FUEL LINE AND METHOD FOR ITS MANUFACTURE AND ITS USE

Description

TECHNICAL FIELD

[0001] The present invention relates to a line, in particular for fuels in the automotive sector, made of thermoplastic material, a method for producing such a line and uses of such lines. STATE OF THE ART

[0002] The use of fuel lines based on layered structures made of plastics, particularly polyamide, has been state of the art for some time. Due to the requirements regarding fuel permeability, as well as the required mechanical properties (e.g., impact strength, elongation at break), and internal and external chemical resistance at a wide range of temperatures, multi-layer pipes are preferred. These pipes feature high thermal resilience, high length stability, and great resistance to the fuels they carry. Among other things, a low permeability value is relevant here. This low permeability value must be met not only for the fuel itself, but also for any additives or other small components it may contain.Furthermore, resistance to washing out of components or parts of the multilayer structure is required.

[0003] US-A-2014 / 246111 discloses fuel lines for the automotive sector that have at least five layers and include barrier layers, adhesion promoter layers, and other functional layers. In particular, a fluoropolymer layer is provided on the inner side, and a layer of EVOH (ethylene-vinyl alcohol copolymer) serves as a barrier layer.

[0004] EP-A-1645412 describes lines for fuel cells made of thermoplastic materials. A layer of a polyamide molding compound is proposed as the inner layer, and a wide variety of possible subsequent layers are suggested, including EVOH layers. No specific examples of layer structures are given, and to ensure a bond between any EVOH layer and the polyamide inner layer, the requirement for an adhesion promoter in the form of a separate, additional layer is explicitly mentioned.

[0005] US-A-2009 / 269532 describes a cable consisting of at least two layers, both made of polyamide. The core element is to equip the inner layer only with an organic stabilizer and expressly not with a copper stabilizer. One advantage emphasized is that such structures are said to be more resistant to aging than the prior art, particularly in contact with hot air, and more resistant to contact with corrosive liquids. Where three-layer structures with a central EVOH layer are disclosed, they always have organic stabilization on the inside and copper stabilization on the outside.

[0006] US-A-2015 / 353792 describes adhesion promoter materials for use, for example, in multilayer fuel lines. Complex copolyamides with a general structure A / B / C, for example, of type 6 / 612 / 12, are proposed, and it is demonstrated that this can ensure adhesion between two different polyamide layers.

[0007] EP-A-445706 proposes layered structures for fuel lines comprising at least three layers of at least two different polyamides. As a comparative example, a layered structure with an inner layer of impact-modified polyamide 6, an intermediate layer of EVOH, and an outer layer of impact-modified polyamide 6 is used, and it is shown that such a structure is not sufficiently resistant to cold shock.

[0008] GB 2390658 discloses, among other things, a fuel line with a barrier layer made of EVOH with an inner layer made of polyamide 6 and an outer layer made of polyamide 612, or with an inner and outer layer made of polyamide 612. Elongations at break of 150% are achieved. Preferably, the inner layer is made of polyamide 612 or 610 and directly borders the EVOH layer. Specifically disclosed are structures in which only three layers are present and in which the outer layers consist exclusively of polyamide 610, polyamide 612, or polyamide 6.

[0009] EP-A-1036968 discloses fuel lines comprising at least four layers, including a barrier layer made of EVOH and, as an adhesion promoter layer to an outermost layer made of polyamide 12 or polyamide 11, a layer based on lactam or amino acid or based on polyamide 69.

[0010] EP-A-1216826 discloses a multilayer composite with an EVOH layer as a fuel line, wherein a polyamide-polyamine copolymer is proposed as the material for an adhesion promoter layer to an outer layer, in particular based on polyamide 12. Due to the apparently poor adhesion of polyamides to EVOH, it is proposed to design a polyamide-based layer directly adjacent to the EVOH barrier layer as a special mixture, whereby a plurality of polyamides as well as the presence of a polyamine-polyamide copolymer are considered necessary to ensure good adhesion even after prolonged contact with fuels. In the specific examples, the inner layer is always designed as a polyamide 6 layer due to the required resistance to fuels.Although further possibilities of other polyamides are described, no reference is made to specifically preferred polyamides, for example with regard to particularly good adhesion to the barrier layer on the one hand and resistance to specific chemicals on the other.

[0011] Another prior art fuel line can be found in EP-A-1 452 307. This also features an EVOH-based barrier layer. To ensure adhesion to the barrier layer and good resistance to peroxide, it is specifically proposed that the inner layer be formed not from a polyamide 6 homopolymer, but from a blend of polyamide homopolymers containing a compatibilizer. Here, too, various polyamide homopolymers are specified, but generally without specific information about which polyamide homopolymers exhibit particularly good adhesion to the barrier layer and resistance to specific chemicals.

[0012] Furthermore, reference should be made to the two documents EP-A-1 036 968 and EP-A-1 162 061, which also describe thermoplastic multilayer composites having an EVOH layer as a barrier layer. Adjacent to this layer, EP-A-1 162 061 describes a layer of a polyamide-based molding compound, with a variety of possible polyamides being specified in general terms. However, the examples specifically disclose only an inner layer of polyamide 6. EP-A-1 036 968 specifically emphasizes the improved adhesion of copolyamides to EVOH barrier layers. Layers of blends of polyamide and polyolefin, or polyamide layers, are always specified as inner layers.

[0013] EP-A-1 884 356 describes a thermoplastic multilayer composite in the form of an extruded hollow profile, comprising a thermoplastic outer layer and at least one further layer, wherein the outer layer is formed from a mixture based on at least one polyamide (PA) and 20 to 80 parts by weight of at least one polyamide elastomer (TPE-A), and the hollow profile was produced at extrusion speeds of over 20 m / min, so that the produced hollow profile has a higher elongation at break of over 200% compared to an otherwise identical hollow profile produced at lower extrusion speeds. Only structures in which mixtures of lactam-based polyamides (specifically PA12 and PA6) are used as the outer layer, or mixtures of PA12 with polyetheramide with PA6 rigid blocks are used. PRESENTATION OF THE INVENTION

[0014] Accordingly, it is an object of the present invention to provide an improved multi-layer composite in the form of a hollow body enclosing an interior space. In particular, the objective is to provide a good barrier effect with as few different layers as possible, i.e., while avoiding adhesion promoter layers, particularly with a very high elongation at break, especially with an elongation at break of greater than 300%, i.e., excellent mechanical properties, particularly with regard to cold impact and elongation at break, and good washout resistance.

[0015] This object is achieved by a multi-layer composite according to claim 1.

[0016] The proposed multi-layer composite consists of three layers: an inner layer bordering the interior, a middle layer bordering this, and an outer layer bordering the middle layer and sealing the multi-layer composite to the outside. Therefore, apart from the middle layer serving as a barrier layer, an inner layer, and an outer layer, there are no further layers, in particular no adhesion promoter layers. What may be present is an additional innermost layer, which is then made conductive. In this case, the inner layer does not border directly on the interior, but indirectly via this innermost layer. However, all layers still border one another directly, i.e.The innermost layer, which directly borders the interior, borders the inner layer on the outside, the inner layer borders the middle layer, and the middle layer borders the outer layer, and the outer layer is the outermost layer of the multi-layer composite.

[0017] The inner layer is based on polyamide 6, the middle layer is based on EVOH, and the outer layer is based on a mixture of polyamide 6 and at least one other polyamide, namely polyamide 612, polyamide 614, polyamide 616, polyamide 618 or a mixture thereof.

[0018] Surprisingly, it turns out that this specific selection of materials, in the specified layer sequence, can provide the stated properties without the need for adhesion promoter layers, while unexpectedly meeting the existing test criteria, particularly for the automotive fuel line sector. In particular, an elongation at break of over 300% according to ISO 527 can be achieved.

[0019] The invention therefore relates to a multi-layer composite in the form of a hollow body enclosing an interior space, consisting of three layers, an inner layer adjacent to the interior space, a middle layer adjacent to this, and an outer layer adjacent to the middle layer and closing off the multi-layer composite to the outside, wherein, if necessary, a further innermost layer can be provided, which then directly borders the inner layer and is provided with a conductive finish.

[0020] The inner layer is based on polyamide 6, the middle layer is based on EVOH and the outer layer is based on a mixture of (A) polyamide 6 and (B) at least one other polyamide selected from the following group: polyamide 612, polyamide 614, polyamide 616 and polyamide 618.

[0021] The other polyamide is not polyamide 6.

[0022] According to the invention, the material of the outer layer, or preferably even all of the layers of the multilayer composite, does not contain any polyamide elastomers (TPE-A), such as from the group of polyetheramides, polyesteramides, polyetheresteramides, polyetheresteretheramides and mixtures thereof.

[0023] A first preferred embodiment is characterized in that the outer layer contains a plasticizer, e.g., based on sulfonamides or hydroxybenzoic acid esters, in particular selected from N-butylbenzenesulfonamide (BBSA), an impact modifier, and an adhesion promoter. This allows the impact strength required for the aforementioned applications to be achieved.

[0024] Suitable hydroxybenzoic acid ester-based plasticizers include, for example, systems such as the following: 2-hexyldecyl-4-hydroxybenzoate, hexyloxyethoxyethyl p-hydroxybenzoate; hexyloxypropoxypropyl p-hydroxybenzoate; hexyloxybutoxybutyl p-hydroxybenzoate; octyloxyethoxyethyl p-hydroxybenzoate; octyloxypropoxypropyl p-hydroxybenzoate; octyloxybutoxybutyl p-hydroxybenzoate; 2'-ethylhexyloxyethoxyethyl p-hydroxybenzoate; 2'-ethylhexyloxypropoxypropyl p-hydroxybenzoate; 2'-ethylhexyloxybutoxybutyl p-hydroxybenzoate; decyloxyethoxyethyl p-hydroxybenzoate; decyloxypropoxypropyl p-hydroxybenzoate; decyloxybutoxybutyl p-hydroxybenzoate, or mixtures thereof. According to a further preferred embodiment, the outer layer preferably contains at least the following additional components: (C1) a plasticizer, particularly preferably selected from BBSA, HDPB (2-hexyldecyl-4-hydroxybenzoate, CAS 148348-12-3) or a mixture thereof, (C2) at least one impact modifier, and (C3) at least one adhesion promoter.

[0025] The proportion of plasticizer (C1) is preferably in the range of 3-12 percent by weight or in the range of 5-8 percent by weight.

[0026] The proportion of impact modifier (C2) is preferably in the range of 10-30 weight percent, or in the range of 10-20 weight percent.

[0027] The proportion of adhesion promoter (C3) is preferably in the range of 3-12 percent by weight or in the range of 5-10 percent by weight.

[0028] These quantities of components (C1)-(C3) are to be understood as 100 percent by weight based on the total mass of the material for producing the outer layer.

[0029] Preferably, the outer layer consists exclusively of components (A), (B), (C1), (C2) and (C3) and optionally additives, which particularly preferably consist of a copper stabilizer and a color masterbatch.

[0030] A further preferred embodiment of the proposed multilayer composite is characterized in that the impact modifier of the outer layer (or also the inner layer) is an ethylene / α-olefin copolymer, particularly ethylene / butylene or ethylene / propylene copolymer, grafted with an anhydride, in particular maleic anhydride. Mixtures of various such systems are also possible.

[0031] Furthermore, the adhesion promoter of the outer layer is preferably a polyethylene grafted with an anhydride, in particular with maleic anhydride, in particular an LLDPE grafted in this way.

[0032] According to a further preferred embodiment, the outer layer of the multi-layer composite can consist of: (A) 5-35% by weight of polyamide 6; (B) 30-60% by weight of at least one of the other polyamides selected from the following group: polyamide 612, polyamide 614, polyamide 616, and polyamide 618; (C) 20-40% by weight of further components other than (A) and (B); where the sum of components (A)-(C) constitutes 100% by weight of the material for producing the outer layer.

[0033] Preferably, the other components (C) are composed as follows: (C1) 3-8 weight percent plasticizer; (C2) 9-30 weight percent impact modifier; (C3) 3-10 weight percent adhesion promoter; (C4) 0-3 weight percent additives, in particular processing aids, UV stabilizers, heat stabilizers, pigments, masterbatch carriers, or mixtures thereof. The proportions of (C1)-(C4) refer to the 100 weight percent of the material for producing the outer layer, formed by the sum of (A) - (C).

[0034] Preferably, the other polyamide (B) is exclusively polyamide 616 or 612.

[0035] The multilayer composite is preferably characterized in that the at least one of the other polyamides (B) of the outer layer (5) selected from the following group: polyamide 612, polyamide 614, polyamide 616 and polyamide 618, or all when present in a mixture, has a relative solution viscosity, measured in m-cresol according to ISO 307 (2007) at a temperature of 20 °C, in the range of 2.0-2.5, preferably of 2.15-2.44.

[0036] The at least one of the other polyamides (B) of the outer layer (5) selected from the following group: polyamide 612, polyamide 614, polyamide 616 and polyamide 618 further preferably has a melting point in the range of 180-240°C, preferably 185-225°C.

[0037] More specifically, the preferably used polyamide 612 or 616 of the outer layer has a relative solution viscosity, measured in m-cresol according to ISO 307 (2007) at a temperature of 20 °C, in the range of 2.10-2.25, and / or a melting point in the range of >200 °C.

[0038] It is further preferred that the polyamide 6 of the outer layer has a relative solution viscosity measured in sulfuric acid (1 g polyamide in 100 ml sulfuric acid) according to ISO 307 (2007) at a temperature of 20 °C in the range of 3.0-3.8, preferably 3.30-3.7, particularly preferably 3.35-3.5, and / or that the polyamide 6 of the outer layer has a melting point in the range of 200-240 °C, preferably 210-230 °C.

[0039] The inner layer may preferably have a copper stabilization, preferably based on CuI, in a proportion in the range of 0.01-0.10 weight percent, or in a proportion of 0.03-0.07 weight percent.

[0040] Furthermore, the inner layer can contain an impact modifier, preferably in a proportion in the range of 10-25 weight percent or in a range of 10-20 weight percent. The impact modifier is preferably an ethylene / α-olefin copolymer grafted with an anhydride, especially maleic anhydride, especially an ethylene / butylene or ethylene / propylene copolymer grafted in this way. Mixtures of various such systems are also possible. Here, the weight percent refers to 100 weight percent of the material used to produce the inner layer.

[0041] The multi-layer composite can further preferably be characterized in that the inner layer consists of: (A_I) Polyamide 6, preferably with a relative solution viscosity, measured in sulfuric acid (1 g polyamide in 100 ml sulfuric acid) according to ISO 307 (2007) at a temperature of 20 °C, in the range of 3.5-3.8, preferably 3.6-3.75. (B_I) 10-30 weight percent impact modifier (C_I) 0.01-0.1 weight percent copper stabilizer (D_I) 0-15 weight percent, preferably 5-10 or 0-1 weight percent additives, preferably selected from the group: conductivity additives, crystallization accelerators, processing aids, lubricants, and mixtures thereof, wherein the sum of components (A_I)-(D_I) adds up to 100 weight percent of the material for producing the inner layer.

[0042] Preferably, the inner layer is made conductive, especially if there is no other innermost layer. In this case, the proportion of component (D_I) is typically in the range of 5-15 weight percent, and in the range of 5-10 weight percent (based on the sum of components (A_I)-(D_I)) is formed by a conductivity additive.

[0043] A further preferred embodiment is characterized in that the component (D_I) contains at least one conductivity additive, this component is formed by a conductivity additive alone, preferably in a proportion in the range of 0.1-15 percent by weight, based on the total mass of the inner layer.As electrically conductive materials within the meaning of the conductivity additive, particles of metal fibers, metal powder, metal oxide powder, conductive carbon black, conductive carbon fiber, conductive carbon nanotubes, conductive graphite powder, conductive graphite fiber, graphene, bronze powder, bronze fiber, steel powder, steel fiber, iron powder, iron fiber, copper powder, copper fiber, silver powder, silver fiber, aluminum powder, aluminum fiber, nickel powder, nickel fiber, tungsten powder, tungsten fiber, gold powder, gold fiber, copper-manganese alloy powder, copper-manganese fiber, and combinations thereof or mixtures thereof can be mixed into the inner layer as component (D_I). When the inner layer is provided with electrical conductivity in this way, the inner layer preferably has an electrical surface resistance of not more than 10 8 < Ω or not more than 10 6 < Ω, preferably not more than 10 Ω.The proportion of the electrically conductive material is preferably determined such that the electrical surface resistance of the inner layer falls within the specified range. Preferably, the conductive particles of the conductivity additive have an average cross-sectional diameter of about 0.1 microns to about 100 microns. The conductive particles may be coated with a coating to provide coated conductive particles as the conductive particles.

[0044] The middle layer typically consists of an EVOH with an ethylene content in the range of 20-25 weight percent, preferably in the range of 25-30 weight percent.

[0045] The inner layer of such a structure preferably has a thickness in the range of 0.3-0.6 mm, preferably in the range of 0.4-0.5 mm.

[0046] The middle layer preferably has a thickness in the range of 0.05-0.2 mm, preferably in the range of 0.075-0.125 mm.

[0047] The outer layer preferably has a thickness in the range of 0.3-0.6 mm, preferably in the range of 0.4-0.5 mm.

[0048] The innermost layer preferably has a thickness in the range of 0.08 - 1 mm, preferably in the range of 0.1 - 0.9 mm.

[0049] As far as the overall structure is concerned, the total wall thickness of the multilayer composite is preferably in the range of 0.5-2.5 mm, more preferably in the range of 0.75-1.5 mm.

[0050] Preferably, the proposed multilayer structure is / is produced in a coextrusion process.

[0051] The multi-layer composite can be in the form of a line which can be designed at least in sections as a corrugated pipe, preferably as a fuel line for internal combustion engines, in particular in the automotive sector.

[0052] According to a preferred embodiment, the line consists exclusively of the inner layer, the middle layer and the outer layer.

[0053] If there is an innermost layer, it is preferably made of polyamide-based or thermoplastic fluoropolymer materials.

[0054] The polyamide base is then preferably selected from the group consisting of: PA 6, PA 12, PA 612, PA 10T / 6T, PA 1212, PA 66, PA 11, PA 106, PA 1012, PA 10T / 612, PA 10T / 610, PA 9T. Such an innermost layer based on polyamide contains a conductivity additive and can additionally contain plasticizers, impact modifiers, adhesion promoters, and / or additives. For example, 1-15 weight percent conductivity additive, 3-8 weight percent plasticizer, 9-30 weight percent impact modifier, 3-10 weight percent adhesion promoter, 0-3 weight percent additives, in particular processing aids, UV stabilizers, heat stabilizers, pigments, masterbatch carriers, or mixtures thereof, the remainder being formed by the polyamide or the mixture of polyamides. The proportions of refer to the 100 weight percent of the material used to produce the innermost layer.

[0055] The thermoplastic fluoropolymer for the innermost layer is preferably based at least on ethylene and tetrafluoroethylene, with or without further blocks selected from the group: propylene, in particular hexafluoropropylene blocks, hexene, in particular perfluorohexene blocks, preferably as a fluorine-containing ethylenic polymer having a carbonyl group, which particularly preferably does not contain an amide, imide, urethane or urea group.

[0056] According to a further preferred embodiment, the innermost layer may consist of the following components: (a) 75-100% by weight, preferably 85-98% by weight, of said polyamide base or fluoropolymer based at least on ethylene and tetrafluoroethylene, with or without hexafluoropropylene blocks and / or perfluorohexene blocks, preferably with carbonyl groups; (b) 0-25% by weight of additives other than (c); (c) 0.1-20% by weight of conductivity additive; where components (a) and (c) add up to 100% by weight of the material of the innermost layer.

[0057] Component (b) is preferably selected from at least one additive from the following group: antioxidants, processing aids, UV stabilizers, heat stabilizers, pigments, masterbatch carriers, lubricants or mixtures thereof.

[0058] Particularly preferably, component (c) contains at least one additive for increasing electrical conductivity, preferably in the form of particles of metal fibers, metal powder, metal oxide powder, conductive carbon black, conductive carbon fiber, conductive carbon nanotubes, conductive graphite powder, conductive graphite fiber, graphene, bronze powder, bronze fiber, steel powder, steel fiber, iron powder, iron fiber, copper powder, copper fiber, silver powder, silver fiber, aluminum powder, aluminum fiber, nickel powder, nickel fiber, tungsten powder, tungsten fiber, gold powder, gold fiber, copper-manganese alloy powder, copper-manganese fiber and combinations thereof.

[0059] Component (c) preferably contains at least one conductivity additive in a proportion in the range of 1-15% by weight, in particular in a proportion of 3-8% by weight, based on the total mass of the innermost layer.

[0060] When the innermost layer is provided with electrical conductivity in this way, it preferably has an electrical surface resistance of not more than 10 8 < Ω or not more than 10 6 < Ω, preferably not more than 10 Ω. The proportion of the electrically conductive material is preferably determined such that the electrical surface resistance of the inner layer falls within the stated range. Preferably, the conductive particles of the conductivity additive have an average cross-sectional diameter of about 0.1 micron to about 100 microns. The conductive particles may be coated with a coating to provide coated conductive particles as the conductive particles.

[0061] Furthermore, the present invention relates to a process for producing a multi-layer composite as described above, wherein the process is preferably characterized in that at least 2, preferably all 3 or 4 layers are formed into a hollow body, particularly preferably into a pipe or a conduit or a container, in a continuous and / or discontinuous process, preferably in an extrusion blow molding, a tandem extrusion, a sheathing process or a coextrusion process.

[0062] Furthermore, the present invention relates to the use of such a multi-layer composite as a line for internal combustion engines, in particular in the automotive sector, in particular for fuel (e.g. diesel or gasoline), urea or coolant.

[0063] Further embodiments are specified in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Preferred embodiments of the invention are described below with reference to the drawings, which are for illustrative purposes only and are not to be construed as limiting. In the drawings: Fig. 1: a fuel line with three layers in a sectional view perpendicular to the direction of travel; Fig. 2: a fuel line with four layers in a sectional view perpendicular to the direction of travel. DESCRIPTION OF PREFERRED EMBODIMENTS

[0065] Figure 1 shows an exemplary fuel line 1 according to the invention in a section transverse to the main direction of travel.

[0066] The cross-sectional area can be constant over the main direction, ie the pipe can have an essentially hollow cylindrical shape.

[0067] However, the cross-sectional area can also vary across the main direction, for example in the form of a corrugated pipe.

[0068] An inner space 2 is enclosed by the pipe wall. Radially extending outward from the inner space 2 is an inner layer 3, which borders and defines the inner space 2 with its inner surface 7. This inner layer is made of polyamide 6 without any other polyamide components.

[0069] Directly adjacent to the inner layer 3 without an intermediate adhesion promoter layer there is a middle layer 4 in the sense of a barrier layer, which is made of EVOH.

[0070] Directly adjacent to this middle layer 4 and again without an intermediate bonding layer, the outer layer 5 follows. The outer layer 5 is based on polyamide 616 in a mixture with PA 6. The outer surface 6 of the outer layer 5 defines the outer boundary of the cable.

[0071] An alternative exemplary fuel line according to the invention is shown in Figure 2Here, in addition to the three layers described above, there is another innermost layer 7, which seals off the fuel line to the inside and, in this case, borders directly on the interior space 2. This innermost layer is made conductive, ie, it contains additives made of conductive particles, such as conductive soot. Raw materials used:

[0072] Polyamide 6 (I) (outer layer): η rel = 3.4 (sulfuric acid); T m measured by DSC according to ISO 11357 (2011) = 222 °C. Polyamide 612 (outer layer): η rel = 2.3 (m-cresol); T m measured by DSC according to ISO 11357 (2011) = 218 °C. Polyamide 616 (outer layer): η rel = 2.2 (m-cresol); T m measured by DSC according to ISO 11357 (2011) = 196 °C. Polyamide 12 (outer layer, VB): Grilamid L25, high-viscosity polyamide 12, commercial product of EMS-CHEMIE AG, Domat / Ems, Switzerland Melt volume rate (MVR): 275°C / 5 kg, ISO 1133; T m measured by DSC according to ISO 11357 (2011) = 178 °C. Polyamide 610 (outer layer, VB): Grilamid 2S 20 natural, polyamide 610 with a relative viscosity of 1.9-2.0, commercial product of EMS-CHEMIE AG, Domat / Ems, Switzerland; T m measured by DSC according to ISO 11357 (2011) = 213 °C. Polyamide 6 (II) (inner layer): η rel = 3.7 (sulfuric acid); T m measured by DSC according to ISO 11357 (2011) = 222 °C.Ethylene vinyl alcohol (barrier layer): An ethylene / vinyl alcohol copolymer (EVOH) was used as the material for the barrier layer. Specifically, the material used in the examples was a product from KURARAY, available under the name EVAL ®< under the product designation F170B and with an ethylene content of 27 mol%. It is available in Europe from EVAL Europe NV in Zwijindrecht, Belgium. Plasticizer (outer layer): BBSA (N-butylbenzenesulfonamide) was used as the plasticizer (WM). This is available under the brand name Uniplex 214 from Lanxess. Impact modifier (for inner and outer layers): Acid-modified ethylene / α-olefin copolymers, namely maleic anhydride-grafted ethylene-butylene and ethylene-propylene copolymers, and their blends, were used as impact modifiers (SZM). Impact modifier of the inner layer: MVR value (measured at 230°C / 2.16 kg) of 1.2 g / 10 min (ASTM D1238), DSC glass transition temperature according to ISO standard 11357-2 (2013) of -65 °C, available under the name Tafmer MH5020C from Mitsui Chemicals. Impact modifier of the outer layer and the inner layer of the comparative example: MVR value (measured at 230 °C / 2.16 kg) of 1.3 g / 10 min (ASTM D1238), DSC glass transition temperature according to ISO standard 11357-2 (2013) of -60 °C, available under the name Tafmer MC201 from Mitsui Chemicals. Copper stabilizer (inner layer): CuI / KI (weight ratio 1:6) was used as the copper stabilizer in a proportion of 0.05 weight percent based on the total mass of the inner layer. The copper(I) iodide is commercially available from Merck KGaA, and the potassium iodide is available from Liquichem Handelsgesellschaft mbH.Adhesion promoter (outer layer): A maleic anhydride-grafted LLDPE was used as the adhesion promoter (HVM). It is available from Mitsui Chemicals under the name Admer NF358E. It has an MFR (190°C, 2.16 kg) of 1.6 g / 10 min (ASTM D1238), a density of 0.91 g / cm3 (ASTM D1505), and a Vicat softening point of 82 °C (ASTM D1525). The Tm, measured by DSC according to ISO 11357-3 (2011), is 120 °C. Masterbatch (outer layer): Euthylene Black, a carbon black-based (40%) color masterbatch based on PE, available from BASF (Ludwigshafen, Germany). Production of the test specimens:

[0073] Tubes were co-extruded at melt temperatures between 210 and 260 °C under vacuum of -56 mbar and an extrusion speed of 32.8 m / min. Tubes with an outer diameter of 8 mm and a wall thickness of 1 mm were used as test specimens. The length of the tube was adjusted according to test requirements. The thickness of the inner layer was 0.45 mm, that of the middle layer 0.10 mm, and that of the outer layer 0.45 mm. Work carried out on the pipe structures Tests:

[0074] Leaching : Tested according to SAE J2260 with test fuel FAM-B (according to SAE J1681 (2000)) - Test 96 hours, 60 °C, closed tube of 200 cm; maximum extract according to VW TL 52712 6 g / m 2< .

[0075] Cold behavior : is tested according to TL 52712 in accordance with VW standard PV 3905. The ball falls from a height of 65 cm. At least 10 test specimens are measured, and the number of fractures is expressed as a percentage.

[0076] Pipe tensile test :Pipe tensile tests were conducted according to ISO 527-2 (2012). Test specimens with a length of 150 mm (for tensile tests in the extrusion direction) or 10 mm (for tensile tests transverse to the extrusion direction) were used. The test temperature was 23 °C and the test speed was 100 mm / min (for tests in the extrusion direction) or 25 mm / min for tests transverse to the extrusion direction.

[0077] Specifically, the following measurements were carried out according to ISO 527: elongation at break in the extrusion direction, elongation at break transverse to the extrusion direction, yield stress in the extrusion direction, yield stress transverse to the extrusion direction.

[0078] Layer adhesion : was tested according to SAE J2260.

[0079] Relative viscosity : DIN EN ISO 307 (2007), in 0.5 wt.% m-cresol solution or 1 wt.% sulfuric acid solution (PA6) at a temperature of 20 °C.

[0080] Thermal behavior (Melting point T m , enthalpy of fusion and glass transition temperature (T g ): ISO standard 11357-1 (2016), -2 (2013) and -3 (2011), granules, differential scanning calorimetry (DSC) was carried out at a heating rate of 20 °C / min. Table 1: Composition and structure B1 B2 VB1 Unit Outer layer inner layer Outer layer inner layer Outer layer inner layer Polyamide 612 % by weight 44.25 - - - 72 - Polyamide 616 % by weight - - 44.25 - - - Polyamide 6 (I) % by weight 25.0 - 25.0 - - - Polyamide 6 (II) % by weight - 78.55 - 78.55 - 70.1 tractor unit (Tafmer MC201) % by weight 20.0 - 20 - 18 19.5 tractor unit (Tafmer MH5020C) % by weight - 20.00 - 20 - - HVM Weight 5.0 - 5.0 - - - World Cup % by weight 5.0 - 5.0 - 10 5.0 CuI / KI % by weight - 0.05 - 0.05 - - Black masterbatch % by weight 0.75 1.4 0.75 1.4 - 5.4 Table 2: Mechanical and chemical test results B1 B2 VB1 Yield stress in extrusion direction N / mm 2 35 38 30 Yield stress transverse to the extrusion direction N / mm 2 37 42 32 Elongation at break in extrusion direction % 344 366 300 Elongation at break transverse to the extrusion direction % 320 330 280 Cold shock, - 25 °C, ball mass 880 g % No break No break 20 Cold shock, -40 °C, ball mass 500 g % No break No break 40 Washout resistance, according to TL 52712 g / m 2 5.6 4.4 33.7 Layer adhesion Layers cannot be separated Layers cannot be separated Outer layer separable

[0081] While all examples demonstrate acceptable mechanical suitability for automotive applications, the low-temperature behavior of the pipes constructed according to the invention is an unexpected and significant improvement over the comparative example. The comparative example clearly fails to meet industrial requirements. The structures according to the invention also exhibit unexpectedly advantageous elongation at break. The molding compounds of all examples can be co-extruded, but only the examples according to the invention demonstrate good adhesion between the outer layer and the intermediate EVOH layer.

[0082] The unexpectedly good suitability of pipes constructed according to the invention for this application is also demonstrated by their excellent leaching resistance. The industrial requirement according to TL 52712 is a leaching of less than 6 g / m² of pipe surface. This requirement is met here only with the examples according to the invention.

[0083] In order to allow further comparison with prior art structures, in particular for comparison with the examples of EP-A-1 884 356, the structures given in Table 3 were prepared by the same procedure and tested for properties as given in Table 4. Table 3: Compositions and structure of further comparative examples VB2 and VB3 VB2 VB3 Unit Outer layer inner layer Outer layer inner layer Polyamide 6 (I) % by weight 42.5 42.5 Polyamide 6 (II) % by weight 83 Polyamide 12 % by weight 42.5 Polyamide 610 % by weight 83 Grilon XE 3871 % by weight 42.5 tractor unit (Tafmer MC201) % by weight 15 10 15 tractor unit (Tafmer MH5020C) % by weight 10 World Cup % by weight 7 7 Table 4: Mechanical and chemical test results VB2 and VB3 VB2 VB3 Yield stress in extrusion direction N / mm 2 30 28 Yield stress transverse to the extrusion direction N / mm 2 32 30 Elongation at break in extrusion direction % 298 276 Elongation at break transverse to the extrusion direction % 280 249 Cold shock, -25°C, ball mass 880 g % 30 30 Cold shock, -40°C, ball mass 500 g % 40 40 Washout resistance, according to TL 52712 g / m 2 42 48 Layer adhesion Outer layer separable Outer layer separable

[0084] Reworking the structures from D1 exhibits poor mechanical properties, particularly in terms of impact strength and leaching. The poor composition / combination of the layers also leads to layer separation.

[0085] The order of the additives (plasticizers) is reversed in D1, thus the composition and structure of D1 deviates from the inventive structure, i.e. the compositions and sequences of the layers as claimed.

[0086] What is particularly noteworthy in connection with the D1 is that the inner layers of the D1 are mostly treated with plasticizer, which makes leaching unacceptable. LIST OF REFERENCE SYMBOLS 1 fuel line 5 Outer layer 2 Interior of 2 6 Outside area of ​​1 3 inner layer 7 Inner surface of 1 4 middle class 8 innermost layer of 1

Claims

1. Multilayer composite (1) in the form of a hollow body enclosing an inner space (2), consisting of three layers, an inner layer (3) adjoining the inner space (2), a middle layer (4) adjoining the inner layer and an outer layer (5) adjoining the middle layer (4) and bordering the multilayer composite (1) to the outside, wherein the inner layer (3) is based on polyamide 6, the middle layer (4) is formed on the basis of EVOH, and the outer layer (5) is based on a mixture of (A) polyamide 6 and (B) at least one other polyamide selected from the following group: polyamide 612, polyamide 614, polyamide 616 and polyamide 618, wherein the material of the outer layer is free from polyamide elastomers (TPE-A) or consisting of four layers, the said three layers (3-5) and a further innermost layer (8) directly adjacent to the said innermost layer (3), and being conductive.

2. Multilayer composite according to claim 1, characterised in that the outer layer (5) contains at least the following further constituents: (C1) a plasticizer, in particular preferably selected as a hydroxybenzoic acid ester- or sulfonamide-based plasticizer, in particular BBSA, HDPB or a mixture thereof (C2) at least one impact modifier, and (C3) at least one adhesion promoter, the proportion of plasticiser (C1) preferably being in the range of 3-12% by weight or in the range of 5-8% by weight, and / or wherein the proportion of impact modifier (C2) is preferably in the range of 10-30% by weight, or in the range of 10-20% by weight, and / or wherein the proportion of adhesion promoter (C3) is preferably in the range of 3-12% by weight or in the range of 5-10% by weight, in each case based on the total mass of the material used to produce the outer layer as 100 percent by weight, wherein preferably the outer layer (5) consists exclusively of the components (A), (B), (C1), (C2) and (C3) and optionally additives, in particular consisting of a copper stabilizer and a colour masterbatch wherein preferably the impact modifier (C2) is an ethylene / α-olefin copolymer, in particular ethylene / butylene or ethylene / propylene copolymer, or mixtures thereof, grafted with an anhydride, in particular with maleic anhydride, and / or in that the adhesion promoter (C3) is a polyethylene grafted with an anhydride, in particular with maleic anhydride, in particular an LLDPE grafted in this way.

3. Multilayer composite according to any of the preceding claims, characterized in that the outer layer (5) consists of: (A) 5-35 % by weight of polyamide 6; (B) 30-60% by weight of at least one of said other polyamides selected from the following group: polyamide 612, polyamide 614, polyamide 616 and polyamide 618; (C) 20 to 40 % by weight of other components different from (A) and (B); wherein the sum of components (A)-(C) is 100% by weight of the material used to produce the outer layer, preferably the other components (C) being composed as follows: (C1) 3-8 weight percent plasticizer; (C2) 9-30 weight percent impact modifier; (C3) 3-10 weight percent adhesion promoter; (C4) 0-3% by weight of additives, in particular processing aids, UV stabilizers, heat stabilizers, pigments, masterbatch carriers or mixtures thereof, where the proportions of (C1)-(C4) are based on the 100 weight percent of the material for producing the outer layer formed by the sum of (A) - (C).

4. Multilayer composite according to one of the preceding claims, characterized in that at least one of the said other polyamides (B) of the outer layer (5), selected from the following group: polyamide 612, polyamide 614, polyamide 616 and polyamide 618, has a relative solution viscosity, measured in m-cresol according to ISO 307 (2007) at a temperature of 20°C, in the range 2.0-2.5, preferably 2.15-2.4, and / or in that at least one of the said other polyamides (B) of the outer layer (5), selected from the following group: polyamide 612, polyamide 614, polyamide 616 and polyamide 618, has a melting point in the range 180-240°C, preferably 185-225°C, and / or in that the polyamide 6 (A) of the outer layer (5) has a relative solution viscosity measured in sulphuric acid according to ISO 307 (2007) at a temperature of 20°C in the range of 3.0 - 3.8, preferably 3.30-3.7, and / or in that the polyamide 6 (A) of the outer layer (5) has a melting point in the range from 200 - 240 °C, preferably from 210-230 °C.

5. Multilayer composite according to one of the preceding claims, characterized in that the inner layer (3) has a copper stabilization, preferably based on CuI, in a proportion in the range of 0.01-0.10 weight percent, or in a proportion of 0.03-0.07 weight percent, and / or in that the inner layer (3) contains an impact modifier, preferably in a proportion in the range of 10-25% by weight or in a range of 10-20% by weight, the impact modifier preferably being an ethylene / α-olefin copolymer grafted with an anhydride, in particular with maleic anhydride, in particular ethylene / butylene or ethylene / propylene copolymer grafted in this way, and mixtures thereof and wherein the weight percentages are each based on 100 weight percent of the material for producing the inner layer (3).

6. Multilayer composite according to any of the preceding claims, characterized in that the inner layer (3) consists of: (A_I)Polyamide 6, preferably having a relative solution viscosity measured in sulphuric acid according to ISO 307 (2007) at a temperature of 20 °C in the range 3.5-3.8, preferably 3.6-3.75;(B_I)10-30 weight percent impact modifier(C_I)0.01-0.1 weight percent heat stabilizer, preferably based on copper(I)(D_I)0-15 % by weight, preferably 5 - 10 or 0 - 1 weight percent additives, preferably selected from the group: conductivity additives, crystallization accelerators, processing aids, lubricants, and mixtures thereof where the sum of the components (A_I) - (D_I) add up to 100% by weight of the material used to produce the inner layer (3).

7. Multilayer composite according to any of the preceding claims, characterized in that the middle layer (4) consists of an EVOH, preferably an EVOH with an ethylene content in the range of 20-25 percent by weight, preferably in the range of 25-30 percent by weight.

8. Multilayer composite according to any of the preceding claims, characterized in that the inner layer (3) has a thickness in the range 0.3-0.6 mm, preferably in the range 0.4-0.5 mm, and / or that the middle layer (4) has a thickness in the range of 0.05-0.2 mm, preferably in the range of 0.075-0.125 mm, and / or that the outer layer (5) has a thickness in the range of 0.3-0.6 mm, preferably in the range of 0.4-0.5 mm, and / or that, if present, the innermost layer (8) has a thickness in the range of 0.08 - 1 mm, preferably in the range of 0.1 - 0.9 mm, whereby preferably the total wall thickness of the multilayer composite is in the range of 0.5-2.5 mm, preferably in the range of 0.75-1.5 mm.

9. Multilayer composite according to any of the preceding claims, characterised in that it is produced in a co-extrusion process.

10. Multilayer composite according to one of the preceding claims, characterized in that the at least one polyamide (A) of the outer layer (5) is selected from polyamide 612, polyamide 616 or a mixture thereof, preferably consisting only of polyamide 612.

11. Multilayer composite according to one of the preceding claims in the form of a pipe which can be structured at least in sections as a corrugated pipe, preferably as a fuel pipe for internal combustion engines, in particular in the automotive sector, wherein preferably the pipe consists exclusively of the inner layer (3), the middle layer (4) and the outer layer (5).

12. Multilayer composite according to one of the preceding claims, characterized in that the innermost layer (8) is based on polyamide or on a thermoplastic fluoropolymer, wherein the polyamide base is preferably selected from the group consisting of PA 6, PA 12, PA 612, PA 10T / 6T, PA 1212, PA 66, PA 11, PA 106, PA 1012, PA 10T / 612, PA 10T / 610, PA 9T, and / or the thermoplastic fluoropolymer is preferably based at least on ethylene and tetrafluoroethylene, with or without further blocks selected from the group: propylene blocks, in particular hexafluoropropylene blocks, hexene blocks, in particular perfluorohexene blocks, preferably as a fluorine-containing ethylenic polymer with a carbonyl group, which in particular preferably does not contain any amide, imide, urethane or urea group, and / or that the innermost layer (8) consists of the following components: (a) 75-100% by weight, preferably 85-98% by weight of said polyamide base or fluoropolymer based on at least ethylene and tetrafluoroethylene, with or without hexafluoropropylene blocks and / or perfluorohexene blocks, preferably with carbonyl groups; (b) 0-25 % by weight of additives other than (c); (c) 0.1-20 weight percent conductivity additive; wherein the components (a) and (c) to 100 weight percent of the material of the innermost layer (8).

13. Multilayer composite according to claim 12, characterized in that component (b) is selected from at least one additive from the following group: antioxidants, processing aids, UV stabilizers, heat stabilizers, pigments, masterbatch carriers, lubricants or mixtures thereof, and / or that component (c) contains at least one additive for increasing electrical conductivity, preferably in the form of particles of metal fibres, metal powder, metal oxide powder, conductive carbon black, conductive carbon fibre, conductive carbon nanotubes, conductive graphite powder, conductive graphite fibre, graphene, bronze powder, bronze fibre, steel powder, steel fibre, iron powder, iron fibre, copper powder, copper fibre, silver powder, silver fibre, aluminium powder, aluminium fibre, nickel powder, nickel fibre, tungsten powder, tungsten fibre, gold powder, gold fibre, copper-manganese alloy powder, copper-manganese fibre and combinations, and / or in that component (b) contains at least one conductivity additive, in a proportion in the range of 1-15% by weight, in particular in a proportion of 3-8% by weight, based on the total mass of the innermost layer.

14. Method for producing a multilayer composite according to one of the preceding claims, characterised in that at least 2, preferably all 3 or 4 layers, are formed into a hollow body, in particular preferably into a pipe or a tube or a container, in a continuous and / or discontinuous process, preferably in an extrusion blow moulding, tandem extrusion, sheathing or coextrusion process.

15. Use of a multilayer composite according to one of claims 1-13 as a tube for internal combustion engines, especially in the automotive sector, especially for fuel, urea or coolant