Composite filter membrane for increased flowability

Abstract

The present invention relates to the field of composite membranes. More specifically, the present invention relates to a composite filter membrane comprising a filtration layer, a support layer containing at least one through hole, and an intermediate layer sandwiched between the filtration layer and the support layer.

Description

[Technical field]

[0001] The present invention relates to improvements in the field of composite filter membranes. More specifically, the present invention relates to a supported composite filter membrane comprising a series of ducts, a method for its manufacture and uses of said composite filter membrane. [Background technology]

[0002] Polymeric filter membranes are usually supported on a support layer, which mechanically strengthens the filtration layer of said filter membrane. The filtration layers of such filter membranes often have low mechanical strength. This is all the more true for thin filtration layers, i.e. those with a thickness of less than 200 μm. The filter membrane is usually attached to the support by mechanical fastening. Solutions of this type are known from US Pat. No. 5,399,623, US Pat. No. 5,499,633 and US Pat. No. 5,499,643. Furthermore, filter membranes are known from US Pat. No. 5,499,623, in which the filtration layer is chemically bonded to the support layer.

[0003] Patent document 4 describes a membrane comprising a support layer having a plurality of holes and a filtration layer chemically bonded to the support layer. Furthermore, the membrane described in Patent document 4 is characterized by the presence of drainage channels under the support layer. Although the presence of said channels leads to improved drainage of the filtered liquid, the fluidity of the membrane is greatly restricted by the size and position of said plurality of holes on the support layer, hindering the movement of said liquid. A drawback of the membrane described in Patent document 4 is that the support layer requires a high open surface area (OSA) in the range of at least 10% to a maximum of 60% to allow sufficient fluidity. This has the disadvantage of weakening the structural integrity of the support layer. Furthermore, this also affects the surface available for bonding of the filtration layer and the support layer, which is required for the backwashability of the membrane.

[0004] Thus, although advances in the field of filter membranes have provided improved composite filter membranes, there is a need to provide a membrane having higher fluidity while retaining the ability to allow backwashing and overcoming other disadvantages of the prior art. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent No. 0662341 [Patent Document 2] European Patent No. 1462154 [Patent Document 3] Patent Publication No. 2009045559 [Patent Document 4] International Publication No. 15140355 Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide a filter membrane that avoids at least some of the drawbacks of the prior art. It is a further object of the present invention to provide a filter membrane that allows for improved properties, such as higher flowability, improved structural integrity, and backwashability. [Means for solving the problem]

[0007] In a first aspect, the present invention provides a composite filter membrane comprising: a filtration layer made from a semi-permeable first polymeric material and allowing liquid flow therethrough; a support layer made from a second polymeric material different from the first polymeric material and including at least one through hole provided for draining a flow of liquid; The middle class, Equipped with The intermediate layer is made of a first polymeric material and is sandwiched between the filtration layer and the support layer, thus being disposed above the support layer but below the filtration layer, the intermediate layer being solvent bonded to the support layer and comprising a series of ducts (one or more ducts) connected to at least one, preferably more, through-holes of the support layer. In other words, the series of ducts comprises one or more openings connected to at least one opening of at least one through-hole, thereby allowing a liquid flow to pass through the filtration layer, the intermediate layer and the support layer via said series of ducts. In other words, the series of ducts allows a liquid flow to exit the semi-permeable filtration layer, be collected in said series of ducts and conveyed to at least one through-hole, where the flow is discharged. In other words, the series of ducts connects to at least one through-hole of the support layer, and said series of ducts is configured to discharge the liquid flow that has passed through the filtration layer and the intermediate layer through said at least one through-hole of the support layer.

[0008] In a second aspect, the present invention provides a method for producing a composite filter membrane according to the present invention, comprising the steps of: (b) providing on the support layer made of a second polymeric material a layer of duct-forming material, the duct-forming material being a material adapted to form, for example by dissolving, a series of ducts, in a configuration partially covering the entire surface of the support layer and at least covering at least one through-hole present in said support layer (so that at least one opening of the duct is connected to at least one through-hole); (c) providing a layer of filtration layer-forming material on the layer of duct-forming material provided in step (b); (d) solvent bonding the support layer and the layer of filtration layer-forming material provided in step (c) with a first solvent, causing adhesion between the support layer and the layer of filtration layer-forming material, thereby forming a filtration layer 2; and (e) at least partially dissolving the duct-forming material with a second solvent, thereby forming an intermediate layer made of a first polymeric material having a series of ducts, solvent bonded to the support layer.

[0009] According to an embodiment of the present invention, step (b) comprises: (c1) providing a filtration layer dope on the layer of duct-forming material; and (c2) stiffening the filtration layer dope provided in step (c1), for example by phase inversion using a third solvent, thereby providing a filtration layer.

[0010] According to an embodiment of the present invention, the method includes the steps of: (c) providing a layer of a filtration layer-forming material, preferably comprising a packing material selected from one or a combination of hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), cross-linked polyvinylpyrrolidone (PVPP), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyethylene glycol (PEG), and glycerol; and (f) dissolving the packing material contained in the filtration layer with a fourth solvent.

[0011] According to an embodiment of the present invention, in step (a) the layer of duct-forming material is provided to cover the support layer with a specific coverage of the support layer of about 10% to about 75%, in particular about 20% to about 50%.

[0012] In a third aspect, the present invention relates to the use of a composite filter membrane as defined according to the invention as a filtration membrane in the wastewater treatment industry, preferably as a membrane in an MBR (membrane bioreactor).

[0013] With specific reference now to the drawings, it is emphasized that the description shown is by way of example and is intended only as an explanatory discussion of various embodiments of the present invention. These drawings are presented to provide what is believed to be the most useful and simplest explanation of the principles and conceptual aspects of the present invention. In this regard, no attempt has been made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. This description, taken together with the drawings, will make apparent to those skilled in the art how some forms of the present invention may be actually embodied. [Brief description of the drawings]

[0014] [Figure 1]FIG. 1, also abbreviated as FIG. 1, is a cut-away cross-sectional view of a composite filter membrane where the filtration layers have been cut to expose a series of ducts remaining in the intermediate layer. [Diagram 2] FIG. 2, also abbreviated as FIG. 2, illustrates a possible duct forming material according to the present invention, where the duct forming material is a PVA web, resulting in a specific coverage of 50% of the support layer. [Diagram 3] FIG. 3, also abbreviated as FIG. 3, illustrates how a composite filter membrane according to the present invention may be manufactured in a roll-to-plate manufacturing line. [Figure 4] FIG. 4, also abbreviated as FIG. 4, shows a cross-section of a composite filter membrane according to the present invention. [Diagram 5] FIG. 5A, also abbreviated as FIG. 5A, illustrates the perforations in the support layer of the composite filter membrane shown in FIG. 4. FIG. 5B, also abbreviated as FIG. 5B, illustrates the support layer of the composite filter membrane shown in FIG. 4, in which adjacent perforations are equally spaced and arranged on the support layer according to a grid pattern. An enlarged view of the perforations is provided. [Figure 6] FIG. 6A, also abbreviated as FIG. 6A, shows the duct forming material utilized to form the ducts in the composite filter membrane shown in FIG. 4, where the duct forming material is a PVA web, resulting in a specific coverage of the support layer of 35%. A close-up of the web is provided. FIG. 6B, also abbreviated as FIG. 6B, shows a further close-up of the close-up shown at the bottom of FIG. 6A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention will now be further described. In the following sections, various aspects of the present invention are defined in more detail. Each aspect defined therein may be combined with any other aspect(s) unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature(s) indicated as being preferred or advantageous. When describing the compounds of the present invention, the terms used shall be construed according to the following definitions, unless the context indicates otherwise. As used herein, the terms "about" and "approximately" referring to measurable values ​​such as parameters, amounts, durations, etc., are meant to encompass variations of ±10% or less, preferably ±5% or less, more preferably ±1% or less, and even more preferably ±0.1% or less from the stated value, as long as such variations are appropriate for carrying out the disclosed invention. It is understood that the values ​​to which the modifiers "about" or "approximately" refer are themselves specifically and preferably disclosed. As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. By way of example, "a compound" means one compound or more than one compound.

[0016] In the context of the present invention, the term "layer" refers to a plane or sheet of material that is, for example, physically and / or chemically different from the object or plane or sheet above or below it, in other words, a sheet of material that is different from the material above or below it.

[0017] In the context of the present invention, the term "filtration layer" refers to a layer capable of removing / separating a phase of matter from another phase of matter, e.g. removing solids from a liquid or gas. Thus, the filtration layer according to the present invention is semi-permeable, thereby allowing for example liquids or gases to pass from a first side to a second side of the filtration layer, thereby allowing at least partial separation of the solid phase and said liquid phase in case of a solid-liquid mixture. By "layer of filtration layer-forming material" we refer to a layer made of a material that results in a filtration layer after solvent bonding with the support layer. The filtration layer-forming material is made of a first polymeric material or a filtration layer dope applied to said first polymeric material, from which the intermediate layer is also made.

[0018] In the context of the present invention, the term "support layer" refers to a layer that is provided to mechanically support another layer. Generally, a support layer is made of a harder material to resist deformation of the layer to which it is attached.

[0019] In the context of the present invention, the term "intermediate layer" refers to a layer located between the support layer and the filtration layer.

[0020] In the context of the present invention, the term "specific coverage" refers to the coverage of the support layer by the duct-forming material, for example, the mesh-like duct-forming material, when the duct-forming material contacts the support layer, and the specific coverage is expressed as a percentage value.In other words, the specific coverage is the area where either the filtration layer, the filtration layer dope, or the already applied filtration layer cannot reach the support layer, so that entanglement cannot occur.For example, when the filtration layer dope is used to cover the duct-forming material on the support layer, the specific coverage is the percentage of the area of ​​the total support layer area that is not wetted by the filtration layer dope and is therefore under the solid duct-forming material.

[0021] In the context of the present invention, the term "open surface area" or OSA refers to the area of ​​the through holes relative to the total area of ​​the support layer (including the through holes), expressed as a percentage value.

[0022] In the context of the present invention, the term "through hole" refers to an opening in an object, which usually extends from one surface of the object in the thickness direction of the object. In the context of the present invention, at least one through hole is provided in the support layer, i.e. at least one opening is provided in the support layer, which extends in the thickness direction of said support layer, i.e. connecting opposite faces of the support layer. It may extend perpendicularly or obliquely to the opposite faces of the support layer.

[0023] In the context of the present invention, the term "series of ducts" refers to one duct, two ducts or a plurality of ducts, for example three or more ducts. In the context of the present invention, the term "diameter of a series of ducts" refers to the diameter of the circular cross section of the duct, the cross section being taken perpendicular to the longest dimension of said duct. It is clear that the maximum diameter of a series of ducts is equal to the diameter of the wire from which the duct-forming material is made, since the ducts are formed by infusing the duct-forming material. In the context of the present invention, the term "intersecting ducts" refers to at least two ducts that intersect to provide a common space for said ducts. In the context of the present invention, the term "duct-forming material" refers to a layer of material that provides the formation of ducts in the composite filter membrane.

[0024] In the context of the present invention, the term "pattern" or "pattern feature" refers to any regularly repeating arrangement, especially a design made from the repetition of lines, shapes, on a surface.

[0025] In the context of the present invention, the term "hydrophilic packing material" refers to a material in which interactions with water and other polar substances are thermodynamically more favorable than interactions with oil or other hydrophobic or non-polar solvents.

[0026] FIG. 1 shows a composite filter membrane 1 according to an embodiment of the present invention, comprising a filtration layer 2 made of a semi-permeable first polymeric material, a support layer 3 made of a second polymeric material different from the first polymeric material and containing at least one through hole 4, and an intermediate layer 5, the intermediate layer 5 being made of the first polymeric material, sandwiched between the filtration layer 2 and the support layer 3, solvent bonded to the support layer 3, and comprising a series of ducts 7 connected to the at least one through hole 4 of the support layer 3, said series of ducts 7 being configured to drain the liquid flow that has passed through the filtration layer 2 and the intermediate layer 5 through the at least one through hole 4 of the support layer 3. The intermediate layer 5 essentially only partially covers the support layer 3 due to the presence of the ducts 7 in the support layer 3, thereby resulting in a lack of contact with the surface of the support layer 3 at the location of said ducts. As shown in FIG. 1, there are multiple through holes. Preferably, more than one through hole is included in the support layer, but only at least one through hole is required. Furthermore, in FIG. 1, a series of ducts 7 is also shown, which are present between the filtration layer 2 and the support layer 3. According to the present invention, the series of ducts 7 may include one or more ducts. The series of ducts 7 shown in FIG. 1 includes a number of ducts, all parallel to one another, at least one of which connects the filtration layer 2 with at least one through hole 4 of the support layer 3, i.e. is provided so that the phase to be filtered by the composite filter membrane 1 passes through the filtration layer 2, is discharged by said series of ducts 7 and is conducted by said series of ducts 7 to at least one through hole present in the support layer 3. In other words, said series of ducts can connect to at least one through hole 4, thereby forming a passage that allows a liquid or gas to flow from one side of the composite membrane according to the present invention (for example, the side where the filtration layer 2 is exposed) to another side of the membrane (for example, the side where the support layer 3 is exposed), and vice versa.For example, when the membrane according to the invention is used for the separation of a solid-liquid mixture, the solid-liquid mixture is in contact with the side of the membrane on which the filtration layer 2 is exposed, the filtration layer 2 being semi-permeable, and the liquid first flows through the filtration layer 2, from there through a duct present in the intermediate layer 5 and from the duct 7 through at least one through hole 4 present in the support layer 3, thereby allowing the flow to exit the composite membrane on the side of the composite membrane 1 on which the support layer 3 is exposed. In FIG. 1, the filtration layer 2 is made of a semi-permeable first polymer material, while the support layer 3 is made of a second polymer material different from the first polymer material, this support layer 3 comprising at least one through hole 4, and the intermediate layer 5 is made of the first polymer material (the same material as the filtration layer 2).

[0027] The series of ducts 7 can be obtained by a duct-forming material 12 sandwiched between the support layer 3 and the filtration layer 2, the material of which at least partially leaches out, resulting in a series of ducts 7 at the location of said duct-forming material 12.

[0028] The introduction of the intermediate layer 5 containing a series of ducts into the composite filter membrane 1 allows the number of through holes 4 in the support layer 3 to be reduced, which brings several advantages. Firstly, the number of through holes 4 in the support layer can be reduced, which means less machining is required to provide the support layer 4 (? through holes 4), leading to a reduction in manufacturing time and associated costs. Secondly, the strength and rigidity of the membrane can be maintained, since fewer through holes 4 need to be present on the support layer 3 to provide the same flowability as in the current state of the art filter membranes. Thirdly, the flowability and / or pressure loss obtained with the existing filtration layer 2 can be improved by the use of the intermediate layer 5 according to the invention. In other words, with the same number of through holes 4, the presence of a series of ducts 7 sandwiched between the filtration layer 2 and the support layer 3 can allow a higher flowability and a lower pressure loss compared to a membrane without said series of ducts 7. Fourthly, the presence of said series of ducts 7, preferably parallel to the support layer 3, leads to an improved horizontal flow of the filtrate and a more uniform distribution of the filtrate on the support layer 3, which is also beneficial to the pressure loss and / or flowability achieved. Fifth, with fewer through holes in the support layer, more bonding surface is available, allowing for stronger bonding between the support layer and the filtration layer, enhancing the backwashability of the composite filter membrane of the present invention. The filtration layer 2, support layer 3, intermediate layer 5 and duct-forming material 12, as well as other embodiments and aspects of the present invention, are now further described below.

[0029] filtration layer The filtration layer 2 referred to herein refers to a solid layer or film made of a first polymeric material, which is continuous and has a structure that allows one or more components to be selectively transported through it. In other words, the filtration layer is semi-permeable. The filtration layer 2 is preferably a filtration membrane. The filtration layer 2 used herein allows one or more compounds to be separated from a feed, which may be liquid or gas, and transported through the filtration layer 2, for example to a location where they can be collected. The filtration layer 2 is a semi-permeable membrane. The filtration layer 2 may be characterized by a certain permeability to one or more compounds. The permeability selectivity can be determined by any kind of separation mechanism, such as, but not limited to, the characteristic pore size of the filtration layer 2 (e.g., microporous or nanoporous filtration membranes), or the characteristic attraction of a particular charge type (e.g., ion exchange membranes).

[0030] In a specific embodiment of the present invention, the thickness of the filtration layer 2 is in the range of about 5 μm to 900 μm, preferably in the range of 100 μm to 500 μm.

[0031] According to the invention, the filtration layer 2 is made of a first polymer material comprising at least a first polymer 10. In a further embodiment of the invention, the first polymer 10 is a compound that is a blend of one or more of the following groups: polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinylidene chloride, polyvinyl chloride, chlorinated polyvinyl chloride, chlorinated polyethylene, polyaryletherketone, polyetheretherketone, sulfonated polyetheretherketone, polychlorotrifluoroethene, polyetherimide, polyimide, polyamideimide, polyacrylonitrile, polyurethane, polyphenylene sulfide, cellulose acetate, cellulose triacetate, grafted variants of any of these polymers, and copolymers of any of these polymers. The amount of the compound of the first polymer 10 in the (dry) (final) filtration layer 2 is advantageously at least 5% by weight, advantageously at least 10% by weight, advantageously at least 25% by weight, advantageously at least 35% by weight, advantageously at least 50% by weight.

[0032] The filtration layer 2 is advantageously a membrane with a high polymer content, which refers to a filtration layer 2 obtained by phase separation using a membrane-forming solution, also called dope, of the filtration layer 2, the ratio of the polymer content to the solvent content being at least 0.15% by weight, advantageously at least 0.20% by weight, advantageously at least 0.25% by weight and advantageously not exceeding 0.50% by weight.

[0033] The thickness of the filtration layer 2 and the intermediate layer 5 can vary within wide limits and usually depends on the type of application for which the composite membrane is intended to be used. In some cases, it is desirable for the membrane layer to be as thin as possible. However, in some applications, for example high flux membranes, a thicker filtration layer 2 may be desirable. When using high flux membranes, a high filtrate drainage capacity may be desirable. This can be achieved by the presence of a series of ducts 7 in the intermediate layer 5 that are large enough to accommodate the required volume. To achieve this, the diameter of the ducts can be increased. In doing so, the thickness of the filtration layer 2 will advantageously also be increased.

[0034] The filtration layer 2 according to the invention can be obtained by subjecting the polymer solution to a phase separation process. Phase separation, also called phase inversion, is a known process in which demixing between the polymer and the solvent is induced. As a result of demixing, the polymer precipitates, thereby forming a membrane lattice with the desired structure (pore size, pore structure, etc.). Further process steps can be performed to completely remove the solvent (e.g., possibly washing in a hot water bath) and to obtain the final pore structure (e.g., removing the pore former by washing in a bleach solution). Demixing can be induced based on several techniques. One possibility is thermally induced phase separation (TIPS), in which demixing is induced by a temperature change at the interface of the polymer solution. Another possibility is to induce a chemical reaction in the polymer solution, causing demixing. This is called reaction induced phase separation (RIPS). Very often, however, demixing is induced by phase diffusion. The polymer solution is contacted with another phase, which is a liquid (liquid-induced phase separation or LIPS) or gas (vapor, called vapor-induced phase separation or VIPS) that is a non-solvent for the polymer but miscible with the solvent of the polymer solution. The liquid or vapor diffuses through the polymer solution, causing a local change in the composition of the polymer solution and inducing demixing. As a result, the polymer precipitates out of the solution. LIPS is also called immersion precipitation. It is convenient to note that any phase separation process can be applied to make the filtration layer 2 as described herein. In this specification of the present invention, when referring to "stiffening / stiffening the dope of the filtration layer 2", it refers to the act of forming a membrane by precipitation of the polymer by phase separation with a solvent.

[0035] According to a particular embodiment of the present invention, the filtration layer 2 is at least partially made of a first polymer 10, which is a dope of the filtration layer 2 that needs to be stiffened. The dope of the filtration layer 2 is stiffened by means of a solvent that needs to be in contact with the dope of the filtration layer 2. In a particular embodiment, the filtration layer 2 is a dope of the filtration layer 2 made of polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) or N-ethylpyrrolidone (NEP), where NMP or NEP is the solvent used in the phase separation process.

[0036] When the filtration layer 2 is obtained by a phase separation process, the liquid filtration layer 2 (the dope of the filtration layer 2) is poured onto the duct-forming material 12. The dope of the filtration layer 2 is then brought into contact with a solvent and the dope is stiffened, thereby starting the phase separation process. This means that the material used for the duct-forming material 12 is compatible and does not interfere with the phase separation process, more specifically with the solvent used in said process. This mainly requires the resistance of the duct-forming material 12 with the solvent used in said phase separation process, at least when stiffening is performed. In principle, any compatible polymer material can be used as the duct-forming material 12, as long as it can be dissolved in a solvent that does not substantially adversely affect (e.g. completely dissolves) the support layer 3 and the filtration layer 2, either during the phase separation process or during post-treatment steps. In fact, the support layer 3 and the filtration layer 2 may be dissolved in the same solvent as the duct forming material 12, but in these circumstances, in order to allow the filtration layer 2 and the support layer 3 to retain their functionality, the time of using said solvent must be carefully monitored to avoid dissolution or substantial shape change of the membrane layer.

[0037] Advantageously, the filtration layer 2 comprises an outer layer (hereinafter also referred to as skin or skin layer) containing pores that determine the permselectivity of the entire filtration layer 2. The pores of the skin are usually smaller than the pores in the interior of the filtration layer 2. Advantageously, the skin extends to the support layer 3, i.e. the skin forms an edge in contact with the support layer 3 along at least a part of the periphery of the filtration layer 2. Advantageously, the skin forms an edge in contact with the support layer 3, which edge completely surrounds or encloses the filtration layer 2 on the support layer 3. It can be seen that no additional sealing is required, since the skin seals the filtration layer 2 along the edge(s). This skin edge is therefore a sealed edge, which can be obtained when the membrane is cast directly on the support layer 3 as a polymer solution.

[0038] According to an embodiment of the present invention, the compound of the first polymer 10 may be an organic binder forming the matrix or lattice of the membrane, in which a hydrophilic filling material may optionally be dispersed. Such filling material is a pore former that must be removed before the use of the composite membrane according to the present invention. The removal can be performed in a post-treatment step, for example by washing with a bleach solution (for example for PVP). The filling material may be an organic polymer, advantageously a combination of one or more polymers from the group comprising hydroxypropylcellulose (HPC), carboxymethylcellulose (CMC), polyvinylpyrrolidone (PVP), cross-linked polyvinylpyrrolidone (PVPP), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyethylene glycol (PEG) and glycerol. Preferably, according to an embodiment of the present invention, the filtration layer 2 comprises pores with a pore size ranging from about 0.5 nm to 50 μm, preferably from about 5 nm to 5 μm, most preferably from about 0.05 μm to 0.5 μm. The filler material dispersible in the filtration layer prior to use can be one or a combination of two or more filter media from the group including, but not limited to, amines, such as monoethanolamine (MEA), diethanolamine (DEA), polyethyleneimine (PEI), aminopropyltrimethoxysilane, and polyethyleneiminetrimethoxysilane. The filler material can be one or a combination of amide- or amine-containing polymers, such as, but not limited to, polyamide (PA), polyurethane (PUR), polyvinylamine (PVArm), and melamine.

[0039] In a further embodiment of the invention, the filtration layer 2 further comprises a hydrophilic packing material 12, advantageously one or a combination of two or more from the group: hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), cross-linked polyvinylpyrrolidone (PVPP), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyethylene glycol (PEG) and glycerol.

[0040] In a further embodiment of the present invention, the filtration layer 2 comprises about 1% to about 15% by weight of the hydrophilic filling material 12 described above.

[0041] support layer According to the invention, the support layer 3 is made of a second polymeric material different from the first polymeric material, and the support layer 3 comprises one or more through holes 4 that allow the drainage of the filtrate filtered by the semi-permeable filtration layer 2 across the composite filter membrane 1. The support layer 3 provides structural support to the intermediate layer 5, which is in direct contact with the support layer 3 and the filtration layer 2, ensuring the desired mechanical strength. In other words, the support layer provides structural rigidity and drainage of the filtrate. In particular, the support layer 3 improves the rigidity of the composite filter membrane 2 (composite filter membrane 1 or filtration layer 2), thereby reducing the risk of rupture or damage of the intermediate layer 5 and the filtration layer 2. This is particularly important when the composite filter membrane 1 of the invention is subjected to backwashing.

[0042] Said through holes 4 extend over the entire thickness of the support layer 3 from one outer surface to the opposite outer surface. The through holes may penetrate the support layer at an oblique angle, thus at an angle greater or less than 90 degrees, but preferably extend along a direction perpendicular to both surfaces of the support layer, thus penetrating the support layer at an angle of about 90 degrees. If the support layer comprises several through holes, these through holes are advantageously not connected to each other in the support layer 3. The through holes 4 may have any cross-sectional shape that the skilled person considers appropriate, i.e. have the shape of a regular geometric figure, for example a circular, square, polygonal such as a hexagonal, star-shaped or slit-shaped hole, or the through holes 4 may have any other suitable shape. However, it is preferred that the through holes 4 have a circular or polygonal cross section. According to a further preferred embodiment, the through holes 4 advantageously have the shape of a substantially cylinder or prism, advantageously with an axis perpendicular to the outer surface of the support layer.

[0043] The support layer 3 advantageously exhibits an open surface area (OSA) of at least 0.01%. When defining the total area, the peripheral edges of the support layer 3 that may be fluid-tight sealed are ignored. The OSA of the support layer 3 is advantageously not too low, on the one hand, as it is necessary to provide a sufficient flux through the face of the support layer 3, and on the other hand, not too high, so as not to impair the strength of the support layer 3. A high OSA leads to larger and / or more numerous through holes 4, which makes the support layer 3 less rigid and more prone to bending.

[0044] In a further embodiment of the present invention, the support layer 3 has a plurality of through holes 4 and has an open surface area (OSA) in the range of about 0.01% to about 10%, particularly about 0.1% to 5%, of the total area of ​​the support layer 3. In a particular embodiment, the support layer 3 is made of polycarbonate (PC) or polyvinyl chloride (PVC) and has an OSA in the range of about 0.01% to about 10%, particularly about 0.1% to 5%. The size of the through holes 4 is in the range of about 0.1 mm to about 4.0 mm, particularly about 0.1 mm to about 1.0 mm.

[0045] The support layer 3 is preferably wider than the filtration layer 2 in order to provide a sealing periphery.

[0046] The support layer 3 may be a single layer of material or may be a multi-layer structure, where successive layers may be made of different materials, including non-polymers such as metals. Alternatively, the support layer 3 may be formed of a structure formed of different compounds, with a gradient of one or more compounds throughout the structure, such that at the outer surface of the support layer 3 that forms the interface with the filtration layer 2, the compounds of the second polymer 11 are present in sufficient amounts to cause a sufficiently strong interaction with the compounds of the first polymer 10.

[0047] According to the invention, the second polymer material from which the support layer 3 is made comprises at least a second polymer. The compound of the second polymer 11 can be chosen from a wide range of compounds and can be polysulfone (PSU), polyethersulfone (PESU), grafted variants thereof, or a copolymer of any one of the polymers. The compound of the second polymer 11 can be polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), grafted variants thereof, or a copolymer of any one of the polymers. The compound of the second polymer 11 can be polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), grafted variants thereof, or a copolymer of any one of the polymers. The compound of the second polymer 11 can be a polymer of the polyaryletherketone (PAEK) family, for example polyetheretherketone (PEEK), grafted variants of any of these polymers, for example sulfonated polyetheretherketone (PEEK-WC), or a copolymer of any one of these polymers. The compound of the second polymer 11 may be polychlorotrifluoroethene (PCTFE), polyetherimide (PEI), polyimide (PI), polyamideimide, polyacrylonitrile (PAN), polyurethane (PUR), in particular thermoplastic polyurethane, a grafted variant of any of these polymers, or a copolymer of any one of these polymers. The compound of the second polymer 11 may be polyphenylene sulfide (PPS), cellulose acetate (CA), cellulose triacetate (CTA), a grafted variant of any of these polymers, or a copolymer of any of these polymers. The second polymer 11 compound may be polycarbonate (PC), poly(methyl methacrylate) (PMMA), polyamide (e.g., nylon), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), polychlorotrifluoroethylene (PCTFE), polybutylene terephthalate (PBT) and polyphenylene sulfide (PPS), grafted variants of any of these polymers (aminated, sulfonated or acrylated, etc.), or copolymers of any of these polymers.The compound of the second polymer 11 can be polyethylene (PE), chlorinated polyethylene (CPE), polypropylene (PP), poly(ethylene terephthalate) (PET), optionally modified by copolymerization, such as PET-G (glycol modified), amorphous PET (PET-A) or PET-GAG (multilayer PET-G foil with A-PET core). Combinations of the compounds listed above can also be used to prepare the support layer 3.

[0048] Thus, according to an embodiment of the present invention, the support layer 3 comprises a second polymer 11, the compound of which is a blend of one or more polymers selected from polycarbonate, polyester, poly(methyl methacrylate), nylon, polystyrene, acrylonitrile-butadiene-styrene, polychlorotrifluoroethylene, polybutylene terephthalate, polyethylene, polypropylene, poly(ethylene terephthalate), polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinylidene chloride, chlorinated polyethylene, polyvinyl chloride, chlorinated polyvinyl chloride, polyaryletherketone, polyetheretherketone, sulfonated polyetheretherketone, polychlorotrifluoroethene, polyetherimide, polyimide, polyamideimide, polyacrylonitrile, polyurethane, polyphenylene sulfide, cellulose acetate, cellulose triacetate, grafted variants of any of these polymers, and copolymers of any of these polymers.

[0049] The amount of the compound of the second polymer 11 in the support layer 3 is advantageously at least 5% by weight, advantageously at least 10% by weight, advantageously at least 25% by weight, advantageously at least 35% by weight, advantageously at least 50% by weight, based on the weight of the support layer. The support layer 3 may contain reinforcing or filling materials such as glass fibers, basalt fibers, metal fibers, carbon nanotubes and glass beads. According to an embodiment of the invention, the area of ​​the support layer 3 covered by both the intermediate layer 5 and the filtration layer 2 is preferably at least 90%, more preferably at least 99.9% of the available area on the support layer. The thickness of the support layer can vary within a wide range, but according to the invention, the preferred thickness of the support layer 3 is about 50 μm to about 1000 μm.

[0050] Middle Tier According to the invention, the intermediate layer 5 is arranged between the support layer 3 and the filtration layer 2. In other words, the intermediate layer 5 is sandwiched between the support layer 3 and the filtration layer 2. The intermediate layer is formed by dissolving the part or parts of the duct-forming material 12, which is preferably completely covered by the filtration layer 2. After leaching of the duct-forming material, a series of ducts is formed, which at least partially cover the through holes 4 of the support layer 3 and provide access thereto. In this way, the series of ducts formed after dissolving the duct-forming material connects to at least one through hole, thereby allowing the flow of liquid to pass through the filtration layer 2, the intermediate layer 5 and the support layer 3 via said series of ducts 7. The ducts 7 in the intermediate layer 5 are preferably substantially parallel to the support layer, but can also be present obliquely in the support layer. Thus, according to the invention, the intermediate layer 5 is formed by at least partial dissolution of the duct-forming material 12, which is sandwiched between the support layer 3 and the filtration layer 2. The duct-forming material 12 is therefore substantially absent in the composite filter membrane 1 according to the invention, and is only present before the membrane is utilized for its intended filtration purpose. According to the invention, the intermediate layer 5 is made from a first polymeric material, which is the same polymeric material from which the filtration layer is made.

[0051] According to an embodiment of the present invention, the combined thickness of the filtration layer 2 and the intermediate layer 5 is in the range of about 50 μm to 1 mm. According to an embodiment of the present invention, the thickness of the intermediate layer is about 10% to 90% of the combined thickness of the filtration layer 2 and the intermediate layer 5, in one embodiment about 20% to about 60% of the combined thickness of the filtration layer 2, advantageously 33% of said combined thickness.

[0052] In one embodiment of the invention, the intermediate layer 5 is in a plane parallel to the support layer 3 and at least partially covers said support layer 3. In a further embodiment of the invention, the ducts of the series of ducts 7 have a diameter of about 10 μm to about 750 μm, advantageously about 100 μm to about 350 μm. In a further embodiment of the invention, the series of ducts 7 comprises crossing ducts 8, which allow the distribution of the discharged liquid on the composite membrane and facilitate the discharge of the liquid. Thus, the ducts 8 of the series of ducts 7 may or may not be accessible to each other, but preferably they are accessible to each other. In a further embodiment of the invention, the ducts 7 are arranged according to a regular geometric pattern 9 selected from herringbone, checkerboard, etc. Since the series of ducts 7 present in the intermediate layer is obtained by leaching of the duct-forming material 12, the pattern of the series of ducts 7 is obtained directly from the pattern of the duct-forming material 12.

[0053] Duct forming material According to an embodiment of the invention, the duct-forming material 12 is applied onto the support layer 3 in the form of a pattern, such as a mesh, prior to application of the filtration layer 2, e.g. prior to the phase separation process used in applying and manufacturing the filtration layer 2 onto the support layer 3. To enable the intermediate layer 5 to be applied at the desired location on the support layer 3, the duct-forming material 12 is preferably applied using a printing technique.

[0054] The duct-forming material 12 may not be resistant to the solvent used to harden the filtration layer 2, i.e., the first solvent. When in contact with the first solvent, the duct-forming material 12 dissolves and may lose its shape more or less after a while. In order to ensure that the duct-forming material 12 retains its shape and allows the formation of a series of ducts, it is preferable to keep the contact time with the first solvent as short as possible. The contact time is preferably 10 minutes or less, more preferably 0.1 seconds to 10 minutes.

[0055] In a further preferred embodiment of the present invention, the duct-forming material 12 covers the support layer 3 at a specific coverage of about 10% to about 75%, particularly about 20% to about 50%, of the surface area of ​​the support layer.

[0056] The application of the duct forming material 12 can be carried out using various techniques, such as (i) screen printing, (ii) single layer printing techniques (3D printing), (iii) electrospinning, etc., or any other technique deemed appropriate by the skilled artisan.

[0057] Screen printing (i) is a printing technique in which a mesh is used to transfer ink to a substrate, except in areas that have been blocked by a blocking stencil. A blade or squeegee is moved across a screen, filling the open mesh openings with ink, and a reverse stroke brings the screen momentarily into contact with the substrate along the contact line. This causes the ink to wet the substrate and be drawn out of the mesh openings as the screen bounces back after the blade has passed. Since one color is printed at a time, several screens can be used to create a multicolored image or design.

[0058] Single layer printing techniques (ii) are similar to 3D printing, with the difference that instead of building multiple layers, only one layer is built. Using the Fused Deposition Modeling technique, a continuous filament of thermoplastic material extruded from a nozzle can be deposited on a horizontal surface, i.e. as a layer. The nozzle can be moved in three dimensions, and the movements are computer controlled. In this way, a given shape can be created.

[0059] Electrospinning (iii) is a fiber production method that uses electrical forces to draw electrically charged threads of a polymer solution or melt to fiber diameters on the order of a few hundred nanometers. Electrospinning combines characteristics of both electrospray and conventional solution dry spinning of fibers. The process does not require the use of solidification chemistry or high temperatures to produce solid threads from solution. This makes the process particularly suitable for producing fibers using large, complex molecules. Electrospinning from molten precursors is also performed. This method ensures that no solvent can be carried over into the final product.

[0060] FIG. 2 shows an example of a duct forming material 12 according to the invention, which is a PVA web, resulting in a specific coverage of the support layer of 50%. More specifically, FIG. 2 shows a web of PVA with a height of 0.1 mm, a wire width of 1 mm, and a square side length of 3.25 mm, resulting in a specific coverage of the support layer of 50%. The web shown in FIG. 2 is not circular. The height of the wire is measured on the cross section of the wire, the height being measured along a direction perpendicular to the plane of the support layer and the width being measured along a direction parallel to the support layer. The web can be made of PVA so that it is water soluble and dissolves in a further process, leaving the ducts in the intermediate layer sandwiched between the support layer and the filtration layer. PVA dissolves in relatively cold water (25° C. to 40° C.).

[0061] If the duct-forming material 12 is not soluble in the solvent used to stiffen the filtration layer 2, multiple ducts can be obtained in the intermediate layer 5 by exposing the assembled membrane to a suitable solvent, which leaches out the intermediate layer 5, resulting in a series of ducts 12 (?7) positioned between the support layer 3 and the filtration layer 2.

[0062] The polymer of the duct-forming material 12 is often soluble in the solvent (which allows solvent bonding to occur), but this is not essential. The polymer must retain its structure for a long enough time until the filtration layer 2 reaches its solid structure, which may be a contact time of the order of a few seconds to a few minutes. The layer of duct-forming material 12 provides a pattern 9 of interconnected ducts in the intermediate layer 5 across the entire surface of the support layer 3, said pattern 9 being obtained by leaching out the duct-forming material 12 after the composite filter membrane 1 has been assembled and the first polymer 10 and the second polymer 11 have been bonded.

[0063] From the above, it can be seen that the layer of duct-forming material 12 is applied over a portion of the surface of the support layer 3. Parts of the surface of the support layer will not be covered by the duct-forming material and at these locations the support layer 3 will be in contact with the filtration layer 2 and a solvent bond may be established between these layers. Thus, the layer of duct-forming material 12 may be applied on the support layer according to a regular geometric pattern 9, such as a herringbone or checkerboard pattern covering about 10% to 75% of the support layer 3.

[0064] In a preferred embodiment, the duct forming material 12 is formed by the use of crossed wires having a diameter (if the cross section of the duct forming material has a circular cross section) or height of about 10 μm to about 750 μm, advantageously about 100 μm to about 350 μm. The wires do not necessarily have to be circular and can be selected from a variety of shapes, including but not limited to circular, elliptical, rectangular, semicircular, etc. The layer of duct forming material 12 can be attached to the support layer 3 at the through holes 4 or by spot welding. There is no need to connect the intermediate layer 5 to other locations on the support layer 3, as the layer of duct forming material 12 will then melt.

[0065] Advantageously, the duct forming material 12 may be made from the same material as the filling material that may be present in the filtration layer 2. In this way, the formation of the pores in the filtration layer 2 and the formation of the intermediate layer 5 containing the series of ducts 7 can be achieved simultaneously in a single post-processing step. The duct forming material 12 may be made from an organic polymer, advantageously one or a combination of hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), cross-linked polyvinylpyrrolidone (PVPP), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyethylene glycol (PEG) and glycerol.

[0066] In order to create a series of ducts 7 with the highest capacity to discharge the phase to be filtered and thus improve the flowability, it is advisable to apply a layer of duct-forming material 12 to cover at least a part, preferably all, of the through holes 4 in the support layer 3. In other words, it is advisable to apply a layer of duct-forming material 12 to cover at least a part, in particular at least 80%, 85%, 90%, 95%, 99%, preferably all, of the open surface area of ​​the support layer 3. In this way, when the duct-forming material 12 dissolves, a series of ducts 7 connect with the through holes 4 on the support layer 3. In this way, the discharge of the filtrate through the series of ducts 7 and through holes 4 is achieved with improved flowability. In the manufacture of the composite filter membrane 1, for example, a gel-like substance forming the duct-forming material 12 is applied according to a pattern 9 to the outer surface of the support layer 3 over the entire through holes 4 in said support layer 3. The gel-like substance penetrates or covers the through holes 4 of the support layer 3 accordingly. After solidification of the gel-like substance, a layer of duct-forming material 12 is formed. The duct-forming material may then be covered with a layer of filtering layer-forming material.

[0067] According to an embodiment of the present invention, the filtration layer 2 is a porous layer of a first polymer 10 and the support layer 3 is a sheet of a second polymer 11, which typically includes a plurality of through holes 4. The first polymer 10 and the second polymer 11 are selected so that polymer entanglement can be obtained. Typically, a common solvent for the first polymer 10 and the second polymer 11 is used to at least partially dissolve the first polymer 10 and the second polymer 11, allowing bond formation between the first polymer 10 and the second polymer 11 by polymer entanglement.

[0068] As mentioned above, the bonding between the intermediate layer 5 and the support layer 3 is achieved by solvent bonding. In this process, the surface layer of the support layer 3 is softened or (at least partially) dissolved by the action of a solvent. Advantageously, the solvent that brings about the solvent bonding is the same solvent used in the phase separation process for the manufacture of the filtration layer 2 (meaning the solvent that stiffens the dope of the filtration layer 2). This makes the polymer chains of the support layer 3 sufficiently mobile to interact with the polymer chains of the layer of the filtration layer-forming material. Furthermore, if the polymers of the layer of the filtration layer-forming material and the polymers of the support layer 3 are compatible, it is possible to achieve sufficiently strong intermolecular interactions, such as, but not limited to, (partial) interpenetration and entanglement between the chains of the two polymers that occur at the interface between the layer of the filtration layer-forming material and the support layer 3. Surprisingly, when the phase separation is carried out to stiffen the dope of the filtration layer 2, these intermolecular interactions do not disappear but become permanent, resulting in a strong bond.

[0069] It will be understood that in order to obtain a bond between the support layer 3 and the intermediate layer 5, the intermediate layer 5 and the support layer 3 must share an interface where the compound of the first polymer 10 (contained in the filtration layer 2 and the layer of the filtration layer-forming material) can interact with the support layer 3 at a molecular level. Thus, at least the outer surface layer of the support layer 3 that forms the interface with the intermediate layer 5 to be formed, and possibly the entire support layer 3, comprises or consists of a compound of the second polymer 11 that can interact with the first polymer 10 of the filtration layer 2 / layer of the filtration layer-forming material / intermediate layer 5. Both the compound of the first polymer 10 and the compound of the second polymer 11 must be present at the interface, and further, for the interaction between the first polymer 10 and the second polymer 11 to occur, the compounds of the first polymer 10 and the second polymer 11 must be compatible, e.g., have similar Hildebrand solubility parameters. Due to molecular mobility and interactions between the first polymer 10 and the second polymer 11, advantageously, the polymer chains of the compound of the first polymer 10 penetrate and / or become entangled with the polymer chains of the compound of the second polymer 11 at the interface between the intermediate layer 5 and the support layer 3.

[0070] In a second aspect, the present invention provides a method for producing a composite filter membrane 1 as defined in accordance with the present invention, comprising the steps of: (a) providing a support layer 3 having at least one through hole 4; (b) providing on said support layer 3 a layer of duct-forming material 12 configured to partially cover the entire surface of the support layer 3 and to at least cover at least one through hole 4 of said support layer 3; (c) providing a layer of filtration layer-forming material on the layer of duct-forming material 12 provided in step (b), thereby covering the duct-forming material 12; (d) solvent bonding the support layer 3 and the layer of filtration layer-forming material with a first solvent, causing adhesion between said support layer 3 and said layer of filtration layer-forming material, thereby forming a filtration layer 2; and (e) at least partially dissolving the duct-forming material 12 provided in step (b) with a second solvent, thereby forming an intermediate layer 5 having a series of ducts 7.

[0071] According to an embodiment of the present invention, step (b) includes the steps of (c1) providing a dope of the filtration layer 2 on the layer of duct forming material 12, and (c2) stiffening the dope of the filtration layer 2 provided in step (c1) with a third solvent, thereby providing the filtration layer 2.

[0072] According to an embodiment of the present invention, the method includes the steps of: (c) providing a layer of a filtration layer-forming material, preferably comprising a packing material selected from one or a combination of hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), cross-linked polyvinylpyrrolidone (PVPP), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyethylene glycol (PEG) and glycerol; (f) dissolving the filling material contained in the filtration layer 2 with a fourth solvent; Further includes.

[0073] According to an embodiment of the invention, the method further comprises carrying out steps (d) and (e) contemporary with a common solvent or mixture of solvents, i.e. the first solvent and the second solvent are the same. According to a further embodiment of the invention, the method further comprises carrying out steps (e) and (f) contemporary with a common solvent or mixture of solvents, i.e. the second solvent and the fourth solvent are the same.

[0074] According to an embodiment of the present invention, in steps (a)(b), the method comprises providing a layer of duct forming material 12 covering the support layer 3 with a specific coverage of the support layer of about 10% to about 75%, in particular about 20% to about 50%.

[0075] FIG. 3 shows a series of steps that allow the production of the composite filter membrane 1 according to the present invention in a roll-to-plate production line. Hereinafter, steps A to J will be described in detail, which are general methods for producing the composite filter membrane 1 according to the present invention. For example, but not limited to, the series of steps may include the following consecutive steps: step A, unrolling the untreated support material; step B, perforating the untreated support material and providing through holes; step C, washing the perforated support material, thereby obtaining a usable support layer; step D, applying a layer of duct-forming material on the support layer; step E, applying a layer of filtration layer-forming material, such as a filtration layer dope; step F, washing; step G, post-treatment; step H, conditioning and drying; step I, cutting the obtained composite filter membrane; step J, laminating the obtained composite filter membrane. The steps described in FIG. 3 may differ, for example, based on the technology of forming the filtration layer, for example, when no filtration layer dope is required and the filtration layer can be placed directly on the layer of duct-forming material, or when no post-treatment step is required, for example. The above listed steps are explained in more detail below.

[0076] Process A: Deployment The coil with the untreated support material is placed horizontally so that the axis of the coil is perpendicular to the direction of production. This process is usually called "uncoiling" and can be stretched using accumulators. Accumulators can be implemented in case the coil needs to be replaced without stopping production. Equipment for uncoiling and positioning the coils is well known in all kinds of manufacturing industries.

[0077] Process B: Drilling The sheet material comprises through holes 4 for draining the filtered water. The through holes 4 are preferably circular, for example with a diameter of 1 mm. The through holes 4 are preferably arranged in a pitch pattern at a clearly defined distance from each other. The most obvious patterns are square, triangular or rectangular. Other patterns are also possible. The through holes 4 do not necessarily have to be circular, but may for example be rectangular in shape, triangular, oval, etc. It is not necessary to perforate the entire surface. A defined margin (non-perforated material) is left surrounding the perforated area.

[0078] Various techniques can be provided for creating the through holes 4. The most common technique for perforating sheet material is "die-cutting". For small surfaces, flat-bed punches are suitable. For larger surfaces, rotary punches must be considered.

[0079] Step C: Washing A cleaning step must be performed to remove dust and residues from the perforation process. This can be done with a high airflow or dust removal device. Also, degreasing of the film material cannot be ignored. If degreasing is not done properly, the adhesion of the filter layer 2 will not be efficient enough. On the other hand, if the perforation process is performed without adding lubricants, the degreasing step can be simplified. The degreasing may be performed at the production site by the material supplier. For example, EtOH or isopropyl alcohol can be used as degreasing agents. When used in large quantities, other industrial agents may be more suitable.

[0080] Step D: Applying a layer of duct forming material In this step D, a specific embodiment of the first step of the manufacture of the composite filter membrane 1 according to the present invention is described, in which a step (a) is performed in which a layer of duct-forming material 12 is provided on the support layer 3, the layer being configured to partially cover the entire surface of the support layer 3 and at least cover at least one through hole 4 present in said support layer 3. The layer of duct-forming material 12 must be applied so that it is positioned relative to the support layer 3 and fixed to each other. This layer of duct-forming material 12 is sacrificial, since it is removed in the manufacturing process after the layer of filtration layer-forming material is cast and solidified (if the layer of filtration layer-forming material is a filtration layer dope) or after a pre-made filtration layer is placed on the support layer. After the removal of the duct-forming material 12, the duct 6 is exposed. The choice of material for the layer of duct-forming material 12 depends on the ability of said material to create thin wires that connect to each other and maintain their shape, for example when a filtration layer dope (also called membrane dope) is cast on it, and during the solidification process of said filtration layer dope. The layer of duct-forming material 12 can be applied by coating or by laminating as a pre-made mesh material. The screen printing process can be an interesting industrial process used for coating the layer of duct-forming material 12 by using a liquid solution that can be spread in a checkered pattern on the surface of the support layer 3. By carrying out the process several times, two or more layers can be applied and the required height can be created. The liquid solution must be viscous to avoid running out and losing its shape. The viscosity must be increased to a nearly solid state before carrying out the next step of the manufacture (the coating process of the filtration layer 2). In this case, additional steps (for example UV curing or evaporation by heat) are most likely to be carried out. Furthermore, the layer of duct-forming material 12 can be created, for example with the aid of 3D printing techniques. By passing a polymer filament through a heated extrusion nozzle, the polymer melts and reforms into thinner filaments that can be placed on the support layer. By moving the extruder in a specific path, a mesh-like pattern is created.The intermediate layer 5 obtained by leaching out the layer of duct-forming material 12 may be organic, advantageously one or a combination of hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), cross-linked polyvinylpyrrolidone (PVPP), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyethylene glycol (PEG) and glycerol. The layer of duct-forming material 12, usually in the form of a mesh, can also be removed after assembly of the composite filter membrane 1, for example by washing with an aqueous solution (for example in the case of PVP). Removal of the polymer leaves a series of ducts 7 in the intermediate layer 5.

[0081] Step E: Application of the filtration layer In this step, a specific embodiment of the second step of the manufacture of the composite filter membrane 1 according to the invention is described, in which step (b) is performed by providing a layer of a filtration layer-forming material on the layer of duct-forming material 12. The filtration layer 2 obtained from the layer of filtration layer-forming material is a porous or non-porous polymer layer. It allows some to pass and blocks others. Such may be molecules, ions or small particles. The layer of filtration layer-forming material 2 may be a thermodynamically stable polymer solution, in other words a filtration layer dope, or may be provided already rigidified. To create the filtration layer 2 in the filter membrane of the final composition, different techniques can be used. Each technique requires a specific polymer composition, which gives different results (pore size, chemical stability, etc.). For example, to create a porous membrane suitable for MBR (membrane bioreactor) applications, the pore size is preferably in the range of 0.03 μm to 0.3 μm. The filtration layer dope that can be used is a developed composition based on PVDF polymer dissolved in NMP. Additional PVP can be added as a filling material. The filtration layer dope is dissolved in a non-solvent (H 2O), it solidifies by liquid-liquid extraction. This procedure results in an asymmetric structure of pores across the thickness of the filtration layer 2. The smallest pores are on the outside of the formed filtration layer 2 (highest solvent-non-solvent gradient at first contact), creating a thin skin layer. Larger pores are formed in the substructure of the filtration layer 2. Thus, in a further embodiment according to the invention, the step of providing the filtration layer 2 on the layer of duct-forming material 12 comprises (c1) providing a dope of the filtration layer 2 on the layer of duct-forming material 12, and (c2) hardening the dope of the filtration layer 2 of step (c1) by a third solvent, thereby providing the filtration layer 2. According to an embodiment of the invention, the filtration layer 2 is coated on the layer of duct-forming material 12 on the support layer 3. The thickness of the applied layer should be thicker than the thickness of the layer of duct-forming material 12 to avoid defects in the subsequent membrane skin layer. The open areas of the layer of duct-forming material 12 are also filled with the filtration layer dope. To solidify the filtration layer dope, the structure is immersed in water, which acts as a non-solvent. A minimum residence time is required for dilution of the solvent in the membrane structure. The filtration layer 2 is almost solidified in order to start the next process step. The solvent present in the dope of the filtration layer 2 comes into contact with the support layer 3 and partially dissolves the surface. At that point, polymer entanglement occurs. Achieving polymer entanglement is important for the support layer 3 to adhere to the filtration layer 2 so that the composite filter membrane 1 according to the invention can be backwashed. If the support layer 3 does not adhere strongly enough to the filtration layer 2, the pressure exerted by air or liquid during backwashing can cause the filtration layer 2 to peel off from the support layer 3. This bond between the filtration layer and the support layer is only possible if the combination of materials used is properly chosen. More specifically, the materials constituting the layer of filtration layer forming material and the support layer are chosen by softening or at least partially dissolving under the action of a common solvent that can be used, for example, in the filtration layer dope solution. By exposing both the support layer 3 and the layer of filtration layer forming material to such a common solvent, a strong bond is created between the filtration layer 2 and support layer 3 thereby formed through polymer entanglement.The common solvent is usually an aprotic solvent such as N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), dimethylformamide (DMF), dimethylsulfoxide (DMSO) and dimethyl acetate (DMAc). Such bonding can be achieved by a support layer made of polycarbonate (PC) or polyvinyl chloride (PVC) and a filtration layer dope made of polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) or N-ethylpyrrolidone (NEP). Furthermore, the material constituting the layer of duct-forming material 12, for example a water-soluble polymer material, must be such that the layer of duct-forming material 12 is not rapidly dissolved by the common solvent used to bond the layer of filtration layer-forming material 2 and the support layer 3 by polymer entanglement. If the layer of filtration layer-forming material can be dissolved by the common solvent, it is necessary to fine-tune the process so that the duct 6 formed by dissolving the layer of duct-forming material 12 can retain its shape by the common solvent. This step describes a specific embodiment of the fourth step of manufacturing a composite filter membrane 1 according to the invention, which provides step (e) of at least partially dissolving the layer of duct-forming material 12, thereby forming an intermediate layer 5 with a series of ducts 7. Depending on the polymer used for the duct-forming material 12, it may be that the layer of duct-forming material 12 is already fully / partially dissolved after this process step. This is certainly the case when a PVA with low hydrolytic properties is used. On the other hand, if PVP is used for the layer of duct-forming material 12, it must be removed in a later manufacturing step, for example step G.

[0082] Step F: Washing In the washing step, any remaining solvent is washed from the resulting filtration layer 2. This step is an extension of the previous step. The washing step can be carried out with the same solvent as that used to solidify the filtration layer dope, i.e. a non-solvent for the filtration layer dope, if one was used. Furthermore, it has been found that higher temperatures and convection speed up the process.

[0083] Process G: Post-processing Post-treatment is an additional washing step to remove additives such as PVP from the filtration layer 2. Typically, hypochlorite (NaOCl) is used to oxidize the PVP, causing chain scission. In this way, residual PVP can be easily washed away. A slight increase in temperature may be beneficial to reduce the residence time. At this point, the duct-forming material 12 can also be washed away if it has not yet dissolved in the previous manufacturing step. Thus, in a further embodiment according to the invention, the method comprises: (f) dissolving the filling material contained in the filtration layer 2; Further includes:

[0084] Step H: Conditioning and drying In most cases, the composite filter membrane 1 is dried before transportation and / or storage. Drying of the composite filter membrane 1 must be done in a controlled manner. If not done well, the pores in the filtration layer 2 may collapse, resulting in fewer active pores after rewetting. Also, dried, uncollapsed pores may be difficult to rewet. Smaller pores require higher liquid intrusion pressures, exceeding the maximum allowable pressure, especially if the material of the filtration layer 2 is mild or non-hydrophilic. To avoid the above identified drawbacks, the composite filter membrane 1 needs to be conditioned. Conditioning the composite filter membrane 1 means immersing the composite filter membrane 1 for a certain period of time in a warm water bath with a high content of glycerol in the water (up to 30%). The pores need to be filled with this high concentration glycerol solution before drying can occur. Drying can be done by heated air circulating over the surface of the composite filter membrane 1. The glycerol concentration increases during the evaporation of the water. In particular, the small pores are filled with a gel-like glycerol material, which remains after most of the water has evaporated. If it is desired to rewet the composite filter membrane 1, the glycerol dissolves by immersing the membrane in water and can then be easily washed away.

[0085] Process I: Cutting The sheet of composite filter membrane 1 is cut to a specific width and length in preparation for lamination and / or packaging. A minimal amount of space should be left around the composite filter membrane 1 for later handling. Cutting can be easily accomplished with a die cross cutting machine.

[0086] Process J: Lamination For space-saving storage of sheets of the composite filter membrane 1, lamination is recommended. The surface of the composite filter membrane 1 is fragile and needs to be handled carefully. A protective film material between each sheet is a necessary precaution. For lamination and / or packaging of the composite filter membrane 1, several machines are commercially available. In a third aspect, the present invention relates to the use of the composite filter membrane 1 defined by its embodiments. For example, the composite filter membrane 1 can be used in various technical fields and for various purposes as a filtration composite membrane. The composite filter membrane 1 according to the present invention is particularly suitable for use in microfiltration or ultrafiltration processes. Furthermore, the composite filter membrane 1 of the present invention is particularly suitable as a filtration membrane in industrial wastewater treatment, more particularly as a membrane for a membrane bioreactor (MBR). Furthermore, the composite filter membrane 1 according to the present invention is particularly useful as a filtration membrane that can be backwashed. EXAMPLES

[0087] Experimental Department The manufacture of the composite filter membrane 1 shown in FIG.

[0088] FIG. 4 shows a cross-section of a composite filter membrane according to the invention, the composite filter membrane 1 comprising a filtration layer 2 at the top of the figure, a support layer 3 at the bottom of the figure, and an intermediate layer 5 sandwiched between the filtration layer 2 and the support layer 3, the intermediate layer 5 being solvent-bonded to the support layer 3 and comprising a visible duct 6 in the center of the figure. The duct 6 allows, for example, liquid to be discharged through the duct 6 and then through at least one through-hole 4 in the support layer 3. The through-hole 4 is not visible in FIG. 4 due to the way in which the cross-section of the composite filter membrane 1 is photographed. The composite filter membrane 1 shown in FIG. 4 is made of the following materials: support layer 3, PVC; filtration layer 2, the filtration layer dope is based on a PVDF / NMP mixture with PVP as the filling material; a layer of duct-forming material 12, filaments of partially hydrolyzed PVA. The detailed manufacture of the composite filter membrane 1 shown in FIG. 4 is described in Example 1.

[0089] Example 1 The manufacture of the composite filter membrane 1 shown in Figure 4 includes the steps of preparing the support layer 3, applying a layer of duct-forming material 12, applying a layer of filtration layer-forming material (in this case, filtration layer dope) and stiffening it, washing off residual solvent, and post-treatment, conditioning and drying.

[0090] Preparation of the support layer In Example 1, polyvinyl chloride (PVC) was chosen as the material for the support layer 3. PVC is one of the most commonly used thermoplastic polymers worldwide. PVC is widely available in two major categories: rigid and flexible. In our development, the rigid one was chosen. It is available in coils and is still flexible enough to be easily deployed. The material is transparent. The thickness is 300 μm. The sheet was cut to dimensions of 210 mm width and 297 mm length.

[0091] Figure 5A shows the perforation of the support layer 3 of the composite filter membrane 1 shown in Figure 4. Drilling was the preferred choice to create through-holes 4. A square pitch pattern was chosen with a pitch of 13 mm and a diameter of the through-holes 4 of 1.0 mm, see Figure 5B. A margin of a few centimeters was left at the edges. This resulted in a total of 280 through-holes 4 being drilled.

[0092] Figure 5B shows the support layer 3 of the composite filter membrane 1 shown in Figure 4, with adjacent through-holes 4 equally spaced and positioned on the support layer 3 according to the square pitch pattern. An enlarged view of the through-holes 4 is provided.

[0093] Five sheets of the resulting support layer 3 were placed on top of each other on a CNC drilling machine and pressed down with a 3 mm thick aluminum plate, which had the same width and length dimensions as the PVC sheet and was pre-drilled with through holes 4 with a diameter of 1.5 mm.

[0094] Applying a layer of duct forming material A 3D printer was used to apply the duct-forming material 12 onto the perforated support layer 3. Filaments of partially hydrolyzed PVA were used. This type of filament is typically designed to dissolve in water at room temperature. The positioning of the support layer 3 had to be ensured to ensure that the through holes 4 were covered by the printed filament. After several printing attempts, a layer thickness of about 0.5 mm could be achieved.

[0095] FIG. 6A shows a layer of duct forming material 12 utilized to form the ducts 6 in the composite filter membrane 1 shown in FIG. 4, the duct forming material 12 being a PVA web resulting in a specific coverage of the support layer 3 of 35%, with all through holes 4 in the support layer 3 being completely covered as evident from the view shown in FIG. 6B. A close-up of the web is presented. The web is 0.5 mm high, 0.5 mm wide, and a square with each side measuring 2.6 mm long. As the web is made from PVA, it is water-soluble and can be dissolved in further processing leaving channels in the intermediate layer 5 sandwiched between the support layer 3 and the filtration layer 2.

[0096] Figure 6B shows a further enlargement of the enlarged view shown at the bottom of Figure 6A. Figure 6B shows a checkered pattern of PVA material. The shape of the layer of duct forming material 12 can be described as mesh-like. The dimensions of the checkered pattern are wire diameter (D) 0.5 mm, center to center (CTC) distance of 2.6 mm, and clear opening size (COS) of 2.1 mm.

[0097] Application and hardening of the layer of filtration layer forming material The filtration layer dope was pre-prepared in a membrane factory. The dope is based on a PVDF / NMP mixture with PVP as the filler material. Before use, the dope was heated to 40°C in a hot air oven. Casting was done with an Elcometer 4340 motorized film applicator with a doctor blade. The thickness was set at 1.0 mm (this is the wet thickness before solidification). During the coating process, the humidity of the ambient air should be as low as possible to avoid premature skin formation. Therefore, the applicator is placed in a low humidity compartment. After the casting process, the resulting sheet of composite filter membrane 1 was transferred to a second compartment, where the membrane was kept above a 40°C hot water bath. The filtration layer dope was facing downwards. In this way, water vapor can reach the surface of the filtration layer dope and the first skin pores are formed. After 20 seconds, the sheet of composite filter membrane 1 was immersed in a 40°C hot water bath. At this point solidification is complete. The sheet of composite filter membrane 1 was left in a hot water bath for several hours to ensure that the filtration layer 2 was fully formed.

[0098] Washing off residual solvent During solidification of the filtration layer dope, the solvent of the filtration layer dope is diluted in a water bath. In the washing step, the solvent / water mixture was replaced with clean water.

[0099] Evaluation of the resulting product At this point, samples were taken from the resulting sheet of composite filter membrane 1. Surprisingly, the layer of duct-forming material 12 had already dissolved, resulting in open ducts. To summarize the findings, the PVA material used for the layer of duct-forming material 12 was completely dissolved after the washing process, and the dimensions of the open ducts 6 in the intermediate layer formed were close to the dimensions of the wire diameter of the layer of duct-forming material 12 shown in Figure 6B. Furthermore, when an attempt was made to peel the intermediate layer 5 from the lower layer, the intermediate layer 5 had a strong bond with the support layer 3. When the intermediate layer 5 was torn in two, the remainder remained attached to the support layer 3. That is, there was an additional force of polymer entanglement that was stronger than the cohesive force of the intermediate layer 5. Furthermore, the exposed ducts 6 were completely covered by the filtration layer 2, and no defects of the skin layer occurred.

[0100] Post-processing At this point, the pores of the filtration layer 2 are still filled with PVP polymer. A post-treatment step is required to open the pores to ensure that water flow can occur. The procedure is as follows: Prepare a warm water bath at 45°C. Add hypochlorite (NaOCl) until it reaches 2000 ppm. Add HCl to lower the pH to pH 8.0. Immerse a sheet of composite filter membrane 1 in the solution for a minimum of 0.75 hours and a maximum of 4 hours. Rinse the membrane at least three times with warm fresh water.

[0101] Conditioning and drying After post-treatment, the pores are filled with water. If a dry composite filter membrane 1 is required, a conditioning and drying process needs to be carried out. The procedure is as follows:

[0102] 1. Prepare a hot water / glycerol mixture at 50°C. The concentration must be greater than 20% and less than 50%. If the concentration is too low, there may not be enough glycerol remaining after drying to fill all the pores. If the concentration of glycerol is too high, the viscosity will be too high. This high viscosity will adversely affect its ability to mix with fresh water present in the smallest pores.

[0103] 2. Immerse the membrane sheet in the water / glycerol mixture. It is highly recommended to use convection during the residence time, as this will encourage the penetration of the mixture into the pores. This can be done with an aerator.

[0104] 3. After 16 hours, the membrane sheet can be removed from the water / glycerol mixture. A draining step can now take place. A blower can be placed to blow air over the surface of the membrane. After 24-48 hours, depending on the humidity of the surrounding air, the membrane should be dry and ready for storage. The air can be heated to improve the drying procedure.

[0105] Table 1 below shows combinations of materials for the support layer 3, materials for the filtration layer 2, binding solvent, duct forming material 12, and solvents for dissolving the layer of duct forming material 12 suitable for carrying out the present invention. Further combinations of materials and solvents will be apparent to those skilled in the art based on the teachings provided in the present specification. Further examples according to the present invention are provided in Table 1. As examples of support materials, polyvinyl chloride (PVC) and polycarbonate (PC) were investigated. These two materials, when combined with binding solvents NMP or NEP, provide good adhesion between the membrane layer and the support layer 3. As for the duct forming material 12, polyvinyl alcohol (PVA) is slowly soluble in both NMP and NEP and is easily dissolved in H. 2 It is mostly dissolved after a rinse step with O. Polyvinylpyrrolidone (PVP) dissolves much slower in NMP (or NEP) and must be removed in a NaOCl post-treatment step.

[0106] [Table 1] [Explanation of symbols]

[0107] 1 Composite filter membrane 2 filtration layer 3 Support layer 4 Through holes 5. Middle Tier 6 Duct 7 A series of ducts 8 Cross Duct 9 Patterns 10 First Polymer 11 Second Polymer 12 Duct forming materials

Claims

1. A composite filter membrane (1), a filtration layer (2) made from a semi-permeable first polymer material; a support layer (3) made from a second polymeric material different from said first polymeric material and containing at least one through hole (4); the middle class (5) and Equipped with The intermediate layer (5) made from the first polymer material and sandwiched between the filtration layer (2) and the support layer (3); Solvent-bonded to the support layer (3), a series of ducts (7) connected to the at least one through-hole (4) of the support layer (3), the series of ducts (7) configured to discharge the liquid flow that has passed through the filtration layer (2) and the intermediate layer (5) through the at least one through-hole (4) of the support layer (3); Composite filter membrane.

2. 2. The composite filter membrane of claim 1, wherein the series of ducts (7) are recessed onto the filtration layer.

3. 2. The composite filter membrane of claim 1, wherein the series of ducts (7) are formed by dissolving a duct-forming material (12) embedded within the filtration layer (2).

4. Multi-multi claim A composite filter membrane according to any one of claims 1 to 3, wherein the series of ducts (7) are substantially parallel to the support layer (3).

5. 2. The composite filter membrane (1) according to claim 1, wherein the support layer (3) has a plurality of through holes (4) with an open surface area (OSA), defined as the area of ​​the through holes relative to the total area of ​​the support layer (3), expressed as a percentage value in the range of about 0.01% to about 10%, in particular 0.1% to 5%, of the total area of ​​the support layer (3).

6. 2. The composite filter membrane (1) according to claim 1, wherein the diameter of the circular cross section of the ducts (6) of the series of ducts (7) is from about 10 μm to about 750 μm, in particular from about 50 μm to about 500 μm, and more particularly from about 100 μm to about 350 μm.

7. 2. The composite filter membrane (1) of claim 1, wherein the combined thickness of the filtration layer (2) and the intermediate layer (5) ranges from about 50 μm to 1 mm.

8. A method for producing the composite filter membrane (1) according to claim 1, comprising: (a) providing a support layer (3) having at least one through hole (4); (b) providing a layer of duct-forming material (12) on the support layer (3) so as to partially cover the entire surface of the support layer (3) and at least cover the at least one through-hole (4) in the support layer (3); (c) providing a layer of filter layer-forming material on the layer of duct-forming material (12) provided in step (b); (d) solvent bonding the support layer (3) provided in step (a) and the layer of filtration layer-forming material provided in step (c) with a first solvent to cause adhesion between the support layer (3) and the layer of filtration layer-forming material, thereby forming a filtration layer (2); (e) at least partially dissolving the duct-forming material (12) applied in step (b) with a second solvent, thereby forming an intermediate layer (5) having a series of ducts (7); A manufacturing method comprising:

9. Step (c) is (c1) providing a dope for a filtration layer (2) on the layer of duct-forming material (12); (c2) hardening the dope of the filtration layer (2) provided in step (c1) with a third solvent, thereby providing the filtration layer (2); The method of claim 8, comprising:

10. 10. The method according to claim 9, wherein in step (c1), the ratio of polymer content to solvent content of the dope of the filtration layer (2) is at least 0.15% by weight, advantageously at least 0.20% by weight, advantageously at least 0.25% by weight, advantageously not more than 0.50% by weight.

11. 9. The method of claim 8, wherein in step (b), the layer of duct-forming material (12) comprises a regular geometric pattern (9), such as a herringbone pattern or a checkerboard pattern, covering approximately 10% to 75% of the support layer (3).

12. (c) providing a layer of a filter layer-forming material, preferably comprising a filler material selected from one or a combination of hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), cross-linked polyvinylpyrrolidone (PVPP), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyethylene glycol (PEG), and glycerol; (f) dissolving the filler material contained in the filtration layer (2) with a fourth solvent; The method of claim 11, comprising:

13. 9. The method of claim 8, wherein steps (d) and (e) are carried out simultaneously in a common solvent or mixture of solvents, i.e., the first solvent and the second solvent are the same.

14. 13. The method of claim 12, wherein steps (e) and (f) are carried out with a common solvent or mixture of solvents, i.e., the second solvent and the fourth solvent are the same.

15. 9. The method of claim 8, wherein in step (b) the layer of duct-forming material (12) is applied to cover the support layer (3) with a specific coverage of the support layer of about 10% to about 75%, in particular about 20% to about 50%.

16. Use of the composite filter membrane (1) according to any one of claims 1 to 7 as a filtration membrane in the wastewater treatment industry or as a membrane in an MBR (membrane bioreactor).

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