Patent Publication Number: US-2023158439-A1

Title: Surface coated filter and method

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This patent application is a continuation of co-pending U.S. patent application Ser. No. 15/999,284, filed Aug. 17, 2018, which is now pending, which is a nationalization of U.S. PCT Application No. PCT/US2017/017202, filed Feb. 9, 2017, and claims the benefit of U.S. Provisional Patent Application No. 62/297,569, filed Feb. 19, 2016, the entire teachings and disclosure of each of these patent applications are incorporated herein by reference thereto. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to filters, and more particularly, to a coating of the exterior surface of a filter media pack. 
     BACKGROUND OF THE INVENTION 
     Filter media packs are often wrapped with a fabric or paper to enhance the aesthetics of the block of filter media as well as to protect the filter media during handling. Conventionally, the paper wraps are heavy cardstock, and the fabric wraps are polyester nonwovens. These wraps provide some reinforcement for the filter media packs, but they do not protect the filter media from puncturing if dropped or gouged during handling or installation. Additionally, these wraps do not provide strong bonding surfaces for attaching structures, such as seal members or mounting frames, which allows the attached structures to easily tear off. Further, these wraps are often difficult to bind to the filter media, which creates leak paths around the filter media pack. 
     In some instances, the filter media is not coated or covered as discussed in U.S. Pat. No. 7,396,376 to Schrage et al. However, outer skins or protective layers are also proposed as evidenced by U.S. Pat. Nos. 4,410,427 and 6,743,317, both to Wydeven, U.S. Pat. No. 5,820,646 to Gillingham et al, and Japanese Utility Model S60-155921 to Tuchyiya Seisakusho Limited. Additionally, molding techniques for such layers are proposed in U.S. Pat. No. 7,967,886 to Schrage et al., but this proposal requires substantial space and complex, expensive molding tooling and operation. Other slip resistant and textured surface layers have been proposed, including U.S. Publication No. 2014/0217009 by Osterfeld and U.S. Pat. No. 6,080,310 to Bolser et al. 
     Various improvements in the durability, handling, and leak prevention of filter media packs not previously realized in the art can be realized with different aspects or embodiments of the present invention as presented below, thus demonstrating such shortcomings in the state of the art. 
     BRIEF SUMMARY OF THE INVENTION 
     The inventive aspects and embodiments discussed below in the following separate paragraphs of the summary may be used independently or in combination with each other. 
     In one aspect, embodiments of a filter element are provided. The filter element includes a filter media pack having an outer surface. The outer surface extends between a first flow face and a second flow face. A polymeric coating is applied to the outer surface of the filter media pack, and the polymeric coating is not a molded structure. 
     Another aspect is directed to a polymeric coating can have a surface roughness of at least 50 μin. In preferred embodiments, the surface roughness is between about 100 and about 10,000 μin. 
     The polymeric coating preferably penetrates the filter media pack to a depth of at least 9,000 μin. 
     In preferred embodiments, the polymeric coating can be a spray coating layer. Spraying has several advantages. 
     In other embodiments, the polymeric coating can be a roll coating layer. 
     In order to enhance protection of the filter element during handling, the polymeric coating preferably has a Shore A Durometer hardness of between about 60 and about 95. Thus, the polymeric coating is harder than conventional non-woven or paper wraps that are easily punctured or crushed if mishandled. 
     The polymeric coating can include more than one layer, such as at least two layers. Preferably, at least one layer is polyurea. 
     In various embodiments, the polymeric coating is selected from the group consisting of urethane, acrylic, epoxy, silicone, polyurethane, polyurea, polyaspartic, aliphatic polyurea, polystyrene, polyethylene, ethylene-vinyl acetate, polyethylene-vinyl acetate, ethylene propylene diene monomer, polyurea/polyurethane hybrid, and combinations thereof. Additionally, the polymeric coating can optionally include fiberglass, roughening agents or other fillers. 
     The polymeric coating can be applied to a variety of filter element types. In one embodiment, the filter media pack is constructed of a filter media that includes a fluted filter media filter pack having a face sheet and a fluted sheet in a wound or stacked configuration. Unfiltered fluid passes through the face sheet or the fluted sheet to pass from the first flow face to the second flow face. In preferred embodiments, a span from the first flow face to the second flow face is at least 8 centimeters. 
     Additionally, the fluted filter media filter pack can be a wound pack having an annular shape. A leading edge of the wound pack is located at a center of the pack, and a trailing edge of the wound pack terminates along the outer surface, forming a step on the outer surface. The polymeric coating fills in and seals the step, preventing unfiltered fluid flow leakage from the first flow face to the second flow face. Preferably, no additional materials are applied along the step between the polymeric coating and the fluted filter media filter pack. 
     In another embodiment, the filter element is a pleated filter element constructed of a filter media having a plurality of pleat flanks extending between pleat tips at the first flow face and pleat tips at the second flow face. The filter element is configures in such a way that unfiltered fluid must pass through the filter media to pass from the first flow face to the second flow face. The polymeric coating is applied to a leading-most pleat flank and a trailing-most pleat flank and, optionally, along edges of the pleat flanks that extend transverse to the leading-most pleat flank and the trailing-most pleat flank. 
     In order to provide maximum air throughput, preferably, the filter media pack first flow face and a second flow face are free of the polymeric coating. 
     The polymeric coating of the filter element can cover various amounts of the outer surface of the filter media pack. Preferably, the polymeric coating has been applied to at least 25% of a surface area of the outer surface between the first flow face and the second flow face. 
     One advantage of the polymeric coating is that it helps to ensure that the filter element maintains its dimensions during storage. Accordingly, in an embodiment, the filter media pack maintains its volume during a storage period after the polymeric coating has been applied such that the polymeric coating restrains the media pack from expanding and limits any expansion in perimeter of the outer surface to less than 5%, when subjected to 100% humidity for a period of 48 hours. 
     To further enhance the dimension stabilizing capabilities of the polymeric coating, the polymeric coating is preferably impermeable to air and moisture. 
     In certain embodiments, the filter element also includes a border gasket having a housing sealing surface. The border gasket is secured to the polymeric coating in surrounding relation to the filter media pack. 
     Moreover, the border gasket can be molded in place and integrally bonded to the polymeric coating through a seal material of the border gasket. 
     In such cases, preferably, the seal material is of a compatible bonding material to the polymeric coating. In embodiments, the seal material can be at least one of polyurethane, urethane, and silicone. 
     As mentioned above, the polymeric coating can be used with a variety of filter element types. Generally, the filter element will include a filter media pack comprises a filter media having the following properties: a basis weight of between 2 and 4 ounces/square yard; an air permeability of between 5 and 20 cfm (cubic feet per minute) @0.5 inch of water gauge pressure, measured according to ASTM F778-88 (2014); and a Mullens burst strength of at least 15 PSI. 
     Additionally, the filter element may include a filter media pack with filter media having an air filtration initial efficiency of at least 99.6% at removing ISO 12103-1 A2 Fine Test Dust, measured according to ISO 5011. Further, the filter media preferably includes a layer containing at least one of cellulose, polymer, or glass fibers having an average diameter of between 1 and 200 micron. 
     In certain embodiments, the filter media of the filter media pack forms the outer surface of the filter media pack such that the filter media is in contact with the polymeric coating. 
     In order to provide incinerability, the filter element can be free of metal or plastic preformed component parts. 
     In other embodiments, however, the polymeric coating provides a complete surrounding seal between the filter media pack and at least one of a housing gasket or a metal or plastic preformed component part. 
     Further, the polymeric coating can overlap an outermost exterior surface of the metal or plastic preformed component part. 
     Preferably, the polymeric coating has an average thickness of between 0.005 and 0.100 in. 
     In another aspect, an embodiment of a filter element having an enhanced gripping surface is provided. The filter element includes a filter media pack having an outer surface. The outer surface extends between a first flow face and a second flow face. A layer is applied to the outer surface and in surrounding relation of a filtering region of the filter media pack. The layer has a surface roughness of at least 100 μin to provide an outer gripping surface. 
     In a preferred embodiment, the layer is a polymeric coating of a material that is integrally bonded to and penetrates into the outer surface of the air filter media pack. 
     In still another aspect, a filter element comprising: a filter media pack including an outer surface, the outer surface extending between a first flow face and a second flow face; and a layer applied to the outer surface of the filter media pack and covering at least 25% of a span between the first flow face and the second flow face, the outer layer having a an average thickness of between 0.005 and 0.100 inches, wherein the layer being a material that is integrally bonded via the material to the outer surface of the air filter media pack. 
     In still another aspect, a method of applying a liquid coating to a filter element is provided. The first step is providing a filter media pack, and the second step is applying a fluid to an outer periphery of the filter media without molding such that the fluid forms a polymeric coating on the outer periphery. 
     In an embodiment, the applying step is performed using a sprayer spaced a distance from the filter media pack. 
     Further, the sprayer can revolve around the media pack while the media pack is stationary. 
     However, instead, the sprayer can be stationary while the media pack rotates in front of the sprayer. 
     Additionally, the distance between the sprayer and the media pack can change during the applying step. 
     In another embodiment, the applying step is performed using a roller. 
     In certain embodiments, the method of applying a liquid coating to a filter element further includes the step of blocking a first flow face of the filter media pack while applying a polymeric fluid so as to prevent polymeric fluid from being applied to the first flow face. 
     In such embodiments, it may also be provided that a second flow face, diametrically opposed to the first flow face, is not blocked while applying the polymeric fluid. 
     However, the sprayer may be angled relative to the filter media pack so as to prevent coating of the second flow face. 
     Where the filter media pack is a pleated and embossed filter media pack in which a plurality of pleat flanks are each parallel to an axis, the sprayer can be oriented at an angle of between 105° and 150° relative to the axis. 
     Moreover, the sprayer can also be angled downward with respect to gravity. 
     In yet another aspect, a system for applying a coating to a filter element is provided. The system includes a pedestal having a base of a first size that is smaller than a bottom surface of a filter media pack. The system also includes a sprayer that is angled downward with respect to and spaced a distance apart from the pedestal. The sprayer is configured to apply a coating to the filter media pack. The system further includes a plate having a second size that is at least the same size as a top surface of the filter media pack. 
     In an embodiment of the system, the pedestal rotates in front of the sprayer. 
     In another embodiment of the system, the sprayer revolves around the pedestal. 
     Moreover, in either embodiment, the distance between the sprayer and the pedestal can vary during application of the coating. 
     Certain advantages may flow from various aspects discussed above. One potential advantage is the ability of the polymeric coating to stabilize the dimensions of the filter media pack during storage. 
     Another potential advantage that may be realized through the present invention is that the harness of the polymeric coating improves the puncture and crush resistance of the filter media pack during shipping and/or handling as compared to conventional non-woven and paper wraps. 
     Still another potential advantage that may be realized through the present invention is the polymeric coating penetrates into the filter media pack and provides a bonding surface for the gasket, which substantially prevents leak paths between the filter media pack and the gasket seal. 
     Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG.  1    depicts an isometric view of a filter element having a stacked fluted media according to an exemplary embodiment; 
         FIG.  2    depicts a partial cross-sectional view of the filter element depicted in  FIG.  1   ; 
         FIG.  3 A  depicts a detail view of the polymeric coating as shown in  FIG.  2   ; 
         FIG.  3 B  depicts a detail view of an embodiment of the polymeric coating having two layers; 
         FIG.  4    depicts a stacked filter media pack that can be used in the filter element shown in  FIG.  1   ; 
         FIG.  5    depicts the stacked filter media pack of  FIG.  4    with a border gasket; 
         FIG.  6    depicts the stacked filter media pack of  FIG.  4    with a frame; 
         FIG.  7    depicts a partial cross-sectional view of the stacked filter media pack with a frame of  FIG.  6   ; 
         FIG.  8    depicts a cross-sectional view of the stacked filter media pack with a frame of  FIG.  6    filled with seal material; 
         FIG.  9    depicts an isometric view of a second embodiment of a filter element having a stacked fluted filter media; 
         FIG.  10    depicts a stacked fluted filter media with frame that can be used in the embodiment shown in  FIG.  9   ; 
         FIG.  11    depicts a partial sectional view of the filter media pack and frame of  FIG.  10    with a polymeric coating; 
         FIG.  12    depicts an isometric view of the filter media pack of  FIG.  11    with a polymeric coating; 
         FIG.  13    depicts a partial sectional view of the filter media pack of  FIG.  12    with a seal material applied in the frame; 
         FIG.  14    depicts an isometric view the underside of the filter element depicted in  FIG.  9   ; 
         FIG.  15 A  depicts an isometric view of alternate embodiment of a fluted filter element having an annular shape; 
         FIG.  15 B  depicts an isometric view of the filter element of  FIG.  15 A  with a border gasket; 
         FIG.  15 C  depicts an isometric view of the filter element of  FIG.  15 B  also having a mid-mount frame; 
         FIG.  15 D  depicts an isometric view of the filter element of  FIG.  15 A  with just a frame; 
         FIG.  15 E  depicts a partial cross-sectional view of the filter element of  FIG.  15 B  further depicting the adhesive reinforcement structure; 
         FIG.  15 F  depicts a cross-sectional view of the filter element of  FIG.  15 C ; 
         FIG.  15 G  depict a cross-section view of the filter element of  FIG.  15 C  as inserted into a filter housing; 
         FIGS.  16 A-B  depicts an alternate embodiment of a filter element having a pleated filter media; 
         FIG.  17    depicts an isometric view of an embodiment of a rectangular embossed and pleated filter media pack; 
         FIG.  18    depicts a representation of the filter media of the filter media pack of  FIG.  17   ; 
         FIG.  19    depicts a representation of the filter media of  FIG.  18    being folded to form the filter media pack of  FIG.  17   ; 
         FIG.  20    depicts an isometric view of the filter media pack of  FIG.  17    as coated with a polymeric coating; 
         FIG.  21    depicts an isometric view of another alternate embodiment of a cylindrical embossed and pleated filter media pack; 
         FIG.  22    depicts a representation of the filter media of the filter media pack of  FIG.  21   ; 
         FIG.  23    depicts an isometric view of the filter media pack of  FIG.  21    as coated with a polymeric coating; 
         FIGS.  24 - 25    depict isometric views of an embodiment of a system for applying a polymeric coating to a fluted filter media; 
         FIG.  26    depicts an isometric, cross-sectional view of a wound filter element having an adhesive foam gasket as the flexible sealing material according to another exemplary embodiment; 
         FIGS.  27 A and  27 B  depict partial sectional views of the wound filter element of  FIG.  26    as the frame is being located thereon; and 
         FIG.  28    depicts a partial sectional view of the wound filter element of  FIG.  27    with a bonding material filling a channel formed by the frame. 
     
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG.  1    depicts a filter element  10  according to one embodiment. The filter element  10  includes a filter media pack  12  having an outer surface  14  (shown in  FIG.  2   ). The outer surface  14  extends between a first flow face  16  and a second flow face  18 . The outer surface  14  of the media pack  12  is at least partially covered with a polymeric coating  20 . Advantageously, the polymeric coating  20  is not a molded structure and, therefore, requires no mold tooling, which can be expensive to make for various sizes and to maintain. Instead, in preferred embodiments the polymeric coating  20  is applied directly to the outer surface  14  of the filter media pack  12  as a liquid, or other flowable/fluid material, that cures or hardens into a solid coating or layer. 
     The filter media pack  12  includes filter media for removing particulate from a fluid stream. In some instances, the filter media forms the outer surface  14  of the filter media pack  12 . Additionally, the filter element  10  can be formed in such a way as to be free of metal or plastic preformed component parts. Filter elements of the variety that do not include metal are generally able to be incinerated. Nevertheless, embodiments of the filter element can include metal or plastic preformed component parts. 
     Various means can be employed to apply the polymeric coating  20  to the outer surface  14  of the filter media pack  12 . For instance, the polymeric coating  20  can be rolled onto the outer surface  14 . In a preferred embodiment, the polymeric coating  20  is sprayed onto the outer surface  14 . 
     The polymeric coating  20  can cover the entire outer surface  14  or only a portion of the outer surface  14  (see, e.g.,  FIG.  4   ). In a preferred embodiment, the polymeric coating  20  is applied to at least 25% of the outer surface  14  extending between the first flow face  16  and the second flow face  18 . In a more preferred embodiment, the polymeric coating  20  is applied to at least 50% of the outer surface  14  extending between the first flow face  16  and the second flow face  18 . In a most preferred embodiment, the polymeric coating  20  is applied to at least 95% of the outer surface  14  extending between the first flow face  16  and the second flow face  18 . 
     Additionally, in some embodiments, the polymeric coating  20  can extend past the outer surface  14  to cover a portion of the first flow face  16  and/or the second flow face  18 . In other embodiments, the first flow face  16  and the second flow face  18  of the filter media pack  12  are free of the polymeric coating  20  to afford maximum fluid flow therethrough. 
       FIG.  2    illustrates a partial cross-sectional view of the filter embodiment of  FIG.  1   . As illustrated in  FIG.  2   , the polymeric coating  20  is relatively thin in relation to the total size of the filter element  10 . The polymeric coating  20  has an average thickness of between 0.005 and 0.100 inches. More preferably, the polymeric coating  20  has an average thickness between 0.020 and 0.050 inches, and most preferably, the polymeric coating has an average thickness between 0.030 and 0.045 inches. 
     Applying the polymeric coating to the filter media pack  12  as a liquid, fluid, or other flowable material allows the polymeric coating  20 , in some embodiments, to penetrate the filter media pack  12 . Preferably, the polymeric coating  20  penetrates the filter media pack  12  to a depth of 9,000 μin. In this way, the polymeric coating  20  is integrally bonded to the outer surface  14  of the filter media pack  12 . This allows the polymeric coating  20  to extend around and interlock with the fibers of the filter media to increase the bond to the filter media pack  12 . 
     In preferred embodiments, the polymeric coating  20  is applied in such a way as to provide a rough surface. The surface roughness improves gripping during handling and also provides an overall more aesthetically pleasing product.  FIG.  3 A  depicts an exaggerated view of the polymeric coating  20  of  FIG.  2   , which demonstrates the surface roughness in exaggerated form. In a preferred embodiment, the polymeric coating  20  has a surface roughness of at least 50 μin (micro-inches); typically the surface roughness will be less than about 10,000 μin but is not so limited in all embodiments. Surface roughness, as used herein, refers to the average difference between the heights of surface projections  22  compared to surface valleys  24 . More preferably, the surface roughness is at least 1,000 μin, and most preferably, the surface roughness is at least 5,000 μin. Further, the surface roughness is more preferably less than 9,000 μin and more preferably less than 7,000 μin. 
     The polymeric coating  20  advantageously improves the crush strength and burst strength of the filter element so as to avoid damage during shipping and/or handling. In a preferred embodiment, the polymeric coating  20  has Shore A Durometer hardness of between about 60 and about 95. This is significantly harder than conventional filter wraps made of non-woven fabric or paper, which were prone to rip or puncture if dropped or gouged during installation or handling. However, this provides some flexibility in the orthogonal direction. The failure of these conventional wraps as a result of punctures caused damage to the filter media packs and resulted in leak paths around the filter media packs. 
     Additionally, the polymeric coating  20  enhances the hoop strength of the filter media pack  12  while maintaining the flexibility in the radial direction. Stated another way the polymeric coating  20  is not a rigid, inflexible material that could cause ripping or tearing of the filter media if the filter media pack  12  is contorted during installation and/or handling. Instead, the polymeric coating  20  is capable of flexing with the filter media pack  12  during installation and/or handling while also preventing the filter media pack  12  from expanding outward, such as from moisture absorption or residual processing stresses. 
     A variety of suitable materials can be utilized as the polymeric coating  20 . Such materials include: urethane, acrylic, epoxy, silicone, polyurethane, polyurea, polyaspartic, aliphatic polyurea, polystyrene, polyethylene, ethylene-vinyl acetate, polyethylene-vinyl acetate, ethylene propylene diene monomer, polyurea/polyurethane hybrid, and combinations thereof. The polymeric coating can also optionally include fiberglass, roughening agents or other fillers. 
     In a preferred embodiment, the polymeric coating  20  is polyurea. 
     The polymeric coating can be applied to various types of filter media packs  12 . In one embodiment depicted in  FIGS.  1  and  9 - 10   , the filter media pack  12  is constructed of a fluted filter media and particularly stacked strips of fluted filter media. As shown in  FIG.  4   , in one embodiment, the fluted filter media includes a face sheet  26  and a fluted sheet  28  in a stacked configuration to form inlet and outlet flutes, plugged at opposite ends, e.g., adjacent either first flow face  16  or second flow face  18  such that unfiltered fluid must pass through the face sheet  26  or the fluted sheet  28  to pass from the first flow face  16  to the second flow face  18 . Typically, the face sheet  26  will be secured to the fluted sheet  28  and then cut to form strips. These strips of a section of face sheet  26  secured to fluted sheet  28  will then be stacked to form the filter media pack  12 . Alternatively, the face sheet  26  and fluted sheet  28  will be secured together and then wound to form a wound filter media pack  12 . Adhesive or other sealant is located between layers of the filter media pack  12  to close off the flutes and force fluid (such as air) to flow through the media. In a preferred embodiment, a span S from the first flow face  16  to the second flow face  18  is at least 8 centimeters. 
       FIGS.  4 - 8    depict steps for assembling various embodiments of the filter element. Beginning in  FIG.  4   , a stacked filter media pack  12  is provided. The stacked filter media pack  12  has the polymeric coating  20  applied to the outer surface  14 .  FIG.  4    depicts a partially coated filter media pack  12 . However, as noted above, more or less of the outer surface  14  could be coated, such as illustrated in  FIG.  5   . 
     As shown in  FIG.  5   , a border gasket  30  attached proximal to the second flow face  18  of the filter media pack  12 . The border gasket  30  can be a pre-molded part that is adhered or bonded to the polymeric coating  20 . Additionally, the pre-molded border gasket  30  can be stretched around the filter media pack  12  such that the border gasket  30  is held in place by a tight frictional engagement between the border gasket  30  and the polymeric coating  20  as a result of the tension in the stretched border gasket  30 . Further, the border gasket  30  can be molded directly onto the polymeric coating  20 . 
     In a preferred embodiment, the height of the polymeric coating  20  over the span S is greater than the height of the border gasket  30 . This helps to ensure that shear forces on the border gasket  30  are spread over a larger span of the filter media because of the polymeric coating  20 . In conventional filter media packs in which the border gasket was bonded directly to the filter media pack, shear forces on the border gasket were localized on the weaker filter media, which frequently caused the filter media to fail and the border gasket to tear free from the filter media pack. With the present polymeric coating  20 , not only is the border gasket  30  provided with a better sealing or bonding surface, but also the shear forces on the border gasket  30  are spread over a larger span of the filter media because of the polymeric coating  20  instead of localized on the filter media pack  12 . 
     The border gasket  30  can be directly molded to the polymeric coating  20 . In such embodiments, the border gasket  30  is molded in place and integrally bonded to the polymeric coating  20 . In such instances, the border gasket is selected for its compatibility with the polymeric coating  20  such that a strong adhesion is formed. Suitable seal materials include polyurethane, urethane, and silicone. In a preferred embodiment, a polyurethane seal material is used with a polyurea coating  20 . 
     In some embodiments, the border gasket  30  can provide a sealing surface for directly sealing with a filter housing (similar to the border gasket  230  sealing with filter housing  243  depicted representatively in  FIG.  15 G ). 
     As shown in  FIG.  6   , in an alternative embodiment, the filter media pack  12  and polymeric coating  20  could instead be inserted into a frame  32 , including a face structure  34  (shown in  FIG.  7   ). With reference to  FIG.  7   , the frame  32  also includes a protruding ledge  36  that extends around the perimeter of the frame  32  and radially outward.  FIG.  7    shows a partial sectional view of the filter media pack  12  and polymeric coating  20  inserted into the frame  32 . As can be seen, the filter media pack  12  rests against the face structure  34 , and a flexible sealing material  37  is deposited into a peripheral channel  38  between a portion of the frame  32  and the polymeric coating  20  (which has coated the outer surface  14  and penetrated into the filter media pack  12 ). The flexible sealing material  37  prevents leak paths between the frame  32  and the polymeric coating  20 . Next, the peripheral channel  38  is filled with a bonding material  40  as shown in  FIG.  8    to secure the frame  32  to the polymeric coating  20 . In alternative embodiments, flexible sealing material  37  may be attached to the polymeric coating  20  prior to the filter media pack  12 , polymeric coating  20 , and flexible sealing material  37  assembly being inserted into the frame  32 . 
     In a preferred embodiment, the bonding material  40  is a rigid material, such as urethane. A “rigid” bonding material is a seal material  40  having a Shore A Durometer of at least 80. Finally, as shown in  FIG.  1   , an outer gasket  42  for sealing with a filter housing is molded, adhered, or otherwise secured to the protruding ledge  36 . 
     Advantageously, the polymeric coating  20  provides an improved adherent surface to which features can be attached to the filter element  10 . As shown in  FIGS.  5  and  8   , the polymeric coating  20  is receptive to direct molding or bonding with a border gasket  30  or gluing of a frame  32 . Prior wraps, especially polyester nonwovens, are unable to provide surfaces that were compatible with a variety of different structures and/or bonding/sealing agents. 
     In some embodiments, such as in  FIGS.  26 - 28   , the flexible sealing material  737  is a pre-formed, low-density foam gasket adhered to the polymeric coating  720  prior to locating the frame  732 . As depicted in the isometric, sectional view of  FIG.  26   , the foam gasket used as the flexible sealing material  737  may be in the form of a foam tape that has an adhesive applied to a single side. In exemplary embodiments, the foam tape can be a polyester or a polyether foam. Additionally, in some embodiments, the adhesive is a pressure-sensitive adhesive. 
     After the foam gasket is attached to the polymeric coating, the frame  732  is pressed over the foam gasket flexible sealing material  737  as shown in  FIGS.  27 A and  27 B , thereby forming peripheral channel  738 . The interior of the frame  732  includes a stepped region in the form of a protrusion  742  that contacts and compresses the flexible sealing material  737 . Because the polymeric coating  720  and filter media pack  12  may not conform exactly to the shape of the frame  732 , the flexible sealing material  737  provides a seal between the polymeric coating  720  and the frame  732  during manufacturing. For example, radial gaps will occur between the protrusion  742  and the surface created by polymeric coating  720  due to inconsistencies in the shape/dimensions in filter media pack  712 . Thus, inserting the frame  732  over the flexible sealing material  737  will cause the flexible sealing material  737  to compress around the perimeter of the polymeric coating  720  and fill any gaps.  FIG.  27 A  shows the frame  732  sliding over the flexible sealing material  737  and compressing it. As shown in  FIG.  27 B , the frame  732  has been fully inserted over the flexible sealing material  737  and has completely compressed it. Preferably, the flexible sealing material  737  compresses at least 5% around the perimeter of the polymeric coating  720 , and more preferably the flexible sealing material compresses at least 10% around the perimeter of the polymeric coating  720 . However, the flexible sealing material  737  may compress in excess of 75%. 
     As mentioned above, placing the frame  732  over the flexible sealing material  737  creates a channel  738  between the polymeric coating  720  and the frame skirt  746 .  FIG.  28    illustrates that a bonding material  740  fills the channel  738  and, in certain embodiments like those pictured in  FIG.  28   , extends above the frame  732 . The bonding material  740  secures the frame  732  to polymeric coating  720 . The flexible sealing material  737  helps to ensure that the bonding material  740  does not leak out of the frame  732  when the bonding material  740  is poured into the channel  738 . 
     A mold can be used when applying the bonding material  740 . Thus, as shown in  FIG.  28   , the bonding material  740  has the additional structures of a tapered region  747  and an axial seal surface  748 . The axial seal surface  748  can be used to form a seal for sealing with a housing in the axial direction. In other embodiments, a radial seal could be defined. The frame  732  includes the projection  742 , a skirt  746 , radially extending ledge  736 , and an axially extending flange  749  forming a multi-step, stepped profile. In preferred embodiments, the bonding material  740  is made from polyurethane, urethane, or silicone or another material similar to that used for the border gasket  30  discussed in relation to other embodiments (e.g.,  FIGS.  5 ,  15 B,  15 C,  15 E,  15 F, and  15 G ). 
     While the embodiments of  FIGS.  26 - 28    depict a “racetrack” filter element  700  in which the filter media pack  712  is formed by winding filter media around a winding structure  754 , other filter media pack configuration can also be used including, among others, stacked fluted filter media, other wound filter media configurations (e.g., circular), and pleated. 
       FIG.  9    depicts an alternate embodiment of a stacked filter media pack filter element  100 .  FIGS.  10 - 14    depict a method of assembling the filter element  100  shown in  FIG.  9   . In this embodiment, the filter media pack  112  and polymeric coating  120  are substantially similar to the filter media pack  12  and polymeric coating  20  of the previous embodiment of the filter element  10 . According to this embodied method and beginning with  FIGS.  10  and  11   , the stacked filter media pack  112  is inserted into a frame  132  such that an end  133  of the frame  132  is coplanar with the second flow face  118  of the filter element  100 . 
     As shown in  FIG.  11   , the frame  132  includes a tapered leg  144  that forms a tight engagement with the outer surface  114  of the filter media pack  112  and that tapers relative to the side wall of the filter media pack  112 . As with the prior frame  132 , the frame  132  of this embodiment forms a peripheral channel  138  between the filter media pack  112  and the frame  132 , and the frame  132  includes a radially outward extending flange in the form of a protruding ledge  136  that extends around the perimeter of the frame  132 . 
     In this embodied method, the polymeric coating  120  is then applied to the outer surface  114  of the filter media pack  112  and at least a portion of the tapered leg  144  of the frame  132  as depicted in  FIGS.  11 - 12   . The polymeric coating can thus help secure the frame  132  to the filter media pack  112 . As shown in  FIG.  13   , the peripheral channel  138  is filled with seal material  140 . Preferably, the seal material  140  is a rigid material, such as a urethane resin. The tight engagement between tapered leg  144  and the filter media pack  112  helps prevent leakage of seal material  140  prior to curing. 
     As shown in  FIG.  14   , a gasket  146  is molded, adhered, or otherwise secured to the protruding ledge  136  of the frame  132  to complete the construction of the filter element  100 . Like outer gasket  142 , gasket  146  seals the filter element  100  to a filter housing (similar to filter housing  243  shown in  FIG.  15 G ). 
     In another embodiment of a filter element  200  depicted in  FIG.  15 A , the filter media pack  212  is a wound pack having an annular shape, specifically a racetrack shape. Nevertheless, other wound shapes could be created, including oval, round, and shapes having varied radii of curvature on different sides, and the wound pack should not be interpreted as being limited to any particular wound shape. The filter media pack  212  is preferably formed from a single sheet of fluted filter media. The sheet of fluted filter media is preferably provided by a face sheet secured to a fluted sheet. However other forms of filter media may be employed. The filter media has a leading edge  248  at a center  250  of a pack  212  and a trailing edge  252  of the wound pack  212  along the outer surface  214  (shown in  FIGS.  15 E and  15 F ). As depicted in  FIG.  15 A , the leading edge  248  is bonded to a central winding structure  254  to facilitate winding and which influences the final shape of the filter element  200 . However, other embodiments need not incorporate a winding structure  254 . The trailing edge  252  terminates at a location along the outer surface  214  of the last winding, which forms a step  256  in the outer surface  214  of the filter media pack  212 . 
     Once the wound filter media pack  212  is formed, the filter element  200  including the wound filter media pack  212  can be assembled similarly to the filter element  200  having a stacked filter media pack  212 , i.e., according to either the steps depicted in  FIGS.  4 - 8    or the steps depicted in  FIGS.  10 - 14   . As in the previous embodiments, the polymeric coating  220  is applied to the outer surface  214 . In this case, the polymeric coating  220  fills in and seals the step  256  and prevents unfiltered fluid flow leakage. Preferably, the polymeric coating  220  is applied without any additional materials applied along the step  256  between the polymeric coating  220  and the fluted filter media filter pack  212 . For instance, in some embodiments, the use of polymeric coating  220  eliminates the need for an adhesive bead to be laid at the trailing edge  252  extending between the first and second flow faces  216 ,  218 . Further, the polymeric coating  220  can provide an improved aesthetic appearance by hiding step  256 . 
     As shown in  FIG.  15 B , a border gasket  230  can be adhered, bonded, molded, or otherwise secured to an end of the polymeric coating  220 . As shown in  FIG.  15 C , the filter element  200  can also feature a mounting frame  232  with a protruding ledge  236  that extends around at least a portion of the frame  232 . Frame  232  is attached to the polymeric coating. As shown in  FIG.  15 C , the frame is mid-mounted, i.e., the frame  232  is located approximately half-way between the first flow face  216  and the second flow face  218 .  FIG.  15 D  depicts a filter element  200  in which no border gasket  30  is provided and the frame  232  is mounted near the first flow face  216 . The seal would be provided adjacent ledge  236 . 
       FIG.  15 E  depicts a partial cross-sectional view of a filter element  200  in which the second flow face  218  has been reinforced using an adhesive material to create an adhesive reinforcing structure  257 . Such an adhesive reinforcing structure  257  is described in co-pending International Patent Application having serial number PCT/US2015/054739 (referred to as “the &#39;739 application”) filed Oct. 8, 2015, owned by the owner of the instant application, the teachings of which are incorporated herein by reference thereto in their entireties. The combination of the adhesive reinforcing structure  257  and the outer layer polymeric coating  220  described above provides improved stability and strength to the filter media pack  212 . The adhesive reinforcing structure  257  can be applied to one or both flow faces  216 ,  218  of the filter element  200 . 
       FIG.  15 F  depicts a cross-sectional view of the filter element  200  shown in  FIG.  15 C .  FIG.  15 G  depicts a cross-sectional view of the filter element  200  inserted into a filter housing  243 . As can be seen in  FIG.  15 G , the protruding ledge  236  of the frame  232  contacts a shelf region  245  of the housing  243  to position the filter element  200  within the housing  243 . A seal is created between the border gasket  230  and a lower wall region  247  of the filter housing  243  to prevent air bypass around the filter element  200 . In a preferred embodiment, air flows through the first flow face  216  to the second flow face  218  such that the air pressure on the filter element  200  ensures that the frame  232  remains in tight contact with the shelf region  245 . 
     Another embodiment of a filter element  300  is depicted in  FIG.  16 A .  FIG.  16 B  depicts the filter media pack  312 , which includes pleated filter media  358  having a plurality of pleat flanks  360  extending between pleat tips  362  at the first flow face  316  and pleat tips  364  at the second flow face  318 . Unfiltered fluid passes through the filter media  358  to pass from the first flow face  316  to the second flow face  318 . The filter media  358  has a leading-most pleat flank  360   a  and a trailing-most pleat flank  360   b . As shown in  FIG.  16 A , the polymeric coating  320  is applied to the leading-most pleat flank  360   a  and the trailing-most pleat flank  360   b . Additionally, the polymeric coating  320  is applied along the edges of the pleat flanks  360  that extend transverse to the leading-most pleat flank  360   a  and the trailing-most pleat flank  360   b.    
     Still another embodiment of pleated and embossed filter element  400  is provided in  FIGS.  17 - 20   .  FIG.  17    depicts a rectangular filter media pack  412  having a pleated media  458  including a plurality of pleat flanks  460  extending between pleat tips  462  on a first flow face  416  and pleat tips  464  on a second flow face  418 . The pleat flanks  460  depicted in  FIG.  17    alternate between embossed pleat flanks  466  and flat pleat flanks  468 . Embossed pleat flanks  466  have been pressed, shaped, or otherwise formed to include ridges along the entire flank or only a portion of the flank. A system and method of embossing a pleated media and embodiments of an embossed and pleated filter media are provided in U.S. Provisional Application No. 62/243,740, titled “Filter Media Packs, Methods of Making and Filter Media Presses,” filed on Oct. 20, 2015, the teachings of which are incorporated herein by reference thereto in their entireties.  FIG.  18    depicts a portion of the pleat media  458  with the pleats  460  laid out flat. As shown in  FIG.  18   , the pleat flanks  460  alternate between embossed pleat planks  466  and flat pleat flanks  468  at fold lines  470 . When folded along fold lines  470 , the pleated structure takes shape as shown representatively in  FIG.  19   .  FIG.  20    depicts the filter media pack  412  as coated with the polymeric coating  420 . As in the prior embodiments, a border gasket or frame can be molded, adhered, bonded, or otherwise secured to the polymeric coating  420 , as desired by the user. 
     A further embodiment of a pleated and embossed filter element  500  is provided in  FIGS.  21 - 23   .  FIG.  21    depicts a cylindrical filter media pack  512  having pleated media  558  including a plurality of pleat flanks  560  extending between pleat tips  562  on a first flow face  516  and pleat tips  564  on a second flow face  566 . The pleat flanks  460  depicted in  FIG.  21    alternate between embossed pleat flanks  566  and flat pleat flanks  568 .  FIG.  22    depicts a portion of the pleat media  558  with the pleats  560  laid out flat. As can be seen in  FIG.  22   , the pleat flanks  560  alternate between sections of embossed pleat flanks  566  and sections of flat pleat flanks  568 . The interface between these sections provides fold lines  570  by which to form the pleated structure. To create the circular shape of the flow faces  516 ,  518  of the filter media pack  512 , trim sections  572  are removed from the filter media  558  so that the width of the pleat flanks  560  transitions from narrow at a leading-most pleat flank  560   a  to widest at the center of the pleated filter media  558  to narrow again at the trailing-most pleat flank  560   b  (see, e.g.,  FIG.  21   ).  FIG.  23    depicts the filter media pack  512  as coated with the polymeric coating  520 . As in the prior embodiments, a border gasket or frame can be molded, adhered, bonded, or otherwise secured to the polymeric coating  520 , as desired by the user. 
     As discussed, a variety of filter element types can benefit from the polymeric coating  20 . Generally, the filter media packs of the filter elements will have filter media with the following properties: a basis weight of between 2 and 4 ounces/square yard; an air permeability of between 5 and 20 cfm (cubic feet per minute) @0.5 inch of water gauge pressure, measured according to ASTM F778-88 (2014); and a Mullen burst strength of at least 15 PSI. 
     Additionally, the filter media can be described in terms of the air filtration efficiency. A typical filter media of the type used with the present invention will have an initial air filtration efficiency of at least 99.6% at removing ISO 12103-1 A2 Fine Test Dust, measured according to ISO 5011 test standard. Further, the air filtration media can include a layer containing at least one of cellulose, polymer, or glass fibers having an average diameter of between 1 and 200 micron. 
     As discussed above, the polymeric coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720  can be applied to the filter media pack  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712  using a variety of applicator tools. In preferred embodiments, the polymeric coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720  is applied using a sprayer that is spaced apart from the filter media pack  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712 . In embodiments, the sprayer revolves around the filter media pack  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712  while the filter media pack is stationary. However, in other embodiments, the sprayer can be stationary while the filter media pack  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712  rotates in front of the sprayer. 
     Additionally, in certain embodiments, the distance between the sprayer and the media pack changes during the application of the polymeric coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720 . The distance between the sprayer and the filter media pack  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712  can change by moving the sprayer closer to and farther away from the pack or vice versa. One benefit of varying the distance between the sprayer and the filter media pack is to create the aforedescribed surface roughness. When the sprayer is positioned relatively far from the filter media pack  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712 , the atomized polymer liquid from the sprayer forms globules before reaching the filter media pack, which stick to the polymer coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720  already contained on outer surface  14 ,  114 ,  214 ,  314 ,  414 ,  514 ,  714  of the filter media pack  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712  or stick to the filter media pack  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712  and then are covered with a more uniform layer of the liquid polymer coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720 . Upon curing, the polymer coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720  is thus provided with a rough surface for improved gripping and aesthetics. 
     In certain embodiments, the polymeric coating  20  is applied in at least two coats, i.e., the outer surface  14  of the filter media pack  12  is coated a first time with the polymeric coating  20  and then is coated at least a second time with the polymeric coating  20 . The material of the polymeric coating  20  can be the same in each coating step, or the material of the polymeric coating can be different in each coating step, such that the polymeric coating  20  is comprised of at least two layers  20   a ,  20   b  as shown representatively in  FIG.  3 B . While  FIG.  3 B  shows a clean demarcation between layers  20   a ,  20   b , the actual demarcation between layers may produce a varied or mixed layer region at the interface of the layers  20   a ,  20   b . Preferably, in embodiments having multiple different layers  20   a ,  20   b , at least one layer is polyurea. While depicting polymeric coating  20  of the first embodiment of the filter element  10 , the multiple layer coating can be applied to the other embodiments of the filter element, including filter elements  100 ,  200 ,  300 ,  400 ,  500 ,  700 . 
       FIGS.  24  and  25    depict, in simplified form, an exemplary system  600  for applying a coating to a filter media pack  212 . The system  600  includes a pedestal  605  upon which the filter media pack  212  rests. The pedestal  605  has a base  610  (shown in  FIG.  25   ) of a first area that is equal in size or smaller than the first flow face  216  of a filter media pack  212 . The system  600  also includes an applicator  615 , such as a sprayer  620 . In embodiments using a sprayer  620 , the sprayer  620  is angled downward with respect to the pedestal  605  and gravity. The sprayer  620  is also spaced a distance apart from the pedestal  605 . The applicator  615 , such as a sprayer  620 , is configured to apply the polymeric coating  220  to the filter media pack  212 . During application, a blocker plate  625  is placed over the second flow face  218  of the filter media pack  212 . The blocker plate  625  preferably has a shape and size equal to the area and shape of the second flow face  218  of the filter media pack  212 . In this way, the blocker plate  625  prevents liquid polymer from being applied to the second flow face  218  of the filter media pack  212 . Additionally, because of the downward angle of the sprayer  620 , the first flow face  216  is also not coated with the liquid polymer. 
     In one embodiment, during application of the polymeric coating  220 , the pedestal  605  rotates in front of the applicator  615 . In another embodiment, the applicator  615  revolves around the pedestal  605 . In still other embodiments, the applicator  615  can revolve around a rotating pedestal  605 . In such embodiments, the applicator  615  preferably revolves counter to the direction of rotation of the pedestal  605 . 
     Additionally, in embodiments using a sprayer  620 , the distance between the sprayer  620  and the pedestal  605  can vary during application of the polymeric coating  220 . In this way, the spray  620  moves closer to and farther away from the pedestal  605 . This can be used to form the gripping surface or to more uniformly apply the liquid polymeric coating  220  for non-circular filter media packs. 
     While the applicator system  600  was described in terms of the filter element  200 , the system  600  works as well with the other filter embodiments, including filter elements  10 ,  100 ,  300 ,  400 ,  500 ,  700 . 
     For the pleated filter elements (including the embossed and pleated filter elements)  300 ,  400 ,  500 , preferably the sprayer  620  is angled relative an axis A parallel to the pleat flanks  360 ,  460 ,  560  as illustrated in  FIGS.  16 B,  17 , and  21   . That is, the sprayer  620  is angled in a plane parallel to the first flow face  316 ,  416 ,  516  and second flow face  318 ,  418 ,  518 . With respect to axis A, preferably the sprayer  620  is oriented at an angle θ of between 105° and 150°. In a more preferred embodiment, the sprayer  620  is oriented at an angle θ of approximately 120°. Thus, the sprayer  620  can be angled relative to the axis A and downward with respect to gravity, or both. This reduces the amount of overspray into the channels formed between adjacent pleat flanks  360 ,  460 ,  560 . Moreover, if the pleat flanks are sufficiently close together, the polymeric coating can be used to close the channels between adjacent pleat flanks  360 ,  460 ,  560  to effectively create an end cap of the filter media pack  312 ,  412 ,  512 . 
     Advantageously, the filter media packs  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712  featuring the polymeric coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720  are better able to retain their shape during storage. The polymeric coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720  restrains the filter media pack  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712  from expanding as a result of absorption of ambient moisture and, in the case of wound filter elements, coil stresses. Further, it prevents adjacent layers of filter media from delaminating. The polymeric coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720  limits expansion in perimeter of the outer surface to less than 5%, when subjected to 100% humidity for a period of 48 hours. In preferred embodiments, the polymeric coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720  is impermeable to air and moisture such that air and moisture cannot penetrate through the polymeric coating  20 ,  120 ,  220 ,  320 ,  420 ,  520 ,  720  and be absorbed into the filter media pack  12 ,  112 ,  212 ,  312 ,  412 ,  512 ,  712 . 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.