Time temperature indicator

A method for producing a time temperature indicator, comprising the steps of:

• a) applying a metal layer or a metal-containing layer onto a substrate, thus obtaining a first label;
• b) obtaining a photolatent reactive polymer comprising (1) a doped polymer containing a photolatent acid or a photolatent base a dopant, or (2) a functionalized polymer which is functionalized with photolatent acidic groups or photolatent basic groups, whereby, upon irradiation of the photolatent reactive polymer with light, an acid or a base is formed from the photolatent acidic or basic groups or from the photolatent acid or photolatent base, which acid or base reacts with said metal layer or metal-containing layer when brought into contact therewith;
• c) applying the polymer of step b) to a substrate, thus obtaining a second label;
• d) applying the polymer of said second label onto the metal layer or metal containing layer of said first label;
• and
• e) either before, after or at the same time as the applying of step (d), irradiating the photolatent reactive polymer with light.

A time-temperature indicator, comprising:

• a first label comprising
• a first carrier layer,
• a metal layer or a metal-containing layer disposed on one side of said first carrier layer, and
• an adhesive layer, said adhesive layer being disposed on the opposite side of said first carrier layer as said metal layer or said metal-containing layer;
• and
• a second label comprising a second carrier layer and, disposed thereon, a photolatent doped polymer layer, said photolatent doped polymer comprising a polymer and a dopant, wherein
• said dopant is one or more photolatent acid or photolatent base, the dopant having properties such that, upon irradiation with light, an acid or a base is formed from the photolatent acidic or basic groups or from the photolatent acid or photolatent base, which acid or base reacts with the metal of said metal layer or metal-containing layer when brought into contact therewith, wherein said second label is affixed to said first label such that the doped polymer layer of said second label is facing said metal layer or metal-containing layer of said first label.