U.S. patent application number 14/429957 was filed with the patent office on 2015-08-27 for polyphenylene sulfide composite fiber and nonwoven fabric.
This patent application is currently assigned to TORAY INDUSTRIES, INC.. The applicant listed for this patent is TORAY INDUSTRIES, INC.. Invention is credited to Ryoichi Hane, Yohei Nakano, Yoshikazu Yakake.
Application Number | 20150240390 14/429957 |
Document ID | / |
Family ID | 50341430 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150240390 |
Kind Code |
A1 |
Yakake; Yoshikazu ; et
al. |
August 27, 2015 |
POLYPHENYLENE SULFIDE COMPOSITE FIBER AND NONWOVEN FABRIC
Abstract
Provided are a composite fiber which consists primarily of
resins comprising polyphenylene sulfide as their main constituents
and which has both thermal dimensional stability and excellent
thermal bondability, and a nonwoven fabric. The composite fiber
consists primarily of component A and component B, the component A
being a resin that includes polyphenylene sulfide as its main
constituent, the component B being a resin that includes
polyphenylene sulfide as its main constituent, having a higher melt
flow rate than the component A, and forming at least part of the
surface of the fiber.
Inventors: |
Yakake; Yoshikazu;
(Otsu-shi, JP) ; Hane; Ryoichi; (Otsu-shi, JP)
; Nakano; Yohei; (Otsu-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TORAY INDUSTRIES, INC. |
Tokyo |
|
JP |
|
|
Assignee: |
TORAY INDUSTRIES, INC.
TOKYO
JP
|
Family ID: |
50341430 |
Appl. No.: |
14/429957 |
Filed: |
September 18, 2013 |
PCT Filed: |
September 18, 2013 |
PCT NO: |
PCT/JP2013/075134 |
371 Date: |
March 20, 2015 |
Current U.S.
Class: |
442/364 ;
428/373 |
Current CPC
Class: |
D04H 3/14 20130101; Y10T
428/2929 20150115; D04H 1/4382 20130101; D04H 1/4291 20130101; Y10T
442/641 20150401; D04H 3/147 20130101; D04H 3/16 20130101; D04H
3/009 20130101; D01F 8/16 20130101 |
International
Class: |
D01F 8/16 20060101
D01F008/16; D04H 3/009 20060101 D04H003/009 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2012 |
JP |
2012-208019 |
Sep 21, 2012 |
JP |
2012-208020 |
Claims
1. A polyphenylene sulfide composite fiber consisting primarily of
component A and component B, the component A being a resin that
comprises polyphenylene sulfide as its main constituent, the
component B being a resin that comprises polyphenylene sulfide as
its main constituent, having a higher melt flow rate than the
component A, and forming at least part of the surface of the
fiber.
2. The polyphenylene sulfide composite fiber according to claim 1,
wherein at least part of the surface of the fiber has a lower
crystallinity than the center of the cross section of the fiber
when the crystallinity of the fiber surface is measured in the
region from the fiber surface to 1 .mu.m in the radially inward
direction of the fiber.
3. The polyphenylene sulfide composite fiber according to claim 1
or 2, wherein the melt flow rate of the component A (MFR (A)) and
the melt flow rate of the component B (MFR (B)) satisfy the
following formula: 10 (g/10 min).ltoreq.MFR(B)-MFR(A).ltoreq.1000
(g/10 min).
4. The polyphenylene sulfide composite fiber according to claim 1
or 2, which is a core-sheath composite fiber comprising the
component A as a core component and the component B as a sheath
component.
5. A nonwoven fabric made from the polyphenylene sulfide composite
fiber according to claim 1 or 2.
6. The nonwoven fabric according to claim 5, which is a spunbonded
nonwoven fabric.
7. The nonwoven fabric according to claim 6, which is produced by
integrating the polyphenylene sulfide composite fiber by thermal
bonding.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is the U.S. National Phase application of PCT
International Application No. PCT/JP2013/075134, filed Sep. 18,
2013, and claims priority to Japanese Patent Application No.
2012-208019, filed Sep. 21, 2012, and Japanese Patent Application
No. 2012-208020, filed Sep. 21, 2012.
FIELD OF THE INVENTION
[0002] The present invention relates to a polyphenylene sulfide
(sometimes abbreviated as "PPS") composite fiber which consists
primarily of resins comprising PPS as their main constituents and
which is excellent in heat resistance and chemical resistance, and
to a nonwoven fabric made from the fiber.
BACKGROUND OF THE INVENTION
[0003] A PPS resin has excellent characteristics such as heat
resistance, flame retardancy and chemical resistance, and is
suitable for engineering plastics, films, fibers, nonwoven fabrics,
and the like. In particular, nonwoven fabrics utilizing these
excellent characteristics are expected to be used for industrial
applications such as heat-resistant filters, electrical insulating
materials and battery separators.
[0004] There has been proposed, as a nonwoven fabric made from a
PPS resin, a long-fiber nonwoven fabric produced by spinning a PPS
resin and drawing the resulting long fibers to forma fabric by
spunbonding, temporarily bonding the fabric at a temperature not
higher than the first crystallization temperature of the fabric,
heat treating the fabric under tension at a temperature not lower
than the first crystallization temperature, and thermal bonding the
fabric (see Patent Literature 1). However, in such a process with
heat treatment, the crystallinity of the fibers becomes too high,
which leads to insufficient thermal bondability resulting in a
nonwoven fabric of a low mechanical strength.
[0005] Another proposed nonwoven fabric is a heat-resistant
nonwoven fabric produced by spinning fibers comprising 30 wt % or
more of a PPS fiber with a degree of crystallinity of 25 to 50% at
a spinning rate of 6000 m/min or more, and integrating the fibers
by thermal bonding (see Patent Literature 2). However, the fibers
produced by high-speed spinning at a spinning rate of 6000 m/min or
more have a high crystallinity, which leads to insufficient thermal
bondability resulting in a nonwoven fabric of a low mechanical
strength.
[0006] In general, higher crystallinity of synthetic fibers results
in higher thermal dimensional stability and a lower thermal
bondability. In other words, thermal dimensional stability and
thermal bondability are in a trade-off relationship. In particular,
in the case of PPS fibers, achieving both qualities at the same
time is difficult as described above.
[0007] In order to solve this problem, the applicants of the
present invention have proposed a PPS long-fiber nonwoven fabric
having both thermal dimensional stability and excellent thermal
bondability, in particular, a long-fiber nonwoven fabric produced
by drawing and stretching long fibers by hot compressed air and
thermally bonding the resulting web (see Patent Literature 3).
[0008] Indeed, this technique was able to achieve a certain effect
of imparting thermal dimensional stability and improving thermal
bondability, but when the mass per unit area was high, sufficient
thermal bondability could not be obtained.
[0009] Thus, there has not been provided a PPS fiber having both
thermal dimensional stability and excellent thermal bondability or
a PPS nonwoven fabric having a high mechanical strength.
PATENT LITERATURE
[0010] Patent Literature 1: JP 2008-223209 A
[0011] Patent Literature 2: WO 2008/035775
[0012] Patent Literature 3: WO 2011/070999
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a
polyphenylene sulfide composite fiber having both thermal
dimensional stability and excellent thermal bondability and a
nonwoven fabric being made from the fiber and having a high
mechanical strength.
[0014] That is, the present invention includes, according to an
aspect of the invention, a polyphenylene sulfide composite fiber
consisting primarily of component A and component B, component A
being a resin that comprises polyphenylene sulfide as its main
constituent, component B being a resin that comprises polyphenylene
sulfide as its main constituent, having a higher melt flow rate
(hereinafter, melt flow rate is also referred to as MFR) than
component A, and forming at least part of the surface of the
fiber.
[0015] The present invention also includes a nonwoven fabric made
from the polyphenylene sulfide composite fiber.
[0016] The PPS composite fiber of the present invention has both
thermal dimensional stability and excellent thermal bondability.
Hence, the nonwoven fabric of the present invention has both
thermal dimensional stability and excellent mechanical strength,
and therefore can be used for various industrial applications.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0017] An important feature of the composite fiber of embodiments
of the present invention is that the fiber consists primarily of
component A and component B and that each of the components
comprises PPS as its main constituent. With this configuration, the
fiber exhibits excellent heat resistance, flame retardancy and
chemical resistance. The term "consists primarily of" means that
the components account for 90% by mass or more of the total mass of
the fiber. The term "comprises as its main constituent" means that
a particular ingredient accounts for 85% by mass or more of the
total mass of the resin, component, or the fiber.
[0018] Another important feature of the PPS composite fiber of
embodiments of the present invention is that it is a PPS composite
fiber consisting primarily of component A and component B,
component A being a resin that comprises polyphenylene sulfide as
its main constituent, component B being a resin that comprises
polyphenylene sulfide as its main constituent, having a higher melt
flow rate than component A, and forming at least part of the
surface of the fiber.
[0019] In general, fibers produced by a common spinning process
have fiber structure in which orientation and crystallinity
increase from the center of the cross section of the fiber to the
surface of the fiber. This structure is created as follows: cooling
of fibers spun from a spinneret proceeds from the fiber surface
toward the inside of the fibers, and due to the cooling, the
fluidity beneath the fiber surface is reduced, causing the
concentration of spinning stress on the fiber surface, and then
oriented crystallization proceeds therefrom.
[0020] With such fiber structure, even when the fiber as a whole
has a low crystallinity, the fiber surface, which is crucially
important for thermal bonding, has a high crystallinity, resulting
in insufficient thermal bondability.
[0021] The present invention includes a composite fiber consisting
primarily of component A and component B, component A being a resin
that comprises polyphenylene sulfide as its main constituent,
component B being a resin that comprises polyphenylene sulfide as
its main constituent and having a higher melt flow rate than
component A. In this composite fiber, spinning stress is
concentrated on component A, and thereby the orientation and
crystallization of component B is suppressed. Further, at least
part of the fiber surface is formed of component B with suppressed
orientation and crystallinity, and as a result the fiber has
thermal dimensional stability and very excellent thermal
bondability.
[0022] As described above, the fiber comprising polyphenylene
sulfide as its main constituent has a lower crystallinity in at
least part of the fiber surface than in the center of the cross
section of the fiber when the crystallinity of the fiber surface is
measured in the region from the fiber surface to 1 .mu.m in
radially inward direction of the fiber. The fiber provided with
such fiber structure with the opposite configuration to that of the
structure of fibers produced by common spinning process achieves
both thermal dimensional stability and very excellent thermal
bondability.
[0023] The PPS in components A and B preferably contains 93 mol %
or more of p-phenylene sulfide units. The PPS containing 93 mol %
or more of p-phenylene sulfide units, more preferably 95 mol % or
more of p-phenylene sulfide units, provides excellent spinnability
and produces fibers with excellent mechanical strength.
[0024] Components A and B each preferably contain 85% by mass or
more of the PPS resin, more preferably 90% by mass or more of the
PPS resin, further more preferably 95% by mass or more of the PPS
resin, for achieving heat resistance, chemical resistance, and the
like.
[0025] Components A and B each may contain a thermoplastic resin
other than the PPS resin as long as the effects of the present
invention are not impaired. Examples of the thermoplastic resin
other than the PPS resin include polyetherimide, polyethersulfone,
polysulfone, polyphenylene ether, polyester, polyarylate,
polyamide, polyamide-imide, polycarbonate, polyolefin, and
polyether ether ketone.
[0026] Components A and B each may contain additives such as
nucleating agents, delustrants, pigments, antifungal agents,
antimicrobial agents, fire retardants and hydrophilizing agents, as
long as the effects of the present invention are not impaired.
[0027] The MFR of component A of the present invention as measured
in accordance with ASTM D1238-70 (measurement temperature:
315.5.degree. C., applied load: 5 kg) is preferably 50 to 300 g/10
min. When the MFR is 50 g/10 min or more, more preferably 100 g/10
min or more, adequate fluidity is obtained, and thereby an increase
in the back pressure at the spinneret is suppressed and breakage of
fibers during drawing and stretching is prevented. When the MFR is
300 g/10 min or less, more preferably 225 g/10 min or less, an
appropriately high polymerization degree or molecular weight is
obtained, and thereby sufficient mechanical strength and heat
resistance for practical use are obtained.
[0028] Another important feature of embodiments of the present
invention is that the MFR (as measured in accordance with the above
ASTM D1238-70) of component B of the present invention is higher
(i.e., the viscosity is lower) than that of component A. The
difference obtained by subtracting the MFR of component A from the
MFR of component B is preferably 10 g/10 min or more, more
preferably 50 g/10 min or more, further more preferably 100 g/10
min or more. With this condition, spinning stress imposed to
component B is reduced, and thereby the oriented crystallization of
component B is suppressed.
[0029] The difference obtained by subtracting the MFR of component
A from the MFR of component B is preferably 1000 g/10 min or less,
more preferably 500 g/10 min or less, further more preferably 200
g/10 min or less. With this condition, adequate fluidity is
obtained, and thereby stable spinning can be performed.
[0030] The amount of component B is preferably 5 to 70% by mass of
the total amount of the PPS composite fiber. When the amount of
component B is 5% by mass or more, more preferably 10% by mass or
more, furthermore preferably 15% by mass or more, strong thermal
bonding is achieved efficiently. When the amount of component B is
70% by mass or less, more preferably 50% by mass or less, further
more preferably 30% by mass or less, the decrease in mechanical
strength is prevented.
[0031] An important feature of the composite form of the PPS
composite fiber of embodiments of the present invention is that
component B forms at least part of the fiber surface. The advantage
of this configuration is that component B exposed to the surface of
the fiber contributes to thermal bonding. In addition, component A
is preferably successively disposed in the longitudinal direction
of the PPS composite fiber of the present invention. The successive
disposition of component A in the longitudinal direction of the
fiber more effectively concentrates spinning stress on component A
and suppresses the orientation and crystallization of component
B.
[0032] Examples of the composite form of the PPS composite fiber of
the present invention include a core-sheath type of which the cross
section has circle-shaped component A surrounded by concentric
donut-shaped component B, an eccentric core-sheath type in which
the center of component A is not coaxial with the center of
component B, an islands-in-the-sea type containing component A as
the sea component and component B as the island component, a
side-by-side type containing components A and B lying side-by-side,
a segmented pie type in which components A and B are alternately
arranged in radial segments, and a multilobal type containing
several portions of component B arranged around component A. Among
them, preferred is the core-sheath type in which the component B
occupies the entire surface of the fiber and which is excellent in
spinnability.
[0033] The average single fiber fineness of the PPS composite fiber
of the present invention is preferably 0.5 to 10 dtex. When the
average single fiber fineness is 0.5 dtex or more, more preferably
1 dtex or more, further more preferably 2 dtex or more, the
spinnability of the fiber is maintained and frequent breakage of
the fiber during spinning is prevented. When the average single
fiber fineness is 10 dtex or less, more preferably 5 dtex or less,
further more preferably 4 dtex or less, the amount of the extruded
molten resin per spinneret hole is appropriately reduced so that
the spun fibers are sufficiently cooled, thereby preventing the
deterioration of spinnability caused by fusion of the fibers. In
addition, the fiber with such average single fiber fineness can
produce a nonwoven fabric not having varying mass per unit area but
having excellent quality of the surface. Considering the
dust-collecting performance of the nonwoven fabric in use as a
filter or the like, the average single fiber fineness is preferably
10 dtex or less, more preferably 5 dtex or less, and further more
preferably 4 dtex or less.
[0034] The PPS composite fiber of the present invention can be
produced as a multifilament yarn, a monofilament yarn or a staple
yarn, and can also be used to produce any types of fabrics such as
woven fabrics and nonwoven fabrics. The PPS composite fiber of the
present invention is especially preferably used to produce a
nonwoven fabric. This is because, in a nonwoven fabric, the PPS
composite fibers thermally bonded to each other and thereby enhance
the strength of the nonwoven fabric.
[0035] Examples of the nonwoven fabrics include needle punched
nonwoven fabrics, wet-laid nonwoven fabrics, spun lace nonwoven
fabrics, spunbonded nonwoven fabrics, meltblown nonwoven fabrics,
resin-bonded nonwoven fabrics, chemical-bonded nonwoven fabrics,
thermally bonded nonwoven fabrics, tow-opening nonwoven fabrics,
and air-laid nonwoven fabrics. Among them, preferred are spunbonded
nonwoven fabrics, which are excellent in productivity and
mechanical strength.
[0036] The nonwoven fabric made from the PPS composite fiber of the
present invention exhibits a high mechanical strength after thermal
bonding, and therefore the nonwoven fabric of the present invention
is preferably produced by integrating the fibers by thermal
bonding.
[0037] The mass per unit area of the nonwoven fabric of the present
invention is preferably 10 to 1,000 g/m.sup.2. When the mass per
unit area of the nonwoven fabric of the present invention is 10
g/m.sup.2 or more, more preferably 100 g/m.sup.2 or more, further
more preferably 200 g/m.sup.2 or more, the nonwoven fabric exhibits
sufficient mechanical strength for practical use. When the mass per
unit area of the nonwoven fabric of the present invention is 1,000
g/m.sup.2 or less, more preferably 700 g/m.sup.2 or less, further
more preferably 500 g/m.sup.2 or less, the nonwoven fabric exhibits
adequate breathability and thereby will not cause high pressure
drop when used as a filter or the like.
[0038] From the tensile strength in the longitudinal direction, the
tensile elongation in the longitudinal direction and the mass per
unit area of the nonwoven fabric, the product of strength and
elongation per mass per unit area is calculated by the formula
below. The product of strength and elongation per mass per unit
area of the nonwoven fabric made from the thermally bondable
composite fiber of the present invention is preferably 25 or
more.
[0039] Product of strength and elongation per mass per unit
area=longitudinal tensile strength (N/5 cm).times.longitudinal
tensile elongation (%)/mass per unit area (g/m.sup.2)
[0040] When the product of strength and elongation per mass per
unit area is 25 or more, more preferably 35 or more, further more
preferably 40 or more, the nonwoven fabric has sufficient
mechanical strength for use in severe environment. The upper limit
of the product of strength and elongation per mass per unit area is
not particularly defined, but the product of strength and
elongation per mass per unit area of the nonwoven fabric of the
present invention is preferably 100 or less so that the nonwoven
fabric is not too hard to handle.
[0041] Preferred embodiments of processes for producing the PPS
composite fiber and the nonwoven fabric of the present invention
will be described below.
[0042] The PPS composite fiber of the present invention can be
produced by a conventional melt spinning process. For example, for
the production of a core-sheath composite fiber, a PPS resin as the
core component and a PPS resin as the sheath component are melted
in separate extruders, metered, fed to a spinneret for core-sheath
composite spinning, and melt spun into continuous fibers. The
fibers are cooled with a conventional cooling device that blows air
laterally or circularly, an oil is applied to the fibers, and the
fibers are taken up on a winder with a take-up roller to produce a
core-sheath composite fiber as undrawn fibers. When the composite
fiber is desired to be provided in the form of short fibers, the
wound undrawn fibers are drawn with a conventional drawing machine
having a plurality of pairs of rollers at different circumferential
speeds, crimped in a stuffer-box crimper or the like, and cut into
a desired length with a cutter such as an EC cutter. When the
composite fiber is desired to be provided in the form of long
fibers, the wound undrawn fibers are drawn with a drawing machine,
taken up, and, if necessary, subjected to processing such as
twisting and false twisting.
[0043] A process for producing a composite-fiber nonwoven fabric by
spunbonding process, which is a preferred embodiment of the
nonwoven fabric of the present invention, will be described
below.
[0044] Spunbonding process is a production process involving
melting a resin, spinning continuous fibers from the molten resin
by extruding it from a spinneret, cooling and solidifying the
fibers, drawing and stretching the fibers with an ejector,
collecting the fibers on a moving net to form a nonwoven web, and
thermally bonding the web.
[0045] The spinneret and the ejector may be in various shapes such
as a circular shape and a rectangular shape. Inter alia, a
combination of a rectangular spinneret and a rectangular ejector is
preferred so that the amount of compressed air to be used is
relatively small and the continuous fibers hardly fuse to each
other or rub against each other.
[0046] The spinning temperature for melting and spinning the resin
is preferably 290 to 380.degree. C., more preferably 295 to
360.degree. C., further more preferably 300 to 340.degree. C. The
spinning temperature within the above range allows the resin to be
in a stable molten state and to exhibit excellent spinning
stability.
[0047] Components A and B are melted in separate extruders,
metered, and fed to a spinneret for composite spinning, and spun
into composite fibers.
[0048] Cooling of the spun continuous composite fibers may be
performed by, for example, a method in which cold air is forced to
blow over the continuous fibers, a method in which the continuous
fibers are allowed to cool down at ambient temperature around the
fibers, a method in which the distance between the spinneret and
the ejector is adjusted, or a combined method thereof. Cooling
conditions can be appropriately adjusted based on the discharge
rate per spinneret hole, the spinning temperature, the ambient
temperature, and the like.
[0049] The continuous fibers solidified by cooling are drawn and
stretched by compressed air ejected from the ejector. The methods
and conditions for drawing and stretching the fibers by means of
the ejector are not particularly limited, but preferred are methods
that efficiently promote the crystallization of the PPS fibers, in
particular, a method in which the fibers are drawn and stretched at
a spinning rate of 3,000 m/min or more by compressed air that is
heated to 100.degree. C. or higher and then ejected from the
ejector, or a method in which the fibers are drawn and stretched at
a spinning rate of not less than 5,000 m/min and less than 6,000
m/min by compressed air (at normal temperature) ejected from the
ejector that is disposed so that the compressed air outlet of the
ejector is 450 to 650 mm distant from the bottom of the
spinneret.
[0050] The drawn PPS composite fibers are collected on a moving net
to form a nonwoven web, and the obtained nonwoven web is integrated
by thermal bonding to form a nonwoven fabric.
[0051] The thermal bonding can be performed by, for example,
thermal pressure bonding using various types of rolls, such as a
hot embossing roll pair of upper and lower rolls each having an
embossed surface, a hot embossing roll pair of a roll having a flat
(smooth) surface and a roll having an embossed surface, and a hot
calendering roll pair of upper and lower flat (smooth) rolls; and
through-air bonding involving passing hot air through a nonwoven
web in the thickness direction thereof. Among these, preferred is
thermal bonding using a hot embossing roll pair, which improves the
mechanical strength and allows the nonwoven fabric to retain
adequate breathability.
[0052] The emboss pattern on the embossing roll(s) may be circle,
oval, square, rectangle, parallelogram, diamond, regular hexagon,
regular octagon, or the like.
[0053] Regarding the surface temperature of the hot embossing roll
pair, since the PPS composite fiber of the present invention is
very excellent in thermal bondability and thus can be thermally
bonded at a lower temperature than usual, the surface temperature
of the hot embossing roll pair is preferably 150 to 5.degree. C.
lower than the melting point of PPS. When the surface temperature
of the hot embossing roll pair is not lower than the temperature
that is 150.degree. C. lower than the melting point of PPS, more
preferably not lower than the temperature that is 100.degree. C.
lower than the melting point of PPS, further more preferably not
lower than the temperature that is 50.degree. C. lower than the
melting point of PPS, the fibers are sufficiently thermally bonded
and thereby flaking off and fluffing of the resulting nonwoven
fabric are prevented. When the surface temperature of the hot
embossing roll pair is not higher than the temperature that is
5.degree. C. lower than the melting point of PPS, holes in the
press-bonded parts due to melting of the fibers are prevented from
being generated.
[0054] The linear pressure applied by the hot embossing roll pair
during thermal bonding is preferably 200 to 1500 N/cm. When the
linear pressure applied by the hot embossing roll pair is 200 N/cm
or more, more preferably 300 N/cm or more, the fibers are
sufficiently thermally bonded and thereby flaking off and fluffing
of the resulting sheet is prevented. When the linear pressure
applied by the hot embossing roll pair is 1500 N/cm or less, more
preferably 1000 N/cm or less, the raised portions of the embossing
roll(s) are prevented from biting into the nonwoven fabric and
thereby difficulty in removing the nonwoven fabric from the roll(s)
and the breakage of the nonwoven fabric are prevented.
[0055] The bonded area formed by the hot embossing roll pair is
preferably 8 to 40%. When the bonded area is 8% or more, more
preferably 10% or more, further more preferably 12% or more, the
resulting nonwoven fabric will have sufficient strength for
practical use. When the bonded area is 40% or less, more preferably
30% or less, further more preferably 20% or less, the resulting
nonwoven fabric is prevented from being formed into a film-like
fabric that hardly exhibits the advantages of a nonwoven fabric,
such as breathability. In cases where the thermal bonding is
performed with a pair of upper and lower rolls each having raised
and recessed portions, the term "bonded area" herein refers to the
ratio of the area of the nonwoven web in contact with both of the
raised portions of the upper roll and the raised portions of the
lower roll, relative to the total area of the nonwoven web. In
cases where the thermal bonding is performed with a pair of a roll
having raised and recessed portions and a flat roll, the term
"bonded area" herein refers to the ratio of the area of the
nonwoven web in contact with the raised portions of the roll having
raised and recessed portions, relative to the total area of the
nonwoven web.
[0056] For the purpose of improving transportability and
controlling the thickness of the nonwoven fabric, the nonwoven web
before thermal bonding can be temporarily bonded under a linear
pressure of 50 to 700 N/cm with calender rolls at 70 to 120.degree.
C. The calender rolls may be a combination of upper and lower metal
rolls or of a metal roll with a resin or paper roll.
EXAMPLES
[0057] The present invention will be specifically illustrated with
reference to Examples. However, the present invention is not
limited to these Examples. Various alterations and modifications
are possible without departing from the technical scope of the
present invention.
Measurement Methods
[0058] (1) Melt Flow Rate (MFR) (g/10 Min)
[0059] The MFRs of the resins used were measured in accordance with
ASTM D1238-70 under the conditions of a measurement temperature of
315.5.degree. C. and an applied load of 5 kg.
(2) Average Single Fiber Fineness (dtex)
[0060] Ten small samples were randomly taken from the nonwoven web
collected on a net. The surfaces of the samples were photographed
at a magnification of 500 to 1000 times under a microscope. The
widths of ten fibers of each sample, 100 fibers in total, were
measured and the average value was calculated. The fibers were
regarded as having a circular cross section, and therefore the
average width value of the single fiber was regarded as the average
diameter thereof. From the average diameter and the solid density
of the resin used, the weight of the single fiber per 10,000 m in
length was calculated and rounded off to the first decimal place to
determine the average single fiber fineness.
(3) Spinning Rate (m/min)
[0061] The spinning rates V (m/min) were calculated based on the
following formula using the average single fiber fineness F (dtex)
and the discharge rate of the resin per spinneret hole D
(hereinafter abbreviated to discharge rate per hole: g/min) under
various settings.
V=(10000.times.D)/F
(4) Crystallinity
[0062] Fibers were taken from the nonwoven web collected on a net
and were embedded in a resin (a bisphenol epoxy resin, curing time:
24 hours). The embedded fibers were sectioned with a microtome to
prepare a sample of a fiber cross section with a thickness of 2.0
This sample was analyzed by laser Raman spectroscopy under the
conditions described below. From the obtained Raman spectrum, the
full width at half maximum of the phenyl ring-S stretching band
(around 1080 cm.sup.-1) was determined. The full width at half
maximum of the phenyl ring-S stretching band (around 1080
cm.sup.-1) in the Raman spectrum of PPS becomes smaller as
crystallization proceeds with the increase in structural order and
the equalization of the environment around the vibration. Based on
this tendency, the determined value of the full width at half
maximum was used to evaluate the crystallinity (a smaller full
width at half maximum means a higher crystallinity). [0063] Device:
Near-infrared Raman spectrometer (Photon Design) [0064] Conditions:
[0065] Measurement mode: Raman microscope [0066] Objective lens:
.times.100 [0067] Beam diameter: 1 .mu.m [0068] Cross slit: 200
.mu.m [0069] Light source: YAG laser/1064 nm [0070] Laser power: 1
W [0071] Diffraction grating: Single 300 [0072] (Full width at half
maximum: 900) gr/mm [0073] Slit: 100 .mu.m [0074] Detector:
InGaAs/Nippon Roper Raman spectrometer [0075] Measurement Position:
[0076] (1) Surface of the fiber (the region from 0 to 1.0 .mu.m in
the radially inward direction of the fiber when the surface is the
base point (0)) [0077] (2) Center of the cross section of the fiber
(diameter/2) (5) Mass Per Unit Area (g/m.sup.2) of Nonwoven
Fabric
[0078] In accordance with JIS L 1913 (2010) 6.2 "Mass per unit
area", three test pieces each having a size of 20 cm.times.25 cm
were taken per meter of width of a sample, the masses (g) of the
test pieces in standard conditions were measured, and the average
value thereof was expressed in terms of mass per m.sup.2
(g/m.sup.2).
(6) Product of Strength and Elongation Per Mass Per Unit Area of
Nonwoven Fabric
[0079] In accordance with JIS L 1913 (2010) 6.3.1, three test
samples long in the longitudinal direction of the fabric were
taken, and tensile strength test was performed on each of the test
samples under the conditions of a sample size of 5 cm.times.30 cm,
a clamp distance of 20 cm, and a stretching rate of 10 cm/min to
determine the strength at break of the sample. The determined
strength at break was taken as the longitudinal tensile strength
(N/5 cm). The elongation of the sample at the maximum load was also
measured at an accuracy of 1 mm to determine the elongation rate
(i.e., the length elongated from the original length). The
determined elongation rate was taken as the longitudinal tensile
elongation (%). The average of the determined longitudinal tensile
strength (N/5 cm) and the average of the determined longitudinal
tensile elongation (%) were calculated and rounded off to the whole
number. Then, from the longitudinal tensile strength (N/5 cm) and
the longitudinal tensile elongation (%) calculated in this manner,
and the mass per unit area (g/m.sup.2) determined in the above (5),
the product of strength and elongation per mass per unit area was
calculated by the following formula and rounded off to the whole
number.
[0080] Product of strength and elongation per mass per unit
area=longitudinal tensile strength (N/5 cm).times.longitudinal
tensile elongation (%)/mass per unit area (g/m.sup.2)
(7) Thermal Shrinkage Rate (%) of Nonwoven Fabric
[0081] In accordance with JIS L 1913 (2010) 6.10.3 "Dimensional
change rate under dry heat conditions", the measurement was
performed. The inside temperature of a constant temperature dryer
was set at 200.degree. C. and heat treatment was performed for 10
minutes.
Example 1
Component A
[0082] A 100 mol % linear polyphenylene sulfide resin (Toray
Industries, Inc., product number: E2280, MFR: 160 g/10 min) was
dried in nitrogen atmosphere at 160.degree. C. for 10 hours and
used as component A.
Component B
[0083] A 100 mol % linear polyphenylene sulfide resin (Toray
Industries, Inc., product number: M2588, MFR: 300 g/10 min) was
dried in nitrogen atmosphere at 160.degree. C. for 10 hours and
used as component B.
Spinning and Nonwoven Web Forming
[0084] The component A was melted in an extruder for a core
component, and the component B was melted in an extruder for a
sheath component. The components A and B were metered to provide an
A:B mass ratio of 80:20. The components were spun from a
rectangular-shaped core-sheath spinneret with a hole diameter
(.PHI.) of 0.55 mm at a discharge rate per hole of 1.37 g/min at a
spinning temperature of 315.degree. C. to form continuous
core-sheath composite fibers. The spun fibers were cooled and
solidified in an atmosphere at a room temperature of 20.degree. C.,
and were passed through a rectangular ejector disposed at a
distance of 550 mm from the spinneret. The fibers were drawn and
stretched by the air that was heated to 200.degree. C. with an air
heater and ejected from the ejector at an ejector pressure of 0.17
MPa. The drawn fibers were collected on a moving net to form a
nonwoven web. The obtained core-sheath composite long fibers had an
average single fiber fineness of 2.9 dtex. The spinning rate was
4,797 m/min. The crystallinity was lower in the surface of the
fibers than in the center of the cross section of the fibers. The
occurrence of the breakage of the fibers during 1 hour spinning was
zero and thus good spinnability was observed.
Temporary Bonding and Thermal Bonding
[0085] The nonwoven web was then temporarily bonded under a linear
pressure of 200 N/cm and at a temporary bonding temperature of
90.degree. C. using a pair of upper and lower metal calendering
rolls installed in the production line. The nonwoven fabric was
then thermally bonded under a linear pressure of 1000 N/cm and at a
thermal bonding temperature of 200.degree. C. using an embossing
roll pair which provided a 12% bonded area and which consisted of
an upper metal roll having a polka-dot emboss pattern and a lower
flat metal roll, to give a core-sheath composite long-fiber
nonwoven fabric. The obtained core-sheath composite long-fiber
nonwoven fabric had a mass per unit area of 260 g/m.sup.2, a
product of strength and elongation per mass per unit area of 54 and
thermal shrinkage rates of 0.1% in the longitudinal direction and
0.0% in the transverse direction.
Example 2
Component A
[0086] The same PPS resin as in Example 1 was used as component
A.
Component B
[0087] The same PPS resin as in Example 1 was used as component
B.
Spinning and Nonwoven Web Forming
[0088] Core-sheath composite spinning and nonwoven web forming were
performed in the same manner as in Example 1 except that the
ejector pressure was 0.15 MPa. The obtained core-sheath composite
long fibers had an average single fiber fineness of 3.2 dtex. The
spinning rate was 4,317 m/min. The crystallinity was lower in the
surface of the fibers than in the center of the cross section of
the fibers. The occurrence of the breakage of the fibers during 1
hour spinning was zero and thus good spinnability was observed.
Temporary Bonding and Thermal Bonding
[0089] The nonwoven web was temporarily and thermally bonded to
give a core-sheath composite long-fiber nonwoven fabric in the same
manner as in Example 1. The obtained core-sheath composite
long-fiber nonwoven fabric had amass per unit area of 260
g/m.sup.2, a product of strength and elongation per mass per unit
area of 51, and thermal shrinkage rates of 0.1% in the longitudinal
direction and 0.1% in the transverse direction.
Example 3
Component A
[0090] The same PPS resin as in Example 1 was used as component
A.
Component B
[0091] The same PPS resin as in Example 1 was used as component
B.
Spinning and Nonwoven Web Forming
[0092] Core-sheath composite spinning and nonwoven web forming were
performed in the same as in Example 1. The obtained core-sheath
composite long fibers had an average single fiber fineness of 2.9
dtex. The spinning rate was 4,797 m/min. The crystallinity was
lower in the surface of the fibers than in the center of the cross
section of the fibers. The occurrence of the breakage of the fibers
during 1 hour spinning was zero and thus good spinnability was
observed.
Temporary Bonding and Thermal Bonding
[0093] The nonwoven web was temporarily and thermally bonded to
give a core-sheath composite long-fiber nonwoven fabric in the same
manner as in Example 1 except that the thermal bonding temperature
was 140.degree. C. The obtained core-sheath composite long-fiber
nonwoven fabric had a mass per unit area of 260 g/m.sup.2, a
product of strength and elongation per mass per unit area of 62 and
thermal shrinkage rates of 0.1% in the longitudinal direction and
0.0% in the transverse direction.
Example 4
Component A
[0094] The same PPS resin as in Example 1 was used as component
A.
Component B
[0095] The same PPS resin as in Example 1 was used as component
B.
Spinning and Nonwoven Web Forming
[0096] Core-sheath composite spinning and nonwoven web forming were
performed in the same manner as in Example 1. The obtained
core-sheath composite long fibers had an average single fiber
fineness of 2.9 dtex. The spinning rate was 4,797 m/min. The
crystallinity was lower in the surface of the fibers than in the
center of the cross section of the fibers. The occurrence of the
breakage of the fibers during 1 hour spinning was zero and thus
good spinnability was observed.
Temporary Bonding and Thermal Bonding
[0097] The nonwoven web was temporarily and thermally bonded to
give a core-sheath composite long-fiber nonwoven fabric in the same
manner as in Example 1 except that the thermal bonding temperature
was 240.degree. C. The obtained core-sheath composite long-fiber
nonwoven fabric had a mass per unit area of 260 g/m.sup.2, a
product of strength and elongation per mass per unit area of 50 and
thermal shrinkage rates of 0.1% in the longitudinal direction and
0.1% in the transverse direction.
Comparative Example 1
Component A
[0098] The same PPS resin as in Example 1 was used as component
A.
Component B
[0099] Component B was not used.
Spinning and Nonwoven Web Forming
[0100] The component A was melted in an extruder, metered, and spun
from a rectangular-shaped single-component spinneret with a hole
diameter (.PHI.) of 0.50 mm at a discharge rate per hole of 1.37
g/min at a spinning temperature of 315.degree. C. The spinning and
nonwoven web forming were performed in the same manner as in
Example 2. The obtained single-component long fibers had an average
single fiber fineness of 2.4 dtex. The spinning rate was 4,920
m/min. The crystallinity was higher in the surface of the fibers
than in the center of the cross section of the fibers. The
occurrence of the breakage of the fibers during hour spinning was
zero and thus good spinnability was observed.
Temporary Bonding and Thermal Bonding
[0101] The nonwoven web was temporarily and thermally bonded to
give a single-component long-fiber nonwoven fabric in the same
manner as in Example 1 except that the thermal bonding temperature
of the embossing roll pair was 260.degree. C. The obtained
single-component long-fiber nonwoven fabric had amass per unit area
of 260 g/m.sup.2, a product of strength and elongation per mass per
unit area of 4 and thermal shrinkage rates of 0.0% in the
longitudinal direction and 0.1% in the transverse direction.
TABLE-US-00001 TABLE 1 Example Example Example Example Comparative
Unit 1 2 3 4 Example 1 Resin Component -- -- PPS PPS PPS PPS PPS A
Melting .degree. C. 281 281 281 281 281 point MFR g/10 160 160 160
160 160 min Component -- -- PPS PPS PPS PPS Not used B Melting
.degree. C. 281 281 281 281 point MFR g/10 300 300 300 300 min Mass
ratio [component A: -- 80:20 80:20 80:20 80:20 100:0 component B]
Spinning Spinning temperature .degree. C. 315 315 315 315 315
Spinneret hole diameter mm 0.55 0.55 0.55 0.55 0.50 Discharge rate
per g/min 1.37 1.37 1.37 1.37 1.37 spinneret hole Temperature of
.degree. C. 200 200 200 200 200 compressed air Ejector pressure MPa
0.17 0.15 0.17 0.17 0.15 Average single fiber dtex 2.9 3.2 2.9 2.9
2.4 fineness Spinning rate m/min 4797 4317 4797 4797 4920 Full
width Fiber -- 12.8 13.3 12.8 12.8 10.8 at half surface maximum
Center of -- 10.4 10.4 10.4 10.4 12.8 cross section of fiber
Temporary Temperature .degree. C. 90 90 90 90 90 bonding Linear
pressure N/cm 200 200 200 200 200 Thermal Temperature .degree. C.
200 200 140 240 260 bonding Linear pressure N/cm 1000 1000 1000
1000 1000 Nonwoven Mass per unit area g/m.sup.2 260 260 260 260 260
fabric Product of strength and -- 54 51 62 50 4 elongation per mass
per unit area Thermal Longitudinal % 0.1 0.1 0.1 0.1 0.0 shrinkage
Transverse % 0.0 0.1 0.0 0.1 0.1 rate
[0102] As shown in Table 1, Examples 1 to 4, in which the PPS of
the sheath component had a lower viscosity than the PPS of the core
component, had a lowered crystallinity on the surface of the
fibers. The core-sheath composite long-fiber nonwoven fabrics made
therefrom had greatly improved values of the product of strength
and elongation per mass per unit area and more excellent mechanical
strength, as compared with the single-component long-fiber nonwoven
fabric of Comparative Example 1.
[0103] The nonwoven fabric made from the thermally bondable
composite fiber of the present invention has both thermal
dimensional stability and excellent mechanical strength, and is
therefore suitable for various industrial filters, electric
insulating materials, battery separators, membrane materials for
water treatment, heat insulating materials, hazmat suits, and the
like.
* * * * *