Patent Publication Number: US-2009240222-A1

Title: Absorbent article

Description:
TECHNICAL FIELD 
     The present invention relates to an absorbent article suitably applicable to a top sheet (surface material) for a disposable diaper, a sanitary napkin, a panty liner, an incontinence pad, and the like. 
     BACKGROUND ART 
     Heretofore, an absorbent article has been known in which crosswise emboss lines are formed in both end portions of a top sheet in a longitudinal direction, and in which lengthwise emboss lines are formed in an approximately center portion thereof (see Patent Document 1). In such an absorbent article, the lengthwise emboss lines act to spread body fluid in the longitudinal direction, thereby preventing the body fluid from spreading in the cross direction. The crosswise emboss lines act to spread the body fluid in the cross direction, thereby preventing the body fluid from spreading in the longitudinal direction. In this way, the body fluid is prevented from leaking out from the end portions of the absorbent article in both the cross direction and the longitudinal direction. 
     However, since a conventional absorbent article is configured to prevent the body fluid from leaking out by controlling the spreading direction of the body fluid on the surface of its top sheet as described above, the absorbent article fails to keep the spread area of body fluid on the surface of the top sheet small when the body fluid has high viscosity like water-like feces or menstrual blood, and accordingly does not easily pass through the top sheet. 
     The present invention has been made to solve the aforementioned problem, and aims to provide an absorbent article capable of controlling the spread area of body fluid on the surface sheet thereof. 
     Patent Document 1: Japanese Patent Application Publication No. 2004-298271 
     DISCLOSURE OF THE INVENTION 
     An absorbent article according to the present invention includes a surface sheet made of a liquid permeable fiber nonwoven fabric and shaped in a waveform. Fibers constituting the surface sheet are more oriented in a longitudinal direction of the surface sheet than in a cross direction thereof. The waveform is continuously formed in the longitudinal direction, and a top area and a bottom area of the waveform each extend in a direction crossing the longitudinal direction of the surface sheet. A fiber density in a wall area between the top area and the bottom area of the waveform is set lower than a fiber density of the top area or the bottom area. 
     With use of the absorbent article according to the present invention, components in body fluid that easily pass through the surface sheet mainly pass through the surface sheet through the wall area while only high viscosity components thereof remain on the surface sheet. This increases the viscosity of the remaining body fluid, whereby the spread area of the body fluid on the surface sheet can be kept small. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a schematic view showing an overall configuration of a disposable diaper illustrated as an embodiment of the present invention. 
         FIG. 2  is a schematic view showing a cross section configuration along a longitudinal-direction of a top sheet illustrated as the embodiment of the present invention. 
         FIG. 3  is an upper surface view showing a configuration of the top sheet illustrated as the embodiment of the present invention. 
         FIG. 4  is a schematic view showing orientation of fibers in a shape forming region shown in  FIG. 3 . 
         FIG. 5  is a schematic view for explaining a method of manufacturing the top sheet illustrated as the embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A water absorbent article according to the present invention is applicable to a disposal diaper as shown in  FIG. 1 , for example. Hereinafter, a configuration of a disposable diaper illustrated as an embodiment of the present invention will be described with reference to the drawings. It should be noted that an absorbent article according to the present invention is not limited to this embodiment, and is also applicable to a top sheet for, for example, a sanitary napkin, a panty liner, an incontinence pad or the like. 
     [Overall Configuration of Disposable Diaper] 
     As shown in  FIG. 1 , a disposable diaper  1  described as the embodiment of the present invention includes a water absorbent article  2 , and is configured of a front waistband region  3  and a back waistband region  4  in front and back ends thereof in a longitudinal direction and a crotch region  5  located between the front waistband region  3  and the back waistband region  4 . The front waistband region  3  includes wing portions  6  and the back waistband region  4  includes wing portions  7 . The wing portions  6  and  7  each extend in a lateral side direction of the disposable diaper  1 . When the disposable diaper  1  is worn, the wing portions  6 ,  7  overlap each other with the wing portions  6  placed on the inner side and are joined with each other with a tape fastener  8 . 
     Cuffs  10  are formed at both cross direction side portions of the water absorbent article  2  so as to extend in a longitudinal direction along cross direction side edges  2   a  of the water absorbent article  2 . Each of the cuffs  10  is formed by folding back a sheet member  9  that forms a surface layer over the cross direction side portions of the water absorbent article  2  and the wing portions  6 . At a longitudinal direction center portion of the water absorbent article  2 , this cuff  10  is folded and thus formed to project from the surface of the water absorbent article  2  at an approximately constant range (height), and a string-like elastic member  11  is attached to a tip edge  10   a  of each of the cuffs  10  in an elastic state. 
     The attaching of the elastic members  11  causes the tip edges  10   a  of the cuffs  10  to shrink in the longitudinal direction, thereby forming gathers in the cuffs  10 , and also causes a force of pulling both longitudinal direction sides of the water absorbent article  2  toward the center side thereof to act through the cuffs  10 . Thereby, the water absorbent article  2  is provided with tendencies to be bent in the longitudinal direction with the side of a top sheet  21 , which will be described later, facing inward, and to have the cuffs  10  stand like walls at the longitudinal direction center portion of the water absorbent article  2 . 
     At the longitudinal direction center portion of the water absorbent article  2 , a string-like elastic member  12  is provided in a location shifted from a fixed edge of each of the cuffs  12  outwardly in the cross direction of the water absorbent article  2  (toward the cross direction side edge  2   a ). The elastic member  12  is provided in an elastic state so as to extend along the cross direction side edge  2   a  and the fixed edge. The attaching of this elastic member  12  causes the cross direction side portion of the water absorbent article  2  to form gathers. 
     [Configuration of Water Absorbent Article] 
     As shown in  FIG. 2 , the water absorbent article  2  includes: the liquid permeable top sheet (surface sheet)  21  formed of a fiber nonwoven fabric; a liquid impermeable back sheet (back surface sheet)  22  formed of a plastic film, a composite material of a plastic film and a nonwoven fabric, or the like; and a liquid absorbent core (absorber)  23  interposed between the top sheet  21  and the back sheet  22  and joined to at least one of the top sheet  21  and the back sheet  22 . 
     A material usable for the liquid absorbent core  23  is a mixture of particulate or fibrous super absorbent polymer and fluff pulp, a mixture of particulate or fibrous super absorbent polymer, fluff pulp and thermoplastic synthetic resin fiber, or other similar mixtures, the mixtures each being compressed in a desired thickness. In addition, the entire liquid absorbent core  23  is desirably covered with tissue paper in order to prevent deformation thereof and dropping-off of the polymer particles. As the polymer particles, a starch type, a cellulose type, or a synthetic polymer type is usable. 
     [Configuration of Top Sheet] 
     As shown in  FIG. 3 , in the top sheet  21 , multiple shape forming regions R 1  are each formed to extend in the longitudinal direction of the absorbent article, and are arranged in a direction (cross direction) crossing the longitudinal direction of the absorbent article. In each of the shape forming regions R 1 , a waveform composed of a top area T, a bottom area B, and a wall area W between the top area T and the bottom area B is continuously formed in the longitudinal direction, as shown in  FIG. 2 . In addition, as shown in  FIG. 4 , fibers  24  constituting the top sheet  21  are more oriented in the longitudinal direction of the top sheet  21  than in the cross direction. The fibers  24  are formed, for example, by fusion bonding of the fibers in the top area T or the bottom area B, so that the fiber density in the wall area W is lower than the fiber density of the top area T or the bottom area B. Instead, the fibers  24  may be formed by cutting off the fibers or bonding portions of the fibers in the wall area W, so that the fiber density in the wall area W is lower than the fiber density of the top area T or the bottom area B. Otherwise, the fibers  24  may be formed by drawing the fibers in the wall area W to make the fiber diameter in the wall area W smaller (thinner) than the fiber diameter in the top area T and the bottom area B, so that the fiber density in the wall area W is lower than the fiber density of the top area T or the bottom area B. Specifically, the fiber densities in the top area T and the bottom area B are each set within a range of 0.05 [g/cm 3 ] to 0.2 [g/cm 3 ] inclusive, while the fiber density in the wall area W is set within a range of 0.005 [g/cm 3 ] to 0.15 [g/cm 3 ] inclusive. 
     When the waveform composed of the top area T, the bottom area B, and the wall area W is continuously formed in the longitudinal direction of the top sheet  21  as described above, body fluid is more likely to spread along the bottom areas B, whereby the spread direction of the body fluid can be controlled. In addition, when the fiber density in the wall area W is made lower than the fiber density in the top area T or the bottom area B, components of the body fluid that easily pass through the top sheet  21  mainly pass through the top sheet  21  through the wall areas W and only high viscosity components are left on the surface of the top sheet  21 . Thus, the viscosity of the body fluid is so high that the spread area of the body fluid can be kept small. As a result, this leads to a reduction in the area where the body fluid adheres to the skin, and prevents the body fluid from leaking out from the absorbent article. Incidentally, when the fibers in the top area T and the bottom area B are fusion bonded, the fibers are fixed in a manner crossing the orientation direction of the fibers, and the fibers are surely oriented and extend between the adjacent fusion bonded portions. 
     As shown in  FIG. 3 , the shape forming regions R 1  are located in a position shifted to the side of the back waistband region  4 . The top sheet allows low viscosity body fluid such as urine to pass therethrough, but hardly allows high viscosity body fluid such as water-like feces to pass therethrough. In addition, the high viscosity body fluid is highly likely to spread on the back side of the absorbent article. Moreover, in the case where the top sheet is shaped in the waveform as described above, the irritation of the skin increases. Thus, it is desirable to provide the shape forming regions R 1  only to a minimum necessary extent. For these reasons, by locating the shape forming regions R 1  in the position shifted to the side of the back waistband region  4 , the spread area of high viscosity body fluid can be kept small and the irritation of the skin can be minimized. 
     A non-shape forming region R 2  is formed between each adjacent two of the shape forming regions R 1 . The non-shape forming region R 2  extends in the longitudinal direction and has a cross direction dimension of 0.2 [mm] to 0.3 [mm] inclusive. The formation of the non-shape forming region R 2  between the shape forming regions R 1  prevents a situation where the body fluid spreads because the wall areas W in the shape forming regions R 1  are accordion-folded. In addition, this configuration allows the tension of the top sheet  21  to be maintained at the time of manufacturing the top sheet  21 , thereby preventing the top sheet  21  from becoming loose and crinkled. 
     The top area T and the bottom area B each have dimensions within ranges of 0.2 [mm] to 3 [mm] inclusive in the longitudinal direction and of 3 [mm] to 100 [mm] inclusive in the cross direction, and the wall area W has dimensions within ranges of 0.3 [mm] to 5 [mm] inclusive in the longitudinal direction and of 3 [mm] to 100 [mm] inclusive in the cross direction. In addition, the height dimension of the waveform from the bottom portion to the top portion is within a range of 0.3 [mm] to 3 [mm] inclusive. 
     As described above, the fiber densities in the top area T and the bottom area B are higher than the fiber density in the wall area W. For this reason, when the area ratios of the top area T and the bottom area B are set high, the permeability of body fluid is lowered. To avoid this, it is necessary to decrease the area ratio of the wall area W by decreasing the area ratios of the top area T and the bottom area B. The increase in the area ratio of the wall area W, however, leads to reduction in the strength of the top sheet  21 , whereby skin rubbing or the like is more likely to cause tearing of the top sheet  21  or deformation of the waveform. Therefore, the top sheet  21  is desirably formed in the aforementioned dimensions. 
     [Top Sheet Manufacturing Method] 
     The foregoing waveform of the top sheet  21  can be formed by feeding a fiber nonwoven fabric into between rollers  31   a  and  31   b  while applying an appropriate tension to the fiber nonwoven fabric (see  FIG. 5(   a )). On the surface of each of the rollers  31   a  and  31   b , concave and convex patterns, for example, as shown in  FIG. 5(   b ) are formed. The dimensions D 1 , D 2 , and D 3  of the upper extremity, the lower extremity, and the length between each adjacent two of the upper extremities of convex portions  33  of multiple trapezoidal shapes formed in the roller  31   a  in the longitudinal direction and the dimensions D 4 , D 5 , and D 6  of the upper extremity, the lower extremity, and the length between each adjacent two of the upper extremities of convex portions  34  of multiple trapezoidal shapes formed in the roller  31   a  in the cross direction are determined appropriately depending on the dimensions of the waveform and shape forming regions to be formed. Note that, an apparatus shown in  FIG. 5  is configured so that the concave and convex patterns of the rollers  31   a  and  31   b  are meshed with each other, that is, convex portions of the roller  31   a  are respectively meshed with concave portions of the roller  31   b . Thus, the top portions and the bottom portions of the waveform of the top sheet  21  respectively correspond to the concave portions of the roller  31   a  and the convex portions of the roller  31   b . Accordingly, the density of the wall areas in the top sheet  21  can be changed by adjusting the depths and the like of the rollers  31   a  and  31   b  as needed. 
     OTHER EMBODIMENTS 
     Heretofore, the embodiment to which the present invention made by the present inventors is applied has been described. However, the present invention is not limited by the description and the drawings that are provided according to this embodiment and constitute a part of the disclosure of the present invention. For example, a nonwoven fabric may be formed on the surface, at the side of the liquid absorbent core  23 , of the shape forming regions in the top sheet  21 . The nonwoven fabric has a density within a range of 0.005[g/cm 3 ] to 0.10 [g/cm 3 ] inclusive, and thus is more bulky than the top sheet  21 . When the liquid absorbent core is covered with a high density sheet, high viscosity body fluid has nowhere to go even once passing through the top sheet, and thus leaks out to remain on or flow over the top sheet  21 . For this reason, by providing the bulky nonwoven fabric having the density within the range of 0.005 [g/cm 3 ] to 0.10 [g/cm 3 ] inclusive, high viscosity body fluid flows toward the liquid absorbent core  23  after passing through the top sheet  21 , whereby the contact area between the body fluid and the skin can be reduced more easily. 
     Moreover, in this case, a sheet covering the liquid absorbent core  23  and having a density within a range of 0.05 [g/cm 3 ] to 0.25 [g/cm 3 ] inclusive may be provided between the bulky nonwoven fabric and the liquid absorbent core  23 . When the density in the top sheet  21  is lowered, the components of the absorbent core  23  may get out to the surface of the absorbent article  2  through the top sheet  21 . The covering of the liquid absorbent core  23  with the sheet having the density within the range of 0.05 [g/cm 3 ] to 0.25 [g/cm 3 ] inclusive prevents the components of the liquid absorbent core  23  from getting out. Furthermore, to add another word or two, it is obvious that all other embodiments, examples, application techniques and the like made based on the foregoing embodiments by those skilled in the art fall under the category of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to atop sheet (surface material) for a disposable diaper, a sanitary napkin, a panty liner, an incontinence pad or the like.