Abstract:
The invention relates to a method for the continuous production of a flexible liquid-absorbing web material having two outer layers, at least one of which is formed by a textile material, between which are inserted at least two stretchable-elastic intermediate layers that are pre-stressed with respect to said layers and comprise filaments or bands arranged running in opposite directions to each other and obliquely with respect to the production direction. The intermediate layers shorten and gather the web material substantially transversely to the production direction thereof when the intermediate layers are relieved of stress. Powder-form or fibre-form inserts, which have absorbent properties for liquids, such as urine, blood, water or sweat, or resorbing properties, such as release of medicinal substances, cosmetic ingredients or for generating heat/cold, are introduced into the free spaces of the elastic intermediate layer.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Textile absorbent materials capable of expanding in one coordinate direction at least to create room for the increased volume due to imbibition of liquid to be absorbed are more particularly needed in connection with disposable articles such as baby diapers, incontinence products and femcare hygiene, and also in the sector of absorbent articles for packaging and food technology. 
         [0002]    This function is traditionally performed by suitable combination products comprising pulp, superabsorbent granules or fibers and liquid-distributing layers comprising synthetic nonwovens, pulp or cotton. 
         [0003]    In recognition of the responsibility toward sustainability of the Earth&#39;s natural resources and the conscious approach to the consequences of their use, it is industry&#39;s responsibility to minimize the consumption of raw materials and packaging materials and also the transportation energy for manufacture and sales as far as possible. As far as the production of hygiene articles is concerned, this means primarily a reduction in primary energy requirements, pulp, transportation volume, packaging films and cardboard and waste volume. 
         [0004]    Numerous projects are known particularly in the field of baby diapers, not only from the literature but also from industrial design, seeking to partially or completely replace the absorbency of cellulose/pulp by using superabsorbent granules (superabsorbents) and succeeding. It is technically, economically and ecologically desirable for, for example, modern baby diapers or adult incontinence articles to be completely converted to pulp-free absorbent pads in order that the influence of using disposable articles on climate change may be kept as small as possible. 
       PRIOR ART 
       [0005]    Two fundamentally different approaches are known in order to reduce/eliminate the pulp from baby diapers, incontinence products and femcare hygiene articles:
       1. replace the pulp by using stretch- or swell-capable thermoplastics as binders between the granules of superabsorbent to retain adherence as the superabsorbent swells up, to join in the swelling movement and to ensure substrate integrity even in the moist state.   2. incorporate the superabsorbent between two or more carrier layers in discrete sections in the manner of a quilted blanket, in which case the volume enlargement of the superabsorbent due to its swelling due to liquid imbibition takes place alternatively due to elasticity of one or more carrier layers, shirring or stretching of one or more carrier layers during the installation of the superabsorbent in the laminate, or by suitable bonding between the individual carrier layers such that targeted, local rupturing of this bond due to bursting pressure is made possible by the swelling of the superabsorbent.       
 
         [0008]    EP 724 418 describes the production of a laminate which consists of two outer plies, of which at least one ply is hydrophilic and which are glued to each other using a water-sensitive pressure-sensitive adhesive, so that isolated unglued sections can punctiformly incorporate superabsorbent which, in the swollen state, specifically breaks open the gluing and achieves the laminate volume increase needed for the swell volume. It has to be assumed that only limited integrity can be achieved for the laminate in the swollen state. 
         [0009]    US 20020102392 proposes a method for producing an absorption-capable laminate with incorporated sections of superabsorbents and elastic properties. Sections of superabsorbents are positioned via a vacuum system, between two outer plies, of which one is shirred in the longitudinal direction using a profiled roller, and transversely to the manufacturing direction, to obtain a longitudinally extendable laminate, wherein the elasticity and shining can be increased by using elastic films or nonwovens. 
         [0010]    US20020115969 discloses a method for the longitudinally continuous production of a laminate with individual sheetings of superabsorbents which have been installed with hot glue between two outer plies such that strips of superabsorbent-covered and superabsorbent-free regions in each case are formed transversely to the manufacturing direction. 
         [0011]    The production of a laminate comprising two outer plies with punctiformly incorporated sections of superabsorbents is described in WO 2004071539 and WO 2004071363. A textured vacuum roller is used to cause a first outer layer to develop depressions, which are filled with superabsorbents and fibers and bonded to the second outer layer. Comparable products have long also been used as supports in surgery and patient care. 
       DESCRIPTION OF THE INVENTION 
       [0012]    Superabsorbents undergo a weight increase of 2500-5000% as they imbibe liquid. The associated increase in volume has to be accommodated through suitable flexibility on the part of the surrounding carrier material. This is in principle not a problem in the case of conventional pulp/superabsorbent pads, since the pulp allows expansion in all three dimensions. In the case of so-called superabsorbent laminates, in which superabsorbent granules or superabsorbent/fiber mixtures are fixed using pressure-sensitive adhesive or thermally between two or more plies of nonwovens, film, tissue or the like, this function has to be made possible by the outer plies of the laminate, whether through stretching or through geometric flexibility. But at all times the containment of the superabsorbent has to be ensured without one of the outer plies breaking or the lamination tearing open. It is further desirable that this laminate be elastically extendable not just perpendicularly to its production plane but also within this plane itself in order not only to facilitate the volume enlargement on the part of the superabsorbent due to liquid imbibition but also to combine with other components of the above-identified hygiene articles in not impairing their flexibility and ability to conform to the particular body contour. 
         [0013]    The invention accordingly has for its object to provide a production method enabling the continuous production of absorption-capable textile sheeting material with high manufacturing capacity and, as a result, cost-effectively, wherein the end product has not only area-elastic properties to optimally adapt to the body contour of the user but also volume-elastic properties to accommodate large amounts of liquid. 
         [0014]    This object is achieved according to the invention by virtue of the fact that owing to the incorporation of superabsorbents and one or more elastic interplies, consisting of individual threads, strands or bands between two outer plies of a thusly produced laminate, this laminate is made extendable essentially transversely to the production direction and shirred in the relaxed state to the extent that the elastic interplies contain individual sections of superabsorbent in the manner of a quilted blanket and create room for the expansion of the laminate on fluid imbibition perpendicularly to and within the manufacturing plane. For use within the context of modern ultra-thin and elastic hygiene articles, it is important that the laminate thus produced is completely elastic and extendable and conforms perfectly to the body contour in both the dry and the moist state. 
         [0015]    As a result of the shining and texturing thus achieved on the skin-sided surface of the laminate, or to be more precise on that side from where the liquid to be imbibed comes into contact with the laminate and advantageously in association with an appropriately hydrophilic and transportation-capable outer layer, an excellent conductance of liquid not only in the dry but also in the moist state is ensured. Furthermore, a laminate produced in this way is always permeable perpendicularly to its manufacturing plane in the region of the gluing of the elastic plies even in the swollen state without being hindered by the swelling of the superabsorbent, so that the texture of the surface and the choice of appropriate outer layer ensure transportation performance even on the skin-remote side and the skin-sided outer layer can be optimized in respect of back-wetting/skin moisture. 
         [0016]    According to the invention, first the front end of the first outer textile layer  20  is applied to the end portion of an elongate rod- or tube-shaped core  5  and, by imposing an advancement movement around the core, folded into a shape which is closed in a hoselike form. 
         [0017]    In the further course of the advancement movement on the core, through tapering of the cross section of the core, the circumference of this hose is shortened to the effect that excess material is ducted through ducting rails or rods  8  outside the hose into suitable cutouts in the core  5 ; subsequently, two or more driven feed devices  11 ,  14  which ring the mold and are contrarotatory in pairs loosely withdraw groups of elastic threads or strands  50 ,  53  from circumferentially spaced-apart individual guides  17  and place them with friction-caused low pre-tensioning around the first outer material layer in the course of the advancement on the core. Areal pattern  32  of elastic threads or strands which surrounds the tube of the first outer sheeting of material in a cruciformly symmetrical manner has a pressure-sensitive adhesive  29  applied to it in thread form, which wets and enfolds the essentially bare elastic threads. In the continued course of the forward feed movement, the cross section of the core is enlarged to tauten the hose of the first outer sheeting of material and thereby cause it to come into contact with the elastic threads and finally be brought into a flat shape. On both sides of this flat hose, a pair of advancement or contact rollers  38  is used to bond two individual sheets of the second outer material layer  32  onto the free surface of the first outer material sheeting  20  and the elastic threads  17  provided with the pressure-sensitive adhesive  29 . As this bond is being formed, individual tracks of superabsorbent  47  are introduced on both sides of the hose of the first outer sheeting of material, between it and the supplied second outer sheeting of material. Finally, the hose thus produced is severed lengthwise into individual sheetings and these are traversingly wound onto individual rolls or deposited in boxes. 
         [0018]    As a result of the folding-in of the hose of the first sheeting of material and producing the circumferential elasticity of the hose by spreading apart the first outer sheeting of material by expanding the elastic thread pattern  32 , with respect to comparable winding processes for elastic hoses based on pre-tensioned threads or bands (for example WO 03041627, DE 102004026070) an appreciable reduction in complexity by eliminating the drive for individual guides of the threads and increased productivity in proportion with the transverse extensibility of the laminate are produced since, according to experience, the manufacturing speed is limited by the limiting speed of the ring-shaped feed devices. The width of the applicator system for the pressure-sensitive adhesive  29  is furthermore reduced to the same degree. 
         [0019]    Since, following application of the elastic threads or bands to the hose of the first outer sheeting of material, these threads or bands only touch punctiformly and are otherwise bare, a pressure-sensitive adhesive applied spirally or meanderingly is forced through the areal pattern of the elastic threads, preferably in order that these elastic threads are enfolded and are oriented essentially around the threads after spreading apart of the hose of the first outer sheeting of material, as a result of which a glue pattern which corresponds to the areal pattern  32  ( FIG. 4 ) is produced, which owing to the enfolding of the elastic threads bonds these adheringly not only to the first but also to the second outer sheeting of material in the further course of the advancement movement on the core. 
         [0020]    It has proven to be advantageous to form the core  5 , in accordance with  FIG. 2   a , from guiding struts  35  which guide the material sheeting  20  and storage struts  38  ( FIG. 2   a ) arranged thereinbetween into which excess material of the hose of material sheeting  20  is forced during the tapering of the core through corresponding guiding rails  8  ( FIG. 2   b ). 
         [0021]    The first outer material layer, once it has been pressed into the storage struts, can easily be maintained by negative pressure, introduction of compressed air or by electrostatic charging in a position closely bearing against the guiding and storage struts of the core, and be pulled with low friction over the core. 
         [0022]    Spreading the core apart after the elastic interlayers and the pressure-sensitive adhesive have been applied is advantageously achieved when guiding struts, which are mutually opposite pairwise, gradually widen in the further course of the core in their expansion direction transversely to the longitudinal axis of the core and a further pair of guiding struts is decreased in its width to the same degree, so that the hose of the first outer layer is continuously pulled out of the storage struts and pulled taut over the tips of the guiding struts and is thus brought into sheetlike contact with the pressure-sensitively glued elastic plies ( FIG. 2   c ), lastly brought into a flat state, in the continued course of the advancement movement by further synchronous pairwise widening or, respectively, width reduction of the guiding struts while maintaining essentially the same length of circumference ( FIG. 2   d ). 
         [0023]    Advantageously, the core  5  for this process is disposed to be perpendicular in its longitudinal direction such that the advancement rolls  56  are situated at the lower end of core  5  ( FIG. 1 ). 
         [0024]    The superabsorbent  47  is advantageously supplied in separate volumetrically or weight-dosed continuous individual lines or tracks which are either introduced into the glue-free regions of the areal pattern in an intermittent manner by pulsating compressed air or pistons, or are intermittently deflected in line with the areal pattern  32  in a direction transversely to the centrifugal direction of the hose of the first outer sheeting of material. For simplicity of use, it can be sufficient to allow these individual tracks to trickle down continuously, in which case it is advantageous to supply two individual tracks per cassette of the areal pattern. 
         [0025]    It may be useful and advantageous for the hose of the first outer material sheeting  20  to be relaxed in the transverse direction by reducing the width of the guiding struts before being supplied into the tensile rolls  56 , so that it has a slight degree of waviness at the time the second outer sheeting  44  is supplied, as a result of which small pockets are formed in the region of the nonglued zones of areal pattern  26 , which facilitate the laydown of superabsorbent  33 . 
         [0026]    In a further development of the invention, this waviness can be suitably policed to control the ratio of the widths of the first and second outer sheetings of material relative to each other to the extent that the laminate thus produced has a higher degree of waviness on the side of the first outer layer than on the side of the second outer layer. This makes it possible to minimize the particular costly material of the outer layers  20  and  44  while keeping the swell volume of individual cassettes the same. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0027]    In the description which follows the present invention is explained in more detail in connection with the drawings which schematically illustrate how the method according to the invention is carried out in the production of area-elastic absorption-capable sheeting material. In the drawings 
           [0028]      FIG. 1  shows a highly schematicized depiction of the side view of the essential functional elements of a device which can be used to carry out the method according to the invention; 
           [0029]      FIG. 2   a  shows the construction of the core comprising guiding and storage struts; 
           [0030]      FIG. 2   b  shows the construction of the core comprising guiding and storage struts and guiding rails in the region of the tapering of the core; 
           [0031]      FIG. 2   c  shows the construction of the core in the region of the spreading apart of the core; 
           [0032]      FIG. 2   d  shows the construction of the core after spreading apart is complete; 
           [0033]      FIG. 3  shows the arrangement of individual guides in one of the feed means provided in the device as per  FIGS. 1 and 2  for applying groups of untensioned or lightly tensioned threads or strands; 
           [0034]      FIG. 4  shows the areal pattern, obtained on using two oppositely driven feed means as per  FIG. 3 , of elastic threads or strands and of applied pressure-sensitive adhesive in a sheeting material produced in the manner of the invention; 
           [0035]      FIG. 5   a  shows the areal pattern, obtained on using two oppositely driven feed means as per  FIG. 3 , of elastic threads or strands and of punctiformly supplied pulverulent filler material in a sheeting material produced in the manner of the invention; 
           [0036]      FIG. 5   b  shows the areal pattern, obtained on using two oppositely driven feed means as per  FIG. 3 , as elastic threads or strands and of pulverulent filler material supplied continuously in discrete individual lines in a sheeting material produced in the manner of the invention; 
           [0037]      FIG. 5   c  shows the areal pattern, obtained on using two oppositely driven feed means as per  FIG. 3 , as elastic threads or strands and of pulverulent filler material supplied continuously in discrete individual lines, intermittently deflected transversely to the production direction in a sheeting material produced in the manner of the invention; 
           [0038]      FIG. 6  shows a schematic depiction of the laminate produced according to the invention on unweighting the hose of the first sheeting of material and the incorporated elastic interplies transversely to the manufacturing direction thereof before introducing the superabsorbent and bonding to the second outer layer; 
           [0039]      FIG. 7   a  shows a schematic depiction of a detail from the cross section of the core on using two storage struts between respectively two guiding struts and policing the sectionwise intake of the first outer layer by positioning the guiding rails; and 
           [0040]      FIG. 7   b  shows areal patterns of elastic threads of the elastic sheeting material produced according to  FIG. 7   a , in the planar, relaxed state. 
       
    
    
       [0041]    The device  2  depicted in a simplified and highly schematicized manner in  FIG. 1 , for carrying out the inventive method consists of an elongate core  5  having in this case a square cross section, which is surrounded by two feed means  11 ,  14  which are spaced apart from each other in the longitudinal direction. These feed means are rotationally driven in opposite directions illustrated by the arrows a and b. Individual guides  17  for elastic threads, bands or strands are spaced apart from each other on these ring-shaped feed means in the circumferential direction in each case through which individual guides the elastic elements are withdrawn to their wound package in the axial direction, leading them in the direction of core  5 . 
         [0042]    From a rotatably mounted and driven material roller  26 , a first textile layer  20  is preferably conveyed under sheeting tension control, folded via a forming shoulder  6  into a hose of rectangular cross section and laid onto the front end of core  5  formed by multiple struts  35 ,  38  in this example ( FIG. 2   a ). Advantageously, the overlap of the first textile layer  20  is fixed here in the course of forming the hose by applying a pressure-sensitive adhesive, welding or mechanical arrest. 
         [0043]    This hose thus formed is subsequently guided over the cross-sectionally tapered core, so that the hose merely guides the core on the ends of the guiding struts  35 , which shorten in their width, and inbetween material of the hose is guided using guiding rails or wires  8  in vacant spaces formed by storage struts  38  disposed between the guiding struts ( FIG. 2   b ). 
         [0044]    This hose, thus shortened in its circumference, is subsequently guided by two contrarotatingly turning feed means  11 ,  14 . In the feed means, individual elastic threads, bands or strands  50 ,  53  are each withdrawn by circumferentially spaced-apart individual guides  17  of stationary packages or rolls and laid down onto the hose of the first outer material layer  20 . The superposition of the rotary motions of the two feed means  11 ,  14  by the advancement of the first material layer  20  results in an oppositely diagonal pattern of the elastic elements  50 ,  53 , which only contacts the first layer material layer on the tips of the guiding rails  35  of core  5 , but is otherwise bare,  FIG. 3 . 
         [0045]    In the continued course of advancement on the core, the elastic threads  50 ,  53  have pressure-sensitive adhesive applied to them, preferably as a curtain of spiraling or meandering threads, which on impingement on the bare oppositely diagonal pattern of elastic threads  50 ,  53  is diverted by these and preferentially wets and enfolds the elastic threads, but specifically cross-over points between threads  50  and  53 ,  FIG. 4 . 
         [0046]    In the continued course of advancement on the core  5 , the latter is spread in its cross section such that any two opposite guiding struts are expanded in their width, and a complementary pair of guiding struts is reduced in its width, to the effect that initially the material of the first layer  20  remaining in the storage struts  38  of the core  5  is continuously detached and the hose of the first material layer  20  is tensioned taut over the ends of the guiding rails  35  ( FIG. 2   c ). This brings the hose of the first material sheeting  20  into sheetlike contact with the pattern of elastic elements  17  and of the pressure-sensitive adhesive applied thereto. The process of pairwise widening of the guiding struts  35  and the attendant diminution of complementary guiding struts is continued in the course of the continued advancement of the hose of the first material sheeting  20  over the core  5  to the effect that ultimately the hose of the first material sheeting  20  is only guided over the ends of two guiding struts  35  of core  5  and hence is virtually planar. 
         [0047]    In a further step in the course of the advancement, this hose thus formed into a flat shape is introduced into a device of two driven opposite advancement elements, here two rolls or rollers  56 , which supply in the last instance the advancement for withdrawing the first outer layer  20  of the material roll  26  and the transportation of all materials over the core. 
         [0048]    The advancement rollers  56  provide withdrawal and feeding, preferably under sheeting tension control, of an individual sheeting each of the second outer layer  44  of two mutually spaced-apart, rotatingly driven devices of material rolls  41 , on both sides of the material sheeting  20 , and sheetlike bonding thereof to the first material layer  20  and the elastic areal pattern  32  via the pressure-sensitive adhesive  29 . 
         [0049]    As the flattened hose of the first material sheeting  20  is brought together with the supplied planar lengths of the second material sheeting  44  by the advancement unit  56 , a superabsorbent  47  is introduced on both sides of the hose in a perpendicular manner such that, in line with the areal pattern  32 , individual lines or tracks adapted individually volumetrically or grammetrically to the advancement speed of the hose of the first material sheeting  20  are continuously trickled in, resulting in a product pattern as per  FIG. 5   b ; alternatively these tracks are mechanically or pneumatically deflected transversely to the flow direction in accordance with areal pattern  32  in an intermittent or oscillating manner (product pattern as per  FIG. 5   c ) or these tracks are deflected either by pulsating or intermittent compressed air, mechanical pistons or mechanical deflection of the conveying means transversely to the flow direction of the hose of the first material sheeting  20  onto the centers of the regions of this hose which are free of pressure-sensitive adhesive and formed by the areal pattern  32  (product pattern of  FIG. 5   a ). 
         [0050]    After the pressure-sensitive adhesive is set, advantageously by the contact pressure of the advancement rolls  56 , and after bonding the two outer layers  20  and  44  among themselves to the incorporated elastic elements  50 ,  53  therebetween with inclusion of the superabsorbent introduced, this multi-ply hose thus formed is severed longitudinally into individual sheetings in the course of the continued advancement movement, which sheetings can selectively be transversingly wound up on rolls movement or deposited in boxes or coiled up. 
         [0051]    In a further development of the inventive method described here, the width of the flat hose comprising a first textile layer  20  and areal pattern of elastic elements  32 , having been spread apart into the flat state,  FIG. 2   d , can be relaxed and shirred by reducing the width of the guiding rails  35  such that bonding to the otherwise essentially flat second outer layer  44  produces an elastic, absorption-capable sheeting material which has on the outside surface formed by the first textile layer a higher degree of shirring than the side formed by the second outer layer,  FIG. 6 . 
         [0052]    In a further development of the inventive method it can be desirable and advantageous for the planar sheeting material produced in this way to be endowed transversely to its production direction with sections of differing shirring for the external plies and thus differing swell volume, leading by controlling the superabsorbent distribution transversely to the production direction of the sheeting material to an advantageous transverse distribution of absorbency.  FIG. 7   a  illustrates, by way of example, how in this case of two storage struts  38  per guiding strut pair  38 , by means of suitably disposing the guiding rails  8  in the respectively formed-out storage sections of core  5  in the transverse direction to the advancement direction, differing sheeting widths of the excess sheeting material of the first outer layer  20  due to the tapering of the core  5  are introduced. If in the continued course of the advancement movement and spreading apart of the core  5 , initially the spreading of the storage struts  38  serves to contact, on the tips thereof, the material sheeting  20  with the pressure-sensitive adhesive  29  of the elastic plies  50 ,  53  and then the spreading apart of core  5  is continued within the meaning of  FIGS. 2   b - d  and the combination with the superabsorbent and the second outer layer  44  is completed, a longitudinally severed sheeting material which in the relaxed, planar state has a strutwise variation in the transverse direction of the shining of the external layers and hence ultimately of absorbency is ultimately formed,  FIG. 7   b.    
         [0053]    It can be advantageous to achieve the function of pressing the first textile layer into the vacant spaces of the storage struts instead of the guiding rails  8  by negative-pressure from the guiding core, by static charge build-up on the first material sheeting  20  versus the struts  35 ,  38  of the core, or by applying compressed air to the outside surface of the hose of the first material layer  20 . 
         [0054]    It can further be sensible and advantageous to achieve the functions of the respectively four guiding and storage struts from  FIGS. 2   a  and  2   b  by means of a correspondingly higher number of struts in order that specifically in the case of large sheeting widths for the first outer layer  20  or high storage requirements a good conductance of material may be achieved on tapering the cores  5 . 
         [0055]    Even if the isolation of individual sections of superabsorbents in glue-free regions of an otherwise mutually glued-together sheeting material comprising two outer layers  20 ,  44  and incorporating elastic plies  50 ,  53  is advantageous for the swelling effect and volume enlargement on the part of superabsorbent  47  in the liquid imbibition in accordance with the intended use, it can be sensible to wet the second outer layer  44  with an additional slight layer of pressure-sensitive adhesive before combining with the first outer layer  20  in a sheetlike manner or in longitudinal strips in order that the superabsorbent may be fixed as sheetlike as possible to thereby preempt any possible clumping of this material before commencement of liquid imbibition and to improve the haptics of the sheeting material thus produced. 
       DESIGNATIONS OF ELEMENTS IN DRAWINGS 
       [0000]    
       
         
           
               2  Overall device 
               5  Core 
               6  Forming shoulder of first textile layer 
               8  Guides of first textile layer 
               11  First guide means 
               14  Second guide means 
               17  Individual guide of elastic threads 
               20  First textile layer 
               23  Forming shoulder 
               26  Material roll of first textile layer 
               29  Pressure-sensitive adhesive 
               32  Areal pattern of elastic threads 
               35  Guiding struts of core 
               38  Storage struts of core 
               41  Material roll of second textile layer 
               44  Second textile layer 
               47  Superabsorbent 
               50  Individual thread of first interply 
               53  Individual thread of second interply 
               56  Tensile device