MEDIUM- OR HIGH-VOLTAGE ELECTRIC DEVICE

Abstract

The invention relates to an electrical device (1,20,30) comprising a cross-linked layer (3, 4, 5, 21, 22, 23, 31, 32) produced from a polymer composition comprising: at least one polymer A comprising at least one epoxy function; and a cross-linking agent B comprising at least one reactive function that can react with the epoxy function of said polymer A in order to allow the cross-linking of said polymer A. The device is characterised in that the polymer composition also comprises a compound C comprising: at least one aromatic group; and a reactive group that can physically interact with the hydroxyl function formed by the opening of said epoxy function during the cross-linking of polymer A.

Description

The present invention relates to an electrical device of the electric cable or electric cable accessory type. It typically but not exclusively applies to the fields of low-voltage (in particular of less than 6 kV), medium-voltage (in particular from 6 to 45-60 kV) or high-voltage (in particular greater than 60 kV, and which can range up to 800 kV) power cables, whether they are direct current or alternating current.

Power cables typically comprise a central electrical conductor and at least one electrically insulating layer crosslinked by techniques well known to a person skilled in the art, in particular by the peroxide route.

The peroxide route is tending to be increasingly avoided with respect to the decomposition products of peroxide, which exhibit disadvantages during the manufacture of the cable, indeed even once the cable is in the operational configuration. This is because, during the crosslinking, the peroxides decompose and form crosslinking by-products, such as, in particular, methane, acetophenone, cumyl alcohol, acetone, tert-butanol, α-methylstyrene and/or water. The formation of water from cumyl alcohol is relatively slow and can occur after several months, indeed even a few years, once the cable is in the operational configuration. The risk of breakdown of the crosslinked layers is thus significantly increased. In addition, if the methane formed during the crosslinking stage is not discharged from the crosslinked layers, risks related to the explosiveness of methane and its ability to ignite cannot be ignored. This gas can also cause damage once the cable is put into service. Even if solutions exist for limiting the presence of methane within the cable, such as, for example, heat treating the cable in order to accelerate the diffusion of methane outside the cable, they become lengthy and expensive when the thickness of the crosslinked layers is high.

Mention may be made, as example of crosslinking process not using the peroxide route, of the document U.S. Pat. No. 4,826,726, which describes a heat-resistant electric cable comprising an elongated electrical conductor surrounded by a crosslinked layer obtained from a composition comprising an ethylenic copolymer comprising an oxirane functional group and a polymeric compound, as crosslinking agent, of the copolymer of ethylene and of unsaturated dicarboxylic acid anhydride type.

However, once said composition has been crosslinked, the layer obtained does not exhibit optimum properties of tensile strength and elongation at break, in particular during the life of the electric cable (cf. aging).

The aim of the present invention is to overcome the disadvantages of the techniques of the prior art by providing an electrical device, of the electric cable or electric cable accessory type, comprising a crosslinked layer, the manufacture of which significantly limits the presence of crosslinking by-products, such as, for example, methane and/or water, while guaranteeing optimum mechanical properties (tensile strength and elongation at break) during the life of the electrical device.

A subject matter of the present invention is an electrical device comprising a crosslinked layer obtained from a polymer composition comprising:

• • at least one polymer A comprising at least one epoxy functional group, and
  • a crosslinking agent B comprising at least one reactive functional group capable of reacting with the epoxy functional group of said polymer A in order to make possible the crosslinking of said polymer A, characterized in that the polymer composition additionally comprises a compound C comprising:
  • at least one aromatic group, and
  • a reactive group capable of interacting physically with the hydroxyl functional group formed by the opening of said epoxy functional group during the crosslinking of the polymer A.

By virtue of the invention, the crosslinked layer makes it possible to avoid the use of organic peroxide while guaranteeing, on the one hand, a high level of crosslinking and, on the other hand, very good mechanical properties of the type consisting of tensile strength and elongation at break according to French standard NF EN 608 11-1-1, during the life of the electrical device.

In addition, the crosslinked layer of the invention exhibits the advantage of being economical, easy to process, in particular by extrusion, and easy to manufacture since it does not require resorting to restrictive venting processes.

The Compound C

The reactive group of the compound C is in particular capable of interacting physically with the hydroxyl functional group which is formed during the crosslinking of the polymer A with the compound B. In other words, the reactive group of the compound C is not capable of interacting chemically with the hydroxyl functional group formed from the epoxy functional group of the polymer A during the crosslinking of the polymer composition. It thus does not modify the chemical structure of said hydroxyl functional group; in particular, it is not capable of forming a chemical bond of the covalent type with said hydroxyl functional group.

More particularly, said reactive group is capable of forming van der Waals' bonds and/or hydrogen bonds with the hydroxyl groups originating from the epoxy functional groups of the polymer A, once opened.

The compound C makes it possible to significantly limit, indeed even to prevent, the epoxy functional groups liable to have not reacted during the crosslinking of the polymer composition from reacting chemically by etherification with the hydroxyl groups originating from the epoxy functional groups, once opened.

The compound C will thus sterically hinder the hydroxyl groups originating from the epoxy functional groups already opened and will thus significantly limit, indeed even prevent, the etherification of the epoxy functional groups liable to have not reacted during the crosslinking.

The compound C can be different from the polymer A and from the crosslinking agent B. It is preferably an organic compound.

The compound C can be a polymeric or nonpolymeric compound.

“Nonpolymeric compound” is understood to mean a compound other than a polymer. In other words, this compound does not in particular result from the covalent linking of a large number of identical or different monomer units and more particularly does not result from the covalent linking of at least two identical or different monomer units.

Particularly preferably, the compound C is an antioxidant.

The reactive group of the compound C can be a hydrogen atom, in particular in the form of a hydroxyl (OH) group and/or of an amine (NH) group, it being possible for the amine to be of the primary or secondary type.

The aromatic group of the compound C can be a benzene group or one of its derivatives.

According to a first alternative form, the aromatic group together with the reactive group can form a phenol group.

Preferably, the phenol group is disubstituted in the ortho position.

Mention may be made, by way of examples, of the following compounds, comprising at least one phenol group disubstituted in the ortho position:

• • 2-methyl-4,6-bis[(octylthio)methyl]phenol (Irgastab KV10; CAS No. 110553-27-0);
  • benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-, 1,1′-(2,2-bis((3-(3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)-1-oxopropoxy)methyl)-1,3-propanediyl) ester (Irganox 1010; CAS No. 6683-19-8);
  • 3,5-bis(1,1-dimethylethyl)-4-hydroxybenzenepropanoic acid octadecyl ester (Irganox 1076; CAS No. 2082-79-3);
  • 1,3,5-trimethyl-2,4,6-tris[3′,5′-di(tert-butyl)-4′-hydroxybenzyl]benzene (Irganox 1330; CAS No. 1709-70-2);
  • thiodiethylene bis{3-[3,5-di(tert-butyl)-4-hydroxyphenyl]propionate} (Irganox 1035; CAS No. 41484-35-9).

Particularly preferably, the phenol group is a di(tert-butyl)-4-hydroxyphenyl group. Mention may be made, by way of examples, of Irganox 1010, Irganox 1076, Irganox 1330 or Irganox 1035.

In this first alternative form, the compound C can thus be Irganox 1035 or else a compound which is not Irganox 1035.

According to a second alternative form, the aromatic group together with the reactive group form an aminobenzene group, the amine of which is of the primary or secondary type. Mention may be made, by way of examples, of 1,2-dihydro-2,2,4-trimethylquinoline or poly(1,2-dihydro-2,2,4-trimethylquinoline) (CAS No. 26780-96-1).

The compound C of the invention can additionally comprise a thioether group. Mention may be made, by way of examples, of Irgastab KV10 or Irganox 1035.

The polymer composition in accordance with the invention can comprise at most 10.0 parts by weight of compound C per 100 parts by weight of polymer(s) in the composition, preferably at most 5.0 parts by weight of compound C per 100 parts by weight of polymer(s) in the composition, preferably at most 2.0 parts by weight of compound C per 100 parts by weight of polymer(s) in the composition and particularly preferably at most 1.0 part by weight of compound C per 100 parts by weight of polymer(s) in the composition.

The polymer composition in accordance with the invention can comprise at least 0.01 part by weight of compound C per 100 parts by weight of polymer(s) in the composition and preferably at least 0.1 part by weight of compound C per 100 parts by weight of polymer(s) in the composition.

In the present invention, when reference is made to “100 parts by weight of polymer(s)”, this is understood to mean preferably the polymer or polymers other than the crosslinking agent B and the compound C in the polymer composition (when the crosslinking agent B and/or the compound C are in the polymer form).

The Polymer A

The epoxy functional group (i.e., the epoxide functional group) or the polymer A is more particularly an oxirane functional group (i.e., an ethylene oxide group).

Preferably, the epoxy functional group can be contributed by a compound comprising said epoxy functional group, it being possible for this compound to be chosen from glycidyl esters. Thus, the polymer of the invention can comprise glycidyl ester groups.

The polymer A of the invention can comprise at most 10% by weight of epoxy functional group and preferably at most 5% by weight of epoxy functional group.

The polymer A of the invention can comprise at least 0.1% by weight of epoxy functional group and preferably at least 1% by weight of epoxy functional group.

According to a first alternative form, the epoxy functional group of the polymer A can be grafted to said polymer. The polymer comprising at least one epoxy functional group of the invention is, according to this first alternative form, an epoxy-grafted polymer. In other words, the polymer according to the invention can be a polymer comprising at least one epoxy functional group grafted to the macromolecular chain (i.e., main chain or backbone) of said polymer. The ends of the macromolecular chain of the polymer may or may not for their part be grafted with the epoxy functional group.

According to a second alternative form, the polymer comprising at least one epoxy functional group of the invention can be a copolymer obtained from at least two monomers, one of the two monomers comprising said epoxy functional group. Said monomer comprising said epoxy functional group can be chosen from the following compounds: butenecarboxylic acid monoglycidyl ester, glycidyl methacrylate, glycidyl acrylate, methylglycidyl acrylate, methylglycidyl methacrylate, itaconic acid glycidyl ester, 7,8-epoxy-1-octyl methacrylate, itaconic acid methylglycidyl ester, 7,8-epoxy-1-octyl vinyl ether, vinyl glycidyl ether, allyl glycidyl ether and 2-methyl-2-propenyl glycidyl ether.

Mention may be made, by way of example, as polymer comprising at least one epoxy functional group, of a copolymer of ethylene and glycidyl methacrylate.

The polymer A of the invention is more particularly an organic polymer, making it possible in particular to shape the polymer composition by extrusion.

The polymer A can comprise at least one polyolefin. The term “polyolefin” as such means generally olefin polymer of the olefin homopolymer or copolymer type. Preferably, said olefin polymer is a noncyclic olefin polymer.

In the present invention, it will be preferable to use an ethylene polymer (ethylene homo- or copolymer) or a propylene polymer (propylene homo- or copolymer).

The first alternative form of the invention can be used with an epoxy-grafted olefin homopolymer or an epoxy-grafted olefin copolymer.

The second alternative form of the invention can be used with a copolymer obtained from an olefin monomer and a monomer comprising at least one epoxy functional group, as described above.

The polymer composition of the invention can comprise more than 50.0 parts by weight of polymer(s) comprising at least one epoxy functional group (i.e., polymer A) per 100 parts by weight of polymer(s) (i.e., polymer matrix) in the polymer composition; preferably at least 70 parts by weight of polymer(s) A per 100 parts by weight of polymer(s) in said polymer composition; and particularly preferably at least 90 parts by weight of polymer(s) A per 100 parts by weight of polymer(s) in said polymer composition.

In the present invention, when reference is made to “100 parts by weight of polymer(s)”, this is understood to mean preferably the polymer or polymers other than the crosslinking agent B and the compound C in the polymer composition (when the crosslinking agent B and/or the compound C are in the polymer form).

Particularly advantageously, the constituent polymer or polymers of the polymer composition are solely one or more olefin-based polymer(s) (i.e., olefin homopolymer and/or copolymer).

In a specific embodiment, the polymer of the invention can additionally comprise at least one acrylate functional group. This acrylate functional group advantageously makes it possible to render the polymer of the invention supple and more flexible.

According to a first alternative form, the acrylate functional group can be grafted to the polymer of the invention. The polymer of the invention is, according to this first alternative form, an acrylate-grafted polymer. In other words, the polymer according to the invention can be a polymer comprising at least one acrylate functional group grafted to the macromolecular chain (i.e., main chain or backbone) of said polymer. The ends of the macromolecular chain of the polymer may or may not, for their part, be grafted with the acrylate functional group.

According to a second alternative form, the polymer of the invention can be a copolymer obtained from at least two monomers, one of the two monomers comprising said acrylate functional group. Mention may be made, by way of example, of the terpolymer of ethylene, methyl acrylate and glycidyl methacrylate.

The Crosslinking Agent B

The crosslinking agent B of the invention can be a polymeric compound or a nonpolymeric compound. Preferably, the crosslinking agent is other than the polymer A.

It will be preferable to use a nonpolymeric compound as compound B since this type of crosslinking agent advantageously makes it possible to improve the resistance to electrical breakdowns of the crosslinked layer, in particular according to the standard IEC 62539, at 20° C., based on the Weibull distribution.

When the crosslinking agent of the invention is of the “nonpolymeric” type, it does not result from the covalent linking of a large number of identical or different monomer units and preferably it does not result from the covalent linking of at least two identical or different monomer units.

The reactive functional group of the crosslinking agent is capable of reacting with the epoxy functional group of the said polymer in order to make possible the crosslinking of said polymer. It will react directly with the epoxy functional group after opening the epoxy during a rise in temperature.

The reactive functional group of the crosslinking agent can be chosen from an anhydride functional group, a carboxyl functional group and an amine functional group.

When the crosslinking agent comprises at least one amine functional group, the amine functional group is a primary or secondary amine.

In a specific embodiment, the crosslinking agent can comprise at least two reactive functional groups. These two reactive functional groups can be identical or different and can be chosen without distinction from an anhydride functional group, a carboxyl functional group and an amine functional group.

The crosslinking agent can preferably comprise an amine functional group and a carboxyl functional group.

The crosslinking agent can preferably comprise two amine functional groups.

Mention may be made, as examples of nonpolymeric crosslinking agent, of amino acids, diamines, anhydrides, Lewis acids or Brønsted acids.

The preferred nonpolymeric crosslinking agent of the invention is chosen from:

• • a nonpolymeric compound comprising at least one amine functional group and at least one carboxyl functional group, i.e. an amino acid,
  • a nonpolymeric compound comprising at least one anhydride functional group, preferably in combination with a crosslinking catalyst, and
  • one of their mixtures.

The amino acid typically comprises two functional groups: a carboxyl —COOH functional group and an amine functional group which is preferably of the primary amine —NH₂ type. The carbon chain separating the carboxyl functional group from the amine functional group can comprise from 1 to 50 carbon atoms and preferably from 1 to 20 carbon atoms. Conventionally, the carboxyl and amine functional groups can be positioned at the ends of the main carbon chain of said amino acid, the main carbon chain preferably being an unbranched chain. The amino acid can also be an α-amino acid, which is defined by the fact that the amine functional group is bonded to the carbon atom adjacent to the carboxyl functional group (the α carbon).

Mention may be made, as preferred example, of 11-aminoundecanoic acid.

When the crosslinking agent is a nonpolymeric compound comprising an anhydride functional group, the composition can additionally comprise a crosslinking catalyst or, in other words, said nonpolymeric compound comprising an anhydride functional group is combined, in the polymer composition, with a crosslinking catalyst.

The nonpolymeric compound comprising an anhydride functional group is more particularly an organic compound. In other words, the nonpolymeric compound comprising an anhydride functional group is composed solely of carbon and of hydrogen and optionally of oxygen.

More particularly, said nonpolymeric compound comprising an anhydride functional group additionally comprises an aliphatic chain comprising at least five carbon atoms, it being possible for this chain to be saturated or unsaturated.

Mention may be made, by way of example, of dodecenylsuccinic anhydride.

Mention may be made, as examples of polymeric crosslinking agent, of copolymers of olefin and unsaturated monocarboxylic acid, copolymers of olefin and unsaturated dicarboxylic acid or copolymers of olefin and unsaturated dicarboxylic acid anhydride. The olefin cited for these copolymers is preferably ethylene.

The polymer composition in accordance with the invention can comprise an amount of crosslinking agent B in an amount necessary and sufficient to obtain the crosslinked layer.

By way of example, the polymer composition in accordance with the invention can comprise at most 15.0 parts by weight of crosslinking agent B per 100 parts by weight of polymer(s) in the composition, preferably at most 10.0 parts by weight of crosslinking agent B per 100 parts by weight of polymer(s) in the composition and preferably at most 5.0 parts by weight of crosslinking agent B per 100 parts by weight of polymer(s) in the composition.

The polymer composition in accordance with the invention can comprise at least 0.1 part by weight of crosslinking agent B per 100 parts by weight of polymer(s) in the composition and preferably at least 0.5 part by weight of crosslinking agent B per 100 parts by weight of polymer(s) in the composition.

In the present invention, when reference is made to “100 parts by weight of polymer(s)”, this is understood to mean preferably the polymer or polymers other than the crosslinking agent B and the compound C in the polymer composition (when the crosslinking agent B and/or the compound C are in the polymer form).

Filler-Comprising Polymer Composition

The polymer composition of the invention can additionally comprise a filler.

The filler of the invention can be an inorganic or organic filler. It can be chosen from a flame-retardant filler and an inert filler (or noncombustible filler).

By way of example, the flame-retardant filler can be a hydrated filler chosen in particular from metal hydroxides, such as, for example, magnesium dihydroxide (MDH) or aluminum trihydroxide (ATH). These flame-retardant fillers act mainly by the physical route by decomposing endothermically (e.g., release of water), which has the consequence of lowering the temperature of the crosslinked layer and of limiting the propagation of the flames along the electrical device. The term “flame retardant properties” is used in particular.

For its part, the inert filler can be chalk, talc, clay (e.g., kaolin), carbon black or carbon nanotubes.

According to a first alternative form, carbon black, as electrically conducting filler, may be preferred in order to obtain a semiconducting crosslinked layer and may be introduced into the polymer composition in an amount sufficient to render the composition semiconducting.

According to a second alternative form, carbon black may be used in a small amount in order to improve the dielectric properties of an electrically insulating layer.

The polymer composition can comprise at least 5 parts by weight of fillers per 100 parts by weight of polymer in the composition, preferably at least 10 parts by weight of filler per 100 parts by weight of polymer in the composition and more preferably still at least 20 parts by weight of filler per 100 parts by weight of polymer in the composition.

The addition of a filler as described in the invention can result in a rise in temperature during the processing of the polymer composition and for this reason bring about premature crosslinking of the polymer composition. Thus, in order to prevent any premature crosslinking of the polymer composition, it is preferable for the addition of the filler to be carried out so that there is no premature crosslinking of the polymer composition during its processing. More particularly, the crosslinking agent can advantageously be added to the polymer composition in a stage separate from and subsequent to that of the addition of the filler.

According to another characteristic of the invention and in order to guarantee an “HFFR” (Halogen-Free Flame Retardant) electrical device, the electrical device, or in other words the components which make up said electrical device, preferably does/do not comprise halogenated compounds. These halogenated compounds can be of any nature, such as, for example, fluoropolymers or chloropolymers, such as polyvinyl chloride (PVC), halogenated plasticizers, halogenated inorganic fillers, and the like.

Additives

The composition can typically additionally comprise additives in an amount of 5 to 20 parts by weight per 100 parts by weight of polymer in the composition. The additives are well known to a person skilled in the art and can, for example, be chosen from protective agents (e.g., UV stabilizers, agents for combating copper), processing aids (e.g., plasticizers, viscosity reducers) and pigments.

As mentioned above, the polymer composition can also comprise a crosslinking catalyst in order to help in the crosslinking. This crosslinking catalyst can more particularly be used when the nonpolymeric crosslinking agent of the invention comprises a reactive functional group of the anhydride type.

The crosslinking catalyst can be a catalyst of the Lewis base type or, in other words, a nucleophilic chemical entity, one of the constituents of which has a pair or more of free or nonbonding electrons on its valence layer.

By way of examples, the crosslinking catalyst can be chosen from imides, tertiary amines, imidazoles and one of their mixtures.

Crosslinking catalysts of phenol type would be preferred in the context of the invention, this catalyst being in particular a Lewis base, such as, for example, 2,4,6-tris(dimethylaminoethyl)phenol.

When the polymer composition comprises a crosslinking catalyst, in particular in the presence of a nonpolymeric crosslinking agent comprising a reactive functional group of the anhydride type, the polymer composition can comprise from 0.01 to 2.0 parts by weight of crosslinking catalyst per 100 parts by weight of polymer and preferably from 0.05 to 1.0 part by weight of crosslinking catalyst per 100 parts by weight of polymer.

The Crosslinked Layer and the Electrical Device

In the present invention, the crosslinked layer can be easily characterized by the determination of its gel content according to the standard ASTM D 2765-01.

More particularly, said crosslinked layer can advantageously have a gel content, according to the standard ASTM D 2765-01, of at least 40%, preferably of at least 50%, preferably of at least 60% and particularly preferably of at least 70%.

The electrical device of the invention can be an electric cable or an electric cable accessory.

According to a first embodiment, the device according to the invention is an electric cable comprising an elongated electrically conducting component surrounded by said crosslinked layer.

According to a second embodiment, the device according to the invention is an electric cable accessory, said accessory comprising said crosslinked layer. Said accessory is more particularly intended to be used in combination with at least one electric cable, the crosslinked layer being intended to surround at least one end of an electric cable. The accessory can in particular be an electric cable joint or termination.

The crosslinked layer of the invention can be an electrically insulating layer or semiconducting layer.

According to a first embodiment, the crosslinked layer of the invention can be an electrically insulating layer.

The crosslinked layer of this first embodiment in addition advantageously exhibits a significantly improved resistance to electrical breakdown.

More particularly, “electrically insulating layer” is understood to mean a layer, the electrical conductivity of which can be at most 1.10⁻⁹ S/m (siemens per meter) (at 25° C.).

When the electrical device of the invention is an electric cable, at least two alternative forms of this first embodiment are possible.

According to a first alternative form of the first embodiment, the crosslinked layer of the invention is directly in physical contact with the elongated electrically conducting component. Reference is made, in this case, in particular to low-voltage cable.

The polymer composition used to form the low-voltage cable preferably comprises at least one filler, as defined above in the invention.

In addition, the polymer of the invention can advantageously comprise said acrylate functional group.

According to a second alternative form of the first embodiment, the electric cable of the invention additionally comprises a first semiconducting layer and a second semiconducting layer, the first semiconducting layer surrounding the elongated electrically conducting component, the electrically insulating layer surrounding the first semiconducting layer and the second semiconducting layer surrounding the electrically insulating layer. Reference is made, in this case, in particular to medium- or high-voltage cable.

The polymer composition used to form the medium- or high-voltage cable and more particularly the electrically insulating layer of said cable preferably does not comprise filler or else does not comprise filler in an amount sufficient to modify the electrical properties of the electrically insulating layer.

In addition, the polymer of the invention can advantageously not comprise said acrylate functional group.

According to a second embodiment, the crosslinked layer of the invention can be a semiconducting layer. This semiconducting layer can be at least one of the semiconducting layers of a medium- or high-voltage cable as defined above.

Consequently, the polymer composition of the invention can additionally comprise an electrically conducting filler in an amount sufficient to render the polymer composition semiconducting. Mention may be made, for example, as electrically conducting filler, of carbon black.

More particularly, “semiconducting layer” is understood to mean a layer, the electrical conductivity of which can be at least 1.10⁻⁹ S/m (siemens per meter), preferably at least 1.10⁻³ S/m, and preferably can be less than 1.10³ S/m (at 25° C.).

When the electrical device of the invention is an electric cable, the latter can comprise a first semiconducting layer surrounding the elongated electrically conducting component, an electrically insulating layer surrounding the first semiconducting layer and a second semiconducting layer surrounding the electrically insulating layer, the crosslinked layer of the invention being at least one of these three layers, preferably at least two of said three layers and preferably said three layers. Reference is made, in this case, in particular to medium- or high-voltage cable.

In the present invention, the elongated electrically conducting component of the electric cable can be a metal wire or a plurality of metal wires, which is/are or is/are not twisted, in particular made of copper or of aluminum, or one of their alloys.

When the electrical device of the invention is an electric cable accessory, said accessory more particularly surrounds at least one end of an electric cable, said end being that which is intended to be combined with said accessory.

The accessory can typically be a hollow longitudinal body, such as, for example, an electric cable joint or termination, in which at least a portion of an electric cable is intended to be positioned.

The accessory comprises at least one semiconducting component and at least one electrically insulating component, these components being intended to surround an end of an electric cable. The semiconducting component is well known for controlling the geometry of the electric field, when the electric cable, in combination with said accessory, is under voltage.

The crosslinked layer of the invention can be said semiconducting component and/or said electrically insulating component.

When the accessory is a joint, the latter makes it possible to connect together two electric cables, the joint then surrounding, in part, these two electric cables. More particularly, the end of each electric cable intended to be connected is positioned inside said joint.

When the device of the invention is an electric cable termination, the latter surrounds, in part, an electric cable. More particularly, the end of the electric cable intended to be connected is positioned inside said termination.

The crosslinked layer of the invention can be a layer extruded or a layer molded by processes well known to a person skilled in the art. When the electrical device is an electric cable, the crosslinked layer is preferably an extruded layer. When the electrical device is an electric cable accessory, the crosslinked layer is preferably a molded layer.

Another subject matter of the invention is a process for the manufacture of an electrical device of the electric cable type according to the invention, characterized in that it comprises the following stages:

• • i. extruding the polymer composition around an elongated electrically conducting component, in order to obtain an extruded layer, and
  • ii. crosslinking the extruded layer of stage i.

Stage i can be carried out by techniques well known to a person skilled in the art, using an extruder.

During stage i, the temperature within the extruder should preferably not exceed the temperature of opening of the epoxy functional group with the polymer, in order to prevent any crosslinking within the extruder. By way of example, the temperature for processing the polymer composition by extrusion is less than 200° C. and preferably less than 150° C.

There is thus obtained, at the extruder outlet, a layer extruded around said electrically conducting component which may or may not be directly in physical contact with said electrically conducting component.

At the extruder outlet, the extruded layer is thus a “noncrosslinked” layer.

“Noncrosslinked” is understood to mean a layer, the gel content of which according to the standard ASTM D 2765-01 is at most 20%, preferably at least 10%, preferably at least 5% and particularly preferably 0%.

Prior to stage i, the constituent components of the polymer composition of the invention can be mixed, in particular with the polymer A in the molten state, in order to obtain a homogeneous mixture. The temperature within the mixer can be sufficient to obtain a polymer A in the molten state but is limited in order to prevent the opening of the epoxy functional group of the polymer and thus the crosslinking of the polymer A.

The homogeneous mixture is then granulated by techniques well known to a person skilled in the art. These granules can subsequently feed an extruder in order to carry out stage i.

Stage ii can be carried out by the thermal route, for example using a steam tube or a bath of molten salt, these techniques being well known to a person skilled in the art. By way of example, the crosslinking temperature is less than 300° C. and preferably less than or equal to 250° C.

At the extruder outlet, the composition extruded in the form of a layer around the electrically conducting component can subsequently be subjected to a temperature sufficient in order to be able to open the epoxy functional group of the polymer A and thus to cause the crosslinking agent to react with the opened epoxy functional group. An extruded and crosslinked layer is then obtained.

Other characteristics and advantages of the present invention will become apparent in the light of the description of a nonlimiting example of an electric cable according to the invention made with reference to the figures.

FIG. 1 represents a diagrammatic view in cross section of an electric cable according to a preferred embodiment in accordance with the invention.

FIG. 2 represents a diagrammatic view of an electrical device according to the invention comprising a joint in longitudinal section, this joint surrounding the end of two electric cables.

FIG. 3 represents a diagrammatic view of an electrical device according to a first alternative form of the invention comprising a termination in longitudinal section, this termination surrounding the end of a single electric cable.

FIGS. 4a to 4f exhibit spectra of infrared absorbance as a function of the time (0 h, 24 h, 96 h and 168 h) for crosslinked layers in accordance with the invention and not in accordance with the invention.

FIG. 5 exhibits histograms of tensile strength according to the French standard NF EN 60811-1-1 at 0 h, 24 h, 96 h and 168 h for crosslinked layers in accordance with the invention and not in accordance with the invention.

FIG. 6 exhibits histograms of elongation at break according to the French standard NF EN 60811-1-1 at 0 h, 24 h, 96 h and 168 h for crosslinked layers in accordance with the invention and not in accordance with the invention.

For reasons of clarity, only the components essential for the understanding of the invention have been represented diagrammatically, this being done without observing a scale.

The medium- or high-voltage power cable 1, illustrated in FIG. 1, comprises an elongated central conducting component 2, in particular made of copper or of aluminum. The power cable 1 additionally comprises several layers positioned successively and coaxially around this conducting component 2, namely: a first semiconducting layer 3 referred to as “inner semiconducting layer”, an electrically insulating layer 4, a second semiconducting layer 5 referred to as “outer semiconducting layer”, an earthing and/or protective metal shield 6 and an external protective cladding 7.

The electrically insulating layer 4 is an extruded and crosslinked layer obtained from the polymer composition according to the invention.

The semiconducting layers are also extruded and crosslinked layers which can be obtained from the polymer composition according to the invention.

The presence of the metal shield 6 and of the external protective cladding 7 is preferential but not essential, this cable structure being as such well known to a person skilled in the art.

FIG. 2 represents a device 101 comprising a joint 20 surrounding, in part, two electric cables 10a and 10b.

More particularly, the electric cables 10a and 10b respectively comprise an end 10′a and 10′b which are intended to be surrounded by the joint 20.

The body of the joint 20 comprises a first semiconducting component 21 and a second semiconducting component 22 separated by an electrically insulating component 23, said semiconducting components 21, 22 and said electrically insulating component 23 surrounding the ends 10′a and 10′b respectively of the electric cables 10a and 10b.

This joint 20 makes it possible to electrically connect the first cable 10a to the second cable 10b, in particular by virtue of an electrical connector 24 positioned at the center of the joint 20.

At least one of the components chosen from the first semiconducting component 21, the second semiconducting component 22 and said electrically insulating component 23 can be a crosslinked layer as described in the invention.

The first electric cable 10a comprises an electrical conductor 2a surrounded by a first semiconducting layer 3a, an electrically insulating layer 4a surrounding the first semiconducting layer 3a, and a second semiconducting layer 5a surrounding the electrically insulating layer 4a.

The second electric cable 10b comprises an electrical conductor 2b surrounded by at least one first semiconducting layer 3b, an electrically insulating layer 4b surrounding the first semiconducting layer 3b, and a second semiconducting layer 5b surrounding the electrically insulating layer 4b.

These electric cables 10a and 10b can be those described in the present invention.

At said end 10′a, 10′b of each electric cable 10a, 10b, the second semiconducting layer 5a, 5b is at least partially denuded in order for the electrically insulating layer 4a, 4b to be at least partially positioned inside the joint 20, without being covered with the second semiconducting layer 5a, 5b of the cable.

Inside the joint 20, the electrically insulating layers 4a, 4b are directly in physical contact with the electrically insulating component 23 and the first semiconducting component 21 of the joint 20. The second semiconducting layers 5a, 5b are directly in physical contact with the second semiconducting component 22 of the joint 20.

FIG. 3 represents a device 102 comprising a termination 30 surrounding a single electric cable 10c.

More particularly, the electric cable 10c comprises an end 10′c intended to be surrounded by the termination 30.

The body of the termination 30 comprises a semiconducting component 31 and an electrically insulating component 32, said semiconducting component 31 and said electrically insulating component 32 surrounding the end 10′c of the electric cable 10c.

At least one of the components chosen from the semiconducting component 31 and the electrically insulating component 32 can be a crosslinked layer as described in the invention.

The electric cable 10c comprises an electrical conductor 2c surrounded by a first semiconducting layer 3c, an electrically insulating layer 4c surrounding the first semiconducting layer 3c, and a second semiconducting layer 5c surrounding the electrically insulating layer 4c.

This electric cable 10c can be that described in the present invention.

At said end 10′c of the electric cable 10c, the second semiconducting layer 5c is at least partially denuded in order for the electrically insulating layer 4c to be at least partially positioned inside the termination 30, without being covered with the second semiconducting layer 5c of the cable.

Inside the termination 30, the electrically insulating layer 4c is directly in physical contact with the electrically insulating component 32 of the termination 30. The second semiconducting layer 5c is directly in physical contact with the semiconducting component 31 of the joint 30.

EXAMPLES

1. Filler-Free Electrically Insulating Compositions

Filler-free crosslinkable compositions, the amounts of the compounds of which are expressed in parts by weight per 100 parts by weight of polymer, the polymer being in this instance solely Polymer/Epoxy, are collated in table 1 below. Compositions I1 to I6 are in accordance with the invention, whereas compositions C1 and C2 correspond to comparative compositions.

TABLE 1a
Compositions	I1	I2	I3	I4	I5	C1
Polymer/Epoxy	100	100	100	100	100	100
Crosslinking	0.75	0.75	0.75	0.75	0.75	0.75
agent
Irgastab KV10	1.0	0	0	0	0	0
Irganox 1010	0	0.5	0	0	0	0
Irganox 1076	0	0	0.9	0	0	0
Irganox 1330	0	0	0	0.44	0	0
Irganox 1035	0	0	0	0	0.45	0
Irganox PS802	0	0	0	0	0	0.58

	TABLE 1b
	Compositions	I6	C2
	Polymer/Epoxy	100	100
	Crosslinking agent	0.75	0.75
	Aromatic amine	0.3	0
	Nonaromatic amine	0	0.15

The compounds of tables 1a and 1b have the following origins:

• • Polymer/Epoxy is a copolymer of ethylene and glycidyl methacrylate (GMA) sold by Arkema under the reference Lotader AX8840, this copolymer comprising 8% by weight of GMA;
  • Crosslinking agent is 11-aminoundecanoic acid sold by Sigma-Aldrich under the reference 11-Aminoundecanoic acid;
  • Irgastab KV10 is an antioxidant sold by BASF under the reference Irgastab KV10 (CAS No. 110553-27-0);
  • Irganox 1010 is an antioxidant sold by BASF under the reference Irganox 1010 (CAS No. 6683-19-8);
  • Irganox 1076 is an antioxidant sold by BASF under the reference Irganox 1076 (CAS No. 2082-79-3);
  • Irganox 1330 is an antioxidant sold by BASF under the reference Irganox 1330 (CAS No. 1709-70-2);
  • Irganox 1035 is an antioxidant sold by BASF under the reference Irganox 1035 (CAS No. 41484-35-9);
  • Irganox PS802 is an antioxidant sold by BASF under the reference Irganox PS802 (CAS No. 693-36-7);
  • Aromatic amine is the antioxidant 1,2-dihydro-2,2,4-trimethylquinoline sold by Flexsys under the reference Flectol TMQ (CAS No. 26780-96-1); and
  • Nonaromatic amine is the antioxidant N,N′-diethylhydroxylamine (tertiary amine) sold by Sigma-Aldrich under the reference N,N-Diethylhydroxylamine (CAS No. 3710-84-7).

The compositions collated in tables 1a and 1b are processed as follows.

In a first step, for each composition (I1 to I6, C1 and C2), the crosslinking agent and the antioxidant are mixed with the polymer in the molten state in an internal mixer of twin-screw or Buss type, the temperature within the mixer not exceeding 130° C. in order to prevent the opening of the epoxy functional group of the polymer and to thus prevent the crosslinking of the polymer. The homogeneous mixture thus obtained is subsequently granulated.

In a second step, the granules are subsequently introduced into a single-screw extruder and extruded at a maximum temperature of 130° C., in order to prevent any crosslinking of the polymer in the extruder.

The extrusion is carried out around a copper conducting wire with a section of 1.5 mm². An electric cable comprising an extruded and noncrosslinked layer in direct contact with the conducting wire is obtained.

In a third step, the extruded layer is crosslinked by supplying heat, at a temperature of 200° C., said electric cable being passed inside a steam tube under a steam pressure of 15 bar.

2. Semiconducting Compositions

A crosslinkable semiconducting composition I7 in accordance with the invention, the amounts of the compounds of which are expressed in parts by weight per 100 parts by weight of polymer, the polymer in this instance being solely Polymer/Epoxy, is collated in table 2 below.

TABLE 2
Composition   I7
Polymer/Epoxy 100
Amino acid    0.38
Antioxidants  1.5
Carbon black  42.9

The compounds of table 2 have the following origins:

• • Polymer/Epoxy is a copolymer of ethylene and glycidyl methacrylate (GMA) sold by Arkema under the reference Lotader AX8840, this copolymer comprising 8% by weight of GMA;
  • Amino acid is an 11-aminoundecanoic acid sold by Sigma-Aldrich under the reference 11-Aminoundecanoic acid;
  • Antioxidants is a mixture of 0.5 part by weight of Irganox PS802 and of 1.0 part by weight of Irganox 1035, these antioxidants being sold by BASF; and
  • Carbon black is carbon black sold by Cabot under the reference Carbon Black VXC500.

Composition I7 in table 2 is processed according to the same procedure as that described for the compositions of tables 1a and 1b, except for the fact that the carbon black is first of all mixed with the molten polymer and then the crosslinking agent and the antioxidants are incorporated in said mixture. The addition of the crosslinking agent in a stage separate from and subsequent to the addition of the carbon black makes it possible to prevent any premature crosslinking of the polymer composition which may occur subsequent to the rise in temperature brought about by the addition of the carbon black. The crosslinking agent is thus added to the filler-comprising mixture once the mixture has cooled to a temperature of less than 130° C.

3. Characterization of the Crosslinked Compositions

3.1. Infrared Absorbance Spectra

FIGS. 4a to 4d exhibit spectra of infrared absorbance as a function of the time (0 h, 24 h, 96 h and 168 h) for crosslinked layers in accordance with the invention (compositions I2, I3, I4 and I6).

For the compositions according to the invention, these absorbance spectra show that, during aging, up to 168 h, compound C of the invention performs its role perfectly, namely it prevents the etherification reactions since the peaks in the vicinity of 1200 cm⁻¹ remain stable and are characteristic of the stability in the number of ether functional groups formed. In addition, the peak in the vicinity of 915 cm⁻¹, corresponding to the epoxy functional group, also remains unchanging.

FIGS. 4e to 4f exhibit spectra of infrared absorbance as a function of the time (0 h, 24 h, 96 h and 168 h) for crosslinked layers not in accordance with the invention (compositions C1 and C2).

These absorbance spectra show that, during aging and starting from 24 h for composition C1 and from 96 h for composition C2, the antioxidant used does not succeed in preventing the etherification reactions since the peaks in the vicinity of 1200 cm⁻¹ vary, this variation being characteristic of the etherification of the epoxy groups of the polymer A.

3.2 Tensile Strength Test

FIG. 5 exhibits histograms of tensile strength according to the French standard NF EN 60811-1-1, at 0 h, 24 h, 96 h and 168 h, for crosslinked layers in accordance with the invention (compositions I2, I3, I4 and I6) and not in accordance with the invention (compositions C1 and C2).

It is clearly apparent that, after aging for 168 h, the compositions according to the invention exhibit a tensile strength (i.e., maximum strength achieved before breaking) of at least 10 mPa, in contrast to compositions C1 and C2, which exhibit a strength of at most 8 mPa.

3.3. Elongation at Break Test

FIG. 6 exhibits histograms of elongation at break according to the French standard NF EN 60811-1-1, at 0 h, 24 h, 96 h and 168 h, for crosslinked layers in accordance with the invention (compositions I2, I3, I4 and I6) and not in accordance with the invention (compositions C1 and C2).

It is clearly apparent that, after aging for 168 h, the compositions according to the invention exhibit a deformation at elongation (i.e., maximum elongation achieved before breaking) of at least 280%, in contrast to compositions C1 and C2, which exhibit a deformation of at most 70%.

Claims

1. An electrical device having a crosslinked layer obtained from a polymer composition comprising:

at least one polymer A comprising at least one epoxy functional group, and

a crosslinking agent B comprising at least one reactive functional group capable of reacting with the epoxy functional group of said polymer A in order to make possible the crosslinking of said polymer A,

wherein the polymer composition additionally comprises a compound C comprising:

at least one aromatic group, and

a reactive group capable of interacting physically with the hydroxyl functional group formed by the opening of said epoxy functional group during the crosslinking of the polymer A.

2. The device as claimed in claim 1, wherein the compound C is different from the polymer A and from the crosslinking agent B.

3. The device as claimed in claim 1, wherein the compound C is an antioxidant.

4. The device as claimed in claim 1, wherein the reactive group of the compound C is a hydrogen atom.

5. The device as claimed in claim 1, wherein the reactive group of the compound C is in the form of a hydroxyl (OH) group and/or of an amine (NH) group.

6. The device as claimed in claim 1, wherein the aromatic group of the compound C is a benzene group or one of its derivatives.

7. The device as claimed in claim 1, wherein the aromatic group together with the reactive group form a phenol group.

8. The device as claimed in claim 7, wherein the phenol group is disubstituted in the ortho position.

9. The device as claimed in claim 7, wherein the phenol group is a di(tert-butyl)-4-hydroxyphenyl group.

10. The device as claimed in claim 1, wherein the aromatic group together with the reactive group form an aminobenzene group, the amine of which is of the primary or secondary type.

11. The device as claimed in claim 1, wherein the polymer composition comprises at most 10 parts by weight of compound C per 100 parts by weight of polymer(s) in the composition.

12. The device as claimed in claim 1, wherein the polymer A comprises at least one compound chosen from glycidyl esters.

13. The device as claimed in claim 1, wherein the polymer A comprises at most 10% by weight of epoxy functional group.

14. The device as claimed in claim 1, wherein the polymer A comprises at least 0.1% by weight of epoxy functional group.

15. The device as claimed in claim 1, wherein the epoxy functional group of the polymer A is grafted to said polymer.

16. The device as claimed in claim 1, wherein the polymer A is a copolymer obtained from at least two monomers, one of the monomers comprising said epoxy functional group.

17. The device as claimed in claim 1, wherein the polymer A additionally comprises at least one acrylate functional group.

18. The device as claimed in claim 1, wherein the crosslinking agent B is a polymer compound or a nonpolymer compound.

19. The device as claimed in claim 1, wherein the reactive functional group of the crosslinking agent B is chosen from an anhydride functional group, a carboxyl functional group and an amine functional group.

20. The device as claimed in claim 19, wherein the amine functional group of the crosslinking agent is a primary amine or a secondary amine.

21. The device as claimed in claim 1, wherein the crosslinking agent B comprises at least two reactive functional groups.

22. The device as claimed in claim 19, wherein the crosslinking agent comprises an amine functional group and a carboxyl functional group.

23. The device as claimed in claims 19 and 21, characterized in that the crosslinking agent comprises two amine functional groups.

24. The device as claimed in claim 1, wherein said device is an electric cable comprising an elongated electrically conducting component surrounded by said crosslinked layer.

25. The device as claimed in claim 1, wherein said device is an electric cable accessory, said accessory comprising said crosslinked layer.

26. The device as claimed in claim 25, wherein the accessory is an electric cable joint or termination.

27. The device as claimed in claim 1, wherein the crosslinked layer is an electrically insulating layer.

28. The device as claimed in claim 1, wherein the crosslinked layer is a semiconducting layer.

29. The device as claimed in claim 1, wherein said device further comprises a first semiconducting layer (3) surrounding the elongated electrically conducting component (2), an electrically insulating layer (4) surrounding the first semiconducting layer (3) and a second semiconducting layer (5) surrounding the electrically insulating layer (4), the crosslinked layer being at least one of these three layers.