Patent Application
20090257687
The present invention relates to packaging. More specifically, the present invention relates to a laminated package usable in microwave cooking applications.
While once relegated to heating up leftovers and popping an occasional bag of popcorn, microwaves have now become a cooking staple in many homes. Whether making an entire meal or zapping a side dish, microwaves provide a quick and easy alternative to conventional cooking methods.
Although generally quicker and easier than conventional cooking, microwave cooking is not without its drawbacks. Microwaves tend to dry out food that should be moist and tend to soften foods that should be crisp. As a result, some flavor and appeal may be lost when cooking in the microwave. Moreover, the microwave product may lose some of the nutritional value of its conventionally cooked counterpart.
To combat the above-described problems associated with microwave cooking, several products and methods have been tried. For example a number of packages have become available that are designed for microwave cooking. In most applications, the packaging is relatively standard packaging for a frozen product, i.e., it is designed to be stored in the freezer with foodstuffs therein, but can then be transferred to the microwave for cooking. Such packages consist of a thermoplastic laminate having multiple layers of thermoplastic materials.
In the conventional packaging, foodstuffs contained within the package contact one of the thermoplastic layers. However, when certain products are prepared in these conventional packages, particularly products having high moisture content and/or having sauces or spices included for flavoring, the heated-up products contacting the thermoplastic deform the thermoplastic. This deformation may be manifested as scorch-marks, marring, bubbling, charring or the like. This deformation of the thermoplastic may or may not create a food contamination problem, but at the very least, the visual effect of the bubbled, melted plastic is unappealing to a user. In fact some users assume the product is bad based on the visual deformities and may refuse to eat the product, or worse, refuse to again buy the product.
Accordingly, there is a need in the art for an improved package designed for microwave cooking. There is a need in the art for a package in which foodstuffs can be frozen and subsequently cooked in a microwave. There also is a need in the art for a microwave cooking package that effectively cooks the foodstuffs contained therein without damaging the foodstuffs or the package.
The present invention addresses the foregoing needs in the art by providing an improved package for microwave cooking. It is also contemplated that the packaging could be used in other types of cooking, for example, cooking in a conventional oven
In one aspect of the present invention, a package includes an inner ply and an outer ply laminated to the inner ply. The inner ply contact foodstuffs contained within the package. The inner ply is a paper-based product having a wet tensile strength property such that it will not deteriorate in the presence of high-moisture foods. The paper-based product also has a scorching temperature above the temperature of the foodstuffs when heated. The outer ply includes a polymer film.
In another aspect, a multi-layer package for use in cooking foodstuffs includes an inner ply, an outer ply, and a vent. The inner ply contacts the foodstuffs and is a paper-based product having a scorching temperature above a maximum temperature reached by the foodstuffs during microwave heating of the foodstuffs. The outer ply is laminated to the inner ply and is a polymer film. The vent is disposed in the pressure to relieve pressure within the package during microwave cooking.
These and other aspects and objects of the invention will be apparent from the following description and attached figures, in which preferred embodiments of the present invention are described and depicted.
As described above, many commercial packaging products used for storing and subsequently microwaving food products are known. A conventional package 10 is illustrated in
An improved microwave-cooking package 20 according to a first embodiment of the invention is illustrated in
The inner ply 22 preferably is a paper-based layer and the outer ply 24 preferably is a polymer film or a thermoplastic. The paper-based product used to form the inner ply preferably is one of Kraft paper, bleached Kraft paper, parchment paper, greaseproof paper, glassine paper, rice paper, or cellophane. Although not limiting to this disclosure, the inventor has conducted tests with the following commercially available papers: Reynolds parchment 10900-01331, Fox River WOGR, and Wausau Nos. GG 243W00, GN404838, GF323182, GF235174, GN214933, and GF205204.
Preferably, the paper product comprising the inner ply 22 has a wet tensile strength between about 10% and about 50%. More preferably, the wet tensile strength of the inner ply is between about 20% and about 30%. The inventor has found that when the inner ply is formed of a paper product having a wet tensile strength that is less than about 10%, the package will deteriorate, particularly when higher moisture foods, namely foods having a moisture content of between about 65% and about 85% are contained in the package. Preferably, the package of the invention can be used with foods having moisture contents in this range, and more preferably with foods in the range of about 70% to about 75% moisture content. Paper products having higher wet tensile strength products also can be used, although such paper products tend to be more expensive.
The paper-based product comprising the inner layer 22 preferably also is characterized in that it has a scorching temperature that is above a maximum temperature the foodstuffs contained within the package will reach during cooking. Accordingly, burning or charring of the inner ply 12 will not occur when the package is heated in the microwave. Preferably, the scorching temperature of the inner layer is above about 290° F.
The package 20 according to the foregoing description is particularly well-suited for use with foodstuffs having high-moisture content resulting from their inclusion of sauces or excess water used for steaming the product. As a result of their high-moisture content, when the products contained within the package 20 are heated, steam is created that inflates the package. The package according to the present invention preferably includes a venting mechanism that allows the steam to be exhausted before the package becomes deformed or, in an extreme case, explodes.
In one example, venting is partially accomplished by virtue of the characteristics of the inner ply. Specifically, the porosity of the paper product comprising the inner ply is such that the steam generated in the package can escape through the pores in the paper. For example, paper products having a porosity of between about 29 and about 15,000 sec/100 ml are believed to be effective in such an embodiment. Once through the paper-based inner ply, the steam preferably is then vented out an opening formed between the inner ply and the outer ply or through the outer ply.
The outlet may be always open to the atmosphere, or it may be selectively opened. For instance, the outlet 28 may include a seal that is sealed until some event occurs to open or break the seal. The seal may be resealable, or it may be a single-use seal. In one preferred embodiment, the seal is pressure activated such that when sufficient pressure builds up behind the seal, the seal will open and allow excess steam to escape. In this manner, the venting mechanism acts as a bleed valve behind which a relatively large amount of pressure must build up before any of the pressure is bled off. When minimal steam is desired in the package, the seal may open at a relatively low pressure, whereas when it is desirable to maintain an amount of the steam in the package during cooking, for example, to steam the contents of the package, the seal opens at a relatively higher pressure.
The seal comprising the outlet may be formed in a number of ways. For instance, the seal may be formed by including a one-way valve at the outlet which allows steam to exhaust. In another embodiment, an adhesive is used that creates a temporary bond between the inner ply and the outer ply at the outlet. The bond is temporary in that a sufficient force, i.e., resulting from an elevated pressure, in the channel upstream of the bond will overcome the adhering force of the adhesive, thus causing the bond to break. The inner ply and the outer ply thus separate and steam exhausts. The bond preferably is sufficiently strong that the bond is sealed at all times other than cooking, for example, to prevent leaking from the package and/or to prevent contaminants from entering the package.
In another embodiment, a temporary bond also may be formed to close the channel, but the bond in this embodiment comprises a heat seal that is broken at a predetermined temperature obtained by the package and/or the contents within the package, i.e., a predetermined venting temperature. Specifically, the outlet includes a heat seal that melts or de-adheres when the package and/or the contents of the package reach the venting temperature. The heat seal may consist of a pattern in which the adhesive between the inner and outer plies is arranged. The heat seal could comprise more than just the outlet 28. In fact, the heat seal could form any or all of the channel 26. As will be understood, steam will only pass through the heat-sealed portion of the package when a sufficient temperature is reached to open the heat seal.
In the embodiments described above, steam passes through the inner ply of the laminate packaging material through pores inherent in the inner ply. Alternatively, the inner ply may be perforated or otherwise manufactured to include pores, for example, micropores. In another embodiment, a slit or similar opening may be formed through the inner ply in communication with the channel 26.
In yet another embodiment of the invention, the porosity of the paper is sufficiently low that steam will not permeate the paper. In this embodiment, a different venting mechanism preferably is provided that selectively allows and prohibits passage of steam there through, i.e., to selectively vent steam from or retain steam in the package. An exemplary configuration of this embodiment is illustrated in
In yet another embodiment of the invention, instead of using a channel through which steam escapes to an outlet, an aperture may be formed directly through all plies comprising the package, and steam is allowed to vent through this aperture. The aperture may be completely open during cooking, for example, a tab could be applied to cover the whole prior to use, which tab is removed by a user prior to cooking. Alternatively, the aperture may uncover during the cooking process. For example, a cover may cover the aperture by virtue of a heat sensitive adhesive that melts during cooking. The melting of the adhesive combined with the pressure within the container forces the aperture to become uncovered, thereby venting the package.
Any number of adhesives may be used to seal the package, to laminate the layers, and/or to create the destructible heat seal. Specifically, the invention contemplates the use of water-based, solvent-based, hot melt, and solventless adhesives Some commercial adhesives tested by the inventor include H. B. Fuller WC 3460 ZZ; H. B. Fuller PWF-3007; Royal 20394; Royal 20123; Hycar 26288; Hycar 26315; Dow Primacor 5986, 5990, 59801, and 59901; and Dow Hypod™ DPOD 4501 and 8501. As should be appreciated, any adhesive that could contact the food stuffs contained within the package should preferably be safe for human consumption.
As described above, the preferred package according to the invention is formed by laminating two layers or plies. The lamination preferably is maintained using an adhesive. Solvent-based, solvent-free, and water-based adhesives are known in the art, and may be used to bond the plies 12, 14. The inventors have found, however, that water-based adhesives may be less desirable when the product contained in the package has a relatively high moisture content, as the water-based adhesives tend to re-liquefy during heating, thus resulting in delamination of the plies. The above-mentioned adhesives also may be used to form the vents and/or heat seals described above.
As noted above, the outer ply preferably is a polymer film. Such films are generally preferred for the outer ply because their appearance, especially when printed on, is preferable. As described above, the polymer film preferably is laminated to the inner, paper ply. The polymer film may be an oriented polyester (OPET) film, such as DuPont Mylar 813/48 gauge, EB 11/48 gauge, or 822/48 gauge. Alternatively, the polymer film may be an oriented polypropylene (OPP) film such as AET films AQS/70 gauge. Of course, one of the ordinary skill may appreciate that other polymer films could be used, including other OPET and OPP films, and films other than OPET and OPP.
The invention is not limited to packages having two plies. It is anticipated that additional plies also may be used. Moreover, one or more plies used in the preferred microwave package may be coated, for example, to aid in lamination and/or to provide a barrier layer. When adhesives are used either during formation of the package, such a barrier layer may be required to ensure that the adhesives cannot contact the foodstuffs, for example, because the adhesives are not FDA-approved.
Although the invention is described as having an inner, paper ply and an outer polymer ply, both plies could be made of paper. By eliminating the polymer ply, the package may be more environmentally-friendly. Using biodegradable adhesive also may be desirable. The package also may include only a single ply. For example, the single ply would be the inner, paper ply. In this arrangement, the inner ply preferably would be at least partially coated with an adhesive that would facilitate formation of the single ply into a package or a pouch. The adhesive preferably would be heat-sensitive and would melt at a predetermined temperature to vent the container, or alternative venting mechanisms, such as those described above, could be used.
The foregoing embodiments of the invention are representative embodiments, and are provided for illustrative purposes. The embodiments are not intended to limit the scope of the invention. Variations and modifications are apparent from a reading of the preceding description and are included within the scope of the invention. The invention is intended to be limited only by the scope of the accompanying claims.
