Note: Descriptions are shown in the official language in which they were submitted.
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DISPOSABLE DIAPER
BACKGROUND OF THE INVENTION
The present invention relates to a disposable diaper
perticularly characterized in side flaps provided with
elastic members therein,
There have already been proposed various types of
disposable diaper. Concerning those of well known art
including side flaps provided with elastic members
adapted to exert appropriate pressure around the wearer's
legs, two types of diaposable diaper have been proposed,
i.e., the one comprising a liquid-absorbent core sandwiched
between a liquid-permeable topsheet and a liquid-lmpermeable
backsheet and the side flaps formed by the areas of said two
sheets laterally extending from opposite outer side edges of
said core so as to contain in said side flaps to exert
pressure around the wearer's legs, and the other employing
as a part of said side flaps the third sheet made of material
provided separately of said topsheet and said backsheet.
In such diaper of the prior art, said elastic member
usually has a tensile strength of 100 to 600g so that the
elastic member may exert effective pressure and establish
desired seal around the wearer's leg.
Preferably, said elastic member should exhibit a high
contraction percentage as being mounted on the diaper and
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even the conventional diaper has intended to achieve such a
high contraction percentage of said elastic member. However,
a relatively high rigidity of the side flap on which said
elastic member is mounted disadvantageously has limited said
contraction percentage. To solve such a problem, it may be
contemplated that the elastic member permitting said desired
contraction to be obtained, i.e., the elastic member being
excellent in its elasticity and high in its stretching
stress is employed. However, it is not easy to obtain such
elastic member by the technique presently available and an
unacceptable cost will result even if such elastic member is
obtained.
In the case of the diaper having said side flap at least
partially formed by said topsheet, said problem will become
more serious when said topsheet of a relatively high rigidity
is employed in order to realize a desired characteristic
thereof. Consequently, types and structures of said topsheet
which may be adopted are limited.
An essential object of the present invention is to provide
improved disposable diapers having said side flaps without
limiting both types and structures of said topsheet.
SUMMARY OF THE INVENTION
According to the present invention, the object as set
forth above is achieved by a disposable diaper including a
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liquid-permeable topsheet, a liquid-impermeable backsheet,
a liquid-absorbent core sandwiched between these two sheets,
and side flaps extending laterally from opposite side edges
of said core and provided with associated elastic members,
wherein each of said side flaps is disposed outside said
topsheet and includes a third sheet forming at least a part
of said side flap; wherein said third sheet has a rigidity
as measured by the Clark rigidity tester according to The
Japanese Industrial Standard(P8143) longitudinally of the
diaper lower than that of said topsheet; and wherein said
elastic member is adhered at least to said third sheet.
To assure that said elastic member exhibits a predetermined
contraction percentage even when said elastic member is
adhered also to said backsheet forming a part of said side
flaps, said topsheet has a rigidity of 90mm or higher as
measured by said tester; said backsheet has a rigidity lower
than 60mm as measured by said tester; said third sheet has a
rigidity of 10 to 80mm as measured by said tester; said
elastic member has a tensile strength of 70 to 700g; and
said third sheet has a water pressure resistance of 20mm or
higher as measured by the water pressure resistance tester
according to The Japanese Industrial Standard(L1092) and is
of air-permeable nature.
According to the present invention, the third sheet
having a rigidity lower than that of the topsheet forms a
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part of the side flap and the elastic member for fitness
around the wearer's leg is bonded at least to said third
sheet. Such feature of the invention advantageously
increases a contraction percentage, in other words, a
contraction extent (i.e., length) with respect to the case in
which said part of the side flap is constructed by the area
of said topsheet extending laterally from the outer side edge
of the core. With a consequence, said side flap developing a
shrinkage due to the presence of the elastic member therein
well follows and accommodates movement of the wearer's leg and
exerts appropriate pressure around the leg for an effective
seal, minizing possible leakage of fluids which would otherwise
occur between the side flap and the leg. Furthermore, the
present invention permits said topsheet of a relatively high
rigidity depending on factors such as quality and structure
of its material to be selectively employed independently of
said elastic member.
Further advantage of the diaper constructed according to
the present invention lies in that the rigidities not only of
said third sheet but also of said topsheet and said backsheet
as well as the tensile strength of said elastic member are
respectively specified within the predetermined associated
ranges and thereby it is assured to achieve the above-
memtioned effect even when said elastic member is bonded to
said backsheet.
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Still another advantage of the diaper
constructed according to the present invention lies in
that the water pressure resistance of said third sheet
is also specified within the predetermined range and
thereby it is assured to minimize a possible trouble
that a quantity of body fluids excreted on said
topsheet might flow down onto the surface of said third
sheet or permeate between said third sheet and said
backsheet being in contact with said third sheet and
result in leakage along the outer side edge of said
side flap.
According to a further broad aspect of the
present invention, there is provided a disposable
diaper which includes a liquid-permeable topsheet, a
liquid-impermeable backsheet, a liquid-absorbent core
sandwiched between these two sheets, and side flaps
made of different material from the core and extending
laterally from opposite side edges of the core and
provided with associated elastic members. Each of the
side flaps is disposed outside the topsheet and
includes a third sheet forming at least a part of the
side flap. The third sheet has a rigidity
longitudinally of the diaper lower than that of the
topsheet. The elastic member is adhered at least to
the third sheet. The rigidity of the topsheet is 90 mm
or higher as measured by the Clark rigidity tester
according to The Japanese Industrial Standard (P8143).
The backsheet has a rigidity lower than 60 mm as
measured by the said tester. The rigidity of the third
sheet is 10 to 80 mm as measured by the said tester.
The elastic member has a tensile strength of 70 to 700
g. The third sheet has a water pressure resistance of
20 mm or higher as measured by the water pressure
resistance tester according to The Japanese Industrial
Standard (L1092) and is of air-permeable nature. The
third sheet has also been subjected to waterproofing.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a plan view showing an unfolded
diaper as partially broken away; and
Figs. 2A through 2H illustrate various
manners in which important parts of the diaper may
be arranged in accordance with the present
invention.
PREFERRED EMBODIMENTS
The invention will now be described more in
detail by way of example in reference with the
accompanying drawing.
Referring to Fig. 1, a diaper comprises a
liquid-permeable topsheet 1, a liquid-impermeable
backsheet 2, a liquid-absorbent core 3 sandwiched
between these two sheets, and a pair of side flaps 4
extending laterally from opposite
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side edges of said core 3. Each of the side flaps 4
comprises an area 1a of the topsheet 1 extending from the
associated outer side edge of the core 3, an area 2a of the
backsheet 2 extending from the outer side edge by an extent
longer than the topsheet area 1a, and a third sheet 6 joined
onto a zone of the backsheet area 2a on which the topsheet
is absent. Between the backsheet area 2a and the third
sheet 6 forming together a part of the side flap 4, there is
provided a longitudinally elastic member 5 adhered to the
third sheet 6. It should be understood that this elastic
member 5 may be adhered to both the backsheet 2 and the
third sheet 6.
Fig. 2 illustrates various manners in which the elastic
member 5 and the third sheet 6 may be arranged. Fig. 2A
illustrates an arrangement in which the inner side edge of
the third sheet 6 is adhesively sandwiched between the
topsheet area 1a and the backsheet area 2a adjacent the
respective outer side edges thereof. Fig. 2B illustrates
an arrangement in which the inner side edge of the third
sheet 6 is joined onto the upper surface of the topsheet
area 1a along the outer side edge thereof. Fig. 2C
illustrates an arrangement in which the inner side edge of
the third sheet 6 is joined not only onto the backsheet area
2a but also onto the topsheet area 1a along the outer side
edge thereof which has been folded back down- and inwardly.
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Fig. 2D illustrates an arrangement in which the inner side
edge of the third sheet 6 is joined first onto the backsheet
area 2a and then onto the topsheet area 1a along the outer
side edge thereof which has been folded back up- and
inwardly. Fig. 2E illustrates an arrangement in which the
inner side edge of the third sheet 6 is joined onto the
backsheet area 2a and at the same time to the outer side
edge of the topsheet area 1a in abutting relationship. Fig.
2F illustrates an arrangement in which the inner side edge
of the third sheet 6 is joined onto the backsheet area 2a
with a gap maintained with respect to the outer side edge of
the topsheet area 1a. Fig. 2G illustrates an arrangement
in which the inner side edge of the third sheet 6 is joined
onto the upper surface of the topsheet area 1a along its
outer side edge and the outer side edge of said third sheet
6 is folded back up- and inwardly so as to wrap the elastic
member 5 therein. Finally Fig. 2H illustrates an arrangement
in which the inner side edge of the third sheet 6 is
adhesively sandwiched between the respective outer side edges
of the topsheet area 1a and the backsheet area 2a with the
outer side edge of the third sheet being folded back up- and
inwardly so as to wrap the elastic member 5 therein.
The topsheet 1 has a unique structure adapted to quickly
guide a quantity of body fluids excreted thereon towards the
core 3 and thereby to effectively reduce a possible flowing
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of the body fluids once absorbed by the core 3 back to the
upper surface of the topsheet 1.
A preferable embodiment of such structure is a nonwoven
fabric having a basic weight, i.e., a weight per unit area,
of 25 to 35g/m2 and a thickness of 1 to 2mm, comprising a
top layer of a higher density and a back layer of a lower
density melt-bonded together. Component fibers of such
nonwoven fabric may be selectively combined from a group
consisting of polypropyrene, polyethylene,`conjugated
polyethylene/polypropyrene, and conjugated polyester/
polyethylene. Such two-layered topsheet 1 has a rigidity of
90mm or higher as measured by the Clark rigidity tester
according to The Japanese Industrial Standard(P8143)
longitudinally of the diaper.
The third sheet 6 may be selectively used from a group
consisting of a melt-bonded nonwoven fabric, a span-bonded
nonwoven fabric, a water-jet treated nonwoven fabric, all
these being made of hydrophobic fibers, such nonwoven fabric
subjected to waterproofing treatment, hydrophobic plastic
film, and such film provided with a plurality of apertures.
The third sheet 6 is air-permeable and has a water pressure
resistance of 20mm or higher, preferably of 30mm or higher
and most preferably of 40mm or higher as measured the water
pressure resistance tester according to Japanese Industrial
Standard(L1092). This third sheet 6 has a basic weight
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lower than that of the topsheet 1, a rigldity of 10 to 80mm
as measured in said manner longitudinally of the diaper and
a rigidity of 5 to 80mm as measured transversely of the
diaper.
The backsheet 2 is made of conventionally used material
such as a polyethylene film and has a rigidity of 60mm or
less both longitudinally and transversely of the diaper as
measured according to said JIS.
It is preferred to adjust said rigidity longitudinall
of the diaper to 50 to 100mm at a section consisting of the
backsheet 2 and the third sheet 6.
The elastic member 5 comprises, for example, a plurality
of rubber filaments, urethane rubber piece or urethane foam
piece and a tensile strength thereof is adjusted to 70 to
700g so as to exert appropriate pressure around the wearer's
leg. The elastic member 5 has its outer side edge spaced by
3mm or longer from the outer side edge of the topsheet 1
having said rigidity which is relatively high.
Now the reason why said rigidity of the third sheet 6
longitudinally of the diaper has been set to 10 to 80mm will
be explanined. A contraction percentage of the elastic
member 5 is significantly influenced by said longitudinal
rigidity in the side flap 4, particularly in the third sheet
6 which overlies the side flap 4 and, when the tensile
strength of the elasitc member 5 is set to 70 to 700g in
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consideration of appropriate pressure to be exerted around
the wearer's leg, the contraction percentage of the elastic
member 5 adhesively sandwiched between the third sheet 6 and
the backsheet 2 having said rigidity of 60mm or less optimally
increases as indicated by an experimental result of an Example
as will be described later so that the elastic member
effectively accommodates movement of the wearer's leg and
substantially no gap is developed between the region of the
`side flap 4 carrying the elastic member 5 and the wearer's
leg, thus effectively preventing a quantity of body fluids
from leakage.
When said rigidity of the third sheet 6 is higher than
80mm, the contraction percentage of the elastic member 5
adhesively sandwiched between the third sheet 6 and the
backsheet 2 would be as small as in the conventional diaper.
When said rigidity is lower than 1Omm, on the contrary, said
contraction percentage would certainly increase but the sheet
material having said rigidity would exhibit a significantly
low strength, and a basic weight of said sheet material
would be too low to be agreeable to the touch, if said sheet
material is fibrous nature.
(Example)
(1) A diaper construction (comparison)
The diaper comprised a topsheet, a backsheet, a core
sandwiched between said two sheets and elastic members disposed
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in respective side flaps consisting of said two sheets and
extending from opposite outer side edges of said core.
Details of the respective members were following:
Topsheet : a nonwoven fabric consisting of top and
bottom layers melt-bonded together, said
top layer having a basic weight of 10g/m2
and made of conjugated polyethylene/
polypropyrene fibers and said bottom
layer having a basic weight of 20g/m2 and
made of conjugated polyester/polyethylene
fibers. Having a longitudinal rigidity
of 140mm and a transverse rigidity of
75mm as measured by the Clark rigidity
tester according to JIS(P8143).
Core : fluffy pulp formed in a mat-like piece,
having a rigidity of 10 + 5g cm as
measured by the taber tester.
Backsheet : a polyethylene film having a rigidity of
50mm both in longitudinal and transverse
directions as measured by said Clark
rigidity tester.
Elastic member : a urethane film having a tensile strength
of 250g. Mounted at a condition
stretched twice as long as its original
condition (150mm long and 20mm wide).
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It should be noted that said elastic member is bonded to
said topsheet and said backsheet respectively by four lines
of hot-melt adhesive applied on the top and bottom surface
thereof, and the inner side edge of said elastic member is
spaced from the outer side edge of said core.
(2) A diaper construction (present invention)
The diaper was constructed as has been described in
reference with Fig. 2B.
As the third sheet, a polypropyrene span-bonded nonwoven
fabric was used, which has a basic weight of 20g/m2, a
longitudinal rigidity of 50mm and a transverse rigidity of
40mm as measured by said Clark rigidity tester. The other
details were same as in said (1).
(3) Experimental result on the contraction percentage of the
elastic member
Opposite ends of the respective side flaps on the
opposite extensions of said elastic members respectively
mounted in diapers constructed according to said (1) and (2)
were gripped by hands and the side flaps were stretched
until gathers which had been formed by the respective side
flaps disappeared. Length of each elastic member after the
hold on the opposite ends of the side flap had been loosed
and the elastic member had contracted again from said
stretched condition (i.e., twice the original length of
150mm) was measured. Then, ratio of the length in the
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contracted condition of each elastic member to its stretched
length (150mm) was determined. The diaper of said (1)
exhibited a contraction percentage of 40% and the diaper of
said (2) exhibited a contraction percentage of 60%.
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