Note: Descriptions are shown in the official language in which they were submitted.
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
NONWOVEN BREATHABLE COMPOSITE BARRIER FABRIC
BACKGROUND OF THE INVENTION
The present invention is directed to cloth-like, liquid-impervious, breathable
composite
barrier fabrics. More particularly, the present invention is directed to cloth-
like, liquid-
impervious, breathable film-nonwoven composite fabrics having biological
liquid barrier
capabilities for use as, for example, sterilization wrap, surgical draping,
surgical gowns,
cover garments, such as over-suits, and the like.
Surgical gowns, surgical drapes, and sterile wrap and sterilization peel
pouches
(hereinafter collectively "surgical articles"), in order to function
satisfactorily, must achieve
a balance of properties, features and performance characteristics. Such
surgical articles
have, as a principal matter, been designed to greatly reduce, if not prevent,
the
transmission through the surgical article of biological liquids and/or
airborne
contaminates. In surgical procedure environments, such liquid sources include
the gown
wearer's perspiration, body fluids from the patient, such as blood, and life
support
liquids, such as plasma and saline. Examples of airborne contaminates include,
without
limitation, biological contaminates, such as bacteria, viruses and fungal
spores. Such
contaminates may also include particulate material such as, without
limitation, lint,
mineral fines, dust, skin scales and respiratory droplets. A measure of the
barrier fabric's
ability to prevent the passage of such airborne materials is sometimes
expressed in terms
of filtration efficiency.
Such surgical articles further should be comfortable during use, that is,
while being worn.
The breathability of the surgical article, that is, its rate of water vapor
transmission, is an
important measure of how comfortable a surgical article is to use. Other
characteristics of
surgical articles that impact upon the eomfort of the article during use
include, without
limitation, the drapeability, cloth-like feel and hand and cool, dry feel of
the articles.
1
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
Surgical articles also require a minimum level of strength and durability in
order to
provide the necessary level of safety to the user of the article, particularly
during surgical
procedures.
Finally, surgical articles desirably are inexpensive to manufacture, utilizing
lightweight
materials that enhance the comfort of the wearer during use, but also reduce
the cost of
such articles.
The use of liquid impervious, breathable multilayer barrier fabrics of various
constructions is known. Surgical articles formed from liquid repellent
fabrics, such as
fabrics formed from nonwoven webs or layers, have provided acceptable levels
of liquid
imperviousness, breathability, cloth-like drapeability, strength and
durability, and cost.
However, the need exists nonetheless for improved cloth-like, liquid-
impervious,
breathable barrier materials for use in forming surgical articles, as well as
other garment
and over-garment applications, such as personal protective equipment
applications (i.e.,
workwear, for example), in which some or all of the above performance
characteristics
and features are desirable or necessary. Other personal protective equipment
applications
include, without limitation, laboratory applications, clean room applications,
sueh as
semiconductor manufacturing, agriculture applications, mining applications,
environmental applications, and the like.
Moreover, personal care articles such as adult incontinent products and infant
or child
care diapers or garments such as training pants may utilize components with
these
desirable properties.
SUMMARY OF THE INVENTION
The present invention is drawn to a breathable barrier material having a first
nonwoven
layer and a first microporous film bonded together to form a composite
laminate. A
second microporous filin and a second nonwoven layer are bonded to the
composite
2
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
laminate to form the barrier material. In another aspect, the present
invention is drawn to
a breathable barrier material where the first and second films are disposed
between the
nonwoven layers. Either or both of the nonwoven layers may be made of a
spunbond
web. Either or both films may be configured as a monolayer or multilayer film.
In another aspect of the present invention, the multilayer film may be made of
a core layer
constituting about 85% of the total film thickness and a skin layer
constituting about 15%
of the total film thickness. In another embodiment two skin layers may be
provided, each
disposed on opposite sides of the core layer. The two skin layers may each
constitute
about 7.5% of the total film thickness. Breathability may be imparted to the
film by use of
suitable fillers. As such, the film may be manufactured from about 30% to
about ~5% by
weight polyolefin resin and from about 70% to about 25% by weight of filler.
In still another aspect, the present invention may have a water vapor
transmission rate of
at least about 500 grams per square meter per 24 hours, or in some embodiments
at least
about 5000 grams per square meter per 24 hours.
The material itself may be created by bonding the prebonded composite laminate
to the
second film and second nonwoven layer to create bond points in the material
and void
spaces between the first and second films. The void spaces between films may
enhance
liquid and viral barrier properties in the barrier material by creating a
boundary that
minimizes passage of liquids and/or viral components through the barrier
material. These
voids may also serve to trap such liquids and/or viral components between the
films.
Such a material may be found useful in applications directed to surgical
gowns, surgical
drapes, sterilization peel pouches, industrial protective garments, personal
care articles,
and other applications wherein the use of a breathable barrier thermoplastic
elastorneric
polyolefin is desirable.
These and other objects are achieved by the improved cloth-like, liquid-
impervious,
breathable barrier material disclosed and claimed herein.
3
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
BRIEF DESCRIPTION OF THE DRAWINGS
FIG.1 is a cross-sectional view of an exemplary barrier material of the
present invention.
FIG. 2 is a cross-sectional side view of a multilayer film for use in the FIG.
1 barrier
material. The right side of the film has been separated to facilitate its
description .
FIG. 3 is a schematic view of a process for making the FIG.1 barrier material.
FIG. 4 is a SEM Micrograph of the FIG.1 barrier material at 50x magnification.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to an improved cloth-like, liquid-
impervious, breathable
barrier material, which possess a unique balance of performance
characteristics and
features making the material suitable for use in forming surgical articles, as
well as other
garment and over-garment applications, such as personal protective equipment
applications. Referring to the drawings, one embodiment of the barrier
material of the
present invention is illustrated. In this embodiment, the barrier material 10
is a laminate
comprising four layers--a top nonwoven layer 12 formed, for example, of
spunbond
filaments, a bottom nonwoven layer 1~ formed, for example, of spunbond
filaments, a first
middle breathable filin 14 formed, for example, of a microporous film, and a
second
middle breathable film 16 formed, for example, of a microporous film. The
individual
layers of barrier material 10 are laminated, bonded or attached together by
known means,
including thermal-mechanical bonding, ultrasonic bonding, adhesives, stitching
and the
like.
As used herein, the terms "layer" or "web" when used in the singular can have
the dual
meaning of a single element or a plurality of elements. As used herein, the
term "laminate"
means a composite material made from two or more layers or webs of material
which
4
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
have been bonded or attached to one another. As used herein, the terms
"nonwoven
fabric" or "nonwoven web" mean a web having a structure of individual fibers
or
filaments that are interlaid, but not in an identifiable, repeating manner as
in a knitted or
woven fabric.
Commercially available thermoplastic polymeric materials can be advantageously
employed in making the fibers or filaments from which top nonwoven layer 12
and
bottom nonwoven layer 18 are formed. As used herein, the term " polymer" shall
include,
but is not limited to, homopolymers, copolymers, such as, for example, block,
graft,
random and alternating copolymers, terpolymers, etc., and blends and
modifications
thereof. Moreover, unless otherwise specifically limited, the term "polymer"
shall include
all possible geometric configurations of the material, including, without
limitation,
isotactic, syndiotactic, random and atactic symmetries. As used herein, the
terms
"thermoplastic polymer" or "thermoplastic polymeric material" refer to a long-
chain
polymer that softens when exposed to heat ayld returns to the solid state when
cooled to
ambient temperature. Exemplary thermoplastic materials include, without
limitation,
polyvinyl chlorides, polyesters, polyamides, polyfluorocarbons, polyolefins,
polyurethanes, polystyrenes, polyvinyl alcohols, caprolactams, and copolymers
of the
foregoing.
Nonwoven webs that may be employed as the nonwoven layers 12 and 18 of the
present
invention may be formed by a variety of known forming processes, including
spunbonding, airlaying, meltblowing, or bonded carded web formation processes.
For
example, in the embodiment of the present invention shown in the drawings
herein, top
layer 12 and bottom layer 18 are both spunbond nonwoven webs, which have been
found
advantageous in forming barrier material 10. Spunbond nonwoven webs are made
from
melt-spun filaments. As used herein, the term "meltspun filaments" refers to
small
diameter fibers and/or filaments that are formed by extruding a molten
thermoplastic
material as filaments from a plurality of fine, usually circular, capillaries
of a spinneret
with the diameter of the extruded filaments then being rapidly reduced, for
example, by
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
non eductive or eductive fluid drawing or other well known spunbonding
mechanisms.
Lastly, the melt-spun filaments are deposited in a substantially random manner
onto a
moving carrier belt or the like to form a web of substantially continuous and
randomly
arranged, melt-spun filaments. Spunbond filaments generally are not tacky when
they are
deposited onto the collecting surface. The production of spunbond nonwoven
webs is
described in U.S. Pat. No. 4,340,563 to Appel et al., U.S. Pat. No. 3,692,618
to Dorschner et
al., U.S. Pat. No. 3,802,81 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and
3,341,394 to
Kinney, U.S. Pat. No. 3,502,538 to Peterson, and U.S. Pat. No. 3,542,615 to
Dobo et al., all
of which are incorporated herein by reference. The melt spun filaments formed
by the
spunbond process are generally continuous and have average diameters larger
than 7
microns based upon at least 5 measurements, and more particularly, between
about 10
and 100 microns. Another frequently used expression of fiber or filament
diameter is
denier, which is defined as grams per 9000 meters of a fiber or filament.
Spunbond webs generally are stabilized or consolidated (pre-bonded) in some
manner
immediately as they are produced in order to give the web sufficient integrity
and
strength to withstand the rigors of further processing into a finished
product. This pre-
bonding step may be accomplished through the use of an adhesive applied to the
filaments as a liquid or powder which may be heat activated, or more commonly,
by
compaction rolls. As used herein, the term "compaction rolls" means a set of
rollers above
and below the nonwoven web used to compact the web as a way of treating a just
produced, melt-spun filament, particularly spunbond, web, in order to give the
web
sufficient integrity for further processing, but not the relatively strong
bonding of later
applied, secondary bonding processes, such as through-air bonding, thermal
bonding,
ultrasonic bonding and the like. Compaction rolls slightly squeeze the web in
order to
increase its self-adherence and thereby its integrity.
An exemplary secondary bonding process utilizes a patterned roller arrangement
for
thermally bonding the spunbond web. The roller arrangement typically includes
a
patterned bonding roll and a smooth anvil roll which together define a thermal
patterning
6
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
bonding nip. Alternatively, the anvil roll rnay also bear a bonding pattern on
its outer
surface. The pattern roll is heated to a suitable bonding temperature by
conventional
heating means and is rotated by conventional drive means, so that when the
spunbond
web passes through the nip, a series of thermal pattern bonds is formed. Nip
pressure
within the nip should be sufficient to achieve the desired degree of bonding
of the web,
given the line speed, bonding temperature and materials forming the web.
Percent bond
areas within the range of from about 10 percent to about 20 percent are
typical for such
spunbond webs.
Each nonwoven layer 12 and/or 18 may itself comprise a single layer of
meltspun fabric,
for example a spunbond or meltblown layer, or each nonwoven layer 12 and/or 18
may
comprise a plurality of separate nonwoven layers comprising any of identical
layers,
similar layers, or different layers. For instance, each of the nonwoven layers
12,18 may
comprise a spunbond layer and a meltblown layer, or a first spunbond layer, a
meltblown
layer, and a second spunbond layer. Additional layers and combinations are
possible as
well, depending on the intended use of the product. In any of the embodiments,
any of the
nonwoven layers may be treated with an antistatic agent, a surfactant to
impart
hydrophilicity, or any other useful surface modifying agents so long as such
an agent
does not interfere with the intent of the invention.
The middle breathable films 14 and 16 may be formed of any microporous film
that can be
suitably bonded or attached to the top and bottom layers 12,18 to yield a
barrier material
having the unique combination of performance characteristics and features
described
herein. One suitable class of film materials includes at least two basic
components: a
thermoplastic polyolefin polymer and a filler. These (and other) components
rnay be
mixed together, heated and then extruded into a monolayer or multilayer film
using any
one of a variety of film-producing processes known to those of ordinary skill
in the film
processing art. Such film making processes include, for example, cast
embossed, chill and
flat cast, and blown film processes.
7
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
Generally, on a dry weight basis, based on the total weight of the film, each
film 14 and 16
will include from about 30 to about 75 weight percent of the thermoplastic
polyolefin
polymer, or blend thereof, and from about 25 to about 70 percent filler.
Suitable polymers
for use in the films include polyethylene, blends of polyethylenes,
polypropylene, blends
of polypropylenes, blends of polyethylene and polypropylene, blend
combinations of
polyethylene or polypropylene with suitable amorphous polymers, copolymers
made
from ethylene a~.zd propylene monomers, and blends of such copolymers with
polyethylenes or polypropylenes or suitable amorphous polymers, serni-
crystalline/ amorphous polymers, "heterophasic' polymers, or combinations
thereof.
Examples of useful polymers are EXXPOL~, EXCEED, and EXACTTM polymers from
Exxon Chemical Company of Baytown, Texas; ENGAGE, ACHIEVE, ATTAIN~,
AFFINITY, and ELITE~ polymers from Dow Chemical Company of Midland, Michigan;
CATALLOY~ polymers from Basell USA Inc. of Wilmington, Delaware.
Other useful polymers and polymer blends used alone or in combination may be
formed
from or include homopolymers, copolymers and blends of polyolefins, ethylene
vinyl
acetate (EVA), ethylene ethyl acrylate (EEA), ethylene acrylic acid (EAA),
ethylene methyl
acrylate (EMA), ethylene butyl acrylate (EBA), polyester (PET), nylon (PA),
ethylene vinyl
alcohol (EVOH), polystyrene (PS), polyurethane (PU), and olefinic
thermoplastic
elastomers which are multistep reactor products wherein an amorphous ethylene
propylene random copolymer is molecularly dispersed in a predominately
semicrystalline
high polypropylene monomer/low ethylene monomer continuous matrix. Other
additives
and ingredients may be added to the films 14, 16 provided such additives do
not
significantly interfere with the ability of the film layer to function in
accordance with the
teachings of the present invention. Such additives and ingredients can
include, for
example, antioxidants, stabilizers, and pigments.
In addition to the polyolefin polymer, as stated, the films 14 and 16 also
include a filler. As
used herein, a "filler" is meant to include particulates and other forms of
materials that
may be added to the filin polymer extrusion blend, will not chemically
interfere with the
8
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
extruded film, but are able to be uniformly dispersed throughout the filin.
Generally, the
fillers will be in particulate form and may have a spherical or non-spherical
shape with
average particle sizes in the range of about 0. 1 to about ~ microns. Both
organic and
inorganic fillers are contemplated to be within the scope of the present
invention provided
that they do not interfere with the film formation process, or the ability of
the film to
function in accordance with the teachings of the present invention. Examples
of suitable
fillers include calcium carbonate (CaCOs), various kinds of clay, silica
(Si02), alumina,
barium carbonate, sodium carbonate, magnesium carbonate, talc, barium sulfate,
magnesium sulfate, aluminum sulfate, titanium dioxide (TiOa.), zeolites,
cellulose-type
powders, kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum
hydroxide,
pulp powder, wood powder, cellulose derivatives, chitin and chitin
derivatives. A suitable
coating, such as, for example, stearic acid, may also be applied to the filler
particles.
As mentioned herein, films 14 and 16 may be formed using any one of the
conventional
processes known to those familiar with film formation. The polyolefin polymer
and filler
are mixed in appropriate proportions given the ranges outli~.led herein and
then heated
and extruded into a monolayer or rnultilayer film as required. In order to
provide uniform
breathability as reflected by the water vapor transmission rate of the filin,
the filler should
be uniformly dispersed throughout the polymer blend and, consequently,
throughout
each film layer itself. For purposes of the present invention, a film is
considered
"breathable" if it has a water vapor transmission rate of at least 300 grams
per square
meter per 24 hours (g/m2/24 hours), as calculated using the test method
described herein.
Other embodiments of this invention contemplate water vapor transmission rates
of at
least 500 grams per square meter per 24 hours (g/m2/24 hours), and still other
embodiments contemplate water vapor transmission rates of at least 5000 grams
per
square meter pex 24 hours (g/m~/24 hours).
Generally, once the film is formed, it will have a weight per unit area of
less than about 80
grams per square meter (gsm) and after stretching and thinn?n_g, its weight
per unit area
will be from about 10 gsm to about 25 gsm.
9
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
The films used in the example of the present invention described below are
multilayer
films, such as the ABA-type film described below. It should be understood that
other
types of films, such as monolayer films, are also considered to be within the
scope of the
present invention provided the forming technique is compatible with filled
films.
Referring to FIG. 2, there is shown, not to scale, an exemplary ABA-type
multilayer film 20
that, for purposes of illustration, has been split apart at the right side of
the drawing. Such
a film may form one or both of the filins 14 and/or 16. In this embodiment,
the multilayer
film 20 includes a core layer 22 made from the extrudable thermoplastic
polymers
described above. The core layer 22 has a first exterior surface 24 and a
second exterior
surface 26. The core layer also has a core thickness 28. Attached to the first
exterior surface
24 of the core layer 22 is a first skin layer 30 which has a first skin
thickness 32. Attached to
the second exterior surface 26 of the core layer 22 is an optional second skin
layer 34 which
has a second skin thickness 36. In addition, the rnultilayer film 10 has an
overall thickness
38.
One embodiment of such a multilayer film of the present invention, for
example, provides
the core layer 22 with a combination of from about 26% to about 30% by weight
of a linear
low density polyethylene (LLDPE) copolymer, from about 15% to about 18% by
weight of
a single-site (metallocene) catalyzed copolymer, and from about 53% to about
57% by
weight particulate calcium carbonate. Skin layers 30 and 34 may comprise, for
example, a
combination of about 26% CATALLOY~, from about 7% to about 10% polypropylene
random copolymer (RCP), and from about 57% to about ~0% by weight particulate
calcium carbonate. The core layer 22 constitutes about 85 % of the total film
thickness 38.
Such multilayer films 20 may be formed by a wide variety of processes well
known to
those of ordinary skill in the film forming industry. Two particularly
advantageous
processes are cast film coextrusion processes and blown film coextrusion
processes. In
such processes, the two or three layers are formed simultaneously and exit the
extruder in
a multilayer form. Due to the extremely thin nature of the multilayer films
according to
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
the present invention such processes will most likely prove to be the most
advantageous
though it also may be possible to form multilayer films using separate
extrusion processes.
Each film as initially formed generally is thicker and noisier than desired,
as it tends to
make a "rattling" sound when shaken. Moreover, each filin does not have a
sufficient
degree of breathability as measured by its water vapor transmission rate.
Consequently,
each film is heated to a temperature equal to or less than about 5° C.
below the melting
point of the polyolefin polymer and then stretched using an in-line machine
direction
orientation (MDO) unit to at least about two times (2x) its original length to
thin the filin
and render it porous. Further stretching of the films 14,16, to about three
times (3x), four
times (4x), or more, their original length is expressly contemplated in
connection with
forming films 14 and/or 16 of the present invention.
The films 14 and 16 after being stretch-thinned should have an "effective"
film gauge or
thickness of from about 0.2 mil to about 1.2 mil in some embodiments. In other
embodiments, it is contemplated that the effective gauge be from about 0.2 mil
to about
0.6 mil. The effective gauge is used to take into consideration the voids or
air spaces in
breathable film layers. For normal, non-filled, non-breathable films, the
actual gauge and
effective gauge of the filin typically will be the same. However, for filled
films that have
been stretch-thinned, as described herein, the thickness of the film will also
include air
spaces. In order to disregard this added volume, the effective thickness is
calculated
according to the test method set forth herein.
Referring now to FIG. 3, a process for preparing a barrier material 10
according to the
present invention is illustrated. One of the films, for example film 14 is
formed using any
type of conventional film forming equipment 40, such as cast or blown film
equipment.
The film 14 having a formulation as described herein then is passed through a
film
stretching apparatus 42 to stretch and thin the filin to an effective gauge of
0.6 mil or less.
One type of suitable film stretching apparatus is a Machine Direction Orienter
unit, Model
11
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
No. 7200, available from the Marshall & Williams Company, having offices in
Providence,
R.I.
While the film 14 is being stretched, a nonwoven layer, for example spunbond
nonwoven
layer 12 is formed. A conventional spunbond nonwoven web manufacturing
process, as
described herein, can be used to form the nonwoven layer 12. As shown in FIG.
3, the
spunbond web 12 is formed of substantially continuous and randomly arranged,
melt-
spun filaments, that are deposited onto a moving continuous forming wire 44
from
extruders 46. The webs of randomly arranged, melt-spun filaments then can be
pre-
bonded by passing the web through a pair of compaction rolls (not shown) to
give the
web sufficient integrity and strength for further processing. One or both of
the compaction
rolls may be heated to aid in bonding the web 12. Typically, one of the
compaction rolls
also has a patterned outer surface that imparts a discrete bond pattern with a
prescribed
bond area to web 12. The opposing compaction roll usually is a smooth anvil
roll,
although this roll also may have a patterned outer surface if desired.
Once the film 14 has been sufficiently stretch-thinned and oriented, and the
spunbond
web 12 has been formed, the film layer 14 and web 12 are brought together and
laminated
to one another using a pair of laminating or bonding rolls 48, 50, as shown in
FIG. 3, or
other conventional bonding means, in order to produce a composite laminate 52
of the
present invention.
It should be noted that bonding roll 48 is a pattern roll, whereas second
bonding roll 50 is
a smooth roll. Both rolls are driven by conventional means, such as, for
example, electric
motors (not shown). Pattern roll 48 is a right circular cylinder that may be
formed of any
suitable, durable material, such as, for example, steel, to reduce wear on the
rolls during
use. Pattern roll 48 has on its outermost surface a pattern of raised bonding
area. An
intermittent pattern of discrete, regularly repeating bonding points can be
suitably
employed, for example, as is conventional in the art. The bonding areas on
pattern roll 48
form a nip with the smooth or flat outer surface of opposed positioned anvil
roll 50.
12
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
Anvil roll 50 also is a right circular cylinder that can be formed of any
suitable, durable
material, such as, for example, steel, hardened rubber, resin-treated cotton
or
polyurethane.
The pattern of raised bonding areas on the pattern roll 48 is selected such
that the area of
at least one surface of the resulting composite laminate 52 occupied by bonds
after
passage through the nip formed between pattern rolls 48, 50 ranges from about
10 percent
to about 30 percent of the surface area of the barrier material. The bonding
area of the
composite laminate 52 may be varied to achieve the above-mentioned percent
bond area,
as is known in the art.
In accordance with one embodiment of this invention, bonding may be
accomplished
using a Rarnisch bond pattern. The Ramisch bond pattern has a bond area of
about 8% to
about 14%, a pin density of about 52 pins/in2, and a pin depth at 8% bond area
of about
0.052 inch. The Ramisch bond pattern is a relatively deep, open pattern
suitable for use in
stretch applications. However any suitable conventional thermal bonding means
may be
used for thermally bonding the layers including, but not limited to, standard
heat rolls,
ultrasound and through-air-bonding. The temperature of the outer surface of
the pattern
roll 48 may be varied by heating or cooling relative to the smooth roll 50.
Heating and/or
cooling can affect, for example, the degree of lamination of the individual
layers forming
the laminate 52. Heating and/or cooling of pattern roll 48 and/or smooth roll
50 may be
effected by conventional means (not shown) well known in the art. The specific
ranges of
temperatures to be employed in forming the laminate 52 are dependent on a
number of
factors, including the types of polymeric materials employed in forming the
individual
layers of the laminate 52, the dwell time of the individual layers within the
nip and the nip
pressure between the pattern roll 48 and anvil roll 50. After laminate 52
exits the nip
formed between bonding rolls 48, 50, the laminate 52 may be wound onto roll 54
for
subsequent processing.
13
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
The second film 16 and nonwoven layer 18 may be formed from sinvlar materials
and in a
manner similar to that of the first film 14 and nonwoven layer 12 respectively
as depicted
in FIG. 3. Once the film 16 is stretch-thinned, in order to produce the
barrier material 10 of
the present invention, the film. 16, nonwoven layer 18, and laminate 52 are
brought
together and laminated to one another using a pair of laminating or bonding
rolls as
shown in FIG. 3, or other conventional bonding means.
It should be apparent that the composite laminate 52 is thus double bonded
whereas the
filin 16 and nonwoven layer 18 are single bonded to the composite laminate 52.
FIG. 4
depicts the resulting barrier material 10 depicting voids between the films 14
and 16, that
is, each film 14 and 16 is separate between the bonded regions. It is believed
that these
voids enhance liquid and viral barrier properties in the barrier material 10
by creating a
boundary that minimizes passage of liquids and/or viral components through the
barrier
materia110 and may serve to trap such liquids and/or viral components between
the films
14 and 16.
Modifications in the above-described process will be readily apparent to those
of ordinary
skill in the art without departing from the spirit and scope of the present
invention. For
example, after the barxier material 10 is formed, it may continue in line for
further
processing and converting. Or, different apparatus may be used for stretch-
thinning the
films 14,16. Other known means for bonding and laminating the filins 14,16 to
nonwoven
layers 12, 18 may be used, provided the resulting barrier material 10 has the
required
properties described herein. Finally, formation of the films 14,16 and/or
nonwoven layers
12, 18 may take place at a remote location, with rolls of the individual
layers unwound
and fed to the nip formed between pattern roll 48 and smooth roll 50. Also,
for certain
applications, it may be advantageous to have a two component material that can
be
formed as above described by omitting one of the spunbond webs, for example.
Typical
spunbond weights for such applications are between about 0.6 osy to about 1.5
osy,
commonly between about 0.9 osy to about 1.3 osy. These materials may also be
thermally
or adhesively laminated to the stretch-thinned film to form the composite. In
whatever
14
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
manner bonding is accomplished, the existence of the voids between filins
should be
maintained.
Having described certain embodiments of the present invention, a sample
barrier material
was tested to further illustrate the present invention and to teach one of
ordinary skill in
the art the manner of carrying out the present invention. The results of the
measurements
of certain physical properties of the barrier materials so formed, and the
test procedures
used, are set forth below.
Test Procedures
The following test procedures were used to analyze the sample and comparative
barrier
materials identified below.
Mocon Water Vapor Transmission Rate Test
A suitable technique for determining the WVTR (water vapor transmission rate)
value of a
material is the test procedure standardized by INDA (Association of the
Nonwoven
Fabrics Industry), number IST-70.4-99, entitled "STANDARD TEST METHOD FOR
WATER VAPOR TRANSMISSION RATE THROUGH NONWOVEN AND PLASTIC
FILM USING A GUARD FILM AND VAPOR PRESSURE SENSOR" which is incorporated
by reference herein. The INDA procedure provides for the determination of
WVTR, the
permeance of the film to water vapor and, for homogeneous materials, water
vapor
permeability coefficient.
The INDA test method is well known and will not be set forth in detail herein.
However,
the test procedure is summarized as follows. A dry chamber is separated from a
wet
chamber of known temperature and humidity by a permanent guard film and the
sample
material to be tested. The purpose of the guard film is to define a definite
air gap and to
quiet or still the air in the air gap while the air gap is characterized. The
dry chamber,
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
guard film, and the wet chamber make up a diffusion cell in which the test
film is sealed.
The sample holder is known as the Permatran-W model 100K manufactured by
Mocon/Modern Controls, Inc, Minneapolis, Mien. A first test is made of the
WVTR of the
guard film and air gap between an evaporator assembly that generates 100
percent
relative humidity. Water vapor diffuses through the air gap and the guard film
and then
mixes with a dry gas flow which is proportional to water vapor concentration.
The
electrical signal is routed to a computer for processing. The computer
calculates the
transmission rate of the air gap and guard film and stores the value for
further use.
The transmission rate of the guard film and air gap is stored in the computer
as Calf. The
sample material is then sealed in the test cell. Again, water vapor diffuses
through the air
gap to the guard film and the test material and then mixes with a dry gas flow
that sweeps
the test material. Also, again, this mixture is carried to the vapor sensor.
The computer
then calculates the transmission rate of the combination of the air gap, the
guard film, and
the test material. This information is then used to calculate the transmission
rate at which
moisture is transmitted through the test material according to the equation:
TRntest material = TR-pest material, gnardfilrn, airgap- Z'R-lguardfilnr,
airgap
Calculations:
WVTR: The calculation of the WVTR uses the formula:
WT~TR=Fpsar (Z'~RHlApsar (Z'~(1-.RH)~
where:
F=The flow of water vapor in cc/min.,
pear (T)=The density of water in saturated air at temperature T,
RH=The relative humidity at specified locations in the cell,
A=The cross sectional area of the cell, and,
psar (T)=The saturation vapor pressure of water vapor at temperature T.
16
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
EXAMPLE
A barrier material according to the present invention was made. The film
formulation was
cast into a multilayer filin having a core layer that contained on a total
weight percent
basis based upon the weight of the film, 26-30% by weight of a Ziegler-Natta
catalyzed
linear low density polyethylene (LLDPE) copolymer, about 15% to about 18% by
weight of
a single-site (metallocene) catalyzed copolymer, and from about 53% to about
57% by
weight particulate calcium carbonate. The skin layers each contained, a
combination of
about 34% CATALLOY~, from about 7% to about 10% polypropylene random copolymer
(RCP), and about 5~% by weight particulate calcium carbonate. The core layer
constituted
about 85 % of the total film thickness. The CaCOs in the core and skin layers
was coated
with from about 0.5 to 3.0% behenic acid based upon the weight of the CaCOs,
having a
0.9 to 1.3 micron average particle size and a top cut of 8 microns.
The spunbond facing layers were both 0.60 ounces per square yard nonwoven webs
formed from extrudable thermoplastic resins of hornopolymer polypropylene from
BP/Amoco 2% titanium dioxide (white), 0.09% anti-static compound and 0.91 SCC
11111
blue color concentrate. T'he spunbond filaments were essentially continuous in
nature and
had an average fiber size of 2.0 dpf.
One of the films and nonwoven layers were laminated together to form an 18.5
g/ma
composite laminate having a MOCON value of 7466 g/mz/24hr using Ramisch
pattern
thermal bonding rolls, as described herein. The pattern roll had a bonding
temperature of
about 185° F. and the smooth anvil roll had a temperature of about
145° F. The nip
pressure formed between the rolls was about 440 psig. The second film alone
had a basis
weight of 18.5 g/m~ and together with the second nonwoven layer in an unbonded
configuration had a MOCON value of 6293 g/m2/24hr. The second film and
nonwoven
layer were thermally bonded to the composite laminate using a C-star pattern.
This
attempt was a partial success in that a breathable barrier material having a
MOCON value
of 3079 g/m~/24hr was created. However, this test run did not reach the
desired target
17
CA 02523782 2005-10-26
WO 2005/017248 PCT/US2004/005032
range for breathability of 5500 g/m2/24hr. The material did exhibit improved
resistance to
low surface tension fluids by 2.7 times compared to a control. Bacteriophage
testing was
conducted in accordance with ASTM F 1671-97b and 22 out of 22 samples passed
the test.
A second sample of barrier material was created with increased calcium
carbonate level in
the skin (57 to 65%) having the same properties as the first; however, in this
sample the
second film and nonwoven layer were thermally bonded to the composite laminate
using
the Ramisch bond pattern. The MOCON of this barrier material was in the range
of 4500-
6500 g/m'-/24hr, and the bacteriophage results were 31 out of 32 samples
passing the test.
It is contemplated that the improved cloth-like, liquid impervious, breathable
barrier
material constructed in accordance with the present invention will be tailored
and
adjusted by those of ordinary skill in the art to accommodate various levels
of
performance demand imparted during actual use. Accordingly, while this
invention has
been described by reference to certain specific embodiments and examples, it
will be
understood that this invention is capable of further modifications. This
application is,
therefore, intended to cover any variations, uses or adaptations of the
invention following
the general principles thereof, and including such departures from the present
disclosure
as come within known or customary practice in the art to which this invention
pertains
and fall within the liixiits of the appended claims.
18
