CONDUCTIVE FILTER CARTRIDGE AND METHOD FOR MAKING SAME

Abstract: Conductive filter cartridges are made by fabricating a multilayer unit which includes a filter layer and a spacer layer which are generally constructed in spiral form whereby the spacer layers define flow channels which contact the flow of particulate entrained air and direct such air to be filtered through the filter layers. The spacer layers are fabricated from materials which are electrically conductive throughout the spacer layer are connected to a source of reference potential to continuously remove electrical static charge and thereby prevent accumulation of dangerous levels of charge buildup in a non-conductive filtering unit.

Description: CONDUCTIVE FILTER CARTRIDGE AND METHOD FOR MAKING SAME Field of the Invention The present invention relates to a filter cartridge having antistatic properties and a method for making such a filter cartridge. Background of the Invention When large quantities of electrically chargeable powdered materials, such as small polymer coated iron granules referred to as "carrier" particles and/or finely ground toner particles that make up the developer mix in electrophotographic copiers, are transported at high speeds, their characteristic of picking up static electricity can cause significant difficulties in a filtering or separating process. The problem of electrostatic charge build—up is similarly true in the field αf handling grain and grain products such as flour and meal, wherein separating solid particulate material from fluids is accomplished. For instance, in certain cleaning and/or filtering operations related to electrophotographic copiers toner particles are brought into mutual frictional contact with a cleaning apparatus, causing the build—up of static electricity to be so great that a static electrical discharge can cause severe shocks to workers, result in a toner dust explosion or create an electrical field proximate to the collecting apparatus which can result in damage to sensitive electronic components located within the field. When the potential is sufficiently high, a spark may jump to a surface of lower potential with the possibility of either igniting the fluid or any flammable material in the immediate area or cause an explosion when the fluid is a suspension of toner dust in the entrained air. This latter possibility becomes particularly damaging since cleaning operations for electrophotographic copiers are generally accomplished in an area which includes sensitive electronic office—related apparatus which could be adversely effected by such an explosion. There is a need, therefore, for a means of effectively removing such electrical static charge build-up, especially for applications in which small chargeable particles are removed from the fluid stream and more particularly relating to the need to minimize the safety hazard when handling toner dust particles. In U.S. Patent 3,986,530, it is suggested to solve the static electrical problem by carrying out the filtering process in contact with a knotted or woven cloth which is used as the filter media and contains electrically conductive thread composed of 10 to 90 weight percent electroless metal plated staple fibers, and 90 to 10 weight percent of metallic filaments in an amount of 0.1 to 1.0 thread per cm width of the cloth. Use of a filter media such as described above as part of a filter cartridge, however, is inadequate to effectively dissipate the dangerous build—up of electrical charges which occur during the cleaning and/or filter operations described above. It is also known from U.S. Patent 4,322,232 to treat the problem by use of a filter media wherein a conductive strand formed from a synthetic filamentary yarn and knit into a loop pile is also intended to function to remove electrostatic charges. This expedient to solve the problem of continuous and adequate removal of the electrostatic charges by treating the filter media was also found to provide insufficient antistatic properties. Another prior art proposal, U.S. Patent 3,933,643, discloses the use of a porous, resilient, electrically conductive permeable filter media which comprises carbonaceous conductive material for dissipating static electrical charges accumulating in the filter media during fluid passage. A modification further teaches that the filter media can be connected to an external power supply suitable for maintaining a controlled uniform electrical potential across the filter media to assist in the retention of particles of opposite charge during filtration. The purpose of the external connection to an electrical power supply is to establish a controlled uniform electrical potential across the filter media which can also be accomplished by grounding the conductive filter media. From a consideration of the prior art, it appeared that the attempt to effectively solve the static charge build—up problem was to have some type of conductive material or electrical charge included in the filter media, especially for applications in which very small particles are to be removed from the fluid stream. However, there continues to be an unsolved problem for applications in which toner particles are to be removed, during cleaning or dust removal operation effecting electrophotographic copiers. In such cleaning processes static electricity is generated at extremely high potentials and none of the prior art devices have an effective way to continuously dissipate the charge build—up and thereby maintain the filter cartridge as part of the cleaning equipment at a low and safe potential. The ability to continuously dissipate electrical static charge build-up on the filter unit is extremely necessary, particularly to effectively and speedily satisfy the service requirement for high volume electrophotographic copying equipment. Therefore, an object of the present invention is to provide a filter cartridge which has conductive properties which will continuously and effectively remove dangerous static electrical potentials from the particle entrained fluids. A further object of the invention is the provision of the filter cartridge which will allow the establishment of continuously maintaining low voltage potential on the filter cartridge without an external power supply while avoiding the hazards of a high potential discharge from the filter cartridge into the filtered fluid. SUMMARY OF THE INVENTION The above objects of this invention are accomplished by providing a filter cartridge for removing particulate material entrained in air comprising: a multilayer unit having opposed end surfaces, and including a filter layer and a spacer layer, at least one surface of the filter layer contacting the spacer layer in said unit, said spacer layer being constructed to define flow channels which contact the flow of particulate entrained air and direct such air to said filter layer which holds the particulate material removed from the air passing through said filter layer, said spacer layer comprising electrically conductive material disposed throughout said spacer layer for defining an electrical pathway therethrough; and means coupled to said spacer layer to connect it to a source of reference potential to remove continuously electrical static charge and thereby prevent build—up of charge on said filter cartridge. Yet a further object of the present invention is to accomplish, in a method of making a filter cartridge, comprising the steps of: a) winding a filter layer and a corrugated conductive spacer layer about a core to form a filter unit; b) sealing the alternative open pleats of the corrugated spacer layer to define flow channels so that particulate entrained air enters said flow channels through unsealed pleats and the particle entrained air passes through the filter layer before exiting the cartridge; c) sealing the free end of the conductive spacer layer to said unit to prevent unwinding; and d) providing a conductive outer surface to define an electrical pathway for removing continuously electrical static charge and prevent charge build-up on the unit. The method further includes the step of attaching at least one conductive end cap to the end of the filter unit. BRIEF DESCRIPTION OF THE DRAWINGS Some of the objects of the invention having been stated, other objects will appear as the description proceeds when taken in connection with the accompanying drawings, in which: FIG. 1 is a lengthwise sectional view of the filter cartridge containing a two layer construction according to the present invention with end caps and an external conductor for grounding the unit; FIG. 2 is a sectional view on the line 2-2 of FIG. 1; FIG. 2A is an enlarged sectional view of the two layer construction of the filter cartridge; FIG. 2B is a sectional view on line 2B of FIG. 2A; FIG. 3 is a sectional view taken on line 3-3 of FIG. 1; FIG. 4 is a sectional view taken on line 4-4 of FIG. 1; FIG. 5 is a lengthwise sectional view of a filter cartridge containing a four layer construction according to the present invention with end caps and an external conductor for grounding the unit; FIG. 5A is an enlarged sectional view of the four layer construction of the filter cartridge; FIG. 5B is a sectional view on line 5B of FIG. 5A; FIG. 6 is a sectional view taken on line 5—5 of FIG. 5; FIG. 7 is a sectional view taken on line 7—7 of FIG. 5; FIG. 8 is a sectional view taken on line 8—8 of FIG. 5; FIG. 9 is a perspective view of a sandwich construction having a filter layer and a corrugated conductive spacer layer sealed to a core; FIG. 10 is a perspective view of a four layer sandwich construction having alternating filter layers and corrugated conductive spacer layers sealed to a core; FIG. 11 is an end view with part broken away of a pleated filter according to the invention; FIG. 12 shows a lengthwise view of the cartridge of FIG. 11 with a part broken away and showing an external conductor for grounding this unit; FIG. 13 is an end view with part broken away of a modification of a pleated filter according to this invention; FIG. 14 is an end view of a four—sided filter; FIG. 15 is a section view taken on line 15—15 of FIG. 14 and showing an external conductor for grounding of the individual conductive spacer layers. DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS While the present invention will be described hereinafter with particular reference to the accompanying drawings, it is to be understood at the outset that persons skilled in the applicable arts will be able to modify the present invention while accomplishing the favorable result to be described. Accordingly, the following description is to be understood, from the outset, as a broad teaching disclosure directed to persons skilled in the art, and not as being restrictive upon the scope of the invention. Components for fluid filtration are commonly made from a multilayer material which is formed by at least one filter layer and at least one spacer layer. The filter layer of our preferred embodiment must be sufficient to remove minute particles from a fluid air stream, e.g., at least 25 micron in size or larger and preferably 0.1 to 10 micron in size. Commonly made filter layers can be inorganic, such as alumina, silica, fiberglass, glass or made from organic polymers such as nylon, Dacron, polyethylene or polypropylene, or resins such as phenolic, vinyl chlorides or malamine. Animal or vegetable fibers such as cellulose or cotton may also be used. These materials may be blended if desired and formed into filter material by well-known methods such as winding, felting, needling, flocculating, etc., the elements usually being held together by the applications of appropriate binders which are applied during filter material fabrication. In addition, it is known to impregnate carbon into the filter material during fabrication. Carbon is said to be impregnated into the filter material to assist in the retention of particles of opposite charge during filtration. The fluid—impermeable spacer layer which is the subject of our invention can comprise any flexible material sufficiently strong to prevent fluid passage even at high pressures. It is desirable that this layer, as well as the filter layer, be relatively thin to maximize filter surface area for a given filter volume. The spacer layer material must also be sufficiently pliable to permit crimping into corrugated form and winding it around a core without fracturing to prevent fluid passage even at high pressures. Particularly suitable fluid impermeable materials include polyesters such as polyethylene terephthalate and polyvinyl materials such as polyvinyl chloride, polyvinyl acetate, polyolefins such as polyethylenes and polypropylene, all of which can be coated with anti-static coating compositions such as a polystyrene sulfonic acid sold as ' Versa TL 121 by National Starch Co. Other useful anti—static coating c'ompositions are ammonium or potassium salt forms of polystyrene sulfonate known as Versa TL 125 and Versa TL 126; also a quaternary ammonium salt coated from organic solvents; and N-[para—(4-(para—methoxy anilino) anilino) phenyl] 1,4— enzyl quinone imine (U.S. Patent 4,237,194) coated from a 31 acetone in water solution. For example, a high density polyethylene can be impregnated with 5—25 weight percent of a conductive carbon black powder to provide a suitable spacer material, .02—.2 cm thick having a 7 3 2 conductivity of 10 —10 ohms/cm . Other useful spacer material can be metal foil, expanded and flattened metal, woven wire screen, perforated screen, welded wire screen in fabric or mesh form made from aluminum, steel, stainless steel, copper and any other suitable conductive metal. Other suitable fluid impermeable material can be polyethylene, papers, nylon or fiberglass impregnated with a conductive material such as con¬ ductive carbon black powder. In addition, suitable spacer layer material can include conductive metallic wire laminated to supporting materials such as polyvinyl chloride, nylon and paper. The fluid flow path will be described with reference to Figs. 1, 2, 2A and 2B with regard to a two-layered filter cartridge. As shown therein, the filter unit of our invention is formed from a multilayered flat filter layer 1 and a corrugated spacer layer 3, made from a polyethylene material impregnated with a conductive carbon, which are both sealed along the length to a core (4) which may be hollow or solid and then spirally wound until the desired diameter is reached. The spacer layer is then wrapped around the finished filter cartridge and sealed along the entire length of the cartridge at 16, to provide an outer conductive liner 2 for the cartridge. The sealant 15 as shown in Figs. 9 and 10 is chosen to adhere a multilayer web construction of either two or four layers to the core 4 wherein the multilayers can be rolled onto the core 4 prior to curing the adhesive and the adhesive can be cured after the spiral filter construction is formed. Sufficient sealing composition is also employed to provide the desired seal 5 along one edge of the spacer layer and between adjacent layers of the multilayer web but in amounts less than will migrate through the filter layer and cause undesirable sealing of the opposite surface on the same spiral end. The opposite edge is left unsealed. The spiral wound construction of this invention is thus selectively sealed at each spiral end surface and along the end widths to assure that fluid entering the cartridge through openings 7 at one spiral end surface must pass through a filter layer prior to being removed from the cartridge through exit opening 7a and then through opposing outlet 12. The flow channel is illustrated by reference number 8. The spiral wound construction also insures that particle entrained air entering at 9 is diffused by filler material 11 which effects flow of the particle entrained fluid uniformly to all openings 7, of the spacer areas across the entire width of the edge portion of the spirally wound cartridge. Generally the arrangement is such that one spacer layer adjacent to or contacting a first surface of each filter layer is open to the atmosphere on a first spiral end surface and closed to the atmosphere on the second spiral end surface. The position of the fluid—impermeable spacer layer or layers is such as to prevent contact of spacer layers open on opposing spiral end surfaces. To prevent unfiltered fluid from passing through the center of a hollow core 4, the center of the core would be sealed. The filter cartridge thus formed is preferably provided with an end cap 10 which is sealed to the end of the unit by means of seal 6. Only the upstream end cap need be conductive. The adhesive for seal 6 is chosen so that it provides the necessary conductivity to define an electrical pathway from the conductive spacer layers to the conductive end cap which is grounded by conductor means 13. Since most sealing compositions are resinous in nature and non—conductive, they must be blended with a sufficient amount of finely divided carbon to provide an electrically conductive bond between the conductive spacer layers and the end caps 10. As an alternative, the end cap 10 can be mechanically sealed to the filter cartridge thereby eliminating the need for a conductive seal 6. In the case where the filter cartridge is used in a proposed vacuum cleaning operation, an end cap with a fitting which is compatible with a vacuum cleaner hose is connected to the upstream end of the cartridge. As stated above, the end cap can be filled with coarse bonded non-woven polyester strand filler material 11 which functions to prevent the collected toner particles from falling out of the cartridge. Other suitable filler materials can be spun glass, fiberglass, steel wool or any metallic wool, open cell polyurethane or neoprene foam, expanded metal or expanded pressboard or chip board. The polyester filler 11 must be generally sufficiently porous not to impede a uniform flow of the particle entrained air to all openings on the upstream side of the cartridge and yet fine enough to prevent the collected particles from falling out when the spent filter cartridge is removed from the cleaning equipment. Our preferred embodiment is illustrated by Figures 5—8 and Figures 5A—5B which show a spiral-wound filter constructed by winding corrugated spacer layers 20 and 21, e.g., an impregnated polyethylene web support of different pleat sizes in interleaved relationship with two filter layers 1 on to a central core 4 to form a spiral filter. Winding of these multilayers is continued until the desired diameter is reached. Spacer layer 20 on the air entering (upstream) side 7 must be made of conductive material. The filter layers and spacer layers are collectively sealed at 15 along the length of the core 4 to secure them to the core as illustrated in Figure 10 and then the space between the small spacer 21 and the filter layer 1 is sealed at 5 along one edge of the rolled filter cartridge. The opposite edge of these layers is left unsealed. Conversely, the space between the layer spacer 20 and the filter layer 1 is sealed at 5 along one edge of the opposite edge of the rolled filter cartridge. Therefore, the sealed edges of the two spacers 20 and 21 are opposite each other. This means that the particle entrained air enters inlet 9 is diffused by filler material 11 and flows uniformly into one of the air spaces 7 at the upstream end of the filter cartridge, through the flow channel 8 between the upstream spacer 20 and the filter layer 1 and then passes through the filter layer and exits the cartridge through the open space 7a between the downstream 21 spacer and the filter layer. After winding the cartridge to the desired diameter, the layers of filter material and the smaller spacer layer 21 are cut with the exception of upstream spacer layer 20 which is wrapped around the filter cartridge and sealed to the outer surface at 16 to prevent unwinding and to define an electrical pathway to a means for removing the electrical charge build—up from the filter cartridge. In the preferred embodiment, appropriate conductive end caps 14 are attached and sealed at 6 with a conductive composition to the end of the filter cartridge to meet the needs of the intended use. In the case of using the filter cartridge in a vacuum cleaning operation the upstream end cap is grounded as indicated by electrical connection 13 with a fitting which is compatible with a vacuum cleaner housing or cleaner hose. However, this ground is usually supplied by the metal filter housing which is part of the cleaning equipment and is in contact with the end cap so that only special cases would require a separate ground connection to the filter cartridge. The invention is not limited to filter cartridges having end caps, since most of the spiral filter cartridges are initially made without end caps. The conductive end portion of the spacer layers can be grounded through a separate connection or the metal ends of the filter housing. Finally, as previously noted, the end cap is filled with a layer of coarse bonded non— oven polyester strand filter material 11 which acts to prevent the collected toner from falling out. We have found that selection of the large corrugated spacer 20 is critical for designing a filter cartridge to maximize the load capacity for holding toner particles. As seen above, the toner particles are collected on the surface of the filter material 1 and in this collected position acts as a porous filter cake, making it possible to fill the entire space provided by the upstream spacer 20. Therefore, the height of the corrugations and the . number of crimp per inch can be varied to maximize the space available to collect toner or other types of dust particles. On the other hand, the design of the corrugation for the downstream spacer 21 need only provide sufficient space for air to pass to the atmosphere from exit opening 7a at a reasonable pressure drop. The filter media 1 need only be sufficiently porous to remove the smallest toner particles since it is used primarily as a surface filter. While the large spacer 20 must be made of conductive material, the smaller spacer 21 can be made of either conductive or non—conductive material. It should also be noted that in the preferred embodiment the larger spacer material 20 can be made of permeable or impermeable material; however, it and end caps must be made of conductive material in order to bleed off the electrical static charge build-up that is gen- erated within the filter cartridge and dissipated by means of conductor means 13. The conductive spacer layers of the invention therefore provide a method for the dissipation of static charges that may rapidly build up in the pores of non—conductive filter media. This invention eliminates the hazard of high static electrical charge accumulation that may cause sparking across the filter media resulting in the ignition or explosion of filter dust. The spacer layers as shown in Figure 1 or Figure 5 may also be employed to form a conventional pleated filter cartridge as shown in Figure 11 and Figure 12 where the filter media 31 is pleated and the pleats are arranged in the form of an annulus about a perforated core 33. A conductive spacer layer 32 of the type used in Figure 1 or Figure 5 conforms to the pleated filter media and can be connected to a ground as indicated by conductor means 13. The conductive spacer layer in this embodiment must be made of permeable material to allow the particle entrained air to pass through the spacer layer and permit loading of the filter media 31. The spacer layer also acts to hold the pleats of the filter media 31 apart and thus increase the load capacity of the filter media. This type of filter cartridge is preferably provided with end caps 34 which are bonded to the opposite ends of the pleated filter cartridge, such end caps having a center hole 30 to exit the filtered fluid. Suitable conductive sealing compositions 35 are used to bond the end caps 34 to the pleated filter cartridge which can also be grounded by conductor means 13. A similar type of construction is shown in Figure 13 in which a spacer layer 36 is made of a permeable material which is wound tight against the pleated knuckles of the filter media 31 to hold the pleats in place during loading of the filter media. The filter cartridge as shown in Figure 14 and 15 illustrates a four-sided frame type of construction which is another embodiment of our invention. Frame 44 which may be made of conductive or non—conductive material holds a continuous layer of pleated filter media 42 and individual conductive spacer layers 43 and non-conductive spacer layer 48. Figure 15 illustrates the filter unit arrangement wherein one layer of filter media 42 is alternated with a conductive upstream spacer layer 43 and a conductive or non—conductive downstream spacer layer 48. The spacer layer material as previously described above can be corrugated and conductive or non—conductive depending on its function within the particular filter cartridge. The flow of the particle enhanced air is shown by 47 wherein the particle- ladened fluid enters the upstream spacer which is open to the atmosphere and passes through the filter media for surface loading of the filter. Electrical connectors 45 are necessary at each upstream spacer layer and coupled to electrical ground 46 to remove static charge build-up from the filter unit. Finally, sealant 41 functions to seal the filter unit to the frame 44. The adhesive sealant 41 can be chosen so that it provides the necessary conductivity to define an electrical pathway from the conductive filter unit to the electrical ground 46. Whether the sealant must be conductive or non— onductive depends upon the conductivity of frame 44, and individual upstream spacer layers 43. A further modification of the frame type filter can be to use filter media 42 with non—conductive corrugated spacer layers 43 and 48 and locate a conductive face screen on the upstream side of the filter unit to dissipate static charge build-up to ground. Such a face screen could be made of the same material described for the spacer layer and must be permeable to the flow of the particle entrained air. A number of advantages result from the filter cartridge of the present invention. For example, the filter cartridge of the present invention allows for the conductive spacer layers to be in intimate contact with the flow of the particle entrained fluid being filtered. This unique design results in a filter cartridge which continually dissipates the electrical static charge build—up and functions to maintain the filter cartridge at a very low potential during a filtering operation, e.g., the cartridge is usually at a potential of no more than 100 volts during a continuous filtering operation. In addition, the collecting apparatus using the inventive filter cartridge does not create an electrical field which can damage sensitive electronic components located within the field. In addition, the effective dissipation of electrical static charge build— p is accomplished while maintaining a low pressure d op across the filter cartridge during the major portions of the life cycle of the cartridge. The filter cartridge of the present invention has the advantage of being readily adaptable to fill a number of useful filtering applications. While we have specifically disclosed the problem relating to the removal of toner particles from electrophotographic equipment, the filter cartridge and the concept of the present invention contained therein can be used in most cleaning applications where the problem of dangerous static charged build—up occurs, e.g., in the field of handling grain and grain products such as flour and meal. The filter cartridge of the present invention can be modified to include various shapes and sizes to fit the particular application for which its use is intended. Furthermore, it is also possible to modify the design of the conductive spacer material in order to maximize the loading capacity of the filter cartridge . The use of conductive spacer layer provides an opportunity to design the filter media to meet the specific requirements of the fluid being filtered. For example, it is possible to use either non—conductive or conductive filter media in the filter cartridge of the present invention. The filter cartridge of the present invention results in a self—contained disposable unit which does not require specifically designed equipment or a special housing for its use.

Claims: We Claim: 1. A filter cartridge for removing particulate material entrained in air comprising: a multilayer unit having opposed end surfaces, and including a filter layer and a spacer layer, at least one surface of the filter layer contacting the spacer layer in said unit, said spacer layer being constructed to define flow channels which contact the flow of particulate entrained air and direct such air to said filter layer which holds the particulate material removed from the air passing through said filter layer, said spacer layer comprising electrically conductive material disposed throughout said spacer layer for defining an electrical pathway ' therethrough; and means coupled to said spacer layer to connect it to a source of reference potential to continuously remove electrical static charge and thereby prevent build—up of charge on said filter cartridge. 2. A filter cartridge according to Claim 1, wherein there are a plurality of filter layers and conductive spacer layers. 3. A filter cartridge according to Claim 1, wherein the conductive spacer layers are corrugated and define spiral flow channels. 4. A filter cartridge according to Claim 3, wherein the corrugated conductive spacer layer form the outer liner for said filter cartridge. 5. A filter cartridge according to Claim 3, further including at least one conductive end cap electrically connected to said filter cartridge. 6. A filter cartridge according to Claim 4 further includes filler material disposed in the conductive end cap to distribute the particle entrained air uniformity to the flow channels. 7. A filter cartridge as set forth in Claim 2, wherein the spacer layer defining the upstream flow channel is conductive. 8. A filter cartridge according to Claim 1, wherein the conductive spacer layers are separated as individual members. 9. A filter cartridge according to Claim 1, in which the spacer layer includes a material selected from the group consisting of polyester, polyvinyl polyamide, papers or fiberglass coated or impregnated with an antistatic composition. 10. A filter cartridge according to Claim 8, in which the polyvinyl is selected from the group consisting of polyvinyl chloride, polyvinyl acetate or polyolefins such as polyethylene or polypropylene. 11. A filter cartridge according to Claim 9, wherein the antistatic composition is selected from the group consisting of a) polystyrene sulfonic acid; b ammonium or potassium salt forms of polystyrene sulfonate; c) quaternary ammonium salt coated from organic solvents; d) 1,4—benzyl quinone imine coated from a 3% acetone in water solution; and e) conductive carbon black powder. 12. A filter cartridge according to Claim 1, in which the spacer layer includes a material selected from the group consisting of metal foil, expanded and flattened metal woven wire screen, perforated screen, welded wire screen in fabric or mesh form made from a conductive metal. 13. A filter cartridge according to Claim 1, wherein the filter layer is pleated and arranged in the form of an annulus around a perforated core, a conductive spacer layer surrounds the outside surface of the filter layer and is connected to ground by means of end caps attached to the opposite ends of said pleated filter cartridge. 14. A method of making a filter cartridge comprising the steps of: a) winding a filter layer and a corrugated conductive spacer layer about a core to form a filter unit; b) sealing the alternative open pleats of the corrugated spacer layer to define flow channels so that particulate entrained air enters said flow channels through unsealed pleats and the particle entrained air passes through the filter layer before exiting the cartridge; c) sealing the free end of the conductive spacer layer to said unit to prevent unwinding; and d) providing a conductive outer surface to define an electrical pathway for continuously removing electrical static charge and prevent charge build—up on the unit. 15. A method of making a filter cartridge according to Claim 1, further including the step of attaching at least one conductive end cap to the end of said filter unit. 16. The method of making a filter cartridge according to Claim 1, wherein there are a plurality of filter layers and conductive spacer layers.

Inventors: MEDAJ THOMAS D, SOULES WILLIAM J, MEDAJ, THOMAS, D., SOULES, WILLIAM, J.
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1986
Main classification: B01D46
IPC codes: B01D46, H05F3