Abstract:
A side seal assembly for a shrink wrap packaging system is located downstream in the feed direction from a wrapping station to join first and second plies together and enclose each of the products in individually wrapped packages. The side seal assembly includes a heated side seal mechanism to form the side seal weld and separate the selvage film. The assembly includes an indexing mechanism to index the side seal mechanism and expose a clean surface to the film without removal or extensive servicing of the assembly and the heretofore requisite downtime for the system. The sealing and cutting functions are combined into a single, stationary component thereby reducing the number of movable parts. Moreover, indexing the side seal mechanism operatively exposes a clean, free of resin build-up, peripheral edge of the side seal mechanism to the plies, without the need to stop production for extended periods of time while consistently producing a thin side seal weld on the package.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to the art of film wrapping systems for use in wrapping objects with shrink wrap film and more particularly to improvements directed to making a side seal in the film. 
     A wide variety of systems are known for wrapping packages in thermoplastic film. Typical thermoplastic films utilized in such shrink wrap packaging systems include polyolefin, PVC and LDPE. More recent machines for wrapping packages in thermoplastic film utilize a continuous longitudinal or side sealer and an end sealer which moves at approximately the velocity of the packages as they travel through the machine so that it is not necessary to stop the packages while performing the end sealing operation. 
     One type of continuous side seal mechanism utilizes an elongate heated wire oriented in the direction of travel of the packages to heat and weld film plies and subsequently separate excess plastic film from the package. A variant of this type of side seal mechanism employs a fixed blade to heat and weld film plies, which simultaneously may cut the excess or waste film away from the welded seam. Another type of side sealing mechanism commonly utilized in shrink wrap packaging systems utilizes upper and lower rotating rollers or elements between which the plies of the film pass to form the weld. These rotary wheel side seal mechanisms employ a single mechanism to perform the dual operations of sealing the two plies of film together to form the weld and cutting the film to separate the excess selvage film outboard of the weld. 
     Side seal mechanisms of these and other prior art designs typically produce a relatively thick or wide seal on the wrapped package. One advantage of covering products in shrink wrap film is that the wrapping completely envelops the product without distracting from the aesthetic appeal of the package. Retailers and consumer product manufacturers desire packaging that does not interfere with nor detract from the product. A thick or wide side seal is therefore viewed as undesirable, particularly for low profile packages such as audio compact disc packages where the side seal is positioned on the thin side or height of the CD case. 
     Additionally, each of these prior techniques requires very high temperatures of the sealing mechanism to accomplish both the welding and separation functions. Typically, temperatures on the order of 500° F. or greater are required to heat the film to a molten state for separation of the selvage from the package. 
     Thus, while prior side seal mechanisms are seemingly simple, they require significant and complex maintenance efforts to maintain proper operation. The high temperatures required for separation of the selvage film results in sputtering of the molten film onto the components of the side seal mechanism. Such an accumulation of molten film or thermoplastic material on the heated welding or cutting mechanism may interfere with efficient heat transfer resulting in inferior weld formation and cutting operation. Additionally, the constant rubbing of the film on the cutting mechanism rubs off a coating on the cutting mechanism intended to increase thermal efficiency. Moreover, as a result of this inferior performance, the side sealer components must typically be serviced or repaired at least weekly and often daily. 
     Additionally, other complicating factors are involved in the servicing of these known side sealer mechanisms, which lead to extended service times. First there is an increased down time to allow for cooling of the system components. Moreover, these prior systems have relatively complicated disassembly and reassembly procedures to remove the film deposited on the components and maintain their serviceability. Finally, critical and detailed calibration and adjustment are required each time the side seal mechanism is broken down, cleaned and reassembled. 
     Therefore, a need exists in the shrink wrap packaging industry for a side seal mechanism which can readily accommodate a wide variety of film materials and repeatedly and consistently produce a thin, narrow, clean and accurate side seal weld and separation of the selvage material without the demanding service and maintenance requirements associated with known side seal mechanisms. 
     SUMMARY OF THE INVENTION 
     These and other objectives have been achieved with this invention, which in one embodiment includes a side seal assembly for a shrink wrap packaging system. The shrink wrap packaging system in one embodiment includes a feed conveyor to deliver a series of products to a wrapping station. The wrapping station may include a pair of film inverter rods, which are adjustable for spacing from one another to correspond to the height of the product being wrapped. A film delivery unit dispenses a supply of two-ply film in a direction generally perpendicular to the feed direction of the products. The two-ply film may be inverted by the inverter rods at the wrapping station where the products are inserted between the plies of the film. The system may also include a film inverter rod adjustment mechanism to adjust the spacing between the rods. 
     The shrink wrap system also includes a side seal assembly located downstream in the feed direction from the wrapping station to join the first and second plies together and enclose each of the products in individually wrapped packages. The side seal assembly includes a heated side seal mechanism to form the side seal weld and separate the selvage film. The assembly includes an indexing mechanism to index the side seal mechanism and expose a clean surface to the film without removal or extensive servicing of the assembly and the heretofore requisite downtime for the system. A heat shrink tunnel in one embodiment is located downstream from the sealing mechanisms to heat the film and thereby shrink it around the product as is well known in the industry. 
     Another aspect according to this invention is a method for wrapping a series of products in film. The method comprises the steps of serially feeding the products in a feed direction to a wrapping station, delivering film to the wrapping station, serially wrapping each of the products with the film, sealing the plies together to form a side seal weld with a stationary side seal mechanism, cutting a selvage portion of the film outboard of the side seal weld from a remainder of the film wrapped around the respective product with the side seal mechanism, and periodically indexing the side seal mechanism to expose a different portion thereof to the plies. 
     The side seal assembly according to this invention overcomes the problems and disadvantages associated with the prior side seal mechanisms. Advantageously, the sealing and cutting functions are combined into a single, stationary component thereby reducing the number of movable parts. Moreover, indexing the side seal mechanism operatively exposes a clean, free of resin build-up, peripheral edge of the side seal mechanism to the plies, without the need to stop production for extended periods of time while consistently producing a thin side seal weld on the package. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a top view of a film wrapping system and associated method according to one embodiment of this invention; 
         FIG. 2  is a perspective view of a side seal assembly of the system of  FIG. 1 ; 
         FIG. 3  is a side elevational view of components of the side seal assembly continuously joining plies of film to make a side seal weld; 
         FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is an isolated side elevational view of the side seal mechanism continuously joining plies of film to make a side seal showing one embodiment of the film path; 
         FIG. 6  is a top plan view of components of the side seal assembly forming the side seal weld and cutting selvage film from the remainder of the film; 
         FIG. 7A  is a side elevational view of the side seal mechanism continuously joining plies of film to make a side seal showing one embodiment of the film path prior to indexing; 
         FIG. 7B  is a side elevational view of the side seal mechanism continuously joining plies of film to make a side seal showing one embodiment of the film path after indexing; 
         FIG. 8  is a side elevational view of the side seal mechanism continuously joining plies of film to make a side seal showing an alternative embodiment of the film path prior to indexing; 
         FIG. 9A  is a perspective view of an alternative embodiment of the side seal mechanism; and 
         FIG. 9B  is a side elevational view of the alternative embodiment of the side seal mechanism shown in  FIG. 9A  continuously joining plies of film to make a side seal. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , a top view of an exemplary automatic high-speed film wrapping system  10  according to one embodiment of this invention is shown. The system  10  generally includes a feed conveyor  12 , a film delivery unit  14 , a wrapping station  16 , a side seal assembly  18 , an end sealer  20 , associated downstream conveyor(s)  22  and a heat shrink tunnel  24 . Products P to be wrapped in film  26  enter the system  10  via a feed conveyor  12 . The conveyor  12  delivers the spaced-apart and generally aligned products P to the wrapping station  16  where a folded film  26  from a film roll  28  in the film delivery unit  14  surrounds each product P. The folded film  26  enveloping each product is sealed proximate its free edges  30 ,  30  by the side seal assembly  18  to form a tube of film  26  enclosing the spaced products P. The film selvage  32  ( FIG. 6 ) at the sealed edge  34  is severed and removed. The film  26  between the adjacent products P is sealed and severed at the end sealer  20  to produce individual sealed packages of the product P. 
     The system  10  wraps a product P in a flexible plastic film  26  in which the travel of the product P is essentially continuous through the system lo in a feed direction indicated by arrow A. The film  26  may be any one of a variety of films well known in the art including PVC, LDPE and polyolefin and is supplied to the system  10  as a folded web at right angles to the feed direction of the product P (shown in  FIG. 1 ) through the system. The film  26  is provided to upper and lower inverter rods  36  of the wrapping station  16  where the film  26  is redirected and turned inside out to travel in the feed direction with the products P delivered by the feed conveyor  12 . 
     The feed conveyor  12  pushes products P into the wrapping station  16  to cause them to be enclosed by the folded film  26  supplied by film delivery unit  14  on the top, bottom, and one side of the product P with the other side of the product P adjacent to the free edges  30 ,  30  of the folded film  26  being open initially. The product P thus enclosed in the web of film  26  travels with the film  26  past the side seal assembly  18  in  FIG. 1  which seals the folded film  26  proximate and inboard of the two free edges  30 ,  30  together to form a continuous tube of film which envelops the succession of products P which are being fed into the system  10  by feed conveyor  12 . The side seal mechanism  18  also severs the excess width  32  of film  26  from the tube. A selvage accumulator  38 , such as a vacuum or other take-up mechanism, removes this selvage  32 . 
     As the product P progresses further through the system  10 , the end sealing mechanism  20  seals the trailing edge of each package while simultaneously sealing the leading edge  42  of the succeeding package in the system and it also severs one package from the other while the packages are traveling without stopping through the system  10 . The end seal mechanism  20  in one embodiment is so designed that it travels a short distance with the product P at substantially the same velocity while the seal is being made. After the seal has been made, the sealing mechanism  20  releases from the film  26  and returns to its original position to repeat the transverse seal for the next product. The wrapped product may then be conveyed through the shrink tunnel  24  for shrinking of the film around the product. While exemplary embodiments of the film delivery unit  14 , wrapping station  16 , end sealer  20  and shrink tunnel  24  are shown and described herein as part of the system, specific models or embodiments of these and other components could readily be varied or changed as known by one of ordinary skill in this art without departing from the scope of this invention. One example of a film delivery unit compatible with this invention is described in U.S. Pat. No. 6,817,163, which is assigned to the assignee of this invention and hereby incorporated entirely by reference. 
     Because the product P being wrapped in the film  26  proceeds through the system  10  at a substantially uniform velocity, the system  10  is capable of operating at film web speeds as high as 120 feet per minute although 60 to 100 feet per minute is a more typical speed. The system  10  is capable of wrapping in excess of one product P per second. 
     Turning now particularly to  FIGS. 2-6 , the novel side seal assembly  18  in accordance with this invention will be described. As shown in  FIGS. 2 and 3 , the side seal assembly  18  includes two jaws  44  and  46 , the first jaw being a top or upper jaw  44  and the second being a bottom or lower jaw  46 . The jaws  44 ,  46  are vertically movable relative to each other by a small pneumatic piston and cylinder arrangement  48 . The pneumatic piston and cylinder arrangement  48  allows for vertical adjustment of the jaws  44 ,  46  relative to each other to allow for a spacing between the components for a user to feed the film  26  between the jaws  44 ,  46 . A set of alignment rollers  50  are rotationally mounted to respective blocks  52  which are each secured to a plate  54  mounted on opposite ends of a post  56 . A mounting block  58  secures the post  56  to the leading edge of a lower chassis  62 . 
     The upper jaw  44  includes an upper chassis  64  and, likewise, the lower jaw  46  includes the lower chassis  62 . Chassis screws  66  at opposite ends of the upper chassis  64  are secured to a post  67  mounted upon plate  69 . A pneumatic piston  40  is also mounted on the plate  69  and linkage  71  is coupled to the upper end of the piston  40 . The linkage  71  is also coupled to a mounting block  73 , the function of which will be described later herein. 
     A pair of feed rollers  68   a ,  68   b  are provided downstream from the alignment rollers  50  adjacent the upstream end of the assembly  18 . Each of the feed rollers  68   a ,  68   b  are mounted for rotation on a respective shaft  70   a ,  70   b  in the associated chassis  62 ,  64 . A pair of discharge rollers  72   a ,  72   b  are located adjacent a downstream end of the side seal assembly  18  and each of the discharge rollers  72   a ,  72   b  are likewise rotationally mounted on a respective shaft  74   a ,  74   b  that is mounted in the associated chassis  62 ,  64 . 
     A traction belt  76   a  runs about the feed roller  68   a  and discharge roller  72   a , and which is elevated above the side seal mechanism  86  by idler pulley  78  so that belt  76   a  is not overly exposed to the heated side seal mechanism  86 . Pulley  78  is rotationally mounted to shaft  80  that is secured to bracket  82  mounted to upper chassis  64 . Conversely, lower traction belt  76   b  runs about feed roller  68   b  and discharge roller  72   b . Traction belts  76   a ,  76   b  work in unison to pull the two free edges  30 ,  30  of the folded film  26  through the assembly  18  into contact with a side seal mechanism  86 . Traction belts  76   a ,  76   b  are guided by their respective traction belt guides  84   a ,  84   b , which are secured to upper and lower jaws  44 ,  46 , respectively. The lower traction belt guide  84   b  has an opening  85  to accommodate the vertical adjustment of the peripheral edge  202  of the side sealing mechanism  86  below the vertical level of film  26 . 
     The side seal assembly  18  according to this invention advantageously includes a side seal mechanism  86  that is stationary and operatively coupled to a heater (not shown) and an indexing mechanism  102 . The side seal mechanism  86  is stationary in the sense that it is fixed or non-moving during the side seal operation; however, the mechanism  86  is adjustable without being removed from the assembly  18  as will be described herein. The side seal mechanism  86  is positioned between the feed and discharge rollers  68   a ,  72   a  and is mounted on hub  98  on the shaft  88  by single set screw  100 . The side seal mechanism  86  is heated generally to a temperature greater than 350° F. to 600° F., typically to a temperature greater than 400° F. to 600° F., preferably to a temperature greater than 500° F. to 600° F. 
     The shaft  88  on which the side seal mechanism  86  is mounted is hollow so that electrical wiring  87  can be run to the sealing mechanism  86  to heat it. The shaft  88  projects from the upper chassis  64  through the block  73  such that when the side seal assembly  18  is not in operation, the piston  40  lifts the block  73  and the shaft  88  via linkage  71  so that the stationary side seal mechanism  86  is disengaged from the film  26 . As such, the film  26  is not damaged or melted due to contact with the side seal mechanism  86  when the assembly  18  is not in operation. As the system  10  begins to wrap and seal products, the piston  40  draws the stationary side seal mechanism  86  downwardly via linkage  71  and block  73  into sealing operational contact with the film  26  for production. 
     The side seal assembly  18  holds two free edges  30 ,  30  of the folded film  26  together, and guides the layers through the side seal mechanism  86 . The side seal mechanism  18  seals the two plies to form a side seal weld and separates a selvage portion  32  ( FIG. 6 ), which is guided away so as not to reattach to the newly formed weld. 
     The shaft  88  on which the side seal mechanism  86  is mounted is hollow so that electrical wiring (not shown) can be run to the sealing mechanism  86  to heat it. The mechanism  86  can be indexed so a rotary electrical connection (not shown) of known type may be used so that twisting of the wiring does not occur. The electrical wiring engages a circular ceramic heater element (not shown) seated within the sealing mechanism  86  with the heat extending toward the film plies  26  and sealing an adjacent area of the film  34  ( FIG. 6 ). Also, a temperature controller (not shown) may be incorporated to accommodate various types of film  26 . 
     The shaft  88  is operatively coupled to an indexing mechanism  102  which may be manually indexed by disengaging a locking mechanism  106  from an index housing  104 , thereby exposing a different region of peripheral edge  202  of the side seal mechanism  86  to the film (see  FIG. 2 ). As shown in  FIGS. 7A and 8 , the side seal mechanism  86  is indexed through an angle of rotation to expose a different portion of the mechanism  86  to the film  26  for sealing. Additionally, the path of the film  26  may be adjusted relative to the center of the mechanism  86  to increase or decrease the dwell downtime or exposure of the film  26  to the heated sealing mechanism  86 . The side seal mechanism  86  can be locked in the new position by again engaging the locking mechanism  106  with the index housing  104 . Alternatively, the heated stationary side seal mechanism  86  may be indexed automatically based on a measurable variable, such as, the operating temperature of the side seal mechanism  86 , thickness of the film  26 , average speed of film  26  traveling in feed direction A, vertical height of the side seal mechanism  86 , degree of sealing of the film  26 , accumulated operating time or any combination thereof, to provide a clean, free of resin build-up  204 , peripheral edge  202 . 
     Referring to  FIGS. 7A and 7B , during operation the elevated temperatures required for forming weld  34  and separation of the selvage film  32  results in sputtering and accumulation of the molten film  26  onto the surface of mechanism  86 . Over time, such an accumulation of molten film  26  on the mechanism  86  and its peripheral edge  202  may interfere with efficient heat transfer to the film  26  and result in inferior weld  34  formation. Accordingly, the side sealing mechanism  86  may be indexed to expose a different portion of the peripheral edge  202  of the mechanism  86 , which is clean and free of resin build-up. 
     In one embodiment shown in  FIGS. 9A and 9B , the side seal mechanism  86  is generally circular, but alternatively it may also be generally shaped as an n-sided polygon where n is equal to or greater than  5 . The side seal mechanism  86  may be further characterized with a beveled peripheral edge  202 . In an alternative embodiment, it may be desirable to include a plurality of beveled notches  206  at the peripheral edge  202 . 
     To produce a thin, clean weld  34  and to accommodate appropriate welding and cutting temperatures the side seal mechanism  86  in one embodiment is cold rolled steel or aluminum, which is coated with process such as TFE-LOK® in which PTFE particles are embedded into the surface of the mechanism  86 . The TFE-LOK® provides enhanced heat conductivity to the sealing mechanism  86 . The coating process for the mechanism  86  may be accomplished according to U.S. Pat. Nos. 3,279,936; 3,502,493 and 4,051,275, each of which is hereby incorporated by reference entirely. Due in part to the thermally efficient conductivity afforded to the sealing mechanism  86  by such a coating, the sealing mechanism  86  of this invention may be significantly thinner than some prior systems. 
     From the above disclosure of the general principles of the present invention and the preceding detailed description of at least one preferred embodiment, those skilled in the art will readily comprehend the various modifications to which this invention is susceptible. Therefore, I desire to be limited only by the scope of the following claims and equivalents thereof.