U.S. patent application number 12/190900 was filed with the patent office on 2010-02-18 for elastomeric bicomponent fibers comprising block copolymers having high flow.
Invention is credited to John E. FLOOD, Dale L. Handlin, JR..
Application Number | 20100038815 12/190900 |
Document ID | / |
Family ID | 34961513 |
Filed Date | 2010-02-18 |
United States Patent
Application |
20100038815 |
Kind Code |
A1 |
FLOOD; John E. ; et
al. |
February 18, 2010 |
ELASTOMERIC BICOMPONENT FIBERS COMPRISING BLOCK COPOLYMERS HAVING
HIGH FLOW
Abstract
Bicomponent fibers having a sheath-core morphology where the
sheath is a thermoplastic polymer and the core is an elastomeric
compound are made which can be continuously extruded from the melt
at high production rates. The elastomeric compound comprises a
coupled, selectively hydrogenated block copolymer having high flow.
The block copolymer has at least one polystyrene block of molecular
weight from 5,000 to 7,000 and at least one polydiene block of
molecular weight from 20,000 to 70,000 and having a high vinyl
content of 60 mol % or greater. The bicomponent fibers are useful
for the manufacture of articles such as woven fabrics, spunbond
non-woven fabrics or filters, staple fibers, yarns and bonded,
carded webs. The bicomponent fibers can be made using a process
comprising coextrusion of the thermoplastic polymer and elastomeric
compound to produce fibers at greater than 800 mpm and having a
denier from 0.1 to 50 g/9000 m.
Inventors: |
FLOOD; John E.; (Cypress,
TX) ; Handlin, JR.; Dale L.; (Houston, TX) |
Correspondence
Address: |
Michael A. Masse;KRATON Polymers U.S. LLC
Intellectual Property Asset Manager, 3333 Highway 6 South, Rm. CA-110
Houston
TX
77082
US
|
Family ID: |
34961513 |
Appl. No.: |
12/190900 |
Filed: |
August 13, 2008 |
Current U.S.
Class: |
264/172.15 |
Current CPC
Class: |
D04H 1/435 20130101;
D04H 1/4334 20130101; Y10T 428/2913 20150115; C08L 53/025 20130101;
C08L 51/006 20130101; Y10T 428/2929 20150115; D04H 3/16 20130101;
C08F 297/04 20130101; D01F 8/10 20130101; Y10T 428/2931 20150115;
D04H 1/4382 20130101; C08F 297/044 20130101; D01F 8/06 20130101;
Y10T 428/2967 20150115; D04H 1/4291 20130101; C08L 51/006 20130101;
C08L 2666/04 20130101; C08L 51/006 20130101; C08L 53/00 20130101;
C08L 51/006 20130101; C08L 2666/02 20130101; C08L 53/025 20130101;
C08L 53/00 20130101; C08L 53/025 20130101; C08L 2666/02 20130101;
C08L 53/025 20130101; C08L 2666/04 20130101 |
Class at
Publication: |
264/172.15 |
International
Class: |
D01D 5/34 20060101
D01D005/34 |
Claims
1-16. (canceled)
17. A process to produce the bicomponent fiber of claim 1
comprising coextrusion of a thermoplastic polymer and an
elastomeric compound wherein the thermoplastic polymer and the
elastomeric compound are forced using separate melt pumps to
extrude through a die to form one or more fibers having a sheath
primarily consisting of the thermoplastic polymer and a core
primarily consisting of the elastomeric compound at a rate of at
least 500 meters per minute such that the bicomponent fiber has a
denier per filament from 0.1 to 30 grams per 9000 meters.
18. The process of claim 17 wherein the polydiene blocks E and
E.sub.1 have a vinyl content from 73 to 83 percent.
19. The process of claim 17 wherein the bicomponent fibers have a
denier per filament from 1 to 10 grams per 9000 meters.
20. The process of claim 17 wherein the bicomponent fibers are
extruded at a rate of at least 2000 meters per minute.
21-25. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
provisional patent application Ser. No. 60/549,570, filed Mar. 3,
2004, entitled Block Copolymers having High Flow and High
Elasticity.
FIELD OF THE INVENTION
[0002] The invention relates to bicomponent fibers comprising a
thermoplastic polymer sheath and an elastomeric core. In particular
the elastomeric core comprises a block copolymer of mono alkenyl
arene and conjugated diene blocks having high flow. The invention
also relates to processes for producing bicomponent fibers. The
invention further relates to articles made from bicomponent
fibers.
BACKGROUND
[0003] Fibers made from elastic materials find use in a variety of
applications ranging from woven fabrics to spunbond elastic mats to
disposable, personal hygiene items. It would be of particular
interest to use styrenic block copolymers for such applications.
However, the typical phase-separated nature of block copolymer
melts leads to high melt elasticity and high melt viscosity. In
order to process styrenic block copolymers through small orifices,
such as found in fiber spinnerets, expensive and specialized melt
pump equipment would be required. Further, the high melt
elasticities lead to fracture of the fiber as it exits the die,
preventing the formation of continuous elastomeric fibers. As a
result, styrenic block copolymers have been found to be exceedingly
difficult to process into continuous elastic fibers at high
processing rates.
[0004] A further problem with styrenic block copolymers is their
inherent stickiness in the melt. Because of this character, melt
spun fibers of styrenic block copolymers tend to stick together, or
self-adhere, during processing. This effect is not desired and can
be, in fact, tremendously problematic when separate, continuous
fibers are the goal. In addition to the result of an unacceptable
fiber product, the self-adhesion of the fibers leads to equipment
fouling and expensive shut-downs. Efforts to apply styrenic block
copolymers in elastic fiber production have to date been met with
significant challenges.
[0005] Himes taught the use of triblock/diblock copolymer blends as
one approach to make elastomeric fibers in U.S. Pat. No. 4,892,903.
These types of compositions have been found to have high
viscosities and melt elasticities which have limited them to
formation of discontinous and continuous fibers such as used in
melt-blown, non-woven applications.
[0006] Bicomponent fibers comprising acid functionalized styrenic
block copolymers have been taught by Greek in European Patent
Application 0 461 726. Conventional, selectively hydrogenated
styrenic block copolymers which were acid functional were used to
form side-by-side bicomponent fibers with polyamides. While the
acid functionalization provided increased adhesion between the two
components, it is well known in the art that acid functionalization
leads to even higher melt viscosities and melt elasticities than in
unfunctionalized block copolymers. Further, the side-by-side
morphologies taught by Greak would not prevent the inherently
sticky fibers from self-adhering during processing.
[0007] Bonded non-woven webs made using bicomponent fibers
comprising, among other polymers, conventional styrenic block
copolymers and having a variety of morphologies has been taught by
Austin in U.S. Pat. No. 6,225,243. In particular, the sheath-core
morphologies, with the core being comprised of styrenic block
copolymers, provided fibers of suitably low stickiness to form
non-woven webs.
[0008] However, high viscosity and melt elasticity of conventional
styrenic block copolymers continues to prevent high speed spinning
of continuous elastomeric fibers. The present invention addresses
these longstanding needs by providing a high melt flow block
copolymer which is able to be formed into continuous elastomeric
bicomponent fibers.
SUMMARY OF THE INVENTION
[0009] In one aspect, the present invention is a bicomponent fiber
comprising a thermoplastic polymer sheath and an elastomeric core
wherein the elastomeric core comprises a selectively hydrogenated
block copolymer having an S block and an E or E.sub.1 block and
having the general formula:
S-E-S,(S-E.sub.1).sub.n,(S-E.sub.1).sub.nS,(S-E.sub.n).sub.nX
or mixtures thereof, wherein: [0010] a. prior to hydrogenation the
S block is a polystyrene block; [0011] b. prior to hydrogenation
the E block is a polydiene block, selected from the group
consisting of polybutadiene, polyisoprene and mixtures thereof,
having a molecular weight from 40,000 to 70,000; [0012] c. prior to
hydrogenation the E.sub.1 block is a polydiene block, selected from
the group consisting of polybutadiene, polyisoprene, and mixtures
thereof, having a molecular weight from 20,000 to 35,000; [0013] d.
n has a value of 2 to 6 and X is the residue of a coupling agent;
[0014] e. the styrene content of the block copolymer is from 13 to
25 weight percent; [0015] f. the vinyl content of the polydiene
block prior to hydrogenation is from 70 to 85 mol percent; [0016]
g. the block copolymer includes less than 15 weight percent of
units having the general formula:
[0016] S-E or S-E.sub.1 [0017] wherein S, E and E.sub.1 are as
already defined; [0018] h. subsequent to hydrogenation about 0 to
10% of the styrene double bonds have been hydrogenated and at least
80% of the conjugated diene double bonds have been hydrogenated;
[0019] i. the molecular weight of each of the S blocks is from
5,000 to 7,000; and [0020] j. the melt index of the block copolymer
is greater than or equal to 12 grams/10 minutes according to ASTM
D1238 at 230.degree. C. and 2.16 kg weight.
[0021] In another aspect the invention is an article such as an
elastomeric mono filament, a woven fabric, a spunbond non-woven
fabric, a melt blown non-woven fabric or filter, a staple fiber, a
yarn or a bonded, carded web comprising the bicomponent fiber
described herein.
[0022] In a further aspect the invention is a process to produce a
bicomponent fiber comprising coextrusion of a thermoplastic polymer
and an elastomeric compound comprising a selectively hydrogenated
block copolymer as described herein wherein the thermoplastic
polymer and the elastomeric compound are forced using separate melt
pumps through a die to form one or more fibers having a sheath
primarily composed of thermoplastic polymer and a core comprised of
the elastomeric compound at a rate of at least 500 meters per
minute such that the resulting bicomponent fiber has a denier per
filament of 0.1 to 10 grams per 9000 meters.
[0023] Importantly, the invention comprises an elastomeric compound
in the core having high melt flow which allows processing of
bicomponent fibers on commercial-type equipment at high rates. The
high melt flow of the elastomeric core compound can be achieved
with selectively hydrogenated block copolymers having high vinyl
contents, sufficiently low molecular weights, or by some
combination of these features.
[0024] The elastomeric core compound may further comprise a
thermoplastic polymer which is compositionally the same or
different from the sheath material. Incorporation of a
thermoplastic polymer in the elastomeric core may increase the
core-sheath compatibility, increase the core-sheath adhesion,
increase the processability of the elastomeric compound, and/or
improve the material economics.
FIGURES
[0025] FIG. 1 shows a cross-section of a bundle of bicomponent
fibers of the present invention. The thermoplastic polymer sheath
is apparent as an annular region surrounding each elastomeric
core.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] The bicomponent fibers of the present invention comprise a
thermoplastic polymer sheath and an elastomeric compound core
comprising a selectively hydrogenated block copolymer. The
bicomponent fiber is made by a coextrusion process in which the
thermoplastic polymer and the elastomeric compound core are metered
to a die or spinneret separately. Such a coextruded bicomponent
fiber can have a variety of morphologies including, but not limited
to, sheath-core, side-by-side, islands in the sea, bilobal,
trilobal, and pie-section.
[0027] In the present invention it is important that the sheath
form the majority of the outside surface of the fiber. In
particular, the sheath-core morphology wherein the sheath forms a
covering about the core is preferred. In this preferred morphology,
the core may be centered in the fiber cross-section or may be
off-center. The sheath may cover the core in a complete fashion
over the circumference of the fiber or may be only partially
covering over the circumference of the fiber. In the case where the
covering is partial about the circumference, the morphology is
distinguished from side-by-side morphologies in that the core makes
up the majority of the volume of the fiber. The volume ratio of the
sheath to the core in the present invention is from 5/95 to 49/51.
The preferred range of sheath to core volume ratio is 10/90 to
40/60 and the most preferred range is 20/80 to 30/70. The sheath
consists primarily of a thermoplastic polymer and the core consists
primarily of an elastomeric compound. As used herein "consists
primarily" means greater than 80% on a volume basis.
[0028] The elastomeric compound core comprises a selectively
hydrogenated block copolymer having an S block and an E or E.sub.1
block and having the general formula:
S-E-S,(S-E.sub.1).sub.n,(S-E.sub.1).sub.nS,(S-E.sub.1).sub.nX
or mixtures thereof, wherein: (a) prior to hydrogenation, the S
block is a polystyrene block; (b) prior to hydrogenation, the E
block or E.sub.1 block is a polydiene block, selected from the
group consisting of polybutadiene, polyisoprene and mixtures
thereof. The block copolymer can be linear or radial having three
to six arms. General formulae for the linear configurations
include:
S-E-S and/or (S-E.sub.1), and/or (S-E.sub.1).sub.nS
wherein the E block is a polydiene block, selected from the group
consisting of polybutadiene, polyisoprene and mixtures thereof,
having a molecular weight of from 40,000 to 70,000; the E.sub.1
block is a polydiene block, selected from the group consisting of
polybutadiene, polyisoprene and mixtures thereof having a molecular
weight of from 20,000 to 35,000; and n has a value from 2 to 6,
preferably from 2 to 4, an more preferably an average of
approximately 3. By example, the general formula for the radial
configurations having three and four arms include:
##STR00001##
wherein the E.sub.1 block is a polydiene block, selected from the
group consisting of polybutadiene, polyisoprene and mixtures
thereof, having a molecular weight of from 20,000 to 35,000; and X
is a coupling agent residue.
[0029] As used herein, the term "molecular weights" refers to the
true molecular weight in g/mol of the polymer or block of the
copolymer. The molecular weights referred to in this specification
and claims can be measured with gel permeation chromatography (GPC)
using polystyrene calibration standards, such as is done according
to ASTM 3536. GPC is a well-known method wherein polymers are
separated according to molecular size, the largest molecule eluting
first. The chromatograph is calibrated using commercially available
polystyrene molecular weight standards. The molecular weight of
polymers measured using GPC so calibrated are styrene equivalent
molecular weights. The styrene equivalent molecular weights may be
converted to true molecular weights when the styrene content of the
polymer and the vinyl content of the diene segments are known. The
detector used is preferably a combination ultraviolet and
refractive index detector. The molecular weights expressed herein
are measured at the peak of the GPC trace, converted to true
molecular weights, and are commonly referred to as "peak molecular
weights".
[0030] The block copolymers of the present invention are prepared
by anionic polymerization of styrene and a diene selected from the
group consisting of butadiene; isoprene and mixtures thereof. The
polymerization is accomplished by contacting the styrene and diene
monomers with an organoalkali metal compound in a suitable solvent
at a temperature within the range from about -150.degree. C. to
about 300.degree. C., preferably at a temperature within the range
from about 0.degree. C. to about 100.degree. C. Particularly
effective anionic polymerization initiators are organolithium
compounds having the general formula RLi.sub.n where R is an
aliphatic, cycloaliphatic, aromatic, or alkyl-substituted aromatic
hydrocarbon radical having from 1 to 20 carbon atoms; and n has a
value of 1 to 4. Preferred initiators include n-butyl lithium and
sec-butyl lithium. Methods for anionic polymerization are well
known and can be found in such references as U.S. Pat. No.
4,039,593 and U.S. Reissue Pat. No. Re 27,145.
[0031] The block copolymers of the present invention can be linear,
linear coupled, or a radial block copolymer having a mixture of 2
to 6 "arms". Linear block copolymers can be made by polymerizing
styrene to form a first S block, adding butadiene to form an E
block, and then adding additional styrene to form a second S block.
A linear coupled block copolymer is made by forming the first S
block and E block and then contacting the diblock with a
difunctional coupling agent. A radial block copolymer is prepared
by using a coupling agent that is at least trifunctional.
[0032] Difunctional coupling agents useful for preparing linear
block copolymers include, for example, methyl benzoate as disclosed
in U.S. Pat. No. 3,766,301. Other coupling agents having two, three
or four functional groups useful for forming radial block
copolymers include, for example, silicon tetrachloride and alkoxy
silanes as disclosed in U.S. Pat. Nos. 3,244,664, 3,692,874,
4,076,915, 5,075,377, 5,272,214 and 5,681,895; polyepoxides,
polyisocyanates, polyimines, polyaldehydes, polyketones,
polyanhydrides, polyesters, polyhalides as disclosed in U.S. Pat.
No. 3,281,383; diesters as disclosed in U.S. Pat. No. 3,594,452;
methoxy silanes as disclosed in U.S. Pat. No. 3,880,954; divinyl
benzene as disclosed in U.S. Pat. No. 3,985,830;
1,3,5-benzenetricarboxylic acid trichloride as disclosed in U.S.
Pat. No. 4,104,332; glycidoxytrimethoxy silanes as disclosed in
U.S. Pat. No. 4,185,042; and oxydipropylbis(trimethoxy silane) as
disclosed in U.S. Pat. No. 4,379,891.
[0033] In one embodiment of the present invention, the coupling
agent used is an alkoxy silane of the general formula
R.sub.x--Si--(OR').sub.y, where x is 0 or 1, x+y=3 or 4, R and R'
are the same or different, R is selected from aryl, linear alkyl
and branched alkyl hydrocarbon radicals, and R' is selected from
linear and branched alkyl hydrocarbon radicals. The aryl radicals
preferably have from 6 to 12 carbon atoms. The alkyl radicals
preferably have 1 to 12 carbon atoms, more preferably from 1 to 4
carbon atoms. Under melt conditions these alkoxy silane coupling
agents can couple further to yield functionalities greater than 4.
Preferred tetra alkoxy silanes are tetramethoxy silane ("TMSi"),
tetraethoxy silane ("TESi"), tetrabutoxy silane ("TBSi"), and
tetrakis(2-ethylhexyloxy)silane ("TEHSi"). Preferred trialkoxy
silanes are methyl trimethoxy silane ("MTMS"), methyl triethoxy
silane ("MTES"), isobutyl trimethoxy silane ("IBTMO") and phenyl
trimethoxy silane ("PhTMO"). Of these the more preferred are
tetraethoxy silane and methyl trimethoxy silane.
[0034] One important aspect of the present invention is the
microstructure of the polymer. The microstructure relevant to the
present invention is a high amount of vinyl in the E and/or E.sub.1
blocks. This configuration can be achieved by the use of a control
agent during polymerization of the diene. A typical agent is
diethyl ether. See U.S. Pat. No. Re 27,145 and U.S. Pat. No.
5,777,031, the disclosure of which is hereby incorporated by
reference. Any microstructure control agent known to those of
ordinary skill in the art of preparing block copolymers to be
useful can be used to prepare the block copolymers of the present
invention.
[0035] In the practice of the present invention, the block
copolymers are prepared so that they have from about 60 to about 85
mol percent vinyl in the E and/or E.sub.1 blocks prior to
hydrogenation. In another embodiment, the block copolymers are
prepared so that they have from about 65 to about 85 mol percent
vinyl content. In still another embodiment the block copolymers are
prepared so that they have from about 70 to about 85 mol percent
vinyl content. Another embodiment of the present invention includes
block copolymers prepared so that they have from about 73 to about
83 mol percent vinyl content in the E and/or E.sub.1 blocks.
[0036] In one embodiment, the present invention is a hydrogenated
block copolymer. The hydrogenated block copolymers of the present
invention are selectively hydrogenated using any of the several
hydrogenation processes know in the art. For example the
hydrogenation may be accomplished using methods such as those
taught, for example, in U.S. Pat. Nos. 3,494,942; 3,634,594;
3,670,054; 3,700,633; and Re. 27,145, the disclosures of which are
hereby incorporated by reference. Any hydrogenation method that is
selective for the double bonds in the conjugated polydiene blocks,
leaving the aromatic unsaturation in the polystyrene blocks
substantially intact, can be used to prepare the hydrogenated block
copolymers of the present invention.
[0037] The methods known in the prior art and useful for preparing
the hydrogenated block copolymers of the present invention involve
the use of a suitable catalyst, particularly a catalyst or catalyst
precursor comprising an iron group metal atom, particularly nickel
or cobalt, and a suitable reducing agent such as an aluminum alkyl.
Also useful are titanium based catalyst systems. In general, the
hydrogenation can be accomplished in a suitable solvent at a
temperature within the range from about 20.degree. C. to about
100.degree. C., and at a hydrogen partial pressure within the range
from about 100 psig (689 kPa) to about 5,000 psig (34,473 kPa).
Catalyst concentrations within the range from about 10 ppm to about
500 ppm by wt of iron group metal based on total solution are
generally used and contacting at hydrogenation conditions is
generally continued for a period of time with the range from about
60 to about 240 minutes. After the hydrogenation is completed, the
hydrogenation catalyst and catalyst residue will, generally, be
separated from the polymer.
[0038] In the practice of the present invention, the hydrogenated
block copolymers have a hydrogenation degree greater than 80
percent. This means that more than from 80 percent of the
conjugated diene double bonds in the E or E.sub.1 block has been
hydrogenated from an alkene to an alkane. In one embodiment, the E
or E.sub.1 block has a hydrogenation degree greater than about 90
percent. In another embodiment, the E or E.sub.1 block has a
hydrogenation degree greater than about 95 percent.
[0039] In the practice of the present invention, the styrene
content of the block copolymer is from about 13 percent to about 25
weight percent. In one embodiment, the styrene content of the block
copolymer is from about 15 percent to about 24 percent. Any styrene
content within these ranges can be used with the present invention.
Subsequent to hydrogenation, from 0 to 10 percent of the styrene
double bonds in the S blocks have been hydrogenated in the practice
of the present invention.
[0040] The molecular weight of each of the S blocks in the block
copolymers of the present invention is from about 5,000 to about
7,000 in the block copolymers of the present invention. In one
embodiment, the molecular weight of each of the S blocks is from
about 5,800 to about 6,600. The S blocks of the block copolymers of
the present invention can be a polystyrene block having any
molecular weight within these ranges.
[0041] In the practice of the present invention, the E blocks are a
single polydiene block. These polydiene blocks can have molecular
weights that range from about 40,000 to about 70,000. The E.sub.1
block is a polydiene block having a molecular weight range of from
about 20,000 to about 35,000. In one embodiment, the molecular
weight range of the E block is from about 45,000 to about 60,000,
and the molecular weight range for each E.sub.1 block of a coupled
block copolymer, prior to being coupled, is from about 22,500 to
about 30,000.
[0042] One advantage of the present invention over conventional
hydrogenated block copolymer is that they have high melt flows that
allow them to be easily molded or continuously extruded into shapes
or films or spun into fibers. This property allows end users to
avoid or at least limit the use of additives that degrade
properties, cause area contamination, smoking, and even build up on
molds and dies. But the hydrogenated block copolymers of the
present invention also are very low in contaminants that can cause
these undesirable effects, such as diblocks from inefficient
coupling. The block copolymers and hydrogenated block copolymers of
the present invention have less than 15 weight percent of diblock
content, such diblocks having the general formula:
SE or SE.sub.1
wherein S, E and E.sub.1 are as previously defined. In one
embodiment, the diblock level is less than 10 percent in another
embodiment less than 8 percent. For example, where the structure of
the hydrogenated block copolymer is (S-E.sub.1).sub.2X, the block
copolymer contains less than 10% of the S-E.sub.1 species. All
percentages are by weight.
[0043] One characteristic of the hydrogenated block copolymers of
the present invention is that they have a low order-disorder
temperature. The order-disorder temperature (ODT) of the
hydrogenated block copolymers of the present invention is typically
less than about 250.degree. C. Above 250.degree. C. the polymer is
more difficult to process although in certain instances for some
applications ODT's greater than 250.degree. C. can be utilized. One
such instance is when the block copolymer is combined with other
components to improve processing. Such other components may be
thermoplastic polymers, oils, resins, waxes or the like. In one
embodiment, the ODT is less than about 240.degree. C. Preferably,
the hydrogenated block copolymers of the present invention have an
ODT of from about 210.degree. C. to about 240.degree. C. This
property can be important in some applications because when the ODT
is below 210.degree. C., the block copolymer may exhibit creep that
is undesirably excessive or low strength. For purposes of the
present invention) the order-disorder temperature is defined as the
temperature above which a zero shear viscosity can be measured by
capillary rheology or dynamic rheology.
[0044] For the purposes of the present invention, the term "melt
index" is a measure of the melt flow of the polymer according ASTM
D1238 at 230.degree. C. and 2.16 kg weight. It is expressed in
units of grams of polymer passing through a melt rheometer orifice
in 10 minutes. The hydrogenated block copolymers of the present
invention have a desirable high melt index allowing for easier
processing than similar hydrogenated block copolymers that have
higher melt indexes. In one embodiment, the hydrogenated block
copolymers of the present invention have a melt index of greater
than or equal to 12. In another embodiment, the hydrogenated block
copolymers of the present invention have a melt index of at least
15. In still another embodiment, the hydrogenated block copolymers
of the present invention have a melt index of at least 40. Another
embodiment of the present invention includes hydrogenated block
copolymers having a melt index of from about 20 to about 100. Still
another embodiment of the present invention includes hydrogenated
block copolymers having a melt index of from about 50 to about
85.
[0045] In a further embodiment, the elastomeric compound core is
further comprised of a thermoplastic polymer. In this embodiment,
the elastomeric core contains up to 50% by weight of a
thermoplastic polymer such as polypropylene, linear low density
polyethylene, polyamides, poly(ethylene terephthalate),
poly(butylene terephthalate), poly(trimethylene terephthalate) and
other thermoplastics as described herein in reference to the sheath
composition.
[0046] In a still further embodiment, the elastomeric core of the
bicomponent fiber comprises a selectively hydrogenated block
copolymer having a vinyl content in the range of about 20 to about
60 mol percent. In this embodiment, the block copolymer has a total
true molecular weight such that it has high melt index according to
the description presented herein.
[0047] The present invention includes a sheath composed primarily
of a thermoplastic polymer. Exemplary thermoplastic polymers
include, for example, ethylene homopolymers, ethylene/alpha-olefin
copolymers, propylene homopolymers, propylene/alpha-olefin
copolymers, impact polypropylene copolymers, butylene homopolymers,
butylene/alpha olefin copolymers, and other alpha olefin copolymers
or interpolymers.
[0048] Representative polyethylenes include, for example, but are
not limited to, substantially linear ethylene polymers,
homogeneously branched linear ethylene polymers, heterogeneously
branched linear ethylene polymers, including linear low density
polyethylene (LLDPE), ultra or very low density polyethylene (ULDPE
or VLDPE), medium density polyethylene (MDPE), high density
polyethylene (HDPE) and high pressure low density polyethylene
(LDPE).
[0049] When the thermoplastic polymer is polyethylene, the melt
flow rate, also referred to as melt flow index, must be at least 25
g/10 min at 230.degree. C. and 2.16 kg weight according to ASTM
D1238. The preferred type of polyethylene is linear low density
polyethylene.
[0050] Representative polypropylenes include, for example, but are
not limited to, substantially isotactic propylene homopolymers,
random alpha olefin/propylene copolymers where propylene is the
major component on a molar basis and polypropylene impact
copolymers where the polymer matrix is primarily a polypropylene
homopolymer or random copolymer and the rubber phase is an
alpha-olefin/propylene random copolymer. Suitable melt flow rates
of polypropylenes are at least 10 g/10 min at 230.degree. C. and
2.16 kg according to ASTM D1238. More preferred are melt flow rates
of at least 20 g/10 min. Polypropylene homopolymers are the
preferred type of polypropylene.
[0051] Examples of ethylene/alpha-olefin copolymers and
propylene/alpha-olefin copolymers include, but are not limited to,
AFFINITY, ENGAGE and VERSIFY polymers from Dow Chemical and EXACT
and VISTAMAXX polymers from Exxon Mobil. Suitable melt flow rates
of such copolymers must be at leas 10 g/10 min at 230.degree. C.
and 2.16 kg weight according to ASTM D1238.
[0052] Still other thermoplastic polymers included herein are
polyvinyl chloride (PVC) and blends of PVC with other materials,
polyamides and polyesters such as poly(ethylene terephthalate),
polybutylene terephthalate) and poly(trimethylene terephthalate).
Regardless of the specific type, the thermoplastic polymer must
have a melt flow rate suitable for processing into fibers or
components of fibers.
[0053] It is sometimes desirable to use processing aids and other
additives in the elastomeric core compound. Exemplary of such aids
and additives are members selected from the group consisting of
other block copolymers, olefin polymers, styrene polymers,
tackifying resins, polymer extending oils, waxes, fillers,
reinforcements, lubricants, stabilizers, and mixtures thereof.
[0054] In the embodiments of the present invention it is especially
useful to include resins compatible with the rubber E and/or
E.sub.1 blocks of the elastomeric compound. This serves to promote
the flow of the elastomeric compound. Various resins are known, and
are discussed, e.g., in U.S. Pat. Nos. 4,789,699; 4,294,936; and
3,783,072, the contents of which, with respect to the resins, are
incorporated herein by reference. Any resin can be used which is
compatible with the rubber E and/or E.sub.1 blocks of the
elastomeric compound and/or the polyolefin, and can withstand the
high processing (e.g., extrusion) temperatures. Generally,
hydrogenated hydrocarbon resins are preferred resins, because of
their better temperature stability. Examples illustrative of useful
resins are hydrogenated hydrocarbon resins such as low molecular
weight, fully hydrogenated .alpha.-methylstyrene REGALREZ.RTM.
(Eastman Chemical), ARKON.RTM.P (Arakawa Chemical) series resins,
and terpene hydrocarbons such as ZONATAC.RTM.501 Lite (Arizona
Chemical). The present invention is not limited to use of the
resins listed here. In general, the resin may be selected from the
group consisting of C.sub.5 hydrocarbon resins, hydrogenated
C.sub.5 hydrocarbon resins, styrenated C.sub.5 resins,
C.sub.5/C.sub.9 resins, styrenated terpene resins, fully
hydrogenated or partially hydrogenated C.sub.9 hydrocarbon resins,
rosins esters, rosins derivatives and mixtures thereof. One of
ordinary skill in the art will understand that other resins which
are compatible with the components of the composition and can
withstand the high processing temperatures, and can achieve the
objectives of the present invention, can also be used.
[0055] The bicomponent fiber may also comprise a wax to promote
flow and/or compatibility. Suitable waxes are those having a
congealing point of from 50 to 70.degree. C. Suitable amounts of
wax are from 0.1 to 75% w, preferably from 5 to 60% wt based on the
weight of the elastomeric compound. Animal, insect, vegetable,
synthetic and mineral waxes may be used with those derived from
mineral oils being preferred. Examples of mineral oil waxes include
bright stock slack wax, medium machine oil slack wax, high melting
point waxes and microcrystalline waxes. In the case of slack waxes
up to 25% w of oil may be present. Additives to increase the
congealing point of the wax may also be present.
[0056] The bicomponent fiber may also comprise an oil. The oil may
be incorporated to improve the processability of the fiber or to
enhance its softness. Especially preferred are the types of oil
that are compatible with the E and/or E.sub.1 of the block
copolymer. While oils of higher aromatics content are satisfactory,
those petroleum-based white oils having low volatility and less
than 50% aromatic content are preferred. The oils should
additionally have low volatility, preferable having an initial
boiling point above about 260.degree. C. The amount of oil employed
varies from about 0 to about 300 parts by weight per hundred parts
by weight rubber, or block copolymer, preferably about 20 to about
150 parts by weight.
[0057] The elastomeric compound is typically stabilized by the
addition of an antioxidant or mixture of antioxidants. Frequently,
a sterically hindered phenolic stabilizer is used, or a
phosphorus-based stabilizer is used in combination with a
sterically hindered phenolic stabilizer, such as disclosed in
Japanese patent No. 94055772; or a combination of phenolic
stabilizers is used, such as disclosed in Japanese patent No.
94078376.
[0058] Other additives such as pigments, dyes, optical brighteners,
bluing agents and flame retardants may be used in the bicomponent
fibers of the present invention.
[0059] The bicomponent fibers of the present invention can be used
to form a variety of articles. These articles include elastic mono
filaments, woven fabrics, spunbond non-woven fabrics or filters,
melt-blown fabrics, staple fibers, yarns, bonded, carded webs, and
the like. Any of the processes typically used to make these
articles can be employed when they are equipped to extrude two
materials into a bicomponent fiber.
[0060] In particular, non-woven fabrics or webs can be formed by
any of the processes known in the art. One process, typically
referred to as spunbond, is well known in the art. U.S. Pat. No.
4,405,297 describes a typical spunbond processes. The spunbond
process commonly comprises extruding the fibers from the melt
through a spinneret, quenching and/or drawing the fibers using an
air flow, and collecting and bonding the non-woven web. The bonding
of the non-woven web is typically accomplished by any thermal,
chemical or mechanical methods, including water entanglement and
needle punch processes, effective in creating a multiplicity of
intermediate bonds among the fibers of the web. The non-woven webs
of the present invention can also be formed using melt-blown
process such as described in U.S. Pat. No. 5,290,626. Carded webs
may be formed from non-woven webs by folding and bonding the
non-woven web upon itself in the cross machine direction.
[0061] The non-woven fabrics of the present invention can be used
for a variety of elastic fabrics such as diapers, waist bands,
stretch panels, disposable garments, medical and personal hygiene
articles, filters, and the like.
[0062] Elastic mono-filaments of the present invention are
continuous, single, bicomponent fibers used for a variety of
purposes and can be formed by any of the known methods of the art
comprising spinning, drawing, quenching and winding. As used
herein, staple fiber means cut or chopped segments of the
continuously coextruded bicomponent fiber.
[0063] Yarns of the bicomponent fibers can be formed by common
processes. U.S. Pat. No. 6,113,825 teaches the general process of
yarn formation. In general, the process comprises melt extrusion of
multiple fibers from a spinneret, drawing and winding the filaments
together to form a multi-filament yarn, extending or stretching the
yarn optionally through one or more thermal treatment zones, and
cooling and winding the yarn.
[0064] The articles of the present invention can be used alone or
in combination with other articles made with the bicomponent fibers
or with other classes of materials. As an example, non-woven webs
can be combined with elastic mono-filaments to provide elastic
stretch panels. As another example, non-woven webs can be bonded to
other non-elastomeric non-woven webs or polymeric films of many
types.
[0065] In the process of producing the bicomponent fiber of the
present invention two separate single screw extruders are used to
extrude the sheath polymer and core polymer into two separate melt
pumps. Following the melt pumps, the polymers are brought together
into their bicomponent configuration in the spinneret via a series
of plates and baffles. Upon exiting the spinneret the fibers are
cooled/quenched via a cold air quench cabinet. After quenching the
fibers are drawn via an aspirator or a series of cold rolls. In the
case that cold rolls are used, the fibers are taken up onto a
winder. In the case that an aspirator is used, the fibers are
allowed to collect in a drum beneath the aspirator.
[0066] One important aspect of the process is the rate at which the
bicomponent fibers may be produced. The high flow characteristics
presented by the inventive fibers allows high extrusion rates. This
is important from a practical sense since commercial equipment
operates at high extrusion rates. In this way, economic throughputs
can be achieved. In the present invention, extrusion rates of at
least 800 meters per minute (mpm) are required. More preferred are
rates about 1000 mpm or greater and most preferred are rates about
2000 mpm or greater.
[0067] For the applications disclosed herein, fine denier fibers
are preferred. These fine denier fibers are extremely efficient
elastic materials in the sense that very small amounts of material
can be used to affect elastic behavior in articles so composed. In
the present invention bicomponent fibers having a denier (grams per
9000 m fiber) from 0.1 to 30 can be made. More preferred are fibers
having a denier from 0.5 to 20 g, 9000 m and most preferred are
fibers having a denier from 1 to 10 g/9000 m.
EXAMPLES
[0068] The term "elastic" is used herein to mean any material
which, upon application of a biasing force, is stretchable, that
is, elongatable at least about 60 percent (i.e., to a stretched,
biased length which is at least about 160 percent of its relaxed
unbiased length) and which, will recover at least 50 percent of its
elongation upon release of the stretching, elongating force. A
hypothetical example would be a one (1) inch sample of a material
which is elongatable to at least 1.60 inches (4.06 cm) and which,
upon being elongated to 1.60 inches (4.06 cm) and released, will
recover to a length of not more than 1.27 inches (3.23 cm). Many
elastic materials may be elongated by much more than 60 percent
(i.e., much more than 160 percent of their relaxed length), for
example, elongated 100 percent or more, and many of these will
recover to substantially their initial relaxed length, for example,
to within 105 percent of their initial relaxed length, upon release
of the stretching force.
[0069] The elasticity was measured on yarns formed from the
bicomponent fibers as the percent strain recovery at 100 percent
elongation. The yarn consisted of a multiplicity of individual
continuous fibers ranging in number from 36 to 144 depending upon
the number of holes in the spinneret. The yarn was stretched
manually to 100% elongation and then allowed to relax. The relaxed
length of the yarn was then measured and the percent recovery
calculated. In this method the elasticity is determined as the
percent recovery.
[0070] As used herein, the term "tenacity" refers to the measure of
tensile strength of a yarn as measured in grams per denier.
Examples 1-8
[0071] Bicomponent fibers with a polypropylene sheath and a SEBS
elastomer core at sheath/core ratios of 30/70 and 20/80 were made
according to the following description. The polypropylene sheath
was a nominal 38 MFR homopolymer (5D49) from The Dow Chemical
Company. The elastomer core (Polymer 7) was a nominal 50 MFR, high
vinyl (vinyl content=75 mol %), coupled SEBS copolymer (coupling
efficiency=96%) with an 18% styrene content, a styrene MW of 6600
and a midblock molecular weight of 60,000.
[0072] The fibers were made using a conventional, commercial-type
high speed spinning process using bicomponent technology and
spinnerets from Hills Inc.
[0073] Table 1 gives typical spinning performance and mechanical
properties of the fibers. From Table 1, one can see that high speed
spinning can be achieved (Examples 3 5, and 8) as well as
reasonable fiber tensile strength and elongation-to-break (Examples
1, 2, 4, 6, 7). Exceptionally high spinning speeds were attainable.
The sheath-core bicomponent fibers (Examples 3 and 5) were spun at
2700 mpm.
Examples 9-13
[0074] Bicomponent fibers with a polypropylene sheath and a SEBS
elastomer core at sheath/core ratios of 30/70 and 20/80 were made
according to the following description. The polypropylene sheath
was a nominal 38 MFR homopolymer (5D49) from The Dow Chemical
Company. The elastomer core (Polymer 5) was a 31 MFR, high vinyl
(vinyl content=76%), coupled SEBS copolymer (coupling
efficiency=94%) with an 18% styrene content, a styrene MW of 6200
and a midblock molecular weight of 56,000.
[0075] The fibers were made via a conventional, commercial-type
high speed spinning process using bicomponent technology and
spinnerets from Hills Inc.
[0076] Good tensile properties could be achieved with the 31 MER
elastomer (Examples 9, 11 and 12). The attainable spinning speed
was in the range of 1500 to 1800 mpm.
Examples 14-25
[0077] Bicomponent fibers with a polypropylene sheath and a SEBS
elastomer core at sheath/core ratios of 30/70 and 20/80 were made
according to the following description. The polypropylene sheath
was a nominal 38 MFR homopolymer (5D49) from The Dow Chemical
Company. The elastomer core (Polymer 6) was a nominal 20 MFR, high
vinyl (vinyl content=76%), coupled SEBS copolymer (coupling
efficiency=95%) with an 19% styrene content, a styrene MW of 6100
and a midblock molecular weight of 50,000.
[0078] The fibers were made via a conventional, commercial-type
high speed spinning process using bicomponent technology and
spinnerets from Hills Inc.
[0079] The results of Table 3 demonstrate that a lower melt flow
elastomer has a detrimental effect on the spinning performance
(maximum spinning speed) but the tensile properties are still
considered to be reasonable for an elastic fiber. Table 3 also
shows that as the polypropylene becomes a greater portion of the
fiber cross-section that spinning performance improves and that
even relatively low melt flow elastomers can offer good spinning
performance with the correct sheath/core ratio. In addition, the
polypropylene improves the tensile strength of the fibers as its
concentration increases but probably has a negative effect on the
fiber elasticity.
Examples 26-36
[0080] Bicomponent fibers with a polypropylene sheath and a SEBS
elastomer core at sheath/core ratios of 30/70 and 20/80 were made
according to the following description. The polypropylene sheath
was a nominal 38 MFR homopolymer (5D49) from The Dow Chemical
Company. The elastomer core was a blend with polypropylene (5D49)
and an elastomer (Polymer 7). Blend 1 was a blend of 10 wt % Dow
5D49 polyproplene with 90 wt % Polymer 7. Blend 2 was a blend of 20
wt % Dow 5D49 polypropylene with 80 wt % Polymer 7.
[0081] The fibers were made via a conventional, commercial-type
high speed spinning process using bicomponent technology and
spinnerets from Hills Inc. Table 4 demonstrates that elastomer
blends with polypropylene made good elastomeric cores for
bicomponent elastic fibers. High spinning speeds and good tensile
and elastic properties were achieved.
[0082] A comparative monocomponent fiber (Example 36) is also shown
in Table 4. The monocomponent fiber consisted only of the elastomer
compound (Polymer 7) and no thermoplastic polymer sheath. Low
spinning speeds were required and the fibers exhibited unacceptable
stickiness during the spinning process. The resulting monocomponent
fibers self-adhered and could not be separated.
Examples 37-39
[0083] Bicomponent fibers were also spun via a single air aspirator
to simulate a spunbond process. Air pressure in the aspirator was
used to affect the maximum spinning speed, i.e., the higher the
pressure the higher the spinning speed. For all of the examples the
polymer throughput per hole (0.35 g/hole/min) is the same.
[0084] Example 37 was a comparative monocomponent fiber of 5D49
polypropylene alone. The maximum air pressure reached 40 psi before
fibers began to break. The fibers of this thermoplastic polymer had
no elasticity.
[0085] Example 38 used a 5D49 polypropylene sheath and a 50 MFR
elastic core (Polymer 7) at a 20/80 ratio to produce elastic
spunbond fibers. The maximum spinning speed was 20 psi before
filmaments began to break. Example 39 was a bicomponent fiber of
polypropylene (5D49) and a 20 MFR elastomer (Polymer 6) at a
sheath/core ratio of 40/60. The maximum spinning speed was 25 psi
before fibers began to break. The bicomponent fibers of Examples 38
and 39 were elastic.
Example 40-45
Examples 40 through 44 demonstrate sheath/core bicomponent fibers
using Dow ASPUN polyethylene as the thermoplastic polymer sheath
(6811A) and Polymer 7 as the elastomeric core. These examples
demonstate that polyethylene can also be used as a sheath for
bicomponent elastic fibers.
[0086] The fibers were made via a conventional, commercial-type
high speed spinning process using bicomponent technology and
spinnerets from Hills Inc.
Example 46
[0087] A bicomponent elastic fiber was made with a relatively low
melt flow rate, low vinyl elastomer (Polymer 8) according to the
following description. Polymer 8 was a nominal 9 MF, 38% vinyl
coupled SEBS elastomer. It has a styrene block molecular weight of
5000, a midblock molecular weight of 47,000, and a coupling
efficiency of 94%. The nominal styrene content is 18 wt %. The
sheath for this fiber is a nominal 12 MER homopolymer
polypropylene. While this example demonstrates that bicomponent
fibers can be made using low vinyl block copolymers, a higher melt
flow rate elastomer would be preferred for optimal spinning
performance.
TABLE-US-00001 TABLE 1 Spinning Elongation Highest Denier per
Sheath/Core Speed Tenacity at Break Elasticity Spinning Spinneret
filament Example Ratio (mpm) (g/dn) (%) (%) Speed # of holes (dpf)
1 20/80 500 0.3 500 70 -- 72 15 2 20/80 1400 0.6 320 80 -- 72 5.4 3
20/80 -- -- -- -- 2700 72 -- 4 30/70 500 0.3 550 -- -- 72 15 5
30/70 -- -- -- -- 2700 72 -- 6 20/80 500 0.2 560 -- -- 36 27 7
20/80 1500 0.3 280 -- -- 36 7.6 8 20/80 -- -- -- -- 3000 36 --
TABLE-US-00002 TABLE 2 Ex- Sheath/ Spinning Tenac- Elongation
Highest am- Core Speed ity at Break Elasticity Spinning ple Ratio
(mpm) (g/dn) (%) (%) Speed 9 20/80 500 0.3 470 -- -- 10 20/80 -- --
-- -- 1500 11 30/70 500 0.3 570 -- -- 12 30/70 1400 0.7 250 75 --
13 30/70 -- -- -- -- 1800
TABLE-US-00003 TABLE 3 Spinning Elongation Highest Denier per
Sheath/Core Speed Tenacity at Break Elasticity Spinning filament
Example Ratio (mpm) (g/dn) (%) (%) Speed (dpf) 14 20/80 500 0.3 500
-- -- 14.5 15 20/80 1000 0.5 310 -- -- 7.5 16 20/80 -- -- -- --
1100 -- 17 30/70 500 0.3 490 -- -- 14.5 18 30/70 1400 0.7 250 80 --
5 19 30/70 -- -- -- -- 1500 -- 20 40/60 500 0.5 660 -- -- 14.5 21
40/60 1400 0.8 320 -- -- 5 22 40/60 -- -- -- -- 1900 -- 23 50/50
500 0.5 660 -- -- 14.5 24 50/50 1400 0.9 330 50 -- 5 25 50/50 -- --
-- -- 2500 --
TABLE-US-00004 TABLE 4 Highest Spinning Elongation Spinning
Sheath/Core Speed Tenacity at Break Elasticity Speed
Comments/denier per Example Core Ratio (mpm) (g/dn) (%) (%) (mpm)
filament (dpf) 26 Blend 1 0/100 -- -- -- -- 800 No sheath, very
sticky 27 Blend 1 20/80 500 0.1 660 -- -- 21 dpf 28 Blend 1 20/80
1500 0.2 310 75 -- 7.7 dpf 29 Blend 1 20/80 2000 0.4 200 -- -- 6
dpf 30 Blend 1 20/80 -- -- -- -- 2700 -- 31 Blend 2 0/100 -- -- --
-- 800 No sheath, very sticky 32 Blend 2 20/80 500 0.2 530 -- -- 21
dpf 33 Blend 2 20/80 1500 0.3 200 70 -- 7.7 dpf 34 Blend 2 20/80
2000 0.4 160 75 -- 6 dpf 35 Blend 2 20/80 -- -- -- -- 3000 -- 36
Polymer 7 0/100 -- -- -- -- 800 No sheath, very sticky
TABLE-US-00005 TABLE 5 Sheath/ Max Spinning Core Speed Elasticity
Example Sheath Core Ratio (psi) (%) 37 5D49 -- 100/0 40 0 38 5D49
Polymer 7 20/80 20 -- 39 5D49 Polymer 6 40/60 25 75
TABLE-US-00006 TABLE 6 Denier Spinning per Elongation Highest
Sheath/Core Speed filament Tenacity at Break Elasticity Spinning
Example Ratio (mpm) (g/9000 m) (g/dn) (%) (%) Speed 40 20/80 300
17.6 0.1 660 -- -- 41 20/80 500 11.6 0.1 680 -- -- 42 20/80 -- --
-- -- -- 500 43 30/70 500 11.6 0.1 580 60 -- 44 30/70 1000 5.2 0.2
360 50 -- 45 30/70 -- -- -- -- -- 1000
TABLE-US-00007 TABLE 7 Spinning Elongation Sheath/Core Speed
Tenacity at Break Elasticity Example Ratio (mpm) (g/dn) (%) (%) 46
20/80 500 0.02 480 80
* * * * *