Note: Descriptions are shown in the official language in which they were submitted.
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NONWOVEN FILLER LAMINATE WITH BARRIER PROPERTIES
BACKGROUND OF THE INVENTION
The present invention is directed to a single-use, disposable absorbent
laminate containing a
nonwoven web bonded to a breathable film. Such laminates have a wide variety
of uses, especially
in the areas of limited use and disposable items including, but not limited
to, surgical and health
care related products such as surgical drapes and gowns, disposable work wear
such as coveralls
and lab coats and personal care absorbent products such as diapers, training
pants, incontinence
garments, sanitary napkins, bandages, wipes and the like. Many of these
products require highly
engineered components and yet, at the same time, are required to be limited
use or disposable
items. By limited use or disposable, it is meant that the product and/or
component is used only a
small number of times or possibly only once before being discarded.
For example, surgical drapes have been designed to greatly reduce, if not
prevent, the transmission
of liquids through the surgical drape. In surgical procedure environments,
such liquid sources
include patient liquids such as blood, saliva and perspiration, and life
support liquids such as
plasma and saline. In earlier times, surgical drapes were made of cotton or
linen. Surgical drapes
fashioned from these materials, however, permitted transmission or "strike-
through" of various
liquids encountered in surgical procedures. In these instances, a path was
established for
transmission of biological contaminates, either present in the liquid or
subsequently contacting the
liquid, through the surgical drape. Additionally, in many instances, surgical
drapes fashioned from
cotton or linen provided insufficient barrier protection from the transmission
therethrough of
airborne contaminates. Furthermore, these articles were costly, and of course
laundering and
sterilization procedures were required before reuse.
Presently, disposable surgical drapes have largely replaced linen surgical
drapes. Advances in such
disposable surgical drapes include the formation of such articles from liquid
absorbent fabrics
and/or liquid impervious films which prevent liquid strike-through. For
example, see JP 8080318
assigned to Kyowa Hakko Kogyo K K; U.S. Pat. No. 5,546,960 assigned to
Molnlycke A B; and
WO 96/09165 assigned to Exxon. In this way, biological contaminates carried by
liquids are
prevented from passing through such fabrics. However, in some instances,
surgical drapes formed
from absorbent fabrics and/or liquid impervious films sacrifice other drape
properties, such as
meeting Class 1 flammability requirements per NFPA 702-1980, tear strength,
being relatively "lint
free" i.e., not containing loose fibrous elements. Class 1 flammability
requirements are met when a
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material takes 20 seconds or greater for a flame from a standardized ignition
source to spread 5
inches according to NFPA 702-1980 test conditions.
In some instances, surgical drapes fashioned from liquid absorbent fabrics
alone, such as fabrics
formed from hydrophilic fibers, sufficiently absorb liquids and are more
breathable than nonporous
materials. However, the breathability provided by such nonwoven fabrics has
generally occurred at
the expense of liquid barrier properties of the drape. The desire for improved
liquid absorptivity and
fluid impervious barrier properties has resulted in the lamination of
absorbent nonwoven webs to
various film or barrier layers. One commercially available application of this
configuration is used
in the creation of surgical drapes. The surgical drape sold under the
tradename Klinidrape~ and
assigned to Molnlycke AB, is believed to comprise a liquid absorbent nonwoven
top sheet
containing inherently hydrophilic rayon staple (discontinuous) fibers, a fluid-
impermeable
intermediate sheet of polyethylene, a bottom sheet of cellulose, and adhesive
components to attach
the top and bottom sheets to the polyethylene sheet. Although the above
described Klinidrape~ has
liquid absorptivity and fluid impermeability, the drape produces relatively
numerous lint particles,
relies upon adhesive type bonds, and does not pass the Class 1 flammability
requirements of NFPA
702-1980.
For such drapes the lamination of nonwoven fabrics to films improves the
strength and fluid barrier
attributes. Spunbonded fabrics containing continuous synthetic filaments have
been laminated with
films for consideration in surgical drape applications. Such laminate fabrics
do not drastically
increase the drape density and are relatively low in cost. One such laminated
fabric, comprising a
multilayer film bonded to a support layer, such as a hydrophobic spunbonded
fabric layer, is
disclosed in GB 2296216, which is assigned to Kimberly-Clark Worldwide, and is
described as
having applications for surgical drapes. However, since the spunbonded fabric
component of the
above laminate fails to exhibit hydrophilic properties, the drapes made from
such laminate fabric
lack fluid absorbency.
Another laminate, disclosed in WO 96/09165 and assigned to Exxon, comprises a
microporous film
adhesively bonded between an outer nonwoven layer containing hydrophobic
spunbonded filaments
and a hydrophilic nonwoven inner layer. With respect to applications as
surgical drapes, the film
component provides a barrier to fluid, while the spunbonded component provides
strength to the
drape. This laminate, however, utilizes adhesive bonding to attach the film to
the nonwoven
substrate.
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Microporous films are well known in the art and in some embodiments typically
consist of a film
containing some quantity of a particulate filler material dispersed therein.
These films with
particulate filler material are known as filled films. Under typical
processing conditions for making
a filled film microporous, the particulate filled films are stretched and/or
crushed between
compression rollers so as create voids in and around the particles. This
renders the films breathable
and permits the transmission of water vapor and other gases through micropores
developed in and
through the film in the regions containing and proximate to the voids while
normally inhibiting the
transmission of liquids such as water. Filled films treated in the stretching
manner typically result in
breathable films having water vapor transmission rates of at least 300 grams
per square meter per
24 hours (300 g/mz/24 hrs).
One approach to facilitate processing and the subsequent lamination of filled
films to other
materials constructions is to form surface or "skin" layers on one or both
sides of the filled film.
Frequently these additional film layers have lower amounts of filler content
or are monolithic film
layers, or are combinations of both. Such multilayered filled films comprise
base or "core" layers
that contain pore developing fillers and skin layers that optionally contain
such pore developing
fillers or other fillers and additives. Typically the core layers provide the
bulk of the strength and
barrier attributes of the entire film while the skin layers contribute but
provide additional desired
attributes. Stretching and/or crushing processing conditions performed on
these films can also
render them films breathable. For a multilayered filled film with pore
developing fillers in all layers
stretching and/or crushing creates voids around the particles as described
above and examples of
such films are described in U.S. 6,045,900 by Haffner, et al. For a
multilayered filled film with
reduced, minimal or with no pore developing fillers present, breathability of
the film can be
achieved. This is done by proper selection of the polymeric components, their
content contribution
in each skin, and by appropriate processing of the multilayered film, for
example stretching the film
so that the skin layers are sufficiently thinned to permit transmission of
water vapor and other
gases. McCormack, et al, describes examples of such films in U.S. 6,075,179.
One problem has been long recognized and encountered with the above material
constructions in
thermal lamination to other material constructions. That problem is that known
attempts to
thermally point bond a nonwoven fabric layer to a microporous thermoplastic
film frequently result
in a laminate that fails to meet blood strikethrough requirements as described
in ASTM-F1670-95.
An example of this problem is cited as the comparative example in U.S.
6,23,767 where the use of
thermal point bonding to join a multi-layer stretched thinned microporous film
to a nonwoven
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resulted in a laminate that fails the ASTM-F1670-95 test. To surmount this
problem U.S. 6,238,767
describes smooth roll calendering techniques that j oin the microporous film
and the nonwoven.
The difficulty in obtaining thermal bonded laminates of nonwovens and
microporous films that
pass the ASTM-F1670-95 test is further increased when the nonwoven webs are
treated with a
fugitive surfactants. It is believed that when such webs are thermal bonded to
microporous films,
some portion of fugitive surfactant present on the web is driven by the heat
and pressure of the
thermal bonding process into the film itself at the bond areas. When liquid
such as water, blood, or
urine contacts this surfactant present in the microporous regions of the film
the surface tension of
the liquid decreases sufficiently to result in the passage of liquid through
the microporous network.
Such laminates fail to pass the blood strikethrough criteria set forth in ASTM-
F1670-95. It is
believed that the pressures and temperatures used in the thermal bonding
process create intimate
contact among the surfactant, the polymers of the nonwoven fabric, and the
polymers and other
materials present in the elm at bonded regions. This is believed to result in
the presence of
surfactant in the microporous regions that reduces the surface tension of
liquid that contacts these
regions and allows the liquid to pass through the laminate.
A common technique used to negate the effect of surfactant contamination in
the film is to avoid it
altogether by attaching the film via an adhesive to the surfactant treated
nonwoven web. So long as
the bond is non-thermal and the film and surfactant treated nonwoven are
physically separated,
surface tension reduction of liquids in the microporous regions is eliminated
or at least minimized.
An alternative technique is to thermally bond the film to a surfactant free
web. Once the bond is
established, as a subsequent step, the film/nonwoven laminate can be topically
treated with the
surfactant to be rendered hydrophilic. U.S. 5,901,706 by Griesbach, et al,
describes such laminates,
made by adhesive attachment or by thermal bonding followed by surfactant
treatment, suitable for
surgical drapes.
Consequently, until the present invention, it was believed that microporous
films thermally bonded
to nonwoven webs with surfactant treatments could not reliably provide the
liquid barrier necessary
to enable the film/nonwoven laminate to pass the blood strikethrough criteria
of ASTM-F1670-95.
SUMMARY OF THE INVENTION
The present invention is drawn to a disposable, absorbent laminate containing
one or more layers of
surfactant-treated meltspun nonwoven thermally bonded to a breathable film and
a method of
making the same. Such a laminate is useful for surgical drapes and would have
applications for
gowns, disposable work wear such as coveralls and lab coats and personal care
absorbent products
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such as diapers, training pants, incontinence garments, sanitary napkins,
bandages, wipes and the
like. In accordance with the invention the laminate should provide superior
liquid absorptivity,
exhibit relatively low levels of lint particles, pass the blood strikethrough
criteria of ASTM-F1670-
95, meet the Class 1 flammability requirements of NFPA 702-1980, and maximize
drape strength
all at a relatively low cost. As such, the present invention is drawn to a
laminate comprising a
nonwoven web having been treated with a surfactant and a stretched film. The
stretched film
comprises a core layer and at least one skin layer. The core layer has a
percentage by weight of a
micropore developing filler material incorporated therein. The stretched film
has been stretched in
at least one direction to some percentage of its original size until a desired
degree of vapor
permeability is reached. The film is thermally bonded to the surfactant
treated nonwoven. The end
result is a laminate that forms both a breathable barrier and passes blood
strikethrough in
compliance with ASTM F1670-95 and has an exposed face that is capable of
absorbing aqueous
liquids.
In another embodiment, the invention is drawn to a breathable absorbent
laminate compliant with
ASTM F1670-95. The laminate comprises a nonwoven web treated with a
surfactant. The
nonwoven web is thermally bonded at a plurality of bond points to a multilayer
polyolefm resin
film, at least some of the bond points form attachments between the web and
the multilayer film. At
least one layer of the multilayer film contains a percentage by weight of a
micropore developing
filler.
In other embodiments, the invention is a surgical drape consisting of a
thermally bonded laminate
made from a stretched multilayered filled film and a surfactant treated,
hydrophilic and absorbent
meltspun nonwoven web.
The laminates of the present invention satisfy the need in the art for
materials that provide
improved liquid absorptivity while passing blood strikethrough criteria set
forth in ASTM-F1670-
95, as well as, providing comfort, improved drape strength, and having
relative low levels of lint
particles, while meeting the Class 1 flammability requirements of NFPA 702-
1980 (flame
propagation of 20 seconds or greater).
The laminates of the present invention may be formed from thermal bonding a
film that contains at
least one microporous layer and one or more nonwoven fabric layers so as to
include at least one
layer of hydrophilic meltspun fabric. In general, the filaments of the
contemplated nonwoven
fabrics are made from hydrophobic polymeric material. These materials are made
hydrophilic by
treating with a hydrophilic chemical additive, such as a surfactant, in or on
the filaments.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a portion of a cross-section of an embodiment of the laminate
of the present
invention.
FIG. 2 depicts a portion of a cross-section of a further embodiment of the
laminate of the present
invention.
FIG. 3 depicts a portion of a cross-section of another embodiment of the
laminate of the present
invention.
FIG. 4 depicts a portion of a cross-section of yet another further embodiment
of the laminate of the
presentinvention.
FIG. 5 depicts one possible process for forming the multilayer films depicted
in FIG. 3 and 4.
FIGs. 6-9 depict photomicrographs of various examples of film cross-sections
DETAILED DESCRIPTION OF THE INVENTION
As used herein the ternz "polymer" generally includes but is not limited to,
homopolymers,
copolymers, such as for example, block, graft, random and alternating
copolymers, terpolymers,
etc. and blends and modifications thereof. Furthermore, unless otherwise
specifically limited, the
term "polymer" shall include all possible geometrical configurations of the
molecule. These
configurations include, but are not limited to isotactic, syndiotactic and
random symmetries.
As used herein, the term "nonwoven fabric or "web" refers to a fabric that has
a structure of
individual fibers or filaments which are randomly and/or unidirectionally
interlaid in a mat-like
fashion. Nonwoven fabrics can be made from a variety of processes including,
but not limited to,
air-laid processes, wet-laid processes, hydroentangling processes, staple
fiber carding and bonding,
and solution spinning. Suitable nonwoven fabrics include, but are not limited
to, spunbonded
fabrics, meltblown fabrics, wet-laid fabrics, hydroentangled fabrics,
spunlaced fabrics and
combinations thereof. The basis weight of nonwoven fabrics is usually
expressed in ounces of
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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).
As used herein, the term "meltspun fabric" refers to a nonwoven web of
filaments or fibers, which
are formed by extruding a molten thermoplastic material, or coextruding more
than one molten
thermoplastic material, as filaments or fibers from a plurality of fine,
usually circular, capillaries in
a spinneret with the diameter of the extruded filaments or fibers. Meltspun
fabrics include, but are
not limited to, spunbonded fabrics and meltblown fabrics and are characterized
as having thermal
bonding junctions throughout the fabric.
As used herein, the term "spunbonded fabric" or "spunbond fabric" refers to a
web of small
diameter continuous filaments which are formed by extruding a molten
thermoplastic material, or
coextruding more than one molten thermoplastic material, as filaments from a
plurality of fine,
usually circular, capillaries in a spinneret with the diameter of the extruded
filaments rapidly
reduced, for example, by non-eductive or eductive fluid-drawing or other well
known spunbonding
mechanisms. These small diameter filaments are substantially uniform with
respect to each other.
The diameters that characterize these filaments range from about 7 to 45
microns, preferably from
about 12 to 25 microns. The production of spunbonded nonwoven webs is
illustrated in patents
such as Appel et al., U.S. Pat. No. 4,340,563; Dorschner et al., U.S. Pat. No.
3,692,618; Kinney,
U.S. Pat. Nos. 3,338,992 and 3,341,394; Levy, U.S. Pat. No. 3,276,944;
Peterson, U.S. Pat. No.
3,502,538; Hartman, U.S. Pat. No. 3,502,763; Dobo et al., U.S. Pat. No.
3,542,615; and Harmon,
Canadian Patent No. 803,714.
As used herein, the term "meltblown fabrics" refers to a fabric comprising
fibers formed by
extruding a molten thermoplastic material through a plurality of fine, usually
circular, die
capillaries as molten threads or filaments into a high velocity gas (e.g. air)
stream that attenuates the
filaments of molten thermoplastic material to reduce their diameters, which
may be to "rilicrofiber"
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 disbursed
meltblown fibers. The
meltblown process is well-known and is described in various patents and
publications, including
NRL Report 4364, "Manufacture of Super-Fine Organic Fibers" by V. A. Wendt, E.
L. Boone, and
C. D. Fluharty; NRL Report 5265, "An Improved Device for the Formation of
Super-Fine
Thermoplastic Fibers" by K. D. Lawrence, R. T. Lukas, and J. A. Young; and
U.S. Pat. No.
3,849,241 issued Nov. 19, 1974 to Buntin et al.
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As used herein, the term "microfibers" means small diameter fibers having an
average diameter not
greater than about 100 microns, for example, having a diameter of from about
0.5 microns to about
50 microns. More specifically microfibers may also have an average diameter of
from about 1
micron to about 20 microns. Microfibers having an average diameter of about 3
microns or less are
commonly referred to as ultra-fme micro~bers.
As used herein the term "multilayer laminate" means a laminate wherein some of
the layers are
spunbond (S) and some meltblown (M) such as a spunbond/meltblown/spunbond
(SMS) laminate
and others as disclosed in U.S. Patent 4,041,203 to Brock et al., U.S. Patent
5,169,706 to Collier, et
al, U.S. Patent 5,145,727 to Potts et al., U.S. Patent 5,178,931 to Perkins et
al. and U.S. Patent
5,188,885 to Timmons et al. Such a laminate may be made by sequentially
depositing onto a
moving forming belt first a spunbond fabric layer, then a meltblown fabric
layer and last another
spunbond layer and then bonding the laminate in a manner described below. Such
fabrics usually
have a basis weight of from about 0.1 to 12 osy (about 3.4 to 400 gsm), or
more particularly from
about 0.4 to about 3 osy (about 14 to 100 gsm). Multilayer laminates may also
have various
numbers of meltblown layers or multiple spunbond layers in many different
configurations and may
include other materials like films (F) or coform materials, e.g. SMMS, SM,
SFS, etc.
As used herein, the term "multilayered film" or multilayered filled film"
means a film with multiple
contacting adjacent layers, each layer is uniformly distributed in planar
dimension of the film.
As used herein, the term "spunlaced fabrics" refers to a web of material
consisting of one or more
types of non-continuous fibers, where the fibers are hydroentangled to achieve
mechanical bonding
without binder materials or thermal bonding.
As used herein, the term "wet-laid fabrics" refers to fabrics formed by a
process, such as a paper-
making process, wherein fibers or filaments dispersed in a liquid medium are
deposited onto a
screen such that the liquid medium flows through the screen, leaving a fabric
on the surface of the
screen. Fiber bonding agents may be applied to the fibers in the liquid medium
or after being
deposited onto the screen. Wet-laid fabrics may contain natural and/or
synthetic fibers.
As used herein, the term "hydroentangle" or "hydroentangling" refers to a
process wherein a web of
material consisting of one or more types of fibers or filaments are subjected
to high-velocity water
jets, which entangle the fibers to achieve mechanical bonding.
As used herein, the terms "breathable" and "microporous" refer to a material
which allows the
passage of vapor and/or gas therethrough, but forms a barner against the
passage therethrough of
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liquids. The term generally refers to a material which is permeable to water
vapor having a
minimum water vapor transmission rate (WVTR) of about 100 g/m2/24 hours. The
WVTR of a
fabric is water vapor transmission rate which, in one aspect, gives an
indication of how comfortable
a fabric would be to wear. WVTR is measured as indicated below and the results
are reported in
grams/m2/24 hours. However, often applications of breathable barriers
desirably have higher
WVTRs and breathable barriers of the present invention can have VWTRs
exceeding about 300
g/m2/24 hrs, 800 g/m2/24 hrs, 1500 g/mz/24 hrs or even exceeding 3000 g/m2/24
hrs. Breathable
films are well known in the art and may be produced by any known method.
As used herein the term "thermal point bonding" involves passing a fabric, web
of fibers, or
multiply fabrics and/or webs of fibers to be bonded between a heated calender
roll and an anvil roll.
The calender roll is usually, though not always, patterned in some way so that
the entire fabric is
not bonded across its entire surface, and the anvil roll is usually flat. As a
result, various patterns
for calender rolls have been developed for functional as well as aesthetic
reasons. One example of a
pattern is taught in U.S. Patent 3,855,046 to Hansen and Pennings. Typically,
the % bonding area
varies from around 10% to around 30% of the area of the fabric laminate web.
As is well known in
the art, the bonding holds the laminate layers together as well as imparts
integrity to each individual
layer by bonding filaments and/or fibers within each layer.
As used herein, the term "ultrasonic bonding" means a thermal point bonding
process performed,
for example, by passing the fabric between a sonic horn and anvil roll as
illustrated in U.S. Patent
4,374,888 to Bornslaeger.
As used herein, "fugitive surfactant" and "surfactant" means a chemical agent
that renders the
polymer surfaces hydrophilic and can be extracted to some degree from those
surfaces by aqueous
fluids.
As used herein, the term "machine direction" or MD means the direction of a
fabric in the direction
in which it is produced. The term "cross machine direction" or CD means the
opposite direction of
the fabric, i.e. a direction generally perpendicular to the MD.
As used herein the term "recover" and "retract" refers to a contraction of a
stretched material upon
termination of a biasing force following stretching of the material by
application of the biasing
force. For example, if a material having a relaxed, unbiased length of one (1)
inch was elongated 50
% by stretching to a length of one and one half (1.5) inches the material
would have a stretched
length that is 150 % of its relaxed length. If this exemplary stretched
material contracted, that is
recovered to a length of one and one tenth (1.1) inches after partial to
complete release of the
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biasing and stretching force, the material would have recovered 80 % (0.4
inch) of its elongation.
As used herein, a "micropore developing filler" is meant to include
particulates and other forms of
materials which can be added to a polymer and which will not chemically
interfere with or
adversely affect the extruded film made from the polymer but are able to be
uniformly dispersed
throughout the film. Generally, the micropore developing fillers will be in
particulate form and
usually will have somewhat of a spherical shape with average particle sizes in
the range of about
0.5 to about 8 microns. The film will usually contain at least about 30 % of
micropore developing
filler based upon the total weight of the elm layer. Both organic and
inorganic micropore
developing fillers are contemplated to be within the scope of the present
invention provided that
they do not interfere with the film formation process, the breathability of
the resultant film or its
ability to bond to a fibrous polyolefm nonwoven web.
Looking to FIG. 1, a laminate 10, in accordance with the present invention is
depicted comprising a
surfactant treated nonwoven web 12 bonded to a multilayered film 14. Bonding
of the web 12 to the
film 14 is accomplished at least in part at bond points 16 by thermal point
bonding, i.e., through the
use of heat and/or pressure as with heated bonding rolls, at least one of
which is patterned. The
multilayered film 14 comprises a plurality of layers which may include a core
layer 18 and one or
more skin layers 20 on either side of the core layer 18. Each skin layer 20
may further include
extrudable thermoplastic polymers and/or additives that provide specialized
properties to the film
14.'As depicted in FIG. l, at least one skin layer 20 (in the FIG. 1
embodiment two are depicted)
and the nonwoven web 12 are positioned in a juxtaposed, face-to-face, or
surface-to-surface
relationship with respect to each other. The web 12 and the elm 14, or both
are joined to one
another over the entire surface or at least at some portion of their
respective surfaces, such as at
thermal bond points 16. The web 12 or the film 14 of the laminate 10 may have
a shape and size
independent from the other. However, in many embodiments the web 12 and the
film 14 are
generally similar in shape and are coextensive with each other.
In some embodiments, as described below, the nonwoven web 12 may comprise a
surfactant treated
spunbond layer. Other embodiments include nonwoven webs 12 comprising at least
one
spunbonded layer in combination with one or more meltblown fabric layers,
wherein one or more
of the fabric layers are made hydrophilic by incorporating a surfactant in or
on the respective
fabrics thereby rendering the nonwoven web absorbent.
Further embodiments such as depicted in FIG. 2, contemplate that the
multilayered film 14 may be
sandwiched between two nonwoven webs 12 and 22. Each nonwoven web 12 and/or 22
may itself
comprise a single layer of meltspun fabric, for example a spunbond or
meltblown fabric, or each
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nonwoven web 12 and/or 22 may comprise a plurality of separate nonwoven webs
wherein each
separate nonwoven web 12 or 22 are any of identical webs, similar webs, or
different webs. For
instance, each of the webs 12, 22 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 webs may be treated with surfactant to become
hydrophilic and
any of the webs may be treated with other surface modifying agents.
FIG. 3 depicts an embodiment of the invention similar to FIG. 1, however FIG.
3 replaces the
single layer nonwoven web with a multilayer nonwoven web 24. Any one or all of
the layers of the
nonwoven web 24 may be treated with a surfactant and adjacent layers of the
nonwoven web 24
may be made of polymers that are thermally miscible. In the embodiment of FIG.
3, the nonwoven
web 24 comprises a spunbond/meltblown/spunbond (SMS) laminate having a first
spunbond layer
26, a meltblown layer 28, and a second spunbond layer 30. As in FIG. 1 the
FIG. 3 film 14
comprises a plurality of layers which may include the core layer 18 and one or
more skin layers 20
on either side of the core layer 18. Each skin layer 20 may include extrudable
thermoplastic
polymers and/or additives that provide specialized properties to the film 14.
As depicted in FIG. 3,
any of the embodiments contemplated may arrange the film 14 so that it forms
an exterior surface
of the laminate 10.
FIG. 4 depicts another embodiment which sandwiches the multilayered film 14
between at least one
nonwoven web 22 (it should however be understood that nonwoven web 12 may be
substituted)
and at least one multilayered nonwoven web 24. Any one or all of the layers of
any one of or all of
the nonwoven webs may be treated with surfactant but at least one nonwoven
layer in at least one
nonwoven web is desirably hydrophilic. While various combinations are
contemplated one possible
embodiment of the laminate 10 comprises the nonwoven web 24 which itself
comprises a
spunbond/meltblown/spunbond (SMS) laminate of first spunbond layer 26, a
meltblown layer 28,
and a second spunbond layer 30 laminated to the film 14. The nonwoven web 12
is bonded to the
opposite side of the film 14 thereby sandwiching the film 14 between webs 22
and 24. At least one
of the layers 26, 28, or 30 is surfactant treated.
As should be evident from the above explanations and the FIGs., numerous
combinations and
quantities of single and/or multiple layer webs and films are possible..
Furthermore, numerous
possibilities exist with respect to which of these layers and/or webs also are
pretreated with
surfactant. In any event, in each of the embodiments, the film 14 may serve to
block external liquid
penetration through the laminate 10. As such, the film 14 is attached to at
least one adjacent layer of
11
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the laminate 10. In any of the embodiments the film 14 may be attached to the
nonwoven web 12,
22, and/or 24 of the laminate 10 by thermal point bonds 16.
In certain embodiments, the film 14 may comprise an extrudable polyolefin
containing multiple
layers, where at least one of those layers contains micropore developing
filler or fillers. Looking
still to FIG. 4, it can be seen that the core layer 18 of the film 14 may
contain such micropore
developing filler 32. The micropore developing filler 32 provides properties
to the core layer 18
such as breathability to be obtained via proper processing. As such, this
filler 32 may be dispersed
throughout the core layer 18. Typically the films 14 are made breathable by
the addition of the filler
32 to the film 14 during the film forming process and then by the subsequent
stretching of the film
so as create voids in and around the filler 32. This renders the film
breathable and permits the
transmission of water vapor and other gases through micropores developed in
and through the film
in the regions containing and proximate to the voids while normally inhibiting
the transmission of
liquids such as water. The micropore developing filler 32 may also be included
in the skin layers 20
for desirable properties such as breathability, anti-block, improved
attachment to nonwoven webs,
and the like. Of course, all embodiments including those depicted in FIGS. 1-
3, contemplate the use
of such micropore developing filler 32.
Most typically, such filler material 32 used in the core layer 18 of the film
14 is primarily utilized
in, for example, a weight percentage ranging from about 25 % to about 60 %,
based upon the total
weight of the layer 18. The amount of filler material 32 may vary widely as
long as the desired
degree of liquid impermeability of the entire film 14 is maintained.
Suitable polymers for the core layer 18 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
that can be
included in the polymeric portion of the core layer 18 are EXXPOL~, EXCEED,
and EXACTTM
polymers from Exxon Chemical Company of Baytown, Texas; ENGAGE~, ACHIEVE~,
ATTAIN~ , AFFINITY~, and ELITE~ polymers from Dow Chemical Company of Midland,
Michigan; CATALLOY~ polymers from Basell USA Inc. of Wilmington, Delaware.
Other useful
polymers include elastomeric thermoplastic polymers.
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Each skin layer 20 may be made from polymers which provide such properties as
antimicrobial
activity, water vapor transmission, adhesion and/or antiblocking properties
and may include
micropore developing fillers 32. Suitable polymers for the skin layer 20 or
layers 20 include
polymers and polymer blends used alone or in combination of homopolymers,
copolymers and
blends of polyolefins, CATALLOY~ polymers, 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 olefmic 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.
For more detailed description of films having core and skin layers see US
Patents 5,695,868,
6,075,179, and 6,238,767 to McCormaclc et al. assigned to common assignee
which is incorporated
herein by reference in its entirety.
Examples of some possible micropore developing filler materials 32
incorporated in the core layer
18 include calcium carbonate (CaC03), various kinds of clay, silica (SOz),
alumina, barium sulfate,
sodium carbonate, talc, magnesium sulfate, titanium dioxide, zeolites,
aluminum sulfate, cellulose-
type powders, diatomaceous earth, magnesium sulfate, magnesium carbonate,
barium carbonate,
kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum hydroxide, pulp
powder, wood
powder, cellulose derivative, polymer particles, chitin and chitin
derivatives. The micropore
developing filler materials 32 may optionally be coated with a fatty acid,
such as stearic acid, or a
larger chain fatty acid such as behenic acid, which may facilitate the free
flow of the particles (in
bulk) and their ease of dispersion into the polymer matrix. Silica containing
fillers may also be
present in an effective amount to provide antiblocking properties.
Filler materials that may be incorporated in the skin layers) 20 include
calcium carbonate (CaC03),
various kinds of clay, silica (SOZ), etc. Particularly useful fillers are
silica containing fillers, such as
diatomaceous earth, when present in effective amounts to provide anti-blocking
properties to the
film.
In one multilayered film 14, the core layer 18 may comprise a polyethylene
filled with about 60
by weight calcium carbonate serving as the micropore developing filler 32. The
skin layers 20 may
contain appropriate CATALLOY~ polymers. Such CATALLOY~ polymers may contain
copolymers of ethylene. The skin layers 20 may also contain additives to
impart anti-blocking
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attributes. The ratio of the total of the skin layers 20 to the core layer 18
may be approximately 4.5
to 12% by weight. In other multilayered films 14 the core layer 18 is as
described above but the
skin layers 20 may contain polymeric blends of appropriate CATALLOY~ polymers
with EVA
polymers with about 28% vinyl acetate content with or without the addition of
diatomaceous earth
or other additives to impart anti-blocking attributes .
It is contemplated that the absorbent component of the laminate 10 is any one
of or all of the
nonwoven webs 12, 22, and/or 24. 'The webs may be formed from a number of
processes including,
but not limited to, spunbonding and meltblowing processes. Regardless of the
number of layers or
their specific configuration, the actual materials used to manufacture any of
the nonwoven webs
may comprise monocomponent and/or multicomponent, or conjugate, synthetic
filaments and/or
fibers that may be produced from a wide variety of thermoplastic polymers that
are known to form
fibers or filaments.
Suitable polymers for forming the nonwoven webs of the present invention
include, but are not
limited to, polyolefms, e.g., polyethylene, polypropylene, polybutylene, and
the like. Of the suitable
polymers for forming conjugate fibers, particularly suitable polymers for the
high melting
component of the conjugate fibers include polypropylene, copolymers of
propylene and ethylene
and blends thereof, polyesters, and polyamides, more particularly
polypropylene. Particularly
suitable polymers for the low melting component include polyethylenes, more
particularly linear
low density polyethylene, high density polyethylene and blends thereof. Most
suitable component
polymers for conjugate fibers are polyethylene and polypropylene. Especially
suitable polymers for
forming the nonwoven webs include polymers of narrow molecular weight
distribution such as
metallocene catalyzed polypropylene, and in particular inelastic metallocene-
catalyzed
polypropylene. In addition, the polymer components may contain thermoplastic
elastomers blended
therein or additives for enhancing the crimpability and/or lowering the
bonding temperature of the
fibers, and enhancing the abrasion resistance, strength and softness of the
resulting webs. Yet other
suitable polymer additives include polybutylene copolymers and ethylene-
propylene copolymers.
In some of the embodiments, one or more hydrophilic additives are added to the
polymer melt in
order to form hydrophilic meltspun fabrics. Particularly useful hydrophilic
additives include
surfactants that are nontoxic, have a low volatility and are sufficiently
soluble in the molten or
semi-molten polymers. Additionally, the hydrophilic additive is desirably
thermally stable at
temperatures up to 175 degree C. and sufficiently phase separates such that
the additive migrates
from the bulk of the polymer filament towards the surface of the polymer
filament as the filament
solidifies without requiring the addition of heat. Once at the polymer
surface, the additive alters the
14
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polymer surface such that the surface of the polymer rapidly wets upon contact
with (by reducing
the surface tension of) an aqueous fluid. Such additives include, but are not
limited to, one or a
combination of additives selected from the following classes of additives: (i)
polyoxyalkylene
modified fluorinated alkyls, (ii) polyoxyallcylene fatty acid esters, (iii)
polyoxyalkylene modified
polydimethyl siloxanes and PEG-terephthalate (polyethylene glycol modified
terephthalate) and
(iv) ethoxylated alkyl phenols. An example of a suitable polyoxyalkylene
modified fluorinated
alkyl is FC-1802, a product of the Minnesota Mining and Manufacturing Company.
An example of
a suitable polyoxyalkylene fatty acid ester is PEG-400 ML, a product of Henkel
Corporation/Energy Group. An example of a suitable polyoxyalkylene modified
polydimethyl
siloxane is MASIL~ SF-19, a product of PPG Industries. An example of suitable
ethoxylated alkyl
phenol is Triton~ 102, a product of Union Carbide. The choice of one or more
additives depends
upon, for example, cost, compatibility with the polymeric material, and the
overall contribution to
the properties of the laminate. The treatment to render hydrophobic polymers
hydrophilic by adding
surfactant to the polymer melt is illustrated in patents such as Pike et al.,
U.S. Pat. No. 5,759,926
that is herein incorporated by reference in its entirety.
Additionally and/or alternatively, the hydrophilic additives, especially
surfactants, may be added to
the meltspun fabric following fabric formation. Suitable methods of applying
the hydrophilic
additives to a meltspun fabric include, but are not limited to, foam coating,
spray coating, or
solution coating. For those embodiments where the hydrophilic properties of
the absorbent fabric
are due to hydrophilic additives added on the surfaces of the fabric
filaments, the hydrophilic
additives may include any additive which is thermally stable at temperatures
up to 60°C. Once on
the filament surface, the additive changes the inherent hydrophobicity of the
filament surface such
that the filament surface wets upon contact with (by reducing the surface
tension of) an aqueous
fluid. Such additives include, but are not limited to, those identified above
and having thermal
stabilities up to 60°C. Any such additive is suitable for the present
invention as long as it does not
negatively impact desired properties of the resulting laminate. Further, the
hydrophilic meltspun
fabrics and other components comprising the absorbent laminate of the
invention may also be
treated with any lrnown antistatic agent. The treatment to render hydrophobic
polymers hydrophilic
by surface treatment of the fibers is illustrated in patents such as Krzysik
et al., U.S. Pat. No.
6,204,208 that is herein incorporated by reference in its entirety.
Generally, the concentration of the hydrophilic additive in or on the
filaments or fibers that
comprise the meltspun fabric (e.g., spunbonded filaments or meltblown
microfibers) may comprise
about 0.05 % by weight to about 5.0 % by weight. Moreover, the concentration
of the hydrophilic
CA 02467807 2004-05-19
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additive in or on the filaments or fibers that comprise the meltspun fabric
may comprise about 0.1
by weight to about 1.5 % by weight.
The choice of one or more hydrophilic additives depends upon, for example,
cost, compatibility
with the polymeric material, and the overall contribution to the properties of
the finished drape. The
hydrophilic meltspun webs provide superior liquid absorptivity to the
laminates of the present
invention compared to conventional, namely hydrophobic, spunbonded fabrics.
For use as a
surgical drape, the laminates of the present invention provide equivalent
liquid absorptivity without
being flammable compared to commercially available absorbent drapes. In some
embodiments, the
hydrophilic meltspun fabrics may have a basis weight of from about 15 to about
140 grams per
square meter (gsm). In other embodiments, the hydrophilic meltspun fabrics may
have a basis
weight of from about 20 to about 60 grams per square meter (gsm).
The hydrophilic meltspun webs of the present invention may also be treated
with or contain various
chemicals in order to impart additional desirable characteristics. Any such
chemical is suitable for
the present invention as long as the chemical does not negatively impact
desired properties of the
laminate. For example, the hydrophilic meltspun webs may be treated with any
lrnown antistatic
agent, fire retardant, or other desirable chemical finish. Furthermore, for
hospital related end uses
for the laminates of this invention, it may be desired to treat the webs so
that they become
electrically conductive to prevent the build-up of a static charge. One
possible way to achieve this
result is to apply a conventional salt solution, such as lithium nitrate, to
the web of continuous
filaments before or after formation of the meltspun fabric. As an embodiment,
the surfactant and
salt solution are combined and then applied to the meltspun fabric iri a
single treatment step.
In the practice of this invention, a single nonwoven web layer 12 may be
laminated to a ftlm layer
14, similar to that depicted in FIG. 1. An example of such is a spunbond (S)/
film (F) laminate.
Alternatively, a plurality of nonwoven web layers may also be incorporated
into the laminate,
similar to the FIGS. 2-4 embodiments according to the present invention.
Examples of such
materials can include, for example, SFS multilayered laminate composites.
Additional examples
include meltblown (M)/F laminates, SMS/F laminates. In fact, any combination
of a surfactant
treated nonwoven web, layer, or single layer within a nonwoven web coupled
with a microporous
film is contemplated. In one possible embodiment, the laminate can be used as
a surgical drape. In a
surgical drape embodiment, the outermost layer that faces away from the
patient may contain a
hydrophilic meltspun web.
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In the case where the laminate 10 consists of a hydrophilic meltspun fabric
and a film (i.e., the FIG.
1 embodiment or a similar construction), the film should desirably contact the
patient. The film
may have projections as described in U.S. 5,546,960 or other three dimensional
features that
minimize contact with the patient. As a surgical drape the laminate of the
present invention may
also be provided with one or more fenestrations (not shown). In some such
applications, each
fenestration is generally sized for overlying the operating site of the
patient and for providing a
health care provider a means of accessing the site. The fenestration may
extend through one or
more or the surgical drape layers and may vary in size depending upon the
intended use of the
surgical drape. Additionally, the surgical drape may contain other components
such as an incise
material, a release layer over an incise material, a pouch for storing
surgical equipment, and any
other surgical drape component known to those of ordinary skill in the art.
While this described
embodiment is directed to surgical drapes there are many other applications
for the laminates of the
present invention. Other applications include, but are not limited to, patient
prep pads, examination
table covers, patient mattress bed covers or liners, and the like.
The components of the laminate of the present invention may be manufactured by
any method of
making similar laminates known to those of ordinary skill in the art. The
hydrophilic meltspun
fabric may be prepared by adding a hydrophilic chemical additive to the
polymer melt and
subsequently forming meltspun filaments or fibers. Alternatively, the
hydrophilic chemical additive
may be coated onto the meltspun fabric. These methods may also be used to
render hydrophilic
other nonwoven fabrics made from inherently hydrophobic polyolefins that are
used in conjunction
with the meltspun fabric in the absorbent drape. Thermal bonding together
hydrophilic meltspun
fabrics and films suitable for the invention may result by passing such
materials through a nip
formed by co-rotating heated rolls that are pressed together, by ultrasonic
methods, and other means
that join together in defined areas the adjacent facing surfaces of the
hydrophilic meltspun fabric
and the film.
Some of the previously disclosed embodiments of the present invention (not
shown) use a
multilayer film 14 comprising a particulate filled core layer 18 and a single
skin layer 20. In at least
one of the most basic configurations, one skin layer 20 is attached, usually
simultaneously due to
the coextrusion process, to a first exterior surface of the core layer 18 to
form the multilayer film
14. In embodiments having this configuration, the multilayer film 14 defines
an overall thickness
where a first skin layer 20 defines a first skin thickness comprising about 10
% or less than of the
overall effective thickness of the multilayer film 14.
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The effective thickness of a film is used to take in-to consideration the
voids or air spaces in
breathable film layers. For normal, non-filled, non-breathable films, the
actual thickness and
effective thickness of the film will typically be the same. However, for
filled films that have been
stretch-thinned, as described herein, the thickness of the elm will also
include air spaces. In order
to disregard this added volume, the effective thickness is calculated
according to the test method
described below.
For example, in some embodiments the thickness of the first skin layer 20 may
be manufactured so
as to not exceed about 5 microns. In other embodiments the thickness of the
first skin layer 20 may
be manufactured so as to not exceed about 3 microns. In still other
embodiments the thickness of
the first skin layer 20 may be manufactured so as to not exceed about 2
microns. These thicknesses
can be reached by stretching the film 14 to such a degree so as to thin the
multilayer film 14 to
within the dimensions defined herein.
In the case of a multilayer film 14 comprising a core layer 18 sandwiched
betweemtwo skin layers
as shown in each of FIGS. 1-4, a possible embodiment provides that the first
skin and the second
15 skin layers 20 have a combined thickness which does not exceed about 15 %
of the overall
thickness of the multilayer film 14. Another embodiment provides that the
first skin and the second
skin layers 20 have a combined thickness which does not exceed more than about
8 % of the overall
thickness of the multilayer film 14. Other embodiments provide that the first
skin and the second
skin layers 20 have a combined thickness which does not exceed more than about
6 % of the overall
20 thickness of the multilayer film 14. The skin layers 20 could also be made
not to exceed about 3
of the overall thickness of the multilayer film 14.
Moreover, there is no requirement that each skin layer 20 be the same
dimension. For instance, one
of the skin layers 20 could range from about 0 to about 15 % whereas the other
skin layer 20 could
range from about 15 % to about 0 %. In some embodiments the film 14 in the
final laminate may
have a film thickness of from about 0.3 mil (about 8 microns) to about 1 mil
(0.025 mm). In other
possible embodiments, the film 14 may have a film thickness of from about 0.5
mil (about 13
microns) to about 0.8 mil (about 20 microns). Also, the film 14 in the final
laminate may have a
film basis weight of less than about 25 grams per square meter (gsm).
Moreover, the film 14 in the
final laminate may have a film basis weight of less than about 20 gsm. Again,
these thickness and
basis weight ranges can be used for any of the embodiments contemplated
herein.
In any event, once the particulate filled film 14 has been formed, it is then
stretched to create voids
around or in close proximity to the filler particles throughout the core layer
18 which provides the
18
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layer 18 with its breathability. Proper selection of type and amount of
polymer and fillers in each
skin layer 20 ensures that these layers 20 do not prevent transmission of
water vapor and other
gases through film 14 after stretching. In forming the individual layers 28
and 30 of the film 14, the
layers 28 and 30 may be coextruded to ensure interfacial contact and alleviate
processing
complexity. Processes for forming film 14 are generally known. The film 14 can
be made from
either cast or blown film equipment, can be coextruded and can be embossed if
so desired.
Additionally, the film 14 can be stretched or oriented by passing the film 14
through a film
stretching unit. Generally, this stretching may take place in the CD or MD or
both.
The inventors discovered that by stretching the multilayered film 14 described
in the embodiments
and thermally bonding them under specific conditions with a meltspun web
pretreated with a
surfactant results in a laminate that reliably prevents the strikethrough of
aqueous based fluids. The
composition of the layers in the film and the percentage thickness of each
layer are factors in
maintaining a measure of breathability while consistently retaining liquid
strike through protection
after the stretched film is thermally point bonded to a nonwoven web made
absorbent via treatment
of the web by a surfactant. Additionally important is that in stretching the
film, it retains significant
continuity in the skin layers adjacent to the surfactant treated nonwoven web
while the core layer is
made microporous.
The inventors have further discovered that allowing the multilayered films to
retract after stretching
and before thermally bonding them with a surfactant treated meltspun fabric
comprises one method
to produce laminates that reliably prevent the strikethrough of aqueous based
fluids. Retraction of
stretched multilayered films has been mentioned in connection with stretched
multilayered films
containing micropore developing fillers, as for example in the previously
cited U.S. 6,045,900
patent. Such retraction has been observed to improved physical attributes in
the resultant film such
as greater elongation prior to rupture in the direction of stretching. With
respect to the invention,
applying appropriate processing conditions (e.g. stretching and retraction) to
the extruded film
before lamination to surfactant treated nonwoven webs have been identified as
factors that enhance
and/or maintain desired fluid barrier properties.
Referring to FIG. 5, a process for forming the laminate 10 of FIG. 2 and 4 is
shown. A coextrusion
film apparatus 34 forms the film 14 that has multiple layers consisting of
skin and core layers (not
shown). Typically the apparatus 34 will include two or more polymer extruders
36. In one method
of fabrication, the film 14 is extruded into a pair of nip or chill rollers 38
one of which may be
patterned so as to impart an embossed pattern to film 14. This is particularly
advantageous to
reduce the gloss of the film and give it a matte finish. In another method the
film 14 is extruded
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onto a chilled roll which can have a smooth~or matte finish. Typically, the
film 14, as initially
formed, will have an overall thiclrness of approximately 25 to 60 micrometers
with, in the case of
multilayer films, the total skin or bonding layer having an initial thickness
that may be about 3% to
30% of the total thiclrness, for example.
From the coextrusion film apparatus 34 the film 14 is directed to a film
stretching unit 40 such as a
machine direction orienter (MDO), which is a commercially available device
from vendors such as
the Marshall and Williams Company of Providence, R.I. Such an apparatus 40 has
a plurality of
paired stretch rolls 42. These pairs of stretch rolls move at predetermined
speeds that may rotate
faster, slower or at the same speed relative to each other. Typically the
stretch rolls move at a
progressively faster speeds to progressively stretch and thin the film 14 in
the machine direction of
the film which is the direction of travel of the Elm 14 through the process as
shown in FIG. 5. Some
of the stretch rolls 42 may optionally move at slower speeds compared to
preceding stretch rollers
42 in order to allow retraction of film 14 also in the machine direction. The
stretch rolls 42 are
generally heated for processing advantages. In addition, the unit 40 may also
include rolls (not
shown) upstream and/or downstream from the stretch rolls 42 that may be used
to preheat the film
14 before stretching and heat or cool it after stretching.
After exiting the film stretching unit 40 the stretched Elm 14 is allowed to
retract by an amount
substantially less than the amount it was stretched. This retraction is
achieved by rotating the heated
calender rolls 44 so that the speed ratio of the film in the nip formed by
rolls 44 to the speed of the
last set of stretching rollers in the stretching unit 40 is less than 100%,
and may desirably range
between about 70 to 90%.
One possible film 14 can be seen, inter alia, on FIG. 4 wherein the film
comprises a multilayered
film 14 with the core layer 18 comprising a polyethylene Elled with about 60 %
by weight calcium
carbonate which serves as the micropore developing filler 32 and the skin
layers 20 comprising a
polymeric blend of 50% EVA with about 28% vinyl acetate content and 50%
CATALLOY~ I~S-
357P and 5% by weight of antiblock additive. The ratio of the skin layers to
the core layer may
range from about 4.5 to 12% by weight. The initial thickness of the skin
layers 20 on either side of
the core layer 18 may be the same. The removal of such fillers 32 from the
skin layers 20 is
possible via in-line Elm formation and lamination to nonwovens.
Still looking to FIG. 5, once the multilayered film 14 is extruded, it is
stretched via the stretching
unit 40 with stretch roll temperatures of about 160°F to about
220°F. After the Elm 14 has been
sufficiently thinned but before the stretched film passes through the last set
of stretch rolls 42, the
CA 02467807 2004-05-19
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film 14 is retracted slightly while maintained between the temperatures of
about 160°F to about
220°F. After the film 14 exits the stretching unit 40 it is further
retracted before it is thermally
bonded to the nonwoven web or webs 12, 22, and/or 24 at the calendering rolls
44. This
accumulative retraction is believed to deliver the beneficial effect of
thickening and reducing any
holes formed in the skin layers 20. Films subjected to this treatment may be
made to possess
breathability between about 300 - 3500 VWTR.
In some embodiments, the multilayered film 14 and the nonwoven webs for
example 12 and 22 are
next brought together and laminated to one another using heated calendering
rolls 44 consisting of a
smooth steel roll and a patterned steel roll. These rolls 44 form a discrete
bond pattern with a
prescribed bond surface area for the resultant laminate. Generally, the
maximum bond point surface
area for a given area of surface on one side of the laminate 10 will not
exceed about 50 % of the
total surface area. There are a number of discrete bond patterns which may be
used, all generally
having a bond point surface area between 15 and 30 %. Once the laminate 10
exits the calendering
rolls 44, it may be wound up into a roll 46 for subsequent processing.
Alternatively, the laminate 10
may continue in-line for further processing or conversion.
A similar process may also be used to create a laminate 10 of a film 14 and a
single nonwoven web
for example, web 12 as shown in FIG. 1 and 3. The modifications to the
previously described
process include use of only one nonwoven web layer 12, the arrangement of the
nonwoven web 12
and the film 14 so that the desired skin layer 20 is adjacent to the desired
face of the nonwoven web
12, and adjustment of bonding temperatures in calendering rolls 44 so that the
thermal point
bonding occurs between the film 14 and the nonwoven 12.
The temperatures to which the film 14 is heated while stretching will depend
on the composition of
the film as well as the breathability and other desired end properties of the
laminate 10. In most
cases the film will be heated to a temperature no higher than 5 degrees C
below the melting point of
the core layer in the film. The purpose for heating the film is to allow it to
be stretched quickly
without causing film defects. The amount of stretching will depend on the
polymeric composition,
but, in general, the film may be stretched to about 300% or more of its
original length (that is, a one
crn length, for example, will be stretched to 3 cm) but less than the amount
that tends to result in
elm defects. For most applications, for example, the stretch will be to at
least 200% of the original
film length and, frequently, in the range of about 250% to 500%. Lamination of
nonwoven webs to
the film is achieved via heat and compressive force imparted by the
calendering rolls 44. The
strength of the thermal point bond that attaches the hydrophilic nonwoven web
and the film
21
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together is measured by peel strength. After thernial bonding the laminate 10
may be heated or
cooled, if desired, by methods (not shown) known to those skilled in the art.
The present invention is described above and below by way of examples, which
are not to be
construed in any way as imposing limitations upon the scope of the invention.
On the contrary, it is
to be clearly understood that other embodiments, modifications, and
equivalents thereof which,
after reading the description herein, may suggest themselves to those skilled
in the art without
departing from the spirit of the present invention and/or the scope of the
appended claims. In the
examples reference in made to certain data that was measured by certain tests.
These tests are
described below.
Film Thickness The overall thickness of the film was measured in cross-section
from
photomicrographs. One method for obtaining the photomicrographs used a Field
Emission
Scanning Electron Microscopy (FESEM) and the following preparation procedure.
Each film
sample was submersed in liquid nitrogen and cut on impact with a razorblade.
The freshly cut
cross-section was mounted to a specimen stub in an upright position using
copper tape. Scanning
electron photomicrographs were taken at approximately 2000X magnification to
show each
respective film structure. Three separate specimens and two corresponding
photomicrographs for
each specimen were prepared for each multilayer film sample and measurements
were taken
directly off these photographs. A reference scale was super-imposed on each
photomicrograph for
calibration of the measurements. At least three measurements for each
microphotograph were made
thereby creating a set of at least eighteen data points or measurements for
each film sample to be
used in determining the thickness. From each set of data points for a
corresponding film sample an
average thickness value for each film sample was calculated in microns.
Effective Thickness The effective thickness of a film material was calculated
by dividing the basis
weight of the film by the density of the polymers) and fillers forming the
film. Densities can be
readily determined from vendor information or commonly available references.
To obtain the
effective thickness of a film material in units of inches, the weight per unit
area measured in ounces
per square yard (osy) was multiplied by 0.001334 (a metric to English
conversion factor) and the
result was divided by the density of the polymer formulation in grams per
cubic centimeter (g/cc).
Water Vapor Transmission Rate Test: The water vapor transmission rate (WVTR)
for the sample
materials was calculated in general accordance with ASTM Standard E96-80.
Circular samples
measuring three inches (7.62 cm) in diameter were cut from each of the test
materials and a control,
which was a piece of CELGARD~ 2500 film from Hoechst Celanese Corporation of
Sommerville,
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N.J. CELGARD~ 2500 film is a microporous polypropylene film. Three specimens
were prepared
for each material. The test dishes were number 681 Vapometer cups distributed
by 'Thwing-Albert
Instrument Company of Philadelphia, Pa. One hundred milliliters (ml) of
distilled water was poured
into each Vapometer cup and individual samples of the test materials and
control material were
placed across the open tops of the individual cups. Screw-on flanges were
tightened to form a seal
along the edges of each cup (no sealant grease was used), leaving the
associated test material or
control material exposed to the ambient atmosphere over a 6.5 centimeter (cm)
diameter circle
having an exposed area of approximately 33.17 square centimeters. The cups
were weighed and
placed in a forced air oven set at a temperature of 37 degree C. ( 100, degree
F.). The oven was a
constant temperature oven with external air circulating through it to prevent
water vapor
accumulation inside. A suitable forced air oven is, for example, a Blue M
Power-O-Matic 60 oven
distributed by Blue M Electric Co. of Blue Island, Ill. After 24 hours, the
cups were removed from
the oven and weighed again. The preliminary test water vapor transmission rate
values were
calculated as follows:
Test WTITR = (grams weight loss over 24 hours) x 315.5 (glmzl24 hrs)
The relative humidity within the oven was not specifically controlled. Under
predeternlined set
conditions of 100 degree F (37 degree C.) and ambient relative humidity, the
VWTR for the
CELGARD~ 2500 film control has been determined to be 5000 grams per square
meter for 24
hours (g/m~ /24 hrs). Accordingly, the control sample was run with each test
and the preliminary
test values were corrected to set condition using the following equation:
WVTR = (Test WVTRlcorr.trol WVTR) x 5000 glrn2/24 hrs (glnZ2/24 hrs)
Other methods for determining WVTRs are possible using other testing systems.
One specific test
system used to measure the WVTR values for some of the films and laminates of
the Examples and
Comparative Examples was the PERMATRAN-W 100K water vapor permeation analysis
system,
commercially available from Modern Controls, Inc. (MOCON) of Minneapolis,
Minn.
Blood Strikethrou h~-~Test: Blood Barrier results were measured in accordance
with ASTM F1670-
95. In this test a specimen is subjected to a synthetic blood simulant for a
specified time and
pressure sequence. Visual observation alone is used to determine when, or if,
penetration occurs.
Results are reported as pass ("compliant") or fail.
Hydrostatic Pressure (Hydrohead) Test: The hydrostatic 'pressure test measures
the resistance of
nonwoven materials to the penetration of water under low hydrostatic pressure.
This test procedure
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is in accordance with Method 5514--Federal Test Methods Standard No. 191A,
AATCC Test
Method 127-89 and INDA Test method 80.4-92, modified to include a support of
synthetic fiber
window screen material available at any hardware store. The test head of a
Textest FX-300
Hydrostatic HeadTester, available from Schmid Corp., having offices in
Spartanburg, S.C. was
filled with purified water. The purified water was maintained at a temperature
between 65degree F.
and 85 degree F. (18.3 and 29.4 degree C.), which was within the range of
normal ambient
conditions (about 73 degree F. (23 degree C.) and about 50% relative humidity)
at which this test
was conducted. An 8 inch by 8 inch (20.3 cm by 20.3 cm) square sample of the
test material was
placed such that the test head reservoir was covered completely. The sample
was subjected to a
standardized water pressure, increased at a constant rate until leakage was
observed on the outer
surface of the sample material or the desired hydrostatic pressure was
achieved. Hydrostatic
pressure resistance was measured at the first sign of leakage in three
separate areas of the sample.
This test was repeated for eve specimens of each sample material. The
hydrostatic pressure
resistance results for each specimen were averaged and recorded in millibars
(mbar). A higher
value indicates greater resistance to water penetration.
Peel Test: To determine peel strength a laminate is tested for the amount of
tensile force which will
pull the layers of the laminate apart. Values for peel strength are obtained
using a 4 inch (10.2 cm)
width of fabric, a wider clamp width and a constant rate of extension of 12
inches (30.5 cm) per
minute. The film side of the specimen is covered with masking tape or some
other suitable material
to prevent the film from ripping apart during the test. The masking tape is on
only one side of the
laminate and so does not contribute to the peel strength of the sample. The
sample is delaminated
by hand a sufficient amount to allow it to be clamped into position. The
specimen is clamped in, for
example, an Instron Model TM, available from the Instron Corporation, 2500
Washington St.,
Canton, Mass. 02021, or a Thwing-Albert Model INTELLECT II available from the
Thwing-Albert
Instrument Co., 10960 Dutton Rd., Philadelphia, Pa. 19154, which have at least
4 inches (10.2 cm)
long parallel clamps. The sample specimen is then pulled apart at 180 degrees
of separation at a rate
of 300 mm (about 12 inches) per minute and the tensile strength recorded in
grams force per 4
inches as the average based on the generated curve.
Absorbency Test: This test is performed according to Federal Government
Specification ULT-T-
595b. It is made by cutting a test sample 4 inches by 4 inches (10.2 cm by
10.2 cm), weighing it,
and then saturating it with water for three minutes by soaking. The sample is
then removed from the
water and hung by one corner for 30 seconds to allow excess water to be
drained off. The sample is
then reweighed, and the difference between the wet and dry weights is the
water pickup of the
sample expressed in grams per 4" by 4" sample. The percent absorbency (%
Absorbency) is
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obtained by dividing the total water pick-up by the dry weight of the sample
and multiplying by
100.
Examples of the Invention
All the films in the Examples were multilayered ftlms with two outer or skin
layers in each example
being the same and sandwiching an intermediate or core layer. All films were
cast ftlms and all the
films were embossed prior to stretching to yield a matte finish on one of the
exterior surfaces.
Tables 1, 2 and 3 contain measurements and determinations made according to
the methods
previously described that characterize selected attributes of the laminates of
the ftlms.
EXAMPLE 1
For this example, the film used was a cast coextruded skin-core-skin or "ABA"
film having a core
layer which contained by weight approximately 39% Dow 3310, approximately 2.8%
Dowlex
4012, both available from DowChemical Co., 0.2% of CIBA B900 anti-oxidant and
58%
Supercoat~, a ground, stearic acid coated CaC03, available from English China
Clay. The two
outer or skin layers on opposite sides of the core layer comprised 4.5 percent
of a polymeric blend
of 50% 760.36 ethylene vinyl acetate (EVA) from Exxon Chemical Company and 50%
KS357P
CATALLOY~ polymer from Basell USA Inc. (Wilmington, DE), with approximately 4
percent
Ampacet 10115 antiblock agent. Ampacet 10115 antiblock agent comprises
approximately 20
weight percent Superfloss~ diatomaceous earth and is available from Ampacet
Corporation of
Tarry-town, N.Y. The three layer film was extruded using cast extrusion
equipment of the type
~ described to give an unstretched film having a thickness of approximately 51
microns (2 mils). The
film was wound up on a roll and later sent through a Machine Direction
Orienter (1VID0). The
MDO unit was preheated to 185 to 210 degree F. (85 degree C. to 99 degree C.)
and the ftlm was
stretched approximately 4x while at these temperatures. By saying the film was
stretched 4x it is
meant that, for example, a 1 meter long film would be stretched to a resultant
length of 4 meters.
Each of the two skin layers comprised approximately 2.25 percent of the
overall film by weight. As
a result, the core layer represented approximately 95.5 percent of the film by
weight. After
stretching but before thermal bonding with the nonwoven webs, the film was
allowed to retract
20% without the application of additional heat. The basis weight of the final
film was
approximately 21 grams per square meter (gsm) and the actual thickness of the
resultant film was
approximately 20 microns. See FIG. 6 for a photomicrograph of this example.
The nonwoven webs consisted of a 0.4 osy spunbond and a 0.8 osy
spunbond/meltblown/spunbond
(SMS) nonwoven web with a surfactant treatment. The spunbond, about 14 gsm
basis weight, was
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made of filaments of about 1.8 denier extruded from a copolymer of ethylene
with 3.5% propylene
(resin 6D43, available from Union Carbide Corp.) which were thermally point
bonded. The SMS
fabric had a basis weight of 0.8 osy and consisted of 0.29 osy spunbond outer
layers from
appropriate polypropylene resins such as Montell PF 304 and 0.22 meltblown
center layer from
appropriate polypropylene resins such as Exxon 37466. After the spunbond and
meltblown layers
were thermal point bonded, the SMS laminate was dipped in a bath of Gemtex SM-
33 surfactant
and water and subsequently dried to add about 1% Gemtex SM-33 by weight onto
the nonwoven
fabric.
The stretched film and the nonwoven webs were then thermally bonded together
at calender
temperatures of 245°F (118 degree C.) for the pattern roll and
260°F (127 degree C.) for the anvil
roll at a speed of 800 FPM (244 meters per minute).
EXAMPLE 2
The laminate of Example 2 was made in the same manner as Example 1 except that
the skin layer
formulation consists of 96% CATALLOY KS-084P polymer from Basell USA.
EXAMPLE 3
The laminate of Example 3 was made in the same manner as Example 1 except that
the core layer
of the film was produced using 35% Supercoat and approximately 62% Dow 3310.
The resulting
film was measured to have a basis weight of approximately 17.3 gsm and an
actual film thickness
of about 19 microns. See FIG. 7 for a photomicrograph of this example.
EXAMPLE 4
The film for the laminate consisted of a core layer which contained by weight
approximately 42%
Dow 3310 available from DowChemical Co., similar trace amount and type of
antioxidant as
described in Example 1, and 58% CaC03 as also described in Example 1. The two
outer or skin
layers on opposite sides of the core layer comprised 6 percent of KS084P
CATALLOY~ polymer
from Basell USA Inc. (Wilmington, DE). No diatomaceous earth or other anti-
slip agents or fillers
were added to the skin layer material. The three-layer film was extruded using
cast extrusion
equipment of the type described to give an unstretched film having a thickness
of approximately 51
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microns (2 mils). The film was wound up on a roll and later sent through a
Machine Direction
Orienter (MDO). The MDO unit stretch rolls were heated progressively from
approximately 150 to
210degree F. (66 degree C. to 99 degree C.) The film was stretched
approximately 4x while at these
temperatures. Each of the two skin layers comprised approximately 3 percent of
the overall film by
weight. As a result, the core layer represented approximately 94 percent of
the film by weight.
After stretching but before thermal bonding with the nonwoven webs, the film
was allowed to
retract 10% without the application of additional heat. The resulting film was
measured to have a
basis weight of approximately 23.1 gsm and an actual film thickness of about
23 microns.
The nonwovens of Example 1 were thermally bonded to the film using calender
rolls similar to that
of Example 1 but with the patterned roll at 230 degree F. (110 degree C.), the
smooth roll at 180
degree F. (82 degree C.)and a bonding speed of 330 FPM.
Attributes of the resulting laminate were measured using Hydrohead and Peel
tests. Because of the
time delay specified in ASTM 1670 test method, the barrier attributes of the
laminate were accessed
by Hydrohead testing. A value of at least 300 mbar was selected as a value to
prescreen samples for
subsequent testing using ASTM 1670 procedures. (Samples with tested Hydrohead
values below
300 mbars tend to fail the ASTM 1670 tests.) The laminate of this comparative
example did not
consistently achieve the desired 300 mbar value. The Peel test accessed the
strength of thermal
bonding of the surfactant treated 0.8 osy SMS to the film. Results are
recorded in Table 1.
EXAMPLE 5
The film consisted of the same materials as Example 4 and was stretched and
bonded as described
in Example 4 with the following differences: 3.4x stretch and 18% retraction.
Laminate attributes
for the Peel and hydrohead tests are recorded in Table 1 and Table 2
respectively. The laminates of
this example consistently achieved Hydrohead values of 300 mbar or greater.
The Peel values
assessing the thermal bond between the film and the surfactant treated
nonwoven are significantly
greater. Because the film was stretched less and retracted more, the resulting
film was measured to
have a basis weight of approximately 29.7 gsm and an actual film thickness of
about 25 microns.
This greater thickness is believed to be the reason for the difference in
Hydrohead and Peel values.
EXAMPLE 6
The film and resulting laminate for Example 6 are the same as Example 4 except
that the skin
layers comprise 12% by weight of the film. Since the Peel values are similar
for Comparative
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Examples 3 and 7, the extra amount of polymer in the skin layers is concluded
to be in access of
that needed to promote acceptable attachment of the hydrophilic nonwoven. WVTR
values were
not determined for this sample. The resulting film was measured to have a
basis weight of
approximately 20.2 gsm and an actual film thickness of about 23 microns.
COMPARATIVE EXAMPLE 1
This laminate consisted of a 1.0-osy hydrophilic spunbond thermally laminated
to a multilayered
film that contained no fillers. The hydrophilic spunbond was made according to
the method
described for when hydrophilic chemical additives are added to the polymer
melt as described in
U.S. Patent 5,901,706. The hydrophilic chemical additive was MASIL~ SF-19, a
surfactant
product of PPG Industries. The multilayered film consisted of a 0.6 ml film
having two skin layers,
each contributing 30% by weight to the film's composition. The each skin layer
was made of 65
of CATALLOY~ polymer 71-1, 25 % of Exxon's 3445, 5 % of low density
polyethylene (Quantum
Chemical's NA 334) and 5 % of Ti02 concentrate (Ampacet 110210, 50/50 blend in
polypropylene). The core layer was made of 25 % of CATALLOY~ polymer 71-1, 30
% of
Exxon's 3445, 5 % of low density polyethylene (Quantum Chemical's NA 334) and
40 % of Ti02
concentrate. The film was stretched l.Sx at temperatures of about 140 -
160°F (60 - 71 degree C.).
The resulting film was measured to have a basis weight of approximately 15.4
gsm and an actual
film thickness of about 10 microns. See FIG. 8 for a photomicrograph of this
example.
The nonwoven and the film were thermal bonding together using heated steel
calender rolls
consisting of a patterned roll having a measured temperature of 174°F (
79 degrees C.) and a
smooth roll having a measured temperature of 146 degrees F (63 degree C.) at a
line speed of 25
FPM (7.6 meters per minute). The nonwoven contacted the pattern roll and the
film contacted the
anvil roll.
The calculated effective thickness for this film compares favorably with the
actual measured
thickness, as is shown in Table 3; the difference being 14%. This difference
is attributed to
variations in individual measured basis weight values of film specimens used
to determine the
average GSM value, variations in density values reported in published
references for the filler
components, and undetectable micropores. This difference is at least half as
small as the 31% or
greater differences determined between the effective and actual thickness
values for each of the
other samples (Examples 1, 3 to 6, Comparative Example 2, and presumably
Example 2 which is
similar to Example 1). This distinction between the actual and effective film
thickness values for
Comparative Example 1 for all the other examples supports the existence of
microporous structures.
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COMPARATIVE EXAMPLE 2
This laminate consisted of the 1.0-osy hydrophilic spunbond thermal bonded to
a multilayered film
that contained calcium carbonate (CaC03) similar to that used for Example 1 as
the micropore
developing filler in all film layers. The hydrophilic spunbond was the same as
described in
Comparative Example 1. The multilayered film consisted of skin layers made of
60 % CaC03 in an
custom formulated high viscosity butene-rich APAO polymer from Huntsman and a
core layer of
55% CaC03, 22% Dowlex 2035 LLDPE and 23% AffinityTM EG-8200 LLDPE, both from
Dow
Chemical. Each skin layer made up 10% of the film by weight. The film was
stretched
approximately 3x at temperatures of about 140 - 160°F. The resulting
film was measured to have a
basis weight of approximately 29.2 gsm and an actual film thickness of about
22 microns. See FIG.
9 for a photomicrograph of this example.
The nonwoven and the film were thermal bonding together using heated steel
calender rolls
consisting of a patterned roll having a measured temperature of 200°F
degrees and a smooth roll
having a measured temperature of 170 degree °F and a line speed of 150
FPM. The nonwoven
contacted the pattern roll and the film contacted the anvil roll.
TABLE 1
ASTM
Sam le % Peel WVTR 1670
Absorbenc Av ; Results
m
Comparative 556 67 Less than Pass
Example 1 100
Comparative 563 58 1818 Fail
Example 2
Example 1 475 32 3520 Pass
Example 2 475 52 1000 Pass
Example 3 475 56 101 Pass
Example 4 475 45 Less than ---
100
Example 5 475 95 113 ---
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TABLE 2
All
Specimens
Passing Final Actual Final
300
Hydrohead Film Film Thickness
Sam le value GSM microns
Example 1 Yes 20.8 20.4
Example 4 No 23.1 22.7
Example 5 Yes 29.7 25.4
Example 6 No 20.2 22.8
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TABLE 3
Effective
Actual Avg. Effective Skin/total
Sam le Total Film Total film
Thickness thickness
Tliickness ratio,
Comparative Example10.0 11.4 76
1
Comparative Example22.0 15.2 19
2
Example 1 20.4 10.1 8
Example 3 18.8 11.4 6
Example 4 22.7 12.6 12
Example 5 25.4 16.2 12
Example 6 22.8 11.8 23
While the invention has been described in connection with some possible
embodiments, it is to be
understood that the invention is not limited to those embodiments. On the
contrary, all alternatives,
modifications and equivalents as can be included within the scope and spirit
of the invention
defined in the appended claims are intended to be covered.
31
