FR2876766A1 - Tube, useful e.g. in the transport of aggressive fluids, comprises: an interior layer (comprising a modified fluorinated polymer and optionally an electro conducting product); optionally binding layer; and a vulcanized elastomer layer - Google Patents

Abstract

Tube (I), comprises: an interior layer (A) (comprising a modified fluorinated polymer (which is grafted by irradiation of a compound mixed with a fluorinated polymer) and optionally an electro conducting product) in contact with a circulating fluid; optionally binding layer; and a vulcanized elastomer layer.

Description

Field of the invention

  The present invention relates to tubes based on vulcanized elastomer and fluoropolymer which has been modified by irradiation grafting, more particularly tubes having an inner layer comprising a modified fluoropolymer (B1) by irradiation grafting and a layer outer vulcanized elastomer.

  These tubes are useful in the manufacture of fuel system elements for example for fuel supply pipes, bringing gasoline from the tank to the injection system, for the tubing between the fuel tank and the fuel tank. filling port as well as for the return pipes for petrol vapors. They can also be used to carry coolant and to transfer fluids from a fuel cell (fuel-ce / 1).

  Grafting a graftable compound onto a polymer chain is a well known operation that is already widely employed to modify the physicochemical properties of polymers. Thus, maleic anhydride is grafted onto a polyolefin (polyethylene, polypropylene) in the molten state in an extruder. To do this, a radical initiator whose decomposition temperature must be carefully selected is added to the molten mixture. The grafting using a radical initiator on a fluoropolymer which comprises hydrogen atoms in its structure is much less easy. Thus, this explains that the grafting of maleic anhydride on PVDF has been poorly described.

  In addition, the content of maleic anhydride grafted onto PVDF is generally low, the grafting yield is therefore poor. A large part of ungrafted maleic anhydride thus remains, which must be removed in another step. The extrusion grafting technique also uses high temperatures and shear that can degrade the fluoropolymer chains and release hydrofluoric acid which, if not carefully removed, can be troublesome. In the remainder of the description, reference will be made to a modified fluoropolymer, also denoted (BI), to designate a fluoropolymer modified by grafting under irradiation.

  It has now been found that grafting by means of irradiation makes it possible to obtain grafting which is more effective than grafting by means of a radical initiator, which leads to a very good adhesion between the layer comprising the modified fluoropolymer. and the vulcanized elastomer layer.

  PRIOR ART AND THE TECHNICAL PROBLEM The international application WO 99/48678 describes a process for adhesion of a fluoropolymer to an elastomer by incorporation of antimony trioxide and adhesion agents such as organophosphonium salts. to the elastomer.

  EP 683725 describes tubes consisting successively of an inner layer of PVDF (polyvinylidene fluoride), a coextrusion binder and an outer layer of vulcanized elastomer. They have the advantage of having good resistance to aggressive chemical fluids and being a barrier to many fluids, in particular gasoline and fluids used in air conditioning circuits. However, they can be fragile at low temperatures. It is known to improve the impact resistance of PVDF but it is to the detriment of its chemical resistance and its barrier properties.

  In the manufacture of multilayer pipes, it is necessary that there is good interfacial adhesion between the layers so as to have good flexibility and a decrease in the creasing of the tubes.

  It has now been found that a tube having an outer layer of vulcanized elastomer and an inner layer comprising a modified fluorinated polymer (BI), optionally mixed with a fluorinated polymer (B2), has a good compromise of properties, namely good chemical resistance. of the inner layer in which the fluid flows and a good adhesion between the two layers.

  In addition, it is sometimes necessary for the inner layer to be conductive. The friction of a solvent on the inner layer of a tube can indeed generate electrostatic charges, the accumulation of which can lead to an electric discharge (spark) capable of igniting the solvent with catastrophic consequences (explosion). Also, is it sometimes necessary to make these conductive parts.

  It is known to lower the surface resistivity of resins or polymeric materials by incorporating conductive and / or semiconductor materials such as carbon black, steel fibers, carbon fibers, particles (fibers, platelets, spheres) metallized with gold, silver or nickel. Among these materials, carbon black is more particularly used, for economic reasons and ease of implementation. Apart from its particular electroconductive properties, the carbon black behaves like a charge such as for example talc, chalk, kaolin. Thus, it is known to those skilled in the art that as the level of charges increases, the viscosity of the polymer / filler mixture increases. Similarly, as the charge rate increases, the flexural modulus of the charged polymer increases and its impact resistance decreases. These known and predictable phenomena are explained in "Handbook of Fillers and Reinforcements for Plastics" edited by HS Katz and JV Milewski - Van Nostrand Reinhold Company ISBN 0-442-25372-9, see in particular Chapter 2, Section II for loads in general and Chapter 16, Section VI for carbon black in particular. As for the electrical properties of carbon black, the technical bulletin "Ketjenblack EC - BLACK 94/01" of the company AKZO NOBEL indicates that the resistivity of the formulation drops very sharply when a critical rate of carbon black, called threshold of percolation , is reached. As the carbon black content increases further, the resistivity decreases rapidly to a stable level (plateau area). It is therefore preferred, for a given resin, to operate in the plateau zone, where a dosing error will have only a small influence on the resistivity of the compound.

  PVDF has a fragile behavior in multiaxial shock. The addition of an agent to make it electroconductive as a carbon black will make it even more fragile. The various ways to improve the impact resistance properties most often involve the incorporation of soft elastomeric phases which may have core-shell type morphologies in a PVDF matrix. The major disadvantage of such an association is a sharp decrease in chemical resistance, especially when hot.

  It has now been found that it is possible to increase the impact resistance of a tube having a modified fluoropolymer inner layer and a vulcanized elastomer outer layer by using for the inner layer a particular composition comprising, in addition to the fluoropolymer modified (B1) optionally mixed with a fluoropolymer (B2), a polyethylene bearing epoxy functions and an impact modifier selected from elastomers and very low density polyethylenes.

  Figures 1/2 and 2/2 are views of tubes according to the invention.

  In FIG. 1/2, a tube 1 comprises an inner layer 2 and an outer layer 3.

  In FIG. 2/2, a tube 4 comprises an inner layer 5, a binder layer 6 and an outer layer 7.

Description of the invention

  The present invention relates to a tube having in its radial direction, from the inside to the outside: 1) a so-called inner layer intended to come into contact with a circulating fluid, said inner layer comprising (i) a modified fluoropolymer ( BI) by irradiation grafting of a graftable compound optionally mixed with a fluorinated polymer (B2), (ii) optionally an electroconductive product, 2) optionally a layer of binder, 3) a vulcanized elastomer layer.

  According to one particular form of the invention, the inner layer comprises, in addition to the modified fluorinated polymer (BI) optionally mixed with a fluorinated polymer (B2), and optionally an electroconductive product, a polyethylene carrying epoxy functional groups and an impact modifier chosen from the elastomers and very low density polyethylenes.

  The tubes of the invention have many advantages; They resist cold shock (-40 C), they have excellent flexibility, they can be made antistatic, they have a very good resistance to chemicals and can carry aggressive fluids, and they are a barrier to very many fluids such as for example gasoline automobiles, air conditioning fluids, even for a small thickness of the inner layer, E they are clean that is to say that the inner layer contains essentially no product migrating such as oligomers or plasticizers, so there is no risk that the fluid flowing in the tube causes these products that could clog devices placed on the circuit of this fluid, E the inner and outer layers do not do not delaminate under the effect of a mechanical and / or thermal stress.

  The process used to obtain the modified fluoropolymer (B1) consists in: a) melt blending a fluoropolymer and at least one graftable compound, b) the mixture obtained is formed into films, plates, granules or powder, c) irradiating this mixture in the solid state by irradiation (may be radiation y, 3 or X) under a dose of between 1 and 15 Mrad, optionally after removing the residual oxygen, d ) to remove the ungrafted graftable compound and the residues released by grafting, in particular HF.

  The inner and outer layers can be coextruded or extruded sequentially. By coextrusion, each layer is melt fed with an extruder into a coextrusion head which produces concentric flows forming the tube. This technique is known in itself. The tube is then passed through a heating furnace or tunnel to effect vulcanization (cross-linking) of the elastomer. It is recommended during the coextrusion to use a coextrusion head in which the elastomer flow remains at a sufficiently low temperature (generally of the order of 80 to 120 C) not to cause vulcanization before formation of the tube and especially clog the extruder. It is also possible to manufacture by coextrusion a tube that does not comprise the elastomer layer and then to pass this tube through a so-called cladding device or at the right angle to cover it with the elastomer layer. Then just as above to pass the tube in a furnace or a heating tunnel to perform the vulcanization of the elastomer.

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

  By way of example of monomer, mention may be made of vinyl fluoride; vinylidene fluoride (VF2); 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); perfluoro (1,3 dioxole); perfluoro (2,2-dimethyl-1,3-dioxole) (DP); the product of formula CF2 = CFOCF2CF (CF3) OCF2CF2X wherein X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2 = CFOCF2CF2SO2F; the product of formula F (CF2) nCH2OCF = CF2 wherein n is 1, 2, 3, 4 or 5; the product of formula R 1 CH 2 OCF = CF 2 in which R 1 is hydrogen or F (CF 2) z and z is 1, 2, 3 or 4; the product of formula R3OCF = CH2 wherein R3 is F (CF2) z- and z is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoropropene.

  The fluoropolymer may be a homopolymer or a copolymer, it may also include non-fluorinated monomers such as ethylene.

  Advantageously, the fluorinated polymer is chosen from: homo-and copolymers of vinylidene fluoride (VF2) preferably containing at least 50% by weight of VF2, the copolymer being chosen from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP ), trifluoroethylene (VF3) and tetrafluoroethylene (TFE), homo- and copolymers of trifluoroethylene (VF3), copolymers, and especially terpolymers, combining the residues of the chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE), hexafluoropropylene units. (HFP) and / or ethylene and optionally VF2 and / or VF3 units.

  Preferably, the fluoropolymer is polyvinylidene fluoride (PVDF) homopolymer. 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 sec -1 using a capillary rheometer. these PVDFs are well suited to extrusion and injection, preferably the PVDF has a viscosity ranging from 300 Pa.s to 1200 Pa.s, the viscosity being measured at 230 ° C., at a shear rate of 100 s -1 using a capillary rheometer.

  Preferably, the fluoropolymer is a PVDF homopolymer or a VF2-HFP copolymer containing at least 50% by weight of VF2, advantageously at least 75% by weight of VF2 and preferably at least 85% by weight of VF2.

  The MFI (abbreviation for Melt Flow Index) of the fluoropolymer is advantageously 5 and 30 g / 10 min (at 230 ° C. under a load of 5 kg) for a PVDF homopolymer and between 5 and 30 ° C. g / 10min (at 230 ° C. under a load of 5 kg) for a copolymer of VF2 and HFP.

  PVDF marketed under the brand KYNAR 710, KYNAR 720, KYNARFLEX 2850, KYNAR SUPER FLEX 2500 are perfectly suited for this formulation.

  As regards the modified fluorinated polymer (BI), this is obtained by grafting under irradiation of a graftable compound on a fluoropolymer. The fluoropolymer is modified by grafting the graftable compound by irradiation (radiations y, 13 or 1) under an irradiation dose of between 10 and 200 kGray, preferably between 10 and 150 kGray. Said fluoropolymer is premixed in the molten state to the graftable compound by all the known melt blending techniques of the prior art, preferably with the aid of an extruder.

  Then, the mixture of the fluoropolymer and the graftable compound is irradiated (radiations y, 13 or 1) allowing grafting of the reactive function on the fluoropolymer. This results in a grafting of the graftable compound at a level of 0.1 to 5% by weight (that is to say that the graftable grafted compound corresponds to 0.1 parts for 99.9 to 95 parts of fluoropolymer) preferably from 0.5 to 5%, preferably from 1 to 5%. The graftable graft compound content depends on the initial content of the graftable compound in the fluoropolymer / graftable compound mixture to be irradiated. It also depends on the effectiveness of the grafting, and therefore the duration and energy of the irradiation. Irradiation with a cobalt bomb is preferred.

  The graftable compound that has not been grafted and the residues released by grafting, in particular HF, are then removed. This operation can be performed according to techniques known to those skilled in the art. 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-methyl pyrrolidone, and then to precipitate the polymer in a non-solvent, for example in water or in an alcohol.

  This is one of the advantages of this irradiation grafting process that higher graftable graftable compound 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 graftable compound per 99 parts of the fluoropolymer), or even greater than 1.5%, whereas with a conventional grafting process in an extruder, the content is of the order of 0.1 to 0.4%.

  On the other hand, the grafting by irradiation takes place cold, typically at temperatures below 100 C, or even 70 C, so that the mixture of the fluoropolymer and the graftable compound is not in the molten state as for a conventional grafting process in an extruder. An essential difference is therefore that, in the case of a semi-crystalline fluorinated polymer (as for PVDF for example), the grafting takes place in the amorphous phase and not in the crystalline phase, while homogeneous grafting occurs. in the case of an extruder grafting. The graftable compound is therefore not distributed identically on the chains of the fluoropolymer in the case of radiation grafting and in the case of grafting in an extruder. The modified fluorinated product therefore has a different distribution of the graftable compound on the chains of the fluoropolymer compared to a product which would be obtained by grafting in an extruder.

  During this grafting step, it is preferable to avoid the presence of oxygen. A nitrogen or argon sweep of the fluoropolymer / graftable compound mixture is therefore possible to remove oxygen.

  As regards the graftable compound, it has at least one C doubleC double bond and at least one polar function which may be a function: carboxylic acid, carboxylic acid salt, carboxylic acid anhydride, epoxide carboxylic ester, silyl, carboxylic amide, hydroxy, isocyanate.

  Mixtures of several graftable compounds are also conceivable.

  Examples of graftable compounds are methacrylic acid, acrylic acid, undecylenic acid, zinc, calcium or sodium undecylenate, maleic anhydride, itaconic anhydride and crotonic anhydride. , acrylate or glycidyl methacrylate, allyl glycidyl ether, vinyl silanes such as vinyl trimethoxysilane, vinyl triethoxysilane, vinyl triacetoxysilane, γ-methacryloxypropyltrimethoxysilane.

  Preferably, to obtain good adhesion between the inner and outer layers of the tube, maleic anhydride or zinc, calcium or sodium undecylenates will be chosen. These graftable compounds also have the advantage of being solid which facilitates their introduction into an extruder. Maleic anhydride is very particularly preferred because it makes it possible to obtain excellent adhesion between the inner and outer layers of the tube.

  Due to the presence of a C = C double bond on the graftable compound, it is not excluded that the graftable compound polymerizes to give polymer chains grafted onto the fluoropolymer or free, that is to say not attached to the fluorinated polymer. By polymer chain is meant a sequence of more than 10 units of the graftable compound. In the context of the invention, it is preferable to limit the presence of grafted or free polymer chains, thus to seek to obtain chains of less than 10 units of the graftable compound. Preferably, it will be limited to chains of less than 5 units of graftable compounds, and even more preferably of less than 2 units of graftable compound.

  Similarly, it is not excluded that there is more than one C = C double bond on the graftable compound. For example, graftable compounds such as allyl methacrylate, trimethylolpropane trimethacrylate or ethylene glycol dimethacrylate may be used. However, the presence of more than one double bond on the graftable compound can lead to crosslinking of the fluoropolymer, thus to a change in the rheological properties or even to the presence of gels, which is not desired. It can then be difficult to obtain a good grafting performance while limiting the crosslinking. Also, the graftable compounds containing only one C doubleC double bond are preferred. The preferred graftable compounds are therefore those having a single C = C double bond and at least one polar function.

  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 polymerize or even to give rise to crosslinking. Maleic anhydride is very particularly preferred.

  The modified fluoropolymer has all the characteristics of the fluoropolymer before modification, in particular its very good chemical resistance and its very good resistance to oxidation, as well as its thermomechanical behavior.

  With regard to the electroconductive product these are all the conductors of electricity. Examples include metals and carbon products. As an example of carbon-based products, mention may be made of graphite, carbon black, carbon nanotubes and carbon fibers. It would not be outside the scope of the invention using several electroconductive elements. The carbon-based products that can be used are described in Handbook of fillers 2 ", published by Chem Tec Publishing 1999, page 62 ≈2.1.22, page 92 ≈2.1.33 and page 184 ≈2.2.2.

  Advantageously, the electroconductive product is chosen from carbon blacks. The carbon blacks, can be semiconducting black conductors, these carbon blacks, have a low BET surface. Of the carbon blacks that can be used, those of MMM Carbon are particularly satisfactory. Blacks having a nitrogen adsorption surface area of less than 500 m 2 / g are particularly preferred. Advantageously, these carbon blacks have a nitrogen adsorption surface of less than 100 m 2 / g. Among these different types ENSACO 250 is particularly suitable for the application because it disperses well and ensures good electrical conduction.

  Regarding the binder layer, is meant any product that allows adhesion between the inner layer and the vulcanized elastomer layer. By way of example, mention may be made of mixtures of fluorinated polymer, PMMA and optionally of acrylic elastomer of the core shell type; PMMA may comprise copolymerized (meth) acrylic acid. These binders are described in US Pat. No. 5,274,276. Mention may also be made of mixtures based on poly (meth) acrylates modified by imidization and optionally containing a fluorinated polymer; they are described in patents US 5939492, US 6040025, US 5795939 and EP 726926.

  This layer is optional in the case where the inner layer has itself a very good adhesion to the outer layer. With regard to the vulcanized elastomer layer, the vulcanizable synthetic or natural elastomers suitable for the practice of the present invention are well known to those skilled in the art, the term elastomer in the definition of the present invention meaning that it can consist of mixtures of several elastomers.

  These elastomers or elastomer mixtures have a compression set (D.R.C.) at 100 C less than 50 (Yo generally between 5 and 40% and preferably less than 30%.

  Among these, mention may be made of natural rubber, polyisoprene having a high level of double bond in the cis position, a polymerized emulsion based on styrene / butadiene copolymer, and polybutadiene having a high level of double bond in the cis position obtained by nickel, cobalt, titanium or neodynium catalysis, a halogenated ethylene / propylene / diene terpolymer, a halogenated butyl rubber, a styrene / butadiene block copolymer, a styrene / isopropene block copolymer, the halogenated products of the above polymers, an acrylonitrile copolymer butadiene, an acrylic elastomer, a fluoroelastomer, chloroprene, nitrile rubbers with incorporation of chlorinated paraffins, especially NBR rubbers, chlorinated polymers such as chlorosulfonated polyethylene (CSM), chlorinated polyethylene (CPE), PVC rubbers nitriles (especially NBR-PVC). It may also be an epichlorohydrin rubber, a copolymer of epichlorohydrin and ethylene oxide (equimolar or not) or, preferably, a terpolymer of epichlorohydrin, ethylene oxide and 'allyl glycidyl ether.

  If the tube of the invention does not comprise a binder layer, it is recommended that the elastomer be selected from functionalized elastomers, elastomers having acrylate units, halogenated elastomers and epichlorohydrin rubbers. As regards the functionalized elastomers, this function is advantageously a carboxylic acid or carboxylic acid anhydride function. In the case where the elastomers mentioned above do not contain carboxylic acid or anhydride radicals of said acids (which is the case of most of them), said radicals will be provided by grafting, in known manner, the elastomers mentioned above. above or by mixtures of elastomers, for example with elastomers with acrylic units such as acrylic acid. Preferably, the vulcanizable elastomers mentioned above comprise a content by weight of carboxylic acid or dicarboxylic anhydride radicals of between 0.3 and 10% relative to said elastomers.

  Similarly, it is possible to mix elastomers that have no functions, no acrylate units, that are not halogenated and that are not epichlorohydrin rubbers with at least one elastomer chosen from functionalized elastomers, the elastomers having acrylate units, halogenated elastomers and epichlorohydrin rubbers.

  Among the elastomers mentioned above, it is possible to choose those included in the following group: carboxylated nitrile elastomers, acrylic elastomers, carboxylated polybutadienes, grafted ethylene / propylene / diene terpolymers or mixtures of these polymers with the same elastomers but non-grafted nitriles, polybutadienes, ethylene / propylene / diene terpolymers, alone or in admixture.

  Vulcanization systems suitable for the present invention are well known to those skilled in the art and therefore the invention is not limited to any particular type of system.

  When the elastomer is based on unsaturated monomer (butadiene, isoprene, vinylidene norbornene ...), there may be mentioned four types of vulcanization systems: S sulfur systems associated with usual accelerators such as metal salts of dithiocarbamates (zinc dimethyl dithiocarbamate, tellurium, etc.), sulferamides, etc. These systems may also contain zinc oxide associated with stearic acid.

  Sulfur-donor systems in which the majority of the sulfur used for bypassing comes from sulfur-containing molecules such as the organosulfur compounds mentioned above.

  Phenolic resin systems consisting of difunctional, halogen-containing formophenolic resins associated with accelerators such as stannous chloride, zinc oxide.

  Peroxide systems. All free radical donors can be used (dicumyl peroxides, etc.) in combination with zinc oxide and stearic acid.

  When the elastomer is acrylic (butyl polyacrylate with acid or epoxy functions or any other reactive function allowing crosslinking), the usual crosslinking agents based on diamines (orthotoluidyl guanidine, diphenylguanidine, etc.) or blocked diamines (carbamate d hexamethylene diamine, etc.).

  The elastomeric compositions can be modified for certain particular properties (improvement of the mechanical properties for example) by the addition of fillers such as carbon black, silica, kaolin, aluminum, clay, talc, chalk etc. These fillers can be surface-treated with silanes, polyethylene glycols or any other coupling molecule. In general, the filler content in parts by weight is between 5 and 100 per 100 parts of elastomers.

  In addition, the compositions may be softened by plasticizers such as mineral oils derived from petroleum, esters of phthalic acid or sebacic acid, liquid polymeric plasticizers such as low molecular weight polybutadiene optionally carboxylated, and other plasticizers well known to those skilled in the art.

  The vulcanization agent combinations used are such that they must allow complete crosslinking of the elastomer according to kinetics leading to good properties of resistance to the separation of the elastomer layer and the inner layer or layer of binder.

  As regards the inner layer, this comprises (i) a modified fluoropolymer (B1) optionally mixed with a fluorinated polymer (B2), (ii) optionally an electroconductive product.

  This inner layer comprises from 100 to 5 parts, preferably from 100 to 50 parts, of modified fluorinated polymer (BI) for 0 to 95 parts, preferably 0 to 50 parts, of fluoropolymer (B2).

  The fluorinated polymer (B2) is any fluoropolymer described above. (B1) can be obtained from a fluoropolymer which is not necessarily of the same nature as the fluoropolymer (B2). For example, (B1) may be a homo- or copolymer of modified VF2 and (B2) may be a polytetrafluoroethylene.

  It can also be envisaged that (B1) is a modified fluorinated polymer obtained from a fluoroelastomer and that (B2) is a thermoplastic fluorinated polymer. Conversely, (BI) may be a modified fluorinated polymer obtained from a fluorinated thermoplastic and (B2) an elastomeric fluoropolymer.

  The proportion of electroconductive product is from 0 to 25% by weight, based on the modified fluoropolymer optionally mixed with a fluoropolymer.

  According to one particular form of the invention, the inner layer comprises, in addition to the modified fluorinated polymer (B1) optionally mixed with a fluorinated polymer (B2), and optionally an electroconductive product, a polyethylene bearing epoxy functions and an impact modifier chosen from the elastomers and very low density polyethylenes.

  More specifically, the inner layer then comprises: at 30% by weight of a mixture (A) comprising: a polyethylene bearing epoxy functions, an impact modifier chosen from elastomers and very low density polyethylenes, said impact modifier being wholly or partly functionalized at 70% by weight of a mixture (B) comprising: - a modified fluoropolymer (B1), a fluorinated polymer (B2).

  It may also include an electroconductive product.

  With regard to the mixture (A) and first polyethylene carrying epoxy functions, it may be a polyethylene on which epoxy functional groups or a copolymer of ethylene and a unsaturated epoxide.

  With regard to copolymers of ethylene and an unsaturated epoxide, mention may be made, for example, of ethylene copolymers of an alkyl (meth) acrylate and an unsaturated epoxide or copolymers of ethylene, a saturated carboxylic acid vinyl ester and an unsaturated epoxide. The amount of epoxide can be up to 15% by weight of the copolymer and the amount of ethylene of 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, it is a copolymer of ethylene of an alkyl (meth) acrylate and an unsaturated epoxide.

  Preferably the alkyl (meth) acrylate is such that the alkyl has 1 to 5 carbon atoms.

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

  Examples of alkyl acrylate or methacrylate which can be used are, in particular, methyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, acrylate and the like. 2-ethylhexyl. Examples of unsaturated epoxides that may be used include: aliphatic glycidyl esters and ethers such as allyl glycidyl ether, vinyl glycidyl ether, glycidyl maleate and itaconate, glycidyl acrylate and methacrylate, and esters and alicyclic glycidyl ethers such as 2-cyclohexene-glycidyl ether, cyclohexene-4,5-diglycidylcarboxylate, cyclohexene-4-glycidyl carboxylate, 5-norbornene-2-methyl-2-glycidyl carboxylate and endocis-bicyclo (2.2 , 1) -5-heptene-2,3-diglycidyl dicarboxylate.

  With regard to the mixture (A) and now of the impact modifier and first of the elastomers, mention may be made of SBS, SIS, SEBS block polymers and ethylene / propylene (EPR) or ethylene / propylene / diene elastomers ( EPDM). As for the very low density polyethylenes, they are, for example, polyethylenes obtained by metallocene catalysis having a density for example between 0.860 and 0.900. Mention may be made, for example, of the polyethylenes marketed by Dow Chemical under the brand name Affinity, in particular Affinity EG 8100 G, Affinity EG 8150 G and Affinity KC 8852 G. Acrylic elastomers are not suitable because they cause a permeability to gasoline. Acrylic elastomers refer to acrylic elastomers which are unsuitable because they cause permeability to gasoline. Acrylic elastomers refer to elastomers based on at least one monomer chosen from acrylonitrile, alkyl (meth) acrylates and core shells. As regards the core-shell copolymer, it is in the form of fine particles having an elastomer core and at least one thermoplastic shell (most often made of PMMA), the particle size is in general less than the pm and advantageously between 50 and 300 nm.

  Advantageously, an ethylene / propylene (EPR) or ethylene / propylene / diene (EPDM) elastomer is used. The functionalization may be provided by grafting or copolymerization with an unsaturated carboxylic acid. It would not depart from the scope of the invention using a functional derivative of this acid. Examples of unsaturated carboxylic acid are those having 2 to 20 carbon atoms such as acrylic, methacrylic, maleic, fumaric and itaconic acids. Functional derivatives of these acids include, for example, anhydrides, ester derivatives, amide derivatives, imide derivatives and metal salts (such as alkali metal salts) of unsaturated carboxylic acids. Preferred among these functional derivatives are acid anhydrides including maleic anhydride.

  The products of the EXXELOR VA range, in particular the EXXELOR VA 1803, are preferred.

  Unsaturated dicarboxylic acids having 4 to 10 carbon atoms and their functional derivatives, particularly their anhydrides, are particularly preferred grafting monomers. These grafting monomers include, 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 acid, x-methylbicyclo (2,2,1) -hept-5-ene-2,3-dicarboxylic acid, maleic, itaconic, citraconic, allylsuccinic anhydrides cyclohex-4-ene1,2-dicarboxylic acid, 4-methylenecyclohex-4-ene-1,2-dicarboxylic acid, bicyclo (2,2,1) hept-5-ene-2,3-dicarboxylic acid, and x-methylbicyclo ( 2,2,1) hept-5-ene-2,2-dicarboxylic acid. Maleic anhydride is advantageously used.

  Various known methods can be used to graft a grafting monomer onto a polymer. For example, this can be done by heating the polymers at elevated temperature, from about 150 to about 300 C, in the presence or absence of a solvent with or without a radical generator. The amount of the grafting monomer may be suitably selected but is preferably from 0.01 to 10%, more preferably from 600 to 2% based on the weight of the polymer to which the graft is attached.

  With regard to the proportions for the particular form of the invention, those of the mixture (A) are from 5 to 30%, advantageously from 5 to 10%, for respectively 95 to 70%, advantageously from 95 to 90%, of ( B). The proportion of polyethylene carrying epoxy functions may be from 1 to 2 parts per 5 parts of the impact modifier.

  For the mixture (B), there are 100 to 5 parts, preferably 100 to 50 parts, of modified fluoropolymer (B1) for 0 to 95 parts, preferably 0 to 50 parts, of fluoropolymer (B2).

  The proportion of electroconductive product is between 0 and 25% by weight relative to the totality of the mixture (A) and of the mixture (B).

  As regards the preparation of the compositions of the invention they can be prepared by melt blending of the constituents according to the usual techniques of thermoplastics.

  The inner and outer layers may also contain additives which may be: dyes; the pigments; antioxidants; - flame retardants; UV stabilizers; nanofillers; the nucleating agents.

  The tubes of the invention may have an outside diameter of between 8 mm and 25 cm. The thickness of the inner layer may be between 15 and 400 μm, preferably between 15 and 200 μm, that of the optional binder between 5 and 100 μm.

Examples

  The gas permeability of the tubes is measured by a static method at 23 C with fuel C containing 15% methanol (static method).

PRODUCTS USED

  KYNAR 720: PVDF homopolymer marketed by the company MFI ARKEMA = 14 g / 10min at 230 C under 5 kg and melting point 169 C. HYDRIN 2000: copolymer of epichlorohydrin with ethylene oxide ZEON CHEMICAL .

  KYNAR ADX 120: modified PVDF containing 1% of grafted maleic anhydride obtained according to the procedure described below, starting from a KYNAR 720. EXXELOR VA 1803: EPR elastomer grafted with maleic anhydride, of MFI 3 g / 10 min (230 ± 2.16 kg).

  LOTADER 8840: copolymer of ethylene and glycidyl methacrylate from the company ARKEMA and MVI (Melt Volume Index) 5 cm3 / 10 min (190 C 2.16 kg). It contains 92% ethylene and 8% glycidyl methacrylate by weight.

  Preparation of the Kynar ADX 120: A mixture of PVDF Kynar 720 from the company ARKEMA and 2% by weight of maleic anhydride is prepared. This mixture is prepared using a twin-screw extruder operating at 230 ° C. and 150 rpm at a flow rate of 10 kg / h.

  The granulated product thus prepared and bagged in sealed aluminum bags, then the oxygen is removed using a sweep with a stream of argon. These bags are then irradiated with gamma radiation (Cobalt 60 bomb) at 3 Mrad (10 MeV acceleration) for 17 hours. A grafting rate of 50% is determined, this rate is verified after a solubilization step in N-methyl pyrrolidone and then precipitation in a water / THF mixture (50/50 by weight). The product obtained after the grafting operation is then placed under vacuum overnight at 130 ° C. to evacuate the residual maleic anhydride and the hydrofluoric acid released during the irradiation.

  The final grafted maleic anhydride content is 1% (analysis by infrared spectroscopy on the C = 0 band around 1780 cm -1).

  Preparation of the elastomer: A composition is carried out in an internal mixer comprising 15 parts by weight: HYDRIN 2000 100 stearic acid 1 carbon black FEF N550 Extrusil (Degussa silica) 20 MgO 3 CaCO 3 This composition is mixed on a cylinder with 1 part of ZISNET F (ZEON CHEMICAL triazine).

Example 1

  A tube based on 70% by weight of Kynar 720 and 30% by weight of ADX 120 is extruded (on a Werner 40 extruder) into a diameter of 6/7 mm (inner layer), then taken up on a sheathing installation. elastomer, extruding the HYDRIN composition at 90 ° C. through a sheathing die (outer layer).

  The tube is placed in an oven at 170 ° C. for 20 minutes.

  Example 2 (Comparative): The conditions of Example 1 are repeated, but no ADX 120 is used. The inner layer is therefore composed only of KYNAR 720.

Example 3

  The conditions of Example 1 are repeated, but a mixture comprising a mixture of Kynar 720 (64% by weight), with 30% of Kynar ADX 120, 1% of LOTADER 8840 and 5% of EXXELOR is used for the inner layer. VA 1803. This mixture once produced has a nodular type morphology with an average size of dispersed phase less than 5 microns.

Claims (11)

  1. Tube having in its radial direction, from the inside towards the outside: 1) a so-called inner layer intended to come into contact with a circulating fluid, said inner layer comprising (i) a modified fluoropolymer (B1) by an irradiation grafting of a graftable compound optionally mixed with a fluorinated polymer (B2), (ii) optionally an electroconductive product, 2) optionally a layer of binder, 3) a vulcanized elastomer layer.   2. Tube according to claim 1 wherein the fluoropolymer has in its chain at least one monomer chosen from compounds containing a vinyl group capable of opening to polymerize and which contains, directly attached to this vinyl group, at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.   The tube of claim 2 wherein the fluoropolymer that is modified is a PVDF homopolymer or a VF2-HFP copolymer.   4. Tube according to one of claims 1 to 3 wherein the graftable compound has at least one C = C double bond and at least one polar function which may be a carboxylic acid function, carboxylic acid salt, dicarboxylic anhydride or carboxylic acid, epoxide, carboxylic acid ester, silyl, carboxylic amide, hydroxy and isocyanate.   The tube of claim 4 wherein the graftable compound contains only one C = C double bond. 10   The tube of claim 5 wherein the graftable compound is maleic anhydride.   7. Tube according to one of claims 1 to 6 wherein the electroconductive product is a carbon black.   8. The tube of claim 7 wherein the carbon black has a nitrogen adsorption surface of less than 100 m 2 / g.   9. The tube of claim 8 wherein the carbon black is ENSACO 250.   10. Tube according to any one of the preceding claims wherein the inner layer comprises a polyethylene bearing epoxy functions and an impact modifier selected from elastomers and very low density polyethylenes.   11. The tube of claim 10 wherein the inner layer comprises: 5 to 30% by weight of a mixture (A) comprising: a polyethylene bearing epoxy functions, - a shock modifier selected from elastomers and very low polyethylenes density, said impact modifier being wholly or partly functionalized, 95 to 70% by weight of a mixture (B) comprising: a modified fluoropolymer (B1), a fluorinated polymer (B2).   and optionally an electroconductive product.