BACKGROUND OF THE INVENTION 
     This invention relates generally to filters and more particularly, but not by way of limitation, to collapsible filter apparatus for removing particulates from an airstream adapted for use in a paint booth. 
     Filters, including air filters, are used for a variety of applications. Generally, an air filter fits in a housing and has a filter media which removes undesired particles from a fluid, typically an airstream. Depending on its specific application, the filter media is adapted to remove dust, dirt, paint, fumes and/or other particles. 
     In paint booths, i.e., paint overspray control or paint arrester applications, a filter is placed in the exhaust airstream of the paint booth or similar structure. Paint spray residual that does not adhere to the article being painted is entrained in the airstream of the exhaust porting from the paint booth. The airstream passes through the filter positioned at an air intake before it is exhausted into the environment. 
     A few types of filters are commonly used in paint booths and similar applications. One is a rigid, non-collapsible, framed filter. The framed filter is designed to fit snugly in the modular frame of the exhaust airstream of the paint booth. A framed filter typically requires no clips or other additional parts to secure the filter to the modular frame of the paint booth, but does require the use of a rear supporting grid either built into the filter or placed behind the filter in the modular frame to prevent the filter from being drawn through the modular frame into the exhaust duct. 
     Shipping, storing and disposing non-collapsible framed filters is expensive and burdensome due to the volume of the filters. However, such volume is necessary in an expanded state in order to effectively and efficiently remove and entrain paint from an airstream. 
     Another type of filter which attempts to overcome these disadvantages is a frameless accordion-type filter media typically manufactured in long sections, i.e., twenty to thirty feet long, and cut to length to fit a particular modular frame of the paint booth. The expandable/collapsible filter medium is formed of paperboard, cardboard and/or honeycomb to create an inexpensive and effective filter means. The collapsible design of these filters greatly reduces the shipping, storage and disposal costs of the filter. However, the filter must be cut and a rear supporting grid typically must be used to secure the filter. Also, clips or wire fasteners must be used to secure the edges of the filter to the modular frame of the air intake. 
     Another attempt to overcome these disadvantages is illustrated in U.S. Pat. No. 5,252,111 to Spencer, deceased et al., which is incorporated herein by reference. This patent describes a multi-ply expandable filter media formed of honeycomb and a corresponding expandable frame. However, the frame lacks strength because it is not continuous and appears to require the use of a rear supporting grid. 
     Thus, there is a need for improved filter apparatus which are collapsible, expandable, strong and which do not require the use of clips or a rear supporting grid. 
     SUMMARY OF THE INVENTION 
     The present invention provides improved filter apparatus which meet the needs described above. 
     The invention includes filter apparatus for removing air entrained particulates comprising a collapsible filter media. The filter media has a periphery. A continuous frame extends around and attaches to the periphery of the filter whereby the filter media and attached frame together can be lengthwise collapsed. 
     The invention also includes a filter apparatus comprising a collapsible filter media. The filter media has a first end substantially parallel to a second end and a top substantially parallel to a bottom. The first and second ends each have an upper portion and a lower portion. The filter apparatus also has a frame for supporting the filter media. The frame has an upper frame member connecting the upper portion of the first end and the upper portion of the second end and spanning the top of the filter media. The frame has a lower frame member connecting the lower portion of the first end to the lower portion of the second end and spanning the bottom of the filter media. The frame has a plurality of fold points located on the upper frame member and on the lower frame member such that the upper frame member and the lower frame member can be folded to collapse the filter media lengthwise between the first end and the second end. 
     The invention further includes a filter apparatus configurable between a collapsed state and an expanded state. The filter apparatus is a corrugated filter media for removing particulates from an airstream. The filter media has a periphery comprising a first end and a second end, the filter media being collapsible between the first and second ends. The filter apparatus includes a continuous frame for supporting the filter media extending around the periphery of the filter media and connecting to the first end and the second end of the filter media. The frame has a plurality of fold points at which the frame can be folded such that the frame together with the filter media are lengthwise collapsible, whereby an overall height of the filter apparatus in the collapsed state is not significantly greater than the overall height of the filter apparatus in an expanded state. 
     It is therefore an general object of the present invention to provide improved filter apparatus. Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially cutaway front elevation view of the apparatus of the present invention shown in an expanded state. 
     FIG. 2 is a sectional view along lines  2 — 2  of FIG.  1 . 
     FIG. 3 is a front elevation view of the apparatus of the present invention shown in a collapsed state. 
     FIG. 4 is a front elevation view of an alternate embodiment of the present invention shown in a collapsed state. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, presently preferred embodiments of the invention and their operation are illustrated. Like reference numerals generally refer to like parts throughout the drawings and this description. 
     Directional terms—specifically including but not limited to upper, lower, top, bottom, upstream, downstream, left and right—have been used throughout the specification and claims. These directional terms have been used solely for clarity in describing the application and do not limit the invention to any specific orientation. In other words, filter apparatus  10  of the present invention can be rotated about any of its axes and still function as intended. 
     Referring to FIG. 1, the filter apparatus of the present invention is shown and designated generally by the numeral  10 . Apparatus  10  has a filter media  12  for removing particulates from a fluid flow such as an airstream. Filter media  12  is preferably a rectangular shaped, multi-ply media such as that described in U.S. Pat. No. 3,075,337 to Erhard C. Andreae, which patent is incorporated herein by reference. Alternately, filter media  12  is formed as described in U.S. Pat. No. 5,051,118 to Robert Andreae, which patent is incorporated herein by reference. 
     Referring to FIG. 1, filter media  12  has a periphery  14 . Periphery  14  includes a first end  16  which has an upper portion  18  and a lower portion  20 . Periphery  14  of filter media  12  also includes a second end  22  which is substantially parallel to first end  16 . Second end  22  has an upper portion  24  and a lower portion  26 . Periphery  14  of filter media  12  also has a top  28  substantially parallel to a bottom  30 . Opposite ends of top  28  connect with upper portion  18  of first end  16  and to upper portion  24  of second end  22 , respectively. Similarly, opposite ends of bottom  30  connect to lower portion  20  of first end  16  and to lower portion  26  of second end  22 , respectively. The junctions of ends  16 ,  22 , top  28  and bottom  30  form four corners  32  at approximate right angles such that filter media  12  is substantially rectangular in shape. 
     Referring to FIGS. 1 and 2, filter media  12  is preferably an accordion-type, multi-ply corrugated filter which separates particles from an airstream by inertia. More specifically, filter media  12  has a first media member or upstream wall  34 . First media member  34  has upstream folds  36  which are substantially parallel and extend from top  28  to bottom  30  of periphery  14  of filter media  12 . First media member  34  also has downstream folds  38  which are substantially parallel and extend from top  28  to bottom  30  of periphery  14  of filter media  12 . First media member  34  has walls  40  extending from top  28  to bottom  30  which are the portions of first media member  34  which separates upstream folds  36  and downstream folds  38 . 
     First media member  34  has a plurality of apertures  42  disposed in first media member. Preferably, apertures  42  are circular, are located upon downstream folds  38  and are vertically and horizontally aligned as shown in FIG.  1 . Most preferably, apertures  42  are slightly offset on downstream folds  38  such that approximately 60% of an aperture  42  is positioned on one side of a downstream fold  38  and 40% of the aperture  42  is positioned on the other side of the downstream fold  38 . The offset nature of apertures  42  helps to create a swirling effect which increases the efficiency of removing particles from the airstream. 
     Filter media  12  has a second media member or downstream wall  44  attached in complementary relationship with first media member  34 . Similar to the structure of first media member  34 , second media member  44  has upstream creases  46  and downstream creases  48  extending from top  28  to bottom  30 . Upstream creases  46  and downstream creases  48  are separated by walls  50 . Second media member  44  has holes  52  positioned on walls  50  of second media member  44 , i.e., located between upstream creases  46  and downstream creases  48 . As with apertures  42  of first media member  34 , holes  52  of second media member  44  are aligned vertically and horizontally. 
     First media member  34  and second media member  44  are positioned in a complementary relationship with each other. Upstream folds  36  of first media member  34  are aligned with upstream creases  46  of second media member  44 . Similarly, downstream folds  38  of first media member  34  are aligned with downstream creases  48  of second media member  44 . First media member  34  of second media member  44  are attached by any suitable means including glue, staples and other bonding means. In a preferred embodiment, the front of upstream creases  46  of second media member  44  is glued to the back of upstream folds  36  of first media member  34 . 
     In a preferred embodiment, walls  50  of second media member  44  are wider than walls  40  of first media member  34  such that V-shaped chambers  54  are created between first media member  34  and second media member  44 , i.e., between walls  40  of first media member  34  and walls  50  of second media member  44 . 
     When first media member  34  and second media member  44  are attached, apertures  42  of first media member  34  are offset from holes  52  in second media member  44 . Most preferably, apertures  42  and holes  52  are offset in both vertical and horizontal directions. The offset orientation of apertures  42  and holes  52  creates a swirling effect on the particle ladened airstream such that the particles are deposited on the first and second media members  34 ,  44  such that substantially clean free air exits through the rear of the filter. 
     In a preferred embodiment, first media member  34  and second media member  44  are each formed of a single piece of two ply, 47 pound per msf (1000 square feet) paper board. In high moisture environments, 53 pound paper board forms first media member  34  and 47 pound paper board forms second media member  44 . However, many materials are suitable as the filter media of the present invention, specifically including but not limited to cardboard, fiber weave, mesh, polyester, fiberglass, aluminum and combinations thereof. 
     In addition to first and second media members  34 ,  44 , additional media members can be added, i.e., such as third and fourth media members to improve the efficiency of removing particles in the airstream. Any additional media members can also be formed of a variety of filter materials. In another alternate embodiment, first media member  34  is formed of paperboard as previously described and second media member  44  is formed of thin polyester material as described in U.S. Pat. No. 5,051,118. 
     Referring to FIG. 1, filter apparatus  10  has a frame  56  attached to periphery  14  of filter media  12 . Frame  56  has an upper frame member  58  connecting upper portion  18  of first end  16  of periphery  14  of filter media  12  to upper portion  24  of second end  22  of periphery  14  of filter media  12 . Similarly, frame  56  has a lower frame member  60  connecting the lower portion  20  of first end  16  of periphery  14  of filter media  12  to lower portion  26  of second end  22  of periphery  14  of filter media  12 . Upper frame member  58  and lower frame member  60  span top  28  and bottom  30 , respectively, of periphery  14  of filter media  12 , but do not attach to top  28  or bottom  30 . 
     Frame  56  also includes left frame member  62  and right frame member  64 . Ends of left frame member  62  connect to an end of upper frame member  58  and to an end of lower frame member  60 , respectively. Similarly, ends of right frame member  64  connect to an end of upper frame member  58  and to an end of lower frame member  60 , respectively. In an expanded or unfolded state as shown in FIG. 1, upper frame  58  is substantially parallel to lower frame member  60 . Similarly, left frame member  62  is substantially parallel to right frame member  64  such that frame  56  forms a rectangle. 
     Left frame member  62  is attached to first end  16  of periphery  14  of filter media  12 . Similarly, right frame member  64  is attached to second end  22  of periphery  14  of filter media  12 . Attachment may be accomplished by any suitable means such as gluing, tacking, bonding, stapling, etc., but preferably is attached by glue. 
     Preferably, frame members  58 ,  60 ,  62 ,  64  are formed of a single piece of 200 pound per inch, B-fluted, corrugated double-face cardboard. Most preferably, frame members  58 ,  60 ,  62 ,  64  form a continuous frame  56 . “Continuous” as used herein means an unbroken member; however, a broken member having a gap or splice  66  interposed between or connecting adjacent ends  68  of frame  56  is included within the definition of continuous as used herein. Most preferably, ends  68  of frame  56  overlap and are glued to form the “continuous” frame  56 . Overlapping ends  68  of frame  56  are preferably located either on upper frame member  58  or lower frame member  60  to create a stronger frame, as opposed to left or right frame member  62 ,  64 . Moreover, the orientation of adjacent ends  68  proximately located and attached to filter media  12  is included within the definition of “continuous.” 
     Referring to FIGS. 1 and 3, frame  56  has a plurality of fold points  70  which enable frame  56  and attached filter media  12  together to be lengthwise collapsed, i.e., collapsed between left frame member  62  and right frame member  64 . A “fold point” is a predetermined location at which the frame can be folded to facilitate configuring or transitioning apparatus  10  between an expanded state and a collapsed state. Preferably, fold points  70  are weakened areas in the material of frame  56 . When frame  56  is formed of cardboard, fold points  70  may be created by scoring with a scoring head. 
     In the preferred embodiment shown in FIG. 3, fold points are positioned such that in the collapsed state each the upper frame member  58  and the lower frame member  60  forms an L-shape. In this preferred embodiment, each upper frame member  58  and lower frame member  60  has four fold points. Upper frame member  58  has a first fold point  72  located at the junction between upper frame member  58  and right frame member  64  and a second fold point  74  located at the junction of left frame member  62  and upper frame member  58 . A third fold point  76  is spaced from first fold point a distance approximately equal to the collapsed length of filter apparatus  10  such that third fold point  76  is located adjacent the second fold point  74  in a collapsed state. A fourth fold point  78  is located approximately equidistant between second fold point  74  and third fold point  76 . First portion  80  of upper frame member  58  extends between first fold point  72  and third fold point  76 ; second portion  82  of upper frame member  58  extends between third fold point  76  and fourth fold point  78 ; third portion  84  of upper frame member  58  extends between second fold point  74  and fourth fold point  78 . 
     Fold points  70  on lower frame member  60  are similarly located. Lower frame member  60  has a first fold point  72 ′ located at the junction between lower frame member  60  and left frame member  62  and a second fold point  74 ′ located at the junction of right frame member  64  and lower frame member  60 . A third fold point  76 ′ is spaced from first fold point a distance approximately equal to the collapsed length of filter apparatus  10  such that third fold point  76 ′ is located adjacent the second fold point  74 ′ in a collapsed state. A fourth fold point  78 ′ is located approximately equidistant between second fold point  74 ′ and third fold point  76 ′. First portion  80 ′ of lower frame member  60  extends between first fold point  72 ′ and third fold point  76 ′; second portion  82 ′ of lower frame member  60  extends between third fold point  76 ′ and fourth fold point  78 ′; third portion  84 ′ of lower frame member  60  extends between second fold point  74 ′ and fourth fold point  78 ′. 
     In the collapsed state illustrated in FIG. 3, the overall height of filter apparatus  10  is not significantly greater than the overall height of the filter in the expanded state. In a preferred embodiment, the overall height of filter apparatus  10  is the same in both the collapsed and expanded states. First portion  80 ,  80 ′ has a length approximately equivalent to the collapsed length of filter apparatus  10 . Second portion  82 ,  82 ′ and third portion  84 ,  84 ′ are approximately equidistant. Second portion  82  abuts third portion  84  which abuts left frame member  62 . Similarly, second portion  82 ′ abuts third portion  84 ′ which abuts right frame member  64 . 
     Referring to FIG. 4, an alternate orientation of fold points  70  is illustrated. Each the upper frame member  58  and the lower frame member  60  has six fold points such that in the collapsed state each the upper frame member  58  and the lower frame  60  forms a U-shape as illustrated in FIG.  4 . 
     In operation, filter apparatus  10  is shipped and stored in a collapsed state as shown in FIG. 3 (or in the alternate embodiment shown in FIG.  4 ). When ready for use, filter apparatus  10  is configured to an expanded state by pulling left frame member  62  and right frame member  64  in opposite directions, resulting in fold points  70  flexing, until upper frame member  58  and lower frame member  60  are approximately straight and parallel. The filter apparatus  10  is then placed in a modular frame fitted for the particular size of filter apparatus  10 . It is unnecessary to secure filter apparatus  10  to the modular frame of the paint booth with clips. It is also unnecessary to use a rear supporting grid since the accordion design of the filter media  12  prevents collapse between upper frame member  58  and lower frame member  60 . 
     An airstream containing undesired particles such as paint particles is pulled toward filter apparatus  10 . The airstream passes through apertures  42  of first media member  34  and then through holes  52  of second media member  44 , with the particles being deposited in various locations of first media member  34  and second media member  44 . The filtered air may pass through one or more second stage filter systems—typically dense polyester weave filters—before the airstream, now substantially free of particles, passes through the exhaust of the filter unit into the environment. When filter apparatus  10  is full or loaded with particles, filter apparatus  10  is removed from the modular frame and may be collapsed by pushing left frame member  62  toward right frame member  58 . Filter apparatus  10  can then be suitably disposed of. 
     Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those inherent therein. While preferred embodiments of the present invention have been illustrated for the purpose of the present disclosure, changes in the arrangement and construction of parts and the performance of steps can be made by those skilled in the art, which changes are encompassed within the scope and spirit of the present invention as defined by the appended claims.
The invention provides a filter apparatus for removing air entrained particles comprising a collapsible filter media. The filter media has a periphery. A continuous frame extends around and attaches to the periphery of the filter media whereby the filter media and attached frame together can be lengthwise collapsed.