Field of the invention

The present invention relates to a fluoropolymer-based impact-resistant barrier composition. Fluoropolymers, for example those based on vinylidene fluoride CF2=CH2 (VDF) such as PVDF (polyvinylidene fluoride) , are known to offer excellent mechanical stability/ properties, very high chemical inertness and good ageing resistance. These qualities are exploited in a variety of different application fields. For example, mention may be made of the manufacture of extruded or injection-moulded parts for the chemical engineering or microelectronics industry, the use in the form of an impermeable jacket for transporting gases or hydrocarbons, production o± films or coatings for protection purposes in the architectural field, and the production of protective elements for electrical engineering applications. The composition of the invention may be used in combination with JLayers of other materials.

The content of french appln 04-11186 filed on 20 oct 04, of french appln 04-11070 filed on 19 oct 04 and US provisionnal specification 60/64 ^* 7318 filed on 26 January 05 are incorporated in this application.

Prior art and the technical problem

The excellent chemical resistance and high impermeability of fluoropolymers is unfortunately combined with a poor low-temperature impact strength. To improve the mechanical properties at low temperature, impact modifiers of the acrylic-based core-shell particle type are most often used. These impact modifiers, apart frrom the fact that they have to be used in a large amount in order to obtain a significant reinforcement, substantially modify the chemical resistance of the ffluoropolymer, reduce its solvent resistance, increase its swellability and appreciably increase its permeability. A particularly impact-resistant and impermeable composition has now been

found that can adhere directly to substrates such as polyamide or polyolefin substrates. The composition exhibits excellent resistance to solvents, such as alcohol- based fuels, and very low permeability. Brief description of the invention

The present invention relates to a composition comprising, the total being 100%:

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

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

(advantageously between 1 and 60%) by weight of (A) + (B) .

The present invention also relates to structures comp_rising a layer made of the above composition, that is to say the structure may be either a monolayer, and therefore consist of one layer of the above composition, or a multilayer, and therefore include a layer made of the above composition. This structure is useful for making devices for storing or 'transferring fluids, in particular in cars and heavy goods vehicles. The fluids may for example be petrol, diesel, hydraulic brake fluid, compressed air for the brake circuit of heavy goods vehicles, and hydraulic clutch circuit fluid. The invention also relates to these devices, which may be tanks, pipes, hoses and containers. These structures may include other layers made of other materials, and may be manufactured by standard techniques, such as extrusion, coextrusion, coextrusion-blow moulding, coating and extrusion-coating. These structures are also useful for storing and transporting chemicals, cosmetics, solvents and perfumes. As regards the multilayer structures, in a

specific embodiment it has been surprisingly discovered that a very strong and cohesive adhesion can be attained when (Bl) is a flexible fluoropolymer. The term flexible fluoropolymer relates to a fluoropolymer having a tens ile modulus between 50 and 1000 MPa (as measured according to ISO R 527 at 23°C) , preferably between 100 and 750 MPa and even more preferably between 200 and 600 MPa.

Detailed description of the invention

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

With regard to ethylene/unsaturated epoxide copolymers, mention may be made, for example, of copolymers of ethylene with an alkyl (rneth) acrylate and with an unsaturated epoxide, or copolymers of ethylene with a vinyl ester of: a saturated carboxyldc acid and with an unsaturated epoxide. The amount of epoxide may be up to 15% by weight of the copolymer and the amount of ethylene at least 50% by weight. Advantageously, the proportion of epoxide is between 2 and 12% by weight. Advantageously, the proportion of alkyl (meth)acrylate is between 0 and 40% by weight and preferably between 5 and 35% by weight.

Advantageously, this is an ethylene/allcyl (meth) acrylate/unssturated epoxide copolymer.

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

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

Examples of alkyl acrylates and methacrylates that can be used are especially methyl methacrylate, methyl acrylate, ethyl acrylate, n-fc>utyl acrylate, isobutyl acrylate and 2-ethylhexyl acrylate. Examples of unsaturated epoxides that can be used are especially: aliphatic glycidyl esters and ethers, such as allyl glycidyl ether, vinyl glycidyl ether, glycidyl maleate, glycidyl itaconate, glycidyl acrylate and glycidyl methacrylate; and - alicyclic glycidyl esters and ethers, such as 2- cyclohexen-1-yl glycidyl ether, glycidyl cyclohexene-4, 5- dicarboxylate, glycidyl cyclohexene-4-carboxylate, glycidyl 2-methyl-5-norbornene-2-carboxylate and glycidyl endo-cis- bicyclo 2.2.1] hept-5-ene-2, 3-dicarboxylate.

With regard to blend (A) and now the impact modifier, and firstly elastomers, mention may be made of SBS, SIS and SEBS block polymers and ethylene-propylene (EPR) or ethylene-propylene-d±ene monomer (EPDM) elastomers. As regards the very low-density polyethylenes, these are, for example, metallocene polyethylenes of density between for example 0.860 and 0.900. Acrylic elastomers are not suitable as they cause permeability to petrol. The term "acrylic elastomers" denotes elastomers based on at least one monomer chosen from acrylonitrile, alkyl

(meth) acrylates and core/shell copolymers. As regards core/shell copolymers, these are in the form of fine particles having an elastomer core and at least one thermoplastic shell (usually PMMA) , the size of the particles generally toeing less than 1 μm and advantageously between 50 and 300 nm.

Advantageously, an ethylene-propylene (EPR) or ethylene- propylene-diene monomer (EPDM) elastomer is used. The functionalization may be provided by grafting or copolymerizing with an unsaturated carboxylic acid. It would not be outside the scope of the invention to use a

functional derivative of this acid. Examples of unsaturated carboxylic acids are those having 2 to 20 carbon atoms, such as acrylic, methacrylic, maleic, fumaric and itaconic acids. The functional derivatives of these acids comprise, for example, anhydrides, ester derivatives, amide derivatives, im±de derivatives and metal salts (such as alkali metal salts) of unsaturated carboxylic acids .

Unsaturated dicarboxylic acids having 4 to 10 carrbon atoms and their functional derivatives, particularly their anhydrides, are particularly preferred grafting monomers.

These grafting monomers comprise, for example,. maleic, fumaric, itacon±c, citraconic, allylsuccinic, c^clohex-4- ene-1, 2-dicarboxylic, 4-methylcyclohex-4-ene-1, 2- dicarboxylic, bi cyclo [2.2.1]hept-5-ene-2, 3-dicarboxylic and x-methylbicyclo [ 2.2.1]hept~5-ene-2, 3-dicarboxylic acids and maleic, itaconic, citraconic, allylsuccinic, c^clohex-4- ene-1, 2-dicarboxylic, 4-methylenecyclohex-4 -ene-1, 2- dicarboxylic, bi cyclo [2.2.1] hept-5-ene-2, 3-dicarboxylic and x-methylbicyclo [2.2.1]hept-5-ene-2, 2-dicarboxylic anhydrides. Advantageously, maleic anhydride is used.

Various known processes may be used to graft a grafting monomer onto a polymer. For example, this may be carried out by heating the polymers to a high temperatuxe, about 150 to about 300 ⁰ C, in the presence or absence of a solvent and with or without a radical initiator. The amount of grafting monomeir may be chosen appropriately, b>ut it is preferably from 0.01 to 10%, better still from βOO ppm to 2%, with respect to the weight of the polymer onto which the graft is attached.

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

vinyl group, at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.

As examples of monomers, mention may be made of vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene

(VF3); chlorotrifluoroethylene (CTFE); 1, 2-difluoro- ethylene; tetrafluoroethylene (TFE); hexafluoropropylene

(HFP); perfluoro (alkyl vinyl) ethers, such as perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyJL) ether

(PPVE) ;

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

As examples, the fluoropolymer is chosen from:

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

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

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

Advantageously, the fluoropolymer is a poly (vinylidene fluoride) (PVDF) homopolymer or copolymer. Preferably, the PVDF contains, by weight, at least 50%, more preferably at least 75% and better still at least 85%, VDF. The comonomer is advantageously HFP. Advantageously, the PVDF has a viscosity ranging from 100 Pa. s to 2000 Pa. s, the being measured at 230 ⁰ C with a shear rate of 100 s ^"1 using a capillary αrheometer. These PVDFs are well-suited to

extrusion and to injection moulding. Preferably, the PVDF has a viscosity ranging from 300 Pa. s to 1200 Pa. s, the viscosity being measured at 230 ⁰ C with a shear rate of 100 s ^"1 using a capillary rheometer. By way of example of functionalized fluoropolymer mention may be made of functionalized PVDF, that is a PVDF comprising monomer units of VDF and of at least one functional monomer having a least one functional group that may be one of the following groups : a carboxylic acid, a carboxylic acid salt, a carbonate, a carboxylic acid anhydride, an epoxide, a carboxylic acid esterr, a silyl, an alkoxysilane, a carboxylic amide, a hydroxyl, an isocyanate. The functionalized PVDF is prepared in suspension, in emulsion or in solution by copolymerizing VDF with said at least one functional monomer and optionally at least another comonomer.

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

As examples of unsaturated grafting monomers, mention may be made of carboxylic acids and their derivatives, acid chlorides, isocyanates, oxazolines, epoxydes , amines and hydroxides. Examples of unsaturated carboxyLic acids are those having 2 to 20 carbon atoms such as acrylic, methacrylic, maleic, fumaric and itaconic acids. The

functional derivatives of these acids comprise, for example, anhydrides, ester derivatives, amide derivatives, imide derivatives and metal salts (such as alkali metal salts) of unsaturated carboxylic acids. Mention may also be made of undecylenic acid and zinc undecylenate_

Unsaturated dicarboxylic acids having 4 to 10 carbon atoms and their functional derivatives, particularly their anhydrides, are particularly preferred grafting monomers.

Step a) is carried out in any blending devdLce, such as extruders or mixers used in the thermoplastics industry.

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

After step a) it is found that the fluoropolymer/unsaturated monomer blend has lost about 10 to 50% of the unsaturated monomer that had been introduced at the start of step a) . This proportion depends on the volatility and the nature of the unsaturated monomer. In fact, the monomer has been vented in the extruder or the mixer and it ±s recovered in the venting circuits. With regard to step c) , the products recovered after step b) are advantageously packaged in polyethylene bags and the air expelled, the bags then being sealed. During this grafting step, it is preferable to avoid the presence of oxygen. Flushing the fluoropolymer/graftable compound blend with nitrogen, or argon is therefore possible in order to eliminate the oxygen.

As regards the method of irradiation, it is possible to use, without distinction, electron irradiation, better

known as beta irradiation, and photon irradiation, better known as gamma irradiation. Advantageously, the dose is between 2 and 6 Mrad and preferably between 3 and 5 Mrad. This results in the unsaturated monomer being grafted to an amount of 0.1 to 5 wt% (that is to say the grafted unsaturated monomer corresponds to 0.1 to 5 parts per 99.9 to 95 parts of fluoropolymer) , advantageously 0.5 to 5 wt% and preferably 0.5 to 1.5 wt% ; better still 0.7 to 1.5 wt% ; better still 0.8 to 1.5 wt% ; better still 0.9 to 1.5 wt% ; better still 1 to 1.5 wt%. The grafted unsaturated monomer content depends on the initial content of the unsaturated monomer in the fluoropolymer/unsaturated monomer blend to be irradiated. It also depends on the grafting efficiency, and therefore on the duration and the energy of the irradiation.

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

As an example of a functionalized fluoropolymer, mention may also be made of one that is grafted with an unsaturated monomer, but via a radical route. The unsaturated monomer may be chosen from those mentioned above. This method is

less effective than radiation grafting - it is not possible to graft more than 0.8% of unsaturated monomer and there is a risk of degrading the fluoropolymer. However, this product may be suitable for simple operating conditions.

One of the advantages of this radiation grafting process is that it is possible to obtain higher grafted unsaturated monomer contents than with conventional grafting processes using a radical initiator. Thus, typicaLly, with the radiation grafting process, it is possible to obtain contents of greater than 1% (one part of unsaturated monomer per 99 parts of fluoropolymer) , orr even greater than 1.5%, whereas with a conventional grafting process carried out in an extruder, the content is around 0.2 to 0.8%. Moreover, radiation grafting takes place "cold", typically at temperatures below 100 ⁰ C, or even below 70 ⁰ C, so that the fluoropolymer/unsaturated monomex blend is not in the melt state, as in the case of a. conventional grafting process carried out in an extruder. One essential difference is therefore that, in the case of a semicrystalline fluoropolymer (as is the case with PVDF for example) the grafting takes place in the amorphous phase and not in the crystalline phase, whereas homogeneous grafting is produced in the case of grafting carried out in an extruder. The unsaturated monomer is therefore not distributed along the fluoropolymer chains in the same way in the case of radiation grafting as in the case of grafting carried out in an extruder. The modified fluoropolymer therefore has a different distribution of the graftable compound along the fluoropolymer chains compared with a product obtained by grafting carried out in an extruder.

As examples of functionalized fluoropolymers , mention may also be made of those in which a functional monomer or a species carrying a functional group has been incorporated during trie polymerization. By way of example such

incorporation comes from the chain transfer agent. Such functionalized fluoropolymers are disclosed in patents US 5 415 958,- US 6 680 124 and US 6 703 465 and patent application US 2004-0191440, the contents of which are incorporated into the present application.

With regard to the fluoropolymer (Bl) _r this may be chosen from the same polymers as (B2) . (Bl) may be the same polymer as (B2), but not functionalized, or it may be different. As regards the specific embodiment in which (Bl) is a flexible polymer Preferably, the viscosity (measured at 230 ⁰ C at a shear rate of 100 s-1 using a capillary rheometer) of the flexible fluoropolymer ranges from 100 to 1500 Pa. s. Preferably, the crystallization temperature (measured by DSC according to ISO 11357-3) of the flexible fluoropolymer is from 50 to 120 ⁰ C, more preferably from 85 to 110 ⁰ C.

With regard to the proportions, those of (A) are advantageously from 5 to 10% per 95 to 90% of (B) respectively. The proportion of the polyethylene carrying epoxy functional groups may be from 1 to 2 parts per 5 parts of impact modifier. The proportion of (B2) is advantageously between 25 and 35% by weight of (A) + (B) if the composition of the invention is to adhere to a polyolefin. The proportion of (B2) is advantageously between 45 and 55% by weight of (A) + (B) if the composition of the invention is to adhere to a polyamide.

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

The compositions of the invention may furthermore contain at least one additive chosen from: dyes; pigments; antioxidants;

fire retardants;

UV stabilizers; nanofillers; nucleating agents.

The invention also relates to structures. As examples of structures according to the inveation, mention may be made of those comprising, in succession: an inner layer in contact with th.e fluid to be transported or to be stored, consisting of the composition of the invention, and, directly attached to the said inner layer a polyolefin outer layer. This structure is useful for petrol tanks or tubes.

In the above structures, a layer of functionalized polyolefin having functional groups capable of reacting with the functional groups of the fluoropolymer (B2) may be placed between the layer of the composition of the invention and the polyolefin layer. For example, if maleic anhydride has been grafted onto the fluoropolymer (B2), the functionalized polyolefin layer consists of a polyethylene carrying epoxy functional groups. Such polymers were mentioned previously. Advantageously, the layer of functionalized polyolefin consists of an ethylene/glycidyl methacrylate copolymer and possibly a glycidyl methacrylate/alkyl acrylate copolymer, optionally blended with polyethylene.

In the above structures, the inner ¹ layer in contact with the fluid to be transported or stored may contain carbon black, carbon nanotubes or any other additive capable of making said layer conductive in orrder to prevent the build¬ up of static electricity.

As examples of structures accoirding to the invention, mention may also be made off those comprising, in succession:

a layer consisting of the composition of the invent ±on placed between two polyolefin layers. This structure is useful for petrol tanks in motor vehicles.

As examples of structures according to the invention, mention may also be made of those comprising, in succession: a polyolefin layer placed between two layers consisting of the composition of the invention. This structure is useful for petrol tubes and hoses in filling stations.

In the above structuires, a layer of functionalized polyolefin having functional groups capable of reacting with the functional groups of the fluoropolymer (B2) may be placed between the one or two layers of the composition according to the invention and the one or two polyolefin layers. For example, if maleic anhydride has been grafted onto the fluoropolymer (B2), the functionalized polyolefin layer consists of a polyethylene carrying epoxy functional groups. Such polymers were mentioned previously. Advantageously, the layer of functionalized polyolefin consists of an ethylene/g-lycidyl methacrylate copolymer and possibly a glycidyl methscrylate/alkyl acrylate copolymer, optionally blended with polyethylene.

Examples

The following polymers were used:

Kynar ^® ADX 120: a functional PVDF homopolymer grafted with maleic anhydride, from Arkema, with an MVI (Melt Volume Index) of 7 cm ³ /10 min (230°C/5 kg) .

Kynar ^® 720: A PVDF homopolymer from Arkema with an MIVI (Melt Volume Index) of 7 cm ³ /10 min (230°C/5 kg) . Kynar ^® ADX 140: a functional PVDF homopolymer grafted with maleic anhydride, from Arkema, with an MVI (Melt Volume Index) of 0.6 cm ³ /10 min (23O°C/5 kg) .

Kynar ^® 740: A PVDF homopolymer from Arkema with an KIVI (Melt Volume Index) of 1 cm ³ /10 min (230°C/5 kg) .

LOTADER ^® 884O: an ethylene/glycidyl methacrylate copolymer from Arkema with an MVI (Melt Volume Index) of 5 cm ³ /10 min (190°C/2.16 kg) and containing 92% ethylene and 8% glycidyl methacrylate by weight. FINATHENE ^® 3802 HDPE: a high-density polyethylene from Arkema with an MFI of 0.2 g/10 min (2.16 kg/190°C) . Its density is 0.938.

EXXELOR ^® VA 1803: an EPR elastomer grafted with maleic anhydride, with an MFI of 3 g/10 min (230°C-2.16 kg) .

Example 1: according to the invention

A Kynar 740 (44 wt%)/Kynar ADX 140 (50 wt%) /LOTADER 8840 (1 wt%) /EXXELOR VA 1803 (5 wt%) blend was produced at 230 ⁰ C in a Werner 40-type extruder. This blend, once produced, has a nodular morphology, the mean size of the dispensed phase being less than 5 μm. This formulation was injection- moulded to form a bar, which was tested using the notched Charpy impact method (ISO 179-1:2000) at -40 ⁰ C. A toughness value of 26 kJ/m ² was obtained. For comparison, pure Kynar 720 under the same conditions has a toughness of 5 kJ/m ² . Example 1 bis : according to the invention

A Kynar 720 (44 wt%) /Kynar ADX 120 (50 wt%) /LOTADER 8840 (1 wt%) /EXXELOR VA 1803 (5 wt%) blend was produced at 230°C in a Werner 40-type extruder. This blend, once produced, has a nodular morphology, the mean size of the disperrsed phase being less than 5 μm. This formulation was injection- moulded to form a bar, which was tested using trie notched Charpy impact method (ISO 179-1:2000) at -40 ⁰ C. A toughness value of 10 k:J/m ² was obtained. Example 2: according to the invention

The blend prepared in Example 1 was coextruded over a Lotader 8840 itself coextruded over a Finathene 3802 HDPE. This coextrusion was carried out in a McNeil extruder at 24O ⁰ C. The three-layer tube had a diameter of 32 mm and a thickness of 3 mm (2600 μm of HDPE, 100 μm of Lotader 8840 and 300 μm of the blend prepared in Example 1) . The adhesion obtained between the Lotader and the formulation

of Example 1 was 55 N/cm. The PE/Lotader interface could not be peeled. This tube had a permeability to CElO at 4O°C of 1 g/m ² /day (petrol CElO con-tains 45% iso-octane, 45% toluene and 10% ethanol by volume) .

The tube was subjected to a bail drop test with a 500 g ball from a height of 1 m at -30 ⁰ C. No cracking could be observed on the internal layer and the external layer of the tube.

As a. comparison, the same tube made of pure ADX 120 instead of the blend of Example 1 also had a permeability to CE lO of 1_ g/rrr/day . However, when this tube was subj ected to t he same impact test , a crack on tine internal layer and t he exte rnal layer of the tube was observed .