U.S. patent application number 10/434552 was filed with the patent office on 2004-11-11 for nonwoven breathable composite barrier fabric.
Invention is credited to Bowen, Uyles W., Mathis, Michael P., Rotella, John A., Schild, Lisa A..
Application Number | 20040224596 10/434552 |
Document ID | / |
Family ID | 33416714 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040224596 |
Kind Code |
A1 |
Mathis, Michael P. ; et
al. |
November 11, 2004 |
Nonwoven breathable composite barrier fabric
Abstract
A breathable barrier material having a first nonwoven layer and
a first microporous film bonded together to form a composite
laminate. A second microporous film and a second nonwoven layer are
bonded to the composite laminate and second film to form the
barrier material such that the films are disposed between the
nonwoven layers. The composite laminate is bonded to the second
film and second nonwoven layer thereby creating 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.
Inventors: |
Mathis, Michael P.;
(Marietta, GA) ; Rotella, John A.; (Marietta,
GA) ; Bowen, Uyles W.; (Canton, GA) ; Schild,
Lisa A.; (Roswell, GA) |
Correspondence
Address: |
KIMBERLY-CLARK WORLDWIDE, INC.
401 NORTH LAKE STREET
NEENAH
WI
54956
|
Family ID: |
33416714 |
Appl. No.: |
10/434552 |
Filed: |
May 9, 2003 |
Current U.S.
Class: |
442/382 ;
428/196; 428/34.1; 442/110; 442/389; 442/394; 442/398; 442/400;
442/76 |
Current CPC
Class: |
B32B 2307/7265 20130101;
B32B 27/32 20130101; A61B 46/40 20160201; Y10T 442/2418 20150401;
Y10T 442/668 20150401; B32B 27/20 20130101; B32B 2535/00 20130101;
Y10T 442/2139 20150401; B32B 27/12 20130101; Y10T 442/68 20150401;
Y10T 442/678 20150401; B32B 37/0084 20130101; Y10T 442/674
20150401; B32B 2307/724 20130101; Y10T 428/13 20150115; Y10T
428/2481 20150115; Y10T 442/66 20150401; B32B 5/26 20130101 |
Class at
Publication: |
442/382 ;
428/196; 442/394; 442/389; 442/400; 442/398; 442/076; 442/110;
428/034.1 |
International
Class: |
B65D 001/00 |
Claims
We claim:
1. A breathable barrier material comprising: a first nonwoven
layer; a first microporous film bonded to the first nonwoven layer
to form a composite laminate; a second microporous film; and a
second nonwoven layer bonded to the composite laminate and second
film to form the barrier material.
2. The material of claim 1 wherein the first and second films are
disposed between the nonwoven layers.
3. The material of claim 1 wherein one of the nonwoven layers
comprises a spunbond web.
4. The material of claim 1 wherein the first and second nonwoven
layers comprise first and second spunbond webs.
5. The material of claim 1 wherein one of the nonwoven layers
comprises at least one layer of a meltblown polyolefin and at least
one layer of a spunbond polyolefin.
6. The material of claim 1 wherein one of the films comprises a
monolayer film.
7. The material of claim 1 wherein one of the films comprises a
multilayer film.
8. The material of claim 7 wherein the multilayer film comprises a
core layer constituting about 85% of the total film thickness and a
skin layer constituting about 15% of the total film thickness.
9. The material of claim 7 wherein the multilayer film comprises a
core layer constituting about 85% of the total film thickness and
two skin layers each constituting about 7.5% of the total film
thickness disposed on opposite sides of the core layer.
10. The material of claim 1 wherein one of the films comprises from
about 30% to about 75% by weight polyolefin resin and from about
70% to about 25% by weight of filler having an average size less
than about 10 microns.
11. The material of claim 7 wherein each of the film layers
comprise from about 30% to about 75% by weight polyolefin resin and
from about 70% to about 25% by weight of filler having an average
size less than about 10 microns.
12. The material of claim 1 wherein one of the films comprises from
about 30% to about 45% by weight polyolefin resin and from about
70% to about 55% by weight of filler.
13. The material of claim 7 wherein each of the film layers
comprise from about 30% to about 45% by weight polyolefin resin and
from about 70% to about 55% by weight of filler.
14. The material of claim 1 wherein the laminate has a water vapor
transmission rate of at least about 500 grams per square meter per
24 hours.
15. The material of claim 1 wherein the laminate has a water vapor
transmission rate of at least about 5000 grams per square meter per
24 hours.
16. The material of claim 1 wherein the laminate has a water vapor
transmission rate of from about 500 to about 5000 grams per square
meter per 24 hours.
17. The material of claim 1 wherein the nonwoven layers comprise
about 98% random copolymer of polypropylene and polyethylene with
1.5-3.5% ethylene content.
18. The material of claim 1 wherein one of the nonwoven layers
comprises an antistatic treatment.
19. The material of claim 1 wherein the material is thermally
bonded.
20. The material of claim 1 comprising a surgical gown.
21. The material of claim 1 comprising a surgical drape.
22. The material of claim 1 comprising a sterilization peel
pouch.
23. The material of claim 1 comprising an industrial protective
garment.
22. The material of claim 1 comprising a thermoplastic elastomeric
polyolefin.
24. The material of claim 1 comprising a personal care article.
25. The material of claim 1 comprising bonding the composite
laminate to the second film and second nonwoven layer so that the
material is breathable, maintains fluid barrier properties, and
passes bacteriophage testing in compliance with ASTM F
1671-97b.
26. The material of claim 1 comprising void spaces between the
first and second films.
27. The material of claim 1 comprising thermally bonding the
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.
Description
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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, such as semiconductor manufacturing,
agriculture applications, mining applications, environmental
applications, and the like.
[0007] 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
[0008] 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
film and a second nonwoven layer are bonded to the composite
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.
[0009] 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 75% by weight polyolefin resin and from about 70% to
about 25% by weight of filler.
[0010] 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.
[0011] 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.
[0012] 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
elastomeric polyolefin is desirable.
[0013] These and other objects are achieved by the improved
cloth-like, liquid-impervious, breathable barrier material
disclosed and claimed herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross-sectional view of an exemplary barrier
material of the present invention.
[0015] 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.
[0016] FIG. 3 is a schematic view of a process for making the FIG.
1 barrier material.
[0017] FIG. 4 is a SEM Micrograph of the FIG. 1 barrier material at
50.times. magnification.
DETAILED DESCRIPTION OF THE INVENTION
[0018] 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 18
formed, for example, of spunbond filaments, a first middle
breathable film 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.
[0019] 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 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.
[0020] 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 and 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.
[0021] 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
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. 3,802,817 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.
[0022] 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.
[0023] 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
bonding nip. Alternatively, the anvil roll may 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.
[0024] 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.
[0025] 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 10 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 may 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.
[0026] 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 and propylene monomers, and blends of
such copolymers with polyethylenes or polypropylenes or suitable
amorphous polymers, semi-crystalline/amorphous polymers,
"heterophasic" polymers, or combinations thereof. Examples of
useful polymers are EXXPOL.RTM., EXCEED.RTM., and EXACT.TM.
polymers from Exxon Chemical Company of Baytown, Tex.; ENGAGE.RTM.,
ACHIEVE.RTM., ATTAIN.RTM., AFFINITY.RTM., and ELITE.RTM. polymers
from Dow Chemical Company of Midland, Mich.; CATALLOY.RTM. polymers
from Basell USA Inc. of Wilmington, Dela.
[0027] 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.
[0028] 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 film polymer extrusion blend, will not chemically
interfere with the extruded film, but are able to be uniformnly
dispersed throughout the film. 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 7
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
(CaCO.sub.3), various kinds of clay, silica (SiO.sub.2), alumina,
barium carbonate, sodium carbonate, magnesium carbonate, talc,
barium sulfate, magnesium sulfate, aluminum sulfate, titanium
dioxide (TiO.sub.2), 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.
[0029] 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 outlined herein and then
heated and extruded into a monolayer or multilayer film as
required. In order to provide uniform breathability as reflected by
the water vapor transmission rate of the film, 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/m.sup.2/24 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/m.sup.2/24 hours), and still other
embodiments contemplate water vapor transmission rates of at least
5000 grams per square meter per 24 hours (g/m.sup.2/24 hours).
[0030] 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 thinning, its weight per unit area will be
from about 10 gsm to about 25 gsm.
[0031] 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.
[0032] 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 films 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 multilayer film 10 has an overall
thickness 38.
[0033] 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.RTM., from about 7% to about 10%
polypropylene random copolymer (RCP), and from about 57% to about
70% by weight particulate calcium carbonate. The core layer 22
constitutes about 85% of the total film thickness 38.
[0034] 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 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.
[0035] Each film as initially formed generally is thicker and
noisier than desired, as it tends to make a "rattling" sound when
shaken. Moreover, each film 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.degree. 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 (2.times.) its
original length to thin the film and render it porous. Further
stretching of the films 14, 16, to about three times (3.times.),
four times (4.times.), or more, their original length is expressly
contemplated in connection with forming films 14 and/or 16 of the
present invention.
[0036] 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 film 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.
[0037] 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 film to an effective gauge of 0.6 mil or less. One
type of suitable film stretching apparatus is a Machine Direction
Orienter unit, Model No. 7200, available from the Marshall &
Williams Company, having offices in Providence, R.I.
[0038] 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.
[0039] 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.
[0040] 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.
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.
[0041] 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.
[0042] In accordance with one embodiment of this invention, bonding
may be accomplished using a Ramisch bond pattern. The Ramisch bond
pattern has a bond area of about 8% to about 14%, a pin density of
about 52 pins/in.sup.2, 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.
[0043] The second film 16 and nonwoven layer 18 may be formed from
similar 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.
[0044] It should be apparent that the composite laminate 52 is thus
double bonded whereas the film 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 material 10 and may serve to trap such liquids
and/or viral components between the films 14 and 16.
[0045] 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 barrier 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 films 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 manner
bonding is accomplished, the existence of the voids between films
should be maintained.
[0046] 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.
[0047] Test Procedures
[0048] The following test procedures were used to analyze the
sample and comparative barrier materials identified below.
[0049] Mocon Water Vapor Transmission Rate Test
[0050] 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.
[0051] 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.
[0052] The sample holder is known as the Permatran-W model 100K
manufactured by Mocon/Modern Controls, Inc, Minneapolis, Minn. 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.
[0053] 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 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:
TR.sup.-1.sub.test material=TR.sup.-1.sub.test material, guardfilm,
airgap-TR.sup.-1.sub.guardfilm, airgap
[0054] Calculations:
[0055] WVTR: The calculation of the WVTR uses the formula:
WVTR=F.rho..sub.sat(T)RH/Ap.sub.sat(T)(1-RH))
[0056] where:
[0057] F=The flow of water vapor in cc/min.,
[0058] .rho..sub.sat(T)=The density of water in saturated air at
temperature T,
[0059] RH=The relative humidity at specified locations in the
cell,
[0060] A=The cross sectional area of the cell, and,
[0061] .rho..sub.sat(T)=The saturation vapor pressure of water
vapor at temperature T.
EXAMPLE
[0062] A barrier material according to the present invention was
made. The film formulation was cast into a multilayer film 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.RTM., from about 7% to about 10% polypropylene
random copolymer (RCP), and about 57% by weight particulate calcium
carbonate. The core layer constituted about 85% of the total film
thickness. The CaCO.sub.3 in the core and skin layers was coated
with from about 0.5 to 3.0% behenic acid based upon the weight of
the CaCO.sub.3, having a 0.9 to 1.3 micron average particle size
and a top cut of 8 microns.
[0063] The spunbond facing layers were both 0.60 ounces per square
yard nonwoven webs formed from extrudable thermoplastic resins of
homopolymer polypropylene from BP/Amoco 2% titanium dioxide
(white), 0.09% anti-static compound and 0.91 SCC 11111 blue color
concentrate. The spunbond filaments were essentially continuous in
nature and had an average fiber size of 2.0 dpf.
[0064] One of the films and nonwoven layers were laminated together
to form an 18.5 g/m.sup.2 composite laminate having a MOCON value
of 7466 g/m.sup.2/24 hr using Ramisch pattern thermal bonding
rolls, as described herein. The pattern roll had a bonding
temperature of about 185.degree. F. and the smooth anvil roll had a
temperature of about 145.degree. F. The nip pressure formed between
the rolls was about 440 psig. The second film alone had a basis
weight of 18.75 g/m.sup.2 and together with the second nonwoven
layer in an unbonded configuration had a MOCON value of 6293
g/m.sup.2/24 hr. 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.sup.2/24 hr was created. However,
this test run did not reach the desired target range for
breathability of 5500 g/m.sup.2/24 hr. 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.
[0065] 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.sup.2/24
hr, and the bacteriophage results were 31 out of 32 samples passing
the test.
[0066] 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 limits of the appended
claims.
* * * * *