Patent Publication Number: US-6991592-B2

Title: Method of folding flat bottom bag

Description:
FIELD OF THE INVENTION 
   The present invention relates to methods of making packages. In particular, the invention relates to methods of folding leak resistant, flat bottom bags. 
   BACKGROUND 
   Bags are a common form of packaging and are readily available. Bags are generally flexible; they easily conform to the shape of the item being retained; and they are relatively inexpensive to produce. Over the years, methods for making flat bottom bags have changed, from manually folding paper sheets to form the bags, to mechanical processes for automatically folding paper sheets to form the bags. 
   A common bag configuration is a flat bottom bag with gusseted sides. Both the standard, brown paper grocery bag and brown paper lunch bag are such flat bottom bags. A standard flat bottom bag is illustrated in  FIG. 13 , showing the various flaps and folds. Such a configuration, in addition to the paper material, is not resistant to water or other liquid, due to the bottom fold configuration. Indeed, such a construction easily allows passage of liquid therethrough. 
   Other bottom fold configurations for flat bottom bags are known. 
   One method for folding paper flat bottom bags (also referred to as block-shaped bottom bags) having a fold configuration different than the grocery bag, discussed above, is described in U.S. Pat. No. 3,266,387, Finke et al. The bag produced by Finke et al. is illustrated in  FIG. 14 , showing the various flaps and folds, The process of Finke et al. begins tubular bags (i.e., unfinished bags having a non-sealed bottom). The teachings of Finke et al. include folding the bottom, changing the bag orientation direction, and then raising the corner pleats. 
   Improvements are desirable. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a method for folding a bottom for a flat bottom, non-paper bag. The process is an automated, robotic system that eliminates the need for operator interaction in order to fold or otherwise manipulate the bag during the bottom folding process. 
   The method begins with an unfinished bag, already formed into a general shape having a sleeve defining a longitudinal direction and a transverse direction, the sleeve having a mouth end and a bottom end and defining an interior. At the bottom end is an unfinished base portion. The method of the invention then folds the unfinished bag, by a sequence of steps at a variety of process stations, to provide a completed bag. 
   In one particular embodiment, the method of the invention is directed to folding a bag, including opening an unfinished base portion of an unfinished flat bottom bag and extending the gussets transversely, forming a fin extending transversely across the unfinished base portion, and then folding a first end and a second end of the fin against the unfinished base portion to form a base. Using such a method, at least 20 bags/minute can be folded. In some embodiments, at least 40 bags/minute can be folded. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective side view of a first step in the method of the present invention, with the package blank at a first process location. 
       FIG. 2  is a perspective end view of a second step in the method of the present invention, with the package blank in a first position, at the first process station. 
       FIG. 3  is a perspective end view of a third step in the method of the present invention, at the first process station, with the package blank in a second position. 
       FIG. 4  is a perspective end view of a fourth step in the method of the present invention, with the package blank in a third position, at a first portion of a second process station. 
       FIG. 5  is a perspective side view of the fourth step, at a second portion of the second process station. 
       FIG. 6  is a perspective end view, from the opposite side of  FIGS. 2 ,  3  and  4 , of a fifth step in the method of the present invention, with the package blank at a third process station. 
       FIG. 7  is a perspective side view, of the fifth step, with the package blank exiting the third process station. 
       FIG. 8  is a perspective top side view, of a holding step for the package blank, between the third process station and a fourth process station. 
       FIG. 9  is a perspective top side view, from the opposite side of  FIG. 8 , of a sixth step in the method of the present invention, with the package blank entering the fourth process station. 
       FIG. 10  is the same view as  FIG. 9 , with the package blank within the fourth process station. 
       FIG. 11  is a schematic depiction of two steps which occur to the package blank at the fourth process station. 
       FIG. 12  is a schematic depiction of a final step which occurs to the package blank to form the completed package. 
       FIG. 13  is a schematic depiction of the bottom of a conventional paper flat bottom bag. 
       FIG. 14  is a schematic depiction of the bottom of a paper flat bottom bag made by the process of U.S. Pat. No. 3,266,387 to Finke et al. 
   

   DETAILED DESCRIPTION 
   Process speed is a factor in whether or not processes are commercially successful. The present invention provides a fast, fully automated process for folding non-paper, flat bottom bags having side gussets. The process includes using modern technology, such as robotics and programmable motion controllers. 
   The bags folded by the method of the present invention are “non-paper”, meaning, that at least the outer surfaces of the bags are not a cellulosic material. The preferred material from which the bag is made is a sheet of polymeric material, such as polyethylene (either high density or low density), polypropylene, polyester, or blends thereof. 
   The polymeric sheet may be a layered co-extrusion of two or more types of materials. The polymeric sheet may include a base paper or cellulosic layer onto which a polymeric layer is adhered. As another alternative, the polymeric sheet may include a reinforcing or strengthening scrim, paper, or fibers. 
   The polymeric sheet may have a surface coating on one or both sides of the sheet. Any coating may be applied to the formed polymeric sheet or may be co-extruded with the polymeric sheet. One preferred surface coating is a UV-resistant coating, present on the side of the sheet that will be the outer surface of the bag. A UV coating, in addition to reducing any harmful effect from exposure to UV, increases the gloss of the material and reduces scuffing of any printing on the surface. 
   Typically, the sheet material has a thickness of about 2 to 10 mil, and is usually about 5 mil thick. 
   A polymeric bag is preferred over paper or other cellulosic bags, in general, because the polymeric bag is resistant to passage of moisture or liquid therethrough (i.e., is leak resistant), and is tear and puncture resistant. 
   Unfinished bags, which include a sleeve defining a mouth, a partially folded bottom, and side gussets, are used as the feed material for the folding process of the present invention. Such unfinished bags can be folded by commercially available packaging machines. One example of a machine that provides an unfinished bag is a W&amp;H Triumph bag machine, which is available from Windmoeller &amp; Hoelscher Corp. Other examples of machines that provide such an unfinished bag are available from H. G. Weber &amp; Co., Inc., and Fisher &amp; Krecke. 
   The process includes, in general, opening the partially folded bottom of the unfinished bag, first by lifting an end flap to provide sufficient room for a bottom opening mechanism to fit within the various bottom flaps. Once situated, the bottom opening mechanism pulls the bag bottom taught in the transverse direction, forming a fin where the two edges of the bag material join. A sharp crease is formed defining the fin between the base portions of the bag bottom, and the two edges f the bag material are seamed, to seal the fin. The fin is creased and sealed while the bag is moving in its transverse direction. After the fin is sealed, the direction of bag movement is changed. While the bag is moving in its longitudinal direction, the fin ends, or flaps, are folded against the base of the bag bottom. The flaps are sealed to the bottom, resulting in a flat bottom bag. A label may be added to the bottom of the bag. 
   In a more detailed description of the process of this invention, the process includes, in general, supplying partially folded bags to the process machine from a typical flat-bottom bag forming machine, with the bottom unsealed. These bags are loaded into a holder, such as a magazine. 
   From the holder, the partially folded bags are transported to a first station and stopped so that the centerline of the unsealed bottom is aligned with a mechanism to open the folded, but unsealed bottom. The bag is oriented so that during transport, the leading edge is the unsealed bottom and the trailing edge is the mouth of the bag. While stationary, the unsealed bottom is opened, or “reformed”, in such a manner that the original fold lines are used to maintain the flat bottom configuration while forming a sealable profile. A seal area is defined by the overlap material used in a conventional flat bottom forming operation. In accordance with the process of the present invention, two steps can be used to define the seal area. 
   In the first step, the bottom is opened enough to allow a bottom opening mechanism, such as a set of finger mechanisms, to drop into the open bottom and transversely stretch the bottom. In the stretched form, the two edges of the package material meet, forming a fin across the bottom of the unfinished bag. 
   The bag, with the finger mechanisms still positioned inside, is transported to a sealing area. At a first location in the sealing area, the bag bottom passes through a station that provides further definition between the fin and the bag bottom. This first location or station flattens the bottom and forms a semi-sharp crease between the bottom and the fin. A second portion of this station forms a sharper crease between the bottom and the fin. This defining of the fin is accomplished using various plates, press rolls and creasing blades. 
   Once the fin is sharply creased, the bag progresses to a continuous motion sealer, which seals the two fin layers together by the application of heat and pressure. A rotary band sealer is a preferred sealer for this operation. While the seal is warm, the fin is deflected down toward the bottom to facilitate subsequent folding. 
   Exiting from the sealing area, the bag changes its travel direction and is brought to a folding station. The folding station has guides, which fold the fin end flaps back onto the bag bottom. As the flaps are folded in, an adhesive is applied to hold the flaps in position against the bottom. Pressure is applied to iron the flaps against the bottom, and a finished bag is produced. 
   A label may be positioned over the bottom to provide a more refined look to the bottom. 
   Using the process of the invention, described in detail below, bags can be completed at a rate of at least 20–25 bags/minutes per process line. Depending on the polymeric sheet material used for the bags, 40–60 bags/minutes can be folded; such a rate can be obtained when a 5 mil thick high density polyethylene material is used. 
   The finished bag typically has a length, from its mouth to the bag bottom, of about 12–30 inches, and a width of about 6–18 inches, although the process equipment could be scaled to accommodate virtually any size bag. Bags as small as 3 inches wide and 6 inches tall, which are often used for packaging coffee, can also be made by this process. For a bag 6–14 inches wide, the side gussets are typically about 3–6 inches deep (per side), however, gusset depths of 2–9.5 inches are also common. 
   The finished bag can be used to hold any type of item, but it typically used for granular items. Because of the polymeric material, the bag is particularly suited for items that are often stored outside in the elements or in locations where the bag could get wet, such as in a garage or storage shed. Examples of items for which the bag is particularly suited include dog food, cat food and other palletized animal food, bird seed, cat litter and other bedding, sorbent materials, and fertilizer. 
   After the bag is folded and filled, the mouth is typically sealed. The seal may be made with adhesive, stitching, staples or other mechanical fasteners, or merely by melting the bag material together. For some products, a reclosable zipper closure may be added to the mouth of the bag. Such a zipper closure may be present on the unfinished bag, so that the bag progresses through the bottom folding process with the zipper already present at the mouth end, or, the zipper closure may be added to the bag after folding the bottom. 
   A specific example of a process according to the present invention is described in detail, below, with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. 
   Referring to  FIG. 1 , a partially folded bag  10  is illustrated. Partially folded bag  10  has a first, bottom end  12  and an opposite second end  14 . In the completed package, opposite end  14  will be the mouth or top of the package, through which items are placed and removed from the package. Throughout this discussion, the direction between bottom end  12  and mouth end  14  is referred to as the longitudinal direction. Extending between ends  12 ,  14  is a front face  16  and an opposite, back face (not illustrated). Partially folded bag  10  also has a first side edge  20  and an opposite second side edge  22 . Although not visible in  FIG. 1 , first side edge  20  is defined by a first sidewall, and second side edge  22  is defined by a second sidewall. Each of the sidewalls includes inwardly folded, expandable, longitudinal gussets extending from end  12  to end  14 . Throughout this discussion, the direction across face  16 , from side edge  20  to side edge  22 , is referred to as the transverse direction. 
   At the point in the process illustrated in  FIG. 1 , partially folded bag  10  is preformed with the front and back faces and sidewalls formed. The top of the bag, at second end  14 , is in its final configuration, configured for use as a mouth of the final package. First end  12  is partially folded and is considered “unfinished”. In this unfinished state, first end  12  has a first flap  24  which has a first bottom edge  13 , a second flap  26  which has a second bottom edge  15 , a first edge flap  28  on first side edge  20  and a second edge flap  30  on second side edge  22 . Such a partially folded bag  10  as illustrated in  FIG. 1  can be produced, for example, on a W&amp;H Triumph bag machine, which is available from Windmoeller &amp; Hoelscher Corp. Such bag folding machines are common in the packaging industry. 
   Once folded, partially folded bag  10  is fed to a first station of the current process, for example by a conveyor belt; such a first station is illustrated in  FIG. 1 , where partially folded bag  10  is positioned on support surface  102 , on its back face. Partially folded bag  10  may be secured to surface  102 , for example, by a holding mechanism, such as a vacuum or suction cups. While secured to surface  102 , partially folded bag  10  is positioned evenly between a bottom opening and holding mechanism, such as two suction cups  108 , one on each side of partially folded bag  10 . Partially folded bag  10  is also positioned so that a lifting source, such as a stream of air from air nozzle  104 , raises flap  24  up from the rest of partially folded bag  10 , in particular, from second flap  26 . The stream or jet of air from nozzle  104  is sufficient to raise flap  26 . 
   Referring now to  FIG. 2 , partially folded bag  10 , with flap  24  raised, is gripped by suctions cups  108  on edge flaps  28 ,  30  while being maintained on surface  102  by a retaining mechanism, such as by suction cups  106 . Suction cups  108  pull edge flaps  28 ,  30  out from the center of partially folded bag  10 , thus inverting the side gussets of partially folded bag  10 . At this stage, partially folded bag  10  has an opened bottom. 
   The bottom of partially folded bag  10  is opened in such a manner to allow an extending mechanism, such as fingers  110 , sufficient room to slide within partially folded bag  10  between edge  13  of flap  24  and edge  15  of flap  26 . In  FIG. 2 , outer fingers  110  and inner fingers  112  are illustrated progressing into the opened partially folded bag  10 . 
   Once within opened partially folded bag  10 , fingers  110 ,  112  stretch partially folded bag  10  and pull partially folded bag  10  taught across its width, as illustrated in  FIG. 3 ; in particular, fingers  110 ,  112  pull edge flaps  28 ,  30  apart. Bottom end  12  of partially folded bag  10  is reformed by this transverse stretching process. During this process, suction cups  108  retract, allowing partially folded bag  10  to tightly stretch, so that flap edge  13  and flap edge  15  are brought together forming a fin  36  extending from a base  38 . It is preferred that suction cups  108  release and retract prior to fingers  110 ,  112  stretching partially folded bag  10 . Fingers  110 ,  112  extend into fin  36  and terminate approximately at fold line  35 , which is due to the tension from fingers  110 ,  112  on edge flaps  28 ,  30 . This fold line  35  is a soft fold line, meaning, that fold line  35  is not a sharp crease having a definite line of demarcation, but rather, has an indefinite crease. 
   Partially folded bag  10 , with reformed bottom end  12 , is conveyed, for example, by a carriage assembly, to a second station that includes a creasing mechanism, as shown in  FIGS. 4 and 5 . Prior to entering creaser mechanism  114 , partially folded bag  10  includes soft fold line  35 ; after being acted on by creaser mechanism  114 , partially folded bag  10  has a sharp, distinct fold line  35 . 
   Referring to  FIG. 4 , partially folded bag  10  is illustrated moving transversely from right to left of the drawing into a first portion of a creaser mechanism  114 , with fingers  110 ,  112  retained in place within fin  36 . Creaser mechanism  114  includes a foot  116  which rests on and applies pressure to base  38  of partially folded bag  10 . As partially folded bag  10  moves under foot  116 , more distinction from fin  36  and base  38  is created, forming a sharper fold line  35 . 
   From foot  116 , partially folded bag  10  moves transversely to a second portion of creaser mechanism  114 . During this process to the second portion, fingers  110 ,  112  are removed from fin  36 . The second portion of creaser mechanism  114 , illustrated in  FIG. 5 , as sharp creaser mechanism  117 , includes various devices to form a sharp crease between fin  36  and base  38 . Shown in  FIG. 5  are first and second creasing rollers  118  and first and second creasing wheels  120 . Rollers  118  have a wide, flat area that further applies pressure to and presses base  38  of partially folded bag  10 . A pressure plate  119  can be included to provide further pressure on base  38 . Rollers  118  may apply pressure directly to base  38 , or to plate  119 , which in turn transfers the pressure to base  38 . Wheels  120  have a thin area, such as a peripheral edge, that forms a sharp crease or fold between fin  36  and base  38 . 
   The resulting bases  38 , one on each side of fin  36 , include an angled edge  42  at each side  20 ,  22  of partially folded bag  10 . Edges  42  meet at peak  40  at fin  36 . The portion of base  38  defined by angled edges  42  and extending past sides  20 ,  22  forms a flap  44 , which has fin  36  bisecting it. Each side  20 ,  22  of partially folded bag  10  has a flap  44 . It is this flap  44  what will provide a seal area that is later folded and sealed to base  38 . 
   From creasing mechanism  114 , partially folded bag  10 , having a sharp fold line  35  between fin  36  and base  38 , progresses to a third station to seal edge  13  to edge  15  in order to form a permanent seam at fin  36 . Referring to  FIG. 6 , partially folded bag  10 , progressing as indicated transversely from left to right of the drawing, nears a sealing station  121 . Preferably, sealing station  121  includes a sealing mechanism that provides the desired seal. In the embodiment illustrated, sealing station  121  includes a continuous sealer, such as a rotary band sealer  122 . Various movement devices, such as feed rollers  124  and conveyor band  126 , feed partially folded bag  10  into rotary band sealer  122 . An example of a suitable rotary band sealer  122  is Model AN ST225 available from Steeltec. Fin  36  is sealed by sealing station  121 . Particularly, a seal is formed by rotary band sealer  122  between the material present between edge  13  to fold line  35  and edge  15  to fold line  35 . 
   Partially folded bag  10 , with sealed fin  36 , exits sealing station  121  (e.g., rotary band sealer  122 ) in  FIG. 7 . Partially folded bag  10  progresses, still transversely, to a temporary or holding station at roller  128 . Partially folded bag  10  is conveyed adjacent to roller  128  until partially folded bag  10  contacts stop  130 , where partially folded bag  10  awaits entry into the next station. In  FIG. 8 , side edge  22  of partially folded bag  10  is illustrated against stop  130 . When pressure is sensed by stop  130  (e.g., when the presence of partially folded bag  10  against stop  130  is sensed) and a sufficient time interval has passed since the previous partially folded bag  10 , partially folded bag  10  progress under roller  128  at a bottom closing station which folds flaps  44 . When progressing under roller  128  to and through the bottom closing station, partially folded bag  10  moves longitudinally. 
     FIG. 9  illustrates partially folded bag  10  progressing under roller  128  to closing mechanism  132  at the bottom closing station;  FIG. 10  illustrates partially folded bag  10  farther under roller  128  and being acted on by closing mechanism  132 . Closing mechanism  132  includes a pair of inner bars  134  and a pair of outer bars  136 , one of each of bars  134 ,  136  on each side of partially folded bag  10 . Bars  134 ,  136  are positioned so that inner bar  134  is positioned closer to a centerline of partially folded bag  10  than outer bars  136  are. Inner bar  134  has a first end  134   a  and an opposite second end  134   b.    
   Partially folded bag  10  progresses between bars  134 ,  136 , specifically, so that flap  44  passes over outer bar  136  and base  38 , and possibly a portion of flap  44 , pass under inner bar  134 . Inner bar  134  is configured so that the bottom surface of bar  134  (e.g., the surface against partially folded bag  10 ) lowers as it progresses from first end  134   a  to second end  134   b . Similarly, outer bar  136  has a first end  136   a  and an opposite second end  136   b . However, outer bar  136  is configured so that the top surface of bar  136  (e.g., the surface against partially folded bag  10 ) raises as it progresses from first end  136   a  to second end  136   b . Either or both bars  134 ,  136  may be bars having a generally rectangular shaped, or, either or both bars  134 ,  136  may have a tapered, beveled, or wedge shape. In the embodiment illustrated in  FIGS. 9 and 10 , inner bar  134  is a plate and outer bar  136  is a tapered or wedge bar, having a greater thickness at second end  136   b  than at first end  136   a.    
   As partially folded bag  10  progresses longitudinally, flap  44 , one on each side  20 ,  22  of partially folded bag  10 , enters between upper bevel bar  134  and outer bar  136 . As partially folded bag  10  further progresses between bars  134 ,  136 , fin  36  is folded by inner bar  134  and outer bar  136  at flaps  44 . The upward tapered or beveled surface on outer bar  136  folds flap  44  upward, while inner bar  134  holds fin  36  and the rest of base  38  down. A crease results between flap  44  and the rest of base  38 . 
   Additionally at this bottom closing station, a sealant, such as hot melt adhesive, is applied to base  38  prior to flaps  44  being folded down against base  38 . Adhesive  46  is illustrated being applied to base  38  in  FIG. 11  by applicators  48 . After adhesive  46  is applied, flaps  44  are folded against base  38 , as illustrated in  FIG. 11 , and preferably tacked with pressure. Although not illustrated, various devices, including rollers, bars, arms, etc. can be used to fold flaps  44  against adhesive  46 . Rollers can be used to apply pressure to flaps  44 . 
   A label  50  can be applied to partially folded bag  10  after flaps  44  have been sealed to base  38 , as illustrated in  FIG. 12 . Label  50  can be applied in the same process as the folding of partially folded bag  10 , described above, or can be applied in a different process removed from the one described above. Still further, label  50  could be applied manually, although this is not preferred. 
   The resulting finished package has an interior that is defined by a sleeve having a mouth at mouth end  14  for providing access to the interior and a base at end  12  opposite the mouth. The sleeve is defined by side edges  20 ,  22  and face panel  16  and an opposite face panel (not illustrated). Label  50 , if present, would cover flaps  44 . 
   The above specification, examples and data provide a complete description of the manufacture and use of the structure of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.