Tearable container closure and envelope comprising same

1. An envelope adapted to be permanently closed and later opened, the envelope comprising:

a front panel and a rear panel having top, bottom, and opposite side edge margins, the front and rear panels being joined together along the bottom and side edge margins and being unjoined along the top edge margins, the joined edge margins and the panels defining an envelope interior and the unjoined top edge margins defining an envelope opening in communication with the envelope interior; and

a closure having a top edge margin, a bottom edge margin joined to the top edge margin of the rear panel, and a height extending from the bottom edge margin of the closure to the top edge margin, the closure having opposite sides and a width extending from one to the other of the opposite sides, the closure having an interior surface, an exterior surface, and a thickness extending from the exterior surface to the interior surface, the envelope being configured such that the interior surface of the closure is sealable to the front panel of the envelope to permanently close the envelope opening, the closure comprising:

a closure panel extending along the width of the closure and defining at least a portion of each of the exterior and interior surfaces of the closure, the closure panel being formed of a first polymeric material having a tear strength, and

a tear band coextruded with the closure panel to form the closure, the tear band extending along the width of the closure at a location spaced apart from the top of the closure along the height of the closure and being formed of a second polymeric material having tear strength that is lower than the tear strength of the first polymeric material;

wherein the tear band overlies a portion of the closure panel along a segment of the height of the closure to form a composite tearable section of the closure including the tear band and said portion of the closure panel; and

wherein the tear band has a thickness which is from about 50% to about 80% of the thickness of the closure.

2. An envelope as set forth in claim 1 wherein the tear band has an outboard side that defines a portion of one of the interior surface and the exterior surface of the closure panel.

3. An envelope as set forth in claim 2 wherein the tear band has an inboard side and a thickness extending from the outboard side to the inboard side, the thickness of the tear band being less than the thickness of the closure.

4. An envelope as set forth in claim 1 wherein the first polymeric material and the second polymeric material comprise a polymer of the same type.

5. An envelope as set forth in claim 4 wherein the first polymeric material comprises one of low-density polyethylene and linear low-density polyethylene.

6. An envelope as set forth in claim 4 wherein the second polymeric material comprises a high density polyethylene.

7. An envelope as set forth in claim 4 wherein the second polymeric material comprises a polyethylene-foaming agent blend.

8. An envelope as set forth in claim 4 wherein the second polymeric material comprises said polymer of the same type as said polymer of the first polymeric material and another polymer of another type, said other polymer of said other type being between about 1 and about 75 wt % of the second polymeric material.

9. An envelope as set forth in claim 8 wherein said other polymer of said other type is between about 15 and about 35 wt % of the second polymeric material.

10. An envelope as set forth in claim 9 wherein the first polymeric material has a tensile strength at yield point and the second polymeric material has a tensile strength at yield point, the tensile strength at yield point of the second polymeric material being greater than the tensile strength at yield point of the first polymeric material.

11. An envelope as set forth in claim 1 wherein the second polymeric material comprises an immiscible polymer blend.

12. An envelope as set forth in claim 1 wherein a tensile force required to reach a yield point of the composite tearable structure is greater than a tear force required to tear the composite tearable structure along the width the of the closure.

13. An envelope as set forth in claim 12 wherein a ratio of said tensile force to said tear force is at least about 3.

14. An envelope as set forth in claim 13 wherein said ratio is from about 4 to about 75.

15. An envelope as set forth in claim 1 wherein the tear band has an outer side and forming at least one raised element protruding from the outer side along the width of the closure.

16. An envelope as set forth in claim 1 wherein the closure panel comprises first and second tear guides formed in one of the interior surface and the exterior surface of the closure, the first tear guide being spaced apart above the tear band and the second tear guide being spaced apart below the tear band, each of the first and second tear guides comprising a formation extending along the width of the closure panel selected from the group of formations consisting of one of a projection extending outward from said one of the interior surface and the exterior surface and a depression formed in said one of the interior surface and the exterior surface.

17. An envelope as set forth in claim 1 wherein the closure includes a tear guide formation extending along the width of the closure and configured to guide tearing of the closure along a tear line at a location aligned along the height of the closure with the tear band, the closure further comprising at least one raised element extending along the width of the closure adjacent the tear line configured to inhibit the closure from tearing in a direction transverse to the tear line when the closure is being torn along the tear line.

18. An envelope as set forth in claim 17 wherein the tear guide formation comprises one of a groove, a depression, and a raised element.

19. An envelope as set forth in claim 17 wherein the tear guide formation is formed on one of the interior surface and the exterior surface of the closure and the raised element is formed on the other of the interior surface and the exterior surface of the closure.

20. An envelope as set forth in claim 17 wherein the tear band has a top edge and a bottom edge spaced apart along the height of the closure, the tear guide formation comprising a top tear guide formation defining a top tear line adjacent the top edge of the tear band, the closure further including a bottom tear guide formation extending along the width of the closure and configured to define at a bottom tear line spaced apart from the top tear line and located adjacent the bottom edge of the tear band.

21. An envelope as set forth in claim 20 wherein the at least one raised element comprises a plurality of raised elements spaced apart along the height of the closure between the top and bottom tear lines.

22. An envelope adapted to be permanently closed and later opened, the envelope comprising:

a front panel and a rear panel having top, bottom, and opposite side edge margins, the front and rear panels being joined together along the bottom and side edge margins and being unjoined along the top edge margins, the joined edge margins and the panels defining an envelope interior and the unjoined top edge margins defining an envelope opening in communication with the envelope interior; and

a closure having a top edge margin, a bottom edge margin joined to the top edge margin of the rear panel, and a height extending from the bottom edge margin of the closure to the top edge margin, the closure having opposite sides and a width extending from one to the other of the opposite sides, the closure having an interior surface, an exterior surface, and a thickness extending from the exterior surface to the interior surface, the envelope being configured such that the interior surface of the closure is sealable to the front panel of the envelope to permanently close the envelope opening, the closure comprising:

a closure panel extending along the width of the closure and defining at least a portion of each of the exterior and interior surfaces of the closure, the closure panel being formed of a first polymeric material having a tear strength, and

a tear band coextruded with the closure panel to form the closure, the tear band extending along the width of the closure at a location spaced apart from the top of the closure along the height of the closure and being formed of a second polymeric material having tear strength that is lower than the tear strength of the first polymeric material;

wherein the tear band overlies a portion of the closure panel along a segment of the height of the closure to form a composite tearable section of the closure including the tear band and said portion of the closure panel;

wherein the tear band has a thickness which is from about 25% to about 95% of the thickness of the closure;

wherein the tear band has a top edge and a bottom edge spaced apart along the height of the closure, the closure comprising a top tear guide formation extending along the width of the closure and defining a top tear line adjacent the top edge of the tear band, the closure further comprising a bottom tear guide formation extending along the width of the closure and defining a bottom tear line spaced apart from the top tear line and located adjacent the bottom edge of the tear band; and

wherein the tear band has an outer side and comprises a plurality of raised elements protruding from the outer side and extending along the tear band, the plurality of raised elements being spaced apart along the height of the closure between the top and bottom tear lines.