Abstract:
An improved method and apparatus for enabling unsupported packaging film (e.g., low density polyethylene, linear low density polyethylene, and high density polyethylene) to be sealed in a tube in the process of making a flexible package. A “following belt” is provided which allows for a sandwiching effect to be imported on the film as it passes through its welding zone. In the prior art, while in this welding zone the polyethylene film would move with a conventional band seal assembly. But the opposite side of the polyethylene film would have to move relative to a drag iron this causing potential friction, seam failure and poor tracking. The present invention&#39;s use of a following belt allows the elements on both sides of the unsupported film to move with the film.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    The present application claims the benefit and priority of pending U.S. provisional patent application No. 60/406,548, entitled “Method and Apparatus for Providing an Improved Seam Seal in a Vertical Form Fill and Package Apparatus”, filed Aug. 27, 2002. The present application also incorporates the entirety of said provisional application by reference, even incorporating figures used in the provisional which may not be initially used in the non-provisional, but might be added at applicant&#39;s discretion. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention generally relates to vertical form fill and seal (a.k.a. “VFFS”) packaging machines, and particularly relates to the provision of an improved method and subapparatus for providing an improved seam seal in vertical form fill and seal packaging machines.  
           [0004]    [0004] 2 . Description of Related Art  
           [0005]    Vertical form fill and seal machines operate by transforming packaging material from a flat roll into a tube and sealing the edges of the flat to form the seam. This is referred to as the seam seal. Packaging machines operate in a variety of ways, including “intermittent motion” and “continuous motion”.  
           [0006]    Packaging machines also run a variety of film-type packaging materials. Such films are referred to as resistance film and polyethylene (a.k.a., “poly”) film. Resistance film is typically laminate film consisting of typically 3 to 7 layers with the sealing layer the inside layer. The multiple layers provide support for the sealing layer. Polyethylene film is typically a single layer film. The sealing process requires the two separate polyethylene layers to reach the melt point of the material and under pressure the layers are bonded together.  
           [0007]    Supported films such as the resistance films are easier to process due to the supporting layers. Polyethylene presents a problem when the film reaches the melting point and is unsupported; a consistent bond or weld cannot be achieved if other forces are acting on the film such as product filling the package, or friction due to relative movement when the film is in motion.  
           [0008]    Intermittent motion machines can overcome the problem with machine timing to allow the seal to set or with attachments that provide support while the film is stopped, such as shown in U.S. Pat. No. 5,987,853. Continuous motion machines are machines designed to operate with the film in continuous motion. Significant benefits exist due to the continuous motion; these allow for designs that increase dwell time for the end or transverse seal, less velocity differential between product being filled and the packaging material. However, the continuous motion of the film tends to cause a problem with running unsupported films such as polyethylene.  
           [0009]    Currently known seam seal assemblies for continuous motion machines consist of heated endless belts and stationary drag irons, between which the film is drawn and sealed. Stationary drag irons are positioned on the exterior of the forming tube assembly, and are used in conjunction with a heated endless belt assembly known as a “band seal assembly”. The band seal assembly and the stationary drag irons capture the flat overlapped seal therebetween. Heat and pressure is applied from the band seal assembly against the flat overlapped seal, which being captured from behind by the drag iron, melts and provides a welded seal. The band seal assembly draws the film downwardly, and the process continues. The disadvantage of this configuration is that since the inner layer is in constant drag against the forming tube assembly, this relative “dragging” movement between the overlapped seal and the drag irons can cause poor tracking and tearing, and can pull the seal apart. The condition exists regardless of the type of film the machine is using but is especially a problem when processing an unsupported film.  
           [0010]    Therefore it may be seen that there is a need in the art for an improved VFFS configuration which provides an improved seam seal.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    The present invention overcomes deficiencies in the prior art by providing a device for use with vertical form fill and seal machines which reduces the drag of film on the forming tube and reduces the influence the drag has on the film tracking.  
           [0012]    Generally described, the invention relates to a product packaging method including the use of film, having an overlap seam, and a drag iron, the method comprising the steps of capturing the overlap seam between a sealing band portion and an endless following band portion, and moving the sealing band portion, overlap seam portion, and endless following band portion in tandem together while providing sufficient pressure and heat from the sealing band portion sufficient to provide a seal corresponding to the drag iron raised portion.  
           [0013]    Therefore it is an object of the present invention to provide improved packaging machinery.  
           [0014]    It is a further object of the present invention to provide an improved packaging method.  
           [0015]    It is a further object of the present invention to provide an improved packaging method which includes the use of roll-fed unsupported film, which is then manipulated into an elongate tube which can accept product, the product contained by longitudinal and transverse seals.  
           [0016]    It is a further object of the present invention to provide an improved vertical form fill and seal machine which provides an improved seam seal for use with unsupported film such as a polyethylene film.  
           [0017]    It is a further object of the present invention to provide a vertical form fill and seal (VFFS) apparatus which is efficient.  
           [0018]    It is a further object of the present invention to provide a VFFS apparatus which has reduced downtime.  
           [0019]    It is a further object of the present invention to provide a VFFS apparatus which provides improved tracking features through use of a following belt.  
           [0020]    Other objects, features, and advantages of the present invention will become apparent upon reading the following detailed description of the preferred embodiment of the invention when taken in conjunction with the drawing and the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)  
       [0021]    Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:  
         [0022]    [0022]FIG. 1 is an illustrative view showing the forming tube assembly  20  with a forming shoulder assembly  21  which is configured to form an elongate sheet of film  5 , having longitudinal edges  5 E, such that the edges overlap a distance “D”, and a seal  6  can be provided.  
         [0023]    [0023]FIGS. 2A and 2B are illustrative sequential views generally showing the interaction between the moving support apparatus  50 , the band seal assembly  30 , the forming tube assembly  20 , and the film  5 . In FIG. 2A the band seal assembly  30  is spaced apart and is not in contact with the film  5 . However, in FIG. 2B the band seal assembly  30  has been brought into contact with the film  5 , pressing the film  5  against the following belt  60  of the moving support apparatus  50 , thus causing the following belt to move along with the film and the endless sealing band  32  of the band seal assembly  30 .  
         [0024]    [0024]FIGS. 3A, 3B and  3 C are different views of the same components. FIG. 3A is a front elevational view of the moving support apparatus  50 , without a following belt  60  in place. FIG. 3B is a side elevational view of that shown in FIG. 3A. FIG. 3C is similar to that of FIG. 3B except that the base  51  of the apparatus  50  is separated from the cover  52 , and the roller is not shown in dotted line.  
         [0025]    [0025]FIG. 4 is a partial illustrative, partial cross-sectional view of a band seal assembly  30  positioned on one side of a film layer  5  to be welded, and the moving support apparatus  50  with the endless belt  60  in place. The band seal assembly  30  is shown illustratively and the moving support apparatus  50  is shown in longitudinal cross section taken down its center.  
         [0026]    [0026]FIG. 5 is a pictorial view of the moving support apparatus  50 , with the following belt  60  shown partially in dotted line and partially in its conventional woven form at  60 W. This drawing is not to scale. A top guide roller  61  is rotatably mounted about a roller mount  62  such that it rotates about a generally horizontal axis.  
         [0027]    [0027]FIG. 6 is a transverse cross-sectional view of the moving support apparatus  50 , with the cross section taken below the roller, showing the base  51 , the cover  52 , and the contact ridge  54  (including the compliant material  55 ).  
         [0028]    [0028]FIG. 7 shows a portion of the wall of the forming tube assembly  20 , showing the recessed mount provided by the wall of the forming tube assembly  20 , and the mounting elements  56  for mounting the moving support apparatus  50  to the forming tube assembly.  
         [0029]    FIGS.  8 - 11  are various views of an alternative version  150  of the moving support apparatus which includes two supporting rollers for the endless following belt  160 .  
         [0030]    [0030]FIG. 8 is a front elevational view of the lower portion of the moving support apparatus  150  which includes a second roller  161 .  
         [0031]    [0031]FIG. 9 is a pictorial view of the alternate moving support apparatus  150 .  
         [0032]    [0032]FIG. 10 is a pictorial view of the upper portion of the alternate moving support apparatus  150 , including a base  151 , and a cover  152 .  
         [0033]    [0033]FIG. 11 is a view of that shown in FIG. 10, with the cover  151  separated from the base  151 , such as might be needed for repair or cleaning.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.  
         [0035]    General Construction and Operation  
         [0036]    The device consists of a member defining a narrow cross section contact surface laminated with a compliant material and positioned on the forming tube assembly, combined with the use of a low profile “following belt” constructed from a low coefficient of friction material. The film is sandwiched between a servo-driven sealing belt and the idling following belt. Friction forces are reduced because the following belt is free to rotate. The following belt also acts as a tracking belt, due to the film being pressed against the following belt as it is moved around its constrained path.  
         [0037]    The following belt allows the inside lap of the film to move freely in the direction of film travel thus tracking down the tube. The narrow cross section contact surface provides allows the sealing belt to only contact a small area of the film thus transferring the heat in a concentrated area. The concentrated area is brought to the melt point and bonded together while traversing down the tube. Without the following belt the seal would tend to be pulled apart by the friction forces acting on the film while moving and without the small cross section pressure would be transferred to an area too large to allow the seal to bond before product enters the package and pulling the seal apart.  
         [0038]    The result is the provision of an apparatus for use in vertical form fill seal machines that enables unsupported packaging film (such as low density polyethylene, linear low density polyethylene and high density polyethylene) to be sealed into a tube in the process of making a flexible package. The device that attaches to the forming tube or forming collar assembly that functions as a seal support as the seam is being welded or bonded.  
         [0039]    Elements List  
         [0040]    Polyethylene film  5   
         [0041]    Seam seal  6   
         [0042]    Forming Tube Assembly  20   
         [0043]    Band Seal Assembly  30   
         [0044]    Base  31  (w/heater)  
         [0045]    Endless sealing band  32   
         [0046]    Moving Support Apparatus  50   
         [0047]    Base  51  (defines return channel  51   c )  
         [0048]    Cover  52   
         [0049]    Contact ridge assembly  53  (includes contact ridge  54  and compliant material  55 )  
         [0050]    Endless following belt  60   
         [0051]    Roller  61   
         [0052]    Roller mount  62   
         [0053]    Alternative Moving Support Apparatus  150   
         [0054]    Base  151  (defining return channel  151   c )  
         [0055]    Cover  152   
         [0056]    Endless Following Belt  160   
         [0057]    Lower Roller  161   
         [0058]    The Polyethylene Film Used  
         [0059]    The polyethylene film  5  is conventional, and the type of flat overlap seam configuration is likewise conventional. It should be understood that this technology could also be used for non-poly applications.  
         [0060]    Forming Tube Assembly  20   
         [0061]    The forming tube assembly is generally conventional, except to the extent that a particular mount may be used to mount the moving support  50  thereto.  
         [0062]    Band Seal Assembly  30   
         [0063]    The band seal assembly  30  is conventional and includes a base  31  (see, e.g., FIG. 2A). Heat is provided from the base  31  to the endless sealing band  32  as needed.  
         [0064]    Moving Support Apparatus  50   
         [0065]    This is one of the main parts of the invention.  
         [0066]    Generally described, the moving support apparatus provides a following belt  60 , which “idles” along a defined track defined therefor.  
         [0067]    One section of the following belt path is situated outside the forming tube assembly, such that it can contact the polyethylene film, and in fact can cooperate with the sealing band  32  of the band seal assembly  30  as discussed in further detail elsewhere. Another section of the following belt path is a return path located between the base  51  and the cover  52 , discussed in detail elsewhere.  
         [0068]    The Moving Support Apparatus  50  includes the following components:  
         [0069]    Base  51  (defines return channel  51   c )  
         [0070]    Cover  52  (a.k.a. following belt support member)  
         [0071]    Contact ridge assembly  53  (includes contact ridge  54  and compliant material  55 )  
         [0072]    Compliant material  55  (part of contact ridge  54 )  
         [0073]    Endless following belt  60   
         [0074]    Belt Guide Roller  61   
         [0075]    Roller mount  62   
         [0076]    The base  51  is configured to be mounted in a recess (See FIG. 7) in the forming tube assembly  20 , and to support a cover  52  mounted thereto. The base  51  is generally planar, being approximately {fraction (3/16)} (0.185)″ thick and having a generally rectangular outline being approximately 1 inch wide and sixteen inches long. Of course these dimensions are for general reference only and should not be construed as limiting.  
         [0077]    The back side of the base  51  (the side facing away from the band seal assembly  30 ) is substantially flat (except possibly for various mounting pins, slots, etc.). However, the front side of the base defines a channel  51 C (see FIG. 5 for example) which could be referenced as a “return channel”. When the base  51  is attached to the cover  52 , these two members define the “return tunnel” of rectangular transverse cross section. This return tunnel defines a path for a given portion of a following belt to return from the end of its working path to be returned to the beginning of this working path as described in detail elsewhere.  
         [0078]    The cover  52  is likewise generally flat, with two opposing primary planar faces (with one slight exception on the front primary planar surface). These faces consist of an interior primary planar surface and an exterior primary planar surface with a contact ridge assembly  53  (which includes a “hard” contact ridge  54  and compliant material  55  thereon) extending along a partial longitudinal length of the cover  52 . This contact ridge  54  assembly  53  facilitates a concentration of pressure as needed for polyethylene film welding.  
         [0079]    In one embodiment, the contact ridge  54  is 13.75 inches long, ⅛″ wide, and 0.060″ high, although other suitable dimensions may be used without departing from the spirit and scope of the present invention.  
         [0080]    The compliant material  55  is made of silicone rubber (50-60 durometer) although other materials may be used without departing from the spirit and scope of the present invention. It is ⅛″ wide, and 0.040″-0.060″ thick.  
         [0081]    Teflon tape (not shown) may be used to tape the compliant material  55  to the contact ridge, although the compliant material  55  may include its own adhesive as needed.  
         [0082]    The endless following belt  60  in one embodiment is made of woven Teflon fibers. In one embodiment, the endless belt is approximately ½″ wide and 0.015″ thick.  
         [0083]    As noted above, the cover  52  has a generally rectangular outline; however it includes “yoke” configuration facilitated by a rectangular notch in its upper edge. This yoke allows for the mounting of a belt guide roller  61  by use of a dowel pin or other means known in the art, so as to allow the guide roller  61  to idle freely within the notch, with the rotational axis of the roller  61  being substantially perpendicular to the longitudinal axis of the main cylindrical body of the forming tube assembly  20 .  
         [0084]    The roller  61 , combined with the base  51  and the cover  52 , define an endless belt path for the endless belt  60 . This path could be considered to have two general segments, a working segment, and a nonworking segment. The working segment is where the endless belt is “doing work” or in other words is assisting in the welding process. The nonworking segment is where the belt is not assisting in the welding process.  
         [0085]    The positioning of the belt will now be explained by reference to FIG. 4, which as may be seen illustrates the belt  60  in place. Starting at a point A on the belt  60  which is in contact with the roller  61 , the belt  60  then extends downwardly and against the front face of the cover  52  proximate point B. When the band seal assembly is in place for operation, the exemplary following belt section proximate point B would be captured between the Teflon-tape-covered contact ridge  54  and the polyethylene film being welded. This following belt section when in operation would move along with the polyethylene film, while sliding relative to the contact ridge. At this time, the polyethylene film is being welded. Continuing to follow the belt path, towards the end of the “weld zone”, the exemplary following belt portion then comes to the bottom of the cover  52 , disengages the polyethylene film proximate point C, and then “returns” up through the channel  51   c  defined by the base  51 , until it comes out of the channel and reaches point A described above.  
         [0086]    Operation  
         [0087]    Operation from the point of view of the machine operator should be similar to prior art operation, once all elements are in place.  
         [0088]    Operation is generally as follows: The various elements are all positioned in their relative positions such as shown in FIG. 4 and FIG. 2A, for example. The band seal assembly  30  is moved into its operating position such as shown in FIG. 2B, such that the endless sealing band  32  of the band sealer assembly  30  is in sufficient contact with the polyethylene film such that the polyethylene film is “sandwiched” between the endless sealing band  32  (which supplies the heat) and the endless woven Teflon following belt  60 . As the band seal assembly  30  operates, it moves downwardly along with the film  5 , the film  5  moving as shown by the arrows in FIG. 2B under the influence of conventional endless drive belts such as vacuum belts known in the art. The film likewise pulls downwardly on the endless following belt  60 , causing it to move around its endless path as shown by the arrows in FIG. 2B. This provides improved seam seal production as the polyethylene film is held by two moving surfaces, thus reducing its tendency to tear by friction while under heat from the band seal assembly. It may also be understood that such a configuration provides improved tracking for the film  5 .  
         [0089]    Alternative Embodiments  
         [0090]    An alternative embodiment to the moving support apparatus  50  is such as shown as  150  in FIGS.  8 - 11 . Under this configuration, the endless belt  160  is supported by two rollers, one at each end, instead of just one roller. Furthermore, either of or each of the upper supporting roller can include slightly raised flanges at each longitudinal end to discourage the belt  161  from rolling off the rollers.  
         [0091]    Conclusion  
         [0092]    Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.