DE102009005692A1 - Filter medium, process for its preparation and its use - Google Patents

Abstract

Disclosed is a filter medium comprising at least one foam layer applied to a fabric, wherein the filter medium has an air permeability of 20 to 120 l / dmmin at 200 Pa pressure difference. Furthermore, a method for producing this filter medium is described in which a foam is applied to a fabric and dried. This filter medium is used in industrial dedusting.

Description

The The invention relates to a filter medium, a method for its production and its use for industrial dedusting.

filter media for industrial dedusting must be the chemical and thermal conditions in the filter system accordingly be constructed. The on the surface of the filter medium Filtered dusts are removed by periodic cleaning usually by means of compressed air pulses (jet-pulse) removed, the be introduced from the clean gas side. The pressure loss over the medium is thus kept within specified limits. Usually be either needle felt or polytetrafluoroethylene (PTFE) membrane laminates used as carrier material here needle felt or Can serve tissue.

tissue alone are for filter systems with jet-pulse cleaning only partially suitable. It can only small Flow rates are chosen, otherwise both the pressure loss behavior as well as the emission values would reach an unsatisfactorily high level.

Of the The present invention is therefore based on the object, a filter medium to provide, not those known from the prior art Disadvantages.

According to the invention this is achieved by a filter medium comprising at least one foam layer applied to a fabric, the filter medium having an air permeability of 20 to 120 l / dm ² min at a differential pressure of 200 Pa. The common term for the physical size is air permeability, although in many cases, for. B. after combustion, is no longer pure air composition.

With this area for air permeability is achieved that in industrial dedusting in sufficient Way gas can pass through the filter medium.

The Filter medium according to the invention combines the advantages a fabric, such as high dimensional stability, wide availability and an attractive price level, with a good separation performance and low differential pressure. It has been shown that by the Apply at least one, more conveniently several, good on the carrier and well adhering layers of a stable, fine-pored foam on a suitable tissue a filter medium which can be produced both in terms of emission reduction, as well as with respect to the differential pressure behavior in the range moved by needle felt or membrane filter media. The one on the filter media surface Filtered dust can be safely removed by the cleaning process be removed on the upstream side, it results in a permanent favorable pressure loss behavior.

Compared to established needle felt products for the high temperature range, the filter medium of the invention has a significant price advantage with comparable deposition results, since it can be completely dispensed with the use of very expensive fiber polymers. When comparing with membrane laminates, there are several advantages: It is possible to perform the coating in one step; For membrane laminates, on the other hand, a membrane with a defined useful width has to be produced in advance in a separate and complex process as web material, and then the lamination of glass fabric and membrane takes place. These process steps do not necessarily take place at the same location. In contrast to the membrane laminate, a width specification is practically not given in the filter medium according to the invention. Furthermore, in the case of the laminates, due to the combination of two layers formed, there is a certain risk that the active filter layer will be lost over the surface (delamination). The risk of loss of function due to abrasion damage z. B. in the installation of filter bags against the very lightweight membrane is much lower. Finally, with the filter medium according to the invention with relatively short set-up times, smaller quantities in different widths can be realized. Another advantage of the filter medium according to the invention is the fact that the connection of the porous foam layer with the carrier is made flat, while in the membrane laminates, the compound is more selectively given to the raised crosshairs points, in the deeper areas, the membrane is stretched like a tarpaulin, without having an intense connection with the wearer. In the case of abrasion phenomena, this can have the consequence that the membrane is preferably removed at the raised points and, as a consequence, detachment also occurs in the deeper areas. Especially in the lower-lying areas but preferably the flow takes place, since there is a lower flow resistance. In the case of foam coating, even in the case of a removal at the raised areas, the foam layer would adhere to the lower areas and continue to perform the filtration task NEN.

Under the term "foam layer" in the sense of the present Invention is a solid, and thereby porous and permeable to air Layer understood that made from a foam by drying can be. A PTFE membrane is made of a foil-like Condition produced by stretching the sheet, because in the stretching process a three-dimensional network of PTFE Fibrils arise. The pore size is through determines the degree of stretching. The membrane is in its useful width fixed and must in a further procedural step with be connected to a stable carrier. The foam layer On the other hand, it is applied directly to the support during the drying step formed in a defined form and connected to the carrier. The application step can be repeated to a defined Apply foam. The pore size of the foam gets through the recipe and the foam generation as well as the drying step certainly.

In the filter medium according to the invention adhere Foam layers both to the carrier and - if more than one is present - to each other, and so, that during use, e.g. B. in a filter system, do not delaminate.

The Filter medium according to the invention may comprise several layers have the foam layer, which chemically and / or physically may be the same or different. For example can the filter medium according to the invention 1 to 5, preferably 2 or 3 foam layers. If several foam layers Applied to the tissue, so they are conveniently stacked on one side of the fabric.

Of the Term "tissue" within the meaning of the present invention is the generic term for manual or machine-made Weaving products such as cloth, velvet, velor, plush, Terry and in particular other textile fabrics from at least two right-angled or almost right-angled ones Thread systems.

The Longitudinal threads are called a chain or warp threads. The transverse threads are called Shot or weft threads. Connected are the threads by the type of connection of the thread crossing. Fadenverkreuzung means that threads in a certain rhythm (the Binding is called) above or below the transverse Go through threads. So that a tissue sufficiently slide is, should the warp and weft threads mostly relative be tightly woven. That is why the tissues show, with a few exceptions a closed goods image.

In the filter medium according to the invention can Fabric used with endless threads and / or textile yarns become.

When Thread materials for the fabrics may be preferred temperature-stable polymers, such as. Polyester, polyphenylene sulfide, aromatic polyamides, polyimide, PTFE (polytetrafluoroethylene), PBI (Polybenzimidazole), PBO (poly-p-phenylene-benzobisoxazole) or PEEK (polyetheretherketone), or inorganic materials, such as various Glass types (eg E, C, or AR glass), basalt, silica or mineral fibers, for example aluminum silicate, calcium magnesium silicate, be used. It is also possible to use tissue with 2 or 3 to use several, mutually different fibers. With these Thread materials can have the advantages described above can be achieved in a particularly favorable manner.

When especially suitable for the invention Filter medium have a twill or atlas binding with for the coating particularly suitable, comparatively slight height differences in the tissue surface proved. The (glass) fabric threads are usually Filament yarns, it can also be twice or triple twisted warp or weft threads with different Thread strength are used.

In a preferred embodiment of the filter medium according to the invention, the binding of the coating can be improved by portions of textured yarn components. Particularly advantageously, the textured glass yarns are used in the weft yarn, here for example, it is possible to replace a part of the multifilament yarns in a twisted yarn by textured portions. Thus, a triple-twisted weft yarn can be constructed from one, two or even three textured single yarns. Also in the warp yarns is the partial use of textured yarns, e.g. B. a textured yarn in the triple thread quite possible. Furthermore, yarns with non-textured yarns and yarns with textured yarns may also be used together in a predetermined order. The open pores who reduced by the use of proportions of textured yarns.

at Spun yarns are also common on polymer materials Base of staple fibers available and for use suitable in the carrier fabric.

It is favorable for the commercial application that both the support materials, d. H. the tissue, as well the coating components, d. H. the foam layer, under the thermal and chemical conditions of the respective filtration process the period of their use are stable. The user usually becomes several years of service required. The materials should So be selected in view of these requirements.

In a preferred embodiment of the filter medium according to the invention, the basis weight of the fabric, in particular of the glass fabric, is at least 350 g / m ² , for applications with jet-pulse cleaning particularly preferably 650 g / m ² to 850 g / m ² . A jet-pulse cleaning has a much higher stress on the filter medium due to the acceleration forces in the cleaning of the filter cake. First, an acceleration in the radial direction outwards, which is stopped abruptly when reaching the circular shape, then the filter material is accelerated by the re-entering flow again and hits at high speed on the Stützkorbdrähte, causing a momentary deceleration and friction effects Episode has. In order to survive this process many times, strength reserves are favorable. In addition, the denser fabric adjustment is beneficial to limit dust seepage in the acceleration / deceleration phases to the clean gas side. The basis weight data are preferably for glass yarns, when using other materials, the basis weight changes according to the material density, which the expert can easily determine due to his expertise.

As has already been explained above, is on the fabric at least one foam layer applied. The pores of this foam layer are preferably 1 .mu.m to 300 .mu.m, in particular 2 microns to 100 microns and especially 2 microns up to 50 μm. Become with these pore sizes the above advantages of the invention Filter medium achieved in a particularly favorable manner. Cheap is it doing a small pore size at close To adjust distribution.

In a particularly preferred embodiment of the invention Filter medium PTFE is used for foam coating, because thus the advantages described above in particularly favorable Way can be achieved and it turns out to be special proved suitable for the filter medium according to the invention Has.

Either the pore size as well as the air permeability can by the size distribution of the bubbles in the foam used to make the foam layer, be set, for. B. by the recipe (type and proportion of Foam generation component and foam stabilizer), the foaming aggregate (Generation principle, eg mixer with rotor / stator mixing head, speed control, Pin geometry, material and number in the mixing head), the foam aging in the conveyor system, the foam stability and also the dryer as well as the drying conditions.

By an increase in the proportion of foaming agent in the recipe For example, foaming can be facilitated by the foam. It creates a larger foam volume. To one Foam with a low mean bubble size to produce is its stabilization with conventional stabilizers cheap, because the smaller bubbles a higher have internal tension and have a tendency to stabilize without stabilization by reducing the mutual contact areas to assemble into larger foam bubbles.

Of the Expert knows how to set the above parameters, a favorable for the present invention Size distribution of the bubbles in the foam to reach. Typical recipes and suitable operating parameters exemplify the embodiments and can serve as a basis for the skilled person.

The aim is to produce a very uniformly fine-pored foam structure, which can be well anchored to the fabric surface or on an existing foam layer. The adhesion of the coating to the fabric surface can be achieved by partially sinking the foam coating into the fabric structure. The sinking can take place both at the crossing points of the warp and weft threads, as well as in cavities between the individual capillaries of the fabric threads. Furthermore, a (partial) melting of coating components, such as the fluorocarbon compounds explained in more detail below, or the addition of binders, such as acrylates, urethanes or polyvinyl acetates, Conveniently in amounts up to 35%, preferably 10-25%, bring about a physical attachment of the foam layer to the substrate. Also, a pressing or impressions of the foam layer can be used to improve the adhesion to the substrate but also between the foam layers. Here, the contact pressure and the construction of the pressing device should be chosen so that no destruction of the foam is caused.

Furthermore consists according to a preferred embodiment the possibility of using suitable additives preferably in amounts up to 35%, preferably 10-25%, a chemical Binding or interaction of the foam coating with opposite bring about the carrier material chemically reactive structures. As examples of these additives are silica or organosilicon components, such as. B. crosslinkable Polydimethylsiloxanes, to name.

The addition of solid, finely ground fillers, in particular in amounts of up to 60%, preferably 15-40%, such as. As quartz powder or other forms of SiO ₂ , gypsum, lime, talc, titanium dioxide, fiber short cuts with a fiber length of 3 to 10 mm, in particular 3 to 6 mm or glass beads, can be used to increase the coating stability. Typical particle sizes (with the exception of fiber short cuts) are in the range from 0.2 to 100 .mu.m, preferably a range of less than 20 .mu.m, with which the increased bond strength can be achieved in a particularly favorable manner.

In a preferred embodiment, the filter medium of the invention has a protective equipment, for example, with a coating weight of 10-70 g / m ² , preferably 30-60 g / m ² , based on friction-reducing substances, such as fluoropolymers, silicones or graphite.

Further the filter medium according to the invention can be a conductive Substance, wherein these in the tissue and / or the foam layer incorporated or applied to it. Examples of the conductive materials are coal and finely divided forms of metals, such. B. Powder or (short) fibers.

object The present invention further provides a method of preparation a filter medium, with a foam applied to a fabric and subsequently dried, whereby drying, i. H. the removal in particular of the water from the foam, a foam layer is formed on the fabric.

at the for the inventive method used materials are those described above.

following is the production of a filter medium according to the invention with special consideration of a glass fabric and a PTFE foam layer described as a particularly preferred embodiment, but it is expressly stated that this Method analogous readily to other materials, as above described can be applied.

at the production of the filter medium according to the invention there is a possibility of at least shares (if lower temperature resistant supports are present, up to 100% of the appropriate fluoropolymer; for partial use of PTFE or fillers on the inorganic carrier only up to 50% of the thermoplastic and the rest of PTFE, just for cost reasons to use; at low temperature resistant polymers almost any ratio from 20% fluorothermoplastics is possible) other fluorocarbon compounds (as PTFE), in particular fluorothermoplasts, add, so as to advantageously an adhesion improvement to achieve. For this purpose, perfluoroalkoxy polymers such as PFA (perfluoroalkoxy polymer, copolymer of tetrafluoroethylene and perfluorovinyl ether) or MFA (copolymer of tetrafluoroethylene and perfluoro-methyl-vinyl ether) are used. Other alternatives are copolymers based on tetrafluoroethylene and hexafluoropropylene (FEP) or tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride (THV), all of which have a lower melting point compared to PTFE exhibit.

In a preferred embodiment of the invention Method may include drying at 100 ° C to 150 ° C, especially about 120 ° C, for 1 to 3 minutes respectively.

In a further preferred embodiment of the invention Method may follow sintering after drying, preferably at a temperature of 340 ° C to 380 ° C, in particular about 350 ° C, for 3 to 5 minutes is carried out.

In this sintering treatment accompanying substances are at least partially thermally degraded, the Foam material, e.g. As PTFE, achieved a higher packing density and thus a higher stability. An alternative or addition is the admixture of the mentioned fluorothermoplastic components, when exceeding the lower melting point (examples: PFA 310 ° C, FEP 260 ° C) by about 20-30 ° C also improved adhesion and stabilization of the foam structure achieved.

Especially in the sintering treatment at higher temperatures can depending on the recipe mass losses occur, so that the coating weight of the foam layer after the sintering treatment low than before the sintering treatment can be.

Of the Stable foam, in particular the PTFE-stable foam, for the production The foam layer can be used with one in the textile industry common foam blenders are made, as he z. For example the carpet backing is used. The to Use of coming chemicals can be water-based dispersions be; foam generation can be achieved through the use of surfactant components and the controlled shearing action on the liquid formulation done in the mixer head. For this purpose, the z. B. Pins made of stainless steel or also plastic moldings, centrally arranged in the mixing head, usually cylindrical shaped rotor can be set in rotary motion. On the inner wall the likewise cylindrically shaped, concentrically arranged mixing head Pins are also attached to the fed recipe of a to suspend intense shearing. Important criteria of foam quality and foam stability are the rate of disintegration and dewatering. The person skilled in the art knows that for the production of the stable foam applicable method and the necessary substances.

Of the Foam applied to the fabric should desirably not, in particular not completely, sinking into the tissue and not when drying, z. B. in an oven, disintegrate because it represents the separation-active filter media surface. The pore distribution in the applied and dried foam layer results from the foam structure of the stable foam. The foam recipe So should be sufficiently stable, so that the foam does not Applying to the tissue at the contact surface disintegrates and is not absorbed by this.

In a preferred embodiment of the invention Process for the preparation of the filter medium is the Foam weight 150 g / l to 300 g / l, preferably 200 g / l to 300 g / l, as thus foam layers for the inventive Filter medium can be produced with which the above described advantages are achieved particularly favorable can.

The Foam weight (defines the air or water content in the foam) also provides information about the wetting or penetration behavior of the foam. A high water content leads to a faster Wetting of the carrier and has a higher penetration depth and decay rate result. Typical parameters can be found in the Examples of the experimental procedure. Furthermore the expert knows methods and necessary materials, to set these parameters.

Of the from the blender unit escaping foam can via a suitable compound, for. B. a plastic tube, for a promoted in this area usual order system with which the job is done on the fabric surface. For example, a table-top squeegee or a squeegee are suitable or blanket squeegee. It can also be a job by means of Zwickelfoulard or foam padder. The foam application can be done before Intake of the fabric web into a dryer as evenly as possible over the Goods width done.

about the viscosity of the batch liquor, the foam density, the Foam viscosity, foam stabilization and temperature can control the penetration depth of the applied foam and on the carrier material can be adjusted. The person skilled in the art is aware how he can adjust the parameters and he can by simple Routine experiments determine the optimal parameters and then adjust.

It is particularly advantageous that only so much foam is applied that during drying the evaporation of the water contained in the foam takes place without crack formation in the dry foam layer. Cracking in the foam layer would result in a significant deterioration in the filtration efficiency of the filter medium, as it would be a preferred point of penetration. The application rates may be 10-50 g / m ² , preferably 20 to 40 g / m ² , more preferably 30 to 40 g / m ² , per line. The total application amount when more than 1 layer is applied is preferably 10-70 g / m ² . With these amounts, the above advantages are achieved in a particularly favorable manner.

The aqueous foam is dried during drying, for. B. when passing through an oven, the water gradually removed by evaporation or evaporation. With sufficient stabilization, the foam structure is maintained throughout the drying process. The formulation of the formulation with additions of foam-stabilizing components or components which give the foam layer more flexibility, such as. As polyurethanes or soft set acrylates, allows further litigation without damaging the foam layer (eg., Winding after drying).

Around the tissue in the later application, especially before mechanical To protect load from the support basket wires, can additionally a full bath impregnation of the filter medium with protective equipment based on friction reducing chemicals are carried out. Fluoropolymers, silicones, have proven to be particularly suitable and graphite. The process may advantageously be prior to foam coating be performed, but is also possible as aftertreatment. With this impregnation can be both mechanical Stresses as well as chemical influences on the fabric material intercept.

When Particularly advantageous is the full bath order one PTFE formulation in combination with a sintering step, the one particularly chemical resistant equipment allowed. There is also the possibility of the temperature at the Carrier adapt and at least proportionally less temperature resistant and to use less high melting aids, such as PFA, MFA, FEP or THV.

• Schaumgewichte: 150–300 g/l, vorzugsweise 200–300 g/l;
• Auftragsmenge/Strich: 10–50 g/m², vorzugsweise 20–45 g/m², besonders bevorzugt 30–40 g/m²;
• Luftdurchlässigkeit des Gewebes: 100–250 l/dm²min, bevorzugt 120–160,
• Luftdurchlässigkeit des Filtermediums: 20–100 l/dm²min, bevorzugt 30–80 l/dm²min, besonders bevorzugt 35–50 l/dm²min;
• Gesamtauftragsmenge: 10–70 g/m²; vorzugsweise 15 g/m² bis 50 g/m², besonders bevorzugt 20 g/m² bis 45 g/m² und ganz besonders bevorzugt 30 bis 40 g/m²;
• Rakelspalt: 0,1 bis 0,3 mm;
• Trocknen 100–150°C, bevorzugt 120°C während 1–3 Minuten;
• Sintern 340–380°C, bevorzugt 350°C, während 3–5 Minuten;
• Porengrößen der Schaumschicht: min. ca. 1 μm bis 300 μm, bevorzugt 2 μm bis 100 μm, besonders bevorzugt 2 μm bis 50 μm;
• Auflagenstärke: 0,5 bis 1,0 mm
• Die Dicke des eingesetzten Gewebes hängt von Flächengewicht und Bindung ab und beträgt günstigerweise 0,2 bis 1,2 mm;

Some of the data of the filter medium according to the invention and of the method according to the invention already described above are summarized below.

• Foam weights: 150-300 g / l, preferably 200-300 g / l;
• Application amount / line: 10-50 g / m ² , preferably 20-45 g / m ² , more preferably 30-40 g / m ² ;
• Air permeability of the fabric: 100-250 l / dm ² min, preferably 120-160,
• Air permeability of the filter medium: 20-100 l / dm ² min, preferably 30-80 l / dm ² min, more preferably 35-50 l / dm ² min;
• Total order quantity: 10-70 g / m ² ; preferably 15 g / m ² to 50 g / m ² , more preferably 20 g / m ² to 45 g / m ² and most preferably 30 to 40 g / m ² ;
• Blade gap: 0.1 to 0.3 mm;
• Drying 100-150 ° C, preferably 120 ° C for 1-3 minutes;
• Sintering 340-380 ° C, preferably 350 ° C, for 3-5 minutes;
• Pore sizes of the foam layer: min. about 1 μm to 300 μm, preferably 2 μm to 100 μm, particularly preferably 2 μm to 50 μm;
• Pad thickness: 0.5 to 1.0 mm
• The thickness of the fabric used depends on basis weight and bond, and is desirably 0.2 to 1.2 mm;

object The present invention further relates to the use of the invention Filter media for industrial dedusting. Can do this the filter media of the invention analogous the previously used by the prior art filter media be used.

The following examples in conjunction with the attached figures explain the invention without, however, restricting it to in which

1 the results of the filter test after VDI 39 26 and

2 show the results of a long-term test.

Examples

It the following formulations were prepared 1 to 4, wherein the abbreviation "GT" parts by weight means.

• 1. 80 GT PTFE dispersion
• 20 GT polyester urethane dispersion
• 0.5 GT fatty amine derivative (Dicrylan Foamer HP, Huntsman Textile effects)
• 7 GT ammonium alkylamine stearate

• 2. 85 GT PTFE dispersion
• 15 GT polyester urethane dispersion
• 0.5 GT fatty amine derivative (Dicrylan Foamer HP, Huntsman Textile Effects)
• 15 GT ammonium alkylamine stearate
• 2.5 GT acrylic copolymer emulsion (Dicrylan Thickener HV 30, Fa. Huntsman) adjust some ammonia to pH

• 3. 100 GT PTFE dispersion
• 0.5 GT fatty amine derivative (Dicrylan Foamer HP, Huntsman Textile Effects)
• 15 GT ammonium alkylamine stearate
• 2.36 GT Acrylic Copolymer Emulsion (Dicrylan Thickener HV 30, Fa. Huntsman) Adjust ammonia to pH

• 4. 100 GT PTFE dispersion
• 0.5 GT fatty amine derivatives (Dicrylan Foamer HP, Huntsman Textile effects)
• 10 GT ammonium alkylamine stearate
• 2.17 Acrylic copolymer emulsion (Dicrylan Thickener HV 30, Fa. Huntsman adjust some ammonia to pH

• Viscosity of the starting liquor: 5-8 dPas
• pH value of the starting liquor: 8.5-9.5
• Foam density 180-210 g / l

• Mixer settings: Pump 20 l / h Mixhead 400 l / min, density 1300 g / l

It are commercially available water-based dispersions, no further water was added in the examples. assignment on (glass) tissue by means of a table doctor or a squeegee.

For the filtration tests shown below, Formulation Example 1 was applied in three successive strokes to a 445 g / m ² basis weight glass cloth already provided with PTFE protective equipment. It is a twill weave with a material thickness of 0.55 mm and an average air permeability of 235 l / dm ² min. The total coverage of the foam coating is 40 g / m ² , the air permeability of the finished filter medium on average 36 l / dm ² min.

to Evaluation of the obtained filter media became the following Filter tests performed.

1. Filter test according to VDI 3926 with 100 cleaning cycles

The results are in the table and the 1 shown.

Compared with high-quality, complex-to-produce impregnated PTFE needle felt, the foam-coated glass fabric shows a comparable emission behavior. The clean gas concentration is consistently at the same, very low level of less than 1 mg / m ³ . As far as the differential pressure behavior is concerned, the filter medium according to the invention starts at a noticeably higher level, but it is noteworthy that the differential pressures equalize at the end of the experiment. For a longer test run, it is therefore to be expected that the foam-coated glass fabric will show a more favorable differential pressure behavior.

The differential pressure is expected to be higher than standard polyester needled felt, but the emission is lower by a factor of 5, which makes it suitable for applications with severe limits. In addition, there is the much higher temperature resistance of the filter medium according to the invention. Table results of the filter test test conditions time-controlled, cleaning after 270 s, 100 cycles (equivalent to 450 min) Test dust: Pural SB (Lot 140512) raw gas concentration: 4.8-5.2 g / bm ³ Filter surface load: 3 m / min Temperature: room temperature test result quality Glass fabric with PTFE foam coating PTFE needle felt with impregnation Standard polyester needle felt Weight [g / m ² ] before test 470 701 534 after test 500 795 664 Air permeability at ⎕p = 200 Pa [l / (dm ² min)] before test 36 105 147 after test 9 19 45 mean differential pressure [Mbar] 100th cycle 6.0 5.7 2.8 dust deposition [G] after 100. cleaning 0.5 1.4 2.0 Total emission [mg / bm ³ ] 1.-100. cycle 0.47 0.52 2.48

The filter test was carried out on the basis of VDI 3926

2. Long-term test (filter hose in pilot plant filter plant)

The results are in the 2 shown.

While in the filter test over 100 cleaning cycles based on VDI 3926 showed significant advantages of the standard polyester needle felt with respect to the differential pressure behavior compared to the filter medium according to the invention, you will find in the long-term test for the inventive foam-coated glass fabric a similar course as the standard polyester needle felt. The absolute difference between the differential pressures initially increases and then decreases significantly again until the end of the experiment. The relative difference drops from 239% to 33%. From an extrapolation of the available data, it becomes clear that the differential pressures and thus the energy consumption will first equalize over a longer service life. Subsequently, the filter medium according to the invention over long stretches of its operating time - which corresponds to a multiple of the test time - in all probability have a more favorable differential pressure behavior than the standard polyester needle felt.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - VDI 39 26 [0052]
• - VDI 3926 [0061]
• - VDI 3926 [0063]

Claims (23)

A filter medium comprising at least one foam layer applied to a fabric, the filter medium having an air permeability of from 20 to 120 l / dm ² min. The filter medium of claim 1, wherein 1 to 5 foam layers are applied. Filter medium according to one of the preceding claims, wherein the thread material for the fabric is a polymer and / or is an inorganic material. The filter medium of claim 3, wherein the polymer is selected is polyester, polyphenylene sulfide, aromatic polyamides, Polyimide, polytetrafluoroethylene, polybenzimidazole, poly-p-phenylene-benzobisoxazole or polyetheretherketone. Filter medium according to claim 3, wherein the inorganic Material is selected from glasses, basalt, silica, mineral fibers or mixtures of two or more of these materials Filter medium according to one of the preceding claims, wherein the fabric comprises a proportion of textured yarn components. The filter medium of any one of the preceding claims, wherein the fabric has a basis weight of at least 350 g / m ² . Filter medium according to one of the preceding claims, wherein the foam layer pores having a pore size in the range of 1 .mu.m to 300 .mu.m, in particular 2 .mu.m to 100 microns, especially 2 microns to 50 microns Filter medium according to one of the preceding claims, wherein the foam layer comprises polytetrafluoroethylene. Filter medium according to one of the preceding claims, wherein the foam layer contains aggregates containing a Effect binding or interaction with the tissue. The filter medium of claim 10, wherein the aggregate Silica or organosilicon components. Filter medium according to one of the preceding claims, wherein the foam layer fillers to increase having coating stability. The filter medium of claim 12, wherein the filler comprises solid, finely-ground fillers, such as quartz powder or other forms of SiO ₂ , gypsum, chalk, talc or titanium dioxide, a fiber cut or glass beads. Filter medium according to one of the preceding claims, with protective equipment based on friction reducing Substances is applied. The filter medium of claim 14, wherein the protective equipment selected from the group of fluoropolymers, silicon and graphite is. Process for producing a filter medium according to one of claims 1 to 15, wherein a foam on a Tissue is applied and dried. Process for producing a filter medium according to Claim 16, wherein the foam comprises fluorocarbon compounds. The method of claim 17, wherein the further fluorocarbon compound is a fluorothermoplastic. Method according to one of claims 16 to 18, wherein the drying at about 100 ° C to 150 ° C. for 1 to 3 minutes Method according to one of claims 16 to 19, wherein after drying, sintering at a temperature of 340 ° C to 380 ° C for 3 to 5 minutes he follows. Method according to one of claims 16 to 20, wherein the foam weight 150 g / l to 300 g / l, preferably 200 g / l to 300 g / l. A method according to any one of claims 16 to 21, wherein the application amount of the foam is 10 to 70 g / m ² . Use of the filter medium according to one of the claims 1 to 15 for industrial dedusting.