CA2294160A1 - Medical packaging material and process for making same - Google Patents

Abstract

A medical packaging substrate formed by hydroentangling a cellulosic-based web with a bonded spunbond web is provided by the present invention. The substrate is usable to form medical packages for surgical instruments, medical devices, and medical appliances. The fabric is gas-pervious so that gas sterilization techniques may be used to sterilize the contents of any package made from the material. The material is susceptible to being made bacterial-impervious so as to prevent the passage of bacteria within certain standards.

Description

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.

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 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, 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 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.

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 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 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.

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 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 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 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 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, 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 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.

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.

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, 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 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 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 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.

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, 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 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 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 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.

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 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 available from Kimberly-Clark Corporation. The data in the following table sets forth the comparative results.

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a a m m 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 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.

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' 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 CA 02294160'1999-12-21 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.

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.

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.

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 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.

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 should be understood that aspects of the various embodiments may be interchanged, both in whole or in part.

Claims (22)

WHAT IS CLAIMED IS:

1. A method for forming a composite material from a cellulosic-based web and a bonded spunbond web, said method comprising the steps of:
a) bringing either the upper or lower surface of a cellulosic-based web into contact with the upper or lower surface of a bonded polymeric spunbond web, said spunbond web comprising a substantially continuous bonded structure;
b) hydraulically entangling said webs to form a composite material;
c) and saturating said composite material with a binder.

2. The method of claim, 1 wherein said spunbond web comprises a polymer chosen from the group consisting of polyolefins, polyesters, polyamides, and copolymers and blends thereof.

3. The method of claim 2, wherein said polymer comprises a polyester.

4. The method of claim 1, wherein said binder is a latex.

5. The method of claim 1, wherein said binder is applied to said composite material in an amount sufficient to result in a pickup of from about 15 percent to about 60 percent.

6. The method of claim 1, further comprising the step of wet-pressing said composite material prior to saturating with said binder.

7. The method of claim 1, wherein said entanglement step is performed in three phases with the first phase being performed at about 400 psig and the second and third phases being performed at about 800 psig each.

8. The method of claim 1, further comprising the step of calendering said composite material after saturating with said binder.

9. The method of claim 1, further comprising the step of subjecting said composite material after being saturated with binder to a process for transforming said material into an acceptable bacteria barrier for use in forming packaging for sterilized medical devices.

10. The method of claim 9, wherein said transformation process utilizes a polymer that forms a bacteria-impermeable porous coating on said composite material.

11. The method of claim 1, further comprising the step of bringing either the upper or lower surface of a second cellulosic-based web into contact with the other of the upper or lower surface of said bonded polymeric spunbond web and hydraulically entangling said cellulosic-based web, said second cellulosic-based web, and said bonded polymeric spunbond web to form a composite material.

12. The method of claim 11, further comprising the step of bringing a third cellulosic-based web into contact with the non-contacted surface of said second cellulosic-based web and then hydraulically entangling said cellulosic-based web, said second cellulosic-based web, said third cellulosic-based web, and said bonded polymeric spunbond web to form a composite material.

13. A method for forming a composite material from a cellulosic-based web and a bonded spunbond web, said method comprising the steps of:
a) bringing a surface of a first cellulosic-based web into contact with one surface of a bonded polyester spunbond web, said spunbond web comprising a substantially continuous bonded structure;
b) bringing a surface of a second cellulosic-based web into contact with the other surface of the bonded polyester spunbond web;
c) hydraulically entangling said webs to form a composite material;
d) drying said composite material; and e) saturating said composite material with a binder.

14. The method of claim 13, further comprising the step of calendering said composite material after saturating with said binder.

15. The method of claim 13, further comprising the step of treating said composite material with a bacteria barrier-forming agent.

16. A method for forming a composite material from a cellulosic-based web and a bonded spunbond web, said method comprising the steps of:
a) bringing a surface of a first cellulosic-based web into contact with one surface of a bonded polyester spunbond web, said spunbond web comprising a substantially continuous bonded structure;
b) bringing a surface of a second cellulosic-based web into contact with the other surface of the bonded polyester spunbond web;
c) hydraulically entangling said webs to form a composite material;
d) wet-pressing said composite material;
e) drying said composite material;
f) saturating said composite material with a latex binder;
and g) calendering said composite material.

17. The method of claim 16, further comprising the step of treating said composite material with a bacteria barrier-forming agent.

18. A hydraulically entangled composite material comprising a cellulosic-based material and a bonded polymeric spunbond material, said composite material being substantially saturated with a binder, said material having a machine direction tear strength of at least about 350 grams, a cross machine tear strength of at least about 450 grams, an estimated Dart Impact failure weight of at least about 300 grams and a cumulative pore number of at least about 3,000,000.

19. The composite material of claim 18, wherein said composite material has been subjected to a bacteria barrier treatment process.

20. The composite material of claim 18, wherein said material has been calendered.

21. A package for housing a medical device or surgical instrument, wherein said package is formed, at least in part, from the composite material of claim 18.

22. A package for housing a medical device or surgical instrument, wherein said package is formed, at least in part, from the composite material of claim 19.