Method of making self-supporting pleated filter

A self-supporting, pleated filter, and method of making the same. The method includes forming a plurality of pleats in a filter media that extend along a front face and a rear face. The pleats include a plurality of pleat tips and sloping side surfaces generally perpendicular to the direction of pleating. At least one planar reinforcing strip oriented in the direction of pleating is bonded to the pleat tips on the front face. At least one reinforcing member is positioned along the rear face of the filter media. The filter media is then cut to size. Frame members are applied for some applications. The reinforcing member may be a reinforcing strip oriented in the direction of pleating and bonded to the rear face of the filter media prior to the step of forming the plurality of pleats. A second planar reinforcing strip may optionally be bonded to the reinforcing strip pleat tips. The reinforcing member, the first reinforcing strip and the second reinforcing strip can be aligned to form a truss structure. Alternatively, reinforcing strips oriented perpendicular to the direction of pleating are bonded to the rear face of the filter media prior to the step of forming the pleats. In another embodiment, a reinforcing member is applied to the rear face of the filter media after the pleats have been formed. The reinforcing member is positioned along at least one of the sloping side surfaces of the pleats on the rear face in a direction perpendicular to the direction of pleating. In another embodiment, a scrim is positioned along the rear face of the filter media. The scrim can be bonded to the frame members, the filter media and/or a portion of the frame members extend over a perimeter of the scrim to secure it to the pleated filter.

BACKGROUND OF THE INVENTION

The surface area of filter media is a major factor in determining flow resistance (i.e., pressure drop) and loading capacity of a pleated filter. The surface area of a pleated filter media is determined by the size of the pleated filter, the depth of the pleats, and the pleat density. Since the external dimensions of pleated filters are often restricted by the particular application, the number of pleats per inch (pleat density) can be increased to improve filtration performance.

The ability of air filter media to withstand operating pressures is typically dependent upon the pleat count, the pleat depth and the stiffness of the filter media. The filter media can become unsteady when air pressure is applied to one side. In the event the pleats deform or collapse, a portion of the surface area can be reduced and the pressure drop across the filter element will increase, further increasing the force applied to the filter media.

U.S. Pat. No. 5,618,324 (Sommer, et al.) discloses a self-supporting, accordion folded filter element that includes a planar reinforcing strips bonded to the pleat tips by an adhesive.

A filter element available from Columbus Industries available under the product designation Microshield utilizes a glue bead to provide longitudinal stabilization. The glue bead is applied before the folding of the filter media and connects the folds with one another at the point of application. However, the glue beads require a large quantity of melt bonding agent, resulting in increased cost. Additionally, the glue beads require the pleats to be closely spaced, limiting application of this technique to pleat counts generally greater than about six pleats per inch.

U.S. Pat. No. 4,547,950 (Thompson) discloses a method of spacing the folds of a pleated filter media using a tapered assembly comb having uniformly spaced teeth. Subsequently, a rigid divider is inserted into the separated and folded media to produce a uniformly spaced filter media. Thompson does not disclose automated filter element manufacturing.

Therefore, there is a need for an automated method of manufacturing a pleated filter that has good flow characteristics and exhibits sufficient stability so that the pleats do not collapse or deform when subjected to operating pressure.

SUMMARY OF THE INVENTION

The present invention is directed to a self-supporting, pleated filter for air filtration, and method of making the same. The method of the present invention provides for assembly of the pleated filter by an automated process at a high rate of manufacturing. The pleated filter of the present invention can be used with or without a reinforcing frame structure. The present method and apparatus may utilize conventional filter media, electret media, or a variety of other media suitable for air filtration, such for furnace applications.

In one embodiment, the method of making the self-supporting pleated filter includes forming a plurality of pleats in a filter media that extend along a front face and a rear face. The pleats include a plurality of pleat tips and sloping side surfaces generally perpendicular to the direction of pleating. At least one reinforcing strip oriented in the direction of pleating is bonded to the pleat tips on the front face to form a pleated filter. At least one reinforcing member is positioned along the rear face of the filter media. The filter media is then cut to size. Frame members are optionally applied for some filtration applications. Alternatively, the self-supporting pleated filter can be used without a frame or inserted into a permanent frame that permits the media to be easily changed.

In one embodiment, the step of positioning at least one reinforcing member includes locating one or more elongated reinforcing members oriented in the direction of pleating to the rear face of the filter media prior to the step of forming the plurality of pleats. A plurality of pleats are then formed in the reinforcing member during the step of forming the pleats in the filter media. The pleats formed in the reinforcing member define reinforcing member pleat tips. A second reinforcing strip may optionally be bonded to the reinforcing member pleat tips. In one embodiment, the reinforcing member, the first reinforcing strip and the second reinforcing strip are aligned to form a truss structure. The reinforcing member can optionally be bonded to the filter media.

In another embodiment, the plurality of reinforcing members oriented perpendicular to the direction of pleating are located on the rear face of the filter media prior to the step of forming the pleats. A plurality of pleats are formed in the reinforcing member during the step of forming the pleats in the media. A second reinforcing strip oriented in the direction of pleating may be bonded to the pleat tips of the rear face over the reinforcing member.

In another embodiment, the reinforcing member is inserted into the pleats on the rear face of the filter media after the pleats have been formed. At least one reinforcing member is positioned along at least one of the sloping side surfaces of the pleats on the rear face in a direction perpendicular to the direction of pleating. A second reinforcing strip oriented in the direction of pleating may optionally be bonded to the pleat tips on the rear face over the reinforcing member.

In another embodiment, a scrim is positioned along the rear face of the filter media. The scrim can be bonded to the pleat tips along the rear face. In one embodiment, a portion of the frame members extend over a perimeter of the scrim to secure it to the pleated filter. A scrim refers to a porous mesh, netting or screen. The scrim can be constructed from various metals, plastics or paper-based products.

In another embodiment, a scrim can be substituted for the reinforcing strips located along the front face. The scrim is bonded to the pleat tips on the front face to form a pleated filter. Any of the reinforcing members disclosed herein can be used along the rear face of the pleated filter.

The present method may also include the step of heat setting one or more of the filter media and the reinforcing members after forming the pleats. The step of applying the frame members typically includes positioning a portion of the frame members onto a portion of the front face and the rear face of the filter media. An adhesive is typically applied between the perimeter of the filter media and the frame members. The present method may be performed using a fully automated system. The reinforcing members and reinforcing strips may be constructed from various paperboard products, polymeric materials such as films, or metals configured as elongated strips, scrims, strands or filaments.

The present invention is also directed to a self-supporting pleated filter. The filter media has a plurality of pleats defining a plurality of pleat tips and sloping side surfaces extending along a front face and a rear face. The pleat tips extend perpendicular to a direction of pleating. A planar reinforcing strip oriented in the direction of pleating is bonded to the pleat tips along the front face of the pleated filter. A reinforcing structure is provided along the rear face of the pleated filter. A frame optionally extends around the perimeter of the filter media. In another embodiment, the pleated filter may be inserted into, and subsequently removed from, a reusable frame.

In one embodiment, the reinforcing structure includes one or more reinforcing members extending in the direction of pleating generally along the contour of the pleat tips and sloping side surfaces of the rear face. In one embodiment, the reinforcing members are bonded to the filter media. A generally planar second reinforcing strip oriented in the direction of pleating is bonded to reinforcing member pleat tips on the pleated reinforcing member. In one embodiment, the reinforcing member, the first reinforcing strip and the second reinforcing strip are positioned to define a truss structure.

In another embodiment, the reinforcing structure includes at least one reinforcing member oriented perpendicular to the direction of pleating that is positioned generally along at least one of the sloping side surfaces of the rear face. In one embodiment, the frame extends over distal ends of the reinforcing member. The reinforcing member may also be bonded to the filter media.

In another embodiment, the reinforcing structure includes a scrim that extends over the rear face of the pleated filter. In one embodiment, a portion of the frame extends over a perimeter of the scrim and onto the rear face of the filter media.

In another embodiment, a scrim is substituted for the reinforcing strip located along the front face. The scrim is bonded to the pleat tips on the front face to form a pleated filter. Any of the reinforcing members disclosed herein can be used along the rear face of the pleated filter.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic illustration of a system20for performing the method of the present invention. Filter media22is typically provided on a continuous roll24. The media22may be slit to the desired width at slitting station26. The media22may optionally be preheated at a heating station28to facilitate processing. In the illustrated embodiment, the heating station28is an infrared heater.

In one embodiment, a reinforcing member30is applied to a rear face32of the media22at a location34. As will be discussed in detail below, the reinforcing member30may be applied as one or more continuous strips oriented in the direction of pleating36, as discrete reinforcing members oriented perpendicular to the direction of pleating36, or a variety of other configurations. The reinforcing member30may optionally be bonded to the media22using a variety of techniques, such as adhesive bonding, thermal bonding, solvent bonding, or ultrasonic bonding. In this embodiment, the location34is upstream of rotary-score pleater38that scores the media22and the reinforcing member30prior to pleating. The rotary-score pleater38and pleat folding station40may be modified to accommodate the increased thickness in the filter media22at the location of the reinforcing member30.

The assembly of the media22and the reinforcing member30is advanced through the rotary-score pleater38to a pleat folding station40. Infrared heaters42may optionally be provided for heat-setting the pleats44. The pleats44are retained in an accumulator46until being advanced to a pleat spacing device48that retains the pleats44in the desired pleat spacing. Pleat formation and pleat spacing may be performed by a variety of methods, such as disclosed in U.S. Pat. No. 4,798,575 (Siversson); U.S. Pat. No. 4,976,677 (Siversson); and U.S. Pat. No. 5,389,175 (Wenz).

The pleated filter media60is expanded to the desired pleat spacing in the pleat spacing device48. One or more elongated, planar reinforcing strips62are applied to the pleat tips along the front face64at the station68to maintain the pleat spacing. The reinforcing strips62can be bonded to the pleat tips by various techniques, such as adhesive bonding, thermal bonding, solvent bonding, or ultrasonic bonding. The pleated filter media60and the reinforcing strip62define a pleated filter72that can be cut, machined handled or otherwise processed. The reinforcing strips62provide dimensional stability to the pleats44of the pleated filter72. The pleated filter72can be used in filtration applications, with or without a frame structure, or as an insert into a permanent/reusable frame.

In another embodiment, a scrim62extending substantially across the entire front face64is substituted for the planar reinforcing strips62. The scrim is bonded to the pleat tips to provide dimensional stability to the pleated filter72. Use of a scrim62extending across the front face64may be used in combination with any of the reinforcing members discussed herein.

In the illustrated embodiment, one or more elongated, planar reinforcing strips66are optionally bonded to the rear face32of the pleated filter media60at the station68. In one embodiment, the reinforcing strips66are located over the reinforcing member30and opposite the reinforcing strips62to form truss structures (seeFIG. 6).

In one embodiment, a continuous strip of frame material80is applied to the ends of the pleated filter media60parallel to the direction of pleating36. An adhesive, such as a hot melt adhesive, is applied to a first flange of a U-shaped channel formed from the frame material80at the station87. The adhesive for sealing the ends of the pleats44is applied at station88. A hot melt adhesive is applied to the second flange of the U-shaped channel at station90. The frame material80is bent into its U-shaped configuration at station94. The ends U-shaped channel extend partially onto the front face64and rear face32of the pleated filter media60(seeFIG. 5). An assembly including the endless web of pleated filter media60and attached frame material80is cut at station86to desired lengths. Alternatively, the pleated filter comprising the pleated filter media60and the reinforcing strips62can be cut to size before application of the frame material80.

The pleated filter media60and side frames members92are rotated900at location91to permit application of the end frame members96at a station98. Alternatively, the frame members92,96can be configured as two box structures that are positioned over the first and second faces32,64, respectively, of the pleated filter72, with overlapped circumferential portions, such as disclosed in U.S. Pat. No. 5,782,944 (Justice). In another embodiment, the frame member members92,96can be configured as a one-sided die-cut frame that is folded around the pleated filter72.

In embodiments where the pleated filter media60is used without frame members92,96, the pleated filter72exits the system20after the cutting station86. Alternatively, a pleated filter100with a frame (seeFIG. 2) exits the system20. The pleated filters72,100are typically enclosed in suitable packaging.

Pleat spacing is typically about 3 to about 6 pleats per 2.54 centimeters (1 inch). Pleat depth and the thickness of the filter100is typically about 2.54 centimeters to about 101.6 centimeters (1 inch to 4 inches). For HVAC applications, the length and width of the filter100is typically 30.5 centimeters×30.5 centimeters (12 inches ×12 inches) to about 50.8 centimeters×76.2 centimeters (20 inches ×30 inches). Reference to the front face64or rear face32is for purposes of description only and does not indicate an orientation of the pleated filter100. For example, the reinforcing member30may be positioned upstream or downstream in the air flow.

The resulting pleated filter100in accordance with the present invention is self-supporting. A pleated filter is self-supporting as defined herein when the portion of the pleats44that are not directly supported by the reinforcing member30or the reinforcing strips62,66do not collapse or bow excessively when subjected to the air pressure typically encountered in forced air ventilation systems.

Stiffness of the filter media22is a factor in determining the suitability of a particular filter media for use in the present invention. A Taber V-5 Stiffness Tester, Model 150-B, made by Teledyne Taber of North Tonawanda, N.Y., can be used to evaluate the stiffness of the filter media. The V-5 stiffness tester operates by bending a specimen about 38.1 millimeters wide by about 38.1 millimeters long (1.5 inches by 1.5 inches) to a prescribed angular of deflection and measuring the force, in stiffness units ranging from 0-10, used to obtain this deflection. In many heating, ventilating and air conditioning (HVAC) applications, the air pressure is generally about 125 Pa to about 249.1 Pa (0.5 to 1.0 inch column of water) and the face velocity is approximately 91.5 meters per minute (300 feet per minute). For HVAC filtration applications, the minimum stiffness value is greater than about 1.2 stiffness units, and preferably greater than about 1.5 stiffness units and more preferably greater than about 2 stiffness units.

The U-shaped channel of the side frame members92serve to further stabilize the pleated filter media60and to seal the ends of the pleats44to prevent air bypass in the final pleated filter100. In one embodiment, a viscous adhesive such as a foamed adhesive, a filled adhesive or a caulk is used to seal the ends of the pleats44to the frame members92,96. Latex caulk is well suitable for this purpose since it is low cost and has low volatile organic content. On the other hand, latex caulks have a long set time. Therefore, other adhesives, such as hot melt adhesives, are utilized to bond the two sides of the U-shaped channel formed from the frame material80to the pleat tips44. A variety of techniques may be used for applying the frame members92,96to the pleated filter, such as disclosed in U.S. Pat. No. 4,731,047 (Lobb).

FIG. 3is a top schematic illustration of one embodiment of the present method for making a self-supporting pleated filter. The reinforcing member30is oriented in the direction of pleating36along the rear face32. In one embodiment, the reinforcing member30is bonded to the filter media22. In the illustrated embodiment, the reinforcing member30is strips about 0.64 centimeters to about 2.54 centimeters (0.25 inches to about 1 inch) wide. The filter media22and reinforcing member30are subject to a pleating operation at station40, resulting in pleats being formed in the reinforcing members30. The pleated reinforcing members30include reinforcing member pleat tips120.

The reinforcing strip62is applied to the front face64of the pleated filter media60at the station68to form the pleated filter72(seeFIG. 1). The reinforcing strip66is also bonded to the reinforcing member pleat tips120at the station68. The reinforcing strips62,66provide added dimensional stability to the pleated filter media60to facilitate machine handling. Frame material80is optionally applied to the edges of the pleated filter media60parallel to the direction of pleating36to form side frame members92, as previously discussed. The combination of the pleated reinforcing member30, the reinforcing strips66along the rear face32and the reinforcing strip62along the front face form a truss structure that gives the pleated filter media60its self-supporting properties (seeFIG. 6). The pleated filter media60and frame material80are cut to length at the cutting station86. Alternatively, the pleated filter72can be cut to size prior to application of the frame material80.

FIG. 4is a top schematic illustration of an alternate method in accordance with the present invention. The reinforcing member30is applied to the media22at discrete locations along the rear surface32perpendicular to the direction of pleating36. The reinforcing member30may optionally be bonded to the filter media22. The assembly of the filter media22and the reinforcing member30is subject to the pleating operation at the station40so that the reinforcing member30is simultaneously pleated with the filter media22.

The reinforcing strip62is applied to the front face64of the pleated filter media60at the station68to form the pleated filter72(seeFIG. 1). Reinforcing strips66are optionally applied to the pleat tips along the rear face32at the station68. In the embodiment illustrated inFIG. 4, the side frame members92preferably extend onto the rear face32of the pleated filter media60so that stresses imposed on the reinforcing members30are transmitted to the frame members92.

Turning back toFIG. 1, the reinforcing member30may optionally be inserted directly into the pleated filter media60at a station70. The reinforcing member30can be preformed to correspond to the pleat tips and sloping side surfaces of the pleats44(seeFIG. 7). The reinforcing member30may optionally be bonded to the pleated filter media60. In one embodiment, the station70is located upstream of the station68where the reinforcing strip66is applied to the rear face32. In this embodiment, the reinforcing strip66helps to retain the reinforcing member31to the pleated filter media60. Alternatively, the reinforcing member30may be inserted into the pleats of the pleated filter media60at station70′ located downstream of the station68.

The reinforcing member30may be a scrim extending across the rear face32prior to forming the frame members92,96. The stations70or70′ may be used to position a scrim along the rear face32. The scrim may optionally be adhesively bonded to the pleated filter media60. In this embodiment, the reinforcing strip62will be applied to the front face64to maintain pleat spacing and facilitate machine handling, but the reinforcing strip66along the rear face32may be unnecessary.

The filter media22may be paper, porous films of thermoplastic or thermoset materials, nonwoven webs of synthetic or natural fibers, scrims, woven or knitted materials, foams, or electret or electrostatically charged materials. The filter media22may also include sorbents, catalysts, and/or activated carbon (granules, fibers, fabric, and molded shapes). Electret filter webs can be formed of the split fibrillated charged fibers as described in U.S. Pat. No. RE 30,782. These charged fibers can be formed into a nonwoven web by conventional means and optionally joined to a supporting scrim such as disclosed in U.S. Pat. No. 5,230,800 forming an outer support layer. Alternatively, the filter media22can be a melt blown microfiber nonwoven web, such as disclosed in U.S. Pat. No. 4,817,942 which can be joined to a support layer during web formation as disclosed in that patent, or subsequently joined to a support web in any conventional manner. The reinforcing member30and the reinforcing strips62,66may be constructed from various paper products, polymeric materials, or metals. These materials can be configured as strips, films, scrims, strands or filaments. The frame members are typically paper products, such as chipboard, or polymeric materials.

FIGS. 5 and 6illustrate a self-supporting pleated filter200that corresponds with the method illustrated inFIG. 3. The pleated filter media60is retained within a pair of opposing side frame members92and end frame members96. The reinforcing member30ofFIG. 3corresponds generally to the reinforcing member202that extends in the direction of pleating36and generally follows the contour of the pleat tips204and sloping side surfaces206,208. That is, the reinforcing member202extends into the pleats along the z-axis. The z-axis is the axis perpendicular to a plane defined by the front face64or the rear face32of the pleated filter media60. The reinforcing member202has a plurality of reinforcing member pleat tips210. Reinforcing strip66is optionally bonded to the reinforcing member pleat tips210along the rear face211. Reinforcing strip62is oriented in the direction of pleating36and bonded to the pleat tips204along the front face212and opposite the reinforcing member202to form a truss structure.

FIG. 7is a perspective view of an alternate self-supporting pleated filter230that corresponds generally to the method illustrated inFIG. 4. The reinforcing member30corresponds generally to the reinforcing member232. The reinforcing member232extends into the pleats along the z-axis, perpendicular to the rear face32. The reinforcing member232can be bonded to the pleated filter media60, retained by the side frame members92, or a combination thereof. The reinforcing strip66may optionally be provided along the rear face32. In the illustrated embodiment, the reinforcing member232has a V-shape that extends along a pair of opposing side surfaces234,236of two pleats238. In an alternate embodiment, the reinforcing structure232extends across a single pleat. In one embodiment, the reinforcing member232is a metal scrim.

FIG. 8illustrates an alternate reinforcing structure250that is deposited in the pleats252, rather than being pleated with the filter media60. The reinforcing structure250is typically inserted into the pleats252of the pleated filter media60prior to application of the optional reinforcing strip66. In the embodiment illustrated inFIG. 8, the reinforcing structure250extends along a single pleat252and includes side extensions254that extend parallel to the rear face32over additional pleats. In order to minimize pressure drop across the pleated filter media60, the reinforcing structure250is a porous material, such as a scrim. The reinforcing structure250may be retained to the pleated filter media60by bonding, by the optional reinforcing strip66and/or by the side frame members92. In an alternate embodiment, the reinforcing structure250has a triangular shape corresponding to the shape of the pleats252.

FIG. 9illustrates an alternate pleated filter270with a continuous reinforcing structure272extending across the rear surface32of the filter media60. Reinforcing strips62are located along the front face64(seeFIG. 1). Reinforcing strip66is optionally provided on the rear face32over or under the reinforcing structure272. The reinforcing structure272may be retained to the pleated filter media60by bonding to the frame members92,96and/or the filter media60, by the optional reinforcing strip66and/or by the side frame members92. The continuous reinforcing structure272may be a scrim, mesh, screen or other porous material. In an alternate embodiment, the continuous reinforcing structure272is bonded to the pleat tips along the front face64in place of the reinforcing strips62.

The complete disclosures of all patents, patent applications, and publications are incorporated herein by reference as if individually incorporated. Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein.