FILTER ELEMENT AND METHOD FOR THE MANUFACTURE THEREOF

Abstract: A filter element (10) comprises a porous, thick-walled, integral, self-supporting, resin impregnated and bonded fibrous, tubular filter structure (11) having a hollow core (15); an inner shell (20) of a first large pore size porous media adjacent the hollow core and forming the majority of the filter structure; and an outer shell (21) of a second small pore size porous media, finer than the first porous media and adjacent the inner shell, the first and second porous media being resin impregnated and bonded. A method for the manufacture of a porous, thick-walled, integral, self-supporting, resin impregnated fibrous tubular filter element comprises the steps of forming a hollow inner shell of a first large pore size porous media; forming an outer shell of a second small pore size porous media, onto the inner shell, finer than the first porous media; impregnating the inner shell and the outer shell with a resin binder; and curing the resin to form an integral, self-supporting, resin impregnated and bonded fibrous, tubular filter element.

Description: FILTER ELEMENT AND METHOD FOR THE MANUFACTURE THEREOF TECHNICAL FIELD The present invention relates to filter elements and a method for their manufacture. More particularly, a filter element is provided comprising resin impregnated and bonded fibrous materials and having a higher efficiency than known filter elements comprising resin impregnated and bonded fibrous material. BACKGROUND ART Filter elements which are self-supporting resin impregnated and bonded fiber structures are well known in the art. Preferred embodiments of such filters are described in U.S. Pat. No. 2,539,767 and 2,539,768 to Anderson are produced and sold by the Assignee herein under the trademark MICRO-KLEAN® (Cuno, Incorporated, Meriden, Connecticut) wherein the bonding systems are water soluble thermosetting resins. Broadly, these filter elements are relatively rigid, self-supporting, porous thick- walled, tubular members composed entirely of a resin impregnated and bonded fibrous material. The filter elements are used for filtering liquids and gases by flowing radially inwardly under a differential pressure. Typically the filter elements are designed to obtain maximum contaminant capacity consistent with their filtration efficiency by providing a fibrous structure of a graded porosity, with the size of the pores progressively increasing rapidly outwardly toward the outer surface. By virtue of such graded porosity, or density, as the fluid flows inwardly through progressively smaller pores, the paniculate contaminant to be filtered out penetrates to varying depths according to its size. Thus, the filter elements can accommodate more solids without effecting flow, with a consequently longer, effective life before the elements need replacing. For example, in Anderson, the graded porosity in the filter elements is accomplished by vacuum accreting resin-impregnated fibers from an aqueous uniform dispersion of such fibers under controlled conditions as to the amount of vacuum used in effecting such accretion and as to the composition and characteristics of the fibrous stock used. This approach to producing rigid, self-supporting, porous, thick-walled tubular filter elements has been usefully employed for over 40 years. It has, however, presented distinct limitations to the development and production of higher efficiency filter elements capable of removing ever-smaller contaminant particles. As is well known to the art, achieving such high filtration efficiencies requires the use of very small diameter fibers such as glass microfibers. Aqueous dispersions containing significant amounts of such fine fibers exhibit very slow formation rates during the required vacuum accretion. In many cases, it has proven impossible to form, by vacuum accretion, the required thick-walled tubular filter elements from such fine fiber dispersions. Similarly, it has proven difficult, if not impossible, to impregnate, dry, and cure such filter elements because of the high resistance to liquid or gas flow. Using the current state-of-the-art MICRO-KLEΛN® process, the highest efficiency cartridge that can be produced is practically limited to an 8 micrometer nominal (90 percent particle removal efficiency) rating. There are other approaches to producing high efficiency filter cartridges but all involve the use of expensive raw materials and/or processes. Accordingly, there is a well-defined industrial need for low-cost, economical rigid, self- supporting resin impregnated and bonded filter elements with nominal filtration ratings of less than 8 micrometers, that the prior art has not been able to satisfy. DISCLOSURE OF THE INVENTION It is therefore an object of the present invention to provide a filter element, comprising resin bonded fibers, having a higher efficiency than existing filter elements of this type. It is another object of the present invention to provide a higher efficiency filter element comprising an inner shell of a first porous media and an outer shell of a second porous media, more fine than the first porous media. It is yet another object of the present invention to provide a method for th manufacture of a higher efficiency filter element comprising two layers of resi impregnated and bonded fiber materials. At least one or more of the foregoing objects, together with the advantag thereof over known methods which shall become apparent from the specification whi follows, are accomplished by the invention as hereinafter described and claimed. In general, the present invention provides a filter element comprising porous, thick-walled, integral, self-supporting, fibrous, tubular filler structure havi a hollow core; an inner shell of a first large pore size porous media adjacent the hollo core and forming a significant portion of the filter structure; and an outer shell of second small pore size porous media, finer than the first porous media and adjacent t inner shell, the first and second porous media being resin impregnated and bonded. The present invention also provides a method for the manufacture of porous, thick-walled, integral, self-supporting, fibrous, tubular filter element comprisi the steps of forming a hollow inner shell of a first large pore size porous media; formi an outer shell of a second small pore size porous media, onto the inner large pore si shell finer than the first porous media; impregnating the inner shell and the outer sh with a water soluble thermosetting resin binder; and curing the resin to form an integr self-supporting, fibrous, tubular filter element. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of the filter element of the present inventio with a portion partially broken away; Fig. 2 is a cross section, taken substantially along line 2-2 of Fig. 1; Fig. 3 is a longitudinal section, taken substantially along line 3-3 of Fig. and Fig. 4 is an enlarged fragmentary view of the area circled in Fig. 4. PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION Apart from the novelty of the filter elements taught by the present inventio filter elements of this type arc well known in the art as is their method of manufactu As previously indicated these are produced, for example, as described in Assigne U.S. Pat. Nos. 2,539,767 and 2,539,768 to Anderson, the entire disclosures of whi are incorporated herein by reference. In the current MICRO-KLEAN® production process, the Anderson process has been modified so that the fibers are vacuum accreted from a uniform aqueous dispersion and then, subsequently, vacuum impregnated with a water soluble thermosclting resin. Accordingly, the filter elements of the presen invention generally comprise a relatively rigid self-supporting, porous, thick-walled, tubular member composed entirely of resin-impregnated and bonded fibrous materials. Typically, filter elements of this type are sealingly arrayed within a filte housing which allows for the ingress of a fluid, liquid or gas, to be filtered and th egress of a filtrate. " Within the housing or cartridge, means are provided to direct the fluid to the radially outermost surfaces of the element where the fluid then flows radially inwardly under pressure and is filtered, to exit axially via a central hollow core. It is to be understood that the environment for such use is well known and does not constitut novelty of the present invention. Accordingly, such housings and the passage of th fluid have not been depicted. In similar fashion, to provide tighter, more efficient filler elements of thi type, it has become necessary to seal the ends of the filter elements in order to preven the by-pass of the filter by the unfillercd fluid or contamination by the filtered particles. One particularly useful means of effecting such sealing is to employ a gasket at each end comprising a polyethylene closed cell foam. Such foams are well known in the art, preferred brand being sold by Volteck of Lawrence, Mass. under the registere trademarks VOLARA and MINICEC, the former being preferred. The use of suc gaskets for scaling filter elements of this type is described in U.S. Pat. Nos. 5,015,31 and 5,028,327 owned by the Assignee of record, the subject matter of which i incorporated herein by reference. With reference to the drawings, the filter element of the present inventio is depicted in Fig. 1, indicated generally by the numeral 10. The filter element 1 preferably comprises a cylindrical structure or body 11 having an outer surface 12 opposed ends 13 and 14 and a hollow axial core 15. The outer surface 12 may provid grooves 16, to provide increased surface area and contaminant capacity. The element 10 is intended to be used for filtering liquids and gases whic are caused to flow radially inwardly under a differential pressure. Heretofore, in orde to obtain the maximum life consistent with the filtering efficiency, the fibrous struct of the filter element 10 has comprised a graded porosity, with the size of the po progressively increasing radially outwardly toward the outer surface 12. By virtue such graded porosily, or density, as the fluid flowed inwardly through progressiv smaller pores, the particulate contaminants to be filtered penetrated to varying dep according to their size. The filter element 10 of the present invention employs an incrementa graded porosity; however, in contradiction to prior art the porosity gradation has b reversed, that is, the pores are most numerous and their sizes the smallest at the ou surface 12 of the body 1 1. More particularly, the body 11 actually comprises t components, an inner shell 20 of generally large pore size and an outer shell 21 of sm pore size. The inner shell 20 is bounded at its inner diameter or wall 22 by the holl axial core 15 and an outer diameter or wall 23, forming a thickness which compri approximately 30 to about 70 percent of the overall element thickness. Similarly, inner diameter or wall 24 of the outer shell 21 is continuous with the outer diame wall 23 of inner shell 20 while the radially outer wall 25 is continuous with the ou surface 12. As depicted in the drawings, particularly Fig. 4, the outer surface 12 provide grooves 16, which are individual annular rings. The bottom 26 of each gro or ring 16 is located within the outer shell 21. Alternatively, for other embodime within the scope of the present invention, the outer surface 12 can be free grooves 16. In order to manufacture the filler element 10 according to the pres invention, a fibrous material is mixed with water or other suitable dispersant to for slurry. Subsequently, one or more perforate formers or dies are immersed in the slu in a felting lank holding the aqueous dispersion of fibers and the fibers are caused to accreted upon the formers by application of a vacuum suction imposed upon the inte of the formers. By the control of the degree of vacuum and the length of time o which the vacuum is applied, in conjunction with the proper selection and control of characteristics of the fiber, a filter carcass is produced of the depth, or thickness porosity that is desired. This procedure is terminated when an adequate volume of fibers have accreted to form the inner shell 20. After formation thereof, a substantial portion water or dispersing agent is removed by drawing hot air through the former and shell 20. The former is then immersed in a second aqueous dispersion of fiber selected to form the tighter, smaller pore size of the outer shell 21. This st overfelting the inner shell 20, is controlled by the degree of vacuum and continue a duration of time adequate to produce an outer shell having the intended thick After formation of the shell 21 , a substantial portion of the water or dispersing again removed by drawing hot air through the former, inner shell 20 and outer shel In order to impart to the filter element strength and rigidity, as well waterproof the fibers so that they will not become soggy, or soft in the presen water or other fluids, a resin is used to impregnate the fibers and to bond them tog in a relatively fixed relationship. The amounts of resin used may vary betwee percent and 60 percent by total weight of the filter element. Various resins incl thermosetting resins such as phenol formaldehyde condensation products, formaldehyde condensations products and the melamine resins may be Thermoplastic resins may also be employed, such as polystyrene. Preferred resin melamine and phenolic resins. Resin impregnation is conducted by immersing the dried composite of shell 20 and outer shell 21 in a tank of resin and applying a vacuum through the f for a sufficient period of lime for all of the fibers to be contacted. Generally, abo minutes will suffice but, of course, time is a function of the vacuum as well as th and density of the filter clement and hence, the method of the present invention s not be limited thereby. After impregnation, the filter element is cured by heat under temperatur time conditions appropriate for Ihe curing of the particular resin used. In the final the filter cartridge is sized to accurate dimensions by cutting or trimming mechan as by means of a knife, saw or grinder (see the U.S. Pat. No. 2,539,767 to Ande The fibers employed to manufacture the inner shell 20 can comprise ac nylon, polyester, cellulose and mixtures thereof. These fibers have average dia ranging from about 10 to 40 micrometers and provide a pore size ranging from ab 5 to about 50 micrometers, with 10 to 20 micrometers being preferred. The fibers employed in the overfelting step to form the outer shell 21 selected to provide a very tight, small pore size second porous media. As such, t fibers can comprise acrylic, nylon, polyester, cellulose and mixtures thereof lo whi a relatively high percentage of glass microfibers have been added. Amounts of t latter range from about 5 to about 30 weight percent. Average glass microfi diameters can be selected ranging from about 0.5 mm to 5 mm. Because of the unique structure of the filler element made according to t present inveniton, it is now possible to remove substantially finer particles than via t use of a conventional fibrous filter element. A comparison is presented in Tabl hcreinbelow between a MICRO-KLEAN® filter element, characterizing the known a and a filter element according to the present invention. TABLE I PARTICLE SIZE FOR INDICATED INITIAL PARTICLE REMOVAL EFFICIENCY 50% 90% 95% 98% 99% Prior Art* 4.6 7.9 8.9 9.9 11.6 (micrometers) High Efficiency^ (c) 3.1 3.4 3.8 4.3 (micrometers) a) tighest prior art MICRO-KLEAN® efficiency b) tighest efficiency for filter element according to the present invention c) could not be measured By reviewing the data presented in Table I, it should now be appreciated t the relatively open inner shell formed by the first porous media and overfelled ou shell of the second porous media, being much finer than the first porous media, results in a unique filter element which can filter much finer particles with high efficiency. For use in high efficiency filter applications, it is necessary that the filte clement 10 employ an extremely effective scaling means. Referring to Figs. 1 and 3, thermally bonded to each end 13 and 14 of clement 10 is a thermoplastic polymer close cell foamed sealing gasket 29. Each gasket 29 provides an effective sealing surfac between the ends of the cartridge 10 and the sealing edge of the filter housing (no shown). The gaskets arc typically in the form of a donut shaped disc circle which i adhered to the filter ends 13, 14 concentrically with the hollow axial core 15. Typicall the gasket may be of a diameter somewhat smaller than the outside diameter of the filte element 10, and have an inside diameter somewhat larger than the internal diameter o the filter element. Typically the discs arc 1/16 to 3/32 of an inch thick. This dimensio could be increased if necessary to compensate for troublesome sealing configuration that require more resiliency or depth to provide sufficient sealing. The foam is obtaine in sheet form and cut into discs of the desired size and shape. The gaskets 29 are applied to the filter element 10 by heating the ends 13 14 of the element 10 to a temperature sufficiently high to thermally melt bond th gaskets 29 to the cartridge end when the gasket is contacted with the hard filter elemen surface. Such tcmpcralurc may be determined readily and is empirically derived but i below the temperature al which the element starts to deteriorate, melt and/or fuse an is also below a temperature that completely melts the gasket. However, it has bee found that the cells inside the gasketing material insulate the heated lower surface i contact with Ihc heated ends of the filter 10 from the remaining portion of the gasketin material and thus, only the lower surface of the gasket is sufficiently heated to mel bond itself to the ends of Ihe filler element 10. Such heating can be accomplished wit a hot plate, infrared energy, hot air, etc. A number of techniques are available fo heating the end of Ihe clement which are simple to accomplish and to automate. The closed cell configuration of the polymer is also desirable because i provides resiliency or spring back that allows compensation for out of alignment or ou of flatness of the end of Ihc cartridge. Additionally, Ihc closed cell configuratio provides sealing between cells through which the fluid cannot seep or flow. The use of a solid polymeric gasket would be inadequate because although it might bond to the filter element by the mere healing of the end of the cartridge, it would either completely melt and deform and/or would not provide sufficient resiliency for the sealing edges of the filter housing to embed therein. For a more complete description of these sealing gaskets, reference can be made to U.S. Pat. No. 5,015,316 and 5,028,327, noted hercinabove. The filter housings used in conjunction with the filter element of this invention are well known in the art. The cartridges may be used in varying lengths or multiples of a single length, slacked one on top of another. In such arrangements all Ihe cartridges in multiple height slack arrangements are thermally bonded with a hot melt polymer, e.g., polypropylene, to assure alignment and permanent bonding for positive sealing against bypass. The filter elements may be used for removing particulate contaminants which are fibrous, abrasive or gelatinous from fluids such as gas, alcohol, glycols, coolants, fuels, oils, lubricants, cosmetics, paints and varnishes, syrups, compressed air, water or sensitive process liquids, e.g. , dcmincralizcd water, food products, beverages, photographic solutions and, particularly, magnetic oxide slurries for producing magnetic recording media. Based upon Ihc foregoing disclosure, it should now be apparent that the filter element of the present invention will carry out the objects set forth hereinabove. It should also be apparent to those skilled in the art that the method of the present invention can be practiced lo manufacture a high efficiency filter element having an outer shell of smaller pore size porous media than that of the inner shell. Similarly, the selection of fibers and bonding resins which may be employed to prepare the filter element can readily be determined by those skilled in the art, depending upon the filtration desired. It is, therefore, to be understood that any variations evident fall within the scope of the claimed invention and thus, the overall structure and size of the filter element, as well as the pore size can be varied to suit the ultimate application and can be determined without departing from the spirit of the invention herein disclosed and described. Moreover, the scope of the invention shall include all modifications variations that may fall within the scope of the attached claims.

Claims: CLAIMS What is claimed is: 1. A filter clement comprising: a porous, thick-walled, integral, self-supporting, resin imprcgnalcd bonded fibrous, tubular filter structure having a hollow core; an inner shell of a first large pore size porous media adjacent hollow core; and an outer shell of a second small pore size porous media, finer than first porous media and adjacent said inner shell, said first and second por media being resin impregnated and bonded. 2. A filter element, as set forth in claim 1 , wherein said first porous media compr fibers selected from the group consisting of acrylic, nylon, polyester, cellulose mixtures thereof. 3. A filter clement, as set forth in claim 2, wherein said fibers have aver diameters ranging from about 10 to 40 micrometers. 4. A filter clement, as set forth in claim 3, wherein said first porous media prov pore sizes ranging from about ranging from about 5 to about 50 microns. 5. A filter element, as set forth in claim 1 , wherein said second porous m comprises fibers selected from the group consisting of acrylic, nylon, polyes cellulose and mixtures thereof with glass microfibers. 6. A filter clement, as set forth in claim 5, wherein said glass microfibers hav average diameter ranging from about 0.5 to about 5 micrometers. 7. A filter clement, as set forth in claim 6, wherein said glass microfibers comp from about 5 lo about 30 weight percent of said outer shell. 8. A filter element, as set forlh in claim 1 , wherein said inner shell comprises fro about 30 to 70 percent of the diameter of said element. 9. A filter clement, as set forlh in claim 1 , wherein said tubular filter structur provides an outer wall having a plurality of circumferential grooves. 10. A filter element, as set forth in claim 1, further having opposed ends carryin gaskets seals, thermally bonded thereto. 11. A method for the manufacture of a porous, Ihick-wallcd, integral, self-supporting resin imprcgnalcd and bonded fibrous, tubular filter element comprising the step of: forming a hollow inner shell of a first large pore size porous media; forming an outer shell of a second small pore size porous media, onto sai inner shell, finer than said first porous media; impregnating said inner shell and said outer shell with a resin binder; and curing said resin to form an integral, self-supporting, resin impregnated an bonded fibrous, tubular filter element. 12, A method, as set forlh in claim 11 , wherein said step of forming said hollow inne shell employs fibers selected from the group consisting of acrylic, nylon polyester, cellulose and mixtures thereof. 13. A method, as set forlh in claim 12, wherein said fibers have average diameter ranging from about 10 to 40 micrometers. 14. A method, as set forlh in claim 13, wherein said first porous media provides por sizes ranging from about 5 to about 50 microns. 15. A method, as set forth in claim 11 , wherein said step of forming said outer sh employs fibers selected from the group consisting of acrylic, nylon, polyeste cellulose and mixtures thereof with glass microfibers. 16. A method, as scl forlh in claim 15, wherein said glass microfibers have average diameter ranging from about 0.5 to about 5 micrometers. 17. A method, as set forth in claim 16, wherein said glass microfibers comprises fro about 5 to about 30 weight percent of said outer shell. 18. A method, as set forth in claim 11 , wherein said inner shell comprises from abo 30 to 70 percent of Ihe diameter of said element. 19. A method, as set forth in claim 11 , including the additional step of providing plurality of circumferential grooves in said outer shell. 20. A method, as scl forlh in claim 11 , including the additional step of thermal bonding gaskets seals to opposed ends of said filter elements.

Inventors: HAMLIN THOMAS, HAMLIN, THOMAS
Applicants: CUNO INC, CUNO INCORPORATED
Application year: 1993
Main classification: B01D27
IPC codes: B01D27, B01D29, B01D39, B01D46