EP3642275A1

EP3642275A1 - Polymer composition comprising a polar dielectric liquid

Info

Publication number: EP3642275A1
Application number: EP18755504.0A
Authority: EP
Inventors: Christelle Mazel; Gabriele Perego; Dimitri Charrier; Daphn MERLE
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2017-06-21
Filing date: 2018-06-20
Publication date: 2020-04-29
Also published as: FR3068038B1; KR102267280B1; KR20200010347A; BR112019027039A2; FR3068038A1; WO2018234697A1

Abstract

The invention relates to a polymer composition comprising at least one thermoplastic polymer material, characterized in that the composition also comprises at least one polar dielectric liquid, and at least one nanofiller.

Description

COM POSI Tl ON POLYMER ELECTRICAL QU A T E N T IO N

POLAI RE

The invention relates to a polymer composition comprising at least one thermoplastic polymer material, at least one polar dielectric liquid and at least one nano-filler, a method for preparing said polymer composition, a cable comprising at least one electrically insulating layer obtained from of said polymeric composition, and a method of preparing said cable.

The invention typically, but not exclusively, applies to electrical cables intended for the transmission of energy, in particular to medium-voltage (in particular 6 to 45-60 kV) or high-voltage (in particular greater than 60 kV) energy cables, and up to 400 kV), whether DC or AC, in the fields of overhead, underwater, terrestrial, or aeronautical transmission.

A medium or high voltage power transmission cable generally includes from the inside to the outside:

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

an inner semiconductor layer surrounding said elongated electrically conductive element;

an electrically insulating layer surrounding said internal semiconducting layer;

an outer semiconducting layer surrounding said insulating layer; and

optionally an electrically insulating protective sheath surrounding said outer semiconductor layer.

In particular, the electrically insulating layer may be a polymer layer based on a crosslinked polyolefin such as a crosslinked polyethylene (XLPE) or a crosslinked elastomer of ethylene-propylene or ethylene-propylene-diene. Crosslinking is usually carried out during the step of extruding the polymer composition around the elongated electrically conductive member. The use of a crosslinked polyolefin makes it possible to provide a layer having satisfactory electrical and mechanical properties and to lead to a cable that can operate at a temperature greater than 70 ° C., or even equal to 90 ° C. However, several problems are encountered. On the one hand, crosslinked materials can not be recycled. On the other hand, crosslinking (vulcanization) to produce a homogeneous layer requires specific reaction conditions (eg in terms of time and temperature) which reduce the speed of manufacture of the cable and increase its cost of production. Finally, the crosslinking can sometimes start prematurely in the extruder and / or the extruder head, inducing degradation of the quality of the layer obtained, especially its dielectric properties.

Alternatives have therefore been proposed such as a thermoplastic layer of low density polyethylene (LDPE) or high density (HDPE). However, a cable comprising such an electrically insulating layer can not operate at a temperature greater than about 70 ° C for a thermoplastic layer of LDPE and greater than 80 ° C for a thermoplastic layer of HDPE, inducing a limitation of the power that can be transported in said cable and methods of manufacture.

It is also known to make an electrically insulating layer composed of several paper ribbons or a paper-polypropylene composite impregnated with a large amount of dielectric liquid (e.g., oil impregnated paper cable). The dielectric liquid completely fills the voids in the layer and prevents partial discharges and damage to the cable insulation. However, the manufacture of this type of electrically insulating layer is very complex and expensive.

The choice of the dielectric liquid will depend on the intended application (ie the type of electrical equipment) and its compatibility with the solid insulation it is supposed to impregnate and / or with which it forms an intimate mixture. Among the conventional dielectric liquids, mention may be made of oils mineral (eg naphthenic oils, paraffinic oils, aromatic oils or polyaromatic oils), vegetable oils (eg soybean oil, linseed oil, rapeseed oil, corn oil or castor oil) or synthetic oils such as hydrocarbons aromatic (alkylbenzenes, alkylnaphthalenes, alkylbiphenyls, alkydiarylethylenes, etc.), silicone oils, ether-oxides, organic esters or aliphatic hydrocarbons.

In particular, the international application WO 02/03398 A1 describes a cable comprising at least one electrical conductor and at least one extruded electrically insulating layer based on a dielectric liquid in intimate mixture with a thermoplastic polymer material comprising a propylene homopolymer or a copolymer of propylene with at least one olefin comonomer selected from ethylene and an olefin a different from propylene. The dielectric liquid is an aromatic hydrocarbon comprising at least one alkylaryl hydrocarbon having at least two non-condensed aromatic rings (e.g., dibenzyltoluene or a mixture of 85% by weight of monoxylylxylene and 15% by weight of dixylylxylene). International application WO 02/03398 A1 indicates that the dielectric liquid is free of polar compounds in order to absorb a minimal amount of water and to avoid the formation of defects in the insulating layer related to the presence of water vapor during hot extrusion. However, aromatic hydrocarbons (alkylbenzenes, alkylnaphthalenes, alkylbiphenyls, alkydiarylethylenes) have a high cost and generally induce safety and / or environmental problems (e.g. certain aromatic hydrocarbons are considered carcinogenic).

90 to 95% of the market for dielectric liquids is covered by mineral oils because of the low cost of these "natural" products, obtained directly by refining crude oil. The chemical composition of a mineral oil is extremely complex (several thousand different molecules) and can vary widely. The chemical composition of a mineral oil is therefore generally defined by its content of paraffinic carbon (Cp), its content of naphthenic carbon (Cn) and its aromatic carbon content (Ca). Mineral oils can also contain a small percentage of hydrocarbon molecules which in their structure include heteroatoms such as nitrogen, sulfur or oxygen (eg polar compounds). The polar compound content of a mineral oil can be determined according to ASTM D2007-02. However, mineral oils have lower oxidation stability and dielectric strength than aromatic hydrocarbons. Moreover, it is known from the international application WO 2004/066318 A1 that the electrical properties of a cable comprising at least one electrical conductor and at least one extruded electrically insulating layer based on a thermoplastic polymer material intimately mixed with a mineral oil as a dielectric liquid, can be deteriorated by the presence of these polar compounds, especially in terms of dielectric losses.

There is therefore still a need for electrical cables comprising an electrically insulating layer having electrical properties comparable to those obtained with an XLPE crosslinked layer, while guaranteeing good mechanical properties.

Thus, the object of the present invention is to overcome the drawbacks of the prior art and to provide an economical polymer composition comprising materials, in particular recyclable, that can lead to an electrically insulating layer having improved electrical properties, particularly in terms of rigidity. dielectric, while guaranteeing low dielectric losses.

The object of the present invention is also to provide a cable, in particular at medium or high voltage, which can operate at temperatures above 70 ° C and having improved electrical properties, especially in terms of dielectric strength, while ensuring low dielectric losses.

The objects are achieved by the invention which will be described below.

The invention firstly relates to a polymer composition comprising at least one polymer material at least one dielectric liquid polar, and at least one nano-charge.

The combination of a polar dielectric liquid with at least one nano-charge, or in other words a nano-sized charge, makes it possible to obtain an electrically insulating layer of an electric cable having improved dielectric strength while guaranteeing little dielectric losses.

Furthermore, the polymer composition of the invention also makes it possible to increase the operating temperature of a cable at 90 ° C. to 110 ° C.

Finally, the polymer composition of the invention also has a reduced electrical conductivity, making it possible to use it advantageously in an electrically insulating layer of an electric cable, in particular a high-voltage direct current cable, well known under the Anglicism "High Voltage Direct Current" (HVDC).

In the present invention, the term "polar" means a compound comprising positive and negative partial charges, the barycentre of positive partial charges not coinciding with the center of gravity of the negative partial charges. The positive and negative partial charges appear in polar covalent bonds, in particular in covalent bonds between two atoms of different electronegativity, for example covalent bonds between a carbon atom or a hydrogen atom and an atom chosen from an atom. oxygen, nitrogen, sulfur, fluorine, chlorine, bromine, iodine, or phosphorus.

According to a first embodiment, the dielectric liquid may comprise at least 2.5% by weight of polar compounds relative to the total weight of dielectric liquid. Preferably, the dielectric liquid may comprise at least one polar mineral oil having at least 2.5% by weight of polar compounds relative to the total weight of the polar mineral oil.

According to a second embodiment, the dielectric liquid may comprise at least one mineral oil and at least one polar compound of benzophenone type, acetophenone or a derivative thereof. Preferably, the dielectric liquid may comprise at least 2.5% by weight of polar compounds relative to the total weight of dielectric liquid.

According to a third embodiment, the dielectric liquid may comprise at least 2.5% by weight of polar compounds relative to the total weight of dielectric liquid, and the dielectric liquid may further comprise at least one mineral oil and at least one compound polar benzophenone type, acetophenone or a derivative thereof.

In the present invention, the amount of polar compounds in the dielectric liquid can be easily determined according to ASTM D2007-02.

The polymer composition of the invention may thus preferably comprise at least 2.5% by weight of polar compounds relative to the total weight of the polymer composition.

The nano-charge of the invention is a nanoscale charge.

The nano-charge (s) of the invention typically have at least one of their nanoscale dimensions (10 ^-9 meters).

In the present invention, the term "nano-charge" is understood to mean an elementary particle. A set of elementary particles may be an agglomerate or aggregate of elementary particles.

More particularly, the nano-charge (s) of the invention (ie one or more elementary particles) may have at least one of their dimensions of at most 2000 nm (nanometers), preferably at most 1000, preferably at most 800 nm, preferably at most 600 nm, and more preferably at most 400 nm.

In addition, the nano-charge (s) of the invention may have at least one of their dimensions of at least 1 nm, and preferably at least 5 nm.

Preferably, the nano-filler (s) of the invention may have at least one of their dimensions ranging from 1 to 800 nm. Considering several nano-fillers according to the invention, the term "dimension" is understood to mean the number-average dimension of all the nano-charges of a given population, this dimension being conventionally determined by well-known methods of the skilled person.

The size of the nano-fillers according to the invention may for example be determined by microscopy, in particular by scanning electron microscope (SEM) or by transmission electron microscope (TEM).

At least one of the nano-fillers, or more particularly the nano-fillers included in the polymer composition, may have a form factor strictly greater than or equal to 1, and preferably at most 10.

The at least one nano-charge (s) is / are preferably of the spherical type, or in other words it (s) has / have a form factor substantially equal to 1.

In the present invention, the form factor is typically the ratio between the largest dimension of a nano-charge (such as for example the length of a nano-charge when it is of the lamellar or cylindrical type) and the most small dimension of the nano-charge (such as, for example, the thickness of a nano-charge of the lamellar type, or the diameter of a nano-charge of the cylindrical type).

The nano-filler of the invention may preferably have a BET specific surface area of at least 100 m ² / g, preferably at least 120 m ² / g, and preferably at least 150 m ² / g The nano-filler may have a BET specific surface area of at most 1000 m ² / g, and preferably at most 500 m ² / g.

In the present invention, the surface area can be easily determined according to DIN 9277 (2010). The polymer composition of the invention may comprise at most 10.0% by weight of nano-filler, preferably at most 5.0% by weight of nano-filler, and preferably at most 3.0% by weight of nano charge, based on the total weight of the polymer composition.

The polymer composition of the invention may comprise at least

0.2% by weight of nano-filler, preferably at least 0.5% by weight of nano-filler, and preferably at least 1.0% by weight of nano-filler, relative to the total weight of the polymer composition.

The nano-filler of the invention may preferably be a mineral nano-filler which may be chosen from alkaline earth metal carbonates, alkaline earth metal sulfates, metal oxides, metalloid oxides, metal silicates, and siloxanes.

For exemple :

the nano-fillers of alkaline-earth metal carbonates may be nano-fillers of calcium carbonate,

the nano-fillers of alkaline-earth metal sulphates may be nano-fillers of barium sulphate,

the nano-fillers of metal oxides can be nano-fillers of alumina, of zinc oxide, of titanium dioxide,

the nano-fillers of metalloid oxides may be nano-fillers of silicon dioxide (silica), in particular nano-fillers of fumed silica, the expression "fumed silica" being well known under the Anglicism "fumed silica" "

the nano-fillers of metal silicate can be, for example, nano-fillers of aluminum (for example nano-fillers of aluminum silicate and of hydrated magnesium such as montmorillonite),

the nano-fillers of siloxanes may be nano-fillers of silsesquioxanes (for example nano-fillers of Trisilanolphenyl Polyhedral SilSesquioxane (TP-POSS)).

Preferably, the nano-fillers of the invention may be nano-fillers of metal oxides and / or nano-fillers of metalloid oxides.

The nano-charge of the invention can be a charge called "treated" or

" not treated ".

"Treated load" means a surface-treated filler, or in other words, a surface-treated filler. Said surface treatment advantageously makes it possible to modify the properties of load surface, for example to improve the compatibility of the load with the thermoplastic polymer material, in particular to improve the homogeneity of the load with the thermoplastic polymer material. One can speak of filler treated with a compatibilizing agent. The nano-filler of the invention is preferably a filler treated with a hydrophobic surface treatment. We can then speak of hydrophobic treated nano-filler, the expression "hydrophobic treated" being well known under the anglicism "hydrophobic treated".

In a particularly preferred embodiment, the polymer composition of the invention may comprise at least one compatibilizing agent.

Said compatibilizing agent advantageously makes it possible to improve the compatibility between the nano-filler and the thermoplastic polymer material. It favors more particularly the physicochemical interactions at the interface between said nano-filler and said polymer material to obtain in particular a better mixing homogeneity (dispersion and / or distribution) between said nano-filler and said polymer material.

According to a first variant, the nano-filler of the invention is a filler treated with a compatibilizing agent, or a filler intended to be treated with a compatibilizing agent. Preferably, said compatibilizing agent is of the hydrophobic type.

As such, the polymer composition of the invention may comprise:

at least one nano-filler treated with a compatibilizing agent, this type of filler being readily available commercially, and / or

at least one untreated nano-filler, the composition further comprising a compatibilizing agent intended to be grafted on the surface of said nano-filler.

As an example of treated nano-filler, mention may be made of nano-fillers comprising, on their surface, siloxane and / or silane groups. The silane groups may be of the chlorosilane type.

As an example of a nano-charge intended to be treated, mention may be made of any type of filler which has not undergone any prior treatment during their incorporation into the polymer composition of the invention, the polymer composition of the invention then comprising a compatibilizing agent combining an organic peroxide with an unsaturated silane, in order to obtain in a subsequent step a nano-charge comprising siloxane groups on its surface.

According to a second variant, the polymer composition may comprise a polymer, as compatibilizing agent, comprising groups intended to improve the compatibility between the nano-filler and the thermoplastic polymer material.

For example, said polymer may be a graft polymer maleic anhydride, and preferably a polyolefin grafted maleic anhydride.

According to a third variant, the first and second variants can be combined.

In the present invention, the dielectric liquid may comprise at least about 70% by weight of mineral oil, and preferably at least about 80% by weight of mineral oil, based on the total weight of the dielectric liquid.

The mineral oil is usually liquid at about 20-25 ° C.

The mineral oil may be selected from naphthenic oils and paraffinic oils, and preferably from naphthenic oils.

Mineral oil is obtained from the refining of a crude oil.

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

In a particular embodiment, the polar compound of the benzophenone type, acetophenone or one of their derivatives represents at least About 2.5% by weight, preferably at least about 3.5% by weight, and still more preferably at least about 4% by weight, based on the total weight of the dielectric liquid. With this minimum amount of polar compound, the dielectric strength is improved.

The dielectric liquid may comprise at most about 30% by weight, preferably at most about 20% by weight, and even more preferably at most about 15% by weight, of polar compound of benzophenone type, acetophenone or a derivative thereof, by relative to the total weight of the dielectric liquid. This maximum quantity ensures moderate dielectric loss or low (eg. Less than 10 ^{"about 3),} and also to avoid migration of the dielectric liquid from the electrically insulating layer.

The polar compound of the benzophenone type, acetophenone or one of their derivatives may correspond to the following formula (I):

in which R ¹ and R ² , which are identical or different, are aryl, alkyl, alkylene-aryl groups, the R ¹ and R ^{2 groups} being able to be connected together by the element A representing a single bond or a - (CH _{2) group} ) _n - with n equal to 1 or 2.

The aryl group may comprise one or more aromatic rings, condensed or non-condensed, and preferably non-condensed.

The aryl group may comprise from 5 to 20 carbon atoms, and preferably from 5 to 15 carbon atoms.

Each aromatic ring may comprise one or more heteroatoms such as a nitrogen atom, a sulfur atom or an oxygen atom.

Each aromatic cycle can be substituted by one or more X substituents selected from a halogen atom, an alkyl group or an alkoxy-O-alkyl group. An alkyl group is preferred.

The halogen atom as substituent X on an aromatic ring is preferably a chlorine or fluorine atom, and more preferably a chlorine atom.

The alkyl group as substituent X on an aromatic ring may have from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, and more preferably from 2 to 4 carbon atoms.

The alkyl group of the alkoxy-O-alkyl group as substituent X on an aromatic ring may have from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, and more preferably from 2 to 4 carbon atoms. .

The aromatic ring or rings preferably do not include protic polar substituents such as -OH, -SH, -NH, or -NH ₂ .

The aryl group is preferably a phenyl group, a naphthyl group or a pyridyl group, and more preferably a phenyl group.

The alkyl group as R ¹ and / or R ^{2 group} may have 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms.

In the present invention, the alkyl group can be cyclic, linear or branched.

The alkylene-aryl group is a mixed group that includes an aryl group as defined in the present invention and an alkylene group. The alkylene group of the alkylene-aryl group is directly connected to the ketone function of the compound of formula (I).

The alkylene group can be linear, cyclic or branched, and preferably linear.

In particular, the alkylene group may have from 1 to 5 carbon atoms. Preferably, the alkylene group is - (CH ₂ ) _P - with 1 <p <5; a group - (CH R) _p i- with 1 <Pi <5 and R being an alkyl group, preferably having 1 to 5 carbon atoms; a statistical group - (CHR) _m i- (CH ₂ ) _m 2- 0-e. comprising iru -CH ₂ - and m ₂ -CHR-), with 1 ≤ mi + m ₂ ≤ 5, and R being an alkyl group, preferably having 1 to 5 carbon atoms; or a - (CH R) p _{2 -} (CH ₂ ) p ₃ - (CHR ') p ₄ - (i) group comprising p ₂ -CH ₂ -, P 3 -CHR- and p ₄ -CH R'-) with 1 ≤ p ₂ + P 3 + p ₄ ≤ 5, and R and R 'being different alkyl groups, each preferably having 1 to 5 carbon atoms, preferably 1 <nr 1 <4, 1 <m ₂ <4, 1 <p ₂ <3, 1 <p ₃ <3 and 1 <p ₄ <3.

In the present invention, a statistical group means that the radicals which constitute it (eg -CH ₂ -, -CH R- and / or -CHR'-) may be randomly positioned within the alkylene group.

R (respectively R ') can be a methyl, ethyl, propyl or isopropyl group.

When the alkylene group is branched (e.g., the presence of at least any one of R or R '), it may also be branched to the aryl group of said alkylene-aryl group.

The alkylene-aryl group may be a benzyl group (alkylene-aryl group in which the alkylene group is a CH ₂ and the aryl group is a phenyl).

The compound of formula (I) is of benzophenone type when the groups R ¹ and R ² are aryl groups; acetophenone type when one of R ¹ or R ² is an aryl group and the other is an alkyl group; and one of their derivatives when the groups R ¹ and R ² are alkyl groups or one of the groups R ¹ or R ² is an alkylene-aryl group and the other is an alkyl, aryl or alkylene-aryl group.

According to a first variant of the invention, at least one of said groups R ¹ or R ² of the compound of formula (I) is a phenyl group. According to a second variant of the invention, the groups R ¹ and R ² of the compound of formula (I) are aryl groups. Preferably, at least one of them comprising a phenyl group, and more preferably both aryl groups each comprise a phenyl group.

According to a third variant, the groups R ¹ and R ² of the compound of formula (I) are each phenyl groups, preferably unsubstituted.

According to a particularly preferred embodiment of the invention, the compound of formula (I) may be benzophenone, dibenzosuberone, fluorenone or anthrone, and preferably benzophenone.

The ratio of the number of aromatic carbon atoms to the total number of carbon atoms in the dielectric liquid may be less than about 0.3; and more preferably less than about 0.2.

With this low ratio, safety issues related to the toxicity of the dielectric liquid are minimized.

The ratio of the number of aromatic carbon atoms to the total number of carbon atoms in the dielectric liquid can be determined according to ASTM D3238.

The mineral oil may comprise one or more polar compounds different from the polar compound of benzophenone type, acetophenone or a derivative thereof and in particular different from the compound of formula (I).

However, it will be preferred that these polar compounds other than the polar compound of the benzophenone type, acetophenone or one of their derivatives or different from the compound of formula (I) represent at most approximately 2.5% by weight, and more preferably at most 1.5% by weight. % by weight, relative to the total weight of the dielectric liquid.

An oil containing such proportions of polar compounds may be a refined oil.

Preferably, the dielectric liquid has a boiling point greater than about 250 ° C.

Thus, the dielectric liquid of the polymer composition of the invention which combines a mineral oil and a benzophenone compound, acetophenone or a derivative thereof can be safely handled at ambient temperature (low volatility) and at the temperatures required by the process of forming the electrically insulating layer (eg extrusion), while ensuring the formation of a homogeneous mixture homogeneous with the polymeric material of the polymer composition of the invention.

In the present invention, the thermoplastic material may be based on polyolefin, and preferably based on polypropylene. The thermoplastic polyolefin-based polymeric material may comprise at least one polyolefin homopolymer or copolymer.

The polypropylene thermoplastic polymer material may comprise at least one homopolymer or copolymer of propylene (Pi), and optionally at least one homopolymer or copolymer of olefin a (P ₂ ).

The combination of polymers Pi and P ₂ may advantageously make it possible to obtain a thermoplastic polymer material having good mechanical properties, in particular in terms of elastic modulus, and electrical properties.

In particular, the propylene copolymer Pi may be a random copolymer of propylene.

By way of examples of propylene copolymers Pi, mention may be made of propylene and olefin copolymers, the olefin being especially chosen from ethylene and an olefin a different from propylene.

The olefin which is different from propylene may correspond to the formula CH ₂ = CH-R ³ , in which R ³ is a linear or branched alkyl group having from 2 to 10 carbon atoms, in particular being chosen from the following olefins: butene, 1-pentene; 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and a mixture thereof.

The olefin of the propylene-olefin copolymer is preferably at most 15 mol% and more preferably at most 10 mol% of the copolymer. Copolymers of propylene and ethylene are preferred as the propylene copolymer Pi.

The propylene copolymer Pi preferably has an elastic modulus of about 600 to about 1200 MPa. The propylene homopolymer P 1 preferably has an elastic modulus of about 1250 to 1600 MPa.

The propylene homopolymer or copolymer P 1 may have a melting point greater than about 130 ° C, preferably greater than about 140 ° C, and more preferably from about 140 to 165 ° C.

In particular, the propylene homopolymer P 1 can have a melting temperature of about 165 ° C and the propylene copolymer P 1 can have a melting temperature of about 140 to 150 ° C.

The propylene homopolymer or copolymer Pi may have a melting enthalpy of from about 30 to 100 J / g.

In particular, the propylene homopolymer P 1 can have a melting enthalpy ranging from about 80 to 90 J / g and the propylene copolymer P 1 can have a melting enthalpy ranging from about 30 to 70 J / g.

The propylene homopolymer or copolymer Pi may have a melt index ranging from 0.5 to 3 g / 10 min, measured at about 230 ° C. with a load of approximately 2.16 kg according to the ASTM D1238-00 standard.

According to a preferred embodiment of the invention, the propylene homopolymer or copolymer Pi represents from 40 to 70% by weight approximately of the thermoplastic polymer material.

The olefin homopolymer or copolymer of olefin at P ₂ may correspond to the formula CH ₂ = CH-R ⁴ , wherein R ⁴ is a hydrogen atom or a linear or branched alkyl group having 1 to 12 carbon atoms, and in particular be selected from the following olefins: ethylene, propylene, 1-butene, isobutylene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1 -dodecene, and one of their mixtures.

The propylene olefin, 1-hexene or 1-octene is preferred. The homopolymer or copolymer of olefin P ₂ may be:

a heterophase copolymer comprising a thermoplastic phase of the propylene type and a thermoplastic elastomer phase of the copolymer type of ethylene and of an olefin,

- a polyethylene, or

- one of their mixtures.

The thermoplastic elastomer phase of the heterophase copolymer may represent at least about 20% by weight, and preferably at least about 45% by weight, relative to the total weight of the heterophase copolymer.

The olefin of the thermoplastic elastomer phase of the heterophasic copolymer may be propylene.

The polyethylene may be a linear low density polyethylene (LLDPE). In the present invention, the term "linear low density polyethylene" means linear polyethylene having a density ranging from about 0.91 to about 0.925.

Preferably, the thermoplastic polymer material of the invention may comprise at least said heterophase copolymer and at least said polyethylene.

According to a preferred embodiment of the invention, the olefin homopolymer or copolymer P ₂ represents from 30 to 60% by weight approximately of the thermoplastic polymer material.

The thermoplastic polymer material of the polymer composition of the invention is preferably heterophasic (i.e. it comprises a plurality of phases). The presence of several phases generally comes from mixing two different polyolefins, such as a mixture of polypropylene and a copolymer of propylene or polyethylene.

The polymer composition of the invention comprises a homogeneous intimate mixture of the dielectric liquid and the thermoplastic polymer material (eg, it forms a homogeneous phase). The mass concentration of the dielectric liquid in the polymer composition is preferably less than or equal to the saturation mass concentration of said dielectric liquid in the thermoplastic polymer material.

The saturation mass concentration at 20-25 ° C is generally in the range of about 15 to 20%. It can be determined by the liquid absorption method. In particular, plates (eg of dimensions 200 mm × 200 mm × 0.5 mm) made of the thermoplastic polymer material of the polymer composition are prepared from the corresponding raw materials, in particular by molding. Samples of these plates are weighed (initial weight = P ₀ ) and then immersed at about 20 ° C. in the dielectric liquid of the polymer composition. The mass concentration of saturation is measured by determining the weight change (in percentage) of the samples after different immersion times (eg 3, 6, 9, 12 and 15 days) and after having cleaned and dried their surface (final weight = P _f ). The absorption of the dielectric liquid is determined according to the following formula:

% of dielectric liquid absorption = [(Pf-Po) / Po] 100

The saturation concentration is reached when P _f shows a variation of less than 1% with respect to the increase in the total weight corresponding to P _f -P ₀ .

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

According to a particular embodiment, the polar compound of benzophenone type, acetophenone or a derivative thereof represents from 0.1 to 1.8% by weight, preferably from 0.21 to 1.2% by weight, and more preferably 0.24 to 0.9% by weight, based on the total weight of the polymer composition. According to a particular embodiment, the thermoplastic polymer material is from 70% to 98% by weight, preferably from 80 to 95% by weight, and more preferably from 88 to 97% by weight, relative to the weight. total of the polymer composition The polymer composition may further comprise one or more additives.

The additives are well known to those skilled in the art and may be selected from antioxidants, anti-UV agents, anti-copper agents, anti-water tree agents, pigments and a mixture thereof.

The polymer composition of the invention may typically comprise from about 0.01 to 5% by weight, and preferably from about 0.1 to 2% by weight of additives, based on the total weight of the polymeric composition.

More particularly, the antioxidants make it possible to protect the polymer composition from the thermal stresses generated during the steps of manufacturing the cable or operating 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 which may be mentioned 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), the l, 3,5-trimethyl-2,4,6-tris (3,5-di-ieri-butyl-4-hydroxybenzyl) benzene (Irganox ^® 1330), 4,6-bis (octylthiomethyl) -o-cresol (Irgastab ^® KV10), 2,2'-thiobis (6-ieri-butyl-4-methylphenol) (Irganox ^® 1081), the 2,2'-thiodiethylene bis [3- (3,5-di-ieri-butyl-4-hydroxyphenyl) propionate] (Irganox ^® 1035), 2,2'-methylenebis (6-tert-butyl-4-methyl phenol), the l, 2-bis (3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl) hydrazine (Irganox ^® MD 1024), or 2,2'-oxamido bis (ethyl-3 (3,5 -di-ferf-butyl-4-hydroxyphenyl) propionate). Examples of thioesters include the didodecyl-3,3'-thiodipropionate (Irganox ^® PS800), distearyl thiodipropionate (Irganox PS802) or 4,6-bis (octylthiométhyle) -o-cresol (Irganox ^® 1520).

Examples of sulfur-based antioxidants include dioctadecyl-3,3'-thiodipropionate or didodecyl-3,3'-thiodipropionate.

For examples of antioxidants phosphorus-based, there may be mentioned tris (2,4-di-tert-butylphenyl) phosphite (Irgafos ^® 168) or bis (2,4-di-ferf- butylphenyl ) pentaerythritol diphosphite (Ultranox 626 ^®).

Examples of amine antioxidants include phenylene diamines (eg, 1PPD or 6PPD), diphenylamine styrene, diphenylamines, mercapto benzimidazoles and 2,2,4-trimethyl-1,2-dihydroquinoline. polymerized (TMQ).

Examples of mixtures of antioxidants include Irganox B 225 which comprises an equimolar mixture of Irgafos 168 and Irganox 1010 as described above.

The polymer composition is a thermoplastic polymer composition. It is therefore not crosslinkable.

In particular, the polymer composition does not comprise crosslinking agents, silane coupling agents, peroxides and / or additives which allow crosslinking. Indeed, such agents degrade the thermoplastic polymer material.

The polymer composition is preferably recyclable.

The subject of the invention is a process for the preparation of the polymer composition according to the first subject, characterized in that it comprises at least one step i) of mixing the various constituents of the polymer composition as defined in the first article of the invention. the invention.

In particular, the mixing is carried out according to the following substeps:

ia) when the dielectric liquid comprises a mineral oil and at least one polar compound of benzophenone type, acetophenone or one of their derivatives, mixing the mineral oil and the polar compound of benzophenone type, acetophenone or a derivative thereof (as defined in the first subject of the invention), in order to form a dielectric liquid as defined in the first object of the invention, and ib) mixing a thermoplastic polymer material and at least one nano-filler, as defined in the first subject of the invention, with the dielectric liquid as obtained in the preceding substep ia).

The thermoplastic polymer material of sub-step ib) is generally in the form of granules of polymer (s), in particular granules of at least one homopolymer or copolymer of propylene Pi and optionally at least one homopolymer or copolymer of olefin P ₂ as defined in the first subject of the invention.

The mixture of the sub-step ia) can be carried out using any apparatus for dissolving the polar compound of benzophenone type, acetophenone or a derivative thereof and optionally the additive (s) (especially when they are in the form of solid powders) in mineral oil.

The sub-step i-a) is preferably carried out at a temperature ranging from about 20 to 100 ° C, preferably from about 50 to 90 ° C, and more preferably at a temperature of about 75 ° C.

Sub-step i-a) generally lasts from 15 minutes to 1 hour, and preferably from 20 to 30 minutes.

At the end of the sub-step i-a), a stable and transparent solution is obtained.

The mixture of the sub-step i-a) may further comprise the additive (s) as defined in the invention (e.g. antioxidant).

According to a first variant, the mixture of the sub-step ib) can be carried out by mixing the dielectric liquid obtained in the sub-step ia) with the thermoplastic polymer material or the polymeric compounds which constitute it, and the nano-charge, in particular using an internal mixer, in particular with tangential rotors or with intermeshing rotors, or with a continuous mixer, in particular with screw or counter rotating double screw, or with a mixer of "Buss extruder" type.

According to a second variant, the sub-step ib) can be carried out by impregnating granules of a thermoplastic polymer material as defined in the first subject of the invention with the dielectric liquid, in particular by mixing the polymer granules with the dielectric liquid, the nano-filler being added in a subsequent step described below. Said mixture of the polymer granules with the dielectric liquid is made by heating the resulting mixture so that the granules absorb the dielectric liquid, the temperature of the mixture ensuring that the thermoplastic polymer material remains in the solid state (i.e. granules). These granules can then be mixed in an extruder with the nano-filler. More particularly, the nano-filler of the polymer composition of the invention may be incorporated in an extruder with the granules of polymeric material impregnated with the dielectric liquid. The assembly is thus homogenized in the molten state within the extruder, the extruder being able to be of the continuous mixer type, in particular with a screw or counter rotating double screw (eg "Berstorff twin screw extruder"), or of the type mixer "Buss extruder". The rod obtained at the extruder outlet is cooled and granulated, the granules obtained being able to feed an extruder to manufacture the cable of the invention according to a method as defined below.

The third object of the invention is a cable comprising at least one elongated electrically conductive element, and at least one electrically insulating layer obtained from a polymer composition as defined in the first subject of the invention.

The electrically insulating layer of the invention is a non-crosslinked layer.

The electrically insulating layer of the invention is preferably a recyclable layer. The electrically insulating layer of the invention may be an extruded layer, especially by methods well known to those skilled in the art.

In the present invention, the term "electrically insulating layer" means a layer whose electrical conductivity can be at most 1.10 ^-9 S / m, and preferably at most 1.10 ^-10 S / m (siemens per meter). (at 25 ° C).

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

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

The elongate electrically conductive element may be a single-body conductor such as, for example, a wire or a multi-body conductor such as a plurality of twisted or non-twisted metal wires.

The elongated electrically conductive member may be aluminum, aluminum alloy, copper, copper alloy, and one of their combinations.

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

a first semiconductor layer surrounding the elongated electrically conductive element,

an electrically insulating layer surrounding the first semiconductor layer, said electrically insulating layer being as defined in the invention, and

a second semiconductor layer surrounding the electrically insulating layer.

The electrical cable described above comprising the first semiconductor layer, the electrically insulating layer and the second semiconductor layer may be an HVDC cable. In the present invention, the term "semiconductor layer" means a layer whose electrical conductivity can be at least 1.10 ^"9 S / m (Siemens per meter), preferably at least 1.10 ^{" 3} S / m and preferably may be less than 1.10 ³ S / m (at 25 ° C).

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 cable may further comprise an electrically insulating sheath surrounding the second semiconductor layer, and may be in direct physical contact therewith.

The electrical cable may further comprise a metal screen surrounding the second semiconductor layer. In this case, the electrically insulating sheath surrounds said metal screen.

This metal screen may be a "wired" screen composed of a set of copper or aluminum conductors arranged around and along the second semiconductor layer, a so-called "ribbon" screen composed of one or more ribbons conductive metallic copper or aluminum placed (s) optionally helically around the second semiconductor layer or a conductive metal strip of aluminum laid longitudinally around the second semiconductor layer and sealed with glue in the zones overlapping parts of said ribbon, or a so-called "sealed" screen of metal tube type optionally composed of lead or lead alloy and surrounding the second semiconductor layer. This last type of screen makes it possible in particular to provide a moisture barrier that tends to penetrate the electrical cable radially.

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 "wired" screen and a screen called "ribbon".

All types of metal screens can play the role of grounding 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 swelling layers in the presence of moisture can be added between the second semiconductor layer and the metal screen, these layers to ensure longitudinal sealing of the electric cable to water.

The fourth subject of the invention is a method of manufacturing an electric cable according to the third subject of the invention, characterized in that it comprises at least one step 1) of extruding the polymer composition according to the first object of the invention around an elongated electrically conductive member to provide an electrically insulating (extruded) layer surrounding said elongate electrically conductive member.

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

In step 1), the extruder output composition is said to be "non-crosslinked", the temperature as well as the processing time within the extruder being optimized accordingly.

At the extruder outlet, an extruded layer is thus obtained around said electrically conductive element, which may or may not be directly in physical contact with said elongated electrically conductive element.

The method does not preferably include a step of crosslinking the layer obtained in step 1).

Other features and advantages of the present invention will become apparent in the light of the description of nonlimiting examples of compositions according to the invention and of the cable according to the invention with reference to the following figure:

Figure 1 shows a schematic view of an electric cable according to a preferred embodiment according to the invention. For the sake of clarity, only the essential elements for understanding the invention have been shown schematically, and this without respect of the scale.

The medium or high voltage power cable 1, illustrated in FIG. 1, comprises an elongated central electrically conductive element 2, in particular made of copper or aluminum. The energy cable 1 further comprises several layers arranged successively and coaxially around this central elongated electrically conductive element 2, namely: a first semiconductor layer 3 called "internal semiconductor layer", an electrically insulating layer 4, a second semiconductor layer 5 called an "external semiconductor layer", a metal screen 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 according to the invention.

Semiconductor layers 3 and 5 are thermoplastic (i.e. uncrosslinked) extruded layers.

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

EXEM PLES

1. Polymer compositions

Table 1 below collects polymeric compositions whose amounts of the compounds are expressed in parts by weight per hundred parts by weight of polymer (s) in the polymer composition.

The composition C1 is a comparative composition, and the composition It is in accordance with the invention. The polymers in these compositions are three in number, namely: a propylene copolymer (Pi), a linear low density polyethylene (P ₂ ), and a heterophasic propylene copolymer (P ₂ ).

TABLE 1

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

- A propylene random copolymer sold by Borealis under the reference Bormed RB 845 MO, in the form of granules;

Linear low density polyethylene marketed by Exxon Mobil Chemicals under the reference LLDPE LL 1002 YB, in the form of granules;

- Heterophasic propylene copolymer sold by Basell Polyolefins under the reference Adflex Q 200F, in the form of granules;

Mineral oil marketed by Nynas under the reference Nytex 810, the oil comprising 10% aromatic carbon atoms, 43% naphthenic carbon atoms and 47% paraffinic carbon atoms;

Benzophenone marketed by Sigma-Aldrich under the reference B9300; - Nano-charges marketed by Aérosil under the reference Aérosil R 974, these nano-charges have the following characteristics:

- spherical elementary particles with a form factor substantially equal to 1, whose diameter is less than 100 nm,

- specific surface area (BET): 170 ± 20 m ² / g,

silica particles (SiO ₂ ) surface-treated with DDS (dimethyl dichlorosilane); and

Antioxidant sold by Ciba under the reference Irganox B 225 which comprises an equimolar mixture of Irgafos 168 and Irganox 1010.

Compositions C1 and II comprise the following quantities of polar compounds (determined according to ASTM 2007-02), relative to the total weight of the polymer composition:

Composition Cl: 4.8% by weight,

- Composition II: 4.8% by weight.

More particularly, mineral oil and benzophenone form a dielectric liquid according to the invention. The benzophenone (polar compound) is thus present in an amount of 4.8% by weight relative to the total weight of dielectric liquid.

2. Preparation of non-crosslinked layers

The compositions summarized in Table 1 are implemented as follows.

The mineral oil, antioxidant and benzophenone were mixed with stirring at about 75 ° C to form a dielectric liquid.

The dielectric liquid was then mixed with the propylene copolymer, the linear low density polyethylene and the heterophasic copolymer, in a mixer to impregnate the polymer granules. with the dielectric liquid. The mixture is carried out at a temperature of 80 ° C. At this temperature, the polymer granules are not in the molten state and therefore remain in the solid state.

Said granules impregnated with dielectric liquid were then incorporated, together with the nano-filler, in a twin screw extruder at a temperature of about 145 to 180 ° C. and then melted at about 200 ° C. (screw speed: 80 rpm), in order to obtain an extruded rod. The extruded rod is then cooled and granulated by techniques well known to those skilled in the art. Pellets of polymer composition are thus obtained according to composition C1 and composition II, respectively.

Cables were manufactured with a laboratory extruder, from granules of composition C1 and granules of composition II respectively, and subjected to electrical characterizations. Each of the cables included:

an electrically conductive element with a cross section of 1.4 mm,

a first semiconductor layer surrounding said electrically conductive element, an electrically insulating layer obtained from the polymer composition of the invention or a comparative polymer composition surrounding said first semiconductor layer, and

a second semiconductor layer surrounding said electrically insulating layer. The cables had a total outside diameter of about 6.1 mm and a total length of about 3.64 m. They were stripped of the second semiconductor layer to a thickness of 150 μm and a length of 87 cm.

The electrically insulating layer had a thickness of 1.5 mm (inner and outer radius respectively of 1.4 mm and 2.9 mm). The semiconductor layers were thermoplastic layers having the following composition: 48% by weight of random propylene copolymer (Bormed RB 845 MO); 20% by weight of a heterophasic copolymer (Adflex Q 200F); 25% by weight of carbon black (Vulcan XC 500); 6.5% by weight of a mineral oil (Nytex 810) and 0.5% by weight of antioxidant.

3. Characterization of uncrosslinked layers

The dielectric strength of the layers, or in other words DC dielectric breakdown resistance, expressed in kV / mm, was performed on 700 μm thick plate-shaped samples obtained from the extruded compositions. described above. The device used for this type of measurement is HVTS C2000, with a step-up voltage of 5kV every 30 minutes, from 50kV to 300kV DC.

Statistical analysis (Weibull model) was performed on 10 experimental values of dielectric strength obtained.

The tangent delta (tanδ) (or loss factor) at 25 ° C., 90 ° C. and 130 ° C. of the layers as prepared above was measured by dielectric spectroscopy using an apparatus sold under the name commercial Alpha-A by Novocontrol Technologies.

The tangent of the loss angle gives an indication of the energy dissipated in a dielectric in the form of heat.

The tests were carried out on samples of thickness close to 0.5 mm, over a frequency range of 40 to 60 Hz with a voltage of 500 V adapted according to the thickness of the sample tested, in order to apply a field 1 kV / mm. A temperature of 25 ° C, 90 ° C or 130 ° C was applied during the various tests. 4. Results

The 25 ° C tangent delta results obtained from the compositions Cl and II are both less than 2 × 10 ^-4 , and are substantially the same.The results of 90 ° C tangent delta obtained from the compositions Cl and Both are less than 3 x 10 ^-4 , and are substantially the same.

In addition, the 50 Hz plate DC resistance obtained with the composition II is at least 20% higher than that obtained with the composition Cl.

Thus, the polymer composition according to the invention has better dielectric properties (i.e. better electrical insulation), for substantially identical dielectric losses (tangent delta).

More particularly, the dielectric breakdown resistance (i.e. dielectric strength) of the layer obtained from the composition II according to the invention is significantly improved over that obtained from the comparative composition C1.

Claims

REV EN D I CATI ON S

A polymer composition comprising at least one thermoplastic polymer material, characterized in that the composition further comprises at least one polar dielectric liquid, and at least one nano-filler having a specific surface area (BET) of at least 100 m ² / g -

2. Composition according to claim 1, characterized in that the nano-charge has at least one of its dimensions of at most 2000 nm, and preferably at most 1000 nm.

3. Composition according to any one of the preceding claims, characterized in that the nano-filler is a mineral filler, preferably selected from alkaline earth metal carbonates, alkaline earth metal sulfates, metal oxides, metalloid oxides, metal silicates, and siloxanes.

4. Composition according to any one of the preceding claims, characterized in that the dielectric liquid comprises at least 2.5% by weight of polar compounds relative to the total weight of dielectric liquid.

5. Composition according to any one of the preceding claims, characterized in that the dielectric liquid comprises at least one mineral oil, and optionally a polar compound.

6. Composition according to any one of the preceding claims, characterized in that the dielectric liquid comprises at least one polar compound of benzophenone type, acetophenone or a derivative thereof.

7. Composition according to any one of the preceding claims, characterized in that the thermoplastic polymer material is based on polyolefin, preferably based on polypropylene.

8. Composition according to any one of the preceding claims, characterized in that the polymer composition comprises a compatibilizing agent to improve the compatibility of said nano-filler with the thermoplastic polymer material.

9. Composition according to any one of the preceding claims, characterized in that the dielectric liquid comprises at least 70% by weight. weight of mineral oil, based on the total weight of the dielectric liquid.

10. Composition according to any one of claims 5 to 9, characterized in that the mineral oil is selected from naphthenic oils and paraffinic oils.

11. Composition according to any one of claims 5 to 10, characterized in that the polar compound of benzophenone type, acetophenone or a derivative thereof represents at least 2.5% by weight, relative to the total weight of the dielectric liquid.

12. Composition according to any one of claims 5 to 11, characterized in that the polar compound of benzophenone type, acetophenone or a derivative thereof corresponds to the following formula (I):

13. Composition according to claim 12, characterized in that the compound of formula (I) is benzophenone, dibenzosuberone, fluorenone or anthrone.

15. Composition according to any one of the preceding claims, characterized in that the dielectric liquid represents from 1% to 20% by weight, relative to the total weight of the polymer composition.

16. Composition according to any one of the preceding claims, characterized in that the thermoplastic polymer material comprises at least one homopolymer or copolymer of propylene Pi, and at least one homopolymer or copolymer of olefin P ₂ .

17. Composition according to claim 16, characterized in that the propylene homopolymer or copolymer Pi represents from 40 to 70% by weight of the thermoplastic polymer material.

18. Composition according to any one of the preceding claims, characterized in that the nano-charge is a treated filler.

19. Cable comprising at least one elongated electrically conductive element, and at least one electrically insulating layer obtained from a polymer composition as defined in any one of the preceding claims.

20. Cable according to claim 19, characterized in that the electrically insulating layer is a non-crosslinked layer.

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, characterized in that the composition further comprises at least one polar dielectric liquid. , and at least one nano-charge.