US20090297071A1

US20090297071A1 - Flexible bag with vent for pressure release

Info

Publication number: US20090297071A1
Application number: US12/472,572
Authority: US
Inventors: Rusty E. Koenigkramer; David J. Anzini
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2008-05-28
Filing date: 2009-05-27
Publication date: 2009-12-03
Also published as: WO2009146324A1

Abstract

A flexible bag having a reclosable zipper construction in which material is provided on the inside face of one or both zipper flanges that results in a weak seal area or an unsealed area when the side seals are made. The weak seal area or unsealed area is located on the product side of the zipper closure profiles. Elevated pressure inside the bag will cause the weak seal area of the side seal to fail as intended or will cause the zipper flanges in the unsealed area to separate, resulting in a venting action during cooking of the bag contents. For example, steam inside the bag can escape through the vent or vents while the zipper remains closed. Preferably the bag has a bottom gusset so that it can stand upright in a microwave oven. The bag may be opened to add contents, resealed and then heated.

Description

RELATED PATENT APPLICATION

This application claims the benefit, under Title 35, United States Code, §119(e), of U.S. Provisional Application No. 61/056,691 filed on May 28, 2008.

BACKGROUND

Historically, reclosable bags having press-to-close or slide-to-close reclosable feature were designed for food storage applications such as non-refrigerated and refrigerated storage. These bag products were manufactured from a combination of polyethylene resins with a reclosable feature. More recently, such reclosable bag products have been designed for high-temperature applications; for example, they are microwavable.
This invention relates to a flexible bag for use in the microwaving of cookable items, and more specifically pertains to the controlled venting of any pressure or steam generated within the bag during microwaving to assure that such is effectively released to the atmosphere.
Venting packages work well when the contents are pre-packaged, but in many cases it may be desirable to add ingredients to the package contents just before heating. For example, one may wish to add spices to the package contents prior to heating. There is a need for improvements in reclosable bags or pouches designed for high-temperature applications that will allow ingredients to be added to the package before cooking.

BRIEF SUMMARY

Disclosed herein are flexible bags having a reclosable zipper construction in which material is provided on the inside face of one or both zipper flanges that results in a weak seal area or an unsealed area when the side seals are made. The weak seal area or unsealed area is located on the product side of the zipper closure profiles. Elevated pressure inside the bag will cause the weak seal area of the side seal to fail as intended or will cause the zipper flanges in the unsealed area to separate, resulting in a venting action during cooking of the bag contents. For example, steam inside the bag can escape through the vent or vents while the zipper remains closed. Preferably the bag has a bottom gusset so that it can stand upright in a microwave oven. The bag may be opened to add contents, resealed and then heated. Many different styles of closure profiles can be incorporated into this design.
One aspect of the invention is a bag comprising a receptacle having a mouth and an interior volume, and a reclosable structure installed in the mouth of the receptacle. The receptacle comprises first and second walls that bound the interior volume and first and second side seal regions that include respective marginal portions of the first and second walls. The reclosable structure comprises first and second zipper strips, the first zipper strip comprising a first base web attached to the first wall and a first closure profile projecting from the first base web, and the second zipper strip comprising a second base web attached to the second wall and a second closure profile projecting from the second base web, the first and second closure profiles being mutually interlockable. A first portion of the first base web is weakly sealed to a first portion of the second base web in a weak seal area of the first side seal region, and a second portion of the first base web is weakly sealed to a second portion of the second base web in a weak seal area of the second side seal region. The first portions of the first and second base webs in the first weak seal area have a seal strength such that the first portions of the first and second base webs will separate from each other, thereby forming a vent, when the pressure inside the interior volume of the receptacle increases to a sufficient level, thereby allowing gas to escape from the interior volume into the ambient atmosphere via the vent during cooking of product contained within the interior volume of the receptacle while the mouth of the receptacle is in a fully closed state.
Another aspect of the invention is a bag comprising a receptacle having a mouth and an interior volume, and a reclosable structure installed in the mouth of the receptacle. The receptacle comprises first and second walls that bound the interior volume and first and second side seal regions that include respective marginal portions of the first and second walls. The reclosable structure comprises first and second zipper strips, the first zipper strip comprising a first base web attached to the first wall and a first closure profile projecting from the first base web, and the second zipper strip comprising a second base web attached to the second wall and a second closure profile projecting from the second base web, the first and second closure profiles being mutually interlockable. A first portion of the first base web is not sealed to a first portion of the second base web in a portion of the first side seal region, and a second portion of the first base web is not sealed to a second portion of the second base web in a portion of the second side seal region. The first portions of the first and second base webs form a vent when the pressure inside the interior volume of the receptacle increases to a sufficient level, thereby allowing gas to escape from the interior volume into the ambient atmosphere via the vent during cooking of product contained within the interior volume of the receptacle while the mouth of the receptacle is in a fully closed state.
A further aspect of the invention is a bag comprising a receptacle having a mouth and an interior volume, and a reclosable structure installed in the mouth of the receptacle. The receptacle comprises first and second walls that bound the interior volume and first and second side seal regions that include respective marginal portions of the first and second walls. The reclosable structure comprises first and second extruded plastic zipper strips, the first zipper strip comprising a first base web attached to the first wall and a first closure profile projecting from the first base web, and the second zipper strip comprising a second base web attached to the second wall and a second closure profile projecting from the second base web, the first and second closure profiles being mutually interlockable. Prior to formation of the first and second side seal regions, the first base web comprised a band-shaped surface area which extended the entire length of a face of the first base web, the band-shaped surface area being made of a first resin that forms a weak seal area with an opposing surface area made of a second resin different than said first resin during formation of the first side seal region.
Other aspects of the invention are disclosed and claimed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing a plan view of a reclosable bag in accordance with a first embodiment.

FIG. 2 is a drawing showing a sectional view of one upper portion of the bag depicted in FIG. 1, the section being taken along line 2-2 seen in FIG. 1.

FIG. 3 is a drawing showing a sectional view of another upper portion of the bag depicted in FIG. 1, the section being taken along line 3-3 seen in FIG. 1.

FIG. 4 is a drawing showing the same sectional view as that seen in FIG. 3, except that opposing portions of the zipper base webs in a weak seal area are shown in an unsealed and separated state, thereby forming a vent that is in flow communication with the interior volume of the bag.

FIG. 5 is a drawing showing a sectional view of a mouth portion of a bag in accordance with a second embodiment.

FIG. 6 is a drawing showing a sectional view of a side seal portion of a bag in accordance with the second embodiment.

FIG. 7 is a drawing showing the same sectional view as that seen in FIG. 6, except that opposing portions of the zipper base webs in a weak seal area are shown in an unsealed and separated state, thereby forming a vent that is in flow communication with the interior volume of the bag.

FIG. 8 is a drawing showing a sectional view of a mouth portion of a bag in accordance with a third embodiment.

FIG. 9 is a drawing showing a sectional view of a side seal portion of a bag in accordance with the third embodiment.

FIG. 10 is a drawing showing the same sectional view as that seen in FIG. 9, except that opposing unsealed portions of the zipper base webs are shown separated, thereby forming a vent that is in flow communication with the interior volume of the bag.

FIG. 11 is a drawing showing a sectional view of a side seal portion of a bag in accordance with a fourth embodiment.

Reference will hereinafter be made to the drawings in which similar elements in different drawings bear the same reference numerals.

DETAILED DESCRIPTION

The vented reclosable bags disclosed herein are designed to withstand the particular temperature and pressure conditions attending microwave cooking. Each reclosable bag is made of flexible material, such as polypropylene, plastic lamination films or other high-melting-temperature flexible material. Each reclosable bag has a reclosable structure, e.g., a zipper comprising a pair of extruded plastic zipper strips having mutually interlockable closure profiles. The zipper has a construction which allows the formation of one or more vents for pressure relief during cooking of the bag contents. The vents are located on the product side of the zipper closure profiles at the side edges of the bag. Optionally, the bag may be constructed with a bottom gusset that enables the bag to stand upright inside a microwave oven. For each embodiment disclosed hereinafter, the plastic film used to construct the bag may be thin for single-use bags or thick for multiple-use bags.
The reclosable structure remains closed as the pressure inside the bag increases during cooking. For example, the bag and its contents may be placed inside a microwave oven, which oven is then set to cook the bag contents. During this process, the pressure buildup inside the bag is relieved by the release of steam through the one or more vents formed in the reclosable bag. The pressure relief prevents the bag from bursting or otherwise having its integrity compromised.
FIGS. 1-4 depict one embodiment of a high-temperature reclosable bag suitable for use in cooking food. The bag shown in FIG. 1 comprises a receptacle 2 made of flexible material, such as polypropylene film, plastic lamination film, other higher-melting-temperature material, or a combination of two or more of the foregoing types of flexible material. A web of flexible high-temperature material is folded web to form a front panel 4, a rear panel (not shown in FIG. 1) and a bottom gusset 8 and then heat sealed (or ultrasonically welded) in marginal regions adjacent the top edges and the side edges of the folded web. The side seals are indicated by hatched regions 16 and 18 in FIG. 1. The top seal is not indicated in FIG. 1, but would include marginal portions at the top edges of the front and rear panels, as is well known in the art. The resulting receptacle 2 has an interior volume (not shown) for food product and a mouth in which a reclosable plastic zipper 10 having flanges is installed. In this embodiment, the zipper 10 comprises two zipper strips having mutually interlockable closure profiles 22 and 24 projecting from respective base webs 12 and 14 that are joined to the front and rear bag panels (hereinafter “walls”) 4 and 6, respectively, as seen in the sectional view presented in FIG. 2. These base webs are joined to the bag walls by heat sealing or ultrasonic welding and extend across the mouth of the receptacle from one side seal 16 to the other side seal 18 (indicated by hatching in FIG. 1).
The construction of the side seals 16 and 18 varies in an elevational direction. In the portions of the side seal regions disposed above the horizontal dashed line 8 (which indicates the apex of the bottom gusset) seen in FIG. 1, respective confronting marginal portions of the front and rear panels of the receptacle are sealed together except where the ends of the base webs of zipper 10 intervene. The ends of the zipper base webs are also joined together in the side seals 16 and 18, with the adjoining marginal portions of the front and rear panels being joined to the fused zipper ends. Below the horizontal dashed line 8, respective marginal portions of the front panel and rear panels of the receptacle and intervening marginal portions of the two panels of the bottom gusset are all sealed together in the side seals 16 and 18.
Still referring to FIG. 1, the side seals 16 and 18 also includes respective areas 20 and 20′ (located below the closure profiles) where the zipper base webs are weakly sealed together. This can be accomplished by producing a zipper in which each base web has coextruded material on its inside face. FIG. 2 shows a sectional view of an upper portion of the reclosable bag depicted in FIG. 1, the section being taken along line 2-2 seen in FIG. 1, which is located away from the side seals. As seen in the sectional view of FIG. 2, the base web 12 has coextruded material 26 on its inside face, while the base web 14 has coextruded material 28 on its inside face. This coextruded material extends along the entire length of each base web.
The coextruded materials 26 and 28 may be the same or dissimilar. In either case, the coextruded materials are different than the resin material of the remainder of the zipper (hereinafter “base resin”). The materials are selected so that when the side seals are formed, e.g., by the application of heat and pressure, the coextruded materials 26 and 28 will form a weak or minimal seal, whereas the base resin of the respective zipper strips will form a strong permanent seal in areas above and below the weak seal.
FIG. 3 shows a sectional view of another upper portion of the bag depicted in FIG. 1, the section being taken along line 3-3 seen in FIG. 1, which is located in side seal region 18. A person skilled in the art of manufacturing reclosable packaging will appreciate that the zipper closure profiles will be substantially deformed, i.e., crushed, in the side seal regions, which crushed profiles become part of the side seal, as seen in FIG. 3. At the time when the bag is produced, the coextrusion material 26 and 28 is heat sealed and forms a sufficient bond such that the bag is sealed to form a weak seal area in the side seal region below the closure profiles.
When the package (i.e., bag with food contents) is placed in a microwave oven and heated, internal pressure builds up. The closure profiles 22 and 24 (see FIG. 2) can be made to stay closed when subjected to this increase in internal pressure. As the internal pressure continues to increase, one or both of the two weak seals (e.g., weak seal 20′ seen in FIG. 3) at the side seals of the bag open up, allowing steam to escape from the interior volume of the receptacle, thereby relieving the package internal pressure. FIG. 4 shows the same sectional view as that seen in FIG. 3, except that opposing portions of the zipper base webs in weak seal area 20′ are shown in an unsealed and separated state, thereby forming a vent 30 that is in flow communication with the interior volume of the bag.
In accordance with the embodiment depicted in FIGS. 2-4, the coextruded materials 26 and 28 are disposed on opposing inside faces of the base webs 12 and 14 respectively. Both coextrusions could be a peel seal resin designed to form a peel seal when heat and pressure are applied during bag manufacture and to open later when the bag internal pressure reaches a desired level during cooking. The zipper strips and bag are typically made of polyethylene-based materials. In instances where the bag material is a laminate film, the film surface that the zipper (made of polyethylene-based material) seals to is typically also a polyethylene-based material.
Exemplary polyethylene-based materials that could be used as the zipper base resin include, but are not limited to: high-density polyethylene (HDPE); medium-density polyethylene (MDPE); low-density polyethylene (LDPE); linear low-density polyethylene (LLDPE); cyclic olefin copolymers (a commercial example is Ticona's TOPAS resin); and combinations of the foregoing. Polyethylene-based materials that could be used as base resins, but more likely would be used in combination with the base resins identified in the preceding sentence, include, but are not limited to, ultra-low-density polyethylene (ULDPE); very low-density polyethylene (VLDPE); elastomers; plastomers; metallocene-catalyzed polyethylene; and combinations of the foregoing.
For polyethylene-based base resins, the coextrusions could be a resin that has a higher seal initiation temperature than that of the particular polyethylene-based material from which the zipper is made. Examples of such resins include polypropylene-based material or polyester-based material. In accordance with further alternatives, the coextruded material 26 can be different than the coextruded material 28. For example, coextruded material 26 could be a peel seal resin while coextruded material 28 could be a resin, such as a polypropylene-based material, having a higher seal initiation temperature than that of polyethylene-based material used as the base resin.
As used in the preceding paragraph and hereinafter, the term “polypropylene-based materials” includes, but is not limited to: polypropylene homopolymers; polypropylene copolymers; ethylene/propylene copolymers; metallocene-catalyzed polypropylene; polypropylene-based elastomers; and combinations of the foregoing.
In accordance with a further embodiment depicted in FIGS. 5-7, a weak seal area can be formed in each side seal by coextruding a layer 32 material on the inner face of only one of the two base webs of the zipper, e.g., on base web 12 as shown in FIG. 5. In the case where the zipper strips and the bag material are made of polyethylene-based materials, the coextrusion 32 could be a peel seal resin or a resin that does not seal well to the particular polyethylene-based base resin, such as a polypropylene-based material. In the case where the zipper strips and the bag material are made of a polypropylene-based material, the coextrusion could be a peel seal resin or a resin that does not seal well to the particular polypropylene-based base resin, such as a polyethylene-based material. Alternatively, in both of the foregoing cases, the coextrusion 32 could be a biodegradable resin such as polylactic acid or a polyhydroxyalkanoate. The result, shown in FIG. 6, is a weakly sealed area 20′ in the side seal 18, which weakly sealed area will open, as shown in FIG. 7, when the bag internal pressure reaches a desired level during cooking.
Typical peel seal resins that could be used are DuPont Appeel 11D542 and Basell PB8640. Any of the various grades of resin sold for peelable film or lidstock could also be used.
In accordance with another embodiment depicted in FIGS. 8-10, a vent can be formed in each side seal by applying a coating 34 of heat-resistant material, such as nitrocellulose, on the inner face of one of the two base webs of the zipper, e.g., on base web 12, as shown in FIG. 8. The heat-resistant coating is preferably applied on the inner face of base web 12 at least in the areas of the side seals. This technique can be applied in both the case where the zipper strips and the bag material are made of polyethylene-based materials and the case where the zipper strips and the bag material are made of polypropylene-based materials. The presence of a heat-resistant material on a zipper base web in the side seal region prevents the coated base web from being heat sealed to the confronting base web in the side seal region, thereby forming a vent that opens in response to a sufficient pressure increase inside the receptacle. FIG. 9 shows the vent 30 in a closed state; FIG. 10 shows the vent 30 in an open state. In the alternative, both base webs can have confronting portions which are coated with a heat-resistant material.
In accordance with alternative embodiments, the pressure-release area can be located above the closure profiles, i.e., on the consumer side of the profiles rather than on the product side. Such embodiments would have utility in cases where the unopened bag filled with product is sold with the zipper open. In this case the weakly sealed or unsealed area in the side seal could be above or below the closure profiles of the open zipper.
FIG. 11 is a sectional view, taken through the side seal, of an embodiment wherein a weak seal area has been formed in the side seal by coextruding a layer 32 material on the inner face of base web 12 at an elevation higher than the elevation of the closure profiles. In the case where the zipper strips and the bag material are made of polyethylene-based materials, the coextrusion 32 could be a peel seal resin or a resin that does not seal well to the particular polyethylene-based base resin, such as a polypropylene-based material. In the case where the zipper strips and the bag material are made of a polypropylene-based material, the coextrusion could be a peel seal resin or a resin that does not seal well to the particular polypropylene-based base resin, such as a polyethylene-based material. Alternatively, in both of the foregoing cases, the coextrusion 32 could be a biodegradable resin of a type previously described. Any of the various grades of resin sold for peelable film or lidstock could also be used.
In accordance with further alternative embodiments, a weak seal area or a vent can be formed in a side seal region at the interface of a zipper flange and a confronting portion of the bag wall. For example, the embodiment depicted in FIGS. 5-7 could be altered by placing the coextrusion 32 on the outside face of the lower zipper flange rather than on the inside face. Similarly, the embodiment depicted in FIGS. 8-10 could be altered by placing the coating 34 on the outside face of the lower zipper flange rather than on the inside face. In addition, the embodiment depicted in FIG. 10 could be altered by placing the coextrusion 32 on the outside face of the upper zipper flange rather than on the inside face.
With respect to all embodiments disclosed above, a person skilled in the art will appreciate that the broad scope of the invention includes reclosable bags having only one vent as well as bags having two or more vents.
While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for members thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation to the teachings of the invention without departing from the essential scope thereof. Therefore it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A bag comprising a receptacle having a mouth and an interior volume, and a reclosable structure installed in said mouth of said receptacle, said receptacle comprising first and second walls that bound said interior volume and first and second side seal regions that include respective marginal portions of said first and second walls, said reclosable structure comprising first and second zipper strips, said first zipper strip comprising a first base web attached to said first wall and a first closure profile projecting from said first base web, and said second zipper strip comprising a second base web attached to said second wall and a second closure profile projecting from said second base web, said first and second closure profiles being mutually interlockable, wherein a first portion of said first base web is weakly sealed to a first portion of said second base web in a weak seal area of said first side seal region, and a second portion of said first base web is weakly sealed to a second portion of said second base web in a weak seal area of said second side seal region, said first portions of said first and second base webs in said first weak seal area having a seal strength such that said first portions of said first and second base webs will separate from each other, thereby forming a vent, when the pressure inside said interior volume of said receptacle increases to a sufficient level, thereby allowing gas to escape from said interior volume into the ambient atmosphere via said vent during cooking of product contained within said interior volume of said receptacle while said mouth of said receptacle is in a fully closed state.

2. The bag as recited in claim 1, wherein said first portion of said first base web in said weak seal area of said first side seal region comprises a layer of a first resin, and a second portion of said first base web adjacent said first portion of said first base web and not in said weak seal area of said first side seal region is made of a second resin different than said first resin.

3. The bag as recited in claim 2, wherein said second resin is a polyethylene-based material and said first resin is selected from a group of resins which do not seal well to that polyethylene-based material.

4. The bag as recited in claim 3, wherein said first resin is a polypropylene-based material or a polyester-based material.

5. The bag as recited in claim 2, wherein said second resin is a polypropylene-based material and said first resin is selected from a group of resins which do not seal well to that polypropylene-based material.

6. The bag as recited in claim 5, wherein said first resin is a polyethylene-based material.

7. The bag as recited in claim 2, wherein said first resin is a biodegradable resin such as polylactic acid or a polyhydroxyalkanoate.

8. The bag as recited in claim 2, wherein said first resin is a peel seal resin.

9. The bag as recited in claim 2, wherein said first portion of said second base web in said weak seal area of said first side seal region comprises a layer of a third resin different than said first and second resins, and a second portion of said second base web adjacent said first portion of said first base web and not in said weak seal area of said first side seal region is made of said second resin.

10. A bag comprising a receptacle having a mouth and an interior volume, and a reclosable structure installed in said mouth of said receptacle, said receptacle comprising first and second walls that bound said interior volume and first and second side seal regions that include respective marginal portions of said first and second walls, said reclosable structure comprising first and second zipper strips, said first zipper strip comprising a first base web attached to said first wall and a first closure profile projecting from said first base web, and said second zipper strip comprising a second base web attached to said second wall and a second closure profile projecting from said second base web, said first and second closure profiles being mutually interlockable, wherein a first portion of said first base web is not sealed to a first portion of said second base web in a portion of said first side seal region, and a second portion of said first base web is not sealed to a second portion of said second base web in a portion of said second side seal region, said first portions of said first and second base webs forming a vent when the pressure inside said interior volume of said receptacle increases to a sufficient level, thereby allowing gas to escape from said interior volume into the ambient atmosphere via said vent during cooking of product contained within said interior volume of said receptacle while said mouth of said receptacle is in a fully closed state.

11. The bag as recited in claim 10, wherein said first portion of said first base web is coated with a heat-resistant material.

12. The bag as recited in claim 11, wherein said heat-resistant material is nitrocellulose.

13. A bag comprising a receptacle having a mouth and an interior volume, and a reclosable structure installed in said mouth of said receptacle, said receptacle comprising first and second walls that bound said interior volume and first and second side seal regions that include respective marginal portions of said first and second walls, said reclosable structure comprising first and second extruded plastic zipper strips, said first zipper strip comprising a first base web attached to said first wall and a first closure profile projecting from said first base web, and said second zipper strip comprising a second base web attached to said second wall and a second closure profile projecting from said second base web, said first and second closure profiles being mutually interlockable, wherein prior to formation of said first and second side seal regions, said first base web comprised a band-shaped surface area which extended the entire length of a face of said first base web, said band-shaped surface area being made of a first resin that forms a weak seal area with an opposing surface area made of a second resin different than said first resin during formation of said first side seal region.

14. The bag as recited in claim 13, wherein said second resin is a polyethylene-based material and said first resin is selected from a group of resins which do not seal well to that polyethylene-based material.

15. The bag as recited in claim 14, wherein said first resin is a polypropylene-based material or a polyester-based material.

16. The bag as recited in claim 13, wherein said second resin is a polypropylene-based material and said first resin is selected from a group of resins which do not seal well to that polypropylene-based material.

17. The bag as recited in claim 16, wherein said first resin is a polyethylene-based material.

18. The bag as recited in claim 13, wherein said first resin is a biodegradable resin such as polylactic acid or a polyhydroxyalkanoate.

19. The bag as recited in claim 13, wherein said first resin is a peel seal resin.

20. The bag as recited in claim 13, wherein said first resin is totally resistant to heat sealing.