Retortable container

DETAILED DESCRIPTION It is a primary purpose of the present invention to provide a retortable plastic container which is a substantial unobvious improvement over the nonretortable plastic container covered by U.
S.
Pat.
No.
3,606,958 of Coffman in that, unlike the Coffman container, the present invention can survive in a commercial canning retorter without significant unacceptable distortion.
In such retorts, containers and their contents of food or beverage are subjected to elevated temperatures (approximately 260 degrees F) for an extended period of time such that harmful microorganisms therein are killed.
It is an object of the present invention to provide a retortable plastic container into which food, beverages, or other consumable contents may be first placed and sealed after which both the container and its contents may be heated within a retort chamber to approximately 260 degrees F without evidencing significant permanent distortion of the container.
It is another object of the present invention to manufacture a retortable plastic container being capable of competing with metal cans and glass jars in the food canning industry and also being capable of surviving radiation in a microwave oven without undergoing significant and permanent distortion.
The inventor is aware that plastic containers, particularly those manufactured by SPPF and SFP technologies, are severely prone to deformation during the process of retortion.
The process of extruding a molten plastic into a single or multilayered sheet causes a polymer orientation that on cooling induces internal stresses within the plastic material.
Such internal stresses may vary in intensity within the extruded sheet.
Furthermore, the subsequent heating step in SPPF technology, in which the heated billets or blanks remain in the solid phase, does not effectively relieve these internal stresses, even though the blanks are heated sufficiently to facilitate forming.
Thus, it is necessary to heat the plastic blanks above the crystalline melting point in order to effectively relax or relieve the internal stresses introduced by the sheet extruding step