Abstract:
In a method and device for applying a thread to a moving substrate, a thread is continuously dispensed to a pick-up point adjacent to the point of contact of two rotating wheels ( 2, 3 ) that are inclined towards each other. The peripheries of the wheels have fingers ( 7 ) which hook the thread and move it to one side or the other as the wheels rotate, and then deposit the thread extended between the fingers 180° from the pick-up point. Long spaces between the fingers ( 7 ) on one wheel or the other make it possible to lay the thread longitudinally ( 8   b ) or in a long diagonal line instead of merely in a lateral zigzag pattern. The method and device may be used to make an absorbent article, such as a diaper.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method for applying a thread onto a relatively moving substrate. The present invention also relates to devices for carrying out the method. 
     Such a method and device for applying a thread onto a relatively moving substrate is described in Swedish Patent No. 209 771. It describes how lengths of thread can be laid substantially transversely over longitudinal threads moving thereunder to thereby form a net elastic web. Two wheels inclined towards each other above the substrate of longitudinal threads almost touch at the top. Each of the wheels is provided on its periphery with uniformly spaced fingers which alternatingly hook a thread dispensed centrally from a spool to said point of contact between the inclined wheels, as the wheels rotate. The alternating hooks thus move away from each other as they are moved with the periphery of their respective wheels, thereby gradually extending the thread, somewhat in the manner of a “cat&#39;s cradle”, in a zigzag pattern from one wheel to the other, reaching its broadest extent directly above the substrate and diametrically opposite to the pick-up point of contact between the two wheels. In the method and device shown in this Swedish patent specification, the transversely extended threads, upon reaching their point of greatest extension, are cut by a knife and glued to the longitudinal threads. 
     By this known method and device however with uniformly spaced fingers and where the threads are cut off in transverse lengths, only a transverse pattern can be created with the thread. In the manufacture of elastic pants products such as pants diapers cut end-to-end from a web, it is necessary to lay elastic threads transversely in the waist area for example, and longitudinally to elasticize the leg openings for example. Up to now this has involved a number of different separate process procedures making the method complex, and thus costly and/or prone to error, and different threads which have to be glued separately, at least at their ends, and this can give rise to a number of loose ends in the product. 
     SUMMARY OF THE INVENTION 
     All of these problems are solved by the method described herein. In this way it is possible to apply a single or several parallel elastic threads continuously along a pants diaper web of indefinite length, thus providing both transverse elasticity in the waist portion and sealing elasticity around one or more leg openings as well as longitudinal elasticity over the crotch portion, as will be evident from the detailed description of the present invention. 
     One inventive device for carrying out the method according to the invention removes certain of the projecting elements from one or both of the wheels enabling the device to lay down the thread continuously with both transverse zigzag portions and entirely longitudinal and/or inclined longitudinal portions. 
     A second inventive device for carrying out the method according to the invention includes projections that can be shaped so that certain of them release the thread from engagement, thus creating the same pattern as with the device described above but with a different elasticity in the longitudinal portions. 
     According to one particularly advantageous embodiment of the invention, the projecting elements or fingers are mounted externally on belts running on the inclined wheels, which in this case are pulleys. The belts run on the inclined pulleys from the pick-up point to the points diametrically opposite therefrom. The belts leave the front inclined pulleys there however, keeping the thread in its extended zigzag/longitudinal pattern. The thread can either be pressed by suitable means, a roller for example, off the projections into application against the substrate or the belts can be twisted inwards by virtue of a second pair of pulleys being vertically aligned or oppositely inclined to the first pair of wheels/pulleys, or the two methods can be combined. According to a preferred practical embodiment, two pairs of inclined wheels in spaced longitudinal and transverse relationship transfer the thread, preserving its zigzag/longitudinal pattern, to a conveyor belt carrying fingers or projections running in two parallel rows. 
     The method according to the present invention can be used with particular advantage in, but is not limited to, the manufacture of disposable absorbent articles such as diapers, pant diapers, sanitary briefs, incontinence shields etc. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail below with reference to several examples shown in the accompanying drawings of which: 
     FIG. 1 shows the principle of the invention with reference to a schematic representation in perspective of an embodiment of the device; 
     FIG. 2 shows in a solid line the thread pattern produced by the embodiment shown in FIG. 1, i.e. with one projecting element removed and in a dashed line thread extensions that do not occur due to removal of the one projecting element; 
     FIG. 3 shows in a solid line the thread pattern produced by an embodiment of the present invention (not shown) with two consecutive projecting elements left off one wheel and in a dashed line the thread extensions that do not occur due to removal of the two consecutive projecting elements. 
     FIG. 4 shows in a solid line the thread pattern produced by an embodiment of the present invention (not shown) with several groups of consecutive projecting elements left off the two wheels and in a dashed line the thread extensions that do not occur due to removal of the several groups of consecutive projecting elements. 
     FIG. 5 shows the pattern which can be produced by using four parallel pairs of inclined wheels in accordance with the invention, and 
     FIG. 6 shows an unfinished cut out diaper component with the pattern shown in FIG.  5 . 
     FIGS. 7A and 7B show a longitudinal view and an end view respectively of a schematic drawing of one practical embodiment of a device according to the invention for carrying out the method according to the invention. 
     FIGS. 8A and 8B show a longitudinal view and an end view respectively of a schematic drawing of a second practical preferred embodiment of a device according to the invention for carrying out said method. 
     FIG. 9 shows a longitudinal section through one type of rotating finger cap which can be used. 
     FIG. 10 is a pictorial representation of a pant diaper substrate with an elastic pattern (not shown) bonded to the substrate. 
     FIG. 11 is a pictorial representation of the pant diaper substrate of FIG. 10 with an elastic pattern (not shown) with an absorption unit fastened on the pant substrate. 
     FIG. 12 is a pictorial representation of the pant substrate of FIG. 10 with an elastic pattern (not shown) with an absorption unit of a second embodiment fastened to the pant substrate. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As can be seen in FIG. 1, a substrate web  1 , which can be the cohesive pants layer of a pants diaper for example, moves beneath two rotating wheels  2 ,  3 . These wheels  2 ,  3  are inclined towards each other and almost touch each other at their uppermost points. A thread  4 , which in this case can be an elastic cotten spun rubber thread or a LYCRA elastic thread is dispensed from a spool  5  and runs through a thread guide  6  to the point of contact between the two wheels  2 ,  3 . There the thread is hooked to one side or the other by the projecting elements or fingers  7  distributed around the outer periphery of each wheel and which cross each other at the point of contact. To produce a zigzag pattern the projecting elements or fingers  7  are arranged evenly spaced on converging portions of the two wheels alternatingly hooking the thread. As the wheels  2 ,  3  rotate, as indicated by the arrows A and B in the drawing, the respective fingers, with the thread hooked thereto will diverge, extending the thread between them in a broader and broader zigzag pattern, until reaching a lowermost point directly above the moving substrate web where means, a roller extending across the width of the substrate for example (not shown in FIG.  1 ), are arranged to push the thread out of engagement with the fingers  7  after having established adhesive contact with the substrate, thus laying out the thread in a zigzag pattern. It is also possible to provide the moving substrate with two rows of pins along the lateral margins thereof, to which the thread is transferred in its extended pattern to be subsequently sandwiched between two layers of non-woven fabric for example. Further embodiments are described below in connection with the discussion of FIGS. 7A,  7 B,  8 A,  8 B. 
     Certain selected fingers or series of fingers may be left off one or the other wheel to lay the thread, longitudinally (as shown in FIG. 1,  2  and  3 ) or obliquely longitudinally as shown in FIGS. 4,  5  and  6 , in addition to laying the thread in the basic zigzag pattern. In the example shown in FIG. 1 the thread is hooked and lain in the basic uniform zigzag pattern with the exception that one finger has been eliminated from the wheel  3 , thus producing a longitudinal extension  8   a  of the thread, which is preserved in the longitudinal portion  8   b  of the thread in adhesive contact with the substrate  1 . 
     This effect can of course be achieved in other ways; for example by designing certain of the fingers in such a way that they release the previously hooked thread before reaching adhesive contact with the substrate. This can alleviate problems with excessive transverse stretching of the thread. 
     The thread, which can be elastic, can also be laid between two layers of non-woven material which adhere to each other. 
     This has several advantages which will become evident from the explanation below. 
     FIG. 2 shows in a solid line the pattern of the thread produced by the device as configured in FIG. 1, with one finger being eliminated from one wheel, thus producing one longitudinal section  8   b  in the otherwise basic zigzag pattern of the thread  4 . FIG. 3 shows the pattern produced when two fingers are eliminated from one wheel. FIG. 4 shows in a solid line pattern, which is very useful in the production of diapers and pants diapers as will become evident below. This pattern is produced by first eliminating a pair of fingers  7   a ,  7   b  from each wheel, thereby creating a diagonal portion  9   a . The eliminated finger  7   c  produces a longitudinal section  8   b , which is followed by a diagonal section  9   b , oppositely oriented to the diagonal portion  9   a , and which is produced by eliminating a pair of fingers  7   d ,  7   e  from each wheel. The dashed lines show the thread extensions that would have occurred if the fingers were not eliminated. 
     Four patterns of this type  4   a ,  4   b ,  4   c , and  4   d  are laid out in parallel as shown in FIG.  5  and applied to an elasticized pants type diaper. To do this four pairs of inclined wheels are necessary. FIG. 6 shows an elasticized pants diaper component  1 ′ in its unassembled state cut out of the substrate web with the four patterns  4   a ,  4   b ,  4   c ,  4   d . The zigzag pattern areas at either end are transversely elasticized to provide an elastic waist. The two side columns  4   a  and  4   d  have the zigzag areas slanted to provide a concave edge surface to accomodate the protruding belly shape of the typical toddler, as described in Swedish Patent Application 9402867-7. The longitudinal crotch elastics provide leg sealing elastic and elastic pockets for urine and feces respectively and can be used in conjunction with the absorbent products described in SE 9404567-1. 
     Thus four parallel continuous threads provide lateral elasticity around the waist and longitudinal elasticity around the legs and in the crotch area. Each of the threads need only be severed at its ends thus making handling of the elastic very simple. 
     A further advantage is that if the threads are sandwiched between two layers of non-woven fabric, then each of the threads only needs to be bonded at its ends by gluing for example. The convoluted zigzag pattern will hold the rest of each thread in place since the non-woven fabrics are bonded to each other holding the zigzag pattern in place. 
     The method according to the invention can also be applied by using a device where the inclined wheels are pulleys and the projecting elements or fingers are fixed externally on belts running between said pulleys and second pulleys which are vertically oriented or even inclined oppositely to the first pair of pulleys. The fingers follow the periphery of the first inclined pulleys, functioning in exactly the same manner as the wheels with peripherally fixed fingers. The belts then leave the inclined pulleys when reaching the bottom directly above the substrate, keeping the thread extended in the desired pattern between the two belts. The threads can either be pressed by suitable means (e.g. a roller) off the fingers on the belts, and for example be sandwiched between two layers of non-woven fabric or the orientation of the second pulleys can be such that the thread slips naturally off the fingers as the belts are twisted. 
     FIGS. 7A and 7B show one practical embodiment of the device according to the invention. A pair of inclined pulleys  15 , 16  carry belts  22   a,b  which run over opposite pulleys  18  to follow a path essentially parallel to the substrate  1 . The belts  22   a,b  are provided with projections or fingers  17  spaced with appropriate longer gaps  23  to achieve the desired zigzag/longitudinal pattern. The thread  4 , which in this case is an elastic thread, runs from a spool (not shown) in the direction of the arrow E 1  along the entire upper run of the belts, where the fingers  17  carried by the belts  22   a,b  are held in crossed configuration with the thread running between them. Upon reaching the pulleys  15 ,  16 , the belts  22   a,b  carrying the fingers  17  diverge creating the desired zigzag/longitudinal pattern which is preserved as the belts leave the pulleys and proceed along the lower run. A roller  19  running between the belts  22   a,b  along the lower run presses the thread in the zigzag/longitudinal pattern from the fingers  17  and onto the substrate  1  moving in direction S which has just been sprayed with glue  21  from a gluing unit  20 , thus embedding the thread and preserving the desired zigzag/longitudinal pattern. 
     In order to prevent friction between the thread  4  and the fingers  17  from causing excessive tension and breakage of the thread as the fingers diverge, each finger  17  is provided with a rotating cap  24  (See FIG. 9) which rotates freely on a finger pin  25  via either a journal bearing (not shown) or a rolling contact bearing  26 . 
     FIGS. 8 a  and  8   b  show in a longitudinal view and an end view respectively another preferred practical embodiment of the present invention using finger-equipped intermediate transfer belts  31   a,b,c,d  between two pairs of finger-equipped inclined wheels  27 ,  28  and  29 ,  30  and the moving substrate  1 . The two pairs of inclined wheels  27 ,  28  and  29 ,  30  are spaced both longitudinally and laterally as can be seen in the drawing to provide two zigzag/longitudinal patterns on the substrate which are almost contiguous side-by-side. Each pair of inclined wheels receives between converging fingers a thread fed from one of two spools (not shown) in the direction E 2 , whereupon the diverging fingers of the rotating wheels create the zigzag/longitudinal pattern in the manner described above. As the fingers reach the bottom of the rotating wheel, the thread is transferred, preserving the zigzag/longitudinal configuration of the thread, onto fingers  34  carried on belts  31   a,b,c,d  arranged in parallel relation to each other. There is one transfer belt  31   a,b,c,d  for each inclined wheel  27 ,  28 ,  29 ,  30 . The thread after arriving at the substrate is then pressed into glue  21  which has been sprayed onto the substrate, in the same manner as was described above in conjunction with FIGS. 7A and 7B. 
     This arrangement with intermediate transfer belts prevents glue from penetrating into the finger cap bearings  26  (see 
     FIG. 9) and preventing the finger caps  24  from rotating, and thereby giving rise to thread friction and thread breakage. 
     The intermediate transfer belts  31   a,b,c,d , in contrast to the embodiment shown in FIG. 8 a  with longer gaps  32   b  corresponding to those  32   a  on the inclined wheels, can be provided a continuous tightly spaced series of fingers covering the entire belt. This eliminates the need for synchronization of the belts to the wheels while still preserving the original zigzag/longitudinal pattern produced by the inclined wheels  27 ,  28  and  29 ,  30 . This also enables the pairs of wheels to be changed as needed to produce different patterns, without replacing or synchronizing the intermediate transfer belts  31   a,b,c,d . Having a continuous tightly space series of fingers on each transfer belt also makes it possible to run belts at slightly different speeds so that one belt will advance during a complete cycle an intergral number of fingers in relation to the other belt in each pair of belts. This will enable one to achieve zigzag patterns which are skewed i.e. do not advance uniformly while moving from one side to the other (see patterns  4   a  and  4   d  in FIGS. 5 and 6) or are even retrograde from one side to the other. 
     It is also possible to arrange pairs of inclined wheels in direct series in order to superimpose different patterns on top of each other, for example a longitudinal pattern super-imposed on a zigzag pattern to provide both longitudinal and transverse elasticity and/or strength. 
     FIG. 10 shows a pant substrate  10  of a non-woven material and an elastic stretched as the elastic pattern described in connection with FIGS. 1-6. Pant substrate  10  may include a urine opening  14  and an anal opening  15 . 
     FIG. 11 shows an absorption unit comprising two parts  12  and  13  where the first part  12  is arranged to cover the urine opening  14  in the pant substrate  10  and where the second part  13  is arranged to cover the anal opening  15 . The absorption part  12 , comprising an outer liquid impermeable cover  16 , is fastened at its periphery against the pant substrate  10 . 
     The space inside said cover  16  may be filled with an absorbent material, such as cellulosic fluff and/or absorbent gel. 
     The absorption part  13  for feces comprises an outer liquid impermeable cover  17  fastened at its periphery against the pant. The space inside the cover  17  is preferably empty as it intended to keep feces inside the cover. 
     In FIG. 12, an absorption unit  11  covers both the urine opening  14  and the anal opening  15 . The absorption unit  11  may comprise absorbent material inside a cover  16 . 
     The absorbent articles according to FIG. 11 and 12 can be modified. The important thing is, in contrast to known absorbent articles that a pant is formed which pant is in close contact with the user&#39;s skin all over the pant and proximate the user&#39;s urethral opening and anus and that the absorption unit is arranged on the outside of the pant and is held up by it. 
     The elastic pant can be designed with small holes  14 ,  15  because they are held in place and kept open by the elastic properties of the pant. 
     When feces or urine is excreted, they will pass through their respective holes and into their respective pockets in the absorption unit. 
     The urine and feces collecting parts  12 ,  13  can be fastened to the pant tightly sealed to the portions of the elastic pant immediately surrounding the respective ones of said holes. 
     The front pocket, absorption part,  12  may be filled and weighted down with urine without it pulling the elastic pant out of position in contact with the user. Since the two parts  12  and  13  are separated from each other the feces and urine will not mix, which is advantageous for preventing irritation to the skin. 
     The cover  16  and  17  can be made of elastic material to be able to expand as they are filled with feces or urine. The covers  17  and  18  can also be folded as a bellows to expand as they are filled.