U.S. patent application number 09/949078 was filed with the patent office on 2002-03-14 for fine-fibers-dispersed nonwoven fabric, process and apparatus for manufacturing same, and sheet material containing same.
This patent application is currently assigned to JAPAN VILENE CO., LTD.. Invention is credited to Kawabe, Masaaki, Minami, Akinori.
Application Number | 20020031967 09/949078 |
Document ID | / |
Family ID | 18758623 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020031967 |
Kind Code |
A1 |
Minami, Akinori ; et
al. |
March 14, 2002 |
Fine-fibers-dispersed nonwoven fabric, process and apparatus for
manufacturing same, and sheet material containing same
Abstract
Disclosed is a fine-fibers-dispersed nonwoven fabric comprising
dispersed fine fibers having a fiber diameter of 4 .mu.m or less
and a fiber length of 3 mm or less, wherein an adhesion rate of
substances adhered to the nonwoven fabric is 0.5 mass % or less.
Further, a process and an apparatus for manufacturing the
fine-fibers-dispersed nonwoven fabric, as well as a sheet material
comprising the fine-fibers-dispersed nonwoven fabric are also
disclosed.
Inventors: |
Minami, Akinori; (Ibaraki,
JP) ; Kawabe, Masaaki; (Ibaraki, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3213
US
|
Assignee: |
JAPAN VILENE CO., LTD.
|
Family ID: |
18758623 |
Appl. No.: |
09/949078 |
Filed: |
September 10, 2001 |
Current U.S.
Class: |
442/340 ;
442/363 |
Current CPC
Class: |
D04H 1/54 20130101; Y10T
442/64 20150401; Y10T 442/614 20150401; D04H 1/732 20130101 |
Class at
Publication: |
442/340 ;
442/363 |
International
Class: |
D04H 003/00; D04H
005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 8, 2000 |
JP |
2000-272523 |
Claims
1. A fine-fibers-dispersed nonwoven fabric comprising fine fibers
having a fiber diameter of 4 .mu.m or less and a fiber length of 3
mm or less in a dispersed state, wherein an adhesion rate of
substances adhered to said nonwoven fabric is 0.5 mass % or
less.
2. The fine-fibers-dispersed nonwoven fabric according to claim 1,
wherein the adhesion rate of substances adhered is 0.08 mass % or
less.
3. The fine-fibers-dispersed nonwoven fabric according to claim 1,
wherein the fine fibers contained in the nonwoven fabric are not
substantially entangled.
4. The fine-fibers-dispersed nonwoven fabric according to claim 1,
wherein the fiber diameter of the fine fiber is 2 .mu.m or
less.
5. The fine-fibers-dispersed nonwoven fabric according to claim 1,
wherein the fine fibers are formed from island components remaining
after removing a sea component from islands-in-sea type fibers.
6. The fine-fibers-dispersed nonwoven fabric according to claim 1,
wherein the fine fibers are formed from one or more organic
components.
7. The fine-fibers-dispersed nonwoven fabric according to claim 1,
wherein the fine fibers are fused.
8. A process for manufacturing a fine-fibers-dispersed nonwoven
fabric comprising the steps of: ejecting aggregates of fine fibers
having a fiber diameter of 4 .mu.m or less and a fiber length of 3
mm or less, or a group of the aggregates, and/or mechanically
dividable fibers capable of generating fine fibers having a fiber
diameter of 4 .mu.m or less and a fiber length of 3 mm or less, or
aggregates of the mechanically dividable fibers, from a nozzle into
a gas by an action of a compressed gas, to thereby divide the
aggregates or the group thereof into the fine fibers, and/or divide
the mechanically dividable fibers or the aggregates thereof into
the fine fibers, and disperse the resulting fine fibers; collecting
the dispersed fine fibers to form a fiber web; and bonding the
fiber web to obtain the fine-fibers-dispersed nonwoven fabric.
9. The process according to claim 8, wherein, in addition to the
fine-fibers aggregates or the group thereof, and/or the
mechanically dividable fibers or the aggregates thereof, other
fibers or the aggregates thereof are ejected from the nozzle.
10. The process according to claim 8, wherein bundled aggregates of
fine fibers are ejected from the nozzle.
11. The process according to claim 8, wherein before supplying the
fine-fibers aggregates or the group thereof, and/or the
mechanically dividable fibers or the aggregates thereof to the
nozzle, adhered substances are removed from the fine-fibers
aggregates or the group thereof, and/or the mechanically dividable
fibers or the aggregates thereof.
12. The process according to claim 8, wherein a gas stream passing
through the nozzle is substantially a laminar flow.
13. The process according to claim 8, wherein the fine-fibers
aggregates or the group thereof, and/or the mechanically dividable
fibers or the aggregates thereof are ejected from the nozzle and
brought into collision with a colliding means placed in front of
the nozzle.
14. An apparatus for manufacturing a fine-fibers-dispersed nonwoven
fabric comprising (1) a nozzle capable of ejecting aggregates of
fine fibers having a fiber diameter of 4 .mu.m or less and a fiber
length of 3 mm or less, or a group of the aggregates, and/or
mechanically dividable fibers capable of generating fine fibers
having a fiber diameter of 4 .mu.m or less and a fiber length of 3
mm or less, or aggregates of the mechanically dividable fibers,
into a gas by an action of a compressed gas; (2) a means for
supplying the compressed gas to the nozzle; (3) a dispersing
chamber for dividing the fine-fibers aggregates or the group
thereof, and/or the mechanically dividable fibers or the aggregates
thereof ejected from the nozzle into a gas by an action of the
compressed gas into the fine fibers, and dispersing the fine
fibers; (4) a support on which the fine fibers dispersed in the gas
in the dispersing chamber are collected to form a fiber web; and
(5) a thermal fusing means for heating the fiber web on the
support.
15. A sheet material comprising at least one layer of a
fine-fibers-dispersed nonwoven fabric layer containing dispersed
fine fibers having a fiber diameter of 4 .mu.m or less and a fiber
length of 3 mm or less, wherein an adhesion rate of substances
adhered to said nonwoven fabric layer is 0.5 mass % or less.
16. The sheet material according to claim 15, further comprising
one or more reinforcing layers.
17. A process for manufacturing a sheet material comprising the
steps of: ejecting aggregates of fine fibers having a fiber
diameter of 4 .mu.m or less and a fiber length of 3 mm or less, or
a group of the aggregates, and/or mechanically dividable fibers
capable of generating fine fibers having a fiber diameter of 4
.mu.m or less and a fiber length of 3 mm or less, or aggregates of
the mechanically dividable fibers, from a nozzle into a gas by an
action of a compressed gas, to thereby divide the aggregates or the
group thereof into the fine fibers, and/or divide the mechanically
dividable fibers or the aggregates thereof into the fine fibers,
and disperse the resulting fine fibers; collecting the dispersed
fine fibers on a reinforcing substrate to form a fiber web on the
reinforcing substrate; and bonding the fiber web, and the fiber web
and the reinforcing substrate to obtain the sheet material
comprising the fine-fibers-dispersed nonwoven fabric layer and the
reinforcing layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a fine-fibers-dispersed
nonwoven fabric, a process and an apparatus for manufacturing the
same, as well as a sheet material comprising the same.
[0003] 2. Description of the Related Art
[0004] Many functions can be imparted to a nonwoven fabric by
appropriately combining a selection of fibers used, processes for
manufacturing a fiber web, and/or processes for bonding a fiber
web, and therefore, the nonwoven fabric has wide applications. For
example, a nonwoven fabric composed of fine fibers having a fiber
diameter of 4 .mu.m or less and a fiber length of 3 mm or less has
excellent filtering characteristics, and thus, can be preferably
used as a gas or liquid filter. Further, the nonwoven fabric has a
good pliability, and thus, can be preferably used as an interlining
cloth.
[0005] One of the conventional processes for manufacturing such a
nonwoven fabric composed of fine fibers having a fiber diameter of
4 .mu.m or less and a fiber length of 3 mm or less comprises the
steps of forming a fiber web from islands-in-sea type composite
fibers, namely, fibers prepared by dispersing resin components
(islands components), difficult to be removed by a particular
solvent, into a resin component (sea component) capable of being
removed by the particular solvent, in accordance with a carding
method or an air-laid method, entangling fibers by an action of
needles or a water jet to form an entangled fiber web, and then,
removing therefrom the sea components of the islands-in-sea type
composite fibers by the solvent to generate the fine fibers of the
island components. This process can provide a nonwoven fabric
composed of fine fibers having a fiber diameter of 4 .mu.m or less
and a fiber length of 3 mm or less. Nevertheless, the fine fibers
are present as bundles in the nonwoven fabric, and thus, the
nonwoven fabric is not too different from a fabric composed of
thick fibers, and therefore, the filtering characteristics or
pliability are not sufficient.
[0006] There is a known process for manufacturing a nonwoven
fabric, which process can remedy the bundles of the fine fibers.
The process comprises the steps of taking up fine fibers having a
fiber diameter of 4 .mu.m or less and a fiber length of 3 mm or
less from a slurry containing dispersed fine fibers, to form a
fiber web, and then bonding the fiber web. This process can provide
a nonwoven fabric composed of the dispersed fine fibers.
Nevertheless, the fiber web formed by taking up the fine fibers
from slurry has a high apparent density, because the fine fibers
therein are closely bonded with each other. Therefore, when the
nonwoven fabric is used as a filter, a pressure loss becomes
high.
SUMMARY OF THE INVENTION
[0007] Accordingly, the object of the present invention is to
remedy the above disadvantages of the prior art, and provide a
nonwoven fabric composed of fine fibers dispersed therein, namely,
a fine-fibers-dispersed nonwoven fabric, wherein the fine fibers
are in contact with each other to a lesser degree.
[0008] The inventors of the present invention engaged in intensive
research to remedy the above disadvantages of the prior art, and as
a result, found the reasons for the high apparent density of the
fiber web prepared by taking up from slurry. First, surface-active
agents are used to disperse the fine fibers, and/or sizing agents
are used to fix the fine fibers to each other. The surface-active
agents and/or the sizing agents are adhered on the surfaces of the
fine fibers, and the adhered surface-active agents and/or the
adhered sizing agents serve to raise a degree of adhesion of the
fine fibers. Secondly, when the fiber web is formed by taking up
from a slurry, a solvent (such as water) dispersing the fine fibers
is removed in such a way that the solvent moves in a direction of
thickness of the fiber web. Therefore, the fine fibers are
orientated in a direction crossing at right angles to the thickness
direction of the fiber web, and are closely adhered to each other.
The present invention is based on the above findings.
[0009] Other objects and advantages of the present invention will
be apparent from the following description.
[0010] In accordance with the present invention, there is provided
a fine-fibers-dispersed nonwoven fabric comprising fine fibers
having a fiber diameter of 4 .mu.m or less and a fiber length of 3
mm or less in a dispersed state, wherein an adhesion rate of
substances adhered to the nonwoven fabric is 0.5 mass % or
less.
[0011] The fine-fibers-dispersed nonwoven fabric of the present
invention includes a very small amount of adhered substances, such
as the surface-active agents or sizing agents, and thus, the degree
of adhesion of the fine fibers is at a lower level. Therefore, the
fine-fibers-dispersed nonwoven fabric contains an appropriate
amount of voids having an appropriate size, and a pressure loss of
the fine-fibers-dispersed nonwoven fabric is small. Further, in the
fine-fibers-dispersed nonwoven fabric of the present invention, the
fine fibers are not present in the form of bundles but in the
dispersed state, and thus, the fine-fibers-dispersed nonwoven
fabric has excellent properties, such as filtering characteristics
and pliability, due to the containing of the fine fibers.
Therefore, the fine-fibers-dispersed nonwoven fabric of the present
invention contains an appropriate amount of voids having an
appropriate size, exhibits a small pressure loss, and has excellent
properties, such as filtering characteristics and pliability, due
to the containing of the fine fibers.
[0012] In accordance with the present invention, there is provided
a process for manufacturing a fine-fibers-dispersed nonwoven fabric
comprising the steps of:
[0013] ejecting aggregates of fine fibers having a fiber diameter
of 4 .mu.m or less and a fiber length of 3 mm or less, or a group
of the aggregates, and/or mechanically dividable fibers capable of
generating fine fibers having a fiber diameter of 4 .mu.m or less
and a fiber length of 3 mm or less, or aggregates of the
mechanically dividable fibers, from a nozzle into a gas by an
action of a compressed gas, to thereby divide the aggregates or the
group thereof into the fine fibers, and/or divide the mechanically
dividable fibers or the aggregates thereof into the fine fibers,
and disperse the resulting fine fibers;
[0014] collecting the dispersed fine fibers to form a fiber web;
and
[0015] bonding the fiber web to obtain the fine-fibers-dispersed
nonwoven fabric.
[0016] In the process of the present invention, a solvent as a
medium used for dispersing the fine fibers in the conventional
process is not required, as the fine fibers are dispersed into a
gas, and thus, it is not necessary to use the surface-active agents
or sizing agents required in the process using a solvent as a
dispersing medium. Therefore, according to the process of the
present invention, the nonwoven fabric wherein an adhesion rate of
the substances adhered to the fine-fibers-dispersed nonwoven fabric
is 0.5 mass % or less, i.e., the nonwoven fabric containing the
fine fibers adhered to each other to a lesser degree, can be easily
prepared. Further, the nonwoven fabric containing the uniformly
dispersed fine fibers can be easily prepared, because the
fine-fibers-dispersed nonwoven fabric is prepared by ejecting the
fine-fibers aggregates (particularly, the bundled aggregates) or
the group thereof, and/or the mechanically dividable fibers or the
aggregates thereof, from the nozzle into the gas by an action of
the compressed gas, to thereby divide the aggregates or the group
thereof into the fine fibers, and/or divide the mechanically
dividable fibers or the aggregates thereof into the fine fibers,
and disperse the resulting fine fibers.
[0017] In accordance with the present invention, there is also
provided an apparatus for manufacturing a fine-fibers-dispersed
nonwoven fabric comprising
[0018] (1) a nozzle capable of ejecting aggregates of fine fibers
having a fiber diameter of 4 .mu.m or less and a fiber length of 3
mm or less, or a group of the aggregates, and/or mechanically
dividable fibers capable of generating fine fibers having a fiber
diameter of 4 .mu.m or less and a fiber length of 3 mm or less, or
aggregates of the mechanically dividable fibers, into a gas by an
action of a compressed gas;
[0019] (2) a means for supplying the compressed gas to the
nozzle;
[0020] (3) a dispersing chamber for dividing the fine-fibers
aggregates or the group thereof, and/or the mechanically dividable
fibers or the aggregates thereof ejected from the nozzle into a gas
by an action of the compressed gas into the fine fibers, and
dispersing the fine fibers;
[0021] (4) a support on which the fine fibers dispersed in the gas
in the dispersing chamber are collected to form a fiber web;
and
[0022] (5) a thermal fusing means for heating the fiber web on the
support.
[0023] In accordance with the present invention, there is also
provided a sheet material comprising at least one layer of a
fine-fibers-dispersed nonwoven fabric layer containing dispersed
fine fibers having a fiber diameter of 4 .mu.m or less and a fiber
length of 3 mm or less, wherein an adhesion rate of substances
adhered to the nonwoven fabric layer is 0.5 mass % or less.
[0024] The sheet material of the present invention contains the
layer of the fine-fibers-dispersed nonwoven fabric (hereinafter
referred to as the fine-fibers-dispersed nonwoven fabric layer),
and therefore, the fine-fibers-dispersed nonwoven fabric layer
includes a very small amount of adhered substances, such as the
surface-active agents or sizing agents, and thus, the degree of
adhesion of the fine fibers in the fine-fibers-dispersed nonwoven
fabric layer is at a lower level. Therefore, the
fine-fibers-dispersed nonwoven fabric layer contains an appropriate
amount of voids having an appropriate size, and a pressure loss of
the fine-fibers-dispersed nonwoven fabric layer is small. Further,
in the fine-fibers-dispersed nonwoven fabric layer, the fine fibers
are not present in the form of bundles but in the dispersed state,
and thus, the fine-fibers-dispersed nonwoven fabric layer has
excellent properties, such as filtering characteristics and
pliability, due to the containing of the fine fibers. Therefore,
the sheet material of the present invention contains an appropriate
amount of voids having an appropriate size, exhibits a small
pressure loss, and has excellent properties, such as filtering
characteristics and pliability, due to the containing of the fine
fibers.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1 schematically illustrates an embodiment of the
apparatus for manufacturing the fine-fibers-dispersed nonwoven
fabric of the present invention.
[0026] FIG. 2 is an electron microscope photograph of the surface
of the fine-fibers-dispersed nonwoven fabric layer in the composite
nonwoven fabric prepared in Example 4.
[0027] FIG. 3 is an electron microscope photograph of the surface
of the fine-fibers-dispersed nonwoven fabric layer in the composite
nonwoven fabric prepared in Comparative Example 2.
[0028] FIG. 4 is an electron microscope photograph of the surface
of the fine-fibers-dispersed nonwoven fabric layer in the composite
nonwoven fabric prepared in Example 5.
[0029] FIG. 5 is an electron microscope photograph of the surface
of the fine-fibers-dispersed nonwoven fabric layer in the composite
nonwoven fabric prepared in Example 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] The fine-fibers-dispersed nonwoven fabric of the present
invention contains fine fibers having a fiber diameter of 4 .mu.m
or less and a fiber length of 3 mm or less, so that excellent
properties, such as filtering characteristics or pliability, are
exhibited. When the fine-fibers-dispersed nonwoven fabric of the
present invention contains the fine fibers having a smaller fiber
diameter, the nonwoven fabric exhibits more excellent properties.
Therefore, the fiber diameter is preferably 3 .mu.m or less, more
preferably 2 .mu.m or less. In general, fibers having a smaller
fiber diameter become more pliable, and fine fibers are easily
entangled with each other. Thus, it would be more difficult to
uniformly disperse such fine fibers, and thus to obtain advantages
due to the containing of the fine fibers. On the contrary, the fine
fibers in the fine-fibers-dispersed nonwoven fabric of the present
invention are uniformly dispersed, and therefore, the above
properties are improved, with the fiber diameter of the fine fibers
becoming smaller. There is no particular lower limit of the fiber
diameter of the fine fibers, but about 0.01 .mu.m is
appropriate.
[0031] The term "fiber diameter" as used herein with respect to a
fiber having a circular cross-sectional shape means a diameter of
the circle. For a fiber having a non-circular cross-sectional
shape, a diameter of a circle having an area the same as that of
the non-circular cross-sectional shape is regarded as the
diameter.
[0032] The fine fibers forming the fine-fibers-dispersed nonwoven
fabric of the present invention have a fiber length of 3 mm or less
so that the fine fibers exhibit an excellent dispersibility. If the
fine fibers have a fiber length of more than 3 mm, a degree of
freedom thereof and the dispersibility become lowered. The fiber
length is preferably 2 mm or less. The lower limit of the fiber
length of the fine fiber is not particularly limited, but is
appropriately about 0.1 mm. The fine fibers cut into a fiber length
of 3 mm or less in such a way that they have a uniform fiber length
are preferable.
[0033] The term "fiber length" as used herein means a value
measured in accordance with JIS L 1015 (a testing method for
man-made staple fibers), the B method (an amended method for staple
diagram).
[0034] The fine fibers used in the present invention may be
prepared from any material, such as an organic or inorganic
material, for example, an organic material, such as polyamide based
resin, polyvinyl alcohol based resin, polyvinylidene chloride based
resin, polyvinyl chloride based resin, polyester based resin,
polyacrylonitrile based resin, polyolefin based resin (such as
polyethylene based resin, or polypropylene based resin),
polystyrene based resin (such as crystalline polystyrene, or
amorphous polystyrene), aromatic polyamide based resin, or
polyurethane based resin; or an inorganic material, for example,
glass, carbon, potassium titanate, silicon carbide, silicon
nitride, zinc oxide, aluminum borate, or Wollastonite.
[0035] In general, the fine fibers made of one or more organic
materials have a rigidity lower than that of the fine fibers made
of inorganic materials, and thus are softer than the latter. The
former fine fibers are easily entangled with each other, and
therefore, it is more difficult to uniformly disperse the former
fine fibers, and thus to obtain advantages due to the containing of
the fine fibers. On the contrary, the fine fibers in the
fine-fibers-dispersed nonwoven fabric of the present invention are
uniformly dispersed, and therefore, properties due to the
containing of the fine fibers made of organic materials, such as
bulkiness, hand and feel, and elasticity, are improved.
[0036] The fibers contained in the fine-fibers-dispersed nonwoven
fabric of the present invention must be bonded with each other to
maintain the shape of the nonwoven fabric. Preferably, the fine
fibers are fusible, because the shape of the nonwoven fabric can be
maintained by the fusion of the fine fibers, and the fine fibers
are rarely dropped. The fusible fine fiber may be a fiber
containing a thermoplastic resin on at least a part of the surface
of the fine fiber. The material for the surface of the fine fiber
may be, for example, a crystalline thermoplastic resin, such as a
polyolefin based resin (such as polyethylene based resin, or
polypropylene based resin), polyvinylidene chloride based resin,
polyester based resin, polyamide based resin, crystalline
polystyrene; or an amorphous thermoplastic resin, such as polyvinyl
chloride based resin, amorphous polystyrene based resin,
polyacrylonitrile based resin, or polyvinyl alcohol based
resin.
[0037] Preferably, the fine fiber is composed of two or more
components having a melting point different from each other,
because a form or shape of the fine fiber may be maintained due to
the presence of at least one non-fusible component. When the fine
fiber is a composite fiber composed of two or more components, the
cross-sectional shape may be, for example, a sheath-core type, an
eccentric type, an islands-in-sea type, a side-by-side type, a
multiple bimetal type, or an orange type.
[0038] Preferably, each of the fine fibers has a diameter that does
not substantially change in an axial direction of the fiber,
namely, has substantially the same diameter, so that the
fine-fibers-dispersed nonwoven fabric has an excellent uniformity.
The fine fibers having substantially the same diameter that does
not substantially change in an axial direction of the fiber may be
prepared, for example, by removing sea components from
islands-in-sea type fibers obtained by a composite spinning method,
such as a method for extruding and compositing island components
into sea components under the condition that a spinning nozzle is
controlled. In general, the fine fibers prepared by removing sea
components from islands-in-sea type fibers are liable to form
bundled aggregates of the fine fibers derived from island
components, to be in close contact with each other, and easily
entangled with each other. Therefore, it would be difficult to
uniformly disperse such fine fibers, and thus to obtain advantages
due to the containing of the fine fibers. On the contrary, even in
the form of bundled aggregates the fine fibers can be uniformly
dispersed in the fine-fibers-dispersed nonwoven fabric of the
present invention, and therefore, properties due to the containing
of the fine fibers are obtained. Further, bundled aggregates of the
fine fibers prepared by removing sea components from islands-in-sea
type fibers are liable to be cohered, and thus, it would be
difficult to uniformly disperse such fine fibers. On the contrary,
even in the form of the bundled aggregates the fine fibers can be
uniformly dispersed in the fine-fibers-dispersed nonwoven fabric of
the present invention, and therefore, properties due to the
containing of the fine fibers are obtained.
[0039] The fine fibers used in the present invention may be
undrawn, but preferably are drawn, because a good mechanical
strength is thus obtained.
[0040] As above, the fine fibers are dispersed in the
fine-fibers-dispersed nonwoven fabric of the present invention, and
thus, the properties due to the containing of the fine fibers can
be obtained. An amount of the fine fibers contained in the
fine-fibers-dispersed nonwoven fabric is preferably 20 mass % or
more, more preferably 50 mass % or more, most preferably 100 mass
%, so that the properties due to the containing of the fine fibers
can be obtained.
[0041] The fine-fibers-dispersed nonwoven fabric of the present
invention may contain, in addition to the fine fibers defined as
above, (1) fibers having a fiber diameter of more than 4 .mu.m and
a fiber length of 3 mm or less, hereinafter referred to as thick
fibers, (2) fibers having a fiber diameter of 4 .mu.m or less and a
fiber length of more than 3 mm, hereinafter referred to as long
fibers, or (3) fibers having a fiber diameter of more than 4 .mu.m
and a fiber length of more than 3 mm, hereinafter referred to as
thick-long fibers. Of these fibers, the long fibers and the
thick-long fibers having a fiber length of more than 3 mm exhibit a
poor dispersibility, and may affect the dispersibility of the fine
fibers. Thus, it is preferable to use the thick fibers having a
fiber length of 3 mm or less.
[0042] The upper limit of the fiber diameter of the thick fiber
used is not particularly limited, but is appropriately about 50
.mu.m, because the uniformity of the fine-fibers-dispersed nonwoven
fabric may be affected when the fiber diameter of the thick fibers
is too thick in comparison with the fiber diameter of the fine
fibers.
[0043] The thick fibers have a fiber length of preferably 2 mm or
less, so as to have an excellent dispersibility. The lower limit of
the fiber length of the thick fiber is not particularly limited,
but is appropriately about 0.1 mm. The thick fibers, which are cut
into a fiber length of 3 mm or less in such a way that they have a
uniform fiber length, are preferable.
[0044] As the fine fibers, the thick fibers may be prepared from
any material, such as an organic or inorganic material, for
example, an organic material, such as polyamide based resin,
polyvinyl alcohol based resin, polyvinylidene chloride based resin,
polyvinyl chloride based resin, polyester based resin,
polyacrylonitrile based resin, polyolefin based resin (such as
polyethylene based resin, or polypropylene based resin),
polystyrene based resin (such as crystalline polystyrene, or
amorphous polystyrene), aromatic polyamide based resin, or
polyurethane based resin; or an inorganic material, for example,
glass, carbon, potassium titanate, silicon carbide, silicon
nitride, zinc oxide, aluminum borate, or Wollastonite.
[0045] When the thick fibers are fusible, the shape of
fine-fibers-dispersed nonwoven fabric of the present invention can
be maintained by the fusion of the thick fibers. The fusible thick
fiber may be a fiber containing a thermoplastic resin on at least a
part of the surface of the thick fiber. The material for the
surface of the thick fiber may be, for example, a crystalline
thermoplastic resin, such as polyolefin based resin (such as
polyethylene based resin, or polypropylene based resin),
polyvinylidene chloride based resin, polyester based resin,
polyamide based resin, crystalline polystyrene; or an amorphous
thermoplastic resin, such as polyvinyl chloride based resin,
amorphous polystyrene based resin, polyacrylonitrile based resin,
or polyvinyl alcohol based resin.
[0046] Preferably, the thick fiber is composed of two or more
components having a melting point different from each other,
because a form or shape of the thick fiber may be maintained due to
the presence of at least one non-fusible component, when one of the
components is fused. When the thick fiber is a composite fiber
composed of two or more components, the cross-sectional shape may
be, for example, a sheath-core type, an eccentric type, an
islands-in-sea type, a side-by-side type, a multiple bimetal type,
or an orange type.
[0047] The thick fibers may be undrawn, but preferably are drawn
because a good mechanical strength is thus obtained.
[0048] As above, the fine fibers are dispersed in the
fine-fibers-dispersed nonwoven fabric of the present invention, and
thus, the properties due to the containing of the fine fibers can
be obtained. That is, the fine fibers are not present in the form
of bundles, and thus, the properties due to the containing of the
fine fibers can be obtained.
[0049] In the fine-fibers-dispersed nonwoven fabric of the present
invention, an adhesion rate of substances (such as surface-active
agents or sizing agents) adhered to the fine-fibers-dispersed
nonwoven fabric is as low as 0.5 mass % or less, so as to prevent
the fine fibers therein from closely adhering to each other. The
above advantageous effect can be enhanced as the adhesion rate is
lowered. Therefore, the adhesion rate is preferably 0.3 mass % or
less, more preferably 0.1 mass % or less, still more preferably
0.08 mass % or less, still more preferably 0.06 mass % or less,
still further more preferably 0.04 mass % or less, most preferably
0.02 mass % or less.
[0050] The adhesion rate of the adhered substances is very low in
the fine-fibers-dispersed nonwoven fabric of the present invention,
and the possibility of a dropping of the adhered substances from
the fine-fibers-dispersed nonwoven fabric becomes very low when the
fine-fibers-dispersed nonwoven fabric is used. This can provide
various effects. For example, although a conventional nonwoven
fabric may be used as a filter for physically adsorbing and
removing dust materials contained in a fluid to be treated, the
filter per se, i.e., the conventional nonwoven fabric per se,
generally generates pollutants, and its role as a filter is
deteriorated. On the contrary, in the fine-fibers-dispersed
nonwoven fabric of the present invention or the sheet material
containing at least one fine-fibers-dispersed nonwoven fabric layer
of the present invention, the adhered substances are present in a
small amount. Therefore, the possibility of the dropping of the
adhered substances is very low, and the fine-fibers-dispersed
nonwoven fabric of the present invention or the sheet material of
the present invention may be preferably used as a filter.
[0051] The adhesion rate of the adhered substances means a
percentage of a mass of the adhered substances to a mass of the
fine-fibers-dispersed nonwoven fabric, namely, a value calculated
from the equation (1):
A=(ms/mf).times.100 (1)
[0052] wherein A denotes the adhesion rate (%), ms denotes a mass
(g) of the adhered substances, and mf denotes a mass (g) of the
fine-fibers-dispersed nonwoven fabric.
[0053] It is difficult to lower an adhesion rate of adhered
substances to a level of 0.5 mass % or less by forming a fiber web
by, for example, a wet-laid method, from the fine fibers used in
the present invention, using surface-active agents or sizing
agents, and then treating the web with a water jet.
[0054] The term "adhered substances" as used herein includes an
extract (hereinafter referred to as a hot-water extract) obtained
by dipping the fine-fibers-dispersed nonwoven fabric in hot water
at, for example, 80 to 100.degree. C. for 15 minutes; and an
extract (hereinafter referred to as a hot-methanol extract)
obtained by dipping the fine-fibers-dispersed nonwoven fabric in
hot methanol for 15 minutes. The hot-water extract is, for example,
a sizing agent, such as acrylamide, sodium polyacrylate, sodium
polyalginate, polyethylene oxide, methyl cellulose,
carboxymethylcellulose, hydroxymethylcellulose, or polyvinyl
alcohol. The hot-methanol extract is, for example, a surface-active
agent, i.e., a compound having one or more hydrophilic groups and
one or more lipophilic groups, such as a nonionic surface-active
agent.
[0055] The fine-fibers-dispersed nonwoven fabric of the present
invention may be a unilayered fabric or contain two or more
fine-fibers-dispersed layers. When the fabric contains two or more
fine-fibers-dispersed layers, various characteristics may be
imparted. For example, filtering characteristics may be enhanced if
the fabric contains two or more fine-fibers-dispersed layers, the
contents of the fine fibers therein being different from each
other.
[0056] The fibers, such as the fine fibers and thick fibers,
forming the fine-fibers-dispersed nonwoven fabric of the present
invention are bonded preferably by a fusion of the fibers, such as
the fine fibers and thick fibers. This is because, when the fibers
(such as the fine fibers and thick fibers) are bonded by fusion,
the fine-fibers-dispersed nonwoven fabric is bonded without
disturbing the arrangement of the fine fibers, the fine fibers are
not closely adhered, and the fine-fibers-dispersed nonwoven fabric
contains an appropriate amount of voids having an appropriate size.
Further, it is preferable that the fine fibers are not entangled,
because the fine fibers are liable to be closely adhered if
entangled.
[0057] The fine-fibers-dispersed nonwoven fabric of the present
invention may be composed only of the layer containing the
dispersed fine fibers, but the strength of such a fabric is liable
to be weak, and thus, the fine-fibers-dispersed nonwoven fabric of
the present invention may contain one or more reinforcing layers,
to enhance the strength. Materials forming the reinforcing layer
are, for example, threads, a net, a woven fabric, a knitted fabric,
a fiber web, or a usual nonwoven fabric.
[0058] An apparent density of the fine-fibers-dispersed nonwoven
fabric of the present invention can be as low as 0.005 g/cm.sup.3,
because the fine fibers are not closely adhered to each other. The
apparent density of the fine-fibers-dispersed nonwoven fabric of
the present invention may be about 0.005 to 0.1 g/cm.sup.3.
[0059] The term "apparent density" as used herein means a value
calculated by dividing a mass per unit area (g/cm.sup.2) by a
thickness (cm). The thickness is measured when no load is applied.
The mass per unit area is measured by a method disclosed in
Japanese Industrial Standards (JIS) L1085: 1998, 6.2.
[0060] The fine-fibers-dispersed nonwoven fabric of the present
invention has an excellent uniformity, and the mass per unit area
of the fine-fibers-dispersed nonwoven fabric of the present
invention can be as low as 1 g/m.sup.2. The mass per unit area of
the fine-fibers-dispersed nonwoven fabric of the present invention
can be about 1 to 100 g/m.sup.2.
[0061] The fine-fibers-dispersed nonwoven fabric of the present
invention contains the fine fibers, and exhibits various excellent
characteristics, such as filtering characteristics, pliability,
wiping-off capacity, and/or opacifying properties. Therefore, the
fine-fibers-dispersed nonwoven fabric of the present invention, or
the sheet material containing at least one fine-fibers-dispersed
nonwoven fabric layer of the present invention, may be used in many
applications, for example, as a gas or liquid filter (such as a
HEPA filter, a bag filter, or a cartridge filter), a substrate for
a deodorizing filter, a substrate for a mask (such as a surgical
operation mask or an industrial mask), a filter press, a drape for
a surgical operation, a gown for a surgical operation, a diaper
cover, a battery separator, or a water absorption sheet (for
example, for a moistening device).
[0062] The fine-fibers-dispersed nonwoven fabric of the present
invention may be produced by, for example, the following
method.
[0063] In the first place, the aggregates (particularly, bundled
aggregates) of fine fibers having a fiber diameter of 4 .mu.m or
less and a fiber length of 3 mm or less, or a group of the
aggregates (particularly, the bundled group of the bundled
aggregates), and/or mechanically dividable fibers capable of
generating fine fibers having a fiber diameter of 4 .mu.m or less
and a fiber length of 3 mm or less, or aggregates (particularly,
bundled aggregates) of the mechanically dividable fibers are
prepared. When the adhesion rate of the substances adhered to the
fine-fibers aggregates or the group thereof, and/or the
mechanically dividable fibers or the aggregates thereof is 0.5 mass
% or less (preferably 0.3 mass % or less, more preferably 0.1 mass
% or less, still more preferably 0.08 mass % or less, still more
preferably 0.06 mass % or less, still more preferably 0.04 mass %
or less, most preferably 0.02 mass % or less), the
fine-fibers-dispersed nonwoven fabric of the present invention may
be easily produced.
[0064] The fine-fibers aggregates with a low adhesion rate or the
group thereof with a low adhesion rate, or the mechanically
dividable fibers with a low adhesion rate or the aggregates thereof
with a low adhesion rate may be prepared, for example, by washing
commercially available fine-fibers aggregates or the group thereof,
or the mechanically dividable fibers or the aggregates thereof with
a solvent such as acetone to a level of 0.5 mass % or less with
respect to the adhesion rate. Alternatively, the fine-fibers
aggregates with a low adhesion rate or the group thereof with a low
adhesion rate may be prepared, for example, by extracting and
removing sea component from islands-in-sea type fibers obtained by
a composite spinning method or a melt blend spinning method or the
group thereof. Further, the adhesion rate of the resulting
aggregates or the group thereof may be lowered by washing with a
solvent such as acetone after extracting and removing the sea
component from the islands-in-sea type fibers. When the adhered
substances are removed, static electrical charges are prone to be
generated on the surfaces of the fine fibers, and the fine fibers
are easily dispersed due to an electrical repulsion between the
fine fibers.
[0065] When the fine fibers in the fine-fibers-aggregates or the
group thereof used are in an entangled state, a uniform dispersion
of the fine fibers would become difficult even by an action of a
compressed gas as mentioned below, or the fine fibers must be
treated with the compressed gas many times. Therefore, it is
preferable to use the aggregates wherein the fine fibers are not
entangled, or the group of such aggregates. For example, it is
preferable not to use fine fibers aggregates prepared by beating
mechanically dividable fibers by a beater, pulps beaten by a
beater, or fine fibers aggregates prepared by a flash spinning
method, because the fine fibers are entangled to each other.
Further, it is possible to use the mechanically dividable fibers
capable of generating fine fibers having a fiber diameter of 4
.mu.m or less and a fiber length of 3 mm or less by an action of
the compressed gas, or aggregates of the mechanically dividable
fibers, such as whole aromatic polyamide fine fibers or the
aggregates thereof, or cellulose fibers prepared by a solvent
extraction method, or the aggregates thereof. Furthermore, it is
preferable that the thick fibers or the aggregates thereof used are
washed with acetone or the like to prepare the thick fibers or the
aggregates thereof with a lower adhesion rate.
[0066] Thereafter, the fine-fibers aggregates or the group thereof,
and/or the mechanically dividable fibers or the aggregates thereof,
and optionally the thick fibers or the aggregates thereof, are
supplied to a nozzle while an action of the compressed gas is
applied to the fine-fibers aggregates or the group thereof, and/or
the mechanically dividable fibers or the aggregates thereof, and
optionally the thick fibers or the aggregates thereof, so that they
are ejected from the nozzle to a gas to thereby divide and disperse
the fine fibers from the fine-fibers aggregates or the group
thereof, and/or divide the mechanically dividable fibers or the
aggregates thereof into the fine fibers, and dispersing the
resulting fine fibers. When the thick fibers or the aggregates
thereof are used, they are supplied to a nozzle to thereby disperse
the thick fibers, or divide and disperse the thick fibers from the
aggregates.
[0067] Preferably, the gas stream passing through the nozzle is
substantially a laminar flow. When the gas stream passing through
the nozzle is substantially a laminar flow, the fine fibers are
rarely entangled, and thus are easily dispersed. In general, the
fine fibers passed through the nozzle are prone to be entangled, if
the fiber diameter of the fine fibers passed through the nozzle is
as thin as 4 .mu.m or less, particularly 2 .mu.m or less, and thus
have a low rigidity, i.e., high pliability, the fine fibers are in
the form of the bundled aggregates or the group of the bundled
aggregates, particularly, the bundled aggregates derived from the
island components of the islands-in-sea type fibers, particularly
the group of such bundled aggregates, or the fine fibers are
composed of the organic materials, and thus have a low rigidity,
i.e., a high pliability. Nevertheless, the entanglement of such
fine fibers may be inhibited, using the gas stream in the form of a
substantially laminar flow. The substantially laminar flow may be
generated by using a Venturi tube as the nozzle.
[0068] The nozzle may have a constant cross-sectional area in a
direction of flow from the supplier to the ejecting opening.
Alternatively, the cross-sectional area may be continuously or
discontinuously increased or decreased in the direction of flow; or
continuously or discontinuously increased and then decreased, or
continuously or discontinuously decreased and then increased in the
direction of flow. Further, the ejected fine-fibers aggregates or
the group thereof, and/or the ejected mechanically dividable fibers
or the aggregates thereof may be brought into collision with a
colliding means, such as a baffle plate, placed in front of the
nozzle, to enhance the generating rate of the fine fibers from the
fine-fibers aggregates or the group thereof, and/or the
mechanically dividable fibers or the aggregates thereof, and the
dispersibility of the resulting fine fibers. When the gas stream
passing through the nozzle is a substantially laminar flow, it is
preferable to use the colliding means, such as the baffle plate,
for promoting the dispersion, because the laminar flow has a poor
action in the division and dispersal of the fine fibers.
[0069] Any gas may be used as the compressed gas, and a compressed
air may be preferably used for the production of the
fine-fibers-dispersed nonwoven fabric. A passing rate of the
compressed gas at the ejecting opening of the nozzle is preferably
100 m/sec or more, so that the compressed gas can sufficiently
generate the fine fibers from the bundled aggregates of the fine
fibers, or the groups of the bundled aggregates, and disperse the
resulting fine fibers, and/or sufficiently divide the mechanically
dividable fibers or the aggregates thereof into the fine fibers,
and disperse the resulting fine fibers. The gas passing rate is a
value calculated by dividing a flowing amount (m.sup.3/sec) under 1
atmosphere of the gas ejected from the nozzle by a cross-sectional
area (m.sup.2) of the ejecting opening of the nozzle. A pressure of
the compressed gas is preferably 2 kg/cm.sup.2 or more, so that the
compressed gas can sufficiently generate the fine fibers from the
bundled aggregates of the fine fibers or the group of the bundled
aggregates, and disperse the resulting fine fibers, and/or
sufficiently divide the mechanically dividable fibers or the
aggregates thereof into the fine fibers, and disperse the resulting
fine fibers.
[0070] The gas as a dispersing medium in which the fine-fibers
aggregates or the group thereof ejected from the nozzle are
dispersed, and/or the mechanically dividable fibers or the
aggregates thereof ejected from the nozzle are divided and
dispersed is not particularly limited, but preferably is an air in
view of the production of the fine-fibers-dispersed nonwoven
fabric.
[0071] When the adhesion rate of the substrates adhered to the
fine-fibers aggregates or the group thereof, and/or the
mechanically dividable fibers or the aggregates thereof is low,
static electrical charges are prone to be generated by a friction
between the-nozzle and the fine-fibers aggregates or the group
thereof, and/or the mechanically dividable fibers or the aggregates
thereof. Therefore, the fine fibers repel each other, and may be
collected under the condition that the fine fibers are not easily
closely adhered to each other.
[0072] Then, the dispersed fine fibers, and optionally thick
fibers, are collected to form a fiber web. The fine fibers may be
collected on a support such as a perforated roll or a net. The fine
fibers may be collected by allowing to fall due to gravity-drop or
by forcing the drop by use of a suction from a position under the
support. In the latter case, a strong suction results in a close
adhesion of the fine fibers as the fine fibers are taken up from
the slurry, and therefore, the suction must be appropriately
adjusted.
[0073] Subsequently, the fibers in the fiber web is bonded to form
the fine-fibers-dispersed nonwoven fabric. The bonding method is
not particularly limited, but for example, a method for fusing
fibers (i.e., the fine fibers and/or the thick fibers), a method
for adhering the fibers with a binder such as emulsion or latex, or
a method for entangling the fibers with a fluid jet such as a water
jet, or a combination thereof may be used. Of these methods, the
method for fusing the fibers is preferable, because the fine fibers
can be bonded to each other while maintaining a state in which they
are not closely adhered. It is preferable not to use the method for
entangling the fibers with the fluid jet such as the water jet,
because the fine fibers are prone to be closely adhered due to a
pressure of the fluid jet.
[0074] In addition to the basic process for manufacturing the
fine-fibers-dispersed nonwoven fabric of the present invention as
above, it is preferable that, prior to the ejection of the
fine-fibers aggregates or the group thereof, and/or the aggregates
of the mechanically dividable fibers from the nozzle by the action
of the compressed gas, the fine-fibers aggregates or the group
thereof are separated into smaller aggregates or the group thereof,
and/or the aggregates of the mechanically dividable fibers are
separated into smaller aggregates, or dispersed, mixed in a mixer
or the like, to facilitate the uniform dispersion.
[0075] Further, after the formation of the fiber web on the support
and before the bonding of the fiber web, the fiber web collected on
the support may be supplemented again to one or more nozzles, and
the fine fibers re-ejected from one or more nozzles, re-dispersed
in the gases, and re-collected on one or more supports to form a
fiber web. Such a procedure may be repeated.
[0076] It is possible to use jointly the fine-fibers aggregates or
the group thereof, and/or the mechanically dividable fibers or the
aggregates thereof so that the resulting fine-fibers-dispersed
nonwoven fabric contains two or more kinds of fine fibers having
different fiber diameters. Further, the fine-fibers aggregates or
the group thereof containing two or more kinds of fibers different
from each other with respect to a fiber diameter, the mechanically
dividable fibers or the aggregates thereof containing two or more
kinds of fibers different from each other with respect to a fiber
diameter, and/or the thick fibers or the aggregates thereof
containing two or more kinds of fibers different from each other
with respect to a fiber diameter may be supplemented to the nozzle
while continuously or discontinuously varying a composition
thereof, so that the fine-fibers-dispersed nonwoven fabric
containing layers or regions having various apparent densities in a
thickness direction of the nonwoven fabric may be prepared.
[0077] When collecting the dispersed fine fibers to form the fiber
web, the fine fibers may be collected on a reinforcing material
such as threads, a net, a woven fabric, a knitted fabric, a fiber
web, or a usual nonwoven fabric, to form a laminate. The
fine-fibers-dispersed nonwoven fabric of the present invention may
be enhanced with respect to the strength by forming the above
laminate, and thus, may be used in applications to which a strength
is required. Alternatively, the laminate can be produced by forming
the fine-fibers-dispersed nonwoven fabric of the present invention
and then laminating the resulting fine-fibers-dispersed nonwoven
fabric and a reinforcing material such as threads, a net, a woven
fabric, a knitted fabric, a fiber web, a usual nonwoven fabric, or
a film, to obtain the above advantages.
[0078] After the formation of the fine-fibers-dispersed nonwoven
fabric of the present invention, the nonwoven fabric may be
treated, for example, electrostatically charged. Further, a water
repellency or hydrophilicity may be imparted.
[0079] The apparatus for manufacturing the fine-fibers-dispersed
nonwoven fabric of the present invention will be described
hereinafter referring to FIG. 1 schematically illustrating an
embodiment thereof. In this connection, the apparatus will be
explained when the aggregates (particularly, the bundled
aggregates) of fine fibers having a fiber diameter of 4 .mu.m or
less and a fiber length of 3 mm or less are used.
[0080] The fine fibers having a fiber diameter of 4 .mu.m or less
and a fiber length of 3 mm or less are incorporated into a mixing
apparatus (such as a mixer) 10 in the form of the bundled
aggregates of the fine fibers aggregates, optionally together with
the thick fibers or the aggregates thereof. in the mixing apparatus
10, the bundled aggregates are divided into smaller bundled
aggregates, or the fine fibers are dispersed, loosened, or
mixed.
[0081] The loosened or mixed fine fibers and/or bundled aggregates
(and optionally the thick fibers and/or the aggregates thereof) are
supplied from the mixing apparatus 10 via a supplying tube 11 to a
nozzle 30. An appropriate conveying gas from a conveying-gas
supplying apparatus (not shown) placed on the mixing apparatus 10
may be used. A compressed gas is introduced from a compressed-gas
inlet 20 into the supplying tube 11 at an inside position from and
near to the nozzle 30. By an action of the compressed gas, bundled
aggregates (and optionally the thick fibers and/or the aggregates
thereof) are conveyed from the mixing apparatus 10 via the
supplying tube 11 to the nozzle 30, and vigorously ejected from the
nozzle 30 into a gas 40a in a dispersing chamber 40. Upon the
ejection into the gas 40a, and the fine fibers 70 are generated
from the bundled aggregates and dispersed in the dispersing chamber
40, by an interaction of a difference of an atmospheric pressure in
the nozzle 30 and that in the gas 40a, and a turbulent flow formed
between the ejected compressed gas and the gas 40a. Further, the
dispersion of the fine fibers 70 ejected from the nozzle 30 is
facilitated by bringing the fine fibers 70 into collision with a
wall 45 of the dispersing chamber 40. The wall 45 serves as a
colliding means. Further, a colliding means, such as a baffle
plate, can be located between the ejecting opening of the nozzle 30
and the wall 45. A distance between the ejecting opening of the
nozzle 30 and a flat region in the colliding means to be used for
the colliding is preferably 1 to 100 mm, more preferably 5 to 40
mm, still more preferably 5 to 30 mm, still more preferably 10 to
30 mm, most preferably 10 to 20 mm.
[0082] The fine fibers 70 dispersed in the gas 40a in the
dispersing chamber 40 fall down in the dispersing chamber 40 and
are collected on a support 50 of a net mounted on a bottom of the
dispersing chamber 40 to form a fiber web 80. In the apparatus for
manufacturing the fine-fibers-dispersed nonwoven fabric of the
present invention as shown in FIG. 1, a gas suction apparatus 60
can be placed under the support 50 mounted on the bottom of the
dispersing chamber 40 to suck the gas 40a in the dispersing chamber
40 and facilitate the collection of the fine fibers 70. The inside
of the dispersing chamber 40 may be or may not be hermetically
sealed from the outside.
[0083] The support 50 for collecting the fiber web 80 thereon is a
rotating endless belt which conveys the fiber web 80 to supplying
tubes 12, 13 in a direction of an arrow a in FIG. 1. Then, the
fiber web 80 is similarly supplied via supplying tubes 12, 13 to
nozzles 31, 32. The fiber web may be re-supplied to two nozzles as
shown in FIG. 1, or to one nozzle or three or more nozzles.
Alternatively, when a sufficient dispersion is achieved, the fiber
web may be directly conveyed to a thermal fusing apparatus 90 as
mentioned below.
[0084] A compressed gas is also introduced from compressed-gas
inlets 21, 22 into each of the supplying tubes 12, 13 at an inside
position from and near to each of the nozzles 31, 32. By an action
of the compressed gases, the fine fibers (and optionally the thick
fibers) supplied from the fiber web 80 are conveyed via the
supplying tubes 12, 13 to the nozzles 31, 32, and vigorously
ejected from the nozzles 31, 32 into gases 41a, 42a in dispersing
chambers 41, 42, respectively. Upon the ejections, the fine fibers
71, 72 are dispersed, respectively. Further, the dispersion of each
of the fine fibers 71, 72 ejected from the nozzles 31, 32 is
facilitated by bringing the fine fibers 71, 72 into collision with
walls 46, 47 of the dispersing chambers 41, 42, respectively. The
walls 46, 47 serve as a colliding means. Further, colliding means
can be located between the ejecting openings of the nozzles 31, 32
and the walls 46, 47.
[0085] The fine fibers 71, 72 dispersed in the gases 41a, 42a in
the dispersing chambers 41, 42 fall down in the dispersing chambers
41, 42, respectively and are collected on a support 51 of a net
mounted on the bottoms of the dispersing chambers 41, 42. More
particularly, the fine fibers 71 dispersed in the gas 41a in the
dispersing chamber 41 fall down in the dispersing chamber 41 and
are collected on the support 51 to form a unilayered fiber web 81.
Then, the unilayered fiber web 81 is conveyed by a rotating endless
belt support 51 to the dispersing chamber 42 in a direction of an
arrow b in FIG. 1. The fine fibers 72 dispersed in the gas 42a in
the dispersing chamber 42 fall down in the dispersing chamber 42
and are collected on the unilayered fiber web 81 carried on the
support 51 to form a laminated fiber web 82. The resulting
laminated fiber web 82 does not have a clear bi-layered structure,
because the fine fibers of the unilayered fiber web 80 are
re-dispersed.
[0086] In the apparatus for manufacturing the fine-fibers-dispersed
nonwoven fabric of the present invention as shown in FIG. 1, a gas
suction apparatus 61 can be placed under the support 51 which is
mounted on the bottoms of the dispersing chambers 41, 42 to suck
the gases 41a, 42a in the dispersing chambers 41, 42 and facilitate
the collection of the fine fibers 71, 72. The support 51 and the
gas suction apparatus 61 can be placed for a plurality of
dispersing chambers as shown in FIG. 1, but may be placed for each
of a plurality of dispersing chambers, respectively.
[0087] Thereafter, the laminated fiber web 82 is conveyed by the
endless belt support 51 to the thermal fusing apparatus 90 where
the fine fibers, and optionally the thick fibers, are fused by an
action of heat to form a heat-fused nonwoven fabric 83. The
resulting heat-fused nonwoven fabric 83 is reeled up on a reeling
machine 100.
[0088] The sheet material of the present invention comprises at
least one layer of the above-mentioned fine-fibers-dispersed
nonwoven fabric. That is, the sheet material of the present
invention may be a unilayered sheet composed only of the
above-mentioned fine-fibers-dispersed nonwoven fabric layer, or may
contain one or more layers of the above-mentioned
fine-fibers-dispersed nonwoven fabric, and one or more reinforcing
layers. The reinforcing layer may be, for example, a thread layer,
a net layer, a woven fabric layer, a knitted fabric layer, a fiber
web layer, or a usual nonwoven fabric layer. The laminate of the
fine-fibers-dispersed nonwoven fabric layer and the reinforcing
layer may be produced, for example, by collecting the
fine-fibers-dispersed fiber web on the reinforcing layer, and then
bonding the fiber web with the reinforcing layer, or by bonding the
fine-fibers-dispersed nonwoven fabric layer and the reinforcing
layer by an appropriate bonding means.
[0089] The sheet material of the present invention contains the
fine-fibers-dispersed nonwoven fabric layer, and exhibits various
excellent characteristics, such as filtering characteristics,
pliability, wiping-off capacity, and/or opacifying properties.
Therefore, the sheet material of the present invention may be used
in many applications, for example, as a gas or liquid filter (such
as a HEPA filter, a bag filter, or a cartridge filter), a substrate
for a deodorizing filter, a substrate for a mask (such as a
surgical operation mask or an industrial mask), a filter press, a
drape for a surgical operation, a gown for a surgical operation, a
diaper cover, a battery separator, or a water absorption sheet (for
example, for a moistening device).
EXAMPLES
[0090] The present invention will now be further illustrated by,
but is by no means limited to, the following Examples.
Example 1
[0091] Islands-in-sea type fibers (fineness=1.7 dtex) having 25
island components of high-density polyethylene and polypropylene in
a sea component of polylactic acid were prepared by a composite
spinning method, and cut to a fiber length of 1 mm. The resulting
islands-in-sea type fibers were dipped in a 10 mass % aqueous
solution of sodium hydroxide, and the sea component of polylactic
acid was extracted and removed by hydrolysis. Then, the product was
air-dried to obtain bundled aggregates of the fine fibers A (a
fiber diameter=2 .mu.m; a fiber length=1 mm; adhesion rate of
adhered substances=less than 0.02 mass %; sectional shape=circle,
and islands-in-sea type) wherein high-density polyethylene and
polypropylene were coexistent in each of the fine fibers. The
resulting fine fibers A were drawn but not fibrillated. Each of
fine fibers had substantially the same diameter in an axial
direction thereof.
[0092] On the other hand, islands-in-sea type fibers (fineness=2
dtex) having 61 island components of crystalline polystyrene in a
sea component of polyester copolymer were prepared by a composite
spinning method, and cut to a fiber length of 0.5 mm. The resulting
islands-in-sea type fibers were dipped in a 10 mass % aqueous
solution of sodium hydroxide, and the sea component of polyester
copolymer was extracted and removed by hydrolysis. Then, the
product was air-dried to obtain bundled aggregates of the fine
fibers B (a fiber diameter=1.1 .mu.m; a fiber length=0.5 mm;
adhesion rate of adhered substances=less than 0.02 mass %) of
crystalline polystyrene. The resulting fine fibers B were drawn but
fibrillated. Each of fine fibers had substantially the same
diameter in an axial direction thereof.
[0093] Thereafter, the fine-fibers-dispersed nonwoven fabric of the
present invention was produced by an apparatus similar to the
manufacturing apparatus of the present invention as shown in FIG.
1. More particularly, the bundled aggregates of the fine fibers A
and the bundled aggregates of the fine fibers B were charged into
the mixer 10 at a mass ratio of 25:75, and loosened and mixed. The
mixture of the aggregates of fine fibers was supplied to the nozzle
30 having an orifice with a continuously narrowing cross-sectional
circular shape (diameter at an ejecting opening=3.2 mm), and at the
same time, a compressed air (pressure=6 kg/cm.sup.2) was introduced
from the compressed-gas inlet 20 at an inside position near to the
nozzle 30. The mixture of the aggregates of fine fibers 70 was
ejected from the nozzle 30 (wherein a laminar flow was formed) to
the air at the dispersing chamber 40 and the fine fibers 70 were
dispersed in the dispersing chamber 40. The gas passing rate at the
ejecting opening of the nozzle 30 was 1600 m/s.
[0094] Subsequently, the dispersed fine fibers 70 were collected on
a nonwoven fabric substrate (a spun-bonded nonwoven fabric of
polyester fibers; a mass per unit area=30 g/m.sup.2; not shown)
placed on the support 50 of a net, while the air was sucked at a
suction rate of 2 m.sup.3/min by a suction box 60 located under the
support.
[0095] Then, the spun-bonded nonwoven fabric substrate carrying the
dispersed fine fibers thereon was directly conveyed to an oven 90
at 130.degree. C. and heated for 3 minutes, whereby the fine fibers
were thermally fused to form a fine-fibers-dispersed nonwoven
fabric layer by the high density polyethylene components in the
high density polyethylene-polypropylene fine fibers, and the
fine-fibers-dispersed nonwoven fabric layer and the spun-bonded
nonwoven fabric substrate were also thermally fused to obtain a
composite nonwoven fabric (mass per unit area=40 g/m.sup.2;
thickness=1.1 mm). The fine-fibers-dispersed nonwoven fabric layer
had a mass per unit area of 10 g/m.sup.2; thickness of 1 mm; and an
apparent density of 0.01 g/cm.sup.3. The adhesion rate of adhered
substances, i.e., a percentage of total masses of the adhered
substances extracted by dipping the fine-fibers-dispersed nonwoven
fabric layer in hot water for 15 minutes and the adhered substances
extracted by dipping the fine-fibers-dispersed nonwoven fabric
layer in hot methanol for 15 minutes to a mass of the
fine-fibers-dispersed nonwoven fabric layer, was less than 0.02
mass %.
[0096] Four sheets of the resulting composite nonwoven fabrics were
superimposed, and HEPA filtering characteristics [wind velocity=5.3
cm/s; test particles=DOP (di-(2-ethylhexydyl)phthalate)] were
examined. A capturing efficiency for particles of 0.3 .mu.m was
99.98%, which satisfied a desired value of 99.97%, and a pressure
loss was as low as 175 Pa, which satisfied a desired value of 400
Pa or less.
Comparative Example 1
[0097] The bundled aggregates of the fine fibers A and the bundled
aggregates of the fine fibers B were prepared as in Example 1, and
mixed at a mass ratio of 25:75, and then, a nonionic surface-active
agent was added thereto at an amount of 10 mass % with respect to a
total mass of the bundled aggregates of the fine fibers A and the
bundled aggregates of the fine fibers B.
[0098] The resulting mixture was added to a slurry containing
acrylamide as a sizing agent, and the aggregates of fine fibers
were divided and dispersed by a mixer. The slurry was diluted to
obtain a diluted slurry.
[0099] The diluted slurry was taken up on a nonwoven fabric
substrate (a spun-bonded nonwoven fabric of polyester fibers; a
mass per unit area=30 g/m.sup.2) placed on the support of a net.
Then, the spun-bonded nonwoven fabric substrate carrying the
dispersed fine fibers thereon was conveyed to an oven at
130.degree. C. and heated for 3 minutes whereby the fine fibers
were thermally fused to form a fine-fibers-dispersed nonwoven
fabric layer by the high density polyethylene components in the
high density polyethylene-polypropylene fine fibers, and the
fine-fibers-dispersed nonwoven fabric layer and the spun-bonded
nonwoven fabric substrate were also thermally fused to obtain a
composite nonwoven fabric (mass per unit area=50 g/m.sup.2;
thickness=0.3 mm). The fine-fibers-dispersed nonwoven fabric layer
had a mass per unit area of 20 g/m.sup.2; thickness of 0.2 mm; and
an apparent density of 0.1 g/cm.sup.3. The adhesion rate of adhered
substances, i.e., a percentage of total masses of the adhered
substances extracted by dipping the fine-fibers-dispersed nonwoven
fabric layer in hot water for 15 minutes and the adhered substances
extracted by dipping the fine-fibers-dispersed nonwoven fabric
layer in hot methanol for 15 minutes to a mass of the
fine-fibers-dispersed layer, was 1.5 mass %.
[0100] Two sheets of the resulting composite nonwoven fabrics were
superimposed, and HEPA filtering characteristics [wind velocity=5.3
cm/s; test particles=DOP] were examined. A capturing efficiency for
particles of 0.3 .mu.m was 98%, which did not satisfy a desired
value of 99.97%, and a pressure loss was 560 Pa higher than a
desired value of 400 Pa or less. The fine-fibers dispersing
nonwoven fabric layer was examined by an electron microscope and it
was revealed that some parts of the bundled aggregates of the fine
fibers A and B were not dispersed, and thus the bundled shape was
maintained.
Example 2
[0101] The bundled aggregates of the fine fibers A prepared as in
Example 1 and aggregates of polyester fine fibers (Teijin Ltd.;
fineness=0.11 dtex; fiber diameter=3.2 .mu.m; a fiber length=3 mm;
adhesion rate of adhered substances=less than 0.02 mass %) which
was washed with acetone to remove adhered substances (mainly a
fiber auxiliary) were charged into the mixer at a mass ratio of
60:40, and loosened and mixed. The polyester fine fibers were drawn
and not fibrillated. Each of polyester fine fibers had
substantially same diameter in an axial direction thereof.
[0102] The mixture of the aggregates of the fine fibers was
supplied to a cylindrical ejector having a cross-sectional circular
shape at an ejecting opening (diameter=7 mm), and at the same time,
a compressed air (pressure=6 kg/cm.sup.2) was introduced from the
compressed-gas inlet at an inside position near to the cylindrical
ejector. The mixture of the aggregates of the fine fibers was
ejected from the cylindrical ejector (wherein a spiral flow was
formed) to the air at dispersing chamber and the fine fibers were
generated and dispersed in the dispersing chamber. The gas passing
rate at the ejecting opening of the cylindrical ejector was 160
m/s.
[0103] Subsequently, the dispersed fine fibers were collected on a
nonwoven fabric substrate (a spun-bonded nonwoven fabric of
polyester fibers; a mass per unit area=30 g/m.sup.2) placed on the
support of a net, while the air was sucked at a suction rate of 2
m.sup.3/min by a suction box located under the support.
[0104] Then, the spun-bonded nonwoven fabric substrate carrying the
dispersed fine fibers thereon was directly conveyed to an oven at
130.degree. C. and heated for 3 minutes whereby the fine fibers
were thermally fused to form a fine-fibers-dispersed nonwoven
fabric layer by the high density polyethylene components in the
high density polyethylene-polypropylene fine fibers, and the
fine-fibers-dispersed nonwoven fabric layer and the spun-bonded
nonwoven fabric substrate were also thermally fused to obtain a
composite nonwoven fabric (mass per unit area=50 g/m.sup.2;
thickness=3 mm). The fine-fibers-dispersed nonwoven fabric layer
had a mass per unit area of 20 g/m.sup.2; thickness of 2.9 mm; and
an apparent density of 0.007 g/cm.sup.3. The adhesion rate of
adhered substances, i.e., a percentage of total masses of the
adhered substances extracted by dipping the fine-fibers-dispersed
nonwoven fabric layer in hot water for 15 minutes and the adhered
substances extracted by dipping the fine-fibers-dispersed nonwoven
fabric layer in hot methanol for 15 minutes to a mass of the
fine-fibers-dispersed layer, was less than 0.02 mass %.
[0105] The composite nonwoven fabric contained the
fine-fibers-dispersed nonwoven fabric layer, and thus, exhibited
excellent filtering characteristics and pliability.
Example 3
[0106] Islands-in-sea type fibers (fineness=8.8 dtex) having about
3900 island components of poly-4-methylpentene in a sea component
of polyester copolymer were prepared by a melt blend spinning
method, and cut to a fiber length of 0.5 mm. The resulting
islands-in-sea type fibers were dipped in a 10 mass % aqueous
solution of sodium hydroxide, and the sea component of polyester
copolymer was extracted and removed by hydrolysis. Then, the
product was air-dried to obtain bundled aggregates of the fine
fibers C (a fiber diameter=0.4 .mu.m; a fiber length=0.5 mm;
adhesion rate of adhered substances=less than 0.02 mass %) of
poly-4-methylpentene. The resulting fine fibers C were drawn but
not fibrillated.
[0107] Further, the bundled aggregates of the fine fibers A were
prepared as in Example 1.
[0108] Thereafter, the bundled aggregates of the fine fibers A and
the bundled aggregates of the fine fibers C were charged into the
mixer at a mass ratio of 50:50, and loosened and mixed. The mixture
of the aggregates of the fine fibers was supplied to a Venturi tube
having a cross-sectional circular shape at an ejecting opening
(diameter=8.5 mm) and a cross-sectional circular shape at a
fibers-supplying side (diameter=3 mm), and a compressed air
(pressure=6 kg/cm.sup.2) was introduced from the compressed-gas
inlet at an inside position near to the Venturi tube. The mixture
of the aggregates of the fine fibers was ejected from the Venturi
tube (wherein a laminar flow was formed) to the air at dispersing
chamber and the aggregates of the fine fibers were brought into
collision with a baffle plate placed in front of the Venturi tube
and dispersed. The distance between the baffle plate and the
ejecting opening of the Venturi tube was 15 mm. The gas passing
rate at the ejecting opening of the Venturi tube was 118 m/s.
[0109] Subsequently, the dispersed fine fibers were collected on a
nonwoven fabric substrate (a spun-bonded nonwoven fabric of
polyester fibers; a mass per unit area=30 g/m.sup.2) placed on the
support of a net, while the air was sucked at a suction rate of 2
m.sup.3/min by a suction box located under the support.
[0110] Then, the spun-bonded nonwoven fabric substrate carrying the
dispersed fine fibers thereon was directly conveyed to an oven at
130.degree. C. and heated for 3 minutes, whereby the fine fibers
were thermally fused to form a fine-fibers-dispersed nonwoven
fabric layer by the high density polyethylene components in the
high density polyethylene-polypropylene fine fibers, and the
fine-fibers-dispersed nonwoven fabric layer and the spun-bonded
nonwoven fabric substrate were also thermally fused to obtain a
composite nonwoven fabric (mass per unit area=40 g/m.sup.2;
thickness=0.9 mm). The fine-fibers-dispersed nonwoven fabric layer
had a mass per unit area of 10 g/m.sup.2; thickness of 0.8 mm; and
an apparent density of 0.013 g/cm.sup.3. The adhesion rate of
adhered substances, i.e., a percentage of total masses of the
adhered substances extracted by dipping the fine-fibers-dispersed
layer in hot water for 15 minutes and the adhered substances
extracted by dipping the fine-fibers-dispersed layer in hot
methanol for 15 minutes to a mass of the fine-fibers-dispersed
layer, was less than 0.02 mass %.
[0111] The composite nonwoven fabric contained the
fine-fibers-dispersed nonwoven fabric layer, and thus, exhibited
excellent filtering characteristics and pliability.
Example 4
[0112] The bundled aggregates of the fine fibers A were prepared as
in Example 1, and the bundled aggregates of the fine fibers C were
prepared as in Example 3.
[0113] Thereafter, the bundled aggregates of the fine fibers A and
the bundled aggregates of the fine fibers C were charged into the
mixer at a mass ratio of 5:95, and loosened and mixed. The mixture
of the aggregates of the fine fibers was supplied to a Venturi tube
with a truncated cone shape having a cross-sectional circular shape
at an ejecting opening (diameter=8.5 mm) and a cross-sectional
circular shape at a fibers-supplying side (diameter=3 mm), and a
compressed air (pressure=6 kg/cm.sup.2) was introduced from the
compressed-gas inlet at an inside position near to the Venturi
tube. The mixture of the aggregates of the fine fibers was ejected
from the Venturi tube (wherein a laminar flow was formed) to the
air at dispersing chamber and the fine fibers were brought into
collision with a baffle plate placed in front of the Venturi tube,
and dispersed. The distance between the baffle plate and the
ejecting opening of the Venturi tube was 15 mm. The gas passing
rate at the ejecting opening of the Venturi was 118 m/s.
[0114] Subsequently, the dispersed fine fibers were collected on a
nonwoven fabric substrate (a spun-bonded nonwoven fabric of
polyester fibers; a mass per unit area=30 g/m.sup.2) placed on the
support of a net, while the air was sucked at a suction rate of 2
m.sup.3/min by a suction box located under the support.
[0115] Then, the spun-bonded nonwoven fabric substrate carrying the
dispersed fine fibers thereon was conveyed to an oven at
130.degree. C. and heated for 3 minutes, whereby the fine fibers
were thermally fused to form a fine-fibers-dispersed nonwoven
fabric layer by the high density polyethylene components in the
high density polyethylene-polypropylene fine fibers, and the
fine-fibers-dispersed nonwoven fabric layer and the spun-bonded
nonwoven fabric substrate were also thermally fused to obtain a
composite nonwoven fabric (mass per unit area=40 g/m.sup.2;
thickness=0.8 mm). The fine-fibers-dispersed nonwoven fabric layer
had a mass per unit area of 10 g/m.sup.2; thickness of 0.7 mm; and
an apparent density of 0.014 g/cm.sup.3. The adhesion rate of
adhered substances, i.e., a percentage of total masses of the
adhered substances extracted by dipping the fine-fibers-dispersed
layer in hot water for 15 minutes and the adhered substances
extracted by dipping the fine-fibers-dispersed layer in hot
methanol for 15 minutes to a mass of the fine-fibers-dispersed
layer, was less than 0.02 mass %.
[0116] The composite nonwoven fabric contained the layer of
dispersed fine fibers with submicron, and thus, exhibited very
excellent filtering characteristics and pliability.
[0117] FIG. 2 is an electron micrograph of the surface of the
fine-fibers dispersing nonwoven fabric layer. As apparent from FIG.
2, the bundled aggregates of the fiber fibers were divided into the
fine fibers and the fine fibers were uniformly dispersed.
Comparative Example 2
[0118] The bundled aggregates of the fine fibers A were prepared as
in Example 1, and the bundled aggregates of the fine fibers C were
prepared as in Example 3.
[0119] Then, potassium lauryl phosphate (Takemoto Yushi) as a fiber
auxiliary was added at an amount of 0.6 mass % with respect to a
total mass of the bundled aggregates of the fine fibers A and the
bundled aggregates of the fine fibers C.
[0120] Subsequently, the procedure described in Example 4 was
repeated, using the same composition of the fibers as in Example 4,
whereby the fine fibers were thermally fused to form a
fine-fibers-dispersed nonwoven fabric layer by the high density
polyethylene components in the high density
polyethylene-polypropylene fine fibers, and the
fine-fibers-dispersed nonwoven fabric layer and the spun-bonded
nonwoven fabric substrate were also thermally fused to obtain a
composite nonwoven fabric (mass per unit area=40 g/m.sup.2;
thickness=0.8 mm). The fine-fibers-dispersed nonwoven fabric layer
had a mass per unit area of 10 g/m.sup.2; thickness of 0.7 mm; and
an apparent density of 0.014 g/cm.sup.3. The adhesion rate of
adhered substances, i.e., a percentage of total masses of the
adhered substances extracted by dipping the fine-fibers-dispersed
layer in hot water for 15 minutes and the adhered substances
extracted by dipping the fine-fibers-dispersed layer in hot
methanol for 15 minutes to a mass of the fine-fibers-dispersed
layer, was 0.6 mass %.
[0121] FIG. 3 is an electron micrograph of the surface of the
fine-fibers dispersing nonwoven fabric layer. As apparent from FIG.
3, some parts of the bundled aggregates of the fine fibers A, C
were not divided, and the bundled shapes remained.
Example 5
[0122] The bundled aggregates of the fine fibers A were prepared as
in Example 1, and the bundled aggregates of the fine fibers C were
prepared as in Example 3.
[0123] Thereafter, the bundled aggregates of the fine fibers A and
the bundled aggregates of the fine fibers C were charged into the
mixer at a mass ratio of 25:75, and loosened and mixed.
[0124] Subsequently, the procedure described in Example 2 was
repeated, whereby the fine fibers were thermally fused to form a
fine-fibers-dispersed nonwoven fabric layer by the high density
polyethylene components in the high density
polyethylene-polypropylene fine fibers, and the
fine-fibers-dispersed nonwoven fabric layer and the spun-bonded
nonwoven fabric substrate were also thermally fused to obtain a
composite nonwoven fabric (mass per unit area=40 g/m.sup.2;
thickness=0.8 mm). The fine-fibers-dispersed layer had a mass per
unit area of 10 g/m.sup.2; thickness of 0.7 mm; and an apparent
density of 0.014 g/cm.sup.3. The adhesion rate of adhered
substances, i.e., a percentage of total masses of the adhered
substances extracted by dipping the fine-fibers-dispersed layer in
hot water for 15 minutes and the adhered substances extracted by
dipping the fine-fibers-dispersed layer in hot methanol for 15
minutes to a mass of the fine-fibers-dispersed layer, was less than
0.02 mass %.
[0125] The composite nonwoven fabric contained the layer of
dispersed fine fibers with submicron, and thus, exhibited excellent
filtering characteristics and pliability.
[0126] FIG. 4 is an electron micrograph of the surface of the
fine-fibers dispersing nonwoven fabric layer. As apparent from FIG.
4, although a few bundled aggregates were not completely divided
into the fine fibers, almost all of the bundled aggregates were
divided into the fine fibers, and the fine fibers were uniformly
dispersed.
Example 6
[0127] The bundled aggregates of the fine fibers A were prepared as
in Example 1, and the bundled aggregates of the fine fibers C were
prepared as in Example 3.
[0128] Thereafter, the bundled aggregates of the fine fibers A and
the bundled aggregates of the fine fibers C were charged into the
mixer at a mass ratio of 25:75, and loosened and mixed.
[0129] Subsequently, the procedure described in Example b 4 was
repeated, whereby the fine fibers were thermally fused to form a
fine-fibers-dispersed nonwoven fabric layer by the high density
polyethylene components in the high density
polyethylene-polypropylene fine fibers, and the
fine-fibers-dispersed nonwoven fabric layer and the spun-bonded
nonwoven fabric substrate were also thermally fused to obtain a
composite nonwoven fabric (mass per unit area=40 g/m.sup.2;
thickness=0.8 mm). The fine-fibers-dispersed nonwoven fabric layer
had a mass per unit area of 10 g/m.sup.2; thickness of 0.7 mm; and
an apparent density of 0.014 g/cm.sup.3. The adhesion rate of
adhered substances, i.e., a percentage of total masses of the
adhered substances extracted by dipping the fine-fibers-dispersed
layer in hot water for 15 minutes and the adhered substances
extracted by dipping the fine-fibers-dispersed layer in hot
methanol for 15 minutes, to a mass of the fine-fibers-dispersed
layer, was less than 0.02 mass %.
[0130] The composite nonwoven fabric contained the layer of
dispersed submicron fine fibers, and thus, exhibited very excellent
filtering characteristics and pliability.
[0131] FIG. 5 is an electron micrograph of the surface of the
fine-fibers dispersing nonwoven fabric layer. As apparent from FIG.
5, the bundled aggregates were completely divided into the fine
fibers, and the fine fibers were uniformly dispersed.
[0132] As explained, the fine-fibers-dispersed nonwoven fabric of
the present invention includes a very small amount of adhered
substances, such as the surface-active agents or sizing agents, and
thus, the degree of adhesion of the fine fibers is at a lower
level. Therefore, the fine-fibers-dispersed nonwoven fabric
contains an appropriate amount of voids having an appropriate size,
and a pressure loss of the fine-fibers-dispersed nonwoven fabric is
small. Further, in the fine-fibers-dispersed nonwoven fabric of the
present invention, the fine fibers are not present in the form of
bundles but in the dispersed state, and thus, the
fine-fibers-dispersed nonwoven fabric has excellent properties,
such as filtering characteristics and a pliability, due to the
containing of the fine fibers.
[0133] In the process of the present invention, a medium (such as a
solvent) used for dispersing the fine fibers in the conventional
process is not required, but the fine fibers are dispersed into a
gas, and thus, it is not necessary to use the surface-active agents
or sizing agents required in the process using a solvent as a
dispersing medium. Therefore, according to the process of the
present invention, the nonwoven fabric wherein an adhesion rate of
the substances adhered to the fine-fibers-dispersed nonwoven fabric
layer is 0.5 mass % or less, i.e., the nonwoven fabric containing
the fine fibers adhered to each other to a lesser degree, can be
easily prepared.
[0134] Further, the nonwoven fabric containing the uniformly
dispersed fine fibers can be easily prepared, because the
fine-fibers-dispersed nonwoven fabric is prepared by ejecting the
fine-fibers aggregates or the group thereof, and/or the
mechanically dividable fibers or the aggregates thereof, from the
nozzle into the gas by an action of the compressed gas.
[0135] As above, the present invention was explained with reference
to particular embodiments, but modifications and improvements
obvious to those skilled in the art are included in the scope of
the present invention.
* * * * *