High stability, high precision membrane assembly and method of production thereof

Abstract

The present invention relates to a method of producing a new and advantageous membrane assembly. The present invention relates to a membrane assembly provided by such method comprising a porous carrier material having a thickness of about 50 μm - 5000 μm; at least one skin layer membrane on at least one side of the porous carrier material, wherein said at least one skin layer membrane has a thickness of about 0,5 μm - 40 μm and a pore density of at least about 500 pores / cm.

Description

[0001] High stability, high precision membrane assembly and method of production thereof

[0002] Description

[0003] The present invention relates to a method of producing a new and advantageous membrane assembly. The present invention relates to a membrane assembly provided by such method comprising a porous carrier material having a thickness of about 50 pm - 5000 pm; at least one skin layer membrane on at least one side of the porous carrier material, wherein said at least one skin layer membrane has a thickness of about 0,5 pm - 40 pm and a pore density of at least about 500 pores / cm2

[0004] Background of the invention

[0005] Track-etched membranes are some of the most precise and homogenous membranes that can be bought on an industrial scale. Unlike most conventional membranes available on the market, the circular capillary pores of track-etched membranes, also referred to as “true-pore membranes”, are uniform in size and distribution allowing for the selective transport of substances.

[0006] These qualities make track-etched membranes particularly attractive for applications requiring precise separation and high selectivity in various fields, including water purification, medical diagnostics, and venting applications.

[0007] Track-etched membranes are used for surface filtration, meaning that particles bigger than the pore size are retained on the surface of the membrane, essentially acting as a “sieve”. Aside from size exclusion other physical and chemical parameters such as the surface charge, hydrophobicity, pore density, pore shape, operating temperature and choice of membrane material may also contribute to their separation efficiency.In contrast, membranes such as phase inversion membranes, sintered membranes, or expanded membranes, are categorized as depth filters, whose pores comprise tortuous pathways of the porous structure itself, capturing particles throughout the entire thickness of the membrane via mechanical interception, diffusion and / or adsorption. Depth filters, in particular phase inversion membranes and sintered membranes, typically exhibit a much larger pore size distribution and thickness than track-etched membranes.

[0008] Track-etching technology involves the intricate production of micropores within a thin membrane material and is well known in the art per se. A polymer film, most commonly polycarbonate or polyester, is penetrated via irradiation with a heavy ion beam. The heavy ion beam travels through the film in a straight line and damages the film, creating the “tracks”. The film is typically UV treated and subsequently subjected to a physical or chemical etching step to create micropores of equivalent size in a highly precise and controlled manner along the formed tracks.

[0009] A disadvantage of track-etched membranes is the large loss of flow rate, due to the strong barrier effect of the capillary pore structure, especially when the pore density is low. This effect can be partially counterbalanced by a reduced thickness compared to other membrane types, but basically it cannot be overcome. Especially in case of venting applications with liquid barrier requirements, the small thickness (typically 12 pm to 36 pm) to counterbalance the low flow rate characteristics, leads to early breakthrough times.

[0010] Another drawback, especially for hydrophobic and oleophobic track-etched membranes, is their susceptibility against membrane fouling over time. This may include pore blocking, or the accumulation of particles or substances on the membrane surface or within the membrane pores themselves. In case of thicker depth filters (typical ranging from 100 pm to 400 pm in thicknesses), it takes longer for the contamination to work its way through the pore structure.Owing to their porous structure and small thickness, track-etched membranes are often fragile and prone to tearing or deformation under high pressure or mechanical stress. Especially in case of venting or filtration applications, they must be supported using standard non-woven materials. Such non-wovens support the membrane, but always bear the risk of delamination or contamination.

[0011] Further, the working temperature is reduced to the level of delamination temperature for venting applications in particular, which is much lower than the melting temperature of the track-etched membrane.

[0012] These properties exclude laminated track-etched membranes from high temperature applications.

[0013] A further, commercial, disadvantage of track-etched membranes is the need for highly expensive high energy ion accelerators like cyclotrons. Energy consumption and therefore the cost required to generate the tracks on the membrane correlate with the thickness of the membrane materials.

[0014] Still a further issue with track-etched membranes is their limitation to certain membrane materials. Extruded polymer films (e.g. PTFE, PP and PE) and cast polymer films (e.g., nitrocellulose and PES) are not suitable for track-etching, which is mostly restricted to membranes made of polycarbonate or polyester. Whereas treatment by laser drilling is advantageously not limited by the material of the polymer membrane, the membrane thickness still proves a major challenge. To date, the commercial production of membranes with a thickness as small as 5 pm - 20 pm via laser drilling is not considered financially viable due to the high energy consumption and time necessary to drill the pores.

[0015] It is therefore of great industrial interest to provide membranes with a reduced thickness, while minimizing the associated draw-backs and providing a highly flexiblemethod for the production of such membranes with cheaper alternatives for the generation of pores to those known in the art.

[0016] Besides the track-etching technology, other precise surface filters commercially available are made from aluminum oxide (e. g. Anapore membranes, Cytiva) or other inorganic or metallic substrates. Using non-polymeric base materials results in heavy issues regarding mechanical stability due to rigidity and challenges processing the membranes or connecting the membranes to polymer based devices. Therefore, these non-polymeric membranes are only usable for heavily specialized niche applications.

[0017] Summary of the Invention

[0018] According to the present invention, the technical problem is solved in a first aspect by providing a membrane assembly comprising a porous carrier material having a thickness of about 10 pm - 10000 pm; and at least one skin layer membrane on at least one side of the porous carrier material, wherein said at least one skin layer membrane has a thickness of about 0.5 pm - 40 pm, more preferably 1.0 pm - 40 pm, and a pore density of at least about 500 pores / cm2

[0019] A further aspect of the invention relates to a structure comprising a membrane assembly as described above, and a support substrate such as a woven or non-woven support substrate.

[0020] The invention further relates to the use of a membrane assembly as described above or a structure as described above in microfluidic applications, venting applications, high-temperature applications, liquid barrier applications, lateral flow applications, particle capturing, air purification, liquid filtration, and / or diagnostics.

[0021] A further aspect relates to a method of producing a membrane assembly as described above, comprising a porous carrier material and at least one skin layer membrane comprising the following steps:a. Providing a porous carrier material precursor in the form of a particle- filled raw film; and

[0022] b. Forming or applying as a coating at least one skin layer on at least one side of said particle-filled raw film; and

[0023] c. Imparting a pore density to the at least one skin layer to form a skin layer membrane, preferably by means of

[0024] i. Heavy ion beam treatment, preferably with a cyclotron, more preferably with a low-energy tandem accelerator; and subsequent track-etching treatment, wherein the coated film obtained in step b is immersed in a suitable etching solution, optionally wherein the coated film is subjected to a UV- or solvent treatment to facilitate pore formation prior to immersion in said suitable etching solution; or

[0025] ii. Laser drilling preferably using an excimer laser, femtosecond laser or CO2 laser, wherein the laser drilling is performed by drilling one hole per pulse or several holes per pulse simultaneously, preferably at least about 1000 holes per pulse simultaneously, more preferably at least about 5000 holes per pulse simultaneously; or

[0026] iii. Imprinting, e.g.

[0027] (a) Melting micro-structures into the at least one skin layer;

[0028] (b) Melting nano-structures into the at least one skin layer; or (c) Perforation of the softened skin layer;

[0029] and

[0030] d. Removing filler particles from the particle-filled raw film, preferably by dissolving the filler particles in a washing solution or an etching solution, or by melting the particles to obtain the membrane assembly comprising a porous carrier material and the at least one skin layer membrane; and e. Optionally optimizing the pore size, functionality and / or surface chemistry.

[0031] As used herein, the terms “melting micro-structures” and “melting nano-structures” represent preferred embodiments of imprinting.Still a further aspect of the invention relates to a membrane assembly comprising a porous carrier material and at least one skin layer membrane, which is obtainable by a method as described above.Detailed description

[0032] The present invention relates to a novel and advantageous kind of membrane assembly comprising a porous carrier material having a thickness of about 10 pm -10000 pm, preferably 50 pm - 5000 pm; and at least one skin layer membrane having a thickness of about 0.5 pm - 40 pm, preferably 1 pm - 40 pm, with a pore density of at least about 500 pores / cm2on at least one side of the porous carrier material.

[0033] In preferred embodiments, the membrane assembly may comprise a porous carrier material and one skin layer membrane. In other preferred embodiments, the membrane assembly may comprise a porous carrier material and two skin layer membranes, preferably one at each of the opposing sides of the porous carrier material, respectively.

[0034] In preferred embodiments, the membrane assembly may consist of a porous carrier material and one skin layer membrane. In other preferred embodiments, the membrane assembly may consist of a porous carrier material and two skin layer membranes, one at each of the opposing sides of the porous carrier material, respectively.

[0035] In preferred embodiments, besides a supporting function the porous carrier material may provide an additional separation function.

[0036] In preferred embodiments, the porous carrier material is a depth filter that allows particles to enter the porous material and that catches the particles inside the material within its tortuous pathways and has a narrow part in the range of the respective pore size.

[0037] In further preferred embodiments, the porous carrier material is generated by a template method, which generally refers to a fabrication approach. In general, a preformed template with a specific structure (e.g., pores, patterns, or a scaffold) is usedto create a membrane. The membrane material is deposited or formed around the template, and the template is subsequently removed.

[0038] Membranes and porous materials generated by the template method are known to the skilled person (of. EP0477689, US4242464, US5514378, US8944257, US2010155325, WO0234819, EP2342907, EP4397397, US10865516, WO2012097967).

[0039] The porous carrier material may further be one of: anodized aluminum oxide (AAO) membrane, polymer template membrane, metal template membrane, phase inversion membrane, expanded membrane, sintered membrane, non-woven membrane, woven membrane, colloidal crystal template membrane, or any other suitable membrane or porous material known in the art.

[0040] In preferred embodiments, the porous carrier material is a depth filter generated by a template method.

[0041] In some preferred embodiments, the membrane assembly comprises a porous carrier material having a thickness of about 10 pm - 10000 pm, preferably 50 pm - 5000 pm at least two skin layer membranes, each having a thickness of about 0,5 pm - 40 pm, preferably 1 pm - 40 pm, respectively, each with a pore density of at least about 500 pores / cm2on at least one side of the porous carrier material, wherein the at least two skin layer membranes are not layered on top of each other or overlap.

[0042] The porous carrier material may stabilize the skin layer membrane.

[0043] The pore density of a membrane is a crucial parameter to define the overall performance of a given membrane.In preferred embodiments, the pore density of the at least one skin layer membrane is at least about 10 pores / cm2, preferably at least about 50 pores / cm2, more preferably at least about 100 pores / cm2, even more preferably at least about 200 pores / cm2, even more preferably at least about 300 pores / cm2, even more preferably at least about 400 pores / cm2, even more preferably at least about 500 pores / cm2, even more preferably at least about 1000 pores / cm2, even more preferably at least about 10,000 pores / cm2, even more preferably at least about 100,000 pores / cm2, even more preferably at least about 200,000 pores / cm2, even more preferably at least about 300,000 pores / cm2, even more preferably at least about 400,000 pores / cm2, even more preferably at least about 500,000 pores / cm2, even more preferably at least about 600,000 pores / cm2, even more preferably at least about 700,000 pores / cm2, even more preferably at least about 800,000 pores / cm2, even more preferably at least about 900,000 pores / cm2, even more preferably at least about 1,000,000 pores / cm2, even more preferably at least about 1,100,000 pores / cm2, even more preferably at least about 1,200,000 pores / cm2, more preferably at least about 1,300,000 pores / cm2, even more preferably at least about 1,400,000 pores / cm2, more preferably at least about 1,500,000 pores / cm2, even more preferably at least about 1,600,000 pores / cm2, even more preferably at least about 1,700,000 pores / cm2, even more preferably at least about 1,800,000 pores / cm2, even more preferably at least about 1,900,000 pores / cm2, even more preferably at least about 2,000,000 pores / cm2, even more preferably at least about 2,500,000 pores / cm2, even more preferably at least about 3,000,000 pores / cm2, even more preferably at least about 3,500,000 pores / cm2, even more preferably at least about 4,000,000 pores / cm2, even more preferably at least about 4,500,000 pores / cm2, even more preferably at least about 5,000,000 pores / cm2, even more preferably at least about 5,500,000 pores / cm2, even more preferably at least about 6,000,000 pores / cm2, even more preferably at least about 6,500,000 pores / cm2, most preferably at least about 7,000,000 pores / cm2.

[0044] The pores of the at least one skin layer membrane may be distributed uniformly or non-uniformly, preferably uniformly.

[0045] The pores of the porous carrier material may be distributed uniformly or non-uniform ly, preferably uniformly.In some preferred embodiments, the membrane assembly may comprise two skin layer membranes, one at each of the opposing sides of the porous carrier material, wherein the two skin layer membranes have the same or different pore densities.

[0046] In some preferred embodiments, the membrane assembly may comprise two skin layer membranes, one at each of the opposing sides of the porous carrier material, wherein the two skin layer membranes both have a uniform or non-uniform pore distribution, or one skin layer membrane has a uniform pore distribution, and the other skin layer membrane has a non-uniform pore distribution.

[0047] The pore shape of the porous carrier material may be cylindrical, conical, funnel-like, slit-shaped, conical, hourglass shaped and / or cigar-like or spongy. Preferably it is spongy, i.e. highly disordered with tortuous pathways, preferably along with a high porosity (percentage of voids vs. bulk material) as possible.

[0048] The pore shape of the at least one skin layer membrane may be cylindrical, conical, funnel-like, slit-shaped, conical, hourglass shaped and / or cigar-like, preferably cylindrical.

[0049] In some preferred embodiments, the membrane assembly may comprise two skin layer membranes, one at each of the opposing sides of the porous carrier material, wherein the two skin layer membranes have pores of the same or different shape independently selected from the group consisting of cylindrical, conical, funnel-like, slit-shaped, conical, hourglass shaped and / or cigar-like, preferably cylindrical.

[0050] The pores of the porous carrier material and / or the at least one skin layer membrane may be arranged either parallel or at an angle to each other.In preferred embodiments, the pore density of the at least one skin layer membrane can be imparted onto the skin layer by any method selected of track-etch, laser drilling, imprinting, micro-melting, or nano-melting treatment. Laser drilling and / or imprinting are especially preferred.

[0051] The thickness of a membrane affects the overall performance of a given membrane in a myriad of ways. Thicker membranes generally boast a higher resistance to mechanical stress than thinner membranes, e.g., tearing, puncturing, or pressure-induced deformation. Simultaneously, an increase in membrane thickness affects the transport properties. A decrease in permeability, diffusion and rate of particle transfer due to the increased travel distance required for particles to pass the membrane may be observed for thicker membranes (e. g. see law of Hagen-Poiseuille describing the pressure drop in a laminar flow of an incompressible and Newtonian fluid through a cylindrical pipe with a heavy dependency on the length of the pipe). Thicker membranes typically exhibit lower heat transfer and higher energy consumption to drive processes like filtration or diffusion, while also increasing material cost. Meanwhile, thinner membranes may allow to circumvent some of the drawbacks described above but may require a supporting structure to offset their increased susceptibility to mechanical stress. The ideal membrane strikes a balance between these properties to meet the requirements for the specific application. For example, in electrochemical applications, the thickness of ion-conductive membranes may influence the ionic conductivity, resistance and overall performance of the electrochemical cell. In biological applications, such as drug delivery, the thickness may influence the biocompatibility of the membrane and the rate of controlled drug release. Thickness of a membrane generally refers to the geometrical thickness of a membrane, unless specified otherwise.

[0052] The thickness of the porous carrier material is not particularly limited. Due to the target significantly larger voids and higher porosity compared to the skin-layer, the flow and thus performance is defined by the small pore-structure of the skin-layer and not by the carrier. The pressure drop of the flow rate through the carrier could be magnitudes lower, compared to the pressure drop generated by the high-precision skin-layer structure.Preferably, the thickness of the porous carrier material is about 1 pm - 10000 pm, more preferably about 50 pm - 5000 pm, even more preferably about 60 pm - 4000 pm, even more preferably about 70 pm - 3000 pm, even more preferably about 80 pm - 2000 pm, even more preferably about 90 pm - 1000 pm, even more preferably about 100 pm - 900 pm, even more preferably about 110 pm - 800 pm, even more preferably about 120 pm - 700 pm, even more preferably about 130 pm - 600 pm, even more preferably about 140 pm - 500 pm, most preferably about 150 pm - 300 pm.

[0053] Preferably, the thickness of the porous carrier material is at least about 1 pm, more preferably at least about 50 pm, even more preferably at least about 60 pm, even more preferably at least about 70 pm, even more preferably at least about 80 pm, even more preferably at least about 90 pm, even more preferably at least about 100 pm, even more preferably at least about 110 pm, even more preferably at least about 120 pm, even more preferably at least about 130 pm, even more preferably at least about 140 pm, most preferably at least about 150 pm.

[0054] Preferably, the thickness of the porous carrier material is about 10000 pm or less, more preferably about 5000 pm or less, even more preferably about 4000 pm or less, even more preferably about 3000 pm or less, even more preferably about 2000 pm or less, even more preferably about 1000 pm or less, even more preferably about 900 pm or less, even more preferably about 800 pm or less, even more preferably about 700 pm or less, even more preferably about 600 pm or less, even more preferably about 140 pm or less, most preferably about 150 pm or less.

[0055] Preferably, the thickness of the at least one skin layer membrane is about 0.5 pm - 30 pm, preferably about 0.6 pm - 28 pm, even more preferably about 0.75 pm - 26 pm, even more preferably about 0.9 pm - 24 pm, even more preferably about 1.0 pm - 22 pm, even more preferably about 1.1 pm - 20 pm, even more preferably about 1.2 pm -18 pm, even more preferably about 1.3 pm - 16 pm, even more preferably about 1.4pm - 14 pm, even more preferably about 1.5 pm - 12 pm, even more preferably about 1.6 pm - 10 pm, even more preferably about 1.7 pm - 8.5 pm, even more preferably about 1.8 pm - 7 pm, even more preferably about 1.9 pm - 5.5 pm, most preferably about 2 pm - 4 pm. According to further preferred embodiments, the thickness of the at least one skin layer membrane is about 0.5 pm - 3.0 pm, more preferably 0.5 pm -2.5 pm, even more preferably 0.5 pm - 2.0 pm and even more preferably 0.5 pm - 1.5 pm.

[0056] Preferably, the thickness of the at least one skin layer membrane is at least about 0.5 pm, preferably at least about 0.6 pm, even more preferably at least about 0.75 pm, even more preferably at least about 0.9 pm, even more preferably at least about 1.0 pm, even more preferably at least about 1.1 pm, even more preferably at least about 1.2 pm, even more preferably at least about 1.3 pm, even more preferably at least about 1.4 pm, even more preferably at least about 1.5 pm, even more preferably at least about 1.6 pm, even more preferably at least about 1.7 pm, even more preferably at least about 1.8 pm, even more preferably at least about 1.9 pm, most preferably at least about 2 pm.

[0057] Preferably, the thickness of the at least one skin layer membrane is about 30 pm or less, preferably about 28 pm or less, even more preferably about 26 pm or less, even more preferably about 26 pm or less, even more preferably about 24 pm or less, even more preferably about 22 pm or less, even more preferably about 20 pm or less, even more preferably about 18 pm or less, even more preferably about 16 pm or less, even more preferably about 14 pm or less, even more preferably about 12 pm or less, even more preferably about 10 pm or less, even more preferably about 8.5 pm or less, even more preferably about 7 pm or less, even more preferably about 5.5 pm or less, most preferably about 4 pm or less.

[0058] In some preferred embodiments, the membrane assembly may comprise two skin layer membranes, one at each of the opposing sides of the porous carrier material, whereinthe two skin layer membranes have the same or a different thickness. It is preferred that the at least one skin layer is the outer layer which faces outwards, e.g. towards the sample collection side.

[0059] The thickness of the membrane assembly is generally the sum of the thickness of the individual layers, i.e. the porous carrier material and the at least one skin layer membrane.

[0060] Without being limited to a single method, the thickness of the membranes and porous materials disclosed herein may be measured by any of micrometer or dial gauge, calipers, scanning electron microscopy (SEM), optical microscopy, confocal microscopy, stylus profilometry, optical profilometry, ellipsometry, Fourier Transform Infrared Spectroscopy (FTIR), X-ray reflectometry (XRR), atomic force microscopy (AFM), micro- or nano-computed tomography or any other suitable method known in the art.

[0061] The thickness of the membranes disclosed herein may be measured according to standardized methods including but not limited to DIN EN ISO 2808, DIN 32567, and DIN 4593.

[0062] All technical standards cited in connection with the present invention, such as DIN standards, refer in each case to the last edition in force prior to the priority day of this patent application.

[0063] The pore size of membranes is a further key factor in determining the overall performance of a given membrane. Larger pores excel at separating larger particles, e.g., bacteria and viruses, boast a higher permeability, requiring less energy input to achieve a certain flow rate, and are less susceptible to clogging, while being generally more robust. This comes at the cost of a loss of selectivity and fine filtration ability compared to membranes with smaller pore sizes.Preferably, the porous carrier material has a larger pore size than the skin layer, thereby enabling the porous carrier material to act as a prefilter or enabling the at least one skin layer membrane to act as a high precision filter depending on the orientation of the membrane assembly to the application and the number of skin layer membranes of which the membrane assembly is comprised.

[0064] In preferred embodiments, the porous carrier material has a pore size of about 5 nm -300 pm, preferably of about 10 nm - 250 pm, more preferably of about 100 nm - 200 pm, even more preferably of about 200 nm - 150 pm, even more preferably of about 400 nm - 100 pm, even more preferably of about 600 nm - 90 pm, even more preferably of about 800 nm - 80 pm, even more preferably of about 1 pm - 80 pm, even more preferably of about 5 pm - 80 pm, most preferably of about 10 pm - 80 pm, even more preferably of about 10 pm - 70 pm, even more preferably of about 10 pm - 60 pm, most preferably of about 10 pm - 50 pm.

[0065] According to especially preferred embodiments, the porous carrier material has a pore size of about 10 pm - 80 pm and a porosity of 70 % - 80 %.

[0066] In preferred embodiments, the at least one skin layer membrane has a pore size of about 1 nm - 100 pm, preferably about 2 pm - 50 pm, more preferably about 3 pm - 45 pm, even more preferably about 4 pm - 40 pm, even more preferably about 5 pm - 35 pm, even more preferably about 6 pm - 30 pm, even more preferably about 7 pm - 25 pm, even more preferably about 8 pm - 20 pm, even more preferably about 9 pm - 15 pm, most preferably about 10 nm - 10 pm.

[0067] Without being limited to a single method, the pore size of the membranes and porous materials disclosed herein may be measured by any of scanning electron microscopy (SEM), transmission electron microscopy (TEM), gas adsorption and desorption (BET), bubble point testing, mercury intrusion porosimetry, light extrusion porosimetry,dynamic light scattering (DLS), atomic force microscopy (AFM), capillary flow porometry, X-ray computed tomography or any other suitable method known in the art.

[0068] In some preferred embodiments, the membrane assembly may comprise two skin layer membranes, one at each of the opposing sides of the porous carrier material, wherein the two skin layer membranes have the same or a different pore size.

[0069] In some preferred embodiments, the membrane assembly may comprise two skin layer membranes, one at each of the opposing sides of the porous carrier material, wherein the two skin layer membranes have the same or different pore densities and the same or different pore sizes and the same or different thicknesses.

[0070] In some preferred embodiments, the pores of the porous carrier material and / or the at least one skin layer membrane are distributed randomly and partially overlap.

[0071] In some preferred embodiments, the pores of the porous carrier material and / or the at least one skin layer membrane are highly ordered and do not overlap.

[0072] As used herein, pore size and porosity describe different properties of a porous material. Pore size refers to the characteristic dimension of individual pores (e.g., mean or maximum equivalent pore diameter), typically reported as above in nm or pm, and it strongly influences selectivity and particle retention. Porosity refers to the fraction of void volume within the material relative to total volume, typically and herein reported as a percentage, and it strongly influences permeability and pressure drop. A material may exhibit large pore size but low porosity (few pores), or small pore size but high porosity (many pores). Both properties interact with thickness and tortuosity to determine overall transport.

[0073] The porosity of a membrane may significantly influence the flow rate, particle transport efficiency, membrane fouling diffusion and mechanical stability.In preferred embodiments, the porous carrier material has a porosity of at least about 15%, preferably at least about 20%, even more preferably at least about 25%, even more preferably at least about 30%, even more preferably at least about 35%, even more preferably at least about 40%, even more preferably at least about 45%, most preferably at least about 50%.

[0074] In preferred embodiments, the at least one skin layer membrane has a porosity of at least about 1%, preferably least about 2%, preferably least about 3%, preferably least about 5%, preferably least about 10%, preferably least about 15%, preferably at least about 20%, even more preferably at least about 25%, even more preferably at least about 30%, even more preferably at least about 35%, even more preferably at least about 40%, even more preferably at least about 45%, even more preferably at least about 50%, even more preferably at least about 55%, even more preferably at least about 60%, even more preferably at least about 65%, and most preferably at least about 70%.

[0075] According to preferred embodiments the at least one skin layer membrane has a porosity in the range of 70%-80%.

[0076] In some preferred embodiments, the porosity of the at least one skin layer membrane is higher than the porosity of the porous carrier material.

[0077] In some preferred embodiments, the porosity of the skin layer membrane is equal to the porosity of the porous carrier material.

[0078] In some preferred embodiments, the porosity of the skin layer membrane is smaller than the porosity of the porous carrier material.In some preferred embodiments, the membrane assembly comprises two skin layer membranes, one at each of the opposing sides of the porous carrier material, wherein the two skin layer membranes have the same or different porosities.

[0079] In preferred embodiments, the porous carrier material and the at least one skin layer membrane independently comprise polyolefines, polyurethanes, polyacrylates, polyepoxides, polyamides, polyimides, polycarbonates, and / or polyesters, preferably sustainable and / or environmentally friendly polyolefines, polyurethanes, polyacrylates, polyepoxides, polyamides, polyimides, polycarbonates and / or polyesters and / or mixtures thereof.

[0080] In preferred embodiments, the porous carrier material and the at least one skin layer membrane independently comprise polylactic acid, cellulose, and / or lignin.

[0081] Preferably, the porous membrane material and the at least one skin layer membrane comprise the same materials as described above.

[0082] In some preferred embodiments, the membrane assembly may comprise two skin layer membranes, one at each of the opposing sides of the porous carrier material, wherein the two skin layer membranes comprise the same or a different material as defined above.

[0083] In preferred embodiments, the membrane assembly has a flowrate of at least about 0.1 -20 x 106mL / min cm2, preferably of at least about 0.5 - 10 x 106mL / min cm2, more preferably of at least about 1.0 - 5 x 106mL / min cm2, at 1 bar pressure.

[0084] The invention further relates to a structure comprising a membrane assembly as described above, and a further carrier such as a woven or non-woven support substrate to provide mechanical strength, flexibility and stability to the membraneassembly. Different from the membranes they support, woven and non-woven support substrate do not directly contribute to the separation or filtration process.

[0085] The non-woven support substrate may be porous and / or fibrous structures. The nonwoven support substrates may be produced by bonding together fibers using mechanical, thermal or chemical methods forming a random, mat-like structure boasting a higher flexibility and lower cost of production compared to woven substrates. The non-woven support substrate may comprise polypropylene (PP), polyester (PET), polyethylene (PE), polyamides (e.g., nylon), polysulfone (PS), polyethersulfone (PES), polyvinylidene fluoride (PVDF), polyether ether ketone (PEEK), cellulose, composite blends and / or any other suitable fiber.

[0086] The woven support substrate may comprise interlaced fibers or threads forming a highly uniform, grid-like or crisscross pattern. The woven support substrate may boast increased mechanic stability and durability more suitable for high-pressure applications compared to non-woven support structures. The woven support substrate may comprise polypropylene (PP), polyester (PET), polyethylene (PE), polyamides (e.g., nylon), glass fiber, aramids (e.g., Kevlar), polyvinylidene fluoride (PVDF), polyether ether ketone (PEEK), cellulose, composite blends and / or any other suitable fiber.

[0087] Non-woven supports include fibrous webs consolidated without weaving, such as spunbond, meltblown, needle-punched, hydroentangled, wet-laid, or multilayer laminates (e.g., SMS). Non-limiting examples include spunbond PET or PP, meltblown PP, cellulose-based papers, glass microfiber mats, and PTFE / ePTFE backings. The support substrate may be surface-treated (e.g., corona, plasma, or primer) to enhance adhesion and wetting.

[0088] The invention further relates to the use of a membrane assembly as described above or a structure as described above in microfluidic applications, venting applications, high-temperature applications, liquid barrier applications, lateral flow applications, particle capturing, air purification, liquid filtration, and / or diagnostics.Membrane assembly production

[0089] The invention further relates to a method of producing a membrane assembly as described above, comprising a porous membrane material and at least one skin layer. The membrane layer is suitable for further modification, such as imparting a porosity via track-etching, laser drilling, imprinting, thereby advantageously combining the high stability and protection level of the porous membrane material with the high separation precision of the skin layer membrane.

[0090] In a first step, a porous carrier material precursor in the form of a particle-filled raw film is provided.

[0091] In preferred embodiments, filler particles are mixed with a precursor material to generate a particle-filled mixture, wherein the filler particles are insoluble in the precursor material, e.g., salts, other polymers or metals, and wherein the filler particles have diameters less than the thickness of the final particle-filled raw film.

[0092] In preferred embodiments, the filler particles of the particle-filled raw film have a diameter that is less than the thickness of the porous carrier material, preferably less than 1 / 3 of the final particle-filled raw film, more preferably 1 / 5 of the final particle filled raw film.

[0093] Generally, the filler particles can be selected from any suitable material as long as the particles may be dissolved under suitable conditions determined by the respective filler material e.g. acid treatment, washing with water or aqueous solutions, heat etc... Preferably the filler particles are selected from the group consisting of inorganic or organic salts, metals, polymers and any suitable mixtures thereof.Inorganic salts may be preferred. Even more preferable are non-toxic, thermally stable inorganic salts with a high hardness according to Mohs hardness scale like carbonate and / or sulfate salts.

[0094] Especially preferred embodiments relate to sodium sulfate, in particular sodium sulfate having particle size of particle size of 0-500 pm, more preferably sodium sulfate having a particle size of particle size of 0-149 pm, or calcium carbonate, in particular calcium carbonate having a particle size of 0-150 pm, more preferably calcium carbonate having a particle size of particle size of 0-105 pm. Sodium sulfate may be removed by water washing. Calcium carbonate may be removed by acid treatment.

[0095] In various preferred embodiments, the filler particles themselves may comprise a coating.

[0096] Preferably, the mixture is melted, preferably in an extruder, and transformed into the particle-filled raw film by extrusion or casting techniques known to the skilled person, wherein the melting point of the filler particles is above the melting point of the precursor material. Preferably, the softening point of the particles is above the melting point of the precursor material.

[0097] In preferred embodiments, the precursor material is dissolved in a suitable solvent and mixed with the filler particles, wherein the solvent is not allowed to dissolve the filler particles. The mixture is then transformed into the particle-filled raw film, comprising raw film material and the filler particles, by casting techniques, e.g. solvent film casting, used to produce e. g. polycarbonate films (Pokalon series, Lofo High Tech Films GmbH) or used for the preparation of adhesive tapes, known to the skilled person and a subsequent drying treatment to remove the solvent from the particle-filled raw film.

[0098] Preferably, the solvent is selected from the group consisting of water, organic solvents and / or other sustainable solvents, preferably water and / or other sustainable solvents,wherein the group of other sustainable solvents comprises ethyl lactate, d-limonene, glycerol, glycerol carbonate, cyrene, supercritical CO2, acetone, ethanol, ionic liquids and mixtures thereof.

[0099] Generally, the formation of voids within the particle-filled raw film is to be avoided, unless required to develop special characteristics of the material.

[0100] The above particle-filled mixture may also contain at least one additive, such as a reinforcing additive, preferably selected from but not limited to glass fiber, plasticizers, carbon black to fine tune the characteristics of the final porous carrier material.

[0101] In non-limiting preferred embodiments, the precursor material of the particle-filled raw film is added as fully polymerized polymers, pre-polymers, or oligomers with suitable cross-linking agents, respectively, or monomers. In case precursor material other than fully polymerized polymers is used, the cast film is preferably polymerized by methods known in the art selected from but not limited to thermal curing, UV curing, radical polymerization, chemical curing, microwave curing, infrared (IR) curing plasma polymerization, catalytic polymerization, and / or electron beam curing. As used herein, the terms “fully polymerized polymers”, “polymerized polymer” and / or “polymer” are used interchangeably.

[0102] Preferably, the fully polymerized polymers, pre-polymers, oligomers or monomers are selected from the group comprising (poly)olefines, (poly)urethanes, (poly)acrylates, (poly)epoxides, (poly)amides, (poly)imides, (poly)carbonates, and / or (poly)esters, preferably such that the final porous carrier material comprises sustainable and / or environmentally friendly polymers, wherein the sustainable and / or environmentally friendly polymers comprise polylactic acid, cellulose, lignin, any other suitable compound, and mixtures thereof.Nevertheless, a skilled person will recognize, that the presented approach is capable to be transferred to every kind of polymer, which precursors could be either molten or dissolved in a solvent. In preferred embodiments, the at least one fully polymerized polymer is selected from the group comprising polyolefines, polycarbonates, polyactides, polyesters, sustainable and / or environmentally friendly polymers and mixtures thereof, preferably sustainable and / or environmentally friendly polymers, wherein the sustainable and / or environmentally friendly polymers comprise polylactic acid, cellulose, lignin, any other suitable compound, and mixtures thereof. Polycarbonates and polyactides are in particular preferred.

[0103] In preferred embodiments, the at least one pre-polymer is selected from the group comprising polyolefine pre-polymers, polycarbonate pre-polymers, polyester prepolymers, pre-polymers forming sustainable and / or environmentally friendly polymers, and mixtures thereof, preferably pre-polymers forming sustainable and / or environmentally friendly polymers, wherein the pre-polymers forming sustainable and / or environmentally friendly polymers comprise polylactic acid pre-polymers, cellulose pre-polymers, lignin pre-polymers, any other suitable pre-polymers and mixtures thereof. Polycarbonate pre-polymers and polylactic acid pre-polymers are in particular preferred.

[0104] In preferred embodiments, the at least one oligomer is selected from the group comprising polyolefine oligomers, polycarbonate oligomers, polyester oligomers, oligomers forming sustainable and / or environmentally friendly polymers, and mixtures thereof, preferably oligomers forming sustainable and / or environmentally friendly polymers, wherein the oligomers forming sustainable and / or environmentally friendly polymers comprise polylactic acid oligomers, cellulose oligomers, lignin oligomers, any other suitable oligomers, and mixtures thereof. Polycarbonate oligomers and oligomers pre-polymers are in particular preferred.

[0105] In preferred embodiments, the at least one monomer is selected from the group comprising styrenes, urethanes, acrylates, epoxides, amides, any other suitable compound class, and mixtures thereof.In preferred embodiments, the at least one cross-linking agent is selected from the group comprising unsaturated organic compounds, epoxides, carboxylic acids, amides, amines, isocyanates, cyanates, or any other suitable class of compounds.

[0106] The ratio of the particle to the raw film material defines the final porosity of the porous carrier material. In preferred embodiments, the content of the filler particles in the rawfilm material and / or the particle-filled raw film and / or the at least one particle-filled skin layer by volume is 15 - 90%, preferably 15 - 80%, more preferably 20 - 80 %, more preferably 30 - 80 %, even more preferably 40 - 80 %, even more preferably 40 - 80 %, most preferably 50 - 80 %.

[0107] The size of the filler particles defines the size of the voids and therefore the final pore size. In preferred embodiments, the filler particles have a diameter of about 5 nm - 500 pm, preferably 5 nm - 300 pm, more preferably of about 10 nm - 250 pm, more preferably of about 100 nm - 200 pm, even more preferably of about 200 nm - 150 pm, even more preferably of about 400 nm - 100 pm, even more preferably of about 600 nm - 90 pm, even more preferably of about 800 nm - 80 pm, even more preferably of about 1 pm - 70 pm, even more preferably of about 5 pm - 60 pm, most preferably of about 10 pm - 50 pm.

[0108] In a second step, at least one skin layer is formed on at least one side of the particle-filled raw film or applied as a coating.

[0109] In preferred embodiments, the particle-filled mixture is cast on an at least one preformed skin layer. In preferred embodiments, the particle-filled material obtained as a liquid mixture according to certain preferred embodiments is cast or extruded in such a way that a skin layer is formed on at least one side, e.g., by deposition of the filler particles, or the material is cast on a thin film that forms the skin layer, preferably wherein the thin film is applied to a transport band via spray coating or extruding. Alternatively, the skin layer is applied by spraying a solution comprising at least one polymer, pre-polymer, oligomer or monomer on said particle-filmed raw film.Alternatively, an at least one preformed skin layer is laminated or molten on said particle-filled raw film. Alternatively, a mixture comprising pre-polymers, oligomers or monomers is polymerized on the surface of the particle-filled raw film in a grafting reaction. Advantageously, the particle-filled film stabilizes the skin layer and significantly reduces wrinkle formation, reducing the scrap rate and costs associated with malformed skin layers.

[0110] In preferred embodiments, the at least one skin layer formed is free of filler particles. Alternatively, the at least one skin layer formed is a particle-filled skin layer comprising filler particles, wherein the ratio of the filler particle diameter of the at least one particle-filled skin layer to the particle diameter of the particle-filled raw film significantly smaller, preferably 1:100, more preferably 1:10.

[0111] In case multiple skin layers are formed or applied as a coating on the particle-filled raw film, any combination of particle-filled skin layer and skin layer without filler particles may be applied. In a non-limiting example, a particle-filled skin layer is applied on one side of the particle-filled raw film and a skin layer without filler particles is applied on the opposing side of the particle-filled raw film.

[0112] In case the final membrane assembly requires a high mechanical strength, it can be supported by woven, non-woven or other suitable support structures known in the art throughout and after the production process, wherein the particle-filled mixture is directly cast or extruded into the supporting structure, making it an integral part of the final membrane assembly and simultaneously reducing the porosity of the porous carrier material.

[0113] In a third step, a pore density is imparted onto the at least one skin layer to form a skin layer membrane.In preferred embodiments, the pore density is imparted onto the at least one skin layer by means of heavy ion beam treatment and subsequent track-etching treatment. The heavy ion beam treatment, also referred to as beaming, “damages” the skin layer, forming highly ordered tracks. Pores are formed within these tracks by subsequent track-etching treatment, preferably by submerging the whole skin layer in a suitable etching solution that slowly dissolves the skin layer material. Preferably the heavy ion beam treatment is performed with a cyclotron. In even more preferred embodiments, the skin layer is so thin that it enables use of a low energy tandem accelerator to form the required tracks. Optionally, the beamed skin layer is subjected to an UV treatment or a solvent treatment to facilitate pore formation, which is a commonly employed method in the field of track-etching (P. Apel, 2001 Radiation Measurements, 2001, 34(1-6), 559-566; Apel P. Y, Korchev Y. E., Siwy Z., Spohr R., Yoshida M. 2001 Nucl. Instrum. Methods Phys. Res., Sect. B 2001, 184, 337; A. H. Khayrat, S. A. Durrani, Radiation Measurements, 1995, 25(1-4), 163-164).

[0114] The filler particles contained within the particle-filled raw film are dissolved in either the same etching solution used for track-etching or in a subsequent washing or etching solution. Preferably, the porous carrier material and the skin layer membrane are inert towards said subsequent washing or etching solution dissolving the filler particles of the particle-filled film to avoid the pore-size of the skin layer membrane being altered during the removal of the filler particles.

[0115] In preferred embodiments, the filler particles are removed from the particle-filled raw film prior to the heavy ion beam treatment or the track-etching treatment. Advantageously, the risk of forming conical pores due to “one-sided” etching is hereby significantly reduced.

[0116] In various preferred embodiments, an additional dissolution or etching step may be performed to at least partially open the skin layer in defined areas and reveal the filler particles of the particle-filled raw film. This step may aid in adjusting the skin layer in case it ends up being too thick, or there are skin layers on both sides of the particle-filled film, covering the filler particles of the particle-filled raw film yet to be removed for a later dissolution or etching step.

[0117] In various preferred embodiments, structures, holes and / or channels are selectively etched into specific, predetermined areas of the skin layer, resulting in a porous carrier material with defined areas of release for gases and liquids. Membrane assemblies of this nature may be beneficial for microfluidic applications and others. In some preferred embodiments, only the porous carrier material, preferably a depth filter, acts as a membrane. In preferred embodiments, a porosity is imparted onto the remaining skin layer.

[0118] In various preferred embodiments, the filler particles may also be removed from the formed porous carrier material comprising a sealed skin layer on one side of the porous carrier material without having imparted a porosity onto the skin layer. Membrane assemblies of this nature may be used for example in lateral flow applications.

[0119] Alternatively, a porosity may be imparted onto the at least one skin layer by laser drilling using a excimer laser, femtosecond laser, CO2 laser, or any other suitable laser, wherein the laser drilling is performed by drilling several pores simultaneously or drilling one pore at a time.

[0120] Although laser drilling may also be performed one pore at a time, the usage of interference patterns to drill several pores at once makes this method to impart a porosity onto the at least one skin layer especially advantageous. The penetration depth and therefore energy consumption required to drill the pores is highly dependent on the thickness of the skin layer that has to be removed and is therefore performed preferably for skin layers of appropriately low thickness, e.g. a thickness of about 3 - 4 pm or less. By reducing the thickness of the skin layer to a minimum a competitive production speed and cost can be achieved. A big advantage compared to tracketching is that laser drilling is largely independent of the material of the skin layer because the pores are burned into the skin layer. Track-etching procedures areoptimized for polycarbonates and polyester materials and can only be applied to materials that form stable tracks and can be effectively etched or dissolved to form the membrane pores. Another advantage over “classical” track-etching treatments is that treatment by laser drilling will result in highly ordered single pores that do not show any overlap, unless specifically designed. In contrast, track-etching methods result in randomly distributed tracks and pores that may partially overlap and bear the risk of thus forming a larger pore with the potential for point leakage.

[0121] In various preferred embodiments, when several pores are drilled simultaneously while performing laser drilling to impart a porosity to the at least one skin layer, at least about 10 pores are drilled per pulse simultaneously, preferably at least about 50 holes per pulse simultaneously, more preferably at least about 100 holes per pulse simultaneously, more preferably at least about 500 holes per pulse simultaneously, more preferably at least about 1000 holes per pulse simultaneously, more preferably at least about 2000 holes per pulse simultaneously, more preferably at least about 3000 holes per pulse simultaneously, more preferably at least about 4000 holes per pulse simultaneously, more preferably at least about 5000 holes per pulse simultaneously, more preferably at least about 6000 holes per pulse simultaneously, more preferably at least about 7000 holes per pulse simultaneously, more preferably at least about 8000 holes per pulse simultaneously, more preferably at least about 9000 holes per pulse simultaneously, more preferably at least about 10000 holes per pulse simultaneously, more preferably at least about 20000 holes per pulse simultaneously, more preferably at least about 30000 holes per pulse simultaneously, more preferably at least about 40000 holes per pulse simultaneously, more preferably at least about 50000 holes per pulse simultaneously, more preferably at least about 60000 holes per pulse simultaneously, more preferably at least about 70000 holes per pulse simultaneously, more preferably at least about 80000 holes per pulse simultaneously, more preferably at least about 90000 holes per pulse simultaneously, more preferably at least about 100000 holes per pulse simultaneously, more preferably at least about 200000 holes per pulse simultaneously, more preferably at least about 300000 holes per pulse simultaneously, more preferably at least about 400000 holes per pulse simultaneously, more preferably at least about 500000 holes per pulse simultaneously, more preferably at least about 700000 holes per pulse simultaneously,more preferably at least about 800000 holes per pulse simultaneously, more preferably at least about 900000 holes per pulse simultaneously, more preferably at least about 1000000 holes per pulse simultaneously, most preferably at least about 2000000 holes per pulse simultaneously.

[0122] In various preferred embodiments, laser drilling can be applied to multiple skin layers on opposing sides of the porous carrier material, to impart different pore structures, pore sizes and pore densities to each of the skin layers, respectively.

[0123] In various preferred embodiments, a porosity is imparted onto the at least one skin layer by melting micro structures into the at least one skin layer.

[0124] In various preferred embodiments, a porosity is imparted onto the at least one skin layer by melting nano structures into the at least one skin layer.

[0125] Imprinting comprising micro- and nano-melting comprises heating a template with structures in the size and shape of the target pore structures to a temperature higher than the melting point of a membrane material, or to a temperature at which the membrane material softens enough but lower than the melting point of the template. The template is made of a material, preferably a metal or alloy, with a higher melting point than the membrane material. The liquid or softened membrane material is then pressed into the template such that it penetrates the whole thickness of the template and the preformed micro- or nanostructures penetrate the membrane material to form pores or a porosity. Templates and / or membrane material can be heated.

[0126] Imprinting of the skin layer can be carried out by perforation of the softened skin layer. After partial heating or controlled solvent exposure, the dense surface becomes viscoelastic without fully melting, so openings can be introduced by a pin roller, stamp, micro-needle array, or laser. Because the bulk remains comparatively solid, hole geometry is better defined and the risk of collapse or smear is reduced. The resultingmicroperforations relieve the transport resistance of the otherwise nonporous skin and can be tuned via temperature, dwell time, and perforation density to achieve target flux and selectivity in final operation.

[0127] In various preferred embodiments, a porosity is imparted onto the at least one skin layer by removing filler particles from the skin layer, wherein the skin layer is a particle-filled skin layer comprising filler particles.

[0128] The porosity is imparted to the skin layer by a templating or imprinting process. The terms “templating” and “imprinting” can be used interchangeably herein. In general, a removable phase and / or a patterned tool is used to define void features in a membrane precursor prior to solidification. For example, a porogen (e.g., particles, droplets, or fibers) may be dispersed in a polymer solution or curable composition, the composition may be cast or coated to form a precursor layer, and the precursor may be solidified by curing, cooling, and / or phase inversion. The porogen is then removed by leaching, dissolution, extraction, or decomposition to form pores. Alternatively or additionally, a mold or stamp may be contacted with the precursor to imprint surface porosity.

[0129] The imprinting step is configured to form, in a single patterning operation, (i) a pore structure in a skin layer of the membrane and (ii) an additional micro- and / or nanoscale surface relief. The additional micro- and / or nano-scale surface relief may be superimposed on, surrounding, or spatially coordinated with the pore structure so as to provide a hierarchical, multi-length-scale topography. Such hierarchical topography is operable to modify surface wetting behavior and, in certain embodiments, to increase hydrophobicity and / or water repellency, including by promoting a Cassie-Baxter wetting state and / or lotus-effect-like performance. The micro- and / or nano-scale surface relief may comprise protrusions, recesses, ridges, pillars, grooves, re-entrant features, or combinations thereof, and may be defined by a structured mold, stamp, or roll used during imprinting.The methods presented herein to impart a porosity onto the at least one skin layer are not limiting and do not exclude other suitable methods.

[0130] In further preferred embodiments, a porosity is imparted onto the at least one skin layer by treatments other than a track-etching treatment.

[0131] In further preferred embodiments, a porosity is imparted onto the at least one skin layer by treatments other than a laser drilling treatment.

[0132] In further preferred embodiments, a porosity is imparted onto the at least one skin layer by treatments other than by imprinting or melting nano structures into the skin layer.

[0133] In further preferred embodiments, a porosity is imparted onto the at least one skin layer by treatments other than by removing filler particles from the skin layer, wherein the skin layer is a particle-filled skin layer comprising filler particles.

[0134] In preferred embodiments, a porosity is imparted onto an at least one skin layer that has not yet been applied or formed on at least one side of the particle-filled film and the obtained skin layer membrane is subsequently laminated onto the particle-filled raw film.

[0135] In a fourth step, the filler particles are removed from the particle-filled raw film by dissolving the filler particles in a washing solution or an etching solution to obtain the membrane assembly comprising a porous carrier material and the at least one skin layer membrane.

[0136] The washing solution may comprise a solvent that dissolves the filler particles without having them undergo any chemical changes by reacting with them, which is suitable for example for water-soluble salts and polymers. The etching solution may comprisea substance that chemically attacks and dissolves the filler particles by undergoing chemical reactions, which is suitable for example for metals and poorly soluble salts, such as CaCOs. Alternatively, the filler particles may also be removed in a melting process. Removal by melting requires the melting point of the filler particles to be lower than the melting point of the membrane material. This could be the case if a polymer solution is used to make the particle-filled raw film, or if the polymer material is efficiently cross-linked and the original melting point (e.g., in the case of an extrusion process) has been significantly increased. This situation could also arise if monomers are used to make the particle-filled raw film, which are polymerized around the filler particles. In this case, however, the filler particles would have to be salts with a very low melting point (such as organic salts) or other polymers that are not cross-linked in the entire cross-linking process but retain their original melting point, or which are even degraded by the cross-linking process itself, which would lead to an additional reduction in the melting point. Ultimately, the way in which the filler particles are removed is highly dependent on the particle-filled raw film material and the filler particles themselves.

[0137] In various preferred embodiments, the filler particles are removed by melting.

[0138] In various preferred embodiments, the filler particles are removed from the particle-filled raw film prior to or after laser drilling treatment.

[0139] The methods disclosed herein to generate a porous carrier material are not limiting and do not exclude other suitable methods such as phase inversion, stretching of polymer films, sintering, nanofiber material membranes, cryogels, foams or other methods to produce porous carrier materials that can be combined with a skin layer suitable for imparting a porosity, in particular a porosity suitable for high precision membrane applications.

[0140] In a further non-limiting embodiment, the at least one skin layer described above is preferably applied to a sintered porous carrier material.In a further non-limiting embodiment, the at least one skin layer described above is preferably applied to a stretched porous carrier material.

[0141] In a further non-limiting embodiment, the at least one skin layer described above is preferably applied to a nano-fiber porous carrier material.

[0142] In a further non-limiting embodiment, the at least one skin layer described above is preferably applied to a nano-fiber porous carrier material.

[0143] In a further non-limiting embodiment, the at least one skin layer described above is preferably applied to porous carrier material produced by phase inversion.

[0144] The final membrane assembly may be optimized by applying different coatings to change the surface chemistry, add functionalities or adjust the pore size. In non-limiting examples, applying thicker coatings may reduce the pore sizes. Additional etching or dissolution steps may open the pore structure, which might for example be appropriate if not all the voids of the porous carrier material are interconnected. Various coating techniques are known in the art.

[0145] In preferred embodiments, the filler particles of the particle-filled raw film are removed before imparting a porosity onto the skin layer.

[0146] In case the filler particles themselves are coated, the coating preferably remains inside the porous carrier material and / or the skin layer membrane after the filler particles have been removed.

[0147] In preferred embodiments, the filler particles of the particle-filled raw film are removed after imparting a porosity onto the skin layer.In case the at least one skin layer is a particle-filled skin layer, the filler particles of the particle-filled skin layer and the particle-filled raw film are removed simultaneously in a single dissolution step or in separate dissolution steps, more preferably simultaneously in a single dissolution step.

[0148] In preferred embodiments, the filler particles of the particle-filled raw film are removed before forming or applying as a coating at least one skin layer on at least one side of said particle-filled raw film.

[0149] In case the at least one skin layer is a particle-filled skin layer comprising filler particles, the filler particles of the particle-filled skin layer are preferably removed before or after forming or applying as a coating the at least one skin layer on at least one side of said particle-filled raw film.

[0150] Finally, the invention also relates to a membrane assembly comprising a porous carrier material and at least one skin layer membrane, which is obtainable by any of the methods as described above.Figures

[0151] FIG. 1: Schematic particle-filled raw film with one skin layer. In order to add clarity to the sketch, the ratio of carrier-thickness to skin-layer thickness was shifted significantly to the skin-layer. It is understood, that the skin-layer is designed to be significantly thinner than the corresponding carrier layer.

[0152] FIG. 2: Schematic particle-filled raw film with two skin layers. In order to add clarity to the sketch, the ratio of carrier-thickness to skin-layer thickness was shifted significantly to the skin-layer. It is understood, that the skin-layer is designed to be significantly thinner than the corresponding carrier layer.

[0153] FIG. 3: Schematic particle-filled raw film with one skin layer with beamed tracks. In order to add clarity to the sketch, the ratio of carrier-thickness to skin-layer thickness was shifted significantly to the skin-layer. It is understood, that the skin-layer is designed to be significantly thinner than the corresponding carrier layer.

[0154] FIG. 4: Schematic particle-filled raw film with a single skin layer membrane onto which a pore density was imparted by track-etching or laser drilling or imprinting. In order to add clarity to the sketch, the ratio of carrier-thickness to skin-layer thickness was shifted significantly to the skin-layer. It is understood, that the skin-layer is designed to be significantly thinner than the corresponding carrier layer.

[0155] FIG. 5: Membrane assembly comprising one skin layer membrane after removal of the filler particles from the particle-filled raw film to form the porous carrier material. The upper porous carrier material may act as a depth filter and the lower skin layer membrane as a surface filter. In order to add clarity to the sketch, the ratio of carrierthickness to skin-layer thickness was shifted significantly to the skin-layer. It is understood, that the skin-layer is designed to be significantly thinner than the corresponding carrier layer.FIG. 6: Polycarbonate film with removed sodium sulfate particles with a skin-layer and imprinted pores with a diameter of 10 pm, estimated skin-layer thickness 2-3 pm (cf. Example 10.). Measured on a Leica DMRXA microscope using reflected light and dark-field methods.

[0156] (A) Top view, light areas are free floating skin-layer sections, dark parts are covered with polymer of the carrier forming the connection between skin-layer and carrier.

[0157] (B) Zoom into the skin-layer structure floating over a void.

[0158] (C) Zoom into the carrier layer, showing free floating and polymer covered areas.

[0159] (D) Dark-field measurement to enhance the skin-layer structure.

[0160] (E) Dark-field measurement to enhance the carrier structure after removal of the particles.

[0161] FIG. 7: Improper skin-layer if it is applied not in the right way. It is broken and does not cover the full surface of the sample. Material: PLAwith removed sodium sulfate particles and an imprinted 1p urn pore structure. Example 9 with a skin-layer showing defects during skin-layer casting.

[0162] FIG.8: Laser-drilled pore structure (5 pm, 20 pm pitch). PLA with calcium carbonate particles still inside the sample (cf. Example 16).

[0163] (A) Zoom into the skin-layer. 5 pm pore structures slightly visible, with the calcium carbonate particle underneath.

[0164] (B) Same picture with focus on the particle underneath, showing how the skin-layer covers it.

[0165] FIG.9: Sample with imprinted 10 urn pore structure and a too thick skin-layer. PLAwith calcium carbonate particles still inside the material. If the skin-layer is applied too thick the pore structure does not penetrate it and no connection to the porous carrier is established (cf. Example 12).

[0166] (A) Pore-structure at the surface.

[0167] (B) Zoom into the particle layer. No pore structure visible, due to the too thick skin-layer.FIG.10: Laser-drilled sample (5 pm, 10 pm pitch). PLAbase material with calcium carbonate particles removed (cf. Example 17). Laser: Pharos Light Conversion, 343 nm, 300 kHz, with telescope and f=56 mm, beam diameter approx. 3 pm, single beam. Sputter the sample with 2-3 nm of gold. Otherwise, the microscope images will be very blurred because light is sampled from all depths. From the first laser pulse onwards, gold is completely ablated. Parameter field with 1000-8000 pulses per position and varying power levels. 20x20 pulses each with 20 pm spacing.

[0168] (A) Zoom into the skin-layer with pores floating over a void.

[0169] (B) Picture of the same sample, still containing the salt crystals. Perforated skinlayer covers the particles in a thin layer.Examples

[0170] Provision of porous carrier materials

[0171] Example 1 :

[0172] Polylactide PLE 111-A, Natureplast was fed into an extruder (ZE24, Three-Tec) with a rate of 2.43 kg / h together with sodium sulfate (particle size 0-105 pm) with a rate of 6.57 kg / h and extruded through a gap of 500 pm at a temperature of 180 °C. A film in a thickness of 500 pm was obtained and the particles could be removed by water to > 95% to yield a porous carrier film with a porosity of 73%.

[0173] Example 2:

[0174] Polylactide PLE 111-A, Natureplast was fed into an extruder (ZE24, Three-Tec) with a rate of 2.4 kg / h together with sodium sulfate (particle size 0-149 pm) with a rate of 7.6 kg / h and extruded through a gap of 700 pm at a temperature of 180 °C. A film in a thickness of 700 pm was obtained and the particles could be removed by water to > 95% to yield a porous carrier film with a porosity of 73%.

[0175] Example 3:

[0176] Polylactide PLE 111-A, Natureplast was fed into an extruder (ZE24, Three-Tec) with a rate of 2.4 kg / h together with sodium sulfate (particle size 0-149 pm) with a rate of 7.6 kg / h and extruded through a gap of 700 pm at a temperature of 180 °C. A film in a thickness of 700 pm was obtained and the particles could be removed by water to > 95% to yield a porous carrier film with a porosity of 76%.

[0177] Example 4:

[0178] Polycarbonate Durabio D5380 was fed into an extruder (ZE24, Three-Tec) with a rate of 2.4 kg / h together with calcium carbonate (particle size 0-105 pm) with a rate of 5.6kg / h and extruded through a gap of 500 pm at a temperature of 260°C. A film in a thickness of 500 pm was obtained and the particles could be removed by acidic treatment to > 95% to yield a porous carrier film with a porosity of 70%.

[0179] Example 5:

[0180] Polycarbonate Durabio D5380 was fed into an extruder (ZE24, Three-Tec) with a rate of 2.43 kg / h together with calcium carbonate (particle size 0-105 pm) with a rate of 6.57 kg / h and extruded through a gap of 500 pm at a temperature of 260°C. A film in a thickness of 500 pm was obtained and the particles could be removed by acidic treatment to > 95% to yield a porous carrier film with a porosity of 73%.

[0181] Example 6:

[0182] Polycarbonate Durabio D5380 was fed into an extruder (ZE24, Three-Tec) with a rate of 1.68 kg / h together with calcium carbonate (particle size 0-105 pm) with a rate of 5.32 kg / h and extruded through a gap of 500 pm at a temperature of 260°C. A film in a thickness of 500 pm was obtained and the particles could be removed by acidic treatment to > 95% to yield a porous carrier film with a porosity of 76%.

[0183] Example 7:

[0184] Polycarbonate Durabio D5380 was fed into an extruder (ZE24, Three-Tec) with a rate of 1.35 kg / h together with sodium sulfate (particle size 0-149 pm) with a rate of 3.65 kg / h and extruded through a gap of 500 pm at a temperature of 260°C. A film in a thickness of 500 pm was obtained and the particles could be removed by water to > 95% to yield a porous carrier film with a porosity of 73%.

[0185] Example 8:

[0186] Polycarbonate Durabio D5380 was fed into an extruder (ZE24, Three-Tec) with a rate of 1.20kg / h together with sodium sulfate (particle size 0-149 pm) with a rate of 3.80 kg / h and extruded through a gap of 500 pm at a temperature of 260°C. A film in athickness of 500 pm was obtained and the particles could be removed by water to > 95% to yield a porous carrier film with a porosity of 76%.

[0187] Example 9:

[0188] Polylactide PLE 111-A, Natureplast was fed into an extruder (ZE24, Three-Tec) with a rate of 2.4 kg / h together with calcium carbonate (particle size 0-149 pm) with a rate of 7.6 kg / h and extruded through a gap of 500 pm at a temperature of 180 °C. A film in a thickness of 500 pm was obtained and the particles could be removed by acidic treatment to > 95% to yield a porous carrier film with a porosity of 76%.

[0189] Provision of a membrane comprising porous carrier material precursor in the form of a particle-filled raw film and a skin-Layer

[0190] Example 10:

[0191] A skin layer was added to the filled film of example 8. A ultra-thin film was cast on a PTFE plate by using a dope of 2 % polycarbonate Durabio D5380 in dichloro methane by using common film casting methods. The obtained film with a thickness of 3 pm was added to the filled carrier by melting it to the surface at 220 °C and a pressure of 50 g / cm2The particles could be removed > 95% by extracting the material with water. The skin-layer could not be removed by tearing or by heat or any other methods.

[0192] Example 11:

[0193] A skin layer was added to the filled film of example 3. A ultra-thin film was cast on a PTFE plate by using a dope of 3 % polylactide PLE 111 -A in dichloro methane by using common film casting methods. The obtained film with a thickness of 2 pm was added to the filled carrier by melting it to the surface at 170 °C and a pressure of 50 g / cm2. The particles could be removed > 95% by extracting the material with water. The skinlayer could not be removed by tearing or by heat or any other methods.Example 12:

[0194] Askin layer was added to the filled film of example 8. A commercially available extruded thin polycarbonate film was used. The film with a thickness of 12 pm was added to the filled carrier by melting it to the surface at 170 °C and a pressure of 50 g / cm2. The particles could be removed > 95% by extracting the material with water.

[0195] The skin-layer could not be removed by tearing or by heat or any other methods. This approach shows, that all kinds of thin films can be attached to the filled carrier. In this case, however, the thickness of the skin-layer was too thick, resulting in blind-pores of the imprinted structure. This example points out, that the right thickness is crucial for success.

[0196] Imprinting

[0197] Example 13:

[0198] A filled film with a skin layer according to example 9 was used and a micro-structure was imprinted into the skin-layer by using a PDMS template with columns with a diameter of 10 pm and a height of 10 pm. The template and the carrier were heated to 170 °C and a pressure of 200 g / cm2was applied. The template penetrated the skinlayer and the particles could be removed afterwards by acidic treatment to a degree of > 90%.

[0199] Example 14:

[0200] A fil led film without a skin layer according to example 8 was used, and a micro-structure was imprinted into the skin-layer by using a PDMS template with columns with a diameter of 10 pm and a height of 10 pm. The template and the carrier were heated to 220 °C and a pressure of 200 g / cm2was applied. The molten polymer formed the skinlayer due to compression effects. The template penetrated the skin-layer, and the particles could be removed afterwards by water to a degree of > 90%.Example 15:

[0201] A filled film without a skin layer according to example 9 was used, which was compressed by calendaring to a thickness of 350 pm, and a micro-structure was imprinted into the skin-layer by using a PDMS template with columns with a diameter of 10 pm and a height of 10 pm. The template and the carrier were heated to 170°C and a pressure of 200 g / cm2was applied. The molten polymer formed the skin-layer due to compression effects. The template penetrated the skin-layer, and the particles could be removed afterwards by water to a degree of > 90%.

[0202] Laser-Drilling

[0203] Example 16:

[0204] A filled film with a skin layer according to example 9 was used and a micro-structure was added by laser drilling 5 pm pores into the skin-layer using a Pharos Light Conversion, 434 nm and 300 kHz with a pitch (distance hole to hole) of 20 pm. The pores penetrated the skin-layer, and the particles could be removed afterwards by acidic treatment to a degree of > 90%.

[0205] Example 17:

[0206] A filled film with a skin layer according to example 9 was used and a micro-structure was added by laser drilling 5 pm pores into the skin-layer using a Pharos Light Conversion, 434 nm and 300 kHz with a pitch (distance hole to hole) of 10 pm. The pores penetrated the skin-layer, and the particles could be removed afterwards by acidic treatment to a degree of > 90%.

Claims

Claims1. Membrane assembly comprising:a porous carrier material having a thickness of about 10 pm - 10000 pm; andat least one skin layer membrane on at least one side of the porous carrier material, wherein said at least one skin layer membrane has a thickness of about 0,5 pm - 40 pm, preferably 1 ,0 pm - 40 pm, and a pore density of at least 500 pores / cm22. Membrane assembly according to claim 1 , wherein the pore density of the skin layer membrane is imparted onto the skin layer by track-etch, laser drilling, imprinting comprising micro or nano-melting treatment.

3. Membrane assembly according to claim 1 or 2, wherein the porous carrier material has a thickness of about 50 pm - 5000 pm, preferably 100 pm - 500 pm, preferably about 150 pm - 300 pm.

4. Membrane assembly according to any one of claims 1 -3, wherein the skin layer membrane has a thickness of about 0.5 pm - 30 pm, more preferably about 0.5 pm - 4 pm, even more preferably about 0.5 pm - 2 pm.

5. Membrane assembly according to any one of claims 1-4, wherein the porous carrier material has a larger pore size than the skin layer.

6. Membrane assembly according to any one of claims 1-5, wherein the porous carrier material has a pore size of 5 nm - 300 pm, preferably 10 pm - 50 pm.

7. Membrane assembly according to any one of claims 1 -6, wherein the skin layer membrane has a pore size of 1 nm - 50 pm, preferably 10 nm - 10 pm.

8. Membrane assembly according to any one of claims 1-7, wherein the porous carrier material has a porosity of at least 15 %, preferably at least 50 %, more preferably at least 70%.

9. Membrane assembly according to any one of claims 1 -8, wherein the skin layer membrane has a pore density of at least 500 pores / cm2, preferably at least 2,000,000 pores / cm2.

10. Membrane assembly according to any one of claims 1 -9, wherein the skin layer membrane has a larger porosity density than the porous carrier material.

11. Membrane assembly according to any one of claims 1-9, wherein the skin layer membrane has a smaller porosity than the porous carrier material.

12. Membrane assembly according to any one of claims 1-9, wherein the skin layer membrane and the porous carrier material have an equal porosity.

13. Membrane assembly according to any one of claims 1-12, wherein the porous carrier material acts as a prefilter for the skin layer membrane14. Membrane assembly according to any one of claims 1-13, wherein the porous carrier material and the at least one skin layer membrane independently comprise polyolefines, polyurethanes, polyacrylates, polyepoxides, polyamides, polyimides, polycarbonates, polyesters, and / or sustainable polymers, preferably sustainable polymers, wherein the group of sustainable polymers comprises polylactic acid, cellulose, lignin and / or mixtures thereof.

15. Membrane assembly according to any one of claims 1-14, wherein the porous carrier material and the at least one skin layer membrane are comprised of the same material.

16. Membrane assembly according to any one of claims 1-15, wherein the membrane assembly has a flowrate of at least 0.1 - 20 x 106mL / min cm2, preferably of at least about 0.5 - 10 x 106mL / min cm2, more preferably of at least about 1.0 - 5 x 106mL / min cm2, at 1 bar pressure.

17. Membrane assembly according to any one of claims 1-16, wherein the membrane assembly comprises two skin layer membranes, preferably one at each of the opposing sides of the porous carrier material, respectively.

18. Membrane assembly according to claim 17, wherein the two skin layer membranes have the same or different pore densities.

19. Membrane assembly according to claim 17 or 18, wherein the two skin layer membranes have the same or different pore sizes.

20. Membrane assembly according to any one of claims 17-19, wherein the two skin layer membranes are made of the same or different materials.

21. Membrane assembly according to any one of claims 1-20, wherein the pores of the porous carrier material and / or the at least one skin layer membrane are distributed randomly and partially overlap.

22. Membrane assembly according to any one of claims 1-20, wherein the pores of the porous carrier material and / or the at least one skin layer membrane are highly ordered and do not show any overlap.

23. A structure comprising a membrane assembly according to any one of claims 1 -22, and a support substrate such as a woven or non-woven support substrate.

24. Use of a membrane assembly according to any one of claims 1 -22 or a structure according to claim 23 in microfluidic applications, venting applications, high- temperature applications, liquid barrier applications, lateral flow applications, particle capturing, air purification, liquid filtration and / or diagnostics.

25. Method of producing a membrane assembly according to any one of claims 1- 24 comprising a porous carrier material and at least one skin layer membrane comprising the following steps:a. Providing a porous carrier material precursor in the form of a particle- filled raw film; andb. Forming or applying as a coating at least one skin layer on at least one side of said particle-filled raw film; andc. Imparting a pore density onto the at least one skin layer to form a skin layer membrane, preferably by means ofi. Heavy ion beam treatment, preferably with a cyclotron, more preferably with a low-energy tandem accelerator; and subsequent track-etching treatment, wherein the coated film obtained in step b. is immersed in a suitable etching solution, optionally wherein the coated film is subjected to a UV- or solvent treatment to facilitate pore formation prior to immersion in said suitable etching solution; orii. Laser drilling preferably using an excimer laser, femtosecond laser or CO2 laser, wherein the laser drilling is performed by drilling one hole per pulse or several holes per pulse simultaneously, preferably at least about 1000 holes per pulse simultaneously, more preferably at least about 5000 holes per pulse simultaneously; oriii. Imprinting comprising(a) Melting micro-structures into the at least one skin layer; or (b) Melting nano-structures into the at least one skin layer; or (c) Perforation of the softened skin layer;iv. Removing filler particles from the skin layer, wherein the skin layer is a particle-filled skin layer comprising filler particles, preferably wherein removal of the filler-particles from the particle-filled skin layer is performed simultaneously during removal of the filler particles from the particle-filled raw film in step d.d. Removing filler particles from the particle-filled raw film by dissolving the filler particles in a washing solution or an etching solution, or by melting the particles to obtain the membrane assembly comprising a porous carrier material and the at least one skin layer membrane; and e. Optionally optimizing the pore size, functionality and / or surface chemistry.

26. The method of claim 25, wherein providing a porous carrier material precursor in the form of a particle-filled raw film in step a. is performed byi. Mixing a raw film material, filler particles and preferably at least one additive to obtain a particle-filled mixture; andii. Casting or extruding said particle-filled mixture to form a particle- filled raw film; andiii. Optionally curing and / or polymerizing said particle-filled raw film;oriv. Mixing a raw film material comprising monomers with particles, to obtain a particle-filled mixture, casting said particle-filled mixture to form a particle-filled raw film and polymerizing said particle filled raw film.

27. The method of claim 26, wherein the raw film material is melted to obtain said liquid mixture and the filler particles are not melted.

28. The method of claim 26, wherein the raw film material is dissolved in a suitable solvent to obtain said liquid mixture and the filler particles are not dissolved in said solvent and removing the solvent after step ii., preferably by drying.

29. The method of claim 28, wherein the solvent is selected from the group consisting of water, organic solvents and / or other sustainable and / or environmentally friendly solvents and / or mixtures thereof, preferably sustainable and / or environmentally friendly solvents, wherein the group of sustainable and / or environmentally friendly solvents comprises ethyl lactate, d- limonene, glycerol, glycerol carbonate, cyrene, supercritical CO2, acetone, ethanol, ionic liquids and mixtures thereof.

30. The method of any of claims 26-29, wherein the raw film material comprises at least one of fully polymerized polymers or at least one of prepolymers, oligomers with at least one suitable cross linking agent, and / or monomers.

31. The method of claim 30, wherein the at least one fully polymerized polymer is selected from the group comprising polyolefines, polycarbonates, polyesters, sustainable and / or environmentally friendly polymers, and mixtures thereof, preferably sustainable and / or environmentally friendly polymers, wherein the sustainable and / or environmentally friendly polymers comprise polylactic acid, cellulose, lignin and mixtures thereof.

32. The method of claim 30, wherein the at least one pre-polymer is selected from the group comprising polyolefine pre-polymers, polycarbonate pre-polymers, polyester pre-polymers, pre-polymers forming sustainable and / or environmentally friendly polymers, and mixtures thereof, preferably prepolymers forming sustainable and / or environmentally friendly polymers, wherein the pre-polymers forming sustainable and / or environmentally friendly polymers comprise polylactic acid pre-polymers, cellulose pre-polymers, lignin pre-polymers and mixtures thereof.

33. The method of claim 30, wherein the at least one oligomer is selected from the group comprising polyolefine oligomers, polycarbonate oligomers, polyester oligomers, oligomers forming sustainable and / or environmentally friendly polymers, and mixtures thereof, preferably oligomers forming sustainable and / or environmentally friendly polymers, wherein the oligomers forming sustainable and / or environmentally friendly polymers comprise polylactic acid oligomers, cellulose oligomers, lignin oligomers and mixtures thereof.

34. The method of claim 30, wherein the at least one monomer is selected from the group comprising styrenes, urethanes, acrylates, epoxides, amides and mixtures thereof.

35. The method according to any one of claims 30 and 32-33, wherein the at least one cross-linking agent is selected from the group comprising unsaturated organic compounds, epoxides, carboxylic acids, amides, amines, isocyanates and cyanates.

36. The method according to any one of claims 25-35, wherein the filler particles of the particle-filled raw film have a diameter that is less than the thickness of the porous carrier material.

37. The method according to any one of claims 25-36, wherein the filler particles are selected from the group consisting of salts, metals and polymers, preferably carbonate salts and or sulfate salts.4938. The method according to any one of claims 26-37, wherein the at least one additive is a reinforcing additive, said reinforcing additive being selected from the group consisting of glass fiber, plasticizer, carbon black, polymer fibers, and carbon fibers, preferably wherein the filler particles are chemically inert against said solvent.

39. The method according to any one of claims 26-38, wherein the particle-filled mixture is cast or extruded into a supporting structure, which forms an integral part of the whole membrane assembly, wherein the supporting structure comprises woven or non-woven structures.

40. The method according to any one of claims 26-39, wherein said curing or polymerization of the particle-filled raw film is performed by thermal curing, UV curing, chemical curing, moisture curing, radiation curing, preferably electron beam curing or radical polymerization.

41. The method according to any one of claims 25-40, wherein no voids are formed during production of the particle-filled raw film.

42. The method according to any one of claims 25-41, wherein the content of the filler particles in the raw-film material and / or the particle-filled raw film and / or the at least one particle-filled skin layer by volume is about 15% to 80% by volume, preferably about 50% to 80% by volume.

43. The method according to any one of claims 25-42, wherein forming the at least one skin layer on the at least one side of said particle-filled raw film is performed by one ofi. Casting the particle-filled mixture obtained according to claim 26 step i. on an at least one preformed skin layer; or ii. Spray coating a solution comprising at least one polymer, prepolymer oligomer or monomer on said particle-filled raw film; or iii. Laminating an at least one preformed skin layer on said particle- filled raw film; oriv. Casting or extruding said particle-filled mixture of claim 26 step ii.such that said at least one skin layer is formed during step ii.; or50v. Polymerizing a mixture comprising oligomers or monomers on the surface of said particle-filled raw film in a grafting reaction.

44. The method according to any one of claims 25-42, wherein the at least one skin layer formed is a particle-filled skin layer comprising filler particles, preferably wherein the ratio of the filler particle diameter of the at least one particle-filled skin layer to the particle diameter of the particle-filled raw film is 1:100, preferably 1:10.

45. The method according to any one of claims 25-44, wherein the skin layer is opened in specific, predetermined areas prior to imparting the pore density according to claim 25, step c. by etching to form defined areas of release on the skin layer.

46. The method according to any one of claims 25-45, wherein the etching solution used to dissolve the filler particles is the same etching solution used for tracketching treatment in step c.

47. The method according to any one of claims 25-46, wherein step d. of claim 25 is performed prior to step b. or step c.

48. The method according to any one of claims 25-47, wherein step c. of claim 25 is performed prior to step a. or step b. and the obtained at least one skin layer membrane is laminated onto the particle-filled raw film obtained in step b..

49. The method according to any one of claims 25-48, wherein optimizing the pore size, functionality and / or surface chemistry is performed by applying a membrane coating and / or immersing the membrane assembly in an etching or dissolution solution.

50. Membrane assembly comprising a porous carrier material and at least one skin layer membrane, which is obtainable by a method according to any one of claims 25-49.

Images