Abstract:
This invention provides a process and apparatus ( 38 ) for the manufacture of disposable absorbent cores from a continuous web ( 40 ), wherein a plurality of first and second core elements ( 40   a   , 40   b ) are cut from the same continuous web ( 40 ). The object of the invention is achieved by rotating each of first and second core elements ( 40   a   , 40   b ) about axes perpendicular to the plane of the core element and subsequently combining a first core element ( 40   a ) and a second core element ( 40   b ) in proximal relationship to form the absorbent core. Preferably each of the first and second core elements ( 40   a   , 40   b ) are rotated through 90° in mutually counter-rotating directions.

Description:
The invention relates to a process for manufacturing profiled disposableabsorbent cores, without waste of the absorbent core material; and to an apparatus for performing the process. In particular, diapers or training pants may be made by the process of the invention having absorbent cores with an hourglass-shape for better fit around the legs of the wearer, but the process may also be applied to feminine hygiene articles, adult incontinence articles, and other disposable absorbent articles. 
     Disposable absorbent articles have become very popular in the market place today. Many of these articles include features such as absorbent cores providing a variety of functions including improved containment characteristics and better, more comfortable fit. 
     An overriding consideration in the construction of a disposable absorbent article is the cost of manufacturing the article, including the materials cost. The present invention provides methods for manufacturing absorbent cores for absorbent articles with little or no wasted material. Thus, the absorbent cores made by the process of the present invention can be provided at relatively lower cost than many of the absorbent cores that are currently manufactured using techniques in which material is wasted. Processes which reduce or avoid material waste are disclosed in the following references. 
     U.S. Pat. No. 4,760 764, issued on 2 nd  Aug. 1988, relates to manufacturing methods for disposable diapers which have an “egg-timer” profile. It is proposed to reduce production costs by making effective use of the absorbent core, and in particular by avoiding waste by cutting out and throwing away a part of the absorbent core. This is achieved by providing “nested panels” in a single side panel web and then rearranging the panels, for example as shown in FIG. 4 of the patent to form an absorbent pad. 
     WO96/21411, published on 18 th  Jul. 1996, discloses a method for manufacturing shaped or contoured absorbent cores made from multiple pieces or layers. Wherein the multiple pieces or layers are cut from the same continuous web with “zero scrap”. 
     It is an object of the present invention to provide an alternative method of achieving waste-saving benefits, and associated reduction of material costs. 
     The invention provides a process and apparatus for the manufacture of disposable absorbent cores from a continuous web, wherein a plurality of first and second core elements, are cut from the same continuous web. 
     SUMMARY OF THE INVENTION 
     The object of the invention is achieved by rotating each of first and second core elements about axes perpendicular to the plane of the core element and subsequently combining a first core element and a second core element in proximal relationship to form the absorbent core. Preferably each of the first and second core elements are rotated through 90° in mutually counter-rotating directions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of an apparatus for use in the process of the present invention; 
     FIG. 2 shows a side elevation view of the apparatus of FIG. 1; 
     FIGS. 3 a  and  3   b  show rear and front elevation views of the apparatus of FIG. 1; 
     FIG. 4 shows a schematic side elevation view of a production line assembly comprising an apparatus of the present invention; 
     FIG. 5 a  shows a plan view of core elements after cutting, according to one embodiment of the process of the present invention. FIG. 5 b  shows a plan view of an absorbent core made by combining a first core element and a second core element of FIG. 5 a.   
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Incontinence management articles, such as non-cloth disposable diapers, have traditionally utilized absorbent structures which comprise entangled masses of fibers, i.e. non woven fibrous webs. These webs imbibe aqueous fluids, including discharged body fluids, both by an absorption mechanism where fluid is taken up by the fiber material itself, and especially by a wicking mechanism where fluid is acquired by, distributed through and stored in the capillary interstices between the fibers. These webs often comprise loosely compacted, low density layers of absorbent fibers, such as carded cotton webs, air-laid cellulose fibers, comminuted wood pulp fibers, and the like. Fibrous webs used in such absorbent articles also often include certain absorbent gelling materials usually referred to as “hydrogels”, “super absorbent” or “hydrocolloid” materials to store large quantities of the discharged body fluids. Known technology to manufacture such cores includes air laying the fibers into shaped cavities on a screened drum to form the shape of the core and control the quantity of material used per core. Excess overfill of the shaped cavities is removed and returned to the incoming air stream by a scarfing roll. The Absorbent Gelling Materials (AGM) are added to the airstream along with the fiber materials. This process allows for many alternative shapes to be produced via changes in screen, laydown drum, configuration. Therefore the shape of the material is achieved via “molding” the fibers into shaped cavities. This process provides shape without trim, which in turn results in minimal scrap. Examples of such cores are disclosed in U.S. Pat. No. 4,673,402, issued 16 th  Jun. 1987 and U.S. Pat. No. 4,935,022, issued 19 th  Jun. 1990. 
     An alternative absorbent material potentially capable of providing capillary fluid transport would be open-celled polymeric foams. If made appropriately, open-celled polymeric foams could provide features of capillary fluid acquisition, transport and storage required for use in high performance absorbent cores for absorbent articles such as diapers. Absorbent articles containing such foams could possess desirable wet integrity, could provide suitable fit throughout the entire period the article is worn, and could avoid changes in shape during use. In addition, absorbent articles containing such foam structures could be easier to manufacture on a commercial scale. For example, absorbent diaper cores could simply be stamped out of continuous foam sheets and could be designed to have considerably greater integrity and uniformity than air-laid fibrous absorbent cores containing particulate absorbent gelling materials. 
     Shaped or contoured absorbent cores made from open-celled foam materials are disclosed in U.S. Pat. No. 5,147,345, issued 15 th  Sep. 1992. This patent discloses absorbent cores comprising a fluid acquisition/distribution component that can be fibrous or foam based, as well as fluid storage/redistribution component that comprises a hydrophilic, flexible, open-celled polymeric foam. FIG. 9 discloses one such shaped or contoured core having an hourglass-shaped fluid redistribution/storage layer comprising an open-cell absorbent foam. Forming shaped or contoured absorbent cores or layers from foam materials is not without problems. The hourglass-shaped foam layer is typically made from a single rectangular piece of foam. This rectangular piece of foam can be notched, cut or otherwise severed from the hourglass-shaped piece. In carrying out these operations, a significant amount of unusable foam scrap can be created. Indeed it has been found that, in forming hourglass-shaped foam pieces, as much as 15% to 25% of the total foam material used can end up as unusable scrap. 
     The present invention relates to a process and apparatus for manufacturing an absorbent core having “zero scrap”, thus eliminating the steps for disposing or recycling surplus material. 
     FIG. 1 shows a perspective view of an apparatus  38  according to the present invention. The apparatus comprises a rotating drum  60 . The drum  60  applies discrete first and second core elements  40   a ,  40   b  to a receiving web  1 . In FIG. 1 an incoming web  40  is fed to the apparatus  38  and is cut in a nested pattern (see, for example, FIG.  5 ), and the discrete first and second core elements  40   a ,  40   b  of the incoming webs are held on vacuum shells  80   a ,  80   b  which are arranged around the circumference of the rotating drum  60 . The receiving web  1 ; the incoming web  40 ; and the cutting roll  39  are not shown in FIG. 1 to simplify this illustration. 
     The drum  60  is rotated about a main axis of the apparatus. In the embodiment illustrated in FIGS. 1,  2 ,  3   a  and  3   b  the main axis is oriented horizontally, but this main axis need not necessarily be horizontal in all cases. 
     The vacuum shells  80   a ,  80   b  are mounted on rotatable shafts  81  and are rotatable about an axis A which is radial with respect to the drum  60 . Alternate vacuum shells  80   a ,  80   b  are rotatable in mutually counter-rotating directions, preferably plus and minus 90° from the starting position. The means for providing the rotation each of the rotatable shafts  81  may suitably be provided by a rack and pinion arrangement, and a cam follower which runs around a shell turning cam. The shell turning cam is shaped so that the rack and pinion operate to rotate alternate vacuum shells  80   b  through 90° during a first part of the cycle, prior to transfer of the second core element,  40   b  of the incoming web to the receiving web  1 , and then return the vacuum shells  80   b  to their original orientation by rotating them back through minus 90° during a second part of the cycle after the transfer. 
     In addition, during the first part of the cycle, a shell lifting cam acts to “lift” the vacuum shell  80   b  radially outwards from the drum  60 . This action helps to apply the second core element  40   b  of the incoming web  40  to the receiving web  1  at a transfer step. During the second part of the cycle, after the cut core element  40   b  of the incoming web has been transferred to the receiving web  1 , the vacuum shells  80   b  are “withdrawn” radially inwards with respect to the drum  60 . During the second part of the cycle, or subsequent to the second part of the cycle, the vacuum shells  80   a  (i.e. those vacuum shells which have not been rotated during the first part of the cycle) are rotated through minus 90°and are “lifted” radially outwards from the drum  60 . This action helps to apply the first core elements  40   a  of the incoming web  40  to the receiving web  1  at a transfer step. Finally the vacuum shells  80   a  are “withdrawn” radially inwards with respect to the drum  60 , and the cycle is ready to repeat. 
     In the embodiment of the invention shown in FIGS. 1 and 2 the first and second core elements  40   a  and  40   b  are rotated through plus 90° and minus 90° respectively in order to provide an hourglass-shaped core suitable for use in an absorbent article such as a diaper. 
     Typically, an absorbent article is assembled from an absorbent pad element, or core which is encased between a liquid-pervious topsheet and a liquid impervious backsheet. In a preferred embodiment, the cores are comprised of airfelt or foam, within a cellulosic tissue envelope, to provide integrity to the core in use. The backsheet is coated on its inner surface with beads or spirals of adhesive, for affixing the backsheet to the core. Continuous bands of elastic are fed from metering rolls past a glue nozzle. An S-wrap arrangement of the rolls feeding the bands of elastic minimises deformation of the elastic band and allows for accurate control of the speed of the elastic. The elastic bands are fed into the direction of transport at a lower speed than the cores, the backsheet and the topsheet, so that the elastic bands are stretched. 
     In a particularly preferred embodiment of the present invention a receiving web (which may be, for example, either the backsheet or the topsheet) passes at a constant speed of transport to the infeed side  4  of an assembly  2  for periodically changing the speed of web (illustrated in FIG.  4 ). In the assembly  2 , the receiving web  1  can be slowed down, or stopped and is contacted by the apparatus of the invention  38 . The apparatus  38  comprises means for providing the core elements. The web  1  leaves the outfeed side  6  of the assembly  2  at the constant web speed. The speed of the receiving web portions located upstream and downstream from the assembly  2  along upstream trajectory  3  and downstream trajectory  5  is not affected by the change in speed of those parts of the receiving web  1  that are passing through the assembly  2 . 
     FIG. 4 shows the assembly  2  for changing the speed of a flexible receiving web  1  of relatively low tear strength. By flexible, it is meant that the receiving web  1  can be transported along a curvilinear trajectory and will adapt its shape so as to conform to the trajectory. The receiving web  1  is formed of flexible material, such as paper, airfelt, plastic etc. and can be comprised of the topsheet  121 , the backsheet  123  or any combination thereof. 
     The receiving web  1  is transported along the upstream trajectory  3  with a constant velocity of transport V 0 , in the machine direction F. The upstream trajectory  3  is formed by the length of the receiving web  1  which extends to the right of the first guide roller  9  in FIG. 4, and which is moving towards the infeed side  4  of the assembly. After passing through the assembly, the receiving web  1  exits at the outfeed side  6  and is transported at constant velocity V 0  along the downstream trajectory  5 , which extends to the left of the guide roller  11 . The upstream and downstream trajectories need not correspond to the machine direction, and can be formed by straight-line or curvilinear paths. 
     The guide rollers  9  and  11  are rotationally connected to the frame  35 . The guide rollers  9 ,  11  have a fixed position. The receiving web  1  is looped around an upstream and a downstream transport roller  13 ,  15  which are mounted on a sled  41 . The sled  41  is cyclically translated along the frame  35 , generally parallel to the machine direction F, by drive motor  36 . 
     An intermediate trajectory  7   a ,  7   b ,  7   c  of the receiving web  1  is located between the upstream guide roller  9  and the downstream guide roller  11 , and comprises a first section  7   a  and a third section  7   c,  of variable length, located between the upstream guide roller  9  and the upstream transport roller  13  and the downstream transport roller  15  and the downstream guide roller  11  respectively. The second section  7   c  of the intermediate trajectory  7  is located between the transport rollers  13  and  15  and is of constant length. 
     Because of the symmetry of the intermediate trajectory  7   a ,  7   b ,  7   c , the increase in length of the first section  7   a , upon displacement of the sled  41  opposite to the machine direction F and away from the equilibrium position  39 , is compensated by an equal decrease in length of the third section  7   c , and vice versa. As the length of the second section  7   b  is constant, the whole intermediate trajectory  7   a ,  7   b ,  7   c  is independent of the position of the sled  41  with respect to the frame  35 . 
     When the part of the receiving web that is located along the second section  7   b  of the intermediate trajectory  7   a ,  7   b ,  7   c , is stationary (or at least it is slower than the speed of the web speed V 0 ) relative to the frame  35 , the web  1  is contacted by the applicator means  38  which is positionally stationary (or at least slower) with respect to the frame  35 . After the apparatus  38  has interacted with the receiving web  1 , the web is accelerated along the section  7   b  of the intermediate trajectory towards the outfeed side  6  of the assembly  2 , and is supplied to the downstream trajectory  5  with web speed V 0 . 
     The guide rollers  9 ,  11  and the transport rollers  13 ,  15  are driven by a drive member in the form of a closed loop  50  and pulleys  52 ,  53  and  54 . The loop  50  is partly parallel to the intermediate trajectory  7   a ,  7   b ,  7   c . The loop  50  is driven at a constant speed which is equal to the speed of transport V 0 , of the web  1  by a single drive motor  51 . By driving the guide rollers  9 ,  11  and the transport rollers  13 ,  15 , the strain exerted on the web  1  is minimised and can be limited to the acceleration forces, which are acting to change the speed of the web. Further details of suitable assembly are disclosed in EP-A-0 652 175, published on 10 th  May 1995. 
     FIG. 5 shows a web  40  which has been cut into discrete core elements  40   a ,  40   b . Second core elements  40   b  are subsequently rotated about their axis A. 
     The first and second core elements  40   a ,  40   b  are either mutually adhered, or are adhered to the receiving web  1 , or both. This may be done using any conventional method such as by gluing with adhesives, such as melt adhesives, or use of self-adhesive components, or by use of ultrasonic welding, heat sealing or the like.