WO2011020582A1

WO2011020582A1 - Plastic fuel container for motor bikes or automotive hybrid cars

Info

Publication number: WO2011020582A1
Application number: PCT/EP2010/004958
Authority: WO
Inventors: Bernd Hoecker; Klaus Müller; Ines Schwarz
Original assignee: Basell Polyolefine Gmbh
Priority date: 2009-08-18
Filing date: 2010-08-12
Publication date: 2011-02-24

Abstract

A multilayered plastic fuel container for motor bikes driven by combustion engines or for hybrid cars driven by a combination of electrical energy and combustion engine comprises at least one support layer composed of a thermoplastic polymer and one cover layer arranged thereupon comprising a metal foil. In between the support layer and the cover layer another intermediate layer may be arranged advantageously. The plastic fuel container is prepared by extruding, laminating and thermoforming two half shells and thereafter welding them together at their edges.

Description

Plastic fuel container for motor bikes or automotive hybrid cars

The present invention relates to a novel multilayered plastic fuel container for motor bikes driven by combustion engines or hybrid cars driven by a combination of electrical energy and combustion engine.

The invention further relates to a multistep process for the production of said multilayered plastic fuel container by extruding, laminating, thermoforming and welding. All known fuel containers for motor bikes and hybrid cars, as well, are normally composed of metal covered by a paint or lacquer layer. The metal is for that purpose in a first step formed into two half shells which are thereafter welded together along a welding seam and finally are painted. The filler-cap as well as some appropriate exit for the fuel are already integrated thereby, whereas the filler-cap acts simultaneously as a degassing valve.

Such fuel containers are known in different sizes, shape and colors, as motor bikes are known, as well, in widely different shape and colors. The disadvantage of all such fuel containers made of metal, however, is always their heavy weight.

The object of the present invention was to provide a fuel container for motor bikes and hybrid cars, which is light in weight, but which still maintains the same high quality level in terms of mechanical strength, durability, scratch resistance, barrier properties and thermal stability and which should be prepared by a low-cost method of manufacturing.

Said object is achieved by a multilayered plastic fuel container as mentioned initially comprising at least one support layer comprising a thermoplastic polymer and at least one cover layer comprising a metal foil. Surprisingly, such composite material permits the preparation of a fuel container for motor bikes driven by combustion engines or hybrid cars driven by a combination of electrical energy and combustion engine whose structure is based essentially on thermoplastic polymer and which nevertheless has sufficient strength for motor bike and hybrid car purposes. The wall thickness necessary for such strength is not so great as to be uneconomic.

Surprisingly, it has been found that the stiffness of a plastic fuel container can be markedly improved via lamination to metal foil. For example, it is possible to achieve a stiffness level which hitherto has been unachievable via straight plastics-parts applications, an example for that being a container composed of acrylonitrile-butadiene-styrene copolymer (ABS) well known for its high stiffness. This applies particularly to situations where the containers have exposure to relatively high temperatures.

The arrangement of the layers in the plastic fuel container is variable. Thus, the cover layer of metal may be the outer side of the fuel container in one embodiment. However, it may, as well, also cover the inner surface of the plastic fuel container. In another embodiment, a sandwich structure may be suitable, where the cover layer of metal covers the outer and the inner surface of the plastic fuel container. With such sandwich structure, a further improvement in stiffness is possible. The properties of the fuel container can be further varied within a particularly wide range by way of controlled modification of the thermoplastic polymer for the support layer, which can be impact-modified, provided with mineral fillers, or glassfiber-reinforced, and the mechanical properties can thus be matched to the requirements of motor bikes, without any resultant effect on the surface properties and the surface quality of the fuel containers.

The support layer composed of thermoplastic polymer can comprise, based in each case on the weight of the support layer, from 1 to 60 % by weight, preferably from 5 to 50 % by weight, particularly preferably from 10 to 40 % by weight, of reinforcing fillers. Examples of these reinforcing fillers are barium sulfate, magnesium hydroxide, talc with average grain size in the range from 0.1 to 10 pm, measured to DIN 66 1 15, wood, flax, chalk, glass beads, coated glass fibers, short, long, or other glass fibers, or a mixture for these. The support layer can moreover also comprise respectively advantageous amounts of further additives, e.g. light stabilizers, UV stabilizers, heat stabilizers, pigments, carbon blacks, lubricants, and processing aids, flame retardants, blowing agents, and the like.

According to the invention, the thermoplastic polymer used for the support layer comprise polymers such as polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polysulfones, polyether ketones, polyesters, such as polyethylene terephthalate, polybutylene terephthalate or polyalkylene naphthalate, polycycloolefins, polyacrylates, polymethacrylates, polyamides, such as poly-epsilon-caprolactam or polyhexamethylene- adipineamide or polyhexamethylenesebacineamide, polycarbonate, poly- urethanes, polyacetals, such as polyoxymethylene (POM) or polystyrene (PS). Thermoplastic polymers principally suitable here are homopolymers and copolymers. In this connection, copolymers composed of propylene and ethylene or composed of ethylene or propylene and of other olefins having from 4 to 10 carbon atoms are particularly worthy of mention, as are co- or terpolymers composed of styrene and of relatively small proportions of butadiene, alpha-methylstyrene, acrylonitrile, vinylcarbazole, or esters of acrylic, methacrylic, or itaconic acid.

In order to improve the cost-effectiveness of production of the plastic fuel container, the support layer can also comprise amounts of up to 60 % by weight, based on the total weight of the support layer, of reclaimed materials recycled from the polymers already mentioned.

According to the invention, the term polyoxymethylene (POM) means homo- and copolymers of aldehydes, such as formaldehyde or acetaldehyde, but preferably of cyclic acetals. A characteristic of POM is that there are constantly recurring carbon-oxygen bonds forming a distinctive feature of the molecular chain. The melt flow index (Ml) of POM is usually in the range from 5 to 50 g/10 min, preferably from 5 to 30 g/10 min, measured to ISO 1 133 at a temperature of 230 °C with a load of 2.16 kg.

If the intention is to use polyester for the support layer, materials clearly preferable for this purpose are polyethylene terephthalate (PET) or polybutylene terephthalate (PBT). Both are high-molecular-weight esterification products of terephthalic acid and ethylene glycol and, respectively, butylene glycol. According to the invention, the Ml of particularly suitable polyesters is in the range from 5 to 50 g/10 min, preferably from 5 to 30 g/10 min, measured to DIN 1133 at a temperature of 230 °C with a load of 2.16 kg.

Copolymers of styrene that can be used for the support layer of the plastic fuel container are in particular copolymers having up to 45 % by weight, preferably having up to 20 % by weight, of acrylonitrile within the polymer. The Ml of these copolymers is typically in the range from 1 to 25 g/10 min, preferably from 4 to 20 g/10 min, measured to DIN 1133 at a temperature of 230 °C with a load of 2.16 kg. Further terpolymers of styrene comprise up to 35 % by weight, in particular up to 20 % by weight, of acrylonitrile within the polymer and up to 35 % by weight, preferably up to 30 % by weight, of butadiene. The abbreviated term ABS is also used for these terpolymers, whose Ml is typically in the range from 1 to 40 g/10 min, preferably from 2 to 30 g/10 min, measured to DIN 1133 at a temperature of 230 °C with a load of 2.16 kg.

Further thermoplastics used for the support layer of the plastic fuel container are in particular polyolefins, such as PE and PP, among which particular preference is given to use of PP. According to the invention, PP means homo- and copolymers of propylene. Copolymers comprise subordinate amounts of monomers copolymerizable with propylene, e.g. 1 -olefins having 2 or 4 to 8 carbon atoms. If necessary, it is also possible to use two or more co monomers. Thermoplastics which may be mentioned as particularly suitable for the support layer of the plastic fuel container are homo-polymers of propylene or copolymers composed of propylene and up to 50 % by weight of further 1 -olefins having up to 8 carbon atoms. These copolymers are normally random copolymers, but can also be block copolymers.

The polymerization reaction for production of PP can normally take place at a pressure in the range from 1 to 100 bar (from 0.1 to 10 MPa) in suspension or in the gas phase and in the presence of a Ziegler-Natta catalyst system. Preference is given here to catalyst systems which comprise not only a titanium-containing solid component but also co- catalysts in the form of organoaluminum compounds and electron-donor compounds.

Ziegler-Natta catalyst systems generally comprise a titanium-containing solid component, in particular halides or alcoholates of tri- or tetravalent titanium, and moreover a halogen-containing magnesium compound, inorganic oxides, such as silica gel, as support material, and electron-donor compounds. Particular electron-donor compounds that may be mentioned are carboxylic acid derivatives or ketones, ethers, alcohols, or organosilicon compounds.

The titanium-containing solid component can be prepared by known processes. It is preferably prepared by a process described in more detail in DE 195 29 240.

Co-catalysts suitable for the Ziegler-Natta catalyst systems are not only trialkylaluminum compounds but also compounds in which an alkyl group has been replaced by an alkoxy group or by a halogen atom, such as chlorine or bromine. The alkyl groups can be identical or different. Linear or branched alkyl groups can also be used. According to the invention, it is preferable to use trialkylaluminum compounds whose alkyl groups comprise from 1 to 8 carbon atoms, examples being triethylaluminum, triisobutylaluminum, trioctylaluminum, or methyldiethylaluminum, or a mixture thereof.

However, PP can also be produced in the presence of metallocene as catalyst. Metallocenes are complex compounds having a layered structure and comprising metals from the transition groups of the Periodic Table of the Elements plus organic, preferably aromatic, ligands. To permit their use for production of PP, the metallocene complexes are advantageously applied to a support material. Support materials which have proven advantageous are the inorganic oxides also used for preparation of the titanium-containing solid component in Ziegler-Natta catalysts.

Metallocenes usually used comprise, as central atom, titanium, zirconium, or hafnium, among which zirconium is preferred. The central atom has pi- bonding to at least one pi system, which is embodied by a cyclopentadienyl group. In the great majority of instances, the cyclopentadienyl group has additional substituents, which can be used to control the activity of the catalyst. Preferred metallocenes comprise central atoms bonded by way of two similar or different pi-bonds to two pi-systems, and these may also simultaneously be a constituent of appropriate heteroaromatic systems.

A suitable co-catalyst for the metallocene is in principle any compound which can convert the neutral metallocene to a cation and can stabilize the metallocene. Furthermore, as can be found in EP 427 697, the co-catalyst or the anion formed therefrom should not enter into any further reactions with the metallocenium cation formed. The cocatalyst used is preferably an aluminum compound and/or a boron compound. The formula of the boron compound is preferably R¹⁸ _xNH_4-xBR¹⁹4,R¹⁸xPH4-xBR¹⁹4,R¹⁸ ₃CBR¹⁹4, or BR¹⁹ ₃, in which x is a number from 1 to 4, preferably 3, the radicals R¹⁸ are identical or different, preferably identical, and are Ci-C-io-alkyl or C₆-Ci₈-aryl, or two radicals R¹⁸ together with the atoms connecting them form a ring, and the radicals R¹⁹ are identical or different, preferably identical, and are C6-Ci₈-aryl, which can be alkyl, haloalkyl, or fluorine substituted. In particular, R¹⁸ is ethyl, propyl, butyl, or phenyl, and R¹⁹ is phenyl, pentafluorophenyl, 3,5- bistrifluoromethylphenyl, mesityl, xylyl or tolyl. EP 426 638 describes boron compounds as co-catalyst for metallocenes.

However, it is more preferable that the co-catalyst used is an aluminum compound, such as alumoxane and/or an alkyla!uminum compound.

It is particularly preferable that the co-catalyst used is an alumoxane, in particular of linear type or of cyclic type, and in both of the compounds here there can also be organic radicals present which are identical or different and can be hydrogen or a Ci-C2o-hydrocarbon group, such as a C-i-de- alkyl group, a C₆-C₁₈-aryl group, or benzyl. The support layer of the plastic fuel container can take the form of injection- molded, extruded, or compression-molded sheet in various thicknesses and sizes. Preferred layer thicknesses for the support layer are in the range from 1 to 20 mm, particularly preferably from 2 to 15 mm. The cover layer pursuant to the instant invention can be composed of different metal foils such as aluminum foil or iron foil or a foil of noble metal such as silver or it may comprise chromium. In a preferred embodiment the cover layer comprises an aluminum foil or iron or chromium.

According to the invention, another additional intermediate layer is provided between the support layer and the cover layer of metal to improve their adhesion strength. A particular material that can be used for the additional intermediate layer is thermoplastic polymer. Preferably a thermoplastic polymer which is the same as that used previously for the support layer. This combination produces a particularly firmly adhering bond between the support layer and the cover layer of metal. According to the invention, the intermediate layer is in the shape of a thin web or else preferably a thin nonwoven, with thickness in the range from 0.001 to 1 mm, preferably from 0.005 to 0.5 mm.

A thermoplastic polymer material preferably used for the intermediate layer is a PP which has been produced in the presence of metallocene as catalyst and whose Ml is in the range from 10 to 60 g/10 min, measured to DIN 1133 at a temperature of 230 °C with a load of 2.16 kg.

The intermediate layer composed of a web or a nonwoven thermoplastic polymer can also advantageously be a resin-saturated nonwoven. Acrylate resins, phenolic resins, urea resins, or melamine resins can in particular be employed here as saturating resin. The degree of saturation with resin here can be up to 300 %. This means that practically the entire surface of the intermediate layer has been heavily saturated with resin, which then amounts to 300 % of the weight of the straight intermediate layer without resin. The degree of saturation with resin is preferably from 15 to 150 %, particularly preferably from 80 to 120 %. According to the invention, the weight of the intermediate layer is in the range from 15 to 150 g/m², preferably from 30 to 70 g/m². The invention also provides a process for production of the plastic fuel container by the technique of reverse coating by an injection-molding method. In order to strongly bond the support layer, whose layer thickness is typically in the range from 0.01 to 20 mm, the intermediate layer and the cover layer comprising a metal to give a firmly adhering composite, the initial charge in the technique of reverse coating by an injection-molding method places the material for the intermediate layer and the material for the cover layer on one of the sides into one half of an injection mold and, if desired, another intermediate layer and a cover layer on the other side into the other half of the injection mold. Once the mold has been closed, the thermoplastic polymer is injection-molded at a temperature in the range from 150 to 330 °C and at high pressure of from 5 to 2500 bar (= from 0.5 to 250 MPa) into the compartment between the intermediate layers which are present on each side. The mold temperature is generally from 8 to 160 °C on each side. Once the thermoplastic has been injected under the conditions stated, the mold has the shape of a half shell for a plastic fuel container and is cooled to ambient temperature. The cooling time for this is in the range from 0.01 to 5.0 min.

In another version of the process, a prefabricated laminate whose layer thickness is in the range from 0.02 to 3.0 mm or, as an alternative to this, individual foils (overlay, metal foil, resin) are first laminated to a nonwoven (about 30 g/m²; metallocene polymer, ^®Novolen). Material for a further prefabricated laminate is then prefabricated with the desired thickness and shape. The two variants are then placed in the respective mold halves of an injection-molding compartment, the mold is closed, and then the thermoplastic polymer is injected using a temperature of at least 170 °C and a pressure of at least 50 bar (5 MPa) between these, into the compartment.

The procedure that takes place in compression molding is in principle the same. The single difference is that the thermoplastic is introduced in the form of pellets between the individual foils inserted in the layer sequence, and is exposed to pressure of at least 5 bar and to a press temperature of at least 100 °C on each side, for a press time of at least 30 sec.

The same procedure has proven outstandingly successful in practice with injection-compression molding and transfer molding.

In order to combine the thus prepared half shells to result into the ready fuel container, the half shells are welded together at their respective edges. The welding is preferably performed by means of friction-welding or vibration-welding keeping thereby the welding seam limited to a relatively small area, but strong in mechanical strength. This technology uses an oscillating vibration to create friction heat. The amplitude lies in the range of from 0.25 to 2.5 mm, whereas the frequency (v) ranges from 80 to 300 Hz. In addition a pressure of from 0.5 up to 8 MPa is applied.

In order to give even clearer explanation of the invention for the person skilled in the art, the drawings attached show in detail the principle of the plastic fuel container in the structure and during production.

Figure 1 shows a typical layered structure for the plastic fuel container from side view.

Reference numerals indicate how the aluminum foil 1 and the intermediate layer 2 are arranged on top of each other.

Figure 2 shows two formed/thermoformed half shells for the plastic fuel container before their combination schematically in side view. In this illustration reference numbers show the thermoplastic polymer 3 of the support layer and the combination 4 of the intermediate layer 2 and the aluminum foil 1 arranged in this embodiment at the outer surface.

Figure 3 shows the ready prepared plastic fuel container schematically in side view.

The reference number in figure 3 indicates the welding seam 5 connecting both half shells of the plastic fuel container at their respective edges and extending in vertical direction. As a matter of course, the filler-cap and the exit for the fuel are essential parts of the ready prepared plastic fuel container, but have nevertheless not been shown in this schematic illustration.

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Claims

Patent claims

1. A multilayered plastic fuel container comprising at least one support layer composed of a thermoplastic polymer and at least one cover layer arranged thereupon comprising a metal foil.

2. The plastic fuel container as claimed in claim 1 , wherein the cover layer is arranged on the outer side of the container and/or on the inner side of the container.

3. The plastic fuel container as claimed in claim 1 or claim 2, which comprises, as thermoplastic polymer for the support layer, polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polysulfones, polyether ketones, polyesters, such as polyethylene terephthalate, polybutylene terephthalate or polyalkylene naphthalate, polycycloolefins, polyacrylates, polymethacrylates, polyamides, such as poly-epsilon-caprolactam or poly- hexamethyleneadipineamide or polyhexamethylenesebacineamide, polycarbonate, polyurethanes, polyacetals, such as polyoxymethylene (POM) or polystyrene (PS), or a combination of these.

4. The plastic fuel container as claimed in one or more of claims 1 to 3, wherein the thermoplastic polymer of the support layer also comprises an amount of from 1 to 60 % by weight, preferably from 5 to 50 % by weight, particularly preferably from 10 to 40 % by weight, based in each case on the weight of the support layer, of reinforcing fillers.

5. The plastic fuel container as claimed in claim 4, wherein the thermoplastic polymer of the support layer comprises, as reinforcing fillers, barium sulfate, magnesium hydroxide, talc with average grain size in the range from 0.1 to 10 pm, measured to DIN 66 115, wood, flax, chalk, glass beads, coated glass fibers, or short, long, or other glass fibers, or a mixture of these.

6. The plastic fuel container as claimed in one or more of claims 1 to 5, wherein the support layer is an injection-molded or extruded or compression-molded sheet whose layer thickness is in the range from 1 to 20 mm, preferably from 2 to 15 mm.

7. The plastic fuel container as claimed in one or more of claims 1 to 6, wherein the cover layer comprises a metal foil such as an aluminum foil of an iron foil or a foil of noble metal like silver or a chromium foil.

8. The plastic fuel container as claimed in one or more of claims 1 to 7, wherein an additional intermediate layer is provided between the support layer and the cover layer and wherein the material used for the additional intermediate layer is thermoplastic polymer, preferably a thermoplastic polymer which is the same as that used for the support layer.

9. The plastic fuel container as claimed in one or more of claims 1 to 8, wherein the intermediate layer is in the shape of a thin web or a thin nonwoven, having a thickness in the range from 0.001 to 1 mm, preferably from 0.005 to 0.5 mm.

10. The plastic fuel container as claimed in one or more of claims 1 to 9, wherein the intermediate layer is composed of a thermoplastic polymer resin-saturated nonwoven and wherein acrylate resins, phenolic resins, urea resins, or melamine resins are used as saturating resin.

11. The plastic fuel container as claimed in one or more of claims 1 to 10, wherein the weight of the intermediate layer is in the range of from 15 to 150 g/m², preferably from 30 to 70 g/m².

12. A process for the production of a plastic fuel container as claimed in one or more of claims 1 to 11 , in which the technique used comprises reverse-coating by an injection-molding method and the initial charge comprises the material for the intermediate layer, the cover layer, and the heat-cured layer, in each case in the form of sheet-like structures, and the thermoplastic polymer for the support layer is then bonded thereto via reverse-coating by an injection-molding process.

13. A process as claimed in claim 12, wherein the thermoplastic polymer for the support layer is injection-molded at a temperature in the range from 150 to 330 °C and at high pressure of from 5 to 2500 bar (= from 0.5 to 250 MPa) into the compartment between the intermediate layers which are present on each side and wherein the mold temperature is from 8 to 160 °C on each side.

14. A process as claimed in claim 12 or 13, wherein the half shells are welded together at their respective edges by means of friction welding or vibration welding.

15. Use of a plastic fuel container as claimed in one or more of claims 1 to 11 for motor bikes driven by combustion engines.

16. Use of a plastic fuel container as claimed in one or more of claims 1 to 11 for automotive hybrid cars driven by a combination of electrical energy and combustion engine.

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