Abstract:
A disposable diaper includes a backsheet comprising an elastic inner layer and an inelastic outer layer. The elastic inner layer, in a transversely stretched state, is joined to the inelastic outer layer at a plurality of intermittently disposed spots. The spots are lined up to form a series of imaginary lines disposed on a bias between the longitudinal and transverse directions of the disposable diaper. In each of areas between the spots, defined by a plurality of intersecting imaginary lines that pass through a plurality of the spots that are closely arranged in succession, the inelastic outer layer is free to separate from the elastic inner layer upon contraction (relaxation) of the elastic inner layer, and thereupon the outer layer forms a plurality of longitudinal pleats. The pleats, formed by relaxing the transversely stretched inner layer, are disposed in a direction that is substantially normal to the direction of stretching.

Description:
RELATED APPLICATION 
     The present application is a continuation-in-part of application Ser. No. 08/937,515, filed Sep. 25, 1997 now abandoned, entitled “DISPOSABLE DIAPER”. 
    
    
     BACKGROUND THE INVENTION 
     This invention relates to a disposable diaper and more particularly to such a diaper having a plurality of pleats formed by a backsheet thereof. 
     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. Hei 3-122824 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 non woven fabric intermittently joined to each other so that these layers may be in the form of a single member that is elastic for stretch and contraction. 
     However, the woven fabric, in the form of the elastic inner layer constituent of the known backsheet, may often lose the softness that is peculiar to nonwoven fabrics once it has been joined to the plastic film elastic outer layer that is another constituent of the backsheet. Consequently, the soft touch required for the diaper is apt to be deteriorated in comparison with the case in which the nonwoven fabric is used alone 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 that are inelastic. 
     SUMMARY OF THE INVENTION 
     In view of the problems as have been described above, it is a principal object of the invention to provide a disposable diaper having a backsheet having desired softness as well as elasticity and being obtainable at a relatively low cost. 
     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 said backsheet, in at least said front waist region, comprises and elastic inner layer and an inelastic outer layer that is overlapped with said elastic inner layer; and said elastic inner layer and said inelastic outer layer are joined to each other at a plurality of intermittently arranged spots. The inner and outer layer are spot joined together when said elastic inner layer is in a condition of being stretched transversely of said diaper so that, in areas disposed between imaginary intersecting lines that each pass through and are described by a plurality of said spots that are closely arranged in succession, said inelastic outer layer is free to separate from said elastic inner layer and, upon relaxation of stretching of the inner elastic layer, form a plurality of pleats. 
     The disposable diaper according to the invention is characterized by the backsheet that comprises, at least in the front waist region, the described elastic inner layer and the inelastic outer layer. The inelastic outer layer separates from the elastic inner layer as the latter is contracted so as to form a plurality of pleats that are convex away from the inner layer, that is outward. Such pleats formed in the inelastic outer layer effectively provide the diaper with the comfortable soft touch that is peculiar to a nonwoven fabric. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an embodiment of the disposable diaper according to the invention with portions partially broken away; 
         FIG. 2  is a diagram showing a part of a backsheet of the diaper; 
         FIG. 3  is a sectional view taken along a line III—III in  FIG. 2 ; 
         FIG. 4  is a fragmentary plan view showing the backsheet in its stretched state; 
         FIG. 5  is a fragmentary sectional view taken along the line V—V on  FIG. 4  looking in the direction of the arrows and showing the backsheet as being in its stretched state; and 
         FIG. 6  is a view similar to  FIG. 3  showing a variant of the backsheet. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a pull-on or pants type diaper  1  in a perspective view with a portion broken away. The diaper  1  is shown in  FIG. 1  as contracted transversely. The diaper  1  comprises a liquid-permeable topsheet  2  intended to contact the wearer&#39;s skin, a backsheet  3  and a liquid-absorbent core  4  disposed between these two sheets  2 ,  3 . The topsheet  2  and the backsheet  3  are over laid, with the core  4  therebetween, 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  by which a laminated is formed. This laminate defines a front waist region  6 , a rear waist region  7  and a crotch region  8  entering 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 longitudinal direction of the diaper along their transversely opposite side edges  9  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, that are disposed between the topsheet  2  and the backsheet  3 . These elastic members  13 ,  14  are secured under appropriate tension to inner surface(s) of the topsheet  2  and/or the backsheet  3 , the backsheet  3  consists of an elastic inner layer  3 A, that is stretchable and contractible, 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  22  extending longitudinally of the diaper  1 . 
       FIG. 2  is a fragmentary plan view showing a portion of the backsheet  3  enclosed by an imaginary line  20  that is shown 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 contractible material such as elastomer film of thermoplastic synthetic resin or rubber.  FIGS. 2 and 3  show the elastic inner layer  3 A in its relaxed, contracted state. The inelastic outer layer  3 B is made of substantially unstretchable and uncontractible fibrous material, such as inelastic spun bond non woven fabric containing thermoplastic synthetic fibers, and has a plurality of pleats  22  extending substantially in the longitudinal direction of the diaper  1 . The elastic inner layer  3 A and the inelastic outer layer  3 B are joined together at the spots  21  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  are arranged closely along imaginary lines extending in predetermined directions. Referring to FIG.  2 , the spots  21  are arranged along a plurality of substantially parallel imaginary lines  26  ascending obliquely to the right ascending and a plurality of substantially parallel imaginary lines  27  descending obliquely to the right. Each pair of adjacent lines  26  and each pair of adjacent lines  27  cross each other to produce each defined area in the depicted shape of a lozenge  28 . In each of the areas  28 , upon relaxation and contraction of the elastic layer  3 A, portions of the inelastic outer layer  3 B separate from the elastic inner layer  3 A and thereby form the previously mentioned pleats  22 . 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. 
       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  is transversely expanded to also become flat. Referring to  FIG. 4 , the imaginary lines  26 ,  27  passing through the spots  21  i.e., the lines  26 ,  27  along which the spots  21  are arranged, are inclined at angle of approximately 45 degree with respect to the transverse 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 to a predetermined elongation percentage. Then, an original web of the inelastic layer  3 B is placed upon the stretched 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 joined at the spots in a predetermined pattern. The backsheet  3  may be cut out from this laminated sheet. The contraction of the elastic inner layer  3 A causes the pleats  22  to be formed in a direction that is orthogonal to the direction in which the elastic inner layer  3 A is contracted. It should be understood that the pattern of the pleats depends on the pattern of the spots  21 . 
     With the diaper  1 , having a 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. That is because portions the inelastic outer layer  3 B separate from the elastic inner layer  3 A in each of the areas  28  so as to form the pleats  22 . 
       FIG. 6  is a sectional 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 also joined to each other at spots  21 . In each of the areas  28 , the inelastic third layer  3 C separates from the elastic inner layer  3 A in a direction opposite to the inelastic outer layer (downward as viewed in  FIG. 6 ) so as to form pleats  31  having crests  32 . An apparent thickness corresponding to the distance between the crests  29 ,  32  presented by the backsheet  3  of such structure in its contracted state is substantially larger than the thickness presented by the backsheet  3  in its stretched state. Such contracted backsheet  3  is comfortably soft and has a large cushioning effect. 
     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 having been stretched by 30–100%, and a thickness of 0.01–0.1 mm. The elastic film preferably used has 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 bulk density of 15–200 g/m 2 . The size and pattern of the spots  21  may be selected so that they do not substantially affect the elasticity of the elastic inner layer  3 A and can cause the pleats  22  to form, whereby 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 being spaced apart from an adjacent spot  21  by 1–5 mm. The imaginary lines  26 ,  27  described by the spots  21 , and are successively adjacent one to another, may be either straight or curved. In the case of the embodiment shown by  FIG. 4 , the spots  21 , are each defined by a circle having a diameter of approximately 1.8 mm, are spaced apart one from by a center-to-center distance of approximately 4 mm so as to form the imaginary straight lines  26 ,  27 , respectively. Each pair of adjacent imaginary straight lines  26  and each pair of imaginary adjacent straight lines  27  are both 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 as shown in  FIG. 6 . 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  7 , so as to form the pleats  22  in only these regions of the diaper  1 . 
     The entire disclosure of Japanese Patent Application No. Hei 8-259571 filed on Sep. 30, 1996 including specification, claims, drawings and abstract are incorporated herein by reference in its entirety. 
     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 other wise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.