Abstract:
A disposable diaper includes a backsheet consisting essentially of an elastic inner layer and an inelastic outer layer made of fibrous material. The inelastic outer layer is joined to the elastic inner layer in its stretched state at a plurality of spots for joining intermittently arranged on the elastic inner layer in its stretched state. In each of areas enclosed by a plurality of intersecting lines each defined by a plurality of the spots for joining closely arranged in succession, the inelastic outer layer is free to float off from the elastic inner layer and thereupon to form a plurality of pleats as the elastic inner layer is made free to contact.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a disposable diaper and more particularly to such a diaper having a plurality of pleats formed by a backsheet thereof.  
           [0002]    It is well known in the art of disposable diapers to make a backsheet thereof from an inner layer of plastic film and an outer layer of nonwoven fabric in order to improve a touch of the diaper. For example, Japanese Laid-Open Utility Model Application No. Hei3-122824 discloses a disposable diaper comprising a backsheet consisting of an elastic outer layer of plastic film or rubber film and an elastic inner layer of nonwoven fabric intermittently joined to each other so that these layers may be elastic for stretch and contraction in the form of a single member.  
           [0003]    However, the nonwoven fabric as the elastic outer layer making a constituent of the known backsheet may often lose a softness peculiar to nonwoven fabrics once it have been joined to the plastic film as the elastic inner layer making another constituent of the backsheet. Consequently, a soft touch required for the diaper is apt to be deteriorated in comparison with the case in which the nonwoven fabric is used independently for the backsheet. Such known backsheet is disadvantageous also from an economical viewpoint, since the elastic nonwoven fabric and film are generally more expensive than those which are inelastic.  
         SUMMARY OF THE INVENTION  
         [0004]    In view of the problems as has been described above, it is a principal object of the invention to provide a disposable diaper having a backsheet having a desired softness as well as an elasticity and being obtainable at a relatively low cost.  
           [0005]    The object set forth above is achieved, according to the invention, by a disposable diaper having a front waist region, a rear waist region and a crotch region therebetween, said diaper comprising a liquid-permeable topsheet, a liquid-impermeable backsheet and a liquid-absorbent core disposed therebetween, wherein:  
           [0006]    said backsheet in at least said front waist region comprises an elastic inner layer and an inelastic outer layer and overlapped with said elastic inner sheet;  
           [0007]    and said elastic inner layer and said inelastic outer layer are joined to each other at a plurality of intermittently arranged spots, with said elastic inner layer being stretched transversely of said diaper so that, in areas enclosed by intersecting lines each described by a plurality of said spots closely arranged in succession, said inelastic outer layer is free to float off from said elastic inner layer and thereupon to form a plurality of pleats as said elastic inner layer is made free to contract transversely of said diaper.  
           [0008]    The disposable diaper according to the invention is characterized by the backsheet at least in the front waist region comprising the elastic inner layer and the inelastic outer layer. The inelastic outer layer floats off from the elastic inner layer as the latter is contracted so as to form a plurality of pleats being convex outward. Such pleats formed by the inelastic outer layer effectively provides the diaper with a comfortable soft touch peculiar to the nonwoven fabric.  
           [0009]    Other and further objects, features and advantages of the invention will appear more fully from the following description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a perspective view showing an embodiment of the disposable diaper according to the invention as partially broken away;  
         [0011]    [0011]FIG. 2 is a diagram showing a part of a backsheet of the diaper;  
         [0012]    [0012]FIG. 3 is a sectional view taken along a line III-III in FIG. 2;  
         [0013]    [0013]FIG. 4 is a fragmentary plan view showing the backsheet as being in its stretched state;  
         [0014]    [0014]FIG. 5 is a fragmentary sectional view showing the backsheet as being in its stretched state; and  
         [0015]    [0015]FIG. 6 is a view similar to FIG. 3 showing a variant of the backsheet. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    [0016]FIG. 1 shows a pull-on or pants type diaper  1  in a perspective view as partially broken away. The diaper  1  is shown in FIG. 1 as contracting transversely of the diaper  1 . The diaper  1  comprises a liquid-permeable topsheet  2  intended to contact the wearer&#39;s skin, a backsheet  3  intended to contact no the wearer&#39;s skin and a liquid-absorbent core  4  disposed between these two sheets  2 ,  3 . The topsheet  2  and the backsheet  3  are put one upon another and bonded to each other by means of hot melt adhesive (not shown) over their portions extending outward beyond a peripheral edge of the absorbent core  4  with which a laminate is formed. This laminate defines a front waist region  6 , a rear waist region  7  and a crotch region  8  extending between these two waist regions  6 ,  7 . The front and rear waist regions  6 ,  7  are put flat and joined together at a plurality of intermittent spots arranged in the vertical direction of the diaper along their transversely opposite side edges so as to define a waist-opening  11  and a pair of leg-openings  12 . These openings  11 ,  12  are provided with circumferentially extending elastic members  13  and  14 , respectively, which are disposed between the topsheet  2  and the backsheet  3 . These elastic members  13 ,  14  are secured with appropriate tensions to inner surface(s) of the topsheet  2  and/or the backsheet  3 . The backsheet  3  consists of an elastic inner layer  3 A being stretchable and contractable and an inelastic outer layer  3 B. Of the front and rear waist regions  6 ,  7  and the crotch region  8 , at least the front waist region  6  has a plurality of spots  21  at which the elastic inner layer  3 A and the inelastic outer layer are joined to each other and a plurality of pleats extending vertically of the diaper  1 .  
         [0017]    [0017]FIG. 2 is a fragmentary plan view showing a portion of the backsheet  3  enclosed by an imaginary line  20  in FIG. 1 and FIG. 3 is a sectional view taken along a line III-III in FIG. 2. The elastic inner layer  3 A is made of at least transversely stretchable and contractable material such as elastomer film of thermoplastic synthetic resin or rubber. FIGS. 2 and 3 show the elastic inner layer  3 A in its contracted state. The inelastic outer layer  3 B is made of substantially unstretchable and uncontactable fibrous material such as inelastic spun bond nonwoven fabric containing thermoplastic synthetic fibers and has a plurality of pleats  22  extending substantially in the vertical direction of the diaper  1 . The elastic inner layer  3 A and the inelastic outer layer  3 B are unitized together by the spots  21  for joining at which a portion of synthetic resin contained in at least one of these layer  3 A,  3 B is molten and then solidified. The spots  21  for joining are arranged closely along imaginary lines extending in predeterminded directions. Referring to FIG. 2, the spots  21  are arranged along a plurality of parallel imaginary lines  26  obliquely rightward ascending and a plurality of parallel imaginary lines  27  obliquely rightward descending. Each pair of adjacent lines  26  and each pair of adjacent lines  27  cross each other to define each lozenge area  28 . In each of the areas  28 , the inelastic outer layer  3 B floats off from the elastic inner layer  3 A so as to form the previously mentioned pleats  22 . While both the configuration and the number of the pleats  22  are indeterminate, the pleats  22  may have one or more crest(s)  29  within each of the areas  28 , as seen in FIG. 3 showing the pleats  22  in a sectional view.  
         [0018]    [0018]FIGS. 4 and 5 show the backsheet  3  being transversely stretched in a plan view and in a sectional view, respectively. The backsheet  3  is stretched as the elastic inner layer  3 A is elastically stretched until the pleats  22  of the inelastic outer layer  3 B are completely unfolded. Thereupon, the backsheet  3  becomes substantially flat as shown and the diaper  1  itself shown in FIG. 1 as transversely contracted becomes also flat. Referring to FIG. 4, the lines  26 ,  27  described by the spots  21  for joining, i.e., the lines  26 ,  27  along which the spots  21  are arranged are inclined at angle of approximately 45° with respect to the horizontal direction. The illustrated embodiment of the backsheet  3  may be obtained in a manner as illustrated by FIGS. 4 and 5. Specifically, an original web of the inner layer  3 A which is elastic for stretch and contraction is stretched at a predeterminded elongation percentage. Then, an original web of the inelastic layer  3 B is placed upon the original web of the inner layer  3 A. The original webs of these layers  3 A,  3 B thus placed one upon another are fed between a pair of thermally embossing rolls to obtain a laminated sheet having the spots  21  for joining of a predeterminded pattern. The backsheet  3  may be cut off from this laminated sheet. The contraction of the elastic inner layer  3 A causes the pleats  22  to be formed in the direction which is orthogonal to the direction in which the elastic inner layer  3 A is contracted. It should be understood that a pattern of the pleats depends on the pattern of the spots  21  for joining.  
         [0019]    With the diaper  1  having the backsheet  3  constructed as has been described above, a comfortable soft touch peculiar to the nonwoven fabric can be maintained in spite of the laminate structure of the backsheet  3  with the plastic or rubber film. It is for the reason that the inelastic outer layer  3 B floats off from the elastic inner layer  3 A in each of the areas  28  so as to form the pleats  22 .  
         [0020]    [0020]FIG. 6 is a view similar to FIG. 3 showing a variant of the backsheet  3  used for the invention. This embodiment of the backsheet  3  comprises, in addition to the elastic inner layer  3 A and the inelastic outer layer  3 B, an inelastic third layer  3 C. The inelastic third layer  3 C is made of material similar to the fibrous material of the inelastic outer layer  3 B, for example, of spun bond nonwoven fabric containing thermoplastic synthetic fibers. The inelastic third layer  3 C is joined to the elastic inner layer  3 A at the spots  21  at which the inner and outer layers  3 A,  3 B are joined to each other. In each of the areas  28 , the inelastic third layer  3 C floats off from the elastic inner layer  3 A in the direction opposite to the inelastic outer layer (downward as viewed in FIG. 6) so as to form pleats  31  having a crest  32 . An apparent thickness corresponding to a dimension between the crests  29 ,  32  presented by the backsheet  3  of such structure in its contracted state is substantially larger than that presented by the backsheet  3  in its stretched state. Such backsheet  3  is comfortably soft and has a high cushioning effect.  
         [0021]    To implement the invention, the elastic inner layer  3 A forming a constituent of the backsheet  3  is preferably made of elastic film having an elastic recovery of 60˜100% after stretched by 30˜100% and a thickness of 0.01˜0.1 mm. The elastic film is preferably used with an elastically deformable tension. The inelastic outer layer  3 B and the inelastic third layer  3 C are preferably made of nonwoven fabric having a basis density of 15˜200 g/m 2 . Size and pattern of the spots  21  for joining may be selected so that they do not substantially affect the elasticity of the elastic inner layer  3 A and can form the pleats  22  providing the diaper  1  with a desired softness. This is achieved, for example, by the spots  21  each having an area of 0.7˜9 mm 2  and spaced apart from the adjacent spot  21  by 1˜5 mm. The lines  26 ,  27  described by the spots  21  successively adjacent one to another may be either straight or curved. In the case of the embodiment shown by FIG. 4, the spots  21  each defined by a circle having a diameter of approximately 1.8 mm are spaced apart one from another by a center-to-center distance of approximately 4 mm so as to form the straight lines  26 ,  27 , respectively. Both each pair of adjacent straight lines  26  and each pair of adjacent straight lines  27  are spaced apart in parallel with each other by approximately 20 mm, respectively. The spots at which the inelastic outer layer  3 B and the inelastic third layer  3 C are joined to the elastic inner layer  3 A, respectively, may be separately provided instead of providing them commonly for the inelastic outer layer  3 B and the inelastic third layer  3 C as shown. Concerning the elastic inner layer  3 A, it is not essential for the elastic inner layer  3 A to cover the diaper  1  entirely. It is also possible to provide it on a part of the diaper  1 , for example, along transversely opposite side edges of the front waist region  6  and/or the rear waist region  7  so as to form the pleats  22  only these regions of the diaper  1 .  
         [0022]    The entire disclosure of Japanese Patent Application No. Hei8-259571 filed on Sep. 30, 1996 including specification, claims, drawings and abstract are incorporated herein by reference in its entirety.  
         [0023]    Having described our invention as related to the embodiments shown in the accompanying drawings, it is our intention that the invention be not limited by any of the details of description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.