Packages materials for shielded food containers used in microwave ovens

Claim 1

A package for heating of food material representing a low load in a microwave environment employing a conductive sheet in close proximity to a dielectric material that is selected to minimize failure of the dielectric material during microwave heating, comprising: a conductive sheet, the conductive sheet being exposed to microwave radiation when the package is placed in a microwave oven and the oven is energized, the conductive sheet having an edge, the conductive sheet causing a gain in electrical field strength greater than 3 near at least a portion of an edge; a rigid, dimensionally stable dielectric support for the conductive sheet, the dielectric support being mechanically associated with the conductive sheet to maintain dimensional stability of the combination of the dielectric support and the conductive sheet, the dielectric support extending beyond at least a portion of an edge of the conductive sheet, the dielectric support being spaced less than 0.5 inch from the conductive sheet, the dielectric support being composed of material selected to avoid failure of the dielectric support in high electrical fields which may exist near the conductive sheet during microwave irradiation, the dielectric support material having a dielectric loss factor less than 0.005, the dielectric support material having a failure temperature greater than 101° C.; the package being an intrinsically nonarcing package; food supported by the package, the food representing a low load in a microwave oven cavity, where microwave cooking is continued for a predetermined period of time desired according to the food selected for the package when the package is placed in a microwave oven cavity.

Claim 34

A method for selecting packaging material for use in a shielded microwave container having a gain greater than 3, comprising the steps of: determining the gain of a shield to be used in a microwave food package; selecting a package material having a dielectric loss factor E" less than 0.1; further selecting a package material having a combination of dielectric loss factor E", heat capacity C p , density ρ and failure temperature T f , such that during microwave heating for a predetermined microwave heating time Δt dependent upon the food substance to be heated in the food package: ##EQU14## where T i is the initial temperature of the package material, ω is the angular frequency of the microwave oven, Eo is the dielectric constant of free space, and Erms is the maximum electric field strength to which the package material is subjected during microwave heating; and, constructing a microwave food package having a gain greater than 3 and where the shield is spaced from the selected package material less than 0.1 inch.

Claim 35

A method for selecting packaging material for use in a shielded microwave container having a gain greater than 3, comprising the steps of: determining the gain of a shield to be used in a microwave food package; selecting a package material having a dielectric loss factor E" less than 0.1; further selecting a package material having a combination of dielectric loss factor E", heat capacity C p , density ρ and failure temperature T f , such that during microwave heating for a predetermined microwave heating time Δt dependent upon the food substance to be heated in the food package: ##EQU14## where T i is the initial temperature of the package material, ω is the angular frequency of the microwave oven, Eo is the dielectric constant of free space, and Erms is the maximum electric field strength to which the package material is subjected during microwave heating; and, constructing a microwave food package having a gain greater than 3 and where the shield is spaced from the selected package material less than 0.1 inch.

Claim 41

A method of making a package containing a food product during heating in a microwave oven, said method comprising: determining the gain of a conductive member adjacent a food product in a microwave field; selecting a dielectric packaging material that has a dielectric loss factor sufficiently low such that said material will not detrimentally heat when said food product, said material and said conductive member are exposed to microwave radiation for heating said food product; and, making a package including said conductive member and a package portion made of said packaging material.

Claim 42

A method of making a package containing a food product during heating in a microwave oven, said method comprising: determining the gain of a conductive member adjacent a food product in a microwave field; selecting a dielectric packaging material that has a dielectric loss factor sufficiently low such that said material will not detrimentally heat when said food product, said material and said conductive member are exposed to microwave radiation for heating said food product; and, making a package including said conductive member and a package portion made of said packaging material.