Easy-opening container and closure with radiation-weakened bond and method therefor

Abstract

An easy-opening container and a closure and method therefor are provided. The closure is bonded to a base portion of the container by a bond that can be weakened by radiation, such as microwave radiation. The bond can be weakened after a retort process or other operation so that the bond and, hence, the container is strong enough to resist the forces associated with retort processing but easily opened by a consumer or other user. Either or both of the closure and the base portion can be formed of plastic, and the container can be hermetically sealed for containing food or for other uses.

1 . An easy-opening, retortable container comprising: 
 a base portion having a bottom and side defining an interior space and an opening thereto; and    a plastic membrane of sufficient size to cover the opening and having an outer peripheral area attached to the base portion by a radiation weakened bond having a predetermined tensile force strength; and    wherein the predetermined tensile force strength of the weakened bond allows easy-opening of the container by peeling the membrane from the base portion.    
   
   
       2 . An easy-opening, retortable container according to  claim 1  wherein the base portion is formed of plastic.  
   
   
       3 . An easy-opening, retortable container according to  claim 1  wherein the base portion includes a plastic end ring fusion bonded to a body member, the end ring having an outer peripheral area adapted to be joined to the side of the base portion and defining the opening, the plastic membrane being attached to the end ring by the bond.  
   
   
       4 . An easy-opening, retortable container according to  claim 1  wherein the predetermined tensile force strength is less than about 14 pounds.  
   
   
       5 . An easy-opening, retortable container according to  claim 1  wherein the membrane and the base portion are formed of a high barrier material to prevent transmission of moisture and oxygen therethrough.  
   
   
       6 . An easy-opening, retortable container according to  claim 1  wherein the membrane is formed of a co-extruded sheet of polypropylene and ethylene vinyl alcohol.  
   
   
       7 . An easy-opening, retortable container according to  claim 1  wherein the membrane includes oxygen scavengers disposed in polyolefin.  
   
   
       8 . An easy-opening, retortable container according to  claim 1  wherein the bond is formed of an adhesive.  
   
   
       9 . An easy-opening, retortable container according to  claim 8  wherein the adhesive is formed of polyurethane.  
   
   
       10 . An easy-opening, retortable container according to  claim 1  wherein the bond is weakened by microwave radiation.  
   
   
       11 . An easy-opening, retortable container comprising: 
 a base portion having a bottom and side defining an interior space and an opening thereto; and    a plastic membrane of sufficient size to cover the opening and having an outer peripheral area attached to the base portion by a bond having a predetermined shear force strength and configured to be radiation weakened to have a predetermined tensile force strength; and    wherein the predetermined shear force strength of the bond is sufficient to withstand forces created during retort processing of the container, and the predetermined tensile force strength of the bond allows easy-opening of the container by peeling the membrane from the base portion.    
   
   
       12 . An easy-opening, retortable container according to  claim 11  wherein the base portion is formed of plastic.  
   
   
       13 . An easy-opening, retortable container according to  claim 11  wherein the base portion includes a plastic end ring fusion bonded to a body member, the end ring having an outer peripheral area adapted to be joined to the side of the base portion and defining the opening, the plastic membrane being attached to the end ring by the bond.  
   
   
       14 . An easy-opening, retortable container according to  claim 11  wherein the predetermined shear force strength is at least about 20 psi, and the predetermined tensile force strength is less than about 14 pounds.  
   
   
       15 . An easy-opening, retortable container according to  claim 11  wherein the membrane and the base portion are formed of a high barrier material to prevent transmission of moisture and oxygen therethrough.  
   
   
       16 . An easy-opening, retortable container according to  claim 11  wherein the membrane is formed of a co-extruded sheet of polypropylene and ethylene vinyl alcohol.  
   
   
       17 . An easy-opening, retortable container according to  claim 11  wherein the membrane includes oxygen scavengers disposed in polyolefin.  
   
   
       18 . An easy-opening, retortable container according to  claim 11  wherein the bond is formed of an adhesive.  
   
   
       19 . An easy-opening, retortable container according to  claim 18  wherein the adhesive is formed of polyurethane.  
   
   
       20 . An easy-opening, retortable container according to  claim 11  wherein the bond is adapted to be weakened by microwave radiation.  
   
   
       21 . An easy-opening closure for hermetic sealing of an open end of a retortable container, the closure comprising: 
 a plastic end ring having an outside peripheral area adapted to be joined to the open end of the retortable container and an intermediate area extending radially inward from the outer peripheral area and defining an opening to allow access therethrough to the interior of the container; and    a plastic membrane of sufficient size to cover the opening and having an outer peripheral area overlapping and attached to the intermediate area of the end ring by a bond having a predetermined shear force strength and configured to be radiation weakened to have a predetermined tensile force strength; and    wherein the predetermined shear force strength of the bond is sufficient to withstand forces created during retort processing of the container, and the predetermined tensile force strength of the bond allows easy-opening of the container by peeling the membrane from the end ring.    
   
   
       22 . An easy-opening closure according to  claim 21  wherein the plastic end ring is configured to be fusion welded to the container.  
   
   
       23 . An easy-opening closure according to  claim 21  wherein the end ring is formed of plastic.  
   
   
       24 . An easy-opening closure according to  claim 21  wherein the predetermined shear force strength is at least about 20 psi, and the predetermined tensile force strength is less than about 14 pounds.  
   
   
       25 . An easy-opening closure according to  claim 21  wherein the membrane is formed of a high barrier material to prevent transmission of moisture and oxygen therethrough.  
   
   
       26 . An easy-opening closure according to  claim 21  wherein the membrane is formed of a co-extruded sheet of polypropylene and ethylene vinyl alcohol.  
   
   
       27 . An easy-opening closure according to  claim 21  wherein the membrane includes oxygen scavengers disposed in polyolefin.  
   
   
       28 . An easy-opening closure according to  claim 21  wherein the bond is formed of an adhesive disposed between the plastic end ring and the plastic membrane.  
   
   
       29 . An easy-opening closure according to  claim 28  wherein the bond is formed of polyurethane.  
   
   
       30 . An easy-opening closure according to  claim 21  wherein the bond is adapted to be weakened by microwave radiation.  
   
   
       31 . A method of hermetically sealing an open end of a retortable, easy-opening container, the method comprising: 
 providing a plastic base portion defining an opening;    disposing a plastic membrane to cover the opening of the base portion;    forming a bond between the membrane and the base portion; and    weakening the bond by irradiating the bond such that the bond allows easy opening of the container by peeling the membrane from the base portion.    
   
   
       32 . A method according to  claim 31  wherein said providing step comprises fusion welding an end ring to a body member to form the base portion of the container.  
   
   
       33 . A method according to  claim 31  wherein said weakening step comprises irradiating the bond with microwave radiation.  
   
   
       34 . A method according to  claim 33  wherein said weakening step comprises irradiating the bond with microwave radiation for at least about 10 minutes.  
   
   
       35 . A method according to  claim 31  wherein said forming step comprises forming the bond such that the bond has a shear force strength of at least about 20 psi and wherein said weakening step comprises weakening the bond such that the bond has a tensile force strength of less than about 14 pounds.  
   
   
       36 . A method according to  claim 31  further comprising co-extruding a sheet of polypropylene and ethylene vinyl alcohol to form the plastic membrane.  
   
   
       37 . A method according to  claim 31  further comprising disposing oxygen scavengers in polyolefin to form the plastic membrane.  
   
   
       38 . A method according to  claim 31  wherein said forming step comprises disposing an adhesive between the plastic membrane and the base portion and urging the plastic membrane and the base portion together.  
   
   
       39 . A method according to  claim 31  further comprising retorting the container after said forming step and prior to said weakening step.