Importance

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Abstract

An indicator composition and process capable of changing color in relationship to its exposure to a temperature above and below a base line temperature and to the time of said exposure, for monitoring the time-temperature history of a substrate, depositable as a layer on said substrate, comprising a dispersion of either a binder comprising a reaction inert, neutral finely divided absorbent, in the presence of a reactant comprising a salt of an acid or an organic compound substituted by at least one moiety which, in ionic form, is an anion or a binder/reactant, comprising at least one solid organic polymer whose constituent units contain, as a covalent substituent, at least one moiety which, in ionic form, is an anion; as indicator, at least one acid sensitive pH dye and as activator, at least one base. This composition and process may be utilized to form a solid state device for monitoring integral values of time and temperature during storage of perishables. The device is a single solid indicating layer deposited upon a substrate. The time required for the color change and the activation energy of the device can be varied by varying the concentration and nature of reactants, catalysts, additives and polymeric binder/reactant matrix. The color change can be gradual or abrupt and exhibited as a continuous strip, as alphanumeric symbol(s) or as a line array which can be read by a bar code reader.

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First Claim