Patent Application
20100072196
1. Technical Field
The present invention relates to a food package that vents in a controlled manner when it is heated in a microwave and method of making the same.
2. Description of Related Art
The snack food industry markets some snack foods in food packages that comprise a base and a lid sealed onto the base. The base generally comprises a bowl or other liquid retaining shape with a rim, and a lid is typically sealed along the rim of the base. Foods that are sold in such packaging include chili, soup, cheese sauce, salsa, dips and other mixtures of solid and/or liquid food products. Foods that are packaged in this way are often consumed directly from the base after the lid is removed.
Additionally, many such packaged foods are intended to be consumed at elevated temperatures, and the most convenient method of heating them is in a microwave oven. The microwave oven is an appliance that can be found in many homes and businesses. During operation, a microwave oven floods the cooking chamber with non-ionizing microwave radiation, usually at a frequency of about 2.45 GHz. Many food molecules (for example water molecules) are electric dipoles, which means they are positively charged at one end and a negatively charged at the other end. As the microwave radiation passes through the food, the dipole molecules rotate as they try to align themselves with the alternating electric field of the microwaves. This rotation and movement causes the food to heat up as the rotating molecules impact other molecules, putting them into motion. Microwave heating is highly efficient on liquid water (which a relatively polar molecule), and much less so on fats and sugars (which are less polar).
However, placing into a microwave and heating a scaled food package described above with a water-containing food or food product inside causes serious problems. Most such packaged foods are packaged with a “headspace.” The headspace is the region between the food inside the food package and the lid. The headspace will absorb moisture from the food inside the package, and during microwave heating the air in the headspace tends to heat up very quickly. This heated air, in turn, expands and increases the pressure level inside the food package. Once enough pressure had built up inside the food package to a large enough degree, the sealant between the lid and the base fails rapidly and the food package vents uncontrollably. The result is usually a loud, explosion-like sound accompanied by the ejection of food from the package and onto the walls of the microwave oven.
The main solution to this problem in the prior art is to provide instructions to the consumer to vent the food package before heating it in the microwave. This approach is problematic for several reasons. First, the consumer may not vent the food package as instructed because he or she did not read, forgot to follow, or chose not to follow the instructions provided. Second, in the case of several different food product packages being bundled and sold together with the intention of being heated and consumed together, the consumer would be required to disassemble the food package bundle, vent each food package individually, and reassemble the bundle before heating them together. In any case, the consumer is inconvenienced by this prior art solution.
Consequently, a need exists for a food product package that vents in a controlled manner when heated in a microwave oven.
The present invention places a microwave susceptor in radiant communication with the lid used to seal the food package. In one embodiment, the susceptor heats and weakens the sealant that holds the lid onto the base at a predetermined location, allowing the failure of the lid during microwave heating to occur in a controlled fashion. In a preferred embodiment, the susceptor is placed on top of the material that comprises the food package above the sealant via an adhesive microwave susceptor tab. In another embodiment, the susceptor is incorporated into the food packaging material adjacent to the sealant. In still another embodiment, the susceptor is located on or integral to the lid at a location within a perimeter defined by the sealant. In another embodiment, the food package comprises a flexible sleeve incorporating a microwave susceptor in radiant communication with the lid and/or sealant.
Optionally, in one embodiment, at least one flap guard can be included at the edge of the food package, as a part of the flexible sleeve, near the susceptor. Including a flap guard further reduces the likelihood that the venting food package will spray food particles onto the walls of the microwave.
The resultant food product package is relatively simple and inexpensive to manufacture, yet overcomes the problems in the prior art by allowing the food package to vent in a controlled fashion during heating in a microwave oven. The above as well as additional features and advantages of the present invention will become apparent in the following written detailed description.
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein:
The present invention is directed towards a food package that, when heated in a microwave, vents in a controlled fashion, and method of making the same. The term “food package” as used herein is defined as a package designed to contain food inside of it. In its broadest sense, the “package” portion of the food package generally comprises at least one wall and at least one seal. The type of food package that usually undergoes microwave heating before the food inside is consumed comprises a sturdy, bowl-shaped base with a lid sealed to the rim of the base. However, the principles of the present invention in its broadest sense are applicable to any food package containing a seal that is likely to rupture in an uncontrolled fashion while the food inside is being heated by a microwave oven.
Referring to
Many commercial food processors subject food packages to a retort process in order to sterilize the package and the food inside. During the retort process, the food package is heated to temperatures between about 250° F. and about 260° F. for at least 30 minutes. The seal 40 created by most retort grade heat activated sealants used in the food packaging industry, therefore, is typically capable of surviving the high temperatures and potential pressure spikes that can occur during sterilization procedures. The seal 40 is so strong that, when it does fail during microwave heating, it tends to fail violently and uncontrollably due to the high levels of heat and pressure that have built up inside the headspace of the food package. This violent and uncontrolled failure is typically accompanied by a loud explosion or popping sound, and in some cases by the ejection of food from the food package at the point of failure. Experimental results have shown that the violent failure of the food packaging seal can occur after about 30 seconds to about 45 seconds of heating.
The present invention allows food packages that would otherwise suffer uncontrolled venting during microwave heating to vent in a controlled fashion. Controlled venting is accomplished by providing a microwave susceptor as a part of the food package on or near one wall of the food package, preferably the lid, which causes the lid to fail at a known location before substantial heat and pressure have built up inside the headspace of the food package. A microwave susceptor, as that term is used herein, is defined as a material that has the ability to absorb microwave radiation and convert it into heat. This heat is then transferred to any surface adjacent to or near the susceptor, causing that surface to heat up. Conversion of microwave energy to heat in this maimer has been used for microwave heating foods which require crust browning, such as frozen pizzas. Microwave susceptor materials that can be used in accordance with the present invention are well known in the art, and are described in U.S. Pat. Nos. 5,107,089 and 4,833,007 (the disclosures of which are incorporated herein by reference) among many others.
The susceptor is typically gray or blue-gray in color, and is usually made of ceramics or metals (aluminum, nickel, antimony, copper, molybdenum, iron, chromium, tin, zinc, silver, gold, and various alloys of these metals) or both. In one embodiment, the susceptor is created by physical vapor deposition of aluminum onto a polyester film. Physical vapor deposition is a method of depositing aluminum onto polyester film that is generally well known in the industry. However, many different types of metals and ceramics and polymer films can be used to create a susceptor that can be used in accordance with the present invention.
In the present invention, this heat energy radiated by the susceptor is used to weaken the lid at a specific location. In one embodiment, the susceptor location corresponds to the sealant that holds the lid onto the base, and weakens the lid's adherence to the base by heat weakening, or softening, the sealant between the lid and the base. Thus, the susceptor is in radiant communication with the sealant. In another embodiment, the susceptor is in radiant communication with the lid, thereby causing a portion of the lid to melt and controllably fail. As used herein, the term “radiant communication” between a susceptor and a sealant or a lid is defined as the orientation of the susceptor and the sealant or lid being such that heat radiates (or transfers, typically by conduction) from the susceptor surface to the sealant or lid as the susceptor absorbs microwaves. For a seal created using a polypropylene based sealant, typically the sealant will controllably fail when it is heated to a temperature above 280° F., and preferably to a temperature between about 280° F. and about 300° F. At the time of controlled failure, the pressure inside the food package is, in one embodiment, between about 1 psi and 15 psi. For other types of heat activated sealants, and for different types of polymer films used to make the lid, different temperatures and pressures may be required to weaken it enough to allow it to fail in a controlled fashion.
The embodiments depicted in
