GB2196234A - Packaging materials for foodstuffs - Google Patents

Abstract

A lid for an ovenable container containing foodstuff to be heated by microwaves comprises a paper sheet having a central region surrounded by an annular metallic region. The lid is applied to the container by crimping the annular metallic region around the rim of the container. The central region is transparent to microwaves and the metallic region blocks microwaves from softening the container rim. <IMAGE>

Description

SPECIFICATION Packaging materials for foodstuffs This invention relates to packaging materials for foodstuffs, and in particular concerns a packaging material to be used as a lid for a tray or other container which contains foodstuffs.

For the purposes of providing convenience, it is now known to package and sell foodstuffs in containers which are designed to be placed in ovens, so that the foodstuff contained therein can be cooked and in the preferred case, the food can subsequently be consumed from the same container. Preferably, the container is disposable and when the foodstuff has been consumed it is simply a matter of disposing of the container by placement in a trash or other receptacle. The user therefore has the convenience of being provided with hot foodstuff without having to utilise separate crockery and he is saved the time consuming task of subsequently washing and drying crockery.The use of ovenable containers, as they are sometimes described, is substantial, is increasing, and is expected to continue to increase to a greater extent as the convenience of this method of cooking is experienced by more and more people.

The present invention is concerned with a lid device for applying over foodstuff contained in a container which has foodstuff to be cooked by placement of the container with the covering lid in an oven. The container will preferably be of a disposable nature i.e. it may be of paper and/or plastics construction, but the present invention is concerned principally with the lid construction, and therefore it is to be noted that the invention is not to be considered in its widest aspect as being limited to any particular form of container or container material.

There are known so-called complete ovenable dinners which are sold in packages comprising a container having a lid of a metallic foil material, and covering the metallic foil material is a plastic dome. This assembly is contained in a cardboard box. The foodstuff contained in the container makes up a complete dinner insofar as it will typically comprise meat, potatoes and one or two vegetables.

The assembly is designed so that the foodstuff can be cooked in a conventional gas, electric or solid fuel fired oven or it can also be cooked in a microwave oven, or it can be steamed and to this end the outer case usually carries instructions indicating how the assembly is to be used in the respective cooking methods. Thus, when the food is to be cooked in a conventional oven, or is to be steamed, the plastic dome is removed, and the container with a foil lid is simply placed in the oven or the steaming apparatus and the food is cooked in accordance with instructions given on the outer case.The container is of the plastics disposable type, and the foil lid serves the purpose of retaining moisture inside the container on the one hand, and on the other hand serves to conduct heat away from the rim of the plastic container to avoid softening thereof which can happen if the rim becomes too hot during cooking.

When it is desired to microwave cook the food, the plastic dome is removed, the foil is then removed, and the plastic dome is repositioned over the container and this assembly is inserted in a microwave oven. It is necessary to remove the metallic foil, because the microwaves cannot penetrate the foil and additionally, the foil can give rise to electric arcing in the microwave oven.

Obviously, this arrangement has considerable disadvantages if for no other reason than that the user must carefully read the instructions and remove the plastic dome, metallic foil and so on including repositioning of the plastic dome depending upon the method of cooking utilised. An error in any of these procedures could result in impairment or wastage of the food.

The present invention is concerned with the provision of a suitable lid for such application, but which also in aspects thereof has wider application.

The lid acording to the invention is of a type which essentially is usable in microwave cooking of foodstuff but it can be used in conventional cooking if desired.

In accordance with a first aspect of the invention, a lid for a container in which foodstuff can be cooked by microwave heating comprises a sheet material for application over the foodstuff and connected to or for connection to the rim of the container, said sheet comprising a central portion which is penetrable by microwave energy to permit the cooking of foodstuff thereunder, and a peripheral portion which is of a different composition from the central portion and is designed to conduct heat away from the adjacent rim portion of the container and/or the foodstuff in the container at the region of the rim.

The peripheral portion may contain a metallic layer or coating for the purposes of conduction away of the heat from the rim of the container. The metallic portion may comprise a foil, a blocked layer, or a printed layer, and the presence of the metallic material is the means whereby the peripheral portion is of a different composition from the central portion.

Preferably the peripheral portion includes a metallic foil layer which is adhered or otherwise secured to the remainder of the sheet, and the foil has good deadfold characteristics enabling the peripheral portion to be crimped round the container rim for the holding of the lid to the container.

By this construction, a number of advantages are obtained in that the foodstuff can be microwaved without removing the lid according to the invention and yet the peripheral portion will conduct heat away from the rim of the container whereby the container can be of plastics material and of a disposable nature and yet the rim will not suffer deleterious softening during the cooking operation.Also, by virtue of the fact that the peripheral portion is only crimped round the container rim the lid will on the one hand act to retain steam between the lid and container during cooking thereby to maintain a moist environment in the vicinity of the food, which is desirable, but at the same time the lid will be such as to permit some of the steam to leak past the crimped peripheral portion and the container whereby the creation of too high pressure between the lid and container during cooking is avoided.

The metallic foil peripheral portion is preferably on the side of the lid which faces the container rim so that the metallic surface will contact directly on the container rim and curling and arcing during microwave cooking will be prevented.

In an alternative construction, instead of the peripheral portion being crimped round the container rim, it may be directly adhered thereto by means of an adhesive or sealing arrangement, although in this construction, the use of an intermediate adhesive or heat sealing material, may effect the capability of the heat conducting metallic layer to conduct away heat from the container rim. Furthermore, in such construction, when cooking of the foodstuff takes place, it will be necessary to puncture the lid to avoid excessive pressure build-up.

In any of the arrangements described above, the package comprising container and lid can be placed not only in a microwave oven, but it can also be placed in a conventional oven, and therefore compairing the arrangement according to the invention with the prior art arrangement discussed above, the plastic dome, which is an expensive. part of the packaging, can be eliminated and the user is not required to remove and re-apply lidding layers or components as in the prior art arrangement. Accordingly, there is much less likelihood of errors during cooking.

The concept of providing a liddable material with a central portion through which the microwaves can pass, in combination with a peripheral portion of a different composition whereby the peripheral portion can be crimped to a container is also novel regardless of whether or not that peripheral portion is designed as indicated above, to be heat conductive in nature. In this second aspect of the invention, the peripheral portion may simply be reinforced in some fashion so as to have good deadfold characteristics. For example plastic strips or the like could be provided at the periphery of the sheet material lid, so as to be capable of being crimped round a container rim, the plastic strips being such as to remain in the crimped position.This crimpable edge could also form a means for blocking the passage of microwaves in the region of the periphery of the lid thereby to protect the container rim, when such container is of synthetic plastics material.

The base material of the lidding sheet according to the invention may be any suitable material such as paper or plastic film, but it is preferred that in each case the surface of the sheet which faces the foodstuff should be provided with a finish of a nature which is non-absorbent to the foodstuff liquid content such as moisture, grease, oil or the like so as to avoid soiling of the lid by virtue of contact with the foodstuff. In this connection, it might be mentioned that the lid according to the invention when it is applied to the container holding the foodstuff i.e. before final packaging and transportation, the lidding material is preferably applied so as to have tension therein whereby if the foodstuff contacts the lidding material it will be held reasonably securely in position during transit.

In one specific embodiment, the base material for the lidding sheet is paper on one side of which is coated a polymeric resin such as a polyester resin cured to a hard impermeable coating which faces the foodstuff, and the peripheral portion has applied thereto a ring of metallic, preferably aluminium, foil.

Where reference is made herein to containers, it is to be understood that this expression covers not only relatively deep containers such as trays, but covers also relatively shallow containers such as saucers and plates.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, wherein: Fig. 1 is a perspective and exploded view of a lidding sheet according to one embodiment of the invention; Fig. 2 is a perspective view showing the sheet of Fig. 1 with the layers adhered, and also positioned in relation to a container with foodstuffs therein, and to be lidded by the lidding sheet; and Fig. 3 is a sectional elevation through the assembly of container, foodstuff and lidding material shown in Fig. 2 but when packaged ready for transportation.

Referring to the drawings, in Fig. 1 is shown a lidding sheet in exploded perspective view to indicate the respective layers of the sheet. It should be mentioned that these layers could in fact be sheets or films or extrudates or simply coatings of liquid films, adhesives or the like. In the example shown, the iidding sheet comprises a base material layer 10 which suitably is of paper, to the underside of which is applied a polymeric material layer 12 of the same size. The layers 10, 12 are circular as shown. The third layer which is adhered to the underside of layer 12 comprises a ring 14 of a heat conductive material such as a metallic foil and the three layers are laminated together to the form shown in Fig.

2. The outer diameter of the ring 14 is the same as that of each of layers 10 and 12, and the top surface of the paper 10 may be provided with decorative and/or instructional printing or the like.

The resulting lidding sheet 16 as shown in Fig. 2 is for application to a container, in this case a shallow plastics material dish 18 which contains the food indicated generally by reference 20. The food may suitably take the form of a complete dinner comprising potatoes, meat and one or two vegetables.

The lidding sheet 16 is applied to the container 18 in that the heat conductive ring 14 is arranged to face downwards and to be brought into contact with the rim 22 of the plate 18. The portion of the lid and sheet material as shown in Fig. 3 which lies within the ring 14 may in fact flex and be tensioned as the lidding sheet 16 is applied to the container 18. Attachment of the lidding sheet 16 to the container 18 is by crimping the peripheral portion of the lidding sheet including ring 14 around the rim 22 of the container 18 as shown in Fig. 3, so that the metal foil 14 is in fact crimped round the rim 22. The metal foil has good deadfold characteristics, and therefore the peripheral portion of the lidding sheet 16 will remain crimped around the rim 22.

The centre portion 24 of the lidding sheet which covers the food is in fact transparent to microwave energy so that the package shown in Fig. 3 can be placed in a microwave oven for the cooking of the food 20. During the microwave cooking, the conductive peripheral portion 14 will serve to carry away heat from the interior of the package on the one hand, and on the other hand shields the rim 22 from direct influence of the microwave energy which could cause softening of the container rim.

Additionally, the centre portion 24 traps the moisture inside the package thereby to preserve the desired environment inside the package, but if the pressure inside the package increases above a predetermined level, then the pressure is relieved by the environment escaping past the crimped peripheral portion of the liding sheet 16.

The layer 12 is of a material which is such as to provide a barrier to the passage of liquids, oils and grease from the foodstuff to the paper layer 10. It is important that the paper layer 10 should not be soiled by the foodstuffs after packaging has been completed, and during transportation and display.

The package according to the embodiment illustrated can of course be placed in a conventional oven for the cooking of the foodstuff therein, and in such conventional cooking the metallic peripheral portion including ring 14 will again serve as a means for conducting heat away from the rim to prevent softening of same.

It is important that the heat be conducted away from the container rim as the rim would otherwise tend to distort under the heat of the environment and the weight of the foodstuffs. The food in fact tends to keep the base of the material relatively cool by acting as a heat sink.

The lidding sheet of course prevents contamination of the food during handling and transportation, and also serves to locate the food and prevent it from moving during transportation and during cooking. By retaining the atmosphere inside the package, the lid also prevents drying out of the foodstuffs during cooking.

The layer 12 may be a heat resistant polymeric material in the form of a coating, varnish, ink, adhesive or extrudate which is resistant. to the aqueous or fatty contents of food.

It also serves to protect the paper layer 10 from the serious effects of heating in conventional ovens, but the combined layers 10 and 12 form no barrier to the transmission therethrough of microwave energy enabling the food to be cooked in a microwave oven. The layer 12 may be for example an extrusion coating or lamination of polyethylene terephthalate or a coating of a thermoset resin, but other materials such as nylon or a crosslinkable adhesive may be used such as isocyanate or epoxy adhesive, the adhesive serving to adhere the layer 10 and the foil ring 14, then the whole assembly being heated to cross-link the adhesive to form the heat resistant layer 12.

The paper layer 10 may be a fully bleached paper pulp layer of weight 100 g/m2, and the ring 14 may be an appropriately shaped ring of metal foil such as a micron aluminium foil, or a metallic ink coating or blocked surface.

Although a lidding sheet of circular configuration has been shown, it is to be appreciated that the invention is not to be considered as limited to such shape.

The base material 10 and the coating 12 may be replaced by a single polymeric film material, and the bringing together of the base material 10, the coating 12 and the ring 14 or simply the base material and ring 14 as the case may be may be effected in any suitable manner such as by laminating webs of materials and subsequently punching and cutting the materials to form the lidding sheets or by pre-punching the layers to appropriate form, and then bringing the layers together in a laminating process. Again, the lidding sheets may be produced by laminating layers 10, 12 and a layer of metallic foil, followed by cutting through the foil but not the layers 10 and 12 to remove certain portions of the foil, leaving only rings 14 on the webs 10 and 12, fol lowed by the cutting of the lidding sheets from such laminated web.

The lids may be produced individually or in the form of a continuous strip of material, the latter being prepared for machine packaging applications.

The shape and size of the individual lids may vary widely depending upon the shape and size of the container with which they are to be used. A particularly convenient presentation for continuous material for use in automatic packaging is that of a plurality of individual sections each consisting of an overall paper or plastics web having a peripheral metal foil welded or adhered to it, with each section being. connected to the next by means of one or two bridges or tabs of material which may serve to provide a conveniently graspable tag or tags on the final package enabling the lids to be stripped therefrom when required.

The materials from which the individual components of the lids and containers can be made vary widely but may be chosen from appropriate food grade materials. The container may be of any one of a number of known non-metallic food container materials, for example coated card or crystallised polyethylene terephthalate. The metal foil when used for the lid is preferably aluminium foil.

The base sheet 10 may be a special grade of treated paper. The water vapour permeability of the cover sheet may be chosen according to the particular food product being packaged, and according to whether the annular region of the lid is to be sealed to the edge of the tray in addition to being folded around it. Even where sealing is done, e.g. to preserve the food inside for longer, the operation of sealing is much facilitated by the dead fold properties of the metal foil at the periphery of the cover.

Both tray and cover may of course be printed with appropriate designs or instructions as desired.

It is found that by treating the edge of the base material with a metallic foil or coating or the like enables crimping of the edge of the lidding sheet around the edge of the rim or flange of the container and the lidding sheet will remain in position to protect the food when in transit and during the chilling and for the steam generated in the cooking or heating process to escape past the crimped edge.

The application of the lidding sheets to the containers in accordance with the embodiment would be by hand, but it is possible to apply the lidding sheets by means of specially adapted machinery.

Claims (10)

1. A lid for a container in which foodstuff can be cooked by microwave heating comprising a sheet material for application over the foodstuff and connected to or for connection to the rim of the -container, said sheet comprising a central portion which is penetrable by microwave energy to permit the cooking of foodstuff thereunder, and a peripheral portion which is of a different composition from the central portion and is designed to conduct heat away from the adjacent rim portion of the container, and or the foodstuff in the container at the region of the rim.

2. A lid according to Claim 1, wherein said peripheral portion contains a metallic layer or coating for the purposes of conduction away of the heat from the rim of the container.

3. A lid according to Claim 2, wherein the metallic portion comprises a foil, a blocked layer, or a printed layer, and the presence of the metallic material is the means whereby the peripheral portion is of a different composition from the central portion.

4. A lid according to Claim 3, wherein the peripheral portion includes a metallic foil layer which is adhered or otherwise secured to the remainder of the sheet, and the foil has good deadfold characteristics enabling the peripheral portion to be crimped round the container rim for the holding of the lid to the container.

5. A lid for a container in which foodstuff can be cooked by microwave heating comprising sheet material having a central portion through which the microwaves can pass and a peripheral portion of a different composition rendering the peripheral portion suitable for being crimped to a container rim.

6. A lid according to any preceding claim comprising a base sheet of paper or plastics film defining said central portion and having a peripheral portion treated so as to have said different composition from the central portion.

7. A lid according Claim 6, wherein said base sheet is of paper coated on the side which is to face the foodstuff a polymeric resin such as a polyester resin cured to a hard impermeable coating.

8. A lid according to Claim 6 or 7 wherein the base sheet is a fully bleached paper pulp layer of weight 100 g/m2.

9. A lid for a container substantially as hereinbefore described with reference to the accompanying drawings.

10. A package comprising an ovenable container and a lid according to any one of the preceding claims.