U.S. patent application number 16/691128 was filed with the patent office on 2020-07-02 for propylene-based spunbond fabrics with faster crystallization time.
The applicant listed for this patent is ExxonMobil Chemical Patents Inc.. Invention is credited to Saifudin M. Abubakar, Qi Song.
Application Number | 20200208315 16/691128 |
Document ID | / |
Family ID | 68916592 |
Filed Date | 2020-07-02 |
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United States Patent
Application |
20200208315 |
Kind Code |
A1 |
Abubakar; Saifudin M. ; et
al. |
July 2, 2020 |
Propylene-Based Spunbond Fabrics With Faster Crystallization
Time
Abstract
A method of forming filaments can include: extruding a polymer
composition to form a plurality of filaments, wherein the polymer
composition comprises 75 wt % to 99 wt % of a propylene-ethylene
copolymer, 0.5 wt % to 15 wt % of a propylene-based thermoplastic
polymer, and 0.005 wt % to 1 wt % of a nucleator; and forming a
spunbond material from the plurality of filaments.
Inventors: |
Abubakar; Saifudin M.;
(Shanghai, CN) ; Song; Qi; (Shanghai, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Chemical Patents Inc. |
Baytown |
TX |
US |
|
|
Family ID: |
68916592 |
Appl. No.: |
16/691128 |
Filed: |
November 21, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62785261 |
Dec 27, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08L 23/16 20130101;
D10B 2321/022 20130101; D04H 3/007 20130101; D10B 2321/021
20130101; D04H 1/56 20130101; D04H 3/14 20130101; C08L 23/16
20130101; C08L 23/12 20130101 |
International
Class: |
D04H 1/56 20060101
D04H001/56 |
Claims
1. A method comprising: extruding a polymer composition to form a
plurality of filaments, wherein the polymer composition comprises
75 wt % to 99 wt % of a propylene-ethylene copolymer, 0.5 wt % to
15 wt % of a propylene-based thermoplastic polymer, and 0.005 wt %
to 1 wt % of a nucleator; and forming a spunbond material from the
plurality of filaments.
2. The method of claim 1, wherein the propylene-ethylene copolymer
has an ethylene content of 1.5 wt % to 20 wt % and a propylene
content of 80 wt % to 98.5 wt % based upon the total weight of the
propylene-ethylene copolymer.
3. The method of claim 1, wherein the propylene-ethylene copolymer
has a melt flow rate (MFR) (ASTM D-1238, 2.16 kg weight @
230.degree. C.) of 10 g/10 min to 120 g/10 min.
4. The method of claim 1, wherein the propylene-based thermoplastic
polymer is a homopolymer of propylene.
5. The method of claim 1, wherein the propylene-based thermoplastic
polymer is a random propylene copolymer having a comonomer content
of 4 wt % or less based upon the total weight of the random
propylene copolymer.
6. The method of claim 1, wherein the polymer composition consists
of the propylene-ethylene copolymer, the propylene-based
thermoplastic polymer, and the nucleator.
7. The method of claim 1, wherein the polymer composition consists
of the propylene-ethylene copolymer, the propylene-based
thermoplastic polymer, the nucleator, and a slip aid.
8. The method of claim 1, wherein the polymer composition further
comprises one or more additives selected from the group consisting
of a stabilizer, an antioxidant, a filler, a slip aid, a colorant,
a mold release agent, a wax, and a processing oil.
9. The method of claim 1, wherein the polymer composition is
extruded through a spinneret at a melt temperature of 270.degree.
C. or less, thereby forming the plurality of filaments.
10. A spunbond fabric made by the method of claim 1.
11. A spunbond fabric having a machine direction (MD) and a cross
direction (CD) comprising a polymer composition that comprises 75
wt % to 99 wt % of a propylene-ethylene copolymer, 0.5 wt % to 15
wt % of a propylene-based thermoplastic polymer, and 0.005 wt % to
1 wt % of a nucleator.
12. The spunbond fabric of claim 11, wherein the propylene-ethylene
copolymer has an ethylene content of 1.5 wt % to 20 wt % and a
propylene content of 80 wt % to 98.5 wt % based upon the total
weight of the propylene-ethylene copolymer.
13. The spunbond fabric of claim 11, wherein the propylene-ethylene
copolymer has a melt flow rate (MFR) (ASTM D-1238, 2.16 kg weight @
230.degree. C.) of 10 g/10 min to 120 g/10 min.
14. The spunbond fabric of claim 11, wherein the propylene-based
thermoplastic polymer is a homopolymer of propylene.
15. The spunbond fabric of claim 11, wherein the propylene-based
thermoplastic polymer is a random propylene copolymer having a
comonomer content of 4 wt % or less based upon the total weight of
the random propylene copolymer.
16. The spunbond fabric of claim 11, wherein the polymer
composition consists of the propylene-ethylene copolymer, the
propylene-based thermoplastic polymer, and the nucleator.
17. The spunbond fabric of claim 11, wherein the polymer
composition consists of the propylene-ethylene copolymer, the
propylene-based thermoplastic polymer, the nucleator, and a slip
aid.
18. The spunbond fabric of claim 11, wherein the polymer
composition further comprises one or more additives selected from
the group consisting of a stabilizer, an antioxidant, a filler, a
slip aid, a colorant, a mold release agent, a wax, and a processing
oil.
19. The spunbond fabric of claim 11, wherein the spunbond fabric
exhibits a permanent set of 20% or less in either or both of the MD
and the CD, said permanent set being determined on the basis of
said spunbond fabric having a basis weight of greater than 10
gsm.
20. The spunbond fabric of claim 11, wherein the spunbond fabric
exhibits either or both of (i) a 50% unloading force in the MD less
than or equal to 2.5 N/5 cm, and (ii) a 50% unloading force in the
CD less than or equal to 0.9 N/5 cm, said 50% unloading force
determined on the basis of said spunbond fabric having a basis
weight of 10 gsm or greater.
21. The spunbond fabric of claim 11, wherein the spunbond fabric
exhibits a hysteresis of 45% or less in either or both of the MD
and the CD of the spunbond fabric, said hysteresis being determined
on the basis of said spunbond fabric having a basis weight of 10
gsm or greater.
22. The spunbond fabric of claim 11, wherein the spunbond fabric
exhibits either or both of (i) a peak load of 20 N or less in the
MD, and (ii) a peak load of 10 N or less in the CD, said peak loads
being determined on the basis of said spunbond fabric having a
basis weight of 10 gsm or greater.
23. An article formed from the spunbond fabric of claim 11.
24. The article of claim 23, wherein the article is selected from
the group consisting of diaper tabs, side panels, leg cuffs, top
sheet, back sheet, tapes, feminine hygiene articles, swim pants,
infant pull up pants, incontinence wear components, and bandages.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Ser. No.
62/785,261, filed Dec. 27, 2018, herein incorporated by
reference.
BACKGROUND
[0002] The present disclosure relates to methods for forming
spunbond materials from polymer compositions, and to composites and
articles formed from such spunbond materials.
[0003] Nonwoven fabrics comprised of processed polymers are in high
demand for their use in multiple kinds of products including
clothing and hygienic fabrics such as diapers, surgical masks,
surgical gowns, and the like. Of the nonwoven fabrics, spunbond
fabrics are particularly attractive because of the breathability
such fabrics offer. In addition, many spunbond process lines are in
existence, which allows for a substantial degree of manufacturing
throughput.
[0004] Spunbond processes typically involve passing a polymer
composition through an extruder (optionally in combination with one
or more additives such as coloring agents, resin modifiers, and the
like), in which the polymer composition is melted. The molten
polymer composition passes through a spinneret comprising a
plurality of small holes through which the molten polymer
composition passes, thereby forming molten polymer composition
filaments. Cool or quench air is passed over the filaments as they
exit, with the aim of cooling the filaments so as to solidify them,
before they are deposited onto a collection surface such as a
moving belt where the filaments form a web. Frequently, spunbond
processes employ some means of bonding to bond the filaments of the
web together as they move along the collection surface. Examples
include hydroentanglement, needlepunching, thermal bonding, and
chemical bonding. After the fabrics are bonded, they may be further
treated as they move farther along the moving collection belt
(e.g., by dyeing, resin coating, or the like), after which they are
rolled up and ready for shipment. For more details on spunbond
processes in general, see Lim, H. A Review of Spun Bond Process.
Journal of Textile and Apparel, Technology and Management, Vol. 6,
Issue 3 (Spring 2010).
[0005] Typically, polymers such as styrene-block copolymers, olefin
block copolymers (OBCs), thermoplastic polyurethanes (TPUs),
polyester-polyurethane copolymers (such as spandex, also known as
elastane), polypropylenes, high density polyethylenes, polyesters,
polyamides, and others are used in the polymer compositions in
these spunbond processes. An alternative to such polymer
compositions typically used in spunbond processes is desired.
[0006] Various attempts at using polymer compositions comprising
100% or nearly 100% of an elastomer such as a propylene-ethylene
copolymer have been made. The difficulty encountered in such
attempts is one of trade-offs: in order to obtain properties
suitable for processing of the polymer composition (e.g., one or
more of sufficiently high MFR, melt strength, and crystallinity,
and/or sufficiently rapid crystallizability), the elasticity of the
final product is frequently impaired. For instance, chain scission
of polymer chains to result in shorter average chains (and
therefore higher MFR, as desired for good processability) tends to
impair the elasticity of the resulting article. To overcome these
shortfalls in elastomeric compositions such as propylene-ethylene
copolymers, blends are frequently used instead, combining high-MFR
polymers with low-MFR polymers, and/or combining high- and
low-crystallinity polymers, to form the polymer composition to be
processed into spunbond and other nonwoven materials. While some of
these solutions may provide the desired processability, they suffer
from excessive complication, poor elastic properties of the
resultant nonwoven, or both. On the other hand, modifying the
compositions to improve simplicity and/or elasticity of the end
product frequently results in compositions that are not easily
processed. Obtaining a suitably low MFR for the maintenance of
elastic properties typically requires the extrusion of the polymer
composition to be operated at higher temperatures; however, this,
in turn, means that the polymer composition will not crystallize as
readily or as quickly upon being extruded, such that, by the time
it is deposited onto a collecting surface from the extruder, it
will still be too tacky and amorphous, making it incapable of
further adequate processing (e.g., further bonding, calendering,
rolling up, and the like).
[0007] Background references may include U.S. Pat. Nos. 6,218,010;
6,342,565; 6,525,157; 6,635,715; 7,863,206; and 8,013,093 that
describe previous attempts to use propylene-ethylene copolymers in
spunbonding processes. This attempt encountered significant
difficulty in processing the propylene-ethylene copolymer, such
that significant amounts of high-MFR polypropylene were required in
the blend just to obtain suitable processability (which
significantly impaired the desired elasticity and tensile strength
of the resulting nonwovens).
SUMMARY
[0008] The present disclosure relates to methods for forming
spunbond materials from polymer compositions, and to composites and
articles formed from such spunbond materials. More specifically,
the present invention uses a nucleator in conjunction with a
propylene-ethylene copolymer to decrease the polymer
crystallization time, which makes the propylene-ethylene copolymer
more processable.
[0009] A first embodiment is a method comprising: extruding a
polymer composition to form a plurality of filaments, wherein the
polymer composition comprises 75 wt % to 99 wt % of a
propylene-ethylene copolymer, 0.5 wt % to 15 wt % of a
propylene-based thermoplastic polymer, and 0.005 wt % to 1 wt % of
a nucleator; and forming a spunbond material from the plurality of
filaments.
[0010] A second embodiment is a spunbond fabric made by the method
of the first embodiment.
[0011] A third embodiment is a spunbond fabric having a machine
direction (MD) and a cross direction (CD) comprising a polymer
composition that comprises 75 wt % to 99 wt % of a
propylene-ethylene copolymer, 0.5 wt % to 15 wt % of a
propylene-based thermoplastic polymer, and 0.005 wt % to 1 wt % of
a nucleator.
[0012] A fourth embodiment is an article formed from the spunbond
fabric of the third embodiment. The article may be selected from
the group consisting of diaper tabs, side panels, leg cuffs, top
sheet, back sheet, tapes, feminine hygiene articles, swim pants,
infant pull up pants, incontinence wear components, and
bandages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The following figures are included to illustrate certain
aspects of the embodiments, and should not be viewed as exclusive
embodiments. The subject matter disclosed is capable of
considerable modifications, alterations, combinations, and
equivalents in form and function, as will occur to those skilled in
the art and having the benefit of this disclosure.
[0014] FIG. 1 is an illustration of a typical hysteresis curve
provided for purposes of illustrating the determination of various
elasticity properties described herein.
[0015] FIG. 2 is an illustration of an ideal hysteresis curve.
[0016] FIG. 3 is the 100% hysteresis curve for the first cycle in
the machine direction (MD) for control and nucleated inventive
samples.
[0017] FIG. 4 is the 100% hysteresis curve for the second cycle in
the MD for control and nucleated inventive samples.
[0018] FIG. 5 is the 100% hysteresis curve for the first cycle in
the cross direction (CD) for control and nucleated inventive
samples.
[0019] FIG. 6 is the 100% hysteresis curve for the second cycle in
the CD for control and nucleated inventive samples.
DETAILED DESCRIPTION
[0020] The present disclosure relates to methods for forming
spunbond materials from polymer compositions, and to composites and
articles formed from such spunbond materials. More specifically,
the present invention uses a nucleator in conjunction with a
propylene-ethylene copolymer to decrease the polymer
crystallization time, which makes the propylene-ethylene copolymer
more processable.
[0021] The compositions of the present invention include polymer
compositions that comprise 75 wt % to 99 wt % of a
propylene-ethylene copolymer, 0.5 wt % to 15 wt % of a
propylene-based thermoplastic polymer, and 0.005 wt % to 1 wt % ppm
of a nucleator. Without being limited by theory, it is believed
that as spunbond filaments of the foregoing composition cool and
solidify, the nucleator causes the propylene-based thermoplastic
polymer to crystallize more rapidly than in the absence of the
nucleator. Then, the crystallized propylene-based thermoplastic
polymer acts as nucleation sites for the propylene-ethylene
copolymer to crystallize Therefore, the entire polymer composition
crystallizes more quickly than without the nucleator.
Propylene-Ethylene Copolymer
[0022] The propylene-ethylene copolymer is preferably a
propylene-ethylene random copolymer having crystalline regions
interrupted by non-crystalline regions. Without being limited by
theory, it is believed that the non-crystalline regions may result
from regions of non-crystallizable polypropylene segments and/or
the inclusion of comonomer units. The crystallinity and the melting
point of the propylene-ethylene random copolymer are reduced
compared to highly isotactic polypropylene by the introduction of
errors (stereo and region defects) in the insertion of propylene
and/or by the presence of comonomer.
[0023] Preferably, however, the introduction of comonomer is
limited to specific amounts, so as to maintain adequately high
crystallinity of the copolymer for spunbond processing purposes.
Thus, the copolymer preferably has an ethylene content of about 1.5
wt % to about 20 wt %, or about 5 wt % to about 10 wt %, or about
10 wt % to about 15 wt % based upon the total weight of the
propylene-ethylene copolymer. Propylene-derived units form the
balance of the copolymer of such embodiments (that is, the
copolymer comprises about 80 wt % to about 98.5 wt % propylene, or
about 90 wt % to about 95 wt %, or about 85 wt % to about 90 wt
%).
[0024] The propylene-ethylene copolymer has a melt flow rate (MFK)
of about 10 g/10 min (dg/min) to about 120 g/10 min, or about 15
g/10 min to about 100 g/10 min, or about 25 g/10 min to about 50
g/10 min, or about 10 g/10 min to about 40 g/10 min. The MFR is
measured in accordance with ASTM D1238-13 at 230.degree. C. and
2.16 kg weight.
[0025] The propylene-ethylene copolymer may have a single peak
melting transition as determined by differential scanning
calorimetry (DSC). In one embodiment, the copolymer has a primary
peak transition of about 60.degree. C. to about 70.degree. C.
(preferably about 60.degree. C. to about 65.degree. C.), with a
broad end-of-melt transition of about 80.degree. C. to about
105.degree. C., such as about 85.degree. C. to about 95.degree. C.,
or about 88.degree. C. to about 92.degree. C.
[0026] The peak "melting point" ("T.sub.m") is defined as the
temperature of the greatest heat absorption within the range of
melting of the sample. However, the copolymer may show secondary
melting peaks adjacent to the principal peak, and/or at the
end-of-melt transition. For the purposes of this disclosure, such
secondary melting peaks are considered together as a single melting
point, with the highest of these peaks being considered the T.sub.m
of the copolymer. The propylene-ethylene copolymer may have a
T.sub.m ranging from a low of any one of about 58.degree. C.,
59.degree. C., 60.degree. C., 61.degree. C., 62.degree. C.,
63.degree. C., 64.degree. C., and 65.degree. C., to a high of any
one of about 62.degree. C., 63.degree. C., 64.degree. C.,
65.degree. C., 66.degree. C., 67.degree. C., 68.degree. C.,
69.degree. C., and 70.degree. C., provided the high is greater than
the low.
[0027] The method of determination by DSC is as follows: DSC data
may be obtained using a Perkin-Elmer DSC 7. About 5 mg to about 10
mg of a sheet of the polymer to be tested should be pressed at
approximately 200.degree. C. to 230.degree. C., then removed with a
punch die and annealed at room temperature for 48 hours. The
samples should then be sealed in aluminum sample pans. The DSC data
should be recorded by first cooling the sample to -50.degree. C.
and then gradually heating it to 230.degree. C. at a rate of
10.degree. C./minute. Keep the sample at 230.degree. C. for 10
minutes before a second cooling-heating cycle is applied. Both the
first and second cycle thermal events should be recorded. The
melting temperature is measured and reported during the second
heating cycle (or second melt).
[0028] The DSC procedure may be continued to determine the heat of
fusion and the degree of crystallinity of the polymer sample. The
percent crystallinity (X %) should be calculated using the formula,
X %=[area under the curve (Joules/gram)/B(Joules/gram)]*100, where
B is the heat of fusion for the homopolymer of the major monomer
component. These values for B may be found from the Polymer
Handbook, Fourth Edition, published by John Wiley and Sons, New
York 1999. A value of 189 J/g (B) is used as the heat of fusion for
100% crystalline polypropylene, the major component of the
propylene-ethylene copolymer of various embodiments described
herein.
[0029] The propylene-ethylene copolymer may have heat of fusion
(H.sub.f) of about 17.5 to about 25 J/g, or about 18 to about 22
J/g, or about 19 to about 20 J/g. The propylene-ethylene copolymer
may have a percent crystallinity of about 5% to about 15%, or about
9% to about 11%, or about 10% to about 10.5%. H.sub.f and percent
crystallinity are determined according to the DSC procedure as
described above.
[0030] The propylene-ethylene copolymer may have a density of about
0.850 g/cm.sup.3 to about 0.920 g/cm.sup.3, or about 0.860
g/cm.sup.3 to about 0.890 g/cm.sup.3, or about 0.860 g/cm.sup.3 to
about 0.870 g/cm.sup.3, at room temperature as measured per ASTM
D1505-18.
[0031] The propylene-ethylene copolymer may have a weight average
molecular weight ("Mw") of about 100,000 g/mole to about 130,000
g/mole, or about 115,000 g/mole to about 125,000 g/mol. The
propylene-ethylene copolymer may have a number average molecular
weight ("Mn") of about 40,000 g/mole to about 60,000 g/mole, or
about 50,000 g/mole to about 55,000 g/mol. The propylene-ethylene
copolymer may have a z-average molecular weight ("Mz") of about
180,000 g/mole to about 200,000 g/mole, or about 185,000 g/mole to
about 195,000 g/mol. The propylene-ethylene copolymer may have a
molecular weight distribution MWD (defined as Mw/Mn) ranging from
about 1.6 to about 3.25, or about 1.75 to about 2.25, or about 1.9
to about 2.1.
[0032] The propylene-ethylene copolymer may have a Shore A Hardness
(as determined in accordance with ASTM D2240-15e1) of about 60 to
about 80, or about 65 to about 75, or about 69 to about 72.
[0033] The Vicat softening temperature of the propylene-ethylene
copolymer (determined in accordance with ASTM D1525-17e1) may be
about 40.degree. C. to about 60.degree. C., or about 48.degree. C.
to about 52.degree. C., or about 49.degree. C. to about 52.degree.
C.
[0034] Processes suitable for preparing the propylene-ethylene
copolymer may in some embodiments include metallocene-catalyzed or
Ziegler-Natta catalyzed processes, including solution, gas-phase,
slurry, and/or fluidized bed polymerization reactions. Suitable
polymerization processes are described in, for example, U.S. Pat.
Nos. 4,543,399; 4,588,790; 5,001,205; 5,028,670; 5,317,036;
5,352,749; 5,405,922; 5,436,304; 5,453,471; 5,462,999; 5,616,661;
5,627,242; 5,665,818; 5,668,228; and 5,677,375; PCT Publications WO
96/33227 and WO 97/22639; and European Publications EP-A-0 794 200,
EP-A-0 802 202, and EP-B-634 421, the entire contents of which are
incorporated herein by reference.
[0035] In certain preferred embodiments, the propylene-ethylene
copolymer is a reactor blend. That is, it is a blend of effluents
from two or more polymerization reactor zones, such as parallel
solution polymerization reactors, each zone including a
metallocene-catalyzed polymerization process. Particularly suitable
are those polymerization processes and reactors as described in
U.S. Pat. Nos. 6,881,800 and 8,425,847, which are incorporated
herein by reference.
[0036] Although propylene-ethylene copolymers are described above
as having only two monomers (i.e., propylene and ethylene), in some
embodiments, the propylene-ethylene copolymers can have a comonomer
in addition to ethylene, and/or having comonomer(s) different from
ethylene, so long as the MFR, T.sub.m, and crystallinity (or
H.sub.f) of the propylene-ethylene copolymers remain within the
ranges described above with respect to the propylene-ethylene
copolymers. For instance, the propylene-ethylene copolymers may be
a propylene-.alpha.-olefin copolymer comprising units derived from
propylene and one or more comonomer units derived from a C.sub.4 to
C.sub.20 .alpha.-olefin in addition to, or instead of, ethylene.
The propylene-.alpha.-olefin copolymer may optionally further
comprise one or more comonomer units derived from dienes. In some
embodiments, then, the .alpha.-olefin comonomer units may derive
from, for example, 1-butene, 1-hexane, 4-methyl-1-pentene and/or
1-octene. In one or more embodiments, the diene comonomer units may
derive from 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene,
divinyl benzene, 1,4-hexadiene, 5-methylene-2-norbornene,
1,6-octadiene, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene,
1,3-cyclopentadiene, 1,4-cyclohexadiene, dicyclopentadiene, or a
combination thereof.
[0037] The polymer compositions described herein can include 75 wt
% to 99 wt % of a propylene-ethylene copolymer, or 80 wt % to 99 wt
% of a propylene-ethylene copolymer, or 90 wt % to 99 wt % of a
propylene-ethylene copolymer.
Propylene-Based Thermoplastic Polymer
[0038] As described above, the propylene-based thermoplastic
polymer is believed to crystallize first and act as a nucleator for
the crystallization of the propylene-ethylene copolymer. The
polymer compositions described herein can include 0.5 wt % to 15 wt
% of a propylene-based thermoplastic polymer, or 1 wt % to 10 wt %
of a propylene-based thermoplastic polymer, or 0.5 wt % to 5 wt %
of a propylene-based thermoplastic polymer.
[0039] Propylene-based thermoplastic polymers include those
polymers that primarily comprise units derived from the
polymerization of propylene. In certain embodiments, at least 96%
of the units of the propylene-based thermoplastic polymer derive
from the polymerization of propylene. That is, the propylene-based
thermoplastic polymer may be a random propylene copolymer having a
comonomer content of 4 wt % or less based upon the total weight of
the random propylene copolymer. Example of comonomers include the
.alpha.-olefin comonomer units described above relative to the
propylene-ethylene copolymers. Alternatively, the propylene-based
thermoplastic polymer is a homopolymer of polypropylene.
[0040] The propylene-based thermoplastic polymers may have a
melting temperature (T.sub.m) that is greater than 120.degree. C.,
or greater than 155.degree. C., or greater than 160.degree. C. In
some embodiments, the propylene-based thermoplastic polymers may
have a T.sub.m that is less than 180.degree. C., or less than
170.degree. C., or less than 165.degree. C.
[0041] The propylene-based thermoplastic polymers may have a heat
of fusion (H.sub.f) that is equal to or greater than 80 J/g, or
greater than 100 J/g, in or greater than 125 J/g, or greater than
140 J/g as measured by DSC.
[0042] The propylene-based thermoplastic polymers may include
crystalline and semi-crystalline polymers. These polymers may be
characterized by a crystallinity of at least 40% by weight, or at
least 55% by weight, or at least 65%, or at least 70% by weight as
determined by DSC. Crystallinity may be determined by dividing the
heat of fusion of a sample by the heat of fusion of a 100%
crystalline polymer, which is assumed to be 189 J/g for isotactic
polypropylene.
[0043] In general, the propylene-based thermoplastic polymers may
be synthesized having a broad range of molecular weight and/or may
be characterized by a broad range of MFR. For example, the
propylene-based thermoplastic polymers can have an MFR of at least
2 g/10 min, or at least 4 g/10 min, or at least 6 g/10 min, or at
least 10 g/10 min, where the MFR is measured according to ASTM
D1238-13, 2.16 kg at 230.degree. C. In some embodiments, the
propylene-based thermoplastic polymer can have an MFR of less than
2,000 g/10 min, or less than 400 g/10 min, or less than 250 g/10
min, or less than 100 g/10 min, or less than 50 g/10 min, where the
MFR is measured according to ASTM D1238-13, 2.16 kg at 230.degree.
C.
[0044] The propylene-based thermoplastic polymers may have an Mw of
from about 50 to about 2,000 kg/mole, or from about 100 to about
600 kg/mole. They may also have a Mn of from about 25 kg/mole to
about 1,000 kg/mole, or from about 50 kg/mole to about 300 kg/mole,
as measured by GPC with polystyrene standards.
[0045] The propylene-based thermoplastic polymers include a
homopolymer of a high-crystallinity isotactic or syndiotactic
polypropylene. This polypropylene can have a density of from about
0.85 g/cm.sup.3 to about 0.91 g/cm.sup.3, with the largely
isotactic polypropylene having a density of from about 0.90
g/cm.sup.3 to about 0.91 g/cm.sup.3. Optionally, the propylene
based thermoplastic polymer includes isotactic polypropylene having
a bimodal molecular weight distribution.
[0046] The propylene-based thermoplastic polymers may be
synthesized by any appropriate polymerization technique known in
the art such as, for example, slurry, gas phase, or solution, using
catalyst systems such as conventional Ziegler-Natta catalysts or
other single-site organometallic catalysts like metallocenes, or
non-metallocenes.
Nucleators
[0047] Nucleating agents can be present in the polymer compositions
of the present disclosure at 0.005 wt % to 1 wt %, or 0.01 wt % to
0.5 wt %, or 0.05 wt % to 0.1 wt %. The amount of nucleating agent
depends on the efficacy thereof. For example, sodium benzoate is a
relatively weak nucleator and should be used in higher
concentrations as compared to a more potent nucleator like
HYPERFORM.RTM. HPN-68L (available from Milliken Chemicals).
[0048] Examples of nucleating agents include, but are not limited
to, sodium benzoate, talc, HYPERFORM.RTM. additives (e.g.,
HPN-68L), MILLAD.RTM. additives (e.g., MILLAD.RTM. 3988, available
from Milliken Chemicals), and organophosphates (e.g., NA-11 and
NA-21, available from Amfine Chemicals).
[0049] The nucleator can be added to the components of the polymer
composition as is. Alternatively, the nucleator can be blended with
the propylene-based thermoplastic polymer before adding it to the
components of the polymer composition. Typically, this is called a
nucleator master batch.
Additives
[0050] The polymer compositions of some embodiments optionally
include one or more additives. Any additive known to be suitable in
a spunbonding process may be employed with the propylene-ethylene
copolymers.
[0051] In some preferred embodiments, any additives are present in
the polymer composition in an amount of 10 wt % or less, or 6 wt %
or less, such as 3 wt % or less. In various embodiments, the
additive(s) are present in amounts less than or equal to 10 wt %, 9
wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt %, 4 wt %, 3 wt %, 2 wt %, 1 wt
%, and 0.5 wt % based upon the weight of the polymer
composition.
[0052] Examples of additives include, but are not limited to,
stabilizers, antioxidants, fillers, slip aids (or, alternatively,
slip agents or slip additives), colorants, mold release agents,
waxes, and processing oils. Primary and secondary antioxidants
include, for example, hindered phenols, hindered amines, and
phosphites. Other additives such as dispersing agents, for example,
ACROWAX.TM. C (available from Lonza), can also be included.
Catalyst deactivators may also be used including, for example,
calcium stearate, hydrotalcite, and calcium oxide, and/or other
acid neutralizers known in the art.
[0053] In one or more embodiments, useful slip aids include those
compounds or molecules that are incompatible with the polymeric
matrix of the fibers and therefore migrate to the surface of the
fiber, once formed. In one or more embodiments, the slip aids form
a monolayer over the surface (or a portion thereof) of the fiber.
In these or other embodiments, useful slip aids are characterized
by relatively low molecular weight, which can facilitate migration
to the surface. Types of slip aids include fatty acid amides as
disclosed in Handbook of Antiblocking, Release and Slip Additives,
George Wypych, Page 23. Examples of fatty acid amides include, but
are not limited to, behenamide, erucamide, N-(2-hdriethyl)
erucamide, Lauramide, N,N'-ethylene-bis-oleamide, N,N'-ethylene
bisstearmide, oleamide, oleyl palmitamide, stearyl erucamide,
tallow amide, and mixtures thereof.
[0054] Other additives include, for example, fire/flame retardants,
plasticizers, vulcanizing or curative agents, vulcanizing or
curative accelerators, cure retarders, processing aids, and the
like. The aforementioned additives may also include fillers and/or
reinforcing materials, either added independently or incorporated
into an additive. Examples include carbon black, clay, talc,
calcium carbonate, mica, silica, silicate, combinations thereof,
and the like. Other additives which may be employed to enhance
properties include antiblocking agents or lubricants.
[0055] Any additive, may be included in the polymer composition in
neat form, or as a master batch. When additives are present as a
master batch, the % by weight of the additive master batch (that
is, the wt % of the carrier resin-plus-additive) is taken as the
amount of additive included in the polymer composition. Thus, where
an additive is included in master batch form, 10 wt % of that
additive would mean 10 wt % of the master batch (i.e., the combined
amount of carrier resin and additive would be 10 wt %). Any
suitable carrier resin may be used to form an additive master
batch, such as polypropylene, polyethylene, propylene-ethylene
copolymers, and the like.
Processing the Polymer Compositions
[0056] The formation of nonwoven fabrics from the foregoing polymer
compositions may include manufacture of fibers by extrusion. The
extrusion process may be accompanied by mechanical or aerodynamic
drawing of the fibers. The fiber and fabrics of the present
invention may be manufactured by any technique and/or equipment
known in the art, many of which are well known. For example,
spunbond nonwoven fabrics may be produced by spunbond nonwoven
production lines produced by Reifenhauser GmbH & Co., of
Troisdorf, Germany. The Reifenhauser system utilizes a slot drawing
technique as described in U.S. Pat. No. 4,820,142.
[0057] More particularly, spunbond or spunbonded fibers include
fibers produced, for example, by the extrusion of molten polymer
filaments from either a large spinneret having several thousand
holes or with banks of smaller spinnerets containing, for example,
as few as 40 holes. The temperature at which the spinneret is
operated (i.e., the "melt temperature" of the extruder) may be
about 270.degree. C. or less, or from about 180.degree. C. to about
260.degree. C., or about 200.degree. C. to about 250.degree. C.
That is, processes according to some embodiments may include
extruding the polymer composition through a spinneret at a
temperature of about 270.degree. C. or less, or from about
180.degree. C. to about 270.degree. C. Throughput preferably ranges
from about 0.10 ghm (gram/hole/min) to about 0.30 ghm, or from
about 0.15 ghm to about 0.25 ghm.
[0058] After exiting the spinneret, the molten filaments are
quenched by a cross-flow air quench system, then pulled away from
the spinneret and attenuated (drawn) by high speed air. There are
generally two methods of air attenuation, both of which use the
Venturi effect. The first method draws the filament using an
aspirator slot (slot draw), which may run the width of the
spinneret or the width of the machine. The second method draws the
filaments through a nozzle or aspirator gun. Filaments formed in
this manner may be collected on a collecting surface, such as a
screen ("wire") or porous forming belt to form a web of cooled
fibers. The web can then be passed through compression rolls and
then between heated calender rolls where raised lands on one or
both rolls bond the web at points covering, for example, 10% to 40%
of its area to form a nonwoven fabric (e.g., point-bonding). In
another embodiment, welding of the deposited fibers can also be
effected using convection or radiative heat. In yet another
embodiment, fiber welding can be effected through friction by using
hydro entangling or needle punch methods.
[0059] The fibers and/or webs may furthermore be annealed.
Annealing may be carried out after the formation of fiber in
continuous filament or fabrication of a nonwoven material from the
fibers. Annealing may partially relieve the internal stress in the
stretched fiber and restore the elastic recovery properties of the
blend 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 amorphous and semicrystalline
phases. This may lead 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), may be adequate for the
restoration of the elastic properties in the fiber.
[0060] Thermal annealing of the fibers can be conducted by
maintaining the fibers (or fabrics made from the fibers) at
temperatures, for example, between room temperature up to
160.degree. C., or alternatively to a maximum of 130.degree. C. for
a period between a few seconds to less than 1 hour. A typical
annealing period is 1 to 5 minutes at about 100.degree. C. The
annealing time and temperature can be adjusted based upon the
composition employed. In other embodiments, the annealing
temperature ranges from 60.degree. C. to 130.degree. C., or may be
about 100.degree. C.
[0061] In certain embodiments, for example conventional continuous
fiber spinning, annealing can be done by passing the fiber through
a heated roll (godet) without the application of conventional
annealing techniques. Annealing may desirably be accomplished under
very low fiber tension to allow shrinking of the fiber in order to
impart elasticity to the fiber. The above-referenced passing of
fibers through heated calender rolls may accomplish such annealing
steps. Similar to fiber annealing, the nonwoven web may desirably
be formed under low tension to allow for shrinkage of the web in
both machine direction (MD) and cross direction (CD) to enhance the
elasticity of the nonwoven web. In other embodiments, the bonding
calender roll temperature ranges from 35.degree. C. to 85.degree.
C., or at a temperature of about 60.degree. C. The annealing
temperature can be adjusted for any particular blend. These
calender roll temperatures may be less than typically used due to
the high concentration of the elastomer component (e.g.,
propylene-ethylene copolymer as described above) in the polymer
composition being processed.
Nonwoven Materials
[0062] The nonwoven material resulting from the processing of
various embodiments may be spunbond nonwoven material, e.g., a
spunbond fabric or fiber. The spunbond material may exhibit
hysteresis in either or both of the machine direction (MD) and
cross direction (CD) in a second cycle of testing of 45% or less,
or 10% to 45%, or 20% to 40%, or 25% to 35%. "Hysteresis" is
defined and determined according to the description in the
"Examples" section below for "hysteresis (%)."
[0063] The nonwoven material may also exhibit permanent set (after
2 cycles of testing) 0% to 20%, or 2% to 15% or 4% to 10% (again,
in either or both of the MD and CD).
[0064] The nonwoven material may further exhibit 50% unloading
force, on 2nd cycle and in either or both of MD and CD, of greater
than or equal to 0.1 N/5cm to 5.0 N/5 cm, or 0.5 N/5cm to 4.0 N/5
cm, or 1 N/5cm to 3.0 N/5 cm. The 50% unloading force can be
determined on the basis of a spunbond fabric having a basis weight
of 10 grams per square meter (gsm).
[0065] The nonwoven material may also or instead exhibit a peak
load of 10 N or less, or 1 N to 10 N, or 2 N to 8 N, or 5 N to 10 N
in the CD. The nonwoven material may also or instead exhibit a peak
load of 20 N or less, or 1 N to 20 N, or 5 N to 15 N, or 10 N to 20
N in the MD.
[0066] "Permanent set," "50% unloading force," and "Peak Load" are
each defined and determined on a second cycle of hysteresis testing
according to the description given below in the "Examples" section,
in particular in the discussion of hysteresis testing.
[0067] Further, the nonwoven material may also exhibit superior
tensile strength and elasticity, such as elongation at maximum
strain of greater than or equal to 250%, or greater than or equal
to 270%, or greater than or equal to 277%. The tensile strength of
the nonwoven material in the MD and/or CD may be such that the
material can withstand a force (that is, the breaking force of the
nonwoven material may be) of 6 N to 30 N, or 10 N to 25 N or 15 N
to 20 N.
[0068] Each of the aforementioned elasticity properties (i.e.,
permanent set, 50% unloading force, and hysteresis %), and each of
the aforementioned tensile strength properties (i.e., breaking
force, elongation at maximum strain) are measured on the basis of a
nonwoven material having basis weight of 10 gsm or greater, or
about 10 gsm to 500 gsm, or about 10 gsm to 100 gsm, or about 25
gsm to 200 gsm, or about 50 gsm to 300 gsm, or about 100 gsm to 500
gsm.
Composites
[0069] The spunbond materials of various embodiments may form a
nonwoven fabric layer of a multilayer composite. For instance, the
spunbond material may, during its processing or after processing,
be combined with one or more layers of other woven or nonwoven
material, such as one or more other spunbond layers, one or more
meltblown layers, and the like, to form a composite. Suitable
composites include S, SS, SSS, SMS, MSM, MSxM, SMxS, SMM, MMS, and
the like, where each S represents a spunbond layer in the
composite, and each M represents a meltblown layer in the composite
(with each sub-script x representing an integer from 1-10,
indicating repetition of the labeled layer). The spunbond material
described hereinabove may form any one or more of the spunbond
layers in the composites of such embodiments.
[0070] Another example is an SSMMS construction, wherein the outer
S substrate may be a bi-component stretch laminate (for example, PE
sheath/PP core), the inner S may be an elastic nonwoven web, the
meltblown (M) layers may comprise one or more crystalline
polyolefins (PP, PE), propylene-based elastomers, and blends
thereof, and the outer S layer may comprise a bi-component web with
an elastic nonwoven core and a polyolefin sheath. The elastic
nonwovens may further be modified by any suitable additives known
to those skilled in the art, such as titanium dioxide to improve
opacity.
Spunbond Articles
[0071] The fibers and nonwoven fabrics of the present invention may
be employed in several applications. In one or more embodiments,
they may be advantageously employed in diapers and/or similar
personal hygiene articles, for example in such applications as
diaper tabs, side panels, leg cuffs, top sheet, back sheet, tapes,
feminine hygiene articles, swim pants, infant pull up pants,
incontinence wear components, and bandages. In particular, they can
be employed as the dynamic or stretchable components of these
articles such as, but not limited to, the elastic fastening bands.
In other embodiments, the fibers and nonwoven fabrics may be
fabricated into other protective garments or covers such as medical
gowns or aprons, surgical drapes, sterilization wraps, wipes,
bedding, or similar disposable garments and covers. These materials
may also find applications in protective covers, home furnishing
such as bedding, carpet antiskid padding, wall coverings, floor
coverings, window shades, scrims, and any other application in
which traditional fabrics have been used previously.
[0072] In other embodiments, the fibers and fabrics of the present
invention can be employed in the manufacture of filtration media
(gas and liquid). For example, particular applications include use
in functionalized resins where the nonwoven fabric can be
electrostatically charged to form an electret.
[0073] Further, the fibers and fabrics of the present invention may
be employed in any of the structures and other end-use
applications, or in conjunction with any of the additives and other
compositions described in U.S. Pat. Nos. 7,902,093; 7,943,701; and
8,728,960.
EXAMPLE EMBODIMENTS
[0074] A first embodiment is a method comprising: extruding a
polymer composition to form a plurality of filaments, wherein the
polymer composition comprises 75 wt % to 99 wt % of a
propylene-ethylene copolymer, 0.5 wt % to 15 wt % of a
propylene-based thermoplastic polymer, and 0.005 wt % to 1 wt % of
a nucleator; and forming a spunbond material from the plurality of
filaments. This embodiment may optionally include one or more of
the following: Element 1: wherein the propylene-ethylene copolymer
has an ethylene content of 1.5 wt % to 20 wt % and a propylene
content of 80 wt % to 98.5 wt % based upon the total weight of the
propylene-ethylene copolymer; Element 2: wherein the
propylene-ethylene copolymer has a melt flow rate (MFR) (ASTM
D-1238, 2.16 kg weight @ 230.degree. C.) of 10 g/10 min to 120 g/10
min; Element 3: wherein the propylene-based thermoplastic polymer
is a homopolymer of propylene; Element 4: wherein the
propylene-based thermoplastic polymer is a random propylene
copolymer having a comonomer content of 4 wt % or less based upon
the total weight of the random propylene copolymer; Element 5:
wherein the polymer composition consists of the propylene-ethylene
copolymer, the propylene-based thermoplastic polymer, and the
nucleator; Element 6: wherein the polymer composition consists of
the propylene-ethylene copolymer, the propylene-based thermoplastic
polymer, the nucleator, and a slip aid; Element 7: wherein the
polymer composition further comprises one or more additives
selected from the group consisting of a stabilizer, an antioxidant,
a filler, a slip aid, a colorant, a mold release agent, a wax, and
a processing oil; and Element 8: wherein the polymer composition is
extruded through a spinneret at a melt temperature of 270.degree.
C. or less, thereby forming the plurality of filaments. Example of
combinations include, but are not limited to, Elements 1 and 2 in
combination and optionally in further combination with one of
Elements 3 and 4; one of Elements 5-7 in combination with Elements
1 and/or 2 and optionally in further combination with one of
Elements 3 and 4; one of Elements 5-7 in combination one of
Elements 3 and 4; and Element 8 in combination with one or more of
Elements 1-7.
[0075] A second embodiment is a spunbond fabric made by the method
of the first embodiment optionally including one or more of
Elements 1-8.
[0076] A third embodiment is a spunbond fabric having a machine
direction (MD) and a cross direction (CD) comprising a polymer
composition that comprises 75 wt % to 99 wt % of a
propylene-ethylene copolymer, 0.5 wt % to 15 wt % of a
propylene-based thermoplastic polymer, and 0.005 wt % to 1 wt % of
a nucleator. This embodiment may optionally include one or more of
the following: Element 1; Element 2; Element 3; Element 4; Element
5, Element 6; Element 7; Element 9: wherein the spunbond fabric
exhibits a permanent set of 20% or less in either or both of the MD
and the CD, said permanent set being determined on the basis of
said spunbond fabric having a basis weight of greater than 10 gsm;
Element 10: wherein the spunbond fabric exhibits either or both of
(i) a 50% unloading force in the MD less than or equal to 2.5 N/5
cm, and (ii) a 50% unloading force in the CD less than or equal to
0.9 N/5 cm, said 50% unloading force determined on the basis of
said spunbond fabric having a basis weight of 10 gsm or greater;
Element 11: wherein the spunbond fabric exhibits a hysteresis of
45% or less in either or both of the MD and the CD of the spunbond
fabric, said hysteresis being determined on the basis of said
spunbond fabric having a basis weight of 10 gsm or greater; and
Element 12: wherein the spunbond fabric exhibits either or both of
(i) a peak load of 20 N or less in the MD, and (ii) a peak load of
10 N or less in the CD, said peak loads being determined on the
basis of said spunbond fabric having a basis weight of 10 gsm or
greater. Example of combinations include, but are not limited to,
Elements 1 and 2 in combination and optionally in further
combination with one of Elements 3 and 4; one of Elements 5-7 in
combination with Elements 1 and/or 2 and optionally in further
combination with one of Elements 3 and 4; one of Elements 5-7 in
combination one of Elements 3 and 4; one or more of Elements 9-12
in combination with one or more of Elements 1-7; and two or more of
Elements 9-12 in combination.
[0077] A fourth embodiment is an article formed from the spunbond
fabric of the third embodiment optionally including one or more of
Elements 1-7 and 9-12. Further, the article may be selected from
the group consisting of diaper tabs, side panels, leg cuffs, top
sheet, back sheet, tapes, feminine hygiene articles, swim pants,
infant pull up pants, incontinence wear components, and
bandages.
[0078] Unless otherwise indicated, all numbers expressing
quantities of ingredients, properties such as molecular weight,
reaction conditions, and so forth used in the present specification
and associated claims are to be understood as being modified in all
instances by the term "about." Accordingly, unless indicated to the
contrary, the numerical parameters set forth in the following
specification and attached claims are approximations that may vary
depending upon the desired properties sought to be obtained by the
embodiments of the present invention. At the very least, and not as
an attempt to limit the application of the doctrine of equivalents
to the scope of the claim, each numerical parameter should at least
be construed in light of the number of reported significant digits
and by applying ordinary rounding techniques
[0079] One or more illustrative embodiments incorporating the
invention embodiments disclosed herein are presented herein. Not
all features of a physical implementation are described or shown in
this application for the sake of clarity. It is understood that in
the development of a physical embodiment incorporating the
embodiments of the present invention, numerous
implementation-specific decisions must be made to achieve the
developer's goals, such as compliance with system-related,
business-related, government-related and other constraints, which
vary by implementation and from time to time. While a developer's
efforts might be time-consuming, such efforts would be,
nevertheless, a routine undertaking for those of ordinary skill in
the art and having benefit of this disclosure.
[0080] While compositions and methods are described herein in terms
of "comprising" various components or steps, the compositions and
methods can also "consist essentially of" or "consist of" the
various components and steps.
[0081] To facilitate a better understanding of the embodiments of
the present invention, the following examples of preferred or
representative embodiments are given. In no way should the
following examples be read to limit, or to define, the scope of the
invention.
EXAMPLES
Hysteresis Testing
[0082] Hysteresis tests were carried out as follows. Test samples
measuring 150 mm length by 50 mm width were stretched to 100%
elongation at a cross-head speed of 500 mm/min At the point of 100%
elongation, the samples were held for 1 second before being allowed
to return to the starting position, also at a speed of 500 mm/min
The samples were then held in the un-stretched position for 30
seconds, and the elongation cycle was repeated a second time.
During the second cycle, the percent elongation reached at a load
of 0.1 N was measured. The test was conducted at 20.degree. C. and
50% relative humidity. The extension of the sample was plotted
against the load (force) applied to stretch the sample through each
cycle, generating a hysteresis curve. From the hysteresis curve,
one can also determine peak load (N), 50% unloading force (N/5 cm)
(also referred to as retractive force at 50%), permanent set, and
hysteresis (%). The hysteresis properties of each fabric sample can
be tested in either the machine direction (MD) or cross direction
(CD).
[0083] FIG. 1 is a generic model hysteresis curve provided for
purposes of illustrating the determination of hysteresis data
herein. As shown in FIG. 1, the first cycle provides data to
generate the curve OACD. The second cycle provides data to generate
the curve EBCD'.
[0084] "Peak load" is the force exerted upon the sample when it is
at maximum elongation during the hysteresis testing. In FIG. 1, the
peak load is the Y-axis value at point A.
[0085] "50% unloading force" is the force per width of sample (N/5
cm) exerted by a sample at 50% elongation, measured as the sample
retracts from 100% elongation during the first hysteresis cycle. In
FIG. 1, the 50% unloading force is the Y-value at point H.
[0086] "Permanent set" quantifies the increase in length
experienced by the sample after completion of the first cycle of
extension and relaxation, representing how much the sample has been
permanently stretched as a result of the first extension and
relaxation cycle. With reference to FIG. 1, it can be seen that as
all force is removed after the first cycle, the extension of the
sample does not return to 0; instead, it lies at a point D. The
permanent set can be determined by dividing the line OD by the line
OF (representing the maximum extension of the sample during
testing), and multiplying by 100%. That is, with reference to FIG.
1, permanent set is (OD/OF) times 100%.
[0087] "Hysteresis (%)" is defined as the quotient of hysteresis
divided by mechanical hysteresis. Hysteresis and mechanical
hysteresis are determined from the hysteresis curve. With reference
to FIG. 1, hysteresis (%) may be determined as the area defined by
curve OACD, divided by the area defined by OAFO, multiplied by
100%. That is, with reference to FIG. 1, hysteresis (%) is
(OACD/OAFO) times 100%.
[0088] For visual reference regarding hysteresis, FIG. 2
illustrates an ideal hysteresis curve for elastic materials,
indicating an approximate conformity to Hooke's law (and
illustrating a return of the elastic material to its original
length upon removal of the strain, that is, a permanent set of 0%).
Desirably, for a given basis weight, a nonwoven will exhibit a
combination of (i) low hysteresis; (ii) low permanent set; (iii)
high 50% unloading force; and (iv) low peak load; all properties
being determined in the 2nd cycle of hysteresis testing.
[0089] Example 1. Nonwoven fabrics were produced from three
different polymer compositions according to Table 1 under the
process parameters according to Table 1.
TABLE-US-00001 TABLE 1 Nonwoven Fabric Composition and Process
Parameters Comparative 1 Comparative 2 Sample 1 Formulation (wt %)
EXXONMOBIL .TM. 3.0 100.0 0.0 PP3155 VISTAMAXX .TM. 6202* 0.0 0.0
0.0 VISTAMAXX .TM. 7050* 94.0 0.0 94.0 Nucleator Master Batch** 0.0
0.0 3.0 Slip Master Batch *** 3.0 0.0 3.0 Processing Parameters
Basis Weight (gsm) 45 15 45 Melt Temperature (.degree. C.) 218 235
218 Die Temperature (.degree. C.) 220 237 211 Throughput (kg/h) 500
300 250 Cabin Pressure (rpm) 950 700 900 Suction Blow (rpm) 850 800
800 Mono Exhauster (rpm) 1400 800 1300 Quench Temperature (.degree.
C.) 10 10 10 Bonding Temperature 65 144 65 (.degree. C.) *VISTAMAXX
.TM. is a propylene-ethylene copolymer commercially available from
ExxonMobil). *Nucleator Master Batch = polypropylene resin
(EXXONMOBIL .TM. PP3155, available from ExxonMobil Chemical
Company) with 1 wt % nucleator (HYPERFORM .RTM. HPN-68L, available
from Milliken Chemical) **Slip Master Batch = polypropylene resin
(EXXONMOBIL .TM. PP3155, available from ExxonMobil Chemical
Company) with 15 wt % slip additive
[0090] The crystallinity and physical properties are provided in
Tables 2 and 3, respectively. The T.sub.1/2 data is the speed at
which the fibers crystallize The inventive Sample 1 crystallizes
significantly faster than Comparative 1 because Sample 1 has the
nucleator incorporated therein.
TABLE-US-00002 TABLE 2 Fiber Crystallinity Properties Comparative 1
Comparative 2 Sample 1 T.sub.1/2 at 125.degree. C. (mm) 5.126 --
1.323 T.sub.1/2 at 125.degree. C. (mm) 6.127 -- 2.500 Tc1 (.degree.
C.) 48.14 -- 54.85 .DELTA.H1 (melt) (J/g) 8.53 -- 9.19 Calculated
Crystallinity (%) 4.5 -- 4.9 Tc2 (.degree. C.) 89.24 116.87 129.46
.DELTA.H2 (melt) (J/g) 5.86 107.33 58.57 Calculated Crystallinity
(%) 3.1 56.8 4.5
TABLE-US-00003 TABLE 3 Fiber Physical Properties Comparative 1
Comparative 2 Sample 1 Fiber Size (.mu.m) 25.3 17.9 27.8 MD Force
(N) 22 29 19 CD Force (N) --* 28 --* MD Strain (%) 181 68 212 CD
Strain (%) >267* 58 >267* *Did not break at machine force
limitation.
[0091] FIG. 3 is the 100% hysteresis curve for the first cycle in
the MD for control and nucleated inventive samples. FIG. 4 is the
100% hysteresis curve for the second cycle in the MD for control
and nucleated inventive samples. FIG. 5 is the 100% hysteresis
curve for the first cycle in the CD for control and nucleated
inventive samples. FIG. 6 is the 100% hysteresis curve for the
second cycle in the CD for control and nucleated inventive samples.
The nonwoven fabric hysteresis data for 100% elongation and 200%
elongation are provided in Tables 4 and 5, respectively. The
figures make evident that the Sample 1 has a narrower and lower
hysteresis that is closer to the ideal hysteresis curve for an
elastomeric composition.
TABLE-US-00004 TABLE 4 Nonwoven Fabric Hysteresis (100% Elongation)
Comparative 1 Sample 1 Direction MD CD MD CD Permanent Set (%) 13.1
20.1 15.0 21.1 2.sup.nd Corrected Permanent Set (%) 6.0 3.8 6.2 4.8
F.sub.fapply (t.sub.before) (N) Cycle 1 15.9 3.4 14.5 3.1 Cycle 2
15.0 3.2 13.7 2.9 Hysteresis (%) Cycle 1 70.9 66.6 73.0 69.8 Cycle
2 42.8 40.1 44.7 42.2 Force 50% Unloading Cycle 1 2.0 0.5 1.7 0.4
(N) Cycle 2 1.9 0.5 1.6 0.4 Load Loss Cycle 1 82.9 79.5 84.9 82.3
Cycle 2 52.8 48.7 55.7 52.0
TABLE-US-00005 TABLE 5 Nonwoven Fabric Hysteresis (200% Elongation)
Comparative 1 Sample 1 Direction MD* CD MD CD Permanent Set (%) --
51.2 45.7 56.7 2.sup.nd Corrected Permanent Set (%) -- 7.2 9.9 8.0
F.sub.fapply (t.sub.before) (N) Cycle 1 -- 5.4 25.4 5.5 Cycle 2 --
5.0 23.1 5.1 Hysteresis (%) Cycle 1 -- 75.1 81.8 76.3 Cycle 2 --
45.2 50.8 46.5 Force 50% Unloading Cycle 1 -- 0.1 0.2 0.1 (N) Cycle
2 -- 0.1 0.1 0.1 Load Loss Cycle 1 -- 95.4 98.6 96.7 Cycle 2 --
72.8 89.5 76.2 *Fiber broke.
[0092] Therefore, the present invention is well adapted to attain
the ends and advantages mentioned as well as those that are
inherent therein. The particular embodiments disclosed above are
illustrative only, as the present invention may be modified and
practiced in different but equivalent manners apparent to those
skilled in the art having the benefit of the teachings herein.
Furthermore, no limitations are intended to the details of
construction or design herein shown, other than as described in the
claims below. It is therefore evident that the particular
illustrative embodiments disclosed above may be altered, combined,
or modified and all such variations are considered within the scope
and spirit of the present invention. The invention illustratively
disclosed herein suitably may be practiced in the absence of any
element that is not specifically disclosed herein and/or any
optional element disclosed herein. While compositions and methods
are described in terms of "comprising," "containing," or
"including" various components or steps, the compositions and
methods can also "consist essentially of" or "consist of" the
various components and steps. All numbers and ranges disclosed
above may vary by some amount. Whenever a numerical range with a
lower limit and an upper limit is disclosed, any number and any
included range falling within the range is specifically disclosed.
In particular, every range of values (of the form, "from about a to
about b," or, equivalently, "from approximately a to b," or,
equivalently, "from approximately a-b") disclosed herein is to be
understood to set forth every number and range encompassed within
the broader range of values. Also, the terms in the claims have
their plain, ordinary meaning unless otherwise explicitly and
clearly defined by the patentee. Moreover, the indefinite articles
"a" or "an," as used in the claims, are defined herein to mean one
or more than one of the element that it introduces.
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