably has an elastic modulus ranging from approximately 50 to 300 MPa.

[0062] According to one embodiment of the invention, the two heterophasic propylene copolymers have a different elastic modulus. Preferably, the polymer composition comprises a first heterophasic propylene copolymer having an elastic modulus ranging from about 50 to 550 MPa, and particularly preferably ranging from about 50 to 300 MPa; and a second heterophasic propylene copolymer having an elastic modulus ranging from about 600 to 1200 MPa, and more particularly preferably ranging from about 800 to 1200 MPa.

[0063] Advantageously, the first and second heterophasic propylene copolymers have a melt flow index as defined in the invention.

[0064] These combinations of propylene Pi copolymers can advantageously improve the mechanical properties of the semiconducting layer. In particular, the combination makes it possible to obtain optimized mechanical properties of the semiconducting layer, in particular in terms of elongation at break, and flexibility; and / or makes it possible to form a more homogeneous semiconducting layer, in particular promotes the dispersion of the dielectric liquid in the propylene polymer(s) of said semiconducting layer.

[0065] According to a preferred embodiment of the invention, the propylene copolymer P i or the propylene copolymers Pi when there are several of them, represent(s) at least approximately 50% by weight, preferably approximately 55 to 90% by weight, and particularly preferably approximately 60 to 90% by weight, relative to the total weight of polymer(s) in the polymer composition.

[0066] The homophasic propylene copolymer Pi may represent at least 20% by weight, and preferably from 30 to 70% by weight, relative to the total weight of polymer(s) in the polymer composition.

[0067] The heterophasic propylene copolymer Pi or the heterophasic propylene copolymers Pi when there are several of them, may represent from 5 to 95% by weight approximately, preferably from 50 to 90% by weight approximately, and particularly preferably from 60 to 80% by weight approximately, relative to the total weight of polymer(s) in the polymer composition.

[0068] Other polymers in the polymer composition

[0069] The polymer composition may further comprise a homopolymer or a copolymer of olefin P2.

[0070] Said olefin homopolymer or copolymer P2 is preferably different from said propylene homopolymer or copolymer Pb

[0071] The olefin of the olefin copolymer P2 may be chosen from ethylene and an olefin α corresponding to the formula CH2=CH-R2, in which R2 is a linear or branched alkyl group having from 1 to 12 carbon atoms.

[0072] The olefin a is preferably chosen from the following olefins: propylene, 1-butene, isobutylene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and a mixture thereof.

[0073] Propylene, 1-hexene or 1-octene type α-olefin is particularly preferred.

[0074] The combination of Pi and P2 polymers makes it possible to obtain a polymer composition having good mechanical properties, particularly in terms of elastic modulus, and electrical properties.

[0075] The olefin homopolymer or copolymer P2 is preferably an ethylene polymer.

[0076] The ethylene polymer preferably comprises at least about 80 mol% of ethylene, particularly preferably at least about 90 mol% of ethylene, and more particularly preferably at least about 95 mol% of ethylene, relative to the total number of moles of the ethylene polymer.

[0077] According to a preferred embodiment of the invention, the ethylene polymer is chosen from low density ethylene polymers (LDPE), linear low density ethylene polymers (LLDPE), medium density ethylene polymers (MDPE), and high density ethylene polymers (HDPE); in particular according to standard ISO 1183A (at a temperature of 23°C).

[0078] Preferably, the ethylene polymer is an LLDPE.

[0079] In the present description, the expression "low density" means having a density ranging from approximately 0.91 to 0.925, said density being measured according to ISO 1183A (at a temperature of 23°C).

[0080] In the present description, the expression "medium density" means having a density ranging from approximately 0.926 to 0.940, said density being measured according to the ISO 1183A standard (at a temperature of 23°C).

[0081] In the present description, the expression "high density" means having a density ranging from 0.941 to 0.965, said density being measured according to ISO 1183A (at a temperature of 23°C).

[0082] The ethylene polymer preferably comprises at least about 80 mol% of ethylene, particularly preferably at least about 90 mol% of ethylene, and more particularly preferably at least about 95 mol% of ethylene, relative to the total number of moles of the ethylene polymer.

[0083] The mole percentage of ethylene in the ethylene polymer can be determined by nuclear magnetic resonance (NMR), for example according to the method described in Masson et al., Int. J. Polymer Analysis & Characterization, 1996, Vol.2, 379-393.

[0084] The ethylene polymer preferably has a flexural modulus of at least 150 MPa, and particularly preferably at least 400 MPa, determined according to the ISO 178 method. Furthermore, in comparison with other partially crystalline ethylene polymers, the ethylene polymer preferably has a melting point of at least 110°C measured by DSC.

[0085] According to a preferred embodiment of the invention, the olefin homopolymer or copolymer P2 represents from 5 to 30% by weight approximately, and particularly preferably from 10 to 20% by weight approximately, relative to the total weight of polymer(s) in the polymer composition.

[0086] According to a particularly preferred embodiment of the invention, the polymer composition comprises two propylene copolymers Pi such as a homophasic propylene copolymer and a heterophasic propylene copolymer or two different heterophasic propylene copolymers; and a homopolymer or copolymer of olefin P2 such as an ethylene polymer. This combination of propylene copolymers Pi and a homopolymer or copolymer of olefin P2 makes it possible to further improve the mechanical properties of the semiconducting layer, while ensuring good thermal conductivity.

[0087] The propylene copolymer(s) Pi and the olefin homopolymer or copolymer P2 may represent at least 80% by weight, preferably at least 90% by weight, and particularly preferably at least 95% by weight relative to the total weight of polymer(s) in the polymer composition.

[0088] More particularly, the polymer composition may comprise only the propylene copolymer(s) Pi and the olefin homopolymer or copolymer P2, as defined in the invention, as polymer(s).

[0089] The propylene copolymer(s) Pi and the olefin homopolymer or copolymer P2 are not necessarily miscible within the polymer composition. In other words, their miscibility is not essential to obtain a semiconducting layer with an improved surface condition, in particular a smooth appearance and / or with a reduction in the number of protrusions, preferably while ensuring good mechanical properties.

[0090] The polymer composition of the cable of the invention comprises at most approximately 10% by weight, preferably at most approximately 8% by weight, and particularly preferably at most approximately 5% by weight, of polar polymer(s) relative to the total weight of polymer(s) in the polymer composition.

[0091] In the present description, the expression "polar" means that the polymer of this type comprises one or more polar functions, such as for example acetate, acrylate, hydroxyl, nitrile, carboxyl, carbonyl, ether, ester groups, or any other groups of a polar nature well known in the prior art such as in particular silane groups. For example, a polar polymer is a polymer chosen from ethylene copolymers of the type ethylene and vinyl acetate copolymer (EVA), ethylene and butyl acrylate copolymer (EBA), ethylene and ethyl acrylate copolymer (EEA), ethylene and methyl acrylate copolymer (EMA), and ethylene and acrylic acid copolymer (EAA).

[0092] The polymer composition preferably does not comprise polar polymer(s). Indeed, these can reduce the resistance to thermal aging (e.g. thermal stability) of the semiconducting layer of the invention; when they are used in large quantities, they can make the semiconducting layer peelable, which is not the desired effect in the context of the present invention; and polar residues can migrate into the neighboring insulating layer and thus deteriorate the electrical loss angle (delta tangent) as well as negatively influence the distribution of space charges.

[0093] The composition of the invention is a homogeneous composition in that it is in the form of a single polymer phase in the case where the polymers are miscible, or in the form of at least two phases, the first being uniformly dispersed in the second to form a homogeneous composition.

[0094] When the composition is in the form of at least two phases, the presence of several phases may come from the mixture of two different polyolefins, such as a mixture of different propylene polymers or a mixture of a propylene polymer and an ethylene polymer.

[0095] The polymers used in the polymer composition have the advantage of not producing significant phase separation in the molten state, facilitating their kneading and extrusion to form the semiconducting layer.

[0096] The dielectric liquid

[0097] The polymer composition of the invention preferably further comprises a dielectric liquid, in particular forming an intimate mixture with the polymers of the polymer composition.

[0098] The dielectric liquid improves the conductive charge / propylene polymer interface. The presence of the dielectric liquid thus makes it possible to obtain better dielectric properties (i.e. better electrical insulation), and in particular better dielectric strength of the semi-conductor layer obtained from the polymer composition. Its presence can also make it possible to improve the mechanical properties and / or the resistance to aging of said semi-conductor layer.

[0099] Dielectric liquid is also well known to those skilled in the art as "dielectric oil" or "dielectric fluid".

[0100] Examples of dielectric liquids that may be mentioned are mineral oils (e.g. naphthenic oils, paraffinic oils or aromatic oils); vegetable oils (e.g. soybean oil, linseed oil, rapeseed oil, corn oil or castor oil); or synthetic oils such as aromatic hydrocarbons (alkylbenzenes, alkylnaphthalenes, alkylbiphenyls, alkydiarylethylenes, etc.), silicone oils, ether oxides, organic esters, or aliphatic hydrocarbons.

[0101] Aromatic hydrocarbons, silicone oils, and aliphatic hydrocarbons are preferred as synthetic oils.

[0102] According to a particular embodiment, the dielectric liquid represents from 1% to 20% by weight approximately, preferably from 2 to 15% by weight approximately, and particularly preferably from 3 to 12% by weight approximately, relative to the total weight of the polymer composition.

[0103] The dielectric liquid preferably comprises at least one mineral oil.

[0104] Mineral oil is generally liquid at about 20-25°C.

[0105] The mineral oil is advantageously chosen from naphthenic oils and paraffinic oils.

[0106] Mineral oil is obtained from the refining of crude oil.

[0107] According to a particularly preferred embodiment of the invention, the oil mineral comprises a paraffinic carbon (Cp) content ranging from about 45 to 65 atomic percent, a naphthenic carbon (Cn) content ranging from about 35 to 55 atomic percent, and an aromatic carbon (Ca) content ranging from about 0.5 to 10 atomic percent.

[0108] The dielectric liquid may comprise at least about 70% by weight of mineral oil, preferably at least about 80% by weight of mineral oil, and particularly preferably at least about 90% by weight of mineral oil relative to the total weight of the dielectric liquid.

[0109] According to a preferred embodiment of the invention, the dielectric liquid comprises a mineral oil and at least one polar compound of the benzophenone, acetophenone or one of their derivatives type.

[0110] In a particular embodiment, the polar compound of the benzophenone, acetophenone or one of their derivatives represents at least approximately 2.5% by weight, preferably at least approximately 3.5% by weight, and particularly preferably at least approximately 4% by weight, relative to the total weight of the dielectric liquid.

[0111] According to a preferred embodiment of the invention, the polar compound of benzophenone, acetophenone or one of their derivatives is chosen from benzophenone, dibenzosuberone, fluorenone and anthrone. Benzophenone is particularly preferred.

[0112] The dielectric liquid may comprise at most approximately 30% by weight, preferably at most approximately 20% by weight, and even more preferably at most approximately 15% by weight, of polar compound of the benzophenone, acetophenone or one of their derivatives type, relative to the total weight of the dielectric liquid. This maximum quantity makes it possible to guarantee moderate, or even low, dielectric losses (e.g. less than approximately 10 3), and also to avoid the migration of the dielectric liquid out of the electrically insulating layer.

[0113] According to a preferred embodiment of the invention, the polar compound of benzophenone, acetophenone or one of their derivatives is chosen from benzophenone, dibenzosuberone, fluorenone and anthrone. Benzophenone is particularly preferred.

[0114] Additives

[0115] The polymer composition may further comprise one or more additives.

[0116] The additives are well known to those skilled in the art.

[0117] The additives may be chosen from antioxidants, processing aids such as lubricants, metal deactivators, compatibilizing agents, coupling agents, anti-UV agents, water tree reducing compounds, pigments, and a mixture thereof.

[0118] The polymer composition may typically comprise from 0.01 to 5% by weight approximately, and preferably from 0.1 to 2% by weight approximately of additive(s), relative to the total weight of the polymer composition.

[0119] More particularly, the antioxidants make it possible to protect the polymer composition from thermal stresses generated during the stages of manufacturing the cable or operation of the cable.

[0120] The antioxidant may be chosen from hindered phenols, aromatic amines, nitrogenous aromatic heterocyclics, sulfur-based antioxidants, and phosphorus-based antioxidants, and preferably from hindered phenols.

[0121] Examples of hindered phenols include pentaerythritol-tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (Irganox® 1010), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox® 1076), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (Irganox® 1330), 4,6-bis(octylthiomethyl)-o-cresol (Irgastab® KV10 or Irganox® 1520), 2,2'-thiobis(6-tert-butyl-4-methylphenol) (Irganox® 1081), 2,2'-thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (Irganox® 1035), 2,2'-methylenebis(6-tert-butyl-4-methylphenol) or tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate (Irganox® 3114).

[0122] Examples of aromatic amines that may be mentioned are phenylene diamines (eg paraphenylene diamines such as 1PPD or 6PPD), diphenylamine styrene, di-phenylamines, or 4- ( 1 -methyl 1-1 -phenylethyl 1) -N- [4- ( 1 -methyl 1-1 -phenylethyl l)phenyl] aniline (Naugard 445).

[0123] Examples of nitrogen-containing aromatic heterocyclics include mercaptobenzimidazoles or quinoline derivatives such as polymerized 2,2,4-trimethyl-1,2 dihydroquinolines (TMQ), and preferably mercaptobenzimidazoles.

[0124] Examples of sulfur-based antioxidants include thioethers such as didodecyl-3,3'-thiodipropionate (Irganox® PS800), distearylthiodipropionate or dioctadecyl-3,3'-thiodipropionate (Irganox® PS802), bis[2-methyl-4-{3-n-alkyl (C12 or CM) thiopropionyloxy]-5-tert-butylphenyl]sulfide, thiobis-[2-tert-butyl-5-methyl-4,1-phenylene] bis[3-(dodecylthio)propionate], or 4,6-bis(octylthiomethyl)-o-cresol (Irganox® 1520 or Irgastab® KV10).

[0125] Examples of phosphorus-based antioxidants include phosphites or phosphonates, such as tris(2,4-di-tert-butylphenyl) phosphite (Irgafos® 168) or bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite (Ultranox® 626).

[0126] The metal deactivator may be chosen from nitrogen-containing aromatic heterocycles, and aromatic compounds comprising at least one -NH-C(=O)- function, and preferably from aromatic compounds comprising at least one -NH-C(=O)- function. The presence of oxygen in the metal deactivator is important in order to be able to permanently immobilize the metal ions.

[0127] Examples of nitrogen-containing aromatic heterocyclics include quinoline derivatives such as polymerized 2,2,4-trimethyl-1,2 dihydroquinolines (TMQ).

[0128] As examples of aromatic compounds comprising at least one -NH-C(=O)- function, mention may be made of those comprising two -NH-C(=O)- functions, preferably comprising two -NH-C(=O)- functions covalently bonded, and more particularly preferably comprising a divalent group -NH-C(=O)-C(=O)-NH- or -C(=O)-NH-NH-C(=O)-, such as 2,2' oxamidobis- [ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (Naugard XL-1), 2',3-bis[[3-[3,5-di-tert-butyl-4-hydroxy phenyl] propionyl]] propionohydrazide or l,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl) hydrazine (Irganox® 1024 or Irganox® MD 1024), or oxalyl bis(benzylidenehydrazide) (OABH).

[0129] The polymer composition of the semiconducting layer of the invention is a thermoplastic polymer composition. It is therefore not crosslinkable.

[0130] In particular, the polymer composition does not comprise crosslinking agents, silane coupling agents, peroxides and / or additives which enable crosslinking. Indeed, such agents degrade the polymer(s) of the polymer composition.

[0131] The polymer composition is preferably recyclable.

[0132] The composition may further comprise inert inorganic fillers such as chalk, kaolin or talc; and / or halogen-free mineral fillers intended to improve the fire behavior of the polymer composition.

[0133] The inert inorganic fillers and / or the halogen-free mineral fillers may represent at most approximately 30% by weight, preferably at most approximately 20% by weight, particularly preferably at most approximately 10% by weight, and more particularly preferably from 0.1 to 5% by weight approximately, relative to the total weight of the polymer composition.

[0134] In order to guarantee an electrical cable called "HFFR" for the anglicism "Halogen Free Flame Retardant", the cable of the invention preferably does not include halogenated compounds. These halogenated compounds can be of any nature, such as for example fluorinated polymers or chlorinated polymers such as polyvinyl chloride (PVC), halogenated plasticizers, halogenated mineral fillers, etc.

[0135] The semiconductor layer

[0136] The semiconducting layer of the cable of the invention is preferably a non-crosslinked layer, or in other words a thermoplastic layer.

[0137] In the invention, the expression "non-crosslinked layer" or "thermoplastic layer" means a layer whose gel content according to standard ASTM D2765-01 (xylene extraction) is at most approximately 30%, preferably at most approximately 20%, particularly preferably at most approximately 10%, more particularly preferably at most approximately 5%, and even more particularly preferably 0%.

[0138] In one embodiment of the invention, the semiconducting layer, preferably not crosslinked, has a tensile strength of at least approximately 7 MPa, preferably at least approximately 10 MPa, and particularly preferably at least approximately 12.5 MPa.

[0139] Tensile strength is measured by a dumbbell tensile test. H2, especially at a pulling speed of 25 mm / min.

[0140] In a particularly preferred embodiment of the invention, the semiconducting layer, preferably not crosslinked, has an elongation at break of at least approximately 150%, preferably at least approximately 250%, and particularly preferably at least approximately 350%.

[0141] The elongation at break is measured by a tensile test on an H2 dumbbell specimen, in particular at a tensile speed of 25 mm / min.

[0142] The semi-conductive layer of the cable of the invention is preferably a recyclable layer.

[0143] The semiconductor layer of the invention may be an extruded layer, in particular by methods well known to those skilled in the art.

[0144] The semi-conducting layer has a variable thickness depending on the type of cable envisaged. In particular, when the cable according to the invention is a medium voltage cable, the thickness of the semi-conducting layer is typically from 0.3 to 1.5 mm approximately, and more particularly from 0.5 mm approximately. When the cable according to the invention is a high voltage cable, the thickness of the semi-conducting layer typically varies from 1.0 to 4 mm (for voltages of the order of approximately 150 kV) and up to thicknesses ranging from 3 to 5 mm approximately for voltages above 150 kV (very high voltage cables). The aforementioned thicknesses depend, typically and among other things, on the size of the elongated electrically conductive element.

[0145] In the present description, the term "semiconductor layer" means a layer whose electrical conductivity may be strictly greater than 1.108 S / m (Siemens per meter), preferably at least 1.103 S / m, and preferably may be less than 1.103 S / m, measured at 25°C, in direct current.

[0146] In the present description, the term “semiconductor layer” means a layer whose volume resistivity (measured at 90°C) is less than or equal to 1000 [Q*m].

[0147] The semi-conducting layer of the invention may comprise at least 50% by weight of a propylene polymer, at most 10% by weight of polar polymer(s), relative to the total weight of polymer(s) in the polymer composition and at least one conductive filler chosen from acetylene blacks, and optionally one or more additives, the aforementioned ingredients being as defined in the invention.

[0148] The proportions of the different ingredients in the semi-conductor layer may be identical to those as described in the invention for these same ingredients in the polymer composition.

[0149] The cable

[0150] The electrical cable may comprise at least one elongated electrically conductive element, and the semi-conductive layer as defined in the invention, said layer semiconductor surrounding said elongated electrically conductive element.

[0151] The elongated electrically conductive element may be a single-body conductor such as, for example, a metal wire or a multi-body conductor such as a plurality of twisted or untwisted metal wires.

[0152] The elongated electrically conductive element may be aluminum, aluminum alloy, copper, copper alloy, and preferably copper or copper alloy.

[0153] The cable may further comprise an electrically insulating layer.

[0154] According to the present invention, the expression "electrically insulating layer" means a layer whose electrical conductivity can be at most 1.108 S / m (Siemens per meter) approximately, preferably at most 1.109 S / m, and particularly preferably at most 1.10 10 S / m (Siemens per meter), measured at 25°C in direct current.

[0155] The electrically insulating layer more particularly has an electrical conductivity lower than that of the semiconducting layer. More particularly, the electrical conductivity of the semiconducting layer may be at least 10 times greater than the electrical conductivity of the electrically insulating layer, preferably at least 100 times greater than the electrical conductivity of the electrically insulating layer, and particularly preferably at least 1000 times greater than the electrical conductivity of the electrically insulating layer.

[0156] The electrically insulating layer of the invention preferably surrounds the elongated electrically conductive element.

[0157] The electrically insulating layer may be an internal or external semiconductor layer.

[0158] In other words, when the semiconductor layer is an inner semiconductor layer, the electrically insulating layer surrounds the semiconductor layer.

[0159] In a preferred embodiment, the inner semiconductor layer is in direct physical contact with the elongated electrically conductive element.

[0160] In the present description, the expression "in direct physical contact" means that no layer, of any nature whatsoever, is interposed between said elongated electrically conductive element and the semiconducting layer. In other words, the cable does not comprise any intermediate layer(s), in particular any layer(s) comprising at least one polymer, positioned between said elongated electrically conductive element and the semiconducting layer.

[0161] In a preferred embodiment, the inner semiconductor layer is in direct physical contact with the electrically insulating layer.

[0162] When the semiconductor layer is an external semiconductor layer, it may surround the electrically insulating layer.

[0163] In a preferred embodiment, the outer semiconductor layer is in direct physical contact with the electrically insulating layer.

[0164] The semiconducting layer of the cable of the invention is preferably an internal semiconducting layer. Indeed, in high voltage AC cable applications, it is particularly advantageous for at least the internal semiconducting layer between the elongated electrically conductive element and the electrically insulating layer to have a smooth surface condition since the gradient of the AC electric field in the cable under operating or testing conditions is higher in this area.

[0165] The electrically insulating layer is preferably made of a thermoplastic polymer material, and particularly preferably obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene, in particular comprising at least one homophasic propylene homo- or copolymer and / or at least one heterophasic propylene homo- or copolymer, and optionally at least one ethylene polymer.

[0166] According to a preferred embodiment of the invention, the electrical cable comprises several semiconducting layers surrounding the elongated electrically conductive element, at least one of the semiconducting layers being as defined in the invention (or being obtained from a polymer composition as defined in the invention).

[0167] According to a particularly preferred embodiment of the invention, the cable comprises: - at least one elongated electrically conductive element, in particular positioned in the center of the cable, - a first semiconductor layer (inner semiconductor layer) surrounding the elongated electrically conductive element, - an electrically insulating layer surrounding the first semiconductor layer, and - a second semiconductor layer (outer semiconductor layer) surrounding the electrically insulating layer, at least one of the semiconductor layers, preferably the first semiconductor layer, and particularly preferably both semiconductor layers, being as defined in the invention (or being obtained from a polymer composition as defined in the invention).

[0168] In a particular embodiment, the first semiconductor layer, the electrically insulating layer and the second semiconductor layer constitute a three-layer insulation. In other words, the electrically insulating layer is in direct physical contact with the first semiconductor layer, and the second semiconducting layer is in direct physical contact with the electrically insulating layer.

[0169] The cable may further comprise an outer protective sheath surrounding the elongated electrically conductive element, and preferably surrounding the semiconducting layer as defined in the invention.

[0170] The outer protective sheath may be in direct physical contact with the latter, more particularly when the semiconducting layer is an external semiconducting layer.

[0171] The outer protective sheath may be an electrically insulating sheath.

[0172] The electrical cable may further comprise an electrical screen (e.g. metallic) surrounding the semi-conductor layer as defined in the invention. In this case, the outer protective sheath surrounds said electrical screen and the electrical screen is between the outer protective sheath and the semi-conductor layer.

[0173] This metal screen may be a so-called "wire" screen composed of a set of copper or aluminum conductors arranged around and along the second semi-conductor layer, a so-called "ribboned" screen composed of one or more copper or aluminum conductive metal ribbons possibly laid in a helix around the semi-conductor layer or a conductive aluminum metal ribbon laid longitudinally around the semi-conductor layer and made watertight using glue in the overlapping areas of parts of said ribbon, or a so-called "watertight" screen of the metal tube type possibly composed of lead or lead alloy and surrounding the semi-conductor layer. This latter type of screen makes it possible in particular to act as a barrier to moisture which tends to penetrate the electric cable in a radial direction.

[0174] The metal screen of the electric cable of the invention may comprise a so-called "wired" screen and a so-called "waterproof" screen or a so-called "wired" screen and a so-called "ribboned" screen.

[0175] All types of metal screens can act as earthing for the electrical cable and can thus carry fault currents, for example in the event of a short circuit in the network concerned.

[0176] Other layers, such as layers that swell in the presence of moisture, can be added between the second semi-conductor layer and the metal screen, these layers making it possible to ensure the longitudinal watertightness of the electric cable.

[0177] The cable of the invention relates more particularly to the field of electric cables operating in direct current (DC) or alternating current (AC).

[0178] Cable manufacturing process

[0179] The electric cable in accordance with the first subject of the invention can be obtained according to a process comprising at least one step 1) of extrusion of the polymer composition as defined in the first subject of the invention around an elongated electrically conductive element, to obtain a semi-conductive layer (extruded) surrounding said elongated electrically conductive element.

[0180] Step 1) can be carried out by techniques well known to those skilled in the art, for example using an extruder.

[0181] During step 1), the composition at the extruder outlet is said to be “non-crosslinked”, the temperature and the processing time within the extruder being optimized accordingly.

[0182] At the extruder outlet, an extruded layer is therefore obtained around said electrically conductive element, which may or may not be in direct physical contact with said elongated electrically conductive element.

[0183] Preferably, the method does not include a step of crosslinking the layer obtained in step 1).

[0184] The electrically insulating layer and / or the semi-conducting layer(s) of the electric cable of the invention can be obtained by successive extrusion or by co-extrusion.

[0185] Prior to the extrusion of each of these layers around at least one elongated electrically conductive element, all of the constituents necessary for the formation of each of these layers can be metered and mixed in a continuous mixer of the BUSS co-kneader type, twin-screw extruder or another type of mixer suitable for polymer mixtures, in particular filled ones. The mixture can then be extruded in the form of rods, then cooled and dried to be put into the form of granules, or the mixture can be put directly into the form of granules, by techniques well known to those skilled in the art. These granules can then be introduced into a single-screw extruder in order to extrude and deposit the composition around the elongated electrically conductive element to form the layer in question.

[0186] The different compositions can be extruded one after the other to successively surround the elongated electrically conductive element, and thus form the different layers of the electrical cable of the invention.

[0187] They can alternatively be extruded concomitantly by co-extrusion using a single extruder head, co-extrusion being a process well known to those skilled in the art.

[0188] Whether in the granule formation step or in the cable extrusion step, the operating conditions are well known to those skilled in the art. In particular, the temperature within the mixing or extrusion device may be higher than the melting temperature of the majority polymer or of the polymer having the highest melting temperature, among the polymers used in the composition to be put into artwork. Brief description of the drawings

[0189] The attached drawings illustrate the invention: [Fig.l] [Fig.l] schematically represents a structure, in cross-section, of a cable according to the invention according to a first embodiment.

[0190] Other characteristics and advantages of the present invention will appear in the light of the examples which follow with reference to the annotated figures, said examples and figures being given for illustrative purposes and in no way limiting.

[0191] [Fig.l] represents a schematic view of an electric cable according to a preferred embodiment in accordance with the invention.

[0192] For reasons of clarity, only the elements essential for understanding the invention have been represented schematically, and this without respecting the scale.

[0193] The medium or high voltage electric cable 1 according to the first subject of the invention, illustrated in [Fig.l], comprises a central elongated electrically conductive element 2, in particular made of copper or aluminum. The electric cable 1 further comprises several layers arranged successively and coaxially around this central elongated electrically conductive element 2, namely: a first semi-conductive layer 3 called the “internal semi-conductive layer”, an electrically insulating layer 4, a second semi-conductive layer 5 called the “external semi-conductive layer”, a metal earthing and / or protective screen 6, and an outer protective sheath 7.

[0194] The electrically insulating layer 4 is an extruded thermoplastic layer (i.e. non-crosslinked).

[0195] The semi-conducting layer 3 is an extruded thermoplastic layer (i.e. non-crosslinked) obtained from the polymer composition as defined in the invention.

[0196] The semi-conducting layer 5 is an extruded thermoplastic layer (i.e. non-crosslinked).

[0197] The presence of the metal screen 6 and the outer protective sheath 7 is preferential, but not essential, this cable structure being as such well known to those skilled in the art.

[0198] Example

[0199] Polymer compositions

[0200] Table 1 below presents polymer compositions whose quantities of compounds are expressed as a percentage by weight relative to the total weight of the polymer compositions.

[0201] Composition II is a polymer composition in accordance with the invention, the com position Cl is a composition representing the state of the prior art. [Tables 1] Polymer composition II Cl Statistical propylene copolymer 47.75 47.75 Ethylene polymer 10 10 Heterophasic propylene copolymer 10 10 Conductive filler 1: acetylene black 25 0 Conductive filler 2: furnace black 0 25 Antioxidant 1.25 1.25 Metal deactivator 0.5 0.5 Dielectric liquid 5.5 5.5

[0202] The origin of the constituents collected in Table 1 is as follows: - Statistical propylene copolymer is a statistical copolymer of ethylene and propylene, marketed by LyondellBasell Industries under the reference Moplen RP210G - Ethylene polymer is an LLDPE type polymer using hexene as a co-monomer, marketed by the company INEOS under the reference BPD 3642; - Heterophasic propylene copolymer is a special copolymer of ethylene and propylene, marketed by LyondellBasell Industries under the reference Hifax CA7441 A - Conductive charge 1 is an acetylene black, marketed by the company Denka under the reference Denka Black Granular; - Conductive Charge 2 is a high purity electroconductive furnace black, marketed by the company Orion Engineered Carbons under the reference Printex Kappa 10; - Antioxidant is an antioxidant marketed by the company BASF under the reference Irganox B225; - Metal deactivator is a metal deactivator marketed by BASF under the reference Irganox MD 1024; and - Dielectric liquid is marketed by the company Nynas, under the reference Nyflex BNS 28.

[0203] Preparation of a strip obtained from polymer composition II

[0204] The following constituents: dielectric liquid, and antioxidant of the polymer composition referenced in Table 1, are dosed and mixed with stirring at approximately 75°C, in order to form a dielectric liquid.

[0205] The dielectric liquid is then mixed with the following constituents: propylene copolymer, polyethylene of the polymer composition referenced in Table 1, in a container. Then, the resulting mixture and the conductive filler are mixed using a co-oscillating single-screw mixer ("Buss kneader") at a temperature of approximately 145 to 180°C, then melted at approximately 200°C.

[0206] The resulting homogenized and melted mixture is then cooled and formed into granules.

[0207] The pellets were then hot extruded to form a strip.

[0208] A 0.3 mm thick strip was extruded on a single-screw extruder equipped with a flat die in order to allow a surface condition test to be carried out. The extrusion temperatures are chosen according to the processing properties of the polymer matrix and so as to obtain an extruded strip showing practically no deformation coming from the polymer matrix itself (e.g. unmelted, gels, particles coming from undesired crosslinking, particles coming from degradation of one of the polymers of the polymer matrix). In addition, particular care is taken to avoid deformations caused by the release of volatile substances possibly contained in the polymer composition. This thus makes it possible to measure protrusions or deformations linked mainly to the process of dispersion and distribution of the conductive filler in the polymer matrix.

[0209] Characterization of the surface condition of the strips

[0210] The test was carried out as follows: the extruded strip obtained above is held under constant mechanical tension by a system of speed-regulated rollers and set in motion by a winder. It thus advances into a measurement zone of an optical detection system which consists of a light source on one side of the measurement zone and a camera on the other side of the measurement zone. The orientation of the detection system relative to the moving strip surface is tangential. The in-line camera coupled to a computer simultaneously records images of the extruded strip surface and performs an image analysis. The result is a detailed description of the number of defects present on the strip surface, classified by size and shape. The measurement is made by reflection. The results obtained are shown in Table 2 below and indicate the number of defects or protrusions per m2.

[0211] Results

[0212] The results of the above-mentioned surface condition test, and other mechanical and electrical tests are collected in Table 2 below.

[0213] The breaking strength and elongation at break tests are carried out according to Standard NF EN 60811-1-1, using a device marketed under reference 3345 by the company Instron. The breaking strength and elongation at break are measured by a tensile test on an H2 dumbbell specimen, in particular at a tensile speed of 25 mm / min; in the initial state, or after thermal aging in air, for example in an oven. The thermal aging conditions chosen are as follows: duration of approximately 240 hours (10 days), and isothermal and observed temperature of approximately 135°C.

[0214] The “PEA measurement” indicated in the table corresponds to a measurement carried out according to the so-called PEA test (for “Pulsed Electro-Acoustic test bench”).

[0215] The principle of the PEA electroacoustic test is to subject a dielectric sample having a charge density p(x), placed between a high voltage electrode and a ground electrode, to a pulsed electric field which induces a variation of the electrostatic forces on the electric charges contained in the sample. As these electrostatic forces are in equilibrium with the elastic forces, the pulsed field induces the formation of elastic waves (acoustic waves). By using a piezoelectric transducer, these acoustic waves are detected and converted into an electrical signal which is the reflection of the charge density within the sample. This electrical signal is measured after amplification. Note that acoustic waves are also generated at the interfaces between the sample and the electrodes, which must be taken into account.

[0216] More precisely, the PEA test is a dynamic measurement of the spatial distribution of charges in a solid dielectric material. In the test used, it is not an electrical pulse strictly speaking that is used, but a step, which allows a more precise measurement to be obtained. To induce surface charges, the step signal is superimposed on a DC bias voltage. The acoustic wave that results from the application of this voltage (DC bias + step type pulse) is detected by a piezoelectric sensor which in turn provides a signal voltage that contains the information reflecting the charge distribution. In order to carry out the measurement at a controlled temperature, the sample, the electrodes and the piezoelectric sensor are placed in a thermostatically controlled enclosure (oven). [Tables 2] II Cl Number of protrusions per m2 39 440 Maximum height of protrusions in pm 65 140 Tensile strength [MPa] 24.9 23.1 Elongation at break [%] 710 730 Tensile strength [MPa] after 336 h @ 135°C in air oven 22.2 22.1 Elongation at break [%] after 336 h @ 135°C in air oven 489 475 Volume resistivity [Ohm*m] @ 30 °C 0.130 0.038 Volume resistivity [Ohm*m] @ 90 °C 0.140 0.044 Volume resistivity [Ohm*m] @ 105 °C 0.150 0.052 PEA measurement result (direct current): field maximum electrical capacity obtained in [kV / mm] on SC sandwich + TPHV 11 insulation, under applied field stress of 40 kV / mm. 42 50

[0217] All of these results show that the semiconductor layer of the invention has a good surface condition, in particular a smooth appearance and a very low number of protrusions, while guaranteeing good mechanical and electrical properties.

[0218] We will especially notice a significant improvement in performance in the PEA test, particularly important for good stability of an HVDC isolation system.

Claims

Claims

1. Electric cable comprising at least one semi-conducting layer obtained from a polymer composition comprising at least 50% by weight of a propylene polymer and at most 10% by weight of polar polymer(s), relative to the total weight of polymer(s) in the polymer composition, and at least one conductive filler chosen from acetylene blacks.

2. Electric cable according to claim 1, characterized in that the polymer composition comprises at least 6% by weight of conductive filler relative to the total weight of the polymer composition.

3. An electric cable according to claim 1 or 2, characterized in that the conductive filler is in the form of particles, nodules or aggregates whose primary particles have a dimension of at most 50

4. llili. Electric cable according to any one of the preceding claims, characterized in that the conductive filler has a specific surface area according to the BET method ranging from 50 to 150 m2 / g.

5. An electrical cable according to any one of the preceding claims, characterized in that the polymer composition comprises at least 60% by weight of propylene polymer(s) relative to the total weight of polymer(s) in the polymer composition.

6. An electrical cable according to any one of the preceding claims, characterized in that the propylene polymer is a propylene copolymer Pi chosen from a homophasic propylene copolymer and a heterophasic propylene copolymer.

7. An electrical cable according to any one of the preceding claims, characterized in that the polymer composition further comprises a homopolymer or a copolymer of olefin P2.

8. Electric cable according to claim 7, characterized in that the olefin homopolymer or copolymer P2 is an ethylene polymer.

9. Electric cable according to any one of the preceding claims, characterized in that the polymer composition comprises at most 5% by weight of polar polymer(s) relative to the total weight of polymer(s) in the polymer composition.

10. An electrical cable according to any one of the preceding claims, characterized in that the polymer composition further comprises a dielectric liquid.

11. An electrical cable according to any one of the preceding claims, characterized in that the semiconducting layer is a non-crosslinked layer.

12. An electrical cable according to any preceding claim, characterized in that it comprises at least one elongated electrically conductive element, and the semi-conductive layer surrounds said elongated electrically conductive element.

13. Electrical cable according to any one of the preceding claims, characterized in that it further comprises an electrically insulating layer.

14. An electrical cable according to any one of the preceding claims, characterized in that it comprises: - at least one elongated electrically conductive element, - a first semi-conductive layer surrounding the elongated electrically conductive element, - an electrically insulating layer surrounding the first semi-conductive layer, and - a second semi-conductive layer surrounding the electrically insulating layer, at least one of the semi-conductive layers being as defined in any one of the preceding claims.

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