Easily openable closure for a retortable container having a metal end to which a membrane is sealed

Abstract

A retortable, easily openable closure of the type having a metal end and a membrane closure heat-sealed thereto, wherein the metal end has a coating of a heat-seal composition comprising a food-compatible metal-coating composition blended with polypropylene. The polypropylene disperses within the food-compatible metal-coating composition during curing of the coating on the metal end such that an outer surface of the coating defines a multitude of separate, spaced islands of polypropylene dispersed within the food-compatible metal-coating composition so as to form bonding sites. The membrane closure's lower surface has a heat-seal layer of polypropylene for sealing to the coating on the metal end.

1 . A retort container assembly for producing a retort container, the retort container assembly comprising: 
 a container body having a top end;    a metal end joined to the top end of the container body, the metal end defining an opening through which contents of the container are dispensed, an upper surface of the metal end that surrounds the opening having a coating of a heat seal composition comprising a food-compatible metal-coating composition blended with polypropylene, the polypropylene dispersing within the food-compatible metal-coating composition during curing of the coating on the metal end such that an outer surface of said coating defines a multitude of separate, spaced islands of polypropylene dispersed within the food-compatible metal-coating composition so as to form bonding sites; and    a membrane for attachment to the metal end to seal closed the opening thereof, a lower surface of the membrane having a heat-seal layer thereon for heat-sealing to the polypropylene bonding sites on the coating on the metal end, the heat-seal layer comprising polypropylene and bonding to the membrane with a bond strength exceeding that between the heat-seal layer and the coating on the metal end.    
   
   
       2 . The retort container assembly of  claim 1 , wherein the coating on the metal end comprises about 1 to 20 weight percent polypropylene.  
   
   
       3 . The retort container assembly of  claim 2 , wherein the coating comprises about 10 weight percent polypropylene.  
   
   
       4 . The retort container assembly of  claim 1 , wherein the coating comprises epoxy and polypropylene.  
   
   
       5 . The retort container assembly of  claim 1 , wherein the membrane includes a foil layer, and the heat-seal layer of polypropylene is bonded to the foil layer.  
   
   
       6 . The retort container assembly of  claim 5 , wherein the membrane further includes a layer of polyethylene terephthalate, the foil layer being disposed between the layers of polypropylene and polyethylene terephthalate.  
   
   
       7 . A process for forming a seal between a metal end of a container and a closure membrane such that a peel strength of the seal is substantially unaffected by a retort process and such that the seal has a controlled low peel strength rendering the seal readily openable, the process comprising the steps of: 
 providing the membrane to have a heat-seal layer exposed on a side of the membrane to be sealed to the metal end, the heat-seal layer comprising a layer of polypropylene;    providing the metal end to have a coating of a heat seal composition comprising a food-compatible metal-coating composition blended with polypropylene, the polypropylene dispersing within the food-compatible metal-coating composition during curing of the coating on the metal end such that an outer surface of said coating defines a multitude of separate, spaced islands of polypropylene dispersed within the food-compatible metal-coating composition so as to form bonding sites for bonding to the polypropylene heat-seal layer on the membrane; and    attaching the membrane to the metal end by heat-sealing the heat-seal layer on the membrane to the coating on the metal end via said bonding sites, wherein the coating on the metal end is formulated such that the heat-seal layer on the membrane bonds to the coating with a bond strength less than that between the heat-seal layer and the membrane, whereby failure occurs between the heat-seal layer and the coating when the membrane is pulled to open the container.    
   
   
       8 . The process of  claim 7 , wherein the entire outer surface of the coating is provided to have a substantially uniform distribution of said islands of polypropylene.  
   
   
       9 . The process of  claim 7 , wherein the coating on the metal end is provided to have about 1 to 20 percent polypropylene by weight.  
   
   
       10 . The process of  claim 7 , wherein the coating is formulated of epoxy and polypropylene.