CA1184512A - Filter element having microporous filter membrane - Google Patents
Filter element having microporous filter membraneInfo
- Publication number
- CA1184512A CA1184512A CA000408403A CA408403A CA1184512A CA 1184512 A CA1184512 A CA 1184512A CA 000408403 A CA000408403 A CA 000408403A CA 408403 A CA408403 A CA 408403A CA 1184512 A CA1184512 A CA 1184512A
- Authority
- CA
- Canada
- Prior art keywords
- membrane
- filter
- filter element
- sealing
- porous
- 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.)
- Expired
Links
Abstract
FILTER ELEMENT HAVING MICROPOROUS
FILTER MEMBRANE
ABSTRACT
A filter element comprising a hydrophilic nylon microporous filter membrane having a preformed substantially non porous sealing area of non-porous tape heat sealed to the membrane and a filter housing having preferably a hydrophobic thermoplastic sealing surface in thermoplastic sealing relationship with the sealing area.
Preferably, the filter membrane is a pleated cylindrical membrane and the housing includes end caps thereto.
The preferred pleated cylindrical membrane is produced from an elongated porous filtration area longitudinally bordered by the substantially non-porous sealing areas. Such a membrane may be produced by applying a heat sealable non-porous tape along the longitudinal borders of the filtration area. The filter element is particularly useful for the filtration of aqueous liquids, particularly parenteral or body liquids.
FILTER MEMBRANE
ABSTRACT
A filter element comprising a hydrophilic nylon microporous filter membrane having a preformed substantially non porous sealing area of non-porous tape heat sealed to the membrane and a filter housing having preferably a hydrophobic thermoplastic sealing surface in thermoplastic sealing relationship with the sealing area.
Preferably, the filter membrane is a pleated cylindrical membrane and the housing includes end caps thereto.
The preferred pleated cylindrical membrane is produced from an elongated porous filtration area longitudinally bordered by the substantially non-porous sealing areas. Such a membrane may be produced by applying a heat sealable non-porous tape along the longitudinal borders of the filtration area. The filter element is particularly useful for the filtration of aqueous liquids, particularly parenteral or body liquids.
Description
FILTER ELEMENT HAVING A~lCROPOROlJS
FILTER MEh~BRANE
1. FIELC) OF THE INYENTION
__ _ _ _ __ This invention relates to filter elements utilizing hydrophilic microporous membrane as the filtration media, and more particularly to filter elernents utilizing cylindrical pleated nylon membrane7 said filter elements being suitable for the filtration of aqueous fluids, in particular parenteral or body liquidsO
FILTER MEh~BRANE
1. FIELC) OF THE INYENTION
__ _ _ _ __ This invention relates to filter elements utilizing hydrophilic microporous membrane as the filtration media, and more particularly to filter elernents utilizing cylindrical pleated nylon membrane7 said filter elements being suitable for the filtration of aqueous fluids, in particular parenteral or body liquidsO
2. PRIOR ART
In many applications it is necessary to totally remove particles having dimensions in the submicrometer range. For this purpose, it is well known in the art to use q thin polymeric layer that is rendered highly porous with a substantially uniform pore size. Such layers are commonly termed microporous filtration mernbrane.
One characteristic of such microporous filter membrane is that they are extremely fragile and easily rupture when subjected to deformation due to rough handling9 bending, or fluid pressure. Since even the most minute crack or break will destroy the effectiveness, it is necessary to ose extreme care in manufacture and use.
,,,,~, ~
Microporous filter membrane find many uses in industry9 science and educationO A common industrial application is thc "cold"
sterilization of pharmaceuticals and the stabilization of alcoholic beverages. In cold sterilization, the membrane has a sufficiently small pore size to block the passage of all bacteria present in the unf;ltered fluid supplied to the upstream side. In the production of alcoholic beverages, the removal of bacteri~, yeqst and molds9 stabilizes and clarifies the beverage. In the production of phar-maceuticals, the removal of bacteria is ~n essential step for obvious health reasons. In all of these applications it is essential that the filter mernbrane used be hydrophilic in order to filter such aqueous flui~s.
There are many types of filter membranes available and processes for producing such membrane.
Nylon microporous filter membrane is well known in the art, for example, U.S. Patent No. 3,876,738 to Marinaccio et al tl975) describes a process for preparing nylon microporous membrane by quenching a solution of a film forming polymer in a non-solvent system for the polymer. EuropeGn Patent Application 0 005 536 to Pall, published in 1979, describes a similar type pro-cess for producing nylon membrane~
Other type polymeric microporous membranes, including nylon and processes for producing such membranes are described, for example in the following U~S. Patents:
In many applications it is necessary to totally remove particles having dimensions in the submicrometer range. For this purpose, it is well known in the art to use q thin polymeric layer that is rendered highly porous with a substantially uniform pore size. Such layers are commonly termed microporous filtration mernbrane.
One characteristic of such microporous filter membrane is that they are extremely fragile and easily rupture when subjected to deformation due to rough handling9 bending, or fluid pressure. Since even the most minute crack or break will destroy the effectiveness, it is necessary to ose extreme care in manufacture and use.
,,,,~, ~
Microporous filter membrane find many uses in industry9 science and educationO A common industrial application is thc "cold"
sterilization of pharmaceuticals and the stabilization of alcoholic beverages. In cold sterilization, the membrane has a sufficiently small pore size to block the passage of all bacteria present in the unf;ltered fluid supplied to the upstream side. In the production of alcoholic beverages, the removal of bacteri~, yeqst and molds9 stabilizes and clarifies the beverage. In the production of phar-maceuticals, the removal of bacteria is ~n essential step for obvious health reasons. In all of these applications it is essential that the filter mernbrane used be hydrophilic in order to filter such aqueous flui~s.
There are many types of filter membranes available and processes for producing such membrane.
Nylon microporous filter membrane is well known in the art, for example, U.S. Patent No. 3,876,738 to Marinaccio et al tl975) describes a process for preparing nylon microporous membrane by quenching a solution of a film forming polymer in a non-solvent system for the polymer. EuropeGn Patent Application 0 005 536 to Pall, published in 1979, describes a similar type pro-cess for producing nylon membrane~
Other type polymeric microporous membranes, including nylon and processes for producing such membranes are described, for example in the following U~S. Patents:
3,642,668 to Bailey et al (1972~;
4,203,847 to ~ (19~0), 41203~848 to Grandine, II (1980~; and 4,247,498 to Castro 9 ~ 19 80~.
Commercially available nylon microporous filter membranes are available from Pall Ccrp., Glencove9 N~Yo ~
under the trademark ULTIPOR N66 and N66 POSIDYNE. Another commercially significant filter membrane made of polyvi-nylidene fluor:ide is available from Millipore Corp~, Bedford, Massachusetts, under the trademark DURAPORE.
This membrane is probably produced by the aforementioned G ndine, II patents~
Additionally, the Assignee of this application is selling cationically charged modified nylon microporous filter membrane under the trademark ZETAPOR. These mem-branes are described and claimed in Canadian Patent ~o.
1,166,411 to Barne~ et al and Canadian Patent ~o. 19156,410 to o~trrlc~~r o~ al. _arnes et al describes the use of charged modified membrane for the filtrat:ion of high purity water (18 meyohm-centimeter resistivity) used in the electronics industry, and Ostre_ her et al describes the use of charged modified membrane for the filtration of parenteral or body liquids. Additionally, it should be noted that these filter membranes are typically rein-forced by various meansO A unique method of reinforcement is described in co-pending Canadian Patent Application Serial No~ 417,737 to Barnes et al.
Al I of the aforementioned membranes, besides being used in sheet form, are used in various type filter elements. Generally9 the fitter element comprises the filter membr(lne and a filter housing with a sealing surface in sealing relationship with a sealing area of the membrane. A well known type filter element is the pleated cartridge type fllter element described, for example, in U.S~ Patent No. 3,457,339 to Pall et al (1969~. Another well known type of filter element is the hermetically sealed intravenous unit described in U~S.
Patent No. 4,113,6~7 to Leason ~1970).
In the critical applic~tions for such filter elements, ;t is imperative that the filter membrane not be damaged during produc-tion and that the filtrate not bypass the filter membrane. Either situation could be catastropic, for example, allowing contaminants to enter the blood stream of a patient. It is therefore necessary that on undamaged seal exist between the sealing area of the membrane and the ~ealing surface oF the filter housing to prevent leakage around the filter membrane. In order to insure such integrity, the filter element is "integrity tested" to insure the integrity of the filter elernent. This is gener~lly accomplished by ~ "bubble point" test of the filter element by methods well known in the art. A particular type of integrity testing device for filter cartridges is commercially available under the name ZETAWATCH, from AMF Cuno Division?
Meriden, Connecticut and described and claimed in the Assignee's IJ.. S. Patent ~o., 4, 384, 474. This integrity tester is self contained and electrically monitors the individual cartridge element's integrity within a multiple cartridge housing. Other methods of such integrity testing are described in "Non Destructive Test For Bacterial Retentive Filters" by Ben Trasen which was published in the September/October 1979 issue of the Journal of Parenteral Drug Association, pages 273-2798. Ai I of the known integrity tests require a thorough wetting of the membrane and sealing surfaces assooiated therewith to provide an aocurate determination of integrity. If the filter membrane is broken, even microscopically, if the membrane is improperly installed, or if the membrane sealing surfaces are not completely wetted, bubbles will appear immediately at the point of the break or leakq Ac~ditionally, any filter element must, particularly when used to filter parenteral or biological liquids, hove a minimum of extractable contaminants introduced into the filtrate~ These contaminants may be harmful toxins when introduced into a patient. Specifically9 any filter elernent must meet the test standards of the industry, e.g.
ASTM D-3861-79.
Still further, fiiter elements used to filter parenteral or bio-logical lîquids should be heut sterilizable and autoclavable, without deterioration or discoloration of the housing or membrane or deterioration of the seal between the membrane and housing. A
preferred housing material is polypropylene which is hydrophobic.
Several methods of sealing filter elements have been employed in the past. These methods include pressure clampin~, heat sealing, ultrasonic welding, adhesive and solvent bonding, and injection molding, These prior art methods fail to provide on occasion the 100% positiv~ seal which is necessc ry to prevent leakages. In partiaular where microporous filter membranes are used in the filter element, there is some danger when usirig these methods that the delicate filter media will be damaged during the seuling process~
Known methods of pressure clamping and other mechanical interlocking systems tend to distort the filter membrurle or actwlly damage the membrane at the clamping edges9 thereby destroying the integrity of the membrane and al lowing contaminants to pass through. Also conditions such as time, qnd hent stress relieving CGn allow the pressure seal to relax. Additionally, this method is particularly complicqted when a pleated filter cartridge is assembled, Known methods of heat s~aling, sonic welding and related thermo-mechanical bonding methods may also damage the filter membrane at the sealing edges, The use of adhesives or solvent bonding has disadvantages in ~hat another material is introduced into the filter element that can lead to extractable contarninants. C)ften the constituents of an adhesive or solven~ system may also damage the filter membrane.
The foregoing methods of sealing the filter housing to a filter membrane are particularly troublesome when a hydrophobic sealing surface is in contact with a hydrophilic sealing area, This is often the case when the filter element is used to filter biological or parenteral liquids where it is very highly desirable to use a polypro-pylene housing, (which is resistant to autoclaving and heat steriliza-tion) and undesirable to use adhesives or solvents for sealing (to avoid high extractables). For such elements, the housing is usual Iy thermoplastically sealed to the membrane, inc:reasing the chances for damage to the sealing areas of the membrane~ Additionally, it appears that the hydrophobic sealing surface of the housing in contact with the porous hydrophilic sealing area of the membrnne increases the chances that the filter element will not pass industry integrity testsO This is probably brought about by ~he incomplete wetting of the membrane/housing interface which gives a reduced bubble point. For example, it has been found that in the therrnoplastic sealing of polypropylene end caps to cylindrical pleated nylon membrane filter cartridges, an unacceptably low percen~age of the cartridges passed the industry int~ogrity test.
More specifically7 the following prior art references are relevant to the invention described and claimed herein.
U.S. Patent hlo. 1,476,392 to Carroll (1923) describes a process of making a composite film by casting a plastic or flowable cellusoic material9 efg. cellulose acetate, on to a moving wheel from a plurality of compartments to thereby produce a plurulity of adjacent lFilm strips. This reference does not teach or suggest the production of a microporous filter membrane.
U.S. Patent NoO 2,663,660, to Layte (1953) describes a method of assembling filter elements, e.g~ a filter cartridge, by producing an elong~ted strip oF filter paper and foiding elongated tapes of adhesive material on the elongated edges. The filter paper is then cut to size and pleated transversely of the length of the strip, and rolled into an annulus form The outer portions of the adhesive tape material is then moistened with a soitable solvent material for the adhesive materiql of which the tapes are formed and thereafter the ends of the annulus are capped by end caps. The end caps <~re preferably heqvy c~rdboard. ~ does not teach or suggest the use of such a method in conjunction with microporous membrane nor is such a method suitable for producing filter cartridges for filtering parenteral or biological liquids wherein extractables must be minimized.
U.S. Patent ~Jo. 3,013,607, to Jackson et al (1961) relates to a method of end capping tubular filter elements of paper~ cardboard, felt, woven tissue, etc. Thermoplastic end caps are subjected to hecr~
in~;luced in the field of an electric inductance coil in contact with the cap, to a point where the cap is softened so that the edges of the filter can be embedded in the cap to the depth required to bind the parts together. A metallic strip is applied to the edges of the filter and external support jacketJ or the edges of the Filter element and external support jacket are coated with an electrically conductive or semiconductive material, so as to reinforce the filter edges, and enhance the heat conductivity through the edges and end cap.
Jackson et al does not utilize an organic polymeric microporous filter mernbrane and thus does not recognize the problems associated with J~
the integrity testing vf filter elements containing such hydrophilic membrane in conjunction with a hydrophobic end cap.
Additionally, the use of a metalic strip on the edges of the Jackson et al filter limits greatly the application to which the end ___ capped filter elements can be put. For example9 under certain conditions, the metallic strip can corrode and/or contaminate the material being filtered or the medium being filtered~ Such a filter element is completely unacceptable for the fiitration of biological and porenteral liquids~ Still further the use of such a metalic strip on the edges of the filter elements increases the cost of making the filter elements, and complicates the procedure used in corrugating such filter elements.
U.S. Patent No. 3,407,252 to Pall et al (1968) desoribes the production of Q corrugated or pleated filter media in annulus form which utili;2es a ribbon or tape of bonding agent such as a heat sealable and curable epoxy resin, to form a leak-proof seal along the longitudinal meeting of the pleated filter media.
U.S. Patent No~ 3,457,339 to Pall et ai (1969) describes a process for applying preformed end caps to filter sheet material, particularly sheet materials formed of fiber and in substantially tubular shape. The process involves heating the inside face of the thermoplastic end cap to fuse a portion of the cap into a liquid. The liauid is of a viscosity which is capable of penetrating through the pores of the filter sheet. The edges of the cylindrical sheet ~re then embedded in the liquified end cap so that the liquidified thermo-r~ ~
plastic material penetrates through the pores of the embeddedportions of the filter sheet material from one surfsce to the other.
The liquid plastic is then hardened and said to form a substantially continuous leak proof matrix of end s:ap material permeating through the pores of the filter material and bonding the filter sheet ~o the end cap in a leak proof seal.
This process for applying end caps to a filter sheet has the advnnta~e in that it does not require the use of adhesives. If this Pall et al process, however, is utilized using end caps of a hydrophobic material, and a hydrophilic membrane, an excessive percentage of the cartridges do not pass the industry integrity test. It is believed that this is due to the cartridge not being completely wetted at the interface between the hydrophilic membrane and the hydrophobic end cap. Hydrophobic type end caps may be utilized if the cartridge is integrity tested in a non-aqueous solvent. This, however, limits the application of the filter element. If a hydrophilic type end cap, e.g.
polyester, is usedS the cartridge will generally have inferior solvent and chemical resistance and inferior resistance to autoclaving and heat resistance.
This Pall et al prccess requires that the sealing areas of the filter sheet material be porous to permit penetration of the liquified thermoplastic material through the pores of the embedded portion of the filter sheet m~terial from one surface to the other. Additionally, during prosecution Pa!l et al states:
"...The instant process is simple enough to enable rapid manufacture of filter elements with a minimum of manu-faeturing steps and without the necessity of employing bonding agents and components ~_ filter and end cap..."
In effec7 PQII et al teaches away from Applicant's invention which utilizes a substantially non-porous sealing area and which utilizes other components than the actual materials of the filter and end cap.
U.5. Patent No, 3,471,019 to Trasen e~ al (1969~ describes a filter unit comprised of a two-part housing provided with sealing portions adapted to be aligned with eaah other and with a peripheral portion of the filter cornpletely surrounding the central portions of the filter.
In assembly of the unit, the sealing portions of of the housings are pressed against the opposite sides of the filter and the sealincJ portion of at least one of the parts of the housing is heated to cause the material thereof to melt and flow through the aligned pores of the peripheral portions of the filt0r and fused to the seal;ng portion of the oth~r part of the housingO A similar type filter and sealing method is described in U.S. Patent No. 3,782,083 to ~ (1974) wherein the plastic rnaterial runs through the pores of the -filter element forming a fluid tight integral seal closing all sides of the element to flvid flow.
U.S. Patent No. 3,487,943 to Buckman ~1967) describes a filter element made of pleated filter paper. One portion of the filter element is rnodified so that in operation of the filter the liquid flow velocity through the modified portion is less than that through the remainder of the element. The mociified portion may be formed by compressing together a series of pleats or by sealing to a group of pleats on one side of the element a sheet of similar or dissimilar filter material. The similar or dissimilar filter material is sealed to the annulus cartridge over the inner or outer periphery of the cartridge and does not form a continuous edge along the top of the filter near the end cap.
U.S. Patent No/ 3~591,010 to Pall et al (1971) describes a corrugated element having a microporous layer deposited on u substrate sheet provided with portions of reduccd porosity at the areas of the base folds of the corrugations.
U.S. Patent No. 3,815,754 to ~ (i974) describes a box filter wherein the elements of the filter housing are bonded to the filter sheet by fused integration of the housing members through the open pores of the filter element, forming a fluid tight seal all aiong the sides of the Pilter sheet. Such a bond is obtained by9 for example, ultrasonic welding, solvent softening or heat fusion.
U.S. Patent No. 3,865,919 and 3,867,294 to Pal I et ! (1975 describe cylindrical elements having an improved side seam seal which can be bonded ~o end caps in a teak type manner.
U.S. Patent No. 3,9$4~625 to Michalski 51976) describes a filter which includes a plastic housing and an intermediate filter screen~
The peripheral portion of the screen is sealed between the two housing halves by flowing a portion of at least one of the housing halves through the screen and bonding that portion to the o-ther housing half.
U.S. patent No. 4,101,423 to Merrill et al (1978) describes a tubular filtration elemen~ whose ends are impregnated with a suitable sealing adhes;ve. When the adhesive materiai cures7 the end portion provides mechanical support for the tube and blocks the pass~ge of the fluid or the particulate and bacterial contaminant. Merr~ll et al requires that the sealing material used to form the ends must be hydrophiiic when cured, stating "If the sealant rendered the filter adjacent to it hydro-phobic, the filter would not be wetted and would not then offer capillary resistance to the bubble point test gas9 therefore the bubble point could not be used as an indication of filter integrity..." (Col. 9, lines 59 64).
"It will be understood that if the outer layer (of the filter) is formed from a lacquer impregnated paper, the resilient members can safely appiy a sealing force sufficient to block the fluid from the end portions so that a hydrophobic sealing material may be used." (Col. 10, lines 6-10).
The filtration element is supported and sealed within a housing by radial seal force, i.e~ the filtration element and housing are not in thermoplastic sealing relationship to each other~
US. Patent No. 471549688 to Pall (1979) describes the use of thermoplastic end cap applied to the open ends of a filtered tube in accordance with the afor~mentioned U.5. patent No. 3,457,39 to Pall e_ ~f~
U~SO Patent No. 4,193,876 to Leeke et al (1980) describes dryforming the peripheral portion of discs of fllter media, particularly filter media containing non-compressable particulate to suppress edge leakage in filter presses.
In Assignee's U.S Patent No. 4,347,208, a method is described of making a filter cell comprised of two cellulosic fib~r containing filter media having a sealed periphery. The method comprises compressing the periphery of each filter media to form a flange~
The media are then aligned to provide intimate face to face contact between the flanges and a spacer means provided between the media to cause each to dish out-wardly from the other media~ The media and spacer means are then placed into a mold surrounding the flanges. The mold has a means for providing a recom-pression orce to the inner portions of the flanges~
A thermoplastic polymer ls then :injected into the mold to form a seal around the flanges.
Additionally, MICRO-SCREE~ (Registered Trade M~rk) filter cartridges are commercially available from AMF Cuno Division9 Meriden, Connecticut~ comprising-a stainless steel pleated cylindrical screen welded to stainless steel end caps. Shim stock is welded to the screens at both ends to effectively seal off the end so that the end caps can be welded thereon without des-troying the filter screen thereunder~
Still further, DURAPORE TP (Registered Trade-I ~
- 15a ~
mark) filter cartridges have of recent date become commercially available from Millipore Corp., Bedford, ~ .
hi~assachusetts. This cartridge comprises a polyvinylidene fluoride pleated cylindrical membrane fused to polypropylene end caps. Non-porous poiypropylene tape is laminated to the ends of the membrane cylinder prior to pleating. The tape is apparently adhered to the membrane by partial dissolution with n solvent of the tape and/or membr~ne and appli::ation of sufficient pressure to the tape to mechanicallr bind them together. The solvent is then removed by evaporation .
In summary, in most of the prior ar~ uncovered by applicant relating to sealing filters, the fiiter media sealing area is porous, so that when a thermoplastic or sealing surface is applied thereto it flows through the porous media to effect the seal. Other prior art utilizes solvents and solvent adhesives for sealing which can increase extractable contaminants (an undesirable condition when filtering parenteral or biological liquids) and damage, for example, the nylon membrane pore structure. Additionally, none of the printed references uncovered teach or suggest the problems associated with integrity testing a filter element having a hydrophilic microporous fiiter membrane and a filter housing having a hydrophobic thermoplastic sealing surface in thermoplastic sealing relationship with the sealing area of the membrane nor the solution to these problems.
OBJECTS AND SUMMARY OF THE INVENTIO~
It is an object of this invention to provide a filter element which has an effective thermoplastic seal between a hydrophilic nylon membrane and the hydrophobic surface of the filter housing.
It is a further object of this invention to provide an effective seal without the use of adhesives.
It is still a further object of this invention to provide a filter element which is particularly useful for the filtration of aqueous Eluids, in particular bi.olo-gical and parenteral li~uids.
It is yet another object of this invention to provide a filter element comprising a fragile nylon microporous filter membrane in cylindrical form which has reinforced ends permitting the ends to be embedded in a softened thermoplastic end cap without damage to the ends and/or sealing inteyrity of the filter element.
It is still another object of this invention to pro-vide a filter membxane for use in the filter element of this invention.
It is a further object of this invention to provide novel processes for producing the filter elements and filter membranes of this invention.
In accordance with the present invention9 from a broad aspect thereof, there is provided a filter element comprising a hydrophilic organic polymeric microporous membrane having a porous filtration area and sealing edge areas surrounding the filtration area embedded in and in thermoplastic sealing relationship with a hydrophobic poly-,~
- 18 _ meric sealing member o~ a filter housing. The improve-ment resides in that the sealing edge areas have a non-porous tape solventlessly sealed thereto whereby permea-tion of the hydrophobic polymer into the sealing edge area is prevented~
Preferably the filter membrane is in crylindrical form having the non-porous sealing areas at each end of the cylindex and the housing having an end cap at each end of the cylinder.
The filter membrane used in the aforementioned pre-ferred filter element comprises an elongated porous fil-tratlon area longitudinally bordered by the substantially non-porous sealing areas. This filter membrane used may be produced by preparing the filter membrane by known methods and then applying the heat sealable non-porous tape along the longitudinal borders of the filtration areas.
The filter elements of this invention are useful for the filtration of aqueous liquids, particularly parenteral or body liquids.
BRIEF DESCR~PTION OF THE DRAWINGS
Fig. i is a perspective view~ par~ially broken away~ of a preferred filter elernent of this invention.
Fig. 2 is a top view, partially in section; of the filter element of Fig. 1.
Fig. 3 is an enlargecl view in section, tal~en along line 3-3 of Fig. I depicting the sealing surface between the membrane and filte element .
Fig. 4, is a schematic perspective of an apparatus that may be used to prepare a filter membrane by applying a non-porous tape along the longitudinal borders of ~he fii~ration area.
f~5 DETAILED DESCRIPTION OF THE II`IVENTION
Figs. I ~hrough 3 depict a preferred embodiment of th~ fil~er eiement of this invention. The filter element, generally designated (10~ is comprised olF the nylon filter membrane (12) and the filter housing, generally designated (14). The lFiiter membrane is in cylindrical form having the substantially non-porous area of non-porovs tape (16) at each end of the cylinder (18). Referring to Figo 3~
the filter membrcne (i2) is sandwiched between inner ~nd outer layers (20) and (22) of, for example, polypropylene woven netting.
The composite of filter membrane (12) and inner and outer layers (20 & 2~) is pleated transversely to its length and formed into cylinder (18). The cylinder (18) is then sl;pped over a foraminolJs cylindrical core (24) which is provided with apertures (26~ for flow into the open interior of the core (24). The filter membrane (12) and core 124) are then slipped into an outer cylindrical member (28) which is also provicied with apertures (30). The ends of the cylinders are then capped by end caps (32 ~ 34).
The end caps (32&34) qre sealed by thermoplastic fusion to the non-porous areas ~16) of the filter membrane (12). The end caps (32&34~ close off the interior from the exterior of the filter element.
The fiuid can thus flow from the outside to the interior of the filter element, since interior and exterior are completeiy separated by the filter element and sealed of f by the end caps (32&34). The end caps (32~.34) each have a central aperture (36&38) J~
The preformed end caps (32 & 34) are preferably applied ~o the cylindrical membrane (18) by heating an inside face of the thermo-plastlc end cap to a ternperature sufficient to soften and preferably not liquify, a sufficient amovnt of the end cap to form a thermo-plastic seal with the non-porous area at each end of the cylinder. All of the edges of one end of the cylinder are then embedded into the softened end cap. The softened end cap material is then hardened, typically by cooling at ambient conditions, to form a thermoplastic sealing relationship between the sealing curface of the end cap and nonporous al ea thereby forming a leak proof seal.
A method of applying end caps to filter elements is described in the aformentioned U.S. Patent No. 37457~339 to P~lll et al Such a method and apparatus described therein may be modified to apply end caps in this invention. The rnajor differences between the method used in this invention and the P~lll et al method, is that Pall et al liquifies a portion of the end cap which perrneates through the porous sealins surface oF the filter membrane; whereas Applican~s do not require the end cap to b~ liquified and, as clearly indicated herein, the sealing surface of the memberane is non-porousO
End caps of thermoplastic materials are preferred because of the ease of bonding, but it is aiso possible to use thermosetting resins in a thermoplastic, fusable or heat softenable stage of polymerization9 until bonding has been effected, after which the curing of the resin can be completed to produce a structure which can no longer be separated. Such a structure is autoclavable without danger of -destroying the fluid tight seal between the housing portions and the filter membrane and the end cs ps. Thermoplastic resins whose softening point is sufficiently high so that they are not softened under sterlizing autoclaving conditions are preferred for medical use.
Exemplary of the plastic materials which can be used are polyolefins (polyethylene9 polypropylene, polybutylene, polyisobutylene), poly-amides, polyvinylchlorideg polyvinylidene chloride, polyacrylonitrile, polyesters, polycarbonates, polymethacrylate, polyallyl, cmd poly-oxymethylene resins. Polytetrafluorethylene and poiytrifluorochloro~
ethylene can also be used. Polypropylene is preferred for the filtration of biological and parenteral liquids in that it can withs~and autoclavina and sterilizing without discoloration or distortion~ Other type materials, which may be hydrophilic7 are generally unsuitable for such uses due to discoloration, distortion, etc.cuused by tl;e autoclaving ~Jnd sterilization, however they may be used in conjunction with the membrane of this invention for other uses.
The hydrophilic nylon microporous filter membranes used in the filter element of this invention are weii known in the art.
By the use of the term "microporous membrane" as used herein, it is meant a porous single layer, multiple layer or reinforced single or multiple layer membrane, haviny an effective pore size of at least 0.1 microns or larger or an initial bubble point ~IBP) in water of less than 90 psi. A maximum pore size used for such membrane is about 1.2 microns or an IBP of greater than 8 psi. Preferably, but not necess~rily, a single layer membrane is -~3 substantial Iy symmetrical and isotropic. By "symmetrical"9 it is mean- that the pore structure is substantially the same on both sides of the membrane. Asymrnetric membranes, i.e., membranes hqving one si~e formed with a very tight thin layer which is supported by u more porous open structure9 may also be utilized in this invention.
By the use of the term "iso~ropic"9 i~ is meant the membrane has a uniform pore structure throughout the mernbrane.
The microporous nylon membranes used in this invention are hydrophilic. By the use of the term 'Ihydrophilic''~ in describing the membranes, it is meant a membrane which adsorbs or absorbs water.
Generally, such hydrophilicity is produced by a sufficient amount of hydroxide (Ol l-) carboxyl (-COOH), amino (NH2) and/or similar functional groups on the surface of the membrane. Such groups assist in the adsorption and/or absorption of the water onto the membrane, i.e~ 'Iwetting out" of the membrane. Such hydrophilicity is preferable in the filtration of aqueous fluid.
The term "nylon" is intended to embrace film forming poly-amide resins includtng copolymers and terpolymers which inciude the recurring amido grouping.
While, generaliy, the various nylon or polyamide resins are copolymers of diarnine and a dicarboxylic acid, or homopolymers of a lactam and an amino acid, they vary ~..,e'; n crystallinity or solids structure, melting point9 and other physical properties. Preferred nylons for ose in this invention are copolymers of hexamethylene diamine and adipic acid (nylon 66), copolymers of hexamethylene diamine c.nd sebacic acid (nylon 610), and homopo.ymers of poly~-caprolcctam (nylon 6)~ Alternatively, these preferred polycrnide resins have a rctio of methyiene (CH2) to amide (NHCO3 groups within the range about 51 to about 8:1, most preferc.bly ~bout 5:1 tc.
about 7:1. Nylc.n 6 c.nd nylc.n 66 each have a ratio of 6:1, whereas r.ylon 610 has a ratio of 8~1. The nylon polymers are available in a wide variety of grcdes9 which vary apprecicbly with respect to moleculc.r weight, within the range from c.bout IS,000 to about 42,000 (number average molecular weight) and in other characteristics.
The highly preferred species of ~he units cornposing the polrmer chain is polyhexamethylene adipamide, i.e. r.ylon 66, and molecular weights cbove at.out 30,000 c.re preferred. Polymers free of additives are generally preferred, but the additic.n of antioxidants or similar additives may h~ve benefit under some conditions.
The preferred nylon microporous membranes c.re produced from nylon by the me~hod disclosed in U.S. Pc.tent No. 3,8769738 to Marinaccio et al. Another method for producing such membranes is described in the published aforementioned European Patent Application No. 0 005 536 to Pall.
Both of these methods for producing nylon microporous membranes may be described as "quench techniques", i~e. casting or extruding a solution of a film forming polymer ontc a substrate and quenching the cast film.
.~
Broadly, Nlarinclccio et ~I produces microporous membrane by casting or extruding onto a substrate a casting solution of a film forming polymer in a solvent system and quenching in a bath comprised of a nonsolvent system for the polymer.
The aforementioned Pall application describes another similar method which may be used for the conversion of nylon polymer into nylon microporous membrane. Broadly, Pall providcs a process for preparing skinless hydrophilic alcohol insoluble polyamide resin from a polyamide casting solution. The castina solution is formed by inducing nucleation of the solution by the controlled addition of a nonsolvent for the polyamide resin to obtain a visible precipitate olF
polyamide resin particles.
The casting solution, e.g. whether that of h~arinsccio et al or Pall, is then spread on a substrate, i.e. reinforcing web or non-porous substrate, to form a thin film thereon. The cast film is then contacted with the quenching bath comprised of a non-solvent system for the polymer for a time sufficient to form micropores in the film.
The preferred quench bath for forming a nylon microporous mem-brane comprises a nonsolvent system of methanol and water or formic acid arld water.
These preferred nylon membranes, i.e. described in Marinaccio et a! cmd Pall, are characterizecl by an isotropic structure, having a hiah effective surlFace area and a fine internal microstructure of controlled pore dimensions with narrow pore size distribution and adequate pore volume. For example, a representative 0.22 micron r~ted nylon 66 membrane (polyhexarnethylene ~dipamide~ exhibits an Initi~i Bubble Point (IBP~ of ~bout 45 ~o 50 psid, a Foam All Over Point (FAOP) of about 50 to 55psid, provides a flow of from 7û to 80 ml/min of water ~t S psid (47 mm. diameter discs)9 h~s a surface aren (BET, nitrogen adsorption~ of about 13 m2/g ~nd a thickness of ~bout 4.5 ~o 4.75 rr~
In general~ nylon microporous filter membranes are to be cast at thicknesses in the range of from abou~ I mil to about 20 mils, preferably from abou~ I to about 10 mils (wet thickness). After the polymer solution is ~ast and quenched, the membrane is removed from the quench bath and substr~te upon which it was cast and then washed.
The wa~hed membr~ne is then, preferably, laminated to another washed membrane, or optionally l~minated to a web by methods well known in the art, to form ~ reinforced larnin~ted filtration rnem-brane. A unique reinforced membr~ne is described and claimed in C~n~ a nco-pendiny Affle~eff~ Patent Application Serial NoO
417,737 to Barnes et al. Preferably~ lamination is accomplished by passing the plurality of layers jux-taposed upon each other through heated rollers to heat laminate and dry the membranes together. Pr~ferably such drying is under restraint to prevent shrinkage.
Drying of the membranes under restrainst is described in U.S. Defensive Publication ~o. T103,601.
-2~-Generally, any suitable restraining technique may be used while drying, such as winding the membrane tightly about a dry surface, e.g. a drumO Biaxial control is prepare~ an~ tensioning the laminated membrane is con~idered the most preferred.
The final drying and curing temperature for the filtration membrane shoùld be sufficient to dry and cure the membranes.
Preferably this temperature is from cbout 1 200C to 1 400C for minimiz~tion of drying time without embri~tlement or ofher detri-mental e~fects to the membrunes. The totai thickness of the filtration membr~ne is preferably from ~bout 3 mils to about 30 mils and rnost preferclbly t~bout 5 to 1~ rni~s thick (dry ~hickness).
The filtration membrane may then be rolled and stored under ambient conditions for further proc:essiny. After form~tion of the membrane, it may be trec3ted in accordance wi~h Canadian Patent No~ 1,156,410 to Ostr_icher et al to produce a cati.onically charged modified ~icropor~us membrane par-ticularly suitable for the filtration of parenteral or biological liquids; or in accordance with Canadian Patent No. 19166 9 411 to Barnes et al to produce another type cationically charged modified microporous membrane, particularly suitable for the filtration of high purity water~ i~e. at least 18 megohm-cm resis~ivity, required in the manufacture of electronic component.
;28 The preferred form of the nylon filter membrane is an elongated porous filtration areu bordered by substantially non~porcsus sealing qreas of non-porous tape heat sealed to the membrane. This rnembrane is then pleated transversely to its leng~h and formed into cylinder It has been found that the objects of this invention rnay be achieved by application of the tape to only one face of the membraney ~Ithough the tape may be applied to both faces.
In order to produce this preferred form oF the filter membrane, the apparatus of Fig. 4 may be utilized. The apparatus broadly comprises a pair of laminating rollers ~44) through which the nylon microporous membrane (46) passes, supplied from roller (47). The membrane may be produced by any of the rnethods well known in th art, preferably by the aforementioned Marinaccio et al processO Tape supply rollers (48) feed non porous tape (50) across heat shoes (51) and along the lonyitudinal borders just prior to the entrcnce of the membrane (46) into rollers (44). The heat shoes (Sl) are heated to temperatures which are sufficient to soften the solventless adhesive applied to the underside of tape (5û~ and allow bondîng of the tape to the rnembrane (46) upon cooling. Such temperatures depend upon the specific nylon usedl the tape, tape thickness, adhesive, etc. The shoes (51), in s!rder to more accurately control the process and prevent damage to the membrane, may each be individually heated to .~
q~
different temperatures~ Rol lers (44~ apply forces along the longitudinal borders of the membrane to hea~ seal the tape (Sû) to the borders of the membrane ~46). The membrane (46) is then conveyed through pull rollers (52~ to take up roller ~48). An apparatus which has been found to be particularly suited for such procedure is a modif ied Model No. 25 from Larninex7 Inc., Matthews, North Carolina. The apparatus is modified to accept two tape feed rollers (48) rather than a singie roller the full width of the apparatusO
By the use of the term "heat sealable.~.tape" it is meant a tape which can be heat sealed on one surface to a nylon membrane substrate. Preferably, the t~pe is coated with a solventiess meit adhesive which melts at a temperature which is lower than the melt temperature of the tape rnaterial or nylon membrane, and which upon cooling, is capable of bonding the tape to the nylon membrane. The solventless hot melt adhesive should not have such a low melt temperature that it will not adhesively function at typical heat sterilization and autoclave temperatures, e.gO above about 100C.
Such hot melt adhesives are, for example, polyamides and polyolefin type adhesives. A preferred adhesive is polyethylene.
Preferably the tape utilized is a polyester type tape, however3 any polymeric tape may be utiiized which is non-porous, can with-stand the temperatures of use, autoclaving and sealing and does not produce detrimental extractables. Other tapes suitable for such use are polyamides, polyolefins etc. A commercially available and preferred tape having a hot melt adhesive thereon is sold under the -30~ f~
trademark PERMALAM 150 by Laminex Inc. and is a polyester tape having a solventless hot melt adhesive of polyethylene. When using this specifk: tape the heat shoe in contact wi~h the membrune is heated to about 200F ~93C) and the heat shoes in contact with the tape is heated to about 3000F(1490C~.
Scanning Electron M;crographs of the sealing area of the membrane produced by heat sealing the polyester tape to the borders of the membrane indicate thc t the tape completely blocks the surface ~ores of the membrane without significant penetration into the porous membrane~ Thus the tape prevents entry into ~he pores by the softened material of the end cap which is subsequently applied and reinforoes the mernbraner thus decreasing the opportunity for degradation of the membrcme by heat and mechanical stress during production .
The filter element of this invention can thus utilize the preferred hydrophobic: filter housing, e.g polypropylene, is simple and economical to manufacture, and has no solvents employed in manu-facturing to adhere the tape to the membrane or the filter housing to the membrane. The tape also adds to the structural rigidity of the membrane.
For so ccllle~l sterile filtrations, involving biological liquids, the filter element is santiized or s~erilized by autoclaving or hot water flushing prior to use. The filtration element and membrane of this invention are resistant to this type treatment, anci retain their integrity under such conditions. Additionally, the filter element of this invention can withstand nurnerous wetting and drying cycles and high forward flow (Fig. 13 and reverse flow (not shown3 pressures without failure.
Commercially available nylon microporous filter membranes are available from Pall Ccrp., Glencove9 N~Yo ~
under the trademark ULTIPOR N66 and N66 POSIDYNE. Another commercially significant filter membrane made of polyvi-nylidene fluor:ide is available from Millipore Corp~, Bedford, Massachusetts, under the trademark DURAPORE.
This membrane is probably produced by the aforementioned G ndine, II patents~
Additionally, the Assignee of this application is selling cationically charged modified nylon microporous filter membrane under the trademark ZETAPOR. These mem-branes are described and claimed in Canadian Patent ~o.
1,166,411 to Barne~ et al and Canadian Patent ~o. 19156,410 to o~trrlc~~r o~ al. _arnes et al describes the use of charged modified membrane for the filtrat:ion of high purity water (18 meyohm-centimeter resistivity) used in the electronics industry, and Ostre_ her et al describes the use of charged modified membrane for the filtration of parenteral or body liquids. Additionally, it should be noted that these filter membranes are typically rein-forced by various meansO A unique method of reinforcement is described in co-pending Canadian Patent Application Serial No~ 417,737 to Barnes et al.
Al I of the aforementioned membranes, besides being used in sheet form, are used in various type filter elements. Generally9 the fitter element comprises the filter membr(lne and a filter housing with a sealing surface in sealing relationship with a sealing area of the membrane. A well known type filter element is the pleated cartridge type fllter element described, for example, in U.S~ Patent No. 3,457,339 to Pall et al (1969~. Another well known type of filter element is the hermetically sealed intravenous unit described in U~S.
Patent No. 4,113,6~7 to Leason ~1970).
In the critical applic~tions for such filter elements, ;t is imperative that the filter membrane not be damaged during produc-tion and that the filtrate not bypass the filter membrane. Either situation could be catastropic, for example, allowing contaminants to enter the blood stream of a patient. It is therefore necessary that on undamaged seal exist between the sealing area of the membrane and the ~ealing surface oF the filter housing to prevent leakage around the filter membrane. In order to insure such integrity, the filter element is "integrity tested" to insure the integrity of the filter elernent. This is gener~lly accomplished by ~ "bubble point" test of the filter element by methods well known in the art. A particular type of integrity testing device for filter cartridges is commercially available under the name ZETAWATCH, from AMF Cuno Division?
Meriden, Connecticut and described and claimed in the Assignee's IJ.. S. Patent ~o., 4, 384, 474. This integrity tester is self contained and electrically monitors the individual cartridge element's integrity within a multiple cartridge housing. Other methods of such integrity testing are described in "Non Destructive Test For Bacterial Retentive Filters" by Ben Trasen which was published in the September/October 1979 issue of the Journal of Parenteral Drug Association, pages 273-2798. Ai I of the known integrity tests require a thorough wetting of the membrane and sealing surfaces assooiated therewith to provide an aocurate determination of integrity. If the filter membrane is broken, even microscopically, if the membrane is improperly installed, or if the membrane sealing surfaces are not completely wetted, bubbles will appear immediately at the point of the break or leakq Ac~ditionally, any filter element must, particularly when used to filter parenteral or biological liquids, hove a minimum of extractable contaminants introduced into the filtrate~ These contaminants may be harmful toxins when introduced into a patient. Specifically9 any filter elernent must meet the test standards of the industry, e.g.
ASTM D-3861-79.
Still further, fiiter elements used to filter parenteral or bio-logical lîquids should be heut sterilizable and autoclavable, without deterioration or discoloration of the housing or membrane or deterioration of the seal between the membrane and housing. A
preferred housing material is polypropylene which is hydrophobic.
Several methods of sealing filter elements have been employed in the past. These methods include pressure clampin~, heat sealing, ultrasonic welding, adhesive and solvent bonding, and injection molding, These prior art methods fail to provide on occasion the 100% positiv~ seal which is necessc ry to prevent leakages. In partiaular where microporous filter membranes are used in the filter element, there is some danger when usirig these methods that the delicate filter media will be damaged during the seuling process~
Known methods of pressure clamping and other mechanical interlocking systems tend to distort the filter membrurle or actwlly damage the membrane at the clamping edges9 thereby destroying the integrity of the membrane and al lowing contaminants to pass through. Also conditions such as time, qnd hent stress relieving CGn allow the pressure seal to relax. Additionally, this method is particularly complicqted when a pleated filter cartridge is assembled, Known methods of heat s~aling, sonic welding and related thermo-mechanical bonding methods may also damage the filter membrane at the sealing edges, The use of adhesives or solvent bonding has disadvantages in ~hat another material is introduced into the filter element that can lead to extractable contarninants. C)ften the constituents of an adhesive or solven~ system may also damage the filter membrane.
The foregoing methods of sealing the filter housing to a filter membrane are particularly troublesome when a hydrophobic sealing surface is in contact with a hydrophilic sealing area, This is often the case when the filter element is used to filter biological or parenteral liquids where it is very highly desirable to use a polypro-pylene housing, (which is resistant to autoclaving and heat steriliza-tion) and undesirable to use adhesives or solvents for sealing (to avoid high extractables). For such elements, the housing is usual Iy thermoplastically sealed to the membrane, inc:reasing the chances for damage to the sealing areas of the membrane~ Additionally, it appears that the hydrophobic sealing surface of the housing in contact with the porous hydrophilic sealing area of the membrnne increases the chances that the filter element will not pass industry integrity testsO This is probably brought about by ~he incomplete wetting of the membrane/housing interface which gives a reduced bubble point. For example, it has been found that in the therrnoplastic sealing of polypropylene end caps to cylindrical pleated nylon membrane filter cartridges, an unacceptably low percen~age of the cartridges passed the industry int~ogrity test.
More specifically7 the following prior art references are relevant to the invention described and claimed herein.
U.S. Patent hlo. 1,476,392 to Carroll (1923) describes a process of making a composite film by casting a plastic or flowable cellusoic material9 efg. cellulose acetate, on to a moving wheel from a plurality of compartments to thereby produce a plurulity of adjacent lFilm strips. This reference does not teach or suggest the production of a microporous filter membrane.
U.S. Patent NoO 2,663,660, to Layte (1953) describes a method of assembling filter elements, e.g~ a filter cartridge, by producing an elong~ted strip oF filter paper and foiding elongated tapes of adhesive material on the elongated edges. The filter paper is then cut to size and pleated transversely of the length of the strip, and rolled into an annulus form The outer portions of the adhesive tape material is then moistened with a soitable solvent material for the adhesive materiql of which the tapes are formed and thereafter the ends of the annulus are capped by end caps. The end caps <~re preferably heqvy c~rdboard. ~ does not teach or suggest the use of such a method in conjunction with microporous membrane nor is such a method suitable for producing filter cartridges for filtering parenteral or biological liquids wherein extractables must be minimized.
U.S. Patent ~Jo. 3,013,607, to Jackson et al (1961) relates to a method of end capping tubular filter elements of paper~ cardboard, felt, woven tissue, etc. Thermoplastic end caps are subjected to hecr~
in~;luced in the field of an electric inductance coil in contact with the cap, to a point where the cap is softened so that the edges of the filter can be embedded in the cap to the depth required to bind the parts together. A metallic strip is applied to the edges of the filter and external support jacketJ or the edges of the Filter element and external support jacket are coated with an electrically conductive or semiconductive material, so as to reinforce the filter edges, and enhance the heat conductivity through the edges and end cap.
Jackson et al does not utilize an organic polymeric microporous filter mernbrane and thus does not recognize the problems associated with J~
the integrity testing vf filter elements containing such hydrophilic membrane in conjunction with a hydrophobic end cap.
Additionally, the use of a metalic strip on the edges of the Jackson et al filter limits greatly the application to which the end ___ capped filter elements can be put. For example9 under certain conditions, the metallic strip can corrode and/or contaminate the material being filtered or the medium being filtered~ Such a filter element is completely unacceptable for the fiitration of biological and porenteral liquids~ Still further the use of such a metalic strip on the edges of the filter elements increases the cost of making the filter elements, and complicates the procedure used in corrugating such filter elements.
U.S. Patent No. 3,407,252 to Pall et al (1968) desoribes the production of Q corrugated or pleated filter media in annulus form which utili;2es a ribbon or tape of bonding agent such as a heat sealable and curable epoxy resin, to form a leak-proof seal along the longitudinal meeting of the pleated filter media.
U.S. Patent No~ 3,457,339 to Pall et ai (1969) describes a process for applying preformed end caps to filter sheet material, particularly sheet materials formed of fiber and in substantially tubular shape. The process involves heating the inside face of the thermoplastic end cap to fuse a portion of the cap into a liquid. The liauid is of a viscosity which is capable of penetrating through the pores of the filter sheet. The edges of the cylindrical sheet ~re then embedded in the liquified end cap so that the liquidified thermo-r~ ~
plastic material penetrates through the pores of the embeddedportions of the filter sheet material from one surfsce to the other.
The liquid plastic is then hardened and said to form a substantially continuous leak proof matrix of end s:ap material permeating through the pores of the filter material and bonding the filter sheet ~o the end cap in a leak proof seal.
This process for applying end caps to a filter sheet has the advnnta~e in that it does not require the use of adhesives. If this Pall et al process, however, is utilized using end caps of a hydrophobic material, and a hydrophilic membrane, an excessive percentage of the cartridges do not pass the industry integrity test. It is believed that this is due to the cartridge not being completely wetted at the interface between the hydrophilic membrane and the hydrophobic end cap. Hydrophobic type end caps may be utilized if the cartridge is integrity tested in a non-aqueous solvent. This, however, limits the application of the filter element. If a hydrophilic type end cap, e.g.
polyester, is usedS the cartridge will generally have inferior solvent and chemical resistance and inferior resistance to autoclaving and heat resistance.
This Pall et al prccess requires that the sealing areas of the filter sheet material be porous to permit penetration of the liquified thermoplastic material through the pores of the embedded portion of the filter sheet m~terial from one surface to the other. Additionally, during prosecution Pa!l et al states:
"...The instant process is simple enough to enable rapid manufacture of filter elements with a minimum of manu-faeturing steps and without the necessity of employing bonding agents and components ~_ filter and end cap..."
In effec7 PQII et al teaches away from Applicant's invention which utilizes a substantially non-porous sealing area and which utilizes other components than the actual materials of the filter and end cap.
U.5. Patent No, 3,471,019 to Trasen e~ al (1969~ describes a filter unit comprised of a two-part housing provided with sealing portions adapted to be aligned with eaah other and with a peripheral portion of the filter cornpletely surrounding the central portions of the filter.
In assembly of the unit, the sealing portions of of the housings are pressed against the opposite sides of the filter and the sealincJ portion of at least one of the parts of the housing is heated to cause the material thereof to melt and flow through the aligned pores of the peripheral portions of the filt0r and fused to the seal;ng portion of the oth~r part of the housingO A similar type filter and sealing method is described in U.S. Patent No. 3,782,083 to ~ (1974) wherein the plastic rnaterial runs through the pores of the -filter element forming a fluid tight integral seal closing all sides of the element to flvid flow.
U.S. Patent No. 3,487,943 to Buckman ~1967) describes a filter element made of pleated filter paper. One portion of the filter element is rnodified so that in operation of the filter the liquid flow velocity through the modified portion is less than that through the remainder of the element. The mociified portion may be formed by compressing together a series of pleats or by sealing to a group of pleats on one side of the element a sheet of similar or dissimilar filter material. The similar or dissimilar filter material is sealed to the annulus cartridge over the inner or outer periphery of the cartridge and does not form a continuous edge along the top of the filter near the end cap.
U.S. Patent No/ 3~591,010 to Pall et al (1971) describes a corrugated element having a microporous layer deposited on u substrate sheet provided with portions of reduccd porosity at the areas of the base folds of the corrugations.
U.S. Patent No. 3,815,754 to ~ (i974) describes a box filter wherein the elements of the filter housing are bonded to the filter sheet by fused integration of the housing members through the open pores of the filter element, forming a fluid tight seal all aiong the sides of the Pilter sheet. Such a bond is obtained by9 for example, ultrasonic welding, solvent softening or heat fusion.
U.S. Patent No. 3,865,919 and 3,867,294 to Pal I et ! (1975 describe cylindrical elements having an improved side seam seal which can be bonded ~o end caps in a teak type manner.
U.S. Patent No. 3,9$4~625 to Michalski 51976) describes a filter which includes a plastic housing and an intermediate filter screen~
The peripheral portion of the screen is sealed between the two housing halves by flowing a portion of at least one of the housing halves through the screen and bonding that portion to the o-ther housing half.
U.S. patent No. 4,101,423 to Merrill et al (1978) describes a tubular filtration elemen~ whose ends are impregnated with a suitable sealing adhes;ve. When the adhesive materiai cures7 the end portion provides mechanical support for the tube and blocks the pass~ge of the fluid or the particulate and bacterial contaminant. Merr~ll et al requires that the sealing material used to form the ends must be hydrophiiic when cured, stating "If the sealant rendered the filter adjacent to it hydro-phobic, the filter would not be wetted and would not then offer capillary resistance to the bubble point test gas9 therefore the bubble point could not be used as an indication of filter integrity..." (Col. 9, lines 59 64).
"It will be understood that if the outer layer (of the filter) is formed from a lacquer impregnated paper, the resilient members can safely appiy a sealing force sufficient to block the fluid from the end portions so that a hydrophobic sealing material may be used." (Col. 10, lines 6-10).
The filtration element is supported and sealed within a housing by radial seal force, i.e~ the filtration element and housing are not in thermoplastic sealing relationship to each other~
US. Patent No. 471549688 to Pall (1979) describes the use of thermoplastic end cap applied to the open ends of a filtered tube in accordance with the afor~mentioned U.5. patent No. 3,457,39 to Pall e_ ~f~
U~SO Patent No. 4,193,876 to Leeke et al (1980) describes dryforming the peripheral portion of discs of fllter media, particularly filter media containing non-compressable particulate to suppress edge leakage in filter presses.
In Assignee's U.S Patent No. 4,347,208, a method is described of making a filter cell comprised of two cellulosic fib~r containing filter media having a sealed periphery. The method comprises compressing the periphery of each filter media to form a flange~
The media are then aligned to provide intimate face to face contact between the flanges and a spacer means provided between the media to cause each to dish out-wardly from the other media~ The media and spacer means are then placed into a mold surrounding the flanges. The mold has a means for providing a recom-pression orce to the inner portions of the flanges~
A thermoplastic polymer ls then :injected into the mold to form a seal around the flanges.
Additionally, MICRO-SCREE~ (Registered Trade M~rk) filter cartridges are commercially available from AMF Cuno Division9 Meriden, Connecticut~ comprising-a stainless steel pleated cylindrical screen welded to stainless steel end caps. Shim stock is welded to the screens at both ends to effectively seal off the end so that the end caps can be welded thereon without des-troying the filter screen thereunder~
Still further, DURAPORE TP (Registered Trade-I ~
- 15a ~
mark) filter cartridges have of recent date become commercially available from Millipore Corp., Bedford, ~ .
hi~assachusetts. This cartridge comprises a polyvinylidene fluoride pleated cylindrical membrane fused to polypropylene end caps. Non-porous poiypropylene tape is laminated to the ends of the membrane cylinder prior to pleating. The tape is apparently adhered to the membrane by partial dissolution with n solvent of the tape and/or membr~ne and appli::ation of sufficient pressure to the tape to mechanicallr bind them together. The solvent is then removed by evaporation .
In summary, in most of the prior ar~ uncovered by applicant relating to sealing filters, the fiiter media sealing area is porous, so that when a thermoplastic or sealing surface is applied thereto it flows through the porous media to effect the seal. Other prior art utilizes solvents and solvent adhesives for sealing which can increase extractable contaminants (an undesirable condition when filtering parenteral or biological liquids) and damage, for example, the nylon membrane pore structure. Additionally, none of the printed references uncovered teach or suggest the problems associated with integrity testing a filter element having a hydrophilic microporous fiiter membrane and a filter housing having a hydrophobic thermoplastic sealing surface in thermoplastic sealing relationship with the sealing area of the membrane nor the solution to these problems.
OBJECTS AND SUMMARY OF THE INVENTIO~
It is an object of this invention to provide a filter element which has an effective thermoplastic seal between a hydrophilic nylon membrane and the hydrophobic surface of the filter housing.
It is a further object of this invention to provide an effective seal without the use of adhesives.
It is still a further object of this invention to provide a filter element which is particularly useful for the filtration of aqueous Eluids, in particular bi.olo-gical and parenteral li~uids.
It is yet another object of this invention to provide a filter element comprising a fragile nylon microporous filter membrane in cylindrical form which has reinforced ends permitting the ends to be embedded in a softened thermoplastic end cap without damage to the ends and/or sealing inteyrity of the filter element.
It is still another object of this invention to pro-vide a filter membxane for use in the filter element of this invention.
It is a further object of this invention to provide novel processes for producing the filter elements and filter membranes of this invention.
In accordance with the present invention9 from a broad aspect thereof, there is provided a filter element comprising a hydrophilic organic polymeric microporous membrane having a porous filtration area and sealing edge areas surrounding the filtration area embedded in and in thermoplastic sealing relationship with a hydrophobic poly-,~
- 18 _ meric sealing member o~ a filter housing. The improve-ment resides in that the sealing edge areas have a non-porous tape solventlessly sealed thereto whereby permea-tion of the hydrophobic polymer into the sealing edge area is prevented~
Preferably the filter membrane is in crylindrical form having the non-porous sealing areas at each end of the cylindex and the housing having an end cap at each end of the cylinder.
The filter membrane used in the aforementioned pre-ferred filter element comprises an elongated porous fil-tratlon area longitudinally bordered by the substantially non-porous sealing areas. This filter membrane used may be produced by preparing the filter membrane by known methods and then applying the heat sealable non-porous tape along the longitudinal borders of the filtration areas.
The filter elements of this invention are useful for the filtration of aqueous liquids, particularly parenteral or body liquids.
BRIEF DESCR~PTION OF THE DRAWINGS
Fig. i is a perspective view~ par~ially broken away~ of a preferred filter elernent of this invention.
Fig. 2 is a top view, partially in section; of the filter element of Fig. 1.
Fig. 3 is an enlargecl view in section, tal~en along line 3-3 of Fig. I depicting the sealing surface between the membrane and filte element .
Fig. 4, is a schematic perspective of an apparatus that may be used to prepare a filter membrane by applying a non-porous tape along the longitudinal borders of ~he fii~ration area.
f~5 DETAILED DESCRIPTION OF THE II`IVENTION
Figs. I ~hrough 3 depict a preferred embodiment of th~ fil~er eiement of this invention. The filter element, generally designated (10~ is comprised olF the nylon filter membrane (12) and the filter housing, generally designated (14). The lFiiter membrane is in cylindrical form having the substantially non-porous area of non-porovs tape (16) at each end of the cylinder (18). Referring to Figo 3~
the filter membrcne (i2) is sandwiched between inner ~nd outer layers (20) and (22) of, for example, polypropylene woven netting.
The composite of filter membrane (12) and inner and outer layers (20 & 2~) is pleated transversely to its length and formed into cylinder (18). The cylinder (18) is then sl;pped over a foraminolJs cylindrical core (24) which is provided with apertures (26~ for flow into the open interior of the core (24). The filter membrane (12) and core 124) are then slipped into an outer cylindrical member (28) which is also provicied with apertures (30). The ends of the cylinders are then capped by end caps (32 ~ 34).
The end caps (32&34) qre sealed by thermoplastic fusion to the non-porous areas ~16) of the filter membrane (12). The end caps (32&34~ close off the interior from the exterior of the filter element.
The fiuid can thus flow from the outside to the interior of the filter element, since interior and exterior are completeiy separated by the filter element and sealed of f by the end caps (32&34). The end caps (32~.34) each have a central aperture (36&38) J~
The preformed end caps (32 & 34) are preferably applied ~o the cylindrical membrane (18) by heating an inside face of the thermo-plastlc end cap to a ternperature sufficient to soften and preferably not liquify, a sufficient amovnt of the end cap to form a thermo-plastic seal with the non-porous area at each end of the cylinder. All of the edges of one end of the cylinder are then embedded into the softened end cap. The softened end cap material is then hardened, typically by cooling at ambient conditions, to form a thermoplastic sealing relationship between the sealing curface of the end cap and nonporous al ea thereby forming a leak proof seal.
A method of applying end caps to filter elements is described in the aformentioned U.S. Patent No. 37457~339 to P~lll et al Such a method and apparatus described therein may be modified to apply end caps in this invention. The rnajor differences between the method used in this invention and the P~lll et al method, is that Pall et al liquifies a portion of the end cap which perrneates through the porous sealins surface oF the filter membrane; whereas Applican~s do not require the end cap to b~ liquified and, as clearly indicated herein, the sealing surface of the memberane is non-porousO
End caps of thermoplastic materials are preferred because of the ease of bonding, but it is aiso possible to use thermosetting resins in a thermoplastic, fusable or heat softenable stage of polymerization9 until bonding has been effected, after which the curing of the resin can be completed to produce a structure which can no longer be separated. Such a structure is autoclavable without danger of -destroying the fluid tight seal between the housing portions and the filter membrane and the end cs ps. Thermoplastic resins whose softening point is sufficiently high so that they are not softened under sterlizing autoclaving conditions are preferred for medical use.
Exemplary of the plastic materials which can be used are polyolefins (polyethylene9 polypropylene, polybutylene, polyisobutylene), poly-amides, polyvinylchlorideg polyvinylidene chloride, polyacrylonitrile, polyesters, polycarbonates, polymethacrylate, polyallyl, cmd poly-oxymethylene resins. Polytetrafluorethylene and poiytrifluorochloro~
ethylene can also be used. Polypropylene is preferred for the filtration of biological and parenteral liquids in that it can withs~and autoclavina and sterilizing without discoloration or distortion~ Other type materials, which may be hydrophilic7 are generally unsuitable for such uses due to discoloration, distortion, etc.cuused by tl;e autoclaving ~Jnd sterilization, however they may be used in conjunction with the membrane of this invention for other uses.
The hydrophilic nylon microporous filter membranes used in the filter element of this invention are weii known in the art.
By the use of the term "microporous membrane" as used herein, it is meant a porous single layer, multiple layer or reinforced single or multiple layer membrane, haviny an effective pore size of at least 0.1 microns or larger or an initial bubble point ~IBP) in water of less than 90 psi. A maximum pore size used for such membrane is about 1.2 microns or an IBP of greater than 8 psi. Preferably, but not necess~rily, a single layer membrane is -~3 substantial Iy symmetrical and isotropic. By "symmetrical"9 it is mean- that the pore structure is substantially the same on both sides of the membrane. Asymrnetric membranes, i.e., membranes hqving one si~e formed with a very tight thin layer which is supported by u more porous open structure9 may also be utilized in this invention.
By the use of the term "iso~ropic"9 i~ is meant the membrane has a uniform pore structure throughout the mernbrane.
The microporous nylon membranes used in this invention are hydrophilic. By the use of the term 'Ihydrophilic''~ in describing the membranes, it is meant a membrane which adsorbs or absorbs water.
Generally, such hydrophilicity is produced by a sufficient amount of hydroxide (Ol l-) carboxyl (-COOH), amino (NH2) and/or similar functional groups on the surface of the membrane. Such groups assist in the adsorption and/or absorption of the water onto the membrane, i.e~ 'Iwetting out" of the membrane. Such hydrophilicity is preferable in the filtration of aqueous fluid.
The term "nylon" is intended to embrace film forming poly-amide resins includtng copolymers and terpolymers which inciude the recurring amido grouping.
While, generaliy, the various nylon or polyamide resins are copolymers of diarnine and a dicarboxylic acid, or homopolymers of a lactam and an amino acid, they vary ~..,e'; n crystallinity or solids structure, melting point9 and other physical properties. Preferred nylons for ose in this invention are copolymers of hexamethylene diamine and adipic acid (nylon 66), copolymers of hexamethylene diamine c.nd sebacic acid (nylon 610), and homopo.ymers of poly~-caprolcctam (nylon 6)~ Alternatively, these preferred polycrnide resins have a rctio of methyiene (CH2) to amide (NHCO3 groups within the range about 51 to about 8:1, most preferc.bly ~bout 5:1 tc.
about 7:1. Nylc.n 6 c.nd nylc.n 66 each have a ratio of 6:1, whereas r.ylon 610 has a ratio of 8~1. The nylon polymers are available in a wide variety of grcdes9 which vary apprecicbly with respect to moleculc.r weight, within the range from c.bout IS,000 to about 42,000 (number average molecular weight) and in other characteristics.
The highly preferred species of ~he units cornposing the polrmer chain is polyhexamethylene adipamide, i.e. r.ylon 66, and molecular weights cbove at.out 30,000 c.re preferred. Polymers free of additives are generally preferred, but the additic.n of antioxidants or similar additives may h~ve benefit under some conditions.
The preferred nylon microporous membranes c.re produced from nylon by the me~hod disclosed in U.S. Pc.tent No. 3,8769738 to Marinaccio et al. Another method for producing such membranes is described in the published aforementioned European Patent Application No. 0 005 536 to Pall.
Both of these methods for producing nylon microporous membranes may be described as "quench techniques", i~e. casting or extruding a solution of a film forming polymer ontc a substrate and quenching the cast film.
.~
Broadly, Nlarinclccio et ~I produces microporous membrane by casting or extruding onto a substrate a casting solution of a film forming polymer in a solvent system and quenching in a bath comprised of a nonsolvent system for the polymer.
The aforementioned Pall application describes another similar method which may be used for the conversion of nylon polymer into nylon microporous membrane. Broadly, Pall providcs a process for preparing skinless hydrophilic alcohol insoluble polyamide resin from a polyamide casting solution. The castina solution is formed by inducing nucleation of the solution by the controlled addition of a nonsolvent for the polyamide resin to obtain a visible precipitate olF
polyamide resin particles.
The casting solution, e.g. whether that of h~arinsccio et al or Pall, is then spread on a substrate, i.e. reinforcing web or non-porous substrate, to form a thin film thereon. The cast film is then contacted with the quenching bath comprised of a non-solvent system for the polymer for a time sufficient to form micropores in the film.
The preferred quench bath for forming a nylon microporous mem-brane comprises a nonsolvent system of methanol and water or formic acid arld water.
These preferred nylon membranes, i.e. described in Marinaccio et a! cmd Pall, are characterizecl by an isotropic structure, having a hiah effective surlFace area and a fine internal microstructure of controlled pore dimensions with narrow pore size distribution and adequate pore volume. For example, a representative 0.22 micron r~ted nylon 66 membrane (polyhexarnethylene ~dipamide~ exhibits an Initi~i Bubble Point (IBP~ of ~bout 45 ~o 50 psid, a Foam All Over Point (FAOP) of about 50 to 55psid, provides a flow of from 7û to 80 ml/min of water ~t S psid (47 mm. diameter discs)9 h~s a surface aren (BET, nitrogen adsorption~ of about 13 m2/g ~nd a thickness of ~bout 4.5 ~o 4.75 rr~
In general~ nylon microporous filter membranes are to be cast at thicknesses in the range of from abou~ I mil to about 20 mils, preferably from abou~ I to about 10 mils (wet thickness). After the polymer solution is ~ast and quenched, the membrane is removed from the quench bath and substr~te upon which it was cast and then washed.
The wa~hed membr~ne is then, preferably, laminated to another washed membrane, or optionally l~minated to a web by methods well known in the art, to form ~ reinforced larnin~ted filtration rnem-brane. A unique reinforced membr~ne is described and claimed in C~n~ a nco-pendiny Affle~eff~ Patent Application Serial NoO
417,737 to Barnes et al. Preferably~ lamination is accomplished by passing the plurality of layers jux-taposed upon each other through heated rollers to heat laminate and dry the membranes together. Pr~ferably such drying is under restraint to prevent shrinkage.
Drying of the membranes under restrainst is described in U.S. Defensive Publication ~o. T103,601.
-2~-Generally, any suitable restraining technique may be used while drying, such as winding the membrane tightly about a dry surface, e.g. a drumO Biaxial control is prepare~ an~ tensioning the laminated membrane is con~idered the most preferred.
The final drying and curing temperature for the filtration membrane shoùld be sufficient to dry and cure the membranes.
Preferably this temperature is from cbout 1 200C to 1 400C for minimiz~tion of drying time without embri~tlement or ofher detri-mental e~fects to the membrunes. The totai thickness of the filtration membr~ne is preferably from ~bout 3 mils to about 30 mils and rnost preferclbly t~bout 5 to 1~ rni~s thick (dry ~hickness).
The filtration membrane may then be rolled and stored under ambient conditions for further proc:essiny. After form~tion of the membrane, it may be trec3ted in accordance wi~h Canadian Patent No~ 1,156,410 to Ostr_icher et al to produce a cati.onically charged modified ~icropor~us membrane par-ticularly suitable for the filtration of parenteral or biological liquids; or in accordance with Canadian Patent No. 19166 9 411 to Barnes et al to produce another type cationically charged modified microporous membrane, particularly suitable for the filtration of high purity water~ i~e. at least 18 megohm-cm resis~ivity, required in the manufacture of electronic component.
;28 The preferred form of the nylon filter membrane is an elongated porous filtration areu bordered by substantially non~porcsus sealing qreas of non-porous tape heat sealed to the membrane. This rnembrane is then pleated transversely to its leng~h and formed into cylinder It has been found that the objects of this invention rnay be achieved by application of the tape to only one face of the membraney ~Ithough the tape may be applied to both faces.
In order to produce this preferred form oF the filter membrane, the apparatus of Fig. 4 may be utilized. The apparatus broadly comprises a pair of laminating rollers ~44) through which the nylon microporous membrane (46) passes, supplied from roller (47). The membrane may be produced by any of the rnethods well known in th art, preferably by the aforementioned Marinaccio et al processO Tape supply rollers (48) feed non porous tape (50) across heat shoes (51) and along the lonyitudinal borders just prior to the entrcnce of the membrane (46) into rollers (44). The heat shoes (Sl) are heated to temperatures which are sufficient to soften the solventless adhesive applied to the underside of tape (5û~ and allow bondîng of the tape to the rnembrane (46) upon cooling. Such temperatures depend upon the specific nylon usedl the tape, tape thickness, adhesive, etc. The shoes (51), in s!rder to more accurately control the process and prevent damage to the membrane, may each be individually heated to .~
q~
different temperatures~ Rol lers (44~ apply forces along the longitudinal borders of the membrane to hea~ seal the tape (Sû) to the borders of the membrane ~46). The membrane (46) is then conveyed through pull rollers (52~ to take up roller ~48). An apparatus which has been found to be particularly suited for such procedure is a modif ied Model No. 25 from Larninex7 Inc., Matthews, North Carolina. The apparatus is modified to accept two tape feed rollers (48) rather than a singie roller the full width of the apparatusO
By the use of the term "heat sealable.~.tape" it is meant a tape which can be heat sealed on one surface to a nylon membrane substrate. Preferably, the t~pe is coated with a solventiess meit adhesive which melts at a temperature which is lower than the melt temperature of the tape rnaterial or nylon membrane, and which upon cooling, is capable of bonding the tape to the nylon membrane. The solventless hot melt adhesive should not have such a low melt temperature that it will not adhesively function at typical heat sterilization and autoclave temperatures, e.gO above about 100C.
Such hot melt adhesives are, for example, polyamides and polyolefin type adhesives. A preferred adhesive is polyethylene.
Preferably the tape utilized is a polyester type tape, however3 any polymeric tape may be utiiized which is non-porous, can with-stand the temperatures of use, autoclaving and sealing and does not produce detrimental extractables. Other tapes suitable for such use are polyamides, polyolefins etc. A commercially available and preferred tape having a hot melt adhesive thereon is sold under the -30~ f~
trademark PERMALAM 150 by Laminex Inc. and is a polyester tape having a solventless hot melt adhesive of polyethylene. When using this specifk: tape the heat shoe in contact wi~h the membrune is heated to about 200F ~93C) and the heat shoes in contact with the tape is heated to about 3000F(1490C~.
Scanning Electron M;crographs of the sealing area of the membrane produced by heat sealing the polyester tape to the borders of the membrane indicate thc t the tape completely blocks the surface ~ores of the membrane without significant penetration into the porous membrane~ Thus the tape prevents entry into ~he pores by the softened material of the end cap which is subsequently applied and reinforoes the mernbraner thus decreasing the opportunity for degradation of the membrcme by heat and mechanical stress during production .
The filter element of this invention can thus utilize the preferred hydrophobic: filter housing, e.g polypropylene, is simple and economical to manufacture, and has no solvents employed in manu-facturing to adhere the tape to the membrane or the filter housing to the membrane. The tape also adds to the structural rigidity of the membrane.
For so ccllle~l sterile filtrations, involving biological liquids, the filter element is santiized or s~erilized by autoclaving or hot water flushing prior to use. The filtration element and membrane of this invention are resistant to this type treatment, anci retain their integrity under such conditions. Additionally, the filter element of this invention can withstand nurnerous wetting and drying cycles and high forward flow (Fig. 13 and reverse flow (not shown3 pressures without failure.
Claims (13)
1. In a filter element comprising a hydrophilic organic polymeric microporous membrane having a porous filtration area and sealing edge areas surrounding the filtration area embedded in and in thermoplastic sealing relationship with a hydrophobic polymeric sealing member of a filter housing the improvement wherein the sealing edge areas have a non porous tape solventlessly sealed thereto, whereby permeation of the hydrophobic polymer into the sealing edge area is prevented.
2, In a filter element comprising a cylindrical hydrophilic organic polymeric microporous filter membrane having a porous filtration area and sealing edge areas surrounding the filtration area at each end of the cylin-der embedded in and in thermoplastic sealing realtionship with a hydrophobic polymeric end cap member of a filter housing the improvement wherein the sealing edge areas have a non-porous solventlessly tape sealed thereto, whereby permeation of hydrophobic polymer into the seal-ing edge area is prevented.
3. The filter element of claim 2, wherein the membrane is pleated.
4. The filter element of claim 1 or 2, wherein the tape is comprised of polymer film coated with a sol-ventless hot melt adhesive.
5. The filter element of claim 1 or 2, wherein the tape is comprised of a polyester film coated with a heat sealable polyethylene.
6. The filter element of claim 1, wherein the organic polymer is nylon.
7. The filter element of claim 2, wherein the organic polymer is nylon.
8. The filter element of claim 6 or 7, wherein the hydrophobic polymer sealing member is polypropylene.
9. The filter element of claim 1 or 2 9 wherein the organic polymer is polyhexamethylene adipamide.
10. The filter element of claim 1 or 2, wherein the membrane has a pore size of from about .10 to about 1.2 microns.
11. The filter element of claim 1 or 2, wherein the membrane has a pore size of about .2 to about .85 microns.
12. The filter element of claim 1 or 2, further comprising a charge modifying amount of a cationic charge modifying agent bonded to substantially all of the wetted surfaces of the hydrophilic membrane.
13. The filter element of claim 1, wherein the cylinder is formed from a filter membrane comprising an elongated porous filtration area longitudinally bordered by the non-porous tape.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US38337782A | 1982-05-28 | 1982-05-28 | |
| US383,377 | 1982-05-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1184512A true CA1184512A (en) | 1985-03-26 |
Family
ID=23512842
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000408403A Expired CA1184512A (en) | 1982-05-28 | 1982-07-29 | Filter element having microporous filter membrane |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1184512A (en) |
-
1982
- 1982-07-29 CA CA000408403A patent/CA1184512A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4906371A (en) | Filter element having microporous membrane | |
| US4929354A (en) | Filter element having microporous membrane | |
| US4579698A (en) | Process for producing a microporous polymeric filter membrane with adjacent non-porous edge layers and a pleated filter element formed from the membrane | |
| US5114582A (en) | Filter element and spiral-wound membrane cartridge containing same | |
| US6913786B2 (en) | Laminated edge filter structure and method of making | |
| US4184966A (en) | Tubular filter elements with improved side seam seal | |
| US5904846A (en) | Filter cartridge having track etched membranes and methods of making same | |
| EP1044718B1 (en) | Spiral wound type separation membrane element | |
| EP0096306A2 (en) | Filter element having microporous filter membrane | |
| JPS5923846B2 (en) | Tubular filtration element | |
| US6427846B1 (en) | Plastic filtration unit bonded by an L-shaped plastic melt | |
| US6186341B1 (en) | Integrity testable filtration unit using supported hydrophilic porous membranes | |
| JPH0532082B2 (en) | ||
| EP1146944B1 (en) | Perfluorinated thermoplastic filter cartridge | |
| US6280791B1 (en) | Process of making a three-region reinforced microporous filtration membrane | |
| JP3144858B2 (en) | Manufacturing method of precision membrane pleated filter cartridge | |
| US20040118770A1 (en) | Multiple layer membrane and method for fabrication thereof | |
| JP2020512930A (en) | Spiral wound module assembly with integrated pressure monitoring | |
| CA1184512A (en) | Filter element having microporous filter membrane | |
| CA1200766A (en) | Filter element having microporous filter membrane | |
| JP2002509014A (en) | Separation system, membrane module, filter element and method of manufacturing filter element | |
| JPH05111622A (en) | Production of filter element | |
| JPS6359305A (en) | Pleat-shaped filter component made of fluorine resin | |
| JPS59501251A (en) | Filter element with microporous filter membrane | |
| JP2995596B2 (en) | Hydrophilic cartridge filter and method for producing the same |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEC | Expiry (correction) | ||
| MKEX | Expiry |