At present, supermarkets, convenience stores and a variety of other places where refrigerated foods are available are competing with restaurants and fast-food establishments by providing an assortment of ready-made sandwiches and other lunchtime or dinnertime products. Most often, these packages enclose rapidly perishable food products such as a frankfurter or wiener in a bun or other proteinaceous-farinaceous food combinations which are subject to rapid degradation, particularly if the package is torn or bruised. Since these packages are usually transparent so that the potential consumer can observe product quality, the degradation of the meat product or the staling or molding of the bread will be readily apparent to the consumer and the product will go unsold.
It is thus of primary importance that packages be developed which can maximize freshness and which can be made sturdy enough to avoid the problems associated with bumping and bruising of food products during transport and handling. This has particularly been a problem with transparent sandwich-type packages that have to be frozen at some point before sale in order to protect the rapidly perishable food product contained inside. Typically, at the below-freezing low temperatures normally associated with the processing of such food products, commonly around 0.degree. F., the tendency for these food packages to bruise or break is greatly increased, and such damage will typically result in the spoilage of the food product, particularly when it is thawed.
Additionally, it is often the case that these perishable sandwiches or other food products will be of the type that have to be heated before being consumed, for example, in a microwave oven. It is thus quite important that packaging for such food items be capable of withstanding the conditions associated with microwaving without undergoing thermal distortion.
Although there have been attempts to develop frozen food packages which could be heated to microwave temperatures, these prior packages suffered from various drawbacks including lack of an adequate oxygen barrier which greatly restricted shelf life. Additionally, these packages were not made with easy-to-open peelable lids, and thus removal of the product from the packages was extremely difficult. As a result of these drawbacks, the prior freezer-to-microwave packages were extremely limited in function and consumer suitability, and could not be used to preserve a product that was frozen then thawed to a refrigerated state.
An example of this prior package is disclosed in U.S. Pat. No. 3,997,677 (Hirsch et al). The Hirsch et al. patent discloses a hermetically sealed plastic package that can retain a frozen food product and then be microwaved to serving temperatures. The package essentially utilized any one of three materials, polycarbonate, polypentamethylene or polysulfone, none of which is economically feasible to use today. In fact, the hazy, milky medium and high density polyethylenes disclosed in Hirsch are unsuitable for use in a transparent package. The Hirsch package was constructed utilizing the then existing technology of hermetically sealed plastic moisture barrier packages, and simply comprised adding a thermally stable ply to well-known commercially available packaging materials using conventional sealing techniques. The package does not provide oxygen impermeability, and none of the materials it uses are oxygen barriers capable of preventing permeation of oxygen above freezing. Use of the materials described in the Hirsch patent without suitable oxygen barrier layers results in discoloration, oxidative rancidity, and flavor degradation of the food product at temperatures above freezing.
Another problem with the package described in the Hirsch patent is that it provided no means whereby the package could be easily opened. In the package embodiments disclosed, a polyolefin (medium or high density polyethylene or polypropylene) was fusion sealed to a like polyolefin, and thus there was no capability for peeling the package open. The Hirsch package was openable only by cutting or tearing, and a weakened area was provided which comprised a narrowed fused seal that needed to be torn open. Without an easy-open, peelable feature, the Hirsch package was unsuitable for consumer use because its fused seal necessitated opening in an erratic and unreliable manner even when using a sharp tool such as a knife. The drawbacks of prior packages such as those disclosed in the Hirsch patent have thus resulted in their being of limited functionality and effectiveness, and more suitable and versatile freezer-to-microwave packages are highly desired.
There thus exists a need for a peelably sealed, easy-to-open transparent package for containing a perishable food product which can maintain the freshness of the product while frozen and while the product is thawed and kept at refrigerated temperatures, and which can still withstand conditions of a microwave oven so that the product can be cooked without thermal degradation or melting of the package.