THEREWITH

FIELD OF THE INVENTION

The present invention relates to a nonwoven material suitable for use in personal protective equipment.

BACKGROUND OF THE INVENTION

Synthetic fibers are widely used in a number of diverse applications to provide stronger, thinner, and lighter weight products. Synthetic thermoplastic fibers are typically thermos-formable and thus are particularly attractive for the manufacture of nonwoven fabrics, either alone or in combination with other non-thermoplastic fibers (such as cotton, wool, and wood pulp, for example). Nonwoven fabrics, in turn, are widely used as components of a variety of articles, including without limitation absorbent personal care products, such as diapers, incontinence pads, feminine hygiene products, and the like; medical products, such as surgical drapes, sterile wraps, and the like; filtration devices; interlinings; wipes; furniture and bedding construction; apparel; insulation; packaging materials; and others.

The coronavirus (COVID-19) global pandemic has caused a global shortage of medical supplies, and in particular, a shortage of various forms of personal protective equipment (PPEs) used by first responders and healthcare providers. The most significant challenge in this domain is the shortage of facemasks.

There are various types of facemasks available on the market. The N95 or N99 masks are among are the most well-known, and are typically referred to as respirators. Surgical masks are also facemasks, but they have drastically different properties from respirators. N95 and N99 respirators and surgical masks are PPEs used to protect the wearer from airborne particles.

The N95 and N99 respirators are regulated by the Centers for Disease Control and Prevention (CDC), the National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA) and must adhere to the strict performance guidelines established by these organizations. N95 and N99 respirator filters need to have a filtration efficiency of more than 95% of 0.3- micron particles tested at a flow rate of 85 liters per minute for the respirator and 32 L/min for flat sheets. It is desirable that the pressure drop across these masks be less than 60 Pascals for the base filter. When the actual mask is tested, the pressure drops can be much higher and can reach 100 to 200 Pascals.

A surgical mask is a loose-fitting, disposable device that creates a physical barrier between the mouth and nose of the wearer and potential contaminants in the immediate environment. These are often referred to as facemasks, although not all facemasks are regulated as surgical masks. Unlike the N95 respirators, the edges of the surgical mask are not designed to form a seal around the nose and mouth. These are single-use, disposable respiratory protective devices used and worn by healthcare personnel during procedures to protect both the patient and healthcare personnel from the transfer of microorganisms, body fluids, and particulate material. Surgical masks are tested for particle filtration, bacteria capture, and splash resistance.

The technology used in almost all masks for filtration is a polypropylene (PP) meltblown fabric that is electrostatically charged. A nonwoven filter medium that uses a combination of mechanical structure and electret charge provides a means of achieving high initial efficiency and sustained high efficiency. Meltblown PP fabrics are rather fragile and cannot be reused, laundered, or re-sterilized due to potential loss of charge and structural damage. They are often protected by layers of PP spunbond nonwovens made up of larger fibers that protect the meltblown filter layer.

The supply chain to produce these masks includes meltblown fabric manufacturers, spunbond fabric manufacturers, and mask converters who convert the meltblown and spunbond fabrics into masks. Very few companies are vertically integrated to produce both the base materials and the masks. One of the primary challenges in the US and globally due to the pandemic is insufficient converting capacity for making masks. The relative fragility of PP meltblown fabric is a complicating factor as only certain types of automated converting machines can work with such materials. There is a continuing need for improved types of filtration material for use in making personal protective equipment.

SUMMARY OF THE INVENTION

The disclosure provides a nonwoven fabric comprising at least one layer of an electrostatically- charged elastomeric meltblown nonwoven material, the meltblown nonwoven material typically comprising at least 90% by weight of at least one elastomer, based on the total weight of the layer of electrostatically- charged elastomeric meltblown nonwoven material. The nonwoven fabric of the invention is advantageous for use in forming personal protective equipment such as masks used to cover the nose and mouth for purposes of filtering air.

The disclosure includes, without limitation, the following embodiments.

Embodiment 1 : A nonwoven fabric comprising at least one layer of an electrostatically -charged elastomeric meltblown nonwoven material, the meltblown nonwoven material comprising at least 90% by weight of at least one elastomer, based on the total weight of the layer of electrostatically -charged elastomeric meltblown nonwoven material.

Embodiment 2: The nonwoven fabric of Embodiment 1, wherein the at least one elastomer is selected from the group consisting of styrenic elastomers, polyester and copolyester elastomers, polyurethane elastomers, polyamide elastomers, metallocene polyolefin elastomers, ethylene vinyl acetate elastomers, thermoplastic vulcanizates, and combinations thereof.

Embodiment 3 : The nonwoven fabric of any one of Embodiments 1 to 2, wherein the at least one elastomer comprises a thermoplastic polyester elastomer (TPE-ET).

Embodiment 4: The nonwoven fabric of any one of Embodiments 1 to 3, wherein the thermoplastic polyester elastomer has one or more of a shore D hardness in the range of about 45 to about 65D according to ISO 868, and a flexural modulus at 23°C of about 125 MPa to about 350 MPa according to ISO 178. Embodiment 5 : The nonwoven fabric of any one of Embodiments 1 to 4, wherein the at least one layer of electrostatically -charged elastomeric meltblown nonwoven material has a basis weight of about 20 g/m ² to about 60 g/m ² .

Embodiment 6: The nonwoven fabric of any one of Embodiments 1 to 5, wherein the average fiber diameter of the electrostatically -charged elastomeric meltblown nonwoven material is about 1 micron to about 5 microns.

Embodiment 7 : The nonwoven fabric of any one of Embodiments 1 to 6, wherein the at least one layer of electrostatically -charged elastomeric meltblown nonwoven material has a filtration efficiency of about 95% to about 99%, measured according to the test set forth in 42 CFR Part 84 and NIOSH Procedure No. TEB-APR-STP-0058.

Embodiment 8: The nonwoven fabric of any one of Embodiments 1 to 7, wherein the at least one layer of electrostatically -charged elastomeric meltblown nonwoven material has a pressure drop in the range of about 10 to about 50 Pa.

Embodiment 9: The nonwoven fabric of any one of Embodiments 1 to 8, wherein the at least one layer of electrostatically -charged elastomeric meltblown nonwoven material comprises at least one charge stabilizer.

Embodiment 10: The nonwoven fabric of any one of Embodiments 1 to 9, wherein the at least one charge stabilizer is selected from the group consisting of metal salts of fatty acids, titanate salts, silicate salts, and combinations thereof.

Embodiment 11: The nonwoven fabric of any one of Embodiments 1 to 10, wherein the charge stabilizer is magnesium stearate.

Embodiment 12: The nonwoven fabric of any one of Embodiments 1 to 11, wherein the charge stabilizer is present in an amount of up to about 2.5% by weight, based on the total weight of the layer of electrostatically -charged elastomeric meltblown nonwoven material.

Embodiment 13: The nonwoven fabric of any one of Embodiments 1 to 12, wherein the nonwoven fabric consists of a single layer, the single layer being the layer of electrostatically -charged elastomeric meltblown nonwoven material.

Embodiment 14: The nonwoven fabric of any one of Embodiments 1 to 13, wherein the nonwoven fabric comprises multiple layers including the at least one layer of electrostatically -charged elastomeric meltblown nonwoven material.

Embodiment 15: The nonwoven fabric of any one of Embodiments 1 to 14, wherein the nonwoven fabric further comprises multiple layers of polypropylene spunbond nonwoven material.

Embodiment 16: A mask configured to cover the nose and mouth of a user comprising the nonwoven fabric of any one of Embodiments 1 to 15.

Embodiment 17: The mask of Embodiment 16, in the form of a surgical mask or a respirator.

Embodiment 18: A method of making the nonwoven fabric of any one of Embodiments 1 to 15, comprising: melt blowing fibers comprising the at least one elastomer to form an elastomeric nonwoven web; and electrostatically charging the elastomeric nonwoven web to form the electrostatically -charged elastomeric meltblown nonwoven material.

Embodiment 19: The method of Embodiment 18, further comprising pleating the electrostatically- charged elastomeric meltblown nonwoven material.

Embodiment 20: The method of any one of Embodiments 18 to 19, further comprising combining the electrostatically -charged elastomeric meltblown nonwoven material with one or more additional nonwoven materials to form a multi-layer structure.

Embodiment 21: The method of any one of Embodiments 18 to 20, further comprising converting the electrostatically -charged elastomeric meltblown nonwoven material into a mask.

These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific example implementation described herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and example implementations, should be viewed as combinable, unless the context of the disclosure clearly dictates otherwise.

It will therefore be appreciated that this brief summary is provided merely for purposes of summarizing some example implementations so as to provide a basic understanding of some aspects of the disclosure. Accordingly, it will be appreciated that the above described example implementations are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. Other example implementations, aspects and advantages will become apparent from the following detailed description taken in conjunction with the accompanying figures which illustrate, by way of example, the principles of some described example implementations.

DESCRIPTION OF THE DRAWINGS

Having thus described the present disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 is a schematic drawing of a typical meltblowing process;

FIG. 2 is a cross-sectional view of a multi-layer example embodiment of a nonwoven material according to the disclosure;

FIG. 3 is an illustration of an example embodiment of a surgical mask made using the nonwoven material according to the disclosure;

FIG. 4 is an illustration of an example embodiment of a respirator made using the nonwoven material according to the disclosure; FIG. 5 is an illustration of an example embodiment of a reusable respirator with a replaceable filter made using the nonwoven material according to the disclosure; and

FIG. 6 is an SEM image of a nonwoven material made as described in the Experimental section.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As used in this specification and the claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Directional terms, such as “forward,” “rearward,” “front,” “back,” “right,” “left,” “upwardly,” “downwardly,” and the like are words of convenience and are not to be construed as limiting terms.

As used herein, the term “fiber” is defined as a basic element of nonwovens which has a high aspect ratio of, for example, at least about 100 times. In addition, “filaments/continuous filaments” are continuous fibers of extremely long lengths that possess a very high aspect ratio. “Staple fibers” are cut lengths from continuous filaments. Therefore, as used herein, the term “fiber” is intended to include fibers, filaments, continuous filaments, staple fibers, and the like. The term “multicomponent fibers” refers to fibers that comprise two or more components that are different by physical or chemical nature, including bicomponent fibers.

The term “nonwoven” as used herein in reference to fibrous materials, webs, mats, batts, or sheets refers to fibrous structures in which fibers are aligned in an undefined or random orientation. The nonwoven fibers are initially presented as unbound fibers or filaments, which may be natural or man-made. An important step in the manufacturing of nonwovens involves binding the various fibers or filaments together. The manner in which the fibers or filaments are bound can vary, and include thermal, mechanical and chemical techniques that are selected in part based on the desired characteristics of the final product. Nonwoven fabrics or webs have been formed from many processes, which include carding, meltblowing, spunbonding, and air or wet laying processes.

Nonwoven Fabric

The fibers utilized to form the nonwoven fabrics of the present disclosure can vary, and include fibers having any type of cross-section, including, but not limited to, circular, rectangular, square, oval, triangular, and multilobal. In certain embodiments, the fibers can have one or more void spaces, wherein the void spaces can have, for example, circular, rectangular, square, oval, triangular, or multilobal cross- sections. The fibers may be selected from single-component or monocomponent (/.<?.. uniform in composition throughout the fiber) or multicomponent fiber types (e.g., bicomponent) including, but not limited to, fibers having a sheath/core structure and fibers having an islands-in-the-sea structure, as well as fibers having a side-by-side, segmented pie, segmented cross, segmented ribbon, or tipped multilobal cross- sections. In certain embodiments, the fabrics of the invention will include both monocomponent and multicomponent fibers, and will also typically include more than one type of polymer, either different grades of the same polymer or different polymer types.

Fibers used in nonwoven substrates of the present disclosure include an elastomeric component. “Elastomer” and “elastomeric component,” as used herein, refer to any polymer that exhibits a degree of elasticity (e.g. , capable of returning substantially to its original shape or form after being subjected to stretching or deformation).

Although not limited, the elastomers used in the present disclosure typically are thermoplastic elastomers (TPEs), which generally exhibit some degree of elasticity and can be processed via thermoplastic processing methods (e.g., can be easily reprocessed and remolded). Thermoplastic elastomers can comprise both crystalline (/.<?.. “hard”) and amorphous (/.<?.. “soft”) domains and often comprise a blend or copolymer of two or more polymer types. Where the thermoplastic elastomer comprises a copolymer, it may be prepared, for example, by block or graft polymerization techniques. Thermoplastic elastomeric copolymers can, for example, comprise a thermoplastic component and an elastomeric component. In certain copolymeric thermoplastic elastomers, the physical properties of the material can be controlled by varying the ratio of the monomers and/or the lengths of the segments.

Certain exemplary thermoplastic elastomers can be classified as styrenic elastomers (e.g., styrene block copolymers), polyester and copolyester elastomers, polyurethane elastomers, polyamide elastomers, polyolefin blends (TPOs), polyolefins (alloys, plastomers, and elastomers including metallocene polyolefin elastomers), ethylene vinyl acetate elastomers, and thermoplastic vulcanizates. Certain specific elastomers that are useful according to the present invention include, for example, polyisoprene, butadiene rubber, styrene-butadiene rubber, poly(styrene-Z>-butadiene-Z>-styrene) (SBS), poly(styrene-/>-ethene-co-butane-/>- styrene (SEBS), poly(styrene-/>-isoprene-/>-styrene), ethylene propylene diene monomer rubber (EPDM rubber), EPDM rubber/polypropylene (EPDM/PP), polychloroprene, acrylonitrile-butadiene rubber, hydrogenated nitrile rubber, butyl rubber, ethylene-propylene rubber (EPM), silicone rubber, chlorosulfonated polyethylene, polyacrylate rubber, fluorocarbon rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, ethylene-vinylacetate copolymer, styrene-isoprene block copolymer, urethane rubber, and copolymers, blends, and derivatives thereof.

Exemplary commercially available thermoplastic elastomers include, but are not limited to, OnFlex™, Versaflex™, Dynaflex™, Dynalloy™, Versalloy™, and Versollan™ from PolyOne™ Corporation (Avon Lake, OH); RTP 1200, 1500, 2700, 2800, 2900, and 6000 Series Elastomers from RTP Company (Winona, MN); Elastocon 2800, 8000, STK, SMR, CLR, and OF Series TPEs from Elastocon (Rochester, IL); Enflex® and Ensoft® from Enplast (Turkey); Styroflex® SBS, Elastollan®, and Elasturan® from BASF (Florham Park, NJ); KratonMD6705, G1643, MD6717, MD6705, G1643 (Kraton Performance Polymers, Inc., Houston, TX); Affinity™, Amplify™, Engage™, Infuse™, Nordel™, and Versify™ from Dow Chemical (Midland, MI); Vistamaxx™, Santo prene™, and Exact™ from ExxonMobil Chemical Company (Houston, TX); Kalrez®, Neoprene, Hytrel®, Surlyn®, Vamac®, and Viton® from DuPont® Chemicals (Wilmington, DE); Pebax® from Arkema (France); Mediprene® and Dryflex® from Elasto (Sweden); Estagrip® and Estane® from Lubrizol Corporation (Wickliffe, OH); Garaflex™, Garathane™, Vythrene™, and Evoprene™ from AlphaGary (Leominster, MA) and Santoprene® from Advanced Elastomer Systems (Newport, CA). Other exemplary elastomeric materials are described, for example, inUS2010/0029161 to Pourdeyhimi, which is incorporated herein by reference; see also, US5035240 to Braun et al. and US5540976 to Shawver et ak, and Zapletalova et ah, Polyether Based Thermoplastic Polyurethane Melt Blown Nonwovens, Journal of Engineered Fibers and Fabrics, Vol. 1, Issue 1 (2006), which are incorporated herein by reference.

In certain embodiments, the elastomer is a thermoplastic elastomer (TPE), such as a thermoplastic polyurethane elastomer (TPU) or thermoplastic polyester elastomer (TPE-ET). A particularly advantageous TPE-ET is a series of polymers sold under the Hytrel® trade name by DuPont (Wilmington, DE), which are block copolymers consisting of hard crystalline segments of polybutylene terephthalate and soft amorphous segments based on long-chain poly ether glycols. Properties of various HYTREL grades are determined by the ratio of hard to soft segments. Particularly advantageous grades of TPE-ET, such as HYTREL, for use in the present disclosure have a shore D hardness in the range of about 45 to about 65D (tested according to ISO 868), such as about 50D to about 60D, and a flexural modulus at 23°C of about 125 MPa to about 350 MPa (tested according to ISO 178), such as about 150 to about 250 MPa.

In certain embodiments, the elastomer can be used in a blend with one or more additional polymers. In such embodiments, it is advantageous for the blend to be at least 90% by weight of the elastomer, such as at least about 95% by weight elastomer. Example blending partners include polyesters, co-polyesters, polyamides, polyolefins, polyacrylates, or thermoplastic liquid crystalline polymers. Specific examples include biodegradable polymers such as polybutylene succinate (PBS), poly (butylene succinate)-co- (butylene carbonate) (PBS-co-BC), polyethylene carbonate (PEC), polyhydroxyalkanoates (PHA) such as polyhydroxybutyrate (PHB), poly(glycolic acid) (PGA), polycaprolactone (PCL), and combinations thereof. In certain advantageous embodiments, the blending partner is a polyolefin, such as polypropylene. The use of a blending partner can be particularly convenient when the blending partner is commercially available as a masterbatch with a desired additive for the nonwoven material, such as charge stabilizers discussed below.

As explained in greater detail below, the nonwoven fabrics of the present disclosure are electrostatically charged. Due to conductivity within the material and ionic attacks from the environment, it is possible that this charge will decay after a period of time, which can lead to reduction of filtration efficiency. Accordingly, in certain embodiments, one or more charge stabilizer additives adapted to increase filtration efficiency and enhance longevity of the surface charge of the fabric can be added to the elastomer component. Example additives include metal salts of fatty acids such as stearic acid (e.g., magnesium, zinc, or aluminum stearate), titanate salts such as alkaline earth metal titanate salts (e.g., barium titanate or perovskite), silicate salts such as tourmaline, and other mineral materials such as perlite. When present, the amount of this type of additive is typically in the range of less than about 10% by weight of the overall fiber composition, such as less than about 7.5% or less than about 5% (e.g., about 0.1 to about 10% by weight or about 0.1 to about 5% by weight).

The polymer composition can optionally include other components not adversely affecting the desired properties thereof. Examples include, without limitation, antioxidants, particulates, pigments, and the like. These and other additives can be used in conventional amounts.

Nonwoven Fabric Formation

The nonwoven material can be formed using a meltblowing technique. Meltblowing is a process wherein a polymer (or polymers) is melted to a liquid state and extruded through a linear die containing numerous (e.g., several hundred or more) small orifices. As the polymer is extruded, streams of hot air are rapidly blown at the polymer, rapidly stretching and/or attenuating the extruded polymer streams to form extremely fine filaments. The air streams typically stretch or attenuate the molten polymer by many orders of magnitude. The stretched polymer fibers are collected as a randomly entangled, self-bonded nonwoven web. Meltblowing generally is described, for example, in US3849241 to Butin, which is incorporated herein by reference.

As illustrated in FIG. 1, for example, a high-velocity gas jet impinges upon the polymer as it emerges from the spinneret 4. An extruder 1 can feed a polymer to a first die 3 and through spinneret 4. Air enters from air intake 5 and into the air manifold 2. High pressure air is then used to draw the polymer into a fiber which can be collected on collector 6. The drag force caused by the air attenuates the fiber rapidly, and reduces its diameter as much as a hundred times from the nozzle diameter. Melt blown webs are typically reported to have fibers in the range of 0.1-10 pm, high surface area per unit weight, high insulation value, self-bonding, and high barrier properties yet breathability.

Meltblowing is generally capable of providing fibers with relatively small diameters. Diameter and other properties of meltblown fibers can be tailored by modifying various process parameters (e.g. , die design, die capillary size, polymer throughput, air velocity, collector distance, and web handling). Attenuating the air pressure affects fiber size, as higher pressures typically yield finer fibers (e.g., up to about 5 microns, such as about 1-5 microns) and lower pressures yield coarser fibers (e.g., up to about 20 microns, such as about 10-20 microns). In certain embodiments, the nonwoven web comprises meltblown fibers having average diameters of about 20 microns or less, such as about 15 microns or less or about 10 microns or less or about 5 microns or less (e.g., about 1 to about 10 microns or about 1 to about 5 microns in average diameter). By meltblown standards, the use of a relatively large fiber, such as the ranges provided above, can improve breathability of the resulting fabric.

The design of the meltblowing dies can vary. A conventional Exxon-design meltblown technology (i.e., single-row-capillary or impinging-air type die design) has a single row of spinning capillaries with impinging air streams from both sides of the die tip to draw the fibers. The safe operation pressure of this process is less than about 100 bar, for example. The Biax meltblown die technology (i.e., concentric -air design) features multiple rows of spinning nozzles with individual concentric air jets to attenuate the fibers.

It also tolerates high melt pressures at the spinneret and therefore can utilize higher viscosity polymers with a wide operation window. See, e.g., R. Zhao, “Melt Blowing Polyoxy methylene Copolymer,” International Nonw oven Journal, Summer 2005, pp. 19-21 (2005), herein incorporated by reference.

After production of the fibers and deposition of the fibers onto a surface, the nonwoven web can, in some embodiments, be subjected to some type of bonding (including, but not limited to, thermal fusion or bonding, mechanical entanglement, chemical adhesive, or a combination thereof), although in some embodiments, the web preparation process itself provides the necessary bonding and no further treatment is used. In one embodiment, the nonwoven web is bonded thermally using a calendar or a thru-air oven. In other embodiments, the nonwoven web is subjected to hydroentangling, which is a mechanism used to entangle and bond fibers using hydrodynamic forces. For example, the fibers can be hydroentangled by exposing the nonwoven web to water pressure from one or more hydroentangling manifolds at a water pressure in the range of about 10 bar to about 1000 bar. In some embodiments, needle punching is utilized, wherein needles are used to provide physical entanglement between fibers.

The fibrous webs thus produced can have varying thicknesses. The process parameters can be modified to vary the thickness. For example, in some embodiments, increasing the speed of the moving belt onto which fibers are deposited results in a thinner web. Average thicknesses of the nonwoven webs can vary and, in some embodiments, the web may have an average thickness of about 1 mm or less.

The stiffness of the structure can be controlled by employing larger diameter fibers and/or a higher basis weight. In some embodiments, the basis weight of the nonwoven web is about 100 g/m ² or less, about 75 g/m ² or less, about 65 g/m ² or less, about 60 g/m ² or less, about 50 g/m ² or less, or about 40 g/m ² or less. In certain embodiments, the nonwoven fabric has a basis weight of about 20 g/m ² to about 60 g/m ² , such as about 20 to about 50 g/m ² or about 25 to about 35 g/m ² . The basis weight of the fabric can be measured, for example, using test methods outlined in ASTM D 3776/D 3776M-09ae2 entitled “Standard Test Method for Mass Per Unit Area (Weight) of Fabric.” This test reports a measure of mass per unit area and is measured and expressed as grams per square meter (g/m ² ).

The nonwoven web is treated to induce an electrostatic charge within the fibrous material, which enhances filtration efficiency of the material. Electric charge can be imparted to the fibers by various methods including, but not limited to, corona charging, tribocharging, hydrocharging, and plasma fluorination. See, for example, the electric charging techniques set forth in US4215682 to Kubik et al.; US4588537 to Klasse et al.; US4798850 to Brown; US5401446 to Tsai et al.; US6119691 to Angadjivand et al.; and US6397458 to Jones et al., all of which are incorporated by reference herein. In one particular embodiment, the fibrous material is charged using corona charging by treating one or both sides of the nonwoven web with charging bars, such as those available from Simco-Ion, which can be placed close to the surface of the nonwoven web (e.g., about 20 to about 60 mm) and operating at a voltage of about 35 to about 50 kV. The treated nonwoven fabric is electrostatically charged following such treatment, and such materials are sometimes referred to as electret fibrous materials.

Once electrostatically charged, certain embodiments of the nonwoven fabric have a filtration efficiency of about 80% or higher, or about 85% or higher or about 90% or higher or about 95% or higher or about 98% or higher or about 99% or higher (e.g., about 90% to about 99% or about 95% to about 99%), measuring according to the test set forth in the Experimental section herein. Example ranges of pressure drop for certain example embodiments of the nonwoven fabric include about 50 Pa or less or about 45 Pa or less or about 40 Pa or less or about 35 Pa or less, such as a range of about 10 to about 50 Pa or about 20 to about 40 Pa.

Mask Structures

The electrostatically charged nonwoven fabrics described herein are well-suited for use in personal protective equipment, particularly such equipment used as a breathing barrier. One of the benefits of using the material of the present disclosure is the ability to use a broader range of converters to construct protective equipment from the nonwoven material. For example, unlike conventional polypropylene meltblown materials typically used in masks, the nonwoven material described herein is durable enough to be converted into masks by cutting and sewing, which opens up the possibility of using many converters in the industry that do not normally form masks or other filtration equipment.

When used in a mask, in certain applications, the nonwoven material can be used as a single layer of meltblown material due to the relatively high degree of durability of the nonwoven material compared to many meltblown materials. In other embodiments, the nonwoven material is used as part of a multi-layer structure. For example, an example multi-layer structure is shown in FIG. 2, which illustrates a nonwoven material 10 comprising an inner layer 16 of electrostatically charged meltblown elastomer as described herein sandwiched between two outer layers, 12 and 14, of a different fibrous material, such as a spunbond nonwoven material.

Masks constructed using the nonwoven material of the invention can vary in form and will include surgical masks, disposable respirators, and reusable respirators with replaceable filter cartridges. Typically, a mask according to this aspect of the disclosure will be configured to cover the mouth and nose of a user, and will include one or more bands (typically elastomeric) to temporarily affix the mask to the head of the user. These bands typically encircle the head or encircle the ears of the user.

Surgical masks are typically loosely -fitting and adapted for use as a single-use covering of the nose and mouth. FIG. 3 illustrates a surgical mask 20 according to one embodiment that can include a nonwoven material 22, optionally in pleated form as shown. The surgical mask 20 can further include an edge material 24 stitched or otherwise affixed to the nonwoven material 22 and elastic bands 26 adapted to fit over the ears of the user. The nonwoven material 22 can be a single layer of the electrostatically charged meltblown elastomer of the present disclosure or the meltblown elastomer can be part of a multi-layer structure such as shown in FIG. 2. For example, the multi-layer structure could include two outer PP spunbond layers (e.g., about 20-30 g/m ² ) with a meltblown nonwoven material according to the present disclosure therebetween. Various features of surgical masks that can be combined with the fibrous material of the present disclosure are shown, for example, in US2016/0235136 to Palomo et al., which is incorporated by reference herein. An N95 mask or N95 respirator is a particulate-filtering facepiece respirator that meets the U.S. National Institute for Occupational Safety and Health (NIOSH) N95 classification of air filtration, meaning that it filters at least 95% of airborne particles. Respirators have been categorized as being "filtering face- pieces" because the mask body itself functions as the filtering mechanism. Unlike respirators that include mask bodies with attachable filter cartridges or insert-molded filter elements, filtering face-piece respirators are designed to have the filter media cover much of the mask body so there is no need for installing or replacing a filter cartridge. These filtering face-piece respirators commonly come in two configurations: molded respirators and flat-fold respirators. Example embodiment of masks of this type that could be produced using the fibrous material of the invention are shown in US2017/0252590 to Angadjivand et al. and US2019/0307185 to Shiva et al., each of which is incorporated by reference herein.

FIG. 4 illustrates a respirator 30 according to one embodiment that can include a nonwoven material 32 and elastic bands 36 adapted to encircle the head of the user. The nonwoven material 32 is typically in the form of a multi-layer structure that includes the electrostatically charged meltblown elastomer of the present disclosure, such as shown in FIG. 2. In an example embodiment of respirator 30, the material of the present disclosure can be part of a multi-layer structure comprising at least 5 layers, such as a structure comprising outer PP spunbond layers (e.g., about 20-30 g/m ² ), one or more on each side, as well as an interior electrostatically charged meltblown elastomer layer as set forth herein, and one or more interior PP needle-punched layers (e.g., about 100-120 g/m ² ).

Certain mask bodies are reusable and include attachable filter cartridges or insert-molded filter elements that include replaceable filter materials. The electrostatically charged meltblown elastomer of the present disclosure could be used as the filter material in such mask designs as well. The bodies of such masks are typically constructed of a rubber/elastomeric material or other thermoplastic polymer. In some cases, such mask bodies can be made by injection molding or 3D printing. Reusable mask bodies that can accommodate a filter material are shown, for example, in US2015/0352382 to Jayaraman et al., which is incorporated by reference herein.

FIG. 5 illustrates a reusable respirator 40 according to one embodiment that can include a molded or printed mask body 42 adapted to cover the mouth and nose of the user, a replaceable filter insert 44 that can include a filter material such as a nonwoven material comprising the electrostatically charged meltblown elastomer of the present disclosure, and a cap 46 configured for attachment to the mask body to hold the filter insert in place. Although not shown, the respirator 40 would typically further include elastic bands for affixing the respirator to the head of the user, such as shown in FIGS. 3 and 4.

EXPERIMENTAL

A series of meltblown nonwoven webs were formed using HYTREL 5526 elastomer available from DuPont. The meltblown material was made in a series of basis weights from 25 to 60 g/m ² (or gsm). The samples were produced on a Reicofil R4 meltblowing machine where the throughput was kept between 0.3 to 0.5 gram per hole per minute by using a meltblowing die with 35 holes per inch (300 micron capillary). The die to collector distance was kept constant at 400 mm. The air was either 1000 m ³ /meter/hour (for the 25 and 30 gsm samples) or 1,400 m ³ /meter/hour (for the other samples). The 60 gsm sample contained 4% of a PP/magnesium stearate masterbatch (25% MS concentrate) for a total of 1% magnesium stearate.

The nonwoven webs were subjected to in-line corona charging directed to both sides of the web using four charging bars made by Simco-Ion of Hatfield, PA in order to electrostatically charge the web.

The charging settings were 45 kV with a gap of 30 mm. A scanning electron microscope (SEM) image with magnification at 1700X is provided as FIG. 6 for a 60 g/m ² sample.

Samples were tested for filtration efficiency both before and after corona charging using a test set forth in 42 CFR Part 84 and NIOSH Procedure No. TEB-APR-STP-0058 (Revision 3.1 dated 15 January 2020), which was conducted using a Model 8130 Automated Filter Tester manufactured by TSI Incorporated. The test involved challenging the nonwoven material with 0.3 micron salt particles in an aerosol at 32 liters per minute and at room temperature (about 25°C) and a relative humidity of about 30%. The NaCl particles are neutralized and the material is challenged with a salt particle concentration of not more than 200 mg/m ³ . To be designated an N95 respirator, the minimum filtration efficiency achieved by this test must be 95%. Pressure drop was also determined on the TSI 8130 machine for each material simultaneously.

Data for each sample is set forth in Table 1 below. As shown, the corona charging was successful in increasing the filtration efficiency of each sample, and several samples achieved a filtration efficiency of greater than 95%. The pressure drop for each sample was also within an acceptable range for use in masks. As shown, the charging treatment does not materially impact pressure drop.

Table 1

Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing description. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.