Self-Heating Or Self-Cooling Containers

Abstract

A self-heating or self-cooling container for food or drink comprises inner and outer vessels defining a reaction cell between their mutually facing walls is provided. The reaction cell is divided into first and second chambers by a rupturable membrane. A liquid chemical reagent is filled into the second chamber which is at ambient pressure, and a solid chemical reagent is placed in the first chamber which is at sub-atmospheric pressure. The sub-atmospheric pressure in the first chamber causes a rapid and thorough mixing of the chemical reagents, and shaking the container after the initial rupture of the membrane assists that rapid mixing. Preferably the second chamber is elastically deformable to increase its internal volume, for example being formed with corrugated walls. Alternatively the reaction cell may be provided with pressure relief valve means.

1 . A self-heating or self-cooling container for food or drink comprising: 
 an inner vessel made of thermally conductive material for containing the food or drink;    an outer vessel made of a thermally insulating material;    a two-chamber reaction cell formed between the inner and outer vessels, wherein the reaction cell comprises a first chamber formed between the inner and outer vessels, and a second chamber formed in a base portion of the outer vessel, the first and second chambers being mutually separated by a frangible barrier that can be ruptured by depressing a movable bottom wall of the outer vessel, the first chamber containing a first chemical reagent and the second chamber containing a second chemical reagent, wherein the first and second chemical reagents react together, when mixed, in an exothermic or endothermic chemical reaction to cause the heating or cooling of the contents of the inner vessel; and    wherein prior to rupture of the frangible barrier the first chamber is at subatmospheric pressure and the second chamber is at a higher pressure, so that on rupture of the frangible barrier the equalisation of that pressure differential assists the passage of the second chemical reagent into the first chamber to encourage rapid mixing of the chemical reagents in the first chamber.    
   
   
       2 . A container according to  claim 1 , wherein the first chemical reagent is a dry powdered chemical reagent and the second chemical reagent is a liquid chemical reagent, wherein the first chamber is formed between mutually spaced sidewalls of the inner and outer vessels and across a bottom wall of the inner vessel, and further comprising a removable film seal sealing the top of the inner vessel.  
   
   
       3 . A container according to  claim 2 , further comprising a removable lid covering the top of the container to provide a stable support surface for resting the container in an inverted condition on a flat surface, the removable lid establishing a void space between the removable film seal over the top of the inner vessel and the lid so that after inversion of the container, depression of the movable bottom wall of the outer vessel to rupture the frangible barrier, shaking the container further to encourage mixing of the first and second chemical reagents and standing the inverted container on a flat surface, any volume expansion of the contents of the inner vessel is accommodated by stretching of the removable film seal into the void space.  
   
   
       4 . A container according to  claim 1 , wherein the second chamber incorporates a gas release valve for the release to the atmosphere of any gases generated or caused thermally to expand by the chemical reaction between the reagents following rupture of the frangible barrier.  
   
   
       5 . A container according to  claim 1 , wherein the first and second chambers are sealed chambers, and the second chamber is a variable volume chamber capable of expansion to accommodate any gases generated or caused thermally to expand by the chemical reaction between the reagents following rupture of the frangible barrier.  
   
   
       6 . A container according to  claim 5 , wherein the second chamber has a corrugated side wall so that a partial straightening of the corrugations causes the expansion of the internal volume of the second chamber.  
   
   
       7 . A container according to  claim 6 , wherein the variable volume second chamber is also capable of a partial tightening of the corrugations to cause a reduction in the internal volume of the second chamber when the frangible barrier is first ruptured and the pressure equalisation between the first and second chambers causes an initial fall in the pressure prevailing in the second chamber.  
   
   
       8 . A container according to  claim 1 , further comprising a temperature indicator comprising a message or symbol printed on the outside of the container in a temperature-responsive ink which changes colour when a predefined temperature of that outer wall of the container is reached.  
   
   
       9 . A container according to  claim 8 , wherein the message or symbol is printed on the bottom wall of the container so as to be visible only when the container is inverted.  
   
   
       10 . A container according to  claim 1 , wherein the first and second chemical reagents react together to create a product of reaction which is solid or semi-solid.  
   
   
       11 . A container according to  claim 10 , wherein the first and second chemical reagents incorporate chemicals which react together to generate a quantity of gas sufficient that the solid or semi-solid reaction product is rendered porous.  
   
   
       12 . A container according to  claim 11 , wherein the first chemical reagent incorporates a small quantity of sodium bicarbonate, NaHCO3, and the second chemical reagent is acidic, so that on admixture a small quantity of CO2 is evolved, sufficient to render the solid or semi-solid reaction product porous.