Activatable time-temperature indicator system

An activatable time-temperature monitoring system for indicating the accumulation of a combination of time and ambient temperature which exceeds a predetermined time-temperature integral to which an associated perishable product has been exposed

• characterized in that said system comprises
• a) a first element comprising a direct thermal color-forming composition comprising at least a pair of co-reactant components capable of reacting in combination to form said color upon the heating of said composition at least to a threshold temperature;
• and
• b) a second element comprising an activating component capable of, upon contact with said first element composition, initiating said color-forming combination reaction at a second temperature below said threshold and causing said reaction to proceed to formation of said color at an average rate satisfying said predetermined time-temperature integral.

A method of monitoring the useful life of a perishable product which comprises affixing to said product a time-temperature monitoring system for indicating by means of a visually distinct color change signal the accumulation of a combination of time and ambient temperature which exceeds a predetermined time-temperature integral to which an associated, perishable product has been exposed

• characterized in that
• a) said indicator system comprises
• 1) a first element comprising a direct thermal color-forming composition comprising at least a pair of co-reactant components capable of reacting in combination to form said color upon the heating of said composition at least to a threshold temperature, and
• 2) a second element comprising an activating component capable of, upon contact with said first element composition, initiating said color-forming combination reaction at a second temperature below said threshold and causing said reaction to proceed to the formation of said color at an average rate satisfying said predetermined time-temperature integral;
• b) said second element is affixed to said first element to thereby effect said contact between said activator component and said first element color-forming composition;
• c) said first element is affixed to said perishable product substantially simultaneously with said affixing of said second element to said first element;
• and
• d) said perishable product is exposed to ambient temperatures for a time within the period up to the formation of said color and the resulting appearance of said visually distinct signal.