AU2013368273A1

AU2013368273A1 - Filtering face-piece respirator having rounded perimeter

Info

Publication number: AU2013368273A1
Application number: AU2013368273A
Authority: AU
Inventors: Dean R. Duffy
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2012-12-27
Filing date: 2013-12-11
Publication date: 2015-07-09
Anticipated expiration: 2033-12-11
Also published as: WO2014105421A1; EP2938407A1; CN104870057A; BR112015015164A2; JP2016508191A; US20140182601A1; ES2675793T3; CN104870057B; JP6309024B2; RU2608809C1; EP2938407A4; AU2013368273B2; EP2938407B1; KR20150097805A; PL2938407T3

Abstract

A filtering face-piece respirator 10 that includes a harness 14 and a mask body 12. First and second bond lines 30a, 30b are located on opposing sides of the mask body 12 and join a top portion 18 of the mask body 12 to the bottom portion 20. The first and second bond lines 30a, 30b extend from the frontal line of demarcation 22 to upper and lower perimeter segments 24a, 24b. The upper and lower perimeter segments 24a, 24b have an upper linear segment 32a and a lower linear segment 32b, respectively, located between first and second curved portions 34a, 34b. The first and second curved portions 34a, 34b each extend from the respective upper or lower linear segment 32a, 32b to the first and second bond lines 30a, 30b. The invention provides a more rounded finish to the mask body perimeter, which enables the mask body to exhibit a more comfortable fit.

Description

WO 2014/105421 PCT/US2013/074243 FILTERING FACE-PIECE RESPIRATOR HAVING ROUNDED PERIMETER [0001] The present invention pertains to a filtering face-piece respirator that has a curved perimeter where top and bottom portion of the mask body meet. BACKGROUND [0002] Respirators are commonly worn over a person's breathing passages for at least one of two common purposes: (1) to prevent impurities or contaminants from entering the wearer's respiratory system; and (2) to protect other persons or things from being exposed to pathogens and other contaminants exhaled by the wearer. In the first situation, the respirator is worn in an environment where the air contains particles that are harmful to the wearer, for example, in an auto body shop. In the second situation, the respirator is worn in an environment where there is risk of contamination to other persons or things, for example, in an operating room or clean room. [0003] A variety of respirators have been designed to meet either (or both) of these purposes. Some respirators have been categorized as being "filtering face-pieces" because the mask body itself functions as the filtering mechanism. Unlike respirators that use rubber or elastomeric mask bodies in conjunction with attachable filter cartridges (see, e.g., U.S. Patent RE39,493 to Yuschak et al.) or insert-molded filter elements (see, e.g., U.S. Patent 4,790,306 to Braun), filtering face-piece respirators are designed to have the filter media cover much of the whole mask body so that there is no need for installing or replacing a filter cartridge. These filtering face-piece respirators commonly come in one of two configurations: molded respirators and flat-fold respirators. [0004] Molded filtering face piece respirators have regularly comprised non-woven webs of thermally-bonding fibers or open-work plastic meshes to furnish the mask body with its cup-shaped configuration. Molded respirators tend to maintain the same shape during both use and storage. These respirators therefore cannot be folded flat for storage and shipping. Examples of patents that disclose molded, filtering, face-piece respirators include U.S. Patents 7,131,442 to Kronzer et al, 6,923,182, 6,041,782 to Angadjivand et al., 4,807,619 to Dyrud et al., and 4,536,440 to Berg. [00051 Flat-fold respirators - as their name implies - can be folded flat for shipping and storage. They also can be opened into a cup-shaped configuration for use. Examples of flat-fold respirators are shown in U.S. Patents 6,568,392 and 6,484,722 to Bostock et al., and 6,394,090 to Chen. [0006] Although flat-fold respirators are convenient in that they can be folded flat for shipping and storage, these respirators, when folded horizontally, tend to define a sharp or defined point where an upper portion of the mask body perimeter meets the lower portion. This point may pinch the wearer's cheek when the respirator is being worn for extended time periods. The present invention, described below, addresses this discomfort by providing a horizontally foldable respirator that has a new perimeter which eliminates the more sharply defined region where the top portion of the mask body perimeter meets the lower portion. - 1- WO 2014/105421 PCT/US2013/074243 SUMMARY OF THE INVENTION [00071 The present invention pertains to a filtering face-piece respirator that comprises a harness and a mask body. The mask body comprises a filtering structure that has a top portion, a bottom portion, an upper perimeter segment, a lower perimeter segment, a frontal line of demarcation, and first and second bond lines. The first and second bond lines are located on opposing sides of the mask body and join the top portion of the mask body to the bottom portion. The first and second bond lines extend from the frontal line of demarcation to the upper and lower perimeter segments. The upper and lower perimeter segments, when the mask body is laid flat, comprise an upper linear segment and a lower linear segment, respectively, located between first and second curved portions located at opposing ends of the upper and lower linear segments. The first and second curved portions in each of the upper and lower perimeter segments each extend from the respective upper or lower linear segment to the first and second bond lines. [0008] The provision of the first and second curved portions provides a more rounded finish to the mask body perimeter when in the in-use configuration, which enables the mask body to exhibit a more comfortable fit. From an aesthetics standpoint, the mask body also has a more appealing look from view from the side in that the perimeter has a more continuous look. Glossary [0009] The terms set forth below will have the meanings as defined: [0010] "comprises (or comprising)" means its definition as is standard in patent terminology, being an open-ended term that is generally synonymous with "includes", "having", or "containing". Although "comprises", "includes", "having", and "containing" and variations thereof are commonly-used, open ended terms, this invention also may be suitably described using narrower terms such as "consists essentially of', which is semi open-ended term in that it excludes only those things or elements that would have a deleterious effect on the performance of the inventive respirator in serving its intended function; [0011] "clean air" means a volume of atmospheric ambient air that has been filtered to remove contaminants; [0012] "contaminants" means particles (including dusts, mists, and fumes) and/or other substances that generally may not be considered to be particles (e.g., organic vapors, et cetera) but which may be suspended in air; [0013] "crosswise dimension" is the dimension that extends laterally across the respirator, from side to-side when the respirator is viewed from the front; [0014] "cup-shaped configuration" means any vessel-type shape that is capable of adequately covering the nose and mouth of a person; [00151 "curved" means not extending in a straight line; [0016] "exterior gas space" means the ambient atmospheric gas space into which exhaled gas enters after passing through and beyond the mask body and/or exhalation valve; -2- WO 2014/105421 PCT/US2013/074243 [00171 "filtering face-piece" means that the mask body itself is designed to filter air that passes through it; there are no separately identifiable filter cartridges or insert-molded filter elements attached to or molded into the mask body to achieve this purpose; [00181 "filter" or "filtration layer" means one or more layers of air-permeable material, which layer(s) is adapted for the primary purpose of removing contaminants (such as particles) from an air stream that passes through it; [0019] "filter media" means an air-permeable structure that is designed to remove contaminants from air that passes through it; [0020] "filtering structure" means a generally air-permeable construction that filters air; [0021] "first side" means an area of the mask body that is located on one side of a plane that bisects the mask body normal to the cross-wise dimension; [0022] "flange" means a protruding part that imparts structural integrity or strength to the body from which it protrudes; [0023] "folded inwardly" means being bent back towards the part from which extends; [0024] "frontally" or "frontal" means located in a direction extending away from a person's face when the respirator is being worn; [00251 "harness" means a structure or combination of parts that assists in supporting the mask body on a wearer's face; [0026] "integral" means being manufactured together at the same time; that is, being made together as one part and not two separately manufactured parts that are subsequently joined together; [00271 "interior gas space" means the space between a mask body and a person's face; [0028] "leading edge" an unattached edge; [0029] "line of demarcation" means a fold, seam, weld line, bond line, stitch line, hinge line, and/or any combination thereof; [0030] "linear" means extending in a generally straight line; [0031] "major portion" means the filtering portion of the mask body; [0032] "mask body" means an air-permeable structure that is designed to fit over the nose and mouth of a person and that helps define an interior gas space separated from an exterior gas space (including the seams and bonds that join layers and parts thereof together); [0033] "nose clip" means a mechanical device (other than a nose foam), which device is adapted for use on a mask body to improve the seal at least around a wearer's nose; [0034] "perimeter" means the outer edge of the mask body, which outer edge would be disposed generally proximate to a wearer's face when the respirator is being donned by a person; [00351 "pleat" means a portion that is designed to be or is folded back upon itself; [0036] "polymeric" and "plastic" each mean a material that mainly includes one or more polymers and that may contain other ingredients as well; [00371 "plurality" means two or more; -3- WO 2014/105421 PCT/US2013/074243 [00381 "radiused" means having a generally constant curvature; [00391 "respirator" means an air filtration device that is worn by a person to provide the wearer with clean air to breathe; [0040] "second side" means an area of the mask body that is located on one side of a plane that bisects the mask body normal to the cross-wise dimension (the second side being opposite the first side); [0041] "snug fit" or "fit snugly" means that an essentially air-tight (or substantially leak-free) fit is provided (between the mask body and the wearer's face); and [0042] "transversely extending" means extending generally in the crosswise dimension. BRIEF DESCRIPTION OF THE DRA WINGS [00431 FIG. 1 is a front perspective view of a flat-fold filtering face-piece respirator 10, in accordance with the present invention, being worn on a person's face; [0044] FIG. 2 is a top view of the respirator 10 shown in FIG. 1 in a non-opened configuration; [00451 FIG. 3 is a bottom view of the respirator 10 shown in FIG. 1 in a non-opened configuration; [0046] FIG. 4 is a cross-sectional view of the mask body 12 taken along lines 3-3 of FIG. 2; [00471 FIG. 5 is a cross-sectional view of the filtering structure 16 taken along lines 4-4 of FIG. 3; [0048] FIG. 6 is a front view of the mask body 12, which may be used in connection with the present invention; and [0049] FIG. 7 is a left side view of the mask body 12 in accordance with the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [00501 In practicing the present invention, a filtering face-piece respirator is provided that has first and second curved segments on opposing ends of the mask body perimeter segments. These curved segments enable a rounded perimeter to be achieved in the region where the upper portion of the mask body meets the lower portion. The rounded perimeter allows a more comfortable fit to be achieved. [00511 FIG. 1 shows an example of a filtering face-piece respirator 10 that may be used in connection with the present invention to provide clean air for the wearer to breathe. The filtering face piece respirator 10 includes a mask body 12 and a harness 14. The mask body 12 has a filtering structure 16 through which inhaled air must pass before entering the wearer's respiratory system. The filtering structure 16 removes contaminants from the ambient environment so that the wearer breathes clean air. The mask body 12 includes a top portion 18 and a bottom portion 20. The top portion 18 and the bottom portion 20 are separated by a line of demarcation 22. In this particular embodiment, the line of demarcation 22 is a frontal fold at a bond line that extends transversely across the central portion of the mask body from side-to-side. The mask body 12 also includes a perimeter 24 that includes an upper segment 24a and a lower segment 24b. The harness 14 has a first, upper strap 26 that is secured to the top portion 18 of mask body 12 by a staple 29 adjacent to the perimeter 24a. The harness 14 also has a second, lower strap 27 that is secured by a staple 29 to a flange 30a. -4- WO 2014/105421 PCT/US2013/074243 [00521 FIG. 2 shows the respirator 10 in a horizontal flat-folded configuration. The top portion 18 of the respirator mask body 12 has an upper perimeter segment 24a, a frontal line of demarcation 22, and first and second bond lines 30a, 30b. The first and second bond lines 30a, 30b are located on opposing sides 31a, 31b of the mask body 12 and join the top portion 18 of the mask body 12 to the bottom portion 20 (FIG. 1). The first and second bond lines 30a, 30b extend from the frontal fold 22 to the upper perimeter segment 24a. The upper perimeter segment 24a, when the mask body 12 is laid flat, has an upper linear segment 32a located between first and second curved portions 34a and 34b located at opposing ends of the upper linear segment 32a. The first and second curved portions 34a, 34b in the upper perimeter segment 24a extend from the respective upper linear segment 32a to the first and second bond lines 30a, 30b. The mask body 12 also may have flanges 36a and 36b located on opposing sides 31a and 31b, respectively, of the mask body 12. A plane 38 bisects the mask body 12 to define the first and second sides 31a, 31b. The flanges 36a and 36b can be folded inwardly towards the filtering structure 16 in contact therewith. Each flange typically occupies a surface area of about I to 15 square centimeters, more typically about 2 to 12 square centimeters, and still more typically about 5 to 10 square centimeters. An integral flange can have welds or bonds 35 provided thereon to increase flange stiffness. Alternatively, an adhesive layer may be used to increase flange stiffness. The flanges may have a flexural modulus of at least 10 Mega Pascals (MPa), more typically at least 20 MPa when bent along a major surface of the flange. At the upper end, the flexural modulus is typically less than 100 MPa, more typically less than 60 MPa. The flanges 36a, 36b also typically extend away from a bond line 30a, 30b on the mask body 12 at least 2 millimeters (mm), more typically at least 5 mm, and still more typically at least 1 to 2 centimeters (cm). The flanges 36a, 36b may be integrally or non-integrally connected to the major portion of the mask body 12 and may comprise one or more or all of the various layers that comprise the mask body filtering structure 16. Unlike the filtering structure 16, the layers that comprise the flanges 36a, 36b may be compressed, rendering them nearly fluid impermeable. The flanges 36a, 36b may be an extension of the material used to make the mask body filtering structure 16, or they may be made from a separate material such as a rigid or semi-rigid plastic. The mask body perimeter segment 24a also may have a series of bonds or welds 37 to join the various layers of the mask body 12 together. This perimeter segment 24a therefore may not be very fluid permeable. The top portion 18 may include one or more pleat lines that extend from the first bond line 30a to the second bond line 30b transversely. [0053] FIG. 3 shows that the lower perimeter segment 24b also may have a series of bonds or welds 37 to join the various layers. The remainder of the filtering structure 16 - inwardly from the perimeter may be fully fluid permeable over much of its extended surface, with the possible exception of areas where there are bonds, welds, or fold lines. The bottom portion 20 of the mask body 12 has a lower perimeter segment 24b between first and second bond lines 30a, 30b. The lower perimeter segment 24b, when the mask body 12 is laid flat, has a lower linear segment 32b located between first and second curved portions 34a and 34b located at opposing ends of the lower linear segment 32b. The first and second curved portions 34a, 34b in the lower perimeter segment 24b extend from the respective lower -5 - WO 2014/105421 PCT/US2013/074243 linear segment 32b to the first and second bond lines 30a, 30b, respectively. The curved portions 34a, 34b may be curves that have a varying radius or a generally constant radius. The constant radius may be about 10 to 70 millimeters (mm), more typically 20 to 60 mm, and still more typically 30 to 50 mm. The radiused segments may be cut from a mask body blank and are provided along the perimeter segments 24a and 24b (FIG. 1) where the top portion 18 of mask body 12 meets the lower portion 20 at the bond lines 30a, 30b. The upper and lower segments 24a, 24b may be about 10 to 20 cm long, more typically 13 to 19 cm long, and still more typically 15 to 18 cm in length. A smooth radius curve may improve facial contact when the respirator is donned. The radiused cut also may enable the leading edge 39 to match the perimeter along at least a substantial portion thereof. The curved portions 34a, 34b on each of the upper and lower perimeter segments 24a, 24b allow the perimeter segments 24a and 24b to be folded away from each other in a butterfly fashion as shown in FIG. 2. The first and second flanges 36a, 36b are joined to the mask body 12 at the bond lines 30a, 30b and may be rotated or folded about an axis generally parallel to these lines, respectively. The leading edges 39 of the flanges 36a, 36b begin in a location where the bond lines 30a, 30b meet the perimeter 24. The leading edge 39 can be configured to match the perimeter 24 moving in a direction towards the plane 38 that bisects the mask body 12. The leading edge 39 substantially matches the perimeter 24 for approximately 10 to 50% of its total length. The first and second bond lines 30a, 30b are off-set at an angle a from a plane 38 that extends perpendicular to the perimeter 24 of the mask body 12 when viewing the mask body from a top or bottom view in a folded condition. The angle a may be from zero to about 60 degrees, more typically about 30 to 45 degrees. The bottom portion 20 also may include one or more pleat lines that extend from the first bond line 30a to the second bond line 30b transversely. [0054] FIG. 4 illustrates an example of a pleated configuration of a mask body 12 in accordance with the present invention. As shown, the upper portion or panel 18 of the mask body 12 also may include pleats 40 and 41 and half of the frontal line of demarcation 22. The lower portion or panel 20 of the mask body 12 may include pleats 42 and 44 and half line of demarcation 22. The line of demarcation 22 may be a fold and/or bond line that separates the upper and lower portions 18 and 20 of mask body 12. The lower portion 20 of the mask body 12 may include the same, more, or less filter media surface area than the upper portion 18. The mask body 12 also may include a perimeter web that is secured to the mask body along its perimeter. The perimeter web may be folded over the mask body at the perimeter 24. The perimeter web also may be an extension of the inner cover web folded and secured around the edge of segments 24a and 24b. A nose clip 56 (FIGs. 1, 2, 6 and 7) may be disposed on the upper portion 18 of the mask body centrally adjacent to the perimeter segment 24a between the filtering structure 16 and the perimeter web. The nose clip may be made from a pliable metal or plastic that is capable of being manually adapted by the wearer to fit the contour of the wearer's nose. [00551 FIG. 5 shows that the filtering structure 16 may include one or more layers such as an inner cover web 58, an outer cover web 60, and a filtration layer 62. The inner and outer cover webs 58 and 60 may be provided to protect the filtration layer 62 and to preclude fibers from the filtration layer 62 from -6- WO 2014/105421 PCT/US2013/074243 coming loose and entering the mask interior. During respirator use, air passes sequentially through layers 60, 62, and 58 before entering the mask interior. The air that is disposed within the interior gas space of the mask body may then be inhaled by the wearer. When a wearer exhales, the air passes in the opposite direction sequentially through layers 58, 62, and 60. Alternatively, an exhalation valve (not shown) may be provided on the mask body to allow exhaled air to be rapidly purged from the interior gas space to enter the exterior gas space without passing through filtering structure 16. Typically, the cover webs 58 and 60 are made from a selection of nonwoven materials that provide a comfortable feel, particularly on the side of the filtering structure that makes contact with the wearer's face. The construction of various filter layers and cover webs that may be used in conjunction with the support structure of the present invention are described below in more detail. The filtering structure also may have a structural netting or mesh juxtaposed against at least one or more of the layers 58, 60, or 62, typically against the outer surface of the outer cover web 60. The use of such a mesh is described in U.S. Patent Application Publication No. 2010/0154806Al, entitled Expandable Face Mask with Reinforcing Netting. To improve wearer fit and comfort, an elastomeric face seal can be secured to the perimeter of the filtering structure 16. Such a face seal may extend radially inward to contact the wearer's face when the respirator is being donned. Examples of face seals are described in U.S. Patents 6,568,392 to Bostock et al., 5,617,849 to Springett et al., and 4,600,002 to Maryyanek et al., and in Canadian Patent 1,296,487 to Yard. The mask body perimeter 24 also may be folded upon itself in the nose region to achieve a snug fit - see U.S. Patent Application Publication 2011/0315144A1. [0056] FIG. 6 shows the mask body 12 in an in-use configuration. During use, the flanges 36a, 36b are disposed in contact with the first and second sides of the major portion 63 of mask body 12. The flanges 36a, 36b may be folded inwardly towards the mask body. When the flange is pulled in towards the major portion 63 of the mask body 12, the respirator behaves as a molded respirator rather than a flat fold respirator. That is, the respirator takes on a structural cup-shaped configuration better capable of better maintaining that shape during use. Thus, a respirator of the invention, having the flanges 36a, 36b pulled in towards the major portion 63 of the mask body 12 is, in a sense, a hybrid between a molded respirator and a flat-fold respirator. [00571 FIG. 7 too shows the mask body 12 in an in-use configuration. The mask body 12 is shown to have a rounded configuration in the perimeter region 64 where the upper and lower segments 24a, 24b of the mask body meet. The rounded configuration prevents the mask body 12 from pinching the wearer's cheek or otherwise causing discomfort when the respirator 10 is being donned. The Filtering Structure [00581 The filtering structure that is used in connection with the present invention may take on a variety of different shapes and configurations. The filtering structure typically is adapted so that it properly fits against or within the support structure. Generally the shape and configuration of the filtering structure corresponds to the general shape of the mask body. Although a filtering structure has been illustrated with multiple layers that include a filtration layer and two cover webs, the filtering structure -7- WO 2014/105421 PCT/US2013/074243 may simply comprise a filtration layer or a combination of filtration layers. For example, a pre-filter may be disposed upstream to a more refined and selective downstream filtration layer. Additionally, sorptive materials such as activated carbon may be disposed between the fibers and/or various layers that comprise the filtering structure. Further, separate particulate filtration layers may be used in conjunction with sorptive layers to provide filtration for both particulates and vapors. The filtering structure may include one or more stiffening layers that assist in providing a cup-shaped configuration. The filtering structure also could have one or more horizontal and/or vertical lines of demarcation that contribute to its structural integrity. The first and second flanges when used in accordance with the present invention, however, may make unnecessary the need for such stiffening layers and lines of demarcation. [00591 The filtering structure that is used in a mask body of the invention can be of a particle capture or gas and vapor type filter. The filtering structure also may be a barrier layer that prevents the transfer of liquid from one side of the filter layer to another to prevent, for instance, liquid aerosols or liquid splashes (e.g. blood) from penetrating the filter layer. Multiple layers of similar or dissimilar filter media may be used to construct the filtering structure of the invention as the application requires. Filters that may be beneficially employed in a layered mask body of the invention are generally low in pressure drop (for example, less than about 195 to 295 Pascals at a face velocity of 13.8 centimeters per second) to minimize the breathing work of the mask wearer. Filtration layers additionally may be flexible and may have sufficient shear strength so that they generally retain their structure under the expected use conditions. Examples of particle capture filters include one or more webs of fine inorganic fibers (such as fiberglass) or polymeric synthetic fibers. Synthetic fiber webs may include electret-charged, polymeric microfibers that are produced from processes such as meltblowing. Polyolefin microfibers formed from polypropylene that has been electrically-charged provide particular utility for particulate capture applications. An alternate filter layer may comprise a sorbent component for removing hazardous or odorous gases from the breathing air. Sorbents may include powders or granules that are bound in a filter layer by adhesives, binders, or fibrous structures - see U.S. Patents 6,334,671 to Springett et al. and 3,971,373 to Braun. A sorbent layer can be formed by coating a substrate, such as fibrous or reticulated foam, to form a thin coherent layer. Sorbent materials may include activated carbons that are chemically treated or not, porous alumna-silica catalyst substrates, and alumna particles. An example of a sorptive filtration structure that may be conformed into various configurations is described in U.S. Patent 6,391,429 to Senkus et al. [0060] The filtration layer is typically chosen to achieve a desired filtering effect. The filtration layer generally will remove a high percentage of particles and/or or other contaminants from the gaseous stream that passes through it. For fibrous filter layers, the fibers selected depend upon the kind of substance to be filtered and, typically, are chosen so that they do not become bonded together during the molding operation. As indicated, the filtration layer may come in a variety of shapes and forms and typically has a thickness of about 0.2 millimeters (mm) to 1 centimeter (cm), more typically about 0.3 mm to 0.5 cm, and it could be a generally planar web or it could be corrugated to provide an expanded surface area - see, for example, U.S. Patents 5,804,295 and 5,656,368 to Braun et al. The filtration layer -8- WO 2014/105421 PCT/US2013/074243 also may include multiple filtration layers joined together by an adhesive or any other means. Essentially any suitable material that is known (or later developed) for forming a filtering layer may be used as the filtering material. Webs of melt-blown fibers, such as those taught in Wente, Van A., Superfine Thermoplastic Fibers, 48 Indus. Engn. Chem., 1342 et seq. (1956), especially when in a persistent electrically charged (electret) form are especially useful (see, for example, U.S. Pat. No. 4,215,682 to Kubik et al.). These melt-blown fibers may be microfibers that have an effective fiber diameter less than about 20 micrometers (tm) (referred to as BMF for "blown microfiber"), typically about I to 12 tm. Effective fiber diameter may be determined according to Davies, C. N., The Separation OfAirborne Dust Particles, Institution Of Mechanical Engineers, London, Proceedings IB, 1952. Particularly preferred are BMF webs that contain fibers formed from polypropylene, poly(4-methyl- 1 -pentene), and combinations thereof. Electrically charged fibrillated-film fibers as taught in van Turnhout, U.S. Patent Re. 31,285, also may be suitable, as well as rosin-wool fibrous webs and webs of glass fibers or solution-blown, or electrostatically sprayed fibers, especially in microfilm form. Electric charge can be imparted to the fibers by contacting the fibers with water as disclosed in U.S. Patents 6,824,718 to Eitzman et al., 6,783,574 to Angadjivand et al., 6,743,464 to Insley et al., 6,454,986 and 6,406,657 to Eitzman et al., and 6,375,886 and 5,496,507 to Angadjivand et al. Electric charge also may be imparted to the fibers by corona charging as disclosed in U.S. Patent 4,588,537 to Klasse et al. or by tribocharging as disclosed in U.S. Patent 4,798,850 to Brown. Also, additives can be included in the fibers to enhance the filtration performance of webs produced through the hydro-charging process (see U.S. Patent 5,908,598 to Rousseau et al.). Fluorine atoms, in particular, can be disposed at the surface of the fibers in the filter layer to improve filtration performance in an oily mist environment - see U.S. Patents 6,398,847 B 1, 6,397,458 BI, and 6,409,806 BI to Jones et al. Typical basis weights for electret BMF filtration layers are about 10 to 100 grams per square meter. When electrically charged according to techniques described in, for example, the '507 Angadjivand et al. patent, and when including fluorine atoms as mentioned in the Jones et al. patents, the basis weight may be about 20 to 40 g/m 2 and about 10 to 30 g/m 2 , respectively. [0061] An inner cover web can be used to provide a smooth surface for contacting the wearer's face, and an outer cover web can be used to entrap loose fibers in the mask body or for aesthetic reasons. The cover web typically does not provide any substantial filtering benefits to the filtering structure, although it can act as a pre-filter when disposed on the exterior (or upstream to) the filtration layer. To obtain a suitable degree of comfort, an inner cover web preferably has a comparatively low basis weight and is formed from comparatively fine fibers. More particularly, the cover web may be fashioned to have a basis weight of about 5 to 50g/m 2 (typically 10 to 30g/m 2 ), and the fibers may be less than 3.5 denier (typically less than 2 denier, and more typically less than 1 denier but greater than 0.1). Fibers used in the cover web often have an average fiber diameter of about 5 to 24 micrometers, typically of about 7 to 18 micrometers, and more typically of about 8 to 12 micrometers. The cover web material may have a -9- WO 2014/105421 PCT/US2013/074243 degree of elasticity (typically, but not necessarily, 100 to 200% at break) and may be plastically deformable. [0062] Suitable materials for the cover web may be blown microfiber (BMF) materials, particularly polyolefin BMF materials, for example polypropylene BMF materials (including polypropylene blends and also blends of polypropylene and polyethylene). A suitable process for producing BMF materials for a cover web is described in U.S. Patent 4,013,816 to Sabee et al. The web may be formed by collecting the fibers on a smooth surface, typically a smooth-surfaced drum or a rotating collector - see U.S. Patent 6,492,286 to Berrigan et al. Spun-bond fibers also may be used. [0063] A typical cover web may be made from polypropylene or a polypropylene/polyolefin blend that contains 50 weight percent or more polypropylene. These materials have been found to offer high degrees of softness and comfort to the wearer and also, when the filter material is a polypropylene BMF material, to remain secured to the filter material without requiring an adhesive between the layers. Polyolefin materials that are suitable for use in a cover web may include, for example, a single polypropylene, blends of two polypropylenes, and blends of polypropylene and polyethylene, blends of polypropylene and poly(4-methyl- 1 -pentene), and/or blends of polypropylene and polybutylene. One example of a fiber for the cover web is a polypropylene BMF made from the polypropylene resin "Escorene 3505G" from Exxon Corporation, providing a basis weight of about 25 g/m 2 and having a fiber denier in the range 0.2 to 3.1 (with an average, measured over 100 fibers of about 0.8). Another suitable fiber is a polypropylene/polyethylene BMF (produced from a mixture comprising 85 percent of the resin "Escorene 3505G" and 15 percent of the ethylene/alpha-olefin copolymer "Exact 4023" also from Exxon Corporation) providing a basis weight of about 25 g/m 2 and having an average fiber denier of about 0.8. Suitable spunbond materials are available, under the trade designations "Corosoft Plus 20", "Corosoft Classic 20" and "Corovin PP-S-14", from Corovin GmbH of Peine, Germany, and a carded polypropylene/viscose material available, under the trade designation "370/15", from J.W. Suominen OY of Nakila, Finland. [0064] Cover webs that are used in the invention preferably have very few fibers protruding from the web surface after processing and therefore have a smooth outer surface. Examples of cover webs that may be used in the present invention are disclosed, for example, in U.S. Patent 6,041,782 to Angadjivand, U.S. Patent 6,123,077 to Bostock et al., and WO 96/28216A to Bostock et al. Respirator Components [00651 The strap(s) that are used in the harness may be made from a variety of materials, such as thermoset rubbers, thermoplastic elastomers, braided or knitted yam/rubber combinations, inelastic braided components, and the like. The strap(s) may be made from an elastic material such as an elastic braided material. The strap preferably can be expanded to greater than twice its total length and be returned to its relaxed state. The strap also could possibly be increased to three or four times its relaxed state length and can be returned to its original condition without any damage thereto when the tensile forces are removed. The elastic limit thus is preferably not less than two, three, or four times the length - 10- WO 2014/105421 PCT/US2013/074243 of the strap when in its relaxed state. Typically, the strap(s) are about 20 to 30 cm long, 3 to 10 mm wide, and about 0.9 to 1.5 mm thick. The strap(s) may extend from the first tab to the second tab as a continuous strap or the strap may have a plurality of parts, which can be joined together by further fasteners or buckles. For example, the strap may have first and second parts that are joined together by a fastener that can be quickly uncoupled by the wearer when removing the mask body from the face. Alternatively, the strap may form a loop that is placed around the wearer's ears - see e.g., U.S. Patent 6,394,090 to Chen et al. An example of a strap that may be used in connection with the present invention is shown in U.S. Patent 6,332,465 to Xue et al. Examples of fastening or clasping mechanism that may be used to joint one or more parts of the strap together is shown, for example, in the following U.S. Patents 6,062,221 to Brostrom et al., 5,237,986 to Seppala, and EP1,495,785A1 to Chien. The harness also may be in the form of a reusable carriage or an adhesive layer that is provided on the internal surface of the perimeter. [00661 As indicated, an exhalation valve may be attached to the mask body to facilitate purging exhaled air from the interior gas space. The use of an exhalation valve may improve wearer comfort by rapidly removing the warm moist exhaled air from the mask interior. See, for example, U.S. Patents 7,188,622, 7,028,689, and 7,013,895 to Martin et al.; 7,428,903, 7,311,104, 7,117,868, 6,854,463, 6,843,248, and 5,325,892 to Japuntich et al.; 6,883,518 to Mittelstadt et al.; and RE37,974 to Bowers. Essentially any exhalation valve that provides a suitable pressure drop and that can be properly secured to the mask body may be used in connection with the present invention to rapidly deliver exhaled air from the interior gas space to the exterior gas space. [00671 A nose clip that is used in the present invention may be essentially any additional part that assists in improving the fit over the wearer's nose. Because the wearer's face exhibits in the nose region, a nose clip may be used to better assist in achieving the appropriate fit in this location. The nose clip may comprise, for example, a pliable dead soft band of metal such as aluminum, which can be shaped to hold the mask in a desired fitting relationship over the nose of the wearer and where the nose meets the cheek. An example of a suitable nose clip is shown in U.S. Patent 5,558,089 and Des. 412,573 to Castiglione. Other nose clips are described in U.S. Patent Application 12/238,737 (filed September 26, 2008); U.S. Publications 2007-0044803A1 (filed August 25, 2005); and 2007-0068529A1 (filed September 27, 2005). [0068] This invention may take on various modifications and alterations without departing from its spirit and scope. Accordingly, this invention is not limited to the above-described but is to be controlled by the limitations set forth in the following claims and any equivalents thereof. [0069] This invention also may be suitably practiced in the absence of any element not specifically disclosed herein. [00701 All patents and patent applications cited above, including those in the Background section, are incorporated by reference into this document in total. To the extent there is a conflict or discrepancy - 11 - WO 2014/105421 PCT/US2013/074243 between the disclosure in such incorporated document and the above specification, the above specification will control. - 12 -

Claims

1. A filtering face-piece respirator that comprises: (a) a harness; and (b) a mask body that comprises a filtering structure that has a top portion, a bottom portion, an upper perimeter segment, a lower perimeter segment, a frontal line of demarcation, and first and second bond lines, the first and second bond lines being located on opposing sides of the mask body and joining the top portion of the mask body to the bottom portion, the first and second bond lines extending from the frontal line of demarcation to the upper and lower perimeter segments, the upper and lower perimeter segments, when the mask body is laid flat, comprising an upper linear segment and a lower linear segment, respectively, located between first and second curved portions located at opposing ends of the upper and lower linear segments, the first and second curved portions in each of the upper and lower perimeter segments each extending from the respective upper or lower linear segment to the first and second bond lines.

2. The filtering face-piece respirator of claim 1, wherein the first and second curved portions have a generally constant curvature.

3. The filtering face-piece respirator of claim 2, wherein the first and second curved portions have a radius of about 10 to 70 millimeters.

4. The filtering face-piece respirator of claim 3, wherein the first and second curved portions have a radius of about 20 to 60 millimeters.

5. The filtering face-piece respirator of claim 1, wherein the first and second curved portions have a radius of about 30 to 50 millimeters.

6. The filtering face-piece respirator of claim 1, wherein the upper and lower perimeter segments can be folded away from each other in butterfly fashion.

7. The filtering face-piece respirator of claim 1, being a horizontal flat-fold respirator.

8. The filtering face-piece respirator of claim 1, wherein the upper and lower segments are each 10 to 20 cm long.

9. The filtering face-piece respirator of claim 1, wherein the upper and lower segments are each 13 to 19 cm long - 13 - WO 2014/105421 PCT/US2013/074243

10. The filtering face-piece respirator of claim 1, wherein the upper and lower segments are each 15 to 18 cm in length.

11. The filtering face-piece respirator of claim 1, wherein the first and second curved portions have a varying radius.

12. A filtering face-piece respirator that comprises: (a) a harness; and (b) a mask body that comprises a horizontally foldable filtering structure that has a top portion, a bottom portion, an upper perimeter segment, a lower perimeter segment, a frontal line of demarcation, and first and second bond lines, the first and second bond lines being located on opposing sides of the mask body and joining the top portion of the mask body to the bottom portion, the first and second bond lines extending from the frontal line of demarcation to the upper and lower perimeter segments, the upper and lower perimeter segments, when the mask body is laid flat, comprising an upper linear segment and a lower linear segment, respectively, located between first and second curved portions located at opposing ends of the upper and lower linear segments, the upper and lower linear segments being about 13 to 19 cm in length, the first and second curved portions in each of the upper and lower perimeter segments each having a radius of curvature 10 to 70 millimeters and extending from the respective upper or lower linear segment to the first and second bond lines, wherein the upper and lower perimeter segments can be folded away from each other in butterfly fashion when the respirator is placed in a flat folded condition.

13. The filtering face-piece respirator of claim 12, wherein the first and second curved portions have a radius of about 20 to 60 millimeters, and wherein the upper and lower segments are each 15 to 18 cm in length.

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