Package having a microwave reflective layer

Abstract: A food package formed from a high temperature resistant container wherein a major or a total part of the side wall comprises an aluminium laminate shield which reflects microwave radiation.

Description: This invention relates to a food package for controlled heating or cooking of prepared food in hot air, convection, household and microwave ovens. The rapid increase of the microwave oven sale to private households and the development of catering have changed the conditions for the prepared food manufacturers implying great advantages as well as problems. The advantages are evident and connected with the rapid heating in microwaves which make frozen prepared food even more convenient. There are two main problems: The traditional metallic tray is opaque to microwave radiation and is not suitable in microwave ovens as arcing may occur inside the oven cavity resulting in a very bad perception of this package by the consumer. Since metals are not transparent to microwaves and heating is obtained only from the top, when compared to heating in a plastic container, cooking is not only longer but also uneven especially with frozen products for which the bottom layer is still frozen while the top layer is overcooked and unacceptable (dry or burnt). Plastic trays are transparent to microwave radiation but owing to the limited penetration of microwaves and to the different absorptions of microwaves by the components of the products e.g. water and ice, the cooking of frozen products is uneven. Hot spots currently appear in the corners and along the walls of the tray while the centre is still frozen. Development work in the package industry in relation to microwave cooking has dealt with the problem of selective cooking of multicomponent meals in which the individual food components generally require different quantities of microwave energy exposure. For example, US-A-No 3 865 301 describes a shielded container for a plurality of ingredients of a sandwich-type food product that are to be heated or cooked to a different extent and which is opaque to microwave radiation except for radiation-transparent windows. US-A-4 081 646 illustrates a tray in a material transparent to microwave energy with a plurality of compartments, a cover formed of a material that is transparent to microwave radiation and adapted to the tray and a shielding box having walls opaque to microwave energy and bearing apertures at predetermined locations for inserting the tray with the cover therein, in order to control the amount of radiation received by each of the individual components of a meal. In the prior developments very little attention has been paid to uneven cooking of a prepared dish within a single compartment or tray in a microwave oven. In US-A-4351997, there is described a new design for a dual ovenable tray to avoid this uneven cooking in microwave ovens. This design is related to a tray including a bottom wall and a peripheral wall ending with a horizontally extending rim. The rim is coated partly or totally with a material reflecting or opaque to microwave radiation such as an aluminium foil. This provides a package in a tray form which gives an excellent temperature distribution in microwave ovens and is possible to use in hot air, convection and household ovens at temperatures up to 250°C. The present invention relates to technical and economical new solutions to achieve such a package. US-A-4661672, GB-A-1593523 and DE-A-3242402 describe containers for microwave heating using an aluminium laminate shield which are designed so that, when heating takes place, the shield covers at least part of the top or the base of the container. According to the present invention, there is provided a food package formed from a high temperature resistant container having a base and a side wall extending upwardly from said base to a top edge which defines an opening, and a cover positioned over substantially all of either the opening or the surface of the base the cover having aluminium laminated depending side edges adapted to be secured to a major or total part of the side wall characterised in that the cover is laminated with aluminium and provided with lines of weakening capable of being torn by hand to erable removal of the cover from the depending side edges. The high temperature resistant container is conveniently made of a cardboard or paperboard or a plastic material with good thermal resistance, e.g. crystalline polyethylene terephtalate (CPET), polyether sulfone, polyether imide, polymethylpentene or suitable combinations of such materials. The container may be polygonal and may contain, for example, from 3 to 10 sides. Preferably, the corners have angles rather than curves. The aluminium laminate forms a shield and may be a simple laminate with a layer of aluminium foil coated onto the inside or the outside of a layer of plastics or cardboard material i.e. an aluminium plastics laminate or an aluminium cardboard laminate or it may be a complex laminate having at least one layer of aluminium foil, plastics, cardboard or paperboard. The shield may act as an insulating label so that the consumer can handle the tray after reheating without burning his fingers. The aluminium foil may have a thickness of from 4 to 80µm and preferably from 5 to 15 µm. The container is advantageously made of a conventional plastics material such as CPET and the shield is made of an aluminium laminate cover the depending edges of which may advantageously be secured to the side wall of the container by an adhesive, or by suitable seals. The container is preferably provided with a peelable CPET film lid or any other system for easy opening. The lid could also be a simple heat sealable film. In both cases it is preferably pilfer proof. It is also possible to achieve the shielding with an outer cardboard/aluminium laminate covering only the bottom and the side walls of the container. The shield is provided with lines of weakening capable of being torn by hand to enable removal of the bottom of the shield by the consumer just before reheating. This alternative is advantageous because it enables: a) the use of a standard cardboard/aluminium laminate, and b) the use of existing machinery to deposit the shield onto the container. Such machinery is currently used to produce packages for margarine and butter. The container is provided with a peelable lid made of plastic or cardboard. A plastic over cover may also be provided. The shield may be secured to the walls of the container by using glue, by sealing or by mechanical locking. The mechanical locking enables easy removal of the shield should it be desired to recycle the container. The aluminium foil may be coated on the outside of the container, but it is preferably applied on the inside. The container may be formed from a blank having corner flaps which is folded to form the walls and glued in the corner flaps. The food packages of the present invention are very cheap and convenient because they may be formed by a simple adaptation of conventional containers commercially available at the present time. The different designs allow to achieve a shield very close to the product and this is very important. The present invention will now be further illustrated by way of example with reference to the accompanying drawings in which Figure 1 is a cross-sectional view of a package according to the invention, Figure 2 is a top plan view of the package of Figure 1, Figure 3 is a plan view of the package of Figure 1, Figure 4 is an exploded perspective view of a package according to the invention, Figure 5 is an exploded perspective view of a package, and Figure 6 is a plan view of a laminated aluminium/cardboard of the alternative shield of the invention. Referring to Figures 1 to 4 of the drawings the package comprises a high temperature resistant CPET tray 10 having a peelable film lid 11 and is provided with an aluminium laminate cover 12 with depending edges 13 and provided with precut lines of weakening 14, 15 to enable the top of the cover to be removed by tearing off. Fold lines 17 are provided to conform to the shape of the container.The depending edges 13 are glued or sealed to the side walls 16. The top of the laminate cover 12 may be sealed together with the lid 11 and the flange of the container 18. Figure 5 shows a package comprising a high temperature resistant CPET tray 25 having side walls 26, a peelable lid 27 and a plastic cover 28. A cardboard cover 29 partially laminated by coating with aluminium foil 30 is wrapped around the base and side walls of the tray so that the aluminium laminate forms a shield around the total part of the side walls. Figure 6 illustrates the design of the cardboard shield of the figure 5 completely laminated with aluminium. The shield has four depending walls of cardboard/aluminium laminate (50 and 51) containing fold lines (52 and 53) to conform to the shape of the container 25. The bottom (54) is a cardboard/aluminium laminate provided with precut lines (55) and a tab (56) in order to facilitate the removal of the bottom of the shield before reheating. The walls may be glued, sealed or mechanically locked to the tray walls 26.

Claims: A food package formed from a high temperature resistant container (10, 25) having a base and a side wall (16, 26) extending upwardly from said base to a top edge (18) which defines an opening, and a cover (12, 54) positioned over substantially all of either the opening or the surface of the base the cover having aluminium laminated depending side edges (13, 50, 51) adapted to be secured to a major or total part of the side wall (16, 26), characterised in that the cover (12, 54) is laminated with aluminium and provided with lines of weakening (14, 15, 55) capable of being torn by hand to enable removal of the cover from the depending side edges. A food package according to claim 1 wherein the container (10, 25) is quadrangular in shape and at least the two opposite side walls (16, 26) comprise the aluminium laminated side edges (13, 50, 51). A food package according to claim 1 wherein the depending side edges (13, 50, 51) of the cover (12, 54) are secured to the side walls (16, 26) of the container (10, 25) by an adhesive or a seal or by mechanical locking. A food package according to claim 1 wherein the cover (12, 54) is provided with fold lines (17, 52, 53) enabling the depending side edges (13, 50, 51) to contact the side walls (16, 26) of the container (10, 25). A food package according to claim 2 wherein the two aluminium laminated depending side edges (13, 50, 51) are long enough to insure a complete shield of the sides walls (16, 26) of the container (10, 25) after folding. A food package according to claim 1 which comprises a microwave transparent high temperature resistant container (10, 25) provided with an outer cardboard packaging (12, 54) which is totally laminated with an aluminium foil. A food package according to claim 6 wherein the outer cardboard/aluminium laminate packaging (12, 54) covers only the bottom and the side walls of the container (10, 25). A food package according to claim 6 wherein the outer cardboard/aluminium laminate packaging (12, 54) is provided with fold lines (52, 53) enabling the depending edges (50, 51) to contact the side walls of the container. A food package according to claim 6 wherein the cardboard/aluminium laminate packaging (12, 54) is provided with a precut line (55) and a tab (56) in the bottom enabling the bottom (54) to be removed by the consumer before reheating. A food package according to claim 1 wherein the container (10, 25) is provided with peelable plastic film lid (27).

Inventors: SAUNIER CHRISTIANE-MONIQUE, SAUNIER, CHRISTIANE-MONIQUE
Applicants: FRISCO FINDUS AG, FRISCO-FINDUS AG
Application year: 1992
Main classification: B65D81
IPC codes: B65D77, B65D25, B65D81