Stock material or miscellaneous articles – Structurally defined web or sheet – Nonplanar uniform thickness material
Patent
1992-12-17
1994-11-22
Loney, Donald J.
Stock material or miscellaneous articles
Structurally defined web or sheet
Nonplanar uniform thickness material
428166, 428188, B32B 100
Patent
active
053667891
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a sheet material and in particular relates to an extruded plastics sheet material having voids therein.
1. Background of the Invention
Plastics material sheeting is useful for a number of end uses. Rigid or semi-rigid plastics material sheeting may be used, for example, as a packaging material or a cladding material. However, in order to get the best physical properties at least cost, it is preferable that the sheet not be solid and profiled sheets having opposed walls separated by lateral support members have been proposed hitherto. While such structures have greater strength than a solid sheet of equivalent weight, they still have drawbacks. In particular, local failure is likely to result in complete failure of the structure either immediately or by `creep`.
2. Summary of the Invention
The invention seeks to provide a form of plastics material sheet improved in the above respects and which can be produced conveniently and economically.
According to the present invention there is provided a plastics sheet material which comprises a pair of opposed faces between which run a series of elongate voids, the voids being arranged so that there are a series of uninterrupted interconnections between the two opposite faces and the voids being of a cross sectional shape such that there is a substantial absence of sharp corners.
The voids will in practice be parallel to one another and run the length of the sheet material, thus the material can be produced in one pass by extrusion from a die. This means that the material can be produced potentially much cheaper than, for example, an equivalent laminated product. In many cases products can be produced which could not be made by lamination. Furthermore, being produced in one piece, the structural integrity is greater and the variety of configurations which may be employed is very high. The opposed faces may both be external faces, or one or more may be an internal face if the sheet is of a more involved cross-sectional profile.
The interconnections are preferably arranged such that they do not meet the faces at or near right angles but are inclined to the transverse axis of the sheet. Furthermore it is preferred to provide at least two series of interconnections which join one another where they cross, and indeed are extruded integrally. The voids may be enlarged so as to virtually fill the space between the faces leaving only relatively thin interconnections which act like leafs, ribs or beams between the opposed faces. Where the construction is employed it is important that the connection between each beam and the adjacent face is radiussed to avoid sharp angles for the reasons explained more fully hereinafter.
The plastics material employed is preferably a thermo plastic and the sheet maybe formed from many suitable thermo plastics material such as a polyolefin eg polyethylene or polypropelene. Other thermo plastic materials may be employed if desired, as may fillers, colourants and the like.
The thickness of the sheet and cross sectional shape of the voids will be chosen with regard to cost constraints together with the desired mechanical attributes of the finished sheet. The size and number of the voids will be chosen with similar considerations in mind. These considerations might be modified by considerations of ease of manufacture. As compared with a sheet of equivalent dimensions and weight made form the same polymer, the voids in the constructions of the invention enable a lighter and cheaper sheet to be made without impairing its strength owing to the presence of the interconnecting lattice work between the opposed faces. Avoiding sharp corners or angles in the cross sectional shape materially contributes to the mechanical properties of the finished sheet,. In particular, it enhances resistance to torsion, buckling, particularly in the machine direction and impact force while avoiding points at which fractures are likely to start and from which they are likely to be propogated. Thus, as compared with a sheet
REFERENCES:
patent: 4776573 (1988-11-01), Wolf
Loney Donald J.
Marketech Limited
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