DISPOSABLE ABSORBENT ARTICLES HAVING AN INCREASED FIT FOR THE BODY ANATOMY

Abstract: A tridimensional disposable absorbent article having a body facing surface and a garment facing surface, a longitudinal symmetry plane, a front end edge and a rear end edge, and comprising a liquid pervious topsheet, a backsheet joined to said topsheet and an absorbent core intermediate the backsheet and the topsheet. The absorbent core has a front portion, a central portion and a rear portion, and comprises a longitudinally oriented ridge in the central and rear portion having a profile that provides for an increased body fit.

Description: DISPOSABLE ABSORBENT ARTICLES HAVING AN INCREASED FIT FOR THE BODY ANATOMY FIELD OF THE INVENTION The present invention relates to disposable absorbent articles. Disposable absorbent articles are considered to be absorbent devices designed to be worn externally of the body by a user and to receive fluids discharged from the body. In particular the present invention relates to disposable absorbent sanitary napkins, catamenials, incontinence inserts, and pantiliners that are capable of providing enhanced fit for the body and reduced leakage by matching the non-planar surfaces and the non-linear grooves of the body. The disposable absorbent articles comprises an absorbent core having a front portion, a central portion and a rear portion, and comprise a longitudinally oriented ridge in the central and rear portions having a slope that decreases rearwardly. BACKGROUND OF THE INVENTION In their basic form, disposable absorbent articles comprise an absorbent core interposed between a pervious body-contacting element (alternatively referred to as a topsheet or an overwrap) and an impervious protective barrier (alternatively referred to as a backsheet). The absorbent element is, of course, intended to receive and contain the fluids discharged from the body. The body-contacting element is intended to provide comfortable and dry-feeling contact with body surfaces while allowing free passage of fluids therethrough into the absorbent element. The protective barrier is intended to prevent the fluids which are expelled or which escape from the absorbent element from soiling the user's garments. Major disadvantages of known disposable absorbent articles intended to be worn externally of the body, e.g. leakage, wet/dirty feeling, discomfort, are related to the poor body fit achieved by these articles that are either substantially flat prior to use and must then be squeezed or folded into the right shape to follow the body surface, or, alternatively, are shaped before use, but still need improvement in order to get a better fit with the complex shapes of the user's anatomy. Moreover, most known disposable absorbent articles are intended to be applied to the panty, and typically fixed to it by an adhesive, before wearing the panty with the applied absorbent article, and this does not facilitate a good fit with the body anatomy, also owing to differences in wearing habits and in panty styles. With respect to sanitary napkins, different attempts have been made in order to provide such articles with the capability of conforming to the body anatomy. Body conforming sanitary napkins are well known in the art, both those that are flat prior to use, and that are intended to shape or mold in use to match the wearer's anatomy, and those that are shaped prior to use. Sanitary napkins that are generally cupped or boat-shaped and that are intended to catch menses as it runs or drips from the vaginal orifice are known, such as those disclosed e.g. in U.S. Pat. No. 4,655,759, entitled "Reduced leakage menstrual pad with built-in fold lines", Romans-Hess et al., issued on April 7, 1987. A second known type of design includes sanitary napkins that are raised upwardly or humped in their medial portions so as to be near or in contact with the pudendal region when worn, such as for example those described in U.S. Patent No. 4,701 ,177, entitled "Three-dimensional shaped feminine pad with narrow, absorbent centre and winged edges", Ellis et al., issued on October 20, 1987. While these types of sanitary napkins do provide some measures of success in absorbing and containing body exudates, they fail to provide a sanitary napkin that closely conforms to and fits the body anatomy of the pudendal region. One attempt to increase the body fitting capability of sanitary napkin has been to combine both the cupped and the humped shape in the same article, typically achieving a sanitary napkin having a concave front portion combined with a raised rear portion, in order to better fit the variations in the anatomy in longitudinal direction. An example of this type of approach is European Patent EP-B-162451 , in which an anatomically conformable labial pad is disclosed, having a substantially flat front portion and a rear portion comprising a longitudinally oriented projection. The labial pad is rather short since it is intended for partial disposition within the vestibule of a wearer, with the rear projection that has to be inserted between the labia majora in order to occlude the vestibule. A somewhat similar type of structure, although for external disposition only, is described in European Patent EP-B-302523, in which a sanitary napkin is described comprising a substantially flat or concave front portion intended to cover externally the area of the pubic mons, and a longitudinally oriented raised peak in the rear portion that should adjust and mold to the inverted-V shape of the rear portion of the labia. Although this type of structure does provide the sanitary napkin with a certain capability to fit and conform to the anatomy of the wearer, it still cannot actually fit the various complex body shapes of the female anatomy that comprise non-linear grooves and non-planar surfaces. The sanitary napkin of EP-B-302523 is provided with its tridimensional shape by folding or molding an initially flat structure; this involves for example that the raised peak in the rear portion has a rectilinear profile when seen in side view, and therefore it fails to conform properly to the corresponding non-linear profile of the anatomy as seen in longitudinal direction. A thin absorbent article, particularly a sanitary napkin, featuring a tridimensional structure with a concave front portion and a raised rear portion is described in International Patent Application WO 93/15700. The article is particularly suited to be packaged in a very compact embodiment, but the resulting tridimensional structure is not very likely to conform to the wearer's anatomy therefore providing comfort and body fitting. It is therefore an object of the present invention to provide a tridimensional disposable absorbent article, particularly a sanitary napkin, that has a structure capable of conforming to the various complex body shapes of the female anatomy comprising non-linear grooves and non-planar surfaces, in order to provide increased body fit and comfort, and reduced leakage. It is another object of the present invention to provide such an article, which is moreover thin. It is a further object of the present invention to provide a disposable absorbent article that can be applied directly to the user's body, preferably with no need of fastening means for attaching the absorbent article to the undergarment. SUMMARY OF THE INVENTION The present invention refers to a tridimensional disposable absorbent article having a body facing surface and a garment facing surface, a longitudinal symmetry plane, a front end edge and a rear end edge, which comprises a liquid pervious topsheet, a backsheet joined to the topsheet and an absorbent core intermediate the topsheet and the backsheet, the absorbent core comprising a front portion, a central portion and a rear portion. The body facing surface defines a line formed by the intersection of the body facing surface with the symmetry plane, the line being present in a Cartesian x-y system lying within the symmetry plane, with the x-axis defined by the two points of intersection of the longitudinal symmetry plane with the front end edge and the rear end edge, and with the body facing surface facing towards positive y values, the line having a first derivative with respect to said Cartesian x-y system. The article is such that at least one value of the first derivative of the line in the central portion of the absorbent core is larger than at least one value of the first derivative of the line in the rear portion of the absorbent core. BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the following drawings: FIG. 1 is a perspective view of one embodiment of a sanitary napkin according to the present invention; FIG. 2 is a cross-sectional view of the sanitary napkin of FIG. 1 on line 2-2; FIG. 3 is a top view of the sanitary napkin of FIG. 1 ; FIG. 4 is a curve taken from an anatomical section of the body of a wearer, which schematically represents the central non linear groove of the female anatomy as seen in lateral direction; FIGS. 5a, 5b, and 5c are cross-sectional views of the sanitary napkin of FIG. 1 on lines 5a-5a, 5b-5b, and 5c-5c, respectively. DETAILED DESCRIPTION OF THE INVENTION This invention relates to tridimensional disposable absorbent articles which exhibit absorbency for bodily fluids, the protection of the user's garments from soiling, and improved physical comfort to the user, which are also easy to produce and to package and which exhibit enhanced fit to the body and better conformability to the wearer's anatomy by being provided with a tridimensional structure capable of matching the non-linear grooves and the non-planar surfaces of the female body. The disposable absorbent articles are described below by reference to a sanitary napkin or catamenial. The term "sanitary napkin", as used herein, refers to an article which is worn by females externally of the body and adjacent to the pudendal region and which is intended to absorb and contain the various body fluids which are discharged from the body (e.g., vaginal discharges, menses, and/or urine) and which is intended to be discarded after a single use. It should be understood, however, that the present invention is also applicable to other feminine hygiene or catamenial pads such as pantiliners, or other absorbent articles such as incontinence pads, and the like. The term "use", as used herein, refers to the period of time that starts when the absorbent article is actually put in contact with the anatomy of the user. The terms "joined" or "affixed", as used herein, encompasses configurations whereby a first member is directly connected to a second member and configurations whereby a first member is indirectly connected to a second member by connecting the first member to intermediate members which in turn are connected to the second member. As used herein, the term "pudendal" refers to the externally visible female genitalia and is limited to the labia majora, the labia minora, the clitoris, and the vestibule. FIG. 1 is a perspective view of a sanitary napkin 20 of the present invention with its tridimensional structure before use, with most of the portion of the sanitary napkin 20 that faces or contacts the wearer, oriented towards the viewer. By saying "before use", it is meant that the sanitary napkin 20 of the present invention is provided with a tridimensional structure before it is actually worn. The sanitary napkin can nevertheless be packaged in a folded flat configuration, being subsequently unfolded to get the tridimensional shape just before wearing it. As better shown in FIG. 2, the sanitary napkin 20 comprises a liquid pervious topsheet 22, a liquid impervious backsheet 23 joined with the topsheet 22, and an absorbent core 24 positioned between the topsheet 22 and the backsheet 23. The sanitary napkin 20 has two surfaces, a body facing or contacting surface 20a and a garment facing or contacting surface 20b. The body contacting surface 20a is intended to be worn adjacent to the body of the wearer while the garment surface 20b is on the opposite side and is intended to be directed towards the undergarment when the sanitary napkin 20 is worn, e.g. placed against it. Corresponding body facing and garment facing surfaces can also be identified in each single layer that constitutes the sanitary napkin 20, e.g., in the absorbent core 24. The sanitary napkin 20 has a longitudinal symmetry plane S. The term "longitudinal", as used herein, refers to a line, axis or direction in the sanitary napkin 20 that is generally aligned with (e.g., approximately parallel to) a vertical plane which bisects a standing wearer into left and right body halves when the sanitary napkin 20 is worn. The symmetry plane S of the sanitary napkin 20 substantially corresponds to this vertical plane that bisects the standing wearer. While it is preferred that the sanitary napkin 20 is exactly divided by the longitudinal symmetry plane S into two symmetrically equal halves, it is not excluded that the two halves be not specular. The term "transverse", as used herein, refers to a direction that is generally perpendicular to the longitudinal symmetry plane S. The term "longitudinally oriented" refers to a direction, as seen in plan view, comprised within ±45 degrees, of the longitudinal symmetry plane S; the term "transversely oriented" similarly refers to any other direction, as seen in plan view. The terms "front" and "rear", as used herein, refer to portions or edges in the sanitary napkin 20 that are oriented towards the front and rear part of the wearer's body, respectively, when the sanitary napkin 20 is being worn. The sanitary napkin 20 has a periphery 30, that is defined by the outer edges of the sanitary napkin 20. The longitudinal edges 31 of the sanitary napkin 20 are aligned with the longitudinal symmetry plane S, and the ends edges of the sanitary napkin 20 comprise a front end edge 32a and a rear end edge 32b. The absorbent core 24 of the sanitary napkin has a front portion 40, a central portion 42 and a rear portion 44, each one preferably corresponding to approximately one third of the total length of the absorbent core 24. Corresponding front, central and rear portions can be respectively identified in the sanitary napkin 20 also. The sanitary napkin 20 of the present invention is tridimensional since it is provided prior to use with a tridimensional structure that is intended to match the complex body shapes of the female anatomy. The tridimensional structure has preferably a structural tridimensionality, by "structural tridimensionality" being meant that the structure cannot be completely flattened onto a flat surface while keeping its integrity, that is, without being in any case e.g. torn, crushed or squeezed. In other words, the tridimensional structure cannot be achieved by simply folding or pleating an initially flat article, but is inherently owned by the absorbent article according to the present invention. The tridimensional sanitary napkin 20 of the present invention has preferably a substantially constant thickness, that is more preferably less than 5 mm; the sanitary napkin can be therefore considered of the thin type. While the topsheet, the backsheet, and the absorbent core may be assembled in a variety of well known configurations (including so called "tube" products or side flap products), FIG. 1 shows a preferred embodiment of the sanitary napkin 20 in which the topsheet 22 and the backsheet 23 have length and width dimensions generally larger than those of the absorbent core 24. The topsheet 22 and the backsheet 23 extend beyond the edges of the absorbent core 24 to thereby form the periphery 30 of the sanitary napkin 20. The topsheet 22 is compliant, soft feeling, and non-irritating to the wearer's skin. Further, the topsheet 22 is liquid pervious, permitting liquid (e.g. menses and/or urine) to readily penetrate through its thickness. A suitable topsheet 22 may be manufactured from a wide range of materials such as woven and nonwoven materials; polymeric materials such as apertured formed thermoplastic films, apertured plastic films, and hydroformed thermoplastic films; porous foams; reticulated foams; reticulated thermoplastic films; and thermoplastic scrims. Suitable woven and nonwoven materials can be comprised of natural fibres (e.g., wood or cotton fibers), synthetic fibres (e.g., polymeric fibres such as polyester, polypropylene, or polyethylene fibres); or from a combination of natural and synthetic fibres. A preferred topsheet comprises an apertured formed film. Apertured formed films are preferred for the topsheet because they are pervious to body fluids and yet non-absorbent and have a reduced tendency to allow liquids to pass back through and rewet the wearer's skin. Thus, the surface of the formed film which is in contact with the body remains dry, thereby reducing body soiling and creating a more comfortable feel for the wearer. Suitable formed films are described in U.S. Pat. No. 3,929,135, issued to Thompson on December 30, 1975; U.S. Pat. No. 4,324,246, issued to Muliane, et al. on April 13, 1982; U.S. Pat. No. 4,342,314, issued to Radel, et al. on August 3, 1982; U.S. Pat. No. 4,463,045, issued to Ahr, et al. on July 31 , 1984; and U.S. Pat. No. 5,006,394, issued to Baird on April 9, 1991. A preferred topsheet for the absorbent article of the present invention is a formed film described in one or more of the above patents and marketed on sanitary napkins by The Procter & Gamble Company of Cincinnati, Ohio as "DRI-WEAVE". In a preferred embodiment of the present invention, the body or exposed surface of the formed film topsheet is hydrophilic so as to help liquid transfer through the topsheet faster than if the body surface were not hydrophilic so as to diminish the likelihood that menstrual fluid will flow off the topsheet rather than flowing into and being absorbed by the absorbent core. In a preferred embodiment, surfactant is incorporated into the polymeric materials of the formed film topsheet such as is described in U.S. Patent Application Serial No. 07/794,745, Aziz et al., filed on November 19, 1991. Alternatively, the body surface of the topsheet can be made hydrophilic by treating it with a surfactant such as is described in U.S. 4,950,254. The absorbent core 24 may be any absorbent means that is capable of absorbing or retaining liquids (e.g., menses and/or urine). The absorbent core 24 may be manufactured in a wide variety of sizes and shapes (e.g., rectangular, oval, hourglass, asymmetric, etc.) and from a wide variety of liquid-absorbent materials commonly used in sanitary napkins and other absorbent articles such as comminuted wood pulp that is generally referred to as airfelt. Examples of other suitable absorbent materials include creped cellulose wadding, modified cross-linked cellulose fibres (such as those described in U.S. Patent No. 5,217,445 issued to Young, et al. on June 8, 1993), capillary channel fibres (that is, fibres having intra-fibre capillary channels such as those described in U.S. Patent No. 5,200,248 issued to Thompson, et al. on April 6, 1993), absorbent foams (such as those described in U.S. Patent No. 5,260,345, issued to DesMarais, et al. on November 9, 1993 and U.S. Patent No. 5,268,244 issued to DesMarais, et al. on December 7, 1993), thermally bonded airlaid materials (such as those material described in U.S. Patent Application Serial No. 08/141 ,156, entitled "Catamenial Absorbent Structures Having Thermally Bonded Layers For Improved Handling of Menstrual Fluids and Their Use In Catamenial Pads Having Improved Fit and Comfort" filed in the name of Richards, et al. on October 21 , 1993), absorbent sponges, synthetic staple fibres, polymeric fibres, hydrogel-forming polymer gelling agents, peat moss, tissue including tissue wraps and tissue laminates, or any equivalent materials or combinations of materials. Suitable absorbent cores comprising foams are described in European Applications 0 598 833, 0 598 823 and 0 598 834. Suitable absorbent cores comprising tissue laminates with particles of hydrogel-forming polymer gelling agents comprised therebetween are described in International Patent Applications WO 94/01069 and WO 95/17868. The configuration and construction of the absorbent core may also be varied (e.g., the absorbent core may have varying caliper zones, e.g., profiled so as to be thicker in the centre), hydrophilic gradients, superabsorbent gradients, or lower density and lower average basis weight acquisition zones; or may comprise one or more layers or structures. The total absorbent capacity of the absorbent core should, however, be compatible with the design leading and the intended use of the sanitary napkin. Further, the size and absorbent capacity of the absorbent core may be varied to accommodate different uses such as incontinence pads, pantiliners, regular sanitary napkins, or overnight sanitary napkins. Preferably the absorbent articles of the present invention are sanitary napkins which are uniform in thickness. The backsheet 23 and the topsheet 22 are positioned adjacent the garment facing surface 20b and the body facing surface 20a, respectively, of the absorbent core 24 and are preferably joined thereto and to each other by attachment means (not shown) such as those well known in the art. For example, the backsheet 23 and/or the topsheet 22 may be secured to the absorbent core 24 or to each other by a uniform continuous layer of adhesive, a patterned layer of adhesive, or an array of separate lines, spirals, or spots of adhesive. Adhesives which have been found to be satisfactory are manufactured by H. B. Fuller Company of St. Paul, Minnesota under the designation HL-1258 or H-2031. The attachment means will preferably comprise an open pattern network of filaments of adhesive as is disclosed in U.S. Patent 4,573,986 entitled "Disposable Waste-Containment Garment", which issued to Minetola, et al. on March 4, 1986. An exemplary attachment means of an open pattern network of filaments comprises several lines of adhesive filaments swirled into a spiral pattern such as illustrated by the apparatus and method shown in U.S. Patent 3,911 ,173 issued to Sprague, Jr. on October 7, 1975; U.S. Patent 4,785,996 issued to Zieker, et al. on November 22, 1978; and U.S. Patent 4,842,666 issued to Werenicz on June 27, 1989. Alternatively, the attachment means may comprise heat bonds, pressure bonds, ultrasonic bonds, dynamic mechanical bonds, or any other suitable attachment means or combinations of these attachment means as are known in the art. The backsheet 23 is impervious to liquids (e.g., menses and/or urine) and is preferably manufactured from a thin plastic film, although other flexible liquid impervious materials can also be used. In use, the backsheet 23 is interposed between the absorbent core 24 and the user's undergarments. The function of the backsheet 23 is to prevent exudates which may be expelled from or which inadvertently bypass the absorbent core 24 from contacting and soiling the user's undergarments. The backsheet 23 can thus comprise a woven or nonwoven material, polymeric films such as thermoplastic films of polyethylene or polypropylene, or composite materials such as a film-coated nonwoven material. Preferably, the backsheet is a polyethylene film having a thickness of from about 0.012 mm to about 0.015 mm. Exemplary polyethylene films are manufactured by Clopay Corporation of Cincinnati, Ohio, under the designation P18-0401 and by Ethyl Corporation, Visqueen Division, of Terre Haute, Indiana, under the designation XP-39385. The backsheet 23 is preferably embossed and/or matte finished to provide a more clothlike appearance. Further, the backsheet 23 may permit vapours to escape from the absorbent core 24 (i.e., it can be breathable) while still preventing exudates from passing through the backsheet 23. As illustrated in FIGS. 1 and 2, the sanitary napkin 20 has before use a tridimensional structure with a longitudinal oriented ridge 50 in the central and rear portions 42, 44 of the absorbent core 24, such that the line of intersection 46 of the longitudinal symmetry plane S with the body facing surface 20a has a slope decreasing rearwardly, i.e. towards the rear end edge 32b, in the central portion 42 and in the rear portion 44 of the absorbent core 24. This can be seen more clearly in FIG. 2, where the longitudinal sectional view of the sanitary napkin 20 shows the line of intersection 46 with its decreasing slope in the central and rear portions 42, 44. The decreasing slope of said line of intersection 46 can be expressed mathematically if said line of intersection 46 is considered in a Cartesian x-y system lying in the symmetry plane S, wherein the x-axis is defined by the two points of intersection of the longitudinal symmetry plane S with the front end edge 32a and the rear end edge 32b of the sanitary napkin 20, substantially corresponding to the points indicated by numerals 32a and 32b in the cross-section view of the sanitary napkin 20 illustrated in FIG. 2, and wherein the body facing surface 20a faces towards positive y values. With respect to this system of axes one can form the first derivative of the line of intersection 46. According to the present invention, the first derivative of this line 46 in the longitudinal direction has at least one value that is larger in the central portion 42 of the absorbent core 24 than at least one value in the rear portion 44 of the absorbent core 24. This includes the preferred case, illustrated in FIGS. 1 and 2, where the intersection line 46 is always inclined upward towards the rear end edge 32b with two different slopes in the central portion 42 and in the rear portion 44, and also alternative embodiments in which, e.g., the line of intersection 46 is inclined upward in the central portion 42 and downward in the rear portion 44. The consecutive values of the first derivative of the line of intersection 46 can decrease continuously towards the rear end edge 32b, implying that the line of intersection 46 has a curved profile with a continuously decreasing slope, or, alternatively, the first derivative can assume different discrete values along the length of the intersection line 46. For example, it can be constant in either the central portion 42, or in the rear portion 44, or in both, the latter being the case of the embodiment illustrated in FIGS. 1 and 2, where the intersection line 46 is formed by two substantially rectilinear portions having constant slopes, with a slope change at a point 48 of the line of intersection 46 positioned where the central portion 42 of the absorbent core 24 merges the rear portion 44. A line of intersection 46 with the above described profile provides the sanitary napkin 20 of the present invention with a longitudinally oriented ridge 50 in the central and rear portions 42, 44 of the absorbent core 24 having a longitudinal non linear profile that is intended to match in use the central non linear groove of the female anatomy extending from the labia majora to the perineum and into the gluteal groove, and having approximately the shape schematically indicated in the corresponding central and rear portions 42', 44' of the curve G illustrated in FIG. 4, where the matching profile of a line of intersection 46 in a sanitary napkin illustrated in FIGS. 1 to 3 is also shown. The profile of the longitudinally oriented ridge 50 as defined by the line of intersection 46 with its slope decreasing rearwardly can provide the sanitary napkin 20 with an improved fit to the wearer's body. In the preferred embodiment illustrated in FIG. 1 , when going from front to rear, the forward portion of the ridge 50, with a substantially constant slope, is intended to fit the groove between the labia majora. The subsequent portion of the ridge 50 that bridges the central and the rear portions 42, 44 of the absorbent core 24, with its change in slope, has a profile that is capable of matching in use the downwardly concave portion of the central non linear groove of the female anatomy in the region going from the rearward part of the labia majora to the perineum, so as to achieve a continuous contact with the body. This provides for a better comfort and for a more effective interception of the fluids as they are released from the body. Finally, the rearward portion of the longitudinally oriented ridge 50, still belonging to the rear portion 44 of the absorbent core 24 and having a constant slope in the embodiment of FIG. 1 , is intended to extend between the buttocks, but owing to its slighter slope, as compared to the forward portion of the ridge, it is capable of contacting the body without causing any stress between the anatomy and this portion of the sanitary napkin, which could in turn cause discomfort, and/or prevent the desired substantially continuous contact between the ridge 50 and the wearer's anatomy along the entire length of the non linear groove extending from the labia majora up to the gluteal groove. In other words, a ridge 50 with a profile having a slope decreasing rearwardly can get further into this non linear groove, as schematically indicated in FIG. 4. The ridge 50 with the profile indicated by the line 46 is in fact capable of following the profile of the groove, indicated by the curve G, by extending past a line, indicated with the dashed line in FIG. 4, that connects two points along the central groove of the body surface where the sanitary napkin has contact with the anatomy, e.g. the two points where the sanitary napkin contacts the body in correspondence of the forward and rearward portions of the ridge. A ridge shaped with a linear profile as those known in the art cannot extend past this line, since such a ridge substantially corresponds to this line, and hence cannot provide a continuous contact with the body along the entire length of the ridge. In the embodiment of the present invention illustrated in FIGS. 1 and 2 the tridimensional sanitary napkin 20 preferably has a low constant thickness that is less than 5 mm, wherein the tridimensional structure is provided without the use of humps or of regions of different thickness, and it is an inherent feature of the sanitary napkin 20, rather than an added feature, achieved e.g. by bending, folding or joining together an initially planar structure. As shown in the embodiment of the present invention illustrated in FIGS. 1 and 2, the front portion 40 of the absorbent core 24 is preferably upwardly concave, in order to better conform to the wearer's anatomy in the region of the mons pubis. The sanitary napkin 20 illustrated in FIGS. 1 and 2 shows a particularly preferred configuration for the front, central and rear portions 40, 42, and 44 of the absorbent core 24. As viewed in transverse section the front, central and rear portions of the absorbent core 24 have respectively a V shape, a W shape, and an inverted V shape, as better shown in FIGS. 5a, 5b, and 5c, where transverse sections of the sanitary napkin 20 taken on lines 5a-5a, 5b-5b, and 5c-5c respectively of FIG. 1 are illustrated. These different shapes provide the sanitary napkin 20 with the further capability of conforming to the wearer's anatomy in a direction substantially perpendicular to the already defined symmetry plane S. The V shape of the front portion 40 and the inverted V shape of the rear portion 44 merge together gradually in the central portion 42, where the resulting W shape is predisposed to fit the area of the labia majora and of the perineum. In use, the longitudinally oriented ridge 50 is intended to fit the longitudinal central groove as above described, while the side portions 52 bent upwardly can match the groin creases, i.e. the two grooves that are formed between the body and the legs, typically in the area where the panty elastics contact the body. In the preferred embodiment of the present invention illustrated in FIGS. 1 and 2 the sanitary napkin 20 is provided with an increased capability of conforming to the wearer's anatomy than that simply given by the known differentiated transverse shaping of the different portions of the absorbent core 24. The tridimensional structure of the sanitary napkin 20 prior to use is such that the width of the angle γ of the inverted V shaped portion increases towards the rear end edge 32b of the sanitary napkin 20 starting from a minimum preferred value at a position corresponding to the merging of the rear portion 44 with the central portion 42 of the absorbent core 24, where it substantially corresponds to the angle β of the central inverted V part of the W shaped central portion 42, which is in turn substantially constant along the entire length of this portion 42. Therefore the rearward portion of the ridge 50, typically positioned in use between the buttocks, can more easily widen its inverted V shape during the wearing of the product without being restrained, so providing the sanitary napkin with a better conformability to the anatomical configuration of the wearer. A similar feature is preferably provided in the V shaped front portion 40 of the absorbent core 24, where the angle α of the V increases its width towards the front end edge 32a of the sanitary napkin 20 from a minimum preferred value at a point corresponding to the merging of the front portion 40 with the central portion 42. This will allow the portion of the sanitary napkin 20 which is closer to the front end edge 32a to more easily flatten in transverse direction during wearing in order to accommodate the relatively flat front part of the mons pubis, while still providing an overall concave shape to effectively follow the surface of the mons pubis. The angles of the V shaped front portion 40 and/or of the inverted V shaped rear portion 44 of the absorbent core 24, and consequently of the entire sanitary napkin 20, can therefore increase towards respective end edges 32a and/or 32b up to values around 180°, in order to better accommodate the anatomy of the wearer without inducing any substantial stress in the structure, thus providing for a better fit and comfort. The preferred feature of the angles increasing towards respective end edges in the V shaped and inverted V shaped portions is achieved by giving the front portion 40 and/or the rear portion 44 of the absorbent core 24 a cup shaped structure with any means known to the man skilled in the art. For example, in the sanitary napkin 20 of the present invention illustrated in FIGS. 1 and 2 this is achieved by cutting away a narrow V shaped portion of material centered along the longitudinal centreline of initially flat front portion 40 and rear portion 44 of the absorbent core 24, and of the topsheet 22 and the backsheet 23 as well, and having substantially the same length of the front portion 40 and of the rear portion 44, and then joining together the cut edges with known means, e.g. by thermobonding, along the junction lines identified as 52 and 54 in FIG. 3. The final tridimensional structure illustrated in FIGS. 1 and 2 is then achieved by suitably bending the non planar sanitary napkin 20, e.g. along lines of preferential bending, formed in the absorbent core 24 by means of e.g. embossments or partial cuts, such as the embossments 56 in FIG. 3, as can be readily determined by the man skilled in the art. The presence of this preferred feature in the sanitary napkin of the present invention illustrated in FIGS. 1 and 2 can be readily ascertained when folding transversely the sanitary napkin 20 in order to superimpose the front portion 40 or the rear portion 44 of the absorbent core over the central portion 42 along a fold line that approximately in the unfolded sanitary napkin corresponds to a line separating respectively the front portion 40 or the rear portion 44 from the central portion 42: in both cases the folding line will show an angle rather than being rectilinear. In an alternative embodiment of the present invention a tridimensional shape similar to that illustrated in FIGS. 1 to 5c can also be achieved by comprising in a disposable absorbent article a resilient insert having the desired shape, e.g. between the backsheet and the absorbent core. The insert can be comprised for example only in the central and rear portions of the absorbent article, where the ridge with the desired profile is to be provided, or can extend along the entire length of the absorbent article, in order to provide its whole shape. The resilient insert can be made of any known suitable material, e.g. absorbent or non absorbent material, and can be produced e.g. by thermoforming to get the desired tridimensional shape, preferably with a constant thickness. The insert can completely provide the tridimensional structure, or can alternatively contribute to create and to maintain said structure in an already shaped absorbent article. In a preferred embodiment of the present invention the tridimensional absorbent article, e.g. the sanitary napkin 20, is applied by the user directly to the body. The tridimensional structure of the absorbent article and its capability to conform and fit the anatomy of the user can allow the article to stay in place during the use possibly with no need for additional means intended to fasten the article to an undergarment. Moreover, the forward portion of the ridge can be easily identified in the sanitary napkin, which makes it possible to use it as a reference to direct the sanitary napkin into its optimal position on the body. Alternatively, the absorbent article of the present invention can be also provided with a panty fastening means, which provides means to attach the article to an undergarment. For example the panty fastening means may comprise a mechanical fastener such as hook and loop fasteners such as marketed under the tradename VELCRO, snaps or holders. Alternatively, the absorbent article is fastened to the undergarment by means of panty fastening adhesive on the backsheet 23. The panty fastening adhesive provides a means for securing the absorbent article to the panty and preferably a means for securing the absorbent article when soiled to the fold and wrap package for convenient disposal. Typically, at least a portion of the garment facing surface of the backsheet 23, preferably a portion corresponding to the front portion of the absorbent core 24 only, is coated with adhesive to form the panty fastening adhesive. Any adhesive or glue used in the art for such purposes can be used for the panty fastening adhesive herein. Pressure sensitive adhesives are most preferred. Suitable adhesives include Century A-305-IV manufactured by the Century Adhesives Corporation of Columbus, Ohio, and Instant LOK 34-2823 manufactured by the National Starch and Chemical Company of Bridgewater, New Jersey, 3 Sigma 3153 manufactured by 3 Sigma and Fuller H-2238ZP manufactured by the H.B. Fuller Co. The panty fastening adhesive is typically applied to the backsheet by slot coating or spraying in various distribution patterns, such as e.g. continuous or discontinuous strips, intermittent dots, random patterns spirals. The panty fastening adhesive is typically covered with a removable release paper or film in order to prevent the adhesive from drying out or adhering to another surface other than the panty prior to use. Any commercially available release paper or film may be used. Suitable examples include BL 30MG-A SILOX El/O and BL 30 MG-A SILOX 4 P/O available from Akrosil Corporation. The absorbent articles of the present invention, particularly the sanitary napkin 20, have a length that can range among the typical values commonly used for different sizes of said sanitary articles intended for substantially external disposition adjacent to the body of the wearer. Particularly, the central and rear portions 42 and 44 of the absorbent core 24 do not have a length which is smaller than the total maximum length of the labia majora of an average user. Other alternative means to provide a disposable absorbent article of the preferred tridimensional structure, other than cutting, joining and folding, as already explained, may be achieved by providing an absorbent article with an extensible, elastic portion that can be deformed to yield a structure equivalent to the preferred one by e.g. stretching it in transverse direction in the central and rear portions of the absorbent core. The tridimensional absorbent article of the present invention may further comprise an odour-control material for controlling unpleasant odours associated with absorbed body fluids. Any known odour-control agent or any combination thereof that can be suitably included in a disposable absorbent article, including other materials such as binders and/or substrates, can be comprised in the absorbent article of the present invention as the odour-control material. The odour-control material can be incorporated into the absorbent article by methods known in the art, for example layered on or into the absorbent core or mixed within the absorbent core. In an alternate embodiment of the present invention, the tridimensional absorbent article may have two flaps (not shown), each of which are adjacent to and extend laterally from the side edge of the absorbent core. The flaps are configured to drape over the edges of the wearer's panties in the crotch region so that the flaps are disposed between the edges of the wearer's panties and the wearer's thighs. The flaps serve at least two purposes. First, the flaps help serve to prevent soiling of the wearer's body and panties by menstrual fluid, preferably by forming a double wall barrier along the edges of the panty. Second, the flaps are preferably provided with attachment means on their garment facing surface so that the flaps can be folded back under the panty and attached to the garment facing side of the panty. In this way, the flaps serve to keep the sanitary napkin properly positioned in the panty. The flaps may be constructed of various materials including materials used for the topsheet 22, backsheet 23, combinations thereof, and may be a laminate having tissue in the centre. Further, the flaps may be a separate element attached to the main body of the tridimensional absorbent article or can comprise extensions of the topsheet 22 and/or backsheet 23. It is recommended, however, that the flaps have a liquid impervious backsheet to prevent body fluids which reach the flaps from soiling the edges of the wearer's panties. Preferred flaps that are suitable or adaptable to the tridimensional absorbent article of the present invention are disclosed in U.S. Pat. No. 4,687,478 issued to Van Tilburg on Aug. 18, 1987; U.S. Pat. No. 4,589,876 issued to Van Tilburg on May 20, 1986; and U.S. Pat No. 4,608,047 issued to Mattingly on Aug. 26, 1986. Optionally, the tridimensional absorbent article may comprise components that naturally wrap the sides of a wearer's panties. Sanitary napkins having components that naturally wrap the sides of a wearer's panties suitable for use with the tridimensional absorbent article of the present invention are disclosed in U.S. Patent Application Serial No. 08/096,121 entitled "Absorbent Article having Panty Covering Components that Naturally Wrap the Sides of Panties", filed July 22, 1993, in the names of Lavash, et al and U.S. Patent Application Serial No. 08/277733 entitled "Absorbent Articles Having Undergarment Covering Components with Zones of Extensibility", filed July 20, 1994, in the names of Weinberger, et al. In further alternate embodiments of the present invention the tridimensional absorbent article can also comprise additional elements, such as an acquisition layer or a secondary topsheet positioned between the topsheet 22 and the absorbent core 24 or, alternatively, in any other suitable position. Although the disposable absorbent article of the present invention has been described with reference to a sanitary napkin, it can be used beneficially in the context of other disposable absorbent articles such as panty liners and incontinence articles. The disposable absorbent article may thus also have all those features and parts which are typical for products in the context of their intended use.

Claims: WHAT IS CLAIMED IS: 1. A tridimensional disposable absorbent article having a body facing surface and a garment facing surface, a longitudinal symmetry plane, a front end edge and a rear end edge, and comprising a liquid pervious topsheet, a backsheet joined to said topsheet and an absorbent core intermediate said topsheet and said backsheet, said absorbent core having a front portion, a central portion and a rear portion, said body facing surface defining a line formed by the intersection of said body facing surface with said symmetry plane, said line being present in a Cartesian x-y system lying within said symmetry plane, with the x-axis defined by the two points of intersection of said longitudinal symmetry plane with said front end edge and said rear end edge, and with said body facing surface facing towards positive y values, said line having a first derivative with respect to said Cartesian x-y system, said article being characterized in that: at least one value of said first derivative of said line in said central portion of said absorbent core is larger than at least one value of said first derivative of said line in said rear portion of said absorbent core. 2. A disposable absorbent article according to claim 1 , characterized in that all values of said first derivative in said central portion are larger than the values of said first derivative in said rear portion. 3. A disposable absorbent article according to any of claims 1 or 2, characterized in that consecutive values of said first derivative in said central and in said rear portions decrease continuously towards said rear end edge. 4. A disposable absorbent article according to claims 1 or 2, characterized in that said first derivative is constant either in said central portion or in said rear portion, or in both. 5. A disposable absorbent article according to any preceding claim, characterized in that said front portion is upwardly concave. 6. A disposable absorbent article according to any preceding claim, characterized in that the transverse section of said article in said front portion is V shaped defining an angle , in said central portion is W shaped defining an angle β, and in said rear portion is inverted V shaped defining an angle γ. 7. A disposable absorbent article according to claim 6, characterized in that the angle α of the V in said front portion increases towards said front end edge. 8. A disposable absorbent article according to claim 6 or claim 7, characterized in that the angle γ of the inverted V in said rear portion increases towards said rear end edge. 9. A disposable absorbent article according to any preceding claim, characterized in that said disposable absorbent article is provided with a structural tridimensionality, wherein said article cannot be completely flattened onto a flat surface while keeping its integrity. 10. A disposable absorbent article according to any preceding claim, characterized in that said disposable absorbent article is a sanitary napkin or a pantiliner and said article has a constant thickness of less than 5 mm.

Inventors: LAVASH BRUCE WILLIAM, WIERLACHER STEFAN ALOIS, LAVASH, BRUCE, WILLIAM, WIERLACHER, STEFAN, ALOIS
Applicants: LAVASH BRUCE WILLIAM, PROCTER & GAMBLE, WIERLACHER STEFAN ALOIS, LAVASH, BRUCE, WILLIAM, THE PROCTER & GAMBLE COMPANY, WIERLACHER, STEFAN, ALOIS
Application year: 1998
Main classification: A61F13
IPC codes: A61F13