Patent ID: 8183045

Claim:
A method for indicating time and temperature history of a perishable product, said method comprising: (a) providing a supporting film forming a first roll and a plurality of first flat labels adhered to said supporting film, wherein each first label comprises a transparent film and a chelating agent disposed adjacent said transparent film on one side thereof; (b) providing a supporting self-adhesive film forming a second roll and a plurality of second flat labels adhering to said supporting self-adhesive film, wherein each second label comprises a base film, a second reactant layer comprising a second reactant, and a single flat transparent polymeric matrix barrier layer, wherein said second reactant layer is disposed in between said base film and said barrier layer, and said second reactant reacts according to a predetermined chemical reaction with said chelating agent when they come into contact with one another, said barrier layer allowing diffusion of said chelating agent therethrough in a time and temperature dependent manner after said chelating agent comes into contact therewith, and prevents said second reactant from diffusing therethrough; (c) attaching one of said first labels to one of said second labels to form a combined label with said chelating agent in contact with said transparent barrier layer; and (d) attaching said combined label to a package containing a perishable product.