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 substrate;
a cumulative exposure layer supported by the substrate in a viewable, layered configuration, wherein the cumulative exposure layer is configured to undergo an optical change in appearance in response to a cumulative heat exposure; and
a peak exposure layer supported by the substrate in a viewable, layered configuration, the peak exposure layer comprising a meltable solid configured to melt upon exposure to a predetermined peak heat exposure, the peak exposure layer configured to have a light colored appearance due to light scattering, and in response to the melting of the meltable solid the light scattering ceases causing a darkening of the peak exposure layer, the darkening persisting after the meltable solid re-solidifies;
wherein the cumulative exposure layer and the peak exposure layer are functionally separate with visual outputs of the cumulative exposure layer and the peak exposure layer integrated in a single overlapping display.
2. The dual-function heat indicator of claim 1 , wherein the response of the peak exposure layer is not immediate upon exposure to a peak temperature.
3. The dual-function heat indicator of claim 2 , wherein the peak exposure layer is configured to darken in response to exposure to the peak temperature after an exposure of at least two minutes.
4. The dual-function heat indicator of claim 1 , wherein the peak exposure layer darkens in response to a peak temperature being above a threshold temperature, the threshold temperature in a range of about 30-60° C.
5. The dual-function heat indicator of claim 1 , wherein the peak exposure layer darkens in response to a peak temperature below about 60° C.
6. The dual-function heat indicator of claim 1 , wherein the peak exposure layer darkens in response to a peak temperature above about 30° C.
7. The dual-function heat indicator of claim 1 , further comprising a reference ring that has an appearance that is similar to the appearance of the cumulative exposure layer that has undergone the optical change in appearance.
8. The dual-function heat indicator of claim 1 , further comprising a reference ring that has an appearance that is similar to the appearance of the peak exposure layer after darkening in response to a peak temperature.
9. The dual-function heat indicator of claim 1 , further comprising a transparent film that overlies the cumulative exposure layer and the peak exposure layer.
10. The dual-function heat indicator of claim 1 , further comprising an adhesive layer contacting the substrate on a side opposite the cumulative exposure layer and the peak exposure layer.
11. The dual-function heat indicator of claim 1 , wherein the cumulative exposure layer is affected by a temperature that is below a peak temperature of the peak exposure layer.
12. The dual-function heat indicator of claim 1 , wherein the cumulative exposure layer overlies the peak exposure layer.
13. The dual-function heat indicator of claim 1 , wherein the cumulative exposure layer darkens in response to the cumulative heat exposure.
14. The dual-function heat indicator of claim 1 , wherein the cumulative exposure layer comprises a polymerizable diacetylenic compound that darkens in response to the cumulative heat exposure.
15. The dual-function heat indicator of claim 1 , wherein the meltable solid is in the form of particles configured to scatter light prior to melting, the light scattering masking a color of the particles of the meltable solid.
16. The dual-function heat indicator of claim 15 , wherein melting of the meltable solid causes a color of the meltable solid to become more apparent due to a loss of light scattering.
17. The dual-function heat indicator of claim 1 , wherein the peak exposure layer further comprises a colorant the color of which is masked by the meltable solid prior to melting.
18. The dual-function heat indicator of claim 17 , wherein melting of the meltable solid causes the color of the colorant to become more apparent due to a loss of light scattering.
19. The dual-function heat indicator of claim 17 , wherein the colorant is dissolved in particles that scatter light.
20. The dual-function heat indicator of claim 17 , wherein melting of the meltable solid causes the colorant to become dissolved in the meltable solid.
21. The dual-function heat indicator of claim 1 , wherein the meltable solid comprises a polymer.
22. The dual-function heat indicator of claim 21 , wherein the polymer is a side-chain crystallizable polymer.
23. The dual-function heat indicator of claim 1 , wherein the peak exposure layer overlies the cumulative exposure layer.
24. The dual-function heat indicator of claim 1 , wherein the optical change in appearance comprises a lightening of the cumulative exposure layer.
25. The dual-function heat indicator of claim 1 , wherein the meltable solid comprises an alkane, an alkyl ester, or a wax.
26. The dual-function heat indicator of claim 25 , wherein the wax comprises a paraffin wax, a microcrystalline wax, carnauba wax, beeswax, Chinese wax, shellac wax, spermaceti, tallow, palm wax, soy wax, lanolin, wool grease, a waxy polymer, a waxy copolymer, a polyolefin, polyethylene, polypropylene, an ethylene-vinyl acetate copolymer, or an ethylene-acrylic acid copolymer.
27. The dual-function heat indicator of claim 1 , wherein the meltable solid comprises an undecane, a dodecane, a tridecane, a tetradecane, a pentadecane, a hexadecane, a heptadecane, an octadecane, a nonadecane, an eicosane, a heneicosane, a hexanoic acid, a hexadecane or ethyl lactate.
28. The dual-function heat indicator of claim 18 , wherein the colorant is in the form of particles mixed with the meltable solid.
29. The dual-function heat indicator of claim 28 , wherein the meltable solid comprises a polymer.
30. The dual-function heat indicator of claim 29 , wherein the polymer is a side-chain crystallizable polymer.
31. The dual-function heat indicator of claim 30 , wherein the colorant is a dye.
32. The dual-function heat indicator of claim 18 , wherein the colorant is encapsulated by particles of the meltable solid.
33. The dual-function heat indicator of claim 32 , wherein the meltable solid comprises a polymer.
34. The dual-function heat indicator of claim 33 , wherein the polymer is a side-chain crystallizable polymer.
35. The dual-function heat indicator of claim 34 , wherein the colorant is a dye.
36. The dual-function heat indicator of claim 1 , wherein the visual outputs of the cumulative exposure layer and the peak exposure layer are optically readable by a human viewer.