EP3956047A1

EP3956047A1 - Method for producing a multi-layer filter medium and a filter medium produced according to this method

Info

Publication number: EP3956047A1
Application number: EP20785474.6A
Authority: EP
Inventors: Bernhard Schlichter; Martin Winter
Original assignee: Hydac Process Technology GmbH
Current assignee: Hydac Process Technology GmbH
Priority date: 2019-09-28
Filing date: 2020-09-28
Publication date: 2022-02-23
Also published as: CN114173902A; KR20220069922A; US20220241708A1; JP2022549400A; WO2021058821A1; DE102019006765A1

Abstract

The invention relates to a method for producing a multi-layer filter medium, comprising at least the following production steps: providing a woven fabric layer (12) having passage points (24) for fluid; providing a nonwoven fabric layer consisting of a spunbond (18) and having additional passage points (28) for fluid; and connecting the two layers (12, 18), which have been laid on top of one another, along contact points (30) by melting the nonwoven fabric layer (18) in such a way that the additional passage points (28) become enlarged and at least some of the melted spunbond material flows to the contact points and accumulates there, subsequently forming curing solid connection points between the two layers (12, 18).

Description

Method for producing a multi-layer filter medium and a filter medium produced according to this method

The invention relates to a method for producing a multilayer Fil termediums and a filter medium produced by this method.

The pertinent manufacture II processes together with the associated filter media are known in a large number of embodiments.

DE 10 2013 000 932 A1 shows a filter medium, in particular provided for hydraulic filters, with at least one layer comprising at least one first structure, which has warp and weft threads, and at least one further, second structure with predeterminable filtration properties, the respective first structure is at least partially formed from multifilaments in the form of twisted threads.

DE 10 2013 000 933 A1 discloses a multi-layer filter medium for the filtration of fluids which has at least one support layer, one filter layer and one drainage layer, with an additional drainage layer forming a three-dimensional structure being provided to enlarge the flow channels formed for the fluid flowing through. DE 10 2010 025 218 A1 also discloses a multilayered filter medium, on at least one side of which a support structure rests flatly, which consists of at least one individual fabric made up of weft and warp threads, with at least one set of weft and warp threads / or warp threads overlap more than two adjacent warp or weft threads to form a long-floating bond.

In the above-mentioned prior art documents, Herste II methods for obtaining such filter media are also described. Furthermore, filter media for fine filtration in automatic backwash filters (DE 10 2017 002 646 A1, DE 10 2011 1 11 457 A1) are on the market today, with filter materials regularly used for the filter medium based on stainless steel meshes. Compared to known slotted sieves, micro-sieves and similar sieve material, filter fabrics in the range from 5 to 100miti basically offer a particularly high degree of open filter surface and consequently a high dirt holding capacity with minimal pressure loss. Wire meshes have the advantage over plastic meshes that their mechanical and thermal stability is much higher. Furthermore, compared to woven polymer fibers, wire meshes have thinner wires with the same fineness and thus a higher porosity for the fluid to be filtered. For this reason, almost exclusively stainless steel mesh is used in automatic backwash filters.

Due to the periodic backwashing, the filter medium in the backwashing filter experiences high alternating loads. The filter medium is subjected to high mechanical loads due to the regular flow reversal and the constantly changing differential pressure, which significantly limits the service life of the filter material or the filter medium. In order to make the relevant filter medium more stable and therefore more durable, the fine wire mesh layers are often sintered with the coarser, adjacent support and drainage layers. However, the higher mechanical stability purchased in this way has resulted in the following disadvantages in practice:

Sintered fabric structures are generally very expensive due to the complex and energy-intensive manufacturing process involved. The individual fabric layers must be washed thoroughly and calendered beforehand in order to create more contact surfaces between the fabrics, which in turn reduces the open area. The mentioned sintering takes place at high temperatures, usually a few degrees below the melting temperature of the stainless steel used in a vacuum or under a protective gas atmosphere.

Sintering is usually a discontinuous process and sintered fabrics are limited in size by the size of the furnaces used. Typical panel sizes are therefore in the range of approx. 1.2 by 1.2 m. For filter construction, this means that several plates often have to be put together for larger filter devices, which generates additional work steps in the form of welding processes and the associated additional costs. Wire mesh sintered together is rigid and sheet-like and can therefore only be pleated to a limited extent. Furthermore, the porosity and the free open area of a sintered fabric structure decrease significantly, which means for the filtration process that the dirt holding capacity is reduced with higher pressure losses. Experience has shown that the performance losses caused by sintered materials are in the range of approx. 20 to 30% in practice, with the result that a corresponding filter device must be designed to be significantly larger in order to be able to install the additional filter surface required for comparable performances. Based on this prior art, the invention is based on the object of providing a process and product solution for a filter medium which is significantly improved over the known solutions and which is also superior to sintering fabric layers for the filter media structure.

A pertinent object is achieved by a method with the features of patent claim 1 and a filter medium with the features of patent claim 10.

The method according to the invention for producing a multilayer filter medium is characterized by the following production steps:

Providing a fabric layer which has passage points for fluid;

Providing a nonwoven layer consisting of a spunbonded nonwoven, which has further passage points for fluid; and - connecting the two superimposed layers along contact points by melting the fleece layer in such a way that the melted spunbond material runs at least partially to the contact points while enlarging the further passage points and cumulatively solid connection points between the two layers are then generated at these cumulative hardening.

Furthermore, a filter medium according to the invention, in particular produced according to the above method, is characterized in that at least one metallic fabric layer is firmly connected to an at least partially melted nonwoven layer made of plastic material. In contrast to the known filter media solutions involving the sintering of the wire mesh with one another, the mechanical stabilization takes place through the use of a melt fleece as the fleece layer. In this case, the weight per unit area of the fused fleece is preferably selected and the thermal hotmelt bonding process is carried out in such a way that the fused fleece creates an intermediate space with high porosity between the wire meshes to be connected. In contrast to the sintering of the wire mesh, in which the individual layers have to be calendered beforehand in order to be able to form sufficient contact surfaces, the hot melt adhesive keeps the individual mesh layers at a distance. This intermediate space between the fabric layers thus acts as an additional drainage while the melted thermoplastic simultaneously connects and stabilizes the fine filtration layer with the support layer. This drainage makes maximum use of the open filter surface of the fine fabric as a filter medium.

In a preferred embodiment of the method according to the invention, it is provided that the thin nonwoven threads of the nonwoven layer tear off during the melting process, so that the hot melt adhesive formed by the nonwoven layer, in particular where the fabric cover layers do not lie directly against one another with an at least three-layer filter medium, contracts selectively and thereby forms spherical or island-like accumulations in the form of clusters. As a result, the wire mesh layers are ultimately only glued to one another at isolated points and do not form a homogeneous, large-area bond with one another. In this way, the high porosity in the tissue structure is retained and a correspondingly high fluid permeability through the tissue material is still ensured.

Compared to sintered wire mesh structures and other filter media, the porosity and the free open area for the Under no circumstances will filtration of a tissue structure connected in this way. The fused structure is mechanically much more stable and in terms of pressure losses and dirt holding capacity comparable to non-sintered filter media of the type mentioned above.

Compared to sintered wire mesh structures, which are rigid and sheet-like, the structures that are melt-bonded to one another still have a high degree of flexibility, which is advantageous during the intended backwashing of filter elements, since the individual layers of fabric due to the punctual connection via a preferably thermoplastic filter material as a fleece material still have a certain freedom of movement and stored dirt between the interconnected tissues can be better rinsed out.

It has been shown that the spherical, insular or cluster-like connection points between the individual adjacent fabric layers of the filter medium result in thermoplastic bridges that have a dampening effect on the fabric in relation to the load changes to be carried out in one direction Filtration and backwashing of the filter element material in the opposite direction. This has no equivalent in the prior art.

Further advantageous embodiments are the subject of the other sub-claims.

In the following, the method according to the invention and the associated filter medium are explained in more detail using an exemplary embodiment according to the drawing. Show in principle and not to scale representation

Fig. 1 in idealized form a section through a five-layer Filter medium, the individual fabric layers of which are connected to one another via insole-like or cluster-like melting points;

FIG. 2 shows a plan view of a section of a spunbonded nonwoven as it is used in the filter medium according to FIG. 1; FIG. and

3 and 4 show a detail from the filter medium according to FIG. 1 in plan view, in which the spunbonded nonwoven according to FIG. 2 is placed on a wire mesh underneath; once in the partially unconnected or once in the fully connected, melted state.

Fig. 1 shows in the manner of a cross section a preferred Ausfüh approximate form of the filter medium according to the invention using five layers 10, 12 and 14, 16 and 18. The illustration is idealized because due to the bonding, virtually two of the five layers in their original Structure of this kind no longer exist. The filter medium according to Lig. 1 is itself a three-dimensional fabric body, the layers 10, 12 being made up of warp and weft threads 20, 22, whereas the layers 16 and 18 are made of a spunbonded nonwoven. The warp and weft threads 20,

22 fabric layers 10, 12 are preferably made in a plain weave and the individual shutters 20, 22 of each layer 10, 12 delimit individual passage points 24 with a square cross-section, as exemplified in Lig. 3 and 4 for those looking towards the Lig 1 seen, lower layer 12 are shown. In particular, in the present embodiment, the fabric filter layer 10 is constructed in the same way as the Gewebela ge 12. The actual liltration fabric layer 14 differs from the mentioned warp and weft thread layers 10, 12 in that it is formed from what is known as a lilter weave, in which the individual threads 20, 22 do not form any passage points with a free, square opening cross-section, but rather the threads 20, 22 are designed to lie against one another in such a way that the fluid is repeatedly deflected at the tissue threads 20, 22. In this respect, in the area where two adjacent threads are superimposed, the thread deflection creates a type of three-dimensional filter pore that is not tightly closed in a fluid tight manner by the adjacent spun or melt fleece in the melted state.

The spunbond layers 16, 18 introduced between the layers 10 and 14 and 14 and 12 are also designed as three-dimensional surfaces. Such spunbonded nonwovens in the form of the layers 16, 18 are basically known and represent a textile fabric consisting of individual fila elements 26. The filaments 26 are placed on a conveyor belt immediately after the generation and pre-stretching and compressed in the process. As a result of the softening that is still present (thermoplastic property), the filaments 26 solidify and form the spunbonded nonwoven, the aforementioned solidification also being achieved with chemical binders or by so-called needling (WiKipedia). The individual filaments 26 for the spunbonded nonwoven shown in FIG. 2 delimit further passage points 28 with varying free passage cross-sections between them.

In the illustrated five-layer structure of a filter medium according to FIG. 1, the fabric layer 10 arranged at the top when looking at FIG. 1 is a so-called square mesh fabric with individual wires, preferably with a wire thickness in the range from 0.15 to 0.25 mm, wherein the respective mesh size for forming the passage points 24 is between 100 to 600miti. The main function of this first fabric layer 10 is to support and stabilize the sensitive central filter fabric layer 14, which is preferably designed as a “smooth weft”. The information is only given By way of example and in principle, other types of fabric with a comparable thickness / material strength as well as an open filter surface or mesh size can also take on this task. The specified square mesh allows good foldability, especially with pleated filter media structures, and square mesh can also be used when used in so-called smooth sieve baskets within backwash filter devices. Instead of the fabrics shown, Streckme metals, welded grids, microsieves or slotted screens (all not shown) can take on the task at hand. In the present exemplary embodiment, the fabric layer 12 located at the bottom as seen in FIG. 1 is identical to the first layer 10, although this is not mandatory.

The middle fabric filter layer 14 is a so-called weave fabric with a filter fineness of, for example, bqmiti. The wire thickness of the chain 20 is 0.135 mm, for example, and the wire thickness of the weft 22 is 0.09 mm. The weave in question is the finest woven filter layer within the layer structure 10, 12, 14 and, with its filter fineness, determines the overall cleaning performance. Furthermore, with its passage points 24, it causes almost the entire flow resistance for the five-layer filter medium according to FIG. 1. Plain weave fabrics are used in backwash filters of the usual design due to their good backwash properties with filter fineness of less than 10Omiti, preferably of filter fineness between 20 and bqmiti. The wire thicknesses for the warp threads 20 and the weft threads 22 are typically in the order of 30 to 140miti in such braid fabrics.

The spunbond filter layers 16, 18 are regularly based on polyamide with filament or fiber thicknesses of approx. 20 to 40miti with a surface weight of approx. 5 to 40 grams per square meter and a nonwoven thickness of 0.25mm, which means a porosity of 80 % results. In the present exemplary embodiment, however, a co-polyamide spunbonded nonwoven is preferred used, with a melting range between 120 to 135 ° C and an MFI value averaging 30g / 10 minutes at 160 ° degrees. The bonding temperature required for the Herste II process according to the invention is 140 to 160.degree. If necessary, other thermoplastics can also be used for the spunbonded nonwoven layer 16, 18, for example polyester or polyolefin materials. Depending on the choice of spunbond material, the material resistance or chemical resistance of the finished filter medium can be adapted to the respective requirements in practice, with all layers 10, 12, 14, 16 and 18 contributing to the overall filter performance of the element material.

The Herste II method according to the invention is now characterized in that the individual layers 10, 12, 14, 16 and 18 as shown in FIG. 1 are placed on top of one another with their three-dimensional surface extension, as shown. By appropriate melting of the spunbond material at the mentioned temperatures of 140 to 160 ° C, tear the individual, continuous filaments 26 shown in Fig. 2 and due to the surface tension of the plastic material than shrink the filaments 26 to form insular or cluster-like contact points 30 and According to the representation according to FIG. 1, only individual residual filaments 32 remain, which are separated from one another. The fused connections between the individual layers are produced under pressure by, for example, a press or parts of a Laltmaschine acting on the upper and / or lower fabric layer 10, 12 during the heating process (not shown). In particular when using conventional folding machines for pleating the filter medium, the layer joining process can be carried out continuously.

In particular, FIGS. 3 and 4 show how the filament material according to FIG. 2 is initially only placed on the lower fabric layer 12 (see FIG. 3), in order then in the subsequent heating process with tearing open the filament. elements 26 to form the cluster-like contact points 30 (see FIG. 4). The porosity of the overall structure can be adjusted via the amount of hot melt adhesive in the form of the material input for the spunbonded nonwoven layers 16, 18 and the contact pressure during the folding process for a pleated filter medium. Since the fleece filter layers 16, 18 based on the thermoplastics mentioned and only require low application temperatures compared to the sintering of the wire mesh with low surface weights, the production of such a mesh structure, as shown by way of example in FIG. 1, proves to be less energy-intensive and in this respect much cheaper. The calendering of individual fabrics is not required for gluing, whereby the open area of the fine fabric in the form of the middle filter layer 14 is retained to a maximum. In this respect, this saves a further work step and, in turn, corresponding costs. The gluing process mentioned here can in principle be carried out continuously in a folding machine (not shown) immediately after the folding process for a pleated filter mat. This is possible because the temperatures are relatively low at below 200 ° C and no protective gas atmosphere is required. The production of a mesh pack pleated to that extent as a filter medium with stabilized folds then takes place in one work step; namely, the fabrics are folded and the mesh pack produced is heated by an accompanying heater immediately behind the folding knife. This has the advantage that during the thermal bonding process the necessary pressure can also be permanently exerted on the fabric layers during the joining process, and thus the individual fabric layers can form a defined bond with one another.

Since the individual layers of fabric are only glued immediately after the folds have been folded over, the individual layers of fabric can be pleated in this way without any problems. In this respect there is a risk of folds breaking practically impossible, since the individual layers 10, 12, 14, 16, 18 still have sufficient freedom of movement during the folding process.

The gluing of the fabric layers 10, 12, 14 by means of thermoplastic spunbond in the form of the layers 16, 18 enables the production of mechanically stable fabric structures with comparatively little use of material and space. Supporting fabric layers can generally be chosen thinner, which means that more filter material can be accommodated in the same space when the fabric is folded, which in turn increases the power density of the overall filter apparatus or, with given power, the respective filter apparatus can be made correspondingly geometrically smaller than that known solutions.

According to an embodiment not shown in detail, there is also the possibility of providing the fabric layers 10, 12, shown at the top and bottom in FIG. 5, acting as drainage with additional protective and support layers. In addition to additional grids or perforated sheets, helical wire coils running on the outer circumference can also be used for this purpose, as shown by way of example in DE 102 202 73 A1.

The five-layer structure according to FIG. 1 is not mandatory for the execution of the process solution according to the Invention. In this way, structures with more than five layers can also be produced; but preferably also filter media with only three layers. However, it is already sufficient, under certain circumstances, as a pre-stage for a more complex filter medium within the meaning of the invention, to connect only one fabric filter layer with a fleece filter layer, as stated. The filter medium produced in this way can be set up flat or pleated to form a hollow cylinder (not shown), in order then to be provided with end caps or other closing parts at the end to produce an independent, commercially available filter element (not shown). According to the procedure Ren manufactured filter element material or the filter elements are intended as backwash elements in particular for use in backwash filter devices and are particularly suitable for the solid-liquid separation of low-viscosity fluids. In addition to backwash filter applications in water filtration, the technology can also be used in backwash filters for lubricating oil filtration, especially in large engines.

Spunbonded nonwovens made of polyamide material with a weight per unit area of 8 g / m ² and melting temperatures of approx. 130-140 ° C have proven to be useful flat structures. In this respect, the melting time for the connection is approx. 15 minutes, so that short melting times are achieved at a low melting point. In particular, it can be seen that the melted spunbonded nonwoven fabrics contract to the desired extent to the desired extent.

Multi-layer filter media with a structure using a square mesh fabric of 250miti for the support fabric (w = 0.25 mm; d = 0.2 mm) have proven to be particularly advantageous. This is followed by a polyamide spunbonded nonwoven with a basis weight of 8 g / m ² and then a fine filter fabric is used, for example in the form of a smooth filter weave with 50 mm (mesh: 72 x 380; warp: 1 12 mm; weft wire: 73 mm). In the sequence, a polyamide spunbond with a weight per unit area of 8 g / m ² is again used and subsequently a support fabric in the form of a square mesh fabric 250miti (w = 0.25 mm; d = 0.2 mm) is again provided.

Claims

Patent claims

1 . Method for manufacturing a multi-layer filter medium, with at least the following manufacturing steps:

Providing a fabric layer (12) which has passage points (24) for fluid;

Providing a nonwoven layer consisting of a spunbonded nonwoven (18) which has further passage points (28) for fluid; and - connecting the two superimposed layers (12, 18) ent long from contact points (30) by melting the fleece layer (18) in such a way that the melted spunbond material runs at least partially to the contact points (30) while enlarging the further passage points (28) and then cumulatively solid connection points between the two layers (12, 18) are generated at these cumulative hardening.

2. The method according to claim 1, characterized in that the fleece layer (18) when melting with at least partial abandonment of their filament structure and under the effect of the surface tension of the melted fleece material converges to spherical or cluster-like nodes at the assignable contact points (30) , from which the fixed connection points are then formed by curing.

3. The method according to claim 1 or 2, characterized in that the fleece layer (16, 18) each received between two fabric layers (10, 14; 14, 12), forms a three- or five-layer filter medium.

4. The method according to any one of the preceding claims, characterized in that the respective fabric layer (10, 12, 14) is made of warp (20) and weft threads (22), and that the respective Fleece filter layer (16, 18) is formed from at least one plastic thread material.

5. The method according to any one of the preceding claims, characterized in that with a five-layer structure of the filter medium, the two outermost fabric layers (10, 12) are formed from square mesh, that the middle fabric layer designed as a filter layer (14) from a braid is formed, and that the fleece layer (16, 18) is arranged between the respective square mesh and the braid.

6. The method according to any one of the preceding claims, characterized in that the square mesh fabric is used in the fluid filtration on for drainage and that the braid is used for the actual particle cleaning from the fluid.

7. The method according to any one of the preceding claims, characterized in that in the case of a five-layer filter medium, this is included between protective and / or support layers, which are each formed from a perforated plate, a grid or from a helical wire helix.

8. The method according to any one of the preceding claims, characterized in that the respective filter medium is smooth-surfaced or pleated and set up to form a hollow cylinder, forms a filter element or a preliminary stage of a filter element.

9. The method according to any one of the preceding claims, characterized in that at least during the melting of the respective fleece layer (16, 18), the composite layer is obtained by applying a pressing force.

10. Filter medium, in particular produced by a method according to one of the preceding claims, characterized in that at least one metallic fabric filter layer (10, 12, 14) is firmly connected to an at least partially melted fleece filter layer (16, 18) made of plastic material .

1 1. Backwash filter with a filter medium according to claim 10.