U.S. patent application number 13/500152 was filed with the patent office on 2012-08-02 for nonwoven fabric.
This patent application is currently assigned to UNICHARM CORPORATION. Invention is credited to Hiroki Goda, Hideyuki Ishikawa, Satoshi Mizutani, Toru Oba.
Application Number | 20120196091 13/500152 |
Document ID | / |
Family ID | 43856650 |
Filed Date | 2012-08-02 |
United States Patent
Application |
20120196091 |
Kind Code |
A1 |
Mizutani; Satoshi ; et
al. |
August 2, 2012 |
NONWOVEN FABRIC
Abstract
Short fibers of thermoplastic synthetic resin are fusion bonded
to one another to form a nonwoven fabric. The nonwoven fabric is
formed on its upper surface with crests and troughs extending in
parallel to one another. The crests include first crests having a
uniform height dimension from a lower surface of the nonwoven
fabric and second crests having a uniform height dimension from a
lower surface of the nonwoven fabric which is smaller than the
height dimension of the first crests. Density of the nonwoven
fabric gradually increases in the order of the first crests, the
second crests and the troughs. The first crests are formed so that
the density of the first crests remains lower than the density of
the second crests even when the first crests are compressed toward
the lower surface until the first crests becomes flush with the
level of the second crests.
Inventors: |
Mizutani; Satoshi;
(Kanonji-shi, JP) ; Goda; Hiroki; (Kanonji-shi,
JP) ; Ishikawa; Hideyuki; (Kanonji-shi, JP) ;
Oba; Toru; (Kanonji-shi, JP) |
Assignee: |
UNICHARM CORPORATION
Ehime
JP
|
Family ID: |
43856650 |
Appl. No.: |
13/500152 |
Filed: |
September 17, 2010 |
PCT Filed: |
September 17, 2010 |
PCT NO: |
PCT/JP2010/066134 |
371 Date: |
April 4, 2012 |
Current U.S.
Class: |
428/171 |
Current CPC
Class: |
D04H 1/70 20130101; Y10T
428/24603 20150115; D04H 1/54 20130101; D04H 1/542 20130101; A61F
13/51104 20130101; A61F 13/51108 20130101 |
Class at
Publication: |
428/171 |
International
Class: |
D04H 13/00 20060101
D04H013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 9, 2009 |
JP |
2009-235513 |
Claims
1. A nonwoven fabric formed of short fibers of thermoplastic
synthetic resin fusion bonded to one another and having a length
direction, a width direction and a thickness direction extending
orthogonally to one another, including an upper surface and a lower
surface opposed to the upper surface as viewed in the thickness
direction wherein the upper surface is formed with crests and
troughs undulating in the width direction and extending in parallel
to one another in the length direction and the crests comprise
first crests having a uniform height dimension and second crests
having a uniform height dimension measured from the lower surface
wherein the height dimension of the first crests is larger than the
height dimension of the second crests, wherein: density of the
nonwoven fabric gradually increases in order of the first crests,
the second crests and the troughs and the density of the first
crests remains lower than the density of the second crests even
when the first crests are compressed from the upper surface toward
the lower surface until the first crests become flush with the
second crests.
2. The nonwoven fabric defined by claim 1, wherein the nonwoven
fabric has a basis mass in a range of 18 to 100 g/m.sup.2 and each
of the short fibers has a fineness in a range of 1 to 8 dtex and a
fiber length in a range of 20 to 80 mm, and wherein the nonwoven
fabric has been modified to become hydrophilic.
3. The nonwoven fabric defined by claim 1, wherein the short fibers
are conjugate fibers comprising two types of the thermoplastic
synthetic resin having different fusion temperatures and these two
types of the thermoplastic synthetic resin are fusion bonded to
each other via one of the thermoplastic synthetic resins having a
lower fusion temperature.
4. The nonwoven fabric defined by claim 1, wherein the height
dimension of the first crests is in a range of 1 to 5 mm and the
height dimension of the second crests is lower than the height
dimension of the first crests by a range of 0.5 to 2 mm.
5. The nonwoven fabric defined by claim 1, wherein the first crests
and the second crests are formed alternately in the width direction
and each of the troughs is interposed between each pair of the
adjacent the first crest and the second crest.
Description
TECHNICAL FIELD
[0001] The present invention relates to nonwoven fabrics formed of
short fibers of thermoplastic synthetic resin.
[0002] It is conventionally known to fusion bond short fibers of
thermoplastic synthetic resin together and thereby to obtain
nonwoven fabrics. As an example of such nonwoven fabrics, JP
2008-25080 A (PTL 1) discloses a nonwoven fabric having ridges and
grooves extending in parallel to one another in a machine direction
wherein these ridges and grooves alternate in a cross direction
extending orthogonally to the machine direction.
CITATION LIST
Patent Literature
[0003] {PTL 1} JP 2008-25080 A
SUMMARY
Technical Problem
[0004] The ridges in the nonwoven fabric disclosed in PTL 1 include
the relatively high ridges and the relatively low ridges. The
relatively high ridges and the relatively low ridge are formed to
be the same in their basis mass wherein the basis mass of both
these ridges having different height dimensions in the middle
segments thereof in the width direction than the basis mass of the
grooves. Assuming that such a nonwoven fabric is used as the
liquid-pervious inner sheet in the wearing article such as a
disposable diaper or a menstruation napkin and comes in tight
contact with the wearer's skin, the relatively high ridges are
primarily compressed. In the inner sheet at this moment, the
compressed ridges have the density thereof further increased and,
in consequence, bodily fluids are apt to stay in these ridges and
barred from smoothly moving toward the surrounding region of the
lower density. When the ridges are compressed, for example, to the
same level with the relatively low ridges, the ridges having been
compressed in this manner will locally pressed against the wearer's
skin. Eventually, the inner sheet as a whole may not come in soft
and close contact with the wearer's skin and may have an
uncomfortable texture.
[0005] An object of this invention is to provide a nonwoven fabric
improved so that even when the nonwoven fabric is formed on its
upper surface with the ridges and the grooves, bodily fluids
excreted onto the upper surface may not stay in these ridges after
this upper surface has come in close contact with the wearer's
skin.
Solution to Problem
[0006] According to the present invention, there is provided a
nonwoven fabric formed of short fibers of thermoplastic synthetic
resin fusion bonded to one another and having a length direction, a
width direction and a thickness direction extending orthogonally
one to another, including an upper surface and a lower surface
opposed to the upper surface as viewed in the thickness direction
wherein
[0007] the upper surface is formed with crests and troughs
undulating in the width direction and extending in parallel to one
another in the length direction and
[0008] the crests include first crests having a uniform height
dimension and second crests having a uniform height dimension
measured from the lower surface wherein the height dimension of the
first crests is larger than the height dimension of the second
crests.
[0009] The present invention resides in that a density of the
nonwoven fabric gradually increases in order of the first crests,
the second crests and the troughs and the density of the first
crests remains lower than the density of the second crests even
when the first crests are compressed from the upper surface toward
the lower surface until the first crests become flush with the
second crests.
[0010] According to one embodiment of the present invention, the
nonwoven fabric has a basis mass in a range of 18 to 100 g/m.sup.2
and each of the short fibers has a fineness in a range of 1 to 8
dtex and a fiber length in a range of 20 to 80 mm, and the nonwoven
fabric has been modified to become hydrophilic.
[0011] According to another embodiment of the present invention,
the short fibers are conjugate fibers including two types of the
thermoplastic synthetic resin having different fusion temperatures
and these two types of the thermoplastic synthetic resin are fusion
bonded to each other via one of the thermoplastic synthetic resins
having a lower fusion temperature.
[0012] According to still another embodiment of the present
invention, the height dimension of the first crests is in a range
of 1 to 5 mm and the height dimension of the second crests is lower
than the height dimension of the first crests by a range of 0.5 to
2 mm.
[0013] According to yet another embodiment of the present
invention, the first crests and the second crests are formed
alternately in the width direction and each of the troughs is
interposed between each pair of the adjacent first crest and second
crest.
[0014] A measuring method used for measuring "density of nonwoven
fabric" will be described later with reference to FIGS. 5 through
7.
Advantageous Effects of Invention
[0015] The nonwoven fabric according to the present invention has
the crests and the troughs extending in parallel to one another in
the length direction wherein the crests include the first crests
each having a uniform height dimension and the second crests each
having a uniform height dimension which is smaller than the height
dimension of the first crests wherein both of the height dimensions
are defined by a dimension of the nonwoven fabric in the thickness
direction and these crests cooperate with the troughs to form the
upper surface of the nonwoven fabric with the ridges and the
grooves. The density of the nonwoven fabric gradually increases in
the order of the first crest, the second crest and the trough
wherein the density of the first crest is maintained lower than the
density of the second crest even when the first crest is compressed
to the same level as the second crest. On the assumption that such
a nonwoven fabric is used as the inner sheet of the wearing
article, even when the upper surface of the nonwoven fabric comes
in close contact with the wearer's skin and the first crests having
initially been highest are compressed to the same level as the
second crests, the density gradient of the first crests, the second
crests and the troughs is maintained. In principle, bodily fluids
excreted onto the inner sheet are apt to flow from the region
having the relatively low density toward the region having the
relatively high density, specifically, from the first crests to the
second crests, then from the second crest to the troughs. The
stabilized density gradient assures that bodily fluids smoothly
flow toward the troughs without staying in the first crests and the
wearer is free from discomfort feeling of wetness even if the first
crests directly come in contact with the wearer's skin. In
addition, the first crests would not locally press against the
wearer's skin since the density of the first crests remains lower
than that of the second crests. In other words, the nonwoven fabric
according to the present invention has a uniform texture.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a partial perspective view of a nonwoven fabric
according to the present invention.
[0017] FIG. 2 is a photograph of a section of the nonwoven fabric
in a cross direction.
[0018] FIG. 3 is a diagram partially illustrating a process for
manufacturing the nonwoven fabric.
[0019] FIG. 4 is a schematic front elevation view showing a first
array of air jet nozzles.
[0020] FIG. 5 is a diagram illustrating how the section of the
nonwoven fabric is transformed.
[0021] FIG. 6 is a graphic diagram plotting the surface contour of
the nonwoven fabric based on observation.
[0022] FIG. 7 is a photograph showing a cross-section of
fibers.
DESCRIPTION OF EMBODIMENTS
[0023] Details of nonwoven fabrics according to the present
invention will be more fully understood from the description given
hereunder with reference to the accompanying drawings.
[0024] FIG. 1 is a partial perspective view of a nonwoven fabric 1
according to the present invention and FIG. 2 is a 50-fold
magnified photograph exemplarily showing cross-section of the
nonwoven fabric. It should be noted here that the photograph of
FIG. 2 is really an assembly including a plurality of photographs
joined one with another in a width direction since it is impossible
to record the 50-fold magnified photograph of the nonwoven fabric
over its sufficiently wide range in a single shot. The nonwoven
fabric 1 has a length direction, a width direction and a thickness
direction extending orthogonally one to another and designated by
the double-headed arrows A, B and C, respectively. The nonwoven
fabric 1 has an upper surface 2 and a lower surface 3 opposed to
each other in the thickness direction C. The upper surface 2 is
formed with crests 6 and troughs 7 extending in parallel to one
another in the length direction A and undulating in the width
direction B. The crests 6 include first crests 6a having a height
H.sub.a and second crests 6b having a height H.sub.b in the
thickness direction C. The height H.sub.a of the first crests 6a is
larger than the height H.sub.b of the second crests 6b. These first
crests 6a and second crests 6b are arranged alternately in the
width dimension B and between each pair of the adjacent first and
second crests 6a, 6b, each of the troughs 7 is interposed.
[0025] Such nonwoven fabric 1 is formed by subjecting short fibers
(staples) 11 of thermoplastic synthetic resin preferably having a
fineness in a range of 1 to 8 dtex and a fiber length in a range of
20 to 80 mm to blasts of hot air and thereby fusion bonding them to
one another. The nonwoven fabric 1 is suitable for use as a
liquid-pervious inner sheet in a bodily fluid-absorbent wearing
article such as disposable diaper or sanitary napkin and, for such
intended use, the nonwoven fabric 1 preferably has a basis mass in
a range of 18 to 100 g/m.sup.2 and preferably has been previously
treated to become hydrophilic. The nonwoven fabric 1 used as the
inner sheet includes a lower surface 3 being substantially flat and
an upper surface 2 formed with troughs 7 defining grooves each
having a dimension W.sub.c in the width direction B in a range of
0.4 to 2 mm and first crests 6a defining ridges each having a
dimension W.sub.a in the width dimension B in a range of 2 to 5 mm,
which is larger than a dimension W.sub.b of second crests 6b in the
width dimension B. Preferably, a height H.sub.a of the first crests
6a is in a range of 1 to 5 mm, a height H.sub.b of the second
crests 6b is lower than H.sub.a by a range of 0.5 to 2 mm and a
level of the troughs 7 is lower than the height H.sub.a by a range
of 0.7 to 2.5 mm. To facilitate the short fibers 11 to be fusion
bonded to one another and to make the nonwoven fabric 1 elastically
compressible in the thickness direction C, each of the short fibers
11 is preferably prepared in the form of a conjugate fiber made of
two types of synthetic resin having different fusion temperatures.
Such conjugate fibers may be fusion bonded to one another by fusing
the component fibers of which fusion temperature is lower than the
other. Combination of these different types of component synthetic
resin includes, for example, polyethylene/polyester or
polyethylene/polypropylene. The conjugate fiber may be of
core-in-sheath type and side-by-side type. The core-in-sheath type
conjugate fiber may be concentric core type or eccentric core
type.
[0026] FIG. 3 is a diagram partially illustrating a process for
manufacturing the nonwoven fabric 1 and FIG. 4 is a schematic front
elevation view showing a first array of air jet nozzles 910 used in
the process of FIG. 3. Referring to FIG. 3, a conveyor belt 200
which is air-permeable in the thickness direction is loaded with a
carded web 100 formed of the short fibers 11 and runs in a machine
direction MD. The carded web 100 is subjected to blasts of a
plurality of hot air jets 921 ejected from a second air jet nozzle
array 920 and the air jet 921 is sucked by a suction box 922
through the belt 200. The air jet 921 has a temperature not higher
than a level to soften the short fibers 11 and serves to compress
the carded web 100 to a range of 2/3 to 1/4 of its initial
thickness and thereby to stabilize a texture of the carded web 100.
Then the carded web 100 is subjected to blasts of a plurality of
heated air jets 911 ejected from a first air jet nozzle array 910.
The air jets 911 has an airflow rate, a pressure and a temperature
adjusted so that the short fibers 11 may be moved in a cross
direction CD orthogonal to the machine direction MD and may be
fusion bonded to one another.
[0027] Referring to FIG. 4, the first air jet nozzle array 910
includes a plurality of nozzles (not shown) arranged at
predetermined pitches a and b in the cross direction CD, from which
the air jets 911 are ejected toward the carded web 100. These air
jets 911 are sucked by a suction box 915 through the belt 200. The
positions of the air jets 911 arranged at the pitches a and b in
the cross direction CD correspond to the positions of the troughs 7
formed in the nonwoven fabric 1 as shown in FIG. 1. In the carded
web 100, the short fibers 11 located just below the air jets 911
are partially shared half-and-half on both sides about the cross
direction CD, respectively, and these portions shared half-and-half
participate in formation of the first crests 6a and the second
crests 6b while the portions staying immediately below the air jets
911 form the respective troughs 7. The short fibers 11 lying
between each pair of the adjacent air jets 911 are moved in the
cross direction CD to form the first crest 6a or the second crest
6b. Specifically, the short fibers 11 lying between each pair of
the adjacent air jets 911 arranged at the relatively large pitch a
move to form the first crest 6a and the short fibers 11 lying
between each pair of the adjacent air jets 911 arranged at the
relatively small pitch b move to form the second crest 6b. The
first crests 6a formed concurrently with the troughs 7 in this
manner have a height larger than a height of the second crests 6b
and a density lower than a density of the second crests 6b. In the
troughs 7 formed immediately below the respective air jets 911, the
short fibers 11 are compressed in the thickness direction C and
densified.
[0028] When manufacturing the nonwoven fabric 1 by using the
process illustrated in FIGS. 3 and 4, assuming that the carded web
100, for example, having a basis mass in a range of 30 to 50
g/m.sup.2 is conveyed in the machine direction MD at a moderate
speed, for example, at a speed in the order of 10 m/min, an
ejection quantity of the air jets 911 from the first air jet nozzle
array 910 may be set to a low level and the second air jet nozzle
array 920 may be eliminated. On the assumption that such carded web
100 is conveyed at a speed in a range of 30 to 40 m/min, the second
air jet nozzle array 920 may be used preferably in combination with
the first air jet nozzle array 910 to stabilize the carded web 100
in advance.
[0029] In the nonwoven fabric 1 of FIG. 1 obtained in this manner,
a density of the first crests 6a may be adjusted to be lower than a
density of the second crests 6b and a density of the second crests
6b may be adjusted to be lower than a density of the troughs 7 to
achieve a desirable behavior of the nonwoven fabric 1 when such a
nonwoven fabric is used as the liquid-absorbent inner sheet of the
bodily fluid-absorbent wearing article. Specifically, bodily fluids
excreted on the upper surface 2 of the nonwoven fabric 1 move from
the region having a low density toward the region having a high
density. In other words, bodily fluids smoothly move from the first
crests 6a toward the troughs 7 and from the second crests 6b toward
the troughs 7 in accordance with the density gradient of the
nonwoven fabric 1. When the nonwoven fabric 1 is bent and, in
consequence, the first crests 6a and the second crests 6b move
closer to each other, bodily fluids move from the first crests 6a
toward the second crests 6b. Therefore, certain amount of bodily
fluids would not stay in the first crests 6a being first to come in
contact with the wearer's skin and would not create a discomfort
feeling of wetness against the wearer. In addition, even when the
nonwoven fabric 1 is compressed until the first crests 6a are
compressed to the same level with the second crests 6b, the density
of the first crests 6a remains lower than the density of the second
crests 6b. Therefore, even in such a situation, the first crests 6a
would not create a discomfort feeling of wetness against the
wearer. Also, even when the first crests 6a are compressed together
with the second crests 6b, the first crests 6a subjected to a
higher degree of compression than that to which the second crests
6b are subjected would not be pressed against the wearer's skin
more tightly than the second crests 6b, since the density of the
first crests 6a is maintained lower than that of the second crests
6b. Consequently, the texture of the nonwoven fabric would not
become uneven and create a discomfort feeling to wear against the
wearer.
[0030] TABLE 1 indicates primary manufacturing conditions and
evaluation results with respect to the nonwoven fabric 1 as one
example of the present invention together with those with respect
to comparative examples.
[0031] The nonwoven fabric according to the embodiment indicated in
TABLE 1 was manufactured in the equipment exemplarily illustrated
in FIGS. 3 and 4 without using the second air jet nozzle array 920
under the primary conditions as will be described below. In this
embodiment, the running speed of the carded web 100 was
sufficiently low to save use of the second air jet nozzle array
920.
(1) Short fiber (staple): core-in-sheath type conjugate fiber
having fineness in a range of 2.6 to 3.3 dtex, a fiber length in a
range of 38 to 51 mm, polyester as the core component and
polyethylene as the sheath component. (2) Carded web: basis mass of
35 g/m.sup.2 and running speed of 10 m/min in the machine
direction. (3) First air jet nozzle array: nozzle diameter of 1 mm,
nozzle pitch a=4 mm, nozzle pitch b=2.5 mm, distance between nozzle
and conveyor belt of 5 mm, air jet pressure of 0.06 MPa and air
temperature of 140.degree. C.
[0032] The nonwoven fabric indicated in TABLE 1 as Comparative
Example 1 was obtained in the same manufacturing conditions as
those for the Example according to the present invention except the
nozzle pitches, i.e., set to a=4 mm and b=4 mm. The nonwoven fabric
according to this Comparative Example 1 is similar to the Example
according to the present invention in that the crests and the
troughs arranged alternately in the cross direction CD but the
height of the crests is uniform and there is no discrimination
between the first crests and the second crests.
[0033] The nonwoven fabric indicated in TABLE 1 as Comparative
Example 2 was obtained in the same manufacturing conditions as
those for the Example according to the present invention except the
nozzle pitches, i.e., set to a=3.5 mm and b=3 mm. The nonwoven
fabric according to this Comparative Example 2 is similar to the
Example according to the present invention in that the crests and
the troughs arranged alternately in the cross direction CD and the
crests include the first crests and the second crests having a
smaller height than a height of the first crests. However, there is
not a substantial difference in the height between the first crests
and the second crests.
TABLE-US-00001 TABLE 1 Comparative Example Comparative Example 2
1st 2nd Example 1 1st 2nd Crest Crest Trough Crest Trough Crest
Crest Trough Non- Height (mm) 2.43 1.45 -- 2.07 -- 1.91 1.53 --
Compressed Width (mm) 3.81 2.08 0.56 3.52 0.44 2.82 2.17 0.62 state
Sectional area (mm.sup.2) 5.71 1.78 0.16 4.03 0.13 3.31 2.13 0.17
Number of fiber's cross-sections 248.3 147.3 25.3 230.7 23 220
179.3 28 Fiber's density index 43.5 82.8 158.1 57.2 176.9 66.5 84.2
164.7 (number/mm.sup.2) Compressed Height (mm) 1.52 1.50 -- 1.52 --
1.53 1.55 -- state Width (mm) 3.80 1.99 0.56 3.48 0.46 2.77 2.19
0.64 Sectional area (mm.sup.2) 5.07 1.73 0.16 3.59 0.16 1.77 2.10
0.15 Number of fiber's cross-sections 248.3 147.3 25.3 230.7 23 220
179.3 28 Fiber's density index 49.0 85.1 158.1 64.3 143.8 124.3
85.4 186.7 (number/mm.sup.2) Strike-through value (sec) 1.61 2.16
1.96 Q-Max value Load of 10 g/cm.sup.2 0.178 0.373 0.366
(J/cm.sup.2 sec) Load of 30 g/cm.sup.2 0.819 1.027 0.863
[0034] (a) and (b) of FIG. 5 schematically illustrating
cross-sectional shape of the nonwoven fabric as the example of the
present invention taken along in the cross direction CD and (c) of
FIG. 5 is a plan view of a pressure plate 22 used in the step (b)
of FIG. 5. In (a) of FIG. 5, the nonwoven fabric 1 is placed on a
horizontal surface 21 (See FIG. 2 also) in a state free from any
external force, i.e., in a non-compressed state wherein this
nonwoven fabric 1 is formed with the first crests 6a, the second
crests 6b and the troughs 7. In (b) of FIG. 5, the nonwoven fabric
1 was compressed by the pressure plate 22 from above until the
first crests 6a are deformed to be substantially flush with the
second crests 6b. The pressure plate 22 was supported by a pair of
supporters 25 having a height substantially the same as the height
of the second crests 6b. In the example of the present invention
wherein the first crests 6a have a height of 2.43 mm and the second
crests 6b have a height of 1.45 mm, the nonwoven fabric was
compressed until the height of the first crests 6a is reduced to
1.45 mm. The first crest 6a, the second crest 6b and the trough 7
respectively have widths W.sub.a, W.sub.b and W.sub.c and
cross-sectional areas S.sub.a, S.sub.b and S.sub.c respectively
indicated by shaded portions. A method to measure these
cross-sectional areas will be described later with reference to
FIG. 6 and the measurement result was indicated in TABLE 1.
[0035] In the nonwoven fabric as the comparative example 1, the
nonwoven fabric in the non-compressed state was compressed by using
the pressure plate 22 shown in FIG. 5 until a height of the crests
is reduced to 1.52 mm. Also in the nonwoven fabric as the
comparative example 1, cross-sectional areas of the crest and the
trough in the non-compressed state as well as in the compressed
state were measured and the measurement result was indicated in
TABLE 1.
[0036] In the nonwoven fabric as the comparative example 2, the
nonwoven fabric in the non-compressed state was compressed by using
the pressure plate 22 until a height of the first crests which is
relatively large in the non-compressed state is reduced to a height
of the second crests in the non-compressed state, i.e., 1.52 mm.
Also in the nonwoven fabric as the comparative example 2,
cross-sectional areas of the first crest and the second crest in
the non-compressed state as well as in the compressed state were
measured and the measurement result was indicated in TABLE 1.
[0037] FIG. 6 is a graphic diagram plotting the cross-sectional
areas S.sub.a, S.sub.b and S.sub.c of each of the first crests 6a,
the second crests 6b and the troughs 7 illustrated in FIG. 5,
respectively, measured by 3D measuring device wherein the first
crest 6a was partially illustrated. The nonwoven fabric 1 as an
object to be measured has its lower surface 3 placed on the
horizontal surface 21 and undulation of the upper surface as viewed
in a cross-section taken along the cross direction CD was recorded
by an outline P. As 3D measuring device, High-Accuracy Geometry
Measuring System (inclusive of High-Accuracy Stage: KS-1100) and
High-Speed and High-Accuracy CCD-Laser Displacement Gauge inclusive
of Controller: LK-G3000V Set and Sensor Head: LK-G30) manufactured
by Keyence Corporation were used and measuring conditions were set
as follows:
[0038] (Stage: KS-1100) [0039] Range of measurement: 3000
.mu.m.times.30000 .mu.m [0040] Measuring pitch: 20 .mu.m [0041]
Running speed: 7500 .mu.m/sec
[0042] (Measuring Head: LK-G3000V) [0043] Measurement mode: Object
to be measured [0044] Installation mode: Diffuse reflection [0045]
Filtering: 4 times in average [0046] Sampling period: 200 .mu.m
[0047] The measurement record obtained by the 3D measuring device
was processed by Configuration Analysis System KS-H1A (manufactured
by Keyence Corporation) to determine heights of the crests, widths
of the crests and the troughs and cross-sectional areas of the
crests and the troughs. Referring to FIG. 6, respective widths
W.sub.a, W.sub.b and W.sub.c of the first crest 6a, the second
crest 6b and the trough 7 were determined by a method as follows.
Referring to FIG. 6, an intersection point X at which an arbitrary
horizontal line H.sub.z extending in parallel to the horizontal
surface 21 intersects with the outline P extending upward from
below the horizontal line H.sub.z is obtained and, if a segment of
the outline segment P extending between a pair of the adjacent
intersecting points X lies below the horizontal line H.sub.z and a
distance between these two intersecting points X is in a range of
0.4 to 2 mm, this segment extending between these intersecting
points X was defined as the trough 7. A region extending between
each pair of the adjacent troughs 7 is defined as the crest 6 and,
of the adjacent two crests 6, the crest 6 in which a top position
of the outline P is relatively high was defined as the first crest
6a and the crest 6 in which a top position of the outline P is
relatively low was defined as the second crest 6b. It should be
noted here that each pair of the adjacent intersecting points X
spaced from each other by a distance less than 0.4 mm was ignored
and each pair of the adjacent intersecting points X spaced from
each other by a distance of 0.4 mm or more was searched. The
distance by which each pair of the adjacent intersecting points X
are spaced from each other corresponds to the width W.sub.c of the
trough 7. In the process for manufacturing the nonwoven fabric 1
according to the present invention from the carded web 100, it is
not preferable for the present invention to adopt a trough having
the width smaller than 0.4 mm because it will be difficult to form
the first crest 6a and the second crest 6b if the width W.sub.c of
the trough 7 is narrower than 0.4 mm. Also when the width W.sub.c
exceeds 2 mm, it will be difficult to manufacture the nonwoven
fabric 1 according to the present invention and, if the nonwoven
fabric including the troughs each having such width W.sub.c is used
as the inner sheet of the bodily fluid-absorbent article, the
distance between each pair of the adjacent crests 6 will be too
large to assure a desired texture. For this reason, it is not
preferable to adopt such excessively wide troughs 7.
[0048] With respect also to the nonwoven fabric 1 compressed by the
pressure plate 22 until the first crests 6a are compressed downward
to the state as illustrated in (b) of FIG. 5, the outline P was
plotted by the procedure illustrated in FIG. 6 and thereby the
heights H.sub.a, H.sub.b, the widths W.sub.a, W.sub.b, W.sub.c and
the cross-sectional areas S.sub.a, S.sub.b and S.sub.c were
measured. Referring to (c) of FIG. 5, the pressure plate 22 is
formed in its middle region as viewed in the width direction with a
slit 26 extending through the pressure plate 22 in its thickness
direction. This slit 26 allows the 3D measuring device to be
operated so that the sensor head of the laser displacement gauge in
the 3D measuring device may observe the crests 6 and the troughs 7
of the nonwoven fabric 1 in the course of measuring the heights
H.sub.a, H.sub.b and the width W.sub.a, W.sub.b, W.sub.c in the
nonwoven fabric 1 in the compressed state. The result obtained from
the measurement having been carried out in this manner is recorded
in TABLE 1. Measurement of the height, the width and the
cross-sectional area was carried out also on the nonwoven fabric as
comparative examples 1 and 2 in the same manner as in the nonwoven
fabric 1 according to the present invention. The result of these
measurements is also recorded in TABLE 1.
[0049] FIG. 7 is a 50-fold magnified photograph exemplarily showing
a cross-section of the second crest 6b cut in the cross direction
CD. The cut surface was obtained by cutting the nonwoven fabric 1
in the cross direction CD using a sharp cutter, for example, the
substitute edge H-100 for KOKUYO Cutter Knife HA-B (trade name).
This cut surface was photographed at 50-fold magnifications by
using Real Surface View-VE-7800 manufactured by Keyence
Corporation. Cross-sections 11a of the short fibers 11 appear in
this photograph of the cross-section obtained in this manner.
According to the present invention, the number of the
cross-sections 11a (i.e., the number of fiber cross-sections) was
determined with respect to the first crests 6a, the second crests
6b and the troughs 7, then respective ratios between these numbers
and the cross-sectional areas of the first crests 6a, the second
crests 6b and the troughs 7 were determined and the respective
values of these ratios were defined as the respective fiber
densities of the first crests 6a, the second crests 6b and the
troughs 7 in the compressed state and in the non-compressed state.
In this invention, these fiber densities are referred to also as
fiber density indices. TABLE 1 indicates the fiber density indices
in the example of the present invention and the comparative
examples 1 and 2. As will be apparent from TABLE 1, the fiber
density indices of the nonwoven fabric in the example of the
present invention, the fiber density indices of the nonwoven fabric
in the non-compressed state gradually increased in the order of the
first crests 6a, the second crests 6b and the troughs 7. Such
gradient of the fiber density indices was not changed in the
compressed state also. Specifically, in the nonwoven fabric
according to the present invention, even when the first crests 6a
are compressed to the same level as the second crests 6b, the fiber
density of the first crests 6a remains lower than that of the
second crests 6b and therefore bodily fluids excreted on the upper
surface 2 of the nonwoven fabric 1 may smoothly move from the first
crests 6a having a relatively low density to the second crests 6b
and the troughs 7 having a relatively high density.
[0050] When such a nonwoven fabric 1 is used as an inner sheet of
an absorbent article of such as, for example, a disposable diaper,
the nonwoven fabric 1 allows bodily fluids to move quickly from the
upper surface 2 toward the lower surface 3 and this capacity can be
represented, for example, by the strike-through value or Q-Max
value.
[0051] The strike-through value used herein is represented by a
time (unit: sec) required for 10 ml of artificial urine to pass
through the nonwoven fabric in the form of a test piece for
measurement and the smaller the strike-through value, the sooner
the permeation. To measure the strike-through value, the tester
LISTER manufactured by Lenzing Technik Corporation was used.
Specifically, the measuring probe was placed on the nonwoven fabric
and the tester was operated in accordance with EDANA-ERT Section
150.3 liquid strike-though time method prescribed for this tester.
Under the nonwoven fabric, 20 sheets of filter paper (Qualitative
filter paper No. 2 manufactured by ADVANTEC MFS., INC.) were
stacked in substitution for the absorbent article. The artificial
urine was prepared by dissolving 200 g of urea, 80 g of sodium
chloride, 8 g of magnesium sulfate, 3 g of calcium chloride and 1 g
of blue pigment No. 1 in 10 liter of ion-exchange water and 72 mN/m
of this artificial urine was used at a temperature of 20.degree. C.
Result of measurement was indicated in TABLE 1. The strike-through
values measured on the comparative examples 1 and 2 were also
indicated in TABLE 1.
[0052] The Q-Max value corresponds to a quantified heat quantity
drawn from the wearer's skin by the inner sheet when the inner
sheet wetted with bodily fluids comes in contact with the wearer's
skin represented by unit of J/cm.sup.2*sec. The higher the Q-Max
value of the inner sheet is, the larger the heat quantity drawn
from the wearer's skin becomes and, in consequence, the wearer
experiences an abrupt cold sensation. To measure the Q-Max value,
KES-F7-THERMOLABO II Model high-accuracy and high-speed thermal
property measuring device manufactured by KATO TECH CO., LTD. was
used. As the measuring conditions, a temperature of the probe was
set to <room temperature+10.degree. C., Q-Max measurement (cool
sensitivity measurement)> and as the surface temperature of the
probe, two standard levels of 10 g/cm.sup.2 and 30 g/cm.sup.2 were
adopted. As the nonwoven fabric for measurement, 10.times.10 cm was
used and this nonwoven fabric was placed on 3 sheets of qualitative
filter paper No. 2 stacked, a cylinder having an inner diameter of
20 mm was placed on the nonwoven fabric and 10 cc of the artificial
urine was poured into this cylinder about 5 sec, then the cylinder
was removed, 20 sec after the artificial urine had been poured, the
probe was put in contact with the surface of the nonwoven fabric to
measure a heat transfer from the probe to the surface of the
nonwoven fabric. Result of measurement was indicated in TABLE 1. As
will be apparent from comparison of the example of the invention
with the comparative examples, the nonwoven fabric 1 free from
possibility that bodily fluids might stay on the surface 2
exhibited a relatively small Q-Max value.
REFERENCE SIGNS LIST
[0053] 1 nonwoven fabric [0054] 2 upper surface [0055] 3 lower
surface [0056] 6 crest [0057] 6a crest (first crest) [0058] 6b
crest (second crest) [0059] 7 troughs [0060] 11 short fibers [0061]
A length direction [0062] B width direction [0063] C thickness
direction
* * * * *