Absorbent article

Abstract

Provided is an absorbent article having, in an unfolded and extended state, a longitudinal direction, a left-right direction, and a thickness direction that are orthogonal to each other, and having an absorbent core (21) and a core wrap sheet (24) that covers at least part of the skin-side surface and at least part of the non-skin side surface of the absorbent core (21), wherein: the absorbent article comprises an elastic member stretchable in the longitudinal direction or the left-right direction; the absorbent core (21) and the core wrap sheet (24) are fixed to each other with an adhesive (HMA); the absorbent core (21) includes cellulose fibers (22) and a super-absorbent polymer (SAP); and when a portion that is central in the thickness direction when the absorbent core (21) is divided into three equal parts in the thickness direction and that is central when the absorbent core (21) is divided into three equal parts in the left-right direction is defined as a core central portion, in the core central portion, the cellulose fibers (22) are not fixed to each other with the adhesive (HMA), and the average value of the lengths of the cellulose fibers (22) is smaller than the average value of the diameters of the super-absorbent polymer (SAP) in a state after being immersed in physiological saline for 60 minutes and then drained for 15 minutes.

Description

Absorbent article

[0001] The present invention relates to an absorbent article.

[0002] Conventionally, absorbent articles including an absorbent core that absorbs excreta such as urine and feces are known. For example, the absorbent core of a sanitary napkin described in Patent Document 1 comprises fibers such as pulp fibers. In the sanitary napkin of Patent Document 1, fibers such as pulp fibers, and a binder material for fixing the fibers are provided in a web constituting the absorbent core.

[0003] Japanese National Publication of International Patent Application No. 2004-538024

[0004] As in the sanitary napkin of Patent Document 1, when an absorbent article includes an absorbent core in which fibers such as pulp fibers are fixed with a binder, an adhesive or the like, although there is an advantage that the rigidity of the absorbent core is easily increased and the durability of the absorbent core is easily improved, the increased rigidity of the absorbent core reduces the flexibility of the absorbent core, which may cause a decrease in fit during wear. Further, when the absorbent core comprises a superabsorbent polymer, a sufficient space for the superabsorbent polymer to swell within the absorbent core cannot be secured, which may cause a decrease in absorbency.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide an absorbent article with improved fit and absorbency.

[0006] The main invention for achieving the above objective is an absorbent article having an absorbent core and a core wrap sheet covering at least a portion of the skin-facing side and at least a portion of the non-skin-facing side of the absorbent core, having longitudinal, left-right, and thickness directions that are mutually orthogonal in an unfolded and extended state, wherein the article has an expandable member that is expandable and expandable in the longitudinal or left-right direction, the absorbent core and the core wrap sheet are fixed together with an adhesive, the absorbent core comprises cellulose fibers and a superabsorbent polymer, and when the absorbent core is divided into three equal parts in the thickness direction, the central part in the thickness direction, and when the absorbent core is divided into three equal parts in the left-right direction, the central part of the core, in the central part of the core, the cellulose fibers are not fixed together with the adhesive, and the average length of the cellulose fibers is smaller than the average diameter of the superabsorbent polymer after immersion in physiological saline for 60 minutes and draining for 15 minutes. Other features of the present invention will be made clear by description in this specification and the accompanying drawings.

[0007] According to the present invention, it is possible to provide a pant-type absorbent article that makes it easy for the wearer to recognize the position of the leg openings.

[0008] This is a schematic perspective view of diaper 1. This is a plan view of diaper 1 in its unfolded and stretched state, seen from the skin side. This is a plan view of diaper 1 in its unfolded and stretched state, seen from the non-skin side. This is a schematic cross-sectional view of the center line CL in Figure 2. This is an explanatory diagram of the absorbent body 10. This is a schematic cross-sectional view of the absorbent material 20 at position A-A in Figure 5. This is a diagram showing the distribution of fiber lengths of hardwood fibers (hardwood pulp) and softwood fibers (softwood pulp). This is a diagram for explaining the manufacturing method of the absorbent core 21. This is a table showing the change in SAP diameter when SAP is swollen at a predetermined water absorption ratio / water retention ratio. This is a table showing the particle size distribution of SAP used in this embodiment. This is a diagram explaining the fixing of the absorbent core 21 and the non-skin side core wrap portion 24b. This is a diagram explaining a modified example of the absorbent material 20. Figure 13A is a diagram explaining the absorbent material 20 and the skin side polymer layer 70A. Figure 13B is a diagram explaining the absorbent material 20 and the non-skin side polymer layer 70B.

[0009] The following matters will become clear from the description in this specification and the accompanying drawings: (Aspect 1) An absorbent article having an absorbent core and a core wrap sheet covering at least a portion of the skin side and at least a portion of the non-skin side of the absorbent core, having longitudinal, left-right, and thickness directions that are mutually orthogonal in an unfolded and extended state, wherein the article has an expandable member that is expandable and expandable in the longitudinal or left-right direction, the absorbent core and the core wrap sheet are fixed together with an adhesive, the absorbent core comprises cellulose fibers and a superabsorbent polymer, and when the absorbent core is divided into three equal parts in the thickness direction, the central part in the thickness direction, and when the absorbent core is divided into three equal parts in the left-right direction, the central part of the core, in the central part of the core, the cellulose fibers are not fixed together with the adhesive, and the average length of the cellulose fibers is smaller than the average diameter of the superabsorbent polymer after being immersed in physiological saline for 60 minutes and then drained for 15 minutes.

[0010] According to the absorbent article of Embodiment 1, by providing an absorbent core with cellulose fibers and a superabsorbent polymer, the water absorption of the absorbent article is improved, the absorbent core is made easier to move by the expansion and contraction of the expandable member, and the average length of the cellulose fibers is made smaller than the average diameter of the superabsorbent polymer after being immersed in physiological saline for 60 minutes and then drained for 15 minutes. By making the length of the cellulose fibers shorter than in the case where the absorbent article does not have an expandable member and the average length of the cellulose fibers is greater than or equal to the average diameter of the superabsorbent polymer after being immersed in physiological saline for 60 minutes and then drained for 15 minutes, the cellulose fibers of the absorbent core become easier to loosen, so when worn, the superabsorbent polymer swells more easily, the absorbent core can be made to follow the shape and movement of the wearer's body, and the fit and absorbency can be improved.

[0011] (Aspect 2) The absorbent article of Aspect 1, characterized in that, in the unfolded and stretched state, the cellulose fibers have a portion that overlaps with the expandable member when viewed in the thickness direction.

[0012] According to the absorbent article of embodiment 2, the cellulose fibers that overlap with the stretchable member when viewed in the thickness direction are more easily loosened by the contraction of the stretchable member. As a result, when worn, the absorbent core can more easily conform to the shape and movement of the wearer's body, and the portion of the stretchable member that overlaps with the loosened cellulose fibers can more easily come into contact with the wearer's body, thereby improving the fit of the absorbent article.

[0013] (Aspect 3) The absorbent article according to aspect 1 or 2, characterized in that, in the unfolded and extended state, the expandable member is provided on the non-skin side of the absorbent core in the central part in the left-right direction and in the central part of the three equal parts obtained by dividing the absorbent article in the longitudinal direction.

[0014] According to the absorbent article of embodiment 3, when worn, the cellulose fibers of the absorbent core in the part that comes into contact with the wearer's groin area become easier to loosen, so that the part of the stretchable material that overlaps with the loosened cellulose fibers comes into contact with the wearer's body, thereby improving the fit of the part of the absorbent article that comes into contact with the groin area.

[0015] (Aspect 4) The absorbent article is a pant-type absorbent article that is folded in half in the front-to-back direction at the fold in the center of the longitudinal direction and has a pair of waist portions and a crotch portion, the ends of the pair of waist portions on both sides are joined at joints, and the expandable member is expandable in the left-to-right direction and is provided on the crotch side from the joint.

[0016] According to the absorbent article of embodiment 4, the stretching and contracting of the stretchable member makes it easier to loosen the cellulose fibers in the crotch area, thereby improving the fit of the absorbent article in the crotch area.

[0017] (Aspect 5) An absorbent article according to any of aspects 1 to 4, characterized in that, in the unfolded and extended state, it has a pair of leak-proof wall portions on both sides in the left-right direction, the leak-proof wall portion comprises a leak-proof wall sheet along the longitudinal direction and the expandable member, the leak-proof wall portion has an upright portion that can stand up on the skin side and a fixed portion that cannot stand up, the fixed portion has a first fixed portion and a second fixed portion, the first fixed portion is provided outside the upright portion in the longitudinal direction, the second fixed portion is provided outside the upright portion in the left-right direction, and when viewed in the thickness direction, the first fixed portion has a portion that overlaps with the absorbent core.

[0018] According to the absorbent article of embodiment 5, the contraction of the expandable member of the leak-proof wall loosens the cellulose fibers of the absorbent core, making it easier to improve the flexibility of the absorbent core and the portion of the first fixing part that overlaps with the absorbent core when viewed in the thickness direction. This makes it easier to deform the central part in the longitudinal direction of the absorbent core so that it protrudes toward the non-skin side. As a result, the expandable member of the leak-proof wall contracts more linearly, making it easier to stand the leak-proof wall upright and reducing leakage in the left-right direction when worn.

[0019] (Aspect 6) An absorbent article according to any one of aspects 1 to 5, wherein the absorbent article has a post-treatment tape on the non-skin side, the post-treatment tape has a tape fixing portion fixed to the non-skin side of the absorbent article in a manner that prevents peeling, and the tape fixing portion has a portion that overlaps with the absorbent core when viewed in the thickness direction.

[0020] According to the absorbent article of embodiment 6, the cellulose fibers loosen, improving the flexibility of the absorbent core, which makes it easier to dispose of the absorbent article after use using post-treatment tape.

[0021] (Aspect 7) The cellulose fiber is an absorbent article according to any one of aspects 1 to 6, characterized in that it has an adhesive portion bonded to the core wrap sheet with the adhesive and an unadhesive portion not bonded to the core wrap sheet with the adhesive.

[0022] According to the absorbent article of embodiment 7, the presence of an adhesive portion makes it easier to maintain the shape of the absorbent core, while the presence of a non-adhesive portion makes it easier to create a space for the superabsorbent polymer of the absorbent core to swell when it absorbs excrement.

[0023] (Aspect 8) The absorbent core has a polymer layer made of a superabsorbent polymer on the non-skin side, and the polymer layer has a portion in which the particles of the superabsorbent polymer are fixed together with the adhesive, characterized in that the absorbent article is according to any one of aspects 1 to 7.

[0024] According to the absorbent article of embodiment 8, having superabsorbent polymer particles fixed with an adhesive makes it easier to reduce the risk of superabsorbent polymer particles spilling out of the absorbent article.

[0025] (Aspect 9) An absorbent article according to any one of aspects 1 to 8, characterized in that the skin-side polymer layer containing a superabsorbent polymer but not containing liquid absorbent fibers is located on the skin-side side of the core wrap sheet, which is closest to the skin.

[0026] According to the absorbent article of embodiment 9, a highly water-retentive skin-side polymer layer is provided on the skin side, which makes it easier for the absorbent article to retain absorbed excrement in the skin-side polymer layer when worn. When the excrement reaches the absorbent core from the skin-side polymer layer, even if the absorbed excrement in the absorbent core tries to return to the skin side, the skin-side polymer layer can easily reabsorb and retain the excrement, thus reducing the risk of the excrement returning to the wearer's skin.

[0027] (Aspect 10) An absorbent article according to any one of aspects 1 to 9, characterized in that the non-skin side of the core wrap sheet has a non-skin side polymer layer that contains a superabsorbent polymer but does not contain liquid absorbent fibers.

[0028] According to the absorbent article of embodiment 10, when worn, the absorbent core having cellulose fibers facilitates the absorption of excrement, and the non-skin side polymer layer provided on the non-skin side of the absorbent core facilitates the retention of the excrement absorbed by the absorbent core.

[0029] ===Embodiments=== The absorbent article according to the present invention will be described using a pant-type disposable diaper 1 for infants (hereinafter also referred to as "diaper 1") as an example. However, the absorbent article according to the present invention also includes tape-type disposable diapers, panty-type sanitary napkins, absorbent pads, sanitary napkins, and other absorbent articles. Furthermore, the wearer of the absorbent article is not limited to infants, but may be an adult or a living being such as an animal.

[0030] ===Composition of the Pants-Type Disposable Diaper 1=== Figure 1 is a schematic perspective view of diaper 1. Figure 2 is a plan view of diaper 1 in its unfolded and stretched state, seen from the skin side. Figure 3 is a plan view of diaper 1 in its unfolded and stretched state, seen from the non-skin side. Figure 4 is a schematic cross-sectional view of Figure 2 at the center line CL.

[0031] The "stretched state" of diaper 1 refers to the state in which the entire diaper 1 is stretched without wrinkles, specifically, the state in which the dimensions of each component constituting diaper 1 (for example, the absorbent body 10 and waist sections 30, 40, etc., described later) are stretched to match or be close to the dimensions of the individual component. The "unfolded state" of diaper 1 refers to the state in which the pair of side joints 2 provided on both sides of diaper 1 are separated and diaper 1 is opened and unfolded in a planar manner.

[0032] Diaper 1 has mutually perpendicular vertical, horizontal, and front-to-back directions, and has a waist opening BH and a pair of leg openings LH. The upper side in the vertical direction corresponds to the waist opening BH side, and the lower side corresponds to the crotch side. The front side in the front-to-back direction corresponds to the wearer's abdominal side, and the rear side corresponds to the wearer's back side. The horizontal direction is along the stretching direction of the waist elastic members (thread elastic) 33, 43 of the abdominal waist portion 30 and the back waist portion 40. The vertical direction is along the orthogonal direction perpendicular to the stretching direction.

[0033] Diaper 1 is a so-called three-piece type pant diaper having an absorbent body 10 that absorbs liquid and a pair of waist sections 30 and 40. Of the pair of waist sections, the one that covers the front of the wearer is also called the front waist section 30, and the one that covers the back of the wearer is also called the rear waist section 40.

[0034] In the unfolded state shown in Figure 2, the diaper 1 has a longitudinal direction, a left-right direction, and a thickness direction that are perpendicular to each other. The longitudinal direction is along the longitudinal direction of the absorbent body 10 and along the vertical direction of the pant-type diaper 1. The center line C-C shown in Figure 2 etc. indicates the center of the diaper 1 in the left-right direction, and the center line CL indicates the center of the diaper 1 in the longitudinal direction in the unfolded state. The thickness direction is the direction in which the materials constituting the diaper 1 are layered, as shown in Figure 4. In the thickness direction, the side that comes into contact with the wearer's skin is called the skin side, and the opposite side is called the non-skin side. Also, in the unfolded state, the abdominal waist portion 30 and the back waist portion 40 are arranged parallel to each other with a gap in the longitudinal direction, and the absorbent body 10 is stretched between them, with each end of the absorbent body 10 in the longitudinal direction being joined and fixed to the skin side of the nearest waist portion 30, 40, and the external shape is approximately H-shaped in plan view. Then, from this state, the absorbent body 10 is folded in half along the longitudinal center line CL. In this folded state, the ventral body portion 30 and the dorsal body portion 40, which face each other, are joined and connected at the left and right sides, forming a pair of side joint portions 2. The side joint portions 2 are formed by known joining means such as welding or adhesive.

[0035] The absorbent body 10 comprises an absorbent core 20 (details of which will be described later), a liquid-permeable top sheet 12 positioned closer to the skin than the absorbent core 20, and a back sheet 13 positioned further away from the skin than the absorbent core 20. The back sheet 13 has a two-layer structure consisting of a liquid-impermeable sheet 13a and a hydrophobic outer sheet 13b positioned on its non-skin side. However, the absorbent body 10 may also include other sheet members. For example, a second sheet (not shown) may be provided between the top sheet 12 and the absorbent core 20 in the thickness direction.

[0036] A pair of leak-proof wall portions 15 are provided on both sides of the absorbent body 10 in the left-right direction, along the longitudinal direction of the absorbent body 10. In Figure 4, in the left-right direction, a part of the outer sheet 13b (leak-proof wall sheet) extends outward beyond both ends of the absorbent body 20 and is folded in multiple places toward the skin, thereby forming a pair of leak-proof wall portions 15. A leak-proof elastic member 16, such as elastic thread, is attached to the leak-proof wall portion 15 in an extended state along the longitudinal direction of the absorbent body 10, so that the leak-proof wall portion 15 can stand upright toward the skin. Figure 5 is an explanatory diagram of the absorbent body 10. As shown in Figure 5, the leak-proof wall portion 15 has an upright portion 6b that can stand upright toward the skin and a fixed portion 6a that cannot stand upright. In the leak-proof wall portion 15, the fixed portion 6a is the part where the back sheets 13 (outer sheet 13b) are joined together and cannot stand upright. On the other hand, the upright portion 6b is the part that can stand up because the backsheets 13 are not joined together. The fixing portion 6a has a first fixing portion 6a1 provided on the longitudinal side of the upright portion 6b and a second fixing portion 6a2 provided on the left and right sides of the upright portion 6b. When worn, the leakage-proof wall portion 15 stands up due to the contraction of the leakage-proof wall elastic member 16, making it easier to block the lateral flow of excrement. In addition, leg-around elastic members 17, such as thread elastic, are attached to both sides of the absorbent body 10 in the left and right direction, in an extended state along the longitudinal direction of the absorbent body 10.

[0037] Furthermore, the absorbent body 10 has a crotch elastic member 50 that is expandable and contractible in the longitudinal direction, located in the center in the left-right direction and on the non-skin side in the thickness direction compared to the absorbent core 11. Specifically, the crotch elastic member 50 of this embodiment is attached in a state that is stretched along the longitudinal direction between a liquid-impermeable sheet 13a provided on the non-skin side of the absorbent body 20 and an outer sheet 13b located on the non-skin side of the liquid-impermeable sheet 13a in the thickness direction. However, the crotch elastic member 50 only needs to be provided on the non-skin side of the absorbent body 20. For example, it may be provided between the core wrap sheet 24 (non-skin side core wrap portion 24b) and the back sheet 13 on the non-skin side of the absorbent body 20, or, if a crotch elastic member cover sheet (not shown) is provided between the absorbent body 20 and the liquid-impermeable sheet 13a, it may be provided between the absorbent body 20 and the crotch elastic member cover sheet. The presence of the crotch elastic member 50 makes it easier to bring the diaper 1 into contact with the wearer's crotch area when worn, due to the contraction of the crotch elastic member 50.

[0038] The ventral waist section 30 and the dorsal waist section 40 each have a skin-side sheet 31, 41, a non-skin-side sheet 32, 42, and a plurality of waist elastic members 33, 43 made of thread or elastic material. The plurality of waist elastic members 33, 43 are arranged vertically between the skin-side sheet 31, 41 and the non-skin-side sheet 32, 42, and are attached in a state that is stretched horizontally. Due to the elasticity of the waist elastic members 33, 43, the ventral waist section 30 and the dorsal waist section 40 fit to the wearer's waist. Cover sheets 34, 44 may also be provided to cover the upper end of the absorbent body 10 from the skin side. The cover sheets 34, 44 can improve the feel of the longitudinal end of the absorbent body 10 against the skin and prevent the absorbent body 10 from opening up.

[0039] Furthermore, as shown in Figure 2, the planar shapes of the ventral waist portion 30 and the dorsal waist portion 40 are different when unfolded and extended. The ventral waist portion 30 has a vertical length that is approximately the same as the side joint portion 2, and is rectangular in shape that is long in the left-right direction. The dorsal waist portion 40 has a rectangular portion that overlaps with the ventral waist portion 30, and a roughly trapezoidal portion 40E that extends downward from there. An inclined elastic member 47 is provided in the extending portion 40E. The inclined elastic member 47 has a portion that can expand and contract along the left-right direction and a portion that can expand and contract in a direction inclined with respect to the left-right direction. The extending portion 40E and the inclined elastic member 47 can cover the wearer's buttocks.

[0040] The basic structure of diaper 1 has been described above, but the above structure is just one example and is not limited to this. For example, the ventral waist portion 30 and the dorsal waist portion 40 may be formed from a single continuous member, or an outer crotch member connecting the ventral waist portion 30 and the dorsal waist portion 40 may be provided. Also, the elastic members such as the waist elastic members 33, 43 may be sheet-like elastic members instead of elastic threads.

[0041] ===About the absorbent 20=== Figure 6 is a schematic cross-sectional view of the absorbent 20 at position A-A in Figure 5. The absorbent 20 has an absorbent core 21 and a core wrap sheet 24.

[0042] The absorbent core 21 comprises cellulose fibers 22 that absorb liquid and a superabsorbent polymer SAP (hereinafter also simply referred to as "SAP"), and is molded into a vertically elongated shape in plan view. The absorbent core 21 may also contain materials other than cellulose fibers 22 and superabsorbent polymer (for example, thermoplastic resin fibers). Examples of SAP include starch-based, cellulose-based, and synthetic polymer-based superabsorbent polymers.

[0043] The core wrap sheet 24 is a liquid-permeable sheet, and examples thereof include tissue paper, non-woven fabric, and the like. The core wrap sheet 24 maintains the shape of the absorbent core 21 and facilitates the drawing of excrement into the absorbent core 21. The core wrap sheet 24 is a sheet member that covers at least a part of the skin-facing side of the absorbent core 21 and at least a part of the non-skin-facing side of the absorbent core 21. In the diaper 1 of the present embodiment, a single piece of tissue (sheet member) provides a skin-side core wrap portion 24a provided closer to the skin than the absorbent core 21, and a non-skin-side core wrap portion 24b provided closer to the non-skin side than the absorbent core 21. Specifically, while covering the entire non-skin-facing side of the absorbent core 21, the single core wrap sheet 24 has both side portions in the left-right direction folded back from the non-skin side toward the skin side so as to wrap around the absorbent core 21, and has a portion where the core wrap sheets 24 overlap each other on the skin side of the absorbent core 21.

[0044] Note that the core wrap sheet 24 is not limited to this configuration. The skin-side core wrap portion 24a only needs to cover at least a part of the skin-facing side of the absorbent core 21, and the non-skin-side core wrap portion 24b only needs to cover at least a part of the non-skin-facing side of the absorbent core 21. Further, the skin-side core wrap portion 24a and the non-skin-side core wrap portion 24b may be separate sheets.

[0045] Generally, in an absorbent article such as the diaper 1, the more the substances constituting the absorbent core are fixed (adhered) with a binder or an adhesive, the easier it is to maintain the shape of the absorbent core and the easier it is to increase the rigidity of the absorbent core. Therefore, there is an advantage that the durability of the absorbent core is easily improved, and the absorbent article can be worn for a long time. However, by fixing (adhering) the substances in the absorbent core and increasing the rigidity of the absorbent core, there is a risk that the fit and comfort in a worn state may be reduced. In addition, since the substances in the absorbent core are solidified, when a superabsorbent polymer is contained in the absorbent core, there is no space for the superabsorbent polymer to swell even after it absorbs excrement (moisture). As a result, the superabsorbent polymer cannot swell, cannot exhibit its absorption function, and there has been a risk that the absorbency of the absorbent article may be reduced.

[0046] In contrast, the present invention includes an absorbent core 21 and a core wrap sheet 24 provided with a skin-side core wrap portion 24a and a non-skin-side core wrap portion 24b. Further, the diaper 1 has elastic members that can expand and contract in the longitudinal direction (leakage barrier elastic members 16, leg-surrounding elastic members 17, crotch elastic members 50) and elastic members that can expand and contract in the lateral direction (waist-surrounding elastic members 33, 43).

[0047] As shown in Fig. 6, in the absorbent body 20 of the diaper 1, the absorbent core 21 and the core wrap sheet 24 are fixed by an adhesive HMA. In the present embodiment, with a hot-melt adhesive HMA applied to the inner surface of one core wrap sheet, the core wrap sheet is folded back from the non-skin side toward the skin side so as to cover the side end portion of the absorbent core 21, whereby the hot-melt adhesive HMA is provided between the absorbent core 21 and the core wrap sheet 24. Fixing the absorbent core 21 and the core wrap sheet 24 with the adhesive HMA makes it easier to maintain the shape of the absorbent core 21, improves the durability of the absorbent core 21, and facilitates absorption of excrement through the core wrap sheet 24 (the skin-side core wrap portion 24a), thus making it easy to improve the absorbency for excrement.

[0048] When the adhesive HMA is provided between the absorbent core 21 and the core wrap sheet 24, the adhesive HMA easily impregnates the skin side surface and the non-skin side surface of the absorbent core 21. In contrast, in the diaper 1, in the central portion in the thickness direction of the absorbent core 21 and the central portion in the lateral direction thereof, the cellulose fibers 22 are not fixed by the adhesive HMA. Specifically, when the absorbent core 21 is equally divided into three parts in the thickness direction, which are defined as a skin-side portion 21A, a central portion 21B, and a non-skin-side portion 21C in order from the skin side to the non-skin side in the thickness direction, and defined as a one-side portion 21X, a central portion 21Y, and an other-side portion 21Z in order from one side to the other side in the lateral direction, in the core central portion which is the central portion 21B in the thickness direction and the central portion 21Y in the lateral direction, the cellulose fibers 22 are not fixed to each other by the adhesive HMA.

[0049] Furthermore, the average length of the cellulose fibers 22 (average fiber length) is smaller than the average diameter of the superabsorbent polymer SAP after immersion in physiological saline for 60 minutes and then draining for 15 minutes. The state of the superabsorbent polymer SAP after immersion in physiological saline for 60 minutes and then draining for 15 minutes is also referred to as the "post-swelling" state.

[0050] By incorporating the cellulose fibers 22 and superabsorbent polymer SAP described above, diaper 1 improves water absorption as a disposable diaper (absorbent item), while the elastic material makes it easier to move the absorbent core 21, allowing the absorbent core 21 to conform to the shape and movement of the wearer's body when worn, thereby improving the fit and absorbency of diaper 1.

[0051] Specifically, the absorbent core 21 can improve the ability to draw in excrement by providing cellulose fibers 22, and improve the water retention of excrement by providing a highly absorbent polymer SAP. Furthermore, when force is applied from the outside of the absorbent core 21 due to the expansion and contraction of the expandable member, the absorbent core 21 itself becomes more mobile and deformable. As the absorbent core 21 moves and deforms, the cellulose fibers 22 inside the absorbent core 21 become more easily loosened, improving the flexibility of the absorbent core 21. When the average fiber length of the cellulose fibers 22 in the absorbent core 21 is smaller than the average diameter of the SAP after swelling, the fiber length of the cellulose fibers 22 becomes shorter than when the average fiber length of the cellulose fibers 22 is larger than the average diameter of the SAP after swelling. In the absorbent core 21, the average fiber length of the cellulose fibers 22 is smaller than the average diameter of the SAP after swelling. This makes it less likely for the cellulose fibers to entangle with each other, and even if they do entangle, they are easier to separate. As a result, the shorter cellulose fibers 22 are more easily separated within the absorbent core 21. In particular, in the central part of the core (the central part 21B in the thickness direction and the central part 21Y in the left-right direction), the cellulose fibers 22 are not fixed together with adhesive, allowing them to move more easily. This makes it easier for the cellulose fibers 22 within the absorbent core 21 to separate, creating spaces (gaps) between them. When the absorbent core 21 absorbs excrement, the SAP swells more easily in these spaces between the cellulose fibers 22. This reduces the decrease in absorbency caused by restricting the swelling of the SAP, making it easier for the SAP to perform its absorbent function and improving the absorbency of the absorbent core 21. Furthermore, as the cellulose fibers 22 within the absorbent core 21 loosen, the flexibility of the absorbent core 21 is improved, making it easier for the absorbent core 21 to conform to the shape and movement of the wearer's body when worn, thus improving the fit. In other words, the fit and absorbency of the diaper 1 can be improved.

[0052] <Regarding the average fiber length of cellulose fibers 22> In conventional absorbent articles, coniferous tree fibers (also called coniferous tree pulp) were often used as the liquid absorbent fibers in the absorbent material. In the absorbent core 21 of this embodiment, cellulose fibers 22 are used as the absorbent fibers, and cellulose fibers 22 made from hardwood fibers (hardwood pulp) and coniferous tree fibers (coniferous tree pulp) are used. Hardwood fibers are characterized by having a shorter fiber length compared to coniferous tree fibers. In this embodiment, cellulose fibers 22 are used in a ratio of 70% by weight of hardwood fibers and 30% by weight of coniferous tree fibers. In the absorbent core 21 of the diaper 1 of this embodiment, the cellulose fibers 22 are mixed almost uniformly throughout, and the cellulose fibers 22 and SAP are evenly mixed and arranged throughout the absorbent core 21 (see Figure 6). Furthermore, the ratio of hardwood fibers (hardwood pulp) to softwood fibers (softwood pulp) in the cellulose fibers 22 within the absorbent core 21 can be changed. Alternatively, the cellulose fibers 22 may consist of 100% hardwood fibers by weight.

[0053] Figure 7 shows the distribution of fiber lengths for hardwood fibers (hardwood pulp) and softwood fibers (softwood pulp). The horizontal axis represents fiber length (mm), and the vertical axis represents frequency (%). As shown in Figure 7, the average fiber length of softwood pulp is 2.5 mm, and the distribution of fiber lengths is wide (it includes fibers of 3 mm or more; the standard deviation is 1.6). In contrast, the average fiber length of hardwood pulp is 0.79 mm, and the distribution of fiber lengths is narrow (the standard deviation is 0.27). The average fiber length of the cellulose fibers 22 in the absorbent core 21 is 1.3 mm.

[0054] The average fiber length of pulp fibers is measured using the centerline fiber length (Cont) and represents the length-weighted average fiber length L(l). The length-weighted average fiber length is measured as the L(l) value using the Kajaani Fiber Lab Fiber Properties (offline) manufactured by Metso Automation. This method is also recommended in JIS P 8226-2 (Pulp - Method for measuring fiber length by automated engineering analysis, according to the non-polarized method). Furthermore, the average fiber width of pulp fibers, as described below, is measured as FiberWidth.

[0055] The average fiber length is measured excluding fiber clumps, as described in the JIS evaluation method. Therefore, the average fiber length data presented in this specification are the results obtained after excluding fiber clumps, as described later.

[0056] Furthermore, when using fibers other than cellulose fibers, the average fiber length of those fibers shall be measured according to "A7.1 Measurement of fiber length" in Annex A of JIS L 1015:2010, specifically "A7.1.1 Method A (Standard Method): Method for measuring the length of individual fibers on a graduated glass plate." The above method corresponds to the test method specified in ISO 6989, published in 1981.

[0057] In this embodiment, it is preferable that the cellulose fibers 22 include hardwood fibers made from broadleaf trees, as in the absorbent core 21 of the diaper 1. As mentioned above, since hardwood fibers have a short average fiber length of about 0.79 mm, they are less likely to entangle with each other than fibers with a longer average fiber length, and even if they do entangle, they are easier to untangle. Therefore, in the diaper 1, the cellulose fibers 22 in the absorbent core 21 are easily untangled by the expansion and contraction of the expandable member. This makes it easier to create space between the untangled cellulose fibers 22 for the SAP to swell, thus improving the absorbency of the absorbent core 21 (SAP). Specific examples of hardwood fibers include hardwood pulp extracted from eucalyptus.

[0058] Furthermore, as mentioned above, the absorbent core 21 contains a superabsorbent polymer (liquid-absorbing granular material). As the superabsorbent polymer, it is possible to use a so-called "SAP (Super absorbent polymer)," such as a polymer of acrylic acid. The following describes the case in which SAP is used as the superabsorbent polymer.

[0059] A known method for manufacturing the absorbent core 21 involves accumulating crushed pulp, a superabsorbent polymer, and the like. Figure 8 is a diagram illustrating the manufacturing method of the absorbent core 21. Here, we will describe the manufacturing method in which the absorbent core 21 contains cellulose fibers from hardwood and softwood fibers and a superabsorbent polymer (SAP).

[0060] The rotating drum 70 is a hollow cylindrical drum, and multiple recesses 71 are formed on its circumferential surface at a predetermined pitch to serve as molds for filling with absorbent material. When the rotating drum 70 rotates and the recesses 71 enter the material supply unit 80, the absorbent material supplied from the material supply unit 80 is deposited (accumulated) in the recesses 71 by the suction of the suction unit 72.

[0061] The material supply unit 80 with a hood 80a is formed to cover the top of the rotating drum 70, and the material supply unit 80 supplies crushed pulp (hardwood pulp, softwood pulp), obtained by crushing a pulp sheet in a crusher (not shown), to the recess 71 by air transport. The material supply unit 80 also includes a particle supply unit 81 that supplies superabsorbent polymer particles, and supplies superabsorbent polymer particles to the recess 71. The cellulose fibers (hardwood pulp, softwood pulp) and superabsorbent polymer particles are deposited in the recess 71 in a mixed state, and an absorbent core 21 is formed in the recess 71.

[0062] As the rotating drum 70 continues to rotate, the recess 71 containing the absorbent core 21 reaches the bottom of the drum. At this point, the absorbent core 21 detaches from the recess 71 and is placed on a substrate (such as a core wrap sheet 24) that is being transported by a conveyor, and then handed over to the next process.

[0063] Furthermore, when crushing pulp sheets in a crusher, fibers may remain in clumps because the pulp sheets are not completely crushed. As a result, dense clumps of pulp fibers (also called high-density areas) are scattered throughout the absorbent core 21. The presence of these fibrous clumps in the absorbent core 21 makes it easier to maintain the bulk (thickness) of the absorbent core 21, and makes it easier to make the absorbent core 21 softer and improve its cushioning properties.

[0064] <Regarding the average fiber length of cellulose fibers 22 and SAP diameter> In the diaper 1 of this embodiment, the relationship between the average fiber length (1.3 mm) of the cellulose fibers contained in the absorbent core 21 and the diameter of the SAP before and after swelling due to moisture absorption is defined, thereby making it less likely for the swelling of the SAP to be hindered inside the absorbent core 21.

[0065] Figure 9 is a table showing the change in SAP diameter when SAP is swollen at predetermined water absorption and water retention ratios. In Figure 9, the SAP particle size shown on the left side represents the particle size of SAP before swelling, and the SAP diameter shown on the right side represents the average diameter of SAP after swelling according to the water absorption (water retention) ratio. Specifically, it shows the results of calculating the average diameter of each SAP when water (physiological saline solution) was absorbed (dehydrated) at water absorption (water retention) ratios of 10 to 120 times for SAPs with a diameter of 150 to 850 μm before swelling. Here, "water absorption ratio" refers to the value obtained by dividing the saturation amount of water that an absorbent medium such as SAP can absorb and hold by the weight of the absorbent medium before water absorption. Also, "water retention ratio" refers to the value obtained by dividing the amount of water that an absorbent medium such as SAP can hold after releasing (dehydrating) the absorbed water by the weight of the absorbent medium before water absorption.

[0066] The water absorption ratio (water retention ratio) of SAP was measured according to "JIS K 7223-1996 Test Method for Water Absorption of Superabsorbent Polymers" and followed the procedure below. First, the SAP to be measured was prepared under the conditions of temperature: 20°C, relative humidity: 60%, and pressure (standard atmospheric pressure): 1 atm (101.325 kPa) (for example, in a laboratory maintained under these conditions). The SAP was stored in a designated container and shaken upside down at least 10 times to evenly mix the SAP particles. 1.00 g of the mixed SAP was accurately measured using a spatula or similar tool and placed in a nylon net bag prepared separately. For example, a nylon net bag made by overlapping two 200 mm x 200 mm square nylon nets, heat-sealing three sides of the square 5 mm from the edge of the nylon net, and forming a bag with only one side of the square open. As a nylon net, for example, NBC Industries' 250-mesh nylon net (N-No. 250HD) can be used.

[0067] After placing the SAP in a nylon mesh bag, heat-seal the opening of the nylon mesh bag to prevent the SAP from spilling out. Then, pour 1000 ml of saline solution into a beaker and immerse the nylon bag (SAP) in the saline solution so that one side of the bag touches the bottom of the beaker. Secure one side of the top of the nylon bag to the rim of the beaker with a clothespin or similar to prevent the SAP from touching the nylon mesh as much as possible. Leave it in this state for 60 minutes.

[0068] The physiological saline solution used is prepared by placing a 3-liter beaker on an electronic balance, resetting it to zero, adding 27.0 g of sodium chloride (reagent grade 1) to deionized water to make a total of 3000.0 g, and stirring with a stirring rod until the sodium chloride is visibly dissolved.

[0069] After standing for 60 minutes, the nylon bag containing the SAP is removed from the beaker, and the bag is suspended in the air for 15 minutes by clipping the top center of the bag (for example, 5 mm from the top edge and 50 mm from both ends) with a clothespin to allow the water to drain. After 15 minutes, the weight of the nylon bag containing the SAP is measured. This experiment is repeated multiple times (for example, 5 times), and the average of the measured weights is defined as the water-absorbing weight B. This state of SAP is the "swelled" state of SAP.

[0070] Next, the drained nylon bags (SAP) are dehydrated using a centrifuge (HI30) manufactured by Kokusan Co., Ltd. For example, dehydration is performed for 90 seconds at a rotation speed of 850 rpm (150 G). Then, the weight of the dehydrated nylon bags (SAP) is measured. This experiment is repeated multiple times (for example, 5 times), and the average of the measured weights is defined as the water retention weight C.

[0071] The amount of water absorbed by SAP is determined by subtracting the weight K of the nylon net, which was determined in the blank test, from the water absorbed weight B. The water absorption ratio of SAP is calculated by dividing this absorbed amount by the sample weight (1.00 g). Similarly, the amount of water retained by SAP is determined by subtracting the weight K' of the nylon net, which was determined in the blank test, from the water retained weight C. The water retention ratio of SAP is calculated by dividing this retained amount by the original sample weight (1.00 g).

[0072] Furthermore, the diameter of the SAP before and after swelling is measured using a microscope. Based on the results of the measurement of the water absorption ratio (water retention ratio) of the SAP and the measured diameter, a table (Figure 9) showing the relationship between the water absorption ratio of the SAP and the diameter before and after swelling is presented.

[0073] As shown in Figure 9, in the range of 10 to 120 times the water absorption (water retention) ratio of SAP, the average diameter of SAP after swelling (after water absorption and draining) is always larger than the diameter of SAP before swelling (150 to 850 μm). For example, in Figure 9, when the absorption (water retention) ratio is 40 times, the diameter of SAP before swelling is 500 μm (0.5 mm), while the diameter of SAP after swelling (after water absorption) is 2.12 mm. In Figure 9, when the water absorption ratio and the water retention ratio are the same, the average diameter of SAP after swelling is also the same. This is because the diameter of SAP after swelling is determined by the amount of water (physiological saline in this embodiment) held in the SAP. That is, if the amount of water held in SAP after dehydration is equal to the amount of water held in SAP after water absorption, the average diameter of SAP will also be equal.

[0074] In the data shown in Figure 9, the cells indicated by diagonal lines show that the diameter of the SAP after swelling is larger than the average length of the cellulose fibers of the absorbent core 21 (1.3 mm). Specifically, when the diameter of the SAP before swelling is 300 μm or more, the diameter of the SAP after swelling becomes 1.3 mm or more when the water absorption ratio is 55 times or more. In other words, the average diameter of the SAP after swelling becomes larger than the average length of the cellulose fibers of the absorbent core 21 (1.3 mm). Also, when the water absorption ratio is 40 times, if the diameter of the SAP before swelling is 355 μm or more, the average diameter of the SAP after swelling becomes 1.3 mm or more, which is larger than the average length of the cellulose fibers of the absorbent core 21 (1.3 mm).

[0075] Figure 10 is a table showing the particle size distribution of SAP used in this embodiment. As shown in Figure 10, 72% (average value) of the SAP used in this embodiment have a particle size in the range of 300 to 850 μm before swelling. Therefore, according to the data in Figure 9, it can be seen that more than half of the SAP contained in the absorbent core 21 of this embodiment have an average diameter after swelling that is larger than the average length of the fibers of the absorbent core 21 (1.3 mm).

[0076] Thus, because the average length of the fibers in the absorbent core 21 (1.3 mm) is smaller than the average diameter of the SAP after swelling, the cellulose fibers 22 inside the absorbent core 21 are more easily loosened by the expansion and contraction of the expandable members (leak-proof wall elastic member 16, leg elastic member 17, crotch elastic member 50, waist elastic members 33, 43). This makes it easier to create space for the SAP to increase in diameter when it absorbs excrement (liquid), thereby improving the water absorption performance of the SAP.

[0077] Furthermore, it is preferable that the average length of the fibers in the absorbent core 21 (1.3 mm) is smaller than the average diameter of the SAP after it has been immersed in physiological saline for 60 minutes, drained for 15 minutes (swelled), and then dehydrated using a centrifuge or the like. This allows the fiber length of the cellulose fibers 22 to be shorter than when the average length of the fibers in the absorbent core 21 is larger than the average diameter of the SAP after swelling and dehydration. As a result, the cellulose fibers 22 inside the absorbent core 21 can be more easily loosened by the expansion and contraction of the expandable member, creating space for the SAP to expand and making it easier for the SAP to exhibit its absorption function.

[0078] Furthermore, the water absorption ratio of the SAP provided in the absorbent core 21 is preferably 10 times or more and 120 times or less. In other words, the saturation amount of water (physiological saline solution) that the SAP can absorb and hold is preferably 10 times or more and 120 times or less of the weight of the SAP before swelling. This improves the absorption performance of the absorbent core 21 while reducing the risk that the SAP will swell excessively after absorbing excrement, causing the absorbent core 21 to become excessively hard or deformed, which could cause discomfort to the wearer.

[0079] Regarding the SAP in the absorbent core 21, it is preferable that the average diameter of the SAP before swelling (the state of the SAP before immersion in physiological saline) is shorter than the average length of the cellulose fibers in the absorbent core 21. Furthermore, it is more preferable that the average diameter of the SAP before swelling is between 250 μm and 600 μm. The smaller the average diameter of the SAP before swelling, the smaller the area occupied by the SAP within the absorbent core 21 before absorbing excrement (before swelling), making it easier to create a wider area for loosening the cellulose fibers 22 within the absorbent core 21. Therefore, before the SAP swells after absorbing excrement, the movement due to the expansion and contraction of the expandable member makes it easier to loosen the cellulose fibers 22 of the absorbent core 21, thus making it easier to create space for the SAP to swell with the loosened cellulose fibers 22. Therefore, by providing an absorbent core 21 in which the cellulose fibers 22 have been loosened, after swelling, it becomes easier to absorb moisture up to the maximum absorbable capacity of SAP and swell, thereby improving the fit and absorbency of the diaper 1 (absorbent core 21).

[0080] Furthermore, the absorbent material 20 may have the following features. When viewing the diaper 1 in the thickness direction, it is preferable that the cellulose fibers 22 in the absorbent core 21 have a portion that overlaps with the expandable members. In this embodiment, as shown in Figure 5, when viewed in the thickness direction, the absorbent core 21 has a portion that overlaps with the leak-proof wall elastic member 16, the leg elastic member 17, and the crotch elastic member 50, which expand and contract in the longitudinal direction. Therefore, the cellulose fibers 22 in the absorbent core 21 have a portion that overlaps with the expandable members (16, 17, 50).

[0081] As a result, when viewed in the thickness direction, the cellulose fibers 22 that overlap with the stretchable members (16, 17, 50) are more easily affected by the contractile force of the stretchable members (16, 17, 50), making the cellulose fibers 22 more easily loosened. Therefore, the flexibility of the absorbent core 21 with loosened cellulose fibers 22 is improved, making it easier for the absorbent core 21 to conform to the shape and movement of the wearer's body when worn. In addition, the loosened parts of the cellulose fibers 22 are more flexible and softer than the unloosened parts. Therefore, when viewed in the thickness direction, the contractile force of the stretchable members (16, 17, 50) that overlap with the loosened cellulose fibers 22 is more easily applied to the wearer's body, making contact easier. Thus, the fit of the diaper 1 when worn can be improved.

[0082] In the diaper 1 of this embodiment, the cellulose fibers 22 have portions that overlap with the leak-proof wall elastic member 16, the leg elastic member 17, and the crotch elastic member 50, which expand and contract in the longitudinal direction when viewed in the thickness direction, but are not limited to this. The cellulose fibers 22 may have portions that overlap with at least one of the leak-proof wall elastic member 16, the leg elastic member 17, and the crotch elastic member 50 when viewed in the thickness direction, or the cellulose fibers 22 may have portions that overlap with the waist elastic members 33, 43, which expand and contract in the left and right directions, or with other expandable members such as expandable sheets (not shown).

[0083] As described above, the diaper 1 of this embodiment is provided with expandable members that can stretch in the longitudinal direction (leak-proof wall elastic member 16, leg elastic member 17, crotch elastic member 50) and expandable members that can stretch in the left-right direction (waist elastic members 33, 43), but is not limited to this. The expandable members provided in the diaper 1 may consist only of expandable members that can stretch in the longitudinal direction, or only of expandable members that can stretch in the left-right direction. Furthermore, the expandable members that can stretch in the longitudinal direction may be at least one of the leak-proof wall elastic member 16, leg elastic member 17, crotch elastic member 50, and other elastic members, and the expandable members that can stretch in the left-right direction may be at least one of the waist elastic members 33, 43, and other elastic members.

[0084] As shown in Figure 2, when the diaper 1 is unfolded and stretched, if the diaper 1 is divided into three equal parts in the longitudinal direction, and these parts are designated as the ventral part 1A, the central part 1B, and the dorsal part 1B from the ventral side in the longitudinal direction, it is preferable that, in the unfolded and stretched state, the stretchable member of the diaper 1 is located in the central part in the left-right direction and in the central part 1B in the longitudinal direction, on the non-skin side of the absorbent core 21. In the diaper 1 of this embodiment, the crotch elastic member 50 is located in the central part in the left-right direction and in the central part 1B in the longitudinal direction (see Figure 2), and is located on the non-skin side of the absorbent body 20 (absorbent core 21) (see Figure 4).

[0085] In the unfolded and stretched state of diaper 1, the central part in the left-right direction and the central part in the longitudinal direction 1B corresponds to the part that is positioned in the wearer's crotch area when worn, and is the part from which excrement is discharged. Generally, in absorbent articles such as diapers 1, the absorbent core 21 is a highly rigid and thicker component than the top sheet 12, etc. Therefore, the contractile force of the elastic member provided on the non-skin side of the absorbent core 21 does not easily act on the wearer's skin. In contrast, in diaper 1, the cellulose fibers 22 of the absorbent core 21, which are provided between the wearer's skin and the crotch elastic member 50 in the thickness direction, are loosened by the expansion and contraction of the crotch elastic member 50, making the absorbent core 21 softer and allowing the contractile force of the crotch elastic member 50 to act on the wearer's skin via the absorbent core 21. As a result, the portion of the crotch elastic member 50 that overlaps with the loosened cellulose fibers 22 in the thickness direction is more likely to come into contact with the wearer's body, thereby improving the fit of the portion of the diaper 1 that comes into contact with the wearer's crotch when worn.

[0086] Preferably, the absorbent article (a disposable diaper in the form of pants) has a pair of waist sections and a crotch area, as shown in diaper 1, where the unfolded diaper 1 is folded in half in the front-to-back direction at the central fold (central CL) in the longitudinal direction, and the ends of both sides of the pair of waist sections 30 and 40 are joined at side joints 2 (joints).

[0087] When the diaper 1 is a pant-type absorbent item, the stretchable member may be stretchable in the left-right direction and provided on the crotch side of the side joint 2. For example, as shown in Figure 2, the pant-type disposable diaper of this embodiment has an inclined elastic member 47 provided on the crotch side of the side joint 2 and having a portion that stretches along the left-right direction. The inclined elastic member 47 provided on the crotch side of the side joint 2 makes it easier to loosen the cellulose fibers 22 of the absorbent core 21 by stretching and contracting the inclined elastic member 47 at a position close to the wearer's crotch when worn. This makes it easier to improve the flexibility of the region of the absorbent core 21 of the diaper 1 that is close to the crotch, and improves the fit of the diaper 1 in the crotch area when worn.

[0088] Furthermore, as described above, the diaper 1 may have a pair of leak-proof wall portions 15, and each leak-proof wall portion 15 may have an expandable / contractable member (leak-proof wall elastic member 16) along its longitudinal direction. Specifically, when the diaper 1 is unfolded and extended, if the diaper 1 has a pair of leak-proof wall portions 15 on both sides in the left-right direction, each comprising a leak-proof wall sheet (outer sheet 13b) and a leak-proof wall elastic member 16 (expandable / contractable member), the leak-proof wall portion 15 has an upright portion 6b that can stand up on the skin side and a fixed portion 6a that cannot stand up. In such a leak-proof wall portion 15, when the diaper 1 is viewed in the thickness direction, it is preferable that the first fixed portion 6a1 of the fixed portion 6a, which is provided further outward in the longitudinal direction than the upright portion 6b, has a portion that overlaps with the absorbent core 21. In the diaper 1 of this embodiment, as shown in Figure 5, when viewed in the thickness direction, of the first fixing portions 6a1 provided at the ventral end and the dorsal end in the longitudinal direction, the crotch end of each portion overlaps with the absorbent core 21.

[0089] In the absorbent body 10, the fixing portion 6a, which is fixed with hot melt adhesive or the like, is a part that tends to have high rigidity. In contrast, by having an overlapping portion between the absorbent core 21 and the first fixing portion 6a1, the cellulose fibers 22 of the absorbent core 21 become easier to loosen due to the contraction of the leak-proof wall elastic member 16 of the leak-proof wall portion 15, thereby improving the flexibility of the absorbent core 21. As a result, the ends of the absorbent core 21 in the longitudinal direction become more easily deformed. Therefore, due to the contraction of the leak-proof wall elastic member 16, the absorbent core 21 (absorbent body 20) becomes more easily deformed so that the ends of the absorbent core 21 in the longitudinal direction move closer together, and the central part in the longitudinal direction protrudes toward the non-skin side. This makes it easier for the leak-proof wall elastic member 16 of the leak-proof wall portion 15 to contract more linearly, making it easier to make the leak-proof wall portion 15 stand up toward the skin side. Furthermore, the upright leak-proof wall portion 15 makes it easier to reduce lateral leakage of the diaper 1 when it is being worn.

[0090] Furthermore, as shown in Figure 3, the diaper 1 may be provided with a post-treatment tape 90. The post-treatment tape 90 is a roughly rectangular tape-shaped member (tape member) that is long in the vertical direction (longitudinal direction), and is made of a resin material such as polyethylene or polypropylene. In the diaper 1, as shown in Figure 3, it is fixed to the non-skin side of the back waistband portion 40 (the non-skin side of the non-skin side sheet 42) by a tape fixing portion k90 in a state where it is folded once or more times in the longitudinal direction. When the post-treatment tape 90 is unfolded, one side of the post-treatment tape 90 in the vertical direction is fixed to the non-skin side of the back waistband portion 40 by the tape fixing portion k90 in a way that prevents it from being peeled off, and the other side in the vertical direction has an adhesive portion (not shown). An adhesive is applied to the adhesive portion, and before use of the diaper 1 (when the post-treatment tape 90 is folded), a part of the post-treatment tape 90 is folded with the adhesive portion facing inward, protecting the adhesive surface so that the adhesive portion is not exposed to the outside. When disposing of a used diaper 1, the diaper 1 is rolled up vertically so that the skin-facing side of the absorbent body 10 is facing inward. The folded post-disposal tape 90 is then unfolded and stretched to expose the adhesive side, and the adhesive side is wrapped around the diaper 1. This allows the diaper 1 to be kept in a rolled-up state, preventing leakage of excrement and other substances attached to the inside of the diaper 1 (absorbent body 10) to the outside, while the diaper 1 can be disposed of.

[0091] Furthermore, when the diaper 1 has a post-disposal tape 90, it is preferable that the tape fixing portion k90 overlaps with the absorbent core 21 when viewed in the thickness direction of the diaper 1. In the diaper 1, the absorbent core 21 is thicker and more rigid than the other members, but as described above, the cellulose fibers of the absorbent core 21 are loosened by the expansion and contraction movements of the expandable members 16, 17, 50, 33, and 43, improving the flexibility of the absorbent core 21. When the absorbent core and the tape fixing portion k90 of the post-disposal tape 90 overlap in the thickness direction, when the diaper 1 is to be disposed of after wearing it, the diaper 1 with the improved flexibility of the absorbent core 21 is in a state that is easy to deform, making it easier to roll up the diaper 1, and making it easier to maintain the rolled-up state of the diaper 1 with the post-disposal tape 90. In other words, it becomes easier to dispose of the diaper 1 with little force.

[0092] Furthermore, it is preferable that the cellulose fibers 22 of the absorbent core 21 and the core wrap sheet 24 have an adhesive portion sb where they are bonded (fixed) with adhesive HMA, and an unbonded portion hb where the cellulose fibers 22 and the adhesive HMA are not bonded. In other words, as described above, in the absorbent body 20, although the cellulose fibers 22 of the absorbent core 21 and the core wrap sheet 24 are fixed with adhesive HMA, it is preferable that the adhesive portion sb of the adhesive HMA between the core wrap sheet 24 and the absorbent core 21 is not provided over the entire outer surface of the absorbent core 21, but rather that the core wrap sheet 24 and the absorbent core 21 have both a portion where they are bonded with adhesive HMA (adhesive portion sb) and a portion where they are not bonded (unbonded portion hb). In this embodiment, as shown in Figure 11, adhesive HMA is applied between the core wrap sheet 24 and the absorbent core 21 in an Ω pattern along the longitudinal direction, fixing the core wrap sheet 24 and the absorbent core 21 together. Figure 11 illustrates the fixing of the absorbent core 21 to the non-skin side core wrap portion 24b. The portion to which adhesive HMA is applied corresponds to the adhesive portion sb, and the portion to which adhesive HMA is not applied corresponds to the non-adhesive portion hb. Note that the application pattern of adhesive HMA between the core wrap sheet 24 and the absorbent core 21 is not limited to this. Any application pattern such as a spiral pattern or a stripe pattern can be used. Having an adhesive portion sb where the core wrap sheet 24 and cellulose fibers 22 are bonded with adhesive HMA makes it easier to maintain the shape of the absorbent core 21, improves the rigidity of the absorbent core 21 itself, and improves the durability of the absorbent core 21. On the other hand, having a non-adhesive portion hb where the core wrap sheet 24 and cellulose fibers 22 are not bonded with adhesive HMA makes it easier to loosen the cellulose fibers of the absorbent core 21 by the expansion and contraction movement of the expandable members 16, 17, 50, 33, and 43, thus making it easier to create space for SAP to swell within the absorbent core 21 when excrement is absorbed.

[0093] In the above-described embodiment, an example was given in which the cellulose fibers 22 and SAP were evenly distributed within the absorbent core 21, but the invention is not limited to this. The cellulose fibers 22 and SAP may be provided in a predetermined arrangement within the absorbent core 21. Figure 12 is a diagram illustrating a modified example of the absorbent body 20. As shown in the modified example of the absorbent body 20 in Figure 12, the absorbent core 21 has cellulose fibers 22 and SAP, and may have a polymer layer SF made of SAP on the non-skin side of the absorbent core 21. It is preferable that this polymer layer SF has a portion in which the SAP particles are fixed to each other with adhesive HMA. The adhesive HMA that fixes the SAP particles to each other is the adhesive HMA used to fix the core wrap sheet 24 and the absorbent core 21. By having SAP particles fixed with adhesive HMA in this way, the risk of SAP particles spilling out of the diaper 1 can be reduced. Furthermore, by arranging the cellulose fibers 22 on the skin side within the absorbent core 21, it becomes easier to draw excrement into the absorbent core 21, and the polymer layer SF on the non-skin side can absorb and retain the excrement, thereby improving the excrement absorbency of the diaper 1.

[0094] In the above-described embodiment, an absorbent 20 is provided between the top sheet 12 and the back sheet 13 as a component for absorbing excrement, but the embodiment is not limited to this. As shown in Figures 13A and 13B, a polymer layer made of a superabsorbent polymer SAP, separate from the absorbent 20, may be provided between the top sheet 12 and the back sheet 13.

[0095] Figure 13A is a diagram illustrating the absorbent body 20 and the skin-side polymer layer 70A. In Figure 13, the absorbent body 20 and the skin-side polymer layer 70A provided on the skin side of the absorbent body 20 may be located between the top sheet 12 and the back sheet 13. The skin-side polymer layer 70A is an SAP layer provided on the skin side of the outermost skin-side surface of the core wrap sheet 24 of the absorbent body 20, and is a layer that contains highly absorbent polymer SAP but does not contain liquid absorbent fibers. "Liquid absorbent fibers" include water-absorbing fibers such as pulp, for example, wood pulp obtained from coniferous or broad-leaved trees, bagasse, kenaf, bamboo, hemp, cotton (for example, cotton linter), and other non-wood pulps; regenerated cellulose fibers such as rayon fibers; and semi-synthetic fibers such as acetate fibers. The skin-side polymer layer 70A may be in sheet form, or it may be made by molding SAP particles into a predetermined shape. The skin-side polymer layer containing SAP has high water retention. Therefore, in diaper 1, by placing the skin-side polymer layer 70A on the skin side of the absorbent core 20, when diaper 1 is worn, the skin-side polymer layer 70A makes it easier to retain the excrement absorbed by diaper 1. Furthermore, even if the excrement reaches the absorbent core 20 located on the non-skin side from the skin-side polymer layer 70A, and even if the excrement absorbed by the absorbent core 20 tries to return towards the skin side (so-called rewetting), the skin-side polymer layer 70A, located on the skin side of the absorbent core 20, makes it easier to absorb and retain the excrement. Therefore, in diaper 1, the risk of absorbed excrement returning to the wearer's skin is reduced.

[0096] On the other hand, between the top sheet 12 and the back sheet 13, there may be an absorbent core 20 and a non-skin side polymer layer 70B provided on the non-skin side of the absorbent core 20. Figure 13B is a diagram illustrating the absorbent core 20 and the non-skin side polymer layer 70B. The non-skin side polymer layer 70B is an SAP layer provided on the non-skin side of the outermost non-skin side of the core wrap sheet 24 of the absorbent core 20, and is a layer that contains highly absorbent polymer SAP but does not contain liquid absorbent fibers. The non-skin side polymer layer 70B may be in the form of a sheet, or it may be SAP particles molded into a predetermined shape. As a result, when the diaper 1 is worn, the absorbent core 20 (absorbent core 21) having cellulose fibers 22, which is provided on the skin side, can easily draw in and absorb excrement, and the excrement absorbed by the absorbent core 20 can be absorbed and held by the non-skin side polymer layer 70B provided on the non-skin side of the absorbent core 20, thereby improving the absorbency of excrement in the diaper 1.

[0097] While embodiments of the present invention have been described above, these embodiments are intended to facilitate understanding of the present invention and are not intended to limit its interpretation. Furthermore, the present invention can be modified or improved without departing from its spirit, and it goes without saying that the present invention includes equivalents thereof.

[0098] 1. Pants-type disposable diaper (absorbent material) 2. Side seam (joint), 10. Absorbent body, 12. Top sheet, 13a. Back sheet (liquid impermeable sheet), 13b. Back sheet (outer sheet, leak-proof wall sheet), 15. Leak-proof wall section, 16. Leak-proof wall elastic member (stretchable member), 17. Leg circumference elastic member (stretchable member), 20. Absorbent material, 21. Absorbent core, 21A. Skin-side portion, 21B. Central portion, 21C. Non-skin-side portion, 22. Cellulose fiber, 24. Core wrap sheet, 30. Abdominal waist section, 31. Skin-side sheet, 32. Non-skin-side sheet, 33. Waist circumference elastic member (stretchable member), 34. Cover sheet, 40. Back waist section, 41. Skin-side sheet, 42. Non-skin-side sheet, 43. Waist circumference elastic member (stretchable member), 44. Cover sheet, 47 Inclined elastic member (stretchable member), 50 Crotch elastic member (stretchable member), 70A Skin-side polymer layer, 70B Non-skin-side polymer layer, 90 Post-treatment tape, SAP Superabsorbent polymer, HMA adhesive

Claims

1. An absorbent article having an absorbent core having a longitudinal direction, a left-right direction, and a thickness direction that are mutually orthogonal when unfolded and extended, and a core wrap sheet covering at least a portion of the skin-facing side and at least a portion of the non-skin-facing side of the absorbent core, wherein it has an expandable member that is expandable and expandable in the longitudinal direction or the left-right direction, the absorbent core and the core wrap sheet are fixed together with an adhesive, the absorbent core comprises cellulose fibers and a superabsorbent polymer, and when the absorbent core is divided into three equal parts in the thickness direction, the central part in the thickness direction and the central part when the absorbent core is divided into three equal parts in the left-right direction is defined as the core central part, in the core central part, the cellulose fibers are not fixed together with the adhesive, and the average length of the cellulose fibers is smaller than the average diameter of the superabsorbent polymer after being immersed in physiological saline for 60 minutes and then drained for 15 minutes.

2. An absorbent article according to claim 1, characterized in that, in the unfolded and stretched state, the cellulose fibers have a portion that overlaps with the expandable member when viewed in the thickness direction.

3. An absorbent article according to claim 2, characterized in that, in the unfolded and extended state, the expandable member is provided on the non-skin side of the absorbent core in the central portion in the left-right direction and in the central portion of the three equal parts obtained by dividing the absorbent article in the longitudinal direction.

4. An absorbent article according to claim 1 or 2, wherein the absorbent article is a pant-type absorbent article having a pair of waist portions and a crotch portion, which is folded in half in the front-to-back direction at a fold in the center of the longitudinal direction, and the ends of the pair of waist portions are joined at joints, and the expandable member is expandable in the left-to-right direction and is provided on the crotch side of the joint.

5. An absorbent article according to claim 1 or 2, wherein, in the unfolded and extended state, it has a pair of leak-proof wall portions on both sides in the left-right direction, the leak-proof wall portion comprises a leak-proof wall sheet along the longitudinal direction and the expandable member, the leak-proof wall portion has an upright portion that can stand up on the skin side and a fixed portion that cannot stand up, the fixed portion has a first fixed portion and a second fixed portion, the first fixed portion is provided outside the upright portion in the longitudinal direction, the second fixed portion is provided outside the upright portion in the left-right direction, and the first fixed portion has a portion that overlaps with the absorbent core when viewed in the thickness direction.

6. An absorbent article according to claim 1 or 2, wherein the absorbent article has a post-treatment tape on the non-skin side, the post-treatment tape has a tape fixing portion that is irremovably fixed to the non-skin side of the absorbent article, and the tape fixing portion has a portion that overlaps with the absorbent core when viewed in the thickness direction.

7. An absorbent article according to claim 1 or 2, characterized in that the cellulose fibers have an adhesive portion bonded to the core wrap sheet with the adhesive and an unadhesive portion not bonded to the core wrap sheet with the adhesive.

8. An absorbent article according to claim 1 or 2, wherein the absorbent core has a polymer layer made of a superabsorbent polymer on the non-skin side, and the polymer layer has a portion in which the particles of the superabsorbent polymer are fixed together with the adhesive.

9. An absorbent article according to claim 1 or 2, characterized in that it has a skin-side polymer layer containing a superabsorbent polymer but not containing liquid-absorbing fibers, on the skin-side side of the core wrap sheet, which is closer to the skin.

10. An absorbent article according to claim 1 or 2, characterized in that it has a non-skin side polymer layer containing a superabsorbent polymer but not containing liquid absorbent fibers, on the non-skin side of the core wrap sheet, which is on the non-skin side of the most non-skin side surface.

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