Note: Descriptions are shown in the official language in which they were submitted.
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HIGH STRENGTH FABRICS CONSISTING OF THIN
GAUGE CONSTANT COMPRESSION ELASTIC FIBERS
FIELD OF THE INVENTION
[0001] The present invention relates to high strength fabrics made from
thin gauge
constant compression elastic fibers. Garments made with the constant
compression
elastic fibers have a very comfortable feel to the wearer. The garments are
also resistant
to puncture due to the high strength fabric made with the elastic fibers.
BACKGROUND OF THE INVENTION
[0002] In recent years, the demand for greater functionality in fabrics,
over and
beyond the basic function of insulation, has been high due to the changing
lifestyles
across the globe. One such sought after functionality is fabrics of thinner
gauges without
sacrificing the strength and integrity of the fabric. This thinner gauge
fabric allows for
lower packing volumes, a reduction of a feeling of ''bulk" and in the case of
undergarments, a lack of external visibility through the outer garment.
[0003] Synthetic elastic fibers (SEF) are normally made from polymers
having soft
and hard segments to give elasticity. Polymers having hard and soft segments
are
typically poly(ether-amide), such as Pebax or copolyesters, such as Hytrel
or
thermoplastic polyurethane, such as Estane . However, very high elongation SEF
typically utilize hard and soft segmented polymers such as dry spun
polyurethane
(Lycra ) or melt spun thermoplastic polyurethane (Estane ). While these SEF
vary,
from low to very high, in elongation of break, all can be commonly described
as having
an exponentially increasing modulus (strain) with an increase in elongation
(stress).
[0004] Melt spun TPU fibers offer some advantages over dry spun
polyurethane
fibers in that no solvent is used in the melt spun process, whereas in the dry
spinning
process, the polymer is dissolved in solvent and spun. The solvent is then
partially
evaporated out of the fibers. All of the solvent is very difficult to
completely remove
from the dry spun fibers. To facilitate removing the solvent from dry spun
fibers, they
are typically made into a small size and bunched together to create a multi-
filament
(ribbon-like) fiber. This results in a larger physical size for a given denier
as compared
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to a melt spun fiber. These physical characteristics result in more bulk in
the fabric and
the nature of the multi-filament bundle contributes to a loss of comfort.
[0001] Melt spun TPU fibers are made by melt spinning a TPU polymer. TPU
polymers are made from the reaction of three components, i.e., (a) a hydroxyl
terminated
intermediate, which is typically a polyether or polyester end capped with a
hydroxyl
group; (b) a polyisocyanate, such as a diisocy-anate; and (c) a short chain
hydroxyl
terminated chain extender. The hydroxyl terminated intermediate forms the soft
segment
of the TPU polymer while the polyisocyanate and the chain extender forms the
hard
segment of the TPU polymer. The combination of soft and hard segments gives
the TPU
polymer elastic properties. The TPU polymer is also frequently lightly
crosslinked by
using a pre-polymer end capped with a polyisocyanate to give enhanced
properties. The
crosslinking material is added to the melted TPU polymer during melt spinning
of the
fiber.
[0002] It would be desirable to have a TPU elastic fiber which has a
relatively
constant compression between zero and 250% elongation and to make constant
compression garments and/or fabrics containing such TPU fibers. Also, it would
be
desirable for these constant compression fabrics to be thin gauge and to have
a high
puncture resistance. Garments made from such fabrics would offer more comfort
and
confidence to the wearer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] Figure 1 is a photo micrograph of a 70 denier multi-filament of a
commercial
dry spun polyurethane fiber.
[0004] Figure 2 is a photo micrograph of a 70 denier of a melt spun
constant
compression thermoplastic polyurethane fiber of the present invention.
[0005] Figure 3 is a graph showing the X axis as denier vs. the Y axis of
fiber width
squared (square microns). The fiber of this invention is compared to a
commercial dry
spun fiber.
SUMMARY OF THE INVENTION
[0006] It is an object of the present invention to provide a thin gauge,
constant
compression, high strength fiber having an ultimate elongation of at least
400% and
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having a relatively flat and/or constant modulus in the load and unload cycle
between
100% and 200% elongation. This flat and/or constant modulus is evidenced by a
stress
in the load cycle at 100% elongation of less than 0.023 gram-force per denier,
at 150%
elongation of less than 0.023 gram-force per denier, at 200% elongation of
less than
0.053 gram-force per denier; and as evidenced by a stress in the unload cycle
at 200%
elongation of less than 0.027 gram-force per denier, at 150% elongation of
less than
0.018 gram-force per denier, and at 100% elongation of less than 0.015 gram-
force per
denier.
[0010a1 In accordance with one aspect of the present invention, there is
provided a
melt spun elastic fiber made from a crosslinked thermoplastic polyurethane,
wherein said fiber
has an ultimate elongation of at least 400%; wherein the melt spun elastic
fiber shows a stress
value in the load cycle, (i) at 100% elongation of less than 0.226 mN (0.023
gram-force) per
denier, (ii) at 150% elongation of less than 0.353 mN (0.036 grain-force) per
denier, and (iii) at
200% elongation of less than 0.520 mN (0.053 gram-force) per denier; wherein
the melt spun
elastic fiber shows a stress value in the unload cycle (i) at 200% elongation
of less than 0.265
mN (0.027 gram-force) per denier, (ii) at 150% elongation of less than 0.177
mN (0.018 gram-
force) per denier, and (iii) at 100% elongation of less than 0.147 mN (0.015
gram-force) per
denier; and wherein said thermoplastic polyurethane is prepared from a mixture
comprising: (a) a
linear hydroxyl terminated polyester having a number average molecular weight
of from 500 to
10,000, (b) a polyisocyanate, and (c) a glycol chain extender having from 2 to
10 carbon atoms.
10010b] In
accordance with another aspect of the present invention, there is provided a
melt
spun elastic fiber made from a polyester thermoplastic polyurethane prepared
from a reaction
mixture comprising a polyisocyanate, a linear hydroxyl terminated polyester
intermediate, one or
more chain extenders, and a crosslinking agent; wherein the polyisocyanate
comprises diphenyl
methane-4,4 diisocyanate; wherein the linear hydroxyl terminated polyester
intermediate
comprises the reaction product of adipic acid with a 50/50 blend of 1,4-
butanediol and 1,6-
hexanediol, and wherein said intermediate has a number average molecular
weight (Mn) of from
500 to 10,000 and an acid number of less than 1.3; wherein the one or more
chain extenders
comprise 1,4-butanediol; and wherein the crosslinking agent comprises a
polyether crosslinking
agent.
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[0011] An exemplary fiber is made by melt spinning a thermoplastic
polyurethane
polymer, preferably a polyester polyurethane polymer. The fiber is lightly
crosslinked
by adding a crosslinking agent, preferably 5 to 20 weight percent, to the
polymer melt
during the melt spinning process.
[0011a] In some embodiments, a 40 denier monofilament fiber has a width of
less
than 100 .tn.
[0011b] In some embodiments, when the fiber having a denier of 70 is made into
a
fabric and said fabric is tested for puncture strength according to ASTM D751,
said
fabric has a load at failure of greater than 6 pounds.
[0012] A process to produce the fiber involves a melt spinning process
whereby the
fiber is formed by passing the polymer melt through a spinneret. The velocity
of the
fiber exiting the spinneret and the velocity at which the fiber is wound into
bobbins is
relatively close. That is, the fibers should be wound into bobbins at a speed
no more
than 50%, preferably 20%, and more preferably 10%, greater than the speed at
which the
fiber is exiting the spinneret.
[0013] It is another object of the invention to produce fabric with the
thin gauge,
constant compression fiber. In an exemplary embodiment, the fabric is made by
combining, such as by knitting or weaving, the elastic fiber with a hard
fiber, such as
nylon and/or polyester fiber. Fabric made with the novel fiber also has high
burst
strength.
[0014] Clothing garments, such as undergarments, are made from the elastic
fiber.
Such garments offer very good comfort to the wearer.
DETAILED DESCRIPTION OF THE INVENTION
The fiber of this invention is made from a thermoplastic elastomer. The
preferred
thermoplastic elastomer is a thermoplastic polyurethane polymer (TPU). The
invention
will be described using a TPU, but it should be understood that this is only
one
embodiment and other thermoplastic elastomers can be used by those skilled in
the art.
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[0016] The TPU polymer type used in this invention can be any conventional
TPU
polymer that is known to the art and in the literature as long as the TPU
polymer has
adequate molecular weight. The TPU polymer is generally prepared by reacting a
polyisocyanate with an intermediate such as a hydroxyl terminated polyester, a
hydroxyl
terminated polyether, a hydroxyl terminated polycarbonate or mixtures thereof,
with one
or more chain extenders, all of which are well known to those skilled in the
art.
[0017] The hydroxyl terminated polyester intermediate is generally a linear
polyester
having a number average molecular weight (Mn) of from about 500 to about
10,000,
desirably from about 700 to about 5,000, and preferably from about 700 to
about 4,000,
an acid number generally less than 1.3 and preferably less than 0.8. The
molecular
weight is determined by assay of the terminal functional groups and is related
to the
number average molecular weight. The polymers are produced by (1) an
esterification
reaction of one or more glycols with one or more dicarboxylic acids or
anhydrides or (2)
by transesterification reaction, i.e., the reaction of one or more glycols
with esters of
dicarboxylic acids. Mole ratios generally in excess of more than one mole of
glycol to
acid are preferred so as to obtain linear chains having a preponderance of
terminal
hydroxyl groups. Suitable polyester intermediates also include various
lactones such as
polycaprolactone typically made from c-caprolactone and a bifunctional
initiator such as
diethylene glycol. The dicarboxylic acids of the desired polyester can be
aliphatic,
cycloaliphatic, aromatic, or combinations thereof Suitable dicarboxylic acids
which
may be used alone or in mixtures generally have a total of from 4 to 15 carbon
atoms and
include: succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic,
dodecanedioic,
isophthalic, terephthalic, cyclohexane dicarboxylic, and the like. Anhydrides
of the
above dicarboxylic acids such as phthalic anhydride, tetrahydrophthalic
anhydride, or the
like, can also be used. Adipic acid is the preferred acid. The glycols which
are reacted
to form a desirable polyester intermediate can be aliphatic, aromatic, or
combinations
thereof, and have a total of from 2 to 12 carbon atoms, and include ethylene
glycol, 1,2-
propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol,
1,6-
hexanediol, 2,2-dimethy1-1,3-propanediol, 1,4-cyclohexanedimethanol,
decamethylene
glycol, dodecamethylene glycol, and the like, 1,4-butanediol is the preferred
glycol.
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[0018] Hydroxyl terminated polyether intermediates are polyether polyols
derived
from a diol or polyol having a total of from 2 to 15 carbon atoms, preferably
an alkyl diol
or glycol which is reacted with an ether comprising an alkylene oxide having
from 2 to 6
carbon atoms, typically ethylene oxide or propylene oxide or mixtures thereof
For
example, hydroxyl functional polyether can be produced by first reacting
propylene
glycol with propylene oxide followed by subsequent reaction with ethylene
oxide.
Primary hydroxyl groups resulting from ethylene oxide are more reactive than
secondary
hydroxyl groups and thus are preferred. Useful commercial polyether polyols
include
poly(ethylene glycol) comprising ethylene oxide reacted with ethylene glycol,
poly(propylene glycol) comprising propylene oxide reacted with propylene
glycol,
poly(tetramethyl glycol) comprising water reacted with tetrahydrofuran
(PTMEG).
Polytetramethylene ether glycol (PTMEG) is the preferred polyether
intermediate.
Polyether polyols further include polyamide adducts of an alkylene oxide and
can
include, for example, ethylenediamine adduct comprising the reaction product
of
ethylenediamine and propylene oxide, diethylenetriamine adduct comprising the
reaction
product of diethylenetriamine with propylene oxide, and similar polyamide type
polyether polyols. Copolyethers can also be utilized in the current invention.
Typical
copolyethers include the reaction product of THF and ethylene oxide or THF and
propylene oxide. These are available from BASF as Poly THF B , a block
copolymer,
and poly THF R, a random copolymer. The various polyether intermediates
generally
have a number average molecular weight (Mn) as determined by assay of the
terminal
functional groups which is an average molecular weight greater than about 700,
such as
from about 700 to about 10,000, desirably from about 1000 to about 5000, and
preferably
from about 1000 to about 2500. A particular desirable polyether intermediate
is a blend
of two or more different molecular weight polyethers, such as a blend of 2000
Mn and
1000 M,, PTMEG.
[0019] The most preferred embodiment of this invention uses a polyester
intermediate made from the reaction of adipic acid with a 50/50 blend of 1,4-
butanediol
and 1,6-hexanediol.
[0020] The polycarbonate-based polyurethane resin of this invention is
prepared by
reacting a diisocyanate with a blend of a hydroxyl terminated polycarbonate
and a chain
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extender. The hydroxyl terminated polycarbonate can be prepared by reacting a
glycol
with a carbonate.
10021] U.S. Patent No. 4,131,731 discloses hydroxyl terminated
polycarbonates and
their preparation. Such polycarbonates are linear and have terminal hydroxyl
groups
with essential exclusion of other terminal groups. The essential reactants are
glycols and
carbonates. Suitable glycols are selected from cycloaliphatic and aliphatic
diols
containing 4 to 40, and preferably 4 to 12 carbon atoms, and from
polyoxyalkylene
glycols containing 2 to 20 alkoxy groups per molecular with each alkoxy group
containing 2 to 4 carbon atoms. Diols suitable for use in the present
invention include
aliphatic diols containing 4 to 12 carbon atoms such as butanedio1-1,4,
pentanedio1-1,4,
neopentyl glycol, hexanedio1-1,6, 2,2,4-trimethylhexanedio1-1,6, decanedio1-
1,10,
hydrogenated dilinoleylglycol, hydrogenated dioleylglycol; and cycloaliphatic
diols such
as cyclohexanedio1-1,3, dimethylolcyclohexane-1,4, cyclohexanedio1-1,4,
dimethylolcyclohexane-1,3, 1,4-endomethylene-2-hydroxy-5-hydroxymethyl
cyclohexane, and polyalkylene glycols. The diols used in the reaction may be a
single
diol or a mixture of diols depending on the properties desired in the finished
product.
100221 Polycarbonate intermediates which are hydroxyl terminated are
generally
those known to the art and in the literature. Suitable carbonates are selected
from
alkylene carbonates composed of a 5 to 7 membered ring having the following
general
formula:
0
f\o
0
R
where R is a saturated divalent radical containing 2 to 6 linear carbon atoms.
Suitable
carbonates for use herein include ethylene carbonate, trimethylene carbonate,
tetramethylene carbonate, 1,2-propylene carbonate, 1,2-butylene carbonate, 2,3-
butylene
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carbonate, 1,2-ethylene carbonate, 1,3-pentylene carbonate, 1,4-pentylene
carbonate, 2,3-
pentylene carbonate, and 2,4-pentylene carbonate.
[0023] Also, suitable herein are dialkylcarbonates, cycloaliphatic
carbonates, and
diarylcarbonates. The dialkylcarbonates can contain 2 to 5 carbon atoms in
each alkyl
group and specific examples thereof are diethylcarbonate and
dipropylcarbonate.
Cycloaliphatic carbonates, especially dicycloaliphatic carbonates, can contain
4 to 7
carbon atoms in each cyclic structure, and there can be one or two of such
structures.
When one group is cycloaliphatic, the other can be either alkyl or aryl. On
the other
hand, if one group is aryl, the other can be alkyl or cycloaliphatic.
Preferred examples of
diarylcarbonates, which can contain 6 to 20 carbon atoms in each aryl group,
are
diphenylcarbonate, ditolylcarbonate, and dinaphthylcarbonate.
[0024] The reaction is carried out by reacting a glycol with a carbonate,
preferably an
alkylene carbonate in the molar range of 10:1 to 1:10, but preferably 3:1 to
1:3 at a
temperature of 100 C to 300 C and at a pressure in the range of 0.1 to 300 mm
of
mercury in the presence or absence of an ester interchange catalyst, while
removing low
boiling glycols by distillation.
[0025] More specifically, the hydroxyl terminated polycarbonates are
prepared in
two stages. In the first stage, a glycol is reacted with an alkylene carbonate
to form a
low molecular weight hydroxyl terminated polycarbonate. The lower boiling
point
glycol is removed by distillation at 100 C to 300 C, preferably at 150 C to
250 C, under
a reduced pressure of 10 to 30 mm Hg, preferably 50 to 200 mm Hg. A
fractionating
column is used to separate the by-product glycol from the reaction mixture.
The by-
product glycol is taken off the top of the column and the unreacted alkylene
carbonate
and glycol reactant are returned to the reaction vessel as reflux. A current
of inert gas or
an inert solvent can be used to facilitate removal of by-product glycol as it
is formed.
When amount of by-product glycol obtained indicates that degree of
polymerization of
the hydroxyl terminated polycarbonate is in the range of 2 to 10, the pressure
is gradually
reduced to 0.1 to 10 mm Hg and the unreacted glycol and alkylene carbonate are
removed. This marks the beginning of the second stage of reaction during which
the low
molecular weight hydroxyl terminated polycarbonate is condensed by distilling
off
glycol as it is formed at 100 C to 300 C, preferably 150 C to 250 C and at a
pressure of
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0.1 to 10 mm Hg until the desired molecular weight of the hydroxyl terminated
polycarbonate is attained. Molecular weight (Mn) of the hydroxyl terminated
polycarbonates can vary from about 500 to about 10,000 but in a preferred
embodiment,
it will be in the range of 500 to 2500.
[0026] The second necessary ingredient to make the TPU polymer of this
invention
is a polyisocyanate.
[0027] The polyisocyanates of the present invention generally have the
formula
R(NCO)II where n is generally from 2 to 4 with 2 being highly preferred
inasmuch as the
composition is a thermoplastic. Thus, polyisocyanates having a functionality
of 3 or 4
are utilized in very small amounts, for example less than 5% and desirably
less than 2%
by weight based upon the total weight of all polyisocyanates, inasmuch as they
cause
crosslinking. R can be aromatic, cycloaliphatic, and aliphatic, or
combinations thereof
generally having a total of from 2 to about 20 carbon atoms. Examples of
suitable
aromatic diisocyanates include diphenyl methane-4, 4'-diisocyanate (MDI), H12
MDI, m-
xylylene diisocyanate (XDI), m-tetramethyl xylylene diisocyanate (TMXDI),
phenylene-
1, 4-diisocyanate (PPDI), 1,5-naphthalene diisocyanate (NDI), and
diphenylmethane-3,
3'-dimethoxy-4, 4'-diisocyanate (TODI). Examples of suitable aliphatic
diisocyanates
include isophorone diisocyanate (IPDI), 1,4-cyclohexyl diisocyanate (CHDI),
hexamethylene diisocyanatc (HDI), 1,6-diisocyanato-2,2,4,4-tctramethyl hexane
(TMDI), 1,10-decane diisocyanate, and trans-dicyclohexylmethane diisocyanate
(HMDI). A highly preferred diisocyanate is MDI containing less than about 3%
by
weight of ortho-para (2,4) isomer.
[0028] The third necessary ingredient to make the TPU polymer of this
invention is
the chain extender. Suitable chain extenders are lower aliphatic or short
chain glycols
having from about 2 to about 10 carbon atoms and include for instance ethylene
glycol,
diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol,
triethylene
glycol, cis-trans-isomers of cyclohexyl dimethylol, neopentyl glycol, 1,4-
butanediol, 1,6-
hexandiol, 1,3-butanediol, and 1,5-pentanediol. Aromatic glycols can also be
used as the
chain extender and are the preferred choice for high heat applications.
Benzene glycol
(HQEE) and xylenene glycols are suitable chain extenders for use in making the
TPU of
this invention. Xylenene glycol is a mixture of 1,4-di(hydroxymethyl) benzene
and 1,2-
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di(hydroxymethyl) benzene. Benzene glycol is the preferred aromatic chain
extender
and specifically includes hydroquinone, i.e., bis(beta-hydroxyethyl) ether
also known as
1,4-di(2-hydroxyethoxy) benzene; resorcinol, i.e., bis(beta-hydroxyethyl)
ether also
known as 1,3-di(2-hydroxyethyl) benzene; catechol, i.e., bis(beta-
hydroxyethyl) ether
also known as 1,2-di(2-hydroxyethoxy) benzene; and combinations thereof. The
preferred chain extender is 1,4-butanediol.
[0029] The above three necessary ingredients (hydroxyl terminated
intermediate,
polyisocyanate, and chain extender) are preferably reacted in the presence of
a catalyst.
[0030] Generally, any conventional catalyst can be utilized to react the
diisocyanate
with the hydroxyl terminated intermediate or the chain extender and the same
is well
known to the art and to the literature. Examples of suitable catalysts include
the various
alkyl ethers or alkyl thiol ethers of bismuth or tin wherein the alkyl portion
has from 1 to
about 20 carbon atoms with specific examples including bismuth octoate,
bismuth
laurate, and the like. Preferred catalysts include the various tin catalysts
such as
stannous octoate, dibutyltin dioctoate, dibutyltin dilaurate, and the like.
The amount of
such catalyst is generally small such as from about 20 to about 200 parts per
million
based upon the total weight of the polyurethane forming monomers.
[0031] The TPU polymers of this invention can be made by any of the
conventional
polymerization methods well known in the art and literature.
[0032[ Thermoplastic polyurethanes of the present invention are preferably
made via
a "one shot" process wherein all the components are added together
simultaneously or
substantially simultaneously to a heated extruder and reacted to form the
polyurethane.
The equivalent ratio of the diisocyanate to the total equivalents of the
hydroxyl
terminated intermediate and the diol chain extender is generally from about
0.95 to about
1.10, desirably from about 0.97 to about 1.03, and preferably from about 0.97
to about
1.00. The Shore A hardness of the TPU formed should be from 65A to 95A, and
preferably from about 75A to about 85A, to achieve the most desirable
properties of the
finished article. Reaction temperatures utilizing urethane catalyst are
generally from
about 175 C to about 245 C and preferably from about 180 C to about 220 C. The
molecular weight (Mw) of the thermoplastic polyurethane is generally from
about
100,000 to about 800,000 and desirably from about 150,000 to about 400,000 and
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preferably about 150,000 to about 350,000 as measured by GPC relative to
polystyrene
standards.
[0033] The thermoplastic polyurethanes can also be prepared utilizing a pre-
polymer
process. In the pre-polymer route, the hydroxyl terminated intermediate is
reacted with
generally an equivalent excess of one or more polyisocyanates to form a pre-
polymer
solution having free or unreacted polyisocyanate therein. Reaction is
generally carried
out at temperatures of from about 80 C to about 220 C and preferably from
about 150 C
to about 200 C in the presence of a suitable urethane catalyst. Subsequently,
a selective
type of chain extender as noted above is added in an equivalent amount
generally equal
to the isocyanate end groups as well as to any free or unreacted diisocyanate
compounds.
The overall equivalent ratio of the total diisocyanate to the total equivalent
of the
hydroxyl terminated intermediate and the chain extender is thus from about
0.95 to about
1.10, desirably from about 0.98 to about 1.05 and preferably from about 0.99
to about
1.03. The equivalent ratio of the hydroxyl terminated intermediate to the
chain extender
is adjusted to give 65A to 95A, preferably 75A to 85A Shore hardness. The
chain
extension reaction temperature is generally from about 180 C to about 250 C
with from
about 200 C to about 240 C being preferred. Typically, the pre-polymer route
can be
carried out in any conventional device with an extruder being preferred. Thus,
the
hydroxyl terminated intermediate is reacted with an equivalent excess of a
diisocyanate
in a first portion of the extruder to form a pre-polymer solution and
subsequently the
chain extender is added at a downstream portion and reacted with the pre-
polymer
solution. Any conventional extruder can be utilized, with extruders equipped
with
barrier screws having a length to diameter ratio of at least 20 and preferably
at least 25.
[0034] Useful additives can be utilized in suitable amounts and include
opacifying
pigments, colorants, mineral fillers, stabilizers, lubricants, UV absorbers,
processing
aids, and other additives as desired. Useful opacifying pigments include
titanium
dioxide, zinc oxide, and titanate yellow, while useful tinting pigments
include carbon
black, yellow oxides, brown oxides, raw and burnt sienna or umber, chromium
oxide
green, cadmium pigments, chromium pigments, and other mixed metal oxide and
organic
pigments. Useful fillers include diatomaceous earth (superfloss) clay, silica,
talc, mica,
wallostonite, barium sulfate, and calcium carbonate. If desired, useful
stabilizers such as
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antioxidants can be used and include phenolic antioxidants, while useful
photostabilizers
include organic phosphates, and organotin thiolates (mercaptides). Useful
lubricants
include metal stearates, paraffin oils and amide waxes. Useful UV absorbers
include 2-
(2'-hydroxyphenol) benzotriazoles and 2-hydroxybenzophenones.
[0035[ Plasticizer additives can also be utilized advantageously to reduce
hardness
without affecting properties.
[0036] During the melt spinning process, the TPU polymer described above is
may
be lightly crosslinked with a crosslinking agent. The crosslinking agent is a
pre-polymer
of a hydroxyl terminated intermediate that is a polyether, polyester,
polycarbonate,
polycaprolactone, or mixture thereof reacted with a polyisocyanate. A
polyester or
polyether are the preferred hydroxyl terminated intermediates to make the
crosslinking
agent, with a polyether being the most preferred when used in combination with
a
polyester TPU. The crosslinking agent, pre-polymer, will have an isocyanate
functionality of greater than about 1.0, preferably from about 1.0 to about
3.0, and more
preferably from about 1.8 to about 2.2. It is particularly preferred if both
ends of
hydroxyl terminated intermediate is capped with an isocyanate, thus having an
isocyanate functionality of 2Ø
[0037] The polyisocyanate used to make the crosslinking agent are the same
as
described above in making the TPU polymer. A diisocyanatc, such as MDI, is the
preferred diisocyanate.
[0038] The crosslinking agents have a number average molecular weight (Mn)
of
from about 1,000 to about 10,000 Daltons, preferably from about 1,200 to about
4,000
and more preferably from about 1,500 to about 2,800. Crosslinking agents with
above
about 1500 Min give better set properties.
[0039] The weight percent of crosslinking agent used with the TPU polymer
is from
about 2.0% to about 20%, preferably about 8.0% to about 15%, and more
preferably
from about 10% to about 13%. The percentage of crosslinking agent used is
weight
percent based upon the total weight of TPU polymer and crosslinking agent.
[0040] The preferred melt spinning process to make TPU fibers of this
invention
involves feeding a preformed TPU polymer to an extruder, to melt the TPU
polymer and
the crosslinking agent is added continuously downstream near the point where
the TPU
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melt exits the extruder or after the TPU melt exits the extruder. The
crosslinking agent
can be added to the extruder before the melt exits the extruder or after the
melt exits the
extruder. If added after the melt exits the extruder, the crosslinking agent
needs to be
mixed with the TPU melt using static or dynamic mixers to assure proper mixing
of the
crosslinking agent into the TPU polymer melt. After exiting the extruder, the
melted
TPU polymer with crosslinking agent flows into a manifold. The manifold
divides the
melt stream into different streams, where each stream is fed to a plurality of
spinnerets.
Usually, there is a melt pump for each different stream flowing from the
manifold, with
each melt pump feeding several spinnerets. The spinneret will have a small
hole through
which the melt is forced and exits the spinneret in the form of a monofilament
fiber. The
size of the hole in the spinneret will depend on the desired size (denier) of
the fiber.
[0041] The TPU polymer melt may be passed through a spin pack assembly and
exits
the spin pack assembly used as a fiber. The preferred spin pack assembly used
is one
which gives plug flow of the TPU polymer through the assembly. The most
preferred
spin pack assembly is the one described in PCT patent application WO
2007/076380.
[0042] Once the fiber exits the spinneret, it is cooled before winding onto
bobbins.
The fiber is passed over a first godet, finish oil is applied, and the fiber
proceeds to a
second godet. An important aspect of the process to make the fiber of this
invention is
the relative speed at which the fiber is wound into bobbins. By relative
speed, we mean
the speed of the melt (melt velocity) exiting the spinneret in relationship to
the winding
speed. In a normal prior art TPU melt spinning process, the fiber is wound at
a speed of
4-6 times the speed of the melt velocity. This draws or stretches the fiber.
For the
unique fibers of this invention, this extensive drawing is undesirable. The
fibers must be
wound at a speed at least equal to the melt velocity to operate the process.
For the fibers
of this invention, it is necessary to wind the fibers at a speed no greater
than 50% faster
than the melt velocity, preferably no greater than 20%, and more preferably no
greater
than 10%, with no greater than 5% giving excellent results. It is thought that
a winding
speed that is the same as the melt velocity would be ideal, but it is
necessary to have a
slightly higher winding speed to operate the process. For example, a fiber
exiting the
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spinneret at a speed of 300 meters per minute, would most preferable be wound
at a
speed of between 300 and 315 meters per minute.
[0043] The fibers of this invention can be made in a variety of denier.
Denier is a
term in the art designating the fiber size. Denier is the weight in grams of
9000 meters of
fiber length. The fibers of this invention are typically made in sizes ranging
from 20 to
600 denier, preferably 40 to 400, and more preferably 70 to 360 denier.
[0044] When fibers are made by the process of this invention, anti-tack
additives
such as finish oils, an example of which are silicone oils, are usually added
to the surface
of the fibers after or during cooling and just prior to being wound into
bobbins.
[0045] An important aspect of the melt spinning process is the mixing of
the TPU
polymer melt with the crosslinking agent. Proper uniform mixing is important
to achieve
uniform fiber properties and to achieve long run times without experiencing
fiber
breakage. The mixing of the TPU melt and crosslinking agent should be a method
which
achieves plug-flow, i.e., first in first out. The proper mixing can be
achieved with a
dynamic mixer or a static mixer. Static mixers are more difficult to clean;
therefore, a
dynamic mixer is preferred. A dynamic mixer which has a feed screw and mixing
pins is
the preferred mixer. U.S. Patent 6,709,147 describes such a mixer and has
mixing pins
which can rotate. The mixing pins can also be in a fixed position, such as
attached to the
barrel of the mixer and extending toward the centerline of the feed screw. The
mixing
feed screw can be attached by threads to the end of the extruder screw and the
housing of
the mixer can be bolted to the extruder machine. The feed screw of the dynamic
mixer
should be a design which moves the polymer melt in a progressive manner with
very
little back mixing to achieve plug-flow of the melt. The L/D of the mixing
screw should
be from over 3 to less than 30, preferably from about 7 to about 20, and more
preferably
from about 10 to about 12.
[0046] The temperature in the mixing zone where the TPU polymer melt is
mixed
with the crosslinking agent is from about 200 C to about 240 C, preferably
from about
210 C to about 225 C. These temperatures are necessary to get the reaction
while not
degrading the polymer.
100471 The TPU formed is reacted with the crosslinking agent during the
melt
spinning process to give a molecular weight (Mw) of the TPU in final fiber
form, of from
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about 200,000 to about 800,000, preferably from about 250,000 to about
500,000, more
preferably from about 300,000 to about 450,000.
[0048] The spinning temperature (the temperature of the polymer melt in the
spinneret) should be higher than the melting point of the polymer, and
preferably from
about 10 C to about 20 C above the melting point of the polymer. The higher
the
spinning temperature one can use, the better the spinning. However, if the
spinning
temperature is too high, the polymer can degrade. Therefore, from about 10 C
to about
20 C above the melting point of the TPU polymer, is the optimum for achieving
a
balance of good spinning without degradation of the polymer. If the spinning
temperature is too low, polymer can solidify in the spinneret and cause fiber
breakage.
[0049] The unique fiber of this invention has a relatively flat and/or
constant
modulus in the load and unload cycle between 100% and 200% elongation. This
flat
modulus is evidenced by a stress in the load cycle at 100% elongation of less
than 0.023
gram-force per denier, at 150% elongation of less than 0.036 gram-force per
denier, at
200% elongation of less than 0.053 gram-force per denier; and as evidenced by
a stress
in the unload cycle at 200% elongation of less than 0.027 gram-force per
denier, at 150%
elongation of less than 0.018 gram-force per denier, and at 100% elongation of
less than
0.015 gram-force per denier, where all of this data was collected from a 360
denier fiber.
[0050] This flat modulus is also evidenced by a stress in the load cycle at
100%
elongation of less than 0.158 gram-force per denier, at 150% elongation of
less than
0.207 gram-force per denier, at 200% elongation of less than 0.265 gram-force
per
denier; and as evidenced by a stress in the unload cycle at 200% elongation of
less than
0.021 gram-force per denier, at 150% elongation of less than 0.012 gram-force
per
denier, and at 100% elongation of less than 0.008 gram-force per denier, where
all of this
data was collected from a 70 denier fiber.
[0051] The standard test procedure employed to obtain the modulus values
above is
one which was developed by DuPont for elastic yarns. The test subjects fibers
to a series
of 5 cycles. In each cycle, the fiber is stretched to 300% elongation, and
relaxed using a
constant extension rate (between the original gauge length and 300%
elongation). The %
set is measured after the 5th cycle. Then, the fiber specimen is taken through
a 6th cycle
and stretched to breaking. The instrument records the load at each extension,
the highest
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load before breaking, and the breaking load in units of grams-force per denier
as well as
the breaking elongation and elongation at the maximum load. The test is
normally
conducted at room temperature (23 C + 2 C; and 50% 5% humidity).
[0052] The fiber of this invention has an elongation at break of at least
400%, and
preferably about 450 to 500%. The fiber is a monofilament with a round shape.
Referring to FIG. 2, it can be seen that a 70 denier monofilament fiber is
substantially
round in cross sectional shape. FIG. 1 shows a 70 denier monofilament dry spun
fiber
which has a larger cross section width.
[0053] FIG. 3 shows a graph comparing a dry spun fiber with the melt spun
fiber of
this invention. The graph plots the denier (X axis) vs. the fiber width
squared (square
microns). The graph shows that the melt spun fiber of this invention has a
constant slope
on the graph, whereas the dry spun fiber has an expotentially increasing
slope. The
result is that fabric can be made with the fiber of this invention which is
thinner and thus
more comfortable for the wearer.
[0054] Another important feature of the fiber of this invention is that it
exhibits
improved burst strength in fabric compared to dry spun fibers.
[0055] This feature can be shown by performing the Ball Burst Puncture
Strength
Test according to ASTM D751 using a 1 inch diameter ball. This test would
simulate a
finger pushing through the fabric to form a hole. It was very surprising that
the fibers of
this invention show about a 50 to 75% improvement in burst strength as
compared to dry
spun polyurethane fiber. This improved burst strength exists even though the
tensile
strength of the fiber is almost the same.
[0056] The fiber of this invention also has higher heat capacity. The
combination of
flat modulus curve, higher heat capacity, and thinner gauge results in fabric
made with
the fibers of this invention feeling comfortable to the wearer of garments.
[0057] Fabric made using the fibers of this invention can be made by
knitting or
weaving. Often it is preferred to make fabric using other fibers with the TPU
fibers.
Particularly preferred is to use a hard fiber with the elastic fibers of this
invention. Hard
fibers, such as nylon and/or polyester are preferred. The hard fibers improve
the snag
resistance of the fabric over a 100% elastic fiber fabric. A preferred fabric
is one knitted
using alternating fibers, such as a strand of 140 denier TPU/70 denier nylon
alternating
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with a strand of 140 denier TPU (referred to as a 1-1 fabric) or a strand of
140 denier
TPU/70 denier nylon followed by 2 strands of 140 denier TPU (referred to as 1-
2 fabric).
[0058] Garments can be made with the fabric of this invention. The most
preferred
use of the fabric is in making undergarments or tight fitting garments because
of the
comfort provided by the fiber. Undergarments, such as bras and T-shirts as
well as sport
garments used for activities such as running, skiing, cycling or other sports,
can benefit
from the properties of these fibers. Garments worn next to the body benefit
from the flat
modulus of these fibers, because the modulus is even lower once the fibers
reach body
temperature. A garment that feels tight will become more comfortable in about
30
seconds to 5 minutes after the fibers reach body temperature. It will be
understood by
those skilled in the art that any garment can be made from the fabric and
fibers of this
invention. An exemplary embodiment would be a bra shoulder strap made from
woven
fabric and the wings of the bra made from knitted fabric, with both the woven
and the
knitted fabric containing the melt spun TPU fibers of this invention. The bra
strap would
not require an adjustable clasp because the fabric is elastic.
[0059] The invention will be better understood by reference to the
following
examples.
EXAMPLES
[0060[ The TPU polymer used in the Examples was made by reacting a
polyester
hydroxyl terminated intermediate (polyol) with 1,4-butanediol chain extender
and MDI.
The polyester polyol was made by reacting adipic acid with a 50/50 mixture of
1,4-
butanediol and 1,6-hexanediol. The polyol had a Mn of 2500. The TPU was made
by
the one-shot process. The crosslinking agent added to the TPU during the
spinning
process was a polyether pre-polymer made by reacting 1000 Mn PTMEG with MDI to
create a polyether end capped with isocyanate. The crosslinking agent was used
at a
level of 10 wt.% of the combined weight of TPU plus crosslinking agent. Fiber
were
melt spun to make 40, 70, 140 and 360 denier fibers used in the Examples.
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EXAMPLE 1
[0061] This Example is presented to show the relative flat modulus curve of
the fiber
(70 denier) of this invention as compared to an existing prior art melt spun
TPU fiber (40
denier) and a commercial dry spun fiber (70 denier).
[0062] The test procedure used was that described above for testing elastic
properties. An Instron Model 5564 tensiometer with Merlin Software was used.
The
test conditions were at 23 C 2 C and 50% 5% humidity. Fiber length of test
specimens were 50.0 mm. Four specimens were tested and the results are the
mean value
of the 4 specimens tested. The results are shown in Table I.
TABLE I
Units 70 Denier Prior Art This
Invention
Dry Spun Melt Spun 70 Denier
(40 Denier)
1st Load Pull @ 100% g/denier 0.086 0.128 0.157
1st Load Pull @ 150% g/denier 0.127 0.201 0.206
1st Load Pull @200% g/denier 0.174 0.319 0.264
1st Load Pull @ 300% g/denier 0.334 0.749 0.497
1st Unload Pull @ 200% g/denier 0.028 0.035 0.020
1st Unload Pull @ 150% g/denier 0.017 0.021 0.011
1st Unload Pull @ 100% g/denier 0.015 0.015 0.007
% Set After 1st Pull g/denier 39.36% 17.46% 63.89%
5th Load Pull @ 100% g/denier 0.027 0.028 0.017
5th Load Pull @ 150% g/denier 0.042 0.043 0.028
5th Load Pull @ 200% g/denier 0.060 0.064 0.043
5th Load Pull @ 300% g/denier 0.248 0.442 0.266
5th Unload Pull @ 200% g/denier 0.028 0.036 0.020
5th Unload Pull @ 150% g/denier 0.018 0.022 0.012
5th Unload Pull @ 100% g/denier 0.016 0.017 0.009
% Set After 5th Pull g/denier 47.49% 26.76% 71.05%
-6-1h Load Pull Break Load g/denier 1.802 1.876 1.21
6th Load Pull Break g/denier 583.74% 469.31% 450.6%
Elongation
All of the above data are a mean value for 4 specimens tested.
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[0063] From the above data, it can be seen that the melt spun fibers of
this invention
have a relative flat modulus curve during the 5th testing cycle. The first
cycle is usually
disregarded as this is relieving stress in the fiber.
EXAMPLE 2
[0064] This Example is presented to show the width of a melt spun fiber of
this
invention as compared to a commercial dry spun fiber. The width was determined
by
SEM. The results are shown in Table II.
TABLE II
Fiber Width (Microns)
Denier Melt Spun (This Invention) Dry Spun
34.57
48.32 69.32
40 73.30 117.58
70 89.23 228.43
140 127.92
360 198.38
[0065] As can be seen, the dry spun fiber has a much higher width and the
difference
becomes larger as the denier increases.
EXAMPLE 3
[0066] This Example is presented to show the improved burst strength of the
melt
spun TPU fiber of this invention as compared to a commercial dry spun
polyurethane
fiber. 70 denier fibers were used to prepare a signel Jersey knit fabric from
each type of
fiber. The fabric was tested for burst puncture strength according to ASTM
D751. The
results are shown in Table III. The results are a mean of 5 samples tested.
TABLE III
Test Dry Spun Melt Spun
Load at Failure (Ibs) 5.78 9.03
Displacement at Failure (in.) 8.7 10.6
Load/Thick at Failure (lbflin.) 705 1250
Energy to Failure (lbf-in) 23.0 40.8
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[0067] It was very surprising that although the melt spun fibers of this
invention did
not have higher tensile strength than the dry spun fibers, the burst strength
of the melt
spun fibers were higher.
[0068] While in accordance with the Patent statutes, the best mode and
preferred
embodiment has been set forth, the scope of the invention is not limited
thereto, but
rather by the scope of the attached claims.
