Crosslinked polymer coating for electrical device

Abstract

The invention relates to an electrical device comprising a cross-linked layer, wherein said layer is obtained by reacting at least the following compounds: (a) identical or different polymer chains, each comprising at least one -COOH function (and preferably several); and (b) identical or different non-polymer compounds, each containing at least two epoxy functions. Figure for abstract: none

Description

Title of the invention: Crosslinked polymer layer for electrical device technical field

[0001] The present invention relates to the field of electrical devices such as electrical cables or accessories for electrical cables and which comprise a cross-linked layer based on at least one polymer.

[0002] It typically applies, but not exclusively, to the fields of low voltage power cables (in particular below 6kV), medium voltage (in particular from 6 to 45-60 kV) or high voltage (in particular above 60 kV, and up to 800 kV), whether they are direct current or alternating current.

[0003] Power cables typically comprise a central electrical conductor, generally at least one elongated electrically conductive element of the wire or wire strand type, and at least one electrically insulating layer surrounding this central conductive element. This electrically insulating layer can typically be a cross-linked polymer layer, in particular cross-linked polyethylene. Various cross-linking techniques have been described for producing such insulating layers, including techniques using peroxides, which are often referred to generically as the "peroxide route."

[0004] However, the peroxide route is increasingly being avoided because the peroxides used lead to the formation of decomposition products that generally present drawbacks during the manufacture of the cable or accessory and often have a negative impact on the final performance of the cable. Common peroxides, such as dicumyl peroxide, decompose to form by-products including, in particular, methane, acetophenone, cumyl alcohol, acetone, tert-butanol, alpha-methylstyrene, and / or water, which can impair the final properties of the prepared insulating layer.

[0005] When using the peroxide process, it is preferable to eliminate these decomposition products. In particular, if the methane formed is not removed from the cross-linked layers, it poses risks related to its explosiveness and flammability during storage and final application. Therefore, cables incorporating cross-linked layers produced by the peroxide process are generally subject to a degassing phase after their preparation, which prevents their immediate commissioning and increases the complexity of their manufacturing process and the associated costs. This degassing step can be very lengthy (often several days) and involves managing the volatile by-products such as methane that are released. Given the For very long electrical cables, the quantity of decomposition products is ultimately very significant, especially as the thickness of the cross-linked layer increases.

[0006] Certain peroxide decomposition products prove difficult, or even impossible, to eliminate from the formed layer, which can impair the final performance of the cable, or even compromise the insulating properties of the cross-linked layer. Water formation, for example, is particularly insidious because it most often occurs from non-volatile by-products such as cumyl alcohol, and in a relatively slow manner. Thus, it can occur after several months, or even a few years, once the cable is in its operational configuration. This gradual appearance of water within the insulating layer then significantly increases the risk of cable breakdown in the short to medium term.

[0007] Alternative routes to the peroxide route have therefore been developed, aiming to overcome the difficulties associated with peroxide decomposition products. In this context, the use of specific peroxides that limit the formation of these decomposition products has been particularly recommended.

[0008] Other routes besides the peroxide route have also been explored, notably in patent application WO 2014 / 195629 which describes a crosslinked layer obtained from a polymer composition comprising at least one polymer including an epoxy function and a non-polymer crosslinking agent including a reactive function capable of reacting with this epoxy function.

[0009] An object of the present invention is to provide a new route of access to crosslinked layers for electrical cable or electrical cable accessory, avoiding the presence of crosslinking by-products such as methane and water, while obtaining good crosslinking properties suitable for use within a cable or cable accessory.

[0010] To this end, the present invention proposes the implementation of a new crosslinking route not requiring the implementation of peroxide and implementing the reaction of at least one polymer bearing -COOH functions and at least one non-polymer compound bearing at least two epoxy functions.

[0011] More specifically, according to a first aspect, the present invention relates to an electrical device comprising a cross-linked layer, where said layer is obtained by reaction of at least the following compounds: (a) polymer chains, identical or different, each comprising at least one -COOH function (and preferably several); and (b) non-polymer compounds, identical or different, each containing at least two epoxy functions.

[0012] According to a second aspect, another object of the invention is a preparation method of an electrical device comprising a crosslinked layer, comprising a step (e) of preparing said crosslinked layer by applying a mixture comprising: (a) identical or different polymer chains, each comprising at least one -COOH function (and preferably several); and (b) non-polymer compounds, identical or different, each containing at least two epoxy functions.

[0013] The reaction of the COOH groups on the polymer chains (a) and the epoxy groups on the compounds (b) leads to the formation of ester bridges between the polymers (a) and the compounds (b). Furthermore, given the specific presence of at least two epoxy groups on the compounds (b), at least two bridges are formed between a given compound (b) and polymer chains, ultimately resulting in covalent bonding of the polymer chains (a) via compound (b), namely through bonds of the type -(ester bridge)-[compound (b)]-(ester bridge)-. This results in cross-linking of the polymer chains (a) with each other, and thus the formation of a cross-linked polymer composition capable of forming the desired cross-linked layer.

[0014] According to a first interesting embodiment, step (e) of the process of the invention comprises a first step (e1) in which a population of non-crosslinked polymers P, lacking -COOH groups, is subjected to a grafting reaction with -COOH groups, thereby obtaining a population of grafted polymers; and then a step (e2) in which the grafted polymers obtained in step (e1) are contacted with the compounds (b) according to the invention. According to this particular embodiment, the invention can be described as enabling the preparation of a crosslinked polymer layer from a composition of non-crosslinked polymers P, by grafting and then reaction with a coupling agent (compound b).

[0015] The non-crosslinked P polymers used in step (el) can advantageously be chosen from ethylene homopolymers, propylene homopolymers, ethylene copolymers (in particular with comonomers chosen from ethylene oxides and EVA, and rubbers). The grafting step (el) can be carried out according to any technique known per se allowing the covalent bonding of -COOH groups on the P polymers.

[0016] By way of example, according to an interesting embodiment, the non-crosslinked polymers P used in step (e1) are or comprise non-crosslinked polyethylene (PE). In this case, the grafting step (e2) can typically be carried out by impregnating the PE granules with acrylic acid and a very small amount of peroxide. The impregnation is typically done by first placing the PE granules in an oven for several hours at a temperature below the melting point of PE and generally above 20 °C, then adding the peroxide and acrylic acid, and finally leaving the mixture under stirring for several hours at a temperature below the melting point of the granules and generally above 20 °C. These steps are generally followed by an extrusion or mixing step within an internal mixer.

[0017] Alternatively, according to another possible embodiment where the non-crosslinked polymers P used in step (e1) are or comprise PE, the grafting step (e2) can be carried out without using impregnation of the aforementioned type, but by directly incorporating the mixture of PE, acrylic acid, and peroxide into the device used for the mixing step (e.g., a single or twin-screw extruder or an internal mixer). This embodiment is particularly well-suited when the grafting involves compounds that are in solid form.

[0018]

[0019] According to another conceivable embodiment (compatible with the preceding one), the population of non-crosslinked polymers P used in step (e1) are or include a non-crosslinked rubber, in particular a rubber. In this case, the grafting step (e2) can typically be carried out by impregnating the rubber with acrylic acid and a very small amount of peroxide. The impregnation is typically carried out in an oven, into which the peroxide and acrylic acid are added, and finally by leaving the mixture under agitation for several hours. These steps are generally followed by mixing within an internal mixer.

[0020] According to another embodiment, step (e) of the process of the invention can be carried out on polymers (a) bearing -COOH functions immediately after their synthesis. In this context, step (e) can, for example, be carried out on polymers or copolymers resulting from the polymerization of monomers comprising monomers bearing -COOH functions, for example homopolymers or, more often, copolymers resulting from the polymerization of ethylenically unsaturated monomers, including monomers selected, for example, from acrylic acid or methacrylic acid or itaconic acid, acrylic acid being preferred.

[0021] Regardless of its exact method of implementation, the invention makes it possible to obtain a crosslinked layer without having to use an organic peroxide, while nevertheless guaranteeing a high level of crosslinking. The use of an additional peroxide within the framework of the invention is not excluded in absolute terms (and it is even advantageous for carrying out the grafting), but it is advantageous that the reaction of the COOH functions carried by the polymer chains (a) and the epoxy functions carried by the compounds (b) according to the invention takes place in the absence of any peroxide, or at least in contents remaining below 0.5%, typically below 0.4%, for example between 0.1% and 0.4%.

[0022] Furthermore, the method for preparing the crosslinked layer according to the invention has the advantage of being economical, easy to implement, and it does not require resorting to cumbersome degassing procedures.

[0023] The invention also makes it possible to obtain crosslinked layers well suited for use as an insulating layer in an electrical device. The crosslinked layers according to the invention exhibit, in particular, very good resistance to breakdown according to IEC 62539 or very good electrical resistivity according to IEC 60840, and a relatively low polymer composition crosslinking temperature (generally below 300°C, and preferably below or equal to 250°C), for example, on the order of 200°C [

[0024] Various aspects and particular embodiments of the invention are described in more detail below.

[0025] POLYMER CHAINS (a) In order to achieve the most effective crosslinking of the layer, the polymer chains (a) bearing -COOH functionalities implemented according to the invention advantageously comprise at least 0.1% by weight, and preferably at least 0.5% by weight, of -COOH functionalities, relative to the total weight of the polymer chains (a). However, this proportion need not exceed 10% by weight and may, for example, be between 1 and 5% by weight.

[0026] The polymer chains (a) may be chains comprising at least one -COOH function covalently grafted onto a polymer chain (obtained by post-grafting onto a polymer backbone) and / or homo- or co-polymer chains resulting from the polymerization of monomers including monomers bearing -COOH functions, such as, for example, a copolymer of ethylene and acrylic acid

[0027] The polymer chains (a) of the invention can be brought into contact with the compounds (b) in the form of a polymer composition comprising a mixture of polymer chains, only a portion of which consists of the polymer chains (a), the remainder of the composition comprising other polymer chains not bearing -COOH groups. In this case, the chains (a) bearing -COOH groups advantageously constitute at least 50% by mass, preferably at least 70% by mass, and more preferably at least 90% by mass relative to the total mass of the polymer chains present in the polymer composition.

[0028] The polymer chains (a) are advantageously polymers suitable for shaping by extrusion, which facilitates the application of the cross-linked layer.

[0029] Preferably, the polymer chains (a) comprise (or are exclusively) polyolefins. "Polyolefin" here means an olefin copolymer or homopolymer, preferably a non-cyclic olefin. Advantageously, the polymer chains (a) comprise an ethylene homopolymer or copolymer, or a propylene homopolymer or copolymer.

[0030] THE COMPOUND (b) A compound (b) used according to the invention is a compound specifically bearing at least two epoxy functional groups, so as to ensure crosslinking between the polymer chains. A compound (b) is also a non-polymer compound, which therefore is not, in particular, formed by the covalent linking of identical or different monomer units.

[0031] The epoxy functional groups of the compounds (b) employed according to the invention are functional groups containing an oxygen atom bridging two neighboring and bonded carbon atoms, which makes the compounds (b) particular members of the epoxide family (also called oxalkonals or oxiranes). The compounds (b) specifically bear at least two epoxy functional groups, and are therefore more precisely non-polymer diepoxides or multi-epoxides.

[0032] Compounds (b) may advantageously bear at least two glycidyl ester groups. By way of non-limiting example of compound (b), 1,4-butanediol diglycidyl ether may be cited.

[0033] Regardless of the exact nature of the polymers (a) and compounds (b), it is preferable to implement these compounds with an epoxy / COOH molar ratio, corresponding to the total quantity of epoxy groups carried by the compounds (b) relative to the quantity of COOH groups carried by the polymer chains (a), between 0.2 and 2, for example between 0.3 and 1, in particular between 0.4 and 0.8.

[0034] Furthermore, it is generally preferable that the mass ratio (b) / (a), calculated by dividing the total mass of the compounds (b) introduced by the total mass of the polymer chains (a) introduced, be between 0.1% and 15%, preferably between 0.5% and 10%, and for example between 2% and 7%

[0035] Crosslinking Catalyst In an interesting way, the reaction of polymers (a) and polymers (b) can be catalyzed by the presence of a catalyst or promoter for the reaction of the -COOH and epoxy groups. If applicable, this catalyst or promoter can be a base chosen, for example, from among the imidazoles and tertiary amines, an onium compound, a metal salt; or a Lewis acid.

[0036] OTHER COMPOUNDS POTENTIALLY PRESENT IN THE CROSS-CUT LAYER The reaction of the polymers (a) and the compounds (b) carried out according to the invention can advantageously be conducted in the presence of additional compounds, most often mixed beforehand with the polymers (b) before reaction with the compound (b).

[0037] The polymers (a) and compounds (b) can, for example, react in the presence of one or more of the following compounds, which will ultimately be found in the cross-linked layer:

[0038] CHARGES (optional) Compounds (a) and (b) can react in the presence of a charge which can be Mineral or organic. This charge can be chosen from a fire-retardant charge and an inert (or non-combustible) charge.

[0039] By way of example, the flame retardant filler may be a hydrated filler, chosen in particular from among the metal hydroxides such as, for example, magnesium dihydroxide (MDH) or aluminium trihydroxide (ATH).

[0040] The inert charge can be, for its part, chalk, talc, clay (kaolin for example), or carbon black.

[0041] Carbon black may be preferred for obtaining a semiconducting crosslinked layer, and may be introduced into the polymer composition in sufficient quantity to make the composition semiconducting.

[0042] Where appropriate, the filler may be used at a rate of at least 20 parts by weight (preferably at least 30 parts by weight, for example between 40 and 100 parts by weight) of filler per 100 parts by weight of polymer (a).

[0043] The addition of a filler as described in the invention can lead to a temperature rise during the processing of the polymer composition, and thus induce premature crosslinking of the polymer composition. Therefore, to avoid any premature crosslinking of the polymer composition, it is preferable that the filler be added in such a way that there is no premature crosslinking of the polymer composition during its processing. More specifically, the crosslinking agent can advantageously be added to the polymer composition in a separate step, subsequent to the addition of the filler.

[0044] ADDITIVES (optional) Compounds (a) and (b) can react in the presence of additives, which are then preferably present at a rate of less than 25 parts by weight of additives, for example between 1 and 20 parts by weight of additives relative to the weight of polymers (a).

[0045] These additives may include, in particular, protective agents (antioxidants, anti-UV agents, anti-copper agents), processing agents (plasticizers or lubricants), and pigments.

[0046] According to another feature of the invention, and in order to guarantee an electrical device known as HFFR (Halogen-Free Flame Retardant), the electrical device, or in other words the elements that compose said electrical device, does not / preferably do not include halogenated compounds. These halogenated compounds can be of any kind, such as, for example, fluorinated polymers or chlorinated polymers like polyvinyl chloride (PVC), halogenated plasticizers, halogenated mineral fillers, etc.

[0047] THE ELECTRICAL DEVICE The electrical device comprising the cross-linked layer according to the invention may in particular be: - an electrical cable comprising at least one elongated electrically conductive element, surrounded by said cross-linked layer, this layer being, for example, an insulating layer or an outer sheath; or - an accessory for an electrical cable, said accessory comprising said cross-linked layer. An accessory of this type is more specifically intended to be associated with at least one electrical cable, said cross-linked layer being intended to surround at least one end of an electrical cable. An accessory of this type may be, in particular, a junction or a termination.

[0048] CROSS-CUT LAYER USED AS AN INSULATING LAYER According to an interesting embodiment, the cross-linked layer of the invention can be an electrically insulating layer. It then preferably has an electrical conductivity of at most 1.109 S / m (siemens per meter) at 25°C.

[0049] CROSS-CUT LAYER USED AS A SEMI-CONDUCTIVE LAYER According to a second embodiment, the cross-linked layer of the invention can be a semiconducting layer.

[0050] In this case, the polymer composition of the invention further comprises an electrically conductive filler in sufficient quantity to render the polymer composition semiconducting. Carbon black may be cited, for example, as an electrically conductive filler.

[0051] Here, "semiconductor layer" means a layer whose electrical conductivity is at least 1.109 S / m (siemens per meter), preferably at least 1.103 S / m, and generally less than 1.103 S / m (at 25°C).

[0052] POSSIBLE STRUCTURES FOR A CABLE ACCORDING TO THE INVENTION

[0053] According to a first possible embodiment, the cross-linked layer of the invention can be used in an electrical cable as an insulating layer in direct physical contact with an elongated electrically conductive element. This is referred to in particular as a low-voltage cable.

[0054] The polymer composition used to form such a low-voltage cable preferably comprises at least one filler, as defined above in this description

[0055] According to another possible embodiment, the electrical device of the invention is an electrical cable comprising a first semiconductor layer surrounding an elongated electrically conductive element, an electrically insulating layer surrounding said first semiconductor layer, and a second semiconductor layer surrounding said electrically insulating layer, and wherein the cross-linked layer of the invention is at least one of these three layers, preferably at least two of said three layers, and preferably all three layers. In this case, we speak of medium or high voltage cable.

[0056] According to the present invention, the elongated electrically conductive element of the electric cable can be a metallic wire or a plurality of metallic wires, twisted or not, in particular made of copper or aluminum, or one of their alloys.

[0057] POSSIBLE STRUCTURES FOR AN ACCESSORY ACCORDING TO THE INVENTION When the electrical device of the invention is an accessory for an electrical cable, said accessory advantageously surrounds at least one end of an electrical cable, said end being the one intended to be associated with said accessory.

[0058] The accessory can typically be a hollow longitudinal body, such as for example a junction or termination for an electrical cable, in which at least a part of an electrical cable is intended to be positioned.

[0059] The accessory comprises at least one semiconductor element and at least one electrically insulating element, these elements being intended to surround one end of an electrical cable. The semiconductor element is well known for controlling the geometry of the electric field when the electrical cable associated with said accessory is energized.

[0060] The cross-linked layer of the invention may be said semiconductor element and / or said electrically insulating element.

[0061] When the accessory is a junction, the latter allows two electrical cables to be connected together, the junction then partially surrounding these two electrical cables. More specifically, the end of each electrical cable intended to be connected is positioned inside said junction.

[0062] PLACEMENT OF THE CROSS-CUT LAYER ACCORDING TO THE INVENTION

[0063] The cross-linked layer of the invention may be an extruded layer or a molded layer, which may in particular be obtained by extrusion or molding processes well known to those skilled in the art. When the electrical device is an electrical cable, the cross-linked layer is preferably an extruded layer. When the electrical device is an accessory for an electrical cable, the cross-linked layer is preferably a molded layer.

[0064] The crosslinking process, involving the reaction of polymer chains (a) and compounds (b), generally takes place during or after the application of the extruded layer, in particular during or immediately after the aforementioned extrusion or molding.

[0065] According to an embodiment particularly well suited to the manufacture of an electrical cable, the mixture of polymers (a) and compounds (b) is extruded around an elongated conductive element so as to obtain an extruded layer (directly or indirectly in physical contact with said electrically conductive element) where crosslinking according to the invention takes place (reaction of the polymers (a) and compounds (b)) which leads to the formation of a crosslinked layer according to the invention, this crosslinking preferably taking place after the extrusion step.

[0066] Extrusion can be carried out using techniques that are well known per se, in particular by means of an extruder. Preferably, crosslinking phenomena within the extruder are minimized, and for this reason, the temperature inducing the opening of the epoxy functional groups on the compounds (b) is avoided as much as possible. Typically, the extrusion temperature is below 200°C, and preferably below 150°C. Under these conditions, the extruder outlet yields a layer extruded around the electrically conductive element that is substantially non-crosslinked (typically with a gel content according to ASTM D2765-01 of less than 20%, preferably less than 10%, or even less than 5%).

[0067] The various compounds present in the extruded composition (polymers (a) and compound (b) and any fillers or additives) can typically be mixed upstream of the extruder, particularly with the polymer in its molten state, in order to obtain a homogeneous mixture. The temperature within the mixer is then preferably high enough to obtain a polymer in its molten state, but nevertheless low enough to substantially avoid cross-linking upstream and within the extruder.

[0068] Following the application of the substantially crosslinked layer by extrusion, crosslinking can in particular be obtained by raising the temperature of the applied layer above the opening temperature of the epoxy functions, which induces the desired crosslinking within the applied layer.

[0069] According to an embodiment well adapted to the manufacture of an accessory for electrical cable, the mixture of polymers (a) and compounds (b) is molded so as to obtain a molded layer in which crosslinking according to the invention takes place which leads to the formation of a crosslinked layer according to the invention, this crosslinking being able to take place during or after the molding step.

[0070] Here again, the various compounds present in the extruded composition (polymers (a) and compound (b) and any fillers or additives) can typically be mixed upstream of the molding step, particularly with the polymer in the molten state, in order to obtain a homogeneous mixture. The temperature within the mixer is then preferably high enough to obtain a polymer in the molten state, but nevertheless low enough to substantially avoid cross-linking.

[0071] According to a first embodiment, the molding can take place in a mold heated to a temperature high enough to obtain a polymer in a molten state, but low enough, however, to substantially avoid crosslinking. In this case, the molding is then followed by a heat treatment step of the molded layer, raising the temperature of said layer above the opening temperature of the epoxy functional groups, which induces the desired crosslinking.

[0072] According to another generally more interesting method, the molding can be carried out at a sufficiently high temperature to obtain a polymer in a molten state and to induce crosslinking, thereby obtaining the desired crosslinked layer directly after molding.

[0073] The invention will be further illustrated by the Figures in the Annex and the illustrative example below.

[0074] [Fig.1] Fig.1 represents a schematic cross-sectional view of an electrical cable according to an embodiment of the invention.

[0075] [Fig.2] Fig.2 represents a schematic view of a device according to the invention, comprising a junction in longitudinal section, this junction surrounding the end of two electrical cables.

[0076] [Fig.3] Fig.3 represents a schematic view of a device according to the invention, comprising a termination in longitudinal section, this termination surrounding the end of a single electrical cable.

[0077] For reasons of clarity, only the essential elements for understanding the invention have been represented schematically, and this without regard to scale.

[0078] Figure 1 represents a medium or high voltage power cable 1, which includes an elongated central conductive element 2, in particular made of copper or aluminum. The power cable 1 further comprises several layers arranged successively and coaxially around this conductive element 2, namely: a first semiconducting layer 3 called the "inner semiconducting layer", an electrically insulating layer 4, a second semiconducting layer 5 called the "outer semiconducting layer", a metallic grounding and / or protective screen 6, and an outer protective sheath 7.

[0079] The electrically insulating layer 4 is an extruded and crosslinked layer, obtained from the polymer composition according to the invention.

[0080] The semiconducting layers are also extruded and crosslinked layers, which can be obtained from the polymer composition according to the invention.

[0081] The presence of the metallic screen 6 and the outer protective sheath 7 is preferential, but not essential, this cable structure being as such well known to the person skilled in the art.

[0082] Fig. 2 represents a device 101 comprising a junction 20 partially surrounding two electrical cables 10a and 10b.

[0083] More particularly, the electrical cables 10a and 10b comprise respectively an end 10'a and 10'b, intended to be surrounded by the junction 20.

[0084] The junction body 20 comprises a first semiconductor element 21 and a second semiconductor element 22, separated by an electrically insulating element 23, said semiconductor elements 21, 22 and said electrically insulating element 23 surround the ends 10'a and 10'b respectively of the electrical cables 10a and 10b.

[0085] This junction 20 allows the first cable 10a to be electrically connected to the second cable 10b, in particular by means of an electrical connector 24 located in the center of the junction 20.

[0086] At least one of the elements chosen from the first semiconductor element 21, the second semiconductor element 22 and said electrically insulating element 23, may be a crosslinked layer as described in the invention.

[0087] The first electrical 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.

[0088] The second electrical cable 10b comprises an electrical conductor 2b surrounded by at least a 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.

[0089] These electrical cables 10a and 10b can be those described in the present invention.

[0090] At said end 10'a, 10'b of each electrical cable 10a, 10b, the second semiconducting layer 5a, 5b is at least partially exposed so that the electrically insulating layer 4a, 4b is at least partially positioned inside the junction 20, without being covered by the second semiconducting layer 5a, 5b of the cable.

[0091] Inside the junction 20, the electrically insulating layers 4a, 4b are in direct physical contact with the electrically insulating element 23 and the first semiconductor element 21 of the junction 20. The second semiconductor layers 5a, 5b are in direct physical contact with the second semiconductor element 22 of the junction 20.

[0092] Fig. 3 represents a device 102 comprising a termination 30 surrounding a single electrical cable 10c.

[0093] More particularly, the electrical cable 10c includes an end 10'c, intended to be surrounded by the termination 30.

[0094] The body of the termination 30 comprises a semiconductor element 31 and an electrically insulating element 32, said semiconductor element 31 and said electrically insulating element 32 surround the end 10'c of the electrical cable 10c.

[0095] At least one of the elements chosen from the semiconductor element 31 and the electrically insulating element 32 can be a crosslinked layer as described in the invention.

[0096] The electrical cable 10c comprises an electrical conductor 2c surrounded by a first semiconductor layer 3c, an electrically insulating layer 4c surrounding the first semiconductor layer 3c, and a second semiconductor layer 5c surrounding the electrically insulating layer 4c.

[0097] This 10c electrical cable can be that described in the present invention.

[0098] At said end 10'c of the electrical cable 10c, the second semiconductor layer 5c is at least partially stripped so that the electrically insulating layer 4c is at least partially positioned inside the termination 30, without being covered by the second semiconducting layer 5c of the cable.

[0099] Inside the termination 30, the electrically insulating layer 4c is in direct physical contact with the electrically insulating element 32 of the termination 30. The second semiconducting layer 5c is in direct physical contact with the semiconducting element 31 of the junction 30.

[0100] EXAMPLES

[0101] EXAMPLE1

[0102] Step 1: Grafting acrylic acid onto a PE:

[0103] 100 g of polyethylene (LDPE MFI 2), 0.25 g of peroxide (Dicmuyl peroxide) and 3 g of grafting acrylic acid were placed in a glass container. The resulting mixture was stirred at 60 °C to facilitate the impregnation of the molecules into the polymer until complete absorption of the liquids by the granules.

[0104] The mixture was then placed in an internal mixer at 200 °C, and then mixed at this temperature for a period of 5 minutes after the melting of the latter.

[0105] A sample was taken and formed into a thin film, then washed with tetrahydrofuran. FTIR analysis revealed the presence of grafted acrylic acid through the definition of a peak at 1729 cm1.

[0106] Step 2: Crosslinking with an epoxy:

[0107] The grafted polymer obtained in step 1 was placed in an internal mixer at a temperature above its melting point. A catalyst was introduced, and then an amount of 1,4-butanediol diglycidyl ether, maintaining a molar ratio of 0.5 between the epoxy and acid groups, was added. The mixing time was approximately 5 minutes. The mixture was then placed under pressure at a temperature and time determined experimentally by rheological measurement to allow the reaction of the epoxy groups with the carboxylic acid groups.

[0108] EXAMPLE 2

[0109] Example of crosslinking of an acrylic acid-polyethylene copolymer containing 6.5% acrylic acid function MFI 9

[0110] In an internal mixer, 100 g of the copolymer as obtained in step 1 of the previous example was introduced at 100 °C

[0111] After melting this copolymer, the following elements are added to the mixer at 100°C: - The 2-Ethylimidazole catalyst, with a ratio of 2 molar % relative to the carboxylic acid functions present in the polymer. Epoxy: 1,4-butanediol diglycidyl ether with a molar ratio of the number of epoxy functions to the number of carboxylic acid functions of 0.5:1.

[0112] Once all these compounds have been introduced, an additional 5 minutes of mixing are required. No increase in torque was observed at this temperature.

[0113] Once the incorporation was carried out, the crosslinking was carried out under pressure at 190 °C for 12 minutes.

[0114] A hot elongation measurement was carried out according to IEC 60811-507 to validate the crosslinking. Under these crosslinking conditions, the hot elongation reached 15% and the cold elongation was 0%. Thus, the material complies with the requirements of the standard.

Claims

Demands

1. An electrical device comprising a cross-linked layer, wherein said layer is obtained by reaction of at least the following compounds: (a) identical or different polymer chains, each comprising at least one -COOH function (and preferably several); and (b) identical or different non-polymer compounds, each containing at least two epoxy functions.

2. Electrical device according to claim 1, which is an electrical cable comprising at least one elongated electrically conductive element, surrounded by said cross-linked layer, this layer being for example an insulating layer or an outer sheath.

3. Electrical device according to claim 1, which is an accessory for electrical cable, in particular a junction or termination, said accessory comprising said cross-linked layer, preferably intended to be associated with at least one electrical cable, and to surround at least one end of said electrical cable.

4. Electrical device according to any one of claims 1 to 3, wherein the cross-linked layer is an electrically insulating layer.

5. Electrical device according to any one of claims 1 to 3, wherein the cross-linked layer is a semiconducting layer.

6. A method for preparing an electrical device comprising a crosslinked layer, comprising a step (e) of preparing said crosslinked layer, by applying a mixture comprising: (a) identical or different polymer chains, each comprising at least one -COOH function (and preferably several); and (b) identical or different non-polymer compounds, each containing at least two epoxy functions.

7. A process according to claim 6 wherein step (e) comprises: a step (e1) where a population of non-crosslinked P polymers without -COOH functions is subjected to a grafting reaction with -COOH groups, thereby obtaining a population of grafted polymers; then a step (e2) where the grafted polymers obtained in step (e1) are contacted with the compounds (b)

8. A method according to claim 7 wherein the non-crosslinked P polymers implemented in step (11) are or comprise non-crosslinked polyethylene

9. A method according to claim 7 or 8, wherein the non-crosslinked polymers P implemented in step (11) are or comprise a non-crosslinked rubber

10. A process according to claim 6 wherein step (e) is carried out on polymers (a) obtained from the polymerization of monomers comprising monomers bearing -COOH function.

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