Abstract:
A bag having a built-in closure tab is defined. The closure tab is formed from the outer layer of the laminate which makes up the bag. When a user of the bag wishes to close the bag, the user folds or rolls the sides of the bag together down the side of the bag having the tab. The tab is partially separated from the rest of the outer layer of the laminate. A pressure sensitive adhesive disposed on the interior surface of the tab is used to affix the tab to the rolled down portion of the bag, preventing unwanted opening of the bag. The tab may be affixed and removed from the rolled down portion a number of times, thereby allowing the user to open and reseal the bag as many times as desired.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a bag for containing items, such as consumables. More particularly, the invent ion is directed to a bag having a built-in closure tab. 
     BACKGROUND OF THE INVENTION 
     Bags, such as film bags, are utilized extensively in modern society for containing a wide variety of items, such as candies, food items and liquids. A typical film bag is made from a laminate that includes an outer film layer adhesively secured to an inner sealing layer. The outer layer is usually made from a material that facilitates printing. The inner layer is usually made from a material that enables the package to be sealed. Other layers can also be incorporated. Properties, such as permeability to oxygen and moisture, strength, stiffness and other packaging requirements may dictate material selection. The outer and inner layers are both typically made from plastic film, such as polyethylene or polypropylene. 
     The conventional bag is closed by bringing two opposing sides into contact and downwardly folding or rolling them together. When closed, the bag may tend to free itself from the rolled configuration, thereby reopening and exposing its contents to ambient air. Various methods of preventing the conventional bag from reopening have been attempted. Household items such as clothes pins or paper clips have been used to hold the conventional bag closed. Articles of manufacture, such as the Chip-Clip® (a registered trademark of the Chip Clip Company of Dallas, Tex.), have been specially designed as closures for bags. 
     Other attempts to provide a closure mechanism for a conventional bag have tried to provide a closure device with the bag itself. Some bags have been provided with a metal wire or strip along the length of the bag, the wire or strip being easily bent under the user&#39;s manipulation, but resisting the tendency of the bag to open once folded, thus keeping the bag closed. An example of such a bag is disclosed by U.S. Pat. No. 3,618,850 to Palmer. Other bags are provided with nonresiliently flexible strips disposed transversely to the length of the bag. The nonresilient strip is along the top of the bag and extends beyond the side of the bag. Once the top of the bag is rolled down a first side, the extending portion of the strip is folded snugly against a second side, opposite the first side, preventing the bag from unrolling. 
     Still other attempts to seal a bag involve retrofitting a tab or label onto the bag. A first portion of the label is attached to a bottom portion of the bag with a permanent adhesive. The label has a second portion on which a releasable adhesive is disposed. When the bag is closed and folded downwardly, the portion with releasable adhesive may be attached to the folded portion, thereby preventing the bag from unrolling. One example of a bag of this type is disclosed by U.S. Pat. No. 5,582,889 to Pedrini. One problem with a retrofitted closure tab is the expense of manufacturing and handling the tab. 
     It is desirable to provide a bag having a closure device which is not as complex or expensive to produce as those described above. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a bag with a reusable built-in closure tab. The closure tab is formed from the outer layer of the laminate which forms the sides of the bag. Thus, the closure tab is “built-in.” 
     A bag according to the present invention has an inner and an outer layer. A portion of the outer layer is defined as a tab. The tab portion is separated from the remainder of the outer layer (the fixed portion) by precision cutting. After cutting, the tab portion remains attached to the fixed portion only at its base. A pressure sensitive adhesive, rather than a permanent adhesive, is disposed on the under side of the tab portion, attaching the tab to the inner layer. Thus, the tab portion may be easily pulled away from the inner layer, although remaining attached at its base. The pressure sensitive adhesive disposed on the inside of the tab may be used to affix the tab to a rolled down portion of the bag, thereby sealing the bag closed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, that this invention is not limited to the precise arrangements and instrumentalities shown. 
     FIG. 1 is a perspective view of an open bag according to the present invention. 
     FIG. 2 is a perspective view of a closed bag according to the present invention. 
     FIG. 3 is a perspective view of a bag according to the present invention, a built in closure tab being oriented to reveal its under side. 
     FIG. 4 is a cross sectional view of a portion of the side of a bag according to the present invention, taken along line  4 — 4  in FIG.  1 . 
     FIG. 5 is a schematic diagram of one preferred method of forming the film bag laminate according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings, wherein like numerals identify like elements, there is shown a film bag generally identified by the numeral  10 . Positioned on a wall of the package  10  is a closure tab  20 . The film bag according to the present invention is operative for containing articles, such as candies, food and other items. 
     As seen in FIGS. 1 through 3, Bag  10  has a front wall  12  and a back wall  14 . The walls of the bag, and thus, the bag itself are formed from a laminate having at least two layers, the laminate being described in greater detail below. Tab  20  is provided on front wall  12 . In fact, tab  20  is formed from an outer layer  34  of the laminate, as seen in FIG.  4 . 
     In practice, the tab  20  should be substantially coplanar with the remainder of the front bag wall  12  before the bag is opened. Once the user opens the bag and consumes a portion of the contents stored therein, the user brings both sides of the bag together to re-close the top of the bag. The user pulls at least part of the tab  20  away from the plane of the wall  12 . The top of the bag is then rolled or folded down, the roll forming along front wall  12 . The user then engages the tab  20  with the rolled portion, the tab  20  adhering to the folded portion with great enough affinity to prevent the bag from unrolling. 
     FIG. 4 shows a schematic cross section of a portion of the front wall  12 , taken along line  4 — 4  of FIG.  1 . The laminate forming bag  10  comprises an inner layer  30  and an outer layer  34 . The laminate forming bag  10  may comprise various additional layers as may be desired for the packaging of numerous different products. Properties, such as permeability to oxygen and moisture, strength, stiffness and other desired qualities may dictate material selection. 
     The outer layer  34  is preferably formed from oriented polypropylene (OPP) or polyester, specifically polyethylene terephthalate (PET), it being understood that many other polymers, copolymers, and combinations thereof are also suitable. The outer layer  34  is preferably about 1 mil thick, a mil being understood to be {fraction (1/1000)} of an inch. It being frequently desirable to have a bag with color, designs, graphics and other indicia, the outer layer  34  may be reverse printed, as represented by an ink layer  32 . 
     The inner layer  30  is preferably polyethylene. Alternately, inner layer  30  may be formed from any compositions or multi-layer laminates which may be permanently sealed, preferably by heat sealing. The inner layer  30  is substantially uniform across the entire bag, there being no holes, cut outs or regions substantially different than the rest. 
     The outer layer  34  is bonded to the inner layer  30  by a permanent adhesive  28 . While the permanent adhesive  28  is applied, a knock-out zone  16  is provided during manufacture of the bag  10 . The knock-out zone  16  may be mechanically covered when permanent adhesive  28  is applied. More preferably, the laminate may be manufactured, and the knock out zone may be created, using a rotogravure printing process, as discussed below. No permanent adhesive  28  should be applied within the knock-out zone  16 . 
     Thus, the outer layer  34  may be considered to have two portions, the fixed portion and the tab  20 . The fixed portion of outer layer  34  is permanently adhered to inner layer  30 . The area of the outer layer  34  corresponding with knock-out zone  16  forms tab  20  once manufacture of the bag  10  is complete. The knock-out zone  16  should extend to near enough the bottom of the bag  10  as to be capable of releasing the closure tab  20  for effective closure of bag  10 , even when the bag  10  is very nearly empty. 
     The permanent adhesive  28  may be any known adhesive which provides adequate affinity between the outer and inner layers. It is preferable that the permanent adhesive  28  be a conventional solvent or water based adhesive that is dried by evaporation within an oven. It is understood, however, that other adhesives such as energy curable adhesives could also be used. Other acrylic and urethane adhesives, including solventless, are known to be suitable. 
     The tab  20  may be formed by precision die cutting or laser scoring the outer layer  34 . Any process capable of accurately cutting the outer layer  34  while leaving the inner layer  30  in tact may be employed for forming the tab. Suitable laser scoring equipment may be obtained from Laser Machining, Inc. of Somerset, Wis. Laser scoring uses a focused spot of energy to remove material to a specified depth, allowing the unscored portion, here the inner layer  30 , of the laminate to retain package strength and barrier properties. Precision die cutting may also be used, and for purposes of economy, may be preferred. 
     As seen in the drawings, tab  20  is never fully removed from the fixed portion of outer layer  34 . Rather, tab  20  remains tangentially attached to the remainder of outer layer  34  along an adequate line or region such that danger of accidental total separation, such as by ripping, is minimized. As noted above, it is preferable that the tangential attachment be near the bottom of the bag  10 . 
     Within the knock out zone  16 , where permanent adhesive is not dominant, a pressure sensitive adhesive (PSA)  22  is provided. The particular PSA selected for use in the invention may vary depending on the substance chosen for outer layer  34 . Those skilled in the art would readily be capable of selecting a suitable PSA  22  in light of the teachings provided herein. The PSA should, however, have a greater affinity for the interior surface of outer layer  34  than for the inner layer  30  and the exterior surface of outer layer  34 . Conventional preparation techniques for increasing affinity of the ink  32  and PSA  22  to the interior surface of outer layer  34 , such as flame and corona discharge treatment, are well known. A release layer may also be applied to the exterior surface of outer layer  34  to prevent PSA  22  from adhering to the exterior surface thereof when tab  20  is affixed and removed from the roll of the bag  10 . 
     It is preferable to use an adhesive which is pressure sensitive such that the closure tab  20  may be applied and removed a plurality of times from engagement with inner layer  30  and with the fold of bag  10 , as shown in FIG.  2 . 
     In one embodiment of the invention, the pressure sensitive adhesive is a water-based acrylic adhesive, such as Nacor® 72-8761 adhesive, sold by National Starch and Chemical Company, Bridgewater, N.J. The pressure sensitive adhesive  32  is preferably applied to the removable tab portion  20  with a thickness of about 0.07 to 0.25 mils. 
     In one embodiment, PSA  22  is provided in zones, shown as  22   a  through  22   c  in FIG.  4 . When the PSA  22  on the tab  20  is provided in zones, only one zone need be used at a time, keeping the remaining zones free of dust or other potential contaminants. Once the PSA on the zone in use has reached the end of its useful life, the user may expose the next zone for use. Separating each zone is a gutter of a stronger adhesive  24 , shown as elements  24   a  and  24   b  in FIG.  4 . For purposes herein, a “stronger adhesive” is intended to mean any adhesive with a greater affinity to inner layer  30  than the affinity of PSA  22  to inner layer  30 . As such, stronger adhesive  24  may be another PSA or may be a heat curable adhesive. However, for reasons that will become clear below, stronger adhesive  24  should not be so strongly adhered to inner layer  30  as to be inseparable therefrom without causing damage to tab  20  or inner layer  30 . 
     It is preferred to provide an adhesive-free zone  26  at the tip of the tab  20 . The adhesive-free zone  26  may be provided to assist the user in grasping the tab  20  for separation thereof from inner layer  30 . 
     When the PSA  22  is provided in zones, as shown in FIGS. 3 and 4, a user may grasp the tip of tab  20  and pull with an adequate force to separate PSA zone  22   a  from inner layer  30 . The force initially used should not be so great as to separate stronger adhesive  24   a  from inner layer  30 . Thus, the user may initially reveal only zone  22   a , keeping zones  22   b  and  22   c  protected from contamination. With zone  22   a  revealed, the user may roll down the bag  10 , such as one might normally do to close a bag, and affix zone  22   a  to the rolled portion to ensure the bag remains closed. FIG. 2 shows the tab  20  affixed to the rolled portion. 
     In the event PSA  22   a  loses its affinity and fails to properly keep the bag closed or if it is desired to roll the bag down beyond where tab  20  remains affixed to inner layer  30 , the user may reveal an additional PSA zone  22   b . The user may do so by pulling tab  20  away from inner layer  30  with adequate force to separate a first stronger adhesive gutter therefrom, identified by the numeral  24   a  in the drawings. The separation of stronger adhesive  24   a  from inner layer  30  reveals PSA zone  22   b . Tab  20  may then be affixed to the folded portion of the bag  10  via PSA  22   b , in a way similar to that shown in FIG.  2 . 
     Additional PSA zones  22  may be sequentially revealed as needed. It is preferable that the last PSA zone  22  be near the bottom of the bag such that it is capable of holding the bag  10  closed when the bag  10  is very nearly empty and the user rolls or folds the bag  10  downwardly to very near its bottom. 
     It is currently contemplated that three zones of PSA  22 , as shown in the drawings, are adequate for the design of most bags. However, more zones may be desirable for very large bags or bags which a user must open and reseal an excessive number of times before completely consuming products contained therein. 
     The bag laminate according to the present invention is preferably made in a single forming process  100  as shown in FIG.  5  and discussed hereinafter. 
     The outer layer of material  102  is fed through a series of printing stations  104  wherein one or more layers of printed ink are applied to the outer layer in any conventional manner known to those skilled in the art. 
     The outer layer  102  with the printing formed thereon is then fed through first and second adhesive application stations  106 ,  108 . Each adhesive application station includes a rotogravure laminating cylinder  1   10  that has a copper or similar surface which is capable of being engraved, a pan  112  for applying a suitable liquid to the cylinder  110 , and a doctor blade  114  for removing liquid from the non-engraved portions of the cylinder  1   10 . Rotogravure printing processes are well known to those skilled in the art, and are discussed in  Package Printing , by Nelson R. Eldred, Ph. D, Jemlar Publishing Co., Inc, Plainview, N.Y., pages 86-88 (1993). 
     In a preferred embodiment of the present invention, in the first adhesive application station  106 , the surface of a first rotogravure cylinder  110 ′ is engraved so as to deliver the appropriate amount and pattern of pressure sensitive adhesive. The first rotogravure cylinder  110 ′ rotates within a pan of pressure sensitive adhesive  112 ′. As the outer layer  102  passes the cylinder  110 ′, the pressure sensitive adhesive is applied to the layer with a suitable amount of pressure from a roller  116 ′ to force the adhesive to transfer to the outer layer  102 . The non-engraved portion of the first rotogravure cylinder  110 ′ produces a space within the pressure sensitive adhesive layer. 
     The outer layer  102  and pressure sensitive adhesive combination is fed through a dryer  118  to dry the adhesive and then into the second adhesive application station  108 . In the second adhesive application station  108 , the surface of a second rotogravure cylinder  110 ″ is engraved so as to provide a mirror image of the permanent adhesive portion of the film bag laminate. The second rotogravure cylinder  110 ″ rotates within a pan  112 ″ of permanent adhesive. As the outer layer  102  passes the second rotogravure cylinder  110 ″, the permanent adhesive is applied to the outer layer  102  in register with the space left in the pressure sensitive adhesive portion. The outer layer  102  is then fed through a dryer  120  to dry the adhesive. 
     If it is desired to provide the pressure sensitive adhesive in zones as described herein, an additional adhesive application station (not shown) must be provided. The additional application station applies the stronger adhesive, described above, to gutter zones left in the area where pressure sensitive adhesive is otherwise applied by application station  106 . Those skilled in the art would readily be capable of designing the additional application station in light of the teachings provided herein. 
     After the adhesive has sufficiently dried, an inner layer of material  122  is brought into register with the outer layer and the combination is laminated in a conventional manner, such as with heat and pressure, to complete the film bag laminate  124 . 
     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.