Method for producing a multi-layered filter medium

Abstract

The invention relates to a method for producing a multi-layered filter medium (10) for use in an electrostatic separator with filter functionality, comprising the method steps of: a) producing or providing a multi-layered starting layer composite (12), comprising: a.1) an electrically conductive first conductor layer (14), a.2) an electrically conductive second conductor layer (16), and a.3) an intermediate layer (18) arranged between the first conductor layer (14) and the second conductor layer (16), the intermediate layer (18) comprising at least one dielectric layer (20) and at least one activated carbon layer (22), b) severing part of the multi-layered starting layer composite (12), the severing comprising mechanical separation using a separating tool (24), the separating tool (24) having a cutting edge with a cutting bevel angle of 90° or less, wherein at least the first conductor layer (14), the activated carbon layer (22), the dielectric layer (20) and the second conductor layer (16) of the multi-layered starting layer composite (12) are severed, and the severing comprising either b1) a shearing cut, or comprising b2) a bursting cut, or comprising b3) a crush cut, in which the separating tool (24) cuts through one of the conductor layers (14, 16) and at least one dielectric layer (20) of the intermediate layer (18) before the activated carbon layer (22).

Description

[0001] Process for producing a multi-layer filter medium

[0002] Description

[0003] The invention relates to a method for producing a multilayer filter medium for use in an electrostatic precipitator with filter functionality. Also disclosed are a corresponding multilayer filter medium produced by the method and a filter insert comprising the filter medium.

[0004] Modern filtration technology now offers numerous efficient alternatives and further developments to the well-known processes for separating unwanted components from fluid flows, which are mostly based on essentially mechanical separation, usually on a partially permeable filter element, which can, for example, consist of a porous material.

[0005] One of these developments, which is used particularly for gas purification, is so-called electrostatic precipitation, whereby the devices used are also referred to as electrostatic precipitators. In these electrostatic precipitators, the particles to be removed are first ionized by an electrode and then deposited on an oppositely charged collecting electrode. Such electrostatic precipitators are used primarily in industrial plants. However, the performance characteristics of cabin air filters, especially for use in vehicles, are subject to different requirements, for example, the reliable separation of pollen and / or particulate matter and / or odors and / or exhaust gases.

[0006] To meet these requirements for cabin air filters, the concept of electrostatic separation, which in many cases is not strictly speaking filtration, was combined with mechanical separation processes to obtain high-performance filter elements. By combining conventional filter materials with an ionization device, the separation efficiency of filters can be significantly increased in many cases. For the purpose of clear identification, the corresponding filter elements are referred to as electrostatic precipitators with filter functionality within the scope of the present invention. However, it has been observed that the separation efficiency of such filter elements can decrease over the service life of the filter element, which is often attributed to a reduction in the electrostatic charge in the filter material over time.

[0007] To solve this problem, it has been proposed to design electrostatic precipitators with filter functionality in such a way that polarization of the filter material can be induced in the filter insert by applying a voltage to two polarization elements through the creation of an electric field. In combination with an ionization device, this polarization of the filter material can enable efficient separation, which can advantageously usually be maintained over the entire service life of the filter element. Background information on the basic technology is disclosed, for example, in WO 2007 / 135232 A1 or EP 3 448 540 B1.

[0008] Particularly advantageous designs of these electrostatic precipitators with filter functionality can be achieved if the polarization elements are integrated into the filter medium installed in the filter insert. For this purpose, individual layers of the multi-layer filter medium can be designed as electrically conductive layers, which, when a voltage is applied, together cause the polarization of a dielectric filter material arranged between them. By integrating the polarization elements into the filter medium and thus the filter insert, high-performance filter inserts are obtained that, in particular, have an advantageous weight and make it possible to reduce or even completely eliminate the requirements for the equipment required on the vehicle if no vehicle-mounted polarization elements need to be provided to realize the polarization of the dielectric layer.

[0009] However, the fundamentally advantageous design of filter media or filter inserts with integrated electrically conductive layers also presents challenges, particularly in the large-scale production of such products. Despite the potentially advantageous properties of such filter media, the production of corresponding polarizable filter elements for electrostatic precipitators often proves to be very challenging in practice. To ensure proper function, it is necessary to prevent the two layers in the filter medium acting as electrodes from making electrical contact. This is often made difficult by the fact that the layered filter media usually have to be folded for use to create a so-called pleated filter medium.

[0010] The problems described above are particularly serious in the area of ​​large-scale production of such filter elements, i.e. in the area of ​​mass production, as is particularly necessary for supplying the automotive industry. When attempting to implement this on a large scale, it is particularly disadvantageous that for the continuous production of filter media from web-shaped starting materials, which, with regard to the achievable

[0011] Production capacities and process control would be preferred, inevitably a separation of the filter elements from the strand or web-shaped

[0012] layer structure must be carried out. However, this so-called cutting of the web-like layer structure to length causes mechanical and / or thermal stress on the material in the cutting area due to the processes used, such as hot cutting or ultrasonic welding, which can lead, for example, to compression of the filter medium and / or to fusion of the layers. Due to this circumstance, there is a high probability that a short circuit will occur between the conductive layers during the large-scale production of corresponding filter elements or that such a short circuit will occur as a result of the stress experienced later in use. However, a high level of waste in production or a high failure rate in use are in many cases exclusion criteria for applications in the automotive sector, for example, since vehicle manufacturers are typically very cost-sensitive and the industry is characterized by high quality expectations.

[0013] The problem of unwanted contacting of the conductive layers described above arises in particular when the conductive layers are to be formed using coated nonwovens made of, mostly thermoplastic, plastic, which, according to the inventors' findings, is particularly advantageous with regard to the weight of the filter element, the manufacturing costs and the achievable filter performance, since these materials are easily deformable mechanically and often comprise thermoplastic materials whose dimensional stability can be reduced in separation processes at elevated temperatures.

[0014] In the prior art, DE 102023121052 A1 proposed choosing a specific process to solve the problem, with which it is possible to avoid that the cutting and separating of the filter elements takes place through both conductor layers, so that contact between the conductor layers caused or promoted by the cutting cannot occur.

[0015] Even if the problem of direct contact between the conductor layers during cutting can be reliably resolved by the solution disclosed in DE 102023121052 A1, further development of this technology has shown that it involves a relatively high process engineering effort and can be disadvantageous in terms of time and cost efficiency, particularly for large-scale applications. Furthermore, the development of corresponding filter media and the corresponding filter inserts has shown that, with regard to filtration performance and overall weight, it is generally preferable not to provide a peripheral area in which one or both of the conductor layers are missing, either in the longitudinal direction or at the edges.Rather, in the inventors' estimation, the aim for numerous future applications will be for both conductor layers to extend substantially over the corresponding surface of the filter medium, so that these layers reach, for example, to the lateral lamination.

[0016] In the course of the inventors' efforts to solve the problem described above without edge spacing, the inventors have recognized that in addition to the direct contact of the conductor layers, which can be caused by the separation, a further effect occurs with certain multi-layer filter media, which promotes unwanted breakdown as a result of electrical contact between the conductor layers. This effect occurs with multi-layer filter media that have an additional activated carbon layer between the conductor layers. Such multi-layer filter media are particularly preferred with regard to filtration performance. However, it has been observed with these particularly preferred filter media when many classic separation processes are used that the breakdown voltages are particularly adversely affected when the section through the filter medium is made without edge spacing, i.e.through the conductor layers and the activated carbon layer.

[0017] Thus, with a view to a time- and cost-efficient production of such particularly preferred, activated carbon-containing multi-layer filter media, in which the conductor layers should be arranged over the entire surface of the filter medium, a particular challenge is to identify an optimized process control for the separation, which enables the separation of these particularly sensitive filter media that are susceptible to unwanted breakdowns.

[0018] The primary object of the present invention was to eliminate or at least mitigate the above-described disadvantages of the prior art. In particular, it was an object of the present invention to provide a process for producing activated carbon-containing filter media for use in electrostatic precipitators, with which corresponding activated carbon-containing filter media can be produced on an industrial scale in a time- and cost-efficient manner, particularly in continuous or at least semi-continuous processes.

[0019] It was an object of the present invention that the activated carbon-containing filter media should desirably also be producible without edge spacing of the conductor layers, preferably both in the longitudinal direction and in relation to the side edges.

[0020] In the interaction of the two objects described above, it was a particular object of the present invention to optimally match the advantageous method to be specified to the advantageous activated carbon-containing filter media to be specified.

[0021] It was therefore an object of the present invention to resolve the conflict of objectives between optimising the separation efficiency and manufacturability in large-scale industrial processes for the filter media that can be produced using the process to be specified and, at the same time, to design the process to be specified in such a way that it is compatible with technical features that result from the specific structure of the filter elements to be specified.

[0022] A secondary object of the present invention was to provide a filter medium for use in electrostatic precipitators, which can be produced using the specified method and which has little or no edge spacing between the conductor layers and yet advantageously enables high flashover voltages, thus being particularly efficient and simultaneously mechanically very resilient, and which, in combination with an ionization device in filters, can achieve particularly good separation performance. Therefore, a further secondary object of the present invention was that the specified filter media should exhibit a longer replacement interval than the prior art.In addition, a supplementary secondary task was that the filter media to be specified should be particularly light and thin in order to achieve space and weight savings, particularly as a result of dispensing with additional protective and safety layers which serve to reduce the tendency to puncture.

[0023] It was also a secondary object of the present invention to provide a filter insert comprising the corresponding filter medium for use in electrostatic precipitators with filter functionality,

[0024] The inventors of the present invention have now found that the objects described above can be achieved if the separation or cutting of corresponding activated carbon-containing multi-layer filter media through the conductor layers is carried out by means of a mechanical separation with a separation tool which has a cutting bevel angle of 90° or less, if the separation is carried out either as a shear cut or burst cut or alternatively by means of a crush cut which is carried out from a specific direction through the multi-layer filter medium, as defined in the claims.

[0025] Surprisingly, by selecting a shear cut, a burst cut, or a crush cut in the specific process configuration, advantageous breakdown voltages can be achieved even when the cut is made through the conductor layers and the activated carbon layer, resulting in advantageous multilayer filter media whose edge regions do not require any edge spacing. The resulting process is significantly less complex in terms of equipment than the state-of-the-art alternatives and allows for a significantly more time- and cost-efficient process.

[0026] The above-mentioned objects are thus achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the subclaims and the following statements. Those embodiments which are referred to as preferred below are combined in particularly preferred embodiments with features of other embodiments referred to as preferred. Combinations of two or more of the embodiments referred to as particularly preferred below are therefore very particularly preferred. Likewise preferred are embodiments in which a feature of an embodiment referred to as preferred to some extent is combined with one or more further features of other embodiments which are referred to as preferred to some extent. Features of preferred filter media and filter inserts emerge from the features of preferred methods.

[0027] The invention particularly relates to a method for producing a multi-layer filter medium for use in an electrostatic precipitator with filter functionality, comprising the method steps: a) producing or providing a multi-layer starting layer composite, comprising: a.1) an electrically conductive first conductor layer, a.2) an electrically conductive second conductor layer, and a.3) an intermediate layer arranged between the first conductor layer and the second conductor layer, wherein the intermediate layer comprises at least one dielectric layer and at least one activated carbon layer, wherein the activated carbon layer has a basis weight of 50 g / m 2or more, wherein the activated carbon layer has an average thickness of 0.4 mm or more at a test pressure of 1 kPa, b) separating a part of the multi-layer starting layer composite, wherein the separating comprises a mechanical separation using a separating tool, wherein the separating tool has a cutting edge with a cutting bevel angle of 90° or less, wherein the separation takes place at least through the first conductor layer, the activated carbon layer, the dielectric layer and the second conductor layer of the multi-layer starting layer composite, and wherein the separation comprises either b1) a shear cut, or b2) a burst cut, or b3) a crush cut, in which the separating tool separates one of the conductor layers and at least one dielectric layer of the intermediate layer before the activated carbon layer.

[0028] The method according to the invention serves to produce a multilayer filter medium which, by applying an electrical voltage to its conductor layers, is capable of polarizing a dielectric layer arranged between the conductor layers. This makes it suitable as a filter medium in electrostatic precipitators with filter functionality. The multilayer filter medium produced by the method according to the invention can then be further processed in a typical manner and, in particular, marketed in the form of a filter insert.By way of example, a method according to the invention is provided which, in addition to producing a filter insert, comprises the following method step: c) pleating the multi-layered starting layer composite or the multi-layered filter medium, wherein the pleating of the multi-layered filter medium is preferably carried out after method step b) when using a shear cut or a crush cut, wherein the pleating of the multi-layered starting layer composite is preferably carried out before method step b) when using a burst cut.

[0029] The above statements take into account the fact that the inventors' experiments have shown that the three cutting methods identified as advantageous are suitable to varying degrees for processing pleated multilayer filter media. Shear cutting and crush cutting are particularly suitable for processing non-pleated multilayer filter media. In contrast, while burst cutting already shows excellent results with non-pleated multilayer filter media, particularly advantageous results are achieved when cutting pleated filter media. For this reason, the method according to the invention, when using a burst cutting, is particularly well suited for cutting already pleated filter media.

[0030] Based on this finding, two particularly preferred methods can be separated.

[0031] For the processing of non-pleated filter media, a method according to the invention for producing a multi-layer filter medium for use in an electrostatic precipitator with filter functionality is preferred, comprising the method steps: a) producing or providing a multi-layer starting layer composite, comprising: a.1) an electrically conductive first conductor layer, a.2) an electrically conductive second conductor layer, and a.3) an intermediate layer arranged between the first conductor layer and the second conductor layer, wherein the intermediate layer comprises at least one dielectric layer and at least one activated carbon layer, wherein the activated carbon layer has a basis weight of 50 g / m 2or more, wherein the activated carbon layer has an average thickness of 0.4 mm or more at a test pressure of 1 kPa, b) separating a part of the multi-layer starting layer composite, wherein the separating comprises a mechanical separation using a separating tool, wherein the separating tool has a cutting edge with a cutting bevel angle of 90° or less, wherein the separation takes place at least through the first conductor layer, the activated carbon layer, the dielectric layer and the second conductor layer of the multi-layer starting layer composite, and wherein the separation comprises either b1) a shear cut, or b3) a pinch cut, in which the separating tool separates one of the conductor layers and at least one dielectric layer of the intermediate layer before the activated carbon layer.For the processing of pleated filter media, a method according to the invention for producing a multi-layer filter medium for use in an electrostatic precipitator with filter functionality is preferred, comprising the method steps: a) producing or providing a multi-layer starting layer composite, comprising: a.1) an electrically conductive first conductor layer, a.2) an electrically conductive second conductor layer, and a.3) an intermediate layer arranged between the first conductor layer and the second conductor layer, wherein the intermediate layer comprises at least one dielectric layer and at least one activated carbon layer, wherein the activated carbon layer has a basis weight of 50 g / m. 2or more, wherein the activated carbon layer has an average thickness of 0.4 mm or more at a test pressure of 1 kPa, c) pleating the multi-layer starting layer composite to obtain a pleated multi-layer starting layer composite, b) severing a part of the pleated multi-layer starting layer composite, wherein the severing comprises a mechanical severing with a severing tool, wherein the severing tool has a cutting edge with a cutting bevel angle of 90° or less, wherein the severing takes place at least through the first conductor layer, the activated carbon layer, the dielectric layer and the second conductor layer of the multi-layer starting layer composite, and wherein the severing b2) comprises a bursting cut.

[0032] In this respect, the method according to the invention is additionally or alternatively exemplary, additionally comprising the method step for producing a filter insert: d) laminating at least one side of the pleated multi-layer filter medium, preferably at least two sides, particularly preferably at least the long sides, very particularly preferably all sides, with a laminating material, wherein the laminating material is preferably selected from the group consisting of textile fabrics, in particular nonwovens and felts.

[0033] To implement the electrical contact, an electrical contact system can be applied during the production of a filter insert. Thus, an example of a method according to the invention additionally comprises the following method step for producing a filter insert: e) applying an electrical contact system, wherein the electrical contact system is configured to allow a voltage difference to be applied between the first conductor layer and the second conductor layer. The application is preferably carried out by connecting the lamination of the pleated multi-layer filter medium to an electrical contact system.

[0034] An example of a method according to the invention is one in which the electrical contacting system comprises a first contact point and a second contact point for contacting an external voltage source, the voltage source preferably being a high-voltage source. A preferred method according to the invention is one in which the electrical contacting system is a voltage divider.

[0035] The process according to the invention starts from a multi-layer starting layer composite from which the desired multi-layer filter medium is to be produced. An example of a process according to the invention is one in which the multi-layer starting layer composite has an average thickness in the range of 1 to 10 mm, preferably in the range of 1.5 to 7 mm, particularly preferably in the range of 2 to 5 mm, at a test pressure of 1 kPa.

[0036] At least theoretically, it is conceivable that the multi-layer starting layer composite already largely corresponds to the dimensions of the multi-layer filter medium in terms of its dimensions and only needs to be cut to size in the process according to the invention. With a view to producing a large number of multi-layer filter media as time- and cost-efficiently as possible, however, it is preferred if the multi-layer starting layer composite is provided as a strand-like material, i.e. as a material web, from which a larger number of multi-layer filter media can be separated using the process according to the invention. Accordingly, a process according to the invention is preferred, wherein the multi-layer starting layer composite is strand-like, wherein a plurality of multi-layer filter media are preferably produced from the multi-layer starting layer composite in the process.

[0037] The method according to the invention can advantageously be carried out directly after the production of a starting layer composite, which can advantageously be achieved in particular by successively building up the individual layers of the multi-layer filter medium in a substantially continuous process or by combining two multi-layer precursor materials before separation. However, particularly when using strand-like starting layer composites, it is alternatively also possible to carry out the method according to the invention in a separate step following the production process. In this case, a previously produced web-like multi-layer starting layer composite can be provided, for example, on a roll, from which the material can be unwound and cut to length in the method according to the invention.A process according to the invention is conceivable, wherein the multi-layer starting layer composite is provided on a master roll. However, a process according to the invention is preferred, wherein the multi-layer starting layer composite is produced in process step a), preferably by contacting two or more precursor layers, wherein the two or more precursor layers are preferably bonded to one another.

[0038] The method according to the invention defines a particularly advantageous manner in which multi-layer starting layer composites can be cut to size. It can be seen as an advantage of the method according to the invention that the method according to the invention can be used both for cutting side edges and in the course of separating individual filter media from a strand-like material, and in both cases shows excellent results. In principle, the inventors consider the use of the method particularly preferred for separating the longitudinal edges. In the opinion of the inventors, it is particularly preferred if the method according to the invention not only separates the filter media from a strand-like starting layer composite, but also separates the side edges, whereby a portion of material is separated which is referred to as the side region in the context of the present invention.This lateral separation of the side region takes place in accordance with expert understanding along the longitudinal edge of the strand-like material, ie in particular along the web direction, whereas the singulation takes place at least partially transversely to the web direction. Accordingly, a method according to the invention is preferred, wherein the separation in method step b) comprises at least the separation of one side region of the multi-layer starting layer composite, wherein the separation of the side region preferably takes place along the longitudinal edge. A method according to the invention is particularly preferred, wherein the separation in method step b) preferably comprises at least the separation of two side regions of the multi-layer starting layer composite, wherein the separation of the side regions preferably takes place along the two longitudinal edges.Additionally or alternatively, preferably additionally, a method according to the invention is preferred, wherein the separation in method step b) comprises the singulation of a partial layer composite from the initial layer composite, wherein the partial layer composite is the multi-layer filter medium or wherein the multi-layer filter medium is produced from the partial layer composite.

[0039] When using a burst cut for cutting pleated multi-layer filter media, the method according to the invention is particularly suitable for cutting the multi-layer filter medium obliquely to the direction of the pleats, preferably at an angle in the range of 10° to 80° to the pleat direction, particularly preferably at an angle of 15° to 75° to the pleat direction, most particularly preferably at an angle of 20° to 70° to the pleat direction.

[0040] The multi-layer starting layer composite comprises a first and a second electrically conductive conductor layer, as well as at least two further layers arranged between the conductor layers. The electrical conductor layers are intended to generate an electric field during subsequent use in the filter insert under the influence of an electrical voltage applied to the conductor layers, which can polarize the dielectric layers of the intermediate layer arranged between the conductor layers. Those skilled in the art will understand that, in the method according to the invention, parts of the multi-layer starting layer composite are separated or separated, and that the above requirement implies that the produced multi-layer filter medium also comprises the corresponding layers of the multi-layer starting layer composite.

[0041] Further information and preferred configurations of the layers of the multilayer composite starting layer or the multilayer filter media are disclosed below. However, for a better understanding of the invention, it is helpful to first explain the further process steps of the method according to the invention in more detail.

[0042] With regard to these further process steps, it is useful to note at this point that the multilayer starting layer composite has a specific configuration in which, in addition to the two conductor layers and the dielectric layer arranged therebetween, at least one activated carbon layer is also provided in the intermediate layer. This boundary condition indicates that the multilayer starting layer composite is suitable for producing particularly preferred multilayer filter media, namely, multilayer filter media containing activated carbon. A minimum basis weight and a minimum thickness are defined for the activated carbon layer to express that at least a certain dimensioning of the activated carbon layer exists, which determines the problems solved by the invention.

[0043] Within the scope of the method according to the invention, a portion of the multi-layer starting layer composite is subsequently separated. As defined above, this separation occurs at least through the two conductor layers, the activated carbon layer, and the dielectric layer. This definition is to be understood as a further boundary condition and expresses that the cutting of the multi-layer filter medium does not take place by exploiting an edge spacing of one or both conductor layers, in which case the separation would not cut through both conductor layers. At the same time, this boundary condition expresses that the aggravating presence of an activated carbon layer, which the inventors identified as particularly challenging for the manufacturing process, cannot be circumvented by avoiding a cut through the activated carbon layer, for example, by not pulling the activated carbon layer into the edge regions to be trimmed.

[0044] It follows from the above definition that the separation must take place at least through the four layers mentioned, so that the cross-sectional areas are inevitably exposed by the corresponding layers at the separation edge created during the separation and there is no edge spacing, in particular between the first conductor layer and the second conductor layer, during the cut.

[0045] In addition to the layers defined above, further layers can also be provided in the multi-layer starting layer composite, in particular as part of the intermediate layer. Even if it would be at least theoretically conceivable to design such further layers in such a way that the separation does not take place through these layers, the inventors believe that with a view to time and cost efficiency and to obtaining a multi-layer filter medium that is as uniform as possible, it is particularly preferred if the separation takes place not only through the layers defined above, but through all layers of the filter medium. Consequently, a method according to the invention is preferred, wherein the separation in method step b) takes place through the entire multi-layer starting layer composite, i.e. all layers of the starting layer composite.

[0046] A first important requirement of the method according to the invention is that, among the multitude of possible separation methods, a mechanical separation method is selected for the separation, in which the separation takes place using a separation tool. In this respect, the method according to the invention should be viewed in particular in contrast to melting and / or welding separation methods, which, for example, rely on the use of lasers or ultrasound. Even though these methods may be advantageous in other manufacturing processes, for example, in the process according to DE 102023121052 A1, they have proven unsuitable in the inventors' experiments for the gapless processing of multilayer filter media containing activated carbon.At least theoretically, it would be conceivable to combine the separation according to the invention with other, for example non-mechanical separation processes, and to use different methods, for example, for side edge trimming and cutting to length. However, those skilled in the art will understand that deviations from the advantageous separation process proposed in the method according to the invention will be associated with disadvantages in practice, which would have to be compensated for by other advantages in the design of the overall manufacturing process in order to justify their use. Accordingly, the inventors consider it particularly advantageous for most embodiments if the entire cutting of the multi-layer filter media takes place using the method according to the invention, i.e. using the mechanical separation tool.Accordingly, a method according to the invention is preferred, wherein the separation in method step b) is carried out essentially entirely by mechanical separation with the separation tool. Additionally or alternatively, a method according to the invention is also preferred, wherein the separation according to variant b1) is carried out entirely by one or more shear cuts, and / or wherein the separation according to variant b2) is carried out entirely by one or more burst cuts, and / or wherein the separation according to variant b3) is carried out entirely by one or more pinch cuts, in which the separation tool severs one of the conductor layers and at least one dielectric layer of the intermediate layer upstream of the activated carbon layer.

[0047] The inventors' experiments revealed that special requirements must also be placed on the cutting tool. This is defined by the term "cutting bevel angle," familiar to those skilled in the art, which, in the present case, must not be chosen too large, particularly for burst cuts and crush cuts. Schematic representations for determining the cutting bevel angle can be found below in Figure 5. A preferred method according to the invention is one in which the shear cut is performed with a cutting tool whose cutting edge has a cutting bevel angle in the range of 20° to 90°, preferably in the range of 30° to 90°.Additionally or alternatively, a method according to the invention is preferred, wherein the bursting cut is carried out with a cutting tool whose cutting edge has a cutting bevel angle of 40° or less, preferably 30° or less, particularly preferably 20° or less. In turn, additionally or alternatively, a method according to the invention is preferred, wherein the crushing cut is carried out with a cutting tool whose cutting edge has a cutting bevel angle in the range of 25° to 90°, preferably in the range of 25° to 75°, particularly preferably in the range of 30° to 60°.

[0048] In the inventors' opinion, it is particularly advantageous to forgo the use of melting separation processes, particularly in cases where the conductor layers and / or the dielectric layers, in particular the dielectric filter layers, in the intermediate layer consist of thermoplastics, for example polyethylene or polyethylene terephthalate. In this respect, in the area of ​​hot-cutting processes, i.e. processes in which the cutting tools used are brought to elevated temperatures, there may be configurations that can lead to undesired melting of thermoplastics in the multi-layer filter medium, despite the use of an inherently mechanical separation process. Accordingly, the inventors propose that mechanical separation processes in which the cutting tools are not brought to elevated temperatures are particularly preferred.Consequently, a process according to the invention is preferred, wherein the separation in process step b) is carried out using a separation tool whose temperature is less than 100 °C, preferably less than 60 °C, particularly preferably less than 40 °C.

[0049] In addition to the basic category of mechanical separation and the design of the separation tool, the inventors discovered during the development process that, among all conceivable mechanical separation methods, only three specific separation methods are particularly suitable for processing multilayer composites containing activated carbon. These are a shear cut, a burst cut, and, alternatively, a crush cut. The crush cut is subject to the additional requirement that the separation tool must cut through at least one of the dielectric layers before the activated carbon layer. These three separation methods represent alternative solutions for solving the problems described above.

[0050] At least theoretically, it is conceivable to combine these methods in a process according to the invention, for example by singulating a web-like material by means of a shear cut, but trimming the side edges with a corresponding pinch cut. However, with regard to the equipment required to carry out the process and the associated investment requirements, it is particularly preferred if only one of the three techniques is used. Accordingly, a process according to the invention is preferred, wherein the separation in process step b) comprises a pinch cut, in which the separating tool severs one of the conductor layers and at least one dielectric layer of the intermediate layer upstream of the activated carbon layer, and preferably takes place exclusively with a pinch cut.Alternatively, a method according to the invention is preferred, wherein the separation in process step b) comprises a shear cut and is preferably carried out exclusively with a shear cut. Alternatively, a method according to the invention is preferred, wherein the separation in process step b) comprises a burst cut and is preferably carried out exclusively with a burst cut. In this case, the exclusive use of a shear cut or a burst cut, in particular a burst cut, is particularly preferred in the opinion of the inventors.

[0051] The term “crush cut” is clear to a person skilled in the art in the field of process engineering and refers to a type of mechanical cutting in which the cutting tool, in particular a comparatively blunt, for example rounded, blade or wedge, is passed through the material to be cut, the material to be cut being located on a base which offers resistance to the cut, so that the material to be cut is compressed, i.e. squeezed, between the cutting tool and the cutting base. This therefore generally involves a method according to the invention in which the crush cut is made with a cutting tool against a cutting base. Preference is given to a method according to the invention in which the crush cut is made with a rounded blade or a rounded wedge as the cutting tool.Additionally or alternatively, a method according to the invention is preferred, wherein the crush cut is carried out with a rotating cutting tool.

[0052] The term “shear cut” is also clear to those skilled in the field of process engineering and refers to the severing of a material by two cutting edges moving past each other (DIN 8588:2013-08), so that the material is sheared off by shearing forces. In principle, in addition to a cutting edge, a cutting edge can also be used as the counterpart to the shearing, along which the shearing takes place, as is known, for example, from paper cutting machines, so-called guillotines. However, in the opinion of the inventors, it is preferable to carry out the shearing between two cutting edges, i.e. between two parts with a blade, in particular a tapered blade. The two parts of the separating tool for the shear cut can also be designed as rotating elements, e.g. as a rotating cutting knife which is moved past a rigid or rotating second element.In many cases, this therefore involves a method according to the invention, wherein the shear cut is effected by a cutting movement with a first cutting edge of the cutting tool relative to and along a second cutting edge or relative to and along a cutting edge, preferably by a cutting movement with a first cutting edge of the cutting tool relative to and along a second cutting edge. Preference is given to a method according to the invention in which the shear cut is a scissor cut or a plane cut, preferably a scissor cut. Additionally or alternatively, a method according to the invention in which the shear cut is effected using a rotating blade as the cutting tool is also preferred.

[0053] The term "burst cut" is also clear to those skilled in the field of process engineering. A burst cut is performed with a rotating cutting tool whose cutting edge usually has a relatively low cutting bevel angle. The rotating cutting tool is brought into the material to be cut at a speed greater than the speed of the material web and separates it—in contrast to a shear cut—without a counterblade or—in contrast to a crush cut—without an opposing support. Relevant for essentially all embodiments is a method according to the invention, wherein the burst cut is performed with a rotating cutting tool.

[0054] Suitable devices for crush cutting, burst cutting or shear cutting, which can be adapted to the purposes of the present invention, are commercially available from various manufacturers, for example from DIENES Werke für Maschinenteile GmbH & Co. KG, Wilhelm Bilstein GmbH & Co. KG or Hess & Schofield AG.

[0055] For all three cutting methods, it has proven particularly preferable to design the cutting edge of the cutting tool without a serrated or serrated edge, but rather to use a blade with a smooth ground finish. Accordingly, a method according to the invention is preferred in which the cutting edge of the cutting tool has a smooth ground finish. In other words, a method according to the invention is preferred in which the cutting edge of the cutting tool does not have a serrated or serrated edge.

[0056] Of the three separation methods identified as suitable, the shear cut and the burst cut, in particular the burst cut, are preferred for most embodiments in the inventors' estimation. In fact, the inventors' experiments initially showed a less than advantageous separation result for the use of a pinch cut. In the course of further development, however, the inventors recognized that the performance characteristics of multi-layer filter media cut by pinch cutting can be significantly improved if the orientation of the material during the pinch cut is specifically selected. In the inventors' initial experiments, the activated carbon layer was initially the uppermost layer of the intermediate layer, which was the first to be cut by the cutting tool - coming from above - i.e.immediately after the conductor layer, wherein a detrimental effect of the cutting process on the flashover voltage was found. Surprisingly, a more advantageous cutting result can be achieved by turning the multi-layer material to be cut over, so that the dielectric layers of the intermediate layer are severed before the activated carbon layer, wherein particularly advantageous results have been shown when several dielectric layers are severed before the activated carbon layer. Accordingly, a method according to the invention is preferred, wherein the crush cut is carried out such that the separating tool severes one of the conductor layers and at least two dielectric layers of the intermediate layer, preferably all dielectric layers of the intermediate layer, before the activated carbon layer.

[0057] Without wishing to be bound to this theory, the inventors suspect that the pinch cut leads to particularly pronounced mechanical stress on the activated carbon layer, which results in increased formation of activated carbon dust. Without wishing to be bound to this theory, it is assumed that in the case of the less advantageous cutting direction, the activated carbon dust released by the pinch cut sinks into the underlying dielectric layer, i.e. the one severed after the activated carbon layer, and leads to a local increase in the electrical conductivity of the dielectric layer, which subsequently promotes electrical breakdown. By inverting the arrangement, there is at least one dielectric layer which is severed by the cutting tool before activated carbon dust can be formed from the activated carbon layer, which could then trickle into lower layers. In order to prevent the dust formed from trickling in in this way,In order to particularly reliably prevent the resulting dust from being pushed into the lower layers by the cutting tool, the inventors propose that the cutting during the crush cut should be carried out in such a way that the dielectric layer is arranged above the activated carbon layer with respect to the direction of gravity. This not only prevents any resulting dust from being pushed into the following layer by the cutting tool, but gravity can also counteract the dust from "trickling" into the lower layer. A method according to the invention is therefore preferred, wherein the crush cut is carried out in such a way that the cutting tool severs the intermediate layer in the direction of gravity. Building on the knowledge gained regarding the anisotropy of the results obtained as a function of the orientation of the initial layer composite to be cut, in particular relative to the arrangement of the activated carbon layer, the inventors have succeeded in further optimizing the method according to the invention.Based on the assumption that the activated carbon dust generated during cutting has a negative influence on the achievable flashover voltages, the inventors have supplemented the process with an extraction device with which dust generated during cutting can be extracted, preferably directly during cutting or immediately after cutting. Surprisingly, this extraction of the cut surface actually results in an improvement in the flashover voltages measured for the filter media to be produced. Therefore, a process according to the invention is preferred for essentially all embodiments, wherein process step b) additionally comprises the extraction of particles released during separation from the multi-layer starting layer composite, in particular activated carbon dust. A process according to the invention is particularly preferred in which the extraction is carried out using a extraction device.Additionally or alternatively, a method according to the invention is particularly preferred, wherein the suction is carried out with a suction device arranged in the region of the separating tool, and / or wherein the suction is carried out with a suction device arranged behind the separating tool in the conveying direction of the multi-layer starting layer composite, preferably immediately behind the separating tool, wherein the suction device is preferably directed at at least one of the cut edges produced during the separation, preferably all of the cut edges produced during the separation.

[0058] The inventors have found in their own experiments that an improvement in the observed flashover voltages can also be advantageously achieved with a suction system downstream of the entire process, so that the suction takes place as a subsequent, separate step at the edges of the produced multilayer filter media. Although direct suction is thus preferred in principle, a method according to the invention is also considered preferable, comprising, after the production of the individual multilayer filter medium, the suction of the separating edges created in process step b), preferably with a mobile suction device.

[0059] When using an extraction system, a method according to the invention is preferred, wherein the extraction takes place with a volume flow of 2.5 L / s or more, preferably of 5 L / s or more, particularly preferably of 10 L / s or more, and / or wherein the extraction takes place with a negative pressure at the cutting edge of 0.5 kPa or more, preferably 1 kPa or more, particularly preferably 2 kPa or more.

[0060] During development, the inventors of the present invention discovered that, surprisingly, the activated carbon layer in the multi-layer filter medium not only has a detrimental effect on dust formation. The manufacturing processes known from the prior art focused largely on the problem that the conductor layers inserted on both sides of the multi-layer filter medium could contact each other due to the cutting processes used for separation, thereby potentially causing a short circuit. However, the inventors' experiments have shown that the problem of directly contacting conductor layers is greatly reduced in the presence of an activated carbon layer and, in many cases, does not even exist, at least if—as in the process according to the invention—the use of melting separation processes is dispensed with.In the inventors' experiments, advantageously—and surprisingly in light of the problems discussed in the prior art—no significant defects were detected that could be attributed to direct contact between the layers. Therefore, the inventors believe that the observed deterioration in the breakdown voltage is significantly influenced by the activated carbon layer or the dust generated during cutting. In this respect, the inventors cannot rule out the possibility that carbon dust formation already existed in DE 102023121052 A1, which contributed to the problems described therein or, in some cases, possibly even dominated over interlayer contact between the conductor layers.

[0061] Further information on the individual layers of the multi-layer starting layer composite and, indirectly, the multi-layer filter media produced therefrom is disclosed below, as well as preferred embodiments. The separation processes identified within the scope of the present invention have proven to be particularly advantageous in cases where the conductor layers are textile fabrics, in particular made of plastic. Even if, in the opinion of the inventors, an improvement could be expected with the identified separation processes when other conductor layers, for example metallic grid structures, are used, the inventors assume that the increased mechanical stress when cutting through metallic grids is likely to lead to greater damage to the activated carbon layer, which will reduce the positive effect of the process according to the invention or at least make the relevance of the orientation of the material to be cut, i.e. the orientation of the material, i.e. the cutting direction, lessen the risk of injury or damage.H. with a prior severing of the dielectric layers, gains additional relevance. A method according to the invention is preferred, wherein the first conductor layer comprises a first textile fabric, preferably a first textile fabric coated or impregnated at least in sections with an electrically conductive first material, and / or wherein the second conductor layer comprises a second textile fabric, preferably a second textile fabric coated or impregnated at least in sections with an electrically conductive second material.

[0062] The term "textile fabric" is clear to the skilled person and refers to two-dimensional textile products, which can be woven, warp-knitted, needle-punched, or knitted, for example. In accordance with the expert's understanding, non-textile, fiber-containing fabrics, such as paper and cardboard, in which the fibers are primarily held together by binding agents, are not considered textile fabrics. Even though a wide range of textile fabrics could in principle be considered for the textile fabrics of the conductor layers, the inventors have been able to achieve the best performance characteristics with so-called "non-wovens," and in particular with spunbonded nonwovens.A corresponding textile fabric made of a non-conductive material can advantageously be achieved by equipping the textile fabric with a conductive material. According to the inventors' assessment, a variety of possible methods are suitable in principle. Thus, a method according to the invention is preferred, wherein the first textile fabric and / or the second textile fabric, preferably the first textile fabric and the second textile fabric, are a nonwoven fabric, preferably a spunbonded fabric.

[0063] In practice, the person skilled in the art readily distinguishes between an electrically conductive material and an electrically insulating material based on his or her expert and clear technical understanding of these terms. In this respect, a material is considered to be electrically conductive within the scope of the present invention in particular if its specific electrical resistance at 20 °C is 10 6 Q*m or less, preferably at 10 5 Q*m or less, particularly preferably 10 4 Q*m or less. Conversely, a material is considered to be an electrically insulating material within the scope of the present invention if its specific electrical resistance at 20 °C is 10 7 Q*m or more, preferably at 10 9 Q*m or more, particularly preferably at 10 11Q*m or more. Accordingly, metals and alloys, as well as carbon blacks, in particular conductive carbon black, and plastics made conductive by additives, are electrically conductive materials, whereas typical, unmodified plastics such as PET or PE are also electrically insulating materials, as are most glasses and ceramics. The specific electrical resistance of materials is a value that is well known to those skilled in the art and can be found in relevant tables for most materials. The measurement of the specific electrical resistance of other components is carried out in accordance with common practice, either according to DIN EN ISO 3915 from 1999, which is used in particular for particularly conductive materials, or according to IEC 60093 from 1993, which is used for high specific electrical resistances.The question of which of the two standards should be used depends on the requirements of the two regulations as well as the properties of the respective material being examined.

[0064] Those skilled in the art will understand that the electrical conductivity of conductor layers, for example, the first conductor layer, can in many cases, for example, when using composite materials, result from the presence of conductive material paths running through an otherwise largely insulating material. For example, a dielectric fleece whose fibers are coated with a thin layer of conductive carbon black can be an electrically conductive layer, even though the macroscopic resistivity of the composite material is relatively high due to the dielectric carrier material.

[0065] Furthermore, additionally or alternatively, a method according to the invention is preferred, wherein the first textile fabric and / or the second textile fabric, preferably the first textile fabric and the second textile fabric, consist of a plastic to a mass fraction of 80% or more, preferably 90% or more, particularly preferably 95% or more, very particularly preferably substantially 100%, based on the mass of the textile fabric, wherein the plastic is preferably selected from the group consisting of polyacrylonitriles, polyolefins, polyesters and mixtures of these plastics, particularly preferably polyacrylonitriles, polypropylene, polyethylene terephthalate and mixtures of these plastics, especially preferably polyethylene terephthalate.

[0066] Additionally or alternatively, a method according to the invention is also preferred, wherein the first conductor layer and / or the second conductor layer, preferably the first conductor layer and the second conductor layer, are produced or can be produced by equipping the respective textile fabric, in particular the nonwoven fabric, with the respective electrically conductive material using a method which is selected from the group consisting of impregnation, dip coating, in particular using a padding system, spray coating, application coating, in particular by means of a dispersion in the kiss-coat process, and print coating.

[0067] Additionally or alternatively, a method according to the invention is also preferred, wherein the electrically conductive first material and / or the electrically conductive second material, preferably the electrically conductive first material and the electrically conductive second material, are selected from the group consisting of metals, conductive plastics and carbon, preferably carbon, in particular carbon black or graphene, wherein the electrically conductive material is particularly preferably identical for the first conductor layer and the second conductor layer.

[0068] Additionally or alternatively, a method according to the invention is also preferred, wherein the first conductor layer and / or the second conductor layer, preferably the first conductor layer and the second conductor layer, as a result of the coating of the respective textile fabric, are electrically conductive over at least 80% or more of the area, preferably over 90% or more, particularly preferably over 95% or more, very particularly preferably over 98% or more, particularly preferably substantially over the entire area.

[0069] Even though the conductor layers can contribute to the filtration performance of the filter media, particularly when designed as textile fabrics, the inventors consider it advantageous if the conductor layers are designed with sufficient open pores so that they primarily restrict the air flow through the filter medium as little as possible. With regard to the weight of the conductor layers, at least when using textile fabrics, there is a trade-off between the influence on the overall weight of the filter medium and a beneficial stabilizing effect of the conductor layers on the filter medium, thus improving the mechanical properties. In this respect, the inventors have succeeded in identifying suitable basis weights for the textile fabrics that advantageously resolve this trade-off.Against this background, a method according to the invention is preferred, wherein the first conductor layer and / or the second conductor layer, preferably the first conductor layer and the second conductor layer, have an air passage in the range of 500 to 30,000 L / (m) at 200 Pa. 2 s), preferably in the range of 2000 to 20000 L / (m 2 s). Additionally or alternatively, a method according to the invention is also preferred, wherein the first textile fabric and / or the second textile fabric, preferably the first textile fabric and the second textile fabric, have a basis weight in the range from 5 to 200 g / m 2 , preferably in the range of 10 to 150 g / m 2 , particularly preferably in the range of 15 to 50 g / m 2, have. In most relevant structures, the at least one dielectric layer in the intermediate layer primarily functions as a filter layer, so that it makes a significant contribution to particle filtration of the produced filter media. Additionally or alternatively, however, the mechanical properties of the produced filter medium can also be advantageously influenced by means of corresponding dielectric layers in the intermediate layer, for example by providing comparatively stiff protective layers. Preference is given to a method according to the invention wherein the intermediate layer comprises two or more dielectric layers, preferably three or more dielectric layers. Preference is also given to a method according to the invention wherein the multi-layer intermediate layer comprises one or more further layers, preferably dielectric layers, arranged between the first conductor layer and the second conductor layer.

[0070] Additionally or alternatively, a method according to the invention is also preferred, wherein at least one of the dielectric layers, preferably all of the dielectric layers, consists of a dielectric plastic material to a mass fraction of 80% or more, preferably 90% or more, particularly preferably 95% or more, very particularly preferably essentially 100%, based on the mass of the dielectric layer. A method according to the invention is particularly preferred, wherein the dielectric plastic material is selected from the group consisting of polyolefins, in particular polytetrafluoroethylene, polytetrafluoroethylene-propylene, polypropylene, and polyethylene, polyesters, in particular polyethylene terephthalate, polycarbonates, polyamides, polyvinylidene fluoride, polyacrylonitrile, and polylactides.Additionally or alternatively, a method according to the invention is particularly preferred, wherein the dielectric plastic material has a specific electrical resistance at 20 °C of 10. 7 Q*m or more, preferably at 10 9 Q*m or more, particularly preferably at 10 11 Q*m or more.

[0071] For the majority of embodiments, a method according to the invention is preferred, wherein at least one of the dielectric layers is a particle filter layer comprising a third textile fabric. A method according to the invention is preferred, wherein the third textile fabric is a nonwoven fabric, wherein the third textile fabric is preferably selected from the group consisting of needle-punched nonwovens and meltblown nonwovens. Additionally or alternatively, a method according to the invention is preferred, wherein the particle filter layer has a basis weight in the range of 10 to 200 g / m 2, preferably in the range of 15 to 150 g / m 2 , particularly preferably in the range of 20 to 110 g / m 2 , has.

[0072] The method according to the invention serves, in particular, the purpose of dealing with the presence of activated carbon layers in a process-technical manner. According to the inventors, the advantages of the method according to the invention become more apparent the greater the proportion of activated carbon in the multi-layer filter medium, or the thicker the activated carbon layer is. In their own experiments, the inventors found that the adverse influence of activated carbon on cuttability is particularly evident when particulate activated carbon is used in the activated carbon layer, although this would in principle be preferred for particularly advantageous filter performance due to its high surface area.In this respect, it can be seen as a particular advantage of the method according to the invention that it also leads to excellent results when using particulate activated carbon in the activated carbon layer, in particular when the orientation of the layers is taken into account during cutting, as disclosed above.

[0073] Activated carbon is known to those skilled in the art in the field of filtration technology as an important material and is commercially available from numerous manufacturers. It is preferred that the activated carbon layer is formed from a high mass fraction of activated carbon, so that, for example, the proportion of fibers or other carrier materials in the activated carbon layer should be kept as low as possible. Based on the inventors' experiments, this achieves a particularly good separation effect or cleaning performance while simultaneously minimizing thickness and weight. The inventors have found that particularly high-performance filter media can be obtained with activated carbon layers that are as pure as possible, which preferably consist essentially exclusively of activated carbon apart from the binder, and corresponding filter media can advantageously be processed well in the process according to the invention.Accordingly, a process according to the invention is preferred, wherein the activated carbon layer comprises activated carbon in a mass fraction of 80% or more, preferably 90% or more, particularly preferably 95% or more, based on the mass of the activated carbon layer. Additionally or alternatively, a process according to the invention is preferred, wherein the activated carbon is fixed in the activated carbon layer by a binder.

[0074] The inventors have succeeded in identifying particularly preferred ranges for the selection of activated carbon and for the dimensioning of the activated carbon layer, which have resulted in excellent filter performance in their own experiments. A process according to the invention is preferred, wherein the activated carbon is particulate activated carbon, wherein the activated carbon preferably has an average diameter d50 in the range of 0.1 to 4 mm, preferably in the range of 0.2 to 2 mm. Additionally or alternatively, a filter insert according to the invention is also preferred, wherein the activated carbon has a specific surface area of ​​500 m 2 / g or more, preferably 1000 m 2 / g or more, particularly preferably 2000 m 2 / g or more. In addition or alternatively, a process according to the invention is preferred, wherein the activated carbon layer has a basis weight of 75 g / m 2 or more, preferably 150 g / m 2or more. In addition or alternatively, a process according to the invention is preferred, wherein the activated carbon layer has a basis weight in the range of 50 to 1000 g / m 2 , preferably in the range of 100 to 600 g / m 2 , Additionally or alternatively, a method according to the invention is also preferred, wherein the activated carbon layer has an average thickness of 0.5 mm or more, preferably of 0.6 mm or more, particularly preferably of 0.8 mm or more, at a test pressure of 1 kPa.

[0075] Also disclosed is a multi-layer filter medium produced or producible by the method according to the invention.

[0076] Such a multilayer filter medium is preferred, wherein the multilayer filter medium is pleated. Additionally or alternatively, such a multilayer filter medium is also preferred, wherein at least one of the sides of the pleated multilayer filter medium, preferably at least two sides, particularly preferably at least the long sides, and most particularly preferably all sides, are laminated with a lamination material, wherein the lamination material is preferably selected from the group consisting of textile fabrics, in particular nonwovens and felts.

[0077] Finally, a filter insert for use in an electrostatic precipitator with filter functionality, comprising such a multi-layer filter medium, is also disclosed.

[0078] Such a filter insert is preferred, wherein the filter insert comprises the multi-layer filter medium as a pleated filter medium. Such a filter insert is particularly preferred, wherein the filter insert comprises the multi-layer filter medium as a pleated and laminated filter medium.

[0079] Additionally or alternatively, such a filter insert is also preferred, wherein the filter insert comprises an electrical contacting system, wherein the electrical contacting system is designed such that a voltage difference can be applied between the first conductor layer and the second conductor layer, wherein the electrical contacting system is preferably connected to the lamination of the pleated filter medium, particularly preferably in a materially bonded manner.

[0080] Additionally or alternatively, such a filter insert is preferred, wherein the filter insert is a filter insert for an air filter, preferably an interior air filter, particularly preferably an interior air filter for vehicles, in particular for land vehicles.

[0081] The invention and preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying figures. The figures show:

[0082] Fig. 1 is a schematic representation of the method according to the invention in a first preferred embodiment;

[0083] Fig. 2 is a schematic representation of the method according to the invention in a second preferred embodiment; Fig. 3 is a schematic cross-sectional representation through a multi-layer starting layer composite in a preferred embodiment;

[0084] Fig. 4 is a schematic visualization of the influence of the cutting direction on the distribution of activated carbon dust in the multi-layer initial layer composite of Fig. 3;

[0085] Fig. 5 a schematic visualization of a) shear cut, a b) crush cut and a c) burst cut, and

[0086] Fig. 6 a schematic visualization of the use of a burst cut to process a pleated multi-layer filter medium.

[0087] Fig. 1 shows a schematic representation of the method according to the invention for producing a multi-layer filter medium (10) in a first preferred embodiment.

[0088] Fig. 1 and 2 each initially show schematically the production of a multi-layer starting layer composite 12, which is produced from two multi-layer precursor materials 28a, 28b, each of which is provided by a feed roll.

[0089] The structure of the multilayer starting layer composite 12 of Figs. 1 and 2 is illustrated in Fig. 3. Fig. 3 shows a schematic cross-sectional view through the multilayer starting layer composite 12, which comprises a multilayer intermediate layer 18 arranged between a first conductor layer 14 and the second conductor layer 16 and bonded thereto via an adhesive. Both the first conductor layer 14 and the second conductor layer 16 are formed from a PET spunbonded fabric that has been made conductive by a coating of conductive carbon black and whose basis weight is approximately 30 g / m 2 amounts.

[0090] The intermediate layer 18 comprises the activated carbon layer 22, which in the example shown is particulate activated carbon with an average diameter of about 0.25 to 0.6 mm and a specific surface area of ​​about 2000 m 2 / g, wherein the activated carbon layer 22 has a combined basis weight of about 215 g / m 2with about 15 g / m 2 The binder is used. Arranged above the activated carbon layer 22 is the protective layer 26 of the intermediate layer 18, which in the example shown consists of a non-conductive polyester spunbonded fabric. Also arranged between the protective layer 26 and the first conductive layer 14 is the particle filter layer 20, which in the example shown in Fig. 3 is designed as a needle-punched nonwoven.

[0091] In the preferred inventive methods of Figs. 1 and 2, the multilayer filter media 10 are each produced by separating the multilayer filter medium 10 from the strand-like multilayer starting layer composite 12. The separation is carried out using a separating tool 24 in a mechanical separation process, whereby all layers of the multilayer starting layer composite 12, i.e., the first conductor layer 14, the second conductor layer 16, the particle filter layer 20, the activated carbon layer 22, and the protective layer 26, are severed.

[0092] In the preferred inventive method of Fig. 1, the separation takes place by means of a crush cut, in which the multi-layer starting layer composite 12 is compressed between the separating tool 24 and a base 30 during separation, wherein the activated carbon layer 22 in the example shown is the lowermost layer of the intermediate layer 18, so that the dielectric particle filter layer 20 and the protective layer 26, as well as the first conductor layer 14, are severed by the separating tool 24 before the activated carbon layer 22. In the preferred inventive method of Fig. 2, however, the separation takes place by means of a shear cut, in which the separating tool 24 comprises a cutting edge and a cutting edge.

[0093] In the preferred processes according to the invention shown in Figs. 1 and 2, a suction device 32 is used in each case to suck out any activated carbon dust that may occur during separation from the activated carbon layer 22.

[0094] Fig. 4 is a very schematic illustration of the influence of the cutting direction on the distribution of activated carbon dust in the multi-layer starting layer composite 12. Fig. 4 shows two multi-layer starting layer composites 12 which, in terms of their basic structure, correspond to that of Fig. 3, but are oriented in opposite directions with regard to the cutting direction, indicated by the large arrow. Without wishing to be bound by this theory, the inventors assume that activated carbon dust is created during cutting overall, particularly when severing the activated carbon layer 22, which is indicated in Fig. 4 by jagged shapes. The lightning bolts shown indicate which layers are electrically conductive or are energized.4, it can be seen for the left multi-layer initial layer composite 12 that the activated carbon dust only penetrates the already conductive second conductor layer 16 in the cutting direction, thus causing no functional impairment. However, for the right multi-layer initial layer composite 12, it can be seen how the resulting activated carbon dust penetrates the particle filter layer 20 and the protective layer 26 due to the propulsion of the cutting tool 24 and the acting gravity. As a result, these layers exhibit locally increased electrical conductivity, which can cause undesirable breakdown.

[0095] Fig. 5 schematically illustrates the separation of a portion of the multi-layer composite starting layer 12 with a separating tool 24, each by means of a) a shear cut, b) a crush cut, and c) a burst cut. The schematically illustrated separating tools 24 are each designed as rotating separating tools, in particular as disk-shaped rotating blades. Furthermore, Fig. 5 also illustrates how the cutting bevel angle of the cutting edge is determined for each of the separating tools 24 used.

[0096] Fig. 6 schematically visualizes a particularly preferred method according to the invention, in which a pleated multi-layer filter medium 10 is separated by means of a bursting cut using a separating tool 24 designed as a rotating knife, wherein the direction of rotation of the rotating separating tool 24 indicated by the arrow is directed counter to the feed direction of the multi-layer filter medium 10.

[0097] In the following, the invention and preferred embodiments of the invention are further explained and described with reference to experiments carried out.

[0098] Experiment: Unless otherwise specified in individual cases, the experiments were each conducted on a multilayer filter medium whose general structure corresponds to the structure shown in Fig. 3, as further described above. The comparability of the samples in the respective sub-experiments is ensured by using an identical multilayer filter medium structure for all tests in the sub-experiment (unless otherwise disclosed in individual cases). Slightly different multilayer filter media were used between the sub-experiments, which may differ, for example, with regard to the commercial products processed; this is not critical for the evaluation of the invention.

[0099] The test conducted during the experiments involved measuring the polarization voltage that the multilayer filter media could withstand until electrical breakdown. This voltage is also referred to as the breakdown voltage. In the test setup, the breakdown voltage is considered to be reached when, with increasing voltage, the digital display of the ammeter flickers to the third decimal place, i.e., when a current of 0.001 mA is present, at least briefly, indicating that a current is flowing through the multilayer filter medium.

[0100] The inventors' experiments found that the breakdown voltage of a medium is greatest in the flat, unbent state. Bending or folding the filter media results in a lower breakdown voltage and thus presents more challenging conditions. The breakdown voltages for the non-mechanical separation processes disclosed below (i.e., hot-cut / fusion cutting, ultrasonic cutting) were determined on flat media. Since the results obtained in this state were already inadequate, they were not determined in the folded state. For the mechanical separation processes, however, the measurements were carried out in both the pleated and laminated states in order to simulate the most realistic and demanding operating conditions possible.

[0101] Subexperiment A In subexperiment A, the multilayer filter media were cut along their longitudinal edges using various cutting methods, ensuring that the cut passed through all layers. Between four and six samples were measured for each method. The results are shown in Table 1. Table 1 - Measured breakdown voltages in subexperiment A, all measured values ​​in kV.

[0102] From the data compiled in Table 1, it is clear that excellent flashover voltages can be achieved with shear cuts, whereas the melting or welding processes lead to strong reductions in the flashover voltage.

[0103] The results for the crush cut appear ambivalent in Part A. It is clearly evident that very poor but also quite acceptable results can be achieved using the crush cut. In this respect, it should be noted that in the inventors' initial experiments, which are summarized in Part A, the orientation of the layers relative to the

[0104] The cut had not yet been taken into account. Based on the inventors' later experiments, it can be clearly deduced that the orientation of the layers during the crush cut of samples 3, 4, and 5 was probably not in accordance with the invention. Subexperiment B

[0105] In sub-experiment B, the multi-layer filter media were cut along the longitudinal edges using different separation methods in such a way that the cut was made through all layers, with six samples being measured for each method.

[0106] To verify the assumption that the deterioration in the breakdown voltage is due to dust generation, a series of tests combined the crush cut with a downstream extraction system to remove any dust generated. The results are shown in Table 2.

[0107] Table 2 - Measured breakdown voltages in sub-experiment B, all measured values ​​in kV.

[0108] From the data compiled in Table 2, it is clear that consistent improvements in crush cutting can be achieved through the use of suction, while excellent results can be achieved with shear cutting.

[0109] However, the results for the crush cut are still ambiguous in sub-experiment B, as sufficiently high breakdown voltages could not be achieved in all cases. In this respect, it should be noted that the orientation of the layers relative to the cut was not yet taken into account in the inventors' initial experiments, which are summarized in sub-experiment B. Thus, it was deduced from sub-experiment B that other influencing factors must be contributing. Based on the inventors' later experiments, it can also be clearly deduced in this case that the orientation of the layers during the crush cut of samples 3, 4, and 5 was probably not in accordance with the invention.

[0110] Subexperiment C

[0111] In sub-experiment C, the multi-layer filter media were cut along the longitudinal edges using different separation methods in such a way that the cut was made through all layers, with six samples being measured for each method.

[0112] To verify the assumption that the deterioration in the breakdown voltage is due to dust development, multilayer filter media were investigated in subexperiment C, which lacked the activated carbon layer compared to the setup shown in Fig. 3. The results are shown in Table 3.

[0113] Table 3 - Measured breakdown voltages in sub-experiment C, all measured values ​​in kV.

[0114] From the data presented in Table 3, it is clear that in the absence of the activated carbon layer, comparable results can be obtained with both shear cutting and crush cutting, thus underlining that the difficulties observed are indeed due to the activated carbon layer.

[0115] Subexperiment D In subexperiment D, the multilayer filter media were cut along their longitudinal edges in such a way that the cut passed through all layers. In this case, the orientation of the layers relative to the cutting direction was taken into account for the pinch cuts. Four samples were measured for each cutting direction. The results are shown in Table 4.

[0116] Table 4 - Measured breakdown voltages in sub-experiment D, all measured values ​​in kV.

[0117] The data summarized in Table 4 clearly demonstrates that the arrangement of the layers in the pinch cut has a significant influence on the achievable flashover voltages. If the pinch cut is performed with the activated carbon layer at the bottom, so that the upper conductor layer and the two dielectric layers of the intermediate layer are severed before the activated carbon layer, favorable results are also achieved in the pinch cut.

[0118] Overall, however, it is also evident in sub-experiment D that the use of a shear cut is particularly preferred.

[0119] Subexperiment E

[0120] In sub-experiment E, the multilayer filter media were trimmed along the longitudinal edges with a scissor cut such that the cut passed through all layers. For comparison with the state of the art according to DE 102023121052 A1, the comparison was made with multilayer filter media in which the topmost conductor layer did not extend to the side edge. These filter media were trimmed along the longitudinal edges with a pinch cut such that the cut did not pass through the topmost conductor layer, as the topmost conductor layer was spaced apart from the edges. The results are shown in Table 4.

[0121] Table 5 - Measured breakdown voltages in sub-experiment E, all measured values ​​in kV.

[0122] From the data compiled in Table 5, it is clearly evident that the use of a shear cut results in breakdown voltages that are at the same level as or even higher than the values ​​that can be obtained with the significantly more complex method according to the state of the art, thereby proving the advantage of the method according to the invention.

[0123] Subexperiment F

[0124] In sub-experiment F, pleated multilayer filter media were cut at an angle of approximately 45° to the pleat direction using a burst cut such that the cut passed through all layers, separating one edge of the multilayer filter media at a time. In the subsequent measurements, consistently excellent breakdown voltages were achieved, which were essentially identical to those of the unprocessed multilayer filter media. Reference symbols

[0125] 10 multi-layer filter medium

[0126] 12 multi-layer initial layer composite

[0127] 14 first conductor layer 16 second conductor layer

[0128] 18 Intermediate layer

[0129] 20 particle filter layer

[0130] 22 activated carbon layer

[0131] 24 Separating tool 26 Protective layer

[0132] 28a, 28b multilayer precursor material

[0133] 30 underlay

[0134] 32 Suction device

Claims

Claims 1. A method for producing a multi-layer filter medium (10) for use in an electrostatic precipitator with filter functionality, comprising the method steps: a) producing or providing a multi-layer starting layer composite (12), comprising: a.1) an electrically conductive first conductor layer (14), a.2) an electrically conductive second conductor layer (16), and a.3) an intermediate layer (18) arranged between the first conductor layer (14) and the second conductor layer (16), wherein the intermediate layer (18) comprises at least one dielectric layer (20) and at least one activated carbon layer (22), wherein the activated carbon layer has a basis weight of 50 g / m 2or more, wherein the activated carbon layer has an average thickness of 0.4 mm or more at a test pressure of 1 kPa, b) separating a part of the multi-layer starting layer composite (12), wherein the separating comprises a mechanical separation using a separating tool (24), wherein the separating tool (24) has a cutting edge with a cutting bevel angle of 90° or less, wherein the separation takes place at least through the first conductor layer (14), the activated carbon layer (22), the dielectric layer (20) and the second conductor layer (16) of the multi-layer starting layer composite (12), and wherein the separation comprises either b1) a shear cut, or b2) a burst cut, or b3) a pinch cut, in which the separating tool (24) severs one of the conductor layers (14, 16) and at least one dielectric layer (20) of the intermediate layer (18) before the activated carbon layer (22).

2. The method according to claim 1, wherein the separation in method step b) comprises at least the separation of a side region of the multi-layer starting layer composite (12).

3. Method according to one of claims 1 or 2, wherein the separation in method step b) comprises the singulation of a partial layer composite from the initial layer composite (12), wherein the partial layer composite is the multi-layer filter medium (10) or wherein the multi-layer filter medium (10) is produced from the partial layer composite.

4. The method according to any one of claims 1 to 3, wherein the separation in step b) comprises a shear cut.

5. The method according to any one of claims 1 to 4, wherein the separation in step b) comprises a bursting cut.

6. The method according to any one of claims 1 to 5, wherein the separation in method step b) comprises a pinch cut, in which the separation tool (24) separates one of the conductor layers (14, 16) and at least one dielectric layer (20) of the intermediate layer (18) in front of the activated carbon layer (22).

7. The method according to claim 6, wherein the crimp cut is carried out such that the separating tool (24) cuts one of the conductor layers (14, 16) and at least two dielectric layers (20) of the intermediate layer (18), preferably all dielectric layers (20) of the intermediate layer (18), before the activated carbon layer (22).

8. The method according to any one of claims 1 to 7, wherein method step b) additionally comprises the suction removal of particles released during separation from the multi-layer starting layer composite (12).

9. The process according to any one of claims 1 to 8, wherein the activated carbon is particulate activated carbon.

10. The method according to any one of claims 1 to 9, wherein the activated carbon layer (22) has a basis weight in the range of 50 to 1000 g / m 2 has.

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