Doneness indicator for heat-in packaging and method of making same

Abstract

A heat-in package with doneness indicator for heating applications, such as microwave heating of foods or sterilization applications. The doneness indicator comprises indicia printed with thermochromatic ink on the heat-in packaging. The doneness indicator can be sealed from front to back on the heat-in packaging in such a way that the heat transfer to the sealed area is controlled so that the contents contained within the heat-in packaging has adequate time to heat before a color change or other visual transformation is observed in the doneness indicator. Furthermore, the sealed area containing the thermochromatic ink is not in direct contact with the contents within the packaging. The ink changes due to heat conduction through the film. A venting system can further be incorporated to prevent excessive pressure build-up within the packaging.

1 . A heat-in package for heating a food product, the heat-in package comprising:
 a food product;   a flexible plastic film sealed to form a package, wherein the package is adapted to completely encapsulate and retain the food product within the package during heating of the food product; and   a doneness indicator adapted to undergo a visual transformation in response to a temperature change, the doneness indicator being at least partially isolated from the food product by an indicator seal, wherein the indicator seal inhibits heat transfer to the doneness indicator so as to delay the visual transformation such that the food product is maintained at an elevated temperature for a period of time to sufficiently heat the food product before the visual transformation is observed through the flexible plastic film.   
     
     
         2 . The heat-in package of  claim 1 , wherein the doneness indicator is formed from a thermochromatic ink. 
     
     
         3 . The heat-in package of  claim 1 , wherein the doneness indicator is sandwiched between opposing inner surfaces of the flexible plastic film. 
     
     
         4 . The heat-in package of  claim 1 , wherein the flexible plastic film comprises a multilayer film. 
     
     
         5 . The heat-in package of  claim 4 , wherein the multilayer film is formed of two layers, and wherein the doneness indicator is sandwiched between an inner surface of the first layer of the multilayer film, and an opposing inner surface of the second layer of the multilayer film. 
     
     
         6 . The heat-in package of  claim 1 , wherein at least a portion of the flexible film is transparent or semi-transparent. 
     
     
         7 . The heat-in package of  claim 1 , wherein the indicator seal is formed on an outer surface of the package by ultrasonic welding. 
     
     
         8 . The heat-in package of  claim 1 , wherein the food product is selected from the group comprising vegetable, fruits, meat, popcorn, sauce, and combinations thereof. 
     
     
         9 . The heat-in package of  claim 1 , wherein the indicator seal comprises at least one circle. 
     
     
         10 . The heat-in package of  claim 9 , wherein the indicator seal comprises a plurality of circles in concentric arrangement. 
     
     
         11 . A method of making a heat-in package having a doneness indicator for heating a food product, the method comprising:
 providing a food product;   forming a flexible plastic film into a package by sealing, the package adapted to completely encapsulate and retain the food product within the package during heating of the food product;   positioning a doneness indicator on the package, wherein the doneness indicator is adapted to undergo a visual transformation in response to a temperature change; and   sealing the doneness indicator such that the doneness indicator is sealingly isolated from the food product by an indicator seal, wherein the indicator seal inhibits heat transfer to the doneness indicator so as to delay the visual transformation such that the food product is maintained at an elevated temperature for a period of time to sufficiently heat the food product before the visual transformation is observed through the flexible plastic film.   
     
     
         12 . The method of  claim 11 , wherein positioning a doneness indicator on the package comprises printing a thermochromatic ink on one of the opposing inner surfaces of the flexible plastic film, or an exterior surface of the flexible plastic film. 
     
     
         13 . The method of  claim 11 , wherein sealing the doneness indicator comprises forming the indicator seal by ultrasonic welding. 
     
     
         14 . The method of  claim 11 , wherein the doneness indicator is sealed between opposing inner surfaces of the flexible plastic film. 
     
     
         15 . A heat-in package for heating a food product comprising:
 a food product;   a flexible plastic film sealed to form a package, wherein the package is adapted to completely encapsulate and retain the food product within the package during heating of the food product; and   a doneness indicator formed from a thermochromatic ink, wherein the doneness indicator is adapted to undergo a color change in response to a temperature change, the doneness indicator being isolated from the food product by an indicator seal formed by low temperature sealing, wherein the indicator seal inhibits heat transfer to the doneness indicator so as to delay the color change such that the food product is maintained at an elevated temperature for a period of time to sufficiently heat the food product before the color change is observed through the flexible plastic film.   
     
     
         16 . The heat-in package of  claim 15 , wherein the low temperature sealing is accomplished through ultrasonic welding. 
     
     
         17 . The heat-in package of  claim 15 , wherein the doneness indicator is sandwiched between opposing inner surfaces of the flexible plastic film. 
     
     
         18 . The heat-in package of  claim 15 , wherein the flexible plastic film comprises a multilayer film. 
     
     
         19 . The heat-in package of  claim 18 , wherein the multilayer film is formed of two layers, and wherein the doneness indicator is further sandwiched between an inner surface of the first layer of the multilayer film, and an opposing inner surface of the second layer of the multilayer film. 
     
     
         20 . The heat-in package of  claim 15 , wherein at least a portion of the flexible film is transparent or semi-transparent. 
     
     
         21 . A method of making a heat-in package having a thermochromatic doneness indicator, the method comprising:
 providing a food product;   heat sealing a flexible plastic film to form a package, the package adapted to completely encapsulate and retain the food product within the package during heating of the food product;   positioning a thermochromatic doneness indicator on the package, wherein the doneness indicator is adapted to undergo a color change in response to a temperature change; and   sealing the thermochromatic doneness indicator by low temperature sealing, such that the doneness indicator is sealingly isolated from the food product by an indicator seal, wherein the indicator seal inhibits heat transfer to the thermochromatic doneness indicator so as to delay the color change such that the food product is maintained at an elevated temperature for a period of time to sufficiently heat the food product before the color change is observed through the flexible plastic film.   
     
     
         22 . The method of  claim 21 , wherein positioning a thermochromatic doneness indicator on the package comprises printing a thermochromatic ink on one of the opposing inner surfaces of the flexible plastic film, or on an exterior surface of the flexible plastic film. 
     
     
         23 . The method of  claim 21 , wherein the thermochromatic doneness indicator is sealed sandwiched between opposing inner surfaces of the flexible plastic film. 
     
     
         24 . The method of  claim 21 , wherein sealing the thermochromatic doneness indicator comprises forming the indicator seal by ultrasonic welding. 
     
     
         25 . A heat-in package for heating contents within the package, the heat-in package comprising:
 contents to be heated;   a plastic film sealed to form a package, wherein the package is adapted to completely encapsulate and retain the contents within the package during heating of the contents; and   a doneness indicator adapted to undergo a visual transformation in response to a temperature change, the doneness indicator being at least partially isolated from the contents of the package by an indicator seal, wherein the indicator seal inhibits heat transfer to the doneness indicator so as to delay the visual transformation such that the contents of the package are maintained at an elevated temperature for a period of time to sufficiently heat the contents before the visual transformation is observed through the plastic film.   
     
     
         26 . The heat-in package of  claim 25 , wherein the contents is selected from the group comprising food products, medical instruments, dental instruments, pharmaceutical compositions, and combinations thereof. 
     
     
         27 . The heat-in package of  claim 25 , wherein the doneness indicator is sandwiched between opposing inner surfaces of the plastic film. 
     
     
         28 . The heat-in package of  claim 25 , wherein the indicator seal is formed on an outer surface of the package by ultrasonic welding. 
     
     
         29 . The heat-in package of  claim 25 , wherein the indicator seal comprises at least one circle. 
     
     
         30 . The heat-in package of  claim 25 , wherein the indicator seal comprises a plurality of circles in concentric arrangement.