Abstract:
The present invention relates to a coextrusion binder comprising: 
     5 to 30 parts of a polymer (A), itself comprising a blend of a polyethylene (A1) of relative density between 0.935 and 0.980 and of a polymer (A2) chosen from elastomers, very low-density polyethylenes and ethylene copolymers, the (A1)+(A2) blend being cografted with an unsaturated carboxylic acid; 
     95 to 70 parts of a polyethylene (B) of relative density between 0.930 and 0.950; 
     the blend of (A) and (B) being such that: 
     its relative density is between 0.930 and 0.950, 
     the content of grafted unsaturated carboxylic acid is between 30 and 10,000 ppm, 
     the MFI (melt flow index) measured according to ASTM D 1238 at 190° C./21.6 kg is between 5 and 100. 
     This binder is particularly useful for petrol tanks of structure: HDPE/binder/EVOH or PA/binder/HDPE.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is related to a concurrently filed application entitled, “Coextrusion Binder, Its Use For A Multilayer Structure And The Structure Thus Obtained” the inventors being, Jean-Claude Jammet, Christophe Le Roy, Xavier Marical and Jérôme Pascal, Attorney Docket Number ATOCM-172, based on priority French application 99/04261 filed Apr. 6, 1999, said application b orated by reference herein. 
     FIELD OF THE INVENTION 
     The present invention relates to a coextrusion binder, to its use for making a multilayer structure and to the structure thus obtained. 
     SUMMARY OF THE INVENTION 
     More specifically, the coextrusion binder of the present invention comprises: 
     5 to 30 parts of a polymer (A), itself comprising a blend of a polyethylene (A1) of relative density between 0.935 and 0.980 and of a polymer (A2) chosen from elastomers, very low-density polyethylenes and ethylene copolymers, the (A1)+(A2) blend being cografted with an unsaturated carboxylic acid; 
     95 to 70 parts of a polyethylene (B) of relative density between 0.930 and 0.950; 
     the blend of (A) and (B) being such that: 
     its relative density is between 0.930 and 0.950, 
     the content of grafted unsaturated carboxylic acid is between 30 and 10,000 ppm, 
     the MFI (melt flow index) measured according to ASTM D 1238 at 190° C./21.6 kg is between 5 and 100. 
     The present invention also relates to a multilayer structure comprising a layer which comprises the coextrusion binder defined above and, directly attached to the latter, a layer (E) of a nitrogen-containing or oxygen-containing polar resin, such as a layer of a polyamide resin, of an aliphatic polyketone, of a saponified ethylene-vinyl acetate copolymer (EVOH) or of a polyester resin, or else a metal layer. 
     The invention also relates to a structure comprising the above structure and, directly attached to the latter on the binder side, either a polyolefin layer (F) or a layer of a resin chosen from the resins of the layer (E), or else a metal layer. 
     The invention also relates to a structure comprising, respectively, a polyolefin layer (F), a layer of the binder defined above, a layer of a polyamide resin or of a saponified ethylene-vinyl acetate copolymer (EVOH), a layer of the binder defined above and a polyolefin layer (F). 
     These structures are useful for manufacturing flexible or rigid packages, such as sachets, bottles or containers. These packages may be manufactured by coextrusion, lamination or coextrusion-blow moulding. 
     The invention is useful in particular for coextruded hoses or pipes and for motor-vehicle petrol tanks. 
     Petrol tanks usually consist of five layers consisting respectively of: 
     high-density polyethylene (HDPE); 
     a binder; 
     a &lt;polyamide (PA) or a copolymer having ethylene units and vinyl alcohol units (EVOH); 
     a binder; 
     HDPE. 
     Very often, a sixth layer is added between one of the binder layers and one of the HDPE layers. This sixth layer consists of manufacturing scrap resulting from the moulding of the tanks or, for a much smaller quantity, tanks which are off-specification. This scrap and these off-specification tanks are ground up in order to obtain granules. This regrind is then remelted and extruded directly on the plant for coextruding the tanks. This regrind could also be melted and regranulated by an extrusion machine, such as a twin-screw extruder, before it is reused. 
     According to a variant, the recycled product may be blended with the HDPE of the two outermost layers of the tank. It is also possible, for example, to blend the granules of recycled product with the virgin HDPE granules of these two layers. Any combination of these recycling operations may also be used. 
     The amount of recycled material may represent up to 50% of the total weight of the tank. 
     This sixth layer therefore includes all the materials of the multilayer structure, namely HDPE, binders, PA or EVOH. 
     BACKGROUND OF THE INVENTION 
     The prior art has already described multilayer petrol tanks. EP 834,415 describes structures comprising: 
     Polyethylene/Binder/EVOH/Binder/Polyethylene. 
     The binder is a maleic-anhydride-grafted polyethylene having an MFI of 0.1 to 3 and a relative density between 0.920 and 0.930 and it contains 2 to 40% by weight of material insoluble in n-decane at 90° C. It is explained that the grafted polyethylene is dissolved in n-decane at 140° C. and cooled to 90° C., at which temperature products precipitate; it is then filtered and the insoluble content is the percentage by weight which precipitates and is collected by filtration at 90° C. 
     If the content is between 2 and 40%, the binder has good petrol resistance. 
     No example shows such a polymer. The text specifies that the binder is in fact a blend of 2 to 30 parts of a grafted polyethylene having a relative density between 0.930 and 0.980 and of 70 to 98 parts of an ungrafted polyethylene having a relative density between 0.910 and 0.940, preferably 0.915 and 0.935. 
     An attempt has been made to prepare binders and the corresponding structures in accordance with this teaching. It has found that the binders were not reproducible, that is to say the choice of the product by its relative density is not a sufficient indication. 
     It has also been found that these criteria were not sufficient for the binder to withstand petrol, 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described in detail. 
     With regard to the polymer (A1), this is a polyethylene homopolymer or a copolymer of ethylene with a comonomer chosen, for example, from: 
     α-olefins, advantageously those having from 3 to 30 carbon atoms. Examples of α-olefins having 3 to 30 carbon atoms as possible comonomers comprise propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene, 1-dococene, 1-tetracocene, 1-hexacocene, 1-octacocene and 1-triacontene. These α-olefins may be used by themselves or as a blend of two or more of them; 
     the esters of unsaturated carboxylic acids, such as, for example, alkyl (meth)acrylates, the alkyl of which has from 1 to 24 carbon atoms. Examples of alkyl acrylates or methacrylates that can be used are, in particular, methyl methacrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and 2-ethylhexyl acrylate; 
     the vinyl esters of saturated carboxylic acids, such as, for example, vinyl acetate or vinyl propionate. 
     Advantageously, (A1) is a high-density polyethylene (HDPE) of relative density between 0.940 and 0.965. 
     The MFI of (A1) is between 0.1 and 3 at 2.16 kg. 
     The copolymer (A2) may, for example, be an ethylene/propylene elastomer (EPR) or an ethylene/propylene/diene elastomer (EPDM). 
     (A2) may also be a very low-density polyethylene (VLDPE) which is either an ethylene homopolymer or an ethylene/α-olefin copolymer. 
     (A2) may also be a copolymer of ethylene with at least one product chosen from (i) unsaturated carboxylic acids, their salts and their esters, (ii) vinyl esters of saturated carboxylic acids and (iii) unsaturated dicarboxylic acids, their salts, their esters, their half-esters and their anhydrides. 
     (A2) may be a metallocene polyethylene. 
     The amounts of (A1) and (A2) are advantageously 60 to 95 parts of (A1) for 40 to 5 parts of (A2). 
     The blend of (A1) and (A2) is grafted with an unsaturated carboxylic acid, that is to say (A1) and (A2) are cografted. It would not be outside the scope of the invention to use a functional derivative of this acid. 
     Examples of unsaturated carboxylic acids are those having 2 to 20 carbon atoms, such as acrylic, methacrylic, maleic, fumaric and itaconic acids. The functional derivatives of these acids comprise, for example, anhydrides, ester derivatives, amide derivatives, imide derivatives and metal salts (such as alkali metal salts) of unsaturated carboxylic acids. 
     Unsaturated dicarboxylic acids having 4 to 10 carbon atoms and their functional derivatives, particularly their anhydrides, are particularly preferred grafting monomers. 
     These grafting monomers comprise, for example, maleic, fumaric, itaconic, citraconic, allylsuccinic, cyclohex-4-ene-1,2-dicarboxylic, 4-methylcyclohex-4-ene-1,2-dicarboxylic, bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic and x-methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acids and maleic, itaconic, citraconic, allylsuccinic, cyclohex-4-ene-1,2-dicarboxylic, 4-methylenecyclohex-4-ene-1,2-dicarboxylic, bicyclo-[2.2.1]hept-5-ene-2,3-dicarboxylic and x-methyl-bicyclo[2.2.1]hept-5-ene-2,2-dicarboxylic anhydrides. 
     Examples of other grafting monomers comprise C 1 -C 8  alkyl esters or glycidyl ester derivatives of unsaturated carboxylic acids, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, glycidyl acrylate, glycidyl methacrylate, monoethyl maleate, diethyl maleate, monoethyl fumarate, dimethyl fumarate, monomethyl itaconate and diethyl itaconate; amide derivatives of unsaturated carboxylic acids, such as acrylamide, methacrylamide, the monoamide of maleic acid, the diamide of maleic acid, the N-monoethylamide of maleic acid, the N,N-diethylamide of maleic acid, the N-monobutylamide of maleic acid, the N,N-dibutylamide of maleic acid, the monoamide of fumaric acid, the diamide of fumaric acid, the N-mono-ethylamide of fumaric acid, the N,N-diethylamide of fumaric acid, the N-monobutylamide of fumaric acid and the N,N-dibutylamide of fumaric acid; imide derivatives of unsaturated carboxylic acids, such as maleimide, N-butylmaleimide, N-phenylmaleimide; and metal salts of unsaturated carboxylic acids, such as sodium acrylate, sodium methacrylate, potassium acrylate and potassium methacrylate. Maleic anhydride is preferred. 
     Various known processes may be used to graft a grafting monomer onto the blend of (A1) and (A2).The blend can contain at levels between 10 ppm and 5% additives generaly used for processing of polyolefins and such as antioxidants based on substituted phenolic molecules etc., anti UV agents, processing aids such as fatty amides, stearic acid and salt of stearic acid, fluorinated polymers known to prevent extrusion defaults, anti fog agents based on amines, antiblocking agents such as silica or talc, master batches with dyes, nucleating agents etc. 
     For example, this may be carried out by heating the polymers (A1) and (A2) to high temperatures, approximately 150 to approximately 300° C., in the presence or absence of a solvent and with or without a radical initiator. Suitable solvents that may be used in this reaction are benzene, toluene, xylene, chlorobenzene, cumene, etc. Suitable radical initiators which can be used comprise tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-tert-butyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, 1,3-bis(tert-butylperoxyisopropyl)-benzene, acetyl peroxide, benzoyl peroxide, isobutyryl peroxide, bis(3,5,5-trimethylhexanoyl) peroxide and methyl ethyl ketone peroxide. 
     The amount of grafting monomer in the blend of (A1) and (A2) modified by the grafting obtained in the abovementioned manner may be chosen in an appropriate manner, but it is preferably 0.01 to 10%, better still 600 ppm to 6%, with respect to the weight of grafted (A1) and (A2). 
     The amount of grafted monomer is determined by assaying the succinic functional groups by FTIR spectroscopy. 
     The MFI of (A), that is to say of (A1)and (A2) which have been cografted, is 5 to 100/21.6 kg. As regards the polyethylene (B), this is an ethylene homopolymer or copolymer. 
     The relative density of (B) is advantageously between 0.930 and 0.940. 
     The MFI of (B):5 to 100/21.6 kg. 
     According to one advantageous form of the invention, the binder comprises 5 to 20 parts of (A) per 95 to 80 parts of (B). 
     The relative density of the blend (A)+(B) is advantageously between 0.930 and 0.940. 
     The multilayer structure of the present invention consists of the layer comprising the above binder and of a layer (E) of oxygen-containing or nitrogen-containing polar resin, or a metal layer. 
     Examples of preferred polar resins in the layer other than the binder are polyamide resins, an aliphatic polyketone, a saponified ethylene-vinyl acetate copolymer and polyesters. 
     More specifically, they comprise long-chain synthetic polyamides having structural units of the amide group in the main chain, such as PA-6, PA-6,6, PA-6,10, PA-11, PA-6/6,6 and PA-12; a saponified ethylene-vinyl acetate copolymer having a degree of saponification of approximately 90 to 100 mol %, obtained by saponifying an ethylene/vinyl acetate copolymer having an ethylene content of approximately 15 to 60 mol %; polyesters such as polyethylene terephthalate, polybutylene terphthalate and polyethylene naphthenate, blends of these resins, or else aromatic polyesters such as liquid-crystal polymers. 
     The metal layer may, for example, be a sheet, a film or a foil of a metal such as aluminium, iron, copper, tin and nickel or an alloy containing at least one of these metals as the main constituent. The thickness of the film or of the foil may be suitably chosen and is, for example, approximately 0.01 to approximately 0.2 mm. It is common practice to degrease the surface of the metal layer before laminating the binder of the invention to it. The layer of oxygen-containing or nitrogen-containing polar resin (E) may also contain known additives in conventional amounts. 
     The invention also relates to a structure comprising respectively a polyolefin layer (F), a layer of the binder of the invention and either a layer (E) of nitrogen-containing or oxygen-containing polar resin or a metal layer. According to another particular embodiment, the invention relates to a structure respectively comprising an HDPE layer, a layer of the binder of the invention, a layer of EVOH (or of an EVOH alloy) or a layer of polyamide (or based on polyamide), a layer of the binder of the invention and an HDPE layer. Advantageously, it is in the form of rigid hollow bodies having a volume of 0.1 to 200 litres. The total thickness is between 0.2 and 20 mm, the EVOH or the polyamide representing 0.5 to 15% of this thickness, each binder layer 0.2 to 10% and the two HDPE layers the balance. 
     The MFI of the HDPE is preferably 3 to 17 g/10 min. at 190° C./21.6 kg. 
     The MFI of the EVOH is preferably 1 to 10 g/10 min. at 190° C./2.16 kg. 
     Advantageously, the external layer of HDPE may be replaced by two layers, the outer one made of optionally coloured virgin HDPE and the other made of recycled product coming from scrap and cuttings from the extrusion-blow moulding of these hollow bodies. The thickness of the external HDPE layer added to the thickness of the layer of recycled material is essentially the same as in the case of a single HDPE external layer. 
     These structures are useful for making petrol tanks or tubings for filling petrol tanks. 
     The various layers of the structures of the invention may contain additives such as fillers, stabilizers, slip agents, antistatic agents and fire-retardants. 
     The structures of the invention may be manufactured by coextrusion and extrusion-blow moulding processes, known in the field of thermoplastics. 
    
    
     EXAMPLES 
     The examples presented correspond to 5-layer structures from bottles produced by extrusion-blow moulding under the following conditions. 
     Structure of the Bottle 
     3 constituents, 5 layers; 
     HDPE/binder/EVOH/binder/HDPE; 
     thicknesses: 1.2/0.1/0.15 (EVOH) to 0.25 (PA)/0.1/1.2 mm; 
     HDPE: relative density=0.945−0.950 and MFI=5−6 g/10 min. (190° C./21.6 kg); 
     EVOH; ethylene content=29% MFI 1.7 g/10 min. (190° C./2.16 kg). 
     POLYMIDE: copolyamide 6/6,6 such as the 
     ULTRAMID C4FN from BASF. 
     Type of Bottle 
     Cylinder (Ø=70 mm) with 2 plane faces, 0.7 litre, height=270 mm and weight=170 g. 
     Extrusion-blow Moulding Conditions 
     Temperature profiles (° C.): 
     
       
         
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Head 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 HDPE 
                 200 
                 210 
                 220 
                 230 
                 230 
                 230 
               
               
                   
                 Binder 
                 210 
                 220 
                 220 
                 220 
                 220 
                 230 
               
               
                   
                 EVOH 
                 180 
                 190 
                 200 
                 210 
                 220 
                 230 
               
               
                   
                   
               
             
          
         
       
     
     Tooling Diameter of the die=20 mm 
     Diameter of the mandrel=12 mm 
     Gap=4 mm 
     Blowing stretch ratio: approximately 3. 
     Measurement of the Interlayer Peel Strength 
     15×150 mm test-pieces cut from the plane parts of the bottle and conditioned for at least 24 hours at 23° C. and 50% RH; 
     cutter initiation at one of the binder/EVOH or binder/polyamide interfaces; 
     “T” peel test at a crosshead speed of 50 mm/min. The peel strength, expressed in N/cm, is given by the plateau value of the peel force, excluding the starting peak. “MA” denotes maleic anhydride and the weight % of the cografted blend (A) denotes the proportion of the blend A in A+B. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Formulations 
                 Example 1 
                 Example 2 
                 Example 3 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Polymer A1 
                 Relative density (g/cm 3 ) 
                 0.958 
                 0.940 
                 0.950 
               
               
                   
                 MFI (g/10 min./2.16 kg) 
                 0.9 
                 1 
                 1 
               
               
                   
                 % by weight 
                 80 
                 75 
                 90 
               
               
                 Polymer A2 
                 Comonomer 
                 propylene 
                 1-octene 
                 propylene 
               
               
                   
                 Relative density (g/cm 3 ) 
                 0.880 
                 0.870 
                 0.880 
               
               
                   
                 MFI (g/10 min./2.16 kg) 
                 0.2 
                 5 
                 0.2 
               
               
                   
                 % by weight 
                 20 
                 25 
                 10 
               
               
                 Cografted 
                 MA content (ppm) 
                 4000 
                 10000 
                 6000 
               
               
                 blend A 
                 % by weight 
                 20 
                 25 
                 10 
               
               
                 Polymer B 
                 Relative density (g/cm 3 ) 
                 0.934 
                 0.938 
                 0.936 
               
               
                   
                 MFI (g/10 min./21.6 kg) 
                 14 
                 20 
                 18 
               
               
                 A + B blend 
                 Relative density (g/cm 3 ) 
                 0.936 
                 0.934 
                 0.937 
               
               
                   
                 MFI (g/10 min./21.6 kg) 
                 15 
                 18 
                 18 
               
               
                   
                 MA content (ppm) 
                 800 
                 2500 
                 600 
               
               
                 Peel strength 
                 On PA 6/6,6 (N/cm) 
                 70 
                 80 
                 75 
               
               
                   
                 On EVOH 
                 50 
                 55 
                 55 
               
               
                   
               
             
          
         
       
     
     The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. Also, the preceding specific embodiments are to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. 
     The entire disclosure of all applications, patents and publications, cited above, and of corresponding French application 99/04261, are hereby incorporated by reference. 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.