Patent Publication Number: US-2023149750-A1

Title: Face Masks and Methods of Producing Same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 63/036,141, filed Jun. 8, 2020, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Technical Field 
     The disclosure is generally in the field of face masks and methods of producing face masks. 
     Description of Related Art 
     Face masks are used to reduce or avoid exposure to contaminants and pathogens. Face masks may include a substrate that inhibits or blocks passage of particles, liquids, and microorganisms, while permitting passage of air for breathing. Face masks may be provided in a shape, for example, a two-dimensional shape, or a three-dimensional contour, for facilitating wearing, retention, and comfort. 
     A need remains for improved face masks and techniques of making face masks. 
     SUMMARY 
     Improved face masks and techniques of making face masks are provided. In one aspect, the face mask includes a filter body including a composite film, wherein the composite film includes a first layer of a sintered polymeric material, and a second layer of an expanded polymer film secured to the first layer. In preferred embodiments, the filter body is shaped and dimensioned to cover the mouth and nose of a person. The face mask may include one or more straps for securing the filter body over the mouth and nose of a wearer. 
     In another aspect, a process is provided for making a face mask, wherein the process includes (i) providing a composite film including a sintered polymeric material adjacent an expanded polymer film, (ii) thermoforming the composite film to produce a filter body of the face mask, and optionally (iii) attaching one or more straps to the filter body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments may utilize elements and/or components other than those illustrated in the drawings, and some elements and/or components may not be present in various embodiments. Elements and/or components in the figures are not necessarily drawn to scale. Throughout this disclosure, depending on the context, singular and plural terminology may be used interchangeably. 
         FIG.  1 A  is a conceptual diagram showing a front, perspective view of a face mask including a filter body that includes a composite film. 
         FIG.  1 B  is a conceptual diagram showing a partial cross-sectional, perspective view of the face mask of  FIG.  1 A . 
         FIG.  1 C  is a conceptual diagram showing a cross-sectional view of the composite film of the face mask of  FIG.  1 A . 
         FIG.  2    is a conceptual diagram showing a plan view of a precursor composite film including a first layer of a precursor polymeric material adjacent a second layer of a precursor polymer film. 
         FIG.  3    is a conceptual diagram showing a perspective view of a two-part mold assembly for making a face mask. 
         FIG.  4    is a photograph showing a scanning electron microscopy (SEM) image of a precursor sintered polymeric material before thermoforming. 
         FIG.  5    is a photograph showing a scanning electron microscopy (SEM) image of a sintered polymeric material of  FIG.  4    after thermoforming. 
         FIG.  6    is a photograph showing a scanning electron microscopy (SEM) image of a precursor expanded polymeric film (PTFE) before thermoforming. 
         FIG.  7    is a photograph showing a scanning electron microscopy (SEM) image of the polymeric film of  FIG.  6    after thermoforming. 
     
    
    
     It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components illustrated in the drawings or set forth in the following description. 
     DETAILED DESCRIPTION 
     Improved face masks and techniques of making face masks have been developed. In embodiments, a face mask includes a filter body including a composite film. The composite film includes a first layer of a sintered polymeric material, and a second layer of an expanded polymer film secured to the first layer. In a preferred embodiment, the sintered polymeric layer is a stretched sintered polymeric layer and the expanded polymer film is a stretched expanded polymer film. The “stretched” characteristic of these layers and films results at least in part from plastic deformation of these materials, e.g., by a thermoforming process. The face mask may include one or more straps, e.g., a pair of straps, for securing the filter body over the mouth and nose of a wearer. 
     Masks according to the present disclosure may have one or more of the following advantages: easily formable into a variety of shapes, can be sterilized and reused, offers an enhanced seal compared to conventional masks, offers enhanced barrier properties, offers enhanced air flow, offers more rigidity for ease of repositioning, embodies a soft and non-agitating inner surface, and is made from readily available polymeric materials. 
     In embodiments, a process for making a face mask includes providing a composite film including a sintered polymeric material adjacent an expanded polymer film, thermoforming the composite film to produce a filter body of the face mask, and optionally attaching one or more straps to the filter body. In other embodiments, the filter body may be secured within a pouch of another holder/means known in the art for securing a filter body about a person&#39;s mouth and nose. 
       FIG.  1 A  is a conceptual diagram showing a front, perspective view of a face mask  10  including a filter body  11  that includes a composite film  12 .  FIG.  1 B  is a conceptual diagram showing a partial cross-sectional, perspective view of face mask  10  of  FIG.  1 A .  FIG.  1 C  is a conceptual diagram showing a cross-sectional view of part of the composite film  12  of face mask  10  of  FIG.  1 A . In embodiments, composite film  12  includes a first layer  14  of a sintered polymeric material, and a second layer  16  of an expanded polymer film secured to first layer  14 . In a preferred embodiment, first layer  14  includes a stretched sintered polymeric layer. In a preferred embodiment, second layer  16  includes a stretched expanded polymer film. 
     Composite film  12  acts as a barrier for pathogens, liquids, or generally for contaminants, while allowing passage of air. For example, one or both of first layer  14  and second layer  16  may reduce or prevent passage of liquids and contaminants, and both first layer  14  and second layer  16  may substantially permit passage of air. 
     In embodiments, the sintered polymeric material of first layer  14  is laminated to the expanded polymer film of second layer  16 . The layers may be laminated in the course of molding or thermoforming face mask  10 , or otherwise by thermal processing prior to thermoforming. In embodiments, face mask  10  may include an adhesive layer between first layer  14  and second layer  16 . 
     The sintered polymeric material in first layer  14  may include a beaded or particulate material that is thermoformed, or otherwise heat-treated to promote elongation of the beads or particles of the sintered polymeric material. In some embodiments, the sintered polymeric material includes polyethylene. In some preferred embodiments, the sintered polymeric material includes low melt flow polymers such as high density or ultra high molecular weight polyethylene or fractional melt polypropylene. In at least some preferred embodiments, the polymeric material is a low melt flow polymer so that during heat processing, including thermoforming, the sintered porous structure remains suitably intact and porous. In a preferred embodiment, first layer  14  is free of conventional fibrous or fiber-based materials such as melt-blown and/or spunbond materials. For example, first layer  14  may be free of woven fibrous material or nonwoven fibrous material. Thus, in some embodiments, no fiber or fibrous material is present in first layer  14 . 
     The sintered polymeric material in first layer  14  may define voids or pores. The voids or pores may be at least partially interconnected to provide a passage through first layer  14 . In some embodiments, the porosity of the sintered polymeric material may be in a range of 5 microns to 250 microns. 
     The expanded polymer film in second layer  16  may include an expanded fluoropolymer matrix, or other nanofiber materials that can undergo thermoforming without loss of function. For example, the fluoropolymer may include polytetrafluoroethylene (PTFE). In embodiments, the expanded polymer film defines a matrix including nodules and fibrils. In a preferred embodiment, second layer  16  is free of conventional fibrous or fiber-based materials such as melt-blown and/or spunbond materials. For example, second layer  16  may be free of woven fibrous material or nonwoven fibrous material. Thus, in some embodiments, no fiber or fibrous material is present in second layer  16 . 
     While fibrous material may be absent from first layer  14  or the sintered polymeric material of first layer  14 , or from second layer  16  or the expanded polymeric film of second layer  16 , in some embodiments, the face mask  10  may include a separate fibrous layer. For example, face mask  10  may include one or more woven or non-woven layers distinct from first layer  14  or second layer  16 . Thus, in some embodiments, the face mask  10  or filter body  11  may include layers in addition to first layer  14  and second layer  16 . In other embodiments, filter body  11  consists of composite film  12 . Thus, filter body  11  may only include first layer  14  and second layer  16 . 
     First layer  14 , second layer  16 , and composite film  12  as a whole, may have any suitable thickness. In embodiments, first layer  14  has a thickness in a range of 0.005 inch to 0.125 inch (0.1 mm to 3.2 mm). In embodiments, second layer  16  has a thickness in a range of 0.0005 inch to 0.005 inch (0.01 mm to 0.1 mm). In embodiments, composite film  12  has a thickness in a range of 0.0055 inch to 0.130 inch (0.14 mm to 3.3 mm). In embodiments, a ratio of a thickness of first layer  14  to a thickness of second layer  16  may be in a range of 1 to 250. 
     In embodiments, second layer  16  defines an interior surface configured to face the wearer. Without being bound by theory, providing second layer  16  including the expanded polymeric film, for example, a fluoropolymer film, on the interior of the mask promotes forming a contaminant seal against the wearer&#39;s face. Moreover, while fluoropolymers may exhibit reduced friction, the fluoropolymer of second layer  16  may exhibit a threshold amount of friction to grip or retain position against the wearer&#39;s face or skin. 
     Without being bound by theory, composite film  12  exhibits a synergistic effect relative to the independent properties of first layer  14  and second layer  16 . For example, in isolation, a sintered polymeric material may tend to break in response to tensile stresses. Likewise in isolation, an expanded polymer film may tend to overstretch and rupture upon elongation. However in composite film  12 , the combination of first layer  14  and second layer  16  allows further stretching and forming, for example, because first layer  14  supports second layer  16 . Additionally, porosity of the sintered polymeric material in first layer  14  may promote breathability through filter body  11 , compared to a filter body that does not include a porous or sintered material. 
     The combination of first layer  14  and second layer  16  in composite film  12  may also provide some flex during inhalation or exhalation, causing the mask to elastically deform to the wearer&#39;s face to some extent. Such deformation combined with the grip of second layer  16  may promote formation of a contaminant barrier seal. Such a seal may reduce or prevent migration or entry of contaminants along a peripheral region  20  of face mask  10 . 
     In embodiments, peripheral region  20  may be relatively densified compared to rest of filter body  11 . In embodiments, peripheral region  20  may include an additional layer, for example, a reinforcing layer, or a layer that promotes sealing, retention, or contact with wearer&#39;s skin. 
     As shown in  FIG.  1 A , face mask  10  may generally have a shape that conforms to a wearer&#39;s nose and mouth. For example, filter body  11  may have a convex-concave shape and be dimensioned to fit about the wearer&#39;s mouth and noses. In embodiments, filter body  11  is shaped by a thermoforming process, as described elsewhere in the present disclosure. 
     In some embodiments, filter body  11  defines one or more support ribs  22 . Support ribs  22  may provide some flex and promote conforming of face mask  10  to a wearer&#39;s face. Support ribs  22  may also increase the surface area of face mask  10 , which may promote air passage and breathability. Support ribs  22  may also introduce non-uniform and intended thickness variations in composite film  12  that increase the mask&#39;s overall breathability. 
     In some embodiments, face mask  10  further includes a nose piece  24  attached to filter body  11 . For example, nose piece  24  may be separately formed and secured to filter body  11 , by adhesive, weld, fastener, clip, or combinations thereof. In some other embodiments, nose piece  24  may be integrally formed with filter body  11 , for example, in a single molded shape. 
     In some embodiments, face mask  10  further includes an air-valve  26  secured to the filter body. Air-valve  26  may permit relatively rapid exhalation without permitting inhalation, thus promoting breathability during exhalation. For example, the chance of contaminant migration towards the wearer during exhalation is minimal. Because air-valve may not permit inhalation, all inhaled air would pass through first layer  14  and second layer  16 , which constitute a barrier to contaminants. 
     In embodiments, face mask  10  includes one or more straps  18  for securing filter body  11  over the mouth and nose of a wearer. Straps  18  may include one, two, or more straps. Straps  18  may be attached to peripheral region  20  of filter body  11 . For example, straps  18  may be welded to filter body  11 , for example, laminated or heat-welded to peripheral region  20 . In embodiments, straps  18  may be secured to filter body  11 , for example, by adhesive, mechanical fasteners, clips, stitches, staples, or combinations thereof. Straps  18  may be formed of a polymeric material. In some preferred embodiments, straps  18  are elastic and resilient. 
     Filter body  11  and face mask  10  may be formed by thermoforming from a precursor composite, as described with reference to  FIGS.  2  and  3   . 
       FIG.  2    is a conceptual diagram showing a plan view of a precursor composite film  30  including a first layer  34  of a precursor polymeric material adjacent a second layer  36  of a precursor polymer film. The precursor polymeric material in first layer  34  includes substantially sintered or partially sintered polymeric beads, particles, or material, such that thermoforming may result in further sintering, stretching, and shaping of the precursor polymeric material to form the sintered and porous polymeric material in first layer  14 . 
     Without being bound by theory, low melt flow polymers are preferable for use in porous first layer  34 . For example, low or very low melt flow polymers may soften or tackify in response to thermal processing, but yet retain the general shape and continue to support adjacent second layer  36 . The low or very low melt flow polymers may include polyethylene, for example, high density polyethylene (HDPE) or ultra-high molecular weight polyethylene (UHMWPE) or suitable fractional melt polypropylene materials. 
     Precursor polymer film of second layer  36  includes an unexpanded, partially expanded, or expanded polymer film, which is capable of further expansion or stretching, such that thermoforming results in further expansion or stretching to form expanded polymer film in second layer  16 . Such a second layer  36  may be thermoformed in conjunction with first layer  34  while continuing to stretch or expand, and providing relative high airflow with good filtration. Without being bound by theory, it may be difficult to thermoform such a polymer film in second layer  36  without the support of porous sintered/sinterable first layer  34 . 
     Precursor film  30  may be formed by coating, extruding, dispersing, laminating or otherwise depositing of one of first and second layers  34  and  36  on the other of first and second layers  34  and  36 . For example, beads or particles of first layer  34  may be deposited on second layer  36 . In embodiments, first layer  34  is laminated to second layer  36  in precursor film  30 . 
     Precursor film  30  may be molded in a mold assembly to form a face mask, for example, as described with reference to  FIG.  3   . 
       FIG.  3    is a conceptual diagram showing a perspective view of a two-part mold assembly  40  for making a face mask. Mold assembly  40  includes a first mold portion  42  and a second mold portion  44 . Mold assembly  40  may be formed of any suitable material, for example, metal, alloy, ceramic, polymer, glass, or any material that can sustain temperatures associated with thermoforming of precursor film  30  into face masks. 
     Sheet of precursor film  30  may be placed between first mold portion  42  and second mold portion  44 , for example, between lower surface  46  of first mold portion  42  and upper surface  48  of second mold portion  44 . Lower surface  46  and upper surface  48  define a predetermined shape, for example, configured to impart a predetermined curvature and texture to precursor film  30 . In embodiments, first mold portion  42  and second mold portion remove heat from precursor film  30  during processing. Such removal of heat may promote the cooling of thermally processed material to assume and retain the three-dimensional shape imparted by mold assembly  40 . After molding, the precursor film  30  transforms to a composite film, such as composite film  12  of  FIGS.  1 A and  1 B , which includes a stretched sintered polymeric layer and an expanded polymer film, for example, an expanded PTFE film. 
     Precursor material is thermoformed between first mold portion  42  and second mold portion  44 , in response to a predetermined temperature. For example, mold assembly  40  may be heated to a temperature in a range of 250° F. to 450° F. (120° C. to 230° C.). In some embodiments, one or both of precursor film  30  or mold assembly  40  may be heated. Mold assembly  40  may be operated at atmospheric pressure, partial vacuum, or vacuum, or under pressure, as known in the art. 
     Thus, mold assembly  40  subjects precursor film  30  to stretching and forming to form a molded shape, for example, of a face mask such as face mask  11 . 
     The change in the structure of precursor polymer material in first layer  34  to sintered polymer material in first layer  14  by thermoforming is shown in  FIGS.  4  and  5   . 
       FIG.  4    is a photograph showing a scanning electron microscopy (SEM) image of a precursor sintered polymeric material before thermoforming.  FIG.  5    is a photograph showing a scanning electron microscopy (SEM) image of a sintered polymeric material of  FIG.  4    after thermoforming. 
     The change in the structure of polymer film in second layer  36  to expanded polymer film in second layer  16  by thermoforming is shown in  FIGS.  6  and  7   . 
       FIG.  6    is a photograph showing a scanning electron microscopy (SEM) image of a precursor expanded polymeric film (PTFE) before thermoforming.  FIG.  7    is a photograph showing a scanning electron microscopy (SEM) image of the polymeric film of  FIG.  6    after thermoforming. 
     The unformed expanded PTFE shown in  FIG.  6    has filtration properties that make it suitable for use a medical mask (captures small particles at a rate greater than 95% efficiency), but may be too difficult to breathe through. Similarly, the unstretched porous precursor polymeric material shown in  FIG.  4    is formable and breathable, but by itself, may lack the filtration efficiency required by medical masks. Used together as a laminate, and without forming or further thermal treatment, the precursor film  30  offers appropriate filtration efficiency, but may be too restrictive and lacks sufficient breathability, while also lacking a three-dimensional conforming shape. 
     By forming composite film  12  from precursor film  30 , the resulting composite film  12  undergoes stretch, the permeability of the material as a whole is increased, and breathability of the material as a whole is improved. The forming also shapes the precursor film  30  with shape, a feature suitable for the eventual production of face mask  10 . 
     Because the precursor film  30  is formable and can be shaped with a mold assembly such as mold assembly  40 , a variety of geometries can be molded. While this feature enables the formation of multiple sizes, this feature also enables for different amounts of compression and/or stretch of the precursor film  30 . Compression of precursor film  30  may result in a non-porous material with added strength. This feature can be used around the perimeter of the mask, for example, to reinforce anchor points for straps  18 , and can also be used to reinforce the thin walled mask material with structural ribs  22 . Such features may both reduce mask flex (during inhalation and exhalation) and also provide for a convenient means to reposition face mask  10 . Additional stretch in certain regions of the mask may result in a variable wall thickness which can be utilized to create regions in the mask to enhance breathability. 
     Surprisingly, the filtration efficiency of the formed composite film  12  is very well preserved to levels that are similar to that of the precursor film  30 . Similarly, the splash resistance of the formed composite film  12  exceeds that required by most mask standards, for example, being at least as high as 160 mm Hg. 
     Unlike conventional masks, masks according to the present disclosure may not include electret materials. By using polymeric base materials, the mask can be submerged into isopropyl alcohol and sterilized. Performance testing has shown that the filtration efficiencies of the resulting sterilized mask still offer filtration efficiencies above 95%, and thus meet NISOH N95 ratings after sterilization. 
     While processes for forming face masks are described with reference to mold assembly  40 , any suitable system, apparatus, or assembly may be used to form face masks according to the disclosure. Further, while face masks have been described, precursor film  30  may be used to form any suitable air-filtration media, for example, for residential, commercial, or transportation applications. For example, precursor film  30  may be thermally processed or thermoformed in other molds, to provide objects having different shapes or sheet-formed objects apart from face masks. 
     EXEMPLARY EMBODIMENTS 
     Embodiment 1 
     A face mask comprising: a filter body comprising a composite film, the composite film comprising: a first layer of a sintered polymeric material, and a second layer of an expanded polymer film secured to the first layer; and one or more straps for securing the filter body over the mouth and nose of a wearer. 
     Embodiment 2 
     The face mask of Embodiment 1, wherein the second layer defines an interior surface configured to face the wearer. 
     Embodiment 3 
     The face mask of Embodiment 1 or 2, wherein the expanded polymer film comprises an expanded fluoropolymer matrix. 
     Embodiment 4 
     The face mask of Embodiment 3, wherein the fluoropolymer comprises polytetrafluoroethylene (PTFE). 
     Embodiment 5 
     The face mask of any one of Embodiments 1 to 4, wherein the sintered polymeric material comprises polyethylene. 
     Embodiment 6 
     The face mask of any one of Embodiments 1 to 5, wherein the sintered polymeric material is laminated to the expanded polymer film. 
     Embodiment 7 
     The face mask of any one of Embodiments 1 to 6, wherein the filter body consists of the composite film. 
     Embodiment 8 
     The face mask of any one of Embodiments 1 to 7, wherein the filter body has a convex-concave shape and is dimensioned to fit about the wearer&#39;s mouth and noses. 
     Embodiment 9 
     The face mask of any one of Embodiments 1 to 8, wherein the filter body is shaped by a thermoforming process. 
     Embodiment 10 
     The face mask of any one of Embodiments 1 to 9, wherein the filter body defines one or more support ribs. 
     Embodiment 11 
     The face mask of any one of Embodiments 1 to 10, further comprising a nose piece attached to the filter body. 
     Embodiment 12 
     The face mask of any one of Embodiments 1 to 11, further comprising an air-valve secured to the filter body. 
     Embodiment 13 
     The face mask of any one of Embodiments 1 to 12, wherein the first layer has a thickness in a range of 0.005 inch to 0.125 inch (0.1 mm to 3.2 mm). 
     Embodiment 14 
     The face mask of any one of Embodiments 1 to 13, wherein the second layer has a thickness in a range of 0.0005 inch to 0.005 inch (0.01 mm to 0.1 mm). 
     Embodiment 15 
     The face mask of any one of Embodiments 1 to 14, wherein a ratio of a thickness of the first layer to a thickness of the second layer is in a range of 1 to 250. 
     Embodiment 16 
     The face mask of any one of Embodiments 1 to 15, wherein the composite film has a thickness in a range of 0.0055 inch to 0.130 inch (0.14 mm to 3.3 mm). 
     Embodiment 17 
     A process for making a face mask, the process comprising: providing a precursor composite film comprising a precursor polymeric material adjacent a precursor polymer film; thermoforming the precursor composite film to produce a filter body of the face mask; and optionally attaching one or more straps to the filter body. 
     Embodiment 18 
     The process of Embodiment 17, further comprising, after the thermoforming, trimming the composite film. 
     Embodiment 19 
     The process of Embodiment 17 or 18, further comprising, after the thermoforming, attaching a nose piece to the filter body. 
     Embodiment 20 
     The process of any one of Embodiments 17 to 19, further comprising, after the thermoforming, attaching an air-valve to the filter body. 
     Embodiment 21 
     A face mask comprising: a filter body comprising a composite film, the composite film comprising: a first layer of a sintered polymeric material, and a second layer of an expanded polymer film secured to the first layer, wherein the filter body is shaped and dimensioned to cover the mouth and nose of a person. 
     Embodiment 22 
     The face mask of Embodiment 21, wherein the second layer defines an interior surface configured to face the wearer. 
     Embodiment 23 
     The face mask of Embodiment 21 or 22, wherein the expanded polymer film comprises an expanded fluoropolymer matrix. 
     Embodiment 24 
     The face mask of Embodiment 23, wherein the fluoropolymer comprises polytetrafluoroethylene (PTFE). 
     Embodiment 25 
     The face mask of any one of Embodiments 21 to 24, wherein the sintered polymeric material comprises polyethylene. 
     Embodiment 26 
     The face mask of any one of Embodiments 21 to 25, wherein the sintered polymeric material is laminated to the expanded polymer film. 
     Embodiment 27 
     The face mask of any one of Embodiments 21 to 26, wherein the filter body consists of the composite film. 
     Embodiment 28 
     The face mask of any one of Embodiments 21 to 27, further comprising one or more straps configured to secure the filter body over the mouth and nose of a wearer. 
     The detailed description set forth above is provided to aid those skilled in the art in practicing the invention. However, the invention described and claimed herein is not to be limited in scope by the specific embodiments described above, as these embodiments are presented as mere illustrations of several aspects of the invention. Any combinations and modifications of the described methods and components, and compositions used in the practice of the methods, in addition to those not specifically described, will become apparent to those skilled in the art based on the present disclosure and do not depart from the spirit or scope of the present invention. Such variations, modifications, and combinations are also encompassed by the present disclosure and fall within the scope of the appended claims.