U.S. patent application number 10/703795 was filed with the patent office on 2004-05-20 for nonwoven fibrous sheet structures.
Invention is credited to Davis, Michael C., Frankfort, Hans Rudolf Edward, Janis, Rudolph F., Johnson, Stephen Buckner, McGinty, David Jackson, Rudisill, Edgar N., Samuelson, H. Vaughn, Shin, Hyunkook, Vassilatos, George.
Application Number | 20040097158 10/703795 |
Document ID | / |
Family ID | 32303656 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040097158 |
Kind Code |
A1 |
Rudisill, Edgar N. ; et
al. |
May 20, 2004 |
Nonwoven fibrous sheet structures
Abstract
This invention relates to a nonwoven sheet material with high
air permeability and substantial hydrostatic head liquid barrier
properties. The sheet material is comprised of at least 90%, by
weight, melt spun substantially continuous filament polymer fibers
having an average cross sectional area of less than about 90 square
microns. The sheet material has a basis weight of less than 125
g/m.sup.2 and a grab tensile strength of at least 0.7
N/(g/m.sup.2). The invention is also directed to a process for melt
spinning polymer fibers that can be used to make the nonwoven sheet
material of the invention.
Inventors: |
Rudisill, Edgar N.;
(Nashville, TN) ; Davis, Michael C.; (Midlothian,
VA) ; Frankfort, Hans Rudolf Edward; (Kinston,
NC) ; Janis, Rudolph F.; (Hopewell, VA) ;
Johnson, Stephen Buckner; (Wilmington, NC) ; McGinty,
David Jackson; (Midlothian, VA) ; Samuelson, H.
Vaughn; (Chadds Ford, PA) ; Shin, Hyunkook;
(Wilmington, DE) ; Vassilatos, George;
(Wilmington, DE) |
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: |
32303656 |
Appl. No.: |
10/703795 |
Filed: |
November 7, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10703795 |
Nov 7, 2003 |
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09467268 |
Dec 20, 1999 |
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09467268 |
Dec 20, 1999 |
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09273578 |
Mar 22, 1999 |
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09273578 |
Mar 22, 1999 |
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08868529 |
Jun 4, 1997 |
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5885909 |
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60019277 |
Jun 7, 1996 |
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Current U.S.
Class: |
442/401 ;
442/361; 442/364 |
Current CPC
Class: |
D04H 3/16 20130101; Y10T
442/682 20150401; Y10T 442/688 20150401; D01F 8/14 20130101; Y10T
442/659 20150401; D04H 3/14 20130101; Y10T 442/681 20150401; D04H
3/12 20130101; Y10T 442/641 20150401; Y10T 442/637 20150401 |
Class at
Publication: |
442/401 ;
442/361; 442/364 |
International
Class: |
D04H 001/00; D04H
003/00; D04H 005/00; D04H 013/00; D04H 003/16 |
Claims
We claim:
1. A nonwoven fabric comprising at least one nonwoven layer of
spunbond polypropylene fibers, said fabric having a basis weight
between about 13-125 g/m.sup.2, a grab tensile strength in both the
machine- and cross-directions between about 0.9 to 3 N/(g/m.sup.2),
normalized for basis weight, and a combination of Frazier
permeability between about 10 and 30 m.sup.3/min-m.sup.2 and
hydrostatic head between about 66 and 99 cm.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to nonwoven fibrous structures and
more particularly to breathable fabrics and sheet structures formed
from fibers which are held together without weaving or
knitting.
[0003] 2. Description of the Related Art
[0004] Nonwoven fibrous structures have existed for many years and
today there are a variety of different nonwoven technologies in
commercial use. Nonwoven technologies continue to be developed by
those seeking new applications and competitive advantages. One area
where nonwoven fibrous structures are used is in protective
products. Protective products include apparel and other products
that provide protection from things like hazardous chemicals (as
during chemical spill clean ups), blood and body fluids (as in the
medical field), dry particulates, and other hazards such as paint
or asbestos.
[0005] E. I. du Pont de Nemours and Company (DuPont) makes
Sontara.RTM. spunlaced fabrics which are used extensively for
medical gowns and drapes, and for certain applications within the
medical field. Sontara.RTM. spunlaced fabrics have long been used
in the medical field because of their exceptional performance and
comfort. Sontara.RTM. spunlaced fabrics for medical protective
apparel uses are typically comprised of staple length polyester
fiber hydroentangled with woodpulp. The fabric is finished with a
moisture repellent coating.
[0006] Composite nonwovens are also used in medical products such
as gowns and drapes. Each layer in such composites provides certain
properties desirable for a particular end use. One composite
nonwoven is a spunbond/meltblown/spunbond laminate that is
generally known as "SMS". The spunbond outer layers of an SMS
material are comprised of spunbond nonwoven that contribute
strength to the sheet. The inner layer of an SMS material is made
of fine, low denier, meltblown fibers that contribute barrier
properties to the sheet. Such SMS nonwoven materials are described
in U.S. Pat. No. 4,041,203, with further improvements described in
U.S. Pat. Nos. 4,374,888 and 4,041,203.
[0007] A single layer of bonded meltblown fibers can be used alone
to provide a sheet with good barrier properties. However, such a
meltblown fiber sheet does not exhibit sufficient strength to be
used in many end use applications. U.S. Pat. Nos. 4,622,259 and
4,908,163 disclose meltblown fibers with somewhat improved tensile
properties.
[0008] There is a need for fine fibers that exhibit good strength.
There is also a need for a nonwoven structure made of such fine
fibers, which structure exhibits high barrier to fluids, good air
permeability and high strength.
BRIEF SUMMARY OF THE INVENTION
[0009] The invention is directed to a nonwoven sheet comprised of
at least 90%, by weight, melt spun substantially continuous
filament polymer fibers having an average cross sectional area of
less than about 90 square microns. The sheet has a basis weight of
less than 125 g/m2, a grab tensile strength in both the machine and
cross directions, normalized for basis weight and measured
according to ASTM D 5034, of at least 0.7 N/(g/m2), and a
combination of a Frazier permeability and a hydrostatic head
selected from the group of: a Frazier permeability of at least
about 70 m3/min-m2 and a hydrostatic head of at least about 20 cm;
a Frazier permeability of at least about 28 m3/min-m2 and a
hydrostatic head of at least about 25 cm; a Frazier permeability of
at least about 20 m3/min-m2 and a hydrostatic head of at least
about 35 cm; and a Frazier permeability of at least about 1
m3/min-m2 and a hydrostatic head of at least about 80 cm. In a
preferred embodiment of the invention, the sheet has a hydrostatic
head of at least about 40 cm. Preferably, the fibers of the sheet
have an average boil off shrinkage of less than ten percent. The
invention is also directed to a garment made of the nonwoven sheet
of the invention.
[0010] According to the preferred embodiment of the invention, the
fibers of the sheet are comprised of at least 50% by weight of
polyester polymer. More preferably, the fibers of the sheet are
comprised of at least 80% by weight of polyester polymer selected
from the group of polyethylene terephthalate, polypropylene
terephthalate, polybutylene terephthalate polymer. Alternatively,
the fibers of the sheet may be comprised of at least 50% by weight
a nylon polymer, an elastomeric polymer, or a polyolefin polymer
such as polyethylene or polypropylene. The fibers of the sheet may
include additives blended into the polymer fibers such as
fluorocarbons, ultraviolet energy stabilizers, process stabilizers,
thermal stabilizers, antioxidants, wetting agents, pigments,
antimicrobial agents, and antistatic electricity buildup
agents.
[0011] According to an alternative embodiment of the invention, at
least a portion of the fibers of the sheet of the invention may be
formed of at least two separate component polymers. For example,
one of such component polymers may overlay the other of the
component polymers in a sheath-core arrangement. In one preferred
embodiment of the invention, the sheath polymer has a lower melting
temperature than the polymer comprising the core.
[0012] The fibers of the nonwoven sheet of the invention are bonded
together by a method selected from the group of ultrasonic bonding,
thermal bonding, adhesive bonding, and combinations thereof.
[0013] The present invention is also directed to a process for melt
spinning substantially continuous filament polymer fibers having an
average cross sectional area of less than about 90 square microns.
The process includes the steps of extruding a melt spinnable
polymer through a plurality of capillary openings to form fiber
filaments; drawing said extruded fiber filaments by feeding the
extruded filaments into a draw jet so as to apply a drawing tension
to the fiber filaments, the draw jet including a fiber entrance, a
fiber passage where an air jet impact the filaments in the
direction that the filaments are traveling, and a fiber exit
through which the drawn filaments are discharged from the draw jet;
discharging the drawn fiber filaments through the fiber exit of the
draw jet in a downwardly direction at a rate of at least 6000
m/min; guiding the fiber filaments being discharged from the fiber
exit of the draw jet with an extension plate, the extension plate
extending from the draw jet in a direction substantially parallel
to the direction that the fibers are being discharged from the
fiber exit of the draw jet, the fibers passing within 1 cm of said
extension plate over a distance of at least 5 cm; and laying the
fibers discharged from the fiber exit of the draw jet on a
collection surface.
BRIEF DESCRIPTION OF THE DRAWING
[0014] The invention will be more easily understood by a detailed
explanation of the invention including drawings. It should be
understood that the drawings are for explanation only and are not
necessarily to scale. The drawings are briefly described as
follows:
[0015] FIG. 1 is a perspective view of an apparatus for making the
nonwoven sheet of the invention;
[0016] FIG. 2 is a perspective view of another apparatus for making
the nonwoven sheet of the invention;
[0017] FIG. 3 is a chart illustrating one of the properties of the
fibers of the nonwoven sheet of the invention;
[0018] FIG. 4 is second chart illustrating a second property of the
fibers of the nonwoven sheet of the invention;
[0019] FIG. 5 is a third chart illustrating a third property of the
fibers of the nonwoven sheet of the invention;
[0020] FIG. 6 is an enlarged cross sectional view of a sheath-core
bicomponent fiber;
[0021] FIG. 7 is a schematic illustration of another apparatus for
making the nonwoven sheet of the invention; and
[0022] FIG. 8 is a schematic illustration of a portion of an
inventive apparatus for making the nonwoven sheet of the
invention.
DEFINITIONS
[0023] The term "polymer" as used herein, 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.
[0024] The term "polyolefin" as used herein, is intended to mean
any of a series of largely saturated open chain polymeric
hydrocarbons composed only of carbon and hydrogen. Typical
polyolefins include, but are not limited to, polyethylene,
polypropylene, polymethylpentene and various combinations of the
ethylene, propylene, and methylpentene monomers.
[0025] The term "polyethylene" as used herein is intended to
encompass not only homopolymers of ethylene, but also copolymers
wherein at least 75% of the recurring units are ethylene units.
[0026] The term "polypropylene" as used herein is intended to
embrace not only homopolymers of propylene but also copolymers
where at least 85% of the recurring units are propylene units.
[0027] The term "polyester" as used herein is intended to embrace
polymers wherein at least 85% of the recurring units are
condensation products of carboxylic acids and dihydroxy alcohols
with polymer linkages created by formation of an ester unit. This
includes, but is not limited to, aromatic, aliphatic, saturated,
and unsaturated 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.
[0028] The term "melt spun fibers" as used herein means small
diameter fibers which are formed by extruding molten thermoplastic
polymer material as filaments from a plurality of fine, usually
round, capillaries of a spinnerette with the diameter of the
extruded filaments then being rapidly reduced. Melt spun fibers are
generally continuous and have an average diameter of greater than
about 5 microns.
[0029] 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.
[0030] 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 substantially perpendicular
to the machine direction.
[0031] The term "unitary fibrous sheet" as used herein, means woven
or nonwoven fabrics or sheets made of the same types of fibers or
fiber blends throughout the structure, wherein the fibers form a
substantially homogeneous layer that is free of distinguishable
laminations or other support structures.
Test Methods
[0032] In the description above and in the non-limiting 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.
[0033] Fiber Diameter was measured via optical microscopy and is
reported as an average value in microns.
[0034] Fiber Size is the weight in grams of 9000 meters of the
fiber, and was calculated using the diameter of the fibers measured
via optical microscopy and the polymer density, and is reported in
deniers.
[0035] Fiber Cross Sectional Area was calculated using the diameter
of the fibers via optical microscopy based on a round fiber cross
section.
[0036] Spinning Speed is the maximum speed attained by the fiber
filaments during the spinning process. Spinning speed is calculated
from polymer throughput per capillary opening expressed in g/min,
and the fiber size expressed in g/9000 m (1 denier=1 g/9000 m),
according to the following equation: 1 spinning speed ( m / min ) =
[ polymer throughput per opening ( g / min ) ] ( 9000 ) [ fiber
size ( g / 9000 m ) ]
[0037] Thickness is the distance between one surface and its
opposite and was measured according to ASTM D 5729-95.
[0038] 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.
[0039] 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.
[0040] Elongation of a sheet is a measure of the amount a sheet
stretches prior to failure (breaking) in the grab tensile strength
test and was conducted according to ASTM D 5034, which is hereby
incorporated by reference, and is reported as a percent.
[0041] Hydrostatic Head is a measure of the resistance of the sheet
to penetration by liquid water under a static pressure. The test
was conducted according to MTCC-127, which is hereby incorporated
by reference, and is reported in centimeters. In this application,
unsupported hydrostatic head pressures are measured on the various
sheet examples in a manner so that if the sheets do not comprise a
sufficient number of strong fibers, the measurement is not
attainable. Thus, the mere presence of an unsupported hydrostatic
head pressure is also an indication that the sheet has the
intrinsic strength to support the hydrostatic head pressure.
[0042] Frazier Permeability is a measure of air flow passing
through a sheet under at 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.
[0043] 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.
[0044] Blood Strike Through is a measure of the resistance of
fabrics to the penetration of synthetic blood under a continuously
increasing mechanical pressure and was measured according to ASTM F
1819-98.
[0045] Alcohol Repellency is a measure of the resistance of fabrics
to wetting and penetration by alcohol and alcohol/water solutions,
expressed as the highest percentage of isopropyl alcohol solution
that the fabric is capable of resisting (expressed on a 10 point
scale -10 being pure isopropyl alcohol) and was conducted according
to INDA IST 80.6-92.
[0046] Spray Rating is a measure of the resistance of fabrics to
wetting by water and was conducted according to AATCC 22-1996, and
is reported in percent.
[0047] Moisture Vapor Transmission Rate is a measure of the rate of
diffusion of water vapor through a fabric and was conducted
according to ASTM E 96-92, B upright cup, and is reported in
g/m.sup.2/24 hr.
[0048] Trapezoid Tear is a measure of the tearing strength of a
fabric in which a tear had previously been started and was
conducted according to ASTM D 5733, and is reported in Newtons.
[0049] Intrinsic Viscosity (IV) is a measure of the inherent
resistance to flow for a polymer solution. IV is determined by
comparing the viscosity of a 1% solution of a polymer sample in
orthochlorophenol with the viscosity of the pure solvent as
measured at 25.degree. C. in a capillary viscometer. IV is reported
in dl/g, and is calculated using the formula:
IV=.eta.s/c
[0050] Where: 2 s = specific viscosity = flow time of solution flow
time of solvent - 1
[0051] and c is the concentration of the solution in g/100 ml.
DETAILED DESCRIPTION OF THE INVENTION
[0052] The present invention is a nonwoven sheet that exhibits high
strength and an optimum combination of liquid barrier and air
permeability properties. The invention also includes a process for
making such sheets. The nonwoven sheet of the invention is
comprised of at least 90%, by weight, melt spun substantially
continuous filament polymer fibers having an average cross
sectional area of less than about 90 square microns. The sheet has
a basis weight of less than 125 g/m.sup.2, a grab tensile strength
in both the machine and cross directions, normalized for basis
weight and measured according to ASTM D 5034, of at least 0.7
N/(g/m.sup.2), and a combination of a Frazier permeability and a
hydrostatic head selected from the group of:
[0053] a Frazier permeability of at least about 70
m.sup.3/min-m.sup.2 and a hydrostatic head of at least about 20
cm;
[0054] a Frazier permeability of at least about 28
m.sup.3/min-m.sup.2 and a hydrostatic head of at least about 25
cm;
[0055] a Frazier permeability of at least about 15
m.sup.3/min-m.sup.2 and a hydrostatic head of at least about 35 cm;
and
[0056] a Frazier permeability of at least about 1
m.sup.3/min-m.sup.2 and a hydrostatic head of at least about 80
cm.
[0057] The fibers in the nonwoven sheet of the invention are small
denier polymeric fibers that, when made into a sheet structure,
form numerous very small pores. It has been found that when such
melt spun microfibers are used to create a nonwoven fibrous
structure, the resulting fabric sheets have very high air
permeability while also providing excellent liquid barrier and
sheet strength. As the sheet material is comprised of generally
continuous filaments, the sheet material exhibits low linting
characteristics desirable for end use applications such as clean
room apparel and wipes.
[0058] According to a more preferred embodiment of the invention,
the nonwoven sheet is a unitary fibrous sheet comprised of melt
spun substantially continuous filament polymer fibers wherein the
sheet has a basis weight of from 13 g/m.sup.2 to 125 g/m.sup.2 and
substantially all of the fibers are melt spun fibers. More
preferably, the nonwoven sheet of the invention has a basis weight
within the range of 30 to 110 g/m.sup.2, and most preferably within
the range of 50 to 90 g/m.sup.2.
[0059] The properties of the nonwoven sheet may be modified by
varying the cross sections of the fibers. The preferred fibers in
the nonwoven sheet of the invention have a cross sectional area of
between about 20 and about 90 .mu.m.sup.2. More preferably, the
fibers have a cross sectional area of from about 25 to about 70
.mu.m.sup.2, and most preferably from about 33 to about 60
.mu.m.sup.2. It is believed that the properties of the sheet are
determined in part by the physical size of the fibers. Fiber sizes
are conventionally described in terms of denier or decitex. As
denier and decitex relate to the weight of a long length of fiber,
the density of the polymer influences the denier or decitex values.
For example, if two fibers have the same cross section, but one is
made of polyethylene while the other comprises polyester, the
polyester fiber would have a greater denier because it tends to be
more dense than polyethylene. However, it can generally be said
that the preferred range of fiber denier is less than or nearly
equal to about 1. The most compact fiber cross sections, when used
in sheets, appear to yield sheets with pores that are small but not
closed. Fibers with round cross sections and the above cross
sectional areas have been used to make the nonwoven sheet of the
invention. However, it is anticipated that the nonwoven sheets of
the invention might be enhanced by changing the cross sectional
shapes of the fibers.
[0060] It has been found that a sheet of melt spun microfibers can
be made with sufficient strength to form a barrier fabric without
the need for any type of supporting scrim, thus saving the
additional materials and cost of such supporting materials. This
can be achieved by using fibers with good tensile strength, as for
example by using fibers having a minimum tensile strength of at
least about 1.5 g/denier. This fiber strength would correspond to a
fiber strength of about 182 MPa for a polyester fiber or about 118
MPa for a polypropylene fiber. Melt blown fibers would typically be
expected to have tensile strengths from about 26 to about 42 MPa
due to the lack of polymer orientation in the fiber. The grab
tensile strength of the composite nonwoven sheet of the invention
may vary depending on the bonding conditions employed. Preferably,
the tensile strength of the sheet (in both the machine and cross
directions), normalized for basis weight, is from 0.7 to 5
N/(g/m.sup.2), and more preferably from 0.8 to 4 N/(g/m.sup.2), and
most preferably from 0.9 to 3 N/(g/m.sup.2). Fibers having a
tensile strength of at least 1.5 g/denier should provide sheet grab
strengths in excess of 0.7 N/(g/m.sup.2) normalized for basis
weight. The strength of the sheets of the present invention will
accommodate typical end use applications without reinforcement.
[0061] While fiber strength is an important property, fiber
stability is also important. It has been found that microfibers
melt spun at high speed can be made that exhibit low shrinkage even
where the fibers are made of polyester. The preferred sheet of the
invention is made with fibers that have an average boil off
shrinkage of less than 10%. It has been found that when sheets are
produced by the high speed melt spinning process described below
with respect to FIG. 7, that sheets of strong fine denier
poly(ethylene terephthalate) fibers can be made that have a boil
off shrinkage of less than 5%.
[0062] According to one embodiment of the invention, the nonwoven
sheet may be subjected to a heated nip to bond the fibers of the
sheet. The fibers in the bonded sheet appear to be stacked on one
another without having lost their basic cross sectional shape. It
appears that this is a relevant aspect of the invention because
each fiber appears to have not been distorted or substantially
flattened which would close the pores. As a result, the sheet has
good barrier properties as measured by hydrostatic head while still
maintaining a high void ratio, a low density, and high Frazier
permeability. Preferably, the nonwoven sheet of the invention has a
Frazier permeability of at least 15 m.sup.3/min-m.sup.2 and a
hydrostatic head of at least 20 cm. More preferably, the sheet has
a hydrostatic head of at least 25 cm, and even more preferably of
at least 30 cm, and most preferably of at least 35 cm. It is
further preferred that the 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. In the preferred embodiment of the invention, the
sheet has a Frazier air permeability of at least 20
m.sup.3/min-m.sup.2, and more preferably of at least 25 m.sup.3/min
m.sup.2. A fabric having high barrier properties with high
breathability is believed to be desirable as a protective fabric in
the medical field and possibly many other fields.
[0063] It should be recognized that although the nonwoven sheet of
the invention has been characterized by hydrostatic head, that the
small pores will make a good barrier for dry particulate materials.
Thus, with its high Frazier permeability, the sheet of the
invention should make a suitable filtration media. It should be
recognized that the basis weight of the sheet material will have
some effect on the balance of hydrostatic head and permeability
properties. In most cases, it will be desirable from both an
economic and productivity standpoint, as well as from a property
balance standpoint, to have the sheet basis weight be about or
below 75 g/m.sup.2. However, there are potential end uses where
heavier and higher barrier sheet materials would be desirable such
as certain protective apparel applications. In such cases, the
sheet basis weight may be greater than about 75 g/m.sup.2.
[0064] The fibers of the preferred nonwoven sheet of the invention
are comprised of synthetic melt spinnable polymer. The preferred
fiber is comprised of one or more of any of a variety of polymers
or copolymers including polyethylene, polypropylene, polyester,
nylon, elastomer, and other melt spinnable polymers that can be
spun into fibers of less than approximately 1.2 decitex per
filament. More preferably, the fibers are comprised of at least 50%
by weight polyester polymer, such as poly(ethylene terephthalate),
poly(propylene terephthalate), or poly(butylene terephthalate)
polymer. According to other preferred embodiments of the invention,
the fibers may be comprised of at least 50% by weight of a nylon
polymer, a polyolefin polymer such as polyethylene or
polypropylene, or an elastomeric polymer such as polyurethane or
co-polyether ester.
[0065] One polyester that has been used to make very fine and
strong fibers in the nonwoven sheet of the invention is
poly(ethylene terepthalate) having an intrinsic viscosity of 0.5 to
0.6 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. The normal intrinsic
viscosity for a poly(ethylene terepthalate) polyester is in the
range of 0.65 to 0.70 dl/g. Poly(ethylene terepthalate) with an IV
below about 0.6 dl/g is considered to be a low IV polyester, and
has not historically been used in melt spinning because the
filaments break. Applicants have now found that low IV
poly(ethylene terepthalate) can be spun and drawn into fine fibers
with good strength when spun at high spinning speeds. The use of
low IV poly(ethylene terepthalate) has made it possible to spin
finer polyester fibers of less than 0.8 dpf and to spin the fibers
at speeds in excess of 6000 m/min. Surprisingly, it has been found
that such fibers made with low IV poly(ethylene terepthalate) have
good strength equivalent to that of larger poly(ethylene
terepthalate) fibers directly spun from regular IV polyester
normalized for fiber size.
[0066] The fibers of the nonwoven sheet may be spun with one or
more additives blended into the polymer of the fibers. Additives
that may be advantageously spun into some or all of the fibers of
the nonwoven sheet include fluorocarbons, ultraviolet energy
stabilizers, process stabilizers, thermal stabilizers,
antioxidants, wetting agents, pigments, antimicrobial agents, and
antistatic electricity buildup agents. An antimicrobial additive
may be suitable in some healthcare applications. Stabilizers and
antioxidants may be provided for a number of end use applications
where exposure to ultraviolet energy, such as sunlight, is likely.
A static electricity discharge additive may be used for
applications where a build up of electricity is possible and
undesirable. Another additive that may be suitable is a wetting
agent to make the sheet material suitable as a wipe or absorbent or
to allow liquids to flow through the fabric while very fine solids
are collected in the fine pores of the sheet material.
Alternatively, the nonwoven sheet of the invention may be topically
treated with a finish in order to alter the properties of the
nonwoven sheet. For example, a fluorochemical coating can be
applied to the nonwoven sheet to reduce the surface energy of the
fiber surfaces and thus increase the fabric's resistance to liquid
penetration, especially where the sheet must serve as a barrier to
low surface tension liquids. Typical fluorochemical finishes
include ZONYL.RTM. fluorochemical (available from DuPont,
Wilmington, Del.) or REPEARL.RTM. fluorochemical (available from
Mitsubishi Int. Corp, New York, N.Y.).
[0067] In the nonwoven sheet of the invention, a portion of the
fibers may be comprised of at least two separate component
polymers. These polymer components may be arranged in a sheath-core
arrangement, a side-by-side arrangement, a segmented pie
arrangement, an "islands in the sea" arrangement, or any other
known configuration for multiple component fibers. Where the
multiple component fibers have a sheath-core arrangement, the
polymers may be selected such that the polymer comprising the
sheath has a lower melting temperature than the polymer comprising
the core. Such fibers can be more easily thermally bonded without
sacrificing fiber tensile strength. In addition, small denier
fibers spun as multiple component fibers may split into even finer
fibers after the fibers are spun. One advantage of spinning
multi-component fibers is that higher production rates can be
attained depending on the mechanism for splitting the
multi-component fibers. Each of the resulting split fibers may have
a pie-shaped or other-shaped cross section.
[0068] A sheath-core bicomponent fiber is illustrated in FIG. 6
where a fiber 80 is shown in cross section. The sheath polymer 82
surrounds the core polymer 84 and the relative amounts of polymer
may be adjusted so that the core polymer 84 may comprise more or
less than fifty percent of the cross sectional area. With this
arrangement, a number of attractive alternatives can be produced.
For example, the sheath polymer 82 can be blended with pigments
which are not wasted in the core, thereby reducing the costs for
pigments while obtaining a suitably colored material. A hydrophobic
material such as a fluorocarbon may also be spun into the sheath
polymer to obtain the desired liquid repellency at minimal cost. As
mentioned above, a polymer having a lower melt point or melting
temperature may be used as the sheath so as to be amenable to
melting during bonding while the core polymer does not soften. One
very interesting example is a sheath core arrangement using 2GT
polyester as the core and 3GT polyester as the sheath. Such an
arrangement would be suited for radiation sterilization such as
e-beam and gamma ray sterilization without degradation. Other
combinations of multi-component fibers and blends of fibers may be
envisioned.
[0069] The fibers of the nonwoven sheet of the invention are
preferably high strength fibers, which conventionally are made as
fibers that have been fully drawn and annealed to provide good
strength and low shrinkage. Fibers strengthened by high speed melt
spinning are preferred for the present invention. The nonwoven
sheet of the invention may be created without the steps of
annealing and drawing. In particular, it has been found that
spinning microfibers at high spinning speeds causes considerable
changes in the properties of the fibers. Experiments were run with
2GT polyester at a range of spinning speeds to show the effect of
the spinning speed differences on the fiber properties. As
illustrated in the charts in FIGS. 3, 4, and 5, it can be seen that
as the fiber spinning speeds were increased, the tenacity of the
fibers dramatically increased, while the elongation to break and
boil off shrinkage of the fibers dramatically decreased. The 2GT
microfibers spun at high spinning speeds are strong and stable.
Such high production speeds are also desirable for high production
rates of nonwoven sheets. The data is also tabulated in the
following Table A:
1TABLE A Spinning Speed 3998 5029 5761 5943 6401 (m/min) 4372 5500
6300 6500 7000 (yards/min) No. of Filaments 200 200 200 200 200
Fiber Size (denier) 0.5 0.5 0.5 0.5 0.5 Boil Off Shrinkage (%) 50.1
15.1 12.1 7.8 8.1 Tenacity (g/denier) 3.3 -- 3.9 3.9 3.8 Elongation
to Break 49.0 -- 33.0 31.8 33.2 (%)
[0070] The fibers of the nonwoven sheet of the invention may be
bonded together by known methods such as thermal calendar bonding,
through-air bonding, steam bonding, ultrasonic bonding, and
adhesive bonding.
[0071] The nonwoven sheet of the invention can also be used as a
spunbond layer in a spunbond-meltblown-spunbond ("SMS") composite
sheet. In conventional 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. When the nonwoven sheet of the
invention is used for the spunbond layers, in addition to
contributing strength, the spunbond fiber layers can provide
additional barrier properties to the composite sheet.
[0072] The nonwoven sheet of the invention may be 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 while being pneumatically drawn to reduce their size and
impart increased strength. The filaments are deposited on a moving
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 11 microns. These
fibers can be produced as single component fibers, as multiple
component fibers, or as some combination thereof. Multiple
component fibers can be made in various known cross-sectional
configurations, including side-by-side, sheath-core, segmented pie,
or islands-in-the-sea configurations.
[0073] An apparatus for producing high strength monocomponent or
bicomponent melt spun fibers at high speeds is schematically
illustrated in FIG. 7. In this apparatus, two thermoplastic
polymers are fed into the hoppers 140 and 142, respectively. The
polymer in hopper 140 is fed into the extruder 144 and the polymer
in the hopper 142 is fed into the extruder 146. The extruders 144
and 146 each melt and pressurize the polymer and push it through
filters 148 and 150 and metering pumps 152 and 154, respectively.
The polymer from hopper 140 is combined with polymer from hopper
142 in the spin pack 156 by known methods to produce the desired
bicomponent filament cross sections mentioned above, as for example
by using a multiple component spin pack like that disclosed in U.S.
Pat. No. 5,162,074, which is hereby incorporated by reference.
Where the filaments have a sheath-core cross section, a lower
melting temperature polymer is typically used for the sheath layer
so as to enhance thermal bonding. If desired, single component
fibers can be spun from the multiple component apparatus shown in
FIG. 7 by putting the same polymer in both of the hoppers 140 and
142.
[0074] The melted polymers exit the spin pack 156 through a
plurality of capillary openings on the face of the spinneret 158.
The capillary openings may be arranged on the spinneret face in a
conventional pattern (rectangular, staggered, etc.) with the
spacing of the openings set to optimize productivity and fiber
quenching. The density of the openings is typically in the range of
500 to 8000 holes/meter width of the pack. Typical polymer
throughputs per opening are in the range of 0.3 to 5.0 g/min. The
capillary openings may have round cross sections where round fibers
are desired.
[0075] The filaments 160 extruded from the spin pack 156 are
initially cooled with quenching air 162 and then drawn by a
pneumatic draw jet 164 before being laid down. The quenching air is
provided by one or more conventional quench boxes that direct air
against the filaments at a rate of about 0.3 to 2.5 m/sec and at a
temperature in the range of 50 to 25.degree. C. Typically, two
quench boxes facing each other from opposite sides of the line of
filaments are used in what is known as a co-current air
configuration. The distance between the capillary openings and the
draw jet may be anywhere from 30 to 130 cm, depending on the fiber
properties desired. The quenched filaments enter the pneumatic draw
jet 164 where the filaments are drawn by air 166 to fiber speeds in
the range of from 6000 to 12,000 m/min. This pulling of the
filaments draws and elongates the filaments as the filaments pass
through the quench zone.
[0076] Optionally, the end of the pneumatic draw jet 164 may
include a draw jet extension 188, as illustrated in FIG. 8. The
draw jet extension 188 is preferably a smooth rectangular plate
that extends from the draw jet 164 in a direction substantially
parallel to the curtain of filaments 167 exiting the draw jet. The
draw jet extension 188 guides the filaments to the laydown surface
so that the filaments more consistently impinge the laydown surface
at the same location which improves sheet uniformity. In the
preferred embodiment, the draw jet extension is on the side of the
curtain of filaments toward which the filaments move once they are
on the laydown belt 168. Preferably, the draw jet extension extends
about 5 to 50 cm down from the end of the draw jet, and more
preferably about 10 to 25 cm, and most preferably about 17 cm down
from the end of the draw jet. The fiber filaments discharged from
the exit of the draw jet pass within 1 cm of the surface of the
draw jet extension over a distance of at least 5 cm. Alternatively,
the draw jet extension can be placed on the other side of the
filament curtain or draw jet extensions can be used on both sides
of the curtain of filaments. According to another preferred
embodiment of the invention, the draw jet surface facing the
filaments could be textured with grooves or rounded protrusions so
as to generate a fine scale turbulence that helps to disperse the
filaments in a manner that reduces filament clustering and make a
more uniform sheet.
[0077] The filaments 167 exiting the draw jet 164 are thinner and
stronger than the filaments were when they were extruded from the
spin pack 156. The substantially continuous fiber filaments 167 are
strong fibers having a tensile strength of at least about 1.5
g/denier, and having an effective diameter of from 5 to 11 microns.
The filaments 167 are deposited onto a laydown belt or forming
screen 168 as substantially continuous fiber filaments. The
distance between the exit of the draw jet 164 and the laydown belt
is varied depending on the properties desired in the nonwoven web,
and generally ranges between 13 and 76 cm. A vacuum suction is
usually applied through the laydown belt 168 to help pin the fiber
web. Where desired, the resulting web 170 can be passed between
thermal bonding rolls 172 and 174 before being collected on the
roll 178 as bonded web 176.
[0078] Preferably, the bonding rolls 172 and 174 are heated rolls
maintained at a temperature within plus or minus 20.degree. C. of
the lowest melting temperature polymer in the web and the bonding
line speed is in the range of 20 to 100 m/min. In general, a
bonding temperature in the range of 105-260.degree. C. and a
bonding pressure in the range of 35-70 N/mm has been applied to
obtain good thermal bonding of the nonwoven sheet. For a sheet
containing polyethylene, a bonding temperature in the range of
105-135.degree. C. and a bonding pressure in the range of 35-70
N/mm has been applied to obtain good thermal bonding. For a sheet
containing a low melting temperature copolyester or a low melting
temperature polyester such as poly(trimethylene terephthalate), a
bonding temperature in the range of 140-220.degree. C. and a
bonding pressure in the range of 35-70 N/mm has been applied to
obtain good thermal bonding. For a sheet containing a higher
melting temperature polyester such as poly(ethylene terephthalate),
a bonding temperature in the range of 170-260.degree. C. and a
bonding pressure in the range of 35-70 N/mm has been applied to
obtain good thermal bonding.
[0079] Where a topical treatment is applied to the web, such as a
fluorochemical coating, known methods for applying the treatment
can be used. Such application methods include spray application,
roll coating, foam application, and dip-squeeze application
methods. A topical finishing process can be carried out either
in-line with the fabric production or in a separate process
step.
[0080] Another process for making the nonwoven sheet of the
invention is shown in FIG. 1. A low denier melt-spinning system for
making a continuous roll of fabric is generally referred to by the
number 10. The system 10 comprises a continuous belt 15 running
over a series of rollers. The belt 15 includes a generally
horizontal run under a series of one or more spinning beams 20.
Each spinning beam 20 is provided with molten polymer and a large
number of very small holes, for example, holes of 7 to 16 mils in
diameter. The polymer exits through the holes forming a single
fiber at each hole. The fibers are preferably strong and resist
shrinkage. Typically, such fibers are made by quenching, drawing
and annealing the fibers after they are spun so that the polymer
chains are oriented within the fiber. It has now been found that
such fibers may also be made by high speed spinning.
[0081] Once the strong fibers have been formed, the fast moving and
very fine fibers are directed to the moving belt 15. This is no
small task due to the number of fibers and their sensitivity to
turbulent air forces. Suitable guides, preferably including air
baffles, are provided to maintain some control as the fibers are
randomly arranged on the belt 15. One additional alternative for
controlling the fibers may be to electrostatically charge the
fibers and perhaps oppositely charge the belt 15 so that the fibers
will be pinned to the belt once they are laid down. The web of
fibers are thereafter bonded together to form the fabric. The
bonding may be accomplished by any suitable technique including
thermal bonding or adhesive bonding. Hot air bonding and ultrasonic
bonding may provide attractive alternatives, but thermal bonding
with the illustrated pinch rolls 25 and 26 is preferred. It is also
recognized that the sheet material may be point bonded for many
applications to provide a fabric-like hand and feel, although there
may be other end uses for which it is preferred that the sheet be
area bonded with a smoother finish. With the point bonded finish,
the bonding pattern and percentage of the sheet material bonded
will be dictated so as to control fiber liberation and pilling as
well as by other requirements such as sheet drape, softness and
strength. The fabric is then rolled up on a roll 30 for storage and
subsequent finishing as desired.
[0082] While the description of the invention has thus far been
related to melt spun fibers, there may be other spinning
technologies either now developed or yet to be invented that could
provide suitable polymeric fibers. An alternative process for
making the nonwoven sheet of the present invention is shown in FIG.
2. In FIG. 2, there is shown a wetlay nonwoven fabric forming
system generally referred to by the number 50. The wet lay system
50 includes a foraminous or screen belt 55 running over a series of
rollers. A trough 60 is arranged over the belt 55 to deposit a
slurry of liquid and discontinuous fiber thereon. As the slurry
moves along with the belt 55, the liquid passes through the
openings in the belt 55 and into a pan 61 (also called a pit). The
fiber is randomly arranged and is bonded together at the pinch
rollers 65 and 66. It should be recognized that there are a number
of techniques for bonding the fibers together including through air
bonding, resin bonding as well as other suitable bonding
techniques. The nonwoven fabric is then rolled up on a roll 70 for
storage or subsequent finishing.
[0083] This invention will now be illustrated by the following
non-limiting examples which are intended to illustrate the
invention and not to limit the invention in any manner.
EXAMPLES
[0084] In the following examples, nonwoven sheets were produced
using a high speed melt spinning process described above with
regard to the process shown in FIG. 7.
Example 1
[0085] A nonwoven sheet was made from melt spun fibers produced
using the process and apparatus described above with regard to FIG.
7. The fibers were spun from poly(ethylene terephthalate) polyester
resin with an intrinsic viscosity of 0.58 (as measured in U.S. Pat.
No. 4,743,504) available from DuPont as Crystar.RTM. polyester
(Merge 1988). 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. This polyester was
heated to 290.degree. C. in two separate extruders. The polyester
polymer was extruded, filtered and metered from each extruder to a
bicomponent spin pack maintained at 295.degree. C. and designed to
produce a sheath-core filament cross section. However, because both
polymer feeds comprised the same polymer, a monocomponent fiber was
produced. The spin pack was 0.5 meters wide with a depth of 9
inches (22.9 cm) with 6720 capillaries/meter across the width of
the spin pack. Each capillary was round with a diameter of 0.23 to
0.35 mm. The total polymer throughput per spin pack capillary was
0.5 g/min. The filaments were cooled in a 15 inch (38.1 cm) long
quenching zone with quenching air provided from two opposing quench
boxes at a temperature of 12.degree. C. and a velocity of 1 m/sec.
The filaments passed into a pneumatic draw jet spaced 20 inches
(50.8 cm) below the capillary openings of the spin pack where the
filaments were drawn at a rate of approximately 9000 m/min. The
resulting smaller, stronger substantially continuous filaments were
deposited onto a laydown belt located 36 cm below the draw jet
exit. The laydown belt used vacuum suction to help pin the fibers
on the belt. The fibers in the web had an effective diameter in the
range of 6 to 9 microns.
[0086] The 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 web was bonded at a temperature of
250.degree. C., a nip pressure of 70 N/mm, and a line speed of 50
m/min. The bonded sheet was collected on a roll.
[0087] The nonwoven sheet was treated with a standard
fluorochemical finish to reduce the surface energy of the fiber
surface, and thus increase the fabric's resistance to liquid
penetration. The sheet was dipped into an aqueous bath of 2% (w/w)
Zonyl 7040 (obtained from DuPont), 2% (w/w) Freepel 1225 (obtained
from B. F. Goodrich), 0.25% (w/w) Zelec TY antistat (obtained from
Stepan), 0.18% (w/w) Alkanol 6112 wetting agent (obtained from
DuPont). The sheet was then squeezed to remove excess liquid and
dried and cured in an oven at 168.degree. C. for 2 minutes.
[0088] The physical properties of the sheet are reported in Table
1.
Example 2
[0089] A nonwoven sheet was formed according to the procedure of
Examples 1 except that polymer resin used was film grade
poly(ethylene terephthalate) polyester containing 0.6% by weight
calcium carbonate with a typical particle size of less than 100
nanometers, having an intrinsic viscosity of 0.58 dl/g. The
physical properties of the sheet are reported in Table 1.
Example 3
[0090] A nonwoven sheet was formed according to the procedure of
Example 1 except that the polymer resin used was poly(ethylene
terephthalate) polyester with an intrinsic viscosity of 0.67 dl/g
available from DuPont as Crystar.RTM. polyester (Merge 3934). Also,
the sheet bonding temperature was 180.degree. C. instead of
250.degree. C. The physical properties of the sheet are reported in
Table 1.
[0091] The fibers of the nonwoven sheet made in Examples 1-3 were
melt spun at high speed to provide very fine fiber size while
maintaining overall spinning continuity. The low intrinsic
viscosity polyester used in Examples 1 and 2 resulted in fibers
with lower denier that were less sensitivity to turbulence in the
quench region and than the fibers made with the higher intrinsic
viscosity polyester of Example 3. In addition, with the lower
intrinsic viscosity polyester of Examples 1 and 2, spinning was
more robust (i.e., broken filaments did not cause adjacent
filaments to break) than with the higher intrinsic viscosity
polymer of Example 2. The low intrinsic viscosity polyester melt
spun at high speeds maintained filament strength better than has
been the case with low intrinsic viscosity polyester that has been
melt spun at conventional speeds. In Examples 1 and 2, the
polyester polymer with a low intrinsic viscosity of 0.58 dl/g made
smaller size fibers and generally stronger fibers than the
polyester polymer of Example 3, which had a higher intrinsic
viscosity of 0.67dl/g.
Example 4
[0092] A nonwoven sheet was formed according to the procedure of
Example 1 except that 1.5% weight percent cobalt-aluminate based
blue pigment was added to the polymer fed into the extruder that
fed the sheath portion of the bicomponent spinning apparatus. The
polymer from the two extruders fed polymer to the spin pack at
relative feed rates so as to make bicomponent fibers that were 50
weight percent sheath and 50 weight percent core. The pigment added
to the sheath polymer provided the resulting fabric with color and
additional opacity. A bonding temperature of 250.degree. C. was
used. The physical properties of the sheet are reported in Table
1.
Example 5
[0093] A nonwoven sheet was formed according to the procedure of
Examples 1 except different polymers were put in the two extruders
so as to produce bicomponent sheath-core fibers. Poly(trimethylene
terephthalate) polyester with an intrinsic viscosity of 0.45 dl/g
was extruded to produce the fiber sheaths and poly(ethylene
terephthalate) polyester with an intrinsic viscosity of 0.53 dl/g
(available from DuPont as Crystar.RTM. polyester (Merge 3949)) was
extruded to produce the fiber cores. The sheath comprised about 30%
of the fiber cross sections and the core comprised about 70% of the
fiber cross sections. The sheets were bonded at 150.degree. C.
instead of 250.degree. C. The physical properties of the sheet are
reported in Table 1.
Example 6
[0094] A nonwoven sheet was formed according to the procedure of
Example 5 except a bicomponent sheath-core fiber was made by using
a low melt 17% modified di-methyl isophalate co-polyester with an
intrinsic viscosity of 0.61 dl/g produced by DuPont as Crystar.RTM.
co-polyester (Merge 4442) in the sheath and poly(ethylene
terephthalate) polyester with an intrinsic viscosity of 0.53
dl/gavailable from DuPont as Crystar.RTM. polyester (Merge 3949) in
the core. The sheath comprised about 30% of the fiber cross
sections and the core comprised about 70% of the fiber cross
sections. The physical properties of the sheet are reported in
Table 1.
Example 7
[0095] A nonwoven sheet was formed according to the procedure of
Example 5 except a bicomponent sheath-core fiber was made by using
linear low density polyethylene with a melt index of 27 g/10
minutes (measured according to ASTM D1238)(available from Dow as
Aspun.RTM. 6811A) in the sheath and poly(ethylene terephthalate)
polyester with an intrinsic viscosity of 0.53 dl/g available from
DuPont as Crystar.RTM. polyester (Merge 3949) in the core. The
sheath comprised about 30% of the fiber cross sections and the core
comprised about 70% of the fiber cross sections. Also, the sheet
bonding temperature was 120.degree. C. instead of 250.degree. C.
The physical properties of the sheet are reported in Table 1.
Example 8
[0096] A nonwoven sheet was formed according to the procedure of
Example 5 except a bicomponent sheath-core fiber was made by using
a low melt 17% modified di-methyl isophalate co-polyester with an
intrinsic viscosity of 0.61 dl/g produced by DuPont as Crystar.RTM.
co-polyester (Merge 4442) in the sheath and poly(ethylene
terephthalate) polyester with an intrinsic viscosity of 0.53 dl/g
(available from DuPont as Crystar.RTM. polyester (Merge 3949)) in
the core. Also, the draw jet extension as described above with
regard to FIG. 8 was added. The draw jet extension was a 17 cm
long, smooth surface, rectangular plate that extended down from the
exit of the draw jet on the side of the curtain of filaments facing
toward which the filaments move once they are on the laydown belt.
The sheet was bonded at a temperature was 210.degree. C. instead of
250.degree. C. The physical properties of the sheet are reported in
Table 1.
Example 9
[0097] A nonwoven sheet was formed according to the procedure of
Example 8 except the draw jet extension was removed. The physical
properties of the sheet are reported in Table 1.
[0098] Comparing the data from Table 1 for Examples 8 and 9 shows
that the presence of the draw jet extension leads to increased
hydrostatic head and tensile properties.
2 TABLE 1 Example 1 2 3 4 5 6 7 8 9 Spinning Speed (m/min) 6618
7714 4765 6818 4500 7258 3750 8333 7895 Fiber Diameter (.mu.m) 8.6
8.6 9.4 8.3 10.2 8.1 10.0 7.5 7.6 Fiber Size (denier) 0.71 0.70
0.85 0.66 1.00 0.62 0.96 0.54 0.57 Cross Sectional Area 58 58 70 54
82 51 79 44 45 (.mu.m.sup.2) Thickness (mm) 0.36 0.30 0.30 0.36
0.36 0.34 0.31 0.33 0.31 Basis Weight (g/m.sup.2) 71 58 62 71 81 73
60 78 78 Hydrostatic Head (cm) 39 40 20 40 29 38 25 48 42 Blood
Strike Through 2.0 -- 1.2 1.8 1.6 2.2 1.3 -- -- (psig) Water Impact
(g) 0.00 -- 1.50 0.06 0.48 0.05 -- 0.08 0.09 Alcohol Repellency 10
-- 10 10 10 10 -- -- -- Spray Rating (%) 100 -- 100 100 100 100 --
-- -- Frazier Air Permeability 24 39 61 21 34 23 35 18 24
(m.sup.3/min-m.sup.2) Moisture Vapor 1338 -- 1448 1204 1401 1425
1304 -- -- Transmission Rate (g/m.sup.2/24 hr) Mullen Burst
(N/m.sup.2) 0.22 -- 0.24 0.28 0.25 0.59 0.42 -- -- Grab Tensile MD
(N) 117 125 62 126 97 222 142 304 259 Grab Tensile/BW MD 1.6 2.2
1.0 1.8 1.2 3.1 2.4 3.9 3.3 (N/g/m.sup.2) Elongation MD (%) 23 48
27 21 18 17 30 -- -- Grab Tensile XD (N) 82 82 62 69 76 129 73 228
175 Grab Tensile/BW XD 1.2 1.4 1.0 1.0 0.9 1.8 1.2 2.9 2.2
(N/g/m.sup.2) Elongation XD (%) 29 72 56 31 22 17 70 -- --
Trapezoid Tear MD (N) 13 -- 13 18 9 11 27 -- -- Trapezoid Tear XD
(N) 8 -- 12 7 9 8 11 -- --
[0099] The data from Table 1 clearly indicate that a unique
combination of barrier and air permeability may be formed by the
inventive fabric which is not found in other available nonwoven
fabrics. The uses of such fabrics and structures may be
exceptionally broad as the combination or balance of properties has
not been found in a single fabric. Principally, the fabric may be
used in special use apparel such as a medical gown for a surgeon.
It would be for a single use to protect the surgeon or other
medical personnel from hazardous liquids such as contaminated body
fluids. However, during a long and intense operation, the medical
personnel would not be overheating but rather would be quite
comfortable in a garment that breathes. After use, the garment
would preferably be fully recyclable where constituted of a single
polymer which would be readily recycled back to constituent monomer
as compared to other materials which are combinations of dissimilar
polymers or wherein at least one constituent is not a recyclable
polymer.
[0100] The foregoing description and drawings were intended to
explain and describe the invention so as to contribute to the
public base of knowledge. In exchange for this contribution of
knowledge and understanding, exclusive rights are sought and should
be respected. The scope of such exclusive rights should not be
limited or narrowed in any way by the particular details and
preferred arrangements that may have been shown. Clearly, the scope
of any patent rights granted on this application should be measured
and determined by the claims that follow.
* * * * *