MATRIX POLYMERS LIMITED (Moulton Park Business Centre Redhouse Road Moulton Park Northampton NN3 6AQ, GB)
Devereux, Mark (Gordon Ellis & Company Trente Lane Castle Donington Derby DE74 2NP, GB)
| 1. | A rotomoulded article comprising a first layer of rotomouldable material and a second layer of a further rotomouldable material bonded directly thereto. |
| 2. | A rotomoulded article according to claim 1, in which the first layer of rotomouldable material has one or more predetermined characteristics and the second layer of further rotomouldable material bonded directly thereto has one or more other predetermined characteristics whereas to give the article one or more desired properties. |
| 3. | A rotomoulded article according to any preceding claim, in which the first layer provides an external surface of the article. |
| 4. | A rotomoulded article according to any preceding claim, in which the second layer provides an internal surface of the article. |
| 5. | A rotomoulded article according to any of claims 2 to 4, in which the further material of the said second layer has relatively higher mechanical performance when rotomoulded than the material of the first layer. |
| 6. | A rotomoulded article according to claim 5, in which the second layer has better impact resistance than the material of said first layer. |
| 7. | A rotomoulded article according to any of claims 2 to 6, in which the said further material has a relatively high fracture resistance, in particular resistance to crack formation and/or propagation. |
| 8. | A rotomoulded article according to any of claims 3 to 7, in which the first layer provides a relatively smooth finish on the external surface. |
| 9. | A rotomoulded article according to any preceding claim, in which the first layer is harder than the second layer. |
| 10. | A rotomoulded article according to any of claims 3 to 9, in which the external surface is relatively scratch resistant. |
| 11. | A rotomoulded article according to any of claims 3 to 10, in which the external layer can receive paint such as cellulose, acrylic or other suitable paint to provide good surface covering and finish. |
| 12. | A rotomoulded article according to any preceding claim, in which the second layer bonded to the first layer improves the fracture resistance of the said first layer. |
| 13. | A rotomoulded article according to any preceding claim, in which the second layer bonded to the first layer improves the resistance to damage from impact, such as cracking. |
| 14. | A rotomoulded article according to any preceding claim, in which the said material comprises polyamide, such as nylon. |
| 15. | A rotomoulded article according to any preceding claim, in which the said further material comprises polyolefin. |
| 16. | A rotomoulded article according to claim 15, in which the said further material comprises a modified polyolefin. |
| 17. | A rotomoulded article according to any preceding claim, in which the article comprises a container for fuel, such as a fuel tank. |
| 18. | A rotomoulded article according to any preceding claim, in which the material of the first layer comprises one or more of polyolefin, modified polyolefin, polyamide, polypropylene, homopolymer polypropylene, copolymer polypropylene, polyethylene, cross linkable polyethylene, high density polyethylene, linear low density polyethylene, linear medium density polyethylene, low density polyethylene, ethylene vinyl acetate copolymer, ethylene butyl acrylate copolymer, polyolefin plastomer, flexible plastics material with foaming agent, styrene butadiene rubber, plasticised polyvinyl chloride, platicised polyvinyl chloride with foaming agent. |
| 19. | A rotomoulded article according to any preceding claim, in which the further material of the said second layer comprises one or more of polyamide, modified polyolefin, polyethylene, cross linkable polyethylene, polypropylene, homopolymer polypropylene, copolymer polypropylene, linear low density polyethylene, linear medium density polyethylene, high density polyethylene, ethylene vinyl acrylate co polymer, ethylene butyl acetate copolymer, polyolefin plastomer, flexible plastics material comprising foaming agent, styrene butadiene rubber. |
| 20. | A method of rotomoulding an article, the method comprising moulding a first material to form a first layer in a mould and moulding a second layer of a further material directly onto said first layer so that the second layer bonds directly to said first layer. |
| 21. | A method according to claim 20, in which the method involves the use of material and further material as defined in any of claims 1 to 19. |
| 22. | A rotomoulded article substantially as hereinbefore described with reference to the accompanying drawings. |
| 23. | A method substantially as hereinbefore described with reference to the accompanying drawings. |
| 24. | Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims. |
Rotomoulding is a method used in industry to produce articles from plastics materials. Generally, the process involves charging a mould with a rotomouldable material and then heating the material within the mould to cause the material to melt. As the material is heated and melts, the mould is rotated so that the material lines the inside surface of the mould. Heating then often continues to ensure that the material is appropriately cured, following which the article can be allowed to cool in the mould or removed from the mould for cooling.
Many plastics materials are unsuitable for rotomoulding and it has been found that articles which exhibit a number of desired characteristics which cannot be found in a single rotomouldable material cannot be produced or have to be produced using relatively expensive and/or complex methodology.
According to the present invention there is provided a rotomoulded article comprising a first layer of rotomouldable material and a second layer of a further rotomouldable material bonded directly thereto.
Preferably the first layer of rotomouldable material has one or more predetermined characteristics and the second layer of further rotomouldable material bonded directly thereto has one or more other predetermined characteristics whereas to give the article one or more desired properties.
Preferably the first layer provides an external surface of the article and the second layer preferably provides an internal surface thereof. Preferably the further material of the said second layer has relatively higher mechanical performance when rotomoulded than the material of the first layer, and in particular better impact resistance than the material of said first layer.
Preferably the said further material has a relatively high fracture resistance, in particular resistance to crack formation and/or propagation.
Preferably the first layer provides a relatively smooth finish on the external surface.
Preferably the first layer is harder than the second layer. The external surface may be relatively scratch resistant and can desirably receive paint such as cellulose, acrylic or other suitable paint to provide good surface covering and finish.
Preferably the second layer bonded to the first layer improves the fracture resistance of the said first layer and in particular improves the resistance to damage from impact, such as cracking.
The said material may comprise polyamide, such as nylon.
The said further material may comprise polyolefin, and preferably a modified polyolefin.
The article may comprise a container for fuel, such as a fuel tank.
In further embodiments of the invention, the material of the first layer may comprise one or more of polyolefin, modified polyolefin, polyamide, polypropylene, homopolymer polypropylene, co-polymer polypropylene, polyethylene, cross linkable polyethylene, high density polyethylene, linear low density polyethylene, linear medium density polyethylene, low density polyethylene, ethylene vinyl acetate co-polymer, ethylene butyl acrylate co- polymer, polyolefin plastomer, flexible plastics material with foaming agent, styrene butadiene rubber, plasticised polyvinyl chloride, platicised polyvinyl chloride with foaming agent.
The further material of the said second layer may comprise one or more of polyamide, modified polyolefin, polyethylene, cross linkable polyethylene, polypropylene, homopolymer polypropylene, co-polymer polypropylene, linear low density polyethylene, linear medium density polyethylene, high density polyethylene, ethylene vinyl acrylate co-polymer, ethylene butyl acetate co-polymer, polyolefin plastomer, flexible plastics material comprising foaming agent, styrene butadiene rubber.
According to a further aspect of the present invention there is provided a method of rotomoulding an article, the method comprising moulding a first material to form a first layer in a mould and moulding a second layer of a further material directly onto said first layer so that the second layer bonds directly to said first layer.
Preferably the method involves the use of material and further material as described in any of the preceding paragraphs.
Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings in which:- Fig. 1 is a cross-sectional view of a rotomoulded article according to the present invention; Fig. 2 is an enlarged view of the area II of Fig. 1; and Fig. 3 is a table showing material and further material used to produce articles according to the invention, along with the properties of the articles and indications of areas of utility.
A list of abbreviations used in the table is provided in the specification.
Referring to the drawings, and in particular Figs. 1 and 2, there is provided a rotomoulded article 10 comprising a first layer 12 made from rotomouldable material having one or more pre-selected characteristics and a second layer 14 made from a further mouldable material bonded directly thereto, which further material has one or more other predetermined characteristics whereas to give the article 10 desired properties.
In more detail, the first layer 12 comprises an external layer of the article 10 providing an external surface 16. The second layer 14 comprises an internal layer of the article 10 and provides an internal surface 18.
The materials used to produce the layers 12, 14 are pre-selected to give the layers 12,14 certain characteristics when produced by rotomoulding, which characteristics together give the article 10 one or more desired properties.
In the particular embodiment illustrated in Fig. 1, the article 10 is a container for fuel, such as a fuel tank for a motorcycle.
Unlike most fuel tanks, motorcycle fuel tanks are usually visibly prominent on a motorcycle and therefore it is desirable for the fuel tank to be aesthetically pleasing. It is therefore important that one of the characteristics of the external surface 16 is that it is visibly smooth and can receive paint, such as cellulose, acrylic or other paint.
In this particular embodiment, the material used for the layer 12 is a polyamide, and desirably polyamide twelve.
The polyamide gives the external layer 12 the desired smooth external surface 16, relative scratch resistance and fuel barrier characteristics when rotomoulded. However, rotomoulded polyamides are relatively brittle and generally have poor impact resistance. An impact upon a rotomoulded polyamide is likely to cause the production of cracks which can propagate through the layer. This is undesirable in an article such as a fuel tank, where this could result in fuel leakage during impact for example in a collision.
The material used for the inner layer 14 is chosen to address this and is pre-selected to impart improve-impact resistance to the overall article 10.
The material used in this embodiment is a modified polyolefin which is rotomoulded directly onto the inside of the layer 12 to bond directly thereto. It is an important aspect of the invention that there is no use of adhesives or any intermediate tie layers to attach the first and second layers.
It is important that the layer 14 bonds to the external layer 12 to give the article 10 the desired improved impact resistance. The modified polyolefin 14 has relatively good impact properties and mechanical performance and helps to prevent the propagation of cracks in the layer 12. The modified polyolefin is also substantially resistant to fuel, such as petrol whereby to give the article 10 the desired longevity.
The article 10 is produced in accordance with a method of the present invention. The method comprises rotomoulding material to form the first layer 12 in a mould (not shown) and moulding the second layer 14 of a further material directly on to said first layer 12 so that the second layer 14 bonds directly to said first layer 12.
The material for the layer 12 is charged into a mould following which the temperature is elevated to the melt out temperature of the material. As the mould is rotated and the material melts, the layer 12 is formed on the inside of the mould. Any desired curing of the layer 12 can then be carried out, which may include'cooking'of the material at pre-selected temperatures, for pre- selected times under pre-selected conditions.
The further material for the layer 14 is then introduced into the mould, and the temperature sustained until the further material melts. As this happens, the mould is rotated to form the layer 14 on the inside of the layer 12.
As the layer 14 forms, it bonds directly to the layer 12. Again, any desired curing can then be carried out.
Once the article 10 is formed, it is then cooled either inside and/or outside the mould.
Fig. 3 illustrates a number of alternative material and further material combinations that can be used for the first and second layers 12,14, and the articles that can be produced thereby. The table also includes properties of articles produced with those materials, and it will be appreciated that the utilities of the articles given in the table are by way of example only.
Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.
Abbreviations used for material PA Polyamide (all types, including PA6, PA6 : 6, PA11, PA12) MPO Modified (adhesive) Polyolefin PP Polypropylene (homo-and co-polymer) PE Polyethylene (generic) XLPE Crosslinkable polyethylene HDPE High density polyethylene LMDPE Linear medium density polyethylene LLDPE Linear low density polyethylene LDPE Low density polyethylene EVA Ethylene vinyl acetate co-polymer EBA Ethylene butyl acrylate co-polymer POP Polyolefin plastomer SOFT FOAM Flexible material with foaming agent incorporated SBR Styrene butadiene rubber PPVC Plasticised polyvinyl chloride PPVC FOAM Plasticised polyvinyl chloride with foaming agent incorporated