FIELD OF THE INVENTION
The present invention is directed to a film and a film/nonwoven
laminate fabric, having breathability to water vapor and barrier to the passage
of liquid and viruses.
BACKGROUND OF THE INVENTION
Surgical gowns, surgical drapes, surgical face masks, surgical
scrubs, 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 contaminants, such as bacteria, viruses and fungal
spores. Such contaminates may also include particulate material such as, without
limitation, lint, mineral fines, dust, skin squames and respiratory droplets. A
measure of the barrier fabric's ability to prevent the passage of such airborne
materials is sometimes expressed in term 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 comfort of the article during use include, without limitation, the drapeability,
cloth-like feel and hand and cool, dry feel of the articles.
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 multi-layer 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, such as semiconductor manufacturing, agriculture
applications, mining applications, environmental applications, and the like.
Various low surface tension liquids are used in hospitals
and other sites where surgical and medical procedures are performed. Low surface
tension liquids, such as isopropyl alcohol, can combine with blood and other fluids
to create wettable pathways capable of carrying viruses through various surgical
articles mentioned above. For instance, surgical articles formed using microporous
thermoplastic polyolefin-based films and film/nonwoven laminates are inherently
hydrophobic, and resist the passage of blood and other aqueous fluids which might
carry viruses. However, these films and laminates are typically less resistant to
the passage of low surface tension liquids. Thus, when blood or other aqueous fluid
is combined with isopropyl alcohol or another low surface tension liquid, a vehicle
can be formed for carrying blood-bome viruses and the like through the surgical
European patent EP 0 574 160
relates to a strong multi-layer glove comprising a patient contacting
film layer made from an aqueous rubber latex emulsion, a wearer contacting film
layer made from an aqueous emulsion comprising an acrylic copolymer and a fluorocarbon
telomere resin, and an intermediate film layer made from an aqueous emulsion of
natural rubber latex, polyurethane latex, polyacrylamide/acrylic acid and polyethylene
relates to a method and composition for treating carpet yam to enhance
repellency and stain resistance. The yam comprises polymeric fibers and is immersed
in an aqueous medium of anionic or non-ionic fluorochemical compound and an anionic
binding compound. After that, the yam and aqueous medium are heated to remove excess
water from the yam.
US patent 3,125,547
relates to hydrocarbon resins which provide extrudates of smooth glossy
surface films when extruded at high extrusion speeds. Further, a fluorocarbon polymer
is uniformly distributed throughout the hydrocarbon polymer to improve the extrusion
With the foregoing in mind, there is a need or desire for
improved breathable thermoplastic films and film/nonwoven laminates that prevent
the passage of low surface tension liquids, such as isopropyl alcohol, as well as
SUMMARY OF THE INVENTION
The present invention is directed to a breathable multilayer
thermoplastic polymer-based film and film/nonwoven laminate which prevents the passage
ofboth aqueous-based and low surface-tension liquids, thereby providing improved
liquid and viral barrier properties along with breathability to water vapor. The
breathable film includes a core layer including a thermoplastic polymer, a particulate
filler and at least 0.5% by weight of a fluorochemical. The film also includes two
skin layers, one on each side of the core layer. The skin layers each include a
thermoplastic polymer and zero to less than 0.5% by weight fluorochemical, and may
include a particulate filler.
The skin layers are desirably used as thermal bonding layers
to nonwoven web layers on one or both sides of the film. To this end, the skin layers
desirably provide the film with oleophilic surfaces for improved thermal bonding.
The oleophilic surfaces may permit the passage of oil, such as mineral oil, but
do not permit the passage of aqueous liquids through the film. The fluorochemical
present in at least the core layer prevents the passage of low surface tension liquids.
The skin layers in the film help contain, but may not prevent
migration of the fluorochemical from the core layer. Fluorochemicals which are made
using electrochemical fluorination processes may contain sulfonamide groups. There
has been some controversy relative to this chemistry. A less controversial fluorochemical
may be prepared using a different process, such as a telomerization process, and
does not contain any sulfonamide groups.
With the foregoing in mind, it is a feature and advantage
of the invention to provide a breathable thermoplastic barrier film which prevents
passage of aqueous and/or low surface tension liquids, resulting in improved viral
It is also a feature and advantage of the invention to
provide a breathable film/nonwoven laminate fabric which prevents passage of aqueous
and/or low surface tension liquids through the film, resulting in improved viral
It is also a feature and advantage of the invention to
provide various surgical articles which embody the breathable thermoplastic polymer-based
film and/or the film/nonwoven laminate.
BRIEF DESCRIPTION OF THE DRAWINGS
- FIG. 1 is a cross-sectional view of a breathable thermoplastic viral barrier
film according to the invention.
- FIG. 2 is a cross-sectional view of a breathable viral barrier fabric laminate
according to the invention.
- FIG. 3 is a schematic view of a process for making a breathable viral barrier
fabric laminate according to the invention.
- FIG. 4 is a plot of moisture vapor transmission rate versus hydrohead values
using a low surface tension liquid, for various film samples.
The terms "breathable film" or "breathable laminate" refer
to a film or laminate having a water vapor transmission rate ("WVTR") of at least
about 500 grams/m2 -24 hours, suitably at least about 1000 grams/m2-24
hours, desirably at least about 2000 grams/m2-24 hours, using the WVTR
Test Procedure described herein. Breathable materials typically rely on molecular
diffusion of vapor, or vapor passage through micropores, and are substantially liquid
The terms "viral barrier film" or "viral barrier laminate"
refer to a film or film/nonwoven laminate which passes the federal performance standard
for bacteriophage, set forth in ASTM F1671.
The terms "liquid barrier film" or "liquid barrier laminate"
refer to a film or film/nonwoven laminate which passes the federal performance standard
for synthetic blood strikethrough, set forth in ASTM F1670.
The term "low surface tension liquid" refers to a liquid
having a surface tension of 40 dyne/cm or less, measured using ASTM D 1331-89. A
breathable film or film/nonwoven laminate provides barrier to low surface tension
liquid if the film resists penetration to a low surface tension liquid below 40
dyne/cm, alternatively below 30 dyne/cm, alternatively at about 26 dyne/cm, alternatively
between 22 and 40 dyne/cm, alternatively between 26 and 40 dyne/cm under pressure
of 300 millibars for a time of at least 50 minutes, alternatively under pressure
of 300 millibars for a time of at least 30 minutes, alternatively under a pressure
of 150 millibars for a time of at least 50 minutes, alternatively under a pressure
of 150 millibars for a time of at least 30 minutes, alternatively under a pressure
of 19 millibars for a time of at least 50 minutes, alternatively under a pressure
of 19 millibars for a time of at least 30 minutes, using the modified hydrohead
test described herein. The term "hydrohead" refers to hydrostatic head and the terms
should be considered synonymous for this application.
The term "nonwoven fabric or web" means a web having a
structure of individual fibers or threads which are interlaid, but not in a regular
or identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been
formed from many processes such as, for example, meltblowing processes, spunbonding
processes, air laying processes, coforming processes, and bonded carded web processes.
The basis weight of nonwoven fabrics is usually expressed in ounces of material
per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful
are usually expressed in microns. (Note that to convert from osy to gsm, multiply
osy by 33.91.)
The term "spunbonded fibers" refers to small diameter fibers
which are formed by extruding molten thermoplastic material as filaments from a
plurality of fine capillaries of a spinnerette having a circular or other configuration,
with the diameter of the extruded filaments then being rapidly reduced as by, for
U.S. Patent 4,340,563 to Appel et al.
U.S. Patent 3,692,618 to Dorschner et al.
U.S. Patent 3,802,817 to Matsuki et al.
U.S. Patents 3,338,992
3,341,394 to Kinney
U.S. Patent 3,502,763 to Hartmann
U.S. Patent 3,502,538 to Petersen
U.S. Patent 3,542,615 to Dobo et al
. Spunbond fibers are quenched and generally not tacky when they are deposited
onto a collecting surface. Spunbond fibers are generally continuous and often have
average deniers larger than about 0.3, more particularly, between about 0.6 and
The term "meltblown fibers" means fibers formed by extruding
a molten thermoplastic material through a plurality of fine, usually circular, die
capillaries as molten threads or filaments into converging high velocity heated
gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material
to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown
fibers are carried by the high velocity gas stream and are deposited on a collecting
surface to form a web of randomly dispersed meltblown fibers. Such a process is
disclosed for example, in
U.S. Patent 3,849,241
to Butin et al. Meltblown fibers are microfibers which may be continuous
or discontinuous, are generally smaller than about 1.0 denier, and are generally
self bonding when deposited on to a collecting surface.
The term "microfibers" means small diameter fibers typically
having an average fiber denier of about 0.005-10. Fiber denier is defined as grams
per 9000 meters of a fiber. For a fiber having circular cross-section, denier maybe
calculated as fiber diameter in microns squared, multiplied by the density in grams/cc,
multiplied by 0.00707. For fibers made of the same polymer, a lower denier indicates
a finer fiber and a higher denier indicates a thicker or heavier fiber. For example,
the diameter of a polypropylene fiber given as 15 microns may be converted to denier
by squaring, multiplying the result by .89 g/cc and multiplying by .00707. Thus,
a 15 micron polypropylene fiber has-a denier of about 1.42 calculated as (152
x 0.89 x .00707 = 1.415). Outside the United States the unit of measurement is more
commonly the "tex" which is defined as the grams per kilometer of fiber. Tex may
be calculated as denier/9.
The term "film" refers to a thermoplastic film made using
a film extrusion process, such as cast, blown film or extrusion coating. This term
includes films rendered microporous by mixing polymer with filler, forming a film
from the mixture, and stretching the film to create the voids. Additionally, two
or more incompatible polymers could be blended and also stretched to create a microporous
film. Also included are films in which one or more polymers are extracted by a solvent
or other means to create micropores. It also includes monolithic films which rely
on the solubility of water molecules in the solid polymer film, the diffusion of
water molecules through the solid polymer film and evaporation of the water passing
through the film into the surrounding air. In addition, foams with ruptured "cells"
from stretching or "open cells" also are included, provided there is a sufficiently
tortuous path to prevent the passage of aqueous liquids.
The term "microporous" refers to films having voids separated
by thin polymer membranes and films having micropores passing through the films.
The voids or micropores can be formed when a mixture of polymer and filler is extruded
into a film and the film is stretched, preferably uniaxially in the machine direction.
Microporous films tend to have water vapor transmission due to molecular diffusion
of water vapor through the membranes or micropores, but substantially block the
passage of aqueous liquids.
The term "polymer" 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 atactic symmetries.
The term "thermoplastic" refers to a polymer which melts
and flows when heated.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
Referring to FIG. 1, a breathable multilayer barrier film
20 of the invention includes a center (core) layer 30 and two outer (skin) layers
10. The center layer 30 includes a thermoplastic polymer matrix 32, a plurality
of voids 34 within the matrix, and a plurality of filler particles 36 within the
voids. The outer film layers 10 each include a polymer matrix 12 which is typically
different from the polymer matrix 30 of the core layer, and which can be used to
thermally bond the film 20 to a nonwoven web without destroying the integrity of
the core layer 30, as described further below. In the embodiment shown, each outer
layer 10 includes a plurality of voids 14 within the matrix, and a plurality of
filler particles 16 within the voids. In alternative embodiments, the outer layers
10 may be substantially free of voids and/or filler particles, especially where
the skin layers 10 are very thin as described below.
The voids 34 within the core layer, and the voids 14 within
the skin layers, are typically separated by thin polymer membranes within the respective
polymer matrices 12 and 32. The membranes surrounding the voids, illustrated by
numerals 13 and 33 in F1G.1, readily permit molecular diffusion of water vapor from
a first surface to a second surface of the breathable film 20. The rate of water
vapor transfer through film 20 is at least about 500 grams/m2-24 hours,
suitably at least about 1000 grams/m2-24 hours, desirably at least about
2000 grams/m2-24 hours.
The matrix 32 of the core layer 30 can include any suitable
film-forming matrix polymer. Examples of suitable matrix polymers include without
limitation olefin polymers, for instance polyethylene, polypropylene, copolymers
of mainly ethylene and C3-C12 alpha-olefins (commonly known
as linear low density polyethylene), copolymers of mainly propylene with ethylene
and/or C3-C12 alpha-olefins, and flexible polyolefins including
propylene-based polymers having both atactic and isotactic propylene groups in the
main polypropylene chain. Other suitable matrix polymers include without limitation
elastomers, for example polyurethanes, copolyether esters, polyamide polyether block
copolymers, ethylene methyl acrylate, ethylene ethyl acrylate, and ethylene vinyl
acetate copolymers, and combinations of the foregoing. Single-site catalyzed polyolefins
are useful, including those described in
U.S. Patents 5,571,619
Polymers made using single-site catalysts have a very narrow
molecular weight range. Polydispersity numbers (MW/MN) of
below 4 and even below 2 are possible for single-site catalyzed polymers. These
polymers also have a controlled short chain branching distribution compared to otherwise
similar Ziegler-Neft produced type polymers. It is also possible using a single-site
catalyst system to control the isotacticity of the polymer quite closely.
Single-site catalyzed polymers are available from Exxon-Mobil
Chemical Company of Baytown, Texas under the trade name ACHIEVE®
for polypropylene-based polymers and EXACT® and EXCEED®
for polyethylene-based polymers. Dow Chemical Company of Midland, Michigan has polymers
commercially available under the names ENGAGE®and AFFINITY®.
These materials are believed to be produced using non-stereo selective single-site
catalysts. Exxon-Mobil generally refers to their single-site catalyst technology
as "metallocene" catalysts while Dow refers to theirs as "constrained geometry"
catalysts to distinguish them from traditional Ziegler-Natta catalysts which have
multiple reaction sites. Other manufacturers such as Atofina, BASF, Basell, BP-Amoco,
and Hoechst are active in this area.
In one suitable embodiment, the polymer matrix 32 of the
core layer 30 includes a mixture of a first ethylene-alpha olefin copolymer and
a second ethylene-alpha olefin copolymer. The first ethylene-alpha olefin copolymer
is a Ziegler-Natta catalyzed linear low density polyethylene (LLDPE). The LLDPE
may have a melt index (190°C) of about 2-10 grams/10 min., a density of about
0.910-0.925 grams/cm3, and a comonomer content of about 5-25% by weight.
The comonomer may be an alpha-olefin having 3-12 carbon atoms, desirably 6-8 carbon
atoms. One suitable first ethylene-alpha olefin copolymer is DOWLEX®
2244A, available from the Dow Chemical Co.
The second ethylene-alpha olefin copolymer of the core
layer 30 is a single-site catalyzed copolymer having a melt index (190°C) of
about 2-10 grams/10 min., a density of about 0.905-0.915 grams/cm3, and
a comonomer content of about 5-25% by weight. The comonomer may be an alpha-olefin
having 3-12 carbon atoms, desirable 6-8 carbon atoms. One suitable second ethylene-alpha
olefin copolymer is Exxon-Mobil 2MO65, available from the Exxon-Mobil Chemical Co.
The first and second ethylene alpha-olefin copolymers forming
the matrix 32 may be present in a weight ratio of about 10-90 parts by weight first
ethylene-alpha olefin copolymer to about 10-90 parts by weight second ethylene-alpha
olefin copolymer, suitably about 50-80 parts by weight first ethylene-alpha olefin
copolymer to about 20-50 parts by weight second ethylene-alpha olefin copolymer,
desirably about 60-70 parts by weight first ethylene-alpha olefin copolymer to about
30-40 parts by weight second ethylene-alpha olefin copolymer.
In addition to the polymer matrix 32, the core layer 30
includes a particulate filler, suitably a particulate inorganic filler, shown as
filler particles 36 in FIG. 1. Suitable inorganic fillers include without limitation
calcium carbonate, clays, silica, alumina, barium sulfate, sodium carbonate, talc,
magnesium sulfate, titanium dioxide, zeolites, aluminum sulfate, diatomaceous earth,
magnesium sulfate, magnesium carbonate, barium carbonate, kaolin, mica, carbon,
calcium oxide, magnesium oxide, aluminum hydroxide and combinations of these particles.
The mean diameter for the inorganic filler particles 36 should range from about
0.1-10 microns, alternatively about 0.5-7.0 microns, alternatively about 0.8-2.0
The core layer 30 of breathable viral barrier film 20 should
include about 25-80% by weight polymer matrix and about 20-75% by weight filler
particles, suitably about 30-60% by weight polymer matrix and about 40-70% by weight
filler particles, desirably about 40-50% by weight polymer matrix and about 50-60%
by weight filler particles. The voids 34 surrounding the filler particles 36 typically
each have a dimension in at least one direction which is larger than the corresponding
dimension of the enclosed filler particle(s), caused by stretching of the film in
at least one direction as described below.
The core layer 30 also includes at least 0.5% by weight
of a fluorochemical. The maximum level is governed by the level of barrier properties
desired. Suitably, the core layer includes 0.5-5.0% by weight of the fluorochemical,
desirably about 1.0-4.0% by weight of the fluorochemical, particularly about 2.0-3.0%
by weight of the fluorochemical. The amount and type of fluorochemical should be
selected so as not to render the overall film 20 oleophobic, i.e., so that the film
20 is oleophilic. A film 20 is considered to be oleophilic if the film is wet by
an oil such as mineral oil. One way to determine if a microporous film is oleophilic
is to run the oil droplet test described below. If a film 20 is oleophilic, droplets
of mineral oil applied to one film surface will initially wet the surface and subsequently
enter the tortuous path created by the micropores in the film. The mineral oil will
subsequently wet and travel through the micropores until some of the oil finally
reaches the opposite surface of the film.
A film which is oleophobic, on the other hand, will not
be wet by mineral oil applied during the oil droplet test. Oil droplets will typically
remain on one surface of an oleophobic film, forming coherent beaded drops which
do not enter the micropores and do not diffuse through the film. Whether or not
a fluorochemical renders a film oleophobic is believed to be a function of the amount
and type of the fluorochemical in the film, and the extent to which the fluorochemical
migrates out of the layer in which it is placed and becomes concentrated at either
film surface. For purposes of the present invention, the fluorochemical desirably
has limited or no tendency to migrate out of the layer in which it is placed. If
the fluorochemical does migrate, it should be of a type and in an amount so that
the film remains oleophilic notwithstanding the migration of fluorochemical.
The fluorochemical used in the core layer 30 should also
be devoid of sulfonamide linkages. A sulfonamide linkage is exemplified in a fluorochemical
oxazolidinone represented by the following formula:
Fluorochemicals which are devoid of sulfonamide linkages
can be prepared using a telomerization process. An exemplary telomerization process
is represented by the following sequence of equations used to synthesize the fluorinated
alkyl alcohols, as follows:
Organofluorine Chemistry: Principles And Commercial Applications, edited by
R.B. Banks et al., Plenum Press, N.Y. 1994
Fluorochemicals made by a telomerization process are herein
referred to as telomerized fluorochemicals. Other fluorochemicals may also be used.
An additive available from E.I. DuPont deNemours & Co. ("DuPont") is ZONYL™
FTS, a 2-perfluoroalkylethyl stearate. A fluorochemical from DuPont has been compounded
at a 20% level into DOWLEX® 2244A (linear low density polyethylene)
and is referred to as TLF-9536. Fluorosilicones and f]uoroaUoys are also useful
in the invention. Specific useful fluorochemicals are described in
U.S. Patents 5,145,727, issued to Potts et al.
5,459,188, issued to Sargent et al
6,203,889, issued to Quincy III et al
In addition to the core layer 30, the breathable viral
barrier film 20 includes two outer skin layers. Each skin layer 10 includes a polymer
matrix 12. The matrix 12 of the skin layers is preferably formed of a thermoplastic
olefin polymer or polymer combination which facilitates thermal bonding of the breathable
film 20 to one or more nonwoven webs using a thermal bonding process, such as a
calender bonding process, without compromising the breathability or viral barrier
of the film 20. Suitable skin layer polymers include heterophasic propylene-ethylene
copolymers, propylene-ethylene random copolymers, ethylene vinyl acetate, ethylene-methyl
acrylate, amorphous (Ziegler-Natta or single-site catalyzed) ethylene-alpha olefin
copolymers having densities of about 0.89 grams/cm3 or less, amorphous
poly-alpha olefin (APAO) polymers which can be random copolymers or terpolymers
of ethylene, propylene and butene, other substantially amorphous or semi-crystalline
propylene-ethylene polymers, and combinations of the foregoing.
In one suitable embodiment, the polymer matrix 12 of each
skin layer 10 includes a mixture of a heterophasic propylene-ethylene polymer and
an additional random propylene-ethylene copolymer. Heterophasic propylene-ethylene
copolymers are available from Basell USA, Inc. ("Basell") under the trade name ADFLEX®.
Heterophasic polymers are reactor combinations of different polymer compositions
produced, in sequence, in the same reactor and combined together. Heterophasic propylene-ethylene
polymers are described in
U.S. Patent 5,300,365 to Ogale
(herein incorporated by reference), as having the following general composition:
- (a) from about 10 to 50 parts of a propylene homopolymer having an isotactic
index greater than 80, or a copolymer of propylene with ethylene and/or an another
alpha-olefin, containing over 80% propylene and having an isotactic index greater
- (b) from about 5 to 20 parts of a semi-crystalline copolymer fraction, (b) which
copolymer is insoluble in xylene at room or ambient which copolymer is insoluble
in xylene at room or ambient temperature; and
- (c) from about 50 to 80 parts of a copolymer fraction of ethylene with propylene
and/or another alpha-olefin, and optionally with minor amounts of a diene, said
copolymer fraction containing less than 40% ethylene and/or other alpha-olefin,
being soluble in xylene at room temperature, and having an intrinsic viscosity from
1.5 to 4 dl/g.
One suitable heterophasic propylene-ethylene copolymer
is Basell ADFLEX® KS359. This polymer contains about 14% by weight
ethylene and about 86% by weight propylene overall, has a melt flow rate (230°C)
of 12 grams/10 min., and includes three propylene-ethylene copolymer fractions as
The additional random propylene-ethylene copolymer may
include about 90-98% by weight propylene and about 2-10% by weight ethylene, desirably
about 92-96% by weight propylene and about 4-8% by weight ethylene. One suitable
random copolymer is Union Carbide 6D82, which has an ethylene content of about 5.5%
by weight and a melt flow rate (230°C) of 7 grams/10 min.
The polymer matrix 12 may include about 50-95 parts by
weight of the heterophasic propylene-ethylene copolymer and about 5-50 parts by
weight of the additional random copolymer, suitably about 60-90 parts by weight
heterophasic propylene-ethylene copolymer and about 10-40 parts by weight of the
additional random copolymer, desirably about 70-85 parts by weight heterophasic
propylene-ethylene copolymer and about 15-30 parts by weight of the additional random
If the skin layers 10 are very thin, they need not include
filler particles in the matrix. Desirably, the skin layers 10 will include filler
particles 14. Suitable filler particles 16 include any of the filler particles listed
above for the core layer 30. Each skin layer 10 may include about 25-80% by weight
polymer matrix and about 20-75% by weight filler particles, suitably about 30-60%
by weight polymer matrix and about 40-70% by weight filler particles, desirably
about 40-50% by weight polymer matrix and about 50-60% by weight filler particles.
The voids 14 surrounding the filler particles 16 typically each have a dimension
in at least one direction which is larger than the corresponding dimension of the
enclosed filler particle(s), caused by stretching the film as described below.
The skin layers 10 need not include a fluorochemical. However,
it is likely that some fluorochemical from the core layer 30 will migrate to the
skin layers 10. To help preserve the oleophilic and bonding characteristics of the
film 20, the skin layers 10 should contain less than 0.5% by weight fluorochemical,
suitably less than 0.3% by weight fluorochemical, desirably less than 0.1 % by weight
fluorochemical. This way, both skin layers desirably will have oleophilic outer
The core layer 30 of the breathable barrier film 20 should
constitute about 50-98% of the total film mass, suitably about 70-94% of the total
film mass, desirably about 80-90% of the total film mass. The skin layers 10 may
each constitute about 1-25% of the total film mass (2-50% combined), suitably about
3-15% of the total film mass (6-30% combined), desirably about 5-10% of the total
film mass (10-20% combined).
The film 20 is desirably prepared using a conventional
cast coextrusion process. Once the cast film is prepared, it can be stretched to
about 2-7 times its original length in at least one direction, desirably to about
3.5-4.5 times its original length in at least one direction, to cause voids to form
around the filler particles in the core and skin layers. The voids are separated
by thin polymer membranes, creating a tortuous path for permeability of water vapor
but blocking the passage of aqueous and low surface tension liquids. The stretching
may be performed in one direction, desirably the machine direction. The stretching
may be performed using two or more pairs of nipped draw rollers, with each successive
pair turning faster than the preceding pair. One or both draw rollers in each pair
may be heated, so that the film experiences a stretching temperature of about 65-100°C.
The stretched film may have a thickness of about 2-25 microns, suitably about 5-15
microns, desirably about 7-13 microns.
As shown in FIG. 2, the breathable viral barrier film 20
is bonded on at least one side, preferably both sides, to a nonwoven web or webs
40 to form a breathable viral barrier laminate 50. Each nonwoven web 40 may be a
spunbond web, a meltblown web, a bonded carded web, an air laid web, a foam, or
a laminate or composite including one or more nonwoven webs. Either nonwoven web
40 may also be formed or modified using a hydraulic entangling process. The nonwoven
webs 40 may be formed from a variety of thermoplastic polymers including without
limitation polyolefins, polyamides, polyesters, and copolymers and combinations
of these. Preferred polymers include polyolefins, such as polypropylene and/or polyethylene.
Other suitable polymers include copolymers of mainly ethylene and C3-C12
alpha-olefins, having a density of 0.900-0.935 grams/cm3, commonly known
as linear low density polyethylenes. Also included are copolymers of at least 90%
by weight propylene with not more than 10% by weight C2 or C4-C12
Each nonwoven layer 40 may have a basis weight of about
5-50 grams/m2, suitably about 10-40 grams/m2, desirably about
20-30 grams/m2. In one suitable embodi-ment, the nonwoven layer 40 on
one side of the film 20 is a spunbond web, and the nonwoven layer 40 on the other
side of the film 20 is a spunbond-meltblown-spunbond ("SMS") laminate. The individual
spunbond layer is formed from a polypropylene homopolymer or random propylene-ethylene
copolymer including up to 10% by weight ethylene. The polypropylene homopolymer
or copolymer may have a melt flow rate (230°C) of about 2-50 grams/10 min.
The spunbond and meltblown layers in the SMS laminate are also formed from a polypropylene
homopolymer or random propylene-ethylene copolymer containing up to 10% by weight
ethylene, and having a melt flow rate (230°C) of about 2-50 grams/10 min. One
example is when the nonwoven layers 40 and film 20 are laminated together by passing
the layers between heated nip rollers, one of which has an embossing pattern, to
thermally bond the layers at multiple points constituting about 12-18% of the interfacial
area. Alternatively, the layers can be laminated using adhesive or ultrasonic bonding.
FIG. 3 illustrates a process for making a breathable, viral
barrier laminate 50. Precursor multilayer film 18 is formed using a cast coextrusion
process 22. The film is quenched, and is then heated and stretched in the machine
direction using stretching apparatus 24 to form breathable microporous viral barrier
film 20. First nonwoven web 40 may be separately formed, and is forwarded using
conveyor apparatus 25 whereupon the nonwoven web may be treated with antistat, surfactants
and/or other ingredients using dispensers 25A and 25B. Second nonwoven web 40 may
be separately formed, and is forwarded using conveyor apparatus 26 whereupon it
may be treated with antistats, surfactants and/or other ingredients using dispensers
26A and 26B. The nonwoven webs 40 and film 20 are joined, with the film sandwiched
between the two nonwoven webs, using a calender nip assembly including first and
second nip rollers 80 and 82.
As shown in FIG. 3, bonding roll 80 can be a pattern roll,
whereas second bonding roll 82 is a smooth (anvil) roll. Both rolls are driven by
conventional means, such as, for example, electric motors (not shown). Pattern roll
80 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
80 has on its outermost surface a pattern of raised bonding areas. 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 80
form a nip with the smooth or flat outer surface of opposed positioned anvil roll
82; which 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
The pattern of raised bonding areas on the pattern roll
80 is selected such that the area of at least one surface of the resulting barrier
material 50 occupied by bonds after passage through the nip formed between pattern
rolls 80, 82 ranges from about 10 percent to about 30 percent of the surface area
of the barrier material. The bonding area of the barrier material 50 can be varied
to achieve the above-mentioned percent bond area, as is known in the art.
The temperature of the outer surface of the pattern roll
80 can be varied by heating or cooling relative to the smooth roll 82. Heating and/or
cooling can affect, for example, the degree of lamination of the individual layers
forming the barrier material 50. Heating and/or cooling of pattern roll 80 and/or
smooth roll 82 can be effected by conventional means (not shown) well known in the
art. The specific ranges of temperatures to be employed in forming the barrier material
50 are dependent on a number of factors, including the types of polymeric materials
employed in forming the individual layers of the barrier material 50, the dwell
time of the individual layers within the nip and the nip pressure between the pattern
roll 80 and anvil roll 82. After barrier material 50 exits the nip formed between
the bonding rolls 80, 82, the material 50 can be further compressed and guided using
nip rollers 81 and 83, and wound onto roll 84 for subsequent processing.
Modifications in the above-described process will be readily
apparent to those of ordinary skill in the art without departing from the scope
of the present invention. For example, after the barrier material 50 is formed,
it can continue in-line for further processing and converting. Different apparatus
can be used for stretch-thinning the film 20. Other known means for bonding and
laminating the film 20 to nonwoven layers 40 may be used, provided the resulting
barrier material 50 has the required properties described herein. Finally, formation
of the film 20 and/or nonwoven layers 40 can take place at a remote location, with
rolls of the individual layers unwound and fed to the nip formed between pattern
roll 80 and smooth roll 82. Also, for certain applications, it is advantageous to
have a two component material which can be formed as above described by omitting
one of the nonwoven webs, for example. Also, nonwoven layers 40 may either be thermally
or adhesively laminated to the stretch-thinned film to form the composite.
The breathable viral barrier film 20 and/or laminate 50
may be used in a wide variety of surgical articles to provide improved viral barrier
properties, especially when exposed to low surface tension liquids. Surgical articles
include surgical gowns, drapes, face masks, scrubs, sterile wrap, sterilization
peel pouches, fenestration materials, and the like. The breathable viral barrier
film and/or laminate may also be used as personal protective clothing in applications
such as workwear, laboratory applications, clean room applications such as semiconductor
manufacturing, agriculture applications, mining applications, environmental applications,
veterinary applications and the like.
WATER VAPOR TRANSMISSION RATE (WVTR)
A suitable technique for determining the WVTR (water vapor
transmission rate) value of a film or laminate material of the invention 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".
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, 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; Minnesota. A first test is made of the WVTR of the guard film
and the air gap between an evaporator assembly that generates 100% 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 the 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 CalC. 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 than 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:
- WVTR:The calculation of the WVTR uses the formula:
- F = The flow of water vapor in cc/min.,
- gsat(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,
- psat(T)=The saturation vapor pressure of water vapor at temperature
The hydrohead resistance is a measure ofliquid pressure
resistance, which is the ability of a film or laminate to withstand application
of a load of liquid without fracturing, bursting or tearing. The liquid pressure
resistance of a film or laminate depends on its thickness, material composition,
how it is made and processed, the surrounding environment and method of testing.
Hydrohead values are measured generally according to the Hydrostatic Pressure Test
described in Method 5514 of Federal Test Methods Standard No. 191A, which is equivalent
to AATCC Test Method 127-89 and INDA Test Method 80.4-92. The following additional
parameters are pertinent to this invention.
The repellency or barrier ("strikethrough resistance")
properties of a film or laminate of the invention are measured using hydrostatic
head tests with a low surface tension liquid (about 26.4 dynes/cm). A suitable low
surface tension liquid is an aqueous solution of SYNTHRAPOL®KB available
from ICI Americas in Wilmington, DE, diluted to about 0.1 %. The hydrohead method
utilizes a TEXTEST FX3000 Hydrostatic Head Tester under dynamic and static conditions.
Under the dynamic conditions, the specimens are subjected to a steadily increasing
pressure of the low surface tension liquid. The rate of increase is 60 mbar/minute
and the maximum pressure tested is 300 mbar (4 psi). The "strikethrough resistance"
is expressed as the pressure, or the time elapsed at 300 mbar, when the liquid penetrates
the sample. The test is completed after three areas have failed. The "static" conditions
involve subjecting the sample to the low surface tension liquid at a constant pressure
of 19 mbar. The "strikethrough resistance" is expressed as the time elapsed when
the liquid penetrates the sample. The test is completed after three areas have failed.
OIL DROPLET TEST
The oil droplet test is useful to determine whether a film
is oleophilic or oleophobic. The film sample is laid out on a table, and three or
more drops of mineral oil are added to the film surface at spaced apart locations.
One suitable mineral oil is sold by Eckerd Corporation under the name "mineral oil."
This test corresponds to American Association Of Textile Chemists And Colorists
(AATCC) Standard Test 118-1983. In regard to the standard test, mineral oil has
a repellency rating number of one, indicating relatively easy penetration tendency
compared to most other oils.
If the film is oleophobic, the oil droplets will not wet
the surface, and will remain as bead-shaped droplets having contact angles of generally
greater than 90 degrees with the film surface. If the film is oleophilic, the oil
droplets will spread out and wet the surface. The contact angles between the oil
and film surface will be generally less than 90 degrees after about 30 seconds of
contact. If the film is oleophilic and microporous, some of the oil will penetrate
the film and migrate to the other side.
Film samples having a core layer and two outer skin layers
were produced on a cast coextrusion line. The core layer of each film contained
DOWLEX®2244A LLDPE from Dow Chemical Co., Exxon-Mobil 2MO65 single-site
catalyzed ethylene-alpha olefin plastomer from Exxon-Mobil Chemical Co., FILMLINK™
2029, calcium carbonate from Imerys Co. of Roswell, Georgia, and a concentrate of
fluorochemical from E.1. DuPont deNemours & Co. compounded into DOWLEX®2244A
and referred to as TLF9536, in the following weight percentages. Antioxidants, heat
stabilizers, coolants and other additives, such as are supplied by Ciba Specialty
Chemicals, Inc., can also be added.
Core Layer Compositions,
% By Weight
For each film the core layer constituted 85% of the film
mass. The skin layers each constituted 7.5% of the total film mass, and had an identical
composition for all three films. Each skin layer contained 34% by weight Basell
ADFLEX® KS359, which is a heterophasic propylene-ethylene copolymer
combination containing 86% by weight propylene and 14% by weight ethylene. Each
skin layer also contained 8% by weight Union Carbide 6D82 random propylene-ethylene
copolymer (94.5% by weight propylene, 53% by weight ethylene), 57% by weight FILMLINK
2029 calcium carbonate, and 1% by weight additives.
FIG. 4 illustrates the WVTR vs. hydrohead using an aqueous
solution of SYNTHRAPOL® KB (about 26.4 dyne/cm surface tension)
for various breathable film samples. The straight line defined by the rectangular
points illustrates a general relationship between WVTR and hydrohead for generally
similar film samples with different levels of calcium carbonate and other ingredients.
Sample A, the control with 0% fluorochemical, exhibited a hydrohead resistance slightly
above the line. Samples B and C, having 2% and 4% fluorochemical in their respective
core layers, exhibited hydrohead resistances substantially above the line, and more
than 50% higher than the control. These data illustrate that the use of the selected
fluorochemical in the core layer of the three-layer breathable film provides substantially
increased resistance to penetration by low surface tension liquids. The inventive
films, and fabric laminates containing them, should thus exhibit improved resistance
to penetration by viruses in hospital environments where low surface tension liquids
While the embodiments of the invention disclosed herein
are presently considered preferred, various modifications and improvements can be
made without departing from the scope of the invention. The scope of the invention
is indicated by the appended claims.