EP1028794A1 - Construction de matiere filtrante et procede - Google Patents

Construction de matiere filtrante et procede

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Publication number
EP1028794A1
EP1028794A1 EP97945329A EP97945329A EP1028794A1 EP 1028794 A1 EP1028794 A1 EP 1028794A1 EP 97945329 A EP97945329 A EP 97945329A EP 97945329 A EP97945329 A EP 97945329A EP 1028794 A1 EP1028794 A1 EP 1028794A1
Authority
EP
European Patent Office
Prior art keywords
media
layer
filter
fine fiber
fine
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP97945329A
Other languages
German (de)
English (en)
Inventor
Brad Kahlbaugh
Denis J. Dudrey
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Donaldson Co Inc
Original Assignee
Donaldson Co Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Donaldson Co Inc filed Critical Donaldson Co Inc
Priority claimed from PCT/US1997/017435 external-priority patent/WO1999016534A1/fr
Publication of EP1028794A1 publication Critical patent/EP1028794A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material

Definitions

  • the present invention relates to filters, filter constructions, materials for use in filter constructions and methods of filtering.
  • Applications of the invention particularly concern filtering of particles from fluid streams, for example from air streams.
  • the techniques described herein particularly concern the utilization of arrangements having one or more layers of fine fibers in the filter media, to advantage .
  • Fluid streams such as air and gas streams often carry particulate material therein.
  • air intake streams to the cabins of motorized vehicles, to engines for motorized vehicles, or to power generation equipment; gas streams directed to gas turbines; and, air streams to various combustion furnaces often include particulate material therein.
  • cabin air filters it is desirable to remove the particulate matter for comfort of the passengers and/or for aesthetics.
  • air and gas intake streams to engines, gas turbines and combustion furnaces it is desirable to remove the particulate material because it can cause substantial damage to the internal workings to the various mechanisms involved.
  • production gases or off gases from industrial processes or engines may contain particulate material therein. Before such gases can be, or should be, discharged through various downstream equipment and/or to the atmosphere, it may be desirable to obtain a substantial removal of particulate material from those streams.
  • a variety of fluid filter arrangements have been developed for particulate removal. For reasons that will be apparent from the following descriptions, improvements have been desired for arrangements developed to serve this purpose.
  • filter design has typically concerned a trade off of features designed for high filter efficiency and features designed to achieve high capacity (i.e. long filter lifetime) .
  • the "lifetime" of a filter is typically defined according to a selected limiting pressure drop across the filter. That is, for any given application, the filter will typically be considered to have reached its lifetime of reasonable use, when the pressure buildup across the filter has reached some defined level for that application or design. Since this buildup of pressure is a result of load, for systems of equal efficiency a longer life is typically directly associated with higher capacity. Efficiency is the propensity of the media to trap, rather than pass, particulates . It should be apparent that typically the more efficient a filter media is at removing particulates from a gas flow stream, in general the more rapidly the filter media will approach the "lifetime" pressure differential (assuming other variables to be held constant) .
  • Paper filter elements are widely used forms of surface loading media.
  • paper elements comprise dense mats of cellulose fibers oriented across a gas stream carrying particulate material.
  • the paper is generally constructed to be permeable to the gas flow, and to also have a sufficiently fine pore size and appropriate porosity to inhibit the passage of particles greater than a selected size therethrough.
  • the upstream side of the filter paper operates through diffusion and interception to capture and retain selected sized particles from the gas (fluid) stream.
  • the particles are collected as a dust cake on the upstream side of the filter paper.
  • the dust cake also begins to operate as a filter, increasing efficiency. This is sometimes referred to as "seasoning,” i.e., development of an efficiency greater than initial efficiency.
  • a simple filter design such as that described above is subject to at least two types of problems.
  • a relatively simple flaw i.e. rupture of the paper, results in failure of the system.
  • particulate material rapidly builds up on the upstream side of the filter, as a thin dust cake or layer, it eventually substantially blinds off or occludes portions of the filter to the passage of fluid therethrough.
  • filters are relatively efficient, they are not generally associated with long lifetimes of use, especially if utilized in an arrangement involving the passage of large amounts of fluid therethrough, with substantial amounts of particulate material at or above a "selected size" therein; "selected size” in this context meaning the size at or above which a particle is effectively stopped by, or collected within, the filter.
  • filter life is decreased by a factor proportional to the square of the velocity.
  • a pleated paper, surface loaded, filter system when used as a particulate filter for a system that requires substantial flows of air, a relatively large surface area for the filter media is needed.
  • a typical cylindrical pleated paper filter element of an over-the-highway diesel truck will be about 9-15 inches in diameter and about 12-24 inches long, with pleats about 1-2 inches deep.
  • the filtering surface area of media (one side) is typically 37 to 275 square feet.
  • depth media In many applications, especially those involving relatively high flow rates, an alternative type of filter media, sometimes generally referred to as "depth” media, is used.
  • a typical depth media comprises a relatively thick tangle of fibrous material.
  • Depth media is generally defined in terms of its porosity, density or percent solids content. For example, a 2-3% solidity media would be a depth media mat of fibers arranged such that approximately 2-3% of the overall volume comprises fibrous materials (solids), the remainder being air or gas space.
  • a typical conventional depth media filter is a deep, relatively constant (or uniform) density, media, i.e. a system in which the solidity of the depth media remains substantially constant throughout its thickness.
  • substantially constant in this context, it is meant that only relatively minor fluctuations in density, if any, are found throughout the depth of the media. Such fluctuations, for example, may result from a slight compression of an outer engaged surface, by a container in which the filter media is positioned.
  • Gradient density depth media arrangements have been developed. Some such arrangements are described, for example, in U.S. Patents 4,082,476; 5,238,474; and 5,364,456.
  • a depth media arrangement can be designed to provide "loading" of particulate materials substantially throughout its volume or depth.
  • Such arrangements can be designed to load with a higher amount of particulate material, relative to surface- loaded systems, when full filter lifetime is reached.
  • the tradeoff for such arrangements has been efficiency, since, for substantial loading, a relatively low solids media is desired.
  • Gradient density systems such as those in the patents referred to above, have been designed to provide for substantial efficiency and longer life.
  • surface- loading media is utilized as a "polish" filter in such arrangements .
  • a filter media construction is provided.
  • the filter media construction can be used as a filter media in preferred filter arrangements. It may, in some instances, be utilized as one layer of media in a multilayer arrangement, for example. In some arrangements, layers of filter media according to the present invention can be stacked, to create a preferred construction. Herein various layers or volumes of media will sometimes be referred to as "regions".
  • a preferred filter media construction according to the present invention includes a first layer of permeable coarse fibrous media having a first surface.
  • a first layer of fine fiber media is secured to the first surface of the first layer of permeable coarse fibrous media.
  • the first layer of permeable coarse fibrous material comprises fibers having an average diameter of at least 10 microns, typically and preferably about 12 (or 14) to 30 microns.
  • the first layer of permeable coarse fibrous material has a basis weight of no greater than about 50 grams/meter , preferably about 0.50 to 25 g/m , and most preferably at least 8 g/m .
  • the first layer of permeable coarse fibrous media is at least 0.0005 inch (12 microns) thick, and typically and preferably is about 0.001 to 0.010 inch (25-254 microns) thick.
  • the first layer of permeable coarse fibrous material comprises a material which, if evaluated separately from a remainder of the construction by the Frazier permeability test, would exhibit a permeability of at least 150 meters/min, and typically and preferably about 200-450 meters/min.
  • it is a material which, if evaluated on its own, has an efficiency of no greater than 10% and preferably no greater than 5%. Typically, it will be a material having an efficiency of about 1% to 4%.
  • efficiency when reference is made to efficiency, unless otherwise specified, reference is meant to efficiency when measured according to ASTM #1215-89, with 0.78 ⁇ monodisperse polystyrene spherical particles, at 20 fpm (6.1 meters/min) as described herein. Herein this will sometimes be referred to as the "LEFS efficiency".
  • a layer of material utilized in arrangements according to the present invention is characterized with respect to properties it "has” or would exhibit “on its own” or when tested “separately from the remainder of the construction"
  • the layer of material is being characterized with respect to the source from which it is derived. That is, for example, if reference is made to the "coarse” layer of material, in a composite, the description when characterized as referenced above, is with respect to the material and its properties as it would have existed before being incorporated into the construction. Reference in this context is not necessarily being made to the specific numerical characteristics of, or performance of, the layer as it operates in the composite structure.
  • the layer of fine fiber material secured to the first surface of the layer of permeable coarse fibrous media is a layer of fine fiber media wherein the fibers have average fiber diameters of no greater than about 10 microns, generally and preferably no greater than about 8 microns, and typically and preferably have fiber diameters smaller than 5 microns and within the range of about 0.1 to 3.0 microns.
  • the first layer of fine fiber material secured to the first surface of the first layer of permeable coarse fibrous material has an overall thickness that is no greater than about 30 microns, more preferably no more than 20 microns, most preferably no greater than about 10 microns, and typically and preferably that is within a thickness of about 1-8 times (and more preferably no more than 5 times) the fine fiber average diameter of the layer.
  • the preferred upper basis weights for the fine fiber layers are as follows: for a layer of glass fiber material average size 5.1 micron, about 35.8 g/m ; for glass materials average fiber size 0.4 micron, about 0.76 g/m ; and, for glass fibers average size 0.15 micron, about 0.14 g/m 2; for polymeric fine fibers average size 5.1 micron, about 17.9 g/m ; for polymeric fibers average size 0.4 micron, about 0.3 g/m ; and, for polymeric fine fibers 0.15 micron average size, about 0.07 g/m .
  • the most upstream layer of fine fibers has a basis weight of no greater than about 1 g/m , for such applications .
  • the preferred upper limits of the basis weights for the fine fiber layers will be as follows: for glass fibers average size 2.0 micron, about 15.9 g/m ; for glass fibers average size 0.4 micron, about 1.55 g/m ; and, for glass fibers average size 0.15 micron, 0.14 g/m ; for polymeric fine fibers average size 2.0 micron, about 8.0 g/m ; for polymeric fibers average size 0.4 microns, about 0.78 g/m ; and, for polymeric fibers average size 0.15 microns, about 0.19 g/m 2 .
  • the most upstream layer of fine fibers has a basis weight of no greater than about 1 g/m , for such applications.
  • the upper limits given for the air filtration applications, such as air induction systems etc., were based upon fine fiber layer thicknesses of about 5 fiber diameters, and an LEFS efficiency of 50% for the layer.
  • the assumption was based upon five fine fiber thicknesses and an LEFS efficiency of about 90% per layer.
  • the preferred basis weight for any given situation would depend upon such variables as: the application involved (for example coarse or fine particles, or both, to be trapped in operation, high efficiency or lower efficiency needs); the desired life; the fiber material selected; and, the fiber size used.
  • the glass fibers will work well, and the system will involve higher basis weights (for example about 20 g/m ), at higher fiber diameters (for example 2-3 microns) .
  • first or second in reference to a construction, for example surfaces of media, is not meant to refer to any particular location in the media.
  • first surface on its own is not intended to be indicative of whether the surface referred to is upstream or downstream of other surfaces, or positioned above or below other surfaces. Rather, the term is utilized to provide for clarity in reference and antecedent basis.
  • 1-8 fine fiber average diameters is meant to reference a depth or thickness of about 1 times to 8 times the average diameters of the fine fibers in the fine fiber layer referenced.
  • the fine fibers of the first layer of fine fiber media comprise fibers with diameters of no greater than about l/6th, preferably no greater than about 1/lOth and in some instances preferably no greater than about l/20th of the diameters of the fibers in the first layer of permeable coarse fibrous media.
  • the first layer (most upstream in operation) of fine fiber material is constructed and arranged to provide the resulting composite (i.e. the combination of the first layer of permeable coarse media and the first layer of fine fiber media) with an overall LEFS efficiency of at least 8%, preferably at least 10%, typically within the range of 20 to 60%, and most preferably at least 30% and no greater than about 70%.
  • Such composites can then be stacked to create very efficient, for example greater than 97%, and if desired up to 99% or more, filters. They may also be used for less efficiency but very long life filters, at least 10% typically, for example 50-97% efficient.
  • the first (most upstream in operation) layer of fine fiber media is constructed and arranged such that the resulting composite (i.e. the combination of the first layer of permeable fibrous media with the first layer of fine fiber media thereon) has an overall permeability of at least 20 meters/min, and typically and preferably about 30 to 350 meters/min.
  • the term “most upstream” or “outermost” in connection with a fine fiber layer refers to the layer of fine fiber material (average fiber diameter less than 8 microns) in the position to be most upstream, relative to other fine fiber layers, in use. There may be more upstream layers of media (not fine fiber) than the most upstream fine fiber layer.
  • the first layer of permeable coarse fibrous material may be fibers selected from a variety of materials, including for example polymeric fibers such as polypropylene, polyethylene, polyester, polyamide, or vinyl chloride fibers, and glass fibers.
  • a filter construction which includes more than one layer, and preferably at least 3 layers, of fine fiber material.
  • the arrangements will include three or more such layers.
  • each fine fiber layer is a layer within the general description provided above for the first layer of fine fiber media in the media construction as described.
  • each layer of fine fiber material is separated from its next adjacent layer of fine fiber material, by a layer of permeable coarse fibrous material which operates as a spacing layer or spacing matrix.
  • the layers of permeable coarse fibrous material need not be identical, but preferably each is within the general description given with respect to the filter media construction, for the first layer of permeable coarse fibrous media.
  • the overall composite media construction also has a layer of permeable coarse fibrous media, as described, on both the most upstream and most downstream surfaces .
  • the filter construction may comprise a pleated arrangement of the composite, if desired.
  • such an arrangement can have pleats that are 0.25 to
  • Certain preferred arrangements according to the present invention include media as generally defined, in an overall filter construction. Some preferred arrangements for such use comprise the media arranged in a cylindrical, pleated configuration with the pleats extending generally longitudinally, i.e. in the same direction as a longitudinal axis of the cylindrical pattern. For such arrangements, the media may be imbedded in end caps, as with conventional filters.
  • Such arrangements may include upstream liners and downstream liners if desired, for typical conventional purposes.
  • the constructions may be utilized in association with inner wraps or outer wraps of depth media, for example in accordance with the arrangements described in U.S. Patent Application No. 08/426,220, incorporated herein by reference.
  • media according to the present invention may be used in conjunction with other types of media, for example conventional media, to improve overall filtering performance or lifetime.
  • media according to the present invention may be laminated, or otherwise applied, to conventional media, be utilized in stack arrangements; or be incorporated (an integral feature) into media structures including one or more regions of conventional media. It may be used upstream of such media, for good load; and/or, it may be used downstream from conventional media, as a high efficiency polishing filter.
  • Certain arrangements according to the present invention may also be utilized in liquid filter systems, i.e. wherein the particulate material to be filtered is carried in a liquid. Also, certain arrangements according to the present invention may be used in mist collectors, for example arrangements for filtering fine mists from air. According to the present invention, methods are provided for filtering. The methods generally involve utilization of media as described to advantage, for filtering. As will be seen from the descriptions and examples below, media according to the present invention can be specifically configured and constructed to provide relatively long life in relatively efficient systems, to advantage.
  • the preferred filter media constructions comprise a plurality of layers of fine fiber media, i.e. at least two layers, each of the layers of fine fiber media comprising fibers having diameters of no greater than about 8 microns.
  • the plurality of layers of fine fiber media include an outermost layer. Again, by "outermost” in this context, it is meant that there is a layer of fine fibers in the media which, when the media is organized or oriented for use as a filter media, would be positioned more upstream than any other layer of fine fiber material.
  • this outermost layer of fiber fibers includes fibers having an average diameter of no greater than about 5 microns, and a thickness of no greater than about 5 times the fine fiber average diameters in that outermost layer. Thus, it would have a thickness of no greater than about 25 microns maximum, and in typical applications wherein smaller diameters than 5 microns are used, a substantially smaller thickness.
  • this outermost layer of fine fibers is relatively permeable having, on its own, a permeability for air of at least 90 meter/min.
  • a permeability for air of at least 90 meter/min.
  • each layer of permeable coarse fibrous media comprises fibers of at least 10 microns in diameter and preferably each layer has an efficiency, if evaluated separately from the construction, of no greater than about 20%, and more preferably no greater than 10%, for 0.78 ⁇ particles as defined.
  • this media construction includes at least three layers of fine fiber material, although the at least two layers downstream from the "outermost" layer need not necessarily have an average diameter smaller than 5 microns, but rather it would be preferred that they are at least smaller than 8 microns; and, they may be less permeable than the outermost layer of fine fiber material, preferably each having a permeability on its own of at least 45 meter/min.
  • a preferred filter media construction according to the present invention may be defined as having a first layer of permeable coarse fibrous media comprising coarse fibers having an average diameter of at least 10 microns, an efficiency of no greater than about 5%, for 0.78 ⁇ particles, and a first surface on which is positioned a first layer of fine fiber media.
  • the first layer of fine fiber material comprises fibers having an average diameter of no greater than about 5 microns, and a thickness of no greater than about 5 times the average diameter of the fine fibers in this first layer.
  • this material has a permeability, on its own of at least about 90 meter/min.
  • This media construction can be utilized in association with other layers of fine fiber and coarse fiber material, and may even be utilized in overall media constructions that use other types of media, for example in association with paper or glass media or other types of depth media.
  • the media construction of this embodiment may also include a plurality of further layers of fine fiber material, each of which is spaced from the next adjacent one by a layer of coarse fiber media.
  • treatments may be added to the fibers to enhance such characteristics as efficiency, filter life or both.
  • An overall filter construction may be provided, using media according to the present invention, and as defined in either of the above two identified preferred embodiments.
  • Fig. 1 is a schematic representation of a cross section of a theoretical mono-layer fine fiber filter media.
  • Fig. 2 is a schematic representation of a cross section of a theoretical mono-layer coarse fiber filter media.
  • Fig. 3 is a schematic representation of a cross section of a theoretical mono-layer fine fiber filter media; Fig. 3 being of a different media than that shown in Fig. 1.
  • Fig. 4 is a schematic representation of a cross section of a theoretical mono-layer coarse fiber media arrangement having the same percent solidity as the arrangement shown in Fig. 3.
  • Fig. 5 is a schematic fragmentary plane view of a surface of a media construction according to the present invention.
  • Fig. 6 is a schematic cross sectional view of a media according to Fig. 5.
  • Fig. 7 is a schematic fragmentary cross sectional view of a multi-layer media construction according to the present invention.
  • Fig. 8A is a fragmentary schematic perspective view of a pleated media arrangement including a media construction according to the present invention.
  • Fig. 8B is an enlarged fragmentary schematic cross-sectional view of a portion of the arrangement shown in Fig. 8A.
  • Fig. 9 is a schematic representation of a media according to the present invention threaded on a mechanical support structure.
  • Fig. 10 is a side elevational view of a filter arrangement incorporating a filter media construction according to the present invention therein.
  • Fig. 11 is an enlarged fragmentary schematic cross sectional view taken generally along line 11-11 of Fig. 10.
  • Fig. 12 is a scanning electron micrograph of a conventional air-laid polymeric fiber media.
  • Fig. 13 is a scanning electron micrograph of a conventional air-laid glass fiber media.
  • Fig. 14 is a scanning electron micrograph of a conventional two-phase media.
  • Fig. 15 is a scanning electron micrograph of the same conventional two-phase wet-laid glass media as shown in Fig. 14; Fig. 15 being taken of an opposite side of the media from that shown in Fig. 14.
  • Fig. 16 is a scanning electron micrograph of a media according to a first embodiment of the present invention.
  • Fig. 17 is a scanning electron micrograph of a media according to a second embodiment of the present invention.
  • Fig. 18 is a scanning electron micrograph of a media according to a third embodiment of the present invention.
  • Fig. 19 is a scanning electron micrograph of a media according to a fourth embodiment of the present invention.
  • Fig. 20 is a scanning electron micrograph of a media according to a fifth embodiment of the present invention.
  • Fig. 21 is a scanning electron micrograph of the media of Fig. 19, after NaCl loading according to a description herein.
  • Fig. 22 is a plot of data from Experiment 5.
  • Fig. 23 is a plot of certain data from Experiment 6.
  • Fig. 23 A is another plot of data from Experiment 6.
  • Fig. 24 is a scanning electron micrograph of a media according to the present invention shown after NaCl loading.
  • Fig. 25 is a schematic of a custom salt bench used in certain experiments.
  • Fig. 2 is a schematic illustrating a "single" or “mono-" layer of fine fiber media, with a fixed interfiber distance, D x , representing the distance between the surfaces of adjacent fibers.
  • Fig. 2 is a schematic representation depicting a single layer with the same D x but wherein the fiber diameter is about 12 times larger than the fiber diameter in Fig. 1. Comparing Figs. 1 and 2, it is apparent that, for an area of fixed media perimeter (i.e. area) the total amount of air space or void space between the fibers in the arrangement of Fig.
  • Figs. 3 and 4 are intended to schematically represent a single layer of fibers in two depth media systems in which fibers of different sizes are used, but percent solidity or density is held constant. From a review of the figures, it should be apparent that the arrangement with the larger fibers, i.e. the arrangement of Fig. 4, has potentially such large open areas that the filter efficiency is relatively low (but permeability is very high) , by comparison to an arrangement with smaller diameter fibers but the same percent solidity, i.e. the arrangement of Fig. 3. Theoretical considerations of the effects of utilizing smaller fiber diameters have been studied and have been represented quantitatively by the Stokes Number and Interception Parameter. The dimensionless Stokes Number is represented by the following formula:
  • d f fiber size (diameter)
  • d p particle size (diameter)
  • p p particle density
  • v approach velocity
  • ⁇ fluid viscosity
  • the Stokes Number is reflective of inertial impaction. This can be understood by considering the likelihood that as an airstream is distorted or curved around a fiber, a particle within the airstream and directed toward the fiber will leave the airflow (rather than curve with the air flow) and impact the fiber.
  • the variables reflected in the formula above for the Stokes Number logically reflect that, in general, an increase in momentum of the particle (from increasing density and/or velocity) is associated with a greater likelihood that the particle will not flow around the fiber with the airflow stream, but rather that it will leave the airflow stream and directly impact the fiber.
  • the formula indicates that this likelihood is greater when the fiber diameter is smaller, due, at least in part, to the fact that when the fiber diameter is smaller, the fiber will disrupt the airflow stream to a lesser extent. This brings the effected flow field of the airstream, as it curves around the fiber, into closer proximity to the surface of the fiber and increases the likelihood that a lower momentum particle will still leave the air stream sufficiently to encounter (impact) the fiber.
  • Interception Parameter (R) can be represented by the following formula:
  • d p and d f are defined as above.
  • Interception Parameter is velocity and momentum independent, and relates to the size of the particle and the size of the fiber. In general, it relates to the likelihood that a particle (which tends to curve with the airstream, as the airstream is distorted around the surface of the fiber) , will nevertheless encounter the fiber and become trapped. Thus, it does not directly relate to the likelihood that the momentum of the particle will carry it out of the airstream and into the fiber, but rather whether, while within the airflow stream, the particle will nevertheless encounter the fiber. In general, since smaller fibers disrupt the airflow to a lesser extent, and the distortion in the air flow (from linear) occurs closer to the surface of the fiber, smaller fibers are associated with higher efficiencies and a higher rate of interception impactions than larger fibers.
  • the advantages associated with the use of fine fibers in a media are more pronounced with relatively small particles.
  • the advantages of fine fibers may be of particular interest when the filter application will require filtering of small particles, especially those 10 microns or less in size (diameter) .
  • constructions made from fibers on the order of about 0.2 - 5 microns in size would be more difficult to handle (than constructions of coarser fibers) and would tend to collapse in use, creating a very low permeability. That is, it is relatively difficult to maintain a substantially open structure for high loading and high flow therethrough, with a construction merely comprising fibers of 5 microns or below in diameter, since such media typically possesses insufficient mechanical strength (or "body”) to resist collapse. When the media collapses, the spaces between the fibers become relatively small, and the construction, while perhaps quite efficient as a filter, loads fairly rapidly and is not very permeable.
  • Such media has typically found use in pulse cleaned dust collectors.
  • the coarse, surface loading, cellulose media operates in part as an internal trap for small particles. When this occurs, pulse cleaning is less effective since some particles are trapped inside the cellulose media.
  • the fine web when used, generally operates to collect particulates upstream of the surface loading cellulose fibers, facilitating particle release when the reverse pulse is applied.
  • a general approach for the utilization of fine fibers i.e. on the order of 8 or 10 microns or less in diameter, preferably 5 microns or less and typically about 0.1 to 3.0 microns in diameter (average), in filter media has been developed.
  • a very porous, permeable substrate of relatively coarse fibers is used as a support , support matrix or spacing layer for the very fine fiber media.
  • the material can then be configured in a preferred manner, to achieve an efficient, relatively long life, filter.
  • multiple layers of fine fiber media, separated as described are used to advantage. When multiple layers of fine fiber media, separated as described, are used, long-life, highly efficient filtering systems can be readily obtained.
  • the material 1 includes coarse fibers 2 and fine fibers 3.
  • the material 1, however, is not a material in which the fibers of different sizes are mixed together or are intimately entangled, when the material is created. Rather, material 1 generally comprises a layer (having depth) of coarse fibers 2, at least one outer surface of which has had the fine fibers 3 applied thereto. That is, the media comprises a web of fine fibers on at least one outer surface of a structure of coarse fibers. The fine fibers in the web of fine fibers, then, are not mixed in or entangled with the coarse fiber matrix.
  • the layer of coarse fibers 2 is sometimes referred to as a layer of permeable coarse fibrous media or material. It comprises a substrate on which the fine fibers 3 are positioned.
  • Fig. 5 can be visualized as somewhat analogous to a spider web strung between the rails of a fence. (The analogy is most appropriate if it is also assumed that the spider web is positioned and attached at one side or surface of the fence.)
  • the rails, or coarse fibers 2 provide for a very porous open area, and do not substantially interfere with the airflow through the open space.
  • the fine fibers 3 represent the web suspended in or across the open space. Since the majority of the airflow stream through such a material is not substantially disrupted by the coarse fibers 2, the involvement of the coarse fibers 2 in interception impaction and inertial impaction is relatively small. The extremely fine fibers 3, however, are strung across the volume where the substantial airflow will occur.
  • the spiderweb analogy would involve a plurality of fences stacked against one another, each of which having a spiderweb on a side thereof. The effect would be the stacking of spaced-apart fine spiderwebs .
  • Fig. 6 is a fragmentary cross sectional view of material such as that illustrated in Fig. 5.
  • Fig. 6 is schematic in nature. It will be understood that, in general, Fig. 5 is greatly enlarged relative to Fig. 6, so that detail can be understood.
  • Fig. 6 the layer of depth media of coarse fibers is represented generally at 4 and the layer of very fine fibers is illustrated at 5. It will be understood that the fine fibers 5 are applied to surface 6 of the coarse fiber matrix 4.
  • the layer of fine fibers will be configured approximately as a mono-layer, and to not have a thickness much greater than about 1-8 fine fiber diameters. In general, its depth will be no greater than about 10-15 microns at any given location, and typically no greater than about 2-4 microns .
  • the depth of the coarse support media 4 will be varied from system to system.
  • the schematic of Fig. 6 is simply presented to indicate that in general the depth of the coarse media 4 will be relatively great, by comparison of the depth of the layer of fine fibers 5.
  • the construction of Figs. 5 and 6, however, would be expected to be a relatively inefficient filter, especially if a very open layer of fine fibers is used, since a substantially large void volume or interfiber spacing (i.e.
  • material such as that reflected in the schematic of Fig. 5 is arranged in multiple layers, for example, in a stack.
  • a stack of layers, each of which is similar to Fig. 5, would present the relatively fine fibers 3 in a substantially effective density, with respect to likelihood of being encountered by particles in an airflow stream passing through the entire system.
  • the relatively large void volume provided by the very porous coarse fibers 2 would allow for a substantial loading volume, permeability and thus a relatively long lifetime. It can be theorized, therefore, that such a construction can be developed which would be both very efficient as a filter and of relatively long usable lifetime. As the experiments below indicate, in practice this is achieved.
  • a further advantageous aspect of the arrangement shown in Fig. 5 can be understood by considering the effect of such a composite on trapping particles, in operation.
  • the particles will appear primarily trapped on, and secured to, the individual fine fibers, as small individual particles or agglomerations of particles.
  • the fiber spacing between the fine fibers is sufficiently large that a substantial amount of bridging between the fibers does not occur. This is shown in Fig. 21, discussed below. Indeed the fiber spacing is sufficiently large so that as bridging begins to occur, the particle dendrites tend to break up and fall through the layer of fine fiber.
  • a stack can be constructed by alternately applying coarse and fine fibers to a structure, rather than by combining pre-formed composites (or layers) of the type shown in Fig. 5.
  • the effects on filtering should generally be the same, however one or the other type of process, or alternatives, may be preferred for reasons not related to the performance of the final structure.
  • Typical filter media constructions when configured for use to filter, will include multiple layers of media, with at least two layers effectively comprising a coarse framework supporting or spacing fine fibers or fine fiber webs.
  • An example of such an arrangement is shown schematically in Fig. 7.
  • stacked arrangements may be constructed from multiple layers of the same media composite.
  • a gradient can be provided in the stacked arrangement, for example, by using somewhat different composite materials in each layer or applying layers appropriately while making the multi-layer composite.
  • the materials in the various layers for example, may be varied with respect to the average population density of the fine fibers across the open spaces of the coarse support.
  • the diameters of the fine fibers can be varied from layer to layer.
  • arrangements can include one or more layers of one particular construction, and also one or more layers of a different construction or more than one different construction.
  • Construction 10 includes a layer or region 13 of media comprising a coarse support 14 having a thin layer 15 of fine fibers on a surface thereof.
  • layer 15 is on an upstream surface of support 14.
  • Downstream from layer 13 is a similar layer 17 comprising a coarse support 18 and an upstream, thin, fine fiber layer 19.
  • Arrangement 10 includes further layers 20, 21 and 22 analogously constructed to layers 13 and 17.
  • coarse region 25 of layer 22 is positioned most downstream.
  • upstream of the most upstream fine fiber layer 15, is located a layer 27 of coarse fiber, protective, scrim or media .
  • the overall construction 10 of Fig. 7 will only be about 0.020 to 0.060 inch (0.05-0.15 cm) thick, and in some instances even thinner. Thus, it is enlarged and exaggerated greatly in the figure. It comprises a stack of layers of fine fibers, each of which is spaced from the next adjacent fine fiber layer by a coarse separating or support layer or matrix. On each side, i.e. the most upstream side 27 and most downstream side 25, is located a protective layer of coarse scrim or media.
  • the particular arrangement of Fig. 7 is shown with five, discrete, fine fiber layers, but alternate amounts or numbers of layers can be used.
  • each fine fiber layer is not substantially entangled with the separating coarse support fibers, but rather each fine fiber layer generally sits on a surface of a support structure.
  • a principal function of the coarse material in filter media layers according to the present invention is to provide for a framework across which the fine fibers are extended. Another principal function of the coarse material is to provide for spacing between the regions or layers of fine fibers, in the stack, so that the separated layers of fine fibers do not collapse into a relatively dense (.i.e. low permeability and relatively low loading) construction.
  • the coarse support/spacing structure is not typically provided to serve any substantial filtering function. Indeed, it preferably is a material so open and permeable that it does not serve any substantial filtering function.
  • the overall composite i.e. the resulting multi-layered, filter media
  • the overall composite be a relatively flexible arrangement, which can be arranged in a variety of geometric configurations.
  • the coarse support comprise a flexible fiber construction that has sufficient mechanical integrity or "body” to allow for this.
  • this "body” can be provided by a component other than the same coarse fiber material used to space the fine fiber layers, or it can be provided by the overall composite. This will be described below.
  • a It is preferred to select a material which has a very low percentage solidity and a very high permeability, if possible, to enhance the "void space" across which the fine fiber web will extend.
  • it is a material having a single layer permeability when evaluated by the Frazier Perm Test, of at least 150 meters/min, typically at least about 200-450 meters/min.
  • the coarse support/spacing material should be sufficiently thick to keep the layers of fine fibers separated. In general, for some 5 systems the layer of coarse material need not be any thicker than is minimally necessary to achieve this spacing. It is foreseen that a thickness on the order of about 0.001 inch (25 microns) or so will be more than
  • the material or process selected for the coarse substrate may be thicker than about 0.001 inch, for example on the order of about .010 inch (254 microns), the additional thickness is not necessarily
  • each layer of coarse fiber material which separates layers of fine fibers, is no greater than about 0.030 inches (760 microns) thick.
  • the fine fiber layers are
  • 35 thicker layers of scrim or coarse fibers may provide for improvement in "body” or mechanical strength.
  • relatively thick layers may take up an undue or undesirable amount of space in some filter constructions .
  • the particular material from which the fibers of the coarse support are constructed is not critical, in general it will be preferred to select material that is sufficiently strong and tough to withstand manipulations during manufacture and handling, and also to survive operating conditions. It is an advantage of constructions according to the present invention that the media for many effective filter systems can be provided without the use of "electrically charged” or “statically charged” fibers. Thus, certain preferred systems according to the present invention use fibers without static charge applied to them.
  • the coarse support can be provided from readily available fibrous material such as polymeric fibers. Thus, commercially available materials can be chosen as the coarse support or scrim.
  • the material from which the coarse support is formed should be one to which the fine fibers can be readily and conveniently applied.
  • the diameter of the coarse fibers is less important to preferred filter operation, provided the minimal properties described herein are obtained.
  • the fiber diameters of the coarse fibers will be at least about 6 times, and typically and preferably about 20-200 times, the fiber diameters of the fine fibers.
  • the coarse material will comprise a fibrous material having an average diameter of about 10 to 40 microns, and typically 12 microns or larger.
  • the coarse material will typically have a basis weight within the range of 6.0 to 45.0 g/m , for preferred arrangements.
  • the coarse fiber layer may comprise a collection or mix of short fibers or a non- woven substantially continuous fiber matrix.
  • continuous means fibers having an aspect ratio which is sufficiently large to essentially be infinite, i.e. at least 500 or above.
  • Wet-laid materials may be utilized for the non-woven support; however, air-laid also may be used in some systems.
  • fibrous scrims can be used as the coarse support.
  • One such scrim is Reemay 2011, commercially available from Reemay Co. of Old Hickory, IN 37138. In general, it comprises 0.7 oz., spunbonded polyester.
  • the coarse support layer can comprise a mixture of fibers of different materials, lengths and/or diameters .
  • a should be a material that can be readily formed into fibers with the relatively small diameter selected, for application to the coarse support, or into a web or network of such fine fibers.
  • the fine fiber component will be provided with fiber diameters of 8 microns or less, typically less than 5.0 microns, and preferably about 0.1-3.0 microns depending upon the particular arrangement chosen.
  • fiber diameters 8 microns or less, typically less than 5.0 microns, and preferably about 0.1-3.0 microns depending upon the particular arrangement chosen.
  • a variety of filter materials can be readily provided in such diameters including, for example: glass fibers; polypropylene fibers; PVC fibers; and, polyamide fibers. More generally, polyacrylonitrile can be used; polyvinyladine chloride available from Dow Chemicals, Midland, MI as Seran ® F-150 can be used.
  • suitable synthetic polymeric fibers can be used to make very fine fibers including polysulfone, sulfonated polysulfone, polyimid, polyvinylidine fluoride, polyvinyl chloride, chlorinated polyvinyl chloride, polycarbonate, nylon, aromatic nylons, cellulose esters, aerolate, polystyrene, polyvinyl butyryl, and copolymers of these various polymers.
  • the fine fibers can be secured to the coarse support in a variety of manners.
  • the technique used may depend, in part, on the process used for making the fine fibers or web, and the material (s) from which the fine fibers and coarse fibers are formed.
  • the fine fibers can be secured to the coarse support by an adhesive or they may be thermally fused to the coarse fibers.
  • Coarse bicomponent fibers with a meltable sheath could be used to thermally bond the fine fibers to the coarse fibers.
  • Solvent bonding may be used, thermal binder fiber techniques may be applicable, and autogenous adhesion may be used.
  • wet- laid water soluble or solvent based resin systems can be used.
  • Urethane sprays, hot melt sprays, or hot melt sheets may be used in some systems.
  • adhesives for positive securement of the fine fiber web to the coarse support will not be needed.
  • These will at least include systems in which, when the overall composition is made, the fine fiber is secured between layers of coarse material, and this positioning between the two coarse layers is used to secure the fine fiber layer or web in place.
  • the fine fiber layer comprising "fine fibers" or a "network or web" of fine fibers.
  • network or "web” of fine fibers in this context is meant to not only refer to a material comprising individual fine fibers, but also to a web or network wherein the material comprises fine fibers or fibrils which join or intersect one another at nodes or intersections.
  • Fig. 20 An example of such an arrangement is shown in Fig. 20, discussed in greater detail below. From a review of the Fig., it can be seen that the network of fine material generally comprises a plurality of very fine fibers or strands, some of which extend from nodes or points of intersection.
  • a layer of media used in constructions according to the present invention will generally include a coarse support or matrix having a layer or web of fine fibers secured to at least one surface thereof.
  • the coarse support (or matrix) and fine fibers may be generally as previously described.
  • the overall layer may be characterized in a variety of manners, including, for example, simply as comprising coarse and fine fibers as described and also arranged as shown. It is not accurate to characterize preferred media according to the present invention as comprising a "mixture" of the fine fibers with the coarse fibers.
  • the material is not generally constructed as a mixture of such fibers, i.e., an arrangement wherein the fibers are entangled.
  • any given one of the composite layers generally comprises the layer of coarse material having at least one surface on which is applied the fine material. Even when the media is provided in multilayer (stacked) arrangements, the regions of fine fiber and coarse fiber are generally separately encountered as air passes through the "stack".
  • the fine fiber layers are described as “discrete” relative to one another and relative to the coarse fiber layers, it is not meant that there is absolutely no entanglement, but rather the construction is such that the multi-layer, i.e. separated fine fiber layer, environment is provided for filtration, as the fluid to be filtered passes through the arrangement. In general this will mean (when the layers are discrete) that such entanglement that may occur is relatively low. Generally the entanglement between the fine fiber layers and coarse fiber layers, if it occurs at all, will only involve a relatively small percent by weight of the fine fibers, typically less than 15%.
  • the composite layer of media may be characterized with respect to the mass of fine fiber applied per unit area of a surface of the coarse support or scrim. This is sometimes referred to as the basis weight of the fine fiber layer. Such a characterization will be varied depending upon the particular fiber diameter used, the particular material chosen and the fiber diameter and the particular fine fiber population density or filter efficiency desired for the layer.
  • the mass of material from which the fine fibers are formed, applied per unit surface area of scrim or coarse support (or matrix) will be within the range of about 0.2 to 25 g/m 2 , regardless of the particular material used.
  • An alternate method to characterize a typical and preferred media layer in constructions according to the present invention is with respect to the amount of interfiber space open or visible, when looking into the coarse fiber support or scrim (from the fine fiber side) , that is occupied by or covered the fine fibers or web of fine fibers. This method of characterization will be understood, in part, from consideration of Figs. 16-20.
  • Figs. 16-20 are scanning electron micrographs, at various magnifications, of various examples of scrim with a fine fiber web according to the present invention on one surface thereof.
  • the coarse support comprises a matrix of polyester fibers of 25 to 35 microns in diameter.
  • the fine fibers generally comprise glass fibers from about 0.1 to 3 microns in diameter.
  • the percentage of the area of the open pores in the scrim, occupied by the fine fibers, by area, can be estimated from evaluation of SEMs such as that depicted in Figs. 16-20. It is foreseen that for typical and preferred constructions according to the present invention, the average percentage of the open area in the coarse support or scrim occupied by the fine fibers, when evaluated using such a method, will be 55 % or less, typically about 20 to 40% for preferred air filter media. It is not meant to be suggested that constructions outside of these ranges will be inoperative, but rather that such percentages are typical and are associated with generally operable and effective materials.
  • a coarse fiber support structure or matrix comprising fibers having an average diameter of at least 10 microns, and also having an efficiency of 6% or less, for 0.78 ⁇ particles when evaluated as described herein, is improved by application of at least one fine fiber layer thereon, wherein the fine fibers have an average fiber diameter of about 5 microns or less, such that the improved material when tested has an efficiency of at least about 8%, and preferably at least 10%, for the 0.78 ⁇ particles defined, the construction will be one which has at least some of the desirable properties for use in at least certain preferred arrangements according to the present invention.
  • the material comprises a scrim having an efficiency of about 4% or less for 0.78 ⁇ particles, to which sufficient fine fibers have been applied to provide a composite efficiency of at least 10% or more for 0.78 micron particles.
  • the coarse fiber layer is a material having a permeability, without the fine fiber layer applied thereto, of 250-450 meters/min.
  • the fine fiber material is arranged such that the permeability of a single composite layer of the fine fiber/coarse fiber combination is at least about 10 meters/min, more preferably at least about 25 meters/min. In some instances it may be chosen to be significantly higher, i.e. 100-325 meters/min.
  • permeability any given layer of scrim materials; a composite or layer of scrim with at least one layer of fine fiber thereon; and the overall media composite.
  • the numerical references to "permeability" are in reference to the media face velocity (air) required to induce a 0.50 inch H 2 0 restriction across a flat sheet of the referenced material, media or composite.
  • permeability of a media layer is assessed by Frazier Perm Test according to ASTM D737, using a Frazier Perm Tester available from Frazier Precision Instrument Co., Inc., Gaithersburg, MD, or by some analogous test.
  • Typical media arrangements according to the present invention especially when used in auto cabin air filters, ventilation systems or engine air induction systems, will have an overall permeability of at least 6 meters/min, and more preferably 10-20 meters/min, with permeability being a function of the overall efficiency, number of layers and size of selected fibers.
  • overall permeability of at least 6 meters/min, and more preferably 10-20 meters/min, with permeability being a function of the overall efficiency, number of layers and size of selected fibers.
  • efficiency is typically meant to refer generally to the percentage of test particles retained, when the material characterized is tested according to the method of ASTM 1215-89, incorporated herein by reference, and wherein the test material applied is 0.78 micron diameter, mono-dispersed, polystyrene latex spheres, such as those available from Duke Scientific, Palo Alto, CA, tested at 20 feet/min. (about 6 meters/min) .
  • materials according to the present invention can be characterized with respect to either fiber spacing or the amount of fine fiber material applied per unit area of the coarse substrate or scrim (basis weight) .
  • Methods usable to accomplish this are as follows.
  • the method employed here is to scan an SEM photo into a computer for image analysis.
  • Usable SEM magnification depends on the size of the fibers of interest in the media structure and should be selected so the edges of the fibers to be analyzed are distinct from the background. As magnification is increased, the depth of the viewing field is reduced. After scanning, one can use commercially available software such as Visilog (from Noesis Vision of Ville St. Laurent,
  • Fibrous structures are 3-dimensional, while SEM photos represent a projection of a 3-dimensional object onto a plane or area, hence the term "area solidity".
  • the method employed here is to scan an SEM photo into a computer for image analysis, again using commercially available software such as Noesis Visions Visilog.
  • Usable SEM magnification depends on the size of the fibers of interest in the media structure and should be selected so the edges of the fibers to be analyzed are distinct from the background. As magnification is increased, the depth of the viewing field is reduced.
  • commercially available software such as Visilog by Noesis Vision, to separate the image into foreground and background by setting a grayscale threshold value which defines the border between foreground and background, and convert the scanned grayscale image into a binary image (foreground and background) . A more refined separation can be achieved through the use of the erode and dilate commands.
  • An anomaly include convex pores and pores that lie partially inside the original AOI, i.e. the borders of such pores are not fully defined.
  • Software tools can then be used to calculate the perimeter, area, and aspect ratio in pixel dimensions for each cell inside the revised AOI.
  • a shape factor defined as:
  • SEM photos of media samples of appropriate magnification and number to determine the fiber size distribution of the media are taken.
  • magnifications typically range from 1,000 to over 6,000X.
  • a grid of lines can be superimposed onto (a magnified copy of) the SEM.
  • the number of fibers intersecting the randomly selected grid lines can be counted so that the number of intersections per inch of line is known.
  • By accumulating data for a statistically significant number of lines one can calculate average interfiber spaces and devise a distribution of interfiber distances. The procedure should be repeated sufficiently to ensure a representative figure (or distribution) for the sample.
  • Lbs/3000 ft or grams/m can be used to estimate interfiber space dimensions since in typical constructions the fine fiber mat of interest approximates a monofiber layer.
  • volume solidity can be calculated, which is a fiber spacing index.
  • L centerline distance between parallel fibers on opposite sides of assumed square pore.
  • d f mean square fiber diameter.
  • the interfiber distance "b" can be estimated from the following equations:
  • This model corrects for spacing between consecutive layers of fibers, assumes an inter layer distance of L/2, and is considered valid for values of C ⁇ 0.6.
  • the selection will depend in part upon the use to which the filter media is to be applied and how the media is made.
  • the intended use will generally result in a definition, for the filter designer, of the efficiency of the filter and permeability needed.
  • the efficiency for a given use may be defined by means other than by ability to trap 0.78 micron particles under the test conditions provided above.
  • the manufacturer of an automobile may have specific specifications for the operation of a cabin air filter, which the filter engineer is to meet using materials according to the present invention. That specification might be defined with respect to the ability to trap particles under test conditions that are not equivalent to those defined herein with respect to 0.78 micron particles.
  • the engineer could use the techniques described herein to approximate the possible construction, and then develop appropriate testing to see that the specifications provided by the automobile manufacturer are met.
  • the engineer may develop sufficient correlation data to be able to predict performance under one type of condition, based upon tests conducted under another.
  • the design process will begin with the engineer considering available materials, that possess properties according to the present invention.
  • the engineer may select a scrim and obtain various samples of the scrim material with various amounts of fine fiber material applied thereto.
  • the engineer has had various samples of scrim material comprising Reemay 2011 treated with fine fiber glass material in various amounts, on only one surface thereof, to create eight samples in which the fine fiber layers are characterized by the following:
  • the filter engineer could conduct the designing process.
  • the efficiency of the composite for the 0.78 micron particles under the test conditions defined will be the "sum" of the efficiency of each of the layers. For example, if two layers are used, each of which is 35% efficient, an overall efficiency of 1 - [(1 - .35) x (1 - .35)] or 57.75%.
  • the engineer is in a position to be able to determine how many layers and which materials to use, in order to achieve a desired level of efficiency.
  • a general formulation for determining efficiency in a multilayer system was presented. The specific calculation was made according to the following principles:
  • the overall permeability of the composite can be determined from the permeability of the various layers in the composite according to the following mathematical relationship:
  • pi permeability of component layer of composite comprising either: layer of coarse + fine; or layer of coarse alone, depending on construction.
  • the engineer can know what the permeability of the overall composite will be; and, various layers can be chosen to provide a particular desired permeability.
  • the typical face velocity of a cabin air filter is 50-70 ft/min (about 15-24 meters/min) and such an arrangement operates with an air flow of 220-300 ft 3 /min (about 6.2-8.5 metersVmin) .
  • This can, for example, be achieved with a filter made of the following composite: 1.
  • An upstream layer or matrix that is 30% efficient;
  • next downstream layer or matrix that is 35% efficient 3. A next downstream layer or matrix that is
  • the composite would then be about 75% efficient.
  • the engineer may wish, of course, to take into consideration other variables or factors. For example, fewer layers may be associated with a thinner composite, and in some instances a preferred overall organization.
  • Cost, availability of materials for any given layer, and other related factors may be of concern.
  • the resulting physical properties of the composite for example with respect to ease of formation of a pleated construction, may be of concern.
  • the engineer will desire to have all layers of the stack comprise the same composite material. However, in other instances different materials (or efficiencies etc.) may be used in some or all of the layers. It is foreseen that in typical operations, should the engineer determine to have layers of different efficiency in the composite, in general the resulting efficiency gradient will preferably be arranged such that the efficiency of the composite layers generally increases toward the downstream side of the construction. That is, it is presently foreseen that the preferred organization of layers will be such that more efficient composite layers are further downstream than less efficient composite layers, so that longer life results.
  • Media according to the present invention may be arranged in a wide variety of geometric configurations, to advantage.
  • flat sheets can be arranged in a simple stack to form media for a non-pleated panel type filter.
  • the sheets can be arranged as a blanket or wrap around an item, for example as a cylindrical wrap around a cylindrical structure.
  • a media according to the present invention can be provided in a form such that it can be readily pleated. In some instances, this will be accomplished by selecting the spacing scrim such that when stacked, the resulting composite has sufficient strength or "body” to be pleated and to retain the pleated configuration.
  • This is illustrated schematically in Figs. 8A and 8B.
  • filter media 30 is depicted in a pleated, cylindrical configuration.
  • Fig. 8B a portion of the material is shown in exaggerated blow up, so that it will be understood the material comprises a plurality of layers.
  • material 30 includes coarse layers 31 with layers 32 of fine fibers positioned therebetween.
  • the number of pleats whether arranged cylindrically or in a panel, will be about 1 to 15 per inch (or per 2.5 cm) .
  • the number of pleats per distance reported herein is with respect to the inner diameter of the cylindrical construction.
  • a pleated, cylindrical configuration according to the present invention is unique at least for the reason that media according to the present invention greatly exhibits the properties of depth media systems, with respect to loading and operational face velocities.
  • conventional depth media is not generally pleated. More specifically, pleated constructions are generally associated with paper or cellulose surface loaded systems.
  • the principles of the present invention can be utilized to provide an arrangement which operates as a form of depth media, but which can be configured in a pleated manner more similarly to surface loaded cellulose media.
  • the body can be provided by having only one or a few layers of material (in the media) possess sufficient body.
  • one or two layers of scrim in a multilayer system can be enough for this body without requiring all of the layers to possess it.
  • support layers of material within, or on one side or both sides of, the stacked arrangement may be used to provide this body or mechanical integrity.
  • Such a composite can be made using commercially available synthetic or cellulosic fibers as the support layers.
  • a second approach to providing a sinusoidal arrangement without having the coarse scrim layers form pleats is to utilize a mechanical framework to maintain the material in the pleated construction.
  • a schematic with respect to this is illustrated in Fig. 9.
  • mechanical stays 40 are depicted, with media 41 threaded thereon.
  • Pleat tip bonding approaches may also be used.
  • metal ribbons or wires positioned within the various composite layers can be used to maintain a pleated configuration.
  • an advantage of the present invention is that it may be applied in materials providing for a wide variety of geometric configurations. Thus it can be applied in a great many filter constructions to advantage. As indicated above, the properties of the materials may be selected so that the depth needed, for efficient operation, can be varied as desired.
  • Media according to the present invention may be utilized in a very wide variety of air filter constructions. It can be used, for example, as cylindrical pleated material in cylindrical elements. It may also be utilized as pleated material in panel- type filters. It can be used in unpleated forms, for example as sleeve filters inside of other filter elements, or around the outside of other filter elements. It can also be used in unpleated form in cylindrical and panel elements. Indeed, it may find application to replace the media, or a portion of the media in almost any of a wide variety of filtration or filter systems. In some instances, media according to the present invention may be utilized to enhance the operation of other media, for example other types of commercially available media.
  • media according to the present invention may be applied on an upstream side of, a downstream of, or between layers of various media, to achieve preferred filter operation.
  • a high efficiency version of media according to the present invention may be used downstream of various media, as a polish filter.
  • a high load, lower efficiency version of media according to the present invention may be utilized on the upstream side of conventional media, to achieve an increase in overall efficiency by utilization as a high load media on the upstream side.
  • Media according to the present invention may also be utilized between layers of conventional media, in various gradient filter systems or related systems .
  • One type of filter construction according to the present invention is illustrated in Figs. 10 and 11.
  • the filter arrangement 100 depicted includes a housing 101, an outlet tube 102, and a filter element 103. Access to an interior 104 of the housing 101 for maintenance of the filter element 103 is through hatch or cover 105.
  • the filter element 103 generally comprises pleated filter media 110, outer liner 111, and inner liner 112.
  • housing 101 includes inlet 120 for air to be filtered.
  • the air is distributed in chamber 121, before it passes through filter element 103.
  • the air then enters internal chamber or bore 122, and exits the filter element throughout outlet member 102.
  • the filter element 103 includes first and second opposite end caps 130 and 131, respectively.
  • the filter media 110 is secured to, embedded within and extends between, the end caps 130 and 131.
  • End cap 130 is sized and configured to form a radial seal with outlet tube 102, in region 140.
  • End cap 131 closes end 142 of the filter element 103, in a conventional manner.
  • Fig. 11 a portion of the arrangement shown in Fig. 10 is depicted in a schematic cross sectional view. It can be seen that the filter media 110 is a multi-layer arrangement according to the present invention, and contains a plurality of layers 150 of coarse material, and spaced apart layers 151 of fine fiber material. The particular arrangement shown in
  • Fig. 10 has two fine fiber layers 151 spaced apart and sandwiched by a total of three coarse layers 150. Again, according to the principles of the present invention, a variety of alternate arrangements may be utilized as the filter media 110.
  • the media is shown, in Figs. 10 and 11, incorporated in a cylindrical element constructed for radial sealing with the outlet tube.
  • the media may also be used in filter elements for axial sealing arrangements .
  • the invention can be used to prepare media having high loading capacity when compared to surface-loading media, but its loading advantages are believed to be more pronounced when the operation is for filtering a fine particulate matter, by comparison to filtering to collect more coarse matter. Therefore, by pleating the invention and placing it downstream of some depth media, advantages can be obtained, since the depth media would collect the coarse particles relatively efficiently, allowing enhancement of the filtration process due to the high efficiency for fine particular matter of media according to the present invention.
  • the utilization of depth media upstream for more efficient filters is described in U.S. Patents 5,082,476; 5,238,474; and 5,364,436 and using similar techniques but having downstream from the depth media, media according to the present invention, advantages can be obtained.
  • depth media such as those described in the above patents can be used to remove particles, very efficiently, in a size ranges from 2-10 microns upstream from media according to the present invention, with the media according to the present invention used to achieve very high efficiency removal of sub-2 micron materials, downstream.
  • media according to the present invention can be used in a complimentary manner, with more conventional techniques.
  • media according to the present invention may be configured such that it is not pleated, but rather such that it is located downstream of depth media and used in either a panel or cylindrical filter element.
  • the media may be a separable component from a remainder to the filter assembly, such as a serviceable replacement part.
  • the media according to the present invention may also be utilized upstream above the filter components, as a replacement part.
  • filter material comprises a coarse support with a fine fiber web or mat applied to at least one surface thereof.
  • a coarse fiber support can be viewed as having two available surfaces for application of the fine fiber, one on each side of the coarse fiber mat.
  • the coarse material or matrix would serve to separate the fine fiber mats appropriately.
  • the fine fiber layer may be on either the upstream side or the downstream side, of the mat to which it is applied.
  • the factors of most concern regarding the media relate to selecting the materials such that the coarse fibers are well spaced, serve relatively little filtering function, and are appropriately positioned to support the fine fibers and to keep the layers of fine fibers separated from one another in the overall construction.
  • the fine fibers are chosen for their relatively small diameter.
  • a very wide variety of materials can be utilized in constructions according to the present invention, and a wide variety of techniques are applicable to the generation of such materials.
  • techniques for the preparation of fiber materials for use in filter constructions according to the present invention are not within common practices of a filter designer or engineer, but rather are in the field of fiber processing and polymer processing.
  • mists may be utilized in constructions for the filtering of very fine mists from the air.
  • such mists comprise droplets of about 1 micron in size or smaller. At this size, to some extent they can be treated as particles for purposes of evaluating filtration.
  • Certain materials as described herein, then, can be used to trap such mists.
  • high separation efficiency can be obtained without the small interfiber spaces (i.e. pores) typical of high efficiency mist filter media.
  • the small pores of conventional high efficiency media retain the separated liquid due to capillary forces.
  • the retained liquid in such systems rapidly increases buildup of flow resistance to passage of air, which shortens useful filter life.
  • fiber surfaces which are phobic with respect to the fluid being collected can be used to advantage.
  • the invention may also provide advantages when applied to air filtration applications with high efficiency requirements such as HEPA grade or ULPA grade filtration in a ventilation system.
  • the invention may provide advantages in terms of filter life and more reliability through multiple layers. Through redundant filtration, the overall system is less sensitive to media flaws in an individual layer. Q. Further Comments
  • the coarse substrate or matrix provides integrity to the very fine fibers and structure, thus reducing the likelihood that the fine fibers are damaged during manufacturing, handling or use. In the absence of the coarse support or matrix, fine fiber structure is very easily damaged upon contact with other materials.
  • the preferred arrangements of the present invention are often so durable, that it is foreseen some constructions can be prepared which can be washed with liquid or cleaned by an air flush, after use, for some regeneration.
  • Table R2 the table appearing hereinabove in Section "J.” is modified to include an indication of length of fiber and fiber surface area applied in certain ones of the examples, based upon a calculation given an assumed specific gravity of 2.6 grams/cc for glass; and an average fiber diameter of 0.4 microns.
  • the particular material from which the microfibers were formed is not, in many instances, a critical factor to achieving beneficial effects according to the principles described herein.
  • the amount of fiber, for any given diameter, or amount of fiber surface area, for any given fiber is typically more important to achieving the desired filtering effects.
  • Tables Rl, R2, R3 and R4 indicate a more "generic" approach to characterizing amount of fine fiber applied to the substrate which is, in general, non-specific as to the particular material chosen. That is, by evaluating the amount of fine fiber applied per unit area, by length or surface area, one can remove from the evaluation the variable of the specific gravity of the fine fiber material, i.e. the specific composition of the fine fiber material.
  • the calculations utilizing glass fibers indicate a type of performance expected with a certain amount of fiber length, or fiber surface area, per unit area of substrate, for a given diameter fiber.
  • characterizations such as fiber length per unit area are effectively indicators of packing density or solidity. As such, they are relatively descriptive of fiber geometries, particularly at low basis weights.
  • microfiber applications according to the present invention can be utilized in overall compositions which include a region electrostatically charged media therein.
  • Electrostatically charged media sometimes referred to as "electret” media, can be utilized as the substrate to which the microfiber is applied; and/or it can be used as a separate layer of media positioned in an overall multilayered media composite either: (a) upstream from the microfiber material; (b) downstream from the microfiber material; or (c) between layers of microfiber material.
  • electrostatically charged media provides for relatively high initial efficiencies in many applications.
  • a problem with such media is that it tends to lose efficiency for an extended period of time, relative to its initial efficiency.
  • Electrostatically charged media can be used upstream from microfiber media according to the present invention, in order to provide for some enhanced initial efficiencies.
  • Preferred media for such applications would typically be electrostatically charged media such as E30, a charged fiber material available from ALL FELT of Genoa, IL 60135.
  • a basis weight of 30 g/m 2 It has: a basis weight of 30 g/m 2 ; a thickness of 0.024 inches (at 0.5 psi) ; a permeability (fpm) of 600 + ; and, a LEFS efficiency of 43%.
  • the microfibers could be applied directly to an electrostatically charged substrate; or, a charge could be applied to the substrate after the microfibers are applied thereto.
  • a variety of methods of applying electrostatic charges to media can be utilized, including conventional ones, in the approaches as defined in this section. In some instances, commercial materials can be employed.
  • adsorbent will be used to refer to both absorbent and adsorbent materials. That is, the specific nature of the interaction between the captured chemical material, typically organics, and the filter material, is not referenced.
  • activated carbon or charcoal media is used to adsorb odors and various other organics .
  • Fibrous media has been developed which includes therein chemical adsorbents, such as carbon particles.
  • chemical adsorbents such as carbon particles.
  • One such material is AQFTM adsorptive media available from Hoechst Celanese Corp., Charlotte, North Carolina, 28232-6085. It is available in a variety of permeabilities (typically, 137-279 ft/min) , thickness (0.0661 in - 0.0882 in); basis weights (280-382 lb/3000 ft 2 ); MD stiffness (2220-4830 mg) ; and MD Tensile (17-30 lb/in) .
  • a preferred one for the applications described herein is AQF-375C which has the following characteristics :
  • Such media can be utilized in overall arrangements according to the present invention, to advantage.
  • the media could be used, for example, as the support to which the microfibers are applied.
  • such material can be utilized as a region of media either upstream or downstream from the region of microfiber media (with its support) to create an overall composite of advantageous properties.
  • the maximum thickness of media that can be readily pleated is about 0.060 inches, and typically substantially thinner (0.040 inches, often 0.030 inches or less) medias are preferred, for pleated systems.
  • substantially thinner (0.040 inches, often 0.030 inches or less) medias are preferred, for pleated systems.
  • oil treatment of a media such as a cellulose media extends life. This may in part be due to the fact that as oil treated media collects carbonaceous particulates, rather than building dendrites and blocking air flow, the carbonaceous particulates become suspended in the oil. Arrangements involving oil treated media are described, for example, in U.S. Patent 5,238,474, incorporated herein by reference.
  • mass flow sensors downstream from air filtration equipment, are finding increasing use.
  • mass flow sensors are sometimes positioned downstream from the air cleaner.
  • the air cleaner involves treatment such as oil treatment
  • the oil treatment itself contributes to the mass flow leaving the air cleaner or it may contribute to fouling of the equipment.
  • the media may have a tendency to pass more of certain fines, extending filter life due to lower efficiency.
  • media including fine fiber layers as described herein can be used to advantage in place of the oil treated media. Some examples of this are described hereinbelow.
  • the overall thickness of the media should be 0.060 inches (0.15 cm) or less, preferably 0.030 inches (0.076 cm) or less. To accomplish this it may be desirable to limit the number of layers of fine fiber; and, to reduce as far as reasonably possible, the thickness of the spacing layer (s). Preferred spacing fibers for this will be no more than about 0.003 inch (0.0076 cm) thick, most preferably no more than about 0.0015 inch (0.0038 cm) thick.
  • Pleated media from sheets is used in a wide variety of filter constructions.
  • Commonly used media include: cellulose, glass fiber, or synthetic polymer fiber sheets; expanded polytetrafluoroethylene (PTFE) sheets; and sheets of fiber blends. Improved composites, wherein multilayer fine fiber arrangements according to the present invention are applied in conjunction with such media, are feasible.
  • typical expanded polytetrafluorethylene sheets used as filter media have a fibril size of 0.1-0.3 microns, a permeability (fpm) of 2-70; a LFFS efficiency of >80%, typically >90% (typically a DOP efficiency of 80%-99.9999%) .
  • Multiple Fine Fiber Layer Construction or region or “MFFL Construction or region” will be used to refer to a construction of fine fiber according to the present invention. It will generally comprise a plurality (i.e. at least two) of fine fiber layers separated by a spacing layer or matrix arrangement. As indicated by the principles described herein, the utilization of fine fiber layers (of the same or various LEFS efficiencies) , can be used to provide an overall preferred MFFL construction of a preferred efficiency.
  • an MFFL construction having an overall LEFS efficiency of less than, or equal to, 60% total.
  • This could, for example, be readily formed by using three layers of fine fiber spaced by spacing constructions or support constructions (matrices) as described herein. The most downstream layer of fine fiber could be applied directly against the cellulose sheet, if desired.
  • An overall LEFS efficiency of about 60% could be prepared, for example, from three layers exhibiting an average LEFS efficiency of about 25%.
  • the overall thickness would be substantially less than 0.060 inches and would be readily pleatable.
  • This material or region could be readily pleated into an engine filter, in place of a conventional cellulose sheet. It could be used to provide an overall filter construction with an extended life, due to the type of loading that would occur within the MFFL construction, upstream from the cellulose. In the alternative, it could be used to provide a filter element having a lifetime of about the same length as the conventional (pleated cellulose) element, but of smaller size. To an advantage, the overall air cleaner could therefor be redesigned to be smaller.
  • the cellulose (or other sheet) media downstream from the MFFL construction provides for some structural integrity to the overall system.
  • the MFFL construction can be used in instances which involve relatively low face velocities, but also in applications that involve relatively high face velocities, for example in HVAC or cabin air filter applications. Of course it can also be used with HEPA or ULPA filters.
  • MFFL constructions according to the present invention can be used in arrangements which also include oil media.
  • cabin air filtration i.e. filtration of cabin air for vehicles
  • composite arrangements involving MFFL constructions according to the present invention can be incorporated into overall systems to achieve a desired level of efficiency with respect to both, to advantage.
  • single fine fiber layer arrangements can also be used in combination with materials such as electret or carbon adsorption media.
  • materials such as electret or carbon adsorption media.
  • chemical adsorbent filters are desirable.
  • Such material as the activated carbon filter media for example Hoechst Celanese AQF-375C, can be used to accomplish this.
  • Such a media could be provided, for example, upstream from an MFFL construction, according to the present invention.
  • the MFFL construction would be quite efficient for particulate removal in the cabin air filtration system involved.
  • an "electret" construction media having an electrical charge applied thereto, could be used in the overall cabin air filter construction as well .
  • electret media has a high initial efficiency, which diminishes with loading until cake formation begins, with a tendency toward a relatively slow increase in developed pressure differential across the filter, due to its inefficiency with loading.
  • MFFL constructions as described herein can have generally lower initial efficiencies, by comparison to electret. When the two are combined, in general, desirable attributes of each can be implemented. If an electret material is positioned upstream from a MFFL material according to the present invention, advantage can be taken of the relatively high initial efficiency of the electret material.
  • a relatively light (thin) electret material can be used, so as to provide some desirable initial efficiency, but also lower development of undesirable pressure differential.
  • an MFFL construction Downstream from the electret material, an MFFL construction could be used to provide for an overall desirable efficiency and long life (slow build-up of pressure differential) .
  • This combination can be used in association with a carbon loaded media, to also achieve a desirable level of odor adsorption.
  • a typical construction would be, for example, a composite comprising, from upstream to downstream, electret/odor adsorbent media/MFFL construction.
  • Such systems are used in a wide variety of internal combustion engines. They are for example used for vehicles such as automobiles, light trucks, delivery trucks, heavy duty over-the-highway trucks, construction equipment, agricultural equipment, busses, dump trucks, garbage trucks and in air filtration systems for various other equipment.
  • the techniques can be used for air intake systems for engines generally ranging in size from about 100 hp on up to about 3000 hp.
  • media especially pleated media, involving systems as described herein, can be used to provide significant advantage with respect to either efficiency or lifetime, or both, if selected.
  • overall composites having efficiencies up to about 99% or more, based upon individual fine fiber layers having efficiencies of 10% up to 90%, and typically 10% up to 70%, can be achieved.
  • the media can then be pleated with other media such as pleated paper or pleated synthetic media, to provide a desirable overall composite. Indeed in some systems depth media constructions upstream or downstream from the fine fiber arrangement can also be applied. Various approaches to this were described earlier.
  • a media wherein the microfibers comprise glass fibers was used.
  • the media comprised a layer of glass microfibers on a porous polyester scrim (Reemay 2011).
  • the glass microfibers were of various diameters between about 0.1 and 3.0 microns in diameter.
  • the coarse scrim or fiber matrix generally comprised the polyester scrim described above, commercially available under the designation Reemay 2011.
  • the general technique for preparation of the various glass fiber samples was described above with respect to U.S. Patent 5,336,286.
  • the glass fiber media or composite is generally characterized with respect to %LEFS, with the percent indicating efficiency for trapping 0.78 micron particles according to the techniques described herein.
  • Ultra-Web type media or DCI polymeric fiber material Some of the samples described herein are referred to as "Ultra-Web type” media or DCI polymeric fiber material. These media generally comprise the coarse polyester scrim (Reemay 2011) having applied thereto microfibers of the type used in the Donaldson Company Ultra-Web surface loading media applications.
  • the microfibers are generally of a size about 0.1 - 0.5 microns, and generally comprise a polymer.
  • the media or composite is typically characterized with respect to %LEFS, the term having the same meaning as in other applications described above.
  • This experiment evaluates use of a high efficiency media using a relatively open pore and fiber structure according to the present invention, to improve loading (life) relative to a filter media made of the same fine fibers and of approximately the same initial efficiency but of a smaller interfiber spacing.
  • Tobacco smoke was used for several reasons. First, it tends to plug conventional high efficiency filters, with small pores, quickly. The tar in the smoke is an amorphous solid that flows and is subjected to large capillary forces from the small fibers. The capillary forces cause the tobacco smoke residue to coat the fibers and wick into the pores. Second, it is a common contaminant encountered in vehicle cabin air, indoor air, etc.
  • the substrate material was Hovolin 7311.
  • the final LEFS efficiency being lower than the initial LEFS efficiency (for media (b) and (c) ) is believed to be related to the nature of the contaminant. (It is noted that the effect was more pronounced for the single layer system than the multi-layer system. ) Fluids which coat fibers effectively increase the wetted fibers' diameter. Also, as small pores are closed and pressure drop increases, flow and aerosols may be diverted to the larger pores which remain open longer. Relatively small particles (0.78 ⁇ ) passing through large pores, or past larger wet fibers, would have a lower propensity to collect than when the media is not loaded.
  • DOP loading results are consistent with the tobacco smoke loading results.
  • the sum of low efficiency layers resulting in alternating fine-coarse fiber composite structure provides substantial loading (life) benefits over a filtration media with a single fine fiber layer efficiency approximately equivalent to the combined layers of the composite.
  • One measure of filter life is time to a predetermined pressure drop; another is mass of contaminant fed to a predetermined pressure drop. If the predetermined terminal pressure drop is significantly above the restriction where cake formation begins, then cake loading comparisons are being made rather comparisons between media performance. Life comparisons here are made at a restrictions where cake formation is normally completed. In the following tables operation to 2 inches H 2 0 and 5 inches H 2 0 are given. Samples were tested at 10 fpm.
  • Media were loaded on a custom made salt loading bench (schematic shown in Fig. 25), using commercially available components, specifically a TSI constant high output atomizer model 3076 for particle generation, a TSI model 3054 aerosol neutralizer, and a TSI Electrical Aerosol Analyzer (EAA) model 3030 used for particle counting and sizing to measure particle efficiency as test media is loaded.
  • a TSI constant high output atomizer model 3076 for particle generation a TSI model 3054 aerosol neutralizer
  • EAA Electrical Aerosol Analyzer
  • Submicron salt was used as the contaminant, because it is more easy to discern loading differences between various media when this contaminant is used, than when traditional SAE silica dust is used.
  • Composite media with lower layer LEFS efficiency have better loading (life) than composite media comprised of a fewer layers with a higher layer LEFS efficiency. This apparent ability to choose both efficiency and life, independently, differs from many applications of traditional media. With many practices using conventional media, life is gained by sacrificing efficiency.
  • Sample Area 25 square inches (flat square sheet) using a custom test bench (schematic 14) and custom Collison atomizers, TSI 3054 neutralizer
  • a 3-layer composite made from wet-laid hand sheets of glass microfibers that range in size from submicron to about 3 micron on Reemay 2011. overall composite LEFS efficiency 32% single layer efficiency 12% (each)
  • a 3-layer pleatable composite media including scrim having a web made from fine glass fibers (submicron - 3 microns in diameter), demonstrated a significantly greater permeability (13x) and submicron salt loading life (>5x) than a pleatable cellulose surface loading media of approximately equal initial LEFS efficiency.
  • the test velocity of 150 fpm was arbitrary and intended to illustrate a capability of the media. This is not meant to suggest that engine air cellulose media normally operates at 150 fpm face velocity.
  • This experiment was intended to compare the loading results of a gradient embodiment of the invention with an initial LEFS efficiency of about 65% to that of a non-gradient media of equal number of layers and equal LEFS efficiency.
  • the non-gradient media was made from submicron polymeric fiber (Ultra-Web ®-type fiber) deposited onto Reemay 2011 and laminated by hand using 3M Super 77, each layer having an approximately equal LEFS efficiency to the other two layers in the composite.
  • the single layer LEFS efficiency was about 24%.
  • the gradient media was made from submicron polymeric fibers (Ultra-Web ®-type fibers) deposited onto Reemay 2011 with succeeding layers having greater LEFS efficiency than the preceding layers.
  • the gradient chosen was arbitrary, and it is not known if additional life benefits would have been gained with a different selection of layers for the 3 layer gradient composite, at the same overall LEFS efficiency. In this instance, from upstream to downstream, the LEFS efficiencies of the layers were about 10%, 20%, and 40%. These too were hand laminated using 3M Super 77.
  • the gradient version of the invention better utilized the available media volume than a non-gradient equivalent (thickness, perm, and LEFS efficiency) . This is demonstrated by a 66% increase in submicron particle (NaCl) loading of the gradient sample relative to the non-gradient. This again can be explained in terms of the interfiber spacing of the fine fibers.
  • a non- gradient media structure of the same volume and efficiency as a gradient media is more likely to not utilize the loading potential of the fibers towards the downstream side of the media due to cake formation on the upstream side of the non-gradient media. A cake forms sooner on the non-gradient media than the gradient material. This is due to the average distance between fine fibers being smaller for the non-gradient media than that of the lower efficiency upstream layers of the gradient media.
  • the first layer of the nongradient arrangement has a 24% LEFS efficiency, whereas the gradient structure's first layer is 10% efficient. Therefore, a gradient media structure will tend to more effectively utilize all of the available media volume than a non-gradient equivalent.
  • the polymeric fibers were about 0.4 ⁇ with a relatively small fiber size variance.
  • the glass fibers were about
  • the submicron glass fibers were selected to match the median size as the polymeric fiber but having a different distribution about the mean.
  • Wet-laid handsheets were prepared using a standard 8 x 8 inch handsheet former. The glass fibers were placed onto the Reemay 2011 which was supported by a fine plastic mesh which normally collects fibers drained from the slurry. Single layer of fine fiber polymeric media with a 40% LEFS efficiency.
  • the difference in loading for the gradients was about 5% at 5.0 in H 2 0, and the loading of single layer 40% LEFS samples differed by about 10%.
  • the rate at which the media seasoned were very similar for the single layer media.
  • the glass fiber sample increased in efficiency faster than the polymeric fiber version. The reason for this was partially understood at a later point in time when it was discovered that glass fibers of up to about 3 ⁇ were included in the glass fiber stock used to make handsheet samples. This was discovered when SEMS were taken for pore size analysis. The results of this experiment are plotted in Figs. 23 and 23 A.
  • the plot compares the performance of the single layer polymeric fiber version (40% LEFS) with the single layer glass fiber version (40% LEFS).
  • the plot compares the performance of the 3-layer gradient polymeric version (60% LEFS) to the 3-layer gradient glass fiber version (60% LEFS). Note also that for each type (polymer or glass) the media in the form of a gradient system had about 70% more life and about a 33% reduction in penetration. This indicates that efficiency does not have to be sacrificed to gain life, when preferred techniques of the present invention are used.
  • FIGS 12-21 are scanning electron micrographs (SEMs) of various media. The principles according to the present invention can be understood by reviewing the various media depicted.
  • Fig. 12 is a scanning electron micrograph, lOOx magnification, which shows a conventional air laid polymeric fiber media, in particular Kem Wove 8643.
  • Consistency of fiber size is observable. This is a 1.5 denier material. Its LEFS efficiency is 3%. Its thickness is about 0.30 inches. It has a basis weight of about 73 lb/3000 ft , a volume solidity of 1.1% and a permeability of 400 fpm.
  • Fig. 13 is a convention air laid glass fiber media, at lOOx magnification.
  • the particular media is AF18, available from Schuller. Again, consistency of fiber size is viewable. It has an LEFS efficiency of 12%; a thickness of 0.18 inches; a basis weight of 60 lb/3000 ft 2 ; a volume solidity of 0.9%; and a permeability of 230 fpm.
  • the material has a 45% ASHRAE rating and an approximate fiber size of 4.5 ⁇ .
  • Figs. 14 and 15 depict a conventional two- phase media, at 500-fold magnification. Both phases are glass fibers.
  • the media of the two photographs is Hollingsworth & Vose HF343.
  • Fig. 14 is of the upstream side, where the more coarse fibers are located.
  • Fig. 15 is of the downstream side, and a mixture of the finer fibers with the coarse is viewable.
  • HF343 is a wet-laid glass fiber media.
  • the upstream side of the media (phase one) has relatively open, large, coarse, self-supporting fibers intended to capture and store coarse contaminant.
  • the downstream side (second phase) of the media is made of a combination of fine and coarse fibers. The fine fibers provide higher efficiency but lower capacity than the large fibers in phase one.
  • the media has an ASHRAE rating of approximately 60-65%.
  • HF343 has an LEFS efficiency of 23%; thickness of 0.02 inches; a basis weight of 50 lb/3000 ft ; a volume solidity of 7.1%; and a permeability of about 135 fpm.
  • the volume solidity of a fine fiber layer, of the present invention is difficult to measure directly, or indirectly, and becomes more difficult for LEFS efficiencies less than about 15-20%.
  • the primary difficulty lies in estimating the normal local thickness of the fine fiber layer.
  • the fine fibers create a open porous "surface".
  • the topography of the surface resembles that of a spider web draped over a support structure.
  • the surface of the microfiber matrix derives its shape from the fiber structure and voids beneath it (the support structure) , consequently the matrix has many peaks, valleys, ridges and troughs.
  • the thickness dimension used for estimating the solidity is not the dimension from a peak to a valley, but the thickness of the web/layer at a peak, at a valley, or at a local planer region.
  • This geometry has features that are not evident in SEM photos, but are readily apparent when inspected through a stereoscope, at lOx to 40x magnification.
  • the solidity estimates reported for the materials of the invention are derived from estimates of the local thickness normal to fine fiber layer.
  • Fig. 16 is a composite media according to the present invention.
  • the media comprises Schuller glass fiber 106 deposited on Reemay 2011.
  • the fine fiber diameter range extended from submicron up to about 3 microns.
  • the amount of fiber 106 deposited is sufficient for the resulting layer to have a percent efficiency LEFS of 40%.
  • the very fine fibers comprising the layer of fine fibers are readily viewable. Underneath, in some locations, the more coarse fibers can be viewed.
  • the material of Fig. 16 was made of a wet-laid hand sheet of the fine fiber material, deposited onto a Reemay 2011 substrate as described above in the specification.
  • the figure that would represent the ratio of the fiber diameter of the coarse substrate fibers to the fiber diameter of the fine fibers is much greater, than in the media depicted in Figs. 14 and 15.
  • the fine fiber layer permeability is estimated by removing the substrate contribution from the permeability of the composite. For low efficiency- high permeability samples, it was necessary to stack multiple layers to obtain measurable values to compute average permeability.
  • the average area solidity was about 52%.
  • the permeability was about 190 fpm, the volume solidity about 10%, the basis weight 1.5 lb/3000 ft , and the thickness 10 microns .
  • Fig. 17 is another composite media according to the present invention.
  • the media in Fig. 17 is shown at lOOx magnification.
  • the media comprises a DCI (Donaldson Company Inc.) polymeric fine fiber positioned on a coarse substrate comprising Reemay 2011.
  • the DCI polymeric fine fiber was made generally according to the same process used to form fine polymeric fibers for Donaldson's Ultra-Web ® products, a trade secret process.
  • Fig. 18 is another composite media according to the present invention.
  • the media is shown at 100-fold magnification.
  • the media comprises Schuller glass fiber 106 deposited on Reemay 2011.
  • the amount of glass fiber present was sufficient to provide an efficiency (% LEFS) of 12%.
  • the basis weight of the fine fiber layer was about 0.5 lb/3000 ft , and the permeability was about 600 fpm.
  • This material had an average area solidity of about 33% when evaluated at lOOOx magnification.
  • Fig. 19 is another composite media according to the present invention. It comprises DCI polymeric fine fiber deposited on Reemay 2011, depicted at 100- fold magnification. The media depicted had a percent efficiency of 12% LEFS. Again, the web of fine fibers is readily discernible positioned on top of the underlying coarse fiber support. When evaluated at 500x magnification, this material was observed to have an average area solidity of 22%.
  • Fig. 20 is a micrograph of the material shown in Fig. 19, depicted at 500x magnification. The very fine fiber web, on top of the underlying coarse fiber support, is readily discernible.
  • Fig. 21 is a lOOOx magnification of the material shown in Fig. 19, after NaCl loading. The salt particles, trapped on the very fine fibers, are readily discernible on the picture.
  • Fig. 24 NaCl loaded 18% LEFS media is shown, at lOOOx magnification. The NaCl particles are viewable primarily trapped on the fine fibers.
  • the media material of Fig. 24 is DCI fine fiber polymer on a Reemay 2011 coarse substrate.
  • Figs. 16-20 the characteristic of very fine fibers being positioned on top of a coarse substrate is generally discernible. This is the case regardless of the percent efficiency, or the particular material utilized for formation of the fine fibers. In Fig. 21, operation to achieve load on the fine fiber was readily observed.
  • arrangements according to the present invention may be utilized in an environment involving the filtering of fluid streams which contain components that are chemically incompatible with certain types of fiber materials.
  • some air streams may carry chemicals which are damaging to polymeric materials, but not damaging to glass. If such is the case, it will be preferred to construct the filtering material from materials which are resistant to damage under the intended use environment.
  • each diameter might be 5x to lOx larger than defined herein.
  • Such constructions may be usable, for example, to form agglomerates within a depth media or to form a relatively efficient depth media which includes small fibers and is resistant to collapse as loading occurs in unique environments involving the filtering of rather large particles. It is not anticipated that such constructions will be preferred or desirable for most typically encountered industrial and/or engine environments .

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Filtering Materials (AREA)
  • Filtering Of Dispersed Particles In Gases (AREA)

Abstract

L'invention concerne un milieu filtrant préféré. Le milieu comprend une bande de fibres fine fixée à la surface d'un support en fibres grossières. L'invention concerne aussi un milieu filtrant préféré (10) comprenant des couches multiples de milieux (15, 19) en fibres fines séparées par un support (14, 18) en fibres grossières. L'invention concerne également le résultat avantageux de construction de filtres de même que des procédés d'utilisation de ces agencements dans des filtres.
EP97945329A 1997-09-29 1997-09-29 Construction de matiere filtrante et procede Withdrawn EP1028794A1 (fr)

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PCT/US1997/017435 WO1999016534A1 (fr) 1995-11-17 1997-09-29 Construction de matiere filtrante et procede

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US6716274B2 (en) * 2000-09-05 2004-04-06 Donaldson Company, Inc. Air filter assembly for filtering an air stream to remove particulate matter entrained in the stream
US6800117B2 (en) * 2000-09-05 2004-10-05 Donaldson Company, Inc. Filtration arrangement utilizing pleated construction and method
US8252097B2 (en) 2005-12-29 2012-08-28 Environmental Management Confederation, Inc. Distributed air cleaner system for enclosed electronic devices
US7708813B2 (en) 2005-12-29 2010-05-04 Environmental Management Confederation, Inc. Filter media for active field polarized media air cleaner
US9789494B2 (en) 2005-12-29 2017-10-17 Environmental Management Confederation, Inc. Active field polarized media air cleaner
SG170791A1 (en) * 2005-12-29 2011-05-30 Environmental Man Confederation Inc Improved filter media active field polarized media air cleaner
US7686869B2 (en) 2005-12-29 2010-03-30 Environmental Management Confederation, Inc. Active field polarized media air cleaner
US8795601B2 (en) 2005-12-29 2014-08-05 Environmental Management Confederation, Inc. Filter media for active field polarized media air cleaner
US8814994B2 (en) 2005-12-29 2014-08-26 Environmental Management Confederation, Inc. Active field polarized media air cleaner
US8282712B2 (en) * 2008-04-07 2012-10-09 E I Du Pont De Nemours And Company Air filtration medium with improved dust loading capacity and improved resistance to high humidity environment
US20110210081A1 (en) * 2010-02-26 2011-09-01 Clarcor Inc. Fine fiber liquid particulate filter media
KR20160134792A (ko) * 2014-06-26 2016-11-23 이엠디 밀리포어 코포레이션 개선된 먼지 포집 능력을 갖는 필터 구조
CA2982544C (fr) 2015-04-14 2019-09-24 Environmental Management Confederation, Inc. Milieu de filtration ondule pour nettoyeur d'air a polarisation

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