Dual function heat indicator and method of manufacture

1. A dual-function heat indicator comprising:

a substrate;

a cumulative exposure indicator supported by the substrate in a viewable, layered configuration, wherein the cumulative exposure indicator is configured to undergo an optical change in appearance in response to a cumulative heat exposure;

a peak exposure indicator supported by the substrate in the viewable, layered configuration, the peak exposure indicator comprising a meltable solid configured to melt upon exposure to a predetermined peak heat exposure, the meltable solid configured to change color or transparency in response to the melting of the meltable solid, the color or transparency change persisting after the meltable solid re-solidifies; and

a colored background under the meltable solid that is dark relative to the meltable solid, wherein the meltable solid is initially opaque, obscuring the background, and is configured to become transparent after melting and to remain transparent after re-solidifying, revealing the background;

wherein the cumulative exposure indicator and the peak exposure indicator are functionally separate with the visual outputs of the cumulative exposure indicator and the peak exposure indicator integrated in a single overlapping display.

2. The dual-function heat indicator of claim 1 , wherein there is a short delay between exposure to a peak temperature and response of the peak exposure indicator.

3. The dual-function heat indicator of claim 1 , wherein the peak exposure indicator is color-changeable in response to melting of the meltable solid.

4. The dual-function heat indicator of claim 1 , wherein the peak exposure indicator is color-changeable in response to a peak temperature in a range of about 30-60° C.

5. The dual-function heat indicator of claim 1 , wherein the meltable solid has a melting point below about 60° C.

6. The dual-function heat indicator of claim 1 , wherein the meltable solid has a melting point above about 30° C.

7. The dual-function heat indicator of claim 1 , further comprising a reference ring which has an appearance that is similar to the appearance of the cumulative exposure indicator that has undergone the optical change in appearance.

8. The dual-function heat indicator of claim 1 , further comprising a reference ring which has an appearance that is similar to the appearance of the peak exposure indicator after melting of the meltable solid.

9. The dual-function heat indicator of claim 1 , further comprising a reference ring which has an appearance that is similar to the appearance of the cumulative exposure indicator that has undergone the optical change in appearance and that is similar to the appearance of the peak exposure indicator after responding to a peak exposure event.

10. The dual-function heat indicator of claim 1 , further comprising a transparent film that overlies the cumulative exposure indicator and the peak exposure indicator.

11. The dual-function heat indicator of claim 1 , further comprising an adhesive layer contacting the substrate on a side opposite the cumulative exposure indicator and the peak exposure indicator.

12. The dual-function heat indicator of claim 1 , wherein the cumulative exposure indicator is affected by a temperature that is below a peak temperature of the peak exposure indicator.

13. The dual-function heat indicator of claim 1 , wherein the cumulative exposure indicator overlies the peak exposure indicator.

14. The dual-function heat indicator of claim 1 , wherein the cumulative exposure indicator darkens in response to the cumulative heat exposure.

15. The dual-function heat indicator of claim 1 , wherein the cumulative exposure indicator comprises a heat sensing agent that darkens in response to the cumulative heat exposure.

16. The dual-function heat indicator of claim 1 , wherein the cumulative exposure indicator comprises a polymerizable diacetylenic compound that darkens in response to the cumulative heat exposure.

17. The dual-function heat indicator of claim 1 , wherein melting of the meltable solid reveals a background, the background remaining visible after the meltable solid resolidifies.

18. The dual-function heat indicator of claim 17 , wherein the meltable solid is in the form of particles that obscure a background by scattering light.

19. The dual-function heat indicator of claim 18 , wherein melting of the meltable solid causes a color to become more apparent due to a loss of light scattering.

20. The dual-function heat indicator of claim 1 , wherein the meltable solid comprises a polymer.

21. The dual-function heat indicator of claim 20 , wherein the polymer is a side-chain crystalline polymer.

22. The dual-function heat indicator of claim 1 , wherein the peak exposure indicator overlies the cumulative exposure indicator.

23. The dual-function heat indicator of claim 1 , wherein melting of the meltable solid results in the meltable solid darkening in color.

24. The dual-function heat indicator of claim 23 , wherein the meltable solid is in the form of particles that scatter light.

25. The dual-function heat indicator of claim 23 , wherein the peak exposure indicator further comprises a colorant.

26. The dual-function heat indicator of claim 25 , wherein the colorant is dissolved in the particles that scatter light.

27. The dual-function heat indicator of claim 25 , wherein melting of the meltable solid causes the colorant to become dissolved in the meltable solid.

28. The dual-function heat indicator of claim 1 , wherein the cumulative exposure indicator darkens in color in response to the cumulative heat exposure.

29. The dual-function heat indicator of claim 1 , wherein the optical change in appearance comprises a reduction in opacity of the cumulative exposure indicator.

30. The dual-function heat indicator of claim 1 , wherein the optical change in appearance reveals a background.

31. The dual-function heat indicator of claim 30 , wherein the background is the substrate.

32. The dual-function heat indicator of claim 1 , wherein a layer of aluminum is disposed on the substrate.

33. The dual-function heat indicator of claim 30 , wherein revealing the background allows the background to be read.

34. The dual-function heat indicator of claim 1 , wherein the optical change in appearance comprises a lightening of the cumulative exposure indicator.

35. The dual-function heat indicator of claim 1 , wherein the peak exposure indicator further comprises an oil-soluble reducing agent or a meltable or sensitizer-soluble, primary or secondary amine having low water solubility.

36. The dual-function heat indicator of claim 1 , wherein the peak exposure indicator further comprises an oil-soluble reducing agent, oxalic acid, phosphite ester, hydroxybenzoic acid ester, hydrohydroquinone, a hydroquinone derivative such as dimethyhydroquinone, 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), 4-butyl-aniline, a phenol derivative, an organic acid, an acid clay, reactive acid hectorite clay, a phenolic resin, a phenol-acetylene resins, a polyvalent metallic salts of a phenolic resin, a zinc-including modified alkyl phenolic resin, zinc salicylate, a zinc salicylate resin, a 4,4′-isopropylidenebisphenol, 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′-isopropoxydiphenylsulfone, 4-hydroxyphenylbenzenesulfonate, 4-hydroxybenzoyloxybenzylbenzoate, bis-(3-1-butyl-4-hydroxy-6-methylphenyl)sulfone, p-tert-butylphenol, or a polymer based on bisphenol A.

37. The dual-function heat indicator of claim 1 , wherein the peak exposure indicator further comprises 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.

38. The dual-function heat indicator of claim 1 , wherein the peak exposure indicator further comprises heptadecanol, 4-methoxyphenol, pentadecanol, 2,4-di-tert-butyl phenol or benzophenone.

39. The dual-function heat indicator of claim 1 , wherein the meltable solid comprises an alkane, an alkyl ester, or a wax.

40. 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.

41. The dual-function heat indicator of claim 39 , wherein the wax comprises a paraffin wax, a microcrystalline wax, carnauba wax, beeswax, Chinese wax, shellac wax, spermaceti, tallow, palm wax, soy wax, 15 lanolin, wool grease, a waxy polymer, a waxy copolymer, a polyolefin, polyethylene, polypropylene, an ethylene-vinyl acetate copolymer, an ethylene-acrylic acid copolymer.

42. The dual-function heat indicator of claim 1 , wherein the increased transparency of the meltable solid of the peak exposure indicator reveals a background.

43. The dual-function heat indicator of claim 42 , wherein revealing the background allows the background to be read.