Note: Descriptions are shown in the official language in which they were submitted.
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S P E C I F I C A T I O N
NONWOVEN FABRIC AND PROCESS FOR MAKING THE SAME
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an elastically
stretchable nonwoven fabric having a smooth touch to skin and
also to a process for making the same.
RELATED ART
Japanese Patent Application Publication No. 1994-184897
discloses an elastically stretchable web formed by laminating
a fibrous layer of elastically stretchable polymer with a
fibrous layer of inelastic stretchable polymer.
Japanese Patent Application Publication No. 1997-512313
also discloses an elastically stretchable web formed by
laminating the fibrous layer of elasticallystretchable polymer
with the fibrous layer of inelastic stretchable polymer.
Japanese Patent Application Publication No. 1992-11021
discloses an elastically stretchable conjugated thread
comprising a core-sheath-type conjugated fiber of which the
core fiber is made of elastically stretchable urethane and the
sheath fiber is made of inelastic stretchable polyamide.
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Japanese Patent Application Publication No. 1997-316748
discloses an elastically stretchable fabric including a
core-sheath-type conjugated filament as a weft. In this fabric,
the elastomeric core and the non-elastomeric sheath of the
filament are separated from each other and the sheath slackens
to form bellows-like wrinkles as the filament is drawn.
Japanese Patent Publication No. 3262803 discloses an
invention relating to multi-component thermoplastic
continuous filaments obtained by melt spinning, a product
formed of such filaments and a process for forming such a product.
According to the disclosure of the above-cited Publication,
multi-component thermoplastic filaments extruded from the
extruder is introduced through a quenching chamber into a
Lurgi-duct within which the filaments are drawn and split under
the effect of compressed air supplied thereinto. The filaments
split in this manner are accumulated on a collecting surface
formed by perforated screen or the like.
Japanese Patent Application Publication No. 1997-291454
discloses an invention relating to an elastically stretchable
nonwoven fabric. According to the disclosure of the
above-cited Publication, the elastically stretchable nonwoven
fabric is formed using elastically stretchable conjugated
fibers consisting of a hard elastic member comprising
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crystalline polypropylene as a first component and a
thermoplastic elastomer as a second component. The conjugated
fibers may be selected from a group including those of various
types such as side-by-side and sheath-and-core. Such
conjugated fibers can be finished into nonwoven fabric by
various processes such as spun bonding and thermal bonding
processes.
DISCLOSURE OF THE INVENTION
In the web and the nonwoven fabric disclosed in the
above-cited Publication Nos. 1994-184897 and 1997-512313,
respectively, the fibrous layer made of elastically stretchable
polymer is exposed on the surface of the fabric. The fibers
made of such polymer exhibit a relatively high friction
coefficient and correspondingly rough touch. The elastically
stretchable web or non-woven fabric formed by laminating the
fibrous layers tend to be a thick one.
The conjugated thread and the fabric disclosed in the
above-cited Publication Nos. 1992-11021 and 1997-316748, use
the core-sheath type conjugated fiber of which the core is
formed by elastomeric fiber and the sheath is formed by
non-elastomeric fiber. The sheath functions to cover the
elastically stretchable polymer, i.e., the elastomeric fiber
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and thereby to prevent the elastomeric fiber from coming in
direct contact with the user's body. In this way, the
conjugated thread as well as the fabric disclosed in the
above-cited Publications are able to offer a smooth touch to
the skin and a comfortable touch for the user' s body. However,
the sheath fiber presenting bellows-like wrinkles obstructs the
core fiber from elastically contracting and, in consequence,
limits an extension coefficient as well as a contraction
coefficient of the conjugated thread and the fabric. The
conjugated fiber has its sheath formed with the bellows-like
wrinkles and therefore it is difficult for these conjugated
thread and fabric to offer the soft and flexible touch peculiar
to the fiber having a small fineness.
According to the above-cited Publication No. 3262803, the
multi-component thermoplastic filaments are split to a
plurality of more fine filaments within the Lurgi duct and then
formed into a nonwoven fabric. Repective components
constituting the multi-component thermoplastic filament
appear on the surface of this nonwoven fabric in a form of more
fine filaments in accordance with the mixing proportion of these
components. If one of the components is a thermoplastic
elastomer, the filament of such a thermoplastic elastomer will
be exposed on the surface of the nonwoven fabric and a wearer
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of a wearable article made of the nonwoven fabric may experience
a rough touch with poor slip properties of the nonwoven fabric
depending on a proportion of the thermoplastic elastomer
filament.
According to the above Publication No. 1997-291454, the
elastically stretchable conjugated fiber consisting of the hard
elastic member comprising polypropylene as the first component
and the thermoplastic elastomer as the second component are
intermittently welded into an elastically stretchable nonwoven
fabric. The circumferential surface of the conjugated fiber
is defined by zones occupied by polypropylene and zones occupied
by the elastomer. In this case the thermoplastic elastomer is
inevitably exposed on the surface of the nonwoven fabric.
Consequently, this nonwoven fabric may have a rough touch and
poor slip properties. The above Publication No. 1997-291454
describes as one of embodiments a sheath-and-core type
conjugated fiber of which the sheath is formed by polypropylene
as the first component and the core is formed by the elastomer
comprising ethylene-a-olefin copolymer as the second component.
The elastic stretchability of such a conjugated fiber is
governed by the stretchability of the hard elastic member
comprising polypropylene and the stretchability of the
elastomer might be thereby suppressed.
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It is an object of the present invention to provide a novel
elastic nonwoven fabric adapted to have a broad elastic
extension range as well as a broad elastic contraction range
and to offer a smooth touch to the skin.
The present invention has a first aspect relating to a
nonwoven fabric and a second aspect relating to a process for
making the nonwoven fabric.
According to the first aspect of the invention, there is
provided an elastically stretchable nonwoven fabric comprising
elastically stretchable first fibers made of a first polymer
and inelastically stretchable second fibers made of a second
polymer.
The improvement according to the first aspect of the
invention is characterized in that the nonwoven fabric has first
and second surfaces as viewed in its thickness direction, the
first and second surfaces extending in parallel to each other,
the second fiber is attached to the first fiber at attaching
areas formed intermittently along the first fiber and spaced
apart from the first fiber between each pair of the neighboring
attaching areas, each segment of the second fiber spaced apart
from the first fiber between each pair of the neighboring
attaching areas being longer than an associated segment of the
first fiber, and the number of the second fiber is in a range
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of 1 to 16 per each first fiber.
The first aspect of the invention can be implemented in
preferable manners as follows:
( 1 ) the first and second fibers intersect with each other
in such a manners that the first fiber lies inside and the second
fiber lies outside in any one of the first and second surfaces;
(2) the first fiber has on its circumferential surface
first curved surfaces each bulging radially outward from an axis
of the first fiber and second curved surfaces each depressed
radially toward the axis of the first fiber, the first and second
curved surfaces alternately appearing in a circumferential
direction of the first fiber, and each pair of the first curved
surfaces neighboring to each other in the circumferential
direction cooperate with the second curved surface lying
between the pair of the first curved surfaces neighboring to
each other to form a groove extending in a longitudinal
direction of the first fiber so that the second curved surface
defines a bottom of the groove. In the case that the nonwoven
fabric having such a first fiber is used for a wearable article,
these are little chances where the first fiber contacts the skin
of a wearer of the article, because the curved surfaces of the
first fiber cannot contact the skin.
( 3 ) one of the first and second surfaces has a slip angle
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_g_
of 25° to 40° . The nonwoven fabric having the slip angle of
such
a range is suitable for a wearable article and other products .
(4) the first polymer is selected from the group
consisting of thermoplastic polyurethane and thermoplastic
polyurethane containing a lubricant and the second polymer is
selected from the group consisting of polyolefin-based polymer
and polyamide-based polymer.
The object set forth above is achieved, according to the
second aspect of the invention, by an improvement in a process
for making an elastically stretchable nonwoven fabric formed
by elastically stretchable first fibers made of a first polymer
and inelastically stretchable second fibers made of a second
polymer.
The improvement according to the second aspect of the
invention is characterized by that feeding, in a machine
direction, a plurality of conjugated fibers each consisting of
a ffirst ffibrous component made of the ffirst polymer and a second
fibrous component extending in parallel to and releasably
attached to a surface of the first fibrous component and thereby
forming a web from the conjugated fibers having a basis weight
in a range of 10 to 500g/m2, forming the web with a plurality
of attaching areas intermittently formed in at least one
direction of the machine direction and a cross direction
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intersecting orthogonally the machine direction so that the
conjugated fibers can not be separated one from another at the
attaching areas, stretching the web at least in the one
direction within an elastic range of the f first f fibrous component
and under a failure point of the second fibrous component and
thereby separating the first and second fibrous components one
from another between each pair of the attaching areas
neighboring to each other and permanently deforming the second
fibrous component; and allowing the web to contract under an
elastic recovery force of the first fibrous component so that
the first fiber may be obtained from the first fibrous component,
the second fiber may be obtained from the second fibrous
component and the nonwoven fabric may be obtained from the web.
The second aspect of the invention can be implemented in
preferable manners as follow:
( 1 ) the first fibrous component of the conjugated fiber
has on its circumferential surface first curved surfaces each
bulging radially outward from an axis of the first fibrous
component and second curved surfaces each depressed radially
toward an axis of the first fibrous component, the first and
second curved surfaces alternately appearing in the
circumferential direction of the first fibrous component, and
each pair of the first curved surfaces neighboring to each other
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in the circumferential direction cooperate with the second
curved surface lying between the pair of the first curved
surfaces neighboring to each other to form a groove extending
in the longitudinal direction of the first fibrous component
so that the second fibrous component extends in parallel to the
first fibrous component in the groove.
(2) the circumferential length of the conjugated fiber
occupied by the second fibrous component is in a range of 40
to 90~ of the whole circumferential length of the conjugated
f fiber .
(3) the number of the second fibrous component
constituting the conjugated fiber is in a range of 1 to 16 per
one of the first fibrous component.
(4) the first polymer is selected from the group
consisting of thermoplastic polyurethane and thermoplastic
polyurethane containing a lubricant and the second polymer is
selected from the group consisting of polyolefin-based polymer
and polyamide-based polymer.
In the present invention the slip angle is measured in
an apparatus depicted by an accompanying drawing, i . a . Fig . 11.
The measuring method of the slip angle is included in the
explanation of Fig. 11.
The nonwoven fabric according to the present invention,
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even when the nonwoven fabric contains the elastic fiber, allows
the smooth touch of the nonwoven fabric to the article wearer' s
skin to be adjusted by placing in the vicinity of each of the
elastic fiber at least one inelastic fiber which is longer than
the elastic fiber. The smooth touch to the article wearer's
skin can be effectively adjusted by placing a plurality of the
inelastic fibers in the vicinity of the elastic fiber so as to
surround this elastic fiber. Since the segment of the inelastic
fiber defined between a pair of the neighboring attaching areas
in which the inelastic fiber is inseparably attached to the
elastic fiber is longer than the associated segment of the
elastic fiber, the elastic stretchability of the elastic fibers
as well as the nonwoven fabric is not disturbed by the inelastic
fiber .
The process according to the present invention for making
the nonwoven fabric is primarily characterized in that the
conjugated fibers consisting of the elastic fibrous component
and the inelastic fibrous component separably attached to the
surface of the elastic fibrous component are split into the
respective fibrous components so that the inelastic fibers
having a smaller fineness may surround the elastic fiber having
a larger fineness . In this way, the process according to the
present invention can provide thin nonwoven fabric which is
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elastically stretchable and contractible and allows also at
least one of the upper and lower surfaces of the nonwoven fabric
to present a smooth touch and high slip properties of the
inelastic fiber having a smaller fineness instead of those of
the elastic fiber having a larger fineness.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view showing a typical embodiment
of a nonwoven fabric;
Fig. 2 is a photograph showing cross-sections of
conjugated fibers;
Fig. 3 is a diagram tracing the conjugated fibers in
photograph of Fig. 2;
Fig. 4 is a scale-enlarged plan view showing a part of
Fig . 1;
Fig. 5 is a sectional view taken along a line V-V in Fig.
4;
Fig. 6 is a scale-enlarged portion of Fig. 5;
Fig. 7 is a view similar to Fig. 5 illustrating a relative
position of the respective fibers when the nonwoven fabric is
stretched;
Fig. 8 is a photograph similar to Fig. 2 showing a
preferred embodiment of the present invention;
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Fig. 9 is a diagram similar to Fig. 3 showing the preferred
embodiment;
Figs. 10A, lOB and lOC are sectional views of the
conjugated fibers; and
Fig. 11 is a side view of a tester.
DESCRIPTION OF THE BEST MODE FOR WORKING OF THE INVENTION
Details of the nonwoven fabric and the process for making
the same according to the present invention will be more fully
understood from the description given hereunder with reference
to the accompanying drawings.
A substantially hexahedral fragment of nonwoven fabric
1 shown in Fig. 1 in a perspective view has upper and lower
surfaces 2, 3 which extend parallel to each other and define
the thickness of the nonwoven fabric 1 and side surfaces defined
by cut surfaces 4a, 4b, 4c, 4d each intersecting the upper and
lower surfaces 2, 3. The nonwoven fabric 1 comprises
elastically stretchable fibers 11 made of a first thermoplastic
polymer, inelastically stretchable fibers 12 made of a second
thermoplastic polymer and conjugated fiber regions 13 formed
by the elastic fibers 11 and the inelastic fibers 12 which are
joined together side by side. In the nonwoven fabric 1, these
fibers 11, 12 and the conjugated fiber regions 13 are welded,
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adhesively bonded or mechanically intertwined together at a
plurality of attaching area 16 so that these fibers 11, 12 and
the conjugated fiber regions 13 may be substantially fixed in
the area 16. The elastic fibers 11 and the inelastic fibers
12 are obtained by splitting each conjugated fiber 13a
corresponding to each of the conjugated fiber regions 13 into
a f fiber component 21 and a f fiber component 2 2 ( see Fig . 2 ) during
a production process as will be described later. As will be
seen in Fig. 1, the conjugated fiber regions 13 principally lie
in the vicinity of the respective attaching area 16.
In the nonwoven fabric 1, the elastic fibers 11 have a
fineness in a range of 0.1 dtx to 10 dtx and the inelastic fibers
12 have a fineness in a range of 0.05 dtx to 2 dtx. The fineness
of the inelastic fiber 12 is preferably smaller than the
fineness of the elastic fiber 11. Except for the area 16, in
the surrounding area of each of the elastic fibers 11, one to
sixteen of the inelastic fibers 12 extends or extend between
the neighboring areas 16, for example, the area 16a and the area
16b depicted in Fig. 1. In a preferred embodiment of the
nonwoven fabric 1, at least three inelastic fibers 12a, 12b,
12c lie in the surrounding area of the individual elastic fiber
lla (see Fig. 5) and wrap around this elastic fiber lla. In
the vicinity of the areas 16a and 16b, the inelastic fibers 12a,
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12b, 12c are branched and spaced apart from the elastic fiber
lla. Thus the elastic fiber 11 and the inelastic fibers 12 are
repeatedly joined together ( at the areas 16 ) and spaced apart
from each other in a longitudinal direction of the elastic fiber
11. Between the neighboring areas 16a and 16b, each segment
of the inelastic fibers 12a, 12b, 12c is longer than the segment
of the elastic fiber lla, and the elastic fiber lla is
substantially rectilinear and the inelastic fibers 12a, 12b,
12c describe various curves, respectively. On the upper
surface 2 the ratio of the number of the elastic fiber lla to
the number of the inelastic fibers 12a, 12b, 12c is
approximately 1:3. The elastic fiber lla and the inelastic
fibers 12a, 12b, 12c have ends thereof exposed on the cut surface
4a and the number of these ends approximately corresponds to
the number of the elastic fibers lla and the inelastic fibers
12a, 12b, 12c. In other words, a ratio of the ends of the elastic
fibers lla to the ends of the inelastic fibers 12a, 12b, 12c
exposed on the cut surface 4a is approximately 1:3.
Uses of the nonwoven fabric 1 are not specified. The
nonwoven fabric 1 can be used for a wearable article, for example,
a disposable diaper, disposable pants or a disposable medical
gown, and household goods, for example, disposable wipes. In
the nonwoven fabric 1 used in these fields it is preferable that
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a straight distance between the neighboring attaching areas 16a
and 16b on the elastic fiber lla is 0.5 - 10 mm, and that the
lengths of the inelastic fibers 12a, 12b, 12c between the
neighboring attaching areas 16a and 16b are 1.2 - 5 times of
the length of the associated elastic fiber lla.
The elastic fibers 11 are elastically stretched when the
nonwoven fabric 1 of the arrangement as has been described above
is held with the hands and pulled in a direction A or in a
direction B intersecting orthogonally the direction A,
whereupon the inelastic fibers 12 are oriented to extend in the
direction A or in the direction B. Upon releasing from the
pulled condition, an elastic recovery force of the elastic
fibers. 11 causes the nonwoven fabric 1 to shrink to the state
of Fig. 1. It is well known that such an elastic material as
the elastic fiber 11 has a rubbery rough touch, but the presence
of the plural inelastic fibers 12 wrapping around the respective
elastic fibers 11 is effective to provide the upper and lower
surfaces 2, 3 of the nonwoven fabric 1 with a smooth and slipping
touch similar to that of the inelastic fiber 12. In addition,
the smooth and slipping touch of the nonwoven fabric 1 of the
present invention can be controlled by a fineness, a shape of
the cross section and a number of the inelastic fiber 12. The
fineness of the inelastic fibers 12 may be minimized, for
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example, in the order of 0.5 dtx to 1.5 dtx to make the touch
of the upper and lower surfaces 2 , 3 more smooth and flexible .
Fig. 2 is a photograph showing cross-sections of
conjugated fibers 13a used to make the nonwoven fabric 1 and
S Fig. 3 is a diagram tracing the conjugated fibers 13a in the
photograph of Fig. 2. A plurality of the conjugated fibers 13a
appearing in Fig. 2 are substantially identical one to another.
Each of these fibers 13a has a diameter of 25 ~m to 30 ~.m and
comprises a single elastic fiber component 21 and three
inelastic fiber components 22 separably attaching to the
surface of the elastic fiber component 21 substantially at
regular intervals in a circumferential direction. The
conjugated fiber 13a is substantially identical to the
conjugated fiber component 13 depicted in Fig. 1 in construction
as well as in composition. The conjugated fiber 13a can be
obtained by extruding simultaneously an elastic thermoplastic
polymer to form the elastic f fiber component 21 and an inelastic
thermoplastic polymer to form the inelastic fiber component 22
through nozzles of an extruder for melt spinning well known in
the art. The elastic fibrous component 21 has on its
circumferential surface first curved surface portions 51 each
bulging radially outward from an axis of the elastic fibrous
component 21 and second surface portions 52 each depressed
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radially toward the axis of the elastic first fibrous component
21 so that these first and second surface portions 51, 52
alternately appearing in the circumferential direction of the
elastic fibrous component 21. Each pair of first surface
portions 51, 51 neighboring to each other in the circumferential
direction cooperate with the second surface portion 52 lying
between the pair of neighboring first surface portions 51 to
form a groove 53 wherein the second surface portion 51 defines
a bottom of the groove 53 and a total of three grooves 53a, 53b,
53c extend in the longitudinal direction of the elastic fibrous
component 21. The inelastic fibrous component 22 comprises
three inelastic fibrous components 22a, 22b, 22c extending in
the longitudinal direction of the elastic fibrous component 21
in the grooves 53a, 53b, 53c, respectively.
The first polymer to be used to obtain the elastic fiber
component 21 includes a thermoplastic polyurethane, a
thermoplastic polyurethane containing lubricant and any other
thermoplastic elastomers. The second polymer to be used to
obtain the inelastic fiber component 22 includes thermoplastic
polymer which is incompatible with the first polymer and
stretches inelastically. The term "incompatible" used herein
means that a conjugation strength of the inelastic fiber
component 22 to the elastic fiber component 21 is relatively
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low and the inelastic fiber component 22 can be easily separated
or split from the elastic fiber component 21, when the
conjugated fiber 13a is stretched. The second polymer having
such properties may be selected from the group including
polyolefine polymer such as polyethylene or polypropylene and
polyamide polymer such as nylon. Either homopolymer or
copolymer of polypropylene can be used. The inelastic fiber
12 of polypropylene has preferably crystallinity less than 30 ~
and, more preferably, less than 20 ~ and does not include a fiber
to be deemed as a hard elastic f fiber . The crystallinity of the
inelastic fiber 12 is measured by a DSC method in the present
invention. The first elastic fiber component 21 may be made
by thermoplastic polyurethane containing a lubricant such as
fatty amide to facilitate the inelastic fiber component 22 to
be separated easily from the elastic fiber component 21. An
example of the elastic fibrous component 21 is a thermoplastic
polyurethane whose melt viscosity based on JIS K 7311 is 23 x
103 - 180 x 103 poise. An example of the inelastic fiber
component 22 is a polypropylene whose Melt Flow Rate (MFR) is
30 at 230°C and 2.16 kg/cm2. A preferable weight ratio of the
elastic fibrous component 21 to the inelastic fibrous component
22 is 20:80 - 90:10. In a preferable case of the conjugated
fiber 13a, the inelastic fibrous components 22 associated with
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each elastic fibrous component 21 have a circumferential length
occupying 40 ~ to 90 ~ of the whole circumferential length of
the composite fiber 13a. The areas and shapes of the elastic
fibrous component 21 and the inelastic fibrous component 22 in
the cross-section of the conjugated fiber 13a are formed in such
a way that the elastic fiber 11 from the elastic fibrous
component 21 may have a fineness of 0. 1 - 10 dtx and the inelastic
fiber 12 from the inelastic fibrous component 22 may have a
fineness of 0.05 - 2 dtx and less than that of the elastic fiber
11. A preferable inelastic fibrous component 22 may have a flat
cross-section such as an oval shape and the inelastic fiber 12
derived from the inelastic fibrous component 22 may have also
a flat corss-section. If the inelastic fiber 12 has a flat
cross-section, the length of the long axis may be longer than
two times of the length of the short axis so that the inelastic
fiber 12 can be easily bent.
Using such a conjugated fiber 13a, the nonwoven fabric
1 of Fig. 1 is formed in a manner as will be described.
Preferably, the conjugated fiber 13a of continuous type is used.
A plurality of conjugated fibers 13a is supplied in a machine
direction to make a web having a basis weight of 10 g/mZ to 500
g/m2. In the course of making such a web, the attaching areas
16 depicted in Fig. 1 in which the conjugated fibers 13a are
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joined or intertwined together in an inseparable manner may be
formed intermittently in one of the machine direction and the
cross direction intersecting orthogonally the machine
direction by an appropriate treatment, for example, by
embossing the web under heating or by jetting high pressure
columnar water to the web or by blowing a heated air to the web.
This web may be stretched within an elastic range of the elastic
fibrous component 21 and under a failure point of the inelastic
fibrous component 22, for example, by 70 ~ or more in one
direction or in two directions along which the attaching areas
16 are formed intermittently. Thereafter, the web is relieved
from the stretched condition and is contracted by the elastic
recovery force of the elastic fiber component 21 to obtain the
nonwoven fabric 1 depicted in Fig. 1. Between each pair of the
neighboring attaching areas 16, 16, for example, the areas 16a
and 16b in Fig. 1, the conjugated fiber 13a is separated or split
along the interfaces of the elastic fiber component 21 and the
inelastic fiber components 22 into one elastic fiber 11 and
three inelastic fiber components 12. At the same time, the
inelastic fibers 12 also elongate so as to be permanently
deformed and a diameter of each inelastic fiber 12 is reduced.
In the nonwoven fabric 1 obtained by contracting the web,
between each pair of the neighboring areas 16, 16, the elastic
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fibers 11 contract so as to describe a substantially straight
line or a gentle curve while each of the inelastic fibers 12
longer than the elastic fiber 11 describes a curve which is more
complicated than the elastic fibers 11 and intersect the elastic
fibers 11 and the inelastic fibers 12.
Fig. 4 is a scale-enlarged plan view showing the elastic
fibers lla representing the elastic fiber 11 and the inelastic
fibers 12a, 12b, 12c representing the inelastic fiber 12 on the
upper surface 2 of the nonwoven fabric 1 of Fig. 1 obtained in
the manner as has been described above, and Fig. 5 is a sectional
view taken along a line V-V in Fig. 4. In the vicinity of the
areas 16a, 16b, as will be apparent from Fig. 4, the elastic
fiber component 21 and the inelastic fiber components 22 of the
conjugated fiber 13a are not separated, and therefore, the
conjugated fiber 13a forms the conjugated fiber regions 13.
Between each pair of the neighboring areas 16a, 16b on the
elastic fiber lla separated from the inelastic fibers 12a, 12b,
12c, the elastic fiber lla describes a substantially straight
line while the inelastic fibers 12a, 12b, 12c describe various
curves. The inelastic fiber 12b are intersecting the elastic
fiber lla so as to provide crossing points. At the crossing
points the elastic fiber lla lies inside and the inelastic fiber
12b lies outside in the thickness direction of the nonwoven
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fabric 1. On the cut surface shown in Fig. 5, the inelastic
fibers 12a, 12b, 12c are distributed around the elastic fiber
lla so as to surround the elastic fiber lla.
Fig. 6 is a scale-enlarged perspective view of the elastic
fiber lla of Fig. 5. The circumferential surface of the elastic
fiber lla is defined by first curved surface portions 61 each
radially bulging outward from an axis of the elastic fiber lla
with a relatively small curvature radius and second curved
surface portions 62 each radially depressed toward the axis of
the elastic fiber lla so that these first and second curved
surface portions 61, 62 alternately appear on the
circumferential surface of the elastic fiber lla. The second
curved surface portion 62 lies between each pair of the first
curved surface portions 61 neighboring to each other in the
circumferential direction and these first and second curved
surface portions 61, 62 cooperate together to form a groove 63
extending in the longitudinal direction of the elastic fiber
lla. These first curved surface portion 61, second curved
surface portion 62 and groove 63 respectively correspond to the
first surface portion 51, the second surface portion 52 and the
groove 53 of the conjugated fiber 13a depicted by Fig. 3.
With a wearable article made of the nonwoven fabric 1
including the elastic fiber 11 and the inelastic fiber 12
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depicted in Figs. 4, 5 and 6, the article wearer's skin readily
comes in contact with the inelastic fibers 12a, 12b, 12c rather
than with the elastic fiber lla. Consequently, a touch and slip
properties of the nonwoven fabric 1 are similar to those of the
S inelastic fiber 12. This is very true, when the number of the
inelastic fibers 12 intersecting the elastic fiber lla is
relatively large as in the case depicted in Fig . 4 and the elastic
fiber lla having a rough touch and poor slip properties to the
article wearer's skin is embedded among the inelastic fibers
12 on the upper surface 2 of the nonwoven fabric 1. As will
be apparent from Fig. 6, the elastic fiber lla comes in contact
with the article wearer' s skin 69 indicated by imaginary lines
merely in the vicinity of the first curved surface portions 61
but the second curved surface portions 62 rarely comes in
contact with the skin 69. In this way, the circumferential
surface of the elastic fiber lla possibly coming in contact with
the skin 69 is limited to an extremely small area having a small
curvature radius. Compared to an elastic fiber having a
circular cross-section of the same area as that of the elastic
fiber lla, the surface area of the elastic fiber lla coming in
contact with the skin 69 is substantially reduced. The smaller
the surface area of the elastic fiber lla possibly coming in
contact with the skin 69 is, the higher the smooth touch and
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slip properties of the nonwoven fabric 1 to the article wearer' s
skin 69 are. Even if the elastic fiber lla comes in contact
with the skin 69, a gap is left in many cases between the skin
69 and the grooves 63 of the elastic fiber lla and such a gap
serves to relieve the skin 69 from a high humid condition since
the gap allows a vapour generated within the article to escape
outward. The nonwoven fabric 1 according to the invention can
be implemented also in a manner that not the upper surface 2
but the lower surface 3 is constructed as depicted in Fig. 1
or the both surfaces 2 , 3 are constructed as depicted in Fig .
1.
Fig. 7 is a view similar to Fig. 5 showing the nonwoven
fabric 1 being pulled in the direction A indicated in Fig. 4.
The inelastic fibers 12a, 12b, 12c of Fig. 5 move in directions
indicated by arrows P, Q, R and get nearer to the elastic fiber
lla as the elastic fiber lla is stretched in the direction A
so that these inelastic fibers 12a, 12b, 12c may closely
surround the elastic fiber lla as shown in Fig. 7. If most of
the inelastic fibers 12 of Fig . 7 , orientate in the direction
A, the touch and slip properties of the nonwoven fabric 1 may
be further similar to the smooth touch and high slip properties
of the inelastic fibers 11.
Figs. 8 and 9 are views similar to Figs. 2 and 3,
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exemplarily showing the conjugated fiber 13a suitably used in
the present invention. This conjugated fiber 13a has a diameter
of about 15~ and consists of the elastic fibrous component 21
presenting a semicircular cross-section and the inelastic
fibrous component 22 presenting a semicircular cross-section
which are reparably attached together. The conjugated fiber
13a thus presents a substantially circular cross-section and
the inelastic fibrous component 22 appearing on a
circumferential surface of this conjugated fiber 13a occupies
approximately 50~ of the circumferential length of the
conjugated fiber 13a. Also in the nonwoven fabric 1 obtained
from the web comprising these conjugated fibers 13a by
stretching the web and then allowing the web to contract, a
length of the inelastic fiber derived from the inelastic fibrous
component 22 is longer than the elastic fiber derived from the
elastic fibrous component 21. With such inelastic fibers
flexing and/or curving so as to intersect the elastic f fibers ,
the inelastic fibers function to prevent the elastic fibers from
coming in direct contact with the article wearer's skin.
Consequently, the nonwoven fabric obtained from these
conjugated fibers 13a exhibits a smooth touch and high slip
properties to the article wearer' s skin although a level of its
slip properties can not be comparative to those exhibited by
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the nonwoven fabric 1 depicted in Fig. 1.
Since the nonwoven fabric 1 of the invention may be formed
using the web of the conjugated fiber 13a comprising the elastic
fibrous component 21 having the groove 53 as shown in Fig. 3
and the inelastic fibrous component 22 extending in this groove
53, it is easy to obtain the inelastic fiber 12 which has a
fineness smaller than a fineness of the elastic fiber 11.
Figs. 10A, lOB and lOC exemplarily illustrate the
cross-sections of the conjugated fibers 13a. The conjugated
fiber 13a depicted in Fig. l0A presents a cross-section
distinguished from that of the conjugated fiber 13a depicted
in Fig. 9 in that the elastic fibrous component 21 is formed
with a single groove 53. In the case of the conjugated fiber
13a depicted in Fig. lOB, the elastic fibrous component 21 is
formed with a pair of grooves 53. Finally, in the case of the
conjugated fiber 13a depicted in Fig. lOC, the elastic fibrous
component 21 is formed with four grooves 53. In this manner,
it is possible without departing from the scope of the invention
to form the elastic fibrous component 21 with a selective number
of the grooves 53 in a range of one to sixteen.
Fig. 11 is a side view of a tester 70 used in the present
invention to evaluate the nonwoven fabric with respect to its
slip properties. The tester 70 comprises a plate 71 driven by
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an electric motor 73 so that its angle a of a gradient relative
to the horizontal plane may be increased at a predetermined rate
and a block 72 to be covered with the nonwoven fabric to be
evaluated. The plate 71 has its upper surface formed of
stainless steel having a surface roughness of 12.5s as measured
in accordance with JIS B 0601. The block 72 is made of stainless
steel having a weight adjusted to exert a surface pressure of
lOg/cmz upon the nonwoven fabric. The nonwoven fabric is
attached to the block 72 so as to cover the entire lower surface
of the block 72 . The plate 71 supporting the block 72 is rotated
around a pivot 74 so that the angle a increases at a rate of
2°/sec until the block 72 begins to slip over the upper surface
of the plate 71. The angle a at which the block 72 begins to
slip is defined as a slip angle as. The smaller the value of
as is, the higher the slip properties relative to the article
wearer's skin are. Based on the tester 70, clothing fabric for
men' s and women' s shirts and pants as undergarments made of 100 0
cotton exhibit the slip angle as in a range of about 21° to about
25°.
TABLE 1 indicates the slip angle as exhibited by the
examples of nonwoven fabric of the conjugated fiber 13a depicted
in Figs. 2 and 3 and control nonwoven fabrics. The nonwoven
fabrics of the invention were obtained by subjecting the web
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having a basis weight of 50g/m2 to heat embossing both in the
machine direction and in the cross direction. The conjugated
fiber 13a consisted of thermoplastic polyurethane and
polypropylene at a weight ratio in a range of 84.4 . 15.6 to
67.9 : 32.1 and polypropylene occupied about 70 to 90 ~ of the
circumferential length of the conjugated fiber 13a. The
comparative embodiments of nonwoven fabric were made of
thermoplastic polyurethane fiber or polypropylene fiber and
obtained by subjecting the web having a basis weight of 50 g/m2
to heat embossing in the same manner as in the case of embodiments
of the invention . Both in the embodiments of the invention and
in the comparative embodiments, a plurality of heat embossed
zones each of 0 . 3 mm2 were formed at a pitch of 2 mm in the machine
direction as well as in the cross direction. As will be apparent
from TABLE 1, the slip angle as of the nonwoven fabric 1 depends
on the percentage by which polypropylene as the inelastic
fibrous component 22 occupies the circumferential length of the
conjugated fiber 13a. In other words, the invention allows the
slip angle as of the nonwoven fabric 1 to be controlled by
adjusting the proportion of the inelastic fibrous component 22
occupying the circumferential length of the conjugated fiber
13a. When the nonwoven fabric 1 is used in a wearing article,
the slip angle as of the upper surface 2 and/or the lower surface
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3 is controlled preferably in a range of 25° to 40°.
In order to control the slip angle as of the nonwoven
fabric 1, it is possible without departing from the scope of
the invention to use, in addition to those indicated as the
embodiments, the conjugated fiber 13a consisting of
thermoplastic polyurethane and polypropylene at a weight ratio
in a range of 20 : 80 to 90 : 10. It is also possible to use
the conjugated fiber 13a in which polypropylene occupies 40 to
90 0 of the circumferential length of this conjugated fiber 13a.
[ TABLE 1 )
Constituents Length
of conjugated
fiber occupied by
polypropylene Slip
in the whole angle
peripheral
Thermoplastic pol ro lene length of as
~ py
polyurethane conjugate
f fiber ( %
)
Example
84.4 15.6 70.92 39
3
1 .
Example 76, 5 23. 5 75. 04 34
3
2 .
Example 67.9 32. 1 86.07 30
3
3 .
Control 100 - 0 49
1
1 .
Control - 100 100 21
3
2 .
The nonwoven fabric of the present invention can be used
industrially for disposable wearable articles and the nonwoven
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fabric can be industrially manufactured through the
manufacturing process of the present invention.
