Functional sol-gel coating agents

0001F un kti on el Sol -Ge l -Bes ch i ch tu ngsm itte l

0002Technical field

0003The invention relates to functional sol-gel coating compositions which have nanoparticulate additives. In particular, the invention relates to sol-gel coating compositions with an antimicrobial or decorative function.

0004State of the art

0005Developments in the field of nanotechnology in recent years have made it possible to produce ever smaller particles and to stabilize them as a dispersion. Technologies for the production of nanoparticles have been refined or newly developed, the grinding technology for crushing coarse particles has been significantly improved in order to advance into ever smaller dimensions. Because of their large surface area, these smallest particles tend to agglomerate. Therefore, they are usually only stable as dispersions. Aids are usually used that cause steric or electrostatic repulsion of the particles. In many cases it is now possible to produce dispersions whose particles are only a few nanometers in size. This opens up completely new possibilities for many applications.

0006Nanoparticles have considerable advantages, of which, based on the invention, only two are mentioned: on the one hand, such particles have an extremely high specific surface area and are therefore particularly suitable as functional particles. On the other hand, the use of such particles in coatings makes it possible to produce layer thicknesses that are smaller the smaller the particles that have to be anchored in them. The invention takes advantage of these advantages and combines them with the positive properties of a sol-gel coating. This results in completely new types of functional coatings, particularly in the areas of antimicrobial and decorative coatings. Antimicrobial coating

0007A sol-gel coating composition according to the invention with an antibacterial function has an nanoparticulate antimicrobial metal, for example silver, as an additive. The antimicrobial effect of metal ions has been known for a long time. Silver, for example, can be used in various forms as the antimicrobial starting material and is used as a salt, bound as metallic silver in a matrix or used as particulate metallic silver. Soluble silver salts have the disadvantage that they convert very quickly into the antimicrobial silver ions in the aqueous environment and are therefore quickly consumed. A long-term antimicrobial effect cannot be achieved in this way. Longer working times are usually achieved by systems in which the silver is bound in a matrix. For example, a zeolite, glass or titanium dioxide can be used as the matrix. Metallic nanoparticulate silver has a particularly high antimicrobial effectiveness. DE 101 46 050 describes the use of silver particles up to 100 nm in size in a coating material and their antimicrobial effect. The purely organic coatings according to DE 101 46 050 have a layer thickness of several μm. For many applications, especially on glass, however, transparent or optically neutral layers necessary, a requirement that coatings according to DE 101 46 050 cannot meet. In addition, the organic layers of DE 101 46 050 are fundamentally soft and therefore do not have high scratch and abrasion resistance.

0008There is currently a high demand for antimicrobial systems, which is no longer restricted to the medical sector, but also affects everyday areas of life such as the office or household. The range of examples here ranges from computer keyboards to refrigerators to tiles and joints in sanitary facilities. The possibility of making these objects antimicrobial has so far often failed due to the technical feasibility or the high costs. Decorative coating

0009According to the invention, the use of nanoparticulate additives enables the production of decorative coatings with novel properties.

0010Decorative glasses are primarily glasses that have a sandblasted, etched, satin-like and / or colored look.

0011There are several ways to create such effects:

0012The etching of glass is carried out with the very aggressive hydrofluoric acid and therefore poses a great danger to people and the environment.

0013Colored glasses can be produced, for example, by adding certain inorganic oxides to the glass. This process is complex and expensive.

0014An alternative is to achieve the desired effect with a suitable coating. The market also offers coatings that are based on either organic or ceramic materials . Ceramic coatings must be baked at very high temperatures and then slowly cooled in a defined tempering program to avoid pre-tensioning. This process is time-consuming and costly. Before baking, the coating has no adhesion to the surface and is therefore difficult to handle. Usually, the baking takes place immediately after the layer has been applied. If a safety glass is now made from this glass, it must be tempered a second time, this time with rapid cooling. Since two tempering processes entail considerable costs, it would be desirable if both processes - baking the coating and tempering to the safety glass - could be carried out in one step.

0015Organic coatings, on the other hand, are usually cured either by UV or at temperatures up to 250 ° C, but in no case are they resistant to temperatures above 500 ° C. E.g. This creates a problem when coating safety glass. To manufacture safety glass, the glass is subjected to a defined tempering process, in which the glass is briefly heated around the glass softening point and then cooled with air, whereupon the glass is toughened and can no longer be cut or processed. Organic coating can therefore only take place after the tempering process. In addition, such coatings are only slightly scratch-resistant and UV-stable.

0016In many cases, a method would be necessary in which the coating can be applied before processing and hardened only at a later point in time, in the best case in combination with the tempering process.

0017A decorative coating with the following characteristics is desirable:

0018- Pre-curing at low temperatures creates a layer that is abrasion-resistant enough to be stackable and transportable;

0019- This layer can also be processed after this predrying, ie usual work steps such as grinding, drilling, cutting can be carried out;

0020- The layer has a high temperature stability and thus withstands the subsequent tempering process.

0021DESCRIPTION OF THE INVENTION The present invention is intended to provide coating compositions from which coatings can be produced which, in addition to a desired function (an antibacterial or decorative effect), have a high resistance to external influences.

0022This object is achieved according to the invention by a sol-gel coating agent according to one of the independent claims 1 and 32, a coating according to one of the independent claims 16 and 49 and a method for producing a sol-gel coating according to one of the independent claims

0023Claims 21 and 52 solved. Further advantageous aspects, details and refinements of the invention result from the dependent claims, the description and the examples.

0024The present invention is based on the idea of ​​producing functional coatings using a sol-gel process, the function being represented by a nanoparticulate additive. In particular, the function is an antimicrobial and / or a decorative effect.

0025A sol comprises at least one organometallic compound that hydrolyzes under defined conditions and condenses into a gel network. Si, Ti, Fe, Zn, Sn or Zr can be used as a metal component of the organometallic compound. The organometallic compound should contain at least 2 hydrolyzable groups, usually halogens or alkoxy radicals being used. Further radicals bonded to the metal atom can be any functional hydrocarbon chains or further hydrolyzable groups. The organometallic compound is used in the unhydrolyzed, hydrolyzed or partially condensed state. Widespread examples of such organometallic compounds are monomeric or polymeric silicic acid esters, polysilicates and polysiloxanes. In addition, disperse metal oxides can also be added to the sol if they are useful for improving certain properties. Dispere silica, e.g. B. can increase the scratch resistance, disperse titanium dioxide the hydrophilicity of the coating. In the case of decorative coatings in particular, care must be taken to ensure that there are only a few or no organic residues in addition to the hydrolyzable leaving group, since these decompose at high temperatures and can cause discoloration of the layer. TEAS or TMOS are therefore preferred as silanes.

0026The sol also contains a solvent in which the organometallic compound dissolves. To start the hydrolysis and polymerization reactions, an acid or a base and water are added. If an organometallic compound is used that already reacts with the air humidity (eg silicon tetrachloride), the addition of acid and water can be dispensed with. If the solvent is evaporated, the gel hardens through progressive condensation reactions. Ultimately, a metal oxide layer is created, which usually has a high scratch and abrasion resistance. A sol-gel coating is therefore a coating that is applied as a liquid sol to a substrate and condenses there to form a network, the gel. Depending on the starting sol, such layers can be produced in thicknesses between a few nanometers and several micrometers.

0027Additives, in most cases nanoparticles, are added to this sol, which in addition to the excellent layer properties produce at least one other function. Excellent antimicrobial properties can be achieved through the

0028Generate presence of a nanoparticulate metal. The sol-gel coating composition according to the invention can be used to produce coatings which have high transparency and resistance to external influences in addition to the antimicrobial effect. In the context of the present invention, the term “antimicrobial activity” is understood to mean all germicidal or germ-damaging effects, for example, an algicidal action, a fungicidal action or a bactericidal action.

0029Sol-gel coatings made from the sol-gel coating composition according to the invention change the optical properties of the substrate very little or not at all. In contrast to the acrylic lacquers known from the prior art, the optical properties of the substrate appear practically unchanged after the coating. In addition to the high transparency of the coating, there is also no light reflection, so the coating does not reflect.

0030The sol-gel coatings also have high scratch and abrasion resistance, high temperature resistance and high chemical resistance. By combining the antimicrobial properties with excellent mechanical and chemical resistance, the sol-gel coating composition according to the invention can be used in a large number of applications. Surface coatings with antimicrobial properties should basically meet two different requirements. On the one hand, the surface of the antimicrobially active constituents, that is to say the metal particles, should be as large as possible, since this achieves a high antimicrobial effect per amount of antimicrobial active ingredient used. On the other hand, in the vast majority of applications, a high transparency of the antimicrobial coating is expected. Experiments have shown that silver powder, silver oxide and other silver compounds do not have the required properties. The substances are always clumped, cannot be sufficiently dispersed and are therefore not suitable for the production of transparent layers. Only when a nanoparticulate metal is used in a sol-gel system does a coating agent become available that is suitable for the production of highly antimicrobial and at the same time transparent coatings. A nanoparticulate is preferred in the context of the present invention

0031Metal selected from the group consisting of nanoparticulate silver, nanoparticulate copper, nanoparticulate zinc and mixtures thereof. The antimicrobial effect of silver ions has been known for a long time. Silver has an excellent cytotoxic effect with a very low systemic toxicity. In addition, allergic reactions to silver are extremely rare. Like silver, copper has a very high cytotoxic effect with a very low systemic toxicity. Allergies to copper are also extremely rare. Zinc also has a very low systemic toxicity and allergenic effect, but a somewhat lower cytotoxic effect. Metallic particles with a "nanoparticulate metal" are

0032Grain size from 1 nm to 1000 nm. According to preferred embodiments of the present invention, metal particles with a grain size of 1 nm to 100 nm, particularly preferably with a grain size of 5 nm to 50 nm, are used. Due to their small diameter, these nanoscale metal particles are characterized by a very high specific surface, which ensures the antimicrobial effect even when low metal concentrations are added. Less than 5% by weight of metal particles are sufficient to achieve a reliable and long-lasting antimicrobial effect. According to a preferred embodiment of the present invention, the metal particles are in a concentration of 0.005 to 5% by weight, particularly preferably from 0.01 to 0.5% by weight and particularly preferably from 0.01 to 0.1% by weight. % used. In order to produce particularly high-quality antimicrobial sol-gel coating agents, the sol must be such that the metal particles remain largely dispersed in the sol. For this reason, according to an alternative embodiment of the present invention, surface-modified nanoparticulate metals are used. The surface of the nanoparticulate metal is preferably modified by binding (chemical bonding, adsorption, adhesion, etc.) a dispersing aid and / or an adhesion promoter. The surface of the nanoparticulate metal can be modified by linking functional silanes and / or linking polymers or oligomers with a high proportion of OH groups. These modifications influence the dispersibility of the metal particles in the sol and / or the adhesion of the metal particles in the coating. Particularly good results are achieved if the surface modification consists in the binding of the functional silane AMEO and / or the polymer PEG 200.

0033A similar improvement in the dispersion is achieved if the dispersing aid and / or the adhesion promoter is added to the sol. The

0034Additives attach to the metal particles and thus have an effect similar to that of a direct surface modification of the particles. Preferred examples of such additives are functional silanes, such as. B. AMEO, and / or poly- or oligomers with a high proportion of OH groups, such as. B. PEG 200. According to a preferred embodiment of the present invention, the antimicrobial sol-gel coating has a high surface roughness. If the surface roughness is high, the ratio of surface to volume, ie the ratio of the coating / air interface to the bulk phase of the coating, increases significantly. This increases the likelihood that metal particles will be present on the surface of the coating. Since the metal particles on the surface are essentially responsible for the antimicrobial effect, the efficiency of the metal addition increases with increasing roughness. Antimicrobial sol-gel coatings with sufficient surface roughness therefore require significantly less metal than coatings with a smooth surface for the same antimicrobial effect. Depending on the manufacturing process and layer thickness, the roughness can vary between 5 nm and 1000 nm. Roughnesses of 10 to 200 nm average roughness depth are preferred.

0035As already mentioned, the transparency of the antimicrobial coating is one of the particularly advantageous properties of the sol-gel coating according to the invention. The use of nanoparticulate metal makes it possible to produce extremely thin coatings that have sufficient transparency. According to a preferred embodiment of the present invention, the antimicrobial sol-gel coating therefore has a maximum thickness of 500 nm, preferably a maximum thickness of 200 nm.

0036In order to achieve a homogeneous distribution of the metal particles in the sol, they are preferably added to the sol as a dispersion. Preferred dispersants are organic solvents and water. The sol should be such that the metal particles, preferably silver particles, remain largely dispersed in the sol. In this context, it is important to adjust the pH and select a suitable solvent. According to an alternative embodiment of the present invention, a dispersing aid and / or an adhesion promoter is additionally added to the sol before the sol is applied to the substrate. The dispersing agent stabilizes the dispersion.

0037A sol-gel coating composition according to the invention with an antimicrobial function can be used, for example, for coating surfaces that are in contact with food. In particular, a sol-gel coating agent according to the invention can be used for coating refrigerator shelves. Further possible uses can be found, for example, in the sanitary area and in the medical area. For example, the surfaces of toilets, sinks, shower trays, tiles, countertops, etc. are provided with a coating according to the invention. Decorative coatings are produced by adding the components required to produce the decorative effect.

0038In the case of a sandblasted or etched effect, this component is generally a matting agent (see Examples 13 and 14), a silica or a mixture of different silicas, preferably a silica with particle sizes <10 μm, particularly preferably <0.5 μm. When using a mixture of different silicas, these can each have different grain sizes.

0039In the case of colored effects, inorganic pigments are used. It is particularly important to ensure that the color pigments are ground as finely as possible. Particle size <1 μm, in particular particle sizes <200 nm, are preferred here.

0040If necessary, additives such as emulsifiers or dipping aids can be added. Hydrophobic silicas are particularly suitable as auxiliaries. Depending on the type and grain size of the additives used and depending on

0041The method of application and intended use result in different layer thicknesses for decorative sol-gel coatings according to the invention. Usual layer thicknesses are up to 5 μm, in particular up to 1.5 μm.

0042After application, the layer is pre-hardened in a few minutes at room temperature. Higher temperatures can also be used for higher-boiling solvents or to shorten the pre-hardening time. Temperatures of up to 250 ° C are common here.

0043The layer can be cured at room temperature. In order to achieve a high scratch resistance of the coating within a reasonable period of time, curing preferably takes place at a temperature of approximately 400 to 450 ° C. Curing takes place particularly preferably at temperatures> 500 ° C. or> 800 ° C. A limitation of the curing temperature can result from the type and temperature resistance of the nanoparticulate additive and / or the substrate. The coating solution can be designed such that after the

0044Pre-curing allows processing of the substrate to which it is applied.

0045This can be an advantage, especially when coating glass, since a

0046Coating can take place before processing and before the tempering process.

0047The coating solution can be designed in such a way that the curing parameters correspond to the parameters of the glass tempering process. This allows the glass to be tempered and the coating to harden in a single operation. In particular, a link to the ESG process (production of safety glass) is advantageously possible in this way by the curing process and the tempering process being carried out in a common work step.

0048With this coating, a wide range of optical and haptic effects can now be displayed: The transmission of the coating ranges from almost 100% to 0%.

0049The coating can be adjusted from glossy to matt.

0050The feel of the coating varies from smooth to rough.

0051In any case, the coating is characterized by high abrasion and scratch resistance. The use of a sol-gel process for the production of functional sol-gel coatings results in the advantage that the sol is provided with additives and the coating can thus be cost-effectively tailored to individual requirements. According to a preferred embodiment of the present invention, at least one further type of functional molecule is present in the sol-gel coating composition. In addition to the function that has already been introduced, the layer is specifically provided with further properties. For example, the combination of the properties "antimicrobial" and "decorative" is possible. In this case, the coating agent has both the antimicrobial and the decorative additive.

0052In particular, a combination of the properties “antimicrobial” and / or “decorative” with “easy to clean” is advantageous for many applications. The field of use of such coatings extends from household appliances such as refrigerators or furniture to wall and floor tiles in the medical field The possible uses in the sanitary area already mentioned in the section "Antimicrobial Coatings" are included here.

0053If such easy-to-clean surfaces, so-called “easy-to-clean” or “anti-fingerprin” surfaces, are to be produced, then silanes with at least one hydro- and / or oleophobic residue are advantageously used as functional types of molecules. A particularly high “easy-to -Clean "effect can namely be achieved if the coating has both a hydrophobicity and an oleophobicity. Fluorinated hydrocarbon chains are particularly suitable as residues with hydro- and oleophobic properties. Silanes which contain at least one fluorinated hydrocarbon chain are very particularly preferred. Particularly preferred silanes have the general formula

0054(CF_aH_b) - (CF_vH_x)_n - (CF_yH_e.g.)_m - Si- (OR)₃ where: a + b = 3; v, x, y, z = independently of one another 0, 1 or 2 with v + x = 2 and y + z = 2; n = integer from 0 to 20, preferably 3 to 15, particularly preferably 5 or 7; m = integer from 0 to 10, preferably 0 to 5, particularly preferably 2;

0055R = halogen, alkyl radical of chain length C- to C₆, preferably C to C₃ or aminoalkyl radical of chain length Ci to C₆, preferably C to C₃.

0056All of the functional molecules mentioned can in principle also be applied subsequently to the first functional layer. It is important that this upper functional layer is very thin, i.e. has only a few molecular layers. In this way, the function of the underlying layer is not adversely affected. The second layer can be applied with all common coating methods such as dipping, spraying, knife coating, rolling etc.

0057The present invention also includes a functional sol-gel coating which consists of one of the functional sol-gel coating agents described, the coating agent being applied to a substrate. The substrate, ie the object to be coated or the surface to be coated of this object, can in principle consist of any material. Preferred substrates are metal, glass, ceramic, enamel, wood or plastic. Usually sufficient for substrates that have OH groups on the surface, such as. B. glass, ceramic or enamel, the adhesion and abrasion resistance of the coating without further treatment. The present invention also includes a method for producing the functional sol-gel coating described. In its simplest form, this process comprises the production of a sol with nanoparticulate additives, the application of the sol to a substrate and the hardening of the sol. The sol can be applied using all common coating methods such as dipping, spraying, knife coating, rolling, etc.

0058As already described, the functional coating should often be provided with additional properties. Therefore, at least one further type of functional molecule is preferably added to the sol before the sol is applied to the substrate. Such an additional property can also be achieved by applying a further layer. The second layer can be applied with all common coating methods such as dipping, spraying, knife coating, rolling etc. It is important that this upper functional layer is very thin, ie has only a few molecular layers. In this way the antimicrobial effect of the layer underneath is not negatively affected. The gel hardens either at room temperature or at elevated temperature. The temperature depends on the solvent and the layer thickness. In principle, very high temperatures can also be used if the functional nanoparticles permit this. Antimicrobial coatings are preferably cured for a few minutes at up to 200 ° C, while decorative coatings are preferably exposed to temperatures> 400 ° C. In both cases, however, it is also possible to use temperatures higher than those specified. A temperature limitation can result from the type and temperature resistance of the nanoparticulate additives and / or the substrate used as well as from the type of application and the associated requirements for the coatings. E.g. higher scratch resistance can be achieved more quickly by increasing the curing temperature. However, if the scratch resistance is not a requirement for the coating, energy-saving and inexpensive curing can take place at room temperature. The method according to the present invention is inexpensive and very easy to apply. The resulting coating is characterized not only by an outstanding antimicrobial or decorative effect, but also by high scratch and abrasion resistance, high temperature resistance and high chemical resistance. Furthermore, these layers can be made so thin that they do not change the optical properties of the substrate.

0059For particularly high demands on the adhesion of the coating and for substrates that do not allow sufficient adhesion of the coating, the substrate can be pretreated. According to a preferred embodiment of the present invention, the substrate is therefore subjected to a pretreatment step before the sol is applied. Preferred pretreatment steps are oxidation, treatment with acid, treatment with alkali, plasma treatment, corona discharge, flame treatment, flame silicification, UV radiation or sandblasting.

0060Ways of Carrying Out the Invention

0061I. Sol-gel coating with an antimicrobial effect

00621. Preparation of the coating solution

0063Example 1: 90 g of isopropanol are mixed with 23.0 g of tetraethoxysilane and briefly stirred for homogeneous distribution. Then 20.0 g of H₂O least. and then 4.5 g of 1m HCl are added and the mixture is briefly stirred again. Finally, 2.11 g of a 0.2% aqueous silver suspension are added and the mixture is stirred for 20 minutes. The silver particles contained in the silver suspension have a diameter of 10 to 15 μm. After a rest period of 2 hours, the solution is ready for use.

0064Example 2:

006570 g ethanol, 10.7 g H₂O deionized and 0.15 g of 1m HCl are briefly stirred together and 20.0 g of tetraethoxysilane are added. After stirring for 3 h, 1.7 g of a silver suspension (2000 ppm silver in H₂O, particle size about 20 nm) and stirred for a further 5 min.

0066Example 3:

006770 g ethanol, 10.7 g H₂O deionized and 0.15 g of 1m HCl are briefly stirred together and 20.0 g of tetraethoxysilane are added. After stirring for 3 h, 6.8 g of a silver suspension (2000 ppm silver in H₂O, particle size approx. 100 nm) and stirred for a further 5 min. Example 4:

006892.35 g isopropanol, 2.5 g H₂O deionized and 0.15 g of 1 M HCl are briefly stirred together and 5.0 g of tetraethoxysilane are added. After stirring for 3 h, 6.8 g of a silver suspension (2000 ppm silver in H₂O, particle size about 10 nm) and stirred for a further 5 min.

0069Example 5:

0070Solution 1: 33.33 g of a polysilicic acid ester and 5.33 g of TEOS are added to 53.33 g of ethanol and the mixture is briefly stirred to give a homogeneous distribution.

0071Solution 2: 1.6 g of 1 M HCl are added dropwise to 6.4 g of an aqueous colloidal silica solution (40% solids content) with stirring.

0072Solution 3: Solution 2 is added dropwise to solution 1 with stirring.

0073After stirring for 3 h, 6.8 g of a silver suspension (2000 ppm silver in H₂O, particle size about 10 nm) and stirred for a further 5 min.

0074Example 6:

007510.2 g of H are added to 70.1 g of ethanol₂O deionized and given 0.15g HCI. The mixture is then briefly stirred until homogeneous and then 19.5 g of TEOS are added. After stirring for 3 h, 6.7 g of a copper / titanium dioxide suspension (particle size approx. 50 nm) are added and the mixture is stirred for a further 5 min.

0076Coating

0077The coating solutions according to Examples 1 to 5 are applied using the customary coating methods (dipping, spraying, rolling) and then cured at 200 ° C. for 15 minutes. Alternatively, the coatings can also be applied at 80 ° C for 20 minutes or at 5 minutes

0078500 ° C can be cured. Antimicrobial test procedure: Quantitative evaluation of the effectiveness of antimicrobial agents in polymer and hydrophobic materials according to ASTM E 2180; Inoculum carrier: 0.3% technical agar; Inoculum: Staphylococcus aureus, final concentration in agar see table, 1 ml coating per sample; Incubation: Coating: 24h (+/- 2h) at 36 ° C (+/- 1 ° C), germ count: 48h (+/- 2h) at 36 ° C (+/- 1 ° C).

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00802nd Surface modification of the silver particles

0081Example 7:

008270.1 g ethanol, 10.2 g H₂O dist, 0.15 g of 1m HCl are briefly stirred together and 19.5 g of tetraethoxysilane are added. After 3 hours of stirring, 0.5 g of PEG are stirred in and then 6.8 g of a silver suspension (2000 ppm silver in HO, particle size approx. 10 nm) are added and stirring is continued for 5 minutes. The coating solution is then ready for use.

00833rd Improve liability

0084Example 8: An aluminum plate is immersed in a 4% aqueous AMEO solution and then dried at 80 ° C. for 2 hours.

0085The plate is then coated with a coating solution according to Examples 1 to 5.

0086Example 9: The substrate is flamed in a corresponding system, the

0087A suitable silane (e.g. HMDSO, hexamethyldisiloxane) is added to the flame.

0088The surface is now silicated, ie it contains an SiO₂ -Network with many SiOH groups that improve the connection of the antimicrobial layer.

0089The substrate is then coated with a coating solution according to Examples 1 to 5.

00904th Subsequent waterproofing

0091Example 10:

0092A glass plate coated with a coating solution according to Examples 1 to 5 is coated with a commercially available hydrophobic coating solution according to the instructions. Example 11:

0093A 1% solution of a fluorosilane (e.g. F8261 from Degussa) in an alcoholic solvent (e.g. ethanol) serves as the hydrophobic coating solution, which uses a dilute acid (e.g. ENT) as a catalyst₃) was added.

0094This solution is rubbed onto the antimicrobial coating with a cotton cloth.

0095II. Sol-gel coating with a decorative effect

0096Example 12: Solution 1: 33.33 g of a polysilicic acid ester and 5.33 g of TEOS are added to 53.33 g of ethanol and the mixture is briefly stirred until homogeneous.

0097Solution 2: 1.6 g of 1M HCl are added dropwise to 6.4 g of an aqueous colloidal silica solution (40% solids content) with stirring.

0098Solution 3: Solution 2 is added dropwise to solution 1 with stirring. This solution is mixed with 20 g color pigment (e.g. HEUCODUR^®blue 552 from

0099Heubach) and ground in a pearl mill.

0100Example 13:

0101Solution 1: 33.33 g of a polysilicic acid ester and 5.33 g of TEOS are added to 53.33 g of ethanol and the mixture is briefly stirred to give a homogeneous distribution. Solution 2: To 6.4 g of an aqueous colloidal silica solution

0102(40% solids content), 1.6 g of 1 M HCl are added dropwise with stirring.

0103Solution 3: Solution 2 is added dropwise to solution 1 with stirring.

0104Solution 4: 0.49 g of PEG 200 are dispersed in 1.46 g of ethanol using a disperser at the highest possible speed for about 15 min. Solution 3 and 1.34 g of a matting agent (e.g. Acematt^® TS 100 from Degussa) dispersed for a few minutes.

0105Example 14:

0106Solution 1: 33.33 g of a polysilicic acid ester and 5.33 g of TEOS are added to 53.33 g of ethanol and the mixture is briefly stirred to give a homogeneous distribution.

0107Solution 2: 1.6 g of HCl are added dropwise to 6.4 g of an aqueous colloidal silica solution (40% solids content) with stirring.

0108Solution 3: Solution 2 is added dropwise to solution 1 with stirring.

0109After stirring for 3 hours in solution 3, 3.375 g of hydrophobic silica (for example R 805 from Degussa) is first used as the dispersing aid and then a matting agent (for example Acematt)^® TS 100 from Degussa) dispersed.

0110Coating

0111The coating solutions according to Examples 1 to 5 are applied using the customary coating methods (dipping, spraying, rolling) and then cured at 450 ° C. for 5 minutes.

0112Alternatively, the coatings can also be cured for 3 minutes at 700 ° C.