CA2046836C

CA2046836C - Pizza box

Info

Publication number: CA2046836C
Application number: CA 2046836
Authority: CA
Inventors: D. Gregory Beckett
Original assignee: Graphic Packaging Corp
Current assignee: Individual
Priority date: 1991-05-06
Filing date: 1991-07-11
Publication date: 2000-04-04
Anticipated expiration: 2011-07-11
Also published as: CA2046836A1; AU1669892A; WO1992019515A1

Abstract

A pizza box is described for microwave heating of frozen pizza for consumption. The box includes a lower tray portion which receives the pizza, an upper lid portion which encloses the tray and an integral wall portion hingedly joining the upper lid portion and lower tray portion. A continuous electroconductive metal layer having a thickness which is normally microwave opaque is provided extending between the lid portion and the tray portion through the wall portion. A metal layer in the tray portion is provided with an array of slots therethrough, which permits microwave energy conducted from the lid portion to the tray portion by the metal layer, to generate thermal energy to heat the pizza filling and crispen the crust.

Description

TITLE OF INVENTION
PIZZA BOX
FIELD ~OF INVENTION
5 The present invention is directed to box-like structures, particularly adapted for microwave heating of frozen food products, such as frozen pizzas.
BACKGROUND TO THE INVENTION
It is known to heat a variety of foodstuffs for 10 consumptions by the application of microwave energy.
Microwave heating occurs by the excitation of water molecules within the body of the foodstuff. This manner of heating is different from conventional oven heating, which involves heating from exterior of the food 15 product. While both meahods are effective in heating food products, neverthe7.ess one significant difference exists, in that microwave cooking does not produce browning and crispening of the exterior of the product.
This difference is of no significance with some 20 food products but is of: considerable significant with other products, such as those having a pastry shell, for example, a frozen pizza. Frozen pizzas reconstituted in a microwave oven tend to be soggy and lack crispness in the pastry, whereas such crispness is 25 attainable by reconstituting in a conventional oven.
It has been sugg~=sted to supplement microwave cooking to achieve crispness of the type found with conventional oven heating by using a thin metal film in contact with the pie crust. The ability to generate 30 thermal energy from such thin metal films is described, for example, in U.S. Patent No. 4,641,005.
The thermal energy produced by the thin metal film from the incident microwave energy browns and crispens the 35 pie crust with which it is in contact. The utilization of such thin metal- films in box-like structure particularly adapted for pizzas, is described, for 2o~sa3s example, in US Patent Nos. 4,592,914, 4,891,482 and 4,940,867.
While some success in achieving a crispened and browned pie crust can be achieved using such thin metal films, the microwave-reconstituted pizza lacks an evenness of heating and, hence, does not match the quality of product which is attained when a conventional oven is employed.
However, reconstitution of frozen foodstuffs, such as frozen pizzas, by the application of microwave energy generally is much quicker than by a conventional oven and hence is highly desirable. The present invention is directed towards the provision of a box structure for a variety of frozen food products which is able to achieve more even heating during microwave reconstitution of such frozen foodstuffs by the application of microwave energy, as well as crispe:ning and browning the crust.
SUMMARY OF INVENTION
In the present invention, there is provided a box-like structure having a lower tray portion and an upper lid portion cooperating with the lower tray portion to define an enclosure for the foodstuff. Preferably, the upper lid portion is hingedly joined to the lower tray portion through an integral hinge line.
The lower tray portion and upper lid portion have microwave-energy controlling elements associated therewith to control l;.he distribution of microwave energy within the enclosure. By controlling the distribution of microwave energy within the enclosure, a foodstuff may be heated by microwave energy in the most desirable manner consistent with its form to provide a uniformly-cooked product for consumption.
The lower tray portion of the structure may incorporate a microwave energy heating structure whereby a portion of incident microwave energy is converted to thermal energy which is transferred to the foodstuff in contact with the structure. The heating structure may comprise a thin metal film, as described in the aforementioned U.S. Patent No. 4,641,005, a combination of such thin metal film and a grid of electroconductive material, as described in U.S. Patent No. 4,927,991, or a layer of electroconductive material normally opaque to microwave energy and having an array of slots therethrough, as more particularly described in United States Patent No. 5,117,078 ("Amaze-Met"), and assigned to the assignee hereof.
Alternatively, the lower tray portion may incorporate an element which is opaque to microwave energy, such as a layer of aluminum foil. The element may have one or more apertures therein to permit a controlled amount of microwave energy to pass therethrough.
The lower tray portion also may incorporate a combination of an element opaque to microwave energy and a microwave energy heating structure to provide a desired combination of thermal energy generation and microwave energy shielding.
The upper lid portion of the structure may incorporate a microwave energy heating structure, an element at least partially opaque to microwave energy or a combination of the two, as in the case of the lower tray portion. The structure incorporated into the upper lid portion of any particular box-like structure may be the same as that incorporated into the lower tray portion of that box-like strucaure or different from that incorporated into the lower tray portion.
The structure of both the lower tray portion and upper lid portion generally comprises an outer layer of paperboard of sufficient structural strength to provide the box-like structure, an inner layer of polymeric material coincident with the paperboard layer and the elements) incorporated into the lower tray portion and the upper lid portion incorporated therein.
In one preferred embodiment of the present invention, there is provided a novel box-like structure particularly adapted for the microwave reconstitution of frozen pizzas for consumption, comprising a lower tray portion and an upper lid portion hingedly joined to the lower tray portion by wall means to define an enclosure for a frozen pizza.
The lower tray portion supports a thermal energy generating layer of electroconductive material on the inner surface thereof dimensioned to receive thereon a pie crust of a frozen pizza to be reconstituted in the box-like structure.
The lid portion supports a continuous layer of microwave-opaque electroconductive material on the inner surface thereof and dimensioned to shield the frozen pizza substantially from microwave energy incident on the lid of the box-like structure.
The wall means supports a continuous layer of microwave-opaque electroconductive material joined to both the microwave heat susceptor layer and the continuous layer of microwave opaque material.
By this arrangement, the proportion of incident microwave energy to which the frozen pizza is directly exposed may be controlled from none at all when the continuous microwave-opaque layer supported by upper lid portion completely covers the frozen pizza to a controlled minor amount when one or more open areas are provided in the continuous microwave-opaque layer, such as adjacent the centre of the lid.
The incident microwave energy instead is conducted by the continuous layer of microwave-opaque 204.683 electroconductive material supported by the wall means to the microwave heat susceptor layer, so that the microwave energy is converted into thermal energy by the susceptor in contact with the pizza pie crust to heat 5 the pizza for consumption. The generation of thermal energy in contact with the pie crust ensures that the pie crust is both cooked and browned, while the pie filling also is cooked to a form suitable for consumption.

Figure 1 is a perspective view of a pizza box provided in accordance with one embodiment of the invention in a closed position;
Figure 2 is a plan vis:w of a blank from which the pizza box of Figure 1 may be assembled;
Figure 3 is a sectional view of the blank for the pizza box taken along line 3-3 of Figure 2;
Figure 4 is an enlarged form of the sectional view of Figure 3; and Figure 5 is a perspective view of the pizza box of Figure 1 in an open position..
DESCRIPTION OF PREFERRED EMBODIMENT
Referring to the drawings, there is illustrated therein a pizza box 10 suitable for housing and microwave reconstituting a frozen pizza 12 for consumption. The pizza box 10 usually comprises the structure within which the pizza 12 is marketed, or may be provided separately for receipt therein of a frozen pizza 12 from another source.
The pizza box 10 comprises a lower tray portion 14 and a upper lid portion 16 which is joined to the lower tray portion 14 by a wall portion 18 integrally connected to the lower tray portion 14 and upper lid portion 16 by fold lines 20 .and 22.
The pizza box 10 is formed from a unitary blank 24 (see Figure 2) by appropriate folding and gluing of 2o~~~~s panels. The lower tray portion 14 and upper lid portion 16 comprise a main panel 26 of octagonal outline. The octagonal nature of the structure of the pizza box 10 is only one of a variety of convenient shapes which may be adapted. For example, the pizza box 10 may be square shaped.
The main panels 26 are: joined to side panels 28, 30, 32 along fold lines 34, 36 and 38 respectively.
Side panels 28 have wing panels 40 joined thereto along fold lines 42 while side panel 30 connected to the tray main panel 26 has a single wing panel 44 joined thereto along fold line 46 and side, panel 30 connected to the lid main panel 26 has wing panels 48 joined thereto along fold lines 50. The latter arrangement may be reversed, if desired.
To assemble the pizza box 10 from the blank 24, the panels 32 first are folded up about their respective fold lines 28 and the panels 28 and 30 are folded up about their respective fold lines 34 and 36. The inner face of the various wing panels 40, 44 and 48 have adhesive applied thereto enable them to be adhered to the outer face of panels 32. Such adhesive may conveniently be provided with pealable covers to be removed when the pizza box 10 is readily to be assembled. The wing panels 40 and 44 are bent inwardly about their respective fold lines 42 and 46 to engage and adhere to the outer surf=ace of panels 32. The wing panels 48 also are bent inwardly about their fold lines 50, in one instance to engage and adhere to the outer surface of adjacent panels 32. The lid portion 16 then is folded about line 22 and the other wing panels 48 are bent inwardly about their fold line 50 to engage and adhere to the outer surface of the wall portion 18.
The blank 24 compri:~es a lower layer 52 of paperboard or similar stock material having sufficient structural strength to per~~it a relatively rigid box ~0~6836 ;, like structure to be assembled from the blank 24 and an upper layer 54 of polymeric material, such as polyester or polyethylene, which extends for the same dimensions as the paperboard layer 52. Sandwiched between the paperboard layer 52 and the upper polymeric film layer 54 is a continuous metal layer 56 which is of sufficient thickness as normally to be microwave opaque.
As may be seen particularly in Figure 2, the portion 58 of the metal layer 56 located in the tray portion 14 of the pizza box 10 is provided with an array of radially-directed slots 60 through the thickness of the metal layer. The metal layer portion 58 has a generally circular shape to conform in. shape and dimension to the pizza 12 to be housed in the tray. The central region 62 of the metal layer portion 58 is free from metal.
The array of radially-directed slots 60 allows thermal energy to be generated therefrom when the metal layer portion 58 is exposed to microwave energy, as more particularly described in the aforementioned United States Patent No. 5,117,078 ("Amaze-Met").
The slots or apertures 60 are elongate and each is generally no shorter than about 1.75 cm but may extend to any desirable length. An individual slot or aperture may vary in width from about 1 mm to about 2 cm, provided that the length is greater than the width.
The array of radially-directed slots 60 and the central open region 62 may be provided in any convenient manner. Preferably, this structure is provided by selective demetallization of 'the metal layer 58 supported by the polymeric film layer 54, using aqueous etchant in one of the procedures described in U.S. Patent Nos.
4,398,994 and 4,552,614.
The metal layer 58 may comprise any B

~046~~36 electroconductive metal having a thickness so as to normally be microwave opaque. One convenient metal which may be employed in aluminum, which may have a thickness of about 1 to about 15 microns, typically about 7 microns. Aluminum of that thickness is commercially available and may be laminated to polymeric film. Rolls of such laminate may be selectively demetallized, as discussed above, to provide the required outline shape of the metal layer 58 and the etched out array 60 and central region 62. The polymeric film 54 with etched metal layer 56 supported thereon then may be laminated in any convenient manner using conventional laminating adhesives to the paperboard layer 52 to form the blank 24.
OPERATION
In use, the pizza tray 10, in a closed condition as seen in Figure 1, has a frozen pizza 12 seated on the polymeric film layer 54, which also may have a food-grade release agent applied thereon, in coincidence with the metal layer portion 58. When it is desired to heat the frozen pizza 12 for consumption, the pizza tray 10 is exposed to microwave energy.
The continuous microwave opaque metal layer 56 in the lid portion 16 permits no microwave energy to pass directly to the pizza but rather directs the microwave energy, via the metal layer on the wall portion 18 to the metal layer 58 in the lower tray portion 14.
By virtue of the presence of the array 60 of slots, the microwave energy is converted to thermal energy, which then heats the pizza crust and filling. The open centre region 62 ensures that there is no overheating of the pizza in this region. This arrangement permits an even heating of the pizza filling to be achieved, as well as satisfactory browning and crispening of the crust.
The metal layer 56 in the lid portion 16 need not be wholly opaque but rather one or more openings therethrough may be provided, for example, a central opening, to permit a controlled amount of the incident microwave energy to pass through the lid directly to the pizza filling.
SUMMARY OF DISCLOSURE
In summary of this disclosure, the present invention provides a novel box structure which is able to achieve a much more uniform heating of a frozen food product for consumption. Modifications are possible within the scope of this invention.

Claims

1. A box-like structure for the microwave reconstitution of frozen pizzas housed in the structure to edible form, comprising:
a lower tray portion and an upper lid portion hingedly joined to said lower tray portion by wall means to define an enclosure for a frozen pizza, said lower tray portion supporting a thermal energy generating layer of electroconductive material on the inner surface thereof dimensioned to receive thereon a pie crust of a frozen pizza to be reconstituted in said structure, said thermal energy generating layer of electroconductive material comprising an array of generally radially-directed slots through said material dimensioned so as to generate thermal energy in contact with the pizza pie crust when the structure is exposed to microwave energy, said upper tray portion supporting a continuous layer of microwave-opaque electroconductive material on the inner surface thereof and dimensioned to shield the frozen pizza substantially from microwave energy incident on said box-like structure, said wall means supporting a continuous layer of microwave-opaque electroconductive material joined to both said thermal energy generating layer and said continuous layer of microwave opaque material, said thermal energy generating layer of electroconductive material and said continuous layer of microwave-opaque electroconductive material comprising a single unitary element comprised of aluminum foil of thickness of about 1 to about 15 microns, and said box-like structure being formed from a unitary blank comprising an outer layer of paperboard and an inner layer of polymeric material with said thermal energy generating layer of electroconductive material and said continuous layer of microwave-opaque electroconductive material sandwiched therebetween.

2. The structure of claim 1 wherein said continuous layer of microwave-opaque electroconductive material has an aperture therein to permit a controlled degree of incident thermal energy to pass through said upper lid portion into the enclosure.

3. The structure of claim 1 or 2 wherein each of the slots has a longitudinal dimension of at least about 1.75 cm and a transverse dimension from about 1 mm to about 2 cm.

4. The structure of claim 3 wherein said blank is formed by the steps of:
laminating a layer of aluminum foil to a polymeric material layer, applying etchant resistant material to the layer of aluminum foil in regions thereof from which aluminum is not to be removed, applying an etchant for aluminum to said layer of aluminum foil to remove aluminum completely from regions thereof not protected by said etchant resistant material, and laminating the etched material to paperboard layer.

5. The structure of claim 4 wherein said etchant is aqueous sodium hydroxide solution.