POROUS TEXTILE FABRIC, FILTER ELEMENT, METHOD FOR THE PRODUCTION THEREOF AND USE THEREOF

Abstract

The present invention relates to a porous sheet product, to a filter element comprising the porous sheet product, to a method for producing the porous sheet product, to a method for producing the filter element, and to the use of the sheet product and of the filter element.

Claims

1. A porous sheet product having at least one of the following ply A and at least one of the following ply B: A: a porous membrane; and B: a porous separation ply constructed from polyolefin core-sheath fibers, the sheath material having a lower melting temperature than the core material; the porous sheet product exhibiting a radiation resistance of at least 20 kGy.

2. The sheet product as claimed in claim 1, wherein the core material of the porous separation ply B is polypropylene and the sheath material of the porous separation ply B is polyethylene.

3. The sheet product as claimed in claim 1, wherein the porous membrane A is hydrophobic.

4. The sheet product as claimed in claim 1, wherein the porous membrane is constructed from a polymer selected from the group consisting of polyethersulfone, polyvinylidene fluoride and polyolefins and also mixtures thereof.

5. The sheet product as claimed in claim 1, which consists of the ply sequence BAB or BAAB.

6. A method for producing a porous sheet product as claimed in claim 1, comprising: the steps of (1) providing the at least one porous membrane A; (2) providing the at least one porous separation ply B; (3) arranging the at least one porous membrane A and the at least one porous separation ply B to form the porous sheet product.

7. A filter element comprising: a sheet product of claim 1 and at least one anchoring element, and edge regions of the porous membrane A being embedded into the anchoring element in a fluid-tight manner.

8. The filter element as claimed in claim 7, which is an air filter.

9. A method for producing DE the filter element claim 7, comprising: (I) providing a porous sheet product according to claim 1; (II) providing the at least one anchoring element; (III) embedding the edge regions of the porous membrane A into the at least one anchoring element in a fluid-tight manner.

10. The use of the sheet product as claimed in claim 1 or of the filter element of claim 7 for sterile-filtration for the sterile-filtration of air.

Description

[0070] FIG. 1 shows SEM images (SEM stands for scanning electron microscopy) of, in each case, a porous separation ply B of an exemplary sheet product according to the present invention.

[0071] FIG. 2 shows SEM images of a PP/PE core-sheath spunbonded nonwoven at 2000-fold magnification (A) and of a PET spunbonded nonwoven at 1000-fold magnification (B), the nonwovens from FIGS. 2A and 2B exhibiting the same drainage action.

[0072] FIG. 3 shows, in different magnifications, SEM images of a cap section (section through the end caps of the filter element) of a filter element according to the prior art, using a polyester nonwoven instead of a porous separation ply composed of polyolefin core-sheath fibers. Especially in the magnifications B and C, it can be clearly seen that the polyester fibers have not completely melted in the embedding region and that the polyester nonwoven has hardly shrunk back, resulting in bypasses being allowed to form.

[0073] FIG. 4 shows different images of a cap section of a filter element according to the present invention. It can be clearly seen that the porous separation plies B have shrunk back and that the membrane plies A are completely encased in the region of embedding and intimately meshed with the anchoring element, resulting in the avoidance of the formation of bypasses.

[0074] FIG. 5 shows schematically the test setup of Example 1 (water intrusion test), wherein A denotes a measurement instrument (Sartocheck 4 from Sartorius Stedim Biotech GmbH) and C denotes a structure comprising a pleated filter cartridge having two end caps and filter housing B.

[0075] The present invention will be more particularly elucidated on the basis of the following nonlimiting examples.

EXAMPLES

[0076] Various filter units according to the present invention and according to the prior art (pleated filter cartridge having two end caps and filter housing B, specifically a filter capsule, the structure of which is shown in FIG. 5) were tested in accordance with the following test descriptions. The results obtained were the WIT value, as a measure of the integrity of the filter unit against water, and the BCT value (BCT=bacterial challenge test), as a measure of the suitability of the filter unit for sterile-filtration.

Water Intrusion Test (WIT) Conditions

[0077] The upstream side of the filter housing is filled with water. This is followed by application of 1.5 bar of pressure to the system and stabilization for 10 min. During the test time of 10 min, the water intrudes into the first layer of the membrane. The drop in pressure is measured. From the measured volume of the water which is required in order to compensate for the drop in pressure, and from the drop in pressure and also the known test time, the WIT value is calculated as a measure of the water intrusion. The test is carried out with the aid of a Sartocheck 4 measurement instrument from Sartorius Stedim Biotech GmbH.

Bacterial Challenge Test (BCT) Conditions

[0078] The BCT is carried out in accordance with ASTM F838-15, The microbe used is Brevundimonas diminuta. A result of CFU=0 is rated as sterile.

[0079] In the following examples and comparative examples, the following porous separation plies B were used.

TABLE-US-00002 TABLE 2 Mean nonwoven thickness [m] Grammage [g/m.sup.2] PET 1 250 45 PET 2 250 35 PET 3 150 25 PET 4 230 30 PET 5 110 30 PP/PE 450 90

[0080] The hydrophobically modified membrane used was a membrane as described in DE 10 2011 121 018 A1.

[0081] The results of the measurements carried out are specified in Tables 3 to 7 below. If the filter units were irradiated before the particular test, this is specified together with the radiation dose.

Example 1

[0082] The tested filter cartridge, used as capsule, exhibited the ply sequence BAB (PP/PE core-sheath nonwoven//hydrophobically modified membrane//PP/PE core-sheath nonwoven). Individual items (indicated by numbers (No.)) of structurally identical batches in each case were tested.

[0083] The filter capsules of build heights 7, 9 and 10, as specified in the following tables, respectively exhibited a filter area of about 0.06 m.sup.2, 0.17 m.sup.2 and 0.55 m.sup.2.

TABLE-US-00003 TABLE 3 Ply Build Microbial count sequence height Batch No. [CFU] Treatment BAB 9 121 2 0 Irradiated, 28 0 50 kGy 120 1 0 2 0 119 14 0 18 0 BAB 10 141 99 0 108 0

[0084] All the tested filter capsules of batches 119, 120, 121 and 141 were sterile (CFU=0).

TABLE-US-00004 TABLE 4 Ply Build WIT value sequence height Batch No. [ml/10 min] Treatment BAB 9 121 1 0.8 Irradiated, 21 0.8 50 kGy 38 0.8 120 6 1.2 25 1.4 38 0.9 BAB 10 141 107 2.4 115 2.3 93 2.5

[0085] The combination of two PP/PE core-sheath nonwovens with a hydrophobically modified membrane in the ply sequence BAB is, after irradiation, WIT-testable and also capable of sterile-filtration as per BCT in accordance with ASTM F838-15.

Comparative Example 1

[0086] The tested filter cartridges, used in capsules, exhibited the ply sequences PET1//hydrophobically modified membrane//PET1 or PET1//PET2//hydrophobically modified membrane//PET2//PET1.

TABLE-US-00005 TABLE 5 Build Microbial count Ply sequence height Batch No. [CFU] Treatment PET1//PET2// 9 98 54 Film Irradiated, hydrophob. 65 362 50 kGy mod. 24 37 Lawn membrane// 23 12 Lawn PET2//PET1 21 Lawn 177 8 Film 16 Film PET1// 7 458 12 Film hydrophob. 9 468 4 Lawn mod. membrane// PET1

[0087] The designations Film or Lawn indicate a microbial infestation which can already be identified with the naked eye.

TABLE-US-00006 TABLE 6 Build WIT [ml/ Combination height Batch No. 10 min] Treatment PET1//PET2//hydrophob. 9 177 9 15.7 Irradiated, mod. membrane//PET1 12 19.9 50 kGy 14 27.2 18 15.8 PET1//PET2// 9 411 25 31.2 hydrophob. mod. membrane//PET2//PET1 PET1//hydrophob. mod. 9 456 20 20.9 membrane//PET1 115 9 82.1 113 1 78 5 94 466 1 14.5 2 20.2 15 104.3

[0088] The tested combinations of polyester nonwoven with hydrophobically modified membrane are, after irradiation, neither WIT-testable (very high WIT results) nor capable of sterile-filtration as per BCT.

Example 2

[0089] In this example, further filter cartridges according to the present invention, used as capsule, and comparative filter cartridges with various PET combinations as porous separation ply B were tested. The results are summarized in Table 7 below.

TABLE-US-00007 TABLE 7 Proportion (%) of filter cartridges tested as sterile; number of Build cartridges tested Ply sequence height Batch in parentheses Treatment PET1//PET2//hydrophob. 9 200 70% (10) Untreated mod. membrane//PET2//PET1 PET1//PET4//hydrophob. 207 30% (10) mod. membrane//PET4//PET1 PET1//PET5//hydrophob. 208 50% (10) mod. membrane//PET5//PET1 PET1//hydrophob. mod. 239 0% (2) membrane//PET1 PET1//PET3//hydrophob. 245 30% (10) mod. membrane//PET3//PET1 PET1//PET1//hydrophob. 254 20% (5) mod. membrane//PET1//PET1 PP/PE//hydrophob. mod. 9 119 100% (10) Irradiated, membrane//PP/PE 120 100% (10) 50 kGy 121 100% (10)

[0090] As is evident from Table 7, the comparative filter cartridges are not capable of sterile-filtration as per BCT, even without gamma-irradiation. In contrast, the filter units according to the invention remain capable of sterile-filtration as per BCT, even after gamma-irradiation.

[0091] The present invention provides porous sheet products which make it possible to produce improved filter units. Since the sheath material of the polyolefin core-sheath nonwoven melts at a low temperature, the sheet product according to the invention can be pleated and embedded into an anchoring material at low temperatures. If a hydrophobically modified membrane is used as porous membrane ply A, the hydrophobic modification is protected from decomposition due to high processing temperatures. (Decomposition of hydrophobization may lead to the formation of hydrophilic regions, the result being that the properties of the filter may change greatly, and this could result in the impairment of the function of the filter element, especially as air filter. Especially the air-flow capacity and the WIT test behavior could deteriorate.) The sheet products and filter elements according to the invention are both WIT-testable and capable of sterile-filtration as per BCT even after gamma-irradiation, this not being the case for comparable filter elements according to the prior art. Moreover, particularly stable pleatings can be generated in a gentle manner from the sheet products according to the invention.