Patent Application
20100230403
The invention relates to microwave cooking containers comprising shielding from microwave energy. In particular, the invention relates to microwave cooking containers providing improved even heating throughout food that is disposed in the containers, upon cooking in a microwave oven.
Microwave cooking has long been employed to conveniently and quickly cook comestibles, such as comestibles stored at ambient, refrigerated or frozen temperatures. A common disadvantage of microwave cooking of foods and beverages is uneven heating throughout the container. For instance, the outer edges of a food product typically heat faster than the center of the food product. It would therefore be desirable to provide a way to prevent microwaves from acting on selected areas of a product placed in a microwave oven. By preventing or reducing the amount of microwave energy that reaches the product, the amount of energy that is absorbed by the product can be influenced, thus controlling the rate of heating of the product.
Various previous efforts to provide shielding of microwave energy from portions of a container increased the risk for arcing or sparking during microwave cooking, due to the use and configuration of metallic shielding material with microwave containers. In addition, microwave containers for foodstuffs typically include instructions for consumers regarding microwave timing and power, as well as whether or not to peel back or puncture the lidding. However, not all consumers read or follow the instructions precisely, and altering the location of some microwave shielding elements may result in a potentially dangerous configuration of shielding elements. Thus, it would be desirable to provide microwave shielded containers that do not pose a risk of arcing or sparking even if the consumer does not completely comply with the instructions.
An aspect of the invention is directed to a container comprising at least one compartment for holding food comprising a base comprising a shape having a perimeter, and a plurality of sidewalls extending upwardly from the perimeter of the base at an angle therefrom. The at least one compartment comprises a first shield comprising a material opaque to microwave energy disposed on an inner or outer surface of the base and the plurality of sidewalls. The first shield optionally defines an aperture centered on the base, wherein the aperture comprises the same shape as the base. The container further comprises a lidding configured to be sealed on the at least one compartment, the lidding comprising a second shield comprising a material opaque to microwave energy. The second shield may be disposed on the lidding at a predetermined distance from the plurality of sidewalls, or alternatively may cover substantially the entire lidding.
Another aspect of the invention is directed to a container comprising a first compartment comprising a material substantially transparent to microwave energy, a first shield comprising a material substantially opaque to microwave energy disposed on an inner or outer surface of the compartment, and a lidding configured to seal the first compartment, the lidding comprising a second shield comprising a material opaque to microwave energy. The container further comprises a second compartment at least partially surrounding the first compartment, for instance completely surrounding the first compartment. Alternatively, the container comprises a third compartment, in which the second and third compartments each partially surround the first compartment.
A partially shielded microwave container may be employed for heating a shelf-stable, cold or frozen foodstuff in a microwave oven. The application of strategic shielding of only select areas of the product will allow only certain portions, for example a frozen meal, to heat to a higher temperature than that of other portions. By incorporating shielding into the packaging of a shelf-stable, refrigerated or frozen foodstuff, different types of food may be cooked in the same tray with different degrees of heating for each separate food such that each of the foods finish cooking at the same time.
It was discovered that providing two or more microwave energy shields on a single container or container compartment can synergistically provide more even cooking throughout a foodstuff disposed in the container than in an unshielded compartment or a compartment without the specific arrangement of the shields. In particular, it was discovered that shields that reflect microwave energy may be employed to redirect portions of the microwave energy to result in the more even heating of the foodstuff. Moreover, the arrangement of the microwave energy shields poses little to no risk of causing sparking or arcing within a microwave oven during cooking
In an embodiment, a microwave container is provided comprising a material that is substantially transparent to microwave energy or radiation. Any suitable microwave transparent materials may be employed, such as are known in the art. For example and without limitation, crystalline polyethylene terephthalate (CPET) amorphous polyethylene terephthalate (APET), polypropylene (PP), high density polyethylene (HDPE), organic filled polypropylene, paperboard and paper laminations are commonly employed to form containers for microwave cooking of foodstuffs.
A microwave container or package may be provided comprising materials opaque or at least substantially opaque to microwave energy, and therefore will shield portions of a product disposed within the container or package from being exposed to the full amount of microwaves to which other portions of the product are exposed. The package comprises a substance or layer that will reflect, block or absorb the microwaves before they can reach the area of the product that needs to be protected. This blocking substance is defined herein as a “shield.” Any suitable material that is capable of reflecting, blocking, and/or absorbing microwave energy or radiation may be employed as a microwave shield. Such shielding materials may comprise, for example and without limitation, metal, metallic foil, and alloys. A common material for use as a microwave shield is aluminum, such as aluminum alloy 800616, however the shield can be any metal, metal alloy or nonmetal material that effectively blocks, reflects or absorbs microwave energy.
As discussed above, a microwave shield is configured to reflect, block, and/or absorb at least a portion of the microwave energy directed at a container in a microwave oven. In certain embodiments, a first microwave shield is provided in a shape that substantially conforms to the outer structure of at least a portion of a container. Referring to
The microwave tray 140 shown in
In the embodiment shown in
In certain embodiments, the first shield covers the entire base of the compartment and thus does not comprise an aperture. Such a configuration is selected for applications in which a foodstuff has a low specific heat capacity and thus requires greater shielding than foods having a higher specific heat capacity. As used herein, the term “specific heat capacity” is defined as the amount of energy required to raise the temperature of a unit quantity of food by one unit, such as to raise the temperature of one gram of food by one degree Fahrenheit. When a first shield is provided covering the entire container base, microwave energy may enter the container through other, unshielded areas, of the container. For instance, the container may comprise a horizontal or vertical gap between the upper edge of the first shield sidewalls and the outer edge of the second shield.
Similar to the first compartment 150, the tray 140 comprises a second compartment 144 that comprises a base 151 having a shape defined by a perimeter of the base 151. The base 151 comprises one or more sidewalls 153 extending upwardly from the perimeter of the base at an angle therefrom, and having an upper edge 157, the second compartment optionally consisting essentially of one or more materials transparent to microwave energy. The angle may range between about 60 degrees and about 135 degrees with respect to the base, such as about 90 degrees. The one or more sidewalls 153 of the second compartment 144 further comprise an optional lip 155 extending radially from the upper edge 157 of the sidewalls 153. The presence of a lip 155 provides a convenient surface to which a lidding 146 may be adhered or sealed once the compartments have been filled.
In embodiments of the invention, a container may comprise any number of compartments comprising a base and sidewalls as described for tray 140. Any shape suitable for containing materials such as foods may be selected for the one or more compartments. For example and without limitation, geometrical shapes such as rectangles, ovals, circles, squares, trapezoids, semi-circles, triangles, and concentric rings may be suitable for the one or more compartments. Referring to
Referring to
The lidding 146 comprises any suitable, substantially microwave transparent material for sealing microwave containers once a foodstuff has been disposed within the container or container compartment. Typical materials employed as lidding include, for example and without limitation, heat sealable polymeric films, paper, and paperboard laminations. A few examples of heat sealable polymeric films include Toray Lumilid XL5, which comprises heat sealable polyester, Dupont RL31, which comprises biaxially oriented polyester with an ethylene vinyl acetate heat seal layer, and a sealable polyethylene terephthalate/ethylene vinyl acetate film structure. Suitable lidding material should be easy to attach to the container, provide sufficient abrasion and puncture resistance to maintain the integrity of the package during transport, storage and handling, and be easily removed by the consumer.
In certain embodiments, a microwave container may be provided configured generally opposite or upside-down, as compared to the containers of
As noted above, it was discovered that disposing two or more microwave energy shields on a single container or container compartment can synergistically provide a more even cooking of a foodstuff disposed in the container than in a container or container compartment that does not comprise the particular arrangement of the shields. In general terms, a two-shield system comprises one shield disposed on a container compartment (e.g., the foil shield 142 on the first compartment 150) and a second shield disposed on the lidding of the container (e.g., the second shield 152 on the lidding 146). In certain embodiments, the shapes and locations of the first and second shields are substantially complementary: the first shield defines a center aperture, whereas the second shield is located in the center on the opposite side with a gap between the outer edges of the second shield and the perimeter of the container compartment. It was discovered that the first shield works to absorb, transmit and reflect microwave energy from an opposing direction compared to the second shield on the contrasting location of the container. With the combination of the first and second shields of this configuration interacting together, uniform heating is achieved.
In certain embodiments, the first and second shields reflect the microwave energy that enters the container through the unshielded areas to effectively redirect the microwave energy within the container to result in the more even heating of the foodstuff. This is believed to be due to the configuration of the shields that results in energy being allowed to enter the container or container compartment only from the selected direction(s), which evenly controls the rate of heating of a food product.
Moreover, the complementary arrangement of the microwave energy shields poses little to no risk of causing sparking or arcing within a microwave oven during cooking. In particular, it was discovered that keeping the first and second shields independent of each other and at a sufficient distance minimizes the potential for arcing between the shields and possibly resulting in a fire within the microwave oven. During cooking, energy on the shields may build up to an amount of over 3000 volts. Without wishing to be bound by theory, it is believed that when similar pieces of metallic shielding come into close contact, the air molecules may be disrupted and break down, which in turn allows the water molecules to achieve a plasma state. The plasma produces a conductor between two separate shields, thus resulting in an arc or spark bridging the gap between the two shields. Close proximity of the edges of microwave energy shields therefore provides a greater likelihood of sparks leaping between the shields.
Experiments with the location of first and second microwave shields were performed to investigate if food weight and food distribution throughout the microwave container could further act as a significant factor in sparking. It was discovered that sparking is more prone to happen where there is little to no food, such as in the event food contents have shifted towards the front of the container and solidified, leaving the back portion of the container substantially bare of food. This increase in risk of sparking is due to the higher mass amount of microwave energy being reflected, absorbed, and transmitted by the microwave energy shield, as compared to when energy is being absorbed by food located at the back portion of the container. Accordingly, it is preferable to provide an evenly filled microwave container or compartment.
The second shield may interact with the sidewalls of the first shield, such as sidewalls having a height of three quarters of an inch, or one and one-quarter inches, disposed over a container compartment having sidewalls that are approximately one and one-quarter inches tall. Although some microwave shield interaction was evident all around the shielded compartment, the areas of most concern for potential sparking include the corners of the second shield and sidewalls of the first shield having a height of three quarters of an inch. This concern was caused by the capability of the sidewalls of the first shield to readily transfer energy to and melt the sidewalls of a CPET microwave container, in the event that the food load is not sufficient to absorb enough of the microwave energy. Consequently, for embodiments in which the sidewalls of the first shield are not as high as the sidewalls of the container compartment, it is important to provide an evenly distributed food load that comprises a sufficiently high specific heat capacity, to absorb enough of the microwave energy to prevent significant energy transfer to the container sidewalls such that the sidewalls exhibit damage from the transfer of energy.
The location of the second shield is important, as if it is placed off-center and located close to or in contact with the compartment sidewalls, the second shield may be subject to sparking during cooking in a microwave oven. It was discovered that if the second shield is directly lined up with a sidewall of the first shield, there is a significantly greater potential for arcing through the microwave container. Moreover, if the second shield were to be placed off-center or to extend to the sidewall edges of the container and/or the first shield, there would be a higher risk of sparking if more than one of the same type of microwave container were placed together within a microwave. Placing two containers adjacent together and each having such second shields, the two second shields may come into contact with each other if located side by side, and potentially provide sparking between the second shields. Experiments showed that sparks were created when two containers comprising second shields extending to the sidewall edges of the container were placed touching or up to a half of an inch apart, but not when placed farther than half an inch apart.
To avoid potential sparking were a consumer to place two microwave containers having such a shielding configuration too close together in a microwave oven, it would instead be desirable to provide a microwave container that does not pose a risk of sparking regardless of how the consumer positions one or more containers in a microwave oven. A microwave container comprising a second shield centered on the lidding and having a gap of at least one quarter of an inch between the perimeter of the second shield and the sidewalls of the container, and/or the sidewalls of the first shield, has a lower probability of sparking because the second shield is located at a distance from the sidewalls, so there can be no interaction between the two second shields if two of the same microwave containers were put in the microwave oven at the same time. Indeed, experiments testing microwave cooking of such containers placed next to each other resulted in no instances of sparking between the containers.
As noted above, it is a possibility that a consumer will misunderstand or simply not follow the microwave cooking directions for a microwave container, thus it is important to provide containers configured to avoid sparking even when the instructions are not executed correctly. For example, a consumer could pull off the lidding, realize that it was supposed to remain attached, and then replace the lidding loosely over the container. Experiments were performed on microwave containers having different configurations, in which the lidding was removed and then placed back over the container. For a microwave container comprising a first microwave shield with sidewalls having a height of three quarters of an inch and an aperture in the base, as well as a second microwave shield extended to the container sidewalls, this experiment resulted in a fire within the microwave oven. In contrast, no fires or sparks were observed when this experiment was performed using a microwave container having a first microwave shield with sidewalls having a height of one and one-quarter inches (i.e., the same height as the container sidewalls) and an aperture in the base, as well as a second microwave shield centered on the lidding and located at a distance of one half of an inch from the container sidewalls.
Even though there was a vertical gap of half of an inch between the sidewalls of the first shield and the outer edge of the second shield, sparking and fires were still achieved upon exposure to microwave energy. Surprisingly, it was discovered that a horizontal gap of one half of an inch provides less of a risk of arcing and sparking of the shielded containers. Moreover, inclusion of an optional lip, which extends radially from the upper edge of the sidewalls further decreases the risk of sparking. As noted above, for microwave containers having a vertical gap between the first and second shields, the placement and specific heat capacity of the foodstuff within the microwave container play an important role in minimizing the risk of arcing and sparking of the shielded containers.
It is possible that the second shield will not remain properly affixed to the lidding during manufacturing or distribution, for instance resulting in the second shield to be rolled up on itself. Experiments with both of the above-described shielding configurations having a second shield rolled up on itself resulted in no observed fires and/or sparking for the container having a horizontal gap between the two shields, whereas a fire started on the edge of the sidewall of the container having a vertical gap between the two shields.
An example of incorrect handling of the inventive microwave shielded containers is for a consumer to poke holes in the lidding to vent heat and/or steam during microwave cooking Experiments with both of the above-described shielding configurations resulted in no observed fires as a result of forming holes in the lidding. A further example of incorrect handling is for a consumer to partially peel off the second shield from the lidding, thinking that the second shield is supposed to be removed. Experiments with both of the above-described shielding configurations resulted in observed fires and sparking for the shield configuration having a vertical gap between the two shields, but not for the preferred shield configuration having a horizontal gap.
Embodiments of the invention successfully accomplish redirecting of microwave energy, resulting in shielding of a one or more compartment container. With the redirection of microwave energy, the presence of the shields results in a more even heating of a shelf-stable, refrigerated or frozen food product. In addition, a shielded compartment may be paired with a hot compartment to provide a multi-temperature microwavable meal. With the pairing of the invention and a food product, embodiments of the invention are capable of controlling the rate of heating of specific compartments to a desired temperature range, dependent on the food product. It will be appreciated by one of skill in the art that the dimensions of the microwave container, compartments, and shields can and will be changed to fit a specific food product to allow proper microwave energy to penetrate, thereby providing appropriate heating rates.
A foodstuff having a lower specific heat capacity typically has a faster microwave cooking time than the other foods exhibiting a higher specific heat capacity. In an embodiment, to allow different types of foods to cook in a microwave oven to approximately the same temperature following exposure to microwave energy, a faster-cooking food may be disposed in a container compartment positioned amongst or in between slower-cooking foods. Such an arrangement takes advantage of the phenomenon that the foodstuff located in the center of a microwave container cooks more slowly than foodstuff located closer to the peripheral edges of the container.
Referring to
Referring to
The following examples are illustrative of embodiments of the present invention, as described above, and are not meant to limit the invention in any way. As discussed above, various configurations of microwave shields may be provided on a microwave container to provide even heating of food disposed within the container. Experiments were thus conducted to determine the effects of varied sizes and locations of shielding on the outside of the cooking container on temperature of different types of foodstuff.
The experiments of Example 1 were performed on a microwave container comprising CPET as the microwave-transparent container material and aluminum foil as the shielding material. The microwave container tested comprised a two-compartment container having the general shape shown in
After three minutes and fifteen seconds of cooking in an 805 watt Pansonic microwave oven, the temperature of the applesauce was measured, at three depths at each of five locations within the dish.
The experiments of Comparative Example 2 were performed on a microwave container having the same configuration as Example 1, except that no microwave shields were provided on the container. Applesauce was placed in the shielded compartment, the lidding was affixed to the top of the container, and the entire container was frozen. Next, the frozen shielded container was removed from the freezer and placed in a microwave oven. After three minutes and fifteen seconds of cooking in an 805 watt Pansonic microwave oven, the temperatures of the applesauce was measured, at the three depths at each of the same five locations within the dish as Example 1.
Consequently, the results of Example 1 and Comparative Example 2 demonstrated that the microwave shielding of Example 1 is capable of providing a significant improvement in the evenness of heating throughout a container cooked in a microwave oven.
The experiments of Example 3 were performed on microwave containers comprising CPET as the microwave-transparent container material and comprising aluminum foil as the shielding material. Each microwave container tested comprised a first shield of varied size and location on the outside of a two-compartment container having the general shape shown in
For each shielded container, applesauce was placed in the shielded compartment, macaroni and cheese was placed in the unshielded compartment, a lidding was affixed to the top of the container, and the entire container was frozen. Next, each frozen shielded container was removed from the freezer and placed in a microwave oven. After three minutes and fifteen seconds of cooking in an 805 watt Pansonic microwave oven, the temperatures of the foodstuff were measured.
The experiments of Example 4 were performed according to the materials and procedures of Example 3, except that each frozen shielded container was cooked for three minutes and forty-five seconds in a different 805 watt Pansonic microwave oven.
In the microwave container of Example 5, a multi-compartment container was configured to position high specific heat capacity foodstuff in two outer compartments on either side of a central compartment, as shown in
In the microwave container of Example 6, a multi-compartment container was configured to provide a high specific heat capacity foodstuff in a round dish, concentrically surrounding an inner round dish, as shown in
While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. Variations and modifications of the foregoing are within the scope of the present invention. It is also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.
This application claims priority to provisional U.S. Application Ser. No. 61/209,916, filed Mar. 11, 2009, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61209916 | Mar 2009 | US |
