A bi-functionally active packaging material for microwave food products

摘要

A bi-functional laminate which in a microwave oven converts irreversibly, after a time and at a temperature controlled by the components of the laminate, from a microwave screen with absorbing properties to a microwave transparent material with much weaker absorbing properties. The said laminate is constructed from- a plastic film selected for its compatibility for food contact and for its softening temperature which determines the changeover conversion temperature;- a metal layer vacuum deposited on the plastic layer, the metal being deposited to just sufficient thickness to provide a complete screen to microwave transmission at room temperature (transmission less than 1%);- an adhesive and- a paper or paper-board supporting material of a weight selected to give the required heat-up time to the changeover conversion temperature, said supporting material being adhered to said metal layer.