Background

Filters are used for many purposes, such as removing small suspended particulates from fluid flows. Filtration systems can include various technologies for increasing filter efficacy.

Summary

In some aspects, a method of filtering particles is disclosed. The method can include providing a first filter layer. The first filter layer can include a polyolefin polymer and an electret material and the method can further include providing a second filter layer, the second filter layer including a fire-resistant material. The method can include providing a duct having an entrance face and an exit face, and the duct can be configured to accommodate a fluid flow from the entrance face to the exit face. Further, the method can include disposing the first filter layer and the second filter layer such that the first filter layer is nearer to the exit face than is the second filter layer.

In some aspects, a filter assembly is disclosed. The filter assembly can include a first filter layer. The first filter layer can include a polyolefin polymer and an electret material. A second filter layer can also be included, and the second filter layer can include a fire-resistant material. The first filter layer and the second filter layer can be configured to be disposed a fluid flow.

Brief Description of the Drawings

FIG. 1 is schematic system view of a filtration system including cooking equipment and an exhaust system according to exemplary embodiments of the present disclosure.

FIG. 2 is a front view of a filter assembly according to exemplary embodiments of the present disclosure.

FIG. 3 is a rear perspective view of a filter assembly according to exemplary embodiments of the present disclosure.

FIG. 4 is a cross-sectional view of a filter assembly according to exemplary embodiments of the present disclosure.

FIG. 5 is a schematic view of first filter media, specifically illustrating fibers and electret material, according to exemplary embodiments of the present disclosure.

FIG. 6 is a cross-sectional view of a filter assembly disposed in a fluid flow according to exemplary embodiments of the present disclosure. FIG. 7 is a cross-sectional view of a filter assembly disposed in a fluid flow within a duct according to exemplary embodiments of the present disclosure.

Detailed Description

In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense.

Filters can be used in a wide range of applications. In some embodiments, filters may be designed for general air filtration to filter primarily airborne particulates. For example, filters may be designed to filter particles smaller than 10 micrometers in diameter, smaller than 5 micrometers in diameter, smaller than 2.5 micrometers in diameter, smaller than 1.0 micrometer in diameter, smaller than 0 5 micrometers in diameter or smaller than 0.3 micrometers in diameter, among others.

Filters can also be used in a specific location, such as an exhaust hood, for grease filtering in a commercial cooking environment. In commercial kitchens, grease capture in exhaust hoods may be important for health, safety and environmental reasons. However, grease buildup in and around an exhaust hood or an exhaust system may pose a fire hazard. To mitigate the hazard, commercial kitchens typically use airflow interrupters or disrupters, such as baffles. These can be made of a non-flammable material, such as a metal or metal alloy, including stainless steel, galvanized steel or aluminum. The baffle can prevent fire from spreading from the cooking surface into the exhaust system.

However, grease buildup on baffles requires regular cleaning to maintain the baffle’s effectiveness as a fire barrier and a grease collector. Aesthetically, visible grease on a commercial hood baffle can also be undesirable. Removing, cleaning and reinstalling the baffles can be time-consuming, labor-intensive, expensive and dangerous. The present disclosure provides various embodiments of an improved filtration system and filter, particularly a filter media including electret materials. Versus conventional baffles, the present disclosure can provide a low-cost and effective grease-trapping solution that is lightweight and easy to install in an exhaust hood. Portions of the disclosed filtration system can occupy a range hood position traditionally occupied by conventional baffles. Elements of the disclosed filtration system can also augment traditional baffles in an exhaust hood, thereby requiring minimal or no modifications to existing exhaust systems. Other benefits and uses are also foreseen. For clarity, moving from the cooking equipment through the exhaust system and past the blower can be defined as moving downstream, while moving in the opposite direction can be defined as moving upstream. FIG. 1 is a schematic sectional view of a filtration system 40 including cooking equipment 50 and an exhaust system 54. The cooking equipment 50 can be an oven, stove, grill, fryer, broiler or any other commonly used cooking apparatus known to those skilled in the art and can further define a cooking surface 52. The exhaust system 54 can include an exhaust hood 58 defining an exhaust hood flange 60. The exhaust hood flange 60, can releasably or permanently retain a baffle and/or a filter. An exhaust hood intake 59 can be defined by the exhaust hood 58, and can represent an upstream portion of the exhaust hood 58 and/or a portion of the exhaust hood 58 into which gasses or fluid flows enter the exhaust hood 58. The exhaust hood 58 can be positioned to capture all or a portion of grease and other particulates generated by the use of the cooking equipment 50. A blower 66 can, via an exhaust duct 62, create a reduced-pressure area proximate the cooking equipment 50 (relative to ambient pressure) that can encourage grease and other particulates generated by use of the cooking equipment 50 to enter the exhaust system 54 via the exhaust hood 58. In such a system, as illustrated in FIG. 1 , air, gasses, grease and/or particulates can travel into the exhaust system 54 via the exhaust hood 58 and filter assembly 100, as represented by arrow 70. The filtered air, gasses and any remaining grease and/or particulates can then pass through the exhaust duct 62 and blower 66 before exiting the exhaust system 54, as represented by arrow 74. Arrows 70 and 74 represent portions of a fluid flow traveling from the cooking surface 52, through the exhaust hood 58 and out through the rest of the exhaust system 54.

FIG. 2 is a front view of a filter assembly, FIG. 3 is a rear perspective view of a filter assembly and FIG. 4 is a cross-sectional view of a filter assembly. Filter assembly 100 can include a filter frame 104, a first filter layer 108 and a second filter layer 130.

Filter frame 104 may be any suitable size and may be formed from any suitable material. In some embodiments, filter frame 104 may have a substantially rectangular or square frame shape. In some embodiments, filter frame 104 is rigid. Filter frame 104 may be formed from, or may include, a polymeric material, or may be formed from or include a wood or a wood pulp material. Polymeric materials may be injection moldable or compatible with an additive manufacturing process. Lightweight woods such as a balsa wood or cork wood, may be used. Manufactured wood products such as particleboard, fiberboard, or chipboard may be particularly appropriate. In some embodiments, wood pulp materials such as cardboard, paperboard, and the like may be used. In some embodiments, carbon fiber, fiberglass, or composite materials may be used. Length, width, and thickness may be selected based on the desired application, to provide a suitable fit or a range of standardized sizes, to minimize the weight of the overall filter assembly and/or to provide appropriate rigidity or structural stability.

The first filter layer 108 can include a first filter media 112. The first filter media 112 and/or the first filter layer 108 can include a grease-trapping or a grease-filtering material and further can include an electret material 116 or a charge-enhancing additive (which can be seen, for example, in FIG. 5). Each of these aspects of the first filter media 112 and/or the first filter layer 108 will be described below in further detail. The second filter layer 130, which can be a fire-resistant filter media web, can be secured to and bordered by filter frame 104. The second filter layer 130 can include a second filter media 134, which will be described below in further detail.

In various embodiments, the first filter layer 108 and/or second filter layer 130 can be retained by, connected to, releasably connected to, permanently connected to, adjacent, proximate and/or in contact with the frame 104. In various embodiments, the first filter layer 108 and/or second filter layer 130 can be retained by, connected to, releasably connected to, permanently connected to, adjacent, proximate and/or in contact with one another. Magnets, adhesives, mechanical fasteners, biased mechanical fasteners, hook-and-loop panels, tape, double-sided tape, clips, electrostatics, static cling, 3M DUAL LOCK Fasteners, suction devices and/or any other suitable technology for attachment can be used to connect the first filter layer 108 and/or second filter layer 130 to the frame 104, and can also be used to connect the first filter layer 108 to the second filter layer 130.

Backing layer 138 can be used (as in the configuration of FIG. 4) to provide additional structural stability to the filter assembly 100. Backing layer 138 can be secured to, and bordered by, filter frame 104 and can include any suitable material, including a cardboard grid, a scrim, a fiberglass layer or an expanded metal layer. Backing layer 138 can be configured to support the filter assembly 100 without blocking, or while minimally blocking, airflow through the filter assembly 100. The physical dimensions of backing layer 138 may be selected to provide structural support without creating too large of a pressure drop (downstream of the filter assembly 100 versus upstream of the filter assembly 100) when installed and in use. The backing layer 138 can be secured to the first filter layer 108, the second filter layer 130 and/or the frame 104 via any of the same securement technologies described above for securing the filter layers 108, 130 and the frame 104.

FIG. 5 is a view of a portion of the first filter media 112, particularly showing fibers 114 of the first filter media 112 and the electret material 116. Electret material 116 can be a dielectric material that exhibits a quasi-permanent electrical charge. The performance of microfibrous webs used for aerosol filtration can be improved by imparting an electrical charge to the fibers (such as fiber 114), thus forming an electret web (such as the first filter media 112) including the fibers 114 and the electret material 116. In particular, electret materials 116 are effective in enhancing particle capture in aerosol filters. Electret materials 116 in webs 112 can be formed by bombarding melt-blown fibers as they issue from the die orifices, as the fibers 114 are formed, with electrically charged particles such as electrons or ions. Other methods include, for example, charging the fibers 114 after the web 112 is formed, by means of a corona discharge or imparting a charge to the fiber mat by means of carding and/or needle tacking (tribocharging). In addition, a method in which jets of water or a stream of water droplets impinge on a nonwoven web at a pressure sufficient to provide filtration enhancing electret charge has also been described (hydrocharging). In some embodiments, the electret webs 112 of this disclosure are capable of being charged by corona discharge alone, particularly Direct Current (DC) corona discharge, without the need for additional charging mechanisms.

A number of materials have been added to polymeric compositions to modify the properties of the polymeric composition. For example, in US Patent No. 5,914,186 (Yau et al.), heat-resistant anti-static pressure sensitive adhesive tapes are described that comprise a substrate coated with a microparticle adhesive having a diameter of at least 1 micrometer. The microparticles have a conductive coating formed from a polymer electrolyte base polymer, at least one ionic salt of an alkali or alkaline earth metal, and at least one thermal stabilizer selected from the group consisting of hindered amines, salts of substituted toluimidazoles, and mixtures thereof.

A variety of charge-enhancing additives have been developed for use in electret materials 116. US Patent No. 9,815,068 describes electret webs that include a thermoplastic resin and a charge-enhancing additive, where the charge-enhancing additive is a divalent metalcontaining substituted-mercaptobenzimidazolate salt. US Patent No. 10,240,269 describes electret webs include a thermoplastic resin and a charge-enhancing additive, where the chargeenhancing additive is a fused aromatic thiourea, a fused aromatic urea compound, or a combination thereof. The change-enhancing additive may also include a hindered amine light stabilizer compound.

Examples of electret materials 116 that have additives added include electrets with antibacterial additives as described in Japanese Patent Publication JP 08284063 which describes N-n-butylcarbamic acid 3-9 iodo-2-propynyl ester containing either an amidine or guanidine group, and 2-(4-thiazolyl) benzimidazole, and PCT Publication WO 93/14510 which describes hindered amine compounds, nitrogenous hindered phenol compounds, metallic salt hindered phenol compounds, phenol compounds, sulfur compounds, and phosphorous compounds. Japanese Patent Publication JP 06254319 describes the use of metal salts of long chain organic acids in polyolefin electrets to lessen the attenuation of the electrification quantity. European Patent Publication No. EP 623,941 describes the use of Charge Control Agents from various chemical classes in polymer electrets

Also described are processes for producing high stability electret materials 1 16, such as European Patent Publication No. EP 447,166 which describes a process for producing electrets comprising alternating at least two cycles of applying electric charge and subsequently heating, and also describes electrets containing polar high-molecular weight compounds, and US Patent No. 4,874,659 (Ando et al.) which describes a process comprising placing a fiber sheet between a non-contact voltage-applied electrode and an earth electrode and supplying electricity between the electrodes. Useful charge-enhancing additives 1 16 can include a substituted heterocyclic thiol in some embodiments.

The electret webs 112 may exist in a variety of forms. For example, the electret web 112 may be a continuous or discontinuous film, or a fibrous web. Fibrous webs are particularly useful for the formation of filtration media. In some embodiments the web 112 is a non-woven microfibrous web. Typically, microfibers are 1-100 micrometers, or more typically 2-30 micrometers in effective diameter (or average diameter if measured by a method such as scanning electron microscopy) and the microfibers need not have a circular cross-section.

Thermoplastic resins useful in the present disclosure include any thermoplastic nonconductive polymer capable of retaining a high quantity of trapped electrostatic charge when formed into a web and charged. Typically, such resins have a DC (direct current) resistivity of greater than 1014 ohm-cm at the temperature of intended use. Polymers capable of acquiring a trapped charge include polyolefins such as polypropylene, polyethylene, and poly-4-methyl-1- pentene; polyvinyl chloride; polystyrene; polycarbonates; polyesters, including polylactides; and perfluorinated polymers and copolymers. Particularly useful materials include polypropylene, poly-4-methyl-1-pentene, blends thereof or copolymers formed from at least one of propylene and 4-methyl-1 -pentene.

Examples of suitable thermoplastic resins include, for example, the polypropylene resins: ESCORENE PP 3746G commercially available from Exxon-Mobil Corporation, Irving, TX; TOTAL PP3960, TOTAL PP3860, and TOTAL PP3868 commercially available from Total Petrochemicals USA Inc., Houston, TX; and METOCENE MF 650W commercially available from LyondellBasell Industries, Inc., Rotterdam, Netherlands; and the poly-4-methyl-1-pentene resin TPX-MX002 commercially available from Mitsui Chemicals, Inc., Tokyo, Japan.

The charge-enhancing additive 116 can be added in any suitable amount. Typically, the charge-enhancing additive is present in a thermoplastic resin and charge-enhancing additive blend in amounts of up to about 10% by weight, more typically in the range of 0.02 to 5% by weight based upon the total weight of the blend. In some embodiments, the charge-enhancing additive is present in an amount ranging from 0.1 to 3% by weight, 0.1 to 2% by weight, 0.2 to 1.0% by weight or 0.25 to 0.5% by weight.

The blend of the thermoplastic resin and the charge-enhancing additive 116 can be prepared by well-known methods. Typically, the blend is processed using melt extrusion techniques, so the blend may be preblended to form pellets in a batch process, or the thermoplastic resin and the charge-enhancing additive may be mixed in the extruder in a continuous process. Where a continuous process is used, the thermoplastic resin and the charge-enhancing additive may be pre-mixed as solids or added separately to the extruder and allowed to mix in the molten state. Examples of melt mixers that may be used to form preblended pellets include those that provide dispersive mixing, distributive mixing, or a combination of dispersive and distributive mixing. Examples of batch methods include those using a BRABENDER (e. g. a BRABENDER PREP CENTER, commercially available from C.W. Brabender Instruments, Inc.; South Hackensack, NJ) or BANBURY internal mixing and roll milling equipment (e.g. equipment available from Parrel Co.; Ansonia, CT). After batch mixing, the mixture created may be immediately quenched and stored below the melting temperature of the mixture for later processing.

Examples of continuous methods include single screw extruding, twin screw extruding, disk extruding, reciprocating single screw extruding and pin barrel single screw extruding. The continuous methods can include utilizing both distributive elements, such as cavity transfer mixers (e.g. CTM, commercially available from RAPRA Technology, Ltd.; Shrewsbury, England) and pin mixing elements, static mixing elements or dispersive mixing elements (commercially available from e.g., MADDOCK mixing elements or SAXTON mixing elements).

Examples of extruders that may be used to extrude preblended pellets prepared by a batch process include the same types of equipment described above for continuous processing. Useful extrusion conditions are generally those which are suitable for extruding the resin without the additive.

The extruded blend of thermoplastic resin and charge-enhancing additive 116 may be cast or coated into films or sheets or may be formed into a fibrous web 112 using any suitable techniques. Films can be made into a variety of articles including filtration media by the methods described in, for example, US Patent No. 6,524,488 (Insley et al.). Fibrous webs can be made from a variety of fiber types including, for example, melt-blown microfibers, staple fibers, fibrillated films and combinations thereof. Techniques for preparing fibrous webs include, for example, air laid processes, wet laid processes, hydro-entanglement, spunbond processes, melt-blown processes and combinations thereof. Melt-blown and spunbond, non-woven microfibrous webs can be particularly useful as filtration media.

Melt-blown microfibers useful in the present disclosure can be prepared as described in Van A. Wente, "Superfine Thermoplastic Fibers," Industrial Engineering Chemistry, vol. 48, pp. 1342-1346 and in Report No. 4364 of the Naval Research Laboratories, published May 25, 1954, entitled "Manufacture of Super Fine Organic Fibers" by Van A. Wente et al.

Spunbond microfibers may be formed using a spunbond process in which one or more continuous polymeric free-fibers are extruded onto a collector, as described, for example, in US Patent Nos. 4,340,563 and 8,162,153 and US Patent Publication No. 2008/0038976.

Useful melt-blown and spunbond microfibers for fibrous electret filters (108, 112) typically have an effective fiber diameter of from about 1-100 micrometers, more typically 2 to 30 micrometers, in some embodiments from about 7 to 15 micrometers, as calculated according to the method set forth in Davies, C. N., "The Separation of Airborne Dust and Particles," Institution of Mechanical Engineers, London, Proceedings 1 B, 1952.

Staple fibers may also be present in the web 112. The presence of staple fibers generally provides a loftier, less dense web than a web of only blown microfibers. Generally, no more than about 90 weight percent staple fibers are present, more typically no more than about 70 weight percent. Examples of webs containing staple fiber are disclosed in U.S. Pat. No. 4,118,531 (Hauser).

Sorbent particulate material such as activated carbon or alumina may also be included in the web 112. Such particles may be present in amounts up to about 80 volume percent of the contents of the web 112. Examples of particle-loaded webs are described, for example, in U.S. Pat. No. 3,971 ,373 (Braun), U.S. Pat. No. 4, 100,324 (Anderson) and U.S. Pat. No. 4,429,001 (Kolpin et al.).

Various optional additives can be blended with the thermoplastic composition including, for example, pigments, light stabilizers, nucleating agents, primary and secondary antioxidants, metal deactivators, hindered amines, hindered phenols, fatty acid metal salts, triester phosphites, phosphoric acid salts, fluorine-containing compounds and combinations thereof. Particularly suitable additives include HALS (Hindered Amine Light Stabilizers) and antioxidants, as these may also act as charge-enhancing additives. In addition, other charge-enhancing additives may be combined with the thermoplastic composition. Possible charge additives include thermally stable organic triazine compounds or oligomers, which compounds, or oligomers contain at least one nitrogen atom in addition to those in the triazine ring, see, for example, U.S. Patents 6,268,495, 5,976,208, 5,968,635, 5,919,847, and 5,908,598 to Rousseau et al. Another additive known to enhance electrets is “CHIMASSORB 944: (poly[[6-(1 , 1 ,3,3, - tetramethylbutyl) amino]-s-triazine-2,4-diyl][[(2,2,6,6-tetramethyl-4-piperidy l) imino] hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl) imino]]), available from BASF, Ludwigshafen, Germany. The charge-enhancing additives may be N-substituted amino aromatic compounds, particularly tri-amino substituted compounds, such as 2,4,6-trianilino-p-(carbo-2’-ethylhexyl-T- oxy)-1,3,5-triazine commercially available as “UVINUL T-150” from BASF, Ludwigshafen, Germany. Another charge additive is 2,4,6-tris-(octadecylamino)-triazine, also known as tristearyl melamine (“TSM”). Further examples of charge-enhancing additives are provided in U.S. Patent Application Serial No. 61/058,029, U.S. Patent Application Serial No. 61/058,041 , US Patent No. 7,390,351 (Leir et al.), US Patent No. 5,057,710 (Nishiura et al.), and US Patent Nos. 4,652,282 and 4,789,504 (Ohmori et al.).

In addition, the web 112 may be treated to chemically modify its surface. Surface fluorination can be achieved by placing a polymeric article in an atmosphere that contains a fluorine-containing species and an inert gas and then applying an electrical discharge to modify the surface chemistry of the polymeric article. The electrical discharge may be in the form of a plasma such as an AC corona discharge. This plasma fluorination process causes fluorine atoms to become present on the surface of the polymeric article. The plasma fluorination process is described in a number of U.S. Patents: 6,397,458, 6,398,847, 6,409,806, 6,432, 175, 6,562,112, 6,660,210, and 6,808,551 to Jones/Lyons et al. Electret articles that have a high fluorosaturation ratio are described in U.S. Patent 7,244,291 to Spartz et al., and electret articles that have a low fluorosaturation ratio, in conjunction with heteroatoms, is described in U.S. Patent 7,244,292 to Kirk et al. Other publications that disclose fluorination techniques include: U.S. Pat. Nos. 6,419,871 , 6,238,466, 6,214,094, 6,213,122, 5,908,598, 4,557,945, 4,508,781 , and 4,264,750; U S. Publications US 2003/0134515 A1 and US 2002/0174869 A1 ; and International Publication WO 01/07144.

The electret filter media 112 prepared according to the present disclosure can have a basis weight (mass per unit area) in the range of about 10 to 500 g/m2, and in some embodiments, about 10 to 100 g/m2. In making melt-blown microfiber webs 112, the basis weight can be controlled, for example, by changing either the collector speed or the die throughput. The thickness of the filter medium is typically about 0.25 to 20 millimeters, and in some embodiments, about 0.5 to 2 millimeters. Multiple layers of fibrous electret webs 112 are commonly used in filter elements. The solidity of the fibrous electret web 112 typically is about 1% to 25%, more typically about 3% to 10%. Solidity is a unitless parameter that defines the solids fraction of the web. Generally, the methods of this disclosure provide electret webs 112 with generally uniform charge distribution throughout the web 112 without regard to basis weight, thickness, or solidity of the medium. The electret filter medium and the resin from which it is produced should not be subjected to any unnecessary treatment which might increase its electrical conductivity, e.g., exposure to ionizing radiation, gamma rays, ultraviolet irradiation, pyrolysis, oxidation, etc.

The electret web 112 may be charged as it is formed, or the web 112 may be charged after the web 112 is formed. In electret filter medium, the medium is generally charged after the web 112 is formed. In general, any standard charging method known in the art may be used. For example, charging may be carried out in a variety of ways, including tribocharging, corona discharge and hydrocharging. A combination of methods may also be used. As mentioned above, in some embodiments, the electret webs 112 of this disclosure have the desirable feature of being capable of being charged by corona discharge alone, particularly DC corona discharge, without the need of additional charging methods.

Examples of suitable corona discharge processes are described in U.S. Pat. Re. No. 30,782 (van Turnhout), U.S. Pat. Re. No. 31 ,285 (van Turnhout), U.S. Pat. Re. No. 32,171 (van Turnhout), U.S. Pat. No. 4,215,682 (Davis et al.), U.S. Pat. No. 4,375,718 (Wadsworth et al.), U.S. Pat. No. 5,401 ,446 (Wadsworth et al.), U.S. Pat. No. 4,588,537 (Klaase et al.), U.S. Pat. No. 4,592,815 (Nakao), and US Pat. No. 6,365,088 (Knight et al.). Another technique that can be used to charge the electret web 112 is hydrocharging. Hydrocharging of the web 112 is carried out by contacting the fibers 114 with water in a manner sufficient to impart a charge to the fibers 1 14, followed by drying of the web 112. One example of hydrocharging involves impinging jets of water or a stream of water droplets onto the web 112 at a pressure sufficient to provide the web 112 with filtration enhancing electret charge, and then drying the web 112. The pressure necessary to achieve optimum results varies depending on the type of sprayer used, the type of polymer from which the web 112 is formed, the type and concentration of additives to the polymer, the thickness and density of the web 112 and whether pre-treatment, such as corona surface treatment, was carried out prior to hydrocharging. Generally, water pressures in the range of about 10 to 500 psi (69 to 3450 kPa) are suitable. The jets of water or stream of water droplets can be provided by any suitable spray device. One example of a useful spray device is the apparatus used for hydraulically entangling fibers. An example of a suitable method of hydrocharging is described in US Patent No. 5,496,507 (Angadjivand et al.). Other methods are described in US Patent No. 6,824,718 (Eitzman et al.), US Patent No. 6,743,464 (Insley et al.), US Patent No. 6,454,986 (Eitzman et al.), US Patent No. 6,406,657 (Eitzman et al ), and US Patent No. 6,375,886 (Angadjivand et al.). The hydrocharging of the web may also be carried out using the method disclosed in the US Patent No. 7,765,698 (Sebastian et al.).

FIG. 6 is a schematic cross-sectional view of an exemplary filter assembly 100 disposed in a fluid flow 140. In some embodiments, the fluid flow 140 passes through the filter assembly 100 and at least some constituent layers thereof. Specifically, the fluid flow 140 can pass through the second filter layer 130, the first filter layer 108 and the backing layer 138 in sequence.

FIG. 7 is a schematic side view of an exemplary filter assembly 100 disposed in a duct 150. A duct fluid flow 162 can flow through the duct 150 from a duct entrance face 154 to a duct exit face 158. Similar to FIG. 6, in some embodiments, the duct fluid flow 162 passes through the filter assembly 100 and at least some constituent layers thereof. Specifically, the duct fluid flow 162 can pass through the second filter layer 130, the first filter layer 108 and the backing layer 138 in sequence. It can also be seen that the first filter layer 108 is disposed nearer to the duct exit face 158 than is the second filter layer 130, and further that the second filter layer 130 is disposed nearer to the duct entrance face 154 than is the first filter layer 108. In some embodiments, all or a majority of the duct fluid flow 158 passes through the filter assembly 100.

In various embodiments, one or more of the filter layers 108, 130 and the filter media 112, 134 can include different materials or the same material. In particular, one or more of the elements 108, 130, 112, 134 can include fiberglass, steel, stainless steel, aluminum, aluminum foil, perforated aluminum foil, metals, metal alloys, polymers, carbon, ceramics, organic materials, braided materials, fire-resistant materials, 3M N EXTEL Ceramic Fibers and Textiles, cardboard, chip board or any other material known to those skilled in the art.

In some embodiments, one or more of the elements 108, 130, 112, 134 can include fibers that form a non-woven and/or non-knitted material. The non-woven and/or non-knitted material can describe materials that are bonded together by chemical, mechanical, heat or solvent treatments, rather than by knitting or weaving. The non-woven material can be lofty, carded, air-laid or mechanically bonded (such as spun-lace, needle-entangled or needle- tacked). The non-woven material can be bonded (e.g., the fibers are bonded to one another at various locations) or non-bonded.

One or more of the elements 108, 130, 1 12, 134 can include a heat-setting material or a melt material that provides some or all of the bonding in the non-woven material, such as a flake, powder, fiber or a combination thereof. The heat-setting material can include any suitable thermoplastic or thermoset polymer, such as polyester, polyethylene terephthalate (PET), polypropylene (PP) or a combination thereof After melting and/or heat bonding, the flake, powder and/or fiber can melt and bond the fibers together, increasing a strength and stability of the material.

In some embodiments, one or more of the elements 108, 130, 112, 134 can include a flame-resistant (FR) material, oxidized polyacrylonitrile fiber (OPAN), modacrylic, flame-resistant rayon, polyacrylonitrile (PAN), polyphenylene sulfide (PPS), polyethylene terephthalate (PET), polypropylene (PP), kapok fiber, poly lactic acid (PLA), cotton, nylon, polyester, rayon (e.g., non-flame-retardant rayon), wool, basalt, fiberglass, ceramic or a combination thereof. In some embodiments, one or more of the elements 108, 130, 112, 134 can include a conventional filter media material (such as polyolefin) that has been treated or coated to be flame-resistant, a conventional filter media material and a metal mesh and/or a flame-resistant barrier. In some embodiments, the fibers can be bicomponent fibers, or fibers made of more than one material, such as those listed in this disclosure. In various embodiments, the filter media can be pleated, non-pleated and/or multilayered (which can include a multi-layer web including a woven layer, such as a woven basalt layer), based upon application.

One or more of the elements 108, 130, 1 12, 134 can, in various embodiments, include a coating, a heat-setting or melt material (e.g., powder, flakes and/or fibers), a metal fiber, a glass fiber, a ceramic fiber, an aramid fiber, a sorbent, an intumescent material (e.g., a fiber or a particle), mica, diatomaceous earth, glass bubbles, carbon particles or a combination thereof. Examples of flame-resistant materials include any polymer designated as flame-retardant (e.g., as pure materials or as compounds including the materials), aluminum, polyphosphate, phosphorus, nitrogen, sulfur, silicon, antimony, chlorine, bromine, magnesium, zinc, carbon or a combination thereof. Flame-resistant materials can be halogen-containing flame retardants or non-halogenated flame retardants. Examples of coatings or additives can include expandable graphite, vermiculite, ammonium polyphosphate, alumina trihydrate (ATH), magnesium hydroxide (Mg(OH)2), aluminum hydroxide (AI(OH)3), molybdate compounds, chlorinated compounds, brominated compounds, antimony oxides, organophosphorus compounds or a combination thereof.

In some embodiments, one or more of the elements 108, 130, 112, 134 can include airlaid nonwoven web prepared using 90% oxidized polyacrylonitrile (OPAN) staple fiber with a denier diameter of 5.0dtex x 60mm (commercially available under the trade designation ZOLTEK OX) and 10% binding fiber (high temperature polyester binding or melty fiber with a denier diameter of 6.7dtex x 60 mm, commercially available under the trade designation TREVI RA T270) with an area weight of 150 grams per square meter

In some embodiments, one or more of the elements 108, 130, 112, 134 can include airlaid nonwoven web prepared using nylon staple fiber with a denier diameter of 1000 dtex, or denier, and 10% binding fiber (commercially available under the trade designation TREVIRA T270) with an area weight of 550 grams per square meter.

In some embodiments, one or more of the elements 108, 130, 112, 134 can include airlaid nonwoven web prepared using 40% 5.0dtex x 60 mm OPAN staple fiber, 40% 500 dtex, or denier, PET staple fiber (commercially available from David C. Poole Company, Inc , Greenville, SC), and 20% 15 dtex, or denier, binding fiber, such as is commercially available from Huvis (Seoul, South Korea) with an area weight of 225 grams per square meter.

In various embodiments, one or more of the elements 108, 130, 112, 134 can have a constant, substantially constant or variable thickness as measured from a first side (upstream) to a second side (downstream) of the respective layer. In various embodiments, one or more of the elements 108, 130, 112, 134 can have a thickness, or an average thickness, as measured from a respective first side to a respective second side of, of about, of at least or of at most: 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1 mm,

1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm, 2.1 mm, 2.2mm,

2.3mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, 2.9mm, 3.0mm, 3.1mm, 3.2mm, 3.3mm,

3.4mm, 3.5mm, 3.6mm, 3.7mm, 3.8mm, 3.9mm, 4.0mm, 4.5mm, 5.0mm, 5.5mm, 6.0mm,

6.5mm, 7.0mm, 7.5mm, 8.0mm, 8.5mm, 9.0mm, 9.5mm, 10.0mm, 1 1.0mm, 12.0mm, 13.0mm, 14.0mm, 15.0mm, 16.0mm, 17.0mm, 18.0mm, 19.0mm, 20.0mm, 21.0mm, 22.0mm, 23.0mm, 24.0mm, 25.0mm, 30.0mm, 35.0mm, 40.0mm, 45.0mm, 50.0mm, 60.0mm, 70.0mm, 80.0mm, 90.0mm or 100.0mm.

In some embodiments, one or more securement elements 222a, 222b can permanently or releasably secure the filter assembly 100 to another object (such as a baffle). In some embodiments, as shown exemplarily in FIG. 1, the securement elements 222a, 222b can secure the filter assembly 100 to the exhaust hood 58, exhaust hood intake 59 and/or exhaust hood flange 60. In some embodiments, the phrase ‘releasably’ as applied to securement (such as securement elements 222a, 222b) can indicate an easy separation by a user, a separation by a user requiring a low amount of force, a design of the securement element or connector that facilitates easy separation without damaging the elements being connected or secured, and/or the absence of a permanent or lasting securement technology including, but not limited to, weldments, strong adhesives, rivets, brazing, soldering or any other technology known to those skilled in the art.

In various embodiments, the securement elements 222a, 222b can include magnets, adhesives, mechanical fasteners, biased mechanical fasteners, hook-and-loop panels, tape, double-sided tape, clips, electrostatics, static cling, 3M DUAL LOCK Fasteners, suction devices and/or any other suitable technology for releasable or permanent attachment. The adhesives can include (the same or different) pressure-sensitive adhesives (PSAs). PSAs can include tackified natural rubbers, synthetic rubbers, tackified styrene block copolymers, (meth)acrylics, poly(alpha-olefins) and/or silicones. The adhesives can be oxidatively stable (i.e., maintains adhesion over time) and can exhibit low adhesion build over time. The adhesives can also include (meth)acrylic PSAs being from 80 to 100 weight percent of a C3 — C12 alkyl ester component such as isooctyl acrylate, 2-ethyl-hexyl acrylate and/or n-butyl acrylate, and from 0 to 20 weight percent of a polar component such as acrylic acid, methacrylic acid, ethylene vinyl acetate, N-vinyl pyrrolidone and/or styrene macromer. Such (meth)acrylic PSAs can be used as 100% solids, which can be hot-melt coated or processed via a UV-cured low-viscosity syrup. Optionally, the (meth)acrylic PSA’s can be dispersed in a solvent for coating and/or the (meth)acrylic PSA can be synthesized as a latex polymer dispersion for water-based coating.

In operation, grease generated from the cooking equipment or another source rises, or is suctioned, towards the filter assembly. Airborne droplets of grease can be trapped and/or absorbed by the filter assembly, thus reducing or eliminating or reducing the collection of airborne droplets of grease on a baffle (which can be disposed in an exhaust hood flange). The disclosed technologies can also eliminate or reduce grease traveling downstream through the remainder of the exhaust system via a fluid flow or a duct fluid flow. When the filter assembly (or the first filer layer and/or the second filter layer) has accumulated a particular amount, weight or opacity of grease, after a particular time period or after any other metric, it may be desirable to clean or replace all of, or a portion of, the filter assembly. In such a case, the first filter layer, the second filter layer and/or the backing layer can be removed and either discarded and replaced, or cleaned and placed back on the duct, exhaust system, fluid flow or duct fluid flow. In some embodiments, the filter assembly can be secured to a baffle, or to any other portion of the exhaust hood or exhaust system.

The presence of electret materials can increase the efficiency of a given filter layer, such that a given filter layer with electret materials can absorb more airborne grease or other particles than an identical filter layer without the electret materials. The electret materials can attract and/or retain various airborne particles (charged or not) or grease particles, enhancing the filtration abilities of the filter layer. In some embodiments, the fibers of a given filter layer with electret materials can be smaller (having a smaller average denier or diameter), or the fibers of a given filter layer with electret materials can be arranged in a less-dense manner, than fibers of an identical filter layer lacking the electret materials, thus reducing pressure drop caused by the filter layer and/or increasing filtration properties.

Thus, versus conventional baffles or filters without electret materials, the disclosed systems and filtration technologies provide a lightweight and cost-effective grease-trapping solution that reduces or prevents the buildup of grease on exhaust system components (such as a baffle, mounting article, exhaust duct, blower or exhaust hood), can be installed in or proximate a conventional baffle location in an exhaust hood and facilitates the easy removal and replacement of a releasably secured filter assembly.

Examples

Embodiments of the present disclosure can be better understood by reference to the following examples which are offered by way of illustration. The present disclosure is not limited to the examples given.

Table 1. Materials: Multilayer webs (or filter assemblies) including at least one fire-resistant nonwoven or fabric (or second layer) and at least one charged web (or first layer) were combined such that interior faces of the fire-resistant layer and the charged web were in contact. Prepared multilayer webs are presented in Table 2.

Table 2. Multilayer webs:

The filtration performance of the individual and multilayer webs was measured for % penetration (% PEN) and pressure drop (AP) using oleic acid as the aerosol. The filter tester set-up generated oleic acid particles with a small-volume nebulizer (available from DeVilbiss Healthcare, Somerset, PA). Particle volumes and counts were obtained with an Optical Particle Sizer Model 3330 (available from TSI, Inc., St. Paul, MN) and the pressure drop was measured using a Baratron 220 Electronic Manometer (MKS Instruments, Andover, MA).

The oleic acid aerosol was 0.3-10 microns having a total upstream concentration of 2.2x10 ³ -2.9x10 ³ count per cubic centimeter. The generated aerosol was carried through the web samples at a calibrated flow rate of 85 liters per minute (face velocity 220 feet per minute). Total testing time was 40 seconds (20 second rise time and sample time of 20 seconds); n = 4 for each web example. The % PEN is defined as:

% PEN = 100 x (oleic acid concentration downstream / oleic acid concentration upstream)

Using the % PEN and AP, the quality factor (QF) was calculated by the following equation:

-ln(% PEN 1 100) / AP

Therefore, a high QF is an indication of a better filtration performance.

The stability of the charged media was also verified by testing the filtration performance under accelerated aging. The initial QF (Q _o ) was compared to the QF of webs stored in an aging oven controlled at 38 °C and 85% relative humidity. The filtration performance was measured after 1 and 2 weeks of aging. The performance retention is calculated by the following equation:

% Retention (Q _x ) = (Q _x (after aging at 38 °C/85% RH) / Q _o (initial))) x 100 Qi and Q2 designate the retention at 1 and 2 weeks, respectively. The % PEN and QF values are reported for the particle size bin of 1.6 to 2.2 microns (midpoint of 1.9 microns).

Table 3. Filtration Performance:

The fire-stopping media, basalt fabric and OPAN, have high percent penetrations when tested alone, meaning that a large portion of particles within the 1.9-micron size bin pass through the filter. However, combining the fire-stopping media with a charged media layer drops the penetration values -80%. The multilayer constructions also retain their filtration performance after aging for 2 weeks in an environment similar to the expected operating conditions of the filters.

The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the embodiments of the present disclosure. Thus, it should be understood that although the present disclosure has been specifically disclosed by specific embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those of ordinary skill in the art, and that such modifications and variations are considered to be within the scope of embodiments of the present disclosure. The complete disclosures of the patents, patent documents, and publications cited herein are incorporated by reference in their entirety as if each were individually incorporated. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document that is incorporated by reference herein, this specification as written will control.