U.S. patent application number 10/653818 was filed with the patent office on 2004-03-25 for meltblown web.
Invention is credited to Bansal, Vishal, Davis, Michael C., Rudisill, Edgar N..
Application Number | 20040058609 10/653818 |
Document ID | / |
Family ID | 31994680 |
Filed Date | 2004-03-25 |
United States Patent
Application |
20040058609 |
Kind Code |
A1 |
Bansal, Vishal ; et
al. |
March 25, 2004 |
Meltblown web
Abstract
A meltblown fiber comprising at least 20% by weight polyester
selected from the group consisting of poly(ethylene terephthalate)
having an intrinsic viscosity of less than 0.55 dl/g and
poly(trimethylene terephthalate) having an intrinsic viscosity of
less than 0.80 dl/g is provided. The meltblown fibers are collected
as a web that can be incorporated into composite sheet
structures.
Inventors: |
Bansal, Vishal; (Richmond,
VA) ; Davis, Michael C.; (Midlothian, VA) ;
Rudisill, Edgar N.; (Nashville, TN) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
31994680 |
Appl. No.: |
10/653818 |
Filed: |
September 3, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10653818 |
Sep 3, 2003 |
|
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09852380 |
May 10, 2001 |
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Current U.S.
Class: |
442/400 ;
442/361; 442/362; 442/364 |
Current CPC
Class: |
D01F 6/62 20130101; D01D
5/0985 20130101; Y10T 442/68 20150401; B32B 5/26 20130101; Y10T
442/637 20150401; D04H 1/435 20130101; D04H 1/43828 20200501; D04H
1/43835 20200501; D04H 1/559 20130101; D04H 5/06 20130101; Y10T
442/641 20150401; D04H 1/43838 20200501; D04H 1/4374 20130101; Y10T
442/638 20150401; D01F 8/14 20130101; B32B 2262/0253 20130101; D01F
8/06 20130101; D04H 1/4291 20130101; D04H 1/43832 20200501; D04H
1/56 20130101; B32B 2262/0284 20130101 |
Class at
Publication: |
442/400 ;
442/361; 442/362; 442/364 |
International
Class: |
D04H 001/56 |
Claims
What is claimed is:
1. A meltblown fiber comprising at least 20% by weight polyester
selected from the group consisting of poly(ethylene terephthalate)
having an intrinsic viscosity of less than 0.55 dl/g, and
poly(trimethylene terephthalate) having an intrinsic viscosity of
less than 0.80 dl/g.
2. The meltblown fiber of claim 1 wherein the fiber has an average
effective diameter of less than 10 microns, and wherein the
intrinsic viscosity of the poly(ethylene terephthalate) is in the
range of 0.20 to 0.50 dl/g and the intrinsic viscosity of the
poly(trimethylene terephthalate) is in the range of 0.45 to 0.75
dl/g.
3. The meltblown fiber of claim 2 wherein the intrinsic viscosity
of the poly(ethylene terephthalate) is in the range of 0.25 to 0.45
dl/g and the intrinsic viscosity of the poly(trimethylene
terephthalate) is in the range of 0.50 to 0.70 dl/g.
4. The meltblown fiber of claim 1 wherein said fiber is a multiple
component fiber comprised of between 20% and 98% by weight of
poly(ethylene terephthalate) and between 80% and 2% by weight of a
second polymer component.
5. The meltblown fiber of claim 4 wherein said second polymer
component comprises of at least 10% of polyethylene polymer.
6. A web of meltblown fibers, said web comprised of at least 20% by
weight polyester selected from the group consisting of
poly(ethylene terephthalate) having an intrinsic viscosity of less
than 0.55 dl/g, and poly(trimethylene terephthalate) having an
intrinsic viscosity of less than 0.80 dl/g.
7. The web of claim 6 the fibers of the web have an average
effective diameter of less than 10 microns, and wherein the
intrinsic viscosity of the poly(ethylene terephthalate) is in the
range of 0.20 to 0.50 dl/g and the intrinsic viscosity of the
poly(trimethylene terephthalate) is in the range of 0.45 to 0.75
dl/g.
8. The web of claim 7 wherein the intrinsic viscosity of the
poly(ethylene terephthalate) is in the range of 0.25 to 0.45 dl/g
and the intrinsic viscosity of the poly(trimethylene terephthalate)
is in the range of 0.50 to 0.70 dl/g.
9. The web of claim 6 wherein the web is comprised of multiple
component fibers and the web is comprised of between 20% and 98% by
weight of poly(ethylene terephthalate) and between 80% and 2% by
weight of a second polymer component.
10. The web of claim 9 wherein said second polymer component
comprises at least 10% by weight of polyethylene polymer.
11. A composite sheet comprising: a first fibrous layer having a
first side and an opposite second side; a second fibrous layer
bonded to said first side of said first fibrous layer; said first
fibrous layer being a meltblown web comprised of at least 20% by
weight polyester selected from the group consisting of
poly(ethylene terephthalate) having an intrinsic viscosity of less
than 0.55 dl/g, and poly(trimethylene terephthalate) having an
intrinsic viscosity of less than 0.80 dl/g; said second fibrous
layer comprised of at least 95% by weight of meltspun fibers; said
composite sheet having a basis weight of less than 120 g/m.sup.2,
and a hydrostatic head of at least 10 cm.
12. The composite sheet of claim 11 wherein at least 10% of the
meltblown fibers in said first fibrous layer are multiple component
fibers having a length, said multiple component fibers having first
and second polymer components arranged in a manner such that said
first and second polymer components each extend substantially the
complete length of said bicomponent fibers.
13. The composite sheet of claim 12 wherein said first and second
polymer components of said bicomponent meltblown fibers are
arranged in a side-by-side arrangement.
14. The composite sheet of claim 12 wherein said first polymer
component comprises between 20% and 98% by weight of said first
fibrous layer and said second polymer component comprises between
80% and 2% of said first fibrous layer, and said second polymer
component of said first fibrous layer consists essentially of
polyethylene.
15. The composite sheet of claim 14 wherein the meltspun fibers of
said second fibrous layer are multiple component fibers having a
polyester component and a polyethylene component, wherein the
polyester component comprises at least 10% by weight of the second
fibrous layer and the polyethylene component comprises at least 10%
by weight of the second fibrous layer.
16. A garment comprised of the composite sheet of claim 11.
17. A meltblown fiber comprising at least 20% by weight polyester
having a weight average molecular weight of less than 25,000.
18. The meltblown fiber of claim 17 wherein said polyester has a
weight average molecular weight in the range of 5,000 to
22,000.
19. The meltblown fiber of claim 18 wherein said polyester has a
weight average molecular weight in the range of 10,000 to
19,000.
20. The meltblown fiber of claim 17 wherein said polyester is
poly(ethylene terephthalate).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to meltblown fibers, meltblown fiber
webs, and composite nonwoven fabrics that include meltblown fibers.
The meltblown webs of the invention can be incorporated in
composite fabrics suited for use in apparel, wipes, hygiene
products, and medical wraps.
[0003] 2. Description of Related Art
[0004] In a meltblowing process, a nonwoven web is formed by
extruding molten polymer through a die and then attenuating and
breaking the resulting filaments with a hot, high-velocity gas
stream. This process generates short, very fine fibers that can be
collected on a moving belt where they bond with each other during
cooling. Meltblown webs can be made that exhibit very good barrier
properties.
[0005] Meltblown fibers are most typically spun from polypropylene.
Other polymers that have been spun as meltblown fibers include
polyethylene, polyamides, polyesters, and polyurethanes. Polyester
polymers, such as poly(ethylene terephthalate) ("PET") and
poly(trimethylene terephthalate) ("PTT"), are not well adapted for
making fine meltblown fibers. In addition, due to polyester's low
degree of crystallization when formed in meltblown webs and due to
polyester's low crystallization temperature, thermally bonded
meltblown polyester webs tend to be brittle and they exhibit
relatively poor fluid barrier properties, especially when subjected
to mechanical stress. U.S. Pat. No. 5,364,694 discloses the
meltblowing of a blend of PET with another thermoplastic polymer,
such as polyethylene, which is incompatible with PET and has a high
crystallization rate and a low melt viscosity. The second polymer
produces a "viscosity-reducing effect" that decreases the melt
viscosity of the entire blend, so as to facilitate attenuation of
PET when meltblown. U.S. Pat. No. 4,795,668 discloses the
meltblowing of bicomponent fibers wherein one component is PET and
the other component is a more thermally stable polymer such as
polypropylene or polystyrene.
[0006] Meltblown fibers have been incorporated into a variety of
nonwoven fabrics including composite laminates such as
spunbond-meltblown-spunbond ("SMS") composite sheets. In SMS
composites, the exterior layers are spunbond fiber layers that
contribute strength to the overall composite, while the core layer
is a meltblown fiber layer that provides barrier properties.
Traditionally, the spunbond and meltblown layers of SMS composites
have been made of polypropylene fibers. For certain end use
applications, such as medical gowns, it is desirable that SMS
composite sheets have good strength and barrier properties, while
also being as soft and drapeable as possible. While
polypropylene-based SMS fabrics offer good strength and barrier
properties, they tend not to be as soft and drapeable as is
desirable for apparel products. Polypropylene-based SMS fabrics
also have the limitation that they cannot be sterilized with gamma
radiation because such fabrics are discolored and weakened when
sterilized with gamma radiation, and because gamma radiation
sterilization of polypropylene-based SMS fabrics generates
unpleasant odors. A polymer fiber or fabric is generally considered
to be not radiation sterilizable when sterilization of the fabric
with gamma radiation causes a significant reduction in the strength
of the fiber or fabric, noticeably changes the appearance of the
fiber or fabric, or generates an objectionable odor. This inability
to undergo gamma radiation sterilization presents a significant
problem for polypropylene-based SMS fabrics because radiation
sterilization is commonly used throughout the medical industry.
[0007] There is a need for finer polyester meltblown fibers that
when formed into webs exhibit good barrier properties. There is a
further need for meltblown polyester webs that are pliable and do
not experience a significant loss in barrier properties when
mechanically stressed.
BRIEF SUMMARY OF THE INVENTION
[0008] The present invention is directed to a meltblown fiber and a
web of meltblown fibers. The meltblown fiber of the invention
comprises at least 20% by weight polyester selected from the group
consisting of poly(ethylene terephthalate) having an intrinsic
viscosity of less than 0.55 dl/g, and poly(trimethylene
terephthalate) having an intrinsic viscosity of less than 0.80
dl/g. The meltblown fiber of the invention has an average effective
diameter of less than 10 microns. Preferably, the intrinsic
viscosity of the poly(ethylene terephthalate) is in the range of
0.20 to 0.50 dl/g and the intrinsic viscosity of the
poly(trimethylene terephthalate) is in the range of 0.45 to 0.75
dl/g. More preferably, the intrinsic viscosity of the poly(ethylene
terephthalate) is in the range of 0.25 to 0.45 dl/g and the
intrinsic viscosity of the poly(trimethylene terephthalate) is in
the range of 0.50 to 0.70 dl/g. Meltblown fibers of the invention
are preferably formed into a meltblown web.
[0009] According to one preferred embodiment of the invention, the
meltblown fiber is a multiple component fiber comprised of between
20% and 98% by weight of poly(ethylene terephthalate) and between
80% and 2% by weight of a second polymer component comprised of at
least 10% of polyethylene polymer. Meltblown fibers of the
invention are preferably formed into a multiple component meltblown
web comprised of between 20% and 98% by weight of poly(ethylene
terephthalate) and between 80% and 2% by weight of a second polymer
component comprised at least 10% by weight of polyethylene
polymer.
[0010] The present invention is also directed to a composite sheet
having a first fibrous layer having a first side and an opposite
second side, and a second fibrous layer bonded to the first side of
the first fibrous layer. The first fibrous layer is a meltblown web
comprised of at least 20% by weight polyester selected from the
group consisting of poly(ethylene terephthalate) having an
intrinsic viscosity of less than 0.55 dl/g, and poly(trimethylene
terephthalate) having an intrinsic viscosity of less than 0.80
dl/g. The second fibrous layer is preferably comprised of at least
95% by weight of meltspun fibers. In the preferred embodiment of
the invention, the composite sheet has a basis weight of less than
120 g/m.sup.2, and a hydrostatic head of at least 10 cm. According
to a more preferred embodiment of the invention, at least 10% of
the meltblown fibers in the first fibrous layer are multiple
component fibers. More preferably the multiple component meltblown
fibers have a low intrinsic viscosity polyester component and a
polyethylene component. According to the invention, the meltspun
fibers of the second fibrous layer can be multiple component fibers
having a polyester component and a polyethylene component. The
invention is also directed to garments made of the composite sheet
of the invention.
[0011] The present invention is also directed to a meltblown fiber
comprising at least 20% by weight polyester having a weight average
molecular weight of less than 25,000. Preferably, the polyester has
a weight average molecular weight in the range of 5,000 to 22,000.
More preferably, the polyester has a weight average molecular
weight in the range of 10,000 to 19,000.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic diagram of a portion of an apparatus
used for producing meltblown fibers for use in the composite
nonwoven fabric of the invention.
[0013] FIG. 2 is a diagrammatical cross-sectional view of a
composite nonwoven fabric in accordance with one embodiment of the
invention.
[0014] FIG. 3 is a diagrammatical cross-sectional view of a
composite nonwoven fabric in accordance with another embodiment of
the invention.
[0015] FIG. 4 is schematic illustration of an apparatus for
producing the composite nonwoven fabric of the invention.
DEFINITIONS
[0016] The term "polymer" as used herein, generally includes
homopolymers, copolymers (such as for example, block, graft, random
and alternating copolymers), terpolymers, 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
isotactic, syndiotactic and random symmetries.
[0017] The term "polyethylene" as used herein is intended to
encompass not only homopolymers of ethylene, but also copolymers
wherein at least 85% of the recurring units are ethylene units.
[0018] The term "polypropylene" as used herein is intended to
embrace not only homopolymers of propylene but also copolymers
wherein at least 85% of the recurring units are propylene
units.
[0019] The term "polyester" as used herein is intended to embrace
polymers wherein at least 85% of the recurring units are
condensation products of dicarboxylic acids and dihydroxy alcohols
with polymer linkages created
[0020] by formation of an ester unit. This includes aromatic,
aliphatic, saturated, and unsaturated di-acids and di-alcohols. The
term "polyester" as used herein also includes copolymers (such as
block, graft, random and alternating copolymers), blends, and
modifications thereof. A common example of a polyester is
poly(ethylene terephthalate) which is a condensation product of
ethylene glycol and terephthalic acid.
[0021] The term "meltspun fibers" as used herein means fibers which
are formed by extruding molten thermoplastic polymer 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. Meltspun fibers are generally continuous and
have an average diameter of greater than about 5 microns.
[0022] The term "meltblown fibers" as used herein means fibers
formed by extruding a molten thermoplastic polymer through a
plurality of fine, usually circular, capillaries as molten threads
or filaments into a high velocity gas (e.g. air) stream. The high
velocity gas stream attenuates the filaments of molten
thermoplastic polymer material to reduce their diameter to between
about 0.5 and 10 microns. Meltblown fibers are generally
discontinuous fibers. Meltblown fibers carried by the high velocity
gas stream are normally deposited on a collecting surface to form a
web of randomly dispersed fibers.
[0023] The term "spunbond fibers" as used herein, means fibers that
are formed by extruding molten thermoplastic polymer material as
filaments from a plurality of fine capillaries of a spinneret,
drawn, randomly deposited onto a screen and bonded together.
[0024] The term "nonwoven fabric, sheet or web" as used herein
means a structure of individual fibers or threads that are
positioned in a random manner to form a planar material without an
identifiable pattern, as in a knitted fabric.
[0025] The term "multiple component meltblown web" as used herein
means meltblown fibers spun from fine capillaries as molten
filaments containing multiple and distinct polymer components,
which molten filaments are attenuated by a high velocity gas stream
and deposited on a collecting surface as a web of randomly
dispersed fibers.
[0026] As used herein, the "machine direction" is the long
direction within the plane of a sheet, i.e., the direction in which
the sheet is produced. The "cross direction" is the direction
within the plane of the sheet that is perpendicular to the machine
direction.
Test Methods
[0027] In the description above and in the examples that follow,
the following test methods were employed to determine various
reported characteristics and properties. ASTM refers to the
American Society for Testing and Materials, and AATCC refers to the
American Association of Textile Chemists and Colorists.
[0028] Intrinsic Viscosity (IV) is a measure of the inherent
resistance to flow for a polymer solution and was determined by
ASTM D-2857, which is hereby incorporated by reference, and is
reported in dl/g. The solvent and temperature used to study the
intrinsic viscosity of poly(ethylene terephthalate) in a glass
capillary viscometer was hexafluoropropanol with 0.01 M sodium
trifluoroacetate at 35.degree. C. The solvent and temperature used
to study the intrinsic viscosity of poly(trimethylene
terephthalate) in a glass capillary viscometer was
orthochlorophenol at 25.degree. C.
[0029] Weight Average Molecular Weight was measured using size
exclusion chromatography analysis with a triple detector system.
This system allows an absolute molecular weight to be measured
independent of the type of calibration standards. The molecular
weight averages for poly(ethylene terephthalate) were determined in
hexafluoroisopropanol with 0.01 M sodium trifluoroacetate using an
injection volume of 100 microliters operating at 1.000 mL/min flow
rate at 35 C.
[0030] Fiber Diameter was measured via optical microscopy and is
reported as an average value in microns.
[0031] Basis Weight is a measure of the mass per unit area of a
fabric or sheet and was determined by ASTM D-3776, which is hereby
incorporated by reference, and is reported in g/m.sup.2.
[0032] Grab Tensile Strength is a measure of the breaking strength
of a sheet and was conducted according to ASTM D 5034, which is
hereby incorporated by reference, and is reported in Newtons.
[0033] Hydrostatic Head is a measure of the resistance of a sheet
to penetration by liquid water under a static pressure. The test
was conducted according to AATCC-127, which is hereby incorporated
by reference, and is reported in centimeters.
[0034] Frazier Air Permeability is a measure of air flow passing
through a sheet under a stated pressure differential between the
surfaces of the sheet and was conducted according to ASTM D 737,
which is hereby incorporated by reference, and is reported in
m.sup.3/min/m.sup.2.
[0035] Water Impact is a measure of the resistance of a sheet to
the penetration of water by impact and was conducted according to
AATCC 42-1989, which is hereby incorporated by reference, and is
reported in grams.
DETAILED DESCRIPTION OF THE INVENTION
[0036] Reference will now be made in detail to the presently
preferred embodiments of the invention, examples of which are
illustrated below. The present invention is directed to meltblown
polyester fibers that are spun from lower viscosity polyesters in
order to obtain finer fibers. As embodied herein, the meltblown
fibers are comprised of at least 20% by weight polyester selected
from the group consisting of poly(ethylene terephthalate) having an
intrinsic viscosity of less than 0.55 dl/g, and poly(trimethylene
terephthalate) having an intrinsic viscosity of less than 0.80
dl/g. The intrinsic viscosity of poly(ethylene terephthalate)
polyester that has been meltblown in the past has generally been in
the range of 0.65 to 0.80 dl/g. The intrinsic viscosity or "IV" of
a polymer is an indicator of the polymer's molecular weight, with a
higher IV being indicative of a higher molecular weight.
Poly(ethylene terephthalate) with an IV below about 0.55 dl/g is
considered to be a "low IV" polyester. Poly(trimethylene
terephthalate)("PTT") with an IV below about 0.80 dl/g is
considered to be a "low IV" polyester. The low IV polyesters useful
in the present invention have weight average molecular weights of
less than 25,000. Preferably, the polyester has a weight average
molecular weight in the range of 5,000 to 22,000. More preferably,
the polyester has a weight average molecular weight in the range of
10,000 to 19,000.
[0037] Low IV polyester has not been used in making meltblown
fibers or webs. It has been found that when low IV polyester is
meltblown, the fibers produced have a smaller diameter than fibers
meltblown from conventional IV polyester. These smaller diameter
fibers provide improved barrier properties when used in composite
SMS fabrics.
[0038] According to the invention, the fine polyester meltblown
fibers of the invention are produced according to a conventional
meltblowing process. In the meltblowing process, one or more
extruders supply melted polymer to a die tip where the polymer is
fiberized as it passes through fine capillary openings to form a
curtain of filaments. The filaments are pneumatically drawn and
normally broken by a jet of air around the fine capillary openings
in the die. The fibers are deposited on a moving belt or screen, a
scrim, or another fibrous layer. Fibers produced by melt blowing
are generally discontinuous fibers having an effective diameter in
the range of about 0.5 to about 10 microns. As used herein, the
"effective diameter" of a fiber with an irregular cross section is
equal to the diameter of a hypothetical round fiber having the same
cross sectional area.
[0039] In order to make thermally bonded meltblown polyester webs
that are more pliable and durable, the meltblown fibers can be spun
as multiple component fibers wherein one of the fiber components is
comprised of low IV polyester. The fibers in the multiple component
meltblown web of the invention are typically discontinuous fibers
having an average effective diameter of between about 0.5 microns
and 10 microns, and more preferably between about 1 and 6 microns,
and most preferably between about 2 and 4 microns. Multiple
component meltblown webs are formed from at least two polymers
simultaneously spun from a spin pack. Preferably, the multiple
component meltblown web is a bicomponent web made from two
polymers. The configuration of the fibers in the bicomponent web is
preferably a side-by-side arrangement in which most of the fibers
are made of two side-by-side polymer components that extend for a
significant portion of the length of each fiber. Alternatively, the
bicomponent fibers may have a sheath/core arrangement wherein one
polymer is surrounded by another polymer, an "islands-in-the-sea"
arrangement in which multiple strands of one polymer are imbedded
in another polymer, or any other conventional bicomponent fiber
structure. Without wishing to be bound by theory, it is believed
that the attenuation of the meltblown fibers can actually fracture
the multiple component filaments into even finer filaments, some of
which can contain only one polymer component.
[0040] According to the invention, the second polymer component of
the multiple component meltblown web comprises one or more fiber
forming synthetic polymers that are more pliable than polyester.
Preferably, the second component has a melt temperature less than
the melt temperature of the first component so as to help bind the
meltblown fibers upon thermal bonding, which results in a more
pliable web. Preferably, the other polymer or polymers are gamma
radiation stable polymers such as polyethylene. Alternatively, the
second polymer component can be a non-radiation sterilizable
polymer such as polypropylene if the end use for the sheet does not
require that the sheet be radiation sterilizable.
[0041] The preferred multiple component meltblown web of the
invention is a bicomponent meltblown web comprised of low IV PET
and polyethylene. Preferably, the low IV PET component comprises
from 20% to 98% by weight of the meltblown web and the polyethylene
component comprises from 2% to 80% by weight of the meltblown web.
More preferably, the low IV PET component comprises from 55% to 98%
by weight of the meltblown web and the polyethylene component
comprises from 2% to 45% by weight of the meltblown web. Even more
preferably, the low IV PET component comprises from 65% to 97% by
weight of the meltblown web and the polyethylene component
comprises from 3% to 35% by weight of the meltblown web. Most
preferably, the low IV PET component comprises from 80% to 95% by
weight of the meltblown web and the polyethylene component
comprises from 5% to 20% by weight of the meltblown web.
[0042] The fibers of the meltblown web of the invention can be
meltblown using a meltblowing apparatus having capillary die
openings like that shown in FIG. 1 and more fully described in U.S.
Pat. No. 4,795,668, which is hereby incorporated by reference. In
the sectional view of a meltblowing die 20 shown in FIG. 1, two
different polymeric components are melted in parallel extruders 23
and 24 and metered separately through gear pumps (not shown) and
conduits 25 and 26 into the die cavity 22. In the die cavity, the
polymer components form a layered mass in which the two components
segregate as discrete layers. The layered mass is extruded through
a line of capillary orifices 21. Where single component fiber is
desired, the same polymer is supplied by the two extruders 23 and
24, or just one extruder is used. A jet of hot air supplied from
the channels 28 attenuates the emerging polymer filaments. Without
wishing to be bound by theory, it is believed that the air jet may
fracture the filaments into even finer filaments. The resulting
filaments are believed to include bicomponent filaments in which
each filament is made of two separate polymer components that both
extend the length of the meltblown fiber in a side-by-side
configuration. The fine fibers of layer 14 could alternatively be
produced by other know meltblowing processes, as for example by the
process wherein an individual air nozzle surrounds each polymer
capillary, as disclosed in U.S. Pat. No. 4,380,570.
[0043] A composite nonwoven sheet incorporating the meltblown web
of the invention is shown in FIG. 2. The sheet 10 is a three layer
composite fabric in which an inner layer 14 is comprised of very
fine meltblown polymer fibers sandwiched between outer layers 12
and 16, which are each comprised of larger and stronger and bonded
fibers. The very fine fibers of inner layer 14, when formed into
the layer 14, produce a barrier layer with extremely fine passages.
The layer 14 acts as a barrier to fluids but does not prevent the
passage of moisture vapor. The bonded fiber layers 12 and 16 are
comprised of coarser and stronger fibers that contribute strength,
and in some instances barrier, to the composite sheet. A composite
sheet may alternatively be formed as a two layer composite 18, as
shown in FIG. 3. In the two layer composite sheet, the fine
meltblown fiber layer 14 is attached on just one side to the
coarser and stronger bonded layer 12. According to alternative
embodiments of the invention, the composite sheet may be made with
multiple layers of fine meltblown fibers like the layer 14, or it
may be made with more than two layers of coarser and stronger fiber
layers like the layers 12 and 16.
[0044] The larger and stronger bonded fibers of the layers 12 and
16 are preferably conventional meltspun fibers or some other type
of strong spunbond fiber. Preferably, the meltspun fibers are
substantially continuous fibers. Alternatively, the layers 12 and
16 could be an air-laid or wet-laid staple fiber web or a carded
web wherein the fibers are bonded to each other to form a strong
web structure. The fibers of layers 12 and 16 should be made of a
polymer to which polyethylene-containing fine fibers of the core
layer 14 can readily bond. The fibers of layers 12 and 16 are
preferably gamma radiation sterilizable in that they have an outer
layer comprised of a polymer other than polypropylene, such as
polyester, polyethylene, polyamide, or some combination thereof.
Where the composite fabric will not be used in end use applications
where radiation sterilization is used, the fibers of layers 12 and
16 could also be comprised of a polymer such as polypropylene that
is not gamma radiation sterilizable.
[0045] A preferred meltspun fiber for the layers 12 and 16 is a
bicomponent fiber comprised of polyester and polyethylene. The
polyester component contributes to the strength to the fabric while
the polyethylene component makes the fabric softer and more
drapable. In addition, the polyethylene component has a lower
melting temperature than the polyester component of the fiber so as
to make the layers 12 and 16 more readily bondable to the fine
meltblown fibers of the core layer 14 using a thermal bonding
process. Alternatively, layers 12 and 16 could be comprised of a
blend of single polymer component fibers, as for example, a
spunbond web wherein a portion of the fibers are polyethylene
fibers and a portion of the fibers are polyester fibers.
[0046] Preferably, the larger and stronger fibers of the layers 12
and 16 are substantially continuous spunbonded fibers produced
using a high speed melt spinning process, such as the high speed
spinning processes disclosed in U.S. Pat. Nos. 3,802,817;
5,545,371; and 5,885,909; which are hereby incorporated by
reference. According to the preferred high speed melt spinning
process, one or more extruders supply melted polymer to a spin pack
where the polymer is fiberized as it passes through openings to
form a curtain of filaments. The filaments are partially cooled in
an air quenching zone. The filaments are then pneumatically drawn
to reduce their size and impart increased strength. The filaments
are deposited on a moving screen, belt, scrim or other fibrous
layer. Fibers produced by the preferred high speed melt spinning
process are substantially continuous and have a diameter of from 5
to 30 microns. These fibers can be produced as single component
fibers, as multiple component fibers, or some combination thereof.
Multicomponent fibers can be made in various known cross-sectional
configurations, including side-by-side, sheath-core, segmented pie,
or islands-in-the-sea configurations.
[0047] A composite nonwoven fabric incorporating the low intrinsic
viscosity polyester meltblown web described above can be produced
in-line using the apparatus that is shown schematically in FIG. 4.
Alternatively, the layers of the composite sheet can be produced
independently and later combined and bonded to form the composite
sheet. The apparatus shown in FIG. 4 includes spunbonded web
production sections 80 and 94 well-known in the art. The apparatus
of FIG. 4 further includes a meltblown web production section 82
incorporating the meltblowing apparatus described with regard to
FIG. 1 above. For purposes of illustration, the two spunbond web
production sections 80 and 94 and the meltblown web production
section 82 are shown making bicomponent fibers. It is contemplated
that the spunbond web production sections 80 and 94 and the
meltblown web production section 82 could be replaced by units
designed to produce webs having just one polymer component or
having three or more polymer components. It is also contemplated
that more than one spunbond web production section could be used in
series to produce a web made of a blend of different single or
multiple component fibers. Likewise, it is contemplated that more
than one meltblown web production section could be utilized in
series in order to produce composite sheets with multiple meltblown
layers. It is further contemplated that the polymer(s) used in the
various web production sections could be different from each other.
Where it is desired to produced a composite sheet having just one
spunbond layer and one fine fiber layer (as shown in FIG. 3), the
second spunbond web production section 94 can be turned off or
eliminated.
[0048] According to the preferred embodiment of the invention, in
the spunbond web production sections 80 and 94 of the apparatus
shown in FIG. 4, two thermoplastic polymer components A and B are
melted, filtered and metered (not shown) to the spin packs 56 and
96. The melted polymer filaments 60 and 100 are extruded from the
spin packs through spinneret sets 58 and 98, respectively. The
filaments may be extruded as bicomponent filaments having a desired
cross section, such as a sheath-core filament cross section.
Preferably, a lower melting temperature polymer is used for the
sheath section while a higher melting temperature polymer is used
for the core section. The resulting filaments 60 and 100 are cooled
with quenching air 62 and 102. The filaments next enter pneumatic
draw jets 64 and 104 and are drawn by drawing air 66 and 106. The
fibers 67 from the spunbond web production section 80 are deposited
onto forming screen 68 so as to form a spunbond layer 12 on the
belt.
[0049] According to the preferred embodiment of the invention, a
low intrinsic viscosity polyester polymer and another polymer are
combined to make a meltblown bicomponent web in the meltblown web
production section 82. The two polymers C and D are melted,
filtered, and then metered (not shown) into the spin pack 84. The
melted polymers are combined in the spin pack 84 and exit the spin
pack through a line of capillary openings 86 like those described
above with regard to FIG. 1. Preferably, the spin pack 84 generates
the desired side-by-side fiber filament cross section. Alternative
spin pack arrangements can be used to produce alternative fiber
cross sections, such as a sheath-core cross section. A jet of hot
air 88 supplied from the channels 90 impacts on the opposite side
of the exiting filaments 91 and attenuates each filament 91
immediately after each filament exits its capillary opening. The
meltblown filaments 91 are generally fractured during the
attenuation process. The meltblown filament fibers 91 deposit onto
spunbond layer 12 to create the multiple component meltblown web
layer 14.
[0050] Where a second spunbond web production section 94 is used,
substantially continuous spunbond fibers 107 from the spunbond web
production section 80 are deposited onto the meltblown layer 14 so
as to form a second spunbond layer 16 of the composite sheet. The
layers 12 and 16 do not necessarily have to have the same thickness
or basis weight.
[0051] The spunbond-meltblown-spunbond web structure is passed
between thermal bonding rolls 72 and 74 in order to produce the
composite nonwoven web 10 which is collected on a roll 78.
Preferably, the bonding rolls 72 and 74 are heated rolls maintained
at a temperature within plus or minus 20.degree. C. of the lowest
melting temperature polymer in the composite. For the
polyethylene-containing composite sheet of the invention, a bonding
temperature in the range of 115-120.degree. C. and a bonding
pressure in the range of 350-700 N/cm have been applied to obtain
good thermal bonding. Alternative methods for bonding the layers of
the composite sheet include calender bonding, through-air bonding,
steam bonding, and adhesive bonding.
[0052] Optionally, a fluorochemical coating can be applied to the
composite nonwoven web to reduce the surface energy of the fiber
surface and thus increase the fabric's resistance to liquid
penetration. For example, the fabric may be treated with a topical
finish treatment to improve the liquid barrier and in particular,
to improve barrier to low surface tension liquids. Many topical
finish treatment methods are well known in the art and include
spray application, roll coating, foam application, dip-squeeze
application, etc. Typical finish ingredients include ZONYL.RTM.
fluorochemical (available from DuPont, Wilmington, Del.) or
REPEARL.RTM. fluorochemical (available from Mitsubishi Int. Corp,
New York, N.Y.). A topical finishing process can be carried out
either in-line with the fabric production or in a separate process
step. Alternatively, such fluorochemicals could also be spun into
the fiber as an additive to the melt.
[0053] The composite nonwoven sheet preferably has a basis weight
in the range of 10 to 120 g/m.sup.2, and more preferably within the
range of 30 to 90 g/m.sup.2, and most preferably within the range
of 50 to 70 g/m.sup.2. The grab tensile strength of the composite
nonwoven sheet can range widely depending on the thermal bonding
conditions employed. Typical grab tensile sheet strengths (in both
the machine and cross directions) are from 35 to 400 N, and more
preferably from 40 to 300 N, and most preferably from 50 to 200 N.
The inner meltblown fiber layer of the composite sheet typically
has a basis weight of between 2 and 40 g/m.sup.2, and more
preferably between 5 and 30 g/m.sup.2, and most preferably between
12 and 25 g/m.sup.2. The outer layer of the composite contributes
strength, and is some instances barrier, to the composite nonwoven
fabric. Each of the outer layers typically have a basis weight
between 3 and 50 g/m.sup.2, and more preferably between 8 and 40
g/m.sup.2, and most preferably between 12 and 35 g/m.sup.2.
Preferably, the layers of the composite sheet are secured together
by thermal bonding, as for example via the melting of a low melting
temperature component polymer in the fine fiber layer 14 and/or the
larger fiber layers 12 and 16. According to the preferred
embodiment of the invention, the composite sheet exhibits a
hydrostatic head of at least 10 cm, and more preferably of at least
25 cm, and yet more preferably of at least 45 cm, and most
preferably at least 60 cm. It is further preferred that the
composite sheet exhibit a water impact of less than 5 g, and more
preferably less than 2 g, and most preferably less than 0.5 g.
Finally, it is preferred that the composite sheet has a Frazier Air
Permeability greater than 1 m.sup.3/min/m.sup.2, and more
preferably greater than 5 m.sup.3/min/m.sup.2.
[0054] This invention will now be illustrated by the following
examples which are intended to illustrate the invention and not to
limit the invention in any manner.
EXAMPLES
[0055] In Example 1 and Comparative Example A, monocomponent
poly(ethylene terephthalate) meltblown fibers were prepared. These
fibers were meltblown according to the processes described above
with reference to the apparatus shown in FIG. 1 with the same
polymer being used in both sides of the bicomponent meltblown
spinning apparatus.
[0056] In Example 2 and Comparative Example B, monocomponent
poly(trimethylene terephthalate) meltblown fibers were prepared.
These fibers were meltblown according to the processes described
above with reference to the apparatus shown in FIG. 1 with the same
polymer being used in both sides of the bicomponent meltblown
spinning apparatus.
[0057] In Examples 3 and 4, and in Comparative Examples C and D,
bicomponent poly(ethylene terephthalate) meltblown fibers were
prepared and incorporated into a spunbond-meltblown-spunbond
composite sheet. The meltblown fibers were prepared according to
the processes described above with reference to the apparatus of
FIG. 1 with poly(ethylene terephthalate) being used on one side and
polyethylene/poly(butylene terephthalate) blend being used on the
other side of the bicomponent meltblown spinning apparatus. A layer
of these bicomponent meltblown fibers was sandwiched between
spunbond outer layers to make the composite sheet like that shown
in FIG. 2. The spunbond layers were each produced individually
using a high speed melt spinning process like that described above
with regard to the spunbond web production section 80 of the
process shown in FIG. 5. However, instead of preparing all of the
layers in one continuous process as described with reference to
FIG. 5, the spunbond layers were each spun, laid down, and rolled
up separately. The two spunbond layers and the meltblown layer were
subsequently unrolled, combined, and thermally bonded to produce
the spunbond-meltblown-spunbond composite structure.
Example 1
[0058] Meltblown monocomponent fibers were made with poly(ethylene
terephthalate) available from DuPont as Crystar.RTM. polyester
(Merge 3949). The poly(ethylene terephthalate) had an intrinsic
viscosity of 0.63 dl/g and a weight average molecular weight of
35,600. The poly(ethylene terephthalate) was used as received
without any conditioning or drying and had a moisture content of
about 1300 ppm. The poly(ethylene terephthalate) polymer was heated
to 575.degree. F. (300.degree. C.) in separate extruders. The two
polymer components were separately extruded, filtered and metered
to a bicomponent spin pack to coalesce into a monocomponent fiber.
The die of the spin pack was heated to 600.degree. F. (315.degree.
C.). The die had 601 capillary openings arranged in a 24 inch (61
cm) line. The polymer was spun through the each capillary at a
polymer throughput rate of 0.80 g/hole/min. Attenuating air was
heated to a temperature of 615.degree. F. (323.degree. C.) and
supplied at a rate of 225 standard cubic feet per minute (6.4
m.sup.3/min) through two 0.8 mm wide air channels. The two air
channels ran the length of the 24 inch line of capillary openings,
with one channel on each side of the line of capillaries set back 1
mm from the capillary openings. Both streams of poly(ethylene
terephthalate) were supplied to the spin pack at a rate of 12
kg/hr. The filaments were collected on a moving forming screen. As
the poly(ethylene terephthalate) was meltblown, hydrolytic and
thermal degradation occurred which reduced the molecular weight and
hence the intrinsic viscosity of the polymer forming the meltblown
fibers. The poly(ethylene terephthalate) in the meltblown fibers
had an intrinsic viscosity of 0.34 dl/g and a weight average
molecular weight of 16,500. The average fiber diameter is reported
in Table 1.
Comparative Example A
[0059] Meltblown monocomponent fibers were formed according to the
procedure of Example 1 except that the poly(ethylene terephthalate)
was dried for 4 hours at 120.degree. C. prior to meltblowing which
produced a lower moisture content of about 50 ppm. The
poly(ethylene terephthalate) in the meltblown fibers had an
intrinsic viscosity of 0.59 dl/g and a weight average molecular
weight of 31,000. The average fiber diameter is reported in Table
1.
[0060] The undried poly(ethylene terephthalate) with higher moister
content of Example 1 yielded a lower weight average molecular
weight and a lower intrinsic viscosity after spinning than the
dried poly(ethylene terephthalate) with lower moisture content of
Comparative Example A. The presence of additional water in the
higher moisture content example contributed to greater polymer
chain break up than in the lower moisture content example. Table 1
shows that meltblown fibers made of the lower IV poly(ethylene
terephthalate) of Example 1 have a smaller average fiber diameter
than the conventional IV poly(ethylene terephthalate) of
Comparative Example A. The lower intrinsic viscosity and weight
average molecular weight of the poly(ethylene terephthalate) from
the fibers of Example 1 allowed the fibers to be drawn to smaller
average fiber diameters.
Example 2
[0061] Meltblown monocomponent fibers were formed according to the
procedure of Example 1 except that poly(trimethylene terephthalate)
was used in place of the poly(ethylene terephthalate). The
poly(trimethylene terephthalate) resin was had an intrinsic
viscosity of 0.70 dl/g. The poly(trimethylene terephthalate) was
dried for 8 hours at 110.degree. C. This polymer was meltblown
according to the process of Example 1, except that the extruder was
heated to about 518.degree. F. (270.degree. C.) and the die of the
spin pack was heated to about 518.degree. F. (270.degree. C.). The
average fiber diameter is reported in Table 1.
Comparative Example B
[0062] Meltblown monocomponent fibers were formed according to the
procedure of Example 2 except that the poly(trimethylene
terephthalate) resin had a higher intrinsic viscosity of 0.84 dl/g.
The average fiber diameter is reported in Table 1.
[0063] Table 1 shows that meltblown fibers made with the lower
intrinsic viscosity poly(trimethylene terephthalate) of Example 2
have a smaller average fiber diameter than the fibers produced from
the higher intrinsic viscosity poly(trimethylene terephthalate) of
Comparative Example B.
1TABLE 1 MELTBLOWN FIBER PROPERTIES PET PTT Average IV IV Fiber
Diameter Example (dl/g) (dl/g) (micron) 1 0.34 3.6 A 0.59 4.9 2
0.70 2.9 B 0.84 5.5 PET = poly(ethylene terephthalate) PTT =
poly(trimethylene terephthalate)
Example 3
[0064] A meltblown bicomponent web was made with a poly(ethylene
terephthalate) component and a second component comprising a
polyethylene/poly(butylene terephthalate) blend. This meltblown web
was incorporated into a spunbond-meltblown-spunbond composite
sheet.
[0065] In the meltblown web, the poly(ethylene terephthalate)
component was Crystar.RTM. polyester (Merge 3949), available from
DuPont. The poly(ethylene terephthalate) had an intrinsic viscosity
of 0.63 dl/g and a weight average molecular weight of 35,600. The
poly(ethylene terephthalate) was used as received without any
conditioning or drying and had a moisture content of about 1300
ppm. The polyethylene/poly(butyl- ene terephthalate) bicomponent
blend contained 90% by weight linear low density polyethylene with
a melt index of 150 g/10 minutes (measured according to ASTM
D-1238) available from Dow as ASPUN 6831A and 10% by weight
poly(butylene terephthalate) available from Hoechst as Merge 1300A.
The bicomponent polymer blend was prepared by mixing the
polyethylene and poly(butylene terephthalate) in an extruder at
265.degree. C. The poly(ethylene terephthalate) polymer was heated
to 575.degree. F. (300.degree. C.) and the
polyethylene/poly(butylene terephthalate) bicomponent polymer blend
was heated to 510.degree. F. (265.degree. C.) in separate
extruders. The two polymer components were separately extruded,
filtered and metered to a bicomponent spin pack arranged to provide
a side-by-side filament cross section. The die of the spin pack was
heated to 600.degree. F. (315.degree. C.). The die had 601
capillary openings arranged in a 24 inch (61 cm) line. The polymers
were spun through each capillary at a polymer throughput rate of
0.80 g/hole/min. Attenuating air was heated to a temperature of
615.degree. F. (323.degree. C.) and supplied at a rate of 300
standard cubic feet per minute (8.5 m.sup.3/min) through two 0.8 mm
wide air channels. The two air channels ran the length of the 24
inch line of capillary openings, with one channel on each side of
the line of capillaries set back 1 mm from the capillary openings.
The poly(ethylene terephthalate) was supplied to the spin pack at a
rate of 12 kg/hr and the polyethylene/poly(butylene terephthalate)
was supplied to the spin pack at a rate of 12 kg/hr. A bicomponent
meltblown web was produced that was 50 weight percent poly(ethylene
terephthalate) and 50 weight percent polyethylene/poly(butylene
terephthalate). The filaments were collected on a moving forming
screen to produce a meltblown web. The meltblown web was collected
on a roll. The meltblown web had a basis weight of 17
g/m.sup.2.
[0066] As the poly(ethylene terephthalate) was meltblown,
hydrolytic and thermal degradation occurred which reduced the
molecular weight and hence the intrinsic viscosity of the polymer
forming the meltblown fibers. The poly(ethylene terephthalate) in
the meltblown fibers had an intrinsic viscosity of 0.34 dl/g and a
weight average molecular weight of 16,500.
[0067] The spunbond outer layers were bicomponent fibers with a
sheath-core cross section. The spunbond fibers were made using an
apparatus like that described above with regard to FIG. 4. Spunbond
webs with two basis weights (17 g/m.sup.2 and 24 g/m.sup.2) were
produced for use in the outer layers of the composite sheet. The
spunbond bicomponent fibers were made from linear low density
polyethylene with a melt index of 27 g/10 minutes (measured
according to ASTM D-1238) available from Dow as ASPUN 6811A, and
poly(ethylene terephthalate) polyester with an intrinsic viscosity
of 0.63 dl/g and weight average molecular weight of approximately
35,6 00 available from DuPont as Crystar.RTM. polyester (Merge
3949). The polyester resin was crystallized at a temperature of
180.degree. C. and dried at a temperature of 120.degree. C. to a
moisture content of less than 50 ppm before use.
[0068] The poly(ethylene terephthalate) used in the spunbond layers
was heated to 290.degree. C. and the polyethylene was heated to
280.degree. C. in separate extruders. The polymers were extruded,
filtered and metered to a bicomponent spin pack maintained at
295.degree. C. and designed to provide a sheath-core filament cross
section. The polymers were spun through the spinneret to produce
bicomponent filaments with a polyethylene sheath and a
poly(ethylene terephthalate) core. The total polymer throughput per
spin pack capillary was 1.0 g/min for the 17 g/m.sup.2 basis weight
web and 1.0 g/min for the 24 g/m.sup.2 web. The polymers were
metered to provide filament fibers that were 30% polyethylene
(sheath) and 70% polyester (core), based on fiber weight. The
resulting smaller, stronger substantially continuous filaments were
deposited onto a laydown belt with vacuum suction. The fibers in
the two webs (17 g/m.sup.2 and 24 g/m.sup.2 basis weights) had an
effective diameter in the range of 9 to 12 microns. The resulting
webs were separately passed between two thermal bonding rolls to
lightly tack the web together for transport using a point bonding
pattern at a temperature of 100.degree. C. and a nip pressure of
100 N/cm. The line speed during bonding was 206 m/min for the 17
g/m.sup.2 basis weight web and 146 m/min for the 24 g/m.sup.2 basis
weight web. The lightly bonded spunbond webs were each collected on
a roll.
[0069] The composite nonwoven sheet was prepared by unrolling the
17 g/m.sup.2 basis weight spunbond web onto a moving belt. The
meltblown bicomponent web was unrolled and laid on top of the
moving spunbond web. The second roll of the 24 g/m.sup.2 basis
weight spunbond web was unrolled and laid on top of the
spunbond-meltblown web to produce a spunbond-meltblown-spunbond
composite nonwoven web. The composite web was thermally bonded
between an engraved oil-heated metal calender roll and a smooth oil
heated metal calender roll. Both rolls had a diameter of 466 mm.
The engraved roll had a chrome coated non-hardened steel surface
with a diamond pattern having a point size of 0.466 mm.sup.2, a
point depth of 0.86 mm, a point spacing of 1.2 mm, and a bond area
of 14.6%. The smooth roll had a hardened steel surface. The
composite web was bonded at a temperature of 110.degree. C., a nip
pressure of 350 N/cm, and a line speed of 20 m/min. The bonded
composite sheet was collected on a roll. The final basis weight of
this composite nonwoven sheet was 58 g/m.sup.2. The physical
properties of the sheet are reported in Table 2.
Comparative Example C
[0070] A composite sheet was formed according to the procedure of
Example 3 except that the poly(ethylene terephthalate) was dried
for 4 hours at 120.degree. C. prior to meltblowing which produced a
lower moisture content of about 50 ppm. The intrinsic viscosity of
the poly(ethylene terephthalate) polymer in the meltblown fibers
was 0.59 dl/g and the weight average molecular weight was 31,000.
The physical properties of the composite sheet are reported in
Table 2.
[0071] Table 2 shows that a composite sheet made with meltblown
fibers made of the lower viscosity poly(ethylene terephthalate) of
Example 3 exhibits increased hydrostatic head as compared to the
composite sheet of Comparative Example C.
Example 4
[0072] A composite sheet was formed according to the procedure of
Example 3 except that the air flow rate during the melt blowing
process was 310 standard cubic feet per minute (8.8 m.sup.3/min)
instead of 300 standard cubic feet per minute (8.5 m.sup.3/min).
The physical properties of the sheet are reported in Table 2.
Comparative Example D
[0073] A composite sheet was formed according to the procedure of
Comparative Example C except that the air flow rate during the melt
blowing process was 500 standard cubic feet per minute (14.1
m.sup.3/min) instead of 300 standard cubic feet per minute (8.5
m.sup.3/min). The physical properties of the sheet are reported in
Table 2.
[0074] Table 2 shows a composite sheet made with meltblown fibers
made of the lower viscosity poly(ethylene terephthalate) of Example
4 exhibits increased hydrostatic head as compared to the composite
sheet of Comparative Example D.
2TABLE 2 NONWOVEN WEB PROPERTIES Hydro- Grab Grab Meltblown static
Frazier.sup.+ Tensile Tensile PET IV Meltblown Head (m.sup.3/ MD XD
Example (dl/g) PET Mw (cm) min/m.sup.2) (N) (N) 3 0.34 16,500 77 27
143.4 77.5 C 0.59 31,000 40 65 139.8 86.0 4 0.34 16,500 83 28 140.2
81.5 D 0.59 31,000 58 39 147.8 77.5 PET = poly(ethylene
terephthalate) IV = Intrinsic Viscosity Mw = Weight Averaged
Molecular Weight MD = Machine Direction XD = Cross Direction
.sup.+Frazier Air Permeability
* * * * *