Underpants type disposable diaper

1. An underpants type disposable diaper having a front body part and a back body part which are joined at sides, thereby to form a waist opening and a pair of right and left leg openings, wherein

joined sections at sides of the front body part and back body part are formed with a large number of unit fusing portions arranged at uniform intervals, in a longitudinal direction, provided with groups each having continuous unit fusing portions of the same height, and divided into segments according to the groups of unit fusing portions of different heights;

the joined sections are each divided, in a direction from a side end of the waist opening to a side end of the leg opening, into four segments comprising a waist segment, an upper side segment, an intermediate side segment, and a lower side segment,

the segments having a relationship with respect to the number of laminated sheets wherein the number of laminated sheets of the upper side segment is greater than the number of laminated sheets of the waist segment which is greater than or equal to the number of laminated sheets of the intermediate side segment which is greater than the number of laminated sheets of the lower side segment, and

the segments having a relationship with respect to the height in the longitudinal direction of unit fusing portions wherein the height of unit fusing portions of the upper side segment is greater than the height of unit fusing portions of the waist segment which is greater than or equal to the height of unit fusing portions of the intermediate side segment which is greater than the height of unit fusing portions of the lower side segment.

2. The underpants type disposable diaper according to claim 1 , wherein a ratio of distance among the waist segment, the upper side segment, the intermediate side segment, and the lower side segment is 4 to 6:2 to 4:20 to 24:5 to 7.

3. The underpants type disposable diaper according to claim 1 , wherein the height of the unit fusing portion is 0.3 to 3 mm in the waist segment, 0.5 to 5 mm in the upper side segment, 0.3 to 3 mm in the intermediate side segment, and 0.1 to 2 mm in the lower side segment.

4. The underpants type disposable diaper according to any one of claims 1 , 2 and 3 , wherein the joined section has a width of 7 to 10 mm and a length of 100 to 350 mm.

5. The underpants type disposable diaper according to any one of claims 1 , 2 and 3 , wherein intervals between the unit fusing portions are 0.1 to 5 mm.

6. The underpants type disposable diaper according to any one of claims 1 , 2 and 3 , wherein the joined section has a joint strength ranging from 2.0 to 5.0 kg/50 mm.

7. The underpants type disposable diaper according to claim 1 , wherein

the diaper comprises:

an outermost sheet constituting an outside of the diaper,

a holding sheet that is fixed to an inner surface of the outermost sheet so as to cover the inner surface with the waist portion excluded,

an absorber that is fixed to an inner surface of the holding sheet and extends in a front-back direction centering on a crotch portion of the diaper, and

front-back leak prevention sheets that extend from front and back ends of the absorber to the waist portion;

longitudinal directional end portions of the outermost sheet are folded back to innermost surfaces of the diaper at the waist opening, and the resulted folded back portions are respectively fixed to upper surfaces of the waist portions of the leak prevention sheets;

the waist segment is formed by laminated three layers comprising the outermost sheet, one of the front-back leak prevention sheets and one of the folded back portions of the outermost sheet;

the upper side segment is formed by laminated four layers comprising the outermost sheet, one of the front-back leak prevention sheets, the holding sheet, and one of the folded back portions of the outermost sheet;

the intermediate side segment is formed by laminated three layers comprising the outermost sheet, one of the front-back leak prevention sheets and the holding sheet; and

the lower side segment is formed by laminated two layers comprising the outermost sheet and the holding sheet.

8. The underpants type disposable diaper according to claim 1 , wherein

longitudinal directional intervals between unit fusing portions of different heights in different segments are all unified, and vertical directional intervals between unit fusing portions of the same height in one segment are all unified.