Flexible Package With Stress Riser Opening

1 . A sealed package, comprising:

a first side and a second side, wherein the first side and the second side each comprise a laminate material including a product-side layer and a film layer, the product-side layers of the first and second sides at least partially heat sealed together to form a heat seal between the first and second sides such that the heat seal comprises a stress riser,

wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material.

2 . The sealed package of claim 1 , wherein the film layer comprises at least one olefin polymer.

3 . The sealed package of claim 2 , wherein the olefin polymer comprises polypropylene or polyethylene terephthalate.

4 . The sealed package of claim 1 , wherein the film layer comprises a biopolymer.

5 . The sealed package of claim 4 , wherein the biopolymer comprises cellulose.

6 . The sealed package of claim 1 , wherein the product-side layer comprises polyurethane.

7 . The sealed package of claim 1 , wherein the product-side layer comprises polyethylene.

8 . The sealed package of claim 1 , wherein the package has an interior space, the heat seal includes an interior boundary facing the interior space, the interior boundary having a first portion, and the stress riser includes a second portion of the interior boundary extending beyond the first portion of the interior boundary toward the interior space or away from the interior space.

9 . The sealed package of claim 8 , wherein the stress riser comprises a “V” shape.

10 . The sealed package of claim 8 , wherein the stress riser comprises a “U” shape.

11 . The sealed package of claim 1 , wherein the sealed package furthers comprises a food on the inside of the sealed package.

12 . The sealed package of claim 11 , wherein the food comprises a vegetable.

13 . The sealed package of claim 1 , wherein the product-side layer is adapted to rupture at the stress riser and vent steam out of the sealed package between the product-side layer and the film layer.

14 . A method of making a sealed package, comprising the steps of:

(a) providing a laminate material including an product-side layer and a film layer; and

(b) heat sealing the product-side layer of a first portion of the laminate material and the product-side layer of a second portion of the laminate material to form a heat seal comprising a stress riser,

wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material.

15 . The method of claim 14 , wherein the heat sealing step forms a heat seal including an interior boundary facing an interior space of the sealed package, the interior boundary having a first portion, and the stress riser includes a second portion of the interior boundary extending beyond the first portion of the interior boundary toward the interior space or away from the interior space.

16 . The method of claim 15 , wherein the heat sealing step comprises forming a stress riser with a “V” shape.

17 . The method of claim 15 , wherein the heat sealing step comprises forming a stress riser with a “U” shape.

18 . The method of claim 14 , wherein the heat sealing step comprises pressing the first portion and second portion together between two heated dies comprising stress rising faces.

19 . A method of preparing food, comprising:

(a) providing a sealed package comprising a first side and a second side, wherein the first side and the second side each comprise a laminate material including an product-side layer and a film layer, the product-side layers of the first and second sides at least partially heat sealed together to form a heat seal between the first and second sides such that the heat seal comprises a stress riser, wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material, and wherein the sealed package further comprises a food on the inside of the sealed package; and

(b) microwaving the sealed package to heat the food and generate steam;

wherein the pressure of the steam forms a break in the product-side layer at the location of the stress riser, and

wherein the pressure of the steam delaminates the product-side layer and the film layer at the location of the break.

20 . A heat sealing die for heat sealing a package comprising:

(a) a first heat seal jaw having a first primary seal face with a first periphery and a first stress-riser seal face extending outwardly away from the first periphery; and

(b) a second heat seal jaw having a second primary seal face with a second periphery and a second stress-riser seal face extending outwardly away from the second periphery;

wherein the heat sealing die is adapted to compress said first heat seal jaw and said second heat seal jaw about the package to produce a primary heat seal where the first primary seal face and the second primary seal face contact the package and a stress riser adjacent to the primary heat seal where the first stress-riser seal face and the second stress-riser seal face contact the package.

21 . A system for producing a heat-sealed package comprising:

(a) a heat sealing die comprising

(i) a first heat seal jaw having a first primary seal face with a first periphery and a first stress-riser seal face extending outwardly away from the first periphery; and

(ii) a second heat seal jaw having a second primary seal face with a second periphery and a second stress-riser seal face extending outwardly away from the second periphery;

wherein the heat sealing die is adapted to compress said first heat seal jaw and said second heat seal jaw about the package to produce a primary heat seal where the first primary seal face and the second primary seal face contact the package and a stress riser adjacent to the primary heat seal where the first stress-riser seal face and the second stress-riser seal face contact the package; and

(b) a feeder adapted to feed the package between the first heat seal jaw and the second heat seal jaw.