Dual-function heat indicator and method of manufacture

Abstract

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 for monitoring cumulative ambient heat exposure and peak ambient heat exposure, the dual-function heat indicator comprising:
 a substrate;   a cumulative exposure indicator supported by the substrate in a viewable, layered configuration, the cumulative exposure indicator being color-changeable in response to cumulative ambient heat exposure; and   a peak exposure indicator supported by the substrate in a viewable, layered configuration, the peak exposure indicator comprising a first reactant, a second reactant and a meltable solid, the first reactant being chemically co-reactable with the second reactant to provide a color change, the meltable solid physically separating the first reactant from the second reactant, and the color-changing chemical reaction being induced in response to an ambient heat exposure peak temperature exceeding the melting point of the meltable solid;   wherein the dual-function heat indicator indicates at least one of cumulative ambient heat exposure and peak ambient heat exposure by changing color.   
     
     
         2 . A dual-function heat indicator according to  claim 1 , comprising a viewable active area wherein the cumulative exposure indicator and the peak exposure indicator are viewable in the active area with the optical densities of the viewed indicators combined. 
     
     
         3 . A dual-function heat indicator according to  claim 1 , wherein the peak exposure indicator comprises a peak indicator layer of the dual-function heat indicator and the first reactant and the second reactant are particulate and are dispersed in the peak indicator layer. 
     
     
         4 . A dual-function heat indicator according to  claim 1 , wherein the cumulative exposure indicator is transparent prior to changing color and is configured in a first layer and the peak exposure indicator is configured in a second layer, the second layer being disposed between the cumulative exposure indicator and the substrate and the peak exposure indicator being viewable through the cumulative exposure indicator when transparent. 
     
     
         5 . A dual-function heat indicator according to  claim 1 , wherein the cumulative exposure indicator is configured in one layer and the peak exposure indicator is disposed in the same layer as the cumulative exposure indicator. 
     
     
         6 . A dual-function heat indicator according to  claim 1 , 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, optionally, by bearing a pressure-sensitive adhesive layer. 
     
     
         7 . A dual-function heat indicator according to  claim 1 , wherein the first reactant and the second reactant are solid and wherein the meltable solid further comprises a thermal sensitizer to modify the melting point of the peak meltable solid. 
     
     
         8 . A dual-function heat indicator according to  claim 1 , wherein the meltable solid comprises a binder. 
     
     
         9 . A dual-function heat indicator according to  claim 1 , wherein the first reactant comprises a color former and the second reactant comprises a color developer and wherein, optionally, the color former or the color developer, or both the color former and the color developer, are initially colorless. 
     
     
         10 . A dual function heat indicator according to  claim 9 , wherein the color developer is chosen from a group consisting of 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); meltable, or sensitizer-soluble, primary and secondary amines having low water solubility, for example, 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′-isopropoxydiphenylsulfone, 4-hydroxyphenylbenzenesulfonate, 4-hydroxybenzoyloxybenzylbenzoate, bis-(3-1-butyl-4-hydroxy-6-methylphenyl)sulfone, p-tert-butylphenol, or polymers based on bisphenol A. 
     
     
         11 . A dual function heat indicator according to  claim 9 , wherein the color former is chosen from a group consisting of: 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. 
     
     
         12 . A dual-function heat indicator according to  claim 1 , wherein the cumulative exposure indicator comprises at least one thermally sensitive, polymerizable diacetylenic compound containing at least two conjugated acetylenic groups. 
     
     
         13 . A dual-function heat indicator according to  claim 1 , wherein the cumulative heat exposure color change is irreversible and occurs after a predetermined cumulative heat exposure. 
     
     
         14 . A dual-function heat indicator according to  claim 1 , comprising a freeze indicator wherein the freeze indicator is supported by the substrate and wherein, optionally, the freeze indicator is transparent before activation by exposure to a freezing temperature, is supported on the cumulative exposure indicator and the cumulative exposure indicator is viewable through the freeze indicator. 
     
     
         15 . A dual function indicator according to  claim 1 , further comprising a reference surface printed on the substrate. 
     
     
         16 . A dual function heat indicator according to  claim 1 , wherein the substrate is a synthetic sheet or film further comprised of polyethylene, polypropylene, polycarbonate, polyester, polyamide, polyurethane, polyvinyl chloride, polyvinylidene chloride, cellulose-derived materials, aluminum foil, paper, or coated paper. 
     
     
         17 . A dual function heat indicator according to  claim 16 , wherein the substrate is clear or white. 
     
     
         18 . A dual function heat indicator according to  claim 16 , wherein the substrate is a clear polyester film. 
     
     
         19 . A dual function heat indicator according to  claim 1 , wherein the peak indicator comprises a pre-manufactured thermal paper or film having a normal color change activation temperature of greater than 60° C. 
     
     
         20 . A dual function heat indicator according to  claim 19 , further comprising an activator applied to the pre-manufactured thermal paper or film configured to lower the color change activation temperature of the commercially manufactured thermal paper or film to below 60° C. 
     
     
         21 . A dual function heat indicator according to  claim 20 , wherein the activator is an organic solvent. 
     
     
         22 . A dual function indicator according to  claim 20 , wherein the activator is chosen to have a melting point that is approximately the same as a desired predetermined peak ambient temperature threshold that is indicated by the peak exposure indicator. 
     
     
         23 . A dual function heat indicator according to  claim 20 , wherein the activator is chosen from a group consisting of heptadecanol, 4-methoxyphenol, pentadecanol, 2,4-di-tert-butyl phenol or benzophenone. 
     
     
         24 . A dual function heat indicator according to  claim 20 , further comprising a barrier separating the activator from the premanufactured thermal paper or film, the barrier configured to allow the activator to contact the thermal paper in response to an ambient heat exposure peak temperature greater than a predetermined peak temperature, but less than the normal activation temperature of the thermal paper. 
     
     
         25 . A dual function heat indicator according to  claim 24 , wherein the barrier is a meltable solid. 
     
     
         26 . A dual-function heat indicator according to  claim 1 , wherein the peak exposure indicator has a response temperature chosen from the group consisting of: in the range from about 30° C. to about 50° C., in the range of from about 40° C. to about 60° C., in the range of from about 30° C. to about 40° C., in the range of from about 40° C. to about 50° C., in the range of from about 50° C. to about 60° C., in the range of from about 30° C. to about 35° C., in the range of from about 35° C. to about 40° C., in the range of from about 40° C. to about 45° C., in the range of from about 45° C. to about 50° C., in the range of from about 50° C. to about 55° C., in the range of from about 55° C. to about 60° C., about 30° C., about 35° C., about 40° C., about 45° C., about 50° C., about 55° C., of and about 60° C. 
     
     
         27 . A dual-function heat indicator for monitoring cumulative ambient heat exposure and peak ambient heat exposure, the dual-function heat indicator comprising:
 a substrate;   a cumulative exposure indicator supported by the substrate in one viewable layer of the dual-function heat indicator, the cumulative exposure indicator being color-changeable in response to cumulative ambient heat exposure; and   a peak exposure indicator supported by the substrate in another viewable, layer of the dual-function heat indicator, the peak exposure indicator comprising a meltable particulate colored material;   wherein the meltable particulate colored material has an average particle size imbuing the meltable particulate colored material with a light color, the light color being attributable to scattering of visible light by the meltable colored material particles;   wherein melting of the meltable particulate colored material causes the peak exposure indicator to change its visual appearance, the change in appearance being induced by an ambient heat exposure peak reaching a temperature exceeding the melting point of the meltable particulate colored material; and   wherein the dual-function heat indicator indicates cumulative ambient heat exposure or peak ambient heat exposure by changing color.   
     
     
         28 . A dual-function heat indicator according to  claim 27 , wherein the change in appearance of the peak exposure indicator is caused by the meltable particulate colored material darkening in color. 
     
     
         29 . A dual-function heat indicator according to  claim 27 , wherein the change in appearance of the peak exposure indicator is caused by the melting of the meltable particulate material revealing a background. 
     
     
         30 . A dual-function heat indicator according to  claim 27 , wherein the change in appearance of the peak exposure indicator is caused by the melting of the meltable particulate material obscuring a background. 
     
     
         31 . A dual-function heat indicator according to  claim 27 , wherein the meltable particulate colored material comprises a meltable solid and a dye dissolved in the meltable solid. 
     
     
         32 . A heat event indicator for monitoring ambient heat exposure to a temperature traversing a threshold temperature, the heat event indicator comprising:
 a substrate; and   a coalesceable particulate colored material supported by the substrate;   wherein the coalesceable particulate colored material has an average particle size imbuing the coalesceable particulate colored material with a light color, the light color being attributable to scattering of visible light by the coalesceable colored material particles;   wherein coalescence of the coalesceable particulate colored material causes the coalesceable particulate colored material to darken in color, the darkening being induced by an ambient heat exposure event reaching a temperature traversing the threshold temperature; and   wherein the heat event indicator indicates the occurrence of the ambient heat exposure event by changing color.   
     
     
         33 . A heat event indicator according to  claim 32 , wherein the threshold temperature is a peak temperature and the coalesceable particulate colored material is meltable and melts in response to the ambient heat exposure event. 
     
     
         34 . A heat event indicator according to  claim 32 , wherein the threshold temperature is a freezing temperature, the heat event indicator comprises a dispersion of the coalesceable particulate colored material in aqueous liquid medium, wherein the dispersion collapses and the coalesceable particulate colored material coalesces in response to the ambient heat exposure event. 
     
     
         35 . A host product and a dual-function heat indicator according to  claim 1 , the dual-function heat indicator being associated with the host product to monitor the host product for heat exposure; the host product, optionally, being a medical product comprising a heat-sensitive proteinaceous component. 
     
     
         36 . A method of making a dual-function heat indicator for monitoring cumulative ambient heat exposure and peak ambient heat exposure, optionally, being a dual-function heat indicator according to  claim 1 , the method comprising:
 applying a liquid composition comprising a cumulative heat-sensing agent to a substrate, the cumulative heat-sensing agent being color-changeable in response to cumulative ambient heat exposure and being transparent prior to changing color; and   drying the liquid composition on the substrate to provide a dried composition, without changing the color of the heat-sensing agent;   incorporating a peak exposure indicator composition in the liquid composition, the peak exposure indicator composition comprising a first reactant, a second reactant and a meltable solid; or   supporting a peak exposure indicator comprising a first reactant, a second reactant and a meltable solid on the substrate prior to the application of the liquid composition and applying the liquid composition over the peak exposure indicator on the substrate;   wherein the first reactant and the second reactant are chemically co-reactable to provide a color change, the meltable solid physically separates the first reactant from the second reactant in the dried composition or in the substrate-supported peak exposure indicator, and the color-changing chemical reaction is induced in response to an ambient heat exposure peak.   
     
     
         37 . A method according to  claim 36 , comprising applying the peak exposure indicator composition to a discrete area of the substrate prior to applying the liquid composition and applying the liquid composition to the entire area of the peak exposure indicator. 
     
     
         38 . A method according to  claim 37 , wherein the substrate bears a coating of the peak exposure indicator composition, the coating optionally extending over the entire area of the substrate. 
     
     
         39 . A method according to  claim 36 , wherein the first reactant and second reactant are both particulate and the liquid composition comprises an aqueous dispersion of the first reactant, the second reactant and the meltable solid. 
     
     
         40 . A method for treating a thermal substrate configured to respond to an ambient temperature above a first predetermined threshold by changing color, the method comprising:
 applying an activator to the thermal substrate, the activator configured to cause the thermal substrate to change color at an ambient temperature above a second predetermined threshold, the second predetermined threshold substantially lower than the first predetermined threshold.   
     
     
         41 . A method according to  claim 40 , further comprising coating a printable surface of the thermal substrate with the activator. 
     
     
         42 . A method according to  claim 40 , wherein the activator includes a meltable solid. 
     
     
         43 . A method according to  claim 40 , wherein the thermal substrate includes a thermal coating further comprising a first reactant and a second reactant which are chemically co-reactable to provide a color change, wherein the color change is a chemical reaction being induced in response to a peak temperature exceeding the melting point of the activator. 
     
     
         44 . A method according to  claim 40 , wherein the first reactant comprises a color former and the second reactant comprises a color developer and wherein optionally, the color former or the color developer, or both the color former and the color developer are initially colorless. 
     
     
         45 . A method according to  claim 44 , wherein the color developer is chosen from a group consisting of 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); meltable, or sensitizer-soluble, primary and secondary amines having low water solubility, for example, 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′-isopropoxydiphenylsulfone, 4-hydroxyphenylbenzenesulfonate, 4-hydroxybenzoyloxybenzylbenzoate, bis-(3-1-butyl-4-hydroxy-6-methylphenyl)sulfone, p-tert-butylphenol, or polymers based on bisphenol A. 
     
     
         46 . A method according to  claim 44 , herein the color former is chosen from a group consisting of: 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′1-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. 
     
     
         47 . A method according to  claim 40 , further comprising a barrier which prevents direct contact between the activator and the thermal coating. 
     
     
         48 . A method according to  claim 47 , wherein the barrier is a meltable solid with a melting point of about the second threshold temperature, wherein an ambient temperature above the second predetermined threshold causes melting of the barrier triggering the reaction between the first reactant and second reactant to chemically co-react and provide a color change. 
     
     
         49 . A method according to  claim 48 , wherein the meltable solid is chosen to have a melting point that is approximately the same as a desired predetermined peak ambient temperature threshold that is indicated by the peak exposure indicator. 
     
     
         50 . A method according to  claim 40 , wherein the thermal substrate is pre-manufactured thermal paper or pre-manufactured thermal film. 
     
     
         51 . A method according to  claim 40 , wherein the activator is an organic solvent, preferably chosen from a group consisting of: heptadecanol, 4-methoxyphenol, pentadecanol, 2,4-di-tert-butyl phenol or benzophenone, and more preferably the activator is benzophenone. 
     
     
         52 . A method according to  claim 40 , wherein an ambient temperature above the second predetermined threshold causes melting of the activator triggering the reaction between the first reactant and second reactant to chemically co-react and provide a color change. 
     
     
         53 . A peak heat indicator comprising:
 a pre-manufactured thermal substrate normally configured to respond to an ambient temperature above a first predetermined threshold by changing color, and an activator applied to the thermal substrate and configured to interact with the pre-manufactured thermal substrate so that the pre-manufactured substrate changes color to respond to an ambient temperature above a second predetermined threshold by changing color, the second predetermined threshold being substantially lower than the first predetermined threshold.   
     
     
         54 . A peak heat indicator according to  claim 53 , wherein the activator includes a meltable solid having a melting point approximately the same as the second predetermined temperature, wherein an ambient temperature above the second predetermined threshold causes melting of the activator triggering the reaction between the first reactant and second reactant, causing them to chemically co-react and provide a color change. 
     
     
         55 . A peak heat indicator according to  claim 54 , wherein the meltable solid is chosen to have a melting point that is approximately the same as a desired predetermined peak ambient temperature threshold that is indicated by the peak exposure indicator. 
     
     
         56 . A peak heat indicator according to  claim 53 , wherein the thermal substrate includes a thermal coating further comprising a first reactant and a second reactant which are chemically co-reactable to provide a color change wherein the color, change is a chemical reaction being induced in response to a peak temperature exceeding the melting point of the activator. 
     
     
         57 . A peak heat indicator according to  claim 53 , wherein the first reactant comprises a color former and the second reactant comprises a color developer and wherein optionally, the color former or the color developer, or both the color former and the color developer are initially colorless. 
     
     
         58 . A peak heat indicator according to  claim 57 , wherein the color developer is chosen from a group consisting of 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); meltable, or sensitizer-soluble, primary and secondary amines having low water solubility, for example, 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′-isopropoxydiphenylsulfone, 4-hydroxyphenylbenzenesulfonate, 4-hydroxybenzoyloxybenzylbenzoate, bis-(3-1-butyl-4-hydroxy-6-methylphenyl)sulfone, p-tert-butylphenol, or polymers based on bisphenol A. 
     
     
         59 . A peak heat indicator according to  claim 57 ; wherein the color former is chosen from a group consisting of: 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. 
     
     
         60 . A peak heat indicator according to  claim 53 , further comprising a barrier configured to prevent direct contact between the activator and the thermal coating. 
     
     
         61 . A peak heat indicator according to  claim 60 , wherein the barrier is a meltable solid. 
     
     
         62 . A peak heat indicator according to  claim 53 , wherein the thermal substrate is pre-manufactured thermal paper or pre-manufactured thermal film. 
     
     
         63 . A peak heat indicator according to  claim 53 , wherein the activator is an organic solvent, preferably chosen from a group consisting of: heptadecanol, 4-methoxyphenol, pentadecanol, 2,4-di-tert-butyl phenol or benzophenone, and more preferably benzophenone