U.S. patent application number 12/063124 was filed with the patent office on 2008-08-21 for propylene based meltblown nonwoven layers and composite structures.
Invention is credited to Thomas T. Allgeuer, Andy C. Chang, Gert J. Claasen, Antonios K. Doufas, Edward N. Knickerbocker, Hong Peng, Randy E. Pepper, Jozef J. Van Dun.
Application Number | 20080199673 12/063124 |
Document ID | / |
Family ID | 37308808 |
Filed Date | 2008-08-21 |
United States Patent
Application |
20080199673 |
Kind Code |
A1 |
Allgeuer; Thomas T. ; et
al. |
August 21, 2008 |
Propylene Based Meltblown Nonwoven Layers and Composite
Structures
Abstract
The present invention relates to propylene-based nonwoven layers
made by the meltblown process, and laminates incorporating such
layers. The meltblown layers of the present invention comprise
propylene copolymers characterized by having less than 50 percent
crystallinity. The meltblown layers of the present invention show
an improved combination of extensibility and tensile strength. The
laminate structures of the present invention are characterized by a
combination of low bending modulus with high peel strength.
Inventors: |
Allgeuer; Thomas T.;
(Wollerau, CH) ; Chang; Andy C.; (Houston, TX)
; Claasen; Gert J.; (Adliswil, CH) ; Doufas;
Antonios K.; (Lake Jackson, TX) ; Knickerbocker;
Edward N.; (Lake Jackson, TX) ; Peng; Hong;
(Lake Jackson, TX) ; Pepper; Randy E.; (Lake
Jackson, TX) ; Van Dun; Jozef J.; (Zandhoven,
BE) |
Correspondence
Address: |
The Dow Chemical Company
Intellectual Property Section, P.O. Box 1967
Midland
MI
48641-1967
US
|
Family ID: |
37308808 |
Appl. No.: |
12/063124 |
Filed: |
August 3, 2006 |
PCT Filed: |
August 3, 2006 |
PCT NO: |
PCT/US2006/030416 |
371 Date: |
February 7, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60709668 |
Aug 19, 2005 |
|
|
|
Current U.S.
Class: |
428/219 ;
442/328; 442/382 |
Current CPC
Class: |
Y10T 442/66 20150401;
D04H 1/56 20130101; D04H 1/4374 20130101; D04H 1/4291 20130101;
Y10T 442/601 20150401 |
Class at
Publication: |
428/219 ;
442/328; 442/382 |
International
Class: |
D04H 1/42 20060101
D04H001/42; D04H 13/00 20060101 D04H013/00 |
Claims
1. A meltblown fabric which has an MD peak tensile force (F.sub.MD)
per one inch width and normalized to 20 gsm basis weight described
by the following equations a.
F.sub.MD.gtoreq.[-0.00143.times.elong(percent)+0.823] if elongation
is between 20 to 675 percent b. F.sub.MD.gtoreq.0.1 lb if
elongation is greater than or equal to 675 percent and wherein the
fabric comprises at least one copolymer with 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 meltblown fabric of claim 1 in which the at least one
copolymer is characterized as having .sup.13C NMR peaks
corresponding to a regio-error at about 14.6 and about 15.7 ppm,
the peaks being of about equal intensity.
3. The meltblown fabric of claim 1 wherein the comonomer comprises
3 to 20 wt. percent ethylene.
4. The meltblown fabric of claim 1 wherein the comonomer comprises
9 to 20 wt. percent ethylene.
5. The meltblown fabric of claim 1 wherein the copolymer has a MFR
from 25 to 5000.
6. The meltblown fabric of claim 1 wherein the copolymer has
undergone chemically induced chain scission and has a MFR from 50
to 5000.
7. The meltblown fabric of claim 6 wherein the chain scission is
caused by combining the composition with a free radical initiator
prior to extrusion.
8. The meltblown fabric of claim 7 wherein the free radical
initiator is a peroxide type.
9. The meltblown fabric of claim 7 wherein the rheology modifier is
a non-peroxide type.
10. The meltblown fabric of claim 9 wherein the non-peroxide type
rheology modifier is a hydroxyl amine ester.
11. The meltblown fabric of claim 6 wherein the chain scission is
caused by combining the composition with at least one peroxide type
and one non-peroxide type of free radical initiators.
12. The meltblown fabric of claim 1 in which the average fiber
diameter is less than 10 microns.
13. The meltblown fabric of claim 1 which has immediate set of less
than or equal to about 50 percent as measured by a 50 percent 1
cycle test.
14. The meltblown fabric of claim 1 which has retained load greater
than or equal to about 0 percent as measured by a 75 percent 1
cycle test.
15. The meltblown fabric of claim 1 which has retained load greater
than or equal to about 15 percent as measured by a 75 percent 1
cycle test.
16. The meltblown fabric of claim 1 wherein the fabric comprises
less than about 10 percent by weight hPP and/or RCP.
17. The meltblown fabric of claim 1 wherein the fabric comprises
less than about 8 percent by weight hPP and/or RCP.
18. The meltblown fabric of claim 1 wherein the fabric comprises
less than about 6 percent by weight hPP and/or RCP.
19. The meltblown fabric of claim 1 wherein the fabric comprises
less than about 4 percent by weight hPP and/or RCP.
20. A nonwoven laminate comprising the meltblown nonwoven layer of
any one of claims 1-19 and at least one spunbond nonwoven
layer.
21. The nonwoven laminate of claim 20 wherein the spunbond layer
comprises fibers characterized in that a polyethylene based
material comprises at least a portion of the surface of the
fiber.
22. The nonwoven laminate of claim 20 wherein the spunbond layer
comprises a bicomponent fiber.
23. The nonwoven laminate of claim 22 wherein the bicomponent fiber
is in a sheath-core configuration.
24. The nonwoven laminate of claim 23 wherein the spunbond layer
comprises a monofilament fiber.
25. The nonwoven laminate of claim 24 wherein the spunbond layer
comprises a polyolefin other than polyethylene.
26. A nonwoven laminate structure comprising at least two nonwoven
layers, said nonwoven laminate structure being characterized by
having an overall bending modulus according to ASTM D 5732-95 of
0.005 Nmm or less and a peel strength between the nonwoven layers
of more than 2 N/5 cm; wherein at least one of the nonwoven layers
comprises fiber comprising at least one polymer with at least about
50 weight percent of units derived from propylene.
27. The nonwoven laminate structure of claim 26 further
characterized by having hydrohead behavior greater than about 200
mm H.sub.2O normalized to a basis weight of 25 gsm.
28. The nonwoven laminate structure of claim 26 wherein the at
least two nonwoven layers include at least one meltblown layer and
at least one spunbond layer
29. The nonwoven laminate structure of claim 28 further comprising
at least one additional meltblown or spunbond layer.
30. The nonwoven laminate structure of claim 26 wherein at least
one nonwoven layer is a meltblown nonwoven layer which comprises
meltblown fibers comprising a propylene based polymer characterized
by having one or more of the following traits: a. less than 50
percent crystallinity b. flex modulus less than 50 kpsi c. melting
point less than about 140.degree. C.; and/or heat of fusion less
than 80 J/g
31. The nonwoven laminate structure of claim 30 wherein the
meltblown fibers are further characterized as comprising copolymers
of propylene and an alpha-olefin, wherein the alpha olefin is
preferably ethylene.
32. The meltblown nonwoven layer of claim 31 wherein the alpha
olefin is ethylene.
33. The nonwoven laminate structure of claim 30 in which the
propylene based polymer 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 being of about equal intensity.
34. The nonwoven laminate structure of claim 30 wherein the
propylene based polymer comprises 3 to 20 wt. percent ethylene.
35. The nonwoven laminate structure of claim 30 wherein the
propylene based polymer comprises 9 to 20 wt. percent ethylene.
36. The nonwoven laminate structure of claim 30 wherein the
propylene based polymer has an MFR from 25 to 5000.
37. The nonwoven laminate structure of claim 30 wherein the
propylene based polymer has undergone chemically induced chain
scission and has an MFR from 50 to 5000.
38. The nonwoven laminate structure of claim 37 wherein the chain
scission is caused by combining the composition with a free radical
initiator prior to extrusion.
39. The nonwoven laminate structure of claim 38 wherein the free
radical initiator is a peroxide type.
40. The nonwoven laminate structure of claim 38 wherein the free
radical initiator is a non-peroxide type.
41. The nonwoven laminate structure of claim 37 wherein the chain
scission is caused by combining the composition with at least one
peroxide type and one non-peroxide type of free radical
initiators.
42. The nonwoven laminate structure of claim 30 in which the
average fiber diameter of the meltblown fibers is less than about
12 microns.
43. The nonwoven laminate structure of claim 28 in which the
spunbond layer comprises fibers characterized as having
polyethylene based material comprising at least a portion of the
surface of the fiber.
44. The spunbond layer of claim 26 comprising fibers of a
bicomponent structure.
45. The spunbond layer of claim 44 in which the bicomponent fibers
have a sheath-core configuration.
46. A nonwoven laminate comprising at least one meltblown nonwoven
layer and at least one spunbond layer wherein: the at least one
melt blown layer comprises fibers comprising polymer having at
least about 50 weight percent of units derived from propylene; and
the at least one spunbond nonwoven layer comprises fibers
characterized in that a polyethylene based material comprises at
least a portion of the surface of the fiber.
47. The nonwoven laminate of claim 46 wherein the at least one
meltblown layer comprises fibers comprising polymer having at least
about 50 weight percent of units derived from propylene and at
least about 5 weight percent of units derived from a monomer other
than propylene.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to propylene-based nonwoven
layers made by the meltblown process, and laminates incorporating
such layers. The meltblown layers of the present invention comprise
propylene copolymers characterized by having less than 50 percent
crystallinity. The meltblown layers of the present invention show
an improved combination of extensibility and tensile strength and
also exhibit markedly better bonding strength when bonded to
spunbond layers, particularly spunbond layers made from fibers in
which a polyethylene based material comprises at least a portion of
the surface.
BACKGROUND AND BRIEF SUMMARY OF THE INVENTION
[0002] Nonwoven webs or fabrics are desirable for use in a variety
of products such as bandaging materials, garments, disposable
diapers, and other personal hygiene products, including
pre-moistened wipes. Nonwoven webs having high levels of strength,
softness, and abrasion resistance are desirable for disposable
absorbent garments, such as diapers, incontinence briefs, training
pants, feminine hygiene garments, and the like. For example, in a
disposable diaper, it is highly desirable to have soft, strong,
nonwoven components, such as topsheets or backsheets (also known as
outer covers).
[0003] As used herein, the term "nonwoven web", refers to a web
that has a structure of individual fibers or threads which are
interlaid, but not in any regular, repeating manner. Nonwoven webs
have been, in the past, formed by a variety of processes, such as,
for example, air laying processes, meltblowing processes,
spunbonding processes and carding processes, including bonded
carded web processes. These various process each have their own
strengths and weaknesses. For example, spunbonded webs tend to have
higher tensile strength than meltblown webs whereas the meltblown
process tends to produce webs having increased liquid barrier
properties as compared to spunbond nonwovens.
[0004] 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 and softness.
Nevertheless, these fabrics are commonly incorporated into
multicomponent articles, for example, diapers, wound dressings,
feminine hygiene products and the like.
[0005] In comparison, polyethylene-based elastomers, and the fibers
and fabrics made from these polymers, tend to exhibit low modulus
and good elasticity, but they also tend to have low tenacity,
stickiness and exhibit a hand feel which is generally considered as
unacceptable for many applications.
[0006] Tensile strength of nonwovens and tenacity of fibers is
important because the manufacture of multicomponent articles
typically involves multiple steps (for example, rolling/unrolling,
cutting, adhesion, etc.), and webs lacking tensile strength may not
survive one or more of these steps. Fibers with a high tensile
strength (also known as tenacity) are also advantaged over fibers
with a low tensile strength because the former will experience
fewer line breaks, and thus greater productivity will be obtained
from the manufacturing line. Moreover, the end-use of many products
also typically requires a level of tensile strength specific to the
function of the component. Tensile strength must be balanced
against the cost of the process used to achieve the higher tensile
strength or to achieve higher tenacity. Optimized fabrics will have
the minimum material consumption (basis weight) to achieve the
minimum required tensile strength for the manufacture and end-use
of the fiber, component (for example, nonwoven fabric) and
article.
[0007] Hand feel is another important aspect for many nonwoven
structures, particularly those structures intended for use in the
hygiene and medical field. Low modulus is one aspect of hand feel.
Fabrics made from fibers with a low modulus will feel "softer", all
else being 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, for example, hPP, will feel harsher (stiffer)
and will drape less well resulting in a poorer fit. Fabrics made
from polyethylene-based elastomers also tend to lack adequate hand
feel as they tend to have an undesirable feel to the skin commonly
characterized by descriptors such as tacky, sticky, clammy,
rubbery, or wet.
[0008] Fiber extensibility/elasticity is another important criteria
for nonwoven structures, particularly those used in hygiene and
medical applications, because the characteristic translates to a
better comfort and fit as the article made from the fiber will be
able to be more body conforming in all situations. 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.
[0009] A nonwoven meltblown layer which exhibits a combination of
high tensile strength, good elongation and adequate hand feel is
therefore desired and is an aspect of the present invention. It has
been discovered that such extensible/elastic meltblown fabrics can
be made from a particular class of polypropylene, known as
propylene based plastomers and elastomers, without the need for
blending substantial amounts of higher tenacity materials such as
hPP. The propylene based plastomers and elastomers can be
characterized by one or more of the following traits: crystallinity
less than 50 percent; flex modulus less than 50 kpsi; melting point
less than about 140.degree. C. (and even less than about
130.degree. C.); and/or heat of fusion less than 80 J/g. The
propylene based polymer preferably comprises copolymers of
propylene and an alpha-olefin, and the alpha olefin is preferably
ethylene. The ethylene in the preferred embodiment is preferably
present in an amount of from 3 to 20 percent by weight of the
propylene based polymer. Propylene based polymers having ethylene
in an amount of from 9 to 20 percent by weight of the propylene
based polymer are more elastomeric. Such polymers may be referred
to as propylene-based elastomers (PBE). The preferred propylene
based polymer has an MWD of from 2 to 4. The propylene based
polymer typically may have a melt flow rate (prior to any rheology
modifier) in the range of from 1 to 100 g/10 min. Nonwoven
meltblown layers made from propylene based plastomers and
elastomers, without substantial amounts (such as more than about 10
percent by weight (10 wt. percent )) of hPP is therefore another
aspect of the present invention. All percentages specified herein
are weight percentages unless otherwise specified.
[0010] By themselves, for example, these nonwovens may
advantageously be used in filtration applications, or they may be
combined with other materials, including other nonwoven materials.
For structures can have hydrohead performance from 100, preferably
200 to 800 mm H.sub.2O for a 25 gsm basis weight. Higher basis
weights may be able to achieve higher hydrohead performance.
[0011] Used in combination with other materials such as another
nonwoven, film, apertured film, fibers, woven fabric or others,
synergistic properties may be achieved. It is recognized that
performance requirements will vary with applications. As a result,
use of this invention and its various embodiments can take a number
of forms not limited to the descriptions provided herein.
[0012] Because of the relative strengths and weaknesses associated
with the different processes and materials used to make nonwoven
fabrics, composite structures of more than one layer are often used
in order to achieve a better balance of properties. Such structures
are often identified by letters designating the various lays such
as SM for a two layer structure consisting of a spunbond layer and
a meltblown layer, SMS for a three layer structure, or more
generically SM.sub.XS structures. In order to maintain structural
integrity of such composite structures, the layers must be bonded
together. Common methods of bonding include point bonding, adhesive
lamination, and other methods known to those skilled in the art. It
is a continual goal within the art to increase the bonding strength
between the layers in order to provide more durable structures as
long as other desirable properties such as breathability and
flexural modulus are preserved to a certain degree.
[0013] It has been observed, however, that poor bonding strength
between layers is particularly problematic when polyethylene
materials (including bicomponent fibers where polyethylene forms at
least part of the surface of the bicomponent fibers) are used to
make one layer, and propylene materials such as homopolymer
polypropylene ("hPP") or random copolymer polypropylene ("RCP") are
used for an adjacent layer. It would therefore be particularly
desirable to improve the bonding strength between
polyethylene-based layers and polypropylene-based layers in a
nonwoven composite structure.
[0014] It has also been discovered that meltblown fabrics made from
this particular class of polypropylene based materials offers
superior bonding strength to spunbond layers made from fibers
having surfaces comprised of polyethylene based materials. In
addition to providing superior bonding strength between the
meltblown and spunbond layers, the use of these polymers for use in
the meltblown nonwoven webs has been observed to increase the
overall softness as compared to composites in which the meltblown
layers comprise substantial amounts of hPP or RCP.
[0015] Another aspect of the present invention is a nonwoven
laminate comprising a meltblown nonwoven layer and a spunbond
nonwoven layer wherein the meltblown layer comprises meltblown
fibers comprising a propylene based polymer characterized by having
one or more of the following traits: less than 50 percent
crystallinity; flex modulus less than 50 kpsi; melting point less
than about 140.degree. C.; and/or heat of fusion less than 80 J/g.
The propylene based polymer preferably comprises copolymers of
propylene and an alpha-olefin, and the alpha olefin is preferably
ethylene. The ethylene in the preferred embodiment is preferably
present in an amount of from 3 to 20 percent by weight of the
propylene based polymer. The preferred propylene based polymer has
an MWD of from 2 to 4. The preferred propylene based polymer has a
melt flow rate (prior to any rheology modifier) in the range of
from 1 to 100 g/10 min.
[0016] In another aspect of the nonwoven laminates of the present
invention, the spunbond layer comprises fibers characterized in
that a polyethylene based material comprises at least a portion of
the surface of the fiber. The spunbond layer in the nonwoven
laminates of the present invention may comprise a bicomponent
fiber, and if so the bicomponent fiber is preferably in a
sheath-core configuration. Alternatively the spunbond layer may
comprise a monofilament fiber (that is, the fiber will have a
uniform cross section).
[0017] Another aspect of the present invention is a nonwoven
laminate structure comprising at least two nonwoven layers, said
nonwoven laminate structure being characterized by having an
overall bending modulus less than 0.005 Nmm and a peel strength
between the nonwoven layers of more than 2 N/5 cm width.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a plot of Bending Modulus vs. Elongation for the
examples and comparative examples indicated;
[0019] FIG. 2 is a plot of Peak Force vs. Elongation for the
examples and comparative examples indicated;
[0020] FIG. 3 is a plot of Set Strain vs. Elongation for the
examples and comparative examples indicated;
[0021] FIG. 4 is a plot of Retained Load vs. Elongation for the
examples and comparative examples indicated;
[0022] FIG. 5 is a bar graph showing the bending modulus for
laminate structures as indicated; and
[0023] FIG. 6 is a bar graph showing the peel strength for laminate
structures as indicated.
DETAILED DESCRIPTION OF THE INVENTION
[0024] As used herein, the term "nonwoven web" or "nonwoven fabric"
or "nonwoven", refers to a web that has a structure of individual
fibers or threads which are interlaid, but not in any regular,
repeating manner. Nonwoven webs have been, in the past, formed by a
variety of processes, such as, for example, air laying processes,
meltblowing processes, spunbonding processes and carding processes,
including bonded carded web processes.
[0025] As used herein, the term "meltblown" , refers to the process
of extruding a molten thermoplastic material through a plurality of
fine, usually circular, die capillaries as molten threads or
filaments into a high velocity gas (for example, air) stream which
attenuates the filaments of molten thermoplastic material to reduce
their diameter, which may be to a microfiber diameter. Thereafter,
the meltblown fibers are carried by the high velocity gas stream
and are deposited on a collecting surface to form a web of randomly
dispersed meltblown fibers.
[0026] As used herein, the term "spunbonded", refers to the process
of extruding a molten thermoplastic material as filaments from a
plurality of fine, usually circular, capillaries of a spinneret
with the diameter of the extruded filaments then being rapidly
reduced by drawing the fibers and collecting the fibers on a
substrate.
[0027] As used herein, the term "microfibers", refers to small
diameter fibers having an average diameter not greater than about
100 microns. Fibers, and in particular, spunbond and meltblown
fibers used in the present invention can be microfibers. More
specifically, the spunbond fibers can advantageously be fibers
having an average diameter of 15-30 microns, and having a denier
from 1.5-3.0, whereas the meltblown fibers can advantageously be
fibers having an average diameter of less than about 30 microns, or
more advantageously be fibers having an average diameter of less
than about 15 microns, or even more advantageously be fibers having
an average diameter of less than about 12 microns. It also
contemplated that the meltblown fibers may have even smaller
average diameters, such as less than 10, 8 or even 5 microns.
[0028] As used herein, the term "polymer" generally includes, but
is not limited to, homopolymers, copolymers, such as, for example,
block, graft, random and alternating copolymers, terpolymers, etc.,
and blends and modifications thereof. Furthermore, unless otherwise
specifically limited, the term "polymer" shall include all possible
geometrical configurations of the material. These configurations
include, but are not limited to, isotactic, syndiotactic and random
symmetries.
[0029] As used herein, the term "polypropylene based plastomers
(PBP) or elastomers (PBE)" (collectively, these may be referred to
as "PBPE") includes reactor grade copolymers of propylene having
heat of fusion less than about 100 Joules/gm and MWD<3.5. The
PBPs generally have a heat of fusion less than about 100
Joules/gram while the PBEs generally have a heat of fusion less
than about 40 Joules/gram. The PBPs typically have a weight percent
ethylene in the range of 3 to 10 wt percent ethylene , with the
elastomeric PBEs having an ethylene content of from 10 to 15 wt
percent ethylene.
[0030] As used herein, the term "extensible" refers to any nonwoven
material which, upon application of a biasing force, is able to
undergo elongation to at least about 50 percent strain and more
preferably at least about 70 percent strain without experiencing
catastrophic failure.
[0031] The nonwoven material of the present invention will
preferably have a basis weight (weight per unit area) from 10 grams
per square meter (gsm) to 100 gsm. The basis weight can also be
from 15 gsm to 60 gsm, and in one embodiment it can be 20 gsm.
[0032] As used herein, the term "tensile strength" describes the
peak force for a given basis weight when pulled in either the
machine direction (MD) or cross direction (CD) of a nonwoven when
pulled to break. The peak force may or may not correspond to the
force at break or strain at break. "Elongation" unless otherwise
specified, refers to the strain corresponding to the tensile
strength.
[0033] A first aspect of the invention is a meltblown fabric which
has a MD peak tensile force (F.sub.MD) measured in pounds per one
inch width and normalized to 20 gsm basis weight, described by
being greater than [-0.00143.times.elongation (percent)+0.823] if
elongation is between 20 to 675 percent. If elongation is greater
than about 675 percent, F.sub.MD is greater than about 0.1 pounds
(lb). The meltblown fabric comprises at least one copolymer with 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.
[0034] The copolymer is a PBPE having MWD<3.5, and having heat
of fusion less than about 90 Joules/gm, preferably less than about
70 Joules/gm, more preferably less than about 50 Joules/gm. When
ethylene is used as a comonomer, the PBPE has from 3 to 15 percent
of ethylene, or from 5 to 14 percent of ethylene, or 9 to 12
percent ethylene, by weight of the propylene based elastomer or
plastomer. Suitable propylene based elastomers and/or plastomers
are taught in WO03/040442, which is hereby incorporated by
reference in its entirety.
[0035] Of particular interest for use in the present invention are
reactor grade PBPEs having MWD less than 3.5. 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.
[0036] 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.
[0037] The amount of comonomer other than ethylene in the propylene
based elastomer or plastomer is a function of, at least in part,
the comonomer and the desired heat of fusion of the copolymer. If
the comonomer is ethylene, then typically the comonomer-derived
units comprise not in excess of about 15 wt percent of the
copolymer. The minimum amount of ethylene-derived units is
typically at least about 3, preferably at least about 5 and more
preferably at least about 9, wt percent based upon the weight of
the copolymer. If the polymer comprises at least one other
comonomer other than ethylene, then the preferred composition would
have a heat of fusion approximately in the range of a
propylene-ethylene copolymer with 3 to 20 wt. percent ethylene.
Though not intending to be bound by theory, it is thought that
attaining approximately similar crystallinity and crystal
morphology is necessary to achieve similar functionality of said
polymers in a nonwoven.
[0038] The propylene based elastomer or plastomer of this invention
can be made by any process, and includes copolymers made by
Zeigler-Natta, CGC (Constrained Geometry Catalyst), 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
polymer, and propylene/ethylene elastomers and plastomers by The
Dow Chemical Company.
[0039] The density of the propylene based elastomers or plastomers
of this invention is typically at least about 0.850, can be at
least about 0.860 and can also be at least about 0.865 grams per
cubic centimeter (g/cm.sup.3) as measured by ASTM D-792.
[0040] The weight average molecular weight (Mw) of the propylene
based elastomers or plastomers of this invention can vary widely,
but typically it is between 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 homopolymers
and copolymers used in the manufacture of meltblown fabrics,
preferably the minimum Mw is about 20,000, more preferably about
25,000.
[0041] The polydispersity of the propylene based elastomers or
plastomers of this invention is typically between 2 and 3.5.
"Narrow polydispersity", "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, can be less than
about 3.0, can also be less than about 2.8, can also be less than
about 2.5, and can also be less than about 2.3. Polymers for use in
fiber applications typically have a narrow polydispersity. Blends
comprising two or more of the polymers 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 2 and 4.
[0042] The PBPEs for use in the present invention ideally have an
MFR of from 20 to 5000, g/10 min, or alternatively 2000 g/10 min.
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.). MFRs greater than
about 250 were estimated according to the following
correlation:
MFR=9.times.10.sup.18 Mw.sup.-3.3584
[0043] Mw (grams per mole) was measured using gel permeation
chromatography.
[0044] The PBPEs may advantageously be subjected to a chemically
induced chain scissioning agent. Such materials are known to
increase the MFR of the polymers and to reduce their molecular
weight distribution (MWD), thereby improving performance in the
meltblown process. In general, it is preferred that the reactor
grade PBPE have an MFR between 1 to 100 g/10 min, whereas after
chain scission (if any) the PBPE will preferably have an MFR of
from 50 to 5000 g/10 min. Suitable chain scissioning agents include
peroxide and non-peroxide type free radical initiators. For many
applications, non-peroxide type chain scissioning agents are
preferred such as cyclic and open chain hydroxylamine esters. One
particularly preferred chain scissioning agent is the family of
compounds known as hydroxyl amine esters (US2003/0216494 A1, hereby
incorporated by reference). The peroxide process has been reported
to suffer from problems such as discoloration, odor, or smoke,
which can be reduced by using non-peroxide chain scissioning
agents. Further, it has been observed that using hydroxyl amine
esters increases the long term thermal stability and light
stability. In some applications it may be desirable to use more
than one type of chain scissioning agent such as in combination
with peroxides or free-radical agents.
[0045] In one preferred embodiment of this invention, the propylene
based elastomers or plastomers 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, that is, the units derived
from ethylene and/or the unsaturated comonomer(s), in the copolymer
is increased, and (iii) an X-ray diffraction pattern when the
sample is slow-cooled 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 one or both of the following
characteristics: (iv) a B-value when measured according to the
method of Koenig (described below) greater than about 1.03 when the
comonomer content, that is, the units derived from the comonomer
other than propylene, is at least about 3 wt percent, and (v) 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
(WO2/003040442) which is incorporated herein by reference, as
supplemented below.
[0046] B-Value
[0047] "High B-value" and similar terms mean the ethylene units of
a copolymer of propylene and ethylene, or a copolymer of propylene,
ethylene and at least one unsaturated comonomer, is distributed
across the polymer chain in a nonrandom manner. B-values range from
0 to 2. The higher the B-value, the more alternating the comonomer
distribution in the copolymer. The lower the B-value, the more
blocky or clustered the comonomer distribution in the copolymer.
The high B-values of the polymers made using a nonmetallocene,
metal-centered, heteroaryl ligand catalyst, such as described in
U.S. Patent Publication No. 2003/0204017 A1, are typically at least
about 1.03 as determined according to the method of Koenig
(Spectroscopy of Polymers American Chemical Society, Washington,
D.C., 1992), preferably at least about 1.04, more preferably at
least about 1.05 and in some instances at least about 1.06. This is
very different from propylene-based copolymers typically made with
metallocene catalysts, which generally exhibit B-values less than
1.00, typically less than 0.95. There are several ways to calculate
B-value; the method described below utilizes the method of Koenig,
J. L., where a B-value of 1 designates a perfectly random
distribution of comonomer units. The B-value as described by Koenig
is calculated as follows.
[0048] B is defined for a propylene / ethylene copolymer as:
B = f ( EP + PE ) 2 F E F P ##EQU00001##
where f(EP+PE)=the sum of the EP and PE diad fractions; and Fe and
Fp=the mole fraction of ethylene and propylene in the copolymer,
respectively. The diad fraction can be derived from triad data
according to: f(EP+PE)=[EPE]+[EPP+PPE]/2+[PEP]+[EEP+PEE]/2. The
B-values can be calculated for other copolymers in an analogous
manner by assignment of the respective copolymer diads. For
example, calculation of the B-value for a propylene/l-octene
copolymer uses the following equation:
B = f ( OP + PO ) 2 F O F P ##EQU00002##
[0049] For propylene polymers made with a metallocene catalyst, the
B-values are typically between 0.8 and 0.95. In contrast, the
B-values of the propylene polymers made with an activated
nonmetallocene, metal-centered, heteroaryl ligand catalyst (as
described below), are above about 1.03, typically between 1.04 and
1.08. In turn, this means that for any propylene-ethylene copolymer
made with such a nonmetallocene metal-centered, heteroaryl
catalyst, not only is the propylene block length relatively short
for a given percentage of ethylene but very little, if any, long
sequences of 3 or more sequential ethylene insertions are present
in the copolymer, unless the ethylene content of the polymer is
very high.
[0050] .sup.13C NMR
[0051] The propylene ethylene copolymers suitable for use in this
invention typically have substantially isotactic propylene
sequences. "Substantially isotactic propylene sequences" and
similar terms mean that the sequences have an isotactic triad (mm)
measured by .sup.13C NMR of greater than about 0.85, preferably
greater than about 0.90, more preferably greater than about 0.92
and most preferably greater than about 0.93. Isotactic triads are
well known in the art and are described in, for example, U.S. Pat.
No. 5,504,172 and WO 00/01745 which refer to the isotactic sequence
in terms of a triad unit in the copolymer molecular chain
determined by .sup.13C NMR spectra. NMR spectra are determined as
follows.
[0052] .sup.13C NMR spectroscopy is one of a number of techniques
known in the art for measuring comonomer incorporation into a
polymer. An example of this technique is described for the
determination of comonomer content for ethylene/.alpha.-olefin
copolymers in Randall (Journal of Macromolecular Science, Reviews
in Macromolecular Chemistry and Physics, C29 (2 & 3), 201-317
(1989)). The basic procedure for determining the comonomer content
of an olefin interpolymer involves obtaining the .sup.13C NMR
spectrum under conditions where the intensity of the peaks
corresponding to the different carbons in the sample is directly
proportional to the total number of contributing nuclei in the
sample. Methods for ensuring this proportionality are known in the
art and involve allowance for sufficient time for relaxation after
a pulse, the use of gated-decoupling techniques, relaxation agents,
and the like. The relative intensity of a peak or group of peaks is
obtained in practice from its computer-generated integral. After
obtaining the spectrum and integrating the peaks, those peaks
associated with the comonomer are assigned. This assignment can be
made by reference to known spectra or literature, or by synthesis
and analysis of model compounds, or by the use of isotopically
labeled comonomer. The mole percent comonomer can be determined by
the ratio of the integrals corresponding to the number of moles of
comonomer to the integrals corresponding to the number of moles of
all of the monomers in the interpolymer, as described in Randall,
for example.
[0053] The data is collected using a Varian UNITY Plus 400 MHz NMR
spectrometer, corresponding to a .sup.13C resonance frequency of
100.4 MHz. Acquisition parameters are selected to ensure
quantitative .sup.13C data acquisition in the presence of the
relaxation agent. The data is acquired using gated .sup.1H
decoupling, 4000 transients per data file, a 7 sec pulse repetition
delay, spectral width of 24,200 Hz and a file size of 32K data
points, with the probe head heated to 130.degree. C. The sample is
prepared by adding approximately 3 mL of a 50/50 mixture of
tetrachloroethane-d2/orthodichlorobenzene that is 0.025 M in
chromium acetylacetonate (relaxation agent) to 0.4 g sample in a 10
mm NMR tube. The headspace of the tube is purged of oxygen by
displacement with pure nitrogen. The sample is dissolved and
homogenized by heating the tube and its contents to 150.degree. C.
with periodic refluxing initiated by heat gun.
[0054] Following data collection, the chemical shifts are
internally referenced to the mmmm pentad at 21.90 ppm. Isotacticity
at the triad level (mm) is determined from the methyl integrals
representing the mm triad (22.5 to 21.28 ppm), the mr triad
(21.28-20.40 ppm), and the rr triad (20.67-19.4 ppm). The
percentage of mm tacticity is determined by dividing the intensity
of the mm triad by the sum of the mm, mr, and rr triads. For
propylene-ethylene copolymers made with catalyst systems, such as
the nonmetallocene, metal-centered, heteroaryl ligand catalyst
(described above) the mr region is corrected for ethylene and
regio-error by subtracting the contribution from PPQ and PPE. For
propylene-ethylene copolymers the rr region is corrected for
ethylene and regio-error by subtracting the contribution from PQE
and EPE. For copolymers with other monomers that produce peaks in
the regions of mm, mr, and rr, the integrals for these regions are
similarly corrected by subtracting the interfering peaks using
standard NMR techniques, once the peaks have been identified. This
can be accomplished, for example, by analyzing a series of
copolymers of various levels of monomer incorporation, by
literature assignments, by isotopic labeling, or other means which
are known in the art.
[0055] For copolymers made using a nonmetallocene, metal-centered,
heteroaryl ligand catalyst, such as described in U.S. Patent
Publication NO. 2003/0204017, the .sup.13C NMR peaks corresponding
to a regio-error at about 14.6 and about 15.7 ppm are believed to
be the result of stereoselective 2,1-insertion errors of propylene
units into the growing polymer chain. In general, for a given
comonomer content, higher levels of regio-errors lead to a lowering
of the melting point and the modulus of the polymer, while lower
levels lead to a higher melting point and a higher modulus of the
polymer.
Matrix Method for Calculation of B-Values According to Koenig, J.
L.
[0056] For propylene/ethylene copolymers the following procedure
can be used to determine the comonomer composition and sequence
distribution. Integral areas are determined from the .sup.13C NMR
spectrum and input into the matrix calculation to determine the
mole fraction of each triad sequence. The matrix assignment is then
used with the integrals to yield the mole fraction of each triad.
The matrix calculation is a linear least squares implementation of
Randall's (Journal of Macromolecular Chemistry and Physics, Reviews
in Macromolecular Chemistry and Physics, C29 (2&3), 201-317,
1989) method modified to include the additional peaks and sequences
for the 2,1 regio-error. Table A shows the integral regions and
triad designations used in the assignment matrix. The numbers
associated with each carbon indicate in which region of the
spectrum it will resonate.
[0057] Mathematically the Matrix Method is a vector equation s=fM
where M is an assignment matrix, s is a spectrum row vector, and f
is a mole fraction composition vector. Successful implementation of
the Matrix Method requires that M, f, and s be defined such that
the resulting equation is determined or over determined (equal or
more independent equations than variables) and the solution to the
equation contains the molecular information necessary to calculate
the desired structural information. The first step in the Matrix
Method is to determine the elements in the composition vector f.
The elements of this vector should be molecular parameters selected
to provide structural information about the system being studied.
For copolymers, a reasonable set of parameters would be any odd
n-ad distribution. Normally peaks from individual triads are
reasonably well resolved and easy to assign, thus the triad
distribution is the most often used in this composition vector f.
The triads for the E/P copolymer are EEE, EEP, PEE, PEP, PPP, PPE,
EPP, and EPE. For a polymer chain of reasonable high molecular
weight (>=10,000 g/mol), the .sup.13C NMR experiment cannot
distinguish EEP from PEE or PPE from EPP. Since all Markovian E/P
copolymers have the mole fraction of PEE and EPP equal to each
other, the equality restriction was chosen for the implementation
as well. Same treatment was carried out for PPE and EPP. The above
two equality restrictions reduce the eight triads into six
independent variables. For clarity reason, the composition vector f
is still represented by all eight triads. The equality restrictions
are implemented as internal restrictions when solving the matrix.
The second step in the Matrix Method is to define the spectrum
vector s. Usually the elements of this vector will be the
well-defined integral regions in the spectrum. To insure a
determined system the number of integrals needs to be as large as
the number of independent variables. The third step is to determine
the assignment matrix M. The matrix is constructed by finding the
contribution of the carbons of the center monomer unit in each
triad (column) towards each integral region (row). One needs to be
consistent about the polymer propagation direction when deciding
which carbons belong to the central unit. A useful property of this
assignment matrix is that the sum of each row should equal to the
number of carbons in the center unit of the triad which is the
contributor of the row. This equality can be checked easily and
thus prevents some common data entry errors.
[0058] After constructing the assignment matrix, a redundancy check
needs to be performed. In other words, the number of linearly
independent columns needs to be greater or equal to the number of
independent variables in the product vector. If the matrix fails
the redundancy test, then one needs to go back to the second step
and repartition the integral regions and then redefine the
assignment matrix until the redundancy check is passed.
[0059] In general, when the number of columns plus the number of
additional restrictions or constraints is greater than the number
of rows in the matrix M the system is overdetermined. The greater
this difference is the more the system is overdetermined. The more
overdetermined the system, the more the Matrix Method can correct
for or identify inconsistent data which might arise from
integration of low signal to noise (S/N) ratio data, or partial
saturation of some resonances.
[0060] The final step is to solve the matrix. This is easily
executed in Microsoft Excel by using the Solver function. The
Solver works by first guessing a solution vector (molar ratios
among different triads) and then iteratively guessing to minimize
the sum of the differences between the calculated product vector
and the input product vector s. The Solver also lets one input
restrictions or constraints explicitly.
TABLE-US-00001 TABLE A The contribution of each carbon on the
central unit of each triad towards different integral regions. P =
propylene, E = ethylene, Q = 2,1 inserted propylene. Triad name
Structure Region for 1 Region for 2 Region for 3 PPP ##STR00001## L
A O PPE ##STR00002## J C O EPP ##STR00003## J A O EPE ##STR00004##
H C O EEEE ##STR00005## K K EEEP ##STR00006## K J EEP ##STR00007##
M C PEE ##STR00008## M J PEP ##STR00009## N C PQE ##STR00010## F G
O QEP ##STR00011## F F XPPQE ##STR00012## J F O XPPQP ##STR00013##
J E O PPQPX ##STR00014## I D Q PQPPX ##STR00015## F B P Chemical
Shift Ranges A B C D E F G H I 48.00 43.80 39.00 37.25 35.80 35.00
34.00 33.60 32.90 45.60 43.40 37.30 36.95 35.40 34.50 33.60 33.00
32.50 J K L M N O P Q 31.30 30.20 29.30 27.60 25.00 22.00 16.00
15.00 30.30 29.80 28.20 27.10 24.50 19.50 15.00 14.00
[0061] 1,2 inserted propylene composition is calculated by summing
all of the stereoregular propylene centered triad sequence mole
fractions. 2,1 inserted propylene composition (Q) is calculated by
summing all of the Q centered triad sequence mole fractions. The
mole percent is calculated by multiplying the mole fraction by 100.
C2 composition is determined by subtracting the P and Q mole
percentage values from 100.
[0062] DSC Method
[0063] 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 (for
example, 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.
[0064] 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.
[0065] 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. The sample
is subsequently 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.
[0066] Mechanical testing was performed using an Instron (Model
5564) sourced from Instron Corporation (Norwood, Mass.) and
equipped with a 100 N load cell. This instrument was used for the
tensile test and the 50 percent hysteresis test described
below.
[0067] Skewness Index
[0068] 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.
[0069] 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. The equation below 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
##EQU00003##
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 percent) 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.
Gel Permeation Chromatography
[0070] Molecular weight distribution of the polymers is determined
using gel permeation chromatography (GPC) on a Polymer Laboratories
PL-GPC-220 high temperature chromatographic unit equipped with four
linear mixed bed columns (Polymer Laboratories (20-micron particle
size)). The oven temperature is at 160.degree. C. with the
autosampler hot zone at 160.degree. C. and the warm zone at
145.degree. C. The solvent is 1,2,4-trichlorobenzene containing 200
ppm 2,6-di-t-butyl-4-methylphenol. The flow rate is 1.0
milliliter/minute and the injection size is 100 microliters. About
0.2 percent by weight solutions of the samples are prepared for
injection by dissolving the sample in nitrogen purged
1,2,4-trichlorobenzene containing 200 ppm
2,6-di-t-butyl-4-methylphenol for 2.5 hrs at 160.degree. C. with
gentle mixing.
[0071] The molecular weight determination is deduced by using ten
narrow molecular weight distribution polystyrene standards (from
Polymer Laboratories, EasiCal PS1 ranging from 580-7,500,000
g/mole) in conjunction with their elution volumes. The equivalent
polypropylene molecular weights are determined by using appropriate
Mark-Houwink coefficients for polypropylene (as described by Th. G.
Scholte, N. L. J. Meijerink(, H. M. Schoffeleers, and A. M. G.
Brands, J. Appl. Polym. Sci., 29, 3763-3782 (1984)) and polystyrene
(as described by E. P. Otoclia, R. J. Roe, N. Y. Hellman, P. M.
Muglia, Macromolecules, 4, 507 (1971)) in the Mark-Houwink
equation:
{N}=KM.sup.a
where K.sub.pp=1.90E-04, a.sub.pp=0.725 and K.sub.ps=1.26E-04,
a.sub.ps=0.702.
[0072] The meltblown fabrics of the present invention may be made
with 100 percent PBPE or can be blended with other polymers to form
the fibers used to make the fabric. Suitable polymers for blending
with these PBPEs are commercially available from a variety of
suppliers and include, but are not limited to, other polyolefins
such as an ethylene polymer (for example, 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 (for example, homopolymer
polypropylene, polypropylene copolymer, random block polypropylene
interpolymer and the like), thermoplastic polyurethane, polyamide,
polylactic acid interpolymer, thermoplastic block polymer (for
example styrene butadiene copolymer, styrene butadiene styrene
triblock copolymer, styrene ethylene-butylene styrene triblock
copolymer and the like), polyether block copolymer (for example,
PEBAX), copolyester polymer, polyester/polyether block polymers
(for example, HYTEL), ethylene carbon monoxide interpolymer (for
example, 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. If the
PBPE (or blend of PBPEs) used to make the meltblown fabric of the
present invention is blended with one or more other polymers, then
the PBPE(s) preferably comprises at least about 90, more preferably
at least about 92 and more preferably at least about 94 and more
preferably at least about 96 wt percent of the total weight of the
blend.
[0073] It should also be readily recognized that other additives
might also be added as is generally known in the art. Examples of
such additives include antioxidants, ultraviolet light stabilizers,
thermal stabilizers, slip agents, pigments or colorants, processing
aids (such as fluoropolymers), crosslinking catalysts, flame
retardants, fillers, foaming agents, etc.
[0074] Slip agents or antistatic agents may be particularly
beneficial when the PBPE used to make the meltblown fabric contains
more than about 9 wt percent ethylene, as it was observed that such
fabrics tended to stick to the collecting drum or belt making it
difficult to remove. Typical slip agents include oleicamide,
erucamide, or stearicamide, and a typical antistac agent is
glycerol mono stearate (GMS).
[0075] The meltblown fabric can be made in any manner known in the
art. Typical processes include but are not limited to the Exxon
single-row type line, the multirow Biax-Fiberfilm, and the Hills
type line. Description of nonwoven processes are described in the
respective art of the respective companies and in publications such
as The Nonwovens Handbook, Association of Nonwovens Fabrics
Industry, Cary N.C. and Principles of Nonwovens, INDA, Cary N.C.
U.S. Pat. No. 3,849,241 also describes a suitable meltblown
process. These references are hereby incorporated by reference.
[0076] The meltblown fabrics of the present invention will have a
tensile strength (F.sub.MD) of greater than about
[-0.00143.times.elong(percent)+0.823] if elongation (denoted by
elong(percent)) is between 20 to 675 percent and greater than about
0.1 lb if elongation is greater than or equal to 675 percent per
one inch width (normalized to 20 gsm).
[0077] Tensile strength is peak force on a normalized basis to 20
gsm. This is calculated according to the following equation:
F MD = F Peak , MD .times. 20 BasisWt ( gsm ) ##EQU00004##
such that F.sub.Peak,MD is the peak force measured for a 1 inch
wide by 6 inch long strip cut parallel to the machine direction
which is gripped by line contact grips with a spacing of 3 inches.
The sample is pulled to break at a rate of 10 inches per minute.
The resulting F.sub.MD is measured in pounds per 1 inch width.
BasisWt is the basis weight of the nonwoven measured in grams per
square meter. Basis weight is measured for each specimen by
weighing the 1 inch wide by 6 inch long sample strips on a
analytical balance and converting to grams per square meter. Care
is taken to avoid sampling from the edges and defects present in
the web. Defects comprise holes, nonuniform sections, and fiber
aggregations.
[0078] More preferably the meltblown fabrics of the present
invention will have a tensile strength of greater than
[-0.00143.times.elong(percent)+1] and even more preferably greater
than [-0.00143.times.elong(percent)+1.2] per one inch width
(normalized to 20 gsm) for elongation of 20 to 675 percent strain.
Elongation was defined according to the following equation:
Elongation ( % ) = L peak force - L o L o .times. 100 %
##EQU00005##
[0079] such that L.sub.o is the initial length of three inches, and
L.sub.peak force is the length corresponding to the strain at the
F.sub.Peak,MD. Strain is defined as the percent change in length of
the sample.
Strain ( % ) = L - L o L o .times. 100 % ##EQU00006##
such that L is the length of the sample.
[0080] The meltblown fabric of the present invention also
preferably has immediate set of less than or equal to about 35
percent or more preferably less than or equal to about 12 percent
as measured by a 50 percent hysteresis test. The 50 percent
hysteresis test is carried out as follows: a 1 inch wide by 6 inch
long strip cut parallel to the machine direction which is gripped
by line contact grips with a spacing of 3 inches. The sample is
pulled to a strain of 50 percent strain at a rate of 10 inches per
minute. The crosshead is then immediately returned at the same rate
until 0 percent strain. The crosshead is then immediately extended
again at the same rate until a positive tensile force is measured.
This point is defined as permanent set. The strain corresponding to
the onset of the positive force is taken as the immediate set
strain.
[0081] Further, the meltblown fabric of the present invention
preferably has retained load greater than or equal to about 0
percent or even more preferably greater than or equal to about 20
percent as measured by a 50 percent hysteresis test. Retained load
is measured as the force at 30 percent strain during retraction
divided by the force at 30 percent strain during the first
extension. Retained load is taken as this is ratio multiplied by
100 percent.
Hydrohead
[0082] Hydrohead is measure according to EDANA test method: WSP
80.6(05)/. The test method applies to nonwoven fabrics, which are
intended for use as a barrier to penetrating fluids. The
hydrostatic pressure test measures the resistance of nonwoven
fabrics to the penetration of water under varied hydrostatic head
pressures.
[0083] The nonwoven fabric is mounted to form the cover on the test
head reservoir. The specimen is subjected to a standardized water
pressure and a constant rate until leakage appears on the outer
surface of the nonwoven. The test results for the hydrostatic water
pressure test are measured at the point where the first drops of
appear in three separate areas on the specimen. Results are
reported in either centimeters/minute or millibars/minute.
[0084] The preferred meltblown nonwoven fabrics will have hydrohead
performance from 10, preferably 20 to 80 cm H.sub.2O/min for a 25
gsm basis weight. Higher basis weights may be able to achieve
higher hydrohead performance.
Laminate Structures
[0085] In many applications, the meltblown fabrics, such as those
of the present invention, can be improved upon by combining the
meltblown fabric with one or more additional fabric layers bonded
together. Such structures are often identified by letters
designating the various lays such as SM for a two layer structure
consisting of a spunbond layer and a meltblown layer, SMS for a
three layer structure, or more generically SM.sub.xS structures (x
is the number of meltblown layers). Laminate structures,
particularly those comprising the above-described meltblown layers,
is another aspect of the present invention.
[0086] The nonwoven laminates of the present invention comprise at
least two nonwoven layers. It is preferred that at least one of the
nonwoven layers be made using the meltblown process, and at least
one of the nonwoven layers be made using the spunbond process. The
nonwoven laminates of the present invention will be characterized
by their combination of overall structure softness and bonding
strength between the layers.
[0087] Bending modulus is determined by ASTM D 5732-95. The
preferred nonwoven laminates of the present invention will have an
overall normalized bending modulus (E.sub.bend,MD,20gsm) less than
0.06 mNcm more preferably less than 0.04 mNcm and most preferably
less than 0.03 mNcm for a normalized basis weight of 20 gsm. This
is calculated according to the following formula:
E bend , MD , 20 gsm = E bend , MD .times. 20 BasisWt ( gsm )
##EQU00007##
such that E.sub.bend,MD is the as measured bending modulus bending
modulus and BasisWt is the basis weight of the fabric measured in
grams per square meter.
[0088] The preferred nonwoven laminates will also exhibit a peel
strength between the nonwoven layers of more than about 2 N/5 cm,
more preferably greater than about 2.5N/5 cm and most preferably
greater than 3N/5 cm Peel strength is determined by the maximum
force in N required to peel two or more substrates apart from each
other using a specimen with a width of 5 cm.
[0089] The two nonwoven layers may be made of any polymer or
polymer blend capable of forming a nonwoven laminate structure
having an overall bending modulus of about 0.005 Nmm or less and a
peel strength between the nonwoven layers of at least about 2 N/5
cm. It is generally preferred that at least one nonwoven layer be a
meltblown layer, with the above-described meltblown nonwoven
fabrics being particularly preferred. Other meltblown fabrics which
may be suitable for these novel laminates include but are not
limited to those described in US 2005/0106978 and WO
2005/052052.
[0090] It is generally preferred that at least one of the layers be
a spunbond layer and that this spunbond layer be made from fibers
which comprise a polyethylene material. The fiber may be
monofilament or a bicomponent fiber. Bicomponent fibers include all
of the known configurations including sheath-core, side by side,
and islands in the sea configurations. The sheath core fiber is the
preferred bicomponent fiber configuration.
[0091] The spunbond fiber may be made from any suitable material.
Specific embodiments include propylene based polymers, blends
containing propylene based polymers, ethylene based polymers,
blends containing ethylene based polymers, and blends thereof.
Sometimes, improved softness is desired. Embodiments that meet this
need include the spundbond fabrics described in recently filed U.S.
application Ser. Nos. 11/083,891 and 11/068,098 (both or which are
hereby incorporated by reference in their entirety), and spunbond
fiber that comprises a polyethylene material particularly where the
polyethylene material comprises at least a portion of the fiber's
surface. "Polyethylene material" is meant to include any polymer
comprising more than fifty mole percent ethylene. In many cases,
the polymer will include an alpha olefin copolymer and typically
that copolymer will be a C.sub.3-C.sub.20 alpha olefin. Hexene and
octene are preferred copolymers. The polyethylene material can be
made via gas-phase, solution-phase or slurry polymerization or any
combination thereof, using any type of reactor or reactor
configuration known in the art.
[0092] "Polyethylene material" includes many types of material
known in the art, such as the materials known as low density
polyethylene (LDPE), high density polyethylene (HDPE) and linear
low density polyethylene (LLDPE) and blends containing such
materials. Particularly useful polyethylene materials for use in
the spunbond materials of the present invention are the LLDPE
materials. This includes the substantially linear ethylene polymers
which are further defined in U.S. Pat. No. 5,272,236, U.S. Pat. No.
5,278,272, U.S. Pat. No. 5,582,923 and U.S. Pat. No. 5,733,155; the
homogeneously branched linear ethylene polymer compositions such as
those in U.S. Pat. No. 3,645,992; the heterogeneously branched
ethylene polymers such as those prepared according to the process
disclosed in U.S. Pat. No. 4,076,698; and/or blends thereof (such
as those disclosed in U.S. Pat. No. 3,914,342 or U.S. Pat. No.
5,854,045). Each of these references is incorporated herein by
reference.
[0093] The preferred laminate structures can have hydrohead
performance from 100, preferably 200 to 800 mm H.sub.2O for a 25
gsm basis weight. Higher basis weights may be able to achieve
higher hydrohead performance.
Additional Measurement Methods
[0094] Unless otherwise indicated, the following analytical
techniques are used to characterize the materials discussed in the
present application.
[0095] Density Method:
[0096] 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.
[0097] Tensile Test
[0098] A 1 inch wide by 6 inch long strip cut parallel to the
machine direction which is gripped by line contact grips, separated
by 3 inches. 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 3
inches and multiplying by 100. Load equals pounds force per 1 inch
width.
[0099] Tensile strength is defined according to the following
equation:
F MD = F Peak , MD .times. 20 BasisWt ( gsm ) ##EQU00008##
such that F.sub.Peak,MD is the peak force measured according to the
method described above and BasisWt is the basis weight of the
nonwoven measured in grams per square meter. Elongation was defined
according to the following equation:
Elongation ( % ) = L peak force - L o L o .times. 100 %
##EQU00009##
such that L.sub.o is the initial length of three inches, and
L.sub.peak force is the length corresponding to the strain at the
FP.sub.Peak,MD.
[0100] Scanning Electron Microscopy:
[0101] 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.
[0102] 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.
[0103] Fiber diameters were measured by acquiring the images of the
fabrics in at least three different locations. The diameters of at
least 15 fiber diameters were measured from the images using
ImagePro Express image analysis software (Media Cybernetics, Silver
Spring Md.). Care was taken not to measure the same fiber more than
once and not to include measurements of "married" or "roped"
filaments (fibers that were extensively bonded along the fiber
axis). The average and standard deviation of the fiber diameters
were then calculated.
SPECIFIC EMBODIMENTS
[0104] 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.
[0105] The different resins used are presented in Tables 1 and 2.
The process conditions used to synthesize the propylene-ethylene
resins A, B, C, and D are shown in Table 1.
TABLE-US-00002 TABLE 1 PROPYLENE-ETHYLENE RESIN PROCESS CONDITIONS
POLY POLY POLY SOLV C.sub.3 C.sub.2 H.sub.2 MONOM CONTRL CATMTL
VISC. DENS PROD FLOW FLOW FLOW FLOW CONV TEMP EFF. Resin CPOISE
G/CC LB/HR LB/HR PPH PPH SCCM % DEG C. M#/# A 73,151 0.8872 4.5
23.1 7.0 0.3 57.2 61.4 105.0 242,849 B 16,855 0.8761 4.7 23.1 7.0
0.5 117.6 60.9 105.0 274,579 C 68,009 0.8669 4.7 23.1 7.0 0.4 88.4
60.2 105.0 276,983 D 16,720 0.8661 4.9 23.1 7.0 0.6 143.6 60.8
105.0 312,893
The characteristics of the resins are listed in Table 2.
TABLE-US-00003 TABLE 2 RESINS Ethylene Density Content Viscosity
MFR.sup.a Resin Description (g/cc) (wt %) MWD (190.degree. C., cP)
(g/10 min) A propylene-ethylene plastomer 0.8869 4.5 2.5 72650
233.sup.a B propylene-ethylene plastomer 0.8770 8.3 2.3 15900
1059.sup.a C propylene-ethylene elastomer 0.8649 10.5 2.5 71150
238.sup.a D propylene-ethylene elastomer 0.8667 11.0 2.3 14700
1145.sup.a F polypropylene homopolymer 0.902 0.0 n/a n/a 1100.sup.b
G polypropylene homopolymer 0.902 0.0 n/a n/a 350.sup.b H
propylene-ethylene plastomer 0.888 5 n/a n/a 25 I
propylene-ethylene plastomer 0.876 9 n/a n/a 25 J
propylene-ethylene elastomer 0.865 12 n/a n/a 25 P
polypropylene-homopolymer 0.902 0 n/a n/a 25 (peroxide visc broken)
S polypropylene-homopolymer 0.902 0 n/a n/a 25 Density Resin
Description (g/cc) MI, g/10 min.sup.b K ethylene-hexene copolymer
0.933 150 L ethylene-octene copolymer 0.874 500 Q Linear Low
Density Polyethylene 0.950 17 R Enhanced Polyethylene resin 0.936
20 .sup.aASTM D-1238 (230.degree. C., 2.16 kg) .sup.bASTM D-1238
(190.degree. C., 2.16 kg)
Density was measured according to ASTM D-792. Ethylene content was
measured using the NMR method described previously. Molecular
weight distribution (MWD) was measured using the GPC method
described above. Melt flow rate (MFR) was measured according to
ASTM D-1238, condition L (2.16 kg, 230 degrees C.).
[0106] Propylene-ethylene copolymers comprising 4.5-12.0 wt.
percent ethylene were used. For comparison, an ethylene-octene
copolymer and a polypropylene homopolymer were also used. The melt
flow ratio (MFR) of the propylene-ethylene polymers was 25-1145
g/10 min. The melt index (MI) of the ethylene-based resins K and L
were 150 and 500 g/10 min, respectively.
[0107] Inventive and comparative examples were made using a Biax
Fiber-Film meltblown line (Greenville, Wis.) with a variety of
conditions. The spinneret had 128 holes (2 rows of 64 spinnerets),
each of which had a diameter of 0.014 inches. The length to
diameter ratio (L/D) for the 1 inch extruder was 20. In addition to
extruder selection and die selection, the main variables were melt
temperature, air pressure, air temperature, throughput
(grams/hole/minute or ghm) which was controlled by pump speed,
collector drum speed, die-to-collector distance (DCD). Selected
inventive and comparative examples were also made on a Hills type
meltblown line.
[0108] The conditions used to fabricate the inventive and
comparative examples axe shown in Tables 3, 4, and 5. By adjusting
the variables described above, fiber diameter, basis weight, and
the degree of self-bonding was controlled. Samples with only the
number and hyphen designation (that is 1-1 to 6-4 and 7-1 to 9-1)
are the inventive examples, and samples with the designation ending
in the letter `c` (that is 1-1c to 3-3c) are the comparative
examples.
TABLE-US-00004 TABLE 3 FABRIC EXAMPLES Melt Temp Air Pressure Air
Temp Throughput Collector Speed DCD Basis Weight Ex. Resin
(.degree. C.) (psi) (.degree. C.) (ghm) (ft/min) (cm) (gsm) 1-1 A
250 14 250 0.09 15 22 22.2 1-2 A 250 14 250 0.09 15 11 22.3 1-3 A
250 12 250 0.05 8 22 18.8 1-4 A 250 12 250 0.05 9 13.5 21.1 1-5 A
280 13 280 0.10 17 13.5 24.1 1-6 A 284 6 284 0.05 9 13.5 15.2 1-7 A
310 13 310 0.07 24 13.5 21.6 1-8 A 310 9 310 0.05 9 13.5 20.4 2-1 B
247 6.2 245 0.13 8.5 23 44.5 2-2 B 247 4 245 0.06 8 23 23.5 2-3 B
247 6.2 245 0.13 32 23 11.8 3-1 C 250 16 250 0.10 15.5 20 27.7 3-2
C 250 -- -- -- -- -- 25.6 3-3 C 275 7.5 275 0.03 6 21 21.5 3-4 C
275 11 275 0.09 15 21 19.2 4-1 D 250 8 250 0.18 25 25 34.0 4-2 D
250 4 250 0.06 9 25 23.7 4-3 D 250 6 250 0.11 18 25 24.9 5-1 90/10
B/F 247 6 255 0.11 19 23 24.1 5-2 90/10 B/F 247 6 255 0.05 8.5 23
16.6 5-3 90/10 B/F 270 7 255 0.13 21 23 25.1 6-1 75/25 C/G 250 4
250 0.12 20 22 22.9 6-2 75/25 C/G 250 4 250 0.12 20 10 26.6 6-3
75/25 C/G 280 5 280 0.12 20 22 25.3 6-4 75/25 C/G 280 5 280 0.12 20
10 26.7 1-1c F 290 4 285 -- 8.5 10 22.6 1-2c F 290 6.2 285 -- 17.4
10 23.0 1-3c F 290 9.8 285 -- 25.7 10 23.3 1-4c F 247 8 245 -- 8 10
22.5 1-5c F 247 9 245 -- 16 10 20.4 1-6c F 247 12 245 -- 24.4 10
19.8 2-1c K 280 10 280 0.11 16 10 23.4 2-2c K 280 10 280 0.11 16 5
21.8 2-3c K 280 10 280 0.11 16 5 24.2 2-4c K 314 4 310 0.11 16 5
23.6 3-1c L 250 7 250 0.15 25 20 23.0 3-2c L 220 8 220 0.12 19 20
20.4 3-3c L 220 4 220 0.04 7 20 20.9 7-1c F 252 696 275 55 29 150
25.1 8-1c 98.5/1.5 G/X 262 697 276 51 29 150 23.0 9-1 97.5/2.5 H/X
255 407 275 48 34 330 21.7 The letter "c" in the designation
denotes comparative example X is IRGATEC CR76 polymer modifier
available from Ciba Specialty Chemicals, which is a hydroxyl amine
ester in a masterbatch. Samples 7-1, 8-1, 9-1 were made on a Hills
type line. All others in this table were made with Biax 5'' width
meltblown line manufactured by the Biax-Fiberfilm Corporation
(Greenville, Wisconsin, USA)
[0109] Fabric samples made to examine the effect of hydroxylamine
masterbatch level were made. They are described in Table 4.
TABLE-US-00005 TABLE 4 FABRIC EXAMPLES MADE WITH MODIFIED RESINS
Melt Screw Through- X Temp Speed put Mw MFR.sup.a Ex. Resin (wt. %)
(.degree. C.) (rpm) (ghm) (g/mol) (g/10 min) 10-01 H 1.5 250 20
0.13 74500 390 10-02 J 1.5 280 20 0.15 55500 1050 10-03 J 1.5 280
20 0.12 52600 1257 10-04 I 3 280 20 -- 54200 1137 10-05 I 3 250 20
0.12 75100 380 10-06 J 1.5 250 20 -- 65700 596 10-07 J 1.5 250 20
-- 72800 422 10-08 I 1.5 250 20 -- 72200 434 10-09 I 1.5 280 20 --
59200 845 10-10 J 3 250 20 0.08 50600 1432 10-11 J 3 230 20 0.14
83300 268 .sup.aASTM D-1238 (230.degree. C., 2.16 kg)
[0110] Further examples of fabrics made on the Hills type line are
described in Table 5. Notice that the hydrohead performance of
these novel fabrics are comparable to conventional hPP-based
fabrics while imparting the additional desirable bonding
performance.
TABLE-US-00006 TABLE 5 FABRIC EXAMPLES Fabric Weight Hydrohead
Example Resin (g/m.sup.2) (mm) 11-01c S 25 700 11-02c S 35 882
11-03c S 50 1017 11-04c 98.5/1.5 P/X 25 295 11-05c 98.5/1.5 P/X 35
282 11-06c 98.5/1.5 P/X 50 532 11-07c 98.5/1.5 P/X 25 330 11-08c
98.5/1.5 P/X 35 497 11-09 98.5/1.5 H/X 50 402 11-10 98.5/1.5 H/X 25
365 11-11 98.5/1.5 H/X 35 542 11-12 98.5/1.5 H/X 50 480 11-13
98.5/1.5 H/X 20 + 6 + 6 300; 333 11-14 J 25 n/a 11-15 J 50 n/a
11-16 J 100 n/a 11-17c S 139 380; 510 11-18c F 25 n/a 11-19
97.5/2.5 H/X 25 n/a The letter `c` in the designation denotes a
comparative example.
[0111] By plotting the bending moduli against elongation of the
fabrics described in the preceding tables (FIG. 1), the
differentiation of the inventive fibers and the comparative
examples is evident. Inventive fibers describe a region of higher
elongation (greater than about 75 percent) and lower normalized
modulus (less than 0.6 mNcm at 20 gsm) in contrast to the
comparative examples. Functionally, this behavior translates to
fibers that can exhibit better drape (lower bending modulus) and
fibers that can have greater extensibility (higher elongation to
break).
[0112] FIG. 2 shows the normalized peak force plotted against
elongation to break. In contrast to the comparative examples, the
inventive samples occupy a region of higher peak force and
elongation described by the equations: [0113] a.
F.sub.MD.gtoreq.[-0.00143.times.elong(percent)+0.823] if elongation
is between 20 to 675 percent strain. [0114] b. F.sub.MD.gtoreq.0.1
lb if elongation is greater than or equal to 675 percent strain.
This result combined with the result from FIG. 1 demonstrates that
the inventive examples exhibit the novel and desirable combination
of the following properties: better drape (lower bending modulus),
higher extensibility (higher elongation at peak force), and higher
strength (higher normalized peak force).
[0115] There are various aspects of elastomeric behavior. FIG. 3
shows the set strain plotted against elongation for the inventive
examples. The inventive PBP-based fabrics exhibit set strains less
than about 50 percent strain. For more elastic performance,
selection of PBE-based fabrics exhibit the more preferred set
strains of less than about 15 percent. In this way, selected
inventive examples are shown to have lower set, an aspect of
elastomeric behavior. Because the comparative examples hPP examples
exhibited elongations to break less than 50 percent strain, they
were not able to survive this test.
[0116] Another aspect of elastomeric behavior is retractive force.
Retained load is a measure of retractive force. Higher retained
loads correspond to higher retractive force for a given extension
force. FIG. 4 shows the MD retained load plotted against
elongation. PBP based fabrics are shown to have retained loads of
greater than or equal to 0 percent. PBE based fabrics are shown to
have retained loads great than about 15 percent. In applications by
themselves or with other components, PBE based fabrics are shown to
have greater retractive force. Such behavior translates to greater
"holding power" which is necessary for improved fit and comfort. In
many elastic applications, higher holding power is desirable for
its greater mechanical ability to fasten one object to another.
[0117] The tensile and elastic properties discussed previously are
summarized in table 6.
TABLE-US-00007 TABLE 6 TENSILE AND ELASTIC PROPERTIES FOR INVENTIVE
AND COMPARATIVE FABRICS Normalized Normalized Retained Bending
Modulus Tensile Strength Load 30% (mN cm) Elongation (lb/1'' width)
Set Strain strain Example @ 20 gsm avg (%) avg stdev @ 20 gsm avg
stdev (%) avg stdev (%) uncert. 1-1c 1.535 2 0 1.41 1.3 n/a n/a n/a
-- 1-2c 1.408 4 1 1.50 0.5 n/a n/a n/a -- 1-3c 0.858 5 2 1.08 1.3
n/a n/a n/a -- 1-4c 1.069 9 2 1.53 2.0 n/a n/a n/a -- 1-5c 0.871 9
2 1.74 0.0 n/a n/a n/a -- 1-6c 0.956 19 11 1.40 0.3 n/a n/a n/a --
1-1 0.168 244 188 1.21 1.0 26.0 0.8 0.1 0.2 1-2 0.364 187 5 1.20
0.1 29.1 0.3 0.0 0.0 1-3 0.194 177 35 1.51 0.0 25 2 0.4 0.3 1-4
0.364 95 15 1.00 0.1 25.3 0.0 0.0 0.0 1-5 0.228 8 1 1.07 0.0 n/a --
n/a -- 1-6 0.194 85 11 1.02 0.2 n/a -- n/a -- 1-7 0.107 141 92 1.13
0.6 n/a -- n/a -- 1-8 0.228 13 6 1.18 0.2 27.7 -- n/a -- 2-1 n/a
366 106 0.67 0.5 17.9 0.3 9.2 1.1 2-2 0.228 182 38 0.66 0.0 19.2
0.7 5.5 1.0 2-3 0.020 227 28 0.59 0.2 18.8 0.1 6.6 1.1 3-1 0.087
399 149 0.67 0.9 26.5 0.8 n/a -- 3-2 0.107 n/a n/a -- n/a -- n/a --
3-3 0.068 402 154 0.70 0.7 8.6 0.8 28.8 1.9 3-4 0.087 481 102 0.81
1.0 9.1 0.8 28.8 1.6 4-1 0.030 439 89 0.38 0.1 7.5 0.1 35.8 3.2 4-2
0.107 453 159 0.44 0.5 8.1 0.7 32.6 4.4 4-3 n/a 528 159 0.48 0.5
7.6 0.1 35.6 3.5 5-1 0.053 245 16 0.64 0.0 18.0 0.3 8.7 1.6 5-2
0.068 286 49 0.78 0.1 16 1 9.2 2.0 5-3 0.107 154 33 0.64 0.2 17.0
0.2 8.8 0.8 6-1 0.039 141 6 0.63 0.1 15.7 0.1 12.1 1.7 6-2 0.107
165 11 0.64 0.1 16.3 0.2 10.4 1.9 6-3 0.114 185 35 0.72 0.1 16.5
0.3 10.5 0.7 6-4 0.107 167 26 0.64 0.2 15.6 0.5 13.5 1.4 7-1c n/a 5
1 1.76 0.2 n/a -- n/a -- 8-1c n/a 13 2 2.26 0.2 n/a -- n/a -- 9-1
n/a 17 8 0.91 0.2 n/a -- n/a -- 2-1c 0.160 7 2 0.18 0.3 n/a -- n/a
-- 2-2c 0.416 14 7 0.63 0.1 n/a -- n/a -- 2-3c 0.228 12 5 0.53 0.3
n/a -- n/a -- 2-4c 0.236 23 4 0.52 0.1 n/a -- n/a -- 3-1c 0.003 56
8 0.16 0.0 7.3 0.4 45 6 3-2c 0.003 n/a -- 0.18 0.1 9.2 0.7 34 12
3-3c 0.003 28 4 0.14 0.1 n/a -- n/a -- 10-1 n/a 38 51 1.0 0.3 23 2
n/a -- 10-2 n/a 238 90 0.41 0.06 n/a -- 11 1 10-3 n/a 94 24 0.39
0.02 7 1 11.4 0.9 10-4 n/a 359 45 0.51 0.01 n/a -- n/a -- 10-5 n/a
121 72 0.8 0.1 13.6 0.7 n/a -- 10-6 n/a 303 142 0.44 0.06 7 1 10 2
10-7 n/a 200 71 0.8 0.2 6.3 0.6 6.7 0.9 10-8 n/a 283 120 0.6 0.1 11
2 39 3 10-9 n/a 53 12 0.7 0.1 13 1 120 40 10-10 n/a 16 1 0.34 0.08
6.3 0.6 12 6 10-11 n/a 90 31 0.5 0.1 5.3 0.6 5.7 0.6 The letter `c`
in the designation denotes a comparative example.
[0118] Based on the described discoveries, the following table of
preferred ranges for the fibers of this invention is described in
Table 7.
TABLE-US-00008 TABLE 7 PREFERRED RANGES FOR THE INVENTIVE FABRICS
Extensible Elastic Ethylene (wt. %) From >5 to 10 from 10 to 17
Bending Modulus less than about 0.6 less than about 0.3 (mN cm) at
<30 gsm Elongation (%) greater than about 20% greater than about
350% Tensile Strength F.sub.MD .gtoreq. [-O.00143 .times. elong(%)
+ 0.823] if elongation (lbs/1'' width is between 20 to 675%
F.sub.MD .gtoreq. 0.1 lb if elongation is @ 20 gsm) greater than or
equal to 675% Set Strain (50% less than about 50% less than about
15% hysteresis Test) Retained Load at greater than or equal greater
than about 15% 30% (50% hyster- to 0% esis Test)
[0119] Selected meltblown fabrics from Table 5 were chosen for
fabrication into SMxS laminate structures (`S` denotes spunbond
layer, `M` denotes melt blown layer, and `x` denotes the number of
meltblown layers). They were combined with various 20 gsm spunbond
fabrics (Table 8) made with Reicofil 3 technology from Reifenhauser
and point bonded at the recommended temperatures for the various
materials (hPP, PE and bico) with a calendar roll (21 percent
bonding area) to make SMS and SS laminates (Tables 9 and 10).
TABLE-US-00009 TABLE 8 SPUNBOND NONWOVEN FABRICS Basis Weight
Designation Composition Type (gsm) 12-18 P hPP 20 12-19 S hPP 20
12-20 41/59 J/P propylene-ethylene/hPP blend 20 12-21 Q
polyethylene 20 12-22 R polyethylene 20 12-23 70/30 P/Q
hPP/polyethylene (core/sheath) 20 (core/sheath)
[0120] In all cases, inventive laminates made with the meltblown
fabrics of example 11-19, had the lowest or equal to the lowest
bending modulus. This demonstrates that the low modulus of the
meltblown fabrics of the preferred compositional range results in
novel laminates. Low modulus translates to softness and better
drape in end-use.
TABLE-US-00010 TABLE 9 SMXS STRUCTURES AND THEIR BENDING MODULI (N
MM) Spun- Meltblown Layer bond Spunbond 11-04c or Example Layer
Composition Control- 11-18c 11-07c 11-19 13-1c 12-18 P 0.004 13-2c
12-18 P 0.009 13-3c 12-18 P 0.008 13-4 12-18 P 0.006 14-1c 12-19 S
0.003 14-2c 12-19 S 0.007 14-3c 12-19 S 0.008 14-4 12-19 S 0.006
15-1c 12-20 41/59 J/P 0.001 15-2c 12-20 41/59 J/P 0.003 15-3c 12-20
41/59 J/P 0.004 15-4 12-20 41/59 J/P 0.003 16-1c 12-21 Q 0.001
16-2c 12-21 Q 0.003 16-3c 12-21 Q 0.003 16-4 12-21 Q 0.003 17-1c
12-22 R 0.001 17-2c 12-22 R 0.003 17-3c 12-22 R 0.004 17-4 12-22 R
0.003 18-1c 12-23 70/30 P/Q 0.002 (core/sheath) 18-2c 12-23 70/30
P/Q 0.006 (core/sheath) 18-3c 12-23 70/30 P/Q 0.005 (core/sheath)
18-4 12-23 70/30 P/Q 0.004 (core/sheath) The letter `c` in the
designation denotes a comparative example.
[0121] Measurement of the peel strength of these laminates by
cutting a 5 cm wide strip parallel to the machine direction (MD)
and peeling at 100 mm/min in an Instron in a 180.degree. T-peel
geometry shows that laminates made with meltblown fabric 11-19
consistently exhibits the highest peel strengths (FIG. 6). Peel
strength is reported in Newtons per 5 cm width.
[0122] When examined in detail, this result is especially
astonishing. First, SMS structures made with meltblown fabric 11-19
exceeded the peel strength of the spunbond fabrics to themselves
(the "control" in tables 9 and 10 were two spunbond layers as
indicated with no meltblown layer). Second, SMS structures made
with meltblown fabric 11-19 exceeded the peel strength of the hPP
spunbond fabrics (12-18 and 12-19) to hPP meltblown layers (11-18c,
11-04c, or 11-07c). Typically, bonds of dissimilar materials are
weaker. As a result, the laminates made with meltblown example
11-19 exhibit unexpectedly high bond strengths. Lastly, when at
least one spunbond comprises a polyethylene based polymer
(12-21,12-22, and 12-23), the peel strength not only exceeds the
controls meltblown but also laminates comprising hPP based
meltblown (11-18c, 11-04c, or 11-07c). This shows the improved
characteristics of the preferred meltblown compositions and also
the novel laminates that comprise them.
TABLE-US-00011 TABLE 10 SMXS STRUCTURES AND THEIR PEEL STRENGTH
(N/5 CM WIDTH) Meltblown Spun- Spunbond con- 11-04c or Example bond
Composition trol - 11-18c 11-07c 11-19 13-1c 12-18 P 1.6 13-2c
12-18 P 2.3 13-3c 12-18 P 2.1 13-4 12-18 P 5.2 14-1c 12-19 S 2.05
14-2c 12-19 S 3.1 14-3c 12-19 S 3.1 14-4 12-19 S 5 15-1c 12-20
41/59 J/P 0.6 15-2c 12-20 41/59 J/P 1.25 15-3c 12-20 41/59 J/P 1.6
15-4 12-20 41/59 J/P 5.4 16-1c 12-21 Q 1.3 16-2c 12-21 Q 0 16-3c
12-21 Q 0 16-4 12-21 Q 2.6 17-1c 12-22 R 1.9 17-2c 12-22 R 0 17-3c
12-22 R 0 17-4 12-22 R 3.25 18-1c 12-23 70/30 P/Q 3.5 (core/sheath)
18-2c 12-23 70/30 P/Q 0 (core/sheath) 18-3c 12-23 70/30 P/Q 0
(core/sheath) 18-4 12-23 70/30 P/Q 6.3 (core/sheath) The letter `c`
in the designation denotes a comparative example.
* * * * *