U.S. patent application number 11/498481 was filed with the patent office on 2007-02-15 for propylene-based copolymers, a method of making the fibers and articles made from the fibers.
Invention is credited to Andy C. Chang, Byron P. Day, Antonios K. Doufas, Stephen M. Englebert, Joy F. Jordan, Edward N. Knickerbocker, Lizhi Liu, Rajen M. Patel, Hong Peng, Randy E. Pepper, Renette E. Richard, Christian L. Sanders, Varunesh Sharma, Jozef J.I. Van Dun.
Application Number | 20070036972 11/498481 |
Document ID | / |
Family ID | 34963146 |
Filed Date | 2007-02-15 |
United States Patent
Application |
20070036972 |
Kind Code |
A1 |
Chang; Andy C. ; et
al. |
February 15, 2007 |
Propylene-based copolymers, a method of making the fibers and
articles made from the fibers
Abstract
Fibers that exhibit good elasticity or extensibility and
tenacity, and low modulus are prepared from propylene-based
copolymers. The propylene-based copolymers comprise at least about
50 weight percent (wt %) of units derived from propylene and at
least about 8 wt % of units derived from one or more comonomers
other than propylene, e.g., ethylene. Particularly preferred
propylene copolymers are characterized as having .sup.13C NMR peaks
corresponding to a regio-error at about 14.6 and about 15.7 ppm,
the peaks of about equal intensity. In one aspect of the invention,
fibers are subjected to stress-induced crystallization by
subjecting the fiber to tensile elongation during draw.
Inventors: |
Chang; Andy C.; (Houston,
TX) ; Van Dun; Jozef J.I.; (Bellaire, TX) ;
Peng; Hong; (Lake Jackson, TX) ; Pepper; Randy
E.; (Lake Jackson, TX) ; Knickerbocker; Edward
N.; (Lake Jackson, TX) ; Patel; Rajen M.;
(Lake Jackson, TX) ; Day; Byron P.; (Canton,
GA) ; Jordan; Joy F.; (Marietta, GA) ; Doufas;
Antonios K.; (Lake Jackson, TX) ; Liu; Lizhi;
(Lake Jackson, TX) ; Englebert; Stephen M.;
(Woodstock, GA) ; Richard; Renette E.; (Dunwoody,
GA) ; Sanders; Christian L.; (Decatur, GA) ;
Sharma; Varunesh; (Atlanta, GA) |
Correspondence
Address: |
THE DOW CHEMICAL COMPANY
INTELLECTUAL PROPERTY SECTION,
P. O. BOX 1967
MIDLAND
MI
48641-1967
US
|
Family ID: |
34963146 |
Appl. No.: |
11/498481 |
Filed: |
August 3, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11083891 |
Mar 18, 2005 |
7101622 |
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11498481 |
Aug 3, 2006 |
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60554664 |
Mar 19, 2004 |
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Current U.S.
Class: |
428/364 |
Current CPC
Class: |
D01F 6/30 20130101; Y10T
442/681 20150401; Y10T 428/29 20150115; D04H 1/4291 20130101; D04H
1/43828 20200501; Y10T 442/602 20150401; D04H 1/43832 20200501;
Y10T 428/2913 20150115; D04H 3/16 20130101; Y10T 442/601 20150401;
D01F 8/06 20130101; D04H 1/56 20130101; Y10T 442/68 20150401 |
Class at
Publication: |
428/364 |
International
Class: |
D02G 3/00 20060101
D02G003/00 |
Claims
1. A fiber comprising more than 80 weight percent of a reactor
grade propylene copolymer, the copolymer having a MWD of less than
3.5, said copolymer comprising at least about 50 weight percent of
units derived from propylene and at least about 5 weight percent of
units derived from a comonomer other than propylene.
2. The fiber of claim 1 wherein the fiber is characterized as
having a crystallinity index as measured by X-ray diffraction of
less than about 30%.
3. A fiber comprising a propylene copolymer, the copolymer
comprising at least about 50 weight percent of units derived from
propylene and at least about 5 weight percent of units derived from
a comonomer other than propylene, the fiber characterized as having
a crystallinity index as measured by X-ray diffraction of less than
about 30%.
4. The fiber of any of claims 1-3 in which the copolymer comprises
at least about 84 weight percent of units derived from propylene,
and the comonomer other than propylene is ethylene.
5. The fiber of any of claims 1-4 in which the crystallinity index
of the fiber is less than 27%.
6. The fiber of any of claims 1-4 in which the crystallinity index
of the fiber is less than about 20%.
7. The fiber of any of claims 1-6 in which the copolymer is further
characterized as having .sup.13C NMR peaks corresponding to a
regio-error at about 14.6 and about 15.7 ppm, the peaks of about
equal intensity.
8. The fiber of any of claims 1-7 in which the copolymer is further
characterized as having a DSC curve with a T.sub.me that remains
essentially the same and a T.sub.max that decreases as the amount
of the comonomer in the copolymer is increased.
9. The fiber of any of claims 1-6 in which the copolymer is further
characterized as having an X-ray diffraction pattern exhibiting
more gamma-form crystals than a propylene copolymer comparable in
weight average molecular weight except that it is prepared with a
Ziegler-Natta catalyst.
10. The fiber of any of claims 1-9 wherein the copolymer comprises
at least about 98 weight percent of the fiber.
11. The fiber of any of the preceding claims further comprising a
nucleating agent.
12. The fiber of any of the preceding claims in the form of a
monofilament.
13. The fiber of any of the preceding claims in the form of a
bicomponent fiber.
14. The fiber of claim 13 in which the fiber has a sheath/core
configuration.
15. The fiber of claim 14 in which the copolymer comprises the
sheath.
16. The fiber of claim 14 in which the copolymer comprises the
core.
17-42. (canceled)
Description
[0001] This application is being filed contemporaneously with a
related application entitled "EXTENSIBLE AND ELASTIC CONJUGATE
FIBERS AND WEBS HAVING A NONTACKY FEEL" in the names of Joy F.
Jordan et al., Attorney Docket Number 20094 which is incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to fibers made from propylene-based
copolymers. In one aspect, this invention relates to fibers made
from propylene-based elastomers and plastomers while in another
aspect, this invention relates to elastic or extensible fibers made
from the same. In still other aspects, this invention relates to a
method of making elastic fibers from the propylene-based elastomers
and plastomers, and articles made from such fibers.
BACKGROUND OF THE INVENTION
[0003] Propylene-based polymers, particularly homo-polypropylene
(hPP) are well known in the art, and have long been used in the
manufacture of fibers. Fabrics made from hPP, particularly nonwoven
fabrics, exhibit high modulus but poor elasticity. These fabrics
are commonly incorporated into multicomponent articles, e.g.,
diapers, wound dressings, feminine hygiene products and the like.
While polyethylene-based elastomers, and the fibers and fabrics
made from these polymers, exhibit low modulus and good elasticity,
they also exhibit a tenacity, stickiness and hand feel which are
generally considered to be unacceptable for commercial
applications.
[0004] Tenacity is important because the manufacture of
multicomponent articles typically involves multiple steps (e.g.,
rolling/unrolling, cutting, adhesion, etc.). Fibers with a high
tensile strength are advantaged over fibers with a low tensile
strength because the former will experience fewer line breaks (and
thus greater productivity). Moreover, the end-use typically
requires a level of tensile strength specific to the function of
the component. Optimized fabrics have the minimum material
consumption (basis weight) to achieve the minimum required tensile
strength for the manufacture and end-use of the fiber, component
(e.g., nonwoven fabric) and article.
[0005] Low modulus is one aspect of hand feel. Fabrics made from
fibers with a low modulus will feel "softer", all else equal, than
fabrics made from fibers with a high modulus. A fabric comprised of
lower modulus fibers will also exhibit lower flexural rigidity
which translates to better drapability and better fit. In contrast,
a fabric made from a higher modulus fiber, e.g., hPP, will feel
harsher (stiffer) and will drape less well (e.g., it will have a
poorer fit). Fabrics made from polyethylene-based elastomers feels
very tacky and clammy to the skin.
[0006] Fiber elasticity is important because it translates to
better comfort-fit as the article made from the fiber will be more
body conforming. Diapers with elastic components will have less
sagging in general as body size and shape and movement vary. With
improved fit, the general well being of the user is improved
through improved comfort, reduced leakage and a closer resemblance
of the article to cotton underwear.
[0007] Accordingly, interest remains high in a polymer that
exhibits good elasticity and tenacity and low modulus when in the
form of a fiber, and articles made from such fibers.
SUMMARY OF THE INVENTION
[0008] According to one embodiment of this invention, an elastic or
extensible fiber comprises a propylene copolymer, the copolymer
comprising at least about 50 weight percent of units derived from
propylene and at least about 5 weight percent of units derived from
a comonomer other than propylene, the copolymer characterized as
having a crystallinity index as measured by X-ray diffraction of
less than about 40%. Such copolymers with a crystallinity index
between about 20% and about 40% form extensible fibers, while
copolymers with crystallinity indices less than about 20% form
elastic fibers. The comonomer is typically one or more of ethylene
(a preferred comonomer), a C.sub.4-20 .alpha.-olefin, a C.sub.4-20
diene, a styrenic compound, and the like.
[0009] In another embodiment of the invention, the fibers comprise
propylene copolymers further characterized as having at least one
of the following properties: (i) .sup.13C NMR peaks corresponding
to a regio-error at about 14.6 and about 15.7 ppm, the peaks of
about equal intensity, (ii) a DSC curve with a T.sub.me that
remains essentially the same and a T.sub.max that decreases as the
amount of comonomer, i.e., the units derived from ethylene and/or
the unsaturated comonomer(s), in the copolymer is increased, and
(iii) an X-ray diffraction pattern that reports more gamma-form
crystals than a comparable copolymer prepared with a Ziegler-Natta
(Z-N) catalyst. Typically the copolymers of this embodiment are
characterized by at least two, preferably all three, of these
properties. In other embodiments of this invention, these
copolymers are characterized further as also having the following
characteristic: (iv) a skewness index, S.sub.ix, greater than about
-1.20.
[0010] In another embodiment of the invention, the fiber is an
extensible, high tenacity fiber comprising a propylene copolymer,
the copolymer comprising at least about 50 weight percent of units
derived from propylene and at least about 5 weight percent of units
derived from a comonomer other than propylene, the fiber
characterized as having a crystallinity index of less than 30%, a
modulus of less than or equal to about 20 g/den, a retained load at
30% elongation as measured by a 50% 1-cycle test of more than 5%,
and an immediate set as measured by a 50% 1-cycle test of less than
or equal to about 30%. The fiber should be stretchable to at least
100% (i.e. 2.times.) of its original dimension.
[0011] In another embodiment of the invention, the fiber is an
elastic fiber comprising a propylene copolymer, the copolymer
comprising at least about 50 weight percent of units derived from
propylene and at least about 5 weight percent of units derived from
a comonomer other than propylene, the fiber characterized as having
a crystallinity index of less than or equal to about 25%, a modulus
of less than or equal to about 5 g/den, a tenacity of less than or
equal to about 2.5 g/den, a retained load at 30% elongation as
measured by a 50% 1-cycle test of greater than or equal to about
15%, and an immediate set as measured by a 50% 1-cycle test of less
than or equal to about 15%. The fiber should be stretchable to at
least 50% (i.e. 1.5.times.) of its original dimension.
[0012] In another embodiment, the invention is a method of forming
a fiber, the fiber comprising a propylene copolymer, the copolymer
comprising at least about 50 weight percent of units derived from
propylene and at least about 5 weight percent of units derived from
a comonomer other than propylene, the method comprising the steps
of (i) forming a melt of the copolymer, (ii) extruding the melted
copolymer through a die, and (iii) subjecting the extruded
copolymer to a draw down greater than about 200. The fibers are
oriented by subjecting the fiber to tensile elongation during a
drawing operation. In one aspect of this embodiment, the tensile
elongation is imparted in the quench zone of the drawing operation,
i.e., between the spinneret and the godets.
[0013] Though not bound by the following theory, the orientation to
produce these inventive fibers is thought to result in
stress-induced crystallization. This crystallization, in turn,
minimizes fiber blocking (i.e., sticking) and improves hand
feel.
[0014] The fibers of this invention can be made from the
propylene-based copolymers alone, or they can be made from blends
of the propylene-based copolymers and one or more other polymers,
and/or additives and/or nucleators. The fibers can take any form,
e.g., monofilament, bicomponent, etc., and they can be used with or
without post-formation treatment, e.g., annealing. Certain of the
fibers of this invention are further characterized by substantial
breakage before elongation to 300%, others by substantial breakage
before elongation to 200%, and still others by substantial breakage
before elongation to 100%.
[0015] The fibers of this invention are used to manufacture various
articles of manufacture, e.g., fabrics (woven and nonwoven), which
in turn can be incorporated into multicomponent articles such as
diapers, wound dressings, feminine hygiene products and the
like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIGS. 1A, 1B, 1C are photographs of X-ray film that evidence
the smectic phases of polypropylene homopolymers (1A and 1B) and
the alpha phase of a propylene-ethylene copolymer comprising 12
weight percent ethylene (1C).
[0017] FIG. 2 is a graph illustrating the immediate set and modulus
behavior of propylene homo- and copolymers.
[0018] FIG. 3 is a graph illustrating the correlations of immediate
set on crystallinity index of propylene homo- and copolymers.
[0019] FIG. 4 is a graph illustrating the correlation of fiber
modulus on crystallinity index of the inventive propylene copolymer
fibers
[0020] FIG. 5 is a graph illustrating the correlation of retained
load at 30% strain on crystallinity index of the inventive
propylene copolymer fibers.
[0021] FIG. 6 is a graph illustrating the correlation of tenacity
on crystallinity index of the inventive propylene copolymer
fibers.
[0022] FIG. 7 is a graph illustrating the correlation of elongation
and crystallinity index of propylene copolymer fibers.
[0023] FIG. 8 is a graph illustrating the correlation of immediate
set and retained load at 30% strain of the inventive propylene
copolymer fibers.
[0024] FIG. 9 is a micrograph of a nonwoven fabric showing the
self-bonding capability of the inventive fibers made from
propylene-ethylene copolymer containing 12 wt % ethylene.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] "Polymer" means a macromolecular compound prepared by
polymerizing monomers of the same or different type. "Polymer"
includes homopolymers, copolymers, terpolymers, interpolymers, and
so on. The term "interpolymer" means a polymer prepared by the
polymerization of at least two types of monomers or comonomers. It
includes, but is not limited to, copolymers (which usually refers
to polymers prepared from two different types of monomers or
comonomers, although it is often used interchangeably with
"interpolymer" to refer to polymers made from three or more
different types of monomers or comonomers), terpolymers (which
usually refers to polymers prepared from three different types of
monomers or comonomers), tetrapolymers (which usually refers to
polymers prepared from four different types of monomers or
comonomers), and the like. The terms "monomer" or "comonomer" are
used interchangeably, and they refer to any compound with a
polymerizable moiety which is added to a reactor in order to
produce a polymer. In those instances in which a polymer is
described as comprising one or more monomers, e.g., a polymer
comprising propylene and ethylene, the polymer, of course,
comprises units derived from the monomers, e.g.,
--CH.sub.2--CH.sub.2--, and not the monomer itself, e.g.,
CH.sub.2.dbd.CH.sub.2.
[0026] "P/E* copolymer" and similar terms mean a
propylene/unsaturated comonomer (typically and preferably ethylene)
copolymer characterized as having at least one of the following
properties: (i) .sup.13C NMR peaks corresponding to a regio-error
at about 14.6 and about 15.7 ppm, the peaks of about equal
intensity, (ii) a DSC curve with a T.sub.me that remains
essentially the same and a T.sub.max that decreases as the amount
of comonomer, i.e., the units derived from ethylene and/or the
unsaturated comonomer(s), in the copolymer is increased, and (iii)
an X-ray diffraction pattern that reports more gamma-form crystals
than a comparable copolymer prepared with a Ziegler-Natta (Z-N)
catalyst. Typically, the copolymers of this embodiment are
characterized by at least two, preferably all three, of these
properties. In other embodiments of this invention, these
copolymers are characterized further as also having the following
characteristic: (iv) a skewness index, S.sub.ix, greater than about
-1.20.
[0027] With respect to the X-ray property of subparagraph (iii)
above, a "comparable" copolymer is one having the same comonomer
composition within 10%, and the same Mw within 10%. For example, if
an inventive propylene/ethylene/1-hexene copolymer is 9 wt %
ethylene and 1 wt % 1-hexene and has a Mw of 250,000, then a
comparable polymer would have from 8.1-9.9 wt % ethylene, 0.9-1.1
wt % 1-hexene, and a Mw between 225,000 and 275,000, prepared with
a Ziegler-Natta catalyst.
[0028] P/E* copolymers are a unique subset of P/E copolymers. P/E
copolymers include all copolymers of propylene and an unsaturated
comonomer, not just P/E* copolymers. P/E copolymers other than P/E*
copolymers include metallocene-catalyzed copolymers, constrained
geometry catalyst catalyzed copolymers and Z-N-catalyzed
copolymers. For purposes of this invention, P/E copolymers comprise
50 weight percent or more propylene while EP (ethylene-propylene)
copolymers comprise 51 weight percent or more ethylene. As here
used, "comprise . . . propylene", "comprise . . . ethylene" and
similar terms mean that the polymer comprises units derived from
propylene, ethylene or the like as opposed to the compounds
themselves.
[0029] "Metallocene-catalyzed polymer" or similar term means any
polymer that is made in the presence of a metallocene catalyst.
"Constrained geometry catalyst catalyzed polymer", "CGC-catalyzed
polymer" or similar term means any polymer that is made in the
presence of a constrained geometry catalyst.
"Ziegler-Natta-catalyzed polymer", Z-N-catalyzed polymer" or
similar term means any polymer that is made in the presence of a
Ziegler-Natta catalyst. "Metallocene" means a metal-containing
compound having at least one substituted or unsubstituted
cyclopentadienyl group bound to the metal. "Constrained geometry
catalyst" or "CGC" as here used has the same meaning as this term
is defined and described in U.S. Pat. Nos. 5,272,236 and
5,278,272.
[0030] "Random copolymer" means a copolymer in which the monomer is
randomly distributed across the polymer chain. "Propylene
homopolymer" and similar terms mean a polymer consisting solely or
essentially all of units derived from propylene. "Polypropylene
copolymer" and similar terms mean a polymer comprising units
derived from propylene and ethylene and/or one or more unsaturated
comonomers. The term "copolymer" includes terpolymers,
tetrapolymers, etc.
[0031] The unsaturated comonomers used in the practice of this
invention include, C.sub.4-20 .alpha.-olefins, especially
C.sub.4-12 .alpha.-olefins such as 1-butene, 1-pentene, 1-hexene,
4-methyl-1-pentene, 1-heptene, 1-octene, 1-decene, 1-dodecene and
the like; C.sub.4-20 diolefins, preferably 1,3-butadiene,
1,3-pentadiene, norbornadiene, 5-ethylidene-2-norbornene (ENB) and
dicyclopentadiene; C.sub.8-40 vinyl aromatic compounds including
sytrene, o-, m-, and p-methylstyrene, divinylbenzene,
vinylbiphenyl, vinylnapthalene; and halogen-substituted C.sub.8-40
vinyl aromatic compounds such as chlorostyrene and fluorostyrene.
Ethylene and the C.sub.4-12 .alpha.-olefins are the preferred
comonomers used in the practice of this invention, and ethylene is
an especially preferred comonomer.
[0032] The reactor grade propylene copolymers of this invention
comprise at least about 50, preferably at least about 60 and more
preferably at least about 70, wt % of units derived from propylene
based on the weight of the copolymer. Sufficient units derived from
propylene are present in the copolymer to ensure the benefits of
the polypropylene (PP) stress-induced crystallization behavior
during melt spinning, as well as the clear advantage of
polypropylene's tendency to chain scission vs. cross-link during
extrusion. Stress-induced crystallinity generated during draw
facilitates spinning, reduces fiber breaks, and reduces roping.
[0033] It is intended that the term "reactor grade" is as defined
in U.S. Pat. No. 6,010,588 and in general refers to a polyolefin
resin whose molecular weight distribution (MWD) or polydispersity
has not been substantially altered after polymerization.
[0034] Sufficient levels of comonomer other than propylene control
the crystallization such that elastic performance is maintained.
Although the remaining units of the propylene copolymer are derived
from at least one comonomer such as ethylene, a C.sub.4-20
.alpha.-olefin, a C.sub.4-20 diene, a styrenic compound and the
like, preferably the comonomer is at least one of ethylene and a
C.sub.4-12 .alpha.-olefin such as 1-hexene or 1-octene. Preferably,
the remaining units of the copolymer are derived only from
ethylene.
[0035] The amount of comonomer other than ethylene in the copolymer
is a function of, at least in part, the comonomer and the desired
crystallinity of the copolymer. The desired crystallinity index of
the copolymer does not exceed about 40% and for elastic fibers, it
does not exceed about 20%. If the comonomer is ethylene, then
typically the comonomer-derived units comprise not in excess of
about 16, preferably not in excess of about 15 and more preferably
not in excess of about 12, wt % of the copolymer. The minimum
amount of ethylene-derived units is typically at least about 5,
preferable at least about 6 and more preferably at least about 8,
wt % based upon the weight of the copolymer.
[0036] The propylene copolymers of this invention can be made by
any process, and include copolymers made by Zeigler-Natta, CGC,
metallocene, and nonmetallocene, metal-centered, heteroaryl ligand
catalysis. These copolymers include random, block and graft
copolymers although preferably the copolymers are of a random
configuration. Exemplary propylene copolymers include Exxon-Mobil
VISTAMAXX.TM., Mitsui TAFMER.TM. and propylene/ethylene plastomers
or elastomers from The Dow Chemical Company.
[0037] The density of the copolymers of this invention is typically
at least about 0.850, preferably at least about 0.860 and more
preferably at least about 0.865, grams per cubic centimeter
(g/cm.sup.3). Typically the maximum density of the propylene
copolymer is about 0.915, preferably the maximum is about 0.900 and
more preferably the maximum is about 0.890, g/cm.sup.3.
[0038] The weight average molecular weight (Mw) of the copolymers
of this invention can vary widely, but typically it is between
about 10,000 and 1,000,000 (with the understanding that the only
limit on the minimum or the maximum M.sub.w is that set by
practical considerations). For copolymers used in the manufacture
of meltblown fibers, preferably the minimum Mw is about 20,000,
more preferably about 25,000.
[0039] The polydispersity of the copolymers of this invention is
typically between about 2 and about 4. "Narrow polydisperity",
"narrow molecular weight distribution", "narrow MWD" and similar
terms mean a ratio (M.sub.w/M.sub.n) of weight average molecular
weight (M.sub.w) to number average molecular weight (M.sub.n) of
less than about 3.5, preferably less than about 3.0, more
preferably less than about 2.8, more preferably less than about
2.5, and most preferably less than about 2.3. Polymers for use in
fiber applications typically have a narrow polydispersity. Blends
comprising two or more of the copolymers of this invention, or
blends comprising at least one copolymer of this invention and at
least one other polymer, may have a polydispersity greater than 4
although for spinning considerations, the polydispersity of such
blends is still preferably between about 2 and about 4.
[0040] In one preferred embodiment of this invention, the propylene
copolymers are further characterized as having at least one of the
following properties: (i) .sup.13C NMR peaks corresponding to a
regio-error at about 14.6 and about 15.7 ppm, the peaks of about
equal intensity, (ii) a DSC curve with a T.sub.me that remains
essentially the same and a T.sub.max that decreases as the amount
of comonomer, i.e., the units derived from ethylene and/or the
unsaturated comonomer(s), in the copolymer is increased, and (iii)
an X-ray diffraction pattern that reports more gamma-form crystals
than a comparable copolymer prepared with a Ziegler-Natta (Z-N)
catalyst. Typically the copolymers of this embodiment are
characterized by at least two, preferably all three, of these
properties. In other embodiments of this invention, these
copolymers are characterized further as also having the following
characteristic: (iv) a skewness index, S.sub.ix, greater than about
-1.20. Each of these properties and their respective measurements
are described in detail in U.S. Ser. No. 10/139,786 filed May 5,
2002 (WO2003/040442) which is incorporated herein by reference.
[0041] The skewness index is calculated from data obtained from
temperature-rising elution fractionation (TREF). The data is
expressed as a normalized plot of weight fraction as a function of
elution temperature. The separation mechanism is analogous to that
of copolymers of ethylene, whereby the molar content of the
crystallizable component (ethylene) is the primary factor that
determines the elution temperature. In the case of copolymers of
propylene, it is the molar content of isotactic propylene units
that primarily determines the elution temperature.
[0042] The shape of the metallocene curve arises from the inherent,
random incorporation of comonomer. A prominent characteristic of
the shape of the curve is the tailing at lower elution temperature
compared to the sharpness or steepness of the curve at the higher
elution temperatures. A statistic that reflects this type of
asymmetry is skewness. Equation 1 mathematically represents the
skewness index, S.sub.ix, as a measure of this asymmetry. S ix = w
i * ( T i - T Max ) 3 3 w i * ( T i - T Max ) 2 . Equation .times.
.times. 1 ##EQU1##
[0043] The value, T.sub.max, is defined as the temperature of the
largest weight fraction eluting between 50 and 90.degree. C. in the
TREF curve. T.sub.i and w.sub.i are the elution temperature and
weight fraction respectively of an arbitrary, i.sup.th fraction in
the TREF distribution. The distributions have been normalized (the
sum of the w.sub.i equals 100%) with respect to the total area of
the curve eluting above 30.degree. C. Thus, the index reflects only
the shape of the crystallized polymer. Any uncrystallized polymer
(polymer still in solution at or below 30.degree. C.) has been
omitted from the calculation shown in Equation 1.
[0044] Differential scanning calorimetry (DSC) is a common
technique that can be used to examine the melting and
crystallization of semi-crystalline polymers. General principles of
DSC measurements and applications of DSC to studying
semi-crystalline polymers are described in standard texts (e.g., E.
A. Turi, ed., Thermal Characterization of Polymeric Materials,
Academic Press, 1981). Certain of the copolymers of this invention
are characterized by a DSC curve with a T.sub.me that remains
essentially the same and a T.sub.max that decreases as the amount
of unsaturated comonomer in the copolymer is increased. T.sub.me
means the temperature at which the melting ends. T.sub.max means
the peak melting temperature.
[0045] The propylene copolymers of this invention typically have an
MFR of at least about 0.01, preferably at least about 0.05, more
preferably at least about 1 and most preferably at least about 10.
The maximum MFR typically does not exceed about 2,000, preferably
it does not exceed about 1000, more preferably it does not exceed
about 500, further more preferably it does not exceed about 80 and
most preferably it does not exceed about 50. MFR for copolymers of
propylene and ethylene and/or one or more C.sub.4-C.sub.20
.alpha.-olefins is measured according to ASTM D-1238, condition L
(2.16 kg, 230 degrees C.).
[0046] One preferred class of propylene copolymers of this
invention are prepared by nonmetallocene, metal-centered,
heteroaryl ligand catalysis. In certain embodiments, the metal is
one or more of hafnium and zirconium.
[0047] More specifically, in certain embodiments of the catalyst,
the use of a hafnium metal has been found to be preferred as
compared to a zirconium metal for heteroaryl ligand catalysts. A
broad range of ancillary ligand substituents may accommodate the
enhanced catalytic performance. The catalysts in certain
embodiments are compositions comprising the ligand and metal
precursor, and, optionally, may additionally include an activator,
combination of activators or activator package.
[0048] The catalysts used in the practice of this invention
additionally include catalysts comprising ancillary ligand-hafnium
complexes, ancillary ligand-zirconium complexes and optionally
activators, which catalyze polymerization and copolymerization
reactions, particularly with monomers that are olefins, diolefins
or other unsaturated compounds. Zirconium complexes, hafnium
complexes, compositions or compounds using the disclosed ligands
are within the scope of the catalysts useful in the practice of
this invention. The metal-ligand complexes may be in a neutral or
charged state. The ligand to metal ratio may also vary, the exact
ratio being dependent on the nature of the ligand and metal-ligand
complex. The metal-ligand complex or complexes may take different
forms, for example, they may be monomeric, dimeric or of an even
higher order.
[0049] For example, suitable ligands useful in the practice of this
invention may be broadly characterized by the following general
formula: ##STR1## wherein R.sup.1 is a ring having from 4-8 atoms
in the ring generally selected from the group consisting of
substituted cycloalkyl, substituted heterocycloalkyl, substituted
aryl and substituted heteroaryl, such that R.sup.1 may be
characterized by the general formula: ##STR2## where Q.sup.1 and
Q.sup.5 are substituents on the ring other than to atom E, with E
being selected from the group consisting of carbon and nitrogen and
with at least one of Q.sup.1 or Q.sup.5 being bulky (defined as
having at least 2 atoms). Q''.sub.q represents additional possible
substituents on the ring, with q being 1, 2, 3, 4 or 5 and Q''
being selected from the group consisting of hydrogen, alkyl,
substituted alkyl, cycloalkyl, substituted cycloalkyl, heteroalkyl,
substituted heteroalkyl, heterocycloalkyl, substituted
hetercycloalkyl, aryl, substituted aryl, heteroaryl, substituted
heteroaryl, alkoxyl, aryloxyl, silyl, boryl, phosphino, amino,
thio, seleno, halide, nitro, and combinations thereof. T is a
bridging group selected group consisting of --CR.sup.2R.sup.3-- and
--SiR.sup.2R.sup.3-- with R.sup.2 and R.sup.3 being independently
selected from the group consisting of hydrogen, alkyl, substituted
alkyl, cycloalkyl, substituted cycloalkyl, heteroalkyl, substituted
heteroalkyl, heterocycloalkyl, substituted hetercycloalkyl, aryl,
substituted aryl, heteroaryl, substituted heteroaryl, alkoxyl,
aryloxyl, silyl, boryl, phosphino, amino, thio, seleno, halide,
nitro, and combinations thereof. J'' is generally selected from the
group consisting of heteroaryl and substituted heteroaryl, with
particular embodiments for particular reactions being described
herein.
[0050] Also for example, in some embodiments, the ligands of the
catalyst used to make the preferred propylene copolymers of this
invention may be combined with a metal precursor compound that may
be characterized by the general formula Hf(L).sub.n where L is
independently selected from the group consisting of halide (F, Cl,
Br, I), alkyl, substituted alkyl, cycloalkyl, substituted
cycloalkyl, heteroalkyl, substituted heteroalkyl, heterocycloalkyl,
substituted heterocycloalkyl, aryl, substituted aryl, heteroaryl,
substituted heteroaryl, alkoxy, aryloxy, hydroxy, boryl, silyl,
amino, amine, hydrido, allyl, diene, seleno, phosphino, phosphine,
carboxylates, thio, 1,3-dionates, oxalates, carbonates, nitrates,
sulphates, and combinations thereof. n is 1, 2, 3, 4, 5, or 6.
[0051] Certain ligands complex to the metal resulting in complexes
that are useful in the catalysis of the propylene copolymers of
this invention. In one aspect, the 3,2 metal-ligand complexes that
can be generally characterized by the following formula: ##STR3##
where M is zirconium or hafnium; R.sup.1 and T are defined above;
J''' being selected from the group of substituted heteroaryls with
2 atoms bonded to the metal M, at least one of those atoms being a
heteroatom, and with one atom of J''' is bonded to M via a dative
bond, the other through a covalent bond; and
[0052] L.sup.1 and L.sup.2 are independently selected from the
group consisting of halide, alkyl, substituted alkyl, cycloalkyl,
substituted cycloalkyl, heteroalkyl, substituted heteroalkyl,
heterocycloalkyl, substituted heterocycloalkyl, aryl, substituted
aryl, heteroaryl, substituted heteroaryl, alkoxy, aryloxy, hydroxy,
boryl, silyl, amino, amine, hydrido, allyl, diene, seleno,
phosphino, phosphine, carboxylates, thio, 1,3-dionates, oxalates,
carbonates, nitrates, sulphates, and combinations of these
radicals.
[0053] These catalysts and their use to make the preferred
propylene copolymers of this invention are further described in
U.S. Ser. No. 10/139,786 filed May 5, 2002.
[0054] The propylene copolymers used to make the fibers of this
invention have many useful applications. Representative examples
include mono- and multifilament fibers, mono- and bicomponent
fibers, staple fibers, binder fibers, spunbond and meltblown fibers
(using, e.g., systems as disclosed in U.S. Pat. Nos. 4,430,563,
4,663,220, 4,668,566 or 4,322,027), both woven and nonwoven
fabrics, strapping, tape, continuous filament (e.g., for use in
apparel, upholstery) and structures made from such fibers
(including, e.g., blends of these fibers with other fibers such as
PET or cotton). Staple and filament fibers can be melt spun into
the final fiber diameter directly without additional drawing, or
they can be melt spun into a higher diameter and subsequently hot
or cold drawn to the desired diameter using conventional fiber
drawing techniques. It should be understood that the term
"spinning" or "spun" implies commercially available equipment and
spinning rates.
[0055] Certain copolymers used in the practice of this invention
exhibit excellent elasticity, particularly those with a
crystallinity index of less than 20%. Whether or not pre-stretching
is desirable will depend upon the application. For example, the
elastomeric propylene copolymers of this invention can replace the
thermoplastic triblock elastomers as the filament layer in the
stretch bonded laminate process of U.S. Pat. No. 6,323,389. The
filament layer would be stretched, preferably only once, prior to
being sandwiched between the two spunbond layers. In an alternative
example, the elastomeric polymers of this invention can replace the
elastic layer in the necked bonded laminate process of U.S. Pat.
No. 5,910,224. Some pre-stretching of the propylene polymer may be
preferred.
[0056] The polymers of this invention, either alone or in
combination with one or more other polymers (either polymers of the
invention or polymers not of the invention) may be blended, if
desired or necessary, with various additives such as antioxidants,
ultraviolet absorbing agents, antistatic agents, nucleating agents,
lubricants, flame retardants, antiblocking agents, colorants,
inorganic or organic fillers or the like. These additives are used
in a conventional matter and in conventional amounts.
[0057] While the fibers of this invention can comprise a blend of
the propylene copolymers used in the practice of this invention
with one or more other polymers, and the polymer blend ratio can
vary widely and to convenience, in one embodiment of this invention
the fibers comprise at least about 98, preferably at least about 99
and more preferably essentially 100, weight percent of a propylene
copolymer comprising at least about 50, preferably at least about
60 and more preferably at least about 70, weight percent of units
derived from propylene and at least about 5 weight percent of units
derived from a comonomer other than propylene (preferably ethylene
or a C.sub.4-12 .alpha.-olefin), the copolymer characterized as
having a crystallinity index as measured by X-ray diffraction of
less than about 40%. In another embodiment of the invention, the
propylene copolymer comprises one or more P/E* copolymers. As noted
earlier, fibers made from these polymers or polymer blends can take
any one of a number of different forms and configurations.
[0058] Elastic fibers comprising polyolefins are known, e.g., U.S.
Pat. Nos. 5,272,236, 5,278,272, 5,322,728, 5,380,810, 5,472,775,
5,645,542, 6,140,442 and 6,225,243. The polymers used in the
practice of this invention can be used in essentially the same
manner as known polyolefins for the making and using of elastic
fibers. In this regard, the polymers used in the practice of this
invention can include functional groups, such as a carbonyl,
sulfide, silane radicals, etc., and can be crosslinked or
uncrosslinked. If crosslinked, the polymers can be crosslinked
using known techniques and materials with the understanding that
not all crosslinking techniques and materials are effective on all
polyolefins, e.g., while peroxide, azo and electromagnetic
radiation (such as e-beam, UV, IR and visible light) techniques are
all effective to at least a limited extent with polyethylenes, only
some of these, e.g., e-beam, are effective with polypropylenes and
then not necessarily to the same extent as with polyethylenes. The
use of additives, promoters, etc., as noted earlier, can be
employed as desired.
[0059] "Fiber" means a material in which the length to diameter
ratio is typically greater than about 10. Fiber diameter can be
measured and reported in a variety of fashions. Generally, fiber
diameter is measured in denier per filament. Denier is a textile
term which is defined as the grams of the fiber per 9000 meters of
that fiber's length. Monofilament generally refers to an extruded
strand having a denier per filament greater than 15, usually
greater than 30. Fine denier fiber generally refers to fiber having
a denier of about 15 or less. Microdenier (also known as
microfiber) generally refers to fiber having a diameter smaller
than 1 denier, or less than 12 microns for PP.
[0060] "Filament fiber or "monofilament fiber" means a continuous
strand of material of indefinite (i.e., not predetermined) length,
as opposed to a "staple fiber" which is a discontinuous strand of
material of definite length (i.e., a strand which has been cut or
otherwise divided into segments of a predetermined length).
[0061] "Elastic" means that a fiber will have an immediate set of
less than 15% as measured by the 50% 1-cycle test described below
in the Measurement Methods. Elasticity can also be described by the
"permanent set" of the fiber. Permanent set is the converse of
elasticity. A fiber is stretched to a certain point and
subsequently released to the original position before stretch, and
then stretched again. The point at which the fiber begins to pull a
load is designated as the percent permanent set. "Elastic
materials" are also referred to in the art as "elastomers" and
"elastomeric". Elastic material (sometimes referred to as an
elastic article) includes the polymer itself as well as, but not
limited to, the polymer in the form of a fiber, film, strip, tape,
ribbon, sheet, coating, molding and the like. The preferred elastic
material is fiber. The elastic material can be cured or uncured,
radiated or unradiated, and/or crosslinked or uncrosslinked.
[0062] "Nonelastic material" means a material, e.g., a fiber, that
is not elastic as defined above.
[0063] "Homofilament fiber", "monolithic fiber", "monocomponent
fiber" and similar terms mean a fiber that has a single polymer
region or domain, and that does not have any other distinct polymer
regions (in contrast to bicomponent fibers).
[0064] "Bicomponent fiber" means a fiber that has two or more
distinct polymer regions or domains. Bicomponent fibers are also
known as conjugated or multicomponent fibers. The polymers are
usually different from each other although two or more components
may comprise the same polymer. The polymers are arranged in
substantially distinct zones across the cross-section of the
bicomponent fiber, and usually extend continuously along the length
of the bicomponent fiber. The configuration of a bicomponent fiber
can be, for example, a sheath/core arrangement (in which one
polymer is surrounded by another), a side by side arrangement, a
pie arrangement or an "islands-in-the sea" arrangement. Bicomponent
fibers are further described in U.S. Pat. Nos. 6,225,243,
6,140,442, 5,382,400, 5,336,552 and 5,108,820.
[0065] "Meltblown fibers" are fibers formed by extruding a molten
thermoplastic polymer composition through a plurality of fine,
usually circular, die capillaries as molten threads or filaments
into converging high velocity hot gas streams (e.g. air) which
function to attenuate the threads or filaments to reduced
diameters. The filaments or threads are carried by the high
velocity hot gas streams and deposited on a collecting surface to
form a web of randomly dispersed fibers with average diameters
generally smaller than 10 microns.
[0066] "Meltspun fibers" are fibers formed by melting at least one
polymer and then drawing the fiber in the melt to a diameter (or
other cross-section shape) less than the diameter (or other
cross-section shape) of the die.
[0067] "Spunbond fibers" are fibers formed by extruding a molten
thermoplastic polymer composition as filaments through a plurality
of fine, usually circular, die capillaries of a spinneret. The
diameter of the extruded filaments is rapidly reduced, and then the
filaments are deposited onto a collecting surface to form a web of
randomly dispersed fibers with average diameters generally between
about 7 and about 30 microns.
[0068] "Nonwoven" means a web or fabric having a structure of
individual fibers or threads which are randomly interlaid, but not
in an identifiable manner as is the case of a knitted fabric. The
elastic fiber of the present invention can be employed to prepare
nonwoven structures as well as composite structures of elastic
nonwoven fabric in combination with nonelastic materials.
[0069] "Draw" means draw down, which is V.sub.fiber/V.sub.capillary
(approximately equal to D.sup.2.sub.capillary/D.sup.2.sub.fiber if
crystallinity changes from the melt to the fiber are ignored).
V.sub.fiber means the velocity of the fiber at the winder,
V.sub.capillary means the velocity of the fiber as it exits the
spinneret. D.sub.capillary means the diameter of the cross-section
of the capillary, and D.sub.fiber means the diameter of the
cross-section of the fiber at the point of measurement. At constant
denier per filament (dpf), draw down is fixed at a given capillary
diameter regardless of production rate.
[0070] "Stick points" are usually measured by stringing up the
fiber at fixed speeds (e.g., 1000, 2000, 3000 m/min), and then
pressing a glass rod against the front of the fiber bundle at the
bottom of the quench cabinet. The glass rod is raised until the
fiber sticks to the rod. This is repeated 3 times at each speed and
the stick points averaged. The stick point is taken as the distance
down from the spinneret face in centimeters. Typically, for a given
resin, the stick point decreases (crystallization rate is
increased) as the spinning speed increases due to increased
spinning stress and narrower fibers (improved heat transfer).
Spinning stress can also be increased by increasing draw down,
i.e., by using a larger hole die, as mass balance forces the fiber
to come to the same final diameter (at constant take-up speed)
regardless of the initial diameter (spinneret hole size). By
increasing spinning stress, the fiber crystallizes faster, and the
stick point moves up toward the die.
[0071] As used herein, for nonwovens, the term "extensible"
includes materials that are stretchable to at least 150%. "Elastic"
means that a web sample will have an immediate set of less than 15%
as measured by the 50% 1-cycle test described above under Test
Procedures. Elasticity can also be described by the "first cycle
set" of the web. "Set" is as defined in the Test Procedures.
[0072] To quantify a fabric with good formation, the number of
filament aggregates per 2 cm length is measured. Each filament
aggregate is at least 10 times the fiber width in length. Care was
taken to not include thermal and pressure bond points in the 2 cm
length. Over a 2 cm length in random directions, the linear line
count of filament aggregates was taken. Filament aggregates consist
of multiple filaments in parallel orientation fused together. The
filaments are fused for greater than 10 times the width of the
fiber. Filament aggregates are separate from thermal or pressure
bond points. For good web formation, the number of filament
aggregates is lower than 30/2 cm, preferentially lower than 20/2
cm.
[0073] The propylene copolymers used in the practice of this
invention, particularly the P/E* copolymers, can be blended, as
noted above, with other polymers to form the fibers of this
invention. Suitable polymers for blending with these propylene
copolymers are commercially available from a variety of suppliers
and include, but are not limited to, other polyolefins such as an
ethylene polymer (e.g., low density polyethylene (LDPE), ULDPE,
medium density polyethylene (MDPE), LLDPE, HDPE, homogeneously
branched linear ethylene polymer, substantially linear ethylene
polymer, graft-modified ethylene polymer, ethylene-styrene
interpolymers (ESI), ethylene vinyl acetate interpolymer, ethylene
acrylic acid interpolymer, ethylene ethyl acetate interpolymer,
ethylene methacrylic acid interpolymer, ethylene methacrylic acid
ionomer, and the like), polycarbonate, polystyrene, conventional
polypropylene (e.g., homopolymer polypropylene, polypropylene
copolymer, random block polypropylene interpolymer and the like),
thermoplastic polyurethane, polyamide, polylactic acid
interpolymer, thermoplastic block polymer (e.g. styrene butadiene
copolymer, styrene butadiene styrene triblock copolymer, styrene
ethylene-butylene styrene triblock copolymer and the like),
polyether block copolymer (e.g., PEBAX), copolyester polymer,
polyester/polyether block polymers (e.g., HYTEL), ethylene carbon
monoxide interpolymer (e.g., ethylene/carbon monoxide (ECO),
copolymer, ethylene/acrylic acid/carbon monoxide (EAACO)
terpolymer, ethylene/methacrylic acid/carbon monoxide (EMAACO)
terpolymer, ethylene/vinyl acetate/carbon monoxide (EVACO)
terpolymer and styrene/carbon monoxide (SCO)), polyethylene
terephthalate (PET), chlorinated polyethylene, and the like and
mixtures thereof. In other words, the propylene copolymer used in
the practice of this invention can be blended with two or more
polyolefins, or blended with one or more polyolefins and/or with
one or more polymers other than a polyolefin. If the propylene
copolymer used in the practice of this invention, or a blend of
such copolymers, is blended with one or more polymers other than a
propylene copolymer, then the polypropylene copolymer(s) preferably
comprises at least about 50, more preferably at least about 70 and
more preferably at least about 90, wt % of the total weight of the
blend. As noted above, in one embodiment of the invention, the
fiber comprises at least 98 wt % of a propylene copolymer,
preferably a P/E* copolymer. For some applications, particularly
when web uniformity is a concern, the fiber may comprise
significant amounts (for example 10-40 wt % of the total weight of
the blend) of a higher crystalline material such as homopolymer
polypropylene. The amount of the various components in the blend
can be optimized to balance extensibility/elasticity with other
properties such as web uniformity.
[0074] In one embodiment, the propylene copolymer used in the
practice of this invention is a blend of two or more propylene
copolymers. Suitable propylene copolymers for use in the invention,
including random propylene ethylene polymers, are available from a
number of manufacturers, such as, for example, The Dow Chemical
Company, Basell Polyolefins and Exxon Chemical Company. Suitable
conventional and metallocene polypropylene polymers from Exxon are
supplied under the designations ESCORENE and ACHIEVE. The propylene
copolymer used in the practice of this invention can also be
blended with homopolymer polypropylene (h-PP).
[0075] Suitable graft-modified polymers useful as blend polymers in
the practice of this invention are well known in the art, and
include the various ethylene polymers bearing a maleic anhydride
and/or another carbonyl-containing, ethylenically unsaturated
organic radical. Representative graft-modified polymers are
described in U.S. Pat. No. 5,883,188, such as a homogeneously
branched ethylene polymer graft-modified with maleic anhydride.
[0076] Suitable polylactic acid (PLA) polymers for use as blend
polymers in the practice of this invention are well known in the
literature (e.g., see D. M. Bigg et al., "Effect of Copolymer Ratio
on the Crystallinity and Properties of Polylactic Acid Copolymers",
ANTEC '96, pp. 2028-2039; WO 90/01521; EP 0 515203A and EP 0 748
846 A2). Suitable polylactic acid polymers are supplied
commercially by Cargill Dow under the designation EcoPLA.
[0077] Suitable thermoplastic polyurethane (TPU) polymers for use
as blend polymers in the practice of this invention are
commercially available from BASF and from The Dow Chemical Company
(the latter marketing them under the designation PELLETHANE).
[0078] Suitable polyolefin carbon monoxide interpolymers for use as
blend polymers in the practice of this invention can be
manufactured using well known high pressure free-radical
polymerization methods. However, they may also be manufactured
using traditional Ziegler-Natta catalysis, or with the use of
so-called homogeneous catalyst systems such as those described and
referenced above.
[0079] Suitable free-radical initiated high pressure
carbonyl-containing ethylene polymers such as ethylene acrylic acid
interpolymers for use as blend polymers in the practice of this
invention can be manufactured by any technique known in the art
including the methods taught by Thomson and Waples in U.S. Pat.
Nos. 3,520,861, 4,988,781, 4,599,392 and 5,384,373.
[0080] Suitable ethylene vinyl acetate interpolymers for use as
blend polymers in the practice of this invention are commercially
available from various suppliers, including The Dow Chemical
Company, Exxon Chemical Company and Du Pont Chemical Company.
[0081] Suitable ethylene/alkyl acrylate interpolymers for use as
blend polymers in the practice of this invention are commercially
available from various suppliers. Suitable ethylene/acrylic acid
interpolymers for use as blend polymers in the practice of this
invention are commercially available from The Dow Chemical Company
under the designation PRIMACOR. Suitable ethylene/methacrylic acid
interpolymers for use as blend polymers in the practice of this
invention are commercially available from DuPont Chemical Company
under the designation NUCREL.
[0082] Chlorinated polyethylene (CPE), especially chlorinated
substantially linear ethylene polymers, for use as blend polymers
in the practice of this invention can be prepared by chlorinating
polyethylene in accordance with well known techniques. Preferably,
chlorinated polyethylene comprises equal to or greater than 30
weight percent chlorine. Suitable chlorinated polyethylenes for use
as blend polymers in the practice of this invention are
commercially supplied by The Dow Chemical Company under the
designation TYRIN.
[0083] Bicomponent fibers can also be made from the propylene P/E*
copolymers of this invention. Such bicomponent fibers have the
polypropylene polymer of the present invention in at least one
portion of the fiber. For example, in a sheath/core bicomponent
fiber (i.e., one in which the sheath surrounds the core), the
polypropylene can be in either the sheath or the core. Different
polypropylene polymers of this invention can also be used
independently as the sheath and the core in the same fiber,
preferably where both components are elastic and especially where
the sheath component has a higher melting point than the core
component. Other types of bicomponent fibers are within the scope
of the invention as well, and include such structures as
side-by-side conjugated fibers (e.g., fibers having separate
regions of polymers, wherein the polyolefin of the present
invention comprises at least one region of the fiber).
[0084] The shape of the fiber is not limited. For example, typical
fiber has a circular cross-sectional shape, but sometimes fibers
have different shapes, such as a trilobal shape, or a flat (i.e.,
"ribbon" like) shape. The fiber embodiments of this invention are
not limited by the shape of the fiber.
[0085] The fibers of this invention can be made using any
conventional technique including melt blown, melt spun and spun
bond. For melt spun fibers, the melt temperature, throughput, fiber
speed and drawdown can vary widely. Typical melt temperatures range
between 190 and 245C with the higher temperatures supporting higher
throughputs and fiber speeds, particularly for melts of polymers
with a relatively high MFR, e.g., 25 or greater. Throughput,
measured in grams/hole/minute (ghm), typically ranges between 0.1
and 1.0, preferably between 0.2 and 0.7, ghm. Fiber speed typically
ranges from less than 1000 to more than 3000, but preferably
between 1000 and 3000 meters per minute (m/min). Drawdown varies
from less than 500 to more than 2500. Generally, greater draw down
results in a more inelastic fiber.
[0086] The fibers of this invention can be used with other fibers
such as those made from PET, nylon, cotton, Kevlar.TM., etc. to
make elastic and nonelastic fabrics.
[0087] Fabrics made from the elastic fibers of this invention
include woven, nonwoven and knit fabrics. Nonwoven fabrics can be
made various by methods, e.g., spunlaced (or hydrodynamically
entangled) fabrics as disclosed in U.S. Pat. Nos. 3,485,706 and
4,939,016, carding and thermally bonding staple fibers; spunbonding
continuous fibers in one continuous operation; or by melt blowing
fibers into fabric and subsequently calendaring or thermally
bonding the resultant web. These various nonwoven fabric
manufacturing techniques are well known to those skilled in the art
and the disclosure is not limited to any particular method. Other
structures made from such fibers are also included within the scope
of the invention, including e.g., blends of these novel fibers with
other fibers (e.g., poly(ethylene terephthalate) or cotton).
[0088] Fabricated or multicomponent articles that can be made using
the fibers and fabrics of this invention include composite articles
(e.g., diapers) that have elastic portions. For example, elastic
portions are typically constructed into diaper waist band portions
to prevent the diaper from falling and leg band portions to prevent
leakage (as shown in U.S. Pat. No. 4,381,781). Often, the elastic
portions promote better form fitting and/or fastening systems for a
good combination of comfort and reliability. The inventive fibers
and fabrics of this invention can also produce structures which
combine elasticity with breathability. For example, the inventive
fibers, fabrics and/or films may be incorporated into the
structures disclosed in U.S. Pat. No. 6,176,952.
[0089] Both the propylene copolymers and fibers made from the
copolymers can be subjected to post reaction/formation treatments,
e.g. crosslinking, annealing and the like. The benefits and
techniques of annealing are described in U.S. Pat. No. 6,342,565.
These post treatments are applied in their conventional manner.
[0090] The following examples are given to illustrate various
embodiments of the invention. They do not intend to limit the
invention as otherwise described and claimed herein. All numerical
values are approximate. When a numerical range is given, it should
be understood that embodiments outside the range are still within
the scope of the invention unless otherwise indicated. In the
following examples, various polymers were characterized by a number
of methods. Performance data of these polymers were also obtained.
Most of the methods or tests were performed in accordance with an
ASTM standard, if applicable, or known procedures. All parts and
percentages are by weight unless otherwise indicated.
SPECIFIC EMBODIMENTS
[0091] The effect of spinning conditions was examined for polymers
with 25-38 MFR. Elongational stresses achieved by controlling
throughput and take-off rate determined the amount of
stress-induced crystallinity in the fiber and hence the resulting
mechanical properties. Higher elongational stresses achieved at a
draw down greater than 1000 resulted in higher crystallinity and
hence more rigid fibers. More elasticity was preserved at lower
crystallinity or draw down less than 1000. For more elastic fiber,
very low crystallinity or draw down less than 500 was preferred. To
verify that elasticity was maintained, the tensile hysteresis
behavior was measured.
Measurement Methods
[0092] Density Method:
[0093] Coupon samples (1 inch.times.1 inch.times.0.125 inch) were
compression molded at 190.degree. C. according to ASTM D4703-00 and
cooled using procedure B. Once the sample cooled to 40-50.degree.
C., it was removed. Once the sample reached 23.degree. C., its dry
weight and weight in isopropanol was measured using an Ohaus AP210
balance (Ohaus Corporation, Pine Brook N.J.). Density was
calculated as prescribed by ASTM D792 procedure B.
[0094] DSC Method:
[0095] Differential scanning calorimetry (DSC) is a common
technique that can be used to examine the melting and
crystallization of semi-crystalline polymers. General principles of
DSC measurements and applications of DSC to studying
semi-crystalline polymers are described in standard texts (e.g., E.
A. Turi, ed., Thermal Characterization of Polymeric Materials,
Academic Press, 1981). Certain of the copolymers used in the
practice of this invention are characterized by a DSC curve with a
T.sub.me that remains essentially the same and a T.sub.max that
decreases as the amount of unsaturated comonomer in the copolymer
is increased. T.sub.me means the temperature at which the melting
ends. T.sub.max means the peak melting temperature.
[0096] Differential Scanning Calorimetry (DSC) analysis is
determined using a model Q1000 DSC from TA Instruments, Inc.
Calibration of the DSC is done as follows. First, a baseline is
obtained by running the DSC from -90.degree. C. to 290.degree. C.
without any sample in the aluminum DSC pan. Then 7 milligrams of a
fresh indium sample is analyzed by heating the sample to
180.degree. C., cooling the sample to 140.degree. C. at a cooling
rate of 10.degree. C./min followed by keeping the sample
isothermally at 140.degree. C. for 1 minute, followed by heating
the sample from 140.degree. C. to 180.degree. C. at a heating rate
of 10.degree. C./min. The heat of fusion and the onset of melting
of the indium sample are determined and checked to be within
0.5.degree. C. from 156.6.degree. C. for the onset of melting and
within 0.5 J/g from 28.71 J/g for the heat of fusion. Then
deionized water is analyzed by cooling a small drop of fresh sample
in the DSC pan from 25.degree. C. to -30.degree. C. at a cooling
rate of 10.degree. C./min. The sample is kept isothermally at
-30.degree. C. for 2 minutes and heated to 30.degree. C. at a
heating rate of 10.degree. C./min. The onset of melting is
determined and checked to be within 0.5.degree. C. from 0.degree.
C.
[0097] The polypropylene samples are pressed into a thin film at a
temperature of 190.degree. C. About 5 to 8 mg of sample is weighed
out and placed in the DSC pan. The lid is crimped on the pan to
ensure a closed atmosphere. The sample pan is placed in the DSC
cell and the heated at a high rate of about 100.degree. C./min to a
temperature of about 60.degree. C. above the melt temperature. The
sample is kept at this temperature for about 3 minutes. Then the
sample is cooled at a rate of 10.degree. C./min to -40.degree. C.,
and kept isothermally at that temperature for 3 minutes.
Consequently the sample is heated at a rate of 10.degree. C./min
until complete melting. The resulting enthalpy curves are analyzed
for peak melt temperature, onset and peak crystallization
temperatures, heat of fusion and heat of crystallization, T.sub.me,
and any other DSC analyses of interest.
[0098] X-ray Experimental:
[0099] The samples were conveniently analyzed in a transmission
mode using a GADDS system from Bruker-AXS, with a multi-wire
two-dimensional HiStar detector. Samples were aligned with a laser
pointer and a video-microscope. Data were collected using copper
K.alpha. radiation (at a wavelength of 1.54 angstroms) with a
sample-to-detector (SDD) distance of 6 cm. The X-ray beam was
collimated to 0.3 mm. For the 2D area detector in transmission
mode, the radial distance from the center, r, is equal to
SDD.times.(tan 2.theta.), where 2.theta. is equal to the angle
between the incident x-ray beam and the diffracted beam. For Cu
K.alpha. radiation and an SDD of 6 cm, the range of 20 actually
measured was about 0.degree. to 35.degree.. The azimuthal angle,
.phi., ranged from 0.degree.-360.degree.
[0100] Data Analysis:
[0101] Conventionally, the scattering area (or intensity) from
amorphous segments, which lies underneath the diffraction area from
the crystal phase, is determined by profile fitting of a
diffraction profile using an appropriate software package (e.g.,
the Jade software, from Materials Data, Inc, that was used here).
Then, the absolute crystallinity, X.sub.C-Abs, is calculated based
on the ratio of these two area values as given below: X C - Abs = (
1 - I Am I Total ) Equation .times. .times. 2 ##EQU2## where
I.sub.Am is the integrated intensity, after background subtraction,
for the amorphous scattering, and I.sub.Total, is the total
intensity measured and incorporates the scattering and diffraction
of both polymer phases (again, after background subtraction). The
method of determining I.sub.Total is detailed more later.
[0102] However, such an analysis is most accurate only in the
absence of significant preferred orientation (both of the
crystalline and amorphous phases) and for samples with relatively
high crystallinity, where the peaks are strong and well defined. In
the case of the highly oriented, low crystallinity fibers of this
study, conventional profile fitting, using the data for the entire
360.degree. azimuthal range, did not yield a reproducible and
reliable estimate of the shape of the amorphous scattering curve,
I.sub.Am, and a different method for quantifying this value had to
be devised, as will be discussed following the discussion of
I.sub.Total determination below.
[0103] For all samples in this study, whether low or high in
crystallinity or orientation, the total integrated intensity due to
both crystal phase diffraction and amorphous phase scattering, or
I.sub.Total, was obtained as follows. First, the 2D screen was
divided into small bands (concentric circles) of thickness
.DELTA.r. At each r+.DELTA.r distance from the center of the
detector out to the edges of the screen, the intensity was averaged
over 360.degree. (i.e., from .phi.=0.degree. to 360.degree.) to
give I.sub.AVG(r), which was then integrated from r=0 to
r=r.sub.max (or 2.theta. from 0.degree. to 35.degree.) to give
I.sub.Total.
[0104] The amorphous scattering, on the other hand, was not
determined from such a total angular profile. Instead, the
intensities of amorphous scattering were determined in only two
extreme, or particular, directions of .phi. (i.e. using only two
particular azimuthal angles) along the fiber direction
(.phi.=0.degree.), and 2) along a "near equatorial" direction
approximately perpendicular to the fiber direction (12 degrees off
the equatorial direction, or .PHI.4=78.degree.). Along these two
directions, the intensity from 0.degree. to 35.degree. 2.theta. is
essentially all due to amorphous scattering, as crystal peak
diffraction in these two directions is very weak or absent, and a
reliable determination of the true shape of the amorphous peak is
obtained.
[0105] The average of amorphous scattering area, I.sub.Am, for the
entire 0-360 degrees of .phi. was then estimated from
I.sub.Am(.phi.=0.degree.) and I.sub.Am(.phi.=78.degree.) as:
I''.sub.Am=1/2*[I.sub.Am(.phi.=0.degree.)+I.sub.Am(.phi.=78.degree.)]
Equation 3 where, again, I.sub.am(.phi.=0.degree.) is the
integrated intensity of amorphous scattering along the fiber axis
from 0.degree. to 35.degree. 2.theta., and
I.sub.am(.phi.=78.degree.) is the same obtained at an angle
12.degree. off the equatorial (perpendicular) axis. The
crystallinity index, Xc, is then determined similarly to Equation 2
as follows: X C = ( 1 - I Am * I Total ) .times. 100 Equation
.times. .times. 4 ##EQU3## where X.sub.C-Abs has been changed to
X.sub.C to indicate that X.sub.C is an index of the amount of
crystallinity in the sample, not an absolute crystallinity level,
due to the presence of preferred crystal phase orientation.
However, by using Equation 4, the crystallinity index calculated
was found to be reliable and reproducible for samples across a
broad range of crystallinities, from a few percent to about
40%.
[0106] The Amorphous Orientation was obtained by the ratio of
amorphous scattering intensities in the fiber direction to that in
the near equatorial direction, or: Amorphous
Orientation=I.sub.Am(.phi.=0.degree.)/I.sub.Am(.phi.=78) Equation 5
noting that, for oriented fibers, I.sub.Am(.phi.=78.degree.) is
greater than I.sub.Am(.phi.=0.degree.). Based on this definition, a
value of 0 represents perfect amorphous orientation, and 1
represents random orientation. These data were also found to be
quite reproducible and reliable across a broad orientation and
crystallinity range.
[0107] For the crystal orientation, a conventional Hermans'
Orientation function, f.sub.c, was determined using Wilchinsky's
method (J. Appl. Physics, 30, 792 (1959)). The calculated f.sub.c
represents the degree of crystal orientation along the fiber
direction. A value of 1 represents perfect orientation, 0 represent
random orientation, and -0.5 represents perfectly perpendicular
orientation.
[0108] Tensile Test:
[0109] A tow of 144 filaments was loaded between two pneumatically
activated line-contact grips separated by 2 inches. This is taken
to be the gauge length. The flat grip facing is coated with rubber.
Pressure is adjusted to prevent slippage (usually 50-100 psi). The
crosshead is increased at 10 inches per minute until the specimen
breaks. Strain is calculated by dividing the crosshead displacement
by 2 inches and multiplying by 100. Reduced load (g/denier) equals
[load (grams force)/number of filaments/denier per filament].
Elongation was defined according to equation 6: Elongation .times.
.times. ( % ) = L break - L o L o .times. 100 .times. % Equation
.times. .times. 6 ##EQU4## such that L.sub.o is the initial length
of two inches, and L.sub.break is the length at break. Tenacity is
defined according to the equation 7: Tenacity .times. .times. ( g /
den ) = F break .function. ( g ) d .times. f Equation .times.
.times. 7 ##EQU5## such that F.sub.break is the force at break
measured in grams force, d is denier per filament, and f is the
number of filaments in the tow that is being tested.
[0110] 50% 1-Cycle Test:
[0111] The sample was loaded and the grip spacing was set up as
done in the tensile test. The crosshead speed was set at 10 inches
per minute. The crosshead was raised until a strain of 50% was
applied, and then the crosshead was returned at the same crosshead
speed to 0% strain. After returning to 0% strain, the crosshead was
extended at 10 inches per minute. The onset of load was taken as
the immediate set. Reduced load was measured during the first
extension and first retraction of the sample at 30% strain.
Retained load was calculated as the reduced load at 30% strain
during retraction divided by the reduced load at 30% strain during
extension multiplied by 100.
[0112] Nonwoven Measurements:
[0113] Specimens for nonwoven measurements were obtained by cutting
3 inch wide by 8 inch strips from the web in the machine (MD) and
cross direction (CD). Basis weight, in g/m.sup.2, was determined
for each sample by dividing the weight, measured with an analytical
balance, divided by the area. Samples were then loaded into a
Sintech fitted with pneumatically activated line-contact grips with
an initial separation of 3 inches and pulled to break at 12
inches/min. Peak load and peak strain were recorded for each
tensile measurement.
[0114] Elasticity was measured using a 1-cycle hysteresis test to
80% strain. In this test, samples were loaded into a Sintech fitted
with pneumatically activated line-contact grips with an initial
separation of 4 inches. Then the sample was stretched to 80% at 500
mm/min, and returned to 0% strain at the same speed. The strain at
10 g load upon retraction was taken as the % set. The hysteresis
loss is defined as the energy difference between the strain and
retraction cycle. The load down was the retractive force at 50%
strain. In all cases, the samples were measured green or
unaged.
[0115] Filament Aggregates:
[0116] To quantify a fabric with good formation, the following
method was employed. A Nikon SNZ-10 binocular microscope was used
at 10.times. magnification with incident light to count the number
of filament aggregates over a given length. Only filaments
aggregates that intersected the 2 cm line were counted. Each
filament aggregate is at least 10 times the fiber width in length.
Care was taken to not include thermal and pressure bond points in
the 2 cm length. Over a 2 cm length in random directions, the
linear line count of filament aggregates was taken. `Filament
aggregates` consist of multiple filaments in parallel orientation
fused together. The filaments are considered fused, if the length
of fusion persists for greater than 10 times the width of the
fiber. Filament aggregates are separate from thermal or pressure
bond points.
[0117] Scanning Electron Microscopy:
[0118] Samples for scanning electron microscopy were mounted on
aluminum sample stages with carbon black filled tape and copper
tape. The mounted samples were then coated with 100-200 .ANG. of
gold using an SPI-Module Sputter Coater (Model Number 11430) from
Structure Probe Incorporated (West Chester, Mass.) fitted with an
argon gas supply and a vacuum pump.
[0119] The gold coated samples were then examined in a Hitachi
S4100 scanning electron microscope equipped with a field effect gun
and supplied by Hitachi America, Ltd (Shaumberg, Ill.). Samples
were examined using secondary electron imaging mode were measured
using an acceleration voltage of 3-5 kV and collected using a
digital image capturing system.
Experimental Data
[0120] The different resins used are presented in Table 1. In that
Table "X-Ray Crystallinity Index" refers to the crystallinity index
of a rapidly quenched compression molded film sample and is
therefore not directly comparable with crystallinity indices
reported for fiber samples in the subsequent tables.
[0121] Propylene-ethylene copolymers comprising about 9-16 wt. %
ethylene were used in the following examples. For comparison, an
ethylene-octene copolymer and a polypropylene homopolymer were also
used. The melt flow ratio (MFR) of each polymer was 20-40 (or about
a 10-20 melt index (MI) equivalent). TABLE-US-00001 TABLE 1 RESINS
DSC X-Ray MI Heat of Melting Crystallinity Polymer or Density
Melting Points Index Type Description MFR (g/cm.sup.3) (J/g)
(.degree. C.) (%) Ex1 propylene- 5 wt % 25 0.8887 71 115 52
ethylene ethylene MFR Ex2 propylene- 9 wt % 25 0.876 54 104, 134 31
ethylene ethylene MFR Ex3 propylene- 12 wt % 25 0.867 34 51, 124 17
ethylene ethylene MFR Ex4 propylene- 15 wt % 25 0.860 18 124 --
ethylene ethylene MFR C1 homopolymer -- 38 0.900 110 162 -- PP MFR
C2 random PP 3 wt. % 35 0.90 89 143 -- copolymer ethylene MFR C3
metallocene -- 24 0.90 103 149 -- PP MFR C4 ethylene- 38-40 wt % 10
0.870 50 51, 62 -- octene octene MI
In this and the following tables, Ex1-Ex4 are the inventive
examples and C1-C4 are the comparative examples.
[0122] Fibers were spun under a variety of conditions. The main
variables were throughput (grams/hole/minute or ghm), which was
controlled by pump speed, extruder design, and die parameters. The
spinneret had 144 holes, each of which had a diameter of 0.65 mm
and a length/diameter ratio (L/D) of 3.85. The quench air
temperature was 12.degree. C. and was distributed over the three
zones. The air velocities in each of the zones were measured as
0.20, 0.28 and 0.44 m/s using a hot-wire anemometer. Melt
temperature was varied from 190 to 245.degree. C. Draw down was
controlled by a combination of spinning speed and pump rate.
[0123] Six spinning runs were conducted using the propylene
copolymer Ex1. The melt temperature of each run was 220.degree. C.,
the throughput was 0.6 ghm for Runs Ex1/1-3 and 0.3 ghm for Runs
Ex1/4-6, and the spinning speed (meters/minute or m/min) was 1000
m/min for Runs Ex1/1 and Ex1/4, 2000 m/min for Runs Ex1/2 and
Ex1/5, and 3000 m/min for Runs Ex1/3 and Ex1/6. The data are
presented in Table 2. TABLE-US-00002 TABLE 2 SPINNING CONDITIONS
AND X-RAY CHARACTERIZATION OF EX1 FIBERS Crystallinity Crystal Draw
Denier/ Crystal Index, Xc Amorphous Orientation, Run No. Down
Filament Type (%) Orientation fc Ex1/1 421 5.4 smectic &
.alpha. -- -- -- Ex1/2 841 2.7 .alpha. 26.0 0.62 0.887 Ex1/3 1261
1.8 .alpha. 21.3 0.63 0.893 Ex1/4 841 2.7 .alpha. -- -- -- Ex1/5
1681 1.35 .alpha. 33.9 0.72 0.914 Ex1/6 2522 0.9 .alpha. 27.0 0.70
0.911
[0124] Six spinning runs were conducted using the propylene
copolymer Ex2. The melt temperature of each run was 220.degree. C.,
the throughput was 0.6 ghm for Runs Ex2/1-3 and 0.3 ghm for Runs
Ex2/4-6, and the spinning speed (meters/minute or m/min) was 1000
m/min for Runs Ex2/1 and Ex2/4, 2000 m/min for Runs 2/2 and 2/5,
and 3000 m/min for Runs Ex2/3 and Ex2/6. The data are presented in
Table 3. TABLE-US-00003 TABLE 3 SPINNING CONDITIONS AND X-RAY
CHARACTERIZATION OF EX2 FIBERS Crystallinity Crystal Denier/
Crystal Index, Xc Amorphous Orientation, Run No. Draw Down Filament
Type (%) Orientation fc Ex2/1 421 5.4 .alpha. 21.2 0.88 0.922 Ex2/2
841 2.7 .alpha. 23.8 0.76 0.932 Ex2/3 1261 1.8 .alpha. 20.7 0.8
0.956 Ex2/4 841 2.7 .alpha. 15 0.88 0.948 Ex2/5 1681 1.35 .alpha.
16.7 0.8 0.949 Ex2/6 2522 0.9 .alpha. 24.6 0.81 0.961
[0125] Six spinning runs were conducted using the propylene
copolymer Ex3. The melt temperature of each run was 220.degree. C.,
the throughput was 0.6 ghm for Runs 3/1-3 and 0.3 ghm for Runs
3/4-6, and the spinning speed (meters/minute or m/min) was 1000
m/min for Runs 3/1 and 3/4, 2000 m/min for Runs 3/2 and 3/5, and
3000 m/min for Runs 3/3 and 3/6. The data are presented in Table 4.
TABLE-US-00004 TABLE 4 SPINNING CONDITIONS AND X-RAY
CHARACTERIZATION OF EX3 FIBERS Crystallinity Crystal Denier/
Crystal Index, Xc Amorphous Orientation, Run No. Draw Down Filament
Type (%) Orientation fc Ex3/1 421 5.4 .alpha. 12.2 0.88 0.926 Ex3/2
841 2.7 .alpha. 14.7 0.79 0.93 Ex3/3 1261 1.8 .alpha. 17.1 0.74
0.936 Ex3/4 841 2.7 .alpha. 14 0.87 0.930 Ex3/5 1681 1.35 .alpha.
17.8 0.85 0.917 Ex3/6 2522 0.9 .alpha. 19.9 0.76 0.93
[0126] Spinning of Ex1-Ex3 is compared in Table 5. The melt
temperature was 220.degree. C., the draw down 1261, and the
throughput 0.4 ghm for each run. The spinning speed was 2000 m/min
for each run. TABLE-US-00005 TABLE 5 SPINNING CONDITIONS AND X-RAY
CHARACTERIZATION OF DIFFERENT EXAMPLES Crystallinity Index
Amorphous Crystal Resin (%) Orientation Orientation Ex1/7 25.8 0.71
0.938 Ex2/7 12.5 0.89 0.939 Ex3/7 4 0.93 0.849
[0127] Comparative examples C1-C3 were run under the same
conditions as reported in Tables 2, 3 and 4. The results are
presented in Table 6, 7 and 8 respectively. TABLE-US-00006 TABLE 6
SPINNING CONDITIONS AND X-RAY CHARACTERIZATION OF C1 FIBERS
Crystallinity Run Denier/ Crystal Index, Xc Amorphous Crystal No.
Draw Down Filament Type (%) Orientation Orientation, fc C1/1 421
5.4 smectic 26 0.56 -- C1/2 841 2.7 .alpha. 47.9 0.72 0.956 C1/3
1261 1.8 .alpha. 52.3 0.77 0.957 C1/4 841 2.7 .alpha. 58.2 0.7
0.918 C1/5 1681 1.35 .alpha. 61.5 0.63 0.958 C1/6 2522 0.9 .alpha.
53.1 0.91 0.932
[0128] TABLE-US-00007 TABLE 7 SPINNING CONDITIONS AND X-RAY
CHARACTERIZATION OF C2 FIBERS Crystallinity Run Denier/ Crystal
Index, Xc Amorphous Crystal No. Draw Down Filament Type (%)
Orientation Orientation, fc C2/1 421 5.4 smectic -- -- -- C2/2 841
2.7 .alpha. 38.7 0.69 0.92 C2/3 1261 1.8 -- -- -- -- C2/4 841 2.7
.alpha. 38.7 0.72 0.9 C2/5 1681 1.35 -- -- -- -- C2/6 2522 0.9 --
-- -- --
[0129] TABLE-US-00008 TABLE 8 SPINNING CONDITIONS AND X-RAY
CHARACTERIZATION OF C3 FIBERS Crystallinity Run Denier/ Crystal
Index, Xc Amorphous Crystal No. Draw Down Filament Type (%)
Orientation Orientation, fc C3/1 421 5.4 smectic -- -- -- C3/2 841
2.7 .alpha. 37.3 0.59 0.91 C3/3 1261 1.8 -- -- -- -- C3/4 841 2.7
.alpha. 27.5 0.59 0.87 C3/5 1681 1.35 -- -- -- --
[0130] As mentioned before, the most common crystal form for
oriented PP is the .alpha., monoclinic form. However, for quenched
samples of low orientation (low spinning stress), a less-ordered
crystalline form, referred to as paracrystalline, or smectic, also
exists. In this crystal structure, the chains are not in a perfect
three-dimensional lattice, but have a general two-dimensional
order. This smectic crystalline form is achieved by quickly
quenching the melt to a temperature below 70.degree. C. If
temperatures above 70.degree. C. are applied to a polymer with a
smectic crystal phase, the crystals transform to the more stable
alpha form.
[0131] It is surprising that, under the spinning conditions of
Table 5, the inventive fibers made with Ex2-Ex4 all have the alpha
crystal form. Looking at the comparative resin fibers runs, it is
seen that, for the C1-C3 resins (Z/N h-PP, Z/N ethylene (Et) random
copolymer, and metallocene h-PP) resins spun at low draw down (draw
down=421) and relatively slow fiber speed (1000 m/min) (see runs
C1/1 and C2/1 and C3/1 in Tables 6, 7, and 8), the smectic
structure was found (see C1/1 and C3/1 x-ray diffraction patterns
in FIGS. 1A and 1B).
[0132] The fiber properties for all inventive and comparative
fibers are reported in Table 9. TABLE-US-00009 TABLE 9 FIBER
TENSILE AND ELASTIC PROPERTIES FOR SELECTIVE INVENTIVE AND
COMPARATIVE EXAMPLES Run Modulus Elongation Tenacity 30% load 30%
unload Retained load Immediate Number (g/den) (%) (g/den) (g/den)
(g/den) at 30% (%) Set (%) Ex1/1 7.14 146 2.43 0.71 0.02 2.5 26
Ex1/2 10.95 128 2.86 1.41 0.08 5.6 25 Ex1/3 13.00 101 2.89 1.85
0.13 6.9 25 Ex1/4 9.72 152 2.75 1.00 0.16 15.5 25 Ex1/5 13.98 108
2.81 1.69 0.13 7.6 24 Ex1/6 15.84 86 2.94 2.31 0.15 6.7 25 Ex2/1
2.14 145 1.82 0.49 0.07 13.7 10 Ex2/2 4.06 91 2.76 1.31 0.15 11.6
11 Ex2/3 5.85 69 2.48 1.69 0.20 11.6 11 Ex2/4 3.46 134 2.39 0.75
0.10 13.1 11 Ex2/5 6.89 97 2.90 1.71 0.14 8.3 14 Ex2/6 7.72 66 2.56
2.16 0.17 7.7 12 Ex3/1 0.14 208 -- 0.20 0.05 27.7 5 Ex3/2 1.35 120
2.31 0.70 0.13 18.3 5 Ex3/3 2.16 91 2.27 1.03 0.15 14.9 5 Ex3/4
0.49 151 1.87 0.40 0.09 21.8 5 Ex3/5 2.98 89 2.20 1.01 0.15 15.1 6
Ex3/6 1.91 112 1.89 0.14 0.03 22.0 5 C1/1 19.36 276 1.84 0.47 0.00
0.0 30 C1/2 38.93 202 1.95 1.11 0.07 6.7 19 C1/3 50.41 188 2.35
1.44 0.11 7.9 20 C1/4 25.68 240 2.10 1.08 0.05 5.0 16 C1/5 37.87
215 2.15 1.38 0.11 8.1 18 C1/6 52.48 187 2.27 1.69 0.05 2.8 27 C2/1
8.57 199 2.31 0.62 0.00 0.0 29 C2/2 16.66 161 2.56 1.23 0.01 0.9 28
C2/3 11.42 147 2.56 1.62 0.02 1.5 28 C2/4 13.16 182 2.38 0.96 0.00
0.3 29 C2/5 16.24 166 2.35 1.33 0.03 2.2 29 C2/6 21.65 117 2.15
1.66 0.00 0.3 29 C3/1 12.09 178 2.59 0.70 0.00 0.0 33 C3/2 19.21
115 3.52 1.75 0.00 0.0 29 C3/3 24.88 107 3.09 2.10 0.01 0.5 28 C3/4
21.02 163 3.23 1.80 0.05 0.3 28 C3/5 26.50 112 3.00 2.37 0.02 0.9
28
[0133] Plotting the immediate set and moduli of the fibers
described in the preceding tables (FIG. 2), there is clear
differentiation of the inventive fibers and the comparative
examples. Inventive fibers describe a region of lower immediate set
(less than about 22%) and of lower modulus (less than about 22
g/den) in contrast to the comparative examples. Functionally, this
behavior translates to fibers that are easier to stretch (lower
modulus) and fibers that have greater recovery upon deformation
(lower immediate set).
[0134] FIG. 3 shows that the lower immediate set of the inventive
fibers corresponds to crystallinity index regions of less than or
equal to about 30%. Furthermore, there is clear differentiation
from comparative example C1, which had surprisingly low immediate
set.
[0135] FIG. 4 shows the moduli corresponding to the crystallinity
index region less than or equal to about 30%. The crystallinity
index correlates to fiber stiffness measured as fiber modulus,
which in turn correlates to nonwoven drape and hand. The fiber
stiffness of the inventive polymers is significantly lower than for
other propylene polymers and at lower immediate set and therefore
should result in differentiated fiber as well as fabric.
[0136] FIG. 5 shows the retained load at 30% strain in the 50%
1-cycle test corresponding to the crystallinity index region less
than or equal to 30%. Retained load is a measure of retractive
force for a give extension force and is an aspect of elasticity.
Greater retained loads translate to fibers that have greater
"holding power". In many elastic applications, higher holding power
is desirable for its greater mechanical ability to fasten one
object to another.
[0137] FIG. 6 describes the corresponding tenacity of the inventive
fibers when pulled to break. Again, crystallinity is shown to be a
key factor in tenacity. Surprisingly, lower crystallinity
propylene-ethylene copolymer fibers could match or exceed the
tenacity of many higher crystallinity propylene fibers (Table
9).
[0138] Examination of propylene-ethylene fibers melt spun under a
variety of conditions revealed that comonomer (ethylene) content,
spinning speed and quench condition were the prime determining
factors that affected crystallinity index and in turn, tensile and
elastic properties, as is demonstrated above. The crystallinity
index can be seen to increase with increased spinning speed and
reduced throughput. This effect is typical for stress-induced
crystallization, and surprisingly the effect decreases with
increased ethylene content.
[0139] Consideration of property balances allows further
differentiation of the inventive examples. Plotting immediate set
against retained load at 30% strain (FIG. 8) shows a transition to
very low set with retained loads at 30% strain of about 15% and
greater. These coincide with fibers having a crystallinity index of
about 20% and lower (FIG. 5). Consequently, fibers with less than
about 20% crystallinity index describe elastic performance
characterized by greater recovery (lower immediate set) and by
higher retractive force (higher retained load). The subset of the
inventive fibers with less than 10% crystallinity index can be
classified as elastic fiber.
[0140] Based on the described discoveries, the following table of
preferred ranges for the fibers of this invention is described
(Table 10). TABLE-US-00010 TABLE 10 PREFERRED RANGES FOR THE
INVENTIVE FIBERS Intermediate Intermediate Extensible A B Elastic
Ethylene (greater 6 to 17 7 to 17 9 to 17 (wt. %) than 5) to 17
Crystallinity less than 30 less than 27 less than 23 less than 20
Index (%) Immediate Set less than 22 less than 18 less than 14 less
than 10 (50% 1-Cycle Test) Modulus less than 22 less than 18 less
than 14 less than 10 (g/den) Tenacity greater than greater than
greater than greater than (g/den) 1.2 1.2 1.2 1.2 Retained Load
greater than greater than greater than greater than at 30% (50% 2.5
7 11 15 1-Cycle Test) Elongation .gtoreq.50 .gtoreq.50 .gtoreq.50
.gtoreq.50
[0141] Thirty four g/m.sup.2 (1 ounce per square yard (osy))
spunbond nonwovens were produced from the Ex2 and Ex3 resins on a
14'' pilot line using a 25 holes per inch (hpi) spin pack with a
distance between the spin pack and the fiber drawing unit of 48
inches. The polymer was run at 0.6 ghm at a melt temperature of
390.degree. F. (199.degree. C.). Quench air flow (100 feet/min) and
temperature (70.degree. F.) was applied over a distance of 25
inches. The drawing pressure in the fiber draw unit was 4 psi.
After collecting the fibers on the belt, the nonwovens were bonded
using an average pattern roll/anvil roll temperature of 130.degree.
F. (55.degree. C.). The average fiber size of these webs was about
30 microns. The properties of the nonwovens are presented in Table
11 as examples 4/1 and 4/2. The web homogeneity of the inventive
fabrics is excellent as evidenced by the low number of filament
aggregates per linear 2 cm.
[0142] For example 4/3, a 34 g/m.sup.2 spunbond nonwoven was
produced from the Ex2 polymer on a 14'' pilot line using a 50 holes
per inch (hpi) spin pack with a distance between the spin pack and
the fiber drawing unit of 50 inches. The polymer was run at 0.7 ghm
at a melt temperature of 490.degree. F. (255.degree. C.). Quench
air flow of. 100 feet/min and temperature of 77.degree. F. was
applied over a distance of 25 inches. The drawing pressure in the
fiber draw unit was 6 psi. After collecting the fibers on the belt,
the nonwovens were bonded using an average pattern roll/anvil roll
temperature of 130.degree. F. (55C). The properties of this
nonwoven are also presented in Table 11. The web homogeneity of
this nonwoven is not acceptable as demonstrated by the unacceptably
high number of filament aggregates.
[0143] Comparative Example C4/1 is a commercially available hPP
based nonwoven of 15 g/m.sup.2 (0.45 osy). TABLE-US-00011 TABLE 11
NONWOVEN PROPERTIES Ex 4/2 Ex 4/1 (25MFR, Ex 4/3 C 4/1 (25MFR, 12
wt % (25 MFR (38 MFR, Test 9 wt % E) E) 9 wt % E) 0 wt % E) Basis
weight, g/m.sup.2 (osy) 30.4 33.5 33.5 15.3 (0.893) (0.984) 0.986)
(0.45) Peak Tensile Load, 3920 3580 2530 6121* MD, g Peak Tensile
Load, 1500 990 645 1724* CD, g Peak Elongation, MD, % 168 225 174
43* Peak Elongation, CD, % 277 422 217 69* Set, MD, % 26 -- 30 NA
Set, CD, % 33 19 38 NA Hysteresis loss, MD, % 73 -- 77 NA
Hysteresis loss, CD, % 72 45 76 NA Load down, MD, gF 329 -- 198 NA
Load down, CD, gF 83 78 36 NA Crystallinity Index, % 14.0 9.8 -- --
Number of filament 17 29 40 0 aggregates per 2 cm *data normalized
to 1 osy; NA: not available for measurement as webs fail at about
60% strain
[0144] The data show that both the inventive polymers and the webs
made from them are elastic. The crystallinity index, Xc, measured
on fibers in a nonwoven web in between the bond points, is below
20%. The inventive nonwovens are anisotropic in nature (not due to
the nature of the polymer, but rather to non optimized fabrication
conditions).
[0145] As seen from a comparison between Examples 4/1, 4/2, and
4/3, the processing conditions also play a role in producing a
satisfactory nonwoven. For a given spin pack density and quench air
temperature, only certain combinations of throughput and residence
time of the fiber between the spin pack and the fiber drawing unit,
the melt temperature and the quench air flow rate will lead to more
homogeneous web formation.
[0146] Nonwoven fabrics of Ex4/2 are made of predominantly
individual unmarried filaments. However, such filaments are
self-bonding as evidenced by the micrograph of FIG. 9. The bond
points occur at fiber-fiber contacts, and they are about 5 to 50
.mu.m in length. Conventional, mechanically made bond points, e.g.,
those achieved by a patterned calendar roll, are much larger
(100's-1000's microns) in size and consequently, they cannot match
the density of self-bonding points. Furthermore, the large
film-like bond points and the resulting increase in fabric
stiffness and drape degrade hand feel. In this way, self-bonding
has at least three advantages over mechanical bonding, i.e.,
simplicity in manufacture, better fabric drape and better hand
feel.
[0147] While this invention has been described in considerable
detail by the preceding examples, this detail was provided for the
purpose of illustration only and is not to be construed as a
limitation upon the invention as described in the following claims.
All U.S. patents and allowed U.S. patent applications cited above
are incorporated herein by reference.
* * * * *