The enormous growth of precooked dinners and entrees conveniently designed for quick heating and consuming is a well-known. The container starts with a plate or bowl made of plastic-coated paper, thin aluminum sheet, or more commonly of a thermo-formable plastic such as PET or Nylon withstanding oven heating to 400°F without distortion or transfer of its components to the food. Plastic films are commonly used for the lids, replacing the original aluminum foil lids that are not compatible microwaving. Since the package usually remains lidded while being heated, the high temperature required for the plate or bowl extends to the lid as well.
Oxygen barrier assumes significance for dinners and entrees which are either sold refrigerated or at room temperature as opposed to being frozen. As far as the former is concerned, sufficiently thick PET would suffice, especially when the requirement is a shell life in the range of 30 days. However, unrefrigerated products are recommended to either use aluminium foil or incorporate an EVOH/PVDC layer in the lid/tray/bowl.
Tray-lid package is another flexible yet less popular packaging that is also known as “retort pouch” as the packaging is done in the pouch before being retorted at 250°F. This shelf-stable package scores over glass jars or metal cans in these ways: low cost, light weigh, a thin cross connection, and convenient portability.
After the proliferation of microwaveability, PVDC-based non-metallic barrier layers were incorporated rather than the erstwhile aluminium foil.
This package’s successful deployment signified a key achievement. Seal polymers which could be sealed via different food layers were able to endure retorting conditions and remain hermetically sealed for at least a year. In addition, some of the key impediments to be surmounted included constructions exhibiting excellent oxygen barrier, albeit with the inability to contribute undesirable components to the food under retort conditions
The original foil-containing structure was as follows:
> PE / Adhesive / Foil / Primer / Adhesive / PP sealant.
The microwaveable embodiments include:
> PET / PVDC / PP
> Nylon/PVDC/nylon/tie layer/sealant.