Microwave interactive flexible packaging

[0001] This application is a continuation-in-part of U.S. patent application Ser. No. 10/501,003 filed Mar. 7, 2005 now U.S. Pat. No. 7,019,271, which is the National Stage of International Application No. PCT/US03/03779 filed Feb. 7, 2003, which claims the benefit of U.S. Provisional Application No. 60/355,149 filed Feb. 8, 2002; this application also is a continuation-in-part of U.S. patent application Ser. No. 11/054,633 filed Feb. 9, 2005, which claims the benefit of U.S. Provisional Application No. 60/543,364 filed Feb. 9, 2004. The above-referenced applications each are incorporated by reference herein in their entirety.

[0002] The present invention relates to packages for heating or cooking a food item. In particular, the invention relates to a package for heating or cooking a food item in a microwave oven.

[0003] Microwave ovens provide a convenient means of cooking and reheating food items. Frequently, users transport microwaveable food items from home to work or another location by placing the food item in a plastic bag, aluminum foil, plastic wrap, or a plastic container. Although some of such materials or containers may be placed in the microwave oven, such materials or containers often result in the food item being undesirably soggy. In contrast, by merely cooking the food item on a paper plate, napkin, paper towel, or other commonly available substrate, the food item often becomes dried out and hardened.

[0004] Many combinations of materials of different character have been used in microwave packaging to influence the effect of the microwave energy on the food product being heated. These microwave packaging materials may be microwave transparent, for example, paper, paperboard, or many plastics, or they may be microwave interactive, for example, metal foils or thin metal deposits. Microwave transparent materials generally provide, for example, food product support, packaging form, insulation, and vapor barrier functions in packaging. Microwave interactive materials generally provide, for example, enhanced surface heating, microwave shielding, enhanced microwave transmission, and energy distribution functions in packaging. Microwave packaging often is created and configured for a particular food product or type of food product using materials chosen to best exploit the cooking ability of a microwave oven with respect to that food product. However, such packaging typically is provided only with the particular food item and is not independently available for purchase and use with food items prepared by a user.

[0005] Thus, there is a need for a package for a food item that may be used to contain a food item, transport the item between locations, and heat or cook the food product therein. Further, there is a need for a package that provides browning and/or crisping of the food item during microwave heating or cooking. Still further, there is a need for a package that is available for purchase and use with food items prepared by a user.

[0006] The present invention relates generally to a package that can be used for storing, transporting, and heating a food item therein. The package is formed at least partially from at least one material that enhances heating in a microwave oven.

[0007] In one aspect, the present invention is directed to a package for receiving a food item for storage and heating therein. The package comprises at least one opening, at least one mechanism for closing the at least one opening, and an insulating microwave material. The package includes an interior into which the food item is placed, and an interior surface on which the food is supported. The package further may include at least one vent to permit the passage of water vapor therefrom. The vent may be an aperture, perforation, or other suitable feature or, alternatively, may be a closure mechanism that is sealed only partially during heating, thereby permitting water vapor to escape.

[0008] In this and other aspects of the present invention, the closure mechanism may be any suitable mechanism as desired. For example, the interior surface of the package proximate the opening may include an adhesive material covering at least a portion thereof. Alternatively, the closure mechanism may be a zipper or slider-type closure. Alternatively still, the closure mechanism may include a flap extending from an open end of the package, where the flap is adapted to be inserted into the opening.

[0009] In yet another alterative, the closure mechanism may include a flap extending from an open end of the package, where the flap includes a mechanism for releasably sealing the package. In one aspect, the mechanism for releasably sealing the package may include an adhesive material covering at least a portion of the flap, where, for example, the flap is adapted to be folded over the opening such that the adhesive contacts an exterior surface of the package. In another aspect, the mechanism for releasably sealing the package may include a tab extending from the flap that communicates with a corresponding slot in the package.

[0010] In another aspect, the present invention is directed to a package for heating a food product comprising a sleeve formed at least partially from an insulating microwave material and having at least two open ends, where the sleeve has an interior surface comprising an adhesive covering at least a portion thereof for substantially sealing the package. In one aspect, the insulating microwave material comprises expandable insulating cells. In another aspect, the insulating microwave material comprises a susceptor material.

[0011] In yet another aspect, the present invention is directed to a package for storing and heating a food item therein, where the package is formed at least partially from an insulating material including a barrier film. The package comprises an opening through which the food item is received and a closure mechanism proximate the opening for substantially sealing the package. The barrier film may comprise ethylene vinyl alcohol, barrier nylon, polyvinylidene chloride, barrier fluoropolymer, nylon 6, nylon 66, coextruded nylon 6/ethylene vinyl alcohol/nylon 6, silicon oxide coated film, or any combination thereof. In one aspect, the barrier film has an oxygen transmission rate of less than about 80 cc/m²/day. In another aspect, the barrier film has an oxygen transmission rate of less than about 25 cc/m²/day. In yet another aspect, the barrier film has a water vapor transmission rate of less than about 450 g/m²/day.

[0012] In this and other aspects, the present invention contemplates a plurality of packages stacked in a face-to-face relation. The plurality of packages may be placed into a carton comprising an open portion through which the microwave cooking packages may be removed or dispensed.

[0013] Other aspects, features, and advantages of the present invention will become apparent from the following description and accompanying figures.

[0037] The present invention generally is directed to a disposable package for storing a food item, and browning and crisping the food item in a microwave oven. The package may be provided as a sleeve, a pouch, a bag, or any other configuration as desired. Unlike conventional sandwich bags, plastic containers, and the like, the package of the present invention includes features that store the item during transportation and brown and crisp the food item during the heating or cooking cycle in the microwave oven.

[0038] The sleeve or pouch may be provided with one or more features that allow the bag to be sealed during refrigeration, freezing, transportation, heating, or otherwise. In one aspect, the sleeve or pouch is provided with one or more strips of pressure-sensitive adhesive near the periphery thereof so that, after the food item is positioned, the package may be sealed around the edges of the food item. In another aspect, the sleeve or pouch is provided with an open portion for inserting the food item therein, and a flap adjacent thereto. The flap may be folded over to close the end and may be inserted into a slot to secure the food item therein. In yet another aspect, the flap is provided with an adhesive that secures the package when brought into contact with an exterior surface of the package. If desired, the feature for closing the package may be selected to substantially seal the package for protection of the food item during storage in a refrigerator or freezer, or to store or transport a food item that has a liquid component or other components that might tend to fall out of the package.

[0039] In any of the packages contemplated hereby, the sleeve or pouch may include one or more venting mechanisms. For example, the package may be provided with apertures or perforations that permit vapor to escape during cooking. Alternatively, the package may be re-opened partially or completely at one or more ends, edges, or locations to provide venting of the food product.

[0040] The present invention may be best understood by referring to the following figures. For purposes of simplicity, like numerals may be used to describe like features. However, it should be understood use of like numerals is not to be construed as an acknowledgement or admission that such features are equivalent in any manner.

[0041] FIGS. 1-14 depict several exemplary packages that may be formed according to the present invention. The exemplary packages have a sleeve or pouch configuration and are shown to be hand-held type packages. However, it should be understood that other shapes and configurations are contemplated by the present invention. Examples of other shapes encompassed hereby include, but are not limited to, polygons, circles, ovals, cylinders, prisms, spheres, polyhedrons, ellipsoids, and any other shape that may be formed into a three-dimensional package for receiving a food item therein. The shape of the package may be determined by the shape of the food product intended for use therewith, and it should be understood that different packages are contemplated for different food products, for example, sandwiches, corn dogs, pizzas, French fries, soft pretzels, pizza bites, cheese sticks, pastries, doughs, and so forth. Additionally, it should be understood that the present invention contemplates packages for single-serving portions and for multiple-serving portions, and is not restricted to hand-held packages. It also should be understood that various components used to form the packages of the present invention may be interchanged. Thus, while only certain combinations are illustrated herein, numerous other combinations and configurations are contemplated hereby.

[0042] According to one aspect of the present invention shown in FIGS. 1 and 2, the package comprises a sleeve 100 having an interior 110, an exterior surface 115, an open first end 120, and an open second end 125 (shown in dashed lines). Various closure mechanisms may be provided to seal the package for refrigeration, freezing, or transportation. For example, an adhesive strip 130 may be provided on the interior surface 135 of the sleeve 100 proximate the first end 120 and the second end 125. Any suitable adhesive may be used, and in some instances, the adhesive is a pressure-sensitive adhesive. As shown in FIG. 2, after the food item F is placed into the sleeve 100, the respective ends 120, 125 of the sleeve 100 may be pressed together to seal the food item F therein. If desired, the adhesive may be covered with a removable release liner, such as those known in the art.

[0043] Alternatively, as shown in FIGS. 3 and 4, the first end 155 and second end 160 of the sleeve 150 may include flaps 165, 170 that fold into the interior 175 of the sleeve 150 to enclose the food item F therein. Alternatively still, as shown in FIGS. 5 and 6, the flaps 165, 170 may include adhesive strips 172, 174 that are pressed against the exterior 176 of the package 150 to enclose the food product F therein. In another example shown in FIGS. 7 and 8, the flaps 165, 170 may include tabs 180, 185 or other projections that are inserted into corresponding slots 190, 195 in the sleeve 150. While various enclosure mechanisms are provided herein, it should be understood that the present invention contemplates numerous other closure mechanisms.

[0044] According to another aspect of the present invention shown in FIG. 9, the package comprises a pouch 200 having an interior 205, an exterior surface 210, a plurality of sealed edges 215a, 215b, and 215c, and at least one open end 220 or open portion. The pouch 200 may be shaped and sized to receive one or more food items (not shown). For example, as shown in FIG. 10, the pouch 200 may be somewhat rectangular in shape and may include one or more gussets 225 as needed to accommodate larger or thicker food items (not shown), for example, one or more pieces of fried chicken. As shown in FIG. 11, the pouch 200 may be elongated in shape to accommodate, for example, a submarine sandwich, an egg roll, or burrito. As shown in FIG. 12, the pouch 200 may be triangular in shape to accommodate, for example, a slice of pizza. As shown in FIG. 13, the pouch 200 may be substantially square in shape to accommodate, for example, a sandwich, such as a grilled cheese sandwich or a meat and cheese sandwich. As shown in FIG. 14, the pouch 200 may be circular or rounded in shape to accommodate, for example, a pot pie.

[0045] In each of the exemplary packages shown in FIGS. 9-14, various closure mechanisms may be provided. For example, any of the closure mechanisms shown in or described in connection with FIGS. 1-8 may be used, including one or more adhesives strips (FIGS. 1, 2, 5, 6), flaps (FIGS. 3, 4, 5, 6), tabs (FIGS. 7, 8), zippers, which typically comprise at least one elongated ridge and at least one mating and releasably interlocking elongated groove (FIG. 14), sliders, which are zipper-type fasteners that typically include a sliding bar that causes the ridge(s) to engage with the groove(s) as the slider is moved along the opening (FIG. 13), or the like, or any combination thereof, as are known to those of skill in the art. Other closure mechanisms are contemplated hereby.

[0046] Any of the numerous packages contemplated hereby may be formed from one or more microwave energy interactive materials that promote browning and/or crisping of the food item during microwave heating. In one aspect, the package may include one or more susceptor materials. The susceptor material may form all or part of the package as needed or desired to brown or crisp the food item. Thus, for instance, where the package is intended for use with a slice of pizza, the susceptor material may form all or part of the portion of the package in contact with or proximate the crust of the pizza. As another example, where the package is intended for a sandwich or a burrito, substantially all of the interior surface of the package may be provided with a susceptor material.

[0047] A susceptor used in accordance with the present invention may comprise a microwave energy interactive material deposited on or supported by a substrate. Depending on the microwave energy interactive material selected and its positioning in the packaging, the susceptor may absorb microwave energy, transmit microwave energy, or reflect microwave energy as desired for a particular food product. When the food product is placed inside the package, the microwave energy interactive material may be in proximate contact with the surface of the food product, intimate contact with the food product, or a combination thereof, as needed to achieve the desired cooking results.

[0048] The microwave energy interactive material may comprise an electroconductive or semiconductive material. According to one aspect of the present invention, the microwave energy interactive material may comprise 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 for use with the present invention 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 thereof.

[0049] While metals are inexpensive and easy to obtain in both vacuum deposited or foil forms, metals may not be suitable for every application. For example, in high vacuum deposited thickness and in foil form, metals are opaque to visible light and may not be suitable for forming a clear microwave package or component. Further, the interactive properties of such vacuum deposited metals for heating often are limited to heating for narrow ranges of heat flux and temperature. Such materials therefore may not be optimal for heating, browning, and crisping all food products. Additionally, for field management uses, metal foils and vacuum deposited coatings can be difficult to handle and design into packages, and can lead to arcing at small defects in the structure.

[0050] Thus, according to another aspect of the present invention, the microwave interactive energy material may comprise a metal oxide. Examples of metal oxides that may be suitable for use with the present invention 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 for use with the present invention is indium tin oxide (ITO). ITO can be used as a microwave energy interactive material to provide a heating effect, a shielding effect, or a combination thereof. To form the susceptor, ITO typically is sputtered onto a clear polymeric 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.

[0051] Alternatively, 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.

[0052] The substrate used in accordance with the present invention typically comprises an electrical insulator, for example, a polymeric film. The thickness of the film may typically be from about 35 gauge to about 10 mil. In one aspect, the thickness of the film is from about 40 to about 80 gauge. In another aspect, the thickness of the film is from about 45 to about 50 gauge. In still another aspect, the thickness of the film is about 48 gauge. Examples of polymeric 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.

[0053] According to one aspect of the present invention, the polymeric film may comprise polyethylene terephthalate. Examples of polyethylene terephthalate film that may be suitable for use as the substrate include, but are not limited to, MELINEX®, commercially available from DuPont Teijan Films (Hopewell, Va.), and SKYROL, commercially available from SKC, Inc. (Covington, Ga.). Polyethylene terephthalate films are used in commercially available susceptors, for example, the QWIK WAVE® Focus susceptor and the MICRO-RITE® susceptor, both available from Graphic Packaging International (Marietta, Ga.).

[0054] According to another aspect of the present invention, the package may be constructed from materials that provide a water barrier, oxygen barrier, or a combination thereof to the susceptor. Such barrier layers may be formed from a polymer film having barrier properties or from any other barrier layer or coating as desired. Suitable polymer films may include, but are not limited to, ethylene vinyl alcohol, barrier nylon, polyvinylidene chloride, barrier fluoropolymer, nylon 6, nylon 66, coextruded nylon 6/EVOH/nylon 6, silicon oxide coated film, or any combination thereof.

[0055] One example of a barrier film that may be suitable for use with the present invention is CAPRAN® EMBLEM 1200 M nylon 6, commercially available from Honeywell International (Pottsville, Pa.). Another example of a barrier film that may be suitable is CAPRAN® OXYSHIELD OBS monoaxially oriented coextruded nylon 6/ethylene vinyl alcohol (EVOH)/nylon 6, also commercially available from Honeywell International. Yet another example of a barrier film that may be suitable for use with the present invention is DARTEK® N-201 nylon 6,6, commercially available from Enhance Packaging Technologies (Webster, N.Y.).

[0056] Still other barrier films include silicon oxide coated films, such as those available from Sheldahl Films (Northfield, Minn.). Thus, in one aspect, a susceptor may have a structure including a film, for example, polyethylene terephthalate, with a layer of silicon oxide coated onto the film, and ITO or other material deposited over the silicon oxide. If needed or desired, additional layers or coatings may be provided to shield the individual layers from damage during processing.

[0057] The barrier film may have an oxygen transmission rate (OTR) as measured using ASTM D3985 of less than about 20 cc/m²/day. In one aspect, the barrier film has an OTR of less than about 10 cc/m²/day. In another aspect, the barrier film has an OTR of less than about 1 cc/m²/day. In still another aspect, the barrier film has an OTR of less than about 0.5 cc/m²/day. In yet another aspect, the barrier film has an OTR of less than about 0.1 cc/m²/day.

[0058] The barrier film may have an water vapor transmission rate (WVTR) as measuring using ASTM F1249 of less than about 100 g/m²/day. In one aspect, the barrier film has an water vapor transmission rate (WVTR) as measuring using ASTM F1249 of less than about 50 g/m²/day. In another aspect, the barrier film has a WVTR of less than about 15 g/m²/day. In yet another aspect, the barrier film has a WVTR of less than about 1 g/m²/day. In still another aspect, the barrier film has a WVTR of less than about 0.1 g/m²/day. In a still further aspect, the barrier film has a WVTR of less than about 0.05 g/m²/day.

[0059] 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 product. For example, the microwave energy interactive material may be provided as a continuous or discontinuous layer or coating, circles, loops, hexagons, islands, squares, rectangles, octagons, and so forth. Examples of alternative patterns and methods that may be suitable for use with the present invention are provided in U.S. Pat. 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; and 4,890,439; 4,775,771; each of which is incorporated by reference herein in its entirety. Although particular examples of the 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 invention.

[0060] According to yet another aspect of the present invention, the susceptor optionally is laminated to a support. The support may form a partial or complete layer of the susceptor. The support may be formed from paper, paperboard, a low shrink polymer, or any other suitable material. Thus, for example, a metallized polymer film may be laminated to a paper, for example, a kraft paper, or alternatively, a low shrink polymer film, for example, a cast nylon 6 or nylon 6,6 film, or a coextruded film containing such polymers. One such material that may be suitable for use with the present invention is DARTEK, commercially available from DuPont Canada.

[0061] Where the support is paper, the paper may have a basis weight of about 15 to about 80 lbs/ream. In one aspect, the paper support has a basis weight of about 20 to about 60 lbs/ream. In another aspect, the paper support has a basis weight of about 25 lbs/ream. Where the support is paperboard, the support may have a thickness of about 8 to about 28 mils. In one aspect, the paperboard support has a thickness of about 10 to about 20 mils. In another aspect, the paperboard support has a thickness of about 13 mils.

[0062] If desired, the support may be coated or laminated with other materials to impart other properties, such as absorbency, repellency, opacity, color, printability, stiffness, or cushioning. Absorbent susceptors are described in U.S. Provisional Patent Application Ser. No. 60/604,637, filed Aug. 25, 2004, incorporated herein by reference in its entirety. Additionally, the support may include graphics or indicia printed thereon. Where no additional support is present, the insulating material may act as a support for the susceptor, may be in direct contact with the susceptor, and/or may be affixed thereto thermally, adhesively, mechanically, or any combination thereof, as is shown and described herein.

[0063] In another aspect of the present invention, the package includes an insulating microwave material. As used herein, an “insulating microwave material” refers to any arrangement of layers, such as polyester layers, susceptor layers, polymer layers, paper layers, continuous and discontinuous adhesive layers, and patterned adhesive layers that provide an insulating effect. The package may include one or more susceptors, one or more expandable insulating cells, or a combination of susceptors and expandable insulating cells. Examples of materials that may be suitable, alone or in combination, include, but are not limited to, are QwikWave® Susceptor packaging material, QwikWave® Focus packaging material, Micro-Rite® packaging material, MicroFlex® Q packaging material, and QuiltWave™ Susceptor packaging material, each of which is commercially available from Graphic Packaging International, Inc. Any of such materials or other insulating materials may be used to form all or a portion of the packages shown in FIGS. 1-14 and FIGS. 21-23 or contemplated hereby.

[0064] In one aspect of the present invention, the insulating microwave material includes at least one susceptor. By using an insulating microwave material with a susceptor, more of the sensible heat generated by the susceptor is transferred to the surface of the food product rather than to the microwave oven environment. Without the insulating material, some or all the heat generated by the susceptor may be lost via conduction to the surrounding air and other conductive media, such as the microwave oven floor or turntable. Thus, more of the sensible heat generated by the susceptor is directed to the food product and browning and crisping is enhanced. Furthermore, insulating microwave materials may retain moisture in the food item when cooking in the microwave oven, thereby improving the texture and flavor of the food item.

[0065] Various exemplary insulating materials are depicted in FIGS. 15-20. In each of the examples shown herein, it should be understood that the layer widths are not necessarily shown to scale. In some instances, for example, the adhesive layers may be very thin with respect to other layers, but are nonetheless shown with some thickness for purposes of clearly illustrating the arrangement of layers.

[0066] Referring to FIG. 15, the material 300 may be a combination of several different layers. A susceptor, which typically includes a thin layer of microwave interactive material 305 on a first plastic film 310, is bonded for example, by lamination with an adhesive 312, to a dimensionally stable substrate 315, for example, paper. The substrate 315 is bonded to a second plastic film 320 using a patterned adhesive 325 or other material, such that closed cells 330 are formed in the material 300. The closed cells 330 (shown unexpanded) are substantially resistant to vapor migration.

[0067] Optionally, an additional substrate layer 335 may be adhered by adhesive 340 or otherwise to the first plastic film 310 opposite the microwave interactive material 305, as depicted in FIG. 16. The additional substrate layer 335 may be a layer of paper or any other suitable material, and may be provided to shield the food item (not shown) from any flakes of susceptor film that craze and peel away from the substrate during heating. The insulating material 300 provides a substantially flat, multi-layered sheet 350, as shown in FIG. 17.

[0068] FIG. 18 depicts the exemplary insulating material 350 of FIG. 17 after being exposed to microwave energy from a microwave oven (not shown). As the susceptor heats upon impingement by microwave energy, water vapor and other gases normally held in the substrate 315, for example, paper, and any air trapped in the thin space between the second plastic film 320 and the substrate 315 in the closed cells 330, expand. The expansion of water vapor and air in the closed cells 330 applies pressure on the susceptor film 310 and the substrate 315 on one side and the second plastic film 320 on the other side of the closed cells 330. Each side of the material 300 forming the closed cells 330 reacts simultaneously, but uniquely, to the heating and vapor expansion. The cells 330 expand or inflate to form a quilted top surface 360 of cells separated by channels in the susceptor film 310 and substrate 315 lamination, which lofts above a bottom surface 365 formed by the second plastic film 320. This expansion may occur within 1 to 15 seconds in an energized microwave oven, and in some instances, may occur within 2 to 10 seconds.

[0069] FIGS. 19 and 20 depict alternative exemplary microwave insulating material layer configurations that may be suitable for use with any of the various packages of the present invention. Referring first to FIG. 19, an insulating microwave material 400 is shown with two symmetrical layer arrangements adhered together by a patterned adhesive layer. The first symmetrical layer arrangement, beginning at the top of the figure, comprises a PET film layer 405, a metal layer 410, an adhesive layer 415, and a paper or paperboard layer 420. The metal layer 410 may comprise a metal, such as aluminum, deposited along a portion or the entire PET film layer 405. The PET film 405 and metal layer 410 together define a susceptor. The adhesive layer 415 bonds the PET film 405 and the metal layer 410 to the paperboard layer 420.

[0070] The second symmetrical layer arrangement, beginning at the bottom of the drawings, also comprises a PET film layer 425, a metal layer 430, an adhesive layer 435, and a paper or paperboard layer 440. If desired, the two symmetrical arrangements may be formed by folding one layer arrangement onto itself. The layers of the second symmetrical layer arrangement are bonded together in a similar manner as the layers of the first symmetrical arrangement. A patterned adhesive layer 445 is provided between the two paper layers 420 and 440, and defines a pattern of closed cells 450 configured to expand when exposed to microwave energy. In one aspect, an insulating material 300 having two metal layers 410 and 430 according to the present invention generates more heat and greater cell loft.

[0071] Referring to FIG. 20, yet another insulating microwave material 400 is shown. The material 400 may include a PET film layer 405, a metal layer 410, an adhesive layer 415, and a paper layer 420. Additionally, the material 400 may include a clear PET film layer 425, an adhesive 435, and a paper layer 440. The layers are adhered or affixed by a patterned adhesive 445 defining a plurality of closed expandable cells 450.

[0072] Any of the insulating materials shown herein or contemplated hereby may have barrier properties that render the package suitable for storage of a food item therein. Such insulating materials may include a layer of barrier film in addition to the other layers present, or may replace a film layer previously described herein. Various exemplary barrier films that may be suitable for use with the present invention are described above.

[0073] As stated above, any of such insulating materials may be used to form all or part of the various packages contemplated by the present invention. Thus, for example, FIG. 21 depicts the package of FIG. 1 formed from an insulating material, FIG. 22 depicts the package of FIG. 7 formed from an insulating material, and FIG. 23 depicts the package of FIG. 8 formed from an insulating material, where each of FIGS. 1, 9, and 10 illustrate the package upon exposure to microwave energy.

[0074] It should be understood that in any of the packages contemplated hereby, it may be necessary or desirable to configure the package to include portions formed from a material other than an insulating material. For example, in one aspect, a package includes a food-supporting surface formed from a susceptor material, and a food-covering layer formed from an insulating microwave material. Such a package may be useful with food items that have a crust that is desirably browned and crisped, for example, pizza. Likewise, the package may include portions, for example, proximate the edges or the opening that do not have an insulating effect. Thus, for example, the package may be designed to have the flap, zipper, or other closure mechanism attached or affixed to a non-insulating material. In yet another aspect, one or more portions of the package may be laminated or otherwise bonded or assembled or assembled so that portions of the package formed from an insulating material are rendered non-insulating. For example, an insulating material having expandable cells used to form a sleeve may be bonded around all or a portion of the periphery so that the expandable cells can no longer expand. As another example, the package may include portions that include expanding cells that are positioned to maintain the package in an upright position, a flattened position, or any other configuration during cooking. Thus, advantageously, numerous packages may be tailored to various food items to optimize heating in the microwave oven.

[0075] Use of any of the exemplary insulating materials to package and/or cook a food item provides several benefits before, during, and after heating in a microwave oven. First, the water vapor and air contained in the closed cells provides insulation between the food item and the interior surfaces of the microwave oven. The base of a microwave oven, for example, the glass tray found in most microwave ovens, acts as a large heat sink, absorbing much of the heat generated by the susceptor film or within the food item itself. The vapor pockets in the cells formed by the present invention may be used to insulate the food item and susceptor film from the microwave oven surfaces and the vented air in the microwave oven cavity, thereby increasing the amount of heat that stays within or is transferred to the food item.

[0076] Second, the formation of the cells allows the material to conform more closely to the surface of the food item, placing the susceptor film in greater proximity to the food item. This enhances the ability of the susceptor film to brown and crisp the surface of the food item by conduction heating, in addition to some convection heating, of the food item.

[0077] Further, the insulating materials contemplated hereby may be desirable as a packaging material because it adds little bulk to the finished package, yet is transformed into a bulk insulating material without any consumer preparation before cooking.

[0078] According to one aspect of the present invention, a plurality of microwave cooking packages are provided in a nestled, stacked, folded, rolled, or other configuration. Thus, for example, a plurality of packages may be stacked in a face-to-face relation, then folded or rolled and placed in a bag, box, or other carton. The carton may include a portion that tears away using perforations, folds, tabs, or otherwise, to form an open portion through which the microwave cooking packages may be removed or dispensed.

[0079] The user then may dispense or otherwise remove a cooking package from the bag or carton, and place a food item to be cooked into the interior thereof. The package may be sealed by any of various mechanisms, for example, those described above, and placed in the refrigerator, freezer, lunch bag, briefcase, or otherwise, for later use. For example, the food item may be placed in the refrigerator for later consumption by another family member, such as a spouse or child. When the user wants to consume the food item, the packaged optionally is opened for venting (as described above) and the package is placed in the microwave oven. After heating, the food item may be removed from the package if desired. Alternatively, the food item may be consumed while still in the package, and the package may gradually be pulled away from the food item to expose it. If desired, the package may be provided with tear lines or perforations to aid in removal of the food item from the package.

[0080] The present invention is illustrated further by the following examples, which are not to be construed in any way as imposing limitations upon the scope thereof. On the contrary, it is to be clearly understood that resort may be had to various other aspects, modifications, and equivalents thereof which, after reading the description herein, may be suggested to one of ordinary skill in the art without departing from the spirit of the present invention or the scope of the appended claims.

[0081] The conductivity of various susceptor films was evaluated. Indium tin oxide coated (ITO) films were provided by Sheldahl Films (Northfield, Minn.) for evaluation, as indicated in Table 1. Each of the films included one or more layers of a proprietary clear hard coat (“CLHC”) material to protect the individual layers. The films were laminated on the ITO side to 75 gauge DARTEK N-201 nylon 6,6 film using Rohm & Haas Mor-Free 205A/C-66 adhesive applied in an amount of about 1.2 lb/ream. A 48-gauge polyethylene terephthalate (PET) film was evaluated as a control material. The results are presented in Table 1.

[0082]

TABLE 1
				Conduc-
Sam-	Sheldahl		No. of	tivity	Resistivity
ple	No.	Construction	Samples	(mhos/sq)	(ohms/sq)
1	140669	40 ohm/sq ITO	9	0.014 to	71.4 to 38.4
		2 mil PET		0.026
2	159512	250 ohm/sq ITO	4	0.0036 to	277.8 to
		SiOx		0.0037	270.3
		CLHC
		7.5 mil PET
		CLHC
3	159980	50 ohm/sq ITO	9	0.0166 to	60.2 to 57.8
		SiOx		0.0173
		CLHC
		7.5 mil PET
		CLHC
4	control	48 gauge PET	1	0.016 to	62.5 to 58.8
				0.017

[0083] The results indicate that the ITO films form susceptor materials that may be useful to form packages of the present invention. The use of a 7.5 mil PET film may be desirable for packaging applications that require or benefit from some level of stiffness or rigidity. However, it will be understood that ITO may be used to form susceptor materials having a lower basis weight and, therefore, less rigidity, as needed or desired for flexible packaging applications.

[0084] The barrier properties of Samples 2 and 3 from Example 1, each including a silicon oxide (SiOx) barrier layer, also were evaluated. Oxygen Transmission Rate (OTR) was measured at 22.8° C. and 0% relative humidity. Water Vapor Transmission Rate was measured at 37.8° C. and 100% relative humidity. The results are presented in Table 2. The results indicate that a SiOx layer may be used successfully to prepare a barrier susceptor suitable for use with the present invention.

[0085]

TABLE 2
	Sheldahl		No. of	OTR	WVTR
Sample	No.	Construction	Samples	(cc/m2/day)	(g/m2/day)
2	159512	250 ohm/sq	4	<0.0496	0.0841
		ITO
		SiOx
		CLHC
		7.5 mil PET
		CLHC
3	159980	50 ohm/sq ITO	9	<0.0496	0.0143
		SiOx
		CLHC
		7.5 mil PET
		CLHC

[0086] 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 present invention is susceptible of broad utility and application. Many adaptations of the present invention other than those herein described, as well as many variations, modifications, and equivalent arrangements will be apparent from or reasonably suggested by the present invention and the above detailed description thereof, without departing from the substance or scope of the present invention.

[0087] While the present invention is described herein in detail in relation to specific aspects, it is to be understood that this detailed description is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the present invention. The detailed description set forth herein is not intended nor is to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications, and equivalent arrangements of the present invention, the present invention being limited solely by the claims appended hereto and the equivalents thereof.