WO2006042763A1

WO2006042763A1 - Multilayer tube based on a polyamide and a fluoropolymer for transferring fluids

Info

Publication number: WO2006042763A1
Application number: PCT/EP2005/011795
Authority: WO
Inventors: Nicolas Amouroux; Gäelle BELLET; Anthony Bonnet; Fabrice Chopinez
Original assignee: Arkema France
Priority date: 2004-10-19
Filing date: 2005-10-18
Publication date: 2006-04-27

Abstract

The present invention relates to a multilayer tube comprising, in its radial direction from the outside inwards: a polyamide outer layer (1); an inner layer (2) of a composition comprising, the total being 100%, 5 to 30% by weight of a blend (A) comprising: a polyethylene carrying epoxy functional groups, an impact modifier chosen from elastomers and very low density polyethylenes, the said impact modifier being completely or partly functionalized; 95 to 70% by weight of a blend (B) comprising: a fluoropolymer (B1), a functionalized fluoropolymer (B2), the proportion of (B2) being between 1 and 80% by weight of (A)+(B), the layers being successive and adhering to one another in their respective contact region. The inner layer is the layer in contact with the fluid being transported. According to one advantageous embodiment, a layer of functionalized polyolefin having functional groups capable of reacting with the functional groups of the fluoropolymer (B2) is placed between the layer (2) and the layer (3). The tube of the present invention has a very low permeability to the cooling liquid and to its additives (boric acid and its salts). These tubes also exhibit good resistance to fuels and to engine lubrication oils. This tube exhibits very good mechanical properties at low temperature and at high temperature. These tubes may be smooth or corrugated. The invention also relates to the use of these tubes for transporting cooling liquids.

Description

MULTILAYER TUBE BASED ON A POLYAMIDE AND A FLUORQf^LYMER

FOR TRANSFERRING FLUIDS

Field of the invention

The present invention relates to a multilayer tube based on a polyamide and a fluoropolymer for transferring fluids.

As examples of tubes for transferring fluids, mention may be made of petrol pipes, in particular for carrying petrol from the tank to the engine of motor vehicles. As other examples of fluid transfer, mention may be made of the fluids used in fuel cells, CO2 systems for cooling, hydraulic systems, cooling circuits and air-conditioning circuits, and medium-pressure power transfer.

For safety and environmental protection reasons, motor-vehicle manufacturers require these tubes to have not only mechanical properties such as burst strength and flexibility with good cold (-40⁰C) impact strength and high- temperature (125°C) strength, but also a very low permeability to hydrocarbons and to their additives, particularly alcohols such as methanol and ethanol. These tubes must also have good resistance to the fuels and lubrication oils for engines. These tubes are manufactured by coextruding the various layers using standard techniques for thermoplastics.

One particular use relates to tubes for cooling circuits of internal combustion engines, such as engines for cars or lorries. The cooling liquids are in general aqueous solutions of alcohol such as, for example, ethylene glycol, diethylene glycol or propylene glycol. These tubes must also have good mechanical strength and withstand the environment of the engine (temperature, possible presence of oil). They may be smooth (of constant diameter) or corrugated, or they may have corrugated parts and smooth parts.

The content of french appln 04-11188 filed on 20 oct 04, french appln 04- 11571 filed on 29 oct 04, french appln 04-11074 filed on 19 oct 04 and US provisionnal specification 60/ 647055 filed on 26 jan 05 are incorporated in this application.

Prior art and the technical problems Patent US 5 560 398 describres tubes for a cooling circuit, which consist of an outer polyamide layer and an inner layer chosen from polyolefins, fiuoropoiymers, polyesters and EVAs (ethyiene/vinyi acetate copolymers).

Patent US 5 716 684 discloses tubes for cooling circuits, consisting of an outer polyamide layer, a tie consisting of a polyvinylidene fluoride/polyamide blend, and an inner layer made of polyvinylidene fluoride.

Patent US 5 706 864 discloses tubes for cooling circuits, which consist of an outer polyamide layer and an inner layer either made of PVDF or a polyolefin or a polyolefin grafted by a carboxylic acid anhydride. A tie must be placed between these two layers if the external layer is a polyamide and the internal layer a PVDF.

Patent US 5 850 855 discloses tubes for cooling circuits, which consist, in this order, of an outer layer made of an amine-terminated polyamide, a layer of polyethylene grafted by maleic anhydride, and an inner layer made of a polyolefin or HDPE (high-density polyethylene) grafted by silanes. As a variant, they consist, in this order, of an outer layer of an amine-terminated polyamide, a layer of polypropylene grafted by maleic anhydride, and an inner layer that is a polypropylene/EPDM (ethylene-propylene-diene monomer) elastomer blend. Patent EP 1 104 526 discloses a tube having, along its radial direction from the inside outwards, an inner layer, based on a fluororesin (or fluoropolymer) and intended to come into contact with a flowing fluid, characterized in that the inner layer is formed from a blend comprising a semicrystalline thermoplastic fluororesin (for example PVDF) and an ABC triblock copolymer, the three blocks A, B and C being linked together in this order, each block being either a homopolymer or a copolymer obtained from two or more monomers, block A being connected to block B and block B being connected to block C by means of a covalent bond or by an intermediate molecule linked to one of these blocks via a covalent bond or to the other block via another covalent bond, and in that:

-block A is compatible with the fluororesin; -block B is incompatible with the fluororesin and is incompatible with block A;

-biock C is incompatibie with the fiuororesin, biock A and block B; the outer layer of the tube being made of a polyamide. This PVDF-based layer is impact-resistant while still remaining a barrier to petrol. However, adhesion to the polyamide layer remains to be provided.

In all the above structures, the use of a tie is necessary when a PA layer is coextruded with a PVDF layer. These ties have a low resistance to the fluids being transported, resulting in premature ageing of the multilayer structure. Moreover, the use as an internal layer of PVDF poses the problem of the cold impact strength of the structure. The use of conventional impact modifiers for PVDF does appreciably improve the cold impact strength, but it substantially reduces its chemical resistance and increases its permeability to the fluids being transported. The prior art has already disclosed tubes comprising a polyamide outer layer and at least one other layer made of PVDF. In these tubes of the prior art, complicated compositions have been disclosed for ensuring adhesion of the polyamide to the PVDF. In addition, these tubes are not used for cooling liquids.

Patent EP 558 373 discloses a tube for transporting petrol, which respectively comprises a polyamide outer layer, a tie layer and an inner layer in contact with the petrol and consisting of a fluoropolymer.

Patents EP 696 301, EP 740 754 et EP 726 926 disclose tubes for transporting petrol, which comprise respectively a polyamide outer layer, a tie layer, a PVDF (polyvinylidene fluoride) layer, a tie layer and a polyamide inner layer in contact with the petrol.

Other polyamide/PVDF-based tubes for transporting petrol are disclosed in Patents US 5 472 784, US 5 474 822, US 5 500 263, US 5 510 160, US 5 512 342 and US 5 554426.

A functional-fluoropolymer-based blend has now been found that is capable of adhering directly to polyamides, making it possible to produce multilayer structures that are particularly well-suited for transporting fluids. The composition exhibits excellent resistance to solvents, alcoholic fuels and cooling liquid and also a very low permeability. The invention also relates to impact modification made possible by the functionalization of the fluoropolymer by impact modifiers that are insensitive to the fluids being transported.

Brief description of the invention

The present invention relates to a multilayer tube comprising, in its radial direction from the outside inwards: a polyamide outer layer (1 ); an inner layer (2) of a composition comprising, the total being 100%, 5 to

30% by weight of a blend (A) comprising: a polyethylene carrying epoxy functional groups, an impact modifier chosen from elastomers and very low- density polyethylenes, the said impact modifier being completely or partly functionalized;

95 to 70% by weight of a blend (B) comprising: a fluoropolymer (B1 ), a functionalized fluoropolymer (B2), the proportion of (B2) being between 1 and 80% (advantageously 1 and 60%) by weight of (A)+(B), the layers being successive and adhering to one another in their respective contact region. The inner layer is the layer in contact with the transported fluid. In a specific embodiment it has been discovered that a very strong and cohesive adhesion can be attained when (B1 ) is a flexible fluoropolymer. The term flexible fluoropolymer relates to a fluoropolymer having a tensile modulus between 50 and 1000 MPa (as measured according to ISO R 527 at 23°C), preferably between 100 and 750 MPa and even more preferably between 200 and 600 MPa.

Another embodiment relates to a multilayer tube comprising, in its radial direction from the outside inwards: a polyamide outer layer (1 ); a layer (2) of a composition comprising, the total being 100%, 0 to 30% by weight of a blend (A) comprising: a polyethylene carrying epoxy functional groups, an impact modifier chosen from elastomers and very low-density polyethylenes, the said impact modifier being completely or partly functionalized;

100 to 70% by weight of a blend (B) comprising: optionally, a fluoropolymer (B1), a functionalized fluoropolymer (B2), the proportion of (B2) being between 10 and 100%, advantageously 30 to 90% and preferably 40 to 75%, by weight of (A)+(B); a polyolefin inner layer (3); the layers being successive and adhering to each other in their respective contact region. The inner layer is in contact with the transported fluid. In a specific embodiment it has been discovered that a very strong and cohesive adhesion can be attained when (B1 ) is present and is a flexible fluoropolymer. The term flexible fluoropolymer relates to a fluoropolymer having a tensile modulus between 50 and 1000 MPa (as measured according to ISO R 527 at 23⁰C), preferably between 100 and 750 MPa and even more preferably between 200 and 600 MPa.

According to one advantageous embodiment, a layer of functionalized polyolefin having functional groups capable of reacting with the functional groups of the fluoropolymer (B2) is placed between the layer (2) and the layer

(3). According to one advantageous embodiment, the polyamide of the outer layer (1) is a polyamide having amine terminal groups or comprising more amine terminal groups than acid terminal groups.

According to one advantageous embodiment, a layer of a polyamide having amine terminal groups or one comprising more amine terminal groups than acid terminal groups is placed between the outer layer (1 ) and the layer

(2). According to another embodiment, these two preceding embodiments may be combined.

These tubes may have an outside diameter of 6 to 110 mm and a thickness of around 0.5 to 5 mm. Advantageously, the tube for cooling liquids according to the invention has an outside diameter ranging from 8 to 40 mm and a total thickness of 0.8 to 2.5 mm. The outer layer (1 ) represents between 30 and 80% of the thickness of the tube. In the tubes having an inner layer (3), the thickness of the outer layer (1 ) represents between 25 and 50% of the thickness of the tube. The tube of the present invention has a very low permeability to the cooling liquid and to its additives (boric acid and its salts). These tubes also exhibit good resistance to fuels and to engine lubrication oils.

This tube exhibits very good mechanical properties at low temperature and at high temperature. These tubes may be smooth or corrugated. The invention also relates to the use of these tubes for transporting cooling liquids.

Detailed description of the invention

The tubes having a fluoropolymer-based inner layer (2) will firstly be described.

With regard to the polyamide of the outer layer (1), mention may be made of PA-11 and PA-12. Mention may also be made of those of formula X, Y/Z or 6, Y2/Z in which:

X denotes the residues of an aliphatic diamine having from 6 to 10 carbon atoms;

Y denotes the residues of an aliphatic dicarboxylic acid having from 10 to 14 carbon atoms;

Y2 denotes the residues of an aliphatic dicarboxylic acid having from 15 to 20 carbon atoms; and Z denotes at least one unit chosen from the residues of a lactam, the residues of an alpha, omega-aminocarboxylic acid, the unit X1 ,Y1 in which X1 denotes the residues of an aiiphatic diamine and Yi denotes the residues of an aliphatic dicarboxylic acid, the weight ratios Z/(X+Y+Z) and Z/(6+Y2+Z) being between 0 and 15%.

Mention may be made by way of example of PA-6, 10

(hexamethylenediamine and sebacic acid units), PA-6, 12

(hexamethylenediamine and dodecanedioic acid units), PA-6, 14

(hexamethylenediamine and C14 diacide), PA-6, 18 (hexamethylenediamine and C18 diacide) and PA-10, 10 (1 , 10-decane diamine and sebacic acid units).

Mention may also be made of polyamides of formula XTY₁Ar in which: « Y denotes the residues of an aliphatic diamine having from 8 to 20 carbon atoms; β Ar denotes the residues of an aromatic dicarboxycylic acid; • X denotes either the residues of aminoundecanoic acid NH2-(CH2)iθ"

COOH, of lactam 12 or of the corresponding amino acid, or the unit Y,x remains from the condensation of the diamine with an aliphatic diacid (x) having between 8 and 20 carbon atoms or else the unit Y, I remains from the condensation of the diamine with isophthalic acid. X/ Y₁Ar denotes, for example:

- 11/10₁T, which results from the condensation of aminoundecanoic acid, 1 ,10-decanediamine and terephthalic acid;

- 12/12.T, which results from the condensation of lactam 12, 1 ,12-dodecanediamine and terephthalic acid; - 10,10/10,T, which results from the condensation of sebacic acid,

1 ,10-decanediamine and terephthalic acid; and

- 10,l/10,T, which results from the condensation of isophthalic acid, 1 ,10-decanediamine and terephthalic acid.

The inherent viscosity of the polyamide of the outer layer (1 ) may be between 1 and 2 and advantageously between 1.2 and 1.8. The inherent viscosity is measured at 2O⁰C for a 0.5% concentration in metacresol. 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 per 100 to 70% of polyamide respectively. This polyamide may contain the usual additives, such as UV stabilizers, thermal stabilizers, antioxidants, fire retardants, etc.

^" With regard to blend (A) and firstly the polyethylene carrying epoxy functional groups, this may be a polyethylene onto which epoxy functional groups have been grafted or an ethylene/unsaturated epoxide copolymer.

With regard to ethylene/unsaturated epoxide copolymers, mention may be made, for example, of copolymers of ethylene with an alkyle (meth)acrylate and with an unsaturated epoxide, or copolymers of ethylene with a vinyl ester of a saturated carboxylic acid and with an unsaturated epoxide. The amount of epoxide may be up to 15% by weight of the copolymer and the amount of ethylene at least 50% by weight. Advantageously, the proportion of epoxide is between 2 and 12% by weight. Advantageously, the proportion of alkyl (meth)acrylate is between 0 and 40% by weight and preferably between 5 and

35% by weight.

Advantageously, this is an ethylene/alkyl (meth)acrylate/unsaturated epoxide copolymer.

Preferably, the alkyl (meth)acrylate is such that the alkyl possesses 1 to 10 carbon atoms.

The MFI (melt flow index) may for example be between 0.1 and 50 g/10 min (190°C/2.16 kg).

Examples of alkyl acrylates and methacrylates that can be used are especially methyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and 2-ethylexyl acrylate. Examples of unsaturated epoxides that can be used are especially:

- aliphatic glycidyl esters and ethers, such as allyl glycidyl ether, vinyl glycidyl ether, glycidyl maleate, glycidyl itaconate, glycidyl acrylate and glycidyl methacrylate; and - alicyclic glycidyl esters and ethers, such as 2-cyclohexen-1-yl glycidyl ether, glycidyl cyclohexene-4,5-dicarboxylate, glycidyl cyclohexene-4-carboxylate, glycidyl 2-methyl-5-norbornene-2-carboxylate and glycidyl endo-cis-bicyclo 2.2.1] hept-5-ene-2,3-dicarboxylate.

With regard to blend (A) and now the impact modifier, and firstly elastomers, mention may be made of SBS, SIS and SEBS block polymers and ethylene-propylene (EPR) or ethylene-propylene-diene monomer (EPDM) elastomers. As regards the very-low density polyethylenes, these are, for example, metallocene polyethylenes of density between for example 0.860 and 0.900. Acrylic elastomers are not recommended as they cause permeability to the cooling liquid. The term "acrylic elastomers" denotes elastomers based on at least one monomer chosen from acrylonitrile, alkyl (meth)acrylates and core/shell copolymers. As regards core/shell copolymers, these are in the form of fine particles having an elastomer core and at least one thermoplastic shell (usually PMMA), the size of the particles generally being less than 1 μm and advantageously between 50 and 300 nm. It would not be outside the scope of the invention to use these acrylic elastomers, but this would be to the detriment of the permeability to the cooling liquid. For example, 1 to 3 parts of acrylic elastomers per 5 to 10 parts of other impact modifiers may be used. Advantageously, an ethylene-propylene (EPR) or ethylene-propylene-diene monomer (EPDM) elastomer is used. The functionalization may be provided by grafting or copolymerizing with an unsaturated carboxylic acid. It would not be outside the scope of the invention to use a functional derivative of this acid. Examples of unsaturated carboxylic acids are those having 2 to 20 carbon atoms, such as acrylic, methacrylic, maleic, fumaric and itaconic acids. The functional derivatives of these acids comprise, 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. These grafting monomers comprise, for example, maleic, fumaric, itaconic, citraconic, allylsuccinic, cyclohex-4-ene-1 ,2-dicarboxylic, 4- methylcyclohex-4-ene-1 ,2-dicarboxylic, bicyclo[2.2.1]hept-5-ene-2,3- dicarboxylic and x-methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acids and maleic, itaconic, citraconic, allylsuccinic, cyclohex-4-ene-1 ,2-dicarboxylic, 4- methyienecyciohex-4~ene-1 ,2-dicarboxyiic, bicyclo-[2.2.1]hept-5-ene-2,3- dicarboxylic and x-methyl-bicyclo[2.2.1]hept-5-ene-2,2-dicarboxylic anhydrides. Advantageously, maleic anhydride is used.

Various known processes may be used to graft a grafting monomer onto a polymer. For example, this may be carried out by heating the polymers to a high temperature, about 150 to about 300⁰C, in the presence or absence of a solvent and with or without a radical initiator. The amount of grafting monomer may be chosen appropriately, but it is preferably from 0.01 to 10%, better still from 600 ppm to 2%, with respect to the weight of the polymer onto which the graft is attached.

As regards the functionalized fluoropolymer (B2) and firstly the fluoropolymer, this denotes any polymer having in its chain at least one monomer chosen from compounds that contain a vinyl group capable of opening in order to be polymerized and that contains, directly attached to this vinyl group, at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.

As examples of monomers, mention may be made of vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1 ,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers, such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE). The fluoropolymer may be a homopolymer or a copolymer; it may also include non-fluorinated monomers such as ethylene.

As examples, the fluoropolymer is chosen from:

- homopolymers and copolymers of vinylidene fluoride (VDF) preferably containing, by weight, at least 50% VDF, the copolymer being chosen from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3) and tetrafluoroethylene (TFE);

- homopolymers and copolymers of trifluoroethylene (VF3); and - copolymers, and especially terpolymers, combining the residues of chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP) and/or ethylene units and optionally VDF and/or VF3 units.

- mention may also be made of ethylene/tetrafluoroethylene (ETFE) copolymers.

Advantageously, the fluoropolymer is a poly(vinylidene fluoride) (PVDF) homopolymer or copolymer. Preferably, the PVDF contains, by weight, at least 50%, more preferably at least 75% and better still at least 85% VDF. The comonomer is advantageously HFP. Advantageously, the PVDF has a viscosity ranging from 100 Pa. s to 2000 Pa. s, the viscosity being measured at 230⁰C and a shear rate of 100 s^"1 using a capillary rheometer. These PVDFs are well- suited to extrusion and to injection moulding. Preferably, the PVDF has a viscosity ranging from 300 Pa. s to 1200 Pa. s, the viscosity being measured at 230⁰C with a shear rate of 100 s^'1 using a capillary rheometer. By way of example of functionalized fluoropolymer mention may be made of functionalized PVDF, that is a PVDF comprising monomer units of VDF and of at least one functional monomer having a least one functional group that may be one of the following groups : a carboxylic acid, a carboxylic acid salt, a carbonate, a carboxylic acid anhydride, an epoxide, a carboxylic acid ester, a silyl, an alkoxysilane, a carboxylic amide, a hydroxyl, an isocyanate. The functionalized PVDF is prepared in suspension, in emulsion or in solution by copolymerizing VDF with said at least one functional monomer and optionally at least another comonomer.

By way of example of a functionalized fluoropolymer, mention may be made of that grafted with an unsaturated monomer. It may be produced according to a grafting process in which : a) the fluoropolymer is melt-blended with the unsaturated monomer ; b) the blend obtained in a) is made in the form of films, sheets, granules or powder ; c) the products from step b) are subjected, in the absence of air, to photon (γ) or electron (β) irradiation with a dose of between 1 and 15 Mrad; and d) the product obtained in c) is optionally treated in order to remove all or part of the unsaturated monomer that has not been grafted onto the fiuoropoiymer.

As examples of unsaturated grafting monomers, mention may be made of carboxylic acid and their derivatives, acid chlorides, isocyanates, oxazolines, epoxydes, amines and hydroxides. Examples of unsaturated carboxylic acids are those having 2 to 20 carbon atoms such as acrylic, methacrylic, maleic, fumaric and itaconic acids. The functional derivatives of these acids comprise, for example, anhydrides, ester derivatives, amide derivatives, imide derivatives and metal salts (such as alkali metal salts) of unsaturated carboxylic acids.

Mention may also be made of undecylenic acid and zinc undecylenate.

Unsaturated dicarboxylic acids having 4 to 10 carbon atoms and their functional derivatives, particularly their anhydrides, are particularly preferred grafting monomers. Step a) is carried out in any blending device, such as extruders or mixers used in the thermoplastics industry.

With regard to the proportions of the fiuoropoiymer and of the unsaturated monomer, the proportion of fiuoropoiymer is advantageously, by weight, from 90 to 99.9% per 0.1 to 10% of unsaturated monomer respectively. Preferably, the proportion of fiuoropoiymer is from 95 to 99.9% per 0.1 to 5% of unsaturated monomer respectively.

After step a) it has been found that the fluoropolymer/unsaturated monomer blend has lost about 10 to 50% of the unsaturated monomer that had been introduced at the start of step a). This proportion depends on the volatility and the nature of the unsaturated monomer. In fact, the monomer has been vented in the extruder or the mixer and it is recovered in the venting circuits.

With regard to step c), the products recovered after step b) are advantageously packaged in polyethylene bags and the air expelled, the bags then being sealed. During this grafting step, it is preferable to avoid the presence of oxygen. Flushing the fluoropolymer/graftable compound blend with nitrogen or argon is therefore possible in order to eliminate the oxygen. As regards the method of irradiation, it is possible to use, without distinction, electron irradiation, better known as beta irradiation, and photon irradiation, better known as gamma irradiation. Advantageously, the dose between 2 and 6 Mrad and preferably between 3 and 5 Mrad. This results in the unsaturated monomer being grafted to an amount of 0.1 to 5 wt% (that is to say the grafted unsaturated monomer corresponds to 0.1 to 5 parts per 99.9 to 95 parts of fluoropolymer), advantageously 0.5 to 5 wt% and preferably 0.5 to 1.5 wt% ; better still 0.7 to 1.5 wt% ; better still 0.8 to 1.5 wt% ; better still 0.9 to 1.5 wt% ; better still 1 to 1.5 wt%. The grafted unsaturated monomer content depends on the initial content of the unsaturated monomer in the fluoropolymer/unsaturated monomer blend to be irradiated. It also depends on the grafting efficiency, and therefore on the duration and the energy of the irradiation.

With regard to step d), any ungrafted monomer and the residues liberated by the grafting, especially HF can be eliminated by any means. The proportion of grafted monomer relative to the monomer present at the start of step c) is between 50 and 100%. It is possible to wash with solvents that are inert with respect to the fluoropolymer and to the grafted functional groups. For example, when maleic anhydride is grafted, it is possible to wash with chlorobenzene. It is also possible, more simply, to vacuum degas the product recovered at step c), while optionally heating at the same time. This operation may be carried out using techniques known to those skilled in the art. It is also possible to dissolve the modified fluoropolymer in a suitable solvent, such as for example N-methyl pyrrolidone, and then to precipitate the polymer in a non- solvent, for example in water or in an alcohol.

As an example of a functionalized fluoropolymer, mention may also be made of one that is grafted with an unsaturated monomer, but via a radical route. The unsaturated monomer may be chosen from those mentioned above. This method is less effective than radiation grafting - it is possible to graft no more than 0.8% of unsaturated monomer and there is a risk of degrading the fluoropolymer. However, this product may be suitable for simple operating conditions. One of the advantages of this irradiation grafting process is that it is possible to obtain higher grafted unsaturated monomer contents than with conventional grafting processes using a radical initiator. Thus, typically, with the irradiation grafting process, it is possible to obtain contents of greater than 1 % (one part of unsaturated monomer per 99 parts of fluoropolymer), or even greater than 1.5%, whereas with a conventional grafting process carried out in an extruder, the content is around 0.2 to 0.8%. Moreover, the irradiation grafting takes place "cold", typically at temperatures below 100⁰C, or even below 7O⁰C, so that the fluoropolymer/unsaturated monomer blend is not in the melt state, as in the case of a conventional grafting process carried out in an extruder. One essential difference is therefore that, in the case of a semicrystalline fluoropolymer (as is the case with PVDF for example) the grafting takes place in the amorphous phase and not in the crystalline phase, whereas homogeneous grafting is produced in the case of grafting carried out in an extruder. The unsaturated monomer is therefore not distributed along the fluoropolymer chains in the same way in the case of irradiation grafting as in the case of grafting carried out in an extruder. The modified fluoropolymer therefore has a different distribution of the graftable compound along the fluoropolymer chains compared with a product obtained by grafting carried out in an extruder. As examples of functionalized fluoropolymers, mention may also be made of those in which a functional monomer or an element carrying a functional group has been incorporated during the polymerization. By way of example such incorporation comes from the chain transfer agent. Such functionalized fluoropolymers are disclosed in patents US 5 415 958, US 6 680 124 and US 6 703 465 and patent application US 2004-0191440, the contents of which are incorporated into the present application.

With regard to the fluoropolymer (B1), this may be chosen from the same polymers as (B2). (B1) may be the same polymer as (B2), but not functionalized, or it may be different. As regards the specific embodiment in which (B1 ) is a flexible polymer Preferably, the viscosity (measured at 230⁰C at a shear rate of 100 s-1 using a capillary rheometer) of the flexible fluoropolymer ranges from 100 to 1500 Pa. s. Preferably, the crystallization temperature 5

(measured by DSC according to ISO 11357-3) of the flexible fluoropolymer is from 50 to 120⁰C, more preferably from 85 to 11O⁰C.

With regard to the proportions, those of (A) are advantageously from 5 to 10% per 95 to 90% of (B) respectively. The proportion of the polyethylene carrying epoxy functional groups may be from 1 to 2 parts per 5 parts of impact modifier. The proportion of (B2) is advantageously between 35 and 60%, preferably between 45 and 55%, by weight of (A)+(B).

With regard to the preparation of the compositions of the invention, these may be obtained by melt-blending of the constituents using standard techniques for thermoplastics.

The (A)/(B) blends may furthermore contain at least one additive chosen from: dyes; pigments; antioxidants; fire retardants;

UV stabilizers; nanofillers; nucleating agents.

With regard to the embodiment in which the tube includes an inner layer (3), the polyamide of the outer layer (1 ) may be chosen from the polyamides of the outer layer (1 ) described above.

With regard to the layer (2), the nature of the constituents (A) and (B) is the same as that described above. The proportions of (A) are advantageously from 5 to 30% per 95 to 70% of (B) respectively. The proportions of (A) are preferably from 5 to 10% per 95 to 90% of (B) respectively. The proportion of polyethylene carrying epoxy functional groups may be between 1 and 2 parts per 5 parts of impact modifier. The proportion of (B2) is advantageously between 35 and 60%, preferably between 45 and 55%, by weight of (A)+(B). The layer (3) is made of a polyolefin. It may or may not be functionalized or it may be a blend of at least one functionalized polyolefin and/or of at least one unfunctionalized polyolefin.

An unfunctionalized polyolefin is a homopolymer or a copolymer of alpha- olefins or diolefins, such as, for example, ethylene, propylene, 1-butene, 1-octene and butadiene. By way of examples, mention may be made of:

- polyethylene homopolymers and copolymers, particularly LDPE, HDPE, LLDPE (linear low-density polyethylene) or VLDPE (very low-density polyethylene) and metallocene polyethylene; - propylene homopolymers and copolymers;

- ethylene/alpha-olefin copolymers such as ethylene/propylene copolymers; EPRs (abbreviation for ethylene-propylene rubbers); and ethylene/propylene/diene copolymers (EPDM);

- styrene/ethylene-butylene/styrene block copolymers (SEBS), styrene/butadiene/styrene block copolymers (SBS), styrene/isoprene/styrene block copolymers (SIS), styrene/ethylene-propylene/styrene block copolymers (SEPS);

- copolymers of ethylene with at least one product chosen from salts or esters of unsaturated carboxylic acids such as alkyl (meth)acrylate (for example methyl acrylate), or vinyl esters of saturated carboxylic acids such as vinyl acetate (EVA), the proportion of comonomer possibly being as much as 40% by weight.

The functionalized polyolefin may be an alpha-olefin polymer having reactive units (the functional groups); such reactive units are acid, anhydride or epoxy functional groups. By way of example, mention may be made of the above non-functionalized polyolefins that are grafted or are copolymerized or terpolymerized with unsaturated epoxides such as glycidyl (meth)acrylate, or by carboxylic acids or the corresponding salts or esters, such as (meth)acrylic acid (this possibly being completely or partially neutralized by metals such as Zn, etc.) or else with carboxylic acid anhydrides such as maleic anhydride. A functionalized polyolefin is, for example, a PE/EPR blend, the weight ratio of which may vary between wide limits, for example between 40/60 and 90/10, the said blend being cografted with an anhydride, especially maleic anhydride, with a degree of grafting, for example, of 0.01 to 5% by weight.

The functionalized polyolefin may be chosen from the following (co)polymers, grafted with maleic anhydride or glycidyl methacrylate, in which the degree of grafting is, for example, from 0.01 to 5% by weight:

- PE, PP, copolymers of ethylene with propylene, butene, hexene, or octene and containing, for example, from 35 to 80% by weight of ethylene;

- ethylene/alpha-olefin copolymers such as ethylene/propylene copolymers; EPRs (abbreviation for ethylene-propylene rubbers); and ethylene/ propylene/diene copolymers (EPDM);

- styrene/ethylene-butylene/styrene block copolymers (SEBS), styrene/ butadiene/styrene block copolymers (SBS), styrene/isoprene/styrene block copolymers (SIS), styrene/ethylene-propylene/styrene block copolymers (SEPS); - ethylene/vinyl acetate copolymers (EVA), containing up to 40% by weight of vinyl acetate;

- ethylene/alkyl (meth)acrylate copolymers, containing up to 40% by weight of alkyl (meth)acrylate;

- ethylene/vinyl acetate (EVA)/alkyl (meth)acrylate terpolymers, containing up to 40% by weight of comonomers.

The functionalized polyolefin may also be chosen from ethylene/propylene copolymers containing predominantly propylene, these being grafted with maleic anhydride and then condensed with monoaminated polyamide (or polyamide oligomer) (products described in EP-A-O 342 066). The functionalized polyolefin may also be a copolymer or terpolymer of at least the following units: (1) ethylene, (2) an alkyl (meth)acrylate or a vinyl ester of a saturated carboxylic acid and (3) an anhydride such as maleic anhydride or a (meth)acrylic acid or an epoxy such as glycidyl (meth)acrylate. By way of examples of functionalized polyolefins of this latter type, mention may be made of the following copolymers, in which the ethylene preferably represents at least 60% by weight and in which the termonomer (the functional group) represents, for example, from 0.1 to 10% by weight of the copolymer: - ethylene/alkyl (meth)acrylatθ/(meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymers;

- ethyiene/vinyi acetate/maleic anhydride or giycidyi methacrylate copolymers. In the above copolymers, the (meth)acrylic acid may be salified with Zn or Li.

The term "alkyl (meth)acrylate" denotes Ci to Cs alkyl methacrylates and acrylates, and may be chosen from methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate and ethyl methacrylate.

Moreover, the aforementioned functionalized polyolefins may also be crosslinked by any suitable process or agent (diepoxy, diacid, peroxide, etc.); the term functionalized polyolefin also includes blends of the aforementioned polyolefins with a difunctional reactive agent such as a diacid, dianhydride, diepoxy, etc., which is capable of reacting with them or blends of at least two functionalized polyolefins able to react together.

The abovementioned copolymers may be copolymerized so as to form random or block copolymers and may have a linear or branched structure.

The molecular weight, the MFI index and the density of these polyolefins may also vary over a wide range, as those skilled in the art will appreciate. MFI is the abbreviation for Melt Flow Index. It is measured according to the ASTM 1238 standard.

Advantageously, the unfunctionalized polyolefins are chosen from propylene homopolymers or copolymers and any ethylene homopolymer or copolymer of ethylene and a comonomer of higher alpha-olefin type, such as butene, hexene, octene or 4-methyl-1-pentene. Mention may be made, for example, of high-density PP and PE, medium-density PE, linear low-density PE, low-density PE and very low-density PE. These polyethylenes are known to those skilled in the art as being produced by a "radical" process, by "Ziegler"- type catalysis or, more recently, by so-called "metallocene" catalysis.

Advantageously, the functionalized polyolefins are chosen from any polymer comprising alpha-olefin units and units carrying polar reactive functional groups such as epoxy, carboxylic acid or carboxylic acid anhydride functional groups. By way of examples of such polymers, mention may be made of ethylene/aikyl acryiate/maleic anhydride or ethylene/aikyl acryiate/giycidyl methacrylate terpolymers, such as the LOTADER® polymers from the Applicant, or maleic-anhydride-grafted polyolefins such as the OREVAC® polymers from the Applicant, as well as ethylene/aikyl acrylate/(meth)acrylic acid terpolymers. Mention may also be made of propylene homopolymers and copolymers grafted with a carboxylic acid anhydride and then condensed with polyamides or monoaminated polyamide oligomers. The polyolefin of the layer (3) may also contain a functionalized polyolefin having functional groups that can react with the functional groups of the fluoropolymer (B2) of the adjacent layer.

According to one advantageous embodiment, a layer of functionalized polyolefin having functional groups capable of reacting with the functional groups of the fluoropolymer (B2) is placed between the layer (2) and the layer (3).

For example, if maleic anhydride has been grafted onto the fluoropolymer (B2), the functionalized polyolefin layer consists of a polyethylene carrying epoxy functional groups. Such polymers were mentioned previously. Advantageously, the layer of functionalized polyolefin consists of an ethylene/glycidyl methacrylate copolymer and possibly an ethylene/aikyl acrylate copolymer, optionally blended with polyethylene.

Examples The following polymers were used:

Kynar^® 720 : A PVDF homopolymer from Arkema with an MVI (Melt Volume

Index) of 7 cm³/10 min (230°C/5 kg).

Kynar^® ADX 120 : a functional PVDF homopolymer grafted with maleic anhydride, from Arkema, with an MVI (Melt Volume Index) of 7 cm³/10 min (230°C/5 kg).

Kynar^® 740 : a PVDF homopolymer from Arkema with an MVI (Melt Volume

Index) of 1 cm³/10 min (230°C/5 kg). Kynar^® ADX 140 : a functional PVDF homopolymer grafted with maleic anhydride from Arkema, with an MVI (Melt Volume Index) of 1 cm³/10 min (230°C/5 kg).

Paraloid^® EXL 3600 : an MBS impact modifier of the core/shell type (from Rhom and Haas).

LOTADER^® 8840 : an ethylene/glycidyl methacrylate copolymer from Arkema with an MVI (Melt Volume Index) of 5 cm³/10 min (190°C/2.16 kg) and containing 92% ethylene and 8% glycidyl methacrylate by weight. EXXELOR^® VA 1803 : an EPR elastomer grafted with maleic anhydride, with an MFI of 3 g/10 min (230°C-2.16 kg).

Rilsan AESN P110 TL^® : an impact-modified nylon-12 from Arkema. NECHV0^® : a nylon-12 with predominantly amine chain ends from Arkema.

Example 1 : according to the invention A Kynar 740 (44 wt%)/Kynar ADX 140 (50 wt%)/LOTADER 8840 (1 wt%)/EXXELOR VA 1803 (5 wt%) blend was produced at 23O⁰C in a Werner 40-type extruder.

A three layer tube 1.5 mm in thickness and 12 mm in outside diameter, composed of AESN P110 TL as external layer (1250 μm thickness), NECHVO (50 μm in thickness) and the above PVDF alloy as internal layer (200 μm thickness), was extruded on a McNeil line at 230⁰C.

This tube, pendulum-impact tested according to the DIN 73378 standard with a pendulum impact of 7.5 J, showed no fracture at 23⁰C or at -30⁰C.

The tube was aged for 300 h at 130⁰C in a fan oven, the inside of the tube being filled with a cooling liquid composed of 50% water and 50% cooling fluid (Havoline^® product from Texaco), the outside of the tube being in contact with the atmosphere of the chamber. After this ageing, the impact-tested tube showed no fracture at 23⁰C or -30°C.

The permeability of this three-layer tube to the water/Havoline^® mixture at 130°C was 60 g/(m² per 24 h). Example 2 : comparative example

A monolayer tube of 1.5 mm thickness and 12 mm outside diameter, composed of AESN P110 TL, was extruded at 230⁰C on a McNeii line.

This tube, impact-tested according to the DIN 73378 standard with a pendulum impact of 7.5 J showed no fracture at 23°C nor at -30⁰C.

After 300 h of the ageing described in Example 1 , the impact-tested tube fractured in a brittle manner at -30°C, but also at 23°C.

The permeability of this monolayer tube to the water/Haveline^® mixture at 130°C was 260 g/(m² per 24 h).

Example 3 : comparative example

A Kynar 720 (20 wt%)/Kynar ADX 120 (50 wt%)/Paraloid (30 wt%) blend was extruded at 230⁰C in a Werner 40-type extruder.

A three-layer tube of 1.5 mm thickness and 12 mm outside diameter, composed of AESN P110 TL as external layer (1250 μm in thickness), NECHVO (50 μm in thickness) and the above PVDF alloy as internal layer (200 μm in thickness), was extruded at 23O⁰C on a McNeil line.

This tube, impact-tested according to the DIN 73378 standard with a pendulum impact of 7.5 J showed no fracture at 23⁰C nor at -30⁰C. After 300 h of the ageing described in Example 1 , the impact-tested tube fractured in a brittle manner at -30⁰C, but did not fracture at 23°C.

The permeability of this three-layer tube to the water/Haveline^® mixture at 13O⁰C was 130 g/(m² per 24 h).

Claims

1. Multilayer tube comprising, in its radial direction from the outside inwards: a polyamide outer layer (1 ); an inner layer (2) of a composition comprising, the total being 100%, 5 to 30% by weight of a blend (A) comprising: a polyethylene carrying epoxy functional groups, an impact modifier chosen from elastomers and very low- density polyethylenes, the said impact modifier being completely or partly functionalized;

95 to 70% by weight of a blend (B) comprising: a fluoropolymer (BI ), a functionalized fluoropolymer (B2), the proportion of (B2) being between 1 and 80% (advantageously

1 and 60%) by weight of (A)+(B), the layers being successive and adhering to one another in their respective contact region.

2. Multilayer tube comprising, in its radial direction from the outside inwards: a polyamide outer layer (1 ); a layer (2) of a composition comprising, the total being 100%, 0 to 30% by weight of a blend (A) comprising: a polyethylene carrying epoxy functional groups, an impact modifier chosen from elastomers and very low-density polyethylenes, the said impact modifier being completely or partly functionalized;

100 to 70% by weight of a blend (B) comprising: optionally, a fluoropolymer (B1 ), a functionalized fluoropolymer (B2), the proportion of (B2) being between 10 and 100% by weight of (A)₊(B); a poiyoiefin inner iayer (3); the layers being successive and adhering to each other in their respective contact region.

3. Tube according to Claim 2, in which the proportions of (A) are from 5 to 30% per 95 to 70% of (B) respectively.

4. Tube according to any one of the preceding claims, in which the polyamide of the outer layer (1 ) is a polyamide having amine terminal groups or comprising more amine terminal groups than acid terminal groups.

5. Tube according to any one of the preceding claims in which a layer of a polyamide having amine terminal groups or one comprising more amine terminal groups than acid terminal groups is placed between the outer layer (1 ) and the layer (2).

6. Tube according to any one of the preceding claims, in which the impact modifier of the blend (A) is an EPR grafted with maleic anhydride or an

EPDM grafted with maleic anhydride.

7. Tube according to any one of the preceding claims, in which the functionalized fluoropolymer (B2) is a PVDF homopolymer or copolymer grafted with maleic anhydride.

8. Tube according to any one of the preceding claims, in which the fluoropolymer (B1) is a PVDF homopolymer or copolymer.

9. Tube according to any one of Claims 1 and 3 to 8, in which the proportions of (A) are from 5 to 10% per 95 to 90% of (B) respectively.

10. Tube according to any one of the preceding claims, in which the proportion of the polyethylene carrying epoxy functional groups is from 1 to 2 parts per 5 parts of impact modifier.

11. Tube according to any one of the preceding claims, in which the proportion of (B2) is between 35 and 60% by weight of (A)+(B).

12. Tube according to Claim 11 , in which the proportion of (B2) is between 45 and 55% by weight of (A)+(B).

13. Use of the tubes according to any one of the preceding claims for transporting cooling liquids.