Filter module having an edge-reinforced membrane, method for producing the filter module and use thereof

Abstract

A filter module for sterile filtration and virus filtration of fluid media. The filter module includes a filter membrane with a porous edge structure arranged thereon and at least one anchoring element. The filter membrane with the porous edge structure is embedded in the anchoring element and serves as edge reinforcement to improve the connection of the filter membrane to the anchoring element. The texturing or surface roughness of the edge reinforcement provides an interlocking effect between the filter membrane and the anchoring element. The embedding of the filter membrane in the anchoring element provides a fluid-tight connection of the membrane to the anchoring element which prevents the occurrence of leaks in the end region of the filter module. A method for producing the filter module is also described.

Claims

1. A filter module comprising: a filter membrane having an edge region; a porous edge structure connected to the edge region of the filter membrane; and at least one anchoring element, wherein at least part of the filter membrane and at least part of the porous edge structure connected thereto are embedded together in the at least one anchoring element, wherein the porous edge structure is formed as an edge strip which covers the edge region without completely covering a remainder of the filter membrane and reinforces the edge region when embedded with the filter membrane in the at least one anchoring element, and wherein the edge strip sits flush with an end of the filter membrane when embedded in the at least one anchoring element to stabilize the edge region of the filter membrane by reducing a risk of the membrane edge region bending, buckling or breaking off.

2. The filter module as claimed in claim 1, wherein the filter membrane and the porous edge structure connected to the edge region are present as a composite.

3. The filter module as claimed in claim 1, wherein the porous edge structure has a pore size of at least 0.1 μm.

4. The filter module as claimed in claim 1, wherein the porous edge structure is textured or has a surface roughness.

5. The filter module as claimed in claim 1, wherein part of the porous edge structure remains outside the at least one anchoring element and forms a protrusion or overhang.

6. The filter module as claimed in claim 1, wherein the filter membrane is tubular.

7. The filter module as claimed in claim 1, wherein the filter membrane is pleated.

8. The filter module as claimed in claim 1, wherein the filter membrane is constructed from a polymer selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, polyethersulfone, polyamide, polyolefin, cellulose acetate, cellulose, and mixtures thereof.

9. The filter module as claimed in claim 1, wherein the porous edge structure is constructed from a polymer selected from the group consisting of polyethersulfone, polyamide, polyolefin, and mixtures thereof.

10. The filter module as claimed in claim 1, wherein the filter membrane is constructed from polytetrafluoroethylene, and wherein both the porous edge structure and the at least one anchoring element are constructed from polypropylene.

11. The filter module as claimed in claim 1, wherein: the filter membrane and the porous edge structure are constructed from polyethersulfone, and the at least one anchoring element is constructed from polypropylene.

12. The filter module as claimed in claim 1, wherein the porous edge structure is a porous film or a membrane.

13. A method for producing the filter module as claimed in claim 1, comprising the following steps: (a) providing a filter membrane and a porous edge structure, (b) arranging the porous edge structure on at least one edge region on the filter membrane, (c) connecting the filter membrane to the porous edge structure arranged on the at least one edge region, (d) optionally pleating the filter membrane having the porous edge structure arranged on the at least one edge region, (e) optionally welding the filter membrane having the porous edge structure arranged on the at least one edge region along sides of the filter membrane which do not have continuous edge reinforcement, (f) providing at least one anchoring element, (g) softening a subregion of the at least one anchoring element, and (h) embedding the filter membrane having the porous edge structure arranged on the at least one edge region in the softened subregion of the at least one anchoring element.

14. The method as claimed in claim 13, wherein the porous edge structure is textured or is provided with a surface roughness during the connection operation in step (c).

15. A method of filtering a fluid medium, comprising passing the fluid medium through a filter module according to claim 1.

16. The method according to claim 15, wherein the fluid medium is air.

17. The method according to claim 13, comprising pleating the filter membrane having the porous edge structure arranged on the at least one edge region.

18. The method according to claim 13, comprising welding the filter membrane along the sides which do not have continuous edge reinforcement.

19. The method according to claim 17, comprising welding the filter membrane along the sides which do not have continuous edge reinforcement.

20. The filter module as claimed in claim 5, wherein the protrusion or overhang extends outside from an embedding side of the at least one anchoring element at least 1 to 10 mm.

21. The filter module as claimed in claim 1, wherein: the filter membrane has a total area, the edge strip has a width of approximately 2 to 10 mm, and the edge region of the filter membrane covered by the edge strip accounts for about 0.5% to 25% of the total area of the filter membrane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The figures show:

(2) FIG. 1 shows scanning electron microscopy images of a filter module having an edge-reinforced membrane according to the present invention (left) and of a filter module without an edge-reinforced membrane as a comparative example (right). In both cases, the membranes are pleated. As can be gathered from FIG. 1, the edge region of the membrane is uniformly interlocked with the anchoring element in the case of the presence of the edge reinforcement, whereas the edge region of the membrane tends to bend down or bend over in the case of the absence of the edge reinforcement. This becomes apparent especially in the folds of the pleating, which, in a sense, fall over.

(3) FIG. 2 shows the texturing or the surface roughness when looking from above at the example of a filter module according to the invention having a PTFE membrane and a PP edge strip arranged thereon. As can be gathered from FIG. 2, the texture of the nonwoven has pressed into the edge strip. On the basis of the SEM image from FIG. 2, it is possible to determine the gap width of the texturing or the surface roughness.

(4) FIG. 3 shows the nonwoven-attributed texturing or surface roughness of the filter module according to the invention from FIG. 2 when looking from the side. On the basis of the SEM image from FIG. 3, it is possible to determine the penetration depth of the texturing or of the surface roughness.

DETAILED DESCRIPTION

EXAMPLES

(5) The following examples serve to further explain and illustrate the present invention without, however, being restricted thereto.

Example A

(6) The influence of edge reinforcement on filter sterility was evaluated on the basis of bacterial retention. To this end, a filter module having an edge-reinforced membrane and a filter module without an edge-reinforced membrane as a comparative example were tested. In both cases the membrane was constructed from expanded polytetrafluoroethylene. The edge reinforcement of the filter module, which edge reinforcement was sealed on the inflow side, was constructed from polypropylene, as were the end caps used in both cases. Drainage nonwovens composed of polyphenylene sulfide were used for stabilization in both cases.

(7) Table A-1 shows the sterility results from a BC (“Bacteria Challenge”) test for the filter module without an edge-reinforced membrane (Example No. 1 to 10). The BC test was carried out in accordance with ASTM 838-05. The filter module without an edge-reinforced membrane was consistently 10-inch filter cartridges, the ePTFE membrane (length: 241 mm; thickness: 90±10 μm) having a pore size of 0.2 μm. Altogether, five cartridges, each from two different lots, were tested. As can be gathered from Table A-1, the filter module without edge reinforcement already shows a comparatively high microbial count in the untreated state, i.e., nonsteamed state due to the insufficient connection of the membrane to the end cap (see also the SEM image in FIG. 1, right), which ultimately leads to a lack of sterility of the filter module.

(8) Tables A-2 to A-4 show the sterility results for the filter module having an edge-reinforced membrane (Example No. 11 to 36). Here, the BC test was also carried out in accordance with ASTM 838-05. The filter module having an edge-reinforced membrane was, too, consistently 10-inch filter cartridges, the ePTFE membrane (length: 241 mm; thickness: 90±10 μm) having a pore size of 0.2 μm. The porous edge structure used was a PP membrane (thickness: 180±20 μm) in strip form having a pore size of likewise 0.2 μm and an edge region/width of 8 mm, i.e., about 3.3% of the total area of the filter membrane were covered by such a porous edge structure. Heat-sealing was carried out at a temperature of 170° C. and at a pressure of 3 bar. The PPS drainage nonwoven was already concomitantly guided during the sealing operation. As a result of the fiber impression by the nonwoven, a texturing or a surface roughness was produced in the porous edge structure. The average gap width was 16 μm, whereas the average penetration depth was 11 μm, which could be ascertained by scanning electron microscopy (see also the SEM images in FIG. 2 and in FIG. 3). The penetration depth of the edge seal into the end cap was about 1.5 to 2 mm, i.e., a protrusion/overhang of 6 to 6.5 mm protruding from the end cap. Ten cartridges from one lot and also four or twelve cartridges from two further lots were tested. As can be gathered from Tables A-2 to A-4, no significant microbial count is measurable even in the case of an up to 150 times steaming of the filter module having edge reinforcement (134° C. and 30 min for each cycle, followed by cooling with water to about 15° C.). The reason therefor is the improved connection of the edge-reinforced membrane to the end cap (see also the SEM image in FIG. 1, left), the result being that especially leaks in the edge region can be avoided, which leaks would otherwise have an adverse effect on the sterility of the filter module.

Example B

(9) In a further system, the influence of edge reinforcement on filter sterility was evaluated on the basis of bacteriophage retention. To this end, a filter module having an edge-reinforced membrane and a filter module without an edge-reinforced membrane as a comparative example were tested. Here too, 10-inch filter cartridges were consistently used. In both cases, the membrane was constructed from polyethersulfone and had hydrophilic properties due to the addition of polyvinylpyrrolidone, and two plies each of an identical virus membrane were installed as prefilter and main filter. The pore size of the filter membranes was 0.02 μm. Whereas the prefilter was edge-reinforced in the example, the prefilter in the comparative example did not have edge reinforcement. The edge reinforcement, i.e., the porous edge structure, of the filter module, which edge reinforcement was sealed on the prefilter on the inflow side, was likewise constructed from polyethersulfone and had a pore size of 0.65 μm. The thickness of the prefilter membrane and main-filter membrane was 150±10 μm in each case, whereas the thickness of the edge strip was 160±20 μm. Heat-sealing was carried out at a temperature of 270° C. and at a pressure of 4 bar. The texturing or surface roughness was produced by impression of the textured PTFE conveyor belt of the heat sealer. The fiber thickness of the textured conveyor belt was in the region of 400 μm, which could be measured on the basis of microscopy images. Moreover, a penetration depth of about 15 to 20 μm was obtained. The edge region/width and the penetration depth into the end cap were identical to the values from Example A. The end caps were constructed from polypropylene, both in the example according to the invention and in the comparative example. Moreover, PP drainage nonwovens were used in both cases.

(10) Table B shows the sterility results for the filter module without an edge-reinforced membrane (Example No. I) and for the filter module having an edge-reinforced membrane (Example No. II to IV). In the case of the filter module without edge reinforcement, an LRV (“Log 10 Reduction Value”) of 4.3 was ascertained. In contrast to a complete retention, this value merely corresponds to a reduction in the original bacteriophage concentration, i.e., it was additionally possible to detect bacteriophages in the filtrate. By contrast, in the case of the edge-reinforced filter module, an LRV of 6.0 was ascertained, this amounting to a complete retention of bacteriophages. In comparison with the filter module without an edge-reinforced membrane, this is an improvement of about two log levels.

(11) Here, the testing of bacteriophage retention was carried out on the basis of a phage solution composed of Pseudomonas aeruginosa bacteriophages PP7 having a concentration of at least 10.sup.7 PFU/mL, which was filtered at a constant pressure of 2 bar through the filter module to be tested. For the filtration, the fractions were not collected in various containers, but all collected together in one pool. The filtrate thus obtained was subsequently tested for phages.

(12) To analyze the bacteriophage PP7 titer, samples (150 μL aliquot) were incubated with bacteria (150 μL aliquot of an overnight culture, diluted 1:100 in nutrient solution) at room temperature for about 10 minutes. Thereafter, 2.5 mL of 0.8% agar were added and the entire volume was spread on a Petri dish containing 1.5% solid nutrient agar. After an incubation time of 18 to 24 hours at 37° C., the plaques induced by the bacteriophages were counted.

(13) TABLE-US-00001 TABLE A-1 Microbial Applied load Microbial Example Cartridge Lot Treatment microbial [microbes/ count No. No. No. method Test microbe count cm.sup.2] [CFU] 1 1 1 Untreated Brevundimonas dim 8.00 × 10.sup.10 1.43 × 10.sup.7 0 2 2 1 Untreated Brevundimonas dim 8.00 × 10.sup.10 1.43 × 10.sup.7 352 3 3 1 Untreated Brevundimonas dim 8.00 × 10.sup.10 1.43 × 10.sup.7 0 4 4 1 Untreated Brevundimonas dim 8.00 × 10.sup.10 1.43 × 10.sup.7 40 5 5 1 Untreated Brevundimonas dim 8.00 × 10.sup.10 1.43 × 10.sup.7 0 6 1 2 Untreated Brevundimonas dim 8.00 × 10.sup.10 1.43 × 10.sup.7 0 7 2 2 Untreated Brevundimonas dim 8.00 × 10.sup.10 1.43 × 10.sup.7 No longer countable 8 3 2 Untreated Brevundimonas dim 8.00 × 10.sup.10 1.43 × 10.sup.7 400 9 4 2 Untreated Brevundimonas dim 8.00 × 10.sup.10 1.43 × 10.sup.7 338 10 5 2 Untreated Brevundimonas dim 8.00 × 10.sup.10 1.43 × 10.sup.7 52 Bubble point [bar] Test Diffusion [mL/min] Example Cartridge Lot Membrane before after pressure before after No. No. No. area [m.sup.2] sterilization BC test [bar] sterilization BC test 1 1 1 0.56 1.64 1.60 0.70 2.2 1.5 2 2 1 0.56 1.59 1.55 0.70 2.1 1.6 3 3 1 0.56 1.69 1.64 0.70 2.2 1.5 4 4 1 0.56 1.65 1.63 0.70 2.4 1.5 5 5 1 0.56 1.60 1.54 0.70 2.3 1.8 6 1 2 0.56 1.60 1.55 0.70 11.0 1.7 7 2 2 0.56 1.60 1.55 0.70 11.5 2.8 8 3 2 0.56 1.60 1.59 0.70 11.1 2.1 9 4 2 0.56 1.64 1.63 0.70 9.9 1.6 10 5 2 0.56 1.64 1.63 0.70 10.7 1.7

(14) TABLE-US-00002 TABLE A-2 Microbial Applied load Microbial Example Cartridge Lot Treatment microbial [microbes/ count No. No. No. method Test microbe count cm.sup.2] [CFU] 11 1 1 Untreated Brevundimonas dim 8.75 × 10.sup.10 1.46 × 10.sup.7 0 12 2 1 150x Brevundimonas dim 7.50 × 10.sup.10 1.25 × 10.sup.7 0 steamed 13 3 1 Untreated Brevundimonas dim 8.75 × 10.sup.10 1.46 × 10.sup.7 0 14 4 1 150x Brevundimonas dim 7.50 × 10.sup.10 1.25 × 10.sup.7 0 steamed 15 5 1 150x Brevundimonas dim 7.50 × 10.sup.10 1.25 × 10.sup.7 0 steamed 16 6 1 150x Brevundimonas dim 7.50 × 10.sup.10 1.25 × 10.sup.7 0 steamed 17 7 1 Untreated Brevundimonas dim 8.75 × 10.sup.10 1.46 × 10.sup.7 0 18 8 1 150x Brevundimonas dim 7.50 × 10.sup.10 1.25 × 10.sup.7 0 steamed 19 9 1 Untreated Brevundimonas dim 8.75 × 10.sup.10 1.46 × 10.sup.7 0 20 10 1 Untreated Brevundimonas dim 8.75 × 10.sup.10 1.46 × 10.sup.7 0 Bubble point [bar] Test Diffusion [mL/min] Example Cartridge Lot Membrane before after pressure before after No. No. No. area [m.sup.2] sterilization BC test [bar] sterilization BC test 11 1 1 0.60 — — 0.70 — 2.6 12 2 1 0.60 — 1.59 0.70 — 2.9 13 3 1 0.60 — — 0.70 — 2.9 14 4 1 0.60 — 1.58 0.70 — 2.1 15 5 1 0.60 — 1.60 0.70 — 1.4 16 6 1 0.60 — 1.59 0.70 — 5.4 17 7 1 0.60 — — 0.70 — 3.3 18 8 1 0.60 — 1.54 0.70 — 2.9 19 9 1 0.60 — — 0.70 — 2.8 20 10 1 0.60 — — 0.70 — 2.6

(15) TABLE-US-00003 TABLE A-3 Microbial Applied load Microbial Example Cartridge Lot Treatment microbial [microbes/ count No. No. No. method Test microbe count cm.sup.2] [CFU] 21 1 2 25x Brevundimonas dim 8.00 × 10.sup.10 1.33 × 10.sup.7 0 steamed 22 2 2 Untreated Brevundimonas dim 7.75 × 10.sup.10 1.29 × 10.sup.7 0 23 3 2 Untreated Brevundimonas dim 7.75 × 10.sup.10 1.29 × 10.sup.7 0 24 4 2 25x Brevundimonas dim 8.00 × 10.sup.10 1.33 × 10.sup.7 0 steamed 25 1 3 Untreated Brevundimonas dim 7.25 × 10.sup.10 1.32 × 10.sup.7 0 26 2 3 Untreated Brevundimonas dim 7.25 × 10.sup.10 1.32 × 10.sup.7 0 27 3 3 Untreated Brevundimonas dim 7.25 × 10.sup.10 1.32 × 10.sup.7 0 28 4 3 Untreated Brevundimonas dim 7.25 × 10.sup.10 1.32 × 10.sup.7 0 29 5 3 Untreated Brevundimonas dim 7.25 × 10.sup.10 1.32 × 10.sup.7 0 30 6 3 Untreated Brevundimonas dim 7.25 × 10.sup.10 1.32 × 10.sup.7 0 Bubble point [bar] Test Diffusion [mL/min] Example Cartridge Lot Membrane before after pressure before after No. No. No. area [m.sup.2] sterilization BC test [bar] sterilization BC test 21 1 2 0.60 — 1.59 0.70 — 3.8 22 2 2 0.60 — 1.65 0.70 — 3.5 23 3 2 0.60 — 1.65 0.70 — 2.1 24 4 2 0.60 — 1.59 0.70 — 3.0 25 1 3 0.55 — 1.55 0.70 — 1.0 26 2 3 0.55 — 1.54 0.70 — 2.0 27 3 3 0.55 — 1.49 0.70 — 1.7 28 4 3 0.55 — 1.55 0.70 — 2.6 29 5 3 0.55 — 1.53 0.70 — 1.9 30 6 3 0.55 — 1.50 0.70 — 1.9

(16) TABLE-US-00004 TABLE A-4 Microbial Applied load Microbial Example Cartridge Lot Treatment microbial [microbes/ count No. No. No. method Test microbe count cm.sup.2] [CFU] 31 7 3 Untreated Brevundimonas dim 8.50 × 10.sup.10 1.55 × 10.sup.7 0 32 8 3 Untreated Brevundimonas dim 8.50 × 10.sup.10 1.55 × 10.sup.7 0 33 9 3 Untreated Brevundimonas dim 8.50 × 10.sup.10 1.55 × 10.sup.7 0 34 10 3 Untreated Brevundimonas dim 8.50 × 10.sup.10 1.55 × 10.sup.7 0 35 11 3 Untreated Brevundimonas dim 8.50 × 10.sup.10 1.55 × 10.sup.7 0 36 12 3 Untreated Brevundimonas dim 8.50 × 10.sup.10 1.55 × 10.sup.7 0 Bubble point [bar] Test Diffusion [mL/min] Example Cartridge Lot Membrane before after pressure before after No. No. No. area [m.sup.2] sterilization BC test [bar] sterilization BC test 31 7 3 0.55 — 1.54 0.70 — 2.2 32 8 3 0.55 — 1.50 0.70 — 1.8 33 9 3 0.55 — 1.55 0.70 — 2.2 34 10 3 0.55 — 1.50 0.70 — 4.3 35 11 3 0.55 — 1.54 0.70 — 2.2 36 12 3 0.55 — 1.55 0.70 — 1.7

(17) TABLE-US-00005 TABLE B Filter Example Lot area Prediffusion Postdiffusion No. No. [cm.sup.2] Prefilter Main filter [mL/min] [mL/min] I 1 6500 Not sealed Not sealed 11.0 9.5 II 1 5189 Sealed Not sealed 11.0 11.4 III 2 5497 Sealed Not sealed 10.6 11.4 IV 2 5497 Sealed Not sealed 9.6 10.9 Example Lot Fractions Titer, L2 Titer, fractions No. No. [mL] PFU/mL PFU/mL Plaques? LRV I 1 Pool 1.8 × 10.sup.7 8.5 × 10.sup.2      Bacteriophages 4.3 in the filtrate II 1 Pool 1.8 × 10.sup.7 2.0 × 10.sup.1 (*) Complete retention 6.0 III 2 Pool 1.8 × 10.sup.7 2.0 × 10.sup.1 (*) Complete retention 6.0 IV 2 Pool 1.8 × 10.sup.7 2.0 × 10.sup.1 (*) Complete retention 6.0 (*) No phages were detected in the filtrate. The specified values are calculated statistical values in order to be able to estimate the detection limit (see also “Guidance for industry—Q5A viral safetyevaluation of biotechnology products derived from cell lines of human or animal origin”).

(18) A filter module based on an edge-reinforced membrane is provided. The edge reinforcement achieves a fluid-tight connection of the filter membrane to the anchoring element. In particular, the production method can virtually completely prevent the occurrence of leaks in the edge region of the filter module, which leaks would otherwise have an adverse effect on the sterility of the filter module. Advantageously, this can ensure an adequate sterility even over a relatively long period of use, and this means that the filter module is suitable for all those applications that require an absence of bacteria and viruses. The filter module is thus outstandingly suitable for the sterile-filtration and virus filtration of fluid media, particularly of gaseous media, especially of air, as well as of liquid media.