Activatable temperature indicator with time delay

Abstract

Disclosed herein are delayed reaction threshold temperature indicators and methods of making and activating the same, the delayed reaction threshold temperature indicators including a first substrate, first and second layers, and a housing secured to the substrate. The first layer includes a first reactant and an optional meltable polymer, and the second layer includes a meltable polymer and a second reactant. The meltable polymer is configured to keep the first and second reactants from interacting with each other. When exposed to temperatures at and/or above a desired threshold for a period of time, the meltable polymer melts and allows the first and second reactants to come into contact with each other, thereby producing a visual change in appearance.

1 . A delayed reaction threshold temperature indicator comprising:
 a first substrate   a first layer further comprising a first reactant, the first layer positioned on top of the substrate;   a second layer further comprising a meltable polymer and a second reactant, the second layer positioned on top of the first layer;   a removable barrier layer between the first layer and the second layer, the barrier layer substantially impermeable to and preventing contact between the first and second reactants;   a housing secured to the substrate, the housing including a viewing window through which the first and second layers are visible;   wherein after removal of the barrier layer, exposure to a temperature at and/or above the melting point of the meltable polymer for a predetermined period of exposure time allows the first reactant and/or second reactant to migrate toward each other; and   wherein the first and second reactants produce a visual change in appearance after they come into contact with each other.   
     
     
         2 . The indicator of  claim 1 , wherein the visual change in appearance is a change in color. 
     
     
         3 . The indicator of  claim 2 , wherein the change in color is a darkening of the first and second layers visible through the viewing window. 
     
     
         4 . The indicator of  claim 1 , wherein the first layer comprises a second substrate infused or impregnated with the first reactant. 
     
     
         5 . The indicator of  claim 1 , wherein the first layer comprises the meltable polymer with the first reactant initially contained therein. 
     
     
         6 . The indicator of  claim 1 , wherein the first includes a background comprising a pattern, an indicia, or a color darker than an initial color of the first and second reactants prior to their contacting each other. 
     
     
         7 . The indicator of  claim 6 , wherein the background is initially visible through the viewing window and is at least partially obscured by the visual change in appearance. 
     
     
         8 . The indicator of  claim 1 , wherein the melting point of the meltable polymer is in a range from -10° C. to 50° C. 
     
     
         9 . (canceled) 
     
     
         10 . The indicator of  claim 1 , wherein the predetermined period of time is in the range from 5 minutes to 60 minutes. 
     
     
         11 - 12 . (canceled) 
     
     
         13 . The indicator of  claim 10 , wherein the exposure occurs during two or more exposures to a temperature at and/or above the melting point of the meltable polymer. 
     
     
         14 . The indicator of  claim 13 , wherein the meltable polymer resolidifies rapidly when exposed to a temperature below the melting point of the meltable polymer. 
     
     
         15 . The indicator of  claim 14 , wherein resolidification of the meltable polymer comprises recrystallization. 
     
     
         16 . The indicator of  claim 14 , wherein the resolidification of the meltable polymer inhibits migration of the first and/or second reactants through the first and/or second layers. 
     
     
         17 . The indicator of  claim 1 ,
 wherein the molecular weight of the meltable polymer is in the range from 5,000 Da to 30,000 Da.   
     
     
         18 . The indicator of  claim 1 ,
 wherein the first reactant is bromothymol blue or resorcinol.   
     
     
         19 . The indicator of  claim 1 ,
 wherein the weight percent of the first reactant in the first layer is in the range of 0.1% to 10%.   
     
     
         20 . (canceled) 
     
     
         21 . The indicator of  claim 1 ,
 wherein the second reactant is butylamine or 5-(hydroxymethyl)furfural (HMF).   
     
     
         22 - 32 . (canceled) 
     
     
         33 . The indicator of  claim 1 , further comprising a reference area surrounding or adjacent to the viewing window. 
     
     
         34 . The indicator of  claim 33 , wherein the reference area comprises a pattern, a color, or a printed indicia that contrasts with or corresponds to the visual change in appearance caused by the reaction between the first and second reactants. 
     
     
         35 . The indicator of  claim 1 , further comprising;
 at least one of a freeze indicator, a second temperature threshold exposure indicator with a different temperature threshold, and a cumulative time-temperature exposure indicator.   
     
     
         36 - 45 . (canceled)