Dual-function heat indicator and method of manufacture
A dual-function heat indicator for monitoring two or more modes of heat exposure is described. A manufacturing process for the dual-function heat indicator is also described. Dual-function heat indicators as described may be useful for monitoring the exposure of host products, with which the dual-function heat indicators may be associated, to cumulative ambient heat exposure and to a peak ambient heat exposure, and for other purposes.
1. A dual-function heat indicator comprising:
a peak indicator layer including a peak heat exposure indicator;
a cumulative heat exposure layer physically distinct from the peak indicator layer and including a cumulative heat exposure indicator,
wherein the cumulative heat exposure indicator is configured to change color in response to a cumulative ambient heat exposure over time, including an exposure over time to temperatures that are always below a minimum threshold temperature required to cause a color change in the peak heat exposure indicator;
wherein the peak heat exposure indicator is configured to change color in response to a peak temperature exposure above the minimum threshold temperature that is less than two minutes in duration, and the peak temperature exposure does not cause a color change in the cumulative heat exposure indicator;
wherein the peak heat exposure indicator comprises:
a first reactant comprising a leuco dye precursor,
a second reactant comprising a developer for the leuco dye precursor that is reactable with the first reactant in a color-changing reaction, and
a meltable solid separating the first reactant and the second reactant and having a melting point in the range of 30° C. to 60° C.,
wherein the peak heat exposure indicator is configured so that, responsive to the meltable solid melting, the first and second reactants to come into contact with each other, providing a color change from the color-changing reaction,
wherein the cumulative heat exposure indicator is transparent prior to changing color and the peak heat exposure indicator is viewable through the cumulative heat exposure indicator when the cumulative heat exposure indicator is transparent.
2. The dual-function heat indicator of claim 1 , wherein the cumulative heat exposure indicator undergoes a change in optical density in response to cumulative exposure to heat over time and the peak heat exposure indicator undergoes a change in optical density in response to the peak heat exposure above the melting point, and wherein the cumulative heat exposure indicator and the peak heat exposure indicator each have a respective viewable active area, and the cumulative heat exposure indicator viewable active area and the peak heat exposure viewable active area are viewable so that the optical densities of the viewable active areas are combined when viewed.
3. The dual-function heat indicator of claim 1 , wherein the melting point is in the range of 40° C. to 60° C.
4. The dual-function heat indicator of claim 1 , wherein the first reactant and the second reactant are solid and wherein the peak indicator layer has been treated with a thermal sensitizer which modifies the melting point.
5. The dual-function heat indicator of claim 1 , wherein the cumulative heat exposure indicator color change is irreversible.
6. The dual-function heat indicator of claim 1 , wherein the cumulative heat exposure indicator comprises at least one thermally sensitive, polymerizable diacetylenic compound containing at least two conjugated acetylenic groups.
7. The dual-function heat indicator of claim 1 , wherein the first reactant or the second reactant is initially transparent.
8. The dual-function heat indicator of claim 1 , wherein both the first reactant and the second reactant are initially transparent.
9. The dual-function heat indicator of claim 1 , wherein the second reactant is an oil-soluble reducing agent, oxalic acid, phosphite ester, hydroxybenzoic acid ester, hydrohydroquinone, a hydroquinone derivative, dimethylhydroquinone, di-tert-butyl hydro quinone, dialkylhydroquinone, 3-ethoxyphenol, 1,2-diethyl-3-hydroxybenzene, 1,3-diethyl-2-hydroxybenzene, 2,2′-methylenebis(3,4,6-trichlorophenol), meltable, or sensitizer-soluble, primary and secondary amines having low water solubility, 4-butyl-aniline, phenol derivatives, organic acids, acid clays, reactive acid hectorite clay, phenolic resins, phenol-acetylene resins, polyvalent metallic salts of phenolic resins, zinc-including modified alkyl phenolic resin, zinc salicylate, zinc salicylate resin, 4,4′-isopropylidenebisphenol (also known as bisphenol A), 1,7-di(hydroxyphenylthio)-3,5-dioxaheptane, 4-hydroxyethyl benzoate, 4-hydroxydimethyl phthalate, monobenzyl phthalate, bis-(4-hydroxy-2-methyl-5-ethylphenyl)sulfide, 4-hydroxy-4′-isopropoxydiphenyl sulfone, 4-hydroxyphenylbenzenesulfonate, 4-hydroxybenzoyloxybenzylbenzoate, bis-(3-1-butyl-4-hydroxy-6-methylphenyl)sulfone, p-tert-butylphenol, or polymers based on bisphenol A.
10. The dual-function heat indicator of claim 1 , wherein the first reactant is 3,3-bis(p-dimethylaminophenyl)-phthalide, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (crystal violet lactone), 3,3-bis(p-dimethylaminophenyl)-6-diethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide, 3,3-bis(p-dibutylaminophenyl)-phthalide, 3-(N—N-diethylamino)-5-methyl-7-(N,N-dibenzylamino) fluoran, 3-dimethylamino-5,7-dimethylfluoran, 3-diethylamino-7-methylfluoran, 3-(2′-hydroxy-4′-dimethylaminophenyl)-3-(2′-methoxy-5′-chlorophenyl)phthalide, 3-(2′-hydroxy-4′-dimethylaminophenyl)-3-(2′-methoxy-5′-nitrophenyl-phthalide, 3-(2′-hydroxy-4′-diethylaminophenyl)-3-(2′-methoxy-5′-methylphenyl)phthalide, 3-(2′-methoxy-4′-dimethylaminophenyl)-3-(2′-hydroxy-4′-chloro-5′-methylphenyl)-phthalide, benzoylleuco methylene blue, malachite green lactone, N-2,4,5-trichlorophenylleuco auramine, 3-diethylamino-6-methyl-7-chlorofluoran, 3,6-bis(diethylamino)fluoran-γ-(4′-nitro)-anilinolactam, 3-diethylamino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-cyclohexylamino-6-chlorofluoran, or 3-diethylamino-6,8-dimethylfluoran.
11. The dual-function heat indicator of claim 1 further comprising a substrate that supports the cumulative and peak heat exposure indicators.
12. The dual-function heat indicator of claim 11 , further comprising a reference surface printed on the substrate.
13. The dual-function heat indicator of claim 11 , wherein the substrate is clear or white.
14. The dual-function heat indicator of claim 11 , wherein the peak heat exposure indicator is disposed between the cumulative heat exposure indicator and the substrate.
15. The dual-function heat indicator of claim 11 , wherein the cumulative heat exposure indicator is disposed between the peak heat exposure indicator and the substrate.
16. The dual-function heat indicator of claim 11 , wherein the substrate is configured to be conformable with a host product and enables the dual-function heat indicator to be attachable to the host product.
17. The dual-function heat indicator of claim 16 , wherein the substrate is attachable to the host product by bearing a pressure-sensitive adhesive layer.