WO1992019515A1

WO1992019515A1 - Pizzabox for microwave heating

Info

Publication number: WO1992019515A1
Application number: PCT/CA1992/000189
Authority: WO
Inventors: D. Gregory Beckett
Original assignee: Beckett Industries Inc.
Priority date: 1991-05-06
Filing date: 1992-04-29
Publication date: 1992-11-12
Also published as: CA2046836C; CA2046836A1; AU1669892A

Abstract

A pizza box (10) is described for microwave heating of frozen pizza for consumption. The box includes a lower tray portion (14) which receives the pizza (12), an upper lid portion (16) which encloses the tray and an integral wall portion (18) hingedly joining the upper lid portion and lower tray portion. A continuous electroconductive metal layer (56) 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 (14) is provided with an array of slots (60) theretrough, 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

PIZZA BOX FOR MICROWAVE HEATING

vτγi n m? TKVENTION The present invention is directed to box-lik structures, particularly adapted for microwave heatin of frozen food products, such as frozen pizzas. BACKGROUND TO THE INVENTION It is known to heat a variety of foodstuffs fo consumptions by the application of microwave energy. Microwave heating occurs by the excitation of wate molecules within the body of the foodstuff. This manne of heating is different from conventional oven heating, which involves heating from exterior of the foo product. While both methods are effective in heatin food products, nevertheless one significant differenc exists, in that microwave cooking does not produc browning and crispening of the exterior of the product. This difference is of no significance with som food products but is of considerable significant wit other products, such as those having a pastry shell for example, a frozen pizza. Frozen pizza reconstituted in a microwave oven tend to be soggy an lack crispness in the pastry, whereas such crispness i attainable by reconstituting in a conventional oven.

It has been suggested to supplement microwav cooking to achieve crispness of the type found wit conventional oven heating by using a thin metal film i contact with the pie crust. The ability to generat thermal energy from such thin metal films is described for example, in U.S. Patent No. 4,641,005, th disclosure of which is incorporated herein by reference The thermal energy produced by the thin metal film fro the incident microwave energy browns and crispens th pie crust with which it is in contact. The utilizatio of such thin metal films in box-like structu particularly adapted for pizzas, is described, f example, in US Patent Nos. 4,592,914, 4,891,482 and 4,940,867, the disclosures of which are incorporated herein by reference.

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 crispening 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 the 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 i contact with the structure. The heating structure ma comprise a thin metal film, as described in th aforementioned U.S. Patent No. 4,641,005, a combinatio of such thin metal film and a grid of electroconductiv material, as described in U.S. Patent No. 4,927,991, th disclosure of which is incorporated herein by reference, or a layer of electroconductive material normally opaqu to microwave energy and having an array of slot therethrough, as more particularly described in m copending United States patent application Serial No. 535,168 filed June 8, 1990 ("Amaze-Met"), the disclosur of which is incorporated herein by reference, an assigned to the assignee hereof. Alternatively, the lower tray portion ma incorporate an element which is opaque to microwav energy, such as a layer of aluminum foil. The elemen may have one or more apertures therein to permit controlled amount of microwave energy to pas therethrough.

The lower tray portion also may incorporate combination of an element opaque to microwave energy an a microwave energy heating structure to provide desired combination of thermal energy generation an microwave energy shielding.

The upper lid portion of the structure ma incorporate a microwave energy heating structure, a element at least partially opaque to microwave energy o a combination of the two, as in the case of the lowe tray portion. The structure incorporated into the uppe lid portion of any particular box-like structure may b the same as that incorporated into the lower tra portion of that box-like structure or different fro that incorporated into the lower tray portion. The structure of both the lower tray portion an upper lid portion generally comprises an outer layer o paperboard of sufficient structural strength to provide the box-like structure, an inner layer of polymeric material coincident with the paperboard layer and the element(s) 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 electroconductive material supported by the wall mean to the microwave heat susceptor layer, so that th microwave energy is converted into thermal energy by th susceptor in contact with the pizza pie crust to hea the pizza for consumption. The generation of therma energy in contact with the pie crust ensures that th pie crust is both cooked and browned, while the pi filling also is cooked to a form suitable fo consumption. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a perspective view of a pizza bo provided in accordance with one embodiment of th invention in a closed position;

Figure 2 is a plan view of a blank from which th pizza box of Figure 1 may be assembled;

Figure 3 is a sectional view of the blank for th pizza box taken along line 3-3 of Figure 2;

Figure 4 is an enlarged form of the sectional vie of Figure 3; and Figure 5 is a perspective view of the pizza box o Figure 1 in an open position.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawings, there is illustrate therein a pizza box 10 suitable for housing an microwave reconstituting a frozen pizza 12 fo consumption. The pizza box 10 usually comprises th structure within which the pizza 12 is marketed, or ma be provided separately for receipt therein of a froze pizza 12 from another source. The pizza box 10 comprises a lower tray portion 1 and a upper lid portion 16 which is joined to the lowe tray portion 14 by a wall portion 18 integrall connected to the lower tray portion 14 and upper li portion 16 by fold lines 20 and 22. The pizza box 10 is formed from a unitary blank 2 (see Figure 2) by appropriate folding and gluing o 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 surface 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 comprises a lower layer 52 of paperboard or similar stock material having sufficient structural strength to permit a relatively rigid box- like structure to be assembled from the blank 24 and a upper layer 54 of polymeric material, such as polyeste or polyethylene, which extends for the same dimension as the paperboard layer 52. Sandwiched between th paperboard layer 52 and the upper polymeric film laye 54 is a continuous metal layer 56 which is of sufficien thickness as normally to be microwave opaque.

As may be seen particularly in Figure 2, th portion 58 of the metal layer 56 located in the tra portion 14 of the pizza box 10 is provided with an arra of radially-directed slots 60 through the thickness o the metal layer. The metal layer portion 58 has generally circular shape to conform in shape an dimension to the pizza 12 to be housed in the tray. T central region 62 of the metal layer portion 58 is fre from metal.

The array of radially-directed slots 60 allo thermal energy to be generated therefrom when the meta layer portion 58 is exposed to microwave energy, as mo particularly described in my aforementioned copendi United states patent application Serial No. 475,32 ("Amaze-Met").

The slots or apertures 60 are elongate and each generally no shorter than about 1.75 cm but may exte to any desirable length. An individual slot or apertu may vary in width from about 1 mm to about 2 c provided that the length is greater than the width.

The array of radially-directed slots 60 and t central open region 62 may be provided in any convenie manner. Preferably, this structure is provided selective demetallization of the metal layer supported by the polymeric film layer 54, using aqueo etchant in one of the procedures described in U. Patent Nos. 4,398,994 and 4,552,614, the disclosures which are incorporated herein by reference.

The metal layer 58 may comprise an electroconductive metal having a thickness so as to normally be microwave opaque. One convenient meta which may be employed in aluminum, which may have a thickness of about 1 to about 15 microns, typicall 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 opening therethrough may be provided, for example, a centra opening, to permit a controlled amount of the inciden microwave energy to pass through the lid directly to th pizza filling.

SUMMARY OF DISCLOSURE

In summary of this disclosure, the presen invention provides a novel box structure which is abl to achieve a much more uniform heating of a frozen foo product for consumption. Modifications are possibl within the scope of this invention.

Claims

What I claim is:

1. A box-like structure for the microwave reconstitution of foodstuffs housed in the structure to an edible form, which comprises: a lower tray portion and an upper lid portion cooperating with said lower tray portion to define an enclosure for the foodstuff, said lower tray portion and said upper lid portion having microwave-energy controlling elements associated therewith to control the distribution of microwave energy within said enclosure to achieve a desired heating of the foodstuff.

2. The structure of claim 1 wherein said lower tray portion has at least one microwave energy controlling element which is a microwave energy heating element which develops thermal energy from incident microwave energy when in contact with the foodstuff.

3. The structure of claim 1 wherein said lower tray portion has at least one microwave energy controlling element which is at least partially microwave opaque.

4. The structure of claim 1 wherein said lower tray portion has at least one microwave energy controlling element which is a combination of a microwave energy heating element which develops thermal energy from incident microwave energy when in contact with the foodstuff and an element which is at least partially microwave opaque.

5. The structure of claim 1 wherein said upper lid portion has at least one microwave energy controlling element which is a microwave energy heating element which develops thermal energy from incident microwave energy when in contact with the foodstuff.

6. The structure of claim 1 wherein said upper lid portion has at least one microwave energy controlling element which is at least partially microwave opaque.

7. The structure of claim 1 wherein said upper li portion has at least one microwave energy controllin element which is a combination of a microwave energ heating element which develops thermal energy fro incident microwave energy when in contact with th foodstuff and an element which is at least partiall microwave opaque.

8. The structure of claim 2, 3, 4, 5, 6 or 7 wherei said lid portion has at least one microwave energ controlling element which is the same as the at leas one microwave controlling element of the lower tra portion.

9. The structure of claim 2, 3, 4, 5, 6 or 7 wherei said lid portion has at least one microwave energ controlling element which is different from the a least one microwave controlling element of the lowe tray portion.

10. The structure of claim 1 wherein said lower tra portion and said upper lid portion are formed from laminate of an outer paperboard layer, an inne polymeric film layer and at least one microwave-energ controlling element sandwiched therebetween.

11. The structure of claim 10 wherein said microwa energy controlling element is formed from aluminum.

12. A box-like structure for the microwav reconstitution of frozen pizzas housed in the structur to edible form, comprising: a lower tray portion and an upper lid portio hingedly joined to said lower tray portion by wa means to define an enclosure for a frozen pizza, said lower tray portion supporting a thermal ener generating layer of electroconductive material on t inner surface thereof dimensioned to receive thereon pie crust of a frozen pizza to be reconstituted in sa structure, said upper tray portion supporting a continuo 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, and said wall means supporting a continuous layer of microwave-opaque electroconductive material joined to both said microwave heat susceptor layer and said continuous layer of microwave opaque material.

13. The structure of claim 12 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.

14. The structure of claim 12 which is formed from a unitary blank comprising an outer layer of paperboard, an inner layer of polymeric material and said thermal energy generating layer of electroconductive material and said continuous layers of microwave-opaque electroconductive material sandwiched therebetween.

15. The structure of claim 14 wherein said thermal energy generating layer of electroconductive material and said continuous layers of microwave-opaque electroconductive material comprise a single unitary element.

16. The structure of claim 15 wherein said single unitary element is comprised of aluminum foil of thickness of about 1 to about 15 microns.

17. The structure of claim 16 wherein said thermal energy generating layer of electroconductive material comprises 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.

18. The structure of claim 17 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.

19. The structure of claim 18 wherein said blank i formed by the steps of: laminating a layer of aluminum foil to a polymeri material layer, applying etchant resistant material to the layer o aluminum foil in regions thereof from which aluminum i not to be removed, applying an etchant for aluminum to said layer o aluminum foil to remove aluminum completely from region thereof not protected by said etchant resistan material, and laminating the etched material to paperboard layer

20. The structure of claim 19 wherein said etchant i aqueous sodium hydroxide solution.