Abstract:
The present disclosure relates generally to air filter frames. In some embodiments, the air filter frames are nestable. Nestable air filter frames of the type described herein offer significantly reduced shipping volume, and thus shipping costs, while also providing cost-effective manufacturing. Some embodiments relate to an air filter frame including a single strip of framing material forming at least two of the four major frame segments and the frame corner between the two major frame segments. In some embodiments, a single strip of framing material forms at least three of the four major frame segments and two of the frame corners.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to air filters. More particularly, it relates to frame components useful with air filters. 
       BACKGROUND 
       [0002]    Air filters are commonly used in forced air systems (e.g., residential heating and air-conditioning systems) in order to remove dust and dirt particles and the like. Air filter products typically include a filtration media surrounded and supported by a frame. Additional supporting components, such as a mesh screen, adhesive beads, etc., may also be included. However, the frame is not only sized and shaped to partially enclose and support the filtration media, but also sized and shaped so that the air filter product can be inserted or supported in place based upon a particular end-use application. As a point of reference, the three-dimensional shape of an air filter product includes a length, width, and depth. In the case of a rectangular air filter product, for example, a rectangular filtration media is surrounded at its four sides by frame pieces or segments that may be connected at the corners and/or connected to the four side edges of the filtration media. The majority of the filtration media is thus capable of use for its filtering ability, with air flow through the filtration media occurring in the depth direction. Many end-use applications have a filter-receiving housing with established length, width, and depth dimensions; the air filter product&#39;s outer dimensions desirably match one or more of the expected housing length, width and/or depth dimensions to achieve robust retention of the air filter product upon insertion into the housing. 
         [0003]    Air filter frame elements are known to be made from a variety of materials, including metal, plastic, and paperboard. In many instances, a selected construction of the air filter frame is a function of the filtration media format. For example, the filtration media can be formed to a pleated or other three-dimensional shape. The frames associated with these filtration media formats must accommodate the elevated, overall three-dimensional depth. In other instances, the filtration media can be relatively flat or planar (e.g., non-pleated). In theory, the frame could also have a relatively minimal depth (corresponding with that of the flat filtration media format); however, in order to facilitate robust retention within the expected end-use filter-receiving housing, the frame will oftentimes define an elevated depth (as compared to a thickness or depth of the flat filtration media), including side panels or walls projecting well away from a major surface of the filtration media to define an overall depth of the air filter product that corresponds with the depth of the end-use filter-receiving housing. 
         [0004]    The projecting frame format associated with many flat filtration media-based air filter products has been found to present a unique opportunity for reduced shipping costs. In particular, the depth-defining side panels or walls can be formed to extend at a non-perpendicular angle relative to the plane of the flat filtration media. With this design, a first air filter product can nest “inside” the frame of a second air filter product when stacked on top of the other. This nested or stacked arrangement significantly reduces the resultant shipping volume, and thus shipping costs, when the air filter products are delivered in bulk. These same nested arrangements, and thus shipping cost savings, can also be accomplished with other air filter product designs, including pleated filtration media-based products having projecting frame walls or panels establishing the air filter product&#39;s overall depth. 
         [0005]    One example of a nesting frame construction for a flat filtration media air filter product is provided in U.S. Publication No. 2013/0327004, entitled “Framed Air Filter with Offset Slot, and Method of Making,” the entire teachings of which are incorporated herein. The frame design of the &#39;004 Publication is a strip-frame, which means that individual frame pieces are cut as linear strips for a continuous roll of frame material (e.g., chipboard) with very little waste. Four distinct or discrete strips are used to complete a rectangular air filter product. The nested strip frame design of the &#39;004 Publication, while excellent in reducing shipping costs, may come with a penalty in manufacturing productivity due to the need to assemble four strip pieces. 
         [0006]    Standard strip frames for non-nesting filters often have a hinged corner joint, which allows for rapid assembly in manufacturing because the hinge design reduces the number of frame pieces from four to two or even one. However, the hinged frame is not designed to provide filter-to-filter nesting such that the shipping and cost savings described above are not available. 
         [0007]    Single piece nestable frames for flat filtration media air filter products are known, for example fiberglass-based residential air filter products available from Flanders Corp. However, these known frames are die-cut from a single piece of chipboard in a “box frame style” configuration and are accordingly much more expensive than a perimeter-only strip frame. 
       SUMMARY 
       [0008]    The inventors of the present application recognized a need for an air filter having a nestable perimeter strip frame that can be assembled in a cost- and time-efficient manner. 
         [0009]    Aspects of the present disclosure are directed toward air filter frame strips useful for framed air filters, and related methods of assembly and manufacture. 
         [0010]    Some embodiments relate to a frame capable of being used in an air filter, wherein the frame includes four major frame segments, comprising: a single strip of framing material forming at least two of the major frame segments and the frame corner between the two major frame segments; and wherein the frame is nestable. 
         [0011]    Some embodiments relate to a frame capable of being used in an air filter, comprising between two and three strips that cooperatively form the frame; and at least one nestable corner. Some embodiments have at least two nestable corners. 
         [0012]    Some embodiments relate to a frame capable of being used in an air filter, comprising: a material strip including: (1) first and second downstream panels, (2) first and second inner side walls interconnected to a corresponding one of the downstream panels at a fold line, (3) first and second outer side walls interconnected to a corresponding one of the inner side walls at a fold line, (4) first and second upstream panels interconnected to a corresponding one of the outer side walls at a fold line, (5) a joint portion formed at region of intersection between the first and second outer side walls, the joint portion including: (a) a first, vertical score line interconnecting the first and second outer side walls, (b) a second score line in the first outer side wall and extending in non-perpendicular fashion immediately adjacent the first score line, (c) a third score line in the second outer side wall and extending in non-perpendicular fashion immediately adjacent the first score line, (d) a first cut-out portion separating the first and second downstream panels and separating the first and second inner side walls, and (e) a second cut-out portion locating adjacent the joint portion and separating the first and second upstream panels. 
         [0013]    Some embodiments relate to a method of at least partially assembling at least a portion of a frame of a framed air filter, the method comprising: (1) receiving a material strip defining: (a) first and second downstream panels, (b) first and second inner side walls interconnected to a corresponding one of the downstream panels at a fold line, (c) first and second outer side walls interconnected to a corresponding one of the inner side walls at a fold line, (d) first and second upstream panels interconnected to a corresponding one of the outer side walls at a fold line, (e) a joint portion formed at region of intersection between the first and second outer side walls, the joint portion including: (f) a first, vertical score line interconnecting the first and second outer side walls, (g) a second score line in the first outer side wall and extending in non-perpendicular fashion immediately adjacent the first score line, (h) a third score line in the second outer side wall and extending in non-perpendicular fashion immediately adjacent the first score line, (i) a first cut-out portion separating the first and second downstream panels and separating the first and second inner side walls, (j) a second cut-out portion locating adjacent the joint portion and separating the first and second upstream panels; (2) folding the material strip at the joint portion to bring the first and second outer side walls toward one another, including the joint folding at each of the first-third score lines and further including the second and third score lines being brought into substantial abutment to define a corner; (3) further folding the material strip to locate the first inner side wall over the first outer side wall, the first downstream panel over the first upstream panel, the second inner side wall over the second outer side wall, and the second downstream panel over the second upstream panel; wherein following the steps of folding, the material strip is transitioned to define first and second major frame segments intersecting at a corner. 
         [0014]    In some embodiments, the single strip forms three of the major frame segments and two frame corners between the three major frame segments. 
         [0015]    In some embodiments, each major frame segment includes a first side wall and a second side wall and wherein the first side wall and the second side wall are at least one of (1) generally parallel to one another or (2) positioned at an angle of less than about 40 degrees to one another. In some embodiments, each of the first and second side walls have a side wall tilt angle that is between about 95 degrees and about 150 degrees. In some embodiments, each of the first and second side walls have a side wall tilt angle that is between about 100 degrees and about 130 degrees. In some embodiments, the first side wall and second side wall have a foldable connection therebetween. In some embodiments, the foldable connection is at least one of a score line and/or a fold line. Some embodiments further include one or more self-retention features. In some embodiments, the self-retention feature includes at least one locking tab on or adjacent to one or more of the major frame segments; at least one slot on or in one or more of the other major frame segments; and wherein the tab(s) is/are capable of being inserted or tucked into the slot(s). In some embodiments, the self-retention features include an adhesive. In some embodiments, the frame corner is a triangular inwardly folding corner. In some embodiments, the frame corner is asymmetric by between about 0.01 mm and about 1 mm. 
         [0016]    Some embodiments further include air filtration media attached to or adjacent to the frame; and wherein the air filtration media is at least one of pleated or flat. In some embodiments, the air filtration media is at least one of a nonwoven material, an electret-comprising nonwoven material, or a fiberglass-containing material. Some embodiments further include at least one of an open cell structure layer, a porous media layer, a nonwoven scrim layer, a reinforcing filament layer, a netting, and/or a wire mesh. 
         [0017]    In some embodiments, the frame strip includes a hinge joint integrated between two frame sides. When manipulating or folding the frame strip from a flat state toward a final state in which the two frame sides are assembled to a respective edge of an air filter media, the hinge joint facilitates formation of a common corner between the frame sides and side walls of the frame sides arranged at a tilt angle relative to upstream and downstream panels thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view of an exemplary framed air filter in accordance with principles of the present disclosure, viewed from the downstream side of the framed air filter. 
           [0019]      FIG. 2  is a cross-sectional view of a portion of the framed air filter of  FIG. 1 , taken along the line  2 - 2 . 
           [0020]      FIG. 3  is a plan view of an exemplary material strip in a flat state and useful in forming two or more major frame segment components of the framed air filter of  FIG. 1 . 
           [0021]      FIG. 4A  is a simplified perspective view of a portion of the material strip of  FIG. 3  in a folded state. 
           [0022]      FIG. 4B  is a cross-sectional view of a portion of the arrangement of  FIG. 4A , taken along the line  4 B- 4 B. 
           [0023]      FIG. 5A  is a simplified plan view of a portion of the material strip of  FIG. 3  illustrating various geometric relationships in the flat state. 
           [0024]      FIG. 5B  is a simplified plan view of a portion of the material strip of the type generally shown in  FIG. 3  illustrating various geometric relationships in the flat state of an exemplary embodiment. 
           [0025]      FIG. 5C  is a schematic drawing generally showing how the embodiments of  FIG. 5A and 5B  can be folded to create a corner. 
           [0026]      FIG. 6A  is a plan view of another material strip in a flat state. This material strip can be useful in forming two or more major frame segment components of the framed air filter of the type generally shown in  FIG. 1 . 
           [0027]      FIG. 6B  is a plan view of another material strip in a flat state. This material strip can be useful in forming two or more major frame segment components of the framed air filter of the type generally shown in  FIG. 1 . 
           [0028]      FIG. 6C  is a schematic drawing generally showing how the embodiments of  FIG. 6A and 6B  can be folded to create a corner. 
           [0029]      FIG. 7A  is a plan view of another material strip in a flat state. This material strip can be useful in forming two or more major frame segment components of the framed air filter of the type generally shown in  FIG. 1 . 
           [0030]      FIGS. 7B and 7C  are schematic drawings generally showing how the embodiments of  FIG. 7A  can be folded to create a corner. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Although directional terminology such as “top”, “bottom”, “upper”, “lower”, “under”, “over”, “front”, “back”, “up” and “down” may be used in this disclosure, it will be understood that those terms are used in their relative sense only unless otherwise noted. Terms such as “outer”, “outward”, “outwardmost”, “outwardly” and the like mean in a direction generally away from the geometric center of the air filter media. Terms such as “inner”, “inward”, “inwardmost”, “inwardly” and the like mean in a direction generally toward the geometric center of the air filter media. As used herein as a modifier to a property, attribute or relationship, the term “generally”, unless otherwise specifically defined, means that the property, attribute or relationship would be readily recognizable by a person of ordinary skill but without requiring absolute precision of a perfect match (e.g., within +/−20% for quantifiable properties); the term “substantially” means to a high degree of approximation (e.g., within +/−10% for quantifiable properties) but again without requiring absolute precision or a perfect match. 
         [0032]    As used herein, the term “upstream” is used to denote the closed-ended side of a framed air filter, corresponding to the far side of a framed air filter  10  as shown in  FIG. 1  and to the lower side of the framed air filter  10  as shown in  FIG. 2 . Certain figures of the present disclosure are marked with “u” to aid in recognition of the upstream side of the framed air filter and components. 
         [0033]    As used herein, the term “downstream” is used to denote the open-ended side of such a framed air filter (the side to which the filter frame side walls protrude), corresponding to the near side (the visible side) of the framed air filter  10  as shown in  FIG. 1  and to the upper side of the framed air filter  10  as shown in  FIG. 2 . Certain figures of the present disclosure are marked with “d” to aid in recognition of the downstream side of the framed air filter and components. 
         [0034]    The terms upstream and downstream are used purely for convenience of description herein, in recognition of the observation that such framed air filters are often placed into forced air ventilation systems with the closed-ended side of the framed air filter facing the stream of incoming air (i.e., facing upstream) and with the open-ended side of the framed air filter facing downstream (e.g., with the terminal ends of the side walls resting against support flanges of the forced air ventilation system). However, it will be appreciated that in some cases, such framed air filters might be placed in an airstream in the reverse orientation; thus, it is emphasized that the terms “upstream” and “downstream” are used herein merely for convenience of description of the various components of the framed air filter and their geometric relationship, irrespective of how such a framed air filter might be eventually installed into a forced air ventilation system. 
         [0035]    Shown in  FIG. 1  in perspective view from the downstream side is an exemplary framed air filter  10  in accordance with principles of the present disclosure.  FIG. 2  provides a cross-sectional view of a portion of the framed air filter  10  of  FIG. 1 . The framed air filter  10  provides an upstream side  11  a and a downstream side  11   b,  and includes a filer media  12  and a frame  14 . The frame  14  is mounted generally on, and surrounds, a perimeter  16  of the filter media  12 . The framed air filter  10  can be rectangular in shape (which specifically includes square shapes) having corners  18 . The perimeter  16  of the filter media  12  thus can have a generally rectangular shape (which does not preclude irregularities, notches, chamfered or angled corners, or the like, along or in the perimeter  16 ). The frame  14  may thus take the form of a rectangular frame with four elongated frame segments  20  that are each mounted on one of the four major edges of the filter media  12 . For ease of identification, the four major segments  20  of the frame  14  may occasionally be referred to herein by a lettered subscript (e.g., a, b, c, or d). The four major frame segments  20  combine to define four frame corners  22 . 
         [0036]    Some features of the present disclosure relate to formation of two (or more) of the major frame segments  20 , and the corresponding frame corner  22  there between, from a single strip of framing material. To better understand features of the single strip and corresponding manufacturing techniques of the present disclosure (including mounting to the filter media  12 ), an explanation of optional panels or walls provided with each of the frame segments  20  is beneficial. In some embodiments, the frame segments  20  can be highly similar. With this in mind, and as shown in  FIG. 2 , the major frame segments  20  can form or define a downstream panel  30  and an upstream panel  32 . The panels  30 ,  32  can, upon final assembly, be generally parallel to each other and capture (e.g., pinch) a portion  33  of the perimeter  16  of the filter media  12  therebetween. In some embodiments, an inwardmost edge  34  of the downstream panel  30  may be aligned (along an inward-outward direction, as shown in  FIG. 2 ) within e.g., about 2 mm, 1 mm, or 0.5 mm, on average, of an inwardmost edge  36  of the upstream panel  32 . 
         [0037]    The major frame segment  20  further includes an outer side wall  40  and an inner side wall  42 . The outer side wall  40  extends outward and downstream from the upstream panel  32 , and is foldably connected thereto by a fold line  44 . The inner side wall  42  extends outward and downstream from the downstream panel  30 , and is foldably connected thereto by a fold line  46 . The outer and inner side walls  40 ,  42  are connected at a fold line  48 . Such fold lines can be provided by any known method, such as by scoring, partially perforating, or using any other suitable method to provide a path along which a fold may be preferentially formed. Further, at least the fold line  46  may not be a line of folding pre-scored or otherwise pre-imparted into a material of the major frame segment  20 ; any folding or curvature at or between a combination of the upstream panel  32  and the inner side panel  42  can be accomplished by the techniques and equipment used in the assembly process. In some embodiments, all four of the major frame segments  20  ( FIG. 1 ) include the panels  30 ,  32  and the side walls  40 ,  42 , along with the foldable connections therebetween. In this context, the term “foldable” signifies that the major frame segment  20  is formed (i.e., into the general configuration of  FIG. 2 ) by folding the various panels and side walls of the major frame segment  20  relative to each other along the various fold lines (as described in detail below). The term does not denote that the frame segment (or the entirety of the frame  14 ), once formed, is foldable in the sense that it can be collapsed or folded flat. In fact, as will be made clear herein, in various embodiments the frame  14 , once formed, may not be collapsible or foldable. 
         [0038]    In various embodiments, the outer side wall  40  and the inner side wall  42  are positioned at an angle to each other (when viewed in cross section as shown in  FIG. 2 , and as measured by the vertex provided by the fold line  48 ) of less than about  40 ,  30 ,  20 , or  10  degrees. In further embodiments, the outer side wall  40  and the inner side wall  42  can be generally parallel to each other. Regardless, the inner side wall  42  is oriented at a nominal tilt angle T of greater than 90 degrees (preferably at least 95 degrees) to about 150 degrees relative to the downstream panel  30 . For example, in the exemplary embodiment of  FIG. 2 , the inner side wall  42  is oriented at a tilt angle T of approximately 130 degrees from the downstream panel  30 . The designation “nominal” is used in recognition of the fact that this tilt angle T may occur along the elongate length of the major frame segment  20 . Often the outer side wall  40  may form a generally similar angle with respect to the upstream panel  32 . 
         [0039]    In specific embodiments in which the side wall tilt angle T is greater than 90 degrees, the framed air filter  10  may not be nestable. In other embodiments in which the side wall tilt angle T is greater than 90 degrees (e.g., is greater than about 105 degrees), the framed air filter  10  may be nestable. By “nestable” it is meant that multiple framed air filters  10  (of the same shape and size) can be stacked so that they collectively occupy less than 90% of the total height obtained by multiplying the depth of each framed air filter  10  by the number of framed air filters  10 . For purposes of such calculation, the depth of a framed air filter is the distance, along an axis normal to the major plane of the framed air filter, from the farthest downstream point of the framed air filter (which, in the depiction of  FIG. 2  is the fold line  48 ) to the farthest upstream point of the framed air filter (which, in the depiction of  FIG. 2 , is the upstream panel  32 ). 
         [0040]    With the above explanations in mind, and returning to  FIG. 1 , in some embodiments, pairs of the major frame segments  20  (each including the panels and side walls described above) are formed from a single, common material strip. For example, the first and second major frame segments  20   a,    20   b  can be formed from a first material strip  60  (referenced generally), whereas the third and fourth major frame segments are formed from a second material strip  62  (referenced generally). In other embodiments, three or all four of the major frame segments  20   a - 20   d  are formed from a single, common material strip. Regardless, and as described in greater detail below, the single material strip  60 ,  62  integrally forms at least one of the frame corners  22  upon final, folded assembly (e.g., as identified in  FIG. 1 , the first material strip  60  integrally forms the frame corner  22   a  at the intersection of the first and second major frame segments  20   a,    20   b ). 
         [0041]    The material strip(s)  60 ,  62  can be made of any suitable material, such as paperboard, plastic, metal, etc., into which may be imparted fold or score lines as described herein. In some embodiments, the material strip(s)  60 ,  62  can be made of paperboard of thickness in the range of 20-30 thousandths of an inch. In some embodiments, the material strip(s)  60 ,  62  is single-layer paperboard rather than corrugated paperboard. 
         [0042]    With embodiments in which pairs of the major frame segments  20  are formed by two material strips, the first and second material strips  60 ,  62  can be substantially identical.  FIG. 3  provides a plan view of a portion of an exemplary embodiment of the first material strip  60  in a flat state (i.e., prior to folding to the final folded state of  FIGS. 1 and 2 ). It will be understood that geometries, etc., associated with the FIGURES of the present application, including but not limited to the views of  FIGS. 3 and 6 , is not necessarily to scale. As indicated above, the first material strip  60  will be folded/processed to form the first and second major frame segments  20   a,    20   b  (referenced generally in  FIG. 3 , shown in greater detail in  FIG. 1 ), and thus in the flat state forms or includes various sections that will become the panels and side walls (described above) of the first and major frame segments  20   a,    20   b.  Thus, and as identified in  FIG. 3 , the first material strip  60  includes the downstream and upstream panels  30   a,    32   a  of the subsequently created first major frame segment  20   a,  as well as the downstream and upstream panels  30   b ,  32   b  of the subsequently created second major frame segment  20   b.  The outer and inner side walls  40   a ,  42   a  of the subsequently created first major frame segment  20   a  are provided, as are the outer and inner side walls  40   b,    42   b  of the subsequently created second major frame segment  20   b.  As shown, in the flat state, the downstream panels  30   a,    30   b  are generally aligned with one another relative to a length of the material strip  60 , as are the inner side walls  42   a,    42   b,  the outer side walls  40   a,    40   b,  and the upstream panels  32   a,    32   b.  However, only the outer side walls  40   a,    40   b  are contiguous or connected to one another along a length of the material strip  60 . A first cut-out section  70  is formed through a thickness of the material strip  60  that physically separates the first major frame segment downstream panel  30   a  from the second major frame segment downstream panel  30   b,  and physically separates the two inner side walls  42   a,    42   b.  A second cut-out section  72  is formed through a thickness of the material strip  60  that physically separates the first major frame segment upstream panel  32   a  from the second major frame segment upstream panel  32   b.  A side edge  74  of the first upstream panel  32   a  is thus spatially separated from an opposing side edge  76  of the second upstream panel  32   b  in the flat state (in being understood that the first and second upstream panels  32   a,    32   b,  each extend to and terminate at a second, opposite side edge, respectively, that is not shown in the partial view of  FIG. 3 ). The side edges  74 ,  76  may or may not be parallel. In some embodiments, a slightly non-parallel relationship is desired to promote improved fit upon final assembly due to material thickness, process tolerances, etc. 
         [0043]    Aspects of the present disclosure relate to features of the second cut-out section  72  and at an intersection of the two outer side walls  40   a,    40   b  that promote simple or ready transition of the material strip  60  from the flat state (of  FIG. 3 ) to the final assembled state (of  FIG. 1 ) in which the material strip  60  integrally forms one of the frame corners  22  ( FIG. 1 ) as well as two of the major frame segments  20  ( FIG. 1 ). Optional features provided at one or more of the downstream panels  30   a,    30   b  and the inner side walls  42   a,    42   b  that can promote the material strip  60  self-maintaining the folded state are described below. 
         [0044]    A joint section  80  (referenced generally) is defined along a region of intersection between the two outer side walls  40   a,    40   b  by various fold or score lines. As a point of clarification, the outer side walls  40   a,    40   b  can each be viewed as having opposing major edges in the lateral direction, with the corresponding major edges of the outer side walls  40   a,    40   b  being substantially aligned with one another; for example, the first outer side wall  40   a  defines opposing major edges  82   a,    84   a,  whereas the second outer side wall  40   b  defines opposing major edges  82   b,    84   b.  The first major edges  82   a,    82   b  each correspond with, or are defined at, the corresponding fold line  48   a,    48   b  between the respective outer side wall  40   a,    40   b  and the corresponding inner side wall  42   a,    42   b.  The second major edges  84   a,    84   b  each correspond with, or are defined at, the corresponding fold line  44   a,    44   b  between the respective outer side wall  40   a,    40   b  and the corresponding upstream panel  32   a,    32   b.  In a region of the second cut-out section  72 , the second major edges  84   a,    84   b  are exposed or not otherwise connected to any other physical structure of the material strip  60 . Stated otherwise, the joint section  80  can be described as having a trailing edge  86  collectively defined by portions of the second major edges  84   a,    84   b  at the second cut-out section  72 . With these designations in mind, the joint section  80  includes a first or vertical score line  90  formed at the point of intersection of the outer side walls  40   a,    40   b.  The vertical score line  90  can substantially bisect a shape of the second cut-out section  72 . A second score line  92  is formed in the first major frame segment outer side wall  40   a,  extending between the first and second major edges  82   a,    84   a  at an angle that is non-perpendicular and non-parallel relative to the lines defined by the major edges  82   a,    84   a.  For example, the second score line  92  can extend from a point of intersection with the vertical score line  90  at the first major edge  82   a  to the second major edge  84   a  at a location that is laterally off-set or spaced from the vertical score line  90 . In some embodiments, a location of the second score line  92  at the second major edge  84   a  is substantially aligned with the side edge  74  of the first upstream panel  32   a.  A substantially identical third score line  94  is formed in the second major frame segment outer side wall  40   b,  extending between the corresponding first and second major edges  82   b,    84   b.  The third score line  94  can be a substantially mirror image of the second score line  92  relative to the vertical score line  90 , extending from a point of intersection with the vertical score line  90  at the first major edge  82   b  to a point along the second major edge  84   b  that can be substantially aligned with the side edge  76  of the second upstream panel  32   b.  As a point of clarification, the term “score line” is used herein to assist the reader in distinguishing the score lines  90 - 94  from the various fold lines described above. However, the “score lines”  90 - 94  are not limited to being formed by a scoring operation, but instead are more generically fold lines that can be provided by any known method, such as scoring, partially perforating, or using any other suitable method to provide a path along which a fold may preferentially be formed. 
         [0045]    The vertical and second score lines  90 ,  92  combine to define a triangular flap  100   a  in the first outer side wall  40   a.  A substantially similar triangular flap  100   b  is defined in the second outer side wall  40   b  by the vertical and third score lines  90 ,  94 . As shown, the three score lines  90 - 94  substantially intersect at a common point  110  at an intersection of the first major edges  82   a,    82   b.  The three score lines  90 - 94  allow the triangular flaps  100   a,    100   b  to inwardly fold in forming the frame corner  22   a  ( FIG. 1 ), which allows the common point  110  (and thus the first major edges  82   a,    82   b ) to remain spatially stationary while pulling the second major edges  84   a,    84   b  inward toward one another. Further, the second cut-out section  72  optionally spans the full width of the joint section  80  (i.e., distance between the second and third score lines  92 ,  94  at the contiguous second major edges  84   a,    84   b ), allowing the first and second upstream panels  32   a,    32   b  to overlap one another in forming the frame corner  22   a.    
         [0046]    In some embodiments, the corner is not symmetric. In some instances, having non-symmetric corners permits the filters and/or frames to better nest. In some embodiments, one or both of the upstream panels  32   a,    32   b  over or under hanging the corresponding score line  92 ,  94  (e.g., the side edge  74  of the first upstream panel  32   a  can be off-set from the terminal end of the second score line  92  at the second major edge  84   a  and/or the side edge  76  of the second upstream panel  32   b  can be off-set from the terminal end of the third score line  94  at the second major edge  84   b ). Some embodiments include score lines  92 ,  94  with an asymmetric geometry relative to score line  90 . Such an arrangement may help predispose the folded flap to one side during assembly. Additionally or alternatively, such an arrangement may promote improved fit upon final assembly due to material thickness, process tolerances, etc. 
         [0047]    Transitioning of the material strip  60  from the flat state of  FIG. 3  to the final, folded state is reflected in  FIGS. 4A and 4B . For ease of explanation, the downstream panels  30   a,    30   b  ( FIG. 3 ) and the inner side walls  42   a,    42   b  ( FIG. 3 ) are omitted from the views of  FIGS. 4A and 4B . As shown, the material strip  60  has been folded to integrally form the first and second major frame segments  20   a,    20   b  and the frame corner  22   a.  In particular, the first and second outer side walls  40   a,    40   b  have been pulled toward one another, with a structure of the joint section  80  effectively pivoting at the common point  110 . The material strip  60  has folded along each of the score lines  90 - 94  (it being understood that in the views of  FIGS. 4A and 4B , the second score line  92  is hidden), with the second and third score lines  92 ,  94  being brought into substantial abutment with one another. The triangular flaps  100   a,    100   b  (it being understood that the triangular flap  100   a  of the first outer side wall  40   a  is hidden in the views of  FIGS. 4A and 4B ) project or fold inwardly away from a remainder of the corresponding outer side wall  40   a,    40   b.    FIGS. 4A and 4B  illustrates that with the folding action, the trailing edge  86  of the joint section  80  has “lifted” upwardly from a plane of the fold lines  44   a,    44   b  between the second side walls  40   a,    40   b  and the corresponding upstream panel  32   a,    32   b.  The joint section  80  thus has a folded, triangular shape in the final, folded state, and can be arranged or nested against one of the two outer side walls  40   a,    40   b  (in the views of  FIGS. 4A and 4B , the joint section  80  is arranged or nested substantially against the outer side wall  40   a  of the first major frame segment  20   a ). Further, as the outer side walls  40   a,    40   b  are pulled toward one another, the upstream panels  32   a,    32   b  are brought into an overlapping arrangement. For example, in  FIGS. 4A and 4B , the upstream panel  32   b  of the second major frame segment  20   b  is disposed over the upstream panel  32   a  of the first major frame segment  20   a.  Alternatively, the first upstream panel  32   a  can be arranged over the second upstream panel  32   b  during the folding process. Regardless,  FIG. 4B  illustrates that upon completion of the folding process, the material strip  60  in the final folded form defines the tilt angle T in both of the first and second major frame segments  20   a,    20   b.    
         [0048]    A geometric analysis of the joint section  80  is considered in  FIG. 5 , which denotes the relationship between a length H of the outer side walls  40   a,    40   b  and a one-half width distance B of the second cut-out section  72 . The geometric relationship established by the angle of the second and third score lines  92 ,  94  relative to the corresponding second major edge  84   a,    84   b  effectively establishes the nominal tilt angle T ( FIG. 4B ) between the outer side wall  40   a,    40   b  and the corresponding upstream panel  32   a,    32   b  in the final, folded state of the major panel segments  20   a,    20   b  ( FIGS. 1 and 2 ) as described above. For example, in folding the material strip  60  from a square corner in the flat state, the outer side walls  40   a,    40   b  each “push” inwardly in two dimensions at the corresponding triangular flap  100   a,    100   b  by the one-half width distance B, generating a tilt angle T that can be approximated (assuming zero material thickness) as: 
         [0000]      tilt angle ( T )=arc sin ( B/H ). 
         [0049]    Given this relationship, the material strip  60  can be designed to provide a wide range of tilt angles in the resultant frame segment  20  ( FIG. 1 ), and thus in the frame  14  ( FIG. 1 ) as a whole, that in turn can provide varying degrees of nestability as desired for a particular application. By way of several non-limiting examples, assuming an outer side wall length H of ⅞ inch, a one-half width distance B of 1 inch provides a tilt angle T of approximately 125 degrees; a one-half width distance B of 0.5 inch provides a tilt angle T of approximately 107 degrees; a one-half width distance B of 1.5 inches provides a tilt angle T of approximately 149 degrees. 
         [0050]    Returning to  FIG. 3 , the first cut-out section  70  is sufficiently sized so that the downstream panels  30   a,    30   b  and inner side walls  42   a,    42   b  do not interfere with the above-described transitioning of the material strip  60 , and in particular the joint section  80 , from the flat state of  FIG. 3  to the final folded state of  FIGS. 4A and 4B . In general terms, following arrangement of the material strip  60  to the folded state of  FIGS. 4A and 4B  (in which the joint section  80  is folded inwardly and upwardly, and the upstream panels  32   a,    32   b  overlap one another as described above), the inner side walls  42   a,    42   b  are each folded downwardly over the corresponding outer side wall  40   a,    40   b,  and the downstream panels  30   a,    30   b  are each folded/arranged over the corresponding upstream panel  32   a,    32   b  as generally reflected in  FIG. 2 . In some embodiments, it may be beneficial for the material strip  60  to include features whereby the two or more of the inner side walls  42   a,    42   b  and the downstream panels  30   a,    30   b  interface with one another to more robustly self-retain the final, folded state. For example, and as shown in  FIG. 6 , a locking tab  120  and a slot  122  can be provided. The locking tab  120  is formed as a projection from an edge of the one of the upstream panels  30   a,    30   b,  whereas the slot  122  is formed in the other downstream panel  30   a,    30   b . With the exemplary embodiment of  FIG. 6 , the locking tab  120  is provided with the downstream panel  30   a  of the subsequently created first major frame segment  20   a,  whereas the slot  122  is formed in the downstream panel  30   b  of the subsequently created second major frame segment  20   b.  An opposite relationship is equally acceptable. Upon final assembly to the folded state, the locking tab  120  is inserted or tucked into the slot  122  and frictionally retains the material strip  60  in the folded state. A wide variety of other self-retention type features or arrangement are equally acceptable, for example any of the features described in U.S. Publication No. 2013/0327004, entitled “Framed Air Filter With Offset Slot, and Method of Making,” the entire teachings of which are incorporated herein by reference. In summary, the self-retention features, where included, can provide that components of two neighboring major frame segments otherwise integrally formed by a single material strip may interact with each other in a self-stabilizing manner so as to collectively reduce the tendency of the material strip to unfold from the folded state. With additional reference to  FIG. 1 , a thus-formed frame corner  22  of the frame  14  (as integrally formed by the single material strip  60 ) may thus be self-stabilizing while the frame  14  is in a partially assembled condition. 
         [0051]    In related embodiments, locking tabs and/or slots can be provided along the material strip  60  at locations opposite the joint section  80  that facilitate connection between two, separate material strips in completing the frame  14 . For example, with the exemplary embodiment, the first and second material strips  60 ,  62  can provide complimentary, interlocking-type features that assemble to one another in forming the second and fourth frame corners  22   b,    22   d  as would be apparent to one of ordinary skill (and examples of which are provided in the &#39;004 Publication). 
         [0052]    While the discussions above have focused primarily on the exemplary case of two separate material strips  60 ,  62 , it will be appreciated that the present disclosure is not limited to such cases. Thus, the use of the integrated nestable joint as disclosed herein encompasses the use of such a feature in the producing of the complete frame  14  by the folding of a single, integral material strip. The single, integral material strip could include three of the joints as described above that otherwise assist in forming three of the frame corners  22  as part of a folding operation. The fourth frame corner  22  could be defined as the single material strip were folded to bring opposing ends thereof into a substantially abutted relationship (and that may include the interlocking features described above). Regardless, frames  14  of the present disclosure can be formed to any desired shape and size (e.g., standard nominal sizes of 20″×20″×1″, 20″×25″×1″, etc.). 
         [0053]    Complete assembly of the framed air filter  10  includes arranging the one (or more) material strips  60  to the folded state of  FIGS. 4A and 4B ; where two of the material strips  60 ,  62  are provided, the so-folded strips  60 ,  62  are interlocked to one another as described above. With the downstream panel  30  lifted away from the corresponding upstream panel  32 , a suitable bonding adhesive can be deposited on to the exposed downstream face of the upstream panel  32  of each of the major frame segments  20 . An additional bonding adhesive can optionally be deposited between the joint section  80  and the outer side wall  40  to which abutted contact or nesting is desired. In some cases, it may be desirable to apply additional adhesive for attaching the outer and inner side walls  40 ,  42 . The filter media  12  may then be placed into the partially-complete frame  14 , with a bondable border area of the filter media  12  in overlapping relation with at least a portion of the upstream panel  32 . While the exemplary illustration of  FIG. 2  shows the perimeter  16  of the filter media  12  terminating at a particular point between the downstream and upstream panels  30 ,  32 , any suitable design can be used. For example, the edge of the filter media  12  may extend into the space between the outer and inner side walls  40 ,  42  as desired. Additional bonding adhesive may be deposited atop the downstream face of the filter media  12 ; or (depending e.g., on the viscosity of the adhesive and the porosity and wicking characteristics of the filter media  12 ), some of the previously-applied bonding adhesive may penetrate through the filter media  12  and minimize or eliminate the need to apply additional adhesive. The material strip(s)  60 ,  62  is then further folded as described above to bring the downstream panels  30  into contact with the downstream face of the filter media  12 ; where provided, the complimentary interlocking features provided with the material strip(s)  60 ,  62  are engaged to complete the frame  14  and prevent the material strip(s)  60 ,  62  from unfolding as the bonding adhesive cures. 
         [0054]    It has been found that with the designs of the present disclosure, the desired tilt angle T of the outer and inner side walls  40 ,  42  of the completed frame  14  may be largely, or completely, set by the design of the material strips  60 ,  62  themselves, rather than having to use special tooling to dictate the tilt angle T. Such tooling may nevertheless be used if desired. It has further been found that filter frames as disclosed herein, once fully assembled and with the bonding agent fully solidified, are not collapsible. That is, in ordinary handling, packaging, and use of the framed air filters of the present disclosure, the side walls  40 ,  42  cannot be fully flattened outward into the major plane of the filter media  12  to any significant extent, nor can they be flattened inward into the major plane of the filter media  12  to any significant extent, without causing unacceptable damage to the frame  14 . The term “fully flattened” is used in recognition of the fact that it might be possible, especially in the case of a very long (e.g., 25 inches or more) major frame segment, to appreciably deform a section of the frame  14  toward the center of the elongated length of the frame  14 . However, for purposes of denoting a frame as not collapsible, it will be appreciated that even if some such deformation toward the center of the elongated length of the frame  14  is possible, it will not be possible in the sections of the frame  14  that are proximate (e.g., within a few centimeters of) the frame corners  22 . 
         [0055]    Any suitable air filter media can be used as the filter media  12 . The air filter media  12  may conveniently comprise the rectangular-shaped perimeter  16  that in turn may be sized and shaped to match the size and shape of the frame  14  (or vice-versa). The filter media  12  is typically sheet-like, with a length and width that are greater than a thickness of the filter media  12  and with an overall planar configuration (even if pleated). Although  FIGS. 1 and 2  illustrate the filter media  12  as being non-pleated, any suitable filter media format, including pleated, may be used. As a point of reference, one common technique for incorporating a pleated filter media into the “pinch” type frames of the present disclosure is to flatten the pleats on two or four edges of the pleated filter media pack to provide a more planar region to be captured between the downstream and upstream panels  30 ,  32 . In some embodiments, the filter media  12  can comprise an electret-comprising nonwoven material. In some embodiments, the filter media  12  may comprise fiberglass fibers. 
         [0056]    In some embodiments, the filter media  12  (whether pleated or in a substantially flat state or otherwise) may include one or more layers comprising an open cell structure, a porous media, one or more nonwoven scrims, reinforcing filaments, nettings, wire meshes, or any such structure(s) that may be provided along with the filter media  12  (e.g., bonded thereto) and which can be made of any suitable material. Whether inherently, or by way of a reinforcing layer, it may be advantageous that the filter media  12  be sufficiently strong to survive the air pressure applied in conventional forced-air heating and/or cooling systems. Further advantages maybe gained if the filter media  12  is able to enhance the frame strength, for example by distributing the air-pressure load over the various portions of the frame  14 . 
         [0057]    In some embodiments, the filter media  12  may comprise a bondable border area that may be sandwiched between portions of the downstream and upstream panels  30 ,  32 , and may be attached to one or both panels (e.g., by adhesive and/or by mechanical fasteners such as staples). Although not shown in  FIG. 2 , some filter media useful with the present disclosure may be somewhat compressible, such that the capturing of the filter media  12  between the downstream and upstream panels  30 ,  32  and the pressing of the frame  14  may cause the filter media  12  to be compressed (e.g., as much as 10, 20, 30% or more) from its uncompressed thickness. 
         [0058]    Although specific embodiments of the present disclosure have been shown and described herein, it is understood that these embodiments are merely illustrative of the many possible specific arrangements that can be devised in application of the principles of the present disclosure. Numerous and varied other arrangements can be devised in accordance with these principles by those of ordinary skill in the art without departing from the spirit and scope of the present disclosure. Thus, the scope of the present disclosure should not be limited to the structures described in this application, but only by the structures described by the language of the claims and the equivalents of those structures.