Patent Publication Number: US-2016235606-A1

Title: Disposable Absorbent Article with Varied Distribution of Absorbent Particulate Polymer Material and Method of Making Same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 12/485,953, filed on Jun. 17, 2009, which claims the benefit of U.S. Provisional Application No. 61/077,498, filed on Jul. 2, 2008. 
    
    
     FIELD 
     The present disclosure generally relates to an absorbent article, and more particularly to absorbent articles comprising absorbent particulate polymer material. 
     BACKGROUND 
     Absorbent articles, such as disposable diapers, training pants, and adult incontinence undergarments, absorb and contain body exudates. They are also intended to prevent body exudates from soiling, wetting, or otherwise contaminating clothing or other articles, such as, bedding, that come in contact with the wearer. A disposable absorbent article, such as a disposal diaper, may be worn for several hours in a dry state or in a urine loaded state. Accordingly, efforts have been made toward improving the fit and comfort of the absorbent article to the wearer, both when the article is dry and when the article is fully or partially loaded with liquid exudates, while maintaining or enhancing the absorbing and containing functions of the article. 
     Disposable absorbent articles, as disposable diapers, are often purchased and used in a relatively large volume. It has been desirable to make disposable absorbent articles with reduced bulk to reduce space needed for transportation, shelf display, and/or storage. Some absorbent articles, like disposable diapers, have been made thinner by using an absorbent polymer material (also known as super absorbent polymer), such as an absorbent particulate polymer material, as the primary liquid absorbent in the article. Absorbent particulate polymer material absorbs liquid and swells within the article. 
     A wearer may subject some absorbent articles, such as disposable diapers, to one or more rushes of liquid, such as when urinating. Such a wearer typically desires that the absorbent article absorb and hold all such liquid during initial and subsequent rushes of liquid. The rate of absorbency and capacity of the absorbent particulate polymer material may affect the absorbent article&#39;s ability to absorb and hold all liquid during initial and subsequent rushes of liquid. When an absorbent article is not able to absorb and hold all liquid, an undesirable liquid leak may occur. 
     Thus, there remains a desire to enhance the ability of some thin, flexible, and/or inexpensive absorbent articles to absorb and hold one or more rushes of liquid without substantial leakage of liquid from the absorbent article. 
     SUMMARY 
     The present disclosure addresses one or more technical problems such as that described above. In some embodiments, the absorbent article may include: a lateral axis; a longitudinal axis; a front waist region on a first side of the lateral axis; a back waist region on a second side of the lateral axis; a first longitudinal side edge on a first side of the longitudinal axis; a second longitudinal side edge on a second side of the longitudinal axis: a first elastic leg feature proximate to the first longitudinal side edge; a second elastic leg feature proximate to the second longitudinal side edge; a topsheet; a backsheet; and an absorbent core positioned between the topsheet and the backsheet. The absorbent core may include a first area of absorbent particulate polymer material positioned at least partially between the longitudinal axis and the first longitudinal side edge, a second area of absorbent particulate polymer material positioned at least partially between the longitudinal axis and the second longitudinal side edge, and a third area of absorbent particulate polymer material. The first area of absorbent particulate polymer material may be convex relative to the longitudinal axis and concave relative to the first longitudinal side edge. The second area of absorbent particulate polymer material may be convex relative to the longitudinal axis and concave relative to the second longitudinal side edge. The third area of absorbent particulate polymer material may substantially surround the first area of absorbent particulate polymer material and the second area of absorbent particulate polymer material. Further, the first area of absorbent particulate polymer material has a first basis weight, the second area of absorbent particulate polymer material has a second basis weight, and the third area of absorbent particulate polymer material has a third basis weight. The third basis weight may be different than each of the first basis weight and the second basis weight. 
     In some embodiments, an absorbent article may include: a lateral axis; a longitudinal axis; a front waist region on a first side of the lateral axis; a back waist region on a second side of the lateral axis; a first longitudinal side edge on a first side of the longitudinal axis; a second longitudinal side edge on a second side of the longitudinal axis: a first elastic leg feature proximate to the first longitudinal side edge; a second elastic leg feature proximate to the second longitudinal side edge; a topsheet; a backsheet; and an absorbent core positioned between the topsheet and the backsheet. The absorbent core may include a first area of absorbent particulate polymer material, a second area of absorbent particulate polymer material, and a third area of absorbent particulate polymer material. The first area of absorbent particulate polymer material may be concave relative to the longitudinal axis. The second area of absorbent particulate polymer material may be concave relative to the longitudinal axis. The third area of absorbent particulate polymer material may substantially surround the first area of absorbent particulate polymer material and the second area of absorbent particulate polymer material. The first area of absorbent particulate polymer material has a first basis weight, the second area of absorbent particulate polymer material has a second basis weight, and the third area of absorbent particulate polymer material has a third basis weight. The first basis weight may be substantially the same as the second basis weight, and the third basis weight may be different than each of the first basis weight and the second basis weight. 
     In some embodiments, an absorbent article may include: a lateral axis; a longitudinal axis; a front waist region on a first side of the lateral axis; a back waist region on a second side of the lateral axis; a first longitudinal side edge on a first side of the longitudinal axis; a second longitudinal side edge on a second side of the longitudinal axis: a first elastic leg feature proximate to the first longitudinal side edge; a second elastic leg feature proximate to the second longitudinal side edge; a topsheet; a backsheet; and an absorbent core positioned between the topsheet and the backsheet. The absorbent core may include a first area of absorbent particulate polymer material, a second area of absorbent particulate polymer material, and a third area of absorbent particulate polymer material. The first area of absorbent particulate polymer material may extend in a direction substantially parallel with the longitudinal axis and may be disposed on a first side of the longitudinal axis. The second area of absorbent particulate polymer material may extend in a direction substantially parallel to the longitudinal axis and may be disposed on the second side of the longitudinal axis. The third area of absorbent particulate polymer material may substantially surround each of the first area of absorbent particulate polymer material and the second area of absorbent particulate polymer material. The first area of absorbent particulate polymer material has a first basis weight, the second area of absorbent particulate polymer material has a second basis weight, and the third area of absorbent particulate polymer material has a third basis weight. The third basis weight may be different than each of the first basis weight and the second basis weight. 
     Other features and advantages of the disclosure may be apparent from the following detailed description, drawings, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a diaper in accordance with an embodiment of the present disclosure. 
         FIG. 2  is a cross sectional view of the diaper shown in  FIG. 1  taken along the sectional line  2 - 2  of  FIG. 1 . 
         FIG. 3  is a partial cross sectional view of an absorbent core layer in accordance with an embodiment of this disclosure wherein more absorbent particulate polymer material is present toward lateral edges of the diaper than in a central zone of the diaper. 
         FIG. 4  is a partial cross sectional view of an absorbent core layer in accordance with another embodiment of this disclosure. 
         FIG. 5  is a plan view of the absorbent core layer illustrated in  FIG. 3 . 
         FIG. 6  is a plan view of a second absorbent core layer in accordance with an embodiment of this disclosure wherein more absorbent particulate polymer material is present toward lateral edges of the diaper than in a central zone of the diaper. 
         FIG. 7  is a partial sectional view of an absorbent core comprising a combination of the first and second absorbent core layers illustrated in  FIGS. 5 and 6 . 
         FIG. 8A  is a plan view of the absorbent core illustrated in  FIG. 7 . 
         FIGS. 8B-8F  are plan views of absorbent cores having alternative patterns of absorbent material. 
         FIG. 9  is a plan view of the absorbent core in accordance with an embodiment of this disclosure wherein more absorbent particulate polymer material is present toward ends of the diaper than in a central zone of the diaper. 
         FIG. 10  is a plan view of the absorbent core in accordance with an embodiment of this disclosure wherein more absorbent particulate polymer material is present toward lateral edges and ends of the diaper than in a central zone of the diaper. 
         FIG. 11  is a schematic representation of a rheometer. 
         FIG. 12  is a schematic illustration of a process for making an absorbent core in accordance with an embodiment of this disclosure. 
         FIG. 13  is a partial sectional view of an apparatus for making an absorbent core in accordance with an embodiment of this disclosure. 
         FIG. 14  is a perspective view of the printing roll illustrated in  FIG. 13 . 
         FIG. 15  is a partial sectional view of the printing roll illustrated in  FIG. 14  showing absorbent particulate polymer material reservoirs. 
         FIG. 16  is a perspective view of the supporting roll illustrated in  FIG. 12 . 
         FIG. 17  is a perspective view of a printing roll for making an embodiment of this disclosure wherein more absorbent particulate polymer material is present toward ends of the diaper than in a central zone of the diaper. 
         FIG. 18  is a partial sectional view of the printing roll illustrated in  FIG. 17  showing absorbent particulate polymer material reservoirs. 
         FIG. 19  is a perspective view of a printing roll for making an embodiment of this disclosure wherein more absorbent particulate polymer material is present toward lateral edges and ends of the diaper than in a central zone of the diaper. 
     
    
    
     DETAILED DESCRIPTION 
     As summarized above, this disclosure encompasses a disposable absorbent article comprising an absorbent core located in a chassis and comprising absorbent particulate polymer material having a basis weight that varies across the absorbent core. Embodiments of such disposable absorbent articles are described hereinbelow along with embodiments of apparatuses and methods for making disposable absorbent articles. 
     DEFINITIONS 
     As used herein, the following terms have the following meanings: 
     “Absorbent article” refers to devices that absorb and contain body exudates, and, more specifically, refers to devices that are placed against or in proximity to the body of the wearer to absorb and contain the various exudates discharged from the body. Absorbent articles may include diapers, training pants, adult incontinence undergarments, feminine hygiene products, breast pads, care mats, bibs, wound dressing products, and the like. As used herein, the term “body fluids” or “body exudates” includes, but is not limited to, urine, blood, vaginal discharges, breast milk, sweat and fecal matter. 
     “Absorbent core” means a structure typically disposed between a topsheet and backsheet of an absorbent article for absorbing and containing liquid received by the absorbent article and may comprise one or more substrates, absorbent polymer material disposed on the one or more substrates, and a thermoplastic composition on the absorbent particulate polymer material and at least a portion of the one or more substrates for immobilizing the absorbent particulate polymer material on the one or more substrates. In a multilayer absorbent core, the absorbent core may also include a cover layer. The one or more substrates and the cover layer may comprise a nonwoven. Further, the absorbent core is substantially cellulose free. The absorbent core does not include an acquisition system, a topsheet, or a backsheet of the absorbent article. In a certain embodiment, the absorbent core would consist essentially of the one or more substrates, the absorbent polymer material, the thermoplastic composition, and optionally the cover layer. 
     “Absorbent polymer material,” “absorbent gelling material,” “AGM,” “superabsorbent,” and “superabsorbent material” are used herein interchangeably and refer to cross linked polymeric materials that can absorb at least 5 times their weight of an aqueous 0.9% saline solution as measured using the Centrifuge Retention Capacity test (Edana 441.2-01). 
     “Absorbent particulate polymer material” is used herein to refer to an absorbent polymer material which is in particulate form so as to be flowable in the dry state. 
     “Absorbent particulate polymer material area” as used herein refers to the area of the core wherein the first substrate  64  and second substrate  72  are separated by a multiplicity of superabsorbent particles. In  FIG. 8A , the boundary of the absorbent particulate polymer material area is defined by the perimeter of the overlapping circles. There may be some extraneous superabsorbent particles outside of this perimeter between the first substrate  64  and second substrate  72 . 
     “Airfelt” is used herein to refer to comminuted wood pulp, which is a form of cellulosic fiber. 
     “Comprise,” “comprising,” and “comprises” are open ended terms, each specifies the presence of what follows, e.g., a component, but does not preclude the presence of other features, e.g., elements, steps, components known in the art, or disclosed herein. 
     “Consisting essentially of” is used herein to limit the scope of subject matter, such as that in a claim, to the specified materials or steps and those that do not materially affect the basic and novel characteristics of the subject matter. 
     “Disposable” is used in its ordinary sense to mean an article that is disposed or discarded after a limited number of usage events over varying lengths of time, for example, less than about 20 events, less than about 10 events, less than about 5 events, or less than about 2 events. 
     “Diaper” refers to an absorbent article generally worn by infants and incontinent persons about the lower torso so as to encircle the waist and legs of the wearer and that is specifically adapted to receive and contain urinary and fecal waste. As used herein, term “diaper” also includes “pants” which is defined below. 
     “Fiber” and “filament” are used interchangeably. 
     A “nonwoven” is a manufactured sheet, web or batt of directionally or randomly orientated fibers, bonded by friction, and/or cohesion and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitch-bonded incorporating binding yarns or filaments, or felted by wet-milling, whether or not additionally needled. The fibers may be of natural or man-made origin and may be staple or continuous filaments or be formed in situ. Commercially available fibers have diameters ranging from less than about 0.001 mm to more than about 0.2 mm and they come in several different forms: short fibers (known as staple, or chopped), continuous single fibers (filaments or monofilaments), untwisted bundles of continuous filaments (tow), and twisted bundles of continuous filaments (yarn). Nonwoven fabrics can be formed by many processes such as meltblowing, spunbonding, solvent spinning, electrospinning, and carding. The basis weight of nonwoven fabrics is usually expressed in grams per square meter (gsm). 
     “Pant” or “training pant”, as used herein, refer to disposable garments having a waist opening and leg openings designed for infant or adult wearers. A pant may be placed in position on the wearer by inserting the wearer&#39;s legs into the leg openings and sliding the pant into position about a wearer&#39;s lower torso. A pant may be preformed by any suitable technique including, but not limited to, joining together portions of the article using refastenable and/or non-refastenable bonds (e.g., seam, weld, adhesive, cohesive bond, fastener, etc.). A pant may be preformed anywhere along the circumference of the article (e.g., side fastened, front waist fastened). While the terms “pant” or “pants” are used herein, pants are also commonly referred to as “closed diapers,” “prefastened diapers,” “pull-on diapers,” “training pants,” and “diaper-pants”. Suitable pants are disclosed in U.S. Pat. No. 5,246,433, issued to Hasse, et al. on Sep. 21, 1993; U.S. Pat. No. 5,569,234, issued to Buell et al. on Oct. 29, 1996; U.S. Pat. No. 6,120,487, issued to Ashton on Sep. 19, 2000; U.S. Pat. No. 6,120,489, issued to Johnson et al. on Sep. 19, 2000; U.S. Pat. No. 4,940,464, issued to Van Gompel et al. on Jul. 10, 1990; U.S. Pat. No. 5,092,861, issued to Nomura et al. on Mar. 3, 1992; U.S. Patent Publication No. 2003/0233082 A1, entitled “Highly Flexible And Low Deformation Fastening Device”, filed on Jun. 13, 2002; U.S. Pat. No. 5,897,545, issued to Kline et al. on Apr. 27, 1999; U.S. Pat. No. 5,957,908, issued to Kline et al on Sep. 28, 1999. 
     “Substantially cellulose free” is used herein to describe an article, such as an absorbent core, that contains less than 10% by weight cellulosic fibers, less than 5% cellulosic fibers, less than 1% cellulosic fibers, no cellulosic fibers, or no more than an immaterial amount of cellulosic fibers. An immaterial amount of cellulosic material would not materially affect the thinness, flexibility, or absorbency of an absorbent core. 
     “Substantially continuously distributed” as used herein indicates that within the absorbent particulate polymer material area, the first substrate  64  and second substrate  72  are separated by a multiplicity of superabsorbent particles. It is recognized that there may be minor incidental contact areas between the first substrate  64  and second substrate  72  within the absorbent particulate polymer material area. Incidental contact areas between the first substrate  64  and second substrate  72  may be intentional or unintentional (e.g. manufacturing artifacts) but do not form geometries such as pillows, pockets, tubes, quilted patterns and the like. 
     “Thermoplastic adhesive material” as used herein is understood to comprise a polymer composition from which fibers are formed and applied to the superabsorbent material with the intent to immobilize the superabsorbent material in both the dry and wet state. The thermoplastic adhesive material of the present invention forms a fibrous network over the superabsorbent material. 
     “Thickness” and “caliper” are used herein interchangeably. 
     Absorbent Articles 
       FIG. 1  is a plan view of a diaper  10  according to a certain embodiment of the present invention. The diaper  10  is shown in its flat out, uncontracted state (i.e., without elastic induced contraction) and portions of the diaper  10  are cut away to more clearly show the underlying structure of the diaper  10 . A portion of the diaper  10  that contacts a wearer is facing the viewer in  FIG. 1 . The diaper  10  generally may comprise a chassis  12  and an absorbent core  14  disposed in the chassis. 
     The chassis  12  of the diaper  10  in  FIG. 1  may comprise the main body of the diaper  10 . The chassis  12  may comprise an outer covering  16  including a topsheet  18 , which may be liquid pervious, and/or a backsheet  20 , which may be liquid impervious. The absorbent core  14  may be encased between the topsheet  18  and the backsheet  20 . The chassis  12  may also include side panels  22 , elasticized leg cuffs  24 , and an elastic waist feature  26 . 
     The leg cuffs  24  and the elastic waist feature  26  may each typically comprise elastic members  28 . One end portion of the diaper  10  may be configured as a first waist of the diaper  10 . An opposite end portion of the diaper  10  may be configured as a second waist region  32  of the diaper  10 . An intermediate portion of the diaper  10  may be configured as a crotch region  34 , which extends longitudinally between the first and second waist regions  30  and  32 . The waist regions  30  and  32  may include elastic elements such that they gather about the waist of the wearer to provide improved fit and containment (elastic waist feature  26 ). The crotch region  34  is that portion of the diaper  10  which, when the diaper  10  is worn, is generally positioned between the wearer&#39;s legs. 
     The diaper  10  is depicted in  FIG. 1  with its longitudinal axis  36  and its transverse axis  38 . The periphery  40  of the diaper  10  is defined by the outer edges of the diaper  10  in which the longitudinal edges  42  run generally parallel to the longitudinal axis  36  of the diaper  10  and the end edges  44  run between the longitudinal edges  42  generally parallel to the transverse axis  38  of the diaper  10 . The chassis  12  may also comprise a fastening system, which may include at least one fastening member  46  and at least one stored landing zone  48 . 
     The diaper  10  may also include such other features as are known in the art including front and rear ear panels, waist cap features, elastics and the like to provide better fit, containment and aesthetic characteristics. Such additional features are well known in the art and are e.g., described in U.S. Pat. No. 3,860,003 and U.S. Pat. No. 5,151,092. 
     In order to keep the diaper  10  in place about the wearer, at least a portion of the first waist region  30  may be attached by the fastening member  46  to at least a portion of the second waist region  32  to form leg opening(s) and an article waist. When fastened, the fastening system carries a tensile load around the article waist. The fastening system may allow an article user to hold one element of the fastening system, such as the fastening member  46 , and connect the first waist region  30  to the second waist region  32  in at least two places. This may be achieved through manipulation of bond strengths between the fastening device elements. 
     According to certain embodiments, the diaper  10  may be provided with a re-closable fastening system or may alternatively be provided in the form of a pant-type diaper. When the absorbent article is a diaper, it may comprise a re-closable fastening system joined to the chassis for securing the diaper to a wearer. When the absorbent article is a pant-type diaper, the article may comprise at least two side panels joined to the chassis and to each other to form a pant. The fastening system and any component thereof may include any material suitable for such a use, including but not limited to plastics, films, foams, nonwoven, woven, paper, laminates, fiber reinforced plastics and the like, or combinations thereof. In certain embodiments, the materials making up the fastening device may be flexible. The flexibility may allow the fastening system to conform to the shape of the body and thus, reduce the likelihood that the fastening system will irritate or injure the wearer&#39;s skin. 
     For unitary absorbent articles, the chassis  12  and absorbent core  14  may form the main structure of the diaper  10  with other features added to form the composite diaper structure. While the topsheet  18 , the backsheet  20 , and the absorbent core  14  may be assembled in a variety of well-known configurations, preferred diaper configurations are described generally in U.S. Pat. No. 5,554,145 entitled “Absorbent Article With Multiple Zone Structural Elastic-Like Film Web Extensible Waist Feature” issued to Roe et al. on Sep. 10, 1996; U.S. Pat. No. 5,569,234 entitled “Disposable Pull-On Pant” issued to Buell et al. on Oct. 29, 1996; and U.S. Pat. No. 6,004,306 entitled “Absorbent Article With Multi-Directional Extensible Side Panels” issued to Robles et al. on Dec. 21, 1999. 
     The topsheet  18  in  FIG. 1  may be fully or partially elasticized or may be foreshortened to provide a void space between the topsheet  18  and the absorbent core  14 . Exemplary structures including elasticized or foreshortened topsheets are described in more detail in U.S. Pat. No. 5,037,416 entitled “Disposable Absorbent Article Having Elastically Extensible Topsheet” issued to Allen et al. on Aug. 6, 1991; and U.S. Pat. No. 5,269,775 entitled “Trisection Topsheets for Disposable Absorbent Articles and Disposable Absorbent Articles Having Such Trisection Topsheets” issued to Freeland et al. on Dec. 14, 1993. 
     The backsheet  26  may be joined with the topsheet  18 . The backsheet  20  may prevent the exudates absorbed by the absorbent core  14  and contained within the diaper  10  from soiling other external articles that may contact the diaper  10 , such as bed sheets and undergarments. In certain embodiments, the backsheet  26  may be substantially impervious to liquids (e.g., urine) and comprise a laminate of a nonwoven and a thin plastic film such as a thermoplastic film having a thickness of about 0.012 mm (0.5 mil) to about 0.051 mm (2.0 mils). Suitable backsheet films include those manufactured by Tredegar Industries Inc. of Terre Haute, Ind. and sold under the trade names X15306, X10962, and X10964. Other suitable backsheet materials may include breathable materials that permit vapors to escape from the diaper  10  while still preventing liquid exudates from passing through the backsheet  10 . Exemplary breathable materials may include materials such as woven webs, nonwoven webs, composite materials such as film-coated nonwoven webs, and microporous films such as manufactured by Mitsui Toatsu Co., of Japan under the designation ESPOIR NO and by EXXON Chemical Co., of Bay City, Tex., under the designation EXXAIRE. Suitable breathable composite materials comprising polymer blends are available from Clopay Corporation, Cincinnati, Ohio under the name HYTREL blend P18-3097. Such breathable composite materials are described in greater detail in PCT Application No. WO 95/16746, published on Jun. 22, 1995 in the name of E. I. DuPont. Other breathable backsheets including nonwoven webs and apertured formed films are described in U.S. Pat. No. 5,571,096 issued to Dobrin et al. on Nov. 5, 1996. 
     In certain embodiments, the backsheet of the present invention may have a water vapor transmission rate (WVTR) of greater than about 2000 g/24 h/m 2 , greater than about 3000 g/24 h/m 2 , greater than about 5000 g/24 h/m 2 , greater than about 6000 g/24 h/m 2 , greater than about 7000 g/24 h/m 2 , greater than about 8000 g/24 h/m 2 , greater than about 9000 g/24 h/m 2 , greater than about 10000 g/24 h/m 2 , greater than about 11000 g/24 h/m 2 , greater than about 12000 g/24 h/m 2 , greater than about 15000 g/24 h/m 2 , measured according to WSP 70.5 (08) at 37.8° C. and 60% Relative Humidity. 
       FIG. 2  shows a cross section of  FIG. 1  taken along the sectional line  2 - 2  of  FIG. 1 . Starting from the wearer facing side, the diaper  10  may comprise the topsheet  18 , the components of the absorbent core  14 , and the backsheet  20 . According to a certain embodiment, diaper  10  may also comprise an acquisition system  50  disposed between the liquid permeable topsheet  18  and a wearer facing side of the absorbent core  14 . The acquisition system  50  may be in direct contact with the absorbent core. The acquisition system  50  may comprise a single layer or multiple layers, such as an upper acquisition layer  52  facing towards the wearer&#39;s skin and a lower acquisition  54  layer facing the garment of the wearer. According to a certain embodiment, the acquisition system  50  may function to receive a surge of liquid, such as a gush of urine. In other words, the acquisition system  50  may serve as a temporary reservoir for liquid until the absorbent core  14  can absorb the liquid. 
     In a certain embodiment, the acquisition system  50  may comprise chemically cross-linked cellulosic fibers. Such cross-linked cellulosic fibers may have desirable absorbency properties. Exemplary chemically cross-linked cellulosic fibers are disclosed in U.S. Pat. No. 5,137,537. In certain embodiments, the chemically cross-linked cellulosic fibers are cross-linked with between about 0.5 mole % and about 10.0 mole % of a C 2  to C 9  polycarboxylic cross-linking agent or between about 1.5 mole % and about 6.0 mole % of a C 2  to C 9  polycarboxylic cross-linking agent based on glucose unit. Citric acid is an exemplary cross-linking agent. In other embodiments, polyacrylic acids may be used. Further, according to certain embodiments, the cross-linked cellulosic fibers have a water retention value of about 25 to about 60, or about 28 to about 50, or about 30 to about 45. A method for determining water retention value is disclosed in U.S. Pat. No. 5,137,537. According to certain embodiments, the cross-linked cellulosic fibers may be crimped, twisted, or curled, or a combination thereof including crimped, twisted, and curled. 
     In a certain embodiment, one or both of the upper and lower acquisition layers  52  and  54  may comprise a non-woven, which may be hydrophilic. Further, according to a certain embodiment, one or both of the upper and lower acquisition layers  52  and  54  may comprise the chemically cross-linked cellulosic fibers, which may or may not form part of a nonwoven material. According to an exemplary embodiment, the upper acquisition layer  52  may comprise a nonwoven, without the cross-linked cellulosic fibers, and the lower acquisition layer  54  may comprise the chemically cross-linked cellulosic fibers. Further, according to an embodiment, the lower acquisition layer  54  may comprise the chemically cross-linked cellulosic fibers mixed with other fibers such as natural or synthetic polymeric fibers. According to exemplary embodiments, such other natural or synthetic polymeric fibers may include high surface area fibers, thermoplastic binding fibers, polyethylene fibers, polypropylene fibers, PET fibers, rayon fibers, lyocell fibers, and mixtures thereof. According to a particular embodiment, the lower acquisition layer  54  has a total dry weight, the cross-linked cellulosic fibers are present on a dry weight basis in the upper acquisition layer in an amount from about 30% to about 95% by weight of the lower acquisition layer  54 , and the other natural or synthetic polymeric fibers are present on a dry weight basis in the lower acquisition layer  54  in an amount from about 70% to about 5% by weight of the lower acquisition layer  54 . According to another embodiment, the cross-linked cellulosic fibers are present on a dry weight basis in the first acquisition layer in an amount from about 80% to about 90% by weight of the lower acquisition layer  54 , and the other natural or synthetic polymeric fibers are present on a dry weight basis in the lower acquisition layer  54  in an amount from about 20% to about 10% by weight of the lower acquisition layer  54 . 
     According to a certain embodiment, the lower acquisition layer  54  desirably has a high fluid uptake capability. Fluid uptake is measured in grams of absorbed fluid per gram of absorbent material and is expressed by the value of “maximum uptake.” A high fluid uptake corresponds therefore to a high capacity of the material and is beneficial, because it ensures the complete acquisition of fluids to be absorbed by an acquisition material. According to exemplary embodiments, the lower acquisition layer  54  has a maximum uptake of about 10 g/g. 
     A relevant attribute of the upper acquisition layer  54  is its Median Desorption Pressure, MDP. The MDP is a measure of the capillary pressure that is required to dewater the lower acquisition layer  54  to about 50% of its capacity at 0 cm capillary suction height under an applied mechanical pressure of 0.3 psi. Generally, a relatively lower MDP may be useful. The lower MDP may allow the lower acquisition layer  54  to more efficiently drain the upper acquisition material. Without wishing to be bound by theory, a given distribution material may have a definable capillary suction. The ability of the lower acquisition layer  54  to move liquid vertically via capillary forces will be directly impacted by gravity and the opposing capillary forces associated with desorption of the upper acquisition layer. Minimizing these capillary forces may positively impact the performance of the lower acquisition layer  54 . However, in a certain embodiment the lower acquisition layer  54  may also have adequate capillary absorption suction in order to drain the layers above (upper acquisition layer  52  and topsheet  18 , in particular) and to temporarily hold liquid until the liquid can be partitioned away by the absorbent core components. Therefore, in a certain embodiment, the lower acquisition layer  54  may have a minimum MDP of greater than 5 cm. Further, according to exemplary embodiments, the lower acquisition layer  54  has an MDP value of less than about 20.5 cm H 2 O, or less than about 19 cm H 2 O, or less than about 18 cm H 2 O to provide for fast acquisition. 
     The methods for determining MDP and maximum uptake are disclosed in U.S. patent application Ser. No. 11/600,691 (Flohr et al.). For example, according to a first embodiment, the lower acquisition layer  54  may comprise about 70% by weight of chemically cross-linked cellulose fibers, about 10% by weight polyester (PET), and about 20% by weight untreated pulp fibers. According to a second embodiment, the lower acquisition layer  54  may comprise about 70% by weight chemically cross-linked cellulose fibers, about 20% by weight lyocell fibers, and about 10% by weight PET fibers. According to a third embodiment, the lower acquisition layer  54  may comprise about 68% by weight chemically cross-linked cellulose fibers, about 16% by weight untreated pulp fibers, and about 16% by weight PET fibers. In one embodiment, the lower acquisition layer  54  may comprise from about 90-100% by weight chemically cross-linked cellulose fibers. 
     Suitable non-woven materials for the upper and lower acquisition layers  52  and  54  include, but are not limited to SMS material, comprising a spunbonded, a melt-blown and a further spunbonded layer. In certain embodiments, permanently hydrophilic non-wovens, and in particular, nonwovens with durably hydrophilic coatings are desirable. Another suitable embodiment comprises a SMMS-structure. In certain embodiments, the non-wovens are porous. 
     In certain embodiments, suitable non-woven materials may include, but are not limited to synthetic fibers, such as PE, PET, and PP. As polymers used for nonwoven production may be inherently hydrophobic, they may be coated with hydrophilic coatings. One way to produce nonwovens with durably hydrophilic coatings, is via applying a hydrophilic monomer and a radical polymerization initiator onto the nonwoven, and conducting a polymerization activated via UV light resulting in monomer chemically bound to the surface of the nonwoven as described in co-pending U.S. Patent Publication No. 2005/0159720. Another way to produce nonwovens with durably hydrophilic coatings is to coat the nonwoven with hydrophilic nanoparticles as described in co-pending applications U.S. Pat. No. 7,112,621 to Rohrbaugh et al. and in PCT Application Publication WO 02/064877. 
     Typically, nanoparticles have a largest dimension of below 750 nm. Nanoparticles with sizes ranging from 2 to 750 nm may be economically produced. An advantage of nanoparticles is that many of them can be easily dispersed in water solution to enable coating application onto the nonwoven, they typically form transparent coatings, and the coatings applied from water solutions are typically sufficiently durable to exposure to water. Nanoparticles can be organic or inorganic, synthetic or natural. Inorganic nanoparticles generally exist as oxides, silicates, and/or, carbonates. Typical examples of suitable nanoparticles are layered clay minerals (e.g., LAPONITE™ from Southern Clay Products, Inc. (USA), and Boehmite alumina (e.g., Disperal P2™ from North American Sasol. Inc.). According to a certain embodiment, a suitable nanoparticle coated non-woven is that disclosed in the co-pending patent application Ser. No. 10/758,066 entitled “Disposable absorbent article comprising a durable hydrophilic core wrap” to Ekaterina Anatolyevna Ponomarenko and Manias NMN Schmidt. 
     Further useful non-wovens are described in U.S. Pat. No. 6,645,569 to Cramer et al., U.S. Pat. No. 6,863,933 to Cramer et al., U.S. Pat. No. 7,112,621 to Rohrbaugh et al., and co-pending patent application Ser. No. 10/338,603 to Cramer et al. and Ser. No. 10/338,610 to Cramer et al. 
     In some cases, the nonwoven surface can be pre-treated with high energy treatment (corona, plasma) prior to application of nanoparticle coatings. High energy pre-treatment typically temporarily increases the surface energy of a low surface energy surface (such as PP) and thus enables better wetting of a nonwoven by the nanoparticle dispersion in water. 
     Notably, permanently hydrophilic non-wovens are also useful in other parts of an absorbent article. For example, topsheets and absorbent core layers comprising permanently hydrophilic non-wovens as described above have been found to work well. 
     According to a certain embodiment, the upper acquisition layer  52  may comprise a material that provides good recovery when external pressure is applied and removed. Further, according to a certain embodiment, the upper acquisition layer  52  may comprise a blend of different fibers selected, for example from the types of polymeric fibers described above. In some embodiments, at least a portion of the fibers may exhibit a spiral-crimp which has a helical shape. In some embodiments, the upper acquisition layer  52  may comprise fibers having different degrees or types of crimping, or both. For example, one embodiment may include a mixture of fibers having about 8 to about 12 crimps per inch (cpi) or about 9 to about 10 cpi, and other fibers having about 4 to about 8 cpi or about 5 to about 7 cpi. Different types of crimps include, but are not limited to a 2D crimp or “flat crimp” and a 3D or spiral-crimp. According to a certain embodiment, the fibers may include bi-component fibers, which are individual fibers each comprising different materials, usually a first and a second polymeric material. It is believed that the use of side-by-side bi-component fibers is beneficial for imparting a spiral-crimp to the fibers. 
     The upper acquisition layer  52  may be stabilized by a latex binder, for example a styrene-butadiene latex binder (SB latex), in a certain embodiment. Processes for obtaining such lattices are known, for example, from EP 149 880 (Kwok) and US 2003/0105190 (Diehl et al.). In certain embodiments, the binder may be present in the upper acquisition layer  52  in excess of about 12%, about 14% or about 16% by weight. For certain embodiments, SB latex is available under the trade name GENFLO™ 3160 (OMNOVA Solutions Inc.; Akron, Ohio). 
     The absorbent core  14  in  FIGS. 1-8A  generally is disposed between the topsheet  18  and the backsheet  20  and comprises two layers, a first absorbent layer  60  and a second absorbent layer  62 . As best shown in  FIG. 3 , the first absorbent layer  60  of the absorbent core  14  comprises a substrate  64 , an absorbent particular polymer material  66  on the substrate  64 , and a thermoplastic composition  68  on the absorbent particulate polymer material  66  and at least portions of the first substrate  64  as an adhesive for covering and immobilizing the absorbent particulate polymer material  66  on the first substrate  64 . According to another embodiment illustrated in  FIG. 4 , the first absorbent layer  60  of the absorbent core  14  may also include a cover layer  70  on the thermoplastic composition  68 . The absorbent core  14  may also include another layer  69  of thermoplastic composition on the first substrate  64  for anchoring the absorbent particulate polymer material  66  to the first substrate  64 . 
     Likewise, as best illustrated in  FIG. 2 , the second absorbent layer  62  of the absorbent core  14  may also include a substrate  72 , a thermoplastic composition  73  on the substrate, an absorbent particulate polymer material  74  adhered to the second substrate  72  with the thermoplastic composition, and a thermoplastic composition  66  on the absorbent particulate polymer material  74  and at least a portion of the second substrate  72  or first layer of thermoplastic composition for immobilizing the absorbent particulate polymer material  74  on the second substrate  72 . Although not illustrated, the second absorbent layer  62  may also include a cover layer such as the cover layer  70  illustrated in  FIG. 4 . 
     The substrate  64  of the first absorbent layer  60  may be referred to as a dusting layer and has a first surface  78  which faces the backsheet  20  of the diaper  10  and a second surface  80  which faces the absorbent particulate polymer material  66 . Likewise, the substrate  72  of the second absorbent layer  62  may be referred to as a core cover and has a first surface  82  facing the topsheet  18  of the diaper  10  and a second surface  84  facing the absorbent particulate polymer material  74 . The first and second substrates  64  and  72  may be adhered to one another with adhesive about the periphery to form an envelope about the absorbent particulate polymer materials  66  and  74  to hold the absorbent particulate polymer material  66  and  74  within the absorbent core  14 . 
     According to a certain embodiment, the substrates  64  and  72  of the first and second absorbent layers  60  and  62  may be a non-woven material, such as those nonwoven materials described above. In certain embodiments, the non-wovens are porous and in one embodiment has a pore size of about 32 microns. 
     As illustrated in  FIGS. 1-8A , the absorbent particulate polymer material  66  and  74  is deposited on the respective substrates  64  and  72  of the first and second absorbent layers  60  and  62  in small and large clusters  90  and  91  of particles to form a grid pattern  92  comprising land areas  94  and junction areas  96  between the land areas  94 . As defined herein, land areas  94  are areas where the thermoplastic adhesive material does not contact the nonwoven substrate or the auxiliary adhesive directly; junction areas  96  are areas where the thermoplastic adhesive material does contact the nonwoven substrate or the auxiliary adhesive directly. The junction areas  96  in the grid pattern  92  contain little or no absorbent particulate polymer material  66  and  74 . The land areas  94  and junction areas  96  can have a variety of shapes including, but not limited to, circular, oval, square, rectangular, triangular, and the like. 
     The grid pattern shown in  FIG. 8A  is a square grid with regular spacing and size of the land areas. Other grid patterns including hexagonal, rhombic, orthorhombic, parallelogram, triangular, rectangular, and combinations thereof may also be used. The spacing between the grid lines may be regular or irregular. 
     The size of the land areas  94  in the grid patterns  92  may vary. According to certain embodiments, the width  119  of the land areas  94  in the grid patterns  92  ranges from about 8 mm to about 12 mm. In a certain embodiment, the width of the land areas  94  is about 10 mm. The junction areas  96 , on the other hand, in certain embodiments, have a width or larger span of less than about 5 mm, less than about 3 mm, less than about 2 mm, less than about 1.5 mm, less than about 1 mm, or less than about 0.5 mm. 
     The small clusters  90  of absorbent particulate polymer material  66  and  74  are thinner than the large clusters  91  of absorbent particulate polymer material  66  and  74  and impart a lower basis weight of absorbent particulate polymer material  66  and  74  to the area of the absorbent core  14  in which the small clusters  90  are located. Likewise, the large clusters  91  of absorbent particulate polymer material  66  and  74  are thicker than the small clusters  90  of absorbent particulate polymer material  66  and  74  and impart a higher basis weight of absorbent particulate polymer material  66  and  74  to the area of the absorbent core  14  in which the large clusters  91  are located. This creates a varied profile of absorbent particulate polymer material across the absorbent core  14 . 
     As shown in  FIG. 8A , the absorbent core  14  has a longitudinal axis  100  extending from a rear end  102  to a front end  104  and a transverse axis  106  perpendicular to the longitudinal axis  100  extending from a first edge  108  to a second edge  110 . The grid pattern  92  of absorbent particulate polymer material clusters  90  and  91  is arranged on the substrates  64  and  72  of the respective absorbent layers  60  and  62  such that the grid pattern  92  formed by the arrangement of land areas  94  and junction areas  96  forms a pattern angle  112 . The pattern angle  112  may be greater than 0, or 15 to 30 degrees, or from about 5 to about 85 degrees, or from about 10 to about 60 degrees, or from about 15 to about 30 degrees from the longitudinal axis  100  of the absorbent core  14 . 
     As best seen in  FIGS. 7 and 8A , the first and second layers  60  and  62  may be combined to form the absorbent core  14 . The absorbent core  14  has an absorbent particulate polymer material area  114  bounded by a pattern length  116  and a pattern width  118 . The extent and shape of the absorbent particulate polymer material area  114  may vary depending on the desired application of the absorbent core  14  and the particular absorbent article in which it may be incorporated. In a certain embodiment, however, the absorbent particulate polymer material area  114  extends substantially entirely across the absorbent core  14 , such as is illustrated in  FIG. 8A . 
     The first and second absorbent layers  60  and  62  may be combined together to form the absorbent core  14  such that the grid patterns  92  of the respective first and second absorbent layers  62  and  64  are offset from one another along the length and/or width of the absorbent core  14 . The respective grid patterns  92  may be offset such that the absorbent particulate polymer material  66  and  74  is substantially continuously distributed across the absorbent particulate polymer area  114 . In a certain embodiment, absorbent particulate polymer material  66  and  74  is substantially continuously distributed across the absorbent particulate polymer material area  114  despite the individual grid patterns  92  comprising absorbent particulate polymer material  66  and  74  discontinuously distributed across the first and second substrates  64  and  72  in clusters  90  and  91 . In a certain embodiment, the grid patterns may be offset such that the land areas  94  of the first absorbent layer  60  face the junction areas  96  of the second absorbent layer  62  and the land areas of the second absorbent layer  62  face the junction areas  96  of the first absorbent layer  60 . When the land areas  94  and junction areas  96  are appropriately sized and arranged, the resulting combination of absorbent particulate polymer material  66  and  74  is a substantially continuous layer of absorbent particular polymer material across the absorbent particulate polymer material area  114  of the absorbent core  14  (i.e. first and second substrates  64  and  72  do not form a plurality of pockets, each containing a cluster  90  of absorbent particulate polymer material  66  therebetween). In a certain embodiment, respective grid patterns  92  of the first and second absorbent layer  60  and  62  may be substantially the same. 
     In a certain embodiment as illustrated in  FIGS. 1-8A , the amount of absorbent particulate polymer material  66  and  74  may vary along the width  116  of the grid pattern  92  substantially perpendicularly to the longitudinal axis  36  of disposable absorbent diaper  10 . In a certain embodiment, the grid pattern may be divided into absorbent zones  120   a ,  121   a  and  122   a , or another number of zones, in which the amount of absorbent particulate polymer material  66  and  74  per unit area of the absorbent core  14  varies from zone to zone. As used herein, “absorbent zone” refers to a region of the absorbent particulate polymer material area having boundaries that are perpendicular to the longitudinal axis shown in  FIG. 8A . The amount of absorbent particulate polymer material  66  and  74  may, in a certain embodiment, gradually transition from one of the plurality of absorbent zones  120   a ,  121   a , and  122   a  to another. This gradual transition in amount of absorbent particulate polymer material  66  and  74  may reduce the possibility of cracks forming in the absorbent core  14 . 
     In the embodiment illustrated in  FIGS. 1-8A  the first and second side absorbent zones  120   a  and  122  are spaced from one another and extend substantially parallel to the longitudinal axis  36  of the diaper  10  and the central absorbent zone  121   a  extends substantially along the longitudinal axis and between the first and second side absorbent zones  120   a  and  122   a . The absorbent particulate polymer material  66  and  74  present in the first and second side absorbent zones  120  and  122  of the absorbent core  14  has a basis weight greater than the basis weight of the absorbent particulate polymer material  66  and  74  present in the central absorbent zone  121   a  of the absorbent core  14 . According to a certain embodiment, the basis weight of the absorbent particulate polymer material  66  and  74  present in the first and second side absorbent zones  120   a  and  122   a  of the absorbent core  14  is greater than the basis weight of the absorbent particulate polymer material  66  and  74  in the central absorbent zone  121   a  the absorbent core  14 . 
     In the embodiment illustrated in  FIGS. 1-8A , the absorbent particulate polymer material  66  and  74  in the central absorbent zone  121   a  of the absorbent core  14  has a higher basis weight than in the first and second side absorbent zones  120   a  and  122   a  of the absorbent core  14 . When the absorbent core  14  according to this embodiment is subjected to a flush of liquid directed at the central absorbent zone  121   a , liquid that flows over and past the central absorbent zone  121   a  contacts the side absorbent zones  120   a  and  122   a . The first and second side absorbent zones  120   a  and  122   a  have more absorbent particulate polymer material and have greater capacity to absorb such liquid and deter flow of the liquid beyond the side absorbent zones  120  and  122  to prevent leakage. 
     Although the embodiment illustrated in  FIGS. 1-8A  has only three absorbent zones  120 ,  121   a , and  122   a , the absorbent diaper  10  may include any number of absorbent zones having varying basis weights of absorbent particulate polymer. Furthermore, in other embodiments, the absorbent particulate polymer material  66  and  74  may be varied in different patterns such as by placing more absorbent particulate polymer material in the central absorbent zone  121   a  than in the side absorbent zone  120   a  and  122   a  or alternating areas of greater and lesser amounts of absorbent particulate polymer material per unit area of the absorbent core. 
     In  FIG. 8A , the areas of greater absorbent particulate polymer material basis weight  120   a  and  122   a  are substantially parallel and continuous and the absorbent core  14  is substantially rectangular. In certain embodiments, areas of greater absorbent particulate polymer material basis weight may have other shapes such as curved or be intermittent, or both. Furthermore, in certain embodiments, the absorbent core may have different shapes including but not limited to hourglass, oval, round, square and triangular.  FIG. 8B  shows an embodiment comprising continuous areas of greater absorbent particulate polymer material basis weight  120   b  and  122   b  curved inwardly so as to form a concave pattern and adjacent areas of lower absorbent particulate polymer material basis weight  121   b .  FIG. 8C  shows an embodiment comprising continuous areas of greater absorbent particulate polymer material basis weight  120   c  and  122   c  curved inwardly so as to form an hourglass pattern and a central area of lower absorbent particulate polymer material basis weight  121   c .  FIG. 8D  shows an embodiment comprising continuous areas of greater absorbent particulate polymer material basis weight  120   d  and  122   d  curved outwardly so as to form a convex pattern and adjacent areas of lower absorbent particulate polymer material basis weight  121   d .  FIG. 8E  shows an embodiment comprising substantially straight parallel areas of greater absorbent particulate polymer material basis weight  120   e  and  122   e  and adjacent areas of lower absorbent particulate polymer material basis weight  121   e , the parallel areas of greater absorbent particulate polymer material basis weight  120   e  and  122   e  having a length shorter than that of the adjacent areas of lower absorbent particulate polymer material basis weight  121   e .  FIG. 8F  shows an embodiment comprising substantially straight parallel intermittent areas of greater absorbent particulate polymer material basis weight  120   f  and  122   f  and adjacent areas of lower absorbent particulate polymer material basis weight  121   f.    
     Another embodiment of an absorbent core  14 ′ is illustrated in  FIG. 9  and the basis weight of the absorbent particulate polymer material  66  and  74  varies across the absorbent core  14 ′ in a direction substantially parallel to the longitudinal axis  36 . This absorbent core  14 ′ comprises first and second end absorbent zones  123  and  124 , spaced form one another and extending substantially perpendicular to the longitudinal axis of the absorbent core, and a central absorbent zone  125 , extending substantially along the longitudinal axis  36  and between the first and second end absorbent zones  123  and  124 . The basis weight of the absorbent particulate polymer material in the absorbent end zones  123  and  124  of the absorbent core  14 ′ is greater than in the central absorbent zone  125  of the absorbent core  14 ′. In this embodiment, the basis weight of the absorbent particulate polymer material  66  and  74  in the first and second end absorbent zones  123  and  124  of the absorbent core  14 ′ is greater than the basis weight of the absorbent particulate polymer material  66  and  74  in the central absorbent zone  125  of the absorbent core  14 ′. When the absorbent core  14 ′ illustrated in  FIG. 9  is subjected to a flush of liquid directed at the central absorbent zone  125 , liquid that flows past the central absorbent zone  125  encounters end absorbent zones  123  and  124  which have greater capacity to absorb and hold such liquid. 
     Although the absorbent core  14 ′ illustrated in  FIG. 9  has only three absorbent zones  123 ,  124 , and  125 , the absorbent core  14 ′ may include any number of absorbent zones arranged in a variety of different patterns of varying absorbent particulate polymer material basis weights. In other embodiments, the basis weight of the absorbent particulate polymer material  66  and  74  in the central absorbent zone  125  may be greater than in the end absorbent zones  123  and  124  or the absorbent core  14 ′ may include a multitude of alternating absorbent zones of varying absorbent particulate polymer material basis weights. 
     Another embodiment of an absorbent core  14 ″ is illustrated in  FIG. 10  and comprises first and second side absorbent zones  120 ′ and  122 ′ spaced from one another and extending substantially parallel to the longitudinal axis  36 , first and second end absorption zones  123 ′ and  124 ′ spaced from one another and extending substantially perpendicularly to the longitudinal axis  36 , and a central portion  121 ′ and  125 ′ extending substantially along the longitudinal axis  36  and between the first and second side absorbent zones  120 ′ and  122 ′ and between the first and second end absorbent zones  123 ′ and  124 ′. The basis weight of the absorbent particulate polymer material  66  and  74  in the first and second side portions  120 ′ and  122 ′ of the absorbent core  14 ″ is greater than the basis weight of the absorbent particulate polymer material  66  and  74  in the central portion  121 ′ and  125 ′ of the absorbent core  14 ″ and the basis weight of the absorbent particulate polymer material  66  and  74  in the first and second end portions  123 ′ and  124 ′ of the absorbent core  14 ″ is greater than the basis weight of the absorbent particulate polymer material  66  and  74  in the central portion  121 ′ and  125 ′ of the absorbent core  14 ″. When the absorbent core  14 ″ illustrated in  FIG. 10  is subjected to a rush of liquid directed at the central absorbent zone  121 ′ and  125 ′, liquid that flows past the central absorbent zone  121 ′ and  125 ′ encounters and may be absorbed by the side absorbent zones  120 ′ and  122 ′ and the end absorbent zones  123 ′ and  124 ′ which all have greater absorbent particulate polymer material basis weights. As with the other embodiments described hereinabove, it should be understood that the absorbent particulate polymer material  66  and  74  may be arranged in a variety of different patterns of varying absorbent particulate polymer material basis weights. In one such embodiment, the central absorbent zone  121 ′ and  125 ′ may have a higher absorbent particulate polymer material basis weight than the side absorbent zones  120 ′ and  122 ′ and the end absorbent zones  123 ′ and  124 ′. 
     The amount of absorbent particulate polymer material  66  and  74  present in the absorbent core  14  may vary, but in certain embodiments, is present in the absorbent core in an amount greater than about 80% by weight of the absorbent core, or greater than about 85% by weight of the absorbent core, or greater than about 90% by weight of the absorbent core, or greater than about 95% by weight of the core. In a particular embodiment, the absorbent core  14  consists essentially of the first and second substrates  64  and  72 , the absorbent particulate polymer material  66  and  74 , and the thermoplastic adhesive composition  68  and  76 . In an embodiment, the absorbent core  14  may be substantially cellulose free. 
     According to certain embodiments, the weight of absorbent particulate polymer material  66  and  74  in at least one freely selected first square measuring 1 cm×1 cm may be at least about 10%, or 20%, or 30%, 40% or 50% higher than the weight of absorbent particulate polymer material  66  and  74  in at least one freely selected second square measuring 1 cm×1 cm. In a certain embodiment, the first and the second square are centered about the longitudinal axis. 
     The absorbent particulate polymer material area, according to an exemplary embodiment, may have a relatively narrow width in the crotch area of the absorbent article for increased wearing comfort. Hence, the absorbent particulate polymer material area, according to an embodiment, may have a width as measured along a transverse line which is positioned at equal distance to the front edge and the rear edge of the absorbent article, which is less than about 100 mm, 90 mm, 80 mm, 70 mm, 60 mm or even less than about 50 mm. 
     It has been found that, for most absorbent articles such as diapers, the liquid discharge occurs predominately in the front half of the diaper. The front half of the absorbent core  14  should therefore comprise most of the absorbent capacity of the core. Thus, according to certain embodiments, the front half of said absorbent core  14  may comprise more than about 60% of the superabsorbent material, or more than about 65%, 70%, 75%, 80%, 85%, or 90% of the superabsorbent material. 
     In certain embodiments, the absorbent core  14  may further comprise any absorbent material that is generally compressible, conformable, non-irritating to the wearer&#39;s skin, and capable of absorbing and retaining liquids such as urine and other certain body exudates. In such embodiments, the absorbent core  14  may comprise a wide variety of liquid-absorbent materials commonly used in disposable diapers and other absorbent articles such as comminuted wood pulp, which is generally referred to as airfelt, creped cellulose wadding, melt blown polymers, including co-form, chemically stiffened, modified or cross-linked cellulosic fibers, tissue, including tissue wraps and tissue laminates, absorbent foams, absorbent sponges, or any other known absorbent material or combinations of materials. The absorbent core  14  may further comprise minor amounts (typically less than about 10%) of materials, such as adhesives, waxes, oils and the like. 
     Exemplary absorbent structures for use as the absorbent assemblies are described in U.S. Pat. No. 4,610,678 (Weisman et al.); U.S. Pat. No. 4,834,735 (Alemany et al.); U.S. Pat. No. 4,888,231 (Angstadt); U.S. Pat. No. 5,260,345 (DesMarais et al.); U.S. Pat. No. 5,387,207 (Dyer et al.); U.S. Pat. No. 5,397,316 (LaVon et al.); and U.S. Pat. No. 5,625,222 (DesMarais et al.). 
     In a certain embodiment best illustrated in  FIG. 2 , the elasticized leg cuffs  24  may comprise absorbent particulate polymer material  126  which may be laid down directly of the elasticized legs cuffs  24  in the same manner as the absorbent particulate polymer material  66  is laid down on first substrate  64  (described below) or may be formed on a separate substrate and added later. 
     The thermoplastic adhesive material  68  and  76  may serve to cover and at least partially immobilize the absorbent particulate polymer material  66  and  74 . In one embodiment of the present invention, the thermoplastic adhesive material  68  and  76  can be disposed essentially uniformly within the absorbent particulate polymer material  66  and  74 , between the polymers. However, in a certain embodiment, the thermoplastic adhesive material  68  and  76  may be provided as a fibrous layer which is at least partially in contact with the absorbent particulate polymer material  66  and  74  and partially in contact with the substrate layers  64  and  72  of the first and second absorbent layers  60  and  62 .  FIGS. 3, 4, and 7  show such a structure, and in that structure, the absorbent particulate polymer material  66  and  74  is provided as a discontinuous layer, and a layer of fibrous thermoplastic adhesive material  68  and  76  is laid down onto the layer of absorbent particulate polymer material  66  and  74 , such that the thermoplastic adhesive material  68  and  76  is in direct contact with the absorbent particulate polymer material  66  and  74 , but also in direct contact with the second surfaces  80  and  84  of the substrates  64  and  72 , where the substrates are not covered by the absorbent particulate polymer material  66  and  74 . This imparts an essentially three-dimensional structure to the fibrous layer of thermoplastic adhesive material  68  and  76 , which in itself is essentially a two-dimensional structure of relatively small thickness, as compared to the dimension in length and width directions. In other words, the thermoplastic adhesive material  68  and  76  undulates between the absorbent particulate polymer material  68  and  76  and the second surfaces of the substrates  64  and  72 . 
     Thereby, the thermoplastic adhesive material  68  and  76  may provide cavities to cover the absorbent particulate polymer material  66  and  74 , and thereby immobilizes this material. In a further aspect, the thermoplastic adhesive material  68  and  76  bonds to the substrates  64  and  72  and thus affixes the absorbent particulate polymer material  66  and  74  to the substrates  64  and  72 . Thus, in accordance with certain embodiments, the thermoplastic adhesive material  68  and  76  immobilizes the absorbent particulate polymer material  66  and  74  when wet, such that the absorbent core  14  achieves an absorbent particulate polymer material loss of no more than about 70%, 60%, 50%, 40%, 30%, 20%, 10% according to the Wet Immobilization Test described herein. Some thermoplastic adhesive materials will also penetrate into both the absorbent particulate polymer material  66  and  74  and the substrates  64  and  72 , thus providing for further immobilization and affixation. Of course, while the thermoplastic adhesive materials disclosed herein provide a much improved wet immobilization (i.e., immobilization of absorbent material when the article is wet or at least partially loaded), these thermoplastic adhesive materials may also provide a very good immobilization of absorbent material when the absorbent core  14  is dry. The thermoplastic adhesive material  68  and  76  may also be referred to as a hot melt adhesive. 
     Without wishing to be bound by theory, it has been found that those thermoplastic adhesive materials which are most useful for immobilizing the absorbent particulate polymer material  66  and  74  combine good cohesion and good adhesion behavior. Good adhesion may promote good contact between the thermoplastic adhesive material  68  and  76  and the absorbent particulate polymer material  66  and  74  and the substrates  64  and  72 . Good cohesion reduces the likelihood that the adhesive breaks, in particular in response to external forces, and namely in response to strain. When the absorbent core  14  absorbs liquid, the absorbent particulate polymer material  66  and  74  swells and subjects the thermoplastic adhesive material  68  and  76  to external forces. In certain embodiments, the thermoplastic adhesive material  68  and  76  may allow for such swelling, without breaking and without imparting too many compressive forces, which would restrain the absorbent particulate polymer material  66  and  74  from swelling. 
     In accordance with certain embodiments, the thermoplastic adhesive material  68  and  76  may comprise, in its entirety, a single thermoplastic polymer or a blend of thermoplastic polymers, having a softening point, as determined by the ASTM Method D-36-95 “Ring and Ball”, in the range between 50° C. and 300° C., or alternatively the thermoplastic adhesive material may be a hot melt adhesive comprising at least one thermoplastic polymer in combination with other thermoplastic diluents such as tackifying resins, plasticizers and additives such as antioxidants. In certain embodiments, the thermoplastic polymer has typically a molecular weight (Mw) of more than 10,000 and a glass transition temperature (Tg) usually below room temperature or −6° C.&gt;Tg&lt;16° C. In certain embodiments, typical concentrations of the polymer in a hot melt are in the range of about 20 to about 40% by weight. In certain embodiments, thermoplastic polymers may be water insensitive. Exemplary polymers are (styrenic) block copolymers including A-B-A triblock structures, A-B diblock structures and (A-B)n radial block copolymer structures wherein the A blocks are non-elastomeric polymer blocks, typically comprising polystyrene, and the B blocks are unsaturated conjugated diene or (partly) hydrogenated versions of such. The B block is typically isoprene, butadiene, ethylene/butylene (hydrogenated butadiene), ethylene/propylene (hydrogenated isoprene), and mixtures thereof. 
     Other suitable thermoplastic polymers that may be employed are metallocene polyolefins, which are ethylene polymers prepared using single-site or metallocene catalysts. Therein, at least one comonomer can be polymerized with ethylene to make a copolymer, terpolymer or higher order polymer. Also applicable are amorphous polyolefins or amorphous polyalphaolefins (APAO) which are homopolymers, copolymers or terpolymers of C2 to C8 alpha olefins. 
     In exemplary embodiments, the tackifying resin has typically a Mw below 5,000 and a Tg usually above room temperature, typical concentrations of the resin in a hot melt are in the range of about 30 to about 60%, and the plasticizer has a low Mw of typically less than 1,000 and a Tg below room temperature, with a typical concentration of about 0 to about 15%. 
     In certain embodiments, the thermoplastic adhesive material  68  and  76  is present in the form of fibers. In some embodiments, the fibers will have an average thickness of about 1 to about 50 micrometers or about 1 to about 35 micrometers and an average length of about 5 mm to about 50 mm or about 5 mm to about 30 mm. To improve the adhesion of the thermoplastic adhesive material  68  and  76  to the substrates  64  and  72  or to any other layer, in particular any other non-woven layer, such layers may be pre-treated with an auxiliary adhesive. 
     In certain embodiments, the thermoplastic adhesive material  68  and  76  will meet at least one, or several, or all of the following parameters: 
     An exemplary thermoplastic adhesive material  68  and  76  may have a storage modulus G′ measured at 20° C. of at least 30,000 Pa and less than 300,000 Pa, or less than 200,000 Pa, or between 140,000 Pa and 200,000 Pa, or less than 100,000 Pa. In a further aspect, the storage modulus G′ measured at 35° C. may be greater than 80,000 Pa. In a further aspect, the storage modulus G′ measured at 60° C. may be less than 300,000 Pa and more than 18,000 Pa, or more than 24,000 Pa, or more than 30,000 Pa, or more than 90,000 Pa. In a further aspect, the storage modulus G′ measured at 90° C. may be less than 200,000 Pa and more than 10,000 Pa, or more than 20,000 Pa, or more then 30,000 Pa. The storage modulus measured at 60° C. and 90° C. may be a measure for the form stability of the thermoplastic adhesive material at elevated ambient temperatures. This value is particularly important if the absorbent product is used in a hot climate where the thermoplastic adhesive material would lose its integrity if the storage modulus G′ at 60° C. and 90° C. is not sufficiently high. 
     G′ is measured using a rheometer as schematically shown in  FIG. 9  for the purpose of general illustration only. The rheometer  127  is capable of applying a shear stress to the adhesive and measuring the resulting strain (shear deformation) response at constant temperature. The adhesive is placed between a Peltier-element acting as lower, fixed plate  128  and an upper plate  129  with a radius R of e.g., 10 mm, which is connected to the drive shaft of a motor to generate the shear stress. The gap between both plates has a height H of e.g., 1500 micron. The Peltier-element enables temperature control of the material (+0.5° C.). The strain rate and frequency should be chosen such that all measurements are made in the linear viscoelastic region. 
     The absorbent core  14  may also comprise an auxiliary adhesive layer  69 . The auxiliary adhesive may be deposited on the first and second substrates  64  and  72  of the respective first and second absorbent layers  60  and  62  before application of the absorbent particulate polymer material  66  and  74  for enhancing adhesion of the absorbent particulate polymer materials  66  and  74  and the thermoplastic adhesive material  68  and  76  to the respective substrates  64  and  72 . The auxiliary glue  69  may also aid in immobilizing the absorbent particulate polymer material  66  and  74  and may comprise the same thermoplastic adhesive material as described hereinabove or may also comprise other adhesives including but not limited to sprayable hot melt adhesives, such as H.B. Fuller Co. (St. Paul, Minn.) Product No. HL-1620-B. The auxiliary glue may be applied to the substrates  64  and  72  by any suitable means, but according to certain embodiments, may be applied in about 0.5 to about 1 mm wide slots spaced about 0.5 to about 2 mm apart. 
     The cover layer  70  shown in  FIG. 4  may comprise the same material as the substrates  64  and  72 , or may comprise a different material. In certain embodiments, suitable materials for the cover layer  70  are the non-woven materials, typically the materials described above as useful for the substrates  64  and  72 . 
     Method and Apparatus for Making Absorbent Articles 
     A printing system  130  for making an absorbent core  14  in accordance with an embodiment of this invention is illustrated in  FIG. 12  and may generally comprise a first printing unit  132  for forming the first absorbent layer  60  of the absorbent core  14  and a second printing unit  134  for forming the second absorbent layer  62  of the absorbent core  14 . 
     The first printing unit  132  may comprise a first auxiliary adhesive applicator  136  for applying an auxiliary adhesive  69  to the substrate  64 , which may be a nonwoven web, a first rotatable support roll  140  for receiving the substrate  64 , a hopper  142  for holding absorbent particulate polymer material  66 , a printing roll  144  for transferring the absorbent particulate polymer material  66  to the substrate  64 , and a thermoplastic adhesive material applicator  146  for applying the thermoplastic adhesive material  68  to the substrate  64  and the absorbent particulate polymer 66 material thereon. 
     The second printing unit  134  may comprise a second auxiliary adhesive applicator  148  for applying an auxiliary adhesive  73  to the second substrate  72 , a second rotatable support roll  152  for receiving the second substrate  72 , a second hopper  154  for holding the absorbent particulate polymer material  74 , a second printing roll  156  for transferring the absorbent particulate polymer material  74  from the hopper  154  to the second substrate  72 , and a second thermoplastic adhesive material applicator  158  for applying the thermoplastic adhesive material  76  to the second substrate  72  and the absorbent particulate polymer material  74  thereon. 
     The printing system  130  also includes a guide roller  160  for guiding the formed absorbent core from a nip  162  between the first and second rotatable support rolls  140  and  152 . 
     The first and second auxiliary applicators  136  and  148  and the first and second thermoplastic adhesive material applicators  146  and  158  may be a nozzle system which can provide a relatively thin but wide curtain of thermoplastic adhesive material. 
     Turning to  FIG. 13 , portions of the first hopper  142 , first support roll  140 , and first printing roll  144  are illustrated. As also shown in  FIG. 16 , the first rotatable support roll  140 , which has the same structure as the second rotatable support roll  152 , comprises a rotatable drum  164  and a peripheral vented support grid  166  for receiving the first substrate  64 . 
     As also illustrated in  FIG. 14 , the first printing roll  144 , which has the same structure as the second printing roll  156 , comprises a rotatable drum  168  and a plurality of absorbent particulate polymer material reservoirs  170  and  171  in a peripheral surface  172  of the drum  168 . The reservoirs  170  and  171 , best illustrated in  FIG. 15 , may have a variety of shapes, including cylindrical, conical, or any other shape. The reservoirs  170  and  171  may lead to an air passage  174  in the drum  168  and comprise a vented cover  176  for holding adhesive particulate polymer material  66  in the reservoir and preventing the adhesive particulate polymer material  66  from falling or being pulled into the air passage  174 . 
     The first printing roll  144  is designed to produce a certain embodiment like the absorbent core  14  illustrated in  FIG. 5  wherein side absorbent zones  120  and  122  have a higher basis weight of absorbing particulate polymer material  66  and  74  than the central absorbent zone  121 . In the embodiment illustrated in  FIG. 14 , this effect may be achieved by having a corresponding set of reservoirs  170  which are relatively deep and a second set  171  of reservoirs which are relatively shallow, such that the deeper reservoirs  170  carry more absorbent particulate polymer material and deliver more absorbent particulate polymer material  66  to the side absorbent zones  120  and  122  and the more shallow reservoirs  171  hold less adhesive particulate polymer material and deliver less absorbent particulate polymer material  66  to the central zone  121  of the absorbent core  14 . The sets of deeper and shallower reservoirs  170  and  171 , of course, can be arranged in any variety of patterns or configurations to create an absorbent core  14  with any corresponding variety of varying absorbent particulate polymer material basis weights across the absorbent core  14 .  FIG. 15 , in particular, illustrates the difference in volumetric sizes of first and second sets of reservoirs  170  and  171 . 
     Other methods of delivering a varying profile of absorbent particulate polymer basis weights to the absorbent core  14  includes, but is not limited to, applying a higher vacuum in sections of the first and second rotatable support rolls  140  and  152  where more absorbent particulate polymer material is desired or, when the absorbent particulate polymer material is delivered to the absorbent core substrate  64  pneumatically, such as when combining cellulosic fibers with absorbent particulate polymer material, directing the air stream carrying the absorbent particulate polymer material and cellulosic fibers to areas of the absorbent core substrate where a higher basis weight of absorbent particulate polymer material is desired. 
     In operation, the printing system  130  receives the first and second substrate  64  and  72  into the first and second printing units  132  and  134 , respectively, the first substrate  64  is drawn by the rotating first support roll  140  past the first auxiliary adhesive applicator  136  which applies the first auxiliary adhesive to the first substrate  64  in a pattern such as described hereinabove. A vacuum (not shown) within the first support roll  140  draws the first substrate  64  against the vertical support grid  166  and holds the first substrate  64  against the first support roll  140 . This presents an uneven surface on the first substrate  64 . Due to gravity, or by using the vacuum means, the substrate  64  will follow the contours of the uneven surface and thereby the substrate  64  will assume a mountain and valley shape. The absorbent particulate polymer material  66  may accumulate in the valleys presented by the substrate  64 . The first support roll  140  then carries the first substrate  64  past the rotating first printing roll  144  which transfers the absorbent particulate polymer material  66  from the first hopper  142  to the first substrate  64  in the grid pattern  92  which is best illustrated in  FIGS. 5 and 6 . A vacuum (not shown) in the first printing roll  144  may hold the absorbent particulate polymer material  66  in the reservoirs  170  until time to deliver the absorbent particulate polymer material  66  to the first substrate  64 . The vacuum may then be released or air flow through the air passages  174  may be reversed to eject the absorbent particulate polymer material  66  from the reservoirs and onto the first substrate  64 . The absorbent particulate polymer material  66  may accumulate in the valleys presented by the substrate  64 . The support roll  140  then carries the printed first substrate  64  past the thermoplastic adhesive material applicator  136  which applies the thermoplastic adhesive material  68  to cover the absorbent particulate polymer material  66  on the first substrate  64 . 
     Hence, the uneven surface of the vented support grid  166  of the support rolls  140  and  152  determines the distribution of absorbent particulate polymeric material  66  and  74  throughout the absorbent core  14  and likewise determines the pattern of junction areas  96 . 
     Meanwhile, the second rotatable support roll draws the second substrate  72  past the second auxiliary adhesive applicator  148  which applies an auxiliary adhesive to the second substrate  72  in a pattern such as is described hereinabove. The second rotatable support roll  152  then carries the second substrate  72  past the second printing roll  156  which transfers the absorbent particulate polymer material  74  from the second hopper  154  to the second substrate  72  and deposits the absorbent particulate polymer material  74  in the grid pattern  92  on the second substrate  72  in the same manner as described with regard to the first printing unit  132  above. The second thermoplastic adhesive material applicator  158  then applies the thermoplastic adhesive material  76  to cover the absorbent particulate polymer material  74  on the second substrate  72 . The printed first and second substrates  64  and  72  then pass through the nip  162  between the first and second support rolls  140  and  152  for compressing the first absorbent layer  60  and second absorbent layer  62  together to form the absorbent core  14 . 
     In an optional further process step a cover layer  70  may be placed upon the substrates  64  and  72 , the absorbent particulate polymer material  66  and  74 , and the thermoplastic adhesive material  68  and  76 . In another embodiment, the cover layer  70  and the respective substrate  64  and  72  may be provided from a unitary sheet of material. The placing of the cover layer  70  onto the respective substrate  64  and  72  may then involve the folding of the unitary piece of material. 
       FIGS. 17-19  illustrate certain embodiments of printing rolls  144 ′ and  144 ″ for making corresponding embodiments of absorbent cores  14 ′ and  14 ″ illustrated in  FIGS. 9 and 10 , respectively. As shown in  FIGS. 17 and 18 , the printing roll  144 ′ for making the absorbent core  14 ′ illustrated in  FIG. 9  comprises sets of deeper and shallower reservoirs  170 ′ and  171 ′ for forming the end absorbent zones  123  and  124 , which have a higher absorbent particulate polymer material basis weight, and the central absorbent zone  125 , which has a lower absorbent particulate polymer material basis weight, respectively. Likewise, the printing roll  144 ″ has sets of deeper and shallower reservoirs  170 ″ and  171 ″, respectively, for forming the side absorbent zones  120 ′ and  122 ′ and end absorbent zones  123 ′ and  124 ′, having a higher basis weight of absorbent particulate polymer material, and the central zone  121 ′ and  125 ′ having a lower basis weight of absorbent particulate polymer material. 
     Absorbent articles such as the diapers  10  made in accordance with embodiments of this invention may be folded and packaged for distribution and sale. Absorbent articles are typically bi-folded, but may also be tri-folded. After folding, the folded absorbent articles may be stacked to form a stack comprising a plurality of absorbent articles. The stack may then be compressed and encased in a packaging material such as a bag, a pouch, a box, or the like. 
     All patents and patent applications (including any patents which issue thereon) assigned to the Procter &amp; Gamble Company referred to herein are hereby incorporated by reference to the extent that it is consistent herewith. 
     The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.” 
     All documents cited in the Detailed Description are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.