Disposable training pants

A disposable training pant 1 includes a liquid-permeable topsheet, a liquid-impermeable backsheet and an absorbent core disposed therebetween. The liquid-permeable tophseet includes an upper layer sheet and a lower layer sheet. The upper layer sheet is formed with a wetness telling area and the lower layer sheet intermittently bonded to the absorbent core 13 and containing fibrous material adapted to shrink by 10% or more longitudinally of the training pant as it is wetted and intermittently bonded to the absorbent core and thereby intensify a feeling of wetness given to the infant.

BACKGROUND OF THE INVENTION 
This invention relates generally to disposable training pants and more 
particularly to such a pants that can be used when infants grow out of 
diapers and that include a wetness telling area. 
Japanese Laid-Open Patent Application No. Hei4-5961 discloses a topsheet of 
a disposable training pant partially formed with a wetness telling area 
having a hydrophilicity. In a disposable training pant described in 
Japanese Laid-Open Patent Application No. Hei5-59601, the topsheet is 
provided at least over a middle area thereof with a moistness holding 
sheet partially bonded thereto and partially rising from the topsheet. 
In disposable training pants or diapers comprising a liquid-permeable 
topsheet, a liquid-impermeable backsheet and a liquid-absorbent core 
extending between these two sheets, it is well known to keep the topsheet 
in close contact with the absorbent core by intermittently bonding these 
two components to each other so that a quantity of discharged body fluids 
may be transferred to the absorbent core as rapidly as possible. However, 
if the topsheet is bonded to the absorbent core in this manner in the 
disposable training pants or diaper as disclosed in the above-identified 
Applications, transfer of body fluids can be accelerated but only a small 
quantity of body fluids can stay in the wetness telling area or the 
moistness holding sheet and a feeling of wetness given to the infant by 
such area or sheet is correspondingly weakened. 
SUMMARY OF THE INVENTION 
In view of the problem as has been described above, it is a principal 
object of the invention to facilitate a quantity of body fluids to be held 
in a wetness telling area. 
The object set forth above is achieved, according to the invention, by a 
disposable training pant comprising a liquid-permeable topsheet, a 
liquid-impermeable backsheet and a liquid-absorbent core extending 
therebetween which form a front waist region, a rear waist region and a 
crotch region extending therebetween, said topsheet being intermittently 
bonded to said absorbent core and bonded to said backsheet at portions of 
said topsheet and said backsheet extending outward beyond a peripheral 
edge of said absorbent core, on wherein: 
said topsheet contains a fibrous material causing at least a longitudinal 
dimension of said crotch region to shrink by at least 10% as said topsheet 
is wetted so that said topsheet can shrink at least longitudinally of said 
crotch region and at least a shrinkable area of said topsheet can peel off 
upward from said absorbent core and wherein a predetermined area of said 
topsheet has a hydrophilicity higher than that in an area extending around 
said predetermined area and thereby defines a wetness telling area. 
The invention allows the infant to perceive a wetness even if the training 
pant have slipped downward after it was worn, since the topsheet of the 
inventive disposable training pant shrinks longitudinally of the pant 
practically as soon as it is wetted with urine, thereupon peels off from 
the absorbent core and moves upward in close contact with the infant's 
skin. Once having peeled off from the absorbent core, the topsheet remains 
impregnated with the quantity of discharged urine for a long period and 
thereby intensifies a feeling of wetness given to the infant by the 
wetness telling area. 
Other and further objects, features and advantages of the invention will 
appear more fully from the following description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A disposable training pant 1 shown by FIG. 1 in a perspective view comprise 
a front waist region 2, a rear waist region 3 and a crotch region 4. The 
front and rear waist regions 2, 3 are bonded to each other along 
transversely opposite side edges 6, 7 thereof so as to form a 
waist-opening 8 and a pair of leg-openings 9, 10. 
FIG. 2 is a sectional view showing the training pant longitudinally 
unfolded after the front and rear waist regions 2, 3 have been separated 
from each other back and forth along the side edges 6, 7 as partially 
broken away. The training pant 1 comprises a liquid-permeable topsheet 11, 
a liquid-impermeable backsheet 12 and a liquid-absorbent core 13 extending 
between these two sheets 11, 12. The topsheet 11 and the backsheet 12 are 
bonded to each other at portions thereof extending outward beyond a 
peripheral edge of the absorbent core 13 with a plurality of elastic 
members 14 serving to fit the training pant 1 around the infant's waist 
and a plurality of elastic members 16 serving to fit the training pant 1 
around the infant's legs being bonded in elastically stretched conditions 
to inner surface(s) of the topsheet 11 and/or the backsheet 12. 
The topsheet 11 comprises an upper layer sheet 17 and a lower layer sheet 
18. The upper layer sheet 17 defines the entire inner surface of the 
training pant 1 and the lower layer sheet 18 is in the form of a 
rectangular sheet which occupies a transversely middle zone of the 
training pant 1 and extends longitudinally thereof. As will be described 
later in reference with FIG. 3, the lower layer sheet 18 is bonded to a 
bottom surface of the upper layer sheet 17. The upper layer sheet 17 is 
formed by a liquid-permeable nonwoven fabric made of hydrophobic 
thermoplastic synthetic fibers and locally treated so as to become 
hydrophilic and thereby to define a wetness-telling area 19 (indicated by 
a dotted area in FIG. 2). The lower layer sheet 18 is made of a 
liquid-permeable nonwoven fabric adapted to shrink longitudinally by 10% 
or more when it is wetted. As a well known example of such nonwoven 
fabric, Japanese Patent Publication No. Hei6-102068 discloses a nonwoven 
fabric of polyvinyl alcohol fibers obtained by a spinning aqueous solution 
of polyvinyl alcohol having a polymerization degree of 1200.about.3000 and 
a sponification degree of 98.0 or higher. 
As the backsheet 12, a film of thermoplastic synthetic resin is used. 
The absorbent core 13 comprises a liquid-absorbent panel 21 and upper and 
lower liquid-absorbent sheets 22 such as hydrophilic tissue papers of wood 
pulp fibers having a high absorptivity as well as a high diffusibility and 
covering the absorbent panel 21. The absorbent panel 21 contains fluff 
pulp fibers of 50% by weight or higher, water-absorptive polymer particles 
of less than 50% by weight and thermoplastic synthetic fibers of less than 
20% by weight. 
FIG. 3 is a sectional view taken along line III--III (center line) in FIG. 
2. Regarding the topsheet 11, the upper layer sheet 17 is bonded to the 
lower layer sheet 18 by means of intermittently applied first hot melt 
adhesives 31, on one hand, and the lower layer sheet 18 is bonded to the 
upper liquid-absorbent sheet 22 by means of intermittently applied second 
hot melt adhesives 32, on the other hand. The first adhesives 31 should be 
principally urine-insoluble but the second adhesives 32 may be either 
urine-soluble or urine-insoluble as circumstances require. 
When urine is discharged in the training pants 1 constructed as has been 
described above, a quantity of discharged urine rapidly moves into the 
absorbent core 13 because the topsheet 1 remains in close contact with the 
absorbent core 13 for a while. As a time elapses, the lower layer sheet 18 
of the topsheet 11 begins to shrink and the second adhesives 32 begin to 
be solved in urine so far as the second adhesives 32 is of water or 
urine-soluble type. Consequently, an adhesive force tending to maintain 
the lower layer sheet 18 and the liquid-absorbent sheet 22 bonded to each 
other begins to weaken. As the shrinkage progresses and adhesive force 
further weakens, the lower layer sheet 18 is peeled off from the upper 
liquid-absorbent sheet 22 and becomes free to shrink. When the second 
adhesives 32 are of water-urine-insoluble type, the quantity of urine 
permeates the upper liquid-absorbent sheet 22 also in the proximity of 
interfaces between the second adhesives 32 and the upper liquid-absorbent 
sheet 22. Eventually, the wood pulp fibers of the upper liquid-absorbent 
sheet 22 at the interfaces are swelled by the quantity of urine and this 
urine permeates the interfaces until the second adhesives 32 come off from 
the upper liquid-absorbent sheet 22. As a result, the lower layer sheet 18 
is separated from the upper liquid-absorbent sheet 22 and become free to 
shrink. 
FIG. 4 is a sectional view taken along the longitudinal center line of the 
training pant 1 as worn showing a behavior of the topsheet 11 before and 
after discharge of urine. With the training pant 1 curved as shown on the 
infant's body, the quantity of urine discharged makes the lower layer 
sheet 18 of the topsheet 11 free to shrink and consequently peels the 
lower layer sheet 18 upward off from the absorbent core 13 as indicated by 
imaginary lines, allowing the lower sheet 18 to come in close contact with 
the infant's skin. Since the upper layer sheet 17 is integral with the 
lower layer sheet 18, the upper layer sheet 17 forms gathers and moves 
upward together with the lower layer sheet 18 as the lower sheet 18 
shrinks. A portion of the upper layer sheet 17 adapted to move upward is 
formed with the wetness telling area 19. Accordingly, the wetness telling 
area 19 is kept in contact with the infant's skin and is able to fulfill 
its desired function even if the training pant 1 somewhat has slipped down 
after the training pant 1 was worn. If discharge of urine is repeated 
after the topsheet 11 has been peeled off from the absorbent core 13, this 
quantity of urine discharged again will stay in and around the wetness 
telling area 19 for a long period without being readily absorbed by the 
absorbent core 13, giving the infant an intense feeling of wetness. 
With the training pant 1 according to the invention, the lower layer sheet 
18 in the embodiment shown may be replaced by a plurality of threads 
adapted to shrink when they are wetted. As a well known example of such 
threads, Japanese Patent Publication No. Hei6-102068 discloses threads 
made from polyvinyl alcohol. Such threads may be provided so as to extend 
not only longitudinally but also transversely of the training pant 1 to 
accelerate shrinkage as well as peeling off of the upper layer sheet 17 
with respect to the absorbent core 13 occurring when the upper layer sheet 
17 is wetted. To form the upper layer sheet 17 with the wetness telling 
area 19, the individual fibers of the wetness telling area 19 may be 
applied with a suitable agent or water-absorbent fibers may be mixed into 
the individual fibers of the wetness telling area 19 to make the wetness 
telling area substantially hydrophilic. Preferably, the lower layer sheet 
18 is intermittently bonded to the upper liquid-absorbent sheet 22 in 
order that the lower layer sheet 18 can be free to shrink and an area over 
which these two sheets 18, 22 are bonded to each other is smaller in a 
region 37 (FIG. 2) extending outside the transversely opposite side edges 
than in a region 36 (FIG. 2) extending outside the longitudinally opposite 
ends of the wetness telling area 19. Outside said transversely opposite 
side edges of the wetness telling area 19, the lower layer sheet 18 and 
the upper liquid-absorbent sheet 22 may be substantially or completely 
free from being bonded to each other. Preferably, the lower layer sheet 18 
is shrinkable by 10% or higher approximately 10 seconds after the lower 
layer sheet 18 begins to be wetted in order that the infant can perceive a 
wetness as soon as possible after discharge of urine has occurred and 
thereby an effect of training for the infant can be improved. A peel 
strength of the second adhesives 32 used to bond such lower layer sheet 18 
to the upper liquid-absorbent sheet 22 is preferably selected in a range 
from 100 g/25 mm of width under its dry condition to 5 g/25 mm of width 
under its wetted condition. The peel strength under the wetted condition 
is measured after the topsheet 11 has been impregnated with 50% of a 
saturated moisture content and left as it is. As the second adhesives 32, 
it is preferred to employ a rubber hot melt adhesive containing a base 
material such as SBS, SIS, SEBS or SEPS and having a solidifying time less 
than 2 seconds. The upper and lower layers 17, 18 of the topsheet 11 may 
be bonded to each other by the well known heat-sealing technique instead 
of using the first adhesives 31. 
The entire disclosure of Japanese Patent Application No. 8-172325 filed on 
Jul. 2, 1996 including specification, claims, drawings and abstract are 
incorporated herein by refernece in its entirety. 
Having described the invention as related to the embodiment shown in the 
accompanying drawings, it is our intention that the invention be not 
limited by any of the details of description, unless otherwise specified, 
but rather be construed broadly within its spirit and scope as set out in 
the accompanying claims.