EP4003579A1

EP4003579A1 - Mechanically stable ultrafiltration membrane, and method for producing same

Info

Publication number: EP4003579A1
Application number: EP20749860.1A
Authority: EP
Inventors: Tobias Schleuss
Original assignee: Sartorius Stedim Biotech GmbH
Current assignee: Sartorius Stedim Biotech GmbH
Priority date: 2019-07-30
Filing date: 2020-07-29
Publication date: 2022-06-01
Also published as: US20220410081A1; KR20220038162A; DE102019005373A1; CN114173911A; WO2021018971A1; JP2022543561A; JP7420918B2

Abstract

The invention relates to a mechanically stable ultrafiltration membrane and to a method for producing such an ultrafiltration membrane.

Description

Mechanically stable ultrafiltration membrane and process for their

Manufacturing

description

The present invention relates to a mechanically stable ultrafiltration membrane and a method for its production.

Filtration membranes are classified based on their retentive properties and pore sizes. On the basis of the pore size, a general distinction is made between microfiltration membranes (mean pore size: 0.1 to 10 mih), ultrafiltration membranes (mean pore size: 0.01 to less than 0.1 mph), nanofiltration membranes (mean pore size: 0.001 to less than 0.01 pm) and reverse osmosis membranes (mean pore size: 0.0001 to less than 0.001 pm) (see Shang-Tian Yang, Bioprocessing for Value-Added Products from Renewable Resources, 2007).

With regard to the retentive properties of the membranes, a similar definition can be made on the basis of the molecular weight cut-off (MW CO). The MWCO refers to the solute (usually dextrans) with the lowest molecular weight in Daltons at which 90% of the solute is retained by the membrane, or alternatively to the molecular weight of a molecule in Daltons at which a 90% of the molecules with this molecular weight are retained by the membrane. For example, a membrane with a MWCO of 10 kDa retains dextrans of 10 kDa and larger by at least 90%.

When used as intended, ultrafiltration membranes can often be exposed to shocks, for example through pulsation of pumps or other system parts in, for example, cross-flow processes. However, many ultrafiltration membranes show a low impact resistance orthogonal to the filter surface and therefore have a short service life and are not sufficiently stable for some demanding applications. The present invention is therefore based on the object of providing an ultrafiltration membrane which has a high impact resistance orthogonal to the filter surface, as well as a production method for a corresponding ultrafiltration membrane.

This object is achieved by the embodiments characterized in the claims.

In particular, the present invention relates to a method for producing an ultrafiltration membrane, comprising the steps:

(a) applying a first polymer solution to a support layer in order to form a first polymer layer on or partially or completely in the support layer,

(b) bringing the coated support layer from step (a) into contact with a gas which contains a nonsolvent, based on the polymer in the first polymer solution,

(c) applying a second polymer solution to the first polymer layer to form a second polymer layer on the first polymer layer, and

(d) Introducing the multi-coated support layer into a precipitation bath which contains a precipitant, based on the polymer in the first and / or second polymer solution.

An ultrafiltration membrane can be obtained from the method according to the invention which has a high impact resistance orthogonal to the filter surface. This distinguishes it from known ultrafiltration membranes, such as ultrafiltration membranes, which are produced by conventional double coating. In the method according to the invention, a non-solvent-containing gas acts on a first polymer layer (precoating), as a result of which a damping area is created in the first polymer layer. Only then is a second polymer layer (main coating) applied with a time delay. The intermediate contact with a non-solvent-containing gas in step (b) gives the ultrafiltration membrane the damping area and results in an increased impact resistance thereof.

In the present invention, the term “ultrafiltration membrane” denotes a membrane which has a MWCO of 1 kDa to 1,000 kDa. According to the invention, in steps (a) and (c), a first or a second polymer solution is applied to a support layer or the coated support layer to form a first polymer layer on or partially or completely in the support layer or a second polymer layer on the first Forming polymer layer.

The polymer solutions used to manufacture the ultrafiltration membrane are not particularly limited. Any solutions of one or more polymers suitable for membrane formation can therefore be used.

The polymers that are dissolved in the polymer solutions (the membrane-forming polymers) are preferably cellulose derivatives selected from the group consisting of cellulose esters, cellulose nitrate and regenerated cellulose. The polymer solutions can independently of one another comprise one or more, preferably one of these membrane-forming polymers. Examples of cellulose esters are cellulose acetate such as cellulose monoacetate, cellulose diacetate and cellulose triacetate, cellulose propionate, cellulose butyrate and cellulose acetate butyrate.

The solvents used for the polymer solutions are not particularly limited as long as they are capable of dissolving the corresponding polymer (s). The solvents for the corresponding membrane-forming polymer (or each of the membrane-forming polymers) preferably have a solubility of (in each case) at least 2% by weight, in particular at least 5% by weight, more preferably at least, under normal conditions (25 ° C., 1013 hPa) 10% by weight, more preferably at least 20% by weight, particularly preferably at least 30% by weight. Suitable solvents are known to the person skilled in the art. Suitable solvents for cellulose acetate are, for example, ketones (e.g. acetone), dioxane, amides (e.g. dimethylacetamide (DMAc), NN-dimethylpropanamide, 2-hydroxy-N, N-dimethylpropanamide) and N-butylpyrrolidone and mixtures thereof. Suitable solvents for cellulose nitrate are, for example, acetone and ethyl acetate. The polymer solutions can also contain one or more auxiliaries, independently of one another. Suitable auxiliaries are, for example, swelling agents, solubilizers, hydrophilizing agents, pore formers (porogens) and / or nonsolvents for the corresponding polymer. Such auxiliaries are known to the person skilled in the art and are adapted to the membrane-forming polymer. For example, polyethylene glycol (PEG), in particular PEG 1000 or PEG 2000, glycerol or polyvinylpyrrolidone (PVP) can be used as swelling agents or pore formers. The polymer solutions preferably consist, independently of one another, of the corresponding membrane-forming polymer, the solvent and optionally one or more auxiliaries, preferably pore-forming agents, swelling agents and / or a non-solvent.

The term “non-solvent” refers to a liquid that is not able to dissolve the membrane-forming polymer. The nonsolvent for the membrane-forming polymer (or each of the membrane-forming polymers) preferably has a solubility of (in each case) at most 1% by weight, particularly preferably at most 0.1% by weight, under normal conditions.

If the polymer solution contains a nonsolvent (or another precipitant) for the corresponding membrane-forming polymer, the nonsolvent (or precipitant) is present at a maximum concentration that is insufficient to lead to precipitation of the membrane-forming polymer. The polymer solutions preferably consist, independently of one another, of the solvent for the corresponding membrane-forming polymer, the corresponding membrane-forming polymer and a non-solvent (mixture).

Suitable nonsolvents are, for example, water, glycerine, isopropanol, ethanol and mixtures thereof. Suitable non-solvents for cellulose acetate are, for example, water, glycerine, isopropanol, ethanol (with decreasing non-dissolving properties), and mixtures thereof. Suitable nonsolvents for cellulose nitrate are, for example, water and alcohols. Unless stated otherwise, the aforementioned definitions and statements relating to non-solvents apply analogously to all aspects of the present invention. The solids content in the polymer solutions is not subject to any particular restrictions and can be selected, for example, on the basis of the desired filter type. The term “solids content” refers to the content of the pure membrane-forming polymer. In a preferred embodiment, the polymer solutions independently of one another have the same or different solids contents of 2 to 40% by weight, in particular from 5 to 30% by weight, even more preferably from 7 to 20% by weight, particularly preferably from 10 to 16% by weight .-%, on.

The polymer solutions can have different solids contents, which can be selected, for example, on the basis of the desired membrane properties. In a preferred embodiment, the first polymer solution has a higher solids content than the second polymer solution. For example, the first polymer solution can have a solids content of 10 to 30% by weight and the second polymer solution can have a solids content of 5 to 20% by weight, the first polymer solution having a higher solids content than the second polymer solution.

The viscosities of the polymer solutions are not subject to any particular restrictions. For example, the polymer solutions, independently of one another, can have viscosities from 800 to 40,000 mPa * s, in particular from 1000 to 25,000 mPa ^* s, particularly preferably from 3000 to 15,000 mPa * s.

The polymer solutions do not have to be subjected to any defined thermal pretreatments, i.e. it is not necessary to use a thermal pretreatment for the membrane / structure formation. In particular, the polymer solutions preferably have no lower or upper critical solution temperatures.

Processes for applying the polymer solutions are known to the person skilled in the art from the prior art and can be used without particular restrictions in the process according to the invention (for example in step (a) and in step (c)). Such methods are, for example, methods in which the (coated) support layer is guided past a doctor blade system or a slot nozzle, from which the corresponding polymer solution emerges. Step (a) is preferably carried out under Use of a slot nozzle. Step (c) is preferably carried out using a slot nozzle.

According to the invention, in step (a) a first polymer solution (2) is applied to a support layer (1) in order to form a first polymer layer on or partially or completely in the support layer (1). This gives a (simply) coated support layer (as shown by way of example in FIG. 1). In step (c), according to the invention, a second polymer solution (4) is applied to the first polymer layer in order to form a second polymer layer on the first polymer layer (as shown by way of example in FIG. 1). This gives a multi-coated support layer.

In step (a), the first polymer solution can partially or completely penetrate into the support layer. For example, the first polymer layer can penetrate at least 25%, in particular at least 50%, particularly preferably at least 75%, into the support layer.

The support layer can be transported by means of a carrier that is not subject to any particular restriction. Any support suitable for prior art membrane manufacturing processes can be used. The carrier preferably has a flat surface and is inert to the substances used (for example polymer solutions and their constituents). A moving belt (conveyor belt) or a drum (as shown by way of example in FIG. 1) is preferably used as the carrier, which enables the process to be carried out continuously.

In a preferred embodiment, the support layer in step (a) and the coated support layer in step (c) move at a speed of 30 to 500 m / h, in particular from 60 to 400 m / h, particularly preferably from 100 to 300 m / h h, relative to the respective polymer solution when it is applied. That is to say, the (coated) support layer is guided past, for example, a doctor blade system or a slot nozzle for application of the respective polymer solution at the speeds mentioned above. The application temperatures in steps (a) and (c) are not particularly limited. For example, the application temperatures can be from 4 ° C to 40 ° C independently of one another.

According to the invention, in step (b) the coated support layer from step (a) is brought into contact with a gas (3) containing a non-solvent, based on the polymer in the first polymer solution (2) (as shown by way of example in FIG. 1) ). The above definitions and statements with reference to non-solvents apply analogously to the non-solvent contained in the gas, unless otherwise stated. Step (b) is preferably carried out under defined conditions.

A phase separation preferably occurs in the first polymer solution (2) as a result of the contact with the non-solvent-containing gas. The term "phase separation" refers to a phase separation that causes a pre-structuring in the cast film (applied polymer solution), i.e. it restricts the movement of the polymer chains.

The adhesion of the second polymer layer to the first polymer layer can be reduced by a possible phase separation in the first polymer layer. The adhesion can, however, be promoted by the interaction of the solvent of the second polymer layer with the phase-separated layer, i.e. a thin, phase-separated layer (the first polymer layer) can be loosened again when the second polymer solution is applied by a suitable choice of the solvent when applying the second polymer solution good adhesion can be guaranteed.

The content of nonsolvents in the gas is not subject to any particular restrictions. For example, the gas can contain from 1.0 to 20 g / m ³ , in particular from 1.7 to 18 g / m ³ , even more preferably from 3.0 to 16 g / m ³ , particularly preferably from 5.0 to 15 g / m ³ , non-solvent (absolute content of non-solvent), preferably at a temperature of 20 ° C. The gas can also be from 1.0 to 20 g / m ³ , in particular from 1.7 to 19 g / m ³ , even more preferably from 5.0 to 18 g / m ³ , even more preferably from 12 to 17 g / m ³ , particularly preferably from 15 to 17 g / m ³ , Contains nonsolvents (absolute nonsolvent content), preferably at a temperature of 20 ° C. If present, the other constituents of the gas (or gas mixture) are preferably inert towards the substances or devices used. The remaining constituents of the gas (or gas mixture) can be, for example, nitrogen, air, or other gases, preferably nitrogen. Preferably, not only (room) air is used as the gas which contains a non-solvent, based on the polymer in the first polymer solution.

The gas (or the gas mixture) preferably does not contain any oxygen.

For example, the gas containing a nonsolvent based on the polymer in the first polymer solution may contain nitrogen as a carrier gas and a

Non-solvent (mixture), consisting of 50 to 100% by volume of water and 0 to 50

Vol .-% ethanol, preferably 80 to 100 vol .-% water and 0 to 20 vol .-% ethanol, particularly preferably 90 to 100 vol .-% water and 0 to 10 vol .-% ethanol, based on the total amount of nonsolvents , contain or consist of.

The agents that can be used for contacting a coated backing sheet with a non-solvent-containing gas are not particularly limited. For example, the coated support layer can be passed through a chamber (for example by means of a carrier) which has a corresponding gas atmosphere and in which preferably defined conditions are generated. The chamber contains the atmosphere loaded with nonsolvents, which is exchanged in such a way that the composition is retained, but preferably no defined flows result. This can be achieved, for example, by a slight overpressure, which can be discharged into the environment through small gaps, for example. If a closed chamber is used, it is controlled in such a way that the medium is exchanged in such a way that the gas moves through the chamber at speeds of less than 0.2 m / s and no turbulence occurs on the surface of the polymer layer.

In addition, the bringing into contact can take place by supplying a corresponding gas flow, for example in a channel in which preferably defined conditions are generated. Conventional gas supply techniques can be used. For example, the gas volume flow can be 10 to 600 m ³ / h at speeds of 0.3 to 8 m / s (v (gas)), preferably 150 to 300 m ³ / h at 2.5 to 5 m / s.

Step (b) is preferably carried out with the aid of a channel. A desired overflow of the polymer layer can be brought about by means of a channel, the gas being discharged again from the chamber after the overflow. The channel is preferably chosen so that a defined (preferably laminar) flow of the non-solvent-containing gas flows towards the coated support layer at an angle which is between 0 and 45 °, preferably between 0 and 35 °, particularly preferably between 0 and 15 °, lies. The overflow can take place in the process direction or against the process direction. The speed of the gas in the channel is chosen such that an effective overflow speed is 0.3 to 8 m / s, preferably 2.5 to 5 m / s.

The duration of action in step (b) is not subject to any particular restrictions. The duration of action can be, for example, from 500 ms to 20 s, in particular from 1.0 s to 10 s, particularly preferably from 2.0 to 5.0 s. When the aforementioned contact times are used, the desired properties of the ultrafiltration membrane can be developed particularly advantageously. If the contact time is too long, a solid layer could already form, so that case properties could be changed or a (permeable) membrane could not arise.

In a preferred embodiment, the exposure temperature in step (b) is at least 10 ° C below the boiling point of the lowest-boiling constituent (usually the solvent) of the first polymer solution. According to the invention, this boiling point of the lowest boiling polymer solution component is above 50 ° C, i.e. this polymer solution component is in liquid form at 50 ° C. A corresponding exposure temperature is, for example, in a range from 10 to 40 ° C.

The (diffusive) penetration depth of the nonsolvent from the atmosphere, which is formed by the nonsolvent-containing gas, in step (b) into the applied first polymer solution is preferably less than 80%, based on the total depth of the applied first polymer solution. Preferably the Penetration depth at most 50%, more preferably at most 33%, most preferably at most 25%. The penetration depth is preferably at least 5.0%, more preferably at least 10%, most preferably at least 15%.

According to the invention, in step (d) the multi-coated support layer is introduced into a precipitation bath (5) (as shown by way of example in FIG. 1), the precipitation bath (5) being a precipitant, based on the polymer in the first (2) and / or second (4), preferably the second (4), polymer solution. The precipitant used in step (d) is not subject to any particular restriction. According to the invention, the same precipitants can be used as in conventional production processes for polymer membranes. The precipitant leads to a precipitation (phase inversion) of the membrane-forming polymer in the first and / or second polymer layer. The precipitant can be a single compound or a mixture of several compounds. The precipitating agent is preferably contained in a liquid in the precipitation bath, particularly preferably the precipitant itself is a liquid in the precipitation bath or the precipitation bath consists of the precipitant. The precipitant is preferably a non-solvent for the membrane-forming polymer or each of the membrane-forming polymers of both polymer solutions, preferably the precipitation bath consists of a precipitant selected from the group consisting of water, alcohols and water provided with additives, particularly preferably the precipitation bath consists of the Precipitant water.

The temperature of the precipitation bath is not subject to any particular restrictions. For example, the temperature of the precipitation bath can be from 1 ° C to 60 ° C, in particular from 3 to 30 ° C, particularly preferably from 4 to 20 ° C.

The method according to the invention can have a further step

(c1) bringing the multi-coated support layer from step (c) into contact with a gas which contains a non-solvent, based on the polymer in the second polymer solution, between step (c) and step (d),

include. The above-mentioned definitions and statements with respect to the nonsolvent, based on the polymer in the first polymer solution, apply analogously to the nonsolvent, based on the polymer in the second polymer solution. Furthermore, the method according to the invention can have a step

(e) Introducing the multi-coated support layer into one or more sinks (6) after step (d)

include (as shown by way of example in FIG. 1). The sinks used in step (e) are not particularly limited. According to the invention, the same sinks can be used as in conventional manufacturing processes for polymer membranes. Rinsing processes are known to the person skilled in the art and can be selected as required by the requirements for the membrane (for example with regard to residual impurities, extractables, leachables (extractable or leachable substances)). Corresponding sinks can contain, for example, water, monohydric or polyhydric alcohols, or other hydrophilic liquids.

As described above, one or more of the polymer solutions can contain cellulose esters. In order to obtain the corresponding saponification products, the process according to the invention can have a further step

(f) saponifying the cellulose esters

include. The saponification processes used in step (f) are not particularly limited. According to the invention, the same saponification processes can be used as in conventional production processes for polymer membranes, for example by introducing the multi-coated support layer into a lye basin. Examples of common processes relating to saponification are described, for example, in US Pat. No. 7422686-B2. Corresponding lye basins can contain, for example, 50% KOH in water or in alcohols or in mixtures thereof. The exposure time can be, for example, from 1.0 to 30 minutes.

The method according to the invention can have a further step

(g) crosslinking the polymer chains in the polymer layers

include. The crosslinking methods used in step (g) are not particularly limited. According to the invention, the same crosslinking methods as in conventional manufacturing methods for polymer membranes can be used. Corresponding networking processes are for example, a crosslinking of regenerated cellulose by the method as described, for example, in US-7422686-B2.

The method according to the invention can be used to produce an ultrafiltration membrane with more than two polymer layers. For this purpose, step (c) can be carried out several times before step (d), it being possible to use different or identical polymer solutions. The precipitation bath in step (d) can accordingly also contain a precipitant, based on the polymers of the further polymer solutions. Optionally, a further step (b) can take place independently of one another between the multiple steps (c), the corresponding gas containing a nonsolvent, based on the polymer of the polymer solution applied immediately before. The number of steps (c) is correspondingly equal to or greater than the number of steps (b).

Another aspect of the present invention relates to an ultrafiltration membrane obtained by the method according to the invention for producing an ultrafiltration membrane. The above definitions and embodiments apply analogously to this aspect of the present invention. The following definitions and embodiments also apply analogously to the method according to the invention for producing an ultrafiltration membrane. The ultrafiltration membrane according to the invention is preferably a flat membrane.

As stated above, the intermediate contact with a non-solvent-containing gas in step (b) of the method according to the invention gives the ultrafiltration membrane a damping area and results in an increased impact resistance thereof. The shock resistance of an ultrafiltration membrane can be checked on the basis of the occurrence of a convective pressure increase. The higher the number of impacts by a test body that a corresponding ultrafiltration membrane can withstand without the occurrence of a convective pressure increase, the higher its impact resistance. The occurrence of a convective pressure increase therefore indicates a destabilization of the corresponding ultrafiltration membrane. The convective pressure increase can be determined by the following test method (as shown by way of example in FIG. 2). A water-wetted ultrafiltration membrane (11) to be tested is placed in a housing and sealed above and below. A cylindrical test piece (K) with a diameter of 20 mm is repeatedly applied with a force of at least 1 N, but not more than 250 N, preferably with a force of 80 to 120 N, particularly preferably with a force of 85 N Membrane (11) and generates impacts on the membrane (11). Above the membrane (11) (skin side or skin side) there is a pressure Pi and below the membrane (11) there is a pressure P2, with Pi> P2 (for example Pi = 3 bar and P2 = 1 bar). A sensor (S) detects the pressure increase (DR2) below the membrane (1 1). This occurs due to diffusion as long as the membrane (1 1) is intact. If the membrane (1 1) tears due to the action of the test body (K), the diffusive component is followed by a convective component, which is recorded by the sensor (S). As a result, a diffusive proportion of the pressure increase is detected by the sensor (S) as soon as the membrane (11) is damaged by an impact from the test body (K). The number of impacts at which this convective component was detected by the sensor (S) is used as a measure of the impact resistance of the tested membrane (1 1).

In a preferred embodiment of the ultrafiltration membrane according to the invention, a convective pressure increase, as determined by the above test method, takes place with a number of impacts of over 600, more preferably over 700, even more preferably over 800, most preferably over 900.

The ultrafiltration membrane according to the invention preferably has two or more, particularly preferably two, polymer layers arranged one on top of the other on the support layer, the first polymer layer, which is arranged directly on or partially or completely in the support layer, has a damping area on the side facing the second polymer layer, which is arranged on the first polymer layer, borders. The damping area is part of the first polymer layer and is obtained by intermittently bringing it into contact with a non-solvent-containing gas in step (b) of the method according to the invention. In comparison to the remaining area of the first polymer layer, the damping area has a modified, preferably more ductile, pore structure. The support layer of the ultrafiltration membrane is not subject to any particular restrictions. It is therefore possible to use all support layers known to the person skilled in the art from the prior art. For example, the support layer can be a fleece, a woven fabric or an open microfilter membrane. Examples of nonwovens are polyolefin nonwovens, such as PP / PE core sheathed nonwovens and polyester nonwovens. Microfilter membranes can be made of polypropylene, polyethylene, polyamide, polyethersulfone or regenerated cellulose, for example. The support layer is preferably a polyolefin fleece or a polyolefin membrane.

The thickness of the backing layer may, for example from 30 to 300 pm, in particular from 50 to 250 pm, more preferably from 80 to 200 pm _", respectively.

In a preferred embodiment of the ultrafiltration membrane according to the invention, the polymer layers have a sponge structure and the outermost polymer layer (i.e. the second polymer layer in the case of a double-layer membrane) has an outer, retentive skin layer (skin (layer)) (on the sponge structure arranged below). The sponge structure can be continuous or interrupted by a visually visible boundary layer. The term "sponge structure" refers to a structure in which the membrane matrix consists of an open-pored, fine network of polymer material in which pores of a similar size are present in each layer, i.e. no fingers or macrovoid (macroporous) structures. The outer, retentive skin layer preferably has a thickness of 0.01 to 2.0 μm, more preferably 0.05 to 1.0 μm, particularly preferably 0.1 to 0.50 μm. The mean pore size of the outer, retentive skin layer is preferably from 0.5 to 200 nm, more preferably from 1.0 to 150 nm, particularly preferably from 2.0 to 100 nm.

The first polymer layer preferably has a microporous sponge structure with an average pore size of 0.05 to 30 μm, more preferably 0.1 to 10 μm, particularly preferably 1.0 to 5.0 μm. Furthermore, the sponge structure of the first polymer layer preferably penetrates at least 25%, even more preferably at least 50%, particularly preferably at least 75%, into the support layer. The thickness of the first polymer layer is preferably 10 to 100 gm, more preferably 20 to 80 gm, particularly preferably 30 to 60 gm. The first polymer layer preferably penetrates to 5 gm (with a minimum of 25% penetration and a minimum thickness of the first polymer layer of 20 gm) up to 100 gm into the support layer. The thickness of the combination of the first polymer layer and the support layer is preferably from 50 to 350 gm, more preferably from 80 to 250 gm, particularly preferably from 100 to 200 gm.

The thickness of the damping area of the first polymer layer is not subject to any particular restriction. For example, the damping area of the first polymer layer can make up up to 20% of the thickness of the first polymer layer. In particular, the damping area of the first polymer layer can have a thickness of 0.1 to 20 gm, more preferably 0.5 to 10 gm, particularly preferably 1.0 to 5.0 gm. A variation in the thickness of the damping area of the first polymer layer can be achieved, for example, by varying the nonsolvent content in the gas or the exposure time in step (b) of the method according to the invention.

The thickness of the second polymer layer is preferably 20 to 100 gm, more preferably 30 to 80 gm, particularly preferably 35 to 70 gm. The thickness of the second polymer layer is preferably less than or equal to the thickness of the combination of first polymer layer and support layer. The mean pore size of the second polymer layer (below the outer, retentive skin layer) is preferably from 0.1 to 20 gm, more preferably from 0.2 to 10 gm, particularly preferably from 0.5 to 5.0 gm.

The total thickness of the ultrafiltration membrane is not subject to any particular restrictions. For example, the ultrafiltration membrane can have a total thickness of 50 to 400 gm, in particular 80 to 350 gm, particularly preferably 120 to 300 gm.

The polymer layers can independently of one another have an asymmetrical structure (widening of the pores in the course of the layer) or a symmetrical sponge structure. In a preferred embodiment, the first Polymer layer has an asymmetrical sponge structure, which more preferably resembles an hourglass (hourglass) (see FIG. 6). The second polymer layer preferably has an asymmetrical sponge structure. Most preferably, the polymer layers, preferably the first and second polymer layers, taken together have a complex structure (cf. FIG. 6) in which the pores extend from the first main surface through the membrane to the fleece side, ie within the second polymer layer, first widen (asymmetrical sponge structure), the pores inside the membrane, preferably above the fleece layer, then taper (entry into the first polymer layer), and the pores in the course of the structure towards the second main surface, preferably inside of the fleece, expands again.

As defined above, the membrane-forming polymers are preferably cellulose derivatives selected from the group consisting of cellulose ester, cellulose nitrate, and regenerated cellulose, which are subjected to the optional saponification and / or crosslinking processes (optional steps (f) and (g) of the process according to the invention) can be. Accordingly, in a preferred embodiment of the ultrafiltration membrane according to the invention, the polymer layers comprise cellulose derivatives selected from the group consisting of cellulose esters, cellulose nitrate, regenerated cellulose and crosslinked, regenerated cellulose. The polymer layers can, independently of one another, comprise one or more, preferably one of these polymers. The polymer layers particularly preferably comprise cellulose esters, in particular cellulose acetate, or crosslinked, regenerated cellulose, and most preferably consist of them.

The ultrafiltration membrane according to the invention can have more than two polymer layers, as stated above. In this case, the outermost polymer layer has the outer, retentive skin layer. The embodiments and definitions of the second polymer layer can be applied analogously to the further polymer layers. The lower (not outer) polymer layers can each have a damping area independently of one another.

The filtration capacity of the ultrafiltration membrane is not particularly limited. The filtration capacity can, for example, as required Help the pore size of the outer, retentive skin layer be adjusted. For example, the filtration capacity of the ultrafiltration membrane can be designed such that the ultrafiltration membrane does not retain more than 50% of bovine serum albumin.

There is no particular restriction on the possible use of the membrane according to the invention. It can be used for filtration, especially for the filtration of viruses, proteins or macromolecules.

The figures show:

Fig. 1: Exemplary device for carrying out the invention

Procedure

Fig 2: Exemplary device for performing the method for

Checking the shock resistance of the membrane (11)

3: SEM image of the membrane from example 1

FIG. 4: Enlargement of the SEM image from FIG. 3 on the damping area

(23, 33) and the sponge structures (22, 24) of the second and first polymer layers located above / below

Fig. 5: Results of the method for checking the impact resistance of different ultrafiltration membranes (M-1 to M-3)

Fig. 6: Example structure of the membrane according to the invention with different diffusive penetration depths (50%, 33%, 25%) of the non-solvent-containing gas in step (b)

The present invention is illustrated in more detail by means of the following, non-limiting examples.

Determination of the (mean) pore sizes To determine the (mean) pore sizes of the membrane, a method based on membrane cross-sections examined in a scanning electron microscope (SEM) was used (described in P. Poelt et.al., Journal of Membrane Science 2012, Vol. 399-400, pp . 86-94).

Example 1: Production of an ultrafiltration membrane with a damping area and increased impact resistance

A first polymer solution consisting of 75 wt .-% dimethylacetamide (DMAc), 15 wt .-% cellulose acetate (Acetati, type Aceplast PC / FG) and 5 wt .-% PEG 1000, 5 wt .-% water is applied by means of a slot nozzle PP / PE core mantle fleece (OMB-60; Mitsubishi) moving at 100 m / h orthogonally to the outlet opening. The polymer film then passes through a chamber 10 cm in length which contains an atmosphere with 35% relative humidity (rh, relative humidity) at a temperature of 20 ° C. After leaving the chamber, the polymer film is moved orthogonally to the outlet opening of a second application medium (carriage with doctor blade) and a second polymer solution consisting of 78% by weight DMAc, 11% by weight cellulose diacetate (Acetati, type Aceplast PC / FG), 4% by weight of PEG 2000, 4% by weight of glycerol and 3% by weight of water is applied, which is then transferred to a precipitation bath made of water at a temperature of 6 ° C. for phase separation. The remainder of the process described above takes place at room temperature.

The membrane obtained is then passed through several rinsing basins into a basin with 50% KOH, in which the acetyl groups are saponified. The regenerated cellulose membrane has a particular stability in the z-direction compared to comparable single or multi-layer membranes. By means of crosslinking, for example the method described in DE 102004053787 A1, the membrane can be converted into a crosslinked regenerated cellulose membrane (cellulose hydrate membrane), which also has particular mechanical stability. SEM images of the membrane obtained are shown in FIGS. 3 and 4. Example 2: Checking the impact resistance of different ultrafiltration membranes

Two conventional ultrafiltration membranes (M-1 and M-2) made of regenerated cellulose (RC) (a single-layer membrane with an exclusion limit of 100 kDa (M-1) and a multilayer membrane with an exclusion limit of 300 kDa (M-2), which were produced using conventional Cocast method (double coating method) without step (b)) and an ultrafiltration membrane (M- 3) according to the invention made of regenerated cellulose with a damping area and an exclusion limit of 300 kDa, which was produced by means of the method according to the invention, were the aforementioned test method for determination subjected to shock resistance or convective pressure increase. A pressure Pi = 3 bar and a pressure P2 = 1 bar were applied and a cylindrical test specimen with a diameter of 20 mm was repeatedly placed on the membrane with a force of 85 N. The results obtained are shown in FIG. 5 and show that with the ultrafiltration membrane (M-3) according to the invention with a damping area, a significantly increased impact resistance can be achieved in comparison to the conventional ultrafiltration membranes (M-1 and M-2).

Example 3: Production of an ultrafiltration membrane with a damping area and increased shock resistance in a chamber

A first polymer solution consisting of 50 wt .-% acetone, 28 wt .-% dioxane, 2 wt .-% water, 12 wt .-% cellulose acetate (Acetati, type Aceplast PC / FG) and 8 wt .-% glycerin is applied using a doctor blade & Slide is applied to a PP / PE core sheath fleece (OMB-60; Mitsubishi) moving at 70 m / h orthogonally to the outlet opening. Directly adjacent to the slide is a 30 cm long chamber which contains an atmosphere of nitrogen as the carrier gas and 19 g / m ^{3 of} a 1:19 mixture of ethanol and water and is kept at a constant temperature of 20 ° C. A preconditioned atmosphere flows through the chamber in the upper area, which is controlled in such a way that a flow of 0.2 m / s is not exceeded, so that no turbulence occurs in the lower area of the chamber where the polymer film passes through the chamber. The chamber is operated in such a way that there is always an overpressure of 1 mbar in relation to the surrounding space. The environment will Aspirated to properly remove the small amounts of ethanol. After leaving the chamber, the polymer film is moved orthogonally to the outlet opening of a second application medium (slide with doctor blade) and a second polymer solution consisting of 50% by weight of acetone, 28% by weight of dioxane, 2% by weight of water, 12% by weight % Cellulose acetate (Acetati, type Aceplast PC / FG) and 8% by weight glycerine is applied, which is then transferred to a precipitation bath made of water at a temperature of 15 ° C. for phase separation.

The membrane obtained is then passed through several rinsing basins into a basin with 50% KOH, in which the acetyl groups are saponified. The membrane is rinsed and excess alkali is neutralized with dilute acetic acid. The regenerated cellulose membrane has a particular stability in the z-direction compared to comparable single or multi-layer membranes. By means of crosslinking, for example the method described in DE 102004053787 A1, the membrane can be converted into a crosslinked regenerated cellulose membrane (cellulose hydrate membrane), which also has the particular mechanical stability.

List of reference symbols

1 support layer

2 First polymer solution

3 Gas containing nonsolvents (with regard to the first polymer solution)

4 Second polymer solution

5 precipitation bath

6 sinks

1 1 Moistened membrane on a base

21 Outer, retentive skin layer

22 sponge structure (second polymer layer)

23, 33 Damping area

24 sponge structure (first polymer layer)

25 Textile support layer

46 Second polymer layer

47 First polymer layer K test body

M-1 Conventional ultrafiltration membrane (single-layer membrane, RC, 100 kDa)

M-2 Conventional ultrafiltration membrane (multilayer membrane, RC, 300 kDa)

M-3 Ultrafiltration membrane according to the invention (multilayer membrane, RC,

300 kDa)

Pi Pressure that is applied above the membrane (11)

P ₂ pressure which is applied below the membrane (11)

S sensor

Claims

1. A method for producing an ultrafiltration membrane, comprising the steps:

(A) applying a first polymer solution (2) to a support layer (1) in order to form a first polymer layer on or partially or completely in the support layer (1),

(b) bringing the coated support layer from step (a) into contact with a gas (3) which contains a non-solvent, based on the polymer in the first polymer solution (2),

(c) applying a second polymer solution (4) to the first polymer layer to form a second polymer layer on the first polymer layer, and

(d) Introducing the multi-coated support layer into a precipitation bath (5) which contains a precipitant, based on the polymer in the first (2) and / or second (4) polymer solution.

2. The method according to claim 1, wherein the polymer solutions independently of one another have the same or different solids contents of 2 to 40% by weight.

3. The method according to claim 2, wherein the first polymer solution (2) has a higher solids content than the second polymer solution (4).

4. The method according to any one of claims 1 to 3, wherein the polymer solutions independently of one another have viscosities of 800 to 40,000 mPa * s.

5. The method according to any one of claims 1 to 4, wherein the application temperatures in steps (a) and (c) are independently of 4 ° C to 40 ° C.

6. The method according to any one of claims 1 to 5, wherein the support layer (1) in step (a) and the coated support layer in step (c) at a speed of 30 to 500 m / h relative to the respective polymer solution (2, 4 ) move when they are applied.

7. The method according to any one of claims 1 to 6, wherein the gas (3) from 1, 0 to 20 g / m ³ , in particular from 1, 7 to 18 g / m ³ or from 1, 7 to 19 g / m ³ , more preferably from 3.0 to 16 g / m ³ or from 5.0 to 18 g / m ³ , particularly preferably from 5.0 to 15 g / m ³ or from 12 to 17 g / m ³ , contains nonsolvents.

8. The method according to any one of claims 1 to 7, wherein the gas containing a non-solvent, based on the polymer in the first polymer solution, nitrogen as a carrier gas and a non-solvent (mixture) consisting of 50 to 100 vol. % Water and 0 to 50% by volume of ethanol, based on the total amount of nonsolvents.

9. The method according to any one of claims 1 to 8, wherein the duration of action in step (b) is from 500 ms to 20 s.

10. The method according to any one of claims 1 to 9, wherein the exposure temperature in step (b) is at least 10 ° C below the boiling point of the lowest-boiling component of the first polymer solution (2), this boiling point being above 50 ° C.

11. The method according to any one of claims 1 to 10, wherein step (b) is carried out with the aid of a channel in which the non-solvent-containing gas flows towards the coated support layer at an angle between 0 and 45 °.

12. The method according to any one of claims 1 to 11, wherein the penetration depth of the nonsolvent from the atmosphere, which is formed by the nonsolvent-containing gas, in step (b) in the applied first polymer solution is less than 80%, based on the total depth of the applied first polymer solution is.

13. The method according to any one of claims 1 to 12, further comprising the step (c1) bringing the multi-coated support layer from step (c) into contact with a gas which contains a non-solvent, based on the polymer in the second polymer solution (4), between step (c) and step (d).

14. The method according to any one of claims 1 to 13, further comprising the step

(e) Introducing the multi-coated support layer into one or more sinks (6) after step (d).

15. The method according to any one of claims 1 to 14, wherein one or more of the polymer solutions contain cellulose esters.

16. The method of claim 15 further comprising the step

(f) saponifying the cellulose esters.

17. The method according to any one of claims 1 to 16, further comprising the step

(g) crosslinking the polymer chains in the polymer layers.

18. The method according to any one of claims 1 to 17, wherein step (c) is carried out one or more times before step (d), different or identical polymer solutions being used, and, optionally, between the multiple steps (c) independently of one another further steps (b) take place, the corresponding gas containing a non-solvent, based on the polymer of the polymer solution applied immediately before.

19. Ultrafiltration membrane obtained by the method for producing an ultrafiltration membrane according to one of claims 1 to 18.

20. Ultrafiltration membrane according to claim 19, wherein

a convective pressure increase, as determined by the following test method, occurs with a number of impacts of over 600, the test method being characterized in that a test body (K) with a diameter of 20 mm is repeated with a force of at least 1 N but not more than 250 N on a water-wetted ultrafiltration membrane (11) to be tested, which is located in a housing and is sealed above and below, a pressure Pi is applied above the membrane (11) and a pressure P2, with below the membrane (11) Pi> P2, is applied, and a sensor (S) detects the pressure increase below the membrane (11), whereby for the pressure increase to a diffusive part, a convective part is detected by the sensor (S) as soon as the membrane (11) is damaged by an impact of the test body (K).

21. Ultrafiltration membrane according to claim 19 or 20, wherein the

Ultrafiltration membrane two or more arranged one on top of the other

Has polymer layers on a support layer (1) and

the first polymer layer, which is arranged directly on or partially or completely in the support layer (1), has a damping region (23, 33) on the side which adjoins the second polymer layer, which is arranged on the first polymer layer.

22. Ultrafiltration membrane according to claim 21, wherein the polymer layers have a sponge structure (22, 24) and

the outermost polymer layer has an outer, retentive skin layer (21).

23. Ultrafiltration membrane according to claim 22, wherein the outer, retentive skin layer (21) has a thickness of 0.01 to 2.0 μm.

24. Ultrafiltration membrane according to one of claims 21 to 23, wherein the first polymer layer has a microporous sponge structure (24) with an average pore size of 0.05 to 30 μm and

the sponge structure of the first polymer layer (24) penetrates at least 25% into the support layer (1).

25. Ultrafiltration membrane according to one of claims 21 to 24, wherein the support layer (1) has a thickness of 30 to 300 μm,

the first polymer layer has a thickness of 10 to 100 μm, the first polymer layer penetrating at least 25% into the support layer (1),

the second polymer layer has a thickness of 20 to 100 μm, the thickness of the second polymer layer being less than or equal to the thickness of the combination of first polymer layer and support layer (1), and

the damping area (23, 33) of the first polymer layer is up to 20% of the thickness of the first polymer layer.

26. Ultrafiltration membrane according to one of claims 21 to 25, wherein the ultrafiltration membrane has a total thickness of 50 to 400 μm.

27. Ultrafiltration membrane according to one of claims 21 to 26, wherein the polymer layers independently of one another have an asymmetrical or a symmetrical sponge structure (22, 24).

28. The ultrafiltration membrane of claim 27, wherein the first and second polymer layers have an asymmetrical sponge structure.

29. The ultrafiltration membrane according to claim 28, wherein the first and second polymer layers taken together have a complex structure, which is preferably characterized in that the pores initially widen from the first main surface inside the second polymer layer, the pores inside the membrane at The entry into the first polymer layer is then tapered and the pores expand again in the course of the structure towards the second main surface.

30. Ultrafiltration membrane according to one of claims 21 to 29, wherein the polymer layers comprise cellulose derivatives selected from the group consisting of cellulose ester, cellulose nitrate, regenerated cellulose and crosslinked, regenerated cellulose.

31. Ultrafiltration membrane according to one of claims 21 to 30, wherein the ultrafiltration membrane does not retain more than 50% bovine serum albumin.