DE19909841A1 - Multilayer membranes and processes for their manufacture - Google Patents

Abstract

The invention applies to the fields of chemistry and relates to multilayer membranes, such as those used, for example, to separate aqueous alcohol mixtures by means of pervaporation. The aim of the invention is to provide a multilayer membrane having a defect-free, separation-active layer and exhibiting a high separation capacity. To this end, the invention provides multilayer membranes consisting of a dense or microporous supporting material and of at least one single layer which is applied thereto and which is attached to the supporting material by polyelectrolyte complexes, whereby few single layers are applied and the first single layer predominantly covers the surface of the supporting material. The aim of the invention is also accomplished by using a method for producing multilayer membranes in which at least one single layer consisting of at least one anionic polyelectrolyte material or, alternatively, of at least one cationic polyelectrolyte material or of at least one non-stoichiometric polyelectrolyte complex is applied to a dense or microporous supporting material which is functionalized with ionic and/or ionizable groups.

Description

The invention relates to the fields of chemistry, the material-converting Industry, biotechnology and the food industry and concerns Multi-layer membranes, such as those used for the separation of aqueous media Alcohol mixtures are used by means of pervaporation and methods for their Manufacturing.

For the dehydration of organic solvents by means of pervaporation were already numerous dense polymer membranes described, with their help preferred Water is transported (J. Néel in R. Y. M. Huang: Pervaporation Membrane Separation Processes, Elsevier 1991, chap. 1; and J. Néel in R. D. Noble and S. A. Stern: Membrane Separations Technology; Elsevier 1995, chap. 5).

Since the transport through such membranes takes place by means of diffusion, is general aimed to produce membranes with the thinnest possible separation active layers. The phase inversion process is used to manufacture such membranes (S. Loeb, S. Sourirajan, Adv. Chem. Ser. 38, 117 (1962)), which provides asymmetric membranes with an integrated separating layer. the desired membranes can also by a composite structure, such as. B. by the deposition of polyelectrolyte complex layers on a carrier material getting produced.

The build-up of thin layers on solid substrates by means of consecutive alternating polyelectrolyte adsorption was first used in the early nineties (G. Decher, J.-D. Hong, J. Schmitt, Thin Solid Films, 210/211, 831-835 (1992)). About the use of this technique for the production of thin layers for Construction of composite membranes has been little reported to date.

From DE 42 29 530 a polyelectrolyte composite membrane (Symplex) is known, which is used for the dehydration of organic solvents. As polyelectrolytes cellulose sulfate (polyanion) and polydimethyldiallylammonium chloride are used (Polycation) used. This symplex is based on a nonionic microporous Carrier layer applied to ensure mechanical stability. at only one complex layer is built up in this process. But since the porous Support material must be sealed, however, are high in this process Mass use (2-5 mass%) of the symplex-forming components necessary, the due to the manufacturing technology to relatively high layer thicknesses (several 100 nm) to lead.

One made up of a polyelectrolyte complex multilayer system Pervaporation and gas separation membrane has been described (L. Krasemann, B. Tieke J. Membr. Sci., 150, 23-30 (1998)). The porous support material used was before the structure of the polyelectrolyte multilayer complex is technically complex Subjected to plasma treatment. This creates ionic groups on the Surface generated, which improves the adhesion of the adsorbed polyelectrolyte Multi-layer complex on the carrier material by electrostatic Ensure interaction. Due to the porosity of the carrier material is a high number of polyelectrolyte complex layers (≧ 30 double layers corresponding to ≧ 60 individual layers) is necessary to ensure a defect-free, active separator Layer and thus an effective membrane. Another disadvantage of this Membrane is, in addition to the necessary plasma pretreatment of the carrier material and the high number of polyelectrolyte complex layers, the insufficient stability of the Multi-layer polyelectrolyte system with water contents of <24% by mass in the feed.

It is also known (J.-M. Leväsalmi, T. J. McCarthy, Macromolecules, 30, 1752-1757 (1997)) a gas separation membrane based on a polyolefin carrier material and a polyelectrolyte complex multilayer system. However, it is necessary to use the hydrophobic polyolefin carrier before the construction of the polyelectrolyte complex Multi-layer system through a wet chemical modification with Chromosulfuric acid and nitric acid hydrophilize to ionogenic groups generate the adsorption of the first polyelectrolyte layer by electrostatic Allow interactions in the first place. However, an effective membrane is only made through obtain the application of a high number of polyelectrolyte layers.

According to R. M. France, R. D. Short, J. Chem. Soc., Faraday Trans., 93 (17), 3173-3178 (1997) is also known that those introduced by plasma treatment Oxygen functionalities on polymer surfaces are only partially stable and with a solvent inert to the polymer substrate can be washed off. Furthermore, it was shown in this study that at least 40% of the Oxygen functionalities can be assigned to the hydroxyl groups can be regarded as inactive with regard to the formation of polyelectrolyte complexes.

The object of the present invention is to provide a multilayer membrane with a specify a defect-free separating layer and a high separation performance and to produce these using a process that is easier to handle and less expensive.

The object is achieved by what is specified in claims 1 and 19 Invention. Further developments are the subject of the subclaims.

The multilayer membranes according to the invention consist of a dense or microporous carrier material and an active release layer applied to it, this separating layer being made up of at least one single layer. The carrier material is at least chemically the same throughout built up. It is advantageously chemically uniform throughout and structurally asymmetrical constructed. But it is also possible according to the invention that the The carrier material has a consistently similar structure, both chemically and structurally. In In any case, the carrier material itself can also be active with regard to the too processing separation problems.

The active separation layer is provided as a polyelectrolyte complex multilayer system the carrier material with a single layer through a polyelectrolyte complex or in the case of several individual layers on the carrier material, also these Individual layers are connected to one another by a polyelectrolyte complex. In the case of several individual layers, there are those that are applied one on top of the other Individual layers alternating from at least one anionic and from at least one cationic polyelectrolyte material, which after application enters into a complex bond with the previously applied single layer.

According to the state of the art, two such are originally differently charged single layers referred to as double layer.

The anionic polyelectrolyte materials are Sulfonic acid groups and / or their salts and / or around phosphonic acid groups and / or their salts and / or around phosphoric acid groups and / or their salts and / or around carboxyl groups and / or their salts and / or around sulfate groups having homopolymers and / or copolymers of olefinically unsaturated Monomers and / or polysaccharides containing carboxyl groups and / or their Salts.

The cationic polyelectrolyte materials are polymeric amine and / or ammonium or phosphine and / or phosphonium compounds.

According to the invention, the number of individual layers applied is essential less than according to the state of the art.

This is usually followed by 20 to 60 double layers, i.e. 40 to 120 Single layers applied.

According to the solution according to the invention, advantageously only between 1 and 30 individual coats can be applied to be the same or even better To obtain separating effect than according to the prior art. Even more advantageous range between 6 and 12 individual layers according to the invention Solution for achieving a better separation effect.

Furthermore, the layer thicknesses of the individual individual layers are also the active ones Layer in the range of thinner layer thicknesses from the range of known Layer thicknesses settled.

According to the state of the art, on the one hand, relatively thin layer thicknesses for individual and also known as double layers. These are around 1 nm per double layer. Around in the case of such layer thicknesses of the double layers, a sufficient separating effect is achieved a number of layers of 20 to 60 double layers is necessary. In the prior art it is also known to have a smaller number of layers to raise. However, these are then much thicker and are around 500 nm per Double layer.

According to the solution according to the invention, there are therefore a small number of thin layers sufficient to achieve an equally good or substantially improved release effect compared to the prior art.

Likewise, in the case of the solution according to the invention, in particular for the first individual layer on the carrier material, a smaller amount of polyelectrolyte material is necessary than is known from the prior art. With this smaller amount of polyelectrolyte material, however, the surface of the carrier material is for the most part covered. The amount applied is advantageously 5 to 500 μg / cm ² carrier surface, even better 50 to 300 μg / cm ² carrier surface.

After and / or during the application takes place between the carrier material and a complex formation takes place of the applied first single layer. These However, complex formation does not only take place in a near-surface area of the Carrier material instead, but extends at least partially deeper.

This is possible because the carrier material is at least chemically and advantageously is also structured in the same way throughout.

This creates a certain interlocking between the first individual layer and the Carrier material achieved, resulting in a much better adhesion of this first Single layer on the carrier material leads.

The covering of the surface of the substrate with the first applied Single layer takes place to more than 50%, advantageously to more than 80%. Included the material of the first single layer covers the carrier surface during application advantageously in larger islands or in larger areas or in one another connected islands or in interconnected areas.

The membrane according to the invention is used for the dehydration of organic substances, e.g. solvents, or mixtures of substances (aldehydes, ketones, ethers, Alcohols, amines, acids) or for the separation of organic / organic * means Pervaporation or for the separation of water vapor and / or hydrogen sulfide from substances or mixtures of substances, such as B. water vapor and / or Hydrogen sulfide from methane, by means of gas separation. The inventive Membrane should only be used when separating substances or mixtures of substances Find application that behave inert towards the membrane.

The anionic polyelectrolyte component is preferably homo- and / or copolymers containing water-soluble sulfonic acid groups and / or their salts such as. B. Poly (styrenesulphonic acid), poly (styrenesulphonic acid-old maleic anhydride), poly (vinyl sulfonic acid) sodium salt, poly (styrene sulfonic acid) - Sodium salt and / or homo- and / or phosphonic acid groups Copolymers and / or their salts such as. B. poly (vinyl phosphonic acid) and / or Homopolymers and / or copolymers containing phosphoric acid groups and / or their Salts such as B. poly (vinyl phosphoric acid) sodium salt and / or carboxyl groups and / or their salts and / or sulfate group-containing polymeric compounds or homo- and / or copolymers of olefinically unsaturated monomers and / or carboxyl-functionalized polysaccharides and / or their salts.

Water-soluble nitrogen-containing components are preferred as the cationic components Polymer compounds and / or their salts such as. B. polyallylammonium chloride, Polydimethyldiallylammonium chloride, polyvinylpyridinium salts, polyethyleneimine, Polymer compounds containing tetraalkylammonium salt groups and / or Polyvinyl compounds with quaternizable and / or quaternized Nitrogen atoms, amino-functionalized polysaccharides such as. B. Chitosan and their Salts used.

The polyelectrolytes or polyelectrolyte components are preferably in one aqueous solution and are applied to the carrier material. The watery one Solution can optionally contain additional ionic and / or non-ionic additives, such as B. low molecular weight electrolytes such as NaCl contain.

The carrier material can be dense or microporous Flat structure or a membrane, in particular a flat membrane, which is preferably not porous, act. This carrier material consists of a water-insoluble polymer with carboxyl and / or amino and / or Sulfonic acid groups and / or phosphonic acid groups and / or Phosphoric acid groups and / or their salts and / or sulfate groups, preferably is functionalized with carboxyl groups. Such a polymer is either used for Production of the membranes according to the invention used directly as a carrier material or on a fleece as a carrier material, consisting of polyamide, polypropylene, Polyester, polyphenylene sulfide or a fine silk fabric, preferably from solution, upset.

The production according to the invention of the multilayer membrane according to the invention takes place by applying at least one individual layer of at least one anionic or at least one cationic polyelectrolyte material or from at least one separately produced non-stoichiometric polyelectrolyte Complex by consecutively alternating application of the oppositely charged Polyelectrolyte materials on the carrier material. The order in which the individual polyelectrolyte components are applied to the carrier, results from the charge of the carrier material used.

The individual layers are advantageously applied by dipping the Carrier material, if necessary with the individual layers already applied, in a solution, the one or the respective anionic (s) or cationic (s) Polyelectrolyte material (a) or the non-stoichiometric polyelectrolyte Contains complex (s) and possibly additional ionic and / or nonionic additives.

The mass fraction of the polyelectrolyte components in the solutions is between 0.01 and 5 mass%, preferably between 0.03 and 3 mass%.

The carrier material is one with ionic and / or ionizable groups functionalized dense or microporous material.

After each individual layer has been applied, between this individual layer and the previous oppositely charged single layer one Complex formation takes place, which leads to a firm adhesion of the individual layers to one another leads.

After each coating step and / or after all of them have been applied The multilayer membrane according to the invention is preferably with individual layers Water or a mixture of water and an organic solvent, preferably alcohol and especially in a mixing ratio of 4: 1, washed. The multilayer membranes can after the application of a and / or all individual layer (s) and dried after washing. It has proved to be advantageous that the multilayer membrane after each Coating step is dried.

The polyelectrolyte complex layers applied to the carrier represent the actual separation-active layer. The carrier material can also be used Contribute separating effect.

The multilayer membranes according to the invention can by dipping into a, the Aqueous solution containing polyelectrolyte components, or by others known ways of applying a thin layer, such as. B. spraying or spinning Coating, can be obtained.

The multilayer membranes according to the invention are characterized in that by using one with ionic and / or ionizable groups functionalized carrier material a particularly good adhesion between the Polyelectrolyte complex multilayer system and the carrier material is guaranteed. Furthermore, the multilayer membranes according to the invention are characterized by a high water (vapor) permeability or permeability of hydrophilic components as well as good selectivity for water and steam as well as for hydrophilic ones Components versus other components. They are also multiple usable, have a high mechanical stability and are simple manageable. Furthermore, the multilayer membrane manufacturing process stands out due to a low use of polyelectrolytes and the formation of very thin, defined separating layers that allow a high permeate flow.

The invention is explained in more detail below using several exemplary embodiments. For the permeate-related characterization of the multilayer membranes, the parameters permeate flow J in kg / m ² h under the given test conditions (temperature, composition of the feed, permeate-side pressure) and the separation factor α of the multilayer membranes are used. The α-value is a dimensionless variable that is defined as the concentration ratio of the binary mixtures in the permeate to that in the feed.

Unless otherwise stated, the experimental conditions were as follows:
pressure on the permeate side: 2000 Pa
Temperature: 50 ° C

example 1

For the production of a multilayer membrane according to the invention, reference is made to the polymeric carrier material, consisting of a carboxyl-functionalized polyamide-6 with a carboxyl group concentration of 207 µmol / g a polyelectrolyte complex Multi-layer system applied. The multi-layer system is followed by consecutive alternating immersion of the carrier material in aqueous Polyelectrolyte component solutions built up. Between each coating step the polymer carrier is washed with water. As a polyanion or Polycation components are used by polyacrylic acid or polyethyleneimine. the Concentration of the solutions is in each case 20 mmol / l, based on the Monomer unit of the polyelectrolyte components. There are from the polyanion and from Polycation material in each case alternating 6 individual layers, i.e. a total of 12 Single layers or 6 double layers applied.

The amount of layer material applied to the carrier surface is approx. 60 µg / cm ² per individual layer. The layer thickness of the entire separation-active layer on the carrier material is about 7 nm.

With the dehydration of organic solvents the following results are obtained obtain:

Ethanol / water (80/20) T = 50 ° C; J = 0.21 kg / m ² h; α = 2344 Ethanol / water (90/10) T = 50 ° C; J = 0.02 kg / m ² h; α = 1400 2-propanol / water (70/30) T = 50 ° C; J = 0.67 kg / m ² h; α = 4700 2-propanol / water (80/20) T = 50 ° C; J = 0.30 kg / m ² h; α = 4044

Example 2

In the production of the multilayer membrane according to the invention, as in Example 1 proceed, wherein after the application of the last polyelectrolyte layer the Multi-layer membrane is dried at 70 ° C.

With the dehydration of organic solvents the following results are obtained obtain:

Ethanol / water (80/20) T = 50 ° C; J = 0.18 kg / m ² h; α = 3000 Ethanol / water (90/10) T = 50 ° C; J = 0.01 kg / m ² h; α = 1685 2-propanol / water (70/30) T = 50 ° C; J = 0.50 kg / m ² h; α = 6500 2-propanol / water (80/20) T = 50 ° C; J = 0.25 kg / m ² h; α = 5980

Example 3

In the production of the multilayer membrane according to the invention, as in Proceed in Example 1, the polydimethyldiallylammonium chloride being used as the polycation Place of polyethyleneimine is used. There will be a total of 10 Double layers applied.

With the dehydration of organic solvents the following results are obtained obtain:

Ethanol / water (80/20) T = 50 ° C; J = 0.45 kg / m ² h; α = 467 Ethanol / water (90/10) T = 50 ° C; J = 0.21 kg / m ² h; α = 300 2-propanol / water (70/30) T = 50 ° C; J = 0.69 kg / m ² h; α = 605 2-propanol / water (80/20) T = 50 ° C; J = 0.38 kg / m ² h; α = 521

Example 4

In the production of the multilayer membrane according to the invention, as in Example 1 procedure, wherein the polyanion is poly (styrenesulfonic acid) sodium salt Place of polyacrylic acid is used and a total of 10 double layers be applied.

With the dehydration of organic solvents the following results are obtained obtain:

Ethanol / water (80/20) T = 50 ° C; J = 0.62 kg / m ² h; α = 337 2-propanol / water (70/30) T = 50 ° C; J = 0.89 kg / m ² h; α = 589

Example 5

In the production of the multilayer membrane according to the invention, as in Example 1, the polyanion being poly (styrenesulfonic acid) sodium salt and polydimethyldiallylammonium chloride is used as the polycation. It will a total of 10 double layers applied.

With the dehydration of organic solvents the following results are obtained obtain:

Ethanol / water (80/20) T = 50 ° C; J = 0.99 kg / m ² h; α = 289 2-propanol / water (70/30) T = 50 ° C; J = 1.11 kg / m ² h; α = 385

Claims (41)

1. Multi-layer membrane consisting of a dense or microporous Carrier material, which is at least chemically consistently structured in the same way is and of at least one single layer applied thereon, the one represents separating layer and with the carrier material and with several Individual layers are interconnected by polyelectrolyte complexes, compared to the number of individual layers that is known to be applied a much smaller number of individual layers is applied and the Layer thickness of these individual layers in the range of the thinner layer thicknesses the known range of layer thicknesses are settled, and the first Single layer of the active separation layer when compared to known applied amount with smaller amounts for the most part the Covered surface of the carrier material and one with the carrier material Complex formation has entered, which at least partially not only the concerns the area of the carrier material close to the surface. 2. Multi-layer membrane according to claim 1, in which the carrier material consists of a water-insoluble material. 3. Multi-layer membranes according to claim 1, wherein the carrier material is a Is flat membrane or a hollow fiber. 4. Multi-layer membranes according to claim 1, wherein the carrier material is a asymmetric membrane is. 5. multilayer membranes according to claim 1, wherein the carrier material on a Fabric made of fine silk or applied to or deposited on a fleece is, the fleece made of a polyamide, polyester, polypropylene or Polyphenylene sulfide consists. 6. Multi-layer membranes according to claim 1, in which the used Carrier material with ionic and / or ionizable groups functionalized material is. 7. Multi-layer membranes according to claim 1, in which the used Layer material is an anionic or cationic polyelectrolyte material. 8. multilayer membranes according to claim 1, wherein between 1 and 30 Individual layers are applied to the carrier material. 9. Multi-layer membranes according to claim 8, in which 6 to 20 individual layers the carrier material are applied. 10. Multi-layer membranes according to claim 1, wherein the layer thicknesses of the Individual layers of the separating layer between 0.3 and 1.5 nm / individual layer lie. 11. Multi-layer membranes according to claim 10, wherein the layer thicknesses of the Individual layers of the separating layer between 0.5 and 0.9 nm / individual layer lie. 12. Multi-layer membranes according to claim 1, in which the applied amount of the respective individual layers is in the range from 5 to 500 µg / cm ^{2 of} carrier surface. 13. Multi-layer membranes according to claim 12, in which the applied amount of the respective individual layers is between 50 and 300 µg / cm ^{2 of} carrier surface. 14. Multi-layer membranes according to claim 1, wherein the covering of the Surface of the carrier material with the material of the first individual layer of the separating layer in larger islands or in larger areas or in islands connected to each other or in areas connected to each other is done. 15. Multi-layer membranes according to claim 14, wherein the covering of the Surface of the carrier material with the material of the first individual layer of the separation-active layer has taken place to more than 50%. 16. Multi-layer membranes according to claim 14, wherein the covering of the Surface of the carrier material with the material of the first individual layer of the separation-active layer has taken place to more than 80%. 17. Multi-layer membranes according to claim 1, in which the complex formation between the carrier material and the material of the first individual layer of the separation-active layer in large parts of the cover not only in the is done near the surface area of the carrier material. 18. Multi-layer membranes according to claim 1, in which the complex formation between the carrier material and the material of the first individual layer of the separating layer for the predominant part of the cover not only in the is done near the surface area of the carrier material. 19. A method for the production of multilayer membranes according to one of the Claims 1-18, in which one with ionic and / or ionizable groups functionalized dense or microporous carrier material at least one Single layer of at least one anionic polyelectrolyte material or at least one cationic polyelectrolyte material alternately or from at least one non-stoichiometric polyelectrolyte complex applied and depending on the charge of the material on the respective surface, the next Single layer of a material with the opposite charge applied is, after the application of the next individual layer one Complex formation between first between the carrier material and the material the first single layer and then between each opposite charged layer materials takes place and the multilayer membranes after each coating and / or after the application of all individual layers washed and / or dried. 20. The method according to claim 19, wherein the carrier material is a water-insoluble Material containing carboxyl groups and / or carboxylate groups and / or Sulfonic acid groups and / or sulfonate groups and / or phosphonic acid groups and / or phosphonate groups and / or phosphoric acid groups and / or Phosphate groups and / or sulfate groups and / or amino groups and / or Has ammonium groups, is used. 21. The method according to claim 19, wherein a carrier material is used, which consists of one or more carboxyl-functionalized polyamide (s) and / or one or more carboxyl-functionalized polyolefin (s) and / or of one or several reaction product (s) from carboxyl-functionalized polyolefin (s) and Polyamide (s). 22. The method according to claim 19, wherein a carrier material is used, which from one or more amino- and / or ammonium-functionalized Polymer compound (s), preferably aliphatic polyamide (s), consists. 23. The method of claim 19, wherein the preparation of an anionic Single layer, an anionic polyelectrolyte component composed of, preferably water-soluble, polymer compound is used, the carboxyl groups and / or carboxylate groups and / or sulfonic acid groups and / or Sulfonate groups and / or phosphonic acid groups and / or phosphonate groups and / or phosphoric acid groups and / or phosphate groups and / or Has sulfate groups. 24. The method of claim 23, wherein the preparation of an anionic Single layer an anionic polyelectrolyte component is used, which is a Carboxyl groups and / or carboxylate groups and / or sulfonic acid and / or Sulfonate groups and / or phosphonic acid and / or phosphonate groups and / or phosphoric acid and / or phosphate groups and / or sulfate groups having homo- and / or copolymer of olefically unsaturated monomers. 25. The method of claim 23, wherein the preparation of an anionic Single layer an anionic polyelectrolyte component is used, which is a Is polysaccharide containing carboxyl and / or carboxylate groups. 26. The method according to claim 23, wherein as having carboxyl groups Polysaccharide a mixed cellulose ester is used. 27. The method according to claim 19, wherein the preparation of a cationic Single layer a cationic polyelectrolyte component composed of, preferably water-soluble, polymer compound is used, the amino groups and / or Ammonium groups and / or phosphine groups and / or phosphonium groups having. 28. The method of claim 27, wherein for the preparation of a cationic Single layer a cationic polyelectrolyte component is used, the Is polyethyleneimine. 29. The method of claim 27, wherein the preparation of a cationic Single layer a cationic polyelectrolyte component is used, which is a Is polydiallylmethylammonium salt. 30. The method of claim 27, wherein the preparation of a cationic Single layer a cationic polyelectrolyte component is used, the Is polydimethyldiallylammonium chloride. 31. The method of claim 27, wherein the preparation of a cationic Single layer a cationic polyelectrolyte component is used, which is a Is polyallylammonium salt. 32. The method according to claim 27, wherein the preparation of a cationic Single layer a cationic polyelectrolyte component is used, the Is polyallylammonium chloride. 33. The method according to claim 27, wherein the preparation of a cationic Single layer a cationic polyelectrolyte component is used, the Is polyallylamine. 34. The method according to claim 27, wherein the preparation of a cationic Single layer a cationic polyelectrolyte component is used, which is a Is polysaccharide containing amino and / or ammonium groups. 35. The method according to claim 19, wherein the application of the individual layers the carrier material from an aqueous solution of at least one of the Polyelectrolyte materials with a mass fraction of 0.01 to 5 mass%, preferably 0.03 to 3 mass%. 36. The method according to claim 19, wherein the application of the individual layers the carrier material from an aqueous solution of at least one separately produced non-stoichiometric polyelectrolyte complex with a Mass fraction of 0.01 to 5 mass%, preferably 0.03 to 3 mass%, carried out will. 37. The method according to claim 19, wherein the polyelectrolyte component containing solutions additionally with ionic and / or non-ionic Supplements are provided. 38. The method according to claim 19, wherein between 1 and 30 individual layers, preferably between 6 and 20 individual layers on the carrier material be applied. 39. The method according to claim 19, wherein after each application of a single layer with water and / or a mixture of water and an organic one Solvent, preferably alcohol, especially in a ratio of 4: 1, is washed. 40. The method according to claim 19, wherein after the application of each Drying is carried out in a single layer. 41. The method according to claim 19, wherein after the application of the last Drying is carried out in a single layer.