PACKAGING CONTAINER

Abstract: A packaging container particularly suitable for retail sale of pre-prepared foodstuffs comprises an inner generally cup-like portion (2) located substantially entirely within an outer portion (3). The inner portion is formed of a microwave compatible plastics material and is retained within the outer portion e.g. by flaps (12) formed integrally with the outer portion which engage barbs provided on the inner portion. The air gap provided between the inner and outer portions prevents the outer portion from being heated by contact with the food product and accordingly the container can readily be handled after microwave heating of the contents.

Description: PACKAGING CONTAINER This invention relates to a packaging container and in the preferred embodiment provides a packaging container which is particularly suitable for the packaging for retail sale of pre-prepared foodstuffs. Many pre-prepared foodstuffs are sold in a ready- to-heat form, and may be heated either in a conventional oven or a microwave oven. Heating of such foodstuffs in a microwave oven has many well recognized advantages, and it has been found to be particularly advantageous if foodstuffs which are susceptible to being heated in a microwave oven are sold packaged in a container in which the products may be heated using a microwave oven. Certain plastics materials are well suited to the formation of such containers since they can readily and cheaply be formed into a water-tight dish-like container, are not adversely affected by microwave energy, and are able to withstand contact with the product even when the temperature of the product has been raised to boiling point. However, simple plastics containers known heretofore for microwavable food products have suffered from the disadvantage that they readily conduct heat with the result that the temperature of the outside surface of the container rises substantially to the temperature of the contents of the container during microwave heating. It is accordingly very difficult to remove the container from the microwave oven after heating. In this respect, it will be appreciated that many of the plastics suitable for formation of such containers are thermoplastic in nature, and accordingly the containers will soften at elevated temperatures. Such softening makes the containers highly flexible, and great care must be taken when removing the container from the microwave oven in order to avoid spillage of the product. Such careful removal will necessitate careful grasping of the container, and this is difficult if the outer surface temperature of the container approaches that of the heated contents. A similar problem arises in relation to dehydrated food products which are sold in a pot to which boiling water is added in order to re-hydrate the food product. The temperature of the outside surface of such containers will become very high, and the containers themselves will soften at elevated temperature rendering handling of such containers difficult. According to one aspect of the present invention a packaging container comprises an inner plastics generally cup-like portion having an open upper end, a closed lower end, and side walls interconnecting the upper and lower ends; and an outer portion having an open upper end, a closed lower end, and side walls interconnecting the upper and lower ends, wherein the inner portion is in contact with the outer portion at the upper end of the container and the side walls of the inner portion are spaced from the side walls of the outer portion by an air gap. With such a container, the outer surface of the side walls will be substantially thermally isolated from the contents of the container by the air gap and accordingly the outer side walls of the container will remain cool to touch. Further, because the outer portion is not heated significantly during microwave heating of the contents of the container, the physical properties of the outer portion will not be adversely affected with the result that the container will remain rigid and easy to handle, notwithstanding that the temperature of the contents may be at or close to the boiling point thereof. In one preferred embodiment of the invention the outer portion is of cartonboard and the inner portion rests on the upper edge of the outer portion and is supported thereby. In this case, the lower closed end of the inner portion is preferably spaced from the lower end of the outer portion. In this way, the temperature of the lower surface of the carton board outer portion will also remain low during heating of the carton and contents. Preferably, the lower end of the inner portion is spaced from the lower end of the outer portion by an air gap, and the weight of the inner portion is entirely supported on the upper edge of the outer portion. Preferably, the air gap between the inner and outer portions is provided by a substantially closed chamber defined between the inner and outer portions. Preferably, the inner portion is secured to the outer portion in a manner which will ensure that the inner portion is retained within the outer portion if the container is inverted to remove the contents. The inner portion may be retained by means of adhesive, but in the preferred embodiment is retained by a mechanical interlock with the outer portion. Such mechanical interlock can conveniently be provided by providing flaps which extend from the upper end of the outer portion downwardly and inwardly to engage the outer surface of the inner portion at a point intermediate the upper and lower ends. In this case, a suitable projection may be formed on the inner portion to engage the free edge of each flap and resist separation of the inner portion from the outer portion. In a particularly preferred embodiment of the invention the lower end of the inner portion is of a smooth curved concave form when viewed from the open end of the inner portion. This arrangement is advantageous from the point of providing even microwave heating of the contents, and offers the further advantage that the contents can easily be removed from the container using a spoon. It will be appreciated that such an arrangement is not possible in the case of a single-walled container since the container would not, if it had this form, stand on its base. Preferably, the upper edge of the inner portion is in the form of an outwardly directed flange. Such a flange provides a surface to which a cover can be sealed, e.g. by heat sealing, adhesive sealing, or ultrasonic welding. The cover may be of any convenient form, for example a plastic laminate membrane, a paperboard/plastic laminate, treated paperboard, or metal foil. If the closure is of a form compatible with microwave heating then the closure may be left in position during microwave heating provided that a suitable vent hole is provided. Preferably, the carton is completely sealed by the closure when sold, and the vent hole is formed by partially breaking the seal between the closure and the container, or by forming an aperture in the closure itself. In an alternative embodiment of the invention the inner portion and the side walls of the outer portion are an integral plastics member, for example an injection moulding or a thermoforming. In this case the lower end of the outer portion is preferably in the form of a sheet e.g. of cartonboard which is sealed to the lower edge of the side wall of the outer portion. The lower edge of the side wall may incorporate a flange to facilitate such sealing. Whilst particularly suitable for the retail sale of microwave heatable foodstuffs it will be appreciated that the packaging containers of the present invention are of more general applicability. For example, the containers can conveniently be used for the retail sale of dehydrated foodstuffs which are re-hydrated by the addition of boiling water. The containers of the present invention are particularly desirable for this purpose since the thermal insulation provided by the air gaps surrounding the inner portion substantially reduces any undesirable cooling of the contents during the re-hydration period. This thermal insulation is also of advantage in relation to microwave heated products in that it delays cooling of the product after heating. The containers of the present invention may also be advantageously adopted for cold or frozen foodstuffs, for example dessert products. The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawings wherein: Figure 1 is a cross-section taken on the line 1-1 of Figure 2 illustrating a preferred embodiment of the invention; Figure 2 is a plan view of the embodiment of Figure 1 ; Figure 3 illustrates on a smaller scale a blank for use in forming the outer portion of the container of Figures 1 and 2; Figure 4 is a cross-sectional view taken on the line Iv -IV of Figure 5 showing second embodiment of the invention; and Figure 5 is a plan view of the embodiment of Figure 4. Referring firstly to Figures 1 and 2 the packaging container 1 comprises an inner generally cup-like portion 2 located substantially entirely within a carton¬ board outer portion 3. The inner portion 2 is formed of a plastics material which is capable of containing foodstuffs whilst the container is subject to microwave heating to raise the temperature of the foodstuffs. Suitable plastics materials will be well known to those skilled in the art. The inner portion 2 can conveniently be formed by thermo- forming, but may be formed by other forming techniques, for example injection moulding. The outer portion 3 is formed from carton board of a type which is able to withstand microwave energy. The inner portion 2 has an open upper end 4 and a closed lower end 5 interconnected by side walls 6. In the illustrated embodiment of the invention the upper open end of the inner portion is substantially square and the closed lower end is in the form of a smooth concave surface when viewed from the open end. The side walls 6 blend from the square upper end into the rounded lower end. Whilst other configurations for the inner portion are possible, for example the open end may be of any convenient polygonal form, or round, and the closed end may correspond in shape to the upper end or have some different shape, the illustrated arrangement is particularly desirable since it will enable the carton to stack neatly in outer cases or on the shelf in a shop, but will provide an optimum shape for microwave heating of the contents and will enable the contents to be cleanly and easily removed from the carton using a spoon. The outer portion 3 comprises an open upper end 7, a closed lower end 8 and side walls 9 interconnecting the upper and lower ends. In the illustrated embodiment the outer portion is in the form of an inverted truncated square based pyramid - i.e. it is square when viewed in horizontal cross-section and tappers inwardly from the open end 7 towards the closed end 8. The inner portion of the container is in contact with the outer portion at the upper end of the container, and in the illustrated embodiment this is achieved by means of an outwardly extending flange 10 which extends around the entire periphery of the inner portion and rests on the upper edge 11 of the outer portion. The side walls 6 of the inner portion are spaced from the side walls 9 of the outer portion by an air gap. In the illustrated embodiment the lower end 5 of the inner portion is also spaced from the lower end 8 of the outer portion by an air gap. Whilst the provision of an air gap between the lower end 5 of the inner portion and the lower end 8 of the outer portion is desirable it should be understood that this is not an essential feature of the present invention, and many of the advantages of the invention can be derived if the lower end 5 of the inner portion rests on the lower end 8 of the outer portion, or rests on some intervening member, e.g. of insulating material. The provision of the air gap provides a large degree of thermal insulation between the manually graspable external surfaces of the container and the contents. In the case of a container which is filled with pre-prepared microwavable food this offers the particular advantage that after the container and food have been heated in a microwave oven the external surface of the container may be grasped to remove the container from the microwave oven without any discomfort to the user. Further, the insulating effect of the air gap will assist in maintaining the temperature of the contents of the container, if the temperature of the contents is different from ambient temperature. In the case of pre- prepared chilled food this has the particular advantage that the insulation provided by the container will assist in keeping the contents cool between the time when they are removed from the retailer's chilled storage system and the time when they are placed in the domestic refrigerator of the purchaser, or are heated by the purchaser. After heating, the thermal insulation provided by the air gap will lengthen the period during which the contents will remain hot. It will be appreciated that the illustrated container may also be used for many purposes other than pre-prepared microwavable foodstuffs. For example, the container may be used to pack dehydrated foodstuffs which are re-hydrated by the addition of boiling water. The thermal insulation provided by the air gap surrounding the side walls of the inner portion will then prevent discomfort to the person holding the container and will retard cooling of the contents of the container during the necessary dwell period for complete re-hydration. The container may also be used for cold products, for example frozen or chilled desserts. Finally, the container may be found to have uses outside the foodstuffs industry, for example it may be used to package such items as hyacinth bulbs which, after being "prepared" by a heat treatment process must be maintained at a relatively low temperature before they are planted. Preferably, the inner portion is secured to the outer portion to prevent accidental separation of the inner and outer portions. This may be achieved by adhesively securing the inner portion to the outer portion, e.g. at the underside of the flange 10. However, in the illustrated embodiment of the invention a mechanical interlock between the inner and outer portions is provided by means of flaps 12 provided on the outer portion. These flaps are bent inwardly during assembly of the outer portion. The inner portion is formed with outwardly extending barb like projections 13 which, when the inner portion is pushed into the outer portion, cam the flaps 12 outwardly until the barb like portions clear the lower ends of the flaps, whereupon the flaps 12 spring back to the illustrated position and prevent removal of the inner portion from the outer portion. The mechanical interlock illustrated is particularly desirable since it can be achieved using a cartonboard blank 14 as illustrated in Figure 3 which blank 14 can be cut from a sheet of cartonboard economically. It will be noted that by orientating the base 8 of the carton diagonally relative to the grain direction 15 of the cartonboard the blank 14 may be cut from a superficial area of cartonboard no larger than that which would be required to cut the blank without flaps 12. The flaps 12 are, in effect, formed by material which would be cut to waste if a blank devoid of the flaps was produced. The blank 14 accordingly enables the step of adhesively securing the inner portion to the outer portion to be eliminated without any additional cost to the manufacturer. In use, after the inner portion 2 has been charged with the product to be sold the open end 4 is closed by means of a suitable closure. It will be noted that the horizontal surface provided by the flange 10 provides a surface against which a range of conventional closures can be sealed. The open end 4 may, for example, be sealed by means of a plastic film or a plastic/foil laminate, or by means of a cartonboard lid having a plastic coated surface or a surface treated to render it compatible with sealing by adhesive, heat sealing or ultrasonic welding to the upper surface of the flange 10. In a particularly preferred embodiment of the invention the open end 4 is closed by means of a cartonboard closure which is scored to provide ready removal of the lid. Preferably, the lid is such that it can readily be punctured or partly opened to provide a ventilation opening prior to microwave heating of the container and contents. If desired, a clip- over additional lid may be provided over the primary closure. In the event that the primary closure is a foil or plastic film/foil laminate, the primary closure should be completely removed prior to microwave heating. In this case, the clip-over additional lid may be used to close the container during microwave heating. In addition, the clip- over lid can be used to re-close the container after opening. The above described container may be found to be particularly advantageous for the sale of foodstuffs which have been subject to autoclave heating. In particular, the foodstuff may be loaded into the cup-like portion 2 and subject to autoclave heating and sealing by means of a suitable lid before the inner portion 2 is loaded into the outer portion 3. During autoclave heating the inner portion 2 may be supported in a complementary shaped support member e.g. of metal, to prevent undesirable stretching of the plastics material of the inner portion 2 when the temperature of the inner portion and the contents are raised to the autoclave temperature. By this means, a container may be sold in which the contents have been subject to autoclave heating, and yet in which the outer portion 3 has not been subject to autoclave heating. Of course, the advantages outlined above in relation to microwave heating of the container still apply to containers of products which have been subject to autoclave sterilization. Referring now to Figures 4 and 5 there is illustrated a second embodiment of the invention. In this embodiment of the invention a unitary plastics shell 20 provides a generally cup-like inner portion 21 having an open upper end 22, a closed lower end 23 and side walls 24. The unitary plastics shell 20 also provides the side wall 25 of an outer portion which comprises the side wall 25 and a paperboard base 26 secured to a flange 27 provided at the lower edge of the side wall 25. The upper edge of the side wall 25 is connected to the upper edge of the side wall 24 by a flange 28 which is also part of the unitary plastics shell 20. The base 26 is preferably provided with one or more small apertures to prevent any build up of pressure within the chamber 29 defined between the shell 20 and the base 26. However, apart from these aperture the chamber 29 is closed to provide an insulating enclosure surrounding the cup-like inner portion 21. As with the previously described embodiments of the invention after a charge of product has been introduced into the cup-like inner portion 21 the open end 22 is closed by a suitable membrane which can conveniently be sealed to the flange 28. The entire container may then be positioned within a printed sleeve for point of sale display if intended for retail sale. In this respect, the flange 27 and underlying portion of the base 26 provide convenient means for locating the container within the sleeve. The shell 20 must, of course, be formed of a material which is compatible with microwave heating, is suitable for direct contact with foodstuffs, and is capable of withstanding contact with foodstuffs heated to substantially boiling point. Such materials as polypropylene, polyester, or laminates incorporating such materials are particularly desirable since by using such materials the shell 20 may be formed by thermoforming techniques. Thermoforming the shell enables the shell to be manufactured using a minimum amount of plastics material. It is possible, however, that the shell may be formed of other processes, for example by injection moulding. Whilst in the embodiment of the invention illustrated in Figures 4 and 5 the container provides a single compartment for product and is generally of oval shape when viewed from above it will be appreciated that many other arrangements are possible. For example, the shape of the container may be varied to provide for the particular needs of the product to be sold and/or with a view to optimizing the heating characteristics of a microwave oven. Further, the inner portion 21 may be formed with one or more dams to separate different types of foodstuff contained within the container. For example, a central dam may be provided to separate a portion of curry on one side of the dam from a portion of rice on the other side of the dam. If desired, conventional techniques may be used to apply printing or a design to the side wall 25. If desired, a spoon or similar instrument may be secured to the side wall 25 prior to positioning of the container within an outer sleeve whereby when the outer sleeve is opened a spoon will be immediately available for consumption of the contents of the container. The container packaged in this manner may be particularly suitable for sale by cafes, garages, and the like for immediate consumption. It will be noted that in the case of both embodiments described above the lower surface of the inner portion is spaced from the base of the container. Whilst this feature is not essential and workable embodiments of the invention can be produced in which the lower surface of the inner portion rests on the inner surface of the base of the container, the feature of spacing the lower surface of the inner portion from the base of the container offers a particular and significant advantage in the efficient use of a microwave oven to heat the contents of the container. It is well recognized that for most efficient utilization of the microwave energy produced by a microwave oven the item to be heated should be held above the base of the microwave oven. To achieve this it is often necessary to stand the product being heated on some form of spacer, e.g. an upturned plate. Embodiments of the invention in which the lower surface of the inner portion is spaced from the base of the container automatically achieve this effect.

Claims: CLAIMS 1. A packaging container comprising: an inner plastics generally cup-like portion having an open upper end, a closed lower end, and side walls interconnecting the upper and lower ends; and an outer portion having an open upper end, a closed lower end, and side walls interconnecting the upper and lower ends, wherein the inner portion is in contact with the outer portion at the upper end of the container and the side walls of the inner portion are spaced from the side walls of the outer portion by an air gap. 2. A packaging container according to claim 1 wherein outer portion is of cartonboard and the inner portion rests on the upper edge of the outer portion and is supported thereby. 3. A packaging container according to claim 2 wherein the inner portion is secured to the outer portion to prevent separation of the inner portion from the outer portion if the container is inverted. 4. A packaging container according to claim 1 wherein the inner portion and the side walls of the outer portion are formed by a unitary plastics shell and the closed lower end of the outer portion is formed by a base secured to the lower end of the side walls of the outer portion. 5. A packaging container according to any preceding claim wherein the lower closed end of the inner portion is spaced from the lower end of the outer portion, preferably by an air gap so that the weight of the inner portion is entirely supported on the upper edge of the outer portion. 6. A packaging container according to any preceding claim wherein the air gap between the inner and outer portions is provided by a substantially closed chamber defined between the inner and outer portions. 7. A packaging container according to any preceding claim wherein the lower end of the inner portion is of a smooth curved concave form when viewed from the open end of the inner portion. 8. A packaging container according to any preceding claim wherein the upper edge of the inner portion is in the form of an outwardly directed flange to which a cover can be sealed, e.g. by heat sealing, adhesive sealing, or ultrasonic welding.

Inventors: HILL JOSEPH ANTHONY, WOOD JOHNATHAN ROSS, HILL, JOSEPH, ANTHONY, WOOD, JOHNATHAN, ROSS
Applicants: ROBINSON & SONS LTD, ROBINSON & SONS LIMITED
Application year: 1990
Main classification: B65D81
IPC codes: B65D77, B65D81