Time/temperature indicators
AssigneeSun Chemical Corporation
InventorsFarid Azizian, Michael William Leonard
Life of this patent
Estimating the term…
Abstract
By printing a bar code (comprising dark and light regions) or parts of such a bar code with an ink containing a dye, which changes color in the presence of an acid or a base to remove the contrast between the regions of the bar code, and a neutral compound which releases an acid or a base on exposure to energising radiation, a bar code can be produced that becomes unreadable after a pre-determined interval. This can be used as a time/temperature indicator to ensure that products, which might be perishable, associated with such a bar code are not used by the public.
Claims24
A substrate on which is provided:
- a bar code comprising a plurality of bars separated by spaces in a contrasting color, wherein at least some of the bars or the spaces are colored by a dye which will change color in the presence of an add or a base to reduce the contrast between the bars and the spaces,
- and
- an additional layer of the dye and a neutral compound which, on exposure to energizing radiation, forms an acid or a base to initiate a color change in the dye, said additional layer provided as a transparent layer over at least a part of the bar code.
A substrate according to cairn 1, in which the bar code is printed over said additional layer.
A substrate on which is provided:
- a bar code comprising a plurality of bars separated by spaces in a contrasting color, wherein at least some of the bars or the spaces are colored by a dye which will change color in the presence of a base to reduce the contrast between the bars and the spaces,
- and
- a neutral compound which, on exposure to energizing radiation, forms a base to initiate a color change in the dye.
A substrate on which is provided:
- a bar code comprising a plurality of bars separated by spaces in a contrasting color, wherein at least some of the bars or the spaces are colored by a dye which will change color in the presence of an acid or a base to reduce the contrast between the bars and the spaces,
- and
- a neutral compound which, on exposure to energizing radiation, forms an acid or a base to initiate a color change in the dye,
- wherein the dye is a leuco dye in its reduced form and the neutral compound is a thioxanthonium salt cationic photoinitiator.
Dependencies are inferred from the claim text.