Patent Publication Number: US-2003232161-A1

Title: Poly-woven laminated paper bag with window

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates to multiwall bags configured for containing bulk quantities of materials, and more specifically, to such a bag having a paper outer layer and a woven inner layer, and a die cut opening in the paper layer that defines a window to allow the contents of the bag to be visually inspected.  
       BACKGROUND  
       [0002] Bulk quantities of materials are often packaged in multi-layer bags, and not surprisingly, there are numerous styles of bags known in the art. One type of bag has an outer layer of paper such as a kraft paper, and an inner layer of a poly-woven fabric laminated to the paper. One common kind of woven fabric used in such bags is a polypropylene material. Another is a polyethylene woven material. This kind of a bag is typically manufactured from roll stock paper-typically a standard kraft paper, and roll stock woven poly-woven material, often called “scrim.” The scrim layer provides a strong, durable liner for the bag.  
       [0003] Although there are several processes according to which the bags may be made, briefly described, the bags are fabricated by laminating or gluing the polypropylene fabric to the layer of paper to form an elongated continuous flattened blank, or web. The blank is formed into a tube by joining opposite lateral side edges at longitudinally extending seams, and by then cutting the tube into the desired bag lengths with rotating knives. One end of the tube is the closed with the desired end type, for example by stitching or heat sealing one end of the tube to define a closed bottom, leaving the opposite end open for filling and sealing by the end user. Any common type of closure may be used on either end of the bag, including as noted sewn ends, but also including valve ends, pinch ends and block bottom closures. The sides of the bag may be gusseted or flat, depending upon the user&#39;s needs and specifications.  
       [0004] Other process steps may be used as well in manufacturing such bags, for example, printing the outer surface of paper layer with various information such as the identity of the product that will be held in the bag, the manufacturer of the product, and the net weight of the bag, etc. One advantage of bags having a paper outer layer is that these bags are well suited to stacking; the paper tends not to slip when the bags are stacked atop one another, and large stacks of bags therefore tend to be relatively more stable than, for example, stacks of bags having plastic outer layers.  
       [0005] One feature that many bag customers want is a window in the bag that allows the contents of the bag to be viewed and inspected by the end user. Thus, and by way of example, when a bulk bag that contains rice includes a window, the end user is able to inspect the product prior to making a purchase.  
       [0006] Although there are known methods of forming a window in a bulk materials bag, none of the known methods produces a bag that is as reliable or as strong as needed. One method involves making a die cut window in the paper layer and gluing a “patch” over the window on the surface of the paper that will be form the interior of the bag. The patch is a clear or translucent material that is fabricated from one of several materials, selected according to the specifics of the bag type. While this kind of a window bag allows the end user to see the product contained in the bag, the bag is inherently weaker than a non-window bag because the integrity of both the paper layer is disturbed, and the plastic patch typically is not as strong as the paper. The patch thus represents a relatively weak portion of the bag that can rupture or leak during handling and transport.  
       [0007] A completely different type of bag that allows the user to view the contents held in the bag has a scrim layer that is relatively translucent. The scrim is laminated (for example, with glue or resin, or heat treatment) to an outer layer fabricated from a clear or translucent film, such as ethyl vinyl acetate (EVA). The EVA layer is amenable to high quality printing with, for example, colored graphics and the like. Non-printed areas of the EVA layer may be utilized as windows. Bags having an EVA film outer layer tend, however, to form less stable stacks compared to paper bags, since the EVA tends to slide more easily over adjacent bags than paper-paper contact between adjacent EVA bags.  
       [0008] Accordingly, in view of the shortcomings inherent in conventional bags such as those just described, there is an opportunity to supply a window bag that has all of the advantages of conventional bags, yet avoids the shortcomings.  
       SUMMARY OF THE INVENTION  
       [0009] The illustrated embodiment of the bag of the present invention is a multi-layer bag having a layer of translucent poly-woven scrim, and a paper layer that includes a die cut opening that defines a window when the two layers are laminated. The two layers are registered relative to one another prior to lamination so that the position of the window is the same on each successive bag. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] The invention will be better understood and its numerous objects and advantages will be apparent by reference to the following detailed description of the invention when taken in conjunction with the following drawings.  
     [0011]FIG. 1 is a perspective view of an illustrated embodiment of the multi-layer window bag according the present invention, the illustrated bag having gusseted sides, a sewn closed bottom and an open top, and showing a quantity of a bulk commodity contained in the bag interior.  
     [0012]FIG. 2 is a cross sectional view taken along the lines  2 - 2  of FIG. 1, with the bulk commodity removed.  
     [0013]FIG. 3 is detail view taken at the close up circle  3  of FIG. 2.  
     [0014]FIG. 4 is a plan view of a multi-layer blank of material that has been formed into a tube but prior to the blank being cut to form individual bags.  
     [0015]FIG. 5 is a schematic side elevation view of one illustrated embodiment of a processing line for forming the multi-layer blank from which the bag of FIG. 1 is formed.  
     [0016]FIG. 6 is a schematic side elevation view of another illustrated embodiment of a processing line for forming a multi-layer blank or web from which a bag according to the invention may be formed.  
     [0017]FIG. 7 is a schematic perspective view of another illustrated embodiment of a processing line for forming the multi-layer web from which the bag of FIG. 1 is formed.  
     [0018]FIG. 8 is a schematic side elevation view of yet another illustrated embodiment of a processing line showing application of a coating material to the web formed according to the process shown in FIG. 5.  
     [0019]FIG. 9 is a cross sectional view of an alternate embodiment of the multi-layer window bag according to the present invention, taken along lines equivalent of the lines  2 - 2  of FIG. 1, but showing a three-layer bag.  
     [0020]FIG. 10 is a detail view of the bag of FIG. 9 taken at the close up circle  10  of FIG. 9.  
     [0021]FIG. 11 is a schematic side elevation view of one illustrated embodiment of a processing line for forming the multi-layer web from which the bag of FIG. 9 is formed.  
     [0022]FIG. 12 is a schematic perspective view of another illustrated embodiment of a processing line for forming the multi-layer web from which the bag of FIG. 9 is formed.  
     [0023]FIG. 13. is a schematic perspective view of another illustrated embodiment of a processing line for forming the multi-layer web from which the bag of FIG. 9 may be formed.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0024] One illustrated embodiment of the present invention is shown in FIGS. 1 through 3. Another illustrated embodiment is shown in FIGS. 9 and 10. With reference to FIG. 1, bag  10  is shown with the first end  12  open to illustrate a bulk commodity  14  contained in the bag. Bulk commodity  14  is illustrated generally as comprising some generic bulk material, and it will be understood that bag  10  is designed to contain any number of bulk commodities, such as food products and other agricultural products and innumerable other items. The end of bag  10  that is opposite first end  12  is referenced generally with number  16 . For ease of reference first end  12  is referred to as the top end of bag  10 , and opposite end is referred to as bottom end  16 . Bottom end  16  is illustrated as being closed with a conventional sewn closure. After filling, top end  12  also would of course be closed in a conventional manner, for example with a sewn closure or valve closure. The first and second lateral side edges of bag  10  are designated with reference numbers  18  and  20 , respectively, and are illustrated as being defined with conventional gussets.  
     [0025] It is to be appreciated that while the invention is illustrated and described as being embodied in a specific type of bag that has gusseted sides, and a sewn closure on the bottom end, the invention as claimed is applicable to multi-layer bags having other side and end configurations. For example, the invention is applicable to bags having flat side edges and other types of sides, and any type of end closures, including sewn ends, sealed ends, valve ends, pinch bottom ends, etc. As such, the specific bag configuration described herein illustrates the invention only and is not intended as a limitation to the claims appended hereto.  
     [0026] A window  22  is formed in the outer layer of bag  10 , as described in detail below. Window  22  allows for commodity  14  to be viewed through the window.  
     [0027] With reference now to FIG. 2, bag  10  is shown as comprising two layers or plies, an outermost layer  24  and an inner layer  26 . Outermost layer  24  (also referred to herein as paper layer  24 ) is typically a conventional and commercially available kraft paper of suitable weight that is supplied in bulk rolls.  
     [0028] Inner layer  26  comprises a poly-woven fabric, sometimes referred to herein as scrim layer  26 . There are numerous commercially available materials available for use in scrim layer  26 , but in all instances the selected material will have enough translucency to allow the commodity  14  contained in the bag interior to be viewed and inspected through window  22 . Stated otherwise, the material selected for inner layer  26  has sufficient transparency that material contained within the bag may be seen through window  22  with sufficient clarity that a viewer may visually discern and inspect the contents with reasonable clarity. One preferred scrim layer  26  is a woven polypropylene fabric. Another preferred scrim layer  26  is a woven polyethylene fabric. As used herein, “poly-woven fabric” or scrim layer  26  refers to polypropylene and polyethylene fabrics, and other woven fabrics of equivalent functionality. Scrim layer  26  preferably has the desired translucency and a fabric weight in the range of about 500 to 1200 denier, and a weave (referring to the number of weft and warp tapes per inch) within the range of about 4 by 4 to about 15 by 15. A more preferred scrim layer is a poly-woven fabric having a weight of about 800 to 900 denier and a weave of about 8 by 8. However, so long as the desired translucency is maintained, the weight of the fabric and the width of the tape may vary widely from the preferred ranges stated. Inner layer  26  is bonded to outer layer  24  as described below.  
     [0029] With reference now to FIGS. 1 and 3, it may be seen that the woven fibers that define the fabric of inner layer  26  run generally parallel to the longitudinal axis of bag  10  and generally transverse to the longitudinal axis of bag  10 . Thus, for reference purposes, a bag axis is defined as the axis extending in the direction of arrow A in FIG. 1—that is, the axis that extends along the longitudinal axis of the formed bag. The cross-bag axis is transverse to the bag axis, and is illustrated with arrow B in FIG. 1. Using conventional terminology, tapes  40  represent warp tapes (running along the bag axis) and tapes  42  represent weft taps (running transverse to the warp tapes).  
     [0030] There are several process steps according to which bag  10  may be fabricated. Outer layer  24  is, as noted, kraft paper that typically is supplied in a roll. FIG. 4 illustrates a section of a continuous tubular blank or web  44  that comprises an outer layer  24  that has plural die cut windows  22  formed therein, each of which is evenly spaced apart from the next adjacent window, and an inner layer  26  of woven fabric that is visible through the windows. While window  22  shown in the drawings is oval in shape, it will be appreciated that the window can be cut in any shape and that more than one window may be cut into the paper layer. Further, as described in greater detail below, window  22  is cut and registered relative to other materials in the bag so that the position of the window on the bag is always in the desired location. Continuing with reference to FIG. 4, the web  44  has been formed into a tube and the outer layer, in most instances, will be preprinted with various labeling indicia  46  (“ABC CO.”), which is repeated at evenly spaced. As detailed below, once the desired layers have been laminated and formed into a tubular web  44 , the web is cut in the cross bag direction at appropriate intervals (for example, at dashed lines  48 ) to define individual bags having open opposite ends. The bottom end is typically then closed with an appropriate closure, leaving the top end open for filling and sealing by the user. It also is to be understood that the top end may be closed with an appropriate closure and sent to the customer for filing through the open bottom end.  
     [0031] When web  44  includes printed indicia, each die cut window  22  is registered relative to the position of indicia  46  so that the window  22  is positioned in the same position on each finished bag. In all cases the window is registered relative to the cut lines (dashed lines  48 ) so that the window is placed in the same place (relative to the bag top end and bottom end) on each successive bag.  
     [0032] One process for forming bag  10  is shown in FIG. 5 where scrim layer  26  is supplied in a supply roll  50  and the material for outer layer  24  is supplied in a separate supply roll  52 . The material in supply roll  52  has already been die cut with windows  22  and has already been printed with indicia  46 , if the later is desired. Paper layer  24  and scrim layer  26  are fed around appropriate intermediary rolls such as guide rolls  54  and tensioning rolls  56  into and through a nip  58  defined between pinch rolls  60 ,  62 . As detailed below, one or more of the lateral edges of the two layers may be overlapped, or laterally offset relative to one another in the cross bag direction as they come together in order to facilitate seam formation. Alternately, one of the layers  24  or  26  may be wider than the other layer (in the cross bag direction) to facilitate formation of a seam. As the two layers  24  and  26  enter nip  58  a lamination unit  59  (such as a conventional extrusion head) applies a bonding agent such as a resin between the layers. The resin (not shown) is preferably coated onto substantially the entire facing surfaces between the two layers. The pressure applied between the pinch rolls on layers  24  and  26  bonds the layers together. It will be appreciated that there are numerous apparatus available for applying bonding agents such as resin between layers  24  and  26 , including for example extrusion heads, curtain coaters, spray coaters and the like.  
     [0033] After passing through nip  58  the two layer web is either rolled onto a take-up or rewind roll  64  for further processing or is fed directly into the further processing line, namely tube formation and bag cutting, both of which are performed in a conventional manner well known to those of ordinary skill in the art.  
     [0034] As noted above, during formation of the blank from which the finished bag  10  will be formed, one or both of the opposite lateral edges of layers  24  and  26  may be overlapped or laterally stepped or offset relative one another during seam formation. This lateral stepping process is done to facilitate formation of longitudinal seams. There are several ways to form the blank, multi-layer web into a tube by joining opposite edges of the blank in a longitudinal seam. One method is illustrated in the cross sectional illustration of FIG. 2 and is done so that when a tube is formed from the blank the overlapping edges of each layer form a longitudinal seam that has an overlapping portion. Referring specifically to FIG. 2, it may be seen that one lateral edge  28  of outer layer  24  aligns with the adjacent lateral edge  36  of inner layer  26 . The coextensive edges  28  and  36  overlap with the opposite lateral edge  30  of the paper layer  24  to define a longitudinal seam  32 . However, the opposite lateral edge  34  of inner layer  26  (which in the illustration of FIG. 2 is wider in the cross bag direction than layer  24 ) overlaps and extends beyond edge  30  of layer  24  and is adhered to the overlapped portion of inner layer  26 . The combined overlapping regions define a longitudinal seam  38 . Both longitudinal seams  32  and  38  extend in the bag direction. During tube formation, the overlapping portions of the layers are coated with suitable adhesive to bond the seams. As shown in FIG. 2, longitudinal seams  32  and  38  are laterally overlapped. Other seam structures function equally as well as the structure just described.  
     [0035] In some instances the customer may desire a finished bag that has the paper layer on the inside of the bag, and the poly-woven layer on the outside. This is accomplished by forming the tub as described above, but with the paper toward the tube interior. Thus, although the bag of FIG. 1 includes a first layer of paper and a second layer of poly-woven material, the bag may be formed with the first layer either on the inside, or on the outside according to customer preference. Moreover, with a bag that has paper on the inside and the poly-woven scrim on the outside, it may be desirable to add an outer layer of EVA material, which has been preprinted (in the manner described below).  
     [0036] As one alternative to the steps illustrated in FIG. 5, supply roll  52  may be unprinted and without die cut windows. FIG. 6 is similar to the process shown in FIG. 5, except a die cut roll  66  is positioned between supply roll  52  (which in FIG. 6 is a blank web of paper without windows  22  cut therein) and the lamination unit  59 . Die cut roll  66  includes a knife blade registered to cut windows  22  in outer layer  24 .  
     [0037] Yet another alternative processing line for manufacturing a multi-ply blank web according to the present invention is shown in FIG. 7, where outer layer  24  (preprinted with indicia  46  and precut with windows  22 , both of which are registered relative to one another) is supplied from a supply roll  68 . Inner woven layer  26  is similarly supplied from a supply roll  70 . Inner layer  24  and outer layer  26  are fed through a nip  70  defined between pinch rolls  72 ,  74  to bond the two layers together. In the illustration of FIG. 7, one or both of the inner layers and outer layers may be pre-coated on the surface that mates with the opposite layer with a suitable adhesive such as a heat-activated resin. In that case the pinch rolls  72  and  74  may be heated to activate the resin and achieve bonding between the two layers. In the illustration of FIG. 7 the woven fabric is not shown through windows  22  in the bonded multi-layer blank that is being wound onto the rewind roll.  
     [0038]FIG. 8 illustrates the addition of a coating layer to the preformed multi-layer blank of web material. Thus, a supply roll  76  of a blank web  78  that has been preformed and comprises an outer layer  24 , inner layer  26  and windows  22  (fabricated as described above) is provided. Blank web  78  is fed through a nip  80  between pinch rolls  82 ,  84 . A coating layer is applied to the outer layer of blank web  78  (that is, the layer that will form the outer layer of the finished bag  10 —the paper layer) at lamination unit  86 , which typically is an extrusion coating head or similar coating unit. The coating typically is a clear resin that provides additional protection for the bag, and may comprise a conventional plastic-type coating selected from numerous compounds well known to those of skill in the art. The coated web  88  is wound onto take up roll  90  for further processing as described above.  
     [0039] In some instances it is desirable to add yet another layer to the two-layer bag described above to provide added resiliency and other benefits. Such a bag is illustrated in FIGS. 9 and 10, and various processing techniques are shown in FIGS. 11 and 12. Beginning with FIG. 9, bag  100  is identical in structure to bag  10  described above, except in addition to paper layer  24  and inner woven layer  26 , an outermost layer  102  has been added. As such, paper layer  24  has become an intermediate layer. Outermost layer  102  comprises a clear layer of a material such as ethyl vinyl acetate (EVA) or oriented polypropylene (OPP). The outer layer provides additional protection for the bag and additional printing options, since materials such as EVA and OPP may be printed with high quality color graphics. Importantly, because EVA and OPP and similar materials are selected to be highly translucent, these materials when applied as an outer layer  102  do not impact the ability to view the contents  14  contained in the bag through window  22 . It will be appreciated that printed indicia on outer layer  102  (not shown) must be registered relative to window  22  so that the indicia is always in the same position relative to the window on each finished bag. FIG. 10 illustrates outer layer  102  as it lays adjacent inner layer  26  at window  22  to provide added protection for the window. As with the bag illustrated in FIG. 1, the three-layer bag of FIG. 10 may be manufactured with the paper layer on the interior of the bag, the scrim layer in the middle, and the EVA layer on the outside.  
     [0040] Alternative processing methods for manufacturing the tri-layer bag  100  shown in FIGS. 9 and 10 are shown in FIGS. 11, 12 and  13 . It will be appreciated to those of ordinary skill in the art that the same processing variations described above with respect to bag  10  may be applied to processing bag  100 . One processing method is illustrated in FIG. 11 where a supply roll  110  of a blank web  112  that has been preformed and comprises an outer paper layer and an inner poly-woven layer, and which includes windows  22  (fabricated as described above) is provided and fed through a nip  114  between rolls  116 ,  118  where the web  112  is bonded to an outer layer  120  that is supplied from supply roll  122 . Outer layer  120  is a clear material such as EVA or OPP as described and is bonded to the outer paper layer (as shown in FIGS. 9 and 10) with a low density resin applied with a laminator  124 . The three-layer blank  128  (inner poly-woven layer, middle paper layer (with windows) and outer EVA layer) are wound onto a rewind roll  130  for further processing (tube and bag formation as described previously).  
     [0041] As detailed above with reference to the embodiment of bag  10  illustrated in FIGS. 2 and 3, the lateral edges of the three layers defining bag  100  may overlapped or offset relative to one another during seam formation as is known in the art.  
     [0042] Another alternate method for fabricating a three-layer blank web  128  is shown in FIG. 12. There, the two-layer blank  132 , comprising the outer paper layer and the inner poly-woven ply (the outer layer being preprinted with indicia  46  and precut with windows  22 , both of which are registered relative to one another) is supplied from a supply roll  134 . Coating layer  136  (EVA or OPP or the like) is similarly supplied from a supply roll  138 . Two-layer blank  132  and coating layer  136  are fed through a nip  140  defined between heated pinch rolls  142 ,  144  to bond the two layers together. In the illustration of FIG. 12, one or both of the inner layers and outer layers may be pre-coated on the surface that mates with the opposite layer with a suitable adhesive such as a heat-activated resin. It will be appreciated that the written indicia may be provided on the outer paper layer, and that the layers are registered relative to one another so that the window  22  and the printed indicia are always consistently located on each finished bag. In the illustration of FIG. 12 the woven fabric is not shown through windows  22  in the bonded multi-layer blank that is being wound onto the rewind roll.  
     [0043] Finally, in FIG. 13 the outer EVA layer  150  is preprinted with indicia  46 . The printed EVA material is then registered with and laminated to the paper layer to define a two-layer supply roll  153 . The poly-woven scrim  154  is supplied on roll  156 . The materials supplied from the two supply rolls  153  and  156  are fed through a nip  158  between heated press rolls  160  and  162  to bond the layers together, and the three layer web  164  is taken up on a take up roll  166  for further processing as described above. It is important that when the EVA layer, which has been preprinted with indicia  46  is laminated to the paper layer, which has a die cut window  22 , that the two layers are registered so that the window is always in the same position relative to the printing on each bag.  
     [0044] Finally, one further alternative processing method is to laminate a paper layer (without a window) to a preprinted EVA sheet, then die cut a window through the two-layer sheet thus formed (the die cut window is registered relative to the printed indicia), and then laminate the scrim layer to form a three-layer sheet. The three-layer sheet is then formed into finished bags in the manner described above.  
     [0045] While the present invention has been described in terms of a preferred embodiment, it will be appreciated by one of ordinary skill that the spirit and scope of the invention is not limited to those embodiments, but extend to the various modifications and equivalents as defined in the appended claims.