Method for producing a filter membrane having a hole structure made of a plurality of holes, and a filter membrane produced using the method

Abstract

The invention relates to a method for producing a filter membrane having a hole structure made of a plurality of holes. The invention further relates to a filter membrane produced using the method. The problem addressed by the invention is therefore that of proposing a method for producing filter membranes which makes it possible to form filter membranes with holes of the same size in the micrometre / nanometre range and enables a high hole density in an industrially acceptable process time. This problem is solved in that a filling mould with an inverse hole structure is first filled with a liquid filter-membrane material. The filling mould is then rotated about an axis of rotation which is parallel to a surface normal of the liquid level of the liquid filter-membrane material filled in the filling mould, wherein a rotational speed of the rotation is set in such a way that a layer of liquid filter-membrane material remaining on the termination surfaces as a result the liquid filter-membrane material being filled in the filling mould is thinned down to a dewetting.

Description

[0001] Method for producing a filter membrane with a hole structure consisting of several holes and a filter membrane produced using the method

[0002] The invention relates to a method for producing a filter membrane with a perforated structure consisting of multiple holes. The invention further relates to a filter membrane produced by the method.

[0003] Filter membranes are self-supporting, thin films accessible from both sides, with holes, pores, or openings connecting both sides. These membranes allow particles or substances to be filtered from a liquid or gas, thus partially separating them. Filter membranes consist of a porous material whose openings permit only certain components of mixtures or dispersions to pass through, while retaining others. Often, particle size separation or the separation of specific fluid components is achieved.

[0004] Filter membranes are used in various fields. For example, they are used in water and wastewater treatment, the food and beverage industry, pharmaceuticals and medicine, as well as in chemical and biotechnology for the removal of impurities, for separating substances, or for regulating substance concentrations.

[0005] Various methods for manufacturing filter membranes are known from the prior art.

[0006] German patent DE 601 15 250 T2 describes a phase inversion technique for the formation of filter membranes. To produce the filter membrane, a polymer solution is brought into contact with an immiscible solvent, resulting in phase separation. This process creates regions in the polymer solution that are rich in polymer and regions that are rich in solvent. As the polymer hardens, the solvent evaporates, leaving the resulting membrane with a porous structure.

[0007] WO 1995 / 013860 A1 describes a filter membrane produced using nuclear track technology. The starting point is a non-porous film made of a polymer material. This film is irradiated with high-energy particles, such as protons or heavy ions. These particles create traces of damage in the polymer film, which are referred to as nuclear tracks. After irradiation, the film is treated (e.g., chemically etched) to widen and deepen the tracks, thus transforming the nuclear tracks into pores. The widened and deepened tracks then form the passage channels (holes) of the filter membrane.

[0008] In both phase inversion and core track techniques, the through-channels are only statistically distributed, which is disadvantageous for certain applications. In particular, the size distribution and the "pore path" are not well defined, thus reducing the separation specificity. Separation specificity refers to the accuracy and sharpness of the separation of one component of a mixture or dispersion from another component of the same mixture or dispersion.

[0009] Furthermore, lithographic processes for the production of filter membranes are also known. For example, DE 102013203 056 A1 describes a process for producing a microsieve. For this, a photoresist layer is first applied to a substrate. The photoresist layer is then partially covered by a mask, so that only the uncovered areas are illuminated during subsequent illumination. When the photoresist layer is developed, only the illuminated areas remain on the substrate. After the remaining photoresist layer is removed from the substrate, the holes of the microsieve are formed by the areas of the photoresist layer that were dissolved during development.

[0010] Filter membranes are also known in which a base film is perforated using mechanical tools or lasers. When embossed with a mechanical tool, the base film is imprinted with an inverted hole structure. The formation of a filter membrane by laser perforation is described, for example, in EP 1967580 B9. Here, a base film is locally separated using a laser.

[0011] While mechanical or laser perforation can be used to create deterministically distributed through-channels, small through-channel diameters in the micrometer / nanometer range and high hole densities cannot be achieved within industrially acceptable process times.

[0012] The object of the invention is therefore to propose a method for producing filter membranes that enables the formation of filter membranes with uniformly sized holes in the micrometer / nanometer range and a high hole density within an industrially acceptable process time. This object is achieved by a method with the features of claim 1. Advantageous embodiments are found in claims 2 to 20.

[0013] The inventive method for producing a filter membrane with a hole structure consisting of several holes comprises the following steps: a. Providing a liquid filter membrane material whose viscosity can be increased by several orders of magnitude upon curing, b. Providing a filling mold, wherein this filling mold has a filling tray with an inverted hole structure arranged therein, with hole-forming sections, and wherein this inverted hole structure is arranged section by section on a tray bottom of the filling tray, and wherein the hole-forming sections of the inverted hole structure have end faces at their ends facing away from the tray bottom 5a, c. Introducing the liquid filter membrane material into the filling mold until at least the sections of the tray bottom located between the hole-forming sections of the inverted hole structure are covered, d.Rotation of the filling mold about an axis of rotation which is parallel to a surface normal of the liquid level of the liquid filter membrane material filled into the filling mold, and wherein a rotational speed of the rotation is set such that a layer of liquid filter membrane material remaining on the end surfaces of the filling mold after filling the liquid filter membrane material into the filling mold is thinned to the point of dewetting and the resulting exposure of the end surfaces of the inverse hole structure, e. initiation of the curing of the filter membrane material in the filling mold during rotation of the filling mold or after stopping the rotation of the filling mold, f. removal of the cured filter membrane material with the hole structure from the filling mold.In technical terms, "dewetting" refers to the process by which a thinly applied, liquid layer of a material withdraws from or detaches from a surface. With thin liquid layers, surface instabilities can cause the film to rupture. Isolated material residues may remain on the surface, forming droplets. The dewetting of a surface depends on various factors, such as surface chemistry, composition, and surface structure (roughness).

[0014] The term "liquid filter membrane material" is used below when the viscosity of the filter membrane material has not yet been increased by several orders of magnitude through curing. The term "cured filter membrane material" is used when the viscosity of the filter membrane material has been increased by several orders of magnitude through curing.

[0015] The basic idea of ​​the inventive method for producing a filter membrane is to first fill the mold with the inverted hole structure with the liquid filter membrane material. Subsequent rotation of the mold then dewettes the end surfaces of the inverted hole structure, which may have been covered by the introduction of the liquid filter membrane material. Before the curing process begins, this ensures that no continuous layer of liquid filter membrane material lies on the end surfaces. This, in turn, ensures that after the curing of the liquid filter membrane material, channels are indeed formed that pass completely through the cured filter membrane material to create the holes.

[0016] In addition to the hole structure that creates continuous channels for the actual filter function, an inverse filter membrane structure can also have other inverse hole structure elements that also create continuous channels, but these channels then have a different functionality in the finished filter membrane (e.g. to attach the filter membrane to a frame structure in later use).

[0017] A secondary advantage is that excess liquid filter membrane material can be collected during the rotation of the filling tray and used to fill another filling tray.

[0018] In an advantageous embodiment, after the liquid filter membrane material has been introduced into the filling mold and before the filling tray is rotated, the liquid filter membrane material is distributed within the filling mold by means of a distribution device. This enables a homogeneous distribution of the liquid filter membrane material within the filling mold, which in turn is advantageous for achieving a uniform filter membrane layer thickness. A distribution device is particularly advantageous for liquid filter membrane materials with insufficient flowability. According to the invention, the distribution device serves to coarsely distribute the liquid filter membrane material within the filling mold. Fine adjustment of the distribution, in particular ensuring continuous channels for the formation of the holes, is achieved by rotating the filling tray.

[0019] It is proposed that the distribution device is a vibrating device and that the filling mold for distributing the liquid filter membrane material is vibrated by this vibrating device, or that the distribution device is a blow-off device and a gas stream from this blow-off device is directed into the filling tray, or that the distribution device is a squeegee device and a squeegee from this squeegee device is guided along the finishing surface.

[0020] One implementation of the process involves using a polymer as the filter membrane material. This polymer is initially provided in liquid form. During curing, it is then transformed into a solid state.

[0021] It is further proposed that the initiation of curing be thermal and / or by UV radiation and / or by electron irradiation.

[0022] In one embodiment, the UV radiation for initiating the curing process is directed at the liquid level of the liquid filter membrane material poured into the filling mold.

[0023] In another embodiment, the base of the filling mold is permeable to UV radiation, and the UV radiation is directed towards the mold base to initiate curing. In this process, the polymer cures from the bottom up, while remaining liquid at the edges. This simplifies the removal of excess liquid polymer.

[0024] One embodiment provides that the sections forming the holes in the inverse hole structure have a lateral extent in the range of 50 nm to 50 pm, preferably in the range of 100 nm to 30 pm, and more preferably in the range of 1 pm to 10 pm, in a cross-section perpendicular to the longitudinal direction of the holes. However, the cross-sectional dimensioning of the sections forming the holes in the inverse hole structure, which is necessary for filtering a specific component of a mixture or dispersion, can also be limited by the thickness of the filter membrane (usually in the range of 500 nm to 100 pm). In particular, an excessively large aspect ratio of the holes can adversely affect the stability of the inverse hole structure, which in turn can lead to problems when removing the cured filter membrane.The expert will optimize the dimensioning of the hole-forming sections of the inverse hole structure together with the dimensioning of the thickness of the filter membrane.

[0025] The outer contour of the hole-forming sections of the inverse hole structure, in a cross-section perpendicular to the longitudinal direction of the holes, can be round, oval, or polygonal, for example. Furthermore, the outer contour can be a freeform shape formed by a combination of round, oval, and / or angular shapes. Likewise, the outer contour can also be adapted to the outer contour of the particles to be filtered, a component of a dispersion, or a mixture. For example, the outer contour of the hole-forming sections can replicate the outer contour of the relevant particles, so that only particles with such an outer contour can pass through the filter membrane. Within the inverse hole structure, the outer contours of all hole-forming sections can be identical. Likewise, within the inverse hole structure, the outer contours of all hole-forming sections can also differ from one another.

[0026] The longitudinal section of the hole-forming sections of the inverse hole structure can be conical, stepped, or hierarchical, so that the holes in the filter membrane also have a conical, stepped, or hierarchical longitudinal section shape. Such shapes are usually not achievable using traditional methods. Here, a longitudinal section is defined as a cross-section parallel to the longitudinal axis of the hole-forming sections of the inverse hole structure.

[0027] It is proposed that in a plane of the end surfaces of the inverse hole structure, the area sum of the end surfaces lies in the range of 10% to 75%, preferably in the range of 25% to 75%, more preferably in the range of 50% to 75%, and the area sum of the surfaces lying between the end surfaces.

[0028] In an advantageous embodiment of the process, a permeable support structure is placed on a surface of the liquid filter membrane material located at the level of the end faces of the inverted perforation structure in the filling mold prior to the curing of the filter membrane material. This support structure is partially immersed in the liquid filter membrane material. During the curing of the filter membrane material, the partially immersed support structure is then fixed to the cured filter membrane material. When the cured filter membrane material is removed from the filling mold, the cured filter membrane material is removed from the filling mold together with the support structure. The permeable support structure serves to mechanically stabilize the finished filter membrane. At the same time, the support structure should not impede the flow of any medium to be filtered through the filter membrane.Mechanical stabilization is advantageous because the stability of the filter membrane is limited, especially at high hole density, and does not meet the requirements of use.

[0029] In an alternative embodiment of the process, after the filter membrane material has cured in the filling mold, a permeable support structure is placed on a surface of the cured filter membrane material located at the level of the end faces of the inverted perforation structure and locally fixed to the cured filter membrane material using a fixing agent. After the permeable support structure has been fixed to the cured filter membrane material, the cured filter membrane material is removed from the filling mold together with the support structure. Here, too, the permeable support structure serves to mechanically stabilize the finished filter membrane, while simultaneously not impeding the flow of the medium to be filtered through the filter membrane.It is proposed that the fixative be an acrylate, applied to the cured filter membrane material before the permeable support structure is placed, and cured by UV radiation after the support structure is placed. Alternatively, it is proposed that the fixative be a curable polymer, applied to the cured filter membrane material before the support structure is placed, and cured by heat or UV radiation after the support structure is placed.

[0030] In principle, the permeable support structure is designed to be more coarsely porous than the filter membrane. This results in a combination or connection between a coarsely open-pored support structure and a finely porous filter membrane.

[0031] One embodiment specifies that the support structure is a gauze with a mesh size ranging from 75 pm to 200 pm. In another embodiment, the support structure is a sieve with openings having a lateral extent of 75 pm to 200 pm. In yet another embodiment, the support structure is a grid with grid openings having a lateral extent of 75 pm to 200 pm. In a further embodiment, the support structure is a membrane with holes having a lateral extent of 75 pm to 200 pm.

[0032] The filling tray can be designed such that the side walls of the filling tray enclose the inverse hole structure and that the end surfaces of the inverse hole structure extend beyond the side walls at their ends facing away from the tray floor, or that the side walls end at the level of the end surfaces at their ends facing away from the tray floor.

[0033] It is proposed that the liquid filter membrane material be introduced by printing, spraying, or pouring. Evaporation of the liquid filter membrane material, causing it to condense in the filling mold, is also possible. Alternatively, capillary action in the areas between the perforated sections of the inverted hole structure can be utilized. For example, liquid filter membrane material can be introduced at a point between the side wall of the filling tray and the outer area of ​​the inverted hole structure, from where it then distributes itself within the filling mold via capillary action. Furthermore,

[0034] In an advantageous embodiment, the surface energy at the end faces of the inverse hole structure is lower than the surface energy at other sections of the inverse hole structure. This promotes the dewetting of the end faces.

[0035] The end surfaces of the inverted hole structure can be designed to promote dewetting. This can be achieved through appropriate geometric design of the end surfaces. For example, fine roughness can be applied, or the wettability of the end surfaces can be reduced through chemical modification (e.g., chemical treatment).

[0036] The end surfaces of the inverted hole structure can further be provided with a coating (or cover) which increases hydrophobicity.

[0037] It is proposed that, during the rotation of the filling tray, the dewetting of the sealing surfaces be supported by the use of an electric field. The electric field is preferably applied between the liquid filter membrane material and the sealing surfaces of the inverted perforated structure. The electric field alters the surface tension of the liquid filter membrane material, which has a beneficial effect on the dewetting process. Furthermore, a filter membrane formed using the inventive method is proposed.

[0038] Exemplary embodiments of the invention are explained below with reference to the drawings. The drawings show:

[0039] Figs. 1a to 1e show a process flow of an embodiment of the inventive method for producing a filter membrane.

[0040] Figs. 2a to 2f show a further step in an embodiment of the inventive method for producing a filter membrane

[0041] Figs. 3a to 3g show a further process of an embodiment of the invention.

[0042] Method for producing a filter membrane with additional

[0043] support structure

[0044] Figs. 4a to 4h show a further step in an embodiment of the inventive method for producing a filter membrane using an additional distribution device.

[0045] Figs. 5a to 5g show a further step in an embodiment of the inventive method for producing a filter membrane with an additional support structure.

[0046] Figs. 6a to 6I show different versions of the inverse hole structure.

[0047] Figs. 7a to 7b show further embodiments of the inverse hole structure in a top view.

[0048] Figures 1a to 1e show a process of one embodiment of the inventive method for producing a filter membrane 1 (Figure 1f) with a perforated structure consisting of several holes 2 (Figure 1f). The process comprises the following steps: a. Providing a liquid filter membrane material 3, the viscosity of which can be increased by several orders of magnitude upon curing; b. Providing a filling mold 4, wherein this filling mold 4 has a filling trough 5 with an inverted perforated structure 6 arranged therein, with sections forming holes 2, and wherein this inverted perforated structure 6 is arranged section by section on a trough base 5a of the filling trough 5, and wherein the sections forming holes 2 of the inverted perforated structure 6 have end faces 6b at their ends facing away from the trough base 5a (see Figure 1a); c.d. Introduction of the liquid filter membrane material 3 into the filling mold 4 until at least the sections 6a of the inverse hole structure 6 between the holes 2 are covered (see Fig. 1b and Fig. 1c), d. Rotation of the filling mold 4 about an axis of rotation 7, which is parallel to a surface normal of the liquid level of the liquid filter membrane material 3 filled into the filling mold 4 and wherein a rotational speed of the rotation is set such that a layer of liquid filter membrane material 3 remaining on the end surfaces 6b after filling the filling mold 4 is thinned to the point of dewetting and the resulting exposure of the end surfaces of the inverse hole structure, e. Initiation of the curing of the filter membrane material 3 in the filling mold 4 during rotation of the filling mold 4 or after a stop in the rotation of the filling mold 4 (see below).Fig. 1 d), f. Removal of the hardened filter membrane material 3 with the hole structure from the filling mold (see Fig. 1e).

[0049] As shown in Fig. 1c, in the process depicted in Figs. 1a to 1e, the liquid filter membrane material 3 is filled into the filling mold 4 up to the upper end of the inverted hole structure 6, so that the end surfaces 6b of the sections 6a of the inverted hole structure 6 forming the holes 2 are covered. The subsequent rotation of the filling mold 4 spins off excess liquid filter membrane material 3, thereby thinning any remaining layer of liquid filter membrane material 3 on the end surfaces 6b until dewetting occurs on the end surfaces 6b and the end surfaces 6b are exposed. According to the invention, the exposure of the end surfaces 6b means that the liquid filter membrane material 3 on the end surfaces 6b of the inverted hole structure 6 is no longer connected to the liquid filter membrane material 3 located between the sections 6a of the inverted hole structure 6 forming the holes 2.Individual residues of liquid filter membrane material 3 may still remain on the end surfaces 6a of the inverse hole structure 6 after the rotation of the filling mold 4 and the associated dewetting, provided that these residues are not connected with liquid filter membrane material 3 lying between the sections 6a of the inverse hole structure 6 forming the holes 2.

[0050] In the illustrated embodiment of the filling form 4, the filling tray 5 is designed such that the side walls 5b of the filling tray 5 end at the level of the end surfaces 6b with their ends facing away from the tray base 5a.

[0051] Figures 2a to 2e show a further step in an embodiment of the inventive method for producing a filter membrane 1. It is not necessary for the liquid filter membrane material 3 to be filled into the filling mold 4 up to the upper end of the inverted hole structure 6. The amount of liquid filter membrane material 3 filled can also be selected such that the upper end of the inverted hole structure 6 is not covered. Nevertheless, even in this case, at least some liquid filter membrane material 3 may remain on the end surfaces 6a of the inverted hole structure 6 as a result of the filling process (see Figure 2b). Due to the surface tension of the liquid filter membrane material 3, the liquid filter membrane material 3 remaining on the end surfaces 6a of the inverted hole structure 6 may be connected to the liquid filter membrane material 3 lying between the sections 6a of the inverted hole structure 6 that form the holes 2.If the liquid filter membrane material 3 were to harden, this would prevent the formation of a continuous channel or hole. Here too, during the rotation of the filling mold 4 after the liquid filter membrane material 2 has been poured in, any remaining layer of liquid filter membrane material 3 on the end surfaces 6a is thinned until dewetting begins on the end surfaces 6a and the end surfaces 6a are exposed (see Fig. 2c and Fig. 2d). The removal of the formed filter membrane 1 from the filling mold 4 is shown in Fig. 2e.

[0052] In the illustrated embodiment of the filling form 4, the filling tray 5 is designed such that the end surfaces 6a of the inverse hole structure 6 extend beyond the side walls 5b of the filling tray 5 at their ends facing away from the tray bottom 5a.

[0053] Figures 3a to 3g show a further embodiment of the method according to the invention. The process steps shown in Figures 3a to 3d are analogous to those in Figures 1a to 1d. According to Figure 1e, after the filling mold 4 has been rotated, a permeable support structure 8 is placed onto the liquid filter membrane material 3 at the level of the end surfaces 6a of the inverted hole structure 6 (see Figure 3e). The permeable support structure 8 is partially wetted with the liquid filter membrane material 3. During the subsequent curing of the liquid filter membrane material 3, the permeable support structure 8 is then fixed to the cured filter membrane material 3 (see Figure 3f). The cured filter membrane material 3 with the hole structure is then removed from the filling mold 4 together with the support structure 8 (see Figure 3g).

[0054] The support structure 8 is a gauze with a mesh size in the range of 75 pm to 200 pm. However, the invention is not limited to this. For example, the support structure 8 can also be a sieve with openings having a lateral extent in the range of 75 pm to 200 pm, or the support structure 8 is, for example, a grid with grid openings having a lateral extent in the range of 75 pm to 200 pm, or the support structure 8 is, for example, a membrane with holes having a lateral extent in the range of 75 pm to 200 pm.

[0055] Figures 4a to 4h show a further embodiment of the method according to the invention. When filling the liquid filter membrane material 3, it can happen that, due to the surface tension of the liquid filter membrane material 3, the liquid filter membrane material 3 does not distribute itself uniformly in the filling trough 5, and thus the areas between the sections 6a forming the holes 2 of the inverse hole structure 6 are not filled uniformly with liquid filter membrane material 3 (see Figure 4b). Optionally, an additional distribution device can therefore be used. In the process shown in Figures 4a to 4h, the distribution device is a vibrating device, the effect of which is symbolically shown in Figure 4c as a horizontal double arrow 9.This distribution device distributes the filled liquid filter membrane material 3 in the filling mold 4, thus compensating for any uneven distribution of the liquid filter membrane material 3 in the areas between the sections 6a forming the holes 2 of the inverted hole structure 6. Nevertheless, at least some end surfaces 6a of the inverted hole structure 6 may still be covered with liquid filter membrane material 3 (see Fig. 4d). The distribution device serves to coarsely distribute the liquid filter membrane material 3 in the filling mold 4. Dewetting, i.e., exposing the end surfaces 6a, is then carried out by means of the subsequent rotation of the filling mold 4 (see Fig. 4e). The subsequent steps according to Fig. 4f to Fig. 4h then proceed analogously to the steps according to Fig. 1d to Fig. 1f.

[0056] The invention is not limited to the distribution device being a vibrating device. In further embodiments, the distribution device can, for example, also be a blow-off device with which a gas flow is directed into the filling trough. Furthermore, the distribution device can, for example, also be a squeegee device whose squeegee is guided along the end surface. Figures 5a to 5g show a further embodiment of the method according to the invention. This embodiment is identical to the embodiment shown in Figures 3a to 3g, except for the application of the permeable support structure 8. In contrast to the embodiment shown in Figures 3a to 3g, in the embodiment according to Figures 5a to 5g, the permeable support structure 8 is not placed on the liquid filter membrane material 3 at the level of the end surfaces 6a of the inverted hole structure 6, but only after the liquid filter membrane material 3 has hardened.After placement, the permeable support structure 8 is locally fixed to the cured filter membrane material 3 using a fixative (see Fig. 5f). The cured filter membrane material 3 with the perforated structure is then removed from the filling mold 4 together with the support structure 8 (see Fig. 5g). The fixative can, for example, be an acrylate, which is first applied in liquid form at specific points at the interface between the support structure and the filter membrane material 3 and then cured by UV radiation. However, the invention is not limited to acrylate as the fixative. For example, the fixative can also be a curable polymer, which is cured by heat or UV radiation after the permeable support structure 8 has been placed.

[0057] In the illustrated embodiments, the sections 6a of the inverse hole structure 6 forming the holes 2 are designed as column-like elements. These column-like elements have a round outer contour in a cross-section perpendicular to the longitudinal axis of the holes 2. Such a round contour has no sharp corners, thus avoiding the risk of damage to the filter material and reducing the risk of the perforated filter film tearing at the holes 2. However, the invention is not limited to such embodiments. For example, in further embodiments, the sections 6a of the inverse hole structure 6 forming the holes 2 can also be other elongated shapes with a different outer contour than a round one. For example, the outer contour in a cross-section perpendicular to the longitudinal axis of the holes 2 can also be oval or polygonal.In another embodiment, the outer contour in a cross-section perpendicular to the longitudinal axis of the holes 2 forms an outer contour of the particles to be filtered of a component of a dispersion or mixture.

[0058] In addition to the aforementioned column-like design of the sections 6a forming the holes 2 of the inverse hole structure 6, other designs are also possible. For example, in further designs, the outer contour of the sections 6a forming the holes 2 of the inverse hole structure 6 is conical, stepped, or hierarchical in a cross-section parallel to the longitudinal direction of the holes 2. Figures 6a to 6p show exemplary designs of the inverse hole structure 6. Figure 6a shows a top view of a design in the filling tray 5 with the inverse hole structure 6. The sections 6a forming the holes 2 of the inverse hole structure 6 have a square outer contour in a cross-section perpendicular to the longitudinal axis of the holes 2. Figure 6b shows a side view of the filling mold 4 according to Figure 6a. In a cross-section perpendicular to the longitudinal axis of the holes 2, the outer contour is rectangular.In a spatial representation not shown, the sections 6a forming the holes 2 of the inverse hole structure 6 are therefore rectangular.

[0059] Fig. 6c shows another embodiment in a top view of the filling tray 5 with the inverse hole structure 6. The sections 6a of the inverse hole structure 6 forming the holes 2 have a round outer contour in a cross-section perpendicular to the longitudinal axis of the holes 2. Fig. 6d shows a side view of the filling mold 4 according to Fig. 6c. In cross-section perpendicular to the longitudinal axis of the holes 2, the outer contour is rectangular. In a three-dimensional representation (not shown), the sections 6a of the inverse hole structure 6 forming the holes 2 are thus columnar.

[0060] Fig. 6e shows another embodiment in a top view of the filling tray 5 with the inverse hole structure 6. The sections 6a of the inverse hole structure 6 forming the holes 2 have a round outer contour in a cross-section perpendicular to the longitudinal axis of the holes 2. Fig. 6f shows a side view of the filling mold 4 according to Fig. 6e. In cross-section perpendicular to the longitudinal axis of the holes 2, the outer contour is conical, tapering upwards from the bottom of the tray. In a three-dimensional representation (not shown), the sections 6a of the inverse hole structure 6 forming the holes 2 are therefore conical.

[0061] Fig. 6g shows another embodiment in a top view of the filling tray 5 with the inverse hole structure 6. The sections 6a of the inverse hole structure 6 forming the holes 2 have a square outer contour in a cross-section perpendicular to the longitudinal axis of the holes 2. Fig. 6h shows a side view of the filling mold according to Fig. 6g. In cross-section perpendicular to the longitudinal axis of the holes 2, the outer contour is stepped, tapering upwards from the bottom of the tray.

[0062] Fig. 6i shows another embodiment in a top view of the filling tray 5 with the inverse hole structure 6. The sections 6a of the inverse hole structure 6 forming the holes 2 have a cruciform outer contour in a cross-section perpendicular to the longitudinal axis of the holes 2. Fig. 6j shows a side view of the filling mold according to Fig. 6i. In cross-section perpendicular to the longitudinal axis of the holes 2, the outer contour is rectangular. A cruciform outer contour can be formed as a freeform shape from two rectangular shapes.

[0063] Fig. 6k shows another embodiment in a top view of the filling tray 5 with the inverse hole structure 6. The sections 6a of the inverse hole structure 6 forming the holes 2 have a square outer contour in a cross-section perpendicular to the longitudinal axis of the holes 2. Fig. 61 shows a side view of the filling mold 4 according to Fig. 6k. In cross-section perpendicular to the longitudinal axis of the holes 2, the outer contour is hierarchically designed, tapering upwards from the tray base 5a.

[0064] It is also not essential that the elongated structures are arranged perpendicular to the bottom of the trough 5a. Figures 6m and 6n show another embodiment in a top view of the filling trough 5 with the inverted hole structure 6. The sections 6a forming the holes 2 of the inverted hole structure 6 are designed in their outer contours analogous to the embodiment according to Figures 6a and 6b. In contrast, the sections 6a forming the holes 2 are inclined relative to the bottom of the trough 5a and thus obliquely oriented. Figures 6o and 6p show another embodiment in a top view of the filling trough 5 with the inverted hole structure 6. The sections 6a forming the holes 2 of the inverted hole structure 6 are designed in their outer contours analogous to the embodiment according to Figures 6e and 6f. In contrast, the sections 6a forming the holes 2 are inclined relative to the bottom of the trough 5a and thus obliquely oriented.

[0065] In the embodiments of the filling mold 4 shown in Figs. 6a to 6p, the inverse hole structure 6 arranged in the filling tray 5 has sections 6a forming 16 holes 2. However, the invention is not limited to this number. The embodiments of the filling mold 4 shown in Figs. 6a to 61 are expressly to be understood as exemplary. The invention is not limited to these embodiments.

[0066] Figures 7a to 7c show further embodiments of the filling mold 4, in which the sections 6a forming the holes 2 of the inverse hole structure 6 within the filling tray 5 have different outer contours. Figure 7a shows an embodiment in which, within the filling tray 5, sections 6a forming holes 2 have an outer contour that is square in cross-section perpendicular to the longitudinal axis of the holes 2, and sections forming holes 2 have an outer contour that is round in cross-section perpendicular to the longitudinal axis of the holes 2.Figure 7b showed an embodiment in which, within the filling tray, sections forming holes 2 have an outer contour square in cross-section perpendicular to the longitudinal axis of the holes 2, sections forming holes 2 have an outer contour round in cross-section perpendicular to the longitudinal axis of the holes 2, and sections forming holes 2 have an outer contour cross-section cross-shaped perpendicular to the longitudinal axis of the holes 2. Figure 7a showed an embodiment in which, within the filling tray 5, sections forming holes 2 6a have an outer contour triangular in cross-section perpendicular to the longitudinal axis of the holes 2, and sections forming holes 2 6a have an outer contour as a freeform shape consisting of a rectangle and a circle.

[0067] In further embodiments not shown, for example, within the filling tray 5, sections 6a forming holes 2 can be provided with an outer contour that is conical in cross-section along the longitudinal axis of the holes 2, and sections 6a forming holes 2 can have an outer contour that is stepped in cross-section along the longitudinal axis of the holes 2. Here, too, the invention is not limited to these combinations. Due to the oblique orientation of the sections 6a forming holes 2 of the inverse hole structure 6, the longitudinal axes of the formed holes 2 of the filter membrane 1 are also obliquely oriented relative to a surface normal of the surface of the filter membrane 1. The holes 2 then thus run obliquely through the filter membrane 1.

[0068] Preferably, the sections 6a forming the holes 2 of the inverse hole structure 6 have a lateral extent in the range of 500 nm to 100 pm, preferably in the range of 1 pm to 50 pm, and more preferably in the range of 10 pm to 50 pm, in a cross-section perpendicular to the central longitudinal axis of the sections 6a forming the holes 2. Also preferred is a lateral extent in the range of 400 nm to 20 pm, also preferably in the range of 500 nm to 10 pm, also preferably in the range of 600 nm to 5 pm, also preferably in the range of 700 nm to 3 pm, also preferably in the range of 800 nm to 2 pm, and also preferably in the range of 900 nm to 1 pm. Other possible, also preferred, lateral extents are in the range of 200 nm - 800 nm, 200 nm - 600 nm, 200 nm - 400 nm and 250 nm - 300 nm.

[0069] In a plane of the end surfaces of the elongated structures lies a sum of the areas of the end surfaces in the range of 10% to 75%, preferably in the range of 25% to 75%, more preferably in the range of 50% to 75%, a sum of the areas of the surfaces lying between the elongated structures.

[0070] In principle, the edge shape of the holes 2 is influenced by the surface tension of the liquid filter membrane material 3 and by capillary forces acting on the liquid filter membrane material 3 in the areas between the sections 6a of the inverse hole structure 6 that form the holes 2. The smaller the lateral extent of the areas between the sections 6a of the inverse hole structure 6 that form the holes 2, the larger the resulting edge ridge will be at the holes 2.

[0071] After removing the cured filter membrane material 3 with the perforated structure from the filling mold 4, the filling mold 4 with the inverse perforated structure 6 can be cleaned before its next use. Solvents or wetting agents can be used for this purpose, along with mechanical assistance (e.g., ultrasound). Furthermore, it can be advantageous to make the inverse perforated structure 6 from a flexible material and to design it to be removable from the filling tray 5. Stretching and / or bending such an inverse perforated structure 6 can simplify the cleaning process.

[0072] The filter membrane material 3 can, for example, be a polymer that is initially provided in liquid form. The curing of the liquid polymer can then be carried out, for example, thermally and / or by UV radiation and / or by electron irradiation. The UV radiation and / or electron irradiation for initiating the curing is directed at the liquid level of the liquid filter membrane material 3 filled into the filling mold 4. Alternatively, the bottom 5a of the filling tray 5 is permeable to UV radiation, and the UV radiation for initiating the curing is directed towards the end surfaces 6b on the bottom 5a of the tray.

[0073] The liquid filter membrane material 3 is introduced into the processes described above by printing, spraying, or pouring. Depending on the dimensions of the areas between the sections 6a of the inverse hole structure 6 that form the holes 2, capillary action can improve the transport and thus the distribution of the liquid filter membrane material 3 in the filling form 4.

[0074] In further embodiments of the processes described above, the inverse hole structure 6 of the filling mold 4 is designed such that the surface energy at the end surfaces 6b of the inverse hole structure 6 is lower than the surface energy at other sections of the inverse hole structure 6. To reduce the surface energy, the end surfaces 6b of the inverse hole structure 6 are roughened and / or chemically modified compared to the other sections of the inverse hole structure 6. In another embodiment, the end surfaces 6b of the inverse hole structure 6 are provided with a coating that increases hydrophobicity. In a further embodiment of the process, not shown, an electric field is applied between the liquid filter membrane material 3 and the end surfaces 6b of the inverse hole structure 6 during rotation of the filling mold 4.

[0075] The design of the side walls 5b of the filling tray 5 is not limited to the described configurations. In less demanding designs, defined side walls 5b can also be omitted. Other design options for the side walls of the filling tray 5 include different inverted hole structures, for example, elongated holes, a higher hole density, or a barrier-like arrangement. The design of the side walls 5b can also be achieved by incorporating structured edge surfaces outside the inverted hole structure. The specific design depends on the particular usage conditions or subsequent processes in the manufacture of end products.

[0076] In the described embodiments of the method according to the invention, the liquid filter membrane material 3 can, for example, be a formulation with a viscosity of 0.18 Pa*s. The dewetting and the resulting exposure of the end surfaces of the inverted hole structure is achieved, for example, by rotating the filling mold 4 at a speed of 3,400 rpm and for a rotation period of 60 s.

[0077] Furthermore, the liquid filter membrane material 3 can, for example, also be a formulation with a viscosity of 0.56 Pa*s. Dewetting and the resulting exposure of the end surfaces of the inverted hole structure is achieved, for example, by rotating the filling mold 4 at a speed of 5,000 rpm for a rotation period of 90 s.

[0078] The two aforementioned versions of the filter membrane material 3 are to be understood as examples. The invention is not limited to the values ​​mentioned.

[0079] Reference symbol list

[0080] 1 filter membrane

[0081] 2 holes

[0082] 3 Filter membrane material 4 Filling mold

[0083] 5 Filling tray

[0084] 5a Bathtub floor

[0085] 5b Side walls

[0086] 6 inverse hole structure 6a Hole-forming sections

[0087] 6b End surfaces

[0088] 7 axis of rotation

[0089] 8 Support structure

[0090] 9 Direction of action of a distribution device

Claims

Patent claims 1. A method for producing a filter membrane (1) with a hole structure consisting of several holes (2), the method comprising the following steps: a. providing a liquid filter membrane material (3) whose viscosity can be increased by several orders of magnitude upon curing, b. providing a filling mold (4), wherein this filling mold (4) is a filling tray (5) comprising an inverse hole structure 6 arranged therein with hole-forming sections (6a) and wherein this inverse hole structure (6) is arranged section by section on a tray base (5a) of the filling tray (5) and wherein the hole-forming sections (6a) of the inverse hole structure (6) has end faces (6b) at their ends facing away from the bottom of the tub (5a), c. introduction of the liquid filter membrane material (3) into the filling mold (4) until at least the sections (6a) of the tub bottom (5a) forming between the holes (2) of the inverse hole structure (6) are covered, d. rotation of the filling mold (4) about an axis of rotation (7) which is parallel to a surface normal of the liquid level of the liquid filter membrane material (3) filled into the filling mold (4) and wherein a rotational speed of the rotation is set such that a layer of liquid filter membrane material (3) remaining on the end faces (6a) after filling the filling mold (4) is thinned to dewetting and a resulting exposure of the end faces of the inverse hole structure, e.Initiation of the curing of the filter membrane material (3) in the filling mold (4) during rotation of the filling mold (4) or after stopping the rotation of the filling mold (4). f. Removal of the hardened filter membrane material (1) with the hole structure from the filling mold (4).

2. Method according to claim 1, characterized in that after the liquid filter membrane material (3) has been introduced into the filling mold (4) and before the filling mold (4) has been rotated, the liquid filter membrane material (3) is distributed in the filling mold (4) by means of a distribution device.

3. Method according to claim 2, characterized in that the distribution device is a vibration device and the filling form (3) is set into vibration with this vibration device for the distribution of the liquid filter membrane material (3), or that the distribution device is a blow-off device and a gas flow of this blow-off device is directed into the filling trough (5), or that the distribution device is a squeegee device and a squeegee of this squeegee device is guided along the end surfaces (6a).

4. Method according to one of the preceding claims, characterized in that the filter membrane material (3) is a polymer.

5. Method according to one of the preceding claims, characterized in that the initiation of the curing of the filter membrane material (3) is carried out thermally and / or by UV radiation and / or by electron irradiation.

6. Method according to claim 5, characterized in that the UV radiation for initiating the curing is directed onto the liquid level of the liquid filter membrane material (3) filled into the filling mold (4).

7. Method according to claim 5, characterized in that the tray bottom (5a) of the filling mold (4) is permeable to UV radiation and the UV radiation is directed towards the tray bottom (5a) in the direction of the end surfaces (6b) for the initiation of the curing.

8. Method according to one of the preceding claims, characterized in that the sections (6a) forming the holes (2) of the inverse hole structure (6) have an outer contour in a cross-section perpendicular to the longitudinal direction of the holes (2) with a have a round, oval or polygonal shape, or a freeform shape formed by a combination of round, oval and polygonal shapes.

9. Method according to one of the preceding claims, characterized in that the sections (6a) forming the holes (2) of the inverse hole structure (6) have a lateral extent in a cross-section perpendicular to the longitudinal direction of the holes (2) in the range of 50 nm to 50 pm, preferably in the range of 100 nm to 30 pm, more preferably in the range of 1 pm to 10 pm.

10. Method according to one of the preceding claims, characterized in that in a plane of the end surfaces (6b) of the inverse hole structure (6) lies a sum of the areas of the end surfaces (6b) in the range of 10% to 75%, preferably in the range of 25% to 75%, more preferably in the range of 50% to 75%, of the areas lying between the end surfaces (6b).

11. Method according to one of the preceding claims, characterized in that, prior to the curing of the filter membrane material (3) in the filling mold (4), a permeable support structure (8) is placed on a surface of the liquid filter membrane material (3) located at the level of the end surfaces (6b) of the inverse hole structure (6), and that this permeable support structure (8) is partially immersed in the liquid filter membrane material (3), and that during the curing of the filter membrane material (3), the partially immersed, permeable support structure (8) is fixed to the cured filter membrane material (3), and that when the cured filter membrane material (3) is removed from the filling mold (4), the cured filter membrane material (3) is removed from the filling mold (4) together with the support structure (8).

12. Method according to one of claims 1 to 10, characterized in that, after the curing of the filter membrane material (3) in the filling mold (4), a permeable support structure (8) is placed on a surface of the cured filter membrane material (3) located at the level of the end surfaces (6b) of the inverse hole structure (6), and that this permeable support structure (8) is locally fixed to the cured filter membrane material (3) with a fixing agent, and that when the cured filter membrane material (3) is removed from the filling mold (4), the cured filter membrane material (3) is removed from the filling mold (4) together with the support structure (8).

13. Method according to claim 11, characterized in that the support structure (8) is a gauze and this gauze has a mesh size in the range of 75 pm to 200 pm, or that the support structure (8) is a sieve with openings having a lateral extent in the range of 75 pm to 200 pm, or that the support structure (8) is a grid with grid openings having a lateral extent in the range of 75 pm to 200 pm, or that the support structure (8) is a membrane with holes having a lateral extent in the range of 75 pm to 200 pm.

14. Method according to claim 12 or 13, characterized in that the fixing agent is a curable polymer and this curable polymer is applied to the cured filter membrane material (3) before the permeable support structure (8) is applied and that the curable polymer is cured after the permeable support structure (8) is applied by heat or by means of UV radiation.

15. Method according to claim 12 or 13, characterized in that the fixing agent is an acrylate and this acrylate is applied to the cured filter membrane material (3) before the permeable support structure (8) is applied and that the acrylate is cured by means of UV radiation after the permeable support structure (8) has been applied.

16. Method according to one of the preceding claims, characterized in that side walls (5b) of the filling tray (5) enclose the inverse hole structure (6) and that the end surfaces (6b) of the inverse hole structure (6) extend beyond the side walls (5b) at their ends facing away from the tray bottom (5a) or the side walls (5b) terminate at the level of the end surfaces (6b) at their ends facing away from the tray bottom (5a).

17. Method according to one of the preceding claims, characterized in that the introduction of the liquid filter membrane material (3) is carried out by printing, spraying or pouring.

18. Method according to one of the preceding claims, characterized in that the surface energy at the end surfaces (6b) of the inverse hole structure (6) is lower than the surface energy at further sections of the inverse hole structure (6).

19. Method according to claim 18, characterized in that, in order to reduce the surface energy, the end surfaces (6b) of the inverse hole structure (6) are roughened and / or chemically modified compared to the further sections of the inverse hole structure (6), or that the end surfaces (6b) of the inverse hole structure (6) are provided with a coating that increases hydrophobicity.

20. Method according to one of the preceding claims, characterized in that during the rotation of the filling mold (4) an electric field is applied between the liquid filter membrane material (3) and the end surfaces (6b) of the inverse hole structure (6).

21. Filter membrane (1) formed by a method according to one of the preceding claims.

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