EP1934045A1

EP1934045A1 - Multilayer tube for transporting water or gas

Info

Publication number: EP1934045A1
Application number: EP06820289A
Authority: EP
Inventors: Anthony Bonnet; Michael Werth
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2005-10-13
Filing date: 2006-10-12
Publication date: 2008-06-25
Also published as: IL190817A0; CA2625986A1; AU2006300983A1; NO20082147L; WO2007042736A1; FR2892171A1; US20100047495A1; FR2892171B1; CN101326054A

Abstract

The invention relates to a multilayer tube comprising (from the inside to the outside of the tube): an optional layer (C1) consisting of at least one fluorinated polymer; a layer (C2) consisting of a mixture containing at least one functionalised fluorinated polymer and at least one flexible fluorinated polymer having a tensile modulus of between 50 and 1000 MPa (measured in accordance with the ISO R 527 standard at 23°C), advantageously between 100 and 750 MPa and preferably between 200 and 600 MPa; an optional layer (C3) of adhesive binder; a layer (C4) consisting of at least one polyolefin or a mixture of at least one polyolefin with at least one functionalised polyolefin; a barrier layer (C5); and an optional layer (C6) consisting of at least one polyolefin.

Description

MULTILAYER TUBE FOR TRANSPORTING WATER OR GAS

[Field of the invention]

The present invention relates to a multilayer pipe comprising a layer of a functionalized fluoropolymer, a layer of a polyolefin and a barrier layer. The polyolefin may be a polyethylene, especially high density polyethylene (HDPE) or crosslinked polyethylene (PEX noted). The tube can be used for the transport of liquids, in particular hot water, or gas. The invention also relates to the uses of this tube

[Technical problem]

Steel or cast iron tubes are increasingly replaced by plastic equivalents. Polyolefins, especially polyethylenes, are widely used thermoplastics because they have good mechanical properties, they are transformed and allow to weld the tubes together easily. Polyolefins are widely used for the manufacture of tubes for the transport of water or city gas. When the gas is under a high pressure (> 10 bar or more), it is necessary for the polyolefin to be mechanically resistant to the stresses exerted by the gas under pressure.

In addition, the polyolefin may be subjected to an aggressive chemical medium. For example, in the case of water transport, it may contain additives or aggressive chemicals (for example ozone, chlorinated derivatives used for the purification of water such as bleach) which are oxidizing, especially hot). These additives or chemicals can damage the polyolefin over time, especially when the water transported is at a high temperature (this is the case in heating circuits or in water systems for which water is raised to high temperature to eliminate germs, bacteria or microorganisms). A problem to be solved by the invention is therefore to develop a chemically resistant tube. Another problem that the invention intends to solve is that the tube has barrier properties. Barrier means that the tube brakes the migration to the transported fluid of contaminants present in the external medium or contaminants (such as antioxidants or polymerization residues) present in the polyolefin. Barrier also means that the tube slows the migration of oxygen or additives present in the fluid transported to the polyolefin layer.

It is also necessary that the tube has good mechanical properties, in particular good impact resistance and that the layers adhere well to each other (no delamination).

The Applicant has developed a multilayer tube that addresses the problems posed. This tube has in particular good chemical resistance vis-à-vis the transported fluid and the barrier properties mentioned above.

[Prior art]

EP 1484346 published December 08, 2004 describes multilayer structures comprising a fluoropolymer grafted by irradiation. The structures can be in the form of bottles, tanks, containers or pipes. The structure of the multilayer tube according to the invention does not appear in this document.

EP 1541343 published June 08, 2005 discloses a multilayer structure based on a fluoropolymer modified by radiation grafting for storing or transporting chemicals. In this chemical application, we mean products that are corrosive or dangerous, or products that we want to maintain purity. The structure of the multilayer tube according to the invention does not appear in this document. US 6016849 published July 25, 1996 discloses a plastic tube having an adhesion between the inner layer and the outer protective layer between 0.2 and 0.5 N / mm. There is no mention of fluoropolymer modified by radiation grafting.

Documents US 2004/0206413 and WO 2005/070671 describe a multilayer pipe comprising a metal sheath. There is no mention of fluoropolymer modified by radiation grafting.

In these documents of the prior art, there is no description of multilayer pipes comprising a layer of a polyolefin, a layer of a functionalized fluoropolymer and a barrier layer.

The invention relates to a multilayer pipe as defined in claim 1, 23 or 24. It also relates to the use of the tube in the transport of water or a gas, a fuel, and a radiant heating system comprising at least one multilayer tube of the invention.

The invention will be better understood on reading the detailed description which follows, non-limiting examples of implementation thereof, and on examining the appended figure. The previous French application FR 05.10440 as well as the provisional application US 60/754887 whose priorities are claimed are hereby incorporated by reference.

figure

Figure 1 shows a sectional view of a multilayer pipe 9 according to one of the forms of the invention. It is a cylindrical tube having several concentric layers, referenced from 1 to 8. The layers are arranged against each other in the indicated order 1 - * 8: layer 1: layer C ₁ comprising a fluoropolymer; layer 2: layer C ₂ comprising the functionalized fluoropolymer + flexible fluoropolymer mixture; layer 3: layer C ₃ of an adhesion binder; layer 4: layer C ₄ comprising a polyolefin; layer 5: layer of adhesion binder; layer 6: barrier layer C ₅ ; layer 7: layer of adhesion binder; layer 8: layer C ₆ comprising a polyolefin.

[Detailed description of the invention]

With regard to the fluoropolymer, this denotes any polymer having in its chain at least one fluorinated monomer chosen from compounds containing a vinyl group capable of opening to polymerize and which contains, directly attached to this vinyl group, at least a fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.

As an example of a fluorinated monomer, mention may be made of vinyl fluoride; vinylidene fluoride (VDF, CH ₂ = CF ₂ ); trifluoroethylene (VF ₃ ); 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); perfluoro (1,3-dioxole); perfluoro (2,2-dimethyl-1,3-dioxole) (PDD); the formula product

CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ X wherein X is SO ₂ F, CO ₂ H, CH ₂ OH, CH ₂ OCN or CH ₂ OPO ₃ H; the product of formula CF ₂ = CFOCF ₂ CF ₂ SO ₂ F; the product of formula F (CF ₂ J _n CH ₂ OCF = CF ₂ wherein n is 1, 2, 3, 4 or 5, the product of formula R ₁ CH ₂ OCF = CF ₂ wherein R ₁ is hydrogen where F (CF ₂ ) Z and z is 1, 2, 3 or 4, the product of formula R ₃ OCF = CH ₂ in which R ₃ is F (CF ₂ ) _Z - and z is 1, 2, 3 or 4 perfluorobutyl ethylene (PFBE), 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene. The fluoropolymer may be a homopolymer or a copolymer, it may also include non-fluorinated monomers such as ethylene.

By way of example, the fluorinated polymer is chosen from: homo-and copolymers of vinylidene fluoride (PVDF) preferably containing at least 50% by weight of VDF, the copolymer being chosen from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF ₃ ) and tetrafluoroethylene (TFE);

copolymers of TFE and ethylene (ETFE); homo- and copolymers of trifluoroethylene (VF ₃ );

copolymers, and especially terpolymers, combining the residues of the chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP) and / or ethylene units and optionally VDF and / or VF _{3 units} .

Advantageously, the fluoropolymer is a homo- or copolymer PVDF. This fluoropolymer indeed has a good chemical resistance, especially to UV and chemicals, and it is easily converted (more easily than PTFE or ETFE-type copolymers). Preferably the PVDF contains, by weight, at least 50% of VDF, more preferably at least 75% and more preferably at least 85%. The comonomer is advantageously ¹ HFP.

Advantageously, the PVDF has a viscosity ranging from 100 Pa.s to 2000 Pa.s, the viscosity being measured at 230 ^° C., at a shear rate of 100 s ^-1 using a capillary rheometer. these PVDFs are well suited to extrusion and injection, preferably PVDF has a viscosity of 300

Pa.s at 1200 Pa.s, the viscosity being measured at 230 ⁰ C, at a shear rate of 100 s ^"1 using a capillary rheometer.

Thus, PVDF marketed under the trademark KYNAR ^® 710 or 720 are perfectly suited for this formulation. As regards the flexible fluorinated polymer, it is a fluorinated polymer having a tensile modulus of between 50 and 1000 MPa (measured according to ISO R 527 at 23 ° C.), advantageously between 100 and 750 MPa, and preferably between 200 and 600 MPa.

As regards the functionalized fluoropolymer, it is a fluorinated polymer bearing at least one functional group chosen from the following groups: carboxylic acid, carboxylic acid salt, carbonate, carboxylic acid anhydride, epoxide, carboxylic acid ester, silyl, alkoxysilane, carboxylic acid amide, hydroxy, isocyanate. It is a copolymer comprising at least one fluorinated monomer and at least one unsaturated monomer bearing a functional group as defined. The functional group is introduced into the fluoropolymer either by copolymerization or by grafting a monomer carrying a functional group as defined.

The functionalized fluoropolymer may be obtained by copolymerizing a fluorinated monomer with at least one unsaturated monomer bearing a functional group and optionally at least one other comonomer. For example, the functionalized polymer may be a PVDF comprising monomeric units of VDF and a monoesterified unsaturated diacid or vinylene carbonate as described in US 5415958. Another example of a functionalized fluoropolymer is that of a PVDF comprising monomeric units of VDF and itaconic or citraconic anhydride as described in US 6703465 B2. The functionalized fluoropolymer may be prepared by an emulsion, suspension or solution process.

The functionalized fluoropolymer may be obtained by irradiation grafting of at least one unsaturated monomer (described below) on a fluoropolymer. In this case, we will speak for simplification of fluoropolymer grafted by irradiation. The process for obtaining the radiation-grafted fluoropolymer is as follows: a) The fluoropolymer is premixed in the molten state with the unsaturated monomer. For this purpose, all the melt mixing techniques known from the prior art are used. The mixing step is carried out in any mixing device such as extruders or kneaders used in the thermoplastics industry. Preferably, an extruder will be used to form the mixture into granules. The grafting takes place on a mixture (in the mass) and not on the surface of a powder as described for example in US Pat. No. 5,576,106.

b). Then, the mixture of the fluoropolymer and the unsaturated monomer is irradiated (β or γ irradiation) in the solid state using an electronic or photonic source under an irradiation dose of between 10 and 200 kGray, preferably between 10 and 150 kGray. The mixture may for example be packaged in polythene bags, the air is removed and the bags are closed. Advantageously the dose is between 2 and 6 Mrad and preferably between 3 and 5 Mrad. Irradiation with a cobalt-60 bomb is particularly preferred.

The unsaturated monomer content which is grafted is 0.1 to 5% by weight (i.e., the unsaturated grafted monomer corresponds to 0.1 to 5 parts for 99.9 to 95 parts by weight). fluoropolymer), preferably from 0.5 to 5%, preferably from 0.9 to 5%. The grafted unsaturated monomer content is dependent on the initial content of the unsaturated monomer in the fluoropolymer / unsaturated monomer mixture to be irradiated. It also depends on the effectiveness of the grafting, and therefore the duration and energy of the irradiation.

vs). The unsaturated monomer which has not been grafted, as well as the residues released by the grafting, in particular the HF, can then optionally be removed. This last step may be necessary if the non-grafted unsaturated monomer is likely to hinder adhesion or for toxicology problems. This operation can be performed according to the known techniques of the skilled person. Vacuum degassing may be applied, possibly by applying heating at the same time. It is also possible to dissolve the modified fluoropolymer in a suitable solvent such as, for example, N-methylpyrrolidone, and then to precipitate the polymer in a non-solvent, for example in water or in an alcohol, or else washing the fluoropolymer modified with a solvent inert with respect to the fluoropolymer and graft functions. For example, when grafting maleic anhydride, it can be washed with chlorobenzene.

This is one of the advantages of this radiation grafting process that higher graft unsaturated monomer contents can be obtained than with conventional grafting methods using a radical initiator. Thus, typically, with the irradiation grafting method, it is possible to obtain contents greater than 1% (1 part of unsaturated monomer per 99 parts of the fluoropolymer), or even greater than 1, 5%, which is not possible with a conventional grafting process in an extruder

On the other hand, the grafting by irradiation takes place at "cold", typically at temperatures below 100 ^° C., or even 50 ^° C., so that the mixture of the fluorinated polymer and the unsaturated monomer is not the same. molten state as for a conventional grafting process in extruder but in the solid state. An essential difference is therefore that, in the case of a semi-crystalline fluorinated polymer (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 occurs in the case of grafting in a melt extruder. The unsaturated monomer therefore does not distribute identically on the chains of the fluoropolymer in the case of irradiation grafting and in the case of grafting in an extruder. The modified fluorinated product therefore has a different distribution of the unsaturated monomer on the fluoropolymer chains compared to a product that would be obtained by grafting into an extruder. During this grafting step, it is preferable to avoid the presence of oxygen. A nitrogen or argon sweep of the fluoropolymer / unsaturated monomer mixture is therefore possible to remove oxygen.

The fluoropolymer modified by radiation grafting has the very good chemical resistance and the oxidation, as well as the good thermomechanical behavior, of the fluoropolymer before its modification.

As regards the unsaturated monomer, it has a C = C double bond as well as at least one polar function which may be a function:

carboxylic acid,

- carboxylic acid salt,

- carboxylic acid anhydride,

epoxide, carboxylic acid ester,

- silyl,

alkoxysilane,

- carboxylic acid amide,

hydroxy, isocyanate.

Mixtures of several unsaturated monomers are also possible.

Unsaturated carboxylic acids having 4 to 10 carbon atoms and their functional derivatives, particularly their anhydrides, are particularly preferred unsaturated monomers. Examples of unsaturated monomers are methacrylic acid, acrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, undecylenic acid, allylsuccinic acid, and the like. cyclohex-4-ene-1,2-dicarboxylic acid, 4-methyl-cyclohex-4-ene-1,2-dicarboxylic acid, bicyclo (2,2,1) hept-5-ene 2,3-dicarboxylic acid, x-methylbicyclo (2,2,1-hept-5-ene-2,3-dicarboxylic acid, zinc, calcium or sodium undecylenate, maleic anhydride, itaconic anhydride, citraconic anhydride, dichloromaleic anhydride, difluoromaleic anhydride, itaconic anhydride, crotonic anhydride, glycidyl acrylate or methacrylate, allyl glycidyl ether, vinyl silanes such as vinyl trimethoxysilane, vinyl triethoxysilane, vinyl triacetoxysilane, γ-methacryloxypropyltrimethoxysilane.

Other examples of unsaturated monomers include C ₁ -C ₈ alkyl esters or glycidyl ester derivatives of unsaturated carboxylic acids such as methyl acrylate, methyl methacrylate, ethyl acrylate, methacrylate and the like. ethyl acrylate, butyl acrylate, butyl methacrylate, glycidyl acrylate, glycidyl methacrylate, monoethyl maleate, diethyl maleate, monomethyl fumarate, dimethyl fumarate, monomethyl, and diethyl itaconate; amide derivatives of unsaturated carboxylic acids such as acrylamide, methacrylamide, maleic monoamide, maleic diamide, N - monoethylamide maleic, N, N - diethylamide maleic, N - maleic monobutylamide, N, N - dibutylamide maleic, furamic monoamide, furamic diamide, fumaric N-monoethylamide, N, N-diethylamide fumaric, fumaric N-monobutylamide and N, N-dibutylamide furamic; imide derivatives of unsaturated carboxylic acids such as maleimide, N-butylmaleimide and N-phenylmaleimide; and metal salts of unsaturated carboxylic acids such as sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate and zinc, calcium or sodium undecylenates.

Unsaturated monomers are those which have two C = C double bonds which could lead to crosslinking of the fluoropolymer, such as, for example, di- or triacrylates. From this point of view, maleic anhydride as well as zinc, calcium and sodium undecylenates are good graftable compounds because they have little tendency to homopolymerize or even to give rise to crosslinking. Advantageously, maleic anhydride is used. This monomer indeed offers the following advantages: it is solid and can be easily introduced with the fluoropolymer granules to prepare the mixture to be melted, - it makes it possible to obtain good adhesion properties,

it is particularly reactive with respect to epoxide or hydroxy functions,

unlike other unsaturated monomers such as (meth) acrylic acid or acrylic esters, it does not homopolymerise and does not have to be stabilized.

In the mixture to be irradiated, the proportion of fluoropolymer is, by weight, between 80 to 99.9% for respectively 0.1 to 20% of unsaturated monomer. Preferably, the proportion of fluorinated polymer is from 90 to 99% for 1 to 10% of unsaturated monomer, respectively.

As regards the polyolefin, the term refers to a polymer comprising predominantly ethylene and / or propylene units. It may be a polyethylene, homo- or copolymer, the comonomer being chosen from propylene, butene, hexene or octene. It may also be a polypropylene, homo- or copolymer, the comonomer being chosen from ethylene, butene, hexene or octene.

The polyethylene may be in particular high density polyethylene (HDPE), low density (LDPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE). The polyethylene can be obtained using a Ziegler-Natta, Phillips or metallocene catalyst or by the high-pressure process. Polypropylene is iso- or syndiotactic polypropylene.

It can also be a crosslinked polyethylene (denoted PEX). PEX has, compared to a non-crosslinked PE, better mechanical properties (especially good crack resistance) and better chemical resistance. The crosslinked polyethylene may be, for example, a polyethylene comprising hydrolysable silane groups (as described in applications WO 01/53367 or US 20040127641 A1) which has then been crosslinked after reaction between them silane groups. The reaction of silane groups Si-OR between them leads to Si-O-Si bonds which connect the polyethylene chains to each other. The content of hydrolysable silane groups may be at least 0.1 hydrolysable silane groups per 100 units -CH ₂ - (determined by infrared analysis). Polyethylene can also be crosslinked by means of radiation, for example gamma radiation. It may also be a polyethylene crosslinked using a radical initiator of the peroxide type. It is therefore possible to use a PEX of type A (crosslinking using a radical initiator), type B (crosslinking with silane groups) or type C (crosslinking by irradiation).

It may also be a so-called bimodal polyethylene, that is to say composed of a mixture of polyethylenes having different average molecular weights as taught in WO 00/60001. For example, bimodal polyethylene makes it possible to obtain a very interesting compromise of impact and stress-cracking resistance as well as good rigidity and good resistance to pressure.

For pressure-resistant tubes, especially pressurized gas or water transport tubes, polyethylene which has good resistance to slow crack propagation (SCG) and rapid propagation can be advantageously used. of crack (RCP). The grade HDPE XS 10 B marketed by TOTAL PETROCHEMICALS has good crack resistance (slow or fast). It is a HDPE containing hexene as a comonomer, having a density of 0.959 g / cm ³ (ISO 1183), an MI-5 of 0.3 dg / min (ISO 1133), an HLMI of 8 dg / min (ISO 1133), a long-lasting hydrostatic resistance of 11.2 MPa according to ISO / DIS 9080, a resistance to slow crack propagation on notched pipes exceeding 1000 hours according to ISO / DIS 13479.

As regards the functionalized polyolefin, this term denotes a copolymer of ethylene and / or propylene and at least one unsaturated polar monomer. This can be for example chosen from:

(C 1 -C 5) alkyl (meth) acrylates, especially methyl, ethyl, propyl, butyl, 2-ethylhexyl, isobutyl or cyclohexyl (meth) acrylate; unsaturated carboxylic acids, their salts and their anhydrides, in particular acrylic acid, methacrylic acid, maleic anhydride, itaconic anhydride and citraconic anhydride; unsaturated epoxides, especially aliphatic glycidyl esters and ethers such as glycidyl allyl glycidyl ether, vinyl glycidyl ether, maleate and itaconate, glycidyl acrylate and methacrylate, as well as alicyclic glycidyl esters and ethers;

vinyl esters of saturated carboxylic acids, in particular vinyl acetate or vinyl propionate.

The functionalized polyolefin may be obtained by copolymerization of ethylene and at least one unsaturated polar monomer selected from the above list. The functionalized polyolefin may be a copolymer of ethylene and a polar monomer from the above list or a terpolymer of ethylene and two unsaturated polar monomers selected from the above list. The copolymerization takes place at high pressures higher than 1000 bar according to the so-called high-pressure process. The functional polyolefin obtained by copolymerization comprises, by weight, from 50 to 99.9% of ethylene, preferably from 60 to 99.9%, even more preferably from 65 to 99% and from 0.1 to 50%, preferably from 0.1 to 40%, more preferably 1 to 35% of at least one polar monomer from the above list. For example, the functionalized polyolefin is a copolymer of ethylene and an unsaturated epoxide, preferably glycidyl (meth) acrylate, and optionally a (C 1 -C 5) alkyl (meth) acrylate or vinyl ester of saturated carboxylic acid. The content of unsaturated epoxide, especially glycidyl (meth) acrylate, is between 0.1 and 50%, advantageously between 0.1 and 40%, preferably between 1 and 35% and even more preferably between 1 and 20%. . It may be, for example, functionalized polyolefins sold by the company Arkema under the references LOTADER AX8840 (8% glycidyl methacrylate, 92% ethylene, melt-index 5 according to ASTM D1238), LOTADER AX8900 (8% methacrylate). glycidyl, 25% methyl acrylate, 67% ethylene, melt-index 6 according to ASTM D1238), LOTADER AX8950 (9% glycidyl methacrylate, 15% methyl acrylate, 76% ethylene, melt-index 85 according to ASTM D 1238).

The functionalized polyolefin may also be a copolymer of ethylene and an unsaturated carboxylic acid anhydride, preferably maleic anhydride, and optionally a C ₁ -C ₈ alkyl (meth) acrylate or an ester vinylic acid saturated carboxylic acid. The content of maleic anhydride, especially maleic anhydride, is between 0.1 and 50%, advantageously between 0.1 and 40%, preferably between 1 and 35%, and even more preferably between 1 and 10%. It may be, for example, functionalized polyolefins marketed by the company ARKEMA under the references LOTADER 2210 (2.6% maleic anhydride, 6% butyl acrylate and 91.4% ethylene, melt-index 3 according to ASTM D1238), LOTADER 3340 (3% maleic anhydride, 16% butyl acrylate and 81% ethylene, melt index according to ASTM D1238), LOTADER 4720 (0.3% maleic anhydride, 30% ethyl acrylate and 69.7% ethylene, melt index 7 according to ASTM D1238), LOTADER 7500 (2.8% maleic anhydride, 20% butyl acrylate and 77.2% ethylene, melt-index 70 according to ASTM D1238), OREVAC 9309, OREVAC 9314, OREVAC 9307Y, OREVAC 9318, OREVAC 9304 or OREVAC 9305. The term "functionalized polyolefin" also refers to a polyolefin on which is grafted by radical means an unsaturated polar monomer from the above list. The grafting takes place in an extruder or in solution in the presence of a radical initiator. As examples of radical initiators, t-butyl hydroperoxide, cumene hydroperoxide, di-isopropylbenzene hydroperoxide, di-t-butylperoxide, t-butyl- cumyl peroxide, dicumyl peroxide, 1,3-bis- (t-butylperoxy-isopropyl) benzene, benzoyl peroxide, iso-butyryl-peroxide, bis-3,5,5-trimethylhexanoyl -peroxide or methyl-ethyl-ketone-peroxide. The grafting of an unsaturated polar monomer on a polyolefin is known to those skilled in the art, for more details, reference may be made for example to EP 689505, US 5235149, EP 658139, US 6750288 B2, US6528587 B2. The polyolefin on which the unsaturated polar monomer is grafted may be a polyethylene, in particular high density polyethylene (HDPE) or low density polyethylene (LDPE), linear low density polyethylene (LLDPE) or very low density polyethylene (VLDPE). The polyethylene can be obtained using a Ziegler-Natta, Phillips or metallocene catalyst or by the high-pressure process. The polyolefin may also be a polypropylene, especially an iso- or syndiotactic polypropylene. It may also be a copolymer of ethylene and propylene type EPR, or a terpolymer of ethylene, a propylene and a diene type EPDM. It may be, for example, functionalized polyolefins marketed by ARKEMA under the references OREVAC 18302, 18334, 18350, 18360, 18365, 18370, 18380, 18707, 18729, 18732, 18750, 18760, PP-C, CA100.

The polymer on which the unsaturated polar monomer is grafted may also be a copolymer of ethylene and at least one unsaturated polar monomer chosen from:

(C 1 -C 5) alkyl (meth) acrylates, especially methyl, ethyl, propyl, butyl, 2-ethylhexyl, isobutyl or cyclohexyl (meth) acrylate; vinyl esters of saturated carboxylic acids, in particular vinyl acetate or vinyl propionate.

It may be, for example, functionalized polyolefins marketed by ARKEMA under the references OREVAC 18211, 18216 or 18630.

Preferably, the functionalized polyolefin is chosen so that the functions of the unsaturated monomer which is grafted on the fluoropolymer react with those of the polar monomer of the functionalized polyolefin. For example, if a carboxylic acid anhydride, for example maleic anhydride, has been grafted onto the fluoropolymer, the functionalized polyolefin layer may consist of a copolymer of ethylene, an unsaturated epoxide, for example glycidyl methacrylate, and optionally an alkyl acrylate, the ethylene copolymer being optionally mixed with a polyolefin.

According to another example, if an unsaturated epoxide, for example glycidyl methacrylate, has been grafted onto the fluoropolymer, the functionalized polyolefin layer may consist of a copolymer of ethylene and a carboxylic acid anhydride. , for example maleic anhydride, and optionally an alkyl acrylate, the copolymer of ethylene being optionally mixed with a polyolefin.

The multilayer tube and all possible variants are described in greater detail. The multilayer tube comprises (in the order from the inside to the outside of the tube):

Optionally a layer Ci comprising at least one fluorinated polymer;

A layer C2 comprising a mixture of: at least one copolymer comprising at least one fluorinated monomer and at least one monomer carrying a functional group chosen from the following groups: carboxylic acid, carboxylic acid salt, carbonate, carboxylic acid anhydride, epoxide, carboxylic acid ester, silyl, alkoxysilane, carboxylic acid amide, hydroxy, isocyanate, and at least one flexible fluorinated polymer having a tensile modulus between 50 and 1000 MPa (measured according to ISO R 527 at 23 ° C), advantageously between 100 and 750 MPa and preferably between 200 and 600 MPa;

Optionally a layer C ₃ of adhesion binder; A layer C ₄ comprising at least one polyolefin or a mixture of at least one polyolefin with at least one functionalized polyolefin;

A barrier layer C ₅ which is a metal sheath or which comprises EVOH OR a mixture based on EVOH, a PVDF or a PGA; Optionally a layer Ce comprising at least one polyolefin.

According to one variant, the layer C3 is directly attached to the layer C2. According to another variant, the layer C ₄ is directly attached to the optional layer C3 or to the layer C ₂ . According to another variant, the tube comprises a layer Ci, a layer C ₂ , a layer C 3 directly attached to the layer C ₂ , a layer C ₄ directly attached to the layer C 3, a layer C ₅ and a layer Ce.

The inner layer that is in contact with the fluid is either the layer Ci or the layer C ₂ . All the layers of the tube are preferably concentric. The tube is preferably cylindrical. Preferably, the layers adhere to each other in their respective contact areas (i.e., two successive layers are directly attached to each other). advantages of the multilayer pipe The multilayer pipe:

• has a chemical resistance against the transported fluid (via the layer Ci and / or C2); • inhibits the migration of contaminants from the external environment to the transported fluid;

• slows down the migration of the contaminants present in the polyolefin of the layer C ₄ and / or the layer Ce towards the transported fluid;

• slows the migration of oxygen or additives present in the fluid transported to the layer C ₄ ;

• has a very good adhesion between the layers (no delamination).

The optional layer C ₁ This layer comprises at least one fluorinated polymer (this fluoropolymer is not modified by radiation grafting). Preferably, the fluoropolymer is a homo- or copolymer PVDF or a copolymer based on VDF and EFFE-type TFE.

The layer C?

This layer comprises a mixture of at least one functionalized fluoropolymer and at least one flexible fluorinated polymer. It has a function of this chemical and protective bonding with the layer C3 or _C4. It also has an adhesion binder function between the polyolefin layer and the fluoropolymer layer when the latter is present. This mixture makes it possible to obtain a very strong adhesion, which is more of the cohesive type.

The mixture comprises, by weight, from 1 to 99 parts, advantageously from 10 to 90 parts, preferably from 10 to 75 parts, more preferably from 10 to 50 parts, of a functionalized fluoropolymer for 99 to 1 parts, advantageously from 90 to 10 parts, preferably from 90 to 25 parts, even more preferably from 90 to 50 parts of a flexible fluorinated polymer. Preferably, the viscosity of the functionalized fluoropolymer (measured with a capillary rheometer at 230 ^° C. at 100 sec ^-1 ) is between 100 and 1500 Pa · s, advantageously between 200 and 1000 Pa · s and preferably between 500 and 1000. Not.

Preferably, the viscosity of the flexible fluorinated polymer (measured by capillary rheometer at 230 ^° C. at 100 sec ^-1 ) is between 100 and 1500 Pa.s, advantageously between 200 and 1000 Pa.s, preferably between 500 and 1000 Pa. .s.

Preferably, the crystallization temperature of the flexible fluorinated polymer (measured by DSC according to ISO 11357-3) is between 50 and 120 ° C, preferably between 85 and 110 ^° C.

Preferably, the functionalized fluoropolymer is a radiation-grafted fluoropolymer. Preferably, it is a radiation-grafted PVDF. Advantageously, the radiation-grafted PVDF is obtained from a PVDF comprising by weight at least 80%, advantageously at least 90%, preferably at least 95%, even more preferably at least 98% of VDF. Most preferably it is a PVDF homopolymer (i.e. with 100% VDF).

Preferably, the flexible fluorinated polymer is a copolymer PVDF, more particularly a copolymer of VDF and HFP.

The eventual Cs layer

The layer C3 which is arranged between the layer C2 and the layer C ₄ serves to reinforce the adhesion between these two layers. It comprises an adhesion binder that is to say a polymer whose function is to improve the adhesion between these two layers. The adhesion binder can for example comprise at least one functionalized polyolefin optionally mixed with a polyolefin. In the case where a mixture is used, it comprises, by weight, from 1 to 99%, advantageously from 10 to 90%, preferably from 50 to 90%, of functionalized polyolefin for 99 to 1%, preferably 90 to 90% by weight. 10%, preferably 10 to 50%, of polyolefin. The polyolefin which is used for mixing with the functionalized polyolefin is preferably a polyethylene because these two polymers have good compatibility. The layer C ₃ may also comprise a mixture of two or more functionalized polyolefins. For example, it may be a mixture of a copolymer of ethylene and an unsaturated epoxide and optionally an alkyl (meth) acrylate and a copolymer of ethylene and of an alkyl (meth) acrylate.

The layer C ₄

The layer C ₄ comprises at least one polyolefin. It may also comprise at least one polyolefin mixed with at least one functionalized polyolefin. In this case, the mixture comprises, by weight, from 1 to 99%, advantageously from 10 to 90%, preferably from 10 to 50%, of functionalized polyolefin for 99 to 1%, preferably 90 to 10%, preferably from 50 to 90% of polyolefin. The polyolefin which is used for mixing with the functionalized polyolefin is preferably a polyethylene because these two polymers have good compatibility.

In the case of such a mixture, the layer C ₃ can be suppressed if a functionalized polyolefin is used which has functions capable of reacting with the functions grafted onto the fluoropolymer. Thus, for example, if anhydride functional groups have been grafted onto the fluoropolymer, the functionalized polyolefin will advantageously comprise epoxide or hydroxy functional groups. For example still, if epoxy or hydroxy functions have been grafted onto the fluoropolymer, the functionalized polyolefin advantageously comprises anhydride functions. Similarly, this is true also for polyolefin functionalized layer C ₃ . The multilayer tube therefore comprises (in the order from inside to outside the tube):

Optionally a layer Ci of at least one fluorinated polymer;

A layer C2 comprising a mixture of at least one functionalized fluoropolymer and at least one flexible fluorinated polymer;

A layer C ₄ of at least one mixture of a polyolefin and at least one functionalized polyolefin which has functions capable of reacting with the functional groups grafted onto the fluoropolymer;

A barrier layer C ₅ which is a metal sheath or which comprises EVOH OR a mixture based on EVOH, PVDF or PGA;

Optionally a Ce layer of a polyolefin.

The barrier layer C ₅

The function of the barrier layer is to avoid contamination of the fluid, which circulates, including water or gas transported by contaminants. Oxygen and chemicals such as hydrocarbons for example are contaminants. In the more specific case of gases, moisture can be a contaminant.

The barrier layer may be a metal sheath. In addition to its barrier function, the metal sheath also has the function of reinforcing the mechanical strength of the tube. Another advantage of using a metal sheath is to be able to bend or deform the tube without it returning to its original position under the effect of the mechanical stresses generated by the thermoplastic polymer layers. The metal may be steel, copper or aluminum or an alloy of aluminum. It is preferably aluminum or an alloy of aluminum for reasons of corrosion resistance and flexibility. The metal sheath is manufactured according to one of the methods known to those skilled in the art. Reference may be made in particular to the following documents which describe processes for producing plastic / metal composite tubes: US Pat. No. 6,822,205, EP 0581208 A1, EP 0639411 B1, EP 0823867 B1 and EP 0920972 A1. Preferably, the method of: Conforming around the layers of thermoplastic polymers already coextruded (that is to say the layers Ci to C ₄ ) a metal strip having longitudinal edges bent towards a common side and placed in abutment on one another s' extending substantially parallel to the longitudinal axis of the plastic tube,

• then the longitudinal edges are welded together. They therefore form a longitudinal weld joint.

After having welded the longitudinal edges of the metal strip, a tubular metal sheath is thus obtained.

To improve the adhesion of the barrier layer C ₅ , a layer of adhesion binder is advantageously disposed between the barrier layer C ₅ and the polyolefin layer C ₄ and / or between the barrier layer C ₅ and the optional layer of polyolefin Ce. The adhesion binder is, for example, a functionalized polyolefin. It is advantageously a polyolefin on which is grafted a carboxylic acid or a carboxylic acid anhydride, for example (meth) acrylic acid or maleic anhydride. It can therefore be a polyethylene grafted with (meth) acrylic acid or maleic anhydride or a polypropylene on which is grafted (meth) acrylic acid or anhydride maleic. By way of example, mention may be made of the functionalized polyolefins sold by Arkema under the references Orevac 18302, 18334, 18350, 18360, 18365, 18370, 18380, 18707, 18729, 18732, 18750, 18760, PP-C, CA100 or by the company UNIROYAL CHEMICAL under the reference POLYBOND 1002 or 1009 (polyethylene on which is grafted acrylic acid).

The barrier layer C ₅ may also comprise a barrier polymer, for example: • EVOH OR an EVOH-based mixture;

• a PVDF;

• poly (glycolic acid) (PGA). EVOH is also called saponified ethylene-vinyl acetate copolymer. It is a copolymer having an ethylene content of 20 to 70 mol%, preferably 25 to 70 mol%, the degree of saponification of its vinyl acetate component being not less than 95% by weight. mol. EVOH is a good barrier to oxygen. Advantageously, the EVOH has a melt index between 0.5 and 100 g / 10 min (230 ^° C., 2.26 kg), preferably between 5 and 30. It is understood that the EVOH may contain small amounts of other comonomer ingredients, including alpha-olefins such as propylene, isobutene, alpha-octene, unsaturated carboxylic acids or their salts, partial alkyl esters, complete alkyl esters ,. ..

For EVOH-based blends EVOH forms the matrix, i.e., at least 40% by weight of the blend and preferably at least 50%.

PGA refers to poly (glycolic acid), that is to say a polymer containing by weight at least 60%, advantageously 70%, preferably 80% of the following units (1):

(-O-CH ₂ -C (= O) -) (1)

This polymer can be manufactured by heating at a temperature between 120 and 250 ⁰ C the 1,4-dioxane-2,5-dione in the presence of a catalyst such as a tin salt, such as SnCl ₄ . The polymerization is carried out in bulk or in a solvent. PGA can contain the following other units (2) to (6): (-O- (CH ₂ ) _n -OC (= O) - (CH ₂ ) mC (= O)) (2) with n integer inclusive of 1 to 10 and m integer from 0 to 10;

O (3)

(-O-CH-C-)

I 30

(CH ₂ ) _j H

with j integer from 1 to 10; Ri o

^R 2 (4) wherein k is an integer of 2 to 10 and R 1 and R ₂ are each independently of one another H or C 1 -C 10 alkyl;

(-OCH ₂ CH ₂ CH ₂ -OC (= O) -) (5) or

(-O-CH ₂ -O-CH ₂ CH ₂ -) (6)

PGA is described in European Patent EP 925915 B1.

The eventual CR layer

The tube may optionally comprise a layer Ce comprising at least one polyolefin. The polyolefins of the layers C ₄ and Ce may be identical or different. The layer C ₆ makes it possible to mechanically protect the tube (for example against shocks carried on the tube when it is installed), in particular to protect the layer C ₄ or the barrier layer C ₅ when it is present. It also makes it possible to mechanically reinforce the entire tube, which can make it possible to reduce the thicknesses of the other layers. To do this, the layer C ₆ may comprise at least one reinforcing agent, such as, for example, a mineral filler.

Thanks to its good thermomechanical properties, PEX is advantageously used for the layer C ₄ and / or for the layer Ce.

Each of the layers of the multilayer tube, in particular the polyolefin layer or layers, may contain additives usually used in admixture with thermoplastics, for example antioxidants, lubricating agents, colorants, flame retardants, mineral or organic fillers, antistatic agents such as carbon black or carbon nanotubes. The tube may also comprise other layers, such as an insulating outer layer.

Multilayer pipe according to a preferred variant (best mode) Multilayer pipe comprises (in order from the inside to the outside of the pipe):

Optionally a layer Ci comprising at least one PVDF homo- or copolymer;

A layer C2 comprising a mixture of at least one homo- or copolymeric PVDF on which irradiation has been grafted with maleic anhydride and at least flexible PVDF;

A layer C ₃ of adhesion binder;

A layer C ₄ comprising at least one polyethylene, preferably of the PEX type; A barrier layer C ₅ ;

Optionally a layer C ₆ of polyethylene, preferably of the PEX type.

The adhesion binder preferably comprises at least one functionalized polyolefin which has functions capable of reacting with maleic anhydride, optionally mixed with a polyolefin. Advantageously, it is a functionalized polyolefin having epoxide or hydroxy functions. For example, it may be a copolymer of ethylene, an unsaturated epoxide, for example glycidyl methacrylate, and optionally an alkyl acrylate.

Preferably, the barrier layer C ₅ is a metal sheath.

Thickness of the layers Preferably, the layers Ci, C2, C3 and C ₅ each have a thickness between 0.01 and 30 mm, advantageously between 0.05 and 20 mm, preferably between 0.05 and 10 mm. The polyolefin layers C ₄ and C ₆ preferably each have a thickness of between 0.1 and 10000 mm, advantageously between 0.5 and 2000 mm, preferably between 0.5 and 1000 mm. The layer or layers comprising the adhesion binder have a thickness of between 0.001 and 30 mm, advantageously between 0.001 and 10 mm.

Getting the tubes

Tubes without metal sheath are manufactured by coextrusion. When the polyolefin of the layer C ₄ and / or of the optional layer C ₆ is a PEX of type B (crosslinking by silane groups), the non-crosslinked polyolefin is first extruded. The crosslinking is performed after the coextrusion of the layers C2 and C _4, and optionally Ci and C3 layers is completed by heating the extruded tube, for example by the dipping in a hot water swimming pool. When the polyolefin layer C ₄ and / or the optional layer C ₆ is a PEX type A (crosslinking using a radical initiator), the crosslinking is carried out using a radical initiator which thermally active during extrusion.

The tubes with metal sheath are manufactured after coextrusion of the layers Ci to C ₄ , and of the optional layer of adhesion binder between the layer C5 and the layer C ₄ , then a metal strip is wound around the layers thus obtained. . The longitudinal edges may be welded together to form a longitudinal seam. It is then possible to extrude the layer C ₆ and optionally a layer of adhesion binder between the layer C ₅ and the layer C ₆ . When the polyolefin of the layer C ₄ and / or of the optional layer Ce is a PEX type B, the crosslinking takes place by heating the tubes, for example by immersing them in a pool of hot water.

Uses of the tube The multilayer tube can be used for the transport of different fluids. The tube is suitable for the transport of water, especially hot water, especially the transport of hot water network. The tube can be used for transport of heating hot water (temperature above 60 ^° C., or even 90 ^° C.). An interesting example of application is the radiant floor heating (radiant floor) in which the tube used to convey hot water is placed under the floor or the floor. The water is heated by a boiler and conveyed through the tube. Another example is that in which the tube is used to convey hot water to a radiator. The tube can therefore be used for radiant water heating systems. The invention also relates to a network heating system comprising the tube of the invention.

The chemical resistance of the tube is adapted to a water containing chemical additives (generally in small quantities, less than 1%) which can alter the polyolefins, especially polyethylene, especially when hot. These additives may be oxidizing agents such as chlorine and hypochlorous acid, chlorinated derivatives, bleach, ozone, etc.

For applications in which the circulating water is potable water, water for medical or pharmaceutical applications or a biological fluid, it is preferable to have a layer of unmodified fluoropolymer as a layer in contact with water (layer Ci). Microorganisms (bacteria, germs, molds, ...) have little tendency to develop on a fluoropolymer, especially on PVDF. In addition, it is preferable that the layer in contact with the water or the biological liquid is a layer of unmodified fluoropolymer that a fluoropolymer layer modified to prevent the migration of ungrafted (free) unsaturated monomer in the water. water or body fluid.

The barrier properties of the tube make it suitable for the transport of water in contaminated soil by slowing the migration of contaminants to the transported fluid. Barrier properties are also useful to prevent the migration of oxygen into the water (DIN 4726), which can be detrimental in the case where the tube is used to carry hot water for heating (the presence of oxygen is a source of corrosion of the steel or iron parts of the heating system). It is also desired to slow down the migration of the contaminants present in the polyolefin layer (antioxidants, polymerization residues, etc.) towards the transported fluid.

More generally, the multilayer pipe can be used for transporting chemicals, especially those capable of chemically degrading polyolefins.

The multilayer pipe may also be used for transporting a gas, in particular a gas under pressure. When the polyolefin is a PE80 type polyethylene or a PE100, it is especially suitable for holding at pressures greater than 10 bar, or even greater than 20 bar, or even greater than 30 bar. The gas can be of different nature. It can be for example:

A gaseous hydrocarbon (for example town gas, a gaseous alkane, especially ethane, propane, butane, a gaseous alkene, especially ethylene, propylene, butene),

• nitrogen, • helium,

• hydrogen,

• oxygen,

• a gas that is corrosive or likely to degrade polyethylene or polypropylene. For example, it may be an acid or corrosive gas, such as H ₂ S or HCl or HF.

We also mention the interest of these tubes for applications related to air conditioning in which the circulating gas is a cryogen. It can be CO ₂ , including supercritical CO ₂ , HFC or HCFC. The optional layer Ci or the layer C _{2 are} resistant to these gases because they are fluorinated polymers. Preferably, the fluoropolymer of the layers Ci and C ₂ is PVDF because it is particularly resistant. It is possible that the cryogen condenses at certain points of the air conditioning circuit and is liquid. The multilayer pipe can therefore also apply to the case where the cryogenic gas has condensed in liquid form.

the fluid can also be a fuel, for example a gasoline

The multilayer pipe can also be used for transporting a fuel, for example a gasoline, in particular a gasoline containing an alcohol. The gasoline can be, for example, gasoline M 15 (15% methanol, 42.5% toluene and 42.5% isooctane), fuel C (50% toluene, 50% isooctane), and CE10 (10%). % ethanol and 90% of a mixture containing 45% toluene and 45% isooctane, it can also be MTBE.

[Examples]

The following examples illustrate the enhanced adhesion when using a blend of flexible fluoropolymer and functionalized fluoropolymer.

Products used

KYNAR ^® 720: PVDF homopolymer from Arkema, of melt flow 20 g / 10 min (230 ⁰ C, 5 kg) and melting temperature of about 170 ⁰ C.

KYNAR ^® 710: PVDF homopolymer from Arkema, of melt flow 25 g / 10 min (230 ° C, 5 kg) and melting temperature of about 170 ⁰ C.

PVDF-1: KYNAR ^® 720 on which has been radiation-grafted maleic anhydride. The grafting was carried out by mixing in a twin screw extruder KYNAR ^® 720 with 2 wt% maleic anhydride. The mixture is granulated and then bagged in sealed aluminum bags, then the bags and their mixture are irradiated under 3 Mrad with a cobalt-60 bomb for 17 hours. The product is recovered and degassed in vacuo to remove the residual non-grafted maleic anhydride. The content of maleic anhydride grafted is 1% (infrared spectroscopy). The MFR of PVDF-1 is

13 g / 10 min (230 ° C, 5 kg). PVDF-2: KYNAR ^® 710 on which has been radiation-grafted maleic anhydride. The grafting was carried out by mixing in a twin screw extruder KYNAR ^® 710 with 2 wt% maleic anhydride. The mixture is granulated and then bagged in sealed aluminum bags, then the bags and their mixture are irradiated under 3 Mrad with a cobalt-60 bomb for 17 hours. The product is recovered and degassed in vacuo to remove the residual non-grafted maleic anhydride. The content of maleic anhydride grafted is 1% (infrared spectroscopy). The MFR of the PVDF-2 is 16 g / 10 min (230 ^° C., 5 kg).

LOTADER ^® AX 8840: copolymer of ethylene (92%) and glycidyl methacrylate (8%) from the company ARKEMA, of melt-index 5 according to ASTM D 1238

PEX: The PEX layer was obtained from a mixture containing 95% BORPEX ^® ME-2510 grade and 5% MB-51 grade sold by BOREALIS.

The examples relate to multilayer pipes having the following structure:

KYNAR ^® 720 / layer comprising functionalized fluoropolymer / LOTADER ^

AX8840 / PEX

The KYNAR ^® 720 layer is the inner layer and the PEX layer is the outer layer. PEX denotes a crosslinked polyethylene obtained from a polyethylene carrying silane functions. The PEX layer is obtained by extrusion of a mixture of two products marketed by the company

BOREALIS (95% by weight of BORPEX ^® ME-2510 which is the polyethylene carrying the silane functions and 5% of MB-51), then the crosslinking of the mixture by putting the tubes in a pool of hot water for 5 days (70 ⁰ C). Example 1 (comparative)

Manufacturing a multi-layer tube having the following structure: KYNAR ^® (120 .mu.m) / PVDF-1 (50 microns) / Lotader ^® AX8840 (50 .mu.m) / PEX (780 microns)

The tubes are obtained by coextruding a polyethylene layer modified by silane groups (extrusion temperature of about 230 ⁰ C), a layer of Lotader ^® AX8840 (extrusion temperature of the order of 250 ⁰ C) a layer of PVDF-1 and a layer of KYNAR ^® 720 (extrusion temperature of the order of 250 ° C). Then, the tubes are placed in a heated pool to obtain the PEX.

The respective thickness of the layers is (for a tube with an external diameter of 14 mm) of 0.78 mm PEX, 50 μm of LOTADER ^® 8840 and 50 μm of modified KYNAR ^® 720 and 120 μm of KYNAR ^® 720. of PEX is the outer layer. All layers adhere to each other.

Adhesion between the grafted Kynar and LOTADER ^® 8840 layers 5 days after extrusion was measured at 15 N / cm by circumferential peeling. The adhesion is adhesive type.

Example 2 (according to the invention)

The conditions of Example 1 are repeated, but the PVDF-1 layer is replaced by a layer of a mixture comprising 50% of PVDF-1 and 50% of a VDF-HFP copolymer having 16% HFP and having a viscosity at 230 ^° C. of 900 Pa.s at 100 sec ^-1 .

Adhesion between the grafted Kynar and LOTADER ^® 8840 layers 5 days after extrusion was measured at 42 N / cm by circumferential peeling. Membership is cohesive. Example 3 (according to the invention)

The conditions of Example 1 are repeated, but the PVDF-1 layer is replaced by a layer of a mixture comprising 50% of PVDF-2 and 50% of a VDF-HFP copolymer having 16% HFP and having a viscosity at 230 ^° C. of 900 Pa.s at 100 sec ^-1 .

Adhesion between the grafted Kynar and LOTADER ^® 8840 layers 5 days after extrusion was measured at 45 N / cm by circumferential peeling. Membership is cohesive.

Example 4 (comparative)

The conditions of Example 1 are repeated, but the PVDF-1 layer is replaced by a layer of a mixture comprising 50% of PVDF-2 and 50% of a VDF-HFP copolymer having 16% HFP and having a viscosity at 230 ^° C. of 2300 Pa.s at 100 sec ^-1 .

Adhesion between the grafted KYNAR and LOTADER ^® 8840 layers 5 days after extrusion was measured at 20 N / cm by circumferential peeling. The adhesion is adhesive type.

Example 1 shows that when the functionalized fluoropolymer (here a radiation-grafted PVDF) is not diluted, the layer of the polymer has an adhesion with the layer of Lotader ^® AX8840 around 15 N / cm. This adhesion is very much improved (Example 2) when the grafted fluoropolymer is diluted in a flexible fluoropolymer. The adhesion is further improved if a flexible fluoropolymer is used and in the presence of a more fluid grafted fluoropolymer (Example 3). Table I

Claims

1. Multilayer tube comprising (in order from the inside to the outside of the tube): optionally a layer Ci comprising at least one fluoropolymer;

A layer C2 comprising a mixture:

at least one functionalized fluoropolymer,

and at least one flexible fluorinated polymer having a tensile modulus of between 50 and 1000 MPa (measured according to the ISO R 527 standard at 23 ° C.), advantageously between 100 and 750 MPa and preferably between 200 and 600 MPa;

Optionally a layer C ₃ of adhesion binder;

A layer C ₄ comprising at least one polyolefin or a mixture of at least one polyolefin with at least one functionalized polyolefin;

A barrier layer C ₅ ;

Optionally a layer Ce comprising at least one polyolefin.

Multilayer tube according to claim 1, in which the barrier layer C ₅ is a metal sheath or which comprises EVOH or a mixture based on EVOH, a PVDF or a PGA.

3. multilayer pipe according to claim 1 or 2 characterized in that the functionalized fluoropolymer is a copolymer comprising at least one fluorinated monomer and at least one unsaturated monomer bearing a functional group selected from the following groups: carboxylic acid, sodium salt, carboxylic acid, carbonate, carboxylic acid anhydride, epoxide, carboxylic acid ester, silyl, alkoxysilane, carboxylic acid amide, hydroxy, isocyanate.

4. Multilayer pipe according to one of claims 1 to 4 characterized in that the functionalized fluoropolymer is obtained by grafting by irradiation of at least one unsaturated monomer on a fluoropolymer.

5. Multilayer tube according to claim 4 wherein the unsaturated monomer grafted on the fluoropolymer has a C = C double bond and at least one polar function which may be a carboxylic acid function, carboxylic acid salt, carboxylic acid, epoxide, carboxylic acid ester, silyl, alkoxysilane, carboxylic amide, hydroxy or isocyanate

The multilayer tube of claim 5 wherein the unsaturated monomer grafted onto the fluoropolymer is an unsaturated carboxylic acid having 4 to 10 carbon atoms and their functional derivatives, preferably an anhydride.

A multilayer pipe according to claim 5 wherein the unsaturated monomer which is grafted is methacrylic acid, acrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, acid undecylenic acid, allylsuccinic acid, cyclohex-4-ene-1,2-dicarboxylic acid, 4-methyl-cyclohex-4-ene-1,2-dicarboxylic acid, bicyclo 1) hept-5-ene-2,3-dicarboxylic acid, x-methylbicyclo (2,2,1-hept-5-ene-2,3-dicarboxylic acid, zinc, calcium or sodium undecylenate , maleic anhydride, itaconic anhydride, citraconic anhydride, dichloromaleic anhydride, difluoromaleic anhydride, itaconic anhydride, crotonic anhydride, glycidyl acrylate or methacrylate, allyl glycidyl ether vinyl silanes, preferably vinyl trimethoxysilane, vinyl triethoxysilane, vinyl triacetoxysilane, γ-methacryloxypropyltrimethoxysilane.

8. Multilayer pipe according to any one of the preceding claims, characterized in that the viscosity of the fluoropolymer functionalized (measured with a capillary rheometer at 230 ^° C. at 100 sec ^-1 ) is between 100 and 1500 Pa.s, advantageously between 200 and 1000 Pa · s and preferably between 500 and 1000 Pa.s.

9. Multilayer pipe according to any one of the preceding claims, characterized in that the viscosity of the flexible fluorinated polymer (measured by capillary rheometer at 230 ⁰ C to 100 s ^"1 ) is between 100 and 1500 Pa.s, advantageously between 200 and 1000 Pa.s, preferably between 500 and 1000 Pa.s.

10. multilayer pipe according to any one of the preceding claims characterized in that the crystallization temperature of the flexible fluorinated polymer (measured by DSC according to ISO 11357-3) is between 50 and 120 ° C, preferably between 85 and 110 ^° C.

Multilayer tube according to any one of the preceding claims, in which the fluoropolymer of the layer Ci and / or of the layer C2 is a polymer having in its chain at least one monomer chosen from compounds containing a vinyl group capable of open to polymerize and which contains, directly attached to this vinyl group, at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.

12. multilayer pipe according to any one of the preceding claims wherein the fluoropolymer of the layer Ci and / or the layer C2 is a homo- or copolymer of VDF containing at least 50% by weight of VDF or an EFEP.

13. Multilayer tube according to any one of the preceding claims wherein the fluoropolymer on which is grafted unsaturated monomer is a homo- or copolymer of VDF containing at least 50% by weight of VDF or an EFEP.

14. multilayer pipe according to one of the preceding claims characterized in that the layer C3 is directly attached to the layer C2.

15. Multilayer pipe according to one of the preceding claims characterized in that the layer C ₄ is directly attached to the optional layer C ₃ or to the layer C2.

16. multilayer pipe according to one of claims 1 to 13 comprising (in the order inside to outside the tube) a layer Ci, a layer C ₂ , a layer C3 directly attached to the layer C ₂ , a layer C ₄ directly attached to the layer C3, a layer C ₅ and a layer Ce.

17. Multilayer pipe according to any one of the preceding claims wherein the layers adhere to each other in their respective contact zone.

18. Multilayer pipe according to any one of the preceding claims wherein the adhesion binder comprises at least one functionalized polyolefin optionally mixed with a polyolefin.

19. Multilayer tube according to claim 18 wherein the functionalized polyolefin of the adhesion binder has functions capable of reacting with the grafted functions on the fluoropolymer.

20. multilayer tube according to one of claims 1 to 17 wherein the layer C ₃ being absent and the layer C ₄ being in direct contact with the layer C ₂ , the functionalized polyolefin of the mixture has functions capable of reacting with the functions grafted onto the fluoropolymer

21. multilayer pipe according to any one of the preceding claims wherein the polyolefin of the layer C ₄ and / or the layer C is a polymer comprising predominantly ethylene and / or propylene units.

22. Multilayer pipe according to claim 21 wherein the polyolefin is a polyethylene, homo- or copolymer, polypropylene, homo- or copolymer.

The multilayer pipe of claim 22 wherein the polyolefin is a PEX.

24. Multilayer tube comprising (in order from the inside to the outside of the tube):

Optionally a layer Ci comprising at least one fluorinated polymer, preferably as defined in one of claims 12; A layer C2 comprising the mixture as defined in one of claims 1 to 13;

A layer C ₄ comprising a mixture of at least one polyolefin and at least one functionalized polyolefin which has functions capable of reacting with the functions grafted onto the fluoropolymer; A barrier layer C5 which is a metal sheath or which comprises EVOH OR a mixture based on EVOH, PVDF or PGA;

Optionally a layer C ₆ comprising at least one polyolefin.

25. Multilayer pipe comprising (in order from the inside to the outside of the pipe):

Optionally a layer Ci comprising at least one PVDF homo- or copolymer;

A layer C2 comprising at least one homo- or copolymer PVDF onto which maleic anhydride has been grafted by irradiation; A layer C3 of adhesion binder;

A layer C ₄ comprising at least one polyethylene, preferably of the PEX type; A barrier layer C ₅ which is a metal sheath;

Optionally a Ce layer of polyethylene, preferably PEX type.

26. multilayer pipe according to one of claims 24 or 25 wherein the layers adhere to each other in their respective contact zone.

27. multilayer pipe according to one of claims 25 or 26 wherein the adhesion binder comprises at least one functionalized polyolefin having functions capable of reacting with maleic anhydride, optionally mixed with a polyolefin.

The multilayer tube of claim 27 wherein the functionalized polyolefin has epoxide or hydroxy functions.

29. Multilayer pipe according to one of claims 27 or 28 wherein the functionalized polyolefin is a copolymer of ethylene, an unsaturated epoxide, for example glycidyl methacrylate, and optionally an alkyl acrylate.

A multilayer pipe according to any one of the preceding claims wherein a layer of adhesion binder is disposed between C ₅ and C ₄ and / or between C ₅ and C ₆ .

31. Use of a tube as defined in any one of claims 1 to 30 for the transport of water, including hot water, chemicals, a gas.

32. Use of a tube as defined in any one of claims 1 to 30 for conveying a fuel.

33. Use of a tube as defined in any one of claims 1 to 30 for conveying hot water in a radiant floor heating (radiant floor) or for conveying hot water to a radiant element.

34. Use of a tube as defined in any one of claims 1 to 30 in radiant heating systems.

35. Use according to claim 31 characterized in that the gas is a gaseous hydrocarbon, nitrogen, helium, hydrogen, oxygen, a corrosive gas or capable of degrading polyethylene or polypropylene, a cryogen.

36. A method of manufacturing a multilayer pipe as defined in one of claims 1 to 30 having at least one layer of PEX type C wherein: • the different layers of the multilayer pipe are coextruded;

And then exposing the multilayer pipe thus formed to irradiation to crosslink the polyethylene layer (s).

37. Radiant heating system comprising at least one multilayer pipe according to any one of claims 1 to 30.