Film fracture feature for peelable multilayer package lid

Abstract

A package for storing and shipping food products incorporates a multilayer film lid that includes a gas-impermeable exterior layer and a gas-permeable interior layer. The multilayer film lid is heat sealed to a flange of a tray upon which the food product is supported. The gas-impermeable layer may be delaminated from the gas-permeable layer when it is desired to expose the food to atmospheric gases. Separation of the gas-impermeable layer from the gas-permeable layer is facilitated by a film fracture feature included in the heat seal pattern adjacent a pull tab of the lid. The film fracture feature concentrates the separation forces exerted on the tab in a small area so that the gas-permeable layer of the lid readily breaks at the film fracture feature.

What is claimed is:  
     
         1 . A package for a food product, comprising: 
 a tray for supporting a food product, the tray defining an upper surface;    a multilayer film lid attached to the upper surface of the tray by a heat seal that extends about a perimeter surrounding the food product, an outer edge of the heat seal having two substantially straight portions that are joined by a corner portion of the heat seal, the lid having upper and lower layers joined together such that the upper layer can be peeled from the lower layer, the lower layer being permeable to oxygen and the upper layer being substantially impermeable to oxygen, the lid having a pull tab portion that extends out beyond the corner portion of the heat seal; and    a film fracture feature defined in the corner portion of the heat seal proximate the pull tab portion, the film fracture feature comprising a portion of the outer edge of the heat seal formed as a straight-line segment oriented at a non-perpendicular angle to each of the two substantially straight portions of the heat seal, whereby pulling upward on the pull tab portion focuses forces on said straight-line segment to break the lower layer along the film fracture feature and thereby initiate fracture between the upper and lower layers of the lid.    
     
     
         2 . The package of  claim 1 , wherein the film fracture feature includes a second straight-line segment, the two straight-line segments intersecting at a vertex.  
     
     
         3 . The package of  claim 1 , wherein the tray includes a bottom wall for supporting said food product, a side wall extending upwards from said bottom wall and terminating at a top edge, and a flange extending outwardly from said top edge of said side wall and including said upper surface to which said lid is attached by said heat seal.  
     
     
         4 . A package for storing a food product in a modified atmosphere, comprising: 
 a tray for supporting the food product; and    a multilayer film lid attached to the tray with a heat seal between the tray and the lid, said heat seal extending substantially continuously about the product to enclose the food product between said tray and said lid, said lid comprising a multilayer film having a first layer and a second layer removably joined together such that the first layer can be delaminated from the second layer;    wherein the lid includes a pull tab portion and said second layer is positioned between said first layer and said tray such that the first layer may be delaminated from the second layer while leaving said second layer attached to said tray;    wherein the heat seal includes a film fracture feature on an outer edge of the heat seal proximate to said pull tab portion of said lid, said film fracture feature comprising a straight-line segment of the outer edge of the heat seal that intersects another portion of the outer edge of the heat seal and thereby forms a vertex that acts as a stress riser for initiation of the delamination of said first layer from said second layer.    
     
     
         5 . The package of  claim 4 , wherein the tray includes a bottom wall for supporting said food product, a side wall extending upwards from said bottom wall and terminating at a top edge, and a flange connected to said top edge of said side wall, wherein said lid is connected to the flange by the heat seal.  
     
     
         6 . The package of  claim 5 , wherein said flange provides a continuous surface that completely surrounds the top edge of said side wall.  
     
     
         7 . The package of  claim 6 , wherein said tray is generally a quadrilateral including four of said side walls and four corners at the intersections between said side walls, and said flange includes four straight portions respectively joined to the side walls and four corner portions formed at junctures between said straight portions of the flange.  
     
     
         8 . The package of  claim 7 , wherein said heat seal includes four straight portions respectively extending along the four straight portions of said flange and four corner portions respectively located at the four corner portions of said flange, and wherein said film fracture feature is located at one of the corner portions of the heat seal.  
     
     
         9 . The package of  claim 8 , wherein said flange includes a generally planar upper surface extending outwardly from said top edge of said side walls and a stepped surface connected to an outer edge of said upper surface.  
     
     
         10 . The package of  claim 9 , wherein said film fracture feature of the heat-seal pattern does not extend outwardly beyond the upper surface of the flange.  
     
     
         11 . The package of  claim 9 , wherein said generally planar upper surface of the corner portion of the flange having the film fracture feature extends to an outer edge of said corner portion.  
     
     
         12 . The package of  claim 4 , wherein the film fracture feature includes a second straight-line segment, the two straight-line segments intersecting at a vertex.  
     
     
         13 . The package of  claim 4 , wherein the film fracture feature includes at least three straight-line segments that form a vertex at each intersection of said straight-line segments.  
     
     
         14 . The package of  claim 4 , wherein said first layer includes a gas-impermeable film.  
     
     
         15 . The package of  claim 14 , wherein said second layer is a gas-permeable film.  
     
     
         16 . A package for storing a food product in a modified atmosphere, comprising: 
 a tray for supporting said food product thereon including a bottom wall for supporting said food product, a side wall extending upwards from said bottom wall and terminating in a top edge, and a flange connected to the top edge of said side wall, wherein said tray is generally a quadrilateral including four of said side walls and four corners at intersections between said side walls, such that said flange includes four straight portions and four corner portions; and    a lid bonded to said tray with a heat seal between said tray and said lid, said heat seal extending substantially continuously about the product to enclose the food product between said tray and said lid, said lid being a multilayer film having a first layer and a second layer removably joined together, said lid having a pull tab portion;    wherein said first layer is gas-impermeable and wherein said second layer is gas-permeable and is positioned between said first layer and said tray such that said first layer may be delaminated from said second layer;    wherein said heat seal includes four straight portions respectively extending along the four straight portions of said flange and four corner portions respectively located at the four corner portions of said flange, the pull tab portion of said lid extending out beyond one of the corner portions of the heat seal;    wherein the corner portion of the heat seal proximate the pull tab portion includes a film fracture feature comprising a straight-line segment of an outer edge of the heat seal that intersects another portion of the outer edge of the heat seal and thereby forms a vertex that acts as a stress riser for initiation of the delamination of said first layer from said second layer.    
     
     
         17 . The package of  claim 16 , wherein said flange includes a generally planar upper surface extending outwardly from said top edge of said side wall and a stepped surface connected to an outer edge of said upper surface, and wherein said stepped surface is absent in the corner portion of the flange at which the film fracture feature is located such that the upper surface of said flange at said corner portion extends to an outer edge of the flange.  
     
     
         18 . The package of  claim 16 , wherein the film fracture feature includes a second straight-line segment, the two straight-line segments intersecting at a vertex.  
     
     
         19 . A package for storing a food product in a modified atmosphere, comprising: 
 a tray for supporting the food product; and    a multilayer film lid attached to the tray with a heat seal between the tray and the lid, said heat seal extending substantially continuously about the product and creating a heat seal pattern which encloses the food product between said tray and said lid, said lid being a multilayer film having a first layer and a second layer removably joined together such that the first layer can be delaminated from the second layer;    wherein the lid includes a pull tab portion and said second layer is positioned between said first layer and said tray such that the first layer may be delaminated from the second layer while leaving said second layer attached to said tray;    wherein an outside edge of the heat seal pattern defines a film fracture feature proximate the pull tab portion, said film fracture feature comprising two line segments of said outside edge that intersect and thereby form a vertex that acts as a stress riser for initiation of the delamination of said first layer from said second layer.    
     
     
         20 . The package of  claim 19 , wherein each of said line segments is substantially straight.