Abstract:
To facilitate a continuous tight fit of a diaper to a wearer, a disposable diaper having one waist opening and a pair of leg openings is provided with: a front-side section; a back-side section; a crotch section; and a pair of extensible or stretchable leg sheets. Longitudinal peripheral edge regions and inner lateral edge regions of the leg sheets are respectively joined, on one side of the crotch section, to lower edge regions of the front-side section and back-side section and lateral edge regions of the crotch section. The leg sheets each have notches facing inward from the outer lateral edges thereof. The pair of leg openings are defined by joining outer lateral edge regions of the leg sheets adjacent to front-side starting ends of the notches, and outer lateral edge regions of the leg sheets adjacent to back-side starting ends of the notches.

Description:
RELATED APPLICATION 
     This application is a 35 U.S.C. §371 national phase filing of International Patent Application No. PCT/JP2012/050111, filed Jan. 5, 2012, through which and to which priority is claimed under 35 U.S.C. §119 to Japanese Patent Application No. 2011-002161, filed Jan. 7, 2011. 
     TECHNICAL FIELD 
     The present invention relates to a disposable diaper. 
     BACKGROUND ART 
     Known in the art is a disposable diaper which is provided with a single torso opening and a pair of leg openings, which disposable diaper is provided with a front part and back part which are separated from each other in the length direction when the diaper is spread open and with an elastic sheet which is joined with these front part and back part, the side edge regions of the front part and back part being joined by tape fasteners (see PLT 1). If doing this, the elastic sheet contacts the wearer, so the diaper easily follows movement of the wearer and slippage of the diaper downward can be suppressed. 
     CITED REFERENCE LIST 
     Patent Literature 
     PLT 1: Japanese Patent Publication No. 2001-8968A 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the above-mentioned diaper, the tape fasteners are at positions separated from the elastic sheet, so the part of the elastic sheet which adjoins the front part and the part of the elastic sheet which adjoins the back part are not joined with each other. As a result, movement of the wearer causes the leg openings to expand larger and the elastic sheet is liable to separate from the wearer. Therefore, slippage of the diaper downward is liable to be unable to be sufficiently suppressed. Further, since the part of the elastic sheet which adjoins the front part and the part of the elastic sheet which adjoins the back part are not joined with each other, the elastic sheet parts are liable to separate from the front part and back part. 
     Solution to Problem 
     According to a first aspect of the present invention, there is provided a disposable diaper which is provided with a single torso opening and a pair of leg openings, wherein the disposable diaper is provided with a front part and back part and with a crotch part, the front part and back part are separated from each other in the length direction when the diaper is spread open, the crotch part extends in the length direction at an intermediate position in the traverse direction, the diaper is further provided with a pair of leg sheets which have stretchability or elasticity, length direction circumferential edge regions and an inward side edge region of one leg sheet are respectively joined at one side of the crotch part with the bottom edge region of the front part and the bottom edge region of the back part and with the side edge region of the crotch part, whereby that one leg sheet is arranged at one side of the crotch part at the space between the front part and back part, length direction circumferential edge regions and an inward side edge region of the other leg sheet are respectively joined at the other side of the crotch part with the bottom edge region of the front part and the bottom edge region of the back part and with the side edge region of the crotch part, whereby that other leg sheet is arranged at the other side of the crotch part at the space between the front part and back part, the diaper has depressed parts which extend from the two side edges inward when spread open, and leg sheets which adjoin front-side starting ends of depressed parts or the front part and leg sheets which adjoin back-side starting ends of depressed parts or the back part are joined with each other, whereby a pair of leg openings are defined. 
     According to a second aspect of the present invention, there is provided a disposable diaper which is provided with a single torso opening and a pair of leg openings, wherein the disposable diaper is provided with a front part and back part, the front part and back part are separated from each other in the length direction when the diaper is spread open, the diaper is further provided with a leg sheet which has stretchability or elasticity, length direction circumferential edge regions of the leg sheet are respectively joined with substantially the entirety of a bottom edge region of the front part and substantially the entirety of a bottom edge region of the back part, whereby the leg sheet is arranged in the space between the front part and the back part, the diaper has depressed parts which extend from the two side edges inward when spread open, and the leg sheet which adjoins front-side starting ends of depressed parts or the front part and the leg sheet which adjoins back-side starting ends of depressed parts or the back part are joined with each other, whereby a pair of leg openings are defined. 
     According to a third aspect of the present invention, there is provided a disposable diaper which is provided with a single torso opening and a pair of leg openings, wherein the disposable diaper is provided with a front part and back part and with a crotch part, the front part and back part are separated from each other in the length direction when the diaper is spread open, the crotch part extends in the length direction at an intermediate position in the traverse direction, the front part and back part are joined, the diaper is further provided with a pair of leg sheets which have stretchability or elasticity, length direction circumferential edge regions and an inward side edge region of one leg sheet are respectively joined at one side of the crotch part with the bottom edge region of the front part and the bottom edge region of the back part and with the side edge region of the crotch part, whereby that one leg sheet is arranged at one side of the crotch part at the space between the front part and back part, length direction circumferential edge regions and an inward side edge region of the other leg sheet are respectively joined at the other side of the crotch part with the bottom edge region of the front part and the bottom edge region of the back part and with the side edge region of the crotch part, whereby that other leg sheet is arranged at the other side of the crotch part at the space between the front part and back part, an outward side edge region inside a front-side length direction circumferential edge region of one leg sheet or an outward side edge region of one leg sheet which adjoins this or a side edge region of the front part and an outward side edge region inside a back-side length direction circumferential edge region of one leg sheet or an outward side edge region of one leg sheet which adjoins this or a side edge region of the back part are joined, an outward side edge region inside a front-side length direction circumferential edge region of the other leg sheet or an outward side edge region of the other leg sheet which adjoins this or a side edge region of the front part and an outward side edge region inside a back-side length direction circumferential edge region of the other leg sheet or an outward side edge region of the leg sheet which adjoins this or a side edge region of the back part are joined, and intermediate regions between the mutually joined side edge regions are left unjoined, whereby a pair of leg openings are defined. 
     Advantageous Effects of Invention 
     It is possible to promote continued wearing of a diaper by a wearer. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view of a disposable diaper of a first embodiment according to the present invention. 
         FIG. 2  is a spread open view of the diaper of  FIG. 1 . 
         FIG. 3  is a cross-sectional view seen along the line III-III of  FIG. 2 . 
         FIG. 4  is a schematic view which shows a method of production of a diaper of the first embodiment according to the present invention. 
         FIG. 5A  is a view which shows another embodiment of cutaway parts. 
         FIG. 5B  is a view which shows another embodiment of cutaway parts. 
         FIG. 5C  is a view which shows another embodiment of cutaway parts. 
         FIG. 5D  is a view which shows another embodiment of cutaway parts. 
         FIG. 6A  is a view which shows another embodiment of joining. 
         FIG. 6B  is a view which shows another embodiment of joining. 
         FIG. 7A  is a view which shows another embodiment of depressed parts. 
         FIG. 7B  is a view which shows another embodiment of depressed parts. 
         FIG. 8A  is a view which shows another embodiment of a leg sheet. 
         FIG. 8B  is a view which shows another embodiment of a crotch part. 
         FIG. 8C  is a view which shows another embodiment of a crotch part. 
         FIG. 9  is a view which explains dimensions of cutaway parts. 
         FIG. 10  is a plan view of a disposable diaper of a second embodiment according to the present invention. 
         FIG. 11  is a spread open view of the diaper of  FIG. 10 . 
         FIG. 12  is a cross-sectional view seen along the line XII-XII of  FIG. 11 . 
         FIG. 13  is a schematic view which shows a method of production of a diaper of the second embodiment according to the present invention. 
         FIG. 14  is a plan view of a disposable diaper of a third embodiment according to the present invention. 
         FIG. 15  is a spread open view of the diaper of  FIG. 14 . 
         FIG. 16  is a view which shows still another embodiment of a disposable diaper. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1 ,  FIG. 2 , and  FIG. 3  show a first embodiment according to the present invention. Note that, in  FIG. 2 , L indicates a length direction of a diaper  1 , while T indicates a traverse direction which perpendicularly intersects the length direction. 
     Referring to  FIG. 1 ,  FIG. 2 , and  FIG. 3 , the disposable diaper  1  is provided with a front part  4 F, a back part  4 B, and a crotch part  4 C. The front part  4 F and the back part  4 B are respectively positioned at the front side and the back side of the wearer when the diaper is worn. 
     The front part  4 F and the back part  4 B respectively form rectangular shapes and are arranged separated from each other in the length direction L when spread open. Further, at the front part  4 F and the back part  4 B, pluralities of elastic members  5 F and  5 B which extend substantially in parallel in the traverse direction T are provided. In particular, as shown in  FIG. 3 , the front part  4 F and the back part  4 B are provided with two liquid impermeable sheets which are superposed on each other. The elastic members  5 F and  5 B are arranged between these sheets in a stretched state and fastened to these sheets. 
     The crotch part  4 C also forms a rectangular shape. It extends in the length direction L and is joined with the front part  4 F and back part  4 B at an intermediate position in the traverse direction. In this case, the length direction circumferential edge regions  4 CF and  4 CB of the crotch part  4 C are joined to the bottom edge regions  4 FB and  4 BB of the front part  4 F and back part  4 B. As a result, the crotch part  4 C is positioned at the crotch of the wearer when the diaper is worn. 
     This crotch part  4 C is, for example, provided with a liquid impermeable back sheet and an absorbent member which is held at the back sheet. The absorbent member is for example provided with a fiber assembly and highly absorbent polymer particles. 
     The diaper  1  is further provided with a pair of substantially rectangular shape leg sheets  6 L and  6 R, that is, is provided with a left leg sheet  6 L which is positioned at a left side of the crotch part  4 C in  FIG. 1  and  FIG. 2  and a right leg sheet  6 R which is positioned at a right side of the crotch part  4 C. The leg sheets  6 L and  6 R have stretchability or elasticity and preferably have elasticity. 
     The elongation of the leg sheets  6 L and  6 R is preferably 140% or more, more preferably 180% or more. Here, the elongation of a sheet material is found as follows. That is, a 50 mm line segment is drawn on a sheet material in the natural state, then the sheet material is pulled to stretch it and the length B (mm) of the line when the material is completely stretched is measured. Next, the following formula is used to calculate the elongation:
 
Elongation= B/ 50×100(%)
 
     Furthermore, the leg sheet  6 L and  6 R have at least one of liquid impermeability, water repellency, and air permeability. 
     The leg sheets can be comprised from stretchable sheets or elastic sheets. As stretchable sheets, for example, polyethylene, polypropylene, or other thermoplastic resin films can be used. Alternatively, they may be comprised from composite sheets of thermoplastic resin films on which partially cut or weakened nonstretchable nonwoven fabrics are laminated. On the other hand, as the elastic sheets, for example, sheets which are made from nonwoven fabrics comprised of melted elastic fibers of urethane, styrene, or other such thermoplastic elastomer resin and composite sheets of nonwoven fabrics comprised of elastic fibers on which partially cut or weakened nonstretchable nonwoven fabrics are laminated. 
     The length direction circumferential edge regions  6 LF and  6 LB of the left leg sheet  6 L are joined to the bottom edge region  4 FB of the front part  4 F and the bottom edge region  4 BB of the back part  4 B at the left of the crotch part  4 C. Further, the inward side edge region  6 LI of the left leg sheet  6 L is joined to the left side edge region  4 CL of the crotch part  4 C. As a result, the left leg sheet  6 L is arranged at the space  7 L between the front part  4 F and back part  4 B at the left of the crotch part  4 C. 
     Similarly, the length direction circumferential edge regions  6 RF and  6 RB of the right leg sheet  6 R are joined to the bottom edge region  4 FB of the front part  4 F and the bottom edge region  4 BB of the back part  4 B at the right of the crotch part  4 C. Further, the inward side edge region  6 RI of the right leg sheet  6 R is joined to the right side edge region  4 CR of the crotch part  4 C. As a result, the right leg sheet  6 R is arranged at the space  7 R between the front part  4 F and back part  4 B at the right of the crotch part  4 C. 
     Here, the front part  4 F, back part  4 B, crotch part  4 C, left leg sheet  6 L, and right leg sheet  6 R are for example joined with each other by a hot melt adhesive A ( FIG. 3 ). 
     In particular, as shown in  FIG. 2 , the diaper  1 , when spread open, has depressed parts  1 DL and  1 DR which extend inward from the two side edges  1 LE and  1 RE. In the first embodiment according to the present invention, the left leg sheet  6 L has a cutaway part  6 LC which extends inward from the outward side edge  6 LOE, while the right leg sheet  6 R has a cutaway part  6 RC which extends inward from the outward side edge  6 ROE. The above-mentioned depressed parts  1 DL,  1 DR are defined by these cutaway parts  6 LC and  6 RC. Note that, in the first embodiment according to the present invention, the cutaway parts  6 LC and  6 RC respectively form semi-oval shapes which have long axes extending in the length direction. 
     On top of this, the outward side edge region  6 LOF of the left leg sheet  6 L adjoining the front-side starting end  6 LCF of the depressed part  1 DL or cutaway part  6 LC and the outward side edge region  6 LOB of the left leg sheet  6 L adjoining the back-side starting end  6 LCB of the depressed part  1 DR or cutaway part  6 LC are joined with each other. Further, the left side edge region  4 FL of the front part  4 F and the left side edge region  4 BL of the back part  4 B are joined with each other. 
     In the same way, the outward side edge region  6 ROF of the right leg sheet  6 R adjoining the front-side starting end  6 RCF of the cutaway part  6 RC and the outward side edge region  6 ROB of the right leg sheet  6 R adjoining the back-side starting end  6 RCB of the cutaway part  6 RC are joined with each other. Further, the right side edge region  4 FR of the front part  4 F and the right side edge region  4 BR of the back part  4 B are joined with each other. 
     As a result, as shown in  FIG. 1 , the left leg sheet  6 L defines the left leg opening  1 LL, while the right leg sheet  6 R defines the right leg opening  1 LR. Further, the front part  4 F and back part  4 B define a single leg opening  1 W. 
     Here, the outward side edge regions  6 LOF and  6 LOB of the left leg sheet  6 L, the outward side edge regions  6 ROF and  6 ROB of the right leg sheet  6 R, and the left side edge regions  4 FL and  4 BL and right side edge regions  4 FR and  4 BR of the front part  4 F and back part  4 B are respectively, for example, joined by sonic seals and therefore are joined to be unable to be again joined. As a result, the diaper  1  forms a pants shape. 
     In the first embodiment according to the present invention, the cutaway parts  6 LC and  6 RC or depressed parts  1 DL and  1 DR are formed so that the circumferential lengths or inside diameters of the leg openings  1 LL and  1 LR become smaller than the circumferential lengths or inside diameters of the legs of the wearer. 
     When worn, the legs of the wearer are passed through the leg openings  1 LL and  1 LR then the diaper  1  is pulled up. In this case, the leg sheets  6 L and  6 R stretch in accordance with the shapes of the legs of the wearer. Therefore, the leg sheets  6 L and  6 R closely fit against the wearer. 
     Furthermore, the left leg sheet  6 L and the right leg sheet  6 R form ring shapes, so the leg sheets  6 L and  6 R can continue to closely fit against the entire circumferences of the legs of the wearer. As a result, leakage from the pair of leg openings  1 LL and  1 LR can be reliably suppressed. Further, separation of the leg sheets  6 L and  6 R from the front part  4 F and back part  4 B can be suppressed. 
     Here, the length direction length LLO of the outward side edge regions  6 LOF and  6 LOB of the left leg sheet  6 L ( FIG. 1 ) and the length direction length LRO of the outward side edge regions  6 ROF and  6 ROB of the right leg sheet  6 R ( FIG. 1 ) are respectively preferably 5 mm or more. 
     The leg sheets  6 L and  6 R preferably have stretchability or elasticity in two directions perpendicularly intersecting each other, for example, preferably have stretchability or elasticity in the length direction L and the traverse direction T. The leg sheets  6 L and  6 R may also have stretchability or elasticity in only one direction. When the cutaway parts  6 LC and  6 RC are semi-oval shapes which extend in the length direction, the leg sheets  6 L and  6 R preferably have stretchability or elasticity in the length direction L. 
     Furthermore, in the first embodiment according to the present invention, the skin-side surfaces of the leg sheets  6 L and  6 R are smooth. That is, the skin-side surfaces of the leg sheets  6 L and  6 R are not provided with wrinkles. As a result, the leg sheets  6 L and  6 R contact the wearer in the form of not line contact, but surface contact, so the contact of the leg sheets  6 L and  6 R with the wearer is improved. 
     Note that, by breaking the joined parts of the outward side edge regions  6 LOF and  6 LOB of the left leg sheet  6 L or the joined parts of the outward side edge regions  6 ROF and  6 ROB of the right leg sheet  6 R, it is possible to adjust the sizes of the leg openings  1 LL and  1 LR. In this case, the joining strength of the joined parts is preferably 6N/25 mm to 40N/25 mm, more preferably 8N/25 mm to 30N/25 mm. This is to enable the sizes of the leg openings  1 LL and  1 LR to be adjusted by breaking the joined parts while enabling prevention of unintentional breakage of the joined parts at the time of use of the diaper  1 . 
       FIG. 4  schematically shows the method of production of the diaper  1  of the first embodiment according to the present invention. Note that, in  FIG. 4 , MD indicates the machine direction, while CD shows the crossing direction which perpendicularly intersects the machine direction MD. 
     Referring to  FIG. 4 , at step S 11 , the web W 4 F of the front part  4 F and the web W 4 B of the back part  4 B are conveyed in the machine direction MD while being separated from each other in the crossing direction CD. At the next step S 12 , the crotch parts  4 C are superposed on and joined to the front part web W 4 F and the back part web W 4 B while separated in the machine direction MD. At the next step S 13 , leg sheet materials M 6  which later form the leg sheets  6 L and  6 R are superposed on and joined to the front part web W 4 F, back part web W 4 B, and mutually adjoining pairs of crotch parts  4 C. At the next step S 14 , through holes LH which later form the cutaway parts  6 LC and  6 RC are formed in the leg sheet materials M 6 . 
     At the next step S 15 , the crotch parts  4 C and leg sheet materials M 6  are folded along a folding line FL substantially parallel to the machine direction MD whereby the front part web W 4 F and back part web W 4 B are superposed against each other. At the next step S 16 , the front part web W 4 F and back part web W 4 B are joined with each other between the mutually adjoining pairs of the crotch part  4 C and the parts of the mutually facing leg sheet materials M 6  are joined with each other whereby joined parts J are formed separated in the machine direction MD. At the next step S 17 , the assemblies are cut along a cutting line CL running through the joined parts J. As a result, mutually separated diapers  1  are formed. 
     Note that, at step S 12 , back sheets which form the crotch parts  4 C may be joined to the front part web W 4 F and back part web W 4 B, then the absorbent members which form the crotch part  4 C joined to the back sheets. 
     Further, at step S 13 , the leg sheet materials M 6  may be joined with the crotch parts  4 C etc. in the stretched state or conversely may be joined without stretching them. 
     Further, at step S 14 , leg sheet materials M 6  in which through holes LH are formed may be superposed on and joined with the front part web W 4 F, the back part web W 4 B, and the crotch parts  4 C. 
       FIG. 5A ,  FIG. 5B ,  FIG. 5C , and  FIG. 5D  show other embodiments of the cutaway parts  6 LC and  6 RC. The cutaway parts  6 LC and  6 RC respectively form semi-circular shapes in the example which is shown in  FIG. 5A , semi-oval shapes which have long axes extending in the traverse direction in the example which is shown in  FIG. 5B , and asymmetric shapes with respect to the length direction center line C-C in the example which is shown in  FIG. 5C . Further, in the example which is shown in  FIG. 5D , the cutaway parts  6 LC and  6 RC are respectively comprised of slits. 
     Note that, in the examples which are shown in  FIG. 5B  and  FIG. 5D , the leg sheets  6 L and  6 R preferably have stretchability or elasticity in at least the traverse direction T. 
     When the cutaway parts  6 LC and  6 RC are long in the length direction as shown in  FIG. 2 , the leg openings  1 LL and  1 LR can be positioned at the groin part of the wearer. In this case, the worn appearance of the wearer can be streamlined. 
     On the other hand, when the cutaway parts  6 LC and  6 RC are long in the traverse direction such as shown in  FIG. 5B  and  FIG. 5D , the leg openings  1 LL and  1 LR can be positioned at the thigh parts of the wearer. In this case, the moving parts of the wearer can be kept from being tightened and the diaper  1  can be used to cover the body of the wearer over a wide range. 
     Whatever the case, the leg openings  1 LL and  1 LR are formed smaller than the legs of the wearer, so when the diaper is worn, the leg sheets  6 L and  6 R can be reliably closely fit with the legs of the wearer. 
     In the above-mentioned first embodiment according to the present invention, the outward side edge regions  6 LOF and GLOB of the left leg sheet  6 L and the outward side edge regions  6 ROF and  6 ROB of the right leg sheet  6 R are respectively joined in a manner unable to be rejoined. However, these outward side edge regions  6 LOF and  6 LOB and outward side edge regions  6 ROF and  6 ROB can respectively be joined in a manner able to be rejoined by using for example fasteners. 
     That is, in the example which is shown in  FIG. 6A , fasteners such as fasteners including male members  8 M and female members  8 F are provided. The male members  8 M are provided adjoining the outward side edge regions  6 LOF and  6 ROF while projecting outward, while the female members  8 F are provided at the outer surfaces of the back part  4 B so as to overlap the outward side edge regions  6 LOB and  6 ROB. 
     On the other hand, in the example which is shown in  FIG. 6B , the male members  8 M are provided at the inner surfaces of the leg sheets  6 L and  6 R so as to overlap the outward side edge regions  6 LOF and  6 ROF. The female members  8 F are similar to those in the example of  FIG. 6A . 
     In the examples which are shown in  FIG. 6A  and  FIG. 6B  as well, the extents of overlap of the male members  8 M and female members  8 F can be changed so as to adjust the sizes of the leg openings  1 LL and  1 LR. 
       FIG. 7A  and  FIG. 7B  show other embodiments of the depressed parts  1 DL and  1 DR. In the embodiments which were explained up to here, the cutaway part  6 LC was formed in the left leg sheet  6 L so that the outward side edge regions  6 LOF and  6 LOB were formed, while the cutaway part  6 RC was formed in the right leg sheet  6 R so that the outward side edge regions  6 ROF and  6 ROB were formed. As opposed to this, in the example which is shown in  FIG. 7A , the cutaway parts  6 LC and  6 RC are formed so that the outward side edge regions are not formed, while these cutaway parts  6 LC and  6 RC define the depressed parts  1 DL and  1 DR. 
     In this case, the left side edge region  4 FL of the front part  4 F which adjoins the front-side starting end  6 LCF of the cutaway parts  6 LC and the left side edge region  4 BL of the back part  4 B which adjoins the back-side starting end  6 LCB of the cutaway parts  6 LC are joined together. Further, the right side edge region  4 RL of the front part  4 F which adjoins the front-side starting end  6 RCF of the cutaway part  6 RC and the right side edge region  4 BR of the back part  4 B which adjoins the back-side starting end  6 RCB of the cutaway part  6 RC are joined together. 
     In the example which is shown in  FIG. 7B , the leg sheets  6 L and  6 R do not have cutaway parts. However, the traverse direction lengths of the leg sheets  6 L and  6 R are shorter than the traverse direction lengths of the spaces  7 L and  7 R. Therefore, the depressed part  1 DL is defined by the outward side edge  6 LOE of the leg sheet  6 L, the bottom edge of the front part  4 F, and the bottom edge of the back part  4 B. In this case, the left side edge region  4 FL of the front part  4 F which adjoins the front-side starting end  6 LCF of the depressed part  1 DL and the left side edge region  4 BL of the back part  4 B which adjoins the back-side starting end  6 LCB of the depressed part  1 DL are joined with each other. Further, the right side edge region  4 RL of the front part  4 F which adjoins the front-side starting end  6 RCF of the depressed part  1 DR and the right side edge region  4 BR of the back part  4 B which adjoins the back-side starting end  6 RCB of the depressed part  1 DR are joined with each other. 
       FIG. 8A  shows another embodiment of the leg sheets  6 L and  6 R, while  FIG. 8B  and  FIG. 8C  shows other embodiments of the crotch part  4 C. In the embodiments which were explained up to here, the leg sheets  6 L and  6 R were joined to the inside surfaces of the front part  4 F and back part  4 B, that is, the wearer side. As opposed to this, in the example which is shown in  FIG. 8A , the leg sheets  6 L and  6 R are joined to the outside surface  4 FO of the front part  4 F and the outside surface  4 BO of the back part  4 B. 
     In the example which is shown in  FIG. 8B , the absorbent member AD is provided separate from the crotch part  4 C. That is, the crotch part  4 C is provided with a back sheet, but is not provided with an absorbent member. On top of this, the crotch part  4 C is joined with the outside surface  4 FO of the front part  4 F and the outside surface  4 BO of the back part  4 B. 
     On the other hand, in the example which is shown in  FIG. 8C , the crotch part  4 C which is provided with the back sheet and absorbent member is joined with the outside surface  4 FO of the front part  4 FO and the outside surface  4 BO of the back part  4 B. Further, the leg sheets  6 L and  6 R are joined between the two sheets which form the front part  4 F and between the two sheets which form the back part  4 B. 
     Next, the dimensions of the depressed parts  1 DL and  1 DR and the cutaway parts  6 LC and  6 RC will be explained while referring to  FIG. 9 . In the first embodiment according to the present invention, the depressed parts  1 DL and  1 DR are formed so that the length direction length LND of the depressed parts  1 DL and  1 DR is not more than ⅓ of the length direction length LN 1  of the diaper  1  (LND≦(⅓)LN 1 ) and so that the traverse direction length WDD of the depressed parts  1 DL and  1 DR is not more than ⅓ of the traverse direction length WD 1  of the diaper  1  (WDD≦(⅓)WD 1 ). 
     If formed in this way, the leg openings  1 LL and  1 LR can be made smaller in size while the body of the wearer can be sufficiently covered by the diaper  1 . Therefore, the leg sheets  6 L and  6 R can be reliably fit against the legs of the wearer. 
     This was confirmed experimentally as well. That is, a plurality of diapers with different length direction lengths LN 1  and traverse direction lengths WD 1  such as child diapers and adult diapers, that is, LND≦(⅓)LN 1  and WDD≦(⅓)WD 1  diapers and LND&gt;(⅓)LN 1  or WDD&gt;(⅓)WD 1  diapers, were prepared. These diapers were checked for frequency of leakage. With the LND≦(⅓)LN 1  and WDD≦(⅓)WD 1  diapers, low frequencies of leakage were obtained. As opposed to this, with the LND&gt;(⅓)LN 1  or WDD&gt;(⅓)WD 1  diapers, high frequencies of leakage were obtained. 
       FIG. 10 ,  FIG. 11 , and  FIG. 12  show a second embodiment according to the present invention. Referring to  FIG. 10 ,  FIG. 11 , and  FIG. 12 , in the second embodiment, a single leg sheet  6  is provided. This leg sheet  6  has substantially the same traverse direction length as the front part  4 F and back part  4 B. 
     The length direction circumferential edge regions  6 F and  6 B of the leg sheet  6  are respectively joined to the substantial entirety of the bottom edge region  4 FB of the front part  4 F and the substantial entirety of the bottom edge region  4 BB of the back part  4 B. As a result, the leg sheet  6  is arranged in the space  7  between the front part  4 F and the back part  4 B. 
     In particular, as shown in  FIG. 11 , the leg sheet  6  has a pair of cutaway parts  6 C which extend from the side edges  60 E inward. In the second embodiment according to the present invention, the cutaway parts  6 C form semi-oval shapes which have long axes extending in the traverse direction. 
     On top of this, the side edge region  60 F of the leg sheet  6  which adjoins the front-side starting ends  6 CF of the cutaway parts  6 C and the side edge region  60 B of the leg sheet  6  which adjoins the back-side starting ends  6 CB of the cutaway parts  6 C are joined together. 
     As a result, as shown in  FIG. 10 , the leg sheet  6  defines a pair of leg openings  1 LL and  1 LR. 
       FIG. 13  schematically shows a method of production of a diaper  1  of a second embodiment according to the present invention. Note that, in  FIG. 13 , MD indicates a machine direction, while CD indicates a crossing direction which perpendicularly intersects the machine direction MD. 
     Referring to  FIG. 13 , at step S 21 , the web W 4 F of the front part  4 F and the web W 4 B of the back part  4 B are conveyed in the machine direction MD while being separated from each other in the crossing direction CD. At the next step S 22 , leg sheet materials M 6  which later form the leg sheets  6 L and  6 R are superposed on and joined to the front part web W 4 F and back part web W 4 B. At the next step S 23 , the crotch parts  4 C are superposed on and joined to the front part web W 4 F, the back part web W 4 B, and the leg sheet materials M 6  while separated in the machine direction MD. At the next step S 24 , through holes LH which later form the cutaway parts  6 LC and  6 RC are formed in the leg sheet materials M 6 . 
     At the next step S 25 , the crotch parts  4 C and leg sheet materials M 6  are folded along a folding line FL substantially parallel to the machine direction MD whereby the front part web W 4 F and back part web W 4 B are superposed against each other. At the next step S 26 , joined parts J are formed separated in the machine direction MD between the mutually adjoining pair of crotch parts  4 C. At the next step S 27 , the assemblies are cut along a cutting line CL running through the joined parts J. As a result, mutually separated diapers  1  are formed. 
     Note that, regarding steps S 22  and S 23 , it is also possible to join the crotch parts  4 C to the leg sheet materials M 6  in advance and then superpose them on the front part web W 4 F and back part web W 4 B. 
     In the second embodiment according to the present invention, the crotch part  4 C is joined to both the front part  4 F and back part  4 B. However, the crotch part  4 C may also be joined to one of the front part  4 F and back part  4 B or may be not joined to either of them. 
     The rest of the configuration and actions of the second embodiment according to the present invention are similar to the configuration and actions of the first embodiment. 
       FIG. 14  and  FIG. 15  show a third embodiment according to the present invention. If referring to  FIG. 14  and  FIG. 15 , in the third embodiment according to the present invention, in the same way as the first embodiment, a left leg sheet  6 L and right leg sheet  6 R are provided. However, the left leg sheet  6 L and the right leg sheet  6 R are not provided with cutaway parts. Therefore, the two side edges of the diaper  1  are not provided with depressed parts. 
     On top of this, the inside of the front-side length direction circumferential edge region  6 LF of the left leg sheet  6 L or the outward side edge region  6 LOFF of the left leg sheet  6 L adjoining this and the inside of the back-side length direction circumferential edge region  6 LB of the left leg sheet  6 L or the outward side edge region  6 LOBB of the left leg sheet  6 L adjoining it are joined with each other. At this time, the intermediate region  6 LX between the mutually joined outward side edge regions  6 LOFF and  6 LOBB remains without being joined. The left leg opening  1 LL is defined in this way. 
     Similarly, the inside of the front-side length direction circumferential edge region  6 RF of the right leg sheet  6 R or the outward side edge region  6 ROFF of the right leg sheet  6 R adjoining this and the inside of the back-side length direction circumferential edge region  6 RB of the right leg sheet  6 R or the outward side edge region  6 ROBB of the right leg sheet  6 R adjoining it are joined with each other. At this time, the intermediate region  6 RX between the mutually joined outward side edge regions  6 ROFF and  6 ROBB remains without being joined. The right leg opening  1 LR is defined in this way. 
     If doing this, there is no need to form cutaway parts and no trim occurs. 
     The left side edge region  4 FL of the front part  4 F which adjoins the front-side length direction circumferential edge region  6 LF of the left leg sheet  6 L and the left side edge region  4 BL of the back part  4 B which adjoins the back-side length direction circumferential edge region  6 LB of the left leg sheet  6 L may be joined with each other and the right side edge region  4 FR of the front part  4 F which adjoins the front-side length direction circumferential edge region  6 RF of the right leg sheet  6 R and the right side edge region  4 BR of the back part  4 B which adjoins the back-side length direction circumferential edge regions  6 RB of the right leg sheet  6 R may be joined with each other. 
     Note that the rest of the configuration and actions of the third embodiment according to the present invention are similar to the configuration and actions of the first embodiment. 
     In the embodiments which have been explained up to here, the front part  4 F, back part  4 B, and crotch part  4 C are comprised from mutually separate members. However, as shown in  FIG. 16 , the front part  4 F and back part  4 B and the crotch part  4 C which is comprised from the back sheet may also be comprised from a common sheet material and the absorbent member AD may be arranged on this sheet material. Note that, in  FIG. 16 , the leg sheets  6 L and  6 R are omitted. 
     Further, the two sides of the crotch part  4 C or absorbent member in the traverse direction may also be provided with leak-proofing members. The leak-proofing members are, for example, provided with sheets which spread outward in the traverse direction from the traverse direction side edges of the absorbent member. Elastic members which extend in the length direction are provided at the outer ends of these sheets. As a result, leakage can be reliably suppressed. 
     Further, the embodiments which are explained up to here may be combined with each other. That is, for example, in the second and third embodiments, as shown in  FIG. 8A , the leg sheets may also be joined to the outer surfaces of the front part  4 F and back part  4 B. 
     The present invention claims the benefit of Japanese Patent Application No. 2011-002161 the entire disclosure of which is cited here. 
     REFERENCE SIGNS LIST 
       1  disposable diaper 
       1 LL,  1 LR leg openings 
       4 F front part 
       4 B back part 
       4 C crotch part 
       6 L,  6 R leg sheets 
       6 LC,  6 RC cutaway parts 
       6 LOF,  6 LOB,  6 ROF,  6 ROB outward side edge regions