FOAM SHEET

Abstract: An extruded foam sheet material which comprises a foamed plastics material (1) sandwiched on either side by a relatively rigid layer (2, 3), wherein there is applied on at least one surface of such a structure another foam layer (4), so as to give a four layer structure. Such a foam sheet material may be used for containers, either to form the structure of the container itself or to provide a lining therefor.

Description: <"*\ FOAM SHEET This invention relates to foam sheet, and more particularly to extruded foam sheet and composites of the same for trays or boxes, crates, cartons or other containers. 5 The invention is especially concerned with the protection of the contents or items carried in or on the above. Extruded plastics foam is used to make a number of boxes, trays and containers for various products but in especially in the fresh, chilled, frozen and fast food fields. One of the main advantages of foam, apart from its thermal insulation properties, is the fact that it is generally totally impervious to water and moisture. 15 This, however, can also be a disadvantage in certain cases since there are some foods such as meat and fruits, for example, where it is desirous that the Kurrounding packaging absorbs moisture or liquids clinging to, or emitted by, the food. This is desirous 20 for presentation purposes or to reduce the spread of bacteria or fungi. Another advantage of extruded foam is that it can be made to be extremely tough and rigid while still being economical to produce. This toughness and/or rigidity can be achieved by making the foam of a high density. Other better and more economical ways are to "skin" one or both surfaces of the foam by collapsing the surface with low temperature and/or pressure, or to extrusion coat or laminate one or both surfaces of the foam with a thin solid sheet made out of the same or a different raw material. The result is a rigid but generally hard surfaced sheet. While such a sheet is rigid and can support significant weight loads in the applications cited above, the hard surface can damage delicate foods such as fruits, vegetables, cakes etc. Soft foam sheets (i.e. low density foam sheets and foam sheets which have not been "skinned", coated or laminated) on the other hand are ideal for protecting such delicate foods described above. Apart from the foam sheets described above there are no known extruded foam sheets for packaging that are made up of two or more different foam sheets. U.S. Patents Nos. US-A-4059660 and US-A-4119749 (equivalent to GB-A-1477987) disclose a light-weight framed panel comprising a foamed material sandwiched between a cardboard material and a finishing cover, the sandwich structure being further provided over certain areas thereof with a foamed polyurethane layer. U.S. Patent No. US-A-3787259 (equivalent to GB-A-1361890 and GB-A-1412436) discloses a floor covering which has a felt backing sandwiched between two foam layers. "\ However, none of the above patents disclose the foam sheet of the present invention as defined below. 5 The present invention provides an extruded foam sheet material, comprising a foamed plastics material having on both surfaces thereof a relatively rigid layer, wherein there is provided on at least one surface thereof another layer of a foamed plastics material. 10 According to the invention, to a known three layer structure of a foamed plastics material sandwiched on either side by a relatively rigid layer, there is applied on at least one surface of such a structure another foam layer, so as to give a four layer structure. 15 Such a foam sheet material according to the invention may be used for trays or boxes, crates, cartons or other containers (hereinafter referred to for convenience as containers), either to form the structure of the container itself or to provide a lining therefor. 20 The present invention takes advantage of the strength and rigidity of "skinned", coated or laminated foam sheet and adds a soft foam to one or both surfaces *. of the rigid foam structure. The resultant composite foam may be then folded or formed and cut into trays, 25 boxes or other containers so that the soft foam is (to the greater part) in contact with the contents of the container, thereby giving protection against knocks. etc., the "skinned", coated or laminated foam sheet providing the strength and rigidity to support the contents. The invention will be further described, by way of example only, with reference to the accompanying drawing, which is a schematic sectional view of an extruded foam sheet according to the invention. The foam sheet shown in the drawing comprises a core of a foam sheet 1, both surfaces of which are provided with relatively rigid thin sheets 2 and 3 respectively, formed either by collapsing the surfaces of the foam sheet 1 by means of low temperature and/or pressure, or by extrusion coating or laminating the foam layer 1 with a thin solid sheet of the same material as the foam 1 or a different material. The composite structure 1, 2, 3 is a rigid but generally hard surfaced sheet, to which there is applied, according to the invention, another foam sheet 4, usually of softer material than the foam sheet 1. It is envisaged according to a preferred aspect of the invention to use a preferably soft foam sheet with either an open (i.e. relatively porous or sponge-like) cell construction throughout, or- alternatively on its surface, and apply it in the same manner described above to the other foam sheet so that the soft, open cell foam sheet is, in general, in contact with food that emits liquid or moisture or has liquid or moisture clinging to it. The open cell foam types described above absorb or dissipate the unwanted moisture or liquid thereby keeping the food relatively dry. Alternatively, the foam sheet may be arranged so that in use the soft, open cell foam sheet is on the outside of a container formed therefrom, so that evaporation from the open cells will assist in cooling of the contents of the container. The two foam sheets can be joined together by a number of means. The preferred method is to laminate the connecting surfaces by first heating these surfaces and then applying pressure with rollers once the surfaces have been brought into contact. Another method is to extrude the two foam sheets simultaneously and to bring the foam sheets into contact with each under pressure such as by means of two rollers, A further method is to apply the soft foam sheet through pressure rollers after the rigid foam sheet has been softened by the heaters of a thermoforming machine and prior to the combined sheet being thermoformed by a mould. The structure of the combined foam sheet can vary-according to the desired characteristics. Typically the foam sheet has a laminated or "skinned" surface 3 on the outside, a "skinned" surface 2 in the middle between the rigid foam 1 and the soft foam 4 and the soft foam 4 on the other surface. Alternatively, as mentioned previously, the soft foam 4 may be arranged on the outside of a container formed from the sheet. As stated earlier the method of creating a solid skin or sheet 2,3 on the surface of the rigid foam sheet 1 prior to applying the soft foam 4 can be suitably "skinning", extrusion coating or laminating. The preferred basic material for the core of the rigid foam 1 is polystyrene but may also be other thermoplastic materials such as polyethyleneterephthalate (PET), high density polyethylene, styrene copolymers, etc. The preferred basic material for the coating or lamination 2,3 on the rigid foam is polystyrene but may also be any other thermoplastic material or paper or metal foil. The preferred basic material for the soft foam 4 is low density polyethylene but may also be polystyrene or another thermoplastic. It will be appreciated that the foam sheet material of the present invention may be extruded continuously, in contrast for example to the panel disclosed in the above mentioned U.S. Patent Nos. 4059660 and 4119749 where the cardboard layer utilized could not be continuously provided. The soft foam 4 may be suitably shaped to receive individual items of produce to be contained within a container formed from the foam sheet, for example the soft foam 4 may be provided with a series of indentations or cells, formed therein for receiving fruit such as apples or oranges.

Claims: CLAIMS : 1. An extruded foam sheet material, comprising a foamed plastics material (1) having on both surfaces thereof a relatively rigid layer (2, 3), characterized in that there is provided on at least one surface thereof I another layer of a foamed plastics material (4). 2. A foam sheet as claimed in claim 1, characterized in that said rigid layers (2, 3) are formed by collapsing the surfaces of the foamed material (1) by means of low temperature and/or pressure. 10 3. A foam sheet as claimed in claim 1, characterized in that said rigid layers (2, 3) are formed by extrusion coating or laminating the foamed material (1) with a thin solid sheet. 4. A foam sheet as claimed in any of claims 1 to 3, 15 characterized in that the foamed plastics material (4) is of low density polyethylene or polystyrene. 5. A container, characterized by including or consisting of a foam sheet as claimed in any of claims 1 to 4. 20 6. A container, characterized by having a lining of a foam sheet as claimed in any of claims 1 to 4.

Inventors: DEVEREUX CHRISTOPHER PETER, DEVEREUX, CHRISTOPHER, PETER
Applicants: PORTAPAX LTD, PORTAPAX LTD.
Application year: 1987
Main classification: B32B5
IPC codes: B32B5