TECHNICAL FIELD
[0001] The present invention relates to a nonwoven fabric, and a method for producing the
nonwoven fabric.
BACKGROUND ART
[0002] In recent years, a nonwoven fabric made of ultra-fine fibers produced by a melt blown
method or the like has been developed, and is used for various applications. With
respect to a nonwoven fabric containing a polymer having a glass transition temperature
(Tg) of less than 50°C, such as polypropylene and polyethylene, a nonwoven fabric
excellent in the handleability, in which fibers are fused to one another, can be obtained
without performing a post processing such as emboss processing, calender processing,
or spunlace processing.
[0003] However, with respect to a nonwoven fabric containing a polymer that has a Tg of
greater than or equal to 50°C, unless the fibers are fused to one another or three-dimensionally
entangled with one another by performing a post processing, the strength as a nonwoven
fabric is weak, therefore, the handleability is poor, and further, there have been
problems that fluff is prone to occur, and the like.
[0004] Accordingly, for such a nonwoven fabric, in general, a method for solving the problems
has been taken by performing a post processing (for example, Japanese Patent Laying-Open
No.
2012-41644 (PTD 1)).
[0005] However, in the nonwoven fabric that has been subjected to a post processing as described
above, at least some parts of the nonwoven fabric have a high density, as a result
there may be a case where the performances of the air permeability and the like are
affected, therefore, it has been desired to develop a nonwoven fabric that is excellent
in the handleability even though there are few high-density parts.
CITATION LIST
PATENT DOCUMENT
[0006] PTD 1: Japanese Patent Laying-Open No.
2012-41644
SUMMARY OF INVENTION
TECHNICAL PROBLEMS
[0007] The present invention has been made to solve the above problems, and an object of
the present invention is to provide a nonwoven fabric having sufficient strength to
be handled alone and including fibers that contain a polymer having a Tg of greater
than or equal to 50°C as a main component without performing a post processing such
as emboss processing, calender processing, or spunlace processing, and a method for
producing the nonwoven fabric.
SOLUTIONS TO PROBLEMS
[0008] The nonwoven fabric of the present invention is a nonwoven fabric according to claim
1, including fibers that contain a polymer having a glass transition temperature of
greater than or equal to 50°C as a main component, having a vertical strength of greater
than or equal to 1 N/5 cm per 1 g/m
2, and satisfying the following conditions (1) and (2):
- (1) a density is 0.1 to 0.4 g/cm3; and
- (2) a proportion of parts with a density exceeding 0.4 g/cm3 is less than or equal to 3% in a cross section in a thickness direction.
[0009] It is preferred that the nonwoven fabric of the present invention has a fiber fusion
rate of greater than or equal to 15% in a cross section in a thickness direction,
and an average area of parts where fibers are fused of less than or equal to 70 µm
2.
[0010] The nonwoven fabric of the present invention preferably has an average fiber diameter
of 1 to 10 µm.
[0011] The present invention is also to provide a method according to claim 5 for producing
the above-described nonwoven fabric of the present invention, in which a melt blown
method is performed while maintaining a temperature in at least one of (1) a hemispherical
space of 0.5 × collection distance d around a nozzle tip relative to the collection
distance d between the tip of a spinning nozzle and a collection surface of spun fibers,
and (2) a point of 1 cm from the collection surface on the straight line relative
to the collection distance d between the tip of the spinning nozzle and the collection
surface of spun fibers at a temperature higher than the glass transition temperature
by greater than 15°C to 60°C.
ADVANTAGEOUS EFFECTS OF INVENTION
[0012] According to the present invention, a nonwoven fabric having sufficient strength
to be handled alone and including fibers that contain a polymer having a Tg of greater
than or equal to 50°C as a main component without performing a post processing such
as emboss processing, calender processing, or spunlace processing, and a method for
producing the nonwoven fabric can be provided.
BRIEF DESCRIPTION OF DRAWINGS
[0013]
Fig. 1 is a scanning electron microscope (SEM) photograph of a cross section in a
thickness direction of a nonwoven fabric of the present invention.
Fig. 2 is a schematic diagram for illustrating a principle of a method for producing
a nonwoven fabric of the present invention.
Fig. 3 is a schematic diagram for illustrating a principle of the method for producing
a nonwoven fabric of the present invention.
Fig. 4 is a diagram schematically showing one preferred example of the method for
producing a nonwoven fabric of the present invention.
Fig. 5 is a diagram schematically showing another preferred example of the method
for producing a nonwoven fabric of the present invention.
Fig. 6 is a SEM photograph of a cross section in a thickness direction in a case where
a nonwoven fabric is formed by a melt blown method using a polymer having a Tg of
greater than or equal to 50°C, and then the formed nonwoven fabric is subjected to
calender processing as the post processing.
Fig. 7 is a SEM photograph of a cross section in a thickness direction in a case where
a nonwoven fabric is formed by a melt blown method using a polymer having a Tg of
greater than or equal to 50°C, and then the formed nonwoven fabric is subjected to
emboss processing as the post processing.
Fig. 8 is a SEM photograph of a cross section in a thickness direction in a case where
a nonwoven fabric is formed by a melt blown method using a polymer having a Tg of
greater than or equal to 50°C, and then the formed nonwoven fabric is subjected to
spunlace processing as the post processing.
DESCRIPTION OF EMBODIMENTS
[1] Nonwoven fabric
[0014] The nonwoven fabric of the present invention has a vertical strength (strength in
a vertical direction (a direction of flow in producing the nonwoven fabric)) per 1
g/m
2 of greater than or equal to 1 N/5 cm. According to the present invention, a nonwoven
fabric having sufficient strength to be handled alone as a nonwoven fabric can be
obtained without performing a post processing such as calender processing, emboss
processing, or spunlace processing, which generates a part partially with a high density.
The strength of the nonwoven fabric of the present invention is more preferably greater
than or equal to 1.2 N/5 cm, and furthermore preferably 1.5 N/5 cm. In a case where
a nonwoven fabric is formed by a conventional melt blown method, and the formed nonwoven
fabric is not subjected to a post processing such as calender processing, emboss processing,
or spunlace processing (Comparative Example 1 described later), the vertical strength
per 1 g/m
2 becomes significantly poor, but even as compared with such a case, the nonwoven fabric
of the present invention is a nonwoven fabric significantly excellent in the handleability.
[0015] In addition, the nonwoven fabric of the present invention is a nonwoven fabric having
a density of 0.1 to 0.4 g/cm
3. When the density is greater than or equal to 0.1 g/cm
3, preferred form and properties as a nonwoven fabric can be maintained, and when the
density is less than or equal to 0.4 g/cm
3, desired performance such as high permeability can be easily obtained in the nonwoven
fabric. The density of the nonwoven fabric of the present invention is preferably
less than or equal to 0.35 g/cm
3, and more preferably less than or equal to 0.3 g/cm
3, and preferably greater than or equal to 0.1 g/cm
3, and more preferably greater than or equal to 0.11 g/cm
3.
[0016] In addition, in the nonwoven fabric of the present invention, a proportion of parts
with a density exceeding 0.4 g/cm
3 is less than or equal to 3%. In a case where the proportion of parts with a density
exceeding 0.4 g/cm
3 exceeds 3%, unevenness is generated on the nonwoven fabric, and as a result, failures
that the air permeability is affected, uneven strength is generated, and the like
may occur in some cases. The proportion of parts with a density exceeding 0.4 g/cm
3 is more preferably less than or equal to 2.5%, and furthermore preferably less than
or equal to 2%.
[0017] The proportion of parts with a density exceeding 0.4 g/cm
3 in the nonwoven fabric described above is determined as follows. Using a SEM, a 100-times
magnified photograph of the cross section in the thickness direction of the nonwoven
fabric is taken, a straight line of 10 mm of the photograph is observed in the width
direction by visual inspection, the length occupied by the parts with a density exceeding
0.4 g/cm
3 is measured in this straight line, and the proportion is determined by the following
equation:
Note that with the observation of the photograph, it is determined whether or not
the density exceeds 0.4 g/cm
3 by using a function of distance measurement between two points attached to the SEM,
and by investigating the length occupied by the parts with a density exceeding 0.4
g/cm
3.
[0018] Herein, Fig. 1 is photographs of a scanning electron microscope (SEM) of a cross
section in a thickness direction of the nonwoven fabric of the present invention (Example
1 described later, Fig. 1(a) shows a 100-times magnified photograph, and Fig. 1(b)
shows a 1000-times magnified photograph). As shown in Fig. 1, the nonwoven fabric
of the present invention has a fusion part 3 in which fibers 2 are partially fused
(self-fused) to one another although being a nonwoven fabric 1 including fibers that
contain a polymer having a Tg of greater than or equal to 50°C as a main component.
Herein, in a cross section in a thickness direction of nonwoven fabric 1 of the present
invention, the fiber fusion rate is preferably greater than or equal to 15%, more
preferably greater than or equal to 20%, and furthermore preferably greater than or
equal to 25%. In a case where the fiber fusion rate is less than 15%, the proportion
of the parts where fibers are fused to one another occupied in the nonwoven fabric
is extremely low and the strength becomes insufficient, and failures may occur in
the handleability, such that the nonwoven fabric cannot be handled alone, in some
cases. In addition, if the fiber fusion rate is extremely high, there may be a case
where a paper-like seat is formed, the air permeability is affected, or the like,
therefore, the fiber fusion rate of a nonwoven fabric is preferably less than or equal
to 60%, and more preferably less than or equal to 50%.
[0019] The above-described fiber fusion rate of a nonwoven fabric can be calculated, for
example, by the following procedures. At first, using a SEM, a 1000-times magnified
photograph of the cross section in the thickness direction of the nonwoven fabric
is taken, and from the photograph, a proportion of the number of the cut sections
where fibers are fused to one another relative to the number of fiber cut sections
(fiber cross sections) is determined by visual inspection. The proportion of the number
of the cross sections where greater than or equal to two fibers are fused to one another,
occupied in the total number of the fiber cross sections that can be found in each
region is expressed as a percentage on the basis of the following equation:
Fiber fusion rate (%) = (the number of the cross sections where greater than or equal
to two fibers are fused to one another) / (the total number of the fiber cross sections)
× 100. Provided that the number of the fibers whose cross sections can be seen is
counted in each photograph, and in a case where the number of fiber cross sections
are less than or equal to 100, photographs to be observed are added so that the total
number of the fiber cross sections exceeds 100. Further, in the parts where fibers
are in contact with one another, there are a part where fibers are simply in contact
with one another without fusing to one another and a part where fibers are bonded
with fusing to one another, and since the nonwoven fabric is cut for the SEM photography,
the fibers that are simply in contact with one another are separated due to the stress
of each fiber in the cross section. Therefore, in the SEM photograph, it can be determined
that fibers, which are in contact with one another, are fused to one another.
[0020] Further, in the nonwoven fabric of the present invention, an average area of parts
where fibers are fused is preferably less than or equal to 70 µm
2, and more preferably less than or equal to 50 µm
2. Herein, as a conventional example, a SEM photograph of a cross section in a thickness
direction in a case where a nonwoven fabric formed by a melt blown method has been
subjected to a post processing is shown in each of Figs. 6 to 8. Fig. 6 shows SEM
photographs in a case where calender processing has been performed as the post processing
(Comparative Example 3 described later, Fig. 6(a) shows a 100-times magnified photograph,
and Fig. 6(b) shows a 1000-times magnified photograph), Fig. 7 shows SEM photographs
in a case where emboss processing has been performed as the post processing (Comparative
Example 2 described later, Fig. 7(a) shows a 100-times magnified photograph, and Fig.
7(b) shows a 1000-times magnified photograph), and Fig. 8 shows SEM photographs in
a case where spunlace processing has been performed as the post processing (Comparative
Example 4 described later, Fig. 8(a) shows a 100-times magnified photograph, and Fig.
8(b) shows a 1000-times magnified photograph). As is prominent in Figs. 6(b) and 7(b),
in a nonwoven fabric to which calender processing or emboss processing has been performed
as the post processing, a large number of parts where fibers are fused to one another
to the extent of the state that discrimination of the fiber diameter becomes difficult
are formed, and the average area of parts where fibers are fused exceeds 70 µm
2. Since the average area of parts where fibers are fused is less than or equal to
70 µm
2, the nonwoven fabric of the present invention can be distinguished from the nonwoven
fabric to which calender processing or emboss processing has been performed as the
post processing, as is prominent in Figs. 6(b) and 7(b). On the other hand, as shown
in Fig. 8, in the nonwoven fabric to which spunlace processing has been performed,
the parts where fibers are fused are extremely few, and the fiber fusion rate becomes
less than 15%. As described above, when the fiber fusion rate in a cross section in
a thickness direction is greater than or equal to 15%, and an average area of parts
where fibers are fused is less than or equal to 70 µm
2, the nonwoven fabric of the present invention can be clearly distinguished from the
nonwoven fabric to which post processing such as calender processing, emboss processing,
spunlace processing, or the like has been performed.
[0021] It is preferred that the nonwoven fabric of the present invention has an average
fiber diameter within the range of 1 to 10 µm. As described above, it is preferred
that the nonwoven fabric of the present invention contains a fusion part where fibers
are fused to one another, but even in the case, different from the case where calender
processing has been performed (see Fig. 6(b)), or the case where emboss processing
has been performed (see Fig. 7(b)), the fusion is to the extent that the fiber diameter
can be discriminated (Fig. 1(b)), and the average fiber diameter can be calculated.
In the nonwoven fabric of the present invention, in a case where the average fiber
diameter is less than 1 µm, the discharge amount is required to be decreased, and
thus the productivity is lowered, in addition, the discharge pressure becomes unstable,
and thread breakage or polymer lumps may be frequently generated and thus the formation
of a web may become difficult. Further, in the nonwoven fabric of the present invention,
in a case where the average fiber diameter exceeds 10 µm, the denseness may become
poor. In particular, for the reason of achieving a balance between the production
stability and the denseness, the average fiber diameter of the nonwoven fabric of
the present invention is more preferably within the range of 1.2 to 9.5 µm, and particularly
preferably within the range of 1.5 to 9.0 µm.
[0022] The nonwoven fabric of the present invention includes fibers that contain a polymer
having a Tg of greater than or equal to 50°C as a main component.
[0023] In the present invention, the expression "fibers that contain a polymer having a
Tg of greater than or equal to 50°C as a main component" is referred to as fibers
that contain a greater than or equal to 50% by mass of polymer having a Tg of greater
than or equal to 50°C, and the content is preferably greater than or equal to 70%
by mass, more preferably greater than or equal to 80% by mass, furthermore preferably
greater than or equal to 90% by mass, and particularly preferably greater than or
equal to 100% by mass.
[0024] In addition, when the total of the polymers having a Tg of greater than or equal
to 50°C is greater than or equal to 50% by mass, the nonwoven fabric of the present
invention may contain greater than or equal to two different polymers having a Tg
of greater than or equal to 50°C.
[0025] Examples of the polymer used in the present invention and having a Tg of greater
than or equal to 50°C include polyamide, polyphenylene sulfide, polyethylene terephthalate,
and polycarbonate, and from the viewpoint of combining flame retardancy, heat resistance,
and the like, amorphous polyetherimide (PEI) is particularly preferred.
[0026] The amorphous PEI used in the present invention is a polymer containing an aliphatic,
alicyclic or aromatic ether unit and a cyclic imide as a repeating unit, and is not
particularly limited as long as having amorphousness and melt formability. Further,
as long as the amorphous PEI is in a range not inhibiting the effect of the present
invention, a cyclic imide, and a structural unit other than an ether bond, for example,
an aliphatic, alicyclic, or aromatic ester unit, an oxycarbonyl unit, and the like
may be contained in the main chain of the amorphous PEI.
[0027] As the amorphous PEI used in the present invention, a polymer represented by the
following general formula is suitably used. Provided that in the formula, R1 represents
a divalent aromatic residue having 6 to 30 carbon atoms, and R2 represents a divalent
organic group selected from the group consisting of a divalent aromatic residue having
6 to 30 carbon atoms, an alkylene group having 2 to 20 carbon atoms, a cycloalkylene
group having 2 to 20 carbon atoms, and a polydiorganosiloxane group that is chain-stopped
by an alkylene group having 2 to 8 carbon atoms.
[0028] In addition, in the amorphous PEI used in the present invention, the melt viscosity
at 330°C is preferably 100 to 3000 Pa·s. When the melt viscosity of amorphous PEI
at 330°C is less than 100 Pa·s, there may be a case where fiber dust, or resin particles
called shots that occur due to the failure in formation of fibers are frequently generated
during spinning. Further, when the melt viscosity of amorphous PEI at 330°C exceeds
3000 Pa·s, there may be a case where a trouble occurs during polymerization or granulation,
for example, ultra-fine fibers are difficult to be formed, and oligomers are generated
during polymerization. The melt viscosity at 330°C is preferably 200 to 2700 Pa·s,
and more preferably 300 to 2500 Pa·s.
[0029] In the amorphous PEI used in the present invention, the glass transition temperature
is preferably greater than or equal to 200°C. When the glass transition temperature
is less than 200°C, there may be a case where the heat resistance of a nonwoven fabric
to be obtained is poor. Further, as the glass transition temperature of amorphous
PEI is higher, a nonwoven fabric excellent in the heat resistance can be obtained,
therefore, this is preferred, but when the glass transition temperature is extremely
high, the fused temperature may also become high, and thus a polymer may be decomposed
during fusion. The glass transition temperature of the amorphous PEI is more preferably
200 to 230°C, and furthermore preferably 205 to 220°C.
[0030] The molecular weight of the amorphous PEI used in the present invention is not particularly
limited, and in consideration of the mechanical properties, the dimensional stability,
or the processability of the fibers or nonwoven fabric to be obtained, the weight
average molecular weight (Mw) is preferably 1000 to 80000. When amorphous PEI having
a high molecular weight is used, the amorphous PEI is excellent in terms of the fiber
strength, the heat resistance, and the like, therefore, this is preferred, but from
the viewpoint of the cost for producing a resin, the cost for forming into small fibers,
and the like, the weight average molecular weight is preferably 2000 to 50000, and
more preferably 3000 to 40000.
[0031] In the present invention, from the viewpoint of the amorphousness, the melt formability,
and the cost, as the amorphous PEI, a condensate of 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane
dianhydride and m-phenylenediamine or p-phenylenediamine, which mainly has a structural
unit represented by the following formula, is preferably used. This PEI is commercially
available from SABIC Innovative Plastics under the trademark of "ULTEM".
[0032] The fibers containing a polymer having a Tg of greater than or equal to 50°C as a
main component, which are included in the nonwoven fabric of the present invention,
may contain an antioxidant, an antistatic agent, a radical inhibitor, a matting agent,
an UV absorber, a flame retardant, an inorganic substance, and the like within the
range of not impairing the effects of the present invention. As the specific examples
of the inorganic substance, carbon nanotube, fullerene, a silicate such as talc, wollastonite,
zeolite, sericite, mica, kaolin, clay, pyrophyllite, silica, bentonite, and alumina
silicate, a metal oxide such as silicon oxide, magnesium oxide, alumina, zirconium
oxide, titanium oxide, and iron oxide, a carbonate such as calcium carbonate, magnesium
carbonate, and dolomite, a sulfate such as calcium sulfate, and barium sulfate, a
hydroxide such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide,
glass beads, glass flakes, glass powder, ceramic beads, boron nitride, silicon carbide,
carbon black, graphite, and the like are used. Further, for the purpose of improving
the hydrolysis resistance of fibers, a terminal sequestering agent such as a mono-
or di-epoxy compound, a mono- or poly-carbodiimide compound, a mono- or di-oxazoline
compound, and a mono- or di-azirine compound may be contained.
[0033] Furthermore, the nonwoven fabric of the present invention may include fibers other
than the fibers that contain a polymer having a Tg of greater than or equal to 50°C
as a main component, for example, fibers made of polyethylene, polypropylene, ethylene
vinyl acetate, or the like within the range of not impairing the effects of the present
invention. The content of the fibers that contain a polymer having a Tg of greater
than or equal to 50°C as a main component is not particularly limited, and is preferably
greater than or equal to 50% by mass, more preferably greater than or equal to 70%
by mass, furthermore preferably greater than or equal to 90% by mass, and particularly
preferably 100% by mass.
[0034] The thickness of the nonwoven fabric of the present invention is not particularly
limited, and is preferably within the range of 10 to 1000 µm, more preferably within
the range of 15 to 500 µm, and particularly preferably within the range of 20 to 200
µm. In a case where the thickness of the nonwoven fabric is less than 10 µm, the strength
may be lowered, and breakage may occur during processing, and further, in a case where
the thickness of the nonwoven fabric of the present invention exceeds 1000 µm, the
formation of a web may become difficult.
[0035] In addition, in the nonwoven fabric of the present invention, the air permeability
is preferably greater than or equal to 10 cc/cm
2/sec, and more preferably greater than or equal to 20 cc/cm
2/sec, and further preferably less than or equal to 130 cc/cm
2/sec, and more preferably less than or equal to 120 cc/cm
2/sec. By setting the air permeability within the range described above, the nonwoven
fabric of the present invention can be suitably used for the application of a filter
or the like.
[0036] In addition, the basis weight of the nonwoven fabric of the present invention is
not particularly limited, and is preferably within the range of 10 to 1000 g/m
2, and more preferably within the range of 15 to 500 g/m
2. In a case where the basis weight of the nonwoven fabric is less than 10 g/m
2, the strength may be lowered, and breakage may occur during processing, and further,
in a case where the basis weight of the nonwoven fabric exceeds 1000 g/m
2, the case is not preferred from the viewpoint of the productivity.
[2] Method for producing nonwoven fabric
[0037] The present invention is also to provide a method for producing the above-described
nonwoven fabric of the present invention. Note that the above-described nonwoven fabric
of the present invention is a nonwoven fabric including fibers that contain a polymer
having a Tg of greater than or equal to 50°C as a main component, and having a vertical
strength of greater than or equal to 1 N/5 cm per 1 g/m
2. As long as the density is 0.1 to 0.4 g/cm
3, and the proportion of parts with a density exceeding 0.4 g/cm
3 is less than or equal to 3% in a cross section in a thickness direction, the nonwoven
fabric of the present invention may be a nonwoven fabric produced by the method for
producing a nonwoven fabric of the present invention, or may be a nonwoven fabric
not produced by the method for producing a nonwoven fabric of the present invention,
but a nonwoven fabric produced by the method for producing a nonwoven fabric of the
present invention is preferred.
[0038] The method for producing a nonwoven fabric of the present invention is characterized
in that a melt blown method is performed while maintaining a temperature in at least
one of the following (1) and (2) at a temperature higher than the Tg of the polymer
to be a main component by greater than or equal to 10°C.
- (1) A hemispherical space of 0.5 × collection distance d around a nozzle tip relative
to the collection distance d between the tip of a spinning nozzle and a collection
surface of spun fibers.
- (2) A point of 1 cm from the collection surface on the straight line relative to the
collection distance d between the tip of the spinning nozzle and the collection surface
of spun fibers.
[0039] Note that in a case where greater than or equal to two different kinds of polymers
having a Tg of greater than or equal to 50°C are used, the temperature is maintained
at a temperature higher than the Tg of the polymer having the highest Tg by greater
than or equal to 10°C.
[0040] Herein, Figs. 2 and 3 are schematic diagrams for illustrating a principle of the
method for producing a nonwoven fabric of the present invention. Fig. 2 shows a state
that a melt blown method is performed by using a melt blown device 11, and after polymer
fibers 13 are discharged (spun) from a spinning nozzle 12 of melt blown device 11,
discharged (spun) polymer fibers 13 are collected by a rotating roll 14, and a web
(that is in a sheet shape obtained by piling up fibers) 15 is formed. Hot air (primary
air) 16 for spinning is discharged together with polymer fibers 13 from spinning nozzle
12 of melt blown device 11, and flows along the curved surface of roll 14. At that
time, the present inventors found that as cold air flows as accompanying flow 17 toward
spinning nozzle 12, polymer fibers 13 discharged from a tip 12a of spinning nozzle
12 are rapidly cooled before reaching a surface (collection surface of spun fibers)
14a of roll 14, and thus web 15 having low strength and poor handleability is formed.
For this reason, conventionally, it has been required to perform a post processing
such as calender processing, emboss processing, or spunlace (hydroentangle) processing
to impart strength to a web and to form a nonwoven fabric. The temperature of the
primary air (measured using a contact-type temperature sensor) discharged from a tip
of a spinning nozzle, which was actually measured by the present inventors, was 420°C,
but the temperature of the primary air (measured using a contact-type temperature
sensor) reached a collection surface of spun fibers was 145°C.
[0041] In the method for producing a nonwoven fabric of the present invention, as shown
in Fig. 3, a temperature in a hemispherical space A of 0.5 × collection distance d
around a nozzle tip relative to the collection distance d between tip 12a of spinning
nozzle 12 and collection surface 14a of spun fibers 13, a radius x around tip 12a
of spinning nozzle 12 being 0.5 × collection distance d, and/or a temperature in a
point B (not shown) of 1 cm from the collection surface on the straight line relative
to the direct distance d between tip 12a of spinning nozzle 12 and collection surface
14a of spun fibers 13 maintains at a temperature higher than the Tg of the polymer
by greater than or equal to 10°C. Herein, in the method for producing a nonwoven fabric
of the present invention, the temperature in either space A or point B is only required
to be maintained at a temperature higher than the Tg of the polymer by greater than
or equal to 10°C, but the temperatures in both of space A and point B may be maintained
at a temperature higher than the Tg of the polymer by greater than or equal to 15°C.
Further, as in the example shown in Fig. 3, a part of space A and a part of point
B may be overlapped.
[0042] By maintaining the temperature in at least one of the above-described space A and
point B at a temperature higher than the Tg by greater than or equal to 10°C, the
cooling of primary air by the accompanying flow as described above is prevented, and
the nonwoven fabric of the present invention that contains a polymer having a Tg of
greater than or equal to 50°C as a main component and has sufficient strength obtained
by fusing fibers to one another can be produced without performing a post processing
such as calender processing, emboss processing, or spunlace processing (that is, web
15 collected by roll 14 can be used as it is as the nonwoven fabric).
[0043] Herein, in a case where a temperature in hemispherical space A of radius x that is
0.5 × collection distance d around a nozzle tip relative to the collection distance
d between tip 12a of spinning nozzle 12 and collection surface 14a of spun fibers
13 is higher than the Tg by greater than or equal to 10°C, the temperature in a space
around hemispherical space A is not particularly limited. Radius x in hemispherical
space A around tip 12a of spinning nozzle 12 is preferably 3 to 12 cm, and particularly
preferably 5 cm. For example, a temperature in space A can be measured by arranging,
for example, a thermocouple-type thermometer as a thermometer at any position on a
curved surface constituting a hemisphere assumed as a boundary of space A.
[0044] Further, even in a case where a temperature in point B of 1 cm from the collection
surface on the straight line relative to the direct distance d between tip 12a of
spinning nozzle 12 and collection surface 14a of spun fibers 13 is higher by greater
than or equal to 10°C, the temperature in a space around point B is not particularly
limited.
[0045] In the method for producing a nonwoven fabric of the present invention, the temperature
in at least one of space A and point B is maintained so as to be at a temperature
higher than the Tg of a polymer by greater than 15 to 60°C). In a case where a temperature
in at least one of space A and point B is at a temperature less than or equal to the
Tg of a polymer, or is less than 10°C even if being higher than the Tg, the effect
of preventing the cooling of the spun fibers by the accompanying flow is insufficient,
and thus a nonwoven fabric having low strength and poor handleability may be produced.
[0046] Fig. 4 is a diagram schematically showing one preferred example of the method for
producing a nonwoven fabric of the present invention. In the example shown in Fig.
4, a hot air injection device 21 is arranged in the vicinity of tip 12a of spinning
nozzle 12 so as to blow hot air (for the primary air described above, this hot air
is referred to as "secondary air") 22 toward tip 12a of spinning nozzle 12. The arrangement
of hot air injection device 21 is not particularly limited, and hot air injection
device 21 in a shape of continuously forming a circumference surrounding tip 12a of
spinning nozzle 12 may be arranged so that a blowing tip is directed toward tip 12a
of spinning nozzle 12, or multiple hot air injection devices 21 may be arranged around
tip 12a so that a blowing tip is directed toward tip 12a of spinning nozzle 12. For
example, in this way, as described above, by maintaining the temperature in at least
one of the above (1) and (2) at a temperature higher than the Tg of a polymer by greater
than or equal to 10°C, a melt blown method can be performed. Note that as hot air
injection device 21, a conventionally known appropriate hot air injection device can
be used without any particular limitation.
[0047] The temperature of secondary air 22 injected so as to be blown into tip 12a of spinning
nozzle 12 by hot air injection device 21 is not particularly limited as long as the
temperature in at least one of the above (1) and (2) (in particular, a space of the
above-described (1)) can be maintained at a temperature higher than the Tg of a polymer
by greater than or equal to 30°C, and is preferably at a temperature higher than the
Tg of a polymer by 35 to 70°C and more preferably at a temperature higher than the
Tg of a polymer by 35 to 60°C. In a case where the temperature of secondary air 22
is at a temperature higher than the Tg of a polymer by less than 30°C, it becomes
difficult to maintain the temperature in at least one of the above-described (1) and
(2) (in particular, a space of the above-described (1)), and further, there is a tendency
that the fiber fusion is small and the nonwoven fabric strength is weak. Furthermore,
in a case where the temperature of secondary air 22 is higher than the Tg of a polymer
by exceeding 70°C, there is a tendency that the fiber fusion is increased and a paper-like
nonwoven fabric is obtained. Moreover, the flow rate of secondary air 22 is also not
particularly limited as long as the temperature in at least one of the above (1) and
(2) (in particular, a space of the above-described (1)) can be maintained at a temperature
higher than the Tg of a polymer by greater than or equal to 10°C, and is in order
not to disturb the flow of the primary air, preferably within the range of 3 to 12
Nm
3/m, and more preferably within the range of 4 to 10 Nm
3/m.
[0048] Fig. 5 is a diagram schematically showing another preferred example of the method
for producing a nonwoven fabric of the present invention. In the example shown in
Fig. 5, at least a part of a space between tip 12a of spinning nozzle 12 and collection
surface 14a of spun fibers is covered with a cover 31. As a result, the primary air
discharged from tip 12a of the spinning nozzle 12 stays in the space covered with
cover 31 as circulation air 32, and thus the primary air discharged from tip 12a of
spinning nozzle 12 is not rapidly cooled by the accompanying flow as in a case of
not being covered with cover 31. As described above, also in this way, by maintaining
the temperature in at least one of the above (1) and (2) at a temperature higher than
the Tg of a polymer by greater than or equal to 10°C, a melt blown method can be performed.
Note that as long as the temperature in at least one of the above (1) and (2) is maintained
at a temperature higher than the Tg of a polymer by greater than or equal to 10°C,
cover 31 does not need to cover throughout between tip 12a of spinning nozzle 12 and
collection surface 14a of spun fibers. As in the example shown in Fig. 5, it is preferred
that cover 31 is arranged so as to cover throughout between tip 12a of spinning nozzle
12 and collection surface 14a of spun fibers. A material for forming such cover 31
is not particularly limited as long as having heat resistance to the extent that the
cover is not deteriorated due to the temperature of primary air, for example, a metal
such as steel use stainless (SUS), aluminum, and copper can be mentioned, and SUS
is preferred from the viewpoint of the durability, the processability, and the heat
resistance.
[0049] In the method for producing a nonwoven fabric of the present invention, by maintaining
the temperature in at least one of the above (1) and (2) at a temperature higher than
the Tg of a polymer by greater than or equal to 10°C, a melt blown method is performed,
and processes, conditions, and the like that are similar to those in a conventional
melt blown method can be suitably adopted except that a post processing such as calender
processing, emboss processing, or spunlace processing is not performed. As the spinning
conditions, for example, a spinning temperature of 300 to 500°C, a hot air temperature
(primary air temperature) of 300 to 500°C, and an amount of air of 5 to 25 Nm
3 per 1 m of nozzle length can be mentioned as suitable examples, but of course, the
spinning conditions are not limited to these examples.
EXAMPLES
[0050] Hereinafter, the present invention will be specifically described with reference
to examples, however, the present invention is not limited to the following examples
at all.
[Density of nonwoven fabric (g/cm3)]
[0051] The volume of a nonwoven fabric was measured using [basis weight of the nonwoven
fabric] and [thickness of the nonwoven fabric], and from these results, the density
of the nonwoven fabric was calculated.
[Proportion (%) of parts with a density exceeding 0.4 g/cm3]
[0052] Using a scanning electron microscope, a 100-times magnified photograph of a cross
section in a thickness direction of a nonwoven fabric was taken, a straight line of
10 mm of the photograph was observed in a width direction by visual inspection, the
length occupied by parts with a density exceeding 0.4 g/cm
3 was measured in this straight line, and a proportion was determined by the following
equation:
Note that with the observation of the photograph, it was determined whether or not
the density exceeds 0.4 g/cm
3 by using a function of distance measurement between two points attached to the SEM,
and by investigating the length of the parts with a density exceeding 0.4 g/cm
3.
[Vertical strength (strength in vertical direction (direction of flow), N/5 cm)]
[0053] The nonwoven fabric was cut into a piece with a width of 5 cm, and the piece was
extended at a tensile rate of 10 cm/min by using an autograph manufactured by Shimadzu
Corporation in accordance with JIS L 1906, and the load value at the time of breaking
was defined as the vertical strength.
[Melt viscosity]
[0054] The melt viscosity was measured under conditions of a temperature of 330°C and a
shear rate r = 1200 sec
-1, by using Capilograph 1B of Toyo Seiki Seisaku-Sho, Ltd.
[Glass transition temperature (°C)]
[0055] By using a solid dynamic viscoelasticity measuring device, "Rheospectra DVE-V4" manufactured
by Rheology Co. Ltd., the temperature dependency of loss tangent (tan δ) was measured
at a frequency of 10 Hz and at a temperature rise rate of 10°C/min, and the glass
transition temperature was determined from the peak temperature. Herein, the peak
temperature of tan δ means a temperature at which the first derivative value of the
amount of change to the temperature of the value of tan δ becomes zero.
[Fiber fusion rate (%)]
[0056] Using a scanning electron microscope, a 1000-times magnified photograph of a cross
section in a thickness direction of a nonwoven fabric was taken, and from the photograph,
a proportion of the number of cut sections where fibers are fused to one another relative
to the number of fiber cut sections (fiber cross sections) was determined by visual
inspection. A proportion of the number of the cross sections where greater than or
equal to two fibers are fused to one another, occupied in the total number of the
fiber cross sections that can be found in each region was expressed as a percentage
on the basis of the following equation:
Provided that the number of the fibers whose cross sections can be seen is counted
in each photograph, and in a case where the number of fiber cross sections are less
than or equal to 100, photographs to be observed were added so that the total number
of the fiber cross sections exceeds 100.
[Average area of parts where fibers are fused]
[0057] Using a scanning electron microscope, a 1000-times magnified photograph of the cross
section in the thickness direction of the nonwoven fabric was taken, from this photograph,
the area of the parts where fibers are fused was calculated, and the total was divided
by the number of the parts where fibers are fused to obtain the average value.
[Average fiber diameter (µm)]
[0058] The nonwoven fabric was photographed with magnification by a scanning electron microscope,
the diameters of arbitrary 100 fibers were measured, the average value was calculated,
and defined as the average fiber diameter.
[Basis weight of nonwoven fabric (g/m2)]
[0059] In accordance with JIS L 1913, a sample piece of length 20 cm × width 20 cm was taken,
the mass was measured with an electronic balance, the measured mass was divided by
the test piece area 400 cm
2, and the mass per unit area was defined as the basis weight.
[Thickness of nonwoven fabric (µm)]
[0060] In accordance with JIS L 1913, by using the same sample pieces as those in the measurement
of basis weight, the thickness was measured at five positions in each sample piece
with a digital thickness measuring device having a diameter of 16 mm and a load of
20 gf/cm
2 (B1 type, manufactured by Toyo Seiki Seisaku-Sho, Ltd.), and the average value of
the thicknesses at 15 positions was defined as the thickness of the sheet.
[Air permeability of nonwoven fabric (cc/cm2/sec)]
[0061] The air permeability was measured in accordance with a fragile form method of JIS
L 1913 "Test methods for nonwovens".
<Example 1>
[0062] Amorphous polyetherimide having a melt viscosity at 330°C of 500 Pa·s was used, and
extruded with an extruder to be supplied to a melt blown device having a nozzle with
a nozzle hole diameter D (diameter) of 0.3 mm, L (nozzle length) / D = 10, and a nozzle
hole pitch of 0.75 mm. By blowing hot air to the amorphous polyetherimide at a single
hole discharge rate of 0.09 g/min, a spinning temperature of 390°C, a hot air (primary
air) temperature of 420°C, and 10 Nm
3/min per 1 m of nozzle width, a nonwoven fabric having a basis weight of 25 g/m
2 was produced. At this time, a hot air injection device as in the example shown in
Fig. 4 was arranged so that hot air (secondary air) blows into a tip of the spinning
nozzle of the melt blown device, and hot air (secondary air) at a temperature of 260°C
was blown at a flow rate of 2 Nm
3 toward the tip of the spinning nozzle. The direct distance d between the tip of the
spinning nozzle and a receiving surface of a roller receiving the spun fibers was
10 cm, and the temperature measured by a thermometer (AD-5601A (manufactured by A&D
Company, Limited)) arranged so as to be positioned on a hemispherical outer periphery
of a radius x = 5 cm around the tip of the spinning nozzle was 235°C (that is, space
A was maintained at a temperature higher than 215°C that is a glass transition temperature
of the amorphous PEI by 20°C). Further, the temperature measured by a thermometer
(AD-5601A (manufactured by A&D Company, Limited)) arranged so as to be positioned
1 cm from a collection surface on the straight line relative to the direct distance
d between the tip of the spinning nozzle and the collection surface of the spun fibers
was 242°C (that is, point B was maintained at a temperature higher than 215°C that
is a glass transition temperature of the amorphous PEI by 27°C). In this way, a nonwoven
fabric was obtained without performing a post processing. As a SEM photograph of a
cross section in a thickness direction of the obtained nonwoven fabric, a 100-times
magnified photograph is shown in Fig. 1(a), and a 1000-times magnified photograph
is shown in Fig. 1(b).
<Example 2>
[0063] A nonwoven fabric was obtained by using amorphous polyetherimide having a melt viscosity
at 330°C of 900 Pa·s in the similar manner as in Example 1 except that the spinning
temperature was 420°C, the average fiber diameter was 3.7 µm, and the temperature
measured by a thermometer positioned on a hemispherical outer periphery of a radius
x = 5 cm around the tip of the spinning nozzle was 253°C (that is, space A was maintained
at a temperature higher than 215°C that is a glass transition temperature of the amorphous
PEI by 38°C), and the temperature measured by a thermometer arranged so as to be positioned
1 cm from the collection surface on the straight line relative to the direct distance
d between the tip of the spinning nozzle and the collection surface of the spun fibers
was 261°C (that is, point B was maintained at a temperature higher than 215°C that
is a glass transition temperature of the amorphous PEI by 46°C).
<Example 3>
[0064] A nonwoven fabric was obtained in the similar manner as in Example 2 except that
the basis weight was changed to 10 g/m
2.
<Example 4>
[0065] Amorphous polycarbonate having a melt viscosity at 300°C of 100 Pa·s was used, and
extruded with an extruder to be supplied to a melt blown device having a nozzle with
a nozzle hole diameter D (diameter) of 0.3 mm, L (nozzle length) / D = 10, and a nozzle
hole pitch of 0.75 mm. By blowing hot air to the amorphous polycarbonate at a single
hole discharge rate of 0.09 g/min, a spinning temperature of 340°C, a hot air (primary
air) temperature of 370°C, and 10 Nm
3/min per 1 m of nozzle width, a nonwoven fabric having a basis weight of 25 g/m
2 was produced. At this time, a hot air injection device as in the example shown in
Fig. 4 was arranged so that hot air (secondary air) blows into a tip of the spinning
nozzle of the melt blown device, and hot air (secondary air) at a temperature of 210°C
was blown at a flow rate of 2 Nm
3 toward the tip of the spinning nozzle. The direct distance d between the tip of the
spinning nozzle and a receiving surface of a roller receiving the spun fibers was
10 cm, and the temperature measured by a thermometer (AD-5601A (manufactured by A&D
Company, Limited)) arranged so as to be positioned on a hemispherical outer periphery
of a radius x = 5 cm around the tip of the spinning nozzle was 185°C (that is, space
A was maintained at a temperature higher than 135°C that is a glass transition temperature
of the amorphous polycarbonate by 50°C). Further, the temperature measured by a thermometer
(AD-5601A (manufactured by A&D Company, Limited)) arranged so as to be positioned
1 cm from the collection surface on the straight line relative to the direct distance
d between the tip of the spinning nozzle and a collection surface of the spun fibers
was 192°C (that is, point B was maintained at a temperature higher than 135°C that
is a glass transition temperature of the amorphous polycarbonate by 57°C).
<Comparative Example 1>
[0066] A nonwoven fabric was obtained in the similar manner as in Example 2 except that
the hot air injection device was not arranged (the temperature measured by a thermometer
positioned on a hemispherical outer periphery of a radius x = 5 cm around the tip
of the spinning nozzle was 41°C, and the temperature measured by a thermometer arranged
so as to be positioned 1 cm from the collection surface on the straight line relative
to the direct distance d between the tip of the spinning nozzle and the collection
surface of the spun fibers was 110°C).
<Comparative Example 2>
[0067] By using an embossing device, the nonwoven fabric obtained in Comparative Example
1 was subjected to emboss processing as the post processing with an embossing roll
having a lattice pattern under the conditions of a roll temperature of 180°C, a linear
pressure of 50 kg/cm, and a speed of 1 m/min. As a SEM photograph of a cross section
in a thickness direction of the obtained nonwoven fabric, a 100-times magnified photograph
is shown in Fig. 7(a), and a 1000-times magnified photograph is shown in Fig. 7(b).
<Comparative Example 3>
[0068] By using a calender processing device (iron roll), the nonwoven fabric obtained in
Comparative Example 1 was subjected to calender processing as the post processing
under the conditions of a roll temperature of 180°C, a linear pressure of 216 kg/cm,
and a speed of 3.2 m/min. As a SEM photograph of a cross section in a thickness direction
of the obtained nonwoven fabric, a 100-times magnified photograph is shown in Fig.
6(a), and a 1000-times magnified photograph is shown in Fig. 6(b).
<Comparative Example 4>
[0069] By using a hydroentangling device, the nonwoven fabric obtained in Comparative Example
1 was subjected to hydroentangling as the post processing at a speed of 5.0 m/min
using a nozzle having a hole diameter of 0.1 mmφ with hydroentangling treatment at
three stages of 0.5 MPa, 2.0 MPa, and 2.5 MPa. As a SEM photograph of a cross section
in a thickness direction of the obtained nonwoven fabric, a 100-times magnified photograph
is shown in Fig. 8(a), and a 1000-times magnified photograph is shown in Fig. 8(b).
<Comparative Example 5>
[0070] A nonwoven fabric was obtained under the similar conditions as in Example 2 except
that the temperature of the hot air (secondary air) was changed to 240°C. The temperature
measured by a thermometer positioned on a hemispherical outer periphery of a radius
x = 5 cm around the tip of the spinning nozzle was 220°C, and the temperature measured
by a thermometer arranged so as to be positioned 1 cm from the collection surface
on the straight line relative to the direct distance d between the tip of the spinning
nozzle and the collection surface of the spun fibers was 217°C.
[0071] The results are shown in Tables 1 and 2.
[Table 1]
|
Example 1 |
Example 2 |
Example 3 |
Example 4 |
(Raw material forming nonwoven fabric and production conditions) |
Polymer composition of fibers |
PEI |
PEI |
PEI |
PC |
Melt viscosity (Pa•s): 330°C (300°C in Example 4) |
500 |
900 |
900 |
100 |
Glass transition temperature (°C) |
215 |
215 |
215 |
135 |
Spinning temperature (°C) |
390 |
420 |
420 |
340 |
Hot air injection device |
Yes |
Yes |
Yes |
Yes |
Hot air (secondary air) temperature (°C) |
260 |
260 |
260 |
210 |
Collection distance (cm) |
10 |
10 |
10 |
10 |
Temperature in space A (°C) |
235 |
253 |
253 |
185 |
Temperature in point B (°C) |
242 |
261 |
261 |
192 |
Post processing |
No |
No |
No |
No |
(Performance of nonwoven fabric) |
Density (g/cm3) |
0.147 |
0.132 |
0.103 |
0.295 |
Proportion of parts with a density exceeding 0.4 g/cm3 (%) |
0 |
0 |
0 |
1.4 |
Vertical strength per 1 g/m2 (N/5cm) |
1.6 |
1.7 |
1.6 |
1.9 |
Fiber fusion rate (%) |
36 |
28 |
28 |
48 |
Average area of parts where fibers are fused (µm2) |
24 |
33 |
33 |
52 |
Average fiber diameter (µm) |
2.5 |
3.7 |
3.7 |
2.8 |
Basis weight (g/m2) |
25 |
25 |
10 |
25 |
Thickness (µm) |
170 |
189 |
107 |
85 |
Air permeability (cc/cm2/see) |
54 |
75 |
110 |
32 |
[Table 2]
|
Comparative Example 1 |
Comparative Example 2 |
Comparative Example 3 |
Comparative Example 4 |
Comparative Example 5 |
(Raw material forming nonwoven fabric and production conditions) |
Polymer composition of fibers |
PEI |
PEI |
PEI |
PEI |
PEI |
Melt viscosity (Pa•s): 330°C |
900 |
900 |
900 |
900 |
900 |
Glass transition temperature (°C) |
215 |
215 |
215 |
215 |
215 |
Spinning temperature (°C) |
420 |
420 |
420 |
420 |
420 |
Hot air injection device |
No |
No |
No |
No |
Yes |
Hot air (secondary air) temperature (°C) |
- |
- |
- |
- |
240 |
Collection distance (cm) |
10 |
10 |
10 |
10 |
10 |
Temperature in space A (°C) |
41 |
41 |
41 |
41 |
220 |
Temperature in point B (°C) |
110 |
110 |
110 |
110 |
217 |
Post processing |
No |
Emboss |
Calender |
Spunlace |
No |
(Performance of nonwoven fabric) |
Density (g/cm3) |
0.059 |
0.139 |
0.735 |
0.106 |
0.080 |
Proportion of parts with a density exceeding 0.4 g/cm3 (%) |
0 |
23 |
100 |
0 |
0 |
Vertical strength per 1 g/m2 (N/5cm) |
0.1 |
0.6 |
0.9 |
0.9 |
0.2 |
Fiber fusion rate (%) |
0 |
6 |
70 |
0 |
12 |
Average area of parts where fibers are fused (µm2) |
No fiber fusion |
85 |
130 |
No fiber fusion |
No fiber fusion |
Average fiber diameter (µm) |
3.7 |
3.7 |
3.7 |
3.7 |
4.0 |
Basis weight (g/m2) |
25 |
25 |
25 |
25 |
25 |
Thickness (µm) |
423 |
180 |
34 |
236 |
311 |
Air permeability (cc/cm2/sec) |
221 |
25 |
4 |
76 |
156 |
INDUSTRIAL APPLICABILITY
[0072] The nonwoven fabric of the present invention is excellent in the handleability in
spite of having a low density, therefore, not only can be used in combination with
various substrates and other nonwoven fabrics, but also can be used for filters and
the like that are required to have permeability.
REFERENCE SIGNS LIST
[0073] 1: Nonwoven fabric, 2: fibers, 3: fusion part, 11: melt blown device, 12: spinning
nozzle, 12a: tip of spinning nozzle 12, 13: spun amorphous polymer-based fibers, 14:
roll, 14a: roll receiving surface, 15: nonwoven fabric, 16: primary air, 17: accompanying
flow, 21: hot air injection device, 22: secondary air, 31: cover, 32: circulation
air.