Abstract:
A topsheet for a disposable wearing article is formed with a plurality of fine openings each having an area of about 0.16-5 mm 2  and a pant of the peripheral edge of each opening us protuberated upward from upper surface of the topsheet. The topsheet is thereby improved so that body fluids can be rapidly absorbed and stuffiness as well as eruption of the wearer&#39;s skin can be reliably avoided.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a topsheet made of nonwoven fabric having a plurality of fine openings suitable for use as a breathable topsheet material or a breathable and liquid-pervious topsheet material in a disposable wearing article such as a disposable diaper, a disposable sanitary napkin, a disposable incontinent pants or a disposable gown used in medical facilities.  
           [0002]    Japanese Patent Application Publication No. 1986-176346A describes a topsheet made of a nonwoven fabric adapted to be used in an absorbent article. This topsheet is formed by thermally fusible hydrophobic fibers having a fiber diameter smaller than 10μ and a basis weight of 10 g/m 2 . The topsheet has an opening ratio of 10-50% and the minimum opening diameter of 0.3-2 mm wherein the fibers are in a melted state around the openings.  
           [0003]    Japanese Patent Application Publication No. 1988-243360A describes a nonwoven fabric having a plurality of fine openings arranged in a given pattern. This nonwoven fabric has a nonwoven fabric region with of circular or elliptic openings a wherein the nonwoven fabric region has a substantially uniform density of fiber and a substantially smooth surface. The nonwoven fabric with the above-described openings is made by applying high pressure water-jets in columnar streams to a fibrous web supported on a cylinder having a plurality of projections in semispherical shape.  
           [0004]    The nonwoven fabric disclosed in each of the above-identified Publication is intended to be used as a liquid-pervious topsheet in disposable wearing article such as a disposable diaper or a sanitary napkin. The openings formed in the nonwoven fabric are a means to enhance transfer and absorption of body fluids into a liquid-absorbent core covered with this nonwoven fabric. However, when a the wearing article using such nonwoven fabric is worn, the nonwoven fabric having a smooth surface and the wearer&#39;s skin may come in close contact with each other so that most of the openings may be closely covered with the wearer&#39;s skin and thereby rapid absorption of body fluids may be obstructed. In addition, such close contact of the nonwoven fabric with the wearer&#39;s skin may often cause stuffiness and eruption of the wearer&#39;s skin.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of this invention to solve such a problem as possibly occurring in a nonwoven fabric made by the prior art when this nonwoven fabric is used as a topsheet of a disposable wearing article.  
           [0006]    There is provided a, according to this invention, a topsheet made of a nonwoven fabric for a disposable wearing article having upper and lower surfaces and formed with a plurality of openings extending through the upper and lower surfaces.  
           [0007]    The topsheet has a substantially uniform thickness and each of the openings has an area of about 0.16-5 mm 2  wherein only a part of the periphery of the opening is increased in thickness compared to the uniform thickness of the topsheet so as to make the openings protuberate upward from the upper surface. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a perspective view showing a partially cutaway sanitary napkin;  
         [0009]    [0009]FIG. 2 is a fragmentary enlarged view of a topsheet;  
         [0010]    [0010]FIG. 3 is a sectional view taken along a line III-III in FIG. 2;  
         [0011]    [0011]FIG. 4 is a view similar to that in FIG. 2, showing another embodiment of the invention.  
         [0012]    [0012]FIG. 5 is a sectional view taken along a line V-V in FIG. 4;  
         [0013]    [0013]FIG. 6 is a sectional view taken along a line VI-VI in FIG. 5;  
         [0014]    [0014]FIG. 7 is a view similar to that in FIG. 5, showing still another embodiment of the invention; and  
         [0015]    [0015]FIG. 8 is a sectional view taken along a line VIII-VIII in FIG. 7. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    Details of a topsheet made of a nonwoven fabric according to this invention will be more fully understood from the description of a sanitary napkin as a one embodiment of this invention given hereunder with reference to the accompanying drawings.  
         [0017]    [0017]FIG. 1 is a perspective view showing a partially cutaway sanitary napkin  1  using a topsheet  2  according to this invention. The napkin  1  comprises the liquid-pervious topsheet  2 , a liquid-impervious backsheet  3  and a liquid-absorbent core  4  disposed between these two sheets  2 ,  3  wherein the top- and backsheets  2 ,  3  extend outward beyond a peripheral edge of the core  4 , overlaid to each other and bonded together water-tight in these respective extensions. The napkin  1  is defined by a longitudinal direction y and a transverse direction x, both orthogonal to the direction of its thickness and configured to be larger in the longitudinal direction y.  
         [0018]    [0018]FIG. 2 is a fragmentary enlarged view of a the topsheet  2 . The topsheet  2  made of a nonwoven fabric has an upper surface  22  intended to come in contact with the skin of the wearer, a lower surface  23  underlying the core  4 , a fibrous zone  11  formed by a plurality of fibers  6  and a plurality of opening zones  12  surrounded by the fibrous zone  11  and extending between the upper and lower surfaces  22 ,  23  (See FIG. 1 also). The fibrous zone  11  has a basis weight of about 10-100 g/m 2  and preferably comprises hydrophobic fibers by about 80-100% by weight and hydrophilic fibers by about 20-0% by weight wherein the hydrophobic fiber is a thermoplastic synthetic fiber having a fineness of about 0.1-10 dtex. Each of the opening zones  12  has an opening area of about 0.16-5 mm 2  and the total area of these opening zones  12  entirely occupies about 2-60% of a surface area of the topsheet  2 . While the plane shapes as well as the layout of the opening zones  12  on the topsheet  2  are not specified, these opening zones  12  are illustrated to be shaped in elliptic which are larger in the longitudinal direction y and arranged substantially at regular intervals in the longitudinal direction as well as in the transverse direction x.  
         [0019]    [0019]FIG. 3 is a sectional view taken along a line III-III in FIG. 2. While the fibrous zone  11  of the topsheet  2  has a substantially uniform thickness p as a whole, a portion of a peripheral edge defining each of the opening zones  12  extending adjacent its lower end  13  (as viewed in FIG. 2) has a thickness q larger than the thickness p so as to form a protuberance  14  gradually rising above the upper surface of the topsheet  2 . The protuberance  14  gradually decreases in thickness along the peripheral edge of the opening zones  12  and along the direction y as viewed in FIG. 2. A range in which the protuberance  14  and its skirt extends along the peripheral edge of the opening zones  12  is preferably equal to about ¼-½ of the entire circumference of the opening zones  12 . In such topsheet  2 , depending on a particular application thereof, its flat region preferably has a thickness p of about 0.01-5 mm and an apparent density of about 0.01-1.5 g/cm 3 . Preferably, the protuberance  14  has a thickness q which is larger than the thickness p by about 0.1-2 mm and an apparent density than the density of the flat region by about 1.0-5 times.  
         [0020]    When the sanitary napkin  1  using such a topsheet  2  is worn, the topsheet  2  comes in contact with the wearer&#39;s skin at crests of each of the protuberances  14  but the opening zones  12  adjacent to the respective protuberance  14  and the plains contiguous to the respective protuberance  14  tend to form a clearance between the topsheet  2  and the wearer&#39;s skin and thereby to prevent the opening zones  12  from being closed by the wearer&#39;s skin. In this way, menstrual discharge can smoothly flow into the respective opening zones  12  and is rapidly transferred to the core  4 . The clearance between the topsheet  2  and the wearer&#39;s skin serves to improve ventilation between the topsheet  2  and the wearer&#39;s skin. With such sanitary napkin  1 , leakage of menstrual discharge as well as stuffiness or eruption can be effectively avoided. The protuberance  14  formed along the peripheral edges of the respective opening zones  12  are particularly effective to prevent the opening zones  12  from being closed by the wearer&#39;s skin. The protuberance  14  is formed on the part of the opening zone&#39;s peripheral edge which lies aside in the longitudinal direction y toward its lower end  13  as viewed in FIG. 2, so air which would otherwise stay between the topsheet  2  and the wearer&#39;s skin can rapidly flow in the longitudinal direction y as well as in the transverse direction x between each pair of the adjacent protuberance  14 ,  14 . It is possible to form the protuberance  14  so as to be put aside in the longitudinal direction y toward the upper end or in the transverse direction x toward one of the side edges of the opening zone&#39;s peripheral edge as viewed in FIG. 2. The protuberance  14  is formed to have a density higher than that in the region extending therearound and it is not apprehended that the shape of the protuberance might be easily deformed when the protuberance is pressed against the wearer&#39;s skin. The napkin  1  gives somewhat dry touch to its wearer even after absorption of menstrual discharge since the fibrous zone  11  of the topsheet  2  is basically formed by  11  hydrophobic thermoplastic synthetic fiber. It should be understood that the fibrous zone  11  of the topsheet  2  may be treated in desired regions such as the lower surface  23  and/or the peripheral edges of the respective opening zones  12  with an appropriate agent to make these regions hydrophilic.  
         [0021]    [0021]FIG. 4 is a view similar to FIG. 2 but showing another embodiment of the invention, FIG. 2 is a sectional view taken along a line V-V in FIG. 4 and FIG. 6 is a sectional view taken along a line VI-VI in FIG. 5. The topsheet  2  according to this embodiment comprises a nonwoven fabric layer  21  having upper and lower surfaces  22 ,  23  and a thermoplastic synthetic resin film layer  24  bonded to the upper surface  22 . The nonwoven fabric layer  21  is similar to the topsheet  2  illustrated by FIG. 2 in that the layer  21  has the fibrous zone  11  and the opening zones  12 . The film layer  24  comprises a plurality of ribbon-like strips  26  spaced from and extending in parallel to one another in one direction, for example, in the longitudinal direction y. These ribbon-like strips  26  are welded or bonded by adhesion to the nonwoven fabric layer  21  and interrupted in the longitudinal direction by the respective opening zones  12 , so the ribbon-like strips  26  do not cover the opening zones  12 . The ribbon-like strips  26  bonded to the nonwoven fabric, particularly to the fibers  6  forming the peripheral walls  27  of the opening zones  12  and the protuberance  14  serve to protect these opening zones  12  and protuberance  14  from getting out of shape during use of the napkin  1 . Each pair of the adjacent ribbon-like strips  26  are preferably connected to each other by bridges  32  extending in the transverse direction x so that a relative movement of these ribbon-like strips  26  can be restrained and a distance between them can be reliably maintained. The translucent or opaque ribbon-like strips  26  may be used to conceal the core  4  which was sailed with menstrual discharge absorbed therein.  
         [0022]    [0022]FIG. 7 is a view similar to FIG. 5 but showing still another embodiment of the invention and FIG. 8 is a sectional view taken along a line VIII-VIII in FIG. 7. In the topsheet  2  according to this embodiment, the film forming the ribbon-like strips  26  is fibrillated along the side edges  28  of the respective ribbon-like strips  26  to form a plurality of fine naps  33  rising toward the direction above the upper surface  22  of the nonwoven fabric layer  21 . Such ribbon-like strips  26  offer velvet-like touch. The ribbon-like strips  26  having the naps  33  on the side edges thereof are similar to those described in Japanese Patent Application Publication No. 2000-225144A and preferably have a thickness of about 0.001-0.05 mm, a width of about 0.03-3 mm and spaced about 0.1-5 mm apart each other. The naps  33  have a height of with 0.02-5 mm and are formed in the longitudinal direction y with a density of about 10-100 naps/cm.  
         [0023]    While this invention has been described above with respect to the sanitary napkin  1 , the topsheet  2  according to this invention is suitable also as the topsheet for other articles such as a disposable diaper, disposable training pants, disposable incontinent pants and a disposable gown used in medical facilities which particularly require breathable topsheets or breathable liquid-pervious topsheets. The nonwoven fabric forming such topsheet  2  may be formed by bonding or mechanically entangling the fibers  6  together. In the napkin  1  illustrated as the one embodiment of this invention, the backsheet  3  comprises the thermoplastic synthetic resin film and the core  4  comprises fluff pulp or a mixture of fluff pulp and high water absorption polymer grains covered with tissue paper  5  (See FIG. 1). For implementation of this invention, a thickness of the nonwoven fabric was measured under a load of 3 g.  
         [0024]    The topsheet according to this invention has a plurality of the protuberances each formed on a part of the opening zone&#39;s peripheral edge, so it is not apprehended that the opening zones might be closed by the wearer&#39;s skin even when these opening zones come in contact with the wearer&#39;s skin. In this way, the liquid-permeability of the opening zones as well as the breathability in the vicinity of these opening zones are reliably ensured.