Flexible, self-venting retortable container

Abstract

Containers are disclosed, as well as multilayer films used in such containers, which advantageously maintain a high seal strength even after being subjected to retort conditions for sterilization. These retortable containers and multilayer films are also beneficially self-venting upon exposure to microwave heating, when the internal container pressure exceeds a threshold value. The self-venting nature of these containers arises from particular sealing characteristics, in which the seal width differs in defined, self-venting seal regions, relative to non-venting seal regions of a given peripheral seal. Particular structural features and geometries of the self-venting seal regions can be used to improve the location of venting and control of the vented gases.

1 . A retortable container comprising a peripheral seal formed by a sealing layer of a multilayer film,
 the peripheral seal having at least one self-venting seal region with a minimum venting seal width that is less than a minimum non-venting seal width of a non-venting seal region,   wherein the peripheral seal does not include any film layer having a melting temperature of less than 100° C.   
     
     
         2 . The retortable container of  claim 1 , wherein the minimum venting seal width is at most about 3.2 mm (0.125 inches) and the minimum non-venting seal width is at least about 3.2 mm (0.125 inches). 
     
     
         3 . The retortable container of  claim 1 , wherein the minimum venting seal width is from about 2.4 mm (0.094 inches) to about 3.2 mm (0.125 inches). 
     
     
         4 . The retortable container of  claim 1 , wherein the peripheral seal in the self-venting seal region forms an inward protrusion relative to the peripheral seal in the non-venting seal region. 
     
     
         5 . The retortable container of  claim 4 , wherein the inward protrusion, and a line defined by an edge of the container in the non-venting seal region, define a protruded area. 
     
     
         6 . The retortable container of  claim 5 , wherein the protruded area includes a partial circle or a partial ellipse. 
     
     
         7 . The retortable container of  claim 6 , wherein the protruded area further includes a gas discharge opening of a smaller diameter, relative to the diameter of the partial circle or relative to the smallest diameter of the partial ellipse. 
     
     
         8 . The retortable container of  claim 7 , wherein the diameter of the gas discharge opening is at least 4 mm (0.16 inches) and the diameter of the partial circle or the smallest diameter of the partial ellipse is at least 10 mm (0.39 inches). 
     
     
         9 . The retortable container of  claim 5 , wherein the protruded area is a polygon. 
     
     
         10 . The retortable container of  claim 4 , wherein an inner boundary of the self-venting seal region has a shape that conforms substantially to the shape of the inward protrusion, whereby the venting seal width is substantially constant over at least a portion of the self-venting seal region. 
     
     
         11 . The retortable container of  claim 4 , wherein an inner boundary of the self-venting seal region has a shape that does not conform to the shape of the inward protrusion, whereby the venting seal width varies over at least a portion of the self-venting region. 
     
     
         12 . The retortable container of  claim 9 , wherein the protruded area includes a partial circle or a partial ellipse and an inner boundary of the self-venting seal region is formed by line segments. 
     
     
         13 . The retortable container of  claim 1 , wherein the sealing layer of the multilayer film comprises polypropylene. 
     
     
         14 . The retortable container of  claim 13 , wherein the multilayer film further comprises an outer layer comprising biaxially oriented nylon or biaxially oriented polyethylene terephthalate that is optionally separated from the sealing layer by an adhesive layer. 
     
     
         15 . The retortable container of  claim 14 , wherein the multilayer film has a barrier-oxygen transmission rate from about 0.01 to about 4 cc/100 in 2 /24 hours at a temperature of 23° C. (73° F.). 
     
     
         16 . The retortable container of  claim 1 , wherein gas is discharged through the self-venting seal region when the pressure within the container exceeds a threshold pressure from about 2 psig to about 5 psig. 
     
     
         17 . A retortable container comprising a peripheral seal formed by a sealing layer of a multilayer film,
 the peripheral seal having at least one self-venting seal region with a minimum venting seal width that is less than a minimum non-venting seal width of a non-venting seal region,   wherein, following a retort heat treatment, the container has a seal strength from about 40 N/15 mm (15 lb/in) to about 80 N/15 mm (30 lb/in) according to ASTM-F88 with a crosshead speed of 2.12 cm/sec (5 in/min).   
     
     
         18 . The retortable container of  claim 17 , wherein gas is discharged through the self-venting seal region when the pressure within the container exceeds a threshold pressure from about 2 psig to about 5 psig. 
     
     
         19 . A retortable container comprising a peripheral seal formed by a sealing layer of a multilayer film,
 wherein the peripheral seal in a self-venting seal region forms an inward protrusion relative to the peripheral seal in a non-venting seal region, and   the peripheral seal does not include any film layer having a melting temperature of less than 100° C.   
     
     
         20 . The retortable container of  claim 19 , wherein gas is discharged through the self-venting seal region when the pressure within the container exceeds a threshold pressure from about 2 psig to about 5 psig. 
     
     
         21 . A retortable container comprising a peripheral seal formed by a sealing layer of a multilayer film,
 the peripheral seal having at least one self-venting seal region with a minimum venting seal width that is less than a minimum non-venting seal width of a non-venting seal region,   wherein the multilayer film does not delaminate after being subjected to a temperature of 100° C. for 30 minutes.   
     
     
         22 . The retortable container of  claim 21 , wherein the multilayer film does not delaminate after being subjected to a temperature of 100° C. for 60 minutes.