In recent years, microwave ovens have become increasingly popular. This has created an increasing demand for economical, simple, disposable containers which, when used in a microwave oven, produce cooking results, including surface browning and crisping, comparable to those to which people are accustomed with cooking in conventional ovens. For consumer convenience, it is desirable to have the package be so constructed that the food item, together with all or a portion of the package in which it is contained, can be placed directly in the oven.
Paperboard cartons have been found to be an economical way to meet many microwave packaging requirements. In particular, a number of cartons for browning microwave foods have been successfully introduced that are made from paperboard to which a metallized plastic film has been laminated, with the thin metal layer being sandwiched between the plastic film and the paperboard. A suitable adhesive is used to hold the laminated layers together. One laminated material of this kind is shown in U.S. Pat. No. 4,641,005.
Although microwave browning packages of several kinds are now widely sold and the surface browning capability of a metallized film-paperboard laminate used in such packages is widely accepted, the effect of unusual food and package shapes, of multiple layers of microwave absorbing materials and other specialized package configurations on cooking results is not well understood. This is apparently attributable to the complex combination of reflections, refractions and absorptions of microwave radiation occuring in the oven, the food and the packaging. It is also attributable to the different way in which microwaves cook food, as compared to the heating modes of conventional ovens. Accordingly, development of specific package configurations has proceeded slowly and empirically as the microwave cooking possiblities of various food items are explored.
One microwave cooking phenomenon that has been noted is that most foods tend to cook better when they are raised above the floor of the microwave oven. Several prior patents have been directed to packages that elevate food for microwave cooking, e.g., U.S. Pat. Nos. 4,642,434; 4,698,472. However, these packages have had certain disadvantages. For example, a package made from light paperboard, with single-ply walls, may not be able to support heavy food items. In addition, prior packages have been complex and require the development of new or modified packaging machinery. Accordingly, there is a need for simple, effective paperboard package for elevating food for microwave cooking or other forms of cooking where food elevation may be desirable.