MICROWAVE INTERACTIVE LAMINATE

Abstract: A microwave interactive laminate (1) comprises a flexible film (2), microwave interactive metal cooling (3), paper layer (4), and is provided with surface formations (5) whereby a food item (8) may be supported in thermally conductive communication with coating (3) and channels (10) are provided for escape of moisture.

Description: TITLE: "MICROWAVE INTERACTIVE LAMINATE" FIELD OF THE INVENTION This invention relates to a microwave interactive laminate. BACKGROUND ART It has previously been suggested (U.S. Patent 4,267,420, Brastaad) to wrap foodstuffs in a flexible packaging material comprising a microwave interactive layer, for example a polyester film on which is deposited a thin coating of aluminium metal laminated with paper. Similar microwave susceptors have been incorporated into packages (e.g. GB 2,046,060, Seiferth; US 4,190,757, Turpin et al) . In use of microwave interactive packaging, a foodstuff - for example a pizza - is placed upon or wrapped in a sheet of the packaging material and then placed in an energized microwave oven. Some of the microwave energy passes through the wrapping to heat the foodstuff while a portion of the microwave energy heats the metallic coating in thermally conductive communication with the food and thereby browns or crisps the outer surface of the foodstuff. It has been found that when certain foodstuffs, for example fish pieces, are heated in the above manner, the sides and top of the food browns to a greater extent than the base, which becomes moist or soggy. An object of the present invention is to provide a microwave susceptor which avoids or at least ameliorates that disadvantage and which can be manufactured at sufficiently low cost as to be considered disposable. DISCLOSURE OF THE INVENTION According to one aspect the invention consists in a laminate comprising a structural layer and a microwave interactive layer, the laminate having a plurality of surface formations adapted in use to support a food item in thermally conductive communication with the microwave layer while providing at least one space between the food item and the laminate whereby moisture can escape from the supported surface of the food item. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings wherein: Figure 1 shows a portion of a laminate according to the invention in plan. Figure 2 shows a cross-section on line A-A of Figure 1. Figure 3 shows the embodiment of Figure 1 in use in end elevation. Figure 4 shows an enlarged cross-section of a portion of the laminate of Figure 3. Figure 5 shows in cross-section a second embodiment of the invention. The drawings are schematic and not to scale. PREFERRED EMBODIMENTS OF THE INVENTION With reference to figures 1 - 4, there is shown a flexible laminate 1, comprising a film 2, which is coated on one side with a vacuum deposited coating of aluminium metal 3 and which is bonded to a layer of paper 4, so that the metallised layer 3 is sandwiched between film 2 and paper 4. For preference, the film is a polyester such as that sold under the trade mark Melinex 800, available from Imperial Chemical Industries, but may be a polyethylene, nylon, cellophane or other relatively heat stable inert plastic substance. Polyester is preferred for its strength, heat resistance flexibility, and its inertness when in contact with a foodstuff and is preferably of the order of from 12 - 25 microns in thickness. The microwave interactive layer 3 is typically a layer of metal, for example vacuum deposited aluminium metal, such that the surface has a resistance of for example between about 0.4 and 400 ohms per square, preferably from 20 to 300 ohms per square, and usually having a thickness of between about 40 and 700 angstroms. It will be appreciated that the drawings are not to scale and coating 3 is very much thinner than film 2. Paper layer 4 provides the laminate with structural mechanical strength, especially when thin films 2 are employed. The paper layer 4 is bonded to the aluminium coated side of the polyester by means of an adhesive, for example a vinyl adhesive (not shown in the drawings) . A sheet of laminate 1 of indefinite length is provided on one surface with a plurality of surface formations, for example raised protuberances 5 as shown in Figures 1 to 3. Formations 5 may be formed for example by a pressing or embossing process forming a dimple on one side and protrusion of circular plan on the other. For preference, formations 5 are each provided with a flat or resilient upper surface or plateau 6. In use, a foodstuff to be heated is placed upon the laminate of Figure 1 as illustrated in Figure 3 in contact with film 2. The lower surface 7 of food 8, for example a crumbed piece of fish, is supported upon raised formation 5. The upper surface 9 of the food may be in contact either with a like formed sheet (not shown in the drawing), or sheet 1 may be provided with a plain portion (devoid of formations) which may be folded over to provide a flat contact with food upper surface 9. Formations 5 act both to support lower surface 7 of food item 8 upon upper protrusion surfaces 6 and also to define spaces or channels 10 beneath supported food item 8 whereby moisture and other liquids may escape from the lower surface 7 of food item 8, surface of dimples 5 provide sufficient thermally conductive communication between sheet 1 and foodstuff 8 so as to result in browning of the lower surface 7 of foodstuff 8 which does not become soggy. With reference to Figure 5 there is shown a second embodiment of the invention in which a laminate such as shown in Figure 4 comprising polyester film 2, coated with a microwave interactive layer 3, is laminated to a light paper 4 and the laminate is corrugated and is bonded at the corrugation troughs to a liner paper 11. The lower surface 7 of foodstuff 8 may be allowed to rest upon the crests 12 of the polyester corrugations. In use, the corrugation formation provides channels 10 exposed to the underside 7 of the foodstuff 8, whereby moisture or cooking juices may be drained from the under surface of the foodstuff, while at the same time crests 12 provide thermal communication between the microwave interactive layer 3 and foodstuff 8. In other embodiments of the invention, microwave interactive coatings other than aluminium may be employed, for example semi-conductor coatings, metal oxide such as tinoxide or coatings utilising other elemental metals, organic semiconductors, or organic or inorganic conductive inks. The microwave interactive layer need not be continuous and may be provided in discrete islands, or at the plateau of dimples or crests of corrugations and in some embodiments may be omitted from the valleys. Film 2 acts as a carrier upon which aluminium may be vacuum deposited. If the film side of the laminate is in contact with the foodstuff, the film acts as a barrier between the food and aluminium. The structural layer 4 may be made from resin reinforced stocks or papers of various thicknesses, paperboard, or from plastics. However, it will also be understood that layer 4 may be omitted if film 2 is otherwise of sufficient strength to itself constitute a structural layer. The surface formations may be channels, ribs, protrusions or the like and may be made by corrugation, embossing, pressing, vacuum forming, or any suitable means. However, protrusions of circular cross-section are preferred because the resultant wrapping is flexible in two dimensions and is more easily wrapped about a foodstuff. The ratio of plateau area to valley area may be controlled so as to produce a desired browning effect for any particular foodstuff, while optimising the cross-sectional area of channels available for drainage or removal of moisture vapour. In yet other embodiments, the laminate may be formed into a tray, utensil or other receptacle which is thus provided with corrugations, dimples or other formations on its floor. If desired, foodstuffs may be sold pre-packaged in materials as described or else consumers may wrap foodstuffs therein prior to cooking in a microwave oven and thereafter dispose of the wrapping. It is not necessary for the foodstuff to be placed in contact with the film and in some embodiments, contact of the foodstuff with the paper side of the laminate is preferred, the paper surface providing sufficient thermal conductivity to the microwave susceptor layer and having suitable surface formations such as described above. Other embodiments of the invention will be readily apparent to those skilled in the art from the disclosure hereof and all such embodiments are deemed to fall within the scope of the invention disclosed.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A laminate comprising a structural layer and a microwave interactive layer, the laminate having a plurality of surface formations adapted in use to support a food item in thermally conductive communication with the microwave layer while providing at least one space between the food item and the laminate whereby moisture can escape from the supported surface of the food item. 2. A laminate according to Claim 1 wherein the formations are protrusions having a substantially circular cross-seciton. 3. A laminate according to Claim 1 wherein the formations are corrugations. 4. A laminate according to any one of the preceding claims wherein the formations are moulded into the structural layer. 5. A laminate according to any one of the preceding claims wherein the structural layer is a paper or board. 6. A laminate according to any one of the preceding claims including a layer of a plastics film. 7. A laminate according to any one of the preceding claims wherein the microwave interactive layer is vacuum deposited aluminium. 8. A laminate according to Claim 1 comprising a film having a microwave interactive layer on one side and bonded to at least the flute area of a corrugated base. 9. A laminate according to claim 1 comprising a sheet wherein the formations are confined to a zone or region or area thereof. 10. A laminate substantially as herein described with reference to the drawings.

Inventors: CLARK JOHN FREDERICK, CLARK, JOHN, FREDERICK
Applicants: LEIGH MARDON PTY LTD, LEIGH-MARDON PTY. LIMITED
Application year: 1989
Main classification: B32B3
IPC codes: B32B3, B65D81