KR20180078194A - Medium-tension or high-tension electrical cable - Google Patents

Abstract

The present invention is to provide a medium-tension or high-tension electrical cable (1) that includes a cross-linking layer. The cable comprises an electrical conductor (2); a first semiconductor layer (3) surrounding the electrical conductor (2); a second electrical insulating layer (4) surrounding the first layer (3); and a third electrical insulating layer (5) surrounding the second layer (4), wherein at least one of the three layers (3, 4, 5) is a cross-linking layer obtained from a cross-linkable composition including at least one polyolefin and an organic peroxide as a cross-linking agent. In addition, the composition further includes a cross-linking aid including at least two unsaturated moieties, wherein one of the two unsaturated moieties is a vinyl functional group.

Description

[0001] MEDIUM-TENSION OR HIGH-TENSION ELECTRICAL CABLE [0002]

The present invention relates to an electric cable. The present invention applies to power cables of medium or high voltage (in particular exceeding 60 kV, which may range up to 800 kV) power cables, regardless of whether they are DC cables or AC cables, But is not limited thereto.

The intermediate or high voltage electrical cable typically comprises a central electrical conductor, a semiconductive inner layer having a common axis continuously around the electrical conductor, an electrically insulating medium layer and a semiconductive outer layer, Are cross-linked through 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-butyl cumyl peroxide. During the crosslinking of the compositions, the peroxides of this type are degraded to form crosslinking by-products, such as methane, acetophenone, cumyl alcohol, acetone, tert-butanol, a-methylstyrene and / or water. The last two byproducts are formed by the dehydration reaction of cumyl alcohol.

If the methane formed in the cross-linking step is not removed from the crosslinked layer, the risk associated with the explosive nature of methane and its flammability can not be ignored. The gas may also cause damage when the cable is used. Generally, in the case of the structures of medium-pressure and high-voltage cables, when the semiconducting outer layer is surrounded by a metal shielding layer, the gas flows longitudinally along the cable until it reaches the junction and terminals of the electrical equipment Can only spread. Thus, methane can accumulate and exert pressure on the electrical component, which can cause electrical shock. Methods exist to limit the presence of methane in the cable, such as, for example, heat treating 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.

Document US 5 252 676 discloses a three-layer insulation for power cables. These three-layer insulators are obtained from a composition comprising an ethylene copolymer, an organic peroxide as a crosslinking agent, and additives of the type such as 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 by-products and, at the same time, do not provide sufficient thermomechanical properties when the compositions are crosslinked.

It is an object of the present invention to overcome the disadvantages of the prior art by proposing a medium or high voltage electrical cable comprising a crosslinked layer wherein the formation of the crosslinked layer is carried out at the same time while significantly limiting the presence of crosslinking by- Provide optimal thermomechanical properties such as hot creep, which is characterized by an accurate cross-linking 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 Wherein 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 crosslinking agent, the composition comprising two or more unsaturated moieties, one of which is vinyl And a crosslinking auxiliary, which is a functional group, and the vinyl functional group is preferably an ethylenic functional group of the form of CH ₂ = CH-.

The crosslinking adjuvant of the present invention is different from the crosslinking agent, which is a polyfunctional type because it contains two or more unsaturated moieties.

The two or more unsaturated moieties are particularly reactive functional groups of the carbon-carbon double bond type, which can be grafted first to the polyolefin, followed by crosslinking of the polyolefin (i. E., The formation of a three-dimensional structure of the crosslinked polyolefin) .

The crosslinking adjuvant can advantageously significantly reduce the proportion of the organic peroxide used in the crosslinkable composition and thus reduce the amount of methane from the crosslinking by-products generated from the peroxide At the same time, it maintains thermomechanical properties such as excellent thermal creep and satisfactory crosslinking ratio. The thermomechanical properties for the crosslinked layers according to the invention are in accordance with the standard NF EN 60811-2-1 with stresses in the range 100% or less, preferably 80% or less, particularly preferably 60% to 80% Lt; RTI ID = 0.0 > maximum < / RTI >

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

For example, the crosslinking adjuvant may be selected from the group consisting of 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-tetradecadienes; 2,3-diphenyl-1,3-butadiene; Trans, trans-1,4-diphenyl-1,3-butadiene; 1,15-hexadecadien; 1,6-diphenyl-1,3,5-hexatriene; 2,3-dibenzyl-1,3-butadiene; And polybutadiene; Or mixtures thereof.

In a particular preferred embodiment embodiment, the two or more unsaturated moieties of the crosslinking adjuvant is an ethylenic functional group of the vinyl functional group, especially the CH ₂ = CH- form.

In the above case, the cross-linking aid may be 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-tetradecadienes; 1,15-hexadecadienes.

The concentration of the 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 a crosslinking aid, based on 100 parts by weight of the polymer (s) in the crosslinkable composition. The cross-linkable composition may preferably be used in an amount of 0.5 to 2 parts by weight, based on 100 parts by weight of the polymer (s) in the cross-linkable composition.

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

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

The aliphatic peroxide may be an aliphatic peroxide containing one or more tertiary alkyl groups. Mention may be made, as examples of aliphatic peroxides, of:

- Aliphatic peroxycarbonates such as tert-amylperoxy 2-ethylhexylcarbonate, tert-amylperoxy 2-ethylhexylcarbonate, tert-butylperoxyisopropylcarbonate;

- Aliphatic peroxides of tertiary dialkyl such as 1,1-bis (tert-butylperoxy) cyclohexane, 2,5-dimethyl-2,5-bis (tert-butylperoxy) Tert-butyl peroxide, di-tert-butyl peroxide, cyclic peroxides such as 3,6,9-triethyl (2-ethylhexyl) -3,6,9-trimethyl-1,4,7-triperoxonane;

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

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

Compared to aromatic peroxides, aliphatic peroxides have the advantage of not forming cumyl alcohol as a cross-linking by-product during cross-linking of the cross-linkable composition, thereby making it possible to significantly limit the presence of water in the cross-linked layer , While maintaining very good thermomechanical properties.

Of the above-mentioned aliphatic peroxides, preferably aliphatic peroxides of tertiary dialkyls will be used. This is because the peroxides of this type have a very good compromise between the crosslinking rate and the risk of burn-out or pre-crosslinking during use of the composition.

Preferably, the cross-linkable composition does not comprise any aromatic peroxide, especially, for example, dicumyl peroxide or derivatives thereof.

The peroxide-path cross-linking of the crosslinkable compositions according to the present invention can be carried out under the action of heat and pressure, such as using a vulcanization tube under nitrogen pressure, and such cross-linking techniques are well known to those of ordinary skill in the art.

The crosslinkable compositions of the present invention comprise not more than 2.00 parts by weight of an organic peroxide with respect to 100 parts by weight of the polymer (s) in the composition; Preferably not more than 1.50 parts by weight, based on 100 parts by weight of the polymer (s), of an organic peroxide in the composition; Preferably not more than 1.25 parts by weight, based on 100 parts by weight of the polymer (s), of an organic peroxide in the composition; And particularly preferably 1.10 parts by weight or less of organic peroxide, based on 100 parts by weight of the polymer (s) in the composition.

The term "polyolefin" as such generally means an olefin homopolymer or copolymer. The term may in particular mean a thermoplastic polymer or an elastomer.

Preferably, the olefin polymer is an ethylene homopolymer or an 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, copolymers of ethylene and vinyl acetate (EVA), copolymers of ethylene and butyl acrylate (EBA), copolymers of ethylene and methyl acrylate (EMA) Copolymers of 2-hexylethyl acrylate, copolymers of ethylene and alpha-olefins such as polyethylene-octene (PEO), polyethylene-butene (PEO) Polyethylene-butene (PEB), copolymers of ethylene and propylene (EPR) such as ethylene-propylene-diene (EPDM) terpolymers and mixtures thereof. It is hereinafter.

Low density polyethylene (LDPE) is preferably used because it has excellent rheological properties and very good thermomechanical and electrical properties in use by extrusion.

The term "low density" means a density which can be included in the range of 0.910 to 0.940 g / cm3, preferably 0.910 to 0.930 g / cm3, in particular according to the standard ISO 1183 (at a temperature of 23 캜).

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 a polyolefin in an amount greater than 50.0 parts by weight per 100 parts by weight of the polymer (s) (i. E., The polymer matrix) in the composition, preferably greater than or equal to 70 parts per 100 parts by weight of the polymer Polyolefins, particularly preferably at least 90 parts by weight of polyolefins relative to 100 parts by weight of the polymer (s) in the composition.

In a particularly advantageous manner, the crosslinkable composition comprises a polymer matrix consisting solely of a polyolefin or a mixture of polyolefins.

The crosslinkable compositions of the present invention may additionally comprise an aromatic compound comprising a single reactive functional group capable of grafting to the polyolefin and at least one aromatic nucleus. Preferably, the reactive functional group of the aromatic compound is a vinyl functional group. Thus, when the aromatic compound is present in the crosslinkable composition, it does not participate in the cross-linking of the polyolefin as opposed to the crosslinking aid.

The crosslinked layer obtained from the crosslinkable composition is reinforced in the field of electric cables and has a lasting property and provides better water treeing resistance. Particularly to resistance to breakdown, and in particular to the ability to dissipate space charge stored in a high voltage cable under direct current.

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

Examples of the 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 can be mentioned.

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

The grafting of the aromatic compound to the polyolefin polymer chain is typically carried out in the presence of the aliphatic tertiary alkyl peroxide of the present invention during the cross-linking step of the polyolefin according to the radical addition mechanism well known to those of ordinary skill in the art.

The crosslinkable compositions according to the present invention may additionally comprise a protective agent such as one or more antioxidants. The antioxidant protects the composition against thermal constraints that occur during the fabrication of the cable or during the operation of the cable.

The antioxidant is preferably selected from the following:

(3,5-di- t -butyl 4-hydroxyhydrocinnamate) methane, octadecyl 3- (3,5-di- t -butyl- Hydroxyphenyl) propionate , 2,2'-thiodiethylenebis [3- (3,5-di- t -butyl-4-hydroxyphenyl) propionate], 2,2'-thiobis 6- t - butyl-4-methylphenol), 2,2'-methylene-bis (6- t - butyl-4-methylphenol), 1,2-bis (3,5-di - t - butyl-4 (3,5-di- t -butyl-4-hydroxyphenyl) propionate] and 2,2'-oxamido Bis [ethyl 3- ( t -butyl-4-hydroxyphenyl) propionate];

- thio esters, such as 4,6-bis (octyl thiomethyl) - o - cresol, bis [2-methyl -4- {3-n- (C12 or C14) alkylthio propionyloxy} -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 didodecyl 3,3'-thiodipropionate;

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

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

TMQ can have multiple grades, namely:

- a grade of "standard" grade with a low degree of polymerization, ie residual monomers in excess of 1% by weight and residual NaCl in contents of 100 ppm to 800 ppm (parts per million by mass);

- a degree of polymerization of high "high degree of polymerization ", i.e. a residual monomer content of less than 1% by weight and a residual NaCl content of greater than 100 ppm to 800 ppm;

- a grade with a "low residual salt content" rating, ie with a residual NaCl content 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 that the polymer is subjected to during the preparation of the mixture and during extrusion on the cable, Lt; / RTI >

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

Shock retarder; Process aids such as lubricating oil or wax; Compatibilizers; Binder; UV stabilizers; Nonconductive filler; Conductive fillers; And / or other additives and / or fillers well known to those of ordinary skill in the art, such as semiconducting fillers, can additionally be added to the crosslinkable compositions of the present invention.

According to one preferred embodiment, the crosslinked layer of the present invention is an electrically insulating layer (i.e., the second layer). In the case of an electrically insulating layer, the cross-linkable composition does not include any (electrically) conductive fillers and / or semiconductive fillers.

In particular, two or more of the three layers of the cable are crosslinked layers, preferably three layers of cables are crosslinked layers.

When a crosslinkable composition is used in the production of the semiconducting layer (the first layer and / or the third layer), the crosslinkable composition also comprises one or more (electrically) conductive fillers or one or more semiconducting fillers capable of cross- In an amount sufficient to become sexually active.

Particularly, when the electrical conductivity of the layer is 0.001 Sm ^-1 (siemens per meter) or more, semiconducting properties are considered.

The crosslinkable composition used to obtain the semiconducting layer may comprise from 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 may be advantageously selected from carbon black, carbon nanotubes and graphite, or mixtures thereof.

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

In certain embodiments, the first semiconducting layer, the second electrically insulating layer, and the third semiconducting layer comprise a three-layer insulator, generally according to the electrical cable well known in the application of the present invention. That is, the second electrically insulating layer is in direct physical contact with the first semiconducting layer and the third semiconducting layer is in direct physical contact with the second electrically insulating layer.

The electrical cable of the present invention may additionally 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 the length around a third semiconducting layer, and one or more conductive metal strips spirally laid around the third semiconducting layer Quot; strip "shielding layer such as a" strip "shielding layer, or a metal tube surrounding a third semiconducting layer. This type of shielding layer makes it possible to form a barrier against moisture which tends to penetrate the electrical cable, especially in the radial direction.

All types of metal shielding layers can serve to ground the electrical cable and thereby deliver a short circuit in the event of a short circuit in the associated network, for example.

The electrical cable of the present invention may also include an outer protective sheath surrounding the third semiconducting layer, or alternatively surrounding the metal shielding layer, especially when a metal shielding layer is present. The outer protective sheath typically comprises a suitable thermoplastic material such as HDPE, MDPE or LLDPE; Or alternatively can be made of flame retardant or fire resistant materials. 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 when the metal shielding layer is present, and / or between the metal shielding layer and the metal shielding layer when the metal shielding layer and the outer sheath are present. May be added between the outer sheaths and these layers provide longitudinal and / or transverse leakage protection of the electrical cable relative to the water. The electrical conductor of the cable of the present invention may additionally comprise a material that expands in the presence of moisture to obtain a "leaktight core ".

Other features and advantages of the present invention will be described in the context of a non-limiting embodiment of an electrical cable according to the present invention, which is schematically illustrated in a perspective view and a cross-sectional view of an electrical cable in accordance with a preferred embodiment of the present invention. .

For purposes of clarity, only those components that are essential to an understanding of the present invention are shown graphically and are not to scale at a constant rate.

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. The power cable 1 also has a first semiconducting layer 3, also known as an "inner semiconducting layer ", a second electrical insulating layer 4, an" outer semiconducting layer " Layers 3, 4 and 5 comprise a third semiconducting layer 5, a grounding and / or protective metal shielding layer 6, and an outer protective sheath 7, As shown in FIG. Layers 3, 4 and 5 are extruded and crosslinked layers.
The presence of the metal shield layer 6 and the outer protective sheath 7 is preferred, but is not essential, and the structure of the cable itself is well known to those of ordinary skill in the art.

Crosslinkable  Preparation of 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, cross-linkable 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 present invention.

The amount of the constituents of the compositions C1 to C9 shown in Table 1 is expressed in parts by weight (pcr) relative to 100 parts by weight of the polymer in the crosslinkable composition.

The sources of the various constituents of compositions C1 to C9 of Table 1 are as follows:

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

- "BCP" is tert-butyl cumyl peroxide, marketed by Arkema under the trade name Luperox 801;

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

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

- "DVB" is a crosslinking adjuvant divinyl benzene available from Sigma-Aldrich under the trade name divinylbenzene;

- "MDIB" is m-diisopropenyl benzene, available from Sigma-Aldrich under the trade name 1,3-diisopropenylbenzene.

To sufficiently impregnate the polyethylene particles, the compositions C1 to C9 were prepared by mixing the polyethylene particles with the additives peroxide, antioxidant and optionally auxiliaries in a closed vessel located in a roll mixer for 3 hours do. The polyethylene particles were pre-heated to 60 占 폚 before impregnation.

The mixture was then kept at 40 DEG C for 16 hours before being sealed and stored.

Of the composition Characterization

ratio- Crosslinked On the plate, Characterization

● Kinetics and levels of crosslinking

The MDR rheometer (Alpha Technologies) makes it possible to monitor the crosslinking / vulcanization of the material by measuring the change in viscosity of the material (DIN 53529 (1983)).

The chamber containing the sample is formed from two heating plates. The bottom plate of the arc applies a vibration of a constant frequency (100 cycles / mn, i.e. 1.67 Hz) with an amplitude of +/- 0.5 degrees; The top plate measures the reaction of the material, i.e. the resistance of the material to the applied stress. The unit of measurement is torque, expressed in dN.m.

The samples were made from impregnated polyethylene particles, which were cast for 2 minutes without pressure and then with a 3 mm thick plate at a temperature of 120 DEG C in a hydraulic press according to one cycle of 3 minutes under a pressure of 100 bar, And then cooled.

Two discs 35 mm in diameter for completely lining the chamber are cut from the plate using a punch and then placed between two sheets of polyester terpene (R) located in the rheometer chamber.

The measurement is carried out at a temperature of 190 캜, which indicates a tube vulcanization condition. After the initial drop in the torque due to the pre-melting of the material, the viscosity of the material and the resulting torque increase, which is a signal that cross-linking 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 the cross-linking reaches the maximum available. For a given material, an excellent correlation between MH and cross-linking density controlling thermomechanical properties after the cross-linking step is noted.

● Breakdown time

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

It consists of two jaws forming a cylindrical hole that positions the sample to be tested. 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" is used among the two available standard rotors.

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

The samples were made from impregnated polyethylene particles, which were cast for 2 minutes without pressure and then with a 3 mm thick plate at a temperature of 120 DEG C in a hydraulic press according to one cycle of 3 minutes under a pressure of 100 bar, And then cooled.

Four disks with a diameter of 50 mm are cut from the plate using a punch. Two of them are drilled 12 mm in diameter in the center so that they can be stitched to the rotor stem; The other two will be stored intact and placed on the rotor. The entirety is then placed between two sheets of polyester terpene (R) installed in the viscometer chamber.

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

● Measurement of volatile substances (ie, methane) by Sievert technique

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

The samples were made from impregnated polyethylene particles, which were cast into a 1 mm thick plate in a hydraulic press at a temperature of 120 DEG C in a hydraulic press, followed by two minutes without pressure, followed by one cycle of 3 minutes under a pressure of 100 bar, and then cooled.

Subsequently, the disc having a diameter of 6 mm is cut out from 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 apparatus under pressure (helium). The chamber is connected to the 5 ml reservoir by a valve that is under pressure by itself. At the beginning of the test, the pressure in the chamber and in the reservoir are the same. During the temperature cycle, the valve is intermittently opened and closed, reaching a new equilibrium when the valve is opened, and then allowing 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 size change of the chamber with temperature. Thus, real-time recording of the amount of methane released requires precalibration by applying a simulated temperature cycle to the chamber.

While simulating the crosslinking conditions for the various polyethylene layers within the vulcanization tube, the instrument provides a temperature gradient controlled at 1 占 폚 / s.

The cycle is expected to be heated from room temperature to 250 < 0 > C.

The difference between the final pressure and the initial pressure at the same temperature makes it possible to approach methane emissions. The amount of volatile material (ie, methane) is expressed in μmol / g of cross-linked polyethylene.

Crosslinked Plate Characterization

Crosslinking density by measurement of thermal creep

1 mm thick plates are cast from impregnated polyethylene particles. The molding is carried out at a temperature of 120 DEG C in a press in two cycles without pressure and then one cycle in three minutes at 100 bar. 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 DEG C, a pressure of 100 bar, and lasts for 10 minutes. The mold is pre-heated to 190 占 폚. The cooling step is carried out while maintaining a pressure of 100 bar.

The measurement of thermal creep of a material under mechanical stress is determined according to standard NF EN 60811-2-1.

The test is generally referred to as a hot set test (HST), which includes ballasting one end of an H2 dumbbell-shaped specimen having a mass corresponding to a stress application equal to 0.2 MPa, and 15 Lt; RTI ID = 0.0 > 200 C < / RTI > 1 C for 1 minute.

After this time, the maximum heat 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 being expressed as a%, the residual permanent elongation, also known as the residual magnetic (or residual magnetic elongation), is measured.

It is recalled that the more crosslinked the material is, the lower the values of residual magnetic and stress under maximum elongation are.

It is also noted that if the specimen undergoes a break during testing under the combined action of mechanical stress and temperature, then the test result is considered to be a logical failure.

It should be noted that if the elongation does not exceed 100%, the value is considered to be in compliance with the requirements. If the value is exceeded, the test action will be deemed to be non-compliant as well as ruptured.

● Mechanical and thermal aging characteristics

1 mm thick plates are cast using impregnated particles. The casting is carried out in a press at 120 ° C for two minutes without pressure and then one cycle of three minutes at 100 bar. The plate is then cooled under a pressure of 100 bar.

The crosslinking step occurs in a press at a temperature of 190 DEG C under a pressure of 100 bar and lasts for 10 minutes. The mold is pre-heated to 190 占 폚. The cooling step is carried out while maintaining a pressure of 100 bar.

The mechanical properties (elongation and stress at impact) are measured for H2 dumbbell specimens according to standard NF EN 60811-1-1.

Specimens whose thickness is accurately measured are tested after at least 16 hours at room temperature. The traction speed is 200 mm / min. Thus, the value of the initial mechanical property is determined.

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

All the results regarding the characterization of the non-crosslinked and cross-linked plates derived from crosslinkable compositions C1 to C9 are given 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 of XLPE) 113 101 93 104 58 69 67 - - Heat setting at 200 ° C (Hot set) Maximum elongation
(%) 70-75 50-65 60-80 70-95 rupture 60-65 65-80 rupture rupture Residual magnetism
(%) 0 0 0 0 - 0 0 - - Accelerated thermal aging for 7 days at < RTI ID = 0.0 > 135 C & 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 volatile material (methane) released and at the same time maintaining the desired cross-linking density . This is given by the elongation at MH and the heat set test (HST) at 200 ° C.

A comparative example of composition C1 (1.42 pcr BCP) and C4 (1.25 pcr DTBH) has 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 reduced to 1.27 pcr (composition C2) without affecting the above mentioned properties. The same conclusion applies for DVB of Composition C3, which can reduce the amount of peroxide to 1.12 pcr by the addition of 1.0 pcr of DVB. At the same time, the amount of methane released during crosslinking changes from 113 μmol / g of XLPE to 101 μmol / g of XLPE (TVCH) and 93 μmol / g of XLPE (DVB). Compared to composition C1, impact times t1 and t2 for composition C2 and thermal aging at 135 deg. C were improved.

For the aliphatic peroxide (DTBH) associated with Comparative Example C4, the addition of TVCH of 1.0 pcr (Composition C6) or 2.0 pcr (Composition C7) lowered the amount of peroxide to 1.05 pcr without affecting the crosslinking properties I will. The amount of methane released during crosslinking is significantly reduced from 104 μmol / g of XLPE to 69 μmol / g of XLPE (composition C6) and 67 μmol / g of XLPE (composition C7). In this case, the impact time and the heat aging action at 135 占 폚 are also considerably improved.

The reduction without addition of adjuvant (Composition C5) results in a crosslinked system (rupture in HST).

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

Claims (12)

(3) surrounding the electrical conductor (2), a second electrically insulating layer (4) surrounding the first layer (3) and a third electrically insulating layer (4) surrounding the second layer (4) Wherein at least one of the three layers (3,4,5) comprises a semiconductive layer (5), wherein the 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)
Wherein the composition further comprises a crosslinking aid comprising two or more unsaturated moieties, wherein one of the unsaturated moieties is a vinyl functional group of the form CH ₂ = CH-,
Characterized in that the two unsaturated moieties are capable of grafting first to the polyolefin and secondly are capable of participating in the crosslinking of the polyolefin and that the crosslinking aid is a non-polymeric type One). The method according to claim 1,
Wherein the two or more unsaturated moieties of the crosslinking aid are vinyl functional groups. 3. The method according to claim 1 or 2,
Wherein the polyolefin is an ethylene polymer. The method of claim 3,
Wherein the ethylene polymer is low density polyethylene (LDPE). The method according to claim 1,
Wherein the crosslinkable composition comprises greater than 50.0 parts by weight of polyolefin relative to 100 parts by weight of the polymer in the composition. The method according to claim 1,
Wherein the organic peroxide is an aliphatic peroxide. The method according to claim 6,
Wherein the organic peroxide is a tertiary dialkyl aliphatic peroxide. The method according to claim 1,
Wherein the crosslinkable composition additionally comprises an aromatic compound comprising a single reactive functional group capable of grafting to the polyolefin and at least one aromatic nucleus. 9. The method of claim 8,
Wherein the single reactive functional group of the aromatic compound is a vinyl functional group. The method according to claim 1,
Wherein the crosslinked layer is an electrically insulating layer. The method according to claim 1,
Wherein the three layers of the cable are crosslinked layers. The method according to claim 1,
Wherein the crosslinkable composition comprises not more than 2.00 parts by weight of an organic peroxide with respect to 100 parts by weight of the polymer (s) in the composition.

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