Filter element including pleated filter media and filter cartridge and respirator including the filter element

Abstract

A filter element includes pleated filter media including a nonwoven web having polymeric fibers and a plurality of pleat tips. The nonwoven web has a debossed portion on least at some of the pleat tips, and at least one of the following conditions is met. The debossed portion exhibits birefringence while a non-debossed portion of the nonwoven web does not exhibit birefringence. The debossed portion has a retardance profile in which there is an average retardance, and the average retardance is at least three times an average retardance in the non-debossed portion. The debossed portion has a total percent porosity that is less than 80 percent of a total percent porosity of the nonwoven web at the non-debossed portion. A filter cartridge and respirator including the filter element are also disclosed.

Description

[0001] PA101674W002

[0002] FILTER ELEMENT INCLUDING PLEATED FILTER MEDIA AND FILTER CARTRIDGE AND RESPIRATOR INCLUDING THE FILTER ELEMENT

[0003] 5 Cross-Reference to Related Application

[0004] This application claims priority to U.S. Provisional Application No. 63 / 779099, filed March 27, 2025, the disclosure of which is incorporated by reference in its entirety herein.

[0005] Background

[0006] Respirators are often used to cleanse the air that a user breathes and typically include a mask body along with one or more filter elements that are fluidly connected to the mask body. Some respirators include pleated filter media, including those described in U.S. Pat. No. 11,452,891 (Sebastian et al.).

[0007] In unrelated fields, a device for folding a web of material is described in U.S. 6,290,635 (Demmel et al.), and a method of making a folding line in a mesh fabric is disclosed in Int. Pat. Appl. Pub. No.

[0008] 15 WO2009 / 143674 (Chen).

[0009] Summary

[0010] In one aspect, the present disclosure provides a filter element that includes pleated filter media including a nonwoven web having polymeric fibers and a plurality of pleat tips. The nonwoven web has a debossed portion on at least some of the pleat tips, and at least one of the following three conditions is 0 met. 1) The debossed portion exhibits birefringence while the nonwoven web does not exhibit birefringence at a non-debossed portion. 2) The debossed portion has a retardance profile in which there is an average retardance, and the average retardance is at least three times an average retardance at the non-debossed portion. 3) The debossed portion has a total percent porosity as determined by x-ray microtomography that is less than 80 percent of a total percent porosity of the nonwoven web at the non- 5 debossed portion.

[0011] In another aspect, the present disclosure provides a filter cartridge for a reusable respiratory device. The filter cartridge includes a housing and the filter element described herein within the housing. The housing has a coupling element configured to removably couple to the reusable respiratory device and at least one major surface with an air-permeable area. The housing is configured such that substantially all of an ambient air flow is forced through the air-permeable area.

[0012] In another aspect, the present disclosure provides a respirator including a mask body and the above-mentioned filter cartridge connected to the mask body.

[0013] The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The description that follows more 5 particularly exemplifies illustrative embodiments. It is to be understood, therefore, that the following description should not be read in a manner that would unduly limit the scope of this disclosure.Brief Description of the Drawings

[0014] FIGS. 1A to ID illustrate pleated media in filter elements according to some embodiments of the present disclosure.

[0015] FIGS. 2A and 2B are images of scored fiberglass and a debossed nonwoven web comprising polymeric fibers, useful in the practice of the present disclosure, respectively.

[0016] FIG. 2C is a volume-rendered (3D) model for Example 4 generated by the software in the x-ray microtomography analysis described below.

[0017] FIG. 2D is an image of the retardance map for Example 4 generated in the birefringence and retardance analysis described below.

[0018] FIGS. 3 A and 3B illustrate pleated media in filter elements according to some embodiments of the present disclosure, in which FIG. 3 A illustrates some occluded pleat valleys.

[0019] FIGS. 4 A to 4C illustrate an example of a filter element and housing therefore according to some embodiments of the filter cartridge of the present disclosure.

[0020] FIG. 5 illustrates an example of a reusable respirator in which the filter element of the present disclosure may be useful.

[0021] Like reference numbers in the various figures indicate like elements. Some elements may be present in identical or equivalent multiples; in such cases only one or more representative elements may be designated by a reference number, but it will be understood that such reference numbers apply to all such identical elements. Unless otherwise indicated, all figures and drawings in this document are not to scale and are chosen for the purpose of illustrating different embodiments of the present disclosure. In particular, the dimensions of the various components are depicted in illustrative terms only, and no relationship between the dimensions of the various components should be inferred from the drawings, unless so indicated.

[0022] Detailed Description

[0023] Although terms such as "top”, bottom”, “upper”, lower”, “under”, “over”, “up” and “down”, and “first” and “second” may be used in this disclosure, these terms are used in their relative sense only unless otherwise noted. As used herein as a modifier to a property or attribute, the term “generally”, unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within + / - 20 % for quantifiable properties). The term “substantially”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within + / - 10% for quantifiable properties) but again without requiring absolute precision or a perfect match. The term “essentially” means to a very high degree of approximation (e.g., within plus or minus 2 % for quantifiable properties); it will be understood that the phrase “at least essentially” subsumes the specific case of an “exact” match. However, even an “exact” match, or any other characterization using terms such as e.g. same, equal, identical, uniform, constant, and the like, will beunderstood to be within the usual tolerances or measuring error applicable to the particular circumstance rather than requiring absolute precision or a perfect match.

[0024] The term “upstream” is used to denote the side of an entity (e.g. a pleated air filter media) from which moving air impinges on the entity; the term “downstream” is used to denote the side of an entity through which air exits the entity. Terms such as inward, outward, outermost, and the like, are with reference to the upstream-downstream direction of the pleated filter media. The term “lateral”, and terms such as e.g. “laterally inward” and the like, are with reference to a direction along the Pleat Direction of the pleated air filter media, as discussed in detail herein.

[0025] By “occlude”, “occlusive”, and like terms is meant to block so that at least substantially no air can flow therethrough.

[0026] Terms such as "a", "an" and "the" are not intended to refer to only a singular entity but include the general class of which a specific example may be used for illustration. The terms "a", "an", and "the" are used interchangeably with the term "at least one".

[0027] The phrase "comprises at least one of followed by a list including the conjunction “or” refers to comprising any one of the items in the list and any combination of two or more items in the list. The phrase "at least one of followed by a list including the conjunction “or” refers to any one of the items in the list or any combination of two or more items in the list.

[0028] The term "polymer" refers to a molecule having a structure which includes the multiple repetition of units derived, actually or conceptually, from one or more monomers. The term “monomer” refers to a molecule of low relative molecular mass that can combine with others to form a polymer. The term “polymer” includes homopolymers and copolymers, as well as homopolymers or copolymers that may be formed in a miscible blend, e.g., by coextrusion or by reaction. The term “polymer” includes random, block, graft, and star polymers. The term “polymer” encompasses oligomers.

[0029] Pleated filter media in the filter element of the present disclosure comprise a nonwoven web of polymeric fibers. “Nonwoven web” means a plurality of fibers characterized by entanglement or point bonding of the fibers to form a sheet or mat exhibiting a structure of individual fibers or filaments which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven webs of polymer fibers can be made using a variety of processes. In some embodiments, the nonwoven web is a melt blown web, a spunbond web, a carded web, a wet-laid web, or an air-laid web.

[0030] In some embodiments of the filter element of the present disclosure, the nonwoven web of polymeric fibers is made using a melt blowing process, in other words, it is a melt blown web. In a melt blowing process, one or more thermoplastic polymer streams are extruded through a die containing closely arranged orifices. These polymer streams are attenuated by convergent streams of hot air at high velocities to form fine fibers, which are then collected on a surface to provide a melt blown nonwoven fibrous layer. Depending on the operating parameters chosen, the collected fibers may be semi-continuous or essentially discontinuous.In some embodiments of the filter element of the present disclosure, the nonwoven web of polymeric fibers is made by a process known as melt spinning. In melt spinning, the nonwoven fibers are extruded as filaments out of a set of orifices and allowed to cool and solidify to form fibers. The filaments are passed through an air space, which may contain streams of moving air, to assist in cooling the filaments and passing through an attenuation (i.e., drawing) unit to at least partially draw the filaments. Fibers made through a melt spinning process can be “spunbonded,” whereby a web comprising a set of melt spun fibers are collected as a fibrous web and optionally subjected to one or more bonding operations to fuse the fibers to each other. Melt spun fibers are generally larger in diameter than melt blown fibers.

[0031] In some embodiments, the polymeric fibers in the nonwoven web have an effective fiber diameter (EFD) of at least 2 micrometers, at least 2.5 micrometers, or at least 3 micrometers. In some embodiments, the polymeric fibers have an EFD of not more than 30 micrometers, 20 micrometers, 10 micrometers, 8 micrometers, or 6 micrometers. In some embodiments, the polymeric fibers have an EFD in a range from 2 to 30 micrometers, 2 to 10 micrometers, 2 to 8 micrometers, 2 to 6 micrometers, 3 to 8 micrometers, or 4 to 6 micrometers. EFD can be measured using the test method described in the Examples, below.

[0032] In some embodiments, the nonwoven web is a melt-blown nonwoven web, and the fibers exhibit an EFD of less than about 10 micrometers, less than about 8 micrometers, or less than about 6 micrometers, including a range of 2 to 10 micrometers, 2 to 8 micrometers, 2 to 6 micrometers, 3 to 8 micrometers, or 4 to 6 micrometers.

[0033] In some embodiments of the filter element of the present disclosure, the nonwoven web has a thickness of at least about 0.2 millimeter (mm) or at least about 0.3 mm. In some embodiments, the nonwoven web has a thickness of less than about 2.0 mm, 1.7 mm, 1.5 mm, 1.2 mm, 1.0 mm, 0.8 mm, 0.6 mm, 0.5 mm, or 0.4 mm. In some embodiments, the nonwoven web has a thickness in a range from about 0.2 mm to about 1.2 mm or about 0.3 mm to about 0.5 mm. Such thicknesses refer to the thickness of the nonwoven web itself, regardless of the pleated structure. Such thicknesses can refer to the thickness of the nonwoven web before pleating. In some embodiments, the nonwoven web has a basis weight of at least about 25 grams per square meter (gsm), 50 gsm, 70 gsm, or 80 gsm. In some embodiments, the nonwoven web has a basis weight of not more than about 120 gsm or 100 gsm. In some embodiments, the nonwoven web has a basis weight in a range from about 50 gsm to about 120 gsm, from about 50 gsm to about 100 gsm, from about 60 gsm to about 100 gsm, or from about 70 gsm to about 100 gsm.

[0034] The nonwoven web may be made from any suitable polymeric material. The polymeric fibers typically comprise an organic polymer, which is typically a thermoplastic polymer. In some embodiments, the polymeric fibers comprise a semi-crystalline polymer. Examples of suitable polymers for the nonwoven web include polyolefins (e.g., polypropylene, polyethylene, and poly(4-methyl-l -pentene)), polyesters (e.g., polyethylene terephthalate and polybutylene terephthalate), polylactic acid, cyclic polyolefins, and copolymers and blends thereof. Natural fibers may also be useful. In some embodiments, the nonwoven web comprises polyolefin fibers. In some embodiments, the nonwoven web comprises polypropylene fibers. In some embodiments, the polymeric fibers comprise a polymer having a glass transition temperaturenot higher than room temperature. The term “room temperature” as used herein refers to a temperature in a range from 20 °C to 25 °C. The glass transition temperature of a polymer is that reported in Brandrup, J., Immergut, E. H., and Grulke, E. A., Eds., Polymer Handbook, 4thed., Wiley-Interscience, New York, NY, 1999.

[0035] In some embodiments of the filter element of the present disclosure, the nonwoven web exhibits a quasi-permanent electric charge. Polymeric filter material can be quasi-permanently charged, for example, using the process described in U.S. Pat. No. 5,496,507 (Bateman et al.) or a similar process. Charging a filter media causes the fibers of the filter media to capture particulates through the mechanism of electrostatic attraction in addition to mechanical filtration. Because particulates are captured with this additional capture mechanism, charging a filter media can be useful for providing filtration efficiency with a lower pressure drop. In some embodiments, the nonwoven web comprises electret fibers. By an electret material is meant a material (e.g., a polymeric material) that, after a suitable charging processes, exhibits a quasi-permanent electric charge. The electric charge may be characterized by an X-ray Discharge Test as disclosed e.g. in U.S. Patent Publication No. 2011-0290119 (Ylitalo et al.). Examples of suitable electret fibers include split fibrillated charged fibers as described in U.S. Patent RE 30782 (van Turnhout). Such charged fibers can be formed into a nonwoven web by any suitable means such as disclosed in U.S. Pat No.

[0036] 5,230,800 (Nelson). Any suitable charging method may be used. Examples of suitable charging methods include corona charging, hydrocharging, and tribocharging. In some embodiments, a fdter media may be formed from pre-charged electret fibers. In some embodiments, a nonwoven web can be formed, for example, using any of the methods described above, and then post-charged. If desired, the nonwoven web may comprise one or more charging additives, for example, chosen from any of the additives described in U.S. Pat. No. 10,273,612 (Song et al.).

[0037] In some embodiments of the filter element of the present disclosure, the nonwoven web is a melt blown microfiber nonwoven web (e.g. of the general types disclosed in U.S. Pat. No. 4,215,682 (Kubik et al.) and U.S. Pat. No. 7,989,371 (Angadjivand et al.)) that may include at least some fibers that comprise electrets. In some embodiments of the filter element of the present disclosure, the nonwoven web is of the general type described in U.S. Pat. No. 8,162,153 (Fox et al.) or, in some embodiments, is media generally known as tribocharged media.

[0038] In some embodiments of the filter element of the present disclosure, the nonwoven web has a fiber solidity in a range from 9% to 18% or from 10% to 18%. " Solidity " is a nonwoven web property inversely related to density and characteristic of web permeability and porosity (low Solidity corresponds to high permeability and high porosity) and is defined by Equation 1 below.

[0039] 1000 * Web Basis Weight (-^r)

[0040] Solidity (%) = - — - r q \

[0041] Web Thickness (mm) * Fiber Polymer Density ~3)

[0042] Equation 1In some embodiments of the filter element of the present disclosure, the nonwoven web has a Gurley stiffness in a range from 100 milligrams (mg) to 1000 mg. In some embodiments, the nonwoven web has a Gurley stiffness of at least about 100 mg, 150 mg, or 250 mg. In some embodiments, filter media herein has a Gurley stiffness of not more than about 1000 mg, not more than about 600 mg, or not more than about 550 mg. In some embodiments, the filter media has a Gurley stiffness in a range from 150 mg to 350 mg.

[0043] The filter element of the present disclosure includes pleated filter media having a plurality of pleat tips. In pleated filter media, upstream tips alternate with downstream tips. As shown in FIGS. 1A and IB, pleated filter media 110 comprises a plurality of upstream pleats 120 and downstream pleats 130. Each upstream pleat 120 includes an upstream pleat tip 121 and each adjacent pair of upstream pleats 120 defines an upstream pleat valley 122 therebetween. Downstream pleats 130 are in oppositely facing configuration from upstream pleats 120. Each downstream pleat 130 includes a downstream pleat tip 131 and each adjacent pair of downstream pleats 130 defines a downstream pleat valley 132 therebetween. As used herein, the Pleat Direction (Dpin FIGS. IB and 1C, also referred to as the lateral direction) is a direction that is aligned with the long axis of the pleat tips (and that typically mns from one corrugated edge 104 to the other cormgated edge 104’ of the pleated filter media as shown in FIG. 1A).

[0044] A portion of an embodiment of a filter element 101 is shown in a side view in FIG. IB. In some embodiments filter element 101 may be rectangular in shape (which specifically includes square shapes) with four comers; in such embodiments pleated filter media 110 may thus have a generally rectangular perimeter (which does not preclude irregularities, notches, chamfered or angled comers, in the perimeter of filter media 110). In the embodiment shown in FIG. 1A, pleated filter media 110 (and filter element 101) comprises major edges, e.g., four major edges. Major edges (ends) 104 and 104’ (which terminate as exposed pleats) will be referred to herein as cormgated edges, and major edges (ends) 105 and 105’ will be referred to as noncormgated edges, all as shown in FIG. 1 A.

[0045] Filter element 101 comprises an upstream major side 102 and a downstream major side 103 ; pleated filter media 110 thus includes an upstream major face 125 and a downstream major face 135. In some embodiments, filter element 101 may be upstream-downstream symmetrical (e.g., fdter element 101 may be installed in a filter element housing with either major side oriented upstream); in such cases the designation of upstream and downstream sides / faces is interchangeable. In other embodiments, however, filter element 101 is not symmetrical in this manner and the designation of upstream and downstream sides and faces is not interchangeable.

[0046] The longitudinal direction (Di in FIG. 1C) is a direction that is orthogonal to the pleat direction and that typically runs from one noncorrugated edge 105 to the other noncorrugated edge 105’ of the pleated filter media. (Although the terms longitudinal and lateral are used herein for convenience of description, it is not necessary that the longitudinal dimension of pleated filter media 110 must be greater than the lateral (Pleat Direction) dimension of pleated filter media 110.) The upstream-downstream direction (Du.d in FIG.1C) is a direction extending through the filter element from the upstream side 102 to the downstream side 103 and typically corresponds to the overall direction of air flow through the fdter element.

[0047] Further details of pleat geometry are discussed with reference to the side view of FIG. 1C (in which a portion of an example pleated filter media 110 is viewed along the pleat direction Dpwith the later-described optional adhesive dams omitted for clarity). Pleat spacing, pleat height, and pleat distance as defined herein are evaluated with the pleated filter media 110 in a nominally planar configuration in which the pleated filter media 110 exhibits a readily recognizable overall major plane (notwithstanding the local deviations from this plane that are inherent in each pleat), as in FIG. 1C. The pleat height (pleat amplitude) is the distance (Ph in FIG. 1 C) from a first-side pleat tip 121 to a second-side pleat tip 131 , along a direction that is orthogonal to the overall major plane of filter media 110 (i.e., along a direction that is aligned with the upstream-downstream direction Du.d of the pleated media). In some embodiments, a pleated media may exhibit a regularly varying pleat height, for example a predetermined alternating pattern of lower pleat heights interspersed with higher pleat heights.

[0048] In some embodiments, the pleated filter media of the present disclosure has a pleat height of at most about 45 millimeters (mm), 40 mm, 38 mm, 35 mm, 30 mm, 25 mm, 23 mm, 20 mm, 15 mm, or 13 mm. In some embodiments, the pleat height of media 110 is at least about 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, or 12 mm. In some embodiments, the pleat height is in a range from 6 mm to 23 mm, in a range from 10 mm to 23 mm, or any combination of pleat heights listed above.

[0049] The pleat spacing (Psin FIG. 1C) is the distance between nearest-neighbor same-side pleat tips, along a direction that is aligned with the overall major plane of the filter media (i.e., along the longitudinal direction Di of the pleated media). Pleated filter media 110 may have any suitable pleat spacing.

[0050] In some embodiments, the pleated filter media of the present disclosure has a pleat density of at least 7 pleats per inch, at least 8 pleats per inch, at least 9 pleats per inch, at least 10 pleats per inch, at least 11 pleats per inch, at least 12 pleats per inch, at least 13 pleats per inch, at least 14 pleats per inch, at least 15 pleats per inch, not more than 20 pleats per inch, not more than 15 pleats per inch, or a combination thereof.

[0051] In embodiments in which media 110 is tightly pleated, adjacent walls of a pleat may be at least substantially parallel to each other over at least about 70, 80 or even 90 % of the pleat height, on average. Such a tightly pleated media is shown in idealized representation in FIG. ID.

[0052] Filter media may be scored to provide score lines, along which the media can be folded to form pleat tips. Such a pleating operation, which may be conveniently done, for example, by rotary-score pleating, can often result in score lines being readily apparent on at least one major surface of filter media 110 of filter element 101. In some embodiments, both surfaces (upstream and downstream) of filter media 110 are rotary scored to exhibit score lines (noting that any such score lines may or may not be visible on casual inspection of the pleated media and that it may be necessary to physically manipulate (e.g., partially unfold) the pleated media in order to see the score lines).For the filter element of the present disclosure, scoring is carried out using ultrasound. Ultrasonic scoring is a technique that uses the vibrational energy to indent or deboss a web to a pre-determined depth. The purpose of the debossing is to create a fold line for the web. In ultrasonic scoring, the web is placed generally between a flat horn and a patterned anvil. It can also be envisioned that the horn has the pattern, and the opposing anvil is flat. The vibrating horn is brought close to the web and plunged into the web. The web could be stationary or moving as described below.

[0053] In some embodiments, the nonwoven web is placed directly below an ultrasonic horn, and the hom plunges (travels toward the parts) and transmits ultra sonic vibrations into the top of the nonwoven web. The vibrations travel through the top part through at least a portion of the thickness of the nonwoven web. Here, the vibrational energy is converted to heat due to intermolecular friction that melts and fuses at least a portion of the polymeric fibers together. When the vibrations stop, the polymer solidifies under force, producing a debossed portion in the nonwoven web.

[0054] In some embodiments, a continuous mode is useful. In the continuous mode, typically the ultrasonic hom is stationary, and the nonwoven web is moved beneath it. Scanning is a type of continuous mode in which the nonwoven web is scanned beneath one or more stationary horns. In a transverse mode, both the table over which the parts pass and the nonwoven web remain stationary with respect to each other while moving underneath the hom or while the hom moves over them.

[0055] FIGS. 2 A and 2B illustrate fiberglass and a nonwoven web of polymeric fibers useful for the filter element of the present disclosure, respectively. FIG. 2A illustrates fiberglass material 212 which, after scoring, has fractured along a fold line 210. FIG. 2B illustrates a nonwoven web of polymeric fibers, which has been ultrasonically debossed but does not fracture. Instead, the nonwoven web of polymeric fibers has a debossed portion 220 and a non-debossed portion 222. A debossed portion 220 and non-debossed portion 222 are shown in the volume-rendered (3D) model for Example 4 generated by the software in the x-ray microtomography analysis described below, illustrated in FIG. 2C.

[0056] According to the present disclosure, when ultrasonic scoring is carried out under certain conditions to deboss the nonwoven web, birefringence is observed in the debossed portion but not elsewhere in the nonwoven web (e.g., in a non-debossed portion). Materials with structural anisotropy (e.g., polymeric crystals) can have different refractive indices along their principal axes (i.e., parallel and perpendicular axes). The difference in refractive indices is termed birefringence. Retardance refers to how out of phase the two polarization components of the light are that are refracted by a birefringent material and is defined as the difference in optical thicknesses for light polarized along the two axes. Birefringence can be calculated from retardance using the film thickness.

[0057] In some embodiments, the debossed portion has a retardance profile in which there is an average retardance, wherein the average retardance is at least 3, 4, or 5 times an average retardance at the non-debossed portion. For the purposes of the present disclosure, when no birefringence is observed in the non-debossed portion and the retardance is 0, the retardance in the debossed portion is at least 5 nanometers (nm). In some embodiments, the average retardance in the debossed portion is at least 5 nm, at least 7.5 nm,at least 10 rnn, at least 11 rnn, at least 12 rnn, or higher. For the purposes of the present disclosure, the average retardance is a ‘grain-wise’ average retardance, which is calculated as average retardance magnitude and ignores differences in slow-axis orientation. Birefringence and retardance are evaluated using the test method described in the Examples, below. A retardance map for Example 4 is shown in FIG.

[0058] 2D.

[0059] While birefringence and retardance are evaluated using the test method described in the Examples, below, measurement using a Cerna Birefringence Imaging Microscope using a 633-nm filter and polarizer would also be useful for measuring the average retardance. Furthermore, a reduction in background noise would be expected to increase the average retardance of the debossed portion relative to the non-debossed portion.

[0060] According to the present disclosure, when ultrasonic scoring is carried out under certain conditions to deboss the nonwoven web, the debossed portion has a total percent porosity as determined by x-ray microtomography that is less than 80 percent of a total percent porosity of the nonwoven web at the nondebossed portion. In some embodiments, the total percent porosity of the debossed portion is less than 75 percent or less than 70 percent of the total percent porosity of the nonwoven web at the non-debossed portion. Total percent porosity as determined by x-ray microtomography is determined using the test method described in the Examples, below.

[0061] In order to obtain the desired birefringence, retardance, and total percent porosity in the debossed portion, the power supply of the ultrasonic horn is adjusted such that the amplitude of oscillation is more than 10%, more than 20%, at least 30% or at least 50% of the maximum displacement allowed by the equipment. In some embodiments, amplitude of oscillation of the ultrasonic horn is up to and including 100%. While the vibrational energy during ultrasonic scoring is converted to heat due to intermolecular friction that melts the nonwoven web in the debossed portion, the desired birefringence, retardance, and total percent porosity described herein is not observed when the scoring is carried out with a low amplitude of oscillation or when scoring is carried out with heat alone. These results, shown in the Examples, were unexpected.

[0062] In some embodiments, the debossed portion on at least some of the pleat tips is continuous in a pleat direction. In some embodiments, on at least some of the pleat tips, there are multiple, discontinuous debossed portions in a pleat direction. Whether continuous or discontinuous, the debossed portion on at least some of the pleat tips may be linear. The debossed portion may also be substantially linear, which means that the slit can have a slight curvature or slight oscillation. Some oscillation or curvature may result, for example, from the process of ultrasonically scoring a continuous web as would be understood by a person skilled in the art. The debossed portion may also have a wavy or sawtooth pattern with a small amplitude such that the pattern does not affect the ability of the nonwoven web to fold at the debossed portions.

[0063] Ultrasonic scoring at the conditions useful for providing the desired birefringence, retardance, and total percent porosity described herein provides an improvement in pressure drop across the filter elementin comparison to heat scoring at high temperature. As shown in the Examples, below, when ultrasonic scoring was carried out, a pressure drop measured across the unpleated nonwoven web was decreased at least 2%, 5%, 7.5%, or, in some embodiments, at least 10% or more in comparison to the pressure drop measured across the unpleated nonwoven web that had been heat scored at the same pitch. Decreases in pressure drop were more pronounced for higher basis weight nonwoven webs and when the scoring was carried out at higher temperature or amplitude. The pressure drop correlates to an ability of a user to breathe through the filter element. It is desirable to have a filter element with a relatively low pressure drop across the filter media.

[0064] In some embodiments, the pressure drop across the pleated filter media at 85 liters per minute (LPM) air flow rate is not more than about 50 millimeters of water (mmELO), not more than about 40 minfhO. not more than about 30 minfhO. not more than about 20 minfhO. not more than about 15 mniELO. not more than about 12 mniFTO. not more than about 10 mniFTO. not more than about 8 mniFTO. not more than about 5 nimfhO. or not more than about 3 nimfhO. In some embodiments, the pressure drop across the pleated filter media at 85 LPM is at least about 1 mmtLO. at least about 2 mm FLO. at least about 3 mmtLO. at least about 5 mmtLO. at least about 10 mmtLO. or at least about 15 mmtLO. In some embodiments, the media exhibits a Percent Penetration (i.e., DOP initial Percent Penetration, measured according to the procedures disclosed in the Working Examples) of less thanabout 5%, 1.0%, 0.1%, 0.05%, 0.01%, or 0.001% at face velocity of 13.8 cm / s.

[0065] The purpose of pleating a filter element is to increase the area of filter element that is available for filtration and particulate loading. It is desirable that air flows unimpeded through as much of the filter media as possible. If adjacent pleats close off air flow channels, the pressure drop increases, and the available filter media surface area decreases. In some embodiments of the filter element of the present disclosure, at least a majority of the upstream and downstream pleat valleys are at least partially nonoccluded. It is desirable for ambient air to flow through all available channels formed by the pleating process. A difference between occluded and nonoccluded pleat valleys in pleated material 300, 350 is illustrated in FIGS. 3 A and 3B. In FIG. 3 A, approximately half of the channels are at least partially occluded, as illustrated by reference numeral 320. Ambient air can flow more easily through channels 314 than through channels 312.

[0066] FIG. 3B exhibits sharp tips 360 when pleated, with most air channels being not-occluded, as illustrated by channels 362 and 364. Ultrasonic scoring as described above can lead to sharp tips 360 in pleating in contrast to the rounded pleat tips 310 illustrated in FIG. 3 A. As used herein, sharpness of tips 360 refers to a radius of curvature at the pleat tip. A sharp tip as defined as having a radius of curvature less than half of a pleat distance (e.g. a diameter of curvature is less than a width of each pleat). When a radius of curvature is larger than half the pleat distance, occlusion of air channels is more likely to occur. The polymeric material is another factor in forming a sharp pleat tip 360, with materials of higher stiffness more likely to form sharp pleat tips.

[0067] In some embodiments, the filter element of the present disclosure is formed of a single layer of nonwoven material that is sufficiently stiff to be self-supporting once pleated into a pleat pack construction.In these embodiments, the filter media contains a single layer of material which is not coupled to another separate layer of material using any welding, bonding or adhesive treatment. In these embodiments, the filter media can be self-supporting without the use of adhesive to form edge dams or the sealing of the filter media to the interior of a filter cartridge housing. In some of these embodiments, the filter element is formed of a single sheet of non-laminated media that has consistent, or uniform, mechanical properties throughout the thickness of the nonwoven web that is self-supported when pleated. The filter element may have a lower basis weight than other polymeric filter media materials while maintaining a sufficient stiffness to be self-supporting when pleated. The lower basis weight enables a higher pleat count (e.g. folding the filter media more times) which lowers the pressure drop across the filter element. In these embodiments, for example, the filter element can free of fiberglass and / or can be free of any fluorinated material. Further details about such a filter element can be found in co-pending provisional patent application 63 / 572111, filed on March 29, 2024, which is incorporated by reference herein in its entirety.

[0068] In some embodiments, the nonwoven web is laminated, welded (e.g., ultrasonically welded), thermally bonded, or adhesively bonded to a scrim or stiffening element. Stiffening elements can be a woven material, nonwoven material, or metal, for example. Potentially suitable materials to which the nonwoven web can be bonded include paper; porous films of thermoplastic or thermoset materials; microporous membranes such as phase-inversion membranes, other nonwoven polymeric nonwoven webs (e.g., melt blown or spunbond webs, carded webs, wet-laid, or air-laid webs) of synthetic or natural fibers; scrims; plastic netting or mesh; woven or knitted materials; foams; fiberglass media; or laminates or composites of two or more materials. In some embodiments, the lamination may use a hot-melt adhesive that is applied (e.g., by spraying, roll coating, or any suitable method) so as to not unacceptably increase the flow resistance of the media. In some embodiments, adhesive is provided at a coating weight of less than about 15 gsm, 10 gsm, 8 gsm, or 6 gsm. In some embodiments, the nonwoven web of polymeric fibers described above in any of its embodiments is joined to one or more layers of other material before pleating.

[0069] In some embodiments, the filter element of the present disclosure includes at least one layer that comprises a sorbent (e.g. activated carbon), which may be useful, for example, for reducing nuisance odors. Sorbents can be in any suitable form, including granules, fibers, fabric, and molded shapes. In some embodiments, the filter element comprises at least one prefilter layer that is on the upstream side of the nonwoven web of polymeric fibers described above in any of its embodiments, which serves as a primary filtration layer. In some embodiments, such a prefilter layer may capture relatively large particles while allowing smaller particles to pass therethrough so that they may be captured by the nonwoven web. Such a prefilter layer may comprise, for example, polypropylene, polyethylene, polyethylene terephthalate, poly(lactic acid), or blends of these materials.

[0070] In some embodiments, the filter element of the present disclosure comprises a fiberglass layer. The fiberglass layer may take the form of a prefilter layer (that is, on the upstream side of the primary filtration layer). In some embodiments, a fiberglass layer may be on the downstream side of a primary fdtration layer and thus may not function as a prefilter. In some embodiments, fiberglass layers may be provided on boththe upstream and downstream sides of a primary filtration layer. Fiberglass partially fractures when folded (as seen in FIG. 2A) and is a stiff material that can result in a self-supported pleated media; however, it is fragile and prone to breakage. In some embodiments, a fiberglass layer can result in a laminate that is easier to pleat, with a lower pleat spacing and / or higher pleat height, than the primary filtration layer alone. For example, a highly flexible primary filtration layer can be difficult to pleat. Furthermore, combining a fiberglass layer with a nonwoven web of polymeric fibers can provide enhanced physical durability over fiberglass layers when used alone. In some embodiments, the filter element of the present disclosure consists essentially of, or consists of, a primary filtration layer that is the nonwoven web of polymeric fibers described above in any of its embodiments, that is laminated, in some embodiments, adhesively laminated, together with a fiberglass layer. Examples of fiberglass materials that may be suitable for inclusion in a multilayer filtration media as disclosed herein include the products available from Hollingsworth and Vose under the trade designations “HF-13732A”, “HE-14732A”, “HE-1073”, “HF-11732A”, and “HF-0121”.

[0071] A prefilter layer as described above in any of its embodiments may exhibit a Percent Penetration of greater than about 20%, 40%, 60%, 70%, 80%, 90%, or 95%. In some embodiments, any such prefilter layer may be combined with a primary filtration layer that exhibits a Percent Penetration of less than about 10%, 5.0%, 2.0%, 1.0%, 0.4%, 0.2%, 0.1%, 0.05%, or 0.01%. A laminate of at least one primary filtration layer and at least one prefilter layer may, in some embodiments, exhibit a Percent Penetration of less than about 10%, 5.0%, 4.0%, 2.0%, 1.0%, 0.4%, 0.2%, 0.1%, or 0.05%. In some embodiments, a prefilter layer has a thickness of less than about 2.0 mm, 1.5 mm, 1.0 mm, 0.8 mm, 0.6 mm, or 0.4 mm. In some embodiments, a prefilter layer has a basis weight of from at least about 20 gsm, 30 gsm, 40 gsm, or 50 gsm, to at most about 120 gsm, 100 gsm, 80 gsm, or 60 gsm. In some embodiments, a prefilter layer has a pressure drop that is less than 4.0 ininFTO. 3.0 ininFTO. 2.0 ininFTO. 1.5 ininFTO. or 1.0 nmiFTO (tested at face velocity of 14 cm / s).

[0072] In some embodiments, including the embodiments illustrated in FIGS. 1 A to ID, filter element 101 has one or more adhesive edge dams 140. An adhesive edge dam may be located proximate a corrugated edge (104 or 104’) of the pleated filter media. Each dam may be formed of hardened adhesive. In some embodiments, the adhesive may be provided as a liquid that is applied as an elongate bead extending along the longitudinal direction of the media, proximate an edge of the fdter media. Adhesive beads may be applied simultaneously to the upstream and downstream major surfaces of the media, or adhesive beads may be applied to one major surface and then to the other major surface. After the adhesive beads are applied to one or both major surfaces, the media may then be compressed (with the adhesive still in an at least semi-liquid state) along the longitudinal direction of the media to a final pleated configmation (that exhibits the pleat spacing, pleat height, and so on, that is desired to be present when filter element 101 is used). This will cause the adhesive to at least generally fill each pleat valley at a location proximate a corrugated edge of the pleated filter media. The adhesive may then be hardened while the filter media is held in this pleated configuration.The hardened adhesive thus forms a dam 140. In at least some embodiments, pleated filter media 110 comprises a first edge dam 140 at one corrugated edge 104 of the pleated filter media, and a second edge dam 140’ at the other corrugated edge 104’, as shown in FIGS. 1 A to IB (only a single edge dam 140 is visible in the side view of FIG. IB). It will be appreciated that the hardened adhesive portions in upstream pleat valleys 122, and the hardened adhesive portions in downstream pleat valleys 132, act in concert to provide dam 140, even though the adhesive portions in the upstream pleat valleys and those in the downstream pleat valleys are separated from each other by the thickness of the filter media and thus may never physically contact each other. That is, the hardened upstream and downstream adhesive portions collectively form dam 140.

[0073] Dams 140 and 140’ (and optional interior dams 142) can provide structural rigidity to the pleated filter media, which can make the resulting filter element more mechanically robust without having to use, for example, a casing material that might add undesirable weight and / or complexity. It is further noted that the presence of such adhesive dams can allow the achievement of a tight pleating pattern. That is, if a very tight pleating pattern is used, the adhesive dams can act as spacers to provide that adjacent walls of pleats are not pushed completely against each other so that they are so closely spaced (e.g. touching each other) that they disadvantageous^ occlude air flow through the pleat valleys.

[0074] In various embodiments, each adhesive edge dam may be located at a position from about even with the terminal ends of a corrugated edge, to a position that is recessed laterally inward (measured from the centerline of the dam) from the terminal ends of the corrugated edges, no more than about 0.1 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, 2.0 mm, 3.0 mm, or 4.0 mm. By way of specific example, adhesive edge dams 140 and 140’ as shown in the embodiment of FIG. 1A may be located 1 mm to 2 mm laterally inward from the terminal ends of corrugated edges 104 and 104’, and no portion of each adhesive edge dam extends outward beyond the terminal end of the corrugated edge to which it is proximate.

[0075] In some embodiments, an edge dam of hardened adhesive at least substantially or essentially fills the upstream and downstream pleat valleys so that it at least substantially occludes the pleat valleys so as to prevent airflow therethrough. In such a case an edge dam may serve as an edge seal that at least substantially or essentially prevents air (or any other flowing gas or gas mixture) from flowing laterally outward beyond a corrugated edge of the pleated filter media and thus at least partially bypassing the filter media. (The special case in which edge dams function as edge seals may be verified, for example, by mounting the filter element in a filter element housing as described later herein. If the performance of the filter element is substantially unaffected by any external sealing or gasketing that is applied to the filter element, this will indicate that the edge dams are performing as edge seals in the manner described herein.) It will be appreciated that the use of hardened adhesive edge dams 140 that serve as edge seals in this manner may eliminate the need to cover the corrugated edges of the pleated filter element with casing portions or gaskets or to seal the corrugated edges of the pleated filter element by dipping the edges in a sealing material. At the very least, an edge dam can reduce the extent to which such measures may be needed and may thus allow the complexity and cost of filter element 101 to be reduced.If desired, one or more additional interior dams 142 can be provided laterally in between the first and second adhesive edge dams 140 and 140’ as shown in the embodiment of FIG. 1A. Although not necessarily needed for any occluding function, such additional, interior adhesive dams may provide mechanical rigidity to the pleated filter element and may also assist in maintaining the pleats of the filter media in a pleated configuration (e.g., a tightly pleated configuration of the type shown in the embodiment of Fig. ID). The adhesive dams may be spaced at least generally uniformly across the lateral extent of the pleated filter media (as in the embodiment of FIG. 1A), or such spacing may vary as desired. Any number of interior dams (e.g. one, two, three, four, or more) may be present; two such interior dams 142 are depicted in FIG. 1A. Edge dams are discussed in greater detail in U.S. Pat. No. 11,452,891 (Sebastian et al.).

[0076] FIGS. 4 A to 4C illustrate an embodiment of a filter element and housing therefore according to some embodiments of the present disclosure.

[0077] In the embodiment illustrated in the side view of FIG. 4A, the pleated filter element is arcuate. In some embodiments, filter element 401 is planar as made, and is conformed into an arcuate shape in order to be installed into an arcuate receptacle of a filter element housing. Although an arcuate filter element may not be upstream-downstream reversible, it may have other advantages, for example, allowing a filter element housing into which the filter element is installed to be curved so as to follow the contours of a user’s cheek or of a user’s hip. In some embodiments, a convex side of arcuate filter element 401 is an upstream side 402, and a concave side of arcuate filter element 401 is a downstream side 403, as in the exemplary design of FIG. 4A.

[0078] In some embodiments, an arcuate pleated filter media 410 exhibits a shape with single curvature, with the curvature being along a conforming axis Acthat is orthogonal to the pleat direction and is parallel to the longitudinal direction, as shown in FIG. 4A. Such a configuration will be contrasted with a shape that exhibits compound curvature such as a section of a sphere, paraboloid or hyperboloid. This can minimize the chance of any wrinkling or crumpling of the pleated media when it is curved into an arcuate configuration. Other filters (e.g., in respirator mask bodies) are formed into complex, compound-curvature shapes to conform to a human face, for example.

[0079] In some embodiments, filter element 401 may comprise a casing that is a separately made component that is disposed on (e.g., fitted onto or wrapped around) at least portions of filter element 401. If such a casing is present, it will be provided as part of filter element 401 and will not be removable therefrom in ordinary use of filter element 401. Such a casing can be considered a part of a filter element instead of a filter element housing of a respirator. Such a casing may be made of any suitable material such as molded plastic or paperboard. Such casings are described in detail in U.S. Pat. No. 10,751,660 (Legare et al.). In other embodiments, filter element 401 does not include any such casing.

[0080] Filter element 401 may be used, for example, in any application in which it is desired to filter air (which term generally encompasses any breathable gaseous mixture).

[0081] In some embodiments, filter element 401 may be used in any suitable respirator that is configured to filter breathing air. In order to include filter element 401 in a respirator, it may be convenient to installfilter element 401 into the interior of a filter element housing 460 as shown in the illustrated embodiment of FIGS. 4B and 4C. Filter element 401 and filter element housing 460 may be used with any type of respirator, e.g., powered or unpowered, full-mask or half-mask. In some embodiments, such a respirator may comprise at least a mask body that comprises a portion that covers at least the nose and mouth of a user (and, in some embodiments, may take the form of a helmet) to define an interior air space. An exhalation valve may be provided to allow exhaled air to be discharged from the interior air space. Such a respirator may also include a harness assembly that is able to support the mask body on a user’s head. In some embodiments, filter element housing 460 may be mounted in close proximity to the mask body. For example, a single filter element housing may be fluidically connected to the mask body, e.g., at a location in front of the mouth and / or nose of the user. Dual filter element housings may be mounted, e.g., at locations adjacent the right and left cheek of the user. In other embodiments, one or more filter element housings may be located in a unit that is remote from the mask body, e.g., a powered unit that is located on a hip belt and that comprises a fan that motivates the filtered air through a supply tube to the mask body. Filter element housing 460 as depicted in FIGS. 4B and 4C may be suitable, for example, for mounting on a hip belt as part of a so-called powered-air-purifying-respirator (e.g., such as the product available from 3M Company under the trade designation “VERSAFLO TR-600”) that delivers filtered air by way of a hose that fluidically connects filter element housing 460 with a mask body or helmet that resides on a user’s face or head. However, filter element 401 may be installed in a filter element housing of any suitable type.

[0082] Filter element housing 460 comprises at least one major housing portion that is configured to receive at least one filter element 401 and to fluidically connect the filter element to other components of a respirator (e.g., to a mask body). Housing 460 (e.g., major housing portion thereof) may comprise an upstream major face 461 that comprises an air-permeable area 462 (which may conveniently be achieved by providing numerous through-perforations in area 462 of upstream face 461 of filter element housing 460, as shown in FIG. 4B). In some embodiments, housing 460 (e.g., at least a major housing portion thereof) may be made of an organic polymeric resin that is molded (e.g., injection molded, vacuum-formed, or thermoformed) into a desired shape. Other ancillary parts such as latches and fittings may be attached to housing 460 as desired.

[0083] In some embodiments, filter element 401 may be disposable with filter element housing 460 such that, when filter element 401 needs to be changed, the housing 460 is reusable. In such embodiments, filter element housing 460 is not a part of filter element 401 itself and is removably attached to filter element 401. In such cases, housing 460 may comprise a closing portion (not shown in FIGS. 4B and 4C) that is air-impermeable and that may, when closed, serve to securely hold filter element 401 in place within the interior 463 of filter element housing 460. Such a closing portion may be hingedly connected or snap-fitted to housing 460, so that the closing portion can be opened or temporarily removed, a filter element 401 can be removed, and a replacement filter element 401 installed.

[0084] In other embodiments, filter element 401 and a filter element housing 460 may be provided to a user as a unit with filter element 401 non-removably attached to housing 460. Housing 460 containing filterelement 401 will be removably attachable to other components of a respirator to establish a fluidic connection between housing 460 and a mask body of the respirator, so that filtered air can be delivered to the mask body. In such embodiments, housing 460 containing filter element 401 therein may be removed and discarded or recycled, and a new housing and filter element installed in the respirator, at a desired time.

[0085] In the illustrative embodiment of FIG. 4C, interior 463 of housing 460 includes a receptacle 464 that is configured to receive fdter element 401. In the illustrated embodiment of FIG. 4C, receptacle 464 is arcuately shaped to receive an arcuate fdter element. However, it is expressly contemplated that both filter element 401 and housing 460 may have different shapes, for example, housing 460 can be shaped to receive a flat filter, such as that shown in FIG. 1 A. Flat or arcuate shaped filters may also have other shapes (e.g., ovular, circular, polygonal or non-polygonal shaped) having, for example, perimeter portions that are straight and / or curved.

[0086] Receptacle 464 may comprise sidewalls 465 that abut noncorrugated edges 405 and 405’, and sidewalls 467 that abut corrugated edges 404 of pleated filter element 401 when installed within receptacle 464. In some embodiments, the longitudinal distance between sidewalls 465 may be set so that filter element 401 is slightly longitudinally compressed (accordionized) in order to fit within the space between longitudinal sidewalls 465. Such an arrangement may help hold filter element 401 securely in place, while not compressing the pleats of filter element 401 together to such an extent as to disadvantageous^ affect the filtration performance. In some embodiments, a longitudinal distance between longitudinal sidewalls 465 may be at most about 100%, 98%, 96%, or 94 % of the longitudinal length (before being compressed for installation into receptacle 464) of filter element 401.

[0087] If desired, a sealant or potting material (e.g., a hardenable material such as an RTV silicone) may be disposed as ahead along cormgated edges 404 and / or along noncorrugated edges 405 and 405’, e.g., at locations at which these edges are abutted against surfaces 466 of sidewalls 467 and / or 465 of housing 460, as seen in FIG. 4C. Such a material, after hardening, may minimize any air leaks around the edges of filter element 401. It will be appreciated that the presence of edge dams, in particular edge seals, within filter element 401 as discussed herein, may reduce or even eliminate the need for such a material to be used along sidewalls 467 for purposes of minimizing air leakage around corrugated edges 404 of filter element 401. Such a material may of course be used to seal the noncorrugated edges 405 and 405’ of the pleated filter element, against sidewalls 465 of the housing, if desired. Moreover, even if no such material is needed for sealing, such a material may be applied to bond at least some portions of the edges of filter element 401 to surfaces of receptacle 464 if desired to more securely hold filter element 401 in place within housing 460.

[0088] In some embodiments, one or more gaskets (not shown in any Figure) may be provided within interior 464 of filter element housing 460 to assist in securely installing filter element 401 therein. Such a gasket may be permanently attached to housing 460, or it may be removable and replaceable if desired. Such a gasket may be made of a resilient polymeric material such as rubber or silicone. The polymeric material may be solid or a foam. If a foam, it may be an open-cell foam or a closed cell foam. In some embodiments, no such gasket is present.In some embodiments, filter element 401 may be the only filtering component that resides within filter element housing 460. However, in other embodiments, one or more layers of material may reside within housing 460 (e.g., in overlapping relation to or butted up against a major surface of filter element 401) for some additional purpose. Such a layer or layers may contain one or more materials that interact with an airstream to at least partially remove one or more components (e.g., gases, vapors, solid particles, or aerosols) therefrom. The components in the fluid may be sorbed onto or into an active sorbent, may be reacted with a reactive ingredient, or may be exposed to a catalyst. Potentially suitable materials for such uses include activated carbon; alumina and other metal oxides; sodium bicarbonate; metal particles (e.g., silver particles) that can remove a component from a fluid by adsorption, chemical reaction, or amalgamation; catalytic agents such as hopcalite and / or gold (which can catalyze the oxidation of carbon monoxide); clay and other minerals treated with acidic solutions such as acetic acid or alkaline solutions such as aqueous sodium hydroxide; ion exchange resins; molecular sieves and other zeolites; silica; biocides; fungicides and vimcides. Mixtures of any such materials can be employed. In other embodiments, such materials may be provided as particles in a particle-loaded web layer. Combinations of any of these approaches may be used. If desired, such materials may be treated with one or more impregnants to enhance gas removal capability. Examples of treated materials include chemically surface-treated activated carbon.

[0089] In many embodiments, flowing air will locally approach filter element 401, and will locally leave filter element 401, along a direction that is at least generally aligned with the upstream-downstream direction Du-d of the filter element. Such a direction will often be at least generally orthogonal to the pleat direction Dpof the pleated filter media 410. That is, in ordinary use of a pleated filter element 401, there may often be little or no airflow along the long axis of the valleys of the pleated media. In some embodiments, pleated filter element 401 is distinguished from arrangements in which a fluid flows along the valleys in between multiple layers (e.g., stacks or wraps) of pleated media. In some embodiments, pleated filter element 401 is thus distinguished from so-called spiral-wound filters that, as supplied, comprise multiple layers of filter media and in which substantial fluid flow may occur along the long axis of the valleys in between layers of the pleated media.

[0090] In some embodiments, the filter element of the present disclosure is placed within a housing of a respirator, and air is forced through the filter element either by a user breathing (reusable respirator) or by a motor and fan (PAPR). Respirators containing a filter element of the present disclosure may, when worn properly, filter at least 95% of airborne particles having an average diameter of 0.3 micrometer. In some embodiments, such respirators may, when worn properly, filter at least 99% of airborne particles having an average diameter of 0.3 micrometer. In some embodiments, such respirators may, when worn properly, filter at least 99.97% of airborne particles having an average diameter of 0.3 micrometer. In some embodiments, such respirators are at least partially resistant to oily aerosol particles having an average diameter of 0.3 micrometer.

[0091] FIG. 5 illustrates an embodiment of a reusable respirator in which the filter element and / or filter cartridge of the present disclosure may be useful. FIG. 5 illustrates an individual 500 wearing a half-facereusable respirator 502 which is configured to couple to one or more pleat packs 510, each pleat pack containing a pleated filter media (not shown in FIG. 5).

[0092] However, while a half-face reusable respirator (e.g., a reusable respirator that only covers half of the face of individual 500) is illustrated in FIG. 5, it is expressly contemplated that the filter element and / or filter cartridge of the present disclosure may be useful in powered air-purifying respirator (PAPR) filters as well as to other types of reusable respirator, such as full-face respirators, for example.

[0093] In a first embodiment, the present disclosure provides a filter element comprising: pleated filter media comprising a nonwoven web comprising polymeric fibers and a plurality of pleat tips; wherein the nonwoven web comprises a debossed portion on at least some of the pleat tips, and wherein at least one of the following conditions is met: wherein the debossed portion exhibits birefringence while the nonwoven web does not exhibit birefringence at a non-debossed portion; wherein the debossed portion has a retardance profile in which there is an average retardance in the debossed portion, and wherein the average retardance is at least 3, 4, or 5 times an average retardance in the non-debossed portion; or wherein the debossed portion has a total percent porosity as determined by x-ray microtomography that is less than 80 percent of a total percent porosity of the nonwoven web at the non-debossed portion.

[0094] In a second embodiment, the present disclosure provides a filter element comprising: pleated filter media comprising a nonwoven web comprising polymeric fibers and a plurality of pleat tips; wherein the nonwoven web comprises a debossed portion on at least some of the pleat tips, and wherein the debossed portion exhibits birefringence while the nonwoven web does not exhibit birefringence at a non-debossed portion. In a third embodiment, the present disclosure provides the filter element of the second embodiment, wherein the debossed portion has a retardance profile in which there is an average retardance in the debossed portion, and wherein the average retardance is at least three times an average retardance in the non-debossed portion. In a fourth embodiment, the present disclosure provides a filter element comprising: pleated filter media comprising a nonwoven web comprising polymeric fibers and a plurality of pleat tips; wherein the nonwoven web comprises a debossed portion on at least some of the pleat tips, and wherein the debossed portion has a retardance profile in which there is an average retardance in the debossed portion, and wherein the average retardance is at least three times an average retardance at a non-debossed portion. In a fifth embodiment, the present disclosure provides the filter element of any one of the first to fourth embodiments, wherein the average retardance of the debossed portion is at least 10 nanometers, at least 11 nanometers, or at least 12 nanometers.

[0095] In a sixth embodiment, the present disclosure provides the filter element of any one of the first to fifth embodiments, wherein the debossed portion has a total percent porosity as determined by x-ray microtomography that is less than 80 percent of a total percent porosity of the nonwoven web at the non-debossed portion. In a seventh embodiment, the present disclosure provides a filter element comprising: pleated filter media comprising a nonwoven web comprising polymeric fibers and a plurality of pleat tips; wherein the nonwoven web comprises a debossed portion on at least some of the pleat tips, and wherein the debossed portion has a total percent porosity as determined by x-ray microtomography that is less than80 percent of a total percent porosity of the nonwoven web at a non-debossed portion. In an eighth embodiment, the present disclosure provides the filter element of any one of the first to seventh embodiments, wherein the total percent porosity of the debossed portion is less than 75 percent or less than 70 percent of the total percent porosity of the nonwoven web at the non-debossed portion.

[0096] In a ninth embodiment, the present disclosure provides the filter element of any one of the first to eighth embodiments, wherein the nonwoven web comprises at least one of polypropylene fibers, polyethylene fibers, polyester fibers, poly (4-methy 1-1 -pentene) fibers, cyclic olefin copolymer fibers, or poly(lactic acid) fibers. In a tenth embodiment, the present disclosure provides the filter element of any one of the first to ninth embodiments, wherein the polymeric fibers comprise a semi-crystalline polymer having a glass transition temperature not higher than room temperature. In an eleventh embodiment, the present disclosure provides the filter element of any one of the first to tenth embodiments, wherein the nonwoven web comprises polyolefin fibers. In a twelfth embodiment, the present disclosure provides the filter element of any one of the first to eleventh embodiments, wherein the nonwoven web comprises polypropylene fibers. In a thirteenth embodiment, the present disclosure provides the filter element of any one of the first to twelfth embodiments, wherein on at least some of the pleat tips, the debossed portion is continuous in a pleat direction. In a fourteenth embodiment, the present disclosure provides the filter element of any one of the first to thirteenth embodiments, wherein on at least some of the pleat tips, there are multiple, discontinuous debossed portions in a pleat direction.

[0097] In a fifteenth embodiment, the present disclosure provides the filter element of any one of the first to fourteenth embodiments, wherein the nonwoven web exhibits a quasi-permanent electric charge. In a sixteenth embodiment, the present disclosure provides the filter element of any one of the first to fifteenth embodiments, wherein the nonwoven web comprises electret fibers. In a seventeenth embodiment, the present disclosure provides the filter element of any one of the first to sixteenth embodiments, wherein the pressure drop across the pleated filter media at 85 LPM air flow rate is not more than about 50 mmH20, not more than about 40 mmH20, not more than about 30 mmH20, not more than about 20 mmH20, not more than about 15 mmH20, not more than about 12 mmH20, not more than about 10 mmH20, not more than about 8 mmH20, not more than about 5 mmH20, or not more than about 3 mmH20.

[0098] In an eighteenth embodiment, the present disclosure provides the fdter element of any one of the first to seventeenth embodiments, wherein the nonwoven web has a basis weight of at least about 50 grams per square meter, at least about 70 grams per square meter, not more than about 120 grams per square meter, not more than about 100 grams per square meter, or a combination thereof. In a nineteenth embodiment, the present disclosure provides the filter element of any one of the first to eighteenth embodiments, wherein the nonwoven web has a thickness of at least about 0.2 millimeter, at least about 0.3 millimeter, not more than about 2 millimeters, not more than about 1.7 millimeters, not more than about 1.5 millimeters, not more than about 0.5 millimeter, or a combination thereof. In a twentieth embodiment, the present disclosure provides the filter element of any one of the first to nineteenth embodiments, wherein the polymeric fibers have an effective fiber diameter of at least 2 micrometers, at least 2.5 micrometers, or at least 3 micrometers.In a twenty -first embodiment, the present disclosure provides the filter element of any one of the first to twentieth embodiments, wherein the nonwoven web has a Gurley stiffness of not more than 1000 milligrams, not more than 600 milligrams, not more than 550 milligrams, not more than 350 milligrams, at least 250 milligrams, or a combination thereof.

[0099] In a twenty-second embodiment, the present disclosure provides the filter element of any one of the first to twenty -first embodiments, wherein the pleated filter media has a pleat density of at least 7 pleats per inch, at least 10 pleats per inch, at least 15 pleats per inch, not more than 20 pleats per inch, not more than 15 pleats per inch, or a combination thereof. In a twenty -third embodiment, the present disclosure provides the filter element of any one of the first to twenty-second embodiments, wherein the pleated filter media has a pleat height of less than 38 millimeters, less than 25 millimeters, less than 13 millimeters, at least 10 millimeters, at least 6 millimeters, or a combination thereof. In a twenty-fourth embodiment, the present disclosure provides the filter element of any one of the first to thirteenth embodiments, wherein percent penetration of the pleated filter media at 85 LPM air flow rate is not more than 1%, not more than 0.5%, not more than 0.1%, not more than 0.01%, or not more than 0.001%.

[0100] In a twenty -fifth embodiment, the present disclosure provides the filter element of any one of the first to twenty -fourth embodiments, wherein the nonwoven web is a melt blown web, a spunbond web, a carded web, a wet-laid web, an air-laid web, or a combination thereof. In a twenty-sixth embodiment, the present disclosure provides the filter element of any one of the first to twenty -fifth embodiments, wherein the nonwoven web is laminated to a nonwoven scrim, a plastic netting, or a fiberglass layer. In a twentyseventh embodiment, the present disclosure provides the filter element of any one of the first to twentysixth embodiments, wherein the pleated filter media is free of fiberglass. In a twenty -eighth embodiment, the present disclosure provides the filter element of any one of the first to twenty-seventh embodiments, wherein a majority of upstream and downstream pleat valleys are at least partially nonoccluded.

[0101] In a twenty-ninth embodiment, the present disclosure provides a filter cartridge for a reusable respiratory device, the filter cartridge comprising: a housing comprising: a coupling element configured to removably couple to the reusable respiratory device; and at least one major surface with an air-permeable area, wherein the housing is configured such that substantially all of an ambient air flow is forced through the air-permeable area; and the filter element of any one of the first to twenty-eighth embodiments within the housing. In a thirtieth embodiment, the present disclosure provides the fdter cartridge of the twentyninth embodiment, further comprising adhesive coupling the pleated filter media to an interior surface of the housing.

[0102] In a thirty -first embodiment, the present disclosure provides a respirator comprising: a mask body; the filter cartridge of the twenty-ninth or thirtieth embodiment fluidly connected to the mask body. In a thirty-second embodiment, the present disclosure provides the respirator of the thirty-first embodiment, wherein the mask body is a full-facepiece. In a thirty -third embodiment, the present disclosure provides the respirator of the thirty-first embodiment, wherein the mask body is a half-facepiece. In a thirty-fourth embodiment, the present disclosure provides the respirator of any one of the thirty-first to thirty-thirdembodiments, wherein the respirator is a powered air-purifying respirator, and wherein the coupling element is configured to removably couple to the powered air-purifying respirator. In a thirty-fifth embodiment, the present disclosure provides the respirator of the thirty-fourth embodiment, further comprising a remote unit that comprises the filter cartridge, the remote unit being a powered unit comprising a fan and comprising a supply tube that fluidically connects the remote unit to the mask body, whereby filtered air can be delivered from the remote unit to the mask body.

[0103] Examples

[0104] In the following examples, the following abbreviations may be used cm (centimeter), mm (millimeter), pm (micrometer), nm (nanometer), inch (inches), LPM (liters per minute), sec (seconds), min (minutes), kHz (kilohertz), % (percent), °C (degrees Celsius), mg (milligrams), kV (kilovolts), and pA (microamperes).

[0105] Test Procedures

[0106] Effective Fiber Diameter

[0107] The Effective Fiber Diameter (EFD) of a web is evaluated according to the method set forth in Davies, C. N., 'The Separation of Airborne Dust and Particles,' Institution of Mechanical Engineers, London, Proceedings IB, 1952. Unless otherwise noted, the test is run at a face velocity of 13.8 cm / sec for flat filter media.

[0108] Guriev Stiffness

[0109] Gurley Stiffness is measured using a Gurley Stiffness Tester Model 417 IE (Digital), available from Gurley Precision Instruments, Troy, NY. The Stiffness is measured according to the procedures provided in the operating manual for the Tester. For each material, three separate individual physical samples are tested. Each sample is a flat-web (unpleated) sample, cut (e.g. from roll) to a sample dimension of 2 inches by 1.5 inches. If the sample exhibits an identifiable machine direction (downweb direction), the sample is cut so that the long (test) dimension is crossweb with the machine direction of the sample. The sample bends into the downweb direction during the test. Each individual physical sample is tested two times, cycling back and forth from the left and right side of the sample. Results are averaged and are reported in milligrams of force (Gurley Units).

[0110] % Penetration. Pressure Drop, and Quality Factor

[0111] Percent Penetration, pressure drop, filtration Quality Factor (QF), and related parameters of a filtration media sample are obtained using a challenge aerosol containing either DOP (dioctyl phthalate) liquid droplets or NaCl (sodium chloride) solid particulates, in generally similar manner as disclosed in PCT International Publication No. WO 2015 / 199972, published December 30, 2015, and in PCT Publication WO 2015 / 024891, published March 12, 2015, both of which are incorporated by referenceherein. An Automated Filter Tester AFT Model 8130 (TSI, Inc., St. Paul MN) maybe used, with a challenge aerosol that comprises DOP droplets or NaCl particulates, with a mass median diameter in the range of approximately 0.3 pm (e.g., a mass median diameter of approximately 0.26 pm for DOP, and a mass median diameter of approximately 0.33 pm for NaCl). In the following Examples, the challenge aerosol was delivered at a flow rate of 85 liters / min (LPM) to provide a face velocity of 13.8 cm / s, unless otherwise indicated. Testing was performed on flat webs except as noted.

[0112] The particle concentration is measured at the sample inlet and outlet and the Percent Penetration of particles through the filtration web is thus obtained, and the pressure drop through the filtration web is monitored by way of transducers e.g. of the general type available from MKS Instmments (Andover, MA). The equation:

[0113] Equation 2

[0114]

[0115] is used to calculate Quality Factor (QF).

[0116] Parameters which may be measured or calculated from such test procedures include initial Percent Penetration, initial pressure drop, and initial Quality Factor QF. Initial parameters are obtained upon initially exposing the filter media sample to the challenge aerosol, as will be well understood by the ordinary artisan. All Percent Penetration and pressure drop numerical values, ranges, etc. that are present in this document (including both the specification and the claims), will be understood to be initial parameters, using DOP, unless otherwise specified. All such numerical values will be understood to be at a face velocity of 13.8 cm / s.

[0117] Loading tests may be performed by continuously challenging the filter with aerosol over a period of time while monitoring penetration and pressure drop; the test may be stopped after a particular loading of particles is reached or after a clear maximum in the penetration is observed and the final Percent Penetration, final pressure drop, and / or final quality factor at the conclusion of the loading test may be recorded. All particle penetration results are reported as Percent Penetration (e.g. a reported value of 80 means 80 %; a reported value of 0.1 means 0.1 %). Filtration efficiency (e.g., initial or final) may also be obtained, which is 100 minus the Particle Penetration and is likewise reported in percent.

[0118] Birefringence and Retardance

[0119] Sample crystallinity was analyzed on a Nikon Eclipse LV100N POL polarized light microscope with a 4x objective (0.1 NA). The light path used was as follows: lamp, 546-nanometer (nm) filter, rotating linear polarizer, condenser, sample, objective 546-nm circular polarizer, camera. Images were acquired at 4 linear polarizer orientations: 0 degrees (°), 90°, 45°, and 135°. Optical retardance maps were generated using a custom Python script based on the “Four-Frame Algorithm without Extinction Setting” in Shribak and Oldenbourg, Applied Optics, 2003, 42, 16, 3009 to 3017.

[0120]

[0121] sariy polarised input)

[0122]

[0123] From the retardance map, a ‘grain-wise’ average retardance was calculated in the debossed portion, which was calculated as average retardance magnitude and ignored differences in slow-axis orientation. An average retardance was also calculated over a similar, representative area in the nondebossed portion.

[0124] X-ray Microtomography Analysis

[0125] A strip of material (approximately 8 mm wide by 3 cm long) was cut from each nonwoven web such that the strip contained a debossed portion as well as a portion of undisturbed nonwoven web (i.e., a non-debossed portion) for measurement. Each sample assembly was then placed in a plastic tube on the sample stage. The sample was scanned using the SkyScan 1172 Micro-CT X-ray scanner at 1.60 micrometer resolution (no filter, voltage: 40 kV, current: 250 microamperes) and rotated 360 °during scanning along the axis of rotation of the sample. The resulting raw 2D projected scan images were subjected to the process of reconstruction using the SkyScan software to produce individual 2D slices along the axis of rotation spaced at the scanning resolution.

[0126] The SkyScan software was used to binarize (via thresholding) and clean up the dataset as well as to compute the total percent porosity. The total percent porosity was calculated by the software from the total volume of the fibers and the total volume of the dataset according to the equation below.

[0127] Total Dataset Volume — Total Fiber Volume

[0128] Total Porosity (%) X 100 Total Dataset Volume

[0129] The SkyScan software was also used to generate images of the volume-rendered (3D) model for each sample.

[0130] Examples 1 to 4 and Illustrative Examples A to E

[0131] Polypropylene melt-blown nonwoven webs having charged electret moieties were made having basis weights of 75 grams per square meter (gsm) and 95 gsm.

[0132] Examples 1 to 4 and Illustrative Example A were made using a Branson DCX-S power supply with a bar horn vibrating at 20 kilohertz (kHz). The pattern for the debossed portion was on the anvil below the horn. A metal anvil was fabricated with the following dimensions. The anvil was a rectangular machinedsurface which was 3 inches (7.6 cm) long by 0.015 inch (0.038 cm) wide. The anvil was made to mimic a blade pleater.

[0133] The nonwoven web was then passed between the horn and the anvil at a predetermined pitch. The amplitude of oscillation of the bar horn was adjusted at the power supply as a percentage of the maximum displacement allowed by the equipment, which was 10%, 30%, or 100% as shown in the Tables, below.

[0134] A debossed portion and a non-debossed portion were analyzed for each Example and Illustrative Example for birefringence and retardance and using X-ray microtomography as described above. These results, along with the basis weight (b.w.) of the nonwoven web, method (ultrasonic (u.s.) or heat, described below), and temperature or amplitude used for each Example and Illustrative Example, are reported in Table 1, below.

[0135] Table 1. Examples 1 to 4 (Ex. 1 to 4) and Illustrative Examples 1 to 5 (I.E. A to E)

[0136]

[0137] For Illustrative Examples B to E, the 75-gsm and 95-gsm polypropylene nonwoven webs were heat scored using a rotary scoring apparatus at 0 °C and 100 °C. A debossed portion and a non-debossed portion were analyzed for each Illustrative Example for birefringence and retardance and using X-ray microtomography as described above. These results, along with the basis weight (b.w.) of the nonwoven web, method (ultrasonic (u.s.) or heat), and temperature used for each Illustrative Example, are reported in Table 1, above.

[0138] Examples 5 to 13 and Illustrative Examples F to N

[0139] Polypropylene melt-blown nonwoven webs having charged electret moieties were made having basis weights of 75 gsm, 85 gsm, and 95 gsm.

[0140] Examples 5 to 13 were made using a Branson DCX-S power supply with a bar horn vibrating at 20 kilohertz (kHz). The pattern for the debossed portion was on the anvil below the horn. A metal anvil was fabricated with the following dimensions. The anvil was a rectangular machined surface which was 3 inches (7.6 cm) long by 0.015 inch (0.038 cm) wide. The anvil was made to mimic a blade pleater.The nonwoven web was then passed between the horn and the anvil at a predetermined pitch. The amplitude of oscillation of the bar horn was adjusted at the power supply as a percentage of the maximum displacement allowed by the equipment, which was 10%, 30%, or 100% as shown in the Tables, below.

[0141] For Illustrative Examples F to N, the 75-gsm, 85-gsm, and 95-gsm polypropylene nonwoven webs were heat scored using a rotary scoring apparatus at 0 °C, 50 °C, and 100 °C.

[0142] The debossed nonwoven webs were analyzed for pressure drop in a flat condition according to the method described above. The results, including the difference (PD Delta) in pressure drop between ultrasonically (u.s.) scored and comparable heat scored nonwoven webs, are shown in Table 2, below.

[0143] Table 2. Examples 5 to 13 (Ex. 5 to 13) and Illustrative Examples F to N (I.E. F to N)

[0144]

[0145] The debossed nonwoven webs of Examples 1 to 13 and Illustrative Examples A to N can be pleated according to the method described below.

[0146] The debossed nonwoven web can be bent at the debossed lines, and to keep the pleats apart an adhesive glue can be applied and cured between each pleat using the following procedure.

[0147] While in a flat configuration, the nonwoven web with debossed lines can have four beads of hot-melt adhesive (available from Tmxes Company under the trade designation PF-3165) applied to a major surface of the media. The four upstream beads can be applied (by nozzles of a grid melter as the flat media was moved past the grid melter) as elongate stripes that are spaced across the width of the media and extended along the longitudinal length of the media. Of these four beads, first and second can be edge beads that can be applied at locations no more than approximately 2 mm to 3 mm laterally inward from first and second lateral edges of the media. The third and fourth beads can be interior beads that are spaced generally similarly equally across the width of the media between the two edge beads (the lateral spacing between each pair of beads can be in the range of approximately 22 mm to 28 mm). Similar beads can be simultaneously applied to the (opposing) major surface of the nonwoven web (which surface would eventually provide the downstream face of the pleated media). Each downstream bead can be aligned with its corresponding upstream bead, within a lateral distance of approximately 2 mm or less.Before the adhesive beads are fully cooled, the debossed media can be compressed (during which process the media can fold along the score lines) to its final pleated configuration of a pleat spacing. During this process, the adhesive can penetrate into the pleat valleys as the pleats are formed and at least substantially fill the pleat valleys and, at the pleat tips, protmde outward beyond the pleat tips a distance of, on average, approximately 0.5 mm to 1 mm. During this process the adhesive is still sufficiently tacky at the surfaces of the beads so that two portions of an adhesive bead, if meeting in a pleat valley during the folding operation, can adequately bond to each other. The adhesive can be allowed to harden so that each pair of aligned upstream and downstream beads collectively form a dam of hardened adhesive.

[0148] The foregoing Examples have been provided for clarity of understanding only, and no unnecessary limitations are to be understood therefrom. The tests and test results described in the Examples are intended to be illustrative rather than predictive, and variations in the testing procedure can be expected to yield different results. All quantitative values in the Examples are understood to be approximate in view of the commonly known tolerances involved in the procedures used.

[0149] It will be apparent to those skilled in the art that the specific exemplary elements, structures, features, details, configurations, etc., that are disclosed herein can be modified and / or combined in numerous embodiments. All such variations and combinations are contemplated by the inventor as being within the bounds of the conceived invention, not merely those representative designs that were chosen to serve as exemplary illustrations. Thus, the scope of the present invention should not be limited to the specific illustrative structures described herein but rather extends at least to the structures described by the language of the claims, and the equivalents of those structures. Any of the elements that are positively recited in this specification as alternatives may be explicitly included in the claims or excluded from the claims, in any combination as desired. Any of the elements or combinations of elements that are recited in this specification in open-ended language (e.g., comprise and derivatives thereof), are considered to additionally be recited in closed-ended language (e.g., consist and derivatives thereof) and in partially closed-ended language (e.g., consist essentially, and derivatives thereof). Although various theories and possible mechanisms may have been discussed herein, in no event should such discussions serve to limit the claimable subject matter. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document mentioned and / or incorporated by reference herein, this specification as written will control.

Claims

1. What is claimed is:

1. A filter element comprising:pleated filter media comprising a nonwoven web comprising polymeric fibers and a plurality of pleat tips;wherein the nonwoven web comprises a debossed portion on at least some of the pleat tips, and wherein at least one of the following conditions is met:wherein the debossed portion exhibits birefringence while the nonwoven web does not exhibit birefringence at a non-debossed portion;wherein the debossed portion has a retardance profile in which there is an average retardance in the debossed portion, and wherein the average retardance is at least three times an average retardance in the non-debossed portion; orwherein the debossed portion has a total percent porosity as determined by x-ray microtomography that is less than 80 percent of a total percent porosity of the nonwoven web at the non-debossed portion.

2. The filter element of claim 1, wherein the nonwoven web comprises at least one of polypropylene fibers, polyethylene fibers, polyester fibers, poly(4-methyl-l -pentene) fibers, cyclic olefin copolymer fibers, or poly(lactic acid) fibers.

3. The filter element of claim 1 or 2, wherein the polymeric fibers comprise a semi-crystalline polymer having a glass transition temperature not higher than room temperature.

4. The filter element of any one of claims 1 to 3, wherein the nonwoven web comprises polyolefin fibers, or wherein the nonwoven web comprises polypropylene fibers.

5. The filter element of any one of claims 1 to 4, wherein the debossed portion has the retardance profile, and wherein the average retardance in the debossed portion is at least 10 nanometers, at least 11 nanometers, or at least 12 nanometers.

6. The filter element of any one of claims 1 to 5, wherein the total percent porosity of the debossed portion is less than 75 percent or less than 70 percent of the total percent porosity of the nonwoven web at the non-debossed portion.

7. The filter element of any one of claims 1 to 6, wherein on at least some of the pleat tips, the debossed portion is continuous in a pleat direction.

8. The filter element of any one of claims 1 to 6, wherein on at least some of the pleat tips, there are multiple, discontinuous debossed portions in a pleat direction.

9. The filter element of any one of claims 1 to 8, wherein the nonwoven web exhibits a quasipermanent electric charge, or wherein the nonwoven web comprises electret fibers.

10. The filter element of any one of claims 1 to 9, wherein the pressure drop across the pleated filter media at 85 LPM air flow rate is not more than about 50 mniHiO. not more than about 40 nmiFTO. not more than about 30 mmtTO. not more than about 20 nmiFTO. not more than about 15 nmiFTO. not more than about 12 nmiFTO. not more than about 10 nmiFTO. not more than about 8 nmiFTO. not more than about 5 minfhO. or not more than about 3 ininFTO.

11. The filter element of any one of claims 1 to 10, wherein the nonwoven web has a basis weight of at least about 50 grams per square meter, at least about 70 grams per square meter, not more than about 120 grams per square meter, not more than about 100 grams per square meter, or a combination thereof.

12. The filter element of any one of claims 1 to 11, wherein the nonwoven web is a melt blown web, a spunbond web, a carded web, a wet-laid web, an air-laid web, or a combination thereof.

13. The filter element of any one of claims 1 to 12, wherein the nonwoven web is laminated to a nonwoven scrim, a plastic netting, or a fiberglass layer.

14. A filter cartridge for a reusable respiratory device, the filter cartridge comprising:a housing comprising:a coupling element configured to removably couple to the reusable respiratory device; and at least one major surface with an air-permeable area,wherein the housing is configured such that substantially all of an ambient air flow is forced through the air-permeable area; andthe filter element of any one of claims 1 to 13 within the housing.

15. A respirator comprising:a mask body;the filter cartridge of claim 14 fluidly connected to the mask body.

Images