U.S. patent application number 10/666732 was filed with the patent office on 2004-07-08 for nonwoven fabric and process for making the same.
Invention is credited to Kobayashi, Toshio.
Application Number | 20040132374 10/666732 |
Document ID | / |
Family ID | 32032969 |
Filed Date | 2004-07-08 |
United States Patent
Application |
20040132374 |
Kind Code |
A1 |
Kobayashi, Toshio |
July 8, 2004 |
Nonwoven fabric and process for making the same
Abstract
An elastically stretchable nonwoven fabric comprises elastically
stretchable first fibers made of a first polymer and inelastically
stretchable second fibers made of a second polymer. The second
fibers are separably attached to the first fiber at attaching areas
intermittently formed on the first fiber. Between the attaching
areas neighboring to each other the second fibers are spaced apart
from the first fiber and have lengths longer than that of the first
fiber. One to sixteen of the second fibers are provided per each
first fiber.
Inventors: |
Kobayashi, Toshio;
(Kagawa-ken, JP) |
Correspondence
Address: |
LOWE HAUPTMAN GILMAN AND BERNER, LLP
1700 DIAGONAL ROAD
SUITE 300 /310
ALEXANDRIA
VA
22314
US
|
Family ID: |
32032969 |
Appl. No.: |
10/666732 |
Filed: |
September 22, 2003 |
Current U.S.
Class: |
442/328 ;
442/329; 442/334; 442/336; 442/361 |
Current CPC
Class: |
D04H 1/4291 20130101;
Y10T 442/608 20150401; D04H 3/02 20130101; Y10T 442/602 20150401;
D02G 1/18 20130101; D04H 1/4358 20130101; D04H 1/4334 20130101;
Y10T 442/637 20150401; D04H 1/48 20130101; Y10T 442/601 20150401;
Y10T 442/61 20150401; D04H 1/43835 20200501 |
Class at
Publication: |
442/328 ;
442/329; 442/334; 442/336; 442/361 |
International
Class: |
D04H 001/00; D04H
003/00; D04H 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2002 |
JP |
2002-311896 |
Sep 12, 2003 |
JP |
2003-321935 |
Claims
What is claimed is:
1. 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,
said nonwoven fabric being characterized by that: said nonwoven
fabric has first and second surfaces as viewed in its thickness
direction, said first and second surfaces extending in parallel to
each other, said second fiber is bonded to said first fiber at
attaching areas formed intermittently along said first fiber and
spaced apart from said first fiber between each pair of said
attaching areas neighboring to each other, each segment of said
second fiber spaced apart from said first fiber between each pair
of said attaching areas neighboring to each other being longer than
an associated segment of said first fiber, and the number of said
second fiber is in a range of 1 to 16 per each first fiber.
2. The nonwoven fabric according to claim 1, wherein said first and
second fibers intersect with each other in such a manner that said
first fiber lies inside and said second fiber lies outside in one
of said first and second surfaces.
3. The nonwoven fabric according to claim 1, wherein said first
fiber has on its circumferential surface first curved surfaces each
bulging radially outward from an axis of said first fiber and
second curved surfaces each depressed radially toward said axis of
said first fiber, said first and second curved surfaces alternately
appearing in a circumferential direction of said first fiber, and
each pair of said first curved surfaces neighboring to each other
in said circumferential direction cooperate with said second curved
surface lying between said pair of said first curved surfaces
neighboring to each other to form a groove extending in a
longitudinal direction of said first fiber so that said second
curved surface defines a bottom of said groove.
4. The nonwoven fabric according to claim 1, wherein one of said
first and second surfaces has a slip angle of 25.degree. to
40.degree..
5. The nonwoven fabric according to claim 1, wherein said first
polymer is selected from the group consisting of thermoplastic
polyurethane and thermoplastic polyurethane containing a lubricant
and said second polymer is selected from the group consisting of
polyolefin-based polymer and polyamide-based polymer.
6. 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, said process comprising steps of: feeding, in a
machine direction, a plurality of conjugated fibers each consisting
of a first fibrous component made of said first polymer and a
second fibrous component extending in parallel to and releasably
attached to a surface of said first fibrous component and thereby
forming a web from said conjugated fibers having a basis weight in
a range of 10 to 500 g/m.sup.2; forming said web with a plurality
of attaching areas intermittently formed in at least one direction
of said machine direction and a cross direction intersecting
orthogonally said machine direction so that said conjugated fibers
can not be separated one from another at said attaching areas;
stretching said web at least in said one direction within an
elastic range of the first fibrous component and under a failure
point of said second fibrous component and thereby separating said
first and second fibrous components one from another between each
pair of said attaching areas neighboring to each other and
permanently deforming said second fibrous component; and allowing
said web to contract under an elastic recovery force of said first
fibrous component so that said first fiber is obtained from said
first fibrous component, said second fiber is obtained from said
second fibrous component and said nonwoven fabric is obtained from
said web.
7. The process according to claim 6, wherein said first fibrous
component of said conjugated fiber has on its circumferential
surface first curved surfaces each bulging radially outward from
the axis of said first fibrous component and second curved surfaces
each depressed radially toward said axis of said first fibrous
component, said first and second curved surfaces alternately
appearing in a circumferential direction of said first fibrous
component, and each pair of said first curved surfaces neighboring
to each other in said circumferential direction cooperate with said
second curved surface lying between said pair of said first curved
surfaces neighboring to each other to form a groove extending in a
longitudinal direction of said first fibrous component so that said
second fibrous component extends in parallel to said first fibrous
component in said groove.
8. The process according to claim 6, wherein the circumferential
length of said conjugated fiber occupied by said second fibrous
component is in a range of 40 to 90% of the whole circumferential
length of said conjugated fiber.
9. The process according to claim 6, wherein the number of said
second fibrous component constituting said conjugated fiber is in a
range of 1 to 16 per one of said first fibrous component.
10. The process according to claim 6, wherein said first polymer is
selected from the group consisting of thermoplastic polyurethane
and thermoplastic polyurethane containing a lubricant and said
second polymer is selected from the group consisting of
polyolefin-based polymer and polyamide-based polymer.
Description
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] Japanese Patent Application Publication No. 1994-184897 A
(Ref. 1) discloses an elastically stretchable web formed by
laminating a fibrous layer of elastically stretchable polymer with
a fibrous layer of inelastic stretchable polymer.
[0003] Japanese Patent Application Publication No. 1997-512313 A
(Ref. 2) also discloses an elastically stretchable web formed by
laminating the fibrous layer of elastically stretchable polymer
with the fibrous layer of inelastic stretchable polymer.
[0004] In the web and the nonwoven fabric disclosed in the
above-cited Publications, 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.
[0005] Japanese Patent Application Publication No. 1992-11021 A
(Ref. 3) 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.
[0006] Japanese Patent Application Publication No. 1997-316748 A
(Ref. 4) 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.
[0007] The conjugated thread and the fabric disclosed in the
above-cited Publications 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 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.
[0008] Japanese Patent Publication No. 3262803 B (Ref. 5) 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 Ref. 5, 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. According to the
disclosure of Ref. 5, 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. Respective 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 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.
[0009] Japanese Patent Application Publication No. 1997-291454 A
(Ref. 6) discloses an invention relating to an elastically
stretchable nonwoven fabric. According to the disclosure of Ref. 6,
the elastically stretchable nonwoven fabric is formed using
elastically stretchable conjugated fibers consisting of a hard
elastic member comprising 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.
According to Ref. 6 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. Ref. 6 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-.alpha.-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.
REFERENCES
[0010] [Ref. 1] Japanese Patent Application Publication No.
1994-184897 A
[0011] [Ref. 2] Japanese Patent Application Publication No.
1997-512313 A
[0012] [Ref. 3] Japanese Patent Application Publication No.
1992-11021 A
[0013] [Ref. 4] Japanese Patent Application Publication No.
1997-316748 A
[0014] [Ref. 5] Japanese Patent Publication No. 3262803 B
[0015] [Ref. 6] Japanese Patent Application Publication No.
1997-291454 A
SUMMARY OF THE INVENTION
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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 of 1 to 16 per each first fiber.
[0020] The first aspect of the invention can be implemented in
preferable manners as follows:
[0021] (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;
[0022] (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.
[0023] (3) one of the first and second surfaces has a slip angle of
25.degree. to 40.degree.. The nonwoven fabric having the slip angle
of such a range is suitable for a wearable article and other
products.
[0024] (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.
[0025] 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.
[0026] 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 first fibrous
component made of the first 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 500
g/m.sup.2, forming the web with a plurality of attaching areas
intermittently formed in at least one direction of the machine
direction and a cross direction 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
first 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.
[0027] The second aspect of the invention can be implemented in
preferable manners as follow:
[0028] (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 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.
[0029] (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 fiber.
[0030] (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.
[0031] (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.
[0032] In the present invention the slip angle is measured in an
apparatus depicted by an accompanying drawing, i.e. FIG. 11. The
measuring method of the slip angle is included in the explanation
of FIG. 11.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a perspective view showing a typical embodiment of
a nonwoven fabric;
[0034] FIG. 2 is a photograph showing cross-sections of conjugated
fibers;
[0035] FIG. 3 is a diagram tracing the conjugated fibers in
photograph of FIG. 2;
[0036] FIG. 4 is a scale-enlarged plan view showing a part of FIG.
1;
[0037] FIG. 5 is a sectional view taken along a line V-V in FIG.
4;
[0038] FIG. 6 is a scale-enlarged portion of FIG. 5;
[0039] FIG. 7 is a view similar to FIG. 5 illustrating a relative
position of the respective fibers when the nonwoven fabric is
stretched;
[0040] FIG. 8 is a photograph similar to FIG. 2 showing a preferred
embodiment of the present invention;
[0041] FIG. 9 is a diagram similar to FIG. 3 showing the preferred
embodiment;
[0042] FIGS. 10A, 10B and 10C are sectional views of the conjugated
fibers; and
[0043] FIG. 11 is a side view of a tester.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] 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.
[0045] 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, 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 fiber component 21
and a fiber component 22 (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.
[0046] 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 11a (see FIG. 5) and wrap around this
elastic fiber 11a. In the vicinity of the areas 16a and 16b, the
inelastic fibers 12a, 12b, 12c are branched and spaced apart from
the elastic fiber 11a. 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 11a, and the elastic fiber 11a 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 11a to the number of the
inelastic fibers 12a, 12b, 12c is approximately 1:3. The elastic
fiber 11a 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 11a
and the inelastic fibers 12a, 12b, 12c. In other words, a ratio of
the ends of the elastic fibers 11a to the ends of the inelastic
fibers 12a, 12b, 12c exposed on the cut surface 4a is approximately
1:3.
[0047] 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 a straight
distance between the neighboring attaching areas 16a and 16b on the
elastic fiber 11a is 0.5-10 m, 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 11a.
[0048] 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 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.
[0049] FIG. 2 is a photograph showing cross-sections of conjugated
fibers 13a used to make the nonwoven fabric 1 and 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 .mu.m to 30 .mu.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 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.
[0050] 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 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.
[0051] 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 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 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.
[0052] An example of the elastic fibrous component 21 is a
thermoplastic polyurethane whose melt viscosity based on JIS K 7311
is 23.times.10.sup.3-180.times.10.sup.3 poise. An example of the
inelastic fiber component 22 is a polypropylene whose Melt Flow
Rate (MFR) is 30 at 230.degree. C. and 2.16 kg/cm.sup.2. 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 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.
[0053] 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/m.sup.2 to 500 g/m.sup.2. In the
course of making such a web, the attaching areas 16 depicted in
FIG. 1 in which the conjugated fibers 13a are 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
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.
[0054] FIG. 4 is a scale-enlarged plan view showing the elastic
fibers 11a 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 11a separated from
the inelastic fibers 12a, 12b, 12c, the elastic fiber 11a describes
a substantially straight line while the inelastic fibers 12a, 12b,
12c describe various curves. The inelastic fiber 12b are
intersecting the elastic fiber 11a so as to provide crossing
points. At the crossing points the elastic fiber 11a lies inside
and the inelastic fiber 12b lies outside in the thickness direction
of the nonwoven fabric 1. On the cut surface shown in FIG. 5, the
inelastic fibers 12a, 12b, 12c are distributed around the elastic
fiber 11a so as to surround the elastic fiber 11a.
[0055] FIG. 6 is a scale-enlarged perspective view of the elastic
fiber 11a of FIG. 5. The circumferential surface of the elastic
fiber 11a is defined by first curved surface portions 61 each
radially bulging outward from an axis of the elastic fiber 11a with
a relatively small curvature radius and second curved surface
portions 62 each radially depressed toward the axis of the elastic
fiber 11a so that these first and second curved surface portions
61, 62 alternately appear on the circumferential surface of the
elastic fiber 11a. 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 11a. 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.
[0056] With a wearable article made of the nonwoven fabric 1
including the elastic fiber 11 and the inelastic fiber 12 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 11a. Consequently, a touch and slip properties of
the nonwoven fabric 1 are similar to those of the inelastic fiber
12. This is very true, when the number of the inelastic fibers 12
intersecting the elastic fiber 11a is relatively large as in the
case depicted in FIG. 4 and the elastic fiber 11a 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 11a 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 11a 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 11a, the surface area of the elastic fiber 11a coming
in contact with the skin 69 is substantially reduced. The smaller
the surface area of the elastic fiber 11a possibly coming in
contact with the skin 69 is, the higher the smooth touch and slip
properties of the nonwoven fabric 1 to the article wearer's skin 69
are. Even if the elastic fiber 11a 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 11a 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.
[0057] 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 11a
as the elastic fiber 11a is stretched in the direction A so that
these inelastic fibers 12a, 12b, 12c may closely surround the
elastic fiber 11a 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.
[0058] FIGS. 8 and 9 are views similar to FIGS. 2 and 3,
exemplarily showing the conjugated fiber 13a suitably used in the
present invention. This conjugated fiber 13a has a diameter of
about 15.mu. 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
separably 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
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 the nonwoven fabric 1
depicted in FIG. 1.
[0059] 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.
[0060] FIGS. 10A, 10B and 10C exemplarily illustrate the
cross-sections of the conjugated fibers 13a. The conjugated fiber
13a depicted in FIG. 10A 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. 10B, 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.
10C, 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.
[0061] 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 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 10 g/cm.sup.2 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 .alpha. increases at a rate of 2.degree./sec until the block
72 begins to slip over the upper surface of the plate 71. The angle
.alpha. at which the block 72 begins to slip is defined as a slip
angle .alpha..sub.s. The smaller the value of .alpha..sub.s 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% cotton exhibit the
slip angle .alpha..sub.s in a range of about 21.degree. to about
25.degree..
[0062] TABLE 1 indicates the slip angle .alpha..sub.s 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 having a basis weight of 50 g/m.sup.2 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/m.sup.2 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 mm.sup.2 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
.alpha..sub.s 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 .alpha..sub.s 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 .alpha..sub.s of the
upper surface 2 and/or the lower surface 3 is controlled preferably
in a range of 25.degree. to 40.degree..
[0063] In order to control the slip angle .alpha..sub.s 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% of the circumferential
length of this conjugated fiber 13a.
1 TABLE 1 Length occupied by polypropylene in the whole
Constituents of peripheral conjugated fiber (wt %) length of Slip
Thermoplastic conjugate angle polyurethane Polypropylene fiber (%)
.alpha..sub.s 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
[0064] The nonwoven fabric of the present invention can be used
industrially for disposable wearable articles and the nonwoven
fabric can be industrially manufactured through the manufacturing
process of the present invention.
[0065] The nonwoven fabric according to the present invention, 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.
[0066] 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 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.
* * * * *