U.S. patent application number 12/300428 was filed with the patent office on 2009-09-10 for thermal-adhesive bicomponent fiber and method for producing it.
Invention is credited to Hironori Goda.
Application Number | 20090227166 12/300428 |
Document ID | / |
Family ID | 38693994 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090227166 |
Kind Code |
A1 |
Goda; Hironori |
September 10, 2009 |
THERMAL-ADHESIVE BICOMPONENT FIBER AND METHOD FOR PRODUCING IT
Abstract
An essential object of the invention is to provide a
low-modulus, self-extensible thermal-adhesive bicomponent fiber
including polyethylene terephthalate as the fiber-forming resin
component thereof and capable of producing a nonwoven fabric or a
fiber structure that has a high adhesive strength and is bulky and
well drapable. The object of the invention is attained by a
self-extensible thermal-adhesive bicomponent fiber that includes a
fiber-forming resin component and a thermal-adhesive resin
component and is characterized in that the fiber-forming resin
component includes polyethylene terephthalate, that the
thermal-adhesive resin component includes a crystalline
thermoplastic resin having a melting point lower by at least
20.degree. C. than that of the fiber-forming resin component, and
that its breaking elongation is from 130 to 600%, its 100%
elongation tensile strength is from 0.3 to 1.0 cN/dtex and its
120.degree. C. dry heat shrinkage is smaller than -1.0%; and by a
method for producing it.
Inventors: |
Goda; Hironori; (Ehime,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Family ID: |
38693994 |
Appl. No.: |
12/300428 |
Filed: |
May 10, 2007 |
PCT Filed: |
May 10, 2007 |
PCT NO: |
PCT/JP2007/060084 |
371 Date: |
November 11, 2008 |
Current U.S.
Class: |
442/364 ;
264/172.15; 428/373 |
Current CPC
Class: |
D01F 8/14 20130101; D02J
1/22 20130101; D04H 1/54 20130101; Y10T 428/2929 20150115; Y10T
442/641 20150401 |
Class at
Publication: |
442/364 ;
428/373; 264/172.15 |
International
Class: |
D02G 3/02 20060101
D02G003/02; D01D 5/34 20060101 D01D005/34; D04H 13/00 20060101
D04H013/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 12, 2006 |
JP |
2006-133794 |
Claims
1. A self-extensible thermal-adhesive bicomponent fiber comprising
a fiber-forming resin component and a thermal-adhesive resin
component, which is characterized in that the fiber-forming resin
component comprises polyethylene terephthalate, that the
thermal-adhesive resin component comprises a crystalline
thermoplastic resin having a melting point lower by at least
20.degree. C. than that of the fiber-forming resin component, and
that its breaking elongation is from 130 to 600%, its 100%
elongation tensile strength is from 0.3 to 1.0 cN/dtex and its
120.degree. C. dry heat shrinkage is smaller than -1.0%.
2. The thermal-adhesive bicomponent fiber as claimed in claim 1,
which is a core/sheath bicomponent fiber and in which the
fiber-forming resin component constitutes the core component and
the thermal-adhesive resin component constitutes the sheath
component thereof.
3. The thermal-adhesive bicomponent fiber as claimed in claim 1,
wherein the thermal-adhesive resin component is a polyolefin
resin.
4. The thermal-adhesive bicomponent fiber as claimed in claim 1,
wherein the thermal-adhesive resin component is a crystalline
copolyester.
5. A method for producing a thermal-adhesive bicomponent fiber of
claim 1, which comprises cold-drawing an undrawn yarn taken out at
a spinning speed of not higher than 1300 m/min, by from 1.05 to
1.30 times, and then relaxing and thermally shrinking it at a
temperature higher by at least 10.degree. C. than both the glass
transition point of the thermal-adhesive resin component and the
glass transition point of the fiber-forming resin component.
6. The method for producing a thermal-adhesive bicomponent fiber as
claimed in claim 5, wherein the relaxing and thermal shrinking
treatment is effected in hot air.
7. The method for producing a thermal-adhesive bicomponent fiber as
claimed in claim 5, wherein the relaxing and thermal shrinking
treatment is effected in hot water.
8. A thermal-adhesive nonwoven fabric comprising only
self-extensible thermal-adhesive bicomponent fibers of claim 1 and
having a cantilever value of at most 10 cm.
9. A thermal-adhesive nonwoven fabric comprising only
self-extensible thermal-adhesive bicomponent fibers of claim 2 and
having a cantilever value of at most 10 cm.
10. A thermal-adhesive nonwoven fabric comprising only
self-extensible thermal-adhesive bicomponent fibers of claim 3 and
having a cantilever value of at most 10 cm.
11. A thermal-adhesive nonwoven fabric comprising only
self-extensible thermal-adhesive bicomponent fibers of claim 4 and
having a cantilever value of at most 10 cm.
Description
TECHNICAL FIELD
[0001] The present invention relates to a self-extensible
thermal-adhesive bicomponent fiber, which has a low modulus and is
self-extensible in thermal adhesion and which has a soft feel when
formed into a thermal-adhesive nonwoven fabric, and to a method for
producing it.
BACKGROUND ART
[0002] In general, a thermal-adhesive bicomponent fiber such as
typically a core/sheath thermal-adhesive bicomponent fiber that
comprises a thermal-adhesive resin component as the sheath and a
fiber-forming resin component as the core is used as a nonwoven
fabric by forming a fiber web according to a carding method, an
air-laid method or a wet sheet-making method and then melting the
thermal-adhesive resin component through hot air drier treatment or
hot roll treatment to thereby form fiber-fiber bonding to give a
nonwoven fabric. Specifically, this does not use an adhesive
comprising an organic solvent, and its advantage is that the amount
of a harmful substance such as an organic solvent to be released
from it is small. In addition, since its other advantages of high
producibility and cost reduction are great, it has been widely used
as fiber structures such as fiber cushions (hard cotton) and bed
mats, and as nonwoven fabrics.
[0003] Above all, a thermal-adhesive nonwoven fabric typically for
sanitary materials such as paper diapers and sanitary napkins is
required to have softness and drapability like a fabric and have a
suitable, non-paperlike bulkiness, since the nonwoven fabric may be
kept in direct contact with users' skin. Continued investigations
of nonwoven fabrics having such characteristics are made from the
past.
[0004] As one method of thermally adhering a web obtained from
thermal-adhesive fibers, there is known a heat-roll method
comprising thermally pressing and softening a part of the web by
the use of an embossing roll and melt-sealing it. According to the
method, the nonwoven fabric may be readily folded at the boundary
between the heat-sealed region and the non-heat-sealed region, and
the obtained nonwoven fabric may have excellent drapability.
However, since the fibers in the heat-sealed region are pressed and
flattened, the heat-sealed part may become hard and may lose the
bulkiness of nonwoven fabric, and therefore the obtained nonwoven
fabric may have a paperlike feel.
[0005] On the other hand, as another method of thermally adhering a
web obtained from thermal-adhesive fibers, there is known an
air-through method that comprises applying a hot air jet to the
whole of a web to thereby soften or melt the intersections of the
fibers. According to the method, the applied hot air runs through
the web while the bulkiness of the web is left as such in some
degree, and therefore the obtained nonwoven fabric is bulky, not
having a partly hardened region, and the touch of its surface is
smooth. On the other hand, when the nonwoven fabric is folded, it
may have irregular folds and may lose drapability.
[0006] For solving the problems, a method is disclosed in Patent
Reference 1. Specifically, according to a high-speed spinning
method, the orientation index of a thermal-adhesive resin component
is made to be at most 25% and the orientation index of a
fiber-forming resin component is made to be at least 40%, thereby
giving a thermal-adhesive bicomponent fiber having a strong
adhering point strength, melt-fusible at a lower temperature and
having a small degree of thermal shrinkage. The disclosed technique
comprises adhering a blended web of the thermal-adhesive
bicomponent fibers and non-thermal-adhesive fibers according to an
air-through method, thereby producing a nonwoven fabric having
drapability and bulkiness and having a sufficient nonwoven fabric
strength. However, in the current process for production of staple
fibers, the process stability of the high-speed spinning method
could not as yet be said sufficient, and the yield in the method is
low. Further, inconsideration of the property of the obtained
staple fibers, it may be said that the cost performance is not
sufficient and that there may be still many difficult problems in
commercial-base production of staple fibers according to the
high-speed spinning method. Moreover, in case where a
thermal-adhesive nonwoven fabric is formed of only thermal-adhesive
bicomponent fibers, the number of the adhering intersections in the
nonwoven fabric may increase, and therefore, a nonwoven fabric
having a soft feel may be difficult to obtain and a nonwoven fabric
having poor drapability may be obtained. Accordingly, in general,
for the purpose of reducing the number of the adhering
intersections, non-thermal-adhesive fibers are mixed to produce a
nonwoven fabric, but in this case, since the number of the adhering
intersections in the nonwoven fabric decreases, the nonwoven fabric
strength may lower. Accordingly, the nonwoven fabric strength and
the soft feel could not always be on a sufficient level.
[0007] Further, an example to demonstrate a thermal-adhesive
bicomponent fiber, in which the core component is a fiber-forming
resin component and the core component is polyethylene
terephthalate (hereinafter referred to as PET), is not disclosed in
Patent Reference 1. When the core component of a thermal-adhesive
bicomponent fiber is PET, then the melting point of the core
component in the fiber may be sufficiently higher than the melting
point of the sheath component therein, as compared with a
thermal-adhesive bicomponent fiber in which the core component is
polypropylene (hereinafter referred to as PP), and therefore, the
thermal-adhesive strength of the obtained nonwoven fabric may be
further improved. In addition, since the bicomponent fiber in which
the core component is PET is relatively highly rigid, it has a
potential to give a nonwoven fabric having higher bulkiness.
However, even though the bicomponent fibers undrawn at a low draw
ratio or the undrawn bicomponent fibers described in Patent
Reference 1 are formed into nonwoven fabrics, the thermal shrinkage
of the fabrics is still large since the orientation crystallinity
of the core component of the bicomponent fibers used is
insufficient. Moreover, when the high-speed spinning described in
Patent Reference 1 is applied to bicomponent fibers in which the
core component is PET, then the melting temperature of the sheath
component of the bicomponent fibers must be inevitably elevated in
accordance with the melting temperature of the core component of
the bicomponent fibers in spinning the fibers, for the purpose of
preventing rapid solidification of the core component. This
involves a problem of frequent fiber breakage in spinning since the
polymer to constitute the sheath component may deteriorate and the
spinning draft may be large.
[0008] (Patent Reference 1) JP-A-2005-350836
DISCLOSURE OF THE INVENTION
Problems that the Invention is to Solve
[0009] The invention has been made under the background of the
above-mentioned prior art techniques, and its object is to provide
a low-modulus, self-extensible thermal-adhesive bicomponent fiber
comprising polyethylene terephthalate as the fiber-forming resin
component thereof and capable of producing a nonwoven fabric or a
fiber structure that has a high adhesive strength and is bulky and
well drapable.
Means for Solving the Problems
[0010] The present inventors have assiduously investigated for the
purpose of solving the above-mentioned problems, and as a result,
have invented a low-modulus, self-extensible thermal-adhesive
bicomponent fiber that comprises PET as the fiber-forming resin
component thereof and satisfies high adhesive strength, sufficient
bulkiness and drapability, using a crystalline thermoplastic resin
having a lower melting point than PET by at least 20.degree. C., as
the thermal-adhesive resin component of the fiber, and cold-drawing
an undrawn yarn of the fiber taken out at a spinning speed of not
higher than 1300 m/min, by from 1.05 times to 1.30 times under no
heat or with cooling in a coolant, followed by relaxing and
thermally shrinking it at a temperature higher by at least
10.degree. C. than both the glass transition point of the
thermal-adhesive resin component and the glass transition point of
the fiber-forming resin component.
[0011] More concretely, the above-mentioned problems can be solved
by the invention of a self-extensible thermal-adhesive bicomponent
fiber that comprises a fiber-forming resin component and a
thermal-adhesive resin component and is characterized in that the
fiber-forming resin component comprises polyethylene terephthalate
(PET), that the thermal-adhesive resin component comprises a
crystalline thermoplastic resin having a melting point lower by at
least 20.degree. C. than that of the fiber-forming resin component,
and that its breaking elongation is from 130 to 600%, its 100%
elongation tensile strength is from 0.3 to 1.0 cN/dtex and its
12.degree. C. dry heat shrinkage is smaller than -1.0%. In
addition, the above-mentioned problems can be solved by the
invention of a method for producing the thermal-adhesive
bicomponent fiber, which comprises cold-drawing an undrawn yarn of
a bicomponent fiber taken out at a spinning speed of not higher
than 1300 m/min, by from 1.05 to 1.30 times, and then relaxing and
thermally shrinking it at a temperature higher by at least
10.degree. C. than both the glass transition point of the
thermal-adhesive resin component and the glass transition point of
the fiber-forming resin component.
EFFECT OF THE INVENTION
[0012] A nonwoven fabric formed of the low-modulus, self-extensible
thermal-adhesive bicomponent fiber of the invention can have a soft
feel based on the low-modulus characteristic and the
self-extensibility of the thermal-adhesive bicomponent fiber
itself. In addition, the nonwoven fabric may have a high adhesive
strength intrinsic to a thermal-adhesive nonwoven fabric formed of
only thermal-adhesive bicomponent fibers.
BEST MODE FOR CARRYING OUT THE INVENTION
[0013] Embodiments of the invention are described in detail
hereinunder. First, the invention is a bicomponent fiber comprising
a fiber-forming resin component and a thermal-adhesive resin
component. More precisely, the invention is a low-modulus,
self-extensible thermal-adhesive bicomponent fiber that comprises
PET as the fiber-forming resin component thereof and a crystalline
thermoplastic resin having a melting point lower by at least
20.degree. C. than that of PET as the thermal-adhesive resin
component thereof. When the melting point difference between PET
and the thermal-adhesive resin component is less than 20.degree.
C., then it is unfavorable since the fiber-forming resin component
may also melt in a step of melting and adhering the
thermal-adhesive resin component and since a nonwoven fabric or a
fiber structure having a high adhesive strength could not be
produced. Preferably, the melting point difference range is from 20
to 180.degree. C.
[0014] Using a known melting method and spinneret for bicomponent
fibers, the bicomponent fiber may be produced by obtaining an
undrawn yarn of the fiber at a spinning speed of from 100 to 1300
m/min, then cold-drawing it by from 1.05 to 1.30 times, and further
relaxing and thermally shrinking it at a temperature higher by at
least 10.degree. C. than both the glass transition point
(hereinafter this is referred to as Tg) of PET and Tg of the
thermoplastic crystalline resin constituting the thermal-adhesive
resin component and lower by at least 10.degree. C. than the
melting point of the thermal-adhesive resin component, preferably
at a temperature higher by at least 20.degree. C. than Tg of the
two and lower by at least 20.degree. C. than the melting point of
the thermal-adhesive resin component. Concretely, the temperature
higher than both Tg of PET and Tg of the thermoplastic crystalline
resin of the thermal-adhesive resin component is, in many cases, a
temperature higher than Tg (about 70.degree. C.) of PET.
Accordingly, it is desirable that the relaxing and
thermal-shrinking treatment is effected at a temperature not lower
than 80.degree. C., more preferably not lower than 90.degree. C.
Even more preferably, the temperature is not lower than 100.degree.
C. The relaxing and thermal-shrinking treatment may be attained in
hot air or in hot water. This is because, in the invention, the
melting point of the crystalline thermoplastic resin that
constitutes the thermal-adhesive resin component is lower by at
least 20.degree. C. than the melting point of PET, as so mentioned
in the above, and therefore Tg of the thermoplastic crystalline
resin constituting the thermal-adhesive resin component is mostly
lower than Tg of PET. When the temperature in the relaxing and
thermal-shrinking treatment is lower than the above temperature
range, then it is unfavorable since the shrinkage in thermal
adhesion of the bicomponent fiber may increase. When the
temperature in the relaxing and thermal-shrinking treatment is
extremely higher than the temperature range, then the resin of the
thermal-adhesive resin component may soften into pseudo-fusion. The
relaxing and thermal-shrinking treatment may be attained according
to a method of leading a drawn tow to pass through hot air under no
tension at all, or according to a method of overfeeding it in hot
air at from 0.5 to 0.85 times under no tension given thereto.
[0015] Through the above-mentioned relaxing and thermal-shrinking
treatment, the low-drawn fiber may form crystals having a crystal
axis inclined in random directions from the fiber axis direction,
while shrunk in the fiber axis direction by the residual strain
therein. Further, when the fiber is heated, then the crystal size
of the crystals constituting it increases, and therefore when the
crystals existing near to each other are kept in contact with each
other, the crystal size may further increase. Accordingly, there
may occur a phenomenon that the fiber would seemingly extend. This
phenomenon is referred to as self-extension, and the bicomponent
fiber of the invention exhibit the self-extensibility.
[0016] This phenomenon is more remarkable in high-speed spinning at
a spinning speed of not lower than 2000 m/min. The present
inventors' investigations have revealed that, when an undrawn yarn
obtained at a spinning speed of not higher than 1300 m/min is drawn
at a slight draw ratio and then relaxed and thermally-shrunk, then
its self-extension degree may be enlarged, and have reached the
present invention. For example, in case where a core/sheath
bicomponent fiber in which the core component is PET (intrinsic
viscosity: IV=0.64 dL/g) and the sheath component is high-density
polyethylene (MFR=20 g/10 min) is taken out at a spinning speed of
1150 m/min, the self-extension degree of the fiber increases when
the draw ratio is higher than 1.00 time, and the self-extension
degree thereof reaches a maximum level when the draw ratio is 1.20
times. For expressing the self-extensibility of the fiber, it may
be a key point how the orientation of the crystals constituting the
fiber could be kept random relative to the fiber axis before the
crystals grow thick, and for it, therefore, the fiber may well be
greatly shrunk before its crystallization. Accordingly, in a step
of drawing it, when the fiber is cold-drawn by from 1.05 to 1.30
times at a drawing temperature further lower than the drawing
temperature in hot drawing treatment to be effected by the use of
hot water, steam or a plate heater, then the residual strain in the
amorphous part of the fiber may be increased with inhibiting the
orientation crystallization by the drawing, and therefore this is
favorable for obtaining the bicomponent fiber of the invention.
"Cold-drawing" as referred to herein includes not only drawing at
room temperature but also drawing in an atmosphere positively
cooled to a temperature lower than room temperature. Concretely, it
includes a method of drawing under no heat at room temperature, or
in a coolant cooled to a temperature lower than room temperature.
More concretely, a method of cold-drawing in air or drawing in a
cold water bath is preferred. The coolant includes not only air and
water mentioned above, but also vapors such as rare gas, nitrogen
or carbon dioxide inert to the fiber-forming resin component and
the thermal-adhesive resin component that form the bicomponent
fiber of the invention without swelling or dissolving them, as well
as other liquids such as various oils not dissolving PET and the
thermal-adhesive resin component; and the coolant may be suitably
selected from them. The temperature of the coolant in cold-drawing
may be from 0 to 30.degree. C., preferably from 10 to 25.degree.
C.
[0017] Accordingly, in order that the self-extension degree at
120.degree. C. of the bicomponent fiber could be more than 1.0%, or
that is, the dry heat shrinkage at 120.degree. C. of the
bicomponent fiber could be smaller than -1.0%, and that the 100%
elongation tensile strength of the bicomponent fiber could be from
0.3 to 1.0 cN/dtex, the draw ratio must fall within a range of from
1.05 to 1.30 times. When the draw ratio is lower than 1.05 times,
then the 100% elongation tensile strength of the bicomponent fiber
could be at most 1.0 cN/dtex but the self-extension degree thereof
is less than 1.0% and the fiber could not attain the object of the
invention. When the draw ratio is more than 1.30 times, then the
100% elongation tensile strength is more than 1.0 cN/dtex. When a
thermal-adhesive nonwoven fabric is formed of a web of completely,
100-percentage the thermal-adhesive bicomponent fibers of the type,
then the nonwoven fabric could not have the excellent drapability
that is the object of the invention. When the fiber is drawn at the
above-mentioned draw ratio, then the drawing temperature is
preferably lower; and when cold water is used as the coolant, then
the drawing temperature is more preferably from 0.degree. C. to
25.degree. C. The drawing operation at such a low temperature
greatly contributes to increasing the thermal shrinkage of the
obtained bicomponent fiber, since the crystallization of the fiber
owing to orientation and heat generation may be prevented by
removing the heat generated by the bicomponent fiber during
drawing. As mentioned in the above, the 100% elongation tensile
strength of the bicomponent fiber of the invention must be from 0.3
to 1.0 cN/dtex. When the 100% elongation tensile strength is
smaller than 0.3 cN/dtex, then it is unfavorable since the nonwoven
tensile strength may be insufficient and the texture of the
nonwoven fabric may worsen; and when larger than 1.0 cN/dtex, then
it is also unfavorable since the self-extensibility and the
softness (drapability) may be poor.
[0018] In producing the bicomponent fiber of the invention, the
spinning speed must be at most 1300 m/min, preferably at most 1200
m/min, even more preferably from 100 to 1100 m/min. When the
spinning speed is higher than 1300 m/min, then the orientation of
the undrawn yarn may increase but the effect of expressing a high
self-extension degree through low-drawing treatment, which is a
characteristic of the bicomponent fiber of the invention, may
decrease.
[0019] Regarding its profile, the low-modulus, self-extensible
thermal-adhesive bicomponent fiber of the invention may be in any
form of a side-by-side laminated bicomponent fiber of a
fiber-forming resin component and a thermal-adhesive resin
component, or a core-sheath bicomponent fiber where the core
component is a fiber-forming resin component and the sheath
component is a thermal-adhesive resin component. However, preferred
is a core-sheath bicomponent fiber where the core component is a
fiber-forming resin component and the sheath component is a
thermal-adhesive resin component, since the thermal-adhesive resin
component may be disposed in all directions vertical to the fiber
axis direction of the fiber. The core-sheath bicomponent fiber
includes a concentric core-sheath bicomponent fiber and an
eccentric core-sheath bicomponent fiber.
[0020] For the thermal-adhesive resin component, a crystalline
thermoplastic resin must be selected. When an amorphous
thermoplastic resin is selected for it, then the molecular chains
oriented during spinning may be disoriented while melted and
therefore the fiber may thereby greatly shrink. Preferred examples
of the crystalline thermoplastic resin are polyolefin resin and
crystalline copolyester.
[0021] Examples of the polyolefin resin are crystalline polyolefin
resins such as crystalline polypropylene, high-density
polyethylene, middle-density polyethylene, low-density
polyethylene, linear low-density polyethylene. Further, the
crystalline thermoplastic resin to constitute the thermal-adhesive
resin component may be a copolyolefin prepared through
copolymerization of the above-mentioned polyolefin with at least
one unsaturated compound selected from ethylene, propylene,
butene-1, pentene-1, or acrylic acid, methacrylic acid, maleic
acid, fumaric acid, itaconic acid, crotonic acid, isocrotonic acid,
mesaconic acid, citraconic acid or himic acid or their esters or
acid anhydrides.
[0022] Preferred examples of the crystalline copolyester for the
thermal-adhesive resin component are mentioned below. Preferred for
it are copolyesters prepared through copolymerization of an
alkylene terephthalate with any of substituted or sulfonic acid
group-having aromatic dicarboxylic acids such as isophthalic acid,
naphthalene-2,6-dicarboxylic acid, sodium 5-sulfoisophthalate or
potassium 5-sulfoisophthalate, aliphatic dicarboxylic acids such as
adipic acid or sebacic acid, alicyclic dicarboxylic acids such as
1,4-cyclohexamethylene-dicarboxylic acid,
.omega.-hydroxyalkylcarboxylic acid, aliphatic diols such as
polyethylene glycol or polytetramethylene glycol, or alicyclic
diols such as cyclohexamethylene-1,4-dimethanol, so that the formed
copolyester may have an intended melting point. The alkylene
terephthalate may be a polyester obtained starting from 1 to 3
combinations selected from terephthalic acid or its ester-forming
derivatives as the essential dicarboxylic acid component, and
ethylene glycol, diethylene glycol, trimethylene glycol,
tetramethylene glycol, hexamethylene glycol or their derivatives as
the essential diol component. The ester-forming derivative includes
lower dialkyl esters having from 1 to 6 carbon atoms, and a lower
diaryl esters having from 6 to 10 carbon atoms. Preferably, the
ester-forming derivative is are dimethyl ester or diphenyl ester.
It is desirable that the copolymerization ratio of these components
is variously regulated, depending on the copolymerization
components, so that the formed copolymer may have a desired melting
point. Preferably, it is from 5 to 50 mol %. In the invention, when
the fiber-forming resin component is PET, then the thermal-adhesive
resin component may be a polymer blend of at least two crystalline
thermoplastic resins having a melting point lower than that of PET
by at least 20.degree. C., and it may contain an amorphous
thermoplastic resin and a crystalline thermoplastic resin of which
the melting point difference between PET is less than 20.degree. C.
within a range not greatly interfering with the adhesiveness and
the low thermal shrinkability of the fiber.
[0023] The breaking elongation of the low-modulus, self-extensible
thermal-adhesive bicomponent fiber of the invention must be within
a range of from 130 to 600%, preferably from 170 to 450%. When the
breaking elongation of the bicomponent fiber of the invention is
less than 130%, then the orientation of the thermal-adhesive resin
component is too high and the adhesiveness of the fiber may be poor
and therefore the nonwoven fabric strength lowers. When the
breaking elongation of the bicomponent fiber of the invention is
more than 600%, then the strength of the bicomponent fiber is
substantially too low and the strength of the thermal-adhesive
nonwoven fabric could not be increased.
[0024] For controlling the breaking elongation of the bicomponent
fiber to fall within a range of from 130 to 600%, herein employable
is a method of suitably selecting the nozzle orifice diameter
through which the polymer is spun out and the spinning speed,
though varying depending the type of the polymers to be combined
and on the melt viscosity thereof. Above all, the method of
suitably selecting the spinning speed is more effective. Further in
the invention, in order that the breaking elongation is controlled
to fall within the above-mentioned range, it is desirable that the
spinning speed is controlled within a range of from 100 to 1300
m/min, though depending on the type of the polymers and the
combination thereof. When the spinning speed is higher, then the
breaking elongation maybe smaller; and when the spinning speed is
lower, then the breaking elongation may be higher.
[0025] The low-modulus, self-extensible thermal-adhesive
bicomponent fiber of the invention is characterized in that its
120.degree. C. dry heat shrinkage is smaller than -1.0%. Not
specifically defined, the lowermost limit of the dry heat shrinkage
may be -20.0% or so. When a thermal-adhesive nonwoven fabric is
produced, the bicomponent fibers therein may self-extend before
thermal adhesion, thereby further increasing the thickness thereof
in the thickness direction and, in addition, the low-modulus fibers
may be oriented in the thickness direction of the nonwoven fabric,
and therefore, when the compression in the thickness direction
thereof is taken into consideration, then the nonwoven fabric may
have a soft feel, and when it is used as the surface component of
sanitary materials, then the pressing feel to users' skin in the
vertical direction of the fabric may be reduced and further the
drapability of the fabric may be bettered.
[0026] Regarding its cross section, the thermal-adhesive
bicomponent fiber of the invention preferably has a concentric
core/sheath cross section or an eccentric core/sheath cross
section. When the bicomponent fiber has a side-by-side cross
section and when it is formed into a web, then the web may crimp
three-dimensionally and may be thereby greatly shrunk. In such a
case, in addition, the web adhesion strength may be small and the
effect of the invention may be reduced in some degree. Regarding
its cross-sectional profile, the bicomponent fiber may be a solid
fiber or a hollow fiber. Not limited to a round cross section, it
may have a modified cross section, for example, an oval cross
section, a multi-leaved cross section such as a 3-to 8-leaved cross
section, or a multi-angular cross section such as 3- to 8-angular
cross section. The multi-leaved cross section is meant to indicate
a cross-sectional profile that has plural protruding leaves
extending from the center part toward the outer peripheral
direction.
[0027] The fineness of the thermal-adhesive bicomponent fiber of
the invention may be selected depending on the object of the fiber.
Not specifically limited, it may be generally from 0.01 to 500 dtex
or so. By controlling the diameter of the orifice through which
resin is jetted out in spinning, the fiber fineness range may be
attained.
[0028] Not specifically defined, the ratio of the fiber-forming
resin component and the thermal-adhesive resin component may be
selected in accordance with the necessary strength, bulkiness or
thermal shrinkage of the intended nonwoven fabric or fiber
structure. Preferably, the ratio by weight of the fiber-forming
resin component to the thermal-adhesive resin component is from
10/90 to 90/10 or so.
[0029] Regarding its morphology, the fiber may be in any form of
multifilament, monofilament, staple fiber, chop or tow, depending
on the use and the object thereof. In case where the
thermal-adhesive bicomponent fiber of the invention is used as a
staple fiber that requires a carding step, the fiber is preferably
crimped to a suitable degree in order to make the fiber have good
card-through runnability. When formed into a nonwoven fabric, the
thermal-adhesive bicomponent fiber of the invention is especially
effective for improving the drapability the nonwoven fabric having
a random fiber structure. Accordingly, the self-extensible
thermal-adhesive bicomponent fibers of the invention may be formed
into a nonwoven fabric by themselves. If desired, they may be mixed
with any other fibers to produce a nonwoven fabric. For producing a
nonwoven fabric, employable is any of a carding method, an air-laid
method or a wet sheet-making method, in which the fibers are formed
into a web, and then predetermined heat is applied thereto in a hot
air drier or by an embossing roll, thereby thermally adhering the
fibers together to give a soft thermal-adhesive nonwoven fabric of
good drapability having a cantilever value of at most 10 cm.
EXAMPLES
[0030] The invention is described further concretely with reference
to the following Examples, but the invention is not limited at all
by these. In the Examples, the physical data were determined
according to the following methods.
(1) Intrinsic Viscosity (IV):
[0031] The intrinsic viscosity of the polyester was determined as
follows: A predetermined amount of the polymer was weighed, then
dissolved in o-chlorophenol to have a concentration of 0.012 g/ml,
and its viscosity was determined at 35.degree. C. according to an
ordinary method.
(2) Melt Flow Rate (MFR):
[0032] The melt flow rate was determined according to JIS K-7210,
Condition 4 (temperature 190.degree. C., load 21.18 N). Briefly,
polymer pellets before melt spinning were sampled, and the melt
flow rate of the sample was measured.
(3) Melting Point (Tm), Glass Transition Point (Tg):
[0033] The melting point and the glass transition point of the
polymer were measured, using TA Instrument Japan's Thermal Analyst
2200, at a heating rate of 20.degree. C./min.
(4) Fineness:
[0034] The fineness of the bicomponent fiber was measured according
to the method described in JIS L-1015:2005, 8.5.1A Method.
(5) Breaking Tensile Strength, Breaking Elongation, 100% Elongation
Tensile Strength:
[0035] The breaking tensile strength, the breaking elongation and
the 100% elongation tensile strength of the bicomponent fiber were
measured according to the method described in JIS L-1015:2005,
8.7.1 Method. Depending on the efficiency in constant-length heat
treatment thereof, the breaking tensile strength, the breaking
elongation and the 100% elongation tensile strength of the
bicomponent fiber of the invention may vary; and therefore, when
the breaking tensile strength, the breaking elongation and the 100%
elongation tensile strength of the fiber are measured as a single
yarn thereof, then the number of the points of the sample to be
analyzed must increase. The number of the points for measurement is
preferably at least 50. Accordingly, in this, the number of the
points for measurement was 50, and the data of all those points
were averaged to give a mean value for the intended physical data.
In determination of the breaking tensile strength and the breaking
elongation, the tensile strength at a point of 100% elongation in
the load-stress curve is read, and this is the 100% elongation
tensile strength value.
(6) Number of Crimps, Percentage of Crimps:
[0036] The number of crimps and the percentage of crimps of the
bicomponent fiber were determined according to the method described
in JIS L-1015:2005, 8.12.1 and 8.12.2 Methods.
(7) 120.degree. C. Dry Heat Shrinkage:
[0037] The 120.degree. C. dry heat shrinkage of the bicomponent
fiber was measured according to JIS L-1015:2005, 8.15 b), at
120.degree. C.
(8) Web Area Shrinkage:
[0038] The bicomponent fiber web area shrinkage was determined
according to the following method: A card web having a basis weight
of 30 g/m.sup.2 was produced, comprising 100% thermal-adhesive
bicomponent staple fibers cut to have a fiber length of 51 mm; and
the web was cut into a 25 cm.times.25 cm piece. Next, the thus-cut
web was heat-treated, as left in a hot air drier (Satake Chemical
Machinery's hot air circulating constant-temperature drier: 41-S4)
kept at 150.degree. C., for 2 minutes, thereby thermally adhering
the bicomponent fibers together. After thus adhered, the length and
the width dimension of the web were measured, and these were
multiplied to compute the area A.sub.1. According to the following
formula, the area shrinkage was obtained.
Area Shrinkage (%)=[(A.sub.0-A.sub.1)/A.sub.0].times.100
[0039] wherein A.sub.0=5 cm.times.5 cm=625 (cm.sup.2)
(9) Nonwoven Fabric Strength (Adhesion Strength):
[0040] From the thermal-adhered web (thickness 5 mm) obtained in
the above-mentioned method, a test piece having a width of 5 cm and
a length of 20 cm was cut out in the machine direction (in the
direction in which the fiber or web runs in the nonwoven fabric
production process), and its tensile strength was measured at a
pulling rate of 20 cm/min. In this, the chuck distance was 10 cm.
The adhesion strength is obtained by dividing the tensile breaking
strength by the weight of the test piece.
(10) Bending Resistance (Cantilever Value):
[0041] From the thermal-adhered web (thickness 5 mm) obtained in
the above-mentioned method, a test piece having a width of 2.5 cm
and a length of 25 cm was cut out in the machine direction, and
this was tested according to the method of JIS L-1086:1983, 6.12.1.
The cantilever value is only in the machine direction of the
sample.
[0042] Concretely, the cantilever value was measured according to
the following method: On a horizontal bed having a surface smooth
and having a 45-degree inclined surface at its one end, the sample
test piece is put along the bed. Next, one end of the test piece is
accurately registered to one end of the horizontal bed on its
inclined side (joint part of the 45-degree inclined surface and the
horizontal bed), and the position of the other end of the test
piece is measured as the length thereof from one end of the
45-degree inclined surface of the bed. Since the length of the test
piece is 25 cm, this should be 25 cm. Next, the test piece is
gradually slid in the inclined direction according to a suitable
method, and when the center point of one end of the test piece has
reached the same surface as the inclined surface, then the position
of the other end is measured as the length from one end of the
45-degree inclined surface. This value is referred to as A. The
difference between 25 cm and A is the cantilever value of the
sample. 5 sample pieces are thus analyzed on both their surface and
back, and the mean value of the obtained data indicates the
cantilever value of the test sample. Test samples having a larger
cantilever value are harder, and their drapability are worse; and
those having a smaller cantilever value are softer, and their
drapability are better.
Example 1
[0043] As the core component (fiber-forming resin component), used
was polyethylene terephthalate (PET) having IV=0.64 dL/g,
Tg=70.degree. C. and Tm=256.degree. C.; and as the sheath component
(thermal-adhesive resin component), used was high-density
polyethylene (HDPE) having MFR=20 g/10 min and Tm=131.degree. C.
(Tg was lower than 0.degree. C.). These resins were melted at
290.degree. C. and 250.degree. C., respectively. Using a known
core/sheath bicomponent fiber spinneret, these were formed into a
bicomponent fiber in a ratio by weight, core component/sheath
component of 50 wt. %/50 wt. %, and then spun out under the
condition of a jetting rate of 0.70 g/min/orifice and a spinning
rate of 1150 m/min, thereby obtaining an undrawn yarn. The undrawn
yarn was cold-drawn by 1.20 times, and then the cold-drawn yarn was
dipped in an aqueous solution of an oily agent of potassium lauryl
phosphate/polyoxyethylene-modified silicone of 80 wt. %/20 wt. %.
Then, using a staffing box-equipped forced crimper, this was
mechanically crimped at 11 crimps/25 mm. Further, the crimped yarn
was subjected to relaxing and thermal shrinkage treatment and
drying treatment with hot air at 110.degree. C., higher by
40.degree. C. than the glass transition point of the core
component, under no tension, and then cut into pieces having a
fiber length of 51 mm. The single yarn fineness of the
thus-obtained thermal-adhesive bicomponent fiber was 6.4 dtex, the
breaking tensile strength thereof was 0.76 cN/dtex, the breaking
elongation thereof was 442%, the 100% elongation tensile strength
thereof was 0.37 cN/dtex, and the 120.degree. C. dry heat shrinkage
thereof was -2.6%. The web area shrinkage of the web of 100% the
thermal-adhesive bicomponent fibers was -7.5%, the nonwoven fabric
strength thereof was 15.1 kg/g, and the cantilever value thereof
was 8.50 cm.
Comparative Example 1
[0044] A bicomponent fiber was produced under the same condition as
in Example 1, for which, however, the undrawn yarn obtained in
Example 1 was drawn by 2.5 times in hot water at 70.degree. C., and
then further drawn by 1.2 times in hot water at 90.degree. C. The
single yarn fineness of the thus-obtained thermal-adhesive
bicomponent fiber was 2.6 dtex, the breaking tensile strength
thereof was 2.49 cN/dtex, the breaking elongation thereof was
37.1%, and the 120.degree. C. dry heat shrinkage thereof was 2.5 W.
Since the elongation of the thermal-adhesive bicomponent fiber was
less than 100%, the 100% elongation tensile strength thereof could
not be measured. The web area shrinkage of the web of 100% the
thermal-adhesive bicomponent fibers was 5%, the nonwoven fabric
strength thereof was 20.5 kg/g, and the cantilever value thereof
was 12.90 cm.
Comparative Example 2
[0045] A bicomponent fiber was produced under the same condition as
in Example 1, for which, however, the undrawn yarn was not drawn.
The single yarn fineness of the thus-obtained thermal-adhesive
bicomponent fiber was 6.47 dtex, the breaking tensile strength
thereof was 0.60 cN/dtex, the breaking elongation thereof was
460.3%, the 100% elongation tensile strength thereof was 0.37
cN/dtex, and the 120.degree. C. dry heat shrinkage thereof was
-0.7%. The web area shrinkage of the web of 100% the
thermal-adhesive bicomponent fibers was -1.45%, the nonwoven fabric
strength thereof was 14.5 kg/g, and the cantilever value thereof
was 7.90 cm.
Example 2
[0046] A bicomponent fiber was produced under the same condition as
in Example 1, for which, however, the draw ratio in cold drawing
was 1.1 times. The single yarn fineness of the thus-obtained
thermal-adhesive bicomponent fiber was 6.41 dtex, the breaking
tensile strength thereof was 0.65 cN/dtex, the breaking elongation
thereof was 424.1%, the 100% elongation tensile strength thereof
was 0.41 cN/dtex, and the 120.degree. C. dry heat shrinkage thereof
was -1.9%. The web area shrinkage of the web of 100% the
thermal-adhesive bicomponent fibers was -5.6%, the nonwoven fabric
strength thereof was 16.5 kg/g, and the cantilever value thereof
was 8.10 cm.
Example 3
[0047] A bicomponent fiber was produced under the same condition as
in Example 1, for which, however, the draw ratio in cold drawing
was 1.30 times. The single yarn fineness of the thus-obtained
thermal-adhesive bicomponent fiber was 6.22 dtex, the breaking
tensile strength thereof was 0.72 cN/dtex, the breaking elongation
thereof was 381.8%, the 100% elongation tensile strength thereof
was 0.46 cN/dtex, and the 120.degree. C. dry heat shrinkage thereof
was -2.0%. The web area shrinkage of the web of 100% the
thermal-adhesive bicomponent fibers was -6.1%, the nonwoven fabric
strength thereof was 17.1 kg/g, and the cantilever value thereof
was 8.90 cm.
Comparative Example 3
[0048] A bicomponent fiber was produced under the same condition as
in Example 1, for which, however, the draw ratio in cold drawing
was 1.4 times. The single yarn fineness of the thus-obtained
thermal-adhesive bicomponent fiber was 6.14 dtex, the breaking
tensile strength thereof was 0.75 cN/dtex, the breaking elongation
thereof was 346.8%, the 100% elongation tensile strength thereof
was 0.53 cN/dtex, and the 120.degree. C. dry heat shrinkage thereof
was -0.6%. The web area shrinkage of the web of 100% the
thermal-adhesive bicomponent fibers was -1.8%, the nonwoven fabric
strength thereof was 18.4 kg/g, and the cantilever value thereof
was 10.1 cm.
Example 4
[0049] A bicomponent fiber was produced under the same condition as
in Example 1, for which, however, the undrawn yarn was cold-drawn
while cooled in a water bath having a controlled temperature of
20.degree. C. The single yarn fineness of the thus-obtained
thermal-adhesive bicomponent fiber was 6.52 dtex, the breaking
tensile strength thereof was 0.65 cN/dtex, the breaking elongation
thereof was 459.3%, the 100% elongation tensile strength thereof
was 0.39 cN/dtex, and the 120.degree. C. dry heat shrinkage thereof
was -3.2%. The web area shrinkage of the web of 100% the
thermal-adhesive bicomponent fibers was -9.5%, the nonwoven fabric
strength thereof was 15.3 kg/g, and the cantilever value thereof
was 8.13 cm.
Example 5
[0050] A bicomponent fiber was produced under the same condition as
in Example 1, for which, however, the yarn was subjected to
relaxing and thermal shrinking treatment and heat treatment in a
hot water bath at 95.degree. C. with overfeeding it at 0.7 times,
but thereafter it was not dried with hot air. The single yarn
fineness of the thus-obtained thermal-adhesive bicomponent fiber
was 6.58 dtex, the breaking tensile strength thereof was 0.68
cN/dtex, the breaking elongation thereof was 443.3%, the 100%
elongation tensile strength thereof was 0.41 cN/dtex, and the
120.degree. C. dry heat shrinkage thereof was -3.9%. The web area
shrinkage of the web of 100% the thermal-adhesive bicomponent
fibers was -11.4%, the nonwoven fabric strength thereof was 14.9
kg/g, and the cantilever value thereof was 8.90 cm.
Example 6
[0051] As the core component (fiber-forming resin component), used
was polyethylene terephthalate (PET) having IV=0.64 dL/g,
Tg=70.degree. C. and Tm=256.degree. C.; and as the sheath component
(thermal-adhesive resin component), used was crystalline
copolyester (polyethylene terephthalate prepared through
copolymerization with 20 mol % of isophthalic acid and 50 mol % of
tetramethylene glycol) having MFR=40 g/10 min, Tm=152.degree. C.
and Tg=43.degree. C. These resins were melted at 290.degree. C. and
255.degree. C., respectively. Using a known core/sheath bicomponent
fiber spinneret, these were formed into a bicomponent fiber in a
ratio by weight, core component/sheath component of 50 wt. %/50 wt.
%, and then spun out under the condition of a jetting rate of 0.71
g/min/orifice and a spinning rate of 1250 m/min, thereby obtaining
an undrawn yarn. The undrawn yarn was cold-drawn by 1.2 times, and
then the cold-drawn yarn was dipped in an aqueous solution of an
oily agent of potassium lauryl phosphate/polyoxyethylene-modified
silicone of 80 wt. %/20 wt. %. Then, using a staffing box-equipped
forced crimper, this was mechanically crimped at 11 crimps/25 mm.
Further, the crimped yarn was subjected to drying treatment and
relaxing and thermal shrinkage treatment with hot air at 90.degree.
C. under no tension, and then cut into pieces having a fiber length
of 51 mm. The single yarn fineness of the thus-obtained
thermal-adhesive bicomponent fiber was 5.7 dtex, the breaking
tensile strength thereof was 0.94 cN/dtex, the breaking elongation
thereof was 392%, the 100% elongation tensile strength thereof was
0.35 cN/dtex, and the 120.degree. C. dry heat shrinkage thereof was
-3.8%. The web area shrinkage of the web of 100% the
thermal-adhesive bicomponent fibers (however, the thermal-adhering
temperature was changed to 180.degree. C.) was -11.2%, the nonwoven
fabric strength thereof was 12.3 kg/g, and the cantilever value
thereof was 8.30 cm.
INDUSTRIAL APPLICABILITY
[0052] The low-modulus, self-extensible thermal-adhesive
bicomponent fiber of the invention comprises PET as the
fiber-forming resin component, and since the spinning speed in
producing it is low, fiber breakage frequency during spinning is
extremely low. Further, when the bicomponent fiber is used in
producing a nonwoven fabric, then the produced nonwoven fabric is
bulky and has high adhesiveness, high drapability and good
feel.
* * * * *