US Patent No.: 8,282,617 B2
Inventor(s): Masahiro Kaneda, Shikokuchuo, Japan.
Company: Daio Paper Corporation, Ehime, Japan.
Filed: 12/28/07
Issued: 10/9/12

An underpants type disposable diaper, comprising: a barrel-shaped waist portion that includes a ventral-side outer sheet for covering a waist of a wearer on a ventral side and a back-side outer sheet for covering a waist of a wearer on a back side, in which the ventral- and back-side outer sheets are joined together at joined sections at edges on the both sides in a width direction, and the ventral- and back-side outer sheets are not connected but separated at a crotch portion; and an absorber that is connected at a front end portion to the ventral-side outer sheet on an inner surface at a central portion in the width direction and is connected at a back end portion to the back-side outer sheet on an inner surface at a central portion in the width direction, in which an intermediate portion between the front and back end portions is exposed to outside from a separation area between the ventral- and back-side outer sheets at the crotch portion, wherein the absorber has a liquid pervious top sheet arranged on a top side, a liquid impervious sheet arranged on an underside, and an absorbent element interposed between the foregoing sheets to absorb and retain a liquid, a crotch outer sheet is laminated on an underside of the liquid impervious sheet in the absorber so as to be exposed to on an external surface of a product, the crotch outer sheet is higher in stiffness than sheets constituting the ventral- and back-side outer sheets, the crotch outer sheet is disposed in an area ranging in a front-back direction from an intermediate position between the front end portion of the absorber and a crotch-side side edge of the ventral-side outer sheet to an intermediate position between the back end portion of the absorber and a crotch-side side edge of the back-side outer sheet, the underpants type disposable diaper includes: a front-side outer nonoverlap section defined by an area ranging in the front-back direction from the front end portion of the absorber to the front end portion of the crotch outer sheet; a front-side outer overlap section in which the front end portion of the crotch outer sheet and the crotch-side side end of the ventral-side outer sheet overlap each other; a back-side outer nonoverlap section defined by an area in the front-back direction ranging from the back end portion of the absorber to the back end portion of the crotch outer sheet; and a back-side outer overlap section in which the back end portion of the crotch outer sheet and the crotch-side side end of the back-side outer sheet overlap each other, assuming that the number of sheets constituting the outer sheets on the underside of the liquid impervious sheet is B1 at the intermediate portion, A1 at the front- and back-side outer overlap sections, and C1 at the front- and back-side outer nonoverlap sections, there is established a relationship of B1<C1<A1, the ventral-side outer sheet and/or the back-side outer sheet have each a main unit section that constitutes an area identical in an up-down direction to the joined section, and an extension section that extends below the main unit section, and the overlap width of the front-side outer overlap section in the front-back direction and/or the overlap width of the back-side outer overlap section in the front-back direction are shorter than a length of the extension section in the front-back direction and are longer than ½ of the length of the extension section in the front-back direction, on each of the front and back sides.