| abstract |
A time/temperature indicator comprises an activated leuco dye or similar dye, e.g. a vat dye, which undergoes a colour change, for example is bleached, in the presence of a base, in association with a photolatent base. The base is a quaternary ammonium salt, an O-acyloxime, an O-carbamoyloxime, a formamide, an amineimide or an onium salt. The dye and base may be used as a mixture, also comprising a resin and may be printed on substrate. |