Fuel tank having a multilayer structure

FIELD OF THE INVENTION

[0002] This invention relates to automotive fuel tanks and more particularly to a multilayer plastic fuel tank.

BACKGROUND OF THE INVENTION

[0003] European Patent EP 742 236 describes petrol tanks consisting of five layers which are, respectively:

[0004] high density polyethylene (HDPE);

[0005] a binder;

[0006] a polyamide (PA) or a copolymer containing ethylene units and vinyl alcohol units (EVOH);

[0007] a binder;

[0008] HDPE.

[0009] A sixth layer can be added between one of the layers of binder and one of the HDPE layers. This sixth layer consists of manufacturing scraps following molding of the tanks, and to a much smaller extent of non-compliant tanks. These scraps and non-compliant tanks are then ground until granules are obtained. This ground material is then re-melted and extruded directly at the tank co-extrusion plant. This ground material may also be melted and re-granulated by means of an extruding machine such as a twin-screw extruder, before being reused.

[0010] According to one variant, the recycled product can be mixed with the HDPE from the two extreme layers of the tank. It is possible, for example, to mix the granules of recycled product with granules of virgin HDPE of these two layers. It is also possible to use any combination of these two recyclings. The content of recycled material can represent up to 50% of the total weight of the tank.

[0011] European Patent EP 731 308 describes a tube comprising an inner layer comprising a mixture of polyamide and of polyolefin with a polyamide matrix and an outer layer comprising a polyamide. These tubes based on polyamide are useful for transporting petrol and more particularly for bringing the petrol from the motor vehicle tank to the motor and also, but in larger diameter, for transporting hydrocarbons in service stations between the distribution pumps and the underground storage tanks.

[0012] According to another form of the tube, a layer of a polymer comprising ethylene units and vinyl alcohol units (EVOH) can be placed between the inner and outer layers. The structure: inner layer/EVOH/binder/outer layer is advantageously used.

[0013] The tanks described in EP 742 236 which do not have the barrier layer in direct contact with the petrol do admittedly have barrier properties, but they are not sufficient when very low petrol losses are desired. EP 731 308 describes tubes whose outer layer is made of polyamide and the barrier layer is in direct contact with the petrol, wherein the layer made of polyamide is necessary for the mechanical strength of the assembly. Novel structures have now been found which have better barrier properties and which are useful for various objects such as, for example, petrol tanks for motor vehicles.

SUMMARY OF THE INVENTION

[0014] The present invention relates to a plastic fuel tank having a multilayer wall structure, wherein a barrier layer forms an exposed face of the wall and preferably is in direct contact with the fuel contained therein. The barrier layer of the structures of the invention constitutes one of the exposed faces of the structure, i.e. it is not an interior layer of the wall structure. Fuel tank structures embodying the invention have walls with HDPE/barrier layer or HDPE/binder/barrier layer, in which “HDPE” denotes high density polyethylene.

[0015] Preferably, the fuel tank structure comprises successively:

[0016] a first layer of high density polyethylene (HDPE),

[0017] a layer of binder,

[0018] a second layer of EVOH or of a mixture based on EVOH, and

[0019] optionally a third layer of polyamide (A) or a mixture of polyamide (A) and polyolefin (B).

[0020] In the text hereinbelow, the second layer or the combination of the second and the third layer is referred to as the “barrier layer” and forms an exterior face of the wall structure.

[0021] The invention is particularly useful for a fluid such as motor vehicle petrol or volatile hydrocarbon fuels such as gasoline, by avoiding losses through the structure so as not to pollute the environment.

[0022] Objects, features and advantages o this invention include providing a plastic fuel tank which has significantly less hydrocarbon fuel emissions, readily complies with stringent environmental protection standards and requirements, is of economical manufacture and assembly and in service has a long useful life.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] These and other objects, features and advantages of this invention will be apparent from the following detailed description of the best modes, appended claims and accompanying drawings in which:

[0024]
FIG. 1 is a perspective view of an automotive plastic fuel tank according to one presently preferred embodiment of the invention;

[0025]
FIG. 2 is a fragmentary sectional view of a wall of the fuel tank of FIG. 1;

[0026]
FIG. 3 is a fragmentary sectional view of a modified wall of a fuel tank embodying this invention;

[0027]
FIG. 4 is a fragmentary sectional view of a wall of a fuel tank according to another presently preferred embodiment of the invention; and

[0028]
FIG. 5 is an enlarged fragmentary sectional view of a portion of the wall of the fuel tank as in FIG. 4 in the area of a pinch line of the fuel tank.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Referring in more detail to the drawings, FIG. 1 illustrates an automotive plastic fuel tank 10 embodying this invention with a wall 12 having a plastic filler neck or pipe 14 with a flange 16 and a fuel pump module 18 with a cover flange 20 each heat welded to the wall. As shown in FIG. 2, the wall 12 has an exposed outer first layer 22 of HDPE, an inner exposed second layer 24 of EVOH and a binder layer 26 between them which adheres the first and second layers together. The second layer 24 is in contact with liquid fuel in the tank 10 and provides the primary vapor barrier and the first layer 22 provides the primary strength and structural integrity of the tank. The adhesive layer bonds or adheres together the dissimilar first and second layers.

[0030]
FIG. 3 illustrates a modified wall 12′ construction of a fuel tank 10 with an inner first layer 22 of HDPE, an outer exposed second layer 24 of EVOH and a binder layer 26 between them which adheres the first and second layers together. In both forms of the tank, the second vapor barrier layer 26 of EVOH preferably also has a third film or layer 28 of a polyamide (A) or a mixture of a polyamide (A) and a polyolefin (B).

[0031] Preferably, the fuel tank 10 is formed by simultaneously co-extruding all of the layers and adhesive together into a hollow parison which is then placed in a mold with a cavity having the desired shape and configuration of the tank and the parison is blow molded to form the fuel tank.

[0032] The first layer 22 is a high density polyethylene (HDPE) which may also have some carbon black or poly black mixed therein to provide coloration and may include a re-grind layer of HDPE which is composed of re-ground scrap materials from the manufacturing of the fuel tanks 10 and/or salvaged and re-ground HDPE. The first layer 22 and any re-grind layer are preferably of substantially the same composition. The adhesive layer may be of a wide variety of materials and is necessary to attach the layer of HDPE to the vapor barrier second layer and thereby increase the structural integrity of the fuel tank 10 which is paramount for passing various crush resistance specifications in the automotive industry. The second vapor barrier layer is necessary to reduce the amount of hydrocarbon vapors which would diffuse or escape through the fuel tank wall 12 which is composed primarily of HDPE.

[0033] A typical multilayer plastic fuel tank wall 10 has a thickness of between about 3 mm and 10 mm, with an optimal total wall thickness of about 5-6 mm. Nominal values for the individual layers of the multilayer plastic fuel tank 10 are as follows: the first layer 22 comprises between about 90 to 97 percent of the total wall thickness; the binder or adhesive layer 26 comprises between about 1 to 4 percent of the total wall thickness; and the vapor barrier second layer 24 or second and third layers 24,28 comprises between about 2 to 6 percent of the total wall thickness. These ranges of the thickness of the individual layers are illustrative only and can be readily varied during the co-extrusion of the parison for the fuel tank wall 12 during the manufacture of fuel tank 10.

[0034] Throughout a production run of fuel tanks 10, the thickness of the individual layers must be controlled to assure optimum performance and quality of the fuel tank 10 in use. The thickness of the first layer 22 of polyethylene is important because this layer provides structural protection of the vapor barrier layer(s) 24, 28 and also strength and structural integrity of the fuel tank 10 itself. The thickness of the adhesive layer 26 is important to insure adequate attachment between the adjacent layers of HDPE and the vapor barrier layer(s) 24, 28. Finally, the thickness of the vapor barrier layer(s) 24,28 is important to prohibit the permeation of the hydrocarbon vapors through the fuel tank 10 and into the atmosphere.

[0035] As regards the first layer, the high density polyethylene (HDPE) is described in Kirk-Othmer, 4th Edition, Vol. 17, pages 704 and 724-725. It is, according to ASTM D 1248-84, an ethylene polymer with a density at least equal to 0.940. The name HDPE relates both to ethylene homopolymers and its copolymers with small proportions of olefin. The density is advantageously between 0.940 and 0.965. In the present invention, the MFI of the HDPE is advantageously between 0.1 and 50. By way of example, mention may be made of Eltex B 2008® with a density of 0.958 and an MFI of 0.9 (in g/10 min at 190° C. under 2.16 kg), Finathene® MS201B from FINA and Lupolen® 4261 AQ from BASF.

[0036] As regards the second layer, the EVOH copolymer is also referred to as a saponified ethylene-vinyl acetate copolymer. The saponified ethylene-vinyl acetate copolymer to be used according to the present invention is a copolymer with an ethylene content of from 20 to 70 mol %, preferably from 25 to 70 mol %, the degree of saponification of its vinyl acetate component not being less than 95 mol %. With an ethylene content of less than 20 mol %, the barrier properties under conditions of high humidity are not as high as would be desired, whereas an ethylene content exceeding 70 mol % leads to reductions in barrier properties. When the degree of saponification or of hydrolysis is less than 95 mol %, the barrier properties are sacrificed.

[0037] The expression “barrier properties” means the impermeability to gases, to liquids and in particular to oxygen, and to petrol for motor vehicles. The invention relates more particularly to the barrier to petrol or volatile hydrocarbon fuels such as gasoline for motor vehicles.

[0038] Among these saponified copolymers, those which have melt flow indices, under hot conditions, in the range from 0.5 to 100 g/10 minutes are particularly useful. Advantageously, the MFI is chosen between 5 and 30 (g/10 min at 230° C. under 2.16 kg), “MFI”, the abbreviation for “melt flow index” denoting the flow rate in the molten state.

[0039] It is understood that this saponified copolymer can contain small proportions of other comonomer ingredients, including α-olefins such as propylene, isobutene, α-octene, α-dodecene, α-octadecene, etc., unsaturated carboxylic acids or salts thereof, partial alkyl esters, whole alkyl esters, nitrites, amides and anhydrides of the said acids, and unsaturated sulphonic acids or salts thereof.

[0040] As regards the mixtures based on EVOH, they are such that the EVOH forms the matrix, i.e. it represents at least 40% by weight of the mixture and preferably at least 50%. The other constituents of the mixture are chosen from polyolefins, polyamides and optionally functional polymers.

[0041] As a first example of these mixtures based on EVOH of the second layer, mention may be made of the compositions comprising (by weight):

[0042] 55 to 99.5 parts of EVOH copolymer,

[0043] 0.5 to 45 parts of polypropylene and of compatibilizer, the proportions thereof being such that the ratio of the amount of polypropylene to the amount of compatibilizer is between 1 and 5.

[0044] Advantageously, the ratio of the MFI of the EVOH to the MFI of the polypropylene is greater than 5 and preferably between 5 and 25. Advantageously, the MFI of the polypropylene is between 0.5 and 3 (in g/10 min at 230° C. under 2.16 kg). According to one advantageous form, the compatibilizer is a polyethylene bearing polyamide grafts and it results from the reaction (i) of a copolymer of ethylene and of a grafted or copolymerized unsaturated monomer X, with (ii) a polyamide. The copolymer of ethylene and of a grafted or copolymerized unsaturated monomer X is such that X is copolymerized and it can be chosen from ethylene-maleic anhydride copolymers and ethylene-alkyl (meth)acrylate-maleic anhydride copolymers, these copolymers comprising from 0.2 to 10% by weight of maleic anhydride and from 0 to 40% by weight of alkyl (meth)acrylate. According to another advantageous form, the compatibilizer is a polypropylene bearing polyamide grafts which results from the reaction (i) of a propylene homopolymer or copolymer comprising a grafted or copolymerized unsaturated monomer X, with (ii) a polyamide. Advantageously, X is grafted. The monomer X is advantageously an unsaturated carboxylic acid anhydride such as, for example, maleic anhydride.

[0045] As a second example of these mixtures based on EVOH of the second layer, mention may be made of compositions comprising:

[0046] 50 to 98% by weight of an EVOH copolymer

[0047] 1 to 50% by weight of a polyethylene

[0048] 1 to 15% by weight of a compatibilizer consisting of a mixture of an LLDPE polyethylene or metallocene and of a polymer chosen from elastomers, very low density polyethylenes and metallocene polyethylenes, the mixture being co-grafted with an unsaturated carboxylic acid or a functional derivative of this acid.

[0049] Advantageously, the compatibilizer is such that the ratio MFI10/MFI2 is between 5 and 20, in which MFI2 is the mass melt flow index at 190° C. under a load of 2.16 kg, measured according to ASTM D1238, and MFI10 is the mass melt flow index at 190° C. under a load of 10 kg according to ASTM D1238.

[0050] As a third example of these mixtures based on EVOH of the second layer, mention may be made of compositions comprising:

[0051] 50 to 98% by weight of an EVOH copolymer

[0052] 1 to 50% by weight of an ethylene-alkyl (meth)acrylate copolymer,

[0053] 1 to 15% by weight of a compatibilizer resulting from the reaction (i) of a copolymer of ethylene and of a grafted or copolymerized unsaturated monomer X with (ii) a copolyamide.

[0054] Advantageously, the copolymer of ethylene and of a grafted or copolymerized unsaturated monomer X is such that X is copolymerized and it is a copolymer of ethylene and of maleic anhydride or a copolymer of ethylene, of an alkyl (meth)acrylate and of maleic anhydride. Advantageously, these copolymers comprise from 0.2 to 10% by weight of maleic anhydride and from 0 to 40% by weight of alkyl (meth)acrylate.

[0055] As regards the polyamide (A) and the mixture of polyamide (A) and polyolefin (B) of the third layer, the term “polyamide” means the following products of condensation:

[0056] of one or more amino acids, such as aminocaproic acid, 7-aminoheptanoic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid of one or more lactams such as caprolactam, oenantholactam and lauryllactam;

[0057] of one or more salts or mixtures of diamines such as hexamethylenediamine, dodecamethylenediamine, meta-xylylenediamine, bis(p-aminocyclohexyl)methane and trimethylhexamethylenediamine with diacids such as isophthalic acid, terephthalic acid, adipic acid, azelaic acid, suberic acid, sebacic acid and dodecanedicarboxylic acid.

[0058] As examples of polyamides, mention may be made of PA 6 and PA 6-6. It is also advantageously possible to use copolyamides. Mention may be made of the copolyamides resulting from the condensation of at least two α,ω-aminocarboxylic acids or of two lactams or of one lactam and one α,ω-aminocarboxylic acid. Mention may also be made of the copolyamides resulting from the condensation of at least one α,ω-aminocarboxylic acid (or a lactam), at least one diamine and at least one dicarboxylic acid.

[0059] As examples of lactams, mention may be made of those containing from 3 to 12 carbon atoms on the main ring and which can be substituted. Mention may be made, for example, of β,β-dimethylpropiolactam, α,α-dimethylpropiolactam, amylolactam, caprolactam, capryllactam and lauryllactam.

[0060] As examples of α,ω-aminocarboxylic acids, mention may be made of aminoundecanoic acid and aminododecanoic acid. As examples of dicarboxylic acids, mention may be made of adipic acid, sebacic acid, isophthalic acid, butanedioic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, sodium or lithium salts of sulphoisophthalic acid, dimerized fatty acids (these dimerized fatty acids have a dimer content of at least 98% and are preferably hydrogenated) and dodecanedioic acid HOOC—(CH2)10—COOH.

[0061] The diamine can be an aliphatic diamine containing from 6 to 12 atoms, it can be arylic and/or saturated cyclic. As examples, mention may be made of hexamethylenediamine, piperazine, tetramethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, diaminepolyols, isophoronediamine (IPD), methylpentamethylenediamine (MPDM), bis(aminocyclohexyl)methane (BACM) and bis(3-methyl-4-aminocyclohexyl)methane (BMACM).

[0062] As examples of copolyamides, mention may be made of copolymers of caprolactam and of lauryllactam (PA 6/12), copolymers of caprolactam, of adipic acid and of hexamethylenediamine (PA 6/6-6), copolymers of caprolactam, of lauryllactam, of adipic acid and of hexamethylenediamine (PA 6/12/6-6), copolymers of caprolactam, of lauryllactam, of 11-aminoundecanoic acid, of azelaic acid and of hexamethylenediamine (PA 6/6-9/11/12), copolymers of caprolactam, of lauryllactam, of 11-aminoundecanoic acid, of adipic acid and of hexamethylenediamine (PA 6/6-6/11/12) and copolymers of lauryllactam, of azelaic acid and of hexamethylenediamine (PA 6-9/12).

[0063] Advantageously, the copolyamide is chosen from PA 6/12 and PA 6/6-6. The advantage of these copolyamides is that their melting point is less than that of PA 6.

[0064] It is also possible to use any amorphous polyamide which has no melting point.

[0065] The MFI of the polyamides and mixtures of polyamide and of polyolefin of the present invention is measured according to the rules of the art at a temperature of 15 to 20° C. above the melting point of the polyamide. As regards the mixtures based on PA 6, the MFI is measured at 235° C. under 2.16 kg. As regards the mixtures based on PA 6-6, the MFI is measured at 275° C. under 1 kg.

[0066] Polyamide mixtures can be used. Advantageously, the MFI of the polyamides is between 1 and 50 g/10 min.

[0067] It would not constitute a departure from the context of the invention to replace some of the polyamide (A) with a copolymer containing polyamide blocks and polyether blocks, i.e. to use a mixture comprising at least one of the above polyamides and at least one copolymer containing polyamide blocks and polyether blocks.

[0068] The copolymers containing polyamide blocks and polyether blocks result from the copolycondensation of polyamide sequences containing ends that are reactive with polyether sequences containing reactive ends, such as, inter alia:

[0069] I) polyamide sequences containing diamine chain ends with polyoxyalkylene sequences containing dicarboxylic chain ends.

[0070] 2) polyamide sequences containing dicarboxylic chain ends with polyoxyalkylene sequences containing diamine chain ends, obtained by cyanoethylation and hydrogenation of α,ω-dihydroxylated aliphatic polyoxyalkylene sequences known as polyetherdiols.

[0071] 3) polyamide sequences containing dicarboxylic chain ends with polyetherdiols, the products obtained being, in this specific case, polyetheresteramides. These copolymers are advantageously used.

[0072] The polyamide sequences containing dicarboxylic chain ends originate, for example, from the condensation of α,ω-aminocarboxylic acids, lactams or dicarboxylic acids and diamines in the presence of a chain-limiting dicarboxylic acid.

[0073] The polyether can be, for example, a polyethylene glycol (PEG), a polypropylene glycol (PPG) or a polytetramethylene glycol (PTMG). The latter is also known as polytetrahydrofuran (PTHF).

[0074] The number-average molar mass Mn of the polyamide sequences is between 300 and 15,000 and preferably between 600 and 5000. The mass Mn of the polyether sequences is between 100 and 6000 and preferably between 200 and 3000.

[0075] The polymers containing polyamide blocks and polyether blocks can also comprise randomly distributed units. These polymers can be prepared by the simultaneous reaction of the polyether and of polyamide block precursors.

[0076] For example, it is possible to react polyetherdiol, a lactam (or an α,ω-amino acid) and a chain-limiting diacid in the presence of a small amount of water. A polymer is obtained essentially containing polyether blocks, polyamide blocks of very variable length, but also various reagents which have reacted randomly and which are distributed randomly along the polymer chain.

[0077] Whether they originate from the copolycondensation of polyamide and polyether sequences prepared previously or from a one-step reaction, these polymers containing polyamide blocks and polyether blocks have, for example, Shore D hardnesses which can be between 20 and 75 and advantageously between 30 and 70, and an inherent viscosity of between 0.8 and 2.5, measured in meta-cresol at 250° C. for an initial concentration of 0.8 g/100 ml. The MFI values can be between 5 and 50 (235° C. under a load of 1 kg).

[0078] The polyetherdiol blocks are either used as they are and copolycondensed with polyamide blocks containing carboxylic ends, or they are aminated so as to be converted into polyetherdiamines and condensed with polyamide blocks containing carboxylic ends. They can also be mixed with polyamide precursors and a chain-limiter in order to make polymers containing polyamide blocks and polyether blocks having randomly distributed units.

[0079] Polymers containing polyamide and polyether blocks are described in U.S. Pat. Nos. 4,331,786; 4,115,475; 4,195,015; 4,839,441; 4,864,014; 4,230,838 and 4,332,920.

[0080] The ratio of the amount of copolymer containing polyamide blocks and polyether blocks to the amount of polyamide is, on a weight basis, advantageously between 10/90 and 60/40. Mention may be made, for example, of mixtures of (i) PA 6 and (ii) copolymer containing PA 6 blocks and PTMG blocks and mixtures of (i) PA 6 and (ii) copolymer containing PA 12 blocks and PTMG blocks.

[0081] As regards the polyolefin (B) of the mixture of polyamide (A) and polyolefin (B) of the third layer, it can be functionalized or non-functionalized or can be a mixture of at least one functionalized and/or of at least one non-functionalized. For simplicity, functionalized polyolefins (B 1) and non-functionalized polyolefins (B2) have been described below.

[0082] A non-functionalized polyolefin (B2) is conventionally a homopolyrner or copolymer of α-olefins or of diolefins such as, for example, ethylene, propylene, 1-butene, 1-octene or butadiene. By way of example, mention may be made of:

[0083] polyethylene homopolymers and copolymers, in particular LDPE, HDPE, LLDPE (linear low density polyethylene), VLDPE (very low density polyethylene) and metallocene polyethylene.

[0084] propylene homopolymers or copolymers.

[0085] ethylene/α-olefin copolymers such as ethylene/propylene, EPR (abbreviation for ethylene-propylene-rubber) and ethylene/propylene/diene (EPDM).

[0086] styrene/ethylene-butene/styrene (SEBS), styrene/butadiene/styrene (SBS), styrene/isoprene/styrene (SIS) or styrene/ethylene-propylene/styrene (SEPS) block copolymers.

[0087] copolymers of ethylene with at least one product chosen from unsaturated carboxylic acid salts or esters, such as alkyl (meth)acrylate (for example methyl acrylate), or saturated carboxylic acid vinyl esters, such as vinyl acetate, it being possible for the proportion of comonomer to be up to 40% by weight.

[0088] The functionalized polyolefin (B1) can be an α-olefin polymer containing reactive units (functionalities); such reactive units are acid, anhydride or epoxy functions. By way of example, mention may be made of the above polyolefins (B2) grafted or co- or terpolymerized with unsaturated epoxides such as glycidyl (meth)acrylate, or with carboxylic acids or the corresponding salts or esters such as (meth)acrylic acid (it being possible for the latter to be totally or partially neutralized with metals such as Zn, etc.) or alternatively with anhydrides of carboxylic acids such as maleic anhydride. A functionalized polyolefin is, for example, a PE/EPR mixture, in which the weight ratio can vary within a wide range, for example between 40/60 and 90/10, the said mixture being co-grafted with an anhydride, in particular maleic anhydride, according to a degree of grafting of, for example, from 0.01 to 5% by weight.

[0089] The functionalized polyolefin (B1) can be chosen from the following (co)polymers, grafted with maleic anhydride or glycidyl methacrylate, in which the degree of grafting is, for example, from 0.01 to 5% by weight:

[0090] PE, PP, copolymers of ethylene with propylene, butene, hexene or octene containing, for example, from 35 to 80% by weight of ethylene;

[0091] ethylene/α-olefin copolymers such as ethylene/propylene copolymers, EPR (abbreviation for ethylene-propylene-rubber) and ethylene/propylene/diene (EPDM) copolymers.

[0092] styrene/ethyhlene-butene/styrene (SEBS), styrene/butadiene/styrene (SBS), styrene/isoprene/styrene (SIS) or styrene/ethylene-propylene/styrene (SEPS) block copolymers.

[0093] ethylene-vinyl acetate (EVA) copolymers containing up to 40% by weight of vinyl acetate;

[0094] copolymers of ethylene and of alkyl (meth)acrylate, containing up to 40% by weight of alkyl (meth)acrylate;

[0095] ethylene-vinyl acetate (EVA) and alkyl (meth)acrylate copolymers, containing up to 40% by weight of comonomers.

[0096] The functionalized polyolefin (BI) can also be chosen from ethylene/propylene copolymers predominantly containing propylene grafted with maleic anhydride and then condensed with monoamino polyamide (or a polyamide oligomer) (products described in EP-A-0 342 066).

[0097] The functionalized polyolefin (B1) can also be a co- or terpolymer of at least the following units: (1) ethylene, (2) alkyl (meth)acrylate or saturated carboxylic acid vinyl ester and (3) anhydride such as maleic anhydride or (meth)acrylic acid or epoxy such as glycidyl (meth)acrylate. Examples of functionalized polyolefins of the latter type which may be mentioned are the following copolymers, in which ethylene preferably represents at least 60% by weight and in which the termonomer (the function) represents, for example, from 0.1 to 10% of the weight of the copolymer:

[0098] ethylene/alkyl (meth)acrylate/(meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymers;

[0099] ethylene/vinyl acetate/maleic anhydride or glycidyl methacrylate copolymers;

[0100] ethylene/vinyl acetate or alkyl (meth)acrylate/(meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymers.

[0101] In the preceding copolymers, the (meth)acrylic acid can be salified with Zn or Li.

[0102] The term “alkyl (meth)acrylate” in (B 1) or (B2) denotes C1 to C8 alkyl methacrylates and acrylates and can be chosen from methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate and ethyl methacrylate.

[0103] Moreover, the abovementioned polyolefins (B 1) can also be crosslinked by any suitable process or agent (diepoxy, diacid, peroxide, etc.); the expression “functionalized polyolefin” also comprises mixtures of the abovementioned polyolefins with a difunctional reagent such as diacid, dianhydride, diepoxy, etc. which can react with the latter or mixtures of at least two functionalized polyolefins which can react together.

[0104] The copolymers mentioned above, (B1) and (B2), can be copolymerized in a random or block manner and can have a linear or branched structure.

[0105] The molecular weight, the MFI index and the density of these polyolefins can also vary within a wide range, which a person skilled in the art will appreciate. MFI, the abbreviation for melt flow index, is the flow rate in the molten state. It is measured according to ASTM standard 1238.

[0106] Advantageously, the non-functionalized polyolefins (B2) are chosen from polypropylene homopolymers or copolymers and any homopolymer of ethylene or copolymer of ethylene and of a comonomer of higher α-olefinic type such as butene, hexene, octene or 4-methyl-1-pentene. Mention may be made, for example, of PPs, high density PEs, medium density PEs, linear low density PEs, low density PEs and very low density PEs. These polyethylenes are known by those skilled in the art as being produced according to a “radical-mediated” process, according to a catalysis of “Ziegler” type or, more recently, according to a so-called “metallocene” catalysis.

[0107] Advantageously, the functionalized polyolefins (B1) are chosen from any polymer comprising α-olefinic units and units bearing reactive polar functions such as epoxy, carboxylic acid or carboxylic acid anhydride functions. As examples of such polymers, mention may be made of the terpolymers of ethylene, of alkyl acrylate and of maleic anhydride or of glycidyl methacrylate, such as the products Lotader® from ELF Atochem S.A. or polyolefins grafted with maleic anhydride, such as the products Orevac® from ELF Atochem S.A., as well as terpolymers of ethylene, of alkyl acrylate and of (meth)acrylic acid. Mention may also be made of polypropylene homopolymers or copolymers grafted with a carboxylic acid anhydride and then condensed with polyamides or monoamino polyamide oligomers.

[0108] The MFI of (A) and the MFI of (B1) and (B2) can be chosen within a wide range, but it is recommended, in order to facilitate the dispersion of (B), that the MFI of (A) be greater than that of (B).

[0109] For small proportions of (B), for example 10 to 15 parts, it is sufficient to use a non-functionalized polyolefin (B2). The proportion of (B2) and (B1) in the phase (B) depends on the amount of functions present in (B1) as well as their reactivity. Advantageously, (B1)/(B2) weight ratios ranging from 5/35 to 15/25 are used. For small proportions of (B), it is also possible to use only one mixture of polyolefins (B1) to obtain crosslinking.

[0110] According to a first preferred form of the invention, the polyolefin (B) comprises (i) a high density polyethylene (HDPE) and (ii) a mixture of a polyethylene (C1) and a polymer (C2) chosen from elastomers, very low density polyethylenes and ethylene copolymers, the mixture (C1)+(C2) being co-grafted with an unsaturated carboxylic acid.

[0111] According to a second preferred form of the invention, the polyolefin (B) comprises (i) polypropylene and (ii) a polyolefin which results from the reaction of a polyamide (C4) with a copolymer (C3) comprising propylene and a grafted or copolymerized unsaturated monomer X.

[0112] According to a third preferred form of the invention, the polyolefin (B) comprises (i) a polyethylene of LLDPE, VLDPE or metallocene type and (ii) an ethylene-alkyl (meth)acrylate-maleic anhydride copolymer.

[0113] According to a fourth preferred form of the invention, the polyamide (A) is chosen from mixtures of (i) polyamide and (ii) copolymer containing PA 6 blocks and PTMG blocks and mixtures of (i) polyamide and (ii) copolymer containing PA 12 blocks and PTMG blocks; the ratio of the amounts of copolymer and of polyamide by weight being between 10/90 and 60/40. According to a first variant, the polyolefin (B) comprises (i) a polyethylene of LLDPE, VLDPE or metallocene type and (ii) an ethylene-alkyl (meth)acrylate-maleic anhydride copolymer; according to a second variant, the polyolefin comprises two functionalized polymers comprising at least 50 mol % of ethylene units and which can react to form a crosslinked phase.

[0114] As regards the first form, the proportions are advantageously as follows (by weight):

[0115] 60 to 70% of polyamide,

[0116] 5 to 15% of the co-grafted mixture of (C1) and (C2)

[0117] the remainder being high density polyethylene.

[0118] As regards the high density polyethylene, its density is advantageously between 0.940 and 0.965 and the MFI between 0.1 and 5 g/10 min (190° C., 2.16 kg).

[0119] The polyethylene (C1) can be chosen from the polyethylenes mentioned above. Advantageously, (C1) is a high density polyethylene (HDPE) with a density of between 0.940 and 0.965. The MFI of (C1) is (under 2.16 kg-190° C.) between 0.1 and 3 g/10 min.

[0120] The copolymer (C2) can be, for example, an ethylene/propylene elastomer (EPR) or ethylene/propylene/diene elastomer (EPDM). (C2) can also be a very low density polyethylene (VLDPE) which is either an ethylene homopolymer or a copolymer of ethylene and of an α-olefin. (C2) can also be a copolymer of ethylene with at least one product chosen from (i) unsaturated carboxylic acids, salts thereof, esters thereof, (ii) vinyl esters of saturated carboxylic acids, (iii) unsaturated dicarboxylic acids, their salts, their esters, their hemiesters and their anhydrides. Advantageously, (C2) is an EPR.

[0121] Advantageously, 60 to 95 parts of (C 1) are used per 40 to 5 parts of (C2).

[0122] The mixture of (C 1) and (C2) is grafted with an unsaturated carboxylic acid, i.e. (C1) and (C2) are co-grafted. It would not constitute a departure from the context of the invention to use a functional derivative of this acid. Examples of unsaturated carboxylic acids are those containing from 2 to 20 carbon atoms, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid or itaconic acid. The functional derivatives of these acids comprise, for example, the anhydrides, the ester derivatives, the amide derivatives, the imide derivatives and the metal salts (such as the alkali metal salts) of unsaturated carboxylic acids.

[0123] Unsaturated dicarboxylic acids containing 4 to 10 carbon atoms and functional derivatives thereof, particularly their anhydrides, are grafting monomers that are particularly preferred. These grafting monomers comprise, for example, maleic acid, fumaric acid, itaconic acid, citraconic acid, allylsuccinic acid, 4-cyclohexene-1,2-dicarboxylic acid, 4-methyl-4-cyclohexene-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, maleic anhydride, itaconic anhydride, citraconic anhydride, allylsuccinic anhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 4-methylene-4-cyclohexene-1,2-dicarboxylic anhydride, bicyclo(2,2,1)hept-5-ene-2,3-dicarboxylic anhydride and x-methylbicyclo(2,2,1)hept-5-ene-2,2-dicarboxylic anhydride. Maleic anhydride is advantageously used.

[0124] Various known processes can be used to graft a grafting monomer onto the mixture of (C1) and (C2). For example, this can be carried out by heating the polymers (C1) and (C2) to high temperature, about 150° C. to about 300° C., in the presence or absence of a solvent with or without a radical-generator.

[0125] In the mixture of (C1) and (C2) modified by grafting, obtained in the abovementioned manner, the amount of the grafting monomer can be chosen in an appropriate manner, but is preferably from 0.01 to 10%, better still from 600 ppm to 2%, relative to the weight of grafted (C1) and (C2). The amount of the grafted monomer is determined by assaying the succinic functions by FTIR spectroscopy. The MFI of (C1) and (C2) which have been co-grafted is from 5 to 30 g/10 min (190° C.-2.16 kg), preferably 13 to 20.

[0126] Advantageously, the mixture of co-grafted (C1) and (C2) is such that the MFI10/MFI2 ratio is greater than 18.5, MFI10 denoting the flow rate at 190° C. under a load of 10 kg and MFI2 denoting the flow rate under a load of 2.16 kg. Advantageously, the MFI20 of the mixture of co-grafted polymers (C 1) and (C2) is less than 24. MFI20 denotes the flow rate at 190° C. under a load of 21.6 kg.

[0127] As regards the second form of the invention, the proportions are advantageously as follows (by weight):

[0128] 60 to 70% of polyamide,

[0129] 20 to 30% of polypropylene

[0130] 3 to 10% of a polyolefin which results from the reaction of a polyamide (C4) with a copolymer (C3) comprising propylene and a grafted or copolymerized unsaturated monomer X.

[0131] The MFI of the polypropylene is advantageously less than 0.5 g/10 min (230° C.-2.16 kg) and preferably between 0.1 and 0.5. Such products are described in EP 647 681.

[0132] The grafted product of this second form of the invention is now described. To begin with, (C3) is prepared, which is either a copolymer of propylene and of an unsaturated monomer X or a polypropylene onto which is grafted an unsaturated monomer X. X is any unsaturated monomer which can be copolymerized with the propylene or grafted onto the polypropylene and which has a function that can react with a polyamide. This function can be, for example, a carboxylic acid, a dicarboxylic acid anhydride or an epoxide. As examples of monomers X, mention may be made of (meth)acrylic acid, maleic anhydride and unsaturated epoxides such as glycidyl (meth)acrylate. Maleic anhydride is advantageously used. As regards the grafted polypropylenes, X can be grafted onto polypropylene homo- or copolymers, such as ethylene-propylene copolymers predominantly containing propylene (in moles). Advantageously, (C3) is such that X is grafted. The grafting is an operation which is known per se.

[0133] (C4) is a polyamide or a polyamide oligomer. Polyamide oligomers are described in EP 342 066 and FR 2 291 225. The polyamides (or oligomers) (C4) are the products of condensation of the monomers already mentioned above. Mixtures of polyamides can be used. PA-6, PA-11, PA 12, the copolyamide containing units 6 and units 12 (PA-6/12) and the copolyamide based on caprolactam, hexamethylenediamine and adipic acid (PA-6/6.6) are advantageously used. The polyamides or oligomers (C4) can contain acid, amine or monoamine endings. In order for the polyamide to contain a monoamine ending, it suffices to use a chain-limiter of formula R1—NH|R2 in which:

[0134] R1 is hydrogen or a linear or branched alkyl group containing up to 20 carbon atoms,

[0135] R2 is a group containing up to 20 linear or branched alkyl or alkenyl carbon atoms, a saturated or unsaturated cycloaliphatic radical, an aromatic radical or a combination of the above. The limiter can be, for example, laurylamine or oleylamine.

[0136] Advantageously, (C4) is a PA-6, a PA-11 or a PA-12. The proportion of C4 in C3+C4 by weight is advantageously between 0.1 and 60%. The reaction of (C3) with (C4) is preferably carried out in the molten state. For example, (C3) and (C4) can be blended in an extruder at a temperature generally of between 230 and 250° C. The average residence time of the molten material in the extruder can be between 10 seconds and 3 minutes and preferably between 1 and 2 minutes.

[0137] As regards the third form, the proportions are advantageously as follows (by weight):

[0138] 60 to 70% of polyamide,

[0139] 5 to 15% of an ethylene-alkyl (meth)acrylate-maleic anhydride copolymer.

[0140] The remainder is a polyethylene of LLDPE, VLDPE or metallocene type; advantageously, the density of this polyethylene is between 0.870 and 0.925, and the MFI is between 0.1 and 5 (190° C.-2.16 kg).

[0141] Advantageously, the ethylene-alkyl (meth)acrylate-maleic anhydride copolymers comprise from 0.2 to 10% by weight of maleic anhydride, up to 40% and preferably 5 to 40% by weight of alkyl (meth)acrylate. Their MFI is between 2 and 100 (190° C.-2.16 kg). The alkyl (meth)acrylates have already been described above. The melting point is between 80 and 120° C. These copolymers are commercially available. They are produced by radical-mediated polymerization at a temperature which can be between 200 and 2500 bar.

[0142] As regards the fourth form, the proportions are advantageously as follows (by weight):

[0143] According to a first variant:

[0144] 60 to 70% of the mixture of polyamide and of copolymer containing polyamide blocks and polyether blocks,

[0145] 5 to 15% of an ethylene-alkyl (meth)acrylate-maleic anhydride copolymer,

[0146] The remainder is a polyethylene of LLDPE, VLDPE or metallocene type; advantageously, its density is between 0.870 and 0.925, and the MFI is between 0.1 and 5 (190° C.-2.16 kg).

[0147] Advantageously, the ethylene-alkyl (meth)acrylate-maleic anhydride copolymers comprise from 0.2 to 10% by weight of maleic anhydride, up to 40% and preferably 5 to 40% by weight of alkyl (meth)acrylate. Their MFI is between 2 and 100 (190° C.-2.16 kg). The alkyl (meth)acrylates have already been described above. The melting point is between 80 and 120° C. These copolymers are commercially available. They are produced by radical-mediated polymerization at a pressure which can be between 200 and 2500 bar.

[0148] According to a second variant:

[0149] 40 to 95% of the mixture of polyamide and of copolymer containing polyamide blocks and polyether blocks,

[0150] 60 to 5% of a mixture of an ethylene-alkyl (meth)acrylate-maleic anhydride copolymer and of an ethylene-alkyl (meth)acrylate-glycidyl methacrylate copolymer.

[0151] The copolymer with the anhydride was defined in the first variant. The ethylene/alkyl (meth)acrylate/glycidyl methacrylate copolymer can contain up to 40% by weight of alkyl (meth)acrylate, advantageously from 5 to 40%, and up to 10% by weight of unsaturated epoxide, preferably 0.1 to 8%. Advantageously, the alkyl (meth)acrylate is chosen from methyl (meth)acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and 2-ethylhexyl acrylate. The amount of alkyl (meth)acrylate is preferably from 20 to 35%. The MFI is advantageously between S and 100 (in g/10 min at 190° C. under 2.16 kg) and the melting point is between 60 and 110° C. This copolymer can be obtained by radical-mediated polymerization of the monomers.

[0152] Catalysts can be added to accelerate the reaction between the epoxy and anhydride functions. Among the compounds capable of accelerating the reaction between the epoxy function and the anhydride function, mention may be made in particular of:

[0153] tertiary amines such as dimethyllaurylamine, dimethylstearylamine, N-butylmorpholine, N,N-dimethylcyclohexylamine, benzyldimethylamine, pyridine, 4-dimethylaminopyridine, 1-methylimidazole, tetramethylethylhydrazine, N,N-dimethylpiperazine, N,N,N′,N′-tetramethyl-1,6-hexanediamine, a mixture of tertiary amines containing from 16 to 18 carbon atoms, known under the name dimethyltallowamine,

[0154] tertiary phosphines such as triphenylphosphine

[0155] zinc alkyldithiocarbamates

[0156] acids.

[0157] The preparation of the mixtures of the third layer can be carried out by mixing together the various constituents in the molten state in the apparatus usually used in the thermoplastic polymer industry.

[0158] The first layer can consist of a layer of virgin HDPE and a layer of recycled polymers obtained from scraps from the manufacture of the transfer or storage devices or of these non-compliant devices as explained in the prior art already mentioned. This recycled layer is located on the binder layer side. In the text herein below these two layers will be denoted for simplicity by the term “first layer”.

[0159] The thickness of the first layer can be between 2 and 10 mm, that of the second layer between 30 and 500 μm and that of the third layer between 30 μm and 2 mm. The total thickness is usually between 3 and 10 mm.

[0160] A layer of binder can also be placed between the second and the third layer. By way of examples of binders, mention may be made of the functionalized polyolefins (B 1) described above. The binder between the first and second layer and that between the second and third layer may be identical or different. In the descriptions below of binders, the term “polyethylene” denotes both homopolymers and copolymers; such products have been described earlier in the polyolefins of the third layer.

[0161] As a first example of a binder, mention may be made of the mixture of co-grafted (C1) and (C2) described above in the first preferred form of the third layer.

[0162] As a second example of a binder, mention may be made of mixtures comprising:

[0163] 5 to 30 parts of a polymer (D) which itself comprises a mixture of a polyethylene (D1) with a density of between 0.910 and 0.940 and of a polymer (D2) chosen from elastomers, very low density polyethylenes and metallocene polyethylenes, the mixture (D1)+(D2) being co-grafted with an unsaturated carboxylic acid,

[0164] 95 to 70 parts of a polyethylene (E) with a density of between 0.910 and 0.930,

[0165] the mixture of (D) and (E) being such that:

[0166] its density is between 0.910 and 0.930,

[0167] the content of grafted unsaturated carboxylic acid is between 30 and 10,000 ppm,

[0168] the MFI(ASTM D 1238-190° C.-2.16 kg) is between 0.1 and3 g/10 min.

[0169] The MFI denotes the melt flow index.

[0170] The density of the binder is advantageously between 0.915 and 0.920. Advantageously, (D1) and (E) are LLDPEs, and preferably have the same comonomer. This comonomer can be chosen from 1-hexene, 1-octene and 1-butene.

[0171] As a third example of a binder, mention may be made of mixtures comprising:

[0172] 5 to 30 parts of a polymer (F) which itself comprises a mixture of a polyethylene (F) with a density of between 0.935 and 0.980 and of a polymer (F2) chosen from elastomers, very low density polyethylenes and ethylene copolymers, the mixture (F1)+(F2) being co-grafted with an unsaturated carboxylic acid,

[0173] 95 to 70 parts of a polyethylene (G) with a density of between 0.930 and 0.950,

[0174] the mixture of (F) and (G) being such that:

[0175] its density is between 0.930 and 0.950 and advantageously between 0.930 and 0.940,

[0176] the content of grafted unsaturated carboxylic acid is between 30 and 10,000 ppm,

[0177] the MFI (melt flow index) measured according to ASTM D 1238 at 190° C.-21.6 kg is between 5 and 100.

[0178] As a fourth example of a binder, mention may be made of polyethylene grafted with maleic anhydride, having an MFI of 0.1 to 3, a density of between 0.920 and 0.930 and containing 2 to 40% by weight of insolubles in n-decane at 90° C. To determine the insolubles in n-decane, the grafted polyethylene is dissolved in n-decane at 140° C., the solution is cooled to 90° C. and products precipitate; the mixture is then filtered and the insolubles 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 resistance to petrol.

[0179] Advantageously, the grafted polyethylene is diluted in a non-grafted polyethylene and such that the binder is a mixture of 2 to 30 parts of a grafted polyethylene with a density of between 0.930 and 0.980 and from 70 to 98 parts of a non-grafted polyethylene with a density of between 0.910 and 0.940, preferably between 0.915 and 0.935.

[0180] As a fifth example of a binder, mention may be made of mixtures comprising:

[0181] 50 to 100 parts of a polyethylene homo- or copolymer (J) with a density of greater than or equal to 0.9,

[0182] 0 to 50 parts of a polymer (K) chosen from polypropylene homo- or copolymer (K1), poly(1-butene) homo- or copolymer (K2) and polystyrene homo- or copolymer (K3),

[0183] the amount of (J)+(K) being 100 parts,

[0184] the mixture of (J) and (K) being grafted with at least 0.5% by weight of a functional monomer,

[0185] this grafted mixture itself being diluted in at least one polyethylene homo- or copolymer (L) or in at least one polymer of elastomeric nature (M) or in a mixture of (L) and (M).

[0186] According to one form of the invention, (J) is an LLDPE with a density of 0.91 to 0.930, the comonomer containing from 4 to 8 carbon atoms. According to another form of the invention, (K) is an HDPE advantageously with a density of at least 0.945 and preferably from 0.950 to 0.980.

[0187] Advantageously, the functional monomer is maleic anhydride and its content is from 1 to 5% by weight of (J)+(K).

[0188] Advantageously, (L) is an LLDPE in which the comonomer contains from 4 to 8 carbon atoms and, preferably, its density is at least 0.9 and preferably 0.910 to 0.930.

[0189] Advantageously, the amount of (L) or (M) or (L)+(M) is from 97 to 75 parts per 3 to 25 parts of (J)+(K), the amount of (J)+(K)+(L)+(M) being 100 parts.

[0190] As a sixth example of a binder, mention may be made of mixtures consisting of a polyethylene of HDPE, LLDPE, VLDPE or LDPE type, 5 to 35% of a grafted metallocene polyethylene and 0 to 35% of an elastomer, the total being 100%.

[0191] As a seventh example of a binder, mention may be made of mixtures comprising:

[0192] at least one polyethylene or an ethylene copolymer,

[0193] at least one polymer chosen from polypropylene or a propylene copolymer, poly(l-butene) homo- or copolymer, polystyrene homo- or copolymer and preferably polypropylene,

[0194] this mixture being grafted with a functional monomer, this grafted mixture itself optionally being diluted in at least one polyolefin or in at least one polymer of elastomeric nature or in a mixture thereof. In the above mixture which is grafted, the polyethylene advantageously represents at least 50% of this mixture and preferably 60 to 90% by weight.

[0195] Advantageously, the functional monomer is chosen from carboxylic acids and derivatives thereof, acid chlorides, isocyanates, oxazolines, epoxides, amines or hydroxides and preferably unsaturated dicarboxylic acid anhydrides.

[0196] As an eighth example of a binder, mention may be made of mixtures comprising:

[0197] at least one LLDPE or VLDPE polyethylene

[0198] at least one elastomer based on ethylene chosen from ethylene-propylene copolymers and ethylene-butene copolymers

[0199] this mixture of polyethylene and of elastomer being grafted with an unsaturated carboxylic acid or a functional derivative of this acid

[0200] this co-grafted mixture optionally being diluted in a polymer chosen from polyethylene homo- or copolymers and styrene block copolymers

[0201] the binder having

[0202] (a) an ethylene content which is not less than 70 mol %

[0203] (b) a content of carboxylic acid or of its derivative of from 0.01 to 10% by weight of the binder and

[0204] (c) an MFI10/MFI2 ratio of from 5 to 20, in which MFI2 is the mass melt flow index at 190° C. under a load of 2.16 kg, measured according to ASTM D 1238, and MFI10 is the mass melt flow index at 190° C. under a load of 10 kg, according to ASTM D 1238.

[0205] The various layers in the structure of the invention, including the layers of binder, can also contain at least one additive chosen from:

[0206] fillers (mineral fillers, flame-retardant fillers, etc.);

[0207] fibres;

[0208] dyes;

[0209] pigments;

[0210] optical brighteners;

[0211] antioxidants;

[0212] UV stabilizers.

EXAMPLES

[0213] The following products were used:

[0214] EVOH D: ethylene-vinyl alcohol copolymer containing 29 mol % of ethylene, MFI 8 (210° C.-2.16 kg), melting point 188° C., crystallization temperature 163° C., Tg (glass transition temperature) 62° C.

[0215] Mixtures were prepared of polyamide and of polyolefin for the third layer, known as Orgalloy®, and were made from the following products:

[0216] Polyamides (A)

[0217] PA 1: Copolyamide 6/6-6 of medium viscosity with a melting point of 196° C. and a flow index of 4.4 g/10 min according to ASTM 1238 at 235° C. under a weight of 1 kg.

[0218] PA 2: Copolyamide 6/6-6 of medium viscosity with a melting point of 196° C. and a flow index of 6.6 g/10 min according to ASTM 1238 at 235° C. under a weight of 1 kg.

[0219] Polyolefins (B2)

[0220] LLDPE: Linear low density polyethylene with a density of 0.920 kg/l according to ISO 1872/1 and a flow index of 1 g/10 min according to ASTM 1238 at 190° C. under a weight of 2.16 kg.

[0221] HDPE: High density polyethylene with a density of 0.952 kg/l according to ISO 1872/1 and a flow index of 0.4 g/10 min according to ASTM 1238 at 190° C. under a weight of 2.16 kg.

[0222] Polyolefins (B1)

[0223] B1-1: This is a carrier PE with a content of 3000 ppm of maleic anhydride and having a flow index of 1 g/10 min according to ASTM 1238 at 190° C. under a weight of 2.16 kg.

[0224] Antioxidants

[0225] Anti 1: Antioxidant of hindered phenolic type.

[0226] Anti 2: Secondary antioxidant of phosphite type.

[0227] The copolyamide, the polyolefin and the functional polyolefin are introduced, via three independent weight-metering devices (or by simple dry-premixing of the various granulates), into the hopper of a Werner-Pfleiderer co-rotating twin-screw extruder with a diameter of 40 mm, L/D=40 (9 sleeves+4 struts, i.e. a total length of 10 sleeves). The total flow rate of the extruder is 50 kg/h and the spin speed of the screws is 150 rpm and the material temperatures at sleeves 3/4, 6/7 and 7/8 and at the die outlet are, respectively, 245, 263, 265 and 276° C. The extruded rods are granulated and then oven-dried under vacuum for 8 hours at 80° C. The compositions are given in Table 1 below (proportions by weight):

1TABLE 1ProductOrgalloy C1Orgalloy C2Orgalloy C3Orgalloy C4PA164.364.3PA264.364.3LLDPE2727HDPE2727B1-18888Anti 10.50.50.50.5Anti 20.20.20.20.2

[0228] Orgalloy®1: mixture of polyamide 6 and of polyolefin corresponding to the third preferred form of the third layer and consisting (by weight) of:

[0229] 65 parts of PA 6

[0230] 25 parts of linear low density polyethylene of MFI 0.9 g/10 min and density 0.920,

[0231] 10 parts of a copolymer of ethylene, of butyl acrylate and of maleic anhydride in proportions by weight of 91/6/3 and of MFI 5 (190° C.-2.16 kg)

[0232] The binders described in the section “Second example of a binder” are referred to as binder 2a-binder 2d, and their details are given in Table 2 below.

2TABLE 2Formulations of the bindersBinder 2aBinder 2bBinder 2cBinder 2dPolyethyleneComonomer1-octene1-butene1-hexene1-octeneD1Density (g/cm3)0.9190.9170.9180.919MFI (g/10 min; 2.16 kg)4.42.534.4% by weight D1/D1 + D275908075PolyethyleneComonomerpropylene1-butene1-octene1-octeneD2Density (g/cm3)0.8800.9000.8700.870MFI (g/10 min; 2.16 kg)0.22.855% by weight D2/D1 + D225102025Co-graftedMaleic anhydride content3800750040008000mixture D(ppm)% by weight D/D + E20101515PolyethyleneComonomer1-octene1-butene1-hexene1-octeneEDensity (g/cm3)0.9190.9190.9210.920MFI (g/10 min; 2.16 kg)1.110.51Mixture D + EDensity (g/cm3)0.9170.9190.9190.918MFI (g/10 min; 2.16 kg)1.00.80.51.1Maleic anhydride content7607506001200(ppm)

[0233] Next Presently Preferred Embodiment

[0234] As best shown in FIG. 4, another presently preferred embodiment of a multi-layer plastic fuel tank 50 having a tank wall 52 that includes six layers of polymeric material. Starting from the outside of the tank and progressing toward the interior, the fuel tank has an outer layer 54 preferably formed of HDPE, an intermediate layer 56 preferably formed of salvaged and reground material, an adhesive layer 58, a barrier layer 60 preferably formed of EVOH, another adhesive or damper layer 62, and an inner layer 64 that is preferably formed of a polyamide or a polyamide and polyolefin mixture or alloy such as ORGALLOY® which may have a composition generally as described previously. Likewise, the HDPE, regrind, adhesive, damper and EVOH layers may also be of the compositions described previously.

[0235] The HDPE may comprise FINATHENE® MS201 having a density on the order of about 0.950. The adhesive and adhesive/damper layers 58 and 62, respectively, may be a maleic anhydride linear low density polyethylene, such as that sold under the trade name OREVAC® 18334. The barrier layer 60 may be an EVOH copolymer such as that sold under the trade name SOARNOL® DT2903, distributed by ATOFINA in Europe and SOARUS in the United States.

[0236] The regrind layer 56 is preferably salvaged and reground scrap material which is thus a blend of the various materials forming the fuel tank 50. If necessary, to maintain compatibility with the HDPE outer layer 54, the regrind may be diluted with HDPE so that the regrind layer 56 does not have an ORGALLOY® matrix. Advantageously, when the regrind is diluted, an excess of regrind may be produced which may be used for other applications, such as for various valve housings, supports or other arrangements wherein the ORGALLOY® or nylon-based matrix may be beneficial, for example, by way of its increased resistance to permeation of hydrocarbon vapor therethrough.

[0237] The damper layer 62 is provided between the barrier layer 60 and the inner layer 64 to improve the mechanical integrity of the fuel tank, as may be tested with various impact tests known in the art. The damper layer 62 may be, although is not necessarily, of the same material as the adhesive layer 58, although it is not necessary to provide an adhesive between the ORGALLOY® and EVOH layers since they readily adhere to each other. It has been found that directly connecting the ORGALLOY® and EVOH layers can reduce the structural integrity of the fuel tank in at least some designs, because the ORGALLOY® layer does not dissipate impact energy sufficiently to protect the relatively brittle and thin EVOH layer. Therefore, the damper provided between the EVOH and ORGALLOY® layers may be provided primarily to dissipate energy and thereby increase the structural integrity of the fuel tank against impacts or collisions.

[0238] For ease of processing and compatibility with exciting extrusion and blow molding tools, the various layers may have thicknesses similar to those in a conventional six-layer fuel tank, having an outer layer of HDPE, a regrind layer adjacent to the outer layer, an adhesive layer between the regrind layer and a barrier layer of EVOH, and another adhesive layer between the barrier layer and an inner layer of HDPE. In view of the large capital cost for the extrusion and blow molding equipment for fuel tanks, it is desirable that the equipment currently used to form conventional 6-layer fuel tanks can also be used to form the multi-layer fuel tank 50 as described. Accordingly, the inner layer 64 of ORGALLOY® may comprise 30% of the total fuel tank wall 52 thickness, the damper layer 62 may be on the order of 5% of the fuel tank wall thickness, the barrier layer 60 may be 3% of the total thickness, the adhesive layer 58 may be 3% of the total thickness, the regrind layer 56 may be about 40% of the total thickness, and the outer layer 54 may be around 19% of the total thickness. Of course, these thicknesses are merely illustrative of one presently preferred embodiment, and may be changed as desired within the range of current tools, or may be changed more if new or different tooling is employed. Through experimentation, it has been found that the hydrocarbon barrier properties of the ORGALLOY® inner layer 64 are not significantly changed over a range of about 10%-40% of the fuel tank wall thickness providing some flexibility in the design of the fuel tank 50. Desirably, the ORGALLOY® material may be extruded with the same extrusion equipment suitable for polyethylene as in conventional 6-layer fuel tanks, so the processing and manufacturing of the multi-layer fuel tank 50 is very flexible and highly adaptable to current processing machines with the same tools and without requiring any significant changeover.

[0239] When constructed in the manner described, the multi-layer fuel tank 50 exhibits exceptional hydrocarbon barrier performance compared to conventional six layer fuel tanks. This is due in large part to the ORGALLOY® inner layer 64 which is itself an excellent barrier against hydrocarbon permeation, and is far more resistant to permeation of hydrocarbons than HDPE. Thus, the fuel tank has a first barrier layer which includes the ORGALLOY® inner layer 64, and also has a second barrier layer including the EVOH barrier layer 60. These layers 60,64 are provided in series, greatly improving the overall resistance to permeation of hydrocarbons of the fuel tank 50. Both the EVOH barrier layer 60 and the ORGALLOY® inner layer 64 are at least substantially continuous thereby reducing or eliminating permeation windows in the fuel tank 50.

[0240] In fact, as shown in FIG. 5, even in the area of the pinch line 70 of a blow-molded fuel tank 50, the inner layer 64 is continuous, which greatly reduces permeation of hydrocarbon vapors along the pinch line 70. Blow molded fuel tanks are formed by enclosing a parison in a blow mold, closing the mold, and inflating the parison into the mold. Closing the mold also closes the parison and forms a pinch line where the parison is closed between the molds. Permeation along the pinch line is a problem with traditional six layer fuel tanks since the EVOH barrier layer is not continuous in the area of the pinch. Because in conventional six layer fuel tanks the EVOH barrier layer does not seal on itself in the pinch area, a permeation window is defined in the gap between portions of the barrier layer through which hydrocarbon vapors more readily escape. In the multi-layer fuel tank described herein, even if a similar window or gap exists in the barrier layer 60 (as diagrammatically shown in FIG. 5), there is no corresponding window or gap in the inner layer 64, so the extent of hydrocarbon permeation through the pinch line 70 is greatly reduced. Without wishing to be held to any particular theory or numerical range, it is currently believed that approximately 20% to 30% of the hydrocarbon emissions from conventional 6-layer fuel tanks occur through the area of the pinch line. Therefore, the continuous inner layer 64 in the fuel tank 50, even in the area of the pinch line 70, greatly reduces hydrocarbon emission from the fuel tank 50.

[0241] Further, as shown in FIGS. 5 and 6, the ORGALLOY® inner layer 64 has a different rheology than the HDPE inner layer of the conventional six layer fuel tanks. Desirably, the ORGALLOY® inner layer consistently provides a flat interior surface 72 in the area of the pinch line 70 which greatly reduces or eliminates problems that can be encountered with the conventional six layer fuel tank. In the conventional six layer fuel tank, the flow of material during the pinching process is somewhat unpredictable and difficult to control. It is common for a notch or indention to form in the interior surface of the inner layer of HDPE in the area of the pinch line. This notch can reduce the structural integrity of the fuel tank to such things as, for example, internal pressure whereby a fracture or crack may be initiated in the area of the notch. Empirical data has shown that the multi-layer fuel tank 50 has superior mechanical performance including internal pressure resistance as demonstrated by a significant improvement in the burst test performance of the fuel tank. Some empirical testing conducted to date shows that the fuel tank 50 has exhibited increased internal pressure resistance on the order of 20-35% greater then the conventional six layer fuel tank. In addition to forming a continuous, relatively flat inner surface 72, the rheology of the ORGALLOY® layer, which has a lower viscosity then polyethylene, does not affect the thickness or integrity of the EVOH barrier layer in the area of the pinch line 70 to the same extent that is found in conventional six layer fuel tanks. Desirably, in the area of the pinch line 70 the barrier layer 60 of the multi-layer fuel tank does not become as thin as in conventional six layer fuel tanks. This results in still further improved resistance to permeation of hydrocarbon vapors, even in the area of the pinch line 70 of the multi-layer fuel tank 50.

[0242] The greatly improved resistance to permeation of hydrocarbon exhibited by the multi-layer fuel tank 50 over conventional six layer fuel tank, enables the multi-layer fuel tank 50 to meet the very stringent emissions standards enacted or contemplated, for example, in the State of California. These standards include, for example, LEV II and PZEV which require significantly reduced vehicle emissions. While some designs of conventional six layer fuel tanks may meet the requirements of LEV II they will not meet the requirements of the more restrictive regulations of PZEV. The multi-layer fuel tank 50 of the embodiment disclosed provides vastly superior resistance to permeation of hydrocarbons, and can be readily designed to meet the PZEV requirements. In general numbers, to relate the barrier performance of various materials in the polymeric fuel tanks in non-alcoholic or low alcohol fuels such as CARB Ph II, if HDPE is assigned a general permeation rate of 1,000, ORGALLOY® would have a permeation rate of about 1.5, over 600 times lower than the rating for HDPE. For comparison, EVOH may have a permeation rate of 0.6. Therefore, it can be seen that ORGALLOY® by itself, is a vastly superior barrier to hydrocarbon emissions than is HDPE. While nylon based, and hence somewhat susceptible to fuels containing alcohol, ORGALLOY® still provides far superior resistance to hydrocarbon permeation than HDPE. Using similar general ratings, HDPE may have a permeation rate of 1,000 in high alcohol fuels like the test fuel TF1 which contains 10% ethanol, while ORGALLOY® has a permeation rate of only about 225. Therefore, even in high alcohol fuels, ORGALLOY® has a more than 4 times lower permeation rate than HDPE.

[0243] When employed in a fuel tank constructed in the manner described, the overall resistance to hydrocarbon permeation of the multi-layer fuel tank 50 is on the order of 2½ to 3 times better than conventional six-layer fuel tanks for non-alcohol or low alcohol fuels. By way of general relative numbers, if the conventional six-layer fuel tank is rated with a permeation rate of 100 in such fuels, the multi-layer fuel tank 50 has a permeation rate on the order of 30-40. Likewise, the multilayer fuel tank 50 has a permeation rate about ½ that of the conventional six-layer fuel tanks in high alcohol fuels, like TF1. If a conventional six-layer fuel tank has a permeation rating of 100 in high alcohol fuel, the multi-layer fuel tank 50 has a comparative permeation rating of about 45-55. Further, test results have shown that the multi-layer fuel tank 50 is able to provide greatly reduced emissions of about 4 to 7 mg/day in CARB Ph II with an average of about 5 mg/day, and 7 to 10 mg/day in TF1 with an average of about 8 mg/day. These results came from an 80-week soak test at 40° C. of 70 liter fuel tanks. The tanks had a surface area of about 2.1 m2, and a pinch line length of about 2 meters. Under similar test conditions with similar size conventional fuel tanks, the permeation rates for conventional six layer fuel tanks were more than double for CARB Ph II fuel and typically over 60% higher for TF1. It is believed that the permeation rate will not significantly change over the designed life of the fuel tank of 15 years or more.

[0244] Desirably, the multi-layer fuel tank dramatically reduces the emissions of the greatest pollutants, generally designated as aromatics. Aromatics typically include, by way of example without limitation, benzene, Toluene, Ethyl Toluene, Xylene and heavy aromatics. Even in high alcohol fuels, while the overall permeation rate of the multi-layer fuel tank 50 is about ½ half that of a conventional six-layer fuel tank, the emission of aromatics from the multi-layer fuel tank 50 is {fraction (1/10)} that of the conventional six-layer fuel tank. Accordingly, emission of the greatest pollutions is drastically reduced in the multi-layer fuel tank 50. The emission of alcanes and oxygenates is also greatly reduced in the multi-layer fuel tank 50.

[0245] Further, since the inner layer 64 provides a consistent, thick and continuous interior barrier layer, the resistance to hydrocarbon permeation in the multi-layer fuel tank 50 is very consistent from tank-to-tank, day-to-day and month-to-month. There is very little variation in the process and formation of the multi-layer fuel tank 50. Conversely, in the conventional six-layer fuel tank, variations of the thickness in the EVOH layer in any part of the fuel tank can drastically degrade its hydrocarbon permeation performance. Since the EVOH is relatively expensive and brittle, control of the thickness of the EVOH throughout the entire fuel tank is important to the conventional 6-layer fuel tanks which rely on the EVOH layer almost entirely for the resistance to permeation of hydrocarbons. Accordingly, even if some conventional six-layer fuel tanks can be made to meet some of the increasingly strict emission standards, due to process variations including equipment, environment, human influence, and the like, it is unlikely that all or even a significant number of conventional six-layer fuel tanks would meet these increased standards for a given production run.

[0246] Still further, the ORGALLOY® inner layer 64, and the multi-layer fuel tank 50 in general, have superior mechanical performance at higher temperatures as compared to HDPE and fuel tanks employing an inner layer of HDPE as in conventional six layer fuel tanks. The ORGALLOY® inner layer 64 has a significantly higher melting point, generally in the range of about 375° F. to 400° F., then that of HDPE, which may have a melting point in the range of about 255° F. to 275° F. Therefore, the multi-layer fuel tank 50 experiences less deflection of its walls 52 when temperature increases, and greatly reduces or eliminates any risk of melting of the inner layer 64 by even very hot fuel returned to the fuel tank 50, such as from an engine fuel rail. By way of example, without limitation, in some diesel fuel systems, fuel may returned at temperatures up to about 255° F., which is in the range for melting point for the HDPE, and thereby may melt the HDPE or may adversely affect its structural integrity, at least locally and temporarily. In contrast, fuel returned at temperatures of 255° F. does not cause any significant degradation of the ORGALLOY® inner layer 64 since it has a much higher melting temperature. Also, the structural integrity of the multi-layer fuel tank 50, such as may be measured by impact testing, is also better than that of conventional 6-layer fuel tanks, at least in certain temperature ranges, especially higher temperatures. Because the multi-layer fuel tank 50 may exhibit improved structural integrity, there is the potential to reduce the thickness of the fuel tank wall 52 thereby achieving weight and cost savings.

[0247] While generally described with reference to a blow molded fuel tank having a pinch line, the fuel tank construction described herein may be advantageously employed in a thermoforming operation wherein two halves of a fuel tank are generally separately formed and thereafter joined together, such as by welding. The ORGALLOY™ inner layer 64 will still be continuous since the inner layer from one tank half will be welded to the inner layer of the other tank half, to reduce or eliminate permeation windows. In a thermoformed tank, the weld line extends around the entire periphery since the fuel tank is formed in two separate halves. Accordingly, in conventional thermoformed fuel tanks, this weld line between the two tank halves can be a significant source of hydrocarbon emissions. This source of hydrocarbon emissions can be greatly reduced or eliminated with the fuel tank constructed in the manner described, due at least in part to the reduction or elimination of any permeation window and the continuous inner layer of a material that greatly retards hydrocarbon permeation through the tank walls 52.

[0248] Persons of ordinary skill in the art will recognize that the above description of several presently preferred embodiments is provided in terms of illustration of these embodiments and not limitation of the invention. Various substitutions and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. For example, without limitation, the outer layer 54 of HDPE may not be necessary if the re-grind layer 56 has a nylon-based matrix, since the HDPE and re-grind layers may not be compatible. To facilitate welding other components, such as vent valves or the flange of a fuel pump module to the nylon matrix outer layer (in the case where the outer HDPE layer is not employed), these components may be formed from a nylon based material. Further, while the barrier layers of the last disclosed embodiment were set forth as being formed from EVOH and ORGALLOY®, other materials may be used. The EVOH may be removed or replaced by other materials resistant to permeation of hydrocarbons, and likewise, the inner layer may be formed of a polyamide or a different mixture of polyamide and polyolefin than ORGALLOY®. As another example, without limitation, the EVOH material described with reference to the barrier layer 60 may be replaced by another polyamide or a mixture of polyamide and polyolefin such as, for example, ORGALLOY®. This may be more desirable when the multi-layer fuel tank is used with non-alcoholic or low alcohol fuels, since materials like polyamide or mixtures of polyamide and polyolefin such as ORGALLOY® are good barriers against hydrocarbon permeation, especially in non-alcoholic fuels. As still another example, without limitation, while blowmolding and thermoforming techniques were discussed, the multi-layer fuel tank 50 may be made by any suitable process such as by overmolding with polyethylene or the like a film having layers of hydrocarbon barrier material. Of course, in whatever process used to form the fuel tank, other materials may be used as desired for a particular application, and other substitutions or modifications are possible in accordance with the spirit and scope of the invention.

	Number	Date	Country
Parent	09782485	Feb 2001	US
Child	10377470	Feb 2003	US

Fuel tank having a multilayer structure

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Continuation in Parts (1)