WO2005017248A1

WO2005017248A1 - Nonwoven breathable composite barrier fabric

Info

Publication number: WO2005017248A1
Application number: PCT/US2004/005032
Authority: WO
Inventors: Jr. Uyles W. Bowen; Michael P. Mathis; John A. Rotella; Lisa A. Schild
Original assignee: Kimberly-Clark Worldwide, Inc.
Priority date: 2003-05-09
Filing date: 2004-02-20
Publication date: 2005-02-24
Also published as: EP1629144A1; MXPA05011397A; CA2523782A1; US20040224596A1

Abstract

A breathable barrier material having a first nonwoven layer and a first microporous film bonded together to form a composite laminate. A second microporous film and a second nonwoven layer are bonded to the composite laminate and second film to form the barrier material such that the films are disposed between the nonwoven layers. The composite laminate is bonded to the second film and second nonwoven layer thereby creating bond points in the material and void spaces between the first and second films. The void spaces between films may enhance liquid and viral barrier properties in the barrier material by creating a boundary that minimizes passage of liquids and/or viral components through the barrier material.

Description

NONWOVEN BREATHABLE COMPOSITE BARRIER FABRIC

BACKGROUND OF THE INVENTION

The present invention is directed to cloth-like, liquid-impervious, breathable composite barrier fabrics. More particularly, the present invention is directed to cloth-like, liquid- impervious, breathable fi rn-nonwoven composite fabrics having biological liquid barrier capabilities for use as, for example, sterilization wrap, surgical draping, surgical gowns, cover garments, such as over-suits, and the like.

Surgical gowns, surgical drapes, and sterile wrap and sterilization peel pouches (hereinafter collectively "surgical articles"), in order to function satisfactorily, must achieve a balance of properties, features and performance characteristics. Such surgical articles have, as a principal matter, been designed to greatly reduce, if not prevent, the transmission through the surgical article of biological liquids and/ or airborne contaminates. In surgical procedure environments, such liquid sources include the gown wearer's perspiration, body fluids from the patient, such as blood, and life support liquids, such as plasma and saline. Examples of airborne contaminates include, without limitation, biological contaminates, such as bacteria, viruses and fungal spores. Such contaminates may also include particulate material such as, without limitation, lint, mineral fines, dust, skin scales and respiratory droplets. A measure of the barrier fabric's ability to prevent the passage of such airborne materials is sometimes expressed in terms of filtration efficiency.

Such surgical articles further should be comfortable during use, that is, while being worn. The breathability of the surgical article, that is, its rate of water vapor transmission, is an important measure of how comfortable a surgical article is to use. Other characteristics of surgical articles that impact upon the comfort of the article during use include, without limitation, the drapeability, cloth-like feel and hand and cool, dry feel of the articles. Surgical articles also require a minimum level of strength and durability in order to provide the necessary level of safety to the user of the article, particularly during surgical procedures.

Finally, surgical articles desirably are inexpensive to manufacture, utilizing lightweight materials that enhance the comfort of the wearer during use, but also reduce the cost of such articles.

The use of liquid impervious, breathable multilayer barrier fabrics of various constructions is known. Surgical articles formed from liquid repellent fabrics, such as fabrics formed from nonwoven webs or layers, have provided acceptable levels of liquid imperviousness, breathability, cloth-like drapeability, strength and durability, and cost. However, the need exists nonetheless for improved cloth-like, liquid-impervious, breathable barrier materials for use in forming surgical articles, as well as other garment and over-garment applications, such as personal protective equipment applications (i.e., workwear, for example), in which some or all of the above performance characteristics and features are desirable or necessary. Other personal protective equipment applications include, without limitation, laboratory applications, clean room applications, such as semiconductor manufacturing, agriculture applications, mining applications, environmental applications, and the like.

Moreover, personal care articles such as adult mcontinent products and infant or child care diapers or garments such as training pants may utilize components with these desirable properties.

SUMMARY OF THE INVENTION

The present invention is drawn to a breathable barrier material having a first nonwoven layer and a first microporous film bonded together to form a composite laminate. A second microporous film and a second nonwoven layer are bonded to the composite laminate to form the barrier material. In another aspect, the present invention is drawn to a breathable barrier material where the first and second films are disposed between the nonwoven layers. Either or both of the nonwoven layers may be made of a spunbond web. Either or both films may be configured as a monolayer or multilayer film.

In another aspect of the present invention, the multilayer film may be made of a core layer constituting about 85% of the total film thickness and a skin layer constituting about 15% of the total film thickness. In another embodiment two skin layers may be provided, each disposed on opposite sides of the core layer. The two skin layers may each constitute about 7.5% of the total film thickness. Breathability may be imparted to the film by use of suitable fillers. As such, the film may be manufactured from about 30% to about 75% by weight polyolefin resin and from about 70% to about 25% by weight of filler.

In still another aspect, the present invention may have a water vapor transmission rate of at least about 500 grams per square meter per 24 hours, or in some embodiments at least about 5000 grams per square meter per 24 hours.

The material itself may be created by bonding the prebonded composite laminate to the second film, and second nonwoven layer to create bond points in the material and void spaces between the first and second films. The void spaces between films may enhance liquid and viral barrier properties in the barrier material by creating a boundary that rrunixnizes passage of liquids and/ or viral components through the barrier material. These voids may also serve to trap such liquids and/ or viral components between the films.

Such a material may be found useful in applications directed to surgical gowns, surgical drapes, sterilization peel pouches, industrial protective garments, personal care articles, and other applications wherein the use of a breathable barrier thermoplastic elastomeric polyolefin is desirable.

These and other objects are achieved by the improved cloth-like, liquid-impervious, breathable barrier material disclosed and claimed herein. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an exemplary barrier material of the present invention.

FIG. 2 is a cross-sectional side view of a multilayer film for use in the FIG. 1 barrier material. The right side of the film has been separated to facilitate its description .

FIG. 3 is a schematic view of a process for making the FIG. 1 barrier material.

FIG.4 is a SEM Micrograph of the FIG. 1 barrier material at 50x magnification.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an improved cloth-like, liquid-impervious, breathable barrier material, which possess a unique balance of performance characteristics and features making the material suitable for use in forming surgical articles, as well as other garment and over-garment applications, such as personal protective equipment applications. Referring to the drawings, one embodiment of the barrier material of the present invention is illustrated. In this embodiment, the barrier material 10 is a laminate comprising four layers—a top nonwoven layer 12 formed, for example, of spunbond filaments, a bottom nonwoven layer 18 formed, for example, of spunbond filaments, a first middle breathable firm 14 formed, for example, of a microporous film, and a second middle breathable film 16 formed, for example, of a microporous film. The individual layers of barrier material 10 are laminated, bonded or attached together by known means, including thermal-mechanical bonding, ultrasonic bonding, adhesives, stitching and the like.

As used herein, the terms "layer" or "web" when used in the singular can have the dual meaning of a single element or a plurality of elements. As used herein, the term "laminate" means a composite material made from two or more layers or webs of material which have been bonded or attached to one another. As used herein, the terms "nonwoven fabric" or "nonwoven web" mean a web having a structure of individual fibers or filaments that are interlaid, but not in an identifiable, repeating manner as in a knitted or woven fabric.

Cornrnercially available thermoplastic polymeric materials can be advantageously employed in making the fibers or filaments from which top nonwoven layer 12 and bottom nonwoven layer 18 are formed. As used herein, the term " polymer" shall include, but is not limited to, homopolymers, copolymers, such as, for example, block, graft, random and alternating copolymers, terpolymers, etc., and blends and modifications thereof. Moreover, unless otherwise specifically limited, the term "polymer" shall include all possible geometric configurations of the material, including, without limitation, isotactic, syndiotactic, random and atactic symmetries. As used herein, the terms "thermoplastic polymer" or "thermoplastic polymeric material" refer to a long-chain polymer that softens when exposed to heat and returns to the solid state when cooled to ambient temperature. Exemplary thermoplastic materials include, without limitation, polyvinyl chlorides, polyesters, polyamides, polyfluorocarbons, polyolefins, polyurethanes, polystyrenes, polyvinyl alcohols, caprolactams, and copolymers of the foregoing.

Nonwoven webs that may be employed as the nonwoven layers 12 and 18 of the present invention may be formed by a variety of known forming processes, including spunbonding, airlaying, meltblowing, or bonded carded web formation processes. For example, in the embodiment of the present invention shown in the drawings herein, top layer 12 and bottom layer 18 are both spunbond nonwoven webs, which have been found advantageous in forming barrier material 10. Spunbond nonwoven webs are made from melt-spun filaments. As used herein, the term "meltspun filaments" refers to small diameter fibers and/ or filaments that are formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced, for example, by non-eductive or educrive fluid drawing or other well known spunbonding mechanisms. Lastly, the melt-spun filaments are deposited in a substantially random manner onto a moving carrier belt or the like to form a web of substantially continuous and randomly arranged, melt-spun filaments. Spunbond filaments generally are not tacky when they are deposited onto the collecting surface. The production of spunbond nonwoven webs is described in U.S. Pat. No. 4,340,563 to Appel et al., U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,538 to Peterson, and U.S. Pat. No. 3,542,615 to Dobo et al., all of which are incorporated herein by reference. The melt-spun filaments formed by the spunbond process are generally continuous and have average diameters larger than 7 microns based upon at least 5 measurements, and more particularly, between about 10 and 100 microns. Another frequently used expression of fiber or filament diameter is denier, which is defined as grams per 9000 meters of a fiber or filament.

Spunbond webs generally are stabilized or consolidated (pre-bonded) in some manner immediately as they are produced in order to give the web sufficient integrity and strength to withstand the rigors of further processing into a finished product. This pre- bonding step may be accomplished through the use of an adhesive applied to the filaments as a liquid or powder which may be heat activated, or more commonly, by compaction rolls. As used herein, the term "compaction rolls" means a set of rollers above and below the nonwoven web used to compact the web as a way of treating a just produced, melt-spun filament, particularly spunbond, web, in order to give the web sufficient integrity for further processing, but not the relatively strong bonding of later applied, secondary bonding processes, such as through-air bonding, thermal bonding, ultrasonic bonding and the like. Compaction rolls slightly squeeze the web in order to increase its self-adherence and thereby its integrity.

An exemplary secondary bonding process utilizes a patterned roller arrangement for thermally bonding the spunbond web. The roller arrangement typically includes a patterned bonding roll and a smooth anvil roll which together define a thermal patterning bonding nip. Alternatively, the anvil roll may also bear a bonding pattern on its outer surface. The pattern roll is heated to a suitable bonding temperature by conventional heating means and is rotated by conventional drive means, so that when the spunbond web passes through the nip, a series of thermal pattern bonds is formed. Nip pressure within the nip should be sufficient to achieve the desired degree of bonding of the web, given the line speed, bonding temperature and materials forming the web. Percent bond areas within the range of from about 10 percent to about 20 percent are typical for such spunbond webs.

Each nonwoven layer 12 and/ or 18 may itself comprise a single layer of meltspun fabric, for example a spunbond or meltblown layer, or each nonwoven layer 12 and/ or 18 may comprise a plurality of separate nonwoven layers comprising any of identical layers, similar layers, or different layers. For instance, each of the nonwoven layers 12, 18 may comprise a spunbond layer and a meltblown layer, or a first spunbond layer, a meltblown layer, and a second spunbond layer. Additional layers and combinations are possible as well, depending on the intended use of the product. In any of the embodiments, any of the nonwoven layers may be treated with an antistatic agent, a surfactant to impart hydrophilicity, or any other useful surface modifying agents so long as such an agent does not interfere with the intent of the invention.

The middle breathable films 14 and 16 may be formed of any microporous film that can be suitably bonded or attached to the top and bottom layers 12, 18 to yield a barrier material 10 having the unique combination of performance characteristics and features described herein. One suitable class of film materials includes at least two basic components: a thermoplastic polyolefin polymer and a filler. These (and other) components may be mixed together, heated and then extruded into a monolayer or multilayer fil using any one of a variety of film-producing processes known to those of ordinary skill in the film processing art. Such film-making processes include, for example, cast embossed, chill and flat cast, and blown film processes. Generally, on a dry weight basis, based on the total weight of the film, each film 14 and 16 will include from about 30 to about 75 weight percent of the thermoplastic polyolefin polymer, or blend thereof, and from about 25 to about 70 percent filler. Suitable polymers for use in the films include polyethylene, blends of polyethylenes, polypropylene, blends of polypropylenes, blends of polyethylene and polypropylene, blend combinations of polyethylene or polypropylene with suitable amorphous polymers, copolymers made from ethylene and propylene monomers, and blends of such copolymers with polyethylenes or polypropylenes or suitable amorphous polymers, semi- crystalline/ amorphous polymers, "heterophasic' polymers, or combinations thereof. Examples of useful polymers are EXXPOL®, EXCEED®, and EXACT™ polymers from Exxon Chemical Company of Baytown, Texas; ENGAGE®, ACHIEVE®, ATTAIN®, AFFINITY®, and ELITE® polymers from Dow Chemical Company of Midland, Michigan; CAT ALLOY® polymers from Basell USA Inc. of Wilxnington, Delaware.

Other useful polymers and polymer blends used alone or in combination may be formed from or include homopolymers, copolymers and blends of polyolefins, ethylene vinyl acetate (EVA), ethylene ethyl acrylate (EEA), ethylene acrylic acid (EAA), ethylene methyl acrylate (EMA), ethylene butyl acrylate (EBA), polyester (PET), nylon (PA), ethylene vinyl alcohol (EVOH), polystyrene (PS), polyurethane (PU), and olefinic thermoplastic elastomers which are multistep reactor products wherein an amorphous ethylene propylene random copolymer is molecularly dispersed in a predominately semicrystalline high polypropylene monomer/ low ethylene monomer continuous matrix. Other additives and ingredients may be added to the films 14, 16 provided such additives do not significantly interfere with the ability of the film layer to function in accordance with the teachings of the present invention. Such additives and ingredients can include, for example, antioxidants, stabilizers, and pigments.

In addition to the polyolefin polymer, as stated, the films 14 and 16 also include a filler. As used herein, a "filler" is meant to include particulates and other forms of materials that may be added to the film polymer extrusion blend, will not chemically interfere with the extruded film, but are able to be uniformly dispersed throughout the film. Generally, the fillers will be in particulate form and may have a spherical or non-spherical shape with average particle sizes in the range of about 0. 1 to about 7 microns. Both organic and inorganic fillers are contemplated to be within the scope of the present invention provided that they do not interfere with the film formation process, or the ability of the film to function in accordance with the teachings of the present invention. Examples of suitable fillers include calcium carbonate (CaC0₃), various kinds of clay, silica (SiO₂), alumina, barium carbonate, sodium carbonate, magnesium carbonate, talc, barium sulfate, magnesium sulfate, aluminum sulfate, titanium, dioxide (TiO₂), zeolites, cellulose-type powders, kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum hydroxide, pulp powder, wood powder, cellulose derivatives, chitin and chitin derivatives. A suitable coating, such as, for example, stearic acid, may also be applied to the filler particles.

As mentioned herein, films 14 and 16 may be formed using any one of the conventional processes known to those familiar with film formation. The polyolefin polymer and filler are mixed in appropriate proportions given the ranges outlined herein and then heated and extruded into a monolayer or multilayer film as required. In order to provide unif orm breathability as reflected by the water vapor transmission rate of the film, the filler should be uniformly dispersed throughout the polymer blend and, consequently, throughout each film layer itself. For purposes of the present invention, a film is considered "breathable" if it has a water vapor transmission rate of at least 300 grams per square meter per 24 hours (g/m²/24 hours), as calculated using the test method described herein. Other embodiments of this invention contemplate water vapor transmission rates of at least 500 grams per square meter per 24 hours (g/m²/24 hours), and still other embodiments contemplate water vapor transmission rates of at least 5000 grams per square meter per 24 hours (g/m²/24 hours).

Generally, once the film is formed, it will have a weight per unit area of less than about 80 grams per square meter (gsm) and after stretching and thinning, its weight per unit area will be from about 10 gsm to about 25 gsm. The films used in the example of the present invention described below are multilayer films, such as the ABA-type film described below. It should be understood that other types of films, such as monolayer films, are also considered to be within the scope of the present invention provided the forming technique is compatible with filled films.

Referring to FIG. 2, there is shown, not to scale, an exemplary ABA-type multilayer film 20 that, for purposes of illustration, has been split apart at the right side of the drawing. Such a film may form one or both of the films 14 and/ or 16. In this embodiment, the multilayer film 20 includes a core layer 22 made from the extrudable thermoplastic polymers described above. The core layer 22 has a first exterior surface 24 and a second exterior surface 26. The core layer also has a core thickness 28. Attached to the first exterior surface 24 of the core layer 22 is a first skin layer 30 which has a first skin thickness 32. Attached to the second exterior surface 26 of the core layer 22 is an optional second skin layer 34 which has a second skin thickness 36. In addition, the multilayer film 10 has an overall thickness 38.

One embodiment of such a multilayer film of the present invention, for example, provides the core layer 22 with a combination of from about 26% to about 30% by weight of a linear low density polyethylene (LLDPE) copolymer, from about 15% to about 18% by weight of a single-site (metallocene) catalyzed copolymer, and from about 53% to about 57% by weight particulate calcium carbonate. Skin layers 30 and 34 may comprise, for example, a combination of about 26% CATALLOY®, from about 7% to about 10% polypropylene random copolymer (RCP), and from about 57% to about 70% by weight particulate calcium carbonate. The core layer 22 constitutes about 85% of the total film thickness 38.

Such multilayer films 20 may be formed by a wide variety of processes well known to those of ordinary skill in the film forming industry. Two particularly advantageous processes are cast film, coextrusion processes and blown film coextrusion processes. In such processes, the two or three layers are formed simultaneously and exit the extruder in a multilayer form. Due to the extremely ihin nature of the multilayer films according to the present invention such processes will most likely prove to be the most advantageous though it also may be possible to form multilayer films using separate extrusion processes.

Each film as initially formed generally is thicker and noisier than desired, as it tends to make a "rattling" sound when shaken. Moreover, each film does not have a sufficient degree of breathability as measured by its water vapor transmission rate. Consequently, each film is heated to a temperature equal to or less than about 5° C. below the melting point of the polyolefin polymer and then stretched using an in-line machine direction orientation (MDO) unit to at least about two times (2x) its original length to thin the film and render it porous. Further stretching of the films 14, 16, to about three times (3x), four times (4x) or more, their original length is expressly contemplated in connection with forming films 14 and/ or 16 of the present invention.

The films 14 and 16 after being stietch-thinned should have an "effective" film gauge or thickness of from about 0.2 mil to about 1.2 mil in some embodiments. In other embodiments, it is contemplated that the effective gauge be from about 0.2 mil to about 0.6 mil. The effective gauge is used to take into consideration the voids or air spaces in breathable film, layers. For normal, non-filled, non-breathable films, the actual gauge and effective gauge of the film typically will be the same. However, for filled films that have been stietch-thinned, as described herein, the thickness of the film will also include air spaces. In order to disregard this added volume, the effective thickness is calculated according to the test method set forth herein.

Referring now to FIG. 3, a process for preparing a barrier material 10 according to the present invention is illustrated. One of the films, for example fihn 14 is formed using any type of conventional film forming equipment 40, such as cast or blown film equipment. The film 14 having a formulation as described herein then is passed through a film stietching apparatus 42 to stretch and thin the film, to an effective gauge of 0.6 mil or less. One type of suitable film stietching apparatus is a Machine Direction Orienter unit, Model No. 7200, available from the Marshall & Williams Company, having offices in Providence, R.I.

While the film 14 is being stretched, a nonwoven layer, for example spunbond nonwoven layer 12 is formed. A conventional spunbond nonwoven web manufacturing process, as described herein, can be used to form the nonwoven layer 12. As shown in FIG. 3, the spunbond web 12 is formed of substantially continuous and randomly arranged, melt- spun filaments, that are deposited onto a moving continuous forming wire 44 from extruders 46. The webs of randomly arranged, melt-spun filaments then can be pre- bonded by passing the web through a pair of compaction rolls (not shown) to give the web sufficient integrity and strength for further processing. One or both of the compaction rolls may be heated to aid in bonding the web 12. Typically, one of the compaction rolls also has a patterned outer surface that imparts a discrete bond pattern with a prescribed bond area to web 12. The opposing compaction roll usually is a smooth anvil roll, although this roll also may have a patterned outer surface if desired.

Once the film 14 has been sufficiently stietch-thinned and oriented, and the spunbond web 12 has been formed, the film layer 14 and web 12 are brought together and laminated to one another using a pair of laminating or bonding rolls 48, 50, as shown in FIG. 3, or other conventional bonding means, in order to produce a composite laminate 52 of the present invention.

It should be noted that bonding roll 48 is a pattern roll, whereas second bonding roll 50 is a smooth roll. Both rolls are driven by conventional means, such as, for example, electric motors (not shown). Pattern roll 48 is a right circular cylinder that may be formed of any suitable, durable material, such as, for example, steel, to reduce wear on the rolls during use. Pattern roll 48 has on its outermost surface a pattern of raised bonding area. An intermittent pattern of discrete, regularly repeating bonding points can be suitably employed, for example, as is conventional in the art. The bonding areas on pattern roll 48 form a nip with the smooth or flat outer surface of opposed positioned anvil roll 50. Anvil roll 50 also is a right circular cylinder that can be formed of any suitable, durable material, such as, for example, steel, hardened rubber, resin-treated cotton or polyurethane.

The pattern of raised bonding areas on the pattern roll 48 is selected such that the area of at least one surface of the resulting composite laminate 52 occupied by bonds after passage through the nip formed between pattern rolls 48, 50 ranges from about 10 percent to about 30 percent of the surface area of the barrier material. The bonding area of the composite laminate 52 may be varied to achieve the above-mentioned percent bond area, as is known in the art.

In accordance with one embodiment of this invention, bonding may be accomplished using a Ramisch bond pattern. The Ramisch bond pattern has a bond area of about 8% to about 14%, a pin density of about 52 pins/in², and a pin depth at 8% bond area of about 0.052 inch. The Ramisch bond pattern is a relatively deep, open pattern suitable for use in stretch applications. However any suitable conventional thermal bonding means may be used for thermally bonding the layers including, but not Umited to, standard heat rolls, ultrasound and through-air-bonding. The temperature of the outer surface of the pattern roll 48 may be varied by heating or cooling relative to the smooth roll 50. Heating and/ or cooling can affect, for example, the degree of lamination of the individual layers forming the laminate 52. Heating and/ or cooling of pattern roll 48 and/ or smooth roll 50 may be effected by conventional means (not shown) well known in the art. The specific ranges of temperatures to be employed in forming the laminate 52 are dependent on a number of factors, including the types of polymeric materials employed in forming the individual layers of the laminate 52, the dwell time of the individual layers within the nip and the nip pressure between the pattern roll 48 and anvil roll 50. After laminate 52 exits the nip formed between bonding rolls 48, 50, the laminate 52 may be wound onto roll 54 for subsequent processing. The second film 16 and nonwoven layer 18 may be formed from similar materials and in a manner similar to that of the first film 14 and nonwoven layer 12 respectively as depicted in FIG. 3. Once the film 16 is stietch-thinned, in order to produce the barrier material 10 of the present invention, the film 16, nonwoven layer 18, and laminate 52 are brought together and laminated to one another using a pair of laminating or bonding rolls as shown in FIG.3, or other conventional bonding means.

It should be apparent that the composite laminate 52 is thus double bonded whereas the film 16 and nonwoven layer 18 are single bonded to the composite laminate 52. FIG. 4 depicts the resulting barrier material 10 depicting voids between the films 14 and 16, that is, each film 14 and 16 is separate between the bonded regions. It is believed that these voids enhance liquid and viral barrier properties in the barrier material 10 by creating a boundary that minimizes passage of liquids and/ or viral components through the barrier material 10 and may serve to trap such liquids and/ or viral components between the films 14 and 16.

Modifications in the above-described process will be readily apparent to those of ordinary skill in the art without departing from the spirit and scope of the present invention. For example, after the barrier material 10 is formed, it may continue in-line for further processing and converting. Or, different apparatus may be used for stietch-thinning the films 14, 16. Other known means for bonding and laminating the films 14, 16 to nonwoven layers 12, 18 may be used, provided the resulting barrier material 10 has the required properties described herein. Finally, formation of the films 14, 16 and/ or nonwoven layers 12, 18 may take place at a remote location, with rolls of the individual layers unwound and fed to the nip formed between pattern roll 48 and smooth roll 50. Also, for certain applications, it may be advantageous to have a two component material that can be formed as above described by omitting one of the spunbond webs, for example. Typical spunbond weights for such applications are between about 0.6 osy to about 1.5 osy, commonly between about 0.9 osy to about 1.3 osy. These materials may also be thermally or adhesively laminated to the stretch-thinned film to form the composite. In whatever manner bonding is accomplished, the existence of the voids between films should be maintained.

Having described certain embodiments of the present invention, a sample barrier material was tested to further illustrate the present invention and to teach one of ordinary skill in the art the manner of carrying out the present invention. The results of the measurements of certain physical properties of the barrier materials so formed, and the test procedures used, are set forth below.

Test Procedures

The following test procedures were used to analyze the sample and comparative barrier materials identified below.

Mocon Water Vapor Transmission Rate Test

A suitable technique for determining the WVTR (water vapor transmission rate) value of a material is the test procedure standardized by INDA (Association of the Nonwoven Fabrics Industry), number IST-70.4-99, entitled "STANDARD TEST METHOD FOR WATER VAPOR TRANSMISSION RATE THROUGH NONWOVEN AND PLASTIC FILM USING A GUARD FILM AND VAPOR PRESSURE SENSOR" which is incorporated by reference herein. The INDA procedure provides for the determination of WVTR, the permeance of the film to water vapor and, for homogeneous materials, water vapor permeability coefficient.

The INDA test method is well known and will not be set forth in detail herein. However, the test procedure is summarized as follows. A dry chamber is separated from a wet chamber of known temperature and humidity by a permanent guard film and the sample material to be tested. The purpose of the guard film is to define a definite air gap and to quiet or still the air in the air gap while the air gap is characterized. The dry chamber, guard film, and the wet chamber make up a diffusion cell in which the test fil is sealed. The sample holder is known as the Permatran-W model 100K manufactured by Mocon/Modern Controls, Inc, Minneapolis, Minn. A first test is made of the WVTR of the guard film and air gap between an evaporator assembly that generates 100 percent relative humidity. Water vapor diffuses through the air gap and the guard film and then mixes with a dry gas flow which is proportional to water vapor concentration. The electrical signal is routed to a computer for processing. The computer calculates the transmission rate of the air gap and guard film and stores the value for further use.

The transmission rate of the guard film and air gap is stored in the computer as CalC. The sample material is then sealed in the test cell. Again, water vapor diffuses through the air gap to the guard film and the test material and then mixes with a dry gas flow that sweeps the test material. Also, again, this mixture is carried to the vapor sensor. The computer then calculates the transmission rate of the combination of the air gap, the guard film, and the test material. This information is then used to calculate the transmission rate at which moisture is transmitted through the test material according to the equation:

TR^"1 test material ⁼ TR~ ^l test material, guardfilm, airgap- TR^' guardfilm, airgap

Calculations:

WVTR: The calculation of the WVTR uses the formula: WVTR=Fp_sat (T)RH/A_Psat (T)(1-RH)) where:

F=The flow of water vapor in cc/min., P_sat (T)=The density of water in saturated air at temperature T, RH=The relative humidity at specified locations in the cell, A=The cross sectional area of the cell, and, P_sat (T)=The saturation vapor pressure of water vapor at temperature T. EXAMPLE

A barrier material according to the present invention was made. The film formulation was cast into a multilayer film having a core layer that contained on a total weight percent basis based upon the weight of the film, 26-30% by weight of a Ziegler-Natta catalyzed linear low density polyethylene (LLDPE) copolymer, about 15% to about 18% by weight of a single-site (metallocene) catalyzed copolymer, and from about 53% to about 57% by weight particulate calcium carbonate. The skin layers each contained, a combination of about 34% CATALLOY®, from about 7% to about 10% polypropylene random copolymer (RCP), and about 57% by weight particulate calcium carbonate. The core layer constituted about 85% of the total film thickness. The CaCO₃ in the core and skin layers was coated with from about 0.5 to 3.0% behenic acid based upon the weight of the CaCO₃, having a 0.9 to 1.3 micron average particle size and a top cut of 8 microns.

The spunbond facing layers were both 0.60 ounces per square yard nonwoven webs formed from extrudable thermoplastic resins of homopolymer polypropylene from BP/ Amoco 2% titanium dioxide (white), 0.09% anti-static compound and 0.91 SCC 11111 blue color concentrate. The spunbond filaments were essentially continuous in nature and had an average fiber size of 2.0 dpf.

One of the films and nonwoven layers were laminated together to form an 18.5 g/m² composite laminate having a MOCON value of 7466 g/m²/24hr using Ramisch pattern thermal bonding rolls, as described herein. The pattern roll had a bonding temperature of about 185° F. and the smooth anvil roll had a temperature of about 145° F. The nip pressure formed between the rolls was about 440 psig. The second film alone had a basis weight of 18.75 g/m² and together with the second nonwoven layer in an unbonded configuration had a MOCON value of 6293 g/m²/24hr. The second film and nonwoven layer were thermally bonded to the composite laminate using a C-star pattern. This attempt was a partial success in that a breathable barrier material having a MOCON value of 3079 g/m²/24hr was created. However, this test run did not reach the desired target range for breatliabϋity of 5500 g/m²/24hr. The material did exhibit improved resistance to low surface tension fluids by 2.7 times compared to a control. Bacteriophage testing was conducted in accordance with ASTM F 1671-97b and 22 out of 22 samples passed the test.

A second sample of barrier material was created with increased calcium carbonate level in the skin (57 to 65%) having the same properties as the first; however, in this sample the second film and nonwoven layer were thermally bonded to the composite laminate using the Ramisch bond pattern. The MOCON of this barrier material was in the range of 4500- 6500 g/m²/24hr, and the bacteriophage results were 31 out of 32 samples passing the test.

It is contemplated that the improved cloth-like, liquid impervious, breathable barrier material constructed in accordance with the present invention will be tailored and adjusted by those of ordinary skill in the art to accommodate various levels of performance demand imparted during actual use. Accordingly, while this invention has been described by reference to certain specific embodiments and examples, it will be understood that this invention is capable of further modifications. This application is, therefore, intended to cover any variations, uses or adaptations of the invention following the general principles thereof, and including such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and fall within the limits of the appended claims.

Claims

We claim:

1. A breathable barrier material comprising: a first nonwoven layer; a first microporous film bonded to the first nonwoven layer to form a composite laminate; a second microporous film; and a second nonwoven layer bonded to the composite laminate and second film to form the barrier material.

2. The material of claim 1 wherein the first and second films are disposed between the nonwoven layers.

3. The material of claim 1 wherein one of the nonwoven layers comprises a spunbond web.

4. The material of claim 1 wherein the first and second nonwoven layers comprise first and second spunbond webs.

5. The material of claim 1 wherein one of the nonwoven layers comprises at least one layer of a meltblown polyolefin and at least one layer of a spunbond polyolefin.

6. The material of claim 1 wherein one of the films is selected from the group consisting of monolayer films and multilayer films.

7. The material of claim 6 wherein the multilayer film comprises a core layer constituting about 85% of the total film thickness and a skin layer constituting about 15% of the total film thickness.

8. The material of claim 6 wherein the multilayer film comprises a core layer constituting about 85% of the total film thickness and two skin layers each constituting about 7.5% of the total film thickness disposed on opposite sides of the core layer.

9. The material of claim 1 or 6 wherein at least one of the films comprises from about 30% to about 75% by weight polyolefin resin and from about 70% to about 25% by weight of filler having an average size less than about 10 microns.

10. The material of claim 1 or 6 wherein at least one of the films comprises from about 30% to about 45% by weight polyolefin resin and from about 70% to about 55% by weight of filler.

11. The material of claim 1 wherein the laminate has a water vapor transmission rate of at least about 500 grams per square meter per 24 hours.

12. The material of claim 1 wherein the laminate has a water vapor transmission rate of at least about 5000 grams per square meter per 24 hours.

13. The material of claim 1 wherein the laminate has a water vapor transmission rate of from about 500 to about 5000 grams per square meter per 24 hours.

14. The material of claim 1 wherein the nonwoven layers comprise about 98% random copolymer of polypropylene and polyethylene with 1.5-3.5% ethylene content.

15. The material of claim 1 wherein one of the nonwoven layers comprises an antistatic treatment.

16. The material of claim 1 wherein the material is thermally bonded.

17. The material of claim 1 comprising any of a surgical gown, a surgical drape, a sterilization peel pouch, an industrial protective garment, and a personal care article.

18. The material of claim 1 comprising a thermoplastic elastomeric polyolefin.

19. The material of claim 1 comprising bonding the composite laminate to the second film and second nonwoven layer so that the material is breathable, maintains fluid barrier properties , and passes bacteriophage testing in compliance with ASTM F 1671-97b.

20. The material of claim 1 comprising void spaces between the first and second films.

21. The material of claim 1 comprising thermally bonding the composite laminate to the second film and second nonwoven layer to create bond points in the material and void spaces between the first and second films.