Multilayer hollow body with high leaching resistance

Abstract

The invention relates to a multilayer hollow body with high leaching resistance, comprising: I. an inner layer I consisting of a molding composition based on PA612, PA610, PA1010, PA1012 and / or PA1212; iI. Optionally a tackifier layer II consisting of a molding composition based on the following components: a) 0 to 80 parts by weight of a polyamide selected from the group consisting of PA6, PA66, PA6 / 66, b) 0 to 100 parts by weight of a polyamine-polyamide copolymer, c) 0 to 80 parts by weight of a polyamide selected from the group consisting of PA11, PA12, PA612, PA1010, PA1012, PA1212, III. A layer III consisting of an ethylene-vinyl alcohol copolymer molding composition, wherein no more than 0.2 g / m < 2 > of insoluble extract and no more than 7.0 g / m < 2 > of soluble extract are washed out of the multilayer hollow body as the entire system upon first exposure to fuel.

Description

This application is a divisional application of application number 201710850951.1, and the application date of application number 201710850951.1 is September 20, 2017. Technical Field

[0001] The invention provides multilayer hollow bodies with very high leaching resistance by selecting the molding compositions used in the individual layers. The multilayer hollow bodies are mainly hollow profiles for conducting or storing liquid or gaseous media, such as pipes or containers. Background Art

[0002] Flexible pipes for routing liquid or gaseous media in motor vehicles are well known. This problem has previously been solved satisfactorily by single-layer pipes made of polyamide or other thermoplastic molding compositions. In the case of these single-layer pipes, it has been found that the mechanical properties present after installation, such as high elongation at break and high impact resistance, are not significantly altered by cold or heat effects or by contact with the media, even during the service life of the motor vehicle, so that the pipe fails.

[0003] More stringent environmental regulations have led to the discontinuation of the further development and use of single-layer pipes for fuel lines and the abandonment of single-layer fuel containers. In both cases, the automotive industry requires not only adequate fuel resistance, but also an improved barrier effect on fuel components, thereby reducing their emission into the environment. This has led to the development of multilayer hollow bodies, in which, for example, ethylene-vinyl alcohol copolymers (EVOH) are used as barrier layer material. Such multilayer composite materials, which include not only EVOH layers but also further layers based on aliphatic polyamides, are known, for example, from EP 1 216 826 A2.

[0004] Due to their good mechanical properties, their low water absorption capacity and their insensitivity to environmental influences, polyamides are useful materials for both inner and outer layers. However, EVOH is incompatible with polyamides such as PA11, PA12, PA1012 or PA1212 and has only low compatibility with PA612. However, adhesion between adjacent layers is indispensable and can therefore only be ensured by the intervention of an intermediate tackifier layer. In the automotive industry, there has also been a trend for some time towards higher temperatures in the engine compartment, and therefore stability of the hollow bodies used at these temperatures is required. Therefore, solutions comprising a tackifier layer based on, for example, polyolefins are not suitable due to their low resistance to heat deformation. EP 1216826 A2 solves this problem by using a tackifier layer comprising a polyamide selected from PA6, PA66 and PA6 / 66 and a polyamide selected from PA11, PA12, PA612, PA1012 and PA1212.

[0005] For example, the progressive trend towards "downsizing", i.e. reducing the size of components while maintaining the same performance, with the aim of reducing the energy consumption of motor vehicle engines, leads not only to an increase in the temperatures present in the engine compartment but also to a reduction in the size of the injection valves. These valves are nozzles that inject fuel into the intake tract or combustion chamber of an internal combustion engine. The polar components present in the fuel require that the multilayer tubes used are resistant to extraction of components from the materials used. US 6467508 describes the problem of precipitation of such extracts in the fuel and possible clogging of the injection valves. This problem is solved by using "low-precipitation polyamides" in the inner layer. "Low-precipitation polyamides" are washed polyamides which are obtained by an inconvenient and expensive prior extraction with methanol. In this way, troublesome components, such as oligomers, are removed.

[0006] With the progressively decreasing size of the injection nozzles, the automotive industry also needs to reduce not only the extractables which precipitate out in the fuel, but also the extractables which are soluble in the fuel. This need has been intensified by the introduction of hybrid vehicles, since the internal combustion engines of these vehicles are not used for long periods of time. Therefore, soluble extractables in the fuel may also lead to clogging of the injection nozzles via drying-out. Such problematic extractables originate not only from the inner layers of the multilayer tube, but especially from all other layers which cannot be separated from the fuel by barrier layers, such as EVOH layers. Extractables are not only the oligomers described in US6467508, but also additives, such as plasticizers and stabilizers of the molding compositions used. Summary of the invention

[0007] The problem to be solved by the present invention is therefore to provide a composite material consisting of an EVOH layer and at least one polyamide layer, which has a high resistance to heat deformation and a high impact resistance, and in this case also obtains good layer adhesion, the entire multilayer composite having a high resistance to leaching, which means that both insoluble and soluble extractables are at a very low level after contact with the fuel.

[0008] This problem is solved by a multilayer hollow body according to claim 1, comprising the following layers: I. an inner layer (layer I) consisting of a molding composition based on PA612, PA1010, PA1012 and / or PA1212 and copolymers thereof and mixtures thereof; II. Optional adhesion promoter layer (layer II) consisting of a molding composition based on the following components: a) 0 to 80 parts by weight of a polyamide selected from PA6, PA66, PA6 / 66 and mixtures thereof, c) 0 to 80 parts by weight of a polyamide selected from PA11, PA12, PA612, PA1010, PA1012, PA1212 and mixtures thereof, wherein the sum of the parts by weight of components a), b) and c) is 100, and wherein in addition, of the sum of components a) and b), at least 16 parts by weight consist of monomer units derived from caprolactam and / or from the combination of hexamethylenediamine / adipic acid, and of the sum of components b) and c), at least 20 parts by weight consist of monomer units derived from ω-aminoundecanoic acid, laurolactam, from the combination of hexamethylenediamine / dodecane-1,12-dioic acid, from the combination of decane-1,10-diamine / decane-1,10-dioic acid, from the combination of decane-1,10-diamine / dodecane-1,12-dioic acid and / or from the combination of dodecane-1,12-diamine / dodecane-1,12-dioic acid; III. A layer (layer III) consisting of an ethylene-vinyl alcohol copolymer molding composition, Not more than 0.2g / m 2 , preferably not more than 0.18 g / m 2 , more preferably not more than 0.16 g / m 2 Insoluble extracts and not more than 7.0g / m 2 , preferably not more than 6.0g / m 2 , more preferably not more than 5.5g / m 2 The soluble extracts washed out of the multilayer hollow body as a whole on first exposure to the fuel were determined by the method described in the experimental section on multilayer tubes with the same layer structure, a wall thickness of 1 mm and an inner diameter of 6 mm. If the multilayer hollow body has a different wall geometry, it is therefore necessary to convert the individual layer thicknesses to a total wall thickness of 1 mm in order to provide comparability.

[0009] The low extractable content according to the claims is achieved by the choice of polyamide and by the fact that the molding composition of layer I does not contain any plasticizers and the molding composition of layer II preferably also does not contain any plasticizers. It is also advantageous if the molding composition of layer I contains only the necessary amounts of stabilizers and processing aids and the molding composition of layer II preferably also contains only the necessary amounts of stabilizers and processing aids.

[0010] The term "based on" means here that the respective molding composition comprises at least 50% by weight, preferably at least 60% by weight, more preferably at least 65% by weight and particularly preferably at least 70% by weight of these polyamides, in each case based on the entire molding composition. In addition, further additives, as described in detail below, are generally present in order to give a total of 100% by weight. It is further preferred that the molding composition does not contain any further polyamides.

[0011] “Identical layer structure” means that not only the layer sequence and composition of the multiple layers are identical, but also, in the case of different wall thicknesses, the individual layer thicknesses are converted to a total wall thickness of 1 mm.

[0012] The inner layer (layer I) is intended to be in direct contact with the transported or stored medium.

[0013] The multilayer hollow body is preferably a component of a fuel system, for example a fuel line or a fuel container, the fuel further preferably being gasoline.

[0014] In a preferred embodiment, layer I consists of a molding composition based on PA612, PA1010, PA1012 and / or PA1212 and copolymers thereof and mixtures thereof. In this embodiment, it is further preferred that the molding composition of layer II contains neither PA11 nor PA12.

[0015] The polyamide of layer I is more preferably PA 612. In this case, it is further preferred that the molding composition of layer II contains a mixture of PA 612 and PA 6 as polyamide component.

[0016] The amount of component a) present in the molding composition of layer II is at least 10 parts by weight, preferably at least 20 parts by weight, most preferably at least 30 parts by weight, while the upper limit is 60 parts by weight.

[0017] The amount of component c) present in the molding composition of layer II is at least 30 parts by weight, while the upper limit is preferably 70 parts by weight, more preferably 60 parts by weight.

[0018] Layers I, II and III follow directly in succession.

[0019] In another preferred embodiment, layer III is followed on the outside by a further layer, preferably consisting of a polyamide molding composition. It is particularly preferred here that an adjacent layer IV is present on the outside, which contains the same polyamide combination as layer II. Most preferred is a subsequent layer V consisting of a polyamide molding composition based on PA11, PA12 or the same polyamide as layer I; in this way, the mechanical properties required for the application are ensured and at the same time layer III is effectively protected from the penetration of air humidity, which reduces the barrier effect.

[0020] In the context of the present invention, if appropriate for the purposes of the present application, there can additionally be a further layer between layer II and layer III and / or between layer III and layer IV, which is made of a polyamide molding composition based on a polyamide with good adhesion to EVOH. The polyamide is, for example, PA6, PA66 or PA6 / 66.

[0021] In the simplest case, layer II is a blend of components a) and c). Since these polymers are largely incompatible with one another, in the production of blends at conventional processing temperatures (which results in physical mixtures), a sufficient tackifier effect is achieved only within a relatively narrow composition range. Better results are obtained when the polyamide blends are prepared under conditions in which the two polyamides react with one another to a certain extent via end groups or via transamidation reactions to give block copolymers. For this purpose, temperatures of more than 280° C., more preferably more than 300° C., and, if appropriate, the presence of catalysts such as hypophosphorous acid, dibutyltin oxide, triphenylphosphine or phosphoric acid are generally required. It is also possible to start from a polyamide blend which is first prepared under conventional processing conditions and then subject it to a solid phase postcondensation under conditions customary for polyamides. These are generally temperatures of more than 140° C. to a temperature lower than the crystalline melting point T m The temperature is about 5K lower, preferably above 150℃ than T m The reaction time is preferably about 10 K lower and 2 to 48 hours, preferably 4 to 36 hours, more preferably 6 to 24 hours. It is particularly advantageous if one polyamide contains an excess of amino end groups and the other polyamide contains an excess of carboxyl end groups. Finally, the combination of components a) and c) can also be achieved by adding reactive compounds which preferably link the polyamide end groups to each other, such as bisoxazolines, biscarbodiimides, bisanhydrides, diisocyanates or corresponding compounds with three or more functional groups.

[0022] Each component is described in detail below.

[0023] PA6 is prepared by ring-opening polymerization of caprolactam.

[0024] PA66 is prepared by the polycondensation of hexamethylenediamine and adipic acid. Like PA6, it is commercially available in a variety of types.

[0025] PA6 / 66 is a co-condensate from the monomers caprolactam, hexamethylenediamine and adipic acid.

[0026] The lactams and ω-aminocarboxylic acids used as monomers for forming the polyamide contain 4 to 19, in particular 6 to 12, carbon atoms. Particular preference is given to using caprolactam, ε-aminocaproic acid, capryllactam, ω-aminocaprylic acid, laurolactam, ω-aminododecanoic acid and / or ω-aminoundecanoic acid.

[0027] Examples of combinations from diamines and dicarboxylic acids are hexamethylenediamine / adipic acid, hexamethylenediamine / dodecanedioic acid, octamethylenediamine / sebacic acid, decamethylenediamine / sebacic acid, decamethylenediamine / dodecanedioic acid, dodecamethylenediamine / dodecanedioic acid, and dodecamethylenediamine / 2,6-naphthalenedicarboxylic acid. However, not only these but also any other combinations may be used, such as decamethylenediamine / dodecanedioic acid / terephthalic acid, hexamethylenediamine / adipic acid / terephthalic acid, hexamethylenediamine / adipic acid / caprolactam, decamethylenediamine / dodecanedioic acid / ω-aminoundecanoic acid, decamethylenediamine / dodecanedioic acid / laurolactam, decamethylenediamine / terephthalic acid / laurolactam, or dodecamethylenediamine / 2,6-naphthalenedicarboxylic acid / laurolactam.

[0028] PA11 is prepared by polycondensation of ω-aminoundecanoic acid, while PA12 is obtained by ring-opening polymerization of laurolactam. Both polymers are commercially available in various grades.

[0029] PA612 is prepared in a known manner by polycondensation of an equal mixture of hexamethylenediamine and dodecane-1,12-diacid, and PA1010 is prepared in a likewise known manner by polycondensation of an equal mixture of decane-1,10-diamine and decane-1,10-diacid.

[0030] PA1012 is prepared by polycondensation of an equal mixture of decane-1,10-diamine and dodecane-1,12-diacid, while PA1212 is obtained in the same way from dodecane-1,12-diamine and dodecane-1,12-diacid.

[0031] Advantageously, mixtures of different polyamides can also be used here, for example PA12 / PA1012 or PA12 / PA1212. Such mixtures are characterized by particularly high low-temperature impact resistance; they are described, for example, in EP-A-0388583.

[0032] The polyamide molding compositions of layers I, II, IV and V used according to the invention optionally contain further additives as well as the polymer components mentioned. Taking into account the restrictions mentioned below, these further additives are, for example: a) Stabilizers, b) other polymers, c) impact modifiers, d) plasticizers, e) pigments and / or dyes, f) additives that increase conductivity, and g) Processing aids.

[0033] In a preferred embodiment, the molding composition comprises an effective amount of an oxidative stabilizer, more preferably an effective amount of an oxidative stabilizer in combination with an effective amount of a copper-containing stabilizer. Examples of suitable oxidative stabilizers include aromatic amines, sterically hindered phenols, phosphites, phosphonites, sulfur-containing synergists (thiosynergists), hydroxylamines, benzofuranone derivatives, acryl-modified phenols, etc. Most types of such oxidative stabilizers are commercially available, for example under the trade names Naugard 445, Irganox 1010, Irganox 1098, Irgafos 168, P-EPQ or Lowinox DSTDP. Typically, the molding composition contains about 0.01% to about 2% by weight, preferably about 0.1% to about 1.5% by weight of an oxidative stabilizer.

[0034] In addition, the molding compositions may also contain UV stabilizers or light stabilizers of the HALS type. Suitable UV stabilizers are primarily organic UV absorbers, for example benzophenone derivatives, benzotriazole derivatives, oxalanilides or phenyltriazines. HALS-type light stabilizers are tetramethylpiperidine derivatives; these are inhibitors that act as free radical scavengers. UV stabilizers and light stabilizers can advantageously be used in combination. Most types of both are commercially available; the manufacturer's instructions can be followed regarding dosage.

[0035] The molding compositions may additionally comprise hydrolysis stabilizers, for example monomeric, oligomeric or polymeric carbodiimides, or bisoxazolines.

[0036] Examples of further polymers which may be present as additives in the molding composition include polyetheramides or polytetrafluoroethylene (PTFE).

[0037] Impact-modified rubbers for polyamide molding compositions form part of the prior art. They contain functional groups derived from unsaturated functional compounds, which are contained in the main polymer chain or grafted onto the main chain. The most commonly used are EPM or EPDM rubbers that are free-radical grafted with maleic anhydride. Such rubbers can also be used with unfunctionalized polyolefins, such as isotactic polypropylene, as described in EP-A-0683210.

[0038] Plasticizers and their use in polyamides are known. A general overview of plasticizers suitable for polyurethanes can be found in Kunststoffadditive [Plastics additives], C. Hanser Verlag, 2nd edition, page 296.

[0039] Examples of conventional compounds suitable for use as plasticizers include esters of p-hydroxybenzoic acid having 2 to 20 carbon atoms in the alcohol component or amides of arylsulfonic acids having 2 to 12 carbon atoms in the amine component, preferably amides of benzenesulfonic acid.

[0040] Useful plasticizers include ethyl p-hydroxybenzoate, octyl p-hydroxybenzoate, isohexadecyl p-hydroxybenzoate, N-n-octyl toluenesulfonamide, N-n-butylbenzenesulfonamide or N-2-ethylhexylbenzenesulfonamide.

[0041] Examples of suitable pigments and / or dyes include carbon black, iron oxide, zinc sulfide, ultramarine blue, aniline black, pearlescent pigments and metallic flakes.

[0042] Examples of additives that increase conductivity include conductive carbon black or carbon nanotubes.

[0043] Examples of suitable processing aids include alkanes, fatty alcohols, fatty acid amides, stearates such as calcium stearate, paraffins, montanic acid esters or silicones.

[0044] The molding compositions are prepared from the ingredients by melt mixing in a manner known to the person skilled in the art.

[0045] The EVOH of layer III is a copolymer of ethylene and vinyl alcohol. The ethylene content of the copolymer is generally 25 to 60 mol%, in particular 28 to 45 mol%. Many grades are commercially available. See, for example, the company brochure "Introduction to Kuraray EVAL" from Kuraray EVAL Europe. TM Resins", version 1.2 / 9810. In addition to EVOH according to the prior art, the molding compositions may contain further additives customary for barrier layer applications. Such additives are usually part of the know-how of EVOH suppliers.

[0046] When the multilayer composite material according to the present invention is used for the transmission or storage of flammable liquids, gases or dusts, such as fuel or fuel vapor, it is appropriate to make one of the layers forming a part of the composite material conductive. This can be achieved by compounding with a conductive additive by any prior art method. The example of an operable conductive additive includes conductive carbon black, metal flakes, metal powders, metallized glass beads, metallized glass fibers, metal fibers (such as stainless steel), metallized whiskers, carbon fibers (including metallized carbon fibers), intrinsic conductive polymers or graphite fibers. Mixtures of different conductive additives can also be used.

[0047] In the preferred case, the conductive layer is in direct contact with the medium to be transported or stored and has a thickness of no more than 10 9 Ω / square, preferably not more than 106 Specific surface resistance in Ω / square. A measuring method for determining the electrical resistance of multilayer tubes is described in SAE J 2260, November 2004. In this case, layer I is rendered conductive as a whole or it consists of two sublayers, one of which is rendered conductive and the other is not conductive.

[0048] When the multilayer composite material according to the present invention is made into a hollow profile (e.g., a tube) or a container, the composite material can be coated with an additional elastomeric layer. Both the crosslinked rubber composition and the thermoplastic elastomer are suitable for sheathing. The sheathing can be applied to the multilayer composite material with or without an additional tackifier, for example, by coextrusion, extrusion through a crosshead die, or by sliding a prefabricated elastomeric hose over an extruded multilayer tube. The thickness of the sheathing is generally 0.1 to 4 mm, preferably 0.2 to 3 mm.

[0049] Examples of suitable elastomers include chloroprene rubber, ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), epichlorohydrin rubber (ECO), chlorinated polyethylene, acrylate rubber, chlorosulfonated polyethylene, silicone rubber, plasticized PVC, polyetheresteramide or polyetheramide.

[0050] The multilayer composite material can be manufactured in one or more stages, for example by a single stage process of sandwich molding, coextrusion, coextrusion blow molding (for example including 3D blow molding, extruding the parison into open half molds, 3D parison manipulation, suction blow molding, 3D suction blow molding, continuous blow molding) or by a multi-stage process as described in, for example, US 5554425.

[0051] The invention will be illustrated by means of examples in the following experimental part. DETAILED DESCRIPTION

[0052] In the examples, the following components / molding compositions were used: VESTAMID LX9002: Plasticized and impact-modified extrusion molding composition based on PA12 from EVONIK Resource Efficiency GmbH VESTAMID SX8002: Plasticized and impact-modified extrusion molding composition based on PA612 and PA6 from EVONIK Resource Efficiency GmbH VESTAMID SX8001: Plasticized and impact-modified extrusion molding composition based on PA6 from EVONIK Resource Efficiency GmbH EVALF101: EVOH from Kuraray with 32 mol % ethylene.

[0053] Embodiment 1: A five-layer tube with an outer diameter of 8 mm and a total wall thickness of 1 mm was produced by coextrusion with the following layer construction: Layer V: VESTAMID LX9002 Layer IV: VESTAMID SX8002 Tier III: EVALF101 Layer II: Impact-modified extrusion molding composition based on PA612 and PA6, having the following composition: 65.3 wt% PA612 17.5 wt% PA6 16 wt% polyolefin impact modifier 1.2 wt% of stabilizer, and 0.02 wt% calcium stearate as a processing aid Layer I: an impact-modified extrusion molding composition based on PA612 having the following composition: 89.5 wt% PA612 10 wt% polyolefin impact modifier 0.5 wt% of a stabilizer, and 0.02 wt% calcium stearate.

[0054] Comparative Example 1 (According to EP 1216826A2; used in the automotive industry for fuel lines): A four-layer tube with an outer diameter of 8 mm and a total wall thickness of 1 mm was produced by coextrusion with the following layer construction: Layer V: VESTAMID LX9002 Layer IV: VESTAMID SX8002 Tier III: EVALF101 Layer I: VESTAMID SX8001.

[0055] test: a) Tensile test: The multilayer tubes were tested according to DIN EN ISO 527-1 with a takeoff speed of 100 mm / min. The length of the test specimen was about 200 mm, the clamping length was 100 mm, and the strain sensor spacing was 50 mm.

[0056] b) Impact Bending Test: The impact resistance of the multilayer pipes was measured in accordance with DIN 73378 at 23° C. and −40° C. For this purpose, ten pipe sections with a length of approximately 100 mm were used in each case.

[0057] c) Drop weight test: The drop weight test was carried out in accordance with the SAE instructions. This involves allowing a specific weight to fall on a test specimen from a specified drop height. This test is used to determine the impact resistance properties of multilayer tubes under impact according to SAE J2260 and SAE J844. In each case, ten test specimens were measured at -40°C and visually inspected for damage once the test was carried out.

[0058] d) Separation test: The separation test was carried out using a Zwick BZ 2.5 / TN1S tensile testing machine to which a tensile device and a rotating metal wheel were connected so that the layers of the test sample could be separated from each other. The separation test according to DIN EN ISO 2411 was used to determine the adhesion between two layers by measuring the force required to separate the two layers from each other. For this purpose, a tube section of the multilayer tube with a length of 20 cm was longitudinally divided into three parts using a cutting device.

[0059] Before starting the measurement, the sample width is repeatedly measured at different points using a caliper and the average value is entered into the evaluation software.The initially separated end of one layer is then clamped in a clamp that continuously pulls the layer away from the second layer at an angle of 90°.

[0060] The layers are pulled apart at a test speed of 50 mm / min while a graph of the force required in Newtons vs. the displacement in millimeters is recorded. This graph is used to determine the resistance to separation in Newtons per millimeter, which is related to the width of the adhesive contact surface.

[0061] e) Fuel permeability: The permeation measurement is used to determine how much fuel permeates through the fuel line per day and per meter of pipe / square meter of inner pipe area in the case of static storage at 60° C. A pipe section with a length of 300 mm is weighed, then filled with 300 ml of CE10 (composition according to ASTM D471: 45% by volume of toluene, 45% by volume of isooctane and 10% by volume of ethanol) and sealed at both ends. The filled pipe is weighed again in order to be able to determine the mass loss of fuel at specific time intervals and therefore the permeation mass of the fuel. The effective penetration length is 285 mm.

[0062] f) Leaching resistance: Leaching is measured to determine how many grams of soluble and insoluble components are extracted from the multilayer composite after exposure to fuel / m 2Inner tube surface area. To this end, a tube section with a length of 2 m was completely filled with FAM B test fuel (according to DIN 51604-1 / 2) and closed and stored at 60° C. for 96 hours. After cooling, the tube was emptied into a beaker and rinsed with 20 ml of FAM B. The resulting liquid was stored at 23° C. for 24 hours. Thereafter, the test liquid was filtered under reduced pressure at 23° C. and rinsed thoroughly with 20 ml of FAM B. The filtered medium was evaporated at room temperature in a fume hood. The soluble extract was obtained by weighing. The filter was dried at 40° C. for 24 hours and weighed. The insoluble extract was determined by the difference with the original weight of the filter.

[0063] The results are shown in Table 1.

[0064] Table 1 : Layer construction and test results The pipe according to the invention therefore meets the requirements made for fuel lines and has superior leaching resistance compared to the pipes currently used.

Claims

1. A multilayer hollow body comprising the following layers: I. an inner layer (layer I) consisting of a molding composition based on PA11, PA12, PA612, PA1010, PA1012 and / or PA1212 and copolymers thereof and mixtures thereof, which is intended to be in direct contact with the transported or stored medium; II. Adhesion promoter layer (layer II) consisting of a molding composition based on the following components: a) 10 to 60 parts by weight of a polyamide selected from PA6, PA66, PA6 / 66 and mixtures thereof, and c) 30 to 80 parts by weight of a polyamide selected from PA11, PA12, PA612, PA1010, PA1012, PA1212 and mixtures thereof, wherein the sum of the parts by weight of components a) and c) is 100, and wherein in component a), at least 16 parts by weight consist of monomer units derived from caprolactam and / or from the combination of hexamethylenediamine / adipic acid, and in component c), at least 20 parts by weight consist of monomer units derived from ω-aminoundecanoic acid, laurolactam, from the combination of hexamethylenediamine / dodecane-1,12-dioic acid, from the combination of decane-1,10-diamine / decane-1,10-dioic acid, from the combination of decane-1,10-diamine / dodecane-1,12-dioic acid and / or from the combination of dodecane-1,12-diamine / dodecane-1,12-dioic acid; III. Layer composed of ethylene-vinyl alcohol copolymer molding composition (layer III) wherein the molding composition of layer I does not contain any plasticizer and the molding composition of layer II also does not contain any plasticizer and wherein more than 0.2 g / m 2 Insoluble extracts and not more than 7.0g / m 2 of soluble extracts washed out of the multilayer hollow body as a whole upon first exposure to a fuel, which was determined by the method described in the experimental section on multilayer tubes with the same layer structure, a wall thickness of 1 mm and an inner diameter of 6 mm, And wherein the polyamide blend of components a) and c) of layer II is prepared under conditions where the two polyamides react with each other to a certain extent via end groups or via transamidation at temperatures above 280° C. to give block copolymers, and wherein layers I, II and III are directly connected in succession.

2. The multilayer hollow body according to claim 1, characterized in that The polyamide of the molding composition of layer I is PA612.

3. The multilayer hollow body according to claim 1 or 2, characterized in that: It adjoins at least one further layer on the outside.

4. The multilayer hollow body according to claim 3, characterized in that The further layer consists of a polyamide molding composition.

5. The multilayer hollow body according to claim 3, characterized in that A further layer is layer IV comprising the same polyamide combination as layer II.

6. The multilayer hollow body according to claim 3, characterized in that One of the further layers is layer V which follows layer IV and is based on the same polyamide as layer I.

7. The multilayer hollow body according to any one of the preceding claims, characterized in that It is a hollow profile.

8. The multilayer hollow body according to claim 7, characterized in that The hollow profile is a tube or a container.

9. The multilayer hollow body according to claim 7, characterized in that It comprises one or more further layers selected from a conductive layer and an elastomeric covering.

10. The multilayer hollow body according to any one of the preceding claims, characterized in that It is a component of the fuel system.

11. The multilayer hollow body according to claim 10, characterized in that This is a fuel line or a fuel container.

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