Multilayer element for cooling circuits using at least one dielectric fluid

Abstract

The invention relates to the use of at least one element in a cooling circuit using at least one dielectric fluid, wherein the element comprises: - a first layer consisting of a polyamide composition C, characterised in that the composition C comprises 50 to 99.9% by weight relative to the total weight of the composition of a polyamide matrix; - at least one second layer consisting of a composition selected from a composition comprising at least one polyamide, a composition comprising at least one functional polyolefin or a composition comprising at least one barrier polymer; the dielectric fluid is liquid at atmospheric pressure at 23°C and comprises less than 10% by weight of water and glycol ether; and the first layer is intended to be in contact with the dielectric fluid.

Description

[0001]Description Title: Multilayer element for cooling circuits using at least one dielectric fluid Field of the invention The present invention relates to multilayer elements for cooling circuits using at least one dielectric fluid, in particular elements or structures for the transport, distribution or storage of said dielectric fluid intended for the cooling, for example the direct cooling, of battery cells, in particular hybrid and electric vehicles, or for the cooling of computer servers. Technical background Car manufacturers are currently considering the use of direct cooling of traction batteries in hybrid and electric vehicles. It is in fact much more efficient to cool the cells by direct conduction of the fluid with their surface rather than through water-air type exchangers or by conduction through several layers which may include metal in particular.The coolants currently used are mixtures of water and glycol. However, these coolants cannot be used for direct cooling. In fact, when in contact with water, there is a very high risk that the cells will self-ignite and that the fire will spread to the entire battery and then to the vehicle. Since the battery electrodes cannot be in contact with a conductive liquid, water-based coolants cannot be used for direct cooling. Another major risk is that when in contact with water, the cells will self-ignite, causing the fire to spread to the entire battery and then to the vehicle. It is therefore essential to use coolants that do not contain (or contain very little) water and do not conduct electricity in order to avoid any short circuit in the battery that could cause a fire.Direct cooling can be achieved with specific fluids with very low electrical conductivity, called "dielectric fluids". "Dielectric fluids", based on hydrocarbon oils or synthetic esters, are different from the aqueous-based coolants currently used. There is therefore a need to provide transport, distribution or storage elements (or structures) adapted to said dielectric fluids. It is necessary to provide elements which have the following property(ies): - mechanical resistance and in particular not to see its stress or elongation at break modified by more than 50%, in particular by soaking in the dielectric fluid between -60 and 140°C whether in the short term (<168 hours) or in the long term (>10,000 h); - the possibility of being recycled, preferably by a mechanical recycling process; - a resistance to fluid pressure, generally between 1 and 6.bars ; - resistance to chemical attacks from the fluid internally and from various components externally, in particular de-icing salts; - thermal resistance; - resistance to hydrolysis; - low accumulation of electrical charge linked to the friction of the dielectric fluid on the internal surface of said element, in particular in the case of a pipe; - low electrical resistivity, volume or surface, typically less than 10 6Ohms. Surface electrical resistivity measurements can be carried out according to ASTM D257-14 of 2021; - resistance to the release of soluble or insoluble products which can modify the properties of the dielectric fluid or damage one or other of the components of the direct cooling circuit, - resistance to the release of products which harm the dielectric nature of the fluid, in particular of the ionic species type (anionic or cationic). There is a real need to provide such elements which have at least one of these properties throughout the lifetime of the vehicle, in particular between 3000 and 10000 hours, including both the driving phases and the static charging phases of the vehicles on which they are mounted. Summary of the invention The present invention relates to the use of at least one element in a cooling circuit using at least one dielectric fluid,in which the element comprises:- a first layer consisting of a polyamide composition C, characterized in that the composition C comprises from 50 to 99.9% by weight relative to the total weight of the composition of a polyamide matrix; - at least one second layer consisting of a composition chosen from a composition comprising at least one polyamide, a composition comprising at least one functional polyolefin or a composition comprising at least one barrier polymer; the dielectric fluid is liquid at atmospheric pressure at 23°C and comprises less than 10% by weight of water and glycol ether; and said 1st layer being intended to be in contact with said dielectric fluid. Preferably, the polyamide matrix has an average C / N ratio greater than or equal to 5.5, preferably greater than or equal to 6, preferably greater than or equal to 7, preferably greater than or equal to 8, preferably greater than or equal to 9,preferably between 9 and 12. Preferably, composition C has an inherent viscosity between 1 and 1.8, preferably between 1.2 and 1.6, more preferably between 1.3 and 1.6. Preferably, the dielectric fluid comprises one or more compounds chosen from mineral oils and mineral oil derivatives, polyalphaolefins, polyalkylene glycols, silicones, esters with a number-average molar mass between 1000 and 100000 g / mol, for example polyol ester, POE, partially fluorinated polymers having a number-average molar mass of 1000 and 100000 g / mol, for example perfluoropolyethers. Preferably, the dielectric fluid has a density measured according to ISO 1675:2022 at 23°C of between 0.3 and 1.5, preferably between 0.5 and 1.1, advantageously between 0.7 and 1.05, more preferably between 0.8 and 1. Preferably,the dielectric fluid has a kinematic viscosity at 40°C of between 1 and 35 mm2 / s, preferably between 1.5 and 15 mm2 / s, in particular between 2 and 10 mm2 / s and / or a kinematic viscosity at 100°C of between 0.01 and 5 mm2 / s, preferably between 0.1 and 4 mm2 / s, preferably between 0.5 and 3 mm2 / s, more preferably between 0.8 and 2.5 mm2 / s and / or a kinematic viscosity at 25°C of between 5 and 150 mm2 / s, preferably between 10 and 100 mm2 / s, the kinematic viscosity being measured according to standard ISO 3104:2020.Preferably, composition C further comprises from 0.01 to 1.5%, preferably from 0.05 to 0.5%, more preferably 0.1 to 0.4% by weight of a heat stabilizer relative to the total weight of composition C. Preferably, composition C further comprises: - From 10 to 35%, preferably from 15 to 25%, by weight of a flame retardant, preferably a non-halogenated flame retardant,preferably a phosphorus-containing flame retardant; and / or -From 1 to 35% by weight, preferably from 2 to 10% by weight of at least one impact modifier; and / or -From 0.5 to 30% by weight of at least one current-conducting filler; and / or -From 0.1 to 10% by weight of at least one additive.Preferably, composition C comprises a plasticizer content of less than 10%, preferably less than 6%, preferably less than 5%, preferably less than 3%, preferably less than 1%, by weight, preferably composition C is free of plasticizer, such as BBSA. Preferably, the second layer is a layer consisting of a composition chosen from: -a composition comprising at least one polyamide;- a composition comprising at least one functional polyolefin; or- a composition comprising at least one barrier polymer such as a vinyl alcohol copolymer, a fluoropolymer, a polyphenylene sulfide, a polybutylene naphthalate or a polyphthalamide (PPA),preferably an EVOH copolymer. Preferably, the element according to the invention comprises a third layer and optionally a fourth and optionally a fifth layer, in which: -the third layer consists of a composition chosen from:- a composition comprising at least one polyamide, preferably a zinc chloride-resistant polyamide; or -a composition comprising at least one functional polyolefin; or- a composition comprising at least one non-functional polyolefin; or -a composition comprising at least one barrier polymer such as a vinyl alcohol copolymer, a fluorinated polymer, a polyphenylene sulfide, a polybutylene naphthalate or a polyphthalamide, preferably an EVOH copolymer. -the fourth layer,where appropriate, is made up of a composition chosen from:- a composition comprising at least one non-functional polyolefin; or - a composition comprising at least one polyamide.- the fifth layer, where appropriate, is made up of a composition comprising at least one polyamide. Preferably, the element is a pipe for transporting the dielectric fluid. Preferably, the element is a reservoir for storing the dielectric fluid. The present application also relates to a cooling circuit comprising at least one element as described above, in which a dielectric fluid as described above circulates, the layer of composition C being in direct contact with said dielectric fluid. Preferably, the circuit further comprises at least one housing adapted to receive battery cells and provided with an inlet and an outlet allowing the circulation of said dielectric fluid in said housing,said housing being made of a polyamide composition comprising: ode 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7; ode 15 to 65% by weight of reinforcing fibers or fillers.The present invention also relates to a device for the direct cooling of battery cells by a dielectric fluid as described above, comprising: - a dielectric fluid; - At least one housing (BX) adapted to receive battery cells and provided with an inlet and an outlet allowing the circulation of said dielectric fluid in said housing, said housing preferably being made of a polyamide composition comprising: ode 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7; ode 15 to 65% by weight of reinforcing fibers or fillers; - Upstream of the housing (BX),at least one element as described above in the form of a pipe in which said dielectric fluid circulates towards the housing (BX), -Downstream of the housing (BX), at least one element as described above in the form of a pipe in which said dielectric fluid circulates from the housing (BX). The present invention also relates to a device for the direct cooling of battery cells by a dielectric fluid comprising: - A dielectric fluid; - Optionally at least one reservoir (R1) as defined above; - At least one housing (BX) adapted to receive battery cells and provided with an inlet and an outlet allowing the circulation of a dielectric fluid in said housing in direct contact with the battery cells; -Upstream of the housings (BX) at least one element (E1) for the distribution of the dielectric fluid coming from the reservoir to the housings (BX),the element (E1) comprising an inlet for the dielectric fluid and x outlets connected to the boxes (BX), x corresponding to the number of boxes (BX), each of the outlets being connected to a box (BX); -Downstream of the boxes (BX) at least one element (E2) for the recovery of the dielectric fluid coming from the boxes (BX), the element (E2) comprising y inlets for the dielectric fluid and z outlets, y corresponding to the number of boxes (BX) connected to the element (E2) and z corresponding to the number of cooling systems (S1), each of the inlets being connected to a box (BX) and each of the outlets being connected to at least one cooling system (S1); -At least one cooling system (S1), preferably a radiator, allowing the cooling of the dielectric fluid coming from the element (E2); - pipes, possibly connected to each other by connectors, as defined above in which said dielectric fluid circulates between the reservoir (R1),the element (E1), the housings (BX), the element (E2) and the cooling system (S1); -the housings (BX) and the elements (E1) and (E2) being made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers; -The dielectric fluid being as defined above. Preferably, the inlets of the housings (BX) are equipped with a nozzle allowing the dielectric fluid to be sprayed directly onto the battery cells, preferably the nozzle is made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers. Preferably, the pipes are connected to the inlets and / or outlets of the boxes (BX), elements (E1) and (E2) directly or using connectors,preferably made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers. The device may be included in a container comprising an inlet and an outlet each equipped with a pipe as defined above, or a plurality of pipes as defined above connected together by connectors, in which said dielectric fluid circulates. The polyamide composition of the first layer according to the invention, in combination with the other layers, is particularly well suited to the dielectric fluid used in particular for cooling battery cells. Thus, the dielectric fluid will not have its composition modified upon contact with the elements according to the invention comprising the polyamide composition of the invention. Particularly advantageously,after aging for 500 hours at 130°C, the dielectric fluid in contact with the polyamide composition according to the invention does not comprise more than 0.5% by mass, preferably 0.2%, advantageously 0.1% by mass of impurities not initially present. This test is carried out by immersing a “1BA” test piece (according to ISO 527) in 100 mL of dielectric fluid according to the invention. The dielectric fluid is preferably Mobil EV therm Elite 701®. These impurities are quantified in two ways: - the dielectric fluid is filtered and then the residue is weighed after washing and drying (when the mass no longer varies during drying). - The soluble impurities are quantified by liquid chromatography, in particular HPLC by comparing the chromatograms before and after aging of the composition in the fluid. The impurities according to the invention may be additives, monomers or oligomers,plasticizers or fillers initially included in the multi-layer element of the composition or impurities that have migrated through the composition, such as other automotive fluids such as lubricants or greases. Impurities are, for example, phosphorus species and / or BBSA (N-Butyl Benzene Sulfonamide). Fluid pollution by phosphorus species and BBSA can be measured indirectly by monitoring changes in the P and S element contents. These contents can be determined by inductively coupled plasma torch spectroscopy according to ASTM D5185. The migration of antioxidants can be assessed qualitatively and quantitatively by analyzing the fluid using high-performance liquid chromatography coupled with appropriate detection systems for their detection, such as UV photometry,or high-resolution mass spectrometry. The identity of the targeted antioxidants must be confirmed (i) by concordance of the retention times between the substances recorded in the sample chromatograms and those recorded in the analysis of standards, (ii) by concordance of the mass spectra. Preferably, after the aging described above (500 hours at 130°C), the conductivity of the dielectric fluid is less than 1 µS / cm, preferably less than 0.1 µS / cm, more preferably less than 0.01 µS / cm. The resistivity of the fluid is measured according to DIN IEC 60247, which allows the conductivity to be calculated. The water content in the dielectric fluid after aging is determined according to the Karl Fisher method following ISO 760:1978. This aging is carried out by placing the dielectric fluid in contact with a hermetically sealed element according to the invention for 1000 h. The element according to the invention is placed in a controlled atmosphere at 50% relative humidity and at a temperature of 50°C. The wall thickness of the element is 2 mm. The water content in the dielectric fluid after this aging is less than 2% by weight, preferably 1% by weight, in particular 0.5% by weight, advantageously 0.1% by weight, in particular 0.05% by weight (the water content of the fluid before aging is less than 50 ppm). Presentation of the figures [Fig. 1] represents a cooling circuit for battery cells comprising two housings (B1) and (B2) comprising battery cells. Each of the housings (B1) and (B2) comprises an inlet and an outlet allowing the flow of dielectric fluid (3). The cooling circuit also comprises two elements (E1) and (E2) allowing the distribution of the dielectric fluid in the housings (B1) and (B2) via the pipes (T).Detailed description The invention is now described in more detail and in a non-limiting manner in the description which follows. Unless otherwise indicated, all percentages are mass percentages. In the present text, the quantities indicated for a given species can apply to this species according to all its definitions (as mentioned in the present text),including more restricted definitions. It is further specified that the expressions "between… and…" and "from… to…" used in the present description must be understood as including each of the terminals mentioned. The term "polyamide matrix" is intended to designate a composition of one or more polyamides. In the context of the present invention, the polyamide matrix represents more than 50% by weight of polyamide relative to the total weight of the composition. In the context of the present invention, all the components included in the polyamide composition according to the invention are dissolved or dispersed in the polyamide matrix. The term "direct cooling" is intended to designate the cooling of the battery cells by direct contact of said battery cells with the dielectric heat transfer fluid. In so-called "indirect" cooling,the battery cells are not in direct contact with the heat transfer fluid. In indirect cooling processes, there is an element that physically isolates the battery cells from the heat transfer fluid. This element acts as a heat exchanger between the heat transfer fluid and the battery cells. These elements may in particular be in the form of cooling plates, cooling channels, or any other equivalent device allowing such circulation of heat transfer fluid within it. The invention relates firstly to the use of at least one element in a cooling circuit using at least one dielectric fluid, in which the element comprises: - a first layer consisting of a polyamide C composition, characterized in that the composition C comprises from 50 to 99,9% by weight relative to the total weight of the composition of a polyamide matrix; -at least one second layer consisting of a composition chosen from a composition comprising at least one polyamide, a composition comprising at least one functional polyolefin or a composition comprising at least one barrier polymer; the dielectric fluid is liquid at atmospheric pressure at 23°C and comprises less than 10% by weight of water and glycol ether; and said 1, ère layer being intended to be in contact with said dielectric fluid. Preferably, said 1 èrelayer is in contact with said dielectric fluid. Preferably, composition C comprises less than 10%, preferably less than 1%, preferably less than 0.1% of reinforcing fiber, preferably composition C is free of reinforcing fibers. Preferably, the cooling circuit is a direct cooling circuit. The second layer may be a layer consisting of a composition chosen from: - a composition comprising at least one polyamide; - a composition comprising at least one functional polyolefin; or - a composition comprising at least one barrier polymer such as a copolymer comprising vinyl alcohol, a fluorinated polymer, a polyphenylene sulfide, a polybutylene naphthalate or a polyphthalamide (PPA), preferably a copolymer of ethylene and vinyl alcohol (EVOH). The element of the invention may also comprise a third, a fourth,or even a fifth layer. The third layer may consist of a composition chosen from: - a composition comprising at least one polyamide, preferably a polyamide resistant to zinc chloride, preferably a polyamide having a C / N ratio greater than or equal to 7, preferably greater than or equal to 8, preferably greater than or equal to 9,preferably between 9 and 12; or- a composition comprising at least one functional polyolefin; or- a composition comprising at least one non-functional polyolefin; or - a composition comprising at least one barrier polymer as defined above. The fourth layer may consist of a composition chosen from: - a composition comprising at least one non-functional polyolefin; or - a composition comprising at least one polyamide. The fifth layer may consist of a composition comprising at least one polyamide. It should be understood that layer 1 is the innermost. It should be understood that layers 1 to 5 go from the innermost layers (1) to the outermost layer (5). Polyamide matrix of composition CThe composition according to the invention preferably comprises from 50 to 99.9%,preferably from 70 to 99% by weight of polyamide matrix relative to the total weight of composition C. The polyamide(s) of the polyamide matrix are chosen so that the average C / N ratio of the polyamide mixture of the polyamide matrix is ​​greater than or equal to 5.5, preferably greater than or equal to 6, preferably greater than or equal to 7, preferably greater than or equal to 8, preferably greater than or equal to 9, preferably between 9 and 12. In one embodiment, the composition of the invention preferably comprises less than 20% by weight, preferably less than 10% by weight, for example less than 5% by weight, preferably less than 3% by weight, in particular 0% by weight, relative to the total weight of the composition of one or more polyamides having a C / N ratio of less than 7. By average number of carbon atoms per nitrogen atom is meant the average of the number of carbon atoms per pattern,that is to say by chaining between two nitrogen atoms. Within a polyamide, the units are linked to each other by amide functions: -CO-NH-. Thus, there are as many nitrogen atoms as there are amide groups (-CO-NH-). In the case of a homopolyamide of type PA-XY, the number of carbon atoms per nitrogen atom is the average of the X unit and the Y unit. Thus PA612 resulting from the polycondensation of hexanediamine and dodecanedioic acid, is a PA with 9 carbon atoms per nitrogen atom, in other words is a C9 PA, according to the following calculation: (6+12) / 2. In the case of copolyamides, the number of carbon atoms per nitrogen atom is calculated according to the same principle. The calculation is carried out in molar proportion to the different amide units. Thus the coPA- 6.T / 6.6 comprising 60% of 6T and 40% of 66 is in C6.6: 60%x[(6+8) / 2]+40%x[(6+6) / 2] = 6.6. In the case of a polyamide mixture,the number of carbon atoms per nitrogen atom is calculated according to the same principle. The calculation is carried out in molar proportion to the different polyamides. Thus, for a mixture of polyamide A and polyamide B comprising 60% of A and 40% of B, the average C / N ratio is [60% x (C / N ratio of A) + 40% x (C / N ratio of B)] / 2. Preferably, the composition C according to the invention has an inherent viscosity of between 1 and 1.8, preferably between 1.2 and 1.6, more preferably between 1.3 and 1.6. Preferably, the polyamide matrix according to the invention has an inherent viscosity of between 1 and 1.8, preferably between 1.2 and 1.6, more preferably between 1.3 and 1.6. In the sense of the application, the inherent viscosity of the polyamide matrix is ​​measured after dissolution of the polymer matrix. For the purposes of the application, the inherent viscosity is preferably as measured using an "Ubbelohde" tube at 20°C on a 0.5% by weight in m-cresol according to ISO 307 of 2019. The term polyamide refers to both homopolyamide and copolyamide. The nomenclature used to define polyamides is described in ISO 1874-1:2011 "Plastics - Polyamide (PA) materials for molding and extrusion - Part 1: Designation", particularly on page 3 (tables 1 and 2) and is well known to those skilled in the art. Polyamide can be obtained from the polycondensation of lactam units, amino acid units and / or XY units, where X denotes a diamine and Y denotes a dicarboxylic acid (or diacid). Lactams and amino acids contain 4 to 12 carbon atoms. Preferably, they are chosen from pyrrolidinone, 2-piperidinone, caprolactam, aminohexanoic acid, pelargolactam, decanolactam, undecanolactam, 10-aminoundecanoic acid, amino-11-undecanoic acid, amino-12-dodecanoic acid, lauryllactam, enantholactam,caprylolactam. Advantageously, the lactams and amino acids are C11 and C12. The diamine may be aliphatic, linear or branched, or cycloaliphatic, preferably it is linear or branched aliphatic, in particular linear. The dicarboxylic acid may be aliphatic, cycloaliphatic or aromatic, preferably it is aliphatic or aromatic. Concerning the polyamides obtained from the polycondensation of XY units, the diamine (X) may be C4 to C36, in particular C6 to C22, in particular C6 to C18 and the dicarboxylic acid (Y) may be C4 to C36, in particular C6 to C22, in particular C6 to C18. Advantageously, the diamine is chosen from butanediamine, pentanediamine, 2-methyl-1,5-pentanediamine, 1,6-hexamethylenediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 2-methyl-1,8-octanediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 1,10-decanediamine, 1,11-undecanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,12-dodecanediamine, 1,13-tridecanediamine, 1,14-tetradecanediamine, hexadecanediamine, octadecanediamine, octadecenediamine, eicosanediamine, docosanediamine and diamines obtained from fatty acids, 1,3-xylylenediamine (denoted MXD) and 1,4-xylylenediamine (denoted PXD), bis(3,5-dialkyl-4-aminocyclohexyl)-methane, bis(3,5-dialkyl-4-aminocyclohexyl)ethane, bis(3,5-dialkyl-4-aminocyclohexyl)-propane, bis(3,5-dialkyl-4-aminocyclohexyl)-butane, bis-(3-methyl-4-aminocyclohexyl)-methane or 3'-dimethyl-4,4'-diamino-dicyclohexyl-methane commonly called "BMACM" or "MACM" (and noted B hereinafter), p-bis(aminocyclohexyl)-methane commonly called "PACM" (and noted P hereinafter), isopropylidenedi(cyclohexylamine) commonly called "PACP", isophorone-diamine (noted IPD hereinafter) and 2,6-bis(amino methyl)norbornane commonly called "BAMN", in particular 1,10-decanediamine. A non-exhaustive list of cycloaliphatic diamines is given in the publication "Cycloaliphatic Amines" (Encyclopaedia of Chemical Technology, Kirk-Othmer, 4th Edition (1992), pp.386-405). Advantageously, the dicarboxylic acid is chosen from succinic acid, pentanedioic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanoic acid, octadecenoic acid, eicosanedioic acid, docosanedioic acid and fatty acid dimers containing 36 carbons, terephthalic acid (denoted T), isophthalic acid (denoted I), in particular dodecanedioic acid. Advantageously, the diamine is chosen from 1,8-octanediamine, 1,9-nonanediamine, 2-methyl-1,8-octanediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 1,10-decanediamine, 1,3-bis(aminomethyl)cyclohexane (BAC), 1,11-undecanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,12-dodecanediamine, 1,13-tridecanediamine, 1,14-tetradecanediamine, in particular 1,10-decanediamine and the dicarboxylic acid is chosen from sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, tetradecanedioic acid, terephthalic acid (denoted T), isophthalic acid (denoted I), in particular dodecanedioic acid. More preferably, the lactam is lauryllactam, the amino acid is selected from 10-aminoundecanoic acid, amino-11-undecanoic acid, amino-12-dodecanoic acid, the diamine is selected from 2-methyl-1,5-pentanediamine, 1,5-pentanediamine, 1,6-hexamethylenediamine, 1,9-nonanediamine, 2-methyl-1,8-octane-diamine, 1,10-decanediamine and 1,12-dodecanediamine and the dicarboxylic acid is selected from adipic acid, sebacic acid, dodecanedioic acid,terephthalic acid (denoted T) and isophthalic acid (denoted I). According to a very preferred embodiment, the lactam is lauryllactam, the amino acid is chosen from 10-aminoundecanoic acid, amino-11-undecanoic acid, amino-12-dodecanoic acid, the diamine is chosen from butanediamine, 1,5-pentanediamine, 1,6-hexamethylenediamine, 1,10-decanediamine and 1,12-dodecanediamine and the dicarboxylic acid is chosen from adipic acid, sebacic acid, dodecanedioic acid, terephthalic acid (denoted T) and brassylic acid, tetradecanedioic acid. Advantageously, the polyamide present in the composition of the invention is chosen from PA 6, PA 66, PA 56, PA 410, PA412, PA 510, PA 610, PA612, PA 613PA1010, PA10T, PA10T / 1010, PA11, PA12, PA11 / 10T, PA12 / 10T, PA 1012, PA1212, PA 1214 PA 618, PA 12T, PA 1010 / 1012, PA BACT / 6T, PA BACT / 10T, PABACT / 12T, PA MPMDT / 6T, PA MPMDT / 10T, PA MPMDT / 12T, PA MXDT / 6T, PA MXDT / 10T, PA MXDT / 12T, PA11 / BACT / 6T,PA 11 / BACT / 10T, PA 11 / BACT / 12T, PA 11 / MPMDT / 6T, PA 11 / MPMDT / 10T, PA 11 / MPMDT / 12T, PA 11 / MXDT / 6T, PA 11 / MXDT / 10T, PA 11 / MXDT / 12T, PA610 / 6T, PA612 / 6T, and their mixture. Preferably, the polyamide constituting the matrix of the invention is chosen from PA6, PA 66, PA12, PA 11, PA 410, PA412, PA 510, PA 610, PA612, PA 613 PA1010, PA 1012, PA9T, PA10T, PA6T / 10T, PA6T / 1010, PA10T / 1010, PA610 / 6T, PA612 / 6T, and PA11 / 10T, and their mixture. Preferably, the polyamide constituting the matrix of the invention is chosen from PA6, PA66, PA12, PA 11, PA 410, PA412, PA 510, PA 610, PA612, PA 613 PA1010, PA 1012, PA610 / 6T, PA612 / 6T.Polyamide composition The polyamide composition C according to the invention may further comprise at least one heat stabilizer. If present, the heat stabilizer is used in contents of 0.01 to 1.5%, preferably 0.05 to 0.5%, more preferably 0.1 to 0.4% by weight relative to the total weight of the polyamide composition. The heat stabilizer may be chosen from a metal-based stabilizer, an organic stabilizer and a mixture thereof. The metal-based stabilizer may consist of one or more constituents chosen from iron-based or copper-based compounds such as cuprous chloride, cupric chloride, cuprous bromide, cupric bromide, cuprous iodide, cupric iodide, cuprous acetate and cupric acetate. Halides and acetates of other metals such as silver may be mentioned. These copper-based compounds are typically associated with alkali metal halides. A well-known example is the mixture of CuI and KI, where the CuI:KI ratio is typically between 1:5 and 1:15. An example of such a stabilizer is Polyadd P201® from Ciba. Further details on copper-based stabilizers can be found in US Patent 2,705,227. More recently,complexed metal-based stabilizers have appeared, such as complexed coppers such as Bruggolen H3336®, H3337®, H3373® from the Brueggemann company. The metal-based stabilizers are preferably in non-ionic form, advantageously complexed, this advantageously makes it possible to avoid the release of ions into the dielectric fluid which would lead to an increase in the ionic (electrical) conductivity of said dielectric fluid. The organic stabilizer can be chosen, without this list being restrictive, from: - phenolic antioxidants, for example Irganox 245®, Irganox 1010®, Irganox 1098® from BASF, Irganox MD1024® from BASF, Lowinox 44B25® from SI Group, - phosphorus-based stabilizers, such as phosphites, for example Irgafos 168® from Ciba, - a UV absorber, such as Tinuvin 312® from Ciba, - a HALS, as previously mentioned, - an amine-type stabilizer, such as Naugard 445® from Crompton,or of the hindered amine type such as Tinuvin 770® from Ciba, - a polyfunctional stabilizer such as Nylostab S-EED® from Clariant. It is obviously possible to envisage a mixture of two or more of these organic stabilizers. Preferably, the thermal stabilizer is non-halogenated and preferably chosen from amine-type stabilizers. In one embodiment, the stabilizer is a mixture of phenolic antioxidants and phosphites. The polyamide composition (C) according to the invention may further comprise (relative to the total weight of the composition): - From 10 to 35%, preferably from 15 to 25%, by weight of a flame retardant (or flame retardant, or flame retardant), preferably a non-halogenated flame retardant, preferably a phosphorus-containing flame retardant; and / or -From 1 to 30% by weight, preferably from 2 to 10% by weight of at least one impact modifier; and / or -From 0 to 30%, preferably from 1 to 27%,by weight of at least one current-conducting filler; and / or- From 0.1 to 10%, preferably from 0.2 to 5%, by weight of at least one additive.Preferably, the flame retardant is chosen from halogen-free flame retardants, as described in US 2008 / 0274355 and in particular a metal salt chosen from a metal salt of phosphinic acid, a metal salt of diphosphinic acid, a polymer containing at least one metal salt of phosphinic acid, a polymer containing at least one metal salt of diphosphinic acid. The flame retardant may also be chosen from red phosphorus, an antimony oxide, a zinc oxide, an iron oxide, a magnesium oxide, metal borates, such as a zinc borate, melamine pyrophosphates, melamine cyanurates,anti-drip agents of a silicone or fluorinated nature. The flame retardant may also be a mixture of the above-mentioned agents. They may also be halogenated flame retardants such as brominated or polybrominated polystyrene, brominated polycarbonate or brominated phenol. The flame retardant may also be chosen from the metal salt of phosphinic acid of the following formula (I) and the metal salt of diphosphinic acid of the following formula (II):, with R1 and R2, independently of each other, denote a linear or branched C1-C6 alkyl group, or an aryl group; R3 represents a linear or branched C1-C10 alkylene, C6-C10 arylene, C6-C10 alkylarylene, or C6-C10 arylalkylene group, M is an Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na, K ion and / or a protonated amine base m denotes an integer from 1 to 4, n denotes an integer from 1 to 4, x denotes an integer from 1 to 4, n and m being chosen so that the salt is neutral, i.e. it does not carry an electrical charge. Preferably, M represents a calcium, magnesium, aluminum or zinc ion. Preferably, R1 and R2, independently of each other, denote a methyl, ethyl, n-propyl, iso-propyl, n-butyl, tert-butyl, n-pentyl and / or phenyl group. Preferably, R3 represents a methylene, ethylene, n-propylene, iso-propylene, n-butylene, tert-butylene, n-pentylene, n-octylene, n-dodecylene group; phenylene,naphthylene; methylphenylene, ethylphenylene, tert-butylphenylene, methylnaphthylene, ethylnaphthylene, tert-butylnaphthylene; phenylmethylene, phenylethylene, phenylpropylene, or phenylbutylene. The flame retardant may be the product with the trade name ExolitOP 1230® sold by Clariant, which is the aluminum salt of diethylphosphinic acid salt (CAS No. 225789-38-8). More particularly, the flame retardant content is between 10 and 35% by weight, preferably 15 and 25% by weight, and more particularly between 17 and 23% by weight relative to the total weight of the composition. In a preferred embodiment,a synergist agent is also present. The flame retardant synergist agents are in particular as described in WO2005121234. They may be chosen from nitrogen synergists and phosphorus / nitrogen synergists. The synergist agent may be added in a content of between 3 and 20% by weight relative to the total weight of the composition. The polyamide C composition according to the invention may comprise at least one impact modifier. Preferably, it may comprise from 1 to 30%, preferably from 1.5 to 20%, more preferably from 2 to 10%, by weight relative to the total weight of the composition of at least one impact modifier. The impact modifier is advantageously made up of a polymer having a flexural modulus of less than 100 MPa measured according to ISO 178 at 50% RH and a Tg of less than 0°C measured according to standard 11357-2 of 2013. The glass transition temperature Tg of the polyamides is measured using a differential scanning calorimeter (DSC),after a second heating pass, according to ISO 1 1357-2:2013. The heating and cooling rate is 20°C / min. Preferably, the impact modifier consists of one or more polyolefins, some or all of which carry a function chosen from carboxylic acid, carboxylic anhydride and epoxide functions. In particular, the polyolefin may be chosen from an ethylene and propylene copolymer with an elastomeric character (EPR), an ethylene-propylene-diene copolymer with an elastomeric character (EPDM) and an ethylene / alkyl (meth)acrylate copolymer. The composition may comprise up to 20% by weight, relative to the total weight of said composition, of a semi-crystalline polyolefin or a mixture of polyolefins, having a flexural modulus, measured according to ISO 178 at 50% RH, greater than 300 MPa, advantageously greater than 800 MPa. This impact modifier may be a functionalized polyolefin (B1). Preferably,the composition (C) of the invention comprises less than 30%, preferably less than 20%, preferably less than 10%, for example between 2 and 9% by weight of functional polyolefin relative to the total weight of the composition. According to the invention, the term functionalized polyolefin (B1) means the following polymers. The functionalized polyolefin (B1) may be an alpha-olefin polymer having reactive units: functionalities. Such reactive units are carboxylic acid, anhydride, or epoxy functions. By way of example, polyolefins may be mentioned homopolymers or copolymers of alpha olefins or diolefins, such as, for example, ethylene, propylene, butene-1, octene-1, butadiene, and more particularly: - homopolymers and copolymers of ethylene, in particular LDPE, HDPE, LLDPE (linear low density polyethylene), VLDPE (very low density polyethylene,or very low density polyethylene) and metallocene polyethylene, - homopolymers or copolymers of propylene, - ethylene / alpha-olefin copolymers such as ethylene / propylene, EPR (abbreviation for ethylene-propylene-rubber) and ethylene / propylene / diene (EPDM), - styrene / ethylene-butene / styrene (SEBS), styrene / butadiene / styrene (SBS), styrene / isoprene / styrene (SIS), styrene / ethylene-propylene / styrene (SEPS) block copolymers, - copolymers of ethylene with at least one product chosen from salts or esters of unsaturated carboxylic acids such as alkyl (meth)acrylate (e.g. methyl acrylate), or vinyl esters of saturated carboxylic acids such as vinyl acetate (EVA), the proportion of co- monomer up to 40% by weight. These polyolefins described above can be grafted, co-polymerized or terpolymerized by reactive units (the functionalities), such as carboxylic acid functions, anhydrides,or epoxy. More particularly, these polyolefins are grafted or co- or terpolymerized with unsaturated epoxides such as glycidyl (meth)acrylate, or with carboxylic acids or the corresponding salts or esters such as (meth)acrylic acid (which can be neutralized totally or partially by metals such as Zn, etc.) or with carboxylic acid anhydrides such as maleic anhydride. The functionalized polyolefin (B1) can be chosen from the following (co)polymers, grafted with maleic anhydride or glycidyl methacrylate, in which the grafting rate is for example from 0.01 to 5% by weight: - PE, PP, copolymers of ethylene with propylene, butene, hexene, or octene containing for example from 35 to 80% by weight of ethylene; -ethylene / alpha-olefin copolymers such as ethylene / propylene, EPR (short for ethylene-propylene-rubber) and ethylene / propylene / diene (EPDM),- styrene / ethylene-butene / styrene (SEBS), styrene / butadiene / styrene (SBS), styrene / isoprene / styrene (SIS), styrene / ethylene-propylene / styrene (SEPS) block copolymers, - ethylene and vinyl acetate (EVA) copolymers, containing up to 40% by weight of vinyl acetate, - ethylene and alkyl (meth)acrylate copolymers, containing up to 40% by weight of alkyl (meth)acrylate, - ethylene and vinyl acetate (EVA) and alkyl (meth)acrylate copolymers, containing up to 40% by weight of comonomers. A functionalized polyolefin is for example a PE / EPR blend, the weight ratio of which can vary widely, for example between 40 / 60 and 90 / 10, said blend being co-grafted with an anhydride, in particular maleic anhydride, according to a grafting rate for example of 0,01 to 5% by weight. The functionalized polyolefin (B1) may also be chosen from ethylene / propylene copolymers with a majority of propylene grafted with maleic anhydride and then condensed with mono-amine polyamide (or a polyamide oligomer) (products described in EP-A-0342066). The functionalized polyolefin (B1) may also be a co- or terpolymer of at least the following units: (1) ethylene, (2) alkyl (meth)acrylate or saturated carboxylic acid vinyl ester and (3) anhydride such as maleic anhydride or (meth)acrylic acid or epoxy such as glycidyl (meth)acrylate. As examples of functionalized polyolefins of the latter type, the following copolymers may be mentioned, where ethylene preferably represents at least 60% by weight and where the termonomer (the function) represents, for example, 0,1 to 12% by weight of the copolymer: -ethylene / alkyl (meth)acrylate / (meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymers; -ethylene / vinyl acetate / maleic anhydride or glycidyl methacrylate copolymers; -ethylene / vinyl acetate or alkyl (meth)acrylate / (meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymers. In the above copolymers, the (meth)acrylic acid may be salified with Zn or Li. The term "alkyl (meth)acrylate" in (B1) refers to C1-C8 alkyl methacrylates and acrylates, and may be selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate and ethyl methacrylate. Furthermore, the above-mentioned polyolefins (B1) may also be crosslinked by any suitable process or agent (diepoxy, diacid, peroxide,etc.); the term functionalized polyolefin also includes mixtures of the aforementioned polyolefins with a difunctional reagent such as diacid, dianhydride, diepoxy, etc. capable of reacting with them or mixtures of at least two functionalized polyolefins capable of reacting with each other. The copolymers mentioned above (B1) can be copolymerized in a statistical or block manner and have a linear or branched structure. The molecular weight, the MFI index, the density of these polyolefins can also vary to a large extent, which will be appreciated by those skilled in the art. The MFI index, abbreviation of Melt Flow Index, is the melt flow index. It is measured according to the ASTM 1238 standard. Advantageously, the functionalized polyolefins (B1) are chosen from any polymer comprising alpha olefinic units and units carrying polar reactive functions such as epoxy functions,carboxylic acid or carboxylic acid anhydride. Examples of such polymers include terpolymers of ethylene, alkyl acrylate and maleic anhydride or glycidyl methacrylate such as Lotader® from SK Geocentric or polyolefins grafted with maleic anhydride such as Orevac® from SK Geocentric as well as terpolymers of ethylene, alkyl acrylate and (meth)acrylic acid. Mention may also be made of homopolymers or copolymers of polypropylene grafted with a carboxylic acid anhydride then condensed with polyamides or mono-amino oligomers of polyamide, as described in application EP 0342066. More particularly, the functionalized polyolefins (B1) are: -terpolymers of ethylene, alkyl acrylate and maleic anhydride;-terpolymers of ethylene,of alkyl acrylate and glycidyl methacrylate; -polypropylene and polyethylenes grafted with maleic anhydride;-copolymers of ethylene and propylene and optionally of dienemonomer grafted with maleic anhydride; -copolymers of ethylene and octene grafted with maleic anhydride; and their mixture. The functionalized polyolefin (B1) is present in a content of between 0 and 20% by weight, preferably between 1 and 10% by weight relative to the total weight of the composition. The composition according to the invention may comprise at least one non-functionalized polyolefin (B2). A non-functionalized polyolefin (B2) is conventionally a homopolymer or copolymer of alpha olefins or diolefins, such as, for example, ethylene, propylene, butene-1, octene-1, butadiene. Examples include: -homopolymers and copolymers of polyethylene, in particular LDPE, HDPE, LLDPE (linear low density polyethylene,or linear low density polyethylene), VLDPE (very low density polyethylene) and metallocene polyethylene, - homopolymers or copolymers of propylene, - ethylene / alpha-olefin copolymers such as ethylene / propylene, EPR (abbreviation for ethylene-propylene-rubber) and ethylene / propylene / diene (EPDM), - styrene / ethylene-butene / styrene (SEBS), styrene / butadiene / styrene (SBS), styrene / isoprene / styrene (SIS), styrene / ethylene-propylene / styrene (SEPS) block copolymers, - copolymers of ethylene with at least one product chosen from salts or esters of unsaturated carboxylic acids such as alkyl (meth)acrylate (for example methyl acrylate), or vinyl esters of saturated carboxylic acids such as vinyl acetate (EVA),the proportion of comonomer being up to 40% by weight and their mixture. The copolymers mentioned above (B2) can be copolymerized in a statistical or block manner and have a linear or branched structure. Advantageously, the non-functionalized polyolefins (B2) are chosen from homopolymers or copolymers of polypropylene and any homopolymer of ethylene or copolymer of ethylene and a comonomer of higher alpha olefin type such as butene, hexene, octene or 4-methyl-1-pentene. Examples that may be mentioned are PP (PolyPropylene), high density polyethylenes, medium density polyethylenes, linear low density polyethylenes, low density polyethylenes, very low density polyethylenes. These polyethylenes are known to those skilled in the art as being produced according to a radical process, according to a “Ziegler” type catalysis or, more recently,according to a so-called metallocene catalysis. Also preferred are copolymers of ethylene and vinyl acetate (EVA), such as those marketed under the trade name EVATANE® by the Applicant. When the composition according to the invention comprises one or more non-functionalized polyolefins, the MFI of (A) and the MFIs of (B1) and (B2) can be chosen from a wide range; however, to facilitate the dispersion of (B1) and (B2), it is recommended that the viscosities of (B1) and (B2) be close. The non-functionalized polyolefin is present in a content of between 0 and 20% by weight, preferably between 1 and 10% by weight relative to the total weight of the composition. Advantageously, the impact modifier can also be a copolymer formed from polyamide blocks and polyether blocks,the polyamide blocks and the polyether blocks being linked by an ester function. These products are described in document FR 2273021 and sold under the trade name PEBAX® by the company ARKEMA. The copolymers with polyamide blocks (abbreviated below PA) and with polyether blocks (abbreviated below PE) result from the copolycondensation of polyamide blocks with reactive ends with polyether blocks with reactive ends. For example, it is possible to react: - polyether diol, and a polyamide dicarboxylic acid, - polyether diamine and a polyamide dicarboxylic acid, - polyether diol and a polyamide diamine. The polyamide blocks with dicarboxylic chain ends come for example from the condensation of polyamide precursors in the presence of a chain-regulating dicarboxylic acid. Polyamide blocks with diamine chain ends come, for example, from the condensation of polyamide precursors in the presence of a chain-regulating diamine. Thus,the bond between the blocks is either an ester bond or an amide bond. The PA block and PE block polymers may comprise a single PA block and a single PE block. They may also comprise several PA blocks identical in terms of the structure of the monomer(s) constituting the polyamide and identical PE blocks distributed randomly. Said polymers may be prepared by simultaneous reaction of the PE blocks and the precursors of the PA blocks. A polymer is then obtained having PE blocks and PA blocks of very variable length depending on the moment at which the chain regulator intervenes during the formation of the PA block, but also the various reagents having reacted randomly which are distributed randomly (statistically) along the polymer chain. The impact modifier is preferably a polar functional polyolefin. In the context of the present invention,polar functional polyolefin is understood to mean a functional polyolefin as defined above comprising polar monomers such as vinyl acetates, acrylic or methacrylic acids, acrylates, methacrylates and glycidyl methacrylate or a PEBA, preferably the impact modifier is a PEBA. Preferably, composition C comprises less than 15% by weight of apolar functional polyolefin, preferably less than 10% by weight, in particular less than 5% by weight, preferably composition C does not comprise apolar functional polyolefin. Preferably, the impact modifier of the invention is a functional polyolefin, preferably a polyolefin (B1) as described above, comprising at least one heteroatom, preferably at least one nitrogen atom or one oxygen atom. Preferably,the impact modifier of the invention is a functional polyolefin chosen from copolymers of ethylene with at least one product chosen from salts or esters of unsaturated carboxylic acids such as alkyl (meth)acrylate (for example methyl acrylate), or vinyl esters of saturated carboxylic acids such as vinyl acetate (EVA), the proportion of comonomer being able to reach 40% by weight. The polyamide composition according to the invention can also comprise from 0 to 10% by weight of additives relative to the total weight of the composition, preferably from 0.1 to 10%. Preferably, the additives present in the polyamide composition of the invention are chosen from lubricants, organic or inorganic pigments, anti-UV agents, antistatic agents, mineral fillers, such as, for example, talc, silica, calcium carbonate, titanium dioxide, zinc oxide and organic fillers. Preferably,the composition according to the invention comprises a plasticizer content of less than 10%, preferably less than 6%, preferably less than 5%, preferably less than 3%, more preferably less than 1%, by weight relative to the total weight of composition C, preferably the composition according to the invention is free of plasticizer, such as BBSA (BenzylButylSulfonAmide). The polyamide composition (C) according to the invention may comprise current-conducting fillers. Preferably, the first layer consisting of composition (C) has a resistivity of less than 109 Ohm, preferably less than 106 Ohm after aging for at least 168 h at 60°C in the dielectric fluid. The polyamide composition (C) according to the invention may comprise from 0 to 30%, preferably from 1 to 27%, more preferably from 2 to 25%, by weight relative to the total weight of composition C,of at least one current-conducting filler relative to the total weight of the composition. The conductive filler may be chosen from carbon blacks, graphites, graphenes, carbon nanotubes, and metallic fillers such as metallic fibers or metallic powders. These metallic fillers advantageously comprise iron or copper. Preferably, when the current-conducting filler is carbon black or graphite, it is comprised in a content of 15 to 30%, preferably 18 to 27%, by weight relative to the total weight of composition C. When the current-conducting filler is a filler other than carbon black and graphite, for example graphene, carbon nanotubes, it is comprised in a content of 0.5 to 6%, preferably 1 to 5%, by weight relative to the total weight of composition C. In one embodiment, the polyamide composition according to the invention comprises less than 10% by weight,preferably less than 5% by weight, preferably less than 2% by weight, preferably less than 1% by weight, of carbon black and / or black dye, preferably does not comprise carbon black and / or black dye. Preferably, the polyamide composition according to the invention comprises less than 5% by weight, preferably less than 2% by weight, preferably less than 1% by weight, of crosslinked material, preferably the polyamide composition according to the invention does not comprise crosslinked material. Thus and particularly advantageously, the composition C according to the invention is preferably completely heat-meltable, this advantageously allows easy recycling of the composition. The following compositions C according to the invention are preferred (the percentages are given by weight relative to the total weight of the composition C):C1) comprising or consisting of:- 44 to 88,9% by weight of polyamide matrix having an average C / N ratio greater than or equal to 9 -1 to 30% by weight of impact modifier - 10 to 35% by weight of flame retardant - 0.1 to 1% by weight of additives C2) comprising or consisting of: - 79 to 99.9% by weight of polyamide matrix having an average C / N ratio greater than or equal to 9 -0 to 20% by weight of impact modifier - 0.1 to 1% by weight of additives C3) comprising or consisting of: - 49 to 98.9% by weight of polyamide matrix having an average C / N ratio greater than or equal to 9 -1 to 30% by weight of current-conducting filler - 0 to 20% by weight of impact modifier - 0.1 to 1% by weight of additives. C4) comprising or consisting of: - 44 to 88.9% by weight of polyamide matrix preferably having a C / N ratio of from 6 to 9, preferably equal to 6 -5 to 30% by weight of impact modifier - 10 to 35% by weight of flame retardant - 0.1 to 1% by weight of additives C5) comprising or consisting of: - 44 to 98,9% by weight of polyamide matrix having an average C / N ratio greater than or equal to 9 -1 to 30% by weight of impact modifier - 0.1 to 1% by weight of additives C6) comprising or consisting of: - 44 to 93.9% by weight of polyamide matrix having, preferably, a C / N ratio of 6 to 9, preferably equal to 6 -5 to 30% by weight of impact modifier - 0.1 to 1% by weight of additives Polyamide composition forming the subsequent layers In the context of the present invention, the term “subsequent layers”, or higher-ranking layers, is intended to denote the layers other than the first layer; for example, the second, third, fourth or fifth layers may be mentioned. The polyamide is as defined above. Preferably, the composition comprising at least one polyamide constituting the subsequent layers, comprises less than 10% by weight, preferably less than 5% by weight, more preferably less than 1% by weight, preferably does not comprise,of plasticizer such as BBSA (BenzylButylSulfonAmide), relative to the total weight of the composition. If the polyamide layer forming the subsequent layer is the outermost layer or if it is located above the barrier polymer layer then it may comprise up to 14% by weight of plasticizer. Preferably, the composition comprising at least one polyamide constituting the subsequent layers does not comprise current-conducting fillers. Preferably, the composition comprising at least one polyamide constituting the subsequent layers comprises at least 50% by weight, preferably at least 70% by weight, preferably at least 85% by weight, preferably at least 90% by weight, preferably from 70 to 99.8% by weight, preferably from 85 to 99.5% by weight,of at least one polyamide relative to the total weight of the composition. The composition comprising at least one polyamide constituting the subsequent layers may comprise from 0 to 30% by weight of flame retardant. The flame retardant is preferably as described above. In the case where the element according to the invention consists solely of two layers each consisting of a composition comprising at least one polyamide then at least one of these layers, preferably both layers, is (are) consisting of a composition comprising at least one polyamide in which the molar ratio between the carbon and nitrogen atoms (C / N ratio) of the polyamide or, in the case where the composition comprises several polyamides, the average molar ratio between the carbon and nitrogen atoms (C / N ratio) of the polyamides is greater than or equal to 7, more preferably greater than or equal to 8, even more preferably greater than or equal to 9 and preferably between 9 and 12. In this case,in a first embodiment, the 1, ère layer is a layer consisting of a composition comprising at least one polyamide having an average C / N ratio of between 6 and 9 and the 2nd layer is a layer consisting of a composition comprising at least one polyamide having an average C / N ratio greater than or equal to 7, preferably greater than or equal to 8, preferably greater than or equal to 9. In this case, in the second embodiment, the 1 èrelayer is a layer consisting of a composition comprising at least one polyamide having an average C / N ratio of 6 and the 2nd layer is a layer consisting of a composition comprising at least one polyamide having an average C / N ratio greater than or equal to 8, preferably greater than or equal to 9. In the case where the subsequent polyamide layer is the outer layer then the average C / N ratio is greater than or equal to 7, preferably greater than or equal to 8, preferably greater than or equal to 9, preferably between 9 and 12. Preferably, the polyamide composition forming the subsequent layers has a thickness of from 100 to 500 µm, preferably a thickness of from 150 to 450 µm. This layer preferably represents from 10 to 60% of the thickness of the element, advantageously from 15 to 50% of the total thickness of the element,in particular from 20 to 40% of the total thickness of the element.Functional polyolefin composition The composition comprising at least one functional polyolefin according to the invention preferably comprises at least 90% by weight, preferably at least 95% by weight, preferably at least 99% by weight, preferably from 90 to 99.9% by weight, preferably from 95 to 99.8% by weight, of at least one polyolefin relative to the total weight of the composition of which at least 30%, preferably at least 50%, preferably at least 70%, preferably from 30 to 99.9%, preferably from 70 to 99.8% by weight of functional polyolefin.Preferably the composition comprising at least one functional polyolefin is a composition consisting of polyolefin of which at least 30% by weight of at least one functional polyolefin preferably at least 50%, preferably at least 70%, preferably 30 at 99.9%, preferably from 70 to 99.8% by weight of functional polyolefin,preferably the composition comprising at least one functional polyolefin is a composition consisting of functional polyolefin. Preferably the functionalized polyolefins are of type (B1) described above. The reactive function of the at least one functional polyolefin is preferably chosen from maleic anhydride and an epoxide function. The polyolefins which may be included in the functional polyolefin composition and which are not functional polyolefins are polyolefins of type (B2) as described below. Preferably, the functional polyolefin layer comprises less than 10% by weight of fillers, preferably less than 5% by weight of fillers, preferably less than 1% of fillers, preferably is free of fillers. Preferably, the functional polyolefin composition has a thickness of less than 200 µm,preferably a thickness of less than 100 µm. This layer preferably represents less than 20% of the thickness of the element, advantageously less than 15% of the total thickness of the element, in particular less than 10% of the total thickness of the element. Non-functional polyolefin composition The composition comprising at least one non-functional polyolefin according to the invention preferably comprises at least 70% by weight, preferably at least 90% by weight, preferably at least 95% by weight, preferably at least 99% by weight, preferably from 92 to 99.9% by weight, preferably from 96 to 99.6% by weight,of at least one non-functional polyolefin relative to the total weight of the composition. The non-functionalized polyolefins are of type (B2) defined above. Preferably, the at least one non-functional polyolefin is chosen from ethylene or propylene copolymers. The at least one non-functional polyolefin according to the invention may be crosslinked and is, for example, a thermoplastic vulcanizate (TPV) or crosslinked EPDM (ethylene-propylene-diene). The composition comprising at least one non-functional polyolefin may comprise from 0 to 30% by weight of flame retardant. The flame retardant is preferably as described above. Preferably, the non-functional polyolefin composition has a thickness of from 150 to 1000 µm, preferably a thickness of from 200 to 800 µm. This layer preferably represents from 15 to 80% of the thickness of the element, advantageously from 30 to 70% of the total thickness of the element,in particular from 40 to 60% of the total thickness of the element.Barrier polymer composition The composition comprising at least one barrier polymer according to the invention preferably comprises at least 80% by weight, preferably at least 95% by weight, preferably at least 99% by weight, preferably from 85 to 99.9% by weight, preferably from 92 to 99.6% by weight, of at least one barrier polymer relative to the total weight of the composition. The expression "barrier polymer composition" designates a composition making it possible to obtain a barrier layer, that is to say a layer having characteristics of low permeability and good resistance to the various constituents of the fluids, in particular water and the dielectric fluid, that is to say that the barrier layer slows down the passage of the fluid into the other layers of the element,or even outside the element. A barrier layer according to the invention is at least 10 times less permeable than the polyamide composition forming the first layer (inner layer in contact with the dielectric fluid). The barrier polymers are chosen from vinyl alcohol copolymers, polyphthalamides (PPA), fluorinated polymers, polyphenylene sulfide and polybutylene naphthalate, preferably vinyl alcohol copolymers, preferably EVOH, polyphthalamides (PPA), fluorinated polymers, preferably vinyl alcohol copolymers, preferably EVOH, polyphthalamides (PPA), preferably EVOH copolymers. These polymers can be functionalized to improve adhesion to the other layers constituting the element according to the invention. The vinyl alcohol copolymer is a copolymer comprising a vinyl alcohol unit in a content greater than 50% by weight, preferably greater than 70% by weight,this copolymer may be a copolymer of alkylene and vinyl alcohol, preferably a copolymer of ethylene, propylene or butylene and vinyl alcohol, preferably a copolymer of ethylene and vinyl alcohol (EVOH). Preferably, the EVOH copolymer of the invention comprises from 10 to 35 mol% of units derived from ethylene, preferably from 20 to 29 mol%. Polyphthalamides are polyamides comprising a majority of units which comprise at least one aromatic monomer. Preferably, polyphthalamides of the copolyamide 6.T / x type (where x denotes one or more comonomers) such as Zytel HTN® from Dupont, such as Grivory HT® from Ems, such as Amodel® from Solvay, such as Genestar® from Kuraray, such as PPA compositions based on coPA6T / 6I, coPA6T / 66, coPA6T / 6, coPA6T / 6I / 66, PPA9T, coPPA9T / x, PPA10T, coPPA10T / x may be mentioned. Fluorinated polymers are, for example, polyvinylidene fluoride (PVDF),copolymers of ethylene and tetrafluoroethylene (ETFE), copolymers of ethylene, detrafluoroethylene and hexafluoropropylene (EFEP), preferably ETFE. The barrier polymer composition may comprise impact modifiers, in particular from 1 to 20% by weight of impact modifier, preferably from 2 to 15% by weight of impact modifier relative to the total weight of the composition. Preferably, the impact modifier is as defined above. The composition comprising at least one barrier polymer may comprise from 0 to 20% by weight of flame retardant. The flame retardant is preferably as described above. Preferably, the barrier polymer composition has a thickness of less than 300 µm, preferably a thickness of less than 200 µm. This layer preferably represents less than 30% of the thickness of the element, advantageously less than 20% of the total thickness of the element,in particular less than 15% of the total thickness of the element. The compositions of the subsequent layers, in particular the second, third, fourth and fifth layers, preferably comprise from 0.1 to 10% by weight, preferably from 0.2 to 5% by weight, of additives relative to the total weight of the composition. Preferably, the additive is not an impact modifier and is not a plasticizer. The additives are preferably chosen from lubricants, organic or inorganic pigments, anti-UV agents, antistatic agents, mineral fillers, and organic fillers, such as, for example, talc, silica, calcium carbonate, titanium dioxide, zinc oxide and organic fillers, antioxidants. The compositions of the subsequent layers preferably comprise less than 10% by weight, preferably less than 5% by weight, more preferably less than 1% by weight, preferably does not comprise, plasticizer such as BBSA (BenzylButylSulfonAmide),relative to the total weight of the composition. If the subsequent layer is the outermost layer or if it is located above the barrier polymer layer then the composition may comprise up to 14% by weight of plasticizer. In a particularly preferred manner, the elements of the invention may consist of the following layers: -A first layer consisting of a composition comprising at least one polyamide, a second layer consisting of a composition comprising at least one polyamide and optionally a third layer consisting of a composition chosen from a composition comprising at least one functional polyolefin or a composition comprising at least one polyamide; or -A first layer consisting of a composition comprising at least one polyamide, a second layer consisting of a composition comprising at least one polyamide,a third layer consisting of a composition comprising at least one functional polyolefin and a fourth layer consisting of a composition comprising at least one polyolefin; or -A first layer consisting of a composition comprising at least one polyamide, a second layer consisting of a composition comprising at least one polyamide, a third layer consisting of a composition comprising at least one barrier polymer, preferably an EVOH copolymer and a fourth layer consisting of a composition comprising at least one polyamide and optionally a fifth layer consisting of a composition comprising at least one polyamide; or -A first layer consisting of a composition comprising at least one polyamide,a second layer consisting of a composition comprising at least one functional polyolefin and a third layer consisting of a composition comprising at least one polyolefin; or -A first layer consisting of a composition comprising at least one polyamide, a second layer consisting of a composition comprising at least one barrier polymer, preferably EVOH copolymer and a third layer consisting of a composition comprising at least one polyolefin. When the element according to the invention consists of two layers and each of the layers consists of a composition comprising at least one polyamide, then the at least one polyamide of one of the two layers, preferably of the two layers, have an average C / N molar ratio greater than or equal to 7, preferably greater than or equal to 8, preferably greater than or equal to 9, more preferably between 9 and 12. Preferably,the elements of the invention may consist of the following layers: -A first layer consisting of a composition comprising at least one polyamide, a second layer consisting of a composition comprising at least one polyamide, the at least one polyamide of one of the two layers, preferably of the two layers, has an average C / N molar ratio greater than or equal to 7, preferably greater than or equal to 8, preferably greater than or equal to 9, more preferably between 9 and 12; or -A first layer consisting of a composition comprising at least one polyamide, a second layer consisting of a composition comprising at least one polyamide and a third layer consisting of a composition comprising at least one functional polyolefin; or -A first layer consisting of a composition comprising at least one polyamide,a second layer consisting of a composition comprising at least one polyamide and a third layer consisting of a composition comprising at least one polyamide; or -A first layer consisting of a composition comprising at least one polyamide, a second layer consisting of a composition comprising at least one polyamide, a third layer consisting of a composition comprising at least one functional polyolefin and a fourth layer consisting of a composition comprising at least one polyolefin; or -A first layer consisting of a composition comprising at least one polyamide, a second layer consisting of a composition comprising at least one polyamide, a third layer consisting of a composition comprising at least one barrier polymer, preferably EVOH copolymer and a fourth layer consisting of a composition comprising at least one polyamide; -A first layer consisting of a composition comprising at least one polyamide,a second layer consisting of a composition comprising at least one polyamide, a third layer consisting of a composition comprising at least one barrier polymer, preferably EVOH copolymer and a fourth layer consisting of a composition comprising at least one polyamide and a fifth layer consisting of a composition comprising at least one polyamide; or -A first layer consisting of a composition comprising at least one polyamide, a second layer consisting of a composition comprising at least one functional polyolefin and a third layer consisting of a composition comprising at least one polyolefin; or -A first layer consisting of a composition comprising at least one polyamide, a second layer consisting of a composition comprising at least one barrier polymer, preferably EVOH copolymer and a third layer consisting of a composition comprising at least one polyolefin. Preferably,the thickness of the first layer is between 3 and 60%, preferably between 5 and 30%, more preferably between 7 and 20% relative to the total thickness of the element. Preferably, the total thickness of the element is between 0.8 and 3 mm, preferably between 1 and 2 mm, more preferably between 1 and 1.5 mm. Preferably, the thickness of the first layer is between 3 and 60%, preferably between 5 and 30%, more preferably between 7 and 20% relative to the total thickness of the element and the total thickness of the element is between 0.8 and 3 mm, preferably between 1 and 2 mm, more preferably between 1 and 1.5 mm. Dielectric fluid The dielectric fluid according to the invention preferably comprises one or more compounds chosen from mineral oils and mineral oil derivatives, polyalphaolefins, polyalkylene glycols, silicones, esters with a number-average molar mass of between 1000 and 100000 g / mol,preferably between 10000 and 100000 g / mol, preferably between 20000 and 100000 g / mol, preferably between 50000 and 100000 g / mol, for example polyol ester, POE, the partially fluorinated polymers having a number average molar mass 1000 and 100000 g / mol, preferably between 10000 and 100000 g / mol, preferably between 20000 and 100000 g / mol, preferably between 50000 and 100000 g / mol, for example perfluoropolyethers. Preferably, the dielectric fluid according to the invention comprises less than 5% by weight of halogenated compound, preferably does not comprise a halogenated compound. In the context of the present invention, the term halogenated compound means a compound comprising at least one halogen atom. Preferably, the dielectric fluid according to the invention comprises one or more compounds chosen from mineral oils and mineral oil derivatives, polyalphaolefins, polyalkylene glycols, silicones,esters with a number-average molar mass of between 1000 and 100000 g / mol, preferably between 10000 and 100000 g / mol, preferably between 20000 and 100000 g / mol, preferably between 50000 and 100000 g / mol, for example polyol ester, POE. Preferably, the mineral oils and mineral oil derivatives have a number-average molar mass of between 1000 and 100000 g / mol, preferably between 20000 and 100000 g / mol, more preferably between 50000 and 100000 g / mol. Preferably, the dielectric fluid according to the invention has a density at 23°C of between 0.3 and 1.5, preferably between 0.5 and 1.1, advantageously between 0.7 and 1.05, more preferably between 0.8 and 1. The density measurement is carried out according to ISO 1675:2022 at 23°C. Preferably, the dielectric fluid according to the invention has a kinematic viscosity at 40°C of between 1 and 35 mm2 / s, preferably between 1.5 and 15 mm2 / s,in particular between 2 and 10 mm2 / s and / or a kinematic viscosity at 100°C of between 0.01 and 5 mm2 / s, preferably between 0.1 and 4 mm2 / s, preferably between 0.5 and 3 mm2 / s, more preferably between 0.8 and 2.5 mm2 / s and / or a kinematic viscosity at 25°C of between 5 and 150 mm, 2 / s, preferably between 10 and 100 mm2 / s. The kinematic viscosity is measured according to ISO 3104:2020. Preferably, the conductivity of the dielectric fluid is less than 1 µS / cm, preferably less than 0.1 µS / cm, in particular less than 0.01 µS / cm. The resistivity of the fluid is measured according to DIN IEC 60247, which allows the conductivity to be calculated. It is understood that this conductivity corresponds to the conductivity of the dielectric fluid before any use and before aging.Preferably, the dielectric fluid according to the invention:- comprises one or more compounds chosen from mineral oils and mineral oil derivatives, polyalphaolefins, polyalkylene glycols, silicones, esters, for example polyol ester, POE, partially fluorinated polymers of low molecular weight, for example perfluoropolyethers;- a density of less than 1.5, preferably less than 1;- a kinematic viscosity at 40°C of between 1 and 35 mm2 / s, preferably between 1.5 and 15 mm2 / s, in particular between 2 and 10 mm2 / s and / or a kinematic viscosity at 100°C of between 0.01 and 5 mm2 / s, preferably between 0.1 and 4 mm. 2 / s, preferably between 0.5 and 3 mm 2 / s, more preferably between 0.8 and 2.5 mm2 / s and / or a kinematic viscosity at 25°C between 5 and 150 mm 2 / s, preferably between 10 and 1 00 mm2 / s.Mineral oils are preferably mixtures obtained from the distillation of fossil fuels such as petroleum, coal, etc. Mineral oils are composed of hydrocarbons and mainly C15 to C40 alkanes. Preferably, the dielectric fluid is free of halogen, water and glycol ether. Particular dielectric fluids include ExxonMobilMobil EV ThermElite 701® (blend of alkylnaphthenic hydrocarbon bases, PAO & esters), M&I Mivolt DF7® (blend of polyol esters), Engineered FluidsAmpcool AC-110® (blend of hydrocarbon bases and esters) and Shell Diala S4ZX-I® (blends of hydrocarbon bases), but also Croda Xenitron3221® (blends of esters), Total EnergiesEco Friendly® (blends of hydrocarbon bases of biomass origin) and Total Energies Cell Shield® (blends of synthetic oils). The dielectric fluid according to the invention presents, before contact with the elements to be cooled,for example battery cells, a temperature below 40°C, preferably below 30°C, for example between -10 and 30°C. The dielectric fluid according to the invention has, after contact with the elements to be cooled, for example the battery cells, a temperature of between 40 and 110°C, preferably between 40 and 90°C, preferably between 40 and 65°C, advantageously between 40 and 60°C, preferably between 40 and 50°C. Elements according to the invention The elements according to the invention are, for example, elements or structures for the transport, distribution or storage of said dielectric fluids, preferably for the distribution or storage of said dielectric fluids. In one embodiment, the element (or structure) according to the invention is a pipe, preferably for the transport or distribution of the dielectric fluid. Preferably the pipes according to the invention have an internal diameter of between 5 and 25 mm, preferably between 10 and 20 mm,more preferably between 14 and 18 mm. In another embodiment, the element according to the invention is a smooth pipe. In another embodiment, the element according to the invention is a corrugated pipe. In another embodiment, the element (or structure) according to the invention is a reservoir for storing the dielectric fluid. The elements according to the invention may comprise one or more layers, at least one of which is made of composition C. Preferably, the elements according to the invention are made of a layer made of composition C according to the invention. Even more preferably, the elements according to the invention are made of composition C according to the invention. The single-layer structures are produced by extrusion. An industrial “Maillefer” extrusion line is used. This line comprises a single-screw extrusion extruder equipped with a screw with a screw profile adapted to polyamides. In addition,the extrusion line comprises: a die-punch assembly, located at the end of the extrusion head; the inner diameter of the die and the outer diameter of the punch are chosen according to the structure to be produced and the materials that compose it, as well as the dimensions of the tube and the line speed; a vacuum tank with an adjustable depression level. In this tank circulates water maintained at 20°C in general, a gauge is inserted in the front of this tank allowing the element to be shaped in its final dimensions. The diameter of the gauge is adapted to the dimensions of the element, in particular the tube, to be produced, typically from 13.1 to 15 mm for a tube with an external diameter of 13 mm and a thickness of 1.5 mm; a cooling tank in which water is maintained at around 20°C, allowing the element to be cooled along the path from the head to the drawing bench; a diameter gauge; a drawing bench. Before the tests,in order to ensure the best properties for the element and good extrusion quality, it is checked that the extruded materials have a residual moisture content before extrusion of less than 0.08%. Otherwise, an additional step of drying the material is carried out before the tests, generally in a vacuum dryer, for 1 night at 80°C. The elements according to the invention can be used in cooling circuits in the automotive field, in particular in cooling circuits for battery cells, in cooling circuits for energy storage systems, in cooling circuits for computer servers. Preferably, the elements according to the invention are used in cooling circuits in the automotive field,in particular in battery cell cooling circuits. Cooling circuit and device The present application also relates to a cooling circuit using a dielectric fluid comprising at least one element according to the invention, in which a dielectric fluid as defined above circulates, the layer being in direct contact with said dielectric fluid. Said cooling circuit according to the invention may also comprise at least one housing adapted to receive battery cells and provided with an inlet and an outlet allowing the circulation of said dielectric fluid in said housing, said housing preferably being made of a polyamide composition comprising:o from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7;o from 15 to 65% by weight of reinforcing fibers or fillers.In the context of the present invention,cold dielectric fluid means a dielectric fluid whose temperature is lower than 40°C, preferably lower than 30°C, for example between -10 and 30°C and hot dielectric fluid means a dielectric fluid whose temperature is higher than 40°C, preferably between 40 and 110°C, preferably between 40 and 90°C, preferably between 40 and 65°C, advantageously between 40 and 60°C, preferably between 40 and 50°C. The present application relates to a device for the direct cooling of battery cells by a dielectric fluid according to the invention comprising:- A dielectric fluid;- At least one housing (BX) adapted to receive battery cells and provided with an inlet and an outlet allowing the circulation of said dielectric fluid in said housing in direct contact with the battery cells;- Upstream of the housing (BX), at least one pipe according to the invention in which said dielectric fluid circulates towards the housing (BX),- Downstream of the housing (BX),at least one pipe according to the invention in which said dielectric fluid circulates from the housing (BX), the housing (BX) preferably being made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers; the dielectric fluid being as defined according to the invention. Preferably, the fluid entering the housing (BX) is a cold fluid and the fluid leaving the housing (BX) is a hot fluid. The pipes may be connected to the inlet and / or outlet of the housing (BX) directly or using a connector, the connector preferably being made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers. In one embodiment,the inlet of the housing (BX) is equipped with a nozzle, connected to the pipe, allowing the cells to be sprayed with the dielectric fluid. Preferably, the nozzle is made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers. In one embodiment, the device may comprise a reservoir of dielectric fluid, said reservoir preferably being according to the invention and being connected to the other elements of the device by the pipes according to the invention directly or using connectors as defined above. In one embodiment, the hot fluid coming from the housing (BX) is transported to a cooling system. In one embodiment, the cold fluid entering the housing (BX) comes from a reservoir, preferably a reservoir according to the invention. In this embodiment, upstream,the pipe connects the tank to the housing (BX) either directly or via connectors as defined above. In one embodiment, the device comprises several pipes connected to each other using connectors. The connectors are preferably made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having,an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers. The present application also relates to a device for the direct cooling of battery cells by a dielectric fluid comprising: -A dielectric fluid; - Optionally an element according to the invention in the form of a reservoir (R1); -At least one housing (BX) adapted to receive battery cells and provided with an inlet and an outlet allowing the circulation of said dielectric fluid in said housing in direct contact with the battery cells; -Upstream of the at least one housing (BX) at least one element (E1) for the distribution of the dielectric fluid coming from the reservoir to the housings (BX), the element (E1) comprising an inlet for the dielectric fluid and x outlets connected to the housings (BX), x corresponding to the number of housings (BX),each of the outlets being connected to a housing (BX); -Downstream of the housings (BX) at least one element (E2) for recovering the dielectric fluid coming from the housings (BX), the element (E2) comprising y inlets for the dielectric fluid and z outlets, y corresponding to the number of housings (BX) connected to the element (E2) and z corresponding to the number of cooling systems (S1), each of the inlets being connected to a housing (BX) and each of the outlets being connected to at least one cooling system (S1); -At least one cooling system (S1), preferably a radiator, allowing the cooling of the dielectric fluid coming from the element (E2); -elements, in particular in the form of a pipe, according to the invention in which said dielectric fluid circulates between the reservoir (R1), the element (E1), the housings (BX),the element (E2) and the cooling system (S1); -the housings (BX) and the elements (E1) and (E2) being made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers; -The dielectric fluid being as defined according to the invention. Preferably z equals 1. The housings (BX) are preferably housings adapted to receive battery cells and the dielectric fluid. The elements (E1) and (E2) are preferably valves or valves or connectors. Preferably the pipes according to the invention are made of several pipes according to the invention connected together by connectors. Preferably, the pipes are connected to the inputs and / or outputs of the boxes (BX) and elements (E1) and (E2) directly or using a connector. In one embodiment,the inlets of the boxes (BX) are equipped with a nozzle allowing the spraying of the dielectric fluid directly onto the battery cells. The connectors and / or nozzles are preferably made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers. In one embodiment, the device according to the invention is included in a container comprising an inlet and an outlet each equipped with a pipe according to the invention, or a plurality of pipes according to the invention connected together by connectors preferably made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers,and allowing the circulation of said dielectric fluid. In the context of the present invention, connector is understood to mean an interface part allowing the connection between two pipes, the connection between a pipe and a housing, the connection between a pipe and any other element of the device or circuit according to the invention. Preferably, the connectors according to the invention are injected parts, advantageously comprising a polyamide and reinforcing fibers. The device or circuit of the invention may comprise at least one housing, preferably at least 2 housings, preferably at least 6 housings, preferably at least 10 housings, preferably at least 16 housings, for example from 1 to 50 housings, preferably from 1 to 26 housings, preferably from 1 to 16 housings. Preferably, the number of housings is an even number. Examples Unless otherwise stated,the percentages are expressed by weight relative to the total weight of the composition. The evolution of the properties of the first layer according to the invention was evaluated before and after soaking in the fluids Mobil EV therm Elite 701® from the company EXXON MOBIL (Table 1), Ampcool AC-110® from the company Engineered fluids (Table 2), Diala S4 ZX-I® from the company Shell (Table 3) after 168 hours at a temperature of 130°C was measured. Tensile tests on 1BA dumbbells with a thickness of 2 mm were carried out at 23°C according to the ISO 527 standard in order to quantify the differences in properties before and after aging. The evolution of the stress and elongation at break for different comparative compositions and according to the invention are represented below. The 1BA type dumbbells were produced by injection molding for the tensile tests. The following parameters were used: -ENGEL VICTORY 500 hydraulic press,160T- Injection temperature (feed / nozzle): 230C / 250C- Mold temperature: 40°C- Holding time: 20s- Material holding pressure: 622 bars- Cooling time: 15sThe following products were tested:- EI1: Element consisting of a layer of a composition comprising 80.5% PA 11 of Mn 20000 g / mol, 6% PA 6 of Mn 25000 g / mol, 10% Orevac IM800®, 3% PA 610 of Mn 23000 g / mol and 0.5% Anox NBDTL 89® stabilizer sold by SI group- EI2: Element consisting of a layer of a composition comprising 80% by weight of polyamide 12 and 20% by weight of polyolefins functional polyolefins of polar type (Lotader 4700® marketed by SK Geocentric) -EI2: Element consisting of a layer of a composition comprising 80% by weight of polyamide 12 and 20% by weight of functional polyolefins of polar type (Lotader 4700® marketed by SK Geocentric) - EI3: Element consisting of a layer of a composition comprising 55% by weight of polyamide 6,10% by weight of polar functional polyolefins (Lotader AX8900® marketed by SK Geocentric) and 35% of non-polar functional polyolefins (Orevac IM 800® marketed by SK Geocentric) - EC1: Element consisting of a layer of a polypropylene composition (Hostalen, ® PP H1886) -EC2: Element consisting of a layer of a TPV (Santoprene) composition ® 101.87) Tableau 1 Stress loss Elongation loss at break after at break after 168h at 130°C in 168h at 130°C in the fluid fluid dielectric dielectric E I 1 <5% <5% EI 2 <5% <5%EI3 9% 17%EC1 50% 75%EC2 35% 70% Tableau 2 Stress loss Elongation loss at break after at break after 168h at 130°C in 168h at 130°C in the fluid fluid dielectric dielectric E I 1 <5% <5% EI 2 <5% <5%EI ​​3 ND 10%EC1 34% 67%EC2 40% 67% Tableau 3Stress loss Elongation loss at break after at break after 168h at 130°C in 168h at 130°C in the fluid fluid dielectric dielectric E I 1 <5% <5% EI 2 <5% <5% EI3 ND 9%EC1 36% 68%EC2 33% 65%From these first layers, different multilayer structures were prepared (Table 4). These latter present a better compromise of properties compared to the single-layer structures comprising only the inner layer (details for each structure in Table 5). The structures below are 8*1 mm tubes. The values ​​in parentheses correspond to the thicknesses of the different layers expressed in microns. Table 4 monolayer 1 cond-PA11 MLT 1 (100 / 900) cond-PA11 EI 1 monolayer 2 PA 6 MLT 2 (300 / 50 / 650) PA 6 FPO POMLT 3 (400 / 600) PA 6 EI 1 MLT 4 (150 / 50 / 800) cond-PA11 FPO POMLT 5 (200 / 150 / 650) cond-PA11 EVOH EI 1 MLT 6 (150 / 50 / 800) EI 2 FPO POMLT 7 (150 / 50 / 800) EI 1 FPO PO Cond-PA 11 is a composition comprising 64.5% of a PA 11 of Mn 20000 g / mol, 10% Orevac IM800 ® (SKFP), 25% Ensaco 250 G ®(Imerys), 0.5% of stabilizer Anox NBD TL 89® sold by SI group. Composition EI 1 is a composition comprising 80.5% of PA 11 of Mn 20000g / mol, 6% of PA 6 of Mn 25000 g / mol, 10% of Orevac IM800 ® , 3% PA 610 of Mn23000 g / mol and 0.5% Anox NBD TL 89® stabilizer sold by SI group. Composition EI2 is a composition comprising 80% by weight of polyamide 12 and 20% by weight of polar type functional polyolefins (Lotader 4700® marketed by SK Geocentric). PA 6 is a composition comprising 80.5% PA 6 of Mn 25000 g / mol, 10% Orevac IM 800 ® , 3% PA 610 of Mn 23000 g / mol, 6% PA 11 of Mn 20000g / mol and 0.5% stabilizer Anox NBD TL 89® sold by SI group. FPO is Exxelor VA 1801 ® from Exxonmobil PO is PP 83EK10 ® of Sabic EVOH is the EVAL LA170B ®from Kuraray. Table 5 Monolayer 1 MLT 1 provides a structure with better mechanical properties (impact at -40°C) than monolayer 1 while dissipating electrostatic charges Monolayer 2 MLT 2 reduces the increase in water concentration in the dielectric fluid during use (500h at 80°C) and better impact resistance at -40°C compared to monolayers 1 and 2 MLT 3 provides greater durability compared to monolayer 2 (better resistance when exposed to zinc chloride, less pollution of the dielectric fluid and better impact resistance at -40°C) MLT 4 reduces the increase in water concentration in the dielectric fluid during use (500h at 80°C) and better impact resistance at -40°C compared to monolayers 1 and 2 during use (500h at 80°C),dissipate electrostatic charges and better impact resistance at -40°C compared to monolayers 1 and 2 MLT 5 allows to reduce the increase in water concentration in the dielectric fluid MLT 5 (200 / 150 / 650) during use (500h at 80°C), dissipate electrostatic charges and low permeability to the dielectric fluid compared to monolayers 1 and 2 MLT 6 allows to reduce the increase in water concentration in the dielectric fluid MLT 6 (150 / 50 / 800) during use (500h at 80°C), and better impact resistance at -40°C compared to monolayers 1 and 2 MLT 7 allows to reduce the increase in water concentration in the dielectric fluid MLT 7 (150 / 50 / 800) during use (500h at 80°C) and better impact resistance at -40°C compared to monolayers 1 and 2,

Claims

Claims 1. Use of at least one element in a cooling circuit using at least one dielectric fluid, wherein the element comprises:- a first layer consisting of a polyamide composition C, characterized in that the composition C comprises from 50 to 99.9% by weight relative to the total weight of the composition of a polyamide matrix; - at least one second layer consisting of a composition chosen from a composition comprising at least one polyamide, a composition comprising at least one functional polyolefin or a composition comprising at least one barrier polymer; the dielectric fluid is liquid at atmospheric pressure at 23°C and comprises less than 10% by weight of water and glycol ether; and said 1 èrelayer being intended to be in contact with said dielectric fluid.

2. Use according to claim 1 in which the polyamide matrix has an average C / N ratio greater than or equal to 5.5, preferably greater than or equal to 6, preferably greater than or equal to 7, preferably greater than or equal to 8, preferably greater than or equal to 9, preferably between 9 and 12.

3. Use according to claim 1 or 2, in which the composition C has an inherent viscosity of between 1 and 1.8, preferably between 1.2 and 1.6, more preferably between 1.3 and 1.

6. 4.Use according to any one of the preceding claims, in which the dielectric fluid comprises one or more compounds chosen from mineral oils and mineral oil derivatives, polyalphaolefins, polyalkylene glycols, silicones, esters with a number-average molar mass of between 1000 and 100000 g / mol, for example polyol ester, POE, partially fluorinated polymers having a number-average molar mass of 1000 and 100000 g / mol, for example perfluoropolyethers.

5. Use according to any one of the preceding claims, in which the dielectric fluid has a density measured according to ISO 1675:2022 at 23°C of between 0.3 and 1.5, preferably between 0.5 and 1.1, advantageously between 0.7 and 1.05, more preferably between 0.8 and 1.

6. Use according to any one of the preceding claims, in which the dielectric fluid has a kinematic viscosity at 40°C of between 1 and 35 mm2 / s, preferably between 1.5 and 15 mm2 / s, in particular between 2 and 10 mm2 / s and / or a kinematic viscosity at 100°C of between 0.01 and 5 mm2 / s, preferably between 0.1 and 4 mm2 / s, preferably between 0.5 and 3 mm 2 / s, more preferably between 0.8 and 2.5 mm2 / s and / or a kinematic viscosity at 25°C of between 5 and 150 mm2 / s, preferably between 10 and 100 mm2 / s, the kinematic viscosity being measured according to ISO 3104:2020.

7. Use according to any one of the preceding claims, in which composition C further comprises from 0.01 to 1.5%, preferably from 0.05 to 0.5%, more preferably from 0.1 to 0.4%, by weight of a heat stabilizer relative to the total weight of composition C.8.Use according to any one of the preceding claims, wherein composition C further comprises:- From 10 to 35%, preferably from 15 to 25%, by weight of a flame retardant, preferably a non-halogenated flame retardant, preferably a phosphorus-containing flame retardant; and / or- From 1 to 35% by weight, preferably from 2 to 10% by weight of at least one impact modifier; and / or- From 0.5 to 30% by weight of at least one current-conducting filler; and / or- From 0.1 to 10% by weight of at least one additive.

9. Use according to any one of the preceding claims, wherein composition C comprises a plasticizer content of less than 10%, preferably less than 6%, preferably less than 5%, preferably less than 3%, preferably less than 1%, by weight, of. preferably composition C is free of plasticizer, such as BBSA (N-Butyl Benzene Sulfonamide).

10. Use according to any one of the preceding claims, wherein the second layer is a layer consisting of a composition chosen from: - a composition comprising at least one polyamide; - a composition comprising at least one functional polyolefin; or - a composition comprising at least one barrier polymer such as a vinyl alcohol copolymer, a fluorinated polymer, a polyphenylene sulfide, a polybutylene naphthalate or a polyphthalamide (PPA), preferably an EVOH copolymer.

11. Use according to any one of the preceding claims comprising a third layer and optionally a fourth and optionally a fifth layer, wherein: - the third layer consists of a composition chosen from: - a composition comprising at least one polyamide,preferably a zinc chloride-resistant polyamide; or - a composition comprising at least one functional polyolefin; or - a composition comprising at least one non-functional polyolefin; or - a composition comprising at least one barrier polymer such as a vinyl alcohol copolymer, a fluorinated polymer, a polyphenylene sulfide, a polybutylene naphthalate or a polyphthalamide, preferably an EVOH copolymer. - the fourth layer, where appropriate, consists of a composition chosen from: - a composition comprising at least one non-functional polyolefin; or - a composition comprising at least one polyamide. - the fifth layer, where appropriate, consists of a composition comprising at least one polyamide.

12. Use according to any one of claims 1 to 11, wherein the element is a pipe for transporting the dielectric fluid.

13. Use according to any one of claims 1 to 11,wherein the element is a reservoir for storing the dielectric fluid.

14. Cooling circuit comprising at least one element as described in any one of claims 1 to 3 and 7 to 11, in which a dielectric fluid as described according to any one of claims 1 and 4 to 6 circulates, the layer of composition C being in direct contact with said dielectric fluid.

15. Cooling circuit according to claim 14 further comprising at least one housing adapted to receive battery cells and provided with an inlet and an outlet allowing the circulation of said dielectric fluid in said housing,said housing being made of a polyamide composition comprising:o from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7;o from 15 to 65% by weight of reinforcing fibers or fillers.

16. Device for the direct cooling of battery cells by a dielectric fluid as described according to any one of claims 1 and 4 to 6, comprising:- a dielectric fluid;- At least one housing (BX) adapted to receive battery cells and provided with an inlet and an outlet allowing the circulation of said dielectric fluid in said housing, said housing preferably being made of a polyamide composition comprising:o from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7;o from 15 to 65% by weight of reinforcing fibers or fillers;- Upstream of the housing (BX),at least one element as described in any one of claims 1 to 3 and 7 to 11 in the form of a pipe in which said dielectric fluid circulates towards the housing (BX),- Downstream of the housing (BX), at least one element as described in any one of claims 1 to 3 and 7 to 11 in the form of a pipe in which said dielectric fluid circulates from the housing (BX).

17. Device for the direct cooling of battery cells by a dielectric fluid comprising:- A dielectric fluid;- Optionally at least one reservoir (R1) as defined in claim 13;- At least one housing (BX) adapted to receive battery cells and provided with an inlet and an outlet allowing the circulation of a dielectric fluid in said housing in direct contact with the battery cells; -Upstream of the boxes (BX) at least one element (E1) for the distribution of the dielectric fluid coming from the tank to the boxes (BX),the element (E1) comprising an inlet for the dielectric fluid and x outlets connected to the boxes (BX), x corresponding to the number of boxes (BX), each of the outlets being connected to a box (BX);- Downstream of the boxes (BX) at least one element (E2) for recovering the dielectric fluid coming from the boxes (BX), the element (E2) comprising y inlets for the dielectric fluid and z outlets, y corresponding to the number of boxes (BX) connected to the element (E2) and z corresponding to the number of cooling systems (S1), each of the inlets being connected to a box (BX) and each of the outlets being connected to at least one cooling system (S1); -At least one cooling system (S1), preferably a radiator, allowing the cooling of the dielectric fluid coming from the element (E2);- pipes, possibly connected to each other by connectors, as defined in claim 12 in which said dielectric fluid circulates between the reservoir (R1),the element (E1), the housings (BX), the element (E2) and the cooling system (S1); - the housings (BX) and the elements (E1) and (E2) being made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of fibers or fillers of, renfort ;- The dielectric fluid being as defined according to any one of claims 1, 4 to 6.

18. Device according to claim 17, in which the inlets of the boxes (BX) are equipped with a nozzle allowing the spraying of the dielectric fluid directly onto the battery cells, preferably the nozzle is made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers.

19. Device according to any one of claims 16 to 18, in which the pipes are connected to the inlets and / or outlets of the housings (BX), of the elements (E1) and (E2) directly or using connectors, preferably made of a polyamide composition comprising from 35 to 85% by weight of a polyamide matrix preferably having an average C / N ratio greater than or equal to 7 and from 15 to 65% by weight of reinforcing fibers or fillers.20.Device according to any one of claims 16 to 19 included in a container comprising an inlet and an outlet each equipped with a pipe as defined in claim 12, or a plurality of pipes as defined in claim 12 connected together by connectors, in which said dielectric fluid circulates.

Images