FR2468397A1 - FILTER CARTRIDGE, METHOD FOR PRODUCING THE SAME, AND COMPONENTS THEREOF - Google Patents

Abstract

Filtration groups comprising filter membranes and intended to be stacked and linked to each other so as to form monobloc cartridges which can be thrown away after use and which can optionally be housed in a casing which can be thrown away after use. The groups consist of a thin plastic support 88 on the two surfaces of which flat membranes 68 are permanently bonded. The carrier has a central opening, a sealing rim, and on each side, inner and outer circumferential bearing surfaces between which are ribs, the membranes being bonded and sealed to the bearing surfaces and the ribs. Each surface of the support which is close to the central opening comprises circumferential assembly and bracing members making it possible to link the groups placed at a distance from each other and forming a stack. Application in particular to filters for sterilizing liquids.

Description

The invention relates to filtration and more particularly to

  filter membrane cartridges, the components of these cartridges and their manufacturing processes. The filter membranes of various polymers are well known and are generally thin porous structures, whose porosity is between about 50 and% by volume. They are relatively fragile and are generally used together with different types of supports or mechanical reinforcements. Fluid flow rates per unit area across these membranes are a function of pore size, with flow rates decreasing with decreasing pore size. To obtain high flow rates through filters having fine pores, for example less than about 1 μm, filters with relatively large areas are required. These areas have been achieved so far using large individual filters or using several smaller individual filters, mounted in parallel. Leaks or deficiencies should not occur that allow small particles or organisms to pass through these membranes and their supporting elements in delicate applications.

such as sterilization.

  Several small filters have so far been assembled by hand with support plates and associated apparatuses to produce parallel flows, and have been subjected to testing and, if necessary, sterilized, frequently at the point of use, with cost prices and considerable difficulties. It is necessary to restart the operations if the assembly done by hand does not pass the necessary tests. The mechanical parts are generally cleaned and reused, only the filters being replaced. An assembly has also already been made using plastic elements that are discarded after use and mechanically fixed to moving parts relative to each other.

to others.

  Individual large-area filter membranes were supported flat or in rolls or were pleated to fit into small housings. The flat membrane supports are large for a given area of the filters, generally do not discharge after use, and they also require disassembly, cleaning, reassembly and retesting with each filter change. Pleating of fragile membranes creates stress concentrations at the location of the folds, allows the fragile membranes to flex in use, normally requires the interposition of flow-in grilles and placed on one or both sides. upstream and downstream sides, requires filler and adhesives to seal the ends and lap joints and requires a considerable number of hand-made operations. To take into account possible failures of folds, joints or ends, a flat final independent filter is sometimes connected in series with

  folded cartridges to provide an additional guarantee

  in delicate applications, such as sterilization of pharmaceuticals or intravenous fluids. In addition, the use of several different materials in fold-type cartridges increases the sources of products to be extracted into the filtrate. The subject of the invention is essentially new cartridges with membrane filters, new components for these cartridges and a novel process for bonding and sealing a filter membrane to a support. The filter cartridges according to the invention are discarded after use, avoid the folding of the membranes, can easily be manufactured cheaply using automatic machines, the tests for checking their suitability are easy to perform, the number of their parts being minimal and their manufacture according to different dimensions using common parts that can be easily performed. According to an essential feature of the invention, a filtration unit is intended to be bonded to other similar groups in a disposable stack, this group comprising a central opening for passing an axial flow of liquid and comprising a thin support at the top and bottom surfaces. of which porous membranes are affixed, each of these surfaces having bearing surfaces at the inner circumference and the outer circumference as well as interposed ribs delimiting a substantially common plane, the membrane being permanently and permanently attached to said bearing surfaces and said ribs in said plane, each support surface between the inner bearing surface and the central opening including connecting members for connection to complementary assembly members of the superimposed filtration unit, assembling at least one surface extending beyond the surface of the adjacent membrane, said support having internal passages for the liquid and located between said membranes and said central opening, this opening and these passages representing the unique pathways through which the liquid can flow through the group. The support is preferably made of plastic and the membranes are linked

  mechanically to this support by penetrating impregnated

  of the solvated material of the support in the pores of the

  membrane, in a manner to be described later.

  The support structure can be made in any suitable manner in one or more rooms. When the support is in one piece, the inner bearing surface and the connecting members of a support surface are preferably offset relative to the inner bearing surface and the connecting members of the other surface relative to to the axis of the central opening, the inner passages of the support leading to the interior of 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 parts comprises the two outer bearing surfaces which are joined together watertight

to avoid leaks.

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  According to an advantageous embodiment of the filter cartridge according to the invention and disposable after use, it comprises a stack of filtration groups as specified above and connected to each other so as to be secured in a sealed manner to the location of the connecting members by constituting a central axial flow channel, this channel being sealed at one end to prevent the flow of the liquid and having a connecting member connected to the other end and intended for establishing the connection with a liquid conduit, the connecting members connected to each other remotely spacing neighboring membranes to define between them flow channels located outside the groups. These groups preferably comprise supports made of the same plastic material and are bonded to each other by heat or by welding with a solvent at the location of their assembly members. The cartridges may be used in conventional casings comprising an inlet and an outlet 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 way of flow of liquids through the cartridge thus leaves the periphery, passes between the membranes of neighboring filtration groups, through the membranes and by the

  internal passages and leads to the central opening.

  Reverse flow under slightly reduced pressures is also possible because the membranes are bonded to the interposed support ribs and to the edge bearing surfaces and are well supported to

resist the counterpressure.

  Alternatively, the filter cartridges may be mounted and sealed in their own casings disposable after use and may include end covers and a center spacer, the covers including the liquid inlet and the outlet of the container. the cartridge. The covers may be identical and the number of filter groups placed in the cartridge may vary and it is sufficient for this purpose to change the height of the central spacer. The end caps and the housing spacer are preferably made of the same plastic material as the media of the filtration units and are also connected and sealingly secured by welding. Thus, only two materials are used, namely the plastic material of the supports and the housing and the material of the membrane. No adhesive, filler, o-ring or the like is required, which minimizes the infiltration of the products to be extracted and the mechanical forces due to the

  thermal expansion and contraction.

  The invention also relates to a new and advantageous method of sealingly securing a microporous filter on 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 damage to the fliter and occlusions of its filtration volume. This method consists of using a plastic support different from the filter material, to cause the absorption in the pores of the filter of a predetermined quantity of a solvent for the carrier material, which is not a solvent for the filter, to bring the support into contact with the humidified filter, to maintain the contact for a sufficiently long time to cause the solvation of the material situated on the surface of the support and to cause the absorption of a part by the pores of the filter, then remove the solvent, preferably by drying. The pores of the filter are preferably filled with solvent without appreciable excess on the surface. The filter may advantageously be saturated with an excess of solvent and then be rotated to remove excess of this solvent. The necessary contact pressure between the support and the filter is minimal, which avoids the damage

  mechanical damage that may be caused to the membrane.

  The structure of the resultant filter and support assembly is different from, and superior to, structures obtained by the prior art techniques in which the support receives heat, solvent or adhesive. According to the method of the invention, the plastic material of the support does not penetrate into

  or impregnates only the pores of the membrane lying

  ribs or the like without causing a noticeable lateral spread which can cause occlusion of the filter surface. The plastic impregnating material should in principle not pass through the membrane and normally does not

  not, so that parts of the membrane remain

  above the ribs, at a distance from the latter, so as to form oblique channels which pass through it. Tests having been carried out show for example that for a fluid,

  a given pressure and support structure, lower it

  The flow rate caused by the filter produced in accordance with the invention is only about 15%. The ribs have

  preferably a curved surface to minimize contact.

  The binding method according to the invention is applicable to all support structures having a fineness

  as specified, for example, in United States patents.

  United States Nos. 3,854,907, 3,730,353 and 3,371,019.

  Heretofore, the ribbed or thin corrugated supports have not been linked to the filters for occlusion, adjustment or the like. The bonding carried out by the described process can be carried out easily and can provide important protection against pressure excursions which may cause reflux and in some cases it eliminates the need for valves or check valves. The technique according to the invention is also advantageously usable for laminated membranes with fibrous plastic supports such as woven fabrics or nonwoven 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: FIG. 1 is a plan view of a filter cartridge according to the invention; Figure 2 is an elevation; Figure 3 is an axial section; FIG. 4 is an enlarged partial plan view 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; Figure 6 is a cross-section on the line 6-6 of Figure 4; Figure 7 is a cross-section on the line 7-7 of Figure 5; Figure 8 is a cross section along the line 8-8 of Figure 4; Figure 9 is a cross section along the line 9-9 of Figure 5; Figure 10 is a section similar to those of Figures 6 and 7 and shows the two assembled parts and superimposed filter 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; Fig. 12 is a reduced scale partial plan view and shows the rear side of the support piece shown in Fig. 4; Fig. 13 is a reduced scale partial plan view and shows the rear side of the part shown in Fig. 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 reusable conventional support; Fig. 15 is a partial plan view showing an alternative embodiment of the filter support which is in one piece; Fig. 16 is a partial plan view showing the rear side of the support shown in Fig. 15; and

246.8397

  FIG. 17 is a cross-section according to the

line 17-17 of Figure 15.

  Figures 1 to 3 show an autonomous filter cartridge having, for example, 500 cm2 of filter 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 material 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 lid 22 comprises a coupling 32 intended for mounting an outlet pipe or tube or the like which is welded to this lid along a line 34. The lid has under the connector 32 a concentric ring 36 intended to be connected to a filtration unit 38 in a manner to be described in more detail later. The ring 36 and the connector 32 provide communication with a stack of filtration groups or disks 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 air to be vented from the housing upon commissioning. This vent may consist, for example, of a valve or valve opening by hand to evacuate the air and then to be closed. Vent 40 is provided with a

removable cap 41.

  The cover 24 is similar to the cover 22 and has an inlet connector 42 connected along a weld line 44. The cover 24 may also possibly comprise a vent 40 and moreover it is identical to the cover 22. A housing comprising a vent at each end makes it possible to use the cartridge by putting one or the other end at the top. The cover 24 has a ring 46 similar to the ring 36. However, the ring 46 is not connected to the stack of filter disks 38 placed in the housing. On the contrary, the record

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  bottom 38 is sealingly attached to a cap 48 placed at the end of the stack and having outer ribs or the like 49 which rest on the inner periphery of the ring 46 to avoid cutting off the flow at the 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 directs in a central channel located inside the stack, in a manner to be described later, and from there, the filtrate exits through the

  fitting 32 and enters the outlet duct.

  Figures 4 to 13 show an embodiment of the filtration unit 38 which is in two pieces and fits one into the other. The part 50 comprises a plane disk 54 (FIG. 13) which supports projecting concentric ribs 56 and includes notches

  radial forming channels 58 located under the ribs 56.

  The part 50 also comprises a solid flange 60 secured to the base 54 and having 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 outer span 64 define with the surface of the intermediate ribs 56 a common plane to which a filter membrane 68 is bonded by a

  way that 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 inner circumferential bearing surface and which is intended to be permanently connected to a complementary coupling member of the superimposed filtration unit 38 so that the two groups are locked together and so that their neighboring filters 68 are spaced from each other so that the liquid can flow between them. The assembly member 74 may comprise a surface having any desired shape, but advantageously comprises on this surface a tongue in

protrusion as shown.

  The piece 52 fits, as shown in Figures 10 and 11, into the piece 50 to which it is permanently bonded to form a support in one piece for filters 68 related to its upper surface and 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. outer flange 76 which fits into the rim 60 of the workpiece 50, within the bearing surface 62. The workpiece 52 has an inner circumferential bearing surface 78 which, after assembly with the workpiece 50 as 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 86 which comprises as represented a throat that is complementary to the tongue of the organ

assembly 74 of the piece 50.

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

ribs 82.

  As shown in FIG. 10, the completed filtration unit 88 comprises 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 Figure 10 in broken lines, similar filter groups 38 are superimposed and bonded by their connecting members, preferably by solvent welding. The filtration units 38 consisting of a complete support 88 and the two filter membranes 68 may be bonded to form stacks of any desired height and fixed inside the housing 20 in the manner shown in FIG. 3. It is possible to vary the dimensions of the cartridge by changing the number of groups 38 that it contains and by changing the height of the cartridge.

the spacer 26.

  The channels 58 and 84 of the parts 50 and 52, respectively, lead to the orifices 90 and 92 opening onto the central openings 70 and 72 of the parts and 52. When the part 52 is placed in the part 50, the channels 58 and 84 can be aligned with, as a consequence, that the orifices 90 and 92 are also

  to 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 to the radial channels 58 and 84 to then enter through the orifices 80 and 82 into the central opening 70. 72 of the filter element 38. These spaces located between the ribs and the radial channels constitute internal passages allowing the liquid passing through the filtering membranes 68 to flow towards the central opening 70-72, the filtrate thus obtained being running axially

  towards the connection 32 and in the outlet duct.

  All the parts of the cartridge of FIGS. 1 to 3 other than the filtering membranes 68 are preferably made of the same plastic material, for example polycarbonate, and are welded to each other by heat or by a solvent so as to constitute a unitary rigid structure. The obtained cartridge can be sterilized and implemented in an online filtration circuit, then discarded and easily replaced with minimal downtime, work and inconvenience. While it is possible to use an adhesive or other indwelling bonding material to assemble the cartridge parts, the welding as described is more advantageous and can be performed by automated operations. A cartridge thus assembled is only two materials, namely the plastic material constituting the housing and the filter supports and the material in which the membrane is made. This minimum number of materials not only reduces the cost price and the operations concerned, but

  also minimizes the amount of extractables.

  The membranes 68 are microporous films produced by casting or are made of fibers bound or shaped into felt, the pores of which have dimensions preferably of less than 25 μm. These membranes and their method of manufacture using different polymers are well known. Membranes which are supported flat, without wrinkles and which are bonded to the supporting ribs between their peripheral edges are well secured by being prevented from being displaced by the circulation which can take place in one direction or the other and are not subjected to efforts that may be produced by folding or bending during use. The membranes 68 may be bonded to the supports 88 in any desired manner. They are, however, advantageously bound in accordance with the invention by the following method. A predetermined amount of a solvent of the plastic of carrier 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 solvation of the plastic material, which is preferably thermoplastic, of the support and impregnates it into the pores of the membrane above the bearing surfaces and the ribs, but not substantially in the passageways. flow located between the ribs, the fixing thus obtained being narrow and causing a minimum of occlusion of the volume of the filter. A predetermined amount of solvent may be initially dosed and deposited, and then spread over the membrane by capillarity. It has been observed, however, 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 virtually saturates the pores of the membrane without excess and can be easily automated. After a slight contact sufficient to impregnate the plastic into the pores of the membrane, it is dried. It has been found that this is not a difficult operation and it has been observed that normal air drying following a rest period of seconds or less is appropriate. When the materials are judiciously chosen, a rest period of 3 seconds is sufficient. Any suitable solvent of the plastics material

  constituting the support 88 may be used.

  Careful tests have shown that the process described above causes the effective and tight bonding of the membrane by preventing the flow of liquid except through the membrane. They have also shown that the 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 material of the support or when the connection is made under heat and pressure. It seems that the resulting link

  is at least partially mechanical, trans-

  versales performed in these membranes showing extensions of the support material that fill the

neighboring pores of the latter.

  According to a very advantageous embodiment, the support 88 and the housing 20 are made of polycarbonate and the membranes 68 are made by casting polyvinylidene fluoride. The membrane is welded with a solvent to its support, the filter groups are welded to each other by their connecting members and the housing parts are welded to each other by a solvent, the solvent used is trichlorethylene. The connections to the covers 22 and 24 are previously ultrasonically welded with the release of heat. Other suitable materials

can also be used. FIG. 14 represents a variant embodiment of a cartridge of

  filtration consisting of stacked disks 38 arranged in a reusable support 106 of conventional design. The cartridge consists of several filter groups 38 connected to each other by their connecting 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 comprises a coupling 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. filter 38, as well as an outlet orifice 110, the support further comprising a base 114. As shown in FIG. 14, the base 114 and the cover 112 comprise screw threads 116 which are engaged and allow tightening an O-ring 118. Any other suitable waterproof fastener may be used. For sterilization of fluids, a conventional stainless steel casing having a seal and an outer clamping member is preferable. The cover 112 has a recess below the inlet 110 to accommodate the connector 102, the recess surface cooperating with the O-ring 104 to ensure

sealing.

  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 disk comprises at the outer circumference a flange 120 having upper and lower surfaces of span.

  122 and 124. Inner circumferential bearing surfaces

  126 and 128 define with the outer circumferential bearing surfaces 122 and 124 common planes to which the filter membranes are bonded in the manner previously described. Ribs 130 are between the bearing surfaces 122 and 126. Similarly, ribs 132 are between the inner and outer bearing surfaces 124 and 128 on the opposite side of the carrier. The ribs 132 are placed at regular distances on the support surface and intersect, preferably at an angle of 900, to form a grid structure.

  by which liquids can flow.

  The inner circumferential bearing surface 128 is radially offset relative to the bearing surface 126 and is within the latter, the ribs 132 and 132 'penetrating into the gap separating these surfaces so as to constitute a structural support and passages through which liquid can enter the central opening 134. Joining 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. share. As shown in the figures, the connecting members 136 and 138 comprise substantially planar outer surfaces which extend beyond the surface of the membranes bound to the support in their vicinity. The support discs can be alternately stacked with their sides reversed, the connecting members 136 of the adjacent discs being in contact to be permanently connected and the connecting member 138 of a disc being connected to the disc. assembly member 138 of another superimposed disk. As an alternative embodiment, it is possible to produce two sets of support discs which are identical, except that one disc comprises an assembly member which comprises a tongue and the other disc comprises an assembly member which comprises a groove. complementary. The supports according to the embodiment variant shown in FIGS. 15 to 17 can be stacked and bound so as to form a central flow channel and they can be housed in their own casing disposing after use or in a reusable conventional casing and such than

previously described.

  Although the assembly members of the surfaces of the groups 38 and the supports 150 may advantageously be projecting on each surface of the disc above the adjacent membrane to provide a space between the neighboring discs, one may have all or most of

  the desired height to produce a corresponding spacing.

  Although the filter supports as described are circular to facilitate and clarify the drawings and have inner and outer circumferential bearing surfaces, the supports may have any other suitable shape, for example being oval or polygonal and it is of course that the supports having these forms fall within the scope of the invention. On the other hand, although the central flow opening and the cartridge channel are preferably circular and axially disposed, the opening may be biased and may have other desirable shapes. In addition, the term "ribs" as used herein is intended to mean any thin, continuous or discontinuous support structure suitable for providing mechanical support for the filter membrane while providing flow paths for liquids that pass through the filters. In addition, discontinuous or continuous ribs as shown, projecting corrugations, aligned or randomly arranged, and having any desired cross-section

  can, for example, also be used.

  The principle of the invention is intended in

  particular to microporous membranes and ultra-

  filtration, fibrous or cast, having pores whose dimensions are less than about 25 μm and in particular less than about 1 μm. 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 as a sterilization element for liquids. When used as a final filter, pre-filtering materials may be placed in the cartridges to protect the final filtration membranes 68. These coarser filters may be superimposed on the membranes 68 or a cylinder of pre-filtering material may be bonded. on the periphery of the stacked groups 38, the

  as shown in 160 in broken lines in FIG.

  Microporous filter membranes made by casting

are the most advantageous.

  As described above, the housing in three pieces secured that represent Figures 2 and 3

  facilitates the variation of the dimensions of the cartridge.

  The spacer 26 may, however, possibly be omitted and covers having suitable dimensions may have complementary edges and be directly connected.

to one another.

  It goes without saying that the invention has only been described by way of example and that various modifications can

  to be brought without leaving his domain.

Claims (13)

  A filter membrane group to be bonded to similar groups to form after-use integrated stacks, which group includes a central opening (70-72; 134) for axial flow of a liquid and being characterized in that   that it comprises a thin support of plastic material (50-   52; 150) at the top and bottom surfaces of which porous filtering membranes (68) are affixed, each of said surfaces including circumferential inner and outer circumferential surfaces (62, 64, 66, 78; 122, 124, 126,   128) between which are ribs (56-82;   132) delimiting with these bearing surfaces a substantially common plane, the membrane being fixedly attached to the bearing surfaces and the ribs in said plane, each   support surface between the central opening (70-   72; 134) and the inner bearing surface (66-78;   128) comprising an assembly member (74-86; 136-138) intended to be connected to a complementary assembly member of a superimposed filtration unit, the assembly member   at least one of the support surfaces extending   beyond the surface of the adjacent membrane, said support having internal passages (58-84) allowing the liquid to circulate between said membranes and said central opening, this opening and these passages constituting the unique channels by which the liquid can move through the group.   2. Filtration unit according to claim 1, characterized in that said support is in two pieces (50, 52) connected to each other, each of these parts comprising   ribs (56-82), an inner bearing surface (66-   78) and an assembly member (74, 86) on a surface, one of these parts (50) having a sealed outer rim (60) which includes the outer bearing surfaces (62-64) of the two surfaces.   3. Filtration unit according to claim 1, characterized in that said support is in a molded piece of plastic material (150), the inner bearing surface (128) and the assembly member (138) of a surface being within and away from the inner bearing surface (126) and the other surface engaging member (136), said inner passages opening into the space between the inner bearing surfaces . 4. Filtration unit according to claim 3, characterized in that the ribs (132 ') of a support surface extend in the space between the two inner bearing surfaces (126-128), the interstices between the extension of these ribs (1321) forming part of the internal passages which communicate with the central opening (134).   5. Filtration group according to any one   Claims 1 to 4, characterized in that said support   is made of plastic material different from said membrane and the membranes (68) are bonded to this support by plastic material of the latter which penetrates into their pores in contact with said bearing surfaces and the ribs situated between the latter, the pores of the membranes between said ribs containing substantially no material of the support.   6. After-use filter cartridge comprising a plurality of filter groups according to one of   any of claims 1 to 4, characterized in that   the groups are permanently attached to each other by said connecting members (74-86; 136-138) so as to   constitute a stack forming a central channel (70-   72; 134) for axial flow of the liquids, said central flow channel being closed at one end and a connecting member (36; 102) being permanently attached at the other end to allow connection with a flow line of liquid, said connected connecting member (36; 102) forming a spacer which holds the neighboring membranes at a distance to define a channel for the flow of liquid between this member and the adjacent membrane at outside said groups.   7. After-use filter cartridge comprising a plurality of filter groups according to one of   any of claims 1 to 4 and characterized in that   the groups are permanently connected to each other by said connecting members (74-86; 136-138) so as to   constitute a stack and to create a central channel (70-   72; 134), said central flow channel being closed at one end and a connecting member (36; 102) being permanently attached at its other end to permit connection with a flow line of liquid, said linked connecting member forming a spacer which removes the neighboring membranes so as to delimit between said member and the adjacent membrane a flow channel for the liquid outside said groups, said support being made of a plastics material different from that of the membranes and these membranes (68) being bonded to the supports by material of the latter which penetrates into their pores in contact with the bearing surfaces (62, 64, 66, 78; 122, 124, 126, 128 ) and the ribs (56, 82; 130, 132) of the supports, the pores of the membranes located between the ribs containing substantially no material of the support.   8. After-use filter cartridge comprising a plurality of filter groups according to one of   any of claims 1 to 4, characterized in that   said groups are permanently joined to each other by said connecting members (74-86; 136-138) so as to   constitute a stack and to create a central channel (70-   72; 134), said central flow channel being closed off at one end and a connecting member (36; 102) being permanently attached at its other end to permit connection to a flow line of liquid, said linked connecting member forming a spacer and spacing the neighboring membranes so as to define a channel for the flow of liquid between this member and the adjacent membrane outside said groups, said support being made of a plastic material different from that of the membrane, said membranes (68) being bonded to the supports by material of the latter which penetrates into their pores in contact with the bearing surfaces (62, 64, 66, 78; 122, 124, 126, 128) and the ribs (56, 82; 130, 132) of the supports, the pores of the membranes located between the ribs containing substantially no material of the support, all the parts of the cartridge other than the membranes being in the same plastic material and all these parts being welded to each other   to form a monobloc structure.   9. After-use filter cartridge comprising a plurality of filter groups according to one of   any of claims 1 to 4, characterized in that   the groups are permanently connected to each other by said connecting members (74-86; 136-138) so as to   constitute a stack and to create a central channel (70-   72; 134), which channel is closed at one end and a connector member (36; 102) is permanently attached at the other end to allow connection with a liquid flow line, connected spacer-forming connecting member which adjoins neighboring membranes to delimit a liquid flow channel between this member and the adjacent membrane outside said groups, said support being made of a plastic material different from that of the membrane said membranes (68) being bonded to the supports by material of the latter which penetrates into their pores in contact with the bearing surfaces (62, 64, 66, 78, 122, 124, 126, 128) and the ribs ( 56, 82; 130, 132), the pores of the membranes located between the ribs containing substantially no material of the support, said cartridge containing membranes having a pore size of less than about 1 μm and which are intended for sterilization of liquids.   10. After-use filter cartridge comprising a plurality of filter groups according to one of   any of claims 1 to 4, characterized in that   said groups are permanently joined to each other by said connecting members (74-86; 136-138) so as to   constitute a stack and to create a central channel (70-   72; 134) of axial flow of the liquids, said central channel being closed at one end and a connecting member (36; 102) being permanently connected at the other end to allow connection with a liquid flow line, said spacer-shaped connecting member which places the neighboring membranes at a distance in order to delimit between said member and the adjacent membrane a liquid flow channel outside said groups, said support being made of a plastic material different from that of said membrane, the membranes (68) being bonded to the supports by material of the latter which penetrates into their pores in contact with the bearing surfaces (62, 64, 66, 78; 122, 124, 126, 128) and the ribs (56, 82; 130, 132) supports, the pores of the membranes located between the ribs containing substantially no material of the support, said cartridge comprising a housing (20) having at each end a cover (22, 24) and a n spacer element (26) being arranged between them, this spacer member having assembly members (28) complementary to those (30) of the covers and being welded thereto so as to form a one-piece structure, one of the covers having at the closed end of the central flow channel an intake (42) of liquid and the other cover comprising said connecting member (36) connected to   the other end of said central channel (70-72).   11. A method of binding a filter to a plastic support, characterized in that it consists essentially in causing the absorption of a determined amount of solvent by the pores of the filter, this solvent being one for the support. , but not for the filter, to bring the dry support into contact with the filter thus moistened, to maintain contact until said solvent causes the solvation of the support and a part of the latter   infiltrates said pores and then removing the solvent.   The method according to claim 11, characterized in that the pores of the filter are substantially filled with solvent without excess.   13. The method of claim 11, characterized in that an excess of liquid is introduced into the filter to fill the pores and the excess is   eliminated by rotating the membrane.