U.S. patent application number 13/879997 was filed with the patent office on 2014-10-30 for bicomponent fibers and methods for making them.
The applicant listed for this patent is ExxonMobil Chemical Patents Inc.. Invention is credited to Aspy K. Mehta, Galen C. Richeson, Alistair D. Westwood.
Application Number | 20140323003 13/879997 |
Document ID | / |
Family ID | 44908116 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140323003 |
Kind Code |
A1 |
Richeson; Galen C. ; et
al. |
October 30, 2014 |
Bicomponent Fibers and Methods for Making Them
Abstract
The present invention relates to bicomponent polymer fibers, and
to processes for forming those fibers. Bicomponent polymer fibers
are described, having a core comprising a core polymer and a sheath
comprising a sheath polymer, wherein the sheath polymer is a
polyolefin having an Mw less than about 65,000 g/mol. The core
polymer has an Mw at least about 20,000 g/mol greater than the Mw
of the sheath polymer. Processes for forming bicomponent fibers are
also described, comprising (i) forming a molten blend of a core
polymer and a sheath polymer; (ii) extruding the molten polymer
blend using an extrusion die having a length to diameter ratio
greater than or equal to about 10 and under shear conditions
sufficient to drive the sheath polymer to the die wall; and (iii)
forming meltblown fibers having a core comprising the core polymer
and a sheath comprising the sheath polymer.
Inventors: |
Richeson; Galen C.; (Humble,
TX) ; Westwood; Alistair D.; (Kingwood, TX) ;
Mehta; Aspy K.; (Humble, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Chemical Patents Inc. |
Baytown |
TX |
US |
|
|
Family ID: |
44908116 |
Appl. No.: |
13/879997 |
Filed: |
October 18, 2011 |
PCT Filed: |
October 18, 2011 |
PCT NO: |
PCT/US2011/056736 |
371 Date: |
July 10, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61411497 |
Nov 9, 2010 |
|
|
|
Current U.S.
Class: |
442/200 ;
264/172.15; 428/373 |
Current CPC
Class: |
Y10T 428/2929 20150115;
D01F 1/00 20130101; Y10T 442/3154 20150401; D01D 5/40 20130101;
D01F 6/46 20130101; D01D 5/0985 20130101; D01F 8/06 20130101 |
Class at
Publication: |
442/200 ;
428/373; 264/172.15 |
International
Class: |
D01F 8/06 20060101
D01F008/06; D01F 1/00 20060101 D01F001/00 |
Claims
1. A bicomponent polymer fiber having a core comprising a core
polymer and a sheath comprising a sheath polymer, wherein the
sheath polymer is a polyolefin having a weight average molecular
weight (Mw) less than about 65,000 g/mole and wherein the Mw of the
core polymer is at least about 20,000 g/mole greater than the Mw of
the sheath polymer.
2. The polymer fiber of claim 1, wherein the core polymer is
selected from a propylene-based polymer, an ethylene-based polymer,
a propylene-ethylene block copolymer, a styrenic block copolymer,
an acrylate, or a combination of the foregoing.
3. The polymer fiber of claim 1, wherein the core polymer is a
propylene-based polymer comprising from about 5 to about 30 wt %
ethylene and/or a C.sub.4-C.sub.12 alpha olefin and having a triad
tacticity greater than about 90% and a heat of fusion less than
about 75 J/g.
4. The polymer fiber of claim 1, wherein the propylene-based
polymer comprises from about 8 to about 20 wt % ethylene.
5. The polymer fiber of claim 1, wherein the propylene-based
polymer comprises from about 12 to about 18 wt % ethylene.
6. The polymer fiber of claim 1, wherein the Mw of the core polymer
is at least about 75,000 g/mole greater than the Mw of the sheath
polymer.
7. The polymer fiber of claim 1, wherein the Mw of the core polymer
is at least about 100,000 g/mole greater than the Mw of the sheath
polymer.
8. The polymer fiber of claim 1, wherein the Mw of the sheath
polymer is less than about 50,000 g/mole and the Mw of the core
polymer is greater than about 100,000 g/mole.
9. The polymer fiber of claim 1, wherein the sheath polymer is
selected from a polypropylene wax, a polyethylene wax, and
combinations thereof.
10. The polymer fiber of claim 1, wherein the sheath polymer
comprises a backbone of propylene or ethylene with maleic anhydride
grafted to the backbone.
11. The polymer fiber of claim 1, wherein the sheath polymer is a
polyethylene or polypropylene wax comprising at least one
functionalized end group providing a polar character to the
polymer.
12. A nonwoven fabric comprising polymer fibers according to claim
1.
13. A process for forming bicomponent polymer fibers comprising: a.
forming a molten blend of a core polymer and a sheath polymer; b.
extruding the molten polymer blend using an extruder having a die
with a length to diameter ratio greater than or equal to about 10
and under shear conditions sufficient to drive the sheath polymer
to the die wall; and c. forming meltblown fibers having a core
comprising the core polymer and a sheath comprising the sheath
polymer; wherein the sheath polymer is a polyolefin having a weight
average molecular weight (Mw) less than about 65,000 g/mole and
wherein the Mw of the core polymer is at least about 20,000 g/mole
greater than the Mw of the sheath polymer.
14. The process of claim 13, wherein the core polymer is selected
from a propylene-based polymer, an ethylene-based polymer, a
propylene-ethylene block copolymer, a styrenic block copolymer, an
acrylate, or a combination of the foregoing.
15. The process of claim 13, wherein the core polymer is a
propylene-based polymer comprising from about 5 to about 30 wt %
ethylene and/or a C.sub.4-C.sub.12 alpha olefin and having a triad
tacticity greater than about 90% and a heat of fusion less than
about 75 J/g.
16. The process of claim 13, wherein the propylene based polymer
comprises from about 8 to about 20 wt % ethylene.
17. The process of claim 13, wherein the Mw of the core polymer is
at least about 75,000 g/mole greater than the Mw of the sheath
polymer.
18. The process of claim 13, wherein the Mw of the core polymer is
at least about 100,000 g/mole greater than the Mw of the sheath
polymer.
19. The process of claim 13, wherein the Mw of the sheath polymer
is less than about 50,000 g/mole and the Mw of the core polymer is
greater than about 100,000 g/mole.
20. The process of claim 13, wherein the sheath polymer is selected
from a polypropylene wax, a polyethylene wax, and combinations
thereof.
21. The process of claim 13, wherein the sheath polymer comprises a
backbone of propylene or ethylene with maleic anhydride grafted to
the backbone.
22. The process of claim 13, wherein the sheath polymer is a
polyethylene or polypropylene wax comprising at least one
functionalized end group providing a polar character to the
polymer.
23. A nonwoven fabric comprising polymer fibers made according to
claim 13.
24. An article comprising a nonwoven fabric according to claim
23.
25. The fiber according claim 1, further comprising at least one of
carbon black, clay, talc, calcium carbonate, mica, silica,
silicate, hindered phenol, hindered amine, phosphate, sodium
benzoate, oleamide, erucamide, calcium stearate, hydrotalcite, and
calcium oxide.
Description
BACKGROUND OF THE INVENTION
[0001] Propylene-based polymers and copolymers are well known in
the art for their usefulness in the manufacture of meltblown
nonwoven fibers. Such fibers have a wide variety of uses,
particularly when formed into nonwoven fabrics and used in
applications such as medical and hygiene products, clothing, filter
media, and sorbent products, among others. Meltblown nonwoven
fibers are particularly useful in hygiene products, such as baby
diapers, adult incontinence products, and feminine hygiene
products. One consideration with respect to these fibers,
particularly in hygiene applications, is the ability to produce
aesthetically pleasing fabrics having good leakage performance at a
low cost. Good leakage performance is achieved via the elasticity
of the elastic layers of the fabrics, which provides better fit and
conformity to the wearer, resulting in fewer leaks. A common
aesthetic issue with the production of propylene-based nonwoven
fabrics is their often rubbery, tacky, or sticky feel. Further,
tackiness or stickiness can lead to processing problems.
[0002] In the past, aesthetic issues resulting from rubbery or
tacky feel of fibers and fabrics have been addressed in two ways.
First, nonwoven fabrics formed from propylene-based fibers have
been covered with aesthetically pleasing facing layers, resulting
in multilayered compositions. The main drawback of such
compositions is the increased cost that results from the need to
purchase or manufacture facing layers, as well as from added
complexity in the supply chain. Second, bicomponent fibers
(sometimes referred to as "conjugate" fibers) have been prepared
using a spinning process in which separate polymer streams are fed
to a single die or spinneret in order to form fibers comprising two
(or more) polymer compositions. The resulting fibers have
properties of both polymer components. Bicomponent fibers are
commonly classified by their cross-sectional structure. Such
structures may include, but are not limited to, side-by-side,
sheath-core, islands-in-the-sea or segmented-pie cross-sectional
structures. Drawbacks of these traditionally produced bicomponent
fibers are the high cost of the converting equipment required to
allow two polymers to be independently fed to a single die, along
with processing challenges (such as decreased throughput) which
result from running two or more chemically and mechanically
dissimilar polymers.
[0003] It would therefore be beneficial to produce fibers having
desirable properties for use in elastic nonwoven fabrics while
reducing cost and processing issues encountered in the past. The
present invention involves blending a low molecular weight polymer
component with a high molecular weight polymer component to form a
polymer blend. Bicomponent fibers are then formed from the blends
under shear conditions sufficient to cause the low molecular weight
polymer to migrate to the outside of the fiber due to the molecular
weight difference and limited miscibility of the polymers chosen
for use in the blend. The resulting fibers have a core and sheath
structure, with a core formed from the high molecular weight
polymer and a sheath formed from the low molecular weight
polymer.
SUMMARY OF THE INVENTION
[0004] The present invention relates to bicomponent polymer fibers,
and to processes for forming those fibers. In some embodiments, the
invention is directed to bicomponent polymer fibers having a core
comprising a core polymer and a sheath comprising a sheath polymer,
wherein the sheath polymer is a polyolefin having a weight average
molecular weight (Mw) less than about 65,000 g/mol and the core
polymer has an Mw at least about 20,000 g/mol greater than the Mw
of the sheath polymer. In certain embodiments, the core polymer is
a propylene-based polymer comprising from about 5 to about 30 wt %
ethylene and/or a C.sub.4-C.sub.12 alpha olefin and having a triad
tacticity greater than about 90% and a heat of fusion less than
about 75 J/g, and the sheath polymer is an olefin wax. In other
embodiments, the invention is directed to a process for forming
bicomponent fibers comprising (i) forming a molten blend of a core
polymer and a sheath polymer; (ii) extruding the molten polymer
blend using an extrusion die having a length to diameter ratio
greater than or equal to about 10 and under shear conditions
sufficient to drive the sheath polymer to the die wall; and (iii)
forming meltblown fibers having a core comprising the core polymer
and a sheath comprising the sheath polymer. In such processes, the
sheath polymer is a polyolefin having an Mw less than about 65,000
g/mol and the core polymer has an Mw at least about 20,000 g/mol
greater than the Mw of the sheath polymer.
DETAILED DESCRIPTION OF THE INVENTION
[0005] The present invention is directed to bicomponent polymer
fibers having a core comprising a core polymer and a sheath
comprising a sheath polymer, as well as, to processes for forming
such fibers. The core polymer and the sheath polymer are selected
so that the molecular weight difference in the two polymers, as
well as their limited miscibility, allows the polymers to separate
when subjected to shear forces during the extrusion process such
that the core polymer remains in the center of the fiber while the
sheath polymer migrates to the outside of the extrusion die and
forms the outer covering of the fiber.
[0006] While the present application refers to "core" and "sheath"
and "core polymers" and "sheath polymers", these terms are used for
convenience only. It should be noted that the polymers may not
completely separate during the extrusion process, and there may not
be a defined boundary between the core and sheath of the fibers
described herein. Rather, fibers of the invention also include
those fibers having a cross-sectional gradient, in which the
concentration of the sheath polymer is highest at the surface of
the fiber, and the concentration of the core polymer is highest at
the center of the fiber.
[0007] As used herein, the term "copolymer" is meant to include
polymers having two or more monomers, optionally with other
monomers, and may refer to interpolymers, terpolymers, etc. The
term "polymer" as used herein includes, but is not limited to,
homopolymers, copolymers, terpolymers, etc. and alloys and blends
thereof. The term "polymer" as used herein also includes impact,
block, graft, random and alternating copolymers. The term "polymer"
shall further include all possible geometrical configurations
unless otherwise specifically stated. Such configurations may
include isotactic, syndiotactic and random symmetries. The term
"blend" as used herein refers to a mixture of two or more
polymers.
[0008] The term "monomer" or "comonomer" as used herein can refer
to the monomer used to form the polymer, i.e., the unreacted
chemical compound in the form prior to polymerization, and can also
refer to the monomer after it has been incorporated into the
polymer, also referred to herein as a "[monomer]-derived unit",
which by virtue of the polymerization reaction typically has fewer
hydrogen atoms than it does prior to the polymerization reaction.
Different monomers are discussed herein, including propylene
monomers, ethylene monomers, and diene monomers.
[0009] "Polypropylene" as used herein includes homopolymers and
copolymers of propylene or mixtures thereof. Products that include
one or more propylene monomers polymerized with one or more
additional monomers may be more commonly known as random copolymers
(RCP) or impact copolymers (ICP). Impact copolymers are also known
in the art as heterophasic copolymers. "Propylene-based," as used
herein, is meant to include any polymer comprising propylene,
either alone or in combination with one or more comonomers, in
which propylene is the major component (e.g., greater than 50 wt %
propylene). Likewise, "ethylene-based", as used herein, is meant to
include any polymer comprising ethylene, either alone or in
combination with one or more comonomers, in which ethylene is the
major component (e.g., greater than 50 wt % ethylene).
Core Polymer
[0010] Polymers intended for use as the core polymer in the fibers
described herein include any polymers suitable for use in elastic
nonwoven fabrics and articles. Such polymers typically include, but
are not limited to, propylene-based polymers, ethylene-based
polymers, styrenic block copolymers, propylene-ethylene block
copolymers, acrylates, and combinations of the foregoing. In
certain embodiments of the invention, the core polymer has a high
molecular weight relative to the molecular weight of the sheath
polymer. For example, in some embodiments the core polymer has a
weight average molecular weight (M.sub.w) that is at least about
20,000 g/mol greater, or at least about 50,000 g/mol greater, or at
least about 75,000 g/mol greater, or at least about 100,000 g/mol
greater than the M.sub.w of the sheath polymer. In the same or
other embodiments, the core polymer has an M.sub.w greater than
about 75,000 g/mol, or greater than about 100,000 g/mol, or greater
than about 125,000 g/mol.
Propylene-Based Polymers
[0011] In certain embodiments of the present invention, the core
polymer may comprise one or more propylene-based polymers, which
comprise propylene and from about 5 to about 30 wt % of one or more
comonomers selected from ethylene and/or C.sub.4-C.sub.12
.alpha.-olefins. In one or more embodiments, the .alpha.-olefin
comonomer units may derive from ethylene, butene, pentene, hexene,
4-methyl-1-pentene, octene, or decene. The embodiments described
below are discussed with reference to ethylene as the
.alpha.-olefin comonomer, but the embodiments are equally
applicable to other copolymers with other .alpha.-olefin
comonomers. In this regard, the copolymers may simply be referred
to as propylene-based polymers with reference to ethylene as the
.alpha.-olefin.
[0012] In one or more embodiments, the propylene-based polymer may
include at least about 5 wt %, or at least about 6 wt %, or at
least about 7 wt %, or at least about 8 wt %, or at least about 10
wt %, or at least about 12 wt % ethylene-derived units. In those or
other embodiments, the copolymers may include up to about 30 wt %,
or up to about 25 wt %, or up to about 22 wt %, or up to about 20
wt %, or up to about 19 wt %, or up to about 18 wt %, or up to
about 17 wt % ethylene-derived units, where the percentage by
weight is based upon the total weight of the propylene-derived and
.alpha.-olefin derived units. Stated another way, the
propylene-based polymer may include at least about 70 wt %, or at
least about 75 wt %, or at least about 80 wt %, or at least about
81 wt % propylene-derived units, or at least about 82 wt %
propylene-derived units, or at least about 83 wt %
propylene-derived units; and in these or other embodiments, the
copolymers may include up to about 95 wt %, or up to about 94 wt %,
or up to about 93 wt %, or up to about 92 wt %, or up to about 90
wt %, or up to about 88 wt % propylene-derived units, where the
percentage by weight is based upon the total weight of the
propylene-derived and alpha-olefin derived units. In certain
embodiments, the propylene-based polymer may comprise from about 8
to about 20 wt % ethylene-derived units, or from about 12 to about
18 wt % ethylene-derived units.
[0013] The propylene-based polymers of one or more embodiments are
characterized by a melting point (Tm), which can be determined by
differential scanning calorimetry (DSC). For purposes herein, the
maximum of the highest temperature peak is considered to be the
melting point of the polymer. A "peak" in this context is defined
as a change in the general slope of the DSC curve (heat flow versus
temperature) from positive to negative, forming a maximum without a
shift in the baseline where the DSC curve is plotted so that an
endothermic reaction would be shown with a positive peak.
[0014] In one or more embodiments, the Tm of the propylene-based
polymer (as determined by DSC) is less than about 115.degree. C.,
or less than about 110.degree. C., or less than about 100.degree.
C., or less than about 90.degree. C.
[0015] In one or more embodiments, the propylene-based polymer may
be characterized by its heat of fusion (Hf), as determined by DSC.
In one or more embodiments, the propylene-based polymer may have an
Hf that is at least about 0.5 J/g, or at least about 1.0 J/g, or at
least about 1.5 J/g, or at least about 3.0 J/g, or at least about
4.0 J/g, or at least about 6.0 J/g, or at least about 7.0 J/g. In
these or other embodiments, the propylene-based copolymer may be
characterized by an Hf of less than about 75 J/g, or less than
about 70 J/g, or less than about 60 J/g, or less than about 50 J/g,
or less than about 30 J/g.
[0016] As used within this specification, DSC procedures for
determining Tm and Hf include the following. The polymer is pressed
at a temperature of from about 200.degree. C. to about 230.degree.
C. in a heated press, and the resulting polymer sheet is hung,
under ambient conditions, in the air to cool. About 6 to 10 mg of
the polymer sheet is removed with a punch die. This 6 to 10 mg
sample is annealed at room temperature for about 80 to 100 hours.
At the end of this period, the sample is placed in a DSC (Perkin
Elmer Pyris One Thermal Analysis System) and cooled to about
-50.degree. C. to about -70.degree. C. The sample is heated at
10.degree. C./min to attain a final temperature of about
200.degree. C. The sample is kept at 200.degree. C. for 5 minutes
and a second cool-heat cycle is performed. Events from both cycles
are recorded. The thermal output is recorded as the area under the
melting peak of the sample, which typically occurs between about
0.degree. C. and about 200.degree. C. It is measured in Joules and
is a measure of the Hf of the polymer.
[0017] The propylene-based polymer can have a triad tacticity of
three propylene units, as measured by .sup.13C NMR, of 75% or
greater, 80% or greater, 85% or greater, 90% or greater, 92% or
greater, 95% or greater, or 97% or greater. In one or more
embodiments, the triad tacticity may range from about 75 to about
99%, or from about 80 to about 99%, or from about 85 to about 99%,
or from about 90 to about 99%, or from about 90 to about 97%, or
from about 80 to about 97%. Triad tacticity is determined by the
methods described in U.S. Patent Application Publication No.
2004/0236042.
[0018] The propylene-based polymer may have a tacticity index m/r
ranging from a lower limit of 4 or 6 to an upper limit of 8 or 10
or 12. The tacticity index, expressed herein as "m/r", is
determined by .sup.13C nuclear magnetic resonance ("NMR"). The
tacticity index m/r is calculated as defined by H. N. Cheng in 17
MACROMOLECULES, pp. 1950-1955 (1984), incorporated herein by
reference. The designation "m" or "r" describes the stereochemistry
of pairs of contiguous propylene groups, "m" referring to meso and
"r" to racemic. An m/r ratio of 1.0 generally describes a
syndiotactic polymer, and an m/r ratio of 2.0 generally describes
an atactic material. An isotactic material theoretically may have a
ratio approaching infinity, and many by-product atactic polymers
have sufficient isotactic content to result in ratios of greater
than 50.
[0019] In one or more embodiments, the propylene-based polymer may
have a crystallinity of from about 0.5% to about 40%, or from about
1% to about 30%, or from about 5% to about 25%, determined
according to DSC procedures. Crystallinity may be determined by
dividing the Hf of a sample by the Hf of a 100% crystalline
polymer, which is assumed to be 189 joules/gram for isotactic
polypropylene or 350 joules/gram for polyethylene.
[0020] In one or more embodiments, the propylene-based polymer may
have a density of from about 0.85 g/cm.sup.3 to about 0.92
g/cm.sup.3, or from about 0.86 g/cm.sup.3 to about 0.90 g/cm.sup.3,
or from about 0.86 g/cm.sup.3 to about 0.89 g/cm.sup.3 at room
temperature as measured per the ASTM D-792 test method.
[0021] In one or more embodiments, the propylene-based polymer can
have a melt index (MI) (ASTM D-1238, 2.16 kg @ 190.degree. C.), of
less than or equal to about 100 g/10 min, or less than or equal to
about 50 g/10 min, or less than or equal to about 25 g/10 min, or
less than or equal to about 10 g/10 min, or less than or equal to
about 9.0 g/10 min, or less than or equal to about 8.0 g/10 min, or
less than or equal to about 7.0 g/10 min.
[0022] In one or more embodiments, the propylene-based polymer may
have a melt flow rate (MFR), as measured according to ASTM D-1238,
2.16 kg weight @ 230.degree. C., greater than about 1 g/10 min, or
greater than about 2 g/10 min, or greater than about 5 g/10 min, or
greater than about 8 g/10 min, or greater than about 10 g/10 min.
In the same or other embodiments, the propylene-based polymer may
have an MFR less than about 500 g/10 min, or less than about 400
g/10 min, or less than about 300 g/10 min, or less than about 200
g/10 min, or less than about 100 g/10 min, or less than about 50
g/10 min, or less than about 25 g/10 min. In certain embodiments,
the propylene-based polymer may have an MFR from about 1 to about
100 g/10 min, or from about 2 to about 50 g/10 min, or from about 5
to about 25 g/10 min.
[0023] In one or more embodiments, the propylene-based polymer may
have a Mooney viscosity [ML (1+4) @ 125.degree. C.], as determined
according to ASTM D-1646, of less than about 100, or less than
about 75, or less than about 50, or less than about 30.
[0024] In one or more embodiments, the first and second polymers
may have a g' index value of 0.95 or greater, or at least 0.97, or
at least 0.99, wherein g' is measured at the Mw of the polymer
using the intrinsic viscosity of isotactic polypropylene as the
baseline. For use herein, the g' index is defined as: [0025] where
.eta..sub.b is the intrinsic viscosity of the polymer and
.eta..sub.l is the intrinsic viscosity of a linear polymer of the
same viscosity-averaged molecular weight (M.sub.v) as the polymer.
.eta..sub.l=KW.sub.v.sup..alpha., K and .alpha. are measured values
for linear polymers and should be obtained on the same instrument
as the one used for the g' index measurement.
[0026] In one or more embodiments, the propylene-based copolymer
can have a weight average molecular weight (Mw) of from about
50,000 to about 5,000,000 g/mol, or from about 75,000 to about
1,000,000 g/mol, or from about 100,000 to about 500,000 g/mol, or
from about 125,000 to about 300,000 g/mol.
[0027] In one or more embodiments, the propylene-based copolymer
can have a number average molecular weight (Mn) of from about 2,500
to about 2,500,000 g/mole, or from about 5,000 to about 500,000
g/mole, or from about 10,000 to about 250,000 g/mole, or from about
25,000 to about 200,000 g/mole.
[0028] In one or more embodiments, the propylene-based copolymer
can have a Z-average molecular weight (Mz) of from about 10,000 to
about 7,000,000 g/mole, or from about 50,000 to about 1,000,000
g/mole, or from about 80,000 to about 700,000 g/mole, or from about
100,000 to about 500,000 g/mole.
[0029] In one or more embodiments, the molecular weight
distribution (MWD, equal to Mw/Mn) of the propylene-based copolymer
may be from about 1 to about 40, or from about 1 to about 15, or
from about 1.8 to about 5, or from about 1.8 to about 3.
[0030] Techniques for determining the molecular weight (Mn, Mw and
Mz) and MWD may be found in U.S. Pat. No. 4,540,753 (Cozewith, Ju
and Verstrate) (which is incorporated by reference herein for
purposes of U.S. practices) and references cited therein and in
Macromolecules, 1988, Vol. 21, pp. 3360-3371 (Ver Strate et al.),
which is herein incorporated by reference for purposes of U.S.
practices, and references cited therein. For example, molecular
weight may be determined by size exclusion chromatography (SEC) by
using a Waters 150 gel permeation chromatograph equipped with the
differential refractive index detector and calibrated using
polystyrene standards.
[0031] Optionally, the propylene-based polymer may also include one
or more dienes. The term "diene" is defined as a hydrocarbon
compound that has two unsaturation sites, i.e., a compound having
two double bonds connecting carbon atoms. Depending on the context,
the term "diene" in this patent refers broadly to either a diene
monomer prior to polymerization, e.g., forming part of the
polymerization medium, or a diene monomer after polymerization has
begun (also referred to as a diene monomer unit or a diene-derived
unit). Exemplary dienes suitable for use in the present invention
include, but are not limited to, butadiene, pentadiene, hexadiene
(e.g., 1,4-hexadiene), heptadiene (e.g., 1,6-heptadiene), octadiene
(e.g., 1,7-octadiene), nonadiene (e.g., 1,8-nonadiene), decadiene
(e.g., 1,9-decadiene), undecadiene (e.g., 1,10-undecadiene),
dodecadiene (e.g., 1,11-dodecadiene), tridecadiene (e.g.,
1,12-tridecadiene), tetradecadiene (e.g., 1,13-tetradecadiene),
pentadecadiene, hexadecadiene, heptadecadiene, octadecadiene,
nonadecadiene, icosadiene, heneicosadiene, docosadiene,
tricosadiene, tetracosadiene, pentacosadiene, hexacosadiene,
heptacosadiene, octacosadiene, nonacosadiene, triacontadiene, and
polybutadienes having a molecular weight (Mw) of less than 1,000
g/mol. Examples of straight chain acyclic dienes include, but are
not limited to 1,4-hexadiene and 1,6-octadiene. Examples of
branched chain acyclic dienes include, but are not limited to
5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, and
3,7-dimethyl-1,7-octadiene. Examples of single ring alicyclic
dienes include, but are not limited to 1,4-cyclohexadiene,
1,5-cyclooctadiene, and 1,7-cyclododecadiene. Examples of
multi-ring alicyclic fused and bridged ring dienes include, but are
not limited to tetrahydroindene; norbornadiene;
methyltetrahydroindene; dicyclopentadiene;
bicyclo(2.2.1)hepta-2,5-diene; and alkenyl-, alkylidene-,
cycloalkenyl-, and cycloalkylidene norbornenes [including, e.g.,
5-methylene-2-norbornene, 5-ethylidene-2-norbornene,
5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene,
5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene,
and 5-vinyl-2-norbornene]. Examples of cycloalkenyl-substituted
alkenes include, but are not limited to vinyl cyclohexene, allyl
cyclohexene, vinylcyclooctene, 4-vinylcyclohexene, allyl
cyclodecene, vinylcyclododecene, and tetracyclododecadiene. In some
embodiments of the present invention, the diene is selected from
5-ethylidene-2-norbornene (ENB); 1,4-hexadiene;
5-methylene-2-norbornene (MNB); 1,6-octadiene;
5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene;
1,3-cyclopentadiene; 1,4-cyclohexadiene; vinyl norbornene (VNB);
dicyclopentadiene (DCPD), and combinations thereof. In one or more
embodiments, the diene is ENB.
[0032] In some embodiments, the propylene-based polymer may
comprise from 0.05 to about 6 wt % diene-derived units. In further
embodiments, the polymer comprises from about 0.1 to about 5.0 wt %
diene-derived units, or from about 0.25 to about 3.0 wt %
diene-derived units, or from about 0.5 to about 1.5 wt %
diene-derived units.
[0033] In one or more embodiments, the propylene-based polymer can
be grafted (e.g., "functionalized") using one or more grafting
monomers. As used herein, the term "grafting" denotes covalent
bonding of the grafting monomer to a polymer chain of the
propylene-based polymer.
[0034] The grafting monomer can be or include at least one
ethylenically unsaturated carboxylic acid or acid derivative, such
as an acid anhydride, ester, salt, amide, imide, acrylates or the
like. Illustrative monomers include but are not limited to acrylic
acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid,
citraconic acid, mesaconic acid, maleic anhydride, 4-methyl
cyclohexene-1,2-dicarboxylic acid anhydride,
bicyclo(2.2.2)octene-2,3-dicarboxylic acid anhydride,
1,2,3,4,5,8,9,10-octahydronaphthalene-2,3-dicarboxylic acid
anhydride, 2-oxa-1,3-diketospiro(4.4)nonene,
bicyclo(2.2.1)heptene-2,3-dicarboxylic acid anhydride, maleopimaric
acid, tetrahydrophthalic anhydride, norbornene-2,3-dicarboxylic
acid anhydride, nadic anhydride, methyl nadic anhydride, himic
anhydride, methyl himic anhydride, and
5-methylbicyclo(2.2.1)heptene-2,3-dicarboxylic acid anhydride.
Other suitable grafting monomers include methyl acrylate and higher
alkyl acrylates, methyl methacrylate and higher alkyl
methacrylates, acrylic acid, methacrylic acid, hydroxy-methyl
methacrylate, hydroxyl-ethyl methacrylate and higher hydroxy-alkyl
methacrylates and glycidyl methacrylate. Maleic anhydride is a
preferred grafting monomer.
[0035] In one or more embodiments, the grafted propylene based
polymer comprises from about 0.5 to about 10 wt % ethylenically
unsaturated carboxylic acid or acid derivative, more preferably
from about 0.5 to about 6 wt %, more preferably from about 0.5 to
about 3 wt %; in other embodiments from about 1 to about 6 wt %,
more preferably from about 1 to about 3 wt %. In a preferred
embodiment wherein the graft monomer is maleic anhydride, the
maleic anhydride concentration in the grafted polymer is preferably
in the range of about 1 to about 6 wt %, preferably at least about
0.5 wt % and highly preferably about 1.5 wt %.
Preparation of Propylene-Based Polymers
[0036] Polymerization of the propylene-based polymer is conducted
by reacting monomers in the presence of a catalyst system described
herein at a temperature of from 0.degree. C. to 200.degree. C. for
a time of from 1 second to 10 hours. Preferably homogeneous
conditions are used, such as a continuous solution process or a
bulk polymerization process with excess monomer used as diluent.
The continuous process may use some form of agitation to reduce
concentration differences in the reactor and maintain steady state
polymerization conditions. The heat of the polymerization reaction
is preferably removed by cooling of the polymerization feed and
allowing the polymerization to heat up to the polymerization,
although internal cooling systems may be used.
[0037] Further description of exemplary methods suitable for
preparation of the propylene-based polymers described herein may be
found in U.S. Pat. No. 6,881,800, which is incorporated by
reference herein for purposes of U.S. practice.
[0038] The triad tacticity and tacticity index of the
propylene-based copolymer may be controlled by the catalyst, which
influences the stereoregularity of propylene placement, the
polymerization temperature, according to which stereoregularity can
be reduced by increasing the temperature, and by the type and
amount of a comonomer, which tends to reduce the level of longer
propylene derived sequences.
[0039] Too much comonomer may reduce the crystallinity provided by
the crystallization of stereoregular propylene derived sequences to
the point where the material lacks strength; too little and the
material may be too crystalline. The comonomer content and sequence
distribution of the polymers can be measured using .sup.13C nuclear
magnetic resonance (NMR) by methods well known to those skilled in
the art. Comonomer content of discrete molecular weight ranges can
be measured using methods well known to those skilled in the art,
including Fourier Transform Infrared Spectroscopy (FTIR) in
conjunction with samples by GPC, as described in Wheeler and
Willis, Applied Spectroscopy, 1993, Vol. 47, pp. 1128-1130. For a
propylene ethylene copolymer containing greater than 75 wt %
propylene, the comonomer content (ethylene content) of such a
polymer can be measured as follows: A thin homogeneous film is
pressed at a temperature of about 150.degree. C. or greater, and
mounted on a Perkin Elmer PE 1760 infrared spectrophotometer. A
full spectrum of the sample from 600 cm-1 to 4000 cm-1 is recorded
and the monomer weight percent of ethylene can be calculated
according to the following equation: Ethylene wt
%=82.585-111.987X+30.045X2, where X is the ratio of the peak height
at 1155 cm-1 and peak height at either 722 cm-1 or 732 cm-1,
whichever is higher. For propylene ethylene copolymers having 75 wt
% or less propylene content, the comonomer (ethylene) content can
be measured using the procedure described in Wheeler and
Willis.
[0040] Reference is made to U.S. Pat. No. 6,525,157, whose test
methods are also fully applicable for the various measurements
referred to in this specification and claims and which contain more
details on GPC measurements, the determination of ethylene content
by NMR and the DSC measurements.
[0041] The catalyst may also control the stereoregularity in
combination with the comonomer and the polymerization temperature.
The propylene-based polymers described herein are prepared using
one or more catalyst systems. As used herein, a "catalyst system"
comprises at least a transition metal compound, also referred to as
catalyst precursor, and an activator. Contacting the transition
metal compound (catalyst precursor) and the activator in solution
upstream of the polymerization reactor or in the polymerization
reactor of the disclosed processes yields the catalytically active
component (catalyst) of the catalyst system. Any given transition
metal compound or catalyst precursor can yield a catalytically
active component (catalyst) with various activators, affording a
wide array of catalysts deployable in the processes of the present
invention. Catalyst systems of the present invention comprise at
least one transition metal compound and at least one activator.
However, catalyst systems of the current disclosure may also
comprise more than one transition metal compound in combination
with one or more activators. Such catalyst systems may optionally
include impurity scavengers. Each of these components is described
in further detail below.
[0042] In one or more embodiments of the present invention, the
catalyst systems used for producing propylene-based polymers
comprise a metallocene compound. In some embodiments, the
metallocene compound is a bridged bisindenyl metallocene having the
general formula (In.sup.1)Y(In.sup.2)MX.sub.2, where In.sup.1 and
In.sup.2 are identical substituted or unsubstituted indenyl groups
bound to M and bridged by Y, Y is a bridging group in which the
number of atoms in the direct chain connecting In.sup.1 with
In.sup.2 is from 1 to 8 and the direct chain comprises C or Si, and
M is a Group 3, 4, 5, or 6 transition metal. In.sup.1 and In.sup.2
may be substituted or unsubstituted. If In.sup.1 and In.sup.2 are
substituted by one or more substituents, the substituents are
selected from the group consisting of a halogen atom, C.sub.1 to
C.sub.10 alkyl, C.sub.5 to C.sub.15 aryl, C.sub.6 to C.sub.25
alkylaryl, and N- or P-containing alkyl or aryl. Exemplary
metallocene compounds of this type include, but are not limited to,
.mu.-dimethylsilylbis(indenyl)hafniumdimethyl and
.mu.-dimethylsilylbis(indenyl)zirconiumdimethyl.
[0043] In other embodiments, the metallocene compound may be a
bridged bisindenyl metallocene having the general formula
(In.sup.1)Y(In.sup.2)MX.sub.2, where In.sup.1 and In.sup.2 are
identical 2,4-substituted indenyl groups bound to M and bridged by
Y, Y is a bridging group in which the number of atoms in the direct
chain connecting In.sup.1 with In.sup.2 is from 1 to 8 and the
direct chain comprises C or Si, and M is a Group 3, 4, 5, or 6
transition metal. In.sup.1 and In.sup.2 are substituted in the 2
position by a methyl group and in the 4 position by a substituent
selected from the group consisting of C.sub.5 to C.sub.15 aryl,
C.sub.6 to C.sub.25 alkylaryl, and N- or P-containing alkyl or
aryl. Exemplary metallocene compounds of this type include, but are
not limited to,
(.mu.-dimethylsilyl)bis(2-methyl-4-(3,'5'-di-tert-butylphenyl)indenyl)zir-
coniumdimethyl,
(.mu.-dimethylsilyl)bis(2-methyl-4-(3,'5'-di-tert-butylphenyl)indenyl)haf-
niumdimethyl,
(.mu.-dimethylsilyl)bis(2-methyl-4-naphthylindenyl)zirconiumdimethyl,
(.mu.-dimethylsilyl)bis(2-methyl-4-naphthylindenyl)hafniumdimethyl,
(.mu.-dimethylsilyl)bis(2-methyl-4-(N-carbazyl)indenyl)zirconiumdimethyl,
and
(.mu.-dimethylsilyl)bis(2-methyl-4-(N-carbazyl)indenyl)hafniumdimethy-
l.
[0044] Alternatively, in one or more embodiments of the present
invention, the metallocene compound may correspond to one or more
of the formulas disclosed in U.S. Pat. No. 7,601,666. Such
metallocene compounds include, but are not limited to,
dimethylsilyl
bis(2-(methyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)hafni-
um dimethyl, diphenylsilyl
bis(2-(methyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)hafni-
um dimethyl, diphenylsilyl
bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)hafnium
dimethyl, diphenylsilyl
bis(2-(methyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)zirco-
nium dichloride, and cyclo-propylsilyl
bis(2-(methyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)hafni-
um dimethyl.
[0045] In one or more embodiments of the present invention, the
activators of the catalyst systems used to produce propylene-based
polymers comprise a cationic component. In some embodiments, the
cationic component has the formula [R.sup.1R.sup.2R.sup.3AH].sup.+,
where A is nitrogen, R.sup.1 and R.sup.2 are together a
--(CH.sub.2).sub.a-- group, where a is 3, 4, 5 or 6 and form,
together with the nitrogen atom, a 4-, 5-, 6- or 7-membered
non-aromatic ring to which, via adjacent ring carbon atoms,
optionally one or more aromatic or heteroaromatic rings may be
fused, and R.sup.3 is C.sub.1, C.sub.2, C.sub.3, C.sub.4 or C.sub.5
alkyl, or N-methylpyrrolidinium or N-methylpiperidinium. In other
embodiments, the cationic component has the formula
[R.sub.nAH].sup.+, where A is nitrogen, n is 2 or 3, and all R are
identical and are C.sub.1 to C.sub.3 alkyl groups, such as for
example trimethylammonium, trimethylanilinium, triethylammonium,
dimethylanilinium, or dimethylammonium.
[0046] In one or more embodiments of the present invention, the
activators of the catalyst systems used to produce the
propylene-based polymers comprise an anionic component, [Y].sup.-.
In some embodiments, the anionic component is a non-coordinating
anion (NCA), having the formula [B(R.sup.4).sub.4].sup.-, where
R.sup.4 is an aryl group or a substituted aryl group, of which the
one or more substituents are identical or different and are
selected from the group consisting of alkyl, aryl, a halogen atom,
halogenated aryl, and haloalkylaryl groups. In one or more
embodiments, the substituents are perhalogenated aryl groups, or
perfluorinated aryl groups, including but not limited to
perfluorophenyl, perfluoronaphthyl and perfluorobiphenyl.
[0047] Together, the cationic and anionic components of the
catalysts systems described herein form an activator compound. In
one or more embodiments of the present invention, the activator may
be N,N-dimethylanilinium-tetra(perfluorophenyl)borate,
N,N-dimethylanilinium-tetra(perfluoronaphthyl)borate,
N,N-dimethylanilinium-tetrakis(perfluorobiphenyl)borate,
N,N-dimethylanilinium-tetrakis(3,5-bis(trifluoromethyl)phenyl)borate,
triphenylcarbenium-tetra(perfluorophenyl)borate,
triphenylcarbenium-tetra(perfluoronaphthyl)borate,
triphenylcarbenium-tetrakis(perfluorobiphenyl)borate, or
triphenylcarbenium-tetrakis(3,5-bis(trifluoromethyl)phenyl)borate.
[0048] Any catalyst system resulting from any combination of a
metallocene compound, a cationic activator component, and an
anionic activator component mentioned in the preceding paragraphs
shall be considered to be explicitly disclosed herein and may be
used in accordance with the present invention in the polymerization
of one or more olefin monomers. Also, combinations of two different
activators can be used with the same or different
metallocene(s).
[0049] Suitable activators for the processes of the present
invention also include alominoxanes (or alumoxanes) and aluminum
alkyls. Without being bound by theory, an alumoxane is typically
believed to be an oligomeric aluminum compound represented by the
general formula (R.sup.x--Al--O).sub.n, which is a cyclic compound,
or R.sup.x (R.sup.x--Al--O).sub.nAlR.sup.x.sub.2, which is a linear
compound. Most commonly, alumoxane is believed to be a mixture of
the cyclic and linear compounds. In the general alumoxane formula,
R.sup.x is independently a C.sub.1-C.sub.20 alkyl radical, for
example, methyl, ethyl, propyl, butyl, pentyl, isomers thereof, and
the like, and n is an integer from 1-50. In one or more
embodiments, R.sup.x is methyl and n is at least 4. Methyl
alumoxane (MAO), as well as modified MAO containing some higher
alkyl groups to improve solubility, ethyl alumoxane, iso-butyl
alumoxane, and the like are useful for the processes disclosed
herein.
[0050] Further, the catalyst systems suitable for use in the
present invention may contain, in addition to the transition metal
compound and the activator described above, additional activators
(co-activators) and/or scavengers. A co-activator is a compound
capable of reacting with the transition metal complex, such that
when used in combination with an activator, an active catalyst is
formed. Co-activators include alumoxanes and aluminum alkyls.
[0051] In some embodiments of the invention, scavengers may be used
to "clean" the reaction of any poisons that would otherwise react
with the catalyst and deactivate it. Typical aluminum or boron
alkyl components useful as scavengers are represented by the
general formula R.sup.xJZ.sub.2 where J is aluminum or boron,
R.sup.x is a C.sub.1-C.sub.20 alkyl radical, for example, methyl,
ethyl, propyl, butyl, pentyl, and isomers thereof, and each Z is
independently R.sup.x or a different univalent anionic ligand such
as halogen (Cl, Br, I), alkoxide (OR.sup.x) and the like. Exemplary
aluminum alkyls include triethylaluminum, diethylaluminum chloride,
ethylaluminium dichloride, tri-iso-butylaluminum,
tri-n-octylaluminum, tri-n-hexylaluminum, trimethylaluminum and
combinations thereof. Exemplary boron alkyls include triethylboron.
Scavenging compounds may also be alumoxanes and modified alumoxanes
including methylalumoxane and modified methylalumoxane.
[0052] In some embodiments, the catalyst system used to produce the
propylene-based polymers comprises a transition metal component
which is a bridged bisindenyl metallocene having the general
formula (In.sup.1)Y(In.sup.2)MX.sub.2, where In.sup.1 and In.sup.2
are identical substituted or unsubstituted indenyl groups bound to
M and bridged by Y, Y is a bridging group in which the number of
atoms in the direct chain connecting In.sup.1 with In.sup.2 is from
1 to 8 and the direct chain comprises C or Si, and M is a Group 3,
4, 5, or 6 transition metal. In.sup.1 and In.sup.2 may be
substituted or unsubstituted. If In.sup.1 and In.sup.2 are
substituted by one or more substituents, the substituents are
selected from the group consisting of a halogen atom, C.sub.1 to
C.sub.10 alkyl, C.sub.5 to C.sub.15 aryl, C.sub.6 to C.sub.25
alkylaryl, and N- or P-containing alkyl or aryl. In one or more
embodiments, the transition metal component used to produce the
propylene-based polymers is
.mu.-dimethylsilylbis(indenyl)hafniumdimethyl.
Ethylene-Based Polymers
[0053] In further embodiments of the present invention, the core
polymer may comprise one or more ethylene-based polymers, which may
be ethylene homopolymers and/or ethylene copolymers incorporating
one or more comonomers. Various types of ethylene-based polymers
are known in the art. Exemplary ethylene-based polymers include
ethylene-propylene copolymers, low-density polyethylene ("LDPE"),
linear low-density polyethylene ("LLDPE"), and high-density
polyethylene ("HDPE").
[0054] In at least one specific embodiment, the core polymer may be
or include one or more ethylene-propylene copolymers (EP).
Preferably, the EP is non-crystalline, e.g., atactic or amorphous,
but in certain embodiments the EP may be crystalline (including
"semi-crystalline"). The crystallinity of the EP is preferably
derived from the ethylene, and a number of published methods,
procedures and techniques are available for evaluating whether the
crystallinity of a particular material is derived from ethylene.
The crystallinity of the EP can be distinguished from the
crystallinity of the propylene-based polymer by removing the EP
from the composition and then measuring the crystallinity of the
residual propylene-based polymer. Such crystallinity measured is
usually calibrated using the crystallinity of polyethylene and
related to the comonomer content. The percent crystallinity in such
cases is measured as a percentage of polyethylene crystallinity and
thus the origin of the crystallinity from ethylene is
established.
[0055] In one or more embodiments, the EP can include one or more
optional polyenes, including particularly a diene; thus, the EP can
be an ethylene-propylene-diene (commonly called "EPDM"). The
optional polyene is considered to be any hydrocarbon structure
having at least two unsaturated bonds wherein at least one of the
unsaturated bonds is readily incorporated into a polymer. The
second bond may partially take part in polymerization to form long
chain branches but preferably provides at least some unsaturated
bonds suitable for subsequent curing or vulcanization in post
polymerization processes. Examples of EP or EPDM copolymers include
V722, V3708P, MDV 91-9, V878 that are available under the trade
name Vistalon.TM. EPDM from ExxonMobil Chemical Company.
Additionally, several commercial EPDM polymers are available from
The Dow Chemical Co. under the trade names Nordel IP and MG.
[0056] Examples of the optional polyene include, but are not
limited to, butadiene, pentadiene, hexadiene (e.g., 1,4-hexadiene),
heptadiene (e.g., 1,6-heptadiene), octadiene (e.g., 1,7-octadiene),
nonadiene (e.g., 1,8-nonadiene), decadiene (e.g., 1,9-decadiene),
undecadiene (e.g., 1,10-undecadiene), dodecadiene (e.g.,
1,11-dodecadiene), tridecadiene (e.g., 1,12-tridecadiene),
tetradecadiene (e.g., 1,13-tetradecadiene), pentadecadiene,
hexadecadiene, heptadecadiene, octadecadiene, nonadecadiene,
icosadiene, heneicosadiene, docosadiene, tricosadiene,
tetracosadiene, pentacosadiene, hexacosadiene, heptacosadiene,
octacosadiene, nonacosadiene, triacontadiene, and polybutadienes
having a molecular weight (Mw) of less than 1000 g/mol. Examples of
straight chain acyclic dienes include, but are not limited to
1,4-hexadiene and 1,6-octadiene. Examples of branched chain acyclic
dienes include, but are not limited to 5-methyl-1,4-hexadiene,
3,7-dimethyl-1,6-octadiene, and 3,7-dimethyl-1,7-octadiene.
Examples of single ring alicyclic dienes include, but are not
limited to 1,4-cyclohexadiene, 1,5-cyclooctadiene, and
1,7-cyclododecadiene. Examples of multi-ring alicyclic fused and
bridged ring dienes include, but are not limited to,
tetrahydroindene; norbornadiene; methyltetrahydroindene;
dicyclopentadiene; bicyclo(2.2.1)hepta-2,5-diene; and alkenyl-,
alkylidene-, cycloalkenyl-, and cycloalkylidene norbornenes
[including, e.g., 5-methylene-2-norbornene,
5-ethylidene-2-norbornene, 5-propenyl-2-norbornene,
5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene,
5-cyclohexylidene-2-norbornene, and 5-vinyl-2-norbornene]. Examples
of cycloalkenyl-substituted alkenes include, but are not limited to
vinyl cyclohexene, allyl cyclohexene, vinylcyclooctene,
4-vinylcyclohexene, allyl cyclodecene, vinylcyclododecene, and
tetracyclododecadiene.
[0057] LLDPE is typically a copolymer of ethylene and one or more
other alpha-olefins. Such alpha-olefins will generally have 3 to 20
carbon atoms. In certain embodiments, the alpha-olefins are
selected from butene-1, pentene-1,4-methyl-1-pentene, hexene-1,
octene-1, decene-1, and combinations thereof. In other embodiments,
the alpha-olefins are selected from butene-1, hexene-1, octene-1,
and combinations thereof. LLDPEs intended for use herein may be
produced from any suitable catalyst system including conventional
Ziegler-Natta type catalyst systems and metallocene based catalyst
systems. In certain embodiments, LLDPE polymers may have a density
from about 0.89 g/cm.sup.3 to 0.94 g/cm.sup.3, or from about 0.91
g/cm.sup.3 to about 0.94 g/cm.sup.3. Exemplary metallocene
catalyzed linear low density polyethylenes include those available
commercially from ExxonMobil Chemical Company under the name
Exceed.TM. mPE resin.
[0058] HDPE is a semicrystalline polymer available in a wide range
of molecular weights as indicated by either MI or HLMI (melt index
or high-load melt index) and typically has an ethylene content of
at least 99 mole percent (based upon the total moles of HDPE). If
incorporated into the HDPE, comonomers may be selected from butene
and other C.sub.3 to C.sub.20 alpha olefins. In one embodiment, the
comonomers are selected from 1-butene, 4-methyl-1-pentene,
1-hexene, and 1-octene, and mixtures thereof. In certain
embodiments, comonomers may be present in the HDPE up to about 0.68
mole percent, based on the total moles of the HDPE. In further
embodiments, comonomers are present in the HDPE up to about 0.28
mole percent. The density of HDPE is typically greater than 0.94
g/cm.sup.3. In some embodiments, the HDPE may have a density from
about 0.94 g/cm.sup.3 to about 0.97 g/cm.sup.3, or from about 0.95
g/cm.sup.3 to about 0.965 g/cm.sup.3. In the same or other
embodiments, the melting point of the HDPE, as measured by a
differential scanning calorimeter (DSC), may be from about
120.degree. C. to about 150.degree. C., or from about 125.degree.
C. to about 135.degree. C. Further, the HDPE may have a melt index
from about 0.1 g/10 min to about 10.0 g/10 min, or from about 0.2
g/10 min to about 5.0 g/10 min, or from about 0.6 g/10 min to about
2.0 g/10 min.
[0059] HDPE includes polymers made using a variety of catalyst
systems including Ziegler-Natta, Phillips-type catalysts, chromium
based catalysts, and metallocene catalyst systems, which may be
used with alumoxane and/or ionic activators. Processes useful for
preparing such polyethylenes include gas phase, slurry, solution
processes, and the like. Exemplary HDPEs include, but are not
limited to, those commercially available as Marlex TR-130 from
Phillips Chemical Company, M6211 from Equistar Chemical Co., Dow XU
6151.302 from Dow Chemical Co., and HD 7845, HD 6733, HTA 002, HTA
108, HYA 108, Paxon 4700, AD60 007, AA 45004, BA50 100,
Nexxstar.TM. 0111 and MA001 from ExxonMobil Chemical Company.
Styrenic Block Copolymers
[0060] In further embodiments of the present invention, the core
polymer may comprise one or more styrenic block copolymers (SBCs).
The phrase "block copolymer" is intended to include any manner of
block copolymer, including but not limited to diblock, triblock,
and tetrablock copolymers. "Block copolymer" is further meant to
include copolymers having any structure known to those of skill in
the art, including but not limited to linear, radial or multi-arm
star, or multi-branched block copolymers.
[0061] Suitable SBCs include block copolymers of styrene and one or
more conjugated dienes such as SI (styrene-isoprene), SIS
(styrene-isoprene-styrene), SB (styrene-butadiene), SBS
(styrene-butadiene-styrene), and styrene-isoprene-butadiene (SIB).
Styrene block copolymers comprising tetrablock or pentablock
copolymers selected from SISI, SISB, SBSB, SBSI, ISISI, ISISB,
BSISB, ISBSI, BSBSB, and BSBSI are also suitable. The block
copolymers may or may not be hydrogenated.
[0062] In one or more embodiments, the SBC may comprise a
styrene-isoprene-styrene (SIS) block copolymer, a
styrene-butadiene-styrene (SBS) block copolymer, a
styrene-isoprene-butadiene (SIB) block copolymer, or combinations
thereof.
[0063] In one or more embodiments, the SBC may comprise from about
10 to about 45 wt % styrene. In the same or other embodiments, the
styrenic block copolymer component may have a diblock content of
from about 0 to about 85 wt %. Diblock content may be determined by
GPC, and may be manipulated via the reactor settings employed to
produce the styrenic block copolymer component.
[0064] In some embodiments, the SBC may comprise a
styrene-isoprene-styrene (SIS) block copolymer. Such SIS block
copolymers are thermoplastic elastomers having the structure
(S-I)nS, where S is substantially a polystyrene block, I is
substantially a polyisoprene block, and n is an integer of from
about 1 to about 10. The styrene content of the SIS block copolymer
is typically from about 10 to about 45 wt %, or from about 15 to
about 35 wt %, or from about 20 to 30 wt %. The number average
molecular weight (Mn) of the SIS block copolymer may be from about
50,000 to about 500,000. In one or more embodiments, the SIS block
copolymer is a triblock copolymer of the formula above, where n=1,
i.e., a linear polymer of the formula S-I-S wherein S is
substantially a polystyrene block and I is substantially a
polyisoprene block. These block copolymers may be prepared by well
known anionic solution polymerization techniques using lithium-type
initiators such as disclosed in U.S. Pat. Nos. 3,251,905 and
3,239,478, which are hereby incorporated by reference in their
entireties.
[0065] The SIS block copolymers employed herein may have a number
average molecular weight (determined by GPC) in the range of from
about 50,000 to 500,000, or from about 70,000 to about 250,000, or
from about 90,000 to about 175,000, or from about 90,000 to about
135,000. SIS block copolymers may comprise a blend of two or more
different SIS copolymers, which may have the same or different
styrene content, and may be blended to a ratio in the range of from
10:1 to 1:10 parts by weight. The SIS copolymer may be a pure
triblock (one having less than 0.1 wt % of diblock polymer,
preferably 0% diblock polymer), or may contain from about 0.1 to
about 85 wt %, or from about 0.1 to about 75 wt %, or from about 1
to about 65 wt %, or from about 5 to about 50 wt % diblock
copolymer having the structure S-I. This material may be present as
an impurity in the manufacture of the triblock copolymer or may be
separately blended with the triblock as a further technique for
achieving target polystyrene content or modifying the cohesive
properties of the composition. In one or more embodiments, the
balance of the SIS copolymer that is not diblock copolymer may be
in the radial form. In one or more embodiments, the number average
molecular weight of the diblock SI copolymers may range from about
100,000 to about 250,000.
[0066] SIS copolymers may be linear or radial in structure, or a
combination of the two. Radial SIS copolymers may have the same
styrene levels as the linear copolymers discussed above, e.g., from
about 10 to about 45 wt % polymerized styrene. Radial SIS
copolymers useful in the practice of the invention may have a
molecular weight (Mn) of from about 180,000 to about 250,000.
Linear and radial SIS block copolymers of the type described herein
are available commercially and are prepared in accordance with
methods known in the art. Examples of SIS copolymers useful in the
practice of this invention include those available under the trade
names Vector and DPX (from Dexco Polymers LLP), Kraton (from Shell
Chemical Company), Europrene (from Enichem), and Quintac (from
Nippon Zeon). Particularly useful SIS block copolymers include, but
are not limited to, Vector 4111, Vector 4511 and Vector 4113; DPX
552 and DPX 556; Kraton D 1107, Kraton D 1124, Kraton D 1160 and
Kraton D 1161; Europrene SOL T 190 and Europrene SOL T 193; and
Quintac 3421, Quintac 3422, Quintac 3433, and Quintac 3450.
[0067] In some embodiments, the SBC may comprise a
styrene-butadiene-styrene (SBS) block copolymer. Such SBS block
copolymers are thermoplastic elastomers having the structure
(S-B)nS, where S is substantially a polystyrene block, B is
substantially a polybutadiene block, and n is an integer of from
about 1 to about 10. The styrene content of the SBS block copolymer
is typically from about 10 to about 45 wt %, or from about 15 to
about 35 wt %, or from about 20 to 30 wt %. The number average
molecular weight (Mn) of the SBS block copolymer may be from about
50,000 to about 500,000. In one or more embodiments, the SBS block
copolymer is a triblock copolymer of the formula above, where n=1,
i.e., a linear polymer of the formula S-B-S wherein S is
substantially a polystyrene block and B is substantially a
polybutadiene block. These block copolymers may be prepared by well
known anionic solution polymerization techniques using lithium-type
initiators such as disclosed in U.S. Pat. Nos. 3,251,905 and
3,239,478, which are hereby incorporated by reference in their
entireties.
[0068] SBS block copolymers employed herein may have a number
average molecular weight (determined by GPC) in the range of from
about 50,000 to 500,000, or from about 100,000 to about 180,000, or
from about 110,000 to about 160,000, or from about 110,000 to about
140,000. The SBS copolymer may be a pure triblock (one having less
than 0.1 wt % of diblock polymer, preferably 0% diblock polymer),
or may contain from about 0.1 to about 85 wt %, or from about 0.1
to about 75 wt %, or from about 1 to about 65 wt %, or from about 5
to about 50 wt % diblock copolymer having the structure S-B. This
material may be present as an impurity in the manufacture of the
triblock copolymer or may be separately blended with the triblock
as a further technique for achieving target polystyrene content or
modifying the cohesive properties of the composition. In one or
more embodiments, the balance of the SBS copolymer that is not
diblock copolymer may be in the radial form. In one or more
embodiments, the number average molecular weight of the diblock SB
copolymers may range from about 100,000 to about 250,000.
[0069] SBS copolymers may be linear or radial in structure, or a
combination of the two. Radial SBS copolymers may have the same
styrene levels as the linear copolymers discussed above, e.g., from
about 10 to about 45 wt % polymerized styrene. Linear and radial
SBS block copolymers of the type described herein are available
commercially and are prepared in accordance with methods known in
the art. Examples of SBS copolymers useful in the practice of this
invention include those available under the tradenames Vector (from
Dexco Polymers LLP), Kraton (from Shell Chemical Company),
Europrene (from Enichem), and Finaprene (from Fina Chemicals).
Particularly useful SBS block copolymers include, but are not
limited to, Vector 8505, Kraton D 1102, Kraton D 4141, Kraton D
4158, Europrene SOL T 166, and Finaprene 411.
[0070] Radial styrenic block copolymers and other styrenic block
copolymers suitable for use in the present invention include those
described in U.S. Application Publication No. 2009/0133834, which
is incorporated by reference herein in its entirety.
Sheath Polymer
[0071] Polymers intended for use as the sheath polymer in the
fibers described herein include any polymers suitable for use as
feel modifiers in elastic nonwoven fabrics and articles that have a
low molecular weight relative to the core polymer and limited
miscibility in the core polymer. In one embodiment, such polymers
include a polypropylene homopolymer such as Achieve.TM. 6936G1 from
ExxonMobil Chemical Co. Such polymers include, but are not limited
to, olefin waxes including propylene waxes and ethylene waxes and
combinations thereof. In certain embodiments of the invention, the
sheath polymer has a low molecular weight relative to the molecular
weight of the sheath polymer. For example, in some embodiments, the
sheath polymer has a weight average molecular weight (M.sub.w) that
is at least about 20,000 g/mol less, or at least about 50,000 g/mol
less, or at least about 75,000 g/mol less, or at least about
100,000 g/mol less than the M.sub.w of the core polymer. In the
same or other embodiments, the sheath polymer has an M.sub.w less
than about 65,000 g/mol, or less than about 50,000 g/mol, or less
than about 45,000 g/mol, or less than about 40,000 g/mol, or less
than about 35,000 g/mol or less than about 30,000 g/mol, or less
than about 25,000 g/mol, or less than about 20,000 g/mol, or less
than about 15,000 g/mol, or less than about 10,000 g/mol.
[0072] Olefin waxes suitable for use as the sheath polymer may be
polar or nonpolar, branched or unbranched, and may be prepared
using any suitable catalyst system including Ziegler-Natta
catalysts, Phillips-type catalysts, chromium based catalysts, and
metallocene catalyst systems. The olefin waxes may be low, medium,
or high density, such that in some embodiments of the invention,
the waxes may have a density ranging from about 0.88 g/cm.sup.3 to
about 1.0 g/cm.sup.3, or from about 0.89 g/cm.sup.3 to about 0.99
g/cm.sup.3, or from about 0.90 g/cm.sup.3 to about 0.98 g/cm.sup.3.
In the same or other embodiments, the waxes may have a viscosity
from about 100 to about 2000 mPas, or from about 200 to about 1900
mPas, or from about 300 to about 1800 mPas.
[0073] In one or more embodiments, the sheath polymer can be
grafted or functionalized using one or more grafting monomers. The
grafting monomer can be or include at least one ethylenically
unsaturated carboxylic acid or acid derivative, such as an acid
anhydride, ester, salt, amide, imide, acrylates or the like.
Illustrative monomers include but are not limited to acrylic acid,
methacrylic acid, maleic acid, fumaric acid, itaconic acid,
citraconic acid, mesaconic acid, maleic anhydride, 4-methyl
cyclohexene-1,2-dicarboxylic acid anhydride,
bicyclo(2.2.2)octene-2,3-dicarboxylic acid anhydride,
1,2,3,4,5,8,9,10-octahydronaphthalene-2,3-dicarboxylic acid
anhydride, 2-oxa-1,3-diketospiro(4.4)nonene,
bicyclo(2.2.1)heptene-2,3-dicarboxylic acid anhydride, maleopimaric
acid, tetrahydrophthalic anhydride, norbornene-2,3-dicarboxylic
acid anhydride, nadic anhydride, methyl nadic anhydride, himic
anhydride, methyl himic anhydride, and
5-methylbicyclo(2.2.1)heptene-2,3-dicarboxylic acid anhydride.
Other suitable grafting monomers include methyl acrylate and higher
alkyl acrylates, methyl methacrylate and higher alkyl
methacrylates, acrylic acid, methacrylic acid, hydroxy-methyl
methacrylate, hydroxyl-ethyl methacrylate and higher hydroxy-alkyl
methacrylates and glycidyl methacrylate. Maleic anhydride is a
preferred grafting monomer. In certain embodiments herein, the
sheath polymer may be a grafted polymer having a polyethylene or
polypropylene backbone with maleic anhydride grafted to the
backbone. In certain other embodiments, the sheath polymer may be a
polyethylene or polypropylene wax having at least one
functionalized end group, such as for example vinyl tetramethylene
(VTM), providing the polymer with a polar character.
[0074] Exemplary olefin waxes suitable for use as the sheath
polymer in the present invention include, but are not limited to,
those commercially available under the names Licowax and Licocene
(particularly Licowax PE 130, Licowax PE 520, Licocene PE 5301, and
Licocene PP 7502) from Clariant Chemicals, Honeywell A-C
performance additives (particularly A-C 9) from Honeywell
International, and Achieve.TM. (particularly Achieve 6936G1) from
ExxonMobil Chemical Co.
Preparation of Bicomponent Fibers and Fabrics
[0075] The present invention is directed not only to bicomponent
fibers, but also to methods for preparing those fibers. To form the
bicomponent fibers of the invention, a molten blend is prepared
comprising the core polymer and the sheath polymer. The molten
blend is then extruded using an extruder having a die with a length
to diameter ratio greater than or equal to about 10 and under shear
conditions sufficient to drive the sheath polymer toward the die
wall. The resulting bicomponent fibers have a core comprising the
core polymer and a sheath comprising the sheath polymer. While the
terms "core" and "sheath" are used herein for ease of reference, it
should be recognized that the polymers may not completely separate
during the extrusion process, and there may not be a defined
boundary between the core and sheath of the bicomponent fibers
described herein. Rather, fibers of the invention also include
those fibers having a cross-sectional gradient, in which the
concentration of the sheath polymer is highest at the surface of
the fiber, and the concentration of the core polymer is highest at
the center of the fiber.
[0076] Molten blends comprising the core polymer and the sheath
polymer may be prepared by any method that provides an intimate
mixture of the components. Blending and homogenation of polymers
are well known in the art and include single and twin screw mixing
extruders, static mixers for mixing molten polymer streams of low
viscosity, impingement mixers, as well as, other machines and
processes designed to disperse the first and second polymers in
intimate contact. For example, the polymer components and other
minor components can be blended by melt blending or dry blending in
continuous or batch processes. These processes are well known in
the art and include single and twin screw compounding extruders, as
well as, other machines and processes designed to melt and
homogenize the polymer components intimately. The melt blending or
compounding extruders usually are equipped with a pelletizing die
to convert the homogenized polymer into pellet form. The
homogenized pellets can then be fed to the extruder of fiber or
nonwoven process equipment to produce fiber or fabrics.
Alternately, the first and second polymers may be dry blended and
fed to the extruder of the nonwoven process equipment. The blend of
the core and sheath polymers may also be produced by any reactor
blend method currently known in the art. A reactor blend is a
highly dispersed and mechanically inseparable blend of the polymers
produced in situ as the result of sequential polymerization of one
or more monomers with the formation of one polymer in the presence
of another. The polymers may be produced in any of the
polymerization methods described above. The reactor blends may be
produced in a single reactor or in two or more reactors arranged in
series. The blend of the core and sheath polymers may further be
produced by combining reactor blending with post reactor
blending.
[0077] The blended polymer resin may be used to produce fibers and
nonwoven fabric products. As used herein, "nonwoven" refers to a
textile material that has been produced by methods other than
weaving. In nonwoven fabrics, the fibers are processed directly
into a planar sheet-like fabric structure, and are then bonded
chemically or thermally, or interlocked mechanically (or some
combination thereof) to achieve a cohesive fabric.
[0078] The nonwoven fibers and fabrics of the present invention can
be formed by any method known in the art. Preferably, the nonwoven
fibers are produced by a meltblown or spunbond process.
[0079] In a typical spunbond process, polymer is supplied to a
heated extruder to melt and homogenize the polymers. The extruder
supplies melted polymer to a spinneret where the polymer is
fiberized as passed through fine openings arranged in one or more
rows in the spinneret, forming a curtain of filaments. The
filaments are usually quenched with air at a low temperature,
drawn, usually pneumatically, and deposited on a moving mat, belt
or "forming wire" to form the nonwoven fabric. See, for example, in
U.S. Pat. Nos. 4,340,563; 3,692,618; 3,802,817; 3,338,992;
3,341,394; 3,502,763; and 3,542,615.
[0080] The fibers produced in the spunbond process are usually in
the range of from about 10 to about 50 microns in diameter,
depending on process conditions and the desired end use for the
fabrics to be produced from such fibers. For example, increasing
the polymer molecular weight or decreasing the processing
temperature results in larger diameter fibers. Changes in the
quench air temperature and pneumatic draw pressure also have an
affect on fiber diameter.
[0081] In a typical meltblown process, an extruder delivers molten
polymer to a metering melt pump. The melt pump delivers the molten
polymer at a steady output rate to a special melt blowing die,
which may comprise a plurality of fine, usually circular, die
capillaries (also called spinnerets). As the molten polymer
filaments exit the die, they are contacted by high temperature,
high velocity air (called process or primary air). This air rapidly
draws and, in combination with the quench air, solidifies the
filaments. Thereafter, the meltblown fibers are carried by the high
velocity gas stream and are deposited on a collecting surface to
form a web or nonwoven fabric of randomly dispersed meltblown
fibers. Such a process is generally described in, for example, U.S.
Pat. Nos. 3,849,241 and 6,268,203. Meltblown fibers are microfibers
that are either continuous or discontinuous, and, depending on the
resin, may be smaller than about 10 microns (for example, for high
MFR isotactic polypropylene resins such as PP3746G or Achieve.TM.
6936G1, available from ExxonMobil Chemical Company); whereas for
certain resins (for example, Vistamaxx.TM. propylene-based
elastomer, available from ExxonMobil Chemical Company) or certain
high throughput processes such as those described herein, meltblown
fibers may have diameters greater than 10 microns, such as from
about 10 to about 30 microns, or about 10 to about 15 microns. The
term meltblowing as used herein is meant to encompass the meltspray
process.
[0082] It is known that polymer flow under conditions of high shear
can induce segregation of molecules. The extent of segregation and
time required for segregation depend upon the amount of shear
produced. In turn, the level of shear depends upon the process
conditions and the level of immiscibility of the polymer
components. Immiscibility of polymer blend components is a result
of compositional differences and differences in molecular weight of
the blend components, with greater differences leading to a higher
probability of segregation. Process conditions that create shear
and therefore influence segregation include flow velocity (which is
related to the pressure through the die), and the size and/or
cross-sectional area of the die. Segregation is also affected by
the temperature and length of time that the polymer blend is
exposed to the high shear environment. The residence time is
particularly important, because it must be long enough to ensure
that the molecules of the low molecular weight sheath polymer have
sufficient time to migrate to the polymer/die wall interface.
Capillaries with longer length to diameter (L/D) ratios typically
result in longer residence times, thus leading to better
segregation of the polymer components. Conventional meltblown dies
typically have an L/D ratio less than 10, usually less than 5. To
form the bicomponent fibers described herein, the blend of core and
sheath polymers is meltblown through a die with a larger L/D ratio,
for example at least 10, or greater than 10, greater than 15,
greater than 20, greater than 25, greater than 30, greater than 50,
greater than 75, or greater than 100. Under the proper processing
conditions such as those described herein, sufficient shear is
developed using a meltblown die with a high L/D ratio to drive the
sheath polymer to the die wall. The resulting bicomponent fibers
have a sheath comprising the sheath polymer and a core comprising
the core polymer. Such fibers have properties ideal for use in
nonwoven fabric applications, because they have a more desirable
feel than previous fibers due to the sheath layer, while continuing
to provide excellent elastic properties due to the core layer.
[0083] Fabrics formed from the bicomponent fibers described herein
may be a single layer, or may be multilayer laminates. One
application is to make a laminate (or "composite") from meltblown
fabric ("M") and spunbond fabric ("S"), which combines the
advantages of strength from spunbonded fabric and greater barrier
properties of the meltblown fabric. A typical laminate or composite
has three or more layers, a meltblown layer(s) sandwiched between
two or more spunbonded layers, or "SMS" fabric composites. Examples
of other combinations are SSMMSS, SMMS, and SMMSS composites.
Composites can also be made of the meltblown fabrics of the
invention with other materials, either synthetic or natural, to
produce useful articles.
[0084] In some embodiments of the invention, the fibers or fabrics
described herein may be annealed. Annealing partially relieves the
internal stress in a stretched fiber and restores the elastic
recovery properties of the core polymer in the fiber. Annealing has
been shown to lead to significant changes in the internal
organization of the crystalline structure and the relative ordering
of the semi-amorphous and semi-crystalline phases. This leads to
recovery of the elastic properties. For example, annealing the
fiber at a temperature of at least 40.degree. C., above room
temperature but slightly below the crystalline melting point of the
blend, is adequate for the restoration of the elastic properties in
the fiber. Thermal annealing of a polymer blend is conducted by
maintaining the polymer blends or the articles made from a such a
blend at a temperature, for example, between about 25.degree. C.
and about 160.degree. C., or alternatively between about 60.degree.
C. and about 130.degree. C., for a period between a few seconds and
about 1 hour. A typical annealing period is 1 to 5 minutes at
100.degree. C. In nonwoven processes, the fabric web usually passes
through a calender to point bond (consolidate) the web. The passage
of the unconsolidated nonwoven web through a heated calender at
relatively high temperature is sufficient to anneal the fiber and
increase the elasticity of the nonwoven web. The nonwoven web
should be under low tension to allow for shrinkage of the web in
both machine direction (MD) and transverse direction (TD) to
enhance the elasticity of the nonwoven web. In some embodiments,
the bonding calender roll temperature may range from about
60.degree. C. to about 130.degree. C. In another embodiment, the
temperature is about 100.degree. C. The annealing time and
temperature may be adjusted depending upon the composition of a
particular polymer blend.
[0085] A variety of additives may be incorporated into the polymers
used to make the fibers and fabrics described herein, depending
upon the intended purpose. Such additives may include, but are not
limited to, stabilizers, antioxidants, fillers, colorants,
nucleating agents, dispersing agents, mold release agents, slip
agents, fire retardants, plasticizers, pigments, vulcanizing or
curative agents, vulcanizing or curative accelerators, cure
retarders, processing aids, tackifying resins, and the like. Other
additives may include fillers and/or reinforcing materials, such as
carbon black, clay, talc, calcium carbonate, mica, silica,
silicate, combinations thereof, and the like. Primary and secondary
antioxidants include, for example, hindered phenols, hindered
amines, and phosphates. Nucleating agents include, for example,
sodium benzoate and talc. Also, to improve crystallization rates,
other nucleating agents may also be employed such as Ziegler-Natta
olefin products or other highly crystalline polymers. Other
additives such as dispersing agents, for example, Acrowax C, can
also be included. Slip agents include, for example, oleamide and
erucamide. Catalyst deactivators are also commonly used, for
example, calcium stearate, hydrotalcite, and calcium oxide, and/or
other acid neutralizers known in the art.
[0086] The nonwoven products described above may be used in many
articles such as hygiene products including, but not limited to,
diapers, feminine care products, and adult incontinent products.
The nonwoven products may also be used in medical products such as
sterile wrap, isolation gowns, operating room gowns, surgical
gowns, surgical drapes, first aid dressings, and other disposable
items.
Examples
[0087] The following designations are used herein to refer to the
core (C) and sheath (S) polymers used in the following
examples.
[0088] Polymer C1 is a propylene-based polymer comprising propylene
and ethylene, having an ethylene content of about 15 wt %, an MFR
of about 18 g/10 min (230.degree. C., 2.16 kg), and an Mw of about
130,000 g/mol.
[0089] Polymer C2 is an ethylene-propylene copolymer rubber, having
an ethylene content of about 72 wt %, a melt index of about 1.0
g/10 min (190.degree. C., 2.16 kg), and an Mw of about 250,000
g/mol.
[0090] Polymer C3 is an SEBS linear triblock block copolymer having
a styrene content of about 20 wt % and an Mw of about 130,000
g/mol.
[0091] Polymer C4 is an ethylene-based olefin block copolymer
having a melt index of about 5.0 g/10 min (190.degree. C., 2.16 kg)
and an Mw of about 130,000 g/mol.
[0092] Polymer C5 is a propylene-based polymer comprising propylene
and ethylene, having an ethylene content of about 13 wt %, an MFR
of about 79 g/10 min (230.degree. C., 2.16 kg), and an Mw of about
142,000 g/mol.
[0093] Polymer S1 is a polyethylene wax having a viscosity of about
300 mPas, a density of about 0.96-0.98 g/cm.sup.3, and an Mw of
about 14,850 g/mol.
[0094] Polymer S2 is a polyethylene wax having a viscosity of about
650 mPas, a density of about 0.92-0.94 g/cm.sup.3, and an Mw of
about 6,800 g/mol.
[0095] Polymer S3 is a polyethylene homopolymer wax having a
viscosity of about 450 mPas and an Mw of about 7,000 g/mol.
[0096] Polymer S4 is a metallocene-catalyzed polyethylene wax
having a viscosity of about 350 mPas, a density of about 0.96-0.98
g/cm.sup.3, and an Mw of about 4,300 g/mol.
[0097] Polymer S5 is a polypropylene wax having a viscosity of
about 1800 mPas, a density of about 0.90 g/cm.sup.3, and an Mw of
about 27,300 g/mol.
[0098] Polymer S6 is a high melt flow rate homopolypropylene having
an MFR of about 1550 g/10 min (230.degree. C., 2.16 kg) and an Mw
of about 63,000 g/mol.
TABLE-US-00001 Various polymer blends were formed as set forth in
Table 1. Example No. 1 2 3 4 5 6 7 8 9 10 11 Core Polymer, wt % C1
85 85 85 85 50 70 80 C2 85 C3 85 C4 85 C5 90 Sheath Polymer, wt %
S1 15 S2 15 S3 15 S4 15 S5 15 15 15 S6 10 50 30 20 Blend MFR, g/10
min 35.2 33.2 30.4 32.3 11.2 40.5 (230.degree. C., 2.16 kg)
[0099] Having described the various aspects of the compositions
herein, further specific embodiments of the invention include those
set forth in the following lettered paragraphs: [0100] A. A
bicomponent polymer fiber having a core comprising a core polymer
and a sheath comprising a sheath polymer, wherein the sheath
polymer is a polyolefin having a weight average molecular weight
(Mw) less than about 65,000 g/mol and wherein the Mw of the core
polymer is at least about 20,000 g/mol greater than the Mw of the
sheath polymer. [0101] B. The polymer fiber of paragraph A, wherein
the core polymer is selected from a propylene-based polymer, an
ethylene-based polymer, a propylene-ethylene block copolymer, a
styrenic block copolymer, an acrylate, or a combination of the
foregoing. [0102] C. The polymer fiber of any of paragraphs A-B,
wherein the core polymer is a propylene-based polymer comprising
from about 5 to about 30 wt % ethylene and/or a C.sub.4-C.sub.12
alpha olefin and having a triad tacticity greater than about 90%
and a heat of fusion less than about 75 J/g. [0103] D. The polymer
fiber of any of paragraphs B-C, wherein the propylene-based polymer
comprises from about 8 to about 20 wt % ethylene. [0104] E. The
polymer fiber of any of paragraphs B-D, wherein the propylene-based
polymer comprises from about 12 to about 18 wt % ethylene. [0105]
F. The polymer fiber of any of paragraphs A-E, wherein the Mw of
the core polymer is at least about 50,000 g/mol, or at least about
75,000 g/mol greater than the Mw of the sheath polymer. [0106] G.
The polymer fiber of any of paragraphs A-F, wherein the Mw of the
core polymer is at least about 100,000 g/mol greater than the Mw of
the sheath polymer. [0107] H. The polymer fiber of any of
paragraphs A-G, wherein the Mw of the sheath polymer is less than
about 50,000 g/mol and the Mw of the core polymer is greater than
about 100,000 g/mol, or wherein the Mw of the sheath polymer is
less than about 30,000 g/mol and the Mw of the core polymer is
greater than about 125,000 g/mol. [0108] I. The polymer fiber of
any of paragraphs A-H, wherein the sheath polymer is selected from
a polypropylene wax, a polyethylene wax, and combinations thereof.
[0109] J. The polymer fiber of any of paragraphs A-I, wherein the
sheath polymer comprises a backbone of propylene or ethylene with
maleic anhydride grafted to the backbone. [0110] K. The polymer
fiber of any of paragraphs A-J, wherein the sheath polymer is a
polyethylene or polypropylene wax comprising at least one
functionalized end group providing a polar character to the
polymer. [0111] L. A nonwoven fabric comprising polymer fibers
according to any of paragraphs A-K. [0112] M. A process for forming
bicomponent polymer fibers comprising: [0113] i. forming a molten
blend of a core polymer and a sheath polymer; [0114] ii. extruding
the molten polymer blend using an extruder having a die with a
length to diameter ratio greater than or equal to about 10 and
under shear conditions sufficient to drive the sheath polymer to
the die wall; and [0115] iii. forming meltblown fibers having a
core comprising the core polymer and a sheath comprising the sheath
polymer; [0116] wherein the sheath polymer is a polyolefin having a
weight average molecular weight (Mw) less than about 65,000 g/mol
and wherein the Mw of the core polymer is at least about 20,000
g/mol greater than the Mw of the sheath polymer. [0117] N. The
process of paragraph M, wherein the core polymer is selected from a
propylene-based polymer, an ethylene-based polymer, a
propylene-ethylene block copolymer, a styrenic block copolymer, an
acrylate, or a combination of the foregoing. [0118] O. The process
of any of paragraphs M-N, wherein the core polymer is a
propylene-based polymer comprising from about 5 to about 30 wt %
ethylene and/or a C.sub.4-C.sub.12 alpha olefin and having a triad
tacticity greater than about 90% and a heat of fusion less than
about 75 J/g. [0119] P. The process of any of paragraphs N-O,
wherein the propylene based polymer comprises from about 8 to about
20 wt % ethylene. [0120] Q. The process of any of paragraphs N-P,
wherein the propylene based polymer comprises from about 12 to
about 18 wt % ethylene. [0121] R. The process of any of paragraphs
M-Q, wherein the Mw of the core polymer is at least about 50,000
g/mol, or at least about 75,000 g/mol greater than the Mw of the
sheath polymer. [0122] S. The process of any of paragraphs M-R,
wherein the Mw of the core polymer is at least about 100,000 g/mol
greater than the Mw of the sheath polymer. [0123] T. The process of
any of paragraphs M-S, wherein the Mw of the sheath polymer is less
than about 50,000 g/mol and the Mw of the core polymer is greater
than about 100,000 g/mol, or wherein the Mw of the sheath polymer
is less than about 30,000 g/mol and the Mw of the core polymer is
greater than about 125,000 g/mol. [0124] U. The process of any of
paragraphs M-T, wherein the sheath polymer is selected from a
polypropylene wax, a polyethylene wax, and combinations thereof
[0125] V. The process of any of paragraphs M-U, wherein the sheath
polymer comprises a backbone of propylene or ethylene with maleic
anhydride grafted to the backbone. [0126] W. The process of any of
paragraphs M-V, wherein the sheath polymer is a polyethylene or
polypropylene wax comprising at least one functionalized end group
providing a polar character to the polymer. [0127] X. A nonwoven
fabric comprising polymer fibers made according to any of
paragraphs M-W. [0128] Y. An article comprising a nonwoven fabric
according to any of paragraphs M-X. [0129] Z. A fiber according to
any of paragraphs A-Y, further comprising at least one of carbon
black, clay, talc, calcium carbonate, mica, silica, and silicate.
[0130] AA. A fiber according to any of paragraphs A-Z, further
comprising at least one of carbon black, clay, talc, calcium
carbonate, mica, silica, silicate, hindered phenol, hindered amine,
phosphate, sodium benzoate, oleamide, erucamide, calcium stearate,
hydrotalcite, and calcium oxide.
[0131] Certain embodiments and features have been described using a
set of numerical upper limits and a set of numerical lower limits.
It should be appreciated that ranges from any lower limit to any
upper limit are contemplated unless otherwise indicated. Certain
lower limits, upper limits and ranges appear in one or more claims
below. All numerical values are "about" or "approximately" the
indicated value, and take into account experimental error and
variations that would be expected by a person having ordinary skill
in the art.
[0132] To the extent a term used in a claim is not defined above,
it should be given the broadest definition persons in the pertinent
art have given that term as reflected in at least one printed
publication or issued patent. Furthermore, all patents, test
procedures, and other documents cited in this application are fully
incorporated by reference to the extent such disclosure is not
inconsistent with this application and for all jurisdictions in
which such incorporation is permitted.
[0133] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *