EP4288983A1

EP4288983A1 - Electrical cable with improved thermal conductivity

Info

Publication number: EP4288983A1
Application number: EP22706079.5A
Authority: EP
Inventors: Christelle Mazel; Gabriele Perego; Daphné MERLE; Claire GRANGER
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2021-02-03
Filing date: 2022-02-02
Publication date: 2023-12-13
Also published as: WO2022167753A1; US20240304356A1; KR20230138470A; CN116802748A; FR3119484A1

Abstract

The invention relates to a cable comprising at least one electrically insulative layer obtained from a polymer composition comprising at least one polypropylene-based thermoplastic polymer material, at least one dielectric liquid, at least one first thermally conductive inorganic filler having a morphology M1, and at least one second thermally conductive inorganic filler having a morphology M2 that differs from M1.

Description

ELECTRICAL CABLE WITH IMPROVED THERMAL CONDUCTIVITY

The invention relates to a cable comprising at least one electrically insulating layer obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene, at least one dielectric liquid, at least one first thermally conductive inorganic filler having a morphology M1, and at least one second thermally conductive inorganic filler having a morphology M2 different from M1.

The invention applies typically but not exclusively 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 400 kV), preferably at medium voltage, whether direct or alternating current, in the fields of air, submarine, or land electricity transmission.

The invention applies in particular to electric cables having improved thermal conductivity.

A medium or high voltage power transmission cable preferably comprises, from the inside to the outside:

- an elongated electrically conductive element, in particular made of copper or aluminum;

- an internal semiconductor layer surrounding said elongated electrically conductive element;

- an electrically insulating layer surrounding said internal semiconductor layer;

- an outer semiconductor layer surrounding said insulating layer,

- optionally an electric screen surrounding said outer semi-conducting layer, and

- Optionally an electrically insulating protective sheath surrounding said electrical screen.

From international application WO2018167442A1 is known an electric cable comprising at least one elongated electrically conductive element and at least one electrically insulating layer obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene and at least one inorganic filler such as kaolin or chalk. However, the thermal conductivity properties are not optimized.

The object of the present invention is therefore to overcome the drawbacks of the techniques of the prior art by proposing an electric cable, in particular at medium or high voltage, based on propylene polymer(s), said cable being able to operate at temperatures greater than 70°C, and having improved thermal conductivity properties, while guaranteeing good electrical properties, in particular in terms of dielectric strength, and/or good mechanical properties, in particular in terms of elongation at break and resistance to traction.

The object is achieved by the invention which will be described below.

The first subject of the invention is an electric cable comprising at least one elongated electrically conductive element and at least one electrically insulating layer obtained from a polymer composition, characterized in that the polymer composition comprises at least one thermoplastic polymer material based of polypropylene, at least one dielectric liquid, at least one first thermally conductive inorganic filler having a morphology M1, and at least one second thermally conductive inorganic filler having a morphology M2 different from the morphology M1 of the first thermally conductive inorganic filler.

The cable of the invention can operate at temperatures above 70° C., and has improved thermal conductivity properties, while guaranteeing good electrical properties, in particular in terms of dielectric strength, and/or mechanical properties, in particular in terms of elongation at break and tensile strength.

The combination of a thermoplastic polymer material based on polypropylene with at least two thermally conductive inorganic fillers of different morphologies M1 and M2 makes it possible to obtain an electrically insulating layer having improved thermal conductivity properties.

The first and second thermally conductive inorganic fillers The first thermally conductive inorganic filler [respectively the second thermally conductive inorganic filler] may have a thermal conductivity of at least 1 W/mk approximately at 20°C, and preferably of at least 5 W/mk approximately at 20°C .

In the present invention, the thermal conductivity is preferably measured according to the method well known under the anglicism “Transient Plane Source or TPS”. Advantageously, the thermal conductivity is measured using a device marketed under the reference HOT DISK TPS 2500S by the company THERMOCONCEPT.

The first thermally conductive inorganic filler [respectively the second thermally conductive inorganic filler] can be chosen from silicates, boron nitride, carbonates, metal oxides, preferably from silicates, carbonates, and metal oxides, and particularly preferably from silicates and metal oxides.

Among the silicates, mention may be made of aluminum, calcium or magnesium silicates, and preferably aluminum or magnesium silicates, in particular hydrated magnesium silicates.

The aluminum silicates can be chosen from kaolins and any other mineral or clay mainly comprising kaolinite.

In the present invention, the expression "any other mineral or clay mainly comprising kaolinite" means any other mineral or clay comprising at least 50% by weight approximately, preferably at least 60% by weight approximately, and more preferably at least less than 70% by weight approximately, of kaolinite, relative to the total weight of the mineral or the clay.

Kaolins, especially calcined kaolin, are preferred as aluminum silicates.

The magnesium silicates can be chosen from sepiolites, palygorskites and attapulgites.

Sepiolites are preferred as magnesium silicates.

Among the carbonates, mention may be made of chalk, calcium carbonate (eg aragonite, vaterite, calcite, or a mixture of at least two of the aforementioned compounds), magnesium carbonate, limestone, or any other mineral mainly comprising calcium carbonate or magnesium carbonate.

In the present invention, the expression "any other mineral mainly comprising calcium carbonate or magnesium carbonate" means any other mineral comprising at least 50% by weight approximately, preferably at least 60% by weight approximately, and preferably still at least 70% by weight approximately, of calcium carbonate or magnesium carbonate, relative to the total weight of the mineral.

Chalk and calcium carbonate are preferred as carbonates.

Among the metal oxides, mention may be made of aluminum oxide, a hydrated aluminum oxide, magnesium oxide, silicon dioxide, or zinc oxide, and preferably aluminum oxide or silicon dioxide.

In the present invention, aluminum oxide, also well known as "alumina", is a chemical compound with the formula AI2O3.

The hydrated aluminum oxide or hydrated alumina can be a monohydrated or polyhydrated aluminum oxide, and preferably monohydrated or trihydrated.

Examples of aluminum oxide monohydrate include boehmite, which is the gamma polymorph of AIO(OH) or Al2O3.H2O; or the diaspore, which is the alpha polymorph of AlO(OH) or Al2O3.H2O.

By way of example of aluminum oxide polyhydrate, and preferably trihydrate, mention may be made of gibbsite or hydrargillite, which is the gamma polymorph of AI(OH)s; bayerite which is the alpha polymorph of AI(OH)s; or nordstrandite, which is the beta polymorph of AI(OH)s.

Hydrated aluminum oxide is also well known as "aluminum oxide hydroxide" or "alumina hydroxide".

Aluminum oxide is preferred as the metal oxide.

The aluminum oxide (respectively magnesium oxide) is preferably a calcined aluminum oxide (respectively a calcined magnesium oxide).

The silicon dioxide is preferably fumed silica, the expression “fused silica” being well known under the Anglicism “fumed silica”. According to a particularly preferred embodiment of the invention, the first thermally conductive inorganic filler [respectively the second thermally conductive inorganic filler] is chosen from kaolins, chalk, sepiolites and aluminum oxides.

The first thermally conductive inorganic filler [respectively the second thermally conductive inorganic filler] can represent at least 1% by weight approximately, preferably at least 2% by weight approximately, in a particularly preferred manner at least 5% by weight approximately, and so more particularly preferred at least 10% by weight approximately, relative to the total weight of the polymer composition.

The first thermally conductive inorganic filler [respectively the second thermally conductive inorganic filler] preferably represents at most 40% by weight approximately, in a particularly preferred manner at most 30% by weight approximately, and more particularly preferably at most 25% by weight approximately, relative to the total weight of the polymer composition.

The first thermally conductive inorganic filler [respectively the second thermally conductive inorganic filler] can be in the form of particles with a dimension ranging from 0.001 to 3 μm approximately, preferably from 0.01 to 2 μm approximately, in a particularly preferred manner from 0, 05 to 1.5 μm approximately, and more particularly preferably from 0.075 to 1 μm approximately.

By considering several thermally conductive inorganic filler particles 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.

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

The size distribution D50 is preferably measured by laser diffraction, for example using a laser beam diffraction particle sizer. The D50 size distribution indicates that 50% by volume of the particle population has an equivalent sphere diameter less than the given value. The first thermally conductive inorganic filler [respectively the second thermally conductive inorganic filler] may have a specific surface according to the BET method ranging from approximately 1 to 500 m ² /g, preferably from approximately 3 to 450 m ² /g, and in such a way particularly preferred from 5 to 400 m ² /g approximately.

In the present invention, the specific surface of the thermally conductive inorganic filler can be easily determined according to DIN 9277 (2010).

The first thermally conductive inorganic filler [respectively the second thermally conductive inorganic filler] can be “treated” or “untreated”, and preferably “treated”.

“Treated thermally conductive inorganic filler” means a thermally conductive inorganic filler that has undergone surface treatment, or in other words, a surface-treated thermally conductive inorganic filler. Said surface treatment makes it possible in particular to modify the surface properties of the thermally conductive inorganic filler, for example to improve the compatibility of the thermally conductive inorganic filler with the thermoplastic polymer material.

In a preferred embodiment, the first thermally conductive inorganic filler of the invention [respectively the second thermally conductive inorganic filler] is silanized, or in other words is treated to obtain a first silanized thermally conductive inorganic filler [respectively to obtain a second silanized thermally conductive inorganic filler].

The surface treatment used to obtain the silanized thermally conductive inorganic filler can be a surface treatment from at least one silane compound (with or without a coupling agent), this type of surface treatment being well known to man. of career.

Thus, the first silanized thermally conductive inorganic filler of the invention [respectively the second silanized thermally conductive inorganic filler of the invention] may comprise siloxane and/or silane groups at its surface. Said groups can be of the vinylsilane type, alkylsilane, epoxysilane, methacryloxysilane, acryloxysilane, aminosilane or mercaptosilane.

The silane compound used to obtain the first silanized thermally conductive inorganic filler [respectively the second silanized thermally conductive inorganic filler] can be chosen from:

- alkyltrimethoxysilane or alkyltriethoxysilane, such as for example octadecyltrimethoxysilane (OdTMS - C18), octyl (triethoxy)silane (OTES - C8), methyl trimethoxysilane, hexadecyl trimethoxysilane,

- vinyltrimethoxysilane or vinyltriethoxysilane,

- methacryloxylsilane or acryloxysilane, such as for example 3-methacryloxypropyl methyldimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-acryloxypropyl trimethoxysilane, and

- one of their mixtures.

The second thermally conductive inorganic filler is different from the first thermally conductive inorganic filler, in that it has a morphology M2 different from the morphology M1 of the first thermally conductive inorganic filler. The morphology (M1, M2) can be represented by at least one of the parameters chosen from among the size (t1, t2), the shape (f1, f2), and the specific surface (s1, s2).

According to a first embodiment, the first and second thermally conductive inorganic fillers have different sizes (t1, t2).

In this first embodiment:

- the first thermally conductive inorganic filler is in the form of particles preferably having a size distribution D50 of at most approximately 1.5 μm, in a particularly preferred manner of at most 1 μm approximately, and more particularly preferably of at most about 0.9 μm; and

- the second thermally conductive inorganic filler is in the form of particles preferably having a size distribution D50 ranging from approximately 1 to 900 nm, particularly preferably ranging from approximately 10 to 800 nm, and more particularly preferably ranging from 20 at approximately 600 nm, it being understood that [the D50 of the first thermally conductive inorganic filler minus (-) the D50 of the second thermally conductive inorganic filler conductive] is greater than or equal to 100 nm, and preferably greater than or equal to 200 nm, and particularly preferably greater than or equal to 300 nm.

In this first embodiment, the particles of first and second thermally conductive inorganic fillers are preferably in the form of aggregates of particles and/or individual particles.

In this first embodiment, the first thermally conductive inorganic filler is preferably chosen from metal oxides, and particularly preferably from aluminum oxides, and the second thermally conductive inorganic filler is preferably chosen from aluminum oxides. metals, and particularly preferably from aluminum oxides and magnesium oxides.

According to a second embodiment, the first and second thermally conductive inorganic fillers have different shapes (f1, f2), in particular chosen from spherical shapes, aggregates of particles (e.g. of various non-elongated shapes), elongated (e.g. under the shape of fibers, rods, or threads), flat, and elongated and flat.

In this second embodiment:

- the first thermally conductive inorganic filler can be in the form of spherical particles or in the form of aggregates of particles; and

- the second thermally conductive inorganic filler can be in the form of fibers, in particular fibers with a length of between 200 and 2000 nm, a width of between 10 and 30 nm and a thickness of between 5 and 10 nm.

A particle can be defined by a length L and two dimensions DA and DB orthogonal to the length L, with L > (DA, DB). L generally denotes the largest dimension of the particle. The term “shape factor” means the ratio between the length L of a particle and one of the two orthogonal dimensions (DA, DB) of said particle. In the case of a spherical particle, L = DA = DB = diameter of the sphere. In the case of an elongated particle, L” (DA, DB). In the case of a flat particle, DA” (L, DB) OR DB “(L, DA).

In this second embodiment:

- the first thermally conductive inorganic filler is more particularly in the form of particles having a form factor Li/ DAI OR LI/ DBI of at most 3, and particularly preferably ranging from 1 to 2; and

- the second thermally conductive inorganic filler is more particularly in the form of particles having a shape factor L2/DA2 OR L2/DB2 of at least 4, and particularly preferably ranging from 5 to 200.

In this second embodiment, the first thermally conductive inorganic filler is preferably chosen from metal oxides, and particularly preferably from aluminum oxides, and the second thermally conductive inorganic filler is preferably chosen from silicates, and particularly preferably from magnesium silicates.

According to a third embodiment, the first and second thermally conductive inorganic fillers have different specific surfaces (s1, s2).

In this third embodiment:

- the first thermally conductive inorganic filler preferably has a specific surface area according to the BET method ranging from approximately 1 to 300 m ² /g, in a particularly preferred manner ranging from approximately 3 to 200 m ² /g, and more particularly preferably ranging from approximately 5 to 50 m ² /g; and

- the second thermally conductive inorganic filler preferably has a specific surface area according to the BET method ranging from approximately 80 to 500 m ² /g, in a particularly preferred manner ranging from approximately 100 to 450 m ² /g, and more particularly preferably ranging from approximately 150 to 400 m ² /g, it being understood that [the specific surface area of the second thermally conductive inorganic filler minus (-) the specific surface area of the first thermally conductive inorganic filler] is greater than or equal to 100 m ² /g, and preferably greater than or equal to 150 m ² /g, and particularly preferably greater than or equal to 200 m ² /g.

In this third embodiment, the first thermally conductive inorganic filler is preferably chosen from metal oxides, and particularly preferably from aluminum oxides and magnesium oxides, and the second thermally conductive inorganic filler is preferably chosen from silicates, and particularly preferably from magnesium and aluminum silicates. The first, second and third embodiments as defined below can be combined with each other. In other words, the first and second thermally conductive inorganic fillers can have their size, their shape and their specific surface which differ.

The first and second thermally conductive inorganic fillers can be of the same chemical composition or of different chemical composition. The chemical composition of the filler can condition its morphology.

The first thermally conductive inorganic filler/second thermally conductive inorganic filler mass ratio preferably ranges from 0.1 to 9 and particularly preferably from 0.25 to 4.

In an exemplary embodiment according to the invention,

- the first thermally conductive inorganic filler is chosen from metal oxides, such as alumina and silica, in particular calcined alumina. It is in the form of spherical particles, or in the form of aggregates of particles, in particular in the form of aggregates of particles. It has an average particle size D50 of between 200 and 600 nm, in particular of between 300 and 500 nm. It has a specific surface according to the BET method of less than 100 m ² /g, in particular between 1 and 50 m ² /g, for example between 3 and 25 m ² /g, preferably between 5 and 10 m ² / g; and

- the second thermally conductive inorganic filler is chosen from silicates, such as aluminum, calcium or magnesium silicates, and preferably aluminum or magnesium silicates, in particular hydrated magnesium silicates. It is in the form of elongated particles, in particular fibers, these fibers having in particular a length of between 200 and 2000 nm, a width of between 10 and 30 nm and a thickness of between 5 and 10 nm. It has a specific surface according to the BET method greater than 100 m ² /g, in particular between 150 and 450 m ² /g, for example between 200 and 400 m ² /g, preferably between 250 and 350 m ² / g.

The dielectric liquid

The dielectric liquid improves the inorganic filler/polypropylene-based thermoplastic polymer material interface. The presence of the dielectric liquid thus makes it possible to obtain better dielectric properties (ie better insulation electric), and in particular a better dielectric strength of the layer obtained from the polymer composition. It can also make it possible to improve the mechanical properties and/or the resistance to aging of said layer.

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 in a particularly preferred manner from 3 to 12% by weight approximately, relative to the weight total of the polymer composition.

The dielectric liquid can comprise at least one liquid chosen from a mineral oil (e.g. naphthenic oil, paraffinic oil or aromatic oil), a vegetable oil (e.g. soybean oil, linseed oil, rapeseed oil, corn oil or castor oil ), a synthetic oil such as an aromatic hydrocarbon (alkylbenzene, alkylnaphthalene, alkylbiphenyl, alkydiarylethylene, etc.), a silicone oil, an ether-oxide, an organic ester, and an aliphatic hydrocarbon, and preferably from a mineral oil (e.g. naphthenic oil, paraffinic oil or aromatic oil), a vegetable oil (e.g. soybean oil, linseed oil, rapeseed oil, corn oil or castor oil), a synthetic oil such as an aromatic hydrocarbon ( alkylbenzene, alkylnaphthalene, alkylbiphenyl, alkydiarylethylene, etc.), a silicone oil, and an aliphatic hydrocarbon.

The liquid composing the dielectric liquid is generally liquid at approximately 20-25°C.

The dielectric liquid may comprise at least approximately 70% by weight of the liquid making up the dielectric liquid, and preferably at least 80% by weight approximately of the liquid making up the dielectric liquid, relative to the total weight of the dielectric liquid.

Mineral oil is preferred as the liquid composing the dielectric liquid.

The dielectric liquid particularly preferably comprises at least one mineral oil, and at least one polar compound of the benzophenone or acetophenone type, or one of their derivatives.

The mineral oil is preferably chosen from naphthenic oils and paraffinic oils.

Mineral oil is obtained from the refining of crude oil. According to a particularly preferred embodiment of the invention, the mineral oil comprises a paraffinic carbon (Cp) content ranging from approximately 45 to 65 atomic %, a naphthenic carbon (Cn) content ranging from approximately 35 to 55 atomic and an aromatic carbon (Ca) content ranging from approximately 0.5 to 10 atomic %.

In a particular embodiment, the polar compound of benzophenone, acetophenone type or one of their derivatives represents at least 2.5% by weight approximately, preferably at least 3.5% by weight approximately, and in a particularly preferred manner at least 4% by weight approximately, relative to the total weight of the dielectric liquid. The polar compound makes it possible to improve the dielectric strength of the electrically insulating layer.

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

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

One or more additives may form part of the constituents of the dielectric liquid or of the polymer composition.

Additives may be selected from processing aids such as lubricants, compatibilizers, coupling agents, antioxidants, anti-UV agents, antioxidants, anti-copper agents, anti-treeing agents of water, pigments, and a mixture thereof.

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 additives, relative to the total weight of the thermoplastic polymer material based on polypropylene. The antioxidants make it possible to protect the polymer composition from the thermal stresses generated during the stages of manufacture of the cable or operation of the cable.

The antioxidants are preferably selected from hindered phenols, thioesters, sulfur-based antioxidants, phosphorus-based antioxidants, amine-type antioxidants, and a mixture thereof.

Examples of hindered phenols include 1,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine (Irganox® MD 1024), pentaerythritol tetrakis(3-(3, 5-di-te/'t-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-te/'t-butyl-4-hydroxybenzyl)benzene (Irganox® 1330), 4,6-bis(octylthiomethyl) -o-cresol (Irgastab® KV10 or Irganox® 1520), 2,2'-thiobis(6-te/'t-butyl-4-methylphenol) (Irganox® 1081), 2,2'-thiodiethylene bis[ 3-(3,5-di-te/ -butyl- 4-hydroxyphenyl) propionate] (Irganox® 1035), tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate (Irganox® 3114), 2,2'-oxamido-bis(ethyl-3(3,5-di-te/'t-butyl-4-hydroxyphenyl)propionate) (Naugard XL-1), or 2,2'-methylenebis(6 -te/'t-butyl-4-methylphenol).

Examples of sulfur-based antioxidants include thioethers such as didodecyl-3,3'-thiodipropionate (Irganox® PS800), distearyl thiodipropionate or dioctadecyl-3,3'-thiodipropionate (Irganox® PS802), bis[2-methyl-4-{3-n-alkyl (C12 or C14) thiopropionyloxy}-5-te/'t-butylphenyl]sulphide, thiobis-[2-te/7-butyl-5 - methyl-4,1-phenylene] bis [3-(dodecylthio)propionate], or 4,6-bis(octylthiomethyl)-o-cresol (Irganox® 1520 or Irgastab® KV10).

Examples of phosphorus-based antioxidants include tris(2,4-di-te/7-butyl-phenyl)phosphite (Irgafos® 168) or bis(2,4-di-te /7-butylphenyl)pentaerythritol diphosphite (Ultranox® 626).

As examples of antioxidants of the amine type, mention may be made of phenylene diamines (eg paraphenylene diamines such as 1 PPD or 6PPD), diphenylamine styrene, diphenylamines, 4-(1-methyl-1-phenylethyl)- N-[4-(1-methyl-1-phenylethyl)phenyl]aniline (Naugard 445), mercapto benzimidazoles, or polymerized 2,2,4-trimethyl-1,2 dihydroquinoline (TMQ). As examples of mixtures of antioxidants which can be used according to the invention, mention may be made of Irganox B 225 which comprises an equimolar mixture of Irgafos 168 and Irganox 1010 as described above.

The antioxidant can represent from 3% to 20% by weight approximately, and preferably from 5% to 15% by weight approximately, relative to the total weight of the dielectric liquid.

The thermoplastic polymer material based on polypropylene

The polypropylene-based thermoplastic polymer material may comprise a propylene Pi homopolymer or copolymer, and preferably a propylene Pi copolymer.

The propylene homopolymer Pi preferably has an elastic modulus ranging from approximately 1250 to 1600 MPa.

In the present invention, the elastic modulus or Young's modulus of a polymer (known under the anglicism "Tensile Modulus") is well known to those skilled in the art, and can be easily determined according to the ISO 527-1 standard. , -2 (2012). The ISO 527 standard presents a first part, denoted “ISO 527-1”, and a second part, denoted “ISO 527-2” specifying the test conditions relating to the general principles of the first part of the ISO 527 standard.

The propylene homopolymer Pi can represent at least 10% by weight, and preferably from 15 to 30% by weight, relative to the total weight of the thermoplastic polymer material based on polypropylene.

As examples of copolymers of propylene Pi, mention may be made of copolymers of propylene and olefin, the olefin being chosen in particular from ethylene and an olefin ai different from propylene.

The ethylene or the olefin ai different from the propylene of the copolymer of propylene and olefin preferably represents at most 45% by mole approximately, in a particularly preferred manner at most 40% by mole approximately, and more particularly preferably at most 35% by mole, relative to the total number of moles of copolymer of propylene and olefin.

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

The olefin ai different from propylene can correspond to the formula CH2=CH-R ¹ , in which R ¹ is a linear or branched alkyl group having from 2 to 12 carbon atoms, chosen in particular from the following olefins: 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and a mixture thereof.

Propylene and ethylene copolymers are preferred as the propylene Pi copolymer.

The propylene copolymer P1 can be a homophasic propylene copolymer or a heterophasic propylene copolymer.

In the invention, the homophasic propylene copolymer Pi preferably has an elastic modulus ranging from approximately 600 to 1200 MPa, and in a particularly preferred manner ranging from approximately 800 to 1100 MPa.

The homophasic propylene copolymer Pi is advantageously a random copolymer of propylene Pi.

The ethylene or the olefin ai different from the propylene of the homophasic propylene copolymer Pi preferably represents at most 20% by mol approximately, in a particularly preferred manner at most 15% by mol approximately, and more particularly preferably at most 10% in mole approximately, relative to the total number of moles of the homophasic propylene copolymer Pi.

The ethylene or the olefin ai different from the propylene of the homophasic propylene copolymer Pi can represent at least approximately 1% by mole, relative to the total number of moles of homophasic propylene copolymer Pi.

By way of example of a random copolymer of propylene Pi, mention may be made of 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.

The heterophasic (or heterophase) propylene copolymer Pi may comprise a thermoplastic phase of the propylene type and a thermoplastic elastomer phase of the copolymer type of ethylene and an olefin ci2. The olefin O12 of the thermoplastic elastomer phase of the heterophasic propylene copolymer Pi can be propylene.

The thermoplastic elastomer phase of the heterophasic propylene copolymer Pi can 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 Pi.

The heterophasic propylene copolymer Pi preferably has an elastic modulus ranging from approximately 50 to 1200 MPa, and in a particularly preferred manner: either an elastic modulus ranging from approximately 50 to 550 MPa, and more particularly preferably ranging from 50 to 300 MPa about ; or an elastic modulus ranging from approximately 600 to 1200 MPa, and more particularly preferably ranging from approximately 800 to 1200 MPa.

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

The propylene homopolymer or copolymer Pi may have a melting point above approximately 110° C., preferably above approximately 130° C., in a particularly preferred manner above approximately 135° C., and more particularly preferably ranging from 140 to 170°C approximately.

The propylene Pi homopolymer or copolymer can have an enthalpy of fusion ranging from approximately 20 to 100 J/g.

The propylene homopolymer Pi preferably has an enthalpy of fusion ranging from approximately 80 to 90 J/g.

The homophasic propylene copolymer Pi preferably has an enthalpy of fusion ranging from approximately 40 to 90 J/g, and in a particularly preferred manner ranging from 50 to 85 J/g.

The heterophasic propylene copolymer Pi preferably has an enthalpy of fusion ranging from approximately 20 to 50 J/g. The propylene Pi homopolymer or copolymer can have a melt 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.

The homophasic propylene copolymer Pi preferably has a melt 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.

The heterophasic propylene copolymer Pi can have a melt 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.

The propylene Pi homopolymer or copolymer can have a density ranging from 0.81 to 0.92 g/cm ³ approximately; in particular determined according to the ISO 1183A standard (at a temperature of 23°C).

The propylene copolymer Pi preferably has a density ranging from 0.85 to 0.91 g/cm ³ , and in a particularly preferred manner ranging from 0.87 to 0.91 g/cm ³ ; in particular determined according to the ISO 1183A standard (at a temperature of 23°C).

The polypropylene-based thermoplastic polymer material may comprise several different propylene Pi copolymers, in particular two different propylene Pi copolymers, said propylene Pi copolymers being as defined above.

In particular, the polypropylene-based thermoplastic polymer material may comprise a homophasic propylene copolymer (as the first propylene Pi copolymer) and a heterophasic propylene copolymer (as the second propylene Pi copolymer), or two propylene copolymers different heterophasic compounds, and preferably a homophasic propylene copolymer and a heterophasic propylene copolymer.

When the polypropylene-based thermoplastic polymer material 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. According to one embodiment of the invention, the two heterophasic propylene copolymers have a different elastic modulus. Preferably, the polypropylene-based thermoplastic polymer material comprises a first heterophasic propylene copolymer having an elastic modulus ranging from approximately 50 to 550 MPa, and in a particularly preferred manner ranging from approximately 50 to 300 MPa; and a second heterophasic propylene copolymer having an elastic modulus ranging from approximately 600 to 1200 MPa, and more particularly preferably ranging from approximately 800 to 1200 MPa.

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

These combinations of propylene copolymers Pi can advantageously make it possible to improve the mechanical properties of the electrically insulating layer. In particular, the combination makes it possible to obtain optimized mechanical properties of the electrically insulating layer, in particular in terms of elongation at break, and flexibility; and/or makes it possible to form a more homogeneous electrically insulating layer, in particular promotes the dispersion of the dielectric liquid in the thermoplastic polymer material based on polypropylene of said electrically insulating layer.

According to a preferred embodiment of the invention, the propylene Pi copolymer or the propylene Pi copolymers when there are several of them, represent(s) at least 50% by weight approximately, preferably from 55 to 90% by weight. weight approximately, and particularly preferably from 60 to 90% by weight approximately, relative to the total weight of the thermoplastic polymer material based on polypropylene.

The homophasic propylene copolymer Pi can represent at least 20% by weight, and preferably from 30 to 70% by weight, relative to the total weight of the thermoplastic polymer material based on polypropylene.

The heterophasic propylene copolymer Pi or the heterophasic propylene copolymers Pi when there are several of them, can represent from 5 to 95% by weight approximately, preferably from 50 to 90% by weight approximately, and in such a way particularly preferred from 60 to 80% by weight approximately, relative to the total weight of the thermoplastic polymer material based on polypropylene. The polypropylene-based thermoplastic polymer material may further comprise a P2 olefin homopolymer or copolymer.

Said P2 olefin homopolymer or copolymer is preferably different from said P2 propylene homopolymer or copolymer.

The olefin of the olefin copolymer P2 can be chosen from ethylene and an as olefin corresponding to the formula CH2=CH-R ² , in which R ² is a linear or branched alkyl group having from 1 to 12 carbon atoms .

The olefin as 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 one of their mixtures.

The ace olefin of the propylene, 1-hexene or 1-octene type is particularly preferred.

The combination of polymers Pi and P2 makes it possible to obtain a thermoplastic polymer material with good mechanical properties, in particular in terms of elastic modulus, and electrical properties.

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

The ethylene polymer preferably comprises at least about 80% by mole of ethylene, more preferably at least about 90% by mole of ethylene, and more particularly preferably at least about 95% by mole of ethylene. , based on the total number of moles of the ethylene polymer.

According to a preferred embodiment of the invention, the ethylene polymer is a low density polyethylene, a linear low density polyethylene, a medium density polyethylene, or a high density polyethylene, and preferably a high density polyethylene; in particular according to the ISO 1183A standard (at a temperature of 23°C).

The ethylene polymer preferably has an elastic modulus of at least 400 MPa, and particularly preferably at least 500 MPa.

In the present invention, the elastic modulus or Young's modulus of a polymer (known under the anglicism "Tensile Modulus") is well known to those skilled in the art, and can be easily determined according to the ISO 527-1 standard. , -2 (2012). Standard ISO 527 presents a first part, denoted “ISO 527-1”, and a second part, denoted “ISO 527-2” specifying the test conditions relating to the general principles of the first part of the ISO 527 standard.

In the present invention, the expression “low density” means having a density ranging from 0.91 to 0.925 g/cm ³ approximately, said density being measured according to the ISO 1183A standard (at a temperature of 23° C.).

In the present invention, the expression “medium density” means having a density ranging from 0.926 to 0.940 g/cm ³ approximately, said density being measured according to the ISO 1183A standard (at a temperature of 23° C.).

In the present invention, the expression “high density” means having a density ranging from 0.941 to 0.965 g/cm ³ , said density being measured according to the ISO 1183A standard (at a temperature of 23° C.).

According to a preferred embodiment of the invention, the olefin homopolymer or copolymer P2 represents from 5 to 50% by weight approximately, and in a particularly preferred manner from 10 to 40% by weight approximately, relative to the total weight of the thermoplastic polymer material based on polypropylene.

According to a particularly preferred embodiment of the invention, the thermoplastic polymer material based on polypropylene comprises two copolymers of propylene Pi such as a homophasic propylene copolymer and a heterophasic propylene copolymer or two different heterophasic propylene copolymers; and a P2 olefin homopolymer or copolymer such as an ethylene polymer. This combination of propylene copolymers Pi and an olefin homopolymer or copolymer P2 makes it possible to further improve the mechanical properties of the electrically insulating layer, while guaranteeing good thermal conductivity.

The thermoplastic polymer material of the polymer composition of the electrically insulating layer of the cable of the invention is preferably heterophase (ie it comprises several phases). The presence of several phases generally results 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. The polymer composition of the electrically insulating layer of the invention is a thermoplastic polymer composition. It is therefore not labial reticulum.

In particular, the polymer composition does not include crosslinking agents, silane-type coupling agents, peroxides and/or additives which allow crosslinking. In fact, such agents degrade the thermoplastic polymer material based on polypropylene.

The polymer composition is preferably recyclable.

The thermoplastic polymer material based on polypropylene can represent at least 50% by weight approximately, preferably at least 70% by weight approximately, and in a particularly preferred manner at least 80% by weight approximately, relative to the total weight of the polymer composition .

The polymer composition preferably does not comprise any other polymer(s) than those included in the polypropylene-based thermoplastic polymer material.

The thermoplastic polymer material based on polypropylene preferably comprises at least 50% by weight approximately, preferably at least 70% by weight approximately, and in a particularly preferred manner at least 80% by weight approximately, of propylene polymer(s) per relative to the total weight of the polypropylene-based thermoplastic polymer material.

The electrically insulating layer

The electrically insulating layer of the cable of the invention is a non-crosslinked layer or in other words a thermoplastic layer.

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

In one embodiment of the invention, the electrically insulating layer, preferably non-crosslinked, has a thermal conductivity of at least 0.30 W/mK at 40° C., preferably of at least 0.31 W/ mK at 40°C, particularly preferably at least 0.32 W/mK at 40°C, more preferably particularly preferably at least 0.33 W/mK at 40°C, even more preferably at least 0.34 W/mK at 40°C, and even more preferably at least 0 .35 W/mK at 40°C.

In a particular embodiment, the electrically insulating layer, preferably non-crosslinked, has a tensile strength (RT) of at least 8.5 MPa, preferably of at least approximately 10 MPa, and particularly preferably of at least approximately 15 MPa, before aging (according to standard CEI 20-86).

In a particular embodiment, the electrically insulating layer, preferably non-crosslinked, has an elongation at break (ER) of at least approximately 250%, preferably of at least approximately 300%, and particularly preferably of at least approximately 350%, before aging (according to standard CEI 20-86).

In a particular embodiment, the electrically insulating layer, preferably non-crosslinked, has a tensile strength (RT) of at least 8.5 MPa, preferably of at least approximately 10 MPa, and particularly preferably of at least approximately 15 MPa, after aging (according to standard CEI 20-86.

In a particular embodiment, the electrically insulating layer, preferably non-crosslinked, has an elongation at break (ER) of at least approximately 250%, preferably of at least approximately 300%, and particularly preferably of at least approximately 350%, after aging (according to standard CEI 20-86).

The tensile strength (RT) and the elongation at break (ER) (before or after aging) can be carried out according to Standard NF EN 60811-1-1, in particular using a device marketed under the reference 3345 by the company Instron.

Aging is generally carried out at 135°C for 240 hours (or 10 days).

The electrically insulating layer of the cable of the invention is preferably a recyclable layer.

The electrically insulating layer of the invention may be an extruded layer, in particular by methods well known to those skilled in the art. The electrically insulating layer has a variable thickness depending on the type of cable envisaged. In particular, when the cable in accordance with the invention is a medium voltage cable, the thickness of the electrically insulating layer is typically from 4 to 5.5 mm approximately, and more particularly from 4.5 mm approximately. When the cable in accordance with the invention is a high voltage cable, the thickness of the electrically insulating layer typically varies from 17 to 18 mm (for voltages of the order of approximately 150 kV) and to go up to thicknesses ranging approximately 20 to 25 mm for voltages above 150 kV (high voltage cables). The aforementioned thicknesses depend on the size of the elongated electrically conductive element.

In the present invention, the term "electrically insulating layer" means a layer whose electrical conductivity can be at most 1.10 ^-8 S/m (siemens per meter), preferably at most 1.10' ⁹ S/m, and particularly preferably at most ^1.10'1 ° S/m, measured at approximately 25° C. in direct current.

The electrically insulating layer of the invention may comprise at least the thermoplastic polymer material based on polypropylene, at least the first thermally conductive inorganic filler, at least the second thermally conductive inorganic filler, and the dielectric liquid, the aforementioned ingredients being such that defined in the invention.

The proportions of the various ingredients in the electrically insulating layer may be identical to those as described in the invention for these same ingredients in the polymer composition.

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

The cable

The electrically insulating layer of the invention may surround the elongated electrically conductive element.

The elongated electrically conductive element is preferably positioned at the center of the cable. The elongated electrically conductive element can 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.

The elongated electrically conductive member may be aluminum, aluminum alloy, copper, copper alloy, or a combination thereof.

According to a preferred embodiment of the invention, the electric cable comprises:

- at least one semiconductor layer surrounding the elongated electrically conductive element, and

- an electrically insulating layer as defined in the invention.

The electrically insulating layer more particularly has an electrical conductivity lower than that of the semiconducting layer. More particularly, the electrical conductivity of the semiconductor layer can 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 in a particularly preferably at least 1000 times greater than the electrical conductivity of the electrically insulating layer.

The semiconductor layer may surround the electrically insulating layer. The semiconductor layer can then be an outer semiconductor layer.

The electrically insulating layer may surround the semiconductor layer. The semiconductor layer can then be an internal semiconductor layer.

The semiconductor layer is preferably an inner semiconductor layer.

The electrical cable of the invention may further comprise another semi-conducting layer.

Thus, in this embodiment, the cable of the invention may comprise:

- at least one elongated electrically conductive element, preferably positioned in the center of the cable,

- a first semiconductor layer surrounding the elongated electrically conductive element,

- an electrically insulating layer surrounding the first semiconductor layer, and

- a second semiconductor layer surrounding the layer electrically insulating, the electrically insulating layer being as defined in the invention.

In the present invention, the term "semiconducting layer" means a layer whose electrical conductivity can be strictly greater than 1.10 ^-8 S/m (siemens per meter), preferably at least 1.10' ³ S/m, and preferably may be less than 1×10 ³ S/m, measured at 25° C. in direct current.

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 semiconductor layer is in direct physical contact with the electrically insulating layer.

The first semiconductor layer (respectively the second semiconductor layer) is preferably obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene as defined in the invention, and optionally at least one electrically conductive load.

The electrically conductive filler is preferably an amount sufficient for the layer to be semiconductive.

Preferably, the polymer composition at least 6% by weight approximately of electrically conductive filler, preferably at least 10% by weight approximately of electrically conductive filler, preferably at least 15% by weight approximately of electrically conductive filler, and even more preferably at least least 25% by weight of electrically conductive filler, relative to the total weight of the polymer composition.

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

The electrically conductive filler may be carbon black. The first semiconductor layer (respectively the second semiconductor layer) is preferably a thermoplastic layer or an uncrosslinked layer.

The cable may further comprise an outer protective sheath surrounding the electrically insulating layer (or the second semi-conducting layer if it exists).

The outer protective sheath may be in direct physical contact with the electrically insulating layer (or the second semi-conducting layer if it exists).

The outer protective sheath may be an electrically insulating sheath.

The electrical cable may further comprise an electrical screen (e.g. metal) surrounding the second semi-conducting layer. In this case, the electrically insulating sheath surrounds said electrical shield and the electrical shield is between the electrically insulating sheath and the second semi-conducting layer.

This metallic screen can be a so-called "wired" screen composed of a set of copper or aluminum conductors arranged around and along the second semi-conducting layer, a so-called "ribboned" screen composed of one or more ribbons metal conductors in copper or aluminum possibly placed in a helix around the second semi-conductive layer or a metal conductive strip in aluminum placed longitudinally around the second semi-conductive layer and sealed with glue in the areas of overlapping portions of said tape, or of a so-called "sealed" screen of the metal tube type optionally composed of lead or lead alloy and surrounding the second semi-conducting layer. This last type of screen makes it possible in particular to act as a barrier to humidity which tends to penetrate the electrical cable in the radial direction.

The metal screen of the electric cable of the invention may comprise a so-called "wired" screen and a so-called "watertight" screen or a so-called "wired" screen and a so-called "taped" screen.

All types of metal screens can play the role of earthing the electric cable and can thus carry fault currents, for example in the event of a short circuit in the network concerned. Other layers, such as layers that swell in the presence of humidity, can be added between the second semi-conducting layer and the metal screen, these layers making it possible to ensure the longitudinal watertightness of the electric cable.

Brief description of the drawings

[Fig. 1] Figure 1 shows a cable according to the invention.

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

In Figure 1, the medium or high voltage electric cable 1 in accordance with the invention, illustrated in Figure 1, comprises a central elongated electrically conductive element 2, in particular made of copper or aluminum. The electrical cable 1 further comprises several layers disposed successively and coaxially around this central elongated electrically conductive element 2, namely: a first semi-conductive layer 3 called "internal semi-conductive layer", an electrically insulating layer 4, a second semi-conducting layer 5 called "external semi-conducting layer", a metal shield 6 for grounding and/or protection, and an outer protective sheath 7.

The electrically insulating layer 4 is a non-crosslinked extruded layer, obtained from the polymer composition as defined in the invention.

Semiconductor layers 3 and 5 are thermoplastic extruded layers (i.e. non-crosslinked).

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.

Example

A layer in accordance with the invention, ie obtained from a polymer composition comprising at least one thermoplastic polymer material based on polypropylene, at least one dielectric liquid, at least one first filler thermally conductive inorganic filler and at least one second thermally conductive inorganic filler has been prepared.

Table 1 below collates the amounts of the compounds present in the polymer composition in accordance with the invention which are expressed in percentages by weight, relative to the total weight of the polymer composition.

[Tables 1]

TABLE 1

The origin of the compounds in Table 1 is as follows:

- Random propylene copolymer marketed by the company Total Petrochemicals under the reference PPR3221;

- Heterophase propylene copolymer marketed by the company Basell Polyolefins under the reference Adflex® Q 200 F;

- High density polyethylene sold under the trade name Eltex®

A4009 MFN1325 by the company Ineos and whose density is 0.960 g/cm ³ according to standard ISO 1183A at a temperature of 23° C. (MFI=0.9);

- First thermally conductive inorganic filler: calcined alumina sold under the trade name Timal 17 by the company llnivar having an average particle size D50 of 400 nm, a specific surface according to the BET method of 8 m ² /g, and being in the form of aggregates of particles;

- Second thermally conductive inorganic filler: sepiolite (hydrated magnesium silicate) sold under the trade name Pangel S9 by the company Toisa Advanced Materials having a fibrous structure (acicular) and therefore an elongated shape (fibers of length between 200 and 2000 nm, with a width of between 10 and 30 nm and a thickness of between 5 and 10 nm), and having a specific surface according to the BET method of 300 m ² /g;

- Antioxidant marketed by Ciba under the reference Irganox® B 225 comprising an equimolar mixture of Irgafos® 168 and Irganox® 1010; and

- Dielectric liquid comprising 95% by weight of an oil marketed by Nynas under the reference BNS 28, and 5% by weight of benzophenone.

Preparation of the uncrosslinked layer

The following constituents: mineral oil, antioxidant and benzophenone of the polymer composition referenced in Table 1, are measured out and mixed with stirring at approximately 75° C., in order to form a dielectric liquid.

The dielectric liquid is then mixed with the following constituents: heterophase propylene copolymer, random propylene copolymer, high-density polyethylene of the polymer composition referenced in Table 1, in a container. Then, the resulting mixture, the first thermally conductive inorganic filler and the second inorganic filler are mixed using a twin screw extruder (“Berstorff twin screw extruder”) at a temperature of approximately 145 to 180° C., then melted at approximately 200°C (screw speed: 80 rpm).

The resulting homogenized and molten mixture is then put into the form of granules.

The granules were then hot pressed to form a layer.

Polymer composition 11 and polymer composition I2 were thus prepared in the form of an 8 mm thick layer to perform the thermal conductivity measurements.

The same process is used to form the comparative polymer compositions

C1 to C3. The thermal conductivity tests were carried out on the materials according to the method well known under the anglicism “Transient Plane Source or TPS” and using a device marketed under the reference HOT DISK TPS 2500S by the company THERMOCONCEPT. The results corresponding to each of these tests are reported in Table 2 below:

[Tables 2]

TABLE 2

All of these results show that the incorporation of two thermally conductive inorganic fillers of different morphologies as defined in the invention in a polypropylene matrix improves the thermal conductivity properties.

Claims

[Claim 1] Electric cable comprising at least one elongated electrically conductive element and at least one electrically insulating layer obtained from a polymer composition, characterized in that the polymer composition comprises at least one thermoplastic polymer material based on polypropylene, at least one dielectric liquid, at least one first thermally conductive inorganic filler having a morphology M1, and at least one second thermally conductive inorganic filler having a morphology M2 different from the morphology M1 of the first thermally conductive inorganic filler.

[Claim 2] Electric cable according to claim 1, characterized in that the first inorganic filler represents at most 40% by weight, relative to the total weight of the polymer composition, and the second inorganic filler represents at most 40% by weight, relative to the total weight of the polymer composition.

[Claim 3] Electric cable according to Claim 1 or 2, characterized in that the first inorganic filler represents at least 1% by weight, relative to the total weight of the polymer composition, and the second inorganic filler represents at least 1% by weight, relative to the total weight of the polymer composition.

[Claim 4] Electric cable according to any one of the preceding claims, characterized in that the first thermally conductive inorganic filler is chosen from silicates, boron nitride, carbonates, and metal oxides, and the second inorganic filler thermally conductive is chosen from silicates, boron nitride, carbonates, and metal oxides.

[Claim 5] Electric cable according to any one of the preceding claims, characterized in that the second thermally conductive inorganic filler is different from the first thermally conductive inorganic filler, in that the morphology (M1, M2) is represented by at least one of the parameters chosen from among the size (t1, t2), the shape (f1, f2), and the specific surface (s1, s2).

[Claim 6] Electric cable according to any one of the preceding claims, characterized in that the first thermally conductive inorganic filler is in the form of particles having a size distribution D50 of at most 1.5 μm, and the second filler thermally conductive inorganic filler is in the form of particles having a D50 size distribution ranging from 1 to 900 nm, provided that [the D50 of the first thermally conductive inorganic filler minus the D50 of the second thermally conductive inorganic filler] is greater than or equal at 100nm.

[Claim 7] Electric cable according to any one of the preceding claims, characterized in that the first and second thermally conductive inorganic fillers have the same chemical composition.

[Claim 8] Electric cable according to any one of the preceding claims, characterized in that the first thermally conductive inorganic filler has a specific surface area according to the BET method ranging from 1 to 300 m ² /g, and the second thermally conductive inorganic filler has a specific surface area according to the BET method ranging from 80 to 500 m ² /g, it being understood that [the specific surface area of the second thermally conductive inorganic filler minus the specific surface area of the first thermally conductive inorganic filler] is greater than or equal to 100 m ² /g.

[Claim 9] Electric cable according to any one of the preceding claims, characterized in that the first and second thermally conductive inorganic fillers have different shapes (f 1 , f2) chosen from spherical shapes, aggregates of particles, elongated, flat , and flat and elongated.

[Claim 10] Electric cable according to any one of the preceding claims, characterized in that the first thermally conductive inorganic filler is in the form of particles having an aspect ratio LI/DAI OR LI/DBI of at most 3, and the second thermally conductive inorganic filler is in the form of particles having an aspect ratio L2/DA2 or L2/DB2 of at least 4, where L1 is the length of the first inorganic filler particles thermally conductive, l_2 the length of the particles of second thermally conductive inorganic filler, (DAI , DBI,) the orthogonal dimensions of the particles of first thermally conductive inorganic filler at the length Li , (DA2, DB2,) the orthogonal dimensions of the particles of second thermally conductive inorganic filler at length l_2.

[Claim 11] Electric cable according to any one of the preceding claims, characterized in that the first thermally conductive inorganic filler/second thermally conductive inorganic filler mass ratio ranges from 0.1 to 9.

[Claim 12] Electric cable according to any one of the preceding claims, characterized in that the thermoplastic polymer material based on polypropylene comprises a copolymer of propylene and ethylene Pi .

[Claim 13] Electric cable according to any one of the preceding claims, characterized in that the thermoplastic polymer material based on polypropylene comprises a propylene copolymer Pi chosen from a homophasic propylene copolymer and a heterophasic propylene copolymer.

[Claim 14] Electric cable according to any one of the preceding claims, characterized in that the electrically insulating layer is a non-crosslinked layer.

[Claim 15] Electric cable according to any one of the preceding claims, characterized in that it comprises:

- at least one semiconductor layer (3, 5) surrounding the elongated electrically conductive element (2), and

- at least one electrically insulating layer (4) surrounding the elongated electrically conductive element (2), the electrically insulating layer (4) being as defined in any one of the preceding claims.