KR102053756B1 - Medium-tension or high-tension electrical cable - Google Patents

Abstract

The present invention relates to an electrical conductor 2, a first semiconducting layer 3 surrounding the electrical conductor 2, a second electrical insulation layer 4 surrounding the first layer 3 and a third surrounding the second layer 4. Comprising a semiconducting layer (5), wherein at least one of the three layers (3, 4, 5) is a crosslinked layer obtained from a crosslinkable composition comprising at least one polyolefin and an organic peroxide as crosslinker. With regard to the electrical cable (1), the composition further comprises a crosslinking aid comprising at least two unsaturated moieties, wherein one of the two unsaturated moieties is a vinyl functional group.

Description

Medium or high voltage electrical cable {MEDIUM-TENSION OR HIGH-TENSION ELECTRICAL CABLE}

The present invention relates to an electrical cable. The present invention is typically applied to medium voltage (particularly 6 to 45-60 kV) power cables or high voltage (particularly above 60 kV, which can range up to 800 kV) regardless of whether it is a DC cable or an AC cable. This is not restrictive.

Medium or high voltage electrical cables typically comprise a central electrical conductor, a semiconducting inner layer having a common axis continuously around the electrical conductor, an electrically insulating intermediate layer and a semiconducting outer layer, the three layers being provided to a person skilled in the art. Crosslinking is via well known techniques.

Typically, the three crosslinked layers are obtained from a composition based on a polyethylene polymer matrix in combination with an organic peroxide such as dicumyl peroxide or tert-butylcumyl peroxide. While the compositions are crosslinking, this type of peroxide decomposes to form crosslinking byproducts, in particular methane, acetophenone, cumyl alcohol, acetone, tert-butanol, α-methylstyrene and / or water. The last two by-products are formed by dehydration of cumyl alcohol.

If the methane formed in the crosslinking step is not removed from the crosslinked layer, the risks associated with the explosiveness of the methane and its flammability cannot be ignored. The gas may also cause damage when using the cable. Generally for medium and high voltage cables, when the semiconducting outer layer is surrounded by a metal shielding layer, the gas is longitudinally along the cable until it reaches the junction and terminal of the electrical installation (ie, the electrical component). Can only spread. Accordingly, methane can accumulate and exert pressure on electrical components, which can cause electrical shock. There are methods to limit the presence of methane in the cable, such as heat treatment of the cable to promote the release of methane out of the cable, but these methods are time consuming and expensive when the insulation layer is thick.

The document US Pat. No. 5,252,676 discloses a three layer insulator for power cables. These three layer insulators are obtained from compositions comprising additives of the type such as ethylene copolymers, organic peroxides as crosslinkers, and isopropenylbenzene or derivatives thereof. In order to limit the amount of gas generated during the decomposition of the crosslinker, the document proposes to reduce the amount of crosslinker.

However, the crosslinkable compositions used in this document are not suitable for limiting the amount of crosslinking byproducts and at the same time do not provide sufficient thermomechanical properties when the composition is crosslinked.

The object of the present invention is to overcome the disadvantages of the prior art by proposing a medium or high voltage electrical cable comprising a crosslinking layer, the production of the crosslinking layer significantly limiting the presence of crosslinking byproducts such as methane, while It provides optimal thermomechanical properties, such as hot creep, which is characterized by precise crosslinking of the layer.

One aspect of the invention includes an electrical conductor, a first semiconducting layer surrounding the electrical conductor, a second electrically insulating layer surrounding the first layer, and a third semiconducting layer surrounding the second layer, wherein the three In an electrical cable, at least one of the layers is a crosslinked layer obtained from a crosslinkable composition comprising an organic peroxide and at least one polyolefin as a crosslinker, wherein the composition comprises at least two unsaturated moieties, one of which is vinyl It is characterized in that it further comprises a crosslinking aid which is a functional group, the vinyl functional group is preferably an ethylenic functional group of the CH ₂ = CH- form.

The crosslinking aids of the present invention differ from the crosslinkers and are of the multifunctional type because they contain two or more unsaturated moieties.

The at least two unsaturated moieties are especially reactive functional groups of the carbon-carbon double bond type, which can be grafted to the polyolefin firstly, and then secondly to the crosslinking of the polyolefin (ie the formation of the three-dimensional structure of the crosslinked polyolefin). Can participate in

Crosslinking aids can advantageously significantly reduce the proportion of organic peroxides used in the crosslinkable composition, thereby reducing the amount of methane derived from the crosslinking by-products generated from the peroxides. At the same time, thermodynamic properties such as good thermal creep and satisfactory crosslinking rates are maintained. The thermomechanical properties for the crosslinked layer according to the invention are stresses in accordance with standard NF EN 60811-2-1, which ranges from 100% or less, preferably 80% or less, particularly preferably in the range from 60% to 80%. It can be advantageously represented by the maximum thermal elongation under.

Preferably, auxiliaries which do not evaporate during the step of using the crosslinkable composition, in particular by extrusion, will be used as the boiling point is sufficiently high.

For example, crosslinking aids include 1,3-hexadiene; 1,4-hexadiene; 1,5-hexadiene; 2,3-dimethyl-1,3-butadiene; 2-methyl-1,4-pentadiene; 3-methyl-1,3-pentadiene; 4-methyl-1,3-pentadiene; 1,6-heptadiene; 2,4-dimethyl-1,3-pentadiene; 2-methyl-1,5-hexadiene; 4-vinyl-1-cyclohexene; 1,7-octadiene; 2,5-dimethyl-1,5-hexadiene; 2,5-dimethyl-2,4-hexadiene; 5-vinyl-2-norbornene; 1,8-nonadiene; 7-methyl-1,6-octadiene; 1,4,9-decatriene; 2,6-dimethyl-2,4,6-octatriene; Dipentene; 7-methyl-3-methylene-1,6-octadiene; 1,9-decadiene; 3,9-divinyl-2,4,8,10-tetraoxaspiro [5.5] undecane; 1,2,4-trivinylcyclohexane; 1,13-tetradecadiene; 2,3-diphenyl-1,3-butadiene; Trans, trans-1,4-diphenyl-1,3-butadiene; 1,15-hexadecadiene; 1,6-diphenyl-1,3,5-hexatriene; 2,3-dibenzyl-1,3-butadiene; And polybutadiene; Or mixtures thereof.

In certain preferred embodiments, the two or more unsaturated moieties of the crosslinking aid are vinyl functional groups, especially ethylenic functional groups in the form CH ₂ = CH-.

In this case, the crosslinking auxiliary agent is 1,5-hexadiene; 1,6-heptadiene; 1,7-octadiene; 1,8-nonadiene; 1,4,9-decatriene; 1,9-decadiene; 3,9-divinyl-2,4,8,10-tetraoxaspiro [5.5] undecane; 1,2,4-trivinylcyclohexane; 1,13-tetradecadiene; May be selected from 1,15-hexadecadiene.

The concentration of said adjuvant is preferably limited so as not to interfere with the extrusion process of the crosslinkable composition of the present invention. For example, the crosslinkable composition may comprise up to 3 parts by weight of crosslinking aid with respect to 100 parts by weight of the polymer (s) in the crosslinkable composition. It will be desirable for the crosslinkable composition to use from 0.5 to 2 parts by weight of adjuvants relative to 100 parts by weight of the polymer (s) in the crosslinkable composition.

The organic peroxides according to the invention can be selected from organic peroxides well known to those skilled in the art regardless of whether they are aliphatic or aromatic peroxides.

Examples of aromatic peroxides that may be mentioned include dicumyl peroxide and tert-butylcumyl peroxide.

Aliphatic peroxides can be aliphatic peroxides comprising one or more tertiary alkyl groups. Examples of aliphatic peroxides that may be mentioned include the following;

Aliphatic peroxycarbonates such as tert-amylperoxy 2-ethylhexyl carbonate, tert-amylperoxy 2-ethylhexyl carbonate, tert-butylperoxy isopropyl carbonate;

Aliphatic peroxides of tertiary dialkyl, such as 1,1-bis (tert-butylperoxy) cyclohexane, 2,5-dimethyl-2,5-bis (tert-butylperoxy) -3-hexyne, 2, 5-dimethyl-2,5-bis (tert-butylperoxy) -3-hexane, di-tert-amyl peroxide, di-tert-butyl peroxide, cyclic peroxides such as 3,6,9-tree Ethyl-3,6,9-trimethyl-1,4,7-triperoxonan;

Aliphatic peroxyacetals such as butyl 4,4-bis (tert-butylperoxy) valerate; And

Aliphatic peroxyesters such as tert-butylperoxyacetate, tert-amyl peroxyacetate.

Compared to aromatic peroxides, aliphatic peroxides have the advantage of not forming cumyl alcohol as a crosslinking byproduct during crosslinking of the crosslinkable composition, thus making it possible to significantly limit the presence of water in the crosslinked layer. At the same time, they maintain very good thermomechanical properties.

Among the aliphatic peroxides mentioned above, aliphatic peroxides of tertiary dialkyls will preferably be used. The reason is that while using the composition, this type of peroxide has a very good compromise between the rate of crosslinking and the risk of burn-out or pre-crosslinking.

Preferably, the crosslinkable composition does not comprise any aromatic peroxides, in particular dicumyl peroxide or derivatives thereof.

Peroxide-path crosslinking of the crosslinkable compositions according to the invention can be carried out under the action of heat and pressure, such as using vulcanized tubes under nitrogen pressure, and such crosslinking techniques are well known to those skilled in the art.

The crosslinkable compositions of the present invention comprise up to 2.00 parts by weight of organic peroxide with respect to 100 parts by weight of polymer (s) in the composition; Preferably up to 1.50 parts by weight of organic peroxide based on 100 parts by weight of the polymer (s) in the composition; Preferably up to 1.25 parts by weight of organic peroxide with respect to 100 parts by weight of polymer (s) in the composition; And particularly preferably up to 1.10 parts by weight of organic peroxide, based on 100 parts by weight of polymer (s) in the composition.

The term "polyolefin" generally means by itself an olefin homopolymer or copolymer. The term may especially mean thermoplastic polymers or elastomers.

Preferably, the olefin polymer is an ethylene homopolymer or ethylene copolymer.

Examples of ethylene polymers that may be mentioned include linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high density polyethylene (HDPE). : high-density polyethylene), copolymer of ethylene and vinyl acetate (EVA), copolymer of ethylene and butyl acrylate (EBA), ethylene and methyl acrylate (EMA: methyl acrylate) ), Copolymer of 2-hexylethyl acrylate (2HEA: 2-hexylethyl acrylate), copolymer of ethylene and α-olefin, for example polyethylene-octene (PEO: polyethylene-octene), polyethylene-butene ( Copolymers of polyethylene-butene (PEB), ethylene and propylene (EPR) such as ethylene-propylene-diene (EPDM) terpolymers and mixtures thereof It is hereinafter.

It is preferable to use low density polyethylene (LDPE) because low density polyethylene (LDPE) has particularly good rheological properties and very good thermomechanical and electrical properties in use by extrusion.

The term "low density" means in particular a density which can be included in the range of 0.910 to 0.940 g / cm 3, preferably in the range of 0.910 to 0.930 g / cm 3, according to the standard ISO 1183 (at a temperature of 23 ° C.).

Typically, low density polyethylene (LDPE) can be obtained through a polymerization process in a high pressure tubular reactor or an autoclave reactor.

The crosslinkable composition is greater than 50.0 parts by weight with respect to 100 parts by weight of the polymer (s) (ie, the polymer matrix) in the composition, preferably at least 70 parts by weight with respect to 100 parts by weight of the polymer (s) in the composition. Polyolefins, particularly preferably, may comprise at least 90 parts by weight of polyolefin with respect to 100 parts by weight of the polymer (s) in the composition.

In a particularly advantageous manner, the crosslinkable composition comprises a polymer matrix composed of polyolefins alone or a mixture of polyolefins.

The crosslinkable compositions of the present invention may further comprise an aromatic compound comprising a single reactive functional group capable of grafting to the polyolefin and one or more aromatic nuclei. Preferably, the reactive functional group of the aromatic compound is a vinyl functional group. Thus, the aromatic compound, when present in the crosslinkable composition, does not participate in crosslinking of the polyolefin in contrast to the crosslinking aid.

The crosslinked layer obtained from the crosslinkable composition has strengthened and persistent properties in the field of electrical cables and provides better water treeing resistance. In particular it relates to resistance to electrical breakdown, in particular the ability to dissipate the space charge that accumulates in the high voltage cable under direct current.

The aromatic compound may be selected from styrene, styrene derivatives, and isomers thereof.

Examples of styrene derivatives may include compounds having the following general formula;

Wherein X is hydrogen, an alkyl group or an aryl group; R is hydrogen, an alkyl group or an aryl group. In particular, 4-methyl-2,4-diphenylpentene and triphenylethylene may be mentioned.

In the present invention, styrene derivatives of the polycyclic aromatic hydrocarbon (PAH) type may also be considered. In particular, examples of vinyl naphthalene include 2-vinyl naphthalene; Examples of vinylanthracene include 9-vinylanthracene or 2-vinylanthracene; And as examples of vinylphenanthrene, 9-vinylphenanthrene may be mentioned.

Grafting of the aromatic compound to the polyolefin polymer chain is typically performed during the crosslinking step of the polyolefin according to radical addition mechanisms well known to those skilled in the art in the presence of the aliphatic tertiary alkyl peroxides of the present invention.

The crosslinkable composition according to the present invention may further comprise a protective agent such as one or more antioxidants. Antioxidants protect the composition against thermal constraints that occur during the manufacture of the cable or during the operation of the cable.

Antioxidants are preferably selected from:

Tetrakisethylene (3,5-di- t -butyl 4-hydroxyhydrocinnamate) methane, a sterically hindered phenolic antioxidant, octadecyl 3- (3,5-di- t -butyl-4- Hydroxyphenyl) propionate , 2,2'-thiodiethylenebis [3- (3,5-di- t -butyl-4-hydroxyphenyl) propionate], 2,2'-thiobis ( 6- t -butyl-4-methylphenol), 2,2'-methylenebis (6- t -butyl-4-methylphenol) , 1,2-bis (3,5-di- t -butyl-4- Hydroxyhydrocinnamoyl) hydrazine, [2,2'-oxamidobis (ethyl 3- (3,5-di- t -butyl-4-hydroxyphenyl) propionate] and 2,2'-oxamido Bis [ethyl 3- ( t -butyl-4-hydroxyphenyl) propionate];

Thioesters such as 4,6-bis (octylthiomethyl) -o -cresol, bis [2-methyl-4- {3-n- (C12 or C14) alkylthiopropionyloxy} -5- t -butyl Phenyl] sulfide and thiobis [2- t -butyl-5-methyl-4,1-phenylene] bis [3- (dodecylthio) -propionate];

Sulfur-based antioxidants such as dioctadecyl 3,3'-thiodipropionate or dididodecyl 3,3'-thiodipropionate;

Phosphorus-based antioxidants such as phosphites or phosphonates, for example tris (2,4-di- t -butylphenyl) phosphite or bis (2,4-di- t -butylphenyl) pentaerythritol Diphosphites; And

Antioxidants of the amine type, such as polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), the latter type of antioxidants are particularly preferred in the compositions of the invention.

TMQ can have multiple grades, that is:

A “standard” grade having a low degree of polymerization, ie, a grade having a residual monomer in an amount of more than 1% by weight and residual NaCl in a content of 100 ppm to 800 ppm or more;

A “high degree of polymerization” grade having a high degree of polymerization, ie, a grade having residual monomers of less than 1% by weight and residual NaCl of from 100 ppm to 800 ppm or more;

A "low residual salt content" grade, ie a grade having a residual NaCl of less than 100 ppm.

The type of stabilizer and its content in the crosslinkable composition are typically selected as a function of the maximum temperature the polymer will receive during the preparation of the mixture and by extrusion on the cable, which is also the maximum exposure time at that temperature. Depends on

The crosslinkable composition may typically comprise 0.1 to 2 weight percent antioxidant (s). In particular when the antioxidant is TMQ, it may preferably comprise up to 0.7% by weight of antioxidant (s).

Impact retardants; Processing aids such as lubricants or waxes; Compatibilizers; Binders; UV stabilizers; Nonconductive fillers; Conductive fillers; And / or other additives and / or fillers well known to those skilled in the art, such as semiconducting fillers, may additionally be added to the crosslinkable compositions of the present invention.

According to one preferred embodiment, the crosslinked layer of the invention is an electrically insulating layer (ie a second layer). In the case of an electrically insulating layer, the crosslinkable composition does not include any (electrically) conductive fillers and / or semiconducting fillers.

In particular, at least two of the three layers of the cable are crosslinked layers, preferably three layers of the cable are crosslinked layers.

When a crosslinkable composition is used in the manufacture of a semiconducting layer (first layer and / or third layer), the crosslinkable composition may also be used in which the composition which is crosslinkable with one or more (electrically) conductive fillers or one or more semiconducting fillers Include in an amount sufficient to become a last name.

In particular, it is considered that the semiconductor is semiconducting when the electrical conductivity of the layer is greater than 0.001 Sm ⁻¹ (siemens per meter).

The crosslinkable composition used to obtain the semiconducting layer may comprise 0.1 to 40% by weight of (electrically) conductive filler, preferably at least 15% by weight of conductive filler, more preferably at least 25% by weight of conductive filler. have.

The conductive filler can be advantageously selected from carbon black, carbon nanotubes and graphite, or mixtures thereof.

Regardless of whether it is a first semiconducting layer, a second electrically insulating layer and / or a third semiconducting layer, at least one of the three layers is an extruded layer, preferably two of the three layers are extruded layers, more preferably Preferably the three layers are extruded layers.

In one particular embodiment, generally in accordance with electrical cables well known in the field of application of the present invention, the first semiconducting layer, the second electrical insulation layer and the third semiconducting layer constitute a three-layer insulator. That is, the second electrically insulating layer is in direct physical contact with the first semiconducting layer and the third semiconductive layer is in direct physical contact with the second electrically insulating layer.

The electrical cable of the present invention may further comprise a metal shielding layer surrounding the third semiconducting layer.

The metal shielding layer comprises a "wire" shielding layer consisting of an assembly of copper or aluminum conductors arranged along a length around a third semiconducting layer, and one or more conductive metal strips helically spiraling around the third semiconducting layer. It may be a "strip" shield layer that is constructed, or a "leaktight" shield layer, such as a metal tube surrounding the third semiconducting layer. This type of shielding layer makes it possible to form a barrier, in particular against moisture, which tends to penetrate the electrical cable in the radial direction.

All types of metal shielding layers can serve to ground the electrical cable, thus delivering a short circuit in the event of a short circuit in the relevant communication network, for example.

The electrical cable of the present invention may also comprise an outer protective sheath surrounding the third semiconducting layer or optionally surrounding the metal shielding layer, especially when a metal shielding layer is present. The outer protective sheath is typically a suitable thermoplastic material such as HDPE, MDPE or LLDPE; Or optionally made of a flame retardant material or fire retardant material. In particular, if the latter material does not contain halogen, the sheath is referred to as HFFR (Halogen Free Flame Retardant) type.

Other layers, such as a layer that expands in the presence of moisture, may be added between the third semiconducting layer and the metal shielding layer in the presence of the metal shielding layer, and / or the metal shielding layer and the metal shielding layer and in the presence of the outer sheath. It can be added between the outer sheaths and these layers provide longitudinal and / or transverse leakage protection of the electrical cable with respect to water. The electrical conductor of the cable of the invention may further comprise a material which expands in the presence of moisture to obtain a "leaktight core".

Further features and advantages of the present invention will be described in terms of a non-limiting embodiment of the electric cable according to the invention, and FIG. 1 schematically showing a perspective view and a cross-sectional view of the electric cable according to a preferred embodiment according to the invention. This is referred to.

For the sake of clarity, only those elements which are essential for understanding the present invention have been shown schematically, which is not to scale.

The medium or high voltage power cable 1 shown in FIG. 1 comprises an elongated central conductive element 2, in particular made of copper or aluminum. With a continuous common axis around the conductive element 2, the power cable 1 is also the first semiconducting layer 3, also known as the "internal semiconducting layer", the second electrically insulating layer 4, the "external semiconductor". A third semiconducting layer 5, known as a "layer layer", a ground and / or protective metal shielding layer 6, and an outer protective sheath 7, wherein the layers 3, 4 and 5 comprise Can be obtained from Layers 3, 4 and 5 are extruded and crosslinked layers.
The presence of the metal shielding layer 6 and the outer protective sheath 7 is preferred, but not essential, and the structure of the cable itself is well known to those skilled in the art.

Crosslinkable  Preparation of the composition

Crosslinkable Composition C1 C2 C3 C4 C5 C6 C7 C8 C9 Polyolefin 100 100 100 100 100 100 100 100 100 BCP 1.42 1.27 1.12 - - - - - - DTBH - - - 1.25 1.05 1.05 1.05 1.05 1.05 Antioxidant 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 TVCH - 1.00 - - - 1.00 2.00 - - DVB - - 1.00 - - - - - - MDIB - - - - - - - 1.00 2.00

In Table 1, crosslinkable compositions C1, C4, C5, C8 and C9 are referred to as comparative examples and compositions C2, C3, C6 and C7 are referred to as compositions according to the invention.

The amounts of the components of Compositions C1 to C9 described in Table 1 are expressed in parts by weight (pcr) relative to 100 parts by weight of the polymer in the crosslinkable composition.

The sources of the various components of Compositions C1 to C9 of Table 1 are detailed below:

"Polyolefin" is a low density polyethylene sold under the trade name BPD 2000 by the company Ineos;

"BCP" is tert-butylcumyl peroxide sold under the name Luperox 801 by the company Arkema;

"DTBH" is 1,1-bis (tert-butylperoxy) cyclohexane (tertiary dialkyl aliphatic peroxide) sold by the company Arkema under the trade name Luperox 101;

"TVCH" is a crosslinking adjuvant 1,2,4-trivinylcyclohexane sold by BASF under the trade name TVCH;

"DVB" is a crosslinking adjuvant divinylbenzene sold by the company Sigma-Aldrich under the trade name divinylbenzene;

"MDIB" is the adjuvant m-diisopropenylbenzene sold under the name 1,3-diisopropenylbenzene by the company Sigma-Aldrich.

To sufficiently impregnate the polyethylene particles, compositions C1 to C9 are prepared by mixing the polyethylene particles with additives, peroxides, antioxidants and optionally an adjuvant for 3 hours in a closed container located in a roll mixer. do. The polyethylene particles were preheated to 60 ° C. before being impregnated.

The mixture was then left at 40 ° C. for 16 hours before sealing and storing.

Of composition Characterization

ratio- Crosslinked On a plate Characterization

Kinetics and levels of crosslinking

An MDR rheometer (Moving Die Rheometer, Alpha Technologies) makes it possible to monitor the crosslinking / vulcanization of the material by measuring a change in the viscosity of the material (DIN 53529 (1983)).

The chamber containing the sample is formed from two heating plates. The lower plate of the arc applies a vibration of a constant frequency (100 cycles / mn, ie 1.67 Hz) of amplitude ± 0.5 °; The top plate measures the material's response, ie the resistance of the material to the applied stress. The unit of measurement is torque, expressed in dN.m.

Samples are made from impregnated polyethylene particles, which are cast into plates of 3 mm thickness at 120 ° C. in a hydraulic press according to one third of a cycle under pressure of 100 bar for 2 minutes without pressure and Then cooled.

Two disks of 35 mm in diameter for complete lining of the chamber are cut out of the plate using a punch and then placed between two sheets of polyester terpene® located in the rheometer chamber.

The measurement is carried out at a temperature of 190 ° C., which indicates tube vulcanization conditions. After the initial drop in torque due to premelting of the material, the viscosity of the material and the resulting torque increase, which is a signal that crosslinking has occurred.

The parameter of interest is MH, which corresponds to the measured maximum torque. This is the plateau value obtained when the entire system reacts and when crosslinking reaches the maximum value available. For a given material, a good correlation between MH and crosslink density that controls the thermomechanical properties after the crosslinking step is noted.

● Breakdown time

Mooney Viscometer (Monsanto MV2000) makes it possible to measure the viscosity of a material or to monitor its change over time in the case of crosslinkable materials (standard ASTM D1646 (2005)).

It consists of two jaws that form a cylindrical hole for placing the sample under test. At the center of the chamber is a metal disk that rotates at a constant speed of 2 rpm. In the case of the present invention "large" of the two available size rotors is used.

During the measurement, the jaws and the chamber are maintained at a temperature and pressure of 130 ° C.

Samples are made from impregnated polyethylene particles, which are cast into plates of 3 mm thickness at 120 ° C. in a hydraulic press according to one third of a cycle under pressure of 100 bar for 2 minutes without pressure and Then cooled.

Four disks 50 mm in diameter are cut out of the plate using a punch. Two of them are drilled with holes 12 mm in diameter in the center so that they can be sewn onto the rotor stem; The other two will be stored intact and placed on the rotor. The whole is then placed between two sheets of polyester terpene® installed in the viscometer chamber.

The resistance of the material to the rotation of the rotor is measured. Measurements are expressed in Mooney (MU), in arbitrary units. The parameter of interest is the minimum viscosity value ML, measured at time t0 (minutes). ML + 1 is the viscosity value corresponding to ML increased by 1 Mooney unit. This is measured at time t1 (minutes). ML + 2 is the value corresponding to ML increased by 2 Mooney units. This is measured at time t2 (minutes).

Measurement of volatiles (ie methane) by the Sievert technique;

The amount of volatiles produced during the polyethylene crosslinking step and then removed is determined by Sievert method using PCT Pro 2000 (HY-ENERGY, SETARAM).

The sample is made from impregnated polyethylene particles, which are cast into a 1 mm thick plate at 120 ° C. temperature in a hydraulic press according to one cycle of three minutes under pressure of 100 bar for two minutes without pressure and then cooled.

The disc, 6 mm in diameter, is then cut out of the plate using a punch and then accurately weighed to within mg (total mass = 300-350 mg).

The sample is placed in the chamber of the instrument under pressure (helium). The chamber is connected to the 5 ml reservoir by a valve which is itself under pressure. At the beginning of the test, the pressure in the chamber and the reservoir is the same. During the temperature cycle the valve opens and closes intermittently, which leads to a new equilibrium when the valve is opened, and then allows a new pressure in the reservoir to be measured when the valve is closed. The cause of the pressure change is partly due to the release of methane and partly due to the change in size of the chamber with temperature. The real time recording of the amount of methane released thus necessitates precalibration by applying a temperature cycle envisioned to the chamber.

Simulating the crosslinking conditions for the various polyethylene layers in the vulcanization tube, the instrument provides a controlled temperature gradient of 1 ° C / s.

The cycle is expected to be heated from room temperature to 250 ° C.

The difference between the final pressure and the initial pressure at the same temperature gives access to methane emissions. The amount of volatiles (ie methane) is expressed in μmol / g of crosslinked polyethylene.

Crosslinked On a plate Characterization

Crosslink density by measurement of thermal creep

Plates 1 mm thick are cast from impregnated polyethylene particles. The molding is carried out at 120 ° C. temperature in the press according to one cycle of three minutes at 100 bar then two minutes without pressure. The plate is then cooled at a pressure of 100 bar.

The crosslinking step is carried out in a press at a temperature of 190 ° C., a pressure of 100 bar and lasts for 10 minutes. The mold is preheated to 190 ° C. The cooling step is carried out while maintaining a pressure of 100 bar.

Thermal creep measurements of materials under mechanical stress are determined according to standard NF EN 60811-2-1.

This test is commonly referred to as a hot set test (HST), which involves ballasting one end of an H2 dumbbell type specimen having a mass corresponding to a stress application equivalent to 0.2 MPa, and 15 Positioning the assembly in a heated oven at 200 ± 1 ° C. for minutes.

After this time, the maximum thermal elongation under stress of the specimen, expressed as a%, is recorded.

The suspended mass is then removed and the specimen is held in the oven for an additional 5 minutes.

Before expressed as a%, the residual permanent elongation, also known as residual magnetic (or residual magnetic elongation), is measured.

It is recalled that the more crosslinked the material, the lower the value of residual magnetism and maximum elongation under stress.

It is also noted that the test results are logically considered to be a failure if the specimen is broken during testing under the combined action of mechanical stress and temperature.

It should be noted above that if the elongation does not exceed 100% the value is considered to comply with the requirements. If this value is exceeded, the test action will be considered to be noncompliant, as ruptured.

● mechanical and thermal aging characteristics

Plates 1 mm thick are cast using impregnated particles. The casting is carried out at 120 ° C. in a press for 2 minutes without pressure followed by one cycle of 3 minutes at 100 bar. The plate is then cooled under a pressure of 100 bar.

The crosslinking step takes place at a temperature of 190 ° C. under a pressure of 100 bar in the press and lasts for 10 minutes. The mold is preheated to 190 ° C. The cooling step is carried out while maintaining a pressure of 100 bar.

Mechanical properties (elongation and stress at impact) are measured on specimens of H2 dumbbell type in accordance with standard NF EN 60811-1-1.

Specimens with accurate thickness measurements are tested after a minimum of 16 hours at room temperature. The traction speed is 200 mm / min. Thus, the value of the initial mechanical properties is determined.

Specimens with accurate thickness measurements are placed in an oven to accelerate thermal aging (7 days at 135 ° C.) and are then characterized in the same manner. Accordingly, the elongation and stress change with respect to the impact are determined. Regardless of whether it is tensile stress or elongation to impact, the change is considered sufficient when it is between + 25% and -25%.

All results regarding the characterization of the crosslinked plates with the non-crosslinked plates derived from the crosslinkable compositions C1 to C9 are shown in Table 2 below.

Crosslinkable Composition C1 C2 C3 C4 C5 C6 C7 C8 C9 MH
(dN.m) 3.2 3.4 3.2 3.0 2.2 3.2 2.8 1.9 1.2 ML at 130 ℃
(Mooney unit) 9.4 9.7 9.7 9.7 9.1 7.5 7.5 8.8 8.8 t0 (ML + 0)
(min) 15 22 13 17 19 31 25 22 15 t1 (ML + 1)
(min) 45 52 15 49 55 69 64 66 84 t2 (ML + 2)
(min) 66 74 16 79 91 102 104 115 154 CH ₄ Sievert
(μmol / g XLPE) 113 101 93 104 58 69 67 - - Hot set at 200 ° C Elongation
(%) 70-75 50-65 60-80 70-95 rupture 60-65 65-80 rupture rupture Residual magnetic
(%) 0 0 0 0 - 0 0 - - Accelerated thermal aging at 135 ° C. for 7 days Change in tensile stress
(%) -33 0 6 -33 -23 -16 0 +3 +3 Change in elongation at impact
(%) -17 +6 5 -16 -13 -4 +10 +3 -One

The addition of the adjuvant according to the invention makes it possible to significantly reduce the amount of peroxide required for crosslinking, thereby reducing the amount of volatiles (methane) released, while at the same time maintaining the desired crosslink density. Let's do it. This is given by the elongation in the heat setting test (HST) at MH and 200 ° C.

Comparative examples of compositions C1 (1.42 pcr BCP) and C4 (1.25 pcr DTBH) have an MH of about 3.0-3.2 dN.m and an HST elongation in the range of 60-80%.

In the case of cumyl peroxide (BCP), the addition of 1.0 pcr of TVCH allows the amount of peroxide to be lowered to 1.27 pcr (composition C2) without affecting the properties described above. The same conclusion applies to DVB of composition C3, where the addition of 1.0 pcr of DVB can reduce the amount of peroxide to 1.12 pcr. At the same time, the amount of methane released during crosslinking varies from 113 μmol / g XLPE to 101 μmol / g XLPE (TVCH) and 93 μmol / g XLPE (DVB). Compared to composition C1, the heat aging action at impact times t1 and t2 and 135 ° C for composition C2 was improved.

For aliphatic peroxides (DTBH) associated with Comparative Example C4, the addition of 1.0 pcr (composition C6) or 2.0 pcr (composition C7) TVCH lowers the amount of peroxide to 1.05 pcr without affecting the crosslinking properties. To be able. The amount of methane released during crosslinking is significantly reduced from 104 μmol / g XLPE to 69 μmol / g XLPE (composition C6) and 67 μmol / g XLPE (composition C7). In this case, the impact time and thermal aging at 135 ° C. are also significantly improved.

The reduction without addition of the adjuvant (composition C5) causes a crosslinked system (rupture in HST).

Under the same conditions (1.0 pcr TVCH, Composition C8-2.0 pcr TVCH, Composition C9), the use of m-diisopropenylbenzene (MDIB) does not result in a network that is sufficiently crosslinked to pass through HST.

Claims (12)

An electrical conductor 2, a first semiconducting layer 3 surrounding the electrical conductor 2, a second electrical insulation layer 4 surrounding the first layer 3 and a third surrounding the second layer 4 Comprising a semiconducting layer (5), wherein at least one of the three layers (3, 4, 5) is a crosslinked layer obtained from a crosslinkable composition comprising at least one polyolefin and an organic peroxide as a crosslinking agent. In the electric cable (1),
The composition further comprises a crosslinking aid comprising at least two unsaturated moieties, one of the unsaturated moieties being a vinyl functional group in the form CH ₂ = CH-,
Two such unsaturated moieties may first be grafted to the polyolefin, secondly may participate in crosslinking of the polyolefin,
The crosslinking aids reduce the proportion of organic peroxides used in the crosslinkable composition, and the crosslinked layer has a maximum thermal elongation under stress according to standard NF EN 60811-2-1 of 100% or less. An electric cable (1), characterized in that. The method of claim 1,
At least two unsaturated portions of said crosslinking aid are vinyl functional groups. The method according to claim 1 or 2,
And said polyolefin is an ethylene polymer. The method of claim 3,
The ethylene polymer is low-density polyethylene (LDPE: Low-Density PolyEthylene) characterized in that the electric cable. The method of claim 1,
And wherein the crosslinkable composition comprises more than 50.0 parts by weight of polyolefin based on 100 parts by weight of polymer in the composition. The method of claim 1,
And said organic peroxide is an aliphatic peroxide. The method of claim 6,
And wherein said organic peroxide is tertiary dialkyl aliphatic peroxide. The method of claim 1,
Wherein the crosslinkable composition further comprises an aromatic compound comprising a single reactive functional group capable of grafting to the polyolefin and at least one aromatic nucleus. The method of claim 8,
An electric cable, wherein the single reactive functional group of the aromatic compound is a vinyl functional group. The method of claim 1,
And wherein said crosslinked layer is an electrical insulation layer. The method of claim 1,
And wherein the three layers of the cable are crosslinked layers. The method of claim 1,
And wherein the crosslinkable composition comprises up to 2.00 parts by weight of organic peroxide with respect to 100 parts by weight of polymer (s) in the composition.

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