AU2014294222A1 - Disposable diaper - Google Patents

Abstract

A disposable diaper (10) comprising: an absorbent body (40) having an absorbent core; a pair of fastening tapes (90); a waist expansion/contraction sheet having expansion/contraction properties in the product width direction; and a waist holding section that holds the disposable diaper on to the body of a wearer. The waist expansion/contraction sheet has: a rear-side waist expansion/contraction sheet (85) arranged in the rear waist area; and a front-side waist expansion/contraction sheet (86) arranged in the front-side end section in the front waist area. Some of the rear-side waist expansion/contraction sheet is arranged overlapping the rear-side end section of the absorbent core and is arranged overlapping the waist holding section. The front-side waist expansion/contraction sheet is arranged adjacent to the front-side end section of the absorbent core.

Description

English SpecificationUC-547-PCT 1 DESCRIPTION DISPOSABLE DIAPER TECHNICAL FIELD [0001] The present invention relates to a disposable diaper. BACKGROUND ART [0002] Disposable diapers having a front lower-torso region, a back lower-torso region, and a crotch region,, and including an absorbent extending from the crotch region to the front lower-torso region and the back lower-torso region, and a fastening tape for fastening the front lower-torso region and the back lower-torso region to each other, have been known (see, for example, Patent Literature 1). [0003] In general, the fastening tape extends outward in the product width direction from a lateral edge of the back lower-torso region of the disposable diaper. When the disposable diaper of Patent Literature 1 is worn, the crotch region of the disposable diaper is brought adjacent to the crotch area of a wearer and in this state the fastening tape in the back lower-torso region is pulled to the front lower-torso region so that the fastening tape is fastened to the front lower-torso region. [0004] Further, a waist opening of the disposable diaper of the Patent Literature 1 is provided with an elastic member that is elastically extensible in the width direction. The waist opening of the disposable diaper fits around the wearer's waist by way of elastic extension of the elastic member. CITATION LIST PATENT LITERATURE [0005] Patent Literature 1: JP 2006-20665 A TECHNICAL PROBLEM [0006] However, the above disposable diaper had a following problem. In the disposable diaper in Patent Literature 1, a region laterally extending from the fastening tape is spaced from the elastic member. The region laterally extending from the fastening tape and a region in which the elastic member is disposed provide a fit to the wearer's body, respectively. However, the section English Specification_UC-547-PCT 2 between the region laterally extending from the fastening tape and the elastic member may not fit the wearer's body but may rise from the region laterally extending from the fastening tape, or may be uneven with the region laterally extending from the fastening tape. [0007] Further, an absorbent core of the absorbent is formed of absorbent material such as comminuted pulp, which results in an increased thickness in a region in which the absorbent core is disposed compared to a region in which the absorbent core is not disposed. Further, a region in which the elastic member is disposed will increase in thickness after the elastic member has contracted. Thus, the disposable diaper will have an increased thickness in the area neighboring the waist opening, which is greater than the components' thickness. [0008] In the disposable diaper of Patent Literature 1, the elastic member is spaced from the absorbent core. The section between the elastic member and the absorbent core has a thickness smaller than the regions in which the elastic member and the absorbent core are disposed, respectively. Thus, the section between the elastic member and the absorbent core may be uneven with the region in which the elastic member is disposed, and/or the section between the elastic member and the absorbent core may be uneven with the region in which the absorbent core is disposed. [0009] In recent years, user demands (the term "user" is herein used interchangeably with the term "consumer") for disposable diaper have been growing; in particular for disposable diapers for infants, more users request of such diapers to be easy on baby's skin for the sake of skin protection and to have appearances similar to underwear. [0010] In the above-mentioned disposable diaper, however, surface unevenness is created in several portions in the disposable diaper, and some users may feel that such unevenness can cause irritation on baby's skin, or other users may feel that such unevenness emphasizes functionality of disposable diaper and renders an underwear-like appearance. [0011] The present invention addresses the above problem with an object of providing a disposable diaper that is easy on wearer's skin and has an acceptable appearance to satisfy consumer demands. [0012] A disposable diaper (disposable diaper 10) according to the disclosure herein includes a front lower-torso region (front lower-torso region 20), a back English SpecificationUC-547-PCT 3 lower-torso region (back lower-torso region 30), and a crotch region (crotch region 25) between the front lower-torso region and the back lower-torso region; a product longitudinal direction (product longitudinal direction L) from the front lower-torso region to the back lower-torso region; a product width direction (product width direction W) orthogonal to the product longitudinal direction; an absorbent (absorbent 40) extending from the crotch region to at least one of the front lower-torso region and the back lower-torso region, and having an absorbent core; a pair of fastening tapes (fastening tapes 90) disposed on product widthwise outer edges of the back lower-torso region and configured to be fastened to the front lower-torso region; and a waist elastic sheet extending bilaterally from the center in the product width direction of the disposable diaper and being elastically extensible in the product width direction; and a waist holding section in the front lower-torso region and the back lower-torso region, extending along the product width direction for holding the disposable diaper against a wearer's body. In the disclosure, the waist elastic sheet includes: a back waist elastic sheet (back waist elastic sheet 85) disposed at a back edge of the back lower-torso region; and a front waist elastic sheet (front waist elastic sheet 86) disposed at a front edge of the front lower-torso region, a portion of the back waist elastic sheet overlaps a back edge of the absorbent core and the waist holding section, and the front waist elastic sheet is disposed adjacent to a front edge of the absorbent core. BRIEF DESCRIPTION OF DRAWINGS [0013] Fig. 1 is a flat-out, plan view of a disposable diaper according to the embodiment, in a stretched state. Fig. 2 is a plan view of a portion of the disposable diaper according to the embodiment, in a relaxed state. Fig. 3 is a cross-sectional view of the disposable diaper taken along the line F1-F1 shown in Fig. 1. Fig. 4 is a cross-sectional view of the disposable diaper taken along the line F2-F2 shown in Fig. 1. DESCRIPTION OF EMBODIMENTS [0014] Embodiments of a disposable diaper 10 of the present invention will now be described with reference to the drawings. Note that, in the following description of the drawings, the same or like parts are given the same or like reference sign. Note also that the drawings are for schematic depiction only and that dimensional ratios are different from those in a real-world setting. [0015] English Specification_UC-547-PCT 4 Thus, specific dimensions or the like should be determined taking the following explanation into consideration. Note also that, some dimensional relations or ratios may be different between the drawings. [0016] (1) Overall schematic configuration of disposable diaper Fig. 1 is a flat-out, plan view of a disposable diaper 10 according to the embodiment, in a stretched state. Fig. 2 is a plan view of a portion (back edge portion) of the disposable diaper according to the embodiment, in a relaxed state. Fig. 3 is a cross-sectional view of the disposable diaper taken along the line Fl-Fl shown in Fig. 1. Fig. 4 is a cross-sectional view of the disposable diaper taken along the line F2-F2 shown in Fig. 1. [0017] The stretched state shown in Fig. 1 illustrates a state in which a leg elastic zone 75 and an elastic member 81 of leg side gathers 80 have been stretched to such extent that no wrinkles are formed in components of the disposable diaper, for example, a top sheet 50 and a side flap 70. A relaxed state, as opposed to the stretched state, is a state in which the disposable diaper 10 has been taken out from a package if it had been enclosed therein and kept in an atmosphere at a temperature of 20 0 C ± 2 0 C and a relative humidity (RH) of 60% ± 5% for 12 hours. The disposable diaper in the relaxed state has wrinkles in its components, for example, the top sheet 50 and the side flap 70. [0018] The disposable diaper 10 is a disposable diaper of tape type. Here, a tape-type diaper is one whose product widthwise outer edge of the front lower-torso region and product widthwise outer edge of the back lower-torso region are not joined prior to use but are joined via a fastening member such as a fastening tape when the diaper is worn. [0019] The disposable diaper 10 has a front lower-torso region 20, a crotch region 25, and a back lower-torso region 30. The front lower-torso region 20 is the area that will come in contact with the front lower torso (i.e., the belly) of the wearer. The back lower-torso region 30 is the area that will come in contact with the back lower torso (i.e., the back) of the wearer. The crotch region 25 is located between the front lower-torso region 20 and the back lower-torso region 30. [0020] Note that, in the embodiment, a direction from the front lower-torso region 20 to the back lower-torso region 30 is referred to as a product longitudinal direction L, and a direction that is orthogonal to the product longitudinal direction L is referred to as a product width direction W. [0021] English SpecificationUC-547-PCT 5 The disposable diaper 10 includes an absorbent 40 extending from the crotch region 25 to at least one of the front lower-torso region 20 and the back lower-torso region 30. The absorbent 40 is formed by an absorbent core 40a and a core wrap 40b. [0022] The absorbent core 40a may be similar to that of any conventional disposable diapers, and can be suitably formed of well-known members and materials, for example, comminuted pulp and super absorbent polymer. The absorbent core 40a is wrapped by the core wrap 40b in the form of sheet. The external sheet is disposed on a surface on the non-skin-facing side of the disposable diaper. The external sheet is formed by, for example, a nonwoven fabric. [0023] The core wrap 40b is a sheet that covers the absorbent core 40a. At least a portion of a skin-facing surface of the core wrap 40b is formed by a liquid-permeable, filament nonwoven fabric of various kinds or a tissue sheet. For example, an air-through filament nonwoven fabric, spunbond nonwoven fabric, SMS (spunbond-meltblown-spunbond) nonwoven fabric having a mass of about 10-30 g/m 2 or a tissue sheet having a mass of about 10-30 g/m 2 can be used. [0024] A low-stiffness region 110 is disposed in the absorbent 40 in the back lower-torso region, which low-stiffness region is an area that has a basis weight that is lower than other areas of the absorbent or that does not have the absorbent core 40a. The low-stiffness region 110 has a shape in which a product widthwise length gradually decreases from the product widthwise center of an end of the absorbent 40 in the back lower-torso region toward the front lower-torso region. More specifically, the low-stiffness region has a wedged shape in plan view of the disposable diaper. A border line between the absorbent core 40a and the low-stiffness region 110 has an arc shape protruding toward the product widthwise (W) center. The absorbent 40 outward in the product width direction from the low-stiffness region 110 each has a trapezoidal shape narrowing toward the end of the absorbent 40 in the back lower-torso region. [0025] The absorbent core has a thickness at a product longitudinal end and a thickness at a product longitudinal center, the former thickness being smaller than the latter thickness. More preferably, an area in which the absorbent core overlaps the back waist elastic sheet is smaller in thickness than an area in which the absorbent core does not overlap the back waist elastic sheet at the product longitudinal end of the absorbent core. [0026] Thickness can be adjusted by means of embossing for lowering the basis English SpecificationUC-547-PCT 6 weight of the absorbent core. Thickness measurement can be performed using "PEACOCK" dial thickness gauge (available from OZAKI MFG. CO., LTD., Tokyo, Japan). A circular contact point having a diameter of 10 mm is used and a load is adjusted to be 6.0 gf/cm 2 for measuring the area of interest. Thickness measurement is performed for the disposable diaper in the stretched state. [0027] The liquid-permeable top sheet 50 is disposed on a top surface (i.e., skin-facing side) of the absorbent 40. Further, the liquid-impermeable back sheet 60a is disposed on a bottom surface (i.e., non-skin-facing side) of the absorbent 40. An external sheet 60 is disposed on a bottom surface (i.e., non-skin-facing side) of the back sheet 60a. [0028] The back sheet 60a is disposed inward in the product longitudinal direction from a front edge 10F of the disposable diaper, and inward in the product longitudinal direction from a back edge 1OR of the disposable diaper. The back sheet 60a is disposed inward in the product width direction from the product widthwise edges of the disposable diaper. [0029] A side flap 70 is disposed on each product widthwise (W) side margin of the absorbent 40. The side flap 70 is disposed from the front lower-torso region 20 through the crotch region 25 to the back lower-torso region 30, and is disposed outward in the product width direction from the absorbent 40. The side flap 70 is formed by one, or two or more laminated nonwoven fabrics. [0030] A pair of leg openings 35 are respectively formed in the side flaps 70 of the disposable diaper 10. The leg openings 35 are disposed on the respective product widthwise side edges of the disposable diaper, which leg openings 35 are the areas that will encircle the legs of the wearer when the disposable diaper is worn by the wearer. The leg openings 35 are concave toward the product widthwise center of the absorbent body. [0031] Further, the pair of side flaps 70 are individually provided with fastening tapes 90. Each fastening tape 90 is disposed at the product widthwise outer edge of the back lower-torso region, and is configured to be fastened to the front lower-torso region. The fastening tape 90 extends outward in the product width direction from the side flap 70. In the back lower-torso region 30, the fastening tape extends in the product width direction W to be fastened to a non-skin-facing surface of the front lower-torso region 20 and thus holds the disposable diaper 10 against the wearer's body. [0032] English Specification_UC-547-PCT 7 Target sections 95 are disposed on the non-skin-facing surface of the front lower-torso region so that the pair of fastening tapes 90 are fastened thereonto, respectively. [0033] A nonwoven fabric having alternating high basis weight portions and low basis weight portions in the product width direction can be used for the top sheet and the external sheet. In the top sheet formed in this way, suitable extensibility for extensible areas is realized because force will be localized at borders between the high basis weight portions and the low basis weight portions. As a modification example, a nonwoven fabric having alternating high density portions and low density portions at least in the product width direction can be used for the top sheet and the external sheet. The high density portions in the nonwoven fabric having alternating high density portions and low density portions are composed of continuous lines or dots arranged with space from one another. [0034] The nonwoven fabric forming the top sheet or the external sheet is a sheet without thermo-fused regions by dot-pattern or linear embossing, or a sheet having a dot-pattern or linear embossed area by a percentage of 5% to 15%. The percentage of the embossed area is the proportion of the area having embossment. For example, the percentage shows the proportion of the embossed area in the external sheet in relation to the total area of the external sheet. [0035] In the embodiment, the front lower-torso region 20, the back lower-torso region 30, and the fastening tapes 90 form a waist holding section. The waist holding section in the back lower-torso region 30 extends in the product width direction from where an engagement area of the fastening tape 90 is disposed. The waist holding section in the front lower-torso region 20 extends in the product width direction from where the target section 95 is disposed. [0036] A pair of leg elastic zones 75 are respectively disposed in the side flaps 70, which leg elastic zones are inward in the product width direction from the respective leg openings 35 and outward in the product width direction from the absorbent 40, and are extensible in the product longitudinal direction L. [0037] The leg elastic zones 75 may have any configuration as long as they are capable of extending and contracting the leg openings 35 in the product longitudinal direction; for example, the leg elastic zones 75 may be disposed along the respective leg openings 35, or part of the leg elastic zones 75 may be angled relative to the respective leg openings 35. [0038] English SpecificationUC-547-PCT 8 Further, a pair of secondary elastic zones 77 are disposed outward in the product width direction from the respective leg elastic zones 75, straddling the border between the crotch region 25 and the back lower-torso region 30, and being extensible in the product longitudinal direction. As a region in the side flap 70 in which the secondary elastic zone 77 has been formed contracts, the side flap 70 is enabled to conform to the buldging contour of the wearer's buttocks, covering the buttocks with the region. [0039] As used herein, the leg elastic zone 75 and the secondary elastic zone 77 are areas that actually contract in the product longitudinal direction by means of elastic members such as rubber threads, but do not include areas in which elastic members are disposed under non-elasticized conditions. [0040] Each leg elastic zone 75 is formed by three elastic members that are extensible in the product longitudinal direction. Each secondary elastic zone 77 is formed by a single elastic member that is extensible in the product longitudinal direction. The elastic members according to the embodiment are made of elastic polyurethane filaments and/or natural rubber. [0041] A back edge 75R of the leg elastic zone 75 is in the front relative to the fastening tape 90 and inward in the product width direction from the fastening tape. Hence, the region that is in the front relative to the fastening tape 90 and inward in the width direction from the fastening tape 90 will be contracted by the leg elastic zone 75. [0042] A front edge 77F of the secondary elastic zone 77 is disposed in the back relative to a front edge 75F of the leg elastic zone 75. Hence, the region in the back relative to the front edge 75F of the leg elastic zone 75 will be contracted by the secondary elastic zone 77. A back edge 77R of the secondary elastic zone 77 is disposed in the back relative to the back edge of the leg elastic zone. Hence, the region in the back relative to the leg elastic zone 75 will be contracted by the secondary elastic zone 77. [0043] The leg elastic zone 75 can pull the crotch region of the disposable diaper toward the wearer's crotch area. Further, the pulling force by the leg elastic zone can be transferred to the fastening tape 90 via the secondary elastic zone 77. Hence, when the fastening tape 90 is fastened, the region between the fastening tape 90 and the leg elastic zone 75, as well as the region held against the wearer's waist by the fastening tape 90 and the region in which the leg elastic zone 75 is disposed, readily provides a close fit.

English Specification_UC-547-PCT 9 [0044] Furthermore, the region outward in the product width direction from the leg elastic zone can be contracted by the secondary elastic zone, so that the side flap in the back lower-torso region can properly cover the wearer's buttocks. In this way, especially a back portion of the leg opening is protected from being inside-out when worn. Furthermore, the contracting of the leg elastic zone can pull the leg opening toward the wearer's body, preventing displacement of the leg opening. [0045] The leg elastic zone 75 is interposed between the side flap 70 and the external sheet 60. Alternatively, in the region in which the back sheet 60a is interposed between the absorbent 40 and the external sheet 60, the leg elastic zone 75 is interposed between the back sheet 60a and the side flap 70. [0046] The extensibility of the leg elastic zone 75 is preferably 1.7 to 2.4. In the embodiment, the extensibility of the leg elastic zone 75 is set to 1.9 to 2.2. It is noted that, the extensibility is a degree of extension of the leg elastic zone and is defined as follows: leg elastic zone's extensibility = (length of leg elastic zone in stretched state)/(length of leg elastic zone in relaxed state). [0047] Further, the extensibility of the secondary elastic zone 77 is preferably 1.6 to 2.4. It is noted that, the extensibility of the secondary elastic zone 77 is a degree of extension of the secondary elastic zone and is defined as follows: secondary elastic zone's extensibility = (length of secondary elastic zone in stretched state)/(length of secondary elastic zone in relaxed state). [0048] In this description, such extensibility is determined as follows, for example. First, the disposable diaper 10 is taken out of a package if it is enclosed therein. A region to be measured, for example, the leg elastic zone, is then cut out. Here, the external sheet joined to the region to be measured such as the leg elastic zone, is cut out altogether. The extensibility of the cut sample is measured to determine the extensibility of the region of interest. [0049] Each sample is kept in an atmosphere at a temperature of 20 0 C ± 2 0 C and a relative humidity (RH) of 60% ± 5% for 60 minutes, and then the length of the region of interest is measured along the elastically extensible direction. This length measured is defined as "the length of the region of interest (for example, the leg elastic zone) in the relaxed state." [0050] Secondly, the length of the desired region in the elastically extensible English SpecificationUC-547-PCT 10 direction is measured in this state (i.e., the relaxed state), and the length of this desired region in the elastically extensible direction, as the region is stretched to an extent that any wrinkle created by the elastic member is not visually observed in a non-extensible sheet, are measured. This latter length measured is defined as "the length of the region of interest (for example, the leg elastic zone) in the stretched state." Using these measurements, extensibility can be calculated in the above expressions. [0051] It is noted that measurement of "length" herein is intended to take the following approach. A sample is prepared by taking out the disposable diaper 10 from a package if it is enclosed therein and keeping it in an atmosphere at a temperature of 20 0 C 2 0 C and a relative humidity (RH) of 60% ± 5% for 12 hours. [0052] Next, a measuring tape (PVC-coated fiberglass tape; available from Shinwa Rules Co., Ltd., Nigata, Japan) is used along the region to be measured, and the length of the region as such is measured. To measure the length of the region of interest in the stretched state, the disposable diaper 10 in the relaxed state is stretched to an extent that any wrinkle created by the elastic member is not visually observed. In this description, lengths of ten samples were measured according to the above approach, and an average value was calculated, which was defined as length. [0053] Further, a pair of leg side gathers 80, extending in the product longitudinal direction L, are disposed inward from the pair of leg elastic zones 75 (that is, toward the center in the product width direction W). The leg side gathers 80 are raised elastic gathers, disposed along product widthwise inner edges of the side flaps 70 and inward in the product width direction from the leg elastic zones 75. The leg side gathers 80 are disposed inward in the product width direction from the leg elastic zones 75. The leg side gathers 80 can employ any known configurations, specifically, they may be formed by sheet materials different from the side flaps 70. [0054] The disposable diaper 10 has a waist elastic sheet that extends bilaterally from the product widthwise center of the disposable diaper and is elastically extensible in the product width direction. The waist elastic sheet includes a back waist elastic sheet 85 disposed at the back edge of the disposable diaper and a front waist elastic sheet 86 disposed at the front edge of the disposable diaper. It is noted that, in Fig. 1, an imaginary line Li is shown, running through the product widthwise center (midpoints) of the disposable diaper, extending in the product English SpecificationUC-547-PCT 11 longitudinal direction. [0055] When the disposable diaper is in the relaxed state, the back edge 1OR thereof having a product widthwise center and product widthwise outer ends will have a curved shape in which the product widthwise center is recessed inward in the product longitudinal direction from the product widthwise outer ends. When the disposable diaper is in the relaxed state, a back edge of the back waist elastic sheet 85 at the back edge of the disposable diaper, having a product widthwise center and product widthwise outer ends, will also have a curved shape in which the product widthwise center is recessed inward in the product longitudinal direction from the product widthwise outer ends. [0056] Further, when the disposable diaper is in the stretched state (as is shown in Fig. 1), a front edge 85F of the back waist elastic sheet 85, having a product widthwise center and product widthwise outer ends, will have a curved shape in which the product widthwise center is recessed outward in the product longitudinal direction from the product widthwise outer ends. It is noted that, the curved shape of the back waist elastic sheet is not formed in the entirety of the front edge 85F, but partially at the widthwise center of the front edge. [0057] The back waist elastic sheet 85 is disposed between the pair of fastening tapes in the product width direction. A portion of the front edge 85F of the back waist elastic sheet 85 overlaps the absorbent core 40a. The back edge 85R of the back waist elastic sheet 85 is aligned with the back edge of the disposable diaper. The back waist elastic sheet 85 is greater in length in the product width direction than the absorbent core 40a and the back sheet 60a. The back waist elastic sheet extends outward in the product width direction from the absorbent core 40a and from the back sheet 60a. A portion of the back waist elastic sheet 85 overlaps the waist holding section. [0058] When the disposable diaper is in the relaxed state, the front edge 1OF thereof having a product widthwise center and product widthwise outer ends will have a curved shape in which the product widthwise center is recessed inward in the product longitudinal direction from the product widthwise outer ends. When the disposable diaper is in the relaxed state, a front edge 86F of the front waist elastic sheet 86 at the front edge of the disposable diaper, having a product widthwise center and product widthwise outer ends, will also have a curved shape in which the product widthwise center is recessed inward in the product longitudinal direction from the product widthwise outer ends. [0059] English SpecificationUC-547-PCT 12 Further, when the disposable diaper is in the stretched state (as is shown in Fig. 1), a back edge 86R of the front waist elastic sheet 86, having a product widthwise center and product widthwise outer ends, will have a curved shape in which the product widthwise center is recessed outward in the product longitudinal direction from the product widthwise outer ends. It is noted that, the curved shape of the front waist elastic sheet is not formed in the entirety of the back edge 86R, but partially at the widthwise center of the back edge 86R. [0060] The front waist elastic sheet 86 is adjacent to the absorbent core 40a and the target sections 95 in the product longitudinal direction. Specifically, the back edge 86R of the front waist elastic sheet 86 is adjacent to a front edge of the absorbent core 40a and front edges of the target sections 95. The back edge 86R of the front waist elastic sheet 86 is outward in the product longitudinal direction from the absorbent core 40a and from the target sections 95. Here, the front waist elastic sheet 86 being adjacent to the absorbent core 40a and the target sections 95 means that the front waist elastic sheet 86 is spaced from the absorbent core 40a and the target sections 95, respectively, by a distance ranging from 0 mm to 5 mm. [0061] The front edge 86F of the front waist elastic sheet 86 is aligned with the front edge of the disposable diaper. The front waist elastic sheet 86 is greater in length in the product width direction than the absorbent core 40a and the back sheet 60a. The front waist elastic sheet 86 extends outward in the product width direction from the absorbent core 40a and from the back sheet 60a. [0062] The back edge 86R of the front waist elastic sheet 86 is adjacent to the absorbent core 40a and the target sections 95 in the product longitudinal direction. The back edge 86R of the front waist elastic sheet 86 is outward in the product longitudinal direction from the absorbent core 40a and from the target sections 95. [0063] A front edge 60aF of the back sheet 60a is located between the front edge 1OF of the disposable diaper and the front edge of the absorbent core 40a, while a back edge 60aR of the back sheet 60a is located between the back edge 1OR of the disposable diaper and a back edge of the absorbent core 40a. [0064] In the embodiment, a sheet having a property of narrowing (so-called "narrowing sheet") is preferable for the waist elastic sheet, that is, when the sheet is stretched in one direction, the sheet is narrowed in a second direction orthogonal to the stretching direction. [0065] A usable waist elastic sheet can be a sheet formed of an mixture of elastic English Specification_UC-547-PCT 13 filaments that are elastically extensible and non-elastic filaments that are non-elastically extensible, in particular, a spunbond nonwoven fabric sheet having a mass of 20-80 g/m 2 , more preferably 40-75 g/m 2 , and more preferably 50-70 g/m 2 , containing polyurethane filaments as elastic filaments having a denier of 2-6 dtex and at least one of polyolefin filaments, polyester filaments, and polyamide filaments as non-elastic filaments having a denier of 2-6 dtex, with a mixing ratio by weight between the elastic filaments and the non-elastic filaments being 40 : 60 to 60 : 40. In such nonwoven fabric formed of a mixture of elastic filaments and non-elastic filaments, part of a non-elastic filament layer is broken with gear so as to render extensibility. Other waist elastic sheets are also possible as long as one has a narrowing property, which can be relatively readily shaped into the narrowed configuration of the embodiment. It is noted that, the waist elastic sheet is not limited to a nonwoven fabric sheet, but may be formed of a film sheet. Further, a pre-shaped elastic sheet may also be used, having a varying width in the product longitudinal direction or cut so as to protrude inward in the product longitudinal direction. The waist elastic sheet is bonded to the external sheet 60 via hot melt adhesive or thermal processing, for example. [0066] The extensibility of the back waist elastic sheet 85 is preferably 1.4 to 1.8. In the embodiment, the extensibility of the back waist elastic sheet 85 is set to 1.5 to 1.6. It is noted that, the extensibility is a degree of extension of the back waist elastic sheet and is defined as follows: back waist elastic sheet's extensibility = (length of back waist elastic sheet in stretched state)/(length of back waist elastic sheet in relaxed state). [0067] The extensibility of the front waist elastic sheet 86 is preferably 1.3 to 1.7. In the embodiment, the extensibility of the front waist elastic sheet 86 is set to 1.4 to 1.6. It is noted that, the extensibility is a degree of extension of the front waist elastic sheet and is defined as follows: front waist elastic sheet's extensibility = (length of front waist elastic sheet in stretched state)/(length of back front elastic sheet in relaxed state). [0068] With this sheet configuration of the waist elastic sheet, the region in which the waist elastic sheet is disposed (the area neighboring the waist opening) will be in surface contact with the wearer's body. Thus, a desired fit on the wearer is achieved. In contrast, in a configuration in which a plurality of elastic threads are provided, the elastic threads will conform to the wearer's body, yet strictly speaking, portions between the individual elastic threads will not. Hence, the elastic threads provide line contact with the wearer's body, which increases the likelihood of displacement, and thus may fail to properly cover the wearer's body. Because the English SpecificationUC-547-PCT 14 waist elastic sheet is elastic itself, it has enhanced flexibility and is capable of providing a sort of waist cushion. Furthermore, when the waist elastic sheet is in a contracted state, the area in which the waist elastic sheet is disposed tends to gain bulk and is soft to the touch. [0069] In the embodiment, the waist elastic sheet is joined to the sheets that interpose the waist elastic sheet therebetween. Specifically, the waist elastic sheet is interposed between the external sheet 60 and the back sheet 60a. However, in a configuration in which the core wrap 40b extends outward in the product longitudinal direction from the absorbent core 40a, the waist elastic sheet may be interposed between the core wrap 40b and the back sheet 60a or the external sheet 60. The position of the waist elastic sheet is not limited. In the region in which the absorbent is absent, the waist elastic sheet may be interposed between the side flap 70 and the back sheet 60a or the external sheet 60. The waist elastic sheet is bonded, for example, to the external sheet 60 via hot melt adhesive or thermal processing, for example. [0070] In the region in which the waist elastic sheet is disposed, the sheets, specifically, the top sheet, the back sheet, and the waist elastic sheet, are joined to each other via adhesive (hot melt adhesive) that is intermittently applied. Here, "intermittent" application of adhesive means that adhesive is delivered not planar but linearly, creating a meandering or spiral pattern, for example. [0071] The back waist elastic sheet 85, in plan view of the disposable diaper, overlaps a portion of the low-stiffness region 110 of the absorbent. It is noted that, although the back waist elastic sheet 85 partially overlaps the low-stiffness region 110 in the embodiment, the whole back waist elastic sheet 85 may overlap the low-stiffness region 110. [0072] Because such low-stiffness region 110 has been formed, the back waist elastic sheet 85 can elastically extend without obstruction, and when it contracts, the low-stiffness region 110 becomes narrower, shortening the distance between the planking absorbent areas on both sides of the product width direction, so that the absorbent 40 is prevented from rising into an unintended profile. An area in which the low-stiffness region 110 is formed will resists rising. The low-stiffness region 110 being resistant to rising is formed at the product widthwise center of the disposable diaper. Consequently, surface unevenness between the absorbent core and the waist elastic sheet is prevented in the product width direction of the disposable diaper. It is noted that the low-stiffness region is not limited at the back edge of the absorbent, but may also be formed at the front edge of the absorbent.

English Specification_UC-547-PCT 15 [0073] It is noted that, although the waist elastic sheet according to the embodiment is configured to extend and contract in the product width direction, the waist elastic sheet may be configured to extend and contract in the product width direction and the product longitudinal direction. [0074] The fastening tape 90 is attached to a corresponding region in the side flap 70 in the back lower-torso region 30. The fastening tape 90 includes a substrate sheet 91 connected to the side flap 70 and a hook sheet 92 fixed to the substrate sheet 91 and provided with a plurality of engagement hooks as engagement members (not shown) thereon. The hook sheet 92 is a region that is provided with engagement members thereon; and the waist holding section in the back lower-torso region, as mentioned above, is the region that extends from the hook sheet 92 in the product width direction. [0075] The hook sheet 92 is fixed to the substrate sheet 91, more particularly, joined to the substrate sheet 91. The joining of the hook sheet 92 and the substrate sheet 91 is preferably performed with care to avoid stiffening of the fastening tape 90 more than necessary. Specifically, the hook sheet 92 and the substrate sheet 91 are preferably joined with hot melt adhesive, applied intermittently in dots, spirals, or lines. It is noted that the hook sheet 92 and the substrate sheet 91 may also be joined via heat sealing or the like. [0076] The substrate sheet 91 is formed by one, or two or more laminated nonwoven fabrics. A nonwoven fabric made through spunbonding (SB) or spunbond-meltblown-spunbond (SMS) process may be used as the substrate sheet 91. The nonwoven fabric forming the substrate sheet 91 has a basis weight (or a total basis weight if nonwoven fabrics are laminated) of 30-120 g/m 2 , preferably 40-90 g/m 2 . [0077] The fastening tape includes a base 93 that overlaps the external sheet and an extension 94 that extends outward in the product width direction from the external sheet. The base 93 is an area of the substrate sheet 91 which overlaps the external sheet when the fastening tape is deployed. The extension 94 is another area of the substrate sheet 91 which does not overlap the external sheet. When the disposable diaper is in the stretched state as is shown in Fig. 1, a product longitudinal center of the extension is aligned with a product longitudinal center of the base, in the product longitudinal direction. On the other hand, when the disposable diaper is in the relaxed state, the fastening tape is shifted in association with the curving of the back waist elastic sheet 85, so that the product longitudinal English Specification_UC-547-PCT 16 center of the extension comes outward in the product longitudinal direction from the longitudinal center of the base. [0078] As used herein, overlapping of components includes indirect overlapping of components (with other component(s) interposed therebetween) as well as direct overlapping of components. [0079] The target sections 95 are disposed on the non-skin-facing side surface of the external sheet 60 in the front lower-torso region. The target sections 95 are configured to function as a loop in a hook-loop fastening system so that the engagement hooks of the fastening tapes can hook thereon. An air-through nonwoven fabric, for example, may be used for the target sections. [0080] By way of example, a filament nonwoven fabric made of polyolefinic thermoplastic synthetic resin filaments or a polyolefinic thermoplastic synthetic resin film may be used for the target sections 95. The loops on the target sections may be formed of polyolefinic thermoplastic synthetic resin. [0081] Further, a bulky nonwoven fabric may be partially embossed for preventing fluffiness on the surface and used for the target sections 95. [0082] Further, the external sheet 60 of the disposable diaper may be formed by a nonwoven fabric, and indicial marking for the fastening of the fastening tapes 90 may be printed on the non-skin-facing side surface of the back sheet 60a or the external sheet 60 or indicial sheets may be disposed on the non-skin-facing side surface of the back sheet 60a or the external sheet 60, so that the marking or the sheets function as the target sections. [0083] To put the disposable diaper on, a caregiver pulls the fastening tape in the back lower-torso region to the front lower-torso region. As the caregiver brings the fastening tape to the front lower-torso region, he or she fastens the fastening tape to the corresponding target section. [0084] (2) Manufacturing method for disposable diaper The following will explain one example of a manufacturing method for the disposable diaper according to the embodiment. Note that, for methods that will not be explained in the embodiment, any existing method(s) may be used. Further, the manufacturing method to be explained below is merely an example, and other manufacturing method(s) may also be employed. The manufacturing method for the disposable diaper at least includes a component forming step, a English Specification_UC-547-PCT 17 component arranging step, leg-area forming step, and a cutting step. [0085] In the manufacturing method for the disposable diaper, individual disposable diapers are manufactured as follows: a continuous body of a plurality of disposable diapers connected to each other in the product longitudinal direction is made, and then the continuous body is cut to the size of an individual disposable diaper along the product width direction W. [0086] In the component forming step, components of the disposable diaper are formed. Specifically, the absorbent core 40a is formed by layering absorbent material, for example. [0087] In the component arranging step, components of the disposable diaper 10, such as continuous webs of waist elastic sheet and top sheet, the absorbent, the leg elastic zone 75, and secondary elastic zone 77, are arranged on top of a continuous web of back sheet. [0088] Here, for the waist elastic sheet, the front waist elastic sheet 86 of one disposable diaper and the back waist elastic sheet 85 of the adjacent disposable diaper are not yet separated. The side edges of the elastic sheet, which are to be the product widthwise outer edges of the disposable diaper when the disposable diaper is formed, are held with suction means or the like, and the elastic sheet is stretched in the product width direction of the disposable diaper and affixed onto a continuous web. Because the elastic sheet is stretched with its side edges held, the side edges of the elastic sheet are hardly stretched. The extensibility of the side edges of the elastic sheet in the product width direction will be lower than the extensibility of the area between the side edges in the product width direction. [0089] Specifically, the region in which the waist elastic sheet of the disposable diaper is disposed will have three zones having different extensibilities. The three zones in the region in which the waist elastic sheet of the disposable diaper is disposed, are: a central zone located in the product widthwise center of the region, a lateral zone located at each of the product widthwise edges in the region (corresponding to the side edges of the waist elastic sheet), and an intermediate zone between the central zone and the lateral zone; and the relation of these zones in terms of extensibility is: extensibility of the central zone in the product width direction > extensibility of the intermediate zone in the product width direction > extensibility of the lateral zone in the product width direction. [0090] The extensibility of the central zone in the product width direction can be English Specification_UC-547-PCT 18 1.4 to 1.8. The extensibility of the lateral zone in the product width direction is set lower than the extensibility of the central zone in the product width direction, which can be 1.0 to 1.1. The extensibility of the intermediate zone can be set lower than the extensibility of the central zone in the product width direction but higher than the extensibility of the lateral zone in the product width direction, which can be 1.2 to 1.3. It is noted that, the extensibility of the lateral zone in the product width direction can be 1.0 and thus this zone may not be practically stretchable. [0091] Further, the elastic sheet that has been stretched in the product width direction is narrowed in the product longitudinal direction. In particular, the product widthwise center of the elastic sheet is narrowed. Hence, in the stretched elastic sheet, a length in the product longitudinal direction at the product widthwise center is shorter than that at the product widthwise edge. In the elastic sheet that has been affixed in such narrowed state, as shown in Fig. 1, product longitudinal end edges of the elastic sheet, such as the back edge of the front waist elastic sheet and the front edge of the back waist elastic sheet, have curved shapes in which the widthwise centers thereof are recessed from the widthwise outer ends thereof. [0092] In the leg-area forming step, the top sheet 50, the external sheet 60, and the back sheet 60a are cut. As a result, the front edges 77F of the secondary elastic zones 77 are cut, and the leg openings 35 to encircle the wearer's legs are formed. [0093] In the cutting step, the continuous body in which the top sheet 50, the back sheet 60a, the absorbent 40, and other components have been arranged is cut in the product width direction W to the size of a product. In this way, the disposable diaper 10 is manufactured. [0094] As the individual disposable diapers are cut from the continuous body, the waist elastic sheets and the leg elastic zones in the disposable diapers which have been stretched are relaxed, assuming the relaxed state. As the stretched state is relaxed, the waist elastic sheet that has been narrowed due to the stretching is deformed to return to the state before narrowing. Thus, the back edge of the back waist elastic sheet and the front edge of the front waist elastic sheet, which have been straight in the stretched state, are deformed and curved in the relaxed state. [0095] Further, as the individual disposable diapers are cut from the continuous body and assume the relaxed state, the front edge of the front waist elastic sheet contracts by a greater amount compared to the back edge of the front waist elastic sheet, and the back edge of the back waist elastic sheet contracts by a greater English Specification_UC-547-PCT 19 amount compared to the front edge of the back waist elastic sheet. The greater amount of contraction of the front edge of the front waist elastic sheet is attributed to the fact that the front edge of the front waist elastic sheet is more spaced from the absorbent core 40a compared to the back edge of the front waist elastic sheet and hence it is less affected by the stiffness of the absorbent core 40a. The greater amount of contraction of the back edge of the back waist elastic sheet is attributed to the fact that the back edge of the back waist elastic sheet is more spaced from the absorbent core 40a compared to the front edge of the back waist elastic sheet and hence it is less affected by the stiffness of the absorbent core 40a. [0096] The front edge of the front waist elastic sheet contracts by a greater amount compared to the back edge of the front waist elastic sheet, so that the product widthwise center of the front edge of the disposable diaper is recessed inward in the product longitudinal direction from the product widthwise outer ends of the front edge of the disposable diaper, creating a curved shape. Similarly, the back edge of the back waist elastic sheet contracts by a greater amount compared to the front edge of the back waist elastic sheet, so that the product widthwise center of the back edge of the disposable diaper is recessed inward in the product longitudinal direction from the product widthwise outer ends of the back edge of the disposable diaper, creating a curved shape. [0097] (3) Operation and effect The back waist elastic sheet 85 overlaps the back edge of the absorbent core 40a, so that the back waist elastic sheet 85 and the absorbent core 40a are not spaced from each other. Otherwise, for instance, a region between the waist elastic sheet and the absorbent core 40a may be raised, whereby surface unevenness due to thickness difference may become obvious. In contrast, because a portion of the back waist elastic sheet 85 overlaps the back edge of the absorbent core 40a, thickness transition can be gradual in the overlapped area. [0098] Further, a portion of the back waist elastic sheet 85 overlaps the waist holding section. Thus, unwanted situations, in which a region between the waist holding section and the waist elastic sheet is raised or such region causes unevenness with the waist holding section, can be prevented. [0099] Surface unevenness is gradually decreased toward the back edge of the disposable diaper, so that discomfort to skin caused by unevenness can be prevented. Further, an underwear-like appearance is possible because thickness transition in the disposable diaper is smooth. With such disposable diaper, user demands about skin protection and appearance can be satisfied.

English Specification_UC-547-PCT 20 [0100] It is noted that, in the disposable diaper according to the embodiment, the area in which the waist elastic sheet is disposed has a thickness of about 1.5 mm to 3.0 mm in the relaxed state, the area in which the absorbent core is disposed has a thickness of about 3.5 mm to 4.5 mm, and the product longitudinal end of the disposable diaper (the area in which the back sheet is not disposed) has a thickness of about 1.0 mm to 2.0 mm. [0101] The front waist elastic sheet 86 is disposed adjacent to the front edge of the absorbent core 40a, and thus a region having the thickness of the front waist elastic sheet and a region having the thickness of the absorbent core 40a are adjacent to each other. Hence, an underwear-like appearance is also possible in the front lower-torso region due to smooth thickness transition in the disposable diaper. [0102] The front edge 60aF of the back sheet is located between the front edge 10F of the disposable diaper and the front edge of the absorbent core 40a, while the back edge 60aR of the back sheet is located between the back edge of the disposable diaper and the back edge of the absorbent core 40a. The presence and absence of the back sheet in the regions between the absorbent core 40a and the respective product longitudinal ends of the disposable diaper provides change in thickness, which contributes to smoother thickness transition in these regions. [0103] The back edge 86R of the front waist elastic sheet 86 is disposed adjacent to the front edges of the target sections, and the front waist elastic sheet 86 which does not overlap the target sections will contract when the disposable diaper is in the relaxed state. On the other hand, the target sections 95 are the areas necessary for fixing the fastening tapes, and if they should contract, they would be wrinkled and therefore would not fully provide the fastening (joining) of the fastening tapes. Further, compared to other sheet components of disposable diaper, such as the top sheet and the back sheet, a sheet material having a higher basis weight or stiffness is typically used for the fastening tapes. For this reason, contraction of the target sections, onto which the fastening tapes are fastened, can altogether create an impression associable with discomfort. Thus, it is preferable that the front waist elastic sheet is disposed adjacent to the target sections rather than overlapping the target sections. [0104] The top sheet having the high basis weight portions and the low basis weight portions is disposed at least from regions in which the waist elastic sheets are disposed to the respective product longitudinal ends of the disposable diaper. More specifically, when the top sheet is disposed at least from regions in which the English SpecificationUC-547-PCT 21 waist elastic sheets are disposed to the respective product longitudinal ends of the disposable diaper, the top sheet covers the back waist elastic sheet and is continuously disposed therefrom until it reaches the back edge of the disposable diaper, and also the top sheet covers the front waist elastic sheet and is continuously disposed therefrom until it reaches the front edge of the disposable diaper. [0105] Because the top sheet has the high basis weight portions and the low basis weight portions, the low basis weight portions typically contract when the waist elastic sheet is in the contracted state, so that any adjacent high and low basis weight portions become closer to each other. Consequently, when the disposable diaper is in the relaxed state, the area in which the top sheet is disposed typically has increased bulk, providing a certain level of thickness while maintaining a certain level of flexibility. In this way, thickness difference from each product longitudinal end of the absorbent to the corresponding product longitudinal end of the disposable diaper is less obvious. [0106] At least one of the top sheet and the external sheet is formed by a nonwoven fabric sheet having no thermo-fused region by dot-pattern or linear embossing, or a nonwoven fabric sheet having a dot-pattern or linear embossed area by a percentage of 5% to 15%. In the top sheet and/or the external sheet formed by such nonwoven fabric sheet, filaments in the areas in which no thermo-fused region or embossment is formed are allowed a relatively high degree of freedom. Thus, the filament portions having a relatively high degree of freedom typically provide bulk in the relaxed state. In this way, thickness difference from each product longitudinal end of the absorbent to the corresponding product longitudinal end of the disposable diaper is less obvious. [0107] The waist elastic sheet is joined to the sheets that interpose the waist elastic sheet therebetween via adhesive with a relatively small ratio of joined regions, because the adhesive is applied intermittently. When the waist elastic sheet is in the contracted state, greater product thickness and increased flexibility are allowed in non-joined regions (the areas without adhesive). [0108] The thickness of the absorbent core at the product longitudinal end is smaller than the thickness of the absorbent core at the product longitudinal center. The thickness of the disposable diaper gradually changes from the crotch region through the product longitudinal end of the absorbent to the product longitudinal end of the disposable diaper. In this way, surface unevenness of the disposable diaper is less recognizable for users. [0109] English SpecificationUC-547-PCT 22 (4) Other embodiments The content of the present invention has been disclosed as above through the embodiments of the present invention; however, the description and drawings as part of the disclosure should not be understood as limitation to the present invention. After reviewing this disclosure, various alternative embodiments, examples, and practicable techniques will be apparent to those skilled in the art. [0110] In a modification example, a front waist elastic sheet may overlap a front edge of an absorbent core 40a. [0111] In a modification example, a front edge of a back sheet may extend to a front edge of the disposable diaper or may be in the back relative to a front edge of an absorbent core. In a modification example, a back edge of a back sheet may extend to a back edge of the disposable diaper or may be in the front relative to a back edge of an absorbent core. [0112] In a modification example, the product longitudinal lengths of the lateral zones of the disposable diaper may be equal to, or greater than or smaller than the product longitudinal length of the central zone of the disposable diaper. [0113] In a modification example, a back edge of a front waist elastic sheet may overlap front edges of target sections. [0114] In a modification example, a pattern may be provided on a back sheet, which pattern is visible from the non-skin-facing side of the disposable diaper. The pattern may be printed or formed through any one of embossing, thermo-fusing, and ultrasonic sealing. [0115] The pattern is disposed in a region that overlaps an absorbent core. Further, the pattern is not disposed between a front edge of the disposable diaper and a front edge of the absorbent core, and is not disposed between a back edge of the disposable diaper and a back edge of the absorbent core. The pattern is not disposed in areas neighboring the waist and the areas in which the absorbent core is absent and the color of the wearer's skin is generally seen through. In this way, the waist area may resemble that of underwear. [0116] In a modification example, a top sheet may not be formed by a nonwoven fabric sheet having alternating high basis weight portions and low basis weight portions in the product width direction. [0117] English Specification_UC-547-PCT 23 In a modification example, a top sheet may not be formed by a nonwoven fabric sheet having no thermo-fused region by dot-pattern or linear embossing, and may not be formed of a nonwoven fabric sheet having a percentage of dot-pattern or linear embossed area by 5% to 15%. Further, an external sheet may not be formed by a nonwoven fabric sheet having no thermo-fused region by dot-pattern or linear embossing, and may not be formed of a nonwoven fabric sheet having a percentage of dot-pattern or linear embossed area by 5% to 15%. [0118] In a modification example, the adhesive for joining an waist elastic sheet and the sheets interposing the waist elastic sheet therebetween may not be placed intermittently but may be placed all over the surface. [0119] In a modification example, an absorbent core has a thickness at a product longitudinal end thereof and a thickness at a product longitudinal center thereof, and the former thickness may be equal to or greater than the latter thickness. [0120] Hence, it is obvious that the present invention includes various embodiments that are not described herein. Therefore, the technical scope of the present invention is defined solely by matters specifying the invention stated in the scope of the claims which are valid from the above description. [0121] It is appreciated that Japanese Patent Application No. 2013-156040 (filed on July 26, 2013) is incorporated herein in its entirety by reference. INDUSTRIAL APPLICABILITY [0122] A disposable diaper that is easy on wearer's skin and has an acceptable appearance to satisfy consumer demands can be provided. REFERENCE SIGNS LIST [0123] 10: disposable diaper 20: front lower-torso region 25: crotch region 30: back lower-torso region 35: leg opening 40: absorbent 40a: absorbent core 40b: core wrap English Specification_UC-547-PCT 24 50: top sheet 60: external sheet 60a: back sheet 70: side flap 75: leg elastic zone 75F: front edge 75R: back edge 77: secondary elastic zone 77F: front edge 77R: back edge 80: leg side gathers 81: elastic member 85: back waist elastic sheet 85F: front edge 85R: back edge 86: front waist elastic sheet 86F: front edge 86R: back edge 90: fastening tape 91: substrate sheet 92: hook sheet 93: base 94: extension 95: target section 110: low-stiffness region L: product longitudinal direction W: product width direction

Claims (8)

1. A disposable diaper, comprising: a front lower-torso region, a back lower-torso region, and a crotch region between the front lower-torso region and the back lower-torso region; a product longitudinal direction from the front lower-torso region to the back lower-torso region; a product width direction orthogonal to the product longitudinal direction; an absorbent extending from the crotch region to at least one of the front lower-torso region and the back lower-torso region, and having an absorbent core; a pair of fastening tapes disposed on product widthwise outer edges of the back lower-torso region and configured to be fastened to the front lower-torso region; and a waist elastic sheet extending bilaterally from the center in the product width direction of the disposable diaper and being elastically extensible in the product width direction; and a waist holding section in the front lower-torso region and the back lower-torso region, extending along the product width direction for holding the disposable diaper against a wearer's body, wherein the waist elastic sheet includes a back waist elastic sheet disposed at a back edge of the back lower-torso region; and a front waist elastic sheet disposed at a front edge of the front lower-torso region, a portion of the back waist elastic sheet overlaps a back edge of the absorbent core and the waist holding section, and the front waist elastic sheet is disposed adjacent to a front edge of the absorbent core.

2. The disposable diaper according to claim 1, comprising a liquid-impermeable back sheet disposed on a non-skin-facing surface of the absorbent, wherein a front edge of the back sheet is located between a front edge of the disposable diaper and the front edge of the absorbent core, and a back edge of the back sheet is located between a back edge of the disposable diaper and the back edge of the absorbent core.

3. The disposable diaper according to claim 2, wherein a pattern is provided on the back sheet, which pattern being visible from a non-skin-facing side of the disposable diaper, wherein the pattern is disposed in a region that overlaps the absorbent core, but is not disposed between the front edge of the disposable diaper and the front edge of the absorbent core nor between the back edge of the disposable diaper and the back edge of the absorbent core. English Specification_UC-547-PCT 26

4. The disposable diaper according to any one of claims 1 to 3, wherein target sections are disposed on the front lower-torso region for fastening of the fastening tapes, and a back edge of the front waist elastic sheet is disposed adjacent to front edges of target sections.

5. The disposable diaper according to any one of claims 1 to 4, comprising a top sheet disposed on a surface on a skin-facing side of the disposable diaper, wherein the top sheet is disposed at least from regions in which the waist elastic sheets are disposed to the respective product longitudinal ends of the disposable diaper, and the top sheet is formed by a nonwoven fabric sheet having alternating high basis weight portions and low basis weight portions in the product width direction.

6. The disposable diaper according to any one of claims I to 4, comprising: an external sheet disposed on a surface on the non-skin-facing side of the disposable diaper; and a top sheet disposed on a surface on the skin-facing side of the disposable diaper, wherein at least one of the top sheet and the external sheet is formed by a nonwoven fabric sheet having no thermo-fused region by dot-pattern or linear embossing, or a nonwoven fabric sheet having a dot-pattern or linear embossed area by a percentage of 5% to 15%, and the one of the top sheet and the external sheet is disposed at least from the regions in which the waist elastic sheets are disposed to the respective product longitudinal ends of the disposable diaper.

7. The disposable diaper according to any one of claims 1 to 6, wherein the waist elastic sheet is joined via adhesive to the sheets that interpose the waist elastic sheet therebetween, wherein the adhesive is intermittently applied.

8. The disposable diaper according to any one of claims 1 to 7, wherein the absorbent core has a thickness at the product longitudinal end thereof and a thickness at a product longitudinal center thereof, the former thickness being smaller than the latter thickness.