U.S. patent application number 13/696693 was filed with the patent office on 2013-05-30 for nonwoven fabrics made from polymer blends and methods for making same.
The applicant listed for this patent is Galen C. Richeson. Invention is credited to Galen C. Richeson.
Application Number | 20130137331 13/696693 |
Document ID | / |
Family ID | 44263170 |
Filed Date | 2013-05-30 |
United States Patent
Application |
20130137331 |
Kind Code |
A1 |
Richeson; Galen C. |
May 30, 2013 |
Nonwoven Fabrics Made From Polymer Blends And Methods For Making
Same
Abstract
The present invention is directed to polymer blends for use in
nonwoven fabric applications, and to fabrics formed from the
polymer blends. In one or more embodiments, the polymer blends
comprise from about 70 to about 99.9 wt %, based on the total
weight of the composition, of a first propylene-based polymer and
from about 0.1 to about 30 wt % of a second propylene-based
polymer. The first polymer has a melt flow rate of from about 100
to about 5,000 g/10 min, and the second polymer has a melt flow
rate of from about 1 to about 500 g/min, and the second polymer has
either a lower melt flow rate or a higher triad tacticity than the
first polymer.
Inventors: |
Richeson; Galen C.; (Humble,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Richeson; Galen C. |
Humble |
TX |
US |
|
|
Family ID: |
44263170 |
Appl. No.: |
13/696693 |
Filed: |
May 3, 2011 |
PCT Filed: |
May 3, 2011 |
PCT NO: |
PCT/US2011/034967 |
371 Date: |
January 18, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61354882 |
Jun 15, 2010 |
|
|
|
Current U.S.
Class: |
442/415 ;
264/555 |
Current CPC
Class: |
Y10T 442/697 20150401;
D04H 1/56 20130101; D04H 13/00 20130101; D01F 6/46 20130101; D01D
5/0985 20130101; D04H 1/541 20130101 |
Class at
Publication: |
442/415 ;
264/555 |
International
Class: |
D01F 6/46 20060101
D01F006/46; D04H 13/00 20060101 D04H013/00 |
Claims
1. A nonwoven fabric made from a polymer composition comprising: a.
from about 70 to about 99.9 wt %, based on the total weight of the
composition, of a first propylene-based polymer having a melt flow
rate of from about 100 to about 5,000 g/10 min; and b. from about
0.1 to about 30 wt % of a second propylene-based polymer having a
melt flow rate of from about 1 to about 500 g/10 min, wherein the
second propylene-based polymer has at least one of: (i) a lower
melt flow rate than the first propylene-based polymer; or (ii) a
higher crystallinity than the first propylene-based polymer;
wherein the first propylene-based polymer is prepared using a
catalyst system comprising a metallocene catalyst.
2. The fabric of claim 1, wherein the polymer composition comprises
from about 5 to about 15% by weight of the second propylene-based
polymer.
3. The fabric of claim 1, wherein the second propylene-based
polymer is prepared using a catalyst system comprising a
Ziegler-Natta catalyst.
4. The fabric of claim 1, wherein the nonwoven fabric is
meltblown.
5. The fabric of claim 1, wherein the first propylene-based polymer
is a propylene homopolymer.
6. (canceled)
7. The fabric of claim 1, wherein the second propylene-based
polymer is a propylene homopolymer.
8. The fabric of claim 1, wherein the second propylene-based
polymer further comprises from 0.01 to 25% by weight of the second
propylene-based polymer of one or more comonomers selected from
C.sub.2 and/or C.sub.4-C.sub.10 alpha-olefins.
9. The fabric of claim 1, wherein the first propylene-based polymer
has a melt flow rate of from about 500 to about 3000 g/10 min.
10. The fabric of claim 1, wherein the second propylene-based
polymer has a melt flow rate of from about 1 to about 250 g/10
min.
11. (canceled)
12. The fabric of claim 1, wherein the first propylene-based
polymer has a triad tacticity of greater than about 0.94.
13. The fabric of claim 1, wherein the second propylene-based
polymer has a higher triad tacticity than the first propylene-based
polymer.
14. The fabric of claim 1, wherein the first propylene-based
polymer has a meso run length, as determined by .sup.13C NMR,
greater than about 75.
15. (canceled)
16. (canceled)
17. A process for producing nonwoven fabrics comprising: a. forming
a polymer composition comprising: (i) from about 70 to about 99.9
wt %, based on the total weight of the composition, of a first
propylene-based polymer prepared using a catalyst system comprising
a metallocene catalyst and having a melt flow rate of from about
100 to about 5,000 g/10 min; and (ii) from about 0.1 to about 30 wt
% of a second propylene-based polymer having a melt flow rate of
from about 1 to about 500 g/10 min wherein the second
propylene-based polymer has at least one of: (i) a lower melt flow
rate than the first propylene-based polymer; or (ii) a higher
crystallinity than the first propylene-based polymer; b. forming
fibers comprising the polymer composition using a meltblown
process; and c. forming a fabric from the fibers.
18. The process of claim 17, wherein the second propylene-based
polymer has a higher triad tacticity than the first propylene-based
polymer.
19. The process of claim 17, wherein the second propylene-based
polymer is prepared using a catalyst system comprising a
Ziegler-Natta catalyst.
20. The process of claim 17, wherein the first propylene-based
polymer is a propylene homopolymer.
21. (canceled)
22. The process of claim 17, wherein the second propylene-based
polymer is a propylene homopolymer.
23. (canceled)
24. (canceled)
25. The process of claim 17, wherein the first propylene-based
polymer has an MWD of from about 1.0 to about 4.0.
26. The process of claim 17, wherein the first propylene-based
polymer has a meso run length, as determined by .sup.13C NMR,
greater than about 75.
27. The process of claim 17, wherein the fibers are formed using an
extruder having a throughput rate of from about 0.1 to about 3
ghm.
28. The process of claim 27, wherein the throughput rate is from
about 0.3 to about 1.0 ghm.
29. The process of claim 27, wherein the melt temperature of the
extruder is from about 175.degree. C. to about 290.degree. C.
30. The process of claim 17, wherein the air temperature of the
meltblown process is from about 175.degree. C. to about 290.degree.
C.
31. The process of claim 17, wherein the air pressure at the die of
the meltblown process is about 10 kPa to about 215 kPa.
32. The process of claim 17, wherein the fabric has a basis weight
of from about 0.1 to about 500 g/m.sup.2.
Description
PRIORITY CLAIM
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 61/354,882 filed Jun. 15, 2010, the disclosure
of which is fully incorporated herein by reference.
BACKGROUND OF INVENTION
[0002] Polypropylene polymers and polymer blends are well known in
the art for their usefulness in the manufacture of nonwoven
meltblown fabrics. Such fabrics have a wide variety of uses, such
as in medical and hygiene products, clothing, filter media, and
sorbent products, including those designed to absorb water, oil,
and other chemicals. An important aspect of these fabrics,
particularly in sorbent applications, is the fabric's loft, or
thickness at a particular basis weight, with a higher loft being
more desirable. Also desirable is a fabric with minimal roping
(i.e., poor fiber separation) and linting.
[0003] Previously, such propylene-based nonwoven fabrics were
prepared in melt blown processes using Ziegler-Natta catalyzed
polypropylene granules coated with peroxide. The addition of
peroxide serves to vis-break the propylene polymer, resulting in
higher melt flow rates and narrower molecular weight distributions
desirable for melt blown applications. Such peroxide coating also
has drawbacks, however, such as an increase in the complexity and
expense of the melt blowing process and the formation of
decomposition byproducts, making the addition of peroxide
undesirable.
[0004] Metallocene catalyzed propylene-based polymers are also
known in the art and have been used to form meltblown fabrics. See,
for example, U.S. Pat. Nos. 6,010,588, 7,081,299, and 7,319,122,
which are incorporated herein by reference. While propylene-based
polymers having high melt flow rates and narrow molecular weight
distributions have been prepared with such single site catalysts,
thus having the advantage of not requiring post reactor treatment
(such as peroxide coating), those polymers have not resulted in
fabrics exhibiting the loft and resistance to roping desired for
certain absorbent and other applications. One possible way to
increase the loft of a fabric is to use a water quench to cool the
molten fibers of the fabric. This is undesirable too, however,
because the high levels of water quench sometimes needed to produce
satisfactory loft result in an excessive level of residual water in
the fabric.
[0005] It would be desirable, then, to develop a propylene-based
polymer composition that produces meltblown fabrics with high loft
and resistance to roping without requiring post reactor treatment
and minimizing water quenching. The present invention accomplishes
these goals by blending a small amount of a propylene-based polymer
having a lower melt flow rate or a higher level of isotacticity
with a metallocene-catalyzed propylene-based polymer having a high
melt flow rate. Nonwoven fabrics produced from the polymer blends
of the invention have high loft and good resistance to roping and
linting with low levels of residual moisture.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to polymer blends for use
in nonwoven fabric applications, fabrics formed from the polymer
blends, and to methods for forming such fabrics. In one or more
embodiments, the polymer blends comprise from about 70 to about
99.9 wt %, based on the total weight of the composition, of a first
propylene-based polymer and from about 0.1 to about 30 wt % of a
second propylene-based polymer. The first polymer has a melt flow
rate of from about 100 to about 5,000 g/10 min, and the second
polymer has a melt flow rate of about 1 to about 500 g/min. In
various embodiments, the MFR of the first polymer may be higher
than the MFR than the second polymer and/or the triad tacticity
(e.g., crystallinity) of the second polymer may be higher than the
first polymer. In one embodiment, the second polymer has a triad
tacticity greater than about 0.94. Additionally, nonwoven fabrics,
particularly meltblown nonwoven fabrics, formed from the polymer
blends of the invention provide the advantages of a polymer
produced with a metallocene catalyst while maintaining comparable
loft and resistance to linting or roping to fabrics made from
Ziegler-Natta based polymers. These fabrics also have low levels of
residual moisture resulting from their manufacture and are suitable
for use in many commercial applications, including sorbent
articles. In certain applications low levels of "shot" and high
liquid barrier properties are desirable. Blends of high MFR
metallocene based with lower MFR or higher crystallinity
propylene-based polymers reduce "shot" and/or improve barrier
resistance, particularly to water based liquids.
DETAILED DESCRIPTION OF THE INVENTION
[0007] The nonwoven fabrics of the present invention are formed
from polymer blends that comprise from about 70 to about 99.9 wt %,
based on the total weight of the composition, of a first
propylene-based polymer and from about 0.1 to about 30 wt % of a
second propylene-based polymer, where the first polymer has a melt
flow rate of from about 100 to about 5,000 g/10 min, and the second
polymer a melt flow rate of from about 1 to about 500 g/min and
either a lower melt flow rate or a higher triad tacticity than the
first polymer. In one embodiment, the second polymer has a triad
tacticity greater than about 0.94. In one or more embodiments, the
first polymer is produced using a catalyst system comprising a
metallocene catalyst. In the same or other embodiments, the first
polymer is a reactor grade polymer.
[0008] The present invention is also directed to processes for
forming nonwoven fabrics comprising the polymer blends described
herein. In one or more embodiments, such methods comprise the steps
of forming a molten polymer composition, forming fibers comprising
the polymer composition using a meltblown process, and forming a
fabric from the fibers. The molten polymer composition comprises
from about 70 to about 99.9 wt %, based on the total weight of the
composition, of a first propylene-based polymer prepared using a
catalyst system comprising a metallocene catalyst and having a melt
flow rate of from about 100 to about 5,000 g/10 min, and from about
0.1 to about 30 wt % of a second propylene-based polymer having
either a lower melt flow rate and/or a higher triad tacticity
(i.e., crystallinity). In one embodiment, the melt flow rate of
from about 1 to about 500 g/10 min and/or a triad tacticity greater
than about 0.94.
[0009] 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.
[0010] 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.
[0011] In some embodiments of the present invention, each of the
first and second propylene-based polymers comprises polypropylene.
"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-derived units,
either alone or in combination with one or more comonomers, in
which propylene-derived units are the major component (i.e.,
greater than 50 wt % propylene).
First Propylene-Based Polymer
[0012] The polymer blends used to form the nonwoven fabrics of the
present invention comprise a first propylene-based polymer. In one
or more embodiments, the first propylene-based polymer is a reactor
grade propylene polymer produced using a catalyst system comprising
a metallocene compound. By "reactor grade" is meant a polymer that
has not been chemically or mechanically treated after
polymerization in an effort to alter the polymer's average
molecular weight, molecular weight distribution, or viscosity.
Particularly excluded from those polymers described as reactor
grade are those that have been peroxide coated.
[0013] The first propylene-based polymer may be a homopolymer or a
copolymer of propylene-derived units and one or more comonomers
(e.g., C.sub.2 and/or C.sub.4-C.sub.16 alpha olefin-derived units).
When the first polymer is a copolymer, the comonomer content may be
from about 0.01 to about 25 wt %, or from about 0.1 to about 20 wt
%, or from about 1 to about 15 wt %, or from about 1 to about 10 wt
%, based upon the weight of the first polymer. In a preferred
embodiment, the first polymer is a propylene homopolymer (i.e.,
polypropylene homopolymer).
[0014] In one embodiment, the first polymer is predominately
crystalline, meaning it has a melting temperature greater than
about 110.degree. C., or greater than about 115.degree. C., or
greater than about 130.degree. C. The term "crystalline" as used
herein refers to those polymers having a heat of fusion greater
than about 60 J/g, or greater than about 70 J/g, or greater than
about 80 J/g, as determined by Differential Scanning calorimetry
(DSC) at a heating rate of 10.degree. C./minute.
[0015] Crystallization temperature (Tc), melting temperature (Tm),
and heat of fusion (Hf) may be measured as follows. For example,
about 6 to 10 mg of a sheet of the polymer or plasticized polymer
is pressed at approximately 150.degree. C. to 200.degree. C., and
is removed with a punch die. The sample is placed in a Differential
Scanning calorimeter (Perkin Elmer 7 Series Thermal Analysis
System) and heated to 200.degree. C. and held for 10 minutes. The
sample is cooled at 10.degree. C./min to attain a final temperature
of 25.degree. C. The thermal output is recorded and the inflection
point in the thermal output data, indicating a change in the heat
capacity, is determined by electronically differentiating the
thermal output data. The maximum in the differential thermal output
data corresponds to the crystallization temperature of the sample.
The sample is held at 25.degree. C. for 10 minutes and heated at
10.degree. C./min to 200.degree. C. The thermal input is recorded
and the inflection point in the thermal input data, indicating a
change in the heat capacity, is determined by electronically
differentiating the thermal input data. The maximum in the
differential thermal input data corresponds to the melting
temperature of the sample. The area under the melting peak of the
sample, which typically occurs between about 0.degree. C. and about
200.degree. C., is measured in Joules and is a measure of the Hf of
the polymer.
[0016] In one or more embodiments, the first propylene-based
polymer has a melt flow rate, or "MFR" (2.16 kg, 230.degree. C.),
of from about 100 to about 5,000 g/10 min, as determined by ASTM
D-1238. In further embodiments, the first polymer may have an MFR
of from about 350 to about 4,000 g/10 min, or from about 500 to
about 3,000 g/10 min, or from about 750 to about 2,500 g/10 min, or
from about 1,000 to about 2,000 g/10 min.
[0017] In various embodiments, the first propylene-based polymer
has a triad tacticity of less than about 0.96, or less than about
0.95, or less than about 0.94.
[0018] In one or more embodiments, the first propylene-based
polymer may have a weight average molecular weight (Mw) of from
about 40,000 to about 125,000. In the same or other embodiments,
the first polymer may have a number average molecular weight (Mn)
of from about 10,000 to about 60,000. The first polymer may also
have a molecular weight distribution (Mw/Mn, or "MWD") of from
about 1.0 to about 4.0, or from about 1.5 to about 3.5, or from
about 2.0 to about 3.0. Techniques for determining the molecular
weight (Mn and Mw) and molecular weight distribution (MWD) are
found in U.S. Pat. No. 4,540,753 (which is incorporated by
reference herein for purposes of U.S. practice) and references
cited therein and in Macromolecules, 1988, Volume 21, p. 3360
(which is herein incorporated by reference for purposes of U.S.
practice) and references cited therein.
[0019] The first propylene-based polymer is produced using a
catalyst system comprising a metallocene catalyst. In one or more
embodiments, the catalyst system comprises at least one
metallocene, preferably supported using a porous particulate
material, and at least one activator. The catalyst system may also
comprise one or more cocatalysts.
[0020] As used herein, "metallocene" refers generally to compounds
represented by the formula Cp.sub.mMR.sub.nX.sub.q, where Cp is a
cyclopentadienyl ring which may be substituted, or derivative
thereof which may be substituted, M is a Group 4, 5, or 6
transition metal, for example titanium (Ti), zirconium (Zr),
hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium
(Cr), molybdenum (Mo) or tungsten (W), R is a hydrocarbyl group or
hydrocarboxyl group having from one to 20 carbon atoms, X is a
halogen or hydrogen, and m=1-3, n=0-3, q=0-3, and the sum of m+n+q
is equal to the oxidation state of the transition metal.
[0021] Methods for making and using metallocenes are disclosed in,
for example U.S. Pat. Nos. 4,530,914; 4,542,199; 4,769,910;
4,808,561; 4,871,705; 4,933,403; 4,937,299; 5,017,714; 5,026,798;
5,057,475; 5,120,867; 5,278,119; 5,304,614; 5,324,800; 5,350,723,
6,143,686; and 5,391,790.
[0022] The metallocene component selected for use in the catalyst
system of this invention is a metallocene which, when used alone,
produces isotactic, crystalline propylene polymers and, when used
in combination with another metallocene, produces polymers having
the attributes desired for the particular application of interest.
Metallocene catalyst components suitable for preparation of the
first propylene-based polymer include those described in U.S. Pat.
Nos. 6,143,686, 5,145,819; 5,243,001; 5,239,022; 5,329,033;
5,296,434; 5,276,208; and 5,374,752; and EP 549 900 and 576
970.
[0023] Metallocenes are generally used in combination with some
form of activator in order to create an active catalyst system. The
term "activator" is defined herein to be any compound or component,
or combination of compounds or components, capable of enhancing the
ability of one or more metallocenes to polymerize olefins to
polyolefins.
[0024] In one embodiment, ionizing activators are used to activate
the metallocenes. These activators can be "non-ionic" or "ionic"
(also called non-coordinating anion activators or NCA activators).
The ionic activators are compounds such as tri(n-butyl)ammonium
tetrakis(pentafluorophenyl)boron, which ionize the neutral
metallocene compound. Such ionizing compounds may contain an active
proton, or some other cation associated with but not coordinated or
only loosely associated with the remaining ion of the ionizing
compound. Combinations of activators may also be used, for example,
alumoxane and ionizing activators in combinations, for example
those described in WO 94/07928. The non-ionic activator precursors
that can serve as the NCA activators are strong Lewis acids with
non-hydrolyzable ligands, at least one of which is
electron-withdrawing, such as those Lewis acids known to abstract
an anionic fragment from dimethyl zirconocene (biscyclopentadienyl
zirconium dimethyl) e.g., trisperfluorophenyl boron,
trisperfluoronaphthylboron, or trisperfluorobiphenyl boron, and
other highly fluorinated trisaryl boron compounds.
[0025] The term "non-coordinating anion" describes an anion which
either does not coordinate to the cationic metallocene or which is
only weakly coordinated to said cation, thereby remaining
sufficiently labile to be displaced by a neutral Lewis base.
"Compatible" noncoordinating anions are those that are not degraded
to neutrality when the initially formed complex decomposes.
Further, the anion will not transfer an anionic substituent or
fragment to the cation so as to cause it to form a neutral four
coordinate metallocene compound and a neutral by-product from the
anion. Noncoordinating anions useful in accordance with this
invention are those that are compatible and stabilize the
metallocene cation in the sense of balancing its ionic charge in a
+1 state, yet retain sufficient lability to permit displacement by
an ethylenically or acetylenically unsaturated monomer during
polymerization.
[0026] The catalyst systems used to produce the polymers described
herein are preferably supported using a porous particulate
material, such as for example, talc, inorganic oxides, inorganic
chlorides and resinous materials such as polyolefins or other
polymeric compounds. In particular, the catalyst system is
typically the resultant composition from contacting at least the
metallocene component, the activator component, and the support
component.
[0027] Desirable support materials are porous inorganic oxide
materials, which include those from the Periodic Table of Elements
of Groups 2, 3, 4, 5, 13 or 14 metal oxides. Silica, alumina,
silica-alumina, and mixtures thereof are particularly suitable.
Other inorganic oxides that may be employed either alone or in
combination with the silica, alumina or silica-alumina are
magnesia, titania, zirconia, and the like.
[0028] A more detailed description of the metallocene compounds, as
well as activators, support materials, and overall catalyst
systems, suitable for use in the present invention is found in U.S.
Pat. No. 7,081,299, which is incorporated by reference herein in
its entirety. In some embodiments of the invention, the metallocene
used to prepare the first propylene-based polymer is a
silica-supported bridged 2,4 disubstituted indenyl metallocene or
bridged 4-phenyl indenyl metallocene.
[0029] The supported catalyst systems described herein and in the
referenced documents can be used in any suitable polymerization
technique. Methods and apparatus for effecting such polymerization
reactions are well known. The supported catalyst activators can be
used in similar amounts and under similar conditions to known
olefinic polymerization catalysts.
[0030] As used herein, the term "polymerization" includes
copolymerization and terpolymerization and the terms "olefins" and
"olefinic monomer" include alpha olefins, diolefins, strained
cyclic olefins, styrenic monomers, acetylenically unsaturated
monomers, cyclic olefins alone or in combination with other
unsaturated monomers. The metallocene supported catalyst
composition is useful in coordination polymerization of unsaturated
monomers conventionally known to be polymerizable under
coordination polymerization conditions. Monomers suitable for the
polymers of the invention include propylene and C.sub.2 and/or
C.sub.4-C.sub.10 alpha-olefins. Polymerization conditions also are
well known and include solution polymerization, slurry
polymerization, and low pressure gas phase polymerization. The
supported metallocene catalyst compositions described herein are
thus particularly useful in the known operating modes employing
fixed-bed, moving-bed, fluid-bed, or slurry processes conducted in
single, series or parallel reactors.
[0031] Polymerization techniques for olefin polymerization can
include solution polymerization, slurry polymerization, or gas
phase polymerization techniques. Methods and apparatus for
effecting such polymerization reactions are well known and
described in, for example, 12 ENCYCLOPEDIA OF POLYMER SCIENCE AND
ENGINEERING 504 541 (John Wiley and Sons, 1988) and in 2
METALLOCENE-BASED POLYOLEFINS 366 378 (John Wiley and Sons,
2000).
[0032] The polymers of the invention can be prepared with the
catalysts described in either batch, semi-continuous, or continuous
propylene polymerization systems. Desirable polymerization systems
are the continuous processes, including diluent slurry, bulk slurry
(loop and stirred tank), and gas phase (stirred and fluid bed).
Continuous polymerization can be carried out in a single reactor of
any of the above types, in two or more reactors operating in
series, or in two or more reactors operating in parallel. When two
or more reactors are operating in a continuous process, the
multiple reactors can be all of the same type or they may be any
combination of the types.
[0033] Hydrogen gas is often used in olefin polymerization to
control the final properties of the polyolefin, such as described
in POLYPROPYLENE HANDBOOK 76 78 (Hanser Publishers, 1996). Using
the catalyst systems herein, it is known that higher concentrations
(partial pressures) of hydrogen increase the melt flow rate (MFR)
of the polyolefin generated, in particular polypropylene. The MFR
can thus be influenced by the hydrogen concentration, which in turn
influences the optimal fiber manufacturing process temperatures.
Typically, the higher the MFR of the polypropylene, the finer the
fibers and more uniform the coverage can be obtained in the fabric.
Also, higher MFR resins can be processed at lower temperatures. The
final quality of the fabrics made from the fibers comprising the
polymers described herein is thus influenced by hydrogen
concentration during polymerization or the final MFR of the
polymer.
[0034] Polypropylene polymers made from the above described
catalyst systems and processes have improved properties. The
polypropylene tends to be highly isotactic as measured by the meso
run length of the polypropylene chains, while maintaining a
relatively narrow molecular weight distribution. Isotactic
polypropylenes are those polymers wherein the pendent hydrocarbyl
groups of the polymer chain are ordered in space on the same side
or plane of the polymer backbone chain. Using isotactic
polypropylene as an example, the isotactic structure is typically
described as having the pendent methyl groups attached to the
ternary carbon atoms of successive monomeric units on the same side
of a hypothetical plane through the carbon backbone chain of the
polymer, as shown in below:
##STR00001##
[0035] The degree of isotactic regularity may be measured by NMR
techniques, and typical nomenclature for an isotactic pentad is
"mmmm", in which each "m" represents a "meso" dyad or successive
methyl groups on the same side in the plane. Single insertions of
inverted configuration give rise to rr triads as shown below:
##STR00002##
[0036] As is known in the art, any deviation or inversion in the
regularity of the polymer structure lowers the degree of
isotacticity and hence crystallinity of which the polymer is
capable. Ideally, the longer the mmmm runs or meso run lengths, the
more highly isotactic the polypropylene. Defects and inversions
such as the 1, 3 or 2, 1 insertion are undesirable when isotactic
polymer is desired.
[0037] In some embodiments, the first propylene-based polymer of
the present invention may have less than 50 stereo defects per 1000
units, or less than 25 stereo defects per 1000 units, or less than
100 stereo defects per 10,000 units, or less than 80 stereo defects
per 10,000 units, and meso run lengths (MRL) of greater than 50, or
greater than 75, or greater than 100 in yet another embodiment as
indicated by .sup.13C NMR.
[0038] Exemplary commercially available polymers suitable for use
as the first propylene-based polymer include Achieve.TM. propylene
polymers, available from ExxonMobil Chemical Company, and
Metocene.TM. and Moplen.TM. propylene polymers, available from
LyondellBasell.
Second Propylene-Based Polymer
[0039] The polymer blends used to form the nonwoven fabrics of the
present invention comprise a second propylene-based polymer. The
second propylene-based polymer may be a homopolymer or a copolymer
of propylene with one or more C.sub.2 and/or C.sub.4-C.sub.10 alpha
olefins.
[0040] The second propylene-based polymer differs primarily from
the first propylene-based polymer in that it has either a lower MFR
than that described above for the first polymer or a higher
crystallinity. In one or more embodiments herein, the second
propylene-based polymer has an MFR of from about 0.1 to about 500
g/10 min, or from about 1 to about 250 g/10 min, or from about 5 to
about 150 g/10 min, or from about 10 to about 100 g/10 min, or from
about 10 to about 75 g/10 min, as determined by ASTM D-1238 (2.16
kg, 230.degree. C.).
[0041] In other embodiments herein, the second propylene-based
polymer may have an MFR similar to, or even higher than, that of
the first propylene-based polymer, but has a crystallinity higher
than that of the first propylene-based polymer. The crystallinity
is reflected in the level of isotacticity of the polymer, and in
such embodiments the triad tacticity of the second polymer is
greater than about 0.94, or greater than about 0.95, or greater
than about 0.96. As used herein, the "triad tacticity" of a polymer
is the relative tacticity of a sequence of two adjacent propylene
units, a chain consisting of head to tail bonds, expressed as a
binary combination of m and r sequences. It is usually expressed as
the ratio of the number of units of the specified tacticity to all
of the propylene triads in the copolymer. The triad tacticity (mmmm
fraction) of a propylene copolymer can be determined from a
.sup.13C NMR spectrum of the propylene copolymer and the following
formula:
mmFraction=PPP(mm)/(PPP(mm)+PPP(mr)+PPP(rr))
where PPP(mm), PPP(mr), and PPP(rr) denote peak areas derived from
the methyl groups of the second units in the following three
propylene unit chains consisting of head-to-tail bonds:
##STR00003##
[0042] The .sup.13C NMR spectrum of the propylene copolymer is
measured as described in U.S. Pat. No. 5,504,172. The spectrum
relating to the methyl carbon region (19-23 parts per million
(ppm)) can be divided into a first region (21.2-21.9 ppm), a second
region (20.3-21.0 ppm) and a third region (19.5-20.3 ppm). Each
peak in the spectrum was assigned with reference to an article in
the journal Polymer, Volume 30 (1989), p. 1350. In the first
region, the methyl group of the second unit in the three propylene
unit chain represented by PPP (mm) resonates. In the second region,
the methyl group of the second unit in the three propylene unit
chain represented by PPP (mr) resonates, and the methyl group
(PPE-methyl group) of a propylene unit whose adjacent units are a
propylene unit and an ethylene unit resonates (in the vicinity of
20.7 ppm). In the third region, the methyl group of the second unit
in the three propylene unit chain represented by PPP (a) resonates,
and the methyl group (EPE-methyl group) of a propylene unit whose
adjacent units are ethylene units resonates (in the vicinity of
19.8 ppm). The calculation of the triad tacticity is outlined in
the techniques shown in U.S. Pat. No. 5,504,172. Subtraction of the
peak areas for the error in propylene insertions (both 2,1 and 1,3)
from peak areas from the total peak areas of the second region and
the third region, the peak areas based on the 3 propylene
units-chains (PPP(mr) and PPP(rr)) consisting of head-to-tail bonds
can be obtained. Thus, the peak areas of PPP(mm), PPP(mr) and
PPP(rr) can be evaluated, and hence the triad tacticity of the
propylene unit chain consisting of head-to-tail bonds can be
determined.
[0043] In one or more embodiments herein, the second polymer may
comprise low amounts of comonomer, such that the second polymer may
be a random copolymer of polypropylene (RCP) or an impact copolymer
(ICP). Exemplary RCPs typically comprise from about 1 to about 8 wt
% comonomer, or from about 2 to about 5 wt % comonomer. In one or
more embodiments, the RCP comonomer is ethylene.
[0044] In some embodiments of the present invention, the second
polymer is a copolymer of propylene and from about 0.1 to about 25
wt % of one or more comonomers. The comonomers may be linear or
branched. In one or more embodiments, linear comonomers may include
ethylene and/or C.sub.4 to C.sub.10 alpha-olefins, including but
not limited to butene, hexene, and octene. Branched comonomers may
include 4-methyl-1-pentene, 3-methyl-1-pentene, and
3,5,5-trimethyl-1 hexene. In one or more embodiments, the comonomer
can include styrene.
[0045] In some embodiments, the second polymer is a copolymer of
propylene and ethylene (and may comprise other comonomers as well).
For example, the second polymer may comprise from about 75 to about
99 wt % units derived from propylene and from about 1 to about 25
wt % units derived from ethylene. In some embodiments, the second
polymer may comprise from about 2 to about 25 wt % ethylene-derived
units, or from about 3 to about 18 wt % ethylene-derived units, or
from about 5 to about 10 wt % ethylene-derived units.
[0046] Optionally, the second 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" 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 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 cylcoalkylidene 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.
[0047] When one or more dienes is present, the second polymer may
comprise from 0.05 to about 6 wt % diene-derived units. In further
embodiments, the second polymer comprises from about 0.1 to about
5.0 wt % diene-derived units, or from about 0.1 to about 3.0 wt %
diene-derived units, or from about 0.1 to about 1.0 wt %
diene-derived units.
[0048] In one or more embodiments, the second polymer may have a
heat of fusion (Hf) determined according to the DSC procedure
described above, which is greater than or equal to about 0.5 Joules
per gram (J/g), and is less than or equal to about 80 J/g, or less
than or equal to about 75 J/g, or less than or equal to about 70
J/g, or less than or equal to about 60 J/g, or less than or equal
to about 50 J/g. In other embodiments herein, the second polymer
may have a heat of fusion greater than about 80 J/g, or greater
than about 90 J/g, or greater than 100 J/g.
[0049] The first and second polymers may have the same or different
melting point. In some embodiments, the melting point of the second
polymer may be less than the melting point of the first polymer,
such as less than 100.degree. C., or less than 90.degree. C., or
less than or equal to 80, or less than or equal to 75.degree. C. In
other embodiments, the second polymer has a melting point higher
than that of the first polymer, such as greater than 110.degree.
C., or greater than 120.degree. C., or greater than 130.degree. C.
In certain embodiments herein, the first and second polymers both
have a melting point greater than about 110.degree. C., and the
melting point of the second polymer is at least about 5.degree. C.
greater than the melting point of the first polymer.
[0050] The second polymer may further have a triad tacticity of
three propylene units, as measured by .sup.13C NMR, of 75% or
greater, 80% or greater, 82% or greater, 85% or greater, or 90% or
greater. In some embodiments, the triad tacticity of the second
polymer ranges from about 50 to about 99%, or from about 60 to
about 99%, or from about 75 to about 99%, or from about 80 to about
99%, or from about 60 to about 97%. Triad tacticity is determined
by the methods described in U.S. Patent Application Publication
2004/0236042, which is incorporated herein by reference.
[0051] In various embodiments, the second propylene-based polymer
has a higher melting temperature (Tm) than the first
propylene-based polymer. For example, in one embodiment, the first
propylene-based polymer has a melting temperature of about
153-155.degree. C. and the second polymer has a
Tm.gtoreq.156.degree. C. The second propylene-based polymer may be
prepared using a metallocene catalyst system like those described
above with respect to the first polymer. Alternately, the second
polymer may be prepared using any other catalyst known in the art
to produce polymers having the characteristics described herein,
such as other single-site catalysts, Ziegler-Natta catalysts, and
the like. In certain embodiments herein, the second polymer is
produced using a Ziegler-Natta catalyst.
[0052] Exemplary commercially available polymers suitable for use
as the second propylene-based polymer include Achieve.TM. and
ExxonMobil.TM. propylene polymers (such as but not limited to
PP3155E1, PP3155E3, PP3885, PP3864F5, PP3325E1, PP3374E3, and
Achieve.TM. 3854), and Vistamaxx.TM. elastomers, available from
ExxonMobil Chemical Company, Versify.TM. polymers available from
the Dow Chemical Company, and Moplen HP561R, Moplen HP566R, Moplen
HP462R available from Lyondell Basell, PPH9099 and PPH9020
available from Totalfina, HG455FB available from Borealis, HG3600
available from Arco, DR7052.01 available from Dow, 201-CA25
available from Ineos, and PP512P available from Sabic.
Nonwoven Fabrics
[0053] The nonwoven fabrics of the present invention are formed
from a blend of the first and second propylene-based polymers
described herein. In certain embodiments of the present invention,
the fabrics may comprise from about 70 wt % to about 99.9 wt %, or
from about 75 wt % to about 99 wt %, or from about 80 wt % to about
98 wt %, or from about 85 wt % to about 95 wt % of the first
polymer and from about 0.1 wt % to about 30 wt %, or from about 1
wt % to about 25 wt %, or from about 2 wt % to about 20 wt %, or
from about 5 wt % to about 15 wt % of the second polymer.
[0054] In one embodiment, the polymer composition used to form the
nonwoven fabric consists essentially of the first propylene-based
polymer and the second propylene-based polymer. As used herein,
"consists essentially of the first propylene-based polymer and the
second propylene-based polymer" means the nonwoven fabric comprises
less than 2 wt % of other components, based on total weight of the
polymer composition.
[0055] The present invention is directed not only to nonwoven
fabrics, but also to processes for forming nonwoven fabrics
comprising the polymer blends described herein. In one or more
embodiments, such methods comprise the steps of forming a molten
polymer composition comprising the first propylene-based polymer
and the second propylene-based polymer, forming fibers comprising
the polymer composition, and forming a fabric from the fibers.
[0056] The first and second polymers may be blended by any post
reactor method that guarantees 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.
[0057] The blend of the first and second 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 first and second
polymers may further be produced by combining reactor blending with
post reactor blending.
[0058] The blended polymer resin may be used to produce 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 by passing the intermediate
one-dimensional yarn state, and then are either bonded chemically,
thermally, or interlocked mechanically (or both) to achieve a
cohesive fabric.
[0059] The nonwoven fabrics of the present invention can be formed
by any method known in the art. Preferably, the nonwoven fabrics
are produced by a meltblown or spunbond process.
[0060] 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 spinnerette where the polymer is
fiberized as passed through fine openings arranged in one or more
rows in the spinnerette, 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 U.S. Pat. No. 3,542,615.
[0061] 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.
[0062] As used herein, "meltblown fibers" and "meltblown fabrics"
refer to fibers formed by extruding a molten thermoplastic material
at a certain processing temperature through a plurality of fine,
usually circular, die capillaries as molten threads or filaments
into converging high velocity, usually hot, gas streams which
attenuate the filaments of molten thermoplastic material to reduce
their diameter, which may be to microfiber diameter. 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 are generally smaller than about 10
microns, preferably less than about 5 microns. The term meltblowing
as used herein is meant to encompass the meltspray process.
[0063] Commercial meltblown processes utilize extruders having a
relatively high throughput, in excess of 0.3 grams per hole per
minute ("ghm"), or in excess of 0.4 ghm, or in excess of 0.5 ghm,
or in excess of 0.6 ghm, or in excess of 0.7 ghm. The fabrics of
the present invention may be produced using commercial meltblown
processes, or in test or pilot scale processes. In one or more
embodiments of the present invention, the fibers used to form the
nonwoven fabrics are formed using an extruder having a throughput
rate of from about 0.1 to about 3.0 ghm, or from about 0.2 to about
2.0 ghm, or from about 0.3 to about 1.0 ghm.
[0064] The fabrics 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.
[0065] One parameter often used to describe nonwoven fabrics is
their basis weight, or the weight of the fabric per unit of area.
The fabrics of the present invention may have a basis weight of
from about 0.1 to about 500 grams per square meter ("gsm"), or from
about 1 to about 450 gsm, or from about 10 to about 400 gsm, or
from about 25 to about 350 gsm.
[0066] 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.
[0067] 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.
[0068] The fabrics of the present invention are also useful as air
or liquid filters. Examples of filter applications include
automotive and vehicle cabin filters, home ventilation filters,
clean room filters, industrial ash and particulates filters,
surgical and nuisance dust masks, beverage filters, pharmaceutical
filters, medical filters, water purification filters, and
recreational filters such as pool filters. The filters may be
useful in either sheet or cartridge form, and may be multi-layered
or multi-density.
[0069] The fabrics of the present invention are also useful as
sorbent products, such as oil sorbent, chemical sorbent, or water
sorbent articles. Some other specific nonwoven articles include,
but are not limited to, swimwear, outerwear, scrubbing pads, cloth
linings, automotive interior parts, face masks and respirators,
vacuum bags, wipe materials, and other products.
EXAMPLES
[0070] In the examples below, a first propylene-based polymer,
labeled "Component A", and a second propylene-based polymer,
labeled "Component B", were used either individually or blended to
form a polymer resin that was meltblown to form nonwoven fabrics.
The fabrics were formed on a BIAX pilot line, commercially
available from BIAX-Fiberfilm in Greenville, Wis. The pilot line
was equipped with a 3.5'' extruder capable of a throughput of
approximately 300+ lb/hr and a 25'' (0.635 m) wide capillary die
having approximately 200 holes/inch (0.015'' capillary size). The
maximum throughput rate of the extruder was approximately 0.57 ghm.
The line was also equipped with a 1 m diameter single drum
collector. The ambient temperature at the time of testing was
approximately 60.degree. F. (15.5.degree. C.). All fabric examples
reported below had a basis weight of approximately 300 gsm.
[0071] Component A is a metallocene-catalyzed reactor grade
propylene homopolymer having an MFR of about 1550 g/10 min.
[0072] Component B1 is a Ziegler-Natta catalyzed propylene
homopolymer having an MFR of about 36 g/10 min.
[0073] Component B2 is a Ziegler-Natta catalyzed propylene
homopolymer having an MFR of about 65 g/10 min.
[0074] Component B3 is a metallocene-catalyzed propylene-based
elastomer having an ethylene comonomer content of 13 wt % and an
MFR of about 290 g/10 min.
[0075] Component B4 is a peroxide coated Zeigler-Natta catalyzed
propylene homopolymer having an MFR of about 1200 g/10 min.
EXAMPLES
[0076] As used herein, one inch is equivalent to 2.54 centimeters.
Degrees Fahrenheit (.degree. F.) can be converted to degrees
Celsius (.degree. C.) as follows: .degree. C.=(.degree.
F.-32).times.5/9.
Example 1
[0077] In Comparative Example 1, fabrics were prepared using 100 wt
% Component A at varying throughput rates, air temperatures, die
pressures, and water quench rates. The resulting fabrics were
observed visually and tactilely, and the results are reported in
Table 1.
TABLE-US-00001 TABLE 1 (Achieve 6936G1) Air Water Quench Through-
Die Melt Air Pressure (top unit Run put Pressure Temp. Temp. at Die
only; % of No (ghm) (psi) (.degree. F.) (.degree. F.) (psi)
maximum) Observations 1-1 0.30 835 371 342 23.5 30 good 1-2 0.57
1175 371 343 24.5 30 lower loft, stiffer, less ropey 1-3 0.57 1025
371 400 27 65 improved loft, less stiff 1-4 0.57 945 403 375 27 80
ropey 1-5 0.30 790 358 360 17.5 50 soft and lofty, but ropey on top
1-6 0.57 1425 370 357 27 60 stiff, ropey on top 1-7 0.57 1250 370
390 27 60 softer feel 1-8 0.57 1250 373 418 27 60 softer feel 1-9
0.57 1250 382 471 18 70 fabric feels boardy 1-10 0.57 950 377 448
24 70 less boardy, looks ropey 1-11 0.57 1060 384 425 27 80 good
loft, not too stiff, ropey
Example 2
[0078] In Example 2, fabrics were prepared using 95 wt % Component
A and 5 wt % Component B1 at varying throughput rates, air
temperatures, die pressures, and water quench rates. The resulting
fabrics were observed visually and tactilely, and the results are
reported in Table 2.
TABLE-US-00002 TABLE 2 (5% PP3155) Air Water Quench Through- Die
Melt Air Pressure (top unit Run put Pressure Temp. Temp. at Die
only) (% of No. (ghm) (psi) (.degree. F.) (.degree. F.) (psi)
maximum) Observations 2-1 0.30 900 373 380 23 30 very high loft,
more ropey 2-2 0.57 1385 384 391 27 70 less loft, not as ropey 2-3
0.57 1225 399 431 27 70 good uniformity and loft
Example 3
[0079] In Example 3, fabrics were prepared using 90 wt % Component
A and 10 wt % Component B1 at varying throughput rates, air
temperatures, die pressures, and water quench rates. The resulting
fabrics were observed visually and tactilely, and the results are
reported in Table 3.
TABLE-US-00003 TABLE 3 (10% PP3155) Air Water Quench Through- Die
Melt Air Pressure (top unit Run put Pressure Temp. Temp. at Die
only) (% of No. (ghm) (psi) (.degree. F.) (.degree. F.) (psi)
maximum) Observations 3-1 0.30 865 386 428 26 30 very lofty, soft,
some ropiness 3-2 0.30 825 386 426 26 60 damp 3-3 0.30 826 387 427
19.5 40 slightly damp 3-4 0.57 1375 395 427 27.5 60 lower loft,
good abrasion resistance, dry 3-5 0.57 1376 400 442 27.5 70
increased loft 3-6 0.57 1130 398 489 24 85 lower loft 3-7 0.57 1090
408 484 24 85 good loft, dry, soft 3-8 0.57 1090 409 485 20 85 3-9
0.57 1090 409 485 15 85 loose loft, soft
Example 4
[0080] In Example 4, fabrics were prepared using 90 wt % Component
A and 10 wt % Component B2 at varying throughput rates, air
temperatures, die pressures, and water quench rates. The resulting
fabrics were observed visually and tactilely, and the results are
reported in Table 4.
TABLE-US-00004 TABLE 4 (10% PP3885) Air Water Quench Through- Die
Melt Air Pressure (top unit Run put Pressure Temp. Temp. at Die
only) (% of No. (ghm) (psi) (.degree. F.) (.degree. F.) (psi)
maximum) Observations 4-1 0.30 720 409 417 19 40 soft, lofty, low
lint 4-2 0.57 1215 406 410 25 100 low loft, ropey 4-3 0.57 1205 406
410 27 100 better loft 4-4 0.57 1000 412 484 27 100 soft, lofty,
low ropiness 4-5 0.57 1000 412 484 27 100 soft, lofty, low ropiness
4-6 0.57 1000 412 484 27 100 soft, lofty, a little more ropey
Example 5
[0081] In Example 5, fabrics were prepared using 90 wt % Component
A and 10 wt % Component B3 at varying throughput rates, air
temperatures, die pressures, and water quench rates. The resulting
fabrics were observed visually and tactilely, and the results are
reported in Table 5.
TABLE-US-00005 TABLE 5 (10% VM2330) Air Water Quench Through- Die
Melt Air Pressure (top unit Run put Pressure Temp. Temp. at Die
only) (% of No. (ghm) (psi) (.degree. F.) (.degree. F.) (psi)
maximum) Observations 5-1 0.30 960 370 368 22.5 40 soft, lofty,
ropey 5-2 0.30 710 388 406 14 60 5-3 0.57 1280 389 404 25 40 low
loft, slightly ropey 5-4 0.57 1216 387 423 20 100 better loft, less
ropey
Example 6
[0082] In Comparative Example 6, fabrics were prepared using 100 wt
% Component B4 at varying throughput rates, air temperatures, die
pressures, and water quench rates. The resulting fabrics were
observed visually and tactilely, and the results are reported in
Table 6.
TABLE-US-00006 TABLE 6 (PP3546G) Through- Melt Air Run put Temp.
Temp. Air Water No. (ghm) (.degree. F.) (.degree. F.) Rate Quench
Observations 6-1 0.30 408 416 20.5 50 soft, lofty, low lint 6-2
0.30 408 416 20.5 50 soft, lofty, low lint 6-3 0.57 410 414 25 100
soft, lofty, low lint
[0083] As reflected in the Examples and Tables above, the addition
of a small amount of a lower MFR polymer or a polymer with a triad
tacticity greater than about 0.94 or 0.95 or 0.96 (Component B) to
a high MFR metallocene-catalyzed reactor grade homopolypropylene
(Component A) helps to improve loft and reduce ropiness (i.e., poor
filament separation) in meltblown nonwoven fabrics made from the
polymer blend. The addition of a second polymer is believed to
improve the solidification rate of the first polymer by either
increasing the elongation viscosity which allows higher process
temperatures and therefore higher water quench rates for faster
cooling without leaving high residual moisture or by increasing the
crystallization rate by nucleating the metallocene polymer. Faster
solidification or crystallization tends to produce more loft in the
fabric.
[0084] Table 7 (Blends of metallocene-catalyzed polypropylene
meltblown with Ziegler-Natta meltblown). Blend 1=10 wt % of
Component A (a Ziegler-Natta-catalyzed polypropylene having a MFR
of 400 gr/min) and 90 wt % of Component B (a metallocene-catalyzed
polypropylene having a MFR of 1400 gr/min) and Blend 2=20 wt % of
Component A and 80 wt % of Component B, the wt % based upon total
weight of the blend:
TABLE-US-00007 TABLE 7 Die/Air Die/Air Air Air Temp Temp Melt Thru
Rate Permeability Shot Set actual at Die put DCD Actual HH HH (cm3/
Rating Visual Comments Resin (.degree. F.) (.degree. F.) (.degree.
F.) ghm in SCFM mbar in cm2/sec) * shot Quality Component B 480 475
458 0.6 200 350 76.0 30.5 52 2.0 low- Slightly stiff, uniform mod
Component B 480 481 456 0.6 250 400 73.1 29.4 61 1.5 low Soft,
fairly uniform Component B 510 511 486 0.6 250 298 64.3 25.8 48 2.5
mod Very soft, fairly uniform Component B 510 507 486 0.75 200 247
50.1 20.1 55 2.5 mod- Slightly stiff, uniform heavy Component B 510
505 484 0.75 250 298 58.9 23.7 56 2.3 mod Fairly uniform, slightly
stiff Blend 1 480 480 0.6 200 400 65.3 26.2 69 1.3 low Slightly
stiff, uniform Blend 1 480 476 0.6 250 400 56.8 22.8 84 0.8 low
Slightly stiff, fairly uniform Blend 1 480 481 0.6 250 475 65.6
26.3 64 0.8 very Soft, fairly uniform low Blend 1 480 486 0.6 200
450 73.0 29.3 52 1.5 low Soft, fairly uniform Blend 2 510 510 480
0.6 200 425 71.1 28.6 52 1.3 low Soft, very uniform Blend 2 510 512
483 0.6 250 425 70.1 28.2 58 1.0 very Soft, uniform low Blend 2 510
514 486 0.75 200 425 61.6 24.7 54 1.8 low- Slightly stiff, very mod
uniform Blend 2 510 512 486 0.75 250 450 63.9 25.7 63 1.0 low
Slightly stiff, very uniform * Comparison to reference fabrics
having different levels of shot.
[0085] Table 7 (series 2.9-2.18) shows the process conditions and
properties of a melt blown fabric made with a metallocene catalyzed
polymer (.about.1400MFR). Blending a lower MFR polymer made with a
Z--N catalyst (Blend 1 with a 400 MFR reactor grade) allows the
production of fabrics with lower levels of shot at moderately high
throughput rates (0.6 ghm) even at fairly low process temperatures
(480.degree. F.). At high throughput rates (0.75 ghm) and/or high
process temperatures (510.degree. F.), Blend 2 allows the
production of fabrics with greatly reduced shot levels and improved
barrier properties (higher hydrohead or "HH").
[0086] The present invention can be further described as
follows:
1. A nonwoven fabric made from a polymer composition
comprising:
[0087] a. from about 70 to about 99.9 wt %, based on the total
weight of the composition, of a first propylene-based polymer
having a melt flow rate of from about 100 to about 5,000 g/10 min;
and
[0088] b. from about 0.1 to about 30 wt % of a second
propylene-based polymer having a melt flow rate of from about 1 to
about 500 g/10 min, wherein the second propylene-based polymer has
at least one of: (i) a lower melt flow rate than the first
propylene-based polymer; or (ii) a higher crystallinity than the
first propylene-based polymer;
[0089] wherein the first propylene-based polymer is prepared using
a catalyst system comprising a metallocene catalyst.
2. The fabric of 1, wherein the polymer composition comprises from
about 5 to about 15% by weight of the second propylene-based
polymer. 3. The fabric of 1, wherein the second propylene-based
polymer is prepared using a catalyst system comprising a
Ziegler-Natta catalyst. 4. The fabric of 1, wherein the fabric is
meltblown. 5. The fabric of 1, wherein the first propylene-based
polymer is a propylene homopolymer. 6. The fabric of 5, wherein the
first propylene-based polymer is a reactor grade propylene
homopolymer. 7. The fabric of 1, wherein the second propylene-based
polymer is a propylene homopolymer. 8. The fabric of 1, wherein the
second propylene-based polymer further comprises from 0.01 to 25%
by weight of the second polymer of one or more comonomers selected
from C.sub.2 and/or C.sub.4-C.sub.10 alpha-olefins. 9. The fabric
of 1, wherein the first propylene-based polymer has a melt flow
rate of from about 500 to about 3000 g/10 min. 10. The fabric of 1,
wherein the second propylene-based polymer has a melt flow rate of
from about 1 to about 250 g/10 min. 11. The fabric of 1, wherein
the second propylene-based polymer has a melt flow rate of from
about 1 to about 50 g/10 min. 12. The fabric of 1, wherein the
first polymer has a triad tacticity of greater than about 0.94. 13.
The fabric of 1, wherein the second propylene-based polymer has a
higher triad tacticity than the first propylene-based polymer. 14.
The fabric of 1, wherein the first propylene-based polymer has a
meso run length, as determined by .sup.13C NMR, greater than about
75. 15. An article comprising the fabric of 1. 16. The article of
15, wherein the article is selected from one or more of a hygiene
product, a medical product, a filter medium, an oil sorbent
product, a water sorbent product, or a chemical sorbent product.
17. A process for producing nonwoven fabrics comprising:
[0090] a. forming a molten polymer composition comprising: (i) from
about 70 to about 99.9 wt %, based on the total weight of the
composition, of a first propylene-based polymer prepared using a
catalyst system comprising a metallocene catalyst and having a melt
flow rate of from about 100 to about 5,000 g/10 min; and (ii) from
about 0.1 to about 30 wt % of a second propylene-based polymer
having a melt flow rate of from about 1 to about 500 g/10 min
wherein the second propylene-based polymer has at least one of: (i)
a lower melt flow rate than the first propylene-based polymer; or
(ii) a higher crystallinity than the first propylene-based
polymer;
[0091] b. forming fibers comprising the polymer composition using a
meltblown process; and
[0092] c. forming a fabric from the fibers.
18. The process of 17, wherein the second propylene-based polymer
has a higher triad tacticity than the first propylene-based
polymer. 19. The process of 17, wherein the second propylene-based
polymer is prepared using a catalyst system comprising a
Ziegler-Natta catalyst. 20. The process of 17, wherein the first
propylene-based polymer is a propylene homopolymer. 21. The process
of 20, wherein the first propylene-based polymer is a reactor grade
propylene homopolymer. 22. The process of 17, wherein the second
propylene-based polymer is a propylene homopolymer. 23. The process
of 17, wherein the second propylene-based polymer further comprises
from 0.01 to 25% by weight of the second polymer of one or more
comonomers selected from C.sub.2 and/or C.sub.4-C.sub.10
alpha-olefins. 24. The process of 17, wherein the first
propylene-based polymer has a melt flow rate of from about 500 to
about 3000 g/10 min. 25. The process of 17, wherein the first
propylene-based polymer has an MWD of from about 1.0 to about 4.0.
26. The process of 17, wherein the first propylene-based polymer
has a meso run length, as determined by .sup.13C NMR, greater than
about 75. 27. The process of 17, wherein the fibers are formed
using an extruder having a throughput rate of from about 0.1 to
about 3 ghm. 28. The process of 27, wherein the throughput rate is
from about 0.3 to about 1.0 ghm. 29. The process of 27, wherein the
melt temperature of the extruder is from about 175.degree. C. to
about 290.degree. C. 30. The process of 17, wherein the air
temperature of the meltblown process is from about 175.degree. C.
to about 290.degree. C. 31. The process of 17, wherein the air
pressure at the die of the meltblown process is about 10 kPa to
about 215 kPa. 32. The process of 17, wherein the fabric has a
basis weight of from about 0.1 to about 500 g/m.sup.2.
[0093] 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.
[0094] Various terms have been defined above. 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.
[0095] 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.
* * * * *