Indicator for packaging of such as milk is built into opening seal has a chemical that responds to moisture and changes colour over period of days

摘要

The carton used to hold such as milk has an insert [2] set into the opening seal [1]. The insert is covered by a peel off foil [4] and contains a chemical [3] that acts as a moisture indicator. When the foil is removed the colour of the insert changes from dark blue to light blue over a period of days to indicate freshness.