Inherently stable flow-through porous filter element and method for producing such a filter element

Abstract

To provide an essentially stable flow-through porous filter element for filtering foreign matter from a gas stream, which comprises a porous filter body and a surface filtration layer formed on the inflow side of the filter body.SOLUTION: An intrinsically stable, flow-through porous filter element for filtering foreign bodies out of a gas flow, comprising a filter body made of plastic, having an inflow side and an opposite outflow side, wherein a surface filtration layer is formed on the inflow side, wherein the filter body has a three dimensional support structure produced in an additive manufacturing process, wherein the support structure has a plurality of cavities through which gas can flow from the inflow side to the outflow side, and wherein the surface filtration layer at least partially fills the cavities of the three dimensional support structure.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an essentially stable flow-through porous filter element for filtering contaminants from a gas stream. The present invention also relates to a method for making an essentially stable flow-through porous filter element for filtering contaminants from a gas stream. [Background technology]

[0002] Such filter elements are used in factories and plants in various industrial sectors, such as the automotive industry, the chemical industry, the food industry and the production of building materials.

[0003] Previously, the filter body of such filter elements was sintered and then provided with a surface filtration layer, for example in the form of a spray coating. Due to the nature of the process, the filter body is typically manufactured in multiple parts that are then bonded together to form a single filter body. While the sintering process allows for the mass production of inherently stable filter elements, it has certain limitations, for example, regarding the plastics that can be used and the structure of the filter body and / or surface filtration layer. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide an essentially stable flow-through porous filter element for filtering contaminants from a gas stream that does not suffer from these limitations and includes a porous filter body and a surface filtration layer formed on the inlet side of the filter body. [Means for solving the problem]

[0005] According to the present invention, a filter element having inherent stability and flow-permissive porosity therethrough, i.e., an inherently stable flow-through porous filter element for filtering contaminants from a gas stream, is proposed, which comprises a filter body made of plastic, having an inlet side and an opposite outlet side, with a surface filtration layer formed on the inlet side. The filter body is manufactured by an additive manufacturing process and comprises a three-dimensional support structure having a plurality of cavities through which gas can flow from the inlet side to the outlet side. The surface filtration layer at least partially fills the cavities of the three-dimensional support structure.

[0006] The present invention further provides a method for manufacturing an essentially stable flow-through porous filter element for filtering contaminants from a gas stream, the filter body being made of plastic and having an inlet side and an opposite outlet side, the method comprising at least the following steps: manufacturing a three-dimensional support structure by an additive manufacturing process, such that a plurality of cavities are formed in the three-dimensional support structure, through which gas can flow from the inlet side to the outlet side, and partially filling the cavities of the three-dimensional support structure with a coating material to form a surface filtration layer.

[0007] The three-dimensional support structure is fabricated by an additive manufacturing process, particularly laser sintering, stereolithography, particularly UV-based or low-force stereolithography, DLP, binder jetting, particle jetting, or FDM, each of which results in a distinctive structure in the resulting three-dimensional support structure and, if applicable, in other portions of the filter body that are fabricated in the same way, particularly by the same manufacturing process as the three-dimensional support structure.

[0008] Additive manufacturing processes allow filter bodies to be manufactured with desired shapes and mechanical properties, such as strength and rigidity, without the limitations imposed by conventional processes. Additive manufacturing also offers the possibility of manufacturing three-dimensional support structures together with the filter body. Additive manufacturing processes eliminate the need for molds or forms that specify the shape of the parts to be manufactured; instead, parts are generated under computer control based on digital 3D design data. In this way, filter elements of any size and shape can be manufactured in a single process, particularly with integrated filter bodies, and, if applicable, even with the filter body, connecting elements, and at least a portion of the surface filtration layer, or parts for adhering the surface filtration layer applied in a separate manufacturing process, being integrated or manufactured in one piece. Filter bodies and such parts can be manufactured in a single printing process, even if they have different shapes or differ in terms of the materials from which the filter body or individual parts are made. Filter elements manufactured using additive manufacturing processes can be recognized, in particular, by the fact that the filter body manufactured using additive manufacturing processes, and, if applicable, the additional parts, have shapes that typically cannot be achieved using a casting process. Additively manufactured parts may have, for example, cavities or undercuts and protrusions.

[0009] The three-dimensional support structure allows for a permanently durable bond between the surface filtration layer and the filter body, even under heavy loads typically expected during operation (e.g., as a result of a strong inflow of raw gas containing partially abrasive foreign particles and / or the application of pressure pulses during repeated cleaning cycles). The three-dimensional support structure is formed so that the particles of the surface filtration layer (this applies particularly to the particles of the first layer of the surface filtration layer, described in more detail below) can be wedged into the support structure when the surface filtration layer is applied. The cavities are free spaces within the support structure through which gas can flow. In this case, the cavities are formed by the support structure itself. Because the three-dimensional support structure is produced by an additive manufacturing process, it can have cavities, particularly those with so-called parametrically controlled pore configurations. This term is intended to indicate that the cavities or pores formed in the three-dimensional support structure by an additive manufacturing process can be specifically tailored in size and shape to produce a corresponding three-dimensional support structure with cavities.

[0010] The support structure also ensures stability during the manufacturing process of the filter element. In particular, support structures manufactured by additive manufacturing improve the stability of the green compact of the filter element before curing and post-processing.

[0011] The inlet side of the filter body is the side where the gas flow containing the contaminants reaches the filter element during filtering and penetrates the surface filtration layer. The downstream side of the filter body is the side where the gas flow with the contaminants removed leaves the filter element. Therefore, when the filter element is installed, the inlet side faces the raw gas space of the filter system, and the outlet side of the filter body faces the clean gas space of the filter system.

[0012] A plastic filter body is obtained when the filter body has a plastic as its main component. In addition to the main component of plastic, other components may be present in the filter body, for example, in the form of additives or fillers. Whether such additional components are plastic or non-plastic is immaterial. The plastic for producing the filter body can be formed from one polymer material or from several polymer materials (e.g., in the form of a polymer blend or mixed polymer). Hereinafter, when the composition of a plastic is mentioned, for example, in connection with the filter body and / or filter element, this should always be understood to mean that the plastic can be formed from only one polymer material or from several polymer materials. The term polymer material should be understood as a general term and is intended to include both homopolymers composed of the same type of monomers and copolymers, such as block copolymers and other polymers composed of different types of monomers.

[0013] Additively manufactured filter elements can be produced with such high precision that little or no post-processing is required. A wide range of shapes and sizes of filter elements can also be produced this way.

[0014] Possible embodiments and further developments are set out in the dependent claims and are described below. These embodiments and further developments are expressly intended to refer to both the filter element according to the invention and the manufacturing method according to the invention. It is understood that the respectively described embodiments and further embodiments can be combined with each other as desired, unless it is expressly indicated in the individual aspects that they are alternatives to each other.

[0015] In particular, the three-dimensional support structure may comprise a cage structure that is open toward the inlet side. In particular, such a cage structure may be designed so that the material for forming the surface filtration layer is contained in individual cavities. Each cavity forms a type of cage, and the material contained in each cavity is held by the three-dimensional support structure that surrounds the cage. In particular, the cage structure is designed so that the material for forming the surface filtration layer is introduced into each cage after the three-dimensional support structure is manufactured. The material for forming the surface filtration layer can be in particulate form when introduced into at least the cavities of the three-dimensional support structure. The cage structure is then designed so that in each case, the particles introduced into the cavity are held by the cage structure, so that in each case, most of the material introduced into the cavity remains there and is not further transported through the bottom or side boundaries of the cavity. To assist in holding the particles within the cage structure, an adhesive system such as an adhesive can be used. The retention of the material in the cavities may be further enhanced by the fact that the material for forming the surface filtration layer has a configuration and / or is introduced into the cavities such that the particles of the material in the cavities bond with each other to form agglomerates, which often extend across several adjacent cavities and thus form bridge structures that lead to particularly good fixation of the material for the surface filtration layer in the cavities of the cage structure.

[0016] To form a cage-like structure, the three-dimensional support structure can form, in particular, a basket-, cup-, or funnel-shaped cavity, each having a bottom side and an opposite open side, where the open side can face the inlet side so that the material for forming the surface filtration layer can be easily introduced into the cage structure through the open side.

[0017] Each basket-, cup-, or funnel-shaped cavity can have a lateral boundary, e.g., in the form of a side wall, connecting the bottom side to the open side and having an opening through which adjacent basket-, cup-, or funnel-shaped cavities communicate with each other. Such lateral boundaries can block, or at least hinder and / or guide, the lateral movement of the particles of the material forming the surface filtration layer to such an extent that their "dropping out" of the cavity and further transport toward the inlet and / or outlet sides is effectively suppressed. However, through the openings formed in the lateral boundaries, the particles of the material for the surface filtration layer can still connect with each other across adjacent cavities, thus forming aggregates or bridge structures extending across multiple adjacent cavities. In this way, a secure fixation of the material of the surface filtration layer in the three-dimensional support structure is formed.

[0018] In particular, the open side of each cavity may have a front opening, and the bottom side and / or side boundary of each cavity may have a rear opening. In this regard, it is advantageous if, in an orthogonal projection from the open side to the bottom side, multiple rear openings on the bottom side and / or side boundary are located within the area defined by the front openings on the open side. In particular, an orthogonal projection is obtained when the three-dimensional support structure is viewed from the inlet side, looking in a direction perpendicular to the surface of the three-dimensional support structure. In this case, the front openings formed on the inlet side and the openings located within each front opening behind them and positioned closer to the outlet side are visible. These rear openings are defined by structures of the three-dimensional support structure located on the corresponding outlet side, such as structures defining the bottom side of the cavity and structures forming the side boundaries of the cavity. However, in the above-mentioned orthogonal projection, only the portion of each rear opening that is within the area of ​​the front opening on the inlet side is visible. Here, we consider the projected area of ​​this portion of the rear opening on the outlet side in addition to the area of ​​the front opening on the inlet side. Looking perpendicularly at the front openings, multiple rear openings that typically appear small at first glance are visible. For example, the rear openings may in fact be smaller than the respective front openings on the open side. In this case, the rear openings may be arranged in any way relative to the front openings. The rear openings, in particular the rear openings on the bottom side of the cavity of the cage structure further towards the outlet side, may also be made larger than or equal to the respective front openings on the open side. However, in this case, the rear openings should be arranged laterally offset relative to the front openings on the open side, so that some rear openings are always at least partially visible in the aforementioned projection, i.e. when viewed from the inlet side through the front openings on the open side.

[0019] In particular, the open side of each cavity of the three-dimensional support structure can have only one front opening, and thus, in this configuration, each cage structure is associated with exactly one front opening facing the inlet side through which material for forming the surface filtration layer can be admitted into the cage structure.

[0020] The filter body may define a thickness direction extending between its inlet and outlet sides. The surface filtration layer may fill the cavities of the three-dimensional support structure, for example, over at least 10% of its thickness, particularly over at least 25% of its thickness, particularly over at least 50% of its thickness, particularly between 25% and 100%, particularly between 50% and 75% of its thickness. This allows for advantageous connection or bonding between the surface filtration layer and the filter body, particularly the three-dimensional support structure. The greater the proportion of the surface filtration layer embedded in the cavities of the three-dimensional support structure, the more durable the bond between the surface filtration layer and the support structure.

[0021] For example, the surface filtration layer can fill the cavities of the three-dimensional support structure over at least 10% of the thickness of the three-dimensional support structure, particularly over at least 25% of the thickness of the three-dimensional support structure, particularly over at least 50% of the thickness of the three-dimensional support structure, particularly between 25% and 100% of the thickness of the three-dimensional support structure, particularly between 50% and 75% of the thickness of the three-dimensional support structure. This allows for advantageous adhesion of the surface filtration layer to the filter body, particularly the three-dimensional support structure. The more the surface filtration layer is embedded in the support structure, the more durable the bond between the surface filtration layer and the support structure. In extreme cases, the cavities of the three-dimensional support structure can be filled with material from the surface filtration layer over the entire thickness of the three-dimensional support structure. In this case, substantially all of the cavities formed by the three-dimensional support structure will be filled with material from the surface filtration layer. Therefore, the three-dimensional support structure can also be considered part of the surface filtration layer, especially in cases where the portion of the three-dimensional support structure filled with material from the surface filtration layer occupies a large portion of the three-dimensional support structure and / or the surface filtration layer.

[0022] The average degree of filling of the cavities of the three-dimensional support structure with the surface filtration layer material may vary depending on the material composition of the surface filtration layer. This may also be influenced by the application method in which the surface filtration layer material is applied. For example, coating materials or processes that have a strong tendency to form agglomerates between individual particles of the coating material introduced into the cavities of the three-dimensional support structure may already detect strong fixation of the coating material at moderate fill levels, particularly below 50% or between about 30 and 50%, due to the formation of bridge structures spanning multiple adjacent cavities caused by particle agglomeration. Other coating materials or processes, such as liquid-based ones, may require higher fill levels, such as at least 50%, at least 75%, or even up to 100%, to achieve the desired fixation of the coating material in the three-dimensional support structure.

[0023] According to the previous embodiment, the surface filtration layer can be integrally or integrally formed with the filter body. This particularly relates to the three-dimensional support structure, which can be manufactured in the same additive and printing processes as the filter body. In this sense, the filter body and the surface filtration layer are manufactured in one piece. This reduces the number of steps required and lowers manufacturing costs. The cohesion between the filter body and the surface filtration layer is also particularly good when the configurations of the filter body and the surface filtration layer, in particular the support structure or "mother pore structure" of the filter body and the three-dimensional support structure, are only slightly or completely different. In particular, the support structure of the filter body and the three-dimensional support structure can be made of the same material.

[0024] It is further proposed that the surface filtration layer includes a first layer that at least partially, particularly to a large extent, fills the cavities of the three-dimensional support structure. The first layer substantially forms a filling layer of the three-dimensional support structure. The term "to a large extent" refers to the mass of the first layer, i.e., the portion of the first layer that fills the cavities of the support structure (relative to its mass) per surface area of ​​the filter element is greater than the portion of the first layer that is applied to the three-dimensional support structure outside the cavities. In particular, the first layer fills the cavities of the three-dimensional support structure by at least 30%, particularly at least 65%, particularly at least 75%, particularly at least 85%, and particularly at least 95% of its mass. In this way, the first layer provides good fixation of the surface filtration layer in the three-dimensional support structure, and thus to the filter body. Despite good fixation, the filling of this three-dimensional support structure with the material of the first layer can be very porous, so that the flow resistance through the filter element remains within an acceptable range.

[0025] The surface filtration layer can include at least a second layer applied to the first layer from the inlet side. This can be done, for example, so that the second layer forms the surface of the inlet side of the filter body. However, it is also conceivable that in addition to the second layer, the first layer, and possibly the three-dimensional support structure itself, also contribute to forming the surface of the inlet side of the filter body. The first layer can be considered a foundation for the at least second layer. The at least second layer can easily adjust or set which contaminants are filtered from the gas flow before entering the filter body, particularly contaminants of a corresponding size. If applicable, the at least second layer can also include multiple layers stacked on top of each other, each layer forming the initial surface of the gas flow on the inlet side of the filter body in the direction of gas flow during filtering. The second layer, together with the first layer, if applicable, forms a suitable surface filtration layer for the most part. In a further embodiment, the second layer can form the surface of the inlet side of the filter body together with part of the first layer and even part of the three-dimensional support structure.

[0026] The first and second layers can have different pore sizes. In this case, the pore size of the first layer can be larger than the pore size of the second layer. This reduces the pressure loss of gas flow through the filter element because only a relatively small thickness of the inlet-side surface filtration layer needs to have very low porosity. The thickness of this low porosity is determined primarily by the second layer, in cooperation with the first layer and / or the three-dimensional support structure, if applicable. The porosity of the three-dimensional support structure can be very large without affecting its stability. This is where the advantages of additive manufacturing processes can be optimally utilized. The first layer can be formed from a relatively coarse-grained material, and even if the three-dimensional support structure is filled with the material of the first layer, flow resistance remains low and significant pressure loss does not occur as the gas flow passes through the filter element. Flow resistance is essentially determined by the portion of the surface filtration layer where the second material is located. The thickness of this portion can be very small, resulting in an overall low flow resistance.

[0027] In this configuration, most of the foreign matter accumulates on the surface of the surface filtration layer and does not penetrate deep into the filter element in the direction of the gas flow, which makes it easier to clean the filter element, and the filter quality of the filter element can be improved in a short time after cleaning.

[0028] The surface filtration layer can be configured such that the first and second layers form a transition region therebetween and the material of the second layer penetrates and at least partially fills the interstices between the particles of the first layer, thereby providing particularly strong cohesion between the first and second layers of the surface filtration layer.

[0029] The surface filtration layer may form the surface of the filter body, which in some embodiments is formed by the first and second layers, also in cooperation with a three-dimensional support structure, so that foreign matter remains on the surface of the filter body, allowing the filter body to be effectively cleaned.

[0030] At least the second layer may adhere to the first layer or form an inlet surface filling the cavity of the first layer and the three-dimensional support structure over a thickness of up to 50% of the support structure, particularly up to 25% of the thickness, particularly up to 5% of the thickness, particularly up to 1% of the thickness.

[0031] In particular, the pore size of the three-dimensional support structure can be between 100 μm and 2000 μm. The pore size of the second layer of the surface filtration layer can be between 0.1 μm and 20 μm, and the pore size of the first layer of the surface filtration layer can be between 1 μm and 200 μm. The pore size refers to the average pore size that occurs on the surface of the corresponding layer or structure when the first or second layer is made of a granular material and pores are formed between the granular material. The pore size can be determined and measured, in particular, using a pore measurement device. When "pores" or "pore size" are referred to here or below, this term should be understood generally and is intended to include any type of hole, opening, cavity, open microstructure, or other structure in a solid structure that is structured to be permeable to a fluid. For example, in some additive manufacturing processes, by target selection and definition of "voxels" (voxels refer to basic volume elements used to discretely divide a three-dimensional space into these elements for addressing the three-dimensional space, and are similar to "pixels" in two-dimensional objects), it is possible to intentionally create an open microstructure in the objects thus produced (filter elements, filter bodies, surface filtration layers, and especially three-dimensional support structures) that provides the same functionality as pores in the conventional sense of sintered porous bodies produced by conventional methods.

[0032] Pore ​​size can be measured, for example, using a capillary flow porometer, PSM165, from TOPAS. The measurement principle is explained below. When a fluid flows through a medium, a pressure loss occurs, which is strongly influenced by the pore size distribution. The resistance to flow can only be determined by flow tests. The relationship between the effective pressure difference and the resulting volumetric flow rate is measured. In addition to other methods, such as microscopic imaging and corresponding evaluation, pore size can also be determined by applying pressure and measuring the volumetric flow. The operating principle of this measurement is that liquid-filled pores only become gas-permeable at a certain pressure, as the liquid is expelled from the pores. The pore opening pressure (bubble point) depends on the surface tension of the liquid and the pore diameter. Smaller pores require higher pressures. Since a real material always has a distribution of pore sizes, the pressure at which previously liquid-filled pores become gas-permeable corresponds to the opening pressure of the largest pore. By further increasing the pressure, the pore size distribution can be inferred from the progression of the pressure difference and volumetric flow.

[0033] In any case, the second layer can contain PE, PTFE, SiO2, such as microglass, hollow glass, foam glass, solid glass or sand, PPS, aluminum oxide, or a mixture of at least two of the above materials. In particular, the second layer can contain the above materials in particulate form. This allows for better cleaning of the surface filtration layer. Furthermore, the surface filtration layer can also have a bactericidal effect.

[0034] The surface filtration layer can be formed, at least in part, as a coating. In either case, the first and second layers can be formed as coatings, particularly by liquid deposition, spraying, brushing, dip coating, baking, and / or thermal spray processes, such as flame spraying. This results in a uniform surface filtration layer suitable for enabling good filtration performance. Furthermore, the coating can be applied quickly and easily. Furthermore, proven methods can be used to apply the surface filtration layer to the filter body. Generally, coatings obtained from liquid or suspension-based coating processes fill the cavities of the three-dimensional support structure to a greater extent with the surface filtration layer material (especially the first layer material) than with coatings obtained from thermal spray processes, such as flame spraying, or other thermal spray processes. This is because, in the latter process, the material considered for forming the surface filtration layer can form bridges between particles accommodated in different cavities of the three-dimensional support structure. This results in good anchoring of the first layer material even at a relatively low fill level of about 30% of the volume of the cavity of the three-dimensional support structure.

[0035] The three-dimensional support structure can have a framework-like or truss-like configuration with rods connected to each other at nodes. A truss-like configuration is understood to mean that multiple rods are connected to each other at nodes, and therefore the three-dimensional support structure has inherent stability and can survive without additional structures. In addition to good inherent stability with a high porosity, an advantage of a truss-like design is that the formed cavities can have a nearly uniform distribution in the three-dimensional support structure. This allows for the efficient production of durable surface filtration layers. Truss structures have a low self-weight or specific weight compared to their load-bearing capacity. The three-dimensional support structure can also be produced, for example, with a periodic minimum surface, particularly a tri-periodic minimum surface. More generally, the three-dimensional support structure can also be formed from an osteogenic or porous structure. The available space for fluid flow can be particularly large.

[0036] The three-dimensional support structure can have a lattice-like structure forming at least two lattice layers, one of which faces the inlet side, particularly defining the inlet side, and the other lattice layer facing the outlet side. The lattice layers can be connected to each other by rods or webs. The two lattice layers are arranged one behind the other in the flow direction of the gas flow as it passes through the filter element. The lattice layer facing the inlet side can define the inlet side in the sense that no further structure is formed thereon, except for the first and possibly second layers of the surface filtration layer, and thus the position of the filter surface is defined by the inlet side of the three-dimensional support structure. The two lattice layers, or, if present, the additional lattice layer, can be oriented substantially parallel to each other, where "substantially parallel to each other" includes a tilt of plus or minus 10 degrees relative to each other. The lattice-like structure can achieve uniform cavities, particularly with regard to the shape and size of the cavities, which can be easily and quickly filled with the surface filtration layer, particularly its particles. The rods or webs connecting at least two lattice layers to each other extend substantially in the direction of gas flow through the filter element, transverse to the inlet and / or outlet sides. An additional lattice layer may be provided between two lattice layers. A three-dimensional support structure having a total of three lattice layers is particularly preferred. In this case, an additional lattice layer is present between one lattice layer defining the inlet side and the other lattice layer facing the outlet side. The surface filtration layer at least partially fills the intermediate space between the two lattice layers. This allows the surface filtration layer to be firmly and durably adhered to the support structure.

[0037] One and / or the other lattice layer may have a configuration with rods connected to each other at nodes and defining openings. This configuration defines a lattice structure in which a plurality of at least three adjacent rods, in particular four adjacent rods, of each lattice layer surrounds an opening in the lattice layer. Arrangements in which the openings are defined by higher-order polygons are also contemplated. Then, a plurality of n adjacent rods of each lattice layer each surrounds one opening in the lattice layer.

[0038] One and / or the other lattice layer can have a regular lattice structure. The term "regular lattice structure" should be understood to mean that the arrangement of the openings and rods in each lattice layer has a regular pattern with a repeating arrangement of the rods relative to each other and / or the openings. In particular, the arrangement of the rods in each lattice layer then defines regular openings. For example, all openings in a lattice layer can have the same size and / or shape. Alternatively, larger first openings and smaller second, third, etc. openings can be provided, with the arrangement of the first, second, third, etc. openings defining a regular pattern. The advantages of a regular lattice structure are its stability and the generally uniform distribution of openings in the regular lattice structure. This allows for the efficient production of durable surface filtration layers.

[0039] The at least two lattice layers may be arranged such that the openings of one of the two lattice layers are offset from the openings of the other of the two lattice layers, thereby allowing the surface filtration layer, and in particular the particles of the surface filtration layer, to efficiently fill the cavities.

[0040] The three-dimensional support structure may include three lattice layers arranged one behind the other in the flow direction between the inlet and outlet sides of the filter body. The openings in the center lattice layer may be offset from the openings in the other two lattice layers. In particular, each lattice layer has the same configuration of rods and openings. This allows for efficient filling of the cavities with the surface filtration layers, particularly the particles in the surface filtration layers.

[0041] The three-dimensional support structure may include three lattice layers arranged one behind the other in the flow direction between the inlet and outlet sides of the filter body. The openings of the two outer lattice layers may be arranged to coincide with each other. In particular, the lattice layers may each have the same configuration of rods and openings. "Coincident" should be understood as coinciding with the flow direction of the gas flow during filtering.

[0042] The openings in one, the other and / or the central grid layer may be triangular, quadrangular, in particular square, rectangular, rhomboid or rhombus or parallelogram, polygonal, circular and / or elliptical.

[0043] The webs or rods connecting two adjacent lattice layers can be offset from the nodes of the two lattice layers. In particular, they can be positioned centrally between the two adjacent nodes. This means that the webs or rods connecting two adjacent lattice layers start on both lattice layers in the section between the two nodes, especially in the center. In this way, a cage structure is formed between the two adjacent lattice layers, which is suitable for retaining particles of the surface filtration layer, especially particles of the first layer, especially against movement transverse to the plane of the lattice layers. The cage structure itself has as small a surface area as possible so as not to impede gas flow. This arrangement is advantageous, for example, when the two lattice layers are offset so that the nodes of one lattice layer are located in the center of the openings of the other lattice layer. In orthogonal projection, the nodes of one lattice layer are located in the center of the openings of the other lattice layer. In this case, the rods or webs connecting the two lattice layers to each other can be perpendicular to the plane of the two lattice layers and can start from the center of the rods or webs located in the plane of each lattice layer and connecting adjacent nodes of each lattice layer.

[0044] It is also conceivable that the rods or webs connecting two adjacent lattice layers are positioned at the nodes of one lattice layer and offset from the nodes of the other lattice layer. This means that the webs or rods start at the nodes of one lattice layer and terminate at the section between two nodes of the other lattice layer. For example, the webs or rods can start at the nodes of the lattice layer located on the inlet side but terminate at the section between two nodes of the central lattice layer. Similarly, the webs or rods can start at the nodes of the lattice layer located on the outlet side and terminate at the section between two nodes of the central lattice layer. In this way, cage structures are formed between two adjacent lattice layers, which are well suited to retaining particles in the surface filtration layer, particularly the first layer.

[0045] The term lattice layer particularly refers to a layer having several parallel-oriented webs or rods extending in a first direction and several other parallel-oriented webs or rods extending in a second direction. The first and second directions are at an angle to each other, particularly a 90° angle. In this way, the webs or rods together form a lattice or net. Where a web or rod extending in the first direction intersects with a web or rod extending in the second direction, a node is formed. Between two nodes, there is an uninterrupted stretch of the corresponding web or rod.

[0046] The at least two lattice layers define a pore structure. The pore structure typically has a pore diameter between 1 μm and 10,000 μm, especially between 100 μm and 2,000 μm. The pore diameter indicates the maximum diameter of particles (especially circular particles) that can be accommodated in the pores. The two lattice layers create parametric pores, i.e., pores formed by the relative placement of the at least two lattice layers. Thus, the pores in the lattice layers are not randomly positioned but are parametrically controlled. Even seemingly random pores formed in this way can be created parametrically, for example, by using a randomizer to intentionally create randomness in the pores. This is advantageous when printing processes that can handle irregular distributions are used. For example, in stereolithography, particle jetting, and fused deposition modeling, the CAD-defined pore structure is directly implemented in the material. In processes that fuse or bond powders in a powder bed (selective laser sintering, selective laser beam melting, binder jetting), it is preferable to create the laser paths and bonding points in CAD rather than drawing the pore structure as a solid. The irregular structure of the material's grain size, along with the controlled irregularity within certain parameters, then forms the actual pores in the additively manufactured substrate. The webs that define the pores may themselves be porous.

[0047] The filter body may further include a three-dimensional base structure, hereinafter also referred to as a "mother pore structure." The three-dimensional support structure is disposed on the inlet side of the mother pore structure. The mother pore structure has a different structure from the three-dimensional support structure, and the mother pore structure in particular has larger openings or pores than the three-dimensional support structure. The surface filtration layer is disposed on the side of the three-dimensional support structure facing away from the mother pore structure. The mother pore structure provides additional stability to the filter element. The mother pore structure also allows the gas flow swirled by the support structure to settle before leaving the filter element.

[0048] The three-dimensional pore structure may have a larger pore size than the three-dimensional support structure. The filter body may include an ultraviolet-crosslinkable thermosetting polymer material, particularly as a main component for the three-dimensional support structure and, optionally, the pore structure. The main component may include polyethylene, polysulfone or polyphenylene sulfide, polyamide, such as nylon in laser sintering, or polylactide, or a mixture of these materials.

[0049] The mother pore structure and the three-dimensional support structure can be manufactured by an additive manufacturing process, in particular a 3D printing process. In particular, both structures can be manufactured by the same additive manufacturing process. This allows for rapid production of the filter body, and therefore the filter element.

[0050] Both the mother pore structure and the three-dimensional support structure can be formed from a solid material or from a porous material.

[0051] A pore structure can be distinguished from a three-dimensional support structure in that, for example, the pore structure establishes and / or defines the contours of the filter body, whereas the three-dimensional support structure follows this contour of the filter body and establishes a connection with the surface filtration layer.

[0052] It should also be noted that, if desired, the mother hole structure could be manufactured without the use of additive manufacturing processes, however, this would not take advantage of the advantages achievable by additive manufacturing processes.

[0053] The filter body may further include a three-dimensional support structure configured to form or attach additional components to the filter body, such as a filter element head or a filter element foot. Such a three-dimensional support structure may also form a mother pore structure, or the mother pore structure may form such a three-dimensional support structure.

[0054] The filter body may include at least one additional component different from the main component, in particular fibers, in particular staple fibers, or filled plastics, and the additional component may have at least one of the following properties: antistatic, conductive, antibacterial, antifungal, and flame-retardant.

[0055] The filter element can be designed as a hollow body, with the inlet side of the filter body located outside the hollow body and the outlet side of the filter body located inside the hollow body. In cross section, the filter element can be cylindrical, fir-tree, lamellar, or polygonal. Such cross sections are well suited to providing the filter element with sufficient inherent stability while creating as large a surface area as possible on the inlet side of the filter body.

[0056] The filter element may also have a box-like shape, in particular an elongated box-like shape. The box may have two opposing wide side walls formed by the long and wide sides of the box, respectively. At the end faces of the box, two narrow walls extending in the depth direction connect the two wide side walls. Elongated means that the longitudinal extension of the filter element is significantly greater than its width. In any case, the depth extension of the box is significantly smaller than both the longitudinal and width extensions.

[0057] The filter element may further include a filter head and / or a filter foot for closing the hollow filter body at the open end. In particular, the filter foot and / or the filter head may be configured to enhance the inherent stability of the filter element. For example, the filter element may be held or supported on the filter head and / or the filter foot.

[0058] In particular, in this regard, arrangements are envisaged in which the filter head is arranged at a first end of the filter element and the filter foot is arranged at a second end of the filter element opposite the first end.

[0059] In particular, the filter head and / or filter foot can be integrally or monolithically formed with the base. This is intended to specifically express that the filter head and / or filter foot are formed in the same additive process as the base. Such an integral design can improve the stability of the entire filter element by avoiding joints, which are typically weak points. Furthermore, it can avoid process steps during manufacturing, possible retooling, etc. The filter head and / or filter foot can be formed from the same polymer material as the filter body. However, the filter head and / or filter foot are generally non-porous. Of course, the filter head and / or filter foot can also be formed from a respective, specifically adapted polymer material.

[0060] The filter body and, optionally, the surface filtration layer may contain a thermoplastic polymer material as the main component, particularly polyethylene (PE), polypropylene (PP), polyphenylene sulfide (PPS), polyimide (PI), polyamide (PA), polyvinyl alcohol (PVA), polylactide (PLA), or a thermoplastic blend polymer based on these. The main component typically accounts for a larger proportion of the overall composition than the additional components. The filter body and, optionally, the surface filtration layer may contain multiple main components, or the main component may be a blend polymer. The addition of polyvinyl alcohol is particularly useful for creating pore structures, since many polyvinyl alcohols are readily soluble in water. Therefore, cavities can be formed by incorporating polyvinyl alcohol into the material of the filter body or surface filtration layer and then treating it with water. The addition of water also allows for targeted pore formation. This approach allows for the pore structure, particularly the pore size, to be tailored appropriately.

[0061] The filter body and, optionally, the surface filtration layer may comprise, as a main component, a thermosetting polymer material, in particular, an epoxy resin, a phenolic resin, a polyester resin, a melamine resin, a silicone resin, a urethane resin, or a mixed polymer based on these. In particular, polymer materials suitable for stereolithography or laser sintering can be used.

[0062] When the filter body or surface filtration layer is primarily made of a thermosetting polymer material, it is particularly possible that the filter body or surface filtration layer primarily contains an ultraviolet (UV) crosslinkable thermosetting polymer material, such as epoxy acrylate, or a polymer material that crosslinks by heat and / or in a humid environment.

[0063] The filter body and optionally the surface filtration layer may further comprise, in addition to one or more main components, at least one additional component different from the main component.

[0064] Suitable additional components include fibers, especially staple or short fibers. The fibers serve to increase strength and can be provided, for example, as glass fibers, ceramic fibers, or plastic fibers, such as aramid fibers, among others. The fibers can be, for example, carbon fibers. Natural fibers are also possible. Mixtures of such fibers and so-called filled plastics (plastic compounds) can also be used.

[0065] Filled plastics or compounds are processed plastics to which so-called additives (fillers, additives, fibers, etc.) have been added in a specific process, making their properties particularly adaptable.

[0066] The filter element (filter body and possibly the surface filtration layer) may also comprise additional components with antistatic properties, such as soot particles.

[0067] In yet another embodiment, additional components may include conductive particles, for example made of silver or so-called doped plastic particles that have been doped with electrons.

[0068] Other possible additional components may have antibacterial properties. For this purpose, silver, copper or titanium dioxide (T i O2) is possible.

[0069] Yet another possible additional component may have antiseptic properties, which may inhibit fungal growth in the filter body and / or surface filtration layer. Such an additional component may be, for example, copper.

[0070] It has also proven advantageous for the additional components to be flame-retardant. This reduces the flammability of the filter body and, if applicable, the surface filtration layer. This is particularly advantageous in connection with the filtration of combustible dust. Such components can be, for example, plastics based on polyoxymethylene (POM), polysulfone (PSU), or polyphenylene sulfide (PPS). Components based on aluminum trihydrate (ATH), magnesium hydroxide, organic bromine compounds, or layered silicates are also possible.

[0071] Additive manufacturing processes can produce fractal surface structures, which can very efficiently increase the surface area available for filtration for a given size of the filter element. It is also possible to shape the surface of the surface filtration layer in a way that creates a lotus effect, which makes the surface filtration layer easier to clean.

[0072] In particular, the filter element may comprise a filter body manufactured by a photopolymerization-based additive manufacturing process. Continuous liquid interface manufacturing methods are particularly suitable for this purpose. Continuous liquid interface manufacturing methods have the advantage of faster part production speeds compared to other three-dimensional manufacturing methods, since parts are continuously drawn from a polymer solution that hardens in place, as opposed to the predominantly layer-by-layer structure of other three-dimensional manufacturing methods.

[0073] Other additive manufacturing processes are also suitable for producing the proposed filter elements. In selective laser sintering (SLS) or selective laser melting (SLM), spatial structures are produced from powdered starting materials by selectively irradiating them with a laser, resulting in essentially point-like sintering of the powdered starting material in each irradiated volume. The laser is irradiated over an entire layer of powdered starting material, and is intentionally activated only at locations within the layer where sintering of the powdered starting material occurs. In this way, the filter body and, optionally, the surface filtration layer are built up layer by layer. The effect of the laser beam allows for the production of any three-dimensional shape, including undercuts, that cannot be produced by conventional sintering. Furthermore, the pore structure can be easily controlled by appropriately adjusting the laser beam. Another suitable additive manufacturing process is so-called binder jetting, in which powdered starting materials are bound to a binder at selected locations within the layer to produce the filter body and, optionally, the surface filtration layer. In the binder jetting process, powder or granular layers are typically applied onto a height-adjustable table and bound by a binder at the locations of the layer that form the pore walls of the filter body or surface filtration layer. For this reason, a print head that applies a binder instead of ink is used, similar to a normal inkjet printer.

[0074] The present invention will now be described in more detail with reference to the drawings, which should be understood as merely exemplary. The drawings are schematic, not to scale, and show only those features essential to an understanding of the invention. It is understood that additional features may be present, as known to those skilled in the art. In the drawings, like reference numerals respectively indicate identical or corresponding elements. [Brief explanation of the drawings]

[0075] [Figure 1] 1 shows an embodiment of a filter element according to the present invention, comprising a filter head and a filter foot. [Figure 2] 2 is a view showing the central portion of a cross section through the filter element at the position indicated by II-II in FIG. 1. FIG. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the cross-sectional view of FIG. 2. [Figure 4] FIG. 3 is an enlarged perspective view of the three-dimensional support structure of the embodiment of FIG. 2. [Figure 5] 1A-1C illustrate an exemplary method for manufacturing a filter element according to the present invention. [Figure 6] 1 is a schematic diagram illustrating an exemplary method for manufacturing a filter element according to the present invention. [Figure 7] 5A-5C are schematic diagrams illustrating other possible methods of manufacturing a filter element according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0076] The features of the individual exemplary embodiments can also be implemented in other exemplary embodiments, provided that this is technically feasible, and are therefore interchangeable, even if not specifically indicated in each case below.

[0077] FIG. 1 shows a filter element 1 having a plastic filter body 2. The filter body is made from a polymer material by an additive manufacturing process. The filter element 1 has a box-like shape, in particular a narrow box-like shape, whose extension in the longitudinal direction (x-direction in FIG. 1 ) and width direction (y-direction in FIG. 1 ) is significantly greater than its extension in the depth direction (z-direction in FIG. 1 ). In particular, the extension in the longitudinal and / or width direction of the filter element is at least twice, even at least five times, or even at least ten times greater than its extension in the depth direction. The filter element may have approximately the same dimensions in the longitudinal direction x and the width direction y. If desired, the filter element may be somewhat smaller in the width direction y than in the longitudinal direction x, but in any case, the extension in the width direction y is significantly greater than the extension in the depth direction z.

[0078] Furthermore, the filter element 1 has a filter head 3 and a filter foot 4, with the filter head 3 being located at an end on a first side 5 of the filter element 1 and the filter foot 4 being located at an end on a second side 6 of the filter element 1 opposite the first side 5. The embodiment of the filter element 1 shown in FIG. 1 is held by a partition 7 located on an edge of a filter device (not shown in detail), separating an inlet side 8 from an outlet side 9 of the filter device. The inlet side 8, also referred to as the raw gas side, corresponds to the side on which the gas flow containing the contaminants, the so-called raw gas, impinges on the filter element 1, while the outlet side 9, also referred to as the clean gas side, corresponds to the side on which the gas from which the contaminants have been removed, the so-called clean gas, flows out. Thus, the filter element 1 has an inlet side and an outlet side.

[0079] The filter element 1 has a filter head 3 fixed "transversely" to a partition wall 7 arranged at its edge, i.e., it extends from the partition wall 7 in the x-direction. FIG. 1 shows the so-called clean-fluid installation of the filter element 1, in which the side of the filter head 3 protruding beyond the filter body 2 on both sides in the y-direction and facing the filter foot 4 is attached to the partition wall 7 at the outlet side 9, and the filter body 2 of the filter element 1 protrudes through an opening in the partition wall 7. A seal 10 is visible between the filter head 3 and the partition wall 7, which serves to seal between the inlet side 8 and the outlet side 9. This allows the filter element 1 to be replaced from the "clean" outlet side 9. In the exemplary embodiment illustrated here, the filter foot 4 closes one end of the filter body 2, allowing the clean fluid to exit the filter body 2 through the filter head 3.

[0080] Alternatively, a so-called raw gas side installation of the filter element 1 is also conceivable, in which case the filter head 3 is fixed to the partition wall 7 from the inlet side 8 with its side facing away from the filter foot 4. The filter element 1 is therefore installed and removed via the inlet side 8.

[0081] Of course, it is also conceivable to fix the filter element 1 in a hanging manner rather than laterally, and the partition 7 is then provided laterally, preferably horizontally, in the filter device, for example in the form of an intermediate floor between the lower inlet side 8 and the upper outlet side 9. Furthermore, in this hanging installation position of the filter element 1, either a clean gas side installation or a raw gas side installation of the filter element 1 can be provided.

[0082] The filter body 2 consists of a porous, in particular flow-through porous structure, which can be formed in different ways. An exemplary embodiment is shown in Figure 3. A flow-through porous structure is understood to be a structure which forms a coherent body, but which is flow-through porous from the inlet side 8 of the filter body 2 to the outlet side 9 of the filter body 2, i.e. a body (in this case, the filter body 2) which is permeable to the passage of gas.

[0083] Furthermore, the filter body 2 of the filter element 1 according to the present invention is also inherently stable, meaning that it forms a body structure strong enough to support its own weight when held at only one of its longitudinal ends (the filter head) or alternatively at both its longitudinally spaced ends by additional support structures at the filter foot, as shown, for example, in Figure 1. However, beyond the filter body 2, the filter element 1 does not have any additional backbone or support structures made of the same material as the filter body 2. In further embodiments, the filter element can have additional structures, such as springs, that can be inserted into the filter body 2.

[0084] Such filter elements 1 are used, for example, in large industrial plants for purifying exhaust gases and have a length of 1 cm to 5 m, in particular 5 cm to 3 m, a width of 0.55 cm to 200 cm, in particular 1 cm to 100 cm, and a depth of 0.5 cm to 50 cm, in particular 1 cm to 25 cm. 2 25m from 2The surface filtration layer may have a cross-sectional area available for filtration for fluid flow up to 1000 sq. m. If the surface filtration layer is properly structured with protrusions / dimples, surface roughness, fractal geometry, or an otherwise structured surface, the actual available surface area for surface filtration may be much larger than this cross-sectional area.

[0085] Figure 2 shows the cross-sectional profile of the filter body 2 in the central part, away from the edges, along the length of the line II-II in Figure 1. It can be seen that the filter body 2 is formed as a hollow body and, in the example shown, has a fir-tree-shaped cross section 11. However, circular, cylindrical or polygonal cross-sectional areas are also conceivable.

[0086] The fir-tree design is particularly suitable because it creates a larger surface area on the inlet side 8 (outside) than, for example, a smooth cubic cross-section of approximately the same volume of the filter element 1, and is therefore more effective in filtering the raw gas reaching it. The outlet side 9 is located inside the hollow body. After passing through the filter body of the filter element, the purified gas flows approximately perpendicular to the cross-section to the filter head.

[0087] It can be seen that the fir-tree cross section 11 has a series of intermediate walls 12 at intervals, which divide the internal hollow space or cavity into a number of smaller hollow chambers 13. The intermediate walls 12 ensure the stability of the filter body 2, and their number can be selected depending on the desired stability. If the filter body 2 has sufficient inherent stability, it is possible to omit the intermediate walls 12.

[0088] In order to filter foreign matter from the raw gas, the filter body 2 is provided with a surface filtering layer 14 on its inlet side 8, as shown schematically and exemplarily in FIG.

[0089] The surface filtration layer 14 forms the main filter element. The foreign matter (particles) to be filtered are trapped by the small pores on the surface of the surface filtration layer. Such substances do not penetrate at all or only slightly into the interior of the filter body 2, and the filter body 2 mainly functions as a separator between the raw gas side (inlet side 8) and the clean gas side (outlet side 9), through which the clean fluid can pass.

[0090] The surface filtration layer 14 has a porous structure similar to that of the filter body 2, and is disposed on the inlet side 8 of the filter body 2 or partially disposed on the inlet side of the filter body 2. The average pore size in the surface filtration layer 14 is significantly smaller than that of the filter body 2. The average pore size in the surface filtration layer 14 is selected so that foreign matter to be filtered from the raw gas cannot pass through the surface filtration layer 14 and is instead deposited on the surface on the inlet side.

[0091] The filter body 2 may have an average pore size of about 100 μm to 2000 μm in the region outside the surface filtration layer 14, while the filter body in the region where the surface filtration layer 14 is formed has a smaller average pore size, often in the range of 0.1 μm to 200 μm.

[0092] At least the three-dimensional support structure 23, which will be explained in more detail below, ensures a rigid connection of the surface filtration layer 14 to the filter body 2 and is additively manufactured. However, further components of the filter element 1, such as the mother pore structure 40 forming the porous base structure, support structures for further components such as the filter head 3 and / or filter foot 4, as well as the filter head 3 and / or filter foot 4, can also be additively manufactured.

[0093] Additive manufacturing processes are understood to be processes in which a part is built layer by layer by depositing material based on digital 3D design data. In general terms, additive manufacturing processes are also called 3D printing processes. Known additive manufacturing processes are, for example, stereolithography, selective laser sintering (SLS), binder jet or fused layer modeling / manufacturing (FLM).

[0094] Additive manufacturing processes are particularly well suited to producing complex shapes such as undercuts, cavities, and overlaps that cannot be produced using traditional manufacturing methods.

[0095] FIG. 3 shows an exemplary embodiment of a filter element 1 having a filter body 2 with a multi-layer or multi-phase structure. The structure of the filter body 2 includes a support structure. The support structure provides inherent stability to the filter element 1 or filter body 2 and is designed to be sufficiently porous to allow gas flow through the filter body 2 with a relatively low pressure drop. On the inlet side of the support structure, the structure of the filter body 2 includes a basic structure 40 called a "mother pore structure." The mother pore structure 40 is formed with a coarse-pore, gas-permeable structure, but is nevertheless inherently stable, i.e., capable of supporting its own weight without the aid of additional support elements. This coarse-pore structure has larger pore sizes compared to the other layers or phases of the filter body 2, particularly compared to the surface filtration layer 14. The mother pore structure 40 is formed as a truss or framework structure, which provides the filter body 2 with basic stability and a low specific weight.

[0096] The framework structure should be considered as an example, and other structures, e.g., bionic structures, having good inherent stability with the lowest possible specific weight and / or the lowest possible flow resistance are also contemplated. The support structure may further be designed to form additional components in corresponding parts of the filter body 2, such as the filter head or filter foot, or to attach such components to the filter body 2.

[0097] A three-dimensional support structure 23 designed as a truss structure or framework structure is arranged on the inlet side 41 of the mother hole structure 40, which is located to the right of the mother hole structure 40 in FIG. 3 . Like the mother hole structure 40 and the filter body 2, the support structure 23 is a component manufactured by additive manufacturing. Due to additive manufacturing, the support structure 23 can have relatively large cavities 26 between the individual support structure components and still provide sufficient stability to form a stable filter layer, particularly to provide a stable and permanent connection with the surface filtration layer 14. In this embodiment, this is achieved by the support structure 23 having a lattice-like structure including three lattice layers 23.1, 23.3, 23.2 arranged one behind the other in the flow direction of the gas flow.

[0098] FIG. 4 is a perspective view showing the basic structure of the three-dimensional support structure 23. The location of the cross-sectional plane for the cross-sectional view of FIG. 3 is also shown in FIG. 4, with the understanding that neither the first layer 27 and the second layer 28 of the surface filtration layer 14 nor the pore structure 40 are shown in FIG. 4 for clarity. The three-dimensional support structure 23 comprises a first lattice layer 23.1 forming the inlet side of the support structure 23 and defining the inlet side of the filter body 2; a second lattice layer 23.2 forming the outlet side of the support structure 23 and facing the outlet side of the filter body 2; and a third lattice layer 23.3, intermediate between the first lattice layer 23.1 and the second lattice layer 23.2 in the flow direction. Cavities 26 are formed between and within the lattice layers 23.1 to 23.3. The first lattice layer 23.1 is also referred to as the front lattice layer, the second lattice layer 23.2 as the rear lattice layer, and the third lattice layer 23.3 as the center lattice layer.

[0099] The lattice layers 23.1 to 23.3 are aligned substantially parallel to one another. An offset of up to 10° from one another should also be considered substantially parallel. The lattice layers 23.1 to 23.3 are arranged so that the gas flow G impinges on the front lattice layer 23.1 from a substantially normal direction and passes through the rear lattice layers 23.1, 23.2, and 23.3 in that order. Each of the lattice layers 23.1 to 23.3 is formed by rods 24.1 and 24.2 connected to one another at nodes 25.

[0100] The rods 24.1 and 24.2 extend in the plane of the respective grid layer 23.1, 23.2, 23.3, i.e., extend transversely (specifically perpendicularly) to the direction of gas flow as it passes through the grid layers 23.1 to 23.3. Each of the grid layers 23.1 to 23.3 is formed by a set of parallel first rods 24.1 extending in a first direction and a further set of parallel second rods 24.2 extending in a second direction and intersecting the first set of rods. In this embodiment, the second direction is substantially perpendicular to the first direction. The first and second rods 24.1 and 24.2 together define an opening 26.1 (for clarity, only one of these openings 26.1 is labeled in FIG. 4). Each opening 26.1 is formed between two adjacent first rods 24.1 and two adjacent second rods 24.2, resulting in four intersections between these first and second rods 24.1, 24.2. These intersections are also called nodes 25. For each of the three lattice layers 23.1, 23.2, and 23.3, the openings 26.1 form so-called parametrically controlled pores through which gas flow can pass through the corresponding lattice layer 23.1 to 23.3. In particular, two adjacent rods 24.1 aligned parallel to each other and two adjacent rods 24.2 aligned parallel to each other form a respective opening 26.1 between them. The openings 26.1 thus formed have a quadrilateral, particularly a square, shape in FIG. 4. Alternatively, the openings 26.1 may be triangular, square, rectangular, rhomboidal or rhomboidal, parallelogram, polygonal, circular, or elliptical. In alternative embodiments of openings 26.1, the corresponding lattice layer may have correspondingly different arrangements of rods or sets of rods joined together to define respective openings 26.1 having multiple corners, such as honeycomb (hexagonal) openings 26.1. Openings 26.1 may also have different shapes within the corresponding lattice layer, for example alternating pentagons and hexagons.

[0101] The lattice layers 23.1 to 23.3 are interconnected by third rods 24.3, also referred to as lattice layer connecting rods. These lattice layer connecting rods 24.3 extend transversely to the plane of the respective lattice layers 23.1, 23.3, or 23.2, 23.3, connecting them. In particular, the lattice layer connecting rods 24.3 extend perpendicularly to the plane of the respective lattice layers 23.1, 23.3, or 23.2, 23.3, connecting them. In the illustrated embodiment, the front lattice layer 23.1 and the center lattice layer 23.3 are spaced apart from each other by the same distance as the rear lattice layer 23.2 and the center lattice layer 23.3. It is also possible for the distances between the lattice layers 23.1 to 23.3 to be different from each other, i.e., the distance between the lattice layers 23.1 and 23.3 is different from the distance between the lattice layers 23.2 and 23.3. In the illustrated embodiment, the grid layer connecting rods 24.3 are aligned substantially along the direction of gas flow G.

[0102] For the inlet-side front lattice layer 23.1, the lattice layer connecting rods 24.3 are offset from the nodes 25. For the adjacent central lattice layer 23.3, the lattice layer connecting rods 24.3 are also offset from the respective nodes 25. This means, for example, that one end (front end) of each of the lattice layer connecting rods 24.3 starts from one of the first rods 24.1 of the front lattice layer 23.1 in the section between two nodes 25 (more precisely, halfway between the two nodes 25), while the other end (rear end) of the lattice layer connecting rod 24.3 terminates on one of the second rods 24.2 of the central lattice layer 23.3 in the section between two nodes 25 (more precisely, halfway between the two nodes 25). The same applies to the lattice layer connecting rods 24.3, which start at one end from one of the second rods 24.2 in the section between (more precisely, halfway between) the two nodes 25 of the front lattice layer 23.1, and terminate at their other end (rear end) in the section between (more precisely, halfway between) the two nodes 25 of one of the first rods 24.1 of the central lattice layer 23.3. Thus, each lattice layer connecting rod 24.3 connects a first rod 24.1 of one lattice layer 21.1 to a second rod 24.2 of the adjacent lattice layer 24.3 in a region not located at a node 25 (more precisely, halfway between the two nodes 25).

[0103] With this arrangement, the cavities 26 form cage-like structures between them, so-called parametrically controlled pores. The same applies to the lattice layer connecting rods 24.3 which connect the rear lattice layer 23.2 to the central lattice layer 23.3.

[0104] Other orientations of the connecting rods 24.3 are possible, for example, inclined relative to the flow direction of the gas flow G. Arrangements not shown are also conceivable, with correspondingly different offsets of the central lattice layer 23.3 relative to the front lattice layer 23.1. In this case, the connecting rods 24.3 are arranged at the nodes 25 of the front lattice layer 23.1. On the inlet side, the lattice layer connecting rods 24.3 are arranged at the nodes 25, and relative to the adjacent central lattice layer 23.3, the lattice layer connecting rods 24.3 are arranged offset relative to the respective nodes 25. One end (front end) of the lattice layer connecting rods 24.3 would terminate at one of the nodes 25 where the rod 24.1 intersects with the rod 24.2 of the front lattice layer 23.1, and the other end (rear end) of the lattice layer connecting rod 24.3 would terminate between two adjacent nodes 25 on one of the rods 24.1 or 24.2 of the third (middle) lattice layer 23.3. Thus, the lattice layer connecting rods 24.3 will then connect the nodes 25 of the front lattice layer 21.1 to the rods 24.1 or 24.2 of the central lattice layer 24.3 in the areas not located at the nodes 25. This arrangement also allows the cavities 26 to form cage-like structures between them, so-called parametric control holes. The same applies to the lattice layer connecting rods 24.3 connecting the rear lattice layer 23.2 to the central lattice layer 23.3. For the outflow rear lattice layer 23.2, the lattice layer connecting rods 24.3 are located at the nodes 25. However, for the adjacent second (central) lattice layer 23.3, the lattice layer connecting rods 24.3 are located offset from the respective nodes 25.

[0105] In the exemplary embodiment, each of the lattice layers 23.1 to 23.3 has the same regular lattice structure, meaning that the arrangement of the openings 26.1 and rods 24.1, 24.2 in each of the lattice layers 23.1 to 23.3 has a regular pattern with a repeating configuration of the rods 24.1, 24. relative to each other and / or to the openings 26.1.

[0106] In the exemplary embodiment, the front and rear grid layers 23.1 and 23.2 are aligned with each other, and the central grid layer 23.3 is offset from the grid layers 23.1 and 23.2. In particular, the openings 26.1 in the front and rear grid layers 23.1 and 23.2 are aligned with each other in the gas flow direction, and the openings 26.1 in the central grid layer 23.3 are offset laterally, specifically perpendicularly, to the gas flow direction, such that the rods 24.1 and 24.2 in the central grid layer 23.3 are visible in the flow direction behind and in front of the openings 26.1 in the grid layers 23.1 and 23.2, respectively. In the illustrated embodiment, the offset of the central grid layer 22.3 from the front and rear grid layers 23.1 and 23.2 is selected so that the nodes 25 of the central grid layer 23.3 are precisely aligned with the centers of the openings 26.1 in the front and rear grid layers 23.1 and 23.2. In this way, the third rods 24.3 interconnecting the lattice layers 23.1, 23.2, 23.3 can be perpendicular to the plane of the lattice layers 23.1, 23.2, 23.3. Although each of the three lattice layers 23.1, 23.2, 23.3 has the same regular lattice structure, the offset of the central lattice layer 23.3 relative to the other two lattice layers 23.1, 23.2 creates an obstacle to gas flow through the porous structure (three-dimensional support structure 23) defined by the lattice layers 23.1, 23.2, 23.3.

[0107] In this way, with a very simple geometry of the three lattice layers 23.1, 23.2, 23.3, and therefore at little expense, it is possible to embed material for forming the surface filtration layer 14 in the cavities 26.1 of the three-dimensional support structure 23, in particular in the cavity 26.1 between the front lattice layer 23.1 and the central lattice layer 23.3, and form a cage structure that is extremely suitable for holding it there against further transport in the flow direction of the gas flow G.

[0108] The three grating layers 23.1 to 23.3 are described as an exemplary embodiment only, and it is also possible to use only two grating layers in the support structure, or more than two grating layers.

[0109] Cavities 26 are formed between the rods 24.1 and 24.2 within each of the lattice layers 23.1, 23.2, and 23.3, and between the lattice layers 23.1 through 23.3 and the lattice layer connecting rods 24.3. These cavities 26 are interconnected so that, in a three-dimensional view, gas flow G can flow through the cavities 26 from the inlet side 8 to the outlet side 9. A surface filtration layer 14 is disposed in the cavity 26 between the front lattice layer 23.1 and the central lattice layer 23.3. The surface filtration layer 14 is formed by introducing and receiving particles of a first type 27.1 into the cavity 26 so that the particles are embedded therein. Filling of the cavity 26 with particles of the first type 27.1 is achieved so that a first layer 27 having a pore size between 1 μm and 200 μm is formed. For example, the particles of the first type 27.1 may have a particle size of 25 μm to 200 μm. In an exemplary embodiment, the particles of the first type 27.1 are primarily accommodated in the cavities 26 between the front lattice layer 23.1 and the central lattice layer 23.3. In this regard, several particles of the first type 27.1 each occupy one of the cavities 26, partially forming agglomerates, and in some cases even forming agglomerates with particles of the first type 27.1 accommodated in adjacent cavities 26. The first surface filtration layer 27 formed by the interaction of the particles of the first type 27.1 with the three-dimensional support structure 23 thus has a smaller pore size than the three-dimensional support structure 23 itself. The first surface filtration layer 27 forms a foundation upon which further layers, particularly the second surface filtration layer 28 or even another surface filtration layer, can be applied.

[0110] The second surface filtration layer 28 is applied to the first surface filtration layer 27 from the inlet side. The second surface filtration layer 28 forms the surface of the filter element 1 at the inlet side 8. In the illustrated embodiment, the surface is formed exclusively, or at least largely, by the second surface filtration layer 28. The second surface filtration layer 28 is arranged substantially on the three-dimensional support structure 23 and the first surface filtration layer 27, covering them outward. In this embodiment, the second surface filtration layer 28 is composed of a plurality of particles of a second type 28.1 (having a particle size of 0.1 μm to 20 μm), and the second surface filtration layer 28 has a pore size of 0.1 μm to 20 μm. The pore size of the second surface filtration layer 28 is therefore smaller than that of the first surface filtration layer 27 and also smaller than that of the subsequent layers or structures in the direction of gas flow. The size of the particles 28.1 allows them to settle in the pores formed in the first surface filtration layer 27 and at least partially cover the surface of the surface filtration layer 27. The pores of the surface filtration layers 27 and 28 are arranged relative to one another so that a gas flow can pass through them. Due to the small pore size of the second surface filtration layer 28, the filter element 1 including this surface filtration layer 28 can be cleaned well and effectively.

[0111] In a further embodiment, the second surface filtration layer 28 may not completely cover the first surface filtration layer 27 and possibly the three-dimensional support structure 23. In such an embodiment, the first type of particles 27.1 and possibly part of the three-dimensional support structure 23 are exposed to the outside. In this way, the surface of the filter element 1 is formed by the second surface filtration layer 28 cooperating with the first surface filtration layer 27 and possibly the three-dimensional support structure 23.

[0112] During operation, an ever-increasing amount of foreign matter accumulates on the surface filtration layer 14, forming a filter cake whose thickness increases over time and gradually blocks the pores of the surface filtration layer 14. This impairs the flow of gas through the filter element 1, so the surface filtration layer 14 must be cleaned from time to time. Traditionally, this is typically done by applying a compressed air pulse to the filter element 1 from the clean fluid side. To achieve this while the filter element 1 is in operation, for example, a compressed air pulse is applied to the filter element, generating a pressure surge that is transmitted through the filter element 1 to the foreign matter that has accumulated on the filter element 1 as a filter cake, causing the accumulated foreign matter to fall off the surface filtration layer 14, cleaning the pores and making them "empty" again.

[0113] 5 shows a flow diagram of a method for manufacturing an essentially stable flow-through porous filter element 1. In a first step 70, a support structure is manufactured using an additive manufacturing process. Then, in a second step 72, a mother pore structure 40 can be applied to this support structure. Subsequently, in a third step 74, a three-dimensional support structure 23 can be placed on the mother pore structure 40 using the same additive manufacturing process. In this step, a cavity 26 is formed in the three-dimensional support structure 23.

[0114] The steps of forming the support structure (step 70), forming the mother hole structure 40 (step 72), and forming the three-dimensional support structure 23 (step 74), which are described separately herein, may also be performed in a single additive manufacturing process, for example by printing all three structures simultaneously using a 3D printer.

[0115] This is followed in step 76 by forming a surface filtration layer by partially filling the cavities 26 of the three-dimensional support structure 23 with a first type of particles 27.1 to form a first surface filtration layer 27. In the exemplary embodiment, the particles 27.1 primarily fill the cavities 26 formed between the lattice layers 23.1 and 23.3. In step 78, a second surface filtration layer 28 is deposited on the first surface filtration layer 27, with the particles 28.1 partially filling the intermediate spaces formed between the particles 27.1. The second surface filtration layer 28 forms a porous surface on the first surface filtration layer, which has the smallest pore size throughout the filter body 2.

[0116] The entire exemplary method can be performed using additive manufacturing processes. The surface filtration layer can be realized, for example, via material gradients (SLS, SLM, binder jetting), additives in binders or polymers (FDM, SLA, binder jetting), voxels from CAD (particle jetting, binder jetting, multi-jet fusion), machine paths and laser scanning speeds (SLS, SLM). In a further exemplary embodiment, steps 70 to 74 can be performed using additive manufacturing processes, and steps 76 and 78 can be performed using one or more coating processes of the type described at the beginning.

[0117] 6 and 7 show schematically two possible additive manufacturing processes for producing the filter element 1, or at least for producing the filter body 2.

[0118] 6 shows an exemplary process according to the "bottom-up" principle, meaning that the part to be manufactured is built from the "bottom" to the "top". The manufacturing method, shown diagrammatically, proceeds as follows: A lowerable bed 101, also called a carrier plate 101, is placed in a container 100. Plastic particles 103, for example as granules or powder, are applied to this carrier plate 101 in a predetermined dose, for example by means of a dosing aid 102.

[0119] A mixture 104 of adhesive, solvent(s) and / or water is then selectively applied to predetermined locations, for example by a dosing aid 105, where the plastic particles 103 bond to one another and thus form the first layer of the part to be manufactured. The dosing aid 105 can be designed, for example, as a print head (inkjet).

[0120] In the next step, the carrier plate 101 is lowered and the procedure is repeated until the part to be manufactured is completely produced. After that, the loose plastic particles 103 are removed and the water and / or solvent contained in the mixture 104 can be evaporated to form a porous body.

[0121] It is also contemplated that instead of using water and / or solvents, a readily soluble resin may be used to create the porosity, which can ultimately be washed out of the part.

[0122] Such a process is also called a binder jet process.

[0123] It is also conceivable to use a pure adhesive (i.e., an adhesive without added solvents and / or water and without added readily soluble resins) instead of an adhesive mixture, which is selectively applied by the dosing aid 105 to the individual locations and causes them to adhere to each other.

[0124] Another process that operates according to the "bottom-up" principle is the aforementioned selective laser sintering (SLS), in which a laser passes across a layer of powdered starting material to selectively sinter the powder starting material at predetermined locations in the layer.

[0125] Figure 7 shows a schematic of an exemplary process that operates on a "top-down" principle, meaning that the manufactured part is built from the "top" to the "bottom." Figure 7 shows as an example a so-called "continuous liquid interface manufacturing" process. The continuous liquid interface manufacturing process is a stereolithography process, which differs from many other known additive manufacturing processes in that the manufactured part is built continuously.

[0126] Conventional additive manufacturing processes are usually carried out in so-called two-dimensional printing processes, which means that (thin) layers of the part to be manufactured are created, and this process is repeated frequently to create the three-dimensional part to be manufactured, layer by layer.

[0127] In principle, the continuous liquid interface manufacturing process proceeds as follows: A liquid polymer 107, for example a photosensitive synthetic resin, is applied onto a trough-shaped platform 106. The floor 108 of the platform 106 is at least partially transparent to ultraviolet light (UV light). A light source 109 for UV light, for example a projector, is arranged below the platform 106, which emits one or more beams of UV light 110. These are directed onto the liquid polymer either directly or through the floor 108, for example by deflection by mirrors 111, and are precisely focused in the area where the liquid polymer is to harden.

[0128] Furthermore, the setup of the continuous liquid interface manufacturing process has a movable carrier plate 112 that is movable in a direction perpendicular to the platform 106. Thus, by continuously moving the carrier plate 112, the part being manufactured starting from the platform 106 is slowly pulled out of the liquid polymer 107 so that the liquid polymer 107 can flow in. In this way, the last layer of the just manufactured part 113 and the platform 106 always remain covered with the liquid polymer 107 and can be further cured by UV light 110.

[0129] An oxygen-permeable membrane is attached below the liquid polymer 107, which creates a transition phase that remains liquid, a so-called "dead zone" 114, and prevents the liquid polymer 107 from depositing on the floor 108 of the platform 106 and curing, e.g., polymerizing, there. Instead of an oxygen-permeable membrane, other semi-permeable membranes permeable to cure inhibitors other than oxygen or polymerization inhibitors may also be envisaged.

[0130] Thus, the "Continuous Liquid Interface Manufacturing" process represents a continuous printing process, which makes the manufacturing method significantly faster than other processes that build parts layer by layer.

[0131] The selection and composition of polymeric materials used to make plastics is directly related to the manufacturing method, and vice versa.

[0132] The filter body 2 may therefore primarily comprise a thermoplastic polymer material. Examples of such materials include polyethylene (PE), polypropylene (PP), and polyphenylene sulfide (PPS), which have also been used in the past for filter bodies. However, other thermoplastic polymers, such as polyimide (PI), polyamide (PA), polyvinyl alcohol (PVA), polylactide (PLA), or polyetheretherketone (PEEK), or thermoplastic blends, are also contemplated. In particular, thermoplastic polymers classified as "engineering thermoplastics" or "high-performance thermoplastics" are also contemplated.

[0133] Depending on the operating conditions and the resulting required properties of the filter element 1, it is also possible to use thermosetting polymer materials instead of thermoplastic polymer materials. Examples of thermosetting polymer materials include, among others, epoxy resins, phenolic resins, polyester resins, melamine resins, silicone resins, and urethane resins. Here, too, polymer blends based on thermosetting polymer materials are conceivable. The main difference between thermosetting and thermoplastic polymer materials is that in the case of thermosetting, the polymer materials harden, becoming much more cross-linked and therefore no longer meltable. This generally increases the likelihood of cracks occurring.

[0134] UV-crosslinked polymeric materials are particularly suited to continuous additive manufacturing processes, such as continuous liquid interface manufacturing processes. It is also conceivable to replace UV light radiation with other specific radiation in the light spectrum, such as infrared light radiation (IR light radiation). In this case, a polymeric material would be selected that cures, i.e., crosslinks, when exposed to IR light radiation. [Explanation of symbols]

[0135] 1 Filter Element 2 Filter body 3 filter head 4 filter feet 5 First aspect 6 Second aspect 7 Bulkhead 8 Inflow side 9 Outflow side 10 Seals 11 Cross Section 12 Intermediate Wall 13 Hollow chamber 14 Surface filtration layer 23 Three-dimensional support structure 25 nodes 26 Cavity 27 1st layer 28 2nd layer 40 Mother pore structure (basic structure) 41 Inflow side 100 containers 101 Carrier Plate (Floor) 102 Administration aids 103 Plastic particles 104 Mixture 105 Administration aid device 106 Platform 107 Liquid Polymer 108 beds 109 Light source 110 UV light 111 Mirror 112 Carrier Plate 113 parts G Gas flow x Longitudinal direction y width direction z depth direction

Claims

1. An essentially stable flow-through porous filter element (1) for filtering contaminants from a gas stream, comprising: The filter body (2) is made of plastic and has an inlet side (8) and an opposite outlet side (9), and a surface filtration layer (14) is formed on the inlet side (8). The filter body (2) is manufactured by an additive manufacturing process and comprises a three-dimensional support structure (23) having a plurality of cavities (26) through which gas can flow from the inlet side (8) to the outlet side (9); A filter element (1), characterized in that the surface filtration layer (14) at least partially fills the cavity (26) of the three-dimensional support structure (23).

2. 2. The filter element (1) according to claim 1, characterized in that the three-dimensional support structure (23) has a cage structure that is open towards the inlet side (8).

3. 3. The filter element (1) according to claim 1 or 2, characterized in that the three-dimensional support structure (23) forms basket-, cup- or funnel-shaped cavities (26), each having a bottom side and an opposite open side, the open side facing the inlet side (8).

4. 4. The filter element (1) according to claim 3, characterized in that the basket-, cup- or funnel-shaped cavities (26) each have a lateral boundary connecting the bottom side to the open side, and adjacent basket-, cup- or funnel-shaped cavities (26) have openings communicating with each other.

5. the open side of each cavity (26) has a front opening (26.1) and the bottom side and / or side boundary has a rear opening; 5. A filter element (1) according to claim 3 or 4, characterized in that in orthogonal projection from the open side to the bottom side, a plurality of rear openings of the bottom side and / or the lateral boundaries are arranged within an area defined by a front opening (26.1) of the open side.

6. 6. A filter element (1) according to any one of claims 3 to 5, characterized in that the open side of each cavity (26) has only one opening (26.1).

7. 7. The filter element (1) according to claim 1, wherein the filter body (2) defines a thickness direction extending between its inlet side (8) and outlet side (9), and the surface filtration layer (14) fills the cavities (26) of the three-dimensional support structure (23) over at least 10% of the thickness of the surface filtration layer (14), in particular over at least 25% of the thickness, in particular over at least 50% of the thickness, in particular between 25% and 100% of the thickness, in particular between 50% and 75% of the thickness.

8. 8. The filter element (1) according to claim 1, wherein the filter body (2) defines a thickness direction extending between its inlet side (8) and outlet side (9), and the surface filtration layer (14) fills the cavities (26) of the three-dimensional support structure (23) over at least 10% of the thickness of the three-dimensional support structure (23), in particular over at least 25% of the thickness, in particular over at least 50% of the thickness, in particular between 25% and 100% of the thickness, in particular between 50% and 75% of the thickness.

9. 9. The filter element (1) according to any one of claims 1 to 8, characterized in that the surface filtration layer (14) comprises a first layer (27) that at least partially, in particular mostly, in particular substantially completely fills the cavity (26) of the three-dimensional support structure (23).

10. The surface filtration layer (14) comprises at least one second layer (28) applied to the first layer (27) from the inlet side (8), 10. A filter element (1) according to claim 9, characterized in that in particular the second layer (28) forms a surface at the inlet side (8) of the filter body (2).

11. 11. A filter element (1) according to claim 10, characterized in that the second layer (28) at least partially occupies the interstices of the first layer (27).

12. the first layer (27) and the second layer (28) have different pore sizes; A filter element (1) according to claim 10 or 11, characterized in that the pore size of the first layer (27) is greater than the pore size of the second layer (28).

13. In either case, the second layer (28) is made of PE, PTFE, SiO ２ 13. A filter element (1) according to any one of claims 10 to 12, characterized in that it comprises particles of glass, in particular hollow glass, solid glass, foam glass or sand, PPS, aluminum oxide or a mixture of at least two of these materials.

14. 14. A filter element (1) according to any one of claims 1 to 13, characterized in that the surface filtration layer (14) is at least partly formed as a coating, but in each case the first and second layers (27, 28) are formed as coatings, in particular by liquid deposition, spraying, brushing, dip coating, baking and / or thermal spraying processes, in particular flame spraying.

15. 15. A filter element (1) according to any one of claims 1 to 14, characterized in that the three-dimensional support structure (23) has a truss-like configuration with rods (24.1, 24.2) connected to each other at nodes (25).

16. 16. The filter element (1) according to any one of claims 1 to 15, characterized in that the three-dimensional support structure (23) comprises a lattice-like structure forming at least two lattice layers (23.1, 23.2, 23.3), one lattice layer (23.1) facing the inlet side (8), in particular defining the inlet side (8), and the other lattice layer (23.2) facing the outlet side (9), the lattice layers (23.1, 23.2, 23.3) being connected to one another by rods (24.3) or webs.

17. 17. A filter element (1) according to claim 16, characterized in that the one and / or the other grid layers (23.1, 23.2, 23.3) have a configuration with rods (24.1, 24.2) interconnected at nodes (25) and defining openings (26.1).

18. 18. A filter element (1) according to claim 16 or 17, characterized in that the one and / or the other grating layer (23.1, 23.2, 23.3) comprises a regular grating structure.

19. 19. A filter element (1) according to any one of claims 16 to 18, characterized in that the at least two grating layers (23.1, 23.2, 23.3) are arranged such that the openings (26.1) of one of the two grating layers (23.1, 23.2, 23.3) are offset from the openings (26.1) of the other of the two grating layers (23.1, 23.2, 23.3).

20. 20. The filter element (1) according to any one of claims 16 to 19, characterized in that the three-dimensional support structure (23) comprises three lattice layers (23.1, 23.2, 23.3) arranged one behind the other in the flow direction between the inlet side (8) and the outlet side (9) of the filter body (2), and the openings (26.1) of the central lattice layer (23.3) are arranged offset from the openings (26.1) of the other two lattice layers (23.1, 23.2).

21. 21. The filter element (1) according to any one of claims 16 to 20, characterized in that the three-dimensional support structure (23) comprises three lattice layers (23.1, 23.2, 23.3) arranged one behind the other in the flow direction between the inlet side (8) and the outlet side (9) of the filter body (2), the openings (26.1) of the other two lattice layers (23.1, 23.2) being arranged in a coincident manner.

22. 22. A filter element (1) according to any one of claims 16 to 21, characterized in that the openings (26.1) of the one, the other and / or the central grating layer (23.1, 23.2, 23.3) are triangular, quadrangular, in particular square, rectangular, rhomboid or parallelogram, polygonal, circular and / or elliptical.

23. 23. A filter element (1) according to any one of claims 16 to 22, characterized in that the webs or rods respectively connecting two adjacent lattice layers are arranged offset from the nodes of the two lattice layers.

24. 24. The filter element (1) according to any one of claims 1 to 23, characterized in that the filter body (2) further comprises a three-dimensional mother pore structure (40), and the three-dimensional support structure (23) is arranged on the inlet side (41) of the three-dimensional mother pore structure (40).

25. 25. The filter element (1) according to claim 24, characterized in that the three-dimensional mother pore structure (40) has a larger pore size than the three-dimensional support structure (23).

26. The filter element (1) is formed as a hollow body, 26. A filter element (1) according to any one of claims 1 to 25, characterized in that the inlet side (8) of the filter body (2) is arranged outside the hollow body and the outlet side (9) of the filter body (2) is arranged inside the hollow body.

27. 1. A method of manufacturing an essentially stable flow-through porous filter element (1) for filtering contaminants from a gas stream, comprising: A method of manufacturing a filter body (2) made of plastic and having an inlet side (8) and an opposite outlet side (9), manufacturing the three-dimensional support structure (23) by an additive manufacturing process such that a plurality of cavities (26) are formed in the three-dimensional support structure (23) and through which gas can flow from the inlet side (8) to the outlet side (9); forming a surface filtration layer (14) by partially filling the cavities (26) of the three-dimensional support structure (23); 3. A method of manufacturing a three-dimensional support structure (23) comprising a plastic material.

28. 28. The method of claim 27, characterized in that when the three-dimensional support structure (23) is manufactured by the additive manufacturing process, a cage structure is formed that is open towards the inlet side (8).

29. 29. The method according to claim 27 or 28, characterized in that during the production of the three-dimensional support structure (23) by the additive manufacturing process, basket-, cup- or funnel-shaped cavities (26) are formed, each having a bottom side and an opposite open side, the open side facing the inlet side (8).

30. 30. The method of claim 29, wherein for each of the basket-, cup- or funnel-shaped cavities (26), a lateral boundary is formed, the lateral boundary connecting the bottom side to the open side and having openings through which adjacent ones of the basket-, cup- or funnel-shaped cavities (26) communicate with each other.

31. Each cavity (26) has a front opening (26.1) at the open side and a rear opening at the bottom and / or side boundary, 31. Method according to claim 29 or 30, characterized in that in an orthogonal projection from the open side to the bottom side, rear openings of the bottom side and / or the lateral boundaries are located within an area defined by a front opening (26.1) of the open side.

32. 32. A method according to any one of claims 29 to 31, characterized in that only one opening (26.1) is formed on the open side of each cavity (26).

33. 33. The method according to any one of claims 27 to 32, comprising the step of embedding a material into a plurality of cavities (26) of the support structure (23) to form a first layer (27) of the surface filtration layer (14), characterized in that the majority of the material for the first layer fills the plurality of cavities (26) of the three-dimensional support structure (23).

34. 34. The method according to claim 33, comprising the step of applying to said first layer (27) at least one second layer (28), in particular said second layer (28) forming a surface filtration layer (14) on said inlet side (8) of said filter body (2).

35. 35. The method according to any one of claims 27 to 34, characterized in that the surface filtration layer (14) is formed as a coating, in particular by liquid deposition, spraying, brushing, dip coating, baking and / or a thermal spraying process, in particular flame spraying.

36. 36. The method according to any one of claims 27 to 35, characterized in that during the production of the three-dimensional support structure (23) by an additive manufacturing process, in particular by laser sintering or stereolithography, a truss-like configuration is formed of rods (24.1, 24.2, 24.3) or webs connected to one another at nodes (25).

37. During the manufacture of said three-dimensional support structure (23), a lattice-like structure is formed which forms at least two lattice layers (23.1, 23.2, 23.3), one lattice layer (23.1) defining said inlet side (8) and the other lattice layer (23.2) facing said outlet side (9), 37. Method according to any one of claims 27 to 36, characterized in that the grid layers (23.1, 23.2, 23.3) are interconnected by rods (24.3) or webs.

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