Note: Descriptions are shown in the official language in which they were submitted.
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Kappler.9 PATENT
BREATHABLE COMPOSITE BARRIER FABRIC
Background of the Invention
This invention relates to breathable composite barrier
fabrics which are impervious to water-based li~uids but which
allow passage of water vapor. Applications for such fabrics
exist in the field of protective garments for medical
technicians, laboratory workers, and the like where it is desired
to prevent passage of blood or other body fluids to the body of
the worker or from the worker to the patient while allowing
passage of water vapor. Garments with such characteristics
provide enhanced comfort for the wearer by allowing perspiration
to escape, consistent with maintaining a barrier to passage of
liquids.
Breathable multi-layer barrier fabrics of various
combinations of layered material are disclosed in prior art
patents. U.S. Patent No. 4,041,203, issued August 9, 1977, to
Brock et al., discloses a fabric made up of a mat of generally
discontinuous thermoplastic microfibers as a top layer and a web
of substantially continuous, randomly deposited pol~mer filaments
as a bottom layer, the layers being bonded at intermittent
discrete regions. A three-layer fabric having a mat layer on the
outside and a web layer in the middle is also disclosed. The
specific polymer materials used for the mat and the web include
polyolefins such as polypropylene. U.S. Patent No. 4,828,556,
issued May 9, 1989, to Braun et al., discloses a multi-layer
fabric having a first layer of porous melt-blown material, a
second layer comprised of a non-microporous film of polyvinyl
alcohol, and a third layer of porous non-woven material in the
form of a spun-bonded or melt-blown web. The fabric of this
reference is said to be useful for absorbent articles such as
diapers. Numerous prior patents directed to microporous films
are also disclosed and discussed in this reference. Impervious,
absorbent barrier fabrics are disclosed in U.S. Patent No.
4,379,192, issued April 5, 1983, to Wahlquist et al., the fabric
including layers having continuous filament webs, microfiber
mats, and polymeric film, the mats providing an uncompacted
absorbent center layer. While numerous combinations of layers of
various polymeric materials prepared in a desired physical form
are disclosed in these references, the combination of an inner
layer of microporous film and outer layers of spun-bonded
material as disclosed herein is not known by applicant to have
been disclosed or suggested by the prior art.
A breathable fabric for protective garments of the type
mentioned above should provide for wearer comfort by enabling
passage of water vapor resulting from perspiration or humidity in
the environment, as well as forming a barrier to passage of
liquid water or water-based liquid such as blood or other bo~y
fluids. For effectiveness in situations involving handling of a
bleeding patient, the barrier should be effective at elevated
pressure such as two psig to prevent the blood from being
projected through the fabric. In addition, strength and
durability are desired in the fabric as exemplified by tensile
strength of at least 30 pounds and a Mullen burst value of at
least 50 psi. Other characterstics need for such fabric include
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a relatively low cost obtainable by use of readily available
inexpensive materials for the various layers and amenability to
preparing the fabric and making garments by inexpensive methods.
Also, a cloth-like taxture and feel are n~eded to encourage
wearing of the garment.
Summary _ the Inventio_
The present invention is directed to breathable composite
fabrics made up of an inside layer of a film of polyolefin
material in microporous form sandwiched between layers of spun-
bonded polyolefin webs. Desired characteristics of the fabricsin terms of vapor transmission, liquid water blockage, and
necessary strength are obtained by selecting materials having
specified physical properties for the respective layers. The
layers are bonded to one another by ultrasonic bonding at spaced-
apart points.
Fabrics embodying the invention are effectiv~ for use inprotectivè garments where stoppage of fluids such as blood is
required, along with enhanced comfort and breathability of vapors
produced by perspiration. The fabric may be made up of readily
available inexpensive materials for the respective layers, and
they are readily fabricated using simple methods.
It is, therefore, an object of this invention to provide a
composite fabric that is permeable to water vapor but that serves
as a barrier against passage of water-based fluids.
Another object is to provide such a fabric that provides a
barrier to passage of blood at slightly elevated pressure.
Yet another object is to provide a breathable composite
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fabric that may be manufactured at low cost from readily
available layer materials. -
Other objects and advantages of the invention will beapparent from the following detailed description and the appended
claims.
Brief Description of the Drawings
Fig. l is a diagrammatic representation of a cross-sectional
view of a multi-layer composite fabric embodying the invention.
Fig. 2 is a schematic fragmentary perspective view, with
poxtions peeled away, of the fabric o~ Fig. 1.
Description of the Preferred Embodiment
Referring to the drawings, there i5 shown a breathable
composite fabric 10 made up o~ three layers, a top layer 12 of a
spun-bonded polyolefin, a middle layer 14 of a microporous
polyolefin film, and a bottom layer 16 of spun-bonded polyolefin.
The three layers are secured to one another by ultrasonic bonding
at spaced-apart points 1~ throughout the fabric surface.
Top layer 12 may comprise a spun-bonded polyolefin, with
polypropylene being the preferred material. Polyethylene may
also be used. The polypropylene material may have a weight of
one-half to two ounces per square yard, with one ounce being
particularly preferred. The spun-bonded layers provide strength
to the composite fabric, along with a cloth-like surface texture
which enhances its use for garments, as contrasted with film
materials which have a smooth plastic surface. Spun-bonded
polypropylene suitable for this purpose is available from Poly-
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Bond, Inc., under thP designation Poly-bond. Properties of this
material are as follows: weight, 1 ounce per square yard;
thickness, 7.g mils; air permeability, 465 cubic feet air flow
per square yard; Mullen burst, 43; grab strength, machine
direction, pounds to break, 25; cross direction, 17, elongation,
percent, machine direction, 75; cross direction, 17, and
trapezoidal tear strength, machine direction, 7.2 pounds; cross
direction, 4.25 pounds.
The bottom layer 16 may have the same composition as top
layer 12, although material having a lighter weight such as 0.5
ounce per square yard may be used to reduce the overall fabric
weight.
The middle layer 14 may comprise a microporous film of a
polyolefin and preferably propylene. Polyethylene may also be
used. The polypropylene films have a microporous structure with
extremely small random pores 20 extending through the film
matrix, allowing vapor such as water vapor to pass through, while
forming a barrier to pass~ge of liquids. A suitable film
material is available from 3M Disposable Products Division under
the designation, "Scotch~ microporous film.~ Properties of a
designated film suitable for use in this invention are as
follows: thickness, 1.5 mil; weight, 0.85 ounce per square yard;
tensile strength at break (DPD Test Method 106), machine
direction, 2,000g/25mm; cross direction, 950 grams/25mm;
elongation at break (DPD Test Method 106), machine direction,
greater than 100 percent, cross direction, greater than 100
percent. Permeation/barrier properties include a moisture vapor
transmission rate of greater than 5,000 grams per square meter at
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75 F. and 50 percent relative humidity as measured by theinverted cup method; air permeability, less than 400 seconds/50
cc by Gurley Densometer~ measurement and water hold-out, greater
than 65 pounds per square inch as measured by Mullen burst test.
Other microporous films having a transmission rate of greater
than 1,500 b/m2/24 hr. at 86 F. and 48 percent relative humidity
as measured by ASTM E96 and water holdout greater than 50 psi are
acceptable.
Composite fabrics may be prepared by forming a stacked array
of the respective layers and bonding them together under heat and
pressure at discrete, spaced-apart sites by use of ultrasonic
point bonding techniques such as pinsonic bonding. This produces
a strong and durable fabric, consistent with the avoidance of
creating enough fused axeas to interfere with vapor transmission.
The invention is illustrated by the following example:
A composite three-layered fabric was prepared by providing a
stacked array having a middle layer of a 1.5 mil thick layer of
microporous polypropylene film and top and bottom layers of 1.0
oz./square yard spun-bonded polypropylene material and securing
the layers together by ultrasonic point bonding. Samples of ~he
fabric were subjected to liquid penetration tests by being
exposed to a liquid for 5 minutes at atmospheric pressure, one
minute at 2 psig, and 54 minut~s at atmospheric pressure. For
liquid tap water t73 dynes/cm), no penetration was observed.
Liquid synthetic blood (40 dynes/cm) showed no penetration under
the same test conditions, except for one failure out of 10
samples when exposed for 2 minutes at 2 psig, this failure
resulting from an apparent pin hole. Liquid isopropyl alcohol
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showed no penetration at 5 minutes under atmospheric pressure but
did show penetration at 2 minutPs under 2 psig.
Strength properties of samples of the fabria were determined
using test methods specified in ASTM D-751. Results obtained
were as follows: Mullen burst (psi) 75.0; tensile test (pounds)
(machine direction) 39.6; (cross direction) 39.6; trap tear
(pounds) (machine direction) 23.4; (cross direction) 15.6.
Moisture vapor transmission rates through the fabric were
determined by exposing a sample to 50 percent relative humidity
air at 86.4 F, using ASTM E96 test procedure. A transmission
rate of 1973 g/m2/24 hrs. was obtained. The results obtained
demonstrate effectiveness of the fabric in terms of providing a
barrier to water-based liquids while allowing transmission of
water vapor such as to enable breathability.
The above example is not to be understood as limiting the
scope of the invention, which is limited only as indicated by the
appended claims.
