Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MEDICAL PACKAGING MATERIAL AND
PROCESS FOR MAKING SAME
' Field of the Invention
The present invention relates generally to materials useful in
forming packages for the medical field, including packaging for
medical instruments and devices that require sterilization. More
specifically, the present invention relates to a hydroentangfed
composite material formed from a cellulosic web and a polymeric
web, and a process for making such material.
Background of the Invention
Surgical instruments and medical devices and appliances must
be sterilized prior to use. To reduce the time of operative and other
medical procedures and to permit physicians to utilize their skills
more efficiently, it has become increasingly common to package
surgical tools, medical devices, and medical appliances in a manner
in which they are most readily accessible to operating room and
medical personnel. The devices are often packaged in a sterile
environment so that the devices are immediately available for use.
This avoids the older technique of anticipating the various tools and
appliances to be used during the surgery and then sterilizing them for
use just prior to the operation.
Typically, the containers in which the instruments and devices
are packaged are made of a textile or nonwoven fabric which protects
the instruments during sterilization processes that may be performed
while in the container. (As used herein, the term "fabric" is intended
to encompass any sheet-like or web material which is formed in
whole, or in part, from a plurality of fibers.) These packages usually
take the form of bags, pouches, or the like. Such containers preserve
sterility upon subsequent storage until opened and the instruments
used.
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The normal sterilization procedure used by most hospitals and
surgical supply rooms today involves using sterilizing mediums, such
as steam or ethylene oxide gas, to penetrate a porous package in
which the surgical instruments or medical devices are maintained.
The gas flows through pores in the packaging material and sterilizes
the instruments contained therein. One well-known method for the
sterile packaging of surgical instruments and medical devices has the
device sealed within a protective envelope package having at least
one portion which is pervious to sterilizing gas, such as ethylene
oxide, but which is impervious to the passage of bacteria.
Suitable fabrics for packaging surgical instruments and
medical devices must exhibit the combined effects of good
permeability to steam, ethylene oxide, or freon-containing sterilizing
gases and adequate bacterial filtration efficiency in order to prevent
the entry of bacteria into the package. In addition to being
permeable, the fabric should be strong and exhibit relatively high
internal bond, or delamination and tear resistance. Often such
products also possess a certain degree of fluid repellency to prevent
further transmission of the bacteria. Other desired properties for such
packaging is that it be non-toxic in accordance with industry and
federal guidelines, substantially lint-free, odor-free, and drapable.
One example of these gas-pervious, bacteria-impervious
materials which has certain of these properties is a spunbonded
polyolefin material sold by E.I. duPont de Nemours & Company under
the trademark TYVEK~. It is a lightly consolidated or unconsolidated
fabric made from spun bonded sheets of flash-spun polyolefin
(usually polyethylene or polypropylene) pfexifilamentary film-fibril
strands. The general procedure for manufacturing TYVEK~ is
disclosed in U.S. Patent No. 3,169,895 to Steuber.
TYVEK~ exhibits high strength and provides the necessary
pore size distribution to allow for sterilization processes to act on
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instruments contained within a package made, at least in part, from
the material.
' TYVEK~, however, is a purely synthetic material and lacks the
qualities, such as suppleness and softness, which are often inherent
in material made with cellulosic webs. TYVEK~ is also difficult to
print and is not as drapable as fabrics made from cellulosic materials.
Alternatives to DuPont's TYVEK~ product have been
developed. In particular, medical packaging substrates consisting of
paper-based webs that have been saturated with binders such as a
latex have been used for packaging surgical instruments and medical
devices. In most of these substrates, a synthetic staple fiber, such as
a polyester or nylon, is incorporated directly into the wood pulp
furnish for forming a composite web. Latex, usually at a high add-on,
is necessary to bind the synthetic fibers to the cellulose-based web
because, without the latex addition, the fibers would tend to pick or
pull out of the sheet with relative ease. The synthetic fiber that is
incorporated into the product increases the tear resistance of the
medical packaging substrate but generally reduces delamination
resistance and tensile strength. The add-on latex ensures the
necessary delarnination resistance to prevent the substrate from
splitting during its end use. Although such products function well as
medical packaging substrates, their tear, puncture, and delamination
resistances could be improved.
Among other various products which have been used in
forming packages for surgical instruments and medical devices, are
several products marketed by Kimberly-Clark Corporation, the
assignee of the present invention. In particular, products sold under
the trade designations "BP321," "BP388," and "BP360" are all latex-
saturated paper products that are marketed for use as medical
packaging substrates. The three identified products are 100 percent
pulp products which, when subjected to a heat seal coating process,
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are acceptable as a high-strength, puncture and delamination
resistant medical packaging substrate. These paper products exhibit
pore size distributions after being subjected to the heat seal coating
treatment that allow them to remain sufficiently breathable for gas
sterilization techniques but yet sufficiently impervious to prevent
bacteria passage according to industry standards.
To form sterile packaging trays from bacteria barrier fabrics, a
surgical device or medical appliance is typically placed in an
impervious tray or tub and a layer of a gas-pervious, bacteria-
impervious paper or plastic is sealed to flanged edges of the tray.
The sealed package is then exposed to ethylene oxide which
permeates the paper or plastic and sterilizes the contents of the
package. Because the paper or plastic is designed to prevent the
passage of bacteria, the contents of the package will remain sterile
until the seal is broken.
An example of a needle/suture package is disclosed in U.S.
Patent No. 4,183,431 to Schmidt et al. and a package for housing a
medical instrument is shown in U.S. Patent No. 5,031,775 to Kane. A
breather pouch is described in U.S. Patent No. 5,217,772 to Brown et
al. wherein an outer layer of plastic material is heat sealed to the
edges of a TYVEK~ sheet to secure a medical instrument within the
package. In addition, U.S. Patent No. 5,418,022 to Anderson et al.
relates to a microbial-resistant package comprising a spunbonded
olefin sheet material, such as TYVEK~, at least a portion of which
has been stretched or thermally deformed.
As for prior art composite forming processes, pulp fibers andlor
pulp fiber webs have been combined with materials such as, for
example, nonwoven spunbonded webs, meltblown webs, scrim
materials, and textile materials. One known technique for combining
these materials is hydraulic entangling. For example, U.S. Patent No.
4,808,467 to Sus ind discloses a high-strength nonwoven fabric
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made of a mixture of wood pulp and textile fibers entangled with a
continuous filament base web.
Laminates of pulp fibers with textiles and/or nonwoven webs
are disclosed in Canadian Patent No. 841,398 to Shambelan.
5 According to that patent, high pressure jet streams of water may be
used to entangle an untreated paper layer with base webs such as,
for example, a continuous filament web. European Patent Application
No. 128,667 also discloses an entangled composite fabric having an
upper and lower surface. The upper surface is disclosed as having
been formed of a printed re-pulpable paper sheet. The other surface
is disclosed as having been formed from a base textile layer which
may be, for example, a continuous filament nonwoven web.
According to that patent application, the layers are joined by
entangling the fibers of the pulp layer with those of the base layer
utilizing columnar jets of water.
It is believed, however, that such hydroentangling processes
have not been applied to the making of substrates for use in medical
packaging. The hydroentangling process usually results in a fluffier,
more porous material. Obviously, the presence of pores in medical
packaging substrates must be sufficiently controlled so that they meet
bacteria impermeability standards, while at the same time remaining
gas pervious.
Thus, there is still a need for further improved medical
substrates that can be used in forming packages for housing medical
devices and surgical instruments. Such packaging must allow for
known sterilization mediums to enter into the package and sterilize
the enclosed appliances.
Summaryr of the Invention
It is an object of the present invention to provide an improved
medical packaging substrate for creating packages to house surgical
instruments, medical devices, medical appliances, and the like.
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Another object of the present invention is to provide a
composite substrate for use in medical packaging which provides the
necessary tear, puncture, and delamination resistances for such
packaging, while maintaining the ability to allow passage of
sterilization gases therethrough.
A further object of the present invention is to provide a medical
packaging substrate that has certain characteristics found in
hydroentangled cellulosic web composites but which also maintain
sufficient tear, delamination, and puncture resistance necessary for
use in the medical packaging field.
These and other objects are achieved by providing a medical
packaging substrate constructed by hydroentangling a cellulosic-
containing base paper with a bonded polymeric spunbond web.
Specifically, a cellulosic-containing base paper is hydroentangled with
a bonded spunbond fabric, such as REEMAY~-brand fabric, which is
then saturated with a binder material such as a latex. The saturated
entangled composite material may then be subjected to calendering
to compact the fabric and minimize surface roughness.
The resulting material is useful in forming packages for
housing medical devices and surgical instruments. The material also
retains the ability to allow passage of sterilization gases therethrough
so that instruments housed within packaging made from the material
may be sterilized using known processes. The material also avoids
tinting of fibers so that the instruments contained within the packaging
remain free of particulates prior to being used. The resulting material
meets the stretch, tear, delamination, and puncture resistances often
required for packaging medical devices, particularly those with sharp
edges.
The material is designed to be treated with a bacteria barrier
impregnating process to ensure sufficient impermeability to prevent
bacteria contamination of products inside a package made from the
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material. Such processes generally employ a polymer, such as a
urethane, that forms a porous coating on the material. The coating
forms a barrier to bacteria by physically blocking access through the
material. The porosity of the coating, however, is sufficient to avoid
interference with the porosity of the material relative to the passage of
air or gas. One such exemplary bacteria barrier treatment that may
be used is the MICROMOD~ process featured by Rexam Industrial
Corporation of Matthews, North Carolina.
Unlike previous medical packaging substrates, such as
TYVEK~, the synthetic web used in the present invention consists of
a continuous bonded structure instead of individual fibers that have
been flash-spun. Unlike TYVEK~, the presence of wood pulp in the
product gives the appearance and feel, as well as the characteristics
of drapability, whiteness, and printability, found in conventional paper-
based substrates.
Other objects, features and aspects of the present invention
are discussed in greater detail below.
Brief Description of the Drawing
A full and enabling disclosure of the present invention,
including the best mode thereof, to one of ordinary skill in the art is
set forth more particularly in the remainder of the specification,
including reference to the accompanying figure, in which:
Figure 1 is a schematic illustration of the process for forming
the inventive hydroentangled pulp/spunbond composite fabric.
Repeat use of reference characters in the present specification
and drawings is intended to represent the same or analogous
features or elements of the invention.
Detailed Description of Preferred Embodiment
It is to be understood by one of ordinary skill in the art that the
present discussion is a description of exemplary embodiments only
and is not intended as limiting the broader aspects of the present
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invention, which broader aspects are embodied in the exemplary
construction.
The present invention addresses the objectives and needs
discussed above by providing a composite fabric formed from
celluiosic material and bonded polymeric spunbond material. The
celfulosic and spunbond materials may be provided to the process as
webs and then hydroentangled according to known processes. The
resulting composite is then saturated with a binder material such as
latex. The composite fabric may contain from about 10 to about 50
percent by weight of the nonwoven continuous filament spunbond
fabric, and from about 50 to about 90 percent by weight cellulosic-
based fibers.
As used herein, the term "spunbonded filaments" refers to
small diameter continuous filaments which are formed by extruding a
molten thermoplastic material as filaments from a plurality of fine,
usually circular, capillaries of a spinnerette with the diameter of the
extruded filaments then being rapidly reduced by, for example,
eductive drawing and/or other well-known spunbonding processes.
The production of spunbonded non-woven webs, or fabrics, is
illustrated in patents such as, for example, U.S. Patent No. 4,340,563
to Appel et al., U.S. Patent No. 3,692,618 to Dorschner et al., U.S.
Patent No. 3,802,817 to Matsuki et al., U.S. Patent Nos. 3,338, 992
and 3,341,394 to Kinnev, U.S. Patent No. 3,502,763 to Hartman, U.S.
Patent No. 3,502,538 to Levv, and U.S. Patent No. 3,542,615 to
Dobo et al. The disclosures of these patents are hereby incorporated
in their entireties by reference.
Spunbonded fibers are generally not tacky when they are
deposited onto a collecting surface. Spunbonded fibers are generally
continuous and have diameters larger than 7 micrometers, more
particularly between about 10 and 20 micrometers.
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The filamentous webs of continuous spunbond filaments can
be produced from any fiber-forming thermoplastic polymers. Suitable
filaments include monocomponent filaments of a thermoplastic
polymer or a blend of more than one thermoplastic polymer.
Additionally, suitable filaments include multi-component conjugate
filaments that contain at least two component polymers which occupy
distinct cross-sections of the filament along substantially the entire
length of the filament and multicomponent filaments that contain
discrete fibrils of one or more of component polymers within a
filamentous polymer matrix.
Thermoplastic polymers suitable for the continuous filaments
include polyolefins, polyesters, polyamides, and copolymers and
blends thereof. Polyolefins suitable for the conjugate fibers include
polyethylene, e.g., high density polyethylene, medium density
polyethylene, low density polyethylene and linear low density
polyethylene; polypropylene, e.g., isotactic polypropylene,
syndiotactic polypropylene, blends thereof, and blends of isotactic
polypropylene and atactic polypropylene; polybutylene, e.g., poly(1-
butene) and poly(2-butene); polypentene, e.g., poly(1-pentene) and
poly(2-pentene); poly(3-methyl-1-pentene}; poly(4-methyl-1-pentene);
and copolymers and blends thereof. Suitable copolymers include
random and block copolymers prepared from two or more different
unsaturated olefin monomers, such as ethyfene/propylene and
ethylene/butylene copolymers. Polyamides suitable for the conjugate
fibers include nylon 6, nylon 6/6, nylon 4/6, nylon 11, nylon 12, nylon
6/10, nylon 6/12, nylon 12112, copolymers of caprolactam and
alkaline oxide diamine, and the like, as well as blends and
copolymers thereof. Suitable polyesters include polyethylene
terephthalate, polybutylene terephthalate, polytetramethylene
terephthalate, pofycyclohexylene-1,4-dimethylene terephthalate, and
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isophthalate copolymers thereof, as well as blends thereof. Of these
suitable polymers, more desirable polymers are the polyesters.
Spunbonded nonwoven webs are typically bonded subsequent
to web formation by, for example, pattern bonding. As used herein,
5 the term "pattern bonding" refers to a process of bonding a nonwoven
web in a pattern by the application of heat and pressure. Pattern
bonding typically is carried out at a temperature in a range of from
about 80° C to about 180° C and a pressure in a range of from
about
150 to about 1,000 pounds per linear inch (59-178 kg/cm). The
10 pattern employed typically will have from about 10 to about 250
bondslinch2 (1-40 bondslcm2) covering from about 5 to about 30
percent of the web surface area. Such pattern bonding is
accomplished in accordance with known procedures as disclosed in
U.S. Design Patent No. 239,566 to Voat, U.S. Design Patent No.
264,512 to Rogers, U.S. Patent No. 3,855,046 to Hansen et al., and
U.S. Patent No. 4,493,868. The disclosures of these patents are
incorporated herein in their entireties by reference.
Numerous commercially available spunbonded webs are
presently available using different thermoplastic synthetic materials.
The most extensively employed commercial materials are made from
filaments of polyamides, polyesters and polyolefins such as
polyethylene or polypropylene, although other filamentary materials
such as rayon, cellulose acetate and acrylics may also be employed.
Exemplary of the commercially available spunbonded polymeric web
materials that may be employed in the present invention are the gas
bonded nylon filament materials sold under the trademark CEREX,
the lightly needled tacked polyester materials sold under the
trademark REEMAY, by Reemay, fnc. of Old Hickory, Tennessee,
and the thermal bonded polypropylene materials sold under the
trademarks LUTRASIL and CELESTRA. Of course, other
commercially available spunbonded base web materials also may be
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employed with good results. Various basis weights of REEMAY-
brand materials may be used, such as REEMAY 2817, REEMAY
5200, and REEMAY 2275.
The cellulosic-based, pulp fiber, component of the present
composite material may be made from woody and/or non-woody plant
fiber pulp. The pulp may be a mixture of different types and/or
qualities of pulp fibers, or, alternatively, one type or grade of pulp may
comprise 100 percent of the pulp fiber component. For example, a
pulp containing both low-average fiber length pulp and high-average
fiber length pulp (e.g., virgin softwood pulp) may be used. Low-
average fiber length pulp may be characterized as having an average
fiber length of less than about 1.2 mm, usually from about 0.7 mm to
about 1.2 mm. High-average fiber length pulp may be characterized
as having an average fiber length of greater than about 1.5 mm,
usually from about 1.5 mm to about 6 mm.
When used, low-average fiber length pulp may be certain
grades of virgin hardwood pulp and secondary (i.e., recycled) fiber
pulp from sources such as, for example, newsprint, reclaimed
paperboard, and office waste. High-average fiber length pulp may be
bleached and/or unbleached virgin softwood pulps.
Wood pulps of long, flexible fibers that have a low coarseness
index are more useful for the cellulosic layer of the present invention.
Illustrative examples of suitable pulps include southern pines,
northern softwood kraft pulps, red cedar, hemlock, black spruce, and
mixtures thereof. Exemplary commercially available long pulp fibers
suitable for the present invention include those available from
Kimberly-Clark Corporation under the trade designations "Longlac-
19," "Coosa River-54," "Coosa River-5fi" and "Coosa River-57."
The pulp fibers used in the present invention may be unrefined
or may be beaten to various degrees of refinement. Small amounts
of wet-strength resins andlor resin binders may be added to improve
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strength and abrasion resistance. Useful binders and wet-strength
resins include, for example, Kymene 557 H available from the
Hercules Chemical Company and Parez 631 available from American
Cyanamid, Inc. Cross-linking agents and/or hydrating agents, as
known in the art, may also be added to the pulp mixture. Debonding
agents may also be added to reduce the degree of hydrogen bonding
if a very open or loose nonwoven pulp fiber web is desired. One
exemplary debonding agent is available from the Quaker Chemical
Company of Conshohocken, Pennsylvania, under the trade
designation "Quaker 2008." The addition of certain debonding agents
in the amount of, for example, 1 to 4 percent, by weight, of the
composite also appears to reduce the measured static and dynamic
coefficients of friction and improve the abrasion resistance of the
continuous filament-rich side of the composite fabric. The debonder
is believed to act as a lubricant or friction reducer.
The cellulosic layer may also contain hydrophilic synthetic
fibers, e.g., rayon fibers and ethylene vinyl alcohol copolymer fibers,
and hydrophobic synthetic fibers, e.g., polyolefin fibers. Desirably,
the cellulosic layer has a basis weight between about 10 gsm and
about 50 gsm, more desirably between about 15 gsm and about 30
gsm.
The method for forming the inventive composite material
requires that either the upper or lower surface of a cellulosic-based
web be brought into contact with an upper or lower surface of a
bonded polymeric spunbond web. The webs are then
hydroentangled to form the composite material. One method of
bringing the cellulosic-based and polymeric spunbond webs into
contact is by superimposing a coherent pulp fiber sheet over the
continuous filament layer. The coherent pulp fiber sheet may be, for
example, a re-pulpable paper sheet, a re-pulpable tissue sheet or a
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batt of wood pulp fibers. Alternatively, the cellulosic-based web may
be overlayed with the polymeric spunbond web.
In addition, the present invention includes the hydroentangling
of more than just one cellulosic-based layer with just one polymeric
spunbond layer. Two cellulosic-based webs could be used, one
superimposed onto the upper surface of the polymeric spunbond
web, and the other superimposed onto the lower surface of the
polymeric spunbond web. !n this manner, a polymeric spunbond web
is "sandwiched" between the cellulosic-based webs prior to
entanglement. The present invention also contemplates the use of
more than one cellulosic-based web per surface of polymeric
spunbond web. In other words, two or more separate cellulosic-
based webs could be superimposed onto either or both surfaces of
the polymeric spunbond web. The placement of the spunbond web
between two sheets of paper, however, will result in a more supple
and soft composite fabric. in this embodiment, the spunbond web will
provide the desired toughness to the fabric.
The layered webs, after being brought into contact with each
other, are then subjected to a hydraulic entanglement process
described herein so that a composite material suitable for the end use
as a medical packaging substrate is formed. A prominent
characteristic of this composite material is that the hydraulic
entanglement process integrates the layers so that they are no longer
clearly identifiable in the resulting composite. This ensures that the
resulting substrate has the necessary delamination resistance
required for its ultimate end use.
The hydraulically entangled composite fabric may be dried
utilizing a non-compressive drying process. Through-air drying
processes have been found to work particularly well. Other drying
processes which incorporate infra-red radiation, Yankee dryers,
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steam cans, vacuum de-watering, microwaves, and ultrasonic energy
may also be used.
After drying, the hydraulically entangled composite material is
then saturated with a binder such as a stiff acrylic latex so that the
celluiosic webs are sufficiently bonded and the possibility of tinting is
substantially eliminated. The latex-saturated composite may then be
calendered if desired to attain smoothness. Finally, the composite
material may be printed either before or after being subjected to
further calendering processes such as supercaiendering.
Prior to being used as a substrate for the medical packaging
industry, the composite material is subjected to a process which
enhances the substrate's bacteria barrier properties. One example of
such a technique is the MICROMOD~ process by Rexam which fills
larger pores in fabric with particulates that ensure the required barrier
qualities. The material may then be formed into various medical
packaging, as is well known in the art.
Referring to Figure 1 of the drawings, a process for forming the
present hydroentangled pulp/spunbond composite fabric is
schematically illustrated at 10. According to one embodiment of the
present invention, a suspension of pulp fibers is supplied by a head-
box 12 and deposited via a sluice 14 in a uniform dispersion onto a
forming fabric 16 of a conventional papermaking machine. The
suspension of pulp fibers may be diluted to any consistency which is
typically used in conventional papermaking processes. For example,
the suspension may contain from about 0.01 to about 1.5 percent by
weight pulp fibers suspended in water. Water is removed from the
suspension of pulp fibers to form a layer of pulp fibers 18.
A polymeric spunbond web 20 is unwound from a supply roll
22 and travels in the direction indicated by the arrow associated
therewith as the supply roll 22 rotates in the direction of the arrows
associated therewith. The polymeric web 20 passes through a nip 24
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of an S-roll arrangement 26 formed by the stack rollers 28 and 30 on
its way to a position where web 20 will be brought into contact with
pulp layer 18.
Alternatively, the polymeric spunbond web, Pike pulp layer 18,
5 could be supplied to the process directly from a mechanism for
creating the web. In this manner, supply roll 22 would be eliminated,
and web 20 would be fed directly from the web forming process. Pulp
layer 18 could alternatively be fed from a supply roll instead of directly
from a papermaking machine.
10 The nonwoven substrate 20 may be formed by known
continuous filament nonwoven extrusion processes, such as, for
example, known solvent spinning or melt-spinning processes. The
continuous filament nonwoven substrate 20 is preferably a nonwoven
web of continuous melt-spun filaments formed by the spunbond
15 process. As described above, the spunbond filaments may be
formed from any melt-spinnable polymer, copolymers or blends
thereof. For example, the spunbond filaments may be formed from
polyolefins, polyamides, polyesters, polyurethanes, A-B and A-B-A'
block copolymers where A and A' are the thermoplastic endblocks
and B is an elastomeric midblock, and copolymers of ethylene and at
least one vinyl monomer such as, for example, vinyl acetates,
unsaturated aliphatic monocarboxylic acids, and esters of such
monocarboxylic acids. If the filaments are formed from a polyolefin
such as, for example, polypropylene, the nonwoven substrate 20 may
have a basis weight from about 3.5 to about 70 grams per square
meter (gsm). More particularly, the nonwoven substrate 20 may have
a basis weight from about 10 to about 35 gsm. In one particularly
preferred embodiment of the present invention, the polyester
spunbond web has a basis weight of from about 17 gsm to about 35
gsm.
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The polymers may include additional materials such as, for
example, pigments, antioxidants, flow promoters, stabilizers and the
like.
Examples of processes for making hydroentangled composite
fabrics are disclosed in U.S. Patent Nos. 5,389,202, 5,587,225, and
5,573,841, all of which are assigned to the assignee of the present
application and all of which are incorporated in their entireties herein
by reference thereto.
In one aspect of the present invention, the nonwoven
continuous filament substrate may have a total bond area of less than
about 30 percent (as determined by optical microscopic methods)
and a bond density greater than about 100 pin bonds per square
inch. For example, the nonwoven continuous filament substrate may
have a total bond area of from about 2 to about 30 percent and a
bond density of from about 100 to about 500 pin bonds per square
inch. As a further example, the nonwoven continuous filament
substrate may have a total bond area of from about 5 to about 20
percent and a bond density of from about 250 to 350 pin bonds per
square inch.
The pulp fiber layer 18 is then brought into contact with the
upper surface of the nonwoven substrate 20. In the embodiment
depicted in Figure 1, pulp layer 18 is laid on the polymeric web which
rests upon a foraminous entangling surface 32 of a conventional
hydrauiic entangling machine. It is preferable that the pulp layer 18 is
between the nonwoven substrate 20 and the hydraulic entangling
manifolds 34. The pulp fiber layer 18 and nonwoven substrate 20
pass under one or more hydraulic entangling manifolds 34 and are
treated with jets of fluid to entangle the pulp fibers with the filaments
of the polymeric web 20. The jets of fluid also drive pulp fibers into
and through the polymeric web 20 to form the composite material 36.
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The hydraulic entangling may take place while the pulp fiber
layer 18 is highly saturated with water. For example, the pulp fiber
layer 18 may contain up to about 90 percent by weight water just
before hydraulic entangling.
Alternatively, the pulp fiber layer may be an air-laid or dry-laid
layer of pulp fibers. The present invention also contemplates
superimposing a dried pulp sheet on a polymeric web as disclosed
herein, rehydrating the dried pulp sheet, and then subjecting the
rehydrated pulp sheet to hydraulic entangling.
Hydraulic entangling a wet-laid layer of pulp fibers is desirable
because the pulp fibers can be embedded into and/or entwined and
tangled with the polymer web without interfering with "paper" bonding
(sometimes referred to as hydrogen bonding) since the pulp fibers
are maintained in a hydrated state. In addition, the hydraulic
entanglement process results in a composite material having the
previously separate layers of cellulosic-based material and polymeric-
based material integrated in a manner such that delamination
resistance is greatly increased and a substantially unitary composite
product is formed.
The hydraulic entangling may be accomplished utilizing
conventional hydraulic entangling equipment such as may be found
in, for example, in U.S. Patent No. 3,485,706 to van , which is
incorporated herein in its entirety by reference. Another
hydroentangling process is disclosed in U.S. Patent No. 4,144,370 to
Bouolton. Hydroentangled composite nonwoven fabrics of a
continuous filament nonwoven web and a pulp layer are also
disclosed in U.S. Patent No. 5,284,703 to Everhart et al. and U.S.
Patent No. 4,808,467 to Suskind et al., which are also incorporated
herein in their entireties by reference.
The hydraulic entangling of the present invention may be
carried out with any appropriate working fluid such as, for example,
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18
water. The working fluid flows through a manifold which evenly
distributes the fluid to series of individual holes or orifices. These
holes or orifices may be from about 0.003 to about 0.015 inch in
diameter. For example, the inventive composite material may be
formed utilizing a manifold produced by Honeycomb Systems
Incorporated of Biddeford, Maine, containing a strip having 0.007 inch
diameter orifices, 30 holes per inch, and 1 row of holes. Many other
manifold configurations and combinations may be used. For
example, a single manifold may be used or several manifolds may be
arranged in succession.
In the hydraulic entangling process, the working fluid passes
through the orifices at a pressure ranging from about 200 to about
2000 pounds per square inch gage (psig). At the upper ranges of the
described pressures, it is contemplated that the composite fabrics
may be processed at speeds of about 1000 feet per minute (fpm).
The fluid impacts the pulp fiber layer 18 and the nonwoven
substrate 20 which are supported by a foraminous surface 32 which
may be, for example, a single plane mesh having a mesh size of from
about 40X40 to about 100X100. The foraminous surface 32 may also
be a multiple mesh having a mesh size from about 50X50 to about
200X200. As is typical in many water jet treatment processes,
vacuum slots 38 may be located directly beneath the hydro-needling
manifolds or beneath the foraminous entangling surface 32
downstream of the entangling manifold so that excess water is
withdrawn from the hydraulically entangled composite material 36.
Although the inventors should not be held to a particular theory
of operation, it is believed that the columnar jets of working fluid drive
the pulp fibers into and partially through the matrix or nonwoven
network of filaments in the polymeric web. When the fluid jets and
pulp fibers interact with the polymer web, the pulp fibers are
entangled with filaments of the nonwoven web and with each other. If
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19
the nonwoven filament web is too loosely bonded, the filaments are
generally too mobile to form a coherent matrix to secure the pulp
fibers. On the other hand, if the total bond area of the substrate is
too great, the pulp fiber penetration may be poor. Moreover, too
much bond area will also cause a splotchy composite fabric because
the jets of fluid will splatter, splash, and wash off pulp fibers when
they hit the large non-porous bond spots.
The energy of the fluid jets that impact the pulp layer and
substrate may be adjusted so that the pulp fibers are inserted into
and entangled with the continuous filament substrate in a manner that
enhances the two-sidedness of the fabric. That is, the entangling
may be adjusted to produce high pulp fiber concentration on one side
of the fabric and a corresponding low pulp fiber concentration on the
opposite side. Alternatively, the continuous filament substrate may
be entangled with one or more pulp fiber layers on one side and one
or more different pulp fiber layers on the other side to create a
composite fabric with two pulp-rich sides. In that case, hydraulically
entangling both sides of the composite fabric is desirable.
After hydroentanglement, composite material 36 may then be
subjected to a wet-pressing operation. Wet-pressing is performed on
the material to provide a certain smoothness and to increase the
density of the fabric. A typical wet-pressing process involves
employing a wringer-like apparatus consisting of two or more rollers
through which the material is passed. The rollers press the fabric to
remove excess moisture. Alternatively, in certain instances, wet-
pressing can be achieved by using a metal plate-pressing process.
In this particular arrangement, absorbent paper is placed in contact
with the composite material and then both the absorbent paper and
composite material are placed between two or more metal plates. A
force is applied to the metal plates so as to press the materials
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together. In this manner, excess moisture is squeezed from the
composite material.
After being pressed, the fabric is then dried by conventional
means. One example of a conventional means would be a steam-
s heated drum. Another is the through-air dryer shown in Figure 1 at
42 and described as follows.
In the non-compressive drying operation shown in Figure 1
(and without a wet-pressing step), differential speed pickup roll 40
may be used to transfer the material from the hydraulic needling belt
10 to the drying operation. Alternatively, conventional vacuum-type
pickups and transfer fabrics may be used. If desired, the composite
fabric may be wet-creped before being transferred to the drying
operation.
Non-compressive drying of the web may be accomplished
15 utilizing a conventional rotary drum through-air drying apparatus
shown in Figure 1 at 42. The through-dryer apparatus 42 may be an
outer rotatable cylinder 44 with perforations 46 in combination with an
outer hood 48 for receiving hot air blown through the perforations 46.
A through-dryer belt 50 carries the composite fabric 36 over the upper
20 portion of the through-dryer outer cylinder 40. The heated air forced
through the perforations 46 in the outer cylinder 44 of the through-
dryer 42 removes water from the composite fabric 36. The
temperature of the air forced through the composite fabric 36 by the
through-dryer 42 may range from about 200° F (93° C) to about
500° F (260° C). Other useful through-drying methods and
apparatus may be found in, for example, U.S. Patent Nos. 2,666,369
and 3,821,068, both of which are incorporated in their entireties
herein by reference.
After drying, the composite fabric 36 is then saturated with a
binder such as latex. The binder serves to additionally bind the fabric
together and ensures the necessary delamination resistance to
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21
prevent the substrate from splitting and pulling apart during its end
use. The use of a binder also eliminates the potential for tinting by
the fabric. Linting occurs when fibers are released from the material
and result in particulate parts of fibers creating "dust" within packages
made from the material. Other properties improved by the binder
include dimensional stability, resistance to chemical and
environmental degradation, embossability, resiliency, conformability,
moisture and vapor transmission, and abrasion resistance, among
others. One example of a latex that may be used is Hycar 26106
available from the B. F. Goodrich Company, with a glass transition
temperature of 29°C.
Any of the latex binders commonly employed for reinforcing
paper can be utilized and are well known to those having ordinary
skill in the art. Such binders include, by way of illustration only,
polyacrylates, including polymethacrylates, poly(acrylic acid), poly
(methacrylic acid), and copolymers of the various acrylate and
methacrylate esters and the free acids; styrene-butadiene
copolymers; ethylene-vinyl acetate copolymers; nitrite rubbers or
acrylonitrile-butadiene copolymers; polyvinyl chloride); polyvinyl
acetate); ethylene-acrylate copolymers; vinyl acetate-acrylate
copolymers; neoprene rubbers or traps-1,4-polychloroprenes; cis-1,4-
polyisoprenes; butadiene rubbers or cis-and traps-1,4
polybutadienes; and ethylene-propylene copolymers.
Specific examples of commercially available latex binders are
summarized in Table 1 below.
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22
TABLE 1
Suitable Latexes for Saturation
Polymer Type Product Identification
Polyacrylates Hycar~ 26083, 26084, 26120,
26104, 26106, 26322, 26469
B. F. Goodrich Company
Cleveland, Ohio
Rhoplex~ HA-8, HA-12, HA-16
NW-1715, B-15
Rohm and Haas Company
Philadelphia, Pennsylvania
Carboset~ XL-52
B. F. Goodrich Company
Cleveland, Ohio
Styrene-butadiene copolymers Butofan~ 4264, 4262
BASF Corporation
Sarnia, Ontario, Canada
DL-219, DL-283, DL-239
Dow Chemical Company
Midland, Michigan
Nitrite rubbers Hycar~ 1572, 1577, 1570X55,
1562X28
B. F. Goodrich Company
Cleveland, Ohio
Polyvinyl chloride) Vycar~ 352, 552
B. F. Goodrich Company
Cleveland, Ohio
Ethylene-acrylate copolymers Michem~ Prime 4990
Michelman, Inc.
Cincinnati, Ohio
Adcote 56220
Morton Thiokol, Inc.
Chicago, Illinois
Vinyl acetate-acrylate Xlink 2833
copolymers National Starch & Chemical Co.
Bridgewater, New Jersey
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23
The amount of binder added to the paper, on a dry weight
basis, typically wilt be in the range of from about 15 to about 60
percent, based on the dry weight of the paper. In one particular
embodiment, the latex can be added at a dry add-on of around 50
percent by weight. The amount of binder added, as well as the basis
weight of the paper before and after saturation with binder in general
are determined by the application intended for the latex saturated
composite material.
Finally, paper-impregnating or saturating techniques are well
known to those having ordinary skill in the art. Typically, a formed
paper web is exposed to an excess of the impregnating dispersion or
latex, run through a nip, and dried. One particular process passes
the web through squeeze rolls which apply latex from a saturation
latex basin and then provide the web to a number of drying cans held
at temperatures of about 200 ° F (93 ° C) to about 300 °
F ( 149 ° C).
The saturated web is then wound by a roll windup device and is ready
for commercial use. However, the impregnating dispersion may be
applied by other methods, such as brushing, doctor blading, spraying,
and direct and offset gravure printing or coating and the present
invention is not limited to any particular application process.
Generally, the stiffer, as opposed to the stretchable or softer,
latexes are preferred. The stiffness or hardness of a particular latex
binder depends on the type of latex being used, as well as the
manufacturing source of the latex. For example, an acrylic latex with
a glass transition temperature of greater than 20° C is generally
considered to be a "hard" or "stiff' latex, and an acrylic latex with a
glass transition temperature of less than -5° C is generally considered
to be a "soft" latex. Acrylic latexes having glass transition
temperatures between -5° C and 20° C are considered medium
latexes. Styrene butadiene ("SBR") latexes, on the other hand, are
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24
considered hard if they have glass transition temperatures above 20°
C and soft if they have glass transition temperatures below 0° C.
Optionally, the fabric may then be calendered by known
processes using steel calendering rolls. Calendering will add
smoothness to the fabric. Processes such as "supercalendering,"
which use a harder steel roll and a softer, polishing, roll can also be
used. In supercalendering, a high-gloss polish is created. Unlike
TYVEK~, which is often difficult to print, the present invention results
in an easily printable fabric.
The fabric so made may then be treated with a bacteria barrier
to ensure the necessary bacteria impermeability required for use in
forming medical packages. One such exemplary bacteria barrier
technique is provided by Rexam Industries Corporation via their
MICROMOD~ membrane coating process. This process is disclosed
in U.S. Patent No. 5,523,118 to Williams, which is incorporated herein
by reference thereto. This process involves subjecting the fabric to a
technique which fills the large pores with a urethane-based polymer
so that the fabric acts as a bacteria barrier but does not interfere with
the permeability required for other functions. In addition, anti-
microbial agents may be added to the pore-embedded polymer so
that anti-microbial activity will be exhibited by the fabric.
The composite material is then supplied to a maker of medical
packaging which transforms the fabric into the appropriate packaging
necessary for storing medical devices and appliances and surgical
instrumentation.
Although Figure 1 shows a process wherein only one web of
pulp and one web of spunbond filament is employed, it is to be
understood that the fabric can be made with multiple layers of either
web and then subjected to the disclosed hydroentanglement. The
pulp fiber layers used may be identical, or may consist of different
types of pulp in order to achieve desired characteristic peculiar to the
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types of pulp fiber used. Alteratively, layers can be arranged so that
two or more layers of pulp are hydroentangled to only one surface of
the spunbond filament web. Any of these combinations or others that
could be developed is within the scope of the present invention.
5 The hydroentanglement process creates suppleness and
stretchability for the fabric with the spunbond web providing tear
strength that normal cellulosic webs do not have. The latex
saturation provides bonding and ensures a relatively lint-free material.
The calendering process densifies the paper, thus closing up the pore
10 structure and preventing the passage of bacteria through the fabric.
The calendering increases the surface area and thus creates more
structure to intercept passage of the bacteria. Although the
calendering increases the surface area and does fill some of the
pores, the present procedure allows the material to be sufficiently
15 breathable so that sterilization procedures using gas diffusion
processes can be performed. After treatment with a bacteria barrier-
creation process, the material is ready for transformation into medical
packaging.
The following examples are meant to be exemplary procedures
20 only which aid in the understanding of the present invention. In order
to make comparative tests to commercially available products used in
medical packaging, the inventive substrate was made according to
the following example.
EXAMPLE 1
25 Two sheets of dry base paper commercially available from
Kimberly-Clark Corporation under the designation BP22 at 14 pounds
per ream each were, after wetting, hydroentangled directly to
REEMAY~ 2275 (2.2 denier per filament (dpf); 0.75 ounces/yard2).
Hydroentangling was performed on a pilot hydroentangler meeting
the typical characteristics described above. On the first pass of
hydroentangling, 400 psig was applied in order to set the sheets into
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26
place. Second and third passes over the sheets were run at 800 psig
in order to entangle the sheets. Excess water was removed under
vacuum. The composite fabric was then wet-pressed for five minutes
at 200 psig and dried on a steam-heated drum. The dried fabric was
then impregnated with a hard latex sold under the trade name Hycar
26106 (T9= 29°C) at a dry add-on of around 50 percent.
In order to saturate the hydroentangled composite handsheets,
leaders of stiff grade paper were attached to each handsheet to aid in
feeding the sheet through a saturator or size press. While the
saturator employed was constructed in the laboratory, it was
equivalent to the commercially available Model LW-1 Atlas Laboratory
Wringer (Atlas Electric Devices Company, Chicago, Illinois). Each
leader was butted against the edge of the handsheet and taped with
masking tape. The latex binder was charged to an addition funnel
having a stopcock. The funnel was suspended over the rolls of the
saturator by means of a ring stand. The pressure on the saturator
press rolls was adjusted by a mechanical arm which controlled the
amount of binder pick-up. When the pressure was set, the stopcock
of the addition funnel was opened. When the binder formed an even
bead across the leader paper strip, the saturator was started,
providing an even flooding of binder over the handsheet as it passed
between the press rolls. After passing through the saturator, the
leader was removed from the impregnated handsheet and the
handsheet was dried on the can dryer with frequent turning to
minimize migration of the latex binder.
The latex-saturated composite fabric was then subjected to
steel calendering. The material was calendered with two passes
between steel calendering rollers at 20 psig.
The produced fabric was then compared to TY1/EK~ material
available from DuPont, and latex-saturated Base Paper No. 388
(BP388) and Base Paper No. 321 (BP321 ), both commercially
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27
available from Kimberly-Clark Corporation. The data in the following
table sets forth the comparative results.
CA 02294160 1999-12-21
WO 99/00244 28 PCT/US98/13534
as ~ _~ ~ ~ o o
M ~r m n
W cu
D
c
E ~ ~ o c~~o
~E c c ''"'c c
'n ~ '~ ~ ~ ~E
(~ v O (~ M ~ ~ f0
~ ~ 'd U C
o ~ M O ~ O
~ M ~ o ao
U U
N ~ O O O O
~I lt~ N
N ~ ~ 1~ 00 M
UI ~ ~ ~ 'n
c
o
r0 O
N
O O
m UI ~ co
'n
Q ~
c~)
o ao 0
o
~ ....
_ C ~ O ~ ~ 00 r-
c~ O U ~ ... ',. '-'
O ~ O ,~ ~- CC
O O
O ~ ~ N t~ M
M _ ~ O
N e- e- N
0 0 0 0
-.
N ~ ~ ~ ~ N
00
ca
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e- O 000 N LU
~U ~ M M
a a
m m
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WO 99/00244 PCT/LJS98/13534
29
In the above table, column 1 represents the products to which
the inventive composite material of Example 1 was compared.
Column 2 represents the basis weight in grams per square meters of
each of the comparative products. Basis weights were determined by
s ASTM D-3776-85. Column 3 is the thickness of the products in
millimeters. Column 4 represents the porosity in seconds per 100 cc
of air, with the number in parentheses indicating the number of
sheets. Porosity was determined pursuant to the Gurley Hill Porosity
test according to ASTM D-726-84. Column 5 reports tear strengths in
to the MD (machine direction) and CD (cross machine direction) in
grams and were performed in accordance with the Elmendorf Tear
Test, TAPPI methods T414 and T402. The tensile strength is
reported in Column 6 in kilograms per 15 millimeters and was
determined on an Instron machine according to TAPPI method T494.
15 The percentages of stretch in both the machine direction (MD) and
cross machine direction (CD} was determined simultaneously and are
indicated in Column 7.
Column 8 reports the delamination strength in grams per 15
millimeters and was performed on the Instron machine according to
2o the following procedure. First, sample strips of the substrate were cut
to dimensions of 2-1/2 inches x 7-1/2 inches long grain (7-1/2 inch in
the machine direction). Two strips were cut per sample. An electric
hot plate having a six-inch wide solid steel top was then heated to
312° F (156° C) and a piece of steel plate (1-1/2 inch x 6
inches x 1-
25 1/2 inches) with an insulated handle in the center (weight 2640 grams
which was equal to .9692 psi) was placed on top of the hot ptate and
preheated to 312° F (156° C). A 1/8 inch strip of Ideal "black"
paper
delamination tape (1 inch wide) was placed on each side of the
sample to be tested, with one superimposed upon the other, in the
30 long grain direction of the sample. The tape was not preheated. The
sample was then pressed between the hot plate and the steel plate
1
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for 20 seconds at 312° F (156° C), leaving 1 inch of tape on
each
end unpressed. The samples were then cooled and trimmed to 15
mm wide, ensuring that each edge of the Ideal tape was equally
trimmed. An Instron tensile tester model TM-M was then calibrated
s and set up with a cross head speed of 30 cm/min; a chart speed of 3
cm/min; and a full scale load of 2 kilograms. Delamination resistance
was then determined using the Instron in an attempt to delaminate
the sample substrate being tested. Delamination is expressed in the
tables above in grams.
to As indicated, neither the material of Example 1 or TYVEK~
delaminated. Instead, failures occurred at the adhesive interface
during the testing as opposed to within the sheet itself.
Finally, the estimated dart impact is reported in Column 9 and
was performed according to ASTM D-1709-91.
15 The bacteria barrier characteristics of three of the products
were also determined and are reported in the following table.
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31
TABLE 3
3
Descri~~tion Por Cumulative
ize
(micrometers) Pore Number
M~
MFP
Example 1 300 7.5 20.4 3.28 x 106
BP 388 25.5 2.7 9.6 3.40 x 105
BP 321 not tested ___
TYVEK 12.2 1.8 3.8 3.50 X 10'
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32
In Table 3, column 1 identifies the product being tested.
Column 2 is a measure of the pore size in micrometers. The
maximum pore size and the minimum pore size found in the products
are listed in microns with the median flow parameter being given at
50 percent of air flow. This pore size determination was made using
a Coulter Porometer commercially available from Couiter Electronics,
Ltd., Luton Beds, England. The cumulative pore number is given in
exponential terms as pores per square centimeter and is regarded as
an index of sheet tortuosity. Sheet tortuosity is an indication of the
z o extent of tortuous paths created by the pores in a sheet of material.
Obviously, a sheet with numerous tortuous pore paths provide a more
desirable bacteria barrier because the bacteria is more likely to
become trapped in such material.
As can be seen in the comparative data, the present inventive
fabric material compares favorably with the TYVEK~ material.
Although the porosity data of the present invention was not, in this
particular trial, comparable to TYVEK~, the separate treatment with a
MICROMOD~ process would result in an adequate bacteria barrier
useful for packaging medical and surgical instruments.
2 o It is generally accepted that fabrics with cumulative pore
numbers of more than 3 million per square centimeter will perform
adequately as bacteria barriers. Thus, the present product meets
that requirement and is capable of being formed into various medical
packaging.
2 s EXAMPLE 2
In this example, one sheet of dry base paper commercially
available from Kimberly-Clark Corporation under the designation
BP22 was hydroentangled directly to REEMAY~ 2004 (0.40
ounces/yard2, 3.7 mil). On the first pass of the hydroentangling unit
3 o described above, 400 psig was applied in order to set the sheets in
place. The second pass of the hydroentangler was run at 800 psig to
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33
entangle the webs. Finally, a third pass at 0 psig was applied in order
to dry the composite material. Further drying was accomplished on a
dryer can.
The composite material so formed was then saturated at
approximately 45 percent pickup with Hycar 26322. This particular
grade of latex is a high stretch latex. After saturation, the latex-
saturated composite material was subjected to steel calendering at
20 psig for two passes. The resulting product exhibited sufficient tear
and delamination strengths. However, the resulting porosity was
1 o more than that of the product formed in Example 1.
EXAMPLE 3
In this example, the method of Example 2 was used to
hydroentangle BP22 to REEMAY~ 2250 (0.50 ounces/yard2, 4.0 mil).
Like the product of Example 2, the product made according to this
example showed sufficient tear and delamination strengths but was
more porous than the product formed in Example 1.
EXAMPLE 4
In this example, two plies of BP22 were hydroentangled to
REEMAY~ 2004 (described above). The hydroentanglement was
2 o performed in three passes, with the first pass being at 400 psig to set
the webs, and the second and third passes at 800 psig to entangle
the webs. The hydroentangled composite material was then
saturated with Hycar 26469 at 50 percent pickup. The latex-
saturated composite material was then calendered at 20 psig for two
2s passes. The product, although not tested, exhibited good visual
results. The porosity of this product appeared to be slightly more
than that of Example 1.
EXAMPLE 5
In this example, one sheet of BP22 was hydroentangled to
3 o REEMAY~ 227,5. The hydroentanglement was run in two passes,
with a first pass of 400 psig to set the webs and a second pass at 800
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34
psig to entangle the webs. The composite material was then
subjected to the latex saturation and calendering processes
described in Example 4 above. This product exhibited a higher
porosity than the product in Example 1.
EXAMPLE 6
In this example, two plies of BP22 were hydroentangled to a
web of REEMAY~ 2275 (0.75 ounces/yard2, 2.2 dpf). The
hydroentanglement, latex saturation with Hycar 26469, and
calendering processes were identical to those described above in
i o Example 4 wherein hydroentanglement was performed in three
passes, with the first at 400 psig and the second and third at 800
psig.
The resulting product exhibited a total basis weight of 51.6
pounds per ream with a pickup of 50 percent of the latex. The tear
strength measured according to the test described above was 400g.
The product could not be delaminated. The tensile strength was
6.Okg/15mm, and the stretch was 47 percent. The tensile energy
absorption (TEA) was 1420 grams/centimeter x 9.81 x 103 Joules per
square meter and was determined according to TAPPI method T494.
2o The Dart Impact of this product was estimated to be 575 grams. With
respect to bacteria barrier data, the maximum pore size was 300
microns, the minimum pore size was 2.8 microns, and the median
flow parameter was 13.4. The cumulative pore number was 3.00 x
106. Although a preferred embodiment of the invention has been
described using specific terms, devices, and methods, such
description is for illustrative purposes only. The words used are
words of description rather than of limitation. It is to be understood
that changes and variations may be made by those of ordinary skill in
the art without departing from the spirit and scope of the present
3 o invention which is set forth in the following claims. In addition, it
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should be understood that aspects of the various embodiments may
be interchanged, both in whole or in part.
