Disposable face mask with enhanced fluid barrier

Abstract: A disposable face mask (10) that includes a filter body (14) capable of filtering liquids and/or particles of a size appropriate for the mask's (10) intended purposes, while providing excellent breathability and comfort to the wearer for extended periods of time. The filter body (14) is formed from multiple layers of filtration material having various configurations. Such masks (10) may be secured by one or more knitted headbands (16,18) to the head (12) of a wearer. Various gasket-type sealing materials such as plastic film or other materials such as hydrogel may be used to enhance the fluid barrier formed between the periphery of the mask and the wearer's face.

Description: This invention relates generally to face masks capable of preventing the passage of airborne aerosols, particulate matter and/or liquids. More particularly, and not by way of limitation, this invention relates to disposable face masks having an enhanced fluid barrier between the periphery of the mask and a wearer's face. Also, this invention allows using various materials to enhance the filtration capabilities of the resulting mask for the specific operating environment while maintaining good breathability. Disposable face masks have been manufactured for many years. In the medical field, many of these early masks were used in preventing contamination of a patient by the breath of health care personnel. In recent years with increased concern for infection of health care personnel with airborne pathogens, such as the hepatitis B virus, it has become necessary to not only prevent contamination of patients due to exhalation from health care personnel, but also to prevent infection of health care personnel due to inhalation of airborne infection particles. It has become even more important in view of the advent of human immunodeficiency virus (HIV) and the recent increase in infectious tuberculosis associated with many HIV patients. The rapid increase of infectious diseases, particularly AIDS, has made the use of such protective equipment increasingly important. The Center for Disease Control in Atlanta, Georgia, has found that the AIDS virus (HIV) can be passed by contact with body fluids. Contact of AIDS contaminated body fluids with another person's source of body fluids, e.g., eyes, nose, mouth, etc., can pass the disease. Therefore, it is necessary to prevent a patient's body fluids from contacting the face of health care personnel. Aerosols having airborne liquid and solid particles are generated not only by the exhalation of infected patients, but also by certain procedural manipulations and processes that impart energy to any liquid or microbial suspension. Surgical procedures involving use of drills and saws are particularly prolific producers of aerosols which may contain tuberculosis, HIV or other pathogens from an infected patient. Concern with tuberculosis has been increasing since new strains of the disease show strong resistances to multiple types of drug treatment. One type of mask is illustrated in U.S. Patent No. 2,012,505 entitled Mask, issued on August 27, 1935 to S.J. Goldsmith. Another type of disposable face mask is illustrated in U.S. Patent No. 4,319,567 entitled Disposable Face Mask, issued on March 16, 1982 to M. Magidson. This mask is molded and has been especially configured in an effort to avoid leakage of fluid flow past the edges of the mask. Obviously, leakage cannot be tolerated when attempting to control liquids and/or aerosols. U.S. Patent 4,606,341 entitled Noncollapsible Surgical Face Mask, issued August 19, 1986 to Vance M. Hubbard and Welton K. Brunson shows a conventional rectangular face mask having a trapezoidal pleat. For some operating conditions, rectangularly shaped masks, including the mask shown in Patent '341, may have less than an optimal fit to prevent the passage of liquids and aerosols between the periphery of the masks and a wearer's face. Recent developments in surgical face masks have resulted in resistance to liquid penetration from the exterior of such masks. U.S. Patent No. 4,920,960 entitled Body Fluids Barrier Mask, issued on May 1, 1990 to Hubbard, et al., is exemplary of improvements in such masks. U.S. Patent No. 5,020,533 entitled Face Mask with Liquid and Glare Resistant Visor, issued on June 4, 1991 to Hubbard, et al., is an example of incorporating a visor to protect the face of a wearer from liquids during medical procedures. EP-A-0,658,321 discloses a disposable face mask in accordance with the precharacterising portion of Claim 1. FR-A 2,249,643 discloses a face mask designed to prevent the misting up of the glasses of the wearer by using an impermeable membrane. As shown in its Fig. 9, the impermeable membrane may be contained within a filter body. Figs. 14-16 show an impermeable membrane which is affixed to a preformed face mask, and a further impermeable membrane is also provided around the periphery of the face mask. In accordance with the present invention, there is provided a disposable face mask comprising: a filter body having an opening sized to cover the nose and mouth of a wearer, the filter body having top and bottom edges with the top edge arranged to extend across the nose and cheeks of the wearer, and the bottom edge arranged to extend under the chin of the wearer; the filter body comprising an upper portion of generally trapezoidal configuration having a longer side forming the top edge and a lower portion of a generally trapezoidal configuration having a longer side forming the bottom edge; the top edge and the bottom edge having generally matching dimensions and defining in part the opening of the filter body; the upper and lower portions of the filter body being joined along all remaining sides; the filter body having a shorter side opposite from the longer side and generally parallel with the longer side; characterised by: a first strip of sealing material disposed within the filter body adjacent to the opening and extending at least up to, and along, the top edge of the filter body; and a second strip of sealing material disposed within the filter body adjacent to the opening and extending at least up to, and along, the bottom edge of the filter body; the first sealing strip and the second sealing strip cooperating with each other to form a fluid barrier between the opening of the filter body and the face of the wearer. A disposable face mask incorporating the present invention provides an effective fluid barrier or seal with the face of a wearer, and may provide higher filtration capability with respect to aerosols, a sufficiently low pressure drop through the mask for comfortable breathing, and protection from liquid splashes or liquid sprays. In some embodiments, the first strip of sealing material extends partially from the opening; and the second strip of sealing material extends partially from the opening. Preferably, the first strip of sealing material and the second strip of sealing material are each formed from a thin film layer of plastic type material. Suitable materials are polyethylene and polypropylene. Preferably, the first strip of sealing material and the second strip of sealing material comprises hydrogel. Preferably, the dimensions of the upper portion correspond to the dimensions of the lower portion. Preferably, the length of the longer side of the filter body is approximately three times the length of shorter side of the filter body. For example, the mask may be constructed such that the distance from the longer side to the shorter side is approximately equal to the length of the shorter side. Preferably, the mask further comprises opposite sides of the filter body extending between the top edge and bottom edge, and a bonded border formed along the opposite sides of the filter body and along the bottom edge with the bonded border defining in part three closed sides of the filter body. Preferably, the filter body further comprises an intermediate layer of material which is gas permeable in both directions through the filter body and liquid impermeable in the direction from outside the filter body to inside the filter body. Preferably, the filter body comprises an intermediate layer of filter media formed from expanded polytetrafluoroethylene (PTFE). This enhances the filtration capability of the mask. Additionally, the filter body may further comprise a first layer of bicomponent material disposed on one side of the intermediate layer of expanded polytetrafluoroethylene and a second layer of the same bicomponent material disposed on the opposite side of the layer of expanded polytetraflouroethylene. In many preferred embodiments, the mask further comprises first securing means attached to the body adjacent to opposite ends of the top edge and arranged to extend generally about the back of the head of the wearer in an approximate linear continuation from the top edge, the first securing means being arranged to urge the top edge into tight engagement with the wearer to prevent fluid flow between the top edge and the wearer; and second securing means attached to the body adjacent to opposite ends of the bottom edge and arranged to extend generally over the top of the head of the wearer in an approximate linear continuation from the bottom edge, the second securing means being arranged to urge the bottom edge into tight engagement with the wearer to prevent fluid flow between the bottom edge and the wearer. The resulting mask provides an enhanced fluid barrier around the periphery of the mask to prevent the bypass of both liquids and aerosols between the edges of the mask and the wearer's face. For some applications, a single pair of ties may be used to secure the mask to the head and face of the wearer. For other applications, the mask may be secured to the head and face of the wearer with a pair of ear loops, four surgical tie strips or a continuous loop of resilient material. Fluid impervious flaps may be included to extend the coverage area of the face mask and improve the fluid seal in cooperation with the sealing strips between the periphery of the mask and the face of the wearer. Preferably, the first and second securing means are formed from resilient material to provide comfort to the wearer while maintaining a tight peripheral seal for long periods of time. The securing means may be formed from various types of material as desired. Embodiments of the invention provide significant technical advantages by forming a barrier which prevents the passage of liquids and aerosols between the periphery of the mask and the wearer's face. The resulting face mask blocks liquid spray and aerosols from passing through the exterior of the mask or around the edges of the face mask and contacting portions of the wearer's face. The mask provides substantially increased flow area for the passage of air through the mask during normal breathing by the wearer while at the same time allowing the use of filtration media having higher resistance to the passage of liquids and aerosols through the mask. Embodiments of the invention allow optimising the filtration capability for resistance to the passage of aerosols while minimising the restriction to normal breathing caused by wearing the mask and allow for a substantially enhanced fit between the periphery of the mask and the contours of a wearer's face. By forming a gasket-type seal with the first and second sealing strips, normal movement of the face mask associated with breathing and talking by the wearer will not compromise the fluid barrier formed between the sealing strips and the wearer's face. For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description of exemplary non-limiting embodiments of the invention taken in conjunction with the accompanying drawings, in which: FIGURE 1 is a perspective view of a disposable face mask incorporating an embodiment of the present invention illustrated on the head of a wearer; FIGURE 2 is the plan view of the mask shown in FIGURE 1; FIGURE 3a is a drawing in section and in elevation with portions broken away of the mask shown in FIGURE 1 taken generally along lines 3a-3a of FIGURE 2; FIGURE 3b is a drawing in section and in elevation with portions broken away showing a disposable face mask incorporating an alternative embodiment of the present invention; FIGURE 3c is an enlarged sectional view with portions broken away showing an alternative embodiment of the mask of FIGURE 1 with four layers of material including at least one liquid impervious layer; FIGURE 3d is an enlarged sectional view with portions broken away showing another alternative embodiment of the mask of FIGURE 1 with three layers of material including at least one layer of expanded PTFE filter media; and FIGURE 3e is an enlarged drawing with portions broken away showing a further alternative embodiment with hydrogel placed on gasket-type sealing material attached to the interior periphery of the mask of FIGURE 1. The preferred embodiments of the present invention and its advantages are best understood by referring to FIGURES 1-3e of the drawings, like numerals being used for like and corresponding parts of the various drawings. Disposable face masks 10 and 110 incorporating various features of embodiments of the present invention may be used to retard the flow of bacteria, liquids, particulate matter and aerosols from the exterior of the respective mask to the nose and mouth of a wearer. For purposes of this application aerosols are defined as insoluble liquids or particulate matter frequently associated with microbial solutions. The term "fluid" is used within this application to include any gas, liquid, or mixture of gas and liquid. Various types of particulate matter and aerosols may be entrained with such fluids. Embodiments of the invention form a gasket-type seal to provide an enhanced fluid barrier between the periphery of a disposable face mask and the face of a wearer. For purposes of this application, the term "gasket-type seal" means a fluid barrier or pressure tight seal formed by placing a deformable material between two relatively stationary objects. Such gasket-type seals are sometimes referred to as "static seals." A wide variety of gasket-type sealing materials including thin plastic films and/or hydrogels may be satisfactorily used to form a gasket-type seal between the periphery of a face mask and the face of a wearer. Other types of deformable material such as open cell and closed cell foams may also be used to form the desired gasket-type seal. Embodiments of the invention allow optimizing the filtration capability of a disposable face mask to resist the passage of liquids, particulate matter and/or aerosols while at the same time minimizing resistance to normal breathing by a wearer and providing a comfortable fit for extended periods of wear. Embodiments of the invention allow using one or more multiple layers of filter media which may be specifically designed to block the passage of aerosols in addition to liquids. Mask 10 is shown in FIGURE 1 as being positioned on the face of wearer 12 who is illustrated in ghost lines. Mask 10 includes filter body 14 which is secured to wearer 12 by resilient securing members or headbands 16 and 18. Filter body 14 comprises an upper portion 20 and a lower portion 22 which have a generally trapezoidal configuration. Upper and lower portions 20 and 22 preferably have matching exterior dimensions and shape. Upper and lower portions 20 and 22 may be bonded together by heat and/or ultrasonic sealing along three sides of filter body 14. Bonding in this manner adds important structural integrity to mask 10. The fourth side of filter body 14 is open and includes a top edge 24 with an elongated malleable member 26 (see FIGURES 2 and 3a). Malleable member 26 is provided so that top edge 24 of mask 10 can be configured to closely fit the contours of the nose and cheeks of wearer 12. Malleable member 26 is preferably constructed from an aluminum strip with a rectangular cross-section, but may also be a moldable or malleable steel or plastic member. Top edge 24 of upper portion 20 and bottom edge 38 of lower portion 22 cooperate with each other to define the periphery of mask 10 which contacts the face of wearer 12. The present invention allows optimizing the barrier formed between the periphery of mask 10 and the face of wearer 12 and the filtration capability of mask 10 to resist the passage of liquids, particulate matter and aerosols through filtration media 34 while minimizing resistance to normal breathing of wearer 12 resulting from the use of mask 10. The present invention also allows including multiple layers of filter media within filter body 14 including layer 44 of liquid impervious material. As shown in FIGURES 1 and 3a, mask 10 has the general shape of a cup or cone when placed on the face of wearer 12. The present invention allows mask 10 to provide "off-the-face" benefits of a molded-cone style mask while still being easy to package, store and ship. "Off-the-face" style masks provide a larger breathing chamber as compared to soft, pleated masks which contact a substantial portion of the wearer's face. Therefore, "off-the-face" style masks generally permit cooler and easier breathing. The present invention allows optimizing the volume of air contained within filter body 14. If the volume is too large, excessive amounts of exhaled air may be retained within filter body 14 at normal breathing rates. By properly selecting the size of filter body 14, excessive heating of the air within filter body 14 is minimized and dizziness from prolonged periods of rebreathing exhaled air is also minimized. The approximate optimum dimensions for mask 10 as shown in FIGURE 2 include 260.4 mm (10¼ inches) for the major length, dimension A, of the trapezoidal shape of filter body 14. The length of the opening in filter body 14 defined in part by top edge 24 and bottom edge 38, dimension B, is 235.0 mm (9¼ inches) due to approximately 12.7 mm (½ inches) of seal at each junction between upper portion 20 and lower portion 22. The minor length of the parallel portion of trapezoid shaped filter body 14, dimension D, is approximately 84.1 mm (3 5/16 inches). The opening of filter body 14 defined in part by dimensions A and B is generally parallel with minor length, dimension D. Dimensions A and B may be varied by ± 19.1 mm (¾ inches). The width of the trapezoid shape of filter body 14, dimension C, is 88.9 mm (3½ inches). Dimensions C and D may be varied by 6.4 mm (± ¼ inches). The bonded border defining the three closed sides of mask 10, dimension E, is preferably 6.4 mm (¼ inches) in width. The inner portions of top edge 24 and bottom edge 38 which contact the wearer's face, dimension F, are approximately 12.7 mm (½ inches) in width. Strips of gasket-type sealing material 50 and 52 are disposed on the inner portion of top edge 24 and bottom edge 38 respectively. Strips 50 and 52 preferably have approximately the same length as dimension A of filter body 14 and a width of approximately 31.8 mm (1¼ inches). For one application, strips 50 and 52 have a thickness of approximately 0.0127 mm (0.0005 inches). The above dimensions may be modified to accommodate wearers having smaller or larger facial features. However, the ratio between the width of the trapezoid shape which defines mask 10, dimension C, as compared to the minor length of the trapezoid shape, dimension D, should preferably remain at approximately 1 to 1. The preferred ratio between the major length of filter body 14, dimension A, and the minor length, dimension D, is approximately 3 to 1. For other applications, the ratio of dimension A to dimension D may be varied to provide the desired fit as long as dimension A is larger than dimension D and the width is approximately equal to dimension C. Strips 50 and 52 of gasket-type sealing material allow face mask 10 to form a fluid tight barrier with wearers having a wider variety of facial features. An important feature of the present embodiment is forming radius R1 of approximately 28.6 mm (1 1/8 inches) and radius R2 of approximately 76.2 mm (3 inches) in the non-parallel or angled sides of filter body 14. Radii R1 and R2 cooperate with each other and with the three bonded sides of filter body 14 to prevent collapse of filter body 14 during normal breathing by wearer 12. These radii, R1 and R2, help mask 10 retain the desired, off-the-face shape during normal breathing. If the sealed border on the three closed sides of filter body 14 is less than 6.4 mm (¼ inches), mask 10 may tend to collapse during normal breathing. Therefore, an important feature of the present embodiment includes combining radii R1 and R2 with a sealed border of approximately 6.4 mm (¼ inches) in width or greater to provide the desired cone or cup shaped mask covering the nose and mouth of wearer 12 and to maintain a fluid tight barrier with wearer 12's face without collapsing during normal breathing. Radius R2 curves outward from opposite sides of mask 10 and is tangent to radius R1 that curves inward towards the attachment points for headbands 16 and 18. This arrangement serves several important functions. Radii R1 and R2 cooperate with each other and strips 50 and 52 to improve the facial seal performance between the periphery of mask 10 and the face of wearer 12. Radii R1 and R2 allow mask 10 to open with relatively flat surfaces near each end of top edge 24 and bottom edge 38 adjacent to the attachment point for headbands 16 and 18. These flat surfaces adjacent to the attachment points for the headbands 16 and 18 gradually taper away from the opening in filter body 14. The general trapezoidal shape of filter body 14 in cooperation with radii R1 and R2 and the other preferred dimensions and ratios cooperate to minimize collapse of filter body 14 during normal use of mask 10. Radii R1 and R2 cooperate with strips 50 and 52 disposed respectively on the inner portion of top edge 24 and bottom edge 38 to allow mask 10 to fit securely with and to form a tight facial seal with a greater number of different face sizes. Mask 10 is particularly useful with smaller faces which contact the tapered surfaces adjacent to the attachment points for headbands 16 and 18 on the interior of mask 10 as shown in FIGURES 3a and 3b. Radii R1 and R2 assist in maintaining the integrity of mask 10 by providing strength along the three-bonded sides of filter body 14 when mask 10 is fully opened against the face of a wearer. These previously described design features allow for the use of lighter weight or lighter basis material which adds breathability and comfort to mask 10. Without radii R1 and R2 these same lightweight materials would be prone to collapse during inhalation. The 6.4 mm (¼ inches) bonded seal around the three closed sides of filter body 14 contributes to maintaining structural integrity of mask 10 when secured to the face of wearer 12. Various adhesives, ultrasonic seals and/or heat seals may be used to attach strips 50 and 52 of gasket-type sealing material respectively to top edge 24 and bottom edge 38. Ultrasonic seals (sometimes referred to as ultrasonic welds) 42 have been found to be particularly advantageous for attaching strips 50 and 52. For some applications strips 50 and 52 may be formed from polyethylene or polypropylene with a thickness between 0.127 and 0.0127 mm (0.005 and 0.0005 inches). However, other types of thin film and deformable materials with various thicknesses may be satisfactorily used with the present invention. Blow-by associated with normal breathing of wearer 12 is substantially eliminated by properly selecting the dimension and location of malleable strip 26 and gasket-type sealing material 50 with respect to top edge of 24. Malleable strip 26 is preferably positioned in the center of top edge 24 and has a length in the range of fifty percent to seventy percent of the total length, dimension A, of top edge 24. For one embodiment of the present invention, the performance of mask 10 was enhanced by using malleable strip 26 manufactured from quarter-tempered aluminum. For this embodiment, the length of malleable strip 26 was approximately 54 percent of the length of top edge 24 with a thickness of 0.53 mm (0.021 inches) and a width of 5 mm (0.197 inches). The present invention allows designing mask 10 with the optimum periphery to fit the face of wearer 12 and the optimum dimension for strips 50 and 52 to form an enhanced fluid barrier with the nose and face of wearer 12. The present invention allows modification to the length of top edge 24 and bottom edge 38 while maintaining approximately the same surface area for normal breathing through filter media 34. For some applications securing members 16 and 18 are preferably constructed from resilient polyurethane, but may be constructed from elastic rubber or a covered stretch yarn. The covered stretch yarn may consist of an elastomeric material wrapped with nylon or a polyester. For other applications securing members 16 and 18 may comprise double knitted headbands such as circle knitted polyester/LYCRA or nylon/LYCRA. The use of resilient securing members 16 and 18 substantially improves the fluid barrier between the periphery of mask 10 and the face of wearer 12. As illustrated in FIGURE 3a, upper and lower portions 20 and 22 each include an outer mask layer 30 that is preferably constructed from a spun-bonded polypropylene. Outer mask layers 30 may also be constructed from a bi-component and/or powder bonded material such as polyethylene or polypropylene, a cellulastic tissue, or a spun-bonded polyester. Outer mask layers 30 typically have a basis weight range of 15.5 g/m (0.5 ounces per yard) to 31 g/m (1.0 ounces per yard). 27.9 g/m (0.9 ounces per yard) is one of the preferred basis weights for outer layers 30. Inner mask layers 32 are preferably composed of a bicomponent polyethylene and polypropylene. Layers 32 may also be constructed from polyester and/or polyethylene material or cellulastic tissue. Layers 32 typically have a basis weight range of 12.4 g/m (0.4 ounce per yard) to 23.3 g/m (0.75 ounces per yard). 12.8 g/m (0.413 ounces per yard) is one of the preferred basis weights for layers 32. One or more intermediate layers of filter media may be disposed between outer mask layer 30 and inner mask layer 32. Selection of the number and type of intermediate layers of filter media will depend upon the intended use and function for mask 10. In FIGURE 3a, filter body 14 is shown with only one intermediate mask layer 34 which comprises the filter media for the associated mask 10. This layer is preferably constructed from a melt-blown polypropylene, but may be constructed from an extruded polycarbonate, a melt-blown polyester, or a melt-blown urethane. As shown in both FIGURES 3a and 3b, top edge 24 of masks 10 and 110 may be faced with edge binder 36 that extends across the open end of mask 10 and covers malleable strip 26. In a similar manner, bottom edge 38 of face masks 10 and 110 may be encompassed in edge binder 40. Edge binders 36 and 40 are preferably constructed from a spun-laced polyester material. Binders 36 and 40 may also be constructed from a number of thermally bonded bicomponent materials or from polypropylene or polyethylene non-porous plastic films. Strips 50 and 52 are disposed on the interior of filter body 14 adjacent respectively to edge binders 36 and 40. A plurality of sonic bonds 42 are used to attach respectively strip 50 with edge binder 36 and layers 30, 32 and 34 at top edge 24, and strip 52 with edge binder 40 and layers 30, 32 and 34 at bottom edge 38. For face mask 10, the middle portions of strips 50 and 52 are attached respectively to the interior of filter body 14 with approximately 6.4 mm (¼ inches) of gasket-type sealing material extending outwardly from top edge 24 and bottom edge 38. Also, approximately 6.4 mm (¼ inches) of gasket-type sealing material 50 and 52 extend respectively from sonic bonded area 42 into the interior of filter body 14. Face mask 110 shown in FIGURE 3b is similar to face mask 10 except strip 150 and 152 are disposed within the respective edge binders 36 and 38 such that strips 150 and 152 only extend inwardly within filter body 14. Strips 150 and 152 do not extend from top edge 24 and bottom edge 38 as shown for mask 10. FIGURES 3a and 3b thus show only two of the many options available for installing strips of gasket-type sealing material adjacent to the top edge and bottom edge of a face mask in accordance with the present invention. FIGURE 3c shows an alternative embodiment of the present invention in which filter body 14 includes two intermediate layers 34 and 44 of filter media. Layer 44 may be formed from a barrier material that is gas permeable and permits gas (air) to pass through filter body 14 in both directions and is impermeable to liquid passing through mask 10 in at least one direction. Layer 44 is preferably arranged to prevent the passage of liquids from the exterior of filter body 14 through layer 44 to the interior of filter body 14. A more complete description of the construction and operation of such material can be found in U.S. Patent No. 3,929,135 entitled Absorptive Structure Having Tapered Capillaries , issued on December 30, 1975 to Hugh A. Thompson. Such materials are often constructed from a low density polyethylene and include small apertures which prevent liquids from passing therethrough due to the liquid's relatively high surface tension. U.S. Patents '960; '533 and 5,150,703 entitled Liquid Shield Visor for a Surgical Mask with a Bottom Notch to Reduce Glare, issued on September 29, 1992 to Hubbard, et al provide additional information on materials which may be used for layers 30, 32, 34 and 44 and face masks constructed with such materials. Other types of microporous film may be satisfactorily used with the present invention. The use of barrier materials such as layer 44 is particularly important when mask 10 is worn in an environment where the wearer may be exposed to "body fluids". These fluids such as blood, urine and saliva may contain highly contagious germs and viruses. Contact of AIDS-contaminated body fluids with another person's source of body fluids, such as the eyes, nose and mouth, may transmit the disease. Therefore, it is often preferable to include layer 44 which is resistant to the passage of liquids through filter body 14 to prevent body fluids from contacting the nose and mouth of the wearer. FIGURE 3d shows another alternative embodiment of the present invention in which filter body 14 includes intermediate layer 134 of filter media disposed between layers 32. For this particular embodiment of the present invention the inner and outer mask layers 32 are formed from the same type of material. However, various types of material may be used with intermediate mask layer 134. For one embodiment of the present invention intermediate mask layer 134 was formed from an expanded polytetrafluoroethylene (PTFE) membrane. Such materials are manufactured by W. L. Gore & Associates. A more complete description of the construction and operation of such materials can be found in U.S. Patent No. 3,953,566 entitled Process for Producing Porous Products, issued on April 27, 1976 to Robert W. Gore, and U.S. Patent No. 4,187,390 entitled Porous Products and Process Therefor, issued on February 5, 1980 to Robert W. Gore. For some applications and operating environments the use of filter media 134 substantially enhances the performance of the resulting disposable face mask 10. As demonstrated by the previous comments, the generally trapezoidal shape of filter body 14 including the preferred ratios for the dimensions of filter body 14, radii R1 and R2, the width of bonded sides 46, 47 and 48 and strips 50 and 52 of gasket-type sealing material allows a wide variety of materials to be used in the manufacture of the mask layers which comprise filter body 14. The present invention has significantly increased the types of material which may be satisfactorily used in constructing filter body 14. The present invention also allows more options with respect to selecting the number of layers of material used to manufacture filter body 14. Referring to FIGURE 1, mask 10 is illustrated as being located on the face of wearer 12. Upper portion 20 with malleable member 26 located in top edge 24 and strip 50 of gasket-type sealing material conform very closely to the configuration of the nose and cheeks of wearer 12. It is also important that bottom edge 38 with strip 52 fit very closely with the chin of wearer 12 and top edge 24 with strip 50 and the nose and cheeks of the wearer 12 fit very closely since any leaks result in bypass or blow-by of air either entering mask 10 or being discharged from mask 10 when used by wearer 12. Strips 50 and 52 substantially reduce such leakage. Accordingly, securing members 16 and 18 have their ends attached at the junctures between top edge 24 and bottom edge 38 of mask 10 as shown in FIGURE 3a. The arrangement is such that securing member 16 can be placed over the top of the head of wearer 12, as illustrated in FIGURE 1, in alignment with bottom edge 38 of mask 10 so that a direct force is exerted along that line urging bottom edge 38 into sealing engagement with the chin of wearer 12. Similarly, securing member 18 is positioned around the lower base of the skull and in direct alignment with top edge 24 of mask 10 and thus placing a force thereon which tends to move top edge 24 into tighter sealing engagement with the nose and cheeks of wearer 12. As shown in FIGURE 3a, the ends of securing members 16 and 18 are secured at the same location between top edge 24 and bottom edge 38 with no gap between the ends of securing members 16 and 18. The position of attaching securing members 16 and 18 to filter body 14 in cooperation with radii R1 and R2 results in the optimum pull angle to form a fluid tight barrier between strips 50 and 52 disposed on the interior of mask 10 and the face of wearer 12. In addition to having a tight peripheral seal, it is essential that mask 10 have good breathability characteristics. That is, mask 10 should require a low differential in pressure to permit air to flow easily through filter body 14 despite the fact that layers 30, 32 and 34 are formed from material which will filter 1 micron and smaller particles and have a very tight fit between strips 50 and 52 and the face of wearer 12. A low differential pressure for air flow indicates good breathability through a mask 10 and helps to maintain the desired gasket-type seal between the periphery of mask 10 and the face of wearer 12. For one embodiment upper portion 20 and lower portion 22 of mask 10 have a combined surface area through which air can flow of about two hundred and fifty square centimeters (250cm 2 ). Thus, body 14 of mask 10 has a surface area of approximately two hundred and fifty square centimeters which provides enhanced breathability for wearer 12. Tests were run utilizing a flow rate of thirty-two (32) liters per minute across the entire flow area. Approximately thirty masks incorporating the present invention were checked. The masks had a pressure differential ranging from 0.9 to 1.3 mm of water with a mean pressure differential across the mask of about 1.25 mm of water. Such a low differential in pressure across the mask provides excellent breathability characteristics despite the ability of the mask to filter one micron and smaller sized particles with essentially zero edge leakage around the periphery of mask 10. Upper portion 20 and lower portion 22 are shown connected with each other by heat sealing or ultrasonic bonding along sides 46, 47 and 48 to form filter body 14 having a general trapezoidal shape with an open side defined by top edge 24 and bottom edge 38. Securing members 16 and 18 are attached to the corners of top edge 24 and bottom edge 38 at the junction with upper portion 20 and lower portion 22 during ultrasonic bonding of sides 46, 47 and 48 of filter body 14. In FIGURE 3e, layer 54 of hydrogel is shown disposed on strip 50 to further enhance the fluid barrier formed with the face of wearer 12. Various types of hydrogel and other adhesives may be satisfactorily used with the present invention to provide a sticky or tacky surface on strip 50 to contact adjacent portions of the face of wearer 12. For some applications it may be desirable to apply suitable hydrogel-type materials and/or other biocompatible adhesive compounds to strips 50 and 52 for mask 10 and strips 150 and 152 for mask 110. Examples of hydrogel type materials and compounds satisfactory for use with the present invention are shown in U.S. Patent 5,306,504 entitled Skin Adhesive Hydrogel, Its Preparation and Uses; U.S. Patent 5,254,338 entitled External Application Base or Auxiliary Agent and External Application Composition for Human Being or Animal Containing the Same; and U.S. Patent 5,183,664 entitled Thin Film at EC Dressings, Preparation and Use. These three patents are representative of only a few of the many types of hydrogel materials and compounds which may be satisfactorily used with the present invention. In addition to the previously discussed materials, face masks 10 and 110 may be manufactured using a wide variety of non-woven materials and/or microporous films. The teachings of the present invention allow incorporating new, state of the art materials into face masks 10 and 110.

Claims: A disposable face mask (10) comprising: a filter body (14) having an opening sized to cover the nose and mouth of a wearer, the filter body having top and bottom edges with the top edge (24) arranged to extend across the nose and cheeks of the wearer, and the bottom edge (38) arranged to extend under the chin of the wearer; the filter body comprising an upper portion (20) of generally trapezoidal configuration having a longer side forming the top edge and a lower portion (22) of a generally trapezoidal configuration having a longer side forming the bottom edge; the top edge and the bottom edge having generally matching dimensions and defining in part the opening of the filter body; the upper and lower portions of the filter body being joined along all remaining sides; the filter body having a shorter side opposite from the longer side and generally parallel with the longer side; characterised by : a first strip (50,52) of sealing material disposed within the filter body adjacent to the opening and extending at least up to, and along, the top edge of the filter body; and a second strip (150,152) of sealing material disposed within the filter body adjacent to the opening and extending at least up to, and along, the bottom edge of the filter body; the first sealing strip and the second sealing strip cooperating with each other to form a fluid barrier between the opening of the filter body and the face of the wearer. The mask of Claim 1, wherein: the first strip of sealing material extends partially from the opening; and the second strip of sealing material extends partially from the opening. The mask of Claim 1 or Claim 2, wherein the first strip of sealing material and the second strip of sealing material are each formed from a thin film layer of plastic type material. The mask of any preceding claim, wherein the first strip of sealing material and the second strip of sealing material comprises hydrogel. The mask of any preceding claim, wherein: the dimensions of the upper portion correspond to the dimensions of the lower portion. The mask of any preceding claim, wherein the length of the longer side of the filter body is approximately three times the length of shorter side of the filter body. The mask of Claim 6, wherein the distance from the longer side to the shorter side is approximately equal to the length of the shorter side. The mask of any preceding claim, further comprising opposite sides of the filter body extending between the top edge and bottom edge, and a bonded border formed along the opposite sides of the filter body and along the bottom edge with the bonded border defining in part three closed sides of the filter body. The mask of any preceding claim, wherein the filter body further comprises an intermediate layer (44) of material which is gas permeable in both directions through the filter body and liquid impermeable in the direction from outside the filter body to inside the filter body. The mask of any preceding claim, wherein the filter body comprises an intermediate layer (134) of filter media formed from expanded polytetrafluoroethylene (PTFE). The mask of Claim 10, wherein the filter body further comprises a first layer of bicomponent material disposed on one side of the intermediate layer of expanded polytetrafluoroethylene and a second layer of the same bicomponent material disposed on the opposite side of the layer of expanded polytetraflouroethylene. The mask of any preceding claim comprising: first securing means (16) attached to the body adjacent to opposite ends of the top edge and arranged to extend generally about the back of the head of the wearer in an approximate linear continuation from the top edge, the first securing means being arranged to urge the top edge into tight engagement with the wearer to prevent fluid flow between the top edge and the wearer; second securing means (18) attached to the body adjacent to opposite ends of the bottom edge and arranged to extend generally over the top of the head of the wearer in an approximate linear continuation from the bottom edge, the second securing means being arranged to urge the bottom edge into tight engagement with the wearer to prevent fluid flow between the bottom edge and the wearer.

Inventors: BRUNSON KEVIN, RASBERRY FRANK D, RICH ALBERT R JR, BRUNSON, KEVIN, RASBERRY, FRANK D., RICH, ALBERT R. JR.
Applicants: KIMBERLY CLARK CO, KIMBERLY-CLARK WORLDWIDE, INC.
Application year: 1996
Main classification: A41D13
IPC codes: A41D13, A62B18, A61B19