Abstract:
The present invention describes an improved side-sealing machine for use with heat sealable films. Briefly, a cutting and sealing element is located between a set of cooperating guide and alignment members. The downstream guide and alignment member also includes a compression mechanism. This compression mechanism serves to compress the seal created upstream, and to draw the heat away from the film. In some embodiments, the downstream guide and alignment member also serves to separate the film into a surplus portion and a remaining portion, where only the remaining portion is subjected to compression.

Description:
BACKGROUND OF THE INVENTION 
     Machines used to wrap and seal articles and packages in thermoplastic film are well known in the art. Two types of machines are commonly referred to as side-sealing and lap-sealing machines. In the typical side-sealing configuration, an article or set of articles travels, typically via a conveyer belt, toward the machine. A sheet of center-folded plastic film, having two layers, is fed from a direction which is preferably perpendicular to the direction of the conveyer. The two layers of the film are then separated such that the article is placed between the lower layer and the upper layer. On one side of the article is the center-fold, while on the other side, there is an open edge where the two layers are not attached. The machine has a side sealing mechanism, which typically comprises several sets of belts to hold and guide the film, a heating/sealing element that fuses or welds the two free layers together and a cutting element that removes the excess material. Thus, as the article passes by the side sealing mechanism, this open edge is sealed by welding the two layers together, the plastic is cut and the waste is removed and discarded. At this point, the plastic film resembles a tube, with openings at both the leading and trailing ends of the article, but sealed along both sides. As the article continues to advance, an end sealing mechanism is then employed to seal the film at the leading end of the article. The article is further advanced and the end sealing mechanism then seals the film at the trailing end of the article. 
     The sealing and cutting performed by the side sealing unit can be done in a variety of ways. Some of these methods include hot air, hot knife, hot wire, band sealing and hot wheel. The first three approaches (hot air, hot knife and hot wire) accomplish the cutting and sealing processes without the use of pressure. In contrast, the band system compresses the film between two hot blocks and then a cut is made subsequent to the sealing process. Finally, the hot wheel system includes a heated wheel with a blade in the center that cuts the film. 
     In addition to high quality seals, the throughput of the system is also a concern. Many different types of sealing and cutting processes can be used, which perform well at low speeds, such as less than 40 feet per minute. However, at high speeds, such as 60 feet per minute, it becomes difficult to create good quality seals. This problem is exacerbated by thicker films, which require more heat to properly seal, and are obviously more difficult to cut through. 
     A side sealing machine that can operate at high speed and perform high quality seals, even on thick films, would be very beneficial. Such a machine would allow increased throughput and higher quality. In addition, a method of cutting and sealing a film which allows high quality seals and high throughput would be advantageous. 
     SUMMARY OF THE INVENTION 
     The problems associated with the prior art have been overcome by the present invention, which describes an improved side-sealing machine for use with thick films. Briefly, a cutting and sealing element is located between a set of cooperating guide and alignment members. The downstream guide and alignment member also includes a compression mechanism. This compression mechanism serves to compress the seal created upstream, and to draw the heat away from the film. In some embodiments, the downstream guide and alignment member also serves to separate the film into a surplus portion and a remaining portion, where only the remaining portion is subjected to compression. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a representative side-sealing machine of the prior art; 
         FIG. 2  illustrates a side-sealing mechanism in accordance with the present invention; 
         FIG. 3  illustrates an exploded view of the side-sealing mechanism shown in  FIG. 2 ; 
         FIG. 4  illustrates a top view of the side-sealing mechanism shown in  FIG. 2 ; 
         FIG. 5  illustrates an exploded view of one embodiment of a component of the second guide and alignment member; 
         FIG. 6  illustrates one embodiment of the opposing roller of the present invention; and 
         FIG. 7  shows the second guide and alignment member in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a representative side-sealing machine used to encapsulate or wrap an article in thermoplastic film, as described in U.S. Pat. No. 6,526,728. The machine  10  utilizes a conveyer belt  12  operating at a relatively constant speed to deliver articles  8  that are to be encapsulated. The thermoplastic film  1  is center-folded, such that the side with the fold is closed, while the opposite side  6  is open. On this opposite side, there are two layers of film  4 , 5 , which will later be sealed. This center-folded thermoplastic film  1  is fed from a reel (not shown) that is preferably mounted perpendicular to the direction of travel of the conveyer belt  12 . The film is then inverted and separated by an inverter  13  such that the article is enveloped between the two layers  4 , 5 . At this point, the film  1  on one side of the article is closed, while the opposite side  6  remains open. Also, the film at both the leading and trailing ends of the article is not sealed. Downstream from the inverter is the side-sealing mechanism  20 . After proper relative positioning of the article between the layers of the film  4 , 5 , the enveloped article approaches the side-sealing mechanism  20 . 
     The side-sealing mechanism  20  is located on the open side  6  of the enveloped article. The mechanism holds the two layers of film  4 , 5  together, and guides the layers through the sealing and cutting elements. It then welds the two layers together, and cuts off the surplus material. The surplus material is pulled away so as not to reattach to the film while it is still at an elevated temperature. 
       FIG. 2  shows the mechanism  20  used to perform the side sealing operation.  FIG. 3  shows an exploded view of the mechanism  20  of  FIG. 2 . The side sealing mechanism  20  preferably comprises two sets of cooperating pulleys, an upper set  101  and a lower set  102 . These sets work in unison to pull the two layers of film into the mechanism and hold the layers in place. In the preferred embodiment, each of the pulleys has teeth  110  in its channel so as to accept one or more, preferably two, timing belts  120 . The presence of teeth  110  ensures that the timing belt does not slip relative to the pulleys; a common problem with the prior art. In other embodiments, belts without inner teeth may be used. The first set of pulleys  101   a , 101   b  is located above the layers of film, while the second set  102   a , 102   b  is located below the layers. The forward set of pulleys  101   a ,  102   a  comprises a first guide and alignment member  133 . This guide and alignment mechanism  133  also serves to pull the film into the side sealing mechanism  20 . The rear set of pulleys  101   b ,  102   b  comprise a second guide and alignment member  134 . There may optionally be one or more idler pulleys (not shown). Each of these pulleys may also have one or more O-rings mounted in the channel where the belts are located, so as to provide individual channels for each of the timing belts  120 . One or more of the pulleys that comprise the first and second guide and alignment members  101   a ,  101   b ,  102   a ,  102   b  may be driven, such as by an electric motor contained within the side sealing mechanism. In some embodiments, all of the pulleys are driven. In other embodiments, fewer are actively driven by a motor, and the remaining pulleys rotate due to their coupling to the driven pulleys (such as via a belt). In certain embodiments, the front set of pulleys  101   a ,  102   a  are actively driven by a motor, while the back set of pulleys  101   b ,  102   b  may or may not be actively driven. In other embodiments, the rear set of pulleys  101   b ,  102   b  are actively driven by a motor, while the front set of pulleys  101   a ,  102   a  may or may not be actively driven. 
     A sealing and cutting element  140  is located between the first and second guide and alignment members  133 ,  134 , as best seen in  FIG. 4 . 
       FIG. 4  shows a top view of the side sealing mechanism  20 . In this figure, only the upper pulleys  101   a ,  101   b  are visible. The open end  6  of the film is fed into the first guide and alignment member  133 . As described above, there are preferably two belts  120  which surround upper pulleys  101   a ,  101   b . These belts  120  may be parallel to one another. In other embodiments, the belts  120  are not parallel to one another. In the preferred embodiment, as shown in  FIG. 4 , the belts grow farther apart moving from the first pulley  101   a  to the second pulley  101   b . In other words, the belts diverge from the first pulley  101   a  to the second pulley  101   b . The film is cut by heating and cutting element  140 , which is located between the first and second guide and alignment members  133 ,  134 . The cutting element  140  divides the film into a surplus portion  150 , and a remaining portion  155 . The surplus portion  150  is guided by the inner belts  120  (relative to the sealing mechanism) away from the opposing rollers  160 , such that only the remaining portion  155  is compressed by the opposing rollers  160 . 
     Thus, the second guide and alignment member  134  has several functions. First, it helps guide the film through the side sealing mechanism  20 . Second, it separates the cut film into surplus film  150  and a remaining portion  155 , through the use of channels which force the belts  120  to be non-parallel. The second guide and alignment member  134  also has opposing rollers, which compress the still-hot remaining portion  155  to insure a better seal. Finally, the opposing rollers  160  removes heat from the remaining portion  155  as they compress it. 
       FIG. 5  shows an expanded view of one pulley  101   b  of the second guide and alignment member  134 . The components shown include a center axle  170 . A number of additional components are mounted on the center axle  170 . In this embodiment, the pulley channel is separated into two parts  172 ,  173 . These two channel parts  172 ,  173  are placed on either side of opposing roller  160 . As seen in  FIG. 5 , the channel parts  172 ,  173  are formed with teeth that facilitate the use of a timing belt to minimize the slippage of the belts  120 . As noted above, it is possible to use belts without inner teeth if desired. The belts  120  are each adapted to surround one of these two channel parts, and are therefore separated from one another by the opposing roller  160 . Since the opposing roller  160  is positioned between the two channel parts, it may not be necessary to have O-rings, as described above. In some embodiments, only one O-ring  174  is used to further separate the belts  120  as they loop around pulleys  101   b ,  102   b.    
     Although not shown, the pulley channel can be designed as a single component, and the opposing roller can be designed to fit over the channel component, rather than between channel components  172 ,  173 . 
     The opposing rollers  160  may be fabricated in a number of ways. As is also shown in  FIG. 6 , the opposing roller  160  may be made up of a core  161 , and an annular ring  162  surrounding the core  161 . In this embodiment, the core is roughly circular, with a radius of about 2.693 inches. The annular ring  162  has an inner radius that roughly matches the outer radius of the core  161  and an outer radius of 3.062 inches. In some embodiments, the core  161  is made of metal, such as aluminum or steel, although other suitable materials can be used. In some embodiments, the annular ring is constructed of a pliable material, such as rubber, including neoprene or urethane rubber, or metal, such as steel or aluminum. In other embodiments, the core  161  may be a pliable material, while the annular ring is constructed of metal. The combination of a metal core with a pliable annular ring (or a pliable core with a metal annular ring) serves several purposes. First, the metal material is an excellent thermal conductor, and therefore is able to draw heat away from the film as it is being compressed. In some embodiments, the temperature of the film entering the opposing rollers  160  is over 110° F., while the temperature of the film exiting the opposing rollers is roughly 85° F. Thus, the opposing rollers  160  help to cool the film, which further enhances the seal. The rubber material allows the opposing rollers to be positioned to be in interference with each other. The pliability of the rubber allows the rollers to adapt to various film thicknesses. By positioning the opposing rollers  160  this way, the seal is also compressed as it is being cooled. 
       FIG. 7  shows the second guide and alignment mechanism  134 , and specifically the rear pulleys  101   b ,  102   b . As can be seen in the Figure, the pulleys  101   b ,  102   b  are positioned such that there is a guaranteed interference between the two rollers, even in the absence of a film. In some embodiments, the interference is about 0.063 inches. This interference, using urethane rubber creates a pressure of 54 PSI between the opposing rollers, without the presence of any film. This pressure increases with film thickness. In other embodiments, the interference is caused to create pressure greater than about 1 PSI, preferably more than about 20 PSI. 
     The use of this side sealing mechanism  20  allows for increased throughput, especially of thicker films. For example, using a conventional side sealer, 3 mil thick film can be cut and sealed at speeds less than 40 feet per minute. Using the opposing rollers, which serve to compress and cool the seal, speeds in excess of 60 feet per minute were achieved. 
     The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described (or portions thereof). It is also recognized that various modifications are possible within the scope of the claims. Other modifications, variations, and alternatives are also possible. 
     Accordingly, the foregoing description is by way of example only and is not intended as limiting.