KR102267280B1 - Polymer Composition Comprising Polar Dielectric Liquid - Google Patents

Abstract

The present invention relates to a polymer composition comprising at least one thermoplastic polymer material, wherein the composition further comprises at least one polar dielectric liquid and at least one nanofiller.

Description

Polymer Composition Comprising Polar Dielectric Liquid

The present invention relates to a polymer composition comprising at least one thermoplastic polymer material, at least one polar dielectric liquid and at least one nanofiller, a method for preparing said polymer composition, and at least one electrically insulating layer obtained from said polymer composition. It relates to a cable comprising a, and a method of manufacturing the cable.

The present invention typically, but not exclusively, applies to electrical cables for transmission, particularly medium-voltage, whether DC or AC current in overhead, underwater and terrestrial electrical transmission applications, or alternatively in aviation applications. voltage) applies to power cables (especially from 6 to 45-60 kV) or high-voltage power cables (which may in particular be above 60 kV and below 400 kV).

Medium-voltage or high-voltage transmission cables typically run from inside to outside:

- elongate electrically conductive elements, in particular made of copper or aluminum;

- a semiconductor inner layer surrounding said elongate electrically conductive element;

- an electrically insulating layer surrounding said semiconductor inner layer;

- a semiconductor outer layer surrounding said insulating layer; and

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

includes

Specifically, the electrically insulating layer may be a polymer layer based on a crosslinked polyolefin, such as crosslinked polyethylene (XLPE) or ethylene-propylene or ethylene-propylene-diene crosslinked elastomer. Crosslinking is generally performed during the step of extruding the polymer composition around the elongate electrically conductive element. The use of crosslinked polyolefins provides a layer with satisfactory electrical and mechanical properties and provides cables capable of operating at temperatures above 70°C or even 90°C. However, you run into some problems. First, the cross-linked material cannot be recycled. Second, crosslinking (vulcanization) to produce a uniform layer requires specific reaction conditions (eg, in terms of duration and temperature) that decrease the manufacturing speed of the cable and increase production costs. Finally, crosslinking can sometimes start prematurely in the extruder and/or extruder head, resulting in deterioration of the quality of the layer obtained, in particular its dielectric properties.

Accordingly, alternatives have been proposed, such as thermoplastic layers of low density polyethylene (LDPE) or high density polyethylene (HDPE). However, cables comprising such electrically insulating layers cannot operate at temperatures above about 70° C. for the LDPE thermoplastic layer and above 80° C. for the HDPE thermoplastic layer, limiting the power that can be transmitted in the cable and manufacturing methods. may lead to limitations in

It is also known practice to produce an electrically insulating layer composed of several paper strips, or a paper-polypropylene composite impregnated with a large amount of a dielectric liquid (eg, a cable containing paper impregnated with oil). The dielectric liquid completely fills the voids present in the layer, preventing partial discharge and damage to the insulation of the cable. However, this type of electrically insulating layer is very complicated and expensive to manufacture.

The choice of dielectric liquid will depend on the anticipated application (ie, the type of electrical appliance) and the compatibility with the solid insulator into which the dielectric liquid is intended and/or the dielectric liquid is intended to be impregnated and/or the dielectric liquid together form a homogeneous mixture. Among the conventional dielectric liquids, mineral oil (eg naphthenic oil, paraffin oil, aromatic oil or polyaromatic oil), vegetable oil (eg soybean oil, linseed oil, rapeseed oil, corn oil or castor oil) or Mention may be made of synthetic oils such as aromatic hydrocarbons (alkylbenzenes, alkylnaphthalenes, alkylbiphenyls, alkyldiarylethylenes, etc.), silicone oils, ether oxides, organic esters or aliphatic hydrocarbons.

Specifically, international patent application WO 02/03398 A1 describes a thermoplastic polymer material comprising at least one electrical conductor and a copolymer of propylene homopolymer or propylene with at least one olefin comonomer selected from ethylene and α-olefins other than propylene. A cable comprising at least one extruded electrically insulating layer based on a dielectric liquid in a homogeneous mixture with The dielectric liquid comprises at least one alkylaryl type containing at least two non-fused aromatic rings (e.g., dibenzyltoluene, or a mixture of 85 wt% monoxylylxylene and 15 wt% dixylylxylene). aromatic hydrocarbons including hydrocarbons. International patent application WO 02/03398 A1 indicates that the dielectric liquid absorbs a minimal amount of water and contains no polar compounds to prevent the formation of defects in the insulating layer associated with the presence of water vapor during hot extrusion. However, aromatic hydrocarbons (alkylbenzenes, alkylnaphthalenes, alkylbiphenyls, alkyldiarylethylenes) are expensive and usually involve stability and/or environmental concerns (eg, certain aromatic hydrocarbons are thought to be carcinogenic). .

Mineral oil accounts for 90-95% of the dielectric liquid market, due to the low cost of these “natural” products obtained directly by refining crude oil. The chemical composition of mineral oils is very complex (thousands of different molecules) and can vary within wide proportions. Accordingly, the chemical composition of a mineral oil is generally defined by its paraffinic carbon (Cp) content, its naphthenic carbon (Cn) content and its aromatic carbon (Ca) content. Mineral oils may also contain small proportions of hydrocarbon molecules (eg, polar compounds) that contain heteroatoms such as nitrogen, sulfur or oxygen in their structure. The polar compound content of mineral oil can be determined according to standard ASTM D2007-02. However, the stability to oxidation and dielectric behavior of mineral oils are lower than those of aromatic hydrocarbons. Further, from the international patent application WO 2004/066 318 A1, the electrical properties of a cable comprising at least one electrical conductor and at least one extruded electrical insulation layer based on a thermoplastic polymer material in a homogeneous mixture with mineral oil as dielectric liquid It is known that this can be degraded by the presence of such polar compounds, especially in terms of dielectric losses.

Accordingly, there is still a need for an electrical cable comprising an electrically insulating layer that ensures good mechanical properties, while at the same time having electrical properties comparable to those obtained using XLPE crosslinked layers.

It is therefore an object of the present invention to overcome the problems of the prior art and to provide materials, in particular recycling, which can provide an electrically insulating layer with improved electrical properties, in particular in terms of dielectric strength, while at the same time ensuring low dielectric losses. It is to provide an economical polymer composition comprising possible materials.

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

This object is achieved by the invention described below.

A first subject of the present invention is a polymer composition comprising at least one polymer material, at least one polar dielectric liquid and at least one nanofiller.

The combination of a polar dielectric liquid with at least one nanofiller, or nanometer-sized filler, creates an electrically insulating layer of an electrical cable that exhibits improved dielectric strength while ensuring low dielectric loss.

Moreover, the polymer composition of the present invention also allows the operating temperature of the cable to be raised from 90°C to 110°C.

Finally, the polymer composition of the present invention also exhibits reduced electrical conductivity, allowing it to be advantageously used in the electrical insulation layer of electrical cables, more specifically high voltage direct current (HVDC) cables.

In the present invention, the term "polar" refers to a compound comprising a partial positive charge and a negative charge, wherein the barycentre of the partial positive charge does not coincide with the center of mass of the partial negative charge. Partial positive and negative charges are polar covalent bonds, more specifically covalent bonds between two atoms having different electronegativities, such as carbon atoms or hydrogen atoms with oxygen, nitrogen, sulfur, fluorine, chlorine, bromine, It occurs in covalent bonds between atoms selected from iodine or phosphorus atoms.

According to a first embodiment, the dielectric liquid may comprise at least 2.5% by weight of the polar compound relative to the total weight of the dielectric liquid. The dielectric liquid may preferably comprise at least one polar mineral oil having a polar compound in an amount of at least 2.5% by weight 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 the type of benzophenone, acetophenone or derivatives thereof. The dielectric liquid may preferably comprise at least 2.5% by weight of the polar compound relative to the total weight of the dielectric liquid.

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

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

Accordingly, the polymer composition of the present invention may preferably comprise at least 2.5% by weight of the polar compound relative to the total weight of the polymer composition.

The nanofillers of the present invention are nanometer sized fillers.

The nanofiller(s) of the present invention typically have at least one of their dimensions of nanometer size (10 ^-9 meters).

In the present invention, the term "nanofiller" means elementary particles. The assembly of elementary particles may be an aggregate or aggregate of elementary particles.

More specifically, the nanofiller(s) of the present invention (i.e. one or more elementary particles) have at least one of their dimensions of 2000 nm (nanometers) or less, preferably 1000 or less, preferably 800 nm or less, preferably preferably 600 nm or less, and more preferably 400 nm or less.

Furthermore, the nanofiller(s) of the present invention may have at least one of their dimensions of at least 1 nm, and preferably at least 5 nm.

Preferably, the nanofiller(s) of the present invention may have at least one of its dimensions in the range from 1 to 800 nm.

Considering several nanofillers according to the present invention, the term "dimension" means the number-average dimension of all nanofillers in a given population, which dimension is usually measured via methods well known to those skilled in the art.

The dimensions of the nanofiller(s) according to the invention can be measured, for example, by microscopy, in particular by scanning electron microscopy (SEM) or transmission electron microscopy (TEM).

At least one of the nanofillers comprised in the polymer composition, or more specifically the nanofillers, may have an aspect ratio of strictly 1 or more, and preferably 10 or less.

The nanofiller(s) are preferably spherical, ie have an aspect ratio of substantially 1.

In the present invention, the aspect ratio is typically the largest dimension of the nanofiller (e.g., the length of the nanofiller if the nanofiller has a layered or cylindrical shape) and the smallest dimension of the nanofiller (e.g., the nanofiller's layered nano thickness of the filler, or the diameter of a cylindrical nanofiller).

The nanofillers 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 nanofiller may have a BET specific surface area of 1000 m 2 /g or less, and preferably 500 m 2 /g or less.

In the present invention, the specific surface area can be easily determined according to standard DIN 9277 (2010). The polymer composition of the present invention may comprise up to 10.0% by weight of nanofillers, preferably up to 5.0% by weight of nanofillers, and preferably up to 3.0% by weight of nanofillers, relative to the total weight of the polymer composition.

The polymer composition of the present invention may comprise at least 0.2% by weight of nanofiller, preferably at least 0.5% by weight of nanofiller, and preferably at least 1.0% by weight of nanofiller, relative to the total weight of the polymer composition.

The nanofillers of the present invention may preferably be inorganic nanofillers which may be selected from alkaline earth metal carbonates, alkaline earth metal sulfates, metal oxides, metalloid oxides, metal silicates and siloxanes.

For example:

- the alkaline earth metal carbonate nanofiller may be a calcium carbonate nanofiller,

- the alkaline earth metal sulfate nanofiller may be a barium sulfate nanofiller,

- the metal oxide nanofillers may be alumina, zinc oxide and/or titanium dioxide nanofillers,

- the metalloid oxide nanofiller may be a silicon dioxide (silica) nanofiller, in particular a fumed silica nanofiller,

- metal silicate nanofillers can be, for example, aluminum nanofillers (eg magnesium aluminum silicate hydrate nanofillers such as montmorillonite),

- The siloxane nanofiller may be a silsesquioxane nanofiller (eg trisilanolphenyl polyhedral silsesquioxane (TP-POSS) nanofiller).

Preferably, the nanofillers of the present invention may be metal oxide nanofillers and/or metalloid oxide nanofillers.

The nanofillers of the present invention may be "treated" fillers or "untreated" fillers.

The term “treated filler” refers to a filler that has undergone a surface treatment, ie a surface-treated filler. Said surface treatment can advantageously modify the surface properties of the filler, for example to improve the compatibility of the filler with the thermoplastic polymer material, and in particular to improve the homogeneity of the filler with the thermoplastic polymer material. A filler may be referred to as a filler treated with a compatibilizer.

The nanofillers of the present invention are preferably fillers treated with a hydrophobic surface treatment. A nanofiller may then be said to be hydrophobically treated, or, in the well known expression, "hydrophobically treated".

In one particular preferred embodiment, the polymer composition of the present invention may comprise at least one compatibilizer.

The compatibilizer may advantageously enhance the compatibility between the nanofiller and the thermoplastic polymer material. The agent more specifically promotes physicochemical interactions at the interface between the nanofiller and the polymeric material, resulting in particularly good homogeneity of mixing (dispersion and/or distribution) between the nanofiller and the polymeric material.

According to a first variant, the nanofillers of the invention are fillers treated with compatibilizers, or fillers intended to be treated with compatibilizers. The compatibilizer is preferably hydrophobic.

For this purpose, the polymer composition of the present invention comprises:

- at least one nanofiller treated with a compatibilizer (fillers of this type are probably readily commercially available), and/or

- at least one untreated nanofiller, the composition further comprising a compatibilizer intended for grafting to the surface of said nanofiller

may include.

Examples of treated nanofillers that may be mentioned include nanofillers comprising silane and/or siloxane groups on their surface. The silane group may be of the chlorosilane type.

Examples of nanofillers for treatment that may be mentioned include fillers of any type that have not been subjected to any prior treatment when included in the polymer composition of the present invention, in which case the polymer composition of the present invention, in a subsequent step, has its surface A compatibilizer is included in which the organic peroxide is combined with the unsaturated silane to obtain a nanofiller comprising siloxane groups in the phase.

According to a second variant, the polymer composition may comprise, as compatibilizer, a polymer comprising groups intended to enhance the compatibility between the nanofiller and the thermoplastic polymer material.

As an example, the polymer may be a maleic anhydride grafted polymer, and preferably a maleic anhydride grafted polyolefin.

According to the third variant, the first variant and the second variant may 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, relative to the total weight of the dielectric liquid.

Mineral oils are generally liquid at about 20-25°C.

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

Mineral oil is obtained from the refining of crude oil.

According to a particularly preferred embodiment of the present invention, the mineral oil has a paraffinic carbon (Cp) content in the range of about 45 to 65 atomic percent, a naphthenic carbon (Cn) content in the range of about 35 to 55 atomic percent, and about 0.5 to 10 atomic percent. range of aromatic carbon (Ca) content.

In one specific embodiment, the polar compound of the type of benzophenone, acetophenone or derivatives thereof is at least about 2.5% by weight, preferably at least about 3.5% by weight and even more preferably at least about It corresponds to 4% by weight. Due to this minimal amount of the polar compound, the dielectric strength is improved.

The dielectric liquid contains about 30 wt% or less, preferably about 20 wt% or less and even more preferably about 15 wt% or less, of a polar compound of the type of benzophenone, acetophenone or derivatives thereof, relative to the total weight of the dielectric liquid. can be included as This maximum can ensure moderate or even low dielectric losses (eg, ^{less than about 10 -3} ), and can also prevent migration of dielectric liquid from the electrically insulating layer.

Polar compounds of the type of benzophenones, acetophenones or derivatives thereof may correspond to formula I:

[Formula I]

^{(wherein R 1} and R ^{2 ,} which may be the same or different, are aryl, alkyl or alkylene-aryl groups, and the groups R ¹ and R ² are either a single bond or a group —(CH ₂ ) _n —, where n is 1 or 2)).

Aryl groups may include one or more fused or non-fused, and preferably non-fused aromatic rings.

Aryl groups may contain from 5 to 20 carbon atoms and preferably from 5 to 15 carbon atoms.

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

Each aromatic ring may be substituted with one or more substituents X selected from a halogen atom, an alkyl group or an alkoxy-O-alkyl group. Alkyl groups are preferred.

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

The alkyl group as substituent X on the aromatic ring may contain 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 the aromatic ring may contain 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(s) preferably do not contain any polar protic substituents, such as -OH groups, -SH groups, -NH groups or -NH ₂ groups.

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

Alkyl groups as groups R ¹ and/or R ² may contain 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 may be cyclic, linear or branched.

An alkylene-aryl group is a mixed group comprising an aryl group as defined herein, and an alkylene group. The alkylene group of the alkylene-aryl group is linked directly to the ketone function of the compound of formula (I).

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

Specifically, the alkylene group may contain from 1 to 5 carbon atoms.

Preferably, the alkylene group is selected from the group -(CH ₂ ) _p -, where 1≤p≤5; the group -(CHR) _p1 -, wherein 1≤p ₁ ≤5 and R is an alkyl group, preferably containing 1 to 5 carbon atoms; Statistical group -(CHR) _m1 -(CH ₂ ) _m2 - (ie, including m ₁ -CH ₂ - and m ₂ -CHR-), where 1 ≤ m ₁ + m ₂ ≤ 5 and R is alkyl group, preferably containing 1 to 5 carbon atoms); or a statistical group -(CHR) _p2 -(CH ₂ ) _p3 -(CHR') _p4 - (ie, including p ₂ -CH ₂ -, p ₃ -CHR- and p ₄ -CHR'-), wherein 1 ≤ _{p 2} + p ₃ + p ₄ ≤ 5, R and R' are different alkyl groups, each containing preferably 1 to 5 carbon atoms, preferably ₁ ≤ m 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 constituting it (eg -CH ₂ -, -CHR- and/or -CHR'-) may be randomly placed in the alkylene group.

R (or each R′) may be a methyl, ethyl, propyl or isopropyl group.

When the alkylene group is branched (eg, at least the presence of groups R or R′), the alkylene group may also be linked to the aryl group of the alkylene-aryl group via branching.

The alkylene-aryl group can be a benzyl group (an alkylene-aryl group _{wherein the alkylene group is CH 2} and the aryl group is phenyl).

Compounds of formula (I) are of the benzophenone type when the ^{groups R 1} and R ^{2 are aryl groups;} the acetophenone type when one of the groups R ¹ or R ² is an aryl group and the other is an alkyl group; and when the groups R ¹ and R ² are alkyl groups, or when 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, a derivative of the benzophenone type or an acetophenone It is a type of derivative.

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 comprises a phenyl group, more preferably each of the two aryl groups comprises a phenyl group.

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

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

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

Due to this low ratio, safety concerns 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 standard ASTM D3238.

The mineral oil may comprise one or more polar compounds other than polar compounds of the type of benzophenone, acetophenone or derivatives thereof, and specifically other than compounds of formula (I).

However, polar compounds other than polar compounds of the type of benzophenone, acetophenone or derivatives thereof, or such polar compounds other than compounds of formula (I), are not more than about 2.5% by weight, and more preferably about 1.5% by weight relative to the total weight of the dielectric liquid. It would be desirable to correspond to weight percent or less.

Oils containing these proportions of polar compounds may be refined oils.

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

Thus, the dielectric liquid of the polymer composition of the present invention combining a mineral oil and a compound of the type of benzophenone, acetophenone or derivatives thereof can be prepared at room temperature (limitingly volatile) and in a process for forming an electrically insulating layer (e.g. , extrusion) can be operated without risk at the temperatures required for extrusion), while at the same time ensuring the formation of a homogeneous homogeneous mixture of the polymer composition of the invention with the polymer material.

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

The polypropylene-based thermoplastic polymer material comprises _{at least one homopolymer or at least one copolymer of propylene (P 1} ), and optionally at least one homopolymer or at least one copolymer of α-olefin (P ₂ ) can do.

The combination of polymers P ₁ and P ₂ can advantageously make it possible to obtain thermoplastic polymer materials having good mechanical properties, in particular in terms of elastic modulus, and good electrical properties.

Specifically, the propylene copolymer P ₁ may be a statistical propylene copolymer.

_{Examples of propylene copolymers P 1} that may be mentioned include copolymers of propylene and olefins, the olefins being selected in particular from ethylene and α-olefins other than propylene.

α-olefins other than propylene have the formula CH ₂ CH-R ³ , wherein R ³ is in particular the following olefins: 1-butene, 1-pentene; 4-methyl-1-pentene, 1-hexene, 1-octene, 1 -decene, 1-dodecene, and mixtures thereof, which are linear or branched alkyl groups containing 2 to 10 carbon atoms.

The olefins in the copolymer of propylene and olefins preferably account for up to 15 mol % and more preferably up to 10 mol % of the copolymer.

A copolymer of propylene and ethylene is preferred as _{propylene copolymer P 1 .}

The propylene copolymer P ₁ preferably has a modulus of elasticity in the range of about 600 to 1200 MPa.

The propylene homopolymer P ₁ preferably has a modulus of elasticity in the range 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 in the range of about 140 to 165° C.

Specifically, the propylene homopolymer P ₁ may have a melting point of about 165° C., and the propylene copolymer P ₁ may have a melting point in the range of about 140 to 150° C.

The propylene homopolymer or copolymer P ₁ may have an enthalpy of fusion in the range of about 30 to 100 J/g.

Specifically, the propylene homopolymer P ₁ may have an enthalpy of fusion in the range of about 80 to 90 J/g, and the propylene copolymer P ₁ may have an enthalpy of fusion in the range of about 30 to 70 J/g.

The propylene homopolymer or copolymer P ₁ may have a melt flow index in the range of 0.5 to 3 g/10 min measured at about 230°C with a load of about 2.16 kg according to standard ASTM D1238-00.

According to a preferred embodiment of the invention, the propylene homopolymer or copolymer P ₁ corresponds to about 40% to 70% by weight of the thermoplastic polymer material.

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

Preference is given to α-olefin propylene, 1-hexene or 1-octene.

The α-olefin homopolymer or copolymer P ₂ is:

- a heterophasic copolymer comprising a thermoplastic phase of the propylene type and a thermoplastic elastomeric phase of the type of copolymer of ethylene and α-olefin,

- polyethylene or

- mixtures of these

can be

The thermoplastic elastomeric phase of the heterophasic copolymer may account for at least about 20 weight percent, and preferably at least about 45 weight percent, relative to the total weight of the heterophasic copolymer.

The α-olefin on the thermoplastic elastomer of the heterophasic copolymer may be propylene.

The polyethylene may be linear low density polyethylene (LLDPE). As used herein, the term "linear low density polyethylene" means a linear polyethylene having a density in the range of about 0.91 to 0.925.

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

According to a preferred embodiment of the present invention, the α-olefin homopolymer or copolymer P ₂ corresponds to about 30% to 60% by weight of the thermoplastic polymer material.

The thermoplastic polymer material of the polymer composition of the present invention is preferably heterophasic (ie the thermoplastic polymer material of the polymer composition of the present invention comprises several phases). The presence of several phases is generally derived from mixtures of two different polyolefins, such as polypropylene, and copolymers of propylene or copolymers of polyethylene.

The polymer composition of the present invention comprises a homogeneous homogeneous mixture of a dielectric liquid and a thermoplastic polymer material (eg, the polymer composition of the present invention forms a uniform phase).

The mass concentration of the dielectric liquid in the polymer composition is preferably less than or equal to the saturated mass concentration of the dielectric liquid in the thermoplastic polymer material.

At 20-25°C, the saturated mass concentration is generally about 15% to 20%. The saturated mass concentration can be determined by the liquid absorption method. Specifically, a plate made of a thermoplastic polymer material of the polymer composition (eg size 200 mm x 200 mm x 0.5 mm) is prepared from the corresponding starting material, in particular by molding. A sample of this plate is weighed (initial weight = P ₀ ) and then immersed in the dielectric liquid of the polymer composition at about 20°C. Saturated mass concentration measures the change in weight (as a percentage) of a sample after various immersion times (eg, 3, 6, 9, 12 and 15 days) and after its surface has been cleaned and dried (final weight = P _{f ).} is measured by The absorption rate of the dielectric liquid is determined according to the formula:

Absorption % of dielectric liquid = [(P _f -P ₀ )/P ₀ ] × 100.

Saturation concentration is reached when P _f indicates a change of less than 1% relative to the total weight of a corresponding increase in P _f -P _0.

According to a particular embodiment, the dielectric liquid is present in an amount of from about 1% to 20% by weight, preferably from about 2% to 15% by weight and more preferably from about 3% to 12% by weight relative to the total weight of the polymer composition. corresponds to

According to a particular embodiment, the polar compound of the type of benzophenone, acetophenone or derivatives thereof is from about 0.15% to 1.8% by weight, preferably from about 0.21% to 1.2% by weight and more, relative to the total weight of the polymer composition. Preferably it corresponds to about 0.24% to 0.9% by weight.

According to a particular embodiment, the thermoplastic polymer material comprises from about 70% to 98% by weight, preferably from about 80% to 95% by weight and more preferably from about 88% to 97% by weight relative to the total weight of the polymer composition. corresponds to

The polymer composition may further comprise one or more additives.

Additives are well known to those skilled in the art and may be selected from antioxidants, UV stabilizers, copper scavengers, water treeing inhibitors, pigments, and mixtures thereof.

The polymer composition of the present invention may typically comprise from about 0.01% to 5% by weight and preferably from about 0.1% to 2% by weight of the additive relative to the total weight of the polymer composition.

More specifically, the antioxidant protects the polymer composition from thermal stresses generated during the manufacturing or operating phase of the cable.

The antioxidant is preferably selected from hindered phenols, thioesters, sulfur-based antioxidants, phosphorus-based antioxidants, antioxidants of the amine type, and mixtures thereof.

Examples of hindered phenols which may be mentioned are pentaerythrityl-trityl-tetrakis (3- (3,5-di - tert - butyl-4-hydroxyphenyl) propionate) (Irganox ^® 1010), octadecyl-3- (3,5-di - tert - butyl-4-hydroxyphenyl) propionate (Irganox ^® 1076), 1,3,5- trimethyl-2,4,6-tris (3,5-di - tert - Butyl-4-hydroxybenzyl)benzene (Irganox ^® 1330), 4,6-bis(octylthiomethyl)-o-cresol (Irgastab ^® KV10), 2,2'-thiobis(6- tert -butyl-4 -methylphenol) (Irganox ^® 1081), 2,2'-thiodiethylenebis [3- (3,5-di- tert -butyl-4-hydroxyphenyl) propionate] (Irganox ^® 1035), 2 ,2'-methylenebis(6- tert -butyl-4-methylphenol), 1,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine (Irganox ^® MD 1024) and 2,2′-oxamidobis(ethyl 3-(3,5-di- tert -butyl-4-hydroxyphenyl)propionate).

Examples of thio esters that may be mentioned are didodecyl 3,3'-thiodipropionate (Irganox ^® PS800), distearyl thiodipropionate (Irganox ^® PS802) and 4,6-bis(octylthiomethyl) )-o-cresol (Irganox ^® 1520).

Examples of sulfur-based antioxidants that may be mentioned include dioctadecyl 3,3′-thiodipropionate and didodecyl 3,3′-thiodipropionate.

Examples of the phosphorus antioxidant which may be mentioned are tris (2,4-di - tert - butylphenyl) phosphite (Irgafos ^® 168) and bis (2,4-di - tert - butylphenyl) pentaerythrityl diphosphite trityl (Ultranox ^® 626).

Examples of antioxidants of the amine type that may be mentioned are phenylenediamine (eg 1PPD or 6PPD), diphenylaminestyrene, diphenylamine, mercaptobenzimidazole and polymerized 2,2,4-trimethyl- 1,2 dihydroquinoline (TMQ).

An example of a mixture of antioxidants that may be mentioned is Irganox B 225, comprising an equimolar mixture of Irgafos 168 and Irganox 1010 as described above.

The polymer composition is a thermoplastic polymer composition. Accordingly, the polymer composition cannot be crosslinked.

Specifically, the polymer composition does not contain any crosslinking agents, silane-type coupling agents, peroxides and/or additives that enable crosslinking. The reason is that these agents degrade the thermoplastic polymer material.

The polymer composition is preferably recyclable.

A second object of the invention relates to a polymer composition according to the first object, characterized in that it comprises at least one step i) mixing the various constituents of the polymer composition as defined in the first object of the invention. manufacturing method.

Specifically, the mixing is carried out according to the following substeps:

ia) mineral oil (as defined in the first object of the invention), and benzophenone, aceto, if the dielectric liquid comprises at least one polar compound of the type of benzophenone, acetophenone or derivatives thereof mixing a polar compound of the type of phenone or a derivative thereof to form a dielectric liquid as defined in the first object of the present invention, and

i-b) mixing the thermoplastic polymer material as defined in the first object of the invention and at least one nanofiller with the dielectric liquid obtained in substep i-a) above.

The thermoplastic polymer material of substep ib) is generally polymer granules, in particular at least one propylene homopolymer or copolymer P ₁ as defined in the first object of the invention and optionally at least one α-olefin homopolymer or copolymer It is in the form of granules of coalescing P _{2 .}

The mixing of substep ia) can be carried out using any machine that dissolves in mineral oil a polar compound of the type of benzophenone, acetophenone or derivatives thereof and optionally additive(s) (especially when they are in solid powder form). can

Substep i-a) is preferably carried out at a temperature in the range of about 20 to 100 °C, preferably about 50 to 90 °C and more preferably at a temperature of about 75 °C.

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

At the end of substep i-a), a stable and clear solution is obtained.

In addition, the admixture of substep i-a) may comprise additive(s) as defined herein (eg antioxidants).

According to a first variant, the mixing of substep ib) comprises mixing the dielectric liquid obtained in substep ia) with the thermoplastic polymer material or the polymer compound constituting it, and nanofillers, in particular an internal mixer with a tangent rotor or gear rotor, or mixing using a continuous mixer, in particular a screw or counter-rotating twin-screw mixer, or a mixer of the “Buss extruder” type.

According to a second variant, sub-step ib) can be carried out by impregnating the granules of a thermoplastic polymer material as defined in the first object of the invention with a dielectric liquid, in particular by mixing the polymer granules with a dielectric liquid, Nanofillers are added in a subsequent step described below. Said mixing of the polymer granules and dielectric liquid is effected 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 a solid state (ie, in granular form). These granules can then be mixed with the nanofillers in an extruder. More specifically, the nanofillers of the polymer composition of the present invention may be incorporated into the extruder together with granules of polymeric material impregnated with a dielectric liquid. The entire material is then homogenized to a molten state in the extruder; The type of extruder may be a continuous mixer, in particular a screw or counter-rotating twin screw mixer (eg Berstorff twin screw extruder ), or a mixer of the “bush extruder” type. The obtained extrudate is cooled at the extruder outlet, granulated, and the obtained granules can be used to feed the extruder for the production of the cable of the invention according to the process as defined below.

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

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

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

The electrically insulating layer of the present invention may specifically be an extruded layer extruded through a process well known to those skilled in the art.

In the present invention, the term “electrically insulating layer” refers to a layer having an electrical conductivity (at 25° C.) of 1×10 ^-9 S/m or less and preferably 1×10 ^-10 S/m (Siemens per meter) or less. it means.

The cable of the present invention relates more particularly to the field of electrical cables acting on direct current (DC), in particular the field of HVDC-type cables, or electrical cables alternating with alternating current (AC).

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

The elongate electrically conductive element may be a mono-core conductor, such as a metal wire, or a multi-core conductor, such as a plurality of selectively twisted metal wires.

The elongate electrically conductive element may be made of aluminum, aluminum alloy, copper, copper alloy, and combinations thereof.

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

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

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

- a second semiconductor layer surrounding the electrically insulating layer

may include.

The above-described electric cable including 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” may have an electrical conductivity (at 25° C.) of at least 1×10 ⁻⁹ S/m (Siemens per meter), preferably at least 1×10 ⁻³ S/m, preferably It means a layer which may be less than 1×10 ^{3 S/m.}

In certain embodiments, the first semiconductor layer, the electrically insulating layer and the second semiconductor layer constitute a three-layer insulation. That is, the electrical insulating layer is in direct physical contact with the first semiconductor layer, and the second semiconductor layer is in direct physical contact with the electrical insulating layer.

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

Additionally, the electrical cable may include a metal shield surrounding the second semiconductor layer. In this case, an electrically insulating sheath surrounds the metal shield.

This metal shield is a "wire" shield consisting of an assembly of copper or aluminum conductors arranged around and along a second semiconductor layer, one or more conductive metal strips made of copper or aluminum optionally spirally disposed around the second semiconductor layer. , or a "strip" shield consisting of a conductive metal strip made of aluminum, disposed longitudinally around the second semiconductor layer, and providing leak-tightness by means of an adhesive in the overlapping region of the portion of the strip, or optionally lead or lead alloy and may be a "leakproof" shield of the metal tube type that surrounds the second semiconductor layer. This last type of shield can act as a barrier against moisture, which tends to penetrate the electrical cable in particular in the radial direction.

The metal shield of the electrical cable of the present invention may include a "wire" shield and a "leakproof" shield or a "wire" shield and a "strip" shield.

Any type of metal shield can act as earth for an electrical cable and thus carry fault currents, for example in the event of a short circuit in the associated network.

Another layer can be added between the second semiconductor layer and the metal shield, for example a layer that expands in the presence of moisture, which layer ensures longitudinal waterproofing of the electrical cable.

A fourth object of the present invention provides a method comprising at least one step 1) extruding a polymer composition according to the first object of the invention around an elongate electrically conductive element, whereby an (extruded) electrically insulating layer surrounding said elongate electrically conductive element is provided. It is a method for manufacturing an electric cable according to the third object of the present invention, characterized in that it comprises the step of obtaining a.

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

During step 1), the composition leaving the extruder is "non-crosslinked" and the operating temperature and time in the extruder are consequently optimized.

Thus, an extruded layer around the electrically conductive element, which may or may not be in direct physical contact with the elongate electrically conductive element, is obtained at the extruder outlet.

The process preferably does not comprise a crosslinking step of the layer obtained in step 1).

Other features and advantages of the present invention will become apparent in light of the description of the compositions according to the invention and of non-limiting examples of cables according to the invention with reference to the following drawings.
1 shows a schematic diagram of an electric cable according to a preferred embodiment according to the invention;
For purposes of clarity, only elements essential for an understanding of the present invention have been shown schematically and not to scale.

The medium or high voltage power cable 1 illustrated in FIG. 1 comprises a centrally elongated electrically conductive element 2 made in particular of copper or aluminum. In addition, the power cable 1 has several layers arranged continuously and coaxially around this centrally elongate electrically conductive element 2 , namely: a first semiconductor layer 3 known as “inner semiconductor layer”, electrically insulating layer (4), a second semiconductor layer (5) known as the “outer semiconductor layer”, a metal shield 6 for grounding and/or protection, and a protective outer sheath 7 .

The electrically insulating layer 4 is a non-crosslinked extruded layer obtained from the polymer composition according to the invention.

The semiconductor layers 3 and 5 are thermoplastic (ie non-crosslinked) extruded layers.

The presence of a metal shield 6 and a protective outer sheath 7 is preferred, but not essential, such cable constructions per se are well known to the person skilled in the art.

Example

1. Polymer composition

Table 1 below collects and analyzes polymer compositions, wherein the amount of compound is expressed in parts by weight per 100 parts by weight of polymer(s) in the polymer composition.

Composition C1 is a comparative composition and composition I1 is according to the invention.

There were three polymers in this composition: a propylene copolymer (P ₁ ), a linear low density polyethylene (P ₂ ), and a heterophasic propylene copolymer (P ₂ ).

polymer composition C1 I1 propylene copolymer 50 50 Linear Low Density Polyethylene 25 25 Heterophasic Propylene Copolymer 25 25 mineral oil 6 6 benzophenone 0.3 0.3 nano filler 0 2.0 antioxidant 0.3 0.3

The origins of the compounds in Table 1 are:- Statistical propylene copolymer sold by the company Borealis in granular form under the trade name Bormed RB 845 MO;

- linear low-density polyethylene sold by the enterprise ExxonMobil Chemicals in granular form under the trade name LLDPE LL 1002 YB;

- a heterophasic propylene copolymer sold by the enterprise Basell Polyolefins in granular form under the trade name Adflex Q 200F;

- mineral oil sold by the enterprise Nynas under the trade name Nytex 810 (the oil contains 10% aromatic carbon atoms, 43% naphthenic carbon atoms and 47% paraffinic carbon atoms);

- benzophenone sold by the company Sigma-Aldrich under the trade name B9300;

- Nanofillers sold by the company Aerosil under the trade name Aerosil R 974 (these nanofillers have the following characteristics:

- spherical elementary particles having an aspect ratio of substantially 1 and having a diameter of less than 100 nm;

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

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

- antioxidant sold by the enterprise Ciba under the trade name Irganox B 225, comprising an equimolar mixture of Irgafos 168 and Irganox 1010.

Compositions C1 and I1 contain the polar compound (as determined according to standard ASTM 2007-02) in the following amounts, based on the total weight of the polymer composition:

- composition C1: 4.8% by weight,

- Composition I1: 4.8% by weight.

More specifically, mineral oil and benzophenone form a dielectric liquid according to the present invention. Therefore, benzophenone (polar compound) is present in an amount of 4.8% by weight based on the total weight of the dielectric liquid.

2. Preparation of non-crosslinked layers

The compositions collected in Table 1 were used as follows.

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. Mixing is carried out at a temperature of 80°C. At this temperature, the polymer granules are not in a molten state and therefore remain in a solid state.

The granules impregnated with the dielectric liquid were then incorporated in a Berstorff twin screw extruder at a temperature of about 145 to 180° C. together with the nanofiller, and then melted at about 200° C. (screw speed: 80 rpm) to obtain an extrudate. The extrudate is then cooled and granulated using techniques well known to those skilled in the art. This gives granules of the polymer composition according to composition C1 and composition I1 respectively.

Cables were prepared from each of the granules of composition C1 and granules of composition I1 using a laboratory extruder, and electrical characterization was performed. Each cable is:

- 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 surrounding said first semiconductor layer, obtained from a polymer composition of the invention or a comparative polymer composition, and

- a second semiconductor layer surrounding said electrically insulating layer

included.

The cable had an overall outer diameter of about 6.1 mm and an overall length of about 3.64 m. It stripped the second semiconductor layer over 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 radii of 1.4 mm and 2.9 mm, respectively).

The semiconductor layer had the following composition: 48% by weight of a statistical 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); It was a thermoplastic layer with 6.5 wt% mineral oil (Nytex 810) and 0.5 wt% antioxidant.

3. Characterization of non-crosslinked layers

The dielectric strength of the layer, or resistance to dielectric breakdown under continuous current, expressed in kV/mm, was carried out on a plate-shaped sample having a thickness of 700 μm obtained from the extruded composition described above. The instrument used for this type of measurement is a HVTS C2000 with a voltage increase from 50 kV to 300 kV DC in steps of 5 kV every 30 min.

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

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

The tangent of the loss angle represents the energy dissipated in the dielectric in the form of heat.

The test was performed on a sample having a thickness close to 0.5 mm over a frequency range of 40 to 60 Hz with a 500 V voltage adjusted according to the thickness of the test sample to apply an electric field of 1 kV/mm. Temperatures of 25° C., 90° C. or 130° C. were applied during the various tests.

4. Results

The tan delta results at 25° C. obtained from compositions C1 and I1 are both ^{less than 2×10 −4} and are substantially identical.

The tan delta results at 90° C. obtained from compositions C1 and I1 are both ^{less than 3×10 −4} and are substantially identical.

Further, the continuous-current breakdown resistance for the plate at 50 Hz obtained using composition I1 is at least 20% greater than that obtained using composition C1.

Accordingly, the polymer composition according to the present invention exhibits better dielectric properties (ie better electrical insulation) for substantially the same dielectric loss (tangent delta).

More specifically, the dielectric breakdown resistance (ie dielectric strength) of the layer obtained from the composition I1 according to the present invention is significantly improved compared to the layer obtained from the comparative composition C1.

Claims (20)

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 nanofiller having a specific surface area (BET) of at ^{least 100 m 2 /g.} polymer composition. The polymer composition of claim 1 , wherein the nanofiller has at least one of its dimensions of 2000 nm or less. Polymer composition according to claim 1 or 2, characterized in that the nanofiller is an inorganic filler. Polymer composition according to claim 1 or 2, characterized in that the dielectric liquid comprises at least 2.5% by weight of the polar compound relative to the total weight of the dielectric liquid. Polymer composition according to claim 1 or 2, characterized in that the dielectric liquid comprises at least one mineral oil, and optionally a polar compound. Polymer composition according to claim 1 or 2, characterized in that the dielectric liquid comprises at least one polar compound of the type of benzophenone, acetophenone or derivatives thereof. Polymer composition according to claim 1 or 2, characterized in that the thermoplastic polymer material is based on polyolefins. The polymer composition according to claim 1 or 2, characterized in that the polymer composition comprises a compatibilizer for enhancing the compatibility of the nanofiller with the thermoplastic polymer material. Polymer composition according to claim 1 or 2, characterized in that the dielectric liquid comprises at least 70% by weight of mineral oil relative to the total weight of the dielectric liquid. Polymer composition according to claim 5, characterized in that the mineral oil is selected from naphthenic oil and paraffin oil. Polymer composition according to claim 5, characterized in that the polar compound of the type of benzophenone, acetophenone or derivatives thereof corresponds to at least 2.5% by weight relative to the total weight of the dielectric liquid. Polymer composition according to claim 5, characterized in that the polar compound of the type of benzophenone, acetophenone or derivatives thereof corresponds to formula (I):
[Formula I]

^{(wherein R 1} and R ^{2 ,} which may be the same or different, are aryl, alkyl or alkylene-aryl groups, and the groups R ¹ and R ² are a single bond or a group —(CH ₂ ) _n —, where n is 1 or 2)). 13. Polymer composition according to claim 12, characterized in that the compound of formula (I) is benzophenone, dibenzosuberone, fluorenone or anthrone. Polymer composition according to claim 1 or 2, characterized in that the dielectric liquid accounts for 1% to 20% by weight relative to the total weight of the polymer composition. 3 . The thermoplastic polymer material according to claim 1 , wherein the thermoplastic polymer material is of propylene P ₁ . A polymer composition, characterized in that it comprises at least one homopolymer or at least one copolymer and at least one homopolymer or at least one copolymer of α-olefin P _{2 .} Polymer composition according to claim 15 , characterized in that the propylene homopolymer or copolymer P ₁ corresponds to 40% to 70% by weight of the thermoplastic polymer material. Polymer composition according to claim 1 or 2, characterized in that the nanofiller is a treated filler. A cable comprising at least one elongate electrically conductive element and at least one electrically insulating layer obtained from the polymer composition as defined in claim 1 . 19. Cable according to claim 18, characterized in that the electrically insulating layer is a non-crosslinked layer. delete

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