Solution for producing a biodegradable coating, process for producing same, process for coating a substrate, and coated article produced according to said process

Abstract

The present invention relates to a solution for producing a biodegradable coating, to a process for producing same, to a process for coating a substrate with the solution according to the invention, and to a coated article produced according to said process.

Description

[0001] Fraunhofer Society...eV

[0002] P149848PC01

[0003] The present invention relates to a solution for producing a biodegradable coating, a method for producing it, a method for coating a substrate, and a coated object produced therewith.

[0004] A coating, a method for its production, a method for coating a substrate with the solution according to the invention, and a coated article produced therether. Coating agents are thin layers on materials that are applied to the surface of a substrate to improve or modify certain properties. Consumer goods such as cosmetics, personal care and household products, as well as pharmaceutical, agricultural and industrial products, use ingredients that enable these products to form a film or coating on various substrates such as keratinous substrates (e.g., hair and skin), hard surfaces (e.g., wood and metal), pharmaceutical dosage forms, medical devices, foodstuffs, plants, and other non-keratinous substrates (e.g., fabrics and objects).The components that contribute to the formation of a film or coating on the surface of a substrate can be selected from a variety of raw materials such as polymers, especially acrylate copolymers, polyvinylpyrrolidones, synthetic resins, for example polyurethane resins, acrylic resins and oils.

[0005] A disadvantage is their low biodegradability with environmentally harmful effects, so there is an intensive search for toxicologically and ecotoxicologically compatible alternatives that can be made available to the market at a low cost.

[0006] Finally, the pollution of the world's oceans by microplastics poses a major challenge to our society and is omnipresent in daily media reports. Measures, especially a switch to environmentally friendly material alternatives, are necessary. With this goal in mind, consumer goods such as cosmetic products should also be more strictly regulated in the future and be free of microplastics or other polymers that are not biodegradable or only very slowly biodegradable, such as silicones, polyethylene glycols, poly(vinyl) acrylates, polyvinyl alcohols, or synthetic surfactants. Such cosmetic additives currently enter the soil, inland waters, and the world's oceans in enormous quantities via agricultural sewage sludge from wastewater treatment plants, where they are increasingly accumulating.Due to increased environmental awareness, pressure is steadily growing, especially among consumers, to make cosmetic products more environmentally friendly and to avoid microplastics. This is already leading to a noticeable increase in the availability of new natural cosmetic products in drugstores, pharmacies, and beauty salons.

[0007] Nevertheless, the search for functional substitutes proves extremely difficult.

[0008] For example, hair cleansing products (shampoos) can now deliver satisfactory results without problematic substances such as silicones or synthetic emulsifiers. However, the market is still searching for "green" alternatives, especially in the area of ​​hairsprays. Currently, most state-of-the-art hairsprays use petroleum-based, i.e., non-biodegradable, polyvinylpyrrolidone derivatives or silicones dissolved in water / alcohol mixtures, along with other additives such as surfactants, film improvers, or sunscreens. When sprayed onto the hair, the alcohol evaporates, and the polymers (polyvinylpyrrolidone derivatives or silicones) adhere to each individual hair, resulting in a stiffened hold.This hair coating is barely water-soluble, so the polymers are released into the wastewater and ultimately the environment during showering as "microplastics"—partly as non-biodegradable polymer strands, partly as abrasion in the form of microplastic particles. A replacement with natural organic polymers (e.g., chitosan) does not currently appear to be gaining traction in the market. Furthermore, such natural cosmetic hair-strengthening products are currently only offered as hair tonics and not as hairsprays. It is currently not possible to spray natural organic polymers like chitosan from pressurized bottles over an extended period of use. After just a few applications, these polymers clog the nozzle openings, rendering the product unusable. Customer acceptance can only be expected by developing a "green" hairspray. Another approach is the use of shellac from the lac insect.While such products can deliver satisfactory results as hairsprays, their animal-derived origin makes them less acceptable in the natural cosmetics sector. A vegan alternative is desirable.

[0009] Therefore, developing a natural, vegan, and biodegradable hairspray presents a significant chemical and technological challenge, entailing several development risks. In particular, suitable natural and vegan hairspray substances must be identified that can be sprayed without clogging pressure valves. Furthermore, to improve customer acceptance, new, innovative hair styling products should not only ensure the hairstyle stays in place but also care for the hair and scalp.

[0010] In the pharmaceutical industry, film-coated tablets are coated with layers that consist largely of non-biodegradable polymers, such as polyacrylate-based polymers or polyvinylpyrrolidones. Naturally derived polymers, such as synthetic cellulose ethers, are also used. However, all these coatings contain additives such as plasticizers, which ultimately enter the human body and the environment.

[0011] Alternative coating products are also urgently needed for other substrates, such as seeds, fruit, vegetables, mushrooms, etc., instead of the conventional waxes used so far.

[0012] In addition to organic natural substances, inorganic molecules can also be used. For example, the only water-soluble form of silicic acid, monosilicic acid (MKS) - Si(OH)4 -, is bioactive. Scientific studies demonstrate a positive influence not only on skin and hair (Nakanashi et al., Med. Cutan. Iber. Lat. Am. 2017, 45, 29-35; de Auraujo et al., An. Bras. Dermatol. 2016, 91, 331-335), but also on bone formation and a therapeutic potential in terms of preventing Alzheimer's disease (Jurkic et al., Nutrition & Metabolism 2013, 10, 2-12).

[0013] Dissolved calcium carbonate (MC) is naturally absorbed by plants through water and metabolized within the plant to polysilicic acids. For example, polysilicic acids give bamboo and horsetails their high mechanical stability. Various grains (e.g., rice), tubers (e.g., potatoes), and fruits also store higher concentrations of polysilicic acids, which are ingested by humans and animals through the food chain (Currie et al., Annals of Botany, 2007, 100, 1383-1389). Accordingly, silicic acids are ubiquitous in the organisms of humans and animals through food and drinking water intake. After excretion, these polysilicic acids, as dissolved, metabolized MC, re-enter soils and water bodies, thus completing the nutrient cycle.

[0014] The production of silica clusters is well-documented in the literature and schematically illustrated in Figure 1. This process involves a sol-gel reaction in which, in the first step, a tetraalkoxysilane is hydrolyzed under acidic catalysis to form a hydroxysilane, which then condenses into silica clusters in the second step. The following scheme illustrates the sol-gel reaction using the hydrolysis and condensation of TEOS (tetraethoxyethylsilane) as an example. TEOS Si(OC₂Hs)₄ is dissolved in water and / or alcohol, and an acid is added as a catalyst. The TEOS molecules hydrolyze to form silanol groups. These silanol groups condense to form silicon-oxygen bonds (Si-O-Si), releasing water or alcohol. This reaction leads to the formation of silica clusters.

[0015] Figure 1 shows stable silica clusters containing Si atoms Q2 (green residues) and Q3 (blue residues). Figure 1 (left) provides an overview of the basic building blocks of stable silica clusters (from: Chem. Rev. 2021, 121 (15), 9674-9718). Each Si atom is saturated and 4-coordinate. For clarity, reactive terminal silanol and ethoxy groups are not shown. Figure 1 (right) illustrates reactive terminal groups on two selected silica clusters, which can undergo intermolecular crosslinking reactions. These low-molecular-weight silica clusters mainly contain reactive terminal functional groups, -Si-OH or -Si-OR, where R represents an alkyl group (linear, branched, saturated, unsaturated) that can react with each other to form high-molecular-weight silica clusters.

[0016] The TEOS-based synthesis is schematically depicted in Figure 2. Figure 2 shows a reaction scheme for the production of reactive silica species in ethanol cider or bioethanol. A defined reaction process controls the parallel hydrolysis and condensation reactions starting from the liquid sol-gel precursor TEOS. The process can be controlled to produce defined silica clusters by adjusting parameters such as temperature, time, concentration, or the use of microwave technology.

[0017] By controlling the reaction conditions, such as pH, temperature, time, and concentration of reactants, the size and properties of the silica clusters can be controlled. At low temperatures and sufficient dilution, the reactivity is reduced, allowing the production of low-molecular-weight silica clusters.

[0018] EP 2 152 785 Al relates to a polyethoxysiloxane (PES)-IV material obtained by (a) carrying out a first hydrolysis-condensation reaction (HCR) of at most one residue X of one or more different Si compounds of formula I SiX4 (I), in which the residues X are the same or different and denote hydroxy, hydrogen or ethoxy (EtO), acid-catalyzed at an initial pH of 0 to < 7, in the presence of ethanol (EtOH) or an ethanol-water mixture as solvent, over a period of 1 to 24 h at a temperature of 0°C to 78°C, (b) carrying out a second HCR of the material obtained in step (a) with simultaneous removal of the solvent by successive evaporation in a gas-diffusion-tight container at a pressure of 100 to 1013 mbar; preferably at a slight vacuum of 300 mbar to 800 mbar and a temperature of 50 to 78°C until a drastic increase in viscosity occurs (at a shear rate of 10 s).1 (at 4°C) to 0.5 to 2 Pa s, until constant weight and until the formation of a cyclotetrasiloxane of the general formula ((Si)(OH)o,7s(OEt)i,25 x 1 / 64 H2C 4 and a molar mass of 4 * approx. 114 g = approx. 456 g, is carried out; (c) this PES material is cooled in a closed container over a period of a few minutes to a few seconds and (d) the PES material obtained from (c) is converted into an rPES material by a third HKR.

[0019] DE 10 2014 224 654 Al describes a biodegradable silicate hybrid material containing silsesquioxanes and an organic multi-armed linker, wherein the organic multi-armed linker has at least one of the compounds I and is covalently bonded to the silsesquioxanes.

[0020] The object of the present invention is therefore to provide a way to provide substrates with a coating that is biologically safe and readily biodegradable, in a virtually universal manner.

[0021] This problem is solved with regard to a solution for producing a biodegradable coating with the features of claim 1, with regard to a method for producing the solution with the features of claim 13, with regard to a method for coating a substrate with the features of claim 14, and with regard to a coated article produced theretherwith with the features of claim 18. The dependent claims relate to advantageous embodiments. The coating should also exhibit improved biocompatibility, in particular as determined according to DIN ISO 10993-5:2009. In a first aspect, the present invention thus relates to a solution containing silica clusters, producible according to a method comprising the following steps: a) providing at least one alcoholic solution of at least one silane compound selected from the group consisting of tetraalkoxysilanes and mixtures thereof;b) Providing an aqueous solution of at least one acid with a pKa value of < 2.5; c) Mixing the solutions provided in steps a) and b) and mixing thoroughly for 2 hours to 1 week at a temperature of >20 to 70°C; d) Removing at least some of the alcohol from the mixture from step c) and subsequently cooling the concentrated mixture to a temperature of 20 to -25°C; e) Storing the cooled mixture from step d) until a viscosity of 10 to 75 Pa-s is reached; and f) Diluting the solution with an alcohol until a viscosity of 1 mPa-s to <10 Pa-s is reached and / or the solution is diluted to a dry residue content of 0.1 to < 50 wt%, whereby during steps c) to e) crosslinking of the silane compound occurs and at least some of the acid is incorporated into the resulting network via covalent bonds and / or contributes to the crosslinking.

[0022] “Biodegradability” within the meaning of the present invention refers to the property that the coating can be degraded to MKS via, for example, hydrolysis reactions and does not exhibit any toxic properties to humans or other living organisms, such as animals, bacteria, plants, and fungi. Using humans as an example, the coating and its degradation products were tested according to DIN ISO 10993-5:2009 and classified as cytocompatible.

[0023] For the purposes of the present invention, the term "viscosity" means the dynamic viscosity, which is preferably measured using a rheometer of type Physica MCR301 from Anton Paar with a coaxial cylinder measuring attachment of type CC17 / T200 / SS and a shear rate of 10 s⁻¹. 1 is determined at 23 °C.

[0024] The procedure according to steps a) to e) is described in detail in WO 2019 / 068533 Al, the disclosure content of which for carrying out steps a) to e) is therefore also incorporated into the present invention.

[0025] The described process allows the production of silica clusters that can be stored in dispersion or solution, yet are reactive enough to chemically crosslink in situ, i.e., during the coating process, without a subsequent annealing step, forming a homogeneous film on various surfaces. Due to the amorphous nature of the layer, it is completely biodegradable to molecular weight silica (MBS) upon contact with aqueous solution. Therefore, only a natural molecule, MBS, is released into the environment after degradation.

[0026] The synthesis procedure of steps a)-e) according to claim 1 yields condensation products of alkoxysilanes, which exist in the form of viscous sols. Surprisingly, despite the high viscosity, the system is not directly at the gel point, but contains defined silicon oxo clusters, as demonstrated by dynamic light scattering (DLS). These clusters exhibit a narrowly defined size distribution and are not, as expected, highly polydisperse.

[0027] Step f), dilution with an alcohol, leads to a further separation of these clusters and inhibits their further reaction to form a gel. The result is a homogeneous sol of silicon oxo clusters of defined molecular size (DLS), which is free of gel-like components. This is surprising because, in typical dilutions of viscous sols, gel-like components ("clumps") form, which sediment and do not result in a homogeneous liquid.

[0028] Only step f) produces a sol that can be conveyed through hoses without technical problems and applied uniformly to substrates using wet chemical methods. A homogeneous coating is only possible with such uniform sols, as otherwise inhomogeneous layer formation and uneven drying would occur. The dilution carried out in step f) ensures that the resulting clusters do not agglomerate and thus gel, and therefore remain stable during storage. The resulting solution is thus stable.

[0029] Furthermore, it was surprisingly found that the particle size distribution is very narrow, as demonstrated by the small half-width of the particle size distribution. This is particularly advantageous for coatings. The clusters of nearly uniform size interact with the substrate in the same way and, due to their similar reactivity, exhibit homogeneous cross-linking during solvent evaporation. This allows them to form homogeneous layers, which can therefore be very planar and lack particulate topography. This is surprisingly due to the low degree of chemical cross-linking of the clusters according to the invention. The molecular cluster shape is still sufficiently flexible to adapt three-dimensionally during layer curing and to change its formation during layer formation.With nanoparticulate coating sols, this flexible shape adaptation is not guaranteed, and the particles can be seen within the coating. The coatings therefore turn out inhomogeneous and visually unappealing.

[0030] The silica clusters according to the invention preferably have a mean particle diameter (number mean) of <80 nm, more preferably of 2 to 70 nm, and more preferably of 2 to 60 nm. The mean particle diameter can be determined using conventional analytical methods, e.g., dynamic light scattering (DLS, e.g., with a ZetaSizer, Malvern). The individual diameters of a statistically representative number of clusters (e.g., several hundred) are measured and summarized in a size distribution. The number mean is calculated by taking the arithmetic mean of the measured diameters.

[0031] The clusters preferably exhibit an extremely sharp particle size distribution with a full width at half maximum (FWHM) of <50 nm, preferably <40 nm, and more preferably <30 nm.

[0032] The coatings do not require the incorporation of additives, such as plasticizers, which are necessary, for example, in polymer coatings.

[0033] The production process can be carried out entirely in the absence of alkaline reagents – and therefore always in acidic conditions.

[0034] When living organisms, e.g. mammals including humans, come into contact with the manufactured coatings, no substances enter the organism that are not virtually ubiquitous in nature, namely FMD.

[0035] The toxicological and ecotoxicological compatibility of this class of substances is therefore extremely advantageous.

[0036] Silica clusters can be synthesized from a liquid sol-gel precursor by reacting tetraalkoxysilanes, water, and alcohol under acidic catalysis. Siloxane bridges (Si-O-Si bonds) are formed via hydrolysis and condensation reactions.

[0037] The resulting silica clusters are low-molecular-weight and stable in alcohol for months; they polymerize and only upon application of the solution to produce a coating, e.g., by a spraying process, onto a substrate, forming higher-molecular-weight compounds and finally a chemically cross-linked layer. This allows for the formation of closed films on surfaces, e.g., coating hair to strengthen it.

[0038] These low molecular weight silica clusters contain, in addition to the Si-(0Si-)4 groups, reactive terminal functional groups, -Si-OH or -Si-OR, where R stands for an alkyl group, which can react with each other to form high molecular weight silica clusters.

[0039] According to an advantageous embodiment, the silane compound selected in step a) in the process is a mixed or unmixed tetraalkoxysilane according to the general formula Si(OC xH2x+i)4 with x = 1-12, which is preferably selected from the group consisting of tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and mixtures thereof, wherein tetraethoxysilane is particularly preferred. Furthermore, it is preferred that in the process the alcohol from step a) is a monohydric, dihydric or trihydric, branched or unbranched alcohol, which may be aliphatic or aromatic and which is preferably selected from the group consisting of ethanol, propanol, butanol, ethylene glycol, phenol and mixtures thereof, wherein ethanol is preferred.

[0040] It is further advantageous that in the process the acid in step b) is selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, sulfurous acid, sulfonic acids, in particular methanesulfonic acid, carboxylic acids, carboxylic esters, sulfuric acid esters, amino acids, phosphonic acids, phosphoric acid esters, phytic acid and mixtures thereof, wherein nitric acid and methanesulfonic acid are particularly preferred.

[0041] Alternatively or additionally, it is equally preferred that the acid in step b) is 0.01 to 1 N and particularly preferably 0.1 N.

[0042] The acid content in the aqueous solution from step b) is advantageously in the range of 0.01 to 2.0 wt.%, preferably 0.05 to 1.0 wt.% and particularly preferably 0.1 to 0.5 wt.%, based on the total weight of the solution.

[0043] Further preferred embodiments – which may be given alternatively or cumulatively – provide that in the process, the mixing in step c) is carried out by adding the aqueous solution of the acid dropwise to the alcoholic silane solution; or the mixing in step c) is carried out by adding the alcoholic silane solution dropwise to the aqueous solution of the acid; or the mixing in step c) is carried out by simultaneously combining the alcoholic silane solution and the aqueous solution of the acid; and / or the mixing according to step c) is carried out by stirring or shaking; and / or the mixture from step c) is stirred for 2 hours to 168 hours, preferably 4 to 24 hours and particularly preferably for 6 to 18 hours; and / or the temperature in step c) is 20 to 70°C, preferably 20 to 50°C and particularly preferably 25 to 40°C; the pH value of the mixture in step c) is < 5, preferably 1 to 4.9 and particularly preferably 4 to 4.9.It is further preferred that during step d) of the process, 40 to 80 wt.%, preferably 45 to 75 wt.% and particularly preferably 50 to 65 wt.% of the solvent mixture, based on the total mass of the batch provided in step b), is removed; and / or the concentrated mixture from step d) is cooled to a temperature of 20 to -25°C, preferably 10 to -25°C and particularly preferably 4 to -20°C; and / or during step d) at least some of the water from step b) is also removed; and / or during step f) the solution is diluted to a dry residue content of 0.1 to < 50 wt.%, preferably 0.5 to < 20 wt.%, particularly preferably between 1 and < 10 wt.%.

[0044] In the process, step e) is preferably carried out until a viscosity of 10 to 70 Pa-s, preferably 15 to 40 Pa-s and particularly preferably 20 to 25 Pa-s is reached.

[0045] It is also advantageous that in the process in step f) the alcohol is identical to the alcohol used in step a).

[0046] In step a), exactly one alcohol can be used as a solvent and / or exactly one silane compound is dissolved in the solution from step a).

[0047] It is also possible that in step b) an aqueous solution of exactly one acid is provided.

[0048] The process used to produce the solution can be carried out continuously or in batches.

[0049] The solution according to the invention can further comprise at least one active ingredient. This can be in the form of molecules, polymers, ions, or particles. In particular, the active ingredient is selected from the group consisting of pharmaceutical active ingredients or excipients, cosmetically active substances, plant protection products, in particular herbicides, fungicides, insecticides, pesticides, preservatives, food additives, flavorings, fragrances, colorants, chelating additives, in particular carboxylic acid derivatives, pheromones and other attractants, natural products, in particular poly- and oligosaccharides, proteins and protein fragments, resins, oils, fats, fatty acids and derivatives, lignins and lignin derivatives, (partially) functionalized natural products, in particular cellulose ethers such as methylhydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose, wherein preferably, in the process, the at least one active ingredient is introduced into the solution according to step f).

[0050] Preferred active ingredients in the form of molecules, polymers, proteins, ions and particles include, for example,

[0051] • pharmaceutical excipients

[0052] • Natural substances (polysaccharides, resins, waxes, proteins, lipids, fatty acids and fatty acid esters, lignins and lignin derivatives)

[0053] • Partially natural, functionalized substances (ethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, etc.)

[0054] • Dietary supplements, such as vitamins, fiber, fats, flavorings, fragrances

[0055] • Dyes

[0056] • Plant protection products, in particular herbicides, fungicides, insecticides, pesticides

[0057] • Fertilizers

[0058] • Pheromones

[0059] • synthetic polymers

[0060] The active ingredients can be integrated at different points during the preparation of the solution. The active ingredient can be stirred in directly in pure form as a powder or liquid, or it can be pre-dissolved in a solvent (preferably ethanol) or added as a liquid formulation, e.g.

[0061] 1) after step c)

[0062] 2) after step d) - if the active ingredient was pre-dissolved in ethanol, the added ethanol can be removed again.

[0063] 3) after or during step f) If an active ingredient is contained in the solution, it is preferably contained in an amount, based on the total amount of the solution, of 0.01 to 40 wt.%, preferably of 0.5 to 20 wt.%, particularly preferably of 1 to 20 wt.%.

[0064] According to a further aspect, the present invention relates to a method for producing a solution containing silica clusters, comprising the following steps: a) providing at least one alcoholic solution of at least one silane compound selected from the group consisting of tetraalkoxysilanes and mixtures thereof; b) providing an aqueous solution of at least one acid having a pKa value of < 2.5; c) mixing the solutions provided in steps a) and b) and mixing thoroughly for 4 hours to 1 week at a temperature of >20 to 70°C; d) removing at least some of the alcohol from the mixture from step c) and subsequently cooling the concentrated mixture to a temperature of 20 to -25°C; e) storing the cooled mixture from step d) until a viscosity of 10 to 75 Pa·s is reached;and f) diluting the solution with an alcohol until a viscosity of 1 mPa-s to <10 Pa-s is reached and / or the solution is diluted to a dry residue content of 0.1 to < 50 wt%, wherein during steps c) to e) crosslinking of the silane compound takes place and at least part of the acid is incorporated into the resulting network via covalent bonds and / or contributes to the crosslinking.;

[0065] Regarding the details of the procedure, reference is made to the preceding statements.

[0066] Furthermore, the present invention relates to a method for coating a substrate, in which a solution according to the invention as described above, or a solution produced by a method according to the invention, is applied at least partially or completely to a surface of a substrate, excluding a post-condensation step of the silica clusters. The coatings according to the invention are formed in this process.

[0067] It is preferred that a drying step is carried out after the application of the solution, in which heating of the coating to above 120 °C, preferably above 100 °C, particularly preferably above 80 °C is excluded.

[0068] The solution can be applied, for example, by spray coating, dip coating, rotary coating, plasma coating, roller coating, doctor blade coating, brushing, pouring, drum coating process, doctor blade coating, spin coating, doctor blade coating, slot nozzle application, drum coating, fluid bed coating or by means of the Wurster process.

[0069] The resulting coating thicknesses range from 10 nm to 1 mm. This depends heavily on the coating method: dip coating, for example, results in layers < 1 pm. Fluidized bed coatings result in layer thicknesses of > 1 pm up to several hundred pm.

[0070] Preferred layer thicknesses are between 10 nm and 1 mm, preferably between 100 nm and 200 pm, particularly preferably between 1 pm and 100 pm.

[0071] In particular, the substrate can be selected from the group consisting of

[0072] Hair, fur and pelts, human and animal body parts, tissues and cells, such as skin, fingernails and toenails, hooves, feathers,

[0073] Plant substrates, in particular seeds, seedlings, fruit, vegetables, salad, nuts, plants, plant parts, in particular leaves and roots, algae, lichens,

[0074] Insects, especially pest insects such as aphids, tortrix moths and oak processionary caterpillars,

[0075] Fungi, single-celled organisms, like bacteria

[0076] Unprocessed and processed foods as well as pet food

[0077] Dietary supplements

[0078] Pharmaceutical products, especially tablets, such as film-coated tablets,

[0079] Medical devices, in particular implants or contact lenses

[0080] Scaffolds for in-vitro cell culture

[0081] Washing and cleaning products, in particular dishwasher tablets and laundry detergent tablets

[0082] Fertilizer

[0083] Biodegradable (disposable) products, especially plates, bowls, cups and cutlery.

[0084] Furthermore, the present invention relates to a coated object comprising a substrate and a coating applied at least partially to the substrate, produced according to a method for coating a substrate as described above.

[0085] Furthermore, the coatings according to the invention can find applications in the future not only in cosmetics, such as hairspray, hair gel, or nail polish, but also in other fields. Due to their biocompatible and ecotoxicologically safe nature, these coatings can also be applied, for example, in pharmaceuticals (e.g., coating of dosage forms), agricultural technology (e.g., coating of plants and other living organisms, but also fruits, nuts, vegetables), medical technology (coating of non-, partially, and fully resorbable implants), insect control (coating of and against pest insects), the food industry (coating of food, food supplements, or ingredients), or animal care / feed (coating of body parts such as hooves, claws, feathers, etc.).

[0086] Examples of how to perform DLS measurements:

[0087] To determine the mean particle size (number-mean), the samples were diluted 1:10 with ethanol and filtered through a syringe filter (pore size 200 nm). The mean particle diameter was determined by dynamic light scattering (DLS) using a ZetaSizer ZS (Malvern Instruments, UK). Measurements were performed as a triplet assay with at least 12 runs per measurement at 20 °C. The DLS laser had a wavelength of 633 nm, and the scattered light was measured at 173 °C in polystyrene cuvettes (No. 67.754, Sarstedt AG & Co. KG, Germany). Data analysis was performed using OriginPro 2021 software (Origin Lab Corporation, USA).

[0088] Synthesis example 1:

[0089] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed with 290 mL of ethanol. Over 2 h, 0.02 mol of methanesulfonic acid (MSS) in a 0.1 N solution (163 g) are added dropwise to this sol and stirred for 18 h at 40 °C. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 20 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 5.0 wt% and exhibits a viscosity of 1.9 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar. The mean particle diameter was calculated from three separate DLS measurements as described above, taking the arithmetic mean, to be 2.9 nm (20: 1.3 nm, R). 2 : 0.95 nm, FWHM: 1.5 nm) determined (Fig. 3).

[0090] Synthesis example 2:

[0091] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed with 290 mL of ethanol. A 0.1 N nitric acid solution (176.4 g) is added dropwise to this sol over 2 h and stirred for 18 h at 40 °C. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 30 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 10.0 wt% and exhibits a viscosity of 2.1 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar. The mean particle diameter was calculated from three separate DLS measurements as described above, taking the arithmetic mean, to be 56.9 nm (20: 22.3 nm, R). 2 : 0.97 nm, FWHM: 26.3 nm) determined (Fig. 4).

[0092] Synthesis example 3:

[0093] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed with 290 mL of ethanol. Over 2 h, 150 mL of a 0.1 N phytic acid solution is added dropwise to this sol, and the mixture is stirred at 40 °C for 18 h. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 25 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 3.0 wt% and exhibits a viscosity of 2.0 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar.

[0094] Synthesis example 4:

[0095] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed in 290 mL of ethanol. Over 2 h, 0.02 mol of methanesulfonic acid (MSS) in a 0.1 N solution (163 g) are added dropwise to this sol and stirred for 48 h at 30 °C. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 20 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 20.0 wt% and exhibits a viscosity of 2.4 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar.

[0096] Synthesis example 5:

[0097] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed in 290 mL of ethanol. Over 2 h, 0.02 mol of methanesulfonic acid (MSS) in a 0.1 N solution (163 g) are added dropwise to this sol and stirred at 60 °C for 24 h. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 20 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 2.0 wt% and exhibits a viscosity of 2.1 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar.

[0098] Synthesis example 6:

[0099] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed in 290 mL of ethanol. Over 2 h, 0.02 mol of methanesulfonic acid (MSS) in a 0.1 N solution (163 g) are added dropwise to this sol and stirred for 12 h at 60 °C. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 20 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 4.0 wt% and exhibits a viscosity of 1.9 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar.

[0100] Synthesis example 7 (including integration of active ingredients):

[0101] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed in 290 mL of ethanol. Over 2 h, 0.02 mol of methanesulfonic acid (MSS) in a 0.1 N solution (163 g) are added dropwise to this sol and stirred for 18 h at 40 °C. Solvent is then removed from the sol using a rotary evaporator until a viscosity of 1 Pa s is reached. 5 wt% octenidine is dissolved in this sol as the active ingredient. The sol is then matured at -20 °C to a honey-like viscosity of 20 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 5.0 wt% and has a viscosity of 2.0 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar.

[0102] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed in 290 mL of ethanol. Over 2 h, 0.02 mol of methanesulfonic acid (MSS) in a 0.1 N solution (163 g) are added dropwise to this sol and stirred for 18 h at 40 °C. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 20 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 5.0 wt% and exhibits a viscosity of 1.8 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar. 5 wt% of the active ingredient is dissolved in this sol.

[0103] Synthesis example 9 (including integration of active ingredients):

[0104] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed in 290 mL of ethanol. Over 2 h, 0.02 mol of methanesulfonic acid (MSS) in a 0.1 N solution (163 g) are added dropwise to this sol and stirred at 40 °C for 18 h. Subsequently, 1 m% of the active ingredient (Fe₂O₃ nanoparticles) is dispersed in the sol. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 20 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 5.0 wt% and exhibits a viscosity of 1.9 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar.

[0105] Synthesis example 10 (including integration of active ingredients):

[0106] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed in 290 mL of ethanol. Over 2 h, 0.02 mol of methanesulfonic acid (MSS) in a 0.1 N solution (163 g) are added dropwise to this sol and stirred for 18 h at 40 °C. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 20 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 5.0 wt% and exhibits a viscosity of 1.9 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar. 10 wt% rosin was then dissolved in the sol.

[0107] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed in 290 mL of ethanol. Over 2 h, 0.02 mol of methanesulfonic acid (MSS) in a 0.1 N solution (163 g) are added dropwise to this sol and stirred for 18 h at 40 °C. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 20 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 5.0 wt% and exhibits a viscosity of 1.9 mPa s. To determine the dry residue, the sol was dried in a vacuum drying oven for 18 h at 40 °C and 50 mbar. 0.8 wt% tannic acid is then dissolved in the sol.

[0108] Synthesis example 12 (including integration of active ingredients):

[0109] In a 2-liter round-bottom flask, 5 mol (1042 g) of tetraethoxysilane are mixed in 290 mL of ethanol. Over 2 h, 0.02 mol of methanesulfonic acid (MSS) in a 0.1 N solution (163 g) are added dropwise to this sol and stirred at 40 °C for 18 h. Solvent is then removed from the sol using a rotary evaporator to a viscosity of 1 Pa s and subsequently matured at -20 °C to a honey-like viscosity of 20 Pa s. The resulting sol is then diluted with ethanol to a dry residue of 5.0 wt% and exhibits a viscosity of 1.9 mPa s. 0.5 wt% soy protein is then dissolved in the sol.

[0110] Coating example 1:

[0111] A sol produced according to synthesis example 1 was applied to tablets using a fluidized bed system (Glatt, Mini). For this purpose, 70 g of tablets (diameter: 6 mm) were coated for 20 minutes at an oven temperature of 50 °C with a fluidized bed pressure of 55 m³ / h and a nozzle pressure of 1.5 bar (nozzle diameter: 0.5 mm). The sol consumption was 20 g.

[0112] The result was a homogeneous coating of the entire tablet surface. The layer thickness was approximately 10 pm.

[0113] Coating example 2:

[0114] A sol produced according to synthesis example 1 was applied to seeds using a fluidized bed system (Glatt, Mini). For this purpose, 50 g of rye seeds (diameter: 6 mm) were coated for 20 minutes at an oven temperature of 40 °C with a fluidized bed pressure of 55 m³ / h and a nozzle pressure of 1.5 bar (nozzle diameter: 0.8 mm). The sol consumption was 20 g.

[0115] The result was a homogeneous coating on the seeds.

[0116] Coating example 3:

[0117] A sol produced according to synthesis example 4 was applied to a fingernail with a brush. The result was a clear, homogeneous coating on the fingernail.

[0118] Coating example 4:

[0119] A sol prepared according to synthesis example 4 was applied to a fingernail with a brush. After the solvent evaporated, a homogeneous film remained on the fingernail, which could be removed after thorough cleaning with water.

[0120] Coating example 5:

[0121] A sol prepared according to synthesis example 1 was filled into a commercially available spray bottle (pump spray) and sprayed onto the leaves of a hazelnut tree. This resulted in the formation of a layer on the leaf.

[0122] A sol prepared according to synthesis example 5 was placed in a cuvette. A flat glass substrate was coated using a dip coating system (drawing speed: 5 cm / min). The result was a transparent film with a layer thickness of < 1.0 pm.

[0123] Coating example 7:

[0124] A sol produced according to Synthesis Example 7 was applied to a glass contact lens via rotational coating. 400 pL of the sol was deposited onto the contact lens at a rotational speed of 160 rpm and accelerated from 333 rpm / s to 3000 rpm. This final rotational speed was maintained for 40 s, resulting in a transparent layer. A sol from synthesis example 1 was placed in a dipping bath. Apples were immersed in it. The result was a transparent film with a layer thickness of < 1.0 pm. Coating example 9:

[0125] A sol according to synthesis example 1 was filled into a spray bottle. The coating solution was sprayed onto aphids and oak processionary caterpillars, so that they and the plant were coated. Coating example 10:

[0126] One sol each from synthesis examples 9, 10, and 11 was applied to seeds using a fluidized bed system (Glatt, Mini). For this purpose, 50 g of buckwheat seeds (diameter: 6 mm) were processed at an oven temperature of 40 °C with a fluidized bed pressure of 55 m⁻¹. 3 The coating was applied at a rate of / h and a nozzle pressure of 1.5 bar (nozzle diameter: 0.8 mm) for 20 minutes. Sol consumption was 20 g.

[0127] The result was always a homogeneous coating on the seeds.

Claims

Fraunhofer Society e.V. P149848PC01 Patent claims 1. Solution containing silica clusters, prepareable by a process comprising the following steps: a) providing at least one alcoholic solution of at least one silane compound selected from the group consisting of tetraalkoxysilanes, and mixtures thereof; b) providing an aqueous solution of at least one acid having a pKa value of < 2.5; c) mixing the solutions provided in steps a) and b) and mixing thoroughly for 2 hours to 1 week at a temperature of >20 to 70°C; d) removing at least some of the alcohol from the mixture from step c) and subsequently cooling the concentrated mixture to a temperature of 20 to -25°C; e) storing the cooled mixture from step d) until a viscosity of 10 to 75 Pa·s is reached; and f) diluting the solution with an alcohol until a viscosity of 1 mPa-s to <10 Pa-s is achieved and / or the solution is reduced to a dry residue content of 0.1 to < 50 wt.-% is diluted, whereby during steps c) to e) a crosslinking of the silane compound takes place and at least part of the acid is incorporated into the resulting network via covalent bonds and / or contributes to the crosslinking.

2. Solution according to claim 1, characterized in that, in the process, the silane compound selected in step a) is a mixed or unmixed tetraalkoxysilane according to the general formula Si(OC x H2x+i)4 with x = 1-12 is the one that is preferentially selected from the group consisting of tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and mixtures thereof, wherein tetraethoxysilane is particularly preferred.

3. Solution according to one of the preceding claims, characterized in that in the process the alcohol from step a) is a monohydric, dihydric or trihydric, branched or unbranched alcohol, which may be aliphatic or aromatic and which is preferably selected from the group consisting of ethanol, propanol, butanol, ethylene glycol, phenol and mixtures thereof, wherein ethanol is preferred.

4. Solution according to one of the preceding claims, characterized in that, in the process, the acid in step b) is selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, sulfurous acid, sulfonic acids, in particular methanesulfonic acid, carboxylic acids, carboxylic esters, sulfuric acid esters, amino acids, phosphonic acids, phosphoric acid esters, phytic acid and mixtures thereof, wherein nitric acid and methanesulfonic acid are particularly preferred; and / or the acid in step b) is 0.01 to 1 N and particularly preferably 0.1 N; and / or the acid content in the aqueous solution from step b) is in the range of 0.01 to 2.0 wt.%, preferably 0.05 to 1.0 wt.% and particularly preferably 0.1 to 0.5 wt.%, based on the total weight of the solution.

5. Solution according to one of the preceding claims, characterized in that, in the process, the mixing in step c) is carried out by adding the aqueous solution of the acid dropwise to the alcoholic silane solution; or the mixing in step c) is carried out by adding the alcoholic silane solution dropwise to the aqueous solution of the acid; or the mixing in step c) is carried out by simultaneously combining the alcoholic silane solution and the aqueous solution of the acid; and / or the mixing according to step c) is carried out by stirring or shaking; and / or the mixture from step c) is stirred for 2 to 168 hours, preferably 4 to 24 hours and particularly preferably for 6 to 18 hours; and / or the temperature in step c) is 20 to 70°C, preferably 20 to 50°C and particularly preferably 25 to 40°C; the pH value of the mixture in step c) is < 5, preferably 1 to 4.9 and particularly preferably 4 to 4.

9.

6. Solution according to one of the preceding claims, characterized in that, during the process, during step d), 40 to 80 wt.%, preferably 45 to 75 wt.% and particularly preferably 50 to 65 wt.% of the solvent mixture, based on the total mass of the batch provided in step b), is removed; and / or the concentrated mixture from step d) is cooled to a temperature of 20 to -25°C, preferably 10 to -25°C and particularly preferably 4 to -20°C; and / or during step d), at least some of the water from step b) is also removed; and / or during step f), the solution is diluted to a dry residue content of 0.5 to < 20 wt.%, preferably between 1 and < 10 wt.%.

7. Solution according to one of the preceding claims, characterized in that step e) of the method is carried out until a viscosity of 10 to 70 Pa-s, preferably 15 to 40 Pa-s and particularly preferably 20 to 25 Pa-s is reached.

8. Solution according to one of the preceding claims, characterized in that in the process in step f) the alcohol is identical to the alcohol used in step a).

9. Solution according to one of the preceding claims, characterized in that in step a) exactly one alcohol is used as a solvent and / or in the solution from step a) exactly one silane compound is dissolved; and / or in step b) an aqueous solution exactly one acid is provided.

10. Solution according to one of the preceding claims, characterized in that the process is carried out continuously or in batches.

11. Solution according to one of the preceding claims, characterized in that it contains at least one active ingredient, in particular an active ingredient selected from the group consisting of pharmaceutical active ingredients or excipients, cosmetically active substances, plant protection products, in particular herbicides, fungicides, insecticides, pesticides, preservatives, food additives, flavorings, fragrances, colorants, chelating additives, in particular carboxylic acid derivatives, pheromones and other attractants, natural products, in particular poly- and oligosaccharides, proteins and protein fragments, resins, oils, fats, fatty acids and derivatives, lignins and lignin derivatives, (partially) functionalized natural products, in particular cellulose ethers such as methylhydroxyethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose, wherein preferably in the process the at least one active ingredient is introduced into the solution according to step f).

12. Solution according to the preceding claim characterized in that the at least one active ingredient is contained in an amount, based on the total amount of the solution, of 0.01 to 40 wt.%, preferably of 0.5 to 20 wt.%, particularly preferably of 1 to 20 wt.%.

13. Solution according to one of the preceding claims, characterized in that the clusters have a number-averaged mean particle diameter, determined by dynamic light scattering (DLS), of <80 nm, preferably of 2 to 70 nm, more preferably of 2 to 60 nm.

14. Solution according to one of the preceding claims, characterized in that the clusters have a particle size distribution with a full width at half maximum (FWHM) of <50 nm, preferably <40 nm, more preferably <30 nm.

15. A method for preparing a solution containing silica clusters, comprising the following steps: a) providing at least one alcoholic solution of at least one silane compound selected from the group consisting of tetraalkoxysilanes, and mixtures thereof; b) providing an aqueous solution of at least one acid having a pKa value of < 2.5; c) mixing the solutions provided in steps a) and b) and mixing thoroughly for 4 hours to 1 week at a temperature of >20 to 70°C; d) removing at least some of the alcohol from the mixture from step c) and subsequently cooling the concentrated mixture to a temperature of 20 to -25°C; e) storing the cooled mixture from step d) until a viscosity of 10 to 75 Pa·s is reached; and f) diluting the solution with an alcohol until a viscosity of 1 mPa-s to <10 Pa-s is reached and / or the solution is diluted to a dry residue content of 0.1 to < 50 wt.%, wherein during steps c) to e) a crosslinking of the silane compound takes place and at least part of the acid is incorporated into the resulting network via covalent bonds and / or contributes to the crosslinking.

16. Method for coating a substrate, wherein a solution according to one of claims 1 to 14 or a solution produced by a method according to claim 15 is applied at least partially or completely to a surface of a substrate, wherein a post-condensation step of the silica clusters is excluded, so that a coating is formed.

17. Method according to the preceding claim, characterized in that after the application of the solution a drying step is carried out in which heating of the coating to above 120 °C, preferably above 100 °C, particularly preferably above 80 °C is excluded.

18. Method according to one of the two preceding claims, characterized in that the substrate is selected from the group consisting of Hair, fur and pelts, human and animal body parts, tissues and cells, such as skin, fingernails and toenails, hooves, feathers, Plant substrates, in particular seeds, seedlings, fruit, vegetables, salad, nuts, plants, plant parts, in particular leaves and roots, algae, lichens, Insects, especially pest insects such as aphids, tortrix moths and oak processionary caterpillars, Mushrooms Single-celled organisms, such as bacteria Unprocessed and processed foods as well as pet food, Dietary supplements, Pharmaceutical products, especially tablets, such as film-coated tablets, Medical devices, in particular implants or contact lenses Scaffolds for in-vitro cell culture, washing and cleaning agents, in particular dishwasher tablets and Laundry detergent tablets, fertilizers Biodegradable (disposable) products, in particular plates, bowls, cups and cutlery.

19. Method according to any one of claims 16 to 18, characterized in that the coating is produced in a layer thickness of 10 nm to 1 mm, preferably from 100 nm to 200 pm, particularly preferably from 1 pm to 100 pm.

20. Coated object comprising a substrate and a coating applied at least partially to the substrate, manufactured according to a method according to one of claims 16 to 19.

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