WO1993008982A2

WO1993008982A2 - Roll stock for making resealable bags and resealable roll-formed bag

Info

Publication number: WO1993008982A2
Application number: PCT/US1992/009499
Authority: WO
Inventors: G. Barton Borland
Original assignee: Packaging Industries, Inc.
Priority date: 1991-11-08
Filing date: 1992-11-06
Publication date: 1993-05-13
Also published as: WO1993008982A3

Abstract

A roll stock of flexible packaging material is described for forming food product bags which are resealable and yet can be formed by standard form and fill machinery. The roll stock (21) includes eyespots (26) to control the application of a pressure sensitive material (27) and a locating strip (28) to facilitate finding the pressure sensitive strips (27) at discrete locations selected for bag mouths. The invention includes the bag resulting from use of the roll stock, as well as the method of processing the roll stock to provide resealable bag characteristics to the same.

Description

ROLL STOCK FOR MAKING RESEALABLE BAGS AND RESEALABLE ROLL-FORMED BAG

DISCLOSURE

Background of the Invention

The present invention relates to laminated packaging material for forming bags for food products and, more particularly, to a roll stock of such material from which resealable bags can be made, a method of processing the roll stock to enable such bags to be made, and a resealable bag so formed.

Most flexible packaging for food products, such as chips and dry cereals, is formed in a relatively continuous manner by machines which fill the packages with the food product at the same time the packages are formed. These machines are called "form, fill and seal" machines and the flexible packaging material typically is a laminant having a layer of a heat sealable material, e-g-, polyethylene, on one surface of the same. The form, fill and seal machine wraps a web of the packaging material around a forming mandrel with the edges of the web overlapping. These edges are sealed together to form, what is referred to in the art, a fin seal which extends lengthwise of a bag tube, i.e., a tube from which individual bags are made. After a bottom seal transverse to the fin seal is made, the food product desired to be packaged is placed in the bag tube so formed. An upper seal is then made to close the tube bag's mouth. The finished bag is cut from the tube. These operations are interwoven for several bags at the same time. The forming, filling and sealing procedure is continuous and quite fast to provide high volume packaging.

Many flexible packages are filled with more than one serving of the food product in question. For example, packages containing multiple servings of chips and dry cereal are often formed. The problem is that the consumer who opens a form and fill package has to break the heat seal at the upper end (mouth) of the package to have access to the contents. It would be desirable in order to maintain the freshness of the product remaining in a multiple serving bag, to be able to reseal the bag. This desirability has been known for some time. However, no universally acceptable reseal arrangement has been adopted. Because of such, it is not unusual for consumers to attempt to keep the product fresh by folding or rolling the bag top after it is opened. These steps often are futile.

Much effort has been expended toward developing a flexible resealable package which is acceptable. The arrangement described in U.S. Patent No. 4,786,190 is typical in that it provides a bag design for resealing - a design, however, which cannot be made from roll stock to be used on standard form and fill machinery. That is, although this bag design includes both a pressure sensitive adhesive and a destructible heat seal at the bag mouth, the bag itself is formed simply by heat sealing the edges of one or two separate sheets together, a bag design which is foreign to use with standard form. fill and seal machines. The presence of the exposed pressure sensitive adhesive will interfere with the formation, filling and sealing operation, even if the bag design otherwise was adaptable to use by standard form, fill and sealing machinery. If roll stock for this bag design was made, adjacent sheets of the roll stock will stick together.

Others have provided relatively complicated mechanical closure arrangements to effect bag mouth closures. An example is the interlocking arrangements which are similar to a zipper. These arrangements simply have been too expensive, complicated and/or sufficiently prone to failure to warrant adoption for most high volume uses in spite of the need. Efforts to provide a resealable closure have even resulted in the use of auxiliary tapes and the like as described for example in U.S. Patent Nos. 4,722,166 and 4,913,560. This approach is also quite expensive and slow, and its adoption in high volume, form and fill type of flexible packaging has been precluded.

Summary of the Invention

The present invention provides a roll stock of flexible packaging material from which resealable bags for food products can be made economically with standard form and fill machinery. In its basic aspects, the invention is a roll stock of flexible packaging material which not only includes a substrate as is usual, but a pressure sensitive material at discrete locations to provide closures in bags, such as bag mouths, made from such roll stock. In keeping with the invention, a non- pressure sensitive material is also included as part of the roll stock covering the pressure sensitive material to render the same inoperative during subsequent utilization of the roll stock. Most desirably, the non-pressure sensitive material is a heat sealable material, such as polyethylene, ethylene/vinyl acetate copolymers or certain ionomers such as Dupont's SURLYN™. The result is that the covering material has a dual function - it not only covers the pressure sensitive material, it enables a standard heat seal to be formed at the bag mouth at the same location as the pressure sensitive material. In other words, means for forming two different seals are provided at discrete locations on the roll stock, e.g., the locations desired for bag mouths, means for forming an initial heat seal and means for forming a subsequent pressure sensitive seal. The thickness of the heat sealable material at the location at which it covers the pressure sensitive material is selected so that when a heat seal formed by the same is destroyed, the pressure sensitive material will be exposed for forming a subsequent seal at the desired location. The consumer, after the initial heat seal is broken in order to have access to the food product, can reseal the bag mouth with use of the pressure sensitive material.

The pressure sensitive material is provided in a pattern on the roll stock in the preferred arrangement to provide the closures in bags made therefrom at the discrete locations, e.g., at the locations for bag mouths. Other areas of the laminated packaging material at which it may be desired to form heat seals is maintained free of the pressure sensitive material in order to assure that it does not interfere with desired strong heat seals. Most simply, the pattern is applied to a layer of the heat sealable material which is first applied to the substrate, and a subsequent layer of the heat sealable material is applied over the full surface area of the substrate. The result of this construction is that the pressure sensitive material is embedded in heat sealable material. The heat sealable material can be used to form the standard heat seals on a form and fill machine. The heat seal formed at the location of the pressure sensitive material, though, will not have as much heat sealable material involved in the seal as is typical. When the seal is destroyed, the pressure sensitive material will be exposed as discussed above to enable subsequent sealing at its location.

The invention includes not only the roll stock, but a method of processing roll stock to provide the pressure sensitive material and the resulting bag.

Brief Description of the Drawings

With reference to the accompanying two sheets of drawing:

FIG. 1 is a plan view of a piece of a preferred embodiment of flexible packaging roll stock conforming to the invention;

FIG. 2 is an enlarged partial sectional view showing the various layers of such preferred embodiment;

FIG. 3 is a schematic, side elevation view of apparatus for* processing roll stock in accordance with the invention;

FIG. 4 is a generally schematic perspective view of standard form and fill machinery, forming bags from roll stock of the invention;

FIG. 5 is a perspective schematic view of a bag conforming to the instant invention; and

FIGS. 6 and 7 are enlarged schematic sectional views of a bag mouth illustrating the bag mouth with a heat seal enclosure that respectively is intact and destroyed in order to expose pressure sensitive material for resealing.

Description of the Preferred τ.τnbαdiments

The following relatively detailed description is provided to satisfy the patent statutes. However, it will be appreciated by those skilled in the art that various changes and modifications can be made without departing from the invention as defined by the claims.

Reference is first made to FIGS. 5, 6 and 7 for a general overview of a reclosable bag, to simplify an understanding of the subsequent description of the preferred embodiment of the roll stock. A bag, generally referred to by the reference numeral 11, of flexible packaging material includes, as is usual, a pair of upper and lower opposed side walls 12 and 13. As mentioned previously and will be discussed in more detail below, the bag is formed from a tube of flexible packaging material roll stock. It includes a longitudinal fin seal 14 formed by heat sealing together overlapping edges of the roll stock. It also includes a bottom heat seal 16 which is transverse to the fin seal. The bottom seal has to be sufficiently strong to withstand the weight of the food product against the same, as well as movement of the same such as will be discussed. The upper end of the bag, i.e., the bag mouth, is also closed with a heat seal 17. In accordance with the invention, a pattern of a pressure sensitive material 18 is embedded within the heat sealable material 17 at the bag mouth to be exposed when the former is destroyed by the consumer for initial access to the bag's interior. In this connection, the thickness of the heat sealable material covering the pressure sensitive strip is selected so that when the heat seal formed by the same is destroyed, the pressure sensitive material is exposed for forming a subsequent seal at the mouth. The thickness which is actually selected depends in large part on the materials involved and the weight, etc. , of the food product to be packaged. In general, though, the thickness that is selected should be within the range of between about 0.2 mils and about 0.7 mils.

FIGS. 6 and 7 show operation of the seal. FIG. 6 illustrates the heat seal that is formed at the bag's mouth, whereas FIG. 7 illustrates that when the heat seal is broken, the pressure sensitive material will be exposed.

It is important to note that the pressure sensitive material is provided at the location at which it is desired to operate, but not at the other locations at which there is to be a heat seal, such as at the location for the bottom seal, a location at which a strong heat seal is to be provided. For example, if pressure sensitive material was sandwiched between the heat sealable material layers at the location of the bottom seal, there would be a loss in hot tack resulting in product dropping through the bottom seal while the same is molten.

A piece 21 of the roll stock from which the resealable bag is made is illustrated in FIG. 1. (Although roll stock for forming a single bag tube is illustrated, as a practical matter the operations described relative to FIG. 3 form wider roll stock designed for a multiple number of bag tubes. The wider roll stock so formed is then cut into the narrower roll stock illustrated for forming individual bag tubes.) Such roll stock is a la inant made up of a substrate 22 (FIG. 2) such as a metal foil, a polyester, or a cellophane, as is standard practice in the industry. The substrate is selected to be thermally stable if it is to be resistant to heat applied thereto such as to provide the heat sealing to be described below. The substrate includes on one surface, an ink pattern represented at 23 which provides advertising, product identification, etc. A layer 24 of a heat sealable material, such as polyethylene, is provided over the ink. In this connection, a primer or adhesive layer 25 is also provided between the polyethylene layer and the ink to assure good adhesion. Although the layer 24 in this preferred embodiment is polyethylene, insofar as the broad concepts of the invention is concerned the layer 24 could be of any heat sealable material.

A pattern of a pressure sensitive material is provided on layer 24 at those discrete locations for bag mouths or other bag closures. The Ribbon Coater available from Graco/LTI of Monterey, California, can be used to provide the desired pattern. Acumeter of Marlborough, Massachusetts also provides a suitable ribbon coater. To facilitate deposition of the pattern, the printing on the substrate includes "eye spots" 26 which are sensed as will be discussed hereinafter to control the application of pressure sensitive material as the desired pattern. This pattern in the preferred embodiment is made up of strips 27 indicated in FIG. l. Each of the strips has a thickness in the range of between about .5 mils and about 1.5 mils. Its thickness is preferably 1.0 mils. As a means to aid set-up, the printing also can include a locating strip 28 or the like to facilitate finding the pressure sensitive strips 27. Another layer 29 of polyethylene or other heat sealable material is provided over the full surface area of the roll stock to cover the pattern formed by the strips 27. This covering layer should have the characteristics necessary for the material to be compatible with the form, fill and seal machinery with which it is to be used. For example, it should have both slip and hot tack characteristics. A slip concentrate is added to the polyethylene to provide a low enough coefficient of a friction to enable the packaging material to slide over the metal parts of such machinery. "Hot tack" is inherent in the polyethylene resin and comes into play when a food product is dropped into the bag while the bottom seal is still molten - inadequate hot tack causes the product to drop through the bottom seal.

Although in this embodiment layer 29 covers the full surface area of the roll stock, other arrangements are potentially appropriate. For example, two separate heads could be used, one applying a pattern of the pressure sensitive material and the other applying a pattern of heat sealable material only on those locations having the heat seal material. It is also possible that a single pattern applicator could be used to apply both of the materials in the proper order at the same time. A tape with the heat sealable material and the pressure sensitive material could be applied at the discrete locations.

The resulting construction is that the strips 27 are embedded in heat sealable material, i.e., between the layers 24 and 29. Most desirably, the material of the layers 24 and 29 are the same or otherwise compatible with one another so that they combine for heat sealing purposes at those locations not having the strips 27. It is common to provide a film or layer comparable to layer 24 for heat sealing purposes. In this instance the thickness of the layer 24 can be reduced in view of the layer 29 if the bag otherwise has sufficient strength to prevent tearing.

It will be appreciated that the layer 29 renders the strips 27 inoperative until such time as the heat seal at their location is broken. In this connection, the heat seal which will be formed as discussed below at the bag mouth or other closure will be provided at the location of the strip 27 only by the heat sealable material covering such strip. (Of course, the other wall of a bag will not have the pressure sensitive strip of material.) This heat sealable material is most simply polyethylene having a thickness covering the strips 27 in the range of about 0.2 mils to p.7 mils, preferably 0.4 mils.

In one arrangement, the substrate was cellophane having a thickness of about 0.8 mils, the layer 24 was polyethylene having a thickness of about 1.25 mils adhered to the cellophane by a thickness of about .1 mil of adhesive, each of the pressure sensitive strips had a thickness of about 1.5 mils, and the covering layer was also polyethylene having a thickness of about 0.6 mils. The pressure sensitive material was provided as a hot melt by H. B. Fuller of St. Paul, Minnesota, sold with the designation H.L.-2115-X. H. B. Fuller has other hot melts which can be used. Other appropriate melt pressure sensitive adhesives are sold by Swift Adhesive of Downers Grove, Illinois, and by National Starch of Bridgewater, New Jersey.

Although the packaging material is described as having a particular order of materials, the use of the terms "in order" here and in the claims is not meant to require that each of the layers which is described be immediately adjacent other layers in the order. There can be intermediate layers in accordance with standard practice.

FIG. 3 is a simplified diagrammatic view of those aspects of a flexible packaging processing apparatus relevant to the instant invention. A roll of a substrate (not shown) is unwound in a continuous manner to provide a web 31 of the same. Printing is applied to such substrate in accordance with conventional practice to form the printing 23. (This process is not shown. The substrate with the printing thereon is then primed for application of polyethylene as will be described. This priming operation is also conventional and not shown. As indicated at the left portion of the figure, after the printed substrate is primed, it is passed through a station at which a film of polyethylene or other heat sealable material is extruded as a melt via extruder 32 onto the same as it passes through the nip of a chill roll 33 and a pinch roll 34. A chilled back-up roll 36 is provided to cool pinch roll 34. In accordance with conventional practice the film is at least partially solidified to form the layer 29 at the nip previously described. It then passes about chill roll 33 to complete sufficient solidification for the remainder of the process.

The web is then passed by an electric eye represented at 37 which detects the locations of the eye spots 26 to control operation of patterning equipment for applying the pattern of pressure sensitive material to the web. Thar Is, a signal indicative of the presence of an eye spot: is transmitted as represented by line 38 to a pattern controller 39 which controls the operation of solenoid valves represented at 41 for a coating head 42 for applying the pattern of heat sealable material to the web. In one embodiment, a Ribbon Coater from Graco/LTI of Monterey, California, was used as the coating head. A supply of the pressure sensitive material in hot melt form is contained in a reservoir in a hot melt delivery system represented at 43. The pressure sensitive material in melt form is delivered via a heated hose 44 to the head 42. It will be recognized that with such arrangement the strips 27 will be deposited on the web at the desired discrete locations on the layer 24. The covering layer 29 of the heat sealable material is then applied. It is applied over the full surface of the web. This provides a non-stick, heat sealable surface with adequate slip and hot tack to operate on the selected form, fill and seal machinery. The application of the same at the nip between a chill roll 47 and a pinch roll 48 is represented by the showing of the extruder 46. A back-up chill roll 49 for the pinch roll is also illustrated. The web is completed with any other processing steps desired and then formed into a roll 51 in accordance with conventional practice.

FIG. 4 is a simplified schematic perspective view of a standard form, fill and machine utilizing roll stock of the invention. The roll stock, represented by reference numeral 51, is unwound to form a web 52 which after passing about and through various rollers in accordance with conventional practice is wrapped around a mandrel 53 to form a tube 54. The overlapping edges of the material are heat sealed together by a standard mechanism represented by the blocks 56. In this connection, the tube is advanced along the mandrel by conventional apparatus represented by the belts 57. The tube is heat sealed transverse to the fin seal as is represented by blocks 58 to form the bottom seal of a tube bag. The food product desired to be packaged is.fed into the tube bag through the mandrel as is represented by the hopper 59 shown in dotted lines. The upper end of the bag is then sealed to enclose the food product, and the completed bag is severed from the remainder of the tube. These operations also are accomplished by the blocks represented at 58. The bottom seal for the next tube bag is formed simultaneously with the formation of the bag upper seal and the severing, to form a free bag. It will be recognized from the above that operation of the form, fill and seal machine is oblivious of the fact that the roll stock includes an embedded heat sealable material at the location of the mouth of the completed bags. The blocks 59 form a heat seal in the standard manner. However, as will be recognized the completed bag includes the heat seal strip at the bag mouth as discussed previously.

As mentioned at the beginning of the detailed description, Applicant is not limited to the specific embodiments described above. For example, the bag closure having the pressure sensitive material need not necessarily be the bag's mouth. The invention is applicable to providing covered pressure sensitive material at any location(s) at which resealing of a bag penetration may be desired. Moreover, the pressure sensitive material and the covering/heat sealable material can be provided together as a tape, with or without an appropriate backing. Such a tape could be, for example, applied to the edge of the roll stock as it is unrolled into the web to provide a bag closure at the fin seal of bags. The claims and their equivalents define the scope of protection.

Claims

CLAIMSWhat is claimed is:

1. A roll stock of flexible packaging material to be used to make resealable bags for food products comprising, in order: (a.) a* substrate; (b) a pressure sensitive material selected to provide pressure sensitive material at discrete locations for closures in bags made from said roll stock; and (c) a non-pressure sensitive material covering said pressure sensitive material to render the same inoperative during subsequent utilization of said roll stock.

2. The roll stock of claim 1 wherein there is a pattern of said pressure sensitive material.

3. The roll stock of claim 1 wherein said pressure sensitive material has a thickness at said discrete locations of between about .5 mils and 1.5 mils.

4. The roll stock of claim 3 wherein said thickness is about 1.0 mils.

5. The roll stock of claim 1 wherein said non- pressure sensitive material is another sealing material for sealing said closure when said pressure sensitive material is inoperative.

6. The roll stock of claim 1 wherein said substrate is thermally stable, and said non-pressure sensitive covering material is polyethylene having a thickness at said discrete locations in the range of about 0.2 mils to about 0.7 mils.

7. The roll stock of claim 6 wherein said polyethylene has a thickness of about 0.6 mils at said discrete locations.

8. The roll stock of claim 1 wherein said substrate is thermally stable and said non-pressure sensitive material is a heat sealable material at said discrete locations for forming initial heat seal closures thereat that can be destroyed and expose the pressure sensitive material at each of said locations for forming a subsequent seal at each of said closures.

9. The roll stock of claim 8 wherein said heat sealable covering material has a thickness at said discrete locations in the range of about 0.2 mils to about 0.7 mils.

10. The roll stock of claim 8 wherein said laminated packaging material is free of pressure sensitive material at other locations at which it may be desired to form heat seals.

11. The roll stock of claim 8 wherein a layer of heat sealable material is provided on said substrate between said substrate and said pressure sensitive material.

12. The roll stock of claim 11 wherein said covering non-pressure sensitive material is a heat sealable material and said layer is of the same heat sealable material.

13. The roll stock of claim 11 wherein said covering material is another layer of heat sealable material covering substantially the full surface of said substrate having said pressure sensitive material thereon.

14. The roll stock of claim 13 wherein said pressure sensitive material is sandwiched directly between said layers of heat sealable material, thereby to be embedded in heat sealable material.

15. The roll stock of claim 14 wherein said substrate is cellophane and has a thickness of about 0.8 mils, said layer of heat sealable material is polyethylene having a thickness of about 1.25 mils, said pressure sensitive material has a thickness of about 1.0 mils, and said covering layer of heat sealable material is polyethylene having a thickness of about 0.4 mils.

16. A resealable, flexible bag for packaging a food product comprising: (a) a pair of opposed walls which are heat sealed together to form a closure; and (b) a pressure sensitive material at said closure usable to reseal the same after the heat seal thereat is destroyed; and (c) a non-pressure sensitive material at said closure covering said pressure sensitive material thereat until said heat seal is destroyed.

17. The resealable bag of claim 16 wherein said pressure sensitive material has a thickness in the range of between about .5 mils and 1.5 mils.

18. The resealable bag of claim 16 wherein each of said walls when the thickness of said pressure sensitive material is ignored, is about 2.65 mils, and the thickness of said pressure sensitive material is about 1.0 mils.

19. The resealable bag of claim 16 wherein said non-pressure sensitive material is a heat sealable material having a thickness in the range of about 0.2 mils to about 0.7 mils covering said pressure sensitive material.

20. The resealable bag of claim 16 wherein at least one of said walls is provided with a heat sealable material at said closure within which all of said pressure sensitive material thereat is embedded, and said non-pressure sensitive material is said heat sealable material.

21. The roll stock of claim 16 wherein there is a pattern of said pressure sensitive material.

22. A method of processing flexible packaging material of the type used to make bags for food products, comprising in order: (a) providing a roll of a substrate; (b) making a web of said substrate from said roll; (c) applying a pressure sensitive material to discrete locations at which it is desired to define resealable closures in bags made from said packaging material; (d) applying a non-pressure sensitive material over said pressure sensitive material at said discrete locations; and thereafter (e) forming said web into a roll.

23. The method of claim 22 wherein said non- pressure sensitive material is a closure sealing material.

24. The method of claim 22 wherein said step of applying a pressure sensitive material to said discrete locations includes applying a thickness of between about .5 mils and about 1.5 mils of said material to said discrete locations.

25. The method of claim 22 wherein said substrate is thermally stable and further including the step of applying a layer of heat sealable material to said web prior to said application of said pressure sensitive material, and applying said pressure sensitive material to said layer.

26. The method of claim 22 wherein said substrate is thermally stable and said step of applying a non- pressure sensitive material over said pressure sensitive material includes applying a layer of heat sealable material having a thickness in the range of about 0.2 mils to about 0.7 mils over said pressure sensitive material.

27. The method of claim 25 wherein said step of applying a non-pressure sensitive material over said pressure sensitive material includes applying another layer of a heat sealable material over substantially the full surface of said web.

28. The product of the process of claim 22.

29. A roll stock of flexible packaging material to be used to make resealable bags for food products comprising: (a) a thermally stable substrate; (b) heat sealable material on said substrate at locations selected for the formation of heat seals for bags made from said roll stock; and (c) A pattern of a pressure sensitive material embedded in said heat sealable material, said pattern being selected relative to said heat sealable material to provide pressure sensitive material operable to seal closures in bags made from said roll stock by destroying heat seals formed in said bags with said heat sealable material at the locations at which said pressure sensitive material is embedded therein.

30. The roll stock of claim 29 wherein said pattern has a thickness of between about .5 mils and about 1.5 mils.

31. The roll stock of claim 29 wherein said heat sealable material covers substantially all of said pressure sensitive material.

32. The roll stock of claim 31 wherein said heat sealable material covering substantially all of said pressure sensitive material has a thickness thereat in the range of about 0.2 mils to 0.7 mils.