Abstract:
A VFFS bag is provided that is dimensionally stable, aesthetically pleasing, and renders items stored in it highly visible. The bag includes first and second gusseted side walls that span a depth of the bag and front and rear walls that span a width of the bag. The bag has a substantially rectangular closed bottom end. In order to maximize the viewability of stored items and reduce the amount of film material in the bag, the bag has a depth to width ratio of at least 1.5:1 at the bottom end of the bag. Stability is enhanced by sizing the gussets such that they closely approach but do not overlap a line longitudinally bisecting the bag. A VFFS machine also is disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional patent application of U.S. patent application Ser. No. 13/683,395 filed Nov. 21, 2012 and entitled “Rectangular Multi-Substrate Vertical Form, Fill and Seal Bag and Apparatus for Forming and Filling Same”, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to bags for storing items and, more particularly, to multisubstrate vertical form, fill, and seal (VFFS) bags that are simultaneously formed and filled. The invention additionally relates to a machine and a method for forming and filling such bags. 
         [0004]    2. Discussion of the Related Art 
         [0005]    In order to prevent the premature spoilage of produce and other perishable items, bags storing such items often are formed at least in part of an open mesh material. The open mesh ventilates the items in the bag or allows them to “breathe,” increasing the items&#39; shelf life. The use of open mesh material in bags offers the additional advantage of rendering the stored items highly visible to potential purchasers. 
         [0006]    The mesh material can be preformed into the shape of a bag and filled and different times and/or locations using separate forming and filling equipment. Alternatively, the bags can be formed, filled with items, and sealed simultaneously. One such type of bag is a “vertical form, fill, and seal” or “VFFS” bag that is formed and filled while a web is pulled downwardly over a hollow forming tube, then sealed from below, then filled with items, and then sealed from above. VFFS bags however, historically were formed entirely of film. 
         [0007]    More recently, so called “half-and half” or other multisubstrate VFFS bags were introduced that are formed from a web that is part open mesh fabric and part film. Multisubstrate VFFS bags typically are generally square in shape and have both the front and rear walls formed from a strip of a film material that can be printed with indicia providing information about the items stored in the bags. These strips thus often are called “print bands.” In addition to bearing indicia, the strips also add dimensional stability to the hag, permitting the bag to stand more upright. This added dimensional stability enhances the bags&#39; aesthetic appearance and permits more bags to be placed in a given area such as on a store shelf. 
         [0008]    Bags usually are positioned at their point of purchase with the print bands facing outward. Because these bags are generally square in shape, the items in the bags are not easily viewed by potential purchasers, particularly if they are placed closely adjacent to one another on a shelf. This reduced visibility negates or at least mitigates the “viewability” benefits of making bags from an open mesh material in the first place. 
         [0009]    The viewability of items stored in a VFFS bag could be improved by reducing the width of the film strips at the front and rear walls of the bag. However, since the film strips typically contribute the majority of the dimensional stability to a bag, VFFS bags with narrow print bands tend to be dimensionally unstable and, thus, “slouch” rather dramatically. This slouching reduces the aesthetics of the bags and also hinders the orderly placement of bags on shelves next to one another. It also reduces the number of bags that can be placed in a given area, a major concern in grocery stores and other applications where shelf space is at a premium. 
         [0010]    The percentage of open mesh in a bag of a given capacity, and thus its viewability, can be increased by gusseting the mesh side walls of the bag. However, the typical gusseted bag produces a “bunched” structure at the bottom of the bag that prevents the bottom of the bag from lying flat and, thus, reduces the dimensional stability of the filled bag, counteracting one of the benefits sought by adding film strips to the bag. 
         [0011]    The need therefore has arisen to provide a partial mesh VFFS bag that is dimensionally stable, aesthetically pleasing, and enhances the viewability of items stored in the bag. 
         [0012]    The need also has arisen to provide a method and system for producing VFFS bags having the characteristics described above. 
       SUMMARY OF THE INVENTION 
       [0013]    In accordance with a first aspect the invention, a VFFS bag is provided that is dimensionally stable, aesthetically pleasing, and renders items stored in it highly visible. The bag includes first and second side walls that span a depth of the bag. Each of the side walls is formed from an open mesh fabric and has a top edge, a bottom edge, and a pair of longitudinally opposed, vertically extending, side edges. Each of the first and second side walls also is gusseted so as to expand between first and second side edges thereof when filled with items. The bag additionally includes front and rear walls that span a width of the bag, at least one of the front and rear walls being formed at least in part from a film material and having a top edge, a bottom edge, and first and second side edges, each adjoining a respective edge of one of the first and second side walls. The bag further has a substantially rectangular closed bottom end that is formed by bonding the bottom edges of the front and rear walls together with the bottom edges of the first and second side walls being captured therebetween. The bag is generally rectangular in transverse cross section and has a depth to width ratio of at least 1.5:1 at the bottom end of the bag. 
         [0014]    Each of the side walls of the bag may have two vertically extending gussets formed therein. Each of the gussets is located equidistantly between an edge of the associated side wall of the bag and a line that laterally bisects the bag. Each gusset has an apex that approaches but does not overlap a line that longitudinally bisects the bag. 
         [0015]    In accordance with another aspect of the invention, a VFFS machine is provided for forming bags and filling bags with items. The machine includes a forming tube, a feed assembly, a guide arrangement, first and second tuckers, and a sealer assembly. The feed assembly feeds a continuous web to the forming tube and wraps the web around the forming tube, the web having a first edge formed from an open mesh material and a second edge formed from a film material. A sealing device seals the first and second edges of the web together to form a sleeve. The guide arrangement is located beneath a bottom end of the forming tube and shapes the sleeve into a rectangular shape as the sleeve moves therepast so that the sleeve has a front wall, a back wall, and first and second opposed side walls. The tuckers are located beneath the bottom of the forming tube and are disposed opposite one another. They selectively move toward a line axially bisecting the forming tube to gusset the opposed side walls of the sleeve. The sealer assembly is located beneath the guide arrangement and the tuckers, and seals the front and rear walls of the sleeve together with the first and second side walls captured therebetween, thereby forming a bag having a closed bottom end. 
         [0016]    The guide arrangement may comprise four guides such as guide pins disposed beneath the bottom end of the forming tube, the guide pins forming corners of the bag. It may also include fifth and sixth guides disposed beneath the bottom end of the forming tube adjacent centers of the first and second side walls of the sleeve. respectively. In order to inhibit damage to the sleeve during the production process, at least the fifth and sixth guides may be resiliently deflectable by the sleeve. 
         [0017]    Each of the tuckers may be generally in the shape of a sideways “n”, having first and second spaced forming edges separated by a gap and located on opposite sides of the respective one of the fifth and sixth guides. 
         [0018]    Various other features, embodiments and alternatives of the present invention will be made apparent from the following detailed description taken together with the drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration and not limitation. Many changes and modifications could be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout and in which: 
           [0020]      FIG. 1  is a partially cut away perspective view of rectangular VFFS bag constructed in accordance with an embodiment of the present invention, viewed from in front of and from the left side of the bag; 
           [0021]      FIG. 2  is a front elevation view of the bag of  FIG. 1 ; 
           [0022]      FIG. 3  is a sectional plan view taken generally along the lines  3 - 3  in  FIG. 2 ; 
           [0023]      FIG. 4  is an enlarged fragmentary sectional plan view of a portion of  FIG. 2 , illustrating a corner of the bag; 
           [0024]      FIG. 5  is a sectional plan view taken generally along the lines  5 - 5  in  FIG. 2 ; 
           [0025]      FIG. 6  is a partially cut-away perspective view of a portion of a web usable to form the bag of  FIGS. 1-5 ; 
           [0026]      FIG. 7  is a side elevation view showing the bag of  FIGS. 1-5  juxtaposed next two prior art VFFS bags; 
           [0027]      FIG. 8  is a somewhat schematic side elevation view of a VFFS machine that can be used to make the hag of  FIGS. 1-5 ; 
           [0028]      FIG. 9  is a perspective view showing a portion of the VFFS machine of  FIG. 8  in greater detail; 
           [0029]      FIG. 10  is sectional plan view taken generally along the lines  10 - 10  in  FIG. 9 ; 
           [0030]      FIG. 11  is a fragmentary perspective view showing a bottom of the forming tube and the tuckers of the VFFS machine of  FIG. 8 , showing the tuckers in a retracted or non-operational position; 
           [0031]      FIG. 12  is a front elevation view showing a bottom of the forming tube and the tuckers of the VFFS machine of  FIG. 8 , showing the tuckers in an extended or operational position; 
           [0032]      FIG. 13  is a side elevation view showing one of the guide pins of  FIGS. 11 and 12  and the associated portion of the bottom of the forming tube; 
           [0033]      FIG. 14  is a somewhat schematic top plan view of the structures illustrated in  FIGS. 11 and 12 , showing the tuckers in a retracted position; and 
           [0034]      FIG. 15  is a somewhat schematic top plan view of the structures illustrated in  FIGS. 11 and 12 , showing the tuckers in an extended position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    With regard now to the drawing figures, in which like reference numerals designate like parts throughout, a vertical form, fill, and seal (VFFS) bag  20  is illustrated in  FIGS. 1-5 . The bag is made from the web  100  illustrated in  FIG. 6  using the VFFS machine  200  illustrated in  FIGS. 8-15 . 
         [0036]    Turning first to  FIGS. 1-5 , the bag  20  of this embodiment comprises a so-called four-panel VFFS bag having a front wall  22 , a rear wall  24 , and first and second (left and right) side walls  26  and  28 . The bag  20  additionally has top and bottom ends  30  and  32 . The bag  20  is filled with items  34  such as produce or other food products. The term “filled” as used herein does not mean that the entire interior volume of the bag  20  must be occupied by items  34 . Indeed, in commercial applications, a bag  20  typically is “filled” to its rated weight of stored items while the items occupy less than 70%, and quite often less than 50%, of the interior volume of the bag. Items that may be stored in the bag  20  may, for example, maybe nuts, oranges, potatoes, onions, seafood (such as shrimp, mussels, or clams), newspapers, flower bulbs, dried beans, or wrapped candy. 
         [0037]    The bag  20  is generally rectangular along the majority of its length when filled with items  34 , except where it is collapsed at the top end  30  where the opposed front and rear walls  22  and  24  are sealed to one another with the ends of the left and right side walls  26  and  28  captured therebetween. The left and right side walls  26  and  28  are formed from a gusseted open mesh material  38 . At least the outer surface of at least one of the front and rear walls  22  and  24  is formed from a film material  40  extending lengthwise of the bag  20 . Both of the front and rear walls  22  and  24  may he made at least in part from the film material  40 . In the illustrated embodiment, the film material  40  extends the entire length of each of the front and rear walls  22  and  24 . 
         [0038]    In the bag  20  of the illustrated embodiment, the front wall  22  of the bag  20  is formed from the open mesh material  38  overlaid with the film material  40 , while part of the rear wall  24  is formed solely from the film material  40 . More specifically, as seen in  FIGS. 3 and 5 , the rear wall  24  has first and second side edge portions  42  and  44  that are formed from the open mesh material  38  and that face one another with a gap between them. A strip of the film material  40  overlies and is bonded to the edge portions  42  and  44  and bridges the gap. Referring to  FIGS. 2, 4, and 5 , the film material  40  preferably extends the entire width of both the front and rear walls  22  and  24 , but may extend less than the entire width if desired. The strip of film material  40  forming the outer surface of the front wall  22  is heat sealed to underlying mesh fabric material  38  at its edges via seams  46 ,  48  that are approximately 0.64 cm (¼″) to 2.54 cm (1″) wide. The rear wall  24  of the bag  20  has two vertically extending seams  50 ,  52  at the corners thereof where the film material  40  overlaps the edges  42 ,  44  of the open mesh material  38 . Both of the seams  50 ,  52  comprise overlap seams. 
         [0039]    Referring especially to  FIGS. 3 and 5 , the left and right side walls  26  and  28  of the hag  20  are gusseted so as to permit them to expand and increase their capacity upon being filled. In order to increase the depth to width ratio of the hag  20 , each side wall  26 ,  28  preferably is double gusseted so as to have first and second gussets  56 ,  58  positioned on opposite sides of a line “L 1 ” that laterally bisects the bag  20 , that runs through a vertical plane passing through the centers of the side walls  26 ,  28 . Each gusset  56 ,  58  preferably is centered between the line L 1  and a corresponding edge of the bag  20 . Each gusset  56 ,  58  projects into the bag  20  to a point or apex  60 . In order to maximize the depth to width ratio of the bag  20  without causing the gussets  56 ,  58  to overlap each other at the bottom end  32  of the bag  20  and thus reducing the bag&#39;s dimensional stability, the apex  60  of each gusset  56 ,  58  preferably approaches but does not overlap a line “L 2 ” that longitudinally bisects the bag  20 , i.e., that passes through a vertical plane extending though the centers of the front and rear walls  22 ,  24 . The spacing between each apex  60  and the longitudinal bisector L 2  preferably comprises no more than 25%, and more preferably no more than 10%, of the width of the front wall  22 . In the case of a bag having front and rear walls that are each 7.62 cm (3″) wide, the spacing is no more than 1.52 cm (0.6″), and more probably no more than 0.76 cm (0.3″). 
         [0040]    The bag  20  is closed at the bottom end  32 . This closure could come by way of, for example, sewing, clasping, ultrasonic welding, or adhesion. It also could come by way of but thermal bonding. In the illustrated embodiment, both the top and bottom ends  30  and  32  of the bag  20  are closed by thermally bonded seams as seen in  FIGS. 1 and 2 . These seams may take the form of fin or peel seams  62 ,  64  formed by pressing two seal bars together, also as discussed below. They alternatively could be formed by other seams such as overlap seams. The upper and lower seams  62 ,  64  typically have a height H of about 0.95 cm (⅜″) to 1.27 cm (½″). 
         [0041]    The relationship between the gussets  56 ,  58  and the front and rear walls  22 ,  24  at the bottom  32  of the bag  20  prevents the bottom  32  of the bag  20  from bunching and, thus, provides a stable, flat surface upon which the remainder of the bag  20  can be supported as seen in  FIG. 7 , discussed in more detail below. 
         [0042]    A bag  20  constructed is described thus far can have a depth to width ratio, as measured by the ratio of the length of a sidewall  26  or  28  to the length of an adjacent front or rear wall  22  or  24  at the bottom  32  of the bag  20 , where the bag is not deformed by items stored therein, of over 1.5:1 and even of over 1.75:1. The bag  20  is nevertheless dimensionally very stable. The illustrated bag  20  has a width of 7.62 cm (3″) and a depth of 13.34 cm (5.25″), resulting in a depth to width ratio of 1.75:1. 
         [0043]    Referring now to  FIG. 7 , it can he seen that a VFFS bag  20  constructed as described thus far provides comparable or better visibility of stored items than prior art multi-substrate VFFS bags  70  and  80 , yet is remarkably stable. Each of the bags  20 ,  70 , and  80  has a depth of 13.33 cm (5.25″). Bag  70  has a width of 13.33 cm (5.25″), and bag  80  has width of 10.80 cm (4.25″). The bag  20  constructed as a described above has a width of 7.62 cm (3″). Its width thus is about 30% less than that of the bag  80  and over 40% less than that of the bag  70 . Its depth to width ratio is dramatically higher than that of either bag  70  or bag  80 . The bulging that naturally occurs at the sides of each of these bags  20 ,  70 , and  80  from the pressure of the stored items, though less pronounced in the bag  20  than in the prior art bags  70  and  80 , has a visually more dramatic effect due to the increased depth to width ratio of the bag  20  when compared to that of the bags  70  and  80 . Yet the stability of the bag  20  is comparable to or even superior to that of the bags  70  and  80 . The superior stability is particularly evident at the bottom of the bags, were the inventive bag  20  rests very flat against the surface on which it is supported, whereas the bags  70  and  80  appear comparatively “lumpy”. 
         [0044]    It should also be noted at this time that the reduced width to depth ratio of the inventive bag  20  results in substantial cost savings when compared to prior art bags. The “label stock” typically used as the film material of multi-substrate bags is relatively expensive when compared to the open mesh material. By reducing the width to depth ratio, the bag  20  has over 25% less label stock when compared to the bags  70  and  80 , resulting in a considerable cost reduction. 
         [0045]    The illustrated bag  20 , having the aforementioned “footprint” of 7.62 cm×13.33 cm (3″×5.25″), has a storage capacity of three lbs and is about 38.10 cm (15″) high. A bag having the same footprint and a two pound capacity would be about 30.48 cm (12″) high, and a bag having the same footprint and a one-pound capacity would be about 25.40 cm (10″) high. However, the concepts discussed herein are equally applicable to larger or smaller bags of different proportions. 
         [0046]    Referring now to  FIG. 6 , a web  100  is illustrated from which bag  20  can he made. Web  100  is formed from strips of the open mesh material  38  and the film material  40  and has first and second opposed edges  102 ,  104 . A single seamless strip  106  of open mesh material  38  is provided in this embodiment and is preferred for both strength and aesthetics, but two or more such strips could be bonded together, if desired. First and second strips  108 ,  110  of film material  40  are provided in this embodiment. The first strip  108  will ultimately form the outer portion of the rear walls  24  of the bags  20 , and the second strip  110  will ultimately form the outer portion of the front walls  22  of the bags  20 . In the illustrated embodiment in which each finished bag  20  will have a footprint of 7.62 cm×13.33 cm (3″×5.25″), the web  100  has a width of 41.61 cm (16 ⅜″) to 45.40 cm (17.875″). The mesh strip  106  is about 39.37 cm to 41.9 cm (15.5″ to 16.5″) wide, and each film strip  108 ,  110  is about 7.62 cm (3″) wide. The strips  106 ,  108 ,  110  may be bonded together by the VHS machine  200  as described below or may be bonded together by a different machine and supplied to the VFFS machine  200  as a pre-formed web. 
         [0047]    The mesh strip  106  has a first or outer edge forming the first edge  102  of the web  100  and a second edge  112  that is thermally bonded to a first edge  114  of the first film strip  108 . The first film strip  108  also has a second edge forming the second edge  104  of the web  100 . The mesh strip  106  and fl m strip  108  overlap one another to form a seam  116 . The width “D” of the seam preferably is set to provide adequate strength to the bond between the strips  106  and  108  such that the web  100  can function adequately when formed into a bag for storing produce or other items. By securing the mesh strip  106  to the film strip  108  in this configuration, the strength of the bond between the mesh strip  106  and film strip  108  is further enhanced regardless of the amount of overlap due to the integral form of the seal at the seam  116 . This is because the film strip  108  is softened upon heating to the point where the film strip  108  can surround the overlapped portion of the mesh strip  106 . When cooled, the mesh strip  106  is contained at least partially within the film strip  108  to form a unitary structure for the seam  116 . The width “D” of the overlap can be varied between 0.32 cm and 1.27 cm (⅛″ and ½″), depending, for example, upon the particular use to which the web  100  will be put. 
         [0048]    Still referring to  FIG. 6 , the second film strip  110  is bonded to the mesh strip  106  midway between the first and second edges  102  and  104  of the web  100 . This bond may occur across any desired portion(s) of the width of the second film strip  110 , and preferably is performed at edge seams  118 ,  120  that are between 0.32 cm and 1.27 cm (⅛″ and ½″) wide. 
         [0049]    Both of the film strips  108  and  110  may be formed of the same film material  40 . The material may be any film material capable of being heat bonded to itself and to other materials. It preferably is capable of receiving indicia on its inner and/or outer layer(s) and thus as functioning as a print band. A material made in whole or in part from a synthetic resin film material could suffice. One such material, available from the \John Companies of Antigo Wisconsin, is a so-called PET laminate having a thin layer of a relatively high melting point polyester material, serving as a print surface, laminated onto a relatively thick layer of a relatively low melting point linear low density polyethylene (LLDPE) material. The LLDPE material melts during the heat bonding process to seal the film material to adjacent materials. 
         [0050]    The open mesh material  38  may be any open mesh material to which a thermoplastic film strip can be heat bonded to form a seam that is sufficiently strong for use as form, fill, and seal bags. Preferably, the open mesh material  38  also is suitable for processing into bags using high speed bag-making equipment. Woven, knit, scrim, aperated, and extruded net materials are suitable for this purpose and nonwoven fabrics can be used provided they have sufficient openness of construction to allow adequate visibility of a bag&#39;s contents. Suitable woven, knit, or scrim fabrics may be formed from tapes or slit-film ribbon yarns. The yams of the fabric or such yarns and any coatings will generally comprise a thermoplastic resin composition. 
         [0051]    It also is contemplated to form the open mesh material  38  from thermoplastic resin compositions having different melting points, with a higher melting resin being present to provide strength and integrity to the fabric and a lower melting resin being present, either as a discontinuous coating on the surface of the fabric or laminated to or as part of the yarns thereof, e.g., as coextruded tapes, to provide for heat bonding of the yarns of the fabric to one another and, in turn, greater dimensional stability and resistance to fraying. One such material is formed from a number of intersecting filaments, at least some of which are composite filaments formed from a composite material having a high melting point “earlier” portion and a relatively low melting point “bonding” portion. This material is commercially available from the Volm Companies Inc. of Antigo, Wis. under the brand name ULTRATECH®. Permutations of this material are described in U.S. Pat. Pub. No. 2011/0085749, the contents of which are incorporated by reference. Another suitable material is a nonwoven fabric made from coextruded film that has been split and stretched. This material is commercially available from JX Nippon ANCI, Inc. under the brand name CLAF®. CLAF® material and its characteristics are described in more detail, e.g, in U.S. Pat. Nos. 4,929,303 and 5,182,162, the contents of which are hereby incorporated by reference. 
         [0052]    Preferably, the melting point of the film material  40  is at least about 10° C. below the melting point of the open mesh material  38  to facilitate heat sealing without melting or softening of the mesh material  38 . More preferably, the melting point differential is about 30° C. to about 60° C. The resin of the film strips  108 ,  110  should also provide sufficient seal strength and adhesion so that the bags hold product without breaking or failure at or adjacent to the seams during filling, handling, and use. Preferably, the open mesh material  38  and film material  40  are composed of resins and so configured as to provide, longitudinal seams having a strength of at least about 35.5 kPa (5 lb/in2) as measured by ASTM D 5035-95. More preferably, seam strength is at least about 55.2 kPa (8 lb/in2). 
         [0053]    Turning now to  FIGS. 8-15  and initially to  FIGS. 8 and 9 , the bags  20  may be manufactured on a vertical form, fill, and seal machine  200  that forms the web  100  from rolls  202  and  204  of the open mesh material  38  and the film material  40 , respectively, and that forms and fills bags  20  from the web  100 . The machine  200  includes a frame  206 , a web forming station  208 , a product dispenser  210 , and a form, fill, and seal assembly  212 . The web forming station  208  forms a continuous strip of the afore-described web  100  from rolls  202  and  204  of mesh and film  38 ,  40 , respectively. The form, fill, and seal assembly  212  receives batches of items from the product dispenser  210  and simultaneously forms bags  20  from the web  100 , fills those bags  20  with items, and seals the ends of the formed and filled bags  20 . 
         [0054]    Still referring to  FIG. 8 , the web forming station  208  includes first and second takeoff rolls  202  and  204  for the open mesh material  38  and the film material  40 , respectively. The open mesh material  38  preferably is wound onto the roll  202  in a continuous strip. If the fabric is ULTRATECH® or another material with warp and weft filaments, it is preferably wound onto the roll  202  with the warp filaments extending lengthwise of the strip or in the machine direction. The warp filaments may ultimately extend vertically in the finished bags. The second takeoff roll  204  may support a roll of a PET laminated film material  40 , printed with two adjacent repeating patterns of print indicia positioned side-by-side in alignment with each other. A slitter  214  is provided downstream of the takeoff roll  204  and is operable to slit the film material  40  into two indicia-bearing strips or print bands  108 ,  110 . A system  216  of guide rollers and guide bars guides the film strips  108  and  110  and the continuous strip  106  of the open mesh material  38  into a substrate forming assembly  218 , where the edge of the first film strip  108  is thermally bonded to an edge of the mesh strip  106  ( FIG. 6 ), and the other film strip  110  is thermally bonded to the outer surface of the mesh strip  106  in a spaced apart relationship to the first film strip  108 . As discussed above, segments of the film strips  108  and  110  ultimately form the rear and the front walls of the finished bags, respectively. The thermal bonding preferably is performed via a system of heated bars  220  and a platen  222  as is generally known in the art. A suitable system for slitting indicia-bearing film, into two print bands and for heat bonding the print, bands to a substrate is known, for example, from International Publication No. WO 99/58323 to Winiecke, the subject matter of which is hereby incorporated by reference. 
         [0055]    As noted above, the web  100  need not be formed on the vertical form, fill. and seal machine  200 . It could instead be formed by separate converting equipment located either at the same location as the vertical form, fill, and seal machine  200  or at another location, entirely. Optionally forming the web  100  at a remote location would offer the bag manufacturer the option of not having to purchase and handle multiple rolls of different types of materials. It also would reduce the capital expense associated with the purchase and operation of the VFFS machine  200  because the machine would not require a web forming station. 
         [0056]    Referring again to  FIG. 8 , the product dispenser  210  may function to dispense batches of items that have been weighed by a computer-weighing apparatus (not shown) at the proper time in the operating cycle of the machine  200 . Suitable computer weighing apparatuses that can perform this function are shown in U.S. Pat. Nos. 4,538,693 and 4,901,807, which are incorporated herein by reference. 
         [0057]    Referring to  FIGS. 8-10 , the form, fill, and seal assembly  212  includes a vertical forming tube  230  mounted on the frame  206  immediately below the product dispenser  210 , such that items dispensed from the product dispenser  210  are received internally of the vertical forming tube  230 . A forming shoulder  232  is secured to the frame  206  adjacent but spaced from an upper end of the vertical forming tube  230 . A forming shoulder  232  directs the web  100  around the forming tube  230  to form an initially circular tubular sleeve  150  in which, referring briefly to  FIG. 6 , the outer edge  104  of the first film strip  108  of the web  100  overlaps the outer surface of the opposed edge  102  of the mesh strip  106 . A vertical seal bar  234  is supported adjacent the forming tube  230 . The vertical seal bar  234  heat bonds the overlapped edge of the first film strip  108  to the outer edge of the mesh strip  110  at what will ultimately be the corner of the front of the finished bag  20  to form a vertical overlap seam, hence forming the generally tubular sleeve  150 . A pair of advancing belts  236 ,  238  is located on opposite sides of the vertical forming tube  230 . Belts  236  and  238  are periodically driven by synchronized motors  240 ,  242  ( FIG. 10 ) to index the sleeve  150  downwardly along the forming tube  230  the length of one bag  20  and to advance a corresponding amount of the web  100  into contact with the forming shoulder  232  to enable another bag  20  to be formed. 
         [0058]    Referring now to  FIGS. 11-15 , a guide arrangement  250  is provided at the bottom of the forming tube  230  in order to impart the desired rectangular shape to the sleeve  150  as it is converted into a bag  20 , in the illustrated embodiment, the guide arrangement takes the form of at least four, and preferably six, guide pins extending downwardly from the bottom end of the forming tube  230 . Four of these guide pins are “corner” guide pins  252  that are provided at locations that correspond to the corners of the finished bag  20 . These corner guide pins  252  support the sleeve  150  as it as it is drawn past the end of forming tube  230 , thus forming the corners of the bag  20 . Two additional “center” guide pins  254  may be provided at locations corresponding to the centers of the respective side wails  26  and  28  of the bag  20  in order to facilitate the gusseting operation performed by the tuckers  300 ,  302 , described below. All of the guide pins  252 ,  254  may be formed from steel, another metal, or a plastic. Referring especially to  FIG. 13 , each guide pin  252 ,  254  has a tapered outer end  256  to prevent it from snagging on the sleeve  150  and has an inner end  258  that is welded to or otherwise affixed to a collar  260  mounted on the bottom end of and the forming tube  230 . 
         [0059]    At least the center guide pins  254 , and preferably all of the guide pins  252  and  254 , are constructed so as to resiliently deflect or pivot toward the center of the forming tube  230  when the tuckers  300 ,  302  are extended so as to avoid tearing the web  100  or otherwise damaging the sleeve  150 . This deflection is best seen in  FIGS. 12 and 13 . The resilient deflection could be enabled simply by forming an end portion of the guide pin adjacent the inner end  258  in the form of a spring  262 . Alternately, at least the inner end of the guide pin could be made of a relatively resilient material such as a resiliently flexible plastic. 
         [0060]    The illustrated guide arrangement  250  also could be replaced by other structures such as bars so long as they achieve the desired result. 
         [0061]    Referring especially to  FIGS. 11 and 12 , left and right gusseting blades or tuckers  300 ,  302  are provided beneath the discharge opening in the forming tube  230  immediately above the sealing and cutting assembly  350  (described below) and in vertical alignment with the guide pins  254 . The tuckers  300 ,  302  are driven by actuators such as pneumatic cylinders  301  and  303  to fold the center of the left and right side walls  26  and  28  of the hag  20  between the edges of the front and rear vas  22  and  24 , thus forming the afore-mentioned gussets  56 ,  58  in the side walls  26  and  28  of the bag  20 . The depth of the gussets  56 ,  58  is determined by the stroke of the tuckers  300 ,  302  and, as discussed above, approaches the center of the bag  20  without overlapping it in the illustrated embodiment. 
         [0062]    Referring particularly to  FIGS. 11, 12, and 15 , each of the tuckers  300 ,  302  is generally in the shape of a sideways “n”, having first and second spaced forming edges or blades  304  and  306 . The blades  304  and  306  of each tucker are separated by a gap and are located on opposite sides of a respective one of the center guide pins  254 . Each blade  304 ,  306  has an inner end  308 , an outer forming end  310  that contacts the sleeve  150 , a horizontal bottom edge  312 , and an upper edge  314  that slopes downwardly from its inner end  308  to its other end  310 . Both blades  304  and  306  may be bent or otherwise formed integrally with a rear support plate  316  that is attached to the associated pneumatic cylinder  301  or  303 . Each tucker  300  or  302  may be formed of any of a number of rigid, durable materials such as steel. 
         [0063]    Referring again to  FIGS. 8 and 9 , an end sealing and cutting assembly  350  is located beneath the guide arrangement  250  and the tuckers  300 ,  302 . Assembly  350  includes a pair of opposed heated seal bars  352 ,  354  that are selectively movable toward each other to horizontally compress the sleeve  150  above the level of the product in the filled bag  20  to form a fin seal. The fin seal forms the lateral top seam  62  in the bag  20  containing the items and a lateral bottom seam  64  in the next bag  20  to be filled with the items. The combined seam  62 ,  64  is formed by heating the layers of the various materials so to bond front and rear walls  22  and  24  to each other and to the captured ends of the side walls  26  and  28 , generally as seen in  FIGS. 9 and 12 . The seal bars  352  and  354  are moved into the operative position by pneumatic cylinders  356 ,  358  ( FIG. 8 ) when the tuckers  300 ,  302  are in their operative position, assuring that the gussets  56 ,  58  of the side walls  26  and  28  of the bags  20  are securely retained between the front and rear walls  22  and  24  during the sealing process. Cylinders  356 ,  358  could be replaced by synchronized motors, cam-operated mechanisms, or any other devices capable of driving the tuckers  300  and  302  into and out of their operative positions, preferably but not necessarily in a synchronized manner. The assembly  350  also includes a retractable blade (not shown) that severs the filled and sealed bag  20  from the remainder of the sleeve  150  such that the filled and sealed bag  20  falls downwardly onto a slide  360  and is directed to a discharge conveyor  362 , which carries the filled and sealed bag  20  away from VFFS machine  200 . 
         [0064]    In operation, the web  150 , having been formed by the VFFS machine  200  or having been pre-formed, is pulled downwardly over the forming tube  230  from below by operation of the advancing belts  236  and  238 . This movement occurs in discrete increments, with one bag  20  being formed in each increment. As the web  100  is advanced toward the forming tube  230 , the forming shoulder  232  directs the web  100  around the forming tube  230  to form an initially circular tubular sleeve  150  in which the outer edge  104  of the first film strip  108  of the web  100  ( FIGS. 6 and 11 ) overlaps the outer surface of the opposed edge of the mesh strip  106 . As each increment of the sleeve  150  continues to index down the forming tube  230 , the vertical sealing bar  234  heat bonds the overlapped edge of the first film strip  108  to the outer edge of the mesh strip  106 . The sleeve  150  assumes the above-described rectangular shape is it is drawn past the bottom of the forming tube  230  and over the four corner guide pins  252 . Between movement increments, the tuckers  300 ,  302  are advanced to form the gussets  56 ,  58  and are held in their advanced position while the seal bars  352  and  354  are advanced to form the bottom seam  64  in one bag  20  and the top seam  62  in the underlying bag  20 . The newly formed bag  20  is filled at this time by dispensing items through the forming tube  230  from the product dispenser  210 . The tuckers  300 ,  302  are then retracted, and the retractable blade is extended to separate the bag  20  from the underlying bag. The thus separated bag  20  then is directed down the slide  360  and to the discharge conveyor  362 . At the same time, the advancing belts  236  and  238  are operated to index the next section of sleeve  150  downwardly over the guide pins  252  and  254 , and the process is repeated. 
         [0065]    Many changes and modifications could be made to the substrates, web, bags, and production systems and processes disclosed herein without departing from the spirit of the present invention. To the extent that they might not be apparent from the above, the scope of these variations will become apparent from the appended claims.