Indicator of unacceptable temp. rise of frozen food etc. - reveals irreversible colour change as substance melts and soaks indicator pad

摘要

A method of checking and an indicator for revealing, whether the temp. of the prod. partic. a food prod, has at any time exceeded a predetermined value. The indicator employs the change of state of a substance from solid to liq. to produce an irreversible mark on a recording pad. Pref. the substance is contained in a plastic sachet of which part of the wall is ruptured by expansion of the substance as it freezes from liq. to solid state. If the predetermine temp. is exceeded, the substance melts and soaks into an absorbent recording pad. Pref. both sacket and pad are contained in a transparent, plastic envelope. The substance in the sachet is pref. a soln. of sodium chloride or of calcium chloride. The substance pref. has a freezing point between 0 and -40 deg.C. The absorbent recording pad is pref. white in colour. The fault remains obvious even if the temp. is restored subsequently to an acceptably low level. The indicator is inexpensive to produce and easy to use.