Abstract:
The present invention aims to provide a disposable diaper including leak barriers improved in its function to prevent loose passage from infiltrating thereinto and eventually leaching out therethrough. 
     A disposable diaper ( 1 ) is provided with leak barriers ( 21 ) attached to opposite side edges of a crotch region ( 6 ) so that these leak barriers ( 21 ) may raise themselves on an inner sheet ( 3 ). The leak barriers ( 21 ) are formed of a nonwoven fabric made of thermoplastic synthetic fibers having a fineness in a range of 0.5 to 6 dtex and have a specific volume in a range of 9 to 13 cm 3 /g and a thickness in a range of 0.35 to 0.75 mm.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage application under 35 USC 371 of International Application No. PCT/JP2009/052840, filed Feb. 19, 2009, which claims the priority of Japanese Application No. 2008-093139, filed Mar. 31, 2008, the contents of which prior applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to disposable diapers and more particularly to disposable diapers having an improved function to prevent loose passage from leaching out therethrough. 
       BACKGROUND OF THE INVENTION 
       [0003]    In disposable diapers, it is well known to provide the crotch region with the leak barriers attached to its inner side of the crotch region along its opposite side edges so that these leak barriers can be spaced from the inner side of the crotch region. As the measure to improve the leak-barrier efficiency of these barriers, for example, JP 3761896 B1 (PATENT DOCUMENT 1) discloses the invention according to which the hydraulic resistance of these leak barriers is improved by laminating melt blown fibrous layer and spun bonded fibrous layer one on another. 
       SUMMARY OF THE INVENTION 
       [0004]    However, the melt blown fibrous layer is generally formed of densely piled up ultrafine fibers and apt to improve the hydraulic pressure resistance at a cost of breathability of the leak barriers. Furthermore, loose passage generally has a surface tension sufficiently low to infiltrate easily into voids left among thermoplastic synthetic fibers densely piled up in the leak barriers and loose passage might leak out through the barriers. 
         [0005]    In view of the problems as has been described above, it is a principal object of the present invention to provide a disposable diaper including leak barriers improved in its function to prevent loose passage from infiltrating thereinto and eventually leaching out therethrough. 
         [0006]    The object set forth above is achieved, according to the present invention, by an improvement in a disposable diaper having a crotch region, a front waist region extending forward from the crotch region and a rear waist region extending rearward from the crotch region and comprising a liquid-pervious inner sheet, a liquid-impervious outer sheet and a bodily fluid-absorbent structure inclusive of a bodily fluid-absorbent core sandwiched between the inner and outer sheets in the crotch region wherein the crotch region is provided on its inner side along opposite side edges thereof with leak barriers formed of a nonwoven fabric extending across the crotch region further into the front and rear waist regions and adapted to raise themselves on the inner sheet toward diaper wearer&#39;s skin. 
         [0007]    The improvement according to the present invention is characterized in that the nonwoven fabric is formed of thermoplastic synthetic fibers having a fineness in a range of 0.5 to 6 dtex and has a specific volume in a range of 9 to 13 cm 3 /g and a thickness in a range of 0.35 to 0.75 mm. 
         [0008]    In the disposable diaper according to the present invention, the specific volume and the thickness of the nonwoven fabric used to form the leak barriers are appropriately selected and combined with each other to prevent loose passage from leaching out through the leak barriers and at the same time to improve breathability thereof. In this way, the leak-barrier function of the diaper as a whole is improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a partially cutaway perspective view of a disposable diaper according to the present invention. 
           [0010]      FIG. 2  is a sectional view taken along the line II-II in  FIG. 1 . 
           [0011]      FIG. 3  is a schematic diagram illustrating a method to measure a leach rate. 
           [0012]      FIG. 4  is a graphic diagram plotting a measurement result scored on TABLE 1. 
       
    
    
     IDENTIFICATION OF REFERENCE NUMERALS USED IN THE DRAWINGS 
       [0000]    
       
           1  disposable diaper 
           2  inner sheet 
           3  outer sheet 
           4  core 
           5  bodily fluid-absorbent structure 
           6  crotch region 
           7  front waist region 
           8  rear waist region 
           21  leak barrier 
       
     
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Details of the disposable diaper according to the present invention will be more fully understood from the description given hereunder with reference to the accompanying drawings. 
         [0023]      FIG. 1  is a partially cutaway perspective view of the disposable diaper  1 . The diaper  1  comprises a liquid-pervious inner sheet  2 , a liquid-impervious outer sheet  3  and a bodily fluid-absorbent core  4  wherein the diaper  1  has a crotch region  6 , a front waist region  7  defined before the crotch region  6  and a rear waist region  8  defined behind the crotch region  6 . Of the crotch region  6 , the front waist region  7  and the rear waist region  8 , at least the crotch region  6  is occupied by a bodily fluid-absorbent structure  5  formed of the inner and outer sheets  2 ,  3  and the core  4 . The rear waist region  8  is provided on opposite side edges thereof with tape fasteners  13  used to join the front and rear waist regions  7 ,  8  to each other. The inner and outer sheets  7 ,  8  extend outward from a peripheral edge of the core  4  and are put flat and bonded together by hot melt adhesive  14  outside the peripheral edge of the core  4  to form a pair of side flaps  16 , a front end flap  17  and a rear end flap  18 . The front end flap  17  and the rear end flap  18  are respectively provided with waist elastic members  11  attached under tension between the inner sheet  2  and the outer sheet  3  and extending in a transverse direction B of the diaper  1 . Segments of the side flaps  16  extending in the crotch region  6  are respective provided with leg elastic members  12  attached under tension between the inner sheet  2  and the outer sheet  3  and extending in a front-back direction A of the diaper  1 . On an inner side of the diaper  1 , the crotch region  6  is provided along opposite side edges thereof with leak barriers  21 , respectively. These leak barriers  21  extend across the crotch region  6  further into the front waist region  7  and the rear waist regions  8 . Each of these leak barriers  21  has an inner lateral portion  22 , an outer lateral portion  23 , a front end portion  24  and a rear end portion  25  wherein the outer lateral portion  23 , the front end portion  24  and the rear end portion  25  are attached to the inner sheet  2  by hot melt adhesive  26 . The inner lateral portion  22  has its outer end folded to form a sleeve  27  within which an elastic member  28  extend in the front-back direction A under tension. Specifically, at least opposite ends (not shown) of the elastic member  28  are fixed to the inner surface of the sleeve  27  by adhesive. 
         [0024]      FIG. 2  is a sectional view taken along the line II-II in  FIG. 1 . Each of the leak barriers  21  partially attached to the inner side of the diaper  1  in the manner as has been described above has its inner lateral portion  22  lying above the core  4  as viewed in a thickness direction C of the core  4  and adapted to be spaced upward from the inner sheet  2 . The outer lateral portion  23  is attached to the inner side of the associated side flap  16 . Each of the leak barriers  21  additionally has an intermediate portion  29  defined between the inner lateral portion  22  and the outer lateral portion  23 . The intermediate portion  29  cooperates with the inner sheet  2  to form therebetween a pocket  31  adapted to receive body waste and to retain this. 
         [0025]    The elastic members  28  for the leak barriers  21  contract as the diaper  1  is put on the wearer&#39;s body and curved in the front-back direction A. Thereupon the inner lateral portions  22  and the intermediate portions  29  raise themselves on the inner sheet  2  as indicated by imaginary lines in  FIG. 2 . The respective inner lateral portions  22  of the leak barriers  21  raising themselves in this manner come in contact with legs and inguinal region of the wearer (not shown) and thereby prevent bodily fluids from leaking sideways out of the diaper  1 . 
         [0026]    In such diaper  1 , the inner sheet  2  may be formed by liquid-pervious nonwoven fabric and the outer sheet  3  may be formed of a plastic film, a nonwoven fabric or a composite sheet consisting of a plastic film and a nonwoven fabric. The core  4  may be formed by wrapping fluff pulp fibers and/or super-absorbent polymer particles with a tissue paper. The leak barriers  21  may be formed of a nonwoven fabric. 
         [0027]    With this diaper  1  put on the wearer&#39;s body, urine or loose passage flowing on the crotch region  6  in the transverse direction B is prevented by the leak barriers  21  from further flowing. In addition to such primary function, the leak barriers  21  preferably assures an improved breathability and fulfills the other function to prevent loose passage from leaching out of the leak barriers  21 . It should be noted here that a surface tension of loose passage is lower than that of urine and therefore may easily infiltrate into fiber interstices of the nonwoven fabric forming the leak barriers  21 . In consideration of this, the nonwoven fabric to be used as stock material for the leak barriers  21  should be evaluated and selected from the standpoint other than a function of these barriers for blocking undesirable flow of urine. 
         [0028]    TABLE 1 summarizes the results of evaluation tests having been conducted on various types of nonwoven fabrics to determine their propriety as stock material for the leak barriers  21  from the viewpoint as has been described above. In this evaluation test, a spun bonded nonwoven fabric (brevity code: SB or S), a melt blown nonwoven fabric (brevity code: MB or M) and an air-through nonwoven fabric (brevity code: AT) each formed of thermoplastic synthetic fibers having fineness in a range of 0.5 to 6 dtex were combined in various manners to obtain a plurality of nonwoven fabric sheets for evaluation test which were different one from another in thickness and specific volume. On these nonwoven fabric sheets for evaluation test, leach rate of artificial loose passage and breathability were measured and the propriety was determined with respect to each of these nonwoven fabric sheets. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 composi- 
                   
                 basis 
                 specific 
                 leach 
                 breath- 
               
               
                 Sample 
                 tion of non- 
                 thickness 
                 weight 
                 volume 
                 rate 
                 ability (cc/ 
               
               
                 number 
                 woven fabric 
                 (mm) 
                 (g/m 2 ) 
                 (cm 3 /g) 
                 (g/g) 
                 cm 2 *sec) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 SB 
                 0.185 
                 20 
                 9.3 
                 0.58 
                 778 
               
               
                 2 
                 SB 
                 0.403 
                 40 
                 10.1 
                 0.40 
                 389 
               
               
                 3 
                 SB 
                 0.170 
                 18 
                 9.4 
                 0.62 
                 366 
               
               
                 4 
                 SB 
                 0.308 
                 36 
                 8.6 
                 0.52 
                 189 
               
               
                 5 
                 MB 
                 0.356 
                 30 
                 11.9 
                 0.47 
               
               
                 6 
                 MB 
                 0.666 
                 60 
                 11.1 
                 0.32 
               
               
                 7 
                 SB + MB 
                 0.268 
                 28 
                 9.6 
                 0.51 
               
               
                 8 
                 SB + MB 
                 0.526 
                 56 
                 9.4 
                 0.35 
               
               
                 9 
                 SMS 
                 0.790 
                 54 
                 14.6 
                 0.28 
                 72 
               
               
                 10 
                 SMS 
                 1.420 
                 104 
                 13.7 
                 0.02 
                 33 
               
               
                 11 
                 SMS 
                 0.510 
                 29 
                 17.6 
                 0.45 
                 105 
               
               
                 12 
                 SMS 
                 0.850 
                 48 
                 17.7 
                 0.13 
                 45 
               
               
                 13 
                 SMS 
                 0.800 
                 57 
                 14.0 
                 0.20 
                 60 
               
               
                 14 
                 SMS 
                 1.350 
                 114 
                 11.8 
                 0.01 
                 27 
               
               
                 15 
                 SMS 
                 0.450 
                 32 
                 14.1 
                 0.40 
                 63 
               
               
                 16 
                 SMS 
                 0.820 
                 64 
                 12.8 
                 0.12 
                 30 
               
               
                 17 
                 SMS 
                 0.830 
                 60 
                 13.8 
                 0.20 
                 35 
               
               
                 18 
                 SMS 
                 1.450 
                 120 
                 12.1 
                 0.00 
                 17 
               
               
                 19 
                 SMS 
                 0.460 
                 35 
                 13.1 
                 0.36 
                 42 
               
               
                 20 
                 SMS 
                 0.850 
                 70 
                 12.1 
                 0.04 
                 20 
               
               
                 21 
                 SB 
                 0.350 
                 25 
                 14.0 
                 0.52 
                 673 
               
               
                 22 
                 SB 
                 0.600 
                 50 
                 12.0 
                 0.35 
                 276 
               
               
                 23 
                 SMS 
                 0.186 
                 17 
                 10.9 
                 0.58 
                 194 
               
               
                 24 
                 SMS 
                 0.24 
                 26 
                 9.2 
                 0.54 
                 97 
               
               
                 25 
                 AT 
                 0.734 
                 40 
                 18.4 
                 0.32 
                 803 
               
               
                 26 
                 AT 
                 0.718 
                 50 
                 14.4 
                 0.33 
                 684 
               
               
                   
               
             
          
         
       
     
         [0029]    A method of measuring their leach rate, one of evaluation items in TABLE 1, is schematically illustrated by  FIG. 3  and comprises steps of: 
         [0030]    (1) mixing commercially available mayonnaise (made by Q. P. Corporation) with tap water at ratio of 4:1 to produce artificial loose passage, 
         [0031]    (2) collecting about 1 g of artificial loose passage and accurately weighing (Wg) and dropped it onto a middle of a polyethylene film as a low layer, 
         [0032]    (3) weighing filter paper of 100×100 mm (Ag), 
         [0033]    (4) stacking each 150×150 mm of the nonwoven fabric sheet for evaluation, the filter paper and the polyethylene film as a top layer in the order as illustrated on artificial loose passage, 
         [0034]    (5) placing a weight having a bottom surface area of 100×100 mm and weighing 3.5 kg on the polyethylene film as the top layer and left to stand for 30 sec, 
         [0035]    (6) Removing the weight and weighing the filter paper (Bg), and 
         [0036]    (7) calculating a leach rate by the following equation. 
         [0000]    
       
         
           
             
               
                 
                   
                     leach 
                      
                     
                         
                     
                      
                     
                       rate 
                        
                       
                         ( 
                         
                           g 
                            
                           
                             / 
                           
                            
                           g 
                         
                         ) 
                       
                     
                   
                   = 
                   
                     
                       B 
                       - 
                       A 
                     
                     W 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
         [0037]    To measure their breathability, one of the evaluation items indicated in TABLE 1, a breathability resistance value (kPa·s/m) was measured and then the breathablity was calculated from the following equation. 
         [0000]    
       
         
           
             
               
                 
                   
                     breathability 
                      
                     
                       ( 
                       
                         cc 
                          
                         
                           / 
                         
                          
                         
                           cm 
                           2 
                         
                         * 
                         sec 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       124.55 
                       
                         
                           
                             
                               aeration 
                                
                               
                                   
                               
                                
                               resistance 
                               × 
                             
                           
                         
                         
                           
                             1000 
                           
                         
                       
                     
                     × 
                     100 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
         [0038]    On the basis of the leach rate and the breathability measured in the above-mentioned manner, the inventors have found that the nonwoven fabric sheet having a leach rate of 0.50 g/g or less can be determined to be appropriate as stock material for the leak barriers  21  and this leach rate value of 0.50 g/g can be employed as the reference value for determination of the propriety of the leach out preventing ability. With respect to the breathability, the nonwoven fabric sheet having a breathability of 180 cc/cm 2 *sec or higher can be determined to be appropriate for use as the leak barriers  21  since such nonwoven fabric sheet will be substantially free from a problem of stuffiness. Based on such findings, the inventors employed this value as the reference value for determination of the propriety of the breathability. 
         [0039]    In  FIG. 4 , a white circle indicates that the leach rate does not exceed its reference value and the breathability is not less than its reference value and therefore the nonwoven fabric sheet is appropriate for use as the leak barriers. A black circle indicates that the leach rate does not exceed the reference value but the breathability is lower than the reference value and therefore the nonwoven fabric sheet is not appropriate for used as the leak barriers. A while triangle indicates that the breathability is not less than the reference value but the leach rate exceeds the reference value and therefore the nonwoven fabric sheet is not appropriate for use as the leak barriers. A black triangle indicates that the leach rate exceeds the reference value and the breathability is lower than the reference value and therefore the nonwoven fabric sheet is not appropriate for use as the leak barriers. 
         [0040]    As will be apparent from TABLE 1 and  FIG. 4 , the nonwoven fabric sheet having a thickness in a range of 0.35 to 0.75 mm and a specific volume in a range of 9 to 13 cm 3 /g is appropriate as stock material for the leak barriers  21  since such nonwoven fabric sheet has a sufficiently small leach rate and a sufficiently high breathability.