FR2478483A1 - Discardable filter cartridge - has stack of units with membranes sealed to ribbed supports - Google Patents

Abstract

A discardable membrane filter cartridge, esp. for sterilising pharmaceutical and intravenous fluids, consists of a stack of units with a central axial flow cavity. Each unit has porous filter membranes sealed to the upper and lower surfaces of a thin plastic support. Each surface of the support has internal and external peripheral flanges with a series of intermediate ribs, all in the same plane. Between the central cavity and the inner flange is a further flange for connection to the next unit. The support may be a single moulding, or two sections welded together. The connecting flange dimensions leave a gap for external liq. flow. The stack of units can be held in a casing with upper and lower caps attached to a central spacer. For use with cast or fibrous fine filters with pore size down to less than one micron. The number of different materials is reduced, filter membranes do not need folding, and the units are well adapted for automatic leak testing.

Description

 The invention relates to filtration and more particularly to cartridges with filter membranes, to the components of these cartridges and to their manufacturing processes.

 Filter membranes made of various polymers are well known and are generally thin porous structures, the porosity of which is between approximately 50 and 80% by volume. They are relatively fragile and are generally used in conjunction with different types of mechanical supports or reinforcements. The flow rates of liquids per unit area through these membranes are a function of the size of the pores, the flow rates decreasing with the decrease in the size of the pores. To obtain high flow rates through filters with fine pores, for example less than about 1 vm, filters with relatively large areas are required. These areas have so far been achieved using large individual filters or using several smaller individual filters, mounted in parallel. Leaks or faults capable of leaving must not be allowed to occur. pass small particles or organisms through these membranes and their support elements in delicate applications such as sterilization.

 Several small filters have so far been assembled by hand with support plates and associated devices to produce flows in parallel, then have been tested and, if necessary, sterilized, frequently at the place of use, with cost prices and considerable difficulties. The operations must be repeated if the assembly carried out by hand does not pass the necessary tests. Mechanical parts are generally cleaned and reused, only the filters being replaced. An assembly has also already been produced using plastic elements which are discarded after use and mechanically fixed to moving parts relative to each other.

 The individual large-area filter membranes have been supported flat or in cylinders or have been pleated to be placed in compact boxes. The supports of the flat membranes are large for a given surface area of the filters, they do not generally throw out after use and they also require to be dismantled, cleaned, reassembled and subjected to new tests each time the filter is changed. fragile membranes creates concentrations of force at the location of the folds, allows fragile membranes to flex in service, normally requires the interposition of grids allowing flow and placed on one of the sides or on both sides upstream and downstream, requires filler material and adhesives to seal the ends and lap joints and requires a considerable number of manual operations. To take into account possible failures at folds, seals or ends, a final flat independent filter is sometimes fitted in series with the pleated cartridges to provide an additional guarantee during delicate applications, for example the sterilization of pharmaceutical products or intravenous fluids. moreover, the use of several different materials in pleating type cartridges increases the sources of products to be extracted in the filtrate.

 The subject of the invention is essentially new cartridges with filtering membranes, new components intended for these cartridges and a new method of bonding and sealingly fixing a filtering membrane to a support. The filter cartridges according to the invention are thrown away after use, avoid the folding of the membranes, can easily be produced inexpensively using automatic machines, the tests for checking their suitability being easy to perform, the number of their parts being minimal and their manufacture according to different dimensions using common parts which can be easily carried out. Following an essential feature of the invention, a filtration group is intended to be linked to other similar groups in a self-disposing stack after use, this group comprising a central opening intended to allow an axial flow of liquid to pass and comprising a thin support at the upper surface and at the lower surface of which porous membranes are fixed, each of these surfaces comprising bearing surfaces at the inner and outer circumference as well as interposed ribs defining a substantially common plane, l with membrane being fixed in a sealed and permanent manner on said bearing surfaces and said ribs in said plane, each support surface lying between the inner bearing surface and the central opening comprising assembly members intended to be linked to members complementary assembly of the superimposed filtration group, the assembly members of at least one surface extending beyond the surface of the neighboring membrane, said support comprising internal passages intended for the liquid and located between said membranes and said central opening, this opening and these passages representing the only channels by which the liquid can circulate through the group. The support is preferably made of plastic and the membranes are mechanically bonded to this support by making it penetrate the solvated material of the support into the pores of the membrane, in a manner which will be described later.

 The support structure can be made in any suitable manner in one or more pieces. When the support is in one piece, the interior bearing surface and the assembly members of a support surface are preferably offset with respect to the interior bearing surface and the assembly members of the other surface with respect to to the axis of the central opening, the interior passages of the support ending inside the offset between these elements. When the support is in two or more pieces, these are preferably welded to each other so as to form a unitary structure of a single material and one of the pieces has the two outer bearing surfaces which are joined so waterproof to prevent leaks.

 Next: an advantageous embodiment of the filter cartridge according to the invention and disposing after use, it comprises a stack of filtration groups as specified above and linked to each other so as to be secured together at the location of the assembly members by constituting a central axial flow channel, this channel being sealed at one end to prevent the flow of liquid and comprising a connecting member connected to the other end and intended to establish the connection with a liquid conduit, the assembly members linked to each other placing the neighboring membranes at a distance from each other in order to delimit between them flow channels situated outside the groups. preferably have supports of the same plastic and are bonded to each other by heat or by welding with a solvent at the location of their assembly members. The cartridges can be used in conventional boxes comprising an inlet and an outlet intended for liquids and communicating, on the one hand, with the periphery and, on the other hand, with the central opening of the cartridge. The normal liquid flow path through the cartridge therefore starts from the periphery, passes between the membranes of the neighboring filtration groups, through the membranes and through the internal passages and ends at the central opening.

 Reverse flow at slightly reduced pressures is also possible because the membranes are bonded to the interposed support ribs as well as to the bearing surfaces of the edges and are well supported so as to resist back pressure.

 As an alternative embodiment, the filter cartridges can be mounted and be sealed in their own casings which can be discarded after use and which can include covers placed at the ends as well as a central spacer, the covers comprising the liquid inlet and outlet. the cartridge. The covers may be identical and the number of filtration groups placed in the cartridge may vary and it is sufficient for this purpose to modify the height of the central spacer. The covers placed at the ends and the spacer of the housing are preferably made of the same plastic as the supports of the filtration units and are also connected and secured in a sealed manner by welding. Thus, only two materials are used, namely the plastic of the supports and of the housing and the material of the membrane. No adhesive, no filler, no O-ring or the like is required, which minimizes the infiltration of the products. to be extracted and the mechanical forces due to thermal expansion and contraction.

 The invention also relates to a new and advantageous method of sealingly fixing a microporous filter to the edges and the interposed ribs or the like of a support. The process is reliable and reproducible, it can be easily implemented using automatic machines, it minimizes the damage caused to the filter and the occlusions of its filtration volume. This process consists in using a plastic support different from the material of the filters, to cause the absorption in the pores of the filter of a predetermined quantity of a solvent for the material of the support, which is not a solvent for the filter, to bring the support into contact with the filter humidified, to maintain contact for a sufficiently long time to cause the solvation of the material located on the surface of the support and to cause part of it to be absorbed by the pores of the filter, then to remove the solvent, preferably by drying . The pores of the filter are preferably filled with solvent without any noticeable excess on the surface. The filter can advantageously be saturated with an excess of solvent, then be subjected to a rotational movement in order to remove the excess of this solvent. The contact pressure required between the support and the filter is minimal, which avoids mechanical damage that may be caused to the membrane.

 The structure of the resulting assembly formed of the filter and the support is different from, and superior to the structures obtained by the techniques of the prior art, according to which the support receives heat, a solvent or adhesive. In accordance with the process of the invention, the plastic material of the support only penetrates into or impregnates the pores of the membrane lying above the ribs or the like without causing a noticeable lateral spreading which can cause occlusion of the surface of the filter. The impregnating plastic material does not in principle pass through the membrane and normally does not, so that parts of the membrane remain above the ribs, at a distance from the ribs, so as to form oblique channels which pass through it The tests having been carried out show for example that for a given fluid, pressure and support structure, the reduction in the flow rate caused by the filter produced in accordance with the invention is only about 15%. The ribs preferably have a curved surface to minimize contact.

The bonding method according to the invention is applicable to any support structure having a fineness as specified for example in state patents
United States of America NO 3,854,907, NO 3,730,353 and NO 3,471,019.

Until now, supports with fine ribs or undulations have not been linked to filters for occlusion, adjustment or the like. The connection made by the process described can be implemented easily and can provide significant protection against pressure excursions which risk causing backflow and in certain cases it eliminates the need for check valves or valves. The technique according to the invention can also be advantageously used for membranes laminated with fibrous plastic supports such as woven fabrics or non-woven felts and reinforcing filaments linked by passing through a die.

The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting examples and in which
Figure 1 is a plan view of a filter cartridge according to the invention
Figure 2 is an elevation
7a Figure 3 is an axial section
Figure 4 is a partial plan view on an enlarged scale of a part of a two-piece filter support according to the invention
Figure 5 is a partial plan view similar to that of Figure 4 and shows the other part of the support in two parts w
Figure 6 is a cross section along line 6-6 of Figure 4;
Figure 7 is a cross section along line 7-7 of Figure 5 ;;
Figure 8 is a cross section along line 8-8 of Figure 4;
Figure 9 is a cross section along line 9-9 of Figure 5;
Figure 10 is a section similar to those of Figures 6 and 7 and shows the two parts assembled as well as superimposed filtration groups which are illustrated in broken lines;
Figure 11 is a section similar to those of Figures 8 and 9 and shows the two parts of the support assembled
Figure 12 is a partial plan view on a reduced scale and shows the rear side of the support piece shown in Figure 4;
Figure 13 is a partial plan view on a reduced scale and shows the rear side of the part illustrated in Figure 5
Figure 14 is an axial section similar to that of Figure 3 and shows a cartridge according to the invention and mounted in a conventional reusable support t
Figure 15 is a partial plan view showing an alternative embodiment of the filter holder which is in one piece;
Figure 16 is a partial plan view showing the rear side of the support shown in Figure 15; and
FIG. 17 is a cross section along line 17-17 of FIG. 15.

 Figures 1 to 3 show an autonomous filter cartridge having, for example, 500 cm2 of filtering surface. The cartridge comprises a housing 20 comprising at the upper end a cover 22, at the lower end a cover 24 and, between these covers, a spacer sleeve 26. The covers 22 and 24 and the spacer 26 are preferably in the same plastic and are welded to each other by heat or by a solvent at 28 and 30, the covers 22 and 24 having on the edge a tongue and the spacer 26 having complementary grooves. The cover 22 comprises a connector 32 intended for mounting an outlet pipe or tube or the like which is welded to this cover along a line 34. The cover comprises under the connector 32 a concentric ring 36 intended to be connected to a filtration unit 38 in a manner which will be described in more detail below. The ring 36 and the connector 32 provide communication with a stack of groups or filtration discs 38 housed in the housing 20 and an outlet duct (not shown).

 A vent 40 of any suitable type is mounted on the cover 32 to allow the air from the shoemaker to be removed during commissioning. This vent may consist, for example, of a valve or valve opening by hand to evacuate the air and then having to be closed. The vent 40 is provided with a removable cap 41.

 The cover 24 is similar to the cover 22 and has an inlet connector 42 linked along a weld line 44. The cover 24 may also optionally include a vent 40 and moreover it is identical to the cover 22. A housing comprising a vent at each end allows the cartridge to be used by putting one or the other of the ends at the top. The cover 24 includes a ring 46 similar to the ring 36. However, the ring 46 is not linked to the stack of filtration discs 38 placed in the housing. On the contrary, the lower disk 38 is tightly fixed to a cap 48 placed at the end of the stack and comprising external ribs or the like 49 which rest on the internal periphery of the ring 46 in order to avoid cutting traffic at admission.

 When the cartridge is used, a liquid to be filtered enters through the inlet 42, passes around the outer periphery of the stack of filtration groups 38, enters the spaces separating the groups, passes through the filters and heads for in a central channel located inside the stack, in a manner which will be described later, and from there, the filtrate exits through the connector 32 and enters the outlet conduit.

 Figures 4 to 13 show an embodiment of the filtration unit 38 which is in two parts 50 and 52 fitting one into the other. The part 50 comprises a flat disc 54 (FIG. 13) which supports projecting concentric ribs 56 and comprises radial notches forming channels 58 located under the ribs 56.

The part 50 also includes a solid rim 60 integral with the base 54 and comprising upper and lower bearing surfaces 62 and 64. The part 50 further comprises a circumferential inner bearing surface 66. The inner bearing surface 66 and the surface of external bearing 64 define with the surface of the intermediate ribs 56 a common plane to which a filter membrane 68 is linked in a manner which will be described later.

 The two parts 50 and 52 have a central opening 70, 72, respectively, which is intended for the axial flow of liquid. The part 50 comprises a circumferential assembly member 74 which protrudes between the edge of the opening 70 and the internal circumferential surface and which is intended to be permanently connected to a complementary member for connection of the superposed filtration group 38 so that the two groups are locked with each other and so that their neighboring filters 68 are distant from each other so that the liquid can circulate between them. The assembly member 74 may have a surface having any desired shape, but advantageously comprises on this surface a projecting tongue as shown.

 The part 52 fits, as shown in FIGS. 10 and 11, into the part 50 to which it is permanently attached in order to constitute a support in one piece for filters 68 linked to its upper surface and to its lower surface. The part 52 comprises a central flat part 80 (FIG. 12) similar to the part 54 of the part 50 and it also has projecting ribs 82 and radial channels 84 over which the ribs 82 pass. The part 52 has a outer rim 76 which fits into the rim 60 of the part 50, inside the bearing surface 62. The part 52 has an inner circumferential bearing surface 78 which, after assembly with the part 50 in the manner shown in FIGS. 10 and 11, delimits a common plane with the bearing surface 62 and the surface of the ribs 82. The part 52 comprises, between the opening 72 and the bearing surface 78, a projecting assembly member 86 which comprises as shown a groove which is complementary to the tongue of the assembly member 74 of the part 50.

 When the parts 50 and 52 are assembled and bonded to each other, preferably by heat or solvent welding, they form a support 88 in one piece for filter membranes 68. The membranes 68, of which the one is located on the upper surface and the other on the lower surface of the support 88, are permanently linked to the bearing surfaces 66 and 64 and to the top of the ribs 56 as well as to the bearing surfaces 62 and 78 and to the rib surface 82.

 As shown in Figure 10, the completed filtration unit 88 includes a central annular portion which surrounds the opening 70-72 and which consists of the assembly member 74 on one side and the assembly member 86 on the other side, these two bodies being complementary to each other. As shown in FIG. 10 in broken lines, similar filtration groups 38 are superimposed and linked by their assembly members, preferably by solvent welding. The filtration groups 38 consisting of a support CCJmpl @ t 88 and two filter membranes 68 can be linked to form stacks of any desired height and fixed inside the housing 20 as shown in FIG. 3. it is possible to vary the dimensions of the cartridge by modifying the number groups 38 which it comprises and by modifying the height of the spacer 26.

 The channels 58 and 84 of the parts 50 and 52, respectively, lead to orifices 90 and 92 opening onto the central openings 70 and 72 of the parts 50 and 52. When the part 52 is placed in the part 50, the channels 58 and 84 can be brought into alignment with the consequence that the orifices 90 and 92 are also in alignment, but this alignment is not essential.

The space between the ribs 56- and 82 constitutes curved channels through which the liquid passing through the filters 68 can flow towards the radial channels 58 and 84 to then penetrate through the orifices 80 and 82 in the central opening 70- 72 of the f ration element 38. These spaces located between the ribs and the radial canas constitute internal passages allowing the liquid passing through the filtering membranes 68 to flow towards the central opening 70-72, the filtrate thus obtained s 'flowing axially towards the fitting 32 and into the outlet duct.

 All the parts of the cartridge of Figures 1 to 3 other than the filter membranes 68 are preferably made of the same plastic! for example polycarbonate, and are welded to each other by heat or by a solvent so as to constitute a unitary rigid structure. The cartridge obtained can be sterilized and implemented in an in-line filtration circuit, then be discarded and easily replaced with a minimum of downtime, work and inconvenience. Although it is possible to use an adhesive or other permanently bonding substance to assemble the parts of the cartridge, welding as described is more advantageous and can be carried out by automated operations. A cartridge thus assembled does not is that in two materials, namely the plastic material constituting the housing and the supports of the filters and the material in which the membrane is made. This minimum number of materials not only reduces the cost price and the operations involved, but also minimizes the quantity of extractable materials.

 The membranes 68 are microporous films produced by casting or are made of bonded or felt-shaped fibers whose pores are preferably less than 25 μm in size. These membranes and their manufacturing process using different polymers are well known. The membranes which are supported flat, without wrinkles and which are linked to the support ribs between their peripheral edges are well fixed by being prevented from being displaced by the circulation which can take place in one direction or the other and are not subjected to the forces which can be produced by bending or by bending during use.

 The membranes 68 can be linked to the supports 88 in any desired manner. They are however advantageously linked in accordance with the invention by the following method. A predetermined amount of a solvent for the plastic material of the support 88, which is not a solvent for the membrane, is absorbed by the pores of the membrane.

The membrane is slightly tightened against the bearing surfaces and the surface of the ribs of the support. The solvent causes the plastic, which is preferably thermo-plastic, to solvate the support and causes it to penetrate by impregnation into the pores of the membrane situated above the bearing surfaces and the ribs, but practically not in the flow passages located between the ribs, the fixing thus obtained is narrow and causing a minimum of occlusion of the volume of the filter. A predetermined amount of solvent can be initially dosed and deposited, then it spreads on the membrane by capillary action. However, it has been observed that it is preferable to impose a rapid rotational movement on the membrane, to deposit an excess of solvent on it and thus to remove the excess by centrifugal force. This process practically causes saturation of the membrane pores with no excess and it can be easily automated. After a slight contact sufficient to allow the plastic to penetrate into the pores of the membrane, this is dried. It has been found that this is not a difficult operation and it has been observed that normal air drying which follows a rest period of 60 seconds or less is suitable. When the materials are carefully chosen, a rest time of 3 seconds is sufficient. Any suitable solvent for the plastic material constituting the support 88 can be used.

 Careful tests have shown that the process described above causes the effective and tight connection of the membrane by preventing the flow of liquid, except through the membrane. They have also shown that the surface area of the membrane which is occluded and closed to the flow of the liquid is substantially less than when other bonding techniques are used, for example when the solvent is deposited directly on the plastic of the support or when the connection is made with heat and pressure. It seems that the resulting connection is at least partially mechanical, cross sections made in these membranes showing extensions of the support material which fill the pores adjacent to the latter.

 According to a very advantageous embodiment, the support 88 and the housing 20 are made of polycarbonate and the membranes 68 are produced by casting polyvinylidene fluoride. The membrane is welded by a solvent to its support, the filtration units are welded to each other by their assembly members and the parts of the housing are welded to each other by a solvent, the solvent used being trichlorethylene. The connections to the covers 22 and 24 are previously welded by ultrasound with heat generation. Other suitable materials can also be used.

 FIG. 14 represents an alternative embodiment of a filtration cartridge composed of stacked discs 38 arranged in a reusable support 106 of conventional design. The cartridge consists of several filtration groups 38 linked to each other by their assembly members so as to form a central axial flow channel which is closed at the lower end by a cap 100 fixed by connection. The upper end of the central flow channel has a connector 102 consisting of a cylinder provided with an O-ring 104. The support 106 comprises a cover 112 having an inlet 108 through which the liquid is directed to the periphery of the groups 38 and an outlet 110, the support further comprising a base 114.As shown in FIG. 14, the base 114 and the cover 112 have screw threads 116 which are engaged and allow tighten an O-ring seal 118. Any other suitable waterproof attachment can be used. For sterilization of fluids, a conventional stainless steel case with a gasket and an external clamping element is preferable. The cover 112 has a recess below the inlet 110 to accommodate the connector 102, the surface of the recess cooperating with the O-ring 104 to ensure the seal.

 Figures 15 to 17 show an alternative embodiment of a support 150 in one piece of a filtration unit according to the invention. In this embodiment, the disc comprises at the outer circumference a flange 120 having upper and lower surfaces with a bearing surface 122 and 124. Inner circumferential bearing surfaces 126 and 128 delimit planes with the outer circumferential bearing surfaces 122 and 124 to which the filter membranes are linked in the manner described above. Ribs 130 are located between the bearing surfaces 122 and 126. Likewise, ribs 132 are located between the inner and outer bearing surfaces 124 and 128 on the opposite side of the support. The ribs 130 and 132 are placed at regular distances on the support surface and intersect, preferably at an angle of 900, so as to form a grid structure through which liquids can flow.

 The inner circumferential bearing surface 128 is offset radially with respect to the bearing surface 126 and is located inside the latter, the ribs 132 and 132 'penetrating in the interval separating these surfaces so as to constitute a structural support. and passages through which the liquid can enter the central opening 134. Assembly members 136 and 138 are located between the central opening 134 on the one hand, and the bearing surfaces 126 and 128 on the other hand. As shown in the figures, the assembly members 136 and 138 have substantially planar outer surfaces. which extend beyond the surface of the membranes linked to the support in their vicinity. The support discs can be stacked alternately with their sides inverted, the assembly members 136 of the neighboring discs being in contact so as to be linked to remains and assembly member 138 of a disc being linked to the assembly member 138 of another superimposed disc. In an alternative embodiment, it is possible to produce two sets of support discs which are identical, except that 'a disc comprises an assembly member which comprises a tongue and the other disc comprises an assembly member which comprises a complementary groove. The supports according to the alternative embodiment shown in FIGS. 15 to 17 can be stacked and linked so as to form a central flow channel and they can be housed in their own bolt caster which is thrown away after use or in a conventional reusable boot case and such as previously described.

 Although the members for assembling the surfaces of the groups 38 and the supports 150 may advantageously be projecting on each surface of the disc above the neighboring membrane in order to provide a space between the neighboring discs, one may have all or the most of the height desired to produce corresponding spacing.

 Although the filter supports as described are circular to facilitate and clarify the drawings and that they have circumferential interior and exterior bearing surfaces, the supports may have any other suitable shape, for example be oval or polygonal and it is of course that the supports having these forms come ~ in the field of the invention. Furthermore, although the central flow opening and the cartridge channel are preferably circular and arranged in the axis, the opening may be off-center and may have other shapes which may be desirable. term ~ ribs "as used in this specification is intended to designate any fine support structure, continuous or discontinuous, suitable for providing mechanical support to the filter membrane while providing flow paths for liquids passing through In addition, discontinuous or continuous ribs as shown, projecting corrugations, aligned or randomly arranged, and which may have any desired cross-section can, for example, also be used.

 The principle of the invention is intended in particular for microporous and ultrafiltration membranes, fibrous or made by casting, having pores whose dimensions are less than about 25 µm and in particular less than about 1 Vm. The device of the invention can be used as a preliminary filter or as a final filter for blood, bacteria or the like. It is particularly suitable for sterilizing liquids. When used as a final filter, pre-filtering materials can be placed in the cartridges to protect the final filtration membranes 68. These coarser filters can be superimposed on the membranes 68 or a cylinder of pre-filtering material can be linked at the periphery of the stacked groups 38, as shown in 160 in broken lines in FIG. 3.

Microporous filter membranes produced by casting are the most advantageous.

 As described above, the housing in three integral parts represented by Figures 2 and 3 facilitates the variation of the dimensions of the cartridge.

The spacer 26 can however optionally be omitted and covers having suitable dimensions can have complementary edges and be directly linked to each other.

 It goes without saying that the invention has only been described by way of example and that various modifications can be made to it without departing from its field.

Claims (3)

 1. Method for connecting a filter to a plastic support, characterized in that it essentially consists in causing the absorption of a determined quantity of solvent by the pores of the filter (68), this solvent being a solvent for the support (88), but not for the filter, bringing the dry support (88) into contact with the filter thus humidified (68), maintaining contact until said solvent causes the support (88) to solvate ) and that part of the latter infiltrates into said pores, then eliminating the solvent.  2. Method according to claim 1, characterized in that the pores of the filter (68) are substantially filled with solvent without excess.  3. Method according to claim 1, characterized in that an excess of liquid is introduced into the filter (68) in order to fill the pores and the excess is eliminated by rotating the membrane (68) of the filter.