EP2250859B1

EP2250859B1 - Susceptor with corrugated base

Info

Publication number: EP2250859B1
Application number: EP08873213.6A
Authority: EP
Inventors: Terrence P. Lafferty
Original assignee: Graphic Packaging International LLC
Current assignee: Graphic Packaging International LLC
Priority date: 2008-03-14
Filing date: 2008-09-22
Publication date: 2019-08-28
Anticipated expiration: 2028-09-22
Also published as: EP2250859A4; CA2718050A1; WO2009114038A1; EP2250859A1; ES2745821T3; JP5763732B2; JP2011515281A; CA2718050C; JP5421297B2; JP2014053327A

Description

TECHNICAL FIELD

The present disclosure relates to materials, packages, constructs, and systems for heating, browning, and/or crisping a food item in a microwave oven.

BACKGROUND

Microwave ovens provide a convenient means for heating a variety of food items, including sandwiches and other bread and/or dough-based products such as pizzas and pies. However, microwave ovens tend to cook such items unevenly and are unable to achieve the desired balance of thorough heating and a browned, crisp crust. US 4,891,482 A discloses a microwave heating construct in the form of a pizza box formed from a blank that includes a microwave susceptor. The box includes a separate, second microwave susceptor sheet at the bottom thereof, and the box is placed on a spacing member, such that both susceptors are disposed on the upper side of the spacing member. As such, there is a continuing need for improved materials, packages, and other constructs that provide the desired degree of heating, browning, and/or crisping of various food items in a microwave oven.

SUMMARY

This object is solved by a microwave heating construct as per claim 1 and the claims being dependent therefrom.
The present disclosure relates generally to various inventive and non-inventive microwave energy interactive structures that may be used to form sleeves, disks, trays, cartons, packages, and other constructs (collectively "constructs") for improving the heating, browning, and/or crisping of a food item in a microwave oven. The various structures generally comprise a plurality of components or layers assembled and/or joined to one another in a facing, substantially contacting, layered configuration. The layers include at least two microwave energy interactive elements and a dimensionally stable base. Each microwave energy interactive element comprises one or more microwave energy interactive components or segments arranged in a particular configuration to absorb microwave energy, transmit microwave energy, reflect microwave energy, or direct microwave energy, as needed or desired for a particular microwave heating application. Each of the microwave energy interactive elements comprises a susceptor. The susceptor may circumscribe one or more microwave energy transparent areas that allow the passage of microwave energy though the respective susceptor layer.
The base generally may provide thermal insulation between the microwave energy interactive element and the heating environment. In one example, the base comprises a corrugated paper or paperboard and the structure is a thermally insulated susceptor structure.
It has been found that the use of more than one susceptor with an insulating base to form a thermally insulated susceptor structure significantly enhances the heating, browning, and crisping of a food item thereon as compared with either (1) a structure including more than one susceptor layer without a thermal insulating base, or (2) a single susceptor overlying a thermal insulating base. If needed or desired, at least one aperture or cutout may extend through one or more layers of the structure to provide direct heating and/or ventilation to the bottom surface of the food item.
Thus, as per the subject invention, a thermally insulated susceptor structure comprises a dimensionally stable base having a first side and a second side opposite the first side, a first susceptor disposed on the first side of the base, and a second susceptor disposed on the second side of the base. The base includes a plurality of corrugations. The first susceptor, second susceptor, or both the first and second susceptor may circumscribe at least one microwave energy transparent area.
In each of various independent examples, the first susceptor and/or second susceptor may be supported on a polymer film layer and/or may be joined to a respective support layer, for example, paper. The various layers may be arranged in numerous ways in the susceptor structure. The structure also may include one or more additional layers, for example, paper layers, polymer film layers, susceptor layers, and/or corrugated layers.
Any of such structures may be used to form a construct for heating, browning, and/or crisping a food item in a microwave oven. In one example, a microwave heating construct comprises a dimensionally stable corrugated base, a first susceptor layer, and a second susceptor layer. At least one of the first susceptor layer and the second susceptor layer includes a central region including at least one microwave energy transparent area circumscribed by the respective susceptor layer, and at least one of the first susceptor layer and the second susceptor layer includes a peripheral region including at least one microwave energy transparent area circumscribed by the respective susceptor layer.
One or both susceptor layers may include the various microwave energy transparent areas, such that the first susceptor layer may include both the central region and peripheral region, the second susceptor layer may include both the central region and peripheral region, both the first and second susceptor layers may each include a respective central region and peripheral region, or one susceptor layer may contain one region, while the other susceptor layer may include the other region.
In one particular example, the microwave energy transparent areas in the central region are substantially circular in shape, with a greater number of microwave energy transparent areas proximate a center of the construct, and the microwave energy transparent areas in the peripheral region are substantially square in shape. However, numerous other arrangements of microwave energy interactive areas are contemplated.
Various other aspects, features, and advantages of the invention will become apparent from the following description and accompanying figures. Although several different aspects, implementations, and embodiments of the invention are provided, numerous interrelationships, combinations, and modifications of the various aspects, implementations, and embodiments of the invention are contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

The description refers to the accompanying drawings showing non-inventive reference examples as well as embodiments of the invention in which like reference characters refer to like parts throughout the several views, and in which:

FIGS. 1-11 are schematic cross-sectional views of various exemplary and non-inventive microwave energy interactive structures;
FIG. 12 is a schematic perspective view of a microwave energy interactive heating disk that may be formed from a non-inventive microwave energy interactive structure;
FIG. 13 is a schematic perspective view of a non-inventive microwave energy interactive heating tray that may be formed from a microwave energy interactive structure;
FIG. 14A is a schematic top plan view of an inventive microwave heating construct including microwave energy transparent areas;
FIG. 14B is a schematic cross-sectional view of a portion of the inventive construct of FIG. 14A ;
FIGS. 15 and 16 are schematic cross-sectional views of alternate inventive (Fig. 15) and non-inventive (Fig. 16) microwave constructs, which optionally include the arrangement of microwave energy transparent areas of FIG. 14A ; and
FIG. 17 is a schematic top plan view of a commercially available microwave energy interactive heating disk evaluated for comparative purposes; and
FIGS. 18-20 are schematic top plan views of other non-inventive microwave energy interactive heating disks evaluated in accordance with the disclosure.

DESCRIPTION

The present disclosure relates generally to various microwave energy interactive structures that may be used to form microwave heating packages or other constructs that improve the heating, browning, and/or crisping of a food item in a microwave oven. Each of the various structures includes a pair of microwave energy interactive elements overlying at least a portion of a dimensionally stable (e.g., rigid or semi-rigid) base.
One or both of the microwave energy interactive elements may comprise a thin layer of microwave energy interactive material (i.e., a "susceptor") (generally less than about 10 nm (100 angstroms) in thickness, for example, from about 6 to 10 nm (60 to about 100 angstroms) in thickness) that tends to absorb at least a portion of impinging microwave energy and convert it to thermal energy (i.e., heat) at an interface with a food item. The susceptor may be supported on a microwave energy transparent substrate, for example, a layer of paper or polymer film for ease of handling and/or to prevent contact between the microwave energy interactive material and the food item. Susceptor elements often are used to promote browning and/or crisping of the surface of a food item. However, other microwave energy interactive elements may be used.
The base generally may provide thermal insulation between the microwave energy interactive element and the heating environment. In one example, the base comprises a fluted or corrugated paper or paperboard. However, other materials that provide an insulating space or void that can reduce undesirable heat transfer away from the microwave energy interactive element may be used. It will be appreciated that numerous structures having different configurations may be formed with such materials, and that such structures are contemplated.
It has been discovered that a construct formed from a structure including more than one susceptor layer and a layer of corrugated insulating material significantly enhances the heating, browning, and/or crisping of a food item as compared with either (1) a structure including more than one susceptor layer without a corrugated base, or (2) a single susceptor overlying a corrugated base. When the construct is exposed to microwave energy, the susceptor layers convert at least a portion of the impinging microwave energy to thermal energy, which then heats the adjacent food item, and in some cases, the air within the flutes and/or the other susceptor layer(s). As a result, the heating, browning, and/or crisping of the food item may be enhanced significantly. Additionally, while not wishing to be bound by theory, it is believed that the air and other gases between the flutes of the corrugated base provide insulation between the food item and the ambient environment of the microwave oven, thereby increasing the amount of sensible heat that stays within or is transferred to the food item. Some structures also may include apertures that allow moisture to be vented away from the food item, thereby further enhancing browning and/or crisping of the food item.
Various aspects of the invention may be illustrated by referring to the figures, in which several exemplary constructs are depicted schematically. For simplicity, like numerals may be used to describe like features. It will be understood that where a plurality of similar features are depicted, not all of such features necessarily are labeled on each figure. While various exemplary embodiments are shown and described in detail herein, it also will be understood that any of the features may be used in any combination, and that such combinations are contemplated by the invention.
FIG. 1 depicts a schematic cross-sectional view of an exemplary microwave energy interactive structure 100. The structure 100 includes a pair of microwave energy interactive elements 102a, 102b, for example, susceptors, supported on respective microwave energy transparent substrates 104a, 104b, for example, polymer film layers, to collectively define respective susceptor films or susceptor film layers 106a, 106b. Each susceptor film 106a, 106b is joined respectively to a microwave energy transparent, dimensionally stable support or support layer 108a, 108b, for example, paper. The support layers 108a, 108b are joined to opposite sides of a dimensionally stable corrugated base 110.
In this example, the base 110 is a double faced corrugated material comprising a plurality of flutes 112 bound on opposed surfaces by a pair of substantially planar facing layers 114a, 114b, thereby defining a plurality of insulating voids or spaces 116 between the flutes 112 and the facing layers 114a, 114b. It is noted that in the various figures, the flutes or corrugations of the insulating base are shown as having a more angular, sawtooth shape. However, it will be understood that such figures are schematic only, and that the various flutes may have a more rounded, sinusoidal shape.
Not all of such layers may be necessary for a particular microwave heating application. Furthermore, in some cases, the layers of the structure may be rearranged without adversely affecting the heating, browning, and/or crisping capabilities of the structure. For example, FIGS. 2-6 schematically depict several exemplary variations of the microwave energy interactive structure 100 of FIG. 1 , each of which includes two susceptor layers and an insulating base. The various structures 200, 300, 400, 500, 600 include features that are similar to structure 100 shown in FIG. 1 , except for variations noted and variations that will be understood by those of skill in the art. For simplicity, the reference numerals of similar features are preceded in the figures with a "2" ( FIG. 2 ), "3" ( FIG. 3 ), "4" ( FIG. 4 ), "5" ( FIG. 5), or "6" (FIG. 6 ) instead of a "1".
By way of example, FIG. 2 illustrates an exemplary microwave energy interactive structure 200 that is similar to the structure 100 of FIG. 1 , except that structure 200 of FIG. 2 includes a single faced corrugated base 210 comprising a substantially planar facing or layer (or "flat side") 214a and a corrugated or fluted structure or layer ("fluted side") 212 opposite the flat side 214a. Susceptor film 206b and support 208b are joined to the flutes in a substantially planar configuration, such that susceptor film 206b and support 208b extend across and are at least partially joined to the outermost points of the flutes (i.e., across and along the spines of the flutes). Insulating voids 216 lie between substrate 204b and the corrugations 212.
FIG. 3 illustrates an exemplary structure 300 without the support layers 108a, 108b of FIG. 1 . In this example, susceptor films 306a, 306b are joined directly to the facing layers 314a, 314b of the corrugated base 310. Conversely, FIG. 4 illustrates an exemplary structure 400 with an unfaced corrugated base 410. In this example, the flutes 412 are joined directly to support layers 408a, 408b, thereby defining insulating voids 416. It is noted that the relative positions of the susceptor film 406b and support 408b are inverted relative to susceptor film 106b and support 108b of FIG. 1 . This may simplify construction, for example, where the corrugated structure 412 and support 408b are each formed from paper and such layers are being joined together adhesively. However, it is contemplated that the layers may be configured with the support 408b on the outside of the structure 400. It also is noted that, since layers 314a, 314 and layers 408a, 408b may be formed from similar materials (e.g. paper), the structures of FIGS. 3 and 4 may be similar in form and/or function. Nonetheless, both structures 300, 400 are illustrated schematically herein for clarity and completeness. The particular construction selected for a given application may depend on the available materials, the capabilities of the process and/or machinery used to form the structure, and/or numerous other factors.
If desired, any of the various structures may include one or more apertures or cutouts extending through all or a portion of one or more layers. Such apertures may have any shape and/or configuration and may be used for various purposes, as will be discussed further below.
For example, the structure 500 of FIG. 5 is similar to the structure 400 of FIG. 4 , except that the corrugated base 510 has a single facing layer 514b. A plurality of apertures or slits 518 extend through the first susceptor film 506a and support 508a, thereby exposing the corrugations or flutes 512 and insulating voids 516. If desired, the support layer 504a may serve as a food contacting layer or surface in open communication with the insulating voids 516 through apertures 518. In such examples, moisture generated by the food item may pass through apertures 518 into the voids 516, which may serve as venting channels that carry the moisture away from the food item to enhance browning and/or crisping of the food item further.
FIG. 6 schematically depicts another microwave energy interactive structure 600. In this example, the structure 600 is similar to the structure 200 of FIG. 2 , except that the structure 600 of FIG. 6 includes a plurality of apertures or slits 618 extending through the first susceptor film 606a and support 608a, thereby exposing the facing 614 of base 610. In this example, the apertures 618 may provide browning marks that create the impression of heating on a griddle or grill and also may provide some drawing of moisture away from the food item.
In some examples, the structure may include one or more susceptor layers, susceptor film layers, and/or support layers that directly overlie the faces of the flutes or corrugations in a substantially contacting relationship, such that the particular susceptor layer, susceptor film layer, and/or support layer also is corrugated or fluted. For example, FIG. 7 , schematically depicts an exemplary microwave energy interactive structure 700 including a first susceptor film 706a joined to a first support layer 708a, a second susceptor film 706b overlying the fluted or corrugated side of a single faced corrugated base 710, and a third susceptor film 706c joined to a second support layer 708c. The susceptor films 706a, 706b, 706c each comprise a respective layer of microwave energy interactive material 702a, 702b, 702c supported on a respective substrate 704a, 704b, 704c. The base 710 comprises a facing layer 714 and a plurality of flutes 712. The second susceptor film 706b is corrugated and overlies flutes 712. Insulating voids 716 lie between support layer 708a and flutes 712 and between facing layer 714 and flutes 712.
FIGS. 8-12 schematically depict some exemplary variations of the microwave energy interactive structure 700 of FIG. 7 . The various structures 800, 900, 1000, 1100, 1200 include features that are similar to structure 700 shown in FIG. 7 , except for variations noted and variations that will be understood by those of skill in the art. For simplicity, the reference numerals of similar features are preceded in the figures with an "8" ( FIG. 8 ), "9" ( FIGS. 9A and 9B ), "10" ( FIG. 10), or "11" (FIG. 11 ) instead of a "7".
The structure 800 of FIG. 8 is similar to the structure 700 of FIG. 7 , except that the structure 800 of FIG. 8 does not include a third susceptor film 706c and support 708c. Additionally, in this example, a plurality of apertures or slits 818 extend through the first susceptor film 806a and support 808a, such that apertures 818 are in open communication with voids 816 and the second susceptor film 806b overlying the base 810. In some instances, the voids 816 may serve as venting channels to enhance browning and/or crisping of a food item.
The structure 900 of FIG. 9A is similar to the structure 800 of FIG. 8 , except that susceptor layer 806b and the corrugated base 810 are inverted, such that the facing layer 914 is joined to the first support layer 908a In this configuration, the substrate layer 904a may comprise a food-contacting surface. With the structure 900 inverted, as shown in FIG. 9B , substrate 904b may comprise a food contacting surface. In this latter configuration, the apertures 918 lie on the bottom side of the structure 900 adjacent to the floor of the microwave oven. The apertures 918 may provide a thermal insulating benefit and/or may improve air circulation around the structure 900.
FIG. 10 schematically illustrates still another exemplary microwave energy interactive structure 1000. The structure 1000 is similar to the structure 900 of FIG. 9A , without apertures 918. FIG. 11 is similar to the structure 1000 of FIG. 10A without the support layer 1008a.
The various structures shown herein and/or contemplated hereby may be used to form numerous constructs for heating, browning, and/or crisping a food item in a microwave oven. For example, FIG. 12 depicts an exemplary microwave energy interactive construct 1200 (e.g., a disk) having a substantially circular heating surface 1202 (shown schematically by stippling FIGS. 12 and 13 ) suitable for heating, for example, a pizza, panini, or other circular food item thereon. If desired, the edges of the disk 1200 may be upturned to form a tray 1300 having an upturned peripheral area or sidewall 1302 surrounding a heating surface 1304, as shown schematically in FIG. 13 . Such a tray 1300 (and numerous others) may be formed, for example, using conventional thermal and/or mechanical press forming equipment. However, the various microwave energy interactive structures may be used to form all or a portion of any type of construct, for example, a package, carton, disk, sleeve, pouch, platform, and so forth. Any of such constructs may have any suitable shape, for example, square, rectangular, triangular, oval, or any other regular or irregular shape.
Countless other microwave energy interactive structures and constructs are contemplated by the disclosure. As stated previously, any of such structures may include one or more areas that are transparent to microwave energy. Such microwave energy transparent areas transmit microwave energy and, in some instances, may cause the formation of localized electric fields that enhance heating, browning, and/or crisping of an adjacent food item. The transparent areas may be sized, positioned, and/or arranged to customize the heating, browning, and/or crisping of a particular area of the food item to be heated.
For example, FIG. 14A schematically illustrates a top plan view of an inventive microwave heating construct 1400 (e.g., a microwave heating disk) that generally includes a susceptor 1402 (shown with stippling) that circumscribes a plurality of microwave energy transparent areas 1404, 1406 (shown in white). In this example, the disk 1400 has a substantially circular shape. However, any regular or irregular shape may be used.
The disk 1400 includes a central region 1408 and a peripheral region 1410. In the central region 1408 of the disk 1400, the transparent areas 1404 are substantially circular in shape, with the concentration of microwave energy transparent areas 1404 decreasing from the center of the disk 1400 outwardly towards the peripheral region 1410. However, other configurations are contemplated. In the peripheral region 1410, the microwave energy transparent areas 1406 are substantially square in shape and arranged in rows and columns, such that the microwave energy interactive material in the peripheral area has a grid-like appearance. As stated above, the percent transparent area may be varied as needed to achieve the desired heating, browning, and/or crisping of the food item. Such areas may be formed in any suitable manner, as will be described below.
FIG. 14B schematically illustrates a cross-sectional view of a portion of the microwave heating disk 1400 of FIG. 14A . The microwave heating disk 1400 includes a pair of microwave energy interactive elements 1402a, 1402b, for example, susceptors, supported on respective microwave energy transparent substrates 1412a, 1412b, for example, polymer film layers, to collectively define respective susceptor films or susceptor film layers 1414a, 1414b. Each susceptor film 1414a, 1414b is joined respectively to a microwave energy transparent, dimensionally stable support or support layer 1416a, 1416b, for example, paper. Support layer 1416a is joined to the fluted side of a single faced corrugated material 1418a, thereby defining a plurality of insulating voids or spaces 1420a between the flutes 1422a and the support layer 1416a, while substrate layer 1412b is joined to the facing 1424a of the corrugated material 1418a. Susceptor 1402a circumscribes at least one, and in some examples, a plurality, of microwave energy transparent (i.e., inactive) areas 1404 (or 1406, FIG. 14A ).
FIGS. 15 and 16 schematically depict exemplary variations of the microwave energy interactive disk 1400 of FIGS. 14A and 14B . The microwave heating disks 1500, 1600 may include features that are similar to the disk 1400 shown in FIGS. 14A and 14B , except for variations noted and variations that will be understood by those of skill in the art. For simplicity, the reference numerals of similar features are preceded in the figures with a "15" ( FIG. 15) or "16" (FIG. 16 ).
In the example shown in FIG. 15 , the microwave heating disk 1500 includes an additional layer of corrugated material 1518b, with the flutes 1522b being joined to support layer 1516b to define additional insulating voids 1520b adjacent to the flutes 1522b.
In the example shown in FIG. 16 , susceptor film 1614b and support 1614b are disposed between support layer 1616a and the flutes 1622a of the corrugated material 1618a.
Still numerous other structures and constructs are encompassed by the disclosure. Any of such structures described herein or contemplated hereby may be formed from various materials, provided that the materials are substantially resistant to softening, scorching, combusting, or degrading at typical microwave oven heating temperatures, for example, at from about 121,1°C (250°F) to about 218,3 °C (425°F). The particular materials used may include microwave energy interactive materials, for example, those used to form susceptors and other microwave energy interactive elements, and microwave energy transparent or inactive materials, for example, those used to form the base, substrate, and support layers.
The microwave energy interactive material may be an electroconductive or semiconductive material, for example, a metal or a metal alloy provided as a metal foil; a vacuum deposited metal or metal alloy; or a metallic ink, an organic ink, an inorganic ink, a metallic paste, an organic paste, an inorganic paste, or any combination thereof. Examples of metals and metal alloys that may be suitable include, but are not limited to, aluminum, chromium, copper, inconel alloys (nickel-chromium-molybdenum alloy with niobium), iron, magnesium, nickel, stainless steel, tin, titanium, tungsten, and any combination or alloy thereof.
Alternatively, the microwave energy interactive material may comprise a metal oxide. Examples of metal oxides that may be suitable include, but are not limited to, oxides of aluminum, iron, and tin, used in conjunction with an electrically conductive material where needed. Another example of a metal oxide that may be suitable is indium tin oxide (ITO). ITO can be used as a microwave energy interactive material to provide a heating effect, a shielding effect, a browning and/or crisping effect, or a combination thereof. For example, to form a susceptor, ITO may be sputtered onto a clear polymer film. The sputtering process typically occurs at a lower temperature than the evaporative deposition process used for metal deposition. ITO has a more uniform crystal structure and, therefore, is clear at most coating thicknesses. Additionally, ITO can be used for either heating or field management effects. ITO also may have fewer defects than metals, thereby making thick coatings of ITO more suitable for field management than thick coatings of metals, such as aluminum.
Alternatively still, the microwave energy interactive material may comprise a suitable electroconductive, semiconductive, or non-conductive artificial dielectric or ferroelectric. Artificial dielectrics comprise conductive, subdivided material in a polymeric or other suitable matrix or binder, and may include flakes of an electroconductive metal, for example, aluminum.
While susceptors are described in detail herein in the illustrated exemplary constructs, the microwave energy interactive element alternatively or additionally may comprise a foil having a thickness sufficient to shield one or more selected portions of the food item from microwave energy. Such "shielding elements" may be used where the food item is prone to scorching or drying out during heating.
The shielding element may be formed from various materials and may have various configurations, depending on the particular application for which the shielding element is used. Typically, the shielding element is formed from a conductive, reflective metal or metal alloy, for example, aluminum, copper, or stainless steel. The shielding element generally may have a thickness of from about 0.0007239 cm (0.000285 inches) to about 0.127 cm (0.05 inches). In one example, the shielding element may have a thickness of from about 0.000762 cm (0.0003 inches) to about 0.0762 cm (0.03 inches). In another example, the shielding element may have a thickness of from about 0.000889 cm (0.00035 inches) to about 0.0508 cm (0.020 inches), for example, about 0.04064 cm (0.016 inches).
As still another example, the microwave energy interactive element may comprise a segmented foil, such as, but not limited to, those described in U.S. Patent Nos. 6,204,492 , 6,433,322 , 6,552,315 , and 6,677,563 . Although segmented foils are not continuous, appropriately spaced groupings of such segments may act as a shielding element. Such foils also may be used in combination with susceptor elements and, depending on the configuration and positioning of the segmented foil, the segmented foil may operate to direct microwave energy and promote heating rather than to shield microwave energy.
If desired, any of the numerous microwave energy interactive elements described herein or contemplated hereby may be substantially continuous, that is, without substantial breaks or interruptions, or may be discontinuous, for example, by including one or more breaks or apertures that transmit microwave energy therethrough. The breaks or apertures may be sized and positioned to heat particular areas of the food item selectively. The breaks or apertures may extend through the entire structure, or only through one or more layers. The number, shape, size, and positioning of such breaks or apertures may vary for a particular application depending on type of construct being formed, the food item to be heated therein or thereon, the desired degree of shielding, browning, and/or crisping, whether direct exposure to microwave energy is needed or desired to attain uniform heating of the food item, the need for regulating the change in temperature of the food item through direct heating, and whether and to what extent there is a need for venting.
It will be understood that the aperture may be a physical aperture or void in one or more layers or materials used to form the construct (see, e.g., 518, 618, 818, 918; FIGS. 5, 6 , 8, 9A , 9B ), or may be a non-physical "aperture" (see, e.g., 1404, 1406, 1504, 1604; FIGS. 14A-16 ). A non-physical aperture is a microwave energy transparent area that allows microwave energy to pass through the structure without an actual void or hole cut through the structure. Such areas may be formed by simply not applying a microwave energy interactive material to the particular area, or by removing microwave energy interactive material in the particular area, and/or by chemically and/or mechanically deactivating the microwave energy interactive material in the particular area. While both physical and non-physical apertures allow the food item to be heated directly by the microwave energy, a physical aperture also provides a venting function to allow steam or other vapors to escape from the interior of the construct. It will be noted that where chemical deactivation is used, the metal in the deactivated area may be chemically altered, for example, oxidized, such that the non-physical aperture comprises a chemically altered, but microwave energy transparent, form of the metal.
As stated above, any of the microwave energy interactive elements may be supported on substrate comprising a polymer film or other suitable polymeric material. As used herein the term "polymer" or "polymeric material" includes, but is not limited to, homopolymers, copolymers, such as for example, block, graft, random, and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term "polymer" shall include all possible geometrical configurations of the molecule. These configurations include, but are not limited to isotactic, syndiotactic, and random symmetries.
Examples of polymer films that may be suitable include, but are not limited to, polyolefins, polyesters, polyamides, polyimides, polysulfones, polyether ketones, cellophanes, or any combination thereof. Other non-conducting substrate materials such as paper and paper laminates, metal oxides, silicates, cellulosics, or any combination thereof, also may be used.
In one particular example, the polymer film comprises polyethylene terephthalate. Examples of polyethylene terephthalate films that may be suitable for use as the substrate include, but are not limited to, MELINEX®, commercially available from DuPont Teijan Films (Hopewell, Virginia), and SKYROL, commercially available from SKC, Inc. (Covington, Georgia). Polyethylene terephthalate films are used in commercially available susceptors, for example, the QWIKWAVE® Focus susceptor and the MICRORITE® susceptor, both available from Graphic Packaging International (Marietta, Georgia).
The thickness of the film generally may be from about 8.89 µm (35 gauge) to about 0.254 mm (10 mil). In one example, the thickness of the film is from about 10.16 to about 20.32 µm (from about 40 to about 80 gauge). In another example, the thickness of the film is from about 11.43 to about 12.7 µm (from about 45 to about 50 gauge). In still another example, the thickness of the film is about 12.19 µm (48 gauge).
The microwave energy interactive material may be applied to the substrate in any suitable manner, and in some instances, the microwave energy interactive material is printed on, extruded onto, sputtered onto, evaporated on, or laminated to the substrate. The microwave energy interactive material may be applied to the substrate in any pattern, and using any technique, to achieve the desired heating effect of the food item.
For example, the microwave energy interactive material may be provided as a continuous or discontinuous layer or coating including circles, loops, hexagons, islands, squares, rectangles, octagons, and so forth. Examples of various patterns and methods that may be suitable are provided in U.S. Patent Nos. 6,765,182 ; 6,717,121 ; 6,677,563 ; 6,552,315 ; 6,455,827 ; 6,433,322 ; 6,414,290 ; 6,251,451 ; 6,204,492 ; 6,150,646 ; 6,114,679 ; 5,800,724 ; 5,759,422 ; 5,672,407 ; 5,628,921 ; 5,519,195 ; 5,424,517 ; 5,410,135 ; 5,354,973 ; 5,340,436 ; 5,266,386 ; 5,260,537 ; 5,221,419 ; 5,213,902 ; 5,117,078 ; 5,039,364 ; 4,963,424 ; 4,936,935 ; 4,890,439 ; 4,775,771 ; 4,865,921 ; and Re. 34,683 . Although particular examples of patterns of microwave energy interactive material are shown and described herein, it should be understood that other patterns of microwave energy interactive material are contemplated by the present disclosure.
Various corrugated materials may be used to form a microwave energy interactive structure. Corrugated materials have a longitudinal direction that runs along the length of the flutes, and a transverse direction that runs across the flutes. Corrugated materials may be relatively stiff when the material is flexed in the longitudinal direction, and relatively flexible when flexed in the transverse direction. Thus, it is contemplated that structural elements may be added to enhance the rigidity of the construct. Conversely, it also is contemplated that the construct may include elements that weaken the structure, for example, a score line, if needed or desired for a particular application. Single faced corrugated materials that may be suitable include, but are not limited to, flute sizes A, B (154 flutes/linear m (47 flutes/linear ft)), E (295 flutes/linear m (90 flutes/linear ft)), or any other size. Double faced corrugated materials that may be suitable include, but are not limited to, flute sizes B, C, E, and F.
Various materials may be used to form the support. For example, all or a portion of the support may be formed at least partially from a paper or paperboard material. In one example, the support is formed from paper generally having a basis weight of from about 24.4125 to about 97.65 g/m² (from about 15 to about 60 lbs/ream (lb/3000 sq. ft.)), for example, from about 32.55 to about 65.1 g/m² (from about 20 to about 40 lbs/ream). In another example, the paper has a basis weight of about 40.6875 g/m² (25 lbs/ream). In another example, the support is formed from paperboard having a basis weight of from about 97.65 to about 537.075 g/m² (from about 60 to about 330 lbs/ream), for example, from about 130.2 to about 227.85 g/m² (from about 80 to about 140 lbs/ream). The paperboard generally may have a thickness of from about 0.1524 to about 0.762 mm (from about 6 to about 30 mils), for example, from about 0.3048 to about 0.7112 mm (from about 12 to about 28 mils). In one particular example, the paperboard has a thickness of about 0.3048 mm (12 mils). Any suitable paperboard may be used, for example, a solid bleached or solid unbleached sulfate board, such as SUS® board, commercially available from Graphic Packaging International.
As another example, the support may be formed at least partially from a polymer or polymeric material. One polymer that may be suitable is polycarbonate. Other examples of other polymers that may be suitable include, but are not limited to, polyolefins, e.g. polyethylene, polypropylene, polybutylene, and copolymers thereof; polytetrafluoroethylene; polyesters, e.g. polyethylene terephthalate, e.g., coextruded polyethylene terephthalate; vinyl polymers, e.g., polyvinyl chloride, polyvinyl alcohol, ethylene vinyl alcohol, polyvinylidene chloride, polyvinyl acetate, polyvinyl chloride acetate, polyvinyl butyral; acrylic resins, e.g. polyacrylate, polymethylacrylate, and polymethylmethacrylate; polyamides, e.g., nylon 6,6; polystyrenes; polyurethanes; cellulosic resins, e.g., cellulosic nitrate, cellulosic acetate, cellulosic acetate butyrate, ethyl cellulose; copolymers of any of the above materials; or any blend or combination thereof.
The various constructs may be formed according to numerous processes known to those in the art, including using adhesive bonding, thermal bonding, ultrasonic bonding, mechanical stitching, or any other suitable process. Any of the various layers that may be used to form the constructs may be provided as a sheet of material, a roll of material, or a die cut material in the shape of the construct to be formed.
Optionally, one or more panels of the various constructs described herein or contemplated hereby may be coated with varnish, clay, or other materials, either alone or in combination. The coating may then be printed over with product advertising or other information or images. The constructs also may be coated to protect any information printed thereon. Furthermore, the constructs may be coated with, for example, a moisture barrier layer, on either or both sides.
Alternatively or additionally, any of the structures or constructs may be coated or laminated with other materials to impart other properties, such as absorbency, repellency, opacity, color, printability, stiffness, or cushioning. For example, absorbent susceptors are described in U.S. Provisional Application No. 60/604,637, filed August 25, 2004 , and U.S. Patent Application Publication No. US 2006/0049190 A1, published March 9, 2006 . Additionally, the structures or constructs may include graphics or indicia printed thereon.
Various aspects of the disclosure may be understood further from the following examples, which are not intended to be limiting in any manner.

EXAMPLES 1-7

Nestle panini sandwiches were heated to evaluate the performance of various constructs according to the disclosure. Each panini sandwich was placed on the construct being evaluated, placed into an 1100 W Panasonic microwave oven with a turntable, and heated on full power for about 8 minutes. The results are presented in Table 1, in which the various layers of constructs are described from the food-contacting side to microwave oven side. It will be understood that where a metallized film (i.e. susceptor film) forms an outermost layer of the construct, the metallized side of the susceptor film faces inwardly and the polymer film faces outwardly.

Table 1.

Ex.	Construct	Results
1	Commercially available "control" structure with elongate apertures extending through the thickness of the structure, as illustrated schematically in FIG. 17 :	Little browning or crisping of the bread
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paper support
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film, with the metallized side of the film facing down
	• facing layer of a B flute corrugated material
	• flutes of the B flute corrugated material
2	Experimental construct, as illustrated schematically in FIG. 10 :	Improved browning and crisping of the bread relative to the structure of Ex. 1
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paper support
	• facing layer of a single faced B flute corrugated material
	• flutes of the corrugated material
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film, corrugated
3	Experimental construct, as represented schematically in FIG. 9A , with strips of metallized film and support removed from the top side, as illustrated schematically in FIG. 18 :	Improved browning and crisping of the bread relative to the structure of Ex. 1
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paper support
	• facing layer of a single faced B flute corrugated material
	• flutes of the corrugated material
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film, corrugated
4	Experimental construct, as represented schematically in FIG. 9B , with strips of metallized film and support removed from the bottom side, as illustrated schematically in FIG. 18 :	Improved browning and/or crisping of the bread relative to the structure of Ex. 1
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• fluted side of a single faced B flute corrugated material
	• facing layer of the corrugated material
	• paper support
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
5	Experimental construct, as represented schematically in FIG. 8 , with slits extending through metallized film and support on top side of construct (slits transverse to the corrugated metallized film/paper layer, as illustrated schematically in FIG. 19 ):	Improved browning and/or crisping of the bread relative to the structure of Ex. 1
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film overlying paper support
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film, corrugated
	• flutes of a single faced B flute corrugated material
	• facing layer of the corrugated material
6	Experimental construct, as represented schematically in FIG. 5 , with slits extending through metallized film and support (slits oblique to the length of the flutes, as illustrated schematically in FIG. 20 ):	Improved browning and/or crisping of the bread relative to the structure of Ex. 1
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film overlying paper support
	• flutes of a single faced B flute corrugated material
	• facing layer of the corrugated material
	• paper support
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
7	Experimental construct, as represented schematically in FIG. 6 :	Improved browning and/or crisping of the bread relative to the structure of Ex. 1
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film overlying paper support with slits extending through metallized film and support
	• facing layer of a of a single faced B flute corrugated material
	• flutes of the corrugated material
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paper support

EXAMPLES 8-11

Commercially available frozen 9 inch diameter deluxe Tombstone pizzas were heated to evaluate the performance of various constructs according to the disclosure. Each pizza was placed on the construct being evaluated, placed into an 1100 W Panasonic microwave oven with a turntable, and heated on full power for about 8 minutes. The results are presented in Table 2.

Table 2.

Ex.	Construct	Results
8	Double susceptor "control" structure without corrugated base:	Top of pizza overcooked, edges of bottom crust browned, but other areas soggy and undercooked
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paperboard support
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paperboard support
9	Single layer susceptor "control" structure with corrugated base:	Top of pizza overcooked, bottom of crust soggy and not browned
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paper support
	• facing layer of B flute bleached corrugated material
	• flutes of the corrugated material
10	Experimental construct, as represented schematically in FIG. 4 :	Top of pizza in better condition, particularly along edge of pizza, excellent browning and crisping of bottom of crust,
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paper support
	• facing layer of B flute bleached corrugated material
	• flutes of the corrugated material
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paper support
11	Experimental triple susceptor construct, as represented schematically in FIG. 7 :	Top of pizza heated evenly, pizza crust heated, browned, and crisped evenly
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paper support
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film, corrugated
	• B flute bleached corrugated material
	• 12.19 µm (48 gauge) metallized polyethylene terephthalate film
	• paper support

Notably, the construct of Example 10 became significantly hotter beneath the pizza as compared with the construct of Example 8, yet the outer edges outside of pizza did not scorch. Thus, the construct of Example 10 exhibited greater heating power, but more gentle heating than the construct of Example 8. The construct of Example 11 became the hottest when exposed to microwave energy. Thus, more susceptor layers may be used where it is desirable to reach higher temperatures to brown and/or crisp the food item.

EXAMPLES 12-13

Commercially available frozen 25.4 cm (10 inch) diameter deluxe Tombstone pizzas were heated to evaluate the performance of various constructs according to the disclosure. Each pizza was placed on the construct being evaluated, placed into an 1100 W Panasonic microwave oven with a turntable, and heated on full power for about 8 minutes. The results are presented in Table 3.

Table 3.

Ex.	Construct	Results
12	Experimental construct, as represented schematically in FIG. 15 , with the arrangement of microwave energy transparent areas shown in FIG. 14A , with the microwave transparent areas 1404 having a diameter of about 1.27 cm (0.5 in)	Good browning and crisping
13	Experimental construct, as represented schematically in FIG. 16 , with the arrangement of microwave energy transparent areas shown in FIG. 14A , with the microwave transparent areas 1404 having a diameter of about 1.27 cm (0.5 in)	Good browning and crisping

Although certain embodiments have been described with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the invention as defined in the claims. All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are used only for identification purposes to aid the reader's understanding of the various embodiments of the invention, and do not create limitations, particularly as to the position, orientation, or use of the invention unless specifically set forth in the claims. Joinder references (e.g., joined, attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily imply that two elements are connected directly and in fixed relation to each other.
It will be recognized by those skilled in the art, that various elements discussed with reference to the various embodiments may be interchanged to create entirely new embodiments of the invention. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the invention as defined in the claims. The detailed description set forth herein is not intended nor is to be construed to limit the invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications, and equivalent arrangements of the invention.
Accordingly, it will be readily understood by those persons skilled in the art that, in view of the above detailed description of the invention, the invention is susceptible of broad utility and application. Many adaptations of the invention other than those herein described, as well as many variations, modifications, and equivalent arrangements will be apparent from or reasonably suggested by the invention and the above detailed description thereof, without departing from the invention as defined in the claims.
While the invention is described herein in detail in relation to specific aspects or embodiments, it is to be understood that this detailed description is only illustrative and exemplary of the invention and is made merely for purposes of providing a full and enabling disclosure. The detailed description set forth herein is not intended nor is to be construed to limit the invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications, and equivalent arrangements of the invention.

Claims

A microwave heating construct (1400; 1500) comprising:
a dimensionally stable base (1418a; 1518a) having a first side and a second side opposite the first side, the base including a plurality of corrugations (1422a; 1522a);

a first susceptor layer (1402a; 1502a) joined to the base, the first susceptor layer (1402a; 1502a) is disposed on the first side of the base (1418a; 1518b), the first susceptor layer having a substantially planar configuration, so that the first susceptor layer extends across the plurality of corrugations; and

a second susceptor layer (1402b; 1502b) joined to the base, the second susceptor layer (1402b; 1502b) is disposed on the second side of the base (1418a; 1518b), the second susceptor layer having a substantially planar configuration, so that the second susceptor layer extends across the plurality of corrugations,

wherein the construct including the first susceptor layer and the second susceptor layer is for underlying a food item having a lower surface that is desirably at least one of browned and crisped,
wherein
at least one of the first susceptor layer and the second susceptor layer includes a central region (1408) including a microwave energy transparent area (1404; 1504) circumscribed by the respective susceptor layer,

at least one of the first susceptor layer and the second susceptor layer includes a peripheral region (1410) extending around the central region, the peripheral region including a microwave energy transparent area (1406) circumscribed by the respective susceptor layer.
The construct of claim 1, wherein the microwave energy transparent area (1404; 1504) of the central region (1408) is substantially circular in shape.
The construct of claim 1 or 2, wherein the microwave energy transparent area (1406) of the peripheral region (1410) is substantially square in shape.
The construct of any of claims 1 to 3, wherein
the microwave energy transparent area (1404; 1504) of the central region (1408) is a first microwave energy transparent area of a plurality of microwave energy transparent areas of the central region, and
the microwave energy transparent area (1406) of the peripheral region (1410) is a first microwave energy transparent area of a plurality of microwave energy transparent areas of the peripheral region.
The construct of claim 4, wherein the microwave energy transparent areas (1404; 1504) of the central region (1408) are arranged with a greater number of microwave energy transparent areas proximate to a center of the construct.
The construct of claim 4 or 5, wherein the microwave energy transparent areas (1406) of the peripheral region (1410) are arranged in rows and columns, such that the microwave energy interactive material in the peripheral region has a grid-like appearance.
The construct of any of claims 1 to 6, wherein
the first susceptor layer (1402a; 1502a) is disposed between a first polymer film layer (1412a, 1512a, 1612a) and a first paper layer (1416a; 1516a) in a facing, contacting relationship, and
the second susceptor layer (1402b; 1502b) is disposed between a second polymer film layer (1412b; 1512b; 1612b) and a second paper layer (1416b; 1516b) in a facing, contacting relationship.
The construct of claim 7, further comprising a third paper layer (1424a; 1524a) joined to the second side of the base (1418; 1518a) in a substantially planar configuration across the corrugations (1422a; 1522a; 1622a), thereby defining a plurality of insulating voids (1420a; 1520a) between the third paper layer and the second side of the base.
The construct of claim 7, wherein the first paper layer (1416a; 1516a) is joined to the first side of the base (1418; 1518a) in a substantially planar configuration across the corrugations (1422a; 1522a), thereby defining a plurality of insulating voids (1420a; 1520a) between the first paper layer and the first side of the base.
The construct of any of claims 1 to 9, wherein the first susceptor layer (1402a; 1502a) and the second susceptor layer (1402b; 1502b) each comprise a layer of microwave energy interactive material having a thickness of from about 60 to about 100 angstroms.
The construct of claim 10, wherein the microwave energy transparent area (1404; 1504) of the central region (1408) and the microwave energy transparent area (1406) of the peripheral region (1410) each comprise the microwave energy interactive material in a chemically deactivated condition.
The construct of any of claims 1 to 11, wherein the first susceptor layer (1402a; 1502a) and the second susceptor layer (1402b; 1502b) are operative for converting at least a portion of impinging microwave energy into thermal energy.
The construct of any of claims 1 to 12, wherein the microwave energy transparent area (1404; 1504) of the central region (1408) and the microwave energy transparent area (1406) of the peripheral region (1410) are operative for allowing microwave energy to pass through the respective susceptor layer.