A multilayer tubular structure intended for transporting air conditioning fluids.

Abstract

The present invention relates to a multi-layer tubular structure (MLT) intended to transport a heat transfer fluid, the multi-layer tubular structure comprising: at least one layer (1) comprising a composition (1) mainly comprising at least one long-chain polyamide having between 10 and 15 carbon atoms per nitrogen atom and comprising at least 50% aliphatic units relative to the total number of units present in the long-chain polyamide; at least one layer (2) located below said layer (1), comprising a composition (2) mainly comprising at least one polyamide having between 4 and 9 carbon atoms per nitrogen atom, the polyamide comprising at least 50% of aliphatic units relative to the total units present in the polyamide, and the composition (2) comprising at most 12%, in particular at most 6% by weight of polyolefin relative to the total weight of the composition (2), and at most 2% by weight of at least one plasticizer relative to the total weight of the composition (2); Optionally, a layer (3) comprising a composition (3) as defined for composition (1), or a composition (3') comprising mainly short-chain polyamides having between 4 and 7 carbon atoms per nitrogen atom and at least 20% by weight, preferably at least 25% by weight, of at least one polyolefin relative to the total weight of composition (3'), or a composition (4) comprising a polyamide containing at least 50% semi-aromatic units; Equipped with The present invention relates to a multi-layer tubular structure in which layer (1) does not contain continuous fibers, layer (2) is in contact with the transport fluid when layer (3) is not present, and layer (2) occupies at least 50% of the total thickness of the tube.

Description

Technical Field

[0001] The present invention relates to a multilayer tubular structure comprising at least one inner layer made of aliphatic polyamide and at least one outer layer made of aliphatic polyamide. The invention also relates to the use of this structure for transporting heat transfer fluids, specifically refrigerant fluids selected from hydrocarbon compounds, hydrofluorocarbons, ethers, hydrofluoroethers, CO2, NH3, SO2 and fluoroolefins, in particular R134, R-1234yf or R-1234ze in the field of automotive air conditioning, especially R-1234yf or R-1234ze. Background Art

[0002] Tubular structures for transporting heat transfer fluids in the field of automotive air conditioning require two competing properties, which are water permeability and hot burst at 125°C respectively, and these must be above 83 bar.

[0003] Accordingly, long-chain polyamides allow the first property to be met, which renders the use of short-chain polyamides unsuitable for this first property.

[0004] Nevertheless, these same short-chain polyamides provide the hot burst strength, which in turn makes long-chain polyamides unsuitable for this second property.

[0005] Furthermore, the European F-Gas Directive plans the phase-out from the market of refrigerant gases having a high global warming potential GWP. From 100% in 2015, the quantity of refrigerant hydrofluorocarbon (HFC) fluids with a high GWP coefficient must move to 63% between 2018 and 2020, and reach no more than 21% by 2030.

[0006] Since January 2017, new vehicles sold in Europe must, in their initial construction, be adapted for operation of air conditioning with R1234yf.

[0007] This standard is currently only valid in Europe, but it is expected to be expanded to other regions, such as the United States, in the near future.

[0008] The elements of the air conditioning circulation system, specifically the elements of the multilayer tubular structure, are also, -The structure must be watertight to the transported fluid and therefore must have barrier properties against these fluids (especially against fluorocarbon refrigerant compounds, e.g., R134, R-1234yf, and R-1234ze), as well as against water and oxygen. The term "barrier properties" means that the structure is semi-permeable to the fluids in the automotive air conditioning line, thus allowing for minimal fluid release from the air conditioning line into the environment; - To avoid excessive degradation over the long term, it must exhibit chemical resistance to transport fluids, compressor oil, water, and oxygen; - In addition to having sufficient mechanical resistance (especially rupture resistance), the tube must also have sufficient flexibility when both ends are connected to components that can move in relation to each other (particularly in automotive air conditioning systems where mounting and footprint constraints under the hood require bending of the tubular structure), and must allow for vibration damping; -Considering that the transported fluid can be at high temperatures, and the ambient temperature can also be high (specifically, in automotive air conditioning systems, the relevant components may be located near the engine), satisfactory heat resistance must be exhibited, especially with respect to ZnCl2.

[0009] The conventional structures described above for transporting fluids are primarily intended for transporting gasoline, and are far less commonly used for transporting air conditioning fluids such as refrigerants.

[0010] Therefore, European Patent No. 2098580 describes a structure for transporting or storing fluids, comprising at least two layers, one of which comprises two layers consisting of an adhesive composition, i.e., a mixture of long-chain, medium-chain, and short-chain polyamides. These structures are more specifically for transporting gasoline.

[0011] European Patent No. 2098365 describes a multilayer structure comprising at least two layers, one layer containing at least one polymer and not copper, and the other layer containing at least one polymer and at least one stabilizer made from copper for the transport or storage of fluids. The polymers used in both layers are long-chain polyamides. These structures are more specifically for transporting fuels, particularly biodiesel.

[0012] International Publication WO2014 / 114766 describes a structure comprising at least two layers, one of which consists of an adhesive composition mainly comprising one or two polyamides selected from long-chain polyamides, medium-chain polyamides, and short-chain polyamides.

[0013] These structures, more specifically, are for transporting fuel, including gasoline containing alcohol.

[0014] International application WO2017 / 121961 describes a multilayer tubular structure (MLT) comprising, from the outside to the inside, at least one barrier layer (1) made of EVOH or PPA, and, located beneath the barrier layer, at least one inner layer (2) made of an aliphatic polyamide selected from short-chain, medium-chain or long-chain polyamides.

[0015] These structures are intended for transporting fuel, specifically gasoline containing alcohol.

[0016] Currently, tubing materials for transporting refrigerant fluids in automotive air conditioning systems consist of a rigid metal portion (usually aluminum) and a flexible portion made of multilayer tubing. Some of these multilayer tubing are known as plywood; they contain, from the outside to the inside, a first layer made of rubber-type elastomer, a reinforcing braid, a second layer of rubber-type elastomer, and an inner layer made of polyamide.

[0017] Recently, tubular structures other than plywood pipes have been described for transporting refrigerants in automotive air conditioning systems.

[0018] Therefore, international application WO2014 / 125219 describes a thermoplastic resin structure comprising at least one layer made of a composition containing a copolyamide having the formula X / 10.T / Y, particularly for automotive air conditioning. The proportion of X units is 0.4 to 0.8 moles per mole of 10.T, and Y is a semi-aromatic unit.

[0019] International application WO2017 / 103466 describes a structure for transporting refrigerant fluids, particularly R134, R-1234yf, or R-1234ze, in the field of heat transfer fluids, especially automotive air conditioning.

[0020] These structures comprise a fluid contact layer containing at least one type of semicrystalline thermoplastic resin polymer P1, and a layer containing at least one type of semicrystalline thermoplastic resin polymer P2 and continuous fibers.

[0021] Polyamide P1 is specifically a copolymer of ethylene and vinyl alcohol (EVOH) or a semi-aromatic or short-chain polyamide.

[0022] Polyamide P2 is specifically a semi-aromatic, or short-chain or long-chain polyamide.

[0023] However, the presence of continuous fibers in these structures necessitates their extrusion at several stages.

[0024] Prior art tubular structures and aluminum / rubber structures do not make it possible to meet all the criteria defined above, in particular the combination of the first two properties defined above. SUMMARY OF THE INVENTION

[0025] Accordingly, there exists a need to develop a tubular structure for transporting a transfer fluid, in particular a refrigerant, for example R-1234yf or R-1234ze, that enables compliance with the specifications defined above.

[0026] Accordingly, the present invention provides a multilayer tubular structure (MLT) intended for transporting a heat transfer fluid, wherein the multilayer tubular structure comprises: at least one layer (1) comprising a composition (C1) mainly comprising at least one long-chain polyamide having 10 to 15 carbon atoms per nitrogen atom and comprising at least 50% aliphatic units relative to the total of units present in the long-chain polyamide; at least one layer (2) located under said layer (1) comprising a composition (C2) mainly comprising at least one polyamide having 4 to 9 carbon atoms per nitrogen atom, wherein said polyamide comprises at least 50% aliphatic units relative to the total of units present in said polyamide, and said composition (C2) comprises at most 12% by weight of polyolefin, in particular at most 6% by weight of polyolefin, relative to the total weight of said composition (C2), and at most 2% by weight of at least one plasticizer relative to the total weight of said composition (C2); optionally, a layer (3) comprising either a composition (C3) as defined for the composition (C1), or a composition (C3') mainly comprising a short-chain polyamide having 4 to 7 carbon atoms per nitrogen atom and comprising at least 20% by weight, preferably at least 25% by weight of at least one polyolefin relative to the total weight of the composition (C3'), or a composition (C4) comprising a polyamide containing at least 50% of semi-aromatic units; wherein said layer (1) does not contain continuous fibers, The layer (2) is in contact with the transport fluid when the layer (3) is not present. The aforementioned layer (2) accounts for at least 50% of the total thickness of the tube. Regarding multilayer tubular structures.

[0027] The inventors unexpectedly discovered that a tubular structure comprising at least one layer (1) mainly containing at least one long-chain polyamide having 10 to 15 carbon atoms per nitrogen atom, and at least one layer (2) below layer (1) mainly containing at least one polyamide having 4 to 9 carbon atoms per nitrogen atom, can meet the specifications defined above. [Modes for carrying out the invention]

[0028] Regarding layer (1) and composition (1): The phrase "continuous fiber-free" means that layer (1) does not contain continuous fibers, whether it is mineral fiber, polymer, polymer fiber, or a mixture thereof.

[0029] The term "continuous fiber" refers to a continuous fibrous material (specifically, fiberglass or carbon fiber).

[0030] This means that composition (1), which contains at least one C10-C15 long-chain polyamide, may not contain continuous fibers but may contain short or long fibers.

[0031] Advantageously, the layer (1) does not contain fibers. The fibers are defined as short fibers, long fibers, or continuous fibers. This means that composition (1) in this embodiment, which contains at least one C10-C15 long-chain polyamide, does not contain continuous fibers and also lacks short fibers and long fibers.

[0032] The expression "primarily contains at least one type of polyamide" means that the polyamide is present in composition (1) in a proportion of more than 50% by weight relative to the total weight of the composition.

[0033] The term "polyamide" refers to substances equivalent to homopolyamide or copolyamide.

[0034] The nomenclature used to define polyamides is described in ISO standard 1874-1:2011 "Plastiques-Materiaux polyamides(PA) pour moulage et extrusion-Partie1:Designation," particularly on page 3 (Tables 1 and 2), and is well known to those skilled in the art.

[0035] Homopolyamides can be obtained from polycondensation of lactam units, amino acid units, or XY units [where X is a diamine and Y is a dicarboxylic acid (or diacid)], as long as the homopolyamide has 10 to 15 carbon atoms per nitrogen atom.

[0036] The diamine is a linear or branched aliphatic or alicyclic compound, preferably linear or branched aliphatic, and more specifically, linear.

[0037] The dicarboxylic acid may be aliphatic or alicyclic, preferably aliphatic.

[0038] As a result, the lactams and amino acids used to produce homopolyamides must have an average number of carbon atoms (C) per nitrogen atom (N) between 10 and 15.

[0039] Advantageously, the lactam and amino acids are C11 and C12.

[0040] In cases where homopolyamides are obtained from the polycondensation of XY units, the number of atoms per nitrogen atom is calculated from the average number of carbon atoms present in the units from diamine X and diacid Y.

[0041] As a result, as long as the average number of carbon atoms present in the units from diamine X and the units from diacid Y is 10 to 15, the diamine (X) may be C4 to C36, especially C6 to C18, and especially C4 to C12, and the dicarboxylic acid (Y) may be C4 to C36, especially C6 to C18, and especially C6 to C12.

[0042] Advantageously, the diamine is selected from 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, 1,16-hexadecanediamine, and 1,18-octadecanediamine.

[0043] Advantageously, the diamine is selected from 1,10-decanediamine and 1,12-dodecanediamine.

[0044] Advantageously, the dicarboxylic acid is selected from sebaciic acid and dodecanediic acid.

[0045] Advantageously, the diamine is selected from 1,10-decanediamine and 1,12-dodecanediamine, and the dicarboxylic acid is selected from sebacic acid, undecanediic acid, and dodecanediic acid.

[0046] In the case of copolyamides, the number of carbon atoms per nitrogen atom is calculated according to the same principles as in the case of homopolyamides. Various molar ratios of amide units are used in the calculation.

[0047] As a result, the lactams and amino acids used to produce copolyamides may have an average number of carbon atoms (C) per nitrogen atom (N) of less than 10, in particular 6 to 15.

[0048] The diamine X and diacid Y used in the copolyamide may be aromatic diamines and / or diacids, insofar as the polyamide of composition (1) contains at least 50% aliphatic units relative to the total number of units present in the polyamide.

[0049] In one embodiment, at least one polyamide of composition (1) contains at least 60% aliphatic units relative to the total number of units present in the polyamide.

[0050] In another embodiment, at least one polyamide of composition (1) contains at least 70% aliphatic units relative to the total number of units present in the polyamide.

[0051] In another embodiment, at least one polyamide of composition (1) contains at least 80% aliphatic units relative to the total number of units present in the polyamide.

[0052] In another embodiment, at least one polyamide of composition (1) contains at least 90% aliphatic units relative to the total number of units present in the polyamide.

[0053] In another embodiment, at least one polyamide of composition (1) contains 100% aliphatic units relative to the total number of units present in the polyamide. Thus, at least one polyamide of composition (1) consists solely of aliphatic units.

[0054] In one embodiment, the composition (1) mainly comprises a single polyamide, and therefore the single polyamide is present in the composition in a proportion of more than 50% by weight of the total weight of the composition.

[0055] In one embodiment, the polyamide of composition (1) contains at least 60% aliphatic units relative to the total number of units present in the polyamide.

[0056] In another embodiment, the polyamide of composition (1) contains at least 70% aliphatic units relative to the total number of units present in the polyamide.

[0057] In another embodiment, the polyamide of composition (1) contains at least 80% aliphatic units relative to the total number of units present in the polyamide.

[0058] In another embodiment, the polyamide of composition (1) contains at least 90% aliphatic units relative to the total number of units present in the polyamide.

[0059] In another embodiment, the polyamide of composition (1) contains 100% aliphatic units relative to the total number of units present in the polyamide. Thus, the polyamide of composition (1) consists solely of aliphatic units.

[0060] In one embodiment, the layer (1) is composed of a composition (1) mainly comprising at least one long-chain polyamide having 10 to 15 carbon atoms per nitrogen atom and containing at least 50% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0061] In one embodiment, at least one polyamide of composition (1) contains at least 60% aliphatic units relative to the total number of units present in the polyamide.

[0062] In another embodiment, at least one polyamide of composition (1) contains at least 70% aliphatic units relative to the total number of units present in the polyamide.

[0063] In another embodiment, at least one polyamide of composition (1) contains at least 80% aliphatic units relative to the total number of units present in the polyamide.

[0064] In another embodiment, at least one polyamide of composition (1) contains at least 90% aliphatic units relative to the total number of units present in the polyamide.

[0065] In another embodiment, at least one polyamide of composition (1) contains 100% aliphatic units relative to the total number of units present in the polyamide. Thus, the polyamide consists solely of aliphatic units.

[0066] In one embodiment, the layer (1) consists of a composition (1) mainly comprising a single polyamide, and therefore the single polyamide is present in the composition in a proportion of more than 50% by weight relative to the total weight of the composition.

[0067] In one embodiment, the polyamide of composition (1) contains at least 60% aliphatic units relative to the total number of units present in the polyamide.

[0068] In another embodiment, the polyamide of composition (1) contains at least 70% aliphatic units relative to the total number of units present in the polyamide.

[0069] In another embodiment, the polyamide of composition (1) contains at least 80% aliphatic units relative to the total number of units present in the polyamide.

[0070] In another embodiment, the polyamide of composition (1) contains at least 90% aliphatic units relative to the total number of units present in the polyamide.

[0071] In another embodiment, the polyamide of composition (1) contains 100% aliphatic units relative to the total number of units present in the polyamide. Thus, the polyamide of composition (1) consists solely of aliphatic units.

[0072] Advantageously, in all embodiments defined above for composition (1) of layer (1), the lactam is selected from lauryl lactam, the amino acid is selected from aminoundecanoic acid, the diamine is selected from 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, and the dicarboxylic acid is selected from suberic acid, azelaic acid, sebacic acid, undecanediic acid, dodecanediic acid, brassic acid, and tetradecanediic acid.

[0073] More favorably, the lactam is lauryl lactam, the amino acid is aminoundecanoic acid, the diamine is selected from 1,10-decanediamine and 1,12-dodecanediamine, and the dicarboxylic acid is selected from sebacic acid and dodecanediic acid.

[0074] The composition (1) may also include at least one polyolefin.

[0075] Therefore, the composition (1) may contain at least one polyolefin in addition to the at least one polyamide.

[0076] Advantageously, the composition (1) contains at least 30% of one polyolefin.

[0077] Polyolefins may be functionalized or unfunctionalized, or they may be a mixture of at least one functionalized polyolefin and / or at least one unfunctionalized polyolefin. Briefly, polyolefins are denoted as (B), and functionalized polyolefins (B1) and unfunctionalized polyolefins (B2) are described below.

[0078] Non-functionalized polyolefins (B2) are conventionally homopolymers or copolymers of alpha-olefins or diolefins, such as ethylene, propylene, 1-butene, 1-octene, and butadiene. Examples include: - Homopolymers and copolymers of polyethylene, specifically LDPE, HDPE, LLDPE (linear low-density polyethylene), VLDPE (very low-density polyethylene), and metallocene polyethylene; - Homopolymer or copolymer of propylene; - Ethylene / alpha-olefin copolymers, such as ethylene / propylene, EPR (an 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; - A copolymer of ethylene having at least one product selected from salts or esters of unsaturated carboxylic acids, such as alkyl (meth)acrylate (e.g., methyl acrylate), or a vinyl ester of a saturated carboxylic acid, such as vinyl acetate (EVA), where the proportion of the comonomer can reach 40% by weight.

[0079] Functionalized polyolefins (B1) may be polymers of alpha-olefins having reactive units (functionality); such reactive units are acid, anhydride, or epoxy functional groups. Examples include the aforementioned polyolefins (B2) grafted, copolymerized, or tripolymerized with unsaturated epoxides such as glycidyl (meth)acrylate, or with corresponding salts or esters of carboxylic acids or (meth)acrylic acid (which can be completely or partially neutralized with metals such as Zn), or even with carboxylic acid anhydrides such as maleic anhydride. Functionalized polyolefins are, for example, PE / EPR mixtures, the weight ratio of which can vary widely, for example between 40 / 60 and 90 / 10, and the mixture is co-grafted with anhydrides, specifically maleic anhydride, at a grafting rate of, for example, 0.01 to 5% by weight.

[0080] Functionalized polyolefins (B1) can be selected from the following: - Copolymers of ethylene, propylene, butene, hexene, or octene with PE, PP, or maleic anhydride or glycidyl methacrylate (e.g., containing 35-80% by weight of ethylene), with maleic anhydride or glycidyl methacrylate grafts (where the graft rate is, for example, 0.01-5% by weight); - Ethylene / alpha-olefin copolymers, such as ethylene / propylene, EPR (an 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; - A copolymer of ethylene and vinyl acetate (EVA), containing up to 40% by weight of vinyl acetate; - A copolymer of ethylene and alkyl (meth)acrylate, containing up to 40% by weight of alkyl (meth)acrylate; - Contains a copolymer of ethylene, vinyl acetate (EVA), and alkyl (meth)acrylate, up to 40% by weight of the comonomer.

[0081] The functionalized polyolefin (B1) can also be selected from an ethylene / propylene copolymer with mainly maleic anhydride grafted propylene concentrated with a monoamine polyamide (or polyamide oligomer) (the product described in European Patent No. A-0342066).

[0082] Functionalized polyolefin (B1) may also be a copolymer or terpolymer of at least the following units: (1) ethylene, (2) a vinyl ester of an alkyl (meth)acrylate or saturated carboxylic acid, and (3) an anhydride, e.g., maleic anhydride or (meth)acrylic acid or epoxy, e.g., glycidyl (meth)acrylate.

[0083] Examples of the latter type of functionalized polyolefin include: - Ethylene / (meth)acrylate / (meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymer; - Ethylene / vinyl acetate / maleic anhydride or glycidyl methacrylate copolymer; - Ethylene / vinyl acetate or alkyl (meth)acrylate / (meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymer Here, ethylene preferably accounts for at least 60% by weight, and the ter monomer (functionality) accounts for, for example, 0.1 to 10% by weight of the copolymer.

[0084] In the copolymer described above, (meth)acrylic acid can be chlorided with Zn or Li.

[0085] The term "(meth)acrylate alkyl" in (B1) or (B2) refers to methacrylic acid and C1-C8 alkyl acrylate, and can be selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate, and ethyl methacrylate.

[0086] Furthermore, the polyolefin (B1) described above may also be crosslinked by any suitable method or agent (such as diepoxy, diacid, or peroxide); the term “functionalized polyolefin” also includes the polyolefin described above, a mixture with a bifunctional reagent such as diacid, dianhydride, or diepoxy that can react with them, or a mixture of at least two functionalized polyolefins that can react together.

[0087] The copolymers (B1) and (B2) listed above may be copolymerized statistically or sequentially and have a linear or branched structure.

[0088] The molecular weight (MFI) and density of these polyolefins may also vary widely, as will be known to those skilled in the art. The melt flow index (MFI) is a measure of fluidity when melted. It is measured according to standard ASTM 1238.

[0089] Advantageously, the non-functionalized polyolefin (B2) is selected from polypropylene homopolymers or copolymers, any ethylene homopolymer or copolymer, and higher alpha-olefin comonomers, such as butene, hexene, octene, or 4-methyl-1-pentene. Examples of PP include high-density PE, medium-density PE, linear low-density PE, low-density PE, and ultra-low-density PE. These polyethylenes are known to those skilled in the art as products of the "free radical" method, the "Ziegler" catalytic method, or more recently, products from "metallocene" catalysts.

[0090] Advantageously, the functionalized polyolefin (B1) can be selected from any polymer containing alpha-olefin units and units holding polar reactive functional groups, such as epoxy, carboxylic acid, or carboxylic acid anhydride. Examples of such polymers include terpolymers of ethylene, alkyl acrylate, and maleic anhydride or glycidyl methacrylate, e.g., Lotader (trademark) from Applicant; or polyolefins grafted with maleic anhydride, e.g., Orevac (trademark) from Applicant; and terpolymers of ethylene, alkyl acrylate, and (meth)acrylic acid. Further examples include homopolymers or copolymers of polypropylene grafted with carboxylic acid anhydride and then enriched with polyamide or monoamine polyamide oligomers.

[0091] Advantageously, polyolefins are impact modifiers. The impact modifiers are advantageously composed of polymers having a flexural modulus of less than 100 MPa, measured according to standard ISO 178:2010, at 23°C with a relative humidity of 50% RH and a Tg below 0°C (measured at the inflection point of a DSC thermogram according to standard 11357-2:2013).

[0092] Advantageously, the composition (1) contains at least 40% of one polyolefin.

[0093] Advantageously, the composition (1) comprises, with respect to the total weight of the composition (1), at least 3% by weight of at least one polyolefin, particularly at least 6% by weight of at least one polyolefin, especially 6 to 20% by weight, and more specifically 10 to 12% by weight of at least one polyolefin.

[0094] The composition (1) may also include at least one plasticizer.

[0095] Therefore, the composition (1) may contain at least one plasticizer in addition to the at least one polyamide.

[0096] For example, plasticizers are selected from benzenesulfonamide derivatives, e.g., n-butylbenzenesulfonamide (BBSA); ethyltoluenesulfonamide or N-cyclohexyltoluenesulfonamide; hydroxybenzoic acid esters, e.g., 2-ethylhexyl parahydroxybenzoate and 2-decylhexyl parahydroxybenzoate; esters or ethers of tetrahydrofurfuryl alcohol, e.g., oligoethyleneoxytetrahydrofurfuryl alcohol; and esters of citric acid or hydroxymalonic acid, e.g., oligoethyleneoxy malonic acid.

[0097] The use of a mixture of plasticizers is not outside the scope of this invention.

[0098] Advantageously, the composition (1) contains at least one plasticizer in an amount of up to 13% by weight relative to the weight of the composition (1).

[0099] The composition (1) may also include at least one additive.

[0100] The additives optionally used in the compositions of the present invention are prior art additives that have been used in polyamides, are well known to those skilled in the art, and are particularly described in European Patent No. 2098580.

[0101] For example, they include carbon black and carbon nanotubes, specifically antioxidants, heat stabilizers, UV absorbers, light stabilizers, lubricants, inorganic fillers, flame retardants, nucleating agents and dyes, reinforcing fibers, waxes, and antistatic fillers selected from mixtures thereof.

[0102] For example, stabilizers may be UV stabilizers, organic stabilizers, or more generally, combinations of organic stabilizers, such as phenol antioxidants (e.g., of the type Irganox(Trademark) 245, 1098, or 1010 by Ciba-BASF), phosphite antioxidants (e.g., Irgafos(Trademark) 126 and Irgafos(Trademark) 168 by Ciba-BASF), and optionally other stabilizers, such as HALS (Hindered Amine Light Stabilizer, e.g., Tinuvin(Trademark) 770 by Ciba-BASF), anti-UV (e.g., Tinuvin(Trademark) 312 by Ciba), or phosphorus-based stabilizers. Amine antioxidants, such as Crompton's Naugard(Trademark) 445, or polyfunctional stabilizers, such as Clariant's Nylostab(Trademark) S-EED, may also be used.

[0103] This stabilizer may also be a mineral stabilizer, such as a copper-based stabilizer. Examples of such mineral stabilizers include halides and copper acetate. Secondly, other metals such as silver may be considered at will, although these are known to have less effect. These copper-containing compounds are typically accompanied by alkali metal halides, particularly potassium.

[0104] In one embodiment, the composition (1) is given a total of 100% by weight, - 55% to 100% by weight of at least one of the defined C10-C15 long-chain polyamides; - 0-30% by weight of at least one type of polyolefin; - 0 to 13% by weight of at least one plasticizer; - 0-2% by weight of at least one additive Includes.

[0105] In another embodiment, the composition (1) is, with a total of 100% by weight, - 55% to 97% by weight of at least one defined C10-C15 long-chain polyamide; - 3 to 30% by weight of at least one type of polyolefin; - 0 to 13% by weight of at least one plasticizer; - 0-2% by weight of at least one additive Includes.

[0106] In another embodiment, the composition (1) is, with a total of 100% by weight, - 65% to 94% by weight of at least one defined C10-C15 long-chain polyamide; - 6-20% by weight of at least one type of polyolefin; - 0 to 13% by weight of at least one plasticizer; - 0-2% by weight of at least one additive Includes.

[0107] Advantageously, composition (1) does not contain a plasticizer, and composition (1) is composed of the following in total, - 68% to 100% by weight of at least one defined C10-C15 long-chain polyamide; - 0-30% by weight of at least one type of polyolefin; - 0-2% by weight of at least one additive Includes.

[0108] More advantageously, the composition (1) is composed of a total of 100% by weight, - 68% to 97% by weight of at least one defined C10-C15 long-chain polyamide; - 3 to 30% by weight of at least one type of polyolefin; - 0-2% by weight of at least one additive Includes.

[0109] More advantageously, the composition (1) is such that the total is 100% by weight. - 78% to 94% by weight of at least one defined C10-C15 long-chain polyamide; - 6-20% by weight of at least one type of polyolefin; - 0-2% by weight of at least one additive Includes.

[0110] It is clearly evident that a different composition (1) containing or not containing at least one polyolefin and / or at least one plasticizer and / or at least one additive refers to all the embodiments described above.

[0111] In one embodiment, the at least one polyamide in the layer (1) of the tubular structure defined above is selected from PA11, PA12, PA1010, PA1012, PA1210, and PA1212.

[0112] The layer (1) of the tubular structure defined above may be the outermost layer.

[0113] Advantageously, the layer (1) of the tubular structure defined above is the outermost layer of the structure.

[0114] Advantageously, the structure (1) comprises a single layer (1).

[0115] Regarding layer (2) and composition (2): The phrase "primarily contains at least one type of polyamide" is defined above for layer (1).

[0116] Similarly, the term "polyamide" refers to something equivalent to homopolyamide or copolyamide.

[0117] Homopolyamides can be obtained from polycondensation of lactam units, amino acid units, or XY units [where X is a diamine and Y is a dicarboxylic acid (or diacid)], as long as the homopolyamide has 4 to 9 carbon atoms per nitrogen atom.

[0118] The diamine may be linear or branched aliphatic or alicyclic, preferably linear or branched aliphatic, and more specifically, linear.

[0119] The dicarboxylic acid may be aliphatic or alicyclic, preferably aliphatic.

[0120] As a result, the lactams and amino acids used to produce homopolyamides must have an average number of carbon atoms (C) per nitrogen atom (N) between 4 and 9.

[0121] Advantageously, lactams and amino acids are C6.

[0122] In cases where homopolyamides are obtained from the polycondensation of XY units, the number of atoms per nitrogen atom is calculated from the average number of carbon atoms present in the units from diamine X and diacid Y.

[0123] As a result, as long as the average number of carbon atoms present in the units from diamine X and the units from diacid Y is 4 to 9, the diamine (X) may be C4 to C14, especially C4 to C12, and especially C4 to C10, and the dicarboxylic acid (Y) may be C4 to C14, especially C4 to C12, and especially C4 to C10.

[0124] Advantageously, the diamine is selected 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, and 1,14-tetradecanediamine, specifically from 1,6-hexamethylenediamine.

[0125] Advantageously, the dicarboxylic acid is selected from succinic acid, pentaneoic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassic acid, and tetradecanedioic acid, and more specifically from sebacic acid and dodecanedioic acid.

[0126] Advantageously, diamines include 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-buty The dicarboxylic acid is selected from 2-ethyl-1,5-pentanediamine, 1,12-dodecanediamine, 1,13-tridecanediamine, and 1,14-tetradecanediamine, and more specifically from 1,6-hexamethylenediamine, and the dicarboxylic acid is selected from succinic acid, pentanediic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, undecanediic acid, dodecanediic acid, brassic acid, and tetradecanediic acid, and more specifically from sebacic acid and dodecanediic acid.

[0127] The diamine X and diacid Y used in the copolyamide may be aromatic diamines and / or diacids, insofar as the polyamide of composition (2) contains at least 50% aliphatic units relative to the total number of units present in the polyamide.

[0128] In one embodiment, at least one polyamide of composition (2) contains at least 60% aliphatic units relative to the total number of units present in the polyamide.

[0129] In another embodiment, at least one polyamide of composition (2) contains at least 70% aliphatic units relative to the total number of units present in the polyamide.

[0130] In another embodiment, at least one polyamide of composition (2) contains at least 80% aliphatic units relative to the total number of units present in the polyamide.

[0131] In another embodiment, at least one polyamide of composition (2) contains at least 90% aliphatic units relative to the total number of units present in the polyamide.

[0132] In another embodiment, at least one polyamide of composition (2) contains 100% aliphatic units relative to the total number of units present in the polyamide. Thus, the at least one polyamide consists solely of aliphatic units.

[0133] In one embodiment, the composition (2) mainly comprises a single polyamide, and therefore the single polyamide is present in the composition in a proportion of more than 50% by weight of the total weight of the composition.

[0134] In one embodiment, the polyamide of composition (2) contains at least 60% aliphatic units relative to the total number of units present in the polyamide.

[0135] In another embodiment, the polyamide of composition (2) contains at least 70% aliphatic units relative to the total number of units present in the polyamide.

[0136] In another embodiment, the polyamide of composition (2) contains at least 80% aliphatic units relative to the total number of units present in the polyamide.

[0137] In another embodiment, the polyamide of composition (2) contains at least 90% aliphatic units relative to the total number of units present in the polyamide.

[0138] In another embodiment, the polyamide of composition (2) contains 100% aliphatic units relative to the total number of units present in the polyamide. Thus, the polyamide of composition (2) consists solely of aliphatic units.

[0139] In one embodiment, the layer (2) is composed of a composition (2) mainly comprising at least one long-chain polyamide having 4 to 9 carbon atoms per nitrogen atom and containing at least 50% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0140] In one embodiment, the at least one polyamide in composition (2) contains at least 60% aliphatic units relative to the total number of units present in the polyamide.

[0141] In another embodiment, the at least one polyamide of composition (2) contains at least 70% aliphatic units relative to the total number of units present in the polyamide.

[0142] In another embodiment, the at least one polyamide of composition (2) contains at least 80% aliphatic units relative to the total number of units present in the polyamide.

[0143] In another embodiment, the at least one polyamide of composition (2) contains at least 90% aliphatic units relative to the total number of units present in the polyamide.

[0144] In another embodiment, the at least one polyamide of composition (2) contains 100% aliphatic units relative to the total number of units present in the polyamide. Thus, the polyamide of composition (2) consists solely of aliphatic units.

[0145] In one embodiment, the layer (2) consists of a composition (2) mainly comprising a single polyamide, and therefore the single polyamide is present in the composition in a proportion of more than 50% by weight relative to the total weight of the composition.

[0146] In one embodiment, the polyamide of composition (2) contains at least 60% aliphatic units relative to the total number of units present in the polyamide.

[0147] In another embodiment, the polyamide of composition (2) contains at least 70% aliphatic units relative to the total number of units present in the polyamide.

[0148] In another embodiment, the polyamide of composition (2) contains at least 80% aliphatic units relative to the total number of units present in the polyamide.

[0149] In another embodiment, the polyamide of composition (2) contains at least 90% aliphatic units relative to the total number of units present in the polyamide.

[0150] In another embodiment, the polyamide of composition (2) contains 100% aliphatic units relative to the total number of units present in the polyamide. Thus, the polyamide consists solely of aliphatic units.

[0151] Advantageously, in all embodiments defined above for composition (2) of layer (2), the lactam is caprolactam, the amino acid is aminohexanoic acid, the diamine is selected from 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, and 1,10-decanediamine, and the dicarboxylic acid is selected from adipic acid, sebacic acid, undecanediic acid, dodecanediic acid, brassic acid, and tetradecanediic acid.

[0152] More favorably, the lactam is caprolactam, the amino acid is aminohexanoic acid, the diamine is selected from 2-methyl-1,5-pentanediamine, 1,6-hexamethylenediamine, 1,10-decanediamine and 1,12-dodecanediamine, and the dicarboxylic acid is selected from adipic acid, sebacic acid and dodecanediic acid.

[0153] In one embodiment, the lactam is caprolactam, the amino acid is aminohexanoic acid, the diamine is selected from 2-methyl-1,5-pentanediamine, 1,6-hexamethylenediamine, 1,10-decanediamine, and 1,12-dodecanediamine, and the dicarboxylic acid is selected from adipic acid, sebacic acid, and dodecanediic acid.

[0154] The composition (2) may also contain at least one polyolefin in an amount of up to 12% by weight, and in particular up to 6% by weight, relative to the total weight of the composition.

[0155] The polyolefin is as defined for composition (1).

[0156] The composition (2) may also contain at least one plasticizer in an amount of up to 2% by weight relative to the total weight of the composition.

[0157] The plasticizer is as defined for composition (1).

[0158] The composition (2) may also include at least one additive.

[0159] In one embodiment, the additive is present in a proportion of up to 2% by weight relative to the total weight of the composition.

[0160] The additives are as defined for composition (1).

[0161] In one embodiment, the composition (2) is given a total of 100% by weight, - C4-C9 polyamides defined as being on top of at least one type in an amount of 84% to 100% by weight, particularly 90% to 100% by weight; - 0-12% by weight, particularly 0-6%, of at least one polyolefin; - 0-2% by weight of at least one plasticizer; - 0-2% by weight of at least one additive Includes.

[0162] In another embodiment, composition (2) does not contain polyolefins and has a total weight of 100%. - 96% to 100% by weight of at least one type of C4-C9 polyamide as defined above; - 0-2% by weight of at least one plasticizer; - 0-2% by weight of at least one additive Includes.

[0163] Advantageously, composition (2) does not contain a plasticizer, and composition (2) is composed of the following, with a total weight of 100%: - C4-C9 polyamides defined as being on top of at least one type in an amount of 86% to 100% by weight, particularly 92% to 100% by weight; - 0 to 12% by weight, particularly 0 to 6% by weight, of at least one polyolefin; - 0-2% by weight of at least one additive Includes.

[0164] It is clearly evident that different compositions (2) containing or not containing at least one polyolefin and / or at least one plasticizer and / or at least one additive refer to all embodiments of composition (2) described above.

[0165] In one embodiment, the at least one polyamide in the layer (2) of the tubular structure defined above is selected from PA6, PA66, PA6 / 66, PA610, PA410, PA412, and PA612.

[0166] Regarding the optional layers (3) and composition (3): The inner layer (3) may be located within the tubular structure defined above.

[0167] In one embodiment, the layer (3) is present, located inside the layer (3), and in contact with the transport fluid.

[0168] Layer (3) comprises composition (3) as defined above for composition (1), or composition (3) as defined above for composition (2), or composition (3') which mainly comprises short-chain polyamides having 4 to 7 carbon atoms per nitrogen atom and contains at least 20%, preferably at least 25%, of at least one polyolefin relative to the total weight of composition (3'), or composition (4) which contains at least 50% aromatic units.

[0169] Similarly, the term “short-chain polyamide” in composition (3') refers to a substance equivalent to homopolyamide or copolyamide.

[0170] Homopolyamides can be obtained from polycondensation of lactam units, amino acid units, or XY units [where X is a diamine and Y is a dicarboxylic acid (or diacid)], as long as the homopolyamide has 4 to 7 carbon atoms per nitrogen atom.

[0171] The diamine may be linear or branched, aliphatic, or cyclic aliphatic, preferably linear or branched aliphatic, and more specifically, linear.

[0172] The dicarboxylic acid may be aliphatic or cyclic aliphatic, preferably aliphatic.

[0173] As a result, the lactams and amino acids used to produce homopolyamides must have an average number of carbon atoms (C) per nitrogen atom (N) between 4 and 7.

[0174] Advantageously, lactams and amino acids are C6.

[0175] In cases where homopolyamides are obtained from the polycondensation of XY units, the number of atoms per nitrogen atom is calculated from the average number of carbon atoms present in the units from diamine X and diacid Y.

[0176] As a result, diamine(X) may be C4-C10, especially C4-C7, and particularly C4-C6, as long as the average number of carbon atoms present in the units from diamine X and the units from diacid Y is 4-7, and dicarboxylic acid(Y) may be C4-C10, especially C4-C7, and particularly C4-C6.

[0177] Advantageously, the diamine is selected 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, and 1,10-decanediamine, specifically from 2-methyl-1,5-pentanediamine and 1,6-hexamethylenediamine.

[0178] Advantageously, the dicarboxylic acid is selected from succinic acid, pentaneoic acid, adipic acid, suberic acid, azelaic acid, and sebacic acid.

[0179] Advantageously, the diamine is selected from 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, and 1,14-tetradecanediamine, and the dicarboxylic acid is selected from adipic acid, suberic acid, azelaic acid, sebacic acid, and undecanediic acid, specifically from sebacic acid.

[0180] Advantageously, the layer (3) does not contain continuous fibers.

[0181] Advantageously, the layers (1) and (3) do not contain fibers.

[0182] The term "fiber" is defined as described above.

[0183] The composition (3') of the layer (3) contains at least 20% by weight, preferably at least 25% by weight, of at least one polyolefin.

[0184] The polyolefin is as defined for composition (1).

[0185] The composition (3') may also include at least one plasticizer and / or at least one additive.

[0186] Plasticizers and additives are as defined above.

[0187] In one embodiment, the composition (3') is such that the total is 100% by weight. - C4-C9 long-chain polyamides defined as being made of at least one type, in an amount of 54% to 80% by weight, and especially 54% to 75% by weight; - 20-40% by weight, preferably 25-40% by weight, of at least one polyolefin; - 0-4% by weight of at least one plasticizer; - 0-2% by weight of at least one additive Includes.

[0188] The polyamide of composition (4), which contains at least 50% semi-aromatic units, may be a polyphthalamide, specifically PA11 / 10T, where the 10T units thus account for 50% by weight of the total weight of the copolyamide.

[0189] In one embodiment, the inner layer (3), if present, does not contain polyamide of composition (4) which contains at least 50% semi-aromatic units.

[0190] Tubular structure: The tubular structure may comprise at least one layer (1), at least one layer (2), and optionally an inner layer (3).

[0191] In cases where the tubular structure does not include layer (3), layer (2) is in contact with the transported fluid.

[0192] Therefore, the tubular structure comprises at least one layer (1) and at least one layer (2). Thus, the tubular structure of the present invention may comprise several layers (2).

[0193] Regardless of the number of layers present in the tubular structure, each layer (2), or set of layers (2), accounts for at least 50% of the thickness of the tube.

[0194] Regardless of the number of layers present in the tubular structure, the layer(2), or the set of layers(2), accounts for at least 60% of the thickness of the tube.

[0195] Regardless of the number of layers present in the tubular structure, the layer(2), or the set of layers(2), accounts for at least 70% of the thickness of the tube, and particularly 70% to 95% of the thickness of the tube.

[0196] Adhesion between adjacent layers is ensured by a layer of binder, if necessary.

[0197] Advantageously, the tubular structure does not contain a binder layer.

[0198] In cases where layer (3) exists, layer (3) may be a layer in contact with the transported fluid, and the tubular structure comprises at least three layers.

[0199] Advantageously, the layer (3) is the layer in contact with the transport fluid.

[0200] Advantageously, the layer (1) and the composition (2) do not contain plasticizers.

[0201] Advantageously, all layers present within the tubular structure do not contain plasticizers.

[0202] In one embodiment, the inner layer (3) is located within the structure, i.e., within the multilayer tubular structure defined above, and the composition (3) is identical to composition (1).

[0203] Advantageously, the at least one polyamide in the layer (3) of the tubular structure defined above is selected from PA11, PA12, PA11 / 10T, PA6, PA66, PA6 / 66, PA610, PA410, PA412, and PA612, if present.

[0204] Advantageously, the layer (3) does not contain aromatic units.

[0205] More preferably, the at least one polyamide in layer (3), if present, is selected from PA11, PA12, PA6, PA66, PA6 / 66, PA610, PA410, PA412, and PA612.

[0206] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 60% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 60% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0207] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 60% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 70% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0208] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 60% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 80% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0209] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 60% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 90% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0210] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 60% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 100% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0211] The composition (1) contains 100% aliphatic units, and therefore the composition consists of 100% aliphatic units.

[0212] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 70% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 60% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0213] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 70% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 70% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0214] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 70% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 80% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0215] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 70% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 90% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0216] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 70% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 100% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0217] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 80% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 60% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0218] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 80% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 70% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0219] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 80% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 80% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0220] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 80% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 90% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0221] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 80% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 100% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0222] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 90% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 60% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0223] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 90% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 70% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0224] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 90% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 80% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0225] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 90% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 90% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0226] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 90% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 100% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0227] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 100% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 60% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0228] The composition (2) contains 100% aliphatic units, and therefore the composition consists of 100% aliphatic units.

[0229] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 100% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 70% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0230] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 100% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 80% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0231] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 100% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 90% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0232] Advantageously, the at least one polyamide in composition (2) of the multilayer tubular structure, having 4 to 9 carbon atoms per nitrogen atom, contains at least 100% aliphatic units relative to the total number of units present in the polyamide, and the long-chain polyamide in composition (1) contains at least 100% aliphatic units relative to the total number of units present in the long-chain polyamide.

[0233] In one embodiment, the composition (2) of the tubular structure defined above does not contain polyamides other than aliphatic polyamides.

[0234] In another embodiment, the compositions (2) and (1) of the tubular structure defined above do not contain polyamides other than aliphatic polyamides.

[0235] In a modified version of the present invention, the multilayer tubular structure defined above is characterized in that it has two layers (2) and is separated by a layer made of ethylene vinyl alcohol (EVOH) copolymer.

[0236] In this example, the thickness of the two layers (2) always accounts for at least 50%, preferably at least 60%, preferably at least 70%, and especially 70-95% of the total thickness.

[0237] In one embodiment, the multilayer tubular structure defined above is characterized in that the heat transfer fluid is a refrigerant fluid selected from hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, CO2, NH3, SO2, and fluoroolefin compounds.

[0238] In one embodiment, the heat transfer fluid is preferably 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene, 1,2,3,3,3-pentafluoropropene, 1,1,3,3-tetrafluoropropene, 3,3,3-trifluoropropene, 2,3,3-trifluoropropene, 1,1,1,2-tetrafluoroethane, 1,1,2 The refrigerant fluid is selected from 2-tetrafluoroethane, pentafluoroethane, difluoromethane, 1,1-difluoroethane, 1,1,1,2,3,3,3-heptafluoropropane, 1,1,1-trifluoropropane, 1,1,1,3,3,3-hexafluoropropane, 1,1,1,3,3-pentafluoropropane, 1,1,1,3,3-pentafluorobutane, trifluoroiodomethane, and mixtures thereof.

[0239] In one embodiment, the heat transfer fluid is a refrigerant fluid selected from 1,3,3,3-tetrafluoropropene (1234ze) and 2,3,3,3-tetrafluoropropene (1234yf), and in particular, the heat transfer fluid is 2,3,3,3-tetrafluoropropene (1234yf).

[0240] Advantageously, the refrigerant fluid contains a lubricant, preferably selected from mineral oil, silicone oil, natural paraffin, naphthene, synthetic paraffin, alkylbenzene, polyalphaolefin, polyalkylene glycol, polyol ester and / or polyvinyl ether; the lubricant is more preferably polyalkylene glycol or polyol ester.

[0241] In another aspect, the present invention relates to the use of the multilayer tubular structure defined above for transporting heat transfer fluids.

[0242] In another aspect, the present invention relates to the use of the multilayer tubular structure defined above to satisfy an extractability test, the test of which in particular involves filling the multilayer tubular structure (MLT) with Forane, heating the assembly at 60°C for 96 hours, then emptying it by filtering it into a beaker, then evaporating the filtrate from the beaker at room temperature, and finally weighing the residue, the proportion of which is approximately 6 g / m³ 2 It must be below the inner tube surface, and the percentage of residue on the filter should be 1 g / m³. 2 More preferably, 0.5 g / m 2 The following is required regarding use:

[0243] In other words, the present invention is for the use of the multilayer tubular structure defined above, after contacting the multilayer tubular structure MLT with Forane, to reduce the proportion of soluble and insoluble compounds released by the tubular structure as defined above, wherein the proportion of released compounds is determined by an extractability test, which in particular consists of filling the multilayer tubular structure MLT with Forane, heating the assembly at 60°C for 96 hours, then emptying it by filtering it into a beaker, then evaporating the filtrate from the beaker at room temperature, and finally weighing the residue, wherein the proportion is approximately 6 g / m 2 Below the inner tube surface, preferably 1 g / m 2 Preferably 0.5 g / m 2 The following is required regarding use:

[0244] Therefore, the tubular structure reduces the proportion of soluble and insoluble compounds after contact with Forane compared to the structure of the prior art. [Examples]

[0245] Hereafter, the present invention will be illustrated by the following embodiments, but will not be limited thereto.

[0246] The following structures were prepared by extrusion.

[0247] Multilayer tubes are manufactured by co-extrusion. An industrial McNeil multilayer extrusion line is used, equipped with five extruders connected to a multilayer extrusion head with a spiral spindle.

[0248] The screws used are single extrusion screws with screw profiles adapted for polyamide. In addition to five extruders and multi-layer extrusion heads, the extrusion line includes the following: A die-punch assembly located at the end of the co-extrusion head; the inner diameter of the die and the outer diameter of the punch are selected according to the structure being manufactured, the material from which it is composed, as well as the dimensions of the tube and the line speed; A vacuum tank with an adjustable vacuum level. Water circulates within this tank, generally maintained at 20°C, allowing the gauge to be immersed in the water and the tube to be shaped to its final dimensions. The diameter of the gauge is adjusted to the diameter of the tube being manufactured, typically 8.5-10 mm for the tube, with an outer diameter of 8 mm and a thickness of 1 mm; A continuous cooling tank that maintains water at approximately 20°C, allowing the tubing to be cooled along the passage from the head to the drawing bench; Diameter meter; Draw-wing bench.

[0249] Using a three-dimensional shape with five extruders, tubes ranging from two to five layers are manufactured. In cases where the number of layers is less than five, the same material is then supplied to several extruders.

[0250] In the case of a structure with six layers, an additional extruder is connected, and a spiral spindle is added to the existing head to create the inner layers, which are then brought into contact with the fluid.

[0251] Before testing, ensure that the extruded material has a residual moisture content of less than 0.08% from before extrusion to guarantee the best properties and good extrusion quality for the tube. Otherwise, an additional drying step is generally performed on the material before testing, typically overnight in a vacuum dryer at 80°C.

[0252] After the extrusion parameters stabilized and the dimensions of the tube under consideration no longer changed over time, the tube that met the characteristics disclosed in this patent application was removed. The diameter was controlled by a laser diameter meter attached to the end of the line.

[0253] Generally, line speed is typically 20 m / min. It generally ranges from 5 to 100 m / min.

[0254] The screw speed of the extruder depends on the thickness of the layer and the diameter of the screw, as is known to those skilled in the art.

[0255] In general, the temperatures of the extruder and tools (head and connector) must be adjusted to be well above the melting point of the composition under consideration, so that they remain molten and thus prevent the composition from solidifying and clogging the machine.

[0256] The tubular structure was tested under the different parameters shown in Table 1. TIFF0007913865000001.tif113170

[0257] Example 6 consists of one layer (1) and two layers (2), from left to right.

[0258] Example 7 consists of one layer (1), three continuous layers (2) [total thickness of layer (2) = 1350 μm], and one layer (3), from left to right.

[0259] The measurement method and the values ​​corresponding to the scoring are specified in Table 2. TIFF0007913865000002.tif56170

[0260] ( *** Flow measurements were performed using a Lyssy GPM500 / GC coupling at a temperature of 23°C and relative humidity 0% on a film of the same composition as the layer of the tubular structure having permeation cells. The top surface of the cells was swept with the test gas, and the flow through the film below was measured by gas chromatography. Helium was used as the vector gas for sweeping the bottom.

[0261] The permeability of tubular structures is determined by the usual law of permeability for multilayer structures, i.e. (e and P are the thickness and permeability of the multilayer structure, (ei and Pi are the thickness and permeability of each layer of the structure.) It is calculated by [method].

[0262] composition CPA11: This composition is based on polyamide 11 and contains 20% ethylene / ethyl acrylate / anhydride type impact modifier with Mn (molecular weight by number) 29,000 and a mass ratio of 68.5 / 30 / 1.5 (MFI 6 at 190°C, 2.16 kg), and 1.2% organic stabilizers consisting of 0.8% phenol (Lowinox 44B25 from Great Lakes), 0.2% phosphite (Irgafos 168 from Ciba), and 0.2% UV protection (Tinuvin 312 from Ciba). The melting temperature of this composition is 190°C.

[0263] CPA610: represents a composition based on polyamide 610, which has an Mn (number-average molecular weight) of 30,000, and contains 1.2% of an organic stabilizer consisting of 0.8% phenol (Lowinox 44B25 from Great Lakes), 0.2% phosphite (Irgafos 168 from Ciba), and 0.2% anti-UV agent (Tinuvin 312 from Ciba). The melting temperature of this composition is 223°C.

[0264] CPA66: represents a composition based on polyamide 66, which has an Mn (number-average molecular weight) of 32,000, and contains 1.2% of an organic stabilizer consisting of 0.8% phenol (Lowinox 44B25 from Great Lakes), 0.2% phosphite (Irgafos 168 from Ciba), and 0.2% anti-UV agent (Tinuvin 312 from Ciba). The melting temperature of this composition is 264°C.

[0265] CPA6POF: represents a composition based on polyamide 6, which has an Mn (number-average molecular weight) of 18,000, and contains 40% POF, and 1.2% of an organic stabilizer consisting of 0.8% phenol (Lowinox 44B25 from Great Lakes), 0.2% phosphite (Irgafos 168 from Ciba), and 0.2% anti-UV agent (Tinuvin 312 from Ciba). The melting temperature of this composition is 220°C.

[0266] POF: is a composition based on, by mass, 50% of an ethylene / ethyl acrylate / maleic anhydride type impact modifier with a mass ratio of 68.5 / 30 / 1.5 (MFI 6 at 190°C under 2.16 kg), 25% of an ethylene / methyl acrylate / epoxide (GMA type) impact modifier, glycidyl methacrylate with a mass ratio of 67 / 25 / 8 and an MFI of 6 at 190°C under 2.16 kg, and 25% of an ethylene / methyl acrylate / maleic anhydride type impact modifier with a mass ratio of 76 / 18 / 6 and an MFI of 8 at 190°C under 2.16 kg.

[0267] CPA1110TPOF: refers to a composition based on copolyamide 10.T / 11 with a mass ratio of 68 / 32, which has a number-average molecular weight (Mn) of 20,000, contains 30% of POF, and 1.2% of organic stabilizer consisting of 0.8% of phenol (Lowinox 44B25 from Great Lakes), 0.2% of phosphite (Irgafos 168 from Ciba), and 0.2% of anti-UV agent (Tinuvin 312 from Ciba). The melting temperature of this composition is 255°C. POF is a composition based on: 50% of ethylene / ethyl acrylate / maleic anhydride type impact modifier with a mass ratio of 68.5 / 30 / 1.5 (MFI 6 at 190°C under 2.16 kg), 25% of ethylene / methyl acrylate / epoxide (GMA type) impact modifier, glycidyl methacrylate with a mass ratio of 67 / 25 / 8 having an MFI 6 at 190°C under 2.16 kg, and 25% of ethylene / methyl acrylate / maleic anhydride type impact modifier with a mass ratio of 76 / 18 / 6 having an MFI 8 at 190°C under 2.16 kg.

[0268] CPA610POF: refers to a composition based on polyamide 610, which has a number-average molecular weight (Mn) of 32,000, contains 20% of POF, and 1.2% of organic stabilizer consisting of 0.8% of phenol (Lowinox 44B25 from Great Lakes), 0.2% of phosphite (Irgafos 168 from Ciba), and 0.2% of anti-UV agent (Tinuvin 312 from Ciba). The melting temperature of this composition is 223°C.

[0269] CPA66plast: refers to a composition based on polyamide 66, which has a number-average molecular weight (Mn) of 30,000, contains 6% of BBSA (butylbenzenesulfonamide) plasticizer, and 1.2% of organic stabilizer consisting of 0.8% of phenol (Lowinox 44B25 from Great Lakes), 0.2% of phosphite (Irgafos 168 from Ciba), and 0.2% of anti-UV agent (Tinuvin 312 from Ciba). The melting temperature of this composition is 260°C.

[0270] CPA610plast: This composition is based on polyamide 66, which has a manganese molecular weight (Mn) of 32,000 and contains 6% BBSA (butylbenzenesulfonamide) plasticizer and 1.2% organic stabilizers consisting of 0.8% phenol (Lowinox 44B25 from Great Lakes), 0.2% phosphite (Irgafos 168 from Ciba), and 0.2% UV protection (Tinuvin 312 from Ciba). The melting temperature of this composition is 219°C.

Claims

1. A multilayer tubular structure (MLT) intended for transporting heat transfer fluids, The multilayer tubular structure is The composition comprises at least one layer (1), which mainly comprises at least one polyamide having 10 to 15 carbon atoms per nitrogen atom, wherein the at least one polyamide contains at least 50% aliphatic units relative to the total number of units present in the polyamide having 10 to 15 carbon atoms per nitrogen atom, The layer (2) is located below the layer (1) and comprises a composition (2) mainly comprising at least one polyamide having 4 to 9 carbon atoms per nitrogen atom, wherein the polyamide contains at least 50% aliphatic units relative to the total number of units present in the polyamide, and the composition (2) comprises up to 12% by weight of polyolefin and up to 2% by weight of at least one plasticizer relative to the total weight of the composition (2), Optionally, layer (3) is a layer (3) which contains composition (3) as defined for composition (1), or a composition (3') which mainly contains a polyamide having 4 to 7 carbon atoms per nitrogen atom and contains at least 20% by weight of at least one polyolefin relative to the total weight of composition (3'), or a composition (4) which contains a polyamide containing at least 50% semi-aromatic units, and Equipped with, The aforementioned layer (1) does not contain continuous fibers, The layer (2) is in contact with the transported heat transfer fluid when the layer (3) is not present. The aforementioned layer (2) accounts for at least 50% of the total thickness of the tube. Multilayer tubular structure.

2. The multilayer tubular structure according to claim 1, characterized in that the composition (2) contains up to 6% by weight of polyolefin and up to 2% by weight of at least one plasticizer based on the total weight of the composition (2).

3. The multilayer tubular structure according to claim 1 or 2, characterized in that composition (3') mainly comprises a polyamide having 4 to 7 carbon atoms per nitrogen atom and contains at least 25% by weight of at least one polyolefin relative to the total weight of composition (3').

4. The multilayer tubular structure according to any one of claims 1 to 3, characterized in that the layer (3) is present, the layer (3) is on the inside and in contact with the transported heat transfer fluid.

5. The multilayer tubular structure according to any one of claims 1 to 4, characterized in that the layer (1) is the outermost layer of the multilayer tubular structure.

6. The multilayer tubular structure according to any one of claims 1 to 5, characterized in that the composition (1) contains at least one polyolefin in up to 40%.

7. The multilayer tubular structure according to any one of claims 1 to 6, characterized in that the composition (1) contains at least 3% by weight of at least one polyolefin based on the total weight of the composition (1).

8. The multilayer tubular structure according to claim 7, characterized in that the composition (1) contains at least 6% by weight of at least one polyolefin based on the total weight of the composition (1).

9. The multilayer tubular structure according to claim 7 or 8, characterized in that the composition (1) contains at least one polyolefin in an amount of 10 to 12% by weight relative to the total weight of the composition (1).

10. The multilayer tubular structure according to any one of claims 1 to 9, wherein the composition (1) contains at least one plasticizer in an amount of up to 4% by weight relative to the weight of the composition (1).

11. The composition comprises at least one layer (1), which mainly comprises at least one polyamide having 10 to 15 carbon atoms per nitrogen atom, wherein the at least one polyamide contains at least 50% aliphatic units relative to the total number of units present in the polyamide having 10 to 15 carbon atoms per nitrogen atom, The layer (2) is located below the layer (1) and comprises a composition (2) mainly comprising at least one polyamide having 4 to 9 carbon atoms per nitrogen atom, wherein the polyamide contains at least 50% aliphatic units relative to the total number of units present in the polyamide, and the composition (2) comprises up to 12% by weight of polyolefin and up to 2% by weight of at least one plasticizer relative to the total weight of the composition (2), Optionally, layer (3) is a layer (3) which contains composition (3) as defined for composition (1), or a composition (3') which mainly contains a polyamide having 4 to 7 carbon atoms per nitrogen atom and contains at least 20% by weight of at least one polyolefin relative to the total weight of composition (3'), or a composition (4) which contains a polyamide containing at least 50% semi-aromatic units, and Equipped with, The aforementioned layer (1) does not contain continuous fibers, The layer (2) is in contact with the heat transfer fluid that would have been transported if the layer (3) were not present. The aforementioned layer (2) accounts for at least 50% of the total thickness of the tube. A multilayer tubular structure (MLT) intended for transporting heat transfer fluids, A multilayer tubular structure characterized in that layer (1) does not contain a plasticizer.

12. The composition comprises at least one layer (1), which mainly comprises at least one polyamide having 10 to 15 carbon atoms per nitrogen atom, wherein the at least one polyamide contains at least 50% aliphatic units relative to the total number of units present in the polyamide having 10 to 15 carbon atoms per nitrogen atom, The layer (2) is located below the layer (1) and comprises a composition (2) mainly comprising at least one polyamide having 4 to 9 carbon atoms per nitrogen atom, wherein the polyamide contains at least 50% aliphatic units relative to the total number of units present in the polyamide, and the composition (2) contains up to 12% by weight of polyolefin relative to the total weight of the composition (2). Optionally, layer (3) is a layer (3) which contains composition (3) as defined for composition (1), or a composition (3') which mainly contains a polyamide having 4 to 7 carbon atoms per nitrogen atom and contains at least 20% by weight of at least one polyolefin relative to the total weight of composition (3'), or a composition (4) which contains a polyamide containing at least 50% semi-aromatic units, and Equipped with, The aforementioned layer (1) does not contain continuous fibers, The layer (2) is in contact with the heat transfer fluid that would have been transported if the layer (3) were not present. The aforementioned layer (2) accounts for at least 50% of the total thickness of the tube. A multilayer tubular structure (MLT) intended for transporting heat transfer fluids, A multilayer tubular structure characterized in that the aforementioned layer (2) does not contain a plasticizer.

13. The multilayer tubular structure according to claim 12, characterized in that the layer (2) and the layer (1) do not contain a plasticizer.

14. The multilayer tubular structure according to claim 12 or 13, characterized in that all layers present in the multilayer tubular structure do not contain plasticizers.

15. The multilayer tubular structure according to any one of claims 1 to 14, characterized in that the composition (2) contains a maximum of 6% by weight of polyolefin relative to the total weight of the composition (2).

16. The composition comprises at least one layer (1), which mainly comprises at least one polyamide having 10 to 15 carbon atoms per nitrogen atom, wherein the at least one polyamide contains at least 50% aliphatic units relative to the total number of units present in the polyamide having 10 to 15 carbon atoms per nitrogen atom, The layer (2) is located below the layer (1) and comprises a composition (2) mainly comprising at least one polyamide having 4 to 9 carbon atoms per nitrogen atom, wherein the polyamide contains at least 50% aliphatic units relative to the total number of units present in the polyamide, and the composition (2) contains at least one plasticizer in an amount of up to 2% by weight relative to the total weight of the composition (2). Optionally, layer (3) is a layer (3) which contains composition (3) as defined for composition (1), or a composition (3') which mainly contains a polyamide having 4 to 7 carbon atoms per nitrogen atom and contains at least 20% by weight of at least one polyolefin relative to the total weight of composition (3'), or a composition (4) which contains a polyamide containing at least 50% semi-aromatic units, and Equipped with, The aforementioned layer (1) does not contain continuous fibers, The layer (2) is in contact with the heat transfer fluid that would have been transported if the layer (3) were not present. The aforementioned layer (2) accounts for at least 50% of the total thickness of the tube. A multilayer tubular structure (MLT) intended for transporting heat transfer fluids, A multilayer tubular structure characterized in that the composition (2) does not contain polyolefins.

17. The multilayer tubular structure according to any one of claims 1 to 16, characterized in that the polyamide in composition (2) contains at least 60% aliphatic units relative to the total number of units present in the polyamide.

18. The multilayer tubular structure according to any one of claims 1 to 17, characterized in that the polyamide of composition (2) contains at least 60% aliphatic units relative to the total number of units present in the polyamide, and the polyamide of composition (1) having 10 to 15 carbon atoms per nitrogen atom contains at least 60% aliphatic units relative to the total number of units present in the polyamide having 10 to 15 carbon atoms per nitrogen atom.

19. The multilayer tubular structure according to any one of claims 1 to 18, characterized in that the polyamide in the composition (1) consists of aliphatic units.

20. The multilayer tubular structure according to any one of claims 1 to 18, characterized in that the polyamide in composition (2) consists of aliphatic units.

21. The multilayer tubular structure according to any one of claims 1 to 18, characterized in that the polyamide in composition (2) consists of aliphatic units, and the polyamide in composition (1) having 10 to 15 carbon atoms per nitrogen atom consists of aliphatic units.

22. The multilayer tubular structure according to any one of claims 1 to 21, characterized in that the composition (2) does not contain polyamides other than aliphatic polyamides.

23. The multilayer tubular structure according to any one of claims 1 to 22, characterized in that composition (2) and composition (1) do not contain polyamides other than aliphatic polyamides.

24. The multilayer tubular structure according to any one of claims 1 to 23, wherein the layer (2) accounts for at least 70% of the total thickness of the pipe.

25. A multilayer tubular structure according to any one of claims 1 to 24, characterized in that two layers (2) exist and are separated by a layer made of ethylene vinyl alcohol (EVOH) copolymer.

26. A multilayer tubular structure according to any one of claims 4 to 25, characterized in that the layer (3) is present and the composition (3) is the same as composition (1).

27. The heat transfer fluid is hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers, CO ２ NH ３ SO ２ A multilayer tubular structure according to any one of claims 1 to 26, characterized in that the refrigerant fluid is selected from each compound of fluoroolefins.

28. The heat transfer fluid is CO ２ The multilayer tubular structure according to claim 27, characterized in that the refrigerant fluid is selected from fluoropropene, fluoropropane, fluoroethane, and mixtures thereof.

29. The multilayer tubular structure according to claim 27 or 28, characterized in that the heat transfer fluid is a refrigerant fluid selected from 1,3,3,3-tetrafluoropropene (1234ze) and 2,3,3,3-tetrafluoropropene (1234yf).

30. A multilayer tubular structure according to any one of claims 27 to 29, characterized in that the refrigerant fluid contains a lubricant.

31. The multilayer tubular structure according to any one of claims 1 to 30, characterized in that the at least one polyamide of layer (1) is selected from PA11, PA12, PA1010, and PA1012.

32. The multilayer tubular structure according to any one of claims 1 to 31, characterized in that the at least one aliphatic polyamide of layer (2) is selected from PA6, PA66, PA6 / 66, PA610, PA410, PA412, and PA612.

33. A multilayer tubular structure according to any one of claims 1 to 32, characterized in that, if present, the at least one polyamide in layer (3) is selected from PA11, PA12, PA11 / 10T, PA6, PA66, PA6 / 66, PA610, PA410, PA412, and PA612.

34. Use of a multilayer tubular structure according to any one of claims 1 to 33 for transporting a heat transfer fluid.

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