EP1937465A1

EP1937465A1 - Polyamide-based antistatic multilayer tube for transferring fluids

Info

Publication number: EP1937465A1
Application number: EP06841983A
Authority: EP
Inventors: Jean-Jacques Flat; Gaëlle Bellet; Nicolas Amouroux; Benoît BRULE
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2005-10-18
Filing date: 2006-10-17
Publication date: 2008-07-02
Also published as: KR20080056228A; JP2009511311A; FR2892173B1; WO2007057584A1; US20090314375A1; BRPI0617667A2; CN101312824B; CN101312824A; FR2892173A1

Abstract

The present invention relates to a multilayer tube comprising, in succession in its radial direction from the outside inwards: a nylon-11 or nylon-12 polyamide outer layer; a tie layer; an optional EVOH layer; an optional layer made of PA-6 or of PA-6/polyolefin blend having a PA-6 matrix and a polyolefin disperse phase; an inner layer based on PA-6 in contact with the transported fluid. According to the invention, the inner layer comprises by weight, the total being 100%: 40% to 65% of PA-6, 0% to 20% of HDPE, 10% to 30% of at least one polymer P1 selected from impact modifiers and polyethylenes, either or both of the HDPE and P1 being completely or partly functionalized, and 5% to 30% of an electrically conductive material. The tube of the present invention has a very low permeability to petrol, particularly to hydrocarbons and to their additives, especially alcohols such as methanol and ethanol or else ethers such as MTBE or ETBE. These tubes also have a very good resistance to fuels and to lubricating oils for engines. This tube has very good mechanical properties at low temperature or at high temperature. The invention also relates to the use of these tubes for transporting petrol.

Description

ANTISTATIC MULTILAYER TUBE BASED ON POLYAMIDE FOR

TRANSFER OF FLUIDS

The present invention relates to a polyamide antistatic multilayer pipe for the transfer of fluids.

By way of example of tubes for the transfer of fluid, mention may be made of the tubes for gasoline, and in particular for bringing gasoline from the tank to the engine of automobiles. By way of other examples of fluid transfer, mention may be made of the fluids used in the fuel cell, the CO 2 system for cooling and air conditioning, the hydraulic systems and the cooling circuit. , air conditioning and power transfers at medium pressure. The circulation of these fluids can generate electrostatic charges, the accumulation of which can lead to an electric shock. This is important for fluids that can ignite easily like gasoline.

For reasons of safety and preservation of the environment, automobile manufacturers impose on these fuel tubes both mechanical characteristics such as bursting resistance and flexibility with good resistance to cold shocks ( -4O ⁰ C) and at high temperature (125 ⁰ C), and also a very low permeability to hydrocarbons and their additives, especially alcohols such as methanol and ethanol. These tubes must also have good resistance to fuels and engine lubricating oils. In motor vehicles, under the effect of the injection pump, gasoline flows at high speed in the pipes connecting the engine to the tank. In some cases, gasoline friction / inner wall of the tube can generate electrostatic charges, the accumulation of which can lead to an electric discharge (spark) capable of igniting gasoline with catastrophic consequences (explosion). Also, it is necessary to make conductive the inner surface of the tube in contact with gasoline.

These tubes are manufactured by coextrusion of the different layers according to the usual techniques of thermoplastics. The present invention more particularly relates to conductive tubes based on polyamides for the transport of gasoline and in particular, to bring the essence of the tank of an automobile to the engine.

Among the characteristics of the specifications of the gasoline tubes, five are particularly difficult to obtain jointly in a simple way:

- Cold shock resistance (-40 ^° C.), the tube does not break,

- fuel resistance.

- resistance to high temperature (125 ° C), - very low permeability to gasoline,

- Good dimensional stability of the tube in use with gasoline.

In multilayer pipes of various structures, the cold impact resistance remains unpredictable before having carried out the cold shock resistance standard tests.

It is known to lower the surface resistivity of resins or polymeric materials by incorporating conductive and / or semiconductor materials such as carbon black, steel fibers, carbon fibers, particles (fibers, plates, spheres). metallized with gold, silver or nickel. Among these materials, carbon black is more particularly used, for economic reasons and ease of implementation. Apart from its particular electroconductive properties, the carbon black behaves like a filler such as, for example, talc, chalk, kaolin, which leads to an increase in the flexural modulus of the polymer in which the black of the black has been added. carbon. Thus, the incorporation of carbon black in a polyamide may weaken it and the tube comprising this layer may no longer resist shock.

The patent application EP 1036967 describes a multilayer tube based on polyamides, characterized in that it comprises in its radial direction from the inside towards the outside:

an inner layer formed of a polyamide or a mixture of polyamide and polyolefin with a polyamide matrix, this layer having a dispersed charge of electroconductive carbon black producing a surface resistivity of less than

10 ⁶ Ω,

an intermediate layer formed of a polyamide or of a mixture of polyamide and polyolefin with a polyamide matrix, this layer not comprising electroconductive carbon black or an electrically significant amount of this carbon black,

a binder layer,

an outer layer of polyamide, the above layers adhering together in their respective contact zone.

According to one particular form, the conductive inner layer contains 60 to 70 parts of polyamide, 5 to 15 parts of a compatibilizer and the complement to 100% of HDPE (high density polyethylene) as well as carbon black. The patent application EP 1036968 describes a multilayer tube based on polyamides, characterized in that it comprises in its radial direction from the inside to the outside:

a first layer (1) formed of a mixture of polyamide P 1 and polyolefin Pfji with polyamide matrix P ₁ or a first layer (1) formed of a polyamide P 1,

a layer (2a) formed of EVOH,

a layer (2) formed of a copolyamide,

a layer (3) formed of a polyamide P3,

^P 1 ^{and P} 3 may be identical or different, the layers (1), (2a) (2) and (3) being successive and adhering to each other in their respective contact zone.

According to one particular form, the conductive inner layer contains 60 to 70 parts of polyamide, 5 to 15 parts of a compatibilizer and the complement to 100% of HDPE (high density polyethylene) as well as carbon black. The patent application US 2002/0142118 describes a gas tube comprising going from the outside to the inside: an outer layer of PA 6.12, a binder layer based on polyamide polyamine, a layer of EVOH and an inner layer of PA 6 in contact with the gasoline. The PA layer 6 may be conductive; no details are given on its composition. It has now been found that, in the preceding tubes comprising, starting from the outside, a polyamide layer, a binder layer, optionally an EVOH layer, a conductive inner layer in contact with the transported fluid and optionally one or Several other layers, subjected to shocks or other equivalent mechanical stresses, cracks could appear and spread throughout the structure. It was found that the inner layer in contact with the transported fluid had to be formulated in such a way that it could not cause cracking of the tube.

It has also been discovered that the inner layer in contact with gasoline must necessarily contain HDPE to improve the barrier to gasoline.

The present invention relates to a multilayer tube of the above type, successively comprising in its radial direction from the outside to the inside: an outer layer (1) of polyamide 11 or 12,

a binder layer (2),

an optional layer (3) of EVOH,

a possible layer (4) of PA 6 or of a mixture of PA 6 and polyolefin with matrix PA 6 and polyolefin dispersed phase; - an inner layer (5) based on this PA 6 in contact with the transported fluid.

According to the invention, the inner layer (5) in contact with the transported fluid comprises by weight, the total being 100%:

from 40 to 65% (advantageously from 45 to 60%) of PA 6, from 0 to 20%, advantageously from 1 to 20% (preferentially from 5 to

15%) of HDPE, from 10 to 30% (advantageously 15 to 25%) of at least one polymer P1 chosen from impact modifiers and polyethylenes, at least one of HDPE and P1 being functionalized in whole or in part,

from 5 to 30% (advantageously 15 to 30%, preferably 17 to 24%) of an electroconductive material.

Such an inner layer composition (5) makes it possible to produce a multilayer tube which not only perfectly meets the requirements of the specifications of the gasoline tubes as stated above, but which also has electroconductive properties while retaining cold ductility properties.

Thus, the multilayer pipe according to the invention simultaneously has very good conductive and mechanical properties; it is observed in particular that no breakage of multilayer pipes occurs during impact tests at -40 ° C. In a particular form, the PA-based inner layer 6 in contact with the transported fluid comprises by weight, the total being 100%:

from 45 to 49% of PA 6,

- from 8 to 12% of HDPE,

from 18 to 22% of at least one polymer P1 chosen from impact modifiers and polyethylenes, at least one of HDPE and P1 being functionalized in whole or in part,

from 20 to 24% of an electroconductive material.

These proportions of electroconductive material in the composition of the inner layer, comprised between 5 and 30% by weight, advantageously between 15 and 30%, preferably between 17 and 24% and even more preferably between 20 and 24%, make it possible to obtain a surface resistivity of less than 10 ⁶ Ω, the value required for an electroconductive multilayer pipe. The surface resistivity can also be expressed in Ohm / square (Ohm / square), this unit has the dimension of Ohms. These tubes may have an outside diameter of 6 to 10 mm and a thickness of the order of 0.5 to 5 mm. Advantageously, the gasoline tube according to the invention has an outside diameter ranging from 6 to 12 mm, a total thickness of 0.8 mm to 2.5 mm. The thickness of the outer layer (1) is between 25 and 60% of the thickness of the tube. The thickness of all the layers (4) and (5) represents 30 to 50% of the thickness of the tube. If the layer (4) is present, the thickness of the layer (5) advantageously represents 5 to 20% of the thickness of the set of layers (4) and (5).

The tube of the present invention is very little permeable to gasoline, in particular hydrocarbons and their additives, such as alcohols such as methanol and ethanol, or even ethers such as MTBE or ETBE. These tubes also have good resistance to fuels and engine lubricating oils.

This tube has very good mechanical properties at low or high temperature. This tube has excellent electrical properties before and after contact with gasoline. This tube meets the SAE standard J1645 in particular.

The invention also relates to the use of these tubes for transporting gasoline.

As regards the polyamide of the outer layer (1), its inherent viscosity may be between 1 and 2 and advantageously between 1, 2 and 1.8. The inherent viscosity is measured at 20 ° C for a concentration of 0.5% in meta-cresol. The polyamide of the outer layer (1) may contain from 0 to 30% by weight of at least one product chosen from plasticizers and impact modifiers for 100 to 70% of polyamide, respectively. This polyamide may contain the usual additives, such as anti-UV, stabilizers, antioxidants, flame retardants, etc.

The polyamide of the outer layer (1) may contain at least one product chosen from plasticizers, impact modifiers and catalysed or uncatalyzed polyamides.

As regards the plasticizer, it is chosen from benzene sulphonamide derivatives, such as n-butyl benzene sulphonamide (BBSA), ethyl toluene sulfonamide or N-cyclohexyl toluene sulfonamide; esters of hydroxy-benzoic acids, such as 2-ethylhexyl parahydroxybenzoate and 2-decyl hexyl parahydroxybenzoate; esters or ethers of tetrahydrofurfuryl alcohol, such as oligoethyleneoxytetrahydrofurfurylalcohol; esters of citric acid or of hydroxy-malonic acid, such as oligoethyleneoxy malonate. Mention may also be made of decyl hexyl parahydroxybenzoate and ethyl hexyl parahydroxybenzoate. A particularly preferred plasticizer is n-butyl benzene sulfonamide (BBSA).

As regards the impact modifier, mention may be made, for example, of polyolefins, crosslinked polyolefins and elastomers EPR, EPDM, SBS and SEBS, these elastomers being graftable to facilitate their compatibilization with polyamide, polyamide block copolymers and polyether blocks. . These polyamide block and polyether block copolymers are known per se; they are also designated by the name PEBA (polyether block amide) and sold by the applicant under the name PEBAX®. Acrylic elastomers can also be mentioned, for example those of the NBR, HNBR or X-NBR type. Polyolefins useful as impact modifiers are, for example, ethylene-alkyl (meth) acrylate-maleic anhydride copolymers (or glycidyl methacrylate). They are sold by the plaintiff under the name of Lotader®. As regards the catalyzed polyamide, it is a polyamide containing a polycondensation catalyst such as a mineral or organic acid, for example phosphoric acid. The catalyst can be added to the polyamide after it has been prepared by any method, or simply, and it is preferred, to be the remainder of the catalyst used for its preparation. Polymerization and / or depolymerization reactions may be very substantially carried out during the mixing of this catalyzed polyamide and the polyamide of the outer layer. The amount of catalyst may be between 5 ppm and 15000 ppm of phosphoric acid relative to the catalyzed polyamide. The amount of catalyst can be up to 3000 ppm and advantageously between 50 and 1000 ppm. For other catalysts, for example boric acid, the contents will be different and can be chosen suitably according to the usual polycondensation techniques of polyamides.

The proportion of plasticizer may be (by weight) between 0 and 15%

(advantageously between 4 and 8%), the impact modifier between 0 and 20% (advantageously between 5 and 15%), the polyamide catalysed between 0 and 20%

(advantageously between 10 and 20% and preferably between 12 and 17%), and the complement to 100% polyamide of the outer layer.

Advantageously, the polyamide of the outer layer is PA 12. If catalyzed polyamide is added in this polyamide, then this catalyzed polyamide is advantageously PA 1 1.

As regards the compositions of the outer layer, they may be prepared by melt blending of the constituents according to the usual techniques of thermoplastics. The outer layer may also include usual additives polyamides such as UV stabilizers, antioxidants, pigments, flame retardants.

As regards the layer (2) of binder, is meant any product for adhesion of the layers together. By way of example, grafted polyolefins and copolyamides may be mentioned. By way of example, mention may be made of copolyamide 6/12, which is a copolyamide of caprolactam and lauryllactam. The proportions of caprolactam and lauryllactam can vary from 20 to 80% of caprolactam for 80 to 20% of lauryllactam respectively. Advantageously, it is a mixture of a 6/12 copolyamide rich in 6 and a 6/12 copolyamide rich in 12. With regard to the 6/12 copolyamide mixture, one comprising by weight more than 6 that of 12 and the other more than 12 than 6, copolyamide 6/12 results from the condensation of caprolactam with lauryllactam. It is clear that "6" refers to the motifs derived from caprolactam and "12" refers to the motifs derived from lauryllactam. It would not be outside the scope of the invention if caprolactam was replaced in whole or in part by aminocaproic acid; likewise, lauryllactam could be replaced in whole or in part by aminododecanoic acid. These copolyamides may include other reasons, provided that the ratios of proportions of 6 and 12 are respected.

Advantageously, the copolyamide rich in 6 comprises 50 to 90% by weight of 6 for respectively 50 to 10% of 12. Advantageously, the copolyamide rich in 12 comprises 50 to 90% by weight of 12 for respectively 50 to 10% of 6.

As for the proportions of the 6-rich copolyamide and the 12-rich copolyamide, they can be, by weight, 30/70 to 70/30 and, preferably,

40/60 to 60/40. These copolyamide mixtures may also comprise up to 30 parts by weight of other (co) polyamides or grafted polyolefins per 100 parts of the 6-rich and 12-rich copolyamides.

These copolyamides have a melting temperature (DIN 53736B standard) of between 60 and 200 ° C. and their relative viscosity in solution can be between 1, 3 and 2.2 (DIN 53727 standard, solvent m-cresol, concentration

0.5 g / 100 ml, temperature 25 ° C., Ubbelohde viscometer). Their rheology in the molten state is preferably close to that of the materials of the adjacent layers. These products are manufactured by the usual techniques of polyamides. Processes are described in US 4424864, US 4483975, US 4774139, US 5459230, US 5489667, US 5750232 and US

5254641.

Mention may also be made of the binders described in the US patent application

2002/01421 18 whose content is incorporated in the present application. They are polyamines polyamines prepared from polyamines having at least 4 nitrogen atoms and either lactams or a mixture of diamines and diacids. These polyamines polyamines can be mixed with polyamides such as PA 12, PA 6.12 and possibly impact modifiers such as EPR and grafted EPR.

This binder layer may contain stabilizers. According to one form of the invention, this binder layer may contain at least one impact modifier. This impact modifier can be chosen from the impact modifiers described above for the outer layer (1). Regarding the layer (3), the EVOH copolymer is also called saponified ethylene-vinyl acetate copolymer. The saponified ethylene-vinyl acetate copolymer to be used according to the present invention is a copolymer having an ethylene content of 20 to 70 mol%, preferably 25 to 45 mol%, the degree of saponification of its vinyl acetate component. not less than 95 mol%. Of these saponified copolymers, those having melt indexes in the range of 0.5 to 100 g / 10 minutes are particularly useful. Advantageously, the MFI is chosen between 5 and 30 (g / 10 min at 230 ° C. under 2.16 kg). "MFI" abbreviation for "MeIt Flow Index" designates the melt flow index.

It is understood that this saponified copolymer may contain small proportions of other comonomer ingredients, including α-olefins such as propylene, isobutene, α-octene, α-dodecene, α-octadecene, etc., unsaturated carboxylic acids or their salts, partial alkyl esters, complete alkyl esters, nithles, amides and anhydrides of said acids, and unsaturated sulfonic acids or their salts.

The EVOH layer may consist of EVOH-based mixtures. As for EVOH-based blends, they are such that EVOH forms the matrix, ie it represents at least 40% by weight of the mixture and preferably at least 50%. The other constituents of the mixture are chosen from polyolefins, polyamides, impact modifiers, optionally functionalized. The impact modifier can be chosen from elastomers, copolymers of ethylene and an olefin having from 4 to 10 carbon atoms (for example ethylene-octene copolymers) and very low density polyethylenes. Examples of elastomers include EPR and EPDM. EPR (abbreviation for Ethylene Propylene Rubber) refers to ethylene-propylene elastomers and EPDM refers to ethylene-propylene-diene monomer elastomers. By way of example, mention may be made of mixtures comprising, by weight, 50 to 95% of EVOH for respectively 50 to 5% of grafted EPR, advantageously 60 to 95% of EVOH for respectively 40 to 5% of EPR. grafted and preferably 75 to 95% of EVOH for 25 to 5% of grafted EPR, respectively.

By way of example of the mixtures based on EVOH, mention may also be made of compositions comprising: 50 to 95% by weight of an EVOH copolymer,

- 5 to 50% by weight of an elastomer ά / entuellement functionalized in whole or part or a mixture of a functionalized elastomer and another nonfunctional elastomer.

As regards the layer (4), it may be PA 6 or a mixture of PA 6 and PA polyolefin matrix 6 and polyolefin dispersed phase. In PA 6 and polyolefin PA 6 and polyolefin dispersed phase mixtures, the term polyolefin refers to both homopolymers and copolymers, thermoplastics as well as elastomers. It is for example copolymers of ethylene and an alphaolefin. These polyolefins may be PE, EPR EPDM. They can be functionalized in whole or in part. The dispersed phase may be a mixture of one or more non-functionalized polyolefins and one or more functionalized polyolefins. Advantageously, the matrix PA 6 represents 50 to 85% by weight for respectively 50 to 15% of dispersed phase. Preferably, the matrix PA 6 represents 55 to 80% by weight for respectively 45 to 20% of dispersed phase.

In a preferred form, the mixtures of PA 6 and polyolefin matrix PA 6 comprise by weight, the total being 100%: 50 to 90% (advantageously 60 to 80%) of PA 6,

1 to 35% (advantageously 10 to 30%) of HDPE, 1 to 30% (advantageously 5 to 25%) of at least one polymer P1 chosen from impact modifiers and polyethylenes, at least one of HDPE and P1 being functionalized in whole or in part. Advantageously, the impact modifier is chosen from elastomers and very low density polyethylenes. As regards the impact modifier and first of elastomers, mention may be made of SBS, SIS, SEBS block polymers and ethylene / propylene elastomers.

(EPR) or ethylene / propylene / diene (EPDM). As for very low density polyethylenes, they are, for example, metallocenes with a density of, for example, between 0.860 and 0.900.

Advantageously, an ethylene / propylene (EPR) or ethylene / propylene / diene (EPDM) elastomer is used. The functionalization may be provided by grafting or copolymerization with an unsaturated carboxylic acid.

It would not depart from the scope of the invention using a functional derivative of this acid. Examples of unsaturated carboxylic acid are those having 2 to 20 carbon atoms such as acrylic, methacrylic, maleic, fumaric and itaconic acids. Functional derivatives of these acids include, for example, anhydrides, ester derivatives, amide derivatives, imide derivatives and metal salts (such as alkali metal salts) of unsaturated carboxylic acids.

Unsaturated dicarboxylic acids having 4 to 10 carbon atoms and their functional derivatives, particularly their anhydrides, are particularly preferred grafting monomers. Maleic anhydride is advantageously used. The proportion of all of the functionalized HDPE and functionalized P1 with respect to the entire functionalized and non-functionalized HDPE and functionalized and non-functionalized P1 may be comprised (by weight) of between 1 and 80%, advantageously between 5 and 70% and preferably between 20 and 70%. Otherwise expressed, the proportion of HDPE and P1 which are functionalized relative to the total amount of HDPE and P1 may be comprised (by weight) of between 1 and 80%, advantageously between 5 and 70% and preferably between 20 and 70%. .

The mixtures of PA 6 and polyolefin matrix PA 6 may be prepared by mixing the various constituents in the molten state in the usual apparatus of the thermoplastic polymer industry. According to a first form of these PA 6 and polyolefin PA 6 matrix blends, the HDPE is not grafted and P1 is a mixture of a grafted elastomer and an ungrafted elastomer.

According to another form of these mixtures of PA 6 and PA 6 polyolefin matrix, the HDPE is not grafted and P1 is a grafted polyethylene optionally mixed with an elastomer.

As an example of P1, mention may also be made of: a mixture (A) of at least one high-density polyethylene (A1) and at least one copolymer of ethylene (A2), the mixture of (A1) and (A2) being cografted with a monomer such as an acid or an unsaturated carboxylic acid anhydride or derivatives thereof and said mixture (a) having a ratio cografted Ml ₁₀ / Ml ₂ greater than 18.5 (MI ₁ denoting O the flow index at 190 ° C under a load of 10 kg and M1 ₂ the index under a load of 2.16 kg).

(A2) may be selected from EPR, VLDPE, ethylene / alkyl (meth) acrylate copolymers or ethylene / alkyl (meth) acrylate / maleic anhydride copolymers.

Advantageously, the Ml ₁₀ / Ml ₂ ratio is less than 35 and preferably between 22 and 33.

Advantageously, the MI ₂₀ of the mixture (A) of the polymers (A1) and (A2) co-grafted is less than 24, MI ₂₀ denoting the melt index at 190 ° C under a load of 21 6 kg.

The layer (4) may contain stabilizers and one or more plasticizers.

Regarding the inner layer (5), the polymer P1 has already been described in the layer (4) above. The polymer P1 of the layer (5) and that of the layer (4) may be identical or different. The proportions of HDPE and functionalized P1 with respect to the total amount of HDPE and P1 can be chosen within the ranges of values mentioned for the layer (4) above. As an example of an electroconductive material, there may be mentioned carbon black, carbon fibers and carbon nanotubes. It is advantageous to use a carbon black chosen from those having a BET specific surface area, measured according to ASTM D3037-89, of from 5 to 200 m 2 / g, and a DBP absorption, measured according to the ASTM D 2414-90 standard, of 50 to 300 ml / 100g. These carbon blacks are described in the patent application WO 99-33908, the content of which is incorporated in the present application.

The layer (5) may contain stabilizers and one or more plasticizers.

Five inner layer compositions (5) were prepared. The various compounds entering into each of the compositions are detailed in the table below.

Carbon black is supplied by Timcal under the name "Ensaco 250 Granular". The DBP absorption is 190 ml / g and the BET surface is about 65 m ² / g.

The compatibilizer is a maleic anhydride grafted ethylene copolymer.

On a multi-layer Mc Neil® equipment at 20m / min, five tubes of 8mm outer diameter and 1mm thickness of the following structure were extruded: PA12 (outside) / binder / EVOH / layer (4) / layer (5) and thickness (in μm) of layers 400 (outside) / 50/100/400/50.

The tubes 1 to 5 are identical to each other, with the exception of the composition of the inner layer, as described in Ex. 1 to 5 respectively.

The binder is a mixture of (i) 40% by weight of 6/12 copolyamide with 40% of 6 unit and (ii) 60% of 6/12 copolyamide with 70% of 6 unit.

EVOH denotes a copolymer EVOH with 32mol% of ethylene sold under the name Soarnol® DC3203F by Nippon Goshei.

The layer (4) consists of a mixture of 65% of PA 6, 15% of HDPE and 20% of grafted EPR also comprising antioxidants.

All structures were extruded on multi-layer Mc Neil® equipment at 20m / min. Unless otherwise indicated, percentages are by weight.

For each series of tubes 1 to 5, the surface resistivity of the layer (5) was measured to evaluate the electrical properties of the tubes, and the impact test at -40 ° C of GM (General Motors) and of the VW (Volkswagen) standard to evaluate their mechanical properties. The results obtained are shown in the following table:

If for the tubes 1 to 3, according to the invention, the resistivity is much lower than 10 ⁶ ohms, this is not the case for the tube 4 which comprises only a low weight percentage of carbon black (4 % by weight of the total composition). In addition, the tubes 1 to 3 in accordance with the invention pass the impact test at -40 ° C. of the GM standard (General Motors) and the VW (Volkswagen) standard, unlike the tube 5.

Claims

1. Multilayer pipe comprising successively in its radial direction from the outside to the inside: an outer layer (1) of polyamide 11 or 12,

. a binder layer (2), an optional layer (3) of EVOH,

. an optional layer (4) of PA 6 or of a mixture of PA 6 and polyolefin with PA 6 matrix and polyolefin dispersed phase, an inner layer (5) based on PA 6 in contact with the transported fluid, characterized in that the inner layer (5) based on PA 6 comprises by weight, the total being 100%:

from 40 to 65% of PA 6,

from 0 to 20% of HDPE, advantageously from 1 to 20% of HDPE, from 10 to 30% of at least one polymer P1 chosen from impact modifiers and polyethylenes, at least one of HDPE and P1 being functionalized in whole or in part,

from 5 to 30% of an electroconductive material.

2. Tube according to claim 1 wherein the proportions of the layer (5) are, the total being 100%:

45 to 60% PA 6,

- 5 to 15% of HDPE,

15 to 25% of at least one polymer P1 chosen from impact modifiers and polyethylenes, at least one of HDPE and P1 being functionalized in whole or in part,

- 5 to 30% of an electroconductive material.

3. Tube according to claim 1 or 2 wherein the proportion of electroconductive material of the layer (5) is between 15 and 30%.

4. Tube according to claim 3 wherein the proportion of electroconductive material of the layer (5) is between 17 and 24%.

5. Tube according to any one of claims 1 to 4 wherein in the layer (4) mixtures of PA 6 and polyolefin matrix PA 6 comprise by weight, the total being 100%:

50 to 90% of PA 6,

- 1 to 35% of HDPE,

- 1 to 30% of at least one polymer P1 selected from impact modifiers and polyethylenes, at least one of HDPE and P1 being functionalized in whole or in part.

The tube of claim 5 wherein the proportions of the layer (4) are, the total being 100%: 60 to 80% PA 6,

- 10 to 30% of HDPE,

- 5 to 25% of at least one polymer P1 selected from impact modifiers and polyethylenes, at least one of HDPE and P1 being functionalized in whole or in part.

7. Tube according to any one of claims 1 to 6, characterized in that the composition of the inner layer (5) further comprises at least one additive selected from plasticizers and stabilizers.

8. Use of a tube according to any one of claims 1 to 7 for the transport of gasoline.