DE102005024332A1 - Process for the production of ceramic flakes - Google Patents

Abstract

The invention relates to a method for the production of ceramic flakes, comprising the steps A) of providing a suspension of inorganic nanoparticles, B) applying the suspension to a substrate by means of a film casting technique, C) drying the layer of the applied suspension to form green bodies in the form of flakes and D) the thermal densification of the flake green bodies to form the ceramic flakes. DOLLAR A The resulting ceramic flakes are suitable for. As an inert filter material, absorber material, carrier material for active substances or additives for plastics and paints.

Description

The The invention relates to a method for producing ceramic flakes, available therefrom ceramic flakes and their use.

Particulate carrier materials or fillers are getting big these days Quantities used. They are relatively inexpensive and serve e.g. for cleaning of fluid streams by filtration or adsorption or as a carrier of active components, e.g. of catalytic active substances. Often arise by their Use but also problems. Such is the separation of the carrier materials Of the fluids often difficult after use. In addition, substances, with which the support materials loaded after use, difficult or impossible to remove. Insufficient chemical resistance of the substrates prevents processing with aggressive chemicals. As a result, is a reuse frequently not possible, which is disadvantageous in terms of cost and disposal. Of the Use of such carrier materials may also be associated with health concerns.

In the brewing and beverage industry is e.g. the deep or precoat filtration with the filter aid Diatomaceous earth prevalent. Despite good qualities arise Diatomaceous earth also causes problems. Diatomaceous earth may be due to the structure and size respiratory and be carcinogenic in cristobalite form, making elaborate precautions required are. Disposal or rejection during filtration accumulating mud is difficult and expensive. In breweries accumulating filter sludge are currently predominantly in Germany used or landfilled. According to the circular economy and Waste Law, however, is a highest possible recycling desirable.

It There is therefore a need for an alternative to conventional support materials, the above explained Disadvantages, such as difficult separation from the media and the loading, insufficient chemical resistance, Problems with disposal and recycling, does not have. Further should be a variability in the setting of the proportions possible be to adapt to the particular application.

There often size Quantities must be used the material should be relatively inexpensive to produce. The The object of the invention was therefore also in the provision a simple and inexpensive Method for providing the alternative support materials. The procedure should be as possible uniform geometries, especially with regard to the layer thickness, which are also variably adjustable. Also very thin and / or porous materials should be feasible.

• A) Bereitstellen einer Suspension von anorganischen Nanopartikeln,
• B) Aufbringen der Suspension auf eine Unterlage mittels Foliengießtechnik,
• C) Trocknen der Schicht aus der aufgebrachten Suspension unter Bildung von Grünkörpern in Form von Flakes und
• D) thermisches Verdichten der Flake-Grünkörper unter Bildung der keramischen Flakes.

Surprisingly, the object could be achieved by a method for the production of ceramic flakes, which comprises the following steps:

• A) providing a suspension of inorganic nanoparticles,
• B) applying the suspension to a substrate by means of a film casting technique,
• C) drying the layer of the applied suspension to form green bodies in the form of flakes and
• D) thermally compacting the flake green bodies to form the ceramic flakes.

By The inventive method can surprisingly ceramic flakes are produced in a very simple manner and continuously, as carrier materials are suitable. The thickness of the flakes can be easily determined by the layer thickness of the applied suspension and is relatively uniform. On The reason for using nanopowder suspensions are very thin flakes feasible, which also porous could be. It finds essentially no or only a very small aggregate formation between the formed flakes instead. The flakes have a lot good chemical resistance on. In a preferred embodiment nanoparticles are used which are surface-modified,

The 1 and 2 show microscope images of flakes, which were prepared by the process according to the invention.

The flakes produced according to the invention can be made of any conventional ceramic. Examples are silicate ceramics such as porcelain, steatite, cordierite and mullite, oxide ceramics such as ceramics of alumina, magnesia, zirconia, titania, silica, magnesia spinel, aluminum titanate, barium titanate, lead zirconate titanate and ferrites, and nonoxide ceramics such as borides, silicides, carbides or Nitrides, such as silicon carbide, silicon nitride, aluminum nitride, boron carbide and boron nitride ceramics, or mixed ceramics thereof. Preference is given to ceramics of zirconium oxide, stabilized zirconium oxide, silicon oxide, titanium oxide and aluminum oxide. As known to those skilled in the art, such ceramics may contain additives for property enhancement. For example, alumina ceramics may contain, for example, additives such as MgO, Y ₂ O _3, or MnO to increase the sintering rate, and zirconia may be stabilized by doping.

In a first step is a suspension of inorganic nanoparticles provided. The inorganic nanoparticles are to ceramic nanoparticles or to inorganic nanoparticles, the by drying and / or thermal compression in ceramic Transfer materials. The person skilled in these materials are known. It is preferable about ceramic nanoparticles.

at The inorganic nanoparticles may be nanoparticles Metal or semimetal compounds, in particular metal or semi-metal oxides, carbides, nitrides, silicides or borides, where oxides, including Mixed oxides and hydrates thereof are particularly preferred. Examples for semi-metals are B, Si and Ge. It can be a type of nanoparticles or a Mixture of different nanoparticles can be used.

Examples are oxides such as ZnO, CdO, SiO ₂ , GeO ₂ , TiO ₂ (eg rutile, anatase), ZrO ₂ , Y ₂ O ₃ , CeO ₂ , SnO ₂ , Al ₂ O ₃ (especially boehmite, AlO (OH), also as aluminum hydroxide), MgO, CaO, B ₂ O ₃ , In ₂ O ₃ , La ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , Cu ₂ O, Ta ₂ O ₅ , Nb ₂ O ₅ , V ₂ O ₅ , MoO ₃ or WO ₃ ; Carbides such as CdC ₂ or SiC; Nitrides such as BN, AlN, Si ₃ N ₄ and Ti ₃ N ₄ .

Further examples are mixed oxides such as indium tin oxide (ITO), antimony tin oxide (ATO), spinels, ferrites or mixed oxides with perovskite structure such as BaTiO ₃ and PbTiO ₃ , and mixed oxides of aluminum and silicon such as mullite and sillimanite. Optionally, the nanoparticles may be hydrated.

Preferred nanoparticles are Al ₂ O ₃ , ZrO ₂ , stabilized ZrO ₂ (by doping with eg Y, Ca, Mg, Ce and / or Sc), SiO ₂ and TiO ₂ or hydrates thereof, with ZrO ₂ or stabilized ZrO _{2 being} the most are preferred.

The Preparation of these nanoparticles can be done in the usual way, e.g. by flame pyrolysis, plasma processes, colloid techniques, sol-gel processes, controlled germination and growth processes, MOCVD processes and emulsion processes. The inorganic nanoparticles can also from a coarser one Material obtained by crushing. These procedures are described in detail in the literature. The inorganic nanoparticles can also available in stores be. The nanoparticles are preferred by the sol-gel method receive.

At the Sol-gel processes usually become hydrolyzable Compounds of metals or semi-metals with water, optionally under acidic or basic catalysis, hydrolyzed and condensed. The hydrolysis and / or condensation reactions lead to Formation of polycondensates or precursors thereof e.g. with hydroxy, Oxo groups and / or oxo bridges, from which the nanoparticles can form. It can stoichiometric amounts of water, but also used smaller or larger quantities become. The forming sol can be determined by suitable parameters, e.g. Degree of condensation, solvent or pH on the for the composition desired viscosity be set. By suitable, known in the art setting The conditions may include the formation of nanoparticle-containing sols promoted become. Further details of the sol-gel process are e.g. at C.J. Brinker, G.W. Scherer: "Sol-gel Science - The Physics and Chemistry of Sol-Gel Processing ", Academic Press, Boston, San Diego, New York, Sydney (1990).

Examples of hydrolyzable metal or semimetal compounds that can be used in the sol-gel process are alcoholates or halides, alcoholates being preferred. Examples are Si (OCH ₃ ) ₄ , Si (OC ₂ H ₅ ) ₄ , Si (on- or -iC ₃ H ₇ ) ₄ , Si (OC ₄ H ₉ ) ₄ , SiCl ₄ , HSiCl ₃ , Si (OOCCH ₃ ) ₄ , TiCl ₄ , Ti (OCH ₃ ) ₄ , Ti (OC ₂ H ₅ ) ₄ , Ti (2-ethylhexoxy) ₄ , Ti (n-OC ₃ H ₇ ) ₄ or Ti (i-OC ₃ H ₇ ) ₄ , Al (OCH ₃ ) ₃ , Al (OC ₂ H ₅ ) ₃ , Al (OnC ₃ H ₇ ) ₃ , Al (OiC ₃ H ₇ ) ₃ , Al (OnC ₄ H ₉ ) ₃ , Al (O-sec C ₄ H ₉ ) ₃ , AlCl ₃ , AlCl (OH) ₂ , Al (OC ₂ H ₄ OC ₄ H ₉ ) ₃ , ZrCl ₄ , Zr (OC ₂ H ₅ ) ₄ , Zr (OnC ₃ H ₇ ) ₄ , Zr (OiC ₃ H ₉ ) ₄ , Zr (OC ₄ H ₉ ) ₄ , ZrOCl ₂ , Zr (2-ethylhexoxy) ₄ , and Zr compounds having complexing radicals such as β-diketone and (Meth ) acrylic radicals. For the stabilization of zirconium oxide, for example, in the sol-gel process, additionally hydrolyzable compounds or salts of the abovementioned doping elements are added to amounts known to the person skilled in the art.

The Nanoparticles are also referred to as nanoscale solid particles and have an average particle diameter (volume average, Measurement: dynamic laser light scattering with an ultrafine particle analyzer: Ultrafine Particle Analyzer (UPA), Leeds Northrup) below 1 μm, in the Usually below 500 nm. The nanoparticles preferably have a medium Particle diameter of not more than 200 nm, preferably not more than 100 nm and in particular not more than 50 or even 30 nm and in usually more than 1 nm, e.g. 1 to 20 nm.

The Nanoparticles are in particular in the form of a sol or a suspension in a solvent in front. It is preferred that the nanoparticles be modified on the surface are. By the surface modification can be an improvement quality and regularity the flakes obtained can be achieved. Due to the surface modification can agglomerate be reduced between the nanoparticles or flakes. This can also for improved cracking or reduced sintering temperature contribute.

The surface modification of nanoparticles is a known process, as described by the applicant in WO 93/21127 (for example). DE 4212633 ) or WO 96/31572. The preparation of the surface-modified nanoparticles can in principle be carried out in two different ways, namely firstly by surface modification of already prepared nanoparticles with surface modifiers and secondly by preparation of these nanoparticles in the presence of surface modifiers. These two ways are explained in more detail in the aforementioned patent applications.

When Surface modifiers are suitable e.g. organic compounds having at least one functional Group or hydrolyzable silanes with at least one functional Group and inorganic acids, wherein said functional groups with at the surface of the Nanoparticles react and / or interact with existing groups can, so that a surface modification is reached. For example, on the nanoparticles, e.g. Metal oxides, surface groups as residual valencies, the reactive groups represent, e.g. Hydroxy groups or oxy groups with a functional Group of surface modifier interact and / or react.

The Surface modifiers can e.g. covalent, ionic (saltlike) or coordinative bonds to surface the nanoparticles form while among the less preferred pure interactions by way of example Dipole-dipole interactions, Hydrogen bonds and van der Waals interactions. Is preferred the formation of covalent, ionic and / or coordinative Bonds. Under a coordinative bond becomes a complex formation Understood. Accordingly, the surface modifiers may be to complexing agents that include chelating agents. Between the surface modifier and the particle may e.g. an acid / base reaction to Brönsted or Lewis, a complex formation or an esterification take place.

A surface modification the nanoparticle may e.g. by mixing the nanoparticles with suitable ones Surface modifiers optionally in a solvent and in the presence of a catalyst. Frequently, e.g. a several hours stir the components at room temperature for modification. In a convenient procedure the surface modification takes place by chemomechanical reaction. This is described in WO 04/069400 be. Naturally hang appropriate conditions, like temperature, proportions, Duration of implementation, etc., by the specific partners involved and the desired one Occupancy level.

According to the invention preferred It is also that the surface modifier have a relatively low molecular weight. For example the molecular weight may be less than 1,500, especially below 1,000 and preferably below 500 or below 400 or even below 300 amount. This concludes Of course a much higher one Molecular weight of the compounds is not sufficient (e.g., up to 2,000 and more).

Examples for suitable functional groups of surface modifiers for attachment to the nanoparticles are inorganic acid groups or derivatives thereof, carboxylic acid groups, Anhydride groups, acid amide groups, (Primary, secondary tertiary and quaternary) Amino groups, SiOH groups and C-H-acidic groups, e.g. β-dicarbonyl compounds. It can also several of these groups exist simultaneously in one molecule (e.g., betaines, amino acids and EDTA).

The Surface modifiers are preferably selected from saturated or unsaturated Carboxylic acids, Oxacarbonsäuren, Carboxylic acid derivatives, Amines, β-dicarbonyl compounds, inorganic acids and hydrolyzable silanes with at least one non-hydrolysable Group.

Examples for inorganic acids for surface modification The nanoparticles are hydrochloric, nitric, sulfuric and Phosphoric acid and their esters or derivatives thereof.

Examples of surface modifiers are optionally substituted (eg with hydroxy) saturated or unsaturated mono- and polycarboxylic acids (preferably monocarboxylic acids) having 1 to 24 carbon atoms, such as formic acid, acetic acid, propionic acid, butyric acid, pentanoic acid, hexanoic acid, acrylic acid, methacrylic acid, crotonic acid, citric acid, Adipic acid, succinic acid, glutaric acid, oxalic acid, maleic acid, fumaric acid, itaconic acid and stearic acid, and the corresponding derivatives, such as acid anhydrides, chlorides, esters (preferably C ₁ -C ₄ alkyl esters) and amides, for example methyl methacrylate and caprolactam.

Especially preferred are oxacarboxylic acids with 1 to 24 carbon atoms. These are carboxylic acids, the Oxagruppen, so ether bridges (-O-), contained in the alkyl chain. The oxacarboxylic acid can Contain 1, 2, 3 or more oxa groups. Examples are methoxyacetic acid, 3,6-dioxaheptanoic acid and 3,6,9-trioxadecanoic acid (TODS) and their homologues.

Also suitable are amine compounds, such as Ammonium salts and mono- or polyamines. Examples of these surface modifiers are quaternary ammonium salts of the formula NR ¹ R ² R ³ R ^{4 +} X ^- , in which R ¹ to R ⁴ optionally represent different aliphatic, aromatic or cycloaliphatic groups having preferably 1 to 12, in particular 1 to 8 carbon atoms, such as for example, alkyl groups having 1 to 12, in particular 1 to 8 and particularly preferably 1 to 6 carbon atoms (for example methyl, ethyl, n- and i-propyl, butyl or hexyl), and X ^{- is} an inorganic or organic anion, for example acetate, OH ^- , Cl ^- , Br ^- or I ^- ; Mono- and polyamines, in particular those of the general formula R _3-n NH _n , in which n = 0, 1 or 2 and the radicals R independently of one another are alkyl groups having 1 to 12, in particular 1 to 8 and particularly preferably 1 to 6 carbon atoms, and ethylene polyamines. Specific examples are methylamine, dimethylamine. Trimethylamine, ethylamine, aniline, N-methylaniline, diphenylamine, triphenylamine, toluidine, ethylenediamine and diethylenetriamine.

Preferred surface modifiers are also β-dicarbonyl compounds containing, for example, 4 to 12 carbon atoms, such as β-diketones and β-ketocarboxylic acids, and derivatives thereof, such as β-ketocarboxylic acid esters and β-ketocarboxylic acid amides. Examples are 2,4-hexanedione, 3,5-heptanedione, acetylacetone, diacetyl, acetonylacetone acetoacetic acid and acetoacetic acid C ₁ -C ₄ -alkyl esters (acetoacetates), such as ethyl acetoacetate, and acetoacetamides. Further examples of surface modifiers are amino acids, proteins and imines.

For surface modification of the nanoparticles it is also possible to use hydrolyzable silanes having at least one nonhydrolyzable group, eg silanes of the general formula: R _n SiX _(4-n) (I) wherein the radicals X are identical or different and are hydrolyzable groups or hydroxy groups, the radicals R are identical or different and represent non-hydrolyzable groups and n is 1, 2 or 3, preferably 1 or 2.

In the general formula (I), the hydrolyzable groups X, which may be the same or different, are, for example, hydrogen or halogen (F, Cl, Br or I), alkoxy (preferably C _1-6 alkoxy, such as methoxy, ethoxy , n-propoxy, i-propoxy and butoxy), aryloxy (preferably C _6-10 -anyloxy such as phenoxy), acyloxy (preferably C _1-6 acyloxy such as acetoxy or propionyloxy), alkylcarbonyl (preferably C _{2-) 7-} alkylcarbonyl, such as acetyl), amino, monoalkylamino or dialkylamino. Preferred hydrolyzable radicals are halogen, alkoxy and acyloxy groups. Particularly preferred hydrolysable radicals are C _1-4 alkoxy groups, in particular methoxy and ethoxy.

Examples of the nonhydrolyzable radicals R, which may be identical or different, are alkyl (for example C _1-10 -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl and tert-butyl , Pentyl, hexyl, octyl or cyclohexyl), alkenyl (eg C _2-10 alkenyl such as vinyl, 1-propenyl, 2-propenyl and butenyl), alkynyl (eg C _2-10 alkynyl such as acetylenyl and propargyl) , Aryl (preferably C _6-10 aryl, such as phenyl and naphthyl) and corresponding alkylaryls and arylalkyls. The radicals R and X may optionally have one or more customary substituents, such as halogen or alkoxy.

Further the radical R may have a functional group. Special examples for functional Groups are e.g. the epoxide, hydroxy, ether, amino, monoalkylamino, Dialkylamino, optionally substituted anilino, amide, carboxy, acrylic, Acryloyloxy, methacrylic, methacryloyloxy, mercapto, cyano, alkoxy, Isocyanato, aldehyde, alkylcarbonyl, acid anhydride and phosphoric acid groups. These functional groups are via alkylene, alkenylene or Arylene bridge groups, which may be interrupted by oxygen or -NH groups bound the silicon atom. The bridging groups mentioned and, where appropriate present substituents, as in the alkylamino groups, direct e.g. from the above or below alkyl, alkenyl or aryl radicals. Naturally the radical R can also have more than one functional group. Concrete examples of nonhydrolyzable radicals R with functional groups are glycidyloxypropyl, (Meth) acryloyloxypropyl, aminopropyl and 3-isocyanatopropyl.

Prefers used surface modifiers for the Silanes of the formula (I) are alkylsilanes or dialkylsilanes, such as dimethyldiethoxysilane (DMDE), Epoxysilanes, such as glycidyloxypropyltriethoxysilane (GPTES), and aminosilanes, such as 3-aminopropyltriethoxysilane (APTES).

As the dispersant for the suspension, conventional solvents are used. Examples are polar solvents such as water and polar organic solvents and nonpolar solvents. Examples of organic solvents are alcohols, such as aliphatic and alicyclic alcohols having 1 to 8 carbon atoms, for example methanol, ethanol, n- and i-propanol, butanol, ketones, for example acetone, butanone and cyclohexanone, esters, for example ethyl acetate and glycol esters, ethers For example, diethyl ether, dioxane, isopropoxyethanol and tetrahydrofuran, glycol ethers, glycols, eg ethylene glycol, amides and other nitrogen compounds, eg dimethylacetamide, dimethylformamide and acetonitrile, sulfoxides and sulfones, nitro compounds, such as nitrobenzene, halohydrocarbons, such as chloroform, and hydrocarbons substances, for example toluene or hexane. Of course, it is also possible to use mixtures of the solvents. Preferably used solvents are polar solvents, especially water, alcohols, such as C _1-4 alcohols, and ethers.

such Suspensions are well known in the ceramic arts also called slip. In the suspensions may optionally conventional Contain additives such. Defoamers, dispersing aids, Ver liquid, Flow aids and organic binders. Other possible additives are catalysts or starters, such as photoinitiators or thermal starters, to support crosslinking reactions. The pH of the suspension can by an acid or a base can be suitably adjusted.

For the optional Use of organic binders come all the usual, into consideration, in particular, organic binders known to the person skilled in the art those in the for the suspension used solvents solved can be. Particularly preferred examples of these are celluloses and cellulose derivatives, Polyvinyl alcohols and their derivatives, polyvinyl pyrrolidones, polyethylene glycols and their derivatives, e.g. Polyethylene glycol dimethacrylate, and polysaccharides.

In a preferred embodiment is an organic binder that contains a photochemical curable or crosslinkable binder, wherein monomers, oligomers or Polymers can be used. In this case will be common too Starter for the curing reaction added. Preference is given to monomers, oligomers and polymers with UV-crosslinkable functional groups. These binders are well suited to the skilled person known. For the radiation-curable Binders may be e.g. to those with crosslinkable acrylic or epoxy groups act. Examples of suitable photochemically crosslinkable Binders are epoxy acrylates, polyester acrylates, polyether acrylates, Urethane acrylates and functional monomers such as, for example, polypropylene glycol dimethacrylates or acrylic acid.

Possibly can various organic binders are used, e.g. one in the solvent used soluble Binder together with a photochemically curable binder. The photochemical curable or crosslinkable binder may in particular also be a binder, that in the solvent used is soluble. The type of crack pattern and thus the flake geometry can also from the Depend on the proportion of organic binder used and thus be adjusted as desired by appropriate choice of this amount.

The Amount of nanoparticles in the suspension can be widely used vary, e.g. dependent on of the type of nanoparticles used, the optional surface modification and the desired Viscosity. The solids content of the optionally surface - modified nanoparticles in the suspension may e.g. generally 1 vol.% to 70 vol.%.

in the second step is the suspension by means of film casting technique applied to a substrate. The film casting process is a conventional one Procedure and can be in usual Be applied. Here, the suspension is on a pad applied. The backing may be any substrate act. It can be used an endless track. The underlay can e.g. be made of metal or plastic. Preference is given to a polymer support film used.

at Tape casting you leave Run the suspension on the pad, leaving a wet coating film is formed on the surface. The suspension can be easily manually to be poured on the pad. The suspension may e.g. by means of a slot or a Voratsbehälters be applied with adjustable gap on the substrate. The Layer thickness of the wet film can by the order quantity and / or mechanical means such as a squeegee can be set in the desired manner. The foil casting is preferably continuous.

By the subsequent one Dry form inorganic or ceramic flakes (green body), which can easily be detached from the surface. The formation of the Flakes is surprisingly by the formation of crack patterns in the layer during the Drying. The layer thickness leaves as explained above variable over the film casting technique to adjust. Drying may be at room temperature (e.g., about 20 ° C) or elevated temperature respectively. The appropriate duration naturally depends on factors such as. Temperature and amount and type of solvent.

While or after drying dissolve the forming or formed flakes easily from the underlay from. This may be assisted if necessary, e.g. by shaking. To The drying will receive in particular flakes that do not or essentially not adhere to the substrate. For thermal compression can the flakes are removed from the pad or they stay on Underlay and on it are subjected to thermal consolidation.

The latter sets a thermally stable or residue-free combustible surface ahead. The flakes are preferred after drying of the pad away.

in the third step, the green bodies are in shape of flakes (green Flakes) thermally compacted. The thermal densification will also referred to as sintering. The firing temperatures naturally depend on the material properties and can vary widely. The suitable firing temperatures for the respective ceramic materials for thermal consolidation / sintering are well-known to the skilled person and are generally enclosed at least 300 ° C, e.g. in the range of 400 ° C up to 1,200 ° C. The steps from foil casting to for sintering be carried out in a continuous process.

After sintering, ceramic flakes are obtained. Flakes can also be called platelets. The flakes according to the invention are preferably relatively thin platelets. By the method according to the invention, a surprisingly uniform layer thickness of the flakes can be achieved. One of the advantages of the invention is that dimensions can be set very variable as needed. In general, for example, flakes can be produced with average layer thicknesses in the range of 0.1 .mu.m to 1,000 .mu.m. The length and width dimensions can be variably adjusted, for example, in the range from 1 .mu.m to 10 ^-2 m. For example, flakes with a thickness of about 5 .mu.m and a length of 200 to 500 .mu.m can be obtained.

In a preferred embodiment can when using a radiation curable or curable Bindersystems structuring by irradiation done. It can all conventional Exposure method used for photo-curing be, with the structuring by imagewise irradiation results. The structuring preferably takes place after predrying the applied layer. When structuring, where appropriate is further dried, form at the irradiated sites Binders crosslinked flakes with a defined geometry. The Flakes can subsequently detached from the substrate, optionally with the aid of a solvent. Subsequently the flakes are sintered.

to Irradiation can e.g. UV light, laser beams or electron beams are used wherein UV exposure is particularly preferred. The structuring can by imagewise irradiation can on conventional, known to those skilled in the art, e.g. by photolithographic Methods such as mask exposure or laser writing. Such Structuring is advantageous because it allows a more accurate and uniform cracking and flake geometry can be adjusted.

In a further embodiment can after the thermal compression of the flakes a grinding step connect. In this way, the aspect ratio of the flakes can be reduced or set.

The Flakes can be porous. This may be advantageous as it results in e.g. a larger surface or a higher one loading capacity can be achieved. The pores of the flakes are usually fine pores in the sub-micron range (smaller 1 μm). According to the nomenclature of IUPAC, it is micro, meso or macropore Flakes, wherein the mean pore diameter is preferably less than 200 nm, more preferably below 50 nm (mesoporous) and especially below 2 nm (microporous) lies.

The ceramic flakes can e.g. as an inert filter material or absorber material, as additives or reinforcing elements for plastics and lacquers or as support materials, e.g. For Catalyst systems can be used. The flakes can after the implementation the respective application from the respective working media e.g. by Sedimentation, centrifugation and / or filtration / sieving easy being separated as such or loaded with the target substances, e.g. Waste materials, desired Products or agents, such as catalysts are present.

Possible applications especially in the field of catalysis and filtration. In the field of catalysis can the ceramic flakes as hochtem peraturstabile and chemical-resistant carrier catalytically effective substances, e.g. in stirred kettles, Tanks or pipelines.

By the possibility the production of ceramic flakes, with regard to tailored two-dimensional shape and / or the surface chemistry can be can e.g. compared to natural Diatomaceous earth achieves other separation finenesses or quite different filtration tasks become.

The increased Chemical resistance the ceramic flakes allows recycling in strong alkaline cleaning baths, e.g. after use as Filter aid.

Interesting is the combination of inert filter aids with catalytically active materials (eg TiO ₂ (anatase)). For example, inventive ceramic flakes that are inert can be coated or loaded with a catalytically active material such as anatase. However, it is also possible to use ceramic flakes which themselves are catalytically active, for example ceramic flakes made from anatase.

With such catalytically active flakes is e.g. the removal of organic Contamination by UV irradiation possible, e.g. for cleaning liquid or gaseous Media of all kinds. For this The catalytically active flakes are in the medium to be treated given and then with UV light irradiated. As a result, the presence of the catalytically active Flakes become pollutants (organic substances) through the UV irradiation decomposes or decomposes better. In this way, organic contaminants be continuously removed from media by UV exposure.

A favorable feature of the flakes is the combination of a high specific surface area and a large geometric surface. This leads to a good ratio of the amount of flakes used (for example TiO ₂ ) and the amount of UV radiation used to the surface area of flakes which is exposed to UV light.

It also lies a chemically stable carrier and the separation and reuse of the flakes is easy. This opens options in the purification of weakly polluted effluents, e.g. of clinics, though with anatase coated flakes or anatase flakes be used.

Also in depth filtration or precoat filtration can as Alternative to the currently used carrier materials such as kieselguhr, perlites or celluloses, the ceramic flakes of the present invention be used.

The The invention is explained in more detail by the following examples, without limiting them.

example 1

An approximately 40% by weight alcoholic suspension of nanoscale ZrO ₂ , which has been surface-modified with TODS (3,6,9-trioxadecanoic acid), was applied by means of a doctor blade to a polymer support film and dried at room temperature. During the drying of the wet film, its crack pattern formed. This resulted in flakes after complete drying, which detached from the film. The flakes were compacted at 900 ° C for 30 minutes. No aggregate formation was observed between the flakes. 1 and 2 are microscope images of the flakes obtained.

Example 2

An aqueous suspension of a washed, nanoscale γ-Al ₂ O ₃ (50 wt .-%) which is surface-modified with 3,6,9-trioxadecanoic acid (10 wt .-% based on solids) and the binder 4 wt. % (based on solids) polyvinyl alcohol (Mowiol 16/88, Kuraray), was applied according to Example 1 and dried. This resulted in a crack pattern that could be varied by the content of binder in relation to the size of the flakes. The flakes were then compacted at 800 ° C and showed no aggregate formation of the individual flakes.

Example 3

A 40% by weight suspension of nanoscale ZrO ₂ surface-modified with DOHS (3,6-dioxaheptanoic acid) in a solvent mixture of ethanol / MEK (methyl ethyl ketone) in the weight ratio 33:66 with 15% by weight (based on solids) of an acrylate oligomer (Laromer ^® 8765, from BASF) and 2 wt .-% (based on oligomer) Irgacure ^® 500 (from Ciba Geigy) as an initiator according to example 1 was applied to a polymer film and dried. Subsequently, the dried layer was irradiated through a mask with UV light. In this case, crosslinked flakes with a defined geometry are formed at the irradiated points by binder, which were removed from the film by ethanol and sintered at 900 ° C. after subsequent drying in a drying oven. The structure of the flakes is retained and no agglomerates are formed.

Claims (16)

Process for the production of ceramic flakes, the following steps include: A) Provide a suspension of inorganic nanoparticles, B) applying the suspension on a base by means of film casting technique, C) drying the layer of the applied suspension to form green bodies in Shape of flakes and D) thermal densification of the flake green bodies under Formation of ceramic flakes. Method according to claim 1, characterized in that the backing is a polymer backing sheet. Method according to claim 1 or 2, characterized that the suspension is an organic binder or another Additive includes. Method according to claim 3, characterized that the organic binder is a binder that is in the solvent for the Suspension soluble is, and / or a binder which is curable by photochemical means, includes. Method according to one of claims 1 to 4, characterized that the flakes while and / or be removed from the substrate after drying. Method according to one of claims 1 to 5, characterized in that nanoparticles of Al ₂ O ₃ , ZrO ₂ , stabilized ZrO ₂ , SiO ₂ or TiO ₂ are used. Method according to one of claims 1 to 6, characterized that the nanoparticles surface-modified are. Method according to claim 7, characterized in that that the nanoparticles are selected with a surface modifier saturated or unsaturated Carboxylic acids, Oxacarbonsäuren, Carboxylic acid derivatives, Amines, β-dicarbonyl compounds, inorganic acids and hydrolyzable silanes with at least one non-hydrolysable Group surface-modified are. Method according to one of claims 1 to 8, characterized that the inorganic nanoparticles in the suspension are ceramic Nanoparticles are. Method according to one of claims 3 to 9, characterized that the layer of the applied suspension, which is a photochemically curable Binder comprises, by imagewise irradiation is structured to adjust the geometry of the flakes. Method according to one of claims 1 to 10, characterized that the ceramic flakes are ground after thermal densification, about the aspect ratio to reduce. Ceramic flakes, obtainable by a process the claims 1 to 11. Ceramic flakes according to claim 12, characterized in that that they have an average thickness of not more than 1,000 microns. Ceramic flakes according to claim 12 or claim 13, characterized in that the flakes are porous. Ceramic flakes according to any one of claims 12 to 14, which are themselves catalytically active or with a catalytic loaded or coated active substance. Use of ceramic flakes according to one of claims 12 to 15 as an inert filter material, absorber material, carrier material for active substances or additives or reinforcing elements for plastics and paints.