Diaper fastener with two nonwoven fabric components coated with thermoplastic synthetic resin

A disposable diaper includes a pair of tape fasteners 6 that are used to connect front and rear waist regions 8, 10 to each other and are attached to side flaps 14 in the rear waist region 10 of the diaper. Each of the tape fasteners 6 includes fibrous nonwoven fabric made of thermoplastic synthetic resin fiber and thermoplastic synthetic resin coated on a substantially whole area of an outer surface of the fibrous nonwoven fabric wherein the thermoplastic synthetic resin forms a substantially smooth synthetic resin layer on outer surfaces of the respective tape fasteners. Thus, a free portion of each tape fastener is reliably prevented from being disengaged from a target tape even when the outer surface of the tape fastener and an inner surface of an underwear rub together during use of the diaper.

RELATED APPLICATIONS

The present application is based on, and claims priority from, Japanese Application Number 2003-205918, filed Aug. 5, 2003, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a disposable diaper for absorption and containment bodily discharges.

There has already been proposed an open-type disposable diaper defining, in a longitudinal direction, front and rear waist regions and a crotch region extending between these two waist regions, wherein a pair of tape fasteners extending in a transverse direction and used to connect the front and rear waist regions with each other are attached to side flaps of the rear waist region, respectively, and a target tape is attached to the front waist region so that the tape fasteners may be releasably anchored on the target tape (See Japanese Unexamined Patent Application Publication No. 1997-38139, hereinafter referred to as “Citation”).

The tape fasteners are formed from a fibrous nonwoven fabric made of a plurality of thermoplastic synthetic resin fibers entangled one with another. The tape fasteners respectively have fixed portions adapted to be permanently bonded to respective transversely outer ends of the side flaps in the rear waist region and free portions extending outward from the respective fixed portions in the transverse direction. The free portions of the respective tape fasteners are provided on respective inner surf aces thereof with hooks constituting a mechanical fastener. The target tape is provided in the form of a rectangular strip being relatively long in the transverse direction and formed from a bulky nonwoven fabric made of a plurality of thermoplastic synthetic resin fibers entangled one with another. To put the diaper disclosed in Citation on the wearer's body, the side flaps of the rear waist region are placed upon the outer side of the front waist region and then the free portions of the tape fasteners are anchored on the target tape through the intermediary of the hooks to connect the front and rear waist regions with each other. Parent or care personnel puts underwear such as pants or skirt on the wearer having the diaper thereon. Movement of the wearer's body having the diaper put thereon causes the outer surface of the tape fastener and the inner surface of the underwear to rub together.

In the diaper disclosed in Citation, the tape fasteners are formed from the fibrous nonwoven fabric made of a plurality of thermoplastic synthetic resin fibers and the outer surface of each tape fastener is not smooth but relatively rough. Therefore, a certain sliding friction is exerted upon the tape fastener by the underwear as the outer surface of the tape fastener and the inner surface of the underwear rub together. Such sliding friction may cause torsion and/or turning up of the free portion of the tape fastener. In this diaper, the torsion and/or turning up of the free portion of the tape fastener nay be exerted upon the tape fastener and the target tape as shearing force and/or peel force intending to disengage the tape fastener and the target tape from each other. With a consequence, the tape fastener and the target tape may often be unintentionally disengaged from each other.

SUMMARY OF THE INVENTION

In view of the problem as has been described above, it is an object of the present invention to provide a disposable diaper improved so that a free portion of each tape fastener is reliably prevented from being disengaged from a target tape even an outer surface of the tape fastener and an inner surface of an underwear rub together during use of the diaper.

The object set forth above is achieved, according to the present invention, by a disposable diaper defining, in a longitudinal direction, front and rear waist regions and a crotch region extending between the front and rear waist regions wherein a pair of tape fasteners used to connect the front and rear waist regions with each other are attached to a pair of side flaps in the rear waist region, respectively, and the tape fasteners respectively have fixed portions permanently attached to the side flaps in the rear waist region and free portions extending outward from the fixed portions in the transverse direction and adapted to be releasably anchored on an outer side of the front waist region by means of fastening means formed on inner surfaces of the free portions.

The diaper according to the present invention further comprises the following features: Each of the tape fasteners comprises a first fibrous nonwoven fabric made of a plurality of thermoplastic synthetic resin fibers entangled one with another and thermoplastic synthetic resin coated on a generally whole area of an outer surface of the first fibrous nonwoven fabric so that the thermoplastic synthetic resin forms a substantially smooth first synthetic resin layer on an outer surface of the tape fastener.

According to one preferred embodiment of the invention, a kinetic friction coefficient of the tape fastener on its outer surface is 0.4 or less.

According to another preferred embodiment of the invention, at least one of polyethylene-, polypropylene-, polyamide-, polyester-, polyvinyl chloride- and polystyrene-based synthetic resins is used as material for the synthetic resin fiber forming the first fibrous nonwoven fabric and the first synthetic resin layer and one of the synthetic resin fiber and the first synthetic resin layer contains 25% or higher by weight of the same synthetic resin as the synthetic resin used for the other.

According to still another preferred embodiment of the invention, the side flaps of the rear waist region respective comprise a second fibrous nonwoven fabric made of a plurality of thermoplastic synthetic resin fibers entangled one with another and thermoplastic synthetic resin coated on a generally whole area of the outer surface of the second fibrous nonwoven fabric so that the thermoplastic synthetic resin forms a substantially smooth second synthetic resin layer on outer surfaces of the respective side flaps in the rear waist region.

According to further another preferred embodiment of the invention, a kinetic friction coefficient of the respective side flaps in the rear waist region is 0.4 or less.

According to an additional preferred embodiment of the invention, at least one of polyethylene-, polypropylene-, polyamide-, polyester-, polyvinyl chloride- and polystyrene-based synthetic resins is used as material for the synthetic resin fiber forming the second fibrous nonwoven fabric and the second synthetic resin layer and one of the synthetic resin fiber and the second synthetic resin layer contains 25% or higher by weight of the same synthetic resin as the synthetic resin used for the other.

According to further additional preferred embodiment of the invention, the fixed portions of the tape fasteners are permanently bonded to the side flaps in the rear waist region by means of adhesive coated on the first synthetic resin layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Details of a disposable diaper according to the present invention will be more fully understood from the description given hereunder with reference to the accompanying drawings.

FIG. 1is a partially cutaway perspective view showing a diaper1A according to an embodiment of the invention,FIG. 2is a sectional view taken along the line II—II inFIG. 1,FIG. 3is a sectional view taken along the line III—III inFIG. 1andFIG. 4is a sectional view taken along the line IV—IV inFIG. 1. InFIG. 1, a transverse direction is indicated by an arrow L and a longitudinal direction is indicated by an arrow M. As used herein, “inner surfaces” of top- and backsheets2,3, leak-barrier sheets5, tape fasteners6, a target tape7and fibrous nonwoven fabric28refer to the surfaces thereof facing the wearer's skin and “outer surfaces” thereof refer to the surfaces thereof facing away from the wearer's skin.

The diaper1A primarily comprises the liquid-pervious topsheet2facing the wearer's skin, the liquid-impervious backsheet3facing away from the wearer's skin, a liquid-absorbent core4interposed between these top- and backsheets2,3, and a pair of the leak-barrier sheets5. In addition to these component members, the diaper1A has a pair of the flexible tape fasteners6and the flexible target tape7which is relatively long in the transverse direction.

The diaper1A defines, in the longitudinal direction, front and rear waist regions8,10, crotch region9extending between these waist regions8,10, a pair of end flaps11ending in the transverse direction outside longitudinally opposite ends4aof the core4, respectively, and paired side flaps12,13,14respectively extending in the longitudinal direction outside transversely opposite side edges4bof the core4. The paired side flap12in the front waist region8as well as paired side flap14in the rear waist regions10has a length dimension as measured in the transverse direction which is larger than that of the paired side flap13in the crotch region9, so the diaper1A presents a substantially hourglass-like planar shape.

The topsheet2is formed from a hydrophilic fibrous nonwoven fabric15. The backsheet3is formed from a breathable liquid-impervious plastic film16and a hydrophobic fibrous nonwoven fabric17placed upon each other. Of the backsheet3, the film16faces the wearer's skin and the nonwoven fabric17faces away from the wearer's skin. The film16and the nonwoven fabric17have respective surfaces opposed to each other and intermittently bonded to each other by means of adhesive (not shown). The core4extends between the front and rear waist regions8,10and is permanently bonded to at least one of the topsheet2and the backsheet3(i e., the film16). The leak-barrier sheets5are formed from a hydrophobic fibrous nonwoven fabric18. Each of the nonwoven fabric layers15,17,18is made of a plurality of polyolefin-based thermoplastic synthetic resin crimped fibers intertwined one with another. Each of the nonwoven fabric layers15,17,18is made of a plurality of polyolefin-based thermoplastic synthetic resin fibers intertwined one with another and the film16is made of polyolefin-based thermoplastic synthetic resin.

Each of the end flaps11comprises an end portion2aof the topsheet2extending outward from the associated end4aof the core4in the longitudinal direction and an end portion3aof the backsheet3. These end portions2a,3aof these sheets2,3are placed upon and permanently bonded to each other. Tape-like waist-surrounding elastic members19extending in the transverse direction are contractibly attached to the respective end flaps11. Each of the waist-surrounding elastic members19is interposed between the end portion2aof the topsheet2and the end portion3aof the backsheet3and permanently bonded to these sheets2,3while the elastic member19is stretched in the transverse direction at a given ratio.

The respective paired side flaps12,13,14are formed from transversely opposite side edge portions2b,3bof the top- and backsheets2,3, respectively, and fixed side edge portions5aof the leak-barrier sheets5which will be described later more in details. In the respective paired side flaps12,13,14, the side edge portions2bof the topsheet2extend outward slightly beyond the side edges4bof the core4in the transverse direction. The side edge portions3bof the backsheet3as well as the fixed side edge portions5aof the leak-barrier sheets5extend further outward beyond the side edge portions2bof the topsheet2in the transverse direction. These side edge portions2b,3b,5aof these sheets2,3,5are placed one upon another and permanently bonded one to another. Major portions of the paired side flaps12,14in the front and rear waist regions8,10, respectively, are formed from the side edge portions3bof the backsheet3and the fixed side edge portions5aof the leak-barrier sheets5. A plurality of strand-like leg-surrounding elastic members20extending in the longitudinal direction are contractibly attached to the side flaps13in the crotch region9. The leg-surrounding elastic members20are interposed between the side edge portions3bof the backsheet3and the fixed side edge portions5aof the leak-barrier sheets5and are permanently bonded to these sheets3,5as the elastic members20are stretched in the transverse direction at a given ratio.

The leak-barrier sheets5respectively have the fixed side edge portions5alying outside the respective side edges4bof the core4and extending in the longitudinal direction between the front and rear waist regions8,10, movable portions5bnormally biased to rise above the topsheet2and extending in the longitudinal direction between the front and rear waist regions8,10and fixed end portions5clying on the respective end flaps11and collapsed inward in the transverse direction of the diaper1A. The movable portions5bare provided in the vicinity of respective upper edges thereof with stretchable elastic members21extending in the longitudinal direction contractibly attached thereto. These elastic members21are wrapped with parts of the respective movable portions5band permanently bonded to the respective movable portions5b. The fixed end portions5care permanently bonded to the inner surface of the topsheet2along its longitudinally opposite end portions2a. In the leak-barrier sheets5, the elastic members21contract as the diaper1A is let curve in the longitudinal direction with the topsheet2inside, whereupon the movable portions5brise above the topsheet2and form barriers against bodily discharges.

The tape fasteners6are generally rectangular and extend outward from the side flaps14of the rear waist region10in the transverse direction. The respective tape fasteners6have fixed portions22permanently bonded to the transversely outer end portions14aof the respective side flaps14and free portions23extending outward from the respective fixed portions22in the transverse direction. The free portions23are provided on the inner surfaces thereof with a plurality of flexible hooks24(fastening means) extending in a thickness direction of the diaper1A. The free portions23are formed in the vicinity of distal ends thereof with finger-grips25. These free portions23are releasably anchored on the outer surface of the target tape7through the intermediary of the hooks24.

The target tape7is generally rectangular and extends on in the front waist region8in the transverse direction. The target tape7has its inner surface permanently bonded to the outer surface of the backsheet3(i.e., the nonwoven fabric layer17) by means of adhesive (not shown) in intermittent or continuous manner. The target tape7is provided on its outer surface with a plurality of flexible loops26each extending in the thickness direction of the diaper1A so as to describe a circular arc.

FIG. 5is a partially scale-enlarged sectional view showing a tape fastener6in the sectional view ofFIG. 3andFIG. 6is a perspective view showing the diaper1A as put on the wearer's body.

The tape fastener6comprises a fibrous nonwoven fabric28(first fibrous nonwoven fabric) formed from a plurality of thermoplastic synthetic resin fibers27entangled one with another and thermoplastic synthetic resin29with which the nonwoven fabric28is coated over a generally whole area of its outer surface. Thermoplastic synthetic resin29forms a substantially smooth synthetic resin layer30(first synthetic resin layer) on the outer surface of the tape fastener6. It should be understood here that the nonwoven fabric28may be either hydrophilic or hydrophobic.

To coat the nonwoven fabric28with thermoplastic synthetic resin29, a contact coating technique (using a coater) may be utilized. In the contact coating process, a nozzle tip through which the synthetic resin29is discharged in molten state is placed practically in contact with the outer surface of the nonwoven fabric28and thereby the nonwoven fabric28is coated intermittently or continuously with the synthetic resin29.

As material for the synthetic resin fiber27and the synthetic resin layer30constituting the nonwoven fabric28, polyolefin-based thermoplastic synthetic resin may be used. As such polyolefin-based thermoplastic synthetic resin, at least one of polyethylene-, polypropylene-, polyamide-, polyester-, polyvinyl chloride- and polystyrene-based synthetic resins may be used.

It is preferred to use one and same polyolefin-based synthetic resin as material for the synthetic resin fiber27and the synthetic resin layer30. For example, when polyethylene-based synthetic resin is used as material to form the synthetic resin fiber27, it is preferred to use the same polyethylene-based synthetic resin as material to form the synthetic resin layer30. Use of the same type of synthetic resin as material for the synthetic resin fiber27and the synthetic resin layer30is advantageous in that these two components have substantially the same melting point and a compatibility of these two components is correspondingly improved. Specifically, the synthetic resin fiber27and the synthetic resin29can be easily and reliably joined together when the outer surface of the fibrous nonwoven fabric28is coated with the thermoplastic synthetic resin29.

While it is possible to use different types of polyolefin-based synthetic resin as materials for the synthetic resin fiber27and the synthetic resin layer30, respectively, it is essential in this case that one of the synthetic resin fiber27and the synthetic resin layer30should contain 25% or higher by weight of the same synthetic resin as the synthetic resin used for the other. If the content of the material common to the synthetic resin fiber27and the synthetic resin layer30is less than 25% by weight, melting points of the synthetic resin fiber27and the synthetic resin layer30will be different from each other and/or compatibility between the synthetic resin fiber27and the synthetic resin layer30will be deteriorated. For example, if the melting point of the synthetic resin layer30is higher than the melting point of the synthetic resin fiber27and the compatibility between the synthetic resin fiber27and the synthetic resin layer30is insufficient, it will be impossible to join the synthetic resin layer30to the synthetic resin fiber27unless the outer surface of the nonwoven fabric28is coated with the thermoplastic synthetic resin29molten at a high temperature. In some cases, the nonwoven fabric28will become filmy due to the high temperature of the thermoplastic synthetic resin29. If the nonwoven fabric28becomes filmy, stiffness of the tape fasteners6will unacceptably increase and uncomfortably irritate the wearer's skin. The synthetic resin fiber27preferably has a fineness in a range of 0.3 to 10 dtex. The nonwoven fabric28preferably has a basis weight in a range of 20 to 500 g/m2, more preferably in a range of 30 to 300 g/m2and most preferably in a range of 50 to 150 g/m2.

The hooks24attached to the tape fastener6are made of polyolefin-based thermoplastic synthetic resin. In the fixed portion22of the tape fastener6, the synthetic resin layer30is coated with adhesive31and permanently bonded to the inner surface of the fixed side edge portion5aof the associated leak-barrier sheet5(i.e., the fibrous nonwoven fabric18) forming the side flap14in the rear waist region10by means of the adhesive31. The target tape7may be formed from a fibrous nonwoven fabric made of polyolefin-based thermoplastic synthetic resin fiber or by polyolefin-based thermoplastic synthetic resin film. The loops26attached to the target tape7are made of polyolefin-based thermoplastic synthetic resin.

Parent or care personnel may put the diaper1A on the wearer's body, for example, in a sequence as follows: Parent or care personnel may place buttock of the wearer lying face up on the developed diaper1A, then grip the front waist region8and fold the crotch region9of the diaper1A so that the front waist region8may cover the wearer's belly. Now the side flaps14in the rear waist region10may be folded inward with the tape fasteners6being finger gripped so that these side flaps14may be laid on the end flap11and the side flaps12in the front waist region8over the wearer's belly. Finally, the free portions23of the respective tape fasteners6may be anchored on the outer surface of the target tape7by means of the hooks24.

To anchor the tape fasteners6on the target tape7, the free portions23of the respective tape fasteners6may be pressed against the outer surface of the target tape7to put the hooks24and the loops26into mutual engagement. The diaper1A having the front and rear waist regions8,10connected with each other is formed with a waist-hole32and a pair of leg-holes33. Parent or care personnel may put underwear such as pants or skirt on the wearer's body having the diaper1A on. Movement of the wearer's body having the diaper1A on causes the outer surfaces of the tape fasteners6and the inner surface of the underwear to rub together Body fluids discharged on the diaper1A permeate the topsheet2and then are absorbed and retained by the core4.

The thermoplastic synthetic resin29forms the synthetic resin layer30(i.e., first synthetic resin) on the outer surface of the respective tape fasteners6. The synthetic resin layer30is sufficiently smooth to alleviate a sliding friction exerted upon the tape fasteners6by the underwear even when the outer surface of the tape fasteners6and the inner surface of the underwear rub together. In the diaper1A, a sliding friction exerted upon the tape fasteners6is not so significant to cause torsion and/or turning up of the free portions23. Significant torsion and/or turning up of the free portions23of the tape fasteners6would be exerted upon the tape fasteners6as well as upon the target tape7as a shearing force and/or a peel force intending to disengage them from one another. However, the diaper1A is advantageously constructed so that the free portions23of the tape fasteners6are protected from such torsion and/or turning up. In this way, there is no anxiety that a torsion and/or a peel force might be exerted upon the free portions23of the tape fasteners6as well as upon the target tape7and cause these free portions23to be unintentionally disengaged from the outer surface of the target tape7.

The adhesive31coated on the synthetic resin layer30of the fixed portions22is utilized to attach the fixed portions22of the respective tape fasteners6to the side flaps14in the rear waist region10. The adhesive31spreads well on the synthetic resin layer30because this layer30is substantially smooth. Such feature ensures that, even when a substrate on which the fixed portions22of the respective tape fasteners6are to be permanently bonded is the fibrous nonwoven fabric18of which the outer surface is not smooth but relatively rough, these fixed portions22can be reliably bonded to the side flaps14in the rear waist region10.

A kinetic friction coefficient of the tape fastener6on its outer surface is 0.4 or less so that no significant sliding friction is exerted upon the tape fasteners6even when the outer surface of the tape fastener6and the inner surface of the underwear rub together. If the kinetic friction coefficient of the tape fastener6on its outer surface exceeds 0.4, unacceptably high sliding friction will be exerted upon the tape fastener6by the underwear and such sliding friction will cause torsion and/or turning up of the free portion23of the tape fastener6. With a consequence, the free portion23of the tape fastener6and the target tape7engaged with each other will be subjected to a shearing force and/or a peel force. More specifically, the kinetic friction coefficient exceeding 0.4 will make it impossible to maintain the free portion23of the tape fastener6and the target tape7in mutual engagement and may cause the free portion23to be unintentionally disengaged from the target tape7during use of the diaper1A. The kinetic friction coefficient of the tape fastener6on its outer surface was measured in accordance with JIS K 7125 by a method as will be described.FIG. 7schematically illustrates the method for measurement of the kinetic friction coefficient.(1) For measurement of the kinetic friction coefficient, a movable weight50having a smooth lower surface50aand a fixed table51having a smooth upper surface51a. Samples52for measurement of the kinetic friction coefficient each having a width dimension of 30 mm and a length dimension of 30 mm are made from the tape fastener6before attached to the diaper1A and white cloth53(cotton, calico No. 3) used in a color fastness test (JIS L 0803) is prepared.(2) The sample52is fixed to the lower surface50aof the movable weight50using pressure sensitive adhesive double coated tape. The white cloth53is fixed to the upper surface51aof the fixed table51. The movable weight50has a weight of 58 g and its lower surface is subjected to a load of 6.47/cm2.(3) Measurement of the kinetic friction coefficient is achieved by moving the movable weight50at a velocity of 10 cm/mm in a direction indicated by an arrow N1in FIG. 7 and a kinetic friction coefficient is determined on the basis of a frictional force generated as the movable weight50is moved by 5 cm. Specifically, the kinetic friction coefficient is calculated from an equation: μ=FD/FPwherein μ represents a kinetic friction coefficient, FDrepresents a frictional force generated as the movable weight is moved by 5 cm and FPrepresents a force in a vertical direction indicated by an arrow N2generated along a contact surface between the sample52for measurement and the white cloth53.

In the diaper1A, an engagement force at which the free portion23of the tape fastener6is engaged with the target tape7is preferably in a range of 0.3 to 8.0 N/(width dimension of the tape fastener). If the engagement force is less than 0.3 N/(width dimension of the tape fastener), the free portion23of the tape fastener6may sometimes be disengaged from the target tape7as the outer surface of the tape fastener6and the inner surface of the underwear rub together, even when the kinetic friction coefficient of the tape fastener6on its outer surface is 0.4 or less. The engagement force between the free portion23of the tape fastener6and the target tape7was measured by a method as follows:(1) For measurement of the engagement force, AUTOGRAPH available from SHIMAZU Co., Ltd. (software: Trapezium Ver. 1.22 available from SHIMAZU Co., Ltd.) was used as the measuring device. In addition to this device, a fixture for peel measurement (aluminum fixture having a plane slanted at an angle of 45° with respect to a vertical axis between chucks so that a lower end of this plane can be fixed to the lower chuck of AUTOGRAPH), a pressure roller (diameter; 100 mm, width; 44 mm, weight; 700 g, hardness HS70; and reciprocating at a velocity of 5 mm/sec), a stainless plate(stainless flat plate, thickness*2 to 5 mm), a pair of gum tape strips (available from Nitto Denko Corporation, 50 mm×70 mm) and metallic clips were used.(2) A first sample for measurement of the engagement force is made by cutting the tape fastener6away from the diaper1A and a second sample for measurement of the engagement force is made by cutting a generally half of the tape fastener away from the diaper1A, more specifically, so as to bisect the transverse dimension of the target tape7. Then gum tape strips are coated on both surfaces of the finger-grip so that the upper chuck of AUTOGRAPH may grip the finger-grip25of the free portion23of the tape fastener6.(3) The second sample is placed on the smooth upper surface of the stainless plate. The second sample having been smoothed is fixed to the upper surface of the stainless plate using pressure sensitive adhesive single coated tape. Now the first sample is placed on the second sample and these two samples are engaged with each other using the pressure roller (press conditions: single reciprocating at a velocity of 5 mm/min in the longitudinal direction of the first sample). A lower portion of the 135° peel measurement fixture is held by the lower chuck of AUTOGRAPH and the finger-grip25(including the gum tape strips) of the free portion23of the tape fastener6is held by the upper chuck. AUTOGRAPH is operated under conditions as follow: load cell=50 N; pressure range=10 N; tensile velocity=300 mm/min, and distance between the upper chuck and 135° peel measurement fixture=50 mm.(4) the upper and lower chucks are moved away from each other in order to exert a peel force upon the first and second samples and a force generated when the first and second samples are peeled off from each other is measured. Such force generated when the first and second samples are peeled off from each other is measured ten times and an average is calculated from the results of these ten times measurements as the engagement force between the free portion23of the tape fastener6and the target tape7.

FIG. 8is a partially cutaway perspective view showing a diaper1B according to another embodiment,FIG. 9is a sectional view taken along the line IX—IX inFIG. 8andFIG. 10is a partially scale-enlarged sectional view showing a tape fastener6and a side flap14in the rear waist region10in the sectional view ofFIG. 9. InFIG. 8, a transverse direction is indicated by an arrow L and a longitudinal direction is indicated by an arrow M. As used herein, “inner surface” of fibrous nonwoven fabric34refers to its surface facing the wearer's skin and “outer surface” of this nonwoven fabric refers to its surface facing away from the wearer's skin.

The diaper1B primarily comprises the liquid-pervious topsheet2facing the wearer's skin, the liquid-impervious backsheet3facing away from the wearer's skin, a liquid-absorbent core4interposed between these top- and backsheets2,3, and a pair of the leak-barrier sheets5. The diaper1B defines, in the longitudinal direction, front and rear waist regions8,10, crotch region9extending between these waist regions8,10, a pair of end flaps11ending in the transverse direction outside longitudinally opposite ends4aof the core4, respectively, and paired side flaps12,13,14respectively extending in the longitudinal direction outside transversely opposite side edges4bof the core4. The paired side flap12in the front waist region8as well as paired side flap14in the rear waist regions10has a length dimension as measured in the transverse direction which is larger than that of the paired side flap13in the crotch region9, so the diaper1B presents a generally hourglass-like planar shape.

The topsheet2is formed from a hydrophilic fibrous nonwoven fabric15like the topsheet2shown byFIG. 1. The backsheet3is formed from a bulky hydrophobic fibrous nonwoven fabric34(second fibrous nonwoven fabric). The fibrous non woven fabric34is made of a plurality of polyolefin-based thermoplastic synthetic resin crimped fibers intertwined one with another. The core4is permanently bonded to at least one of the topsheet2and the backsheet3. The leak-barrier sheets5are formed by hydrophobic fibrous nonwoven fabric18like them shown byFIG. 1.

Each of the end flaps11comprises an end portion2aof the topsheet2extending outward from the associated end4aof the core4in the longitudinal direction and an end portion3aof the backsheet3. These end portions2a,3aof these sheets2,3are placed upon and permanently bonded to each other. Tape-like waist-surrounding elastic members19extending in the transverse direction are contractibly attached to the respective end flaps11. Each of the waist-surrounding elastic members19is interposed between the end portion2aof the topsheet2and the end portion3aof the backsheet3and permanently bonded to these sheets2,3.

The respective paired side flaps12,13,14are formed from transversely opposite side edge portions2b,3bof the top- and backsheets2,3, respectively, and fixed side edge portions5aof the leak-barrier sheets5. In the respective paired side flaps12,14in the front and rear waist regions8,10, the side edge portions2bof the topsheet2and the side edge portions5aof the leak-barrier sheets5extend outward slightly beyond the side edges4bof the core4in the transverse direction. The side edge portions3bof the backsheet3extend further outward beyond the side edge portions2b,5ain the transverse direction. Major portions of the paired side flaps12,14are formed by the side edge portions3bof the backsheet3. In the side flaps13in the crotch region9, the side edge portions2bof the topsheet2extend outward slightly beyond the side edges4bof the core4in the transverse direction and the side edge portions3bof the backsheet3as well as the side edge portions5aof the leak-barrier sheets5extend outward beyond the side edge portions2bin the transverse direction. In the respective paired side flaps12,13,14, the side edge portions2b,3b,5aof these sheets2,3,5are placed one upon another and permanently bonded together. A plurality of strand-like leg-surrounding elastic members20extending in the longitudinal direction are contractibly attached to the side flaps13in the crotch region9. The leg-surrounding elastic members20are interposed between the side edge portions3bof the backsheet3and the side edge portions5aof the leak-barrier sheets5and are permanently bonded to these sheets3,5as the elastic members20are stretched in the transverse direction.

The leak-barrier sheets5respectively have the fixed side edge portions5alying outside the respective side edges4bof the core4and extending in the longitudinal direction, movable portions5bnormally biased to rise above the topsheet2and extending in the longitudinal direction and fixed end portions5clying on the respective end flaps11and collapsed inward in the transverse direction. The fixed end portions5care permanently bonded to the inner surface of the topsheet2. The movable portions5brise above the topsheet2and form barriers against bodily discharges.

The tape fasteners6extend outward from the side flaps14of the rear waist region10in the transverse direction. The respective tape fasteners6have fixed portions22permanently bonded to the transversely outer end portions14aof the respective side flaps14and free portions23extending outward from the respective fixed portions22in the transverse direction. The free portions23are provided on the inner surfaces thereof with a plurality of flexible hooks24(fastening means) extending in a thickness direction of the diaper1B. The free portions23are formed in the vicinity of distal ends thereof with finger-grips25. These free portions23are releasably anchored on the outer surface of the backsheet3(nonwoven fabric34) through the intermediary of the hooks24.

The tape fastener6comprises fibrous nonwoven fabric28(first fibrous nonwoven fabric) formed by a plurality of thermoplastic synthetic resin fibers27entangled one with another and thermoplastic synthetic resin29with which the nonwoven fabric28is coated over a substantially whole area of its outer surface. Thermoplastic synthetic resin29forms a substantially smooth synthetic resin layer30(first synthetic resin layer) on the outer surface of the tape fastener6. The nonwoven fabric28may be coated with the thermoplastic synthetic resin29using so-called contact coating (using a coater) technique as in the case shown byFIG. 1.

similarly to the case shown byFIG. 1, polyolefin-based thermoplastic synthetic resin may be used as material for the synthetic resin fiber27and the synthetic resin layer30constituting the nonwoven fabric28. As such polyolefin-based thermoplastic synthetic resin, at least one of polyethylene-, polypropylene-, polyamide-, polyester-, polyvinyl chloride- and polystyrene-based synthetic resins may be used. It is preferred to use one and same polyolefin-based synthetic resin as material for the synthetic resin fiber27and the synthetic resin layer30. While it is possible to use different types of polyolefin-based synthetic resin as materials for the synthetic resin fiber27and the synthetic resin layer30, respectively, it is essential in this case that one of the synthetic resin fiber27and the synthetic resin layer30should contain 25% or higher by weight of the same synthetic resin as the synthetic resin used for the other. Fineness of the synthetic resin fiber27as well as basis weight of the nonwoven fabric28may be similar to those in the case shown byFIG. 1.

The hooks24attached to the tape fastener6are flexible and made of polyolefin-based thermoplastic synthetic resin. In the fixed portion22of the tape fastener6, the synthetic resin layer30is coated with adhesive31and permanently bonded to the inner surface of the fixed side edge portion3bof the backsheet3(i.e., the nonwoven fabric34) forming the side flap14in the rear waist region10by means of the adhesive31.

In the side flaps14of the rear waist region10, the nonwoven fabric34(second fibrous nonwoven fabric) forming the backsheet3is coated over a generally whole area of its outer surface with thermoplastic synthetic resin36. Thermoplastic synthetic resin36forms a substantially smooth synthetic resin layer37(second synthetic resin layer) on the outer surface of the side flaps14in the rear waist region10. To coat the nonwoven fabric34with thermoplastic synthetic resin36, a contact coating technique (using a coater) may be utilized like the case in which the nonwoven fabric28is coated with the thermoplastic synthetic resin29.

As material for the synthetic resin fiber35and the synthetic resin layer37constituting the nonwoven fabric34, polyolefin-based thermoplastic synthetic resin may be used. As such polyolefin-based thermoplastic synthetic resin, at least one of polyethylene-, polypropylene-, polyamide-, polyester-, polyvinyl chloride- and polystyrene-based synthetic resins may be used.

It is preferred to use one and same polyolefin-based synthetic resin as material for the synthetic resin fiber35and the synthetic resin layer37. For example, when polyethylene-based synthetic resin is used as material to form the synthetic resin fiber35, it is preferred to use the same polyethylene-based synthetic resin as material for the synthetic resin layer35to form the synthetic resin layer37. Use of a same type of synthetic resin as material for the synthetic resin fiber35and the synthetic resin layer37is advantageous in that these two components have a substantially same melting point and a compatibility of these two components is correspondingly improved. Specifically, the synthetic resin fiber35and the synthetic resin36can be easily and reliably joined together when the outer surface of the fibrous nonwoven fabric34is coated with the thermoplastic synthetic resin36.

While it is possible to use different types of polyolefin-based synthetic resin as materials for the synthetic resin fiber35and the synthetic resin layer37, respectively, it is essential in this case that one of the synthetic resin fiber35and the synthetic resin layer37should contain 25% or higher by weight of the same synthetic resin as the synthetic resin used for the other. If the content of the material common to the synthetic resin fiber35and the synthetic resin layer37is less than 25% by weight, melting points of the synthetic resin fiber35and the synthetic resin layer37will be different from each other and/or compatibility between the synthetic resin fiber35and the synthetic resin layer37will be deteriorated. For example, if the melting point of the synthetic resin layer37is higher than the melting point of the synthetic resin fiber35and the compatibility between the synthetic resin fiber35and the synthetic resin layer37is insufficient, it will be impossible to join the synthetic resin layer37to the synthetic resin fiber35unless the outer surface of the nonwoven fabric34is coated with the thermoplastic synthetic resin36molten at a high temperature. In some cases, the nonwoven fabric34will become filmy due to the high temperature of the thermoplastic synthetic resin36. If the nonwoven fabric34becomes filmy, stiffness of the side flaps14of the rear waist region10will unacceptably increase and uncomfortably irritate the wearer's skin.

Parent or care personnel may put the diaper1B on the wearer's body in substantially the same sequence as in the case ofFIG. 1. However, in the case of the diaper1B, the free portions23of the respective tape fasteners6are pressed against the outer surface of the backsheet3to put the hooks24into engagement with the crimped fibers35forming the nonwoven fabric34. Parent or care personnel may put underwear such as pants or skirt on the wearer's body having the diaper1B on. Movement of the wearer's body having the diaper1B on causes the outer surfaces of the tape fasteners6and the inner surface of the underwear to rub together while causing the outer surface of the side flaps14in the rear waist region10and the inner surface of the underwear to rub together

The thermoplastic synthetic resin29forms the synthetic resin layer30(i.e., first synthetic resin) on the outer surface of the respective tape fasteners6. The synthetic resin layer30is sufficiently smooth to alleviate a sliding friction exerted upon the tape fasteners6by the underwear even when the outer surface of the tape fasteners6and the inner surface of the underwear rub together. A sliding friction exerted upon the tape fasteners6is not so significant to cause torsion and/or turning up of the free portions23. In this way, there is no anxiety that a torsion and/or a peel force might be exerted upon the free portions23of the tape fasteners6as well as upon the backsheet3and might cause these free portions23to be unintentionally disengaged from the outer surface of the backsheet (i.e., nonwoven fabric34).

The thermoplastic synthetic resin36forms the substantially smooth synthetic resin layer37(i.e., second synthetic resin) on the outer surface of the respective side flaps14of the rear waist region10. The synthetic resin layer37is sufficiently smooth to alleviate a sliding friction exerted upon the tape fasteners6by the underwear even when the outer surface of the tape fasteners6and the inner surface of the underwear rub together. A sliding friction exerted upon the side flaps14is not so significant to cause torsion and/or turning up of the side flaps14. Significant torsion and/or turning up of the side flaps14would be transmitted to the tape fasteners6as a shearing force and/or a peel force intending to disengage the free portions of the tape fasteners6and the backsheet3from one another. However, the diaper1B is advantageously constructed so that the side flaps14can be prevented from such torsion and/or turning up and the free portions23of the tape fasteners6as well as the backsheet3can be protected from such torsion and/or turning up. In this way, there is no anxiety that the free portions23might be unintentionally disengaged from the outer surface of the backsheet3.

Similarly to the case ofFIG. 1, the adhesive31is coated on the substantially smooth synthetic resin layer30of the fixed portions22of the tape fasteners6and therefore the adhesive31spreads well on the synthetic resin layer30in the diaper1B also. Even when a substrate on which the fixed portions22of the respective tape fasteners6are to be permanently bonded is the fibrous nonwoven fabric34of which the outer surface is not smooth but relatively rough, these fixed portions22can be reliably bonded to the side flaps14in the rear waist region10.

A kinetic friction coefficient of the tape fastener6on its outer surface is 0.4 or less. If the kinetic friction coefficient of the tape fastener6on its outer surface exceeds 0.4, unacceptably high sliding friction will be exerted upon the tape fastener6by the underwear and such sliding friction will cause torsion and/or turning up of the free portion23of the tape fastener6. With a consequence, the free portion23of the tape fastener6and the backsheet3engaged with each other will be subjected to a shearing force and/or a peel force which may cause the free portion23to be unintentionally disengaged from the backsheet3during use of the diaper1B.

A kinetic friction coefficient of the side flaps14of the rear waist region10on the respective outer surfaces is 0.4 or less so that no significant sliding friction is exerted upon the tape fasteners6even when the outer surface of the tape fastener6and the inner surface of the underwear rub together. If the kinetic friction coefficient of the side flaps14on the respective outer surfaces exceeds 0.4, unacceptably high sliding friction will be exerted upon the side flaps14by the underwear and such sliding friction will cause torsion and/or turning up of the side flaps14. With a consequence, the free portion23of the tape fastener6and the backsheet3engaged with each other will be subjected to high shearing force and/or peel force. More specifically, the kinetic friction coefficient exceeding 0.4 will make it impossible to maintain the free portion23of the tape fastener6and the backsheet3in mutual engagement and may cause the free portion23to be unintentionally disengaged from the backsheet3during use of the diaper1B.

The method for measurement of kinetic friction coefficient of the tape fastener6on its outer surface is same as the case ofFIG. 1. The method for measurement of kinetic friction coefficient of the side flaps on the respective outer surfaces thereof is the same as the method for measurement of kinetic friction coefficient of the tape fastener6except that samples for measurement are prepared by cutting the side flaps14of the rear waist region10away from the diaper1B each in a size of 30 mm width dimension×30 mm length dimension.

In the diaper1B, an engagement force at which the free portion23of the tape fastener6is engaged with the backsheet3(i.e., nonwoven fabric34) is preferably in a range of 0.3 to 8.0 N/(width dimension of the tape fastener). If the engagement force is less than 0.3 N/(width dimension of the tape fastener), the free portion23of the tape fastener6may sometimes be disengaged from the backsheet3as the outer surface of the tape fastener6and the inner surface of the underwear rub together, even when the kinetic friction coefficient of the tape fastener6on its outer surface is 0.4 or less. The engagement force between the free portion23of the tape fastener6and the backsheet3was measured by the same method as in the case ofFIG. 1except that a substantially half of the front waist region8is cut away from the diaper1B, more specifically, so as to bisect the transverse dimension of the front waist region8to prepare second samples for measurement of engagement force.

The topsheet2may be formed from a hydrophobic fibrous nonwoven fabric having a plurality of apertures or plastic film having a plurality of fine apertures. The backsheet3and the leak-barrier sheets5may be formed from a composite nonwoven fabric (SM nonwoven fabric or SMS nonwoven fabric) consisting of a melt blown fibrous nonwoven fabric having a high water-resistance and a spun bond fibrous nonwoven fabric being high in strength as well as in flexibility laminated on at least one side of the melt blown fibrous nonwoven fabric.

Stock materials for the fibrous nonwoven fabric layers15,17,18,28,34constituting the top- and backsheets2,3, the leak-barrier sheets5, the tape fasteners6and the target tape7, respectively, may be selected from a group consisting of spun lace-, needle punch-, melt blown-, thermal bond-, spun bond- and chemical bond-nonwoven fabric layers. Component fibers of these nonwoven fabric layers15,17,18,28,34may be selected from a group consisting of core-sheath conjugate fiber, side-by-side conjugate fiber, modified macaroni fiber, microporous fiber and fused type conjugate fiber.

The core comprises a mixture of particulate or fibrous super-absorbent polymer and fluff pulp or particulate or fibrous super-absorbent polymer, fluff pulp and super-absorbent synthetic resin fiber, in any case, compressed to a desired thickness. The core4as a whole is preferably wrapped with a liquid-pervious sheet such as tissue paper or hydrophilic fibrous nonwoven fabric in order to prevent the core4from getting out of its initial shape or to prevent the polymer from falling off. The polymer may be selected from a group consisting of starch-based polymer, cellulose-based polymer and synthetic polymer.

Permanently bonding of the sheets2,3,5to one another, permanently bonding of the core4to the sheets2,3and permanently bonding of the elastic members19,20,21to the sheets2,3,5may be achieved by use of adhesive. It is preferred to use hot melt adhesive as adhesive (including the adhesive31). In addition to the hot melt adhesive, it is possible to use acrylic adhesive or rubber-based adhesive. The adhesive is coated on the top- and backsheets2,3and the leak-barrier sheets5preferably in any one of spiral, wavy, zigzag, dotted or striped pattern. The top- and backsheets2,3and the leak-barrier sheets5may be coated with the adhesive in such patterns to ensure that these sheets2,3,5are intermittently and permanently bonded one to another, the core3is intermittently and permanently bonded to the sheets2,3and the elastic members19,20,21are intermittently and permanently bonded to the sheets2,3,5.

While the free portions23of the respective tape fasteners6are provided on the respective inner surfaces thereof with the hooks24in both the diaper1A and the diaper1B, it is impossible to coat these inner surfaces of the free portions23with pressure-sensitive adhesive (fastening means). If the free portions23is coated on the respective inner surfaces thereof with the pressure-sensitive adhesive, the target tape7may be formed from a polyolefin-based thermoplastic synthetic resin film. In both the diaper1A and the diaper1B, the fixed portions22of the tape fasteners6and the side flaps14in the rear waist region10may be permanently bonded to each other using welding technique such as heat-sealing or sonic sealing technique instead of using the adhesive31. Alternatively, in the side flaps14in the rear waist region10of the diaper1A, the fibrous nonwoven fabric17(i.e., second fibrous nonwoven fabric) forming the backsheet3may be coated over a substantially whole area of its outer surface with the thermoplastic synthetic resin36to form a substantially smooth synthetic resin layer37(i.e., second synthetic resin layer) on the outer surfaces of the respective side flaps14.

The disposable diaper according to the present invention is primarily characterized in that the tape fastener comprises the first fibrous nonwoven fabric and the thermoplastic synthetic resin coated on the outer surface of the first fibrous nonwoven fabric and the thermoplastic synthetic resin form the substantially smooth first synthetic resin layer on the outer surface of the tape fastener. Such unique arrangement allows the sliding friction exerted upon the tape fastener by the underwear to be alleviated even when the outer surface of the tape fastener and the inner surface of the underwear rub together. Thus the sliding friction exerted upon the tape fastener is not so sufficient to cause torsion and/or turning up of the free portion of the tape fastener. Such torsion and/or turning up of the free portion of the tape fastener can be effectively alleviated and thereby an anxiety can be eliminated that shearing force and/or peel force might be exerted upon the free portion of the tape fastener and the front waist region engaged with each other and the free portion of the tape fastener might be unintentionally disengaged from the front waist region.

In the case of the diaper constructed so that the side flaps of the rear waist region respective comprise the second fibrous nonwoven fabric and the thermoplastic synthetic resin coated on the outer surface of the second fibrous nonwoven fabric, the sliding friction exerted upon the side flaps by the underwear can be effectively alleviated even when the outer surfaces of the respective side flaps and the inner surface of the underwear rub together. This for the reason that the thermoplastic synthetic resin forms the substantially smooth second synthetic resin layer on the outer surfaces of the respective side flaps in the rear waist region In this diaper, the sliding friction exerted upon the side flaps is not so significant to cause torsion and/or turning up of the side flaps. It is possible for this diaper also to prevent the side flaps from torsion and/or turning up and thereby to protect the free portion of the tape fastener and the front waist region from shearing force and/an peel force. In this way, it is not apprehended that the free portion of the tape fastener might be unintentionally disengaged from the front waist region.

In the case of the diaper constructed so that the first synthetic resin layers constituting the fixed potions of the respective tape fasteners and the side flaps of the rear waist region are permanently bonded together by means of the adhesive, the adhesive spreads well on the tape fasteners because the adhesive is coated on the substantially smooth first synthetic resin layer. Such feature ensures that, even when a substrate on which the fixed portions of the respective tape fasteners are to be permanently bonded is the fibrous nonwoven fabric of which the outer surface is not smooth but relatively rough, these fixed portions can be reliably bonded to the side flaps in the rear waist region.