Microwave container assembly

A microwaveable package containing foodstuff is for direct placement with or without opening same, in a microwave oven so that the foodstuff can be microwave cooked. The foodstuff rests on a sheet of microwave receptor material and the package is designed so that there is an air space between the receptor material and the oven support table to prevent the table from acting as a heat sink to drain away heat generated by the receptor material during cooking.

This invention relates to packaging containers for use in connection with 
the microwave heating of foodstuffs. 
It is known to provide in a packaging container which is otherwise 
transparent to microwave energy, a microwave interactive or receptor, 
material which heats up when subjected to the microwave radiation. The 
heating up of the receptor material serves to heat adjacent foodstuff, for 
the crisping or browning of same, it being a disadvantage of conventional 
microwave heating that although the foodstuff will heat up quickly and 
effectively under the influence of microwaves, it is not possible to 
obtain a crisping or browning effect and that certain products such as 
pizzas and chipped potatoes simply become hot and soft, and rather 
unpalatable. 
The said receptor materials however overcome this disadvantage, in that 
said materials quickly heat up under the influence of the microwaves to a 
high temperature and heat from the receptor materials is transferred by 
conduction to the foodstuff. 
Examples of receptor materials and their methods of manufacture and use are 
disclosed in the following published patent specifications: 
U.S. Pat. No. 4,555,605 
U.S. Pat. No. 4,590,349 
U.S. Pat. No. 4,592,914 
U.S. Pat. No. 4,553,010 
U.K. Patent No. 2,046,060B 
A specific known packaging container for use in connection with microwave 
heating of foodstuffs comprises a box constructed of cut and creased 
material, specifically cardboard, and inside the container and resting on 
a base thereof, is provided a sheet of receptor material. The foodstuff , 
chipped potatoes rest on the receptor material and for the cooking of the 
foodstuff, the lid or a panel in the lid is moved to an open position, and 
the container is simply placed in a microwave oven and the assembly 
subjected to microwave energy. Whilst such packaging is sufficiently 
satisfactory to be commercial, if the package rests on a part of the oven 
which acts as a heat sink and conducts away heat from the receptor 
material, the foodstuff takes longer to heat up than it should. 
To some extent this effect can be reduced if an air space can be created 
between the receptor material and the microwave oven support surface 
(support table) on which the package stands. 
Several attempts have been made to overcome this difficulty, and in one 
suggested arrangement, where a packaging container includes a receptor 
layer and a pizza resting thereon, the pizza and receptor material are 
removed, and the container is turned upside down and then the receptor 
material and pizza are placed on the underside of the base of the 
container. Another proposal provides that one portion of the container 
when the container is opened is folded back to form a support to keep the 
remainder of the container which supports the product on the receptor 
material clear of the microwave oven table. 
These arrangements have a certain inconvenience because they require a 
degree of manipulation on the part of the user, and if the user forgets to 
perform such manipulation, then unsatisfactory cooking may result. 
The present invention seeks to deal with this problem from a different 
approach, and in accordance with the invention, there is provided a 
packaging container of cut and creased material containing a foodstuff or 
for containing a foodstuff to be microwaved, wherein the container is 
constructed so as to provide a platform forming the base of the container 
on which the product rests and when placed in a microwave oven, said 
platform being spaced from a support surface or edge defined by the 
container so that the platform will be kept clear of the microwave table 
during microwaving of the product, which is achieved by simply placing the 
container and its contents, with the lid open or removed as required, 
directly into the microwave oven, said platform comprising or including a 
layer of microwave receptor material. 
By the present invention, the container is constructed so that there is 
created within same a platform spaced from a support edge or surface so 
that the container and its contents can be simply placed directly in the 
microwave oven with the support surface or lodge resting on the microwave 
oven table. The user is therefore subjected to the minimum of 
inconvenience. 
The container may have a lid or lid panel which has to be broken or torn 
open in order to expose the contents for cooking, but no further 
manipulation of the container is required. 
The air space located under the platform will form an insulation space to 
prevent loss of heat from the receptor material. In one particular 
embodiment of the invention, the container has a base of the cut and 
creased material, and the receptor material is attached to or rests on the 
base, and around the base are sides or ledges which form legs to separate 
the base from the microwave oven table during the heating process. 
In this construction, the receptor material preferably is deposited on a 
synthetic plastics film in the form of a strip, and the film is laminated 
to a cut and creased blank which forms the container so that the receptor 
material will cover the base. The base may be formed in a panel having a 
main section which forms said base, and edge sections around the sides of 
the main section, said edge sections lying to the inside of walls of the 
container and the edge sections being sealed to the walls by heat sealing 
of the synthetic plastics material film faces which come together by 
virtue of being on the faces of the edge sections and the insides of the 
container walls. 
The legs therefore surrounding the base are of double thickness. 
The container may have four sides, a top and the said base, and it may have 
an outwardly tapering configuration from top to base so that it has the 
form of a truncated pyramid. This facilitates the positioning of the base 
and its edge sections inside the lower edges of the walls, and also 
permits efficient nesting of the containers as the top will fit within the 
said legs when the containers are stacked one on top of another. 
In an alternative arrangement according to the invention, the receptor 
material is anchored between a pair of side walls of the container so as 
to lie above a base panel of the container to provide said air space. The 
receptor material therefore forms a false base in the container on which 
the product rests. This can be achieved by utilising a panel of receptor 
material with respective side edge portions connected to the inner 
surfaces of side walls of the container.

Referring to the drawings, and firstly to FIG. 1, a container blank 
comprises a sheet of cut and creased material which can be folded and 
erected into the container shown in FIG. 6. 
The blank comprises a base panel 10 of rectangular configuration with 
sealing strips 12, 14 and 16 hinged thereto along lines 18, 20 and 22. The 
fourth side of the rectangular base panel 10 is hinged along line 24 to a 
rear wall panel 26 which is generally rectangular and is hinged to a top 
panel 28 along a hinge line 30 at the opposite side of panel 26 from hinge 
line 24. 
The ends of the panel 26 as defined by hinge lines 32 and 34 taper together 
in a direction from hinge line 24 to hinge line 30, and rear panel 26 has 
glue tabs 36 and 38. 
The top panel 28 is also rectangular, but is slightly smaller than panel 10 
so that the resulting container will have a truncated pyramid appearance, 
the purpose of which will be explained hereinafter. 
Top panel 28 has hinged thereto along parallel hinge lines 40 and 42 
container side panels 44 and 46 of which the sides 48, 50 and 52, 54 
diverge in an outwards direction. Panels 44 and 46 have glue tabs 56 and 
58 hinged thereto along hinge lines 50 and 54. 
A front panel 60 with tapering sides 62, 64 is hinged to top panel 28 along 
hinge line 66. 
Tear lines 68 and 70 in panel 28 and leading to tear tab 72 in the front 
panel 60 define a portion of the blank which can be torn away from the 
front and top panels 72 and 28 and be hinged along hinge line 30 to gain 
access to the interior of the container. 
In this example of the invention there is laminated to the blank shown in 
FIG. 1 a plastic film 74 as shown in FIG. 2 which in this case is of 
polyester, and the film 74 is strip metalised with the receptor particles 
as indicated in the area 76 in FIG. 2 so as to form a receptor layer 78 
sandwiched between the film 74 and the blank as shown in FIG. 3. The film 
74 is in fact strip metalised so that the receptor layer will cover the 
base panel 10 as this is the surface on which the product to be microwave 
cooked will rest in the completed container. 
If reference is made to FIG. 4, the erection of the blank of FIG. 1 to 
produce the container will be understood. It should be mentioned that the 
side of the blank which faces inwardly of the container is the side which 
is covered by the film 74. 
To erect the container, the rear panel 26 is folded about fold line 30 and 
the glue tabs 36 and 38 are tucked inwardly. The sides 44 and 48 are 
turned downwardly and are glued to the tabs 36 and 38. It is to be noted 
at this time that the width of the sides 44 and 46 is greater than the 
width of the rear panel 26 so that edge portions 80 and 82 (FIG. 1) 
project beyond the horizontal plane containing fold line 24. These 
projections 80 and 82 serve for sealing to the sealing strips 12 and 16 as 
will be explained. 
Next the glue tabs 56 and 58 are tucked inwardly, and finally the front 
panel 60 is folded downwardly and is glued to the tabs 56 and 58 and the 
position shown in FIG. 4 is reached. The width of the panel 60 is equal to 
the width of panels 44 and 46. 
In FIG. 4 the base panel 10 is shown as having been hinged rearwardly about 
hinge line 24, and the container is shown in FIG. 5 in the inverted 
position in which the contents can be charged into the container through 
the open base side. The base panel 10 covered by the receptor material 76 
can after filling of the container be folded inwardly as indicated by 
arrow 84 until the position shown in FIG. 6 is reached. It will be noticed 
that in -FIGS. 4 and 5 the sealing strips 12, 14 and 16 are folded out of 
the plane of the panel 10, and when the FIG. 6 position is reached the 
sealing strips 12, 14 and 16 lie with their free edges co-planar with the 
free edges of the side panels 44 and 46 and the front panel 60 so that in 
fact the base of the container is recessed for a purpose to be explained 
in relation to FIG. 7. The adjacent portions of the side panels 44 and 46 
and the sealing strips 12, 14 and 16 can now be gripped in sealing jaws 
and pressed together and simultaneously heated in order to seal the 
sealing strips 12, 14 and 16 to the insides of the sides and front of the 
container improving the rigidity of the container, and sealing the 
contents therein. 
The container thus filled with the product is now ready for sale. 
When it is to be used, the user opens the lid section as shown in FIG. 7, 
and simply places the container in a microwave oven on the microwave 
support surface 86 as shown in FIG. 7. It will be seen that the sealing 
strips and adjacent portions of the sides and front of the container form 
legs supporting the base panel 10 clear of the microwave support surface 
86 and thereby creating an insulating air space 88 in which air can 
circulate as indicated by the arrows. This prevents a loss of heat from 
the receptor material as it heats up during the microwave cooking. 
Because of the tapering of the sides of the front side and rear panels of 
the container, the container has a truncated pyramid appearance and by 
forming a recess in the base of the container, so similar containers can 
effectively be nested. Tapering also facilitates the movement of the base 
panel from the FIG. 5 position into the FIG. 6 position. 
Instead of using a laminated receptor film to provide the receptor surface, 
a separate pad may be inserted in the container so as to rest on top of 
the base panel 10. 
Referring now to the embodiment of the invention shown in FIGS. 8, 9 and 
10, in FIG. 8 a conventional blank 100 comprises rectangular base and top 
panels 102, 104 hingedly interconnected by a side panel 106 and the second 
side panel 108 being hinged to base panel 102, and the top panel having a 
glue strip 110. 
The various panels have end flaps 112 which in a conventional manner close 
the ends of the container when erected. 
In this embodiment of the invention an overlay sheet 114 of receptor 
material is positioned so as to overlie the base panel 102 and parts of 
the side panels 106, 108. The receptor sheet has fold lines 116, 118 which 
are spaced by a distance equal to the width of the base panel 102, but the 
fold lines are offset by an amount X relative to the fold lines between 
the base panel 102 and the side panels 106, 108. This distance X being the 
distance by which it is required that the receptor material should be 
located above the base panel 102 in the erected carton in order to provide 
an air insulation space which performs a function similar to the air 
insulation space 88 in the FIGS. 1 to 7 embodiments. 
The sheet 114 in connected to the side panel 106 in the shaded region 120 
by gluing or the like, but is otherwise initially free from connection to 
the blank 100. 
In order to erect the container from the blank shown in FIG. 8, the 
receptor material 114 is first of all folded about line 118 to the 
position shown in full lines in FIG. 9, and following this folding,, the 
side 108 is folded over as indicated in dotted lines in FIG. 9 so as to 
overlie the previously folded portion of the receptor sheet 114, and the 
receptor sheet is glued in the shaded area 122 as shown in FIG. 9 to the 
inside of the side panel 108. In order to complete the erection, the panel 
104 is folded as shown in dotted lines in FIG. 9 to a -position in which 
the glue flap 110 overlies the previously folded side panel 108 and is 
glued thereto. The container is now in a flattened sleeve form and it is 
subsequently erected to three-dimensional form and the glue flaps 112 are 
tucked inwardly in order to, complete the closure. 
If reference is made to FIG. 10, it will be seen that in the finished and 
erected container, the receptor material 114 is spaced from the base panel 
by the said distance X so that an insulating space 124 is formed between 
the receptor material and the surface on which the container will be 
supported when the package is placed in the microwave oven. The product is 
indicated generally by reference numeral 126, and it will be appreciated 
that with such a container when it is to be used, the user simply places 
the container inside the microwave oven. It may be that part of the 
container will have to be opened or it is recommended that it be opened 
for the microwave cooking in a manner similar to that illustrated in FIG. 
7, and in this connection the container may be provided with suitable tear 
strips. 
With the containers according to the invention, in that they are designed 
to have or provide an air space when the package is placed directly in a 
microwave oven, there is minimum inconvenience for the user and more 
consistent and better quality microwave cooking can be effected.