Patent Application
20100006566
It is known that microwave ovens may have “hot spots”, that is, areas in which the microwaves are concentrated and may become amplified, thereby causing a food item in the hot spot to become intensely heated. A single operating mode microwave oven may have only one hot spot in a single, constant location in the microwave oven, while a multiple operating mode microwave oven may have multiple hot spots in various places in the microwave oven at different points in time, thereby reducing the effect of each individual hot spot over the duration of the heating cycle. In many instances, the microwave oven may be provided with a turntable to attempt to mitigate the effect of such hot spots by continuously rotating the food item (and container, where applicable) to distribute the effect of the hot spots over various portions of the food item. However, in other instances, the microwave oven may be designed to utilize such hot spots advantageously with no attempt to mitigate the effect of the hot spot, for example, by specifying to the user which areas of the microwave oven will heat a food item most rapidly (e.g., a beverage).
It also is known that some microwave heating containers that include one or more microwave energy interactive elements may inherently have “hot spots”, that is, areas that are more prone to overheating under certain microwave heating conditions. For example, some microwave heating containers include a microwave energy shielding element to prevent the overheating of particularly vulnerable areas of food item, such as the sides and peripheral margin of the bottom of the food item. Depending on the shape of the shielding element, the food item being heated, the length of the heating cycle, the type of microwave oven, and so on, some areas of the container adjacent to the shielding element may be more prone to scorching than other areas of the container.
The combined effect of the hot spots in the microwave oven and the hot spots in the container may cause substantial overheating and/or charring of the construct. By way of example,
The tray 100 includes a substantially oval base 102, a substantially upstanding wall 104 extending upwardly from the base 102, and a cavity 106 for receiving a food item generally defined by the base 102 and wall 104. The uppermost portion of the wall 104 comprises a rim 108. A microwave energy shielding element 110 overlies a portion of the base 102 and extends upwardly along the wall 104 a substantially uniform distance (e.g., height H) from the base 102, as shown schematically by stippling in
The present inventors have determined that when the tray 100 is heated under no load conditions (i.e., without a food item) in a microwave oven, the tray 100 may tend to overheat and char in the corners 116 of the tray 100 in the areas A adjacent to the shielding element 110. Even more significant charring may occur when the tray 100 is heated under no load conditions in a microwave oven having a single mode with one of the corners 116 positioned in the hot spot of the microwave oven and/or when the tray 100 is heated in a microwave oven without a turntable. Such charring also may occur when a food item is contained in the tray, which may cause overheating and/or overdrying of the adjacent portions of the food item.
Accordingly, there is a need for a method of reducing hot spots in a microwave heating container. There is also a need for a microwave heating container that mitigates the adverse effects of hot spots in a microwave oven. There also is further a need for a container that is capable of being heated in a single operating mode microwave oven and/or a microwave oven without a turntable without being prone to substantial charring.
Other features, aspects, and embodiments of the invention will be apparent from the following description, accompanying figures, and appended claims.
This disclosure is directed to various microwave heating containers or constructs, blanks for forming such constructs, and methods for forming such blanks and constructs. The constructs may be formed partially from a generally disposable material, for example, paper, paperboard, and/or one or more polymeric materials. The constructs include one or more microwave energy shielding elements comprising a metal foil or high optical density material operative for reflecting substantially all of impinging microwave energy. Each microwave energy shielding element may be shaped or contoured as needed to minimize hot spots in the container and/or to mitigate the effect of hot spots in the microwave oven, thereby reducing charring of the construct and the adjacent food item.
In one example, the construct includes a base, a wall, and a microwave energy shielding element overlying at least a portion of the wall. The upper edge of the microwave energy shielding element is curved downwardly towards the base in the area(s) prone to charring. While not wishing to be bound by theory, it is believed that the incurved portion(s) of the microwave energy shielding element reduces the field strength and redistributes the power to other areas of the shielding element, thereby reducing the potential for overheating as compared with a microwave energy shielding element without such incurved portions.
Various other features, aspects, and embodiments of the present invention will be apparent from the following description and accompanying figures.
The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which:
This disclosure is directed to a method of reducing hot spots in a microwave heating construct (e.g., tray or other container). This disclosure is also directed to a method of mitigating the effects of hot spots in a microwave oven. This disclosure is further directed to a microwave heating construct having features that reduce the presence of hot spots in the container and/or mitigate the effects of hot spots in a microwave oven. In accordance with one aspect of the disclosure, the overheating and/or charring experienced with some microwave energy interactive constructs can be significantly reduced or prevented by modifying the shape and/or dimensions of the microwave energy interactive element(s) in the construct.
Various aspects of the disclosure may be illustrated by referring to
The construct 200 is generally elongate in shape (e.g., oval, elliptical, obround, etc.), such that the construct 200 generally includes a pair of ends 210 opposite one another and a pair of opposed lengthwise portions 212 (or side portions) between the ends 210. The base 202 and wall 204 likewise have corresponding ends or end portions and lengthwise side portions or sides (not separately labeled in the figures), with the ends of the lengthwise portions 212 of the wall 204 generally meeting at and defining corners 214 of the construct 200. However, it will be appreciated that with a construct having an at least partially curvilinear shape, it will be difficult to discern precise boundaries between the various end portions and side portions of the base and wall and the corners of the construct, and therefore, such terms are used merely to discuss the relative positions of features, and not to limit the invention in any manner. Further, it will be appreciated that the lengthwise portions 212 of the wall 204 could be characterized as individual walls that meet at and define the corners 214 of the tray 200.
As shown schematically with stippling in
The microwave energy shielding element 216 includes an upper edge 218 that is substantially uniform along the wall 204, except that the upper edge 218 includes a substantially incurved or incurvate portion 218′ that extends downwardly towards the base 202 in each corner 214 of the construct 200, such that the height H1 of the shielding element 216 in the corners 214 of the tray 200 is less than the height H2 of the shielding element 216 along the remaining portions of the wall 204. The present inventors have found that by configuring the shielding element 216 in this manner, charring of the tray 200 is substantially reduced (as compared with tray 100), even when the tray 200 is used in a microwave oven without a turntable or in a single operating mode microwave oven with one of the ends placed in the hot spot of the microwave oven. While not wishing to be bound by theory, it is believed that reducing the height of the shielding element 216 reduces the field strength along the respective portions of the shielding element 216 to minimize overheating of the construct 200, as compared with a microwave energy shielding element without the incurved portions 218′. Further, it is believed that the energy of the hot spot of the microwave oven may be distributed to other areas of the shielding element 216. For example, the energy of the hot spot may be apportioned to the areas A adjacent to the incurved portions 218′ of the shielding element 216, such that any overheating of such areas A is typically minimal. Other possibilities are contemplated.
If some cases, the microwave energy shielding element 216 may further overlie a peripheral margin of the base 202, as shown in
If desired, the shielding element 216 may circumscribe (i.e., surround or enclose) one or more microwave energy transparent areas 222 that allow microwave energy to be transmitted through the container for bulk heating of the food item. In some instances, the microwave energy transparent areas 222 may comprise apertures extending through the thickness of the microwave energy shielding element 216. In this example, the construct 200 includes a first pair of microwave energy transparent areas and a second pair of microwave energy transparent areas 222 in an opposed configuration on opposite lengthwise portions 212 of the construct 200, extending along the transitional area or “boundary” between the base 202 and the wall 204 (such that the microwave energy transparent areas 222 overlie both the base 202 and the wall 204). The microwave energy transparent areas 222 have a generally curvilinear shape, and more particularly, the microwave energy transparent areas have a generally elongate shape (e.g., obround, elliptical, oval, reniform (i.e., kidney bean shaped)). However, each of the microwave energy transparent areas 222 may be shaped, dimensioned, and/or configured within the tray 200 as needed to transmit a sufficient amount of microwave energy for bulk heating of the food item. Further, any number of microwave energy transparent areas may be used, and in some embodiments, the microwave energy transparent areas may be omitted.
Further, it is noted that in the construct 200 of
Further, if needed or desired, other microwave energy interactive elements may be included or omitted from the tray to increase or decrease the respective rate of heating of other areas of the food item proportionally so the food item is heated more evenly during the desired microwave heating cycle (i.e., time). In this example, the tray 200 includes a microwave energy directing element 224 overlying the base 202. The microwave energy directing element 224 generally comprises a plurality of metallic foil segments 226 arranged in a loop. The loop may be dimensioned to induce the resonance of microwave energy. In this example, the microwave energy directing element 224 is substantially elongate (e.g., oval) in shape and substantially centered on the base 202, such that the microwave energy directing element 224 is operative for directing microwave energy towards a center of the base 202. However, differently configured microwave energy drawing elements may be used, as needed for a particular heating application.
To use the construct 200, a food item is placed in the interior space 206 and heated in a microwave oven. The microwave energy shielding element 216 reflects substantially all of the microwave energy impinging thereon, while the upper portion of the wall 204 not covered by the microwave energy shielding element 216, the portion of the base 202 not covered by the microwave energy directing element 226, and the microwave energy transparent areas 222 allow microwave energy to pass through the container 200 to heat the food item. The microwave energy directing element 226 assists with directing microwave energy to the center of the bottom of the food item, which might otherwise be prone to underheating. The present inventors have determined that the exemplary combination and arrangement of microwave energy interactive elements 216, 226 and microwave energy transparent areas (i.e., the areas not covered by microwave energy interactive elements 216, 226, including microwave energy transparent areas 222) of
To design or make a construct according to one method of the disclosure, a construct including a conventional microwave energy shielding element may be evaluated to determine which area(s) of the construct are prone to overheating. Such areas may lie within corners of the construct or along other portions of the wall(s). The dimensions of the microwave energy shielding element then may be reduced as needed in the identified areas of the construct. For example, the upper edge of the identified area may be curved downwardly towards the base of the construct to reduce the height of the shielding element, and therefore the resulting field strength, in the respective area, for example, as shown in
For purposes of illustration, and not limitation, exemplary approximate dimensions of the blank 228 may be as follows: L1=260 mm; L2=193 mm; L3=160 mm; L4=124 mm; L5=123 mm; L6=78 mm; L7=19 mm; L8=23 mm; L9=24 mm; and L10=8.5 mm.
By way of comparison,
For further comparison,
Numerous other microwave heating constructs are encompassed by this disclosure. The constructs may have any shape, dimensions, and combination of microwave energy interactive elements. For example, although a somewhat oval construct with rounded ends is illustrated, other constructs may have the shape of a circle, obround, triangle, square, rectangle, pentagon, hexagon, heptagon, octagon, or any other suitable regular or irregular shape. Such constructs may have no distinct corners (e.g., as with a circle, which may be characterized as having no distinct corners or as comprising a continuous arrangement of corners), or may have one or more distinct corners, as with a triangle, square, or numerous other shapes. Any of such corners may be rounded in shape, and the degree of rounding (i.e., the radius of curvature) may vary for each application. Likewise, any of such constructs may have any suitable number of walls between the corners, and such walls may be substantially straight, curved, or any combination thereof. Accordingly, it will be appreciated that the location of the hot spot(s) (where present) may vary for each construct. For instance, although the illustrated construct includes hot spots at opposite ends of the construct in the corners, one or more hot spots alternately or additionally may be located along the walls or wall portions of the construct. Thus, the number and placement of incurved areas may likewise vary for each construct.
Any of such constructs 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 250° F. to about 425° F. The materials may include microwave energy interactive materials, for example, those used to form microwave energy shielding elements and other microwave energy interactive elements, and microwave energy transparent or inactive materials, for example, those used to form the remainder of the construct.
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, for example, oxides of aluminum, iron, and tin, optionally used in conjunction with an electrically conductive material. Another metal oxide that may be suitable is indium tin oxide (ITO). ITO has a more uniform crystal structure and, therefore, is clear at most coating thicknesses.
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.
The microwave energy interactive material may be used to form one or more microwave energy interactive elements or features that alter the effect of microwave energy during the heating or cooking of the food item. Such elements or features may shield a particular area of the food item from microwave energy, may direct microwave energy towards or away from a particular area of the food item, or may promote browning and/or crisping of a particular area of the food item. In doing so, the various elements reflect, absorb, or transmit microwave energy in various proportions to bring about a desired heating, browning, and/or crisping result.
In the examples illustrated schematically in
Microwave energy reflecting elements may be configured in various ways, depending on the particular application for which the element is used. Larger microwave energy reflecting elements, for example, shielding element 110, 216 may be used where the food item is prone to scorching or drying out during heating, while smaller microwave energy reflecting elements (not shown) may be used to diffuse or lessen the intensity of microwave energy. A plurality of smaller microwave energy reflecting elements, for example, elements or segments 226, also may be arranged to form a microwave energy directing element, for example, microwave energy directing element 224, to direct microwave energy to specific areas of the food item, for example, the center of the bottom of the food item. If desired, the loops may be of a length that causes microwave energy to resonate, thereby enhancing the distribution effect. While one particular microwave energy distributing element is illustrated herein, it will be understood that numerous other patterns and configuration of segments are contemplated hereby. Examples of other microwave energy distributing elements are described in U.S. Pat. Nos. 6,204,492, 6,433,322, 6,552,315, and 6,677,563.
Although particular examples of microwave energy interactive elements are illustrated in
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, for example, as discussed above in connection with microwave energy transparent areas 112, 114, 222. 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 the type of construct being formed, the food item to be heated therein or thereon, the desired degree of shielding, bulk heating, 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, or may be a non-physical “aperture”. 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 microwave energy interactive material to the particular area, or by removing microwave energy interactive material in the particular area, or by mechanically deactivating the particular area (rendering the area electrically discontinuous). Alternatively, the areas may be formed by chemically deactivating the microwave energy interactive material in the particular area, thereby transforming the microwave energy interactive material in the area into a substance that is transparent to microwave energy (i.e., microwave energy inactive). 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. The arrangement of microwave energy interactive and microwave energy transparent areas may be selected to provide various levels of heating, as needed or desired for a particular application.
The microwave energy interactive element may be supported on a microwave inactive or transparent substrate, for example, a polymer film or other suitable polymeric material (to form a microwave energy interactive “web”), for ease of handling and/or to prevent contact between the microwave energy interactive material and the food item. The outermost surface of the polymer film may define at least a portion of the food-contacting surface 236 of the container 200, as indicated in
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.
The microwave interactive element or microwave interactive web may be joined to or overlie a dimensionally stable, microwave energy transparent support or base to form the construct. In one example, the support may comprise a polymer or polymeric material. As another example, the support may comprise a paperboard material, which may be cut into a blank prior to use in the construct. The paperboard may have a basis weight of from about 60 to about 330 lbs/ream (lbs/3000 sq. ft.), for example, from about 80 to about 140 lbs/ream. The paperboard generally may have a thickness of from about 6 to about 30 mils, for example, from about 12 to about 28 mils. In one particular example, the paperboard has a thickness of about 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.
In another aspect, where a more flexible construct is to be formed, the support may comprise a paper or paper-based material generally having a basis weight of from about 15 to about 60 lbs/ream, for example, from about 20 to about 40 lbs/ream. In one particular example, the paper has a basis weight of about 25 lbs/ream.
It will be understood that with some combinations of elements and materials, the microwave energy interactive element(s) may have a grey or silver color that is visually distinguishable from the substrate or the support. However, in some instances, it may be desirable to provide a package having a uniform color and/or appearance. Such a package may be more aesthetically pleasing to a consumer, particularly when the consumer is accustomed to packages or containers having certain visual attributes, for example, a solid color, a particular pattern, and so on. Thus, for example, the present disclosure contemplates using a silver or grey toned adhesive to join the microwave energy interactive element to the support, using a silver or grey toned support to mask the presence of the silver or grey toned microwave energy interactive element, using a dark toned substrate, for example, a black toned substrate, to conceal the presence of the silver or grey toned microwave energy interactive element, overprinting the metallized side of the polymer film with a silver or grey toned ink to obscure the color variation, printing the non-metallized side of the polymer film with a silver or grey ink or other concealing color in a suitable pattern or as a solid color layer to mask or conceal the presence of the microwave energy interactive element, or any other suitable technique or combination of techniques.
The blank 228 may be formed into the tray 200 or other construct in any suitable manner including, but not limited to, various thermal, mechanical, or thermomechanical techniques or devices, or any combination of such techniques and/or devices. Some of such techniques may include press forming techniques, injection molding, adhesive bonding, thermal bonding, ultrasonic bonding, mechanical stitching, or any other suitable process. In the example illustrated in
Further, any of the various components used to form the construct may be provided as a sheet of material, a roll of material, or a die cut material in the shape of the package to be formed (e.g., a blank). For example, as mentioned above, the microwave energy interactive elements 216, 224 may be part of a microwave interactive web (e.g., the microwave energy interactive elements 216, 224 may be supported on a polymer film). In this regard, the tray 200 may be formed by mounting such a microwave interactive web (e.g., which includes a polymer film that carries the microwave energy interactive element 216, 224) within, or otherwise to, a previously formed container (not shown), such as, but not limited to, a previously formed container (e.g., tray) formed from a polymer or polymeric material, as described in U.S. Patent Application Publication No. US 2007-0215611 A1, published Sep. 20, 2007. Also,
While the present invention is described herein in detail in relation to specific aspects and embodiments, 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 and to set forth the best mode of practicing the invention known to the inventors at the time the invention was made. The detailed description set forth herein is illustrative only and 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. 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 present 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. Further, various elements discussed with reference to the various embodiments may be interchanged to create entirely new embodiments coming within the scope of the present invention.
This application claims the benefit of U.S. Provisional Application No. 61/134,619, filed Jul. 11, 2008, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61134619 | Jul 2008 | US |
