Process for preparing filter elements

Abstract

The present invention relates to a polyurethane casting composition obtained or obtainable by a process comprising the step of reacting a polyol component (A) and an isocyanate component (B) comprising at least one polyisocyanate (IC), wherein the polyol component (A) comprises at least one fat-based polyol (a1); and at least one compound (a2) having at least one unsaturated C-C-bond and at least one hydroxy group and a molecular weight in the range of from 100 to 600 g / mol. The present invention also relates to a process for producing a filter element comprising hollow fibers embedded at their end in a cured polyurethane casting composition comprising embedding hollow fibers in the polyurethane casting composition according to the present invention; curing the polyurethane casting composition at a temperature of at least 10°C to obtain a composite element comprising the hollow fibers embedded in the cured polyurethane composition; and treating the composite element under conditions suitable for sterilization, as well as a filter element comprising hollow fibers embedded at their end in a cured polyurethane casting composition obtained or obtainable according to said process. Furthermore, the present invention relates to the use of the polyurethane casting composition according to the invention for preparing a filter element comprising hollow fibers.

Description

[0001] Process for preparing filter elements

[0002] The present invention relates to a polyurethane casting composition obtained or obtainable by a process comprising the step of reacting a polyol component (A) and an isocyanate component (B) comprising at least one polyisocyanate (IC), wherein the polyol component (A) comprises at least one fat-based polyol (a1); and at least one compound (a2) having at least one unsaturated C-C-bond and at least one hydroxy group and a molecular weight in the range of from 100 to 600 g / mol. The present invention also relates to a process for producing a filter element comprising hollow fibers embedded at their end in a cured polyurethane casting composition comprising embedding hollow fibers in the polyurethane casting composition according to the present invention; curing the polyurethane casting composition at a temperature of at least 10°C to obtain a composite element comprising the hollow fibers embedded in the cured polyurethane composition; and treating the composite element under conditions suitable for sterilization, as well as a filter element comprising hollow fibers embedded at their end in a cured polyurethane casting composition obtained or obtainable according to said process. Furthermore, the present invention relates to the use of the polyurethane casting composition according to the invention for preparing a filter element comprising hollow fibers.

[0003] Polyurethane casting compositions which are applied as adhesive or binder are known from the state of the art. For example WO 2021 / 126422 A1 discloses casting compositions and a process for preparing membranes.

[0004] The use of polyurethane encapsulating compounds for the embedding of hollow fibers of filter elements is known, especially for filters that are used in the medical sector, such as the use as embedding material for hollow fibers in dialyzers, and this has been described, for example, in EP844015 B1. The advantage of the polyurethane encapsulating compounds composed of polyurethane is that it is possible to incorporate a proportion by volume of hollow fibers into the dialyzer and achieve an optimal impregnation of the hollow fibers. In addition, the polyurethane described for the production of the filters is hydrolysis-stable, survives the process of superheated steam sterilization undamaged, and in particular has no toxic potential. However, in order to achieve good and rapid curing and a high productivity, catalysts are often used.

[0005] The use of aminic catalysts for preparing polyurethane encapsulating compounds has the disadvantage that these catalysts exhibit high migration properties and can escape from the polyurethane obtained, they are not usable for medical application. DD-A-155777 discloses the use of tin compounds as catalysts for the preparation of polyurethane encapsulating compounds for dialyzers. The catalysts described in DD-A-155777 give a high and constant reactivity, and have established themselves, alongside other organotin compounds, as a standard for PU polyurethane encapsulating compounds in industry. Mention may be made, by way of example, of EP 2 081 973, EP 538673, EP 413265 and EP 329473.

[0006] Still, the adhesion of the polyurethane and the fibers often is not strong enough. The object of the present invention was therefore to provide a polyurethane composition for embedding hollow fibers of filter elements, with strong adhesion between the polyurethane, the fibers embedded therein and the housing material of the filter element.

[0007] According to the present invention, this object has been solved by a polyurethane casting composition, in particular a polyurethane casting composition for embedding hollow fibers, obtained or obtainable by a process comprising the step of reacting a polyol component (A) and an isocyanate component (B) comprising at least one polyisocyanate (IC), wherein the polyol component (A) comprises

[0008] (1 ) at least one fat-based polyol (a1 ); and

[0009] (2) at least one compound (a2) having at least one unsaturated C-C-bond and at least one hydroxy group and a molecular weight in the range of from 100 to 600 g / mol.

[0010] It has surprisingly been found that the polyurethane casting composition can be used to form stable composites which can be further cured under conditions suitable for sterilization which are typically applied for filter elements for medical applications.

[0011] The polyurethane casting composition according to the invention is preferably compact and is preferably used for the embedding of hollow fibers for filter elements, that is to say it is suitable as an embedding compound for hollow fibers for filter elements. Compact polyurethane casting compositions are understood to be compositions having a density generally of from 0.8 g / l to 1.3 g / l, preferably from 0.9 g / l to 1.1 g / l. The polyurethane casting composition according to the invention, after curing has been performed, generally has a Shore D hardness of from 40 to 80. However, the compositions according to the invention preferably have a Shore D hardness of from 55 to 75. Particular preference is given, for example for applications as encapsulating compound in dialysis filters, to a Shore D hardness of from 58 to 73. Shore D hardness relates to DIN 53505 at a temperature of 23° C. Those skilled in the art will choose the composition of the encapsulating compounds accordingly, for example the nature and amount of the components used for the preparation.

[0012] The polyurethane casting composition obtained or obtainable by a process comprising reacting a polyol component (A) and an isocyanate component (B) comprising at least one polyisocyanate (IC).

[0013] The polyol component (A) here comprises (a1) at least one fat-based polyol, preferably having a hydroxyl number of greater than 50 to less than 500 mg KOH / g and a functionality of at least 2,; and at least one compound (a2) having at least one unsaturated C-C-bond and at least one hydroxy group and a molecular weight in the range of from 100 to 600 g / mol.

[0014] OH functionality is to be understood here in the context of the present invention to be the number of alcoholic, acylatable OH groups per molecule. If the particular component is composed of a compound having defined molecular structure, the functionality is given by the number of OH groups per molecule. If a compound is prepared by ethoxylation or propoxylation of a starter molecule, the OH functionality is given by the number of reactive functional groups, for example OH groups, per starter molecule.

[0015] Polyol component (A) comprises components (a1) and (a2) and may comprise further components, for example further polyols or components reactive towards isocyanates. Polyol component (A) may also comprise suitable catalyst or a catalyst combination comprising two or more catalysts.

[0016] Polyol component (A) comprises at least one fat-based polyol as component (a1). Suitable fat -based polyols are preferably those having a hydroxyl number of greater than 50 to less than 500 mg KOH / g, particularly preferably 100 to 300 mg KOH / g and especially 100 to 200 mg KOH / g, and a functionality of at least 2. The OH functionality of the fat -based polyols is preferably in the range from 2 to 3. The OH functionality of the fat-based polyols is particularly preferably from 2.3 to 3 and very particularly preferably from 2.6 to 3.

[0017] A fat-based polyol may be a fat, an oil, a fatty acid or a fatty acid derivative, or be obtained from the aforementioned compounds by physical or chemical modification. Fat-based polyols according to the definition mentioned above are known per se to those skilled in the art or can be obtained by methods known per se.

[0018] Fat-based polyols that can be used are also commonly known fatty acids, preferably natural fatty acids, particularly preferably vegetable fatty acids, especially unsaturated vegetable fatty acids, and also derivatives thereof such as the esters with mono-, di- and / or trialcohols, as long as the further properties with respect to molecular weight and OH functionality are fulfilled.

[0019] However, examples of fat-based polyols that can be used also include ring-opened epoxidized or oxidized fatty acid compounds and / or adducts of fatty acid compounds and alkylene oxides. Preference is given to hydroxylated fatty acids and / or hydroxylated fatty acid derivatives that are obtainable by the aforementioned methods.

[0020] The adducts of OH functional fat-based compounds, for example castor oil or hydroxylated vegetable oils, and alkylene oxides can be prepared by commonly known al koxy lation of the compounds with, for example, ethylene oxide, propylene oxide and / or butylene oxide at temperatures of from 80 to 130° C. and pressures of from 0.1 to 1 MPa, optionally in the presence of customary catalysts such as alkali metal hydroxides or alkali metal alkoxides.

[0021] Furthermore, fat-based polyols that can be used are also hydroxylated fatty acid compounds based on rapeseed oil, soya oil, colza oil, olive oil and / or sunflower oil and / or those based on oleic and / or linoleic acid. Suitable fat-based polyols are in particular polyols based on hydroxylated soya oil. The fat-based polyol used is particularly preferably a vegetable oil without chemical modification. Particular preference is given to castor oil or the alkoxylation product of castor oil, in particular castor oil. The fat-based polyol is especially preferably castor oil which satisfies the provisions of the German Pharmacopeia according to DAB 10. In one particularly preferred embodiment, the component (a1) used is exclusively castor oil.

[0022] According to a further embodiment, the present invention is also directed to the polyurethane casting composition as disclosed above, wherein the fat-based polyol (a1) is selected from the group consisting of castor oil or an alkox- ylated derivative of castor oil.

[0023] Component (a1) preferably has a low water content, for example less than 0.2% by weight. A water content of component (a1) of less than 0.1% by weight is preferred. If a natural oil, by way of example castor oil, is used as component (a1 ), its use is typically preceded by a purification, which may especially include removal of suspended substances and dewatering. Natural oils freed of suspended substances and having the abovementioned water content are particularly suitable as component (a1).

[0024] Polyol component (A) comprises at least one compound (a2) having at least one unsaturated C-C-bond and at least one hydroxy group and a molecular weight in the range of from 100 to 600 g / mol. Compound (a2) may also have further functional groups. Suitable compounds (a2) are in principle known. Suitable compounds preferably have 1 to 3 hydroxy groups, in particular 1 or 2 hydroxy groups. Furthermore, suitable compounds (a2) preferably have 1 to 3 C- C-double bonds, in particular 1 or 2 C-C-double bonds. Preferably, compound (a2) has at least one unsaturated C-C- bond which is connected to a carbonyl group. Suitable compounds (a2) may for example be selected from acrylates or methacrylates.

[0025] Suitable compounds (a2) are preferably selected from the group of hydroxy functionalized acrylates, methacrylates, in particular acrylates and methacrylates selected from the group consisting of 2-hydroxyethy Imethacry late, 2-hydrox- ypropylmethacrylate, 3-hydroxypropylmethacrylate, 4-hydroxybutylmethacrylate, 5-hydroxypentylmethacrylate, 6- hydroxyhexyl methacrylate, pentaerythritol trimethacrylate, triglycerol dimethacrylate, glycerol dimethacrylate, glycerol monomethacrylate, neopentylglycol monomethacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3- hydroxypropyl acrylate, 4-hydroxybutylacrylate, 5-hydroxypentylacrylate, 6-hydroxyhexyl acrylate, pentaerythritol triacrylate, triglycerol diacrylate, glycerol diacrylate, glycerol monoacrylate, and neopentylglycol monoacrylate, more preferably acrylates and methacrylates selected from the group consisting of2-hydroxyethy Imethacry lat and pentaerythritol triacrylate.

[0026] According to a further embodiment, the present invention is also directed to the polyurethane casting composition as disclosed above, wherein compound (a2) is an acrylate or methacrylate having 1 to 3 acrylate or methacrylate groups. Besides components (a1) and (a2), further compounds may be present in polyol component (A), for example further polyols (a3). Suitable polyols are in principle known to the person skilled in the art. All polyols can be used here which are known in polyurethane chemistry and do not fall under the definition of components (a1) and (a2). The polyol component (A) particularly preferably comprises at least one, at least difunctional, polyol (a3) which has a functionality of from 2 to 8 and a hydroxyl number of from 600 to 1350 mg KOH / . These polyols can be obtained by alkox- ylation, preferably ethoxylation or propoxylation, of difunctional or higher-functionality starter molecules, for instance ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol, trimethylolpropane, pentaerythritol, sugar derivatives such as sucrose, hexitol derivatives such as sorbitol and also other dihydric or polyhydric alcohols, or mixtures thereof. Here, the starter molecules are chosen and used in such amounts that the average nominal functionalities are obtained. The nominal functionality in the context of this invention is considered to be the functionality given solely by the functionality and the proportion of the starter molecules. Any reduction in the functionality, for instance by side reactions, is not taken into account.

[0027] According to a further embodiment, the present invention is also directed to the polyurethane casting composition as disclosed above, wherein the polyol component comprises at least one polyol (a3) with a functionality of 2 to 8 and an OH number in the range of from 600 to 1350 mg KOH / g.

[0028] In addition to components (a1) and (a2), the polyol component (A) preferably comprises at least one metal compound that functions as a polyurethane catalyst, wherein the polyurethane catalyst (ac) does not comprise any tin, lead and / or mercury. Polyurethane catalysts greatly accelerate the reaction of the polyols with the polyisocyanates here. Tin, lead and mercury compounds are excluded as polyurethane catalysts as these compounds can have toxic effects and thus the polyurethane encapsulating compounds obtained would not be suitable for producing filter elements such as water filters or dialysis filters.

[0029] In one preferred embodiment, the metal compounds (ac) are selected from the group consisting of zinc compounds, zirconium compounds, bismuth compounds and titanium compounds, preferably zinc compounds, zirconium compounds and bismuth compounds. Examples of possible zirconium catalysts are zirconium carboxylates such as zirconium neodecanoate or complexes formed from zirconium and 1 ,3-dicarbonyl compounds such as zirconium acety- lacetonates. Examples of zinc compounds are for instance zinc carboxylates such as zinc neodecanoate or zinc ricinoleate, zinc carbene compounds or complexes formed from zinc and 1 ,3-dicarbonyl compounds such as zinc acet- ylacetonate.

[0030] According to a further embodiment, the present invention is also directed to the polyurethane casting composition as disclosed above, wherein composition (A) comprises at least one catalyst (ac) selected from the group consisting of zinc compounds, zirconium compounds, bismuth compounds and titanium compounds.

[0031] Particularly preferred metal catalysts (ac) are bismuth catalysts. Organic bismuth catalysts are known in polyurethane chemistry and by way of example include bismuth carboxylates. In the bismuth carboxylates, bismuth is preferably in the oxidation state of 2 or 3, especially 3. For salt formation, carboxylic acids used are preferably carboxylic acids having 6 to 18 carbon atoms, particularly preferably 8 to 12 carbon atoms. Examples of particularly suitable bismuth salts are bismuth(lll) neodecanoate, bismuth 2-ethylhexanoate and bismuth octanoate; bismuth(lll) neodecanoate is particularly preferably used.

[0032] In one preferred embodiment, the bismuth carboxylate is dissolved in a carboxylic acid before being added to the polyol component (A) and added to the reaction in dissolved form. Solvents used are preferably carboxylic acids having 6 to 18 carbon atoms, particularly preferably 8 to 12 carbon atoms. Examples of these are octanoic acid or ne- odecanoic acid. It is preferred that, the solvent used is, the same acid that also forms the carboxylate radical.

[0033] In one preferred embodiment, for the preparation of the polyurethane encapsulating compounds according to the invention, no organic tin compounds are used that are known as catalysts for the polyurethane reaction. More preferably, an organic bismuth or zinc catalyst is used as organic metal catalyst.

[0034] The components (a1) to (a3) and (ac) are preferably used in an amount such that the proportion of the fatty-acid- based polyol (a1) is 60 to 99% by weight, preferably 75 to 98% by weight and particularly preferably 90 to 96% by weight, the proportion of the compound (a2) is 0.2 to 15% by weight, preferably 0.5 to 12% and particularly preferably 1 to 10% by weight, more preferable 2 to 8% by weight, the proportion of the compound (ac) is 0.001 to 1 .0% by weight, preferably 0.02 to 0.5% and particularly preferably 0.04 to 0.2% by weight, and the proportion of the polyol (a3) is 0 to 25% by weight, preferably 0.5 to 10% and particularly preferably 1.0 to 5% by weight, based in each case on the total weight of components (a1) to (a3) and (ac). The polyol component (A) particularly preferably comprises, besides components (a1) to (a3) and (ac), less than 20% by weight, particularly preferably less than 10% by weight and especially less than 5% by weight of further compounds, based in each case on the total weight of components (a1) to (a3) and (ac). The amount of the components is adjusted so that the sum of the components adds up to 100% by weight. In a very particularly preferred embodiment, polyol component (A) comprises no further compounds besides compounds (a1) to (a3) and (ac).

[0035] According to a further embodiment, the present invention is also directed to the polyurethane casting composition as disclosed above, wherein the proportion of the fat-based polyol (a1) in composition (A) is in the range of from 60 to 99.5% by weight, the proportion of polyol (a2) is in the range of from 0.5 to 10% by weight, the proportion the proportion of the catalyst (ac) is in the range of from 0.001 to 1 .0% by weight and the proportion of the polyol (a3) is in the range of from 0 to 25% by weight, based in each case on the total weight of composition (A).

[0036] According to the present invention, polyol component (A) reacts with isocyanate component (B). Isocyanate component (B) comprises at least one polyisocyanate (IC). Suitable polyisocyantes are in principle known. According to the invention, polyisocyante also encompasses diisocyanates. Suitable diisocyanates are for example toluene 2,4-diiso- cyanate, toluene 2,6-diisocyanate, diphenylene methane 2,2'-diisocyanate, diphenylene methane 2,4'-diisocyanate, diphenylene methane 4,4'-diisocy anate, and prepolymers of diphenylene methane 4, 4'-diisocy anate

[0037] According to a further embodiment, the present invention is also directed to the polyurethane casting composition as disclosed above, wherein the polyisocyanate (IC) is selected from the group consisting of toluene 2, 4-diisocy anate, toluene 2,6-diisocyanate, diphenylene methane 2,2'-diisocyanate, diphenylene methane 2,4'-diisocyanate, diphenylene methane 4,4'-diisocy anate, and prepolymers of diphenylene methane 4, 4'-diisocy anate.

[0038] Isocyanate components (B) used may preferably be any aromatic difunctional and higher-functionality isocyanates known in polyurethane chemistry. Isocyanate components (B) may also comprise the isocyanate prepolymers for preparing the polyurethane encapsulating compounds according to the invention. Such isocyanate prepolymers are obtained by reaction of diisocyanates and / or higher-functionality isocyanates (b1) with compounds having isocyanate-reactive groups (b2), preferably diols, where isocyanates are used in excess.

[0039] Isocyanate components b1) used are the customary aromatic di- and / or polyisocyanates or the mixtures thereof. Diisocyanates are especially suitable, for example tolylene diisocyanate (TDI). Diphenylmethane diisocyanates (hereinafter referred to as MDI) are preferred. Where MDI is used, all bicyclic isomers (2,2'; 2,4' and 4,4') can be used, optionally in a mixture with higher polycyclic homologs of diphenylmethane diisocyanate.

[0040] Isocyanate component b1) may additionally be present in modified form, for instance by incorporation of uretdione, carbamate, isocyanurate, carbodiimide, allophanate groups.

[0041] Diol components b2) used are organic polyhydroxy compounds having an OH functionality of from 1 to 3. Mixtures having an average OH functionality in the range of from 1.5 to 2.5 may be used. The OH functionality is preferably in the range from 1 .8 to 2.2; a diol compound having an OH functionality of 2 is particularly preferably used. In particular, alkoxylated diol compounds are preferred as diol component b2). Propylene glycols are particularly preferred as diol component b2).

[0042] Suitable propylene glycols include (mono)propylene glycol and dipropylene glycol and also oligo- and polypropylene glycols, where the latter may be prepared by propoxylation starting from a diol compound.

[0043] The isocyanate (B) preferably has an NCO content of from 12 to 30% by weight, particularly preferably of from 18 to 27% by weight and very particularly preferably of from 20 to 25% by weight. Aromatic isocyanates here in the context of the present invention are isocyanates where an isocyanate group is bonded directly to a carbon atom in an aromatic system. Moreover, for the preparation of the polyurethane encapsulating compounds according to the invention, auxiliaries and / or additives may be used, such as cell regulators, separating agents, pigments, flame retardants, reinforcers such as glass fibers, surface-active compounds and / or stabilizers against oxidative, thermal, hydrolytic or microbial degradation or ageing. These are preferably added to the polyol component (A).

[0044] Preferably, no photo initiators are used according to the present invention. Preferably, the composition according to the present invention is free of photo initiators. In the context of the present invention, free of means that the composition comprises less than 50 ppm of photo initiators, more preferable less than 25 ppm, in particular less than 10 ppm of photo initiators.

[0045] The conversion to the polyurethane encapsulating compound according to the invention is effected preferably without addition of blowing agent, so that the polyurethane according to the invention is a compact polyurethane. However, the polyol component (A) used can in this case comprise small proportions of residual water. The residual water content is preferably below 1% by weight, more preferably below 0.3% by weight, particularly preferably below 0.05% by weight, based on the total weight of component (A) used. In one further embodiment of the invention, customary water scavengers are also added to the polyol component (A). If these are added, the proportion thereof is <20% by weight, preferably <10% by weight and very particularly preferably <5% by weight, based on the total weight of component (A). Particularly preferably, however, no water scavengers are used.

[0046] The feedstocks are also preferably chosen such that the resulting polyurethane encapsulating compounds can be sterilized by radiation or superheated steam if necessary and are non-cytotoxic. This is essentially brought about in that feedstocks are structured such that they either are incorporated into the polyurethane polymer lattice or can no longer migrate out of the polymer, and / or in that the solid polymer is so stable against hydrolysis that no low molecular weight degradation products that may be cytotoxic can be formed.

[0047] For the preparation of the polyurethanes according to the invention, generally the components (A) and (B) are reacted in amounts such that the ratio of equivalents of NCO groups to the sum total of reactive hydrogen atoms is 1 :0.8 to 1 :1.25, preferably 1 :0.9 to 1 :1.15. A ratio of 1 :1 corresponds here to an NCO index of 100.

[0048] The starting components are typically mixed and reacted at a temperature of 0° C. to 100° C., preferably 15° C. to 70° C. The mixing can be effected with the conventional PUR processing machines. In one preferred embodiment, the mixing is effected by means of low-pressure machines or high-pressure machines. The encapsulating compounds are subsequently cast and subjected to curing, for example at temperatures of from 20 to 150° C., preferably 40 to 100° C.

[0049] Casting is to be understood as any measure that gives the initially free-flowing encapsulating compound that form which it has after the curing. Casting is in particular to be understood as the introduction into or application onto a body. Such a body may for example be a surface, a frame, a vessel with at least one opening or a mold with at least one depression. The encapsulating compound can in principle remain in contact with the body or be parted therefrom. The encapsulating compound is preferably not separated from the mold after curing has been carried out, but forms a unit with it.

[0050] The present invention also further relates to a method for producing the polyurethane encapsulating compounds according to the invention. To this end, polyol component (A) and isocyanate component (B) are mixed to give a reaction mixture and left to react to completion to form the polyurethane encapsulating compound. Mixing may be carried out mechanically using a stirrer or a stirring screw or under high pressure in what is known as the countercurrent injection process. Here, in the context of the invention, the mixture of components (A) and (B) is called the reaction mixture for reaction conversions of less than 90%, based on the isocyanate groups.

[0051] According to a further aspect, the present invention is also directed to a process for producing a filter element comprising hollow fibers embedded in a cured polyurethane casting composition comprising the steps of

[0052] (I) embedding hollow fibers in the polyurethane casting composition as disclosed above;

[0053] (ii) curing the polyurethane casting composition at a temperature of at least 10°C to obtain a composite element comprising the hollow fibers embedded in the cured polyurethane composition;

[0054] (ill) treating the composite element under conditions suitable for sterilization.

[0055] According to the present invention, the filter element comprises hollow fibers embedded in the cured polyurethane casting composition. The hollow fibers may be embedded completely in the polyurethane casting composition or at least partially. Preferably, the hollow fibers are at least embedded at one or both ends in the polyurethane casting composition. According to the present invention, the hollow fibers are fixed in the polyurethane casting composition but have an opening on both sides.

[0056] The process according to the present invention comprises steps (I), (ii), and (ill) but may also comprise further steps. According to step (I), hollow fibers are embedded in the polyurethane casting composition as disclosed above.

[0057] During the production of the filter elements, the polyol component (A) and the isocyanate component (B) is preferably mixed and placed into a mold comprising hollow fibers. The encapsulating compound here is particularly preferably introduced into a hollow body which is rotating in a centrifuge and comprises hollow fibers. As a result of centrifugal force, the liquid reaction mixture is transported to each of the two ends of the filter element while surrounding the hollow fibers, and cures to form a compact, essentially clear encapsulation. According to step (ii), the polyurethane casting composition is cured at a temperature of at least 10°C, preferably in the range of from 10 to 80°C, more preferable in the range of from 10 to 60°C to obtain a composite element comprising the hollow fibers embedded in the cured polyurethane composition. The curing time may vary depending on the components used and the temperature applied. Preferably, the curing does not comprise a treatment with UV light.

[0058] The curing step may take place without further assistance by reaction of the NCO groups with reactive hydrogen atoms, especially of the OH groups, optionally at elevated temperature. The curing step is complete as soon as the encapsulating compound has largely reached its final properties, especially its stability.

[0059] The process according to the present invention further comprises step (ill). According to step (ill), the composite element is treated under conditions suitable for sterilization. The treatment according to step (ill) may comprise treatment with steam, in particular superheated steam or treatment with gamma radiation. Preferably, the treatment according to step (ill) results in a further increase of the stability. After step (ill), the encapsulating compound has preferably reached its final hardness.

[0060] Typically, gamma radiation is applied in the range of from 25 to 60 kGy, preferably in the range of from 30 to 40 kGy.

[0061] The process may also comprise further steps, for example a cutting step. The cutting step may preferably take place before step (ill). By means of a subsequent cutting process, the openings of the hollow fibers are usually exposed. The filter element is generally ready for use after step (ill) of the process of the present invention.

[0062] The filter element may also be covered in a packaging before step (ill) is carried out. After step (ill), the filter element may be used after removal of the packaging without further sterilization steps.

[0063] By means of the method according to the invention, it is possible to prepare encapsulating compounds that can preferably be sterilized by gamma radiation or superheated steam and are non-cytotoxic, and can be used for example as a water filter in the treatment or purification of drinking water or for example as a dialysis filter in the medical-technical sector. At the same time, using the polyurethane encapsulating compounds according to the invention, complex structures can be formed and by way of example a high fiber count of more than 12 000 fibers per filter, as required in dialysis filters, can be completely surrounded. In addition, the polyurethane encapsulating compounds according to the invention are hot sterilizable, radiation sterilizable, for example by irradiation with y rays, or wet sterilizable, for example by using peracetic acid, and display no migration of cytotoxic compounds, for instance amine compounds.

[0064] The cured polyurethane encapsulating compounds are resistant to disinfectants. In particular, the encapsulating compounds according to the invention exhibit a low absorption of water, water vapour or boiling hot water. The polyurethane encapsulating compounds according to the invention can be cut over a period of two weeks without formation of fine dust which otherwise may block the pores of the hollow fibers used for the actual filtration. The cured polyurethane encapsulating compounds according to the invention are preferably transparent, non-cytotoxic, and preferably have good adhesion to other materials that typically serve as filter housing, for instance polycarbonates, at elevated temperatures and over a relatively long period of time. The polyurethane encapsulating compounds are stable with respect to percarboxylic acids, and so shaped bodies made of such polyurethane encapsulating compounds can be sterilized, for example, with peracetic acid. The polyurethane encapsulating compounds according to the invention display high hydrophobicity and a sufficient crosslinking density.

[0065] The still free-flowing polyurethane encapsulating compounds can be also be cast without foam formation. At the same time, the polyurethane encapsulating compounds according to the invention, immediately after mixing of the reactive components, display a low mixed viscosity. It is also advantageous that the encapsulating compounds according to the invention and based on polyurethane are processable with all customary types of hollow fiber, such as cuprophane, polysulfone, polycarbonate or cellulose fibers, and the polycarbonates used most often as materials of the filter housing do not require any pretreatment by corona discharge prior to the processing for improving the adhesion strength.

[0066] The polyurethane encapsulating compounds according to the invention are used for preparing for encapsulating filter elements. To this end, a bundle of hollow fibers is embedded at their end in a polyurethane encapsulating compound according to the invention.

[0067] The encapsulating compounds according to the invention feature good biocompatibility and low emission of substances, especially of toxic substances, rapid and uniform curing and good sterilizability. The polyurethane casting composition has good adherence to the hollow fibers and also the outer material of the filter element.

[0068] According to a further aspect, the present invention is also directed to a filter element comprising hollow fibers embedded at their end in a cured polyurethane casting composition obtained or obtainable according to the process as disclosed above.

[0069] Such a filter element can be used as water filter, for example for the treatment or purification of drinking water, or in the medical sector, for example as dialysis filter element.

[0070] According to a further embodiment, the present invention is also directed to the filter element as disclosed above, wherein the filter element is a filter element for use in medicine, in particular wherein the filter element is a dialysis filter element. According to a further embodiment, the present invention is also directed to the filter element as disclosed above, wherein the filter element is a water filter element.

[0071] According to a further aspect, the present invention is also directed to the use of the polyurethane casting composition as disclosed above for preparing a filter element comprising hollow fibers. The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The process of any one of embodiments 1 to 3", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1, 2 and 3". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention.

[0072] 1 . A polyurethane casting composition obtained or obtainable by a process comprising the step of reacting a polyol component (A) and an isocyanate component (B) comprising at least one polyisocyanate (IC), wherein the polyol component (A) comprises

[0073] (1 ) at least one fat-based polyol (a1 ); and

[0074] (2) at least one compound (a2) having at least one unsaturated C-C-bond and at least one hydroxy group and a molecular weight in the range of from 100 to 600 g / mol.

[0075] 2. The polyurethane casting composition according to embodiment 1, wherein the polyol component comprises at least one polyol (a3) with a functionality of 2 to 8 and an OH number in the range of from 600 to 1350 mg KOH / g.

[0076] 3. The polyurethane casting composition according to embodiment 1 or 2, wherein composition (A) comprises at least one catalyst (ac) selected from the group consisting of zinc compounds, zirconium compounds, bismuth compounds and titanium compounds.

[0077] 4. The polyurethane casting composition according to any one of embodiments 1 to 3, wherein the fat-based polyol (a1) is selected from the group consisting of castor oil or an alkoxylated derivative of castor oil.

[0078] 5. The polyurethane casting composition according to any one of embodiments 1 to 4, wherein compound (a2) is an acrylate or methacrylate having 1 to 3 C-C-double bonds.

[0079] 6. The polyurethane casting composition according to any one of embodiments 1 to 5, wherein the polyisocyanate (IC) is selected from the group consisting of toluene 2, 4-diisocy anate, toluene 2,6-diisocy anate, diphenylene methane 2,2'-diisocyanate, diphenylene methane 2,4'-diisocyanate, diphenylene methane 4,4'-diisocy- anate, and prepolymers of diphenylene methane 4,4'-diisocy anate.

[0080] 7. The polyurethane casting composition according to any one of embodiments 1 to 6, wherein the proportion of the fat-based polyol (a1) in composition (A) is in the range of from 60 to 99.5% by weight, the proportion of polyol (a2) is in the range of from 0.5 to 10% by weight, the proportion the proportion of the catalyst (ac) is in the range of from 0.001 to 1 .0% by weight and the proportion of the polyol (a3) is in the range of from 0 to 25% by weight, based in each case on the total weight of composition (A).

[0081] 8. The polyurethane casting composition according to any one of embodiments 1 to 7, wherein the composition is free of photo initiators.

[0082] 9. A process for producing a filter element comprising hollow fibers embedded in a cured polyurethane casting composition comprising the steps of

[0083] (i) embedding hollow fibers in the polyurethane casting composition according to any one of embodiments 1 to 8;

[0084] (ii) curing the polyurethane casting composition at a temperature of at least 10°C to obtain a composite element comprising the hollow fibers embedded in the cured polyurethane composition;

[0085] (iii) treating the composite element under conditions suitable for sterilization.

[0086] 10. A process for producing a filter element comprising hollow fibers embedded in a cured polyurethane casting composition comprising the steps of

[0087] (i) embedding hollow fibers in the polyurethane casting composition;

[0088] (ii) curing the polyurethane casting composition at a temperature of at least 10°C to obtain a composite element comprising the hollow fibers embedded in the cured polyurethane composition;

[0089] (iii) treating the composite element under conditions suitable for sterilization, wherein the polyurethane casting composition is obtained or obtainable by a process comprising the step of reacting a polyol component (A) and an isocyanate component (B) comprising at least one polyisocyanate (IC), wherein the polyol component (A) comprises

[0090] (1 ) at least one fat-based polyol (a1 ); and

[0091] (2) at least one compound (a2) having at least one unsaturated C-C-bond and at least one hydroxy group and a molecular weight in the range of from 100 to 600 g / mol.

[0092] 11 . The process according to embodiment 10, wherein the polyol component comprises at least one polyol (a3) with a functionality of 2 to 8 and an OH number in the range of from 600 to 1350 mg KOH / g. The process according to embodiment 10 or 11, wherein composition (A) comprises at least one catalyst (ac) selected from the group consisting of zinc compounds, zirconium compounds, bismuth compounds and titanium compounds. The process according to any one of embodiments 10 to 12, wherein the fat-based polyol (a1) is selected from the group consisting of castor oil or an alkoxy lated derivative of castor oil. The process according to any one of embodiments 10 to 13, wherein compound (a2) is an acrylate or methacrylate having 1 to 3 C-C-double bonds. The process according to any one of embodiments 10 to 14, wherein the polyisocyanate (IC) is selected from the group consisting of toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, diphenylene methane 2,2'-diisocy- anate, diphenylene methane 2,4'-diisocy anate, diphenylene methane 4,4'-diisocy anate, and prepolymers of diphenylene methane 4,4'-diisocy anate. The process according to any one of embodiments 10 to 15, wherein the proportion of the fat-based polyol (a1) in composition (A) is in the range of from 60 to 99.5% by weight, the proportion of polyol (a2) is in the range of from 0.5 to 10% by weight, the proportion the proportion of the catalyst (ac) is in the range of from 0.001 to 1 .0% by weight and the proportion of the polyol (a3) is in the range of from 0 to 25% by weight, based in each case on the total weight of composition (A). The process according to any one of embodiments 10 to 16, wherein the composition is free of photo initiators. A filter element comprising hollow fibers embedded at their end in a cured polyurethane casting composition obtained or obtainable according to the process according to embodiment 9. A filter element comprising hollow fibers embedded at their end in a cured polyurethane casting composition obtained or obtainable according to the process according to any one of embodiments 10 to 11 . A filter element comprising hollow fibers embedded at their end in a cured polyurethane casting composition obtained or obtainable according to a process for producing a filter element comprising hollow fibers embedded in a cured polyurethane casting composition comprising the steps of

[0093] (I) embedding hollow fibers in the polyurethane casting composition according to any one of embodiments 1 to 8; (ii) curing the polyurethane casting composition at a temperature of at least 10°C to obtain a composite element comprising the hollow fibers embedded in the cured polyurethane composition;

[0094] (ill) treating the composite element under conditions suitable for sterilization.

[0095] 21 . The filter element according to any one of embodiments 18 to 20, wherein the filter element is a filter element for use in medicine, in particular wherein the filter element is a dialysis filter element.

[0096] 22. The filter element according to any one of embodiments 18 to 21, wherein the filter element is a water filter element.

[0097] 23. Use of the polyurethane casting composition according to any one of embodiments 1 to 8 for preparing a filter element comprising hollow fibers.

[0098] 24. A polyurethane casting composition for embedding hollow fibers obtained or obtainable by a process comprising the step of reacting a polyol component (A) and an isocyanate component (B) comprising at least one polyisocyanate (IC), wherein the polyol component (A) comprises

[0099] (1 ) at least one fat-based polyol (a1 ); and

[0100] (2) at least one compound (a2) having at least one unsaturated C-C-bond and at least one hydroxy group and a molecular weight in the range of from 100 to 600 g / mol.

[0101] 25. The polyurethane casting composition according to embodiment 24, wherein the polyol component comprises at least one polyol (a3) with a functionality of 2 to 8 and an OH number in the range of from 600 to 1350 mg KOH / g.

[0102] 26. The polyurethane casting composition according to embodiment 24 or 25, wherein composition (A) comprises at least one catalyst (ac) selected from the group consisting of zinc compounds, zirconium compounds, bismuth compounds and titanium compounds.

[0103] 27. The polyurethane casting composition according to any one of embodiments 24 to 26, wherein the fat-based polyol (a1) is selected from the group consisting of castor oil or an alkoxylated derivative of castor oil.

[0104] 28. The polyurethane casting composition according to any one of embodiments 24 to 27, wherein compound (a2) is an acrylate or methacrylate having 1 to 3 C-C-double bonds. 29. The polyurethane casting composition according to any one of embodiments 24 to 28, wherein the polyisocyanate (IC) is selected from the group consisting of toluene 2,4-diisocy anate, toluene 2,6-diisocy anate, diphenylene methane 2,2'-diisocyanate, diphenylene methane 2,4'-diisocyanate, diphenylene methane 4,4'-diisocy- anate, and prepolymers of diphenylene methane 4,4'-diisocyanate.

[0105] 30. The polyurethane casting composition according to any one of embodiments 24 to 29, wherein the proportion of the fat-based polyol (a1) in composition (A) is in the range of from 60 to 99.5% by weight, the proportion of polyol (a2) is in the range of from 0.5 to 10% by weight, the proportion the proportion of the catalyst (ac) is in the range of from 0.001 to 1 .0% by weight and the proportion of the polyol (a3) is in the range of from 0 to 25% by weight, based in each case on the total weight of composition (A).

[0106] 31 . The polyurethane casting composition according to any one of embodiments 24 to 30, wherein the composition is free of photo initiators.

[0107] 32. A process for producing a filter element comprising hollow fibers embedded in a cured polyurethane casting composition comprising the steps of

[0108] (i) embedding hollow fibers in the polyurethane casting composition according to any one of embodiments 24 to 31;

[0109] (ii) curing the polyurethane casting composition at a temperature of at least 10°C to obtain a composite element comprising the hollow fibers embedded in the cured polyurethane composition;

[0110] (iii) treating the composite element under conditions suitable for sterilization.

[0111] 33. A process for producing a filter element comprising hollow fibers embedded in a cured polyurethane casting composition comprising the steps of

[0112] (i) embedding hollow fibers in the polyurethane casting composition obtained or obtainable by a process comprising the step of reacting a polyol component (A) and an isocyanate component (B) comprising at least one polyisocyanate (IC), wherein the polyol component (A) comprises

[0113] (1 ) at least one fat-based polyol (a1 ); and

[0114] (2) at least one compound (a2) having at least one unsaturated C-C-bond and at least one hydroxy group and a molecular weight in the range of from 100 to 600 g / mol; (ii) curing the polyurethane casting composition at a temperature of at least 10°C to obtain a composite element comprising the hollow fibers embedded in the cured polyurethane composition;

[0115] (ill) treating the composite element under conditions suitable for sterilization. The process according to embodiment 33, wherein the polyol component comprises at least one polyol (a3) with a functionality of 2 to 8 and an OH number in the range of from 600 to 1350 mg KOH / g. The process according to embodiment 33 or 34, wherein composition (A) comprises at least one catalyst (ac) selected from the group consisting of zinc compounds, zirconium compounds, bismuth compounds and titanium compounds. The process according to any one of embodiments 33 to 35, wherein the fat-based polyol (a1) is selected from the group consisting of castor oil or an alkoxy lated derivative of castor oil. The process according to any one of embodiments 33 to 36, wherein compound (a2) is an acrylate or methacrylate having 1 to 3 C-C-double bonds. The process according to any one of embodiments 33 to 37, wherein the polyisocyanate (IC) is selected from the group consisting of toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, diphenylene methane 2,2'-diisocy- anate, diphenylene methane 2,4'-diisocy anate, diphenylene methane 4,4'-diisocy anate, and prepolymers of diphenylene methane 4,4'-diisocy anate. The process according to any one of embodiments 33 to 38, wherein the proportion of the fat-based polyol (a1) in composition (A) is in the range of from 60 to 99.5% by weight, the proportion of polyol (a2) is in the range of from 0.5 to 10% by weight, the proportion the proportion of the catalyst (ac) is in the range of from 0.001 to 1 .0% by weight and the proportion of the polyol (a3) is in the range of from 0 to 25% by weight, based in each case on the total weight of composition (A). The process according to any one of embodiments 33 to 39, wherein the composition is free of photo initiators. A filter element comprising hollow fibers embedded at their end in a cured polyurethane casting composition obtained or obtainable according to the process according to any one of embodiments 32 to 40. The filter element according to embodiment 41 , wherein the filter element is a filter element for use in medicine, in particular wherein the filter element is a dialysis filter element. 43. The filter element according to embodiment 41 , wherein the filter element is a water filter element.

[0116] 44. Use of the polyurethane casting composition according to any one of embodiments 24 to 31 for preparing a filter element comprising hollow fibers.

[0117] The present invention is further illustrated by the following examples.

[0118] EXAMPLES

[0119] 1 . Raw Materials Used

[0120] Polyol 1 DAB castor oil from Alberdingk Boley

[0121] Polyol 2 trifunctional polyether polyol with an OH number of 935 mg KOH / g available from BASF Polyurethanes GmbH

[0122] Polyol 3 2-hydroxyethy I methacrylate available from company Sigma Aldrich

[0123] Polyol 4 pentaerythritol triacry I at , available from company Sigma Aldrich

[0124] Isocyanate 1 isocyanate prepolymer based on MDI, dipropylene glycol and polypropylene glycol and having an NCO content of 23%, available from BASF Polyurethanes GmbH

[0125] Catalyst 1 Bicat 8842 of company Shepherd, prepared from bismuth neodecanoate and N,N,N',N'- tetrakis(2-hydroxyethyl)ethylenediamine

[0126] 2. Examples / Comparative Examples

[0127] To determine the improvement in the adhesion of the polyurethane to a substrate, lap shear samples were produced and tested after a defined time for the determination of the lap shear strength values. The lap shear strength values were determined based on DIN EN 60601 ISO 4587.

[0128] The required amount of isocyanate at an isocyanate index of 105 was added to a corresponding amount of polyol mixture. The amounts are indicated in table 1; all figures in the tables correspond to parts by weight unless otherwise indicated. The amounts of the isocyanate component and the polyol component were selected here such that 100 g of reaction mixture were obtained. The reaction mixture was mixed in a Speedmixer™ PP130 cup at 25° C for 30 s at 1800 rpm by means of a Speedmixer™ from Haunschild.

[0129] After the mixing time of 30 seconds, the reactive mixture was used to bond polycarbonate strips (100 x 25 x 3 mm) made of Makrolon 099 and to produce corresponding lap shear test specimens with an overlap length of 12.5 mm and a gap thickness between the two strips of 0.3 mm, which was adjusted using glass spheres with a diameter of 0.3 mm. After pressing and curing of the polyurethane for 1 hour at room temperature, the samples were additionally cured for 2 hours at 80 °C. After 14 days of storage at room temperature, the corresponding samples were treated with gamma radiation to simulate sterilization (30 kGy gamma-radiation by company Synergy Health Radeberg GmbH). After a total of 28 days, the lap shear strength values of the treated and untreated samples were determined. The results of the measurements are indicated in table 1 .

[0130] Table 1

[0131] A adhesive break between polyurethane and polycarbonate k.B no break between polyurethane and polycarbonate, polycarbonate deformed

[0132] The examples show that the use of vinylic monomers in combination with treatment with gamma radiation results in an improvement of the adhesion of the polyurethane.

[0133] Literature cited

[0134] EP844015 B1

[0135] DD-A-155777

[0136] EP 2 081 973 EP 538 673

[0137] EP 413 265

[0138] EP 329473

Claims

Claims1 . A polyurethane casting composition for embedding hollow fibers obtained or obtainable by a process comprising the step of reacting a polyol component (A) and an isocyanate component (B) comprising at least one polyisocyanate (IC), wherein the polyol component (A) comprises(1 ) at least one fat-based polyol (a1 ); and(2) at least one compound (a2) having at least one unsaturated C-C-bond and at least one hydroxy group and a molecular weight in the range of from 100 to 600 g / mol.

2. The polyurethane casting composition according to claim 1, wherein the polyol component comprises at least one polyol (a3) with a functionality of 2 to 8 and an OH number in the range of from 600 to 1350 mg KOH / g.

3. The polyurethane casting composition according to claim 1 or 2, wherein composition (A) comprises at least one catalyst (ac) selected from the group consisting of zinc compounds, zirconium compounds, bismuth compounds and titanium compounds.

4. The polyurethane casting composition according to any one of claims 1 to 3, wherein the fat-based polyol (a1) is selected from the group consisting of castor oil or an alkoxylated derivative of castor oil.

5. The polyurethane casting composition according to any one of claims 1 to 4, wherein compound (a2) is an acrylate or methacrylate having 1 to 3 C-C-double bonds.

6. The polyurethane casting composition according to any one of claims 1 to 5, wherein the polyisocyanate (IC) is selected from the group consisting of toluene 2,4-diisocy anate, toluene 2,6-diisocy anate, diphenylene methane 2,2'-diisocyanate, diphenylene methane 2,4'-diisocyanate, diphenylene methane 4,4'-diisocyanate, and prepolymers of diphenylene methane 4,4'-diisocy anate.

7. The polyurethane casting composition according to any one of claims 1 to 6, wherein the proportion of the fatbased polyol (a1) in composition (A) is in the range of from 60 to 99.5% by weight, the proportion of polyol (a2) is in the range of from 0.5 to 10% by weight, the proportion the proportion of the catalyst (ac) is in the range of from 0.001 to 1 .0% by weight and the proportion of the polyol (a3) is in the range of from 0 to 25% by weight, based in each case on the total weight of composition (A).

8. A process for producing a filter element comprising hollow fibers embedded in a cured polyurethane casting composition comprising the steps of(i) embedding hollow fibers in the polyurethane casting composition according to any one of claims 1 to 7;(ii) curing the polyurethane casting composition at a temperature of at least 10°C to obtain a composite element comprising the hollow fibers embedded in the cured polyurethane composition; (ill) treating the composite element under conditions suitable for sterilization.

9. A filter element comprising hollow fibers embedded at their end in a cured polyurethane casting composition obtained or obtainable according to the process according to claim 8.

10. The filter element according to claim 9, wherein the filter element is a filter element for use in medicine, in particular wherein the filter element is a dialysis filter element.11 . The filter element according to claim 9, wherein the filter element is a water filter element.

12. Use of the polyurethane casting composition according to any one of claims 1 to 7 for preparing a filter element comprising hollow fibers.

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