Abstract:
This invention provides a method and apparatus for applying tape tabs to a traveling web, for example, for placement of fastening tabs on a running web of disposable diapers. The invention provides a cutting roll positioned to cut segments from a continuous infeeding web of tape material against a rotating anvil. The anvil, which is traveling at a speed equal to or very close to that of the infeeding tape web, carries the tape segments to a point on its tangency where a higher-speed traveling diaper web most nearly approaches, at which point the traveling diaper web is displaced slightly toward the anvil by means of a protuberance acting against the web. This movement causes it to come into contact with the next available tape segment, which becomes adhered to the higher-speed traveling web. This process provides for operation at higher speeds, higher efficiencies, greater flexibility and lower noise levels than previous processes.

Description:
RELATED APPLICATION  
       [0001]    This application is a divisional of co-pending U.S. patent application Ser. No. 09/521,736, filed Mar. 9, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to processes and apparatus for applying tabs to traveling webs. The invention has particular applicability to the manufacture of disposable diapers.  
           [0003]    The history of cutting and applying tape tabs to disposable diaper webs is now entering its fourth decade. Over the course of that time, various types of automatic manufacturing equipment have been developed which produce the desired results with a variety of materials and configurations. This equipment generally included window-knife and slip-and-cut applicators, each having their own advantages and limitations.  
           [0004]    Window-knife applicators are comprised of: one or more rotating heads, each made up of a knife edge and a vacuum plate; a more or less stationary knife, which is configured with a hole (window); and a tape transfer mechanism. Typically, the rotating heads are mechanically configured so as to eliminate head rotation relative to the stationary knife. Each head is passed, once per cycle, across the face of the stationary window knife, through which the infeeding tape is passed. The rotating knife shears the extended length of tape against the sharp inner edge of the hole (window), after which the severed segment is held by the vacuum plate. The rotating head, with the segment of tape held in place by the vacuum plate, continues through its rotation to a point, usually 90 degrees later, where it contacts the traveling web, which is pressed against the exposed adhesive of the tape segment. This contact, usually against some backing device, effects a transfer of the tape tab from the vacuum plate to the traveling web, which then carries the tape tab downstream.  
           [0005]    Window-knife applicators have a few shortcomings, among which are: the difficulty in feeding tape webs with little axial stiffness; the tendency of the infeeding tape to adhere to the window knife-edge; and for exposed adhesive to contaminate the surfaces of the window knife. For effective cutting, some degree of interference between the cutting edges is necessary between the moving and stationary knife faces, so to minimize impact, precision in manufacturing must be maintained and provision must be made for a degree of resiliency. While applicators of this type have been tested to speeds of 1000 cuts per minute, the maximum practical speed capability of current designs is approximately 750 cuts per minute.  
           [0006]    Slip-and-cut applicators are typically comprised of (a) a cylindrical rotating vacuum anvil (b) a rotating knife roll and (c) a transfer device. In typical applications, a tape web is fed at a relatively low speed along the vacuum face of the rotating anvil, which is moving at a relatively higher surface speed and upon which the tape web is allowed to “slip”. A knife-edge, mounted on the rotating knife roll, cuts a segment of tape from the tape web against the anvil face. This knife-edge is preferably moving at a surface velocity similar to that of the anvil&#39;s circumference. Once cut, the tape tab is held by vacuum drawn through holes on the anvil&#39;s face as it is carried at the anvil&#39;s speed downstream to the transfer point where the tape segment is transferred to the traveling web.  
           [0007]    A common problem with slip-and-cut applicators lies in the tendency to accumulate various contaminants on their anvil surfaces. This is most frequently seen in the form of the release compounds found on the non-adhesive side of tape, which is shipped on pre-wound rolls. Where die-cut tapes are fed onto the surfaces of slip-and-cut applicators, it is common to also see an accumulation of adhesive contamination, as the adhesive has been exposed at the tape edges by the die-cutting process. The difference in speed between the tape web and the anvil tends to “wipe” adhesive from the tape web. Contamination of the anvil, whether by release compounds or by fugitive adhesive, interferes with the regularity of slip occurring between the tape and the anvil, causing registration and cut accuracy problems. Frequent cleaning is necessary to maintain any level of productivity.  
           [0008]    Another problem associated with slip-and-cut applicators occurs at the point of cut. Since the web being cut is traveling at a very low velocity compared to the anvil and knife velocity (perhaps {fraction ( 1 / 20 )} th ), the engagement of the knife with the tape web tends to induce a high tensile strain in the tape web. Having been placed under such a high level of stress, the tape web can recoil violently when the cut is finally completed, causing loss of control of the tape web. This “snap-back” effect increases with the thickness of the tape web. Thicker webs tend to prolong the duration of engagement with the knife before completion of the cut, thereby increasing the build-up of strain. This is a common process problem that is usually addressed by the provision of various shock-absorbing devices. One possible solution might have been to reduce the surface velocity of the knife, but substantially different velocities between the knife and anvil result in rapid wear of the knife edge and/or anvil face, depending on relative hardness.  
           [0009]    Continual improvements and competitive pressures have incrementally increased the operational speeds of disposable diaper converters. As speeds increased, the mechanical integrity and operational capabilities of the applicators had to be improved accordingly. As a further complication, the complexity of the tape tabs being attached has also increased. Consumer product manufacturers are offering tapes which are die-cut to complex profiles and which may be constructed of materials incompatible with existing applicators. For instance, a proposed tape tab may be a die-profiled elastic textile, instead of a typical straight-cut stiff-paper and plastic type used in the past. Consequently, a manufacturer may find itself with a window-knife applicator, which cannot feed a tape web with too little axial stiffness. It could also find itself with a slip-and-cut applicator, which cannot successfully apply die-cut tape segments. Furthermore, existing applicators cannot successfully apply tapes whose boundaries are fully profiled, as may be desired to eliminate sharp corners, which might irritate a baby&#39;s delicate skin. This demonstrates a clear need for an improved applicator capable of applying new tape configurations and overcoming other shortcomings of prior art applicators.  
         SUMMARY OF THE INVENTION  
         [0010]    A basic premise of all applicators using prior art has been to cut the tape at one velocity and then to carry it at its final velocity to the transfer point. The assumption has been made that for correct and accurate placement, the tape tab must be moving at the final web velocity. The proposed invention diverges from that premise, eliminating or reducing the shortcomings associated with prior devices.  
           [0011]    In accordance with an important aspect of the invention tape segments are cut and carried at a very low tape web infeed speed. In accordance with a related aspect, problems with transferring a slow-moving segment to a fast-moving web are overcome. Additionally, die-cutting of tape segments to any number of practical shapes is possible, thereby avoiding difficulties associated with prior attempts to do so using previous applicator technology, which required multiple steps to accomplish the same task.  
           [0012]    The invention provides the additional benefit of quiet operation compared to prior art equipment, which uses high speed cutting faces and suffers from the effects of the very high energy levels seen at the point of contact. Generally, these energies, and the sounds that they generate, increase in proportion to the square of the velocity. The present invention benefits from the relatively low speed of the cutting faces and exhibits extremely low noise levels. In fact, the underlying noise of the mechanical drive systems and the traveling web equipment contribute to make the cutting noise level nearly unnoticeable.  
           [0013]    The present invention provides a simplified process wherein a rotary knife or die, with one or more cutting edges, turns against and in coordination with a corresponding vacuum anvil cylinder. An infeeding tape web is fed along the surface of the anvil, which is rotating at a surface velocity equal to or only somewhat greater than that of the tape web. As the tape web passes the nip created between the knife-edges and the anvil surface, segments of tape are parted but not significantly displaced upon the anvil surface. The segments continue downstream on the anvil surface, held securely by forces induced by a vacuum source directed to one or more holes provided for each segment in the anvil surface.  
           [0014]    At a point downstream along the surface of the anvil, the traveling web to which the segments are to be attached is brought into close proximity with the anvil and its tape segments. A mechanically operated device, which may be as simple as a protuberance on a rotating cylinder, presses the target zone of the traveling web against the exposed adhesive of the tape segment as it is presented on the anvil surface. The protuberance preferably has a surface velocity substantially identical to that of the traveling web. Given the extremely low moment of inertia of the tape segment and the aggressive adhesion provided between its exposed adhesive and the compatible surface of the traveling web, each successive segment is successfully transferred to the traveling web, accelerating almost instantly to the speed of the traveling web.  
           [0015]    A key aspect of this invention lies in the method and apparatus used to effect the transfer of the tape segments from the anvil to the traveling web. In accordance with the invention, a vacuum commutation system is configured to remove or reduce the level of vacuum used to hold each tape segment to the anvil surface just before the point of transfer. The materials and finishes selected for the anvil and the transfer protuberance provide a situation in which the coefficient of friction between the protuberance and the traveling web is relatively high, while the coefficient of friction between the tape segment and the anvil is relatively low. The highly aggressive nature of the bond between the adhesive side of the tape segment and the target surface of the traveling web ensures that there is virtually no slippage between the two. This ensures that the traveling web is driven through the point of transfer at its existing velocity, and that any tendency of the tape segment to adhere to the anvil surface will not influence the traveling web. The process requires that some slip occurs, and in accordance with the invention, slip occurs only between the tape segment and the anvil surface.  
           [0016]    This method is extremely effective in that 25 mm tape segments can be accurately transferred at 800 mm spacing to webs traveling at 300 meters per minute or more. This is a web-to-tape velocity ratio of 32:1. Tape to tape positional accuracy has been found to be extremely precise, with standard deviations of less than 1 mm when applied at a 800 mm spacing. Additionally, a speed capability of more than 2,400 tapes per minute is achievable, easily exceeding the limits of any previously known disposable paper product manufacturing process.  
           [0017]    Further objects and advantages of the invention will be apparent from the following detailed description, the attached claims and the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a diagrammatic side view of a Prior Art process;  
         [0019]    [0019]FIG. 2 is a diagrammatic side view illustrating a preferred process of this invention;  
         [0020]    [0020]FIG. 3 is a side view illustrating a further embodiment of the invention;  
         [0021]    [0021]FIG. 4 is a front elevational view of the equipment of FIG. 3 viewed from the right hand side of FIG. 3;  
         [0022]    [0022]FIG. 5 is a side elevational view of yet another embodiment of the invention;  
         [0023]    [0023]FIG. 6 is a front elevational view of the apparatus shown in FIG. 5 as viewed from the right hand side of FIG. 5;  
         [0024]    [0024]FIG. 7 is a perspective view in somewhat diagrammatic form illustrating a further embodiment of the invention; and,  
         [0025]    [0025]FIG. 8 is a diagrammatic side elevational view illustrating yet another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    Referring more particularly to the drawings there is seen in FIG. 1 a diagrammatic illustration of a prior art process for applying tabs to webs in a diaper making process. Web  10  is a composite material used in formation of diapers which is generally formed of various layers of material such as plastic back sheets, absorbent pads and nonwoven topsheets. A series of tape segments  12  are applied to web  10 . In the illustrated process a rotatable vacuum anvil  14  is used to supply the tabs  12  which have an outwardly facing adhesive coated surface used to adhere the tabs  12  to web  10 . Anvil  14  has internally reduced air pressure or vacuum, and a plurality of openings  24  are provided through its surface to enable suction of the tabs segments  12  against the anvil surface  14 . A web of the tape tab forming material  16  is fed by rollers  20  and  22  against the anvil surface  14  where it is cut into segments by a rotary knife  18 .  
         [0027]    In this prior art application the anvil  14  is rotated at a speed such that its outer perimeter, and thus the tabs  12  carried thereby, are moving at a speed approximately equal to that of web  10 . This causes a great deal of slippage to occur between the anvil  14  and the lower speed infeeding web  16 .  
         [0028]    Referring to FIG. 2, the apparatus and process of this invention is shown in diagrammatic fashion. In accordance with the invention, the web  16  is fed to the anvil  24  at a speed such that the web speed of web  16  approximately equals the speed at which the outer periphery of anvil  14  is traveling. If desired, the anvil  14  may rotate at a slightly higher speed than the linear speed of the web  16 . The blades  34  of a rotary cutter  32  are also traveling at a peripheral speed equal to that of anvil  14 . As seen in FIG. 2, after cutting, a series of tabs  12  are carried on the outer surface of anvil  14 . Tabs  12  are held in place by vacuum provided within the interior of anvil  14 . The adhesive-coated surface of web  16  is facing outwardly while a non-tacky or uncoated surface engages the exterior anvil  14 .  
         [0029]    A web  10  of diaper material is caused to travel in a path slightly displaced from the outer surface of rotating anvil  14 , but in close proximity thereto. Just above the web  10  is a rotating wheel  38 , which rotates at a peripheral velocity equal to the lineal velocity of web  10 , which, in turn, is substantially greater than the peripheral velocity of anvil  14 . Anvil  14  may travel at a peripheral velocity either equal to or somewhat greater than the velocity of web  10 . In practice, to realize the benefits of this invention, the peripheral velocity of anvil  14  should not be greater than about 5 times the velocity of web  10 .  
         [0030]    Wheel  38 , as seen in FIG. 2, has a protrusion  36  which extends along its width. The rotational speed of roller  38  is selected so that the protrusion  36  engages web  10  and displaces it into contact with each successive adhesive-coated tab  12 . The slight displacement of web  10  causes it to come into contact with the tab segment  12  which, then, is instantly adhered to the higher speed traveling web  10 . The coefficient of friction between the uncoated side of tab  12  and the metal surface of anvil  14  is low so that the aggressive adhesion between tab  12  and web  10  together with the extremely low moment of inertia of tape tab segment  12  facilitates successful transfer of the tabs  12  to the web  10 , the tabs  12  accelerating almost instantly to the higher speed of web  10 .  
         [0031]    To further facilitate the transfer of tabs  12  to web  10 , a vacuum commutation is provided to remove or substantially reduce the level of vacuum used to hold tape segments  12  to the anvil surface  14  just before the point of transfer. For this purpose, an interior arcuate plenum  25  is situated within anvil  14  in order to provide vacuum only along the portion of anvil  14  which engages web  16  up to a location just short of the transfer point. Thus, the portion of the anvil  14  which does not engage web  16  or tabs  12  is not provided with vacuum.  
         [0032]    While the drawings show the protrusions  36  on cylinder  38  in somewhat exaggerated form, in practice the protrusions  36  can simply be in the form of a lobe on the cylindrical surface as low as 0.030 inch in height, but may, if desired, be of a much greater height.  
         [0033]    Referring to FIGS. 3 and 4, there is seen an arrangement of the apparatus of this invention generally more suited for commercial operation. As viewed in FIG. 3, web  10  is travelling to the left and adhesive-backed tape  16  is fed over a roller  121  onto anvil/drum  114 . Tape web  16  is cut into individual tape tabs by a rotary cutter  132 . As the tape tab segments  12  travel to the top of drum  114  as viewed in FIG. 3, the web  10  is intermittently impacted by lobes  136  located on opposite sides of rotatable wheel  138 . The apparatus is driven by a motor or power supply  130  through various mechanical drive connections generally shown by dotted or phantom lines in FIG. 4.  
         [0034]    As viewed in FIG. 4, a second laterally displaced anvil  115  receives another tape web  16  which is cut into tab segments  12  by blades  135  on a rotary cutter  133 . A pair of lobes or protrusions  139  on a rotatable wheel  137  cause the web  10  to pick up each successive tab segment  12  from the anvil  115  just as in the case of the other anvil  114 . In this manner, tape tabs  12  are applied to each lateral edge of a web which is subsequently formed into a diaper product. These tape tabs  12  may have ends provided with hook and loop fasteners or other fastening means selected for use in connection with the diaper product.  
         [0035]    Also, as seen in FIG. 4, the rotatable anvils  114  and  115  are rotatably driven by a shaft  140 . Similarly, rotary cutters  132  and  133  are mounted on another shaft  142  while the rotatable disks  138  and  137  are mounted on another shaft  144 .  
         [0036]    In FIGS. 5 and 6 there is seen still another embodiment of the invention particularly suited to manufacture of baby diapers having tape tabs thereon. In this case the rotatable anvil  70 , as viewed in FIG. 5, is similar to anvil  14  previously described in detail. A rotary cutter  72  is provided with cutting blades just as in the case of cutter  32 . In this embodiment a rotatable bar  74  is provided with ends  76  and  78  that serve to push a traveling web against a succession of tabs  12  carried by the anvil  70 . In other respects the apparatus and operation of the device shown in FIGS. 5 and 6 is similar to that previously described. As seen in FIG. 6 a second anvil  71  is engaged by a second rotary cutter  73  to cut a second series of tabs for the lateral side of the diapers opposite that engaged by anvil  70 . A second rotary bar  75  is provided with lobes  77  and  79  which serve in the same fashion as lobes  76  and  78  of rotary bar  74 . Also as seen, the anvils  70  and  71  are rotatably mounted on a shaft  80  and rotatable bars  74  and  75  are rotatably mounted on a shaft  82  while cutters  72  and  73  are mounted on shafts  81  and  83 , respectively. All of these devices may be driven, as shown, by a supply of power from a rotating shaft  84  driven by a power supply common to other components of the production line. The arrangement of drive belts, etc., as shown for purposes of illustration, but does not form a part of the invention, since such components of the production line would routinely be designed by engineers skilled in the art.  
         [0037]    In FIG. 7 there is shown, for purposes of clarity, a simplified device in accordance with the invention, illustrating the application of tabs  52  and  54  which have free ends extending laterally from opposite sides of a diaper-forming web  50 . These free ends of tabs  52  and  54  may be provided with loops on one side of the diaper-forming material and hooks on the opposite side to form hook and loop fasteners on the diapers commonly referred to as Velcro®. In other cases, the tabs on at least one side may be coated with a pressure sensitive adhesive protected until use by a release layer.  
         [0038]    As further seen in FIG. 7, an adhesive-coated tape web  61  is fed over a roller  64  onto an anvil  60  similar to anvil  14  previously described. A similar anvil  62  engages a second adhesive-coated web. These webs may have adhesive coated on one-half of their width and a hook or loop-type fastener provided on the opposite half of the width in order to form the laterally extending tabs  52  and  54 . These webs are cut by blades  56  of rotary cutters  58  and blades  57  of a second rotary cutter  59 , respectively. As seen, both of the cutters  58  and  59  are driven by a rotatable shaft  55 . Similarly, anvils  60  and  62  are driven by a central shaft  63 . Rotatable disks  66  and  68  provided with protrusions  65  and  67  serve to deflect the edges of the web  50  toward the respective anvils  60  and  62  in order to simultaneously pick up the tabs  54  and  52  on opposite sides of the web  50 , as shown.  
         [0039]    A still further alternative embodiment of the invention is illustrated in FIG. 8. In this embodiment, a diaper-forming web  210  is intermittently coated with adhesive deposits  204  along the edge of the web  210 . A tab-forming web  202  is fed over a hollow vacuum anvil  216  and cut thereagainst into a series of tabs  208  by blades  219  of a rotary cutter  218 . An intermediate transfer roll  214  also provided with internal vacuum is used to transport the tabs  208  into close proximity with the bottom of web  210 . Again, a traveling drum  238  having lobes  236  is traveling at a speed such that a lobe  236  contacts the web  210  just as an adhesive-coated area  204  is aligned with one of the tabs  208 . Displacement caused by action of the lobe  236  against the web  210  causes the each tab  208  to become adhered to one of the adhesive coated areas  204 . In other respects the operation of the device of FIG. 8 is similar to that previously heretofore described.  
         [0040]    The foregoing descriptions are set forth for illustrative purposes rather than by way of limitation, since it will be apparent to those skilled in the art that various additional embodiments exemplifying the principles of the invention may be devised.